JPH0126627B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to vinyl chloride resins for magnetic coatings, particularly vinyl chloride resins used as binders for magnetic recording media. [Prior Art] Magnetic recording media such as magnetic tapes and magnetic cards are generally manufactured by coating a substrate such as a polyester film with a magnetic paint containing magnetic powder and its binder as a magnetic layer. In recent years, the coercive force and maximum saturation magnetization have been increased,
In order to improve the signal-to-noise ratio and recording density, miniaturized magnetic powders that have a large coercive force and a large specific surface area have come to be used as the above-mentioned magnetic powders. However, such fine magnetic powder is made of vinyl chloride-vinyl acetate-vinyl alcohol terpolymer,
When preparing magnetic paints with conventional binders such as vinyl chloride-vinyl acetate-maleic acid terpolymer or nitrocellulose, there are drawbacks such as thickening of the paint and insufficient dispersibility. .
In addition, low molecular weight surfactants are used as dispersants to improve dispersibility, but the use of large amounts of these dispersants may cause problems such as poor durability of the magnetic recording medium and head stains, so the amount used should be limited. Naturally, there are limits. On the other hand, in order to improve the durability and reliability of magnetic recording media, polyurethane resin, polyester resin,
Especially for recording, it is recommended to add a cross-linking agent that reacts with a flexible material such as acrylonitrile-butadiene rubber and part or all of the binder to form a cross-linked bond to form a cross-linked magnetic layer. This is commonly used with magnetic recording tapes. Therefore, the binder is required to be compatible with these flexible materials and to have appropriate reactivity with the crosslinking agent. Furthermore, in order to improve tape reliability, tapes are increasingly required to have excellent chemical stability and to be less likely to generate decomposition products that can cause deterioration of magnetic powder or corrosion of heads. It's coming. [Problems to be Solved by the Invention] As a result of intensive studies to develop a binder that can meet the high performance requirements of such magnetic recording media, the present inventor has found that by using a specific vinyl chloride copolymer, the binder can achieve high performance. It is possible to obtain a magnetic coating material that maintains dispersibility, prevents thickening, and has excellent reactivity with crosslinking agents, and that magnetic recording media obtained using the coating material have excellent surface smoothness and durability of the coating film. The inventors have discovered that this material has good properties, as well as excellent running properties, magnetic properties, and electromagnetic conversion properties, and have arrived at the present invention. [Means for solving the problem] That is, a mixture of an unsaturated monomer having an epoxy group and an adduct of an alkali metal salt or an ammonium salt of a strong acid containing sulfur or phosphorus is mixed with vinyl chloride and the necessary A copolymer with a vinyl chloride content of 60% by weight or more obtained by copolymerizing with other unsaturated monomers that can be copolymerized with these according to the conditions, and containing sulfur or The present invention provides a resin for magnetic paint, characterized in that the amount of strong acid radicals containing phosphorus is 0.1 to 4.0% by weight, and the amount of epoxy groups is 0.5% by weight or more. The reaction between an unsaturated monomer having an epoxy group and an alkali metal or ammonium salt of a strong acid containing sulfur or phosphorus is usually carried out with stirring at room temperature or under heated conditions. used in this reaction. Examples of unsaturated monomers having an epoxy group include glycidyl ethers of unsaturated alcohols such as allyl glycidyl ether and methacryl glycidyl ether, glycidyl acrylate, glycidyl methacrylate, glycidyl-p-vinyl benzoate, methyl glycidyl itaconate,
Glycidyl esters of unsaturated acids such as glycidyl ethyl maleate, glycidyl vinyl sulfonate, glycidyl (meth)allylsulfonate, epoxide olefins such as butadiene monooxide, vinylcyclohexene monooxide, 2-methyl-5,6-epoxyhexene, etc. can give. Examples of the alkali metal salt or ammonium salt of a strong acid containing sulfur or phosphorus to be added to the epoxy group-containing unsaturated monomer include sodium sulfite,
Sulfites such as sodium thiosulfate, sodium bizincate, ammonium sulfite, and potassium sulfite; Hydrogen sulfates such as sodium hydrogen sulfate, potassium hydrogen sulfate, and ammonium hydrogen sulfate; Phosphate salts such as dipotassium hydrogen phosphate and disodium hydrogen phosphate. Acid hydrogen salts: Phosphites such as sodium hydrogen phosphite and ammonium hydrogen phosphite; Amino sulfonates such as sodium taurine, sodium sulfamate, and potassium sulfanilate; amino sulfates such as sodium 1-aminoethyl sulfate etc. The addition reaction can be carried out in either an aqueous or non-aqueous system, but since the salts used in the addition reaction are water-soluble, an aqueous system or an organic solvent system containing water is preferred, and the reaction is carried out under stirring. be exposed.
The reaction is usually carried out at about 20 to 120°C for 1 to 24 hours, but if the reaction temperature is too high, side reactions will increase. Rather, it is reacted to leave unreacted epoxy group-containing monomers in the resin of the present invention.
It is preferable to set the epoxy group content to 0.5% by weight or more. Catalysts can be used to accelerate addition reactions. Examples of this catalyst include quaternary ammonium salts such as tetrabutylammonium bisulfate, tetrabutylammonium bromide, trimethyllauryl ammonium chloride, benzyltriethylammonium chloride, and boron fluorides such as boron zinc tetrafluoride. The reaction product thus obtained includes an adduct of an alkali metal salt or ammonium salt of a strong acid containing sulfur or phosphorus to an epoxy group-containing unsaturated monomer. For example, the reaction product of allyl glycidyl ether and sodium bisulfite has 3-
Sodium allyloxy-2-hydroxypropanesulfonate is included, and the reaction product of glycidyl methacrylate and sodium hydrogen sulfate includes propyl methacrylate-2-hydroxy-3 sulfate. Similarly, in the reaction product of methallyl glycidyl ether and dipotassium hydrogen phosphate, potassium 3-methallyloxy-2-hydroxypropane phosphate is present in the reaction mixture of butadiene monoxide and diammonium hydrogen phosphate. Among them is ammonium 2-hydroxy-3-butene phosphate. Thus, the reaction mixture used in the present invention contains, in addition to the unreacted epoxy group-containing unsaturated monomer, one or more unsaturated bonds and one or more salts of strong acids containing sulfur or phosphorus. Contains radically copolymerizable unsaturated compounds. The reaction mixture thus obtained is copolymerized as it is, or after removing the inorganic salts and addition reaction catalyst, with vinyl chloride and, if necessary, a monomer copolymerizable therewith in the presence of a radical generator. Examples of unsaturated monomers that can be used in addition to vinyl chloride 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 and vinylidene fluoride; diethyl maleate, butylbenzyl maleate, di-2-hydroxyethyl maleate, dimethyl itaconate, methyl (meth)acrylate, ethyl (meth)acrylate, (meth)acrylic Lauryl acid, (meth)acrylic acid-
Unsaturated carboxylic acid esters such as 2-hydroxypropyl; Olefins such as ethylene and propylene; Unsaturated alcohols such as allyl alcohol and 3-buten-1-ol; Unsaturated nitriles such as (meth)acrylonitrile; Styrene, α-methyl Examples include aromatic vinyls such as styrene and p-methylstyrene. These monomers are used not only to improve the solubility of the resin by controlling the compatibility and softening point of the resin of the present invention and other resins when mixed, but also to improve the properties of the coating film and the coating properties. Appropriate selection is made depending on needs such as process improvement. The resin of the present invention can be produced using any known polymerization method, but from the viewpoint of polymer solubility, solution polymerization, lower alcohols such as methanol or ethanol alone, or decomposition with lower alcohols such as methanol or ethanol as the polymerization medium are recommended. Preferably, it is produced by a suspension polymerization method using a combination with ionic water. Examples of polymerization initiators used in the production of resins include lauroyl peroxide, benzoyl peroxide,
3,5,5-trimethylhexanoyl peroxide, diisopropyl peroxydicarbonate, di-2-ethylhexyl peroxydicarbonate, di-2-ethoxyethyl peroxydicarbonate, t-butyl-peroxypivalate, t- Organic peroxides such as butyl peroxyneodecanoate; 2,2'-azobisisobutyronitrile, 2,2'-azobis-2,4-dimethylvaleronitrile, 4,4'-azobis-4- Examples include azo compounds such as cyanovaleric acid; inorganic peroxides such as ammonium persulfate, potassium persulfate, and ammonium perphosphate. Examples of suspension stabilizers include polyvinyl alcohol, partially saponified polyvinyl acetate, cellulose derivatives such as methylcellulose, hydroxypropylcellulose, and carboxymethylcellulose, polyvinylpyrodone, polyacrylamide,
Examples include synthetic polymeric substances such as maleic acid-styrene copolymer, maleic acid-methyl vinyl ether copolymer, maleic acid-vinyl acetate copolymer, and natural polymeric substances such as starch and 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-mentioned polymerization initiator, reaction mixture of an epoxy group-containing monomer and a salt of a strong acid containing sulfur or phosphorus, vinyl chloride and other monomers, suspending agents, emulsifiers, molecular weight regulators, etc. are added all at once at the start of polymerization. It may be added to the polymerization system, or it may be added in portions during the polymerization. Polymerization is usually carried out at a temperature of 35-80°C and under stirring. The resin of the present invention has an average degree of polymerization of 100 to 900, preferably 200 to 500, and a vinyl chloride content of 60% by weight.
That's all. If the degree of polymerization is less than 100, the abrasion resistance of the magnetic layer will be insufficient, and if it exceeds 900, the viscosity of the paint will be high and the dispersion of the magnetic powder will tend to be insufficient. On the other hand, if the content of vinyl chloride is less than 60% by weight, the compatibility with flexible materials may decrease,
This may cause problems such as a significant decrease in solvent removal from the coating film. In addition, the amount of strong acid radicals bound to the resin is −SO ₃ , −
It is necessary that the content is 0.1 to 4.0% by weight as SO ₄ , -PO ₄ or -PO ₃ . 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 group will become strong, which will not only result in insufficient solubility in solvents but also reduce the moisture resistance of the coating film. death,
Furthermore, agglomeration of the magnetic powder occurs, which worsens the dispersibility. The resin of the present invention thus obtained has the same properties as ordinary vinyl chloride resin binders for magnetic paints.
In general, flexible materials such as polyurethane resin, polyester resin, acrylonitrile-butadiene copolymer, crosslinking agents such as polyisocyanate, and magnetic powder, as well as lubricants, dispersants, antistatic agents, as necessary, It can be prepared and used as a solution in any solvent with known materials such as abrasives. The resin of the present invention can exhibit excellent heat resistance stability due to the epoxy group in the resin, so that it is possible to manufacture a magnetic recording medium that is highly reliable and resistant to head corrosion. Furthermore, by utilizing the reactivity of epoxy groups, it is possible to crosslink coating films with polyamine compounds and polycarboxylic acid compounds. If desired, vinyl chloride-vinyl acetate copolymer resin, vinyl chloride-vinyl acetate copolymer resin, vinyl chloride-vinyl acetate copolymer resin, etc.
Common resin binders for magnetic coatings, such as vinyl alcohol-vinyl acetate copolymer resin, cellulose resin, phenoxy resin, amino resin, epoxy resin, butyral resin, and acrylic resin, are used in combination to the extent that the object of the present invention is achieved. It is also possible. Furthermore, as the magnetic powder, metal magnetic powders such as Fe powder and Co powder are more preferably used, but γ-
Fe ₂ O ₃ , Fe ₃ O ₄ , Co containing γ-Fe ₂ O ₃ , Co containing
Powders of iron oxides such as Fe ₃ O ₄ , barium ferrite, and CrO ₂ powders are also used. [Example] The present invention will be specifically explained below using Examples. Note that the number of copies is based on weight. (Resin synthesis example) Example 1 15 parts of allyl glycidyl ether, 2 parts of sodium bisulfite, and 50 parts of deionized water were placed in an Erlenmeyer flask.
Stir at 50°C. After 2 hours, the mixture was colored pale yellow, and the oil phase was significantly smaller than before the reaction. This mixed solution was placed in an autoclave together with 5 parts of vinyl acetate, 3 parts of sodium lauryl sulfate, 1 part of potassium persulfate, and 150 parts of deionized water, and after degassing, 100 parts of vinyl chloride was added to initiate polymerization at 54°C. . When the pressure of the autoclave reached 5 kg/cm ² , unreacted vinyl chloride was collected to obtain a copolymer dispersion. This was freeze solidified, thoroughly washed with warm water until no bubbles were generated in the washing water, and then dried to obtain copolymer A. Example 2 Copolymer B was obtained in the same manner as in Example 1 except that potassium hydrogen sulfate was used in place of sodium bisulfite. Example 3 20 parts of glycidyl methacrylate, 3 parts of diammonium hydrogen phosphate, and 50 parts of deionized water were placed in a glass autoclave, and after degassing, they were mixed at 50°C for 2 hours. In another stainless steel autoclave, 3 parts of 3-buten-1-ol, 1 part of azobisisobutyronitrile, 0.6 part of methyl cellulose, 0.2 part of polyoxyethylene lauryl ether, 200 parts of methanol.
After degassing, add 100 parts of vinyl chloride.
At the same time as starting polymerization at 53° C., the mixture in the glass autoclave was continuously injected into the stainless steel autoclave, and the injection was completed by the time the pressure in the stainless steel autoclave reached 5 Kg/cm ² . When the pressure further decreased to 3 kg/cm ² , unreacted vinyl chloride was collected, dehydrated and washed to obtain copolymer C. Example 4 Copolymer D was obtained in the same manner as in Example 3 except that diammonium hydrogen phosphate was replaced with taurine sodium salt. Comparative Example 1 Copolymer E was obtained in the same manner as in Example 1 except that the amount of sodium bisulfite was increased to 15 parts. Comparative Example 2 Copolymer F was obtained in the same manner as in Example 1, except that 50 parts of vinyl acetate and 65 parts of vinyl chloride were used. Comparative Example 3 Copolymer G was obtained in the same manner as in Example 3 except that glycidyl methacrylate was replaced with n-propyl methacrylate. Comparative Example 4 Copolymer H was obtained in the same manner as in Example 3 except that diammonium hydrogen phosphate was not used. The properties of these resins were determined from commercially available vinyl chloride-vinyl acetate-maleic acid terpolymer (I) and vinyl chloride-vinyl acetate-vinyl alcohol terpolymer.
It is shown in the table along with (J). The amount of hydroxyl groups in the resin was determined by infrared absorption analysis, the amount of vinyl chloride was determined by quantifying the amount of chlorine by combustion, the amount of epoxy groups was determined by titration, and the amount of strong acid groups was determined by a combination of elemental analysis and infrared absorption analysis. (Evaluation of resin properties) Next, each resin was evaluated as a magnetic coating material and a magnetic recording medium. The results are shown in the table. The evaluation method was as follows. (1) Solubility Prepare a solution consisting of 100 parts of vinyl chloride copolymer, 200 parts of methyl ethyl ketone, and 200 parts of toluene, and visually check the degree of transparency of this solution.
Judgment was made in three stages. (2) Thermal stability Place 1.0 g of vinyl chloride copolymer in a 15 c.c. test tube, plug the opening with absorbent cotton sandwiched with Congo Red test paper, and place in an oil bath at 150°C. The time required for Congo Red test paper to change color due to hydrochloric acid was measured. (3) Dispersion stability 400 parts of metallic iron magnetic powder, 100 parts of vinyl chloride copolymer
A mixture of 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. This dispersed paint was collected in a sample bottle and stored in a constant temperature bath at 25°C, and the state of gel formation was observed. The generation of gel was determined by taking a portion of the dispersed paint onto a glass plate, diluting it with about 5 times the amount of methyl ethyl ketone, mixing with a glass rod, and visually observing the mixture. The results are indicated by 〇△× in order of least gel formation. (4) Glossiness (1) 400 parts of metallic iron magnetic powder, 70 parts of vinyl chloride copolymer
Department, polyurethane resin (Japan Polyurethane Industry)
A mixture of 30 parts of Nipporan 2304 (manufactured by Nippon Polyurethane Industries, Ltd.), 300 parts of methyl ethyl ketone, 300 parts of methyl isobutyl ketone, 300 parts of toluene, and 2 parts of silicone oil was dispersed under high-speed shearing for 90 minutes, followed by dispersion of polyisocyanate (Nippon Polyurethane Industries, Ltd.). Add 15 parts of Coronate L) and 100 parts of cyclohexanone,
The mixture was further dispersed for 90 minutes to form a magnetic paint. The thickness of the obtained magnetic paint was applied to polyester film soil.
It was coated to a 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) Glossiness (2) A magnetic coating film was obtained in the same manner as Glossiness (1) except that polyamide (Versamide 125, manufactured by General Mills) was used instead of polyisocyanate, and the reflectance was measured. (6) Squareness ratio (Br/Bm) The magnetic coating used for gloss evaluation was 12.5 mm
It was cut to 50 mm and measured using a magnetic property measuring machine. (7) Durability The magnetic coating used for gloss evaluation was smoothed with a calendar roll, then heated at 65℃ for 65 hours, and then brought into contact with a rotating drum covered with abrasive paper under a load of 100g. The magnetic paint was rotated at 150 rpm, and the extent to which the magnetic paint adhered to the abrasive paper was visually observed and judged on a three-grade scale of 〇△×. (8) Running performance Using the same method as the durability evaluation, the force generated between the coating film and the rotating drum was measured at 65°C and an atmosphere of 80% relative humidity.
The running resistance was measured using a gauge and judged in three grades: ○△x in descending order of running resistance.

【table】

[Table] *2 Hydroxyl group

Claims (1)

[Claims] 1 A reaction mixture of an unsaturated monomer having an epoxy group and a product obtained by adding an alkali metal salt or ammonium salt of a strong acid containing sulfur or phosphorus to this is copolymerized with vinyl chloride and, if necessary, these. A copolymer with a vinyl chloride content of 60% by weight or more obtained by copolymerization with other unsaturated monomers where possible, and the amount of strong acid radicals containing sulfur or phosphorus bonded to the copolymer. 1 to 4.0% by weight, and the amount of epoxy groups is 0.5% by weight or more.