JPH0448432A - Binder for magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve dispersibility for fine particles of magnetic powder when the powder is dispersed by preparing the binder comprising copolymers of specified amts. of vinyl chloride, epoxy group-contg. vinyl and N-substd. maleimide as the binder. CONSTITUTION:The binder consists of copolymers of vinyl chloride, epoxy group-contg. vinyl and N-substd. maleimide. The amt. of vinyl chloride is 59 - 98 wt.%, which is decided by the following reason. If the amt. is small, solubility of the binder for an org. solvent decreases, while with large amt. of vinyl chloride, the obtd. copolymers become hard with low flexibility. The amt. of epoxy group-contg. vinyl is 1 - 30 wt.%. If the amt. is small, dispersibility of the magnetic powder in the copolymers decreases, while with large amt., the solubility to an org. solvent decreases. The amt. of N-substd. maleimide is 1 - 40 wt.%. With small amt. of this maleimide, dispersibility of the magnetic powder in the copolymers, heat resistance of the copolymers and wearing resistance of the magnetic layer decrease, while with large amt., the obtd. layer becomes brittle. Thereby, fine particles of the magnetic powder can be uniformly disperse.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to a binder for magnetic recording media.

(Prior art) Generally, magnetic recording materials used for magnetic tapes, magnetic disks, etc. are made by applying a magnetic paint containing magnetic powder and a binder onto a base material, applying a magnetic field to orient the magnetic powder, and then drying it. However, in order to obtain a magnetic recording body with excellent magnetic properties, it is necessary to uniformly disperse the magnetic powder in the binder. Conventionally, vinyl chloride-vinyl acetate-vinyl alcohol polymers, mixtures of these polymers and isocyanate compounds, and the like have been known as the above-mentioned binders.
JP-A-62-112217 and JP-A-62-112217 propose a vinyl chloride copolymer consisting of vinyl chloride and 2-hydroxypropyl acrylate as a binder that can disperse Ii-free pigments well. Unexamined Japanese Patent Publication No. 1-
No. 184629 proposes a vinyl chloride copolymer containing an epoxy group.

However, in recent years, magnetic powder has been made into finer particles as the density of magnetic recording bodies has increased, and the above-mentioned binder has been insufficient in dispersibility of the finely divided magnetic powder.

(Problem B to be Solved by the Invention) The present invention has been made in view of the above drawbacks, and it is possible to form a magnetic layer in which finely divided magnetic powder is uniformly dispersed and has excellent magnetic properties. An object of the present invention is to provide a binder for magnetic recording bodies.

(Means for Solving the Problems) The epoxy group-containing vinyl used in the present invention is not particularly limited as long as it has a reactive double bond and an epoxy group. For example, allyl glycidyl ether, meth Glycidyl ether of unsaturated alcohols such as lyl glycidyl ether, glycidyl ester with acrylic acid and methacrylic acid such as glycidyl acrylate, glycidyl methacrylate, unsaturated dicarboxylic acid ester such as methylglycidyl itaconate, glycidyl ethyl maleate, butadiene mono Examples include olefin epoxides such as oxide and vinylcyclohexene monooxide.

The N-substituted maleimide tel used in the present invention is a compound represented by the following formula.

In the formula, R is not particularly limited as long as it is an aliphatic group, an alicyclic group, or an aromatic group having 1 to 20 carbon atoms, and is, for example, N-methylmaleimide, N-n-propylmaleimide, N- Isopropylmaleimide, N-n-butylmaleimide, N-tert-butylmaleimide, N-n-hexylmaleimide, N-cyclohexylmaleimide, N-
Phenylmaleimide, N-2-chlorophenylmaleimide, N-2-methylphenylmaleimide, N-2-ethylphenylmaleimide, N-2,6-cyclophenylmaleimide, N-2,6-dimethylphenylmaleimide, N -benzylmaleimide, N-(2-chlorobenzyl)maleimide, N-(2-methylbenzyl)maleimide, N-naphthylmaleimide, etc., and N-cyclohexylmaleimide and N-phenylmaleimide are preferably used.

The binder for magnetic recording materials of the present invention is a copolymer of vinyl chloride (al), the above-mentioned epoxy group-containing vinyl (b), and N-1 substituted maleimide. The solubility in solvents decreases, and when the amount increases, the copolymer becomes hard and the flexibility decreases, so the content should be 59 to 98% by weight. The dispersibility of magnetic powder decreases,
If the amount increases, solubility in organic solvents decreases, so 1~
30% by weight, and as the content of N-substituted maleimide (c1 decreases, the dispersibility of the magnetic powder in the copolymer, the heat resistance of the copolymer, and the abrasion resistance of the magnetic layer decrease, In this case, the magnetic layer becomes weak, so the content is 1 to 40% by weight.

When the average degree of polymerization of the above copolymer becomes small, the mechanical strength of the magnetic layer decreases, and when it becomes large, the viscosity of the solution when dissolved in an organic solvent becomes too high, reducing the dispersibility of the magnetic powder and the moldability of the magnetic layer. Therefore, 150 to 800 is preferable.

Any method may be used to produce the above-mentioned copolymer; for example, the known suspension polymerization method, emulsion polymerization method, which is usually carried out in the polymerization of vinyl chloride using a radical polymerization initiator,
Examples include solution polymerization method and bulk polymerization method. The suspension polymerization method is preferably employed because the resulting polymer does not contain impurities (and the production cost is relatively low).

In the above suspension polymerization method, the suspension stabilizer is not particularly limited, and for example, partially saponified polyvinyl alcohol, cellulose derivatives, etc. may be used, and the radical polymerization initiator is not particularly limited, such as ,
Organic peroxides such as benzoyl peroxide, dilauroyl peroxide, and tert-butyl peroxy neodecanoate are used. The N-substituted maleimide may be added all at once into the polymerization vessel before the start of polymerization, or may be added in portions during polymerization, or may be added continuously.

In particular, N whose copolymerizability ratio with vinyl chloride is significantly different
- When using an N-substituted maleimide such as phenylmaleimide, it is preferable to add the entire amount in portions during polymerization or to add it continuously because the heat resistance is further improved. Maleimide is acetone,
It is best to use it by dissolving it in an organic solvent such as methanol or dispersing it in water, and the polymerization temperature is generally 3.
Polymerization is generally carried out at 0 to 90°C for 2 to 20 hours.

The second invention of the present invention provides that the above polymer further includes a sulfonic acid group, a sulfonic acid group, a carboxyl group, a phosphoric acid group,
A polymerizable monomer (d) containing at least one selected from the group consisting of a quaternary ammonium base and an amino group is copolymerized.

The above polymerizable monomer fdl may be used alone or in combination of two or more.

The sulfonic acid group or the polymerizable monomer containing a sulfonic acid group is not particularly limited, and examples thereof include 2-acrylamide-2-methylpropanesulfonic acid, sodium metaallylsulfonate, and the like.

As the polymerizable monomer containing the above carboxyl group,
Examples include, but are not limited to, acrylic acid, methacrylic acid, succinic acid mono(meth)acryloyloxyethyl ester, phthalic acid mono(meth)acryloyloxyethyl ester, maleic acid n-butyl monoester, maleic acid, and fumaric acid. Acrylic acid, methacrylic acid, n-butyl maleic acid monoester, and maleic acid are preferably used.

The polymerizable monomer containing a phosphoric acid group is not particularly limited, but examples thereof include acid phosphoxyethyl (meth)acrylate, acid 7dophosphoxybrobyl (meth)acrylate, 3-chloro- Examples include 2-acid 7dophosphoxybrovir (meth)acrylate.

The polymerizable monomer containing the quaternary ammonium base is not particularly limited, but examples include 2-hydroxy-3-methacryloyloxypropyltrimethylammonium chloride, methacryloyloxyethyltrimethylammonium chloride, trimethyl-3-
Examples include methacryloylamide-propylammonium chloride.

The above polymerizable monomer containing an amino group is not particularly limited, but examples include dimethylamino (meth)acrylate, diethylamino (meth)acrylate, N,N-dimethylaminopropylacrylamide,
Examples include ter-butylaminoethyl (meth)acrylate.

If the content of the polymerizable monomer + dl decreases, the dispersibility of the magnetic powder in the copolymer will decrease, and if it increases, the surface smoothness and moisture resistance of the magnetic layer will decrease.
．． 05 to 5% by weight.

The composition of the binder for a magnetic recording medium of the present invention is as described above, and it can be copolymerized with vinyl chloride within a range that does not reduce the basic performance as a binder such as the dispersibility of magnetic powder and heat resistance. Monomers may be copolymerized, and the content is 10% by weight
The following are preferred.

The above monomer is not particularly limited, but
For example, α-olefins such as ethylene and propylene,
Vinyl esters such as vinyl acetate and vinyl propionate; vinyl ethers such as butyl vinyl ether and heptyl vinyl ether; acrylic esters such as methyl acrylate and ethyl acrylate; methacrylic esters such as methyl methacrylate, ethyl methacrylate, and phenyl methacrylate; Aromatic vinyls such as styrene and α-methylstyrene, vinyl cyanides such as acrylonitrile and methacrylonitrile, vinyl halides such as vinylidene chloride and vinyl fluoride, and unsaturated dicarboxylic acids such as dimethyl maleate and dimethyl fumarate. Examples include esters and unsaturated dicarboxylic acid anhydrides such as maleic anhydride.

A method for producing a magnetic paint from the binder for magnetic recording material of the present invention may be any known method. For example, cobal)-r-iron oxide, etc. may be prepared in a solution in which the binder is dissolved in an organic solvent. One example is a method of dispersing magnetic powder.

The content of the binder and magnetic powder in the magnetic paint may be determined as appropriate depending on the conditions for forming the magnetic layer obtained by applying and drying the magnetic paint. The content is preferably 5 to 30% by weight, and the amount of binder added to the magnetic powder is 10 to 1 part by weight per 100 parts by weight of the magnetic powder.
00 parts by weight is preferred.

Examples of the organic solvent include, but are not limited to, toluene, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, and the like.

In addition, in order to improve the abrasion resistance and heat resistance of the magnetic layer, an isocyanate compound may be added to the magnetic paint. At this time, if an acidic compound is used in combination, a crosslinking reaction between the epoxy group and the isocyanate compound may occur. It is preferable to use the above-mentioned acidic compounds in combination, since this progresses easily and further improves the abrasion resistance and heat resistance of the magnetic layer.

The above-mentioned isocyanate compound is not particularly limited, but examples thereof include tolylene diisocyanate, diphenylmethane diisocyanate, dianisidine diisocyanate, hexamethylene diisocyanate, metaxylylene diisocyanate, and a reaction product of trimethylolpropane and tolylene diisocyanate. It will be done. If the amount of the isocyanate compound added is too small, it will not be possible to improve the abrasion resistance, heat resistance, etc. of the magnetic layer, and if it is too large, the crosslinking density will increase and the magnetic layer will become weak. It is preferably 0.3 to 30 parts by weight.

The above acidic compounds are not particularly limited, but include, for example, oxalic acid, malonic acid, succinic acid, phthalic acid, maleic acid, fumaric acid, formic acid, monochloroacetic acid, dichloroacetic acid, trichloroacetic acid, and 0-nitrobenzoic acid. acid, m
-Carboxylic acids such as nitrobenzoic acid, p-nitrobenzoic acid, O-chlorobenzoic acid, m-chlorobenzoic acid, trimellitic acid, pyromellitic acid, sulfites, sulfuric acids, phosphorous acids, phosphoric acids, etc. It will be done. The amount of the acidic compound added should be at least as large as possible (but the effect of promoting the crosslinking reaction between the epoxy group and the isocyanate compound will be reduced, so the amount should be 0.1 to 5 times the chemical equivalent of the epoxy group in the copolymer). is preferred.

(Example) The present invention will be explained in detail below.

In addition, the degree of polymerization of the vinyl chloride copolymer shown in the results,
The composition and each physical property of the magnetic recording medium were measured as follows.

(11 degree of polymerization Measured in accordance with JIS K6721.

(2) Composition After measuring the chlorine content by the oxygen flask combustion method, the component composition was determined using an elemental analyzer (manufactured by gJ Hon Seisakusho, model: CHN coder MT-5).

(3) Glossiness digital variable angle glossy needle (manufactured by Nihon Heavy Industries Co., Ltd., model: VG-
IC).

(4) The base films on which the heat-adhesive magnetic layers have been formed are stacked so that the magnetic layer surfaces are in contact with each other, and after heating at 120°C for 15 minutes with a load of 10 g/cd applied, one edge of the film is heated. If both films peeled off when you lifted it, mark it as ○.
Those that remained adhered were rated as ×.

(5) A sample for gel fraction measurement was immersed in a mixed solvent of toluene-methyl isobutyl ketone (weight ratio 1/1) at 50°C for a day and night, and the undissolved content expressed as a weight percentage of the sample was determined as the gel fraction. did.

In addition, as a sample for measurement, a composition obtained by removing magnetic powder from the magnetic paint obtained in each example was applied onto a glass plate.
The material formed by drying at 00°C for 2 hours and further at 50°C for 24 hours was used.

(6) Square ratio DC magnetization characteristic recording device (manufactured by Yokogawa Electric Corporation, model: T/32
56-30).

8 g of ion-exchanged water, 1 g of hydroxypropylethyl cellulose I, and 8.8 g of dilauroyl peroxide were charged into a jacketed pressure-resistant polymerization vessel equipped with a 151 stirrer and sealed to remove remaining air. 3 kg of vinyl chloride was compressed and then heated to 70° C. using a jacket. Immediately after the temperature inside the vessel reached 70℃, add 10 g of glycidyl acrylate and 7 g of N-cyclohexyl maleimide.
A solution obtained by dissolving 10 g of acetone in 10 g of acetone was used as the amount to be added in one batch, and the mixture was press-injected 40 times at 5-minute intervals to polymerize while stirring.

The reactor was cooled for 5 minutes after the final addition, and after cooling, the remaining unreacted vinyl chloride was discharged outside the reactor, and the polymerization slurry was then taken out, washed with ion-exchanged water, and dried to obtain a copolymer.

The degree of polymerization and composition of the obtained copolymer were measured and the results are shown in Table 1.

Next, the obtained copolymer was dissolved in a mixed solvent of toluene-methyl isobutyl ketone (weight ratio 1/1) to prepare a 15% by weight copolymer solution, and the amount of the prepared solution was 4 times that of the copolymer. A weight of cobalt-T-iron oxide was supplied to a paint conditioner equipped with a 1/8 inch stainless steel pole, and mixed and dispersed for 4 hours to obtain a magnetic paint.

The obtained magnetic paint was applied to a 25 μm thick polyethylene terephthalate film, a magnetic field was applied with a magnetic flux density of 2000 Gs to orient the magnetic powder, and then dried to form a 6 μm thick magnetic layer. A magnetic recording medium was obtained. The squareness ratio and glossiness of the surface of the magnetic layer of the obtained magnetic recording body were measured, and the results are shown in Table 1.

Evidence 1 As shown in Table 1, a copolymer obtained in the same manner as in Example 1 was used except that the type and amount of the composition in the copolymer were changed, and the same as in Example 1 was used. A magnetic recording medium was obtained in the same manner.

The composition and degree of polymerization of the obtained copolymer and the physical properties of the magnetic recording material were measured in the same manner as in Example 1, and the results are shown in Table 1.

As shown in Table 1, a copolymer obtained in the same manner as in Example 1 was used, except that the type and amount of the composition in the copolymer were changed. A magnetic recording medium was obtained in the same manner.

The adhesion of the obtained copolymer, the degree of polymerization, and the physical properties of the magnetic recording material were measured in the same manner as in Example 1, and the results are shown in Table 1.

The prisoner side 1 25! ! 6.8 kg of methanol and 53 g of α-cumyl peroxyneodecanoate were charged into a pressure-resistant polymerization vessel equipped with a jacket and equipped with a stirrer, and the vessel was sealed to remove remaining air. After that, 3.5 g of vinyl chloride was press-fitted. , and then heated to 43° C. using a jacket. Immediately after the internal temperature reached 43°C, 6.75 g of glycidyl acrylate, 4 g of N-cyclohexylmaleimide, and 32.5 g of vinyl chloride were added.
A mixed solution of 1.5 g was added in an amount of 40 times at 5 minute intervals, and polymerization was carried out with stirring. The reactor was cooled for 5 minutes after the final addition, and after cooling, the remaining unreacted vinyl chloride was discharged outside the reactor, and the polymerization slurry was then taken out, washed with ion-exchanged water, and dried to obtain a copolymer. The composition and degree of polymerization of the obtained copolymer and the physical properties of the magnetic recording material were measured in the same manner as in Example 1, and the results are shown in Table 1.

L Comparison 1 A magnetic recording material was obtained in the same manner as in Example 1 using vinyl chloride-vinyl acetate-vinyl alcohol copolymer as the copolymer.

The physical properties of the obtained magnetic recording body were measured in the same manner as in Example 1, and the results are shown in Table 1.

(Margin below) Inuzashi Niji- An isocyanate compound (
Made by Nippon Polyurethane Co., Ltd., trade name: Coronet) L, solid content 70% by weight) was 3 parts by weight as a solid content per 100 parts by weight of the copolymer, and maleic acid as an acidic compound was 13 parts by weight per 100 parts by weight of the copolymer. A magnetic recording material was obtained in the same manner as in Example 1, except that .6 parts by weight (the same chemical equivalent as the epoxy group in the copolymer) was added and mixed to prepare a magnetic coating material. The squareness ratio, glossiness, heat adhesion and gel fraction of the obtained magnetic recording body were measured, and the results are shown in Table 2.

Using each of the magnetic paints obtained in Examples 2 to 6, Example 7
A magnetic recording medium was obtained in the same manner as above. Measure the squareness ratio, glossiness, heat adhesion, and gel fraction of the obtained magnetic recording material,
The results are shown in Table 2.

Technical Comparison Shell 1 Using the magnetic paint obtained in Comparative Example 3, a magnetic recording medium was obtained in the same manner as in Example 7. The squareness ratio, glossiness, heat adhesion and gel fraction of the obtained magnetic recording body were measured, and the results are shown in Table 2.

Table 2 Glycidyl acrylate L
Example 1 Using a copolymer obtained in the same manner as in Example 1 except that 7 g of N-cyclohexylmaleimide and Ig of n-butyl maleate were dissolved in acetone Log, A magnetic recording medium was obtained in the same manner as in Example 1.

The composition, degree of polymerization, and physical properties of the magnetic recording material of the obtained copolymer were measured in the same manner as in Example 1, and the results are shown in Table 3.

As shown in Table 3, using a copolymer obtained in the same manner as in Example 13 except for changing the type and amount of the composition in the copolymer, Example 1 A magnetic recording medium was obtained in the same manner as above.

The composition, degree of polymerization, and physical properties of the magnetic recording material of the obtained copolymer were measured in the same manner as in Example 1, and the results are shown in Table 3.

(Hereinafter, blank spaces) Magnetic recording bodies were obtained in the same manner as in Example 7 using each of the magnetic paints obtained in Examples 13 to 19. The squareness ratio, glossiness, heat adhesion and gel fraction of the obtained magnetic recording body were measured, and the results are shown in Table 4.

(The following is a blank space) (Effect of the invention) The composition of the binder for a magnetic recording medium of the present invention is as described above, and includes a specific amount of vinyl chloride, epoxy group-containing vinyl, and N
- Since it is a copolymer of substituted maleimide, when the finely divided magnetic powder is dispersed, its dispersibility is excellent. Therefore, the magnetic layer formed using the binder for magnetic recording bodies of the present invention has a high squareness ratio (and has appropriate hardness and flexibility), so it has good sliding contact resistance with the magnetic head. A magnetic recording medium with excellent properties can be obtained.Additionally, if an isocyanate compound and an acidic compound are added,
The epoxy group and the isocyanate compound undergo a crosslinking reaction, and a magnetic recording medium with better abrasion resistance and heat resistance can be obtained.

In the second aspect of the present invention, the polymerizable monomer further contains at least one selected from the group consisting of a carboxyl group, a sulfonic acid group, a sulfonic acid group, a phosphoric acid group, a quaternary ammonium base, and an amino group. Because the body is copolymerized, the squareness ratio of the magnetic layer is higher, and the wear resistance is improved.
A magnetic recording medium with better heat resistance etc. can be obtained.

Claims (1)

[Scope of Claims] 1. A copolymer of (a) vinyl chloride, (b) epoxy group-containing vinyl, and (c) N-substituted maleimide, comprising (
A binder for a magnetic recording medium, characterized in that component a) is 59 to 98% by weight, component (b) is 1 to 30% by weight, and component (c) is 1 to 40% by weight. 2, from (a) vinyl chloride, (b) epoxy group-containing vinyl, (c) N-substituted maleimide, and (d) sulfonic acid group, sulfonic acid base, carboxyl group, phosphoric acid group, quaternary ammonium base, and amino group A copolymer with a polymerizable monomer containing at least one selected from the group consisting of 59 to 97% by weight of component (a),
A binder for a magnetic recording medium, characterized in that component (b) is 1 to 30% by weight, component (c) is 1 to 40% by weight, and component (d) is 0.05 to 5% by weight.