JPS6083219A - Binder for magnetic recording body - Google Patents

Abstract

PURPOSE:To improve the dispersibility of magnetic powder when a magnetic coating material is prepd. by using a specified vinyl chloride copolymer as a principal resin component and adding an isocyanate compound as required. CONSTITUTION:A vinyl chloride copolymer contg. 1-3wt% vinyl monomer having a hydroxyl group and 0.05-5wt% acrylic tertiary amine as constituent units is used as a principal resin component, and an isocyanate compound is added as required. When the amount of the vinyl monomer used is >3wt%, the solubility of the copolymer in a solvent, the surface smoothness of a magnetic recording body and the moisture resistance are deteriorated. When the amount is <1wt%, the dispersibility of magnetic powder is deteriorated, and urethane bonds are not well formed by a reaction with the isocyanate compound, so heat curing is not easily carried out. When the amount of the tertiary amine used is >5wt%, the water resistance of the copolymer is deteriorated, and a cross-linking reaction with the isocyanate compound is excessively accelerated to shorten the pot life of a magnetic coating material. When the amount is <0.05wt%, the dispersibility of magnetic powder is deteriorated, and a cross-linking reaction accelerating effect is hardly produced.

Description

DETAILED DESCRIPTION OF THE INVENTION Kihatsu EA 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 made by coating a substrate with a magnetic paint containing magnetic powder and a binder that binds the powder to a substrate such as polyester.
It is obtained by orientation and drying, and is required to have excellent electrical properties and durability such as resistance to sliding contact with a magnetic head. Therefore, binders for magnetic recording media are particularly required to have properties such as 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 excellent abrasion resistance and heat resistance. It is required that it be possible to form a magnetic layer with a high temperature.

Conventionally, hinyl chloride-hinyl acetate-vinyl alcohol-based polymers have been used as those having relatively good properties, and when it is particularly necessary to improve the abrasion resistance of the magnetic layer, the above polymers and incyanate 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.

However, the gist of the present invention is that hydroxyl group-containing vinyl monomers 1-
30% by weight and 0.05-5% by weight of acrylic tertiary amine
The present invention relates to a binder for a magnetic recording medium, characterized in that the main resin component is a vinyl chloride copolymer having as a constituent unit, and optionally contains an incyanate compound.

Kibatsu P! Vinyl chloride in the vinyl chloride copolymer in AK, together with other structural units, gives the magnetic layer appropriate hardness and flexibility; if too little is used, the abrasion resistance of the magnetic recording medium is insufficient and If too much, the solvent solubility tends to decrease, so the content in the copolymer is usually 60 to 95% by weight.

Examples of the hydroxyl group-containing vinyl monomer used as a structural unit of the above copolymer include those having a structural formula as a reaction product of acrylic acid or methacrylic acid and a polyhydric alcohol, and acrylic acid-based or methacrylic acid-based amides. Specific examples of the former include 2- and droxyethyl (meth)acrynote (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 CH2CH2COO(-CH2CH20sn I (n
(C) an integer from 2 to 9, R is hydrogen or methyl group), polypropylene glycol mono(meth)acrylate represented by the following formula to an integer of 6, R is hydrogen or methyl J15), 2-hydroxyethyl-2'-acryloyloxy Examples include (meth)acrylic acid esters such as phthalates,
A specific example of the latter is N-methylol (meth)acrylamide.

These are used alone or in appropriate combinations as constituent units of copolymers, especially 2-hydroxyethyl (meth)
Acrylate, 2-hydroxypropyl (meth)acrylate, and the like are preferably used.

If the fIk used in the vinyl monomer containing a hydroxyl group is too large, problems such as a decrease in the solvent solubility of the copolymer, a decrease in the surface smoothness of the magnetic recording medium, and a decrease in moisture resistance may occur; If the amount is too low, the dispersibility of the magnetic powder tends to decrease, and if necessary, the flex bond due to the reaction with the isocyanate compound contained is not sufficiently formed, making it difficult to heat cure. % by weight is necessary, preferably 2 to 20% by weight.

The acrylic tertiary amine in the present invention refers to a tertiary amine containing an acryloyl group or a methacryloyl group, specifically (meth)acrylic acid such as dimethylaminoethyl (meth)acrylate, diethylamine ethyl'' (meth)acrylate, etc. Suitable examples include esters and dimethylacrylamide, and dimethylaminoethyl acrylate is particularly preferred from the viewpoint of dispersibility of the magnetic powder.

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 may deteriorate or a crosslinking reaction may occur with the incyanate compound contained if necessary. 0.05 to 5% by weight is required in the copolymer because if it becomes too fast, the pot life of the magnetic paint will be shortened, and if it is too small, the dispersibility of the magnetic powder will be poor and the crosslinking reaction promotion effect will be difficult to occur. , and preferably Vi O, 1 to 3% by weight.

The present invention] The binder may further contain ethylene, propylene, maleic anhydride, etc. as a constituent unit of the vinyl chloride copolymer, if necessary, or a homopolymer or copolymer of these. Coalescing may also be used with vinyl chloride-based copolymers. In particular, it is preferable to use ethylene as a constituent unit of the vinyl chloride copolymer from the viewpoint of improving solvent solubility.

The vinyl chloride/I/based copolymer can be obtained by known polymerization methods such as solution polymerization and precipitation polymerization. That is, in the former case, a mixture of equal weights of methyl isobutyl ketone and toluene is used as a suitable solvent,
After removing unreacted monomers, the obtained solution copolymer is used as a raw material for a binder, and in the latter case, n-hexane is used as a suitable solvent. The copolymer is obtained as a fine powder. The polymerization degree of the copolymer is 150 to 60 from the viewpoint of the mechanical strength of the binder and the characteristics of the magnetic paint.
A range of about 0 is preferable.

Examples of cases in which the abrasion resistance and heat resistance of the magnetic layer are particularly enhanced. Examples of isocyanate compounds to be mixed with the magnetic powder together with the above copolymer include (c) tolylene diisocyanate, diphenylmethane diisocyanate, dianisidine diincyanate,
Toridene diisocyanate, hexamethylene diisocyanate, mexylylene diisocyanate) 1,1-trimedyrolpro, <n> 1 mol reacted with 3 mol of tolylene diisocyanate, etc. Product name “Coronate L” from Shiraki Polycretane Industry 4
It is commercially available as b.

The amount of the incyanate compound to be used is usually 0.3 to 30 parts by weight based on 100 parts by weight of the copolymer, since the final coating film will become brittle if it is too large.

To prepare a magnetic paint using the binder of the present invention, a magnetic powder material such as γ-iron acetate is added to the above copolymer dissolved in a solvent such as toluene together with additives such as a surfactant. By adding, kneading and dispersing, an incyanate compound is mixed as necessary, such as when particularly increasing the wear resistance of the magnetic layer, and further, although usually not necessary, a catalyst such as triethylamine is added in some cases to form the magnetic layer P). The order of addition, dispersion means, etc. of the copolymer, incyanate compound, and magnetic material powder in the present invention are not limited at all. In addition, as the solvent used when dissolving the above copolymer to form the binder of the present invention, one or a mixture of two or more of toluene, methyl ethyl ketone, methyl isobutyl ketone, isopropyl alcohol, cyclohexanone, etc. is generally used. 3. The above copolymer is usually used in an amount of 10 to 100 parts by weight per ioo parts by weight of the magnetic material powder, and the magnetic paint is usually prepared to have 5 to 30 weight percent of the above copolymer. Ru.

The binder for magnetic recording materials of the present invention has the above-mentioned structure, and in particular, a specific amount of a hydroxyl group-containing vinyl monomer and an acrylic tertiary amine are contained in the vinyl chloride copolymer, which is the main resin component. Since the copolymer contains vinyl chloride as a constituent unit, the resulting magnetic coating I'i magnetic powder has excellent dispersibility, and a magnetic layer with a high squareness ratio is formed.Also, vinyl chloride is contained in the copolymer. Therefore, in combination with other components, a magnetic layer having appropriate hardness and flexibility is formed.

Furthermore, when the binder of the present invention contains an incyanate compound, the hydroxyl groups introduced into the copolymer contribute to the crosslinking reaction between the copolymer and the incyanate compound, resulting in improved wear resistance and heat resistance. In addition, the active nitrogen introduced into the copolymer by the acrylic tertiary amine promotes the crosslinking reaction, so there is no need to add a low molecular weight catalyst as in the past. The catalyst does not bleed, causing deterioration of the magnetic properties, and the pot life of the obtained magnetic paint does not become short.

The present invention will be explained below with reference to Examples. In the following, "parts" and "%" indicate parts by weight and % by weight, respectively.

In addition, measurements of each property were conducted using the following method.

Squareness ratio If necessary, the magnetic paint to which an incyanate compound has been added is applied onto a 25μ thick polyester film to a dry thickness of 6μ! A magnetic recording medium was prepared by applying tcK, orientation, and drying, and the squareness ratio was measured.

Heat-adhesive magnetic recording material is heated at a temperature of 120°C for 15 minutes to see if it adheres when the magnetic layers are stacked on top of each other. No adhesion (no blocking occurs) as marked on the front. , kasata, × indicates adhesion.

Gel fraction: Vinyl chloride copolymer film Q that does not contain magnetic powder
Toluene-methyl isobutyl ketone (weight ratio l) at 50°C
:1) It is the value (wt%) obtained by dividing the weight of the film after being immersed in a mixed solvent for one day and night by the weight of the film before immersion.
J? ! 1. It serves as a guideline for determining equality.

(Left below) Example 1 Contents with a stirrer 8't41! A mixed solution of methyl isoptylctone and toluene (weight ratio 1:1) 9001i' and Imptyl Nove Oxide 62 were charged into a stainless steel autoclave, and then the air inside the autoclave was removed.

Next, while cooling the autoclave by passing cooling water at 20° C. through the jacket of the autoclave, a monomer mixture consisting of vinyl chloride, 2-hydroxypropyl acrylate and dimethylaminoethyl acrylate was charged with stirring.

After this, hot water was passed through the jacket and heated until the internal temperature reached 35°C to start the polymerization reaction.The temperature of the reaction system was maintained at 35°C for 4 hours.After the above polymerization reaction was carried out for 4 hours, the reaction system was Cool again to 20°C, blow nitrogen gas from the bottom to remove unreacted vinyl chloride, and form a solution of the copolymer.
I got Ft. The amounts of vinyl chloride, 2-hydroxypropyl acrylate, and dimethylaminoethyl acrylate were each 860F1,789.99.

The obtained copolymer solution was precipitated with n-hexane, washed, and then dried at 50° C. for 24 hours to obtain 390 y of slightly yellow powdered copolymer A.

The degree of polymerization of the zelkova butter is 200 and vinyl chloride is 77.7.
%, 2α1 part of 2-hydroxypropyl acrylate, and 2.3 parts of dimethylaminoethyl acrylate.

A 15φ copolymer solution was prepared by dissolving Common Ear 1 Coalescence A in a toluene-methyl isobutyl ketone (weight ratio 1:1) mixture, and then 2.4 times the amount of the copolymer ( After adding T-iron oxide (weight) and mixing and dispersing it in a ball mill for 20 hours to make a magnetic paint, a magnetic recording medium was prepared and the squareness ratio was measured, and a high value of 0.84 was obtained. 11
It was done.

Example 2 Polymerization was carried out according to Example 1 using the same equipment and the same monomers as those used in Example 1. However, the amount of each monomer charged was changed in phase and the polymerization was carried out in n-hexane.

After the polymerization reaction was completed, unreacted vinyl chloride was removed by blowing nitrogen gas from the bottom, and the copolymer was taken out in the form of a slurry, purified by repeated filtration and washing with n-hex, and then heated at 50°C. Copolymer B is dried for 24 hours and becomes a powder.
I got it.

The composition of the copolymer B and the squareness ratio measured by preparing a magnetic recording medium in the same manner as in Example 1 are as shown in Table 1.

In addition, in the same manner as copolymer B, copolymers C, D, E, F, and G having the compositions shown in Table 1 were prepared (A) and the magnetic recording bodies were adjusted. As shown in the table, all α8
It was a high value exceeding .

(Margin below) Table 1 Comparative Example 1 Vinyl chloride produced in the same manner as Resin B of Example 2/
Copolymer of 2-hydroxypropyl acrylate (contains polymerization degree 280.2-HPA 19.0) and vinyl droplet/vinyl acetate/vinyl alcohol copolymer (1).
A magnetic recording medium was prepared in the same manner as in Example 1 with the composition ratios in this order: Vc91/3/6)bVc, and the squareness ratios were set to 1, hα78 and 0.76.

Example 3 Copolymers BG obtained in Example 2 were each dissolved in a toluene-methyl isobutyl ketone (weight ratio 1:1) mixture to prepare a 15% solution.

T-iron oxide in an amount 2.4 times the amount (weight) of the copolymer was added to this solution, mixed and dispersed in a ball mill for 20 hours, and then 0.65 parts of an isocyanate compound (Coronate L, manufactured by Nippon Polyflex Industrial Co., Ltd.) was added. The mixture was added and stirred to obtain a magnetic paint, and this paint was applied onto a polyester film, oriented, and dried to obtain a magnetic recording medium in which the crosslinking reaction had sufficiently progressed.

The squareness ratio and heat adhesion of this magnetic recording material, as well as the gel fraction indicating the crosslinking and reactivity of each copolymer and incyanate, were as shown in Table 2.

2nd Clothing Comparative Example 2 Magnetic recording bodies were prepared in the same manner as in Example 2 for each of copolymers a and b used in Comparative Example 1, and the heat adhesion was measured. Zorocking occurred in both cases. .

Comparative Example 3 Copolymer c having the composition shown in Table 3 in the same manner as Example 2,
d and e were obtained, magnetic paints and magnetic recording bodies were prepared in the same manner as in Example 3, and the squareness ratio and heat adhesion were measured. In addition, the gel fraction, which indicates the crosslinking reactivity between each copolymer and incyanate, was measured. These results are shown in Table 3.

Table 3 Special g “Applicant Sekisui Chemical Co., Ltd. Representative: Mototoshi Fujinuma

Claims (1)

[Scope of Claims] L The main resin component is a vinyl chloride copolymer having 1 to 30% by weight of a hydroxyl group-containing vinyl monomer and 0.05 to 5% by weight of an acrylic tertiary amine as a main resin component. 1. A binder for a magnetic recording medium, which contains an isocyanate compound according to the following. 2. The binder according to item 1, wherein the hydroxyl group-containing vinyl monomer is 2-hydroxypropyl acrylate. & The binder according to item 1 or 2, wherein the acrylic tertiary amine is dimethylaminoethyl acrylate.