JPH0255843B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention is a vinyl chloride resin for magnetic paint (hereinafter referred to as
PVC), particularly PVC used as a binder for magnetic recording media. Generally, magnetic recording media such as magnetic tapes and floppy disks are manufactured by coating a polymer film or sheet with a magnetic paint in which ferromagnetic powder is dispersed in an organic solvent using an organic polymer as a binder. There is. The organic polymer in this magnetic paint is usually
Relatively hard resins such as PVC, polyvinyl butyral, nitrocellulose, and acetylcellulose are often used in combination with soft materials such as polyester, polyurethane, and acrylonitrile butadiene copolymers. Polyisocyanate compounds are often used as thermosetting components for the purpose of improving properties. Therefore, the characteristics of the resin used as a binder include appropriate compatibility with other polymers and reactivity with polyisocyanate.
It is required to work well with magnetic particles and disperse them uniformly into the paint. In recent years, with the increase in the recording density of magnetic recording media and the demand for improved S/N ratios, magnetic particles have become finer and have higher coercive force. In order to form a highly magnetic layer and achieve the above-mentioned improvement in performance as a medium, the dispersion performance of the binder is a decisively important factor. Until now, it has been customary to use a low-molecular-weight surfactant as a dispersant to improve the dispersion of magnetic particles. Therefore, there is a natural limit to the amount of binder that can be used, and furthermore, from the viewpoint of improving the reliability of magnetic recording media, the binder itself is required to have a high degree of dispersion ability. On the other hand, in order to increase the durability and reliability of the media, it is commonly used, especially in recording magnetic tapes, to crosslink the magnetic layer by incorporating a curable compound, typically 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 will be short and uneconomical, and if the reactivity is too slow, the expected improvements in durability and runnability will not be seen. The present inventor conducted an evaluation on PVC to improve the binder that can meet the high performance of magnetic recording media, and found that the vinyl chloride-vinyl alcohol-vinyl acetate copolymer As the ratio of vinyl alcohol increases, the dispersion performance of magnetic particles improves, but the degree of improvement is low and requires the help of a dispersant.In addition, as the amount of vinyl alcohol increases, the pot life becomes shorter and the moisture resistance of the coating film decreases. , the rate of thermal decomposition also becomes faster. On the other hand, vinyl chloride-maleic acid-vinyl acetate copolymer strongly adsorbs to magnetic particles and exhibits excellent dispersion ability, but the paint tends to thicken and gel, and reactions with polyisocyanate tend to occur locally. It is. In an attempt to solve the problems of these typical PVC binders, vinyl chloride-vinyl alcohol-vinyl acetate-maleic acid copolymer has been proposed; Although it has both the reactivity of the coalescence 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, but the polymer deteriorates during saponification and thus 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, When an isocyanate compound is added, the pot life becomes short.On the other hand, if the copolymerized amount of hydroxyethyl acrylate is reduced to an appropriate pot life, the solubility in the solvent decreases, and the solution becomes more likely to gel and thicken. . Containing these conventional alcoholic hydroxyl groups
As a result of intensive studies on how to solve the problems of PVC, we found that a vinyl chloride multi-component copolymer containing specific amounts of carboxylic acid groups and specific hydroxyl groups showed better dispersibility of magnetic particles than expected. The copolymer has good reactivity with polyisocyanate despite its hydroxyl group content, and has excellent chemical thermal stability.Furthermore, this copolymer can be used as a binder and polyisocyanate as a curing agent to form magnetic particles. It was confirmed that a magnetic recording medium obtained by coating a polyester film with a dispersed paint exhibits excellent magnetic properties, electromagnetic conversion properties, and durability, and the present invention was completed. That is, in the present invention, the carboxylic acid group is 0.3 to 5.0% by weight, the hydroxyl group based on the -X-OH group (X is an organic residue) is 0.1 to 2.0% by weight, and the equivalent ratio of the hydroxyl group and the carboxylic acid group is 0.1 to 3.0, the copolymerization ratio of the monomer supplying the carboxylic acid group or the hydroxyl group and other monomers other than vinyl chloride is 3 to 20% by weight. The present invention relates to a resin for magnetic paint, characterized in that the present invention has an average degree of polymerization of 200 to 900. Examples of unsaturated carboxylic acid monomers that provide carboxylic acid groups to the copolymer of the present invention include unsaturated mono- or dicarboxylic acids such as acrylic acid, methacrylic acid, laleic acid, itaconic acid, and crotonic acid, maleic acid, and itaconic acid. Monoalkyl esters of unsaturated dicarboxylic acids, such as, can be used. This monomer contains 0.3 to 5.0% by weight of carboxylic acid groups in the copolymer.
It is used within the range. If it is less than this, the magnetic powder and dispersibility will be poor, and if it is more than this, the paint will tend to gel and thicken. -X-OH in the vinyl chloride copolymer of the present invention
Examples of X constituting the group include C _o H _2o , OC _o H _2o ,
Organic residues typified by COOC _o H _2o and CONHC _o H _2o (n is an integer from 1 to 4) can be mentioned. Examples of unsaturated alcohol monomers that provide the copolymer with hydroxyl groups based on -X-OH groups include:
α,β-unsaturated acids such as (meth)acrylic acid-2-hydroxyethyl ester and (meth)acrylic acid-2-hydroxypropyl ester have 2 carbon atoms.
to 4 alkanol esters, alkanol esters of unsaturated dicarboxylic acids such as mono-2-hydroxypropyl maleate, di-2-hydroxypropyl maleate, mono-2-hydroxybutyl itaconate, 3-butene-1 -ol, olefinic alcohols such as 5-hexen-1-ol, alkanol vinyl ethers such as 2-hydroxyethyl vinyl ether, 2-hydroxypropyl vinyl ether, N
- Acrylamides such as methylol acrylamide and N-methylol methacrylamide. The amount of these unsaturated alcohols used is such that the amount of hydroxyl groups in the copolymer is 0.1 to 2.0% by weight. If it is less than 0.1% by weight, the crosslinking effect with the polyisocyanate will not be exhibited, and if it exceeds 2.0% by weight, the pot life will be too short. In addition, the equivalent ratio of hydroxyl group and carboxylic acid group is 0.1
-3.0; if this ratio exceeds 3.0, the dispersibility of the magnetic powder will decrease significantly, and if it is less than 0.1, there will be no effect of adding the unsaturated alcohol. Note that the carboxylic acid groups and hydroxyl groups in the copolymer of the present invention can be formed by copolymerization by using, for example, an unsaturated carboxylic acid anhydride and glycols instead of the above-mentioned unsaturated carboxylic acids and unsaturated alcohols. It may be introduced by obtaining a copolymer while producing an alkanol ester of an unsaturated carboxylic acid during the reaction. Examples of other comonomers include vinyl acetate,
Carboxylic acid vinyl esters such as vinyl propionate; vinyl ethers such as methyl vinyl ether, isobutyl vinyl ether, and cetyl vinyl ether; vinylidenes such as vinylidene chloride and vinylidene fluoride; diethyl maleate, dibutyl maleate, diethyl itaconate, and methyl (meth)acrylate. , unsaturated carboxylic acid alkyl esters such as ethyl (meth)acrylate; and olefins such as ethylene and propylene. This comonomer is used for the purpose of improving the solubility of the copolymer while controlling the compatibility and softening point of the copolymer and other resin when the two are mixed. However, the amount used is 3 to 20% by weight in the copolymer. If it exceeds 20% by weight, not only will it be difficult for the paint to separate from the solvent, but the softening point of the copolymer will be low, and the heat-resistant running properties of the magnetic recording medium will tend to deteriorate. Moreover, if it is less than 3% by weight, no effect of improving solubility will be exhibited. The degree of polymerization of the copolymer is 200 to 900, preferably 250
~500. If it is less than 200, the abrasion resistance of the magnetic layer is insufficient, and if it exceeds 900, the viscosity of the paint is high and the dispersion of magnetic particles tends to be insufficient. The resin for magnetic coatings of the present invention can be produced using any known polymerization method, but from the viewpoint of polymer solubility, solution polymerization, methanol as a polymerization medium, etc.
Lower alcohol such as ethanol alone or
Preferably, it is produced by a suspension polymerization process using a combination of this and deionized water. Examples of the polymerization initiator used in the production of the resin include lauroyl peroxide, diisopropyl peroxydicarbonate, di-2-ethylhexyl peroxydicarbonate, t-butylperoxypivalate,
Examples include organic peroxides such as 3,3,5-trimethylhexanoyl peroxide, azo compounds such as α,α'-azobisisobutyronitrile, ammonium persulfate, potassium persulfate, and the like. Suspending agents include, for example, polyvinyl alcohol, partially saponified polyvinyl acetate, cellulose derivatives such as methylcellulose, polyvinylpyrrolidone, maleic anhydride-vinyl acetate copolymer, synthetic polymeric substances such as polyacrylamide, and starch. Examples include natural polymeric substances such as gelatin. Examples of the emulsifier include anionic emulsifiers such as sodium alkylbenzenesulfonate and sodium lauryl sulfate, and nonionic emulsifiers such as polyoxyethylene alkyl ether and polyoxyethylene sorbitan fatty acid partial ester. Further, a molecular weight regulator such as trichlorethylene or thioglycol can also be used if necessary. The above-described polymerization initiator, vinyl chloride and other monomers, suspending agents, emulsifiers, molecular weight regulators, etc. may be added to the polymerization system all at once at the start of polymerization, or they may be added in portions during polymerization. You can also do that. Polymerization is usually carried out at a temperature of 35-80°C with stirring. The vinyl chloride copolymer obtained in this way is generally used as a vinyl chloride resin binder for magnetic paints, and is generally used in an arbitrary solvent solution together with a polyurethane resin, a curing agent typified by polyisocyanate, and magnetic powder. It is prepared and ready for use. Typical examples of polyurethane resins include those obtained by reacting polyester polyols or polyether polyols with isocyanates, and those with residual hydroxyl groups are particularly preferred. In addition, vinyl chloride-
Usual resin binders for magnetic coatings, such as vinyl acetate copolymer resin, cellulose resin, phenoxy resin, epoxy resin, butyral resin, acrylic resin, and acrylonitrile-butadiene rubber, may be used in combination within the range where the object of the present invention is achieved. It is also possible to do so. In addition, magnetic powders include γ-Fe ₂ O ₃ , Fe ₃ O ₄ ,
In addition to iron oxide powders such as Co-containing γ-Fe ₂ O ₃ and Co-containing Fe ₃ O ₄ and CrO ₂ powder, metallic powders such as Fe powder and Fe-Co powder are also used. In the present invention, as a hydroxyl group-containing component, the above-mentioned -X-
By changing to OH, the reactivity with isocyanate can be greatly improved, thereby making it possible to significantly reduce the number of hydroxyl groups required for the reaction. Although the reason for this is not clear, it is thought that the hydroxyl groups participating in the reaction are separated from the main chain of the copolymer, increasing the degree of freedom, and that the distribution of the hydroxyl groups is uniform. Note that it is difficult to explain the mechanism of the dramatic improvement in dispersibility. The present invention will be specifically explained below using examples. Note that the number of parts and percentages in each example are based on weight. In addition, the evaluation of the resin for magnetic coatings was based on the following. (1) Solubility 100 parts of vinyl chloride copolymer was stirred and dissolved in a mixed solvent consisting of 200 parts of methyl ethyl ketone, 100 parts of methyl isobutyl ketone, and 100 parts of toluene at 65°C for 1 hour, and the degree of transparency of the solution was visually observed. It was judged on a three-level scale of 〇△×. (2) Potlife: 20 parts of polyisocyanate (Coronate L, manufactured by Nippon Polyurethane Industries, Ltd.) was added to the solution used for the solubility test per 100 parts of vinyl chloride copolymer.
The pot life was defined as the number of days until the solution no longer flowed even when the solution was stored at ℃ and the container was turned upside down. (3) Thermal stability The solution used in the solubility test was cast onto a glass plate kept horizontal with a spirit level to form a 0.2 mm thick sheet, which was then heated in a gear oven at 120°C. Measure the time until blackening. (4) Glossiness 400 parts of cobalt-coated magnetic iron oxide powder (specific surface area
30m ² /g), 60 parts of vinyl chloride copolymer, polyurethane resin (Nitsuporan manufactured by Nippon Polyurethane Industries Co., Ltd.)
After dispersing a mixture of 40 parts of 2304), 300 parts of methyl ethyl ketone, 300 parts of methyl isobutyl ketone, 300 parts of toluene, and 4 parts of lecithin under high-speed shearing for 90 minutes, 15 parts of polyisocyanate (Coronate L manufactured by Nippon Polyurethane Industries, Ltd.) was dispersed. was added and dispersed for an additional 15 minutes to form a magnetic paint. The obtained magnetic paint was applied onto a polyester film to a film thickness of 5 μm, subjected to magnetic field orientation treatment, and then dried. The reflectance of the magnetic coating film at a 60° reflection angle was measured using a gloss meter. (5) Squareness ratio (Br/Bm) The magnetic coating used for gloss evaluation was 12.5 mm x 50
It was cut into mm pieces and measured using a magnetic property measuring machine. (6) Durability The magnetic coating used for gloss evaluation was smoothed with a calender roll, heated at 65℃ for 65 hours, and then brought into contact with a rotating drum covered with abrasive paper under a load of 100g. , Rotate at 150 rpm and visually check the extent to which the magnetic paint adheres to the abrasive paper.〇△×
Judgment was made in three stages. (7) Running performance During durability evaluation, the force generated between the coating film and the rotating drum is measured using a U-gauge, and the running resistance is evaluated in three stages: ○△× in descending order of running resistance. Example 1 100 parts of vinyl chloride, 10 parts of 3-buten-1-ol
180 parts of acetone, and 2 parts of benzoyl peroxide were placed in an autoclave, and after degassing, polymerization was started at a temperature of 50°C. Immediately after, 5 parts of maleic anhydride, 5 parts of vinylidene chloride, and 40 parts of methanol were thoroughly mixed in advance. The resulting mixture was continuously injected into an autoclave, and when the reaction pressure reached 1 Kg/cm ² , unreacted vinyl chloride was collected, 250 parts of water was added, and the mixture was heated to 70°C and copolymerized with the solvent. The copolymer was separated and dried to obtain copolymer A. Example 2 100 parts of vinyl chloride, isobutyl vinyl ether
10 parts of acrylic acid, 180 parts of acetone, and 2 parts of benzoyl peroxide were placed in an autoclave, and after degassing, polymerization was started at 55°C. Continuously inject a mixture of 5 parts of ethyl methacrylate and 45 parts of methanol from separate injection ports until the pressure of the autoclave reaches 2.0 Kg/cm ² , and then further increases the pressure to 1.0 Kg/cm ² . At that time, unreacted vinyl chloride was collected, 250 parts of deionized water was added and heated to separate the solvent and copolymer, and then dried to obtain copolymer B. Example 3 100 parts of vinyl chloride, 18 parts of vinyl acetate, 3 parts of itaconic acid, 180 parts of methanol, 60 parts of deionized water, 0.6 parts of methyl cellulose, 0.2 parts of polyoxyethylene sorbitan fatty acid ester, 0.35 parts of trichlorethylene, 3,3, Charge 0.42 parts of 5-trimethylhexanoyl peroxide into an autoclave,
After degassing, polymerization was started at 58°C, and 2-
A mixed solution of 3 parts of hydroxyethyl methacrylate and 20 parts of methanol was continuously injected into the autoclave, and the injection was finished when the pressure of the autoclave reached 5 Kg/cm ² . After that, when the pressure of the autoclave reached 3 Kg/cm ² , unreacted vinyl chloride was recovered, the copolymer was recovered by dehydration, washed with cold water, and dried to obtain copolymer C. . Example 4 100 parts of vinyl chloride, 14 parts of vinyl acetate, 4 parts of 2-hydroxyethyl vinyl ether, 6 parts of diethyl maleate, 3 parts of itaconic acid, 120 parts of methanol,
120 parts of deionized water, 0.6 parts of methyl cellulose, 0.2 parts of sodium lauryl sulfate, 0.05 parts of 2-mercaptoethanol, and 0.70 parts of lauroyl peroxide were placed in an autoclave, and after degassing, polymerization was started at 60°C.
Kg/ ^cm2 , add a solution of 0.05 parts of bisphenol A dissolved in 0.2 parts of methanol to recover unreacted vinyl chloride, remove the liquid to recover the copolymer, and wash with cold water. Sample D was obtained by drying. Example 5 Maleic anhydride 2 in a degassed autoclave
After adding 100 parts of vinyl chloride and stirring and mixing at room temperature, add 20 parts of propylene glycol and heat at 58℃ for 4 hours.
Mixed for an hour. To this, 10 parts of vinyl acetate, 3,5,
0.5 part of 5-trimethylhexanoyl peroxide,
Methyl cellulose 0.6 part, polyoxyethylene sorbitan fatty acid ester 0.2 part, methanol 150
50 parts of deionized water was added to start polymerization, and when the pressure of the autoclave reached 3 kg/cm ² , unreacted vinyl chloride was collected, dehydrated, washed with water and dried to obtain copolymer E. Obtained. Example 6 100 parts of vinyl chloride, 11 parts of vinyl acetate, 4 parts of itaconic acid, 180 parts of methanol, 60 parts of deionized water, 0.6 parts of methyl cellulose, 0.2 parts of polyoxyethylene sorbitan fatty acid ester, 0.33 parts of trichlorethylene, 3,3, Charge 0.42 parts of 5-trimethylhexanoyl peroxide into an autoclave,
After degassing, polymerization was started at 58°C, and a mixture of 3 parts of N-methylolacrylamide and 20 parts of methanol was continuously injected into the autoclave until the pressure of the autoclave reached 5 kg/cm ² . finished. After that, when the pressure of the autoclave reached 3Kg/cm ² , unreacted vinyl chloride was collected, the liquid was removed, the copolymer was collected, and the copolymer was washed with cold water and dried to obtain copolymer F. Obtained. Comparative Example 1 Copolymer G was obtained in the same manner as in Example 2 except that isobutyl vinyl ether was not used. Comparative Example 2 Copolymer H was obtained in the same manner as in Example 2 except that 2-hydroxyethyl methacrylate was used as 20 parts and that isobutyl vinyl ether was not used. Comparative Example 3 Polymerization was carried out in the same manner as in Example 3, except that 15 parts of itaconic acid was used. Even after 25 hours had passed since the start of polymerization, the pressure in the autoclave had only decreased to 6.5 kg/cm ² , but at this point the reaction was stopped, the polymer was recovered, and it was dried to obtain Copolymer I. Comparative Example 4 Copolymer J was obtained in the same manner as in Example 3, except that 15 parts of hydroxyethyl methacrylate was used. Comparative Example 5 1.0 part of trichlorethylene, 0 part of deionized water
Copolymer K was prepared in the same manner as in Example 3 except that
I got it. Comparative Example 6 Copolymer L was obtained in the same manner as in Example 3, except that the amount of trichlorethylene and methanol was 0 parts, and the amount of deionized water was 240 parts. Comparative Example 7 50 parts of vinyl chloride, 20 parts of vinyl acetate, acetone
Charge 180 parts of benzoyl peroxide and 2 parts of benzoyl peroxide into an autoclave, and after degassing, start polymerization at 55°C, and add vinyl chloride in 5 portions of 10 parts each time the pressure of the autoclave drops by 0.5 Kg/ ^cm2 . 50 parts were injected.
On the other hand, immediately after the start of polymerization, 5 parts of maleic anhydride and 45 parts of methanol were continuously injected into the autoclave, and when the pressure of the autoclave reached 1 Kg/cm ² , unreacted vinyl chloride was recovered. Next, the reaction solution was added to a mixture of 1,000 parts of methanol and 6 parts of 65% nitric acid, and the mixture was stirred and heated at 70°C for 12 hours. Then, 1,000 parts of deionized water was added to mix the copolymer as a medium. It was separated and collected from. Thereafter, 500 parts of acetone and the copolymer were stirred and mixed at 60°C, then 1000 parts of methanol was added, the copolymer was separated and recovered, and further washed with water and dried to obtain a copolymer M. The compositions of these copolymers are commercially available vinyl chloride-vinyl acetate-maleic acid terpolymer (N),
and vinyl chloride-vinyl acetate-vinyl alcohol copolymer (O) are shown in the table. In addition, the percentage of carboxy groups in the copolymer was determined by titration, and
The percentage of hydroxyl groups was determined by infrared absorption analysis. Next, each copolymer was evaluated as a magnetic coating material and a magnetic recording medium. The results are shown in the table.

【table】

【table】

Claims (1)

[Claims] 1 0.3 to 5.0% by weight of carboxylic acid groups, 0.1 to 0.1% of hydroxyl groups based on -X-OH groups (X is an organic residue)
2.0% by weight, a vinyl chloride-based copolymer having an equivalent ratio of the hydroxyl group to the carboxylic acid group of 0.1 to 3.0, which contains other polymers excluding vinyl chloride and the monomer supplying the carboxylic acid group or the hydroxyl group. The copolymerization ratio of monomers is 3 to 20% by weight, and the average degree of polymerization is 200 to 900.
A resin for magnetic paint, characterized by: