Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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TITLE
HOLLOW CATHODE ARRAY FOR PLASMA GENERATION
BACKGROUND OF THE INVENTION
This invention relates to a hollow cathode array for use in the creation
of a discharge plasma. The plasma generated can be used to modify surface
properties of substrates, such as films, fibers, particles and other articles.
Treatment of various substrates, such as polymers, to impart new
surface properties through physical or chemical modif canon is important for
many industries, including the film industry. Wet methods have successfully
been
used for such treatment; however, such wet methods are associated with
problems,
such as waste disposal of solvents. Dry methods, such corona treatments, uv
treatments, laser treatments, x-ray and gamma-ray treatments have also been
utilized with some success. Corona treatment has been in industrial use for
several decades but is generally restricted to simple surface geometries, such
as
web structures. In addition, in some materials the effects of corona
treatments
fade-away with time. Further, there is little control over what functional
groups
may end up on the surface of a treated substrate, and the close distance
between
electrode and substrate can lead to undesirable formation of pin-holes or burn
spots. UV, x-ray, gamma-ray and laser treatments are point sources and cannot
readily be used to treat large areas. In addition, these treatments are
subject to
intensity variations or shading effects which may result in some regions
receiving
less treatment or even being blocked by line-of sight shadowing.
Treatment of rigid, shaped or molded polymeric containers to impart
improved surface properties and gas barrier properties is important to the
food and
beverage industries. Various application methods have been proposed to coat
such containers with a variety of compositions and thereby improve their gas
burner properties. However, there continues to be a need to further increase
the
gas barrier properties of such containers to make them capable of better
retarding
the transmission of gases, such as oxygen and carbon dioxide. There also
continues to be a need for improved surface properties, especially related to
printability, to improve the recycleability of such containers.
Plasma technology has been used in the laboratory for more than 50
years, but it has only recently been practiced on a commercial scale, mainly
driven
by the semiconductor industries. In the plasma treatment of polymers,
energetic
3~ particles and photons generated in the plasma interact strongly with the
polymer
surface, usually via free radical chemistry.
A major advantage of plasma surface treatment as compared with
other treatment processes is the lack of harmful byproducts. There are usually
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toxic or hazardous liquids or gases that must be disposed of. Usually, the
main
process byproducts for plasma treatment are CO, COZ, and water vapor, none of
which is present in toxic quantities. Theoretically, plasmas can be applied to
objects of all possible geometries with varying success using conventional
apparatus and processes. Such objects include webs, films, large solid objects
with complex shapes, and small discrete parts in large quantities, such as
powder.
A major impediment to utilizing plasma processes on an industrial scale is
achieving economically acceptable rates of production. The usefulness of
plasma
processes is readily apparent but the throughput is so low that the processes
are
economically feasible only for products which acquire greatly enhanced value
from the process. Limiting factors include low plasma density and lack of
plasma
confinement. A plasma modification or polymerization system with a capability
for high production rates would lead to rapid growth in the utilization of
plasma
technology on an industrial scale.
Most devices used to generate plasmas for plasma polymerization and
plasma modification are variations of two basic types of electrode
configurations:
internal parallel plate electrodes and external electrodes. The usefulness of
these
two processes is limited by the ease in which they can be scaled up to treat
large
areas while maintaining high plasma density such that minimum residence time
can be achieved. The existing DC hollow cathode plasma reactors offer higher
plasma density and a higher degree of plasma confinement than the internal
parallel plate and external electrodes. However, they cannot be used to treat
large
areas because a large hollow cathode reactor is inherently difficult to scale
up. In
order to achieve a desirable plasma density with a large hollow cathode
reactor
necessary to accommodate large area treatments, such as 60" (152.4 cm) width
substrates, an extremely high voltage is required.
EP 634 778 describes an array of hollow cathodes which generates plasma
for surface etching and removal of "rolling oils" on metal sheets. The hollow
cathode array system comprises a housing having a plurality of uniformly
spaced
openings along one wall of the housing. The hollow cathode plasma is basically
generated in the housing and transported through the openings. The array of
such
openings serve as a distributor, however plasma intensity and uniformity are
not
enhanced. Each opening is about 1/16 inch (0.15 cm) in diameter. The pressure
used in the system of EP'778 is within the range of 0.1 to 5.0 torrs (13.33 to
666.61 Pascal), and the power input is in the range of 0.5 to 3.0 kW.
U.S. Patent 5,686,78 describes a discharge device having a cathode
with a micro hollow array for use in subminiature fluorescent lamps. This
patent
covers devices with dimensions on the scale of the mean free path of electrons
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which is not viable for Iarge area treatments. The electrons undergo
oscillatory
motion within the micro hollows which produces a micro hollow discharge
resulting in increased current capability. In use, the system of U.S.'789 uses
a
pressure of 0.1 ton to 200 torrs (13.33 to 26,664.48 Pascal). The patent does
not
mention reactive plasma, plasma polymerization, or surface modification of
materials.
H. Koch et al. in an article entitled "Hollow cathode discharge
sputtering device for uniform large area thin film deposition," (J.Vac. Sol.
Technol. A9 (4), Jul/Aug 1991, p. 2374) describe hollow cathode discharge
devices which produce higher densities of sputtered particles than
conventional
discharges. In the hollow cathode plasma sputtering process described therein,
a
sputtered target, e.g. Cu, is used as the cathode. The process is primarily a
physical process in which momentum transfer takes place. The article does not
mention using hollow cathode discharge devices in creating reactive plasma for
surface modification or conducting plasma polymerization for depositing a thin
layer on substrate surfaces.
There continues to be a need for a process for surface treatment that
among others (1) is solventless and/or free of harmful by-products, (2) is
versatile
in tailoring the treatment to any surface structure, any size, and/or
chemistry of a
given article, (3) provides a uniform treatment, (4) is capable of a high rate
and a
high throughput, (5) can be used in a batch or continuous process, and (6) can
be
operated at low pressure or under other desirable conditions.
SUMMARY OF THE INVENTION
The present invention concerns a cathode assembly for generating a
plasma comprising a plurality of electrically conductive hollow plasma
generating
cells in an array, the cells being electrically connected to each other.
The present invention also concerns a plasma generating apparatus,
comprising at least one cathode assembly described above; means for supplying
a
plasma precursor gas to the cathode assembly; and means for supplying power to
the cathode assembly.
The present invention further concerns a method of treating a surface
of a substrate comprising positioning the substrate in close proximity to at
least
one cathode assembly described above; supplying at least one plasma precursor
gas to the vicinity of the cathode assembly and the substrate; generating a
plasma
by supplying power to the cathode assembly; and exposing the surface of the
substrate to the plasma for a time sufficient to form a treated surface.
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The present invention also concerns a method for packaging a liquid
in a molded biaxially oriented polymeric container comprising (a) forming a
molded biaxially oriented polymeric container; (b) exposing at least one
surface
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of the container to a plasma generated from a plasma precursor gas comprising
a
hydrocarbon using the cathode assembly of the present im~ention described
herein,
wherein the array is shaped; (c) introducing a liquid into the container; and
(d)
sealing the container.
The present invention further concerns a method for reducing the gas
permeability of a polyester substrate comprising exposing a polyester
substrate to
a plasma generated from a plasma precursor gas comprising a hydrocarbon using
the cathode assembly of the present invention described herein.
BRIEF DESCRIPTION OF THE DRAWINGS
10 FIG. 1 is a diagram of one embodiment of a cathode assembly of the
present invention showing cells having a generally square cross-sectional
shape.
FIG. 2 is a diagram of one embodiment of a cathode assembly of the
present invention showing cells having a generally circular cross-sectional
shape.
FIG. 3 is a diagram of one embodiment of a cathode assembly of the
present invention showing cells having a generally quadrilateral cross-
sectional
shape.
FIG. 4 is a diagram of one embodiment of a cathode assembly of the
present invention showing cells having a generally triangular cross-sectional
shape.
FIG. 5 is a diagram of one embodiment of a cathode assembly of the
present invention showing cells having a generally hexagonal cross-sectional
shape.
FIG. 6 is a diagram of one embodiment of a cathode assembly of the
present invention showing cells having a generally elliptical cross-sectional
shape.
FIG. 7 is a diagram of one embodiment of a cathode assembly of the
present invention showing a cross section of cells having a flat-bottom end
portion.
FIG. 8 is a diagram of one embodiment of a cathode assembly of the
present invention showing a cross section of cells having various shapes as an
end
portion.
FIG. 9 is a diagram of one embodiment of a cathode assembly of the
present invention showing a cross section of cells having various shapes as an
end
portion.
FIG. 10 is a diagram of one embodiment of a cathode assembly of the
present invention showing the cells in a shaped array so configured as to
treat a
shaped substrate.
FIG. 11 is a diagram of one embodiment of a plasma generating
apparatus of the present invention showing two cathode assemblies, one having
a
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dielectric material coating its walls, the other having a dielectric material
disposed
adjacent to at least one cell. Also shown is means of supplying a plasma
precursor
gas, means for supplying power to the cathode assemblies. and a substrate.
FIG. 12 is a perspective cutaway view of one embodiment of a
cathode assembly of the present invention configured to treat a bottle-shaped
container.
FIG. 13 is a sectional view of the embodiment of FIG. 12.
DETAILED DESCRIPTION
Referring initially to FIGS. 1-6 and 10-13, there is generally shown
alternative embodiments of the cathode assembly of the present invention.
Cathode assembly 1 includes a plurality of cells 2 which together form an
array of
individual plasma generators. Each cell is defined by a wall or walls 3. The
cathode assembly comprises a plurality of electrically conductive hollow
plasma
generating cells mounted in an an: ay, the cells being electrically connected
to each
other with such cells being effective in providing uniform plasma treatment to
a
variety of substrates having small or large treatment area.
By "hollow plasma generating cells" is meant a plurality of cells, each
cell being defined by at least one wall. The cells defined by the wall or
walls can
be of any shape. However, for ease of manufacture, the cells, preferably, have
a
generally circular cross-sectional shape, a generally elliptical cross-
sectional
shape, a generally regular or irregular polygonal cross-sectional shape, or
any
combination of such shapes (see FIGS. 1-6 and 10-13). By "regular polygonal"
is
meant a cross-sectional shape selected from the group consisting of: triangle,
quadrilateral, pentagonal, hexagonal, heptagonal, octagonal, and combinations
thereof. For cells possessing irregular polygonal cross-sectional shapes, such
shapes can be the same or different.
The cells can be tube-like having two open ends. Alternatively, the
cells can be further defined either by a base 5 (see in particular FIG. 10)
upon
which one open end of the cell is mounted, or each cell can be further defined
by
an end portion 6 enclosing one end of the cell. Thus, the cell can further
comprise
an end portion enclosing one end of the cell wherein such end portion is
planar,
flat bottomed, U-shaped, V-shaped, or other (see FIGS. 7-9). The tube-like
cells
or the cells further defined by an end portion can be mounted onto a planar or
shaped base 5.
3~ For ease of handling and/or connecting to a power source, the cathode
assembly can further comprise one or more side pieces 8 which can surround the
array of cells. In certain embodiments, side pieces 8 can form all or a
portion of
the wall of a cell. Side pieces 8 can be attached to at least a portion of the
cells on
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the periphery of the array and/or can be attached to the optional base ~.
Holes 4 in
the side pieces can facilitate connection to a power source.
By "plasma" is meant a fully or partially ionized gas generated under
the influence of extreme thermal conditions or an electricimagrtetic field. A
S plasma is a volume of high-energy electric and magnetic fields that rapidly
dissociate any gases present to form energetic ions, photons, electrons,
highly-
reactive chemical species, neutral stable species, excited molecules, and
atoms.
By "array" is meant any configured grouping of cells. This can
include a planar array or a shaped array. An array can further include any
random
arrangement of cells wherein the cells are arranged in such a way as to
provide
treatment to only selected areas of a substrate.
By "electrically conductive" is meant that the wall, walls, and/or
optional end portions or optional base defining the cells or upon which the
cells
can be mounted, comprise material that can conduct electricity. By
"electrically
1 S connected to each other" is meant that when the cathode assembly is
connected to
a power source, by virtue of the electrically conductive material defining
each cell,
the cells are capable of electrical contact with each other. Materials useful
in the
manufacture of the cathode assembly of the present invention include any
electrically conductive material that will not adversely affect the plasma
process,
such as stainless steel, aluminum, titanium, copper, tungsten, platinum,
chromium,
nickel, zirconium, molybdenum or alloys thereof with each other or other known
elements.
The openings of the cells can be of variable cross-sectional
dimensions, but it is preferred that a plurality of the cells in the array
have a ratio
2S of cell cross-sectional area to cell depth in the range of about 0.1 to
about 5.0, with
a range of about 0.25 to about 4.0 being most preferable. Preferably, the
cross-
sectional area ranges of each cell ranges from about 0.25 to about 10 in2
(about 1.6
to about 64.5 cm')
Each cell can be defined by a discrete wall or walls, such walls being
unshared with an adjacent cell (see FIGS. 2, S, 6 and 10). Such cells can be
separated from at least one adjacent cell (see FIG. 6), or can have walls that
are in
contact with at least one wall of at least one adjacent cell (see FIG. 2), or
any
combination thereof. Alternatively, adjacent cells can share at least one
common
wall (see FIGS. 1, 3, 4 and 11 ). Preferably, regular or in egular polygonal
shaped
3S adjacent cells share at least one common wall or have walls that are in
contact
with at least one wall of at least one adjacent cell. Each wall has conducting
capability and is of such a thickness as to possess mechanical integrity.
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All or a portion of at least one wall of at least one cell of the cathode
assembly of the present invention can be coated with a dielectric material 10
(see
FIG. 11, cathode assembly on left}. In addition or alternately, a dielectric
material
can be disposed adjacent to at least one cell of the cathode assembly of the
S present invention (see FIG. 11, cathode assembly on right). Such dielectric
material can include mica, ceramic, or a polymeric material having a high
dielectric constant. The dielectric material can be coated around the edge of
the
cell, cover all or a portion of the surface of a wall of the cell, or cover
surfaces
immediately adjacent the cell. The dielectric material prevents arcing and
shorting
10 out and can quench discharges. Dielectric material can be used to mask
certain
cells thus preventing plasma generation from that cell when the cathode
assembly
is in use. Decorative effects can be made on a substrate by masking certain
cells
during plasma treatment of the substrate.
In order to provide a more uniform plasma treatment, it has been
discovered advantageous to provide at least a portion of the cells adjacent
the
periphery of the array that are smaller in cross-sectional area than the cells
in the
interior of the array. This embodiment compensates for diffusion loss (see
FIGS
2, 3, 4, 5 and 6).
The cells of the cathode can be arranged in a generally planar array, a
preferred embodiment for the treatment of planar substrates 12 (see FIG. 11 ).
Alternatively, the cells of the cathode assembly can be arranged in a shaped
array
in order to accommodate the shape of an article to be treated, for example an
article having a curved, ring-like or other shape 14 (see FIG. 10), such as a
bottle
(see FIGS. 12 and 13). Such shaped, curved arrays can be configured, for
example, to be concave or convex in shape. In FIGS. 12 and 13, cathode
assembly
1 is disposed within bottle-shaped container 20 for plasma treatment of the
inside
surface of the container. Outer electrode 30 is shown having a cellular
configuration but could have a simple flat surface. In the embodiment shown in
FIGS. 12 and 13, the polarity could be reversed and a gas feed provided to
electrode 30 whereby the outer surface of bottle-shaped container 20 could be
treated.
One or more walls of a cell can be substantially perpendicular to the
plane of the entire array (see FIG. 7), or to the plane of that portion of the
array
upon which the particular cell is located. Alternatively, one or more walls of
each
cell can have at least a portion of one wall forming an obtuse angle with the
plane
of the array (see FIGS. 8 and 9), or to the plane of that portion of the array
upon
which the particular cell is located.
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It is preferable that the array's configuration conform to the shape of
the substrate so as to maintain a reasonably uniform spacing between the
assembly
of cells and the portion of the substrate to be treated. Such a resonably
uniform
spacing allows for more even treatment.
S Cathode assemblies of the present invention can be made by machine
cutting the conductive material into pieces of a desired length, width and
thickness
and placing these pieces into a desired array arrangement. Pieces can be fit
together in a slot arrangement, placed in a tight configuration as to be
wedged
together, or welded by a typical sheet metal spot-welding process. Other
methods
of fabrication of the cathode assemblies of the present invention would be
readily
apparent to one of ordinary skill in the art.
The present invention also concerns a plasma generating apparatus,
comprising the cathode assembly described above; means for supplying a plasma
precursor gas to the cathode assembly; and means for supplying power to the
cathode assembly (see FIG. 11 ).
The plasma precursor gas can be supplied by a gas jet 16 (see FIGS. 7,
12 and 13) disposed in relation to the cathode assembly such that the
precursor gas
diffuses to the vicinity of the cells. FIG. 7 shows a manifold 16M connected
to
individual gas jets 16, each located in a cell. FIGS. 12 and 13 also show a
manifold 16M connected to individual gas jets 16 located in the center
electrode,
which is disposed inside bottle 20. The plasma gas can be fed through a plasma
gas feeding line (not shown) and the gas mass flow rate can be controlled by
using
an appropriate plasma gas flow controller, such as a MKS Type 1179A, available
from MKS Instrument, Inc. The flow rate is application dependent. Many
applications can be suitably handled using flow rates of about 0.1 to about
100
standard cubic centimeter per minute (sccm), preferably about 0.5 to about 15
sccm. Other applications can be handled using higher or lower flow rates.
The source of power 18 (see FIG. 11) can be a DC source, or an AC
source operating at an audiofrequency (AF), or radiofrequency (RF). The power
source is connected to the cathode assembly by suitable fasteners (not shown)
which can be, in one embodiment, inserted into holes 4. For many treatment
applications, less than 1 kW of power is needed, preferably about 1 to about
1000
kW is used, most preferably about 5 to about 200 watts. However, there are
applications in which power input higher than 1kW is required to achieve the
3~ desired results. A liquid electrode cooling system can be used in such
cases.
Low pressure (in vacuum) is used in the plasma treatment herein.
Thus, the present plasma generating apparatus further comprises a vacuum
chamber within which the cathode assembly resides, and means for providing a
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vacuum. A suitable vacuum chamber such as a cylindrical stainless steel vacuum
chamber has been found suitable. Commercially available vacuum pumps
comprising a booster pump in combination with a rotary pump, such as
E2M80/EH500, available from Edwards High Vacuum International can be used.
Pressures useful in the present invention can range from about 1 millitorr to
about
100 torrs (0.1333 to 13,332.24 Pascal), preferably about 1 millitorr to about
1 torr
(0.1333 to 133.32 Pascal). Batch or continuous processing is possible when
using
the present plasma generating apparatus or method. Although vacuum systems
tend to lend themselves to batch processing, a continuous operation can be
maintained for sub atmospheric pressures through use of a stage interlock
vacuum
system. By "stage interlock vacuum system" is meant a series of chambers at
differential pressures.
The present invention further concerns a method of treating at least
one surface comprising positioning the at least one surface of the substrate
in close
proximity to at least one cathode assembly described above; supplying at least
one
plasma precursor gas to the vicinity of the cathode assembly and the
substrate;
generating a plasma by.supplying power to the cathode assembly; and exposing
at
least one surface of the substrate to the plasma for a time sufficient to form
a
treated surface.
First, at least one surface of a substrate is positioned in close
proximity to at least one cathode assembly described above. By "close
proximity"
is meant that the substrate is spaced an appropriate distance from the cathode
assembly sufficient to receive plasma treatment. One or more cathode
assemblies
can be used to treat a substrate. Substrates useful for treatment herein
include
fiber, film, particles, and shaped articles, such as bottles or other
containers. The
substrate can be mounted parallel to and spaced a preselected distance from at
least one cathode assembly of the present invention. In using shaped cathode
assemblies, it is preferred that a reasonably uniform distance between the
substrate
and the cells is maintained in order to provide even treatment of the
substrate.
The fiber, film, particle or shaped article substrates can be made from
thermoplastic polymeric materials. Films and rigid containers contemplated for
use in the present invention include those formed from conventional
thermoplastic
polymers, such as polyolefins, polyamides, and engineering polymers, such as
polycarbonates, and the like. The invention is applicable to films and rigid,
i.e.,
shaped, containers, and injection stretch blow molded biaxially oriented
hollow
thermoplastic containers, such as bottles, formed from synthetic linear
polyesters,
such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT),
polyethylene naphthalate (PEN), and the like, including homopolymers and
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copolymers of ethylene terephthalate and ethylene naphthalate wherein up to
about
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~0 mole percent or more of the copolymer can be prepared from the monomer
units ofdiethylene glycol; propane-1,3-diol; butane-1,4-diol;
polytetramethylene
glycol; polyethylene glycol; polypropylene glycol and 1,4-
hydroxymethylcyclohexane substituted for the glycol moiem in the preparation
of
the copolymer; or isophthalic, dibenzoic; naphthalene 1,4- or 2,6-
dicarboxylic;
adipic; sebacic; and decane-1,10-dicarboxylic acid substituted for the acid
moiety
in the preparation of the copolymer. The foregoing description is intended to
be
an illustration of applicable polymeric substrates and not by way of a
limitation on
the scope of the invention.
Second, in the present method, at least one plasma precursor gas is
supplied to the vicinity of the cathode assembly and the substrate. Plasmas
can be
classified into three categories (1) chemically nonreactive plasma; (2)
chemically
reactive but non-polymer-forming plasma; and (3) chemically reactive and
polymer-forming plasma. The plasma precursor gas employed can be chosen
based on the desired treatment to be provided by the plasma. A suitable
precursor
gas can be, for example, nitrogen; hydrogen; oxygen; ozone; nitrous oxide; a
gas
comprising a hydrocarbon, such as methane, ethylene, butadiene or acetylene;
argon; helium; ammonia; and the like; and mixtures of gases such as
hydrocarbon/nitrogen mixtures, air; halides; halocarbons; and polymerizable
monomers. For example, polymer films can be treated with virtually any organic
or metallorganic compound capable of introduction into the plasma discharge
zone. The precursor gas or gases are fed into the vacuum chamber at a desired
gas
flow rate via a gas jet.
A plasma is generated by supplying power to the cathode assembly.
The cathode assembly is connected to a power supply, and the power supply is
turned on to initiate the plasma state. The power is then adjusted to a
desired
power level. The power level can vary depending on the gas flow rate, the size
of
substrate, the distance from the cathode assembly to the anode, a molecular
weight
of the plasma precursor gas, and pressure. The electrical power and gas flow
rates
can be adjusted so as to form an intense plasma discharge in all of the
desired cells
of the cathode assembly. Optionally, magnetic enhancement may be used to focus
the plasma as it exits the cells.
Finally, at least one surface of the substrate is exposed to the plasma
for a time sufficient to form a treated surface. The plasma treatment should
be
maintained for a desired period of time which can range from several seconds
to
several minutes. The treatment time depends on the characteristics of the
plasma
and its interaction with the substrate surface which depend on the operational
parameters under which the plasma is maintained. Such parameters include gas
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flow rate, input power, pressure, discharge power and substrate position.
Treatment time can also depend on the nature of the substrate.
The present invention is useful for packaging beverages. Thus the
present invention further concerns a method for packaging a liquid in a molded
S biaxially oriented polymeric container comprising forming a container;
exposing
at least one surface of the container to a plasma generated from a plasma
precursor
gas comprising a hydrocarbon using the cathode assembly of the present
invention
described herein, wherein the array is shaped; introducing a liquid into the
container; and sealing the container. This method can further comprise purging
the gas from the container prior to introduction of the liquid. This method
can be
suitable for carbonated liquids.
The present invention is suited for improving the gas barrier
performance of polyethylene terephthalate) films and rigid containers used for
packaging foods and beverages, and injection stretch blow molded PET bottles
used for packaging carbonated soft drinks and beer. Thus the present invention
includes a method for reducing the gas permeability of a polyester substrate
comprising exposing at least one surface of a polyester substrate to a plasma
generated from a plasma precursor gas comprising a hydrocarbon using the
cathode assembly of the present invention, described herein.
The present invention is useful in processes including surface cleaning
(removal of organic contamination); etching or ablation (removal of a weak
boundary layer and increasing the surface area); cross-linking or branching of
near-surface molecules, which can cohesively strengthen the surface layer and
hence the physical properties; chemical modification/grafting by deliberate
alteration of the surface region with new chemical functionalities; and thin
film
deposition, alteration of the surface properties of a substrate to tailor
adhesion
needs or a barrier coating to capitalize on the bulk properties of a thin,
pinhole-
free, and highly adherent film in permeant-selective membranes.
EXAMPLE 1
Adhesion Enhancement for Polvimide Film to Conner
Two I2in x l2in (30.48 cm x 30.48 cm) cathode assemblies having a
square cell pattern similar to that shown in FIG. 1 were made out of stainless
steel.
Each cell measured 1 in x I in x 1 in (2.54 cm x 2.54 cm x 2.54 cm), and the
ratio of
the cross-sectional area of the cell to the depth of the cell was equal to
1Ø The
two cathode assemblies were mounted parallel to each other in a vacuum chamber
and each cathode was connected to a DC power supply. Kapton~ polyimide film,
available from E. I. du Pont de Nemours and Company, Wilinington, DE, was
placed between the cathodes at a distance of about tin (5.08 cm) from each
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cathode. A vacuum was induced with a pressure of 150 millitorrs. Ammonia was
introduced into the chamber at a flow rate of 12 standard cubic centimeter per
minute (scan) and power was supplied at a voltage of 560 V. The filin was
exposed to the ammonia plasma for 1 min.
Using a conventional nip-roll process, the treated film was then laminated
with adhesive and copper. The lay-up consisted of 1 oz. (28.34 grams) copper,
a
layer of lmil (0.0254 mm) Pyralux~ sheet adhesive, the polyimide film strip,
another layer of 1 mil sheet adhesive and another layer of 1 oz. (28.34 grams)
copper to form a clad.
I O In order to test the adhesion strength of the copper to the rest of the
clad,
the copper was placed in the upper jaw of an Instron machine and the rest of
the
clad was adhered with two-sided sticky tape to a German wheel. The wheel was
rotated as the copper was peeled with the intent of maintaining a 90 degrees
peel
angle. The draw rate was 2in/min (5.08 cm/min). The bond values in pounds per
linear inch (pli) (newtons per meter (N/m)) and the surface energies for the
control
and the ammonia plasma treated sample are listed below
Sample Bond Value(nli) fN/ml Polar Surface Eneravjdynes/cml
Control 6.9 (1208.19) 10.7
Ammonia-treated 13.0 (2267.3) 23.2
EXAMPLE 2
Barrier Prouerties Enhancement for Polv(ethvlene terephthalate) (PET) Filins
5" X 5" ( 12.7 cm x 12.7 cm) MYL1NEX~ type S PET films,
available from DuPont Co., Wilmington, DE, were placed between the
assemblies, as described in Example I, for plasma thin film deposition to
create a
higher barrier for oxygen permeation through the PET films. A vacuum was
induced with a pressure of 150 millitorrs. Acetylene was introduced into the
chamber at a flow rate of 25 sccm and power was suuplied at a voltage of 640
V.
The film was exposed to the acetylene plasma for 10 min. The treated films
were
then evaluated for Oxygen Permeation Rate, also known as Oxygen Transmission
Rate (OTR) by using OXTRAN~1000 made by Mocon, Inc. by following ASTM
D3985 with 50% Relative Humidity (RH) at 30°C. Results are listed
below.
Sample Thickness (mild (mml OTR (cc/m2/day)
Control 4.94 __ _ D.125 12.57
Acetylene-
Treated 4.88 O.I24 2.48
12
AMENDED SHEET
