U.S. patent application number 13/746077 was filed with the patent office on 2013-05-23 for fluorinating apparatus.
This patent application is currently assigned to 3M Innovative Properties Company. The applicant listed for this patent is 3M Innovative Properties Company. Invention is credited to Gina M. Buccellato, Moses M. David, John H. Huberty, Seth M. Kirk.
Application Number | 20130125816 13/746077 |
Document ID | / |
Family ID | 26968178 |
Filed Date | 2013-05-23 |
United States Patent
Application |
20130125816 |
Kind Code |
A1 |
David; Moses M. ; et
al. |
May 23, 2013 |
Fluorinating Apparatus
Abstract
An apparatus for fluorinating a substrate. The apparatus
includes a vacuum chamber and a means for generating a
fluorine-containing plasma throughout the entire chamber. The
apparatus includes a capacitively-coupled system within the chamber
that has at least one electrode powered by an RF source and at
least one grounded electrode substantially parallel to the powered
electrode. The electrodes are separated by about 25 mm or less.
Inventors: |
David; Moses M.; (Woodbury,
MN) ; Buccellato; Gina M.; (Eagan, MN) ;
Huberty; John H.; (St. Paul, MN) ; Kirk; Seth M.;
(Minneapolis, MN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
3M Innovative Properties Company; |
St. Paul |
MN |
US |
|
|
Assignee: |
3M Innovative Properties
Company
ST. PAUL
MN
|
Family ID: |
26968178 |
Appl. No.: |
13/746077 |
Filed: |
January 21, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13004288 |
Jan 11, 2011 |
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13746077 |
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10293830 |
Nov 13, 2002 |
7887889 |
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13004288 |
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60341564 |
Dec 14, 2001 |
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Current U.S.
Class: |
118/723E |
Current CPC
Class: |
Y10T 428/249953
20150401; Y10T 442/20 20150401; C08J 9/36 20130101; C23C 16/505
20130101; Y10T 428/249955 20150401 |
Class at
Publication: |
118/723.E |
International
Class: |
C23C 16/505 20060101
C23C016/505 |
Claims
1. An apparatus for fluorinating a substrate, which apparatus
comprises: a vacuum chamber; a capacitively-coupled system within
the chamber comprising at least one electrode powered by an RF
source and at least one grounded electrode substantially parallel
to the powered electrode wherein the electrodes are separated by
about 25 mm or less; and a means for generating a
fluorine-containing plasma throughout the entire chamber; wherein
the powered electrode is a rotating drum.
2. The apparatus of claim 1 wherein the electrodes are separated by
about 16 mm or less.
3. The apparatus of claim 1 further comprising a second rotating
drum powered electrode.
4. The apparatus of claim 1 wherein the capacitively-coupled system
comprises a concentric electrode substantially parallel to the
powered drum electrode.
5. The apparatus of claim 1, further comprising a second rotating
drum electrode in the vacuum chamber, and wherein there is a second
concentric electrode substantially parallel to the second rotating
drum electrode.
6. The apparatus of claim 1, wherein the electrodes are separated
by about 13 to 16 mm.
7. The apparatus of claim 1, wherein the vacuum chamber is a
reaction chamber that is evacuable.
8. The apparatus of claim 7, wherein the reaction chamber allows
for the control of pressure and the flow of reactive gasses.
9. The apparatus of claim 8, wherein the reaction chamber comprises
aluminum.
10. The apparatus of claim 9, wherein the at least one electrode
powered by an RF source and the at least one grounded electrode
that has an asymmetric surface area ratio.
11. The apparatus of claim 10, wherein the ratio is from 2:1 to
4:1.
12. The apparatus of claim 11, wherein the RF source is an RF
generator.
13. The apparatus of claim 1, wherein the power source is connected
to the electrode via a network that acts to match the impedance of
the power source with that of a transmission line.
14. The apparatus of claim 1, wherein the apparatus is adapted to
fluorinate more than one article at a time.
15. The apparatus of claim 1, wherein the grounded electrode is
concentric to the powered drum electrode.
16. The apparatus of claim 1, wherein the apparatus further
comprises a feed reel and a take-up reel.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application is a divisional of U.S. Ser. No.
13/004,288, filed Jan. 11, 2011, which is a divisional of U.S. Ser.
No. 10/293,830, filed Nov. 13, 2002 (now U.S. Pat. No. 7,887,889)
which claims priority to U.S. Provisional Patent Application No.
60/341,564, filed Dec. 14, 2001, which is incorporated by
reference.
BACKGROUND
[0002] Plasma-deposited fluorocarbon coatings can impart desirable
properties, such as low surface energy, water-repellency, soil
resistance, and durability, to a treated article. A charge can be
imparted to the treated article, which makes the article suitable
for use in items such as aerosol filters, face masks, air filters,
and electrostatic elements in electro-acoustical devices such as
microphones, headphones, and electrostatic recorders. Accordingly,
plasma fluorination methods that can quickly and efficiently
produce an article with a fluorocarbon coating are desired.
SUMMARY OF INVENTION
[0003] One aspect of the present invention features a plasma
fluorination method to fluorinate porous articles, both on the
surface and in the interior. It also features the resulting
articles.
[0004] One aspect of the present invention is a method of
fluorinating a porous article comprising: providing a reaction
chamber having a capacitively-coupled system comprising at least
one grounded electrode and at least one electrode powered by an RF
source; generating a fluorine-containing plasma in the chamber
thereby causing an ion sheath to form adjacent to the electrodes;
placing a porous article in the ion sheath of the powered
electrode; and allowing reactive species from the plasma to react
with the article surface and interior whereby the article becomes
fluorinated.
[0005] Another aspect of the present invention is a method of
fluorinating a porous article comprising: providing a reaction
chamber having a capacitively-coupled system comprising at least
one electrode powered by an RF source and at least one grounded
electrode that is substantially parallel to the surface of the
powered electrode and separated from the grounded electrode by
about 25 millimeters or less; generating a fluorine-containing
plasma in the chamber at a pressure of about 40 Pascal or less;
placing a porous article between the substantially parallel
electrodes and outside of the ion sheath; and allowing reactive
species from the plasma to react with the article surface and
interior for a total treatment time of over two minutes whereby the
article becomes fluorinated.
[0006] Another aspect of the present invention is a method of
fluorinating a porous article comprising: providing a reaction
chamber having a capacitively-coupled system comprising at least
one electrode powered by an RF source and at least one grounded
electrode that is substantially parallel to the surface of the
powered electrode and separated from the grounded electrode by
about 25 millimeters or less; generating a fluorine-containing
plasma in the chamber thereby causing an ion sheath to form
adjacent to the electrodes; placing a porous article in the ion
sheath of the grounded electrode; and allowing reactive species
from the plasma to react with the article surface and interior for
a total treatment time of about 30 seconds to about 5 minutes
whereby the article becomes fluorinated.
[0007] Another aspect of the present invention is a method of
fluorinating a porous article comprising: providing a reaction
chamber having a capacitively-coupled system comprising at least
one electrode powered by an RF source and at least one grounded
electrode that is substantially parallel to the surface of the
powered electrode and separated from the grounded electrode by
about 13 millimeters or less; generating a fluorine-containing
plasma in the chamber thereby causing an ion sheath to form
adjacent to the electrodes; placing a porous article between the
electrodes; and allowing reactive species from the plasma to react
with the article surface and interior whereby the article becomes
fluorinated.
[0008] The methods may include embodiments wherein the process is
continuous and/or wherein the treatment time is less than about 60
seconds.
[0009] The porous article to be treated may be selected from the
group consisting of foams, woven materials, nonwoven materials,
membranes, frits, porous fibers, textiles, and microporous
articles. The article may have pores smaller that the mean free
path of any species in the plasma. The article may have two
parallel major surfaces and may be treated on one or both major
surface.
[0010] The methods may be carried out with the electrodes separated
by about 25 millimeters or less. In some embodiments, the
electrodes are separated boy about 16 millimeters(mm) or about 13
mm. Another aspect of the invention is an article comprising at
least one fluorinated porous layer having a basis weight of about
10 to about 300 gsm and a thickness of about 0.20 to about 20 mm,
wherein the layer has a Q.sub.200 of greater than about 1.1. The
layer may have an effective fiber diameter of about 1 to about 50
.mu.m.
[0011] Another aspect of the invention is an article comprising a
composite layer comprising a non-fluorine containing porous layer
and a plasma fluorinated layer affixed to the surface and interior
of the porous layer, wherein the composite layer has at least 3700
ppm fluorine or, in another embodiment, at least 5000 ppm.
[0012] Another aspect of the invention is an apparatus for
fluorinating a substrate comprising a vacuum chamber, a
capacitively-coupled system within the chamber comprising at least
one electrode powered by an RF source and at least one grounded
electrode substantially parallel to the powered electrode wherein
the electrodes are separated by about 25 mm or less, e.g., about 16
mm or 13 mm, and a means for generating a fluorine-containing
plasma throughout the entire chamber.
[0013] The powered electrode may comprise one or more rotating
drums. The apparatus can comprise an asymmetric parallel plate
reactor.
[0014] As used in this invention: "microporous membrane" means a
membrane having pore sizes with a lower limit of about 0.05 .mu.m
and an upper limit of about 1.5 .mu.m;
[0015] "plasma fluorocarbon" means a material deposited from a
plasma comprising fluorocarbon species;
[0016] "plasma fluorination" means thin film deposition, surface
modification, and any other plasma-induced chemical or physical
reaction that can fluorinate an article; "porous article" means an
article having pathways open to at least one surface;
[0017] "Q.sub.200" means the quality factor rating of a filter; the
procedure for determining Q.sub.200 is set forth in the Examples
section of this application, and
[0018] "substantially parallel" means the electrodes are
substantially the same distance from each other along their entire
lengths, including concentric electrodes.
[0019] An advantage of at least one embodiment of the present
invention is that it provides a continuous plasma fluorination
method, which allows for efficient, i.e., faster, processing of
articles, especially continuous articles, e.g., long sheets of
material, as are used in roll-to-roll processing.
[0020] Another advantage of at least one embodiment of the
invention is that it provides a durable fluorination treatment
through the bulk of porous articles, including microporous
membranes.
[0021] Another advantage of at least one embodiment of the present
invention is that treatment efficiencies can be obtained by placing
the article to be treated within an ion sheath.
[0022] Another advantage of at least one embodiment of the present
invention is that fluorination efficiency may be achieved by
reducing the space between the powered and grounded electrode to
about 25 mm or less.
[0023] Other features and advantages of the invention will be
apparent from the following drawings, detailed description, and
claims.
BRIEF DESCRIPTION OF DRAWINGS
[0024] FIG. 1 depicts a parallel plate plasma apparatus for
performing the plasma fluorination of the present invention.
[0025] FIG. 2 depicts a single drum plasma apparatus for performing
the plasma fluorination of the present invention.
DETAILED DESCRIPTION
[0026] The present invention provides a plasma fluorination method
to fluorinate a porous article.
[0027] One method embodiment involves providing a reaction chamber
having a capacitively-coupled electrode system wherein an ion
sheath is formed adjacent to at least one electrode when a plasma
is generated in the system. The ion sheath is an area adjacent to
an electrode in which ion bombardment is prevalent. The porous
article to be treated is placed within the ion sheath.
[0028] This method of the invention can be especially effective for
articles with small pores because the ion sheath can force chemical
species from the plasma into small pores of the articles being
treated. This results in surprisingly fast fluorination of the pore
interiors. It was not expected that plasma fluorination could be
achieved within small pores, especially in cases where the pores
are smaller than the mean free path of any species in the
plasma.
[0029] The mean free path (MFP) for a particular species is the
average distance traveled by a species before it collides with
another species. The MFP depends in part on pressure because the
proximity of species influences the collision frequency. For
example, at 0.13 Pa (1 mTorr) and room temperature, the mean free
path of an argon atom is 80 mm. See Brian Chapman, Glow Discharge
Processes, 153 (John Wiley & Sons, New York 1980). Most other
gases, including those used in the present invention, are within
three times (i.e. 26-240 mm) of this value at this pressure. In the
range of pressures useful for plasma fluorination, the mean free
path of argon varies from 80 mm to 0.08 mm (or 80 microns). Other
gases would have similar variations.
[0030] In plasma-treating a porous article, if the pore size is
smaller than the mean free path of the species in the plasma (i.e.,
smaller than about 20 microns), normally the free radical species
generated in the plasma will collide with the pore walls near the
pore opening. The free radicals will react with molecules in the
pore walls near the pore opening rather than traveling into the
depths of the pores. Therefore, one would not expect the plasma
fluorination to penetrate into the depths of the pores, especially
when the pores have tortuous paths.
[0031] Another method embodiment of the present invention involves
providing a reaction chamber having a capacitively-coupled
electrode system in which a powered and grounded electrode are
spaced about 25 mm (one inch), or less, apart and the porous
article to be treated is suspended between the two electrodes and
outside an ion sheath. In this embodiment, the chamber pressure is
maintained at about 40 Pa or less and the total treatment time is
over 2 minutes. This treatment method results in treated articles
having a higher fluorine content, and better oil repellency, than
similar articles treated in a system in which the grounded and
powered electrode are farther apart and the chamber pressure is
higher than about 40 Pa.
[0032] Another method embodiment of the present invention involves
providing a reaction chamber having a capacitively-coupled system
comprising at least one electrode powered by an RF source and at
least one grounded electrode that is substantially parallel to the
surface of the powered electrode and separated from the grounded
electrode by about 25 millimeters or less; generating a
fluorine-containing plasma in the chamber thereby causing an ion
sheath to form adjacent to the electrodes; placing a porous article
in the ion sheath of the grounded electrode; and allowing reactive
species from the plasma to react with the article surface and
interior for a total treatment time of about 30 seconds to about 5
minutes whereby the article becomes fluorinated.
[0033] Another method embodiment of the present invention involves
providing a reaction chamber having a capacitively-coupled system
comprising at least one electrode powered by an RF source and at
least one grounded electrode that is substantially parallel to the
surface of the powered electrode and separated from the grounded
electrode by about 13 millimeters or less; generating a
fluorine-containing plasma in the chamber thereby causing an ion
sheath to form adjacent to the electrodes; placing a porous article
between the electrodes; and allowing reactive species from the
plasma to react with the article surface and interior whereby the
article becomes fluorinated.
Porous Articles
[0034] Porous articles suitable for use in the present invention
include foams, nonwoven materials, woven materials, membranes,
frits, porous fibers, textiles, and microporous articles. These
articles may have pore sizes of about 0.05 micrometers or
greater.
[0035] The porous articles may be made from, e.g., polymers,
metals, glasses, and ceramics. Suitable polymers for the above
articles include polyolefins such as, e.g., polypropylene,
polyethylene, poly-(4-methyl-1-pentene), and combinations thereof,
halogenated vinylpolymers (e.g., polyvinyl chloride), polystyrene,
polycarbonates, polyesters, polyamides, and combinations thereof.
The nonwovens can be formed by a variety of methods, including but
not limited to, carding, use of a rando-webber, spunbonding,
hydrolacing, or blown microfibers. The textiles and cloths can be
formed as nonwovens or as knit or woven materials. The textiles and
cloths preferably have a basis weight in the range of about 10 to
500 grams per square meter more preferably about 15 to 300 grams
per square meter. Porous frits synthesized from polymers, metals,
glasses and ceramics are available commercially in various pore
sizes. The pore size typically varies between 1 and 250 microns and
the fits may have a void volume of between 20 and 80%. Typical
applications of frits include filtration, support media for
membrane cartridges, solvent filters, diffusers, fluidization
supports, bio-barriers, nibs for writing instruments,
chromatographic support media, catalysis support media, etc. Porous
fibers are also commercially available. Typical diameters for these
fibers are up to and around 100 .mu.m and typical pore sizes are
from about 0.001 .mu.m (10 .ANG.) to about 10 .mu.m (1000
.ANG.).
[0036] Suitable microporous films may be prepared by
thermally-induced phase separation (TIPS) methods such as those
described in U.S. Pat. Nos. 4,539,256 (Shipman), 4,726,989;
5,120,594 (Mrozinski); and 5,260,360 (Mrozinski et al.) which
describe such films containing a multiplicity of spaced, randomly
dispersed, equiaxed, nonuniform shaped particles of a thermoplastic
polymer. These films typically have pore sizes with a lower limit
of about 0.05 micrometers and an upper limit of about 1.5
micrometers.
[0037] A suitable porous material may have a basis weight of 10 to
300 gsm (grams per square meter) and a thickness of 0.20 to 20 mm.
The porous material also may have an effective fiber diameter of 1
to 50 .mu.m.
[0038] The porous articles can be any shape, e.g., sheets, rods,
cylinders, etc., as long as they can be placed within an ion sheath
that surrounds an electrode. Typically the articles will be
sheet-like with two major parallel surfaces. The articles may be
discrete articles or may be continuous sheets of material. They may
have any level of hydrophobicity or hydrophilicity before they are
treated.
[0039] The resulting fluorinated porous article may be used alone
or may be incorporated into another article. For example, it may be
incorporated into a multi-layer (two or more layers) article in
which the other layer(s) are fluorinated or unfluorinated and are
porous or nonporous. The multi-layer article may be made by any
method known in the art, e.g., lamination, physical bonding,
etc.
[0040] Porous filter media are frequently employed to filter air
containing solid and/or liquid particles. The particles removed are
often toxic or noxious substances. Scientists and engineers have
long sought to improve filtration performance of air filters. Some
of the most effective air filters use electret articles. Electrets
are dielectric articles that exhibit a lasting charge, that is, a
charge that is at least quasi-permanent. The term
"quasi-permanent"means that the time constants characteristic for
the decay of the charge are much longer than the time period over
which the electret is used.
[0041] The charged nature of the electret enhances the filter's
ability to attract and retain particles such as dust, dirt, and
fibers that are present in the air. Electrets have been found to be
useful in a variety of applications including air, furnace and
respiratory filters, face masks, and electro-acoustic devices, such
as microphones, headphones, and electrostatic recorders.
[0042] Over the years, various methods of making and improving the
filtration performance of nonwoven fibrous electrets have been
developed. These methods include, e.g., bombarding fibers with
electrically charged particles as the fibers issue from a die
orifice, corona charging a nonwoven fibrous web, and hydrocharging
a nonwoven fibrous web.
[0043] While performance is enhanced through the use of electret
charged media, degradation in filter efficiency during exposure or
loading of aerosols containing an oily mist has been exhibited in
some media. This change in performance during loading prompted the
National Institute for Occupational Safety and Health (NIOSH) to
specify testing that requires respirators used in oily mist
environments to be exposed to 200 mg of dioctyl phthalate (DOP)
during certification testing. In order to determine the benefits of
the filters of this invention, the filter penetration was measured
after exposing the sample to 200 mg of aerosolized DOP.
[0044] In addition to penetration, pressure drop of the filter is a
key measurement in designing a filter. Pressure drop is defined as
a reduction in static pressure within an air stream between the
upstream and downstream sides of a filter through which the air
stream passes. A lower pressure drop allows air to flow through the
medium more easily. Lower pressure drop is typically preferred
because it allows less effort or energy to be used to achieve the
desired flow. This is true whether the filter is employed as a
respirator, which a user breathes through; a battery powered
air-purifying respirator; or a home furnace filter.
[0045] To ease the comparison and the design of filters,
researchers often combine penetration and pressure drop into a
single term of Quality Factor, i.e., the quality of the filtration
performance of the material. In this application, quality factor is
based on penetration and pressure drop after exposure to of 200 mg
of dioctyl phthalate, as explained in more detail in the Examples
section. The Quality Factor Rating is referred to as Q.sub.200.
[0046] Some articles of the present invention have Q.sub.200
ratings over 1.1, and in some cases, as high as 1.53. Some articles
also have fluorine concentrations of over 3700 ppm, and in some
cases, as high as 5000 ppm or more.
Apparatus
[0047] An apparatus suitable for the present invention provides a
reaction chamber having a capacitively-coupled system with at least
one electrode powered by an RF source and at least one grounded
electrode. In some embodiments, a grounded electrode is separated
from the powered electrode by about 25 mm or less.
[0048] A suitable reaction chamber is evacuable, has means for
generating a fluorinated plasma throughout the entire chamber and
is capable of maintaining conditions that produce plasma
fluorination. That is, the chamber provides an environment which
allows for the control of, among other things, pressure, the flow
of various inert and reactive gases, voltage supplied to the
powered electrode, strength of the electric field across the ion
sheath, formation of a plasma containing reactive species,
intensity of ion bombardment, and rate of deposition of a film from
the reactive species. Aluminum is a preferred chamber material
because it has a low sputter yield, which means that very little
contamination occurs from the chamber surfaces. However, other
suitable materials, such as graphite, copper, glass or stainless
steel, may be used.
[0049] The electrode system may be symmetric or asymmetric.
Preferred electrode surface area ratios between grounded and
powered electrodes for an asymmetric system are from 2:1 to 4:1,
and more preferably from 3:1 to 4:1. The ion sheath on the smaller
powered electrode will increase as the ratio increases, but beyond
a ratio of 4:1 little additional benefit is achieved. Placing the
sample on the powered electrode is generally preferred because DC
bias would not be shunted to ground. Both electrodes may be cooled,
e.g., by water.
[0050] Plasma, created from the gas within the chamber, is
generated and sustained by supplying power (for example, from an RF
generator operating at a frequency in the range of 0.001 to 100
MHz) to at least one electrode. The RF power source provides power
at a typical frequency in the range of 0.01 to 50 MHz, preferably
13.56 MHz or any whole number (e.g., 1, 2, or 3) multiple thereof.
The RF power source can be an RF generator such as a 13.56 MHz
oscillator. To obtain efficient power coupling (i.e., wherein the
reflected power is a small fraction of the incident power), the
power source may be connected to the electrode via a network that
acts to match the impedance of the power supply with that of the
transmission line (which is usually 50 ohms resistive) so as to
effectively transmit RF power through a coaxial transmission line.
A description of such networks can be found in Brian Chapman, Glow
Discharge Processes, 153 (John Wiley & Sons, New York 1980).
One type of matching network, which includes two variable
capacitors and an inductor, is available as Model # AMN 3000 from
RF Power Products, Kresson, N.J. Traditional methods of power
coupling involve the use of a blocking capacitor in the impedance
matching network between the powered electrode and the power
supply. This blocking capacitor prevents the DC bias voltage from
being shunted out to the rest of the electrical circuitry. On the
contrary, the DC bias voltage is shunted out to the grounded
electrode. While the acceptable frequency range from the RF power
source may be high enough to form a large negative DC self bias on
the smaller electrode, it should not be so high that it creates
standing waves in the resulting plasma, which is inefficient for
plasma fluorination.
[0051] The articles to be treated may be placed in, or passed
through, the evacuable chamber. In some embodiments, a multiplicity
of articles may be simultaneously exposed to the plasma during the
process of this invention.
[0052] In an embodiment in which the article is treated within an
ion sheath, plasma fluorination of discrete planar articles can be
achieved, for example, by placing the articles in direct contact
with the powered electrode. This allows the article to act as an
electrode due to capacitive coupling between the powered electrode
and the article. This is described in M. M. David, et al., Plasma
Deposition and Etching of Diamond-Like Carbon Films, AIChE Journal,
vol. 37, No. 3, p. 367 (1991). In the case of an elongated article,
the article may optionally be pulled through the vacuum chamber
continuously, while maintaining contact with an electrode. The
result is a continuous plasma fluorination of the elongated
article.
[0053] FIG. 1 illustrates a parallel plate apparatus 10 suitable
for the present invention, showing a grounded chamber 12 from which
air is removed by a pumping stack (not shown). Gases to form the
plasma are injected radially inward through the reactor wall to an
exit pumping port in the center of the chamber. Article 14 is
positioned proximate RF-powered electrode 16. Electrode 16 is
insulated from chamber 12 by Teflon support 18.
[0054] It is not necessary to confine the plasma between the
electrodes. The plasma may fill the entire chamber without
diminishing the effectiveness of the plasma fluorination. However,
the plasma will usually appear brighter between the two
electrodes.
[0055] FIG. 2 illustrates single-drum apparatus 100 that is also
suitable for the present invention, especially the method
embodiment that employs an ion sheath. This apparatus is described
in more detail in U.S. Pat. No. 5,948,166. The primary components
of apparatus 100 are rotating drum electrode 102 that can be
powered by a radio frequency (RF) power source, grounded chamber
104 that acts as a grounded electrode, feed reel 106 that
continuously supplies article 108, which is to be treated, and a
take-up reel 110, which collects the treated article. A concentric
grounded electrode (not shown) can be added near the powered
electrode so spacing can be controlled.
[0056] Article 108 is a long sheet that, in operation, travels from
feed reel 106, around drum electrode 102 and on to take-up reel
110. Reels 106 and 110 are optionally enclosed within chamber 104,
or can be outside chamber 104 as long as a low-pressure plasma can
be maintained within the chamber.
[0057] The curvature of the drum provides intimate contact between
the article and the electrode, which ensures that the article
remains within the ion sheath, irrespective of other operating
conditions such as pressure. This can allow a thick article to be
kept within the ion sheath even at high pressures (e.g., 300 to
1000 mTorr). Because the article is supported and carried by the
drum, this intimate contact also enables the treatment of delicate
materials. The intimate contact also ensures that plasma
fluorination is captured by the article, thereby keeping the
electrode clean. It also allows for effective single-sided
treatment when this is desired. However, dual-sided treatment can
be achieved by passing the article through the apparatus twice,
with one side being treated per pass. A drum electrode also
provides a long treatment zone (pi.times.diameter) and provides
symmetric distribution of power across the electrode, which can
have operational advantages. The drum may be cooled or heated to
control the temperature of the article being treated. In addition,
linear dimensions in the direction of current flow are made small
in comparison to the wavelength of the RF radiation, eliminating
the problem of standing waves.
[0058] In other suitable apparatuses, there may be more than one
powered electrode and more than one grounded electrode. One
suitable apparatus for this invention is a reactor comprising two
drum shaped powered electrodes within a grounded reaction chamber,
which has two to three times the surface area of the powered
electrodes. The drums can be configured so that the article to be
treated can travel around and over the two drums in a manner that
allows it to be plasma-treated on both sides (one side is treated
on each drum). The drums may be located in a single chamber or in
separate chambers, or may be in the same chamber, but separated,
such that different treatments can occur around each drum.
[0059] When multiple electrodes are used, they may be powered by a
single RF supply or powered separately. When a single supply is
used, the power is sometimes distributed unequally between the
electrodes. This may be corrected by using a different power supply
for each electrode with oscillator circuits linked to a master
power supply through a phase angle adjuster. Thus any power
coupling between the electrodes through the plasma may be
fine-tuned by adjusting the phase angle between the voltage
waveforms of the master and slave power supplies. Flexibility in
power coupling and adjustment between the different electrodes may
be achieved by this approach.
[0060] In some embodiments, it is desirable to have the grounded
electrode within about 25 mm of the powered electrode on which an
article to be treated is located. Having a grounded electrode close
to a powered electrode was found to be advantageous. It resulted in
articles with high levels of fluorination and oil repellency. It
was further found that, while the proximity of the electrodes
provided advantages, it was not necessary that the plasma be
restricted to the area between the electrodes. While the plasma
glow tended to be brighter between the electrodes, the plasma
filled the entire reaction chamber. In addition, one experiment was
carried out in which the grounded electrode was perforated to more
clearly show that the plasma was not confined. The properties of
the resulting article were as good as those of articles produced
with an unperforated electrode.
[0061] In addition to the capacitive coupling system, the reactor
might include other magnetic or electric means such as induction
coils, grid electrodes, etc.
Methods of Plasma Fluorination
[0062] Other aspects of the invention are further directed to
methods of plasma-treating articles. The methods are carried out in
a suitable capacitively coupled reactor system such as those
described above.
[0063] In different embodiments of methods of the present
invention, a grounded and a powered electrode are spaced apart by
about 25 mm or less, about 16 mm or less, or about 13 mm or less. A
low chamber pressure may be used and can be beneficial in some
embodiments because the lower pressure normally allows bigger ion
sheaths to form. An article to be treated may be placed on the
powered electrode (preferably), the grounded electrode, or may be
suspended between the electrodes. Plasma fluorination of discrete
planar articles can be achieved, for example, by suspending an
article between the electrodes, preferably about halfway between
the electrodes. In this embodiment, the article may be, but does
not need to be, within an ion sheath. If the article is outside of
an ion sheath, e.g., by being suspended, a treatment time of over
two minutes may be required to deposit a fluorinated layer with
good oil repellency properties. However, reducing the space between
the electrodes, e.g., to about 16 mm or about 13 mm, can decrease
the necessary treatment time. Total treatment times of less than
two minutes can be achieved if the article is within an ion
sheath.
[0064] The article to be treated optionally may be pre-cleaned by
methods known to the art to remove contaminants that may interfere
with the plasma fluorination. A useful pre-cleaning method is
exposure to an oxygen plasma. For this pre-cleaning, pressures in
the reactor are maintained between 1.3 Pa (10 mTorr) and 27 Pa (200
mTorr). Plasma is generated with RF power levels of between 500 W
and 3000 W. Other gases may be used for pre-cleaning such as, for
example, argon, air, nitrogen, hydrogen or ammonia, or mixtures
thereof.
[0065] Prior to the plasma fluorination process, the chamber is
evacuated to the extent necessary to remove air and any impurities.
This may be accomplished by vacuum pumps at a pumping stack
connected to the chamber. Inert gases (such as argon) may be
admitted into the chamber to alter pressure. Once the chamber is
evacuated, a source gas containing fluorine is admitted into the
chamber via an inlet tube. The source gas is introduced into the
chamber at a desired flow rate, which depends on the size of the
reactor, the surface area of the electrodes, and the porosity of
the articles to be treated. Such flow rates must be sufficient to
establish a suitable pressure at which to carry out plasma
fluorination, typically 0.13 Pa to 130 Pa (0.001 Torr to 1.0 Torr).
For a cylindrical reactor that has an inner diameter of
approximately 55 cm and a height of approximately 20 cm, the flow
rates are typically from about 50 to about 500 standard cubic
centimeters per minute (sccm). At the pressures and temperatures of
the plasma fluorination (typically 0.13 to 133 Pa (0.001 to 1.0
Torr) (all pressures stated herein are absolute pressures) and less
than 50.degree. C.), the source gases remain in their vapor
form.
[0066] Upon application of an RF electric field to a powered
electrode, a plasma is established. In an RF-generated plasma,
energy is coupled into the plasma through electrons. The plasma
acts as the charge carrier between the electrodes. The plasma can
fill the entire reaction chamber and is typically visible as a
colored cloud.
[0067] The plasma also forms an ion sheath proximate at least one
electrode. In an asymmetric electrode configuration, higher
self-bias voltage occurs across the smaller electrode. This bias is
generally in the range of 100 to 2000 volts. This biasing causes
ions within the plasma to accelerate toward the electrode thereby
forming an ion sheath. The ion sheath appears as a darker area
adjacent to the electrode. Within the ion sheath accelerating ions
bombard species being deposited from the plasma onto, and into, the
porous article.
[0068] The depth of the ion sheath normally ranges from
approximately 1 mm (or less) to 50 mm and depends on factors such
as the type and concentration of gas used, pressure in the chamber,
the spacing between the electrodes, and relative size of the
electrodes. For example, reduced pressures will increase the size
of the ion sheaths. When the electrodes are different sizes, a
larger (i.e., stronger) ion sheath will form adjacent to the
smaller electrode. Generally, the larger the difference in
electrode size, the larger the difference in the size of the ion
sheaths. Also, increasing the voltage across the ion sheath will
increase ion bombardment energy.
[0069] The article to be treated is placed on or near at least one
electrode in the reaction chamber. In the case of an elongated
article, the article optionally may be pulled through the vacuum
chamber continuously. Contact with an electrode does not need to be
maintained. The fluorine species within the plasma react on the
article's surface and interior. A suitable plasma could contain
fluorine and one or more of oxygen, carbon, sulfur, and hydrogen in
various combinations and ratios. The degree of fluorination of the
final article may be controlled by a number of factors, for
example, the components of the plasma, the length of treatment, and
the partial pressure of the plasma components. The plasma
fluorination results in species in the plasma becoming randomly
attached to the article surface (including interior surfaces) via
covalent bonds. The deposited fluorine composition may constitute a
full layer over the entire exposed article surface (including
interior surfaces), may be more sparsely distributed on the
article, or may be deposited as a pattern through a shadow
mask.
[0070] Sources of fluorine include compounds such as carbon
tetrafluoride (CF.sub.4), sulfur hexafluoride (SF.sub.6),
C.sub.2F.sub.6, C.sub.3F.sub.8, and isomeric forms of
C.sub.4F.sub.10 and C.sub.5F.sub.12, as well as hexafluoropropylene
(HFP) trimer (a mixture of perfluoro 2,3,5 trimethyl 3-hexene;
perfluoro 2,3,5-trimethyl 2-hexene; and perfluoro 2,4,5-trimethyl
2-hexene, available from 3M Company).
[0071] Other plasma fluorinations might include deposition of
amorphous films of containing fluorine such as aluminum fluoride,
copper fluoride, fluorinated silicon nitride, silicon oxyfluorides,
etc. Furthermore, these might include the attachment of additional
functional groups.
[0072] For treatments with carbon- or carbon-and-hydrogen-rich
plasma fluorinations, hydrocarbons are particularly preferred as
sources. Suitable hydrocarbon sources include acetylene, methane,
butadiene, benzene, methylcyclopentadiene, pentadiene, styrene,
naphthalene, and azulene. Mixtures of these hydrocarbons may also
be used. Another source of hydrogen is molecular hydrogen
(H.sub.2). Sources of oxygen include oxygen gas (O.sub.2), hydrogen
peroxide (H.sub.2O.sub.2), water (H.sub.2O), nitrous oxide
(N.sub.2O), and ozone (O.sub.3).
[0073] When treatment comprises deposition of a film, it typically
occurs at rates ranging from about 1 to 100 nm/second (about 10 to
1000 Angstrom per second (A/sec)), depending on conditions
including pressure, power, concentration of gas, types of gases,
relative size of electrodes, etc. In general, deposition rates
increase with increasing power, pressure, and concentration of gas,
but the rates will approach an upper limit.
[0074] The articles also may be treated in a manner to provide
different degrees of fluorination in different areas of the
article. This can be achieved, for example, by using contact masks
to selectively expose portions of the porous article to the plasma
fluorination. The mask may be attached to the article or may be a
separate web that moves with the article. By this method, it is
possible to obtain fluorinated areas on an article. The fluorinated
areas may be in any shape that can be achieved using a shadow mask,
e.g., circles, stripes, etc.
[0075] Articles having fluorination gradients may also be produced.
This can be achieved by exposing different areas of an article to
the plasma fluorination treatment for different lengths of
time.
[0076] In the foregoing description, certain terms have been used
for brevity, clarity, and understanding. No unnecessary limitations
are to be implied therefrom beyond the requirement of the prior art
because such terms are used for descriptive purposes and are
intended to be broadly construed. Moreover, the description and
illustration of the invention is by way of example, and the scope
of the invention is not limited to the exact details shown or
described.
EXAMPLES
[0077] This invention may be illustrated by way of the following
examples including the described test methods used to evaluate and
characterize the plasma fluorinated films produced in the
examples.
Plasma Reactor
[0078] A parallel-plate capacitively coupled plasma reactor
(commercially available as Model 2480 from PlasmaTherm of St.
Petersburg, Fla.), typically used for reactive ion etching, was
used to carry out plasma treatments. The reactor had a chamber that
was cylindrical in shape with an internal diameter of 762 mm (30
inches) and height of 150 mm (6 inches) and a circular powered
electrode having a diameter of 686 mm (27 inches) mounted inside
the chamber. The powered electrode was attached to a matching
network and a 3 kW RF power supply that was operated at a frequency
of 13.56 MHz. The chamber was vacuum pumped with a Roots blower
backed by a mechanical pump. Unless otherwise stated, the base
pressure in the chamber was about 1.3 Pa (10 mTorr) or less.
Process gases were metered into the chamber either through mass
flow controllers or a needle valve. Pressure was controlled
independently from flowrate by a butterfly valve. Unless otherwise
stated, all the plasma treatments were done with the sample located
on the powered electrode of the plasma reactor. The samples were
taped to the electrode or secured with a metal frame.
Hydrocharging
[0079] Some samples were hydrocharged before testing. Hydrocharging
can enhance filtration performance of an article by imparting a
permanent charge. Hydrocharging, as taught in U.S. Pat. No.
5,496,507, which is incorporated herein by reference, imparts a
permanent charge onto a media to enhance filtration. This method of
hydrocharging comprises impinging jets of water or a stream of
water droplets onto the sample at a pressure sufficient to provide
the sample with filtration enhancing electret charge. Samples were
placed on a mesh belt support and moved at a belt speed of
approximately 4 inches/second (10.2 cm/sec) through water jets
generated by a pump-assisted water sprayer operating at a water
pressure of 827 kPa (6206 Torr). The water jets were positioned
about 15 cm (6 in) above the belt. Water was simultaneously removed
from the sample by vacuum. Both sides of the samples were
treated.
[0080] The sample was then passed two additional times over a
vacuum to remove additional moisture and then allowed to air-dry
overnight before proceeding with testing.
Test Methods
DOP Penetration and Pressure Drop Test
[0081] Dioctyl phthalate (DOP) loading is a direct measurement of
the resistance of a filter medium to degradation due to exposure to
an oily mist aerosol. The penetration through, and the pressure
drop across, a sample were monitored during prolonged exposure of
the sample to a DOP aerosol under specified conditions. Standard
equipment and test procedures were used for measuring filter
performance.
[0082] The measurements were made using an automated filter tester
(AFT) Model 8130 available from TSI Incorporated, St. Paul, Minn.
that was set up with an oil aerosol generator. DOP % Penetration
was calculated automatically by the AFT instrument.
[0083] DOP % Penetration=100(DOP Conc. Downstream/DOP Conc.
Upstream), where the concentrations upstream and downstream were
measured by light scattering. The DOP aerosol generated by the AFT
instrument was nominally monodisperse with a mass median diameter
of 0.3 micrometers and had an upstream concentration of 85
mg/m.sup.3 to 110 mg/m.sup.3 as measured using a gravimetric
filter. Measurements were performed with the aerosol neutralizer
turned off and a flow rate through the sample of 42.5 liters per
minute (L/min), unless otherwise indicated.
[0084] Samples were tested in the following manner. Samples were
cut and mounted in a sample holder such that an 11.45 cm (4.5 inch)
diameter portion of the sample was exposed to the aerosol. The face
velocity was 6.9 centimeters/second (cm/sec). Each test was
continued until the exposure on the sample was exposed to 200 mg
DOP. The DOP % Penetration and corresponding Pressure Drop data
were determined by the AFT and transmitted to an attached computer
where the data was stored.
Quality Factor
[0085] Quality Factor (Q Factor) is a measurement of filtration
performance. It depends on the aerosol used, aerosol flow rate, and
filter area. The Quality Factor of a sample was calculated by the
following formula:
[0086] Quality Factor (Q)=-ln[% DOP Penetration/100]/Pressure Drop
where Q is in inverse mm H.sub.2O units and Pressure Drop is in mm
H.sub.2O units. Q Factors were reported for a DOP penetration
loading of 200 mg DOP (Q.sub.200) at a flow rate of 42.5 L/min and
a filter diameter of 11.4 cm resulting in a filter area of 103
cm.sup.2.
[0087] The higher the Q.sub.200, the better the filtration
performance.
Oil Repellency Test
[0088] Porous samples were evaluated for oil repellency using 3M
Oil Repellency Test III (February 1994), available from 3M. In this
test, samples were challenged to either penetration or
droplet-spread by oil or oil mixtures having varying surface
tensions. Oils and oil mixtures were given a rating corresponding
to the following:
TABLE-US-00001 Oil Repellency Surface Tension Rating Number Oil
Composition dynes/cm 0* -- -- 1 KAYDOL mineral oil 31 2 65/35 (vol)
mineral oil/n- 28 hexadecane 3 n-hexadecane 26.5 4 n-tetradecane
25.5 5 n-dodecane 24 6 n-decane 22 7 n-octane 20.5 8 n-heptane 18.5
*fails KAYDOL mineral oil
In running the Oil Repellency Test, a porous sample was placed on a
flat, horizontal surface. A small drop of oil composition was
gently placed on the sample. If, after ten seconds it was observed
that the drop was visible as a sphere or a hemisphere, the porous
sample is deemed to pass the test. The reported oil repellency
rating of the sample corresponds to the highest numbered oil or oil
mixture that was repelled.
[0089] It was desirable to have an oil repellency rating of at
least 1, preferably at least 3.
Fluorine Content
[0090] A sample size of about 1 to 3 mg was loaded into an Antek
9000F Fluoride Analysis System available from Antek Instruments,
Houston, Tex. The analysis was based on oxypyrohydrolysis followed
by final analysis with a fluoride ion specific electrode (ISE). The
carbon-fluorine bond was oxypyrohydrolyzed at 1050.degree. C. The
product hydrogen fluoride (HF) is trapped in a buffer solution. The
dissociated fluoride ions were measured with fluoride ISE at a
controlled temperature. The calibration curve was based on
standards prepared with FC-143 (C.sub.7F.sub.15CO.sub.2NH.sub.4) in
the range of 25 ppm fluorine to 1000 ppm fluorine at an injection
of from 10 to 15 .mu.L.
Example 1
[0091] This example illustrates the effect of the combination of an
ion sheath and electrode spacing on Quality Factor (Q-Factor).
[0092] A blown microfiber porous article was made from propylene
(available as EOD.sub.97-13 from ATOFINA Petrochemical, Houston,
Tex.) that was extruded at a temperature of 350.degree. C. and
blown horizontally onto a collector at a distance of about 300 mm
(12 in) from the extruder. The resulting porous article had an
effective fiber diameter 7.5 .mu.m as described in C. N. Davies,
"Air Filtration" Academic Press, 1973. It also had a solidity of
7.7%, a basis weight of 87.5 g/m.sup.2, an effective pore diameter
of 25 .mu.m, and a thickness of about 1.24 mm (49 mils). Web
thickness was measured according to ASTM D1777-64 using a 230 g
weight on a 10 cm diameter disk. In DOP Penetration testing at 42.5
L/min flow of DOP aerosol, the article exhibited a pressure drop of
40 Pa (300 mTorr).
[0093] The porous article was cut into rectangles of about 15
cm.times.30 cm used as samples A to R. The samples were treated on
the powered electrode in the Plasma Reactor with plasma formed from
perfluoropropane (C.sub.3F.sub.8) gas available from 3M Company and
with various electrode separation distances and process conditions
as shown in Table 1. The reactor chamber was pumped down to a base
pressure of less than 1.3 Pa (10 mTorr). C.sub.3F.sub.8 was
introduced into the chamber at a flow rate of 100 or 200 sccm.
Chamber pressure and radio frequency (RF) power were established. A
bright plasma was seen in the inter-electrode space and an ion
sheath, which was darker than the plasma, formed adjacent to the
powered electrode and encompassed the porous article. For each
sample the plasma treatment was continued for one minute. Then the
plasma was extinguished, the gas flow was stopped, the chamber
pressure brought down to below 1.3 Pa (10 mTorr), and the chamber
was vented to atmosphere. The sample was flipped over and the
treatment was repeated on the other side.
[0094] Samples were hydrocharged and measured for DOP penetration.
The DOP Penetration Test was run as described in the Test Method
section above except the flow rate was 85 L/min and the neutralizer
was on. Quality Factors, Q.sub.200, are reported in Table 1.
TABLE-US-00002 TABLE 1 Q.sub.200 Spacing Power Pressure Flow (at 85
Sample (mm) (W) (Pa) (sccm) L/min) 1-A 152 1500 37 100 0.398 1-B
152 1000 67 200 0.086 1-C 152 2000 67 200 0.120 1-D 152 1000 13 100
0.441 1-E 152 2000 13 100 0.335 1-F 152 1500 37 100 0.309 1-G 76
1500 37 100 0.358 1-H 76 1000 67 200 0.094 1-I 76 2000 67 200 0.124
1-J 76 1000 13 100 0.445 1-K 76 2000 13 100 0.422 1-L 76 1500 40
100 0.428 1-M 25 1500 37 100 0.574 1-N 25 1000 67 200 0.376 1-O 25
2000 67 200 0.556 1-P 25 1000 13 100 0.582 1-Q 25 2000 13 100 * 1-R
25 1500 40 100 0.570 * This condition did not run with a stable
plasma.
The benefit of reducing the electrode spacing was clearly seen in
the Q.sub.200 values shown above.
Example 2 and Comparative Example 1
[0095] This example illustrates the effect of reduced electrode
distance on Quality Factor at the standard test conditions (i.e.,
42 L/min and neutralizer off).
[0096] Example 2 was made as Example 1-D except a different
electrode distance, chamber pressure, and standard test conditions
were used as described herein. The electrode spacing was 0.625 in
(16 mm) and chamber pressure was at 6.7 Pa (50 mTorr). The sample
was exposed to the plasma for two minutes on each side. The sample
was measured for Oil Repellency. The Oil Repellency Rating was 5.
The sample was also hydrocharged and measured for DOP penetration.
Q.sub.200 for this sample was 1.53.
[0097] Comparative Example 1 was made as Example 2 (except the
electrode spacing was 76 mm). The sample was hydrocharged and
measured for DOP penetration. Q.sub.200 for this sample was
0.58.
[0098] The results show that decreasing the electrode spacing
provides improved Q.sub.200 qualities.
Example 3 and Comparative Example 2
[0099] This example illustrates the effect of plasma fluorination
within an ion sheath on the oil-repellency characteristics of a
porous article.
[0100] Example 3 was made as Example 1-D except a different
electrode distance, chamber pressure, and standard test conditions
were used as described herein. The electrode spacing was 0.625 in
(16 mm) and chamber pressure was at 16.6 Pa (125 mTorr). The sample
was exposed to the plasma for one minute on each side.
[0101] Comparative Example 2 was made in a manner similar to
Example 3 except the porous article was suspended in the plasma
between the powered electrode and the grounded electrode and about
8 mm from either electrode and thus outside the ion sheath. Because
a plasma existed on both sides of the suspended sample, the sample
did not have to be flipped over. Total treatment time was two
minutes.
[0102] Example 3 and Comparative Example 1 were measured for oil
repellency. The Oil Repellency Rating for Example 3 and Comparative
Example 1 were 5 and 4, respectively. The samples were also
hydrocharged and measured for DOP penetration. Quality Factors were
determined at different amounts of DOP penetration. The results are
shown in Table 2.
TABLE-US-00003 TABLE 2 DOP Quality Factor Penetration Example 3
Comp. Example 2 0 2.59 1.52 20 2.30 1.22 40 2.10 1.02 60 1.93 0.84
80 1.83 0.73 100 1.72 0.62 120 1.61 0.54 140 1.51 0.46 160 1.44
0.40 180 1.37 0.35 200 1.28 0.23
[0103] As seen in the above table, the Quality Factor at 200 mg of
DOP loading was 1.28 for Example 3. In contrast, the quality factor
of Comparative Example 2 was 0.23. The Q Factor results indicate
that plasma fluorination of a porous sample within an ion sheath
was more efficient than plasma fluorination outside an ion
sheath.
Example 4 and Comparative Example 3
[0104] This example illustrates the effect of exposure time and
electrode distance on a porous article treated outside of an ion
sheath.
[0105] Example 4 was made as Comparative Example 2 except the total
treatment time for the sample was 4 minutes. The resulting sample
had an Oil Repellency Rating of 4. The sample was hydrocharged and
measured for DOP Penetration. A Q.sub.200 value of 1.28 was
obtained.
[0106] Comparative Example 3 was made as Example 4. It was made
outside an ion sheath with an electrode spacing of 76 mm and for a
total treatment time of 4 minutes. The sample was hydrocharged and
measured for DOP penetration. A Q.sub.200 value of 0.48 was
obtained.
Example 5
[0107] This example illustrates the effect of plasma fluorination
on the oil-repellency of a porous membrane having small pores.
[0108] Example 5 was made as Example 1-D except the porous article
was different and electrode spacing and chamber pressure were
changed. The porous article was a microporous polyethylene membrane
made according to U.S. Pat. No. 4,539,256 Ex 8 except the film was
stretched to 6 times its original length in one direction. The
membrane had pore diameters of about 0.09 micrometer. The electrode
distance was about 16 mm (0.625 in) and the chamber pressure was 67
Pa (500 mTorr). The sample was exposed to the plasma for about one
minute on each side. The resulting treated sample had an Oil
Repellency Rating of 4. The Oil Repellency Rating of the untreated
sample was 0.
Example 6
[0109] This example illustrates the effect of short exposure times
on the oleophobicity of a porous article.
[0110] Example 6 was made as Example 1-D except the electrode
distance was 16 mm, the chamber pressure was 67 Pa (500 mTorr), the
total exposure times were less than 60 seconds, and the conditions
shown in Table 4 were used. The repellency rating of the untreated
sample was 0.
[0111] Both samples were tested for oil repellency and DOP
penetration. Results are shown in Table 3.
TABLE-US-00004 TABLE 3 Total Time Power Pressure Flow Repel. Sample
(sec) (W) (Pa) (sccm) Rating Q.sub.200 6-A 20 1000 67 100 5 1.17
6-B 10 1000 67 100 4 0.80
[0112] As shown above, Q.sub.200 was over 1.1 at treatment time of
20 seconds.
Example 7
[0113] This example shows the effect of treatment time and
proximity to an ion sheath on treatment effect.
[0114] The samples each consisted of a four-layer stack of the
polypropylene blown microfiber webs. Each layer was made from
polypropylene (available as EOD.sub.97-13 from ATOFINA
Petrochemical) that was extruded at a temperature of 330.degree. C.
with a collector distance of about 300 mm (12 in). The resulting
web had an effective fiber diameter of 7.0 .mu.m, pressure drop of
5.9 Pa (44 mTorr), a solidity of 4.7%, a basis weight of 15
g/m.sup.2 and thickness of about 340 .mu.m (13.5 mils). Each sample
stack was treated with a C.sub.3F.sub.8 plasma in a manner similar
to Example 1 but at various exposure times and with an electrode
separation distance of 16 mm (0.625 in). Two samples were made at
each of three different exposure times, 20 seconds, 120 seconds,
and 240 seconds. For each exposure time, one four-layer sample was
positioned on the lower, powered electrode (within an ion sheath)
and a second four-layer sample was simultaneously positioned
approximately midway between the powered and grounded electrodes
(outside an ion sheath), which were 16 mm apart. Both the samples
on the powered electrode and the suspended samples were flipped
over midway through the treatment. For all samples, the treatment
conditions were 100 sccm C.sub.3F.sub.8, 40 mPa (300 mTorr), and
1000 Watts applied RF power.
[0115] Each sample was analyzed for fluorine content in each of the
four layers. Exposure times, sample position during treatment, and
results are shown in Table 4.
TABLE-US-00005 TABLE 4 Total Fluorine Content in ppm time 1.sup.st
2.sup.nd 3.sup.rd 4.sup.th Sample (sec) Position Layer Layer Layer
layer 7-A 20 Suspended 45 Under 5 Under 5 17 7-B 20 electrode 3828
1249 847 2601 7-C 120 Suspended 70 41 40 137 7-D 120 electrode 9148
4732 3834 6872 7-E 240 Suspended 146 86 95 147 7-F 240 electrode
10475 5539 4826 7598
[0116] As seen in the above table, the concentration of fluorine in
each of the four layers of a sample was substantially more for the
samples within an ion sheath than for those outside the ion
sheath.
Example 8
[0117] This example illustrates the effect of a perforated
electrode on the plasma treatment.
[0118] Example 8 was made as Example 2 except the grounded
electrode had holes with diameters of 4.8 mm (0.188 inches) and
center-to-center spacings of 6.4 mm (0.250 inches), and the chamber
pressure was 67 Pa (500 mTorr). A bright plasma was seen everywhere
in the chamber including the regions on the side of the perforated
grounded electrode opposite the side facing the powered
electrode.
[0119] Example 8 was tested for oil repellency. The Oil Repellency
Rating was 5. This shows that a perforated electrode, which allowed
the plasma to fill the entire chamber more easily than with a
standard electrode, had no detrimental effect on the properties of
the resulting article.
Example 9 and Comparative Examples 4 and 5
[0120] This example illustrates the influence of electrode spacing
on the fluorination of porous and non-porous substrates at
comparable volumetric power densities.
[0121] Samples of Example 9 were made in a manner similar to that
of Example 1-D except the distance between electrodes was varied,
and conditions were changed as described herein. The fluorination
treatment was carried out for a treatment time of 10 seconds with
the C.sub.3F.sub.8 gas flow rate maintained at 100 sccm and the
chamber pressure maintained at 67 Pa (0.500 Torr). Samples A and B
were flipped over and additionally treated on the backside of the
article for another 10 seconds for a total exposure time of 20
seconds. RF power was adjusted to nominally maintain the same power
density per unit volume of space between the two electrodes for the
different electrode distances. The power density for Sample A was
0.171 W/cm.sup.3. The power density for Sample B was 0.179
W/cm.sup.3.
[0122] Comparative Examples 4 and 5 were made as in Sample A and B,
respectively, except the substrate for the Comparative Examples was
a 0.18 mm thick polycarbonate non-porous film and the Comparative
Examples were not flipped over during plasma treatment, so the
total exposure time was only 10 seconds on one side. The oil
repellency of the untreated non-porous films was 0.
[0123] Samples were tested for oil repellency. The varied process
conditions and results are shown in Table 5.
TABLE-US-00006 TABLE 5 Substrate Distance Time Power Repel. Sample
Type (mm) (sec) (W) Rating 9-A porous 16.0 20 1000 5 9-B porous
28.5 20 1900 2 CE-4 non-porous 16.0 10 1000 6 CE-5 non-porous 28.5
10 1900 6
[0124] As seen in Table 5, the results obtained for the porous
substrates were drastically different depending upon the electrode
spacing. The porous article made with an electrode spacing of 16 mm
withstood a No. 5 fluid in the Oil Repellency Test whereas the
porous article made with an electrode spacing of 28.5 mm withstood
only a No. 2 fluid. In contrast, non-porous samples were not
affected by the electrode spacing.
Example 10
[0125] In order to understand the effect of deposition rate of the
fluorocarbon on a porous sample, the treatment conditions used to
make Samples 9-A and 9-B were repeated on Samples 10-A and 10-B,
respectively. The substrates for samples 10-A and 10-B were pieces
of silicon over which a polystyrene film had been spin-coated.
Portions of the substrates were masked with tape to allow for
step-height measurements using a stylus profilometer available as
Alpha-Step 500 from Tencor Instruments, Mountainview, Calif. The
samples were not flipped over. Total exposure time was 120 seconds,
chamber pressure was 67 Pa (500 mTorr) and gas flow rate was 100
sccm. Power was varied as described above to maintain comparable
power densities.
[0126] Samples were tested for oil repellency. The process
conditions and deposition rate results are shown in Table 6.
TABLE-US-00007 TABLE 6 Time Power Distance Flow Deposition Sample
(sec) (W) (mm) (sccm) Rate (nm/s) 10-A 120 1000 16 100 2.16 10-B
120 1900 28 100 2.27
[0127] The measured deposition rate of 2.16 nanometers/second for
sample 10-A was nominally the same as the rate of 2.27
nanometers/second for sample 10-B. Thus the superior repellency
performance of Sample 9-A over Sample 9-B was not due to a higher
deposition rate and thicker film. This illustrates that the
superior article properties provided by the invention are not due
to depositing thicker fluorinated layers, but are due to more
efficient plasma fluorination of article interiors.
Example 11
[0128] This example illustrates the benefit of locating the porous
substrate on the powered electrode for short treatment times.
[0129] Samples for Example 11 were made as in Example 1-D except
the electrode separation distance was 16 mm (0.625 in) and some
process conditions were different as described herein. Sample A was
located on the powered electrode whereas sample B was located on
the grounded electrode. Both samples were secured to the electrode
with removable Scotch tape on the edges. Fluorination was done at a
chamber pressure of 67 Pa (500 mTorr) with a C.sub.3F.sub.8 flow
rate of 100 sccm, and RF power maintained at 1000 W. Both the
samples were treated for 10 seconds, then flipped over and treated
on the opposite side for another 10 seconds for a total treatment
time of 20 seconds.
[0130] The samples were tested for oil repellency and the results
are summarized in Table 7.
TABLE-US-00008 TABLE 7 Electrode Substrate Spacing Time Power
Repel. Sample Location (mm) (sec) (W) Rating 11-A Powered 16.0 20
1000 5 Electrode 11-B Grounded 16.0 20 1000 2 Electrode
[0131] As seen in the table, the oil repellency rating of the
sample located on the powered electrode was significantly better
than the sample located on the grounded electrode.
Example 12
[0132] This example demonstrates the efficacy of the fluorination
process when the electrode spacing is less than 12 mm (0.5 in).
Stable plasma operation is generally not possible with such a small
spacing. By operating the C.sub.3F.sub.8 plasma at a pressure of 67
Pa (500 mTorr) and power of 1000 Watts, a surprisingly stable
plasma was obtained even when the electrode spacing was as low as
6.3 mm (0.25 in). Samples for Example 12 were made as in Example
1-D except the electrode separation distance was 8.6 mm (0.340 in)
for sample 12-A and 6.3 mm (0.25 in) for samples 12-B and 12-C.
Fluorination was done at a chamber pressure of 67 Pa (500 mTorr)
with a C.sub.3F.sub.8 flow rate of 100 sccm, and RF power
maintained at 1000 W. Samples 12-A and 12-B were treated for 10
seconds, then flipped over and treated on the opposite side for
another 10 seconds for a total treatment time of 20 seconds. Sample
12-C was treated in the same manner using the same process
conditions but the treatment time was for 5 seconds per side, a
total treatment time of 10 seconds. The Oil Repellency Ratings of
these samples are summarized in Table 8.
TABLE-US-00009 TABLE 8 Electrode Substrate Spacing Time Power
Repel. Sample Location (mm) (sec) (W) Rating 12-A Powered 8.6 20
1000 5 Electrode 12-B Powered 6.3 20 1000 5 Electrode 12-C Powered
6.3 10 1000 5 Electrode
As can be seen from the data, the Repellency Rating is excellent
even when the treatment times are as small as 10 seconds.
Example 13
[0133] This example demonstrates the effect of treating a porous
article on the grounded electrode with a small electrode
spacing.
[0134] Samples of the web described in Example 1 were plasma
fluorinated at a C.sub.3F.sub.8 flow rate of 83 sccm, a chamber
pressure of 40 Pa (300 mTorr), RF power maintained at 1000 Watts,
and an electrode spacing of 16 mm. Sample 13-A was placed in the
ion sheath adjacent to the powered electrode while sample 13-B was
placed in the ion sheath adjacent to the grounded electrode. The
samples were hydrocharged and tested for DOP penetration using the
standard test method. Q.sub.200 for Example 13-A was 1.24.
Q.sub.200 for Example 13-B was 1.06.
[0135] Various modifications and alterations of this invention will
become apparent to those skilled in the art without departing from
the scope and spirit of this invention and it should be understood
that this invention is not to be unduly limited to the illustrative
embodiments set forth herein.
* * * * *