JPS6230162A - Resin for magnetic coating material - Google Patents

Abstract

PURPOSE:The titled coating resin, consisting of a specific vinylidene chloride based copolymer resin obtained by copolymerizing vinylidene chloride with a vinyl compound having hydroxyl groups, etc., having improved dispersibility of magnetic powder, capable of giving films having good surface smoothness and useful for sound and picture recording tapes, etc. CONSTITUTION:The titled resin consisting of a vinylidene chloride based copolymer resin, obtained by copolymerizing (A) 30-70wt% vinylidene chloride with (B) a vinyl compound having hydroxyl group in an amount to give 0.01-0.7 millimol/g hydroxyl groups and (C) one or two or more copolymerizable monomers and having 10,000-200,000 weight-average molecular weight.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a binder polymer that is a component of a magnetic paint applied to the surface of a so-called coated magnetic recording medium such as an audio-recording tape.

[Conventional technology]

Recording tapes such as cassette tapes, video tapes, and floppy disks are usually made by mixing magnetic powder with polymers called binders, and antistatic agents, lubricants, abrasives, hardening agents, etc., as necessary. It is prepared by thoroughly kneading it together with a solvent in a dispersion mixer such as a ball mill or sand mill. The degree of dispersion of the magnetic coating composition obtained in this way is directly related to the surface smoothness and orientation ratio of the magnetic recording medium, and is the most important factor for the electromagnetic conversion characteristics of the magnetic recording medium. The selection of binder polymer is important to achieve dispersibility. The role of the binder in magnetic tapes is, of course, to fix the magnetic powder to the coating as its name suggests, but it also plays an important role in improving the dispersibility, sufficiency, and orientation of the magnetic powder. For tapes and the like, the smoothness of the magnetic layer coating surface is an important point, and this property is also determined mainly by the properties of the binder. Furthermore, most of the practical physical properties of magnetic tapes, such as abrasion resistance, flexibility, slipperiness, antistatic properties, chemical resistance, and non-adhesiveness, are determined by the binder polymer. As described above, the range of functions required of a binder is extremely wide, so it is not satisfactory to use only one type of binder, and for example, a combination of the following polymers may be used. Vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl acetate-
Vinyl resins such as vinyl alcohol copolymer, polyvinyl butyral, vinylidene chloride-acrylonitrile copolymer, acrylonitrile-butyl acrylate-2-hydroxyethyl methacrylate copolymer, rubber resins such as acrylonitrile-butadiene copolymer, Fibers such as nitrocellulose and acetylcellulose, 4B resins, crosslinkable resins such as epoxy, phenoxy, urethane, etc. Among them, vinylidene chloride resin in particular has a special status because it not only has excellent durability such as solvent resistance and water resistance, but also has excellent dispersibility of magnetic powder and provides a magnetic paint with good spreadability. is occupying.

However, vinylidene chloride resins conventionally known as magnetic paint binders have a vinylidene chloride content of 15 to 3.
0% by weight of vinyl chloride - vinylidene chloride copolymer or vinylidene chloride with a vinylidene chloride content of 70% by weight or more -
It was limited to acrylonitrile copolymers, etc.

The former has insufficient performance due to its low vinylidene chloride content, and although the latter has a special status as a magnetic powder binder, the only solvents that can dissolve it at room temperature are tetrahydrofuran, N, N- Limited to dimethylformamide, etc., it has a problem with solubility in solvents, and furthermore, it tends to thermally decompose and generate hydrochloric acid due to heating during dissolution or temperature rise due to vigorous stirring during compounding. Hydrochloric acid has the problem of causing magnetic paint to gel, making it impossible to apply. Of course, if the content of vinylidene chloride is lowered, the problems of solubility and generation of hydrochloric acid due to thermal decomposition can be solved, but the dispersion performance of the magnetic powder will deteriorate.

[Problem that the invention seeks to solve]

In view of the above, the present inventors have conducted extensive research in order to find a vinylidene chloride resin binder that has excellent dispersibility of magnetic powder, excellent solubility, and is difficult to dehydrochloride, and has accomplished the present invention. It's arrived.

[Means for solving problems]

That is, the present invention provides a vinylidene chloride-based copolymer obtained by copolymerizing vinylidene chloride, a vinyl compound having a hydroxyl group in a side chain, and one or more monomers copolymerizable with these two. A composite resin whose weight average molecular weight is 10,
000 to 200.000, and the content of hydroxyl groups is 0.000 to 200.000.
01 to 0.7 mmol/g and a vinylidene chloride content of 30 to 70% by weight.

As the vinyl compound having a hydroxyl group in the side chain of the present invention,
Esters of double bond unsaturated carboxylic acids such as acrylic acid, methacrylic acid, itaconic acid, crotonic acid and polyhydric alcohols or esters of polyalkylene glycols, i.e. hydroxyalkyl (meth)acrylates,
Specific examples include polyoxyethylene (meth)acrylic acid ester, but 2-hydroxyethyl (meth)acrylate is advantageous in view of the fact that it can introduce many hydroxyl groups with a smaller amount of use and is easily available.

Examples of the carbon-carbon double bond monomer copolymerizable with vinylidene chloride of the present invention include alkyl (meth)acrylate, (meth)acrylonitrile, styrene, vinyl acetate,
Examples include vinyl chloride.

When it is desired that the magnetic recording medium be more flexible,
Choose a material with high internal plasticity such as butyl acrylate, and when you want something as rigid as a floppy disk, use acrylonitrile, methyl methacrylate,
Select from styrene, etc., and make a desired selection such as raising the glass transition point of the resin.

The molecular weight of the vinylidene chloride resin of the present invention is 10,000
Below this, the strength of the resulting magnetic paint film will be low and the abrasion resistance will be unsatisfactory. On the other hand, if it is more than 20,000, the viscosity of the prepared magnetic paint becomes too high and coating becomes difficult.

The content of hydroxyl groups in the vinylidene chloride resin of the present invention is 0.
．． Even if it is less than 0.7 mmol/g
Good magnetic powder dispersibility cannot be obtained even if the amount exceeds g.

The content of vinylidene chloride in the vinylidene chloride resin of the present invention must be 70% by weight or less from the viewpoint of dehydrochloric acid decomposition, and if it is less than 30% by weight, the amount of other monomers used in combination is too large. Therefore, the characteristics of vinylidene chloride resin will be lost.

〔Example〕

Examples of the present invention will be described below. The necessary measurement methods will be described in advance.

■Weight average molecular weight Calibrate using standard polystyrene using gel permeation chromatography.

■Hydroxyl group content The sample resin is reacted with phenyl isocyanate to convert the hydroxyl groups contained into phenyl urethane derivatives. The nitrogen content of the resin before and after this reaction is determined using an NC analyzer (Sumigraph NC-80, manufactured by Sumi Kagaku).

Since the nitrogen added by this derivatization reaction comes from phenyl isocyanate, it is assumed that there were hydroxyl groups in the sample resin equivalent to the added nitrogen.

It is expressed as the number of equivalent moles (mmol) per gram of resin.

(2) Vinylidene chloride content The chlorine content of the resin is determined by the oxygen flask combustion method using Sct+5niger and converted to the vinylidene chloride content.

■ Solubility evaluation sample 3 g of resin was taken and mixed well with 17 g of solvent at room temperature. The solvents used were cyclohexanone, methyl ethyl ketone, and methyl isobutyl ketone, which are widely used as solvents for magnetic coatings.

If the solution was dissolved at room temperature to give a transparent solution, it is marked with an ○, and if it was not sufficiently melted and a cloudy solution was given, it is marked with an X.

■Dechlorination acidity evaluation 5g of sample resin was placed in an Erlenmeyer flask, the conduit stoppered and kept at a constant temperature of 100°C, a constant flow of nitrogen gas was allowed to flow in from the entry pipe, and the exhaust gas was discharged from the exit pipe under stirring. He led her to a beaker filled with water.

The exhaust gas is nitrogen gas containing hydrochloric acid gas generated by thermal decomposition of the sample resin, and this hydrochloric acid gas dissolves into the water in the beaker, increasing the chlorine ion concentration in the water. This change in chlorine ion concentration was measured using an ion concentration meter (Toa Denpa Kogyo, IM-
20E). The chloride ion concentration increased at a constant rate except at the beginning of the measurement. Sample resin Ikg
molar equivalent of hydrochloric acid per hour (Meq/Kg
=Hr).

0 Dispersibility (gloss) evaluation 3.5 g of sample resin was dissolved in 60 g of a 1/1 mixed solvent of cyclohexanone/methyl isobutyl ketone, and magnetic powder (
Mix with 36.5 g of Co -r -F e203),
The mixture was kneaded in a ball mill for 48 hours to prepare a magnetic paint.

After applying this on a glass plate and leaving it in a constant temperature room at 20°C and 65% relative humidity for more than 12 hours, apply a glossy needle (UGV-50).
The 60°-60° specular reflectance was measured using a gas tester) and was defined as the gloss of the sample resin.

A binder that provides good dispersibility of magnetic powder and provides a coating film with good surface smoothness exhibits a high gloss value using this method. This method is widely accepted as a simple method because the dispersibility and smoothness of the binder polymer can be accurately evaluated without actually spending time and money to make the magnetic tape.

Example 1 A seven-mer premix was prepared by dissolving 0.5 parts by weight of lauryl mercaptan in 100 parts by weight of a monomer mixture of vinylidene chloride, 2-hydroxyethyl acrylate, and methyl acrylate at the mixing ratio shown in the attached table. Of this, 5 parts by weight were added to 120 parts by weight of distilled water and 0.0 parts by weight of potassium persulfate.
1 part by weight of sodium dodecylbenzenesulfonate and 0.1 part by weight of sodium dodecylbenzenesulfonate were placed in a glass-lined iron pressure-resistant reactor, and emulsion polymerization was carried out at 50° C. with stirring. After confirming the end of the reaction by lowering the internal pressure of the reactor, an aqueous solution containing the anionic surfactant Eleminol MON-1 (Sanyo Chemical Co., Ltd.) with an effective content of 0.7 parts by weight was added, and then the monomer premix was added. The remainder was added quantitatively over about 10 hours. After confirming the end of the reaction by lowering the internal pressure of the reactor, cool with water and stop stirring. An aqueous solution of calcium chloride is added to the obtained latex to salt out the resin. After sufficiently repeated washing with water, the sample resin was dried to obtain a sample resin.

This resin was identified and performance evaluated using the method described above. The results are shown in Table 1, and the gloss is shown in Table 1.
Also shown in the figure. As is clear from the figure and table, specific regions are shown regarding the content of hydroxyl groups. Resins numbered 2 through 6 are of the present invention.

Example 2 The composition of 100 parts by weight of the monomer mixture was 60 parts by weight of vinylidene chloride, 3.5 parts by weight of 2-hydroxyethyl methacrylate.
The procedure was the same as in Example 1 except that the parts by weight and acrylonitrile were 36.5 parts by weight.

Example 3 Same as Example I except that the composition of 100 parts by weight of the monomer mixture was 50 parts by weight of vinylidene chloride, 7 parts by weight of Blenmar PE200 (NOF, polyethylene glycol monomethacrylate (formula 1)), and 3 parts by weight of methyl methacrylate.
I did the same thing.

Example 4 The composition of 100M parts of the monomer mixture was as follows: 40 parts by weight of vinylidene chloride, 8 parts by weight of Blenmar PP-1000 (NOF, polypropylene glycol methacrylate, formula 2), 35 parts by weight of methyl acrylate, 1 part by weight of methacriconitrile. The procedure was the same as in Example 1 except that the parts were set as .

Comparative Example 1 Example 10 No. 4 except that lauryl mercaptan was not used
When the same procedure was performed, the MW average molecular weight was 283,00
0 resin was obtained.

Comparative Example 2 Commercially available vinylidene chloride 4H fats F216 (Asahi Kasei) and F310 (Dow Chemical) were similarly evaluated.

Comparative Example 3 Commercially available saponified vinyl chloride/vinyl acetate copolymer resin VA
Similar evaluations were made for GH (union carbide).

This item contains many documents related to magnetic paint and magnetic recording,
Since it is a typical binder polymer cited in patent publications, etc., it can be used as a measure of quality performance.

The evaluation results of Example 2.3.4 and Comparative Example 1.2 are shown in Table 2. When viewed in conjunction with Table 1, only the resin of the present invention satisfies all three performances of solubility, dechlorination acid resistance, and dispersibility, and the molecular weight (Comparative Example 1) and hydroxyl group content (Example I
) or vinylidene chloride content (Comparative Example 2), it can be seen that any or all of the three performances will be unsatisfactory.

Vinyl chloride/vinyl acetate copolymers are also considered important as binder polymers, but these simple copolymers have no dispersibility and are therefore not worth using. Therefore, the saponified and hydrolyzed product has good dispersibility. However, although the simple copolymer was stable, when it was made into a saponified product, the dehydrochlorination acidity became worse, as shown in Table 2, and it was worse than F310, which contains a large amount of chlorine. On the other hand, the resin of the present invention does not deteriorate its dehydrochlorination property even if its dispersibility improves.

〔Effect of the invention〕

As shown above, the resin of the present invention not only achieved a marked improvement in performance compared to conventional vinylidene chloride resins, but also showed a significant improvement in practical performance compared to vinyl chloride resins. be.

(Margin below)

[Brief explanation of drawings]

FIG. 1 is a diagram showing the relationship between the hydroxyl group content and gloss (dispersibility) of a copolymer.

Claims (1)

[Claims] (1) A vinylidene chloride copolymer resin made by copolymerizing vinylidene chloride, a vinyl compound having a hydroxyl group in its side chain, and one or more monomers copolymerizable with these two. and its weight average molecular weight is 10,000 to 2
00,000, and the content of hydroxyl groups is 0.01 to 0.00.
7 mmol/g, and the vinylidene chloride content is 30~
A binder polymer for magnetic paints comprising 70% by weight of vinylidene chloride copolymer resin.