Coating processes – Direct application of electrical – magnetic – wave – or... – Plasma
Reexamination Certificate
2001-09-04
2002-10-22
Pianalto, Bernard (Department: 1762)
Coating processes
Direct application of electrical, magnetic, wave, or...
Plasma
C427S131000, C427S209000, C427S249100, C427S255280, C427S577000, C427S580000, C427S585000, C427S595000
Reexamination Certificate
active
06468602
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a magnetic recording medium such as a magnetic disc and the like for use in magnetic disc devices, and a manufacturing method for the same.
RELEVANT ART
In recent years, in the field of magnetic recording, particularly with respect to magnetic discs, remarkable improvements in the recording density have been achieved. In particular, recent improvements in the recording density have continued at a phenomenal pace, achieving rates of approximately 100 times in 10 years. Technologies supporting the improvement of recording density vary widely, however, one of the key concepts that can be mentioned is the technology of controlling the sliding characteristics between the magnetic head and magnetic recording medium.
Sliding of the head on the medium is unavoidable ever since the introduction of the CSS (Contact—Start—Stop) mode which is so-called “Winchester format” as the main mode for hard disc drives, wherein the basic operation comprises the steps of sliding into contact, head flotation, and sliding into contact between the magnetic head and magnetic recording medium. Accordingly, problems relating to tribology between head and medium have become critical technical problems. Thus, properties such as resistance to abrasion and resistance to sliding over the surface of the magnetic recording medium comprise the keys to a reliable product, and efforts continue to develop and improve the protective film, lubricating film, and the like, which coat the magnetic film.
As a protective film for magnetic recording medium, films comprising various materials have been proposed. However, from the perspective of the total performance such as coating performance and durability, carbon films are principally employed.
These carbon films are generally formed according to a spatter-coating method, in which the coating conditions are extremely important due to their direct impact on resistance to corrosion and CSS properties.
In addition, in order to improve the recording density, it is preferable to reduce the flying height of the head, to increase the number of rotations of the medium, and the like. Thus, a superior resistance to sliding is required for the magnetic recording medium. On the other hand, in order to improve the recording density by means of reducing spacing loss, it's preferable to make the protective film thinner, for example to a thickness of 100 Å or less. Hence, a thin, smooth and durable protective film is highly desired.
However, a carbon protective film formed according to the conventional spattering coating method, can sometimes lack durability, when the film is made thin, for example 100 Å or less.
Therefore, a plasma CVD method is currently being studied as a method for providing a carbon protective film with greater strength, compared to that produced by means of the spatter-coating method. This plasma CVD method is disclosed in, for example, Japanese Patent Application, Second Publication No. Hei 7-21858; First Publication Laid Open No. 7-73454; and the like.
However, under the current demands for increased recording density, it is difficult, from the perspective of durability to sliding, to produce a thin protective film to the point where a sufficiently high recording density is achieved without lowering the output properties, according to the aforementioned conventional technology. In addition, the conventional technology poses the problem of low coating rate, which in turn leads to production inefficiency.
In consideration of the aforementioned, the objectives of the present invention are described as follows.
(1) To provide a magnetic recording medium and manufacturing method thereof, that is reliable and capable of providing a sufficiently high recording density, without lowering the output properties.
(2) To provide a method for manufacturing the aforementioned magnetic recording medium in an efficient manner.
DISCLOSURE OF THE INVENTION
The method for manufacturing a magnetic recording medium according to the present invention comprises a method for manufacturing a magnetic recording medium by means of forming a carbon protective film onto the disc, the non-magnetic substrate of which is layered with a non-magnetic base film and magnetic film, using a reactant gas containing carbon atoms as a starting material, according to a plasma CVD method, wherein a mixed gas of hydrocarbon and hydrogen, in which the mixing ratio of hydrocarbon to hydrogen is in the range of 2 to 1~1 to 100 by volume, is used as a reactant gas, while applying a bias to said disc.
The aforementioned hydrocarbon preferably comprises at least one type of hydrocarbon selected from among lower saturated hydrocarbons, lower unsaturated hydrocarbons, and lower cyclic hydrocarbons, and more preferably comprises toluene.
In the case of using toluene, toluene and hydrogen are mixed, with a mixing ratio of toluene to hydrogen preferably in the range of 1 to 15~1 to 20 by volume.
The bias applied to the disc is preferably a high frequency bias.
In addition, formation of a carbon protective film is preferably carried out under high frequency electrical discharge.
When forming a carbon protective film on both sides of the disc at the same time, it is preferable to make the phases of electrical power supplied to each electrode arranged on the respective sides of the aforementioned disc different from each other. The phase difference of electrical power supplied to each electrode is preferably in the range of 90~270°, and in particular, more preferably the opposite phase (i.e., 180°).
The method for manufacturing a magnetic recording medium according to the present invention may comprise a method for manufacturing a magnetic recording medium by means of forming a carbon protective film onto the disc the non-magnetic substrate of which is layered with a non-magnetic base film and magnetic film, using a reactant gas containing carbon atoms as a starting material, according to a plasma CVD method, wherein pulse D.C. bias having a frequency of 1 kHz~100 GHz and pulse width of 1 ns~500 &mgr;s is applied to the disc, when forming (during formation of) the carbon protective film.
The frequency of the pulse D.C. bias applied to the disc is preferably in the range of 10 kHz~1 GHz, and the pulse width is preferably in the range of 10 ns~50 &mgr;s.
The average voltage of the pulse D.C. bias applied to the disc is preferably in the range of −400~−10V.
The aforementioned reactant gas is preferably a mixed gas of hydrocarbon and hydrogen, with a mixing ratio of hydrocarbon to hydrogen in the range of 2 to 1~1 to 100 by volume. The hydrocarbon preferably comprises at least one type of hydrocarbon selected from among lower saturated hydrocarbons, lower unsaturated hydrocarbons, and lower cyclic hydrocarbons.
The magnetic recording medium according to the present invention is provided with a carbon protective film onto the disc, the non-magnetic substrate of which is layered with a non-magnetic base film and magnetic film, that can be formed according to a plasma CVD method while applying pulse D.C. bias having a frequency of 1 kHz~100 GHz and pulse width of 1 ns 500 &mgr;s to the disc.
The method for manufacturing a magnetic recording medium according to the present invention may comprise a method for manufacturing a magnetic recording medium by means of forming a carbon protective film onto the disc, the non-magnetic substrate of which is layered with a non-magnetic base film and magnetic film, using a reactant gas containing carbon atoms as a starting material, according to a plasma CVD method, wherein the temperature of the disc is heated to 100~250° C. prior to forming the aforementioned carbon protective film.
The temperature of the disc is preferably in the range of 150~200° C.
The aforementioned reactant gas is preferably a mixed gas of hydrocarbon and hydrogen, with a mixing ratio of hydrocarbon to hydrogen in the range of 2 to 1~1 to 100 by volume, wherein the hydrocarbon mixed into the reactant gas preferably comprises at least one ty
Ohnami Kazunori
Sakaguchi Ryuji
Sakai Hiroshi
Suzuki Mikio
Pianalto Bernard
Showa Denko K.K.
Sughrue & Mion, PLLC
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