JPH0440779B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a binder for magnetic recording materials that has excellent dispersibility of magnetic powder. Magnetic recording materials used in magnetic recording tapes, magnetic disks, etc. are usually obtained by coating a substrate with a magnetic paint containing magnetic powder and a binder that binds the powder to a substrate such as polyester, and drying it. , excellent electrical properties and durability are required. Therefore, binders for magnetic recording media are particularly required to have excellent dispersibility of magnetic powder in magnetic paints, and as a result, to impart a high squareness ratio to magnetic recording media, as well as to have excellent wear resistance and heat resistance. It is required to be able to form an excellent magnetic layer. Conventionally, vinyl chloride-vinyl acetate-vinyl alcohol polymers have been used as polymers with relatively good properties, and when it is necessary to particularly improve the wear resistance of the magnetic layer, the polymers and isocyanate compounds may be contained. Although binders for magnetic recording bodies have been used, further improvements have been desired. In view of the current state of binders for magnetic recording media, the present invention provides a magnetic layer that has excellent dispersibility of magnetic powder when made into a magnetic coating material, and has excellent abrasion resistance and heat resistance by adding an isocyanate compound if necessary. An object of the present invention is to provide a binder for a magnetic recording body that can form a magnetic recording material. Therefore, the gist of the present invention is to use vinyl chloride, a hydroxyl group-containing vinyl monomer, an acrylic tertiary amine, a copolymer having a different acrylic ester or vinyl acetate as a constituent unit, and optionally an isocyanate compound. A binder for a magnetic recording body characterized by containing the following. Vinyl chloride, which makes up the majority of the copolymer in the present invention, provides appropriate hardness and flexibility to the magnetic layer together with other structural units, and the amount used must be 60 to 95% by weight. . Examples of the hydroxyl group-containing vinyl monomer in the present invention include those having a structural formula as a reaction product of acrylic acid or methacrylic acid and a polyhydric alcohol, acrylic acid-based or methacrylic acid-based amides, etc. Specific examples of the former Examples include 2-hydroxyethyl (meth)acrylate (this represents both 2-hydroxyethyl acrylate and 2-hydroxyethyl methacrylate. The same applies hereinafter), 2-hydroxypropyl (meth)acrylate, 3-chloro-2-hydroxypropyl (meth)acrylate, polyethylene glycol mono(meth)acrylate CH ₂ =CR−COO(−
CH ₂ CH ₂ O) - _o H (n is an integer from 2 to 9, R is hydrogen or methyl group), polypropylene glycol mono(meth)acrylate represented by the following formula

[Formula] (n is an integer from 2 to 6, R is hydrogen or methyl group), 2-hydroxyethyl-2'-acryloyloxyphthalate A specific example of the latter is N-methylol (meth)acrylamide. These are used alone or in appropriate combinations as structural units of copolymers, and in particular, polyethylene glycol monomethacrylate in which n in the above formula is 7 to 9, polypropylene glycol monomethacrylate in which n in the above formula is 5 or 6, and 2-hydroxy Propyl (meth)acrylate and the like are preferably used. The amount of vinyl monomers containing these hydroxyl groups is as follows:
If the amount is too high, the solubility of the copolymer in the solvent will decrease, and if it is too low, the dispersibility of the magnetic powder will tend to decrease, and if necessary, urethane bonds will be sufficiently formed by reaction with the isocyanate compound contained. It is necessary for the amount to be 0.1 to 30% by weight of the copolymer, as it will not be cured by heat and will be difficult to heat cure.
Preferably it is 0.5 to 10% by weight. In the present invention, the acrylic tertiary amine refers to a tertiary amine containing an acryloyl group or a methacryloyl group.
Preferred examples include (meth)acrylic acid esters such as dimethylaminoethyl (meth)acrylate and diethylaminoethyl (meth)acrylate, and dimethylacrylamide. Among these, dimethylaminoethyl acrylate is particularly preferred. The tertiary amine greatly contributes to improving the dispersibility of the magnetic powder, but if the amount is too large, the water resistance of the copolymer will deteriorate, and if it is too small, the dispersibility of the magnetic powder will deteriorate. Since the effect of promoting the crosslinking reaction between the isocyanate compound contained in the copolymer and the above copolymer is less likely to occur, it is necessary that the amount is 0.05 to 15% by weight of the copolymer, preferably 0.1 to 5% by weight. be. The acrylic ester in the present invention refers to an ester of (meth)acrylic acid and an aliphatic alcohol, and an ester of (meth)acrylic acid and an alicyclic alcohol, and therefore refers to the above-mentioned hydroxyl group-containing vinyl monomer and acrylic ester. A monomer different from the tertiary amine, specifically, for example, methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, amyl (meth)acrylate, hexyl (meth)acrylate, cyclohexyl (meth)acrylate, ) Acrylate, heptyl (meth)
Acrylate, octyl (meth)acrylate,
Examples include 2-ethylhexyl (meth)acrylate, nonyl (meth)acrylate, decyl (meth)acrylate, dodecyl (meth)acrylate, tetradodecyl (meth)acrylate, glycidyl (meth)acrylate, etc., which may be used alone or in combination. 1 to 20 in the above copolymer.
It is contained in an amount by weight and contributes to improving solubility in solvents and dispersibility of magnetic powder, and imparting flexibility to the magnetic layer. In the present invention, vinyl acetate may be used instead of the acrylic ester as a constituent unit of the copolymer, and of course may be used in combination, and the content of vinyl acetate in the copolymer is 1~
It accounts for 20% by weight and contributes to improving the solubility in solvents and dispersibility of magnetic powder, and imparting flexibility to the magnetic layer. Copolymers containing each of the above monomers as constituent units include:
Furthermore, if necessary, other polymerizable vinyl monomers such as ethylene and styrene may be added as structural units, and the preferable range of the degree of polymerization is 200 to 600. It can be obtained by known polymerization methods such as polymerization, emulsion polymerization, and suspension polymerization. Isocyanate compounds to be kneaded with the magnetic powder together with the above copolymer when particularly enhancing the abrasion resistance and heat resistance of the magnetic layer include tolylene diisocyanate, diphenylmethane diisocyanate, dianisidithi diisocyanate, tridene diisocyanate, and hexamethylene. Examples include diisocyanate, metaxylylene diisocyanate, and a reaction product of 1 mol of trimethylolpropane and 3 mol of tolylene diisocyanate. The reaction product is, for example, available from Nippon Polyurethane Kogyo Co., Ltd. under the trade name "Coronate L". It is commercially available. The amount of isocyanate compound to be used is preferably 30 parts by weight or less per 100 parts by weight of the above copolymer, since the final coating film will become brittle if it is too large.
It is usually 0.3 parts by weight or more. To create a magnetic paint using the binder of the present invention,
For example, a magnetic powder material such as γ-iron acetate is added to the above copolymer, which is polymerized by solution polymerization and dissolved in a solvent such as toluene, and is kneaded and dispersed to particularly increase the wear resistance of the magnetic layer. A magnetic coating material is obtained by mixing an isocyanate compound as necessary, such as when the temperature is high, and further adding a catalyst such as triethylamine in some cases, although it is not normally necessary. However, the order of addition, dispersion means, etc. of the copolymer isocyanate compound and magnetic material powder in the present invention are not limited at all. The solvent used to dissolve the copolymer to form the binder of the present invention is generally one or a mixture of two or more of toluene, methyl ethyl ketone, methyl isobutyl ketone, isopropyl alcohol, cyclohexanone, and the like. The above copolymer is a magnetic material powder
Usually 25 to 100 parts by weight are used per 100 parts by weight, and magnetic paints are usually prepared with 10 to 30% by weight of said copolymer. The binder for magnetic recording media of the present invention has the above-mentioned structure, and in particular, the copolymer is made of vinyl chloride.
60-95% by weight, hydroxyl group-containing vinyl monomer 0.1-30
% by weight, 0.05-15% by weight of acrylic tertiary amine, and 1-20% by weight of acrylic ester or vinyl acetate different from the former two, so the resulting magnetic paint has excellent dispersibility of magnetic powder. A magnetic layer with a high squareness ratio is formed, and since the copolymer contains vinyl chloride, in combination with other components, a magnetic layer with appropriate hardness and flexibility is formed. It is. Furthermore, when the binder of the present invention contains an isocyanate compound, the hydroxyl groups introduced into the copolymer contribute to the crosslinking reaction between the copolymer and the isocyanate compound, resulting in excellent wear resistance and heat resistance. In addition, the active nitrogen introduced into the acrylic copolymer by the acrylic tertiary amine promotes the crosslinking reaction, so that the magnetic paint can be cured sufficiently even at low temperatures after being applied to the substrate. At this time, unlike conventional methods, it is not necessary to add a low molecular weight catalyst, so the catalyst does not bleed and deteriorate the magnetic properties, and the magnetic coating obtained The pot life of the plant will not be shortened. The present invention will be explained below with reference to Examples. still,
In the following, "parts" and "%" indicate parts by weight and % by weight, respectively. Example 1 80 parts of water in which 0.32 part of polyvinyl alcohol as a suspension stabilizer was dissolved was placed in an autoclave equipped with a stirring bar, a monomer inlet pipe, a nitrogen blowing pipe, a vacuum line, and a thermometer, and then 0.06 part of benzoyl peroxide was added. A mixture of 13 parts of vinyl acetate monomer, 2 parts of 2-hydroxyethyl methacrylate monomer, and 2 parts by weight of dimethylaminoethyl acrylate monomer was added, and the reaction system was purged with nitrogen and degassed in a vacuum line. After removing oxygen, 83 parts by weight of vinyl chloride was introduced and polymerized at 80°C for 18 hours with stirring to obtain a copolymer. The obtained copolymer was centrifuged using a centrifuge, washed with water, thoroughly dehydrated, and air-dried at 50°C for 24 hours.
A white powder polymer was obtained. This powder copolymer was mixed with toluene-methyl isobutyl ketone (weight ratio 1:
1) A 15% copolymer solution was prepared by dissolving it in the mixed liquid. Next, γ-iron oxide was added to this solution in an amount such that γ-iron oxide was 47 parts based on 20 parts of the solid content of the copolymer, and the mixture was mixed and dispersed in a ball mill for 10 hours to obtain a magnetic paint. In addition, magnetic paint was applied onto a 25μ thick polyester film to a dry thickness of 6μ, and the film was left at room temperature.
A magnetic recording medium was prepared by leaving it for 48 hours and drying, and the squareness ratio was measured. As shown in Table 1, the results were excellent, exceeding 0.8. Examples 2 and 3 Copolymers having various compositions shown in Table 1 were prepared in the same manner as in Example 1, magnetic paints were prepared, magnetic recording bodies were obtained, and their squareness ratios were measured. The results were as shown in Table 1. Comparative Example 1 Squareness ratio of a magnetic recording medium obtained by creating a magnetic paint using vinyl chloride-vinyl acetate-vinyl alcohol polymer (weight ratio, in this order: 91:3:6) in the same manner as in Example 1 was measured. The results were as shown in Table 1.

【table】

[Table] Comparative Example 2 A magnetic paint was prepared using a vinyl chloride-vinyl acetate-acrylic acid ester-vinyl alcohol polymer in the same manner as in Example 1, and the squareness ratio of the obtained magnetic recording material was measured. The squareness ratio was 0.77. Example 4 A white powder copolymer was obtained in exactly the same manner as in Example 1, including the types and amounts of raw materials, and the operating method. This copolymer was dissolved in toluene-methyl isobutyl ketone (weight ratio 1:1) to prepare a 15% copolymer solution. After adding γ-iron oxide in an amount of 47 parts and mixing and dispersing in a ball mill for 10 hours, an isocyanate compound (manufactured by Nippon Polyurethane Industries, Ltd.,
0.65 part of Coronate L) was added and stirred to obtain a magnetic paint. The viscosity of this magnetic paint after 24 and 48 hours was measured using a B-type viscometer to check the pot life stability. In addition, magnetic paint was applied onto a 25μ thick polyethylene terephthalate film to a dry thickness of 6μ, and left to dry and harden at room temperature for 48 hours to produce a magnetic recording medium. and gel fraction were investigated. These results are shown in Table 2. Heating adhesion means heating the formed magnetic layer to 120°C.
This test was conducted to see whether or not the magnetic layers adhered when they were heated for 15 minutes at a temperature of
In addition, × indicates adhesion. Gel fraction is the value obtained by immersing a copolymer resin film without magnetic powder in a mixed solvent of toluene-methyl isobutyl ketone (weight ratio 1:1) for one day and night, dividing the weight of the film by the weight of the film before immersion. This is a standard for determining the reaction efficiency of the crosslinking reaction between the copolymer and the isocyanate compound. Examples 5 to 6 In the same manner as in Example 4, copolymers with various compositions as shown in Table 2 were prepared to obtain binders, and the viscosity increase rate of the magnetic paint, the squareness ratio of the magnetic layer, The heat adhesion and gel fraction were examined. The results were as shown in Table 2. Comparative Example 3 In the same manner as in Example 4, copolymers having various compositions as shown in Table 2 were prepared to obtain binders, and magnetic paints and magnetic layers were evaluated. Second result
Shown in the table. Comparative Example 4 Except for adding 0.82 parts of triethylamine as a catalyst to 100 parts of the copolymer obtained in Comparative Example 1,
A binder was obtained in the same manner as in Example 4, and the magnetic paint and magnetic layer were evaluated. The results are shown in Table 2. Comparative Example 5 A 15% solution of vinyl chloride-vinyl acetate-vinyl alcohol polymer shown in Table 2 in toluene-methyl isobutyl ketone (weight ratio 1:1) was prepared,
A binder was obtained in the same manner as in Example 4, and a magnetic paint was prepared. These evaluation results are shown in Table 2. Comparative Example 6 A binder was obtained and a magnetic paint was prepared in the same manner as in Comparative Example 5, except that 0.41 part of triethylamine was added as a catalyst to 100 parts of the copolymer shown in Comparative Example 5. These evaluation results are shown in Table 2.

【table】

Claims (1)

[Claims] 1. 60 to 95% by weight of vinyl chloride, 0.1 to 30% by weight of hydroxyl group-containing vinyl monomer, acrylic tertiary amine
For magnetic recording media containing a copolymer having a structural unit of 0.05 to 15% by weight and 1 to 20% by weight of an acrylic ester or vinyl acetate different from the former two, and if necessary an isocyanate compound. Binder. 2. The binder according to item 1, wherein the hydroxyl group-containing vinyl monomer is polyethylene glycol monomethacrylate. 3. The binder according to item 1, wherein the hydroxyl group-containing vinyl monomer is 2-hydroxypropyl methacrylate. 4. The binder according to any one of Items 1 to 3, wherein the acrylic tertiary amine is dimethylaminoethyl acrylate. 5 Isocyanate compound content is copolymer
Item 1 ~ which is 0.3 to 30 parts by weight per 100 parts by weight
The binder according to any one of item 4.