JPS62185241A - Production of magnetic recording medium - Google Patents

Abstract

PURPOSE:To assure excellent durability without spoiling an electromagnetic conversion characteristic in the high density recording stage by coating and forming magnetic powder and magnetic layer on a nonmagnetic substrate, diluting with a specific mixture, coating the mixture on the magnetic layer and subjecting the coating to reaction curing. CONSTITUTION:The magnetic layer 2 essentially consisting of the magnetic powder and resin binder is coated and formed on the nonmagnetic substrate 1. A polyurethane having 5,000-40,000 average mol.wt. and isocyanate compd. are diluted with an org. solvent and thereafter the soln. is coated on the magnetic layer 2 and is subjected to reaction curing. The wear resistant protective film 3 is made by reaction curing under the condition of 24hr at 60 deg.C. The layer 3 having the low frictional resistance and excellent wear resistance is thereby provided on the magnetic coated film. The durability is assured without spoiling the electromagnetic conversion characteristic in the high density recording stage and the magnetic recording medium which has both the excellent surface smoothness and high durability in combination and can deal with the high density recording is obtd.

Description

[Detailed Description of the Invention] Industrial Application Field The present invention relates to magnetic recording media such as flexible disks and tapes that can be used in information-related equipment, video or audio equipment, etc. The present invention relates to an improved method of manufacturing a high-density recording medium.

Conventional technology In recent years, with the spread and diversification of computers, higher image quality in the field of video equipment, and further miniaturization of external memory systems, magnetic recording media are required to have higher density recording. It's coming.

Hereinafter, an example of the conventional magnetic recording medium mentioned above will be specifically explained with reference to the drawings.

FIG. 3 shows a cross section of a conventional magnetic recording medium. In FIG. 3, 1 is a nonmagnetic support and 2 is a magnetic layer. As the nonmagnetic support 1, a film of polyethylene terephthalate, polyimide, or the like is generally used. The magnetic layer 2 is formed by applying a magnetic paint in which ferromagnetic particles are dispersed in a binder vehicle together with a dispersant, lubricant, abrasive, etc. using a common coating method such as kiss coating, gravure coating, or reverse coating. be done.

In the magnetic recording medium configured as described above, the factors that enable high-density recording are: ■ The coercive force of the ferromagnetic particles is high; ■ The σ8 (saturation magnetization amount) of the ferromagnetic particles is large; ■ The ferromagnetic particles are fine, ■ The ferromagnetic particles are uniformly dispersed in the binder vehicle,
■ The magnetic layer is smooth and has little spacing loss; ■ The magnetic layer has low frictional resistance.

Regarding the above factors (■, ■, ■), various studies have been conducted due to improvements in the manufacturing method of acicular iron oxide, or the appearance of cobalt-coated acicular iron oxide, acicular metallic iron, barium ferrite, etc. It's coming.

In addition, the above-mentioned factor (2) has been solved by improving the binder, examining dispersion aids, magnetic powder surface treatment agents, and theoretically elucidating dispersion technology.

The problem that the invention aims to solve However, in the conventional configuration, the above-mentioned ①.

Regarding element (2), lowering the surface roughness and reducing spacing loss increases the frictional resistance between the head and the coating film.
There are problems in that the head tends to be scratched and the head sticks when running, making it difficult to ensure running performance and durability.

In view of the above-mentioned problems, the present invention provides excellent running performance even in magnetic recording media for high-density recording with low surface roughness by forming an extremely thin hard film with excellent wear resistance on the magnetic layer. It provides durability.

Means for Solving the Problems In order to solve the above problems, the magnetic recording medium of the present invention comprises:
A magnetic layer containing magnetic powder and a resin binder as main ingredients is coated on a non-magnetic support, and the average molecular weight is s o o o ~.
40,000 polyurethane and an isocyanate compound were diluted with an organic solvent, then applied onto the magnetic layer and cured by reaction.

Effect of the present invention With the above configuration, a film with low frictional resistance and excellent wear resistance can be provided on the magnetic coating film, and durability can be ensured without impairing electromagnetic conversion characteristics during high-density recording. The present invention provides a magnetic recording medium compatible with high-density recording that has both excellent surface smoothness and high durability.

Example [Example 1] A magnetic recording medium according to an example of the present invention will be described below with reference to the drawings.

FIG. 1 shows a cross-sectional view of a magnetic recording medium in an embodiment of the present invention. In FIG. 1, 1 is a non-magnetic support, 2 is a magnetic layer mainly composed of magnetic powder and a resin binder,
3 is a wear-resistant protective film made of vinyl chloride-vinyl acetate copolymer and isocyanate.

Here, as the nonmagnetic support 1, a polyethylene terephthalate film having a thickness of 75 μm is used.

Magnetic layer 2 includes magnetic powder: Co-adhered acicular iron oxide 10% dispersant:
lecithin o. 7 Lubricant nioleyl oleate 7 Butyl stearate 3 Binder: Polyurethane resin 14 Nitrocellulose 14 Abrasive 205 4 Anti-wear agent: Carbon powder 6 Solvent: Toluene 15o Methyl ethyl ketone 20o
〃After putting 100 I of cyclohexanone into a paint dispersion machine and thoroughly mixing and kneading it, use it as a crosslinking agent at a ratio of 4 to 4 for the resin component.

After adding % by weight of polyisocyanate and further mixing and stirring to achieve uniform dispersion, it was applied by gravure coating to a dry film thickness of 1.2 μm, and after drying, it was subjected to surface treatment and hardened at 60°C for 24 hours. Ta. This was punched out into a 3-inch disk shape, which is referred to as a conventional example, and is referred to as sample #1.

A protective film is provided on the magnetic layer 2 by applying a polyurethane and isocyanate compound having an average molecular weight of 50 to 40,000 diluted with a suitable organic solvent. This is 60°C2
The abrasion-resistant protective film 3 is obtained by reaction-curing under the conditions of 4 hours.

Samples #2 to #4 are media created by changing the average molecular weight of the polyurethane used for the wear-resistant protective film 3.

As described above, the disks of Samples #1 to #4 were evaluated for the degree of scratches at each fixed pass using the rotary scratch tester shown in FIG. In addition, in the same figure, 5 is a test medium, 6 is a pad, 7 is a load detector, 8 is a load adjustment table,
9 is a rotating power system, 1o is a steel ball, and 11 is a friction detector. The test conditions were 300 rpm and 20y-load.

The results are shown in Table 1.

(Left below) [Example 2] In Example 2, in contrast to Example 1, the polyethylene terephthalate film thickness was 76 μm → 3
4μm Magnetic powder Co coated acicular iron oxide → Metal magnetic binder nitrocellulose → Changed to vinyl chloride-vinyl acetate copolymer, dry film thickness 3. It was formed by coating so that it became oltm. This was cut into a 2-inch disc shape as a conventional example, and designated as sample #5.

Furthermore, as in Example 1, media were prepared by changing the average molecular weight of the polyurethane used for the wear-resistant protective film 3 as samples #6 to #9. Then, using the rotary scratch tester used in Example 1, the rotation speed was 3600 rpm, I Bj;
Table 2 shows the results of evaluation under load conditions.

As is clear from Tables 1 and 2, the samples in which the wear-resistant protective film, which is a feature of the present invention, is provided on the magnetic layer have improved wear resistance and scratch resistance that is 2 to 3 times that of the conventional one. Obtained. Furthermore, the coefficient of friction is also at the same level or lower than that of conventional products.

The thickness of the wear-resistant protective film 3 formed in the above embodiment is about 100 to 200, and the influence on electromagnetic conversion characteristics is about 0.5 dB or less.

As the polyurethane used in the present invention, for example, Takelac E-400 manufactured by Takeda Pharmaceutical Co., Ltd. Nippon Polyurethane Industry's N
Anything with an average molecular weight in the range of 60oO to 40,000, such as R-90 and N2304, may also be used. In addition, as the isocyanate compound, commonly used polyisocyanates (for example, Takenate D1 from Takeda Pharmaceutical Co., Ltd.
03H.

Use Nippon Polyurethane Kogyo's Coronate L-46, etc.).

Further, in this example, a spin code was used as a method for forming the wear-resistant protective film 3, and methyl isobutyl ketone was selected as a solvent suitable for the coating method. This is just one example and does not limit the content of the present invention, and other coating methods such as kiss coating, gravure offset coating, reverse coating, etc. may also be used. Regarding the diluting solvent, as long as it is a good solvent for the above-mentioned materials, use one that matches the respective application conditions.
For example, solvents such as toluene, methyl ethyl ketone, cyclohexanone, isophorone, and butyl acetate may be used.

Effects of the Invention As described above, according to the present invention, a polyurethane and an isocyanate compound having an average molecular weight of 5,000 to 40,000 are diluted with an organic solvent and then applied and cured by reaction on a conventional magnetic layer.
By providing an extremely thin wear-resistant protective film, excellent durability can be ensured without impairing electromagnetic conversion characteristics during high-density recording.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a magnetic recording medium according to an embodiment of the present invention, FIG. 2 is a diagram showing the structure of a rotary scratch tester, and FIG. 3 is a sectional view of a conventional magnetic recording medium. 1...Nonmagnetic support, 2...Magnetic layer,
3...Wear-resistant protective film. Name of agent: Patent attorney Toshio Nakao and 1 other person6-
--Pad 7---Load! &Engine/Q --? 6 to 1 steel spider

Claims (1)

[Claims] A magnetic layer mainly composed of magnetic powder and a resin binder is coated and formed on a non-magnetic support, and polyurethane and isocyanate compounds with an average molecular weight of 5,000 to 40,000 are diluted with an organic solvent and then coated on the magnetic layer. - A method for producing a magnetic recording medium characterized by reaction hardening.