JPS6163923A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve the scratching resistance, etc. of a magnetic recording medium having a protective layer on a thin magnetic film and to improve the workability in a stage for forming the protective layer by using a ladder type silicone resin film as the protective layer. CONSTITUTION:The silicone resin having ladder structure is prepd. by heating the flaky material of an organosiloxane oligomer having the structure expressed by the formula (R is alkyl, phenyl; n is 2-20) and having 500-5000mol.wt. or heating the same in the presence of an acidic catalyst. Such ladder type silicone resin is dissolved in a soln. of n-buranol, etc. and the soln. is coated by spin coating etc. on the thin magnetic film formed directly or indirectly on a substrate and is then calcined to form the protective layer, by which the intended magnetic recording medium is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a magnetic recording medium, and more particularly, it is used in magnetic storage devices such as magnetic disk devices and magnetic drum devices, and is a medium having a protective layer on one surface. The present invention relates to a magnetic recording medium provided with a magnetic recording medium.

(Prior Art) Generally, in this type of magnetic storage device, recording and reproduction are performed using various methods using a magnetic head for recording and reproduction and a magnetic recording medium. In either method, the recording/reproducing magnetic head and the magnetic recording medium are used in static or dynamic contact with each other or under pressure, so a contact friction condition appears, so the gold kJt substrate of the magnetic recording medium In order to protect the magnetic thin film formed on the magnetic thin film, it is necessary to form a protective layer by coating one surface with a δ-retaining film.

Because of its purpose, this protective layer must have properties such as so-called head crush resistance, wear resistance, lubricity, high temperature and high humidity resistance, and no influence on magnetic properties. .

Conventionally, as such a protective film, a sputtered film formed on the surface of a magnetic recording medium by a 5iO23 sputtering method has been used. However, this sputtering method only yields a film that lacks head crush resistance and is technically problematic. In this regard, a technology has recently been developed to form a polysilicate film by coating and baking a tetrahydroxysilane solution, and has achieved some success (Japanese Unexamined Patent Application Publication No. 52-2011).
-20804).

However, although this method of forming a polysilicate film is effective due to the above-mentioned characteristics of the polysilicate film itself, there are problems in the process of forming the film and it is difficult to handle. That is, polysilicic acid is produced by dehydration condensation polymerization of tetrahydroxysilane, but tetrahydroxysilane is very active and must be prepared as an alcohol solution using ethyl alcohol and butyl alcohol as solvents, resulting in a long shelf life. It is short, about 3 months,
Reactions occur and the quality changes easily. In addition, unless the firing temperature is increased to reduce unreacted silanol groups remaining in the polysilicic acid, it is difficult to exhibit performance, and conversely, there is a risk that increasing the temperature will cause magnetic transformation in the magnetic film. Furthermore, during coating, polysilicic acid is formed as the alcohol solvent evaporates, making it difficult to control viscosity, surface tension, film thickness, etc.

(Objective of the Invention) The present invention eliminates the drawbacks associated with the formation of a conventional protective film, provides various good properties as a protective layer with good workability (ease of use), and has particularly excellent industrial productivity. The object of the present invention is to provide a magnetic recording medium with a high degree of compatibility.

(Structure of the Invention) In order to achieve the above object, as a result of repeated experimental research on various coating materials and their ease of use, we focused on the applicability of silicone resins, and in particular, developed a ladder-type silicone resin coating. We have found that it is practically possible to use this method.

Ladder type silicone resin has the following structure with a molecular weight of 5
It is an insoluble, infusible polymer with a ladder-like structure obtained by heating a flake-like substance of an organosiloxane oligomer having a molecular weight of 0 to 5,000 by heating or heating in the presence of an acidic catalyst.

(However, R is an alkyl group or a phenyl group, and n=2-2
0) And, depending on the aspect of R, when R is a CH, group,
CH, groups and CGH9 groups in various ratios, C,
There are different types such as H, groups, etc., and the features are: ■
It has a flake shape and is soluble in many solvents such as alcohol, aromatic hydrocarbons, and esters. ■It has a low viscosity and can be easily subjected to various operations such as spray coating. ■2°O'C Heating at a low temperature and for a short time as shown below (
It is a thermosetting resin that hardens by firing), ■ It will not change in quality simply by storing it in a cool, dark place (5°C). The thickness of the cured coating in 1 can be determined arbitrarily depending on the curing conditions. ■ The cured product is heat resistant. It has outstanding properties.

The more C, H, groups there are in R, the higher the heat resistance becomes.
The more groups there are, the higher the hardness. ■ Excellent adhesion with metals such as iron and aluminum. ■ The cured product has excellent electrical insulation, weather resistance, and corrosion resistance. (Φ The cured coating surface is glass-like, Excellent hardness, scratch resistance, etc.

The present inventors conducted an experiment on single-coat conditions when coating (spin coating) this resin on a magnetic recording medium, and determined the optimum conditions. First, the solvent was n-butanol (boiling point 118°
Only C) was used. As for the solution concentration, as shown in Table 1, the lower the concentration, the harder it is and the thinner the coating.
0.5 wt% is preferred.

According to the experimental results shown in Table 2, firing is more advantageous if it is treated at a higher temperature for a longer time.
In consideration of ferromagnetization in the case of coating a P layer), 200''C, lhr is preferable.It was confirmed that no magnetic transformation occurred under these firing conditions.

(Leaving space below) Dropped amount: Approximately 0.5 mQ Firing (200°C x 1 hr) Scratch test: JISK6718 (using sapphire needle) Judgment method: 0 No scratch Δ Shallow scratch × Deep scratch See (note) in Table 1.

However, the solution concentration is 0°5vt%. Furthermore, the dropping method is preferably performed at a base rotation speed of 200 to 3000 rpm. If the solution is dropped at 20 OrPm (ii+li), centrifugal force is insufficient and the solution does not spread outward well, and unevenness and radial striped patterns are likely to occur after high-speed rotation.

From the above experimental results, a solution of n-butanol as a solvent with a concentration of 0 and 5 wt% was prepared at a substrate rotation speed of 300°rpn+.
It is preferable to remove the powder under 200° C. and bake at 200° C. for 1 hr. This enables a film thickness of 0.08 μm or less that does not cause scratches even under a scratch resistance test load of 60 g.

(Example) After plating N1-P nonmagnetic alloy to a thickness of about 50 μm on a disc-shaped aluminum alloy disk (outer diameter 130 mm, inner diameter 40 mm), and mechanically polishing this N1-P plating film to a mirror finish. A magnetic alloy of Co-N1-P was plated thereon to a thickness of about 0.05 to 0.08 μm.

Furthermore, various protective film forming materials shown below were coated thereon by a spin coating method.

Fork 11 pull Y While rotating the disk-shaped disc at 20 Orpm,
Ladder type silicone oligomer solution (Owens-fQ
0.4 mQ of a 0.5 wt% solution of Ffinois Glass Resin GR650 in n-butanol was dropped around the inner diameter, and after the solution was sufficiently moved to the outside of the disc by centrifugal force, it was rotated at high speed. One film with a thickness of about 0.08 μm was formed. This was left at room temperature (25° C.) for a while and then fired at 200° C. for 1 hour to form a silicon yarn probe 51! crotch on a disc-shaped disk.

Example 2 While rotating the disk-shaped disc at 20 rpm, a ladder-type silicone oligomer solution (○wens-I
0.2 mQ of QQinois class resin GR650 in n-butanol (0.5 wt% solution) was dropped while moving in the radial direction from the inner circumference to the outer diameter until the solution was sufficiently spread on the disk-shaped disc. After that, high-speed rotation, baking, and protective film formation were performed in the same manner as in Example 1.

By the same method as in Example 1, polysilicate Si(○H)4
(Tokyo Ohka 10 C, D in n-butanol 7-ol.

0.4 mQ of 0.5 wt% solution) was applied to form a protective film on the disc-shaped disc.

Comparative Example 2 0.4 mQ of silicone varnish for hard coating (0.5 wt% solution of Toshiba Silicone Tosguard 510 in n-butanol) was prepared in the same manner as in Example 1.
was applied to form a disc-shaped disk 31F, i.

Comparative Example 3 A silicone varnish that cures at a lower temperature than that used in Comparative Example 2 (0.5 w in n-phthanol of Toshiba Silicone Tosguard 520) was prepared using the same method as in Example 1.
t% solution) was applied in an amount of 0.4 mL to form a 5-layer film on a disc-shaped disc.

Based on JISK6718, (0,05R
A scratch test was conducted using a sapphire needle. The results are shown in Table 3.

As can be seen from the test results shown in the same table, no scratches were generated on the surface of any of the 39 examples of the present invention up to a scratch resistance test load of 60 g, and the ladder type silicone resin Combined with the features mentioned above, it exhibits excellent properties and is easy to use. Although Example 2 differs in the amount of coating compared to Example 1, it shows the same results because the dropping method was also changed.

On the other hand, in the case of Comparative Example 1 in which a polysilicate film was formed, although it showed the same results as each of the examples of the present invention in the scratch resistance test, it had the disadvantage of being difficult to handle. Also,
Comparative Examples 2 and 3 show that scratches occur with a slight load.

(Leaving space below) (Note) Judgment method: Same as (note) in Table 1 (Effect of the invention) As is clear from the detailed description below, according to the present invention, the third layer of the magnetic recording medium Since a ladder-type silicone resin film is used as a protective layer, it is possible to form a protective layer with excellent properties, and its formation technology is also easy to use (and workable), so it has great practical effects.

Claims (1)

[Claims] 1. A magnetic recording medium comprising a substrate directly or indirectly coated with a magnetic thin film and a protective layer on the magnetic thin film, characterized in that the protective layer is a ladder-type silicone resin film.