JPH0574621B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a magnetic paint using a vinyl chloride resin, particularly a vinyl chloride resin crosslinked and cured by electron beam irradiation, as a binder for magnetic powder. [Prior Art] Magnetic recording media such as magnetic tapes and magnetic cards are generally manufactured by applying a magnetic paint containing magnetic powder and its binder as a magnetic layer onto a substrate such as a polyester film. . 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 with a large specific surface area have come to be used as the above-mentioned magnetic powders. However, when preparing magnetic paint, fine magnetic powder cannot be used with commonly used binders such as vinyl chloride-vinyl acetate-vinyl alcohol terpolymer, vinyl chloride-vinyl acetate-maleic acid terpolymer, and nitrocellulose. However, there are disadvantages 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 can cause problems such as poor durability of the magnetic recording medium and head stains, so the amount used is limited. Naturally, there are limits. On the other hand, in order to improve the durability, running characteristics, and reliability of magnetic recording media, in addition to flexible materials such as polyurethane resins, polyester resins, and acrylonitrile-butadiene rubber, thermosetting crosslinking agents such as polyisocyanate compounds are used. It is common for magnetic recording media, in particular, to crosslink the magnetic layer by chemical reaction with active hydrogen-containing groups such as hydroxyl groups, carboxyl groups, and amino groups in the binder, which is added to magnetic paints. It is being done. However, with such a thermosetting binder, the curing reaction basically starts the moment the crosslinking agent is added, which causes problems with the pot life of the paint.
Furthermore, the curing speed varies depending on the material in the magnetic coating and the environment, and it is difficult to control, leading to problems such as the storage stability of the coating and variations in the surface formation treatment effect of the coating. Furthermore, it takes a long time for complete curing.
During curing and aging, the surface roughness of the back surface of the substrate that the coating surface comes into contact with tends to change, which tends to cause a decrease in the surface smoothness of the magnetic layer, which is an important property for high-density recording media. From the above points, conventional thermosetting binders have limitations in responding to the remarkable increase in recording density of magnetic recording media and the stabilization, rationalization, and automation of production processes. [Problems to be Solved by the Invention] As a result of intensive study to develop a binder that can improve the performance of such magnetic recording media and rationalize and stabilize the production process, the present inventor discovered that a specific type of vinyl chloride By using a polymer, it is possible to obtain a magnetic coating material that maintains high dispersibility, prevents thickening, and is instantly crosslinked and cured by electron beams, and that a magnetic recording medium obtained using the coating material is
The inventors have discovered that the coating film has good surface smoothness and durability, and has excellent running properties, magnetic properties, and electromagnetic conversion properties, and has thus arrived at the present invention. [Means for solving the problem] That is, at least one kind selected from COOM, SO ₃ M, SO ₄ M, PO ₃ M and PO ₄ M ₂ (M is hydrogen, alkali metal or ammonium, the same applies hereinafter). A polymer obtained by reacting a vinyl chloride polymer having a hydrophilic group and an epoxy group with a monobasic acid having an acryloyl group or a methacryloyl group, wherein the hydrophilic group is converted into COO, SO ₃ , SO ₄ , 0.1-4.0% by weight as PO ₃ or PO ₄ , acryloyl group or methacryloyl group as double bond equivalent
The present invention provides an electron beam-reactive magnetic paint characterized in that the binder of the magnetic powder is a polymer having an average degree of polymerization of 100 to 900 and containing vinyl chloride in an amount of 60% by weight or less. In addition, double bond equivalent means the molecular weight of a polymer per acryloyl group or methacryloyl group bonded to the polymer. The resin according to the invention is generally COOM,
A vinyl chloride polymer having at least one hydrophilic group selected from SO ₃ M, SO ₄ M, PO ₃ M ₂ and PO ₄ M ₂ and an epoxy group has an acid strength expressed by PKa of 3.5. It is obtained by reacting the following monobasic acids having an acryloyl group or a methacryloyl group. COOM, SO ₃ M, SO ₄ M, PO ₃ M ₂ and PO ₄ M ₂
A vinyl chloride polymer having at least one kind of hydrophilic group and an epoxy group selected from (1) a radically polymerizable monomer having the corresponding hydrophilic group and a monomer having an epoxy group, (2) A method of copolymerizing vinyl chloride with other monomers that can be copolymerized as necessary; (3) a method of copolymerizing vinyl chloride using a radical generator having an epoxy group; (3) a method of copolymerizing vinyl chloride with a monomer having an epoxy group; or an epoxy group-containing vinyl chloride polymer obtained by dehydrochlorinating a vinyl chloride polymer and then epoxidizing it with an epoxidizing agent such as percarboxylic acid. It can be obtained by a method such as a partial addition reaction with a compound having a functional group. It is also possible to combine these methods. Examples of monomers having epoxy groups commonly used in the production of vinyl chloride polymers having both hydrophilic groups and epoxy groups include unsaturated monomers such as allyl glycidyl ether and methallyl glycidyl ether. Glycidyl ethers of alcohols, glycidyl esters of unsaturated acids such as glycidyl acrylate, glycidyl methacrylate, glycidyl-P-vinylbenzoate, methylglycidyl itaconate, glycidyl ethyl maleate, glycidyl vinyl sulfonate, glycidyl (meth)allylsulfonate, butadiene Examples include epoxide olefins such as monooxide, vinylcyclohexene monooxide, and 2-methyl-5,6-epoxyhexene. Among the methods for producing vinyl chloride polymers in the present invention, examples of monomers having hydrophilic groups according to the method (1) above include acrylic acid,
unsaturated monocarboxylic acids such as methacrylic acid,
Examples include unsaturated dicarboxylic acids such as fumaric acid and itaconic acid, and their monoesters. Examples of _SO3M include vinylsulfonic acid, methylvinylsulfonic acid, (meth)allylsulfonic acid, styrenesulfonic acid, ethyl (meth)acrylate-2-sulfonate, and 2-acrylamido-2-methylpropanesulfonic acid. , 3-allyloxy-2-hydroxypropanesulfonic acid, and alkali metal salts and ammonium salts of these acids. Examples of SO ₄ M include acids such as ethyl (meth)acrylate-2-sulfate and 3-allyloxy-2-hydroxypropane sulfate, and alkali metal salts or ammonium salts of these acids. An example _{of PO4M2} is (meth)allylic acid-
Propyl 3-chloro-2-phosphate, ethyl (meth)acrylate-2-phosphate, 3-allyloxy-2
-Acids such as hydroxypropane phosphoric acid, and alkali metal or ammonium salts of these acids. Examples of _PO3M2 include acids such as vinylsulfonic acid, acrylamide methanephosphonic acid, ethyl 2 _- phosphonate-(meth)acrylate, 3-allyloxy-2-hydroxypropanephosphonic acid, and the alkali metals of these acids. Examples include salts and ammonium salts. Examples of radical generators having a hydrophilic group in the method (2) above include 4,4'-azobis-4-cyanovaleric acid for COOM, potassium persulfate, ammonium persulfate, etc. for _SO4M ,
Examples of PO ₄ M ₂ include potassium superphosphate and sodium superphosphate. Further, in the method (3) above, examples of compounds used to introduce hydrophilic groups into the resin by polymerizing the copolymer of a monomer having an epoxy group and vinyl chloride include: At COOM,
Malonic acid, phthalic acid, etc. are used in SO ₃ M, sodium sulfite, ammonium sulfite, sodium bisulfite, potassium bisulfite, ammonium thiosulfate, sodium aminoethanesulfonate, sodium sulfanilate, sodium sulfamate, etc. are used in SO ₄ M. , sodium bisulfate, ammonium bisulfate, sodium 2-aminoethyl sulfate, etc., but for PO ₃ M ₂ , sodium hydrogen phosphite,
Ammonium hydrogen phosphite etc., but in PO ₄ M ₂ ,
Examples include dipotassium hydrogen phosphate and disodium hydrogen phosphate. In addition, examples of monomers that may be used as necessary other than monomers having an epoxy group, vinyl chloride, and monomers having a hydrophilic group 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; vinylidenes such as vinylidene chloride and vinylidene fluoride; diethyl maleate, butyl benzyl maleate, di-2-hydroxyethyl maleate, dimethyl itaconate, (meth)acrylic acid Unsaturated carboxylic acid esters such as methyl, ethyl (meth)acrylate, lauryl (meth)acrylate, and 2-hydroxypropyl (meth)acrylate; olefins such as ethylene and propylene;
Examples include unsaturated nitriles such as (meth)acrylonitrile; aromatic vinyls such as styrene, α-methylstyrene, 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 according to the present invention and other resins when they are mixed, but also to improve the properties of the coating film and the coating. Appropriate selection is made depending on the need for improving the manufacturing process. In the copolymerization of a monomer having an epoxy group and vinyl chloride, or the copolymerization of a monomer having an epoxy group and a monomer having a hydrophilic group, and vinyl chloride, other monomers are further copolymerized. A wide variety of known polymerization methods can be used, including the case of polymerization. In addition, a partial polymer reaction between a copolymer of vinyl chloride as a monomer having an epoxy group and other monomers used as necessary, and a compound having a hydrophilic group,
A wide range of known methods can be used depending on process considerations such as the properties of raw materials and separation of products. COOM, SO ₃ M, SO ₄ obtained as above
The vinyl chloride polymer having at least one hydrophilic group selected from M, PO ₃ M ₂ and PO ₄ M ₂ and an epoxy group must contain 0.5% by weight or more of epoxy groups. If it is less than 0.5% by weight, the amount of acryloyl or methacryloyl groups bonded to the resin due to reaction with monobasic acid having acryloyl or methacryloyl groups is small, and the crosslinking reaction by electron beam tends to be insufficient, resulting in the magnetic layer being damaged after electron beam irradiation. durability is insufficient. Further, the monobasic acid having an acryloyl group or a methacryloyl group to be reacted with the vinyl chloride polymer having a hydrophilic group and an epoxy group needs to be a strong acid with an acid strength expressed by PKa of 3.5 or less. Weak acids with a PKa greater than 3.5 do not undergo addition reactions with epoxy groups under mild conditions, so higher temperatures, longer times, or the use of quaternary ammonium salts are required. However, since vinyl chloride polymers are easily dehydrochlorinated by heat, dehydrochlorination of the polymer and addition reaction of hydrogen chloride to epoxy groups precede the desired acryloyl modification reaction, resulting in the formation of the desired modified product. can not be obtained effectively, and
During the reaction, the vinyl chloride polymer deteriorates, resulting in a significant decrease in the thermal stability of the resulting resin. PKa having an acryloyl group or a methacryloyl group used in the production of the resin according to the present invention is
Monobasic acids of 3.5 or less are defined as including those in which the hydrogen atom of the group is replaced with another element.
Specific examples include halogen-substituted (meth)acrylic acids such as chloroacrylic acid, sulfonic acid-containing (meth)acrylic acids such as (meth)2-acrylamido-2-methylpropanesulfonic acid, and ethyl (meth)acrylate-2-sulfonate. Acrylates, (meth)
Examples include sulfuric acid-containing (meth)acrylates such as 2-ethyl acrylate sulfate, and phosphoric acid-containing di(meth)acrylates such as di-2-(meth)acryloxyethyl acid phosphate. The reaction between a vinyl chloride polymer containing a hydrophilic group and an epoxy group and a monobasic acid with a PKa of 3.5 or less can be carried out at room temperature or at 80°C in a solvent that dissolves both.
It progresses easily under relatively mild conditions up to ℃. Of course, it is also possible to react this vinyl chloride polymer in the form of an aqueous dispersion;
If the monobasic acid is soluble in the polymer, it is also possible to directly knead and react the two on a Banbury or roll. In either case, the amount of monobasic acid used is desirably equal to or less than the equivalent molar amount of epoxy groups in the vinyl chloride polymer. If too much excess is used, unreacted monobasic acid remains, which not only increases the risk of increased hygroscopicity of the resulting resin and development of metal corrosive properties, but also increases the risk of the hydrophilic acid in this vinyl chloride polymer. There is a risk that the resulting resin will become insolubilized by inducing a reaction between the functional group and the epoxy group. In addition, during the reaction, a polymerization inhibitor such as hydroquinone, hydroquinone monomethyl ether, and t-butylcatechol is added within a common sense range. The resin according to the present invention thus obtained has an average degree of polymerization of 100 to 900, preferably 200 to 900.
500, the content of vinyl chloride is 60% by weight or more. If the degree of polymerization is less than 100, the wear resistance of the magnetic layer will be insufficient no matter how much electron beam crosslinking is performed.
If it exceeds 900, the viscosity of the paint is high and the magnetic powder tends to be insufficiently dispersed. Furthermore, if the content of vinyl chloride is less than 60% by weight, disadvantages may occur, such as a decrease in compatibility with flexible materials and a marked decrease in solvent removal from the coating film. In addition, the amount of hydrophilic groups bonded to the resin is COO,
0.1-4.0% by weight as SO ₃ , SO ₄ , PO ₃ or PO ₄
It is necessary that 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 resin will become strong, and not only will the solubility in solvents be insufficient, but the moisture resistance of the coating film will decrease. ,
Furthermore, agglomeration of the magnetic powder occurs, which worsens the dispersibility. By reaction with a monobasic acid, an electron beam-curable double bond is introduced into the resin according to the present invention in the form of vic-glycol monoester of the monobasic acid, and cross-linking with the isocyanate compound along with chlorohydrin generated during the reaction. It also makes it possible. The amount of double bonds contributing to electron beam curing needs to be 10,000 or less in terms of double bond equivalent. If the amount of double bonds is small, such as exceeding 10,000 double bond equivalents, the running properties and durability of the magnetic layer after electron beam irradiation will be insufficient. The resin according to the present invention, like the ordinary vinyl chloride resin binder for magnetic coatings, generally constitutes a binder system together with flexible materials such as polyurethane resin, polyester resin, and acrylonitrile-butadiene copolymer. By replacing part or all of the flexible material with other resins, oligomers, or monomers having one or more electron beam-reactive unsaturated bonds, magnetic powder and, if necessary, lubricants, dispersants, etc. It can be used as a dispersion in any solvent by mixing with known materials such as , antistatic agents, and abrasives. If necessary, in addition to the resin according to the present invention, vinyl chloride-vinyl acetate-maleic acid copolymer resin, vinyl chloride-vinyl alcohol-vinyl acetate copolymer resin, cellulose resin,
It is also possible to use common resin binders for magnetic coatings, such as phenoxy resins, amino resins, epoxy resins, butyral resins, and acrylic resins, as long as the object of the present invention is achieved. In addition, magnetic powders include metal magnetic powders such as Fe powder and Co powder, as well as γ-Fe ₂ O ₃ , Fe ₃ O ₄ ,
Co-containing γ-Fe ₂ O ₃ , Co-containing Fe ₃ O ₄ , iron oxide powder such as barium ferrite, and CrO ₂ powder are used. As the active energy ray used for crosslinking the magnetic coating film using the resin according to the present invention, an electron beam produced by an electron beam accelerator is used from the viewpoint of controlling the absorbed dose and ease of introduction into the manufacturing process line. The electron beam used to cure the magnetic coating film has an accelerating voltage of 100 to 750 KV, preferably 150 to 750 KV, in terms of penetrating power.
The absorbed dose is 0.5-20 using a 300KV electron beam accelerator.
It is best to irradiate it so that it becomes a megarad. [Example] The present invention will be specifically explained below using Examples. Note that parts and percentages are based on weight. In addition, the amount of vinyl chloride was determined by quantifying the amount of chlorine through combustion, the amount of double bonds was determined by titration, the amount of epoxy groups was determined by titration, and the amount of hydrophilic groups was determined by a combination of elemental analysis, titration, and infrared absorption analysis. Ta. (Resin synthesis example) Reference example 1 By emulsion polymerizing allyl glycidyl ether and vinyl chloride with potassium persulfate,
4% epoxy group, 0.5% _SO4 , vinyl chloride
An 82% vinyl chloride copolymer was obtained. This copolymer
100 parts of 2-acrylamido-2-methylpropanesulfonic acid (PKa2.0) and 0.01 part of hydroquinone monoethyl ether were dissolved in 200 parts of dimethylformamide, stirred and mixed at 65°C for 3 hours, and then a large amount of The reaction solution was dropped into water, the resin was recovered, and the resin was thoroughly washed by repeatedly washing with water and hot water with strong stirring, and then dried to obtain Resin A. Reference Example 2 Resin B was obtained in the same manner as in Example 1 except that α-chloroacrylic acid (PKa2.5) was used instead of 2-acrylamido-2-methylpropanesulfonic acid. Reference Example 3 By polymerizing glycidyl methacrylate, sodium styrene sulfonate, vinyl acetate and vinyl chloride in methanol with azobisisobutyronitrile, the amount of epoxy groups was 3% and SO ₃
A vinyl chloride copolymer containing 0.5% of vinyl chloride and 72% of vinyl chloride was obtained. 100 parts of this copolymer and 10 parts of di-2-acryloxyethyl acid phosphate (PKa2.3) were mixed together with 0.015 part of hydroquinone monomethyl ether in a high-speed mixer, and then transferred to a kneading roll at 90°C. The sheet-like material obtained by kneading for 10 minutes was pulverized with water in a high-speed stirrer, thoroughly washed with hot water, and then dried to obtain Resin C. Reference Example 4 A copolymer obtained by suspension polymerizing butadiene monooxide, glycidyl methacrylate, vinyl acetate, and vinyl chloride with lauroyl peroxide was carboxy-modified with malonic acid to create a copolymer with 3.5% epoxy groups and 0.9% COO. A vinyl chloride copolymer containing 78% vinyl chloride was obtained. Resin D was obtained using 100 parts of this resin in the same manner as in Example 1. Comparative Reference Example 1 Resin E was obtained in the same manner as in Example 1 except that acrylic acid (PKa4.2) was used instead of 2-acrylamido-2-methylpropanesulfonic acid. Comparative Reference Example 2 When a vinyl chloride copolymer containing epoxy groups was prepared in the same manner as in Example 3 without using sodium styrene sulfonate, the amount of epoxy groups was 3.7%.
Vinyl chloride accounted for 77%. Resin F was obtained using this copolymer in the same manner as in Example 3. Comparative Reference Example 3 When a vinyl chloride copolymer containing epoxy groups was prepared in the same manner as in Example 3 by reducing the amount of glycidyl methacrylate used, the amount of epoxy groups was 0.4%.
SO ₃ was 0.5% and vinyl chloride was 84%. This copolymer was operated in the same manner as in Example 3 to obtain resin G. Comparative Reference Example 4 100 parts of a commercially available vinyl chloride-vinyl acetate-vinyl alcohol terpolymer, 150 parts of toluene and 80 parts of cyclohexanone were placed in a four-necked flask from step 3, heated to dissolve, heated to 80°C, and then placed in a tolyorange. Add 8 parts of 2-hydroxyethyl methacrylate adduct of isocyanate and add 0.0015 parts of tin octylate.
1 part and 0.0015 part of hydroquinone were added, and the mixture was allowed to react at 80°C in a N ₂ stream until the NCO reaction rate reached 90% or more. After the reaction is completed, cool and methyl ethyl ketone
A resin solution H was obtained by adding 100 parts for dilution. The properties of these resins are shown in the table together with commercially available vinyl chloride-vinyl acetate-maleic acid terpolymer (I) and vinyl chloride-vinyl acetate-vinyl alcohol terpolymer (J). Examples 1 to 4 and Comparative Examples 1 to 6 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 Vinyl chloride resin 100 parts, methyl ethyl ketone 200 parts
A solution consisting of 1 part and 200 parts of toluene was prepared, and the degree of transparency of this solution was visually observed and judged on a three-grade scale of ○△x. 2 Thermal stability 1.0g of vinyl chloride resin was placed in a 15cc test tube.
Plug the opening with absorbent cotton sandwiched with Congo Red test paper and place it in an oil bath at 150℃.
The time required for the Congo Red test paper to change color due to the generated hydrochloric acid was measured. 3. Dispersion Stability A mixture consisting of 400 parts of metallic iron magnetic powder, 100 parts of vinyl chloride resin, 300 parts of methyl ethyl ketone, 300 parts of methyl isobutyl ketone, and 300 parts of toluene was dispersed under high-speed shearing 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. Whether a gel is generated or not,
A portion of the dispersed paint was taken out onto a glass plate, diluted with about 5 times the amount of methyl ethyl ketone, mixed using a glass rod, and visually observed. The results are indicated by ○△× in order of decreasing gel formation. 4 Glossiness 400 parts of cobalt magnetic iron oxide powder, 70 parts of vinyl chloride resin, 30 parts of polyurethane resin (Nituporan 2304 manufactured by Nippon Polyurethane Industries Co., Ltd.), 300 parts of methyl ethyl ketone, 300 parts of methyl isobutyl ketone, 300 parts of toluene, silicon After a mixture consisting of 2 parts of oil was dispersed under high-speed shearing for 90 minutes, the resulting magnetic paint was applied onto a polyester film to a film thickness of 5 μm, subjected to magnetic orientation treatment, and then dried. The reflectance of the magnetic coating film at a reflection angle of 60° was measured using a gloss meter. However, for Resin J, after 90 minutes of dispersion mixing, 20 parts of polyisocyanate (Coronate L manufactured by Nippon Polyurethane Industries Co., Ltd.) was added, and then 10 parts of
A similar test was conducted as a magnetic paint by mixing and dispersing the mixture for minutes. 5 Pot Life The magnetic coating film used for gloss evaluation was passed through a calendar roll with 1/2 the normal linear pressure, the reflectance at a reflection angle of 60°C was measured using a gloss meter, and the film was kept for another week.
The coating film left at 23° C. and 50% relative humidity was calendered under the same conditions as above, the gloss was measured, and the pot life was determined by the difference in drop. 6 Squareness ratio (Br/Bm) The magnetic coating film used for gloss evaluation was 12.5 mm x 50
It was cut into mm pieces and measured using a magnetic property measuring machine. 7 Durability, crosslinking The magnetic coating used for gloss evaluation was smoothed with a calendar roll, and then subjected to acceleration voltage using an electrocurtain type electron beam accelerator manufactured by ESI.
After curing the coating film by irradiating electron beam under _N2 atmosphere at 168KV and irradiation dose of 10Mrad, the load was 100g.
The sample was placed in contact with a rotating drum covered with abrasive paper and 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 ○, Δ, and ×. Further, a part of the cured coating film was taken and rubbed with absorbent cotton impregnated with methyl ethyl ketone, and the degree of shedding of the coating film was evaluated on a three-grade scale of ○, Δ, and ×. However, for the coating film using Resin J, heat treatment was performed at 65° C. for 65 hours instead of electron beam irradiation. 8 Running performance The force generated between the coating film and the rotating drum was measured using a U gauge at 65°C and a relative humidity of 80% using the same method as the durability evaluation, and the running resistance was evaluated in three grades: ○△× in descending order of running resistance. . 【table】

Claims (1)

[Claims] 1 COOM, SO ₃ M, SO ₄ M, PO ₃ M ₂ and PO ₄
Obtained by reacting a vinyl chloride polymer having at least one hydrophilic group selected from M ₂ (M is hydrogen, alkali metal, or ammonium) and an epoxy group with a monobasic acid having an acryloyl group or a methacryloyl group. A polymer, wherein the hydrophilic group is COO, SO ₃ , SO ₄ , PO ₃ or PO ₄ 0.1
~4.0% by weight, an average degree of polymerization of 100~ containing acryloyl group or methacryloyl group as double bond equivalent of 10000 or less and vinyl chloride 60% by weight or more
An electron beam-reactive magnetic paint characterized by using a 900 polymer as a binder for magnetic powder.