Note: Descriptions are shown in the official language in which they were submitted.
CA 0224~274 l998-08-lO
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~UNC~lONA~ EPOXY-8ILICONE COATINGS FOR PAPER
M~G~TN~ CLOTHING8 AND A METHOD OF CO~TING SAME
FIELD OF THE lNV~ lON
The present invention is directed to fabrics for
paper making machines that are rendered contamination
resistant by a durable coating that lasts the entire
life of the fabric, while not overly limiting the
permeability of the fabric.
BACRGROUND OF THE lNV~ lON
The modern papermaker employs a highly
sophisticated papermaking machine which is in essence
a device for removing water from the paper furnish.
The water is removed sequentially in three stages or
sections of the machine. In the first or forming
section, the furnish is deposited on a moving forming
fabric and water drained through the fabric to leave
a paper sheet or web having a solids content of about
18 to 25 percent by weight. The formed web is
carried into a press fabric section and passed
through one or more nip presses on a moving press
fabric to remove sufficient water to form a sheet
having a solids content of about 36 to 50 percent by
weight. This sheet is then transferred to the dryer
section of the papermaking machine where dryer
fabrics hold the paper sheet against hot, steam-
heated dryer cylinders to obtain about 92 to 96
percent solids content. The papermaking fabrics
employed on the papermaking machine must perform a
diverse range of functions, according to the position
on the machine, i.e., forming, press or dryer
section.
Forming fabrics used in the papermaking process
are a kind of papermaking fabric which are used in
the forming section of a papermaking machine.
Forming fabrics are generally constructed of
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synthetic yarns joined together, ordinarily by
weaving, in a fabric construction that is
characterized by a high degree of open spaces between
the intersecting yarns. Forming fabrics must
maintain a high degree of openness to insure that
they permit removal of water from the fiber slurry
deposited thereon.
Since water removal capability is a critical
function of the forming fabric, it is necessary to
insure that the fabric retains a high degree of
openness over its lifetime.
- However, the degree of openness of a fabric is
continually reduced during its life. In addition to
the fiber slurry, paper pulp ordinarily contains
additives such as filler clay, pitch, and polymeric
materials that clog the open spaces of the fabric.
The use of recycled fibers has introduced
considerable amounts of contaminants in the form of
inks, adhesives, tars, and polymeric materials, which
20 also clog the open spaces of the fabric. In addition,
forming fabric designs now include multilayer fabrics
that are more susceptible to contamination problems.
Accordingly, it is desirable to provide a fabric
which exhibits an improved degree of contamination
25 resistance. one proposed prior art solution is the
use of contamination resistant yarns in the
construction of the fabric. This has not proved to
be wholly satisfactory since the contamination
resistance provided by such yarns is short-lived
30 and/or ineffective. Another proposed solution calls
for coating or treating paper making fabrics in order
to improve resistance to contaminants. Again, this
method is not wholly successful because the
contamination resistance provided by the coating is
35 short-lived and/or ineffective.
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U.S. Patent nos. 5,207,873 and 5,395,868
describe papermaking fabrics claimed to have
permanent resistance to adhesion of contaminants.
The fabrics are coated with solutions having as their
5 primary components tetrafluoroethylene, urethane
copolymer and polyacrylamide. This coating has not
proven to be totally effective and/or permanent on
paper machine clothing.
One problem generally inherent to coatings or
treatments is that coatings per se are known to
reduce the permeability of a fabric, an undesired
result that inhibits water removal capabilities, the
primary function of a forming fabric. It is
therefore important that any coating applied to a
15 forming fabric reduce permeability as little as
possible.
S~MMARY OF THE lNv~h~lON
An object of the present invention is to provide
a fabric used in the forming, pressing, or drying
20 section of a paper making machine that exhibits an
improved resistance to contamination over the entire
life of the fabric. These fabrics are referred to as
papermachine clothings by those skilled in the art,
and the terms are generally interchangeable.
It is a further object of the invention to
provide a durable coating that lasts the entire life
of the fabric.
It is a further object of the invention to
provide a coating which does not significantly affect
30 the permeability of the fabric.
It is a further object of the present invention
to provide a coating for a fabric used in a
papermaking machine that achieves the aforementioned
objectives.
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The present invention is a coated fabric used in
a papermaking machine that has significantly enhanced
resistance to contamination which lasts over the
entire fabric lifetime. In another aspect, the
invention is a method of coating a fabric used in a
papermaking machine in order to enhance its
resistance to contamination. The coating
formulations disclosed herein have been shown to
substantially improve the contamination resistance of
a fabric while not significantly reducing the
permeability of the fabric, and not increasing the
mass of the fabric to any significant degree. That
is, the present invention provides a thin, low weight
coating for a papermachine clothings that adds
limited mass to the fabric.
The applicants have found that a coating
comprised of a silicon-epoxy resin will render a
paper machine clothing contamination resistant over
the entire fabric lifetime. Suitable silicon-epoxy
coatings include aqueous mixtures that contain
silicone epoxy resins. It is believed that the
silicone-epoxy resins bond with the polyester or
nylon filaments that form the clothing. A suitable
line of silicone-epoxy resin compositions are
available from Decora Industries, Fort Edward, New
York under the trade name Wearlon~. A preferred
formulation is Wearlon~ 2020-98, a three component
formulation of a resin containing a silicone-epoxy
based emulsion, a curing agent and a crosslinking
agent. The components are mixed in-situ in accordance
with the manufacturer's recommendations and applied
to the fabrics and can be further diluted as
necessary.
Effective contamination resistant fabrics have
been prepared where the fabric coating formulation
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contains 5% to about 50~ solids on a weight-weight
basis, with a mass add-on of 0.1 % to 10.0 % based on
the weight of the uncoated fabric. The % mass add on
is:
5 100 X (basis ~eiqht of a drY. coated fabric - basis ~eiqht of a drY uncoated fabric)
( basis ~eight of a dry uncoated fabric
As a general matter, a greater degree of the
original permeability of a coated fabric is retained
when the solids content of the coating or mass add on
of the coating is reduced. Water, a preferred
diluent for aqueous based coatings, may be used to
reduce solids content and consequently % mass add on.
It has been found that fabrics having coating
15 formulations of a solids content in the range of 10%
to 15 % (W/W) or a mass add on of 1% to 3% maintain
a high degree of their original permeability. That
is, on the order of about 90% - 99% of their original
permeability, which is preferred. In other words,
20 permeability is reduced only about 1% - 10% as a
result of the coating. The fabrics can be coated in
any conventional manner, including immersion within
a coating bath, blade or bar coating techniques,
squeegee coating, transfer coating, spray
application, kiss or applicator roll, slot
applicator, and brush applicator. Application with
a kiss roll has been effective. The coating can be
applied in a single pass, or it may be applied in
multiple passes. Subsequent processing requires
removing excess material and then drying or curing
the coating as directed by the manufacture of that
particular material. These methods are well known by
those skilled in the art.
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BRIEF DESCRIPTION OF THE DRAWINGS
Fig. l is a photograph of an uncoated section
of a contaminated fabric at 5X magnification.
Fig. 2 is a computer generated image of figure
1 with the fabric removed in order to show the
contaminants.
Fig. 3 is a photograph of the coated section of
a contaminated fabric at 5X magnification.
Fig. 4 is a computer generated image of figure
3 with the fabric removed in order to show
contaminants, if any.
DETAILED DESCRIPTION OF TRE ~K~r~:KRED EMBODIMENTS
The following examples illustrate the invention
and its applicability.
EXAMP~E 1
A triple layer forming fabric constructed of
polyester filaments was coated on part of, but not
all of its surface with a an aqueous solution of
WEARLON~ 2020-98 silicon-epoxy coating (49% solids
w/w) available from Decora Industries, Inc. of Fort
Edward, N.Y. The coating formulation was applied in
a single layer with a Binks #7 spray gun available
from Binks Mfg. Co. of Franklin Park, Illinois.
Excess liquid was removed with a vacuum. Mass add on
was determined as 8.3% based on the weight of the
uncoated fabric. Portions of the belt were not
coated in order to serve as a control.
The fabric was installed on a pilot machine and
run for 3 days. The machine was running pulp
consisting of 100% old corrugated container (OCC).
The speed of the machine ranged from 460-670 m/min
(1500-2200 ft/min). Needle showers were used at 13.8
bars (200 psi) with no cleaning chemicals. After the
trial, the fabric was removed and analyzed. The
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following figures relate to the appearance and
condition of the fabric after removal.
A contamination analysis was done on the
sections of the fabric. Figures 1 and 3 are
photographs taken at 5X magnification of each
section. The pictures were then scanned into the
computer with a gray color scale. The image was
converted to a bitmap file (* bmp file), and opened
in Microsoft Paintbrush (see Figs. 2 and 4), and the
contaminants were colored in blue. The gray fabric
was removed from the image leaving only the blue
portion. This image was then imported into an image
analysis program which counted the blue pixels and
found a % contaminated area. The results are listed
below:
8AMPLE % CONT~MTN~TED
1 Uncoated 4.1
2 Coated o. 3
All of the areas of the fabric that were coated
exhibited an increase in contamination resistance
over the areas of the fabric which were not coated.
EX~MPLE 2
Silicone epoxy coating formulations of WEARLON~
2020-98 were applied to fabrics at solids content
ranging from 5% to 25% (w/w). Three coats were
applied to a triple layer fabric via kiss roll
applicator. The compositions of the formulations are
provided in Table 1.
Three separate samples of the coated fabrics
were measured for air permeability and mass add on as
a result of coating and the average was taken. At a
coating formulation having 15% solids, mass add on of
the coating, when dry, was determined to be 11.18
g/m2, or 2.7 % based on the weight of the uncoated
fabric.
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The coatings were allowed to cure for a period
of one week. Three samples were cut from each of the
fabrics per given coating and subjected to high
pressure showering for a period of 8 hrs (oscillating
5 needle showers) under the conditions set forth below.
Data is presented in Tables 2 and 3. Mass, as
reported in Table 2, is the mass of a 2" diameter
sample taken from the fabrics.
HIGH PRESSURE SHOWER ~ NGS:
Fabric Tension = 39 PLI 6. 83 kN/m
Size of Fabric
Tested = 107" X 91l 272 cm x 22.9 cm
Fabric Speed
on Machine
= 1500 ft./min 457 m/min
Water Pressure
= 400 psig 27.6 bars
Shower Arm
= 150 strokes/min
20Nozzle were spaced 1" apart across the length of
the shower arm for uniform coverage.
Because of the demanding environment existing in
a high pressure shower test and its duration (in this
case, 400 psig for 8 hours), the test is a good
measure of coating durability.
Table 3 is based on the data of Table 2. Table
3 expresses the data of Table 2 in terms of the
changes in air permeability and mass add-on between
the uncoated fabrics and the coated fabrics exposed
to high pressure showering. Since the air
permeability and mass add on of the showered, coated
fabrics never return to the original levels of
uncoated fabrics, it is evident that the coatings
remain after exposure to the high pressure showering.
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TABLE 1
%Solids
25% 15% 10% 5%
Water(gal) 48.98 69.39 79.59 89.80
Part "A" (gal) 40.82 24.49 16.33 8.16
Part "X" (gal) 2.04 1.22 0.82 0.41
Part "B"(gal)8.16 4.90 3.27 1.63
Total 100.00 100.00 100.00 100.00
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TABLE 2
Belt % 801ids Before 8howered
Showering 1 Week
After Coating After Coating
0 Uncoated 544 544
7 5 532 529
523 526
3 15 519 521
- 1 25 512 525
10 Belt %~olids Before Showered
Showering 1 Week
After Coating After Coating
0 Uncoated 0. 840 0.840
7 5 0.847 0.844
15 5 10 0.850 0.846
3 15 0.863 0.856
1 25 0.876 0.854
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TABLE 3
Perm (% Decrease)
Belt % 801ids Before Showered
8howering 1 Week
After Coating After Coating
0 Uncoated --- ---
7 5 2.33% 2.82%
3.98% 3.37%
3 15 4.59% 4.35%
0 1 25 5.88% 3.49%
Mass (% increase)
Belt %801ids Before Showered
8howering 1 Week
After Coating After Coating
15 0 Uncoated --- ---
7 5 0.75% 0.44%
1.15% 0.71%
3 15 2.70% 1.90%
1 25 4.20% 1.59%
