JP6777218B1 - Magnetic recording medium, magnetic recording / playback device and magnetic recording medium cartridge - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic recording medium capable of exhibiting good running performance at the time of use. SOLUTION: This magnetic recording medium is a tape-shaped magnetic recording medium, and has a substrate, a base layer provided on the base, and a magnetic layer provided on the base layer. On the surface of the magnetic layer, 20 or more and 200 or less dents having a depth of 20% or more of the average thickness of the magnetic layer are formed per 1600 μm2. The logarithmic decrement obtained by the pendulum viscoelasticity test at a temperature of 10 ° C. or higher and 45 ° C. or lower on the surface of the magnetic layer is 0.025 or higher and 0.040 or lower. The difference between the maximum value of the logarithmic decrement and the minimum value of the logarithmic decrement is 0 or more and 0.020 or less. The square ratio in the vertical direction is 65% or more. The average thickness of the magnetic layer is 80 nm or less. The average thickness of the magnetic recording medium is 5.6 μm or less. [Selection diagram] Fig. 1

Description

The present disclosure relates to a magnetic recording medium, a magnetic recording / playback device using the magnetic recording medium, and a magnetic recording medium cartridge.

Tape-shaped magnetic recording media are widely used for storing electronic data. For example, Patent Document 1 describes smoothing the surface of a magnetic layer in order to improve the electromagnetic conversion characteristics of a magnetic recording medium. Further, in the same document, it is described that a lubricant is added to the magnetic layer in order to suppress friction due to contact between the magnetic recording medium and the head.

Japanese Unexamined Patent Publication No. 2006-69553

The tape-shaped magnetic recording medium is housed in, for example, a magnetic recording cartridge. In order to further increase the recording capacity per magnetic recording cartridge, the total thickness of the magnetic recording medium contained in the magnetic recording cartridge is made thinner, and the length of the magnetic recording medium per magnetic recording cartridge (so-called tape length). ) Can be increased. However, a magnetic recording medium having a thin total thickness may be inferior in running stability. In particular, when repetitive recording and / or reproduction is performed, the surface condition (particularly the surface condition related to friction) of a magnetic recording medium having a thin total thickness changes, the running stability deteriorates, and the electromagnetic conversion characteristic deteriorates. May be done.

Therefore, a thin magnetic recording medium having an excellent running stability is desired even after repeated recording and reproduction operations.

The magnetic recording medium as one embodiment of the present disclosure is a tape-shaped magnetic recording medium, and has a substrate, a base layer provided on the base, and a magnetic layer provided on the base layer. .. On the surface of the magnetic layer, 20 or more and 200 or less dents having a depth of 20% or more of the average thickness of the magnetic layer are formed per 1600 μm ² . The logarithmic decrement obtained by the pendulum viscoelasticity test at a temperature of 10 ° C. or higher and 45 ° C. or lower on the surface of the magnetic layer is 0.025 or higher and 0.035 or lower. The difference between the maximum value of the logarithmic decrement and the minimum value of the logarithmic decrement is 0 or more and 0.020 or less. The vertical square ratio of the magnetic recording medium is 65% or more. The average thickness of the magnetic layer is 80 nm or less. The average thickness of the magnetic recording medium is 5.6 μm or less.

The magnetic recording / playback device according to an embodiment of the present disclosure includes a sending unit capable of sequentially sending out the magnetic recording medium, a winding unit capable of winding up the magnetic recording medium sent out from the sending unit, and a sending unit. It is provided with a magnetic head capable of writing information to the magnetic recording medium and reading information from the magnetic recording medium while contacting the magnetic recording medium traveling from the unit to the winding unit.

The magnetic recording medium cartridge as an embodiment of the present disclosure includes the magnetic recording medium and a housing for accommodating the magnetic recording medium.

Since the magnetic recording medium, the magnetic recording / reproducing device, and the magnetic recording medium cartridge as one embodiment of the present disclosure have the above-described configuration, good contact between the surface of the magnetic layer and the head is maintained during traveling.

It is sectional drawing of the magnetic recording medium which concerns on one Embodiment of this disclosure. It is a 1st explanatory view which shows the method of measuring the surface density of a dent in the magnetic recording medium shown in FIG. 2 is a second explanatory view showing a method of measuring the surface density of a recess in the magnetic recording medium shown in FIG. 1. FIG. 3 is a third explanatory view showing a method of measuring the surface density of a recess in the magnetic recording medium shown in FIG. 1. It is schematic explanatory drawing which shows the layout of the data band and the servo band in the magnetic recording medium shown in FIG. It is the schematic explanatory drawing which shows the data band shown in FIG. 3A enlarged. It is sectional drawing which shows typically the cross-sectional structure of the ε iron oxide particles contained in the magnetic layer shown in FIG. It is a graph which shows an example of the SFD curve of the magnetic recording medium shown in FIG. It is 1st explanatory drawing of the method of measuring the logarithmic decrement by the pendulum viscoelasticity test. It is a 2nd explanatory diagram of the method of measuring the logarithmic decrement by the pendulum viscoelasticity test. It is a 3rd explanatory diagram of the method of measuring the logarithmic decrement by the pendulum viscoelasticity test. It is a schematic diagram of the recording / reproduction apparatus using the magnetic recording medium shown in FIG. It is sectional drawing which shows typically the sectional structure of ε iron oxide particle as a modification. It is sectional drawing of the magnetic recording medium as another modification. It is the schematic schematic diagram explaining the deposit to the magnetic head from the magnetic recording medium containing the magnetic layer with relatively low viscoelasticity. It is the schematic schematic diagram explaining the deposit to the magnetic head from the magnetic recording medium containing the magnetic layer with relatively high viscoelasticity.

Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. The explanation will be given in the following order.
1. 1. One Embodiment 1-1. Configuration of magnetic recording medium 1-2. Manufacturing method of magnetic recording medium 1-3. Configuration of recording / playback device 1-4. Effect 2. Modification example

<1. Embodiment>
[1-1 Configuration of Magnetic Recording Medium 10]
FIG. 1 shows a cross-sectional configuration example of the magnetic recording medium 10 according to the embodiment of the present disclosure. As shown in FIG. 1, the magnetic recording medium 10 has a laminated structure in which a plurality of layers are laminated. Specifically, the magnetic recording medium 10 includes a long tape-shaped substrate 11, a base layer 12 provided on one main surface 11A of the base 11, and a magnetic layer provided on the base layer 12. A back layer 14 provided on the other main surface 11B of the substrate 11 is provided. The surface 13S of the magnetic layer 13 is a surface on which the magnetic head travels while being in contact with the magnetic head. The base layer 12 and the back layer 14 are provided as needed and may be omitted. The average thickness of the magnetic recording medium 10 is, for example, 5.6 μm or less.

The magnetic recording medium 10 has a long tape shape, and travels along its own longitudinal direction during the recording operation and the reproduction operation. The magnetic recording medium 10 is preferably used in a recording / reproducing device including, for example, a ring-shaped head as a recording head.

(Hypokeimenon 11)
The base 11 is a non-magnetic support that supports the base layer 12 and the magnetic layer 13. The substrate 11 is in the form of a long film. The upper limit of the average thickness of the substrate 11 is preferably 4.2 μm or less, more preferably 4.0 μm or less. When the upper limit of the average thickness of the substrate 11 is 4.2 μm or less, the recording capacity that can be recorded in one data cartridge can be increased as compared with a general magnetic recording medium. The lower limit of the average thickness of the substrate 11 is preferably 3 μm or more, more preferably 3.2 μm or more. When the lower limit of the average thickness of the substrate 11 is 3 μm or more, the decrease in strength of the substrate 11 can be suppressed.

The average thickness of the substrate 11 is obtained as follows. First, a 1/2 inch wide magnetic recording medium 10 is prepared, cut into a length of 250 mm, and a sample is prepared. Subsequently, the layers other than the substrate 11 of the sample, that is, the base layer 12, the magnetic layer 13, and the back layer 14 are removed with a solvent such as MEK (methyl ethyl ketone) or dilute hydrochloric acid. Next, using a laser holo gauge (LGH-110C) manufactured by Mitutoyo Co., Ltd. as a measuring device, the thickness of the sample substrate 11 is measured at positions of 5 points or more. Then, the measured values are simply averaged (arithmetic mean) to calculate the average thickness of the substrate 11. The measurement position shall be randomly selected from the sample.

The substrate 11 contains, for example, polyesters as a main component. Alternatively, the substrate 11 may contain PEEK (polyetheretherketone) as a main component. The substrate 11 may contain at least one of polyolefins, cellulosic derivatives, vinyl resins, and other polymeric resins in addition to polyesters or PEEK. When the substrate 11 contains two or more of the above materials, the two or more materials may be mixed, copolymerized, or laminated.

The polyesters contained in the substrate 11 include, for example, PET (polyethylene terephthalate), PEN (polyethylene naphthalate), PBT (polybutylene terephthalate), PBN (polybutylene terephthalate), PCT (polycyclohexylene dimethylene terephthalate), PEB. (Polyethylene-p-oxybenzoate) and at least one of polyethylene bisphenoxycarboxylate.

The polyolefins contained in the substrate 11 include, for example, at least one of PE (polyethylene) and PP (polypropylene). Cellulose derivatives include, for example, at least one of cellulose diacetate, cellulose triacetate, CAB (cellulose acetate butyrate) and CAP (cellulose acetate propionate). The vinyl resin contains, for example, at least one of PVC (polyvinyl chloride) and PVDC (polyvinylidene chloride).

Other polymer resins contained in the substrate 11 include, for example, PA (polyamide, nylon), aromatic PA (aromatic polyamide, aramid), PI (polyimide), aromatic PI (aromatic polyimide), PAI (polyamideimide). ), Aromatic PAI (Aromatic Polyamideimide), PBO (Polybenzoxazole, eg Zyrone®), Polyether, PEK (Polyetherketone), Polyetherester, PES (Polyethersulfone), PEI ( It contains at least one of polyetherimide), PSF (polysulphon), PPS (polyphenylene sulfide), PC (polyamide), PAR (polyamide) and PU (polyamide).

(Magnetic layer 13)
The magnetic layer 13 is a recording layer for recording a signal. The magnetic layer 13 contains, for example, a magnetic powder, a binder and a lubricant. The magnetic layer 13 may further contain additives such as conductive particles, an abrasive, and a rust preventive, if necessary.

The magnetic layer 13 has a surface 13S provided with a large number of recesses 13A. Lubricant is stored in these many recesses 13A. It is preferable that the large number of recesses 13A extend in the direction perpendicular to the surface of the magnetic layer 13. This is because the supply of the lubricant to the surface 13S of the magnetic layer 13 can be improved. A part of a large number of recesses 13A may be extended in the vertical direction. Further, the surface 13S of the magnetic layer 13 has 20 or more and 200 or less, preferably 40 or more and 200 or less recesses 13A having a depth of 20% or more of the average thickness of the magnetic layer 13 per 1600 μm ² , for example. More preferably, it is formed in a ratio of 80 or more and 200 or less.

The surface density of the recess 13A of the surface 13S of the magnetic layer 13 can be obtained, for example, as follows. The surface 13S of the magnetic layer 13 is observed by AFM to obtain an AFM image of 40 μm × 40 μm. As the AFM, Dimension3100 and NanoScopeIIIa manufactured by Digital Instruments and its analysis software are used, and as the cantilever, a silicon single crystal is used (Note 1), and the tapping frequency is tuned to 200-400 Hz. Next, the AFM image is divided into 512 × 512 (= 262,144) measurement points, and the height Z (i) (i: measurement point number, i = 1 to 262,144) is measured at each measurement point and measured. The height Z (i) of each measurement point is simply averaged (arithmetic average) and the average height (reference plane) Z _ave (= (Z (1) + Z (2) + ... + Z (262,144))) / 262,144) is calculated. In this case, as the image processing, the data obtained by filtering by Flatten order 2 and planefit order 3 XY is used.
(Note 1) Nano World SPM probe NCH Normal type PointProbe L (cantilever length) = 125 μm

FIG. 2A is an example of the surface 13S of the magnetic layer 13 observed in an enlarged manner. In FIG. 2A, the XY surface is the direction in which the surface 13S of the magnetic layer 13 spreads, and is, for example, a region having a surface area of 40 μm × 40 μm = 1600 μm ² . Further, in FIG. 2A, the Z axis represents the depth of the recess 13A. It is obtained by counting the number of recesses 13A having a depth from the reference plane corresponding to 20% or more of the average thickness (for example, 70 nm) of the magnetic layer 13 in a region having a surface area of 40 μm × 40 μm = 1600 μm ² . FIG. 2B schematically shows the distribution of the plurality of recesses 13A in the region having a surface area of 1600 μm ² shown in FIG. 2A. Specifically, it represents a part of the cross section along the IIB-IIB cutting line of FIG. 2A. In FIG. 2B, the vertical axis corresponds to the depth of the recess 13A along the Z axis, and specifically, the ratio [%] of the depth of the recess 13A to the average thickness (for example, 70 nm) of the magnetic layer 13. Represents. In the cross section of FIG. 2B, the number of recesses 13A having a depth corresponding to 20% or more of the average thickness (for example, 70 nm) of the magnetic layer 13 is two recesses 13A-1 and 13A-2. FIG. 2C schematically shows the distribution of the plurality of recesses 13A in the region having a surface area of 1600 μm ² shown in FIG. 2A. In the example shown in FIG. 2C, the number of recesses 13A having a depth corresponding to 20% or more of the average thickness (for example, 70 nm) of the magnetic layer 13 is 33. The recess 13A shown in FIG. 2C corresponds to the recess 13A shown in FIG. 2A, and the recess 13A-1 and the recess 13A-2 shown in FIG. 2C correspond to the recess 13A-1 and the recess 13A- shown in FIG. 2B, respectively. It corresponds to 2. Further, as described later, the average thickness of the magnetic layer 13 is obtained by processing the magnetic recording medium 10 thinly perpendicular to the main surface of the magnetic recording medium 10 to prepare a sample piece, and the cross section of the test piece is a transmission electron microscope ( Obtained by observing with a Transmission Electron Microscope (TEM).

As shown in FIG. 3A, for example, the magnetic layer 13 preferably has a plurality of servo band SBs and a plurality of data band DBs in advance. FIG. 3A is a schematic explanatory view showing the layout of the data band DB and the servo band SB in the magnetic recording medium 10, and shows the layout in a plane orthogonal to the stacking direction in the magnetic recording medium 10 having a laminated structure. As shown in FIG. 2A, the plurality of servo bands SB are provided at equal intervals in the width direction of the magnetic recording medium 10. The width direction of the magnetic recording medium 10 is a direction orthogonal to both the longitudinal direction of the magnetic recording medium 10 and the stacking direction of the magnetic recording medium 10. A data band DB is provided between the servo bands SB adjacent to each other in the width direction. A servo signal for controlling the tracking of the magnetic head is written in advance in the servo band SB. User data is recorded in the data band DB.

The upper limit of the ratio R _S (= (S _SB / S) × 100) of the total area S _SB of the servo band SB to the area S of the surface 13 S of the magnetic layer 13 is preferably 4 from the viewpoint of ensuring a high recording capacity. It is 0.0% or less, more preferably 3.0% or less, and even more preferably 2.0% or less. On the other hand, the lower limit of the ratio R _S of the total area S _SB of the servo band SB to the surface area S of the magnetic layer 13 is preferably 0.8% or more from the viewpoint of securing a servo track of 5 or more.

Ratio R _S of the total area S _SB servo bands SB to the area S of the surface of the magnetic layer 13, the ratio R _S of the total area S _SB servo bands SB to the area S of the surface of the magnetic layer 13, for example, a magnetic recording The medium 10 can be measured by developing the medium 10 with a ferricolloid developing solution (Sigma-Car Q, manufactured by Sigma High Chemical Co., Ltd.), and then observing the developed magnetic recording medium 10 with an optical microscope. The number of servo band width W _SB and servo band SB is measured from the observation image of the optical microscope. Next, the ratio R _S is calculated from the following formula.
Ratio R _S [%] = (((servo bandwidth W _SB ) x (number of servo bands)) / (width of magnetic recording medium 10)) x 100

The number of servo band SBs is preferably 5 or more, more preferably 5 + 4n (where n is a positive integer) or more. When the number of servo bands SB is 5 or more, it is possible to suppress the influence of the dimensional change in the width direction of the magnetic recording medium 10 on the servo signal and secure stable recording / playback characteristics with less off-track.

The upper limit of the servo bandwidth W _SB is preferably 95 μm or less, more preferably 60 μm or less, and even more preferably 30 μm or less from the viewpoint of ensuring a high recording capacity. The lower limit of the servo bandwidth W _SB is preferably 10 μm or more from the viewpoint of manufacturing a recording head. Servo bandwidth W _SB width is obtained as follows. First, the magnetic recording medium 10 is developed using a ferricolloid developer (Sigma-Car Q, manufactured by Sigma High Chemical Co., Ltd.). Next, the width of the servo bandwidth W _SB can be measured by observing the developed magnetic recording medium 10 with an optical microscope.

As shown in FIG. 3B, the magnetic layer 13 is configured so that a plurality of data tracks Tk can be formed in the data band DB. In this case, the upper limit of the data track width _WTk is preferably 2.0 μm or less, more preferably 1.5 μm or less, and even more preferably 1.0 μm or less from the viewpoint of ensuring a high recording capacity. The lower limit of the data track width _WTk is preferably 0.02 μm or more from the viewpoint of the magnetic particle size.

From the viewpoint of ensuring a high recording capacity, the magnetic layer 13 can record data so that the minimum value of the magnetization reversal distance L is preferably 48 nm or less, more preferably 44 nm or less, and even more preferably 40 nm or less. It is configured. The lower limit of the minimum value of the magnetization reversal distance L is preferably 20 nm or more from the viewpoint of the magnetic particle size.

The upper limit of the average thickness of the magnetic layer 13 is preferably 90 nm or less, particularly preferably 80 nm or less, more preferably 70 nm or less, and even more preferably 50 nm or less. When the upper limit of the average thickness of the magnetic layer 13 is 90 nm or less, when a ring-shaped head is used as the recording head, the magnetization can be uniformly recorded in the thickness direction of the magnetic layer 13, so that the electromagnetic conversion characteristics are improved. be able to.

The lower limit of the average thickness of the magnetic layer 13 is preferably 35 nm or more. When the upper limit of the average thickness of the magnetic layer 13 is 35 nm or more, the output can be secured when the MR type head is used as the reproduction head, so that the electromagnetic conversion characteristics can be improved.

The average thickness of the magnetic layer 13 is obtained as follows. First, a carbon film is formed on the surface 13S of the magnetic layer 13 of the magnetic recording medium 10 and the surface 14S of the back layer 14 by a vapor deposition method, and then a tungsten thin film is deposited on the carbon film covering the surface 13S of the magnetic layer 13 by a vapor deposition method. Further form. These carbon film and tungsten film protect the sample in the flaking treatment described later.

Next, the magnetic recording medium 10 is processed by a FIB (Focused Ion Beam) method or the like to thin it. When the FIB method is used, a carbon film and a tungsten thin film are formed as a protective film as a pretreatment for observing a TEM image of a cross section described later. The carbon film is formed on the magnetic layer side surface and the back layer side surface of the magnetic recording medium 10 by a vapor deposition method, and the tungsten thin film is further formed on the magnetic layer side surface by a vapor deposition method or a sputtering method. The thinning is performed along the length direction (longitudinal direction) of the magnetic recording medium 10. That is, the thinning forms a cross section parallel to both the longitudinal direction and the thickness direction of the magnetic recording medium 10. The cross section of the obtained sliced sample is observed with a transmission electron microscope (TEM) under the following conditions to obtain a TEM image. The magnification and the accelerating voltage may be appropriately adjusted according to the type of the device.
Equipment: TEM (H9000NAR manufactured by Hitachi, Ltd.)
Acceleration voltage: 300kV
Magnification: 100,000 times

Next, using the obtained TEM image, the thickness of the magnetic layer 13 is measured at at least 10 points or more in the longitudinal direction of the magnetic recording medium 10. The average value obtained by simply averaging (arithmetic mean) the obtained measured values is defined as the average thickness of the magnetic layer 13. The position where the measurement is performed shall be randomly selected from the test pieces.

(Magnetic powder)
The magnetic powder contains, for example, powder of nanoparticles containing ε-iron oxide (hereinafter referred to as “ε-iron oxide particles”). High coercive force can be obtained even with fine particles of ε iron oxide particles. It is preferable that the ε-iron oxide contained in the ε-iron oxide particles is preferentially crystal-oriented in the thickness direction (vertical direction) of the magnetic recording medium 10.

FIG. 4 is a cross-sectional view schematically showing an example of the cross-sectional structure of the ε-iron oxide particles 20 contained in the magnetic layer 13. As shown in FIG. 4, the ε-iron oxide particles 20 have a spherical or substantially spherical shape, or have a cubic shape or a substantially cubic shape. Since the ε iron oxide particles 20 have the above-mentioned shape, when the ε iron oxide particles 20 are used as the magnetic particles, they are more magnetic than when the hexagonal plate-shaped barium ferrite particles are used as the magnetic particles. It is possible to reduce the contact area between the particles in the thickness direction of the recording medium 10 and suppress the aggregation of the particles. Therefore, it is possible to improve the dispersibility of the magnetic powder and obtain a better SNR (Signal-to-Noise Ratio).

The ε iron oxide particles 20 have, for example, a core-shell type structure. Specifically, as shown in FIG. 3, the ε-iron oxide particles 20 include a core portion 21 and a shell portion 22 having a two-layer structure provided around the core portion 21. The shell portion 22 having a two-layer structure has a first shell portion 22a provided on the core portion 21 and a second shell portion 22b provided on the first shell portion 22a.

The core portion 21 of the ε-iron oxide particles 20 contains ε-iron oxide. The ε-iron oxide contained in the core portion 21 preferably has ε-Fe ₂ O ₃ crystals as the main phase, and more preferably composed of single-phase ε-Fe ₂ O ₃ .

The first shell portion 22a covers at least a part of the periphery of the core portion 21. Specifically, the first shell portion 22a may partially cover the periphery of the core portion 21, or may cover the entire periphery of the core portion 21. From the viewpoint of making the exchange coupling between the core portion 21 and the first shell portion 22a sufficient and improving the magnetic characteristics, it is preferable to cover the entire surface of the core portion 21.

The first shell portion 22a is a so-called soft magnetic layer, and contains, for example, a soft magnetic material such as α-Fe, Ni-Fe alloy or Fe-Si-Al alloy. α-Fe may be obtained by reducing ε-iron oxide contained in the core portion 21.

The second shell portion 22b is an oxide film as an antioxidant layer. The second shell portion 22b contains α-iron oxide, aluminum oxide or silicon oxide. The α-iron oxide contains, for example, at least one iron oxide of Fe ₃ O ₄ , Fe ₂ O ₃ and Fe O. When the first shell portion 22a contains α-Fe (soft magnetic material), the α-iron oxide may be obtained by oxidizing α-Fe contained in the first shell portion 22a.

Since the ε iron oxide particles 20 have the first shell portion 22a as described above, the ε iron oxide particles (core shell) keep the coercive force Hc of the core portion 21 alone at a large value in order to ensure thermal stability. The coercive force Hc of the particle) 20 as a whole can be adjusted to a coercive force Hc suitable for recording. Further, since the ε-iron oxide particles 20 have the second shell portion 22b as described above, the ε-iron oxide particles 20 are exposed to the air in the manufacturing process of the magnetic recording medium 10 and before the process, and the particle surface. It is possible to suppress deterioration of the characteristics of the ε iron oxide particles 20 due to the occurrence of rust or the like. Therefore, by covering the first shell portion 22a with the second shell portion 22b, deterioration of the characteristics of the magnetic recording medium 10 can be suppressed.

The average particle size (average maximum particle size) of the magnetic powder is preferably 25 nm or less, more preferably 8 nm or more and 22 nm or less, and even more preferably 12 nm or more and 22 nm or less. In the magnetic recording medium 10, a region having a size of 1/2 of the recording wavelength is the actual magnetization region. Therefore, good S / N can be obtained by setting the average particle size of the magnetic powder to half or less of the shortest recording wavelength. Therefore, when the average particle size of the magnetic powder is 22 nm or less, good electromagnetic waves are obtained in a magnetic recording medium 10 having a high recording density (for example, a magnetic recording medium 10 configured to be able to record a signal at the shortest recording wavelength of 50 nm or less). Conversion characteristics (eg SNR) can be obtained. On the other hand, when the average particle size of the magnetic powder is 8 nm or more, the dispersibility of the magnetic powder is further improved, and more excellent electromagnetic conversion characteristics (for example, SNR) can be obtained.

The average aspect ratio of the magnetic powder is preferably 1 or more and 3.0 or less, more preferably 1 or more and 2.8 or less, and even more preferably 1 or more and 1.8 or less. When the average aspect ratio of the magnetic powder is in the range of 1 or more and 3.0 or less, aggregation of the magnetic powder can be suppressed, and when the magnetic powder is vertically aligned in the process of forming the magnetic layer 13, the magnetic powder can be vertically oriented. The resistance applied to the can be suppressed. Therefore, the vertical orientation of the magnetic powder can be improved.

The average particle size and average aspect ratio of the above magnetic powder are obtained as follows. First, the magnetic recording medium 10 to be measured is processed by a FIB (Focused Ion Beam) method or the like to be thinned. Slicing is performed along the length direction (longitudinal direction) of the magnetic tape. That is, this thinning forms a cross section parallel to both the longitudinal direction and the thickness direction of the magnetic recording medium 10. Using a transmission electron microscope (H-9500 manufactured by Hitachi High-Technologies Corporation), the obtained flaky sample contains the entire magnetic layer 13 with respect to the thickness direction of the magnetic layer 13 at an acceleration voltage of 200 kV and a total magnification of 500,000 times. Observe the cross section and take a TEM photograph. Next, 50 particles are randomly selected from the TEM photographs taken, and the major axis length DL and the minor axis length DS of each particle are measured. Here, the major axis length DL means the maximum distance (so-called maximum ferret diameter) between two parallel lines drawn from all angles so as to be in contact with the contour of each particle. On the other hand, the minor axis length DS means the maximum length of the particles in the direction orthogonal to the major axis length DL of the particles.

Subsequently, the semi-major axis DL of the measured 50 particles is simply averaged (arithmetic mean) to obtain the average semi-major axis DL ave. The average major axis length DLave thus obtained is taken as the average particle size of the magnetic powder. Further, the average minor axis length DSave of the measured 50 particles is simply averaged (arithmetic mean) to obtain the average minor axis length DSave. Then, the average aspect ratio (DLave / DSave) of the particles is obtained from the average major axis length DLave and the average minor axis length DSave.

The average particle volume of the magnetic powder is preferably 5500Nm ³ or less, more preferably 270 nm ³ or more 5500Nm ³ or less, still more preferably 900 nm ³ or more 5500Nm ³ or less. When the average particle volume of the magnetic powder is 5500 nm ³ or less, the same effect as when the average particle size of the magnetic powder is 22 nm or less can be obtained. On the other hand, when the average particle volume of the magnetic powder is 270 nm ³ or more, the same effect as when the average particle size of the magnetic powder is 8 nm or more can be obtained.

When the ε iron oxide particles 20 have a spherical shape or a substantially spherical shape, the average particle volume of the magnetic powder can be obtained as follows. First, the average major axis length DLave is obtained in the same manner as the above method for calculating the average particle size of the magnetic powder. Next, the average volume V of the magnetic powder is calculated by the following formula.
V = (π / 6) × (DLave) ³

(Binder)
As the binder, a resin having a structure in which a cross-linking reaction is applied to a polyurethane resin, a vinyl chloride resin, or the like is preferable. However, the binder is not limited to these, and other resins may be appropriately blended depending on the physical properties required for the magnetic recording medium 10. The resin to be blended is not particularly limited as long as it is a resin generally used in the coating type magnetic recording medium 10.

For example, polyvinyl chloride, polyvinyl acetate, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, acrylic acid ester-acrylonitrile copolymer, acrylic acid ester-chloride. Vinyl-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, acrylic acid ester-acrylonitrile copolymer, acrylic acid ester-vinylidene chloride copolymer, methacrylic acid ester-vinylidene chloride copolymer, methacrylic acid ester-chloride Vinyl copolymer, methacrylic acid ester-ethylene copolymer, polyfluorinated vinyl, vinylidene chloride-acrylonitrile copolymer, acrylonitrile-butadiene copolymer, polyamide resin, polyvinyl butyral, cellulose derivative (cellulose acetate butyrate, cellulose die) Acetate, cellulose triacetate, cellulose propionate, nitrocellulose), styrene butadiene copolymer, polyester resin, amino resin, synthetic rubber and the like.

Examples of the thermosetting resin or reactive resin include phenol resin, epoxy resin, urea resin, melamine resin, alkyd resin, silicone resin, polyamine resin, urea formaldehyde resin and the like.

Further, in each of the above-mentioned binders, polar functional groups such as -SO ₃ M, -OSO ₃ M, -COOM, and P = O (OM) ₂ are introduced for the purpose of improving the dispersibility of the magnetic powder. May be. Here, M in the above chemical formula is a hydrogen atom or an alkali metal such as lithium, potassium, or sodium.

Furthermore, as the polar functional group, -NR1R2, -NR1R2R3 ⁺ X ^- as the side chain type having an end group of,> NR1R2 ⁺ X ^- include those of the main chain type. Here, R1, R2, and R3 in the above formula are hydrogen atoms or hydrocarbon groups, and X ^- is a halogen element ion such as fluorine, chlorine, bromine, or iodine, or an inorganic or organic ion. Further, examples of the polar functional group include -OH, -SH, -CN, and an epoxy group.

(lubricant)
The lubricant contained in the magnetic layer 13 contains, for example, a fatty acid and a fatty acid ester. The fatty acid contained in the lubricant preferably contains, for example, at least one of a compound represented by the following general formula <1> and a compound represented by the general formula <2>. The fatty acid ester contained in the lubricant preferably contains at least one of a compound represented by the following general formula <3> and a compound represented by the general formula <4>. When the lubricant contains two kinds of the compound represented by the general formula <1> and the compound represented by the general formula <3>, the compound represented by the general formula <2> and the compound represented by the general formula <3> By including two kinds of the compound represented by the general formula <1> and the compound represented by the general formula <4>, the compound represented by the general formula <2> and the compound represented by the general formula <4> By including two kinds of compounds represented by, the compound represented by the general formula <1>, the compound represented by the general formula <2>, and the compound represented by the general formula <3> are generally included. A compound represented by the general formula <1> and a compound represented by the general formula <3> by containing three types of a compound represented by the formula <1>, a compound represented by the general formula <2>, and a compound represented by the general formula <4>. >, And the compound represented by the general formula <4>, the compound represented by the general formula <2>, the compound represented by the general formula <3>, and the compound represented by the general formula <4>. By containing three kinds of the compounds, or represented by the compound represented by the general formula <1>, the compound represented by the general formula <2>, the compound represented by the general formula <3>, and the compound represented by the general formula <4>. By containing four kinds of compounds, it is possible to suppress an increase in the dynamic friction coefficient due to repeated recording or reproduction in the magnetic recording medium 10. As a result, the runnability of the magnetic recording medium 10 can be further improved.
CH ₃ (CH ₂ ) _k COOH ・ ・ ・ <1>
(However, in the general formula <1>, k is an integer selected from the range of 14 or more and 22 or less, more preferably 14 or more and 18 or less.)
CH ₃ (CH ₂ ) _n CH = CH (CH ₂ ) _m COOH ・ ・ ・ <2>
(However, in the general formula <2>, the sum of n and m is an integer selected from the range of 12 or more and 20 or less, more preferably 14 or more and 18 or less.)
CH ₃ (CH ₂ ) _p COO (CH ₂ ) _q CH ₃・ ・ ・ <3>
(However, in the general formula <3>, p is an integer selected from the range of 14 or more and 22 or less, more preferably 14 or more and 18 or less, and q is a range of 2 or more and 5 or less, more preferably 2 or more and 4 It is an integer selected from the following range.)
CH ₃ (CH ₂ ) _p COO- (CH ₂ ) _q CH (CH ₃ ) ₂ … <4>
(However, in the general formula <4>, p is an integer selected from the range of 14 or more and 22 or less, and q is an integer selected from the range of 1 or more and 3 or less.)

(Additive)
The magnetic layer 13 has aluminum oxide (α, β or γ alumina), chromium oxide, silicon oxide, diamond, garnet, emery, boron nitride, titanium carbide, silicon carbide, titanium carbide, and titanium oxide (titanium carbide) as non-magnetic reinforcing particles. Rutile-type or anatase-type titanium oxide) and the like may be further contained.

(Underground layer 12)
The base layer 12 is a non-magnetic layer containing a non-magnetic powder and a binder. The base layer 12 may further contain at least one additive such as a lubricant, conductive particles, a curing agent, and a rust preventive, if necessary. Further, the base layer 12 may have a multi-layer structure in which a plurality of layers are laminated. The average thickness of the base layer 12 is preferably 0.5 μm or more and 0.9 μm or less, and more preferably 0.6 μm or more and 0.7 μm or less. By reducing the average thickness of the base layer 12 to 0.9 μm or less, the Young ratio of the entire magnetic recording medium 10 is effectively reduced as compared with the case where the thickness of the substrate 11 is reduced. Therefore, tension control for the magnetic recording medium 10 becomes easy. Further, by setting the average thickness of the base layer 12 to 0.5 μm or more, the adhesive force between the base 11 and the base layer 12 is ensured. Moreover, the variation in the thickness of the base layer 12 can be suppressed, and the roughness of the surface 13S of the magnetic layer 13 can be prevented from becoming large.

The average thickness of the base layer 12 is determined as follows, for example. First, a 1/2 inch wide magnetic recording medium 10 is prepared, cut into a length of 250 mm, and a sample is prepared. Subsequently, the base layer 12 and the magnetic layer 13 of the sample magnetic recording medium 10 are peeled off from the substrate 11. Next, using a laser holo gauge (LGH-110C) manufactured by Mitutoyo Co., Ltd. as a measuring device, the thickness of the laminate of the base layer 12 and the magnetic layer 13 peeled off from the base 11 is measured at five or more points. To do. After that, the measured values are simply averaged (arithmetic mean) to calculate the average thickness of the laminate of the base layer 12 and the magnetic layer 13. The measurement position shall be randomly selected from the sample. Finally, the average thickness of the base layer 12 is obtained by subtracting the average thickness of the magnetic layer 13 measured by using TEM as described above from the average thickness of the laminated body.

The base layer 12 preferably has a large number of holes. By storing the lubricant in these many holes, the magnetic layer is formed even after repeated recording or reproduction (that is, even after the magnetic head is brought into contact with the surface of the magnetic recording medium 10 and repeated running). It is possible to further suppress a decrease in the amount of lubricant supplied between the surface 13S of 13 and the magnetic head. Therefore, the increase in the dynamic friction coefficient can be further suppressed.

From the viewpoint of suppressing a decrease in the dynamic friction coefficient after repeated recording or reproduction, it is preferable that the hole portion of the base layer 12 and the recess 13A of the magnetic layer 13 are connected. Here, the fact that the holes of the base layer 12 and the recesses 13A of the magnetic layer 13 are connected means that some of the holes of the base layer 12 and the many recesses 13A of the magnetic layer 13 are connected. It shall include the state where some of them are connected.

From the viewpoint of improving the supply of the lubricant to the surface 13S of the magnetic layer 13, it is preferable that a large number of holes include those extending in the direction perpendicular to the surface 13S of the magnetic layer 13. .. Further, from the viewpoint of improving the supply of the lubricant to the surface 13S of the magnetic layer 13, the holes of the base layer 12 extending in the direction perpendicular to the surface 13S of the magnetic layer 13 and the surface of the magnetic layer 13 It is preferable that the recess 13A of the magnetic layer 13 extending in the direction perpendicular to the 13S is connected.

(Non-magnetic powder of base layer 12)
The non-magnetic powder includes, for example, at least one of inorganic particle powder and organic particle powder. Further, the non-magnetic powder may contain carbon powder such as carbon black. In addition, one kind of non-magnetic powder may be used alone, or two or more kinds of non-magnetic powder may be used in combination. Inorganic particles include, for example, metals, metal oxides, metal carbonates, metal sulfates, metal nitrides, metal carbides, metal sulfides and the like. Examples of the shape of the non-magnetic powder include, but are not limited to, various shapes such as needle shape, spherical shape, cube shape, and plate shape.

(Bundling agent for the base layer 12)
The binder in the base layer 12 is the same as that in the magnetic layer 13 described above.

(Back layer 14)
The back layer 14 contains, for example, a binder and a non-magnetic powder. The back layer 14 may further contain at least one additive such as a lubricant, a curing agent and an antistatic agent, if necessary. The binder and non-magnetic powder in the back layer 14 are the same as the binder and non-magnetic powder in the base layer 12 described above.

The average particle size of the non-magnetic powder in the back layer 14 is preferably 10 nm or more and 150 nm or less, and more preferably 15 nm or more and 110 nm or less. The average particle size of the non-magnetic powder in the back layer 14 is obtained in the same manner as the average particle size of the magnetic powder in the magnetic layer 13 described above. The non-magnetic powder may include those having a particle size distribution of 2 or more.

The upper limit of the average thickness of the back layer 14 is preferably 0.6 μm or less, and particularly preferably 0.5 μm or less. When the upper limit of the average thickness of the back layer 14 is 0.6 μm or less, the thickness of the base layer 12 and the base 11 can be kept thick even when the average thickness of the magnetic recording medium 10 is 5.6 μm or less. , The running stability of the magnetic recording medium 10 in the recording / reproducing device can be maintained. The lower limit of the average thickness of the back layer 14 is not particularly limited, but is, for example, 0.2 μm or more, and particularly preferably 0.3 μm or more.

The average thickness of the back layer 14 is obtained as follows. First, a 1/2 inch wide magnetic recording medium 10 is prepared, cut into a length of 250 mm, and a sample is prepared. Next, using a laser holo gauge (LGH-110C) manufactured by Mitutoyo as a measuring device, the thickness of the magnetic recording medium 10 as a sample is measured at 5 points or more, and the measured values are simply averaged ( (Arithmetic mean) to calculate the average thickness t _T [μm] of the magnetic recording medium 10. The measurement position shall be randomly selected from the sample. Subsequently, the back layer 14 is removed from the magnetic recording medium 10 of the sample with a solvent such as MEK (methyl ethyl ketone) or dilute hydrochloric acid. After that, using the above laser holo gauge again, the thickness of the sample from which the back layer 14 is removed from the magnetic recording medium 10 is measured at 5 points or more, and the measured values are simply averaged (arithmetic mean) to back layer. The average thickness t _B [μm] of the magnetic recording medium 10 from which 14 has been removed is calculated. The measurement position shall be randomly selected from the sample. Finally, the average thickness t _b [μm] of the back layer 14 is obtained from the following formula.
t _b [μm] = t _T [μm] -t _B [μm]

As shown in FIG. 1, the back layer 14 has a surface provided with a large number of protrusions 14A. The large number of protrusions 14A is for forming a large number of recesses 13A on the surface 13S of the magnetic layer 13 in a state where the magnetic recording medium 10 is wound in a roll shape. The large number of recesses 13A is formed, for example, by a large number of non-magnetic particles protruding from the surface of the back layer 14.

(Average thickness of magnetic recording medium 10)
The upper limit of the average thickness (average total thickness) of the magnetic recording medium 10 is preferably 5.6 μm or less, more preferably 5.0 μm or less, particularly preferably 4.6 μm or less, and even more preferably 4.4 μm or less. .. When the average thickness of the magnetic recording medium 10 is 5.6 μm or less, the recording capacity that can be recorded in one data cartridge can be increased as compared with a general magnetic recording medium. The lower limit of the average thickness of the magnetic recording medium 10 is not particularly limited, but is, for example, 3.5 μm or more.

The average thickness tT of the magnetic recording medium 10 is obtained as follows. First, a 1/2 inch wide magnetic recording medium 10 is prepared, cut into a length of 250 mm, and a sample is prepared. Next, using a laser holo gauge (LGH-110C) manufactured by Mitutoyo as a measuring device, the thickness of the sample is measured at 5 or more points, and the measured values are simply averaged (arithmetic mean) and averaged. The value tT [μm] is calculated. The measurement position shall be randomly selected from the sample.

(Coercive force Hc)
The upper limit of the coercive force Hc in the longitudinal direction of the magnetic recording medium 10 is preferably 2000 Oe or less, more preferably 1900 Oe or less, and even more preferably 1800 Oe or less. When the coercive force Hc2 in the longitudinal direction is 2000 Oe or less, the magnetization reacts sensitively with the magnetic field in the vertical direction from the recording head, so that a good recording pattern can be formed.

The lower limit of the coercive force Hc measured in the longitudinal direction of the magnetic recording medium 10 is preferably 1000 Oe or more. When the lower limit of the coercive force Hc in the longitudinal direction is 1000 Oe or more, demagnetization due to leakage flux from the recording head can be suppressed.

The above coercive force Hc is obtained as follows. A measurement sample is prepared by stacking three magnetic recording media 10 and adhering them with a double-sided tape, and then punching them with a punch having a diameter of 6.39 mm. At this time, marking is performed with an arbitrary non-magnetic ink so that the longitudinal direction (traveling direction) of the magnetic recording medium can be recognized. Then, using a vibrating sample magnetometer (VSM), the MH loop of the measurement sample (entire magnetic recording medium 10) corresponding to the longitudinal direction of the magnetic recording medium 10 (traveling direction of the magnetic recording medium 10). To measure. Next, the coating film (base layer 12, magnetic layer 13, back layer 14, etc.) is wiped off with acetone, ethanol, or the like, leaving only the substrate 11. Then, three of the obtained substrates 11 are laminated and adhered with double-sided tape, and then punched out with a punch having a diameter of 6.39 mm to obtain a sample for background correction (hereinafter, simply referred to as a correction sample). After that, the MH loop of the correction sample (base 11) corresponding to the longitudinal direction of the base 11 (traveling direction of the magnetic recording medium 10) is measured using VSM.

In the measurement of the MH loop of the measurement sample (entire magnetic recording medium 10) and the MH loop of the correction sample (base 11), for example, a vibrating sample magnetometer "VSM-P7-" manufactured by Toei Kogyo Co., Ltd. Type 15 "is used. The measurement conditions are: measurement mode: full loop, maximum magnetic field: 15 kOe, magnetic field step: 40 bits, Time constant of Locking amp: 0.3 sec, Waiting time: 1 sec, MH average number: 20.

After obtaining two MH loops, background correction is performed by subtracting the MH loop of the correction sample (base 11) from the MH loop of the measurement sample (entire magnetic recording medium 10). , The MH loop after background correction is obtained. The measurement / analysis program attached to the "VSMP7-15 type" is used for the calculation of this background correction.

The coercive force Hc can be obtained from the obtained MH loop after background correction. The measurement / analysis program attached to the "VSM-P7-15 type" is used for this calculation. It is assumed that all the above-mentioned measurements of the MH loop are performed at 25 ° C. Further, it is assumed that "demagnetic field correction" is not performed when measuring the MH loop in the longitudinal direction of the magnetic recording medium 10.

(Square ratio)
The square ratio S1 of the magnetic recording medium 10 in the vertical direction (thickness direction) is, for example, 65% or more, preferably 67% or more, more preferably 70% or more, still more preferably 75% or more, and particularly preferably 80%. That is all. When the square ratio S1 is 65% or more, the vertical orientation of the magnetic powder becomes sufficiently high, so that a more excellent SNR can be obtained.

The square ratio S1 is obtained as follows. A measurement sample is prepared by stacking three magnetic recording media 10 and adhering them with double-sided tape, and then punching them with a punch having a diameter of 6.39 mm. At this time, marking is performed with an arbitrary non-magnetic ink so that the longitudinal direction (traveling direction) of the magnetic recording medium can be recognized. Then, using a vibrating sample magnetometer (VSM), the MH loop of the measurement sample (entire magnetic recording medium 10) corresponding to the longitudinal direction of the magnetic recording medium 10 (traveling direction of the magnetic recording medium 10). To measure. Next, the coating film (base layer 12, magnetic layer 13, back layer 14, etc.) is wiped off with acetone, ethanol, or the like, leaving only the substrate 11. Then, three of the obtained substrates 11 are laminated and adhered with double-sided tape, and then punched out with a punch having a diameter of 6.39 mm to obtain a sample for background correction (hereinafter, simply referred to as a correction sample). After that, the MH loop of the correction sample (base 11) corresponding to the longitudinal direction of the base 11 (traveling direction of the magnetic recording medium 10) is measured using VSM.

In the measurement of the MH loop of the measurement sample (entire magnetic recording medium 10) and the MH loop of the correction sample (base 11), for example, a vibrating sample magnetometer "VSM-P7-" manufactured by Toei Kogyo Co., Ltd. Type 15 "is used. The measurement conditions are: measurement mode: full loop, maximum magnetic field: 15 kOe, magnetic field step: 40 bits, Time constant of Locking amp: 0.3 sec, Waiting time: 1 sec, MH average number: 20.

After obtaining two MH loops, background correction is performed by subtracting the MH loop of the correction sample (base 11) from the MH loop of the measurement sample (entire magnetic recording medium 10). , The MH loop after background correction is obtained. The measurement / analysis program attached to the "VSMP7-15 type" is used for the calculation of this background correction.

Substituting the saturated magnetization Ms (emu) and residual magnetization Mr (emu) of the obtained background-corrected MH loop into the following equation, the square ratio S1 (%) is calculated.
Square ratio S1 (%) = (Mr / Ms) x 100
It is assumed that all the above-mentioned measurements of the MH loop are performed at 25 ° C. Further, it is assumed that "demagnetic field correction" is not performed when measuring the MH loop in the vertical direction of the magnetic recording medium 10.

The square ratio S2 in the longitudinal direction (traveling direction) of the magnetic recording medium 10 is preferably 35% or less, more preferably 30% or less, even more preferably 25% or less, particularly preferably 20% or less, and most preferably 15%. It is as follows. When the square ratio S2 is 35% or less, the vertical orientation of the magnetic powder becomes sufficiently high, so that a more excellent SNR can be obtained.

The square ratio S2 is obtained in the same manner as the square ratio S1 except that the MH loop is measured in the longitudinal direction (traveling direction) of the magnetic recording medium 10 and the substrate 11.

(SFD)
In the SFD (Switching Field Distribution) curve of the magnetic recording medium 10, the peak ratio X / Y of the main peak height X and the sub-peak height Y near zero magnetic field is preferably 3.0 or more, more preferably 3.0 or more. It is 5.0 or more, more preferably 7.0 or more, particularly preferably 10.0 or more, and most preferably 20.0 or more (see FIG. 5). When the peak ratio X / Y is 3.0 or more, in addition to the ε-iron oxide particles 20 that contribute to actual recording, low coercive force components peculiar to ε-iron oxide (for example, soft magnetic particles and superparamagnetic particles) are magnetic. It can be suppressed that it is contained in a large amount in the powder. Therefore, it is possible to suppress deterioration of the magnetization signal recorded on the adjacent track due to the leakage magnetic field from the recording head, so that a better SNR can be obtained. The upper limit of the peak ratio X / Y is not particularly limited, but is, for example, 100 or less.

The above peak ratio X / Y is obtained as follows. First, the MH loop after background correction is obtained in the same manner as the above-mentioned method for measuring the coercive force Hc. Next, the SFD curve is calculated from the obtained MH loop. A program attached to the measuring machine may be used for calculating the SFD curve, or another program may be used. Let "Y" be the absolute value of the point where the calculated SFD curve crosses the Y axis (dM / dH), and let "X" be the height of the main peak seen near the coercive force Hc in the MH loop. Calculate the peak ratio X / Y. It is assumed that the measurement of the MH loop is performed at 25 ° C. in the same manner as the above-mentioned method for measuring the coercive force Hc. Further, it is assumed that "demagnetic field correction" is not performed when measuring the MH loop in the thickness direction (vertical direction) of the magnetic recording medium 10. Further, the MH loop may be measured by stacking a plurality of samples to be measured according to the sensitivity of the VSM to be used.

(Activated volume Vact)
Activation volume Vact is preferably 8000 nm ³ or less, more preferably 6000 nm ³ or less, still more preferably 5000 nm ³ or less, particularly preferably 4000 nm ³ or less, most preferably 3000 nm ³ or less. When the activated volume Vact is 8000 nm ³ or less, the dispersed state of the magnetic powder becomes good, so that the bit inversion region can be steep, and the magnetization recorded on the adjacent track due to the leakage magnetic field from the recording head. It is possible to suppress the deterioration of the signal. Therefore, a better SNR can be obtained.

The above activated volume Vact is calculated by the following formula derived by Street & Woolley.
Vact (nm ³ ) = kB × T × Χirr / (μ0 × Ms × S)
(However, kB: Boltzmann constant (1.38 × 10 ^-23 J / K), T: temperature (K), Χirr: irreversible magnetic susceptibility, μ0: vacuum magnetic susceptibility, S: magnetic viscosity coefficient, Ms: saturation Magnetization (emu / cm ³ ))

The irreversible magnetic susceptibility Χirr, the saturation magnetization Ms, and the magnetic viscosity coefficient S substituted in the above equation can be obtained by using VSM as follows. The measurement sample used for VSM is produced by stacking three magnetic recording media 10 with double-sided tape and punching them with a punch having a diameter of 6.39 mm. At this time, marking is performed with an arbitrary non-magnetic ink so that the longitudinal direction (traveling direction) of the magnetic recording medium 10 can be recognized. The measurement direction by VSM is the thickness direction (vertical direction) of the magnetic recording medium 10. Further, the measurement by VSM shall be performed at 25 ° C. on the measurement sample cut out from the long magnetic recording medium 10. Further, it is assumed that "demagnetic field correction" is not performed when measuring the MH loop in the thickness direction (vertical direction) of the magnetic recording medium 10. Further, in the measurement of the MH loop of the measurement sample (the entire magnetic recording medium 10) and the MH loop of the correction sample (base 11), the high-sensitivity vibrating sample magnetometer "VSM" manufactured by Toei Kogyo Co., Ltd. -P7-15 type "is used. The measurement conditions are: measurement mode: full loop, maximum magnetic field: 15 kOe, magnetic field step: 40 bits, Time constant of Locking amp: 0.3 sec, Waiting time: 1 sec, MH average number: 20.

(Lossy susceptibility Χirr)
The irreversible magnetic susceptibility Χirr is defined as the slope near the residual coercive force Hr in the slope of the residual magnetization curve (DCD curve). First, a magnetic field of -1193 kA / m (15 kOe) is applied to the entire magnetic recording medium 10, and the magnetic field is returned to zero to be in a residual magnetization state. Then, a magnetic field of about 15.9 kA / m (200 Oe) is applied in the opposite direction to return it to zero again, and the residual magnetization amount is measured. After that, similarly, the measurement of applying a magnetic field 15.9 kA / m larger than the applied magnetic field to return it to zero is repeated, and the residual magnetization amount is plotted against the applied magnetic field to measure the DCD curve. From the obtained DCD curve, the point where the amount of magnetization becomes zero is defined as the residual coercive force Hr, and the DCD curve is further differentiated to obtain the slope of the DCD curve in each magnetic field. In the slope of this DCD curve, the slope near the residual coercive force Hr is Χirr.

(Saturation magnetization Ms)
First, the MH loop after background correction is obtained in the same manner as the above-mentioned method for measuring the coercive force Hc. Next, Ms (emu / cm ³ ) is calculated from the value of the saturation magnetization Ms (emu) of the obtained MH loop and the volume (cm ³ ) of the magnetic layer 13 in the measurement sample. The volume of the magnetic layer 13 is obtained by multiplying the area of the measurement sample by the average thickness of the magnetic layer 13. The method for calculating the average thickness of the magnetic layer 13 required for calculating the volume of the magnetic layer 13 is as described above.

(Magnetic viscosity coefficient S)
First, a magnetic field of -1193 kA / m (15 kOe) is applied to the entire magnetic recording medium 10 (measurement sample), and the magnetic field is returned to zero to be in a residual magnetization state. After that, a magnetic field equivalent to the value of the residual coercive force Hr obtained from the DCD curve is applied in the opposite direction. The amount of magnetization is continuously measured at regular time intervals for 1000 seconds while a magnetic field is applied. The magnetic viscosity coefficient S is calculated by comparing the relationship between the time t and the amount of magnetization M (t) obtained in this manner with the following equation.
M (t) = M0 + S × ln (t)
(However, M (t): magnetization amount at time t, M0: initial magnetization amount, S: magnetic viscosity coefficient, ln (t): natural logarithm of time)

(Friction coefficient ratio (μ _B / μ _A ))
The magnetic recording medium 10 preferably has a dynamic friction coefficient μ _A between the surface 13S of the magnetic layer 13 of the magnetic recording medium 10 and the magnetic head in a state where a tension of 0.4 N is applied in the longitudinal direction of the magnetic recording medium 10. , The friction coefficient ratio (μ _B /) of the dynamic friction coefficient μ _B between the surface 13S of the magnetic layer 13 of the magnetic recording medium 10 and the magnetic head in a state where a tension of 1.2 N is applied in the longitudinal direction of the magnetic recording medium 10. μ _A ) is 1.0 or more and 2.0 or less, more preferably 1.0 or more and 1.8 or less, and even more preferably 1.0 or more and 1.6 or less. When the friction coefficient ratio (μ _B / μ _A ) is within the above numerical range, the change in the dynamic friction coefficient due to the tension fluctuation during traveling can be reduced, so that the traveling of the magnetic recording medium 10 can be stabilized. ..

The dynamic friction coefficient μA and the dynamic friction coefficient μB for calculating the friction coefficient ratio (μB / μA) are obtained as follows. First, as shown in FIG. 8, the magnetic recording medium 10 having a width of 1/2 inch is placed on two 1-inch diameter columnar guide rolls 91 and 92 arranged in parallel with each other separated from each other by a magnetic layer 13. Place so that the surface 13S of the surface 13S is in contact with the surface. The positional relationship between the two guide rolls 91 and 92 is fixed.

Next, the surface 13S of the magnetic layer 13 comes into contact with the magnetic recording medium 10 with respect to the head block (for recording / playback) 93 mounted on the LTO5 drive, and the holding angle θ1 [°] = 5.6 °. To connect the magnetic recording medium 10 to the movable strain gauge 95 by grasping one end of the magnetic recording medium 10 with the jig 94, and suspending the weight 96 from the other end of the magnetic recording medium 10 to apply a tension T0 of 0.4N. Give. The head block 93 is fixed at a position where the holding angle θ1 [°] is 5.6 °. As a result, the positional relationship between the guide rolls 91 and 92 and the head block 93 is also fixed.

Next, the movable strain gauge 95 slides the magnetic recording medium 10 with respect to the head block 93 at a speed of 10 mm / s toward the movable strain gauge 95 by 60 mm. The output value (voltage) of the movable strain gauge 95 at the time of sliding is converted into T [N] based on the linear relationship (described later) between the output value and the load acquired in advance. Obtain T [N] 13 times from the start of sliding of 60 mm to the stop of sliding, and simply average 11 T [N] excluding the first and last two times. _{Provides Save} [N].
After that, the coefficient of dynamic friction μ _A is calculated from the following equation.

The above linear relationship is obtained as follows. That is, the output value (voltage) of the movable strain gauge 95 is obtained for each of the case where a load of 0.4 N is applied to the movable strain gauge 95 and the case where a load of 1.5 N is applied to the movable strain gauge 95. From the two output values obtained and the two loads, a linear relationship between the output value and the load can be obtained. Using the linear relationship, the output value (voltage) by the movable strain gauge 95 during sliding is converted to T [N] as described above.

The dynamic friction coefficient μ _B is measured by the same method as the method for measuring the dynamic friction coefficient μ _A , except that the tension T ₀ [N] applied to the other end is 1.2 N.
The friction coefficient ratio (μ _B / μ _A ) is calculated from the dynamic friction coefficient μ _A and the dynamic friction coefficient μ _B measured as described above.

When the coefficient of dynamic friction between the surface 13S of the magnetic layer 13 and the magnetic head when the tension applied to the magnetic recording medium 10 is 0.6 N is μC, the coefficient of dynamic friction μC (5) for the fifth time from the start of running and the start of running The coefficient of friction ratio (μC (1000) / μC (5)) with the dynamic friction coefficient μC (1000) at the 1000th time is preferably 1.0 or more and 1.9 or less, and more preferably 1.2 or more and 1.8 or less. Is. When the friction coefficient ratio (μC (1000) / μC (5)) is 1.0 or more and 1.9 or less, the change in the dynamic friction coefficient due to multiple running can be reduced, so that the running of the magnetic recording medium 10 is stabilized. be able to. Here, as the magnetic head, a drive corresponding to the magnetic recording medium 10 is used.

(Friction coefficient ratio (μ _{C (1000)} / μ _{C (5)} ))
The dynamic friction coefficient μC (5) and the dynamic friction coefficient μC (1000) for calculating the friction coefficient ratio (μC (1000) / μC (5)) are obtained as follows.

The magnetic recording medium 10 preferably has a coefficient of dynamic friction μ _{C (6)} in the fifth round trip when the magnetic recording medium in a state where a tension of 0.6 N is applied in the longitudinal direction is slid back and forth on the magnetic head five times. _The coefficient of friction ratio (μ _{C (1000)} / μ _{C (5)} ) between ₅₎ and the dynamic friction coefficient μ _{C (1000) at} the 1000th reciprocation when the magnetic head is reciprocated 1000 times is 1.0 to 2. It is .0, more preferably 1.0 to 1.8, and even more preferably 1.0 to 1.6. When the friction coefficient ratio (μ _{C (1000)} / μ _{C (5)} ) is within the above numerical range, the change in the dynamic friction coefficient due to multiple runs can be reduced, so that the running of the magnetic recording medium 10 is stable. Can be made to.

さらに、動摩擦係数μ_C(1000)は、１０００回目の往路の測定をすること以外は動摩擦係数μ_C(5)と同様にして求める。
以上のとおりにして測定された動摩擦係数μ_C(5)及び動摩擦係数μ_C(1000)から、摩擦係数比μ_C(1000)／μ_C(5)が算出される。 The coefficient of dynamic friction μ _{C (5)} and the coefficient of dynamic friction μ _{C (1000)} for calculating the friction coefficient ratio (μ _{C (1000)} / μ _{C (5)} ) are obtained as follows.
The magnetic recording medium 10 is mounted on the movable strain gauge 71 in the same manner as the method for measuring the dynamic friction coefficient μ _A , except that the tension T ₀ [N] applied to the other end of the magnetic recording medium 10 is 0.6 N. Connect with. Then, the magnetic recording medium 10 is slid 60 mm toward the movable strain gauge at 10 mm / s with respect to the head block 74 (outward route) and 60 mm away from the movable strain gauge (return route). This reciprocating operation is repeated 1000 times. Of these 1000 reciprocating movements, the output value (voltage) of the strain gauge was acquired 13 times during the period from the start of sliding of 60 mm on the 5th outbound route to the stop of sliding, and the coefficient of dynamic friction was μ _A. Convert to T [N] based on the linear relationship between the output value and the load obtained in. _Save [N] is calculated by simply averaging 11 pieces excluding the first and last two times. The coefficient of dynamic friction μ _{C (5)} is calculated by the following formula.

Further, the dynamic friction coefficient μ _{C (1000)} is obtained in the same manner as the dynamic friction coefficient μ _{C (5)} except that the 1000th outbound measurement is performed.
From the dynamic friction coefficient μ _{C (5)} and the dynamic friction coefficient μ _{C (1000)} measured as described above, the friction coefficient ratio μ _{C (1000)} / μ _{C (5)} is calculated.

(Logarithmic decrement obtained by pendulum viscoelasticity test)
The logarithmic decrement (hereinafter, simply referred to as logarithmic decrement) determined by the pendulum viscoelasticity test at a temperature of 10 ° C. or higher and 45 ° C. or lower on the surface 13S of the magnetic layer 13 is 0.025 or higher and 0.035 or lower. Further, at a temperature of 10 ° C. or higher and 45 ° C. or lower, the difference between the maximum value of the logarithmic decrement and the minimum value of the logarithmic decrement is 0 or more and 0.020 or less. The logarithmic decrement rate referred to here means that the higher the value, the stronger the viscosity, and the lower the ratio, the stronger the elasticity. The temperature range of 10 ° C. or higher and 45 ° C. or lower is usually a temperature range in which the magnetic recording medium 10 is expected to be used. By optimizing the viscoelasticity of the surface 13S of the magnetic layer 13 in such a temperature range, the pulverization of the constituent material itself of the magnetic layer 13, which is sometimes called powder dropping, is suppressed. As a result, the contact between the magnetic head and the surface of the magnetic layer can be maintained well and stably during the recording operation and / or the reproduction operation of the magnetic recording medium 10.

The logarithmic decrement rate is a value obtained by the following method using, for example, a pendulum viscoelasticity tester. As the pendulum viscoelasticity tester, for example, a rigid pendulum type physical property tester RPT-3000W manufactured by A & D Co., Ltd. can be used. 6 to 8 are explanatory views of the first to third methods for measuring the logarithmic decrement rate by the pendulum viscoelasticity test. Hereinafter, a method for measuring the logarithmic decrement rate will be described with reference to these drawings. However, the illustrated embodiments are exemplary and do not limit the disclosure in any way.

A 1/2 inch wide tape of 25 mm is cut out from the magnetic recording medium 10 to be measured as a measurement sample 100. The cut-out sample 100 for measurement is placed on the substrate 103 with the measurement surface (surface 13S of the magnetic layer 13) facing upward on the sample stage 101 in the pendulum viscoelasticity tester, and there are obvious wrinkles that can be visually confirmed. In the unfinished state, fix it with Kapton tape 105.

Next, a cylindrical cylinder edge 104 with a pendulum (diameter 4 mm) having a mass of 13 g is placed on the measurement surface of the measurement sample 100 so that the long axis direction of the cylinder edge 104 is perpendicular to the longitudinal direction of the measurement sample 100. Put it on. FIG. 6 shows an example of a state in which the cylindrical cylinder edge 104 with a pendulum is placed on the measurement surface of the measurement sample 100 (state viewed from above). In the embodiment shown in FIG. 6, the temperature sensor 102 is installed on the tape so that the temperature of the tape can be measured, and the surface temperature of the substrate 103 can be monitored. The longitudinal direction of the measurement sample 100 is the direction indicated by the arrow in the figure in the embodiment shown in FIG. 6, and refers to the longitudinal direction in the magnetic recording medium 10 from which the measurement sample 100 is cut out. In the present disclosure, "vertical" shall include the range of error allowed in the technical field to which this disclosure belongs. The range of the above error means, for example, a range of less than the exact vertical ± 10 °. Further, as the pendulum 107 (see FIG. 7), a pendulum made of a material (for example, made of metal, alloy, etc.) having a property of being attracted to a magnet is used.

While raising the surface temperature of the substrate 103 on which the measurement sample 100 is placed from 0 ° C. to 50 ° C. at a heating rate of 2.5 ° C./min or less, the pendulum movement is performed and the pendulum 107 and the magnet 106 are attracted to each other. Start (induce initial vibration) by releasing. FIG. 7 shows an example of the state (state seen from the side) of the pendulum 107 in which the pendulum is moving. In the embodiment shown in FIG. 7, the pendulum motion is performed by stopping the energization of the magnet (electromagnet) 106 arranged below the sample stage (turning off the switch) and releasing the attraction in the pendulum viscoelasticity tester. The pendulum movement is stopped by starting and resuming the energization of the electromagnet (turning on the switch) and attracting the pendulum 107 to the magnet 106. During the pendulum movement, the pendulum 107 repeats its amplitude, as shown in FIG. From the result obtained by monitoring the displacement of the pendulum with the displacement sensor 108 while the pendulum repeats the amplitude, a displacement-time curve with the displacement on the vertical axis and the elapsed time on the horizontal axis is obtained. An example of the displacement-time curve is shown in FIG. In FIG. 8, the correspondence between the state of the pendulum 107 and the displacement-time curve is schematically shown. At regular measurement intervals, stationary (adsorption) and pendulum motion are repeated, and the logarithmic decrement rate Δ (no unit) is obtained from the following formula using the obtained displacement-time curve, and this value is obtained from the magnetic recording medium. Let it be the logarithmic decrement of the surface 13S of the magnetic layer 13 of 10. The adsorption time for one adsorption is 1 second or longer (any time is acceptable as long as it is 1 second or longer), and the interval from the end of adsorption to the start of the next adsorption is 6 seconds or longer (arbitrary if it is 6 seconds or longer). Time is fine.) The measurement interval is an interval of time from the start of adsorption to the start of the next adsorption. The humidity of the environment in which the pendulum movement is performed may be any relative humidity as long as the relative humidity is in the range of 40 to 70%.

In the displacement-time curve, the interval from the minimum displacement to the minimum displacement again is defined as one cycle of the wave. Let n be the number of waves included in the displacement-time curve during the measurement interval, and let An be the difference between the minimum displacement and the maximum displacement in the nth wave. In FIG. 8, the interval from the minimum displacement to the minimum displacement of the nth wave is indicated as Tn (for example, T1 for the first wave, T2 for the second wave, and T3 for the third wave). .. To calculate the logarithmic decrement, the difference between the minimum displacement and the maximum displacement that appears next to the nth wave (An + 1 in the above number 1, A4 in the displacement-time curve shown in FIG. 8) is also used, but after the maximum. The portion where the pendulum 107 is stationary (adsorbed) is not used for counting the number of waves. Further, the portion where the pendulum 107 is stationary (adsorbed) before the maximum displacement is not used for counting the wave number. Therefore, in the displacement-time curve shown in FIG. 8, the number of waves is three (n = 3).

[1-2 Manufacturing Method of Magnetic Recording Medium 10]
Next, a method of manufacturing the magnetic recording medium 10 having the above-described configuration will be described. First, a paint for forming an underlayer is prepared by kneading and dispersing a non-magnetic powder, a binder, a lubricant and the like in a solvent. Next, a paint for forming a magnetic layer is prepared by kneading and dispersing a magnetic powder, a binder, a lubricant and the like in a solvent. Next, a coating material for forming a back layer is prepared by kneading and dispersing a binder, a non-magnetic powder and the like in a solvent. For the preparation of the paint for forming the magnetic layer, the paint for forming the base layer, and the paint for forming the back layer, for example, the following solvent, dispersion device, and kneading device can be used.

Examples of the solvent used for preparing the above-mentioned paint include a ketone solvent such as acetone, methyl ethyl ketone, methyl isobutyl ketone and cyclohexanone, an alcohol solvent such as methanol, ethanol and propanol, methyl acetate, ethyl acetate, butyl acetate and propyl acetate. , Ester solvents such as ethyl lactate and ethylene glycol acetate, ether solvents such as diethylene glycol dimethyl ether, 2-ethoxyethanol, tetrahydrofuran and dioxane, aromatic hydrocarbon solvents such as benzene, toluene and xylene, methylene chloride, ethylene chloride, Examples thereof include halogenated hydrocarbon solvents such as carbon tetrachloride, chloroform and chlorobenzene. These may be used alone or may be mixed appropriately.

As the kneading device used for the above-mentioned paint preparation, for example, a continuous twin-screw kneader, a continuous twin-screw kneader that can be diluted in multiple stages, a kneader, a pressure kneader, a roll kneader, or the like can be used. However, the device is not particularly limited to these devices. Further, as the disperser used for the above-mentioned paint preparation, for example, a roll mill, a ball mill, a horizontal sand mill, a vertical sand mill, a spike mill, a pin mill, a tower mill, a pearl mill (for example, "DCP mill" manufactured by Eirich), a homogenizer, and an ultrasonic mill. Dispersing devices such as a sound wave disperser can be used, but the device is not particularly limited to these devices.

Next, the base layer 12 is formed by applying the base layer forming paint to one main surface 11A of the base 11 and drying it. Subsequently, the magnetic layer forming paint is applied onto the base layer 12 and dried to form the magnetic layer 13 on the base layer 12. At the time of drying, it is preferable that the magnetic powder is magnetically oriented in the thickness direction of the substrate 11 by, for example, a solenoid coil. Further, at the time of drying, the magnetic powder may be magnetically oriented in the traveling direction (longitudinal direction) of the substrate 11 by, for example, a solenoid coil, and then magnetically oriented in the thickness direction of the substrate 11. By performing such a magnetic field orientation treatment, the degree of vertical orientation of the magnetic powder (that is, the square ratio S1) can be improved. After the magnetic layer 13 is formed, the back layer forming paint is applied to the other main surface 11B of the substrate 11 and dried to form the back layer 14. As a result, the magnetic recording medium 10 is obtained.

The square ratios S1 and S2 are, for example, the strength of the magnetic field applied to the coating film of the magnetic layer forming paint, the concentration of solid content in the magnetic layer forming paint, and the drying conditions (drying) of the coating film of the magnetic layer forming paint. The desired value is set by adjusting the temperature and drying time). The strength of the magnetic field applied to the coating film is preferably twice or more the coercive force of the magnetic powder. In order to further increase the square ratio S1 (that is, to further reduce the square ratio S2), it is preferable to improve the dispersed state of the magnetic powder in the paint for forming the magnetic layer. Further, in order to further increase the square ratio S1, it is also effective to magnetize the magnetic powder at a stage before the paint for forming the magnetic layer enters the alignment device for magnetically aligning the magnetic powder. The above-mentioned methods for adjusting the square ratios S1 and S2 may be used alone or in combination of two or more.

Then, the obtained magnetic recording medium 10 is subjected to calendar processing to smooth the surface 13S of the magnetic layer 13. Next, the magnetic recording medium 10 subjected to the calendar processing is wound into a roll shape, and then the magnetic recording medium 10 is heat-treated in this state to form a large number of protrusions 14A on the surface 14S of the back layer 14. Transfer to the surface 13S of the magnetic layer 13. As a result, a large number of recesses 13A are formed on the surface 13S of the magnetic layer 13.

The temperature of the heat treatment is preferably 50 ° C. or higher and 80 ° C. or lower. When the temperature of the heat treatment is 50 ° C. or higher, good transferability can be obtained. On the other hand, if the heat treatment temperature is 80 ° C. or lower, the amount of pores becomes too large, and the amount of lubricant on the surface 13S of the magnetic layer 13 may become excessive. Here, the temperature of the heat treatment is the temperature of the atmosphere that holds the magnetic recording medium 10.

The heat treatment time is preferably 15 hours or more and 40 hours or less. When the heat treatment time is 15 hours or more, good transferability can be obtained. On the other hand, when the heat treatment time is 40 hours or less, the decrease in productivity can be suppressed.

Further, the range of pressure applied to the magnetic recording medium 10 during the heat treatment is preferably 150 kg / cm or more and 400 kg / cm or less.

Finally, the magnetic recording medium 10 is cut into a predetermined width (for example, 1/2 inch width). From the above, the target magnetic recording medium 10 can be obtained.

[1-3 Configuration of recording / playback device 30]
Next, with reference to FIG. 9, the configuration of the recording / reproducing device 30 for recording the information on the above-mentioned magnetic recording medium 10 and reproducing the information from the above-mentioned magnetic recording medium 10 will be described.

The recording / reproducing device 30 has a configuration in which the tension applied in the longitudinal direction of the magnetic recording medium 10 can be adjusted. Further, the recording / reproducing device 30 has a configuration in which the magnetic recording medium cartridge 10A can be loaded. Here, for the sake of simplicity, a case where the recording / reproducing device 30 has a configuration in which one magnetic recording medium cartridge 10A can be loaded will be described. However, in the present disclosure, the recording / reproducing device 30 may have a configuration in which a plurality of magnetic recording medium cartridges 10A can be loaded. As described above, the magnetic recording medium 10 is in the form of a tape, and may be, for example, a long magnetic recording tape. The magnetic recording medium 10 may be housed in the housing in a state of being wound around a reel inside the magnetic recording medium cartridge 10A, for example. The magnetic recording medium 10 is adapted to travel in the longitudinal direction during recording and reproduction. Further, the magnetic recording medium 10 may be configured to be capable of recording a signal at the shortest recording wavelength of preferably 100 nm or less, more preferably 75 nm or less, even more preferably 60 nm or less, and particularly preferably 50 nm or less, for example, the shortest recording. It can be used in the recording / reproducing device 30 whose wavelength is within the above range. The recording track width can be, for example, 2 μm or less.

The recording / playback device 30 is connected to an information processing device such as a server 41 and a personal computer (hereinafter referred to as “PC”) 42 via a network 43, and magnetically records data supplied from these information processing devices. It is configured to be recordable on the medium cartridge 10A.

As shown in FIG. 9, the recording / playback device 30 includes a spindle 31, a reel 32, a drive device 33, a drive device 34, a plurality of guide rollers 35, a head unit 36, and a communication interface (hereinafter, I). (Indicated as / F) 37 and a control device 38 are provided.

The spindle 31 is configured so that the magnetic recording medium cartridge 10A can be mounted. The magnetic recording medium cartridge 10A conforms to the LTO (Linear Tape Open) standard, and rotatably accommodates a single reel 10C in which the magnetic recording medium 10 is wound in a cartridge case 10B. A V-shaped servo pattern is pre-recorded on the magnetic recording medium 10 as a servo signal. The reel 32 is configured so that the tip of the magnetic recording medium 10 drawn from the magnetic recording medium cartridge 10A can be fixed.

The drive device 33 is a device that rotationally drives the spindle 31. The drive device 34 is a device that rotationally drives the reel 32. When recording or reproducing data on the magnetic recording medium 10, the drive device 33 and the drive device 34 rotate the spindle 31 and the reel 32, respectively, to drive the magnetic recording medium 10. The guide roller 35 is a roller for guiding the traveling of the magnetic recording medium 10.

The head unit 36 includes a plurality of recording heads for recording a data signal on the magnetic recording medium 10, a plurality of reproduction heads for reproducing the data signal recorded on the magnetic recording medium 10, and the magnetic recording medium 10. It is provided with a plurality of servo heads for reproducing the recorded servo signal. A ring-type head can be used as the recording head, and a magnetoresistive magnetic head can be used as the playback head, but the types of the recording head and the playback head are not limited to this.

The I / F 37 is for communicating with an information processing device such as a server 41 and a PC 42, and is connected to a network 43.

The control device 38 controls the entire recording / playback device 30. For example, the control device 38 records the data signal supplied from the information processing device on the magnetic recording medium 10 by the head unit 36 in response to the request of the information processing device such as the server 41 and the PC 42. Further, the control device 38 reproduces the data signal recorded on the magnetic recording medium 10 by the head unit 36 and supplies the data signal to the information processing device in response to the request of the information processing device such as the server 41 and the PC 42.

[1-4 effect]
As described above, the magnetic recording medium 10 of the present embodiment is a tape-shaped member in which the substrate 11, the base layer 12, the magnetic layer 13, and the back layer 14 are laminated in this order, and the following (1) to (9). ), It is designed to meet each configuration requirement.
(1) On the surface 13S of the magnetic layer 13, 20 or more and 200 or less dents 13A having a depth of 20% or more of the average thickness of the magnetic layer 13 are formed per 1600 μm ² .
(2) On the surface 13S of the magnetic layer 13, 20 or more and 200 or less recesses 13A having a depth of 20% or more of the average thickness of the magnetic layer 13 are formed per 1600 μm ² .
(3) The logarithmic decrement obtained by the pendulum viscoelasticity test at a temperature of 10 ° C. or higher and 45 ° C. or lower on the surface 13S of the magnetic layer 13 is 0.025 or higher and 0.035 or lower.
(4) The maximum value of the logarithmic decrement obtained by the pendulum viscoelasticity test at a temperature of 10 ° C. or higher and 45 ° C. or lower, and the minimum value of the logarithmic decrement rate obtained by the pendulum viscoelasticity test at a temperature of 10 ° C. or higher and 45 ° C. The difference is 0 or more and 0.020 or less.
(5) The square ratio of the magnetic recording medium 10 in the vertical direction is 65% or more.
(6) The average thickness of the magnetic layer 13 is 90 nm or less.
(7) The average thickness of the magnetic recording medium 10 is 5.6 μm or less.

By having such a configuration, the magnetic recording medium 10 of the present embodiment can maintain good electromagnetic conversion characteristics even after the total thickness is reduced and repeated recording or repeated reproduction is performed. By providing a plurality of recesses 13A formed with an appropriate surface density, air entrained during traveling of the magnetic recording medium 10 can be released from the interface between the surface 13S of the magnetic layer 13 and the head, and the pendulum viscoelasticity can be released. It is considered that the contact between the surface 13S of the magnetic layer 13 and the head can be kept good by controlling the logarithmic decrement rate obtained by the test.

<2. Modification example>
(Modification example 1)
In the above embodiment, the ε-iron oxide particles 20 (FIG. 4) having the shell portion 22 having a two-layer structure have been illustrated and described, but the magnetic recording medium of the present technology is, for example, as shown in FIG. , Ε Iron oxide particles 20A having a shell portion 23 having a single layer structure may be included. The shell portion 23 of the ε iron oxide particles 20A has, for example, the same configuration as the first shell portion 22a. However, from the viewpoint of suppressing deterioration of characteristics, the ε-iron oxide particles 20 having the shell portion 22 having the two-layer structure described in the above embodiment are preferable to the ε-iron oxide particles 20A of the first modification.

(Modification 2)
In the magnetic recording medium 10 of the above-described embodiment, the ε-iron oxide particles 20 having a core-shell structure have been illustrated and described. However, the ε-iron oxide particles may contain an additive instead of the core-shell structure. It may have a core-shell structure and may contain additives. In this case, a part of Fe of the ε iron oxide particles is replaced with an additive. Even when the ε-iron oxide particles contain an additive, the coercive force Hc of the entire ε-iron oxide particles can be adjusted to a coercive force Hc suitable for recording, so that the ease of recording can be improved. The additive is a metal element other than iron, preferably a trivalent metal element, more preferably at least one of Al (aluminum), Ga (gallium) and In (indium), and even more preferably Al and Ga. At least one of them.

Specifically, the ε-iron oxide containing the additive is an ε-Fe _2- xMxO ₃ crystal (where M is a metal element other than iron, preferably a trivalent metal element, more preferably Al, Ga and In. At least one of them, and even more preferably at least one of Al and Ga. X is, for example, 0 <x <1).

(Modification 3)
The magnetic powder of the present disclosure may contain a powder of nanoparticles containing hexagonal ferrite (hereinafter referred to as “hexagonal ferrite particle”) instead of the powder of ε-iron oxide particles. The hexagonal ferrite particles have, for example, a hexagonal plate shape or a substantially hexagonal plate shape. The hexagonal ferrite preferably contains at least one of Ba (barium), Sr (strontium), Pb (lead) and Ca (calcium), and more preferably at least one of Ba and Sr. Specifically, the hexagonal ferrite may be, for example, barium ferrite or strontium ferrite. The barium ferrite may further contain at least one of Sr, Pb and Ca in addition to Ba. The strontium ferrite may further contain at least one of Ba, Pb and Ca in addition to Sr.

More specifically, hexagonal ferrite has an average composition represented by the general formula MFe ₁₂ O ₁₉ . However, M is, for example, at least one metal among Ba, Sr, Pb and Ca, preferably at least one metal among Ba and Sr. M may be a combination of Ba and one or more metals selected from the group consisting of Sr, Pb and Ca. Further, M may be a combination of Sr and one or more metals selected from the group consisting of Ba, Pb and Ca. In the above general formula, a part of Fe may be replaced with another metal element.

When the magnetic powder contains hexagonal ferrite particle powder, the average particle size of the magnetic powder is preferably 50 nm or less, more preferably 40 nm or less, and even more preferably 30 nm or less. The average particle size of the magnetic powder is preferably 25 nm or less, 22 nm or less, 21 nm or less, or 20 nm or less. The average particle size of the magnetic powder is, for example, 10 nm or more, preferably 12 nm or more, and more preferably 15 nm or more. Therefore, the average particle size of the magnetic powder containing the hexagonal ferrite particle powder can be, for example, 10 nm or more and 50 nm or less, 10 nm or more and 40 nm or less, 12 nm or more and 30 nm or less, 12 nm or more and 25 nm or less, or 15 nm or more and 22 nm or less. When the average particle size of the magnetic powder is not more than the above upper limit value (for example, 50 nm or less, particularly 30 nm or less), good electromagnetic conversion characteristics (for example, SNR) can be obtained in the magnetic recording medium 10 having a high recording density. Can be done. When the average particle size of the magnetic powder is not less than the above lower limit value (for example, when it is 10 nm or more, preferably 12 nm or more), the dispersibility of the magnetic powder is further improved, and more excellent electromagnetic conversion characteristics (for example, SNR) are obtained. be able to.

When the magnetic powder contains hexagonal ferrite particle powder, the average aspect ratio of the magnetic powder is preferably 1 or more and 3.5 or less, more preferably 1 or more and 3.1 or less, or 2 or more and 3.1 or less, and even more. It can be preferably 2 or more and 3 or less. When the average aspect ratio of the magnetic powder is within the above numerical range, aggregation of the magnetic powder can be suppressed, and further, resistance applied to the magnetic powder when the magnetic powder is vertically aligned in the process of forming the magnetic layer 13. Can be suppressed. This can result in improved vertical orientation of the magnetic powder.

The average particle size and average aspect ratio of the magnetic powder containing the hexagonal ferrite particle powder can be obtained as follows. First, the magnetic recording medium 10 to be measured is processed by a FIB (Focused Ion Beam) method or the like to be thinned. Slicing is performed along the length direction (longitudinal direction) of the magnetic tape. For the obtained flaky sample, a transmission electron microscope (H-9500 manufactured by Hitachi High-Technologies Corporation) was used so that the entire recording layer was included in the thickness direction of the recording layer at an accelerating voltage of 200 kV and a total magnification of 500,000 times. Observe the cross section. Next, 50 particles whose sides are oriented in the direction of the observation surface are selected from the photographed TEM photograph, and the maximum plate thickness DA of each particle is measured. The maximum plate thickness DA obtained in this way is simply averaged (arithmetic mean) to obtain the average maximum plate thickness DAave. Subsequently, the plate diameter DB of each magnetic powder is measured. Here, the plate diameter DB means the maximum distance (so-called maximum ferret diameter) between two parallel lines drawn from all angles so as to be in contact with the contour of the magnetic powder. Subsequently, the measured plate diameter DB is simply averaged (arithmetic mean) to obtain the average plate diameter DBave. Then, the average aspect ratio (DBave / DAave) of the particles is obtained from the average maximum plate thickness DAave and the average plate diameter DBave.

If the magnetic powder contains a powder of hexagonal ferrite particles, average particle volume of the magnetic powder is preferably 5900Nm ³ or less, more preferably 500 nm ³ or more 3400 nm ³ or less, still more preferably 1000 nm ³ or more 2500 nm ³ or less. When the average particle volume of the magnetic powder is 5900 nm ³ or less, the same effect as when the average particle size of the magnetic powder is 30 nm or less can be obtained. On the other hand, when the average particle volume of the magnetic powder is 500 nm ³ or more, the same effect as when the average particle size of the magnetic powder is 12 nm or more can be obtained.

The average particle volume of the magnetic powder is obtained as follows. First, the average maximum plate thickness DAave and the average maximum plate diameter DBave are obtained by the above-mentioned method for calculating the average particle size of the magnetic powder. Next, the average volume V of the ε iron oxide particles is obtained by the following formula.

According to a particularly preferred embodiment of the present technology, the magnetic powder may be barium ferrite magnetic powder or strontium ferrite magnetic powder, more preferably barium ferrite magnetic powder. The barium ferrite magnetic powder contains magnetic particles of iron oxide having barium ferrite as the main phase (hereinafter referred to as "barium ferrite particles"). The barium ferrite magnetic powder has high reliability of data recording, for example, the coercive force does not decrease even in a high temperature and high humidity environment. From this point of view, the barium ferrite magnetic powder is preferable as the magnetic powder.

The average particle size of the barium ferrite magnetic powder is 50 nm or less, more preferably 10 nm or more and 40 nm or less, and even more preferably 12 nm or more and 25 nm or less.

When the magnetic layer 13 contains barium ferrite magnetic powder as the magnetic powder, the average thickness tm [nm] of the magnetic layer 13 is preferably 35 nm ≦ tm ≦ 100 nm, and particularly preferably 80 nm or less. The coercive force Hc measured in the thickness direction (vertical direction) of the magnetic recording medium 10 is preferably 160 kA / m or more and 280 kA / m or less, more preferably 165 kA / m or more and 275 kA / m or less, and even more preferably 170 kA / m. It is m or more and 270 kA / m or less.

(Modification example 4)
The magnetic powder may contain powder of nanoparticles containing Co-containing spinel ferrite (hereinafter referred to as “cobalt ferrite particles”) instead of the powder of ε-iron oxide particles. The cobalt ferrite particles preferably have uniaxial crystal anisotropy. The cobalt ferrite particles have, for example, a cubic shape or a substantially cubic shape. The Co-containing spinel ferrite may further contain at least one of Ni, Mn, Al, Cu and Zn in addition to Co.

The Co-containing spinel ferrite has, for example, an average composition represented by the following formula.
Co _x M _y Fe ₂ O _Z
(However, in the formula (1), M is, for example, at least one metal of Ni, Mn, Al, Cu and Zn. X is within the range of 0.4 ≦ x ≦ 1.0. The value y is a value within the range of 0 ≦ y ≦ 0.3. However, x and y satisfy the relationship of (x + y) ≦ 1.0. Z is within the range of 3 ≦ z ≦ 4. It is a value of. A part of Fe may be replaced with another metal element.)

When the magnetic powder contains cobalt ferrite particle powder, the average particle size of the magnetic powder is preferably 25 nm or less, more preferably 10 nm or more and 23 nm or less. When the average particle size of the magnetic powder is 25 nm or less, good electromagnetic conversion characteristics (for example, SNR) can be obtained in the magnetic recording medium 10 having a high recording density. On the other hand, when the average particle size of the magnetic powder is 10 nm or more, the dispersibility of the magnetic powder is further improved, and more excellent electromagnetic conversion characteristics (for example, SNR) can be obtained. When the magnetic powder contains powder of cobalt ferrite particles, the average aspect ratio of the magnetic powder is the same as that of the above-described embodiment. Further, the average particle size and the average aspect ratio of the magnetic powder are also obtained in the same manner as the calculation method of the above-described embodiment.

The average particle volume of the magnetic powder is preferably 15000 nm ³ or less, more preferably 1000 nm ³ or more 12000 nm ³ or less. When the average particle volume of the magnetic powder is 15000 nm ³ or less, the same effect as when the average particle size of the magnetic powder is 25 nm or less can be obtained. On the other hand, when the average particle volume of the magnetic powder is 1000 nm ³ or more, the same effect as when the average particle size of the magnetic powder is 10 nm or more can be obtained. The average particle volume of the magnetic powder is a method for calculating the average particle volume of the magnetic powder in the above-described embodiment (method for calculating the average particle volume when the ε iron oxide particles have a cubic shape or a substantially cubic shape). ) Is the same.

The coercive force Hc of the cobalt ferrite magnetic powder is preferably 2500 Oe or more, more preferably 2600 Oe or more and 3500 Oe or less.

(Modification 5)
The magnetic recording medium 10 may further include a barrier layer 15 provided on at least one surface of the substrate 11, as shown in FIG. 11, for example. The barrier layer 15 is a layer for suppressing the dimensional change of the substrate 11 according to the environment. For example, as an example of the cause of causing the dimensional change, there is hygroscopicity of the substrate 11, but by providing the barrier layer 15, the rate of water intrusion into the substrate 11 can be reduced. The barrier layer 15 contains, for example, a metal or a metal oxide. Examples of the metal referred to here include Al, Cu, Co, Mg, Si, Ti, V, Cr, Mn, Fe, Ni, Zn, Ga, Ge, Y, Zr, Mo, Ru, Pd, Ag, Ba. , Pt, Au and Ta can be used. As the metal oxide, for example, a metal oxide containing one or more of the above metals can be used. More specifically, for example, at least one of Al ₂ O ₃ , CuO, CoO, SiO ₂ , Cr ₂ O ₃ , TiO ₂ , Ta ₂ O ₅ and Zr O ₂ can be used. Further, the barrier layer 15 may include diamond-like carbon (DLC), diamond, or the like.

The average thickness of the barrier layer 15 is preferably 20 nm or more and 1000 nm or less, and more preferably 50 nm or more and 1000 nm or less. The average thickness of the barrier layer 15 is obtained in the same manner as the average thickness of the magnetic layer 13. However, the magnification of the TEM image is appropriately adjusted according to the thickness of the barrier layer 15.

(Modification 6)
In the above embodiment, a large number of protrusions 14A provided on the surface 14S of the back layer 14 are transferred to the surface 13S of the magnetic layer 13 to form a large number of recesses 13A on the surface 13S of the magnetic layer 13. However, the method of forming a large number of dents 13A is not limited to this. For example, a large number of dents 13A may be formed on the surface 13S of the magnetic layer 13 by adjusting the type of solvent contained in the paint for forming the magnetic layer, the drying conditions of the paint for forming the magnetic layer, and the like.

(Modification 7)
The magnetic recording medium 10 according to the above-described embodiment may be used for the library device. In this case, the library device may include a plurality of recording / reproducing devices 30 according to the above-described embodiment.

Hereinafter, the present disclosure will be specifically described with reference to Examples, but the present disclosure is not limited to the following Examples.

In the following examples and comparative examples, the surface density of the recess having a depth of 20% or more of the average thickness of the magnetic layer, the logarithmic decrement obtained by the pendulum viscoelasticity test in the temperature range of 10 ° C. or higher and 45 ° C. or lower, vertical The square ratio (vertical orientation) in the direction, the average thickness of the magnetic layer, and the average thickness of the magnetic recording medium are values obtained by the measuring method described in the above-described embodiment.

[Example 1]
The magnetic recording medium as Example 1 was obtained as follows.

<Preparation process of paint for forming magnetic layer>
The paint for forming the magnetic layer was prepared as follows. First, the first composition having the following composition was kneaded with an extruder. Next, the kneaded first composition and the second composition having the following composition were added to a stirring tank equipped with a disper and premixed. Subsequently, sand mill mixing was further performed and filtering was performed to prepare a coating material for forming a magnetic layer.

(First composition)
Each component and weight in the first composition is as follows.
-Powder of barium ferrite (BaFe ₁₂ O ₁₉ ) particles (hexagonal plate, average aspect ratio 2.8, average particle volume 1950 nm ³ ): 100 parts by mass-65 parts by mass of cyclohexanone solution of vinyl chloride resin (composition of the solution) is a resin content of 30%, and cyclohexanone 70% by weight was more of a vinyl chloride-based resin as follows:. polymerization degree 300, Mn = 10000, OSO ₃ as a polar group K = 0.07 mmol / g, Contains secondary OH = 0.3 mmol / g ・ Aluminum oxide powder (α-Al ₂ O ₃ , average particle size 0.2 μm): 5 parts by mass

(Second composition)
Each component and weight in the second composition is as follows.
-Vinyl chloride resin: 1.1 parts by mass (The composition of the solution is 30% by mass of the resin content and 70% by mass of cyclohexanone).
-Carbon black: 2 parts by mass (manufactured by Tokai Carbon Co., Ltd., product name: Seast TA)
-As a fatty acid ester, n-butyl stearate: 2 parts by mass-Methylethyl ketone: 121.3 parts by mass-Toluene: 121.3 parts by mass-Cyclohexanone: 60.7 parts by mass

To the paint for forming a magnetic layer prepared as described above, polyisocyanate (trade name: Coronate L, manufactured by Tosoh Corporation): 4 parts by mass and stearic acid: 2 parts by mass as a fatty acid were added as a curing agent.

<Preparation process of paint for forming base layer>
The paint for forming the base layer was prepared as follows. First, the third composition having the following composition was kneaded with an extruder. Next, the kneaded third composition and the fourth composition having the following composition were added to a stirring tank equipped with a disper and premixed. Subsequently, sand mill mixing was further performed and filtering was performed to prepare a coating material for forming a base layer.

(Third composition)
Each component and weight in the third composition is as follows.
-Needle iron oxide powder (α-Fe ₂ O ₃ , average major axis length 0.15 μm): 100 parts by mass-Vinyl chloride resin (resin solution: resin content 30% by mass, cyclohexanone 70% by mass): 55.6 Parts by mass ・ Carbon black (average particle size 20 nm): 10 parts by mass

(4th composition)
Each component and weight in the fourth composition is as follows.
-Polyurethane resin UR8200 (manufactured by Toyo Spinning Co., Ltd.): 18.5 parts by mass-n-butyl stearate as fatty acid ester: 2 parts by mass-Methyl ethyl ketone: 108.2 parts by mass-Toluene: 108.2 parts by mass-Cyclohexanone: 18. 5 parts by mass

Polyisocyanate (trade name: Coronate L, manufactured by Tosoh Corporation): 4 parts by mass and stearic acid: 2 parts by mass as fatty acids were added to the base layer forming paint prepared as described above.

<Preparation process of paint for forming back layer>
The paint for forming the back layer was prepared as follows. The following raw materials were mixed in a stirring tank equipped with a disper and filtered to prepare a coating material for forming a back layer.
-Small particle size carbon black powder (average particle size (D50) 20 nm): 100 parts by mass-Large particle size carbon black powder (average particle size (D50) 300 nm): 0 parts by mass-Polyester polyurethane (Tosoh Co., Ltd.) Made by the company, trade name: N-2304): 100 parts by mass, methyl ethyl ketone: 500 parts by mass, toluene: 400 parts by mass, cyclohexanone: 100 parts by mass

<Applying process>
Using the magnetic layer forming paint and the base layer forming paint prepared as described above, the non-magnetic support was averaged on one main surface of a long polyester film having an average thickness of 4.0 μm after the calendar. It was formed as follows so as to form a base layer having a thickness of 0.6 μm and a magnetic layer having an average thickness of 80 nm. First, a base layer forming paint was applied on one main surface of the polyester film and dried to form a base layer. Next, the magnetic layer was formed by applying a paint for forming a magnetic layer on the base layer and drying it. The weight ratio of the vinyl chloride resin and the polyurethane resin in the binder of the magnetic layer was set to 1: 1 as shown in Table 1 below. Further, when the paint for forming the magnetic layer was dried, the magnetic powder was magnetically oriented in the thickness direction of the film by a solenoid coil. The square ratio in the thickness direction (vertical direction) of the magnetic recording medium was 67%. Subsequently, a paint for forming a back layer was applied onto the other main surface of the polyester film and dried to form a back layer having an average thickness of 0.3 μm. As a result, a magnetic recording medium was obtained.

<Calendar process and transfer process>
Subsequently, a calendar process was performed to smooth the surface of the magnetic layer. Next, a magnetic recording medium having a smoothed surface of the magnetic layer was wound into a roll, and then the magnetic recording medium was heat-treated at 60 ° C. for 10 hours in that state. Then, after rewinding the magnetic recording medium into a roll shape so that the end located on the inner peripheral side is located on the outer peripheral side, the magnetic recording medium is heated at 60 ° C. for 10 hours in that state. The process was performed again. As a result, many protrusions on the surface of the back layer were transferred to the surface of the magnetic layer, and many dents were formed on the surface of the magnetic layer. The number of dents having a depth of 20% or more of the average thickness of the magnetic layer was set to 20 per 1600 μm ² .

<Cutting process>
The magnetic recording medium obtained as described above was cut to a width of 1/2 inch (12.65 mm). As a result, the desired long magnetic recording medium (average thickness 5.6 μm) was obtained.

[Example 2]
By adjusting the temperature of the calendar processing (lower than that of Example 1), the number of dents having a depth of 20% or more of the average thickness of the magnetic layer was increased to 40 per 1600 μm ² . Except for this, a magnetic recording medium as Example 2 was obtained in the same manner as in Example 1 above.

[Example 3]
In the back layer forming paint, the small particle size carbon black powder (average particle size (D50) 20 nm) is 95 parts by mass, and the large particle size carbon black powder (average particle size (D50) 300 nm) is 5 parts by mass. As a part, the number of dents having a depth of 20% or more of the average thickness of the magnetic layer was set to 80 per 1600 μm ² . Except for this, a magnetic recording medium as Example 3 was obtained in the same manner as in Example 1 above.

[Example 4]
In the back layer forming paint, a small particle size carbon black powder (average particle size (D50) 20 nm) is 95 parts by mass, and a large particle size carbon black powder (average particle size (D50) 300 nm) is 5 parts by mass. It was a department. Further, the temperature of the calendar processing was adjusted (lower than that of Example 1). As a result, the number of dents having a depth of 20% or more of the average thickness of the magnetic layer is 100 per 1600 μm ² . Except for this, a magnetic recording medium as Example 4 was obtained in the same manner as in Example 1 above.

[Example 5]
In the back layer forming paint, a small particle size carbon black powder (average particle size (D50) 20 nm) is 90 parts by mass, and a large particle size carbon black powder (average particle size (D50) 300 nm) is 10 parts by mass. It was a department. As a result, the number of dents having a depth of 20% or more of the average thickness of the magnetic layer is 150 per 1600 μm ² . Except for this, a magnetic recording medium as Example 5 was obtained in the same manner as in Example 1 above.

[Example 6]
In the back layer forming paint, a small particle size carbon black powder (average particle size (D50) 20 nm) is 90 parts by mass, and a large particle size carbon black powder (average particle size (D50) 300 nm) is 10 parts by mass. It was a department. Further, the temperature of the calendar processing was adjusted (lower than that of Example 1). As a result, the number of dents having a depth of 20% or more of the average thickness of the magnetic layer is 180 per 1600 μm ² . Except for this, the magnetic recording medium as Example 6 was obtained in the same manner as in Example 1 above.

[Example 7]
The temperature of the calendar processing was adjusted (even lower than that of Example 6). As a result, the number of dents having a depth of 20% or more of the average thickness of the magnetic layer is 200 per 1600 μm ² . Except for this, a magnetic recording medium as Example 7 was obtained in the same manner as in Example 6 above.

[Example 8]
In the back layer forming paint, a small particle size carbon black powder (average particle size (D50) 20 nm) is 95 parts by mass, and a large particle size carbon black powder (average particle size (D50) 300 nm) is 5 parts by mass. It was a department. The temperature of the calendar processing was adjusted (lower than that of Example 1). Further, the weight ratio of the vinyl chloride resin and the polyurethane resin in the binder of the magnetic layer was set to 3: 1 as shown in Table 1. As a result, the number of dents having a depth of 20% or more of the average thickness of the magnetic layer is 100 per 1600 μm ² . Except for this, a magnetic recording medium as Example 8 was obtained in the same manner as in Example 1 above.

[Example 9]
The weight ratio of the vinyl chloride resin and the polyurethane resin in the binder of the magnetic layer was set to 1: 1.5 as shown in Table 1. As a result, the number of dents having a depth of 20% or more of the average thickness of the magnetic layer is 100 per 1600 μm ² . Except for this, a magnetic recording medium as Example 9 was obtained in the same manner as in Example 8 above.

[Example 10]
In the back layer forming paint, a small particle size carbon black powder (average particle size (D50) 20 nm) is 95 parts by mass, and a large particle size carbon black powder (average particle size (D50) 300 nm) is 5 parts by mass. It was a department. The temperature of the calendar processing was adjusted (lower than that of Example 1). Further, as the polyurethane resin in the binder of the magnetic layer, a resin having a glass transition point of 100 ° C. was used as shown in Table 1. As a result, the number of dents having a depth of 20% or more of the average thickness of the magnetic layer is 100 per 1600 μm ² . Except for this, a magnetic recording medium as Example 10 was obtained in the same manner as in Example 1 above.

[Example 11]
In the back layer forming paint, a small particle size carbon black powder (average particle size (D50) 20 nm) is 95 parts by mass, and a large particle size carbon black powder (average particle size (D50) 300 nm) is 5 parts by mass. It was a department. The temperature of the calendar processing was adjusted (lower than that of Example 1). Further, as the polyurethane resin in the binder of the magnetic layer, a resin having a glass transition point of 60 ° C. was used as shown in Table 1. As a result, the number of dents having a depth of 20% or more of the average thickness of the magnetic layer is 100 per 1600 μm ² . Except for this, a magnetic recording medium as Example 10 was obtained in the same manner as in Example 1 above.

[Example 12]
In the step of preparing the coating material for forming a magnetic layer, a powder of strontium ferrite particles (hexagonal plate shape, average aspect ratio 3.0, average particle size 21.3 nm, particle volume 2000 nm ³ ) was used as the magnetic powder. Except for this, a magnetic recording medium as Example 12 was obtained in the same manner as in Example 4 above.

[Example 13]
In the step of preparing the coating material for forming the magnetic layer, powder of ε-iron oxide particles (spherical, average aspect ratio 1.1, average particle size 16 nm, particle volume 2150 nm ³ ) was used as the magnetic powder. Except for this, a magnetic recording medium as Example 13 was obtained in the same manner as in Example 4 above.

[Example 14]
In the step of preparing the coating material for forming a magnetic layer, a cobalt ferrite powder (cube-shaped, average aspect ratio 1.7, average particle size 18.5 nm, particle volume 2200 nm ³ ) was used as the magnetic powder. Except for this, a magnetic recording medium as Example 14 was obtained in the same manner as in Example 4 above.

[Example 15]
In the coating step, a PET (polyethylene terephthalate) film was used instead of the polyester (PEN) film as the substrate on which the magnetic layer forming paint and the base layer forming paint were applied. Except for this, a magnetic recording medium as Example 15 was obtained in the same manner as in Example 4 above.

[Example 16]
In the coating step, a PEEK (polyetheretherketone) film was used instead of the polyester film as the substrate on which the magnetic layer forming paint and the base layer forming paint were applied. Except for this, a magnetic recording medium as Example 16 was obtained in the same manner as in Example 4 above.

[Example 17]
In the coating step, the drying conditions were adjusted so that the square ratio of the magnetic recording medium in the thickness direction (vertical direction) was 65%. Except for this, a magnetic recording medium as Example 17 was obtained in the same manner as in Example 4 above.

[Example 18]
In the coating step, the average thickness of the magnetic layer was set to 80 nm. Except for this, a magnetic recording medium as Example 18 was obtained in the same manner as in Example 4 above.

[Comparative Example 1]
By adjusting the temperature of the calendar processing (higher than that of Example 1), the number of dents having a depth of 20% or more of the average thickness of the magnetic layer was increased to 15 per 1600 μm ² . Except for this, a magnetic recording medium as Comparative Example 1 was obtained in the same manner as in Example 1 above.

[Comparative Example 2]
In the back layer forming paint, a small particle size carbon black powder (average particle size (D50) 20 nm) is 80 parts by mass, and a large particle size carbon black powder (average particle size (D50) 300 nm) is 20 parts by mass. As a part, the number of dents having a depth of 20% or more of the average thickness of the magnetic layer was set to 230 per 1600 μm ² . Except for this, a magnetic recording medium as Comparative Example 2 was obtained in the same manner as in Example 1 above.

[Comparative Example 3]
The weight ratio of the vinyl chloride resin and the polyurethane resin in the binder of the magnetic layer was set to 1: 0 as shown in Table 1. As a result, the number of dents having a depth of 20% or more of the average thickness of the magnetic layer is 100 per 1600 μm ² . Except for this, a magnetic recording medium as Comparative Example 3 was obtained in the same manner as in Example 4 above.

[Comparative Example 4]
The weight ratio of the vinyl chloride resin and the polyurethane resin in the binder of the magnetic layer was set to 4: 1 as shown in Table 1. As a result, the number of dents having a depth of 20% or more of the average thickness of the magnetic layer is 100 per 1600 μm ² . Except for this, a magnetic recording medium as Comparative Example 4 was obtained in the same manner as in Example 4 above.

[Comparative Example 5]
The weight ratio of the vinyl chloride resin and the polyurethane resin in the binder of the magnetic layer was set to 1: 4 as shown in Table 1. As a result, the number of dents having a depth of 20% or more of the average thickness of the magnetic layer is 100 per 1600 μm ² . Except for this, a magnetic recording medium as Comparative Example 5 was obtained in the same manner as in Example 4 above.

[Comparative Example 6]
As the polyurethane resin in the binder of the magnetic layer, a resin having a glass transition point of 30 ° C. was used as shown in Table 1. As a result, the number of dents having a depth of 20% or more of the average thickness of the magnetic layer is 100 per 1600 μm ² . Except for this, a magnetic recording medium as Comparative Example 6 was obtained in the same manner as in Example 4 above.

[Comparative Example 7]
The weight ratio of the vinyl chloride resin and the polyurethane resin in the binder of the magnetic layer was set to 1: 1.5 as shown in Table 1. Further, as the polyurethane resin in the binder of the magnetic layer, a resin having a glass transition point of 30 ° C. was used as shown in Table 1. As a result, the number of dents having a depth of 20% or more of the average thickness of the magnetic layer is 100 per 1600 μm ² . Except for this, a magnetic recording medium as Comparative Example 6 was obtained in the same manner as in Example 4 above.

[Evaluation]
The magnetic recording media of Examples 1 to 18 and Comparative Examples 1 to 7 obtained as described above were evaluated as follows.

(Room temperature SNR)
The SNR (electromagnetic conversion characteristic) of the magnetic recording medium in a 25 ° C environment was measured using a 1/2 inch tape traveling device (manufactured by Mountain Engineering II, MTS Transport) equipped with a recording / playback head and a recording / playback amplifier. .. A ring head having a gap length of 0.2 μm was used as the recording head, and a GMR head having a distance between shields of 0.1 μm was used as the playback head. The relative speed was 6 m / s, the recording clock frequency was 160 MHz, and the recording track width was 2.0 μm. The SNR was calculated based on the method described in the following document. The results are shown in Table 1 as relative values with the SNR of Example 1 as 0 dB.
Y.Okazaki: “An Error Rate Emulation System.”, IEEE Trans. Man., 31, pp.3093-3095 (1995)

(Lower SNR)
After full-scale recording (full volume recording) on the magnetic recording medium at 45 ° C., that is, after recording on the entire recording area over the entire length of the magnetic recording medium, all the recordings on the magnetic recording medium. The SNR when reproducing the information was measured. Next, at 10 ° C., full-scale recording (full volume recording) was performed on the magnetic recording medium, and then the SNR when reproducing all the information recorded on the magnetic recording medium was measured. The difference between the SNR at 45 ° C. and the SNR at 10 ° C. thus obtained was defined as the SNR decrease.

Table 1 summarizes the configurations and evaluation results of the magnetic recording media in each Example and each Comparative Example.

As shown in Table 1, in Examples 1 to 18, 20 or more dents 13A having a depth of 20% or more of the average thickness of the magnetic layer 13 are 20 or more per 1600 μm ^{2 on} the surface 13S of the magnetic layer 13. The logarithmic decrement Δ is 0.025 or more and 0.035 or less, and is logarithmic. Since the difference between the maximum value of the decay rate Δ and the minimum value of the logarithmic decrement rate Δ is 0 or more and 0.020 or less, good results were obtained in both room temperature SNR and SNR deterioration.

In Comparative Example 1, since the recesses 13A having a depth of 20% or more of the average thickness of the magnetic layer 13 are formed at a ratio of 15 per 1600 μm ² , deterioration of the room temperature SNR is observed. The air entrained during the traveling of the magnetic recording medium cannot be sufficiently released from the interface between the surface of the magnetic layer and the head, an air layer is formed between the surface 13S of the magnetic layer 13 and the head, and the magnetic layer 13 It is considered that the surface 13S is not sufficiently in contact with the head. Further, in Comparative Example 2, since the recesses 13A having a depth of 20% or more of the average thickness of the magnetic layer 13 are formed at a ratio of 230 per 1600 μm ² , deterioration of the room temperature SNR is also observed. Furthermore, the decrease in SNR became remarkable. It is considered that the reason for this is that the surface density of the recesses is too high, so that the contact area between the surface 13S of the magnetic layer 13 and the head is reduced.

In Comparative Example 3, the binder of the magnetic layer 13 does not contain a polyurethane resin. Further, also in Comparative Example 4, the weight of the vinyl chloride resin contained in the binder of the magnetic layer 13 is sufficiently larger than the weight of the polyurethane resin. Therefore, the minimum values of the logarithmic decrement rate Δ obtained by the pendulum viscoelasticity test at a temperature of 10 ° C. or higher and 45 ° C. or lower were 0.015 and 0.018, respectively. As a result, deterioration of room temperature SNR was observed and the decrease of SNR was remarkable in all cases. FIG. 12A shows the state around the magnetic head when the SNR decrease in Comparative Examples 3 and 4 was measured. As shown in FIG. 12A, the constituent material of the magnetic layer 13 separated from the magnetic layer 13 is attached to the side of the region where the magnetic recording medium 10 comes into contact with the magnetic head.

In Comparative Example 5, the weight of the vinyl chloride resin contained in the binder of the magnetic layer 13 is sufficiently smaller than the weight of the polyurethane resin. Therefore, the minimum value of the logarithmic decrement rate Δ obtained by the pendulum viscoelasticity test at a temperature of 10 ° C. or higher and 45 ° C. or lower was 0.040. As a result, deterioration of room temperature SNR was observed, and the decrease in SNR was also remarkable.
FIG. 12B shows the state around the magnetic head when the SNR decrease in Comparative Example 5 is measured. As shown in FIG. 12B, the constituent material of the highly viscous magnetic layer 13 separated from the magnetic layer 13 is attached to the surface of the magnetic head in contact with the magnetic recording medium 10.

In Comparative Examples 6 and 7, the variation (difference between the maximum value and the minimum value) of the logarithmic decrement rate Δ obtained by the pendulum viscoelasticity test in the temperature range of 10 ° C. or higher and 45 ° C. or lower was 0.021 and 0.022, respectively. It became. Therefore, although the room temperature SNR was good, the decrease in SNR was remarkable. It is considered that the shape change is likely to occur at a high temperature and the friction of the surface 13S of the magnetic layer 13 is increased.

Although the present disclosure has been specifically described with reference to the embodiment and examples thereof, the present disclosure is not limited to the above-described embodiment and the like, and various modifications are possible.

For example, the configurations, methods, processes, shapes, materials, numerical values, etc. given in the above-described embodiments and modifications thereof are merely examples, and different configurations, methods, processes, shapes, materials, and numerical values may be used as necessary. Etc. may be used. Specifically, the magnetic recording medium of the present disclosure may include components other than the substrate, the base layer, the magnetic layer, the back layer, and the barrier layer. Further, the chemical formulas of the compounds and the like are typical, and the general names of the same compounds are not limited to the stated valences and the like.

In addition, the configurations, methods, processes, shapes, materials, numerical values, and the like of the above-described embodiments and modifications thereof can be combined with each other without departing from the gist of the present disclosure.

Further, in the numerical range described stepwise in the present specification, the upper limit value or the lower limit value of the numerical range of one step may be replaced with the upper limit value or the lower limit value of the numerical range of another step. Unless otherwise specified, the materials exemplified in the present specification may be used alone or in combination of two or more.

As described above, according to the magnetic recording medium as one embodiment of the present disclosure, good electromagnetic conversion characteristics can be maintained even after the total thickness is reduced and repeated recording or repeated reproduction is performed.
The effect of the present disclosure is not limited to this, and any effect described in the present specification may be used. In addition, the present technology can have the following configurations.
(1)
A tape-shaped magnetic recording medium
With the base
The base layer provided on the substrate and
It has a magnetic layer provided on the base layer and has.
On the surface of the magnetic layer, 20 or more and 200 or less recesses having a depth of 20% or more of the average thickness of the magnetic layer are formed per 1600 μm ² .
The logarithmic decrement obtained by the pendulum viscoelasticity test at a temperature of 10 ° C. or higher and 45 ° C. or lower on the surface of the magnetic layer is 0.025 or higher and 0.035 or lower.
The difference between the maximum value of the logarithmic decrement and the minimum value of the logarithmic decrement is 0 or more and 0.020 or less.
The square ratio of the magnetic recording medium in the vertical direction is 65% or more.
The average thickness of the magnetic layer is 80 nm or less.
A magnetic recording medium having an average thickness of 5.6 μm or less.
(2)
The magnetic recording medium according to (1) above, wherein the logarithmic decrement is 0.025 or more and 0.030 or less.
(3)
The magnetic recording medium according to (1) or (2) above, wherein on the surface of the magnetic layer, the recesses are formed at a ratio of 40 or more and 200 or less per 1600 μm ² .
(4)
The magnetic recording medium according to any one of (1) to (3) above, wherein 80 or more and 180 or less recesses are formed on the surface of the magnetic layer at a ratio of 80 or more and 180 or less per 1600 μm ² .
(5)
The magnetic recording medium according to any one of (1) to (4) above, wherein the substrate contains polyester or polyetheretherketone (PEEK) as a main component.
(6)
The magnetic layer contains magnetic powder and contains
The magnetic powder contains hexagonal ferrite containing at least one of Ba (barium) and Sr (strontium), ε-iron oxide or Co (cobalt) -containing spinel-type ferrite, according to the above (1) to (5). The magnetic recording medium according to any one.
(7)
The base layer and the magnetic layer contain a lubricant and contain a lubricant.
The lubricant includes at least one of the compound represented by the following general formula <1> and the compound represented by the following general formula <2>, the compound represented by the following general formula <3>, and the following. The magnetic recording medium according to any one of (1) to (6) above, which comprises at least one of the compounds represented by the general formula <4>.
CH ₃ (CH ₂ ) _k COOH ・ ・ ・ <1>
(However, in the general formula <1>, k is an integer selected from the range of 14 or more and 22 or less.)
CH ₃ (CH ₂ ) _n CH = CH (CH ₂ ) _m COOH ・ ・ ・ <2>
(However, in the general formula <2>, the sum of n and m is an integer selected from the range of 12 or more and 20 or less, more preferably 14 or more and 18 or less.)
CH ₃ (CH ₂ ) _p COO (CH ₂ ) _q CH ₃・ ・ ・ <3>
(However, in the general formula <3>, p is an integer selected from the range of 14 or more and 22 or less, more preferably 14 or more and 18 or less, and q is a range of 2 or more and 5 or less, more preferably 2 or more and 4 It is an integer selected from the following range.)
CH ₃ (CH ₂ ) _p COO- (CH ₂ ) _q CH (CH ₃ ) ₂ … <4>
(However, in the general formula <4>, p is an integer selected from the range of 14 or more and 22 or less, and q is an integer selected from the range of 1 or more and 3 or less.)
(8)
The base layer has a large number of holes and has a large number of holes.
The magnetic recording medium according to (7) above, wherein the recess of the magnetic layer and the hole of the base layer are connected.
(9)
A delivery unit that can sequentially send out tape-shaped magnetic recording media,
A winding unit capable of winding the magnetic recording medium sent out from the sending unit, and a winding unit.
A magnetic head capable of writing information to the magnetic recording medium and reading information from the magnetic recording medium while contacting the magnetic recording medium traveling from the sending portion to the winding portion is provided. ,
The magnetic recording medium is
With the base
The base layer provided on the substrate and
It has a magnetic layer provided on the base layer and has.
On the surface of the magnetic layer, 20 or more and 200 or less recesses having a depth of 20% or more of the average thickness of the magnetic layer are formed per 1600 μm ² .
The logarithmic decrement obtained by the pendulum viscoelasticity test at a temperature of 10 ° C. or higher and 45 ° C. or lower on the surface of the magnetic layer is 0.025 or higher and 0.035 or lower.
The difference between the maximum value of the logarithmic decrement and the minimum value of the logarithmic decrement is 0 or more and 0.020 or less.
The square ratio of the magnetic recording medium in the vertical direction is 65% or more.
The average thickness of the magnetic layer is 80 nm or less.
A magnetic recording / reproducing device having an average thickness of 5.6 μm or less of the magnetic recording medium.
(10)
The magnetic recording / reproducing device according to (9) above, which has a configuration in which the tension applied in the longitudinal direction of the magnetic recording medium can be adjusted.
(11)
With a tape-shaped magnetic recording medium
A housing for accommodating the magnetic recording medium is provided.
The magnetic recording medium is
With the base
The base layer provided on the substrate and
It has a magnetic layer provided on the base layer and has.
On the surface of the magnetic layer, 20 or more and 200 or less recesses having a depth of 20% or more of the average thickness of the magnetic layer are formed per 1600 μm ² .
The logarithmic decrement obtained by the pendulum viscoelasticity test at a temperature of 10 ° C. or higher and 45 ° C. or lower on the surface of the magnetic layer is 0.025 or higher and 0.035 or lower.
The difference between the maximum value of the logarithmic decrement and the minimum value of the logarithmic decrement is 0 or more and 0.020 or less.
The square ratio of the magnetic recording medium in the vertical direction is 65% or more.
The average thickness of the magnetic layer is 80 nm or less.
A magnetic recording medium cartridge having an average thickness of 5.6 μm or less.

10 ... Magnetic recording medium, 11 ... Base, 11A, 11B ... Main surface, 12 ... Underlayer, 13 ... Magnetic layer, 14 ... Back layer, 20, 20A ... ε Iron oxide particles, 21 ... Core part, 22 ... Shell part , 22a ... 1st shell part, 22b ... 2nd shell part, 30 ... Recording / playback device, 31 ... Spindle, 32 ... Reel, 33, 34 ... Drive device, 35 ... Guide roller, 36 ... Head unit, 37 ... Communication interface , 38 ... control device, 41 ... server, 42 ... personal computer, 43 ... network, 100 ... measurement sample, 101 ... sample stage, 103 ... substrate, 104 ... cylindrical cylinder edge with pendulum, 105 ... fixing tape.

Claims (27)

A tape-shaped magnetic recording medium
With the base
The base layer provided on the substrate and
It has a magnetic layer provided on the base layer and has.
The substrates are PET (polyethylene terephthalate), PEN (polyethylene naphthalate), PBT (polybutylene terephthalate), PBN (polybutylene naphthalate), PCT (polycyclohexylene dimethylene terephthalate), PEB (polyethylene-p-oxybenzoate). ) And at least one of polyethylene bisphenoxycarboxylate,
On the surface of the magnetic layer, 20 or more and 200 or less dents having a depth of 20% or more of the average thickness of the magnetic layer are formed per 1600 μm ² .
The logarithmic decrement obtained by the pendulum viscoelasticity test at a temperature of 10 ° C. or higher and 45 ° C. or lower on the surface of the magnetic layer is 0.025 or higher and 0.035 or lower.
The difference between the maximum value of the logarithmic decrement and the minimum value of the logarithmic decrement is 0 or more and 0.020 or less.
The square ratio of the magnetic recording medium in the vertical direction is 65% or more.
The average thickness of the magnetic layer is 80 nm or less.
The average thickness of the magnetic recording medium is 5.4 μm or less. The magnetic recording medium according to claim 1, wherein the logarithmic decrement is 0.025 or more and 0.030 or less. The magnetic recording medium according to claim 1, wherein on the surface of the magnetic layer, the dents are formed at a ratio of 40 or more and 200 or less per 1600 μm ² . The magnetic recording medium according to claim 1, wherein on the surface of the magnetic layer, the dents are formed at a ratio of 80 or more and 180 or less per 1600 μm ² . The magnetic layer contains magnetic powder and contains
The magnetic recording medium according to claim 1, wherein the magnetic powder contains hexagonal ferrite containing at least one of Ba (barium) and Sr (strontium), ε-iron oxide or Co (cobalt) -containing spinel-type ferrite. .. The base layer and the magnetic layer contain a lubricant and contain a lubricant.
The lubricant includes at least one of the compound represented by the following general formula <1> and the compound represented by the following general formula <2>, the compound represented by the following general formula <3>, and the following. The magnetic recording medium according to claim 1, which comprises at least one of the compounds represented by the general formula <4>.
CH ₃ (CH ₂ ) _k COOH ・ ・ ・ <1>
(However, in the general formula <1>, k is an integer selected from the range of 14 or more and 22 or less.)
CH ₃ (CH ₂ ) _n CH = CH (CH ₂ ) _m COOH ・ ・ ・ <2>
(However, in the general formula <2>, the sum of n and m is an integer selected from the range of 12 or more and 20 or less, more preferably 14 or more and 18 or less.)
CH ₃ (CH ₂ ) _p COO (CH ₂ ) _q CH ₃・ ・ ・ <3>
(However, in the general formula <3>, p is an integer selected from the range of 14 or more and 22 or less, more preferably 14 or more and 18 or less, and q is a range of 2 or more and 5 or less, more preferably 2 or more and 4 It is an integer selected from the following range.)
CH ₃ (CH ₂ ) _p COO- (CH ₂ ) _q CH (CH ₃ ) ₂ … <4>
(However, in the general formula <4>, p is an integer selected from the range of 14 or more and 22 or less, and q is an integer selected from the range of 1 or more and 3 or less.) The base layer has a large number of holes and has a large number of holes.
The magnetic recording medium according to claim 6 , wherein the recess of the magnetic layer and the hole of the base layer are connected. The average thickness of the magnetic recording medium is 5.0 μm or less.
The magnetic recording medium according to claim 1. The average thickness of the magnetic recording medium is 4.6 μm or less.
The magnetic recording medium according to claim 1. The average thickness of the magnetic recording medium is 4.4 μm or less.
The magnetic recording medium according to claim 1. The average thickness of the magnetic layer is 50 nm or less.
The magnetic recording medium according to claim 1. The average thickness of the base layer is 0.5 μm or more and 0.9 μm or less.
The magnetic recording medium according to claim 1. The average thickness of the base layer is 0.6 μm or more and 0.7 μm or less.
The magnetic recording medium according to claim 1. The square ratio of the magnetic recording medium in the vertical direction is 67% or more.
The magnetic recording medium according to claim 1. The square ratio of the magnetic recording medium in the vertical direction is 70% or more.
The magnetic recording medium according to claim 1. The square ratio of the magnetic recording medium in the vertical direction is 75% or more.
The magnetic recording medium according to claim 1. The square ratio of the magnetic recording medium in the vertical direction is 80% or more.
The magnetic recording medium according to claim 1. The substrate further has a back layer provided on the opposite side of the substrate layer.
The average thickness of the back layer is 0.6 μm or less.
The magnetic recording medium according to claim 1. The substrate further has a back layer provided on the opposite side of the substrate layer.
The average thickness of the back layer is 0.5 μm or less.
The magnetic recording medium according to claim 1. The magnetic layer contains magnetic powder and contains
The average particle size of the magnetic powder is 12 nm or more and 30 nm or less.
The magnetic recording medium according to claim 1. The magnetic layer contains magnetic powder and contains
The average particle size of the magnetic powder is 12 nm or more and 25 nm or less.
The magnetic recording medium according to claim 1. The magnetic layer contains magnetic powder and contains
The average particle size of the magnetic powder is 15 nm or more and 22 nm or less.
The magnetic recording medium according to claim 1. Dynamic friction coefficient μ between the surface and the magnetic head when the tension applied to the magnetic recording medium is 0.4 N _A And the coefficient of dynamic friction μ between the surface and the magnetic head when the tension applied to the magnetic recording medium is 1.2 N. _B Friction coefficient ratio with (μ) _B / Μ _A ) Is 1.0 or more and 2.0 or less
The magnetic recording medium according to claim 1. When the tension applied to the magnetic recording medium is 0.6N, the coefficient of dynamic friction between the surface and the magnetic head for the fifth time from the start of running of the magnetic recording medium μ _{C (5)} When the tension applied to the magnetic recording medium is 0.6N, the coefficient of dynamic friction between the surface and the magnetic head 1000 times from the start of running of the magnetic recording medium μ _{C (1000)} Friction coefficient ratio with μ _{C (1000)} / Μ _{C (5)} Is 1.0 or more and 2.0 or less
The magnetic recording medium according to claim 1. A delivery unit capable of sequentially sending out the magnetic recording medium according to any one of claims 1 to 24, and a delivery unit.
A winding unit capable of winding the magnetic recording medium sent out from the sending unit, and a winding unit.
A magnetic head capable of writing information to the magnetic recording medium and reading information from the magnetic recording medium while contacting the magnetic recording medium traveling from the sending portion to the winding portion is provided. magnetic recording and reproducing apparatus. The magnetic recording / reproducing device according to claim 25 , which has a configuration in which the tension applied in the longitudinal direction of the magnetic recording medium can be adjusted. The magnetic recording medium according to any one of claims 1 to 24,
A magnetic recording medium cartridge including a housing for accommodating the magnetic recording medium.

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