JPS58153226A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To enhance the dispersibility, surface smoothness and durability by forming the magnetic layer using a binder having a composition contg. specified polyurethane resins. CONSTITUTION:A magnetic layer for magnetic recording is formed using a binder consisting of polyurethane resin having >=0.5 hydroxyl group per molecule on the average and 1,000-<10,000mol.wt., polyurethane resin having 10,000- 100,000mol.wt., and a resin having active hydrogen such as vinyl chloride-vinyl 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 coating a magnetic paint consisting of magnetic powder, a binder component, an organic solvent, and other necessary components on a substrate such as an ester film, and then 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, preurethane resin is known to have relatively good properties.
Furthermore, in order to improve these properties, this polyurethane resin may be combined with a resin having active hydrogen such as vinyl chloride-vinyl acetate-vinyl alcohol copolymer, or a hard thermoplastic resin may be used instead of the conventional polyurethane resin. A combination of a preurethane resin and a soft thermoplastic polyurethane resin has been proposed, but the dispersibility of the magnetic powder is not quite sufficient and the abrasion resistance is not necessarily satisfactory.

The inventors conducted various studies on binder components in view of the current situation, and found that a polyurethane resin having a hydroxyl group and a molecular weight of less than 10,000 and a polyurethane resin having a molecular weight of 10,000 or more are used as binder components for the magnetic layer. For example, when 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 abrasion resistance of the magnetic layer was improved, and that the abrasion resistance of the magnetic layer was further improved when a low molecular weight incyanate compound was used in combination, leading to the present invention.

The molecular weight of the hydroxyl group used in this invention is 1
Polyurethane resin with a molecular weight of less than 0,000 has a low molecular weight and has hydroxyl groups, so it has good affinity with magnetic powder and has excellent dispersibility of the magnetic powder.It also has an improved calendering effect in the surface treatment process, making it easier to form the magnetic layer. Improves surface smoothness. The average number of hydroxyl groups in the resin is 0.5 per molecule.
or more are preferably used, and the molecular weight is 1000
~ less than 10,000 is preferably used, with a molecular weight of 3
000 to 7000 is more preferably used. Specific examples of such polyurethane resins include:
Takerac E-5517 manufactured by Shikinichi Yakuhin Kogyo Co., Ltd.
, Takerac E-550, etc.

Further, the preurethane resin used in combination with the polyurethane resin having a molecular weight of 10,000 or more is the same polyurethane resin as the above-mentioned polyurethane resin, and therefore has extremely good compatibility, making the magnetic layer tough and improving the wear resistance. If the molecular weight is less than too much, the wear resistance of the magnetic layer cannot be sufficiently improved;
If it exceeds 0,000, the magnetic layer may become too hard and brittle, so those with a molecular weight of 10,000 to 10,000 G are preferably used, and a molecular weight of 20,000 to 500.

is more preferably used. Specific examples of such polyurethane resins include Bandex T-5201 and Bandex T-5250 manufactured by Dainippon Ink and Chemicals.

The ratio of the polyurethane resin having a molecular weight of 10,000 or more to the polyurethane resin having a hydroxyl group and a molecular weight of less than 10,000 is within the range of 1:9 to 9:1, preferably 3:7 to 7:1. The amount of polyurethane resin having a molecular weight of 10,000 or more is preferably within the range of 3. If the amount of polyurethane resin 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.

Examples of resins having active hydrogen that can be used in combination with the above-mentioned urethane resins include vinyl chloride-vinyl acetate-vinyl alcohol copolymers, vinyl chloride-vinyl acetate-maleic acid copolymers, and other resins having active hydrogen. Vinyl-vinyl acetate copolymer, nidotetracellulose, acetylcellulose, a7tylbutycellulose, methylcellulose, ethylcellulose, benzylcellulose,
Cellulose resins such as carboxymethylcellulose and droxycellulose, melivinyl acetal resins such as polyvinyl butyral, etc. are preferably used, and specific examples of vinyl chloride-vinyl acetate resins having active hydrogen include , VAGH, VMCH manufactured by U.C.C.
, VMCC, 1 ml S-Lefuku A1 manufactured by Suikagaku Kogyo Co., Ltd., S-Let C C1 made by Suikagaku Kogyo Co., Ltd., and Denkabinil made by Denki Kagaku Kogyo Co., Ltd., and the like. Further, as a specific example of the cellulose resin, Nitrocell 4-S L1/! manufactured by Asahi Kasei Corporation is used. , L1/4, L
l, H1/4, H1/! , Hl, R5, Daicel Nitrocellulose R5"/R8"/2, R8I, R
Specific examples of the polyvinyl acetal resin include Eslec BLS, Eslec BMS, manufactured by Tanezu Chemical Industry Co., Ltd.
Examples include Eslec BL-1 and Denka Butyral 3000 manufactured by Denki Kagaku Kogyo Co., Ltd.

These resins with viscous hydrogen have good affinity with magnetic powder and have excellent dispersibility of magnetic powder, and when used in combination with isocyanate F compounds, active hydrogen reacts with the isocyanate groups in the compound to form cross-linking bonds. This strengthens the toughness of the magnetic layer and improves wear resistance. Therefore, when these active hydrogen-containing resins are used in combination with both of the above polyurethane resins, 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 of both polyurethane resins. If it is too small, the desired effect will not be obtained, and if it is too large, the durability of the magnetic layer will be reduced. There is a possibility that abrasion resistance may be reduced instead.

As the low molecular weight isocyanate compound used in combination with the above-mentioned urethane resin and resin having active hydrogen,
Low molecular weight isocyanate compounds having less than 2 free isocyanate groups, diisocyanates such as 2,4-tolylene diisocyanate, m-7 2-2 diisocyanesi, and usually obtained by reacting 1 mol of siliol with 3 mols of diisocyanesi. Trifunctional low molecular weight isocyanate compounds are preferably used, and when these types of isocyanate compounds are used in combination, the isocyanate groups contained in the isocyanate compound bind the hydroxyl groups and active hydrogen contained in the polyurethane resin. Because it reacts with active hydrogen in the resin and crosslinks, the toughness of the magnetic layer is further strengthened, and its wear resistance is further improved. Specific examples of such low molecular weight isocyanate compounds include, for example, specific examples of low molecular weight isocyanate compounds having less than 2 isocyanate groups, and specific examples of trifunctional low molecular weight incyanate compounds such as Nippon Polyurethane Kogyo Co., Ltd. Examples include Fuda Neshi L1 (taken) D102 manufactured by Takeda Pharmaceutical Co., Ltd. and Desmodur L manufactured by Bayer. The amount used is preferably within the range of 5 to 50% by weight based on the total amount of the above-mentioned urethane resin and resin having active hydrogen used together, and if it is too small, the desired effect may not be obtained. On the other hand, if the amount is too large, the crosslinking density becomes high, which may make the magnetic layer hard and brittle.

Examples of the magnetic powder used in this invention include r-F
elO3 powder, Fe50. Powder, Co-containing r-Fe, O
In addition to B powder, s/co containing Fe, 04 powder, Cry powder, various conventionally known magnetic powders such as metal powders such as Fe powder, Co powder, and Fe-Ni powder are widely included.

Examples of organic solvents include ketone thread solvents such as Schiff 11 hexanone, methyl ethyl ketone, and methyl isobutyl ketone; ester solvents such as ethyl acetate and psal acetate;
Aromatic hydrocarbon solvents such as benzene, toluene, and xylene, alcohol solvents such as isopropyl alcohol, acid amide solvents such as dimethylformamide, sulfoxide solvents such as dimethyl sulfoxide, ether solvents such as tetrahydro7rane, dioxane, etc. The solvent suitable for dissolving the binder component to be used is 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 roll coating, and then dried.

Next, embodiments of the invention will be described.

Example 1 Co-containing r-Fe, 01 magnetic powder 80 parts by weight Takelac E-551T (Take 1) 4.5 parts by weight Yakuhin Kogyo Co., Ltd., hydroxyl group-containing, polyurethane resin, molecular weight 6000) VAGH (U.S. U, C, C Co., Ltd., 91 vinyl chloride-vinyl acetate-vinyl alcohol copolymer) Methyl isobutyl ketone 45 I toluene
45 l After mixing and dispersing this composition in a ball mill for 50 hours, Pandex T-5201
(Polyurethane resin manufactured by Dainippon Ink Chemical Industries, Ltd., molecular weight 2400G) 4.5 parts by weight of methyl isobutyl ketone 9
parts by weight and 9 parts by weight of toluene were added and mixed and dispersed for another 20 hours, and after this mixing and dispersion, 2 parts by weight of a trifunctional low molecular weight isocyanate compound manufactured by Nippon Giri Urethane Kogyo Co., Ltd. was added. A solution of 6 parts by weight of methyl isobutyl ketone and 6 parts by weight of toluene dissolved in a mixed solvent was added and mixed and dispersed for 1 hour 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 into a predetermined width to produce a magnetic tape.

Example 2 In the preparation of the magnetic paint of Example 1, Bandex T-
Pandex T-5205 (polyurethane resin manufactured by Dainippon Ink Chemical Industries, Ltd., molecular weight 65) was used instead of the solution of 5201.
000) was dissolved in a mixed solvent of 15 parts by weight of methyl isobutyl ketone and 15 parts by weight of Fluene. I made a tape.

Comparative Example 1 In the preparation of the magnetic paint of Example 1, -5
The amount of 517 used was changed from 4.5 parts by weight to 9 parts by weight,
A magnetic tape was prepared in the same manner as in Example 1 except that the mixing and dispersion of Bandex T-5201 was omitted.

Comparative Example 2 In the preparation of the magnetic paint of Example 1, Takelac E55
Omit 1T and reduce the usage amount of Bandex T-5201 to 4.
A magnetic tape was produced in the same manner as in Example 1 except that the amount was changed from 5 parts by weight to 9 parts by weight.

The squareness ratio (Br/Bfn) and the surface roughness of the magnetic layer were measured for the magnetic tapes obtained in each example and each comparative example, and the durability was tested. 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 a/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 tapes obtained by the present invention (Examples 1 and 2) have a higher squareness ratio and a lower surface roughness than conventional magnetic tapes (Comparative Examples 1 and 2). This indicates 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. Recognize.

Patent applicant: Hitachi Maxell, Ltd.

Claims (1)

[Claims] L as a binder component has a water increase group and has a molecular weight of 100
A magnetic recording medium 2 having a magnetic layer comprising a polyurethane resin having a molecular weight of less than 0.00, a polyurethane resin having a molecular weight of 10,000 or more, and a resin having active hydrogen.
Magnetic recording medium according to claim 1 containing a compound