JPH0263252B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides tapes, sheets,
It relates to magnetic recording media in the form of cards, drums, or disks. More specifically, the present invention relates to a magnetic recording medium in which the magnetizable layer is cured by actinic light such as ultraviolet rays, and then completely cured by heat treatment.

Traditionally, binders for magnetic recording media include:
Ethyl cellulose, nitrocellulose, polyvinylidene chloride resin, vinyl chloride-vinyl acetate copolymer, styrene-butadiene copolymer, polymethyl methacrylate resin, vinylidene chloride-methyl methacrylate copolymer, polyurethane resin, epoxy resin , polyester resin, butadiene-acrylonitrile copolymer, etc. have been used, but
These binders have the disadvantage that the adhesiveness of the magnetic recording layer is insufficient because the resin component is simply solidified by evaporation of the solvent.

On the other hand, a method has been proposed in which an isocyanate compound is added to the binder as a crosslinking reagent to improve the adhesion to the support and physical properties (Japanese Patent Publication No. 1973-
28048 et al.), but these methods have another disadvantage in that the pot life of the magnetic paint is shortened because reactive compounds are added.

There is also a method of using an ultraviolet curable resin as a binder, as described in JP-A No. 56-8468, but this method requires that magnetic paint containing a large amount of finely powdered magnetic particles is resistant to ultraviolet rays. It has a fatal flaw in that it cannot be completely cured due to insufficient penetration.

Separately, Japanese Patent Publication No. 57-50801 describes a curing method using an electron beam using a radiation-polymerized resin as a binder, but this method not only requires a huge amount of equipment but also makes it difficult to control the curing. However, there are drawbacks such as deterioration of the binder and support proceeding at the same time as curing.

In view of these circumstances, the present inventors have discovered that a binder with a long pot life, no equipment problems and easy control of the curing reaction, and, unlike conventional ultraviolet curable binders, contains a large amount of finely powdered magnetic particles. However, as a result of intensive research to find a new binder that can be completely cured, a curable type consisting of an epoxy resin, a photopolymerizable compound containing a photopolymerizable compound having a carboxyl group in the molecule, and a photosensitizer was developed. The inventors have discovered that the various defects of the conventional binders described above can be overcome by using a resin composition as a binder, and have thus arrived at the present invention.

That is, the present invention provides an epoxy compound (A) having at least two epoxy groups in the molecule and a photopolymerizable compound (B) having a carboxyl group in the molecule.
Alternatively, a magnetic paint containing finely powdered magnetic particles uniformly dispersed in a curable resin composition consisting of a mixture of the compound (B) and another photopolymerizable compound (C) and a photoinitiator is coated on a support. The magnetic recording medium is characterized in that it has a magnetizable layer which is cured by actinic rays after coating and then by heat treatment.

To cure the curable resin composition used as the binder of the present invention, first, the photopolymerizable compound (B) having a carboxyl group in the molecule or the compound (B) and another photopolymerizable compound (C) are activated. A reaction that is cured by light irradiation to form a carboxyl group-containing polymer;
Next, the epoxy compound (A) reacts with the carboxyl group-containing polymer by heating and is completely cured.This type of curing reaction is different from the conventional curing reaction using only ultraviolet light or ultraviolet curing. This is a curing method that is essentially different from a curing reaction based on a combination of a thermosetting reaction using an organic peroxide and a thermosetting reaction using an organic peroxide.

The completely cured product obtained from the curable resin composition used as the binder of the present invention has excellent properties such as adhesion, chemical resistance, water resistance, heat resistance, and flexibility. As a composition, it has the great advantage of being excellent in storage stability.

A curable resin composition that combines an epoxy compound and a photopolymerizable compound has flexibility, heat resistance,
Proposals have been made regarding photocurable or thermosetting resin compositions that provide cured products with excellent adhesive properties and other properties. For example, JP-A-51-101100 proposes a curable resin composition containing an epoxy resin, oligoester acrylate or methacrylate, and amines having active hydrogen. It is stated that this composition cures at a low temperature to give a relatively flexible cured product, but this composition is heat cured using an addition reaction of a polyamine having active hydrogen to an acrylate group or a methacrylate group. Since it is a type resin composition and uses a polyamine having a primary or secondary amino group, it has a drawback of extremely poor storage stability.

Furthermore, Japanese Patent Publication No. 57-13572 describes a compound containing a polyvalent (meth)acrylate (meaning acrylate and methacrylate, hereinafter similarly abbreviated), an epoxy compound, and a phosphoric acid ester having a polymerizable unsaturated bond. A photocurable resin composition has been proposed. It is stated that a cured product with good performance such as flexibility and adhesion can be obtained from this composition, but since it uses phosphoric acid ester, the disadvantage is that the cured product has significantly poor water resistance. have. As described above, there have been some proposals for combining epoxy compounds and (meth)acrylate compounds, but as mentioned above, all of them have serious drawbacks.

In the molecule, which is an essential component of the curable resin composition used as a binder in the present invention,
An epoxy compound (A) having epoxy groups is
It is an epoxy compound having two or more epoxy groups in one molecule, and its epoxy equivalent is 100 to 4000,
Preferably it is 100-1000.

Representative compounds include bisphenol A,
Bisphenol F, halogenated bisphenol A
Representative examples include bisphenol type epoxy resins, which are diglycidyl ethers such as 2, and novolac type epoxy resins, which are polyglycidyl ethers such as phenol novolak and cresol novolak.
polyglycidyl ethers of polyhydric phenols with a valence of more than 2, polyhydric alcohols with a valence of 2 or more such as ethylene glycol, propylene glycol, neopentyl glycol, 1,4-butanediol, 1,6-hexanediol, trimethylolpropane, etc. Polyglycidyl ethers of phthalic acid, isophthalic acid, tetrahydrophthalic acid, hexahydrophthalic acid, polyglycidyl esters of divalent or higher polycarboxylic acids such as adipic acid, aniline, isocyanuric acid, etc. polyglycidyl ethers in which active hydrogen is substituted with a glycidyl group, vinylcyclohexene diepoxide obtained by epoxidizing the olefin bond in the molecule, 3,4-epoxycyclohexylmethyl-
3,4-epoxycyclohexanecarboxylate, 2-(3,4-epoxy)cyclohexyl-
Alicyclic polyepoxy compounds such as 5,5-spiro(3,4-epoxy)cyclohexane-m-dioxane, N,N,N',N'-tetraglycidylmethaxylene diamine, N,N,N', Examples include aminopolyepoxy compounds such as N'-tetraglycidyl 1,3-bis(aminomethyl)cyclohexane. These epoxy compounds can be used alone or in combination of two or more.

In addition, one epoxy group is added in the molecule of allyl glycidyl ether, phenyl glycidyl ether, etc.
It can also be used in combination with its own epoxy compounds.

Among these epoxy compounds having at least two epoxy groups in the molecule, preferred epoxy compounds include diglycidyl ether of bisphenol A, phenol novolac type polyepoxy compounds, cresol novolac type polyepoxy compounds, and polyhydric epoxy compounds. Examples include alcohol polyepoxy compounds.

Examples of the photopolymerizable compound (B) having one or more carboxyl groups in the molecule, which is an essential component of the curable resin composition used as the binder of the present invention, include (i) acrylic acid, methacrylic acid, There are unsaturated carboxylic acid compounds such as itaconic acid, crotonic acid, and fumaric acid, and (ii) compounds represented by the following general formula ().

(In the formula, R ₁ represents hydrogen or a methyl group, R ₁ and R ₃ each represent an aliphatic, aromatic, or alicyclic residue, A represents an ester bond, and m and n each represent 1 to 1. Indicates a positive integer of 3.) In the general formula (), R ₂ is preferably a divalent to tetravalent hydrocarbon group having 2 to 10 carbon atoms or a hydroxyl group-containing hydrocarbon group, and R ₃ is A di- to tetravalent aliphatic polybasic acid residue having 2 to 10 carbon atoms, a di- to tetravalent aromatic polybasic acid residue having 6 to 15 carbon atoms, or a residue having 6 to 10 carbon atoms. 2～
A tetravalent alicyclic polybasic acid residue is preferred.

Examples of the compound represented by the general formula () include the following compounds.

Examples of compounds where m=1 and n=1 include succinic acid mono(meth)acryloyloxyethyl ester, phthalic acid mono(meth)acryloyloxyethyl ester, maleic acid mono(meth)acryloyloxyethyl ester, and tetrahydrophthalic acid. Mono(meth)acryloyloxyethyl ester, hexahydrophthalic acid mono(meth)acryloyloxyethyl ester, endo-bicyclo(2,2,1)-5-heptene-2,3-dicarboxylic acid, mono(meth)acryloyloxy Ethyl ester, tetrahydrophthalic acid mono-2
-(meth)acryloyloxy-1-(phenoxymethyl)ethyl ester, phthalic acid mono-2-hydroxy-3-(meth)acryloyloxypropyl ester, succinic acid mono-2-hydroxy-
Examples include 3-(meth)acryloyloxypropyl ester.

Examples of the compound where m=1 and n=2 include trimellitic acid mono-2-(meth)acryloyloxyethyl ester.

Examples of the compound where m=1 and n=3 include pyromellitic acid mono-2-(meth)acryloyloxyethyl ester.

Examples of the compound where m=2 and n=1 include phthalic acid mono-[2,3-bis(meth)acryloyloxyisopropyl] ester, methyltetrahydrophthalic acid mono-[2,3-bis(meth)
Examples include acryloyloxyisopropyl] ester, tetrahydrophthalic acid mono-[2,3-bis(meth)acryloyloxyisopropyl] ester, and succinic acid mono-[2,3-bis(meth)acryloyloxyisopropyl] ester.

Examples of compounds where m=2 and n=2 include trimellitic acid mono-[4,5-bis(meth)acryloyloxyneopentyl] ester, trimellitic acid mono-[3,4-bis(meth)acryloyloxyisobutyl] There are esters, etc.

Examples of compounds where m=3 and n=2 include trimellitic acid mono-[3,4,5-tris(meth)
Examples include acryloyloxyneopentyl ester.

Examples of compounds where m=3 and n=3 include pyromellitic acid mono-[3,4,5-tris(meth)
Examples include acryloyloxyneopentyl ester.

As the photopolymerizable compound (B), among the above-mentioned compounds, compound (ii) is particularly preferable. These photopolymerizable compounds (B) having a carboxyl group in the molecule can be used alone or in combination of two or more, or in combination with one or more of the other photopolymerizable compounds (C) described below. used.

The amount of the photopolymerizable compound (B) containing one or more carboxyl groups in the molecule in the photopolymerizable compound (B+C) used in the present invention is 10 to 100% by weight. If the amount is less than 10% by weight,
The properties of the resulting cured product, such as adhesion, water resistance, and heat resistance, become insufficient.

The photopolymerizable compound (C) used in the present invention is a photopolymerizable compound having one or more photopolymerizable double bonds in the molecule.

Examples of photopolymerizable compounds having one photopolymerizable double bond in the molecule include (i) styrene;
Styrenic compounds such as α-methylstyrene and chlorostyrene, (ii) methyl (meth)acrylate, ethyl (meth)acrylate, n- and i
-Propyl (meth)acrylate, n-, sec-
and alkyl (meth)acrylates such as t-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, lauryl (meth)acrylate, stearyl (meth)acrylate, methoxyethyl (meth)acrylate, ethoxyethyl (meth)acrylate , alkoxyalkyl (meth)acrylates such as butoxyethyl (meth)acrylate, allyloxyalkyl (meth)acrylates such as phenoxyethyl (meth)acrylate, and hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl (meth)acrylate. , halogen-substituted alkyl (meth)acrylates, or polyoxyalkylene glycol mono(meth)acrylate such as polyethylene glycol mono(meth)acrylate, polypropylene glycol mono(meth)acrylate, etc.
acrylates or substituted alkyl mono(meth)acrylates such as alkoxypolyoxylalkylene mono(meth)acrylate, heterocycle-containing (meth)acrylates such as tetrahydrofurfuryl (meth)acrylate, (iii) ethylene oxide of bisphenol A, and Mono(meth)acrylates of alkylene oxide adducts of bisphenol A, such as propylene oxide adducts; mono(meth)acrylates of alkylene oxide adducts of hydrogenated bisphenol A, such as ethylene oxide and propylene oxide adducts of hydrogenated bisphenol A; ) acrylates, (iv) a molecule obtained by further reacting a terminal isocyanate group-containing compound obtained by reacting a diisocyanate compound with one or more alcoholic hydroxyl group-containing compounds, and an alcoholic hydroxyl group-containing (meth)acrylate. Urethane-modified mono(meth)acrylates having one (meth)acryloyloxy group within the molecule; (v) Epoxy obtained by reacting a compound having one or more epoxy groups within the molecule with acrylic acid or methacrylic acid. mono(meth)acrylates, and
(vi) There are oligoester mono(meth)acrylates obtained by reacting acrylic acid or methacrylic acid and polyhydric carboxylic acid as the carboxylic acid component with a polyhydric alcohol of dihydrity or more as the alcohol component.

Examples of photopolymerizable compounds having two photopolymerizable double bonds in the molecule include (i) ethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, 1,4-butanediol di (meth)acrylate, neopentyl glycol di(meth)acrylate, 1,6-
Alkylene glycol di(meth)acrylates such as hexanediol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, dipropylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate , polypropylene glycol di(meth)
Polyoxyalkylene glycol di(meth)acrylates such as acrylates, substituted alkylene glycol di(meth)acrylates such as halogen-substituted alkylene glycol di(meth)acrylates, (ii) ethylene oxide and propylene oxide adducts of bisphenol A, etc. di(meth)acrylates of alkylene oxide adducts of bisphenol A, di(meth)acrylates of alkylene oxide adducts of hydrogenated bisphenol A, such as ethylene oxide and propylene oxide adducts of hydrogenated bisphenol A; iii) A terminal isocyanate group-containing compound obtained by reacting a diisocyanate compound and two or more alcoholic hydroxyl group-containing compounds in advance is further reacted with an alcoholic hydroxyl group-containing (meth)acrylate; Epoxy di(meth)acrylates obtained by reacting urethane-modified di(meth)acrylates having (meth)acryloyloxy groups, (iv) compounds having two or more epoxy groups in the molecule with acrylic acid and/or methacrylic acid. Acrylates, (v) oligoester di(meth) obtained by reacting acrylic acid or methacrylic acid and polyhydric carboxylic acid as the carboxylic acid component with a polyhydric alcohol of dihydric or higher valence as the alcohol component
There are acrylates, etc.

Examples of photopolymerizable compounds having three or more photopolymerizable double bonds in the molecule include (i) trimethylolpropane tri(meth)acrylate, trimethylolethane tri(meth)acrylate,
Poly(meth)acrylates of trivalent or higher aliphatic polyhydric alcohols such as pentaerythritol tetra(meth)acrylate, poly(meth)acrylates of trivalent or higher halogen-substituted aliphatic polyhydric alcohols, (ii) diisocyanate compounds A terminal isocyanate group-containing compound obtained by reacting a compound containing three or more alcoholic hydroxyl groups in advance with a (meth)acrylate containing an alcoholic hydroxyl group has three or more (meth)acryloyl groups in the molecule. Urethane-modified poly(meth)acrylates having an oxy group, (iii) epoxy poly(meth)acrylates obtained by reacting a compound having three or more epoxy groups in the molecule with acrylic acid or/and methacrylic acid, etc. There is.

The epoxy compound (A) and the photopolymerizable compound (B) having a carboxyl group in the molecule contained in the binder of the present invention, or (B) and another photopolymerizable compound
The blending ratio of the mixture with (C) is epoxy compound (A): photopolymerizable compound [(B) or (B) + (C)] = 10:90-90:
10 (weight ratio), preferably epoxy compound (A): photopolymerizable compound [(B) or (B) + (C)] =
The range is 20:80:20 (weight ratio). If the amount of the epoxy compound (A) is less than 10% by weight, the photopolymerizable compound (B) having a carboxyl group in the molecule described above
The reaction between the epoxy compound (A) and the epoxy compound (A) is substantially too small, making it difficult to obtain a cured product with excellent adhesiveness and heat resistance.

The photoinitiator used in the present invention is a compound that promotes the photopolymerization reaction of a photopolymerizable compound, and includes, for example, ketals such as benzyl dimethyl ketal, benzoin methyl ether, benzoin ethyl ether, and benzoin-i-propyl ether. , benzoins such as benzoin and α-methylbenzoin, 9,10-anthraquinone, 1-chloroanthraquinone, 2-chloroanthraquinone,
Anthraquinones such as 2-ethylanthraquinone, benzophenones such as benzophenone, p-chlorobenzophenone, p-dimethylaminobenzophenone, 2-hydroxy-2-methylpropiophenone, 1-(4-isopropylphenyl) Propiophenones such as -2-hydroxy-2-methylpropiophenone, suberones such as dibenzosuberone, diphenyl disulfide,
Sulfur-containing compounds such as tetramethylthiuram disulfide and thioxanthone, methylene blue,
Examples include pigments such as eosin and fluorescein, which may be used alone or in combination of two or more.

In the present invention, the amount of this photoinitiator is based on the total amount of the epoxy compound (A) and the photopolymerizable compound.
The amount is 0.05 to 20% by weight, preferably 0.5 to 10% by weight.

In the present invention, when it is necessary to promote the reaction between an epoxy group and a carboxyl group, it is effective to add a reaction promoter. As a reaction accelerator,
For example, 2-methylimidazole, 2-ethylimidazole, 2,4-dimethylimidazole, 2-
Ethyl-4-methylimidazole, 2-undecylimidazole, 2-heptadecyl imidazole, 1-vinyl-2-methylimidazole, 2-
Phenylimidazole, 1-vinyl-2-ethylimidazole, imidazole, 2-phenyl-4
-Methylimidazole, 1-vinyl-2,4-dimethylimidazole, 1-vinyl-2-ethyl-
imidazoles such as 4-methylimidazole,
Benzyldimethylamine, 2,4,6-tridimethylaminophenol, triethanolamine,
Triethylamine, N,N'-dimethylpiperidine, α-methylbenzyldimethylamine, N-methylmorpholine, N,N-dimethylaminoethanol, N,N-diethylaminoethanol, N,
These include tertiary amines such as N-dipropylaminoethanol and dimethylaminomethylphenol, and tertiary amine salts such as triacetate and tribenzoate of tridimethylaminomethylphenol, which can be used alone or in combination of two or more. be done.

In the present invention, the amount of these reaction accelerators added is 0.05 to 5% by weight, preferably 0.1 to 3.5% by weight based on the total amount of the epoxy compound (A) and the photopolymerizable compound.
Weight%.

The curable resin composition used as the binder of the present invention is easily produced by stirring and mixing at room temperature or under heating if necessary. Hydroquinone, hydroquinone monomethyl ether,
1-butyl-catechol, p-benzoquinone,
It is desirable to add a known thermal polymerization inhibitor such as 2,5-t-butyl-hydroquinone or phenothiazine. The amount added is 0.001 to 0.1% by weight, preferably 0.001% by weight based on the photopolymerizable compound of the present invention.
~0.05% by weight.

The fine powder magnetic particles used in the present invention include Fe, γ-Fe ₂ O ₃ , Co-containing γ-Fe ₂ O ₃ ,
Fe ₃ O ₄ , Co-containing Fe ₃ O ₄ , cobalt ferrite (CoO・Fe ₂ O ₃ ), CrO ₂ , Co-Ni-p alloy, Co-
Ni-Fe alloy, Co-Ni-Fe-B alloy, Fe-Ni-
Zn alloy, Fe-Mn-Zn alloy, Fe-Co-Ni-P alloy, Ni-Co alloy, Fe-Ti-Si alloy, Fe-Co-
Si alloy, Fe-Ni alloy, Fe-Ag alloy, Fe-Cr-
Known ferromagnetic fine powders such as Co alloy, Fe-Cr-Si alloy, Fe-Mn-Al alloy can be used.

The blending ratio of the fine powder magnetic particles in the magnetic paint consisting of the fine powder magnetic particles and the binder is 30 to 90% by weight, preferably 50 to 85% by weight, more preferably
It is 60-80% by weight.

The curable resin composition used as a binder in the present invention can be used as is by mixing with fine powder magnetic particles, but if viscosity adjustment is required,
It is also possible to use an organic solvent by adding it.

Examples of organic solvents that can be used include alcohols such as methanol, ethanol, i-propanol, n-propanol, and butanol; esters such as methyl acetate, ethyl acetate, n-butyl acetate, ethyl lactate, and acetic acid glycol monoethyl ether; Ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, ethers such as ethyl ether, glycol dimethyl ether, glycol monoethyl ether, dioxane, aromatic hydrocarbons such as benzene, toluene, xylene, methylene chloride, ethylene chloride, Chlorinated hydrocarbons such as carbon tetrachloride, chloroform, trichloroethylene, trichloroethane, perchlorethylene, chlorobenzene, dichlorobenzene, etc., polar solvents such as dimethylformamide, dimethyl sulfoxide, etc. are used alone or in combination of two or more. can do.

The magnetic paint of the present invention may optionally contain plasticizers such as dibutyl phthalate and triphenyl phosphate, dioctyl sulfonodium succinate, t-butylphenol-polyethylene ether, ethylnaphthalene-sulfonic acid, dilauryl succinate, and stearin. Lubricants such as acid zinc, soybean oil lecithin, silicone oil, polyester or polyurethane containing sodium sulfonate groups, and various antistatic agents can also be added.

In the present invention, the kneading machines used for kneading and dispersing the binder and fine powder magnetic particles include two-roll mills, three-roll mills, ball mills, thoron mills, sand grinders, attritors, high-speed impeller dispersers, high-speed stone mills, and high-speed impact mills. These include mills, desolvers, kneaders, high-speed mixers, homogenizers, and ultrasonic dispersers.

To form the magnetic recording layer in the present invention, finely powdered magnetic particles are mixed and dispersed in a binder, or the organic solvent described above is further added thereto, and then coated on a nonmagnetic support. The application method is
Air doctor coat, blade coat,
There are air knife coats, squeeze coats, roll coats, reverse coats, impregnated coats, transfer roll coats, gravure coats, kiss roll coats, cast coats, spray coats, and spin coats.

There is no particular restriction on the shape of the support as long as it is a non-magnetic support, but it is usually tape-shaped, sheet-shaped,
It is used in the form of disks, cards, or drums.

Materials for the non-magnetic support include polyethylene terephthalate, polybutylene terephthalate, polyethylene, polypropylene, polybutadiene,
Polystyrene, polymethyl methacrylate, styrene-acrylonitrile copolymer, styrene-acrylonitrile-butadiene copolymer, celerose triacetate, cellulose diacetate, cellulose acetate butyrate, cellulose acetate propionate, polyvinyl chloride, polyvinylidene chloride, polycarbonate , polyphenylene sulfide, polyamide, polyimide, polyamideimide, phenolic resin, epoxy resin,
Examples include plastics such as unsaturated polyester resin and cured silicone resin, metals such as aluminum, copper, tin, zinc or non-magnetic alloys containing these, ceramics, glass, and various papers. Among these, plastics and metals are suitable. This non-magnetic support may be back coated on the back side for purposes such as anti-static, anti-blocking, anti-transfer, and improved runnability, if necessary.

If a solvent is added to the magnetic paint coated on the support, the solvent is vaporized, a magnetic field is applied to orient the fine powder magnetic particles contained therein, and then actinic rays such as ultraviolet rays or electron beams are immediately irradiated. Then, it is completely cured by heat treatment.

The ultraviolet light sources used include high-pressure mercury lamps,
These include low-pressure mercury lamps, ultra-high-pressure mercury lamps, metal halide lamps, and electrodeless high-pressure mercury lamps. A photoinitiator is not necessarily required when using an electron beam.

In the case of ultraviolet rays, the irradiation amount generally needs to be 100 mj/cm ² or more as an integrated value of ultraviolet rays, preferably 500 to 5000 mj/cm ² . The ambient temperature during ultraviolet irradiation can range from room temperature to around 200℃, but
When supporting plastics and paper, from room temperature
Temperature ranges up to 100°C are preferred. Although ultraviolet irradiation is possible in the presence of air, it is more effective when carried out in the presence of an inert gas such as nitrogen gas, carbon dioxide gas, or argon gas.

For the heat treatment after irradiation with actinic rays, known methods such as infrared heater, hot air heating, and high frequency heating may be used. The heat treatment temperature can be arbitrarily selected depending on the heat resistance of the support, but generally the temperature is 40~
200℃, and 40℃ for plastics and paper.
Temperatures between 100°C and 100°C are preferred. The heat treatment time is several minutes to several hours. The surface of a completely cured magnetic paint is generally smoothed.

As mentioned above, the curable resin composition used as a binder in the present invention includes a conventional ultraviolet curable resin composition and an ultraviolet thermosetting resin composition that uses both ultraviolet curing and thermosetting with an organic peroxide. are essentially different curing reactions, and magnetic paints using this curable resin composition as a binder can be used for magnetic recording with excellent performance such as adhesion to the support used, water resistance, heat resistance, and flexibility. medium can be obtained.

The following points can be mentioned as excellent effects of the curable resin composition used as a binder in the present invention.

(1) The epoxy compound (A) and the photopolymerizable compound [(B) or a mixture of (B) and (C)] have extremely good compatibility, and the viscosity of the magnetic paint can be adjusted freely and as needed. It is also possible to reduce the viscosity significantly.

(2) The magnetic paint has excellent adhesion to the support.

(3) Rapid curing is possible by actinic light curing, and the orientation of fine powder magnetic particles can be fixed immediately, which is particularly advantageous for perpendicular magnetization.

(4) It is possible to completely cure thick coatings, which is difficult with actinic light-curable resins.

The magnetic recording medium of the present invention takes advantage of the above-mentioned advantages and can be used to record magnetic tapes, video tapes, magnetic cards, etc.
It can be used as a wide variety of magnetic recording media such as magnetic disks, floppy disks, magnetic hard disks, and magneto-optical disks, and its industrial significance can be said to be extremely large.

Examples will be given below to explain the present invention more specifically, but of course the present invention is not limited by the Examples.

In the examples, parts simply indicate parts by weight.

Example 1 190 parts of Epicote 828 (manufactured by Yuka Ciel Chemical Co., Ltd.), which is a bisphenol A type epoxy resin, 216 parts of succinic acid monoacryloyloxyethyl ester,
312 parts of tetrahydrofurfuryl acrylate,
100 parts of benzyl dimethyl ketal and N,N-
Five parts of diethylethanolamine were stirred and mixed at room temperature to obtain a uniform transparent curable resin composition. 23 parts of this curable resin composition, 75 parts of γ-Fe ₂ O ₃ , 2 parts of lecithin, and 100 parts of cyclohexanone were placed in a glass bead type high-speed shaker and mixed for 1 hour, resulting in a magnetic coating material with good dispersibility. Obtained.

This magnetic paint was applied onto a 125μ polyethylene terephthalate film using a reverse coater, dried for 10 minutes at room temperature, and then magnetically oriented with a magnetic field of 1000 oersteds. Next, it was calendered with a super calender at 100°C, irradiated with 3000 mJ/cm ² using a 5.6KW water-cooled high-pressure mercury lamp, and then heat-treated at 120°C for 30 minutes. When the adhesion of the magnetic paint was measured using a cross-cut tape peel test, a good result of 100/100 was obtained.

Example 2 90 parts of Epicote 1001 (manufactured by Yuka Ciel Chemical Co., Ltd.), which is a bisphenol A type epoxy resin, 43 parts of succinic acid monoacryloyloxyethyl ester, 204 parts of diacrylate of a 4 mol adduct of bisphenol A ethylene oxide, benzyl 100 parts of dimethyl ketal and 10 parts of N,N-diethylethanolamine were stirred and mixed at room temperature to obtain a uniform transparent curable resin composition. 25 parts of this curable resin composition,
When 70 parts of cobalt-coated γ-Fe ₂ O ₃ , 2 parts of lecithin and 100 parts of cyclohexanone were placed in a glass bead type high speed shaker and mixed for 1 hour, a magnetic paint exhibiting good dispersibility was obtained.

After coating and treatment in the same manner as in Example 1, ultraviolet rays were irradiated, and then heat treatment was performed. Adhesion of magnetic paint measured by cross-cut tape peel test
A good result of 100/100 was obtained.

Comparative Example 1 A magnetic recording medium was obtained in the same manner as in Example 1 except that the heat treatment after irradiation with ultraviolet rays was not performed. The adhesion of the magnetic paint was measured by a cross-cut tape peel test and was found to be poor at 0/100.

Comparative Example 2 A magnetic recording medium was obtained in the same manner as in Example 2 except that the heat treatment after ultraviolet irradiation was not performed. The adhesion of the magnetic paint was determined by a cross-cut tape peel test and was poor at 0/100.

Comparative Example 3 A magnetic recording medium was obtained in the same manner as in Example 1 except that the ultraviolet irradiation in Example 1 was not performed. The adhesion of the magnetic paint was determined by a cross-cut tape peel test and was poor at 0/100.

Comparative Example 4 A magnetic recording medium was obtained in the same manner as in Example 2 except that the ultraviolet irradiation in Example 2 was not carried out.The adhesion of the magnetic paint was measured by a cross-cut tape peel test and was poor at 0/100. It was hot.

Example 3 90 parts of Epicote 1001 (manufactured by Yuka Ciel Chemical Co., Ltd.), which is a bisphenol A type epoxy resin, 50 parts of succinic acid mono-2-hydroxy-3-acryloyloxypropyl ester, and 4 mole adduct of bisphenol A ethylene oxide. diacrylate 100
parts, 50 parts of benzyl dimethyl ketal and N,N
- 10 parts of diethylethanolamine were stirred and mixed at room temperature to obtain a uniform and transparent cured composition. When 40 parts of this curable resin composition, 60 parts of γ-Fe ₂ O ₃ , 2 parts of lecithin, and 180 parts of cyclohexanone were mixed in a glass bead type high-speed shaker for about 1 hour, a magnetic paint exhibiting good dispersibility was obtained. It was done.

The obtained magnetic paint was dropped from a nozzle onto a diamond-ground aluminum substrate for magnetic disks, spin coating was performed using a spinner at 3000 rpm, and the organic solvent was vaporized at 60°C for 30 minutes. The magnetic field was oriented using an Oersted magnetic field. Next, using a 5.6Kw water-cooled high-pressure mercury lamp.
After irradiation with 3500 mJ/cm ² , heat treatment was performed at 120°C for 30 minutes. The adhesion of the magnetic paint was measured using a cross-cut tape peel test, and a good result of 100/100 was obtained.

Claims (1)

[Claims] 1. An epoxy compound (A) having at least two epoxy groups in the molecule and a photopolymerizable compound (B) having a carboxyl group in the molecule, or a combination of this compound (B) and another photopolymerizable compound (C) A magnetic paint containing finely powdered magnetic particles uniformly dispersed in a curable resin composition consisting of a mixture and a photoinitiator is coated on a support, cured by actinic rays, and then cured by heat treatment. A magnetic recording medium comprising a magnetizable layer.