JPS63261523A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve the dispersibility of fine ferromagnetic material powder into a binder so that a magnetic layer having high S/N is obtd. by using respectively specific fine ferromagnetic metallic powder and binder and to lower the surface electric resistance of the magnetic layer so that the electrostatic chargeability thereof and drop-outs are decreased by improving the surface characteristic of the magnetic layer. CONSTITUTION:The fine ferromagnetic metallic powder of a magnetic recording medium provided with the magnetic layer formed by uniformly dispersing the fine ferromagnetic material powder into the binder on a nonmagnetic base is the fine ferromagnetic metallic powder having >=45m<2>/g SBET, >=1,000Oe coercive force and >=7 acicular ratio and further,the binder consists of a polymer which contains the polar group expressed by formula I and has the mol. wt. within a 10,000-100,000 range. The ratio (weight) of the fine ferromagnetic material powder and the binder is 2.5-10. The dispersibility of the respective components in a coating liquid for formation of the magnetic layer is thereby improved. As a result, the surface electric resistance of particularly the magnetic layer of the magnetic recording medium having good video S/N is low and, therefore, the drop-outs are less increased.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a magnetic recording medium, and particularly to a magnetic recording medium containing fine ferromagnetic metal powder with improved durability and surface properties. .

The magnetic recording medium according to the present invention is used as a "magnetic tape,""magneticseed," or "magnetic disk."

[Prior art and its problems]

With the rapid development in the field of magnetic recording technology, the performance of magnetic recording media is increasingly required to be improved, and in particular, high reproduction output is required for short wavelength recording in magnetic recording media for video. Therefore,
Usually, the ferromagnetic powder used in the magnetic layer of this magnetic recording medium is made into highly fine particles, and at the same time, the surface of the magnetic layer is smoothed to obtain a high S/N. However, when the ferromagnetic powder in the magnetic layer is made into fine particles in this way, the powder particles strongly bond and aggregate due to the fine particle nature and magnetism of the powder, making it extremely difficult to uniformly disperse them in the binder. If the ferromagnetic powder is not sufficiently dispersed within the magnetic layer, the uniformity within the magnetic layer will deteriorate.
There was a problem in that the orientation of the powder itself and the surface properties of the magnetic layer were poor, and as a result, a high S/N ratio could not be obtained.

Furthermore, when the ferromagnetic powder is made into finer particles, its specific surface area increases, and the contact interface between the ferromagnetic powder and the binder solution increases, requiring greater energy to disperse the ferromagnetic powder. do. This problem can be solved to some extent by improving the mixing and dispersing machine for the magnetic composition, but there are limits to this. Therefore, a conventional method has generally been adopted in which a surfactant having dispersion ability is added to a magnetic composition. However, when the amount of surfactant added is increased in order to improve the dispersion ability, a new problem arises in that the physical properties of the resulting magnetic layer deteriorate.

Furthermore, magnetic recording media have the problem of charging, and in order to suppress charging properties, carbon black or an antistatic agent is generally added to the composition for forming the magnetic layer.
This method sometimes causes problems with adhesive failure due to a drop in S/N and blooming.

Recently, we have improved the dispersibility of ferromagnetic fine powder in binder,
In addition, improvements have been made to the binder itself in order to impart antistatic properties, such as those with the general formula: -COOX, SOs X, 0
A binder having a polar group consisting of 3Os This binder was noted as achieving the above objectives to some extent. However, even with this type of binder, a satisfactory situation has not yet been reached.

[Means and effects for solving the problems] The present invention solves the problems in the prior art described above, that is, improves the dispersibility of fine ferromagnetic powder in a binder in the magnetic layer of a magnetic recording medium. The purpose is to obtain a magnetic layer with high S/N by using a magnetic layer, and to reduce the charging property of the magnetic layer by lowering the surface electrical resistance by improving the surface properties of the magnetic layer, thereby obtaining a magnetic recording medium with no increase in dropouts. The present inventors have carefully investigated the relationship between the type and molecular weight of the functional group of the polymer used as a binder and the specific surface area (Smty) measured by the BET method of fine ferromagnetic powder. As a result of our research, we have discovered that the above objectives can be achieved by a specific combination of these, and the running properties of the magnetic recording medium can also be significantly improved, leading to the present invention.

That is, the present invention provides a magnetic recording medium in which a magnetic layer in which fine ferromagnetic powder is uniformly dispersed in a binder is provided on a non-magnetic support, wherein the fine ferromagnetic powder has a size of 5 m1.
t is 45rrf/g or more and coercive force is 1.000Oe
ferromagnetic metal fine powder with an acicular ratio of 7 or more, and the binder has a polar group represented by the following general formula: -COOX, -SOsX, -O
S OsX, -pot xt t or -OP OsX
z (However, L, X in the above polar group is -NR+ Rt
Rs Ra (R+, Rt -Rs and R4 are hydrogen atoms, alkyl groups having 1 to 12 carbon atoms, alkenyl groups,
represents a substituted alkyl group or a substituted alkenyl group, and has a molecular weight of 10.000 to 100.000.
A magnetic recording medium characterized in that the ratio (weight) of the ferromagnetic fine powder to the binder is 2.5 to 10, and in particular, the binder is a vinyl chloride-based polymer. The above magnetic recording medium is made of a polymer, polyurethane resin, or polyester resin.

The present invention will be explained in detail below.

The magnetic recording medium of the present invention basically has a magnetic layer in which fine ferromagnetic powder is dispersed in a binder on a non-magnetic support.

And one of the features of the present invention is that this ferromagnetic material is s st
Specific examples of ferromagnetic metals where y is a ferromagnetic metal of 45rrf/g or more include Fe or Fe and other examples such as 'l'iSV%Cr, Mn.

Co, Nt, Cu, Zn, SL, P, Mo, Sn.

There are alloys with metals such as Sb and Ag. These ferromagnetic metals can be prepared, for example, by thermally decomposing an organic acid salt of a ferromagnetic metal and reducing it by contacting it with a reducing gas, by using acicular oxyhydroxides or these containing other metals, or by using these methods. A method of reducing acicular iron oxide obtained by heating oxyhydroxide by contacting it with a reducing gas, a method of thermally decomposing a metal carbonyl compound, a method of evaporating a ferromagnetic metal in a low pressure inert gas, A method of reducing a ferromagnetic material with a reducing substance such as a boron hydride compound, hypophosphite or hydrazine in an aqueous solution of a salt of a metal that can be
It can be manufactured by a method in which ferromagnetic metal powder is electrodeposited using a mercury cathode and then separated from the mercury. The particles of ferromagnetic metal powder thus obtained have a specific surface measured by the BET method! (S sit ) h<
451Tr/g or more, preferably 50rrf/g
It is necessary that it is above.

For iron oxide particles with S sit of 45 rtf/g or less, S
This is because the effect of improving /N cannot be expected much. The ferromagnetic particles having Sm1t of 45 rif/g or more can be obtained by selecting the size of the particles in the starting material and 5m1t. This ferromagnetic metal powder preferably has a coercive force Hc of 1.000 or more when the purpose of the magnetic recording medium used is short wavelength recording.
The acicular ratio of the powder is preferably 7 or more in order to ensure the necessary coercive force Hc and improve the orientation of the magnetic particles.

Another feature of the invention is that the binder used to form the magnetic layer is a polar group represented by the following general formula: C00X, SOs X, -COOX, -
PO, X, or -〇PO3XI (However, X in the above polar group is -NR+
, Rs and R4 represent a hydrogen atom, an alkyl group, an alkenyl group, a substituted alkyl group, or a substituted alkenyl group having 1 to 12 carbon atoms, and have a molecular weight of 10,000 to 100.000.
In particular, the binder is a vinyl chloride copolymer, a polyurethane resin, or a polyester resin. X in the polar group is -NR+ Rt
R2Ra, and R,, R,, R1 and R4 are
Hydrogen atoms, alkyl groups, alkenyl groups, substituted alkyl groups, or substituted alkenyl groups having 1 to 12 carbon atoms, but in these polar groups, R+, Rt, Rs, and R4 may have one or less hydrogen atoms. desirable,
Examples of alkyl groups include methyl group, ethyl group,
Substituted alkyl groups include tolyl and methylol groups, and alkenyl groups include vinyl and propynyl groups. In the present invention, characteristic polar groups include, for example, -000, -SO,, -03Os, -POs
, 0POs etc. and -NH(Cz Hs
) s, NH(Cx Hs) 1ChHrs,
There are combinations such as N (Cx Hs) 4.

The above polar group-containing polymer is generally synthesized by the following reaction. That is, these polymers are -COOH, -5os H, -O3Os H, -P
A resin such as a vinyl chloride polymer, a polyurethane resin, or a polyester resin containing any of Ox Hs or -〇POsHt, and an alkylamine, dialkylamine, trialkylamine,
Reaction products with tetraalkylammonium hydroxide, etc., or copolymers of polymerizable unsaturated (double bond-containing) compounds containing the above polar groups and other copolymerizable compounds, containing the above polar groups Examples include condensates of polyhydric alcohols and diisocyanates, and condensates of dicarboxylic acids containing polar groups as described above and polyhydric alcohols.

In addition to the above-mentioned polar groups, the actual polymer may also contain polar groups such as hydroxyl, epoxy, and isocyano groups, and the molecular weight of the polymer containing these polar groups is approximately 10. 000~100.000
is within the range of If the molecular weight is below the lower limit, the durability of the magnetic layer formed will be poor, while if it is above the upper limit, the solution viscosity will increase, which is disadvantageous in terms of the process.

The present invention is particularly characterized in that the above-mentioned Shigetani body is a vinyl chloride resin, a polyurethane resin, or a polyester resin.

1. A vinyl chloride resin with a polar group introduced into the side chain, which has the following general formula (■) and general formula (I): [wherein, X is the above polar group] Yes, Y represents a monomer having a vinyl group that can be copolymerized with vinyl chloride, 1,
m and n each represent the degree of polymerization of each component. In addition, in the general formula, each component of the polymer is shown as being arranged regularly in sequence for convenience, but in addition to the cases represented by the above general formula, each component is shown as being arranged regularly in a fixed proportion. They may be arranged or randomly arranged. These resins can be synthesized using conventional techniques.

In the above general formula (I>), the vinyl chloride component is related to the strength and solubility of the magnetic layer in a solvent, and its degree of polymerization l
is less than 100, the desired strength cannot be obtained, and 1
If the polymerization degree is higher than 000, the solubility in solvents will be poor, so the preferable degree of polymerization of the vinyl chloride component is within the range of 100 to 1000.In addition, the vinyl component having a polar group in its side chain has magnetic properties due to the polar group. This improves the dispersibility of the ferromagnetic fine powder in the layer, but the degree of polymerization n is 0.
．． If it is less than 1, the effect will be insufficient, and if it is more than 100, it will not contribute much to the dispersibility, and on the contrary, it will cause problems in terms of moisture resistance. Therefore, the degree of polymerization of the vinyl component having a polar group is 0. 1 to 100, and in addition to the above-mentioned copolymerizable monomers, a monomer Y component that can be copolymerized with vinyl chloride from the viewpoint of improving solubility in solvents, crosslinking with isocyanate, and improving coating film strength. It is also possible to copolymerize at least one selected from vinyl acetate, vinyl alcohol, maleic acid, maleic anhydride, acrylic acid, acrylic ester, methacrylic acid, methacrylic ester, acrylonitrile, vinylidene chloride, vinyl propionate, etc. It is.

A polar group is introduced into the side chain of ±Yutate 2LZ Hanging Polyretuff 1M resin. Polyurethane resin is generally obtained by the reaction of a polyhydroxy compound and a polyisocyanate, but the polar group is used as a raw material for polyurethane resin. The polar group can be introduced into the polyurethane resin by mixing the compounds having the polar group or by organizing the hydroxyl groups remaining at the terminal or side chain of the polyurethane resin with the compound having the polar group. The amount of polar groups introduced into the polyurethane resin is 0.01 to 1.0 mm o 1 /
g, preferably 0.1 to 0.5 mm o 1
It is 7g.

If it exceeds the upper limit, intermolecular or intramolecular aggregation occurs, which not only adversely affects dispersibility, but also causes selectivity with respect to the solvent, resulting in the problem that ordinary general-purpose solvents cannot be used.

A polar group is introduced into the side chain of a polyester resin, and the polyester resin is generally synthesized by condensation polymerization of a carboxylic acid component, a polyhydric alcohol component, and a dicarboxylic acid component having the polar group. be able to. Further, the polar group can be introduced into the polyurethane resin by modifying the hydroxyl group remaining at the terminal or side chain with a compound having the polar group. The amount of polar groups introduced into the polyester resin is 0.01 to 1.0 m
not/g, preferably 0.1 to 0.5 mm
It is ol/g. The upper limit amount is the same as for polyurethane resin.

These high molecular weight polymers can be used alone or in combination of two or more as binders.

A high molecular weight polymer conventionally used as a binder can be used together with the above-mentioned characteristic binder of the present invention in an amount not exceeding the above ratio.

Examples of this polymer include vinyl chloride-vinyl acetate copolymer, vinyl chloride-acrylonitrile copolymer, acrylic ester-acrylonitrile copolymer, acrylic ester-vinylidene chloride copolymer, other acrylic acid copolymers, Urethane elastomers, nylon-silicone resins, cellulose derivatives such as nitrocellulose,
Polyvinyl chloride resin, vinylidene chloride-acrylonitrile copolymer, polyamide resin, polyvinyl butyral,
Styrene-butadiene copolymer, phenolic resin, epoxy resin, polyurethane resin, urea resin, melamine resin, polyester resin, chlorovinyl ether-acrylic ester copolymer, methacrylic ester copolymer,
Binding isocyanate blend polymer, amino resin,
There are various types of synthetic rubber.

Furthermore, it is preferable to add a thermosetting polyisocyanate compound as a binder component in order to improve the durability of the magnetic layer. Examples of the polyisocyanate compound include tolylene diisocyanate, 4,4-diphenylmethane diisocyanate, hexamethylene diisocyanate, and xylene diisocyanate. Isocyanates such as diisocyanate, naphthylene-1,5-diisocyanate, 0-)luidine diisocyanate, isophorone diisocyanate, triphenylmethane triisocyanate, products of these isocyanates and polyalcohols, and condensation of isocyanates. There are polyisocyanates produced by Commercial products of these various polyisocyanates include, for example, "Coronate L" and "Coronate".
HLJ, “Coronate 2030 J,” “Coronate 20
31 J, “Coronet 2036 J, “Coronet”
3014 J, "Coronet" 2015 J, r Milioho 1-MRJ, r Millionate MTLJ, "Dalt Sec 1350 J," Dalt Sec 2170 J, "Dalt Sec 2170 J," Dalt Sec 2280 J
(All of the above are product names: Nippon Polyurethane Industries ■), "Takenate D-102J," Takenate D-11
ONJ, “Takenate D-200J,” “Takenate D
-202J, (all manufactured by Shikinichi Yakuhin Kogyo ■), ``Dismosier Shi'', ``Dismodule ILJ, r Dismodule N'', ``Dismodule HL, (all above,
(manufactured by Sumitomo Bayer ■), and these are used alone or in combination of two or more types by taking advantage of the difference in curing reactivity. Further, for the purpose of accelerating curing, it is desirable to use a compound having a large number of functional groups such as hydroxyl groups and amino groups.

Another feature of the present invention is that the mixing ratio (weight) of the ferromagnetic fine powder and the binder is 2.5 to 10.

If it is below the lower limit (insufficient amount of ferromagnetic fine powder), the required magnetic properties cannot be obtained, and if it is above the upper limit (insufficient amount of binder)
In this case, the magnetic layer has poor bonding properties, that is, poor durability.

In addition to the above magnetic layer components, it is also possible to further add reinforcing agents, lubricants, antistatic agents, dispersants, etc. for the magnetic layer.

Reinforcing agents include α-alumina, fused alumina, chromium oxide, corundum, α-iron oxide, silicon nitride, boron nitride,
There are powders of substances with a Mohs hardness of 6 or more, such as silicon carbide, molybdenum carbide, boron carbide, tungsten carbide, diatomaceous earth, and dolomite, with an average particle diameter of o, oos ~ 5 μm, which can be used alone or in a mixture of two or more as desired. . These reinforcing agents are
It is used in proportions within the range of 0 parts by weight.

Lubricants include silicone oil, graphite, molybdenum disulfide, boron nitride, graphite phosphide, tungsten disulfide,
These include fluorinated alcohols, polyolefins, polyglycols, alkyl phosphorus esters, polyphenyl ethers, higher fatty acid esters, higher fatty acid amides, higher fatty acid alcohols, and antioxidants such as alkyl phenols, which are commonly used as additives in lubricating oils. Rust inhibitors such as naphthenic acid, oil agents such as lauryl alcohol, extreme pressure agents such as dibenzyl sulfide, other detergents and dispersants, viscosity index improvers, pour point depressants, antifoaming agents, etc. can also be added. These lubricants are used in proportions ranging from 0.05 to 20 parts by weight per 100 parts by weight of binder.

Antistatic agents include graphite, various carbon blacks, carbon black graft polymers, conductive powders such as tin oxide-antimony oxide compounds, natural surfactants such as saponin, alkylene oxides, glycerin, glycidol, and polypropylene. Various nonionic surfactants such as alcohols and polyhydric alcohol esters, higher alkyl amines, cyclic amines, hydantoin derivatives,
Amides, amines, ester amides, quaternary ammonium salts, lysine, other heterocyclic compounds, various cationic surfactants such as phosphoniums or sulfoniums, carboxylic acids, sulfonic acids, phosphoric acids, sulfuric ester groups, phosphoric esters Examples include various anionic surfactants containing acidic groups such as amine, no acids, aminosulfonic acids, sulfuric acid esters or phosphoric acid esters of amino alcohols, and various amphoteric surfactants such as alkyl betaine types. These antistatic agents may be used alone or in combination of two or more. The above-mentioned antistatic agent not only has the performance as an antistatic agent, but also has properties such as improved dispersibility, improved magnetic properties, improved lubricity, and improved applicability. The antistatic agent is used in an amount of about 0.0% per 100 parts by weight of binder.
01 to 10 parts by weight.

Dispersants include fatty acids having a carbon atom number of 1θ to 22, such as caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid, elaidic acid, linoleic acid, lylunic acid, and stearolic acid; Examples include metal soaps made from fatty acids such as alkali metals, alkaline earth metals, copper, and lead, lecithin, higher alcohols, and sulfuric acid esters and phosphoric acid esters of these alcohols. These dispersants may be used alone or in combination of two or more. The above dispersant is approximately 0 per 100 parts by weight of binder.
．． 01 to 10 parts by weight.

The coating solution for forming the magnetic layer is basically prepared by mixing the above-mentioned components, i.e., by mixing the above-mentioned components in a solvent that can dissolve the selected binder.
It is prepared by dissolving the desired binder, adding fine ferromagnetic powder to the solution, stirring, and uniformly dispersing it. Solvents for preparing the binder solution include ketone solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, isophorone, alcohols such as methanol, ethanol, propatool, butanol, isopropyl alcohol, isobutyl alcohol, methylhexanol, etc. System solvents, methyl acetate, ethyl acetate, butyl acetate, isobutyl acetate,
Ester solvents such as isopropyl acetate, ethyl butyrate, ethyl lactate, ethylene glycol monoacetate, ether solvents such as glycol acetate monoethyl ether, glycol dimethyl ether, glycol monoethyl ether, tetrahydrofuran, dioxane, benzene,
Aromatic hydrocarbon solvents such as toluene, xylene, cresol, and styrene, halogenated hydrocarbon solvents such as methylene chloride, ethylene chloride, carbon tetrachloride, chloroform, and dichlorobenzene, N.

There are various solvents such as N-dimethylformamide, which can be appropriately selected depending on the selected polymeric substance, or can be used in combination of two or more.

These organic solvents are selected so as to be able to completely dissolve the components to be dissolved, and in the case of a mixed solvent, the quantity ratio of each is determined as appropriate along with the selection of the solvent. Furthermore, these solvents must not deteriorate the properties of the ferromagnetic fine powder, which is the main component of the magnetic layer.

For dissolving and dispersing various components in organic solvents, for example, two-roll mill, three-roll mill, ball mill, pebble mill, thoron mill, sand grinder, attritor, high-speed impeller, dispersion machine, high-speed stone mill, high-speed impact mill, etc.
Disper, Nei Goo, high speed mixer, ribbon blender, Coni Goo, intensive mixer, tumbler,
Pregnancies, dispersers, homogenizers, ultrasonic dispersers, etc. are used.

The magnetic layer forming coating liquid after dispersion treatment is coated with air doctor coat, blade coat, air knife coat, etc.
squeeze coat, impregnation coat, reverse roll coat,
It is applied onto a support by various coating methods such as transfer roll coating, gravure coating, cast coating, and spray coating. The amount of coating is 2 μm in dry thickness.
The amount is as follows.

Examples of non-magnetic supports forming the magnetic layer include polyester resins such as polyethylene terephthalate and polyethylene naphthalate, polyolefin resins such as polypropylene, cellulose derivatives such as cellulose diacetate and cellulose triacetate, vinyl chloride resins such as polyvinyl chloride, Plastic film or sheet materials such as polysulfone resin, polycarbonate resin, polyimide resin, or polyamide resin, or foil materials such as metal materials such as aluminum or copper or various ceramic materials;
There are plate-like bodies. These supports may be shaped in advance, or they may be shaped by, for example, cutting after forming a magnetic layer or a back layer (described later). Various pretreatments such as treatment, undercoat treatment, heat treatment, metal vapor deposition treatment, and alkali treatment may be performed.

The magnetic layer coated on the support by the various methods described above is usually subjected to a magnetic field orientation treatment during drying to orient the ferromagnetic particles within the magnetic layer, and then drying is completed.

Where should the magnetic layer forming coating liquid be applied and where should the magnetic field be applied?

Techniques such as cleaning and drying are conventionally known and can be used or applied appropriately for the present invention.

In addition, in the case of a coated product, especially a tape-shaped body (@ki tape) using a plastic film as a support, it is desirable that a back layer with a desired composition be formed on the back surface of the coated product. Components include binders, organic solvents, and inorganic lubricants which have been exemplified and detailed as components of the magnetic layer forming coating liquid, and can be constructed by appropriately selecting them. The inorganic lubricant is a fine powder with an average particle size of 0.8 μm or less, particularly preferably 0.4 μm or less.

The mixing ratio of the binder and the inorganic lubricant in the back layer is within the range of 1:0.1 to 1:4 (weight ratio). Then, as in the case of forming the magnetic layer, fine powder of an inorganic substance as a lubricant is uniformly dispersed in an organic solvent as a binder to prepare a coating liquid for forming a back layer. This coating solution is then applied to the back side of the support on which the magnetic layer is or should be formed, and dried to form a back layer. The coating layer in a magnetic recording medium should be made as thin as possible in order to increase the recording density per unit of the magnetic recording medium, and therefore the thickness of the back layer is preferably about 0.3 to 1.5 μm. The preparation, coating, drying, etc. of the coating liquid for forming the back layer are the same as those for the magnetic layer. At this time, the practitioner may decide as appropriate whether to provide the magnetic layer or the back layer on the support first.

The magnetic layer and back layer coated as described above are subjected to various surface treatments such as calender treatment as desired, and depending on the form of the support, the coated material is coated in the desired form, for example, in the form of a tape, etc.
Cut into shapes such as cards, discs, and sheets, and then store them in various cassettes or storage cases depending on the type of magnetic recording medium, or attach them to a base or laminate them with other materials. Make it a concrete product. In either case, those skilled in the art can easily manufacture the magnetic recording medium of the present invention using or applying conventional techniques.

It can be commercialized.

〔Example〕

Hereinafter, the present invention will be described in detail and specifically based on Examples and Comparative Examples. The measurement results for the samples on each side will be summarized and explained at the end. In addition, "2 parts" in the compounding ratio in each example are all "parts by weight."

One surface of a polyethylene terephthalate film with a thickness of 10 μm as a support was coated with the coating solution for forming a magnetic layer as described below, subjected to magnetic field alignment treatment using a cobalt magnet, and then heated at a temperature of 100 μm. It was dried in a °C atmosphere for 1 minute to form a magnetic layer with a thickness of 4 μm.

No.1-1°-11 Composition: Ferromagnetic Fe-Go-Ni alloy fine powder (S WET: 50rd/mg, coercive force Hc: 1520 Oe, acicular ratio: 8) - 100 parts chloride containing triethylammonium maleate salt Vinyl acetate copolymer (IXIO-' equivalent/g) ----10 parts Polyurethane resin "Nisten 5701 J (trade name: manufactured by Gutdrich, USA) ---10 parts Carbon black.
・−・・・−・−・・・・−・−・・−・・・・・・
1.5 parts alumina fine powder)
−・−・・−・・・−・5 parts stearic acid・
・−・・−・−・−・・・・・・・−・−・・・−・・
・−・−・1 part butyl stearate−・・−・・
−・・−・−・−・−・−・・ 2-part methyl ethyl ketone・・・−・−・・・・・・・−・−・・・
200 parts cyclohexanone・・−・−・−・・−・−
Preparation of 200 parts: The above composition was placed in a sand grinder together with glass beads, mixed for 2 hours, and then subjected to a dispersion treatment. was added and mixed by high speed stirring to prepare a "magnetic layer forming coating solution".

After forming the magnetic layer as described above, it was subjected to calender treatment and thermosetting treatment, and further cut into tapes having a width of 1/2 inch to prepare a magnetic recording tape. This is called “Sample 1”
'.

[Same as Example 1 except that a vinyl chloride vinyl acetate copolymer containing diethylhexyl ammonium maleate salt (1 x 10-S equivalent/g) was used in place of the copolymer in Example 1. A magnetic recording tape was created. This will be referred to as "Sample 2".

Substance B Same as in Example 1 except that in place of the copolymer in Example 1, vinyl chloride vinyl acetate copolymer containing diethylhexyl ammonium phosphate salt (0,5Xl0-' equivalent/g) was used. A magnetic recording tape was created. This will be referred to as "Sample 3".

The same as in Example 1 except that instead of the copolymer in Example 1, a vinyl chloride vinyl acetate copolymer containing triethylhexylammonium phosphate (0,5Xl0-' equivalent/g) was used. A magnetic recording tape was produced in the same manner. One sample is 4''.

[5] The procedure was carried out in the same manner as in Example 1, except that a carboxylic acid-containing diethylhexyl ammonium salt-containing polyurethane resin (5 x 10-' equivalent/g) was used in place of the polyurethane resin in Example 1, and magnetic recording was carried out in the same manner as in Example 1. I made a tape. This is referred to as 2 samples 5@.

Example 5 except that a vinyl chloride vinyl acetate copolymer containing diethylhexylammonium maleate salt (1 x 10-5 equivalent/g) was used in place of the copolymer in Example 5. A magnetic recording tape was prepared in the same manner as above. This is 1 trial F46''.

Example 1 Instead of the copolymer in Example 5, maleic acid-containing vinyl chloride vinyl acetate copolymer (IXIO-' 1 t/g
) was used in the same manner as in Example 5 to produce a magnetic recording tape. This is defined as one sample 7''.

Example 5 except that in place of the copolymer in Example 5, a vinyl chloride vinyl acetate copolymer containing diethylhexyl ammonium phosphate salt (0,5XIO" equivalent/g) was used.
A magnetic recording tape was created in the same manner as in the case of . This will be referred to as "Sample 8".

Actual JLL-1 Same as in Example 5 except that a triethylhexylammonium phosphate salt-containing vinyl chloride vinyl acetate copolymer (0,5Xl0-' equivalent/g) was used instead of the copolymer in Example 5. A magnetic recording tape was created. This is designated as 2 samples 9'.

Example 5 was carried out in the same manner as in Example 5, except that a phosphoric acid-containing vinyl chloride vinyl acetate copolymer (0.5 x 10-% equivalent/g) was used in place of the copolymer in Example 5. A magnetic recording tape was prepared.This will be referred to as one sample 10'.

Comparison ■ - Instead of the copolymer in Example 1 above, maleic acid-containing vinyl chloride vinyl acetate copolymer (IXIO-' equivalent/g)
The procedure was carried out in the same manner as in Example 1 except that
Created magnetic recording tape. This is referred to as "Comparative Sample 1". Comparison 5-1 The same procedure was carried out except that a phosphoric acid-containing vinyl chloride vinyl acetate copolymer (IXIO-' equivalent/g) was used instead of the copolymer in Example 1. A magnetic recording tape was prepared in the same manner as in Example 1. This is referred to as a 2m comparison sample.

The results of measuring (for each sample prepared) the glossiness of the magnetic layer surface, ■ squareness ratio, ■ videotape, ■ surface electrical resistance of the magnetic layer, and ■ dropout are listed in Table 2. The following results were obtained.The methods for each measurement are as follows.

Directional flow■ Glossiness: Japanese Industrial Standard “JIS Z-8741”
Based on this, the incident angle was set at 45° with respect to the surface of the magnetic layer of each sample, and the gloss level of the surface of the magnetic layer of Comparative Sample 1 was set to 100%1.
It was measured as

■ Squareness ratio: For each sample, measure the squareness ratio measuring machine "vSM-3".
External magnetic field 5
．． Measured under 000 Oe.

■ Video S/N: Record each sample on a video tape recorder.
Run it on FUJIX M6J (product name: manufactured by Fuji Photo Film), and measure noise meter r925C,
(manufactured by product name Nijiback ■) to reduce the standard sample to OdB.
”, and the difference in S/N of each sample was determined.

■ Electrical resistance of the magnetic layer surface: Regarding the magnetic layer surface of each sample Digital surface electrical resistance meter rTR-8611A
J (trade name: manufactured by Takeda Riken ■). The measurement conditions were a temperature of 23°C, a relative humidity of 30%, and a sample size of 8 x 8 mm.

(2) Dropout: After running each sample repeatedly for 250 buses, the dropout was measured using a dropout counter as the number of dropouts per minute in which the reproduction output level decreased by 16 dB or more over a period of 15 x 10-' seconds.

(Hereinafter, blank space) C: Vinyl chloride vinyl acetate copolymer containing diethylhexyl ammonium phosphate salt D: Vinyl chloride vinyl acetate copolymer containing triethylammonium phosphate salt (E) = Vinyl chloride vinyl acetate copolymer containing maleic acid (F ): Phosphoric acid-containing vinyl chloride vinyl acetate copolymer (2) Polyurethane resin (10 parts) (U): Polyurethane resin M: Polyurethane resin containing carboxylic acid diethylhexylammonium salt As is clear from the results shown in Table 1 In the sample using the bonding agent bone, which is characteristic of the present invention (no symbol ()), the ferromagnetic fine powder is sufficiently uniformly dispersed in the bonding agent, and the video S/N ratio is not reduced. The magnetic recording medium had a low surface electrical resistance of the magnetic layer and had few dropouts.

〔Effect of the invention〕

Claims (4)

[Claims] (1) In a magnetic recording medium in which a magnetic layer in which fine ferromagnetic powder is uniformly dispersed in a binder is provided on a nonmagnetic support, the fine ferromagnetic powder has an S_B_E_T of 45 m.
^2/g or more, a coercive force of 1,000 Oe or more, and an acicular ratio of 7 or more, the binder contains a polar group represented by the general formula below, and has a molecular weight of consisting of a polymer in the range of 10,000 to 100,000, the ratio (weight) of the ferromagnetic fine powder to the binder
is 2.5 to 10. Polar group: -COOX, -SO_3X, -OSO_3X,
-PO_3X_2 or -OPO_3X_2 [However, X in the above polar group is -NR_1R_2R_3R_4(R_
1, R_2, R_3 and R_4 represent a hydrogen atom, an alkyl group having 1 to 12 carbon atoms, an alkenyl group, a substituted alkyl group or a substituted alkenyl group. ) represents. ] (2) The magnetic recording medium according to claim 1, wherein the binder is a vinyl chloride copolymer. (3) The magnetic recording medium according to claim 1, wherein the binder is a polyurethane resin. (4) The magnetic recording medium according to claim 1, wherein the binder is a polyester resin.