U.S. patent application number 10/014267 was filed with the patent office on 2002-08-01 for jet plasma process and apparatus for deposition of coatings and the coatings thereof.
This patent application is currently assigned to 3M Innovative Properties Company. Invention is credited to Esswein, William H., Gates, Brian J., Kirk, Seth M., Kohler, Gunter A..
Application Number | 20020102361 10/014267 |
Document ID | / |
Family ID | 25443719 |
Filed Date | 2002-08-01 |
United States Patent
Application |
20020102361 |
Kind Code |
A1 |
Kohler, Gunter A. ; et
al. |
August 1, 2002 |
Jet plasma process and apparatus for deposition of coatings and the
coatings thereof
Abstract
The present invention provides a method for the formation of an
organic coating on a substrate. The method includes: providing a
substrate in a vacuum; providing at least one vaporized organic
material comprising at least one component from at least one
source, wherein the vaporized organic material is capable of
condensing in a vacuum of less than about 130 Pa; providing a
plasma from at least one source other than the source of the
vaporized organic material; directing the vaporized organic
material and the plasma toward the substrate; and causing the
vaporized organic material to condense and polymerize on the
substrate in the presence of the plasma to form an organic
coating.
Inventors: |
Kohler, Gunter A.; (Grant
Township, MN) ; Esswein, William H.; (Hudson, WI)
; Kirk, Seth M.; (Minneapolis, MN) ; Gates, Brian
J.; (Eagan, MN) |
Correspondence
Address: |
Office of Intellectual Property Counsel
3M Innovative Properties Company
PO Box 33427
St. Paul
MN
55133-3427
US
|
Assignee: |
3M Innovative Properties
Company
|
Family ID: |
25443719 |
Appl. No.: |
10/014267 |
Filed: |
October 22, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10014267 |
Oct 22, 2001 |
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09759803 |
Jan 12, 2001 |
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09759803 |
Jan 12, 2001 |
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08920419 |
Aug 29, 1997 |
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Current U.S.
Class: |
427/447 ;
427/255.28; 427/255.6; 427/402; 427/569; 428/446; 428/447 |
Current CPC
Class: |
B05D 1/62 20130101; Y10T
428/269 20150115; Y10T 428/31663 20150401; C23C 16/4485 20130101;
Y10T 428/273 20150115; C23C 16/513 20130101 |
Class at
Publication: |
427/447 ;
427/569; 427/255.6; 427/402; 427/255.28; 428/446; 428/447 |
International
Class: |
C23C 016/00; B05D
001/36 |
Claims
What is claimed is:
1. A method for the formation of an organic coating on a substrate
comprising: providing a substrate in a vacuum; providing at least
one vaporized organic material comprising at least one component
from at least one source, wherein the vaporized organic material is
capable of condensing in a vacuum of less than about 130 Pa;
providing a plasma from at least one source other than the source
of the vaporized organic material; directing the vaporized organic
material and the plasma toward the substrate; and causing the
vaporized organic material to condense and polymerize on the
substrate in the presence of the plasma to form an organic
coating.
2. The method of claim 1 wherein the step of causing the vaporized
organic material to condense and polymerize comprises: causing the
plasma to interact with the vaporized organic material and form a
reactive organic species; and contacting the substrate with the
reactive organic species to form an organic coating.
3. The method of claim 1 wherein the step of causing the vaporized
organic material to condense and polymerize comprises: condensing
the vaporized organic material on the substrate in the presence of
the plasma to form reactive species that polymerize to form the
organic coating.
4. The method of claim 1 wherein the substrate is in close
proximity to a radio frequency bias electrode such that the
substrate is exposed to a radio frequency bias voltage.
5. The method of claim 4 wherein the radio frequency bias voltage
is sufficient to provide the coating with a density that is about
10% greater than the density of the major component of the organic
material prior to vaporization.
6. The method of claim 4 wherein the radio frequency bias voltage
is sufficient to provide the coating with a density that is about
50% greater than the density of the major component of the organic
material prior to vaporization.
7. The method of claim 1 wherein the vaporized organic material
comprises vaporized mineral oil.
8. The method of claim 7 wherein the plasma comprises a carbon-rich
plasma and the vaporized organic material comprises vaporized
dimethylsiloxane oil.
9. The method of claim 7 wherein the coating formed comprises a
layer of a carbon-rich material, a layer of dimethylsiloxane that
is at least partially polymerized, and an intermediate layer of a
carbon/dimethylsiloxane composite.
10. The method of claim 1 wherein the step of providing a plasma
comprises generating a plasma in a vacuum chamber by: injecting a
plasma gas into a hollow cathode system; providing a sufficient
voltage to create and maintain a plasma within the hollow cathode
system; and maintaining a vacuum in the vacuum chamber sufficient
for maintaining the plasma.
11. The method of claim 10 wherein the hollow cathode system is a
hollow cathode slot system comprising two electrode plates arranged
parallel to each other.
12. The method of claim 11 wherein the hollow cathode slot system
comprises a first compartment having therein a hollow cathode tube,
a second compartment connected to the first compartment, and a
third compartment connected to the second compartment having
therein the two parallel plates.
13. The method of claim 12 wherein the step of injecting a plasma
gas comprises injecting a carrier gas into the first compartment
and a feed gas into the second compartment.
14. The method of claim 13 wherein a plasma is formed from the
carrier gas in the first compartment.
15. The method of claim 13 wherein a plasma is formed from the
carrier gas and the feed gas in the third compartment.
16. The method of claim 15 wherein the feed gas is selected from
the group consisting of saturated and unsaturated hydrocarbons,
nitrogen-containing hydrocarbons, oxygen-containing hydrocarbons,
halogen-containing hydrocarbons, and silicon-containing
hydrocarbons.
17. The method of claim 10 wherein the hollow cathode system
comprises a hollow cathode tube.
18. The method of claim 10 wherein the hollow cathode system
comprises: a cylinder having an outlet end; a magnet surrounding
the outlet end of the cylinder; and a tube having a leading edge,
wherein the tube is positioned inside the cylinder and recessed
such that the leading edge of the tube is in the plane of the
center line of the magnet.
19. The method of claim 18 wherein the magnet is made of a ceramic
material.
20. The method of claim 18 wherein the tube is made of a ceramic
material.
21. The method of claim 1 wherein the plasma is formed from an
inert gas.
22. The method of claim 21 wherein the coating formed is a single
layer of organic material.
23. The method of claim 21 wherein the polymerized organic material
comprises a layer of multiple organic materials.
24. An organic coating on a substrate preparable by: providing a
substrate in a vacuum; providing at least one vaporized organic
material comprising at least one component from at least one
source, wherein the vaporized organic material is capable of
condensing in a vacuum of less than about 130 Pa: providing a
plasma from a source other than the at least one source of the
vaporized organic material; directing the vaporized organic
material and the plasma toward the substrate; causing the plasma to
interact with the vaporized organic material and form a reactive
organic species; and contacting the substrate with the reactive
organic species to form an organic coating.
25. The organic coating of claim 24 which is one layer of a single
organic material.
26. The organic coating of claim 24 which is one layer of multiple
organic materials.
27. The organic coating of claim 24 comprising multiple layers of
different organic materials.
28. The organic coating of claim 24 which is a silicone
coating.
29. The organic coating of claim 28 wherein the silicone coating
has a density of at least about 1.0.
30. The organic coating of claim 24 which is polymerized mineral
oil.
31. The organic coating of claim 24 which has a density that is at
least about 10% greater than the density of the major component of
the organic material prior to vaporization.
32. The organic coating of claim 31 which has a density that is at
least about 50% greater than the density of the major component of
the organic material prior to vaporization.
33. A non-diamond-like organic coating on a substrate comprising an
organic material comprising at least one major component, wherein
the coating has a density that is at least about 50% greater than
the density of the major component of the organic material prior to
coating.
34. The non-diamond-like organic coating of claim 33 which has
substantially the same composition and structure as that of the
starting material.
35. The non-diamond-like organic coating of claim 33 which is one
layer of a single organic material.
36. The non-diamond-like organic coating of claim 33 which is one
layer of multiple organic materials.
37. The non-diamond-like organic coating of claim 33 comprising
multiple layers of different organic materials.
38. The non-diamond-like organic coating of claim 33 which is a
silicone coating.
39. The non-diamond-like organic coating of claim 38 wherein the
silicone coating has a density of at least about 1.0.
40. The non-diamond-like organic coating of claim 33 which is
polymerized mineral oil.
41. A jet plasma apparatus for forming a coating on a substrate
comprising: a cathode system for generating a plasma; an anode
system positioned relative to the cathode system such that the
plasma is directed from the cathode system past the anode system
and toward the substrate to be coated; and an oil delivery system
for providing vaporized organic material positioned relative to the
cathode system such that the vaporized organic material and the
plasma interact prior to, or upon contact with, the substrate.
42. The jet plasma apparatus of claim 41 wherein the hollow cathode
system is a hollow cathode slot system comprising two electrode
plates arranged parallel to each other.
43. The jet plasma apparatus of claim 42 wherein the hollow cathode
slot system comprises a first compartment having therein a hollow
cathode tube, a second compartment connected to the first
compartment, and a third compartment connected to the second
compartment having therein the two parallel plates.
44. The jet plasma apparatus of claim 41 wherein the hollow cathode
system comprises a hollow cathode tube.
45. The jet plasma apparatus of claim 41 wherein the hollow cathode
system comprises a point source.
46. The jet plasma apparatus of claim 45 wherein the point source
comprises: a cylinder having an outlet end; a magnet surrounding
the outlet end of the cylinder; a tube having a leading edge,
wherein the ceramic tube is positioned inside the cylinder and
recessed such that the leading edge of the ceramic tube is in the
plane of the center line of the magnet.
47. The jet plasma apparatus of claim 41 further including a radio
frequency bias electrode in close proximity to the substrate to be
coated.
48. The jet plasma apparatus of claim 41 wherein the anode system
is an adjustable anode system located substantially below the path
the plasma travels when in operation.
49. The jet plasma apparatus of claim 41 wherein the oil delivery
system comprises an atomizer for forming droplets of the organic
material prior to vaporization.
50. A hollow cathode system comprising: a cylinder having an outlet
end; a magnet surrounding the outlet end of the cylinder; and a
tube having a leading edge, wherein the tube is positioned inside
the cylinder and recessed such that the leading edge of the tube is
in the plane of the center line of the magnet.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to coatings, particularly
organic coatings containing carbon and/or silicon coatings, and to
a method and apparatus for the plasma deposition of such
coatings.
BACKGROUND OF THE INVENTION
[0002] Plasma processes offer the opportunity to make coatings that
can be quite hard, chemically inert, corrosion resistant, and
impervious to water vapor and oxygen. These are often used as
mechanical and chemical protective coatings on a wide variety of
substrates. For example, carbon-rich coatings (e.g., diamond-like
carbon and jet plasma carbon coatings) have been applied to rigid
disks and flexible magnetic media. They have also been applied to
acoustic diaphragms, polymeric substrates used in optical and
ophthalmic lenses, as well as electrostatic photographic drums.
Silicon-containing polymer coatings have been applied to polymeric
and metal substrates for abrasion resistance. Also, silicone
coatings have been applied to polymeric and nonpolymeric substrates
to reduce water permeability and to provide mechanical
protection.
[0003] Carbon-rich coatings, as used herein, contain at least 50
atom percent carbon, and typically about 70-95 atom percent carbon,
0.1-20 atom percent nitrogen, 0.1-15 atom percent oxygen, and
0.1-40 atom percent hydrogen. Such carbon-rich coatings can be
classified as "amorphous" carbon coatings, "hydrogenated amorphous"
carbon coatings, "graphitic" coatings, "i-carbon" coatings,
"diamond-like" coatings, etc., depending on their physical and
chemical properties. Although the molecular structures of each of
these coating types are not always readily distinguished, they
typically contain two types of carbon-carbon bonds, i.e., trigonal
graphite bonds (sp.sup.2) and tetrahedral diamond bonds (sp.sup.3),
although this is not meant to be limiting. They can also contain
carbon-hydrogen bonds and carbon-oxygen bonds, etc. Depending on
the amount of noncarbon atoms and the ratio of Sp.sup.3/sp.sup.2
bonds, different structural and physical characteristics can be
obtained.
[0004] Diamond-like carbon-rich coatings have diamond-like
properties of extreme hardness, extremely low electrical
conductivity, low coefficients of friction, and optical
transparency over a wide range of wavelengths. They can be
hydrogenated or nonhydrogenated. Diamond-like carbon coatings
typically contain noncrystalline material having both trigonal
graphite bonds (sp.sup.2) and tetrahedral diamond bonds (sp.sup.3);
although it is believed the sp.sup.3 bonding dominates. Generally,
diamond-like coatings are harder than graphitic carbon coatings,
which are harder than carbon coatings having a large hydrogen
content, i.e., coatings containing hydrocarbon molecules or
portions thereof.
[0005] Silicon-containing coatings are usually polymeric coatings
that contain in random composition silicon, carbon, hydrogen,
oxygen, and nitrogen (SiO.sub.wN.sub.xC.sub.yH.sub.z). These
coatings are usually produced by plasma enhanced chemical vapor
deposition (PECVD) and are useful as barrier and protective
coatings. See, for example, U.S. Pat. Nos. 5,298,587 (Hu et al.),
5,320,875 (Hu et al.), 4,830,873 (Benz et al.), and 4,557,946
(Sacher et al.).
[0006] Silicone coatings are high molecular weight polymerized
siloxane coatings containing in their structural unit R.sub.2SiO in
which R is usually CH.sub.3 but may be H, C.sub.2H.sub.5,
C.sub.6H.sub.5, or more complex substituents. These silicones
(often referred to as polyorganosiloxanes) consist of chains of
alternating silicon and oxygen atoms (O--Si--O--Si--O) with the
free valences of the silicon atoms joined usually to R groups, but
also to some extent to oxygen atoms that are joined to
(crosslinked) silicon atoms in a second chain, thereby forming an
extended network. These coatings are valued for their toughness,
their lubricity, controlled gas diffusion, and their ability to
lower surface tension desirable for release coatings and water
repellent surfaces. For example, U.S. Pat. No. 5,096,738 (Wyman)
teaches the formation of barrier coatings via the hydrolysis of
trialkoxy methyl silane resulting in highly crosslinked polymer
structures.
[0007] Methods for preparing coatings by plasma deposition, i.e.,
plasma-enhanced chemical vapor deposition, are known; however, some
of these methods have deficiencies. For example, with certain
methods the use of high gas flow, pressure, and power can cause
formation of carbon powder, instead of the desirable smooth, hard
carbon film. U.S. Pat. Nos. 5,232,791 (Kohler et al.), 5,286,534
(Kohler et al.), and 5,464,667 (Kohler et al.) disclose a process
for the plasma deposition of a carbon-rich coating that overcomes
some of these deficiencies. These processes use a carbon-rich
plasma, which is generated from a gas, such as methane, ethylene,
methyliodide, methylcyanide, or tetramethylsilane, in an elongated
hollow cathode, for example. The plasma is accelerated toward a
substrate exposed to a radio frequency bias voltage. Although this
process represents a significant advancement in the art, other
plasma deposition processes are needed for deposition of a wide
variety of carbon- and/or silicon-containing coatings using lower
energy requirements.
[0008] Methods of preparing multilayer coatings are described in
U.S. Pat. Nos. 5,116,665 (Gauthier et al.) and 4,933,300 (Koinuma
et al.), and UK Patent Application Publication No. GB 2 225 344 A
(Eniricerche SpA). These methods are based on glow discharge
processes, which utilize one reactor and successive changes in
process parameters for the construction of multilayer coatings.
These methods, however, have practical and technical limitations. A
batch type process is required if gradual and/or abrupt changes of
layer properties are desired. Those changes are obtained by
deposition on stationary substrates and successive changes in
process conditions. Continuous deposition can be obtained in a
reactor that accommodates a roll-to-roll web transport system.
Multipass operation is required to construct multilayer coatings.
Under those circumstances a gradual change of layer properties
and/or the formation of interfacial layers are difficult to
obtain.
[0009] Thus, plasma deposition processes are needed for deposition
of a wide variety of carbon- and/or silicon-containing coatings
using relatively low energy requirements. Also, plasma deposition
processes are needed that can accommodate a gradual change of layer
properties and/or the formation of interfacial layers.
SUMMARY OF THE INVENTION
[0010] The present invention provides a method for the formation of
an organic coating on a substrate comprising: providing a substrate
in a vacuum; providing at least one vaporized organic material
comprising at least one component from at least one source, wherein
the vaporized organic material is capable of condensing in a vacuum
of less than about 130 Pa; providing a plasma from at least one
source other than the source of the vaporized organic material;
directing the vaporized organic material and the plasma toward the
substrate; and causing the vaporized organic material to condense
and polymerize on the substrate in the presence of the plasma to
form an organic coating.
[0011] The step of providing a plasma preferably includes
generating a plasma in a vacuum chamber by: injecting a plasma gas
into a hollow cathode system; providing a sufficient voltage to
create and maintain a plasma within the hollow cathode system; and
maintaining a vacuum in the vacuum chamber sufficient for
maintaining the plasma. In a preferred embodiment, the hollow
cathode system includes: a cylinder having an outlet end; a magnet
surrounding the outlet end of the cylinder; and a tube having a
leading edge, wherein the tube is positioned inside the cylinder
and recessed such that the leading edge of the tube is in the plane
of the center line of the magnet.
[0012] Also provided is an organic coating on a substrate
preparable by: providing a substrate in a vacuum; providing at
least one vaporized organic material comprising at least one
component from at least one source, wherein the vaporized organic
material is capable of condensing in a vacuum of less than about
130 Pa; providing a plasma from a source other than the at least
one source of the vaporized organic material; directing the
vaporized organic material and the plasma toward the substrate;
causing the plasma to interact with the vaporized organic material
and form a reactive organic species; and contacting the substrate
with the reactive organic species to form an organic coating. The
coating can include one layer of a single organic material or
multiple organic materials. Alternatively, it can include multiple
layers of different organic materials.
[0013] The present invention also provides a non-diamond-like
organic coating on a substrate comprising an organic material
comprising at least one major component, wherein the coating has a
density that is at least about 50% greater than the density of the
major component of the organic material prior to coating. For one
component layer, the non-diamond-like organic coating preferably
has substantially the same composition and structure as that of the
starting material.
[0014] The present invention also provides a jet plasma apparatus
for forming a coating on a substrate comprising: a cathode system
for generating a plasma; an anode system positioned relative to the
cathode system such that the plasma is directed from the cathode
system past the anode system and toward the substrate to be coated;
and an oil delivery system for providing vaporized organic material
positioned relative to the cathode system such that the vaporized
organic material and the plasma interact prior to, or upon contact
with, the substrate.
[0015] The present invention further provides a hollow cathode
system comprising: a cylinder having an outlet end; a magnet
surrounding the outlet end of the cylinder; a tube having a leading
edge, wherein the ceramic tube is positioned inside the cylinder
and recessed such that the leading edge of the ceramic tube is in
the plane of the center line of the magnet.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 is a schematic diagram of a jet plasma vapor
deposition apparatus of the present invention.
[0017] FIG. 2 is an expanded perspective view of one preferred oil
delivery system of the present invention.
[0018] FIG. 3 is an expanded perspective view of another preferred
oil delivery system of the present invention.
[0019] FIG. 4 is a schematic diagram of an alternative jet plasma
vapor deposition apparatus of the present invention.
[0020] FIG. 5 is a cross-sectional side view of a preferred hollow
cathode point source of the present invention.
[0021] FIG. 6 is a plot of the effect of bias on moisture vapor
transmission.
[0022] FIG. 7 is an Auger Spectroscopy depth profile of a coating
of the present invention on a silicon wafer.
DETAILED DESCRIPTION OF THE INVENTION
[0023] The present invention provides methods and systems for
forming organic coatings, particularly carbon-containing coatings
(e.g., carbon-rich coatings as defined above), silicon-containing
coatings (e.g., silicone coatings as defined above), or
combinations thereof, and the coatings themselves. The methods of
forming the coatings occur by means of plasma interaction with a
vaporized organic material, which is normally a liquid at ambient
temperature and pressure. The systems of the present invention can
be used to deposit low cost coatings, which can have a wide range
of specific densities. These coatings can be uniform
multi-component coatings (e.g., one layer coatings produced from
multiple starting materials), uniform one-component coatings,
and/or multilayer coatings (e.g., alternating layers of carbon-rich
material and silicone materials).
[0024] Generally, the coating processes use a plasma (i.e.,
expanded gaseous reactive ionized atoms or molecules and neutral
molecular fragments) and at least one vaporized organic material
containing at least one component, wherein the vaporized organic
material is capable of condensing in a vacuum of less than about 1
Torr (130 Pa). These vapors are directed toward a substrate in a
vacuum (either in outer space or in a conventional vacuum chamber).
This substrate is in close proximity to a radio frequency bias
electrode and is preferably negatively charged as a result of being
exposed to a radio frequency bias voltage. Significantly, these
coatings are prepared without the need for solvents.
[0025] For example, using a carbon-rich plasma in one stream from a
first source and a vaporized high molecular weight organic liquid
such as dimethylsiloxane oil in another stream from a second
source, a one-pass deposition procedure results in a multilayer
construction of the coating (i.e., a layer of a carbon-rich
material, a layer of dimethylsiloxane that is at least partially
polymerized, and an intermediate or interfacial layer of a
carbon/dimethylsiloxane composite). Variations in system
arrangements result in the controlled formation of uniform
multi-component coatings or layered coatings with gradual or abrupt
changes in properties and composition as desired. Uniform coatings
of one material can also be formed from a carrier gas plasma, such
as argon, and a vaporized high molecular weight organic liquid,
such as dimethylsiloxane oil.
[0026] The coatings formed using the jet plasma process described
herein can have a wide variety of properties. They can be tough,
scratch resistant, chemically resistant, and suitable for use as
protective coatings. They can be impermeable to liquids and gases,
and suitable for use as barrier coatings. They can have a
controlled void/pore structure selective for molecular diffusion,
and suitable for use as separation membranes. They can be
transparent and antireflective, and suitable for use as an optical
coating. They can have tailored surface energies and variable
conductivity and resistivity. Hence, the coatings can have a wide
variety of uses.
[0027] Preferred carbon-rich coatings and preferred silicone
coatings are impervious to water vapor and oxygen, and are
generally resistant to mechanical and chemical degradation. They
are also sufficiently elastic such that they can be used on typical
flexible substrates used in, for example, magnetic media and
packaging films.
[0028] Such preferred coatings are highly polymerized and/or
crosslinked materials, i.e., materials having a crosslink density
generally greater than -that obtained if conventional methods of
deposition, such as conventional PECVD methods, are used.
Specifically, for example, the present invention provides a
substrate on which is coated a silicone coating, preferably a
polymerized diorganosiloxane, having a high concentration of
crosslinked siloxane groups (i.e., high Si--O--Si crosslinkage) and
a reduced concentration of organic groups (e.g., methyl groups)
relative to the starting material.
[0029] Preferably, the coatings of the present invention are
non-diamond-like coatings yet generally very dense. The density of
a coating is preferably at least about 10% (and more preferably, at
least about 50%) greater than the major component of the organic
material prior to vaporization (preferably, greater than any of the
starting materials). Typically, the organic starting materials are
in the form of oils, and the resultant coating can have a density
that is preferably at least about 10% (and more preferably, at
least about 50%) greater than that of the oil used in the greatest
amount. With methods of deposition that do not expose the substrate
to a radio frequency bias voltage, there is only a minor increase
(e.g., less than about 10%) in the density of the coatings relative
to the starting materials. Herein, density is measured by the
floating method as described below. Preferred silicone coatings of
the present invention have a density of at least about 1.0.
[0030] Typically, as the radio frequency bias to which the
substrate is exposed in the method described herein increases, the
density and hardness of the coatings increase. As the density and
hardness increase, the barrier properties for water vapor and/or
oxygen (and other gases) increase. It is even possible to get
several s orders of magnitude increase in barrier properties and
hardness using the methods of the present invention.
[0031] The present invention also provides a substrate on which is
coated polymerized mineral oil (i.e., an aliphatic hydrocarbon),
such as Nujol. This provides a decrease in water vapor
transmission, which is believed to be associated with an increase
in density. Thus, one organic material that can be used as a
starting material in the methods of the present invention is
mineral oil. Other such organic materials include other aromatic
and aliphatic hydrocarbons as well as silicon- and
oxygen-containing hydrocarbons such as silicone oil and
perfluoropolyethers, which can be used alone or in combination.
Suitable organic materials are those that have strong bonds in the
backbone that do not break down easily in a vacuum. They can be
aromatic, aliphatic, or combinations thereof (e.g., compounds
containing aralkyl or alkaryl groups). When more than one organic
material is used, they can be mixed prior to vaporization and
provided from one source or they can be provided separately from
separate sources.
[0032] Using the methods described herein, certain physical and
chemical properties of the starting materials are generally
maintained. That is, properties of the starting materials, such as
coefficient of friction, surface energy, and transparency do not
change significantly upon preparing coatings using the methods
described herein, as opposed to conventional plasma processes.
Thus, the methods of the present invention are very different from
conventional plasma processes because the molecules are not
significantly broken down to low molecular weight, reactive,
species with the methods of the present invention. For example, it
is believed that the --Si--O--Si--O-- chain of a silicon oil
remains substantially in tact in the jet plasma process of the
present invention.
[0033] The methods of the present invention include providing a
plasma (e.g., an argon plasma or a carbon-rich plasma as described
in U.S. Pat. No. 5,464,667 (Kohler et al.)) and at least one
vaporized organic material comprising at least one component from
separate sources and allowing them to interact during formation of
a coating. The plasma is one that is capable of activating the
vaporized organic material. It can be generated using well-known
means or the point source described herein. That is, the plasma can
cause the vaporized organic material to become reactive, for
example, as a result of radical formation, ionization, etc.,
although such reactive species are still capable of condensing in a
vacuum to form a polymerized coating. Alternatively, the plasma can
interact with the vaporized organic material as the vaporized
organic material condenses on the surface in a manner such that the
entire thickness of the coating is polymerized. Therefore, the
plasma and vaporized organic material can interact either on the
surface of the substrate or prior to contacting the surface of the
substrate. Either way, the interaction of the vaporized organic
material and the plasma provides a reactive form of the organic
material (e.g., loss of methyl group from silicone) to enable
densification of the material upon formation of the coating, as a
result of polymerization and/or crosslinking, for example. Thus,
the method of the present invention provides the means of high rate
deposition, approaching the condensation rate of the vaporized
organic material; it also provides the means of preparing coatings
where the physical and chemical composition and structure of the
precursor is maintained to a high degree.
[0034] The methods of the present invention preferably include the
use of a radio frequency bias voltage sufficient to provide a
coating having a density that is at least about 10% greater (and
preferably at least about 50% greater) than the density of the
major component of the organic material prior to vaporization.
Preferably, the bias voltage is no more positive than about minus
50 volts, which also creates a plasma at the substrate. More
preferably, the bias voltage is no more positive than about minus
100 volts, and most preferably, no more positive than about minus
200 volts. Typically, the bias voltage can be as negative as about
minus 2500 volts. The specific bias voltage typically depends on
the material of which the substrate is made. This high bias power
can be obtained in conjunction with the use of the hollow cathode
described herein. As mentioned above, the higher the bias power the
higher the density of the coating. With no bias, the density of a
coating made by the method of the present invention is very similar
to that of conventional coatings (e.g., a silicone polymer coating
with no crosslinkage) made by conventional processes (e.g.,
conventional PECVD methods).
[0035] In general, high density coatings (e.g., diamond-like
carbon, jet plasma carbon) are prepared by plasma enhanced chemical
vapor deposition (PECVD), which utilize negatively biased
substrates in contact with radio frequency powered cathodes.
Typically, the system provides ion bombardment of the fragmented
species of feed gas (e.g., acetylene) and ions of carrier gas
(e.g., argon) onto the substrate to cause atomic
arrangement/rearrangement of the coating being formed to a dense
structure. Simultaneously, the cathode is utilized for extensive
fragmentation of the feed gas, as described in U.S. Pat. No.
4,382,100 (Holland). Because the two process parameters, namely the
extensive fragmentation and the ion attraction cannot be controlled
independently, conventional PECVD methods are limited and
unfavorable for high rate deposition. This limitation has been
overcome in U.S. Pat. No. 5,464,667 (Kohler et al.), which teaches
the independent use of the hollow cathode for feed gas
fragmentation and a second cathode to bias the-film substrate to
deposit these fragments.
[0036] The present invention includes modifications of the systems
described in U.S. Pat. Nos. 5,286,534 (Kohler et al.) and 5,464,667
(Kohler et al.), which allow for the deposition of dense coatings
without extensive fragmentation of the starting material.
Significantly, using the process and system of the present
invention, high molecular weight organic starting materials can be
converted into dense coatings without extensive fragmentation and
without a significant loss of physical and chemical properties
inherent to the starting material. These differences between the
coatings of the present invention and coatings produced by
conventional methods are exemplified by Examples 1, 3, and 4 and
Comparative Example A discussed in greater detail below.
[0037] The plasma is generated from a plasma gas using a hollow
cathode system, such as a "hollow cathode tube" (as disclosed in
U.S. Pat. No. 5,286,534 (Kohler et al.)) or a "hollow cathode slot"
(as disclosed in U.S. Pat. No. 5,464,667 (Kohler et al.)),
preferably a slot comprising two electrode plates arranged parallel
to each other, and more preferably, a tube in line with a slot, and
then directed toward and typically past an anode (as described in
U.S. Pat. No. 5,464,667 (Kohler et al.)). In one preferred
embodiment, the hollow cathode slot system includes a first
component having therein a hollow cathode tube, a second
compartment connected to the first compartment, and a third
compartment connected to the second compartment having therein the
two parallel plates. Alternatively, a system referred to herein as
a "point source" can also be used as the hollow cathode system to
generate a plasma. These all form a jet plasma within the hollow
cathode, which is propelled past or toward an anode. This is in
contrast to conventional "plasma jet" systems in which the plasma
is generated between the cathode and anode and a jet stream is
directed out of the cathode/anode arrangement.
[0038] The plasma gas includes a carrier gas, such as argon, and
optionally a feed gas. The feed gas can be any suitable source for
the desired composition of the coating. Typically, the feed gas is
a source for a carbon-rich coating. The feed gas is preferably
selected from the group consisting of saturated and unsaturated
hydrocarbons, nitrogen-containing hydrocarbons, oxygen-containing
hydrocarbons, halogen-containing hydrocarbons, and
silicon-containing hydrocarbons. The vaporized organic material
(preferably a vaporized organic liquid) is typically used to
provide other materials that form uniform multi-component or
multilayer coatings, although the plasma gas could also be the
source of such components. That is, a low molecular weight
silicon-containing compound could be used to generate a plasma.
[0039] Referring to FIG. 1, a particularly preferred jet plasma
apparatus for deposition of such coatings is shown. This apparatus
is similar to that shown in U.S. Pat. No. 5,464,667 (Kohler et al.)
modified for the deposition of two materials either simultaneously
or sequentially. The apparatus includes feed gas source 20 and
carrier gas source 22 connected via flow controllers 24 and 25,
respectively, to inlet tubes 26 and 27, respectively. Carrier gas,
e.g., argon, from the gas source 22 is fed into a vacuum chamber 30
and into a hollow cathode system 40 through an inlet port 28. Feed
gas, e.g., acetylene, from the gas source 20 is fed into the vacuum
chamber 30 and into the hollow cathode system 40 through an inlet
port 29. The hollow cathode system 40 shown in FIG. 1 is divided
into three compartments, i.e., a first compartment 41, a second
compartment 42, and a third compartment 43. The carrier gas, if
used, is fed into the first compartment 41, whereas the feed gas is
fed into the second compartment 42. A plasma can be formed from the
carrier gas in the first compartment and/or from the carrier and
feed gases in the third compartment. This hollow cathode system is
further discussed in U.S. Pat. No. 5,464,667 (Kohler et al.), the
discussion of which is incorporated herein by reference.
[0040] In addition to the hollow cathode system 40, inside the
vacuum chamber 30 is an anode system 60, which may be either
grounded or ungrounded, and which preferably contains an adjustable
shield 61. Also included are a radio frequency bias electrode 70, a
substrate (e.g., polyethylene terephthalate "PET" film) 75, and an
oil delivery system 120. The oil delivery system 120 provides a
vaporized organic liquid for deposition on the substrate. It
includes oil reservoir 122, cooling system 123, oil delivery system
124, evaporator chamber 126, outlet port 128, adjustable divider
plate 130, and substrate protecting shield 129. The divider plate
130 is used to keep the plasma and vaporized liquid separate until
they are close to the substrate. The substrate protecting shield
129 is used to avoid the condensation of vaporized liquid onto the
nonbiased substrate. Both the divider plate 130 and the substrate
protecting shield 129 are optional.
[0041] The substrate 75 is generally unwound from a first roll 76
and is rewound upon a second roll 78, although it can be a
continuous loop of material. The plasma gas, i.e., feed gas alone
or mixture of feed gas and carrier gas, is converted into a plasma
within the hollow cathode system 40. The plasma 160 is then
directed toward the substrate 75, which preferably contacts the
radio frequency bias electrode 70 during deposition of the coating
from the plasma. The substrate can be made of a wide variety of
materials. For example, it can be a polymeric, metallic, or ceramic
substrate. In a preferred embodiment, the substrate is a thin,
i.e., less than 0.05 cm, and flexible polymeric film. Examples of
useful films are oriented polyester, nylon, biaxially oriented
polypropylene, and the like.
[0042] The radio frequency bias electrode 70 is made of metal, such
as copper, steel, stainless steel, etc., and is preferably in the
form of a roll, although this is not necessarily a requirement. For
example, it can be in the form of a plate. The roll is
advantageous, however, because it reduces friction between the
electrode and the substrate, thereby reducing film distortion. More
preferably, the radio frequency bias electrode 70 is water-cooled
to a temperature no greater than about room temperature (i.e.,
about 25.degree. C. to about 30.degree. C.), preferably to a
temperature of about 0.degree. C. to about 5.degree. C., which is
advantageous when heat-sensitive substrates are used. The radio
frequency bias electrode typically has a frequency of about 25 KHz
to about 400 KHz, although it is possible to increase the frequency
range up to and including the megahertz range. It typically has a
bias voltage of about minus 100 volts to about minus 1500 volts.
With the bias voltage applied, an additional plasma is created in
the proximity of the radio frequency bias electrode 70 that
generates a negative potential at the substrate, and attracts the
plasma species 160 toward the substrate 75 for efficient and rapid
deposition.
[0043] To create a plasma, a first DC power supply 80 is
electrically connected directly to the first compartment 41 of the
hollow cathode system 40 by a circuit 82 and to the anode system 60
by a circuit 84. The first DC power supply 80 can be a pulsating DC
power supply, a filtered DC power supply, or other
plasma-generating means with appropriate arc suppression, such as
those used in sputtering systems. An unfiltered pulsating DC power
supply is generally preferred, however. Also, a second DC power
supply 85 is electrically connected directly to the third
compartment 43 of the hollow cathode system 40 by a circuit 87 and
to the anode system 60 also by circuit 84. In this arrangement
chamber 41 and chamber 43 are electrically isolated from each
other. The second DC power supply 85 can be a pulsating DC power
supply, a filtered DC power supply, or other plasma-generating
means with appropriate arc suppression, although a pulsating DC
power supply is preferred. An example of a filtered DC power supply
is a 25 kilowatt filtered DC power supply, such as that available
from Hippotronics Inc., New York, N.Y. Such a power supply
generates a plasma at high currents up to about 10 amperes, and
relatively low voltage, i.e., about minus 100 volts.
[0044] A radio frequency biasing power supply 90 (e.g., PLASMALOC 3
power supply from ENI Power Systems, Inc., Rochester, N.Y.) is
connected to the radio frequency bias electrode 70 by a circuit 92
and to a ground 100 by a circuit 94. The DC power supplies 80 and
85 can also be connected to the ground 100, although this is not a
preferred arrangement. This electrical connection is represented in
FIG. 1 by the dashed line 105. Thus, in this arrangement wherein
all three power supplies are attached to ground 100, the anode
system 60 is grounded. The former arrangement, wherein the anode
system 60 is not grounded, is advantageous when compared to the
latter arrangement. For example, when the anode system 60 is not
grounded, the plasma formed is more stable, because the plasma sees
the anode system as distinct from the grounded metal chamber.
Typically, when the anode system 60 is not grounded, the cross-web
coating thickness, i.e., the coating thickness along the width of
the substrate, is more uniform. Furthermore, the plasma is more
confined and the pattern of deposition can be more readily
controlled by varying the exposure of the plasma to the anode
system 60.
[0045] As stated above, DC power supplies 80 and 85 are preferably
pulsating DC power supplies. This is because pulsating DC power
supplies provide more stable plasma conditions than nonpulsating DC
power supplies, which contributes to uniform plasma deposition
rates and therefore down-web, i.e., along the length of the
substrate, coating uniformity. Furthermore, they allow for the use
of high current flow, and thus high deposition rates, at relatively
low voltage.
[0046] Whether used as the first DC power supply 80 or the second
DC power supply 85, or both, a preferred pulsating DC power supply
is one that provides a voltage that typically passes through zero
about 25 times/second to about 1000 times/second, more preferably
about 25 times/second to about 200 times/second, and most
preferably about 100 times/second to about 120 times/second. This
allows the plasma to extinguish and then reignite as the cathode
reaches its necessary potential. Examples of such pulsating DC
power supplies include the Airco Temescal Model CL-2A power supply
with a 500 mA maximum output and a 120 Hz full-wave rectified DC
voltage from 0 volts to minus 5000 volts. available from Airco
Temescal, Berkeley, Calif. Another version of this power supply
uses two Airco Temescal transformers in parallel, thereby resulting
in a 1 ampere maximum output. These pulsating DC power supplies
were used in the examples described below. Another power supply was
built with a 20 ampere maximum output, and also used in the
examples described below. This was accomplished with a larger size
(1 kilowatt), leakage-type transformer obtained from MAG-CON Inc.,
Roseville, Minn., including full wave rectification to achieve
pulsating DC output. As used herein, a "leakage-type" transformer
is one that provides a stable operating point for a load with a
negative dynamic resistance. Typical output of this 20 ampere power
supply is 0 volts direct current (VDC) to minus 1500 VDC with
current of 0 ampere to 20 amperes. This power supply is current
limited, which prevents formation of high intensity arcs at the
cathode surfaces. If greater currents are required, a larger
leakage-type transformer can be used, or two or more smaller
transformers can be arranged in parallel.
[0047] In particularly preferred embodiments of the present
invention, both power supply 80 and power supply 85 are pulsating
DC power supplies. In such embodiments, a carrier gas is injected
into the first compartment 41 of the hollow cathode system 40 and a
pulsating DC power supply, preferably a 500 mA pulsating DC power
supply, is used to create a plasma from the carrier gas. Although
formation of this initial carrier gas plasma may not always be
necessary when a pulsating DC power supply is used to generate a
plasma in the third compartment 43 of the hollow cathode system 40,
it is necessary for ignition of a plasma in the third compartment
when a nonpulsating filtered DC power supply is used. After initial
ignition of the carrier gas plasma in particularly preferred
embodiments of the present invention, this initial plasma passes
into the second compartment 42 of the hollow cathode system 40
where it is mixed with the feed gas. This mixture then passes into
the third compartment 43 where a second plasma is created using a
pulsating DC power supply. This pulsating DC power supply can be a
1 ampere or 20 ampere power supply, as used in the examples, or it
can be a 500 mA power supply or a 20 ampere, 30 ampere, 50 ampere,
100 ampere, etc., power supply, depending on the desired feed gas
fragment concentration and coating deposition rate.
[0048] In the first compartment 41 of the hollow cathode system 40,
such as a hollow cathode slot system, the voltage created and
maintained is preferably about minus 200 volts to about minus 1000
volts, preferably about minus 200 volts to about minus 500 volts.
The power supplied to this first compartment is typically about 20
watts to about 10,000 watts, preferably about 20 watts to about
1000 watts, and more preferably about 100 watts to about 500 watts.
In the third compartment 43 of the hollow cathode system 40, the
voltage created and maintained is preferably about minus 50 volts
to about minus 500 volts, and more preferably about minus 80 volts
to about minus 120 volts. The power supplied to this second
compartment is typically about 50 watts to about 3000 watts, and
more preferably about 1000 watts to about 3000 watts.
[0049] Given the correct conditions, a stable jet plasma 160 is
formed in the vacuum chamber which spreads out in an extended
pattern generally imaging the shape of the exit slot of the hollow
cathode system 40. Preferred plasmas have a high feed gas fragment
concentration, i.e., fragmentation of the feed gas occurs at a high
rate, so as to provide a rapid deposition rate of the carbon-rich
coating on the substrate 75. That is, the higher the deposition
rate of a coating and the more uniform the coating, the more
desirable the plasma formed, which depends on the system
arrangement and the current and voltage provided. Furthermore, if a
highly uniform coating can be deposited at a relatively high rate
with low power requirements, the more desirable the system with
respect to practical considerations (e.g., cost, safety, and
preventing overheating).
[0050] To monitor the conditions in the vacuum chamber, a variety
of instruments, such as a mass spectrometer, an emission
spectrometer, and a capacitance manometer, can be connected to the
vacuum chamber. A vacuum can be created and maintained within the
vacuum chamber by any means typically used to create a vacuum
(e.g., diffusion pump and/or mechanical pump). The vacuum chamber
is typically maintained at a pressure of about 0.13 Pascals (Pa) to
about 130 Pa, preferably at about 0.13 Pa to about 1.0 Pa. It will
be understood by one skilled in the art that the method and
apparatus described herein can be used in a naturally occurring
vacuum, such as occurs in space.
[0051] In order to deliver liquids in vapor form into vacuum
chamber 30, oil delivery system 120 is used to control oil feed
rate for evaporation. As shown in FIG. 1, oil 121 is delivered from
a reservoir 122 placed in vacuum chamber 30, through oil delivery
orifice 124. This delivers the oil into evaporator 126 for
evaporation and out evaporator outlet port 128 for delivery to the
radio frequency bias electrode 70. Valve system 140 is used to
expose oil 121 to the vacuum so as to become de-aerated. During
this de-aeration process, oil discharge through oil delivery
orifice 124 is prevented by having equal pressure above the liquid
(e.g. oil 121) and at the oil delivery orifice 124. The
configuration of valve system 140 is changed to introduce air into
reservoir 122 in the space above oil 121 to impose a desirable
pressure above the oil. Typically, the oil delivery orifice 124 is
a tube or needle, such as a syringe needle, although other delivery
orifices of other shapes could be used. The oil feed rate is
controlled by proper selection of the temperature of the delivery
means, which controls the viscosity, and the size of the delivery
means, which controls the mass flow rate. Depending on the desired
result, oil feed rate can be varied over a broad range. The
temperature of the oil delivery orifice 124 can be regulated by
cooling system 123. This can be a liquid-, gas-, or electric-cooled
system. The temperature of the oil delivery orifice 124 and the
evaporator 126 can be monitored using a thermocouple, for
example.
[0052] FIG. 1 also shows divider plate 130 and substrate protection
shield 129. Typically, these components are made of quartz,
although any material can be used, such as metal, plastic, or
ceramic, as long as it can withstand the temperatures experienced
in the system during deposition. As stated above, these components
are optional.
[0053] Oil delivery system 120 is shown in greater detail in FIG.
2, along with valve system 140. The oil delivery system 120
includes an oil reservoir 122 and a flash evaporator 126 consisting
of one or more spacers 127 made of a thermally conductive material
(e.g., aluminum). The spacers 127 can be heated by any of a variety
of means, such as variac-controlled cartridge type resistance
heaters (not shown in FIG. 2). A cooling system 123, such as a
water-cooled copper sleeve, that accommodates the oil delivery
orifice 124 (e.g., a needle) is placed into an inlet port 125 of
the flash evaporator 126. The inlet port 125 is preferably situated
at the back region of the flash evaporator 126 and preferably
includes a sleeve insert, such as a silicone rubber sleeve insert,
to prevent heat exchange between the flash evaporator 126 and the
cooling system 123. The tip of the oil delivery orifice 124 (e.g.,
needle), however, is in immediate contact with the heated inlet
port 125 allowing constant and uniform vaporization of the oil. The
individually shaped spacers 127 preferably provide multiple
spacings so that the vaporized oil is guided over the full width of
the flash evaporator 126 several times upwards and downwards (as
shown by the dotted line) before the vapor is discharged uniformly
through an outlet port 128 into the vacuum chamber (not shown in
FIG. 2).
[0054] An atomizer can also be used to atomize the organic material
(i.e., form liquid droplets of the material) prior to vaporizing
the organic material. The atomizer is particularly necessary for
organic materials that are unsaturated, although it can also be
used with saturated organic materials. This is particularly true if
extended periods of vaporization are used (e.g., greater than a few
minutes) because this can clog the orifice of the evaporator. A
system that includes an atomizer is shown in FIG. 3, wherein oil
delivery system 220 is shown in greater detail along with valve
system 140. In this embodiment, the oil delivery system 220
includes an oil reservoir 222, a flash evaporator 226 consisting of
one or more spacers 227, a cooling system 223, oil delivery orifice
224, inlet port 225 in the flash evaporator 226, and an outlet port
228 as described with respect to FIG. 2. Also included to atomize
the organic material is an ultrasonic horn 230 attached to an
ultrasonic converter 229, as is known in the art. A useful
ultrasonic system is a Branson VC54 unit (40 kHz, available from
Sonics and Materials, Inc., Danbury, Conn.), tuned to provide
maximum atomization. Other means by which the organic material can
be atomized are described, for example, in U.S. Pat. No.
4,954,371.
[0055] An alternative jet plasma vapor deposition apparatus 300 is
shown in FIG. 4. This system includes a radio frequency bias
electrode 310 (also referred to herein as a biased chill roll or
simply a chill roll) with a portion of the radio frequency bias
electrode 310 preferably covered by a dark space ground shield 312,
such as an aluminum sheet, to form a discrete deposition area 314.
Preferably, at least about 76% of the surface of the radio
frequency bias electrode 310 is covered by dark space ground shield
312. Dark space ground shield 312 is grounded and placed about 0.3
centimeter (cm) to about 2.5 cm away from the surface of radio
frequency bias electrode 310 to provide a dark space and thus
concentrate the bias wattage over the exposed surface area of radio
frequency bias electrode 310.
[0056] The jet plasma vapor deposition apparatus 300 of FIG. 4 also
includes a hollow cathode system 315, which includes a point source
cathode 316, a feed gas source 317 and a carrier gas source 318,
for generating a plasma, an oil delivery system 320, attached to a
valve system 321, and an anode system 322 (e.g., an anode wire as
described herein). In this arrangement, the oil delivery system 320
and attached valve system 321 are optional. In the specific
embodiment shown in FIG. 4, an imaginary horizontal plane can be
drawn from the center of the radio frequency bias electrode 310 to
the slot opening of the optional oil delivery system 320, dividing
the noncovered surface area (i.e., the deposition area 314) in
half. The point source cathode 316 is placed above the imaginary
plane and the anode system 322 is placed below the imaginary plane.
Plasma extends as a point source from the point source cathode 316
into the vacuum in a cone shape configuration concentrating near
the radio frequency bias electrode 310 and at the anode wire 322.
Although FIG. 4 is not too scale, in one embodiment of this system,
the point source Cathode 316 is placed about 7.5 cm above the
imaginary plane and about 7.5 cm away from the surface of the radio
frequency bias electrode 310. It is tilted from its horizontal
position by about 60.degree. to ensure a downward expansion of the
plasma toward the anode wire 322 and the deposition area. The anode
wire 322 is placed about 17.5 cm below the imaginary plane and
about 5 cm away from the radio frequency bias electrode 310. The
dark space ground shield 312 prevents the anode wire 322 from being
in-line-of-sight with the deposition area. These distances,
lengths, angles, and other dimensions are presented as exemplary
only. They are not intended to be limiting.
[0057] Referring to FIG. 5, a point source cathode 400 is shown,
which enables the generation of a plasma from a small orifice 403
of a hollowed cylinder 402, which is surrounded by a magnet 408,
preferably a circular magnet, and equipped with an electrode, such
as the spherical-H.V. electrode 410. The cathode 400 preferably
includes a water-cooled cylinder 402, which is typically made of
copper, although it can be made of graphite or other electrically
and thermally conductive metals. A tube 404, preferably having a
circular cross section, is inserted inside a bore 406 of the
cylinder 402 having the leading edge 405 recessed within the bore
406 of the cylinder 402 such that it is in the plane of the center
line of a circular magnet 408 that surrounds the cylinder 402 at
its outlet end. The tube 404 is preferably ceramic, although it can
be made of other materials that withstand high temperatures and are
electrical insulators. The external surfaces of the cylinder 402
can be shielded with quartz 412 (as by the use of a quartz sleeve)
to avoid plasma arcing. This arrangement can be better seen in FIG.
5A, which is a cross section of the point source cathode 400 taken
along line A-A, which also shows a water inlet 417 and water outlet
418.
[0058] Using this particular configuration, a stable plasma can be
sustained and contained in region 414 defined by extensions 416 of
the cylinder 402. This configuration of the cylinder 402 along with
the placement of the magnet 408 concentrates the plasma such that
it extends as a point source into the vacuum in a cone shape
configuration. It is important to note that the strongest plasma is
generated if the leading edge 405 of the ceramic tube 404 is
directly in line with the center (with respect to its width) of the
circular magnet 408. Also, the magnetic field flux density is
preferably at least about 0.15 Kgauss, and more preferably, at
least about 1.5 Kgauss. The magnet 408 is preferably made of a
ceramic material, although metallic alloys can be used. Ceramic
materials generally have better temperature stability and a higher
Curie point (i.e., the point at which magnetism is lost), and are
therefore preferred.
[0059] Particularly preferred embodiments of the present invention
include an anode system (60 in FIG. 1 or 322 in FIG. 4), preferably
an adjustable anode system as shown in FIG. 4 of U.S. Pat. No.
5,464,667 (Kohler et al.). The anode system, particularly the
adjustable anode system, contributes to the maintenance of a stable
plasma, and to the uniformity of the coatings. In a preferred
embodiment of the anode system used herein, however, the enclosing
glass box described in U.S. Pat. No. 5,464,667 (Kohler et al.) is
omitted. Typically and preferably, two tungsten wires function as
the anodes. Each wire is of a sufficient diameter to provide the
temperature desired, and of a sufficient length to provide the
coating width desired. Typically, for a temperature of about
800.degree. C. to about 1100.degree. C., two tungsten wires of
about 0.1 cm to about 0.3 cm in diameter function effectively as
anodes with 10 amperes to 20 amperes of electron current sustained
from the plasma. Portions of the wires can be covered as described
in U.S. Pat. No. 5,464.667 (Kohler et al.). Again, the wire
diameter and length are presented as exemplary only. They are not
intended to be limiting. Any anode can be used as long as the
plasma is generated in the cathode and directed toward and past the
anode.
[0060] It is to be understood that one or more additional
evaporators/hollow cathode tubes, slots, or point systems that
generate plasmas as described herein may also be included within
the systems of the present invention. The multiple systems can
provide more than one layer onto the substrate or can provide an
increased rate of deposition.
[0061] The processes and systems of the present invention can be
used to prepare any of a variety of carbon-containing and/or
silicon-containing coatings, such as amorphous highly dense
coatings, layered coatings, and uniform multi-component coatings,
and the like.
[0062] The composition of the coatings can be controlled by means
of the concentration and composition of the feed gas passed through
the hollow cathode, and the organic material vaporized in the
evaporator. The density of the coatings are controlled by means of
the chamber pressure, the electrical power (current -and voltage)
supplied by the DC and radio frequency power supplies. The
conditions for the formation of high density coatings are generally
chosen to balance the bias power to the concentration of the
starting material. That is, the specific power density includes
bias power density, reaction time, and concentration of starting
material. Generally, the specific power density is increased by
higher power density and longer reaction time, and decreased by
increased concentration of the starting material. Generally, the
higher the power density, the more dense the coating.
[0063] The bias power density typically varies from about 0.1
watt/cm.sup.2 to about 10 watts/cm.sup.2 (preferably, about 0.5
watt/cm.sup.2 to about 5 watts/cm.sup.2). The bias voltage
typically varies from about minus 50 volts to about minus 2000
volts (preferably, about minus 100 volts to about minus 1000
volts). The bias current density typically varies from about 0.1
mAmp/cm.sup.2 to about 50 mAmps/cm.sup.2 (preferably, about 1
mAmp/cm.sup.2 to about 5 mAmps/cm.sup.2). The jet plasma voltage
typically varies from about minus 50 volts to about minus 150 volts
(preferably, about minus 80 volts to about minus 100 volts). The
jet plasma current typically is at least about 0.1 Amp (preferably,
at least about 0.5 Amp). The upper limit of the jet plasma current
is typically dictated by the limitation of the power supply.
[0064] The chamber pressure is typically less than about 1 Torr
(130 Pa). Preferably, the pressure in the reaction chamber is less
than about 8 milliTorr (1.0 Pa). Generally, the less the pressure
(i.e., the higher the vacuum), the more dense the coating. The web
speed of the substrate (i.e., the coating rate) typically varies
from about 1 foot/minute to about 1000 feet/minute (0.3
meter/minute to about 300 meters/minute). Preferably, the web speed
is about 0.9 meter/minute to about 6 meters/minute. The reaction
time typically varies from about 0.01 second to about 10 seconds,
and preferably, from about 0.1 second to about 1 second.
[0065] As discussed below and shown in FIG. 6, the application of
high bias power is a factor for obtaining excellent barrier
properties. In order to achieve high bias wattage, the hollow
cathode is typically positioned in line-of-sight of the film
substrate/chill roll. This arrangement makes possible satisfactory
interaction of the jet plasma with the biased film substrate. In
the absence of the plasma, the wattage power that can be applied is
significantly reduced. When the jet plasma stream is shielded from
the biased film substrate, the bias power is also reduced. This
indicates the necessity for a specific apparatus arrangement to
maximize jet plasma flow toward the biased film substrate.
Preferably, the jet plasma system provides both confinement and
directionality of the plasma. Conventional systems utilizing plasma
sources other than the point source of the present invention and
those described in U.S. Pat. Nos. 5,232,791 (Kohler et al.),
5,286,534 (Kohler et al.), and 5,464,667 (Kohler et al.) lack the
combination of confinement and directionality. Thus, preferred
systems of the present invention are improved with respect to these
parameters.
[0066] As stated previously, the plasma is created from a carrier
gas or a mixture of a carrier gas and a feed gas. This is referred
to herein as the "plasma gas." The carrier gas flow rate can be
about 50 standard cubic centimeters per minute (sccm) to about 500
sccm, preferably about 50 sccm to about 100 sccm, and the feed gas
flow rate can be about 100 sccm to about 60,000 sccm. preferably
about 300 sccm to about 2000 sccm. For example, for carbon
deposition rates of about 20 .ANG./second to about 800
.ANG./second, the feed gas flow rate is about 50 sccm to about 350
sccm and the carrier gas flow rate is about 50 sccm to about 100
sccm, with higher feed gas flow rates in combination with lower
carrier gas flow rates (typically resulting in higher deposition
rates). Generally, for harder coatings, the carrier gas flow rate
is increased and the feed gas flow rate is decreased.
[0067] The feed gas, i.e., the carbon source, can be any of a
variety of saturated or unsaturated hydrocarbon gases. Such gases
can also contain, for example, nitrogen, oxygen, halides, and
silicon. Examples of suitable feed gases include, but are not
limited to: saturated and unsaturated hydrocarbons such as methane,
ethane, ethylene, acetylene, and butadiene; nitrogen-containing
hydrocarbons such as methylamine and methylcyanide;
oxygen-containing hydrocarbons such as methyl alcohol and acetone;
halogen-containing hydrocarbons such as methyl iodide and methyl
bromide; and silicon-containing hydrocarbons such as
tetramethylsilane, chlorotrimethyl silane, and tetramethoxysilane.
The feed gas can be gaseous at the temperature and pressure of use,
or it can be an easily volatilized liquid. A particularly preferred
feed gas is acetylene.
[0068] As stated previously, a carrier gas can also be used with
the feed gas to advantage. For example, without the auxiliary
plasma from the carrier gas the feed gas plasma is difficult to
sustain at around minus 100 volts using either a pulsating or a
filtered DC power supply. For example, when using only the feed
gas, with a 1 ampere pulsating DC power supply the voltage rises
occasionally up to about minus 1000 volts, and with a nonpulsating
filtered 10 ampere power supply, the plasma is occasionally
extinguished altogether.
[0069] The carrier gas can be any inert gas, i.e., a gas that is
generally unreactive with the chosen feed gas under the conditions
of pressure and temperature of the process of the present
invention. Suitable carrier gases include, but are not limited to,
helium, neon, argon, krypton, and nitrogen. Typically, higher
weight gases, e.g., argon, are preferred. The terms "inert" and
"carrier" are not meant to imply that such gases do not take part
in the deposition process at all.
[0070] The thickness of coatings produced by the method of the
present invention are typically greater than about 5 nanometers
(nm), preferably about 10 nm to about 1000 nm, however, thicker
coatings are possible, but not typically needed. The substrate
moves through the plasma at a rate designed to provide a coating of
a desired thickness. Referring to FIG. 1, the speed at which the
substrate 75 travels from roll 76 to roll 78 can be about 10
mm/second to about 4000 mm/second, but is typically about 10
mm/second to about 1500 mm/second for the gas flow rates and
pressures and the apparatus described above.
EXAMPLES
[0071] The present invention is further described by the following
nonlimiting examples. These examples are offered to further
illustrate the various specific and preferred embodiments and
techniques. It should be understood, however, that many variations
and modifications can be made while remaining within the scope of
the present invention.
Test Procedures
[0072] A brief description of the tests utilized in some or all of
the following examples will now be given.
[0073] Water vapor permeability of the coatings was measured with a
Permatran W6 Permeability Tester manufactured by Modern Controls,
Inc., Minneapolis, Minn. The ASTM test method F 1249-90 included
aluminum 25 foil and PET film for standard calibration, sample
conditioning overnight, cell filled halfway with deionized water
and 60 minute test with a nitrogen gas pressure of 15 psi
(1.0.times.10.sup.5 Pascals).
[0074] Abrasion resistance was measured by a combination of two
ASTM test methods. The Taber Abrasion Test, ASTM D4060-95 was used
with a "TABER" Abraser Model 503 with "CALIBRASE" C.S-1OF wheels
(Teledyne Taber, North Tonawanda, N.Y.). A 500 g total weight load
evenly distributed on the two CS-1OF wheels was used. The cycles
were varied between 0 and 100 cycles. The second test method was
ASTM D1003 which used a Gardener Hazemeter, "HAZEGARD" System,
Model XL211 (Pacific Scientific, Gardner/Neotac Instrument
Division, Silver Spring, Md.). In this method the percentage of
light scattering was measured before and after the specimen was
Taber abraded. The lower the value, the better the abrasion
resistance and hardness.
[0075] Adhesion was measured by the 90.degree. angle peel adhesion
method. The uncoated side of the film samples was affixed via
double sided adhesive tape to a stainless steel panel. Usually, an
aggressive, silicone based pressure sensitive adhesive tape was
affixed to the coated side using a seven pound roller, rolled two
times each direction over the tape. The specimens were 1.27 cm wide
and about 30.5 cm long. The silicone based tape was removed from
the coating at a speed of twelve inches per minute in a 90.degree.
peel using an Instron Instrument, Model 1122.
[0076] Hardness was measured by an ultramicro hardness tester UMIS
2000 from CSIRO (Australia). The indentation method included a
Berkovich indenter with a 65.degree. cone angle. The indenter was
made from diamond. The hardness values were determined by the
analysis of the loading-unloading data.
[0077] Density was measured by the floating method. Powdered
samples were suspended in liquids of varying density and the
movement of the suspended particles were observed. Upward movement
indicated that the particles were less dense than the liquid;
downward movement indicated that the particles were more dense than
the liquid. No movement indicated identical densities. Final
readings were made after twelve hours when the particles usually
had risen to the top of the liquid or settled at the bottom. Using
liquids with incremental differences in density, the density of the
particles could be bracketed. The liquids with varying densities
used are listed in Table 1.
1 TABLE 1 Liquid Density (g/cm.sup.3) 1-bromoheptane 1.14
2-bromopropane 1.31 1-bromo-2-fluorobenzene 1.601 4-bromoveratrole
1.702
[0078] Thickness and uniformity of the jet plasma coatings on film
substrates were assessed from the interference color produced by
the coatings on silicone wafers. Small pieces of silicone wafers
were positioned at strategic locations on the film substrate prior
to deposition of the coatings. Such a method was suitable for
coatings having thicknesses up to about 1500 .ANG.. For greater
coating thicknesses a step profilometer was used, manufactured by
Tencor Instruments, Mountain View, Calif. The instrument measured
the step formed by the coating and the adjacent uncoated area which
was masked by adhesive tape during deposition.
[0079] Along with the determination of the index of refraction,
thickness of the coatings was also determined from ellipsometric
values obtained from the coatings on silicon wafers. The
measurements were made on an ellipsometer Model 116B, manufactured
by Gaertener Scientific Corporation, Chicago, Ill.
[0080] Static coefficient of friction was measured by the Inclined
Plane Method. The sample, typically about 2 cm wide and 5 cm long,
was fastened on a horizontal plane which could be inclined. The
free ends of a U shaped steel wire (1 mm in diameter) were attached
to stabilizing arms. The rounded end of the U shaped wire (paper
clip like) was placed upright and in a self-supporting manner onto
the sample surface. The inclined plane was raised until sliding of
the U shaped steel wire began. The static coefficient of friction
was equal to the tangent of the angle at which sliding began.
Example 1
[0081] Silicone coatings were deposited on 30 cm wide and 0.074 mm
thick untreated polyethylene terephthalate (PET) in the system
shown in FIG. 4. The system is similar to the deposition chamber
described in U.S. Pat. No. 5,464,;667 (Kohler et al.) with several
modifications, including a point source cathode and an oil delivery
system.
[0082] The system included a biased chill roll, 48.2 cm in diameter
and 33.5 cm wide. Except for the deposition area, about 76% of the
surface of the radio frequency bias electrode was covered by an
aluminum sheet. The aluminum sheet was grounded and placed about
0.6 cm away from the surface to provide a dark space and thus
concentrated the bias wattage over the remaining 24% of the surface
area. An imaginary horizontal plane could be drawn from the center
of the radio frequency bias electrode to the slot opening of the
oil delivery system, dividing the noncovered surface area in half.
The point source cathode was placed about 7.5 cm above the
imaginary plane and about 7.5 cm away from the radio frequency bias
electrode surface. The point source cathode was machined in the
form of a hollowed cylinder and tilted from its horizontal position
by about 60.degree. to ensure a downward expansion of the plasma
toward the anode wire and the deposition area. The anode wire was
placed about 17.5 cm below the imaginary plane and about 5 cm away
from the chill roll. The grounded aluminum sheet prevented the
anode wire from being in-line-of-sight with the deposition
area.
[0083] In contrast to the hollow cathode slot of U.S. Pat. No.
5,464,667 (Kohler et al.), a hollow cathode point source was used
which enabled the generation of a plasma from a small orifice. As
shown in FIG. 5, the cathode consisted of a water-cooled copper
cylinder, 5 cm long. A ceramic tube was inserted into the bore of
the cylinder with the tip recessed to be in the plane of the center
line of the magnet. The bore of the ceramic tube was 0.35 cm. The
circular ceramic magnet was placed as shown in FIG. 5 at the front
end of the cathode, 5.0 cm in outer diameter and 2.0 cm in inner
diameter. The magnetic flux density at the center of the magnet was
measured to be 0.45 Kgauss. The external surfaces of the cathode
were covered with 0.3 cm thick quartz to avoid plasma arcing. A
stable plasma was sustained with 150 sccm argon extending as a
point source from the tip of the cathode into the vacuum and
concentrating near the radio frequency bias electrode and at the
anode wire.
[0084] The anode was similar to that shown in FIG. 4 of U.S. Pat.
No. 5,464,667 (Kohler et al.) except the enclosing glass box was
omitted. Two tungsten wires each 0.1 cm diameter and 40 cm long
functioned as anodes that reached a temperature of 800-1100.degree.
C. with 10-20 amperes of electric current sustained from the
plasma. The midsection of the tungsten wires were covered with
quartz tubing.
[0085] In order to deliver liquids in vapor form into the vacuum
chamber an oil delivery system was developed to control oil feed
rate and thus oil evaporation. This is shown in FIGS. 1 and 4, and
in greater detail in FIGS. 2 and 3. With the valve configuration
shown in FIGS. 2 and 3, the oil was exposed to the vacuum so as to
become de-aerated. This was done by first evacuating chamber 30
(FIG. 1) and then opening valves V1 and V2 and closing valve V4,
with valve V3 set at the desired metering rate. The chamber was
allowed to stabilize and the oil was outgassed until all residual
gases were boiled off. Oil discharge through the oil delivery
needle was prevented by having equal pressure above the liquid and
at the needle. By changing the valve configuration, such that valve
V1 was closed and valves V2. V3, and V4 were opened, air was
introduced into the space above the oil. Valve V3, a flow-metering
valve, was adjusted to control the pressure to impose a desirable
pressure above the oil, as measured by vacuum gauge 141. Once the
desirable pressure was reached, valve V2 was closed. In addition,
oil feed rate was controlled by proper selection of the gauge and
the temperature of the needle. The needle temperature was regulated
by an attached water-temperature controlled copper sleeve.
[0086] As shown in FIG. 2 the evaporator consisted of multiple
aluminum spacers that were heated by two variac-controlled
cartridge type resistance heaters. The copper sleeve accommodating
the oil delivery needle was placed into the inlet port of the
heater. The inlet port was situated at the back region of the
heater and was filled with a silicone rubber sleeve insert to
prevent heat exchange between the heater and the copper sleeve. The
tip of the needle, however, was in immediate contact with the
heated inlet port allowing constant and uniform vaporization of the
oil. The individually shaped aluminum spacers provided multiple
spacings so that the vaporized oil was guided over the full width
of the heater several times upwards and downwards before the vapor
was discharged uniformly through a slot into the vacuum chamber as
shown in FIG. 1.
[0087] The cathodic point source was powered by a 20 ampere maximum
output pulsating DC power supply as described in U.S. Pat. No.
5,464,667 (Kohler et al.). The Airco Temescal CL-2A power supply
consists of a leakage type power transformer that supplies AC power
to a full wave bridge rectifier to yield an output, which is the
absolute value of the transformer output voltage, i.e., the
negative absolute value of a sine wave starting at zero volts and
going to a peak negative value of about 5000 volts open circuit.
Under a purely resistive load of 100 ohms, this power supply would
rise to a voltage of minus 200 volts with the current limited at
500 mA. With an arc plasma as a load, the output voltage of the
power supply climbs to the breakdown voltage of the apparatus and
then the voltage drops immediately to the arc steady state voltage
with current limited to 500 mA. Thus, the leakage transformer
employed acts to limit current flow through the load or plasma in a
manner similar to a resistive ballast in a typical glow discharge
system. More specifically, as the cycle of power supply output
voltage (starting at To) progresses through the 120 Hz waveform
(starting at zero output volts), the voltage increases with time to
a negative voltage value significantly above the arc steady state
voltage. At this point, voltage breakdown occurs in the plasma jet,
an arc is established, and the power supply output drops to the arc
steady state voltage of about minus 100 volts and the saturation
current of the power transformer, about 500 mA for the CL-2A power
supply. As time progresses through the cycle, the power supply
voltage drops below the arc voltage and the arc extinguishes. The
power supply output voltage continues to drop, reaching zero volts
at T.sub.0+{fraction (1/120)} second and the process starts again.
The time period for this entire cycle is {fraction (1/120)} of a
second, or twice the frequency of the AC line input voltage to the
power supply. The operations of the 1 amp power supply and the 20
amp power supply are identical except that the limiting currents
are 1 amp and 20 amps respectively.
[0088] The positive electrode of the power supply was connected to
the anode wires. The radio frequency bias electrode was cooled to
5.degree. C. and connected to an RF biasing power supply (e.g.,
PLASMALOC 3, from ENI Power Systems, Inc., Rochester, N.Y.). The
entire vacuum chamber was grounded electrically. When pumping the
chamber, the pressure in the oil reservoir was the same as the
chamber pressure. The oil (a dimethylsiloxane, 50 centistokes
viscosity 3780 molecular weight, available from Dow Corning under
the trade designation "DC200") was de-aerated during chamber
evacuation. After a de-aeration time of about 15 minutes, air was
introduced into the top portion of the oil reservoir until a
pressure of 325 Pa was obtained. The 22 gauge oil delivery needle
was maintained at 20.degree. C. resulted in an oil feed rate of
0.36 ml/minute. The oil evaporator was heated to about 370.degree.
C. One hundred fifty sccm of argon was introduced into the point
source cathode and a stable plasma was generated and sustained at
minus 100 volts and 15 amperes. The chamber pressure was between
0.13-0.26 Pa. At a web speed of about 3 meters/minute a series of
experiments was conducted by varying the bias power as shown in
FIG. 6.
[0089] As shown in FIG. 6 the barrier properties of the plasma
polymerized silicone coatings improved with increasing bias voltage
and wattage. Contact angles of all the coatings were measured
around 95.degree. (water). The contact angle of the uncoated PET
film was 75.degree..
[0090] An additional sample of the same oil was prepared at a bias
wattage of 400 Watts and a speed of 6 meters/minute. An eleven
layer coating (Sample A) was obtained by reversing the web
direction five times. The coating thickness was about 3800 .ANG. as
measured by step profilometry of a simultaneously coated silicon
chip placed on the PET film. Based on the eleven layer coating
sample, the single layer coatings were estimated to be around 690
.ANG.. The coating of Sample A was analyzed by Rutherford
backscattering for elemental analysis. The analysis yielded in atom
percent: C, 30%; Si, 30%; and O, 40%. The theoretical yield for
monomethylsilicone having a formula of
--(Si(CH.sub.3O.sub.1/2,)O).sub.n-- - in atom percent is: C, 28.6%;
Si, 28.6%; and O, 42.8%. This data, and the IR spectrum, the peak
positions of which are listed in Table 6, below, suggest that
Sample A has a composition similar to that of
monomethylsilicone.
[0091] Table 2 below shows the Taber Abrasion Test results of the
uncoated PET film and the one and eleven layer coatings on PET film
prepared at bias wattage of 400 Watts. The lower the percent haze,
the greater the abrasion resistance. Thus, abrasion resistance of
the jet plasma silicone coatings increased with the increase in
coating thickness.
2 TABLE 2 TABER (% HAZE) 1 LAYER 11 LAYERS CYCLES PET (690
Angstroms) (3800 Angstroms) 0 0 0 0 20 8.5 5.5 2 40 12 8.5 4 60 15
10.5 6.5 80 17 13 8 100 18 14 12
[0092] The hardness of the eleven layer coating (3800 Angstroms) on
a silicon wafer was 8.14 GPa. As shown below in Table 3, the
hardness of the silicone coating was compared with that of an
uncoated silicon chip, a glass microscope slide obtained from VWR
Scientific (catalog number 48300-C25), and conventional
monomethylsiloxane hard coat deposited as described in Comparative
Example A.
3TABLE 3 Penetration Coating Thickness Depth Hardness Sample
[.ANG.] [.ANG.] [G Pa] 11 Layer Coating 3800 1730 8.14 Conventional
by 5000-10,000 4927 1.33 Monomethylsiloxane Hard Coat Glass Slide
2970 2.96 Silicon Wafer 1440 11.96
[0093] This data showed that the silicone coating was significantly
harder than the glass microscope slide, but softer than the silicon
wafer.
[0094] The single layer silicone coatings prepared at 50 and 400
Watt bias power and the eleven layer silicone coating prepared at
400 Watt bias power were evaluated for their adhesion to the PET
substrate film. Ninety degree peel strength measurements were
conducted with a KRATON-based tape (Sealing Box tape #351
commercially available from 3M Company, St. Paul, Minn.). The peel
strength values were around 2.6 kg/cm. Delamination occurred
through cohesive failure of the adhesive. Therefore, the silicone
coating/PET bonding exceeded the peel strength values measured.
Comparative Example A
[0095] The composition of conventionally prepared
monomethylsiloxane was found to be similar to that of jet plasma
polymerized silicone. However, when the properties of the
conventional monomethylsiloxane coatings were compared with those
of certain jet plasma polymerized silicone coatings, significant
differences were observed.
[0096] Monomethylsiloxane (Sample E) was prepared by the following
procedure: 15 ml trimethoxymethylsilane
((CH.sub.3O).sub.3CH.sub.3Si) were added to 85 ml water, the pH
adjusted to 4 by glacial acetic acid and the mixture stirred for
about 5 minutes until the solution became clear. One third of the
solution was placed in an oven at 100.degree. C. for 12 hours. A
colorless residue was obtained and used for several analyses:
density values were between 1.14-1.31 g/cm; the IR spectrum was
nearly identical to that of jet plasma polymerized silicone. WAXS
identified a broad peak at 8.7 .ANG.. Hydrogen was determined by
combustion analysis, which yielded 4.2 wt-% H. Silicon was
determined by gravametric and ICP analyses, which yielded 40.4 wt-%
Si. Because the theoretical values for monomethylsilicone having
the formula --(Si(CH.sub.3O.sub.1/2)O).sub.n-- are 4.47 wt-% H and
41.9 wt-% Si, the sample appears to be monomethylsilicone.
[0097] The rest of the hydrolyzed trimethoxymethylsilane solution
was adjusted to a pH of 8-9 by adding several drops of 1 N KOH
solution and used for the preparation of coatings.
[0098] Coating on silicon wafer: Silicon wafers were immersed in 3
N KOH solution for about one minute, rinsed with distilled water
and dipped in the hydrolyzed trimethoxymethylsilane solution for 10
seconds. The wafers were placed in an oven and heated for 12 hours
at 100.degree. C. The coating was not uniform in thickness and
ranged according to the interference colors from about 100 .ANG. to
several microns. The hardness of the coating was around 1.33
GPA.
[0099] Coating on PET film: The PET film (0.074 mm) was air corona
treated and dipped in the hydrolyzed trimethoxymethylsilane
solution for 10 seconds. The film samples were suspended in an oven
and heated for 12 hours at 100.degree. C. A continuous coating was
obtained. The thickness was between 1-2 microns as measured by a
film thickness gauge (Sony Maonescale Inc., Digital Indicator,
U12A). The coatings did not have gas diffusion barrier properties.
Water vapor permeability values of the coated and uncoated PET film
were identical and around 8 g/(m.sup.2.multidot.day) (measured with
a Permatran W-6 Permeability tester manufactured by Modem Controls,
Inc., Minneapolis, Minn.).
[0100] The following Table 4 summarizes the comparison in
properties of the conventional monomethylsiloxane and the typical
jet plasma polymerized silicone.
4 TABLE 4 Sample A Sample E Jet Plasma Polymerized Conventional
Dimethyl Siloxane Monomethylsiloxane FTIR Spectrum showed the same
Spectrum showed the same peaks as for dimethyl peaks as for
dimethyl siloxane precursor except siloxane precursor except change
in absorbance change in absorbance intensity for methyl and Si-O-
intensity for methyl and Si-O- Si peaks. Si peaks. Experi- C = 30
atom % C = 28.6 atom % mental Si = 30 atom % Si = 28.6 atom %
Elemental O = 40 atom % O = 42.8 atom % Analysis Theo- H = 4.47 wt
% H = 4.2 wt % retical Si = 41.9 wt % Si = 40.4 wt % Elemental
Analysis Density 1.601-1.702 1.14-1.31 [g/cm.sup.3] Hardness 8.14
1.33 [GPA] Water .about.0.01 8 Vapor Perme- ability [g/m.sup.2
.multidot. day] WAXS Broad Peak at 7 .ANG. Broad Peak at 8.7
.ANG.
Example 2
[0101] Carbon-rich coatings were deposited on 30 cm wide and
1.4.times.10.sup.-3 cm thick video grade polyethylene terephthalate
(PET) film having therein less than about 1% SiO.sub.2 slip agent
(OX-50 from Degussa of Germany), which had been corona treated and
wrapped for storage and handling in a packaging film with moisture
barrier characteristics (manufactured by 3M Company, St. Paul,
Minn.). The experiment was similar to Example 3 of U.S. Pat. No.
5,464,667 (Kohler et al.), which is incorporated herein by
reference, except that the hollow cathode slot was replaced by the
hollow cathode point source (i.e., point source cathode) described
above in Example 1. The development of the point source cathode
simplified the cathode system and eliminated several components of
the hollow cathode slot system, including the argon plasma
compartment together with the argon plasma power supply and the
acetylene compartment.
[0102] The point source cathode was placed about 17.5 cm away from
the biased chill roll. After the vacuum system was evacuated to
about 1 mTorr (0.13 Pa), 35 sccm argon and 1000 sccm acetylene were
introduced together into the point source cathode. A stable plasma
was generated and sustained from the orifice of the cathode and
expanded in cone shape toward the deposition area. The DC pulsating
power supply was set at 15 amperes and minus 75 to minus 95 volts.
The radio frequency bias electrode was biased to minus 300 volts.
The power consumption was 320-400 watts. The web speed was about 15
meters/minute. The pressure varied between 2.3 Pa and 3.0 Pa. The
experiment was run for about 3-4 hours during which no significant
changes in the barrier properties of the coating was experienced.
The water vapor permeability stayed constant at around 1
g/(m.sup.2.multidot.day) as compared to an uncoated sample, which
has a water vapor permeability of about 30
g/(m.sup.2.multidot.day)- . The extended time period of a stable
plasma (i.e. about 3-4 hours) is a significant advantage of the
point source cathode. Without the circular magnet the small orifice
becomes plugged by carbon within several minutes.
Example 3
[0103] Silicone coatings were deposited on 15 cm wide and
2.54.times.10.sup.-3 cm thick film available under the trade
designation "KAPTON" film from DuPont de Nemours (Wilmington,
Del.), Type 100H. Except for the addition of an oil delivery system
(described above) all other components of the deposition system
were identical to those described in Example I of U.S. Pat. No.
5,464,667 (Kohler et al.); however, the arrangement of the
deposition system was modified. The hollow cathode slot system was
9 cm away from the chill roll. Drawing an imaginary horizontal
plane from the center of the radio frequency bias electrode to the
cathode, the cathode slot was about 1.6 cm below the plane. The
anode wire was about 4 cm away from the cathode slot and about 6 cm
below the imaginary plane. A Pyrex glass plate (20 cm wide, 5 cm
long, 0.3 cm thick) was placed parallel to and about 0.6 cm below
the imaginary plane reaching from the front of the cathode box
toward the radio frequency bias electrode and leaving about 4 cm
between the glass plate and the front of the chill roll. The oil
evaporator was positioned on the glass plate. The evaporator slot
was about 1.2 cm above the glass plate and about 4 cm away from the
chill roll. Another glass plate was placed upwards at a 45.degree.
angle leaving a slot opening of about 1.5 cm between the glass
plates. This arrangement allowed the oil vapor to be condensed and
polymerized on the film substrate that was in contact with the
biased chill roll. Subsequent condensation of oil vapor above-the
radio frequency bias electrode was avoided to a high degree. The
hollow cathode slot was about 15 cm wide and the graphite plates
had a gap of about 0.6 cm. The radio frequency bias electrode was 5
cm in diameter, 18 cm long, chilled to 5.degree. C. The grounding
box, i.e., anode, was about 20 cm wide and included a 0.1 mm
diameter tungsten wire. All power supplies, including the anode,
were connected to a common ground. After the vacuum chamber was
evacuated to a pressure of about 0.13 Pa, 100 sccm argon was
introduced into the argon plasma chamber, i.e., the first
compartment of the hollow cathode slot system. The plasma was
sustained about minus 450 volts and at a pulsating DC current of
0.5 amp using the Airco Temescal Model CL-2A power supply (maximum
output of 0.5 amp). The hollow cathode slot was powered by the 25
kilowatt nonpulsating filtered DC power supply from Hippotronics to
enhance the argon plasma ignited in the front compartment. The
current was 8000 mA at about minus 100 volts. The Dow Corning DC200
silicone oil having a viscosity of 50 centistokes (cts) and a
molecular weight of 3780 was vaporized according to the procedure
described in Example 1. About 50 cm Kapton film, as described
above, was transported in loop form over the radio frequency bias
electrode and the two rolls of the web drive system. The deposition
time was determined from the web speed, the number of loop turns
and the contact area of the film with the chill roll. The length of
the contact area was 3.3 cm. The film accommodated silicon ships
and germanium crystal to measure the special properties of the
deposited silicone by elipsometry and FTIR spectroscopy,
respectively. Variation in deposition parameters, in particular the
bias power, resulted in significant differences in coating
properties, as shown in Table 5. Table 5 shows the difference in
properties of a nonbiased Sample A and a biased Sample B.
5 TABLE 5 SAMPLE SAMPLE A SAMPLE B BIAS WATTAGE 0 250 BIAS VOLTAGE
0 -1400 DEPOSITION TIME 0.96 second 1.54 second DEPOSITION RATE
0.34 cm/second 0.2 cm/second MOISTURE 55 g/m.sup.2 .multidot. day
2.5 g/m.sup.2 .multidot. day PERMEABILITY ESCA 29.6/48.4/22.0
29.9/48.8/21.2 Atom percent (O/C/Si) INDEX OF REFRACTION 1.327
1.464 THICKNESS 3595 .ANG. 1252 .ANG.
[0104] IR spectra of Sample B and DC200 silicone oil show the
structural changes as a result of biased jet plasma polymerization.
The position and intensity of the absorption peaks are listed in
Table 6 below.
6TABLE 6 ABSORBANCE WAVE INTENSITY SAM- NUMBER ASSIGN- ABSORBANCE
RATIO PLE (cm.sup.-1) MENT INTENSITY (1260/1019) SILI- 1019 Si-O
stretch 0.397 CONE 1091 Si-O stretch 0.326 0.980 OIL 1260 CH.sub.3
rocking 0.389 mode B 1020 Si-O stretch 0.670 1261 CH.sub.3 rocking
0.387 0.578 mode 2151 Si-H stretch 0.011
[0105] Based on the absorbance intensity ratios, the biased jet
plasma polymerization reduced the methyl concentration of the
coating by about 40% and introduced some Si--H bonding. The lack of
absorption peaks for C--H and C--H.sub.2 moieties suggested band
cleavage between the silicon atoms and the methyl groups and the
subsequent polymerization of the formed silicone radicals. As
indicated by the ESCA results, oxygen appeared to be involved in
the polymerization, most likely resulting into Si--O--Si
crosslinkage. In comparison with the atomic percent ratio of a
conventional silicone polymer that has a Si:C:O ratio of
24.95:50.66:24.39, the oxygen concentration of sample B was
significantly higher.
Example 4
[0106] The deposition system, jet plasma conditions, and substrate
were the same as described in Example 3, except that the "KAPTON"
film was wrapped around the chill roll. About 25% of the surface
was exposed to the plasma while the rest was covered with a nylon
cover creating a gap of about 2 mm. The nylon cover was the same as
that used in Example 1 for the protection of the bare chill roll.
DC200 silicone vapor was jet plasma polymerized onto the film for
about 15 minutes while the radio frequency bias electrode was
rotating at about 10 rpm and was biased at about 25 watts and minus
450 volts (sample A, which was prepared according to a process of
the invention). In a second experiment the bias power was increased
to about 250 watts and about minus 1200 volts (sample B, which was
prepared according to a process of the invention). The coatings
were scraped off the film and collected in powder form. A third
sample was collected from a glass plate positioned close to the
chill roll. This sample was considered typical of a nonbiased jet
plasma polymerized silicone coating (Sample C, which was prepared
according to a process of the invention). The data in Table 7 below
compares the carbon and hydrogen analyses of the different
coatings. Table 7 also includes the analysis of the DC200 silicone
oil (Sample D, starting material), the conventional
monomethylsiloxane (Sample E, which was prepared using a
conventional process described in Comparative Example A), and
density values of all the samples.
7TABLE 7 H:C Intensity of Peak SAM- WEIGHT WEIGHT atom Density
(WAXS) PLE % C % H ratio (g/cm.sup.3) Before . . . After A 16.53
4.96 3.6 1.601-1.702 B 15.40 4.43 3.4 1.601-1.702 7.2 C 30.31 7.84
3.1 <1.140 7.2 D 33.47 8.34 3.0 0.96 (from 7.2 literature) E
1.14-1.31 8.7
[0107] Minor changes in the carbon and hydrogen concentrations
occurred when the DC200 silicone oil (Sample D) was jet plasma
polymerized without bias (Sample C). A significant decrease in
carbon and hydrogen concentration was apparent for the biased
samples (Samples A and B). The C:H atom ratio was greater than
three, which substantiated the FTIR spectroscopy results, namely
the loss of methyl groups and the formation of Si--H bonding.
[0108] Samples A, B, C, D, and E were examined by wide angle x-ray
scattering (WAXS) for purposes of identifying the presence of
crystallinity. Data were collected using a Philips vertical
diffractometer, copper K.sub..alpha. radiation, and proportional
detector registry of the scattered radiation. An interference peak
on the order of 7.2 .ANG. was produced by all materials and is the
only structural feature observed. The position of the interference
maximum produced by the oil did not change position upon
polymerization. This indicates that the structural features present
in the oil maintained their approximate arrangement after
undergoing polymerization. The observed peak was sufficiently broad
that the materials were not considered to possess crystallinity,
but rather possessed a structural feature that repeated itself on a
7 .ANG. length scale. Amorphous carbon and amorphous silica, often
used as barrier coatings, produce peaks at considerably higher
angle, normally between 20 and 30 degrees (2Q), which correspond to
distances on the order of 4.5-3 .ANG.. These data indicated that
the polymerized material were distinctly different from amorphous
carbon and silica materials. A different structural feature was
obtained from Sample E, which showed a broad peak at 8.7
Angstroms.
Example 5
[0109] Nujol, an aliphatic hydrocarbon oil was deposited onto the
substrate described in Example 3 using the system arrangement
described in Example 3. Except for the oil delivery, the procedure
was also the same. At a pressure of 1300 Pa in the oil reservoir
the liquid was introduced into the evaporator heated at 280.degree.
C. The oil delivery needle gauge and temperature were 22.degree. C.
and 20.degree. C., respectively. Four loop turns of the film were
made within 123 seconds resulting in a deposition time of 3.5
second. The pressure during jet plasma polymerization stayed most
of the time below 0.26 Pa. The water vapor permeability of the
coating was around 40 g/(m.sup.2.multidot.day). This value was
lower than the water permeability of the uncoated film (>55
g/(m.sup.2.multidot.day)) and thus indicated barrier properties of
a hydrocarbon polymer. The IR spectra of this coating and the
original Nujol showed minor structural changes. The corresponding
absorbance intensity ratios varied between 10% and 20%.
Examples 6-8
[0110] The deposition procedure was similar to that described in
Example 3 except an acetylene/argon mixture was used as the jet
plasma feed gas and a divider in the form of a glass plate was
installed in between the two sources of acetylene/argon feed gas
and silicone vapor. The series of examples illustrated the
formation of multiple layer coatings and showed changes in
properties depending on the position of the divider.
Example 6
[0111] The apparatus arrangement including the hollow cathode slot
system, grounding box and radio frequency bias electrode were
similar to that described in Example 3. The oil delivery system
consisted of a syringe pump, Teflon tubing (about 1 mm in diameter)
connected to the syringe and leading into the vacuum chamber, a 25
gauge microsyringe needle connected to the Teflon tubing and
inserted into the evaporator as described in Example 1. DC 200
silicone oil (50 cts, Dow Corning Inc.) was fed at about 0.05-0.5
ml/minute into the evaporator heated at about 350.degree. C. It
should be emphasized that due to imperfections in the early stages
of the development of the oil delivery system the exact amount of
oil available for evaporation and deposition could not be assessed
from the flow rates indicated by the settings of the syringe pump.
PET film (1.27.times.10.sup.-3 cm thick and 15 cm wide) was used as
the substrate and continuously unwound from a first roll and
rewound upon a second roll at a web speed of 3 m/minute. The
divider was as close as possible to the chill roll, about 0.3 cm.
The argon plasma was sustained at a flow rate of 50 sccm using a DC
pulsating power supply at 0.5 amp and minus 475 volts. The hollow
cathode slot was powered by a 25 kW filtered DC power supply from
Hippotronics. At a flow rate of 200 sccm acetylene the plasma was
sustained at about 8 amps and about minus 100 volts. The radio
frequency bias electrode was cooled to about 10.degree. C. and
biased at about minus 1000 volts. A coating was obtained about 1350
.ANG. thick. The coating on PET film has a static coefficient of
friction of 0.15 and water vapor permeability values of about 2.5
g/(m.sup.2.multidot.day). The FTIR spectrum of a coated germanium
crystal (placed on the PET film) showed mainly absorption bands
characteristic for silicone oil DC 200. After rinsing with toluene
the silicone coating was completely removed, a strong evidence that
no polymerization of the dimethyl silicone oil had occurred.
Example 7
[0112] This example showed the importance and sensitivity of
divider position for dimethyl silicone polymerization. Identical
conditions were used as those described in Example 6 except for
widening the gap between the divider and the film substrate to
about 0.9 cm. The FTIR spectrum was identical to that of Example 6.
However, after thorough rinsing with toluene about 75% of the
coating was removed. This was an indication that the increased
interaction of the plasma carbon with the dimethyl silicone vapor
resulted in partly polymerized dimethyl silicone.
[0113] The partly polymerized silicone coatings were found to be
excellent lubricant coatings. Table 6 summarizes the static
coefficient of friction values obtained on 1.27.times.10.sup.-3 cm
coated "KAPTON" film before and after soxhlet extraction (about 16
hours in toluene). The different thicknesses were obtained by
varying the web speed between about 1-18 meters/minute. The
thickness was estimated from the interference color on coated
silicone wafers. Table 8 shows static coefficient of friction
values that indicate a high degree of lubrication for extremely
thin coatings and for a coating construction which contained both a
highly polymerized silicone portion (matrix) and a less polymerized
or unpolymerized silicone oil.
8TABLE 8 Thickness (.ANG.) 300 250 150 75 40 JP Polymerized
Silicone Oil 0.06 0.06 0.10 0.09 0.10 JP Polymerized Silicone Oil
0.04 0.06 0.11 0.13 0.14 after Soxhlet Extraction
Example 8
[0114] This example confirmed the importance of sufficient divider
spacing for complete polymerization. Conditions were identical with
those in Example 7 except for the greater distance between the
divider and the substrate (about 1.5 cm). The FTIR spectrum was
very similar to the previous one. However, in contrast to Examples
6 and 7, rinsing with toluene did not decrease appreciably the
intensity of the FTIR absorption peaks. Thus, the increased
distance between the divider and the substrate caused a sufficient
interaction between jet plasma carbon and the dimethyl silicone
vapor to warrant a fully polymerized, cross-linked dimethyl
silicone structure with excellent adhesion to the substrate. The
coating on PET film had a static coefficient of friction of 0.23
and water vapor permeability values of about 1.5
g/(m.sup.2.multidot.day). A depth profile of the coating on
silicone wafers was conducted by Auger Spectroscopy. The spectrum
showed two distinct layers: a carbon layer adjacent to the
substrate and a silicone layer with a small interfacial region
between the carbon and the silicone layer as shown in FIG. 7.
[0115] The adhesion of the multi-layer coatings of Examples 6-8
were evaluated by 90.degree. peel strength testing and summarized
in Table 9. In all cases delamination occurred at the interface
between the coating and the adhesive tape. In particular, the high
peel strength values obtained with samples of Example 8 indicated
that the adhesion of the fully polymerized dimethyl silicone layer
to the carbon layer and also the adhesion of the carbon layer to
the PET film substrate were at least 5.5 N/dm or greater. The high
adhesion and the intrinsic low surface energy values of the
silicone coatings suggested their use for release coatings and
other low surface energy coatings.
9 TABLE 9 Peel Strength (N/dm): Example 6 Unpolymerized DC 200 Oil
2.3 Example 7 Partly Polymerized DC 200 Oil 2.7 Example 8 Fully
Polymerized DC 200 Oil 5.8 PET Film Substrate (Control) 5.6
Example 9
[0116] Polyperfluoroether (Fomblin) was another oil that was
polymerized without containing conventional, polymerizable
functionalities. Multi-layer coatings were obtained with excellent
lubrication properties. Apparatus arrangement and process
conditions were similar to those in Example 7. Experimental
evaporated Co/Ni thin film on a PET substrate (3M magnetic
recording film) and 2.5.times.10.sup.-3 cm "KAPTON" film were used
as substrates. The radio frequency bias electrode was biased at
minus 300 volts. The FTIR spectrum of the coating showed absorption
peaks typical for Fomblin; however, when the coated germanium
crystal was washed in FC77, about 75% of the Fomblin was washed
off. The coatings offered a unique multilayer construction in which
the partial polymerized polyperfluoroether top coat functioned as a
lubricant and the jet plasma carbon base as a protective and
priming layer to the substrate. Table 10 shows the static
coefficient of friction values in dependence of coating thicknesses
before and after soxhlet extraction in FC77 (16 hours). In
comparison, Sony Hi 8 ME Co/Ni tape had static coefficient of
friction values between 0.26-0.32.
10TABLE 10 Thickness (.ANG.) 150 100 75 50 35 25 JP Polymerized
0.18 0.20 0.20 0.22 0.24 0.28 Polyperfluoroether JP Polyermized
0.21 0.23 0.24 0.25 0.26 0.33 Polyperfluoroether after Soxhlet
Extraction
Example 10
[0117] Homogeneous coatings were prepared by a procedure utilizing
two feed sources. This method provided the means to obtain new
coating properties. Apparatus arrangement and process conditions
were similar to those described in Example 3. The hollow cathode
slot and the evaporator slot was placed parallel and in proximity
of the radio frequency bias electrode (less than 7 cm). A divider
was omitted. A 2.5.times.10.sup.-3 cm thick and 15 cm wide "KAPTON"
film obtained from DuPont type 100H was used as the film substrate
that was transported in loop form around the two rolis of the web
drive and the radio frequency bias electrode for multiple
deposition passes. The "KAPTON" film also accommodated silicon
wafers. After the main vacuum chamber had been evacuated to a
pressure of about 1 mTorr, 100 sccm argon was introduced into the
argon plasma chamber, i.e., the first compartment of the hollow
cathode slot system. The plasma was sustained at about minus
475volts and a pulsating DC current of about 500 mA,. At a flow
rate of 150 sccm, acetylene was introduced into the mixing chamber.
i.e., the second compartment of the hollow cathode slot system. The
hollow cathode slot was powered by a second pulsating DC power
supply. The plasma current was 1 amp at about minus 100 volts. The
radio frequency bias electrode was cooled to about 5-10.degree. C.
The bias voltage was minus 1500 volts. The dimethylsilicone oil was
introduced into the oil evaporator by way of a microsyringe pump
with a feed of 0.05-0.5 ml/minute. A 25 gauge syringe needle was
used. The run was completed after 20 passes. The coating was about
2800 .ANG. thick and showed excellent water vapor barrier values of
0.17 g/(m.sup.2.multidot.day). The contact angle and the static
coefficient of friction were 99.degree. and 0.22, respectively. The
Auger depth profile showed a uniform composition throughout the
coating including carbon, silicon, and oxygen.
[0118] The present invention has been described with reference to
various specific and preferred embodiments and techniques. It
should be understood, however, that many variations and
modifications may be made while remaining within the spirit and
scope of the invention. All patents, patent applications, and
publications are incorporated herein by reference as if
individually incorporated.
* * * * *