JP2616638B2 - Magnetic recording media - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel magnetic recording medium, and more particularly, to an excellent recording density and an excellent S / N ratio. The present invention relates to a magnetic recording medium having characteristics such as not causing contamination and suitably used as, for example, a magnetic tape, a magnetic sheet, a magnetic disk, and the like.

[0002]

2. Description of the Related Art In recent years, magnetic recording media have been used for, for example, audio equipment, video equipment, computers, and the like, and the demand for such media has been remarkably growing. This magnetic recording medium
Generally, it has a structure in which a magnetic layer comprising a magnetic powder and a binder is provided on a non-magnetic support such as a polyester film, and this magnetic layer usually contains a magnetic powder and a binder. It is formed by applying or transferring a magnetic paint dispersed in a medium to be coated on the non-magnetic support. Conventionally, as the binder,
For example, polyester resin, cellulose resin, polyurethane resin, vinyl chloride resin, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl acetate-vinyl alcohol copolymer, vinyl chloride-vinylidene chloride copolymer,
Organic polymer compounds such as acrylonitrile-butadiene copolymer, phenolic resin, epoxy resin, polyamide resin, polyvinyl butyral, nitrocellulose, cellulose acetate butyrate, acrylic resin, and electron beam curable resin are used. . Each of these binders has advantages and disadvantages, and since it is difficult to obtain a magnetic layer having desirable properties when used alone, two or more binders are usually used in combination. For example, a relatively hard resin such as a vinyl chloride resin, polyvinyl butyral, and nitrocellulose, and a polyester resin, a polyurethane resin, and an acrylonitrile-butadiene copolymer are often used in combination with a soft resin. In many cases, a polyisocyanate compound is used as a curable component for the purpose of improving the durability of the magnetic layer. In recent years, with the demand for improvement in recording density and S / N ratio of magnetic recording media, ferromagnetic powders have become finer, have higher magnetic force, and have higher coercive force. In order to disperse in a magnetic paint to form a smooth and highly-filled magnetic layer and to improve the performance as a recording medium, the dispersion performance of the binder is a very important factor. Heretofore, as a method of improving the dispersibility of ferromagnetic powder, a method of using a dispersant such as a surfactant having a low molecular weight has been generally used, but in this method, when a large amount of the dispersant is used. Since undesired situations such as durability and head contamination of the magnetic recording medium are caused, it is unavoidable that the amount of the magnetic recording medium is restricted, sufficient dispersibility cannot be obtained, and improvement of the reliability of the magnetic recording medium is required. From the viewpoint, the binder itself is required to have a high dispersing ability. On the other hand, in order to increase the durability and reliability of a magnetic recording medium, it is necessary to include a curable compound such as a polyisocyanate compound in a magnetic paint and form a magnetic layer into a crosslinked film, particularly in the field of magnetic tape for recording. Is commonly used in In this case, the binder is required to have appropriate reactivity with a crosslinking agent such as a polyisocyanate compound. SO ₃ M, SO
_{4 M, PO 4 M 2,} PO 3 M 2 (M is an alkali metal or an ammonium group) vinyl chloride resin containing a hydrophilic group such as strong-acid group and a quaternary ammonium salt containing sulfur or phosphorus, such as is It is widely used because of its excellent dispersibility and dispersion stability of ferromagnetic powder and high strength based on the strength of intermolecular force. On the other hand, with the spread of magnetic recording media, the amount of used recording media generated is also increasing steadily. Such a used recording medium is preferably incinerated from the viewpoint of maintaining the confidentiality of the recording. However, if a vinyl chloride resin is used as a binder at this time, hydrogen chloride gas is generated at the time of incineration, and the smoke exhaust treatment is performed. An acid mist may be generated in an incinerator without equipment. Of course, it is also possible to take measures such as adding and burning lime powder, but in this case,
Inevitably increase the generation of ash. In order to eliminate the generation of hydrogen chloride gas at the time of such incineration, it is only necessary to use a binder that does not contain chlorine as a binder, and as a binder that does not contain chlorine, a nitrocellulose resin, an acrylate resin, Styrene resins and the like are known. However, nitrocellulose-based resins inherently have a risk of denitration and explosion, and the magnetic coating material has a high viscosity, so that its ability as a binder for a magnetic recording medium aiming at high-density recording is insufficient. It has also been proposed that a sulfonic acid (salt) group or a phosphoric acid group can be introduced into an acrylate resin or a styrene resin to improve dispersibility (Japanese Patent Application Laid-Open No. 57-13 / 1982).
Nos. 8050 and 57-138051 and 57
JP-A-141020, JP-A-58-108032, JP-B-62-7606), and in the case of an acrylic resin, in order to enhance the dispersibility, the alkyl group is increased to increase the hydrophobicity of the backbone polymer. As a result, the softening point is lowered, which adversely affects the running properties and durability of the magnetic recording medium. On the other hand, styrene-based resins have the disadvantage that the resulting magnetic layer becomes brittle because the intermolecular force is originally smaller than that of vinyl chloride-based resins, so that styrene monomers and hydroxyl-containing monomers are copolymerized. Or mixed with polyurethane resin,
Furthermore, although it is attempted to improve brittleness by adding a polyisocyanate compound to these and crosslinking, it is said that the running property and durability are insufficient as compared with those using a vinyl chloride binder. Have a problem.

[0003]

SUMMARY OF THE INVENTION The present invention overcomes the disadvantages of the binder used in the conventional magnetic recording medium and generates hydrogen chloride gas even after incineration after use. It is an object of the present invention to provide a magnetic recording medium having excellent recording density and S / N ratio obtained by using a binder which is excellent in dispersibility of a ferromagnetic powder and which can improve the performance of a magnetic recording medium. It was done.

[0004]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to develop a magnetic recording medium having the above-mentioned preferable properties. A hydrophilic group is introduced to enhance the dispersibility of the ferromagnetic powder, and an epoxy group is introduced to increase the durability, especially a combination of a polyurethane resin and / or a polyisocyanate compound as a binder. It has been found that the object can be achieved by the magnetic recording medium, and the present invention has been completed based on this finding.

[0005] That is, the present invention provides a non-magnetic support
In a magnetic recording medium having a magnetic layer formed by dispersing a ferromagnetic powder in a binder, at least one selected from a salt type strong acid group containing sulfur or phosphorus and a quaternary ammonium base as the binder. A styrene-based copolymer or an acrylic-based copolymer containing a hydrophilic group and an epoxy group,
Preferably, the present invention provides a magnetic recording medium characterized by using the styrene-based copolymer or the acrylic-based copolymer and a polyurethane resin and / or a polyisocyanate compound.

Hereinafter, the present invention will be described in detail. The magnetic recording medium of the present invention has a magnetic layer formed by dispersing ferromagnetic powder in a binder on a non-magnetic support. The non-magnetic support is not particularly limited and those conventionally used for magnetic recording media, for example, polyester films (eg, polyethylene terephthalate, polyethylene naphthate) having a thickness of about 5 to 50 μm, polypropylene films, cellulose triacetate films, cellulose Any one selected from diacetate film, polycarbonate film and the like can be used.

In the magnetic recording medium of the present invention, as a binder for the ferromagnetic powder, at least one hydrophilic group selected from a salt-type strong acid group containing sulfur or phosphorus and a quaternary ammonium base and an epoxy resin are used. A styrene-based copolymer or an acrylic-based copolymer containing a group is used. Examples of the salt type strong acid group containing sulfur or phosphorus include -SO
_{3 M, -SO 4 M, -PO} 4 M 2, etc. _-PO 3 _{M 2} can be mentioned (However, M is an alkali metal or an ammonium group), and as the quaternary ammonium bases, for example the formula - N ⁺ R ₁ R ₂ R ₃ X ^{− wherein} R ₁ , R ₂ and R ₃ are the same or different organic residues such as alkyl group, alkenyl group, alkoxy group or aryl group, X ⁻ is OH ⁻ , SO ₃ R ₄ ^-, -S
O ₄ R ₅ ^— or —PO ₄ R ₆ R ₇ ^— (R ₄ , R ₅ , R ₆
And R ₇ are organic residues).

The styrenic copolymer or acrylic copolymer containing a salt type strong acid group and an epoxy group used in the present invention may be a vinyl chloride monomer as described in the following (1), (2) or (3). It is produced by a method for producing a polymer-free polymer. (1) a method of copolymerizing the salt type strong acid group-containing monomer, the epoxy group-containing monomer, and the styrene-based or acryl-based monomer; (2) a method of copolymerizing the epoxy-group-containing monomer and the styrene-based monomer A method of adding the salt type strong acid group-containing compound to an epoxy group-containing copolymer obtained from a monomer or an acrylic monomer, (3) using the salt type strong acid group-containing radical initiator,
A method of copolymerizing a styrene-based monomer or an acrylic-based monomer with an epoxy group-containing monomer may, for example, be mentioned.

The monomer having a salt type strong acid group used in the above method (1) includes, for example, vinyl sulfonic acid, methyl vinyl sulfonic acid, (meth) allyl sulfonic acid, styrene sulfonic acid, (meth) acrylic Acid-2-
Alkali metal salts or ammonium salts of organic sulfonic acids such as ethyl sulfonate, 2-acrylamido-2-methylpropanesulfonic acid, 3-allyloxy-2-hydroxypropanesulfonic acid, (meth) acrylic acid-2-ethyl sulfate, 3 -Alkali metal salts or ammonium salts of organic sulfuric acids such as allyloxy-2-hydroxypropane sulfate, (meth) acrylic acid-3-chloro-2-propyl phosphate,
(Meth) acrylic acid-2-ethyl phosphate, alkali metal salt or ammonium salt of organic phosphoric acid such as 3-allyloxy-2-hydroxypropane phosphoric acid, vinylphosphonic acid,
Examples include alkali metal salts and ammonium salts of organic phosphonic acids such as acrylamide methanephosphonic acid, ethyl 2-phosphonate- (meth) acrylate, and 3-allyloxy-2-hydroxypropanephosphonic acid.

The epoxy group-containing monomers used in the methods (1), (2) and (3) include, for example, glycidyl ethers of unsaturated alcohols such as allyl glycidyl ether and methallyl glycidyl ether. Glycidyl esters of unsaturated acids such as glycidyl acrylate, glycidyl methacrylate, glycidyl-p-vinylbenzoate, methyl glycidyl itaconate, glycidyl ethyl malate, glycidyl vinyl sulfonate, glycidyl (meth) allyl sulfonate, butadiene monooxide, vinyl cyclohexene mono Epoxide olefins such as oxides and 2-methyl-5,6-epoxyhexene;

On the other hand, the styrene-based monomers used in the methods (1), (2) and (3) include, for example, styrene, α-methylstyrene, p-methylstyrene, p-methylstyrene,
t-butylstyrene and the like. Examples of the acrylic monomer include methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, cyclohexyl (meth) acrylate, and the like. In the methods (1), (2) and (3), other copolymerizable monomers can be used in combination, if necessary. As other copolymerizable monomers,
Halogen-free monomers can be used.
For example, vinyl acetate such as vinyl acetate and vinyl propionate, vinyl ether such as methyl vinyl ether, isobutyl vinyl ether and cetyl vinyl ether, unsaturated carboxylic acid such as acrylic acid, methacrylic acid, maleic acid and itaconic acid, maleic anhydride, and itaconic anhydride Unsaturated carboxylic anhydrides such as acids, diethyl maleate, butyl benzyl maleate, di-2-hydroxyethyl maleate, diethyl itaconate, methyl (meth) acrylate, ethyl (meth) acrylate,
Lauryl (meth) acrylate, (meth) acrylic acid-2
-Unsaturated carboxylic acid alkyl esters such as -hydroxypropyl; α-olefins such as ethylene and propylene; allyl alcohol; unsaturated alcohols such as 3-buten-1-ol; unsaturated nitriles such as (meth) acrylonitrile; Vinylidene chloride, a hydroxyl group-containing monomer, or the like can be used. Examples of the hydroxyl group-containing monomer include α, β-unsaturated acids having 2 to 8 carbon atoms, such as (meth) acrylic acid-2-hydroxyethyl ester and (meth) acrylic acid-2-hydroxypropyl ester. Alkanol esters, esters of polyalkylene glycol represented by the following formula and (meth) acrylic acid

[0012]

Embedded image

(M is an integer of 2 to 9; n is 2 to 4
R is hydrogen or a methyl group), 2-hydroxyethyl-2 ′-(meth) acryloyloxyphthalate,
Mono (meth) acrylic esters of dihydroxy esters of dicarboxylic acids such as 2-hydroxyethyl-2 ′-(meth) acryloyloxysuccinate, (meth) acrylamides such as N-methylol (meth) acrylamide, and maleic acid diester Alkylene glycol esters of unsaturated dicarboxylic acids such as -2-hydroxyethyl ester, di-4-hydroxybutyl maleate, di-2-hydroxypropyl itaconate,
Olefin alcohols such as 3-buten-1-ol and 5-hexen-1-ol; vinyl ethers such as 2-hydroxyethyl vinyl ether and 2-hydroxypropyl vinyl ether; (meth) allyl-2-hydroxyethyl ether; ) Allyl-2-hydroxypropyl ether, (meth) allyl-3-hydroxypropyl ether, (meth) allyl-2-hydroxybutyl ether, (meth) allyl-3-hydroxybutyl ether, (meth) allyl-4-hydroxybutyl ether, Polio such as mono (meth) allyl ethers of alkylene glycol such as (meth) allyl-6-hydroxyhexyl ether, diethylene glycol mono (meth) allyl ether and dipropylene glycol mono (meth) allyl ether Sialic sharp glycol (meth) monoallyl ether, glycerol mono (meth) allyl ether, (meth) allyl-2-chloro-3-hydroxypropyl ether, (meth) allyl-2-hydroxy -
Mono (meth) allyl ether of hydroxy-substituted (poly) alkylene glycol such as 3-chloropropyl ether, mono (meth) allyl ether of polyhydric phenol such as eugenol and isoeugenol, (meth) allyl-2-hydroxy Examples thereof include (meth) allyl thioethers of alkylene glycol such as ethyl thioether and (meth) allyl-2-hydroxypropyl thioether, vinyl alcohol and (meth) allyl alcohol which do not contain halogen.

These copolymerizable monomers are used for the purpose of obtaining a homogeneous blend by adjusting the compatibility and softening point of the copolymer according to the present invention and other resins when they are mixed. It is selected appropriately. Among these copolymerizable monomers, acrylonitrile is useful as a component that increases the intermolecular force to increase the strength of the magnetic layer, and is also useful in increasing the compatibility with a commonly used polyurethane resin. .

In the above method (1), the above-mentioned salt-type strong acid group-containing monomer, epoxy group-containing monomer, styrene-based monomer or acryl-based monomer may be used as required. By copolymerizing with other possible monomers, the desired copolymer can be obtained.However, the polymerization method is not particularly limited, and any of a solution polymerization method, a suspension polymerization method, an emulsion polymerization method, etc. Methods can also be used. Examples of the polymerization initiator used for the polymerization include lauroyl peroxide, diisopropyl peroxydicarbonate, and di-2.
Organic peroxides such as -ethylhexylperoxydicarbonate, t-butylperoxypivalate, 3,5,5-trimethylhexanoyl peroxide, azo compounds such as α, α'-azobisisobutyronitrile, or Examples thereof include ammonium persulfate and potassium persulfate.

Examples of the suspending agent used in the suspension polymerization include polyvinyl alcohol, partially saponified polyvinyl acetate, cellulose derivatives such as methylcellulose, polyvinylpyrrolidone, maleic anhydride-vinyl acetate copolymer, and polyacrylamide. And natural polymer materials such as starch and gelatin. Further, examples of the emulsifier used in the emulsion polymerization include anionic emulsifiers such as sodium alkylbenzenesulfonate and sodium lauryl sulfate, and nonionic emulsifiers such as polyoxyethylene alkyl ether and polyoxyethylene sorbitan fatty acid partial ester. . If necessary, a molecular weight modifier such as trichloroethylene, thioglycol, dodecylmercaptan and the like can be used. The above-mentioned polymerization initiator, monomer, suspending agent or emulsifier, molecular weight modifier and the like may be added to the polymerization system at once at the start of the polymerization, or may be added separately during the polymerization. The polymerization is usually carried out at a temperature of 35 to 80 ° C. with stirring.

In the above method (2), first, an epoxy group-containing monomer and a styrene monomer or an acrylic monomer are copolymerized with another copolymerizable monomer used as desired. After polymerization to form an epoxy group-containing copolymer, the salt type strong acid group-containing compound is added thereto. In this case, as the polymerization method, any of a solution polymerization method, a suspension polymerization method, and an emulsion polymerization method can be used in the same manner as described above, but it is optimal according to the conditions of the subsequent addition reaction and the characteristics of the copolymer. What is necessary is just to select a suitable manufacturing method. For example, when the addition reaction is performed in an aqueous system, it is advantageous to obtain a copolymer as fine aqueous dispersion particles by emulsion polymerization, and when the addition reaction is performed in a solvent system, a solution polymerization method or methanol or the like is used. A suspension polymerization method using a lower alcohol as a polymerization medium is preferred, but an ordinary suspension polymerization method can also be used.

The salt type strong acid group-containing compound to be added to the epoxy group-containing copolymer thus obtained includes:
For example, sulfites such as sodium sulfite, sodium hydrogen sulfite, and ammonium potassium sulfite, hydrogen sulfates such as sodium hydrogen sulfate, potassium hydrogen sulfate, and ammonium hydrogen sulfate; hydrogen phosphate salts such as dipotassium hydrogen phosphate and disodium hydrogen phosphate And hydrogen phosphites such as sodium hydrogen phosphite and ammonium hydrogen phosphite; aminosulfonates such as sodium taurine, sodium sulfamate and potassium sulfanilate; and sodium thiosulfate.

The addition reaction can be carried out in any of an aqueous system and a non-aqueous system. However, since the salts used in the addition reaction are water-soluble, it is advantageous to carry out the reaction in an aqueous system or an organic medium containing water. . The reaction is usually carried out by heating at a temperature of about 40 to 120 ° C. for 2 to 24 hours, but if the reaction temperature is too high, the copolymer is deteriorated. A catalyst can be used for this addition reaction. Examples of the catalyst include quaternary ammonium salts such as tetrabutylammonium bisulfate, tetrabutylammonium bromide, trimethyllauryl ammonium chloride and benzyltriethylammonium chloride, and boron fluorides such as zinc zinc tetrafluoride. Further, the addition reaction can be caused to proceed simultaneously with the polymerization by preparing a salt or a catalyst necessary for the addition reaction in the polymerization system when preparing the epoxy group-containing copolymer.

In the above method (3), the styrene monomer or acrylic monomer and the epoxy group-containing monomer and another copolymerizable monomer used as desired are used. The desired copolymer can be obtained by copolymerization using the salt type strong acid group-containing radical initiator. Examples of the salt type strong acid group-containing radical initiator used at this time include ammonium persulfate, potassium persulfate, ammonium perphosphate, sodium perphosphate, and the like.

On the other hand, the method for producing the styrene-based copolymer or acryl-based copolymer containing the quaternary ammonium base and the epoxy group includes, for example, (a) the quaternary ammonium base-containing monomer and the epoxy A method of copolymerizing a group-containing monomer with a styrene-based monomer or an acrylic-based monomer and another copolymerizable monomer used as desired, or (b) an epoxy-group-containing monomer And a styrene-based monomer or an acrylic-based monomer and another copolymerizable monomer used as desired to obtain an epoxy-containing styrene-based copolymer or an acrylic-based copolymer. Thereafter, a method of reacting this with a tertiary amine in the presence or absence of an acid can be used.

Examples of the monomer having a quaternary ammonium salt used in the above method (a) include diallylmethylammonium chloride, diallyldimethylammonium stearate, 2-hydroxy-3-allyloxypropyltrimethylammonium chloride, Vinylbenzyltrimethylammonium chloride, (meth) acryloyloxyethyltrimethylammonium chloride,
2-hydroxy-3-methacryloyloxypropyltrimethylammonium chloride, (meth) acryloyloxypropyldimethylbenzyl chloride, (meth) acrylamidopropyltrimethylammonium chloride and the like can be mentioned.

The epoxy group-containing monomer, styrene monomer or acryl monomer used in the above methods (a) and (b) and other copolymerizable monomers used as desired Examples thereof include those exemplified in the description of the styrene-based copolymer or acrylic monomer containing a salt-type strong acid group and an epoxy group, and
The polymerization method is not particularly limited, and the polymerization method exemplified in the method (1) can be used.

With respect to the content of the salt type strong acid group or the hydrophilic group comprising a quaternary ammonium group in the styrene copolymer or the acrylic copolymer thus obtained,
The molecular weight of the copolymer per hydrophilic group is 4,000.
Amounts such as in the range of ４０40,000 are preferred. If the content of the hydrophilic group is more than this, the moisture resistance of the recording medium is lowered, and if it is less than this, the dispersibility of the ferromagnetic powder tends to be lowered, which is not preferable.

On the other hand, an epoxy group is contained in the copolymer in an amount of 0.1%.
It is desirable to contain it at a ratio of 5 to 10% by weight. If this amount is less than 0.5% by weight, the durability is insufficient and
If it exceeds 0% by weight, crosslinking may proceed too much and become brittle. The styrene copolymer has a number average molecular weight of 1
Those having a glass transition temperature of not lower than 000 to 100,000 and a glass transition temperature of 60 ° C. or higher are preferred. If the number average molecular weight is less than 10,000, the durability is insufficient, and if it exceeds 100,000, the viscosity of the magnetic paint becomes too high and the dispersibility of the ferromagnetic powder is lowered, which is not preferable. Further, the glass transition temperature is 6
If the temperature is lower than 0 ° C., the high temperature (40 to 50)
C), which is not preferable.

In the magnetic recording medium of the present invention, a polyurethane resin and a styrene-based or acrylic-based copolymer containing a hydrophilic group and an epoxy group obtained as described above are used as a binder. It is preferable to use a polyisocyanate compound. Examples of the polyurethane resin include those obtained by the reaction of a polyester polyol or a polyether polyol with a polyisocyanate compound, and particularly include those obtained by remaining a hydroxyl group, or a sulfonate or a phosphate, or Those having a quaternary ammonium salt including a betaine type are preferred from the viewpoint of improving the dispersibility of the ferromagnetic powder. Furthermore, as long as the object of the present invention is not impaired, cellulose resin, phenoxy resin, epoxy resin, butyral resin, acrylic resin and acrylonitrile-
Butadiene rubber may be used in combination.

On the other hand, as the polyisocyanate compound, for example, tolylene diisocyanate, 4-methoxy-
1,3-phenylene diisocyanate, 4-isopropyl-1,3-phenylene diisocyanate, 4-chloro-1,3-phenylene diisocyanate, 4-butoxy-1,3-phenylene diisocyanate, 2,4-diisocyanate-diphenyl ether, mesitylene diisocyanate 4,4′-methylenebis (phenyl isocyanate), judylene diisocyanate, 1,5-naphthalene diisocyanate, benzidine diisocyanate,
o-Nitrobenzidine diisocyanate, 4,4'-diisocyanate dibenzyl, 1,4-tetramethylene diisocyanate, 1,6-hexamethylene diisocyanate, 1,10-decamethylene diisocyanate, 1,4-
Diisocyanates such as cyclohexylene diisocyanate, xylylene diisocyanate, 4,4'-methylenebis (cyclohexyl isocyanate), 1,5-tetrahydronaphthalene diisocyanate, and isophorone diisocyanate, and adducts, dimers, and trimers of these with polyols Further, a resin having a urethane bond formed by the reaction of these diisocyanates and polyols, which has an average of 2.3 or more isocyanate groups in one molecule, and has a number average molecular weight of 2,000 or more and 10, Polyurethane resins having a molecular weight of 1,000 or less and a molecular weight of 1,000 or less are less than 20% by weight. Among these, in particular, an average of 2.3 per molecule.
Polyurethane resins having more than one isocyanate group are preferred from the viewpoint of further improving the durability of the obtained recording medium.

As the ferromagnetic powder used in the magnetic recording medium of the present invention, for example, a metal magnetic powder such as iron or cobalt, an alloy iron magnetic powder with nickel or the like mainly composed of iron or cobalt, γ-Fe ₂ O ₃ , Fe ₃ O ₄ , γ-FeO
_x (1.33 <x ≦ 1.5) and iron oxide magnetic powder such as iron oxide magnetic powder, barium ferrite, Fe ₅ C _2, etc. impregnated or coated with cobalt, iron nitrogen magnetic powder, Chromium oxide magnetic powder and the like can be mentioned. These may be used alone or in combination of two or more. In the case of a combination of two or more, it is also possible to use two magnetic layers and to use different magnetic powders for the first layer and the second layer.

In the present invention, in order to provide a magnetic layer on a non-magnetic support, first, in a suitable organic solvent, as a binder, the styrene-based copolymer or the acrylic copolymer and, if desired, After dissolving the polyurethane resin, the polyisocyanate compound, and other resins to be used, the ferromagnetic powder is dispersed therein to prepare a magnetic paint. Preferred examples of the organic solvent include, for example, methyl ethyl ketone, methyl-n-propyl ketone, methyl isobutyl ketone, diethyl ketone, methyl formate, ethyl formate, propyl formate, methyl acetate, ethyl acetate, butyl acetate, acetone, cyclohexanone, tetrahydrofuran, Dioxane, methanol, ethanol, isopropyl alcohol, butanol, methyl cellosolve, butyl cellosolve, cellosolve acetate, dimethylformamide, dimethylsulfoxide, pentane, hexane,
Cyclohexane, heptane, octane, mineral spirits, petroleum ether, gasoline, benzene, toluene,
Xylene, chloroform, carbon tetrachloride, chlorobenzene, perchlorethylene, trichloroethylene and the like can be mentioned. These solvents may be used alone or in combination of two or more.

The magnetic paint is usually prepared such that the organic solvent is 50 to 90% by weight, the binder is 5 to 20% by weight, and the ferromagnetic powder is 10 to 50% by weight based on the total weight. You. The binder is used in an amount of usually 5 to 25 parts by weight, preferably 7 to 20 parts by weight, per 100 parts by weight of the ferromagnetic powder. In addition, the magnetic paint may be any known additive component such as a lubricant, an abrasive, an antistatic agent, a crosslinking regulator, a dispersant, a pigment, an extender, a plasticizer, as long as the object of the present invention is not impaired. , A surfactant, an antioxidant, a stabilizer, an antifoaming agent, and the like.

Examples of the lubricant include higher fatty acids having 8 to 18 carbon atoms, higher alcohols, higher fatty acid amides, higher fatty acid esters, and the like, and specifically, lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid, linoleic acid, and the like. Acid, stearolic acid, stearyl alcohol, palmityl alcohol, lauryl amide, dimethyl stearyl amide, butyl lauryl amide, butyl stearate,
Octyl stearate and the like. Further, silicone oil, fluorine-based oils such as polyperfluoroalkylene oxide and perfluoroalkane, paraffin wax, polyethylene oxide and the like can also be used. In addition, carbon black, graphite, molybdenum disulfide,
Solid lubricants such as tungsten disulfide can also be used.
These lubricants are usually used in a proportion of 1 to 6 parts by weight based on 100 parts by weight of the ferromagnetic powder.

As the abrasive, for example, alumina,
Silicon carbide, chromium oxide corundum and the like are generally used. Further, as an antistatic agent, for example, other than conductive powders such as graphite and carbon black, nonionic surfactants centered on polyalkylene oxides,
Surfactant-based antistatic agents such as cationic surfactants mainly containing quaternary ammonium salts are used. By the way, the reason why the recording medium of the present invention has excellent durability is not always clear, but probably due to surface-bound moisture such as ferromagnetic powder and atmospheric moisture during the manufacturing process,
This is probably because the strong hydrophilic groups in the binder are partially decomposed and separated, and undergo a crosslinking reaction with the epoxy groups in the molecule.

The crosslinking regulator is for promoting such a crosslinking reaction, and the crosslinking regulator includes:
For example, (1) acid phosphate, (2) acid sulfate, (3) carboxylic acid, (4) polythiol compound,
(5) An aminosilane compound or the like is used. As the (1) acidic phosphate ester, a general formula (R ₈ O) _m PO (OH) _3-m ... [1] [R ₈ O (A ₁ O) _n ] _m PO (OH) _3-m ... [2] and _{[R 8 COO (a 1 O} ) n] m PO (OH) 3-m ... [3] (R 8 in the formula is an alkyl group or alkenyl group having 1 to 22 carbon atoms, a phenyl group, an alkyl A phenyl group or an alkenylphenyl group, A ₁ is an alkylene group having 2 to 4 carbon atoms, m is an integer of 1 to 3, and n is an integer of 1 to 30).

The compound represented by the general formula [1] is a phosphoric acid monoester, phosphoric diester, phosphoric acid derived from phosphoric acid and an alkanol or alkenol having 1 to 22 carbon atoms, phenol, alkylphenol or alkenylphenol. Sesquiesters or phosphate triesters, typical examples of which are monododecyl phosphate, sesquidodecyl phosphate,
Dinonylphenyl phosphate and the like.

The compound represented by the general formula [2] is a phosphoric acid monoester derived from phosphoric acid and an alkanol or alkenol having 1 to 22 carbon atoms, a lower alkylene oxide adduct of phenol, alkylphenol or alkenylphenol. , Phosphoric diester, phosphoric acid sesquiester or phosphoric acid triester, typical examples of which are sesquidodecyl polyoxyethylene (n = 3) phosphate, dinonylphenyl polyoxyethylene (n = 4) phosphate And trioleyl polyoxyethylene (n = 4) phosphate.

The compound represented by the general formula [3] is a monoester, diester, sesquiphosphate or phosphorus phosphate derived from phosphoric acid and a lower alkylene oxide of a fatty acid having 2 to 23 carbon atoms. Acid triesters, and specific examples thereof include [C ₁₇ H ₃₅ COO (CH
₂ CH ₂ O) ₁₅ PO (OH) ₂ ], [CH ₂ ＣC (CH ₃ ) C
OO (CH ₂ CH ₂ O)] _1.5 PO (OH) _{1.5 and the} like.

As the (2) acidic sulfuric acid monoester, for example, R ₉ OSO ₂ OH... [4] R ₉ O (A ₂ O) _k SO ₂ OH... [5] and R ₉ COO (A ₂₎ O) _k SO ₂ OH [6] (wherein R ₉ is an alkyl or alkenyl group having 1 to 22 carbon atoms, a phenyl group, an alkylphenyl group or an alkenylphenyl group, and A ₂ is an alkylene having 2 to 4 carbon atoms) Group, k is an integer of 1 to 30).

The compound represented by the general formula [4] is a sulfuric acid monoester derived from sulfuric acid and an alkanol or alkenol having 1 to 22 carbon atoms, phenol, alkylphenol or alkenylphenol,
Specific examples of such a substance include butyl sulfate monoester and oleyl sulfate monoester. The compound represented by the general formula [5] includes sulfuric acid and a compound having 1 to 1 carbon atoms.
22 alkanols or alkenols, phenols, alkyl phenols or lower alkylene oxide adducts of alkenyl phenols derived from sulfuric acid monoesters, specific examples of which include:
Examples include polyoxyethylene (k = 4) dodecyl ether sulfate monoester, polyoxypropylene (k = 6) nonylphenyl ether sulfate monoester, and the like.

The compound represented by the general formula [6] is a sulfuric acid monoester derived from sulfuric acid and a lower alkylene oxide ester of a fatty acid having 2 to 23 carbon atoms,
As the specific examples of such, such as _{C 5 H 11 COO (CH 2} CH 2 O) 2 SO 2 OH CH 2 = C (CH 3) COO (CH 2 CH 2 O) SO 2 OH and the like.

The carboxylic acid (3) is a saturated or unsaturated aliphatic monovalent or polyvalent carboxylic acid, or an aromatic monovalent or polyvalent carboxylic acid. Specific examples thereof include formic acid,
Monochloroacetic acid, dichloroacetic acid, trichloroacetic acid, α-
Chlorobutyric acid, monofluoroacetic acid, monobromoacetic acid, monoiodoacetic acid, p-nitrobenzoic acid, m-nitrobenzoic acid, o-nitrobenzoic acid, m-chlorobenzoic acid, o-chlorobenzoic acid, o-toluic acid, 3, 5-dinitrobenzoic acid, salicylic acid, oxalic acid, malonic acid, maleic acid,
Fumaric acid, phthalic acid, isophthalic acid, terephthalic acid, hemimellitic acid, trimellitic acid, trimesic acid, prenitic acid, melophanic acid, pyromellitic acid, benzenepentacarboxylic acid, melitic acid, phenylpropionic acid, o-phenylene diacetic acid, glyoxylic acid , Pyruvic acid, acetoacetic acid, glycolic acid, (±) -lactic acid, (±) -mandelic acid,
(-)-Malic acid, (±) -malic acid, (+)-tartaric acid,
(-)-Tartaric acid, (±) -tartaric acid, mesotartaric acid, citric acid and the like. The polythiol compound (4) has a general formula

[0041]

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(Wherein R ₁₀ is a substituent and M ₁ is a hydrogen atom or an alkali metal), or a trialkane thiol or a monoalkali metal salt thereof. Examples of the substituent R ₁₀ in the general formula [7] include —SH, —N (CH ₃ ) ₂ ,
_{-NHC 6 H 5, -N (C} 4 H 9) 2, -N (C 8 H 17) 2, -
_{N (C 12 H 25) 2} , -N (CH 2 CH = CH 2) 2, -NHC
₈ H ₁₆ CH = CHC ₈ H ₁₇ and the like.

As the aminosilane compound (5),
For example, N- (2-aminoethyl) -3-aminopropylmethyldimethoxysilane, N- (2-aminoethyl) -3-
Aminopropylmethoxysilane, p- [N- (2-aminoethyl)] aminomethylphenethyltrimethoxysilane, 1- (3-aminopropyl) -1,1,3,3,3-pentamethyldisiloxane, 3- Aminopropyltriethoxysilane, 3-aminopropyltris (trimethylsiloxy) silane, 3- [N-allyl-N- (2-aminoethyl)] aminopropyltrimethoxysilane, N- [3-
(Trimethoxysilyl) propyl] diethylenetriamine, N- [3- (trimethoxysilyl) propyl] triethylenetetramine, 3-trimethoxysilylpropyl-
m-phenylenediamine, 1,3-bis (3-aminopropyl) -1,1,3,3-tetramethyldisiloxane,
α, ω-bis (3-aminopropyl) polydimethylsiloxane, N, N-bis [(methyldimethoxysilyl) propyl] amine, N, N-bis [3- (methyldimethoxysilyl) propyl] ethylenediamine, N, N -Bis [3- (trimethoxysilyl) propyl] amine, N, N
-Bis [3- (trimethoxysilyl) propyl] ethylenediamine, hexamethyldisilazane and the like. Among these crosslinking regulators, polyoxyethylene alkyl ether acid phosphate and aminosilane compounds are also effective as viscosity modifiers for magnetic coatings.

In the present invention, the method for preparing the magnetic paint is not particularly limited, and may be any of those conventionally used in the production of magnetic paints, for example, a ball mill, a mixer, a roll mill, and the like. A method of uniformly mixing and dispersing using a bead mill, gravel mill, sand mill, high-speed impeller, or the like can be used. The dispersion conditions vary depending on the type and size of the ferromagnetic powder to be used, or the application, but generally, the treatment may be carried out at a temperature in the range of room temperature to 100 ° C. for about 5 minutes to 20 hours.

The magnetic layer in the magnetic recording medium of the present invention comprises:
For example, the magnetic paint prepared as described above is applied to at least one surface on the non-magnetic support by any method so that the thickness when dried is usually in the range of 0.5 to 20 μm, Then, it can be formed by drying, or it can be formed by applying and drying the magnetic paint on a base sheet such as release paper to form a magnetic layer, and then transferring it to a support. it can. The coating method, drying method, transfer method, and the like at this time may be any method selected from known methods.

[0046]

Next, the present invention will be described in more detail by way of examples, which should not be construed as limiting the present invention. The evaluation of the magnetic paint was performed as follows. (1) Glossiness A magnetic paint is applied on a polyester film so as to have a coating thickness of 4 μm, is subjected to a magnetic field orientation treatment, and is dried. 60
° The reflectance was measured at the reflection angle. (2) Dispersion stability After the paint used for the evaluation of the glossiness was allowed to stand for 6 hours, it was applied on a polyester film so as to have a coating thickness of 4 μm, subjected to a magnetic field orientation treatment, and then dried. The reflectance at a reflection angle of 60 ° was measured using a gloss meter, and the retention was calculated from the gloss of (1).

(3) Squareness ratio (Br / Bm) The magnetic coating film used for evaluation of glossiness was 12.5 mm × 50 mm.
And measured with a magnetic property measuring machine. (4) Durability The magnetic coating film used for the gloss evaluation was subjected to a smoothing treatment with a calender roll, and then subjected to a heat treatment at 65 ° C. for 65 hours.
Cut to a width of 2.5 mm, apply a load of 100 g, make contact with a rotating drum on which abrasive paper is stuck, rotate at 150 rpm for 30 minutes, and visually observe the degree of adhesion of the magnetic paint to the abrasive paper. C was evaluated in three stages. A: No stain B: Slight stain C: Stain

(5) Solvent resistance The same coating film used for evaluating the glossiness was coated with a film having a width of 12.5 mm and a length of 5 mm.
0 mm, and cut into 20 pieces, tetrahydrofuran 10
50ml into a 150ml glass bottle with lid
Solvent resistance was evaluated according to the following criteria based on the state after ultrasonic treatment at 1 ° C. for 1 hour and the degree of contamination with tetrahydrofuran. A: No deformation and no stain on the coating film B: The shape of the coating film is retained, but the stain is present. C: The coating film disappears and the stain is severe. (6) Amount of hydrogen chloride generated during combustion. The same coating film was cut into 3 mm x 3 mm, and in accordance with JIS K-7217, hydrogen chloride in the combustion gas in the air was absorbed with an aqueous sodium hydroxide solution, and chloride ions in the absorbing solution were converted into silver nitrate / ferric sulfate. Ammonium /
It was determined by the ammonium thiocyanate method. As a blank, a polyester film on which a magnetic coating film was not applied was used.

Production Example 1 20 parts by weight of styrene, 10 parts by weight of acrylonitrile, 15 parts by weight of allyl glycidyl ether, 1 part by weight of 2-hydroxypropyl methacrylate, 2 parts by weight of sodium lauryl sulfate, 1 part by weight of sodium hydrogen carbonate, 4 parts by weight of potassium persulfate Parts by weight and 200 parts by weight of deionized water were charged into a polymerization vessel equipped with a stirrer. After degassing under reduced pressure, the temperature was raised to 80 ° C. to start polymerization. Immediately after the start of the polymerization, a mixture of 36 parts by weight of styrene, 15 parts by weight of acrylonitrile and 4 parts by weight of 2-hydroxypropyl methacrylate was continuously poured into the polymerization vessel over 8 hours. After 10 hours, the conversion of the polymerization is 9
When it reached 6%, it was cooled to obtain an aqueous dispersion. To this aqueous dispersion, 10 parts by weight of methyl ethyl ketone was added, and -3 was added.
After freezing and thawing at 0 ° C. to collect the resin, the resin was washed with water and dried to obtain resin A. Resin A has an epoxy group content of 3.2 wt%, a hydroxyl group content of 0.4 wt%, a styrene unit content of 58 wt%, and a bound acid content of 0.8 wt% as SO _4.
Having a weight average molecular weight of 30,100 and a binding acid of 1
The molecular weight per unit is 12,000 and the glass transition temperature is 7
6 ° C.

Production Example 2 30 parts by weight of styrene, 20 parts by weight of acrylonitrile, 5 parts by weight of sodium styrenesulfonate, 30 parts by weight of methyl methacrylate, 15 parts by weight of glycidyl methacrylate, 0.5 part by weight of sodium hydrogen carbonate, 1 part by weight of sodium sulfite , 0.1 parts by weight of hydroxypropylcellulose, 0.5 parts by weight of polyoxyethylene lauryl ether, 2 parts by weight of azobisisobutyronitrile, 200 parts by weight of methanol and 20 parts by weight of water were charged into a polymerization vessel and degassed under reduced pressure. After polymerization was started at 60 ° C. and cooled after 5 hours, the content was poured into 10 times the amount of water, followed by filtration, washing and drying to obtain resin B. The epoxy group content in resin B is 2.
8 wt%, the total content of styrene and methyl methacrylate units is 62 wt%, the amount of bound acid is 1.0 wt% as SO ₄ , the weight average molecular weight is 19,000, the molecular weight per bound acid is 9,600, glass The transition temperature was 79 ° C.

Production Example 3 20 parts by weight of styrene, 10 parts by weight of acrylonitrile, 12 parts by weight of allyl glycidyl ether, 1 part by weight of 2-hydroxypropyl methacrylate, 0.1 part by weight of methyl cellulose.
1 part by weight, 3 parts by weight of azoisobutyronitrile and 200 parts by weight of deionized water were charged into a polymerization vessel, degassed under reduced pressure while stirring, and then heated to 80 ° C. to initiate polymerization. Immediately after the start of the polymerization, a mixture of 36 parts by weight of styrene, 18 parts by weight of acrylonitrile and 4 parts by weight of 2-hydroxypropyl methacrylate was continuously poured into the polymerization vessel over 4 hours. , N-dimethylstearylamine 4 parts by weight and lactic acid 2 parts by weight
Stirred for hours. After cooling, the resin was dehydrated and washed, and dried to obtain resin C. Resin C has an epoxy group content of 1.5 wt%, a hydroxyl group content of 0.6 wt%, and a styrene unit content of 56 wt%.
%, The content of bound quaternary ammonium salt is 2.8 wt% as dimethylstearylamino group, the weight average molecular weight is 42,000, the molecular weight per bound quaternary ammonium salt is 10,400, and the glass transition temperature is 76 ° C.

Preparation Example 4 Resin D was obtained in the same manner as in Preparation Example 2, except that the disodium salt of 2-acid phosphoxyethyl methacrylate was used instead of sodium styrene sulfonate. . Epoxy group content in the resin D is 2.7 wt%, the total content of styrene and methyl methacrylate units is 63 wt%, the amount of bound acid as PO ₄ 1.
The weight average molecular weight was 21,000, the molecular weight per binding acid was 6,800, and the glass transition temperature was 77 ° C.

Production Example 5 Resin B 'was obtained in the same manner as in Production Example 2, except that cyclohexyl methacrylate was used instead of styrene. Resin B ′ has an epoxy group content of 2.9 wt%, a total amount of cyclohexyl methacrylate and methyl methacrylate of 61 wt%, and a binding acid amount of SO _4.
And the average molecular weight was 21,000.
0, the molecular weight per binding acid was 9,600, and the glass transition temperature was 67 ° C.

Production Example 6 Resin E was obtained in the same manner as in Production Example 2, except that styrene was used instead of sodium styrenesulfonate. Resin E has no binding acid, a total content of styrene and methyl methacrylate units of 66% by weight, an epoxy group content of 3.0% by weight, and a weight average molecular weight of 29,00.
0 and the glass transition temperature was 80 ° C.

Production Example 7 Resin F was obtained in the same manner as in Production Example 2, except that methyl methacrylate was used instead of glycidyl methacrylate. The styrene content in resin F is 31 wt%, the binding acid content is 1.0 wt% as SO ₄ , its weight average molecular weight is 17,000, the molecular weight per binding acid is 9,600, and the glass transition temperature is It was 81 ° C.

Production Example 8 75 parts by weight of methyl methacrylate, 20 parts by weight of butyl acrylate, 5 parts by weight of 2-acid phosphoxyethyl methacrylate, 0.6 parts by weight of azobisisobutyronitrile, 75 parts by weight of toluene, 75 parts by weight of methyl isobutyl ketone
Parts by weight into a polymerization vessel, and after purging with nitrogen,
After reacting for hours, a copolymer solution was obtained, which was dried to obtain resin G
I got After the resin G was purified by reprecipitation, it was analyzed to have a bound acid amount of 1.8 wt% as PO ₄ , a weight average molecular weight of 19,000, and a molecular weight per bound acid of 5,30.
0, the glass transition temperature was 70 ° C.

Examples 1 to 7, Comparative Examples 1 to 4 Cobalt-coated magnetic iron oxide powder (specific surface area: 42 m ² / g)
100 parts by weight, 10 parts by weight of a hard binder of the type shown in Table 1, 10 parts by weight of a polyurethane resin of the type shown in Table 1,
A mixture consisting of 150 parts by weight of a mixed solvent of methyl ethyl ketone / cyclohexanone / toluene (weight ratio 1/1/1), 2 parts by weight of carbon black, 4 parts by weight of alumina, 2 parts by weight of myristic acid, and 1 part by weight of butyl stearate was placed in a sand mill. After high-speed dispersion for 90 minutes, 60 parts by weight of the mixed solvent and 13 parts by weight of a polyisocyanate of the type shown in Table 1 were added thereto, and after further dispersion for 15 minutes, 7 parts by weight of a crosslinking regulator of the type shown in Table 1 Was added and mixed for 5 minutes to prepare a magnetic paint and evaluated. Table 1 shows the results.

The symbol or trade name of each component in the table means the following. MR-110: manufactured by Nippon Zeon Co., Ltd., trade name, vinyl chloride binder H: 1,4-butanediol adipate-MDI polyurethane resin, molecular weight 70,000, hydroxyl group content 0.3 wt
% M: terminal isocyanate type polyurethane, number average molecular weight: 4,000, NCO amount per molecule: 2.8 L: Nippon Polyurethane Co., Ltd., trimethylolpropane-TDI adduct a: Toho Chemical Co., Ltd., polyoxy Ethylene nonylphenyl acid phosphate b: N, N-dibutylaminothiol-S-triazine c: γ-aminopropyltriethoxysilane AG: Resins obtained in Production Examples 1 to 7, respectively

[0059]

[Table 1]

(Note) ND: 0.010 mg / g or less

[0061]

According to the present invention, it is possible to form a magnetic layer in which ferromagnetic powders are oriented and filled at a high density comparable to the case where a conventional vinyl chloride binder is used.
As a result, a magnetic recording medium having an / N ratio, durability and running properties can be obtained, and even if this magnetic recording medium is incinerated, no hydrogen chloride is generated and no environmental pollution is caused.

──────────────────────────────────────────────────続 き Continuation of the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical display location C09D 163/00 PHZ C09D 163/00 PHZ

Claims (2)

(57) [Claims] A magnetic recording medium having a magnetic layer formed by dispersing a ferromagnetic powder in a binder on a non-magnetic support, wherein the binder comprises a salt-type strong acid group containing sulfur or phosphorus, A magnetic recording medium comprising a styrene copolymer or an acrylic copolymer containing at least one hydrophilic group selected from quaternary ammonium bases and an epoxy group. 2. The magnetic recording medium according to claim 1, wherein the binder contains a polyurethane resin and / or a polyisocyanate compound together with the styrene-based copolymer or the acrylic-based copolymer.