JPH04216877A - Magnetic coating resin - Google Patents

Abstract

PURPOSE:To obtain the title resin which maintains high dispersibility and can give a low-viscosity magnetic coating material that forms a magnetic layer with good abrasion resistance by mixing two specified vinyl chloride copolymers. CONSTITUTION:A magnetic coating resin which contains a mixture of a vinyl copolymer (A) having 0.1-5wt.% bound sulfur- or phosphorus-containing strong acid groups and a vinyl chloride copolymer (B) having 0.01-2wt.% bound sulfur- or phosphorus-containing strong acid groups and an average degree of polymerization of 50 to 600 at a weight ratio of A to B of (5:95) to (40:60). The vinyl copolymers are those having strong acid groups introduced from a redox initiator made by using a sulfur- or phosphorus-containing reducing agent. The above- mentioned resin maintains high dispersibility and can give a low-viscosity magnetic coating material that forms a magnetic layer with good 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

2. Description of the Related Art Magnetic recording media such as magnetic tapes and magnetic cards are generally manufactured by coating a substrate such as a polyester film with a magnetic paint containing magnetic powder and its binder as a magnetic layer. 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, strong hydrophilic groups such as carboxyl groups, sulfonic acid groups, and phosphoric acid groups are introduced into the binder to improve affinity for organic solvents due to the hydrophobicity of the binder molecules and magnetic properties due to the strong hydrophilic groups. It has been attempted to improve the dispersibility of magnetic powder by appropriately adjusting the affinity for the powder. Regarding vinyl chloride binder resins into which carboxyl groups, sulfonic acid groups, phosphoric acid groups, etc.
32, 58-114330, 58-150130, 59
-5423, 60-86108, 60-101161,
60-185226, 60-235814, 60-23
8306, 60-238309, 61-39927, 6
1-53367, 61-53368, 61-57640
, 61-83272, 61-96515, 61-104
329, 61-133012, 61-133017, 6
1-133026, 61-158032, 61-172
214, No. 61-243933, etc.

However, if there are too few of these strong hydrophilic groups, the dispersibility of the magnetic powder will be insufficient, and if there are too many, the hydrophilicity of the binder will become too strong. Solubility in solvents such as furan becomes insufficient. In addition, flexible materials such as polyurethane resin and polyester resin are used to improve the durability and reliability of magnetic recording media.
It is commonly used, especially in magnetic recording tapes for recording, to add a crosslinking agent that reacts with part or all of the binder to form a crosslinking bond to the magnetic coating to form a crosslinked coating on the magnetic layer. Therefore, the function of the binder is to be compatible with these flexible materials. If there are too many strong hydrophilic groups, the compatibility with these flexible materials will decrease.

On the other hand, in order to improve the dispersibility of magnetic powder, the viscosity of the magnetic paint has been lowered in order to effectively receive shearing force during the dispersion process and improve the adsorption characteristics of the binder to the magnetic powder. One way to reduce the viscosity is to use a binder with a low degree of polymerization. However, if the degree of polymerization is low, the wear resistance of the magnetic layer will be insufficient.

[0006]

[Problems to be Solved by the Invention] As a result of intensive study to develop a binder that can meet the high performance of such magnetic recording media, the present inventor found that We have discovered that by mixing two types of vinyl chloride copolymers with different average degrees of polymerization, it is possible to obtain a magnetic paint that maintains high dispersibility, has good compatibility with flexible materials, and has low viscosity. , arrived at the present invention.

[0007]

[Means for solving the problem] That is, the amount of strongly acidic roots having sulfur or phosphorus bound is 0.1 to 5 wt.
%, vinyl chloride copolymer with an average degree of polymerization of 10 to 300 (
This resin for magnetic coatings contains a mixture of A) and a vinyl chloride copolymer (B) in which the amount of strongly acidic radicals having sulfur or phosphorus bonded to 0.01 to 2 wt% and an average degree of polymerization of 200 to 600. provided by the invention.

[0008] The vinyl chloride copolymer used in the present invention refers to a copolymer having a vinyl chloride content of 40% by weight or more, which is obtained by copolymerizing vinyl chloride and another unsaturated monomer copolymerizable with vinyl chloride. It is a copolymer of The amount of the strong acid radical containing sulfur or phosphorus bonded to the vinyl chloride copolymer (A) is required to be 0.1 to 5 wt%. The strongly acidic groups bonded are those directly bonded to the main chain and side chains of the vinyl chloride copolymer; for example, SO3
M, -SO4 M, -OPO (OM1) (OM2)
, -PO(OM1)(OM2), (M: hydrogen atom,
Lithium, sodium, potassium, ammonium, M1, M2: hydrogen atom, lithium, sodium,
Potassium, ammonium, alkyl, etc. ) etc.

[0009] If it is less than 0.1 wt%, the dispersibility will be insufficient, and if it is more than 5 wt%, the hydrophilicity will be strong and the solubility in the solvent will be insufficient. The amount of strong acid radicals containing sulfur or phosphorus bonded to the vinyl chloride copolymer (B) is 0.0
It is preferably 1 to 2 wt%, which is smaller than the amount of strong acid radicals bonded to the vinyl chloride copolymer (A). 2w
If it exceeds t%, the hydrophilicity becomes strong and the compatibility with the flexible material decreases.

[0010] In the present invention, the strong acid radical may be introduced by any known method. For example, it can be introduced by the following methods, but among them, one method is the best in terms of process simplicity and polymerization stability. 1. Vinyl chloride and optionally a copolymerizable unsaturated monomer are copolymerized by a redox initiator using a reducing agent containing sulfur or phosphorus. 2. Vinyl chloride and optionally a copolymerizable unsaturated monomer are copolymerized with a radically polymerizable unsaturated monomer having a strong acid group containing sulfur or phosphorus. 3. A strong acid containing sulfur or phosphorus or a salt thereof is added to a copolymer obtained by copolymerizing vinyl chloride, an unsaturated monomer having an epoxy group, and, if necessary, an unsaturated monomer that can be copolymerized. Add.

The amount of the bound strong acid group is determined by changing the amount of the redox initiator, the radically polymerizable unsaturated monomer having a strong acid group containing sulfur or phosphorus, the strong acid containing sulfur or phosphorus, or a salt thereof. You can control it by doing this. The amount of strongly acidic radicals bound can be determined by a combination of elemental analysis and infrared absorption analysis after thoroughly washing the copolymer with water.

In the present invention, as the monomer to be copolymerized with vinyl chloride if necessary, unsaturated monomers having a hydroxyl group such as 2-hydroxyethyl (meth)acrylate and 2-hydroxypropyl (meth)acrylate are used. ; Unsaturated monomers with epoxy groups such as glycidyl (meth)acrylate and allyl glycidyl ether; Vinyl esters of aliphatic carboxylic acids such as vinyl acetate and vinyl propionate; acrylic acid, itaconic acid, methacrylic acid, crotonic acid, maleic acid unsaturated aliphatic carboxylic acids such as acid, fumaric acid, and maleic anhydride, and their monovalent or polyvalent aliphatic alcohol esters; copolymerizable doublets such as vinylidene chloride, styrene, (meth)acrylonitrile, (meth)acrylamide, etc. Examples include olefins having one bond; or dienes having two copolymerizable double bonds such as isobutylene and butadiene, and chlorinated products such as chlorobutadiene.

Examples of the radically polymerizable unsaturated monomer having a strong acid group containing sulfur or phosphorus include vinylsulfonic acid, styrenesulfonic acid, alkylarylsulfosuccinic acid,
Examples include 2-sulfoethyl methacrylate, methallylsulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid, and their sodium, potassium, or ammonium salts.

Salts of strong acids containing sulfur or phosphorus include sulfites such as sodium sulfite, sodium hydrogen sulfite, potassium sulfite, potassium hydrogen sulfite, ammonium sulfite, and ammonium hydrogen sulfite; sodium thiosulfate; sodium hydrogen sulfate, potassium hydrogen sulfate; , hydrogen sulfates such as ammonium hydrogen sulfate; phosphites such as sodium hydrogen phosphite and ammonium hydrogen phosphite; hydrogen phosphates such as disodium hydrogen phosphate and dipotassium hydrogen phosphate;

[0015] As a redox initiator using a reducing agent containing sulfur or phosphorus, a reducing agent such as sodium formaldehyde sulfoxylate or sodium hydrogen phosphite, and a peroxide such as t-butyl hydroperoxide or cumene hydroperoxide are used. It can be a combination of things. The average degree of polymerization of the vinyl chloride copolymer (A) in the present invention is 10 to 150. Similarly, the average degree of polymerization of the vinyl chloride copolymer (B) is 50 to 600.

The average degree of polymerization is the number average degree of polymerization calculated from the number average molecular weight of a standard polystyrene equivalent by gel permeation chromatography (GPC). If the average degree of polymerization of the vinyl chloride copolymer (A) exceeds 150, the viscosity of the paint will be high and the magnetic powder will likely be insufficiently dispersed. The average degree of polymerization of the vinyl chloride copolymer (B) is preferably larger than the average degree of polymerization of the vinyl chloride copolymer (A), and if it is less than 50, the abrasion resistance of the magnetic layer is insufficient. It is.

The resin in the present invention can be obtained by mixing the above two types of vinyl chloride copolymers (A) and (B). The mixing ratio is (A):(B)=5:95-40:
The range of 60 (weight ratio) is particularly preferable; if the ratio of (A) is less than 5, the dispersibility will be insufficient, and the ratio of (B) will be 60.
If it is less than that, the wear resistance of the magnetic layer will be insufficient. The resin mixture obtained in this way has higher dispersibility than a single resin with the same average degree of polymerization and the same amount of strongly acidic radicals containing sulfur or phosphorus, and has a high resistance to wear of the magnetic layer. A magnetic paint with sufficient properties and low viscosity can be obtained. Although the reason is not clear, it is thought that the vinyl chloride copolymer (A) maintains dispersibility and reduces viscosity, and the vinyl chloride copolymer (B) contributes to wear resistance.

[0018]

[Effect of the invention] The resin of the present invention maintains high dispersibility,
It is possible to obtain a magnetic coating material with good abrasion resistance of the magnetic layer and low viscosity.

[0019]

[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, 16 parts of polyurethane resin (Nipporan 2304 manufactured by Nippon Polyurethane Industries Co., Ltd.), 40 parts of methyl ethyl ketone, 24 parts of toluene, and 16 parts of cyclohexanone were added and further dispersed for 60 parts. Polyisocyanate (Coronate L manufactured by Nippon Polyurethane Industries Co., Ltd.)
C3041), 6 parts of MEK, 4 parts of toluene, and 2 parts of cyclohexanone were added, and the mixture was further dispersed for 30 minutes. The obtained paint was coated with a test coater (manufactured by Yasui Seiki, CAD-150).
, equipped with an orientator, coating speed 2 m/s, film thickness 45 μm, drying temperature 90° C.) to coat the polyester film.

The specular reflectance of the magnetic coating film at 60° C.-60° C. 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.
A magnetic measurement device (BHV-30 manufactured by RIKEN DENSHI) was used.
). 3. The viscosity of the magnetic paint prepared with a paint viscosity of 1 was measured at 25° C. and 0.5 rpm using an EM type viscometer (manufactured by Tokyo Keiki). 4. The magnetic coating used for the evaluation of friction abrasion gloss was smoothed with a calendar roll and then heat-treated at 80°C for 48 hours.
The magnetic paint was brought into contact with a rotating drum to which abrasive paper was pasted, and the extent to which the magnetic paint adhered to the abrasive paper was visually observed and evaluated on a three-grade scale of ○, Δ, and ×. Resin synthesis example

[0021]

[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 11.3 parts of allyl glycidyl ether were added. The temperature was raised to 55°C. As soon as the temperature reached 55°C, injection of 0.528 parts per hour of t-butyl hydroperoxide and 0.560 parts per hour of sodium formaldehyde sulfoxyate was started, and further, 2.6 parts of 2-hydroxypropyl acrylate was continuously injected. I started. 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 (I).

[0022]

[Synthesis Example 2] Resin (II) was prepared in the same manner as Synthesis Example 1, except that t-butyl hydroperoxide was used at 0.264 parts per hour and sodium formaldehyde sulfoxyate was used at 0.280 parts per hour. Obtained.

[0023]

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

[0024]

[Synthesis Example 4] Resin (IV) was obtained in the same manner as in Synthesis Example 2, except that sodium hydrogen phosphite was used instead of sodium formaldehyde sulfoxylate.

[0025]

[Synthesis Example-5] Resin (V) was prepared in the same manner as Synthesis Example-1 except that t-butyl hydroperoxide was used at 0.290 parts per hour and sodium formaldehyde sulfoxyate was used at 0.300 parts per hour. Obtained.

[0026]

[Synthesis Example 6] Resin (VI) was obtained in the same manner as in Synthesis Example 1 except that the reaction temperature was changed to 45°C.

[0027]

[Synthesis Example 7] Resin (VII) was obtained in the same manner as in Synthesis Example 1, except that vitamin C was used instead of sodium formaldehyde sulfoxylate.

[0028]

[Synthesis Example 8] Resin (V
III) was obtained.

[0029]

[Table 1]

[0030]

[Table 2]

As can be seen from the above results, compared to Examples 1 and 2 of the present invention, each of the comparative examples has drawbacks for the following reasons. That is, in Comparative Example 1, since only Resin I (corresponding to copolymer (A)) was used, the friction and abrasion properties were poor and the gloss was low.

Comparative Example 2 contains only resin II (corresponding to copolymer (B)), so the viscosity is high and the squareness ratio is also poor. Comparative Example 3 has a high viscosity because it contains only resin V (corresponding to the intermediate between copolymers (A) and (B)). Comparative Example 4 is a blend of Resin IV/II, but since the degree of polymerization of Resin IV is outside the range of copolymer (A), the viscosity is high and the squareness ratio is poor.

Comparative Example 5 is a blend of resin VII/II, but resin V
Since the amount of strong acid roots in II is zero, both gloss and squareness ratio are low. Comparative Example 6 is a blend of Resin I/VIII, but Resin V
Since the degree of polymerization of III is outside the range of copolymer (B),
It has poor friction and abrasion properties and low gloss.

Claims (3)

[Claims] Claim 1: The amount of strongly acidic radicals having bound sulfur or phosphorus is 0.1 to 5 wt%, and the average degree of polymerization is 10 to 1.
50 vinyl chloride copolymer (A) and the amount of strongly acidic radicals having sulfur or phosphorus bonded is 0.01 to 2wt
%, vinyl chloride copolymer with an average degree of polymerization of 50 to 600 (
A resin for magnetic paint containing a mixture of B). Claim 2: The ratio of (A) and (B) is (A):(B)
)=5:95 to 40:60 (weight ratio). 3. The magnetic paint according to claim 1 or 2, wherein the vinyl chloride copolymer has strong acid groups introduced from a redox initiator using a reducing agent containing sulfur or phosphorus. Resin for use.