JPS58153228A - 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 1,000-10,000mol.wt., an isocyanate compound having <2 isocyanate groups, and an isocyanate compound having >=2 isocyanate groups such as 2,4-tolylene diisocyanate or further contg. vinyl chloride-vinyl acetate copolymer or other 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 polyester 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 used, polyurethane resin is known to have relatively good properties.
Furthermore, in order to improve these properties, it has been proposed to use a low molecular weight isocyanate compound in combination with this.
The dispersibility of the magnetic powder is not sufficient, and the wear resistance is not necessarily satisfactory.

In view of the current situation, the inventors conducted various studies on binder components and found that the binder components of the magnetic layer include a polyurethane resin, an incyanate compound having less than 2 incyanesi groups, and 2 or more isocyanate F groups. The present inventors have discovered that when a compound (isocyanate) is used in combination, the dispersibility of the magnetic powder is improved, the surface smoothness of the magnetic layer is further improved, and the abrasion resistance is further improved, and this invention has been completed.

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 urethane resin is used as long as it has a low molecular weight and has hydroxyl groups, the dispersibility of the magnetic powder is particularly good. When a material with a high molecular weight is used, wear resistance becomes particularly good. As a specific example, for example, Takelac E-5517 manufactured by Shikinichi Yakuhin Kogyo Co., Ltd.
, Takelac E-550, Dainippon Ink & Chemicals Co., Ltd.'s Pandex T-5201, Bandex T-5250, and the like.

Incyanate compounds having less than 2 isocyanate groups that are used in combination have relatively good affinity with magnetic powders and excellent dispersibility of magnetic powders, and when used in combination with polyurethane resins having hydroxyl groups, the isocyanate groups can be used in polyurethane resins. Because it reacts with the hydroxyl groups inside and forms a crosslinking bond, the toughness of the magnetic layer is strengthened and its wear resistance is also improved. A specific example of such an isocyanate compound is Mytic NY320AX manufactured by Mitsubishi Kasei Corporation.

Examples of isocyanate compounds having two or more isocyanate groups that are used together with the isocyanate compounds having less than two isocyanate groups are, for example, 2.4-)lylene diisocyanate), m-phenylene diisocyanate), 4-) .4'-bisphenylene diisocyanate), 1,4-cyclohexylene diisocyanate, 1,5-tetrahydronaphthalene diisocyanate), 1,6-hexamethylene diisocyanate, 4-chloro-1,3-phenylene diisocyanate isocyanate), 1.5-
Diisocyanates such as 7-tale diisocyanate and trifunctional low molecular weight isocyanate compounds, which are usually obtained by reacting 1 mol triol with 3 mol diisocyanate, are preferably used, and these types of isocyanate compounds are used in combination. Then, two or more incyanate groups contained in the incyanate compound react with the hydroxyl groups contained in the polyurethane resin and form a crosslinking bond, further strengthening the strength of the magnetic layer and improving wear resistance. will improve further. 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 Copnate L manufactured by Nippon Polyurethane Industries, Ltd.
Examples include #'r*-)0102 manufactured by Takeda Pharmaceutical Co., Ltd., Desmodur L1 manufactured by Bayer, and Lisbon NX manufactured by Dainippon Ink and Chemicals.

The ratio of the isocyanate compound having two or more isocyanate groups to the isocyanate compound having less than two isocyanate groups is within the range of 1:9 to 9:1, preferably 3:7 to 7. versus 3
It is preferable that the amount is within the following range; 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 abrasion resistance will not be sufficiently improved. In addition, the amount of both isocyanate compounds used together in such a usage ratio is 5 to 50% of the total amount of both isocyanate compounds and the above-mentioned polyurethane resin.
It is preferable to use the amount within the range of 1% by weight; if it is too small, the desired effect cannot be obtained, and if it is too large, the crosslinking density becomes high, which may make the magnetic layer hard and brittle.

In this invention, in addition to the polyurethane resin and both isocyanate compounds, vinyl chloride-
Resins that do not have active hydrogen, such as vinyl acetate copolymer, vinylidene chloride resin, acrylonitrile-butadiene copolymer, etc., may be used in combination within the range of 20 to 80% by weight based on the total amount of the binder component. When used in combination, wear resistance is further improved. A specific example of the vinyl chloride-vinyl acetate copolymer used in combination in this way includes VYHH manufactured by U, C, C, Inc. in the United States, and a specific example of the vinylidene chloride resin is Ioan 207D manufactured by Pardish Co., Ltd. -C is mentioned.

Specific examples of the acrylonitrile-butadiene copolymer include 2-Ball 1432J manufactured by Zeon Corporation.

Examples of the magnetic powder used in this invention include r-F
e, O, powder, Fe3O4 powder, Co-containing r-Fe20
3 powder, Co-containing Fe3O4 powder, Cry2 powder,
Various conventionally known magnetic powders such as metal powders such as Fe powder, Co powder, and FeNi powder are widely included.

Examples of organic solvents include ketone solvents such as cyclohexanone, methyl ethyl ketone, and methyl isobutyl ketone, esthetic solvents such as ethyl acetate and butyl acetate, aromatic hydrocarbon solvents such as benzene, toluene, and xylene, and isopropyl alcohol. Solvents suitable for dissolving the binder component used are particularly limited, such as alcohol solvents, acid amide solvents such as dimethylformamide, sulfoxide solvents such as dimethyl sulfoxide, and ether solvents such as tetrahydrofuran and dioxane. They can be used alone or in a mixture 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 roll coating, and then dried.

Next, embodiments of the invention will be described.

Example I Co-containing -Fe, O, magnetic powder 80 parts by weight Takerac E-551T (Take 1) 16 1 manufactured by Yakuhin Kogyo Co., Ltd.
Hydroxyl group-containing polyurethane resin, molecular weight 6000) Methyl isobutyl ketone 48 l Toluene
48 IF After mixing and dispersing this composition in a ball mill for 700 hours, Mytic NY
A solution of 320AX (isocyanate compound manufactured by Mitsubishi Kasei Corporation, inocyanate group number 1.8) in a mixed solvent of 6 parts by weight of methyl isobutyl ketone and 6 parts of toluene was added, and the mixture was further mixed and dispersed for 1 hour. After this mixing and dispersion, 2 parts by weight of Coronate L (manufactured by Nippon Polyurethane Kogyo Co., Ltd., a trifunctional low molecular weight isocyanate compound) dissolved in a mixed solvent of 6 parts by weight of methyl isobutyl ketone and 6 parts by weight of luene was added and mixed for 1 hour. The mixture was dispersed to prepare a magnetic paint. This magnetic paint was applied onto a polyester film with a thickness of 7 μm to a dry thickness of 5 tones, 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 Colinate L was omitted.

Comparative Example 2 In the preparation of the magnetic paint of Example 1, Mytic NY3
2 Omit the mixing and dispersion of GAI, and reduce the amount of Coronate L used by 2.
A magnetic tape was produced in the same manner as in Example 1 except that parts by weight were changed 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 numerical value of the surface roughness was expressed as a center line average (C, L, A). The durability test was conducted by running a magnetic tape of a predetermined length at a running speed of 4.76''/sec while in sliding contact with a magnetic head, and measuring the number of runs until a decrease in output occurred.

The table below shows the results.

As is clear from the table above, the magnetic tape obtained by the present invention (Example 1) has a higher squareness ratio and lower surface roughness than the conventional magnetic tape (Comparative Examples 1 and 2). Moreover, 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, an isocyanate compound having less than 2 isocyanate F groups, 2.
A magnetic recording medium having a magnetic layer comprising an isocyanate compound having the above incyane group.