JPH0312024A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve electromagnetic conversion characteristics and durability by using vinyl chloride-acryl copolymers and thermoplastic polyurethane resin as binder components. CONSTITUTION:Vinyl chloride-acryl copolymers having hydroxyl groups and sulfo groups, and thermoplastic polyurethane resin having a cyclohexyl ring in its molecular chain are used as the binder components for a magnetic recording medium. A compd. essentially comprising fatty acid ester expressed by formula I is used as a lubricant and incorporated into the magnetic layer of the medium. In formula I, R1, R2 are satd. or unsatd. alkyl groups having a straight or branched chain with 1 - 15 carbons, satisfying that the sum of carbon numbers in R1 and R2 is 6 - 16. R3 is a satd. or unsatd. alkyl group having a straight or branched chain with 17 carbons.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to magnetic recording media, and more particularly to improvements in binders thereof.

[Conventional technology]

Magnetic recording media such as magnetic tapes and magnetic disks are manufactured by applying and drying a magnetic paint containing magnetic powder, a binder, etc. onto a non-magnetic support such as a polyester film.

In recent years, in order to improve recording density and S/N ratio, measures have been taken to make magnetic powder finer particles and to increase coercive force and saturation magnetization. On the other hand, there is a strong demand for binders for dispersing these magnetic powders to have excellent dispersibility and dispersion stability.

However, due to the increase in specific surface area due to finer particles of magnetic powder,
With the increase in cohesive force due to high coercive force, it has become difficult to obtain satisfactory dispersibility with conventionally known binders. Therefore, as a means to improve the dispersibility of magnetic powder, a method of applying high shear force when kneading or dispersing magnetic powder and binder is being considered. Thermal decomposition of the agent may occur, and although the dispersion of the magnetic powder improves, the durability of the magnetic layer tends to decrease.

In addition, improvements in dispersibility by adding a dispersant or water have been investigated, but no satisfactory physical properties have been obtained.

In order to prevent this decrease in durability, there is a method of using a thermoplastic polyester polyurethane resin that is wear-resistant and has a high urethane group concentration. This method has the drawback that since the polyester polyurethane resin has poor water resistance, durability deteriorates when the magnetic recording medium is stored or used at high temperatures.

[Problems to be Solved by the Invention] This invention solves the drawback of the above-mentioned conventional products that the magnetic recording layer coating film has poor water resistance, and thereby provides a magnetic material with excellent electromagnetic conversion characteristics and durability. The purpose is to provide recording media.

[Failure to solve the problem]

The present inventors have conducted intensive research to solve the above problems, and as a result, in a magnetic recording medium using metal magnetic powder,
Vinyl chloride acrylic pentapolymer with hydroxyl and sulfo groups as a binder component and cyclohexyl in the molecular chain)
By using a thermoplastic polyurethane resin having a V ring, a magnetic recording medium with excellent electromagnetic characteristics and durability was obtained.

Further, in the magnetic layer of the above magnetic recording medium, the general formula (R,, R, is a linear or branched saturated or unsaturated alkyl/L/ group having 1 to 15 carbon atoms, and R
, and R1 have a total number of carbon atoms of 6 to 16, and R is a linear or branched saturated or unsaturated alkyl group having 17 carbon atoms).

It has been found that by adding a compound whose main component is a fatty acid ester represented by the following formula, a magnetic recording medium can be obtained which has improved running stability and further improved durability.

In the present invention, the vinyl chloride ρ-acrylic copolymer having a hydroxyl group and a sulfo group used has an average degree of polymerization of 400 to 700, which has a hydroxyl group-containing vinyl group and a sulfo group-containing vinyl group as part of the constituent units. It is preferable that the resin has a vinyl chloride content of 75 to 90% by weight. When the content of vinyl chloride is less than 75% by weight, the durability of the magnetic layer deteriorates, and when the content is less than 90% by weight, the solubility of the resin decreases, making it difficult to form into a paint.

The hydroxyl group-containing vinyl group in this copolymer may be a reaction product of acrylic acid or methacrylic acid with a multi-fA alcohol, methylol group-containing acrylamide, or methylo-p group-containing methacrylic acid! There is raremid. Specific examples include 2-hydroxyethyl acrylate, 2-hydroxymethacrylate, 2-hydroxypropyl acrylate, 2-hydroxypropyl methacrylate, N-methylolacrylamide, N-methylolmethacrylamide, and the like.

The content of vinyl groups containing hydroxyl groups in the copolymer is 10 to 20
% is preferred. When this content is less than 10%,
The dispersibility of the magnetic powder decreases, and the amount of reaction between the binder and the polyisocyanate compound added as a crosslinking agent decreases, resulting in a decrease in crosslinking density and poor durability of the magnetic layer. On the other hand, if the content exceeds 20% by weight, the moisture resistance of the magnetic layer will decrease, and the solubility of the resin in a solvent will decrease.

Examples of the sulfo group-containing vinyl group of the copolymer include 2-acrylamido-2-methylpropanesulfonic acid, vinylsulfonic acid, acrylsulfonic acid, and methacrylsulfone.

The content of these sulfo group-containing vinyl)v groups in the copolymer is preferably 0.1 to 4% by weight. When the content was less than 0.1% by weight, the dispersibility of the magnetic powder decreased, and when the content was more than 4% by weight, the moisture resistance of the magnetic layer decreased.
The solubility of the resin in the solvent deteriorates.

Moreover, it is preferable that the average degree of polymerization of the copolymer is 400 to 700. If the degree of polymerization is less than 400, the mechanical strength of the magnetic layer will be insufficient, and if it is more than 700, the solubility of the resin will decrease, making it difficult to form into a paint.

The thermoplastic polyurethane resin used in combination in the present invention needs to be a polyurethane resin having a cyclohexyl ring in its molecular chain.

Cyclohexy/l'fi can be introduced into the polyurethane resin by using a diol having a cyclohexyl ring or by using a diol having a cyclohexyl ring as a chain extender when synthesizing a polyester component for polyurethane synthesis. . For example, a reaction product of 1-4 cyclohexanediol and adipic acid may be mentioned.

By introducing a cyclohexyl ring into the resin, the Tg of the resin can be increased, and the heat resistance, mechanical strength, etc. of the magnetic layer can be improved. Moreover, hydrolysis resistance is also improved.

The content of the segment having a cyclohexyl ring in the polyurethane resin is preferably 50 to 80% by weight.

If the content is less than 50%, the physical properties such as mechanical strength will be insufficient, and if the content is more than 80%, the Tg will be too high.
The membrane becomes brittle or curls.

The number average molecular weight of this thermoplastic polyurethane resin is 15,
A value in the range of 000 to 60,000 is desirable. If the molecular weight is less than 15,000, the physical properties will decrease, and if it is more than 60,000, the solubility will decrease and the viscosity of the paint will increase.
In the present invention, a compound containing a fatty acid ester represented by the general formula as a main component is used as a lubricant. Since this fatty acid ester has a branched structure and an unsaturated bond, it exhibits good fluidity over a wide temperature range, and can impart excellent lubricity to rounded media with appropriate surface tension. As this compound, 2
-hebutyl undediolate, 2-hebutyl undecyl stearate, and 2-heptyl undecyl lyl-tonato.

This lubricant must be added to the magnetic paint in advance.
It is used by dissolving it in a solvent such as toluene or n-hexane and impregnating it into a magnetic coating. As a lubricant, a conventionally known lubricant may be used in combination with this fatty acid ester.

In that case, the amount of fatty acid ester according to the present invention is
It is necessary that the amount is 50% or more based on the total amount of lubricant.

The metal magnetic powder used in the present invention includes Fe, FeN
Any of ferromagnetic powders such as Fe-Co, Fe-Co-Ni, etc. can be used.

In particular, the surface of the metal powder is coated with an AI compound such that At/metal magnetic powder is 1 to 10% by weight, and its specific surface area is 35 to 55 m17 in BET value, and A metal ferromagnetic material that has adsorbed 0.5 to 2.0% by weight of water is desirable.

In addition, B and C are used to improve magnetic properties and corrosion resistance.

A small amount of elements such as N, Si, P, S, Ti, Cr, Mn, Cu, and Zn may be included.

Any conventionally used nonmagnetic sinterable support, solvent, curing agent, and other additives can be used in the present invention.

〔Example〕

Examples of the present invention will be described below in comparison with comparative examples.

In addition, in the following, parts mean parts by weight.

Example 1 A magnetic paint having the following composition was prepared, and this paint was coated to a thickness of 7
A magnetic layer was formed by coating both sides of a 5 μm polyester film so that the thickness after drying would be 2.5 μm, and after drying, a calendering treatment was performed. Next, this was heat cured at 80° C. for 16 hours, and then punched and polished into a disk shape to produce a magnetic disk.

Polyisocyanate compound 6 parts α・
A1.0. 20 parts car pump hook 2 parts 2-hebutylene oleate 7 parts toylene
183 parts cyclohexanone
183 parts Example 2 As the metal iron magnetic powder in Example 1, 5arr45
m! /9, He: 16000e, σB; 130
emu151, AI/Fa2.0%, approximately 0; 0
．． 5% performance magnetic powder, a vinyl chloride-acrylic copolymer with an average degree of polymerization of 420, and a polyester polyurethane resin with a 1-4-cyclohexane dimetatool adipate component of 50%, number average. 5 except for the resin with a molecular weight of 30,000! A magnetic dog was produced in the same manner as in Example 1.

Comparative Example 1 In Example 2, vinyl chloride-vinyl acetate-vinyl alcohol copolymer was used instead of vinyl chloride-vinyl acrylic copolymer, and polyester polyester Vp-VrJ fat I,
Example 2 except that 1-4 cyclohegysandimethano was used.
A magnetic disk was prepared in the same manner as described above.

Comparative Example 2 In Comparative Example 1, 5 BET for gold and iron magnetic powder; 5
5yyr'/F, Hc; 16000e, σ8;
130 emu152, no coating of AI compound, H,O
Same as Comparative Example 1 except that the magnetic powder with a performance of i O, 4% was used, and the polyester polyurethane resin was replaced with VIi fat with a number average molecular weight of 30.000 and a 1-4 butanediol adipate component of 60%. A magnetic disk was created.

The S/N ratio and magnetic resistance of the magnetic denukes obtained in each of the above Examples and Comparative Examples were measured.

The S/N ratio of the magnetic head is 0.35.
The values are shown as relative values when the magnetic disk of Comparative Example 1 is set to the standard (OdB), which is the value measured using the Sendust magnetic head of the shrine. This is regarded as an indicator of the quality of the dispersibility of the magnetic powder.

111it Magnetism is achieved by loading a magnetic floppy disk drive into a 3.5-inch floppy disk drive, and sliding it into contact with a magnetic head under a temperature cycle environment of o'c-so℃. It is expressed as the number of driving passes until it drops to %.

Claims (2)

[Claims] (1) In a magnetic recording medium in which a magnetic coating film containing ferromagnetic metal powder and a binder for binding the same is provided on a non-magnetic flexible support, the binder component is a chloride containing a hydroxyl group and a sulfo group. A magnetic recording medium comprising a vinyl-acrylic copolymer and a polyurethane resin having a cyclohexyl ring in its molecular chain. (2) As a lubricant in the magnetic layer of the magnetic recording medium shown in claim (1), there are general formulas ▲ mathematical formulas, chemical formulas, tables, etc. ▼ (However, R_1 and R_2 are linear chains with 1 to 15 carbon atoms or a branched saturated or unsaturated alkyl group and R_
The sum of the carbon numbers of 1 and R_2 is 6 to 16, and R_3 is 1 carbon number.
A magnetic recording medium characterized in that it contains a compound whose main component is a fatty acid ester represented by (7) a linear or branched saturated or unsaturated alkyl group.