STRUCTURES AND COMPONENTS THEREOF HAVING A DESIRED
SURFACE CHARACTERISTIC TOGETHER WITH METHODS AND
APPARATUSES FOR PRODUCING THE SAME
BACKGROUND OF THE INVENTION
Field Of The Invention
The present invention relates generally to structures and their components
which have been treated with equipment and techniques that produce modifications
to surface characteristics in either the structures or the components. More
particularly, the present invention relates to equipment and techniques for treating
substrates and components having commercial and industrial uses, particularly in
industrial fabrics. Most particularly, the invention relates to plasma treated
components and substrates together with equipment and techniques useful in treating
the same in an efficient and accurate manner.
The prior art has recognized the advantages to be obtained by plasma treating
and deposition techniques, at low pressure and at atmospheric pressure, to achieve
desirable characteristics in a product. Most generally, the products treated in the
prior art are single purpose products which were not intended to be exposed to a
working condition or an active environment where the treated product is subjected
to varying conditions over an extended time period. Furthermore, the prior art
products were not exposed to varied treatment over time in a work environment. For
example, industrial fabrics are frequently required to work under conditions of high
mechanical stress and hostile environments. Special applications, like papeimaking,
require industrial fabrics that generally work in hot, moist and chemically hostile
environments. As such, the fabric may be exposed to high water content in a
formation step, heat, pressure and relatively high water content in a pressing step, and
then, exposed to high temperatures in a drying step. Thus, the fabrics may see a
variety of conditions in the process. Industrial fabrics may also be exposed to varying
conditions in industries such as food processing, waste treatment, assembly line
processes or surface painting and treating techniques.
The art has recognized that it would be desirable to have substrates and
components with certain mechanical properties, such as strength, dimensional
stability, and flexibility over extended periods. While these characteristics are
desired as mechanical properties, it is sometimes desired to have surface properties
which are contrary to these mechanical properties. For instance, it may be desirable
to have a component which exhibits good internal resistance to moisture at its core
while having an external affinity for moisture at its surface. It is not uncommon to
have a conflict develop between the desired mechanical properties and the preferred
surface properties. The prior art has recognized and there have been attempts at
producing a mechanically robust core which supports a surface layer that has specific
characteristics for the desired application. It has been recognized that important
surface layer properties such as hydrophilicity, hydrophobicity, oleophilicity,
oleophobicity, conductivity, chemical resistance and abrasion resistance may not
necessarily be optimized in a single component which optimizes core properties such
as strength, flexibility, and the like.
The present invention addresses the shortcomings of the prior art by providing
structures and components which are treated with a highly efficient and controllable
plasma treatment. If desired, the structure or component may be further enhanced or
modified by exposure to a deposition treatment.
SUMMARY OF THE INVENTION
The present invention provides substrates and components having at least one
inherent surface characteristic thereof modified by equipment and techniques which
are particularly suitable for achieving that modification. The inherent surface
property may be modified by a plasma treatment process which comprises the steps
of providing a plasma treatment chamber which includes one or more hollow
cathodes for generating a plasma within the chamber. The chamber includes means
for focusing the generated plasma at the surface to be treated as it is introduced into
the chamber and reacted with the plasma.
DESCRIPTION OF THE DRAWINGS
Figure 1 is a side elevation of an apparatus in accordance with the invention
for use in treating large, continuous substrates.
Figures 2 through 5 depict individual portions of the apparatus of Figure 1
in more detail.
Figure 6 depicts an apparatus for treating an endless substrate, such as a
papermaking fabric, in accordance with the present invention.
Figure 7 illustrates depicts another variation of an apparauts for treating
industrial sized substrates, such as papermaking fabrics, with an accompanying
structural arrangement for supporting the apparatus.
Glossary
A component is a structural or modular element that is capable of producing
a structure when a plurality thereof are assembled together.
A fabric structure is formed by arranging individual strands in a pattern, such
as by weaving, braiding, or knitting.
A fiber is a basic element of a textile and is characterized by having a length
at least 100 times its diameter.
A filament is a continuous fiber of extremely long length.
A hollow cathode is an energy efficient chamber for generating a plasma.
An industrial fabric is one designed for a working function such as transport
devices in the form of a moving or conveying belt.
An inherent property or characteristic is one that exists prior to any treatment
by plasma or other means.
A monofilament is a single filament with or without twist.
A multifilament yarn is a yarn composed of more than one filament assembled
with or without twist.
A nonwoven structure is a substrate formed by mechanical, thermal, or
chemical means or a combination thereof without braiding, weaving, or knitting..
A plasma is a partially ionized gas; commonly ionized gases are argon, xenon,
helium, neon, oxygen, carbon dioxide, nitrogen, and mixtures thereof.
A strand is a filament, monofilament, multifilament, yarn, string, rope, wire,
or cable of suitable length, strength, or construction for a particular purpose.
A structure is an assemblage of a plurality of components.
A substrate is any structure, component, fabric, fiber, filament, multifilament,
monofilament, yarn, strand, extrudate, modular element, or other item presented for
plasma treatment or coating.
A web is an array of loosely entangled strands.
A yarn is a continuous strand of textile fibers, filaments, or material in a form
suitable for intertwining to form a textile structure.
A 100% solids solution is a fluid such as a monomer, combination of
monomers, or other coating material which includes no carriers or solvent.
A 100% solids bath is a tank filled with a fluid such as a monomer, which
includes no carriers or solvent.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The preferred embodiments will be described with reference to the drawing
Figures wherein like numerals indicate like elements throughout.
Plasma treatment to remove low molecular weight material or surface
impurities will preferably use readily available, inexpensive, environmentally benign
gases. In some applications, plasma treatment alone may be sufficient, however, it
can be followed by coating with metals, ceramics, or polymerizable compounds.
Preferred polymerizable compounds are radiation curable organic monomers
containing at least one double bond, preferably at least two double bonds, especially
alkene bonds. Acrylates are particularly well-suited monomers. Metals suitable for
deposition include, but are not limited to Al, Cu, Mg, and Ti. Ceramics suitable for
deposition include, but are not limited to, silicate-containing compounds, metal
oxides particularly aluminum oxide, magnesium oxide, zirconium oxide, beryllium
oxide, thorium oxides, graphite, ferrites, titanates, carbides, borides, suicides,
nitrides, and materials made therefrom. Multiple coatings comprising metal, ceramic
or radiation curable compound coatings are possible.
Plasma treatment leads to one or more of the following benefits: cleaning,
roughening, drying, or surface activation. Plasma treatment can also lead to chemical
alteration of a substrate by adding to a substrate or removing from a substrate,
functional groups, ions, electrons, or molecular fragment, possibly accompanied by
cross-linking.
All materials are of interest for plasma treatment or application of a secondary
coating. Those of primary interest are polymers, such as aramids, polyesters,
polyamides, polyimides, fluorocarbons, polyaryletherketones, polyphenylene sulfides,
polyolefins, acrylics, copolymers and physical blends or alloys thereof. Preferred
secondary layer coating thickness for polymers is in the range of 0.1 to 100 microns,
more preferably 20 to 100 microns, most preferably 20 to 40 microns. Preferred
metal or ceramic secondary layer coating thickness is in the range of 50 angstroms
to 5 microns, more preferably 100 to 1000 angstroms. A preferred polymer is an
acrylate of acrylic acid or its esters. The preferred acrylates have two or more double
bonds.
Monoacrylates have the general formula
O
II
Rl C - OR4
\ /
C=C (I)
/ \
R2 R3
Wherein R1, R2, R3, and R4 are H or an organic group.
Diacrylates are acrylates of formula I wherein either R1, R2, R3, or R4 is itself
an acrylate group. Organic groups are usually aliphatic, olefinic, alicyclic, or aryl
groups or mixtures thereof (e.g. aliphatic alicyclic). Preferred monoacrylates are those
where R1, R2 and R3 are H or methyl and R4 is a substituted alkyl or aryl group.
Preferred diacrylates have the formula
O O
II II
R1 C R4 C R7
\ / \ / \ / \ / C=C O O C=C (TJ)
/ \ / \
R2 R3 R5 R6 where R\ R2, R3, R5, R6, R7 are preferably H or methyl, most preferably H.
R4 is preferably C2-C20 alkyl, aryl, multialkyl, multiaryl, or multiglycolyl, most
preferably triethylene glycolyl or tripropylene glycolyl. The notation, C2-C20 alkyl,
indicates an alkyl group with 2 to 20 carbon atoms.
R4 in a mono- or multiacrylate is chosen to yield the desired surface properties after
the monomer has been radiation cured to form a surface on a substrate. (See Table
1)
TABLE 1
Formula I can also include triacrylate and other polyacrylate molecules.
Mixtures of diacrylates can be copolymerized, for example a 50:50 mix of two
structurally different diacrylates. Diacrylates can also be copolymerized with other
polymerizable components, such as unsaturated alcohols and esters, unsaturated
acids, unsaturated lower polyhydric alcohols, esters of unsaturated acids, vinyl cyclic
compounds, unsaturated ethers, unsaturated ketones, unsaturated aliphatic
hydrocarbons, unsaturated alkyl halides, unsaturated acid halides and unsaturated nitriles.
Diacrylates of interest also include 1,2-alkanediol diacrylate monomers of formula
O R2
R1CHCH2OC-C=CH2
I (in)
0-C-C=CH2
II I
O R2 where R1 is in an acrylate radical having about 8 to 28 carbon atoms and R2 is
hydrogen or methyl (See for example U.S. Patent 4,537,710).
The agent for promoting polymerization may be radiation, such as UV
radiation or electron beam radiation. In some instances, it may be preferred to use
a photoinitiator, such as an appropriate ketone.
The formulation Sigma-MM-2116 has been developed to impart
hydrophobic/oleophobic characteristics and is a solvent-free, acrylate based
monomer/oligomer mix which contains 50-95% perfluorinated monoacrylate with
fluorine content ranging from 30-64%. The formulation also contains 3-50% multi¬
functional, compatible crosslinking agents, e.g. di- and tri-acrylate monomers. Also
1-20% of an adhesion promoter was added to enhance diacrylate monomers
functionalized with hydroxyl, carboxyl, carbonyl, sulfonic, thiol, or arnino groups.
The high fluorine content lowers the surface energy of the cured coating and turns the
coated yarn into hydrophobic and oleophobic, Teflon-like, material. Combining the
plasma treatment of the surface of the substrate with the functionalization of the
coating with a specialty adhesion promoter formulation helps to achieve an excellent
adhesion between the coating and the substrate while keeping the energy low, making
the surface of the substrate both hydrophobic and oleophobic.
In addition to the formulation for hydrophobicity/oleophobicity, formulations
are also contemplated in applications for electrostatic dissipation and abrasion
resistance.
Figures 1 -7 illustrate apparatuses for treatment of a substrate, such as a fabric,
belt or web. The apparatus 100 consists of a series of opposed entry and exit vacuum
chambers 103 and 105, 107 and 109, 111 and 113, and 115 and 117 flanking
opposed treatment chambers, 120 and 121, 122 and 123, 124 and 125, 126 and 127,
128 and 129, and 130 and 131. The flanking vacuum chambers provide a vacuum
between 1 and 10 torr. The inner flanking vacuum chambers provide a higher degree
of vacuum in a range between 10"4 and 1 torr. The interior treatment chambers are
also under a vacuum. If desired, all of the chambers may be manifold connected and
the vacuum within each chamber controlled by a switching means . Plasma treatment
equipment may be located in the upper vacuum chambers or in the lower chambers
as desired. This makes it possible to treat only the upper surface 98, only the lower
surface 99 or both the upper and lower surfaces. As can be seen from Figure 1, the
treatment chambers are mounted on opposed rollers 140-169 which are in contact
with the substrate 97. The exterior rollers 140, 141, 160 and 161 for chambers 103,
105, 111 and 113 respectively are generally spaced apart by a distance which is less
than the fabric thickness. This causes an initial compression of the fabric and helps
to remove trapped air from the fabric. As the fabric enters a first chamber, it is
compressed between a first pair of large rollers, for instance 162 and 163, which
compress the fabric to almost its maximum density within the vacuum chamber. The
chamber support rollers 142, 143, 158 and 159 are set to this lower compressed
distance so as to retain the fabric in compression. The fabric may pass through an
additional pair of opposed rollers, such as 164 and 165, as it enters a second chamber
under greater vacuum. The fabric is then maintained in contact with rollers 144
through 157 at this compressed distance to retain as much vacuum as possible in the
treatment chamber(s). When the fabric reaches an exit position, it passes through a
first pair of rollers, such as 166 and 167, which are still at the lesser distance. The
fabric then passes through an additional pair of rollers, such as 158 and 159, after
which the fabric is permitted to begin relaxation before passing through the final
rollers 168, 169 and 160 and 161.
Figure 2 shows a representative upper chamber, 126 and a representative
lower chamber, 127, to illustrate one treatment arrangement. In Figure 2, upper
chamber 126 has the hollow cathodes arrays 36, and lower chamber 127 has focusing
magnets 50. The arrangement of Figure 2 will plasma treat only the upper surface
98 of a substrate 97 when it is relatively dense. For an open, less dense substrate, like
a web or open fabric, it may be possible to treat surfaces 98 and 99 at one time.
If desired, additional hollow cathode arrays 36 may be located in the adjacent
lower chamber and additional focusing magnets 50 may be located in the adjacent
upper chamber 126, to simultaneously treat upper surface 98 and lower surface 99.
Figure 2 does not show a gas feed connection for introducing gas to be ionized or
electrical connections linked to the cathodes as these connections will be known to
those skilled in the art as a matter of design choice.
Figure 3 shows a representative upper chamber 128 and a representative
lower chamber 129 in an arrangement for metal deposition. Lower chamber 129 has
resistively heated boats 171 and a supply of aluminum wire 173 on spool 175. As the
wire 173 contacts the resistively heated boats 171, the wire is vaporized. It then
condenses on the lower surface 99. Alternatively, one can create a ceramic coating
by introducing oxygen into chamber 129 to oxidize the aluminum and create
aluminum oxide (A1203).
Figure 4 shows a representative upper chamber 124 and a representative
lower chamber 125 for creating a monomer layer on surface 98. A monomer
vaporizer 180 creates a cloud of monomer vapor which will be deposited through
condensation on the upper surface 98. If desired, a vaporizer 180, shown in phantom
could be located as a mirror image in lower chamber 125.
Figure 5 shows a representative upper chamber 130 that has a bank 82 of UV
emitting lights that irradiate and cure the monomers on surface 98. Alternatively, the
radiation device can be one that emits an electron beam. If the substrate is treated on
both surfaces a second bank 190, as shown in phantom will be located in chamber
131.
Figure 6 illustrates a second apparatus for treatment of a substrate 97. The
substrate is wound around two cylinders 190 and 192 of a type commonly used in
finishing industrial fabrics. In this embodiment there are again multiple chambers
103, 107, 111, 115, 120, 122, 128, and 130 for various purposes as previously
described in connection with Figures 8 through 12. However, this configuration only
seeks to do single surface treatment at this location. In this embodiment, the original
fabric compression is achieved by an exterior roller 196 against roller 192. Assuming
a fabric moving from left to right as indicated by the arrow, the substrate 97 kept
compressed between rollers 160 and 192. A second large compression roller 166
acting against roller 192 is located in chamber 111. Once again the chamber support
rollers continue the compression of the substrate 97 against the opposed roller 192.
A similar arrangement is provided at the exit by rollers 162, 140, 194 and 192.
With reference to Figure 7, there is shown an illustrative embodiment of a
substrate treating apparatus which is particularly suitable for use with a papermaking
fabric. The apparatus 200 is shown as fragmented right portion thereof to recognize
the fact that such an apparatus may be required to be in excess of 10 meters (420
inches) wide. It is presently contemplated that the apparatus 200 would be mounted
in the fabric finishing area of the papermaking fabric manufacturing process. In such
an area, it is common to have a mounting block or foot 202 which moves in a track
or recess in a finishing apparatus. The mount 202 would preferably include a lifting
apparatus 204, such as a hydraulic cylinder to elevate the lower treatment array 206
to the desired height. The lower array 206 includes transverse rollers 208 and 210
which will contact the fabric when located in the desired position. In order to relieve
the strain on the elevation means 204, a support column 214 is provided with a
plurality of apertures 216 so that a pin may be inserted through an aperture 216 to
assist in maintaining a fixed position. The lower treatment array 206 may include a
plurality of treatment chambers within the area 212 or it may include a shielding
device which will assist in maintaining vacuum during treatment with the upper array
220. With respect to upper array 220, it includes a sleeve 222 which is dimensioned
to fit about the support 214. Sleeve 222 will assist in centering the upper array 220
so that the rollers 224 and 226 of upper array 220 will be opposed to the rollers 208
and 210 of the lower array 206. In areas where it is difficult to maintain opposed
roller alignment or positioning, it will be preferable to provide a sleeve for lower
array 206 so that support 214 may act as a centering device. The array 220 may
contain any of the previously described treatment chambers. At present, it is
contemplated that the array 220 will be raised by an overhead pragmatic crane to
allow location of a fabric between the array 206 and 220.
Example
Five samples of a papermaking press felt, of the type having a base fabric and
batt layers, were tightly mounted around a drum. Each sample was approximately 4
feet long and 12 inches wide. The drum was enclosed in a vacuum chamber, and all
samples were subjected to plasma treatment by rotating the drum for 30 minutes at
50 feet per minute (circumference speed) through a 10% argon/90% nitrogen mix
while exposed to 300 watts. After the plasma treatment, some samples were coated
with a surface deposition, by evaporation, of acrylate monomers followed by an
electron beam curing of the monomers. An acrylate monomer evaporator and an
electron beam gun were used to coat and cure the samples. One sample received a
post electron beam plasma treatment. Post plasma treatment was done in the same
manner as the initial preliminary plasma treatment.
TABLE 2
The samples and their treatment are summarized in Table 2. In Table 2 the
abbreviations are as follows: β-CEA is β-carboxyethyl acrylate, HDODA is
hexanediol diacrylate, AUC (RadCure Photomer 6210 from RadCure, a division of
UCB Chemical Co.) is aliphatic urethane acrylate oligomer, and AA is acrylated
amine oligomer (RadCure Ebecryl 7190 from RadCure).
The acrylate monomers in the evaporated mix are listed in the acrylate coating
column. The molar ratio of the monomers are shown in parentheses.
In the treatment column, "Plasma-Acrylate" indicates the sample underwent
plasma treatment followed by acrylate coating. "Plasma-Acrylate-PostAcrPlasma"
indicates the sample underwent plasma treatment, acrylate coating, and a second
plasma treatment.
AU five samples were tested for their ability to absorb water by placing a drop
of water on their surface layer and observing how quickly the drop was absorbed. All
five samples absorbed the water instantaneously upon contact whereas an untreated
control sample took several seconds to absorb the water.
TABLE 3
Four of the samples and the control were also tested for hydrophilicity using a version
of AATCC Test Method 118 modified to test for water repellency rather than oil
repellency. Test liquids #1 through #6, contain solutions of isopropanol and water
in ratios of (on a percentage by volume basis) 2:98, 5:95, 10:90, 20:80, 30:70 and
40:60 respectively. Beginning with the lowest number test liquid, drops were
carefully placed in several locations on the surface of the sample. If surface wetting
did not occur within 10 seconds, this was repeated with the next higher number liquid
until surface wetting occurred within 10 seconds (with the test liquid indicated in the
right hand column in Table 3). Results are shown in Table 3 (where "C" is the
untreated control). Test liquid #1 is the most waterlike and therefore hydrophilic.
Test liquid #6 is the least waterlike and therefore hydrophobic. The results show that
the treated samples are substantially more hydrophilic than the untreated control.
Hydrophilicity is desirable in papermaking press fabrics because hydrophilic fabrics
have low resistence to flow allowing water to pass right through.
The samples were also tested under impulse drying conditions (see TABLES
4 and 5). Each sample was first plasma treated and then coated with a particular
coating. Sample 1 was coated with β-Carboxyethyl Acrylate (BCEA)/Hexandiol
Diacrylate (HDODA). Sample 2 was coated with Aliphatic Urethane Acrylate
Oligomer / Acrylated Amine Oligomer / HDODA. Sample 3 was coated with
Hexandiol Diacrylate (HDODA). Sample 4 was plasma treated, acrylate coated with
β-CEA/ HDODA (50:50) and then plasma treated again. Sample 5 was plasma
treated without subsequent coating.
High temperature felt conditioning trials were then conducted on the Beloit
MTS ID (Impulse Drying) simulator. Trial conditions of pressure (500 psi average),
NRT (35msec), and temperature (400F) were kept constant during the tests. These
testing conditions were chosen to typify the severe conditions the felt must survive
without a sheet in the nip during Impulse Drying operations.
The MTS ID simulator screening trial is conducted under the same conditions
for each felt candidate. Beloit "G" upper platen was used as the hot surface. A de-
ionized water-cooled bottom platen was used during felt conditioning; this keeps the
felt wet and the bottom platen cool during testing. The felt is conditioned for 50,000
cycles; at 2 cycles per second, with paper samples impulse dried at various cycle
increments. The paper sample and felt are impulse dried between the Beloit "G"
platen and a grooved bottom platen. Furnish used for the paper testing was a 38 gsm
C-LWC made on XPM#3 on 2/6/95, #38993. The handsheet tests are conducted at
certain established intervals by hand-feeding a sheet between the felt and the hot
platen. During the test the sheet is free to stick to either the felt, hot platen, both, or
not to either. During handsheet tests, the felt is kept essentially dry before any
impulse. Each sample was evaluated as shown in Tables 4 and 5.
TABLE 4
Sample Baseline 1 2 3 4 5
Stabilization Temperature 282F 282F 27 IF 27 IF 27 IF 270F
Caliper Drop @ 50 psi 0.34 0.39 0.38 0.38 0.41 0.41
Caliper Drop @ 300 psi 0.29 0.29 0.29 0.29 0.30 0.30
Surface Roughness Drop 0.66 0.71 0.69 0.55 0.67 0.71
CFM (start) 60.00 52.00 67.00 67.00 63.00 62.00
CFM (end) 4.00 4.00 4.00 4.00 4.00 4.00
Wt. Loss After 50,000 cycles 0.01 0.01 0.01 0.01 0.01 0.01
Water absorbed from handsheet 0.29 0.49 0.38 0.33 0.32 0.39
Solids out -6.00 -8.00 -4.00 -4.00 -4.00 -4.00
Sticking Factor 1—3 3.00 3.00 3.00 3.00 3.00
TABLE 5
Definitions of terms used in Tables 4 and 5:
1) Stabilization temperature - the temperature the felt should reach without a
sheet in the nip.
2) Caliper drop - the percentage change in felt caliper during conditioning. A
Beloit C-Frame caliper-measuring apparatus was used to measure felt
thickness at 50 psi and at 300 psi.
3) Surface roughness - measurement of the caliper of a foil impression of the felt
surface.
4) CFM - air permeability measurement in CFM/ft2 using a portable Albany
permeability tester.
5) Water absorbed from handsheet - the amount of water being absorbed from
the handsheet during Impulse Drying. A weight decrease indicates that the
felt is densifying and is losing its dewatering capabilities.
6) Solids out - the average change of percent solids (ingoing solids was
controlled).
7) Sheet sticking factor - see Table 6
TABLE 6
Sheet sticking occurred in each of the fabrics, and may be due to any of a number of
factors unrelated to the plasma treatment. More importantly, none of the treated
samples showed signs of surface fusing as was seen in untreated fabrics. This result
is a positive indication that the plasma treatment altered the exterior surface
characteristics of the sample fabrics as intended.