Carbon film and method of forming the same

Details Carbon film and method of forming the same Carbon film and method of forming the same

2001-10-16

2003-12-02

Turner, Archene (Department: 1775)

Stock material or miscellaneous articles

Self-sustaining carbon mass or layer with impregnant or...

C428S195100

Reexamination Certificate

active

06656592

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a carbon film to be formed on the surface of a soft base material such as rubber or plastic (for example, such a carbon film having characteristics as low friction coefficient or low wear, to be used to such as sliding portion of machine parts), and a method of forming the same.
2. Description of the Related Art
Being high in hardness, carbon film is much used to cover the surface of metallic base material demanded to have high hardness as tools or parts of vehicles.
The carbon film is also sometime covered on the surfaces of soft base material such as rubber or plastic. In these cases, if covering the carbon film on the surface of soft base material, it has a merit to decrease frictional resistance on the surface and provide high hardness as maintaining the flexibility of soft base material. For this fact, recently studies and developments have rapidly been advanced for covering the carbon film on the surfaces of soft base material.
For covering the carbon film on the surface of soft base material, for example, the soft base material is located within a closed film forming container, a gas containing carbon is introduced into the container, the gas is made plasma by use of means for making the gas plasma (for example, means as a high frequency discharge), and a carbon film containing carbon as a main component is formed on the surface of soft base material under the plasma.
The soft base material with carbon film formed thus is often used as a sliding member. For example, the soft base material covered with the carbon film is slid together with other article under pressure.
However, the sliding member composed of the soft base material with the carbon film is used under various circumstances. For example, in the sliding member, a predetermined pressure is loaded on the surface of the soft base material with the carbon film, and at this time, friction coefficient of the carbon film is demanded to be low for maintaining a function as the sliding member. For example, when pressure added to the surface of the carbon film on the soft base material is below a certain value, the friction coefficient of the carbon film is low and desirable; however, if being under pressure larger than this value, the friction coefficient of the carbon film is sometimes high, so that the function as the sliding member cannot be maintained.
Further, even if the carbon films are subject to the same pressure, there are cases that the friction coefficient is controlled to be low and controlled to be high.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the invention to provide a carbon film containing carbon as a main component, formed on the surface of a soft base material, enabling to control friction coefficient to be low, and a method of forming this carbon film.
It is another object of the invention to provide a carbon film containing carbon as a main component, formed on the surface of a soft base material, where friction coefficient is controlled to be low in response to pressure to be applied to the surface of the carbon film.
It is a further object of the invention to provide a method of forming the carbon film containing carbon as a main component, formed on the surface of a soft base material, where friction coefficient is controlled to be low in response to pressure to be applied to the surface of the carbon film.
An inventor made studies for solving the problems, and obtained the following findings.
Namely, the carbon film containing carbon as the main component, formed on the surface of soft base material is divided by cracks into a plurality of regions. The carbon film may be produced by, for example, the following carbon film forming apparatus.
FIG. 3
of attached drawings shows an existing carbon film forming apparatus by Plasma CVD Process where methane gas is a raw gas.
This carbon film forming apparatus comprises a film forming container
1
, a vacuum exhaust apparatus
2
, a shower plate
3
, and means for making plasma the gas (herein, a high frequency electrode
5
connected to a high frequency power source
8
via a matching box
7
). The vacuum exhaust apparatus
2
enables to exhaust an air from an interior of the film forming container
1
. The shower plate
3
introduces a gas containing carbon (herein, methane gas) into the film forming container
1
vacuum-exhausted by the vacuum exhaust apparatus
2
. The means for making plasma the gas makes the gas introduced into the film forming container
1
through the shower plate
3
plasma. Incidentally, the high frequency electrode
5
may mount the soft base material
4
thereon. The high frequency electrode
5
is impressed the high frequency voltage from the high frequency power source
8
via the matching box
7
. Thereby, the gas introduced into the container
1
is made plasma which is to be formed at a position shown with numeral
6
in the drawing.
In the carbon film forming apparatus shown in
FIG. 3
, the soft base material
4
is located on the high frequency electrode
5
in the film forming container
1
, and the interior of the container
1
is closed. While the interior of the closed container
1
is vacuum-discharged by the vacuum exhaust apparatus
2
, the methane gas (CH
4
) is introduced as the raw gas from the shower plate
3
, and the interior of the container
1
is maintained at a desired film forming pressure. In general, the pressure within the vacuum container
1
ranges 0.1 to 10 Pa. The high frequency electrode
5
mounting the soft base material
4
thereon is impressed with the high frequency voltage. Then, a methane gas plasma
6
is formed within the film forming container
1
, and carbon being a composing element of methane is deposited on the soft base material
4
. Thus, the carbon film is formed on the soft base material
4
. By the way, the methane gas is employed as the raw gas, and when the carbon film is formed on the soft base material, benzene gas (C
6
H
6
) is generally used other than the methane gas.
FIG. 4
shows a schematically enlarged view of the surface condition of the carbon film grown by use of the methane gas or benzene gas.
Observing the surface of the grown carbon film by means of such as electron microscope, it is seen as shown in
FIG. 4
that numberless cracks A appear in the film, and the film is finely divided into a plurality of regions B due to cracks A. Herein, each of regions B surrounded by cracks A in the carbon film shall be called as “block”.
In a conventional film forming process of the carbon film employing the methane gas or benzene gas as the raw gas, when forming the carbon film on the soft base material, if changing conditions such as an electric power supplied in the formed film, the average area of the block B may be changed. When employing the methane gas as the raw gas, the average area of the block B ranges around 0.01×10
−3
mm
2
to 0.1 to 10
−3
mm
2
, and when the benzene gas is the raw gas, it ranges around 0.06×10
−3
mm
2
to 0.12 to 10
−3
mm
2
.
According to the inventor's studies, it was seen that if using a gas containing carbon as a raw gas to be introduced into a film forming chamber, which is higher molecular than that of benzene (for example, a hydrocarbon higher molecular than such as benzene), otherwise if using a gas containing oxygen atom and including carbon, or using a gas containing oxygen atom, which is added to the gas containing carbon, the average area of the block B might be controlled, so that the carbon film of larger average area of the block B might be obtained.
The inventor made further studies to investigate the relationship between the average area of the block B and the friction coefficient of the carbon film. It was found that a close correlation was present between them. That is, when the average range of the block B was smaller than around 0.15×10
−3
mm
2
, roughness in the surface of the carbon film was large. When it was larger than around 20×10
−3
mm
2

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