JPS58153225A - 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 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 an isocyanate compound having <2 isocyanate groups such as 2,4-tolylenediisocyanate.

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 preester film, and drying the coating.
A material with excellent electrical properties and durability is required. Therefore, the binder component used has excellent dispersibility of the magnetic powder, improves the 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. At the same time, there is a need for something that can improve the abrasion resistance of the magnetic layer and improve its durability.Among the various binder resins currently used, polyurethane resins are known to have relatively good properties.
Furthermore, in order to improve these properties, it has been proposed to use a low molecular weight incyanate compound in combination with this.
The dispersibility of the magnetic powder is not sufficient, and the wear 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.
When an isocyanate compound having 2 or more inocyanate groups is used in combination with an isocyanate compound having 2 or more isocyanate groups, the dispersibility of the magnetic powder is improved, the surface smoothness of the magnetic layer is further improved, and the wear resistance is improved. It was discovered that this could be further improved, and this invention was made.

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 also has hydroxyl groups, so it has good affinity with magnetic powder and has excellent dispersibility of magnetic powder.It also has an improved calendering effect in the surface grating process, and can be used to form a magnetic layer. Improves surface smoothness. The number of water rjIIM in the resin is preferably 0.5 or more as an average value per molecule, and the molecular weight is 1
A molecular weight of 000 to less than 10,000 is preferably used, and a molecular weight of 3,000 to 7,000 is more preferably used. As a specific example of such a polyurethane resin, for example, Takelac E-55 manufactured by Takeda Pharmaceutical Co., Ltd.
17, Takerac E-550, etc.

Further, the polyurethane resin used in combination with the polyurethane resin having a molecular weight of 10,000 or more is the same as the polyurethane resin described above, and therefore has extremely good compatibility, making the magnetic layer tough and improving the abrasion resistance. Molecular weight is 10000
If it is less than 1, the wear resistance of the magnetic layer cannot be sufficiently improved;
If it exceeds 0,000 G, the magnetic layer may become too strong and become brittle, so those with a molecular weight of 1 ooo to 100,000 are preferably used, and a molecular weight of 20,000 to 5 ooo.

is more preferably used. Specific examples of such polyurethane resins include Pandex T-5201 and Bandex T-5205 manufactured by Dainippon Ink and Chemicals.

The ratio of the polyurethane resin having a molecular weight of 10,000 or more to the above-mentioned hydroxyl group-containing urethane resin having a molecular weight of 10,000 or more is within the range of 1:9 to 9:1, preferably 3:7 to 9:1 by weight. The ratio is preferably within the range of 7:3; if the amount of the preurethane resin having a molecular weight of 10,000 or more 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.

The isocyanate compound having less than 2 isocyanate groups used in combination with the above-mentioned urethane resin having a molecular weight of less than 10,000 and the polyurethane resin having a molecular weight of 1000 or more has a relatively good affinity with magnetic powder and is suitable for magnetic powder. It is highly dispersible, and when used in combination with a polyurethane resin having hydroxyl groups, the isocyanate groups react with the hydroxyl groups in the polyurethane resin to form a crosslinking bond, which strengthens the toughness of the magnetic layer and improves its abrasion resistance.

A specific example of such an isocyanate compound is Mytic NY320AX manufactured by Mitsubishi Kasei Corporation.

In addition, examples of incyanate compounds having two or more isocyanate 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 phenylene diisocyanate, 1,4-Schiff-tetrahexylene diisocyanate, l,5-nato-2-hydride p-naphthalene diisocyanate)
, 1,6-hexamethylene diisocyanate, 4-chloro/L/-1,3-phenylene diisocyanate, 1,5
-Diisocyanates such as 7tale diisocyanate 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. When used in combination, two or more isocyanate groups contained in the isocyanate compound are contained in the polyurethane resin! ! ! Because it reacts with groups and forms crosslinks, the toughness of the magnetic tube is further strengthened and its wear resistance is further improved. In particular, when a trifunctional low molecular weight incyanate compound is used in combination, the crosslinking becomes network-like, so that the abrasion resistance of the magnetic layer is significantly improved. Specific examples of such trifunctional low molecular weight incyanate compounds include, for example, Nippon Polyurethane Co., Ltd. Coronate L1 (Takeda Pharmaceutical Co., Ltd.) D102, Bayer Co., Ltd. Desmojou/I/[, Dainichi Ink Chemical Co., Ltd. Examples include Crisbon NX manufactured by Kogyo.

The ratio of the isocyanate compound having two or more inocyanate groups to the above-mentioned isocyanate compound having less than two inocyanate groups is within the range of 1:9 to 9:1, preferably 3:7. ~7 to 3
It is preferable that the amount is within the following range; if the amount of the isocyanyl-F compound having two or more insocyanesi 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 insia-exclusive compounds used in combination in such a usage ratio is 5 to 5 sO based on the total amount of both polyurethane resins.
It is preferable to use it within the range of the weight arc; 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 incyanate compounds, vinyl chloride-
Resins that do not have active hydrogen, such as vinyl acetate copolymer, vinylidene chloride resin, lylubutadiene 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 these resins are used together, the 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 Dioan 20 manufactured by Pardish Co., Ltd. ? Examples include D-C.

As a specific example of the tTh acrylonitrile-butadiene copolymer, Nippor 1432J manufactured by Nippon Zeon Co., Ltd.
Examples include.

Examples of the magnetic powder used in this invention include r-F
elO) powder, Fe, 04 powder, Co-containing r-Fe, 0
1 powder, Co-containing Fe, 04 powder, Cr01 powder, etc.
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 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 alcohols such as isopropyl alcohol. solvent,
Solvents suitable for dissolving the binder component to be used are particularly limited, such as acid amide solvents such as dimethylformamide, sulfoxide solvents such as dimethyl sulfoxide, ether solvents such as Tesilahydro 7rane and dioxane. They can be used alone or in a mixture of two or more.

Incidentally, various commonly used IAM agents such as dispersants, lubricants, abrasives, antistatic agents, etc. may be optionally added to the magnetic paint.

The magnetic recording medium of the present invention may be manufactured according to a conventional method. For example, a magnetic powder, the above-described binder component of the present invention,
A magnetic paint containing an organic solvent and other additives may be applied by any means such as spraying or V-ru coating, and then dried.

Next, embodiments of the invention will be described.

Example I Co-eating r-FelO1 magnetic powder 80 parts by weight Takelac E-5517 (manufactured by Takeda Pharmaceutical Co., Ltd., hydroxyl group-containing polyurethane resin, molecular weight 600G) Methyl isobutyl ketone 32 1 Toluene
32 1 After dispersing this composition in a ball mill for 50 hours, Pandex T-5201
A solution of 8 parts by weight of polyurethane resin (manufactured by Dainippon Ink Chemical Industries, Ltd., molecular weight 2400G) in a mixed solvent of 16 parts by weight of methyl isobutyl ketone and 16 parts by weight of toluene was added, and the mixture was further mixed and dispersed for 20 hours. Next, a solution of 2 parts by weight of Mytic NY320AX (incyanate compound manufactured by Mitsubishi Kasei Corporation, number of isocyanate groups 1.8) dissolved in a mixed solvent of 6 parts by weight of methyl isobutyl kesine and 6 parts by weight of luene was further added, and the mixture was heated for 1 hour. After mixing and dispersing, 2 parts by weight of Kodane L (manufactured by Nippon Polyurethane Kogyo Co., Ltd., a trifunctional low molecular weight isocyanate compound) was dissolved in a mixed solvent of 6 parts by weight of methylisobutylene to ketone and 6 parts by weight of luene. was added and mixed and dispersed for an additional hour to form a magnetic coating material of 1 lIII. This magnetic paint was applied onto a 7 tt thick preester film to a dry thickness of 5 μm, dried, surface treated, and then cut to a predetermined width to produce a magnetic tape.

Comparison f! 41 In the preparation of the magnetic paint according to the implementation example, the amount of Takerac 15SIT used was changed from 8 parts by weight to 16 parts by weight, and the amount of heavy powder (L) used was changed from 2 parts by weight to 4 parts by weight,
Pandex? The mixed dispersion of -5201 and the mixed dispersion of Mytic NY32GAI were omitted. Example 1 except pL
I made magnetic tape in the same way.

Comparison H2 In the preparation of the magnetic paint of Example Ill, Takelac E-
4517 was omitted, and the amount of Bandex T-5201 used was changed from 8 parts by weight to 16 parts by weight, and [Zarani] Sonate L
A magnetic tape was prepared in the same manner as in Example 1, except that the amount used was changed from 2 parts by weight to 4 parts by weight, and the mixing and dispersion of Mytic NY320AX was omitted.

Comparative Example 3 In the preparation of the magnetic paint of Example 1, Takelac E-5
A magnetic tape was prepared in the same manner as in Example 1, except that the amount of 517 used was changed from 8 parts by weight to 16 parts by weight, and the mixing and dispersion of Bandex T-5201 was omitted.

Comparative Example 4 In preparing the magnetic paint of Example 1, the amount of Cosinate L used was changed from 2 parts by weight to 4 parts by weight, and Mytic NY
A magnetic tape was produced in the same manner as in Example 1 except that the mixing and dispersion of 320AX was omitted.

Regarding the magnetic tapes obtained in Examples and Comparative Examples,
The squareness ratio (''/Bm) and the surface roughness of the magnetic layer were measured to test the durability.The surface roughness of the magnetic layer was measured with a stylus type surface roughness meter, and the surface roughness value was It is expressed as center line average (C, L, A).The durability test was conducted by running a predetermined length of magnetic tape at a running speed of 4.76 a/sec while slidingly contacting the magnetic head. This was done by measuring the number of times the vehicle was run until this occurred.

The table below shows the results.

As is clear from the table above, the magnetic tape obtained by the present invention (Example 1) is different from the conventional magnetic tape (Comparative Examples 1 to 4).
The magnetic recording medium obtained by this invention has excellent dispersibility of magnetic powder and has a smooth surface of the magnetic layer. It can be seen that it has good properties and excellent durability.

Claims (1)

[Claims] 1. As a binder component, the molecular weight having a hydroxyl group is 100
Magnetic recording 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, an isocyanate compound having less than 2 incyanate groups, and an isocyanate compound having 2 or more incyanate groups. medium