JPS58153229A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To enhance the dispersibility, surface smoothness and durability by forming the magnetic layer using a binder consisting essentially of polyurethane resin and specified isocyanate compounds. CONSTITUTION:A magnetic layer for magnetic recording is formed using a binder consisting of polyurethane resin having about 1,000-100,000mol.wt., an isocyanate compound having <2 isocyanate groups, an isocyanate compound having >=2 isocyanate groups such as 2,4-tolylene diisocyanate, and a resin having active hydrogen such as vinyl chloridevinyl acetate copolymer, cellulose resin or polyvinyl acetal resin.

Description

Detailed Description of the Invention The present invention relates to a magnetic recording medium, and an object thereof is to provide a magnetic recording medium having a magnetic layer having excellent dispersibility of magnetic powder, good surface smoothness, and excellent durability. It is about providing.

Magnetic recording media are usually made by applying a magnetic paint consisting of magnetic powder, a binder component, an organic solvent, and other necessary components onto a substrate such as a gelatin film, and drying it.
A material with excellent electrical properties and durability is required. Therefore, the binder component used has excellent dispersibility of the magnetic powder, good surface smoothness of the magnetic layer, and can impart excellent electrical properties such as high sensitivity and high S/N ratio to the magnetic recording medium. What is desired is something that can improve the wear resistance of the magnetic layer and improve its durability.

Among the various binder resins currently in use, urethane resin is known to have relatively good properties.
Furthermore, in order to improve these properties, it has been proposed to combine this polyurethane resin with a resin containing active hydrogen, such as vinyl chloride-vinyl acetate-vinyl alcohol copolymer, and a low molecular weight isocyanate compound. Its dispersibility is not quite sufficient, and its abrasion resistance is not necessarily satisfactory.

The inventors conducted various studies on binder components in view of the current situation, and found that the binder components of the magnetic layer include polyurethane resin, an isocyanate compound having less than 2 isocyanate groups, and an isocyanate compound having 2 or more isocyanate groups. When the compound is used in combination with a resin containing active hydrogen, such as vinyl chloride-vinyl acetate-vinyl alcohol copolymer or cellulose resin, the dispersibility of the magnetic powder improves and the surface smoothness of the magnetic layer becomes even better. It was discovered that the wear resistance was further improved, and this invention was made.

The polyurethane resin used in this invention has good affinity with the magnetic powder and has excellent dispersibility of the magnetic powder, and its good toughness also provides good wear resistance of the magnetic layer. Such polyurethane resin has a molecular weight of 100
Those with a low molecular weight of 0 to 100,000 and those with a high molecular weight are preferably used. When a polyurethane resin with a low molecular weight and a hydroxyl group is used, the dispersibility of the magnetic powder is particularly good, and the polymer The abrasion resistance is particularly good when using one of these. As a specific example,
For example, Takelac E-5517 manufactured by Shikinichi Pharmaceutical Co., Ltd.
Examples include Takelac E-550, Pandex T-5201 manufactured by Dainippon Ink and Chemicals, and Pandex T-5250.

In addition, examples of resins having active hydrogen that can be used in combination with the polyurethane resins include vinyl chloride-vinyl acetate-vinyl alcohol copolymers, vinyl chloride-vinyl acetate-maleic acid copolymers, etc. Cellulose resins such as vinyl-vinyl acetate copolymers, nitrocellulose, acetylcellulose, acetylbutylcellulose, methylcellulose, ethylcellulose, benzylcellulose, carboxymethylcellulose, and hydroxycellulose, and polyvinyl acetal resins such as polyvinyl butyral are suitable. used as a
Specific examples of vinyl chloride/lz-vinyl acetate resins having active hydrogen include U and C in the United States.

Examples include VAGHXVMCH and VMCC manufactured by Company C, Eslec A1 Eslec C1 manufactured by Tanemizu Chemical Industry Co., Ltd. and Eslec M1 manufactured by Denki Kagaku Kogyo Co., Ltd. and Denkavinyl manufactured by Denki Kagaku Kogyo Co., Ltd. In addition, as a specific example of the cellulose resin, Nitrocellulose L manufactured by Asahi Kasei Co., Ltd.
1/! , L1/4, LIH1/4, H1/! , Hl, R
5. Etricel P-S R8”/R5 manufactured by Daicel Corporation
"/2, R3I, R52, etc. 16"-, and a specific example of the polyvinyl acetal resin is Eslec BLS manufactured by Tanezu Kagaku Kogyo Co., Ltd.

Esletsu BMS, Esletsu B L = -1, if
Examples include Denka Butyral 3000 manufactured by Kagaku Kogyo Co., Ltd. These active hydrogen-containing resins have good compatibility with the magnetic powder, which affects the dispersibility of the magnetic powder, and when used in combination with an isocyanate compound, the active hydrogen reacts with the isocyanate group in the isocyanate compound, resulting in crosslinking. This strengthens the toughness of the magnetic layer and improves wear resistance. Therefore, when these active hydrogen-containing resins are used together with the polyurethane resin, the dispersibility and wear resistance of the magnetic powder are further improved. The amount used is preferably within the range of 30 to 70% by weight based on the total amount with the polyurethane resin. Too little will not produce the desired effect, and too much will deteriorate the wear resistance of the magnetic layer. There is a risk that the value may actually decrease.

The isocyanate compound having less than 2 isocyanate groups used in combination with the above-mentioned preurethane resin and resin having active hydrogen has a relatively good affinity with the magnetic powder and excellent dispersibility of the magnetic powder, and also has hydroxyl groups. When used in combination with a certain polyurethane resin, the isocyanate group reacts with the hydroxyl group in the polyurethane resin to form a crosslinking bond, thereby strengthening the toughness of the magnetic layer and improving wear resistance. A specific example of such an isocyanate compound is Mytic NY320AX manufactured by Mitsubishi Kasei Corporation.

Examples of isocyanate compounds having two or more inocyanate groups that are used together with the above-mentioned isocyanate compounds having less than two isocyanate groups include 2.4-)lylene diisocyanate, m-phenylene diisocyanate, 4.4'-bis Phenyl diisocyanate, 1,4-cyclohexylene diisocyanate, 1,5-tetrahydronaphthalene diisocyanate, 1,6-hexamethylene diisocyanate, 4-chloro-1,3-phenylene diisocyanate, 1,5-7thalene diisocyanate, etc. Diisocyanates and trifunctional low molecular weight isocyanate compounds, which are usually obtained by reacting 1 mol of triol with 3 mol of diisocyanate, are preferably used, and when these types of isocyanate compounds are used in combination, Incyanate [Two or more incyanate groups contained in the arsenic compound react with the hydroxyl group contained in the polyurethane resin and the active hydrogen in the active hydrogen-containing resin to form a crosslinking bond, thereby increasing the toughness of the magnetic layer. is further strengthened and wear resistance is further improved. In particular, when a trifunctional low molecular weight isocyanate compound is used in combination, the cross-linking becomes network-like, so that the abrasion resistance of the magnetic layer is significantly improved.

Specific examples of such trifunctional low-molecular-weight isocyanate compounds include, for example, Fluone (manufactured by Nippon Polyurethane Industries, Ltd.) L1 Takene (manufactured by Takeshiki Nichishin Kogyo Co., Ltd.), D102 (manufactured by Takeshiki Nichishin Kogyo Co., Ltd.), Desmodur Shi1 (manufactured by Bayer), and Examples include Crispon NX manufactured by Kagaku Kogyo Co., Ltd.

The ratio of the isocyanate compound having two or more inocyanate groups to the above-mentioned isocyanate compound having less than two isocyanate groups is within the range of 1:9 to 9:1, preferably 3:7 to 9:1. 7 to 3
It is preferable that the amount of the isocyanate compound having two or more isocyanate groups is within the range of 1. If the amount of the isocyanate compound having two or more isocyanate groups is too large, the dispersibility of the magnetic powder will not be sufficiently improved, and if it is too small, the wear resistance will not be sufficiently improved. In addition, it is preferable that the amount of both incyanesi compounds used in combination in such a usage ratio be within the range of 5 to 50% by weight based on the total amount of the binder resin used, and if it is too small, it may cause damage to certain areas. If the amount is too high, the crosslinking density may increase, making the magnetic layer hard and brittle.

Examples of the magnetic powder used in this invention include r-F
e, 03 powder, Fe3O4 powder, Co-containing r-Fe, O
.

In addition to powder, Co-containing Fe, O, powder, CrO2 powder, F
Various conventionally known magnetic powders such as metal powders such as e powder, Co powder, and Fe-Ni powder are widely included.

Examples of organic solvents include ketone solvents such as cyclohexanone, methyl ethyl ketone, and methyl isobutyl ketone, ester solvents such as ethyl acetate and butyl acetate, aromatic hydrocarbon solvents such as benzene, toluene, and xylene, and alcoholic solvents such as isopropyl alcohol. -1%L solvents, acid amide solvents such as dimethylformamide, sulfoxide solvents such as dimethyl sulfoxide, ether solvents such as tetrahydro-7rane, dioquinone, etc., which are suitable for dissolving the binder components used. The solvents are not particularly limited and may be used alone or in combination of two or more.

In addition, various additives commonly used in magnetic paints,
For example, dispersants, lubricants, abrasives, antistatic agents, and the like may be optionally added.

The magnetic recording medium of the present invention may be manufactured according to a conventional method. For example, magnetic powder, the above-mentioned binder component of the present invention, an organic solvent, and other additives are placed on a substrate such as a polyester film. The magnetic paint containing the material may be applied by any means such as spraying or rail coating, and then dried.

Next, embodiments of the invention will be described.

Example I Co-containing - Fe, O, magnetic powder 80 parts by weight Takelac E-551T (Bu 1) 6 Manufactured by Yakuhin Kogyo Co., Ltd.
Hydroxyl group-containing polyurethane resin, molecular weight 6000) VAGH (manufactured by U, C, C, USA, chloride 10 parts by weight vinyl-vinyl acetate-vinyl alcohol copolymer) Methyl isobutyl ketone 48 1 silene
48r After mixing and dispersing this composition in a ball mill for 700 hours,! ITETSUKU NY320A
2 parts by weight of X (incyanate compound manufactured by Mitsubishi Kasei, number of isocyanate groups 1.8), methyl isobutyl ketone,
A mixture of 6 parts by weight and 6 parts by weight of toluene was added and mixed and dispersed for another hour, and after this mixing and dispersion, 2 parts by weight of Furonate L (manufactured by Nippon Polyurethane Industries, Ltd., a trifunctional low molecular weight isocyanate compound) was added. was dissolved in a mixed solvent of 6 parts by weight of methyl isobutyl kesine and 6 parts by weight of toluene and mixed and dispersed for 1 hour to prepare a magnetic paint. This magnetic paint was applied onto a polyester film having a thickness of 7 .mu.m to a dry thickness of 5 .mu.m, dried, surface treated, and then cut to a predetermined width to produce a magnetic tape.

Comparative Example 1 In the preparation of the magnetic paint of Example 1, Mytic NY3
A magnetic tape was produced in the same manner as in Example 1, except that the amount of 20AX used was changed from 2 parts by weight to 4 parts by weight, and the mixing and dispersion of Corine) L was omitted.

Comparative Example 2 In the preparation of the magnetic paint of Example 1, Mytic NY3
A magnetic tape was prepared in the same manner as in Example 1, except that the mixing and dispersion of 20AX was omitted and the amount of Coronae (L was changed from 2 parts by weight to 4 parts by weight).

Regarding the magnetic tapes obtained in Examples and Comparative Examples,
The squareness ratio (Br/Bm) and the surface roughness of the magnetic layer were measured to test the durability. The surface roughness of the magnetic layer was measured using a stylus type surface roughness meter, and the surface roughness values were expressed as center fin averages (C, L, A). In addition, the durability test was conducted using a magnetic tape of a specified length at 4.76 eytl/sec.
The table below shows the results of running at a running speed of 100 lbs., while making sliding contact with a magnetic head, and running until a drop in output occurred.

As is clear from the above table, the magnetic tape obtained by the present invention (Example 1) has a higher squareness ratio and lower surface roughness than the conventional magnetic tapes (Comparisons f11 and 2). Furthermore, the durability is improved, and this shows that the magnetic recording medium obtained by the present invention has excellent dispersibility of magnetic powder, good surface smoothness of the magnetic layer, and excellent durability.

Patent applicant: Hitachi Maxell, Ltd.

Claims (1)

[Claims] 1. As a binder component, a polyurethane resin and an isocyanesi compound having less than 2 isocyanate groups; 2.
A magnetic recording medium having a magnetic layer containing an isocyanate compound having the above isocyanate group and a resin having active hydrogen.