JPH04216876A - Magnetic coating resin - Google Patents

Abstract

PURPOSE:To obtain the title resin which maintains high dispersibility and gives a low-viscosity magnetic coating material that forms a magnetic layer with sufficient abrasion resistance by copolymerizing vinyl chloride in the presence of a specified redox initiator so as to form a copolymer having bound strong acid groups in an amount in a specified range. CONSTITUTION:Vinyl chloride and, if necessary, other copolymerizable monomer are copolymerized in the presence of a redox initiator made by using a sulfur- or phosphorus-containing reducing agent (e.g. a combination of a reducing agent, such as sodium formaldehyde sulfoxylate or sodium phosphite, with a peroxide such as t-butyl hydroperoxide) to give a magnetic coating resin comprising a vinyl copolymer having bound strong acid groups in an amount of 0.1-5wt.%. This resin maintains high dispersibility and can give a low-viscosity magnetic coating material that forms a magnetic layer with sufficient abrasion resistance.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vinyl chloride resin used as a binder for magnetic recording media.

0002

[Prior Art] Magnetic recording media such as magnetic tapes and magnetic cards are generally manufactured by coating a medium such as a polyester film with a magnetic paint containing magnetic powder and its binder as a magnetic layer. has been done. In recent years, as the density of magnetic recording media has increased, finer magnetic powders with large specific surface areas have come to be used. Such fine particle magnetic powder has a strong cohesive force between particles, and it is difficult to obtain a uniformly dispersed state.

[0003] For this reason, strongly hydrophilic groups such as carboxyl groups, sulfonic acid groups, and phosphoric acid groups are introduced into the binder to improve the affinity for organic solvents due to the hydrophobicity of the binder molecule and the strong hydrophilic groups described above. The dispersibility of magnetic powder has been improved by suitably harmonizing its affinity for magnetic powder. Regarding vinyl chloride binder resins into which carboxyl groups, sulfonic acid groups, phosphoric acid groups, etc. have been introduced, JP-A-57-44227, 58-1080
32, 58-114330, 58-150130, 59
-5423, 60-86108, 60-101161,
60-185226, 60-235814, 60-23
8306, 60-238309, 61-39927, 6
1-53368, 61-53367, 61-57640
, 61-83272, 61-96515, 61-104
329, 61-133012, 61-133017, 6
1-133026, 61-158032, 61-172
214, 61-243933, etc.

[0004] Vinyl chloride resins into which carboxyl groups, sulfonic acid groups, phosphoric acid groups, etc. have been introduced are obtained by combining vinyl chloride and other unsaturated monomers as necessary with unsaturated monomers having strong hydrophilic groups. A method of copolymerizing vinyl chloride and, if necessary, another unsaturated monomer with a radical generator containing sulfur or phosphorus; There is also a method of adding an alkali metal salt or ammonium salt of a strong acid containing sulfur or phosphorus to a copolymer obtained by copolymerizing other unsaturated monomers as necessary.

However, in the method of copolymerizing an unsaturated monomer having a strong hydrophilic group, it is difficult to control the copolymer composition because the unsaturated monomer having a strong hydrophilic group is water-soluble. In the method of copolymerization using a radical generator containing sulfur or phosphorus, the decomposition rate of the radical generator largely depends on the polymerization temperature and the change in the pH of the polymerization system, so it is difficult to control the amount of strongly hydrophilic groups introduced. is difficult. Furthermore, the method of adding an alkali metal salt or ammonium salt of a strong acid containing sulfur or phosphorus to a copolymer requires a new addition operation after polymerization.
The process becomes complicated.

[0006]

[Problems to be Solved by the Invention] As a result of intensive study in order to develop a binder that can meet the high performance of such magnetic recording media, the present inventor discovered that vinyl chloride and, if necessary, an unsaturated binder that can be copolymerized. By introducing monomers using a redox initiator using a reducing agent containing sulfur or phosphorus, a vinyl chloride copolymer with a bonding amount of 0.1-5 wt% of strongly acidic groups has high dispersibility. It has been discovered that a magnetic paint with low viscosity can be obtained, and the present invention has been achieved.

[0007]

[Means for solving the problem] That is, vinyl chloride and other unsaturated monomers that can be copolymerized as necessary,
Copolymerized with a redox initiator using a reducing agent containing sulfur or phosphorus, the amount of strongly acidic radicals bound is 0.1-5w
t% of a vinyl chloride copolymer is provided by the present invention.

[0008] The vinyl chloride copolymer in the present invention is obtained by copolymerizing vinyl chloride and another unsaturated monomer copolymerizable with vinyl chloride, and has a vinyl chloride content of 40% by weight. This is the above copolymerization. The amount of the strong acid radical containing sulfur or phosphorus bonded to the vinyl chloride copolymer is required to be 0.1-5 wt%. The bonded strong acid group is one that is directly bonded to the main chain and side chain of the vinyl chloride copolymer, and for example, -SO3
M, -SO4 M, -PO (OM1) (OM2),
-OPO(OM1)(OM2), (M: hydrogen, lithium, potassium, sodium, ammonium, M
1, M2: hydrogen, lithium, potassium, sodium, ammonium, alkyl group. ) etc. At 0.1 end, dispersibility becomes insufficient, and at 5 wt% or more, hydrophilicity becomes strong and solubility in solvents becomes insufficient. The amount of strongly acidic radicals can be controlled by varying the amount of redox initiator. The amount of strong acid radicals is determined by elemental analysis and infrared absorption after thoroughly washing the copolymer with water.

As a redox initiator using a reducing agent containing sulfur or phosphorus, a reducing agent such as sodium formaldehyde sulfoxylate or sodium phosphite is used,
-Butyl hydroperoxide, cumene hydroperoxide
Examples include combinations of peroxides such as oxide. In the present invention, as a monomer to be copolymerized with vinyl chloride as necessary, glycyl (meth)acrylate
Unsaturated monomers with epoxy groups such as ester, allyl glycidyl ether; unsaturated monomers with hydroxyl groups such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, etc. ; Vinyl esters of aliphatic carboxylic acids such as vinyl acetate and vinyl propionate;
Acrylic acid, itaconic acid, methacrylic acid, crotonic acid,
Unsaturated aliphatic carboxylic acids such as maleic acid, fumaric acid, maleic anhydride and their monohydric or polyhydric aliphatic alcohol esters; vinylidene chloride, styrene, (meth)
Examples include olefins having one copolymerizable double bond such as acrylonitrile (meth)acrylamide; dienes having two copolymerizable double bonds such as isobutylene and butadiene; and chlorinated products such as chlorobutadiene.

The average degree of polymerization of the vinyl chloride copolymer in the present invention is 100-600. . What is the average degree of polymerization?
This is the number average degree of polymerization calculated from the number average molecular weight in terms of standard polystyrene using gel permeation chromatography (GPC). If the average degree of polymerization of the vinyl chloride copolymer exceeds 600, the viscosity of the paint will be high and the dispersion of the magnetic powder will tend to be insufficient.If the average degree of polymerization is less than 100, the wear resistance of the magnetic layer will deteriorate. It becomes insufficient.

[0011]

[Effect of the invention] The resin of the present invention maintains high dispersibility,
It is possible to obtain a low-viscosity magnetic coating material whose magnetic layer has sufficient wear resistance.

0012

[Examples] The present invention will be explained in more detail with reference to Examples below. Evaluation of resin physical properties was performed as follows. According to the synthesis example, each resin shown in Table 1 was synthesized. Next, each of these resins was evaluated as a magnetic coating material and a magnetic recording medium. The results are shown in Table 2. The evaluation method was as follows.

1. 126 parts of glossy cobalt-modified γ-ferrite, 16 parts of vinyl chloride resin, 106 parts of methyl ethyl ketone, 64 parts of toluene
After high-speed shear dispersion for 180 minutes, the resulting paint was coated with a test coater (manufactured by Yasui Seiki, CAD-150, with orientation device, coating speed 2 m/s, film thickness 45 .mu.m, drying temperature 90.degree. C.) and coated onto a polyester film. 60 of its magnetic coating
The specular reflectance at -60° was measured using a gloss meter (manufactured by Suga Test Instruments).

2. The magnetic coating used for the evaluation of squareness ratio glossiness was 10 mm x 10 mm.
Cut it out and use a magnetic measurement device (BHV- manufactured by Riken Denshi).
30). 3. Paint Viscosity The viscosity of the magnetic paint prepared in 1 above was measured at 25° C. and 0.5 rpm using an EM type viscometer (manufactured by Tokyo Keiki).

[0015]

[Synthesis Example-1] 207 parts of deionized water, 0.14 parts of 28% aqueous ammonia, and 26 parts of sodium lauryl sulfate were placed in an autoclave, and after degassing, 86.1 parts of vinyl chloride and allyl glycidyl ether were added. 11.3 parts of ester were charged, and the temperature was raised to 55°C. As soon as the temperature reached 55°C, injection of 0.264 parts per hour of t-butyl hydroperoxide and 0.280 parts per hour of sodium formaldehyde sulfoxide was started, and 2.6 parts of 2-hydroxypropyl acrylate was continuously added. I started injecting it. The internal pressure of the autoclave is 4kg/c
m2, unreacted vinyl chloride was collected and taken out, salted out, washed and dried to obtain resin (A).

[0016]

[Synthesis Example-2] Resin (B) was prepared in the same manner as Synthesis Example-1 except that t-butyl hydroperoxide was used at 0.528 parts per hour and sodium formaldehyde sulfoxyate was used at 0.560 parts per hour. I got it.

[0017]

[Synthesis Example 3] Resin (C) was obtained in the same manner as in Synthesis Example 1, except that sodium hydrogen phosphite was used in place of sodium formaldehyde sulfoxylate.

[0018]

[Synthesis Example 4] Resin (D) was obtained in the same manner as Synthesis Example 2, except that vitamin C was used instead of sodium formaldehyde sulfoxylate. As can be seen from Tables 1 and 2, Comparative Example 1, which does not have strong acid groups, has low gloss and squareness ratio, and high viscosity.

[0019]

[Table 1]

[0020]

[Table 2]

Claims (2)

[Claims] Claim 1: Vinyl chloride and other copolymerizable unsaturated monomers are copolymerized using a redox initiator using a reducing agent containing sulfur or phosphorus, and the amount of strongly acidic groups bonded is 0. .1-5 wt% vinyl chloride copolymer resin for magnetic paint. 2. The vinyl chloride copolymer magnetic paint resin according to claim 1, which contains an unsaturated monomer having an epoxy group.