JPS62208423A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve a shelf life and running durability at and under a high temp. and high humidity by using a polar group-contg. monomer contg. >=1 kinds of polar groups among a carboxylic acid group, phosphoric acid group, sulfuric acid group and sulfonic acid group or the salts thereof, amino group and ammonia group. CONSTITUTION:A copolymer which contains a vinyl chloride and hydroxyl group-contg. monomer or the vinyl chloride, vinyl acetate and hydroxyl group- contg. monomer and polar group-contg. monomer as constituting components and does not contain a vinyl alcohol as the constituting component is used as a binder. The polar group-contg. monomer is a vinyl monomer contg. a polar group. The carboxylic acid group, phosphoric acid group, sulfuric acid group and sulfonic acid group or the salts thereof, amino group and ammonia group, etc. are preferable as the polar group. >=1 kinds of the polar group-contg. monomers are incorporated into the copolymer and are incorporated at about 0.02-40wt% in total as the constituting unit. The polar group is incorporated into the copolymer at 0.01-15wt% in total.

Description

[Detailed Description of the Invention] ■ Background Technical Field of the Invention The present invention relates to a magnetic recording medium, and relates to physical properties, particularly dispersibility,
and magnetic recording media with good storage properties, running properties, electromagnetic conversion characteristics, etc. under high temperature and high humidity environments.

Prior Art and its Problems Vinyl chloride-vinyl acetate-vinyl alcohol copolymers have been widely used as binder resins for magnetic tapes.

A representative example of this vinyl chloride-vinyl acetate-vinyl alcohol copolymer is commercially available under the trade name "VAG) I" manufactured by UCC Corporation in the United States.

This copolymer is easily soluble in solvents, has good compatibility with other resins, and has a good affinity with magnetic powder due to the hydroxyl group in its molecules, improving its dispersibility. It has the following advantages.

In particular, its dispersibility is good, resulting in excellent magnetic properties such as degree of orientation and maximum residual magnetic flux density, and excellent electromagnetic conversion properties.

However, in recent years, magnetic powders have become finer particles, and these resins no longer necessarily have satisfactory dispersibility.In this type of copolymer, the amount of hydroxyl groups has increased, and monomers that can be copolymerized with vinyl chloride For example, the decrease in dispersibility is compensated for by copolymerizing maleic acid (anhydride).

However, copolymers with increased amounts of hydroxyl groups and copolymers made with monomers that can be copolymerized with vinyl chloride undergo a saponification process for hydrolysis during the manufacturing process, so The resin itself is easily exposed to hydrochloric acid. For this reason, it has poor thermal stability, and therefore has the disadvantage that its physical properties as a magnetic recording medium, particularly its storage stability and running durability under high temperature and high humidity environments, are insufficient.

Further, a vinyl chloride-vinyl acetate-maleic acid copolymer having a monomer having a polar group without undergoing a saponification process is commercially available under the trade name "VMCH" from UCC Company in the United States. However, this material has poor dispersibility and physical properties compared to the quaternary system of vinyl chloride-vinyl acetate-vinyl alcohol-maleic acid copolymer, which involves a saponification step in the manufacturing process, and has been found to have poor dispersibility and physical properties compared to the quaternary system of vinyl chloride-vinyl acetate-vinyl alcohol-maleic acid copolymer, which involves a saponification step in the manufacturing process. Not suitable for dispersion.

In order to solve such problems, the present inventor first developed a copolymer consisting of vinyl chloride-hydroxyl group-containing monomer or
It is proposed that a copolymer consisting of vinyl base-vinyl acetate-hydroxyl group-containing monomer that does not contain vinyl alcohol as a constituent (has not undergone a saponification process) be used as a binder ( Patent application 1986-20719
No. 6).

Since this copolymer is produced without going through a saponification process, it exhibits extremely good properties, especially in terms of storage stability, runnability, and electromagnetic conversion properties under high temperature and high humidity conditions.

However, it is desired to further improve the dispersibility and thermal stability of finely divided magnetic powder.

■ Purpose of the Invention The purpose of the present invention is to use a vinyl chloride copolymer as a binder, which does not involve a saponification step during the production process, to provide excellent dispersibility and thermal stability, especially in high-temperature, high-humidity applications. The purpose of the present invention is to provide a magnetic recording medium that has excellent storage stability and running durability under conditions.

■Disclosure of invention Such objects are achieved by the invention described below.

That is, the first invention provides a magnetic recording medium in which a magnetic paint containing a binder and magnetic powder is coated on a substrate, wherein the binder is vinyl chloride, a hydroxyl group-containing monomer, a polar group-containing monomer, Or it contains a copolymer containing vinyl chloride, vinyl acetate, a hydroxyl group-containing monomer, and a polar group-containing monomer as constituent units, and the hydroxyl group of this hydroxyl group-containing monomer is not directly bonded to the vinyl group, In addition, the polar group-containing monomer is
The present invention is a magnetic recording medium characterized by having one or more polar groups selected from a carboxylic acid group, a phosphoric acid group, a sulfuric acid group, a sulfonic acid group or a salt thereof, an amino group, and an ammonium group.

Further, a second invention provides a magnetic recording medium in which a magnetic paint containing a binder and magnetic powder is coated on a substrate, wherein the binder comprises vinyl chloride, a hydroxyl group-containing monomer, a polar group-containing monomer, Or it contains a copolymer containing vinyl chloride, vinyl acetate, a hydroxyl group-containing monomer, and a polar group-containing monomer as constituent units, and the hydroxyl group of this hydroxyl group-containing monomer is not directly bonded to the vinyl group, In addition, one or more of polar group-containing 111(7) iKL+ phosphoric acid group, sulfuric acid group and sulfonic acid group or their salts, amine group and ammonium group A magnetic recording medium characterized by having a polar group and an epoxy group.

■Specific structure of the invention Hereinafter, a specific configuration of the present invention will be explained in detail.

The present invention relates to a copolymer comprising vinyl chloride and a hydroxyl group-containing monomer, or vinyl chloride, vinyl acetate and a hydroxyl group-containing monomer, and a polar group-containing monomer as a binder. Use one that does not contain vinyl alcohol (has not undergone a saponification process).

The polar group-containing monomer used in the present invention is a vinyl monomer containing a polar group.

As the polar group, a carboxylic acid group, a phosphoric acid group, a sulfuric acid group, a sulfonic acid group or a salt thereof, an amino group, an ammonia group, etc. are preferable.

In this case, carboxylic acid group C0OH, phosphoric acid group po4H
2. Salts of the sulfuric acid group 5O4H and the sulfonic acid group 5O3H may be salts of alkali metals such as K and Na, alkaline earth metals such as Ca and Mg, as well as ammonium salts.

Note that the phosphoric acid group may be a monophosphoric acid ester group having an alkyl group, an aryl group, or the like.

The amino group may be an unsubstituted amino group or a monosubstituted amino group substituted with an alkyl group, an aryl group, or the like.

Furthermore, as ammonium groups, in addition to unsubstituted ones,
It may also be a mono-, di-, or tri-substituted amino group substituted with an alkyl group, an aryl group, or the like.

Further, an acid anion such as a halogen may be bonded to the ammonium group.

The polar group-containing monomer used in the present invention has one or more of the above polar groups. The polar group may be directly bonded to the vinyl group, or may be bonded to a substituent that is bonded to the vinyl group.

As substituents bonded to the vinyl group to which the polar group is bonded,
ROCO-1R-1RN) (CO-1R31-1RNC
OOCO- etc. are preferred.

In this case, R is an alkyl group, in particular a carbon atom number of 1 to 10
, aryl groups (phenyl group, naphthyl group, etc.). Note that these may be further substituted with other substituents.

Usually, only one of these polar groups is bonded directly or indirectly to the vinyl group, but two or more may be bonded to the vinyl group.

Furthermore, other alkyl groups, particularly those having 1 to 10 carbon atoms, aryl groups, etc., and preferably lower alkyl groups may be bonded to the vinyl group.

Specific examples of these polar group-containing monomers are listed below.

(1) Carboxylic acid group-containing monomer l) Acrylic acid 2) Methacrylic acid 3) Crotonic acid 4) Isocrotonic acid 5) Vinyl acetic acid 6) Angelic acid 7) Tiglic acid 8) Allyl acetic acid 9) β,β-dimethylacrylic acid 10) Pyroterepic acid 11) Undecylenic acid 12) Maleic acid 13) Itaconic acid, etc.

(2) Phosphate group-containing monomer 1) ClI2 =CHCOO(R) n-0PO(O
) l) 2 where R: C)+2, c(co 3 )
Substituted or unsubstituted methylene n such as 2: about 1 to 10 2) CH2=CHCOO[C(C)l 3 ) 2
In(co2)1-OPO(OH)2 where ra: about 1 to 10, n: about 1 to 10, etc.

(3) Sulfate group-containing monomer Here, A: H or a cation such as Na, etc.

(4) Sulfonic acid group-containing monomer l) Vinyl sulfonic acid 2) Vinyl sulfonate 3) Styrene sulfonic acid 4) Styrene sulfonate 5) CI(2-C)l (R) n S03 A where R : Substituted or unsubstituted methylene n such as CH2, C(CI+ 3 ) 2, etc. A: Cation such as H or Na, etc. 6) C112=C)l[c(CH3) 21n((:
H2) msO38 where III: about 1 to 10 n: about 1 to 10 8: cations such as H or Na, etc. 7) CH2<H-(nee NH-(CIlz) 2-
5O3A where 8: ■ or cations such as Na, etc.

(5) Amino group-containing monomer l) Acrylamide 2) co2- ClICOO ((:H2) 2-N)
+ 23) Dimethylaminoethyl methacrylate 4)
CH2=CHC0NH(CH2) 2-S03 A where Am11 or a cation such as Na, etc.

(6) Ammonium group-containing monomer 1) cu2=C:1I-Coo(CH2)
3 N-(R')"X-where R': alkyl such as CH3, C2H5, etc. X: GIL,
1st class anion 2) Diallyldimethyl-ammonium bromide etc.

One or more types of such polar group-containing monomers are contained in the copolymer, and the total amount is about 0.02 to 40% by weight as a structural unit.

As a result, a total of 0.01 polar groups were present in the copolymer.
It is contained in an amount of up to 15% by weight, more preferably in an amount of 0.01 to 5% by weight.

When the polar group content is less than 0.01% by weight, dispersibility deteriorates, and when it exceeds 15% by weight, problems arise in terms of solubility, durability, etc.

The polar group-containing monomer used in the present invention also has an epoxy group as a polar group and the other polar groups mentioned above (carboxylic acid group, phosphoric acid group, sulfuric acid group, sulfonic acid group or salts thereof, amino group, and ammonium group). etc.) (hereinafter referred to as epoxy group-containing monomer).

That is, when the above-mentioned polar group is introduced via an epoxy group in the manufacturing process of the polar group-containing monomer, the epoxy group may be left to remain.

In this case, the epoxy group -CH-CH2 is usually unsubstituted.

Furthermore, one or more of the epoxy group and other polar groups may be bonded directly to the vinyl group, or may be bonded to a substituent that is bonded to the vinyl group.

The substituent bonded to the vinyl group to which an epoxy group and one or more other polar groups are bonded may be a group to which the aforementioned polar group is bonded, but ROCO- is particularly preferred.

In this case R is an alkyl group, in particular carbon atoms a1-10
, aryl groups (phenyl group, naphthyl group, etc.).

Note that these may be further substituted with other substituents.

Usually only one of these polar groups is bonded directly or indirectly to the vinyl group, but two or more may be bonded to the vinyl group.

Furthermore, other alkyl groups, particularly those having 1 to 10 carbon atoms, aryl groups, etc., and preferably lower alkyl groups may be bonded to the vinyl group.

Specific examples of the epoxy group-containing monomer are listed below.

Epoxy group-containing monomer where R, R': H, C113, etc. n: about 1 to 10, for example, glycidyl methacrylate, etc. Such epoxy group-containing monomers are contained in the copolymer as a structural unit in a total of 0.02 to 10. Contains 40% by weight.

As a result, the epoxy group and other polar groups are contained in the copolymer in a total amount of 0.01 to 15% by weight. and,
It is preferable that epoxy groups account for 50 to 95% by weight of these polar groups.

When the epoxy group content in the polar group exceeds 95% by weight, dispersibility deteriorates, and when it becomes less than 50% by weight, the effect of the epoxy group content on thermal stability does not appear.

When an epoxy group is contained as a polar group in this way, the heat resistance of the copolymer becomes better.

A copolymer containing such a polar group-containing monomer as a constituent unit contains vinyl chloride and a hydroxyl group-containing monomer as essential constituent units.

The vinyl chloride unit content is 60-95% by weight, more preferably 70-90% by weight.

When the vinyl chloride unit content exceeds 95%, solubility deteriorates.

Moreover, when it is less than 60% by weight, dispersibility deteriorates.

Furthermore, the hydroxyl group of the hydroxyl group-containing monomer used is not directly bonded to the vinyl group, but is bonded to a substituent that is bonded to the vinyl group.

More specifically, the substituent to which this hydroxyl group is bonded and which is bonded to the vinyl group is preferably ROCO-2R-.
In this case, R is an alkyl group, in particular a carbon atom number of 2 to 10
, aryl groups (phenyl group, naphthyl group, etc.), and particularly preferred are alkyl groups having 2 to 5 carbon atoms.

Note that these may be further substituted with other substituents.

The carbon atom in R to which the hydroxyl group is bonded is preferably the one on the terminal side rather than the one bonded to the ester group.

Usually only one of these substituents is bonded to the vinyl group, but two
More than one may be combined.

Furthermore, an alkyl group, particularly one having 2 to 10 carbon atoms, an aryl group, etc., and preferably a lower alkali group may be bonded to the vinyl group.

Among these hydroxyl group-containing monomers, hydroxyalkyl (meth)acrylates are preferred.

Specific examples of these water WR group-containing monomers are listed below.

1) 2- and droxyethyl acrylate 2) 2-hydroxyethyl methacrylate 3) 2-hydroxypropyl acrylate 4) 2-hydroxypropyl methacrylate 5) 3-hydroxypropyl acrylate 6) 3-hydroxypropyl methacrylate 7) 2-hydroxybutyl Acrylate 8) 2-Hydroxybutyl methacrylate 9) 3-Hydroxybutyl acrylate 10) 3-
Hydroxybutyl methacrylate 11) 4-hydroxybutyl acrylate 12) 4-hydroxybutyl methacrylate 13) 5-hydroxypentyl acrylate 1
4) 5-Hydroxypentyl methacrylate 15) 6-
Hydroxyhexyl acrylate 16) 6-hydroxyethyl methacrylate 17) Neopentyl glycol acrylate 1B) Neopentyl glycol methacrylate 19) Allyl carbinol 20) Allyl alcohol 21) Crotyl alcohol 22) Citronellol 23) Phytol 24) Cinnamyl alcohol Like this The hydroxyl group-containing monomer is contained in the copolymer in an amount of 0.02 to 40% by weight as a structural unit.

As a result, 0.01 to 5 hydroxyl groups are present in the copolymer.
Contains % by weight.

When the hydroxyl group content is less than 0.01% by weight, dispersibility deteriorates and the degree of crosslinking by the crosslinking agent described below decreases.
On the other hand, if it exceeds 5% by weight, problems will occur in terms of solubility, durability, etc.

Furthermore, the copolymer may contain vinyl acetate as a structural unit.

Addition of vinyl acetate tends to improve solubility, but when the content of vinyl acetate units exceeds 20% by weight,
The content of vinyl acetate units is 20% by weight or less, since this will result in poor dispersibility.

The number average molecular weight of such copolymers is usually 1000
0 to 30000.

When the number average molecular weight is less than 10,000, physical properties deteriorate,
Moreover, when it exceeds 30,000, the dispersibility deteriorates.

To synthesize such a copolymer, each monomer may be copolymerized according to a conventional method.

Alternatively, the acid group, ammonium group, etc. can be separately introduced according to a conventional method after the copolymer synthesis.

Alternatively, a copolymer containing an epoxy group-containing monomer may be modified.

Such copolymers are used as the main binder for magnetic recording media.

In the present invention, the binder contains a thermoplastic elastomer and/or resin of 70% relative to the total resin content in the binder.
It contains not more than 20% by weight, especially 20 to 70% by weight.

As the thermoplastic elastomer, the following are suitable.

i) Polyurethane elastomer As a thermoplastic elastomer, polyurethane elastomer has an excellent balance of abrasion resistance of the magnetic coating required for magnetic recording media, adhesion with PUT film, and wettability with magnetic material particles. Urethane compounds are particularly suitable for the purpose of the present invention.

Examples of such urethane compounds include 2.4-toluene diisocyanate, 2.6
-Toluene diisocyanate, 1.3-xylene diisocyanate, 1゜4-xylene diisocyanate, 1,
5-naphthalene diisocyanate, m-phenylene diisocyanate, p-phenylene diisocyanate, 3.
3'-dimethyl-4,4'-diphenylmethane diisocyanate, 4,4'-diphenylmethane diisocyanate, 3,3'-dimethylbiphenylene diisocyanate, 4°4'-biphenylene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, dicyclohexylmethane diisocyanate, Desmodur is combined with various polyvalent isocyanates such as Desmodur N and reticulated saturated polyester (ethylene glycol,
Polyhydric alcohols such as diethylene glycol, glycerin, trimethylolpropane, 1,4-butanediol, 1,6-hexanediol, pentaerythritol, sorbitol, neopentyl glycol, 1,4-cyclohexane dimetatool, and phthalate. acids, isophthalic acid, terephthalic acid, maleic acid, succinic acid, adipic acid,
(by condensation polymerization with saturated polybasic acids such as sebacic acid), reticulated saturated polyethers (polyethylene glycol,
Polyurethane elastomers made of polycondensates of various polyesters such as polypropylene glycol, polytetraethylene glycol), caprolactam, hydroxy-containing acrylic esters, and hydroxy-containing methacrylic esters are effective.

ii) Acrylonitrile-butadiene copolymer elastomer An acrylonitrile-butadiene copolymer having a terminal hydroxyl group commercially available as PolyBD Liquid Resin manufactured by Sinclair Vetro Chemical Co., Ltd. or an elastomer such as Hiker 1432j manufactured by Nippon Zeon Co., Ltd.

1it) Polybutadiene Elastomer A prepolymer having a low molecular weight terminal hydroxyl group, such as PolyBD Liquid Resin R-15 manufactured by Sinclair Vetrochemical Co., is suitable, especially in terms of compatibility with thermoplastic plastics and affinity with magnetic powder.

In addition, polybutadiene cyclized product Nippon Synthetic Rubber Co., Ltd. CBR-
M901 also exhibits excellent performance when combined with thermoplastics.

Other suitable thermoplastic elastomers include:
Examples include chlorinated rubber, acrylic rubber, isoprene rubber and its cyclized product (ClR701 manufactured by Japan Synthetic Rubber), epoxy modified rubber, internally plasticized saturated linear polyester (Toyobo Vylon #300), and the like.

In addition, as a thermoplastic resin that can be used instead of or added to such an elastomer component, linear saturated polyester resin, desmophene #800, #110 manufactured by Bayer & Co., Ltd.
Low molecular weight polyester resins, epoxy resins, phenoxy resins, chlorosulfonated polyethylene resins, which are versatile in two-component types with isocyanates such as 0, @2200,
Vinyl isobutyl ether, polyamide resin, polyvinyl butyral resin, polyvinylpyrrolidone resin, etc. can be used.

The binder can also be crosslinked, especially by a compound crosslinker that can react with the hydroxyl groups of the copolymer.

Examples of such crosslinking agents include polyfunctional isocyanate compounds having isocyanate groups or isocyanate-containing compounds mentioned above, as well as butylated melamine resins and the like.

To cure such a binder, it is generally necessary to heat it in a heating oven at 50-80° C. for 6-100 hours.

The magnetic powder used in the magnetic paint of the magnetic recording medium of the present invention includes metal magnetic particles, cobalt-coated iron oxide particles, and γ
-Fe203 particles, barium ferrite particles, etc. may be included.

The mixing ratio of the magnetic powder and these binders is about 10/1 to 1/10 by weight.

It is effective to use various other abrasives, lubricants, antistatic agents, dispersants, etc. in the magnetic paint depending on the purpose.

Note that the thickness of the recording layer containing magnetic particles and a binder is usually about 1 to 7 mm.

As the substrate, any one of polyester film, various resins such as polyamide and polyimide, aluminum metal, glass, etc. may be used depending on the purpose.

Further, various known back coat layers may be provided on the side opposite to the surface on which the recording layer is provided on such a substrate.

Furthermore, recording layers may be provided on both sides of the substrate.

■Specific effects of the invention According to the invention, a polar group-containing monomer as a binder,
Because it is a copolymer of vinyl chloride-hydroxyl group-containing monomer or vinyl chloride-vinyl acetate-hydroxyl group-containing monomer, which can be obtained without going through a saponification process, it is finely divided. High affinity between magnetic powder and binder;
A magnetic recording medium with excellent reliability, durability, and electromagnetic conversion characteristics can be obtained.

The present invention is a copolymer consisting of a vinyl chloride system and a monomer copolymerizable therewith, which does not contain vinyl alcohol as a constituent (has not undergone a saponification process). Since it is used, changes over time in a high-temperature, high-humidity environment are reduced, and the running properties of the magnetic tape in a high-temperature, high-humidity environment can be improved without deteriorating the electromagnetic conversion characteristics.

By using a copolymer that has not gone through the saponification process in the magnetic recording medium during the resin manufacturing process, chemical changes in the resin itself due to dihydrochloric acid and dihydrochloric acid can be prevented, and magnetic properties due to HCl released from the resin can be prevented. This is because it reduces chemical changes in the powder and other magnetic recording medium components, thereby improving the physical properties of the magnetic recording medium, especially its stability over time and running durability under high temperature and high humidity environments. be.

Further, in the present invention, since a copolymer containing a polar group-containing monomer as a constituent component is used, the dispersibility of the magnetic powder in the magnetic paint is extremely good.

Furthermore, when an epoxy group is used as a polar group, the heat resistance of the recording layer becomes higher.

① Specific Examples of the Invention Next, the present invention will be explained in more detail with reference to Examples of the present invention.

Example 1 Magnetic powder shown in Table 1 was prepared.

Table 1 Magnetic powder classification Magnetic powder AM-Fe203 powder B Co-y-Fe203 powder C Metal
Powders and copolymers shown in Table 2 were also prepared.

A magnetic paint was prepared using the magnetic powder and copolymer described above in the combinations shown in Table 3 in the following manner.

Part by weight Magnetic powder 100 Copolymer
10 Polyurethane resin (
Nippon Polyurethane Co., Ltd. Niraporan 2304) 10 Lubricant
1 abrasive
1 methyl ethyl ketone
70 Methyl isobutyl ketone 70
Toluene 70 This mixture was dispersed in a ball mill for about 20 hours. Thereafter, Coronate Polyisocyanate (manufactured by Nippon Polyurethane Co., Ltd.) was added as a crosslinking agent, and the mixture was coated on a 8751 polyester base. After surface treatment, heat hardening treatment is performed,
A magnetic tape with a coating thickness of 5#m was obtained.

The glossiness of these coating compositions before surface treatment was measured using a crossmeter (Murakami type). The results are shown in Table 3.

From the results in Table 3, it can be seen that the glossiness of the examples was significantly improved compared to the comparative examples, and the dispersibility was improved.

Furthermore, Table 3 shows the running accident rate when these magnetic tapes were continuously hit for 24 hours and 48 hours under an environment of 50° C. and 80% RH. The accident rate under an environment of 50° C. and 80% RH is a maximum of 20% in the example, whereas it is as high as a minimum of 55% in the comparative example.

Table 3 All examples and comparative examples showed good electromagnetic conversion characteristics.

From the above, it is clear that the magnetic recording medium of the present invention has good physical properties in addition to excellent electromagnetic conversion properties.

Claims (17)

[Claims] (1) In a magnetic recording medium in which a magnetic paint containing a binder and magnetic powder is coated on a substrate, the binder is vinyl chloride,
Contains a hydroxyl group-containing monomer and a polar group-containing monomer, or a copolymer containing vinyl chloride, vinyl acetate, a hydroxyl group-containing monomer, and a polar group-containing monomer as constituent units, and this hydroxyl group-containing monomer The hydroxyl group of is not directly bonded to the vinyl group, and the polar group-containing monomer is a carboxylic acid group, a phosphoric acid group, a sulfuric acid group, a sulfonic acid group or their salts, an amino group, and an ammonium group. A magnetic recording medium characterized by having one or more types of polar groups. (2) The magnetic recording medium according to claim 1, wherein the copolymer contains 0.01 to 15% by weight of polar groups. (3) The magnetic recording medium according to claim 1 or 2, wherein the copolymer has a vinyl chloride unit content of 60 to 95% by weight. (4) The magnetic recording medium according to any one of claims 1 to 3, wherein the copolymer has a vinyl acetate unit content of 20% by weight or less. (5) The magnetic recording medium according to any one of claims 1 to 4, wherein the copolymer contains 0.01 to 5% by weight of hydroxyl groups. (6) The number average molecular weight of the copolymer is 10,000 to 3,000
The magnetic recording medium according to any one of claims 1 to 5, wherein the magnetic recording medium is 0. (7) The magnetic recording medium according to any one of claims 1 to 6, wherein the binder contains 70% by weight or less of a thermoplastic elastomer and/or resin. (8) The magnetic recording medium according to any one of claims 1 to 7, wherein the copolymer is crosslinked with a crosslinking agent. (9) In a magnetic recording medium in which a magnetic paint containing a binder and magnetic powder is coated on a substrate, the binder is vinyl chloride,
Contains a hydroxyl group-containing monomer and a polar group-containing monomer, or a copolymer containing vinyl chloride, vinyl acetate, a hydroxyl group-containing monomer, and a polar group-containing monomer as constituent units, and this hydroxyl group-containing monomer The hydroxyl group of is not directly bonded to the vinyl group, and the polar group-containing monomer has a carboxylic acid group, a phosphoric acid group, a sulfuric acid group, a sulfonic acid group or their salts, an amino group, and an ammonium group as polar groups. A magnetic recording medium characterized by having one or more polar groups among the groups and an epoxy group. (10) The magnetic recording medium according to claim 9, wherein the copolymer contains 0.01 to 15% by weight of polar groups. (11) The magnetic recording medium according to claim 9 or 10, in which epoxy groups account for 50 to 95% by weight of the polar groups contained in the copolymer. (12) The vinyl chloride unit content of the copolymer is 60 to 95
The magnetic recording medium according to any one of claims 9 to 11, which is % by weight. (13) Vinyl acetate unit content of copolymer is 20% by weight
A magnetic recording medium according to any one of claims 9 to 12 below. (14) The magnetic recording medium according to any one of claims 9 to 13, wherein the copolymer contains 0.01 to 5% by weight of hydroxyl groups. (15) The number average molecular weight of the copolymer is 10,000 to 300
00. The magnetic recording medium according to any one of claims 9 to 14. (16) The magnetic recording medium according to any one of claims 9 to 15, wherein the binder contains 70% by weight or less of a thermoplastic elastomer and/or resin. (17) The magnetic recording medium according to any one of claims 9 to 16, wherein the copolymer is crosslinked with a crosslinking agent.