JPH0681812B2 - Magnetic paint and magnetic recording medium - Google Patents

Description

TECHNICAL FIELD The present invention relates to a magnetic paint using a vinyl chloride resin as a binder for magnetic powder and a magnetic recording medium using the magnetic paint.

[Conventional technology]

Generally, a magnetic recording medium such as a magnetic tape or a floppy disk is manufactured by applying a magnetic paint prepared by dispersing ferromagnetic powder in an organic solvent with an organic polymer as a binder onto a polymer film or sheet. .

As the organic polymer in this magnetic coating material, a relatively hard resin such as PVC, polyvinyl butyral, nitrocellulose, or acetyl cellulose is usually combined with a soft material such as polyester, polyurethane, or acrylonitrile-butadiene copolymer. Often used, also
Usually as a thermosetting component for the purpose of improving the durability of the coating film,
In many cases, polyisocyanate compounds are used. Therefore, as a characteristic of the resin used as a binder, not only the compatibility with other polymers and the reactivity with polyisocyanate are appropriate, but it is well compatible with magnetic powder and uniformly dispersed in the paint. Work is required.

In recent years, magnetic particles have become finer and have higher coercive force with the demand for higher recording density and improved S / N ratio of magnetic recording media. The dispersion performance of the binder is a crucial factor for forming a magnetic layer having a high packing density and improving the performance as the medium.

Until now, it has been customary to use a low molecular weight surfactant as a dispersant in order to improve the dispersion of magnetic powder.
The use of a large amount of a dispersant has its own limit in terms of the durability of the magnetic recording medium and stains on the head, and in addition, from the viewpoint of improving the reliability of the magnetic recording medium, the binder is highly dispersed. It is required to have the ability. On the other hand, in order to improve the durability and reliability of the medium, it is commonly used in recording magnetic tapes in particular to make the magnetic layer a crosslinked coating film by incorporating a curable compound represented by a polyisocyanate compound into the paint. It is required to have appropriate reactivity with polyisocyanate as a binder. In this case, if the reactivity is too good, the pot life of the paint is short and it is uneconomical, and if it is too slow, the expected improvement in durability and runnability is not observed.

The present inventor conducted an improvement study on a binder that responds to the high performance of such a magnetic recording medium for PVC, and obtained an evaluation on a PVC binder known so far, and a vinyl chloride-vinyl alcohol-vinyl acetate copolymer was obtained. As the proportion of vinyl alcohol increases, the magnetic powder's dispersion performance improves, but to a lesser extent, it requires the use of a dispersant, and as the amount of vinyl alcohol increases, the pot life becomes shorter and the moisture resistance of the coating film decreases. In addition, the rate of thermal decomposition also increases. On the other hand, vinyl chloride-maleic acid-vinyl acetate copolymer strongly adsorbs to magnetic powder and exhibits an excellent dispersion ability, but the paint is apt to thicken and gel, and the reaction with polyisocyanate tends to occur locally. is there.

As an attempt to solve the problems of these typical PVC binders, a vinyl chloride-vinyl alcohol-vinyl acetate-maleic acid copolymer has been proposed, which is a vinyl chloride-vinyl alcohol-vinyl acetate copolymer. Although it has both the reactivity of the polymer and the good dispersibility of the vinyl chloride-maleic acid-vinyl acetate copolymer, its level is insufficient. Further, this copolymer is usually obtained by saponifying a vinyl chloride-maleic acid-vinyl acetate copolymer,
Since the polymer deteriorates during saponification, it has poor chemical thermal stability.

As another attempt, a method using a vinyl chloride-hydroxyethyl acrylate-acrylic acid copolymer has been proposed, but if a relatively large amount of hydroxyethyl acrylate is used to satisfy the solubility in a solvent, it is Pot life becomes short when adding isocyanate compound. On the other hand, if the copolymerization amount of hydroxyethyl acrylate is reduced to an appropriate level for pot life, the solubility in a solvent will decrease, and the solution will easily gel and thicken.

[Problems to be Solved by the Invention]

As a result of diligent study on a method for solving the problems of the conventional PVC containing an alcoholic hydroxyl group, the present inventors have found that by using a specific vinyl chloride copolymer, excellent dispersibility of magnetic powder and temporal stability of dispersion are obtained. In addition, it gives good reactivity with polyisocyanate in spite of an extremely small amount of hydroxyl group content, and has excellent chemical thermal stability. Furthermore, this resin is used as a binder, and polyisocyanate is used as a curing agent. It was confirmed that the magnetic recording medium obtained by applying the coating material in which the magnetic powder was dispersed onto the polyester film used had excellent magnetic characteristics, electromagnetic conversion characteristics, and durability.

That is, in the present invention, by using a monoallyl ether of a polyhydroxy compound as a monomer that gives a hydroxyl group, a smaller amount of the hydroxyl group provides sufficient reactivity as compared with other monomers that give a hydroxyl group. Is obtained, the chemical thermal stability is further improved, and in addition, the magnetic coating using the resin of the present invention as a binder can exhibit good dispersion stability, and by using the coating. The inventors have found that the obtained magnetic recording medium has good surface smoothness and durability of the coating film and is excellent in runnability, magnetic characteristics and electromagnetic conversion characteristics, and completed the present invention.

[Means for Solving the Problems]

That is, the first invention of the present invention is a copolymer of vinyl chloride in which at least one component of the binder of the magnetic powder is a hydroxyl group, and a strong acid radical containing a carboxylic acid group or sulfur or phosphorus, and a unit amount for supplying the hydroxyl group. The present invention relates to a magnetic paint characterized in that the body is a monoallyl ether of a polyhydroxy compound, and the second invention is a strong acid in which at least one component of the binder of the magnetic powder contains a hydroxyl group and a carboxylic acid group or sulfur or phosphorus. The present invention relates to a magnetic recording medium comprising a root-containing vinyl chloride copolymer in which a monomer for supplying the hydroxyl group is a resin of a monoallyl ether of a polyhydroxy compound.

The amount of the monoallyl ether of these polyhydroxy compounds used is in the range such that the hydroxyl group is 0.05 to 3.0% by weight, preferably 0.1 to 2.0% by weight in the copolymer. 0.
If it is less than 05% by weight, the effect of crosslinking with polyisocyanate will not be exhibited, and if it exceeds 3.0% by weight, the pot life will be too short.

Examples of monoallyl ethers of polyhydroxy compounds that give hydroxyl groups in the copolymer according to the present invention include allyl-
2-hydroxyethyl ether, allyl-2-hydroxypropyl ether, allyl-3-hydroxypropyl ether, allyl-2-hydroxybutyl ether, allyl-3-hydroxybutyl ether, allyl-4-hydroxybutyl ether, allyl-6-hydroxyhexyl ether Such as alkylene glycol monoallyl ethers, diethylene glycol monoallyl ether, dipropylene glycol monoallyl ether and other polyoxyalkylene glycol monoallyl ethers, glycerin monoallyl ether, allyl-2-chloro-3-hydroxypropyl ether, allyl Halogen-substituted and hydroxy-substituted monoallyl ethers of (poly) alkylene glycols such as 2-hydroxy-3-chloropropyl ether. Ethers, eugenol, and polyhydric monoallyl ethers phenols and their halogen-substituted derivatives such as isoeugenol and the like. In addition to the ethers of allyl alcohol and polyhydroxy compounds exemplified above, a thioether using allyl thiol instead of allyl alcohol can also be used as a monomer that gives a hydroxyl group according to the present invention, and examples thereof include allyl. -2-hydroxyethyl thioether, allyl-2-
Examples thereof include hydroxypropyl thioether.

As a method for providing a carboxylic acid group to the copolymer according to the present invention, a carboxylic acid group-containing monomer is used. Examples of the carboxylic acid group-containing monomer include unsaturated mono- or dicarboxylic acids such as acrylic acid, methacrylic acid, maleic acid, itaconic acid, and crotonic acid, maleic acid, and monoalkyl esters of unsaturated dicarboxylic acids such as itaconic acid. Can be used.
This monomer is preferably used in a range where the carboxylic acid group in the copolymer is 0.3 to 5.0% by weight. If it is less than this range, the dispersibility of the magnetic powder is poor, and if it is more than this range, the coating composition tends to gel and thicken.

Further, it is necessary that the equivalent ratio of the hydroxyl group to the galbonic acid group is 0.1 to 3.0, preferably 0.2 to 2.0, and this ratio is
When it exceeds 3.0, the dispersibility of the magnetic powder remarkably deteriorates, and when it is less than 0.1, the effect of adding the monoallyl ether of the polyhydroxy compound is not obtained.

The monomer for introducing a strong acid radical containing sulfur or phosphorus into the polymer according to the present invention, sulfonic acid, sulfuric acid, phosphoric acid, a strong acid containing sulfur or phosphorus such as phosphonic acid, and alkali metal salts thereof or A radically polymerizable monomer having an ammonium salt may be mentioned. Among the strong acids,
Sulfonic acid and its salts are easily available and there are many types. For example, vinyl sulfonic acid, methyl vinyl sulfonic acid, (meth) allyl sulfonic acid, styrene sulfonic acid,
Examples include acids such as ethyl (meth) acrylic acid-2-sulfonate, 2-acrylamido-2-methylpropanesulfonic acid, and 3-allyloxy-2-hydroxypropanesulfonic acid, and alkali metal salts and ammonium salts thereof. Examples of monomers having sulfuric acid and salts thereof include acids such as ethyl (meth) acrylate-2-sulfate and 3-allyloxy-2-hydroxypropanesulfate, and alkali metal salts or ammonium salts thereof. Further examples of the monomer having a salt of phosphoric acid include (meth)
Acrylic acid-3-chloro-2-propyl phosphate, (meth) acrylic acid-2-ethyl phosphate, 3-allyloxy-
Examples of the monomer having an acid such as 2-hydroxypropanephosphoric acid and its alkali metal salt or ammonium salt and having a salt of phosphonic acid include vinylphosphonic acid, acrylamidomethanephosphonic acid and ethyl 2-phosphonate.
Examples thereof include acids such as (meth) acrylate and 3-allyloxy-2-hydroxypropanephosphonic acid, and alkali metal salts or ammonium salts thereof.

The content of strong acid radicals containing sulfur or phosphorus in the copolymer is SO when the resin is burned by an oxygen combustion flask method and the amount of sulfur or phosphorus in the resin is measured as sulfuric acid or phosphoric acid.
₄ ^- or PO ₄ ^--- as the amount of 0.1 to 4.0 wt%, preferably
Used in the range of 0.3 to 2.0% by weight. If it is less than 0.1% by weight, the dispersibility of the magnetic powder will be insufficient, and if it exceeds 4.0% by weight, the hydrophilicity of the strong acid radical will be strong and the solubility in the solvent will be insufficient, as well as the moisture resistance of the coating film will be reduced. In addition, aggregation of the magnetic powder occurs and returns, resulting in poor dispersibility.

Further, it is also possible to use other copolymerizable monomers in combination, if necessary. Examples of other comonomers include vinyl acetate, vinyl propionate, and other carboxylic acid vinyl esters; methyl vinyl ether, isobutyl vinyl ether, cetyl vinyl ether, and other vinyl ethers; vinylidene chloride, vinylidene fluoride, and other vinylidene; acrylic acid, methacrylic acid. Unsaturated carboxylic acids such as acids, maleic acid and itaconic acid; unsaturated carboxylic acid anhydrides such as maleic anhydride; diethyl maleate, dibutyl maleate, diethyl itaconate, methyl (meth) acrylate,
Unsaturated carboxylic acid alkyl esters such as ethyl (meth) acrylate; olefins such as ethylene and propylene;
Unsaturated nitriles such as (meth) acrylonitrile; aromatic vinyls such as styrene, α-methylstyrene and p-methylstyrene; epoxy-containing monomers such as allyl glycidyl ether, glycidyl methacrylate and vinylcyclohexene monooxide.

These comonomers are used for the purpose of improving the solubility of the copolymer while controlling the compatibility and softening point of the copolymer and the other resin when they are mixed.

Further, particularly when copolymerizing an epoxy-containing monomer with a hydroxyl group-containing monomer and vinyl chloride, sulfur or phosphorus is added to the epoxy group site in the aqueous or non-aqueous system in the process of the copolymerization reaction or before or after the reaction. It is also possible to adopt a method of adding an alkali metal salt or ammonium salt of a strong acid containing. In that case, examples of the alkali metal salt or ammonium salt of a strong acid containing sulfur or phosphorus include potassium sulfite, sodium thiosulfate, ammonium hydrogensulfate, disodium hydrogenphosphate, ammonium hydrogenphosphite, potassium sulfanilate, and persulfate. Examples thereof include potassium sulfate and sodium superphosphate. The method of adding a strong acid salt containing sulfur or phosphorus in the copolymerization of this epoxy group-containing monomer and vinyl chloride is described in JP-A-60-238306 and JP-A-60-238306.
238371 and JP-A-61-53367.

The degree of polymerization of the copolymer is 200 to 900, preferably 250 to 500. If it is less than 200, the wear resistance of the magnetic layer is insufficient and 900
If it exceeds, the viscosity of the paint is high and the dispersion of magnetic powder tends to be insufficient.

The resin for magnetic paint according to the present invention can be produced by any known polymerization method. From the viewpoint of the solubility of the polymer, it is preferable to produce it by solution polymerization or a lower alcohol such as methanol or ethanol as a polymerization medium alone or by a suspension polymerization method using a combination of this and a deionized water, and sulfur. Alternatively, emulsion polymerization is convenient when a water-soluble salt having a strong acid group containing phosphorus is used in the reaction.
Examples of the polymerization initiator used for producing the resin include lauroyl peroxide, diisopropyl peroxydicarbonate, di-2-ethylhexyl peroxydicarbonate, t-butyl peroxypivalate, and 3,5,5-trimethyl hexa Organic peroxides such as noyl peroxide,
Examples thereof include azo compounds such as α, α′-azobisisobutyronitrile, ammonium persulfate and potassium persulfate. Examples of the suspending agent include polyvinyl alcohol, a partially saponified product of polyvinyl acetate, a cellulose derivative such as methylcellulose, polyvinylpyrrolidone, maleic anhydride-vinyl acetate copolymer, a synthetic polymer substance such as polyacrylamide, and starch, Examples include natural polymer substances such as gelatin. Examples of the emulsifier include anionic emulsifiers such as sodium alkylbenzene sulfonate and sodium lauryl sulfate, and nonionic emulsifiers such as polyoxyethylene alkyl ether and polyoxyethylene sorbitan fatty acid partial ester. If necessary, a molecular weight modifier such as trichloroethylene or thioglycol can be used. The above-mentioned polymerization initiator, vinyl chloride and other monomers, suspending agents, emulsifiers, molecular weight modifiers, etc. may be added to the polymerization system all at once, or may be added separately during the polymerization. You can also do it. The polymerization is usually carried out at a temperature of 35 to 80 ° C with stirring.

The vinyl chloride copolymer thus obtained is, like the ordinary vinyl chloride-based resin binder for magnetic paints, generally a polyurethane resin, a curing agent typified by polyisocyanate and an optional solvent solution together with magnetic powder. And prepared for use.

Typical examples of the polyurethane resin include those obtained by reacting polyester polyols or polyether polyols with isocyanates,
Particularly, those having a residual hydroxyl group are preferable. Also, if desired, vinyl chloride-vinyl acetate copolymer resin, fibrin resin, phenoxy resin, epoxy resin, butyral resin,
Ordinary resin binders for magnetic paints such as acrylic resins and acrylonitrile-butadiene rubber can be used together within the range in which the object of the present invention is achieved.

Further, as the magnetic powder, γ-Fe ₂ O ₃ , Fe ₃ O ₄ , Co-containing γ-
In addition to iron oxide powders such as Fe ₂ O ₃ and Co-containing Fe ₃ O ₄ and CrO ₂ powders, metallic magnetic powders such as Fe powders and Fe—Co powders are also used.

In the resin according to the present invention, as the hydroxyl group-containing component,
By changing the above-mentioned hydroxyl group in place of the saponified vinyl acetate portion to the above-mentioned hydroxyl group, the reactivity with isocyanate can be greatly improved, whereby the hydroxyl group required for the reaction can be greatly reduced. Although the reason for this is not clear, the hydroxyl groups participating in the reaction are separated from the main chain of the copolymer and the degree of freedom is increased,
And that the distribution of hydroxyl groups is uniform.

The mechanism of the dramatic improvement in magnetic powder dispersibility is considered to be due to the decrease in the interaction between the carboxyl group and the hydroxyl group, since the reactivity is achieved with a smaller amount of the hydroxyl group, and the dispersion stability of the magnetic paint is stable. It is considered that the high activity is also due to the small interaction with the fatty acid commonly used as a lubricant.

The present invention will be specifically described below with reference to examples. The parts and percentages in each example are based on weight.

Example 1 Acetone (180 parts) and benzoyl peroxide (2 parts) were charged into an autoclave. After deaeration, 100 parts of vinyl chloride and 3 parts of glycerin monoallyl ether were charged. Then, after the polymerization was started at a temperature of 50 ° C., immediately, 3 parts of maleic anhydride, 10 parts of vinylidene chloride and 40 parts of methanol were sufficiently mixed in advance and continuously injected into an autoclave, and the reaction pressure was 1 kg / Unreacted vinyl chloride was recovered at a point of cm ^2, and 250 parts of water was added and heated to 70 ° C. to separate the solvent and the copolymer and then dried to obtain a resin A. This resin was evaluated for suitability for a magnetic recording medium by the test method of evaluation of resin properties (1) described below.

Example 2 120 parts of methanol, 120 parts of deionized water, methyl cellulose
0.6 parts, sodium lauryl sulfate 0.2 parts, lauroyl peroxide 1.
Charge 2 parts into an autoclave, and after degassing, vinyl chloride 100
Parts, vinyl acetate 8 parts, allyl-2-hydroxyethyl ether 5 parts, and itaconic acid 3 parts. Then, when the polymerization was started at 60 ° C. and reached 3 kg / cm ² , unreacted vinyl chloride was recovered, and the copolymer was recovered by deliquoring the liquid, washed with cold water and dried to obtain a resin B. This resin was evaluated by the test method of resin property evaluation (1).

Example 3 Resin C was obtained in the same manner as in Example 2 except that allyl-2-hydroxy-3-chloropropyl ether was used instead of allyl-2-hydroxyethyl ether.
This resin was evaluated by the test method of resin property evaluation (1).

Example 4 150 parts deionized water, 1 part azobisisobutyronitrile,
1 part of polyoxyethylene stearyl ether and 0.1 part of methyl cellulose were charged into an autoclave, and after degassing, 60 parts of vinyl chloride, 2 parts of allyl-2-hydroxypropyl ether, 2 parts of monomethyl maleate and 8 parts of vinyl acetate were charged. Then, the polymerization was started at 60 ° C., and 40 parts of vinyl chloride was continuously injected into the autoclave for 3 to 7 hours after the start of the polymerization, and when the autoclave pressure reached 3 kg / cm ² , The reaction vinyl chloride was recovered, dehydrated, washed with deionized water and dried to obtain a resin D. This resin was evaluated by the test method of resin property evaluation (1).

Example 5 Resin E was obtained in the same manner as in Example 4 except that allyl-6-hydroxyhexyl ether was used instead of allyl-2-hydroxypropyl ether. This resin was evaluated by the test method of resin property evaluation (1).

Comparative Example 1 Resin F was obtained in the same manner as in Example 1 except that 2-hydroxyethyl methacrylate was used instead of glycerin monoallyl ether. This resin was evaluated by the test method of resin property evaluation (1).

Comparative Example 2 180 parts of acetone and 2 parts of benzoyl peroxide were charged into an autoclave, and after deaeration, 100 parts of vinyl chloride and 10 parts of isobutyl vinyl ether were charged. Then, after starting the polymerization at 55 ° C, immediately 4.5 parts of acrylic acid, 1.5 parts of water, and 44 parts of methanol
Part of the liquid mixture and 2-hydroxyethyl methacrylate 5
Part, a mixed solution of 45 parts of methanol continuously from separate inlets, respectively, until the autoclave pressure reaches 2.0 kg / cm ² , the total amount is injected, and when the pressure reaches 1.0 kg / cm ² ,
Unreacted vinyl chloride was recovered, 250 parts of deionized water was added and heated to separate the solvent and the copolymer, and then dried to obtain a resin G. This resin was evaluated by the test method of resin property (1).

Comparative Example 3 Example 4 except that hydroxypropyl methacrylate was used instead of allyl-2-hydroxypropyl ether.
Resin H was obtained in the same manner as described above. This resin was evaluated by the test method of resin property (1).

Comparative Example 4 A resin I was obtained in the same manner as in Comparative Example 2 except that 20 parts of 2-hydroxyethyl metal relate was used and isobutyl vinyl ether was not used. This resin was evaluated by the test method of resin property (1).

Comparative Examples 5-7 180 parts of acetone and 2 parts of benzoyl peroxide were charged into an autoclave, and after deaeration, 50 parts of vinyl chloride and 20 parts of vinyl acetate were charged. Then, the polymerization was started at 55 ° C., and vinyl chloride was injected 10 times at a rate of 0.5 kg / cm ² every time the pressure in the autoclave was lowered by 5 times, for a total of 50 parts injection. On the other hand, immediately after the start of the polymerization, 5 parts of maleic anhydride and 45 parts of methanol were continuously injected into the autoclave, and the pressure of the autoclave was 1 kg / cm.
^When it reached ² , unreacted vinyl chloride was recovered. Next, the reaction solution was added to a mixed solution of 1000 parts of methanol and 6 parts of 65% nitric acid, and the mixture was heated and stirred at 70 ° C for 12 hours, and then 10
Copolymer was separated and recovered from the medium by adding 00 parts of deionized water. Thereafter, 500 parts of acetone and the copolymer were stirred and mixed at 60 ° C., 1000 parts of methanol was added, the copolymer was separated and recovered, further washed with water and dried to obtain a resin J. This resin was evaluated by the test method of resin property evaluation (1).

The compositions of these copolymers are shown in Table 1 together with a commercially available vinyl chloride-vinyl acetate-maleic acid terpolymer (K) and vinyl chloride-vinyl acetate-vinyl alcohol (L). The% of carboxy groups in the copolymer was determined by titration, and the% of hydroxyl groups was determined by infrared absorption analysis.

(Evaluation of Resin Properties (1)) Next, the samples obtained in Examples 1 to 5 and Comparative Examples 1 to 7 were evaluated as magnetic paints and magnetic recording media by the following method. The results are shown in Table 1.

1) Pot life 100 parts of vinyl chloride copolymer, 200 parts of methyl ethyl ketone
Polyisocyanate (Nippon Polyurethane Industry Co., Ltd.) was dissolved in a mixed solvent consisting of 100 parts of methyl isobutyl ketone and 100 parts of toluene with stirring at 65 ° C. for 1 hour.
Manufactured by Coronate L) per 100 parts of vinyl chloride copolymer
The pot life was defined as the number of days until the solution did not flow even when the container was turned upside down and stored at 23 ° C.

2) Reactivity The sheet obtained by casting the solution used in the pot life test on a glass plate is treated at 60 ° C for 24 hours. This sheet 0.
5 g is precisely weighed and mixed with 50 gr tetrahydrofuran for 24 hours, then the insoluble matter is filtered and washed, dried and precisely weighed.

Gel fraction = weight of insoluble matter / weight of sample (%) 3) Thermal stability The solution used in the pot life test was cast on a glass plate that was kept horizontal with a level, and a sheet 0.2 mm thick Then, this is heated in an oil bath at 80 ° C. according to JIS-K-6723, and the time until the Congo red paper is discolored is measured.

4) Gloss 400 parts of cobalt-coated magnetic iron oxide powder (non-surface area 30m ² /
g), vinyl chloride copolymer 50 parts, polyurethane resin (hydroxyl content 0.3%, 1,4-butanediol adipate-MDI system molecular weight 70,000) 40 parts, methyl ethyl ketone 500 parts, methyl isobutyl ketone 300 parts, toluene 300 parts, carbon A mixture consisting of 2 parts of black, 4 parts of alumina, 2 parts of myristic acid, and 1 part of butyl stearate was subjected to high-speed shear dispersion for 90 minutes, and then 15 parts of polyisocyanate (Coronate L manufactured by Nippon Polyurethane Industry Co., Ltd.) was added. It was dispersed for 15 minutes to obtain a magnetic paint. The obtained magnetic coating material was applied onto a polyester film so that the coating film thickness would be 5 μm, subjected to magnetic field orientation treatment, and then dried. Use a gloss meter to measure the magnetic coating 60
The reflectance at the angle of reflection was measured.

5) Dispersion-stabilized product After the coating material used for gloss evaluation was allowed to stand for 1 hour, it was coated on a polyester film so that the coating film thickness was 5 μm.
After magnetic field orientation treatment, it was dried, and the magnetic coating film was measured for reflectance at a 60 ° reflection angle using a gloss meter.

6) Squareness ratio (Br / Bm) The magnetic coating film used for evaluation of glossiness was cut out into 12.5 mm x 50 mm and measured by a magnetic property measuring machine.

7) Durability The magnetic coating used for gloss evaluation was smoothed with a calender roll and then heat-treated at 65 ° C for 65 hours.
And touch the rotating drum with abrasive paper on it,
It was rotated at 0 rpm, and the extent to which the magnetic coating adhered to the abrasive paper was visually observed, and the measurement was carried out at three levels of A, B, and C.

A: No dirt, B: Some dirt, C: Many dirt Example 6 A polymerization vessel was charged with 117 parts of methanol, 0.6 parts of methyl cellulose, and 0.2 parts of polyoxyethylene sorbitan fatty acid partial ester, which was then sealed and degassed under reduced pressure, and then 100 parts of vinyl chloride, 10 parts of vinyl acetate, and allyl-2-hydroxy. 6 parts of propyl ether was charged and stirred at 50 ° C. Thereafter, 0.6 part of 3,5,5-trimethylhexanoyl peroxide was charged to start the polymerization, and at the same time, 8 parts of 3 parts of 2-acrylamido-2-methylpropanesulfonic acid dissolved in 80 parts of methanol was added.
It was continuously charged at a constant speed so that the entire amount was consumed in time. After the reaction for 10 hours, the polymerization vessel was cooled at a pressure of 2 kg / cm ^2, and unreacted vinyl chloride was recovered, then, deliquored, washed and dried to obtain a resin (N). This resin was evaluated for suitability for a magnetic recording medium by the test method of resin property evaluation (2) described below.

Example 7 A resin (O) was obtained in the same manner as in Example 6 except that 2-methacrylic acid-2-ethyl phosphate was used instead of 2-acrylamido-2-methylpropanesulfonic acid. This resin was evaluated by the test method of evaluation of resin characteristics (2).

Example 8 A resin (P) was obtained in the same manner as in Example 6 except that sodium styrenesulfonate was used instead of 2-acrylamido-2-methylpropanesulfonic acid. This resin was evaluated by the test method of evaluation of resin characteristics (2).

Example 9 A resin (Q) was obtained in the same manner as in Example 6 except that eugenol was used instead of allyl-2-hydroxyethyl ether. This resin was evaluated by the test method of evaluation of resin characteristics (2).

Example 10 In a polymerization vessel, acetone 180 ° C., deionized water 70 parts, lauroyl peroxide 2 parts, allyl-2-hydroxy-3-chloropropyl ether 6 parts, 3-allyloxy-2-hydroxypropane ammonium sulfate 10 parts, isobutyl. Charge 10 parts of vinyl ether, and after degassing, charge 100 parts of vinyl chloride.
The temperature was raised to 5 ° C. When the polymerization pressure reached 3 kg / cm ² , unreacted vinyl chloride was recovered under reduced pressure, the reaction solution was mixed with 1000 parts of deionized water, the resin was separated, and dried to obtain a resin (R).

Example 11 A polymerization vessel was charged with 150 parts of deionized water, 1 part of sodium lauryl sulfate and 1 part of potassium persulfate, and after deaeration, 60 parts of vinyl chloride, 3 parts of vinyl acetate and 3 parts of isobutyl vinyl ether.
And 6 parts of allyl-2-hydroxypropyl ether were charged and the temperature was raised to 60 ° C. to initiate polymerization. After the initiation of the polymerization, a mixed solution of 2 parts of sodium styrenesulfonate and 50 parts of water was continuously injected for 10 hours, while 40 parts of vinyl chloride was divided into 4 parts and reacted for 10 hours, and then unreacted vinyl chloride was added. A polymer solution was obtained by collecting. 100 parts of this polymerization liquid was mixed with 5 parts of methyl ethyl ketone, frozen and thawed, and the polymer was collected, washed, and dried to obtain a resin (S). This resin was evaluated by the test method of the resin property evaluation method (2).

Comparative Example 8 2 without using allyl-2-hydroxypropyl ether
A resin (T) was obtained in the same manner as in Example 6 except that 8 parts of -hydroxypropyl methacrylate and 3 parts of 2-acrylamido-2-methylpropanesulfonic acid were charged during the reaction. This resin is used to evaluate resin properties (2)
The test method was evaluated.

Comparative Example 9 A resin (U) was obtained in the same manner as in Comparative Example 8 except that propyl methacrylate was used instead of 2-hydroxypropyl methacrylate. This resin was evaluated by the test method of the resin property evaluation method (2).

Comparative Example 10 A resin (V) was obtained in the same manner as in Example 6 except that 2-acrylamido-2-methylpropanesulfonic acid was not used. This resin was evaluated by the test method of the resin property evaluation method (2).

Comparative Example 11 100 parts of a commercially available vinyl chloride-vinyl acetate-vinyl alcohol copolymer (composition: 91% by weight of vinyl chloride, 3% by weight of vinyl acetate, 6% by weight of vinyl alcohol), 10 parts of sodium 2-chloroethylsulfonate and 500 parts of dimethylformamide were mixed by stirring at 20 ° C., 5 parts of pyridine was added dropwise to this mixed solution little by little, and stirring and mixing was continued for 3 hours.
The obtained reaction liquid was mixed with 5000 parts of deionized water to recover the resin, which was dissolved in tetrahydrofuran, reprecipitated with methanol, and dried to obtain a resin (W). This resin was evaluated by the test method of the resin property evaluation method (2).

Comparative Examples 12 to 14 Acetone 180 parts, benzoyl peroxide 2 parts, vinyl acetate 25
Parts were charged into a polymerization vessel, deaerated, charged with 50 parts of vinyl chloride and started polymerization at 55 ° C., and then a mixed solution of 3 parts of sodium styrenesulfonate and 17 parts of deionized water was continuously and at a constant rate. While injecting over 8 hours, 50 parts of vinyl chloride was charged in 4 portions and reacted for 10 hours, and then unreacted vinyl chloride was recovered to obtain a polymerization solution. 300 parts of methanol and 6 parts of 65% nitric acid were added to this polymerization liquid, and the mixture was heated and stirred at 80 ° C. for 12 hours, and then 1000 parts of deionized water was added to separate the resin. Further, 400 parts of acetone and 5 parts of propion oxide were added, mixed at 60 ° C. for 2 hours and then mixed with 1000 parts of methanol, and the mixture was dehydrated and dried to obtain a resin (X). This resin was evaluated by the test method of the resin property evaluation method (2).

The properties of these resins are the commercially available vinyl chloride-vinyl acetate-
It is shown in Table 2 together with the maleic acid terpolymer (Y) and the vinyl chloride-vinyl acetate-vinyl alcohol terpolymer (Z). The amount of hydroxyl groups in the resin was determined by infrared absorption analysis, the amount of vinyl chloride was determined by quantification of chlorine by combustion, and the strong acid radicals were determined by both elemental analysis and infrared absorption analysis.

(Evaluation of Resin Properties (2)) Next, each resin obtained in Examples 6 to 11 and Comparative Examples 8 to 14 was subjected to evaluation as a magnetic paint and a magnetic recording medium. The results are shown in Table 2. The evaluation method was as follows.

1) Solubility 100 parts of vinyl chloride copolymer, 200 parts of methyl ethyl ketone,
A solution consisting of 200 parts of toluene was prepared, and the degree of transparency of this solution was visually inspected and judged by three levels of A, B, and C.

A: Transparent, B: Insoluble matter low, C: Insoluble matter high 2) Thermal stability 1.0g of vinyl chloride copolymer was placed in a 15cc test tube and the opening was plugged with absorbent cotton with Congo Red test paper sandwiched between them. The sample was placed in an oil bath at 150 ° C., and the time until the Congo red test paper was discolored by the generated hydrochloric acid was measured.

3) Dispersion stability A mixture of 400 parts of metallic iron magnetic powder, 100 parts of vinyl chloride copolymer, 300 parts of methyl ethyl ketone, 300 parts of methyl isobutyl ketone, and 300 parts of toluene was subjected to high speed shear dispersion for 90 minutes. The dispersion paint was sampled in a sample bottle and stored in a thermostat at 25 ° C., and the state of gel generation was observed. Whether or not the gel was generated was determined by taking out a part of the dispersion paint on a glass plate, diluting it with about 5 times the amount of methyl ethyl ketone, mixing it with a glass rod, and visually observing. A, B, and C are shown in order of least gel formation.

4) Gloss 400 parts of metallic iron magnetic powder, 70 parts of vinyl chloride copolymer, polyurethane resin (Nipporan manufactured by Nippon Polyurethane Industry Co., Ltd.)
2304) 30 parts, 300 parts of methyl ethyl ketone, 300 parts of methyl isobutyl ketone, 300 parts of toluene, 4 parts of higher fatty acid, and 2 parts of silicone oil are subjected to high speed shear dispersion for 90 minutes and then polyisocyanate (manufactured by Nippon Polyurethane Industry Co., Ltd.). Coronate L) 15 parts and cyclohexanone 100
Parts were added and further dispersed for 90 minutes to obtain a magnetic paint. The obtained magnetic coating material was applied onto a polyester film so that the coating film thickness would be 5 μm, subjected to magnetic field orientation treatment, and then dried. The reflectance at 60 ° reflection angle of the magnetic coating film was measured using a gloss meter.

5) Squareness ratio (Br-Bm) The magnetic coating film used for evaluation of glossiness was cut out into 12.5 mm x 50 mm and measured by a magnetic property measuring machine.

6) Durability The magnetic coating used for gloss evaluation was smoothed with a calender roll and then heat-treated at 65 ° C for 65 hours.
And contact it with the rotary drum with abrasive paper attached,
It was rotated at 150 rpm, and the extent to which the magnetic paint adhered to the abrasive paper was visually inspected, and it was judged in four stages of A, B, C and D.

A: No stain, B: Slight stain, C: Slight stain, D: Dirty lot 7) Runability In the same way as the durability evaluation, the force generated between the coating film and the rotating drum was 65 ° C and relative humidity. It was measured with a U gauge in an atmosphere of 80%, and judged in three stages of A, B, and C in order of decreasing running resistance.

A: Low, B: Medium, C: High

 ─────────────────────────────────────────────────── --Continued from the front page (56) References JP-A-60-235814 (JP, A) JP-A-60-206876 (JP, A)

Claims (2)

[Claims] 1. At least one component of a binder of magnetic powder is a copolymer of vinyl chloride containing a hydroxyl group and a carboxylic acid group or a strong acid radical containing sulfur or phosphorus, and the monomer supplying the hydroxyl group is a polyhydroxy compound. A magnetic paint characterized by being a monoallyl ether of. 2. At least one component of the binder of the magnetic powder is a vinyl chloride copolymer containing a hydroxyl group and a carboxylic acid group or a strong acid radical containing sulfur or phosphorus, and the monomer supplying the hydroxyl group is a polyhydroxy compound. A magnetic recording medium characterized by using a magnetic coating material which is a resin of monoallyl ether as described above.