JPS60234219A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a magnetic tape which is free from powder dislodging from a back coat layer and sticking of the powder to a magnetic layer and has excellent wear resistance, etc. by forming the back coat laye contg. a phthalocyanine pigment on the rear of a base provided with the magnetic layer on the front. CONSTITUTION:The paint which contains the phthalocyanine pigment powder having preferably <=1.0mu max. grain size and about 0.01-0.5mu average grain size at 2-70wt% by the weight of binder resin and is incorporated therein with a dispersant, lubricating agent and antistatic agent according to need is coated on the rear of the base formed with the magnetic layer of a coating type or consisting of a thin ferromagnetic metallic film, etc. and is dried to provide the back coat layer having 0.01-0.026mu surface roughness. The phthalocyanine pigment has characteristics including the good compatibility and dispersibility with the binder resin, the specific gravity smaller than the specific gravity of the inorg. powder, difficulty in seting in the paint, the high bond strength to the binder resin, etc. and is therefore free from powder dislodging and obviates transfer of the ruggedness of the back coat layer to the magnetic layer. The tape having the excellent electromagnetic conversion characteristic, excellent chromatic S/N, etc. and good durability is thus obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to magnetic recording media, and particularly to magnetic tapes having a magnetic layer on the surface of a support and a layer of Yatsukko-I on the back surface of the magnetic tape. The present invention relates to a magnetic recording medium with improved strength and durability.

BACKGROUND OF THE INVENTION Magnetic recording media such as magnetic tapes, magnetic sheets, and magnetic disks are widely used in the audio, video, and computer fields. Among these, for example, regarding magnetic tape in the video field, when recording and playing back images, the cassette is attached to the video recorder, and the tape is guided to a guide pole or guide roller. While running, the magnetic head rubs and scans the magnetic head. In this way, images can be recorded on magnetic tape, or
mtiGplt-t45m? ;t, +0]j! lJj,
In order to improve the output in the eqA j frequency range, the surface of the magnetic layer is finished to be smooth so that the sliding force of the magnetic tape against the magnetic head does not vary. The magnetic layer is designed to have improved runnability and durability against magnetic heads, guide rollers, and the like.

However, when this magnetic tape is run by a video decoder, not only the front surface of the magnetic tape but also the back surface is rubbed by the guide poles and guide rolls, so that the magnetic layer on the front side has good running properties against the guide rolls and guide rolls. Even if the magnetic tape has good durability, the running performance and durability of the scratched part on the back side of the magnetic tape are not good.
Excessive tension is applied to the running magnetic tape - this causes the magnetic layer to rub excessively against the magnetic head, which not only causes damage to the magnetic layer and flaking of the magnetic powder in the magnetic layer, but also The strength of the winding tension of the magnetic tape fluctuates, and the spinal pressure fluctuates, causing the winding shape to become disordered and the edges of the tape to become uneven, resulting in uneven running of the tape when it is reused. When these things occur, images such as skew, jitter, and chroma S/N or electromagnetic characteristics deteriorate. Therefore, a back coat layer is provided on the back side of the magnetic tape.

As mentioned above, this back coat layer has been devised to improve running properties and durability against guide balls, guide rolls, guide pins, etc., and one of these devises includes incorporating inorganic powder into the resin layer. There is something. This is a method in which the surface of the back coat layer is roughened to reduce the contact area with guide balls, etc., and to reduce the coefficient of friction.
No. 1, JP-A-58-161135, JP-A-57.
-53825 and JP-A-58-2415 both show examples using inorganic powders, and furthermore, many of these also show those with limited particle sizes. However, these Even with the use of inorganic powder, not only is it not possible to obtain sufficient slipperiness, but when the magnetic tape layer comes into contact with guide pins, etc., these pins are scraped, making it difficult to guide the magnetic tape smoothly. Not only may the function of the guide pin be impaired, but when the back coat layer containing the guide pin is rubbed, the bonding force of the particles to the binder is insufficient to resist this, making it easy for particles to fall off. When the magnetic layer and the barracks are removed,
When the two layers come into contact, the protrusions of the hack coat layer may damage the magnetic layer, and the unevenness is also transferred to the magnetic layer, and when the magnetic layer is scanned and the image is reproduced, the chroma shows the degree of color noise in the image. This may impair electromagnetic characteristics such as S/N.

This is because, in general, inorganic powders not only have a wide variety of particle shapes and are not constant, but also have a wide distribution of particle sizes. In general, when the particle shape is spherical, the particles tend to be arranged regularly, and if these particles are arranged regularly on the surface of the bank coat layer, even when one layer of Barafco-1 comes into contact with, for example, a guide ball, these particles will make point contact, which will reduce the coefficient of friction. In addition, if the particles have a narrow particle size distribution, even if the average particle size is the same, there will be no mixing of particularly large particles, which is preferable, but these things are difficult to expect in the case of inorganic powders. Therefore, when inorganic particles are used, it is desirable to use particles with a relatively large particle size in order to improve the running properties of the bank coat layer surface. As mentioned above, it may damage the magnetic layer or impair the electromagnetic properties. From this,
Basokuko-1・Layer surface roughness cut off 0.0
Center line average roughness Ra of 8++n is 0.010 to 0.02
6 μm, it is difficult to reduce the dynamic friction coefficient μ to 0.50 or less and improve pickling properties. Moreover, cut off 0
．． The centerline maximum roughness Rm of 08+w is relatively high compared to spherical particles, which causes disadvantages such as damaging the magnetic layer as described above.

In the case of a hack coat layer using inorganic powder, Ra is 0.
If the thickness is 0.026 μm or more, the sliding property will be good, but due to the influence of transfer on the surface of the magnetic layer, Chroma S/N, Lumine S
/N etc. deteriorates electromagnetic conversion characteristics. Therefore, Ra is 0
．． It is necessary to make the inorganic powder smaller than 0.026 μm, but in order to achieve this, it is necessary to improve the dispersion state of the inorganic powder in the paint used when forming the bank coat layer, and to maintain the dispersion state until the paint is used. It needs to be maintained stably.

In general, inorganic powders such as carbon black, titanium oxide, and calcium carbonate have relatively good dispersibility in organic solvents among inorganic powders, but this is still insufficient.
The particles of these dispersions may aggregate, and if these dispersions are stored for a long period of time, the particles have a large specific gravity, and most of them, except for carbon black, have a specific gravity of 2 to 4, so they may settle.Especially When the average particle size of the inorganic powder is 0.2μ or less, poor dispersion tends to occur, and even after dispersion, the dispersion stability is poor, resulting in aggregated particles being scattered in the back coat layer formed using this paint. Therefore, it is difficult to reduce Ra to 0.026 μm or less.On the other hand, when the average particle size of the inorganic powder is 0.2L, the dispersion state in the paint is good. However, since the raw material particles themselves are large, they tend to settle, resulting in poor dispersion stability, and it is difficult to reduce Ra to 0.026 pm or less. Must be lowered.

If the filling rate of the inorganic powder is lowered in this way, it may cause so-called glabellar adhesion in which the tapes stick to each other when the tape is wound, impair wear resistance and pickling properties, and increase the risk of stake slip. .

In this way, if the Ra of the back coat layer cannot achieve the above target value and sufficient wear resistance and durability are not obtained, problems such as powder falling off of the magnetic layer will occur, and not only will the output fluctuate, but the Electromagnetic conversion characteristics such as chroma S/N will also not be good.

In particular, recently, video equipment such as VH3 video movies and β movies have become smaller and more dense, making them easier to carry. Since video recording is now being done in various situations where people are taking things out with them, it is hoped that magnetic tape will also be compatible with these situations. In other words, the miniaturization and higher density of video equipment has made the path of the magnetic tape more complex, increasing the chances of the tape coming into contact with guide balls, guide rolls, etc., increasing the frequency of friction, and reducing the running performance of -Fi. There is a demand for improvement in abrasion resistance and durability to prevent powder falling off, etc., and for this purpose, it has been desired to achieve the above target values of Ra and μ.

Second, there are problems associated with the use of inorganic powder in the conventional Hasokko-1 layer, and improvements have been desired.

OBJECTS OF THE INVENTION The first object of the present invention is to provide a hack coat layer with excellent abrasion resistance so that the powder contained in the hack coat layer does not fall off.
An object of the present invention is to provide a magnetic recording medium having a bank coat layer such that when the first layer and the magnetic layer come into contact with each other, there is no glabellar adhesion between the two layers.

A second object of the present invention is to provide a rubber material that maintains slipperiness at, for example, Ra = 0.010 to 0.026 μm without increasing the surface roughness, for example, that can reduce the coefficient of dynamic friction to 0.50 or less. An object of the present invention is to provide a magnetic recording medium having a magnetic coating layer.

A third object of the present invention is to provide a magnetic recording medium having a back coat layer formed by coating with a coating liquid having dispersion stability.

Structure of the Invention The above object is achieved by using phthalocyanine pigment powder as the powder contained in the back coat layer.

Since this phthalocyanine pigment is an organic pigment, it is compatible with the binder, and therefore has a large bonding force with the binder, so that it can increase the resistance when rubbed. Therefore, it not only improves wear resistance and durability, but also has good wettability with organic solvents and low specific gravity, making it difficult to settle.
The dispersion stability of the coating liquid for forming can be improved. In addition, as a result of experiments, it is easy to disperse the particles using a ball mill, and the dispersed particles can be easily made into primary particles, and the variation in the particle size distribution of the particles can also be reduced, so the Ra does not need to be much larger than that of the above-mentioned inorganic powder. , the friction coefficient/I can be reduced. As described above, the phthalocyanine pigment powder has excellent properties that are not found in the plate-forming inorganic powder, and the important point of the present invention lies in the novel use of this in place of the above-mentioned inorganic powder. can effectively perform its various functions.

From this, the magnetic recording medium of the present invention has a magnetic layer on one side of the support and a bank coat layer on the other side of the support, in which the bank coat layer is composed of phthalocyanine pigments. It is characterized by containing.

The back coat layer in the present invention is composed of at least a binder resin and a phthalocyanine pigment powder.

The phthalocyanine pigment used in the present invention has the general formula (
Ql h N2 ) a R' n, and Po is 11, D , Na, K X Cu, 8g, [le, ,
Mg, Ca, Zn, Cd, lia.

HgXAl1 SGa, Tr, La, NdXSm
, Eu, Gd, Dy, 110, Er, , Th, T
m,, Yb, Lu, Ti, Sn, Hf, Ph, V, S
b.

Cr, MoXU, Mn, Fe, CoXNi,
Examples include Rh, Pd, Os, and Pt, and n is O~
It is 2. The crystal forms of this phthalocyanine pigment include α, β, γ, χ, π, and ε. Further, the above general formula also includes those having a substituent which can be normally substituted with a phthalocyanine-based substance such as chlorine.

The maximum particle size of the above phthalocyanine pigment powder is 1.0 μm.
The following are preferable, and more preferably the average particle size is 0.
．． 01' to 0.5μ. In this case, it is preferable for the particle size distribution to have little variation for the reasons mentioned above.

However, particles with a wide particle size distribution may also be used, or two or more types of particle groups with different particle size distributions may be mixed and used.

Specific examples of the phthalocyanine pigments include those commonly called phthalocyanine blue and phthalocyanine green.

When the back coat layer is composed of a phthalocyanine pigment and a binder resin, the content of the phthalocyanine pigment powder in the bank coat layer is determined from the physical properties of the coating film and Ra of this layer.

If there is too much phthalocyanine pigment powder, the strength of the coating film will be weakened, which is undesirable, and if it is too little, the surface Ra value of the back coat layer cannot be achieved. From this, it is appropriate to use 2 to 70% by weight of the binder resin.

The back coat layer may further contain additives such as benzoguanamine resin powder and inorganic powder described below.

Then, a bank coat layer consisting of a mixture of these components is formed by coating the dispersion described later on the support described later by the method described later, and the Ra of the formed back coat layer is 0.010, -0. .026 pm, especially 0
．． It is preferable to set it to 010-0.018 pm. Further, it is preferable that μ in this case be 0.50 or less, particularly 0.36 or less.

Inorganic powders used with the above phthalocyanine pigment powders include carbon black, silicon oxide, titanium oxide, aluminum oxide, chromium, silicon carbide, calcium carbide, zinc oxide, α-Fe203, talc, kaolin, calcium sulfate, and nitride. Examples include those made of boron, zinc fluoride, molybdenum dioxide, calcium carbonate, etc., preferably carbon black or titanium oxide, and these also have a function as a roughening agent together with cyanine pigment powder.

Binder resins that can be used in the back coat layer include thermoplastic resins, thermosetting resins, reactive resins, electron beam curable resins, and mixtures thereof.

The thermoplastic resin used as the binder resin has a softening temperature of 150°C or less and an average molecular weight of 10.000 to 20.
0,000, with a polymerization degree of about 200 to 2,000, such as vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, acrylic ester-acrylonitrile Copolymer, acrylic ester-vinylidene chloride copolymer, acrylic ester-styrene copolymer, methacrylic ester-acrylonitrile copolymer, methacrylic ester-vinylidene chloride copolymer, methacrylic ester-styrene copolymer , urethane elastomer, polyvinyl fluoride, vinylidene chloride-acrylonitrile copolymer, acrylonitrile-butadiene copolymer, polyamide resin, polyvinyl butyral, cellulose derivatives (cellulose acetate butyrate, cellulose diacetate, cellulose triacetate, cellulose propionate, nitrocellulose, etc.), styrene-butadiene copolymers, polyester resins, chlorovinyl ether-acrylic acid ester copolymers, amino resins, various synthetic rubber-based thermoplastic resins, and mixtures thereof.

These resins are disclosed in Japanese Patent Publications Nos. 37-6877 and 39-1.
No. 2528, No. 39-19282, No. 40-5349
No. 40-20907, No. 41-9463, No. 4
No. 1-14059, No. 41-16985 No. 42-64
No. 28, No. 42-11621, No. 43-4623,
No. 43-15206, No. 44-2889, No. 44-
No. i7947, No. 44-18232, No. 45-140
No. 20, No. 45-14500, No. 47-18573, No. 47-22063, No. 47-22064, No. 4
No. 7-22068, No. 47-22069, No. 47-2
2070, U.S. Patent No. 4B-27886, U.S. Patent No. 3.144.352, U.S. Patent No. 3,419.420,
No. 3,499.789 and No. 3,713,887 Mei-Goku 1@.

The thermosetting resin or reactive resin used is one that has a molecular weight of 200,000 or less in the state of a coating solution and becomes insolubilized by a reaction such as condensation or addition after coating and drying. Among these resins, those that do not soften or melt before the resin is thermally decomposed are preferred. Specifically, for example, phenol resin, phenoxy resin, epoxy resin, polyurethane curable resin, urea resin, melamine resin, alkyd resin, silicone resin, acrylic reaction resin, vinyl chloride-vinyl acetate resin, methacrylate copolymer. and diisocyanate prepolymers, mixtures of high molecular weight polyester resins and isocyanate prepolymers, urea formaldehyde resins, mixtures of polyester polyols and isocyanates, polycarbonate-type polyurethanes, polyamide resins, low molecular weight glycols, high molecular weight diols, and triphenylmethane triisocyanates. mixtures, polyamine resins, and mixtures thereof.

These resins are disclosed in Japanese Patent Publications Nos. 39-8103 and 40-97.
79 No. 41-7192, No. 41-8016, No. 4
No. 1-14275, No. 42-18179, No. 43-1
No. 2081, No. 44-28023, No. 45-1450
No. 1, No. 45-24902, No. 46-13103,
No. 47-22067, No. 47-22072, No. 47
-22073, 47-28045, 47-28
No. 048, No. 47-28922, No. 5B-4051,
Japanese Unexamined Patent Publication Nos. 57-31919 and 58-60430, Japanese Patent Application Nos. 151964-1982 and 5B-1206
No. 97, No. 58-120698, U.S. Patent No. 3
, 144.353, 3.320, 090, 3.437.510, 3.597,273, 3.78L210, and 3.73L2IL. It is described in.

Examples of electron beam irradiation-curable resins include unsaturated prepolymers,
For example, maleic anhydride type, urethane acrylic type, polyester acrylic type, polyether acrylic type, polyurethane acrylic type, polyamide acrylic type, etc., or as a polyfunctional monomer, ether acrylic type, urethane acrylic type, phosphate ester acrylic type, aryl type , hydrocarbon type, etc.

In order to improve the durability of the back coat layer of the magnetic recording medium according to the present invention, the back coat layer can contain various curing agents, for example, isocyanate.

Aromatic isocyanates that can be used are, for example, tolylene diisocyanate (TI), 4,4'-diphenylmethane diisocyanate (MDI), xylylene diisocyanate (X old), metaxylylene diisocyanate (MXDI) and those active with these isocyanates. There are adducts with hydrogen compounds, and the average molecular weight is 10.
A range of 0 to 3,000 is preferred.

On the other hand, examples of aliphatic isocyanates include hexamethylene diisocyanate (IIMDI), lysine isocyanate, and trimethylhexamethylene diisocyanate (TM
DI) and adducts of these isocyanates and active hydrogen compounds. Among these aliphatic isocyanates and adducts of these isocyanates and active hydrogen compounds, those having a molecular weight in the range of 100 to 3,000 are preferred.

Among the aliphatic isocyanates, non-alicyclic isocyanates and adducts of these compounds with active hydrogen compounds are preferred.

Examples of the adduct of the above-mentioned isocyanate and an active hydrogen compound include an adduct of a diisocyanate and a trivalent polyol. Polyisocyanates can also be used as curing agents, including, for example, a pentamer of diisocyanate, a decarboxylation compound of 3 moles of diisocyanate and water, and the like. Examples of these include an adduct of 3 moles of tolylene diisocyanate and 1 mole of trimethylolpropane, an adduct of 3 moles of metaxylylene diisocyanate and 1 mole of trimethylolpropane, a pentamer of tolylene diisocyanate, and 3 moles of tolylene diisocyanate. There are pentamers made of 2 moles of hexamethylene diisocyanate, etc., and these can be easily obtained industrially.

To form the back coat layer of the magnetic recording medium of the present invention using these isocyanates - Prepare a coating material by mixing and dispersing the above-mentioned resin and various additives described later in an organic solvent as necessary. The isocyanate-loaded plate is coated onto a support, such as a polyester film, and optionally dried. In this case, the amount of isocyane 1- added is preferably 5 to 50% by weight based on the resin. If it is less than 5% by weight, the coating film tends to be insufficiently cured, and if it is more than 50% by weight, the coating film becomes too hard, which is not preferable.

The paint forming the back coat layer may contain additives such as a dispersant, a lubricant, and an antistatic agent, if necessary.

For example, dispersants include lecithin; caprylic acid;
Fatty acids with 8 to 18 carbon atoms (R-
R represented by COOH is a saturated or unsaturated alkyl group having 7 to 17 carbon atoms); an alkali metal (Li, Na, K, etc.) or an alkaline earth metal (Mg
, Ca, Ba, etc.). In addition, higher alcohols having 12 or more carbon atoms, sulfuric esters, and the like can also be used. It is also possible to use commercially available general surfactants. These dispersants may be used alone or in combination of two or more. These dispersants are
No. 28369, No. 44-17945, No. 48
'-15001, U.S. Patent No. 3,587,993
No. 3゜470.021.

In addition, as lubricants, silicone oil, graphite, molybdenum disulfide, tungsten disulfide, fatty acid esters consisting of monobasic fatty acids with 12 to 16 carbon atoms and monohydric alcohols with 3 to 12 carbon atoms, and 17 carbon atoms are used as lubricants. A fatty acid ester consisting of a monobasic fatty acid or more and a monohydric alcohol having a total of 21 to 23 carbon atoms is used. These are described in Japanese Patent Publication No. 43-23889.

In addition, antistatic agents include conductive powders such as carbon black, graphite, tin oxide-antimony oxide compounds, titanium oxide-tin oxide-antimony oxide compounds, and carbon blank graft polymers; natural surfactants such as saponin; alkylene Nonionic surfactants such as oxide, glycerin, and glycidol; cationic surfactants such as pyridine and other heterocycles, phosphonium or sulfonium; carboxylic acid, sulfonic acid, phosphoric acid,
Examples include anionic surfactants containing acidic groups such as sulfate ester groups and phosphate ester groups; amphoteric surfactants such as amino acids, aminosulfonic acids, and sulfuric or phosphoric esters of amino alcohols.

These surfactants that can be used as antistatic agents include U.S. Pat. 2.676゜924, same No. 2,676.975
No. 2,691,566, No. 2,727,86
No. 0, No. 2,730,498, No. 2,742゜37
No. 9, No. 2.739,891, No. 3,068.1
No. 01, No. 3,158,484, No. 3,201,
No. 253, No. 3,210.191, No. 3,294
, No. 540, No. 3,415,649, No. 3.44
1,413, 3,442,654, West German Patent Publication (OLS) 1,942,665, British Patent No. 1,077°317, British Patent No. 1,198,450, etc. First, "Synthesis of surfactants and their applications" by Ryohei Oda et al. (Maki Shoten 1964 edition): A, W., Bayley [+-Fest Active Agent J (Interscience Publications Incorporated 1)
958 edition): "Encyclopedia of Surf Active Agents Volume 2" by TR Sisley
(Chemical Bab Satush Company 1964 edition):
“Surfactant Handbook” 6th printing (Sangyo Tosho Co., Ltd. 1968)
December 20th, 2015>, etc., are described in detail.

These surfactants may be added alone or in combination. These are used as antistatic agents, but may also be used for other purposes, such as dispersion, improving magnetic properties, improving lubricity, and as coating aids.

Solvents to be added to the above paint or diluting solvents when applying this paint include ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; alcohols such as methanol, ethanol, propatool, and butanol; methyl acetate, ITiI: ethyl acid,
Esters such as butyl acetate, ethyl lactate, and ethylene glycol monoacetate-1-; ethers such as glycol dimethyl ether, glycol monoethyl ether, dioxane, and tetrahydrofuran; aromatic hydrocarbons such as Hensen, toluene, and xylene; methylene chloride, Halogenated hydrocarbons such as ethylene chloride, carbon tetrachloride, chloroform, and dichlorohenzene can be used.

In addition, as a support, polyethylene terephthalate,
Examples include polyesters such as polyethylene-2,6-naphthalate, polyolefins such as polypropylene, cellulose derivatives such as cellulose triacetate and cellulose diacetate, and plastics such as polyamide and polycarbonate, but Cu, 77! , metals such as Zn, glass, BN, Si carbide, ceramics such as porcelain, ceramics, etc. can also be used.

An intermediate layer for improving adhesion may be provided between the support and the back coat layer.

As a coating method for forming the above-mentioned Barafco-1 layer on the support, air doctor coat 1-, plate coat
I~, air knife coat, squeeze coat, impregnation coat, reverse roll coat 1~, transfer roll coat 1~, gravure coat, Kisco 1~, cast coat, spray yo 1~, etc. can be used, but are not limited to these.

The magnetic layer of the magnetic recording medium of the present invention may be a coated magnetic layer using magnetic powder, a binder, a dispersant, a lubricant, etc., or may be formed by a vapor deposition method, a sputtering method, a Heber deposition method, etc. It may also be a thin film type magnetic layer.

As the coated magnetic layer, the binder resin, dispersant, antistatic agent, lubricant (0.2 to 20 parts by weight per 100 parts by weight of magnetic powder) used in the above-mentioned back coat layer can be used. In addition, examples of magnetic powder include y-Fe20B, C
o-containing T-Fe20B, Co-coated γ-Fe203, Fe
3O4, Co-containing FeBO4, Co-coated pe304, C
Oxide magnetic material such as r02, e.g. Fe, Ni-5CO%
Fe-Ni alloy, Fe-Co alloy, Fe-Nj-P alloy, Fe-Ni-Co alloy, Fe-Mn-Zn alloy, F
e-Ni-Zn alloy, Fe-Co-Ni-Cr alloy, F
e-Co-Ni-P alloy, Co-Ni alloy, Co-P
Examples include various ferromagnetic materials such as alloys, Co--Cr alloys, and metal magnetic powders containing Fe and Nis Co as main components. Additives to these metal magnetic materials include sl, Cu, and Z.
Elements such as ns A N % P, Mn, Cr, or compounds thereof may be contained. Hexagonal ferrite such as barium ferrite and iron nitride are also used.

An abrasive can also be used in the magnetic layer, and commonly used materials include fused alumina, silicon carbide,
Chromium oxide, corundum, artificial corundum, diamond, artificial diamond, garnet, emery (main ingredients are corundum and magnetite), titanium dioxide, etc. are used.

These abrasives have an average particle diameter of 0.05 to 5 .mu.m, particularly preferably 0.1 to 1 .mu.m.

These abrasives are used in an amount of 1 to 20 parts by weight per 100 parts by weight of magnetic powder.
Added within the market weight range. The coating solvent and coating method for this magnetic layer are the same as those for the bank coat layer.

Effects of the Invention As described above, the present invention makes it possible to improve the adhesion within the bank coat layer by incorporating a phthalocinine pigment into the bank coat layer. When the powder is applied, it blends in well and is firmly fixed within the layer, so even when the hack coat layer is rubbed by a guide ball, for example, there is less powder falling off. It is also possible to reduce the need to scrape off guide pins and the like.

Furthermore, since phthalocyanine pigment powder has good dispersibility even when the particle size is 0.1 μm or less, when it is contained in a back coat layer, Ra can be reduced and its friction coefficient μ can be reduced. This makes it possible to improve the slipperiness of the back coat layer so that the magnetic tape can be wound evenly, and when the magnetic tape is wound, there are no irregularities on the magnetic layer that can cause problems due to the unevenness of the back coat layer. This can reduce the occurrence of damage to electromagnetic conversion characteristics such as chroma S/N, and can also reduce damage to the surface of the magnetic layer.

In addition, phthalocyanine pigment powder has good dispersibility in binder resins and organic solvents, and can improve dispersion stability in coating liquids, as well as contribute to improved productivity and energy savings.

EXAMPLES Next, the present invention will be described in detail with reference to Examples, but the present invention is not limited thereto.

Example 1 The following composition was sufficiently stirred and mixed in a ball mill, and then a polyfunctional isocyanate (Coronet manufactured by Nippon Polyurethane Co., Ltd.) was added.
After adding 10 g of L), the mixture was filtered with a filter having an average particle size of 1 μm.

Co-containing γ-Fe203 100 g Polyurethane (Nistan 5701 manufactured by Gusodolinchi Co., Ltd.) 40 g Nitrocellulose (Seltsuba BTH1/2 manufactured by Fukaisei Co., Ltd.) 20 g Vinyl chloride-vinyl acetate copolymer (U, C, C, manufactured by VAGI Co., Ltd. 10 g lecithin 2
g Myristic acid 1 g Lauric acid 1 g Methyl ethyl ketone 72 g Toluene 50 g Cyclohexanone 80 g Carbon black (Conductesox 975) 2 g This paint was applied on a 12 μm thick polyethylene terephthalate base film under an orienting magnetic field, and Perform drying,
This dried product was calendered to give a magnetic layer thickness of 5 μm.

Next, the composition of Example 1 shown in Table 1 was milled in a ball mill for 5 minutes.
The mixture was kneaded for several hours to make 11 liters of a coating solution. This coating solution was applied to the back surface of the support using a reverse roll and dried to form a bank coat complex with a dry film thickness of 0.7 μm.
The magnetic tape of Example 1 was prepared by slitting it into two widths.

Example 2 The magnetic material of Example 2 was prepared in the same manner as in Example 1 except that a back coat layer was formed using the composition of Example 2 instead of using the composition of Example 1 in Table 1. I made a tape.

Comparative Example 1 In Example 1, the composition of Comparative Example 1 was used instead of the composition of Example 1 in Table 1 for the back coat layer, and the coating solution was prepared by kneading this in a ball mill for 20 hours. A magnetic tape of Comparative Example 1 was prepared in the same manner as in Example 1.

Comparative Examples 2 to 4 Comparisons were made in the same manner as Comparative Example 1, except that the compositions of Comparative Examples 2 to 4 were used instead of the composition of Comparative Example 1 in Table 1 for the back coat layer. Example 2
~4 magnetic tapes were created.

In Table 1, the numbers for composition J indicate parts by weight and the particle size indicates μm, the polyester is Vylon 200 (Toyobo ■t1), and the nitrocellulose is Seltsuba (Asahi Kasei ■).
Polyisocyanate is Corone) L (manufactured by Nippon Polyurethane), CaCO3 is Homocal D (manufactured by Shiraishi Kogyo), and Sio 2 is Aerosil (Nippon Aerosil).
Ti02 is TY-50 (manufactured by Ishiya Sangyo ■), and phthalocyanine blue is a phthalocyanine pigment manufactured by Toyo Ink ■.

The above Examples 1 and 2 and Comparative Examples 1 to 4 were tested for each item shown in Table 2, and the results are shown in the corresponding column of Table 2. ) A similar test was conducted for those without
The results are shown below.

Here, the wear condition is Vidiodesoki (equipment name NV620).
0), each of the above magnetic tapes was passed through the tape 100 times, and the degree of abrasion of the back coat layer was observed using an optical microscope.

If there was powder falling off, scratches would be visible on the surface of the bank coat layer, so this was evaluated based on the strength (more or less).

The damage to the tape was evaluated by visually observing the surface of the hack coat layer of the magnetic tape that had been passed through the video deck 100 times and evaluating the degree of damage as more or less scratched.

Cinching was done by running and winding with the above video deck 4
) was evaluated as good if it was wrapped in an orderly manner, and bad if the tape-wrapped side was not flat and disordered.

After the magnetic tapes of Examples and Comparative Examples were passed through the video deck 100 times, the surface of the guide pin was observed with an optical microscope, and the degree of scratching was evaluated as more or less scratched.

For adhesion, as in the dish cinching test, a 1/2 inch wide magnetic tape was wound with a pressure of I kg, left at 45°C and 80% relative humidity for 24 hours, and then left at room temperature for another 24 hours before wrapping. If there was resistance when putting it back and pulling it apart, it was evaluated as "Yes", and if there was no resistance, it was evaluated as "No".

The coefficient of dynamic friction was measured using a rotating drum type surface property measuring device manufactured by Shinto Kagaku Co., Ltd. with a rod having a diameter of 411 at a load of 30 g and a rotation speed of 159 rpm.

Surface roughness was measured using a three-dimensional roughness measuring device 3E-3R manufactured by Koita Research Institute.
Measured using K.

Chroma S/N (dB) is chroma signal (3,58Mtl
z) to 0.714Vp-p on the luminance signal, playback this recording, extract only the chroma signal, its effective value (S), and the noise level (N) when the chroma signal is removed. ) represents the ratio.

In the dispersibility test, the dispersion liquid was applied to a glass plate using an applicator, and the dispersibility of the particles was evaluated using a microscope into three grades: good, good, and poor.

In the dispersion stability test, the dispersion was allowed to stand for 48 hours, and the degree of sedimentation of the particles and the dispersion were applied to a glass plate using an applicator, and the size of the dispersed particles was observed using a microscope, and the results were classified into three grades: good, good, and poor.
Evaluated in stages.

From the results in Table 2, the hack coat layers of the magnetic tapes of the examples of the present invention all have a particle diameter as small as 0.05 μm, but the Ra value is 0.018 or less, the dynamic friction coefficient is 0.5 or less, and the dispersion In contrast, Comparative Example 1 has a small amount of inorganic powder and has a high coefficient of kinetic friction, causing some wear and adhesion. Since the amount is large, the surface roughness is thick (there is chipping of the pin, poor dispersion stability, Comparative Example 3
In Comparative Example 4, the particles were too large, resulting in poor dispersibility and dispersion stability, and the surface roughness was large, resulting in poor chroma S/N. Comparative Example 4 had too large particles, resulting in many pins being scraped, and the surface roughness was also large. Therefore, it can be seen that the chroma S/N is also poor. Note that those without a back coat layer (without BC) have wear and tape damage, and the winding appearance is disordered.

(Margins below this page) Table 1 (Margins below this page) Table 2 May 7, 1980

Claims (1)

[Claims] (1) A magnetic recording medium having a magnetic layer on one side of a support and a bank coat layer on the other side of the support, characterized in that the bank coat layer contains a phthalocyanine pigment. magnetic recording medium.