Coating processes – Direct application of electrical – magnetic – wave – or... – Plasma
Reexamination Certificate
1999-12-09
2001-04-17
Nguyen, Nam (Department: 1753)
Coating processes
Direct application of electrical, magnetic, wave, or...
Plasma
C427S585000, C427S237000, C427S249700, C204S192120, C204S192150
Reexamination Certificate
active
06217952
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of forming films over the inner circumference (surface) of a cylindrical member and, more particularly, to a method of forming a film consisting of a hard carbon film for enhancing the abrasion resistance of the inner surface of a cylindrical member (part), such as a bushing, a cylinder in which a piston reciprocates or a bearing, and an intermediate film (layer) formed between the hard carbon film and the inner surface of the cylindrical member which is capable of sticking to both the inner surface of the cylindrical member and the hard carbon film with high adhesion.
2. Description of the Prior Art
A hard carbon film is black and has properties similar to those of diamond. A hard carbon film has advantageous properties including a high mechanical hardness, a small friction coefficient with other materials, a high electrical insulation property, a large thermal conductivity and a high corrosion resistance. Accordingly, there have been proposals for coating various devices, including, medical instruments, magnetic heads, tools and such with a hard carbon film.
A hard carbon film is a hydrogenated amorphous carbon film having properties very similar to those of diamond and hence a hard carbon film is often called a diamondlike carbon film (DLC film) or an i-carbon film.
Proposed in JP-A No. 56-6920 is a film forming method of forming a hard carbon film with high adhesion on a surface of a base member. This previously proposed film forming method forms an intermediate film of silicon or a silicon compound over a surface of a base member by sputtering using a gas containing argon gas (Ar gas) and carbon, and then a hard carbon film is formed on the intermediate film.
Such a prior art method of forming a film consisting of an intermediate film and a hard carbon film over the inner surface of a cylindrical member (base member) of carbon tool steel, such as a bushing, will be described with reference to FIG.
10
.
Referring to
FIG. 10
showing a film forming apparatus for carrying out the prior art method of forming a film consisting of an intermediate film and a hard carbon film overlying the intermediate film, a target
37
of an intermediate film forming material, such as silicon or a silicon compound, and a cylindrical member
11
having a bore
11
a
defined by an inner surface
11
b,
are disposed opposite to each other in a vacuum vessel
13
.
Gases are removed through a gas outlet port
17
from the vacuum vessel
13
by an evacuating means, not shown, to evacuate the vacuum vessel
13
. Then, Ar gas, i.e., a sputtering gas, is supplied through a gas inlet port
15
into the vacuum vessel
13
. A negative DC voltage is applied to the target
37
by a first power source
39
and a negative DC voltage is applied to the cylindrical member
11
by a second DC power source
25
.
A plasma is thus produced within the vacuum vessel
13
to make the target
37
sputter by bombarding the surface of the target
37
with ions. Consequently, particles of the material forming the target
37
are deposited over the inner surface
11
b
of the cylindrical member
11
thus forming an intermediate film of silicon or a silicon compound.
Next, a hard carbon film is formed on the intermediate film by a conventional film forming method using an apparatus as shown in FIG.
11
.
Referring to
FIG. 11
, the cylindrical member
11
having its inner surface
11
b
deposited with the intermediate film is placed in a vacuum vessel
13
provided with a gas inlet port
15
and a gas outlet port
17
. The vacuum vessel
13
is evacuated by an evacuating means, not shown. Then, a gas which contains carbon is supplied through the gas inlet port
15
into the vacuum vessel
13
and the pressure in the vacuum vessel
13
is adjusted to a set pressure.
A positive DC voltage is applied to an anode
31
placed within the vacuum vessel
13
by an anode power source
27
, an AC voltage is applied to a filament
33
by a filament power supply
29
, and a negative DC voltage is applied to the cylindrical member
11
by a DC power source
25
. Thus, a plasma is produced in the vacuum vessel
13
to deposit a hard carbon film on the intermediate film formed over the inner surface of the cylindrical member
11
.
The hard carbon film forming method using the apparatus shown in
FIG. 11
uses the plasma produced by the DC voltage applied to the cylindrical member
11
and the plasma produced by the filament
33
energized by an AC voltage and the anode
31
energized by the DC voltage. Either the plasma produced around the cylindrical member
11
or the plasma produced around the filament
33
and the anode
31
contributes mainly to hard carbon film formation depending on the pressure in the vacuum vessel
13
during hard carbon film formation.
For example, when the pressure in the vacuum vessel
13
is 3×10
−3
torr or above, the plasma produced around the cylindrical member
11
mainly contributes to the decomposition of the gas containing carbon to form the hard carbon film.
Although a carbon film can be formed uniformly over the outer surface of the cylindrical member
11
by the dominant contribution of this plasma, a carbon film formed over the inner surface
11
b
defining the bore
11
a
is inferior in adhesion, hardness and quality. This is because the same voltage is applied to the cylindrical member
11
, and the inner surface
11
b
defines a space in which electrodes of the same polarity are disposed opposite to each other, and the plasma prevailing in the bore
11
a
causes an abnormal discharge called hollow discharge. A hard carbon film formed by hollow discharge is a polymerlike film inferior in adhesion and apt to come off the cylindrical member
11
and have a relatively low hardness.
When the pressure in the vacuum vessel
13
is below 3×10
−3
torr, the plasma produced in the neighborhood of the filament
33
and the anode
31
contributes mainly to hard carbon film formation.
Although a hard carbon film can uniformly be formed over the outer surface of the cylindrical member
11
by the dominant contribution of this plasma, the hard carbon film cannot be formed in a uniform thickness with respect to a direction along the axis of the cylindrical member
11
over the inner surface
11
b
defining the bore
11
a.
Carbon ions produced by the plasma produced around the filament
33
and the anode
31
are attracted to the surface of the cylindrical member
11
by the negative DC potential of the cylindrical member
11
to deposit the hard carbon film over the surface of the cylindrical member
11
.
The hard carbon film is formed by a chemical vapor deposition process when the pressure in the vacuum vessel
13
is above 3×10
−3
torr, and the hard carbon film is formed by a physical vapor deposition process when the pressure in the vacuum vessel
13
is below 3×10
−3
torr. Therefore, the thickness of the hard carbon film formed over the inner surface
11
b
of the cylindrical member
11
decreases from the open end of the bore
11
a
downwards with the depth, which occurs when forming a film by a physical vapor-phase epitaxial growth process, such as a vacuum deposition process, when the plasma produced around the filament
33
and the anode
31
contributes mainly to hard carbon film formation. Consequently, the hard carbon film cannot be formed in a uniform thickness over the entire inner surface
11
b
of the cylindrical member
11
.
Similarly, the thickness of the intermediate film formed over the inner surface
11
b
of the cylindrical member
11
decreases from the open end of the bore
11
a
downwards with the depth when the intermediate film is formed by the method previously described with reference to FIG.
10
.
FIG. 12
is a graph showing a thickness distribution in an intermediate film formed over the inner surface of a cylindrical member, in which distance from the open end of the cylindrical member is measured on the horizontal axis and thickness
Koike Ryota
Miya Yukio
Sekine Toshiichi
Sugiyama Osamu
Toida Takashi
Armstrong Westerman Hattori McLeland & Naughton LLP
Citizen Watch Co. Ltd.
Nguyen Nam
Ver Steeg Steven H.
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