JPH03230316A - magnetic recording medium - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a magnetic recording medium, such as a magnetic tape, in which a magnetic layer containing magnetic powder is provided on a non-magnetic substrate.

(Prior art) In recent years, there has been a demand for higher recording densities in magnetic recording media.
For example, magnetic tapes are required to have high saturation magnetic flux density Bm, high squareness ratio Rs (residual magnetic flux density Br/saturated magnetic flux density Bm), low surface roughness, and excellent flexibility and wear resistance. .

Due to the requirement of high S/N ratio, the specific surface area is 30 m”/g to 70
In order to use fine magnetic powder of m''/g and to uniformly disperse it and bond it firmly, the binder is required to have both excellent dispersion performance and strong bonding strength.

However, as the binder, polyester resin, cellulose resin, polyurethane resin, phenol resin, epoxy resin, polyamide resin, vinyl chloride, vinylidene chloride, vinyl acetate, (meth)acrylic acid ester, (meth)acrylamide, Polymers or copolymers such as acrylonitrile, butadiene, styrene, and vinyl ester are commonly used, but none of them can provide sufficient characteristics in terms of both the dispersibility of the magnetic powder and the abrasion resistance of the magnetic layer. There wasn't.

Among these binders, polyurethane resins have been widely used because of their good abrasion resistance, but these resins have the drawbacks of low adsorption ability for magnetic powder and poor dispersibility of the powder.

Therefore, in order to overcome the drawbacks of the above-mentioned ordinary polyurethane resins, it has been proposed to introduce polar groups such as sulfonic acid groups and carboxyl groups into the molecular chain (Japanese Patent Publication No. 58-41565; 92422). However, although these have improved dispersibility, they have the drawback of impairing the abrasion resistance of polyurethane resins.

On the other hand, in order to increase the strength of the binder, it is effective to increase the molecular weight of the binder, but increasing the molecular weight increases the viscosity of the paint in which magnetic powder is dispersed and reduces the dispersibility. . The finer the magnetic powder, the more likely the viscosity of the paint will increase, so there is a need for a method to improve strength that does not depend on an increase in molecular weight.
Crosslinking of binders with polyisocyanate compounds is widely used. In order to enable crosslinking using this polyisocyanate compound, attempts have been made to introduce into the binder a group having active hydrogen, typified by a hydroxyl group, which reacts with an isocyanate group.

However, when a large amount of hydroxyl groups are introduced into the binder, the dispersion stability of the magnetic powder decreases in magnetic coatings containing lubricants such as fatty acids and their esters, making it difficult to stabilize magnetic recording media with good characteristics. Therefore, it becomes impossible to manufacture the product. On the other hand, if the amount of hydroxyl groups is small, crosslinking will be insufficient and the purpose of improving strength will not be achieved, and the isocyanate M of the isocyanate compound will be in excess of the hydroxyl groups of the binder, and the excess isocyanate compound will be released into the air. It reacts with moisture, resulting in the magnetic layer becoming brittle.

In order to prevent the excess isocyanate compound from becoming brittle even if it reacts with moisture in the air, it is necessary to use a urethane prepolymer or moisture-curable polyurethane that has isocyanate groups at both ends, or to use a urethane prepolymer that has isocyanate groups at both ends. It has been proposed to use a low molecular weight polyisocyanate compound and a polyol together (Japanese Patent Publication No. 4B-42486, Japanese Patent Publication No. 52-35525,
Special Publication No. 47-28048). However, these do not provide sufficient durability and cause problems such as poor release from the calendar and adhesion due to incomplete reaction.

(Problems to be Solved by the Invention) As a result of intensive study on the various conventional problems in response to the above-mentioned demands for higher recording density and higher durability of magnetic recording media, the present inventors have developed a specific polyurethane resin. By using it as a binder for magnetic powder and incorporating a specific compound into the magnetic layer, a low-viscosity magnetic paint in which fine magnetic powder is stably dispersed can be obtained. The present invention was completed after confirming that a magnetic recording medium obtained by coating on a magnetic substrate can exhibit excellent magnetic properties, durability, and runnability.

(Means for Solving the Problems) Thus, according to the first invention, a resin having a urethane bond produced by a reaction between a diisocyanate and a polyol and having an average of 2.3 or more isocyanate groups in one molecule. 10.00 when the number average molecular weight is 2.000 or more
0 or less and a component with a molecular weight of 1,000 or less is 20
% of a polyurethane resin and at least one compound selected from the group consisting of polyols, triazinethiols, and polyamines as a magnetic powder binder. be done.

Further, the second invention provides a magnetic recording medium characterized in that the polyurethane resin in the first invention has a polar group having no active hydrogen atom in the molecule.

Furthermore, the third invention provides a magnetic recording medium having a magnetic layer containing the polyurethane resin according to the first invention, a resin having an epoxy group, and triazinethiol as binders for magnetic powder. .

The molecular weight of the polyurethane resin used in the present invention was determined by gel permeation chromatography (hereinafter abbreviated as GPC). The molecular weight distribution was calculated using polystyrene of known molecular weight as a standard.

For polyurethane resins having isocyanate groups, such as the polyurethane resin used in the present invention, GPC measurements were performed after reacting with methanol at room temperature.

The molecular weight of the polyurethane resin used in the present invention is required to be in the range of 2.000 to 10,000 in terms of number average molecular weight. If the number average molecular weight is less than 2,000, the strength is low and it may not be a good binder. If it exceeds 10,000, the viscosity of the paint in which the magnetic powder is dispersed becomes high, resulting in a decrease in dispersibility.

In the polyurethane resin used in the present invention, the molecular weight is 1.
The amount of components with a molecular weight of 1,000 or less is required to be less than 20% (this value was calculated by measuring the molecular weight distribution by GPC and calculating the amount of components with a molecular weight of 1,000 or less).

If the amount of components with a molecular weight of 1,000 or less is greater than this, running properties will be reduced. This is thought to be because sticky substances are deposited on the surface of the magnetic layer.

The number of isocyanate groups in the polyurethane resin used in the present invention must be 2.3 or more on average per molecule. If the amount is less than this, it is not possible to obtain satisfactory mechanical properties and abrasion resistance in which the polyurethane resin can form a sufficient network structure.

Having an average of 2.3 or more isocyanate groups per molecule used in the present invention and a number average molecular weight of 2.000 to 10
,000 and the component with a molecular weight i, ooo or less is 20
% are obtained from organic diisocyanates and polyols having three or more hydroxyl groups alone or in mixtures with diols having linear terminal hydroxyl groups.

Examples of organic diisocyanates include 2.4-) lylene diisocyanate (hereinafter abbreviated as 2.4-TDI), 2.6-
-1-lylene diisocyanate (hereinafter abbreviated as 2.6-TDI), and mixtures thereof, 4,4'-diphenylmethane diisocyanate (hereinafter abbreviated as MDI), p-phenyl diisocyanate, m-phonylene diisocyanate, 1, 5-naphthylene diisocyanate, isophorone diisocyanate, hexamethylene diisocyanate,
Examples include lysine diisocyanate, xylylene diisocyanate, cyclohexane diisocyanate, hydrogenated MD1, and mixtures thereof. Among these, MDI
, 2.4-TDI and mixtures thereof are preferred.

Examples of polyols having three or more hydroxyl groups in the molecule include trimethylolethane, trimethylolpropane,
Low molecular weight tri- and tetraols such as glycerin, pentaerythritol, and triethanolamine, polyethylene ether polyols obtained by adding ethylene oxide, propylene oxide, or butylene oxide to the polyether polyols with a molecular weight of 50 to 3,000 having terminal hydroxyl groups, and polybrobylene. Polyether polyols such as ether polyols and polybutylene ether polyols, polyesters obtained by polycondensing a mixture of the above low molecular weight triols and the above low molecular weight glycols with the above dibasic acids and their acid esters and acid halides. Polyols include polycaprolactone polyols obtained by ring-opening addition polymerization of lactone such as ε-caprolactone in the presence of a mixture of the triol and glycol.

Examples of the diol having a linear terminal hydroxyl group include polyether polyols, polyester polyols, and low molecular weight glycols having molecular weights of 500 to 3,000 and having terminal hydroxyl groups. As polyether polyol,
Ethylene glycol, 1゜2-propylene glycol,
2.3-butylene glycol, 1.4-butylene glycol, 2,2-dimethyl-1,3-propanediol,
Diethylene glycol, 1,5-pentamethylene glycol, 1,6 hexamethylene glycol, 3-methyl-1,5-bentanediol, cyclohexane-1,4
- Glycols such as diol, cyclohexane-1,4-methanol alone or in combination with succinic acid, maleic acid, adipic acid, glutaric acid, pimelic acid, sheric acid, azelaic acid, sebacic acid, phthalic acid,
Examples include those obtained by polycondensation with dibasic acids such as isophthalic acid, terephthalic acid, hexahydroterephthalic acid, and hexahydroisophthalic acid, and their acid esters and acid halides. Further examples include polycaprolactone diols which are subjected to ring-opening addition polymerization in the presence of the above-mentioned glycols such as ε-caprolactone.

As the low molecular weight glycol, the above-mentioned glycols used in the production of the above-mentioned polyesters can be used alone or in mixtures. Further examples include diols in which 2 to 4 moles of ethylene oxide, propylene oxide, butylene oxide, etc. are added to hydroquinone.

When producing the polyurethane resin used in the present invention, organic diisocyanate and polyol N COlo
The H molar ratio is 1.2/1 to 2/1, and if it is outside this range, the excellent performances sought in the present invention cannot be obtained.

In addition, as the polar group having no active hydrogen in the molecule to be introduced into the polyurethane resin in the second invention, SO
J, 504M, C00M, PO(OM'
)z.

Φ NRz (here, M represents an alkali metal, M'
represents an alkali metal or hydrocarbon group, R represents an organic residue such as an alkyl group, an allyl group, an alkenyl group or an alkoxyl group).

The method for introducing polar groups that do not have active hydrogen atoms into the polyurethane resin used in the second invention is to react with these polar groups that do not have active hydrogen atoms in one molecule and isocyanate groups. 1 possible active hydrogen atom
It can be obtained by reacting a compound having at least 1 or more polyurethane resins during the synthesis of a polyurethane resin. Examples of such compounds include sodium phenolsulfonate, 4-sodium sulfobenzyl alcohol, and 4-sodium isethionate.
Sodium sulfophenyl acetate, 4-sodium sulfophenylpropionic acid, 4-sodium sulfoaniline, 4-
Compounds with one active hydrogen atom in the molecule such as sodium sulfobenzamide salicylate, sodium glycolate, sodium p-aminebenzoate, sodium hydroquinone sulfonate, sodium 5-sodium sulfosalicylate, 2-sodium methyl 1. ib7
Compounds with two active hydrogen groups in the molecule, such as tandiol, sodium 5-sodium sulfoisophthalate, sodium 2,4-dioxybenzoate, sodium dimethylolpropionate, and sodium 4,4'bishydroxyphenylbutyrate. Examples include.

It can also be obtained by a method used in the production of polyurethane resins, in which polar groups that do not have these active hydrogen atoms are introduced in advance into the long-chain polyols used in the production of the polyurethane resins by a known method.

The amount of polar groups having no active hydrogen atoms in the polyurethane resin in the second invention is 0.2 or more, preferably 0.5 to 3, and 0.2 or more per molecule of the polyurethane resin.
If the amount is less than 1, the effect of the present invention will not be apparent.

When producing the polyurethane resin used in the present invention, organic metal compounds such as dibutyltin dilaurate, or tertiary amines such as N
- Methylmorpholine, triethylamine, etc. may be added. Further, in order to increase the stability of the resin, antioxidants, ultraviolet absorbers, hydrolysis inhibitors, etc. may be added.

In addition, in producing the polyurethane resin used in the present invention, conventionally known methods can be used, including sufficiently mixing reactants in the presence of a catalyst if desired, and then injecting the reaction mixture into an extruder. and a conventional solution reaction method in which the reaction is carried out in a single or mixed organic solvent such as dimethylformamide, toluene, xylene, benzene, dioxane, cyclohexane, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, ethyl acetate, butyl acetate, etc. Can be used.

The polyol of the compounds used together with the polyurethane resin as a binder for the magnetic powder of the magnetic recording medium of the present invention is a low molecular weight polyol having two or more hydroxyl groups in one molecule used in the synthesis of the polyurethane resin. Examples include high molecular weight polyols such as polyether polyols, polyester polyols, polycaprolactone polyols, and polycarbonate polyols.

The amount of polyol used in the magnetic recording medium of the present invention is:
The amount of hydroxyl groups in the polyol is preferably 0.1 to 1.0 times the chemical equivalent of the amount of isocyanate groups in the polyurethane resin. If it is less than 0.1 times the chemical equivalent, the effect of the present invention will not be apparent, and if it is more than 1.0 times the chemical equivalent, unreacted products will remain and durability will be reduced.

Polyol acts as a dispersant for magnetic powder in the process of manufacturing magnetic paint, that is, the process of mixing and dispersing magnetic powder with a binder, a solvent, etc., so that a magnetic paint with excellent dispersibility can be obtained. In addition, in the process of manufacturing a magnetic recording medium by coating this magnetic paint on a non-magnetic support to form a magnetic layer,
The reaction between the polyurethane resin and the polyol according to the present invention progresses, and the wear resistance and durability of the magnetic recording medium are improved.

Typical examples of triazinethiol among the compounds used together with the polyurethane resin as a binder for the magnetic powder of the magnetic recording medium of the present invention include at least one triazinethiol selected from the group consisting of general two.

The triazinethiol compound represented by the above general formula (1) has various derivatives depending on the substituent R, and specific examples of R include -SH, -N (cH3) z, NHCi
, I(s, N(cJq)z, -N(c1lH+th,
N (c+□ths) 2, - N (cH2Cl・CH
z)z, NHCaH+bC)I=CHCaH+, etc.

The amount of triazinethiol is preferably in the range of 0.1 to 20 parts by weight per 100 parts by weight of the magnetic powder.

If it is less than 0.1 part by weight, it will be difficult to achieve the object of the present invention, and if it is more than 20 parts by weight, the dispersibility of the magnetic powder will actually decrease, and unreacted products will remain, resulting in a decrease in durability.

In the present invention, the triazinethiol compound has a thiol group that acts as a dispersant in the dispersion step of producing a magnetic paint, and a magnetic paint with excellent dispersibility can be obtained. Furthermore, in the steps after applying the magnetic paint and forming the surface, the reaction between the isocyanate groups and thiol groups of the polyurethane resin of the present invention proceeds, improving the abrasion resistance and durability of the magnetic recording medium.

Furthermore, by combining the polyurethane resin having an isocyanate group according to the present invention and a triazine thiol compound, and further combining the resin having an epoxy group that is reactive with a thiol group, it is possible to create a polyurethane resin containing a triazine thiol compound and an epoxy group. Forms crosslinking with resin, significantly improving wear resistance and durability.

Among the compounds used together with the polyurethane resin as a binder for the magnetic powder of the magnetic recording medium of the present invention, polyamine compounds include compounds having two or more amino groups in one molecule, such as ethylenediamine, tetramethylenediamine, Diamines such as pentamethylenediamine, hexamethylenediamine, 〇-phenylenediamine, P-phenylenediamine, 4-aminodiphenylamine, 1.2.3-triaminopropane, tris(2-aminoethyl)methane, tetra( Examples include triamines such as (aminomethyl)methane, diethylenetriamine, and triaminobenzene, and polyamines such as triethylenetetramine and tetraethylenepentamine.

In the magnetic recording medium of the present invention, the amount of amino groups in the polyamine compound is preferably 0.1 to 1.0 times the chemical equivalent of the isocyanate group in the polyurethane resin, and preferably less than 0.1 times the chemical equivalent. If the amount is more than 1.0 times the chemical equivalent, unreacted products will remain and durability will be reduced. Further, the timing of addition is preferably after the middle of the magnetic coating preparation process. If added from the beginning, the magnetic paint will thicken and the pot life will be shortened.

Examples of resins having epoxy groups used in the third invention include epoxy group-containing vinyl chloride resins, epoxy group-containing chlorinated polyvinyl chloride resins, epoxy-modified polyurethane resins, epoxy-modified polyester resins, and epoxy-modified acrylonitrile butadiene resins. Examples include polymer resins and epoxy resins.

The vinyl chloride resin having an epoxy group used in the present invention is composed of (1) vinyl chloride, a radically polymerizable monomer having an epoxy group that can be copolymerized with vinyl chloride, and if necessary copolymerizing with these monomers. (2) Partial dehydrochlorination of polyvinyl chloride or a copolymer resin containing vinyl chloride as a main component by heating or contacting with a dehydrochlorination agent. It can be obtained by epoxidizing a resin treated with hydrogen chloride using an epoxidizing agent such as percarboxylic acid. The chlorinated polyvinyl chloride resin having an epoxy group can be obtained by the method (2) using a chlorinated polyvinyl chloride resin or a chlorinated polyvinyl chloride copolymer resin as a starting material.

Examples of monomers having epoxy groups used in the production of vinyl chloride resins having epoxy groups include glycidyl ethers of unsaturated alcohols such as allyl glycidyl ether and methallyl glycidyl ether, glycidyl acrylate, glycidyl methacrylate, Glycidyl
Glycidyl esters of unsaturated acids such as p-vinyl benzoate, methyl glycidyl itaconate, glycidyl ethyl maleate, glycidyl vinyl sulfonate, glycidyl (meth)allylsulfonate, butadiene monoxide, vinylcyclohexene monooxide, 2-
Examples include epoxide olefins such as methyl-5,6-epoxyhexene.

In addition, examples of monomers having an epoxy group and monomers used as necessary other than vinyl chloride include carboxylic acid vinyl esters such as vinyl acetate and vinyl propionate; methyl vinyl ether, isobutyl vinyl ether;
Vinyl ethers such as cetyl vinyl ether: vinylidene chloride, vinylidene fluoride, etc.: diethyl maleate, butyl benzyl maleate, di-2-hydroxyethyl maleate, dimethyl itaconate, (meth)
Unsaturated carboxylic acid esters such as methyl acrylate, ethyl (meth)acrylate, lauryl (meth)acrylate, and 2-hydroxypropyl (meth)acrylate;Olefins such as ethylene and propylene;Unsaturated carboxylic acid esters such as (meth)acrylonitrile; Saturated nitriles: Examples include aromatic vinyls such as styrene, α-methylstyrene, and p-methylstyrene. These monomers are used not only to improve the solubility of the resin by controlling the compatibility and softening point of the resin of the present invention and other resins when mixed, but also to improve the properties of the coating film and the coating properties. Appropriate selection is made depending on the need for process improvement, etc.

The epoxy modified polyurethane resin has a molecular weight of 1,000
~200,000 are used. molecular weight is 1
,000, the durability of the coating film is insufficient;
If it exceeds 0,000, the viscosity of the paint becomes too high, causing a practical problem. Epoxy modified polyurethane resin is 1
Epoxy resin having two or more functional hydroxyl groups per molecule,
For example, epoxy resins such as bisphenol A type, halogenated bisphenol type, resorcinol type, and bisphenol F type are reacted with dibasic acids such as adipic acid, phthalic acid, dimerizing luic acid, and maleic acid to form terminal hydroxyl groups. It can be synthesized by synthesizing a polyester resin and reacting it with a polyfunctional polyisocyanate. Alternatively, an epoxidizing agent such as percarboxylic acid is applied to a polyurethane resin synthesized from an unsaturated polyester resin obtained by reacting an unsaturated fatty acid such as maleic acid, fumaric acid, or itaconic acid with a polyhydric alcohol. It can also be synthesized by

The epoxy modified polyester resin has a molecular weight of 1.00
0 to 200.000 is used. The molecular weight is 1.
If it is less than 200, the durability of the coating film is insufficient.
, 000, the viscosity of the paint becomes too high, causing a practical problem. Epoxy-modified polyester resin is made by combining unsaturated dibasic acids such as maleic acid, fumaric acid, and itaconic acid or saturated dibasic acids such as phthalic acid, adipic acid, and terephthalic acid with 1,4-butanediol and 1,5-bentanediol. , 1,6-hexanediol, 1,10-decanediol, and an unsaturated polyester resin obtained by thermal condensation with polyols such as butadiene oligomers with hydroxyl groups at both ends are epoxidized using an epoxidizing agent such as percarboxylic acid. obtained by In addition, instead of the above unsaturated polyester resin, a modified unsaturated polyester resin obtained by melt-mixing this and a polycarbonate resin or a saturated polyester resin in the presence of a catalyst and transesterifying the resin may be used as the starting material. good.

Furthermore, as an epoxy-modified acrylonitrile-butadiene copolymer resin, the acrylonitrile content is generally 12
~50% by weight, molecular weight 5.000~soo, ooo
are used. Acrylonitrile content is 12%
If it is less than 50% by weight, it will have poor compatibility with other binders such as polyvinyl chloride and nitrocellulose, which are generally used in magnetic recording media, and if it is more than 50% by weight, the solubility in the solvent will decrease and the dispersibility of the magnetic powder will be greatly reduced. I feel sorry for you. Also, the molecular weight is 5
If it is less than 500.00, the durability of the coating film is low.
If it is greater than 0, the viscosity of the paint is too high to be practical.

Epoxy-modified acrylonitrile-butadiene copolymer resin is made by copolymerizing a radical copolymerizable monomer containing an epoxy group with acrylonitrile and butadiene in the presence of a radical generator, if necessary, and other copolymerizable monomers. While it can be obtained by polymerization, it can also be obtained by partially epoxidizing the double bonds within the acrylonitrile-butadiene copolymer resin using an epoxidizing agent such as percarboxylic acid.

The epoxy resin used in the third invention has a molecular weight of 500 to 200,000.

If the molecular weight is less than 500, the durability of the coating film will be low and unreacted substances may leak onto the surface of the magnetic layer, making it difficult to use. If the molecular weight exceeds 200,000, the viscosity of the coating material will be too high to be practical. Specific examples of epoxy resins include bisphenol A-epichlorohydrin type, those using halogenated bisphenols, resorcinol, bisphenol F, tetrahydroxyphenylethane, etc. instead of bisphenol, and novolac type epoxy resins. Can be mentioned.

In addition, the resin having an epoxy group in the third invention is as follows:
In order to improve the dispersibility of magnetic powder, C00M, SO3M, 504M, and PO3M are added to the resin containing epoxy groups.
z.

It may contain a functional group such as PO4M3 (M is hydrogen, an alkali metal, or ammonium).

In the binder for the magnetic powder of the magnetic recording medium of the present invention, the above-mentioned epoxy group-containing resin is added to about 2% of the total amount of binder components.
0 to about 80% by weight of the polyurethane resin, about 80% by weight of the polyurethane resin.
It is preferable to use it in a proportion of about 20% by weight.

Although the polyurethane resin can be used alone as a binder for the magnetic powder of the magnetic recording medium of the present invention, it is usually used in combination with other binders.

When used in combination with other binders, 10 to 10% of the total binder
It is preferred to use the polyurethane resin in a range of 90% by weight.

Examples of binders used in combination include polyurethane resins other than those of the present invention, vinyl chloride polymers, polyester resins, acrylonitrile-butadiene copolymer resins, (meth)acrylic acid ester acrylonitrile copolymers, (meth)acrylic Acid ester vinylidene chloride copolymer, (meth)acrylic acid ester styrene copolymer, nylon
silicone resin, nitrocellulose-polyamide resin,
Polyvinyl fluoride, vinylidene chloride acrylonitrile copolymer, styrene butadiene copolymer, styrene butadiene acrylonitrile copolymer, polyamide resin, polyvinyl butyral, cellulose derivatives (cellulose acetate butyrate, cellulose acetate propionate, cellulose diacetate, cellulose) triacetate, nitrocellulose, etc.) chlorovinyl ether acrylic ester copolymers, thermoplastic resins such as various synthetic rubbers, phenolic resins, phenoxy resins, urea resins, melamine resins, alkyd resins, silicone resins, acrylic reaction resins, epoxies Examples include thermosetting resins such as polyamide resins and nitrocellulose melamine resins. The ratio of these resins that can be used in combination to the total amount of binder components is 5
Must not exceed 0%.

Furthermore, these binders may have other functional groups known per se, among which, in particular, 5
04M, 503M, SOZM, COOMN
At least one functional group selected from the group consisting of Hz, N''Rz, OH, phosphoric acid group, and phosphoric ester group (where M represents a hydrogen atom or an alkali metal atom, and R represents an alkyl group, an allyl group, Those having organic residues such as alkenyl groups or alkoxyl groups are preferred.The amount of these functional groups is IX per gram of resin.
It is preferable that 10-6 to I x 10-2 equivalents are contained.

The total binder content in the magnetic layer of the magnetic recording medium of the present invention is usually 10 to 100 parts by weight per 100 parts by weight of the ferromagnetic powder.
Parts by weight, preferably 15 to 40 parts by weight.

The magnetic recording medium of the present invention is prepared by mixing the above-mentioned binder with known materials such as magnetic powder, lubricant, abrasive, antistatic agent, and further, if necessary, a dispersant and a solvent mainly composed of ketones. This is processed to obtain a magnetic paint, which is applied onto a non-magnetic film such as polyester film, subjected to orientation treatment and surface formation treatment. Depending on the application, heat treatment for crosslinking or surface polishing is performed before cutting. , incorporation, etc., to obtain the magnetic recording medium of the present invention.

Particularly fine ferromagnetic powders are suitable as the ferromagnetic powder used in the present invention, such as T FezO3, Fe=04, TFedX
Ferromagnetic iron oxide powder such as (1,33<x<1.5), Co-doped ferromagnetic iron oxide powder, ferromagnetic chromium dioxide powder, ferromagnetic metal powder, barium ferrite, Fe
Examples include iron carbide powder such as 5Cz, iron nitride powder, and the like.

The ferromagnetic metal powder is a ferromagnetic metal powder containing iron, cobalt, or nickel, and for example, the metal content in the ferromagnetic metal fine powder is 75% by weight or more, and the metal content is 80% by weight or more. is at least one ferromagnetic metal or alloy (e.g., Af, Fe, Co, Ni, Fe-
Co, Fe-Ni, CoNi, Co-Ni
-Fe), and other components (e.g., Al1.Si, S, 90% T) within a range of 20% by weight or less of the metal content.
i,,V,Cr.

Mn, Cu, Zn, Y, Mo, Rh, Pd
SAg, Sn, sb, Te.

Ba, Ta, W, Re, Au, Hg, Pb
5BiSLa, Ce, Pr.

Mention may be made of alloys which may contain Nd, B, P).

Methods for producing these ferromagnetic powders are already known, and the ferromagnetic powder used in the present invention can also be produced according to these known methods.

There is no particular restriction on the shape of the ferromagnetic powder, but needle-like, granular, dice-like, rice-grain-like, and plate-like shapes can usually be used.

Examples of lubricants that can be used in the present invention include carbon atoms of 8 to 1;
8 fatty acids, higher alcohols, amides, fatty acid esters, etc. can be used, such as caprylic acid, capric acid, lauric acid, myristic acid, valmitic acid, stearic acid, oleic acid, elaidic acid, linoleic acid, lylunic acid, Stearic acid, stearyl alcohol, valmityl alcohol, laurylamide, dimethyl stearylamide, butyl laurylamide, butyl stearate,
Examples include octyl stearate and sorbitan oleate. Also usable are silicone oil, fluorine-based oils such as polyperfluoroalkylene oxide and perfluoroalkane, paraffin wax, and polyethylene oxide.

Furthermore, solid lubricants such as carbon black, graphite, molybdenum disulfide, and tungsten disulfide can also be used. These lubricants are used in an amount ranging from 1 part to 6 parts per 100 parts of magnetic powder.

In addition, as abrasives, TiOz, TiO, ZnO, Ca
O1SnO,, Sin□, (X FezO1, Crz
(h, 0(Aj2z03, ZnS, Mo5z, B
Examples include a5O, CaSO4, MgCO3, BN, SiC, and the like. These inorganic fillers may be used alone or in combination of two or more.

Furthermore, as antistatic agents, conductive fine powders such as carbon black and carbon blank graft polymer; natural surfactants such as saponin; alkylene oxide type,
Nonionic surfactants such as glycerin and glycidol; higher alkylamines, quaternary ammonium salts, salts of pyridine and other heterocyclic compounds, and cationic surfactants such as phosphonium or sulfonium: carboxylic acids, sulfonic acids , anionic surfactants containing acidic groups such as phosphoric acid, sulfuric acid ester groups, and phosphoric ester groups;
Examples include amphoteric activators such as amino acids, aminosulfonic acids, sulfuric acid or phosphoric acid esters of amino alcohols, and the like.

A dispersant can be used in the magnetic recording medium of the present invention if necessary. Examples of dispersants that can be used in the present invention include fatty acids having 10 to 22 carbon atoms (e.g., caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid, elaidic acid, linoleic acid, esters of the above fatty acids and their compounds. Compounds in which part or all of hydrogen has been replaced with fluorine atoms, amides of the above fatty acids, aliphatic amines, higher alcohols, polyalkylene oxide alkyl phosphates, alkyl phosphates, alkyl borates, sarcosinates, alkyl ethers Known dispersants such as esters, trialkyl polyolefin oxy quaternary ammonium salts and lecithin can be mentioned.

The binder used in the present invention is also effective as a binder for a back coat layer applied for the purpose of improving the running properties of a magnetic tape.

(Effects of the Invention) Thus, according to the present invention, a low-viscosity paint in which fine magnetic powder is stably dispersed can be obtained, and a magnetic recording medium obtained using the paint has excellent surface smoothness and durability of the coating film. It has good running properties and excellent magnetic properties.

(Example) The present invention will be described in more detail with reference to Examples below. Note that parts and percentages in the Synthesis Examples, Examples, and Comparative Examples are based on weight unless otherwise specified.

Polyurethane Synthesis Example 1 566.2 g of methyl ethyl ketone, 1000 g of polybutylene adibate with a molecular weight of 1000 (1,00 mol), 2,4 -TD I
208.8g (1.20 mol), MD I
After charging 225.0 g (0.90 mol) and reacting at 80°C for 3 hours, 500 g of a 3% solution of trimethylolpropane in methyl ethyl ketone (0.11 mol as trimethylolpropane) was added for another 6 hours. The reaction was carried out to obtain sample (A). Sample (B) was prepared in the same manner, and the methyl ethyl ketone solution of trimethylolpropane to be added was 1000, 1500 and 1 soo g, respectively.
(c) and CD) were obtained.

The composition of each polyurethane sample is as shown in Table 1.

Polyurethane Synthesis Example 2 Samples (E), (F), and (I) were synthesized in the same manner except that the long chain polyol, diisocyanate compound, and short chain polyol were changed as shown in Table 2.

In addition, after reacting polybutylene adipate with MDl and TDI in the same manner as in Synthesis Example 1, a mixture of the polar group-containing compounds shown in Table 2 in trimethylolpropane was added. React and sample (G) (H)
I got it. The composition of each of these polyurethane samples was determined from commercially available urethane prepolymer (J), moisture-curable polyurethane (
K) is shown in (Table 2).

Yui←Haritoku→− 1) Examples and comparative examples (Part 1) The following tests (1-1) to (1-4) were conducted.

The results are shown in (Table 3).

(11) 400 parts of glossy cobalt-coated magnetic iron oxide powder (specific surface area: 40 m
2/g), the amount of resin other than polyurethane in Table 3,
Polyol in the amount shown in Table 3 and methyl ethyl ketone 4
9 parts, toluene 49 parts, cyclohexanone 32 parts, carbon black 2 parts, alumina 4 parts, myristic acid 2 parts,
After high-speed shear dispersion of a mixture consisting of 1 part of butyl stearate for 90 minutes, polyurethane resin in the amount shown in Table 3, 30 parts of methyl ethyl ketone, 30 parts of toluene, and 20 parts of cyclohexanone were added and dispersed for 30 minutes, and the above mixture was further dispersed. A total of 50 parts of solvent, and for Comparative Example 3, 15 parts of polyisocyanate (Coronate L manufactured by Nippon Polyurethane)
After adding, the mixture was further dispersed for 10 minutes to obtain a magnetic paint. The obtained magnetic paint was applied to a polyester film with a film thickness of 5 μm.
The film was coated so as to have a diameter of m, subjected to magnetic field orientation treatment, and then dried. The reflectance of the magnetic coating film at a reflection angle of 60 parts was measured using a glossmeter.

(1-2) The magnetic coating used for the evaluation of square specific gloss was 6 am x 6
It was cut into mm pieces and measured using a magnetic property measuring machine.

(1-3) The magnetic coating film used for durability and gloss evaluation was smoothed with a calendar roll, then heated at 65°C for 25 hours, and then placed on a rotating drum covered with abrasive paper under a load of 100g. They were brought into contact and rotated at 150 rpm+g for 10 minutes, and the extent to which the magnetic paint adhered to the abrasive paper was visually observed and evaluated in four grades: A, B, C, and D.

A: No stain, B: Slight stain, C: Slight stain, D: Lots of stain (1-4) The force generated between the paint film and the rotating drum was evaluated using the same method as the running performance and durability evaluation. Measurements were made using a U gauge in an atmosphere of 80% relative humidity at 1°C, and the running resistance was graded into three grades: A to C, in descending order of running resistance.

:low, : medium, :expensive 2) Examples and comparative examples (Part 2) The following tests (2-1) to (2-4) were conducted.

The results are shown in (Table 4).

(2-1) 400 parts of glossy cobalt-coated magnetic iron oxide powder (specific surface area: 40t)
a"7g), 50 parts of a resin other than the polyurethane resin of the present invention listed in Table 3, 5 parts of the triazinethiol compound listed in Table 4, 49 parts of methyl ethyl ketone, 49 parts of toluene, 32 parts of cyclohexanone, and 2 parts of carbon blank. parts, alumina 4 parts, myristic acid 2 parts, butyl stearate 1 part
After high-speed shear dispersion for 90 minutes, polyurethane resin was mixed with methyl ethyl ketone in the amount shown in Table 3.
After adding 0 parts, 30 parts of toluene, and 20 parts of cyclohexanone and dispersing for 30 minutes, a total of 50 parts of the above mixed solvent and 15 parts of polyisocyanate (Coronate L manufactured by Nippon Polyurethane ■) for Comparative Example 2 were added. The mixture was further dispersed for 10 minutes to obtain a magnetic paint. The obtained magnetic paint was applied onto a polyester film to a film thickness of 5 μm, subjected to magnetic field orientation treatment, and then dried. The reflectance of the magnetic coating film at a reflection angle of 60 parts was measured using a glossmeter.

(2-2) The magnetic coating film used for the evaluation of square specific gloss was 6 mm x 6
It was cut into mm pieces and measured using a magnetic property measuring machine.

(2-3) The magnetic coating used for durability and gloss evaluation was smoothed with a calendar roll and then heat treated at 65°C for 65 hours, then placed on a rotating drum covered with abrasive paper under a load of 100g. They were brought into contact and rotated at 150 rpm for 10 minutes, and the extent to which the magnetic paint adhered to the abrasive paper was visually observed and evaluated in four grades: A, B, C, and D.

A: No stain, B: Slight stain, C: Slight stain, D: Lots of stain (2-4) Using the same method as in running performance and durability evaluation, the force generated between the paint film and the rotating drum was measured at 65°. C1 Measured using a U gauge in an atmosphere with relative humidity of 80%, and A is ranked in descending order of running resistance.

Judgment was made in three stages: B and C.

A: Low, B: Medium, C: High 3) Examples and comparative examples (part 3) The following tests (3-1) to (3-4) were conducted.

The results are shown in (Table 5).

(3-1) 400 parts of glossy cobalt-coated magnetic iron oxide powder (specific surface area: 40 m
2/g), resins other than polyurethane in the amounts shown in Table 3, 49 parts of methyl ethyl ketone, 49 parts of toluene, 32 parts of cyclohexanone, 2 parts of carbon blank, and 4 parts of alumina.
After high-speed shear dispersion for 90 minutes, a mixture consisting of 1 part of myristic acid, 2 parts of myristic acid, and 1 part of butyl stearate was added with the amount of polyurethane resin shown in Table 3, 30 parts of methyl ethyl ketone, 30 parts of toluene, and 20 parts of cyclohexanone. After dispersing for a minute, add a total of 50 parts of the above mixed solvent, and finally
The polyamine compound in 3 was added in an amount such that the amount of amino groups was 0 to 3 times the chemical equivalent of the amount of isocyanate groups in the polyurethane resin.However, for Comparative Example 2, 15 parts of polyisocyanate (manufactured by Nippon Polyurethane) Coronate) was added and dispersed for an additional 10 minutes to obtain a magnetic paint. The obtained magnetic paint was applied onto a polyester film to a film thickness of 5 μm, subjected to magnetic field orientation treatment, and then dried. Apply the magnetic coating film to 60% using a glossy needle.
The reflectance at partial reflection angle was measured.

(3-2) The magnetic coating film used for evaluation of square specific gloss was cut into 6 mm x 6 mm pieces and measured using a magnetic property measuring machine.

(3-3) The magnetic coating used for durability and gloss evaluation was smoothed with a calendar roll, then heated at 65°C for 25 hours, and then placed on a rotating drum covered with abrasive paper under a load of 100g. The abrasive paper was contacted and rotated at 150 rpm, and the extent to which the magnetic paint adhered to the abrasive paper was visually observed and evaluated in four grades: A, B, C, and D.

A: No stain, B: Slight stain, C: Slight stain, D: Lots of stain (3-4) Using the same method as the evaluation of running performance and durability, the force generated between the paint film and the rotating drum was measured at 65°. C1 Measurement was performed using a U gauge in an atmosphere with relative humidity of 80%, and the running resistance was evaluated in three stages, ABC and C, in descending order of running resistance.

A: Low, : Moderate, : High Procedure (Hoshosho August 27, 1990 Patent Office Commissioner's Palace 1゜2゜3゜Display of the case 1990 Patent Application No. 23780 Name of the invention Magnetic recording medium amendment Relation to the case of a person who does the following: Patent applicant address: 2-6-1 Marunouchi, Chiyoda-ku, Tokyo Name: Zeon Corporation Representative: Takeshi Takizawa 6 Contents of amendment (11 The scope of patent claims is amended as shown in the attached sheet.

(2) Change “Comparative Example 3” in the third line from the bottom of page 37 of the specification to “
Corrected to "Comparative Example 2".

(3) "Table 3" on page 41, line 6 is corrected to Table 1-41.

(4) "Table-3" in the 8th row from the bottom of No. 41 to 1 Table-4
” is corrected.

(5) "Comparative Example 2" in the fifth line from the bottom of page 41 is corrected to "Comparative Example 12."

(6) The explanatory text from "Glossiness" on the 4th line of page 42 to "Measured." on the 5th line of the same page is revised to "Same as (1-1)."

(7) Change the explanatory text from “Durability Evaluation” in the 5th line from the bottom to “C: High” in the 1st line from the bottom of page 42 of the same page by r(1
- Same as 4). Revise to j.

(8) Add "copolymer" next to "-vinyl acetate" in the fifth line from the bottom of the footnote on page 43.

(9) ``Table 3'' on page 44, line 6 is corrected to ``Table 1 Table 5''.

QOI "Table-3" on page 44, line 11 of the same table is 1-Table-5
” is corrected.

0υ "Table-3" in the 6th row from the bottom of No. 44 is 1 Table-5
” is corrected.

On page 44, line 4 from the bottom, "Comparative Example 2" is corrected to "Comparative Example 22."

0. The explanatory text from "Glossiness" in line 6 of page 45 to "measured." in line 7 of the same page is revised to "same as (1-1)."

04) Add 1 per rlO next to I"450 rp+s" in the 9th line from the bottom of page 45.

09 Change the explanatory text from “Durability evaluation” in the third line from the bottom of page 45 to “C: High” in the second line of page 46 by r(1
- Same as 4). ”.

Attached Claim 1: A resin having a urethane bond in its molecule produced by the reaction of a diisocyanate and a polyol, having an average of 2.3 or more isocyanate groups in one molecule, and a number average molecular weight of 2,000. That's all for io, oo.

or less, and the component with molecular weight i, ooo or less is 20%
1. A magnetic recording medium comprising a magnetic layer containing, in addition to a polyurethane resin, at least one compound selected from the group consisting of polyol, triazinethiol, and polyamine as a binder for magnetic powder.

2. The magnetic recording medium according to claim 1, wherein the polyurethane resin has a polar group without an active hydrogen atom in its molecule.

31a) A resin having a urethane bond produced by the reaction of a diisocyanate and a polyol, having an average of 2.3 or more isocyanate groups in one molecule, and a number average molecular weight of 2,000 or more and 10,000 or less. and a magnetic layer containing a polyurethane resin containing less than 20% of components with a molecular weight of 1.000 or less, (b) a resin having an epoxy group, and (c) triazinethiol as a binder for magnetic powder. magnetic recording media.

Claims (1)

[Claims] 1. A resin having a urethane bond in the molecule produced by the reaction of a diisocyanate and a polyol, having an average of 2.3 or more isocyanate groups in one molecule, and a number average molecular weight of 2. 000 to 10,000, and contains less than 20% of components with a molecular weight of 1,000 or less, as well as at least one compound selected from the group consisting of polyols, triazinethiols, and polyamines. A magnetic recording medium characterized by having a magnetic layer containing as a binder. 2. The magnetic recording medium according to claim 1, wherein the polyurethane resin has a polar group without an active hydrogen atom in the molecule. 3. (a) A resin with urethane bonds produced by the reaction of diisocyanate and polyol, having an average of 2.3 or more isocyanate groups in one molecule, and a number average molecular weight of 2,000 or more and 10,000 (b) a resin having an epoxy group; and (c) triazinethiol as a binder for magnetic powder. A magnetic recording medium characterized by: