JPH0721549A - Magnetic recording medium and its production - Google Patents

Abstract

PURPOSE:To satisfactorily disperse even fine magnetic powder in a magnetic layer, to form a magnetic layer excellent in surface properties and magnetic characteristics and to obtain a magnetic recording medium fit for high density recording. CONSTITUTION:At least magnetic powder is mixed with a binder to prepare a magnetic coating material and a magnetic layer is formed by coating a nonmagnetic substrate with the coating material. At this time, an attenuating AC magnetic field having >=1kG initial amplitude and gradually reducing its amplitude is applied to the magnetic powder before mixing with the binder.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a so-called coating type magnetic recording medium in which a magnetic layer is formed by coating a magnetic coating mainly composed of magnetic powder and a binder on a non-magnetic support, and its manufacture. Regarding the method.

[0002]

2. Description of the Related Art Conventionally, as a magnetic recording medium such as a magnetic tape or a floppy disk, a magnetic paint prepared by dispersing a magnetic powder, a resin binder, an organic solvent and various additives on a non-magnetic support. The magnetic layer was formed by coating,
A so-called coating type magnetic recording medium and a so-called metal thin film type magnetic recording medium in which a magnetic layer is formed by directly depositing a ferromagnetic powder on a non-magnetic support by a vacuum thin film forming technique have been proposed. However, the former coating type magnetic recording medium is currently the mainstream because of its excellent productivity and versatility.

By the way, in order to improve the characteristics of high density recording in the above-mentioned coating type magnetic recording medium and to improve the characteristics in the low wavelength region, the magnetic powder should have high coercive force, fineness and dispersibility. It is necessary to improve and to make the surface of the magnetic layer a mirror surface. However, if the magnetic powder is miniaturized, it becomes difficult to disperse the magnetic powder when the magnetic paint is prepared, and the magnetic powder is unevenly present in the magnetic paint. When such a magnetic coating material is applied as it is to a non-magnetic support, only a magnetic layer having poor surface properties and magnetostatic properties can be obtained.

Therefore, in the coating type magnetic recording medium using fine ferromagnetic powder, the ferromagnetic powder is favorably dispersed in the magnetic paint by introducing a polar group into the binder. There is.

[0005]

However, in the magnetic recording medium, the demand for improvement of high density recording characteristics is increasing more and more, and accordingly, the ferromagnetic powder is required to be further miniaturized, and the specific surface area is 45 m ² / An ultrafine ferromagnetic powder with a weight of g or more is used. In such a case, only the conventionally used method such as introducing a polar group into the binder is insufficient in the effect of imparting dispersibility, and cannot cope with the dispersion of the ultrafine ferromagnetic powder as described above. ing.

Therefore, the present invention has been proposed in view of such conventional circumstances, and even when a fine ferromagnetic powder is used, the magnetic powder is dispersed in the magnetic layer with good dispersibility, An object of the present invention is to provide a magnetic recording medium having excellent surface properties and magnetostatic characteristics, and a method for manufacturing the same.

[0007]

In order to achieve the above-mentioned object, the inventors of the present invention have conducted extensive studies, and as a result, when preparing a magnetic paint, prior to mixing magnetic powder with a binder. By applying a damping AC magnetic field whose initial magnetic field is 1 kGauss or more and whose amplitude is gradually attenuated, the dispersibility of the magnetic powder is enhanced and the magnetic powder is highly dispersed in the magnetic paint, and the surface property and static We have come to the knowledge that a magnetic layer having excellent magnetic properties is formed.

The present invention has been completed based on these findings. That is, the magnetic recording medium of the present invention is
In a magnetic recording medium comprising a magnetic layer mainly composed of magnetic powder and a binder on a non-magnetic support, the magnetic powder has an initial magnetic field of 1 k before being mixed with the binder.
The magnetic powder is characterized in that it is a Gauss or more and is applied with a damping AC magnetic field whose amplitude is gradually attenuated.

The magnetic powder is a needle-shaped magnetic powder. Further, the magnetic powder is a plate-shaped magnetic powder. Furthermore, in the method for producing a magnetic recording medium of the present invention, at least when magnetic powder and a binder are mixed to prepare a magnetic coating material, and the magnetic coating material is applied onto a non-magnetic support to form a magnetic layer. It is characterized in that an attenuating AC magnetic field whose initial magnetic field is 1 kGauss or more and whose amplitude is gradually attenuated is applied in advance to the magnetic powder before being mixed with a binder.

The magnetic recording medium to which the present invention is applied is a so-called coating type magnetic recording medium in which a magnetic layer mainly composed of magnetic powder and a resin binder is formed on a non-magnetic support.

The magnetic layer is formed by applying a magnetic coating material prepared by mixing and dispersing at least a magnetic powder and a resin binder in an organic solvent onto a non-magnetic support. Therefore, the surface property and the magnetostatic property are affected by the dispersibility of the magnetic powder in the magnetic paint preparation stage.

Therefore, in the present invention, in order to improve the dispersibility of the magnetic powder in the step of preparing the magnetic coating material, a damping AC magnetic field having an initial magnetic field of 1 kGauss or more and gradually decreasing amplitude is applied to the magnetic powder in advance. I will keep it. FIG. 1 shows a magnetic field application pattern 1 applied to the magnetic powder.
Here is an example: In this way, first, an initial magnetic field H ₁ of ₁ kGauss or more is applied, the magnetic field is gradually attenuated from this initial magnetic field H ₁ to 0 magnetic field, and the magnetic field is swung in the opposite direction to have a magnitude larger than that of the initial magnetic field H ₁ . Increase to a small second magnetic field H ₂ . Then, the magnetic field is gradually attenuated from this second magnetic field H ₂ to a 0 magnetic field, and the magnetic field is further swung in the opposite direction to increase to a _third magnetic field H ₃ which is smaller in magnitude than the second magnetic field H _2. The attenuation AC pattern is set to the nth magnetic field H _n.
Is repeatedly applied to the magnetic powder until H _n ≈0. When the magnetic powder thus magnetized is kneaded and dispersed with a binder and an organic solvent to prepare a magnetic paint, the magnetic powder is uniformly dispersed in the magnetic paint without causing agglomeration or the like. Therefore, by using the magnetic coating material thus prepared, a magnetic layer having excellent surface properties and magnetostatic properties can be formed.

As the magnetic powder to be magnetized in this way, those usually used in this kind of magnetic recording medium can be used, and either acicular magnetic powder or tabular magnetic powder may be used.

As the acicular magnetic powder, for example, γ-Fe ₂
O ₃ , Fe ₃ O ₄ , γ-Fe ₂ O ₃ and a ferride compound of Fe ₃ O ₄ , Co-containing γ-Fe ₂ O ₃ , Co-containing Fe ₃ O ₄ , and Co-containing γ-Fe ₂ O ₃ And Fe ₃ O
₄ , a velide compound, an oxide containing one or more metal elements in CrO ₂ , such as Te, Sb, Fe, Bi, a metal such as Fe, Co, Ni, F
e-Co, Fe-Ni, Fe-Co-Ni, Fe-Co
-B, Fe-Co-Cr-B, Mn-Bi, Mn-A
1, alloys such as Fe—Co—V, needle-like fine particles such as iron nitride, and the like, of which the effect is particularly great when metal needle-like magnetic powder is used. In addition, these acicular magnetic powders contain A for the purpose of preventing sintering during reduction or maintaining the shape.
A light metal element such as 1, Si, P, or B may be contained in an appropriate amount.

As the flat magnetic powder, for example, the general formula M
O · n (Fe ₂ O ₃ ) (where M is Ba, Sr, C
It represents at least one of a and n is 5-6. ) Fine particles of hexagonal ferrite represented by In this case, in order to control the coercive force, Co, T
It is also possible to add at least one of i, Ni, Mn, Cu, Zn, In, Ge and Nb and replace a part of Fe constituting the hexagonal ferrite with these elements.

As the binder mixed with the magnetic powder together with the above magnetic powder, polymers such as vinyl chloride, vinyl acetate, vinyl alcohol, vinylidene chloride, acrylic acid ester, methacrylic acid ester, styrene, butadiene, acrylonitrile, or the like are used. In addition to a copolymer in which two or more kinds are combined, polyester resin, epoxy resin and the like are exemplified. In particular, from the viewpoint of better dispersing the acicular magnetic powder, it is desirable to use a resin containing a sulfonic acid metal salt or a composite resin of a resin containing a sulfonic acid metal salt and another resin.

Further, in addition to the magnetic powder and the binder, additives such as a dispersant, an abrasive, an antistatic agent and a rust preventive which are usually added may be added to the magnetic paint. In this case, the addition conditions such as the compounding ratio of the additives may be the same as those of the ordinary magnetic recording medium.

As the non-magnetic support to which such a magnetic coating is applied, any of those conventionally used in this type of magnetic recording medium can be used. For example, a polymer support composed of a polymer material typified by polyesters, polyolefins, celluloses, vinyl resins, polyimides, and polycarbonates can be given.

[0019]

The magnetic coating material that forms the magnetic layer in the coating type magnetic recording medium is prepared by mixing at least magnetic powder and a binder. When preparing a magnetic paint in this way,
Initial magnetic field is 1 kG prior to mixing magnetic powder with binder
By applying a damping AC magnetic field that is equal to or more than aus and whose amplitude is gradually attenuated, the magnetic powder is uniformly dispersed without causing aggregation or the like when mixed with the binder. Therefore, by coating the non-magnetic support with the magnetic coating material containing the magnetic powder to which the magnetic field is applied in this manner, a magnetic layer having excellent surface properties and magnetostatic characteristics is formed.

[0020]

EXAMPLES Hereinafter, specific examples of the present invention will be described, but it goes without saying that the present invention is not limited to these examples.

Example 1 The magnetic characteristics and powder characteristics of the Fe-based metal acicular magnetic powder used in this example are shown below. The magnetic characteristics were measured with a sample vibrating magnetometer (manufactured by Toei Industry Co., Ltd.), and the specific surface area was measured with a surface area measuring device (manufactured by Shimadzu Corporation) based on the BET one-point method.

Coercive force: 124.1 kA / m Saturation magnetization: 120 Am ² / kg Squareness ratio: 0.49 Specific surface area: 53 m ² / g

A damping AC magnetic field having an initial magnetic field of 15 kGauss was applied to the Fe-based metal acicular magnetic powder having the above characteristics. A magnetic coating material was prepared by mixing, kneading, and dispersing the thus-magnetized Fe acicular magnetic powder, the binder, the additive, and the organic solvent according to the magnetic coating composition shown below. Composition of magnetic coating Fe-based acicular magnetic powder (long axis length 0.34 μm) 100 parts by weight Polyurethane-polyvinyl chloride copolymer 20 parts by weight (polyurethane: polyvinyl chloride = 1: 1) Abrasive (Al ₂ O ₃ ) 3 parts by weight Antistatic agent (carbon powder) 2 parts by weight Methyl ethyl ketone 100 parts by weight Toluene 100 parts by weight Cyclohexanone 50 parts by weight Then, the prepared magnetic paint is applied onto a polyethylene terephthalate (PET) film to form a magnetic recording medium. It was made.

Example 2 A magnetic recording medium was produced in the same manner as in Example 1 except that the acicular magnetic powder having a major axis length of 0.25 μm was used as the magnetic powder.

Example 3 A magnetic recording medium was prepared in the same manner as in Example 1 except that the acicular metal powder having a major axis length of 0.10 μm was used as the magnetic powder.

Comparative Example 1 A magnetic recording medium was manufactured in the same manner as in Example 1 except that the damping AC magnetic field was not applied to the metal acicular magnetic powder.

Comparative Example 2 A magnetic recording medium was produced in the same manner as in Example 2 except that the damping AC magnetic field was not applied to the metal acicular magnetic powder.

Comparative Example 3 A magnetic recording medium was prepared in the same manner as in Example 3 except that the damping AC magnetic field was not applied to the metal acicular magnetic powder.

With respect to the magnetic recording medium manufactured as described above, Mi, which is an index of the viscosity and coating characteristics of the magnetic coating,
¹ / Ms, dispersibility of magnetic powder in the magnetic layer, SFD, and magnetic properties were measured.

The viscosity of the magnetic paint was determined by using a rotary vibration method and a cone plate type viscometer, and the shear rate was 300 (l / l).
It was evaluated by observing a change in viscosity with time when a shearing force was applied in s). Further, Mi ¹ / Ms is an index representing the dispersibility in the dispersion evaluation method by the rotational vibration method, and Mi ¹ is ¹ when the externally applied magnetic field is applied to the magnetic paint by the sample vibration type magnetometer. Is the magnetization after minutes, M
s represents the saturation magnetization amount. It is shown that the higher the Mi ¹ / Ms of the magnetic paint, the higher the degree of dispersion of the magnetic powder.

For the dispersibility of the magnetic powder, a gloss meter (manufactured by Nippon Denshoku Industries Co., Ltd.) was used to measure the glossiness by injecting a light ray on the surface of the magnetic layer at an incident angle of 45 °. Evaluation was performed by converting the relative value into the gloss value of a reference plate having a standard surface according to JIS-8741 as 100%. The value converted into the relative value is referred to as gloss 45.
The larger the gloss 45 is, the more uniformly the acicular magnetic powder is dispersed in the magnetic layer.

The magnetic characteristics were evaluated by measuring the coercive force, the saturation magnetic flux density, the residual magnetic flux density and the squareness ratio with a sample vibrating magnetometer.

FIG. 2 shows the relationship between time and viscosity when a predetermined shearing force is applied to the magnetic paint, and Table 1 shows Mi ¹ / Ms, magnetic properties and gloss 45 and SFD.

[0034]

[Table 1]

First, referring to FIG. 2, the magnetic paint of Example 1 which uses needle-shaped magnetic powder to which a damping AC magnetic field is applied is the magnetic material of Comparative Example 1 which uses needle-shaped magnetic powder to which no magnetic field is applied. The viscosity is lower than that of paint. Further, in Table 1, Mi ¹ / Ms of Examples 1 to 3
Of the magnetic powders of Comparative Examples 1 to 3 in which the major axis lengths of the magnetic powders are the same, the magnetic paints of Examples 1 to 3 are better than the magnetic paints of Comparative Examples 1 to 3. M
i ¹ / Ms is high.

Further, in Table 1, gloss 45, SF
Looking at D and magnetic characteristics, the magnetic recording media of Examples 1 to 3 have higher gloss 45 and improved SFD as compared with the magnetic recording media of Comparative Examples 1 to 3, and the magnetic characteristics are It is good. From this, in the case of using the acicular magnetic powder, applying a damping AC magnetic field to the acicular magnetic powder causes the magnetic powder to be uniformly dispersed in the magnetic paint to obtain a magnetic recording medium having excellent magnetic characteristics. It turned out to be effective.

Example 4 The magnetic properties and powder properties of the flat magnetic powder used in this example are shown below. The magnetic properties are measured with a sample vibrating magnetometer (manufactured by Toei Industry Co., Ltd.), and the specific surface area is BET.
It is measured by a surface area measuring device (manufactured by Shimadzu Corporation) based on the one-point method.

Coercive force: 56.4 kA / m Saturation magnetization: 58.5 Am ² / kg Squareness ratio: 0.45 Specific surface area: 33 m ² / g

A damping AC magnetic field having an initial magnetic field of 15 kGauss was applied to the flat magnetic powder having the above characteristics. A magnetic paint was prepared by mixing, kneading, and dispersing the thus magnetized flat magnetic powder, a binder, an additive, and an organic solvent in accordance with the following magnetic paint composition. Composition of magnetic paint Flat magnetic powder 100 parts by weight Polyurethane-polyvinyl chloride copolymer 12 parts by weight (Polyurethane: polyvinyl chloride = 1: 1) Abrasive (Al ₂ O ₃ ) 3 parts by weight Antistatic agent (carbon powder ) 2 parts by weight Methyl ethyl ketone 100 parts by weight Toluene 100 parts by weight Cyclohexanone 50 parts by weight Then, the prepared magnetic coating material was applied on a polyethylene terephthalate (PET) film, and then longitudinal alignment treatment was performed to prepare a magnetic recording medium. .

Example 5 A magnetic recording medium was prepared in the same manner as in Example 4 except that the magnetic coating material coated on the non-magnetic support was subjected to the vertical alignment treatment.

Comparative Example 4 A magnetic recording medium was produced in the same manner as in Example 4 except that no damping AC magnetic field was applied to the flat magnetic powder.

Comparative Example 5 A magnetic recording medium was produced in the same manner as in Example 5 except that no damping AC magnetic field was applied to the flat magnetic powder.

With respect to the magnetic recording medium manufactured as described above, the dispersibility and magnetic characteristics of the magnetic powder in the magnetic layer were measured under the same conditions as described above. Table 2 shows the measured magnetic properties and gloss 45 and SFD.

[0044]

[Table 2]

As shown in Table 2, in the magnetic recording media of Examples 4 and 5 in which the damping AC magnetic field was applied in advance prior to the mixing of the flat magnetic powder with the binder, the flat magnetic powder was attenuated. The gloss 45 is higher and the SFD is improved as compared with the magnetic recording media of Comparative Examples 4 and 5 to which the alternating magnetic field is not applied, which are subjected to the same orientation treatment.
The magnetic properties are good.

Therefore, even when the flat magnetic powder is used, it is necessary to apply the damping AC magnetic field in advance to the flat magnetic powder before mixing with the binder. It was found that they were uniformly dispersed and were effective in obtaining a magnetic recording medium having excellent magnetic characteristics. Further, it was found that the effect of applying a damping magnetic field to such magnetic powder can be similarly obtained in both cases where the magnetic coating is subjected to the longitudinal orientation treatment and the vertical orientation treatment.

[0047]

As apparent from the above description, in the present invention, at least a magnetic powder and a binder are mixed to prepare a magnetic paint, and the magnetic paint is applied onto a non-magnetic support. As a result, when the magnetic layer is formed, the initial magnetic field is 1 kGa before mixing with the binder in the magnetic powder.
Since an external alternating magnetic field is applied to a damaging AC magnetic field that is more than uss and whose amplitude is gradually attenuated, even when a fine magnetic powder is used, the magnetic powder is well dispersed in the magnetic layer and the surface property and the magnetic property are improved. A magnetic layer having excellent characteristics can be formed. Therefore, according to the present invention, it is possible to obtain a magnetic recording medium suitable for high density recording.

[Brief description of drawings]

FIG. 1 is 1 of a damped AC magnetic field pattern applied to magnetic powder.
It is a schematic diagram which shows an example.

FIG. 2 is a characteristic diagram showing a viscosity characteristic of a magnetic paint.

Claims (4)

[Claims] 1. A magnetic recording medium comprising a magnetic layer mainly composed of magnetic powder and a binder on a non-magnetic support, wherein the magnetic powder is initially mixed with the binder. A magnetic recording medium having a magnetic field of 1 kGauss or more and a magnetic powder to which a damping AC magnetic field whose amplitude is gradually attenuated is applied. 2. The magnetic recording medium according to claim 1, wherein the magnetic powder is acicular magnetic powder. 3. The magnetic recording medium according to claim 1, wherein the magnetic powder is a plate-shaped magnetic powder. 4. A magnetic coating material is prepared by mixing at least a magnetic powder and a binder, and the magnetic coating material is applied onto a non-magnetic support to form a magnetic layer. The initial magnetic field is 1kGa before being mixed with
2. The method for manufacturing a magnetic recording medium according to claim 1, wherein a damaging AC magnetic field having a strength of not less than uss and gradually damped is applied in advance.