JPH0434578B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a magnetic paint that uses vinyl chloride resin (hereinafter referred to as PVC) as a binder for magnetic powder. Generally, magnetic recording media such as magnetic tapes and floppy disks are manufactured by applying magnetic paint, which is made by dispersing ferromagnetic powder in an organic solvent and using an organic polymer as a binder, onto a polymer film or sheet. There is. The organic polymer in this magnetic paint is usually
Relatively hard resins such as PVC, polyvinyl butyral, nitrocellulose, acetylcellulose,
It is often used in combination with soft materials such as polyester, polyurethane, and acrylonitrile-butadiene copolymers, and polyisocyanate compounds are usually used as thermosetting components to improve the durability of the coating film. There are many examples. 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. In order to develop such high-performance magnetic recording media, the present inventor evaluated conventional PVC binders when conducting a study on improving binders using PVC, and found that vinyl chloride-vinyl alcohol-vinyl acetate copolymer As the ratio of alcohol increases, the dispersion performance of magnetic particles improves, but the degree of improvement is low and requires the assistance 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 will be shortened. On the other hand, if the pot life is reduced to an appropriate level of hydroxyethyl acrylate copolymer, the solubility in the solvent will decrease, making the solution 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 polymer containing specific amounts of carboxylic acid groups and specific hydroxyl groups showed better dispersibility of magnetic particles than expected, and that it contained an extremely small amount of hydroxyl groups. Despite this, it provides good reactivity with polyisocyanate and has excellent chemical thermal stability.Furthermore, this copolymer can be used as a binder and polyisocyanate as a curing agent to disperse magnetic particles. It was confirmed that a magnetic recording medium obtained by coating a polyester film with the above-mentioned paint exhibits excellent magnetic properties, electromagnetic conversion properties, and durability, leading to the completion of the present invention. That is, the present invention contains 0.3 to 5.0% by weight of carboxylic acid groups, 0.2 to 2.0% by weight of hydroxyl groups based on -X-OH groups (OH is bonded to the secondary carbon in the organic residue X), The equivalent ratio of the hydroxyl group to the carboxylic acid group is 0.1 to 3.0, and the copolymerization ratio of the carboxylic acid group or the monomer supplying the hydroxyl group and other monomers other than vinyl chloride is 0 to 3% by weight. The present invention relates to a magnetic paint characterized in that a vinyl chloride polymer powder having an average degree of polymerization of less than 200 and an average degree of polymerization of 200 to 900 is used as a binder for the magnetic powder. Examples of unsaturated carboxylic acid monomers used to provide carboxylic acid groups to the polymer of the present invention include unsaturated mono- or dicarboxylic acids such as acrylic acid, methacrylic acid, maleic acid, itaconic acid, and crotonic acid; Examples include monoalkyl esters of acids, unsaturated dicarboxylic acids such as itaconic acid, and the like. This monomer is used in such a range that the amount of carboxylic acid groups in the polymer is 0.3 to 5.0% by weight. When the amount is less than this, the dispersibility of the magnetic powder is poor, and when it is more than this, the paint tends to gel and thicken. -X- in the vinyl chloride polymer according to the present invention
Examples of X constituting the OH group include organic residues such as C _o H _2o , OC _o H _2o and COOC _o H _2o (n is an integer of 2 or more). However, OH
is the secondary carbon in X (carbon with one hydrogen atom)
It is necessary to be connected to This -X-
Examples of unsaturated alcohol monomers that provide hydroxyl groups based on OH groups to the polymer include α,β- such as (meth)acrylic acid-2-hydroxybutyl ester and (meth)acrylic acid-2-hydroxypropyl ester. Alkanol esters of unsaturated dicarboxylic acids having 3 or more carbon atoms, such as mono-2-hydroxypropyl maleate, di-2-hydroxypropyl maleate, mono-2-hydroxybutyl itaconate, etc. , olefin alcohols such as 4-penten-2-ol and 1-hexen-3-ol, and alkanol vinyl ethers such as 2-hydroxypropyl vinyl ether. The amount of these unsaturated alcohols used is
The amount of hydroxyl group in the polymer is 0.2 to 2.0% by weight. If it is less than 0.2% 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. Furthermore, the equivalent ratio of the hydroxyl group and the carboxylic acid group based on the -X-OH group needs to be 0.1 to 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. In this case, the characteristics as a magnetic paint or a magnetic recording medium are generally poor. The carboxylic acid group and hydroxyl group in the polymer according to the present invention may be, for example, an unsaturated carboxylic anhydride and glycols having a hydroxyl group bonded to a secondary carbon, instead of using the above-mentioned unsaturated carboxylic acid and unsaturated alcohol. may be introduced by obtaining a polymer while producing an alkanol ester of an unsaturated carboxylic acid during the polymerization reaction. Examples of other monomers include carboxylic acid vinyl esters such as vinyl acetate and vinyl propionate; vinyl ethers such as methyl vinyl ether, isobutyl vinyl ether, and cetyl vinyl ether; vinylidene such as vinylidene chloride and vinylidene fluoride; diethyl maleate; Examples include unsaturated carboxylic acid alkyl esters such as dibutyl maleate, diethyl itaconate, methyl (meth)acrylate, and ethyl (meth)acrylate; and olefins such as ethylene and propylene. These comonomers may be added to the vinyl chloride polymer as needed.
It can be used within a range of less than % by weight. The degree of polymerization of the polymer according to the invention is from 200 to 900, preferably from 250 to 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 magnetic paint resin according to the present invention can be produced using any known polymerization method, but from the viewpoint of polymer solubility, solution polymerization, lower alcohol such as methanol or ethanol alone as the polymerization medium, 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, and 3,5,5-trimethylhexane. Examples include organic peroxides such as noyl 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. In addition, as an emulsifier,
Examples 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. 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 at 35-80℃
It is carried out under stirring at a temperature of . The vinyl chloride polymer thus obtained is
Like ordinary vinyl chloride resin binders for magnetic paints, they are generally prepared in any solvent solution together with flexible materials such as polyurethane resins, polyester resins, acrylonitrile-butadiene rubber, curing agents typified by polyisocyanates, and magnetic powders. 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-
Common resin binders for magnetic coatings, such as vinyl acetate copolymer resin, cellulose resin, phenoxy resin, amino resin, epoxy resin, butyral resin, and acrylic resin, may be used in combination to the extent that the purpose of the present invention is achieved. is also possible. 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, metal magnetic powders such as Fe powder and Fe-Co powder are also used. In the polymer according to the present invention, by replacing the vinyl acetate moiety with -X-OH as the hydroxyl group-containing component in place of the saponified hydroxyl group, the reactivity with isocyanate can be greatly improved. By this, the number of hydroxyl groups required for the reaction can be significantly reduced. 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 polymer, increasing the degree of freedom, and that the distribution of the hydroxyl groups is uniform. In addition, by bonding the hydroxyl group to a secondary carbon, the pot life can be maintained,
It is possible to achieve both solubility in a solvent and solution viscosity. 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, evaluation of the magnetic paint or magnetic recording medium was based on the following. 1 Solubility 100 parts of vinyl chloride polymer was dissolved in a mixed solvent consisting of 200 parts of methyl ethyl ketone, 100 parts of methyl isobutyl ketone, and 100 parts of toluene under stirring at 65°C for 1 hour, and the degree of transparency of the solution was visually observed. Judgment was made in three stages: ○△×. 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 polymer.
The pot life was defined as the number of days until the solution stopped flowing even when the solution was stored at ℃ and the container was turned upside down. Generally, about 7 to 30 days is desirable. 3 Thermal stability The solution used for 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 heated at 120°C in an open gear to blacken it. Measure the time it takes. 4 Gloss 400 parts of cobalt-coated magnetic iron oxide powder (specific surface area
30m ² /g), 60 parts of vinyl chloride polymer, 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 this magnetic coating film at a reflection angle of 60°C 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 film used for gloss evaluation was smoothed with a calendar roll, heated at 65°C for 65 hours, and then placed in contact with a rotating drum covered with abrasive paper under a load of 100g for 30 minutes. It was rotated at 150 rpm for a minute, and the extent to which the magnetic paint adhered to the abrasive paper was visually observed and judged on a three-point scale of ○△x. 7. Running property 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, 1-hexen-3-ol
25 parts, 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. After injection into the autoclave, the reaction pressure is 1
When the temperature reached Kg/cm ² , unreacted vinyl chloride was collected, 250 parts of water was added, and the mixture was heated to 70°C to separate the solvent and polymer, followed by drying to obtain Polymer A. Example 2 100 parts of vinyl chloride, 180 parts of acetone, and 2 parts of benzoyl peroxide were charged into an autoclave, and after degassing, the temperature was 55%.
After starting the polymerization at °C, immediately add 4.5 parts of acrylic acid,
A mixture of 1.5 parts of water, 44 parts of methanol, 15 parts of 2-hydroxybutyl methacrylate, and 45 parts of methanol.
Continuously inject all of the above mixture from separate injection ports until the pressure of the autoclave reaches 2.0Kg/cm ² , and when the pressure reaches 1.0Kg/cm ² ,
Unreacted vinyl chloride was collected, 250 parts of deionized water was added and heated to separate the solvent and polymer, and then dried to obtain Polymer B. Example 3 100 parts of vinyl chloride, 3 parts of itaconic acid, 180 parts of methanol, 60 parts of deionized water, 0.6 parts of methyl cellulose
part, polyoxyethylene sorbitan fatty acid ester 0.2 part, trichlorethylene 0.35 part, 3,5,
Charge 0.42 parts of 5-trimethylhexanoyl peroxide into an autoclave, and after degassing, start polymerization at 58°C, and continuously inject a mixed solution of 10 parts of 2-hydroxypropyl methacrylate and 20 parts of methanol into the autoclave. The injection was completed by the time the autoclave pressure reached 5 Kg/cm ² . After that, the autoclave pressure is 3Kg/cm ²
When the temperature is reduced, unreacted vinyl chloride is collected, the polymer is recovered by dehydration, washed with cold water, and then dried.
Polymer C was obtained. Example 4 100 parts of vinyl chloride, 5 parts of vinyl acetate, 8 parts of 2-hydroxypropyl vinyl ether, 3 parts of itaconic acid, 120 parts of methanol, 120 parts of deionized water, 0.6 parts of methylcellulose, 0.2 parts of sodium lauryl sulfate,
0.05 part of 2-mercaptoethanol and 0.70 part of lauroyl peroxide were placed in an autoclave, and after degassing,
When polymerization started at ℃ and reached 3 kg/cm ² , a solution of 0.05 part of bisphenol A dissolved in 0.2 part of methanol was added to recover unreacted vinyl chloride, and the polymer was recovered by dehydrating. Polymer D was obtained by washing with cold water and drying. Example 5 Maleic anhydride 5 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 mix at 58℃ for 10 minutes.
Mixed for an hour. Add to this 0.5 parts of 3,5,5-trimethylhexanoyl peroxide, 0.6 parts of methylcellulose, 0.2 parts of polyoxyethylene sorbitan fatty acid ester, 150 parts of methanol, and 50 parts of deionized water.
When the pressure of the autoclave reached 3 kg/cm ² , unreacted vinyl chloride was collected, drained, washed with water and dried to obtain copolymer E. Comparative Example 1 Polymer F was obtained in the same manner as in Example 2, except that 2-hydroxybutyl methacrylate in Example 2 was replaced with 2-hydroxyethyl methacrylate. Comparative Example 2 Polymer G was obtained in the same manner as in Example 2, except that 30 parts of 2-hydroxybutyl methacrylate was 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 and the polymer was recovered and dried to obtain Polymer H. Comparative Example 4 A polymer was obtained in the same manner as in Example 3, except that 20 parts of hydroxypropyl methacrylate was used. Comparative Example 5 1.0 part of trichlorethylene, 0 part of deionized water
Polymer J was obtained in the same manner as in Example 3 except that Comparative Example 6 Polymer K 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, 14 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. Add vinyl chloride in 5 portions of 10 parts each time the autoclave pressure decreases by 0.5 Kg/ ^cm2 . 50 parts were injected.
On the other hand, immediately after the start of polymerization, 10 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 80°C for 12 hours. Then, 1,000 parts of deionized water was added to remove the polymer from the medium. Separated and collected. Thereafter, 500 parts of acetone and the polymer were stirred and mixed at 60° C., then 1000 parts of methanol was added, the polymer was separated and recovered, and further washed with water and dried to obtain a polymer L. The composition of these polymers was changed to commercially available vinyl chloride.
It is shown in the table together with vinyl acetate-maleic acid terpolymer M and vinyl chloride-vinyl acetate-vinyl alcohol terpolymer N. The percentage of carboxy groups in the polymer was determined by titration, and the percentage of hydroxyl groups in the polymer was determined by infrared absorption analysis. Next, each polymer was evaluated as a magnetic coating material and a magnetic recording medium. The results are shown in the table.

【table】

[Table] *2 Vinyl alcohol *3 Dissolves when heated, but turns into a gel when cooled.

Claims (1)

[Claims] 1 Contains 0.3 to 5.0% by weight of carboxylic acid groups and 0.2 to 2.0% by weight of hydroxyl groups based on -X-OH groups (the OH group is bonded to the secondary carbon in the organic residue The equivalent ratio with the carboxylic acid group is 0.1 to 3.0, and the copolymerization ratio of the monomer that supplies the carboxylic acid group or the hydroxyl group and other monomers other than vinyl chloride is 0 to less than 3% by weight. , and the average degree of polymerization is 200
A magnetic paint characterized in that a vinyl chloride copolymer having a molecular weight of 900 to 900 is used as a binder for magnetic powder.