JPH0630152B2 - Method of manufacturing magnetic recording medium - Google Patents

Description

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

B. 2. Description of the Related Art In recent years, with the increase in density and S / N of magnetic materials, especially recording media for video and computers, the particles of magnetic powder used have become smaller. For example, VHS or beta can be expressed in terms of surface area per unit weight. 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. In the near future, powder of 50-60 m ² / g class 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 relating to recording / reproduction, and therefore when the same weight of magnetic powder is applied,
The use of a magnetic material having a small particle size 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, the dispersion of the particles becomes rapidly difficult as the particle diameter decreases, and the dispersion stability also 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, sufficient dispersibility, stability cannot be obtained,
For this reason, a considerable excess of dispersant is 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 by the magnetic powder is mixed with a binder resin as a binder in the coating film to plasticize the magnetic layer or prevent the binder resin from being hardened, so that the mechanical strength of the magnetic layer, especially Young's Significantly reduce the rate. Recently,
With the long recording time of tapes, there is a tendency to reduce the total thickness of the tape by using a thin base film. However, since the stiffness of the tape is proportional to the cube of the tape thickness, the thickness of the tape decreases. The waist becomes remarkably weak, which deteriorates the running characteristics of the thin tape and the head touch of the tape, and thus leads to deterioration of the S / N ratio. Adoption of a super-stretched base film to maintain mechanical properties associated with thinning, especially the stiffness of the tape.
The Young's modulus of the magnetic layer has been increased. Therefore, the decrease in the Young's modulus of the magnetic layer due to an excessive amount of 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 the magnetic powder and do not impair the mechanical properties of the magnetic layer. For example, JP-A-54-94308, 54-143894, 50
In each of the -92103 publications, the magnetic powder is pretreated with a phosphoric acid ester derivative.

In addition, JP-A-51-134899, 53-51703, 53-7898, 5
Each of the 4-46509 publications discloses a method of coating the surface of the magnetic layer with silicone oil.

Further, JP-A-50-108902, 49-97738, 51-33753,
In each publication such as 53-116114 and 54-24000, the surface is treated with an anion activator. However, the above technique cannot be said to be effective for small particles, particularly 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 of the publications 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 mixing the dry magnetic powder with a dispersant bath liquid to adsorb the dispersant on the surface thereof, dissolving the dispersant, mixing with the magnetic powder, stirring, kneading, filtering, drying, pulverizing,
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, and 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.

The modification of the vinyl chloride resin with a sulfonic acid metal salt residue is disclosed in JP-A-57-44227. First, a vinyl chloride resin containing an OH group and, for example, a chlorine atom and a sulfone in a molecule. Dehydrochlorination is carried out with a compound containing an acid metal salt residue to obtain a modified vinyl chloride resin having a sulfonic acid metal salt residue introduced therein.

As for the vinyl chloride copolymer containing free sulfo group (-SO 3 _H), it is disclosed in JP-A-58-108032. However, although a vinyl chloride-based copolymer obtained from such a polymerizable monomer having a free sulfo group may have excellent dispersibility of the magnetic powder in the dispersion step when mixed with a magnetic paint. In the meantime, a sharp increase in viscosity occurs a short time after the end of dispersion until coating, and even if coating is possible, only an unfavorable medium is often obtained. Further, the calender roll is often soiled during the calender treatment after coating, and as a result, in the medium obtained by initially coating and the medium obtained thereafter,
A significant difference in performance was observed, and most media were unsatisfactory S /
It only showed N and output.

C. OBJECT OF THE INVENTION It is an object of the present invention to provide a method for manufacturing a magnetic recording medium which improves the dispersibility of magnetic powder, improves electromagnetic conversion characteristics, and has excellent running durability.

Another object of the present invention is to provide a method of manufacturing a magnetic recording medium which is easy to be surface smoothed by a calendar roll and has good productivity.

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 And a step of primary dispersion of a vinyl chloride-based copolymer having a degree of polymerization of 200 to 600 and magnetic powder; and a step of secondary dispersion by adding polyurethane.

According to the present invention, the vinyl chloride-based copolymer (hereinafter,
It may be simply referred to as the copolymer of the present invention. Contains a sulfo group and / or a phospho group in its constituents in the form of an alkali metal salt or an ammonium salt, the viscosity of the magnetic coating becomes low, the dispersibility of the magnetic powder is improved, and the magnetic layer of the magnetic layer is improved. Good surface smoothness. Moreover, since the above-mentioned copolymer has an epoxy group-containing component, it has been found that the traveling is further stabilized. It is desirable for the running property that the copolymer contains a hydroxyl group.

Since the copolymer of the present invention has a degree of polymerization of 200 to 600, the copolymer acts as a binder resin, and at the same time, the presence of the sulfo group and / or the phospho group in the molecule thereof causes the magnetic powder as described above. Improve the dispersion of. Therefore, this copolymer is first dispersed with magnetic powder,
Next, when polyurethane, which is the original binder resin, is secondarily dispersed, it is possible to uniformly disperse it in the binder resin while sufficiently producing magnetic dispersion.

On the contrary, when the above-mentioned copolymer and polyurethane are mixed at the same time, the adsorption of the copolymer to the magnetic powder hardly occurs and the dispersion of the magnetic powder becomes worse. For this reason, it is difficult to perform good calendering, and electromagnetic conversion characteristics and the like deteriorate.

In addition, as a method of measuring the degree of polymerization, the vinyl chloride copolymer of the present invention is dissolved by heating in cyclohexanone, and the specific viscosity of the solution is measured at 30 ° C. according to JIS K6721. The degree of polymerization is calculated by converting to the JIS specific viscosity used.

The copolymer of the present invention is obtained by copolymerizing a vinyl chloride monomer, a copolymerizable monomer containing an alkali salt of sulfonic acid or phosphoric acid, an epoxy group-containing monomer, a hydroxyl group-containing monomer and, if necessary, another copolymerizable monomer. Can be obtained by This copolymerization method is already known and disclosed in JP-A-60-235814, JP-A-60-238306, and JP-A-60-2383.
No. 09, No. 60-238371, etc. 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 copolymer of the present invention is produced by vinyl synthesis, it is easy to synthesize, and various copolymerization components can be selected, and the characteristics 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.

As the above-mentioned copolymerizable monomer containing a sulfonate, CH ₂ ═CHCO 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 N, M or CH ₂ ═CHCH ₂ OCH ₂ CH (OH) CH ₂ —, Y ² is H, M or CH ₂ ═CHCONCH (CH ₃ ) _Two
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. 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, acrylamide, methacrylamide, maleic acid, maleic acid ester and the like.

This monomer has a strong acid group content of SO ₃ , S
O ₄ , PO ₄ , PO _5, etc. are used in an amount of 0.1 to 4.0% by weight, preferably 0.3 to 2.0% by weight.

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, vinyl cyclohexene monooxide, 2-
Examples include epoxide olefins such as methyl-5,6-epoxyhexene.

This monomer is generally used in the range of 0.5% by weight or more as the amount of epoxy groups in the copolymer. If this proportion is less than 0.5% by weight, heat resistance and crosslinking reactivity are poor.

Further, as the above-mentioned hydroxyl group-containing component that may be contained, there is a monomer having an —X—OH group, which includes (meth) acrylic acid-2-hydroxyethyl ester,
C2-C4 alkanol esters of α, β-unsaturated acids such as (meth) acrylic acid-2-hydroxypropyl ester, maleic acid mono-2-hydroxypropyl ester, maleic acid di-2-hydroxypropyl ester, Alkanol esters of unsaturated dicarboxylic acids such as itaconic acid mono-2-hydroxybutyl ester, 3
-Olefinic alcohols such as butene-1-ol and 5-hexen-1-ol, alkanol vinyl ethers such as 2-hydroxyethyl vinyl ether and 2-hydroxypropyl vinyl ether, acrylamides such as N-methylol acrylamide and N-methylol methacrylamide. Is mentioned.

The amount of hydroxyl groups based on -X-OH groups bonded to the resin is preferably 0.1 to 2.0% by weight. If it is less than 0.1% by weight, the crosslinking effect of the coating film by the isocyanate compound is not exhibited, and if it is more than 2.0% by weight, the pot life of the coating is too short and it is difficult to use. The amount of the hydroxyl group is much smaller than that of the vinyl chloride-vinyl alcohol-vinyl acetate copolymer which has been heretofore known for magnetic coating materials, but the crosslinking reaction with the isocyanate compound is much smaller. Fully 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 above-mentioned copolymer according to the present invention is polymerized by a polymerization method such as emulsion polymerization, solution polymerization, suspension polymerization and bulk polymerization. In any of the methods, known techniques such as a molecular weight modifier, a polymerization initiator and a monomer may be applied in divided or continuous additions, if necessary.

When the amount of the salt-containing monomer of the acidic group in the copolymer used in the present invention is less than 0.1% by weight, the dispersibility of the magnetic powder becomes insufficient, and when it exceeds 4.0% by weight, the hydrophilicity of the strong acid radical becomes strong, Not only the solubility in a solvent becomes insufficient, but also the moisture resistance of the coating film decreases, and further aggregation of magnetic powder occurs, which rather deteriorates the dispersibility.

The proportion (content) of the above copolymer is preferably 0.2 to 12 parts by weight per 100 parts by weight of the magnetic powder in the magnetic layer.
8 parts by weight is even better.

Magnetic powders used in the magnetic layer of the present invention, particularly ferromagnetic powders, include γ-Fe ₂ O ₃ , Co-containing γ-Fe ₂ O ₃ , and Fe.
₃ O ₄ , iron oxide magnetic powder such as Fe ₃ O ₄ containing Co: 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, etc.
Metal magnetic powder containing Cr as a main component such as Fe, Ni and Co: Cr
Various ferromagnetic powders such as O ₂ can be used. 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 for the magnetic layer of the present invention, polyurethane (urethane resin) that improves the durability of the magnetic medium is used.

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, etc.), styrene-butadiene copolymer, polyester resin, chlorovinyl ether- Acrylic ester copolymers, amino resins, various synthetic rubber-based thermoplastic resins, and mixtures thereof are 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 that 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 and a mixture thereof.

The resin _{is, -SO 3 M, -OSO 3 M} , -COO
It may be a resin containing a hydrophilic polar group such as M, —PO (OM ′) 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-based curing agent include bifunctional isocyanates such as tolylene diisocyanate, diphenylmethane diisocyanate, and hexane diisocyanate, Coronate L (manufactured by Nippon Polyurethane Industry Co., Ltd.), and Desmodur L (manufactured by Bayer). Any of functional isocyanates, urethane prepolymers having isocyanate groups at both ends, which have been conventionally used as a curing agent, and polyisocyanates 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. According to the present invention, the magnetic layer 3 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 and the like 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 (R ₁ COO, such as lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid, elaidic acid, linoleic acid, linolenic acid, and behenic acid
H and R ₁ are alkyl or alkenyl groups having 7 to 21 carbon atoms); Alkali metals (Li, Na, K) of the above fatty acids
Etc.) or a metal soap consisting of an alkaline earth metal (Mg, Ca, Ba); a fluorine-containing compound of the above fatty acid ester; an amide of the above fatty acid; lecithin; a trialkylpolyolefinoxy quaternary ammonium salt (where alkyl is carbon). Numbers 1 to 5, olefins such as ethylene and propylene) 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 (where alkyl is 1 to 5 carbon atoms), COOR (R = H or C _{1 to} C ₂₀₎
Dialkyl polysiloxane modified with an alkyl group), dialkoxy polysiloxane (alkoxy has 1 to 4 carbons), monoalkyl monoalkoxy polysiloxane (alkyl has 1 to 5 carbons, alkoxy has 1 carbons)
~ 4 pieces), phenyl polysiloxane, fluoroalkyl polysiloxane (where alkyl is 1 to 5 carbon atoms), etc. Silicon oil; graphite, etc. conductive fine powder; molybdenum disulfide, tungsten disulfide, etc. inorganic fine powder; polyethylene Plastic fine powders of polypropylene, polypropylene, polyethylene vinyl chloride copolymer, polytetrafluoroethylene, etc .; α-olefin polymer; unsaturated aliphatic hydrocarbons that are liquid at room temperature (n-olefin double bond bonded to terminal carbon) Compounds, having about 20 carbon atoms; 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 0.2 to 30 for 100 parts by weight of magnetic powder.
It is added in the range of parts by weight.

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 aminoalcohol, 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.

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 paint is applied is polyester (for example, polyethylene terephthalate, polyethylene-2,6-
Naphthalate), polyolefin (eg polyethylene, polypropylene), cellulose derivative (eg cellulose triacetate, cellulose diacetate, cellulose acetate butyrate, cellulose acetate propionate), polycarbonate, polyvinyl chloride, polyimide, polyamide, polyhydrazide, metal ( It may for example consist of aluminum, copper), paper or the like.

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 7 Co-γ-Fe ₂ O ₃ 100 parts (Hc-630) (BET specific surface area −35 m ² / g) Vinyl chloride-based copolymer 16 parts (composition and addition amount are shown in Table-1) ) Carbon black 4 parts Methyl ethyl ketone 80 parts Cyclohexanone 40 parts Toluene 80 parts The above composition was kneaded and dispersed for 2 hours using a pressure kneader to perform primary dispersion. Transfer the primary dispersion to a disperser, and further add 10 parts of polyester polyurethane (molecular weight of about 80,000) myristic acid 1 part stearic acid 1 part butyl stearate 1 part α-alumina 4 parts methyl ethyl ketone 100 parts cyclohexanone 50 parts toluene 100 parts. After mixing for 1 hour, secondary dispersion was performed for 3 hours using a sand grinder. The obtained dispersion was put 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 solution 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 Gaussian magnet to dry. After drying, a super calender 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 8 Magnetic powder was used as a Fe—Ni alloy (Hc = 1520 Oe, BET53 m ²
/ G), a magnetic coating material was prepared in the same manner as in Example 1 to prepare a magnetic tape. The tape performance is shown in FIG.

Comparative Example 1 In Example 1, the following composition was prepared.

Co-γ-Fe ₂ O ₃ 100 parts (Hc-630) (BET specific surface area −35 m ² / g) Vinyl chloride / vinyl acetate / vinyl 16 parts Alcohol copolymer (VAGH manufactured by UCC) Polyester polyurethane 10 parts (molecular weight approx. 80,000) Copolymer (composition and addition amount are the same as those in Table-1) Myristic acid 1 part Stearic acid 1 part Butyl stearate 1 part Carbon black 4 parts α-alumina 4 parts Methyl ethyl ketone 180 parts Cyclohexanone 90 parts Toluene 180 Parts The above composition was mixed and dispersed in a tank for 1 hour, then kneaded and dispersed in a batch type sand grinder for 6 hours, and then 5 parts of "Coronate L" manufactured by Nippon Polyurethane Company was dispersed for 10 minutes, and then an average pore diameter of 1 µ was obtained. It filtered with the filter which has, and obtained the magnetic paint.

After coating the obtained coating solution on a polyethylene terephthalate film having a thickness of 14μ so that the dry thickness becomes 5μ,
Magnetic field orientation treatment was performed with a 1000 gauss electromagnet, and then dried. After drying, perform super calendar roll treatment,
The magnetic layer was made smooth. Slitting this, 1/2
An inch wide video tape (VHS type) was obtained.

The characteristics of the obtained tape are shown in FIG.

Comparative Example 2 In Example 1, the following composition was prepared.

Co-γ-Fe ₂ O ₃ 100 parts (Hc-620) (BET specific surface area −35 m ² / g) Copolymer 16 parts same as in Example 1 Polyester polyurethane 10 parts (molecular weight about 80,000) Copolymer (composition And the addition amount is the same as in Table-1) Myristic acid 1 part Stearic acid 1 part Butyl stearate 1 part Carbon black 4 parts α-alumina 4 parts Methyl ethyl ketone 180 parts Cyclohexanone 90 parts Toluene 180 parts The above composition in a tank 1 After mixing and dispersing for 6 hours with a batch type sand grinder, 5 parts of "Coronate L" manufactured by Nippon Polyurethane Co., Ltd. was dispersed for 10 minutes, and then filtered with a filter having an average pore size of 1 µ to obtain a magnetic paint. Got

After coating the obtained coating solution on a polyethylene terephthalate film having a thickness of 14μ so that the dry thickness becomes 5μ,
Magnetic field orientation treatment was performed with a 1000 gauss electromagnet, and then dried. After drying, perform super calendar roll treatment,
The magnetic layer was made smooth. Slitting this, 1/2
An inch wide video tape (VHS type) was obtained.

The characteristics of the obtained tape are shown in FIG.

Comparative Example 3 Fe-Ni alloy 100 parts (Hc-1520) (BET specific surface area -53 m ² / g) Vinyl chloride / vinyl acetate / vinyl 16 parts Alcohol copolymer (VAGH manufactured by UCC) Methyl ethyl ketone 40 parts Cyclohexanone 130 parts Toluene 30 Parts The above composition was kneaded and dispersed using a pressure kneader for 2 hours to perform primary dispersion. This primary dispersion was placed in a tank and further polyester polyurethane 10 parts (molecular weight about 40,000) myristic acid 1 part stearic acid 2 parts butyl stearate 1 part carbon black 4 parts α-alumina 5 parts methyl ethyl ketone 50 parts cyclohexanone 155 parts toluene After adding 35 parts and mixing for 1 hour, secondary dispersion was carried out for 3 hours using a sand grinder. 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 solution 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 Gaussian magnet to dry. After drying, a super calender 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.

Comparative Examples 4 and 5 Instead of the copolymer of Example 1, a copolymer having no —SO ₃ K group (see Table 1) (Comparative Example 4) and —SO ₃ K.
A video tape was obtained in the same manner as in Example 1 except that a copolymer having a group (however, the degree of polymerization was 150) (Comparative Example 5) 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) The standard plate is displayed at 100% when measured at an incident angle of 60 °.

RF output: 4MHz using VTR deck for RF output measurement
The RF output was measured at 100 ° C. and showed a value lower than the original output after 100 times of reproduction (unit: dB).

Video S / N: A 50% white signal of 0.36 Vpp was recorded / reproduced 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 decrease, skew, and powder drop were measured. A is good, B is slightly bad, and C is bad (the same applies hereinafter).

Dropout (DO): Load the VHS cassette (Matsushita NV-6200) with the loaded sample into the VHS cassette and run the sample head for 5 minutes. Repeat the test 100 times to increase the dropout before and after the test. It 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: Tape running tester TBT-300 at 25 ℃
At D (Yokohama System Research Institute), wrap the tape 180 ° around the chrome-plated stainless steel 4Φ pin, tape speed 1c
Measured at m / sec and inlet tension of 20 g, and calculated μ _K by the following formula (X ... Exit tension (g)) From these results, when the magnetic layer is formed according to the present invention, the magnetic powder has excellent dispersibility, and the running property and durability are good,
Therefore, it can be seen that the magnetic characteristics and the electrical characteristics are excellent.

Further, regarding the sample of Example 1 and the sample of Comparative Example 1,
When the calender speed and the calender pressure were changed, the results shown in FIGS. 3 and 4 were obtained. According to this, it can be seen that the sample according to the present invention can be easily calendered.

[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, FIG. 2 is a table collectively showing the performance of each tape, and FIGS. It is a graph showing each performance. In addition, in the code | symbol shown in drawing, it is 1 ... non-magnetic support body 2 ... subbing layer 3 ... magnetic layer 4 ... back coat layer.

Claims (1)

[Claims] 1. A polymerization degree of from 200 to 600, which comprises a vinyl chloride constituent, 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. 1. A method for producing a magnetic recording medium, comprising the steps of: firstly dispersing the vinyl chloride-based copolymer and the magnetic powder; and secondly adding polyurethane to perform secondarily dispersion.