JPH0748250B2 - Magnetic recording medium and manufacturing method thereof - Google Patents

Description

Detailed Description of the Invention a. BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium such as a magnetic tape and a magnetic sheet and a method for manufacturing the same.

B. 2. Description of the Related Art In recent years, as magnetic materials, especially video and recording media for computers, have higher density and higher S / N, the particles of the magnetic powder to be used have become smaller.For example, when expressed in surface area per unit weight, VHS or beta magnetic powder BET surface area 25~30m ² / g class magnetic tape standard grade system is used, 30~40m ² / g, the magnetic powder of 40 to 50 m ² / g class super high grade class in high grade class Is used. Also, in the near future, 50-60 m ² / g class powder is about to appear on the market.

Generally, the S / N ratio of a magnetic recording medium is said to be proportional to the square root of the number of particles of the magnetic substance in the recording material for recording / reproducing, so when the same weight of magnetic powder is applied, the particle size is small. The use of magnetic material is more advantageous for improving S / N. However, since the surface area of the particles increases in inverse proportion to the square of the particle diameter, it becomes difficult to disperse the particles as the particle diameter decreases, and the dispersion stability deteriorates.

Usually, in dispersing the magnetic powder, a dispersant sufficient to coat the surface of the magnetic powder particles should be sufficient, but in reality, this does not provide sufficient dispersibility and stability. A large excess of dispersant has been added.
For example, as a dispersant for ferromagnetic powder, various surfactants, particularly fatty acid salts, phosphoric acid esters, alkyl sulfonates, sulfosuccinates, etc. are mainly used.
However, when these conventional dispersants are used, the dispersibility of the ferromagnetic powder at the time of preparation of the magnetic coating is improved, but the magnetic layer obtained by coating the magnetic coating on a support and drying it has high strength. However, the moisture resistance and the like are likely to deteriorate, so that a problem of running property under high temperature and high humidity is likely to occur, and running durability under normal temperature and humidity conditions is often poor.

Further, the dispersant which is not adsorbed to the magnetic powder is mixed with a binder resin as a binder in the coating film to plasticize the magnetic layer or prevent the curing of the binder resin, and therefore the mechanical strength of the magnetic layer, especially Remarkably reduces Young's modulus. Recently, there is a tendency to reduce the total thickness of the tape by using a thin base film as the tape is recorded for a long time. However, since the stiffness of the tape is proportional to the cube of the tape thickness, it is necessary to reduce the thickness. As a result, the waist becomes significantly weaker, which deteriorates the running characteristics of the thin tape and the head touch of the tape, thus leading to deterioration of the S / N ratio. Therefore, in order to keep the mechanical properties associated with the reduction in thickness, particularly the rigidity of the tape, an ultra-stretched base film has been adopted and the Young's modulus of the magnetic layer has been increased. However, the decrease in the Young's modulus of the magnetic layer due to the excess dispersant and other low molecular weight additives significantly deteriorates the mechanical properties of the thin tape.

Various techniques have been disclosed that effectively and stably disperse magnetic powder and do not impair the mechanical properties of the magnetic layer. For example, JP-A-54-94308 and 54-143894.
In Japanese Patent Publication Nos. 50-92103 and 50-92103, magnetic powder is pretreated with a phosphoric acid ester derivative.

Also, JP-A-51-134899, 53-51703, 53-7898
Japanese Patent Publication No. 54-46509 discloses a method of coating the surface of a magnetic layer with silicone oil.

Also, JP-A-50-108902, 49-97738, 51-33753
No. 53-116114, No. 54-24000, etc., the surface is treated with an anionic activator. However, the above technique is not effective for small particles, especially for BET 35-40 m ² / g or more magnetic powder.

Also, JP-A-51-103403, 47-33602, 55-125169
No. 55-73929, 55-73930, 57-42888, 57-102
Each publication such as No. 6 discloses a technique of coating the surface of the magnetic powder with an oligomer or polymer having a functional group capable of adsorbing to the magnetic powder.

These techniques include dissolving the dispersant, mixing with the magnetic powder, stirring, kneading, filtering, drying, pulverizing, in order to adsorb the dispersant on the surface by mixing the dried magnetic powder with the dispersant coating liquid.
Each step of sieving is required.

Therefore, the conventional dispersants are not sufficient to guarantee good dispersion of various fillers including magnetic powder, which is becoming finer and finer, and the magnetic properties, electromagnetic conversion properties and durability required at present are required. Is difficult to satisfy,
There has been a demand for a binder resin-dispersant combination that can improve such properties.

On the other hand, the viscosity distribution of the magnetic powder is adjusted to improve the dispersibility of the magnetic powder in the binder, a surfactant is used as a dispersant, or a hydrophilic group in the binder, such as a hydroxyl group or a phospho, is used. A method has been proposed in which modification is carried out by introducing a group, a sulfo group, a carboxy group or the like to improve the characteristics.

For example, by introducing a sulfonic acid metal salt residue into a polyester resin, JP-A-56-74824 and JP-A-56-74827 disclose that surface smoothness (gloss) and adhesion to a support are improved. 56-13519, 56-74826, 56-74
No. 828, No. 56-74829 and the like disclose dispersibility and improvement of filling properties related to interfacial tension. The sulfonic acid metal group-introduced polyester resin, polyurethane resin, nitrocellulose, vinyl chloride-vinyl acetate resin, etc. There have been many proposals for binder compositions by combining the above.

Further, since vinyl chloride resins have high mechanical strength, vinyl chloride-vinyl acetate copolymers, vinyl chloride-vinylidene chloride copolymers, vinyl chloride-acrylonitrile copolymers or vinyl chloride-vinyl acetate-vinyl alcohol- Maleic anhydride copolymers and the like are prized.

Modification of the vinyl chloride resin with a sulfonic acid metal salt residue is disclosed in JP-A-57-44227.
A dechlorination reaction was carried out between a vinyl chloride resin containing an H group and a compound containing a chlorine atom and a sulfonic acid metal salt residue in one molecule to introduce a sulfonic acid metal salt residue. A modified vinyl chloride resin is obtained.

Further, it disclosed in JP-A-58-108032 for vinyl chloride copolymer containing free sulfo group (-SO ₃ H). However, a vinyl chloride-based copolymer obtained from such a polymerizable monomer having a free sulfo group is
To increase the paint viscosity when mixed with magnetic paint,
Not only does it hinder the process, but also adversely affects the running property of the medium.

Further, in order to improve the running property of the medium, fatty acid has been conventionally added to the magnetic layer as a lubricant. However, since the fatty acid has a carboxyl group, it is easily adsorbed by the magnetic powder. Therefore, in order to fully exert its role as a lubricant, a method of adding the fatty acid after dispersing the magnetic powder has been proposed. There is. For example, JP-A-60-147931 discloses that the running characteristics are improved with a small amount of lubricant by adding and mixing a lubricant (for example, fatty acid) immediately before coating. Further, JP-A-60-187931 also proposes a method in which a lubricant (for example, fatty acid) is added later.

However, even if such a method of adding a fatty acid is used, the conventional binder is weakly adsorbed to the magnetic powder due to the weak adsorption of the binder to the magnetic powder. The effect was not significant.

C. OBJECT OF THE INVENTION An object of the present invention is to provide a magnetic recording medium having improved dispersibility of magnetic powder, improved electromagnetic conversion characteristics, and excellent running durability, and a manufacturing method thereof.

D. Structure of the invention and its action and effect That is, the present invention, a component comprising vinyl chloride, a component containing a sulfo group and / or phospho group in the form of an alkali metal salt or ammonium salt, a component having an epoxy group A vinyl chloride-based copolymer having a degree of polymerization of 200 or less (hereinafter, referred to as a first copolymer) containing a component of vinyl chloride, and a sulfo group and / or a phospho group in the form of an alkali metal salt or an ammonium salt. Characterized in that the magnetic layer contains a vinyl chloride-based copolymer having a degree of polymerization of 220 to 500 (hereinafter referred to as a second copolymer) containing the constituent component contained in 1) and a constituent component having an epoxy group. The present invention relates to a magnetic recording medium.

In addition, the present invention comprises a vinyl chloride component, a component containing a sulfo group and / or a phospho group in the form of an alkali metal salt or an ammonium salt, and a component having an epoxy group having a polymerization degree of 200 or less. Vinyl chloride-based copolymer (hereinafter referred to as “first copolymer”), and a step of primary dispersion of magnetic powder, a constituent comprising vinyl chloride, and an alkali metal salt or ammonium salt of a sulfo group and / or a phospho group. And a step of secondarily dispersing a vinyl chloride-based copolymer having a degree of polymerization of 220 to 500 (hereinafter referred to as a second copolymer) containing a constituent component contained in the form of and a constituent component having an epoxy group. The present invention also provides a method for manufacturing a magnetic recording medium, which comprises:

According to the present invention, since the first and second copolymers contain a sulfo group and / or a phospho group in the component thereof in the form of an alkali metal salt or an ammonium salt, the magnetic paint viscosity is This lowers the dispersibility of the magnetic powder and improves the surface smoothness of the magnetic layer. Moreover, the first and second
It was found that the traveling was further stabilized because the copolymer of (1) had an epoxy group-containing component. It is desirable for the running property that each copolymer contains a hydroxyl group.

Here, it should be noted that the first copolymer has a polymerization degree of 200 or less, which is relatively smaller than that of vinyl chloride resin, which originally has high mechanical strength. Therefore, this copolymer should have good compatibility with other components in the magnetic paint (particularly with the binder resin) and, at the same time, should have both properties of promoting the dispersion of the magnetic powder as described above. become. If the degree of polymerization is not less than 200, the dispersion effect will be weakened, but it is desirable to further set the degree of polymerization to 50 to 150.

Moreover, in addition to the first copolymer, the second copolymer having a higher degree of polymerization is added to the magnetic layer, so that the second copolymer mainly acts as a binder resin. At the same time, the presence of a sulfo group and / or a phospho group in the molecule easily causes adsorption to the magnetic powder, thus helping the dispersion of the magnetic powder in the binder resin system and adding a fatty acid as a lubricant. The effect can be fully exhibited. The effect of this fatty acid, and in addition to this, the epoxy group of the second copolymer improves the running property and running durability of the medium. It is essential that the degree of polymerization of this second copolymer exceeds 200.
A degree of polymerization of 0 is desirable.

As a method for measuring the degree of polymerization, the vinyl chloride-based copolymer of the present invention is heated and dissolved in cyclohexanone, and the specific viscosity of the solution is measured at 30 ° C. according to JIS K6721. Calculate the degree of polymerization by converting to the JIS specific viscosity used.

The first and second copolymers described above are, respectively, a vinyl chloride monomer, a copolymerizable monomer containing an alkali salt of sulfonic acid or phosphoric acid, an epoxy group-containing monomer,
It can be obtained by copolymerizing a hydroxyl group-containing monomer and, if necessary, another copolymer monomer. This copolymerization method is already known and disclosed in JP-A-60-235814 and JP-A-60-235814.
No. 238306, No. 60-238309, No. 60-238371. However, the above-mentioned hydroxyl group may be supplied as a monomer, but may be generated by partial hydrolysis of a copolymer using a fatty acid vinyl such as vinyl acetate as another copolymerizable monomer. Since the first and second copolymers of the present invention are produced by vinyl synthesis, they can be easily synthesized, and various copolymerization components can be selected, so that the properties of the copolymer can be optimally adjusted. .

The metal of the salt of sulfonic acid (sulfo group) or phosphoric acid (phospho group) is an alkali metal (especially sodium, potassium,
Lithium) or ammonium salt, and potassium is particularly preferable in terms of solubility, reactivity, yield and the like.

Examples of the above copolymerizable monomer containing a sulfonate include CH ₂ = CHSO ₃ M, CH ₂ = CHCH ₂ SO ₃ M, CH ₂ = C (CH ₃ ) CH ₂ SO ₃ M, CH ₂ = CHCH _{2 OCOCH (CH 2 COOR) SO 3} M, CH 2 = CHCH 2 OCH 2 CH (OH) CH 2 SO 3 M, CH 2 = C (CH 3) COOC 2 H 4 SO 3 M, CH 2 = CHCOOC 4 H 8 SO ₃ M, CH ₂ = CHCONHC (CH ₃ ) ₂ CH ₂ SO ₃ M, and the like.

As the _{phosphate, CH 2 = CHCH 2 OCH 2} CH (OH) CH 2 -O-PO 3 MY 1, CH 2 = CHCONHC (CH 3) 2 CH 2 -O-PO 3 MY 2, CH ₂ = CHCH ₂ O (CH ₂ CH ₂ O) mPO ₂ MX ^{2 In the} above, M is an alkali metal or ammonium salt, R
Is an alkyl group having 1 to 20 carbon atoms, Y ¹ is H, M or CH
_{2 = CHCH 2 OCH 2 CH (} OH) CH 2 -, Y 2 is H, M or CH ₂ = CHCO
NHC (CH ₃ ) ₂ CH ₂ −, X ¹ is OH or OM, X ² is CH ₂ = CHCH ₂ O (CH ₂ CH ₂ O) m-, OH or OM
Is. Further, n is an integer of 1 to 100 and m is an integer of 1 to 100.

As other copolymerizable monomers to be copolymerized, there are known polymerizable monomers, for example, various vinyl esters, vinylidene chloride, acrylonitrile, methacrylonitrile, styrene, acrylic acid, methacrylic acid, various acrylic acid esters. , Methacrylic acid ester, ethylene,
Propylene, isobutene, butadiene, isoprene, vinyl ether, aryl ether, aryl ester,
Examples thereof include acrylamide, methacrylamide, maleic acid, and maleic acid ester.

The degree of polymerization of the first copolymer of the present invention is preferably 200 or less, and more preferably 30 to 150. If the degree of polymerization is less than 30, the durability will deteriorate, and if it exceeds 200, the dispersing effect will be low.

The second copolymer of the present invention preferably has a degree of polymerization of 200 to 500 and a vinyl chloride content of 60% by weight or more. If the degree of polymerization is less than 200, the wear resistance of the magnetic layer is insufficient, and 500
If it exceeds, the viscosity of the paint is high and the dispersion of the magnetic powder tends to be insufficient. On the other hand, when the content of vinyl chloride is less than 60% by weight, the compatibility with the flexible material is lowered and the release of the solvent from the coating film is apt to be increased.

The amount of strong acid radical bonded to the resin of the present invention is -SO _3, -S
It is necessary that the content of O ₄ , —PO _4, etc. be 0.1 to 4.0% by weight. If it is less than 0.1% by weight, the dispersibility of the magnetic powder will be insufficient, and if it exceeds 4.0% by weight, the hydrophilicity of the strong acid radical will be strong.
Solubility in solvent becomes insufficient.

Examples of the component having an epoxy group include glycidyl ethers of unsaturated alcohols such as allyl glycidyl ether and methallyl glycidyl ether, glycidyl acrylate, glycidyl methacrylate, glycidyl-p.
-Glycidyl esters of unsaturated acids such as vinyl benzoate, methyl glycidyl itaconate, glycidyl ethyl malate, glycidyl vinyl sulfonate, glycidyl (meth) allyl sulfonate, butadiene monooxide, vinylcyclohexene monooxide, 2-
Examples thereof include epoxide olefins such as methyl-5,6-epoxyhexene. This monomer is generally used in a range such that the amount of epoxy groups in the copolymer is 0.5% by weight or more. If this proportion is less than 0.5% by weight,
It becomes difficult to select the conditions for introducing strong acid radicals.

Further, as the above-mentioned hydroxyl group-containing component that may be contained, there is a monomer having an -X-OH group, and examples thereof include (meth) acrylic acid-2-hydroxyethyl ester and (meth). C2-C4 alkanol esters of α, β-unsaturated acids such as acrylic acid-2-hydroxypropyl ester, maleic acid mono-2-hydroxypropyl ester, maleic acid di-2-hydroxypropyl ester, itaconic acid monoester Alkanol esters of unsaturated dicarboxylic acids such as 2-hydroxybutyl ester, olefinic alcohols such as 3-buten-1-ol and 3-hexen-1-ol, 2-hydroxyethyl vinyl ether, 2-hydroxypropyl vinyl ether, etc. Alkanol vinyl ether, N-methylol acrylamide, N- Acrylamide such as Chi roll methacrylamide.

In addition, the amount of hydroxyl groups based on -X-OH groups bonded to the resin is
0.1 to 2.0% by weight is preferable. If it is less than 0.1% by weight, the crosslinking effect of the coating film by the isocyanate compound is not exhibited,
If it is more than 2.0% by weight, the pot life of the paint is too short and it is difficult to use. Although the amount of this hydroxyl group is much smaller than that of vinyl chloride-vinyl alcohol vinyl acetate copolymers which have been known for magnetic coatings, the crosslinking reaction with an isocyanate compound is sufficient. Will be achieved. The reason is not clear, but it is considered that the hydroxyl groups involved in the reaction are separated from the main chain of the copolymer to increase the degree of freedom and that the distribution of the hydroxyl groups in the polymer is uniform. .

The first and second copolymers according to the present invention are polymerized by a polymerization method such as emulsion polymerization, coating solution polymerization, suspension polymerization and bulk polymerization. In any of the methods, known techniques such as a molecular weight modifier, a polymerization initiator, a monomer, a divided addition or a continuous addition can be applied as necessary.

The salt content of the acidic group in the first and second copolymers used in the present invention needs to be 0.1 to 4.0% by weight. If it is less than 0.1% by weight, the dispersibility of the magnetic powder will be insufficient, and if it exceeds 4.0% by weight, the hydrophilicity of the strong acid radical will be strong.
Not only the solubility in a solvent becomes insufficient, but also the moisture resistance of the coating film decreases, and further, the aggregation of the magnetic powder occurs, which rather deteriorates the dispersibility.

The ratio of the first and second copolymers is 0.2 to 1 with respect to the magnetic powder.
It is preferable to use 2 parts by weight, preferably 1 to 8 parts by weight.

Magnetic powder used in the magnetic layer of the present invention, particularly as ferromagnetic powder, γ-Fe ₂ O ₃ , Co-containing γ-Fe ₂ O ₃ , Fe ₃ O ₄ , Co-containing Fe ₃
O ₄ such iron oxide magnetic powder: Fe, Ni, Co, Fe -Ni-Co alloy, Fe
-Mn-Zn alloy, Fe-Ni-Zn alloy, Fe-Co-Ni-Cr alloy,
Fe-Co-Ni-P alloy, Co-Ni alloy and the like, and various ferromagnetic powders such as metal magnetic powder containing Cr, Fe, Ni and Co as a main component: CrO ₂ can be mentioned. Such magnetic powders may be surface-treated with the copolymer of the present invention in advance, or may be mixed with each other when preparing the magnetic coating material.

The magnetic powder used in the present invention exhibits extremely good dispersibility as described above, but in order to further improve the dispersion speed and dispersion stability and reduce the viscosity of the coating liquid, lecithin (preferably powder) is used in some cases. A small amount of a dispersant such as lecithin), oleic acid, or a phosphoric acid ester may be added.

As the binder resin of the magnetic layer of the present invention, it is preferable to use a urethane resin that improves the durability of the magnetic medium.

Furthermore, various conventionally known resins may be used in combination. The thermoplastic resin used in combination has a softening temperature of 150 ° C. or lower, an average molecular weight of about 10,000 to 200,000, and a degree of polymerization of 200 to 2000.
To a degree, for example, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, acrylic ester-acrylonitrile copolymer, acrylic ester-vinylidene chloride copolymer , Acrylic acid ester-styrene copolymer, methacrylic acid ester-acrylonitrile copolymer, methacrylic acid ester vinylidene chloride copolymer, methacrylic acid ester-styrene copolymer, polyvinyl fluoride, vinylidene chloride-acrylonitrile copolymer, butadiene -Acrylonitrile copolymer, polyamide resin, polyvinyl butyral, cellulose derivative (cellulose acetate butyrate, cellulose diacetate, cellulose triacetate, cellulose propionate, nitrocellulose) ), Styrene-butadiene copolymer, polyester resin, chlorovinyl ether-acrylic ester copolymer, amino resin, thermoplastic resin, and mixtures of these various synthetic rubber type or the like is used.

Further, the thermosetting resin or the reactive resin has a molecular weight of about 200,000 or less in the state of the coating liquid, and the molecular weight becomes infinite due to reactions such as condensation and addition. Further, among these resins, those which do not soften or melt before the resin is thermally decomposed are preferable. Specifically, for example, a phenol resin, an epoxy resin, a urea resin, a melamine resin, an alkyd resin, a silicone resin, an acrylic reaction resin, a mixture of a high molecular weight polyester resin and an isocyanate prepolymer, a methacrylate copolymer and a diisocyanate prepolymer. Examples thereof include a mixture, a mixture of polyester polyol and polyisocyanate, a urea formaldehyde resin, a mixture of low molecular weight glycol / high molecular weight diol / triphenylmethane triisocyanate, a polyamine resin or a mixture thereof.

The resin _{is, -SO 3 M, -OSO 3 M} , -COOM, -PO (O
It may be a resin containing a hydrophilic polar group such as M ') ₂ (where M is hydrogen or an alkali metal, M'is hydrogen, an alkali metal or a hydrocarbon residue).

The blending ratio of the vinyl chloride copolymer as the binder resin usable in the present invention and the urethane resin (the total of both is 100 parts by weight) is the vinyl chloride copolymer according to the present invention. 90 to 10 parts by weight, more preferably 80 to 20
It is desirable that it is parts by weight. If the compounding ratio exceeds 90 parts by weight, the coating film becomes too brittle and the durability of the coating film remarkably deteriorates, and the adhesion to the support also deteriorates. Further, if the above-mentioned mixing ratio is less than 10 parts by weight, the magnetic powder is likely to fall off.

Furthermore, by adding a polyisocyanate curing agent to the magnetic coating material containing the copolymer according to the present invention,
The durability can be improved. Examples of such a polyisocyanate curing agent include bifunctional isocyanates such as tolylene diisocyanate, diphenylmethane diisocyanate, and hexane diisocyanate, Coronate L (manufactured by Nippon Polyurethane Industry Co., Ltd.), Desmodur L (manufactured by Bayer), and the like. Any of those conventionally used as a curing agent such as a trifunctional isocyanate or a urethane prepolymer having isocyanate groups at both ends, and any polyisocyanate usable as a curing agent can be used. The amount of the polyisocyanate-based curing agent used is 5 to 80 parts by weight based on the total amount of the binder.

FIG. 1 shows a magnetic recording medium according to the present invention, for example, a magnetic tape, and a subbing layer 2 (this layer may not be provided if necessary) and a magnetic layer 3 on a support 1.
Are stacked. The magnetic layer 3 according to the present invention contains the above-mentioned copolymer, magnetic powder and binder. For the purpose of preventing charging, preventing transfer, etc., the support 1 is preferably provided with a so-called backcoat 4 on the surface opposite to the side provided with the magnetic layer. This layer 4 does not necessarily have to be provided.

In the magnetic layer, in addition to the above-mentioned copolymer, magnetic powder and binder,
Other dispersants, lubricants, abrasives, antistatic agents, etc. may be added as additives.

Dispersants that can be used in combination include caprylic acid, capric acid,
Fatty acids having 8 to 22 carbon atoms such as lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid, elaidic acid, linoleic acid, linolenic acid, and behenic acid (R ₁ COOH, R ₁
Is an alkyl or alkenyl group having 7 to 21 carbon atoms); a metal soap comprising an alkali metal (Li, Na, K, etc.) or an alkaline earth metal (Mg, Ca, Ba) of the above fatty acid; Compounds containing fluorine; amides of the above fatty acids; lecithin; trialkylpolyolefinoxy quaternary ammonium salts (alkyl has 1 to 5 carbon atoms, olefin has ethylene, propylene, etc.) and the like are used. In addition to these, higher alcohols having 12 or more carbon atoms, and other than these, sulfate esters and the like can also be used.

As the lubricant, dialkyl polysiloxane (alkyl has 1 to 5 carbon atoms), COOR (R = H or C _{1 to} C ₂₀ alkyl group) -modified dialkyl polysiloxane dialkoxy polysiloxane (alkoxy has carbon number) 1-4
), Monoalkyl monoalkoxy polysiloxane (alkyl has 1 to 5 carbon atoms, alkoxy has 1 to 4 carbon atoms)
Individual), phenylpolysiloxane, fluoroalkylpolysiloxane (where alkyl is 1 to 5 carbon atoms), etc. Silicon oil; conductive fine powder such as graphite; inorganic fine powder such as molybdenum disulfide and tungsten disulfide; polyethylene, polypropylene , Polyethylene vinyl chloride copolymer, plastic fine powder such as polytetrafluoroethylene; α-olefin polymer; unsaturated aliphatic hydrocarbon liquid at normal temperature (compound in which n-olefin double bond is bonded to terminal carbon, C20); fatty acid esters consisting of fatty acids having 12 to 22 carbon atoms and monohydric alcohol having 1 to 20 carbon atoms, fluorocarbons and the like can be used. These lubricants are added in the range of 0.2 to 30 parts by weight with respect to 100 parts by weight of magnetic powder.

As the abrasive, commonly used materials such as alumina, silicon carbide, chromium oxide, corundum, artificial corundum,
Diamond, artificial diamond, garnet, emery (main components: corundum and magnetite) are used. These abrasives have a Mohs hardness of 5 or more and an average particle size of
Those having a size of 0.05 to 5 μm are used, and particularly preferably 0.1 to 2 μm. These abrasives are added in the range of 0.5 to 20 parts by weight with respect to 100 parts by weight of magnetic powder.

As the antistatic agent, conductive fine powder such as carbon black and carbon black graft polymer; natural surfactant such as saponin; nonionic surfactant such as alkylene oxide type, glycerin type and glycidol type; higher alkylamines, Cationic surfactants such as quaternary ammonium salts, pyridine and other heterocycles, phosphoniums; anionic surfactants containing an acidic group such as carboxylic acid, sulfonic acid, phosphoric acid, sulfuric acid ester group and phosphoric acid ester group; amino acids And amphoteric activators such as aminosulfonic acids, sulfuric acid or phosphoric acid esters of amino alcohols, and the like are used. The conductive fine powder is added in an amount of 0.2 to 20 parts by weight, and the surfactant is added in an amount of 0.1 to 10 parts by weight, based on 100 parts by weight of the magnetic powder. You may add these surfactant individually or in mixture. Although these are used as antistatic agents, they are sometimes used for other purposes such as dispersion, improvement of magnetic properties, improvement of lubricity, and coating aid.

In addition, the following may be used as an additive. Phosphoric acid, sulfamide, guanidine, pyridine, amine, urea, zinc chromate, calcium chromate, strontium chromate and the like can be used, but especially dicyclohexylamine nitrite, cyclohexylamine chromate, diisopropylamine nitrite, diethanolamine phosphate, cyclohexyl ammonium carbonate, hexa The use of methylenediamine carbonate, propylenediamine stearate, guanidine carbonate, triethanolamine nitrite, morpholine stearate or the like (inorganic acid salt or organic acid salt of amine, amide or imide) improves the rust preventive effect. These are used in the range of 0.01 to 20 parts by weight with respect to 100 parts by weight of the ferromagnetic fine powder.

Further, the constituent material of the magnetic layer is mixed with an organic solvent to prepare a magnetic coating material, which is coated on a support. The solvent of the magnetic coating material is a ketone (for example, acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone). , Alcohol (eg methanol, ethanol, propanol, butanol), ester (eg methyl acetate ethyl acetate, butyl acetate, ethyl lactate, glycol acetate monoethyl ether), glycol ether (eg ethylene glycol monoethyl ether, ethylene glycol diethylene ether, dioxane) ), Aromatic hydrocarbons (eg, benzene, toluene, xylene), aliphatic hydrocarbons (eg, hexane, heptane), nitropropane and the like.
The support to which this magnetic coating is applied is polyester (for example, polyethylene terephthalate, polyethylene-2,6-naphthalate), polyolefin (for example, polyethylene,
Polypropylene), cellulose derivative (eg cellulose triacetate, cellulose diacetate, cellulose acetate butyrate, cellulose acetate propionate), polycarbonate, polyvinyl chloride, polyimide, polyamide, polyhydrazide, metal (eg aluminum, copper), paper, etc. May consist of

In the above-mentioned magnetic paint preparation process, according to the present invention,
First, it is extremely important to firstly disperse the above-mentioned first copolymer and magnetic powder, and then to secondly disperse by adding the above-mentioned second copolymer.

That is, at the time of primary dispersion, the magnetic powder is sufficiently and uniformly dispersed by the excellent dispersion effect of the first copolymer, and the first copolymer is sufficiently adsorbed by the magnetic powder. After that, when the second copolymer is added and secondarily dispersed, the second copolymer acting as a binder resin having a larger molecular weight becomes compatible with the magnetic powder and the binder resin. Contribute to improvement,
Dispersion of the magnetic powder is favorably held or promoted. If the first copolymer is added at the time of secondary dispersion contrary to the above, it is not desirable because the dispersion effect becomes insufficient.

E. Examples Hereinafter, the present invention will be described with reference to specific examples. The components, ratios, operation sequences and the like shown below can be variously modified without departing from the spirit of the present invention. In the following examples, all "parts" represent "parts by weight".

Examples 1 to 10 Co-γ-Fe ₂ O ₃ 100 parts Vinyl chloride first copolymer 4 parts (composition and addition amount are shown in Table-1) Methyl ethyl ketone 20 parts Cyclohexanone 40 parts Toluene 20 parts The above composition was kneaded and dispersed for 2 hours using a pressure kneader, Primary dispersed. This primary dispersion was placed in a tank, and further, vinyl chloride type second copolymer 11 parts (composition and addition amount are shown in Table 2) Carbon black 4 parts α-alumina 4 parts Methyl ethyl ketone 20 parts Cyclohexanone 30 After adding 10 parts of toluene and mixing for 1 hour, secondary dispersion was performed for 2 hours using a sand grinder. In addition, a polyester polyol consisting of 1,4-butanediol and adipic acid and diphenylmethane diisocyanate (MD
I) Polyester polyurethane 8.5 parts (Molecular weight about 80,000) Myristic acid 1 part Stearic acid 1 part Butyl stearate 1 part Methyl ethyl ketone 10 parts Cyclohexanone 10 parts Toluene 20 parts Add and mix for 1 hour, then use a sand grinder. Third-order dispersion was performed for 2 hours.

The obtained dispersion was placed in a tank, 5 parts of Coronate L-75 (polyisocyanate manufactured by Nippon Polyurethane Industry Co., Ltd.) was added as a curing agent, the mixture was stirred for 1 hour, and then filtered with a filter having an average pore size of 1 µ. The obtained coating liquid was applied onto 14 μm polyethylene terephthalate so that the thickness after drying would be 5 μm, and magnetic field orientation treatment was performed with a 4000 gauss magnet to dry.

After drying, a super calendar roll treatment was performed to smooth the magnetic layer. The obtained bulk roll was heat-treated to sufficiently harden the magnetic layer, and then slit to 1/2 inch width to obtain a video cassette tape. The characteristics of the obtained tape are shown in FIG.

Example 11 A magnetic coating material was prepared in the same manner as in Example 1 except that the magnetic powder was changed to a Fe—Ni alloy (Hc = 1530 Oe, BET53m ² / g) to prepare a magnetic tape. The tape performance is shown in FIG.

Comparative Examples 1 and 2 Instead of the first copolymer of Example 1, a low molecular weight copolymer having no —SO ₃ K group (see Table 1) (Comparative Example 1) and a —SO ₃ K group were used. A video tape was obtained in the same manner as in Example 1 except that the copolymer (however, the degree of polymerization was 420) (Comparative Example 2) was used. The obtained characteristics are shown in FIG.

Comparative Examples 3, 4, and 5 Instead of the first and second copolymers of Example 1, sodium oleate (Comparative Example 3), alkyl phosphate (“GAFACK RE610” manufactured by Toho Kasei (Comparative Example 4)). , And sodium sulfosuccinate (Comparative Example 5) were used to obtain a video tape under the other conditions similar to those of Example 1. The characteristics of the obtained video tape are shown in FIG.

Comparative Examples 6 and 7 Instead of the second copolymer of Example 1, a low molecular weight copolymer having no —SO ₃ K group (see Table 2) (Comparative Example 6) and a —SO ₃ K group were used. A video tape was obtained in the same manner as in Example 1 except that the copolymer (however, the degree of polymerization was 120) (Comparative Example 7) was used. The obtained characteristics are shown in FIG.

However, each measurement condition was as follows.

Gloss: Murakami Color Research Laboratory variable angle photometer
oss) Measure at 60 ° each and display the standard plate at 100%.

RF output: RF output at 4MHz was measured using a VTR deck for measuring RF output, and a value was shown that was lower than the original output after 100 playbacks (unit: dB) Video S / N: A 50% white signal of 0.36 Vpp was recorded and played back and directly read with a Shibasoku 725D / 1 noise meter.

Running property: The sample tape was run on a video deck continuously at 40 ° C and 80% for 200 hours, and RF output drop, skew, and powder drop were measured. A is good, B is slightly bad, and C is bad (the same applies hereinafter).

Dropout (DO): V on the VHS deck (Matsushita NV-6200)
The test in which the sample loaded in the HS cassette was loaded and the sample head portion was run for 5 minutes was repeated 100 times, and the increase in dropout before and after the test was measured.

Dirt: After running 400 times, the deposits on the head, cylinder and pinch roller were visually judged.

Paint viscosity: Measured with a B-type viscometer (60r.p.m) at 25 ° C.

Dynamic friction coefficient: 25 ° C Tape running tester TBT-300D (Yokohama System Research Institute) wrapped the tape 180 ° around the chrome plated stainless 4Φ pin, tape speed 1cm / sec,
Measure at inlet tension of 20g and calculate μ _k by the following formula From this result, if the magnetic layer is formed according to the present invention,
The magnetic component is excellent in dispersion, running performance and durability are good,
Therefore, it is understood that the magnetic property and the electric property are excellent.

[Brief description of drawings]

 The drawings show the embodiments of the present invention. FIG. 1 is an enlarged cross-sectional view of a part of a magnetic tape, and FIG. 2 is a table collectively showing the performance of each tape. In addition, in the code | symbol shown in drawing, 1 ... non-magnetic support body 2 ... subbing layer 3 ... magnetic layer 4 ... back coat layer.

Claims (2)

[Claims] 1. A polymer having a degree of polymerization of 200 or less, which contains a constituent composed of vinyl chloride, a constituent containing a sulfo group and / or a phospho group in the form of an alkali metal salt or an ammonium salt, and a constituent having an epoxy group. Degree of polymerization including vinyl chloride-based copolymer, component composed of vinyl chloride, component containing sulfo group and / or phospho group in the form of alkali metal salt or ammonium salt, and component having epoxy group A magnetic recording medium, characterized in that a vinyl chloride copolymer of 220 to 500 is contained in the magnetic layer. 2. A polymer having a degree of polymerization of 200 or less, containing a vinyl chloride component, a component containing a sulfo group and / or a phospho group in the form of an alkali metal salt or an ammonium salt, and a component having an epoxy group. Vinyl chloride copolymer,
And a step of primary dispersion of magnetic powder, a constituent comprising vinyl chloride, a constituent containing a sulfo group and / or a phospho group in the form of an alkali metal salt or an ammonium salt, and a constituent having an epoxy group. And a step of adding a vinyl chloride copolymer having a degree of polymerization of 220 to 500 to carry out secondary dispersion, and manufacturing the magnetic recording medium.