JP2620332B2 - Magnetic recording media - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a magnetic recording medium, and more particularly to an improvement in a solid additive added to a magnetic layer.

[Conventional technology]

Conventionally, magnetic recording media have been used to improve durability.
Solid additives such as alumina having a high Mohs hardness have been included in coating films. However, this solid additive having a high Mohs hardness acts as an abrasive for the magnetic head and cleaning sheet that come into sliding contact with the medium, and the shavings of the shaved magnetic head and the cleaning sheet adhere to the magnetic coating film. It has been found that this causes dropout and output fluctuation. Especially for short wavelength magnetic recording media,
Since the surface smoothness of the magnetic surface is improved, even a small attached portion causes output fluctuation and dropout.

[Problems to be solved by the invention]

The present invention solves the drawback that the output fluctuation and the occurrence of dropout increase during use in a short-wavelength magnetic recording medium having a good surface smoothness, thereby providing a highly reliable magnetic recording medium for high-density recording. The purpose is to provide.

[Means for Solving the Problem] The present inventors have conducted intensive studies in view of such circumstances,
It has been found that the increase in output fluctuation during use is reduced if the average particle size of the solid additive having a large Mohs hardness included in the magnetic coating film is 50 times or less the surface roughness of the magnetic coating film. I've reached the point. This is because when the average particle size of the solid additive increases, the portion of the solid additive protruding from the coating film surface increases, and the amount of the magnetic head or cleaning sheet that is in sliding contact with the magnetic recording medium is increased. Is done.

In particular, when a magnetic powder suitable for high-density recording, such as a metal magnetic powder, is used, the surface roughness of the surface of the magnetic layer is reduced in order to further exhibit its performance. In this case, even if a minute foreign matter adheres to the surface of the magnetic layer, it may cause output fluctuation or dropout, so it is necessary to prevent the generation of minute dust as much as possible, so that the medium is stored in the cartridge case. In addition, it is kept in sliding contact with the cleaning sheet to remove dust on the surface of the medium during use. For this reason, it is necessary to suppress scraping of the magnetic head and the cleaning sheet as much as possible. For such a high-density recording medium, the selection of a solid additive having a high Mohs' hardness shows a very large effect.

〔Example〕

 Hereinafter, an example will be described in more detail.

<Preparation of magnetic disk> Metal magnetic powder (coercive force, 1650 Oe, S _BET , 55 m ² / g) 161 parts PVC / vinyl acetate / vinyl alcohol copolymer (UCC, VAG
H) 19.8 parts Polyurethane resin (ME664, manufactured by Mitsubishi Kasei Kogyo Co., Ltd.) 11.8 parts Trifunctional low molecular weight isocyanate compound (Coronate L, manufactured by Nippon Polyurethane Co., Ltd.) 7.8 parts α-Al ₂ O ₃ (average particle size X μm) 32.2 parts Oleyl Olate 16.2 parts Cyclohexanone 240 parts Toluene 240 parts The average particle size X μm of α-Al ₂ O _{3 in} the above composition was changed as shown in Table 1 depending on each of Examples and Comparative Examples.

This composition was kneaded and dispersed in a ball mill for 96 hours to prepare a magnetic paint, which was applied to both sides of a 75 μm thick polyethylene terephthalate film so that the thickness after drying was 2.5 μm, dried, and calendered. After the treatment, a magnetic disk was punched out into a disk having an outer diameter of 86 mm. The surface smoothness of the magnetic disk was controlled by changing the conditions of the calendering process. The magnetic disk was housed in a cartridge case formed of a hard synthetic resin with a cleaning sheet ultrasonically welded to the inner side to obtain a product.

The surface smoothness and the average particle diameter of α-Al ₂ O ₃ were measured for the magnetic disks obtained in the above Examples and Comparative Examples, and the output level, initial output fluctuation,
The output fluctuation after running for 96 hours in an environment of 45 ° C. and 45% RH was measured.

Surface smoothness: The surface roughness of the magnetic coating film was determined using a stylus type surface roughness meter having an R of 2 μm, at a stylus speed of 0.03 mm / sec and a cutoff of 0.08 mm.

Average particle size of α-Al ₂ O ₃ : A cross-sectional photograph of the coating film was taken at 50,000 times, and the diameter of 1,000 α-Al ₂ O ₃ particles was measured. The particle diameter when this value was 50% of the total weight of the previously measured 1,000 particles was defined as the average particle diameter.

Output level: 35kf using our own high-density floppy disk characteristic tester (using Sendust as a magnetic head)
The output level of ci was determined.

Output fluctuation: 300r with the same tester that measured the output level
A signal of 500 kHz is stored in each track at pm, an average output of each 70 bits is obtained, and the average output of the previous 70 bits is compared to obtain an absolute value of the difference. The average value of the absolute value of this difference in all tracks is defined as output fluctuation.

 Table 1 shows the measurement results.

From the above results, in the magnetic disk having the surface smoothness of 0.015 μm or more (Comparative Example 1), the output level is low and the output fluctuation after the initial running is large. Surface smoothness is 0.015μ
Even when the average particle diameter of the solid additive is 50 or more times the surface smoothness of the magnetic disk (Comparative Examples 2 and 3), the output level and the initial output fluctuation are small, but the output fluctuation after running is large. And lack of reliability.

〔The invention's effect〕

As described above, the surface roughness of the magnetic coating film is 0.015 μm.
m or less, the high recording density magnetic recording medium in which the average particle size of the solid additive added to the magnetic coating film is 50 times or less of the surface roughness has a high output level and an increase in output fluctuation during use. Obviously, a small and highly reliable magnetic recording medium is obtained.

Claims (2)

(57) [Claims] In a cartridge case comprising a pair of front and back shells and a cleaning sheet supported on the inner surface of the shell, the magnetic coating has a surface roughness of 0.015 μm or less and is contained in a magnetic layer. The average particle size of alumina is
A magnetic recording medium having a size of 50 or less and stored in a disk shape. 2. The magnetic recording medium according to claim 1, wherein the magnetic powder contained in the magnetic coating film is a metal magnetic powder.