Note: Descriptions are shown in the official language in which they were submitted.
CA 02151329 2005-08-O1
METHOD OF SEAM CLOSURE FOR SHEET TRANSFER AND OTHER PAPER
PROCESSING BELTS
Background of the invention
1. Field of the Invention
The present invention relates to a paper processing
belt used to carry out the transfer of a paper sheet
between sections, or between elements of a section, such
as the individual presses in a press section, of the
paper machine on which it is being manufactured, or to
carry the sheet into other processes. Specifically, the
present invention is a transfer belt which may be joined
into endless form during its installation on a paper
machine with a seam, and a method for closing the seam
region after the coated seamed transfer belt has been so
joined.
2. Description of the Prior Art
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21~132~
At present, the only commercially available
paper processing belt of this type is a transfer
belt . A transfer belt is designed both to carry a
paper sheet through a portion of a paper machine, so
as to eliminate open draws from the machine and to
release the sheet readily to another fabric or belt
at some desired point. By definition, an open draw
is one in which a paper sheet passes without support
from one component of a paper machine to another over
a distance which is greater than the length of the
cellulose fibers in the sheet and is susceptible to
breakage. The elimination of open draws removes a
major cause of unscheduled machine shut-down, the
breakage of the sheet at such a point where it is
temporarily unsupported by a felt or other sheet
carrier. When disturbances in the flow of paper
stock occur, the likelihood of such breakage is quite
strong where the unsupported sheet is being
transferred from one point to another within the
press section, or from the final press in the press
section to the dryer section. At such points, the
sheet usually is at least 50% water, and, as a
consequence is weak and readily broken. Clearly, the
presence of an open draw will place a limitation on
the maximum speed at which the paper machine may be
run.
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A successful sheet transfer belt must carry out
three critical functions on the paper machine: a) to
remove the paper sheet from a press fabric without
causing sheet instability problems; b) to cooperate with
a press fabric in one or more press nips to ensure
optimal dewatering and high quality of the paper sheet;
and c) to transfer the paper sheet in a closed draw from
one press in the press section to a sheet-receiving
fabric or belt in the next press, or presses, in the
press section, or to a dryer pick-up fabric in the dryer
section.
A sheet transfer belt which successfully carries out
these critical functions is shown in U.S. Pat. No.
5,298,124, entitled "Transfer Belt" and issued on Mar.
29, 1994. The transfer belt shown therein has a surface
topography characterized by a pressure-responsive,
recoverable degree of roughness, so that, when under
compression in a press nip, the degree of roughness will
decrease, thereby enabling a thin continuous water film
to be formed between the transfer belt and a paper sheet
to bond the paper sheet to the transfer belt upon exit
from the press nip. When the original degree of roughness
is recovered after exit from the nip, the paper sheet may
be released by the transfer belt, perhaps with
-3-
the assistance of a minimum amount of vacuum, to a
permeable fabric, such as a dryer pick-up fabric.
The sheet transfer belt shown in that patent
comprises a reinforcing base with a paper side and a
back side, and has a polymer coating, which includes
a balanced distribution having segments of at least
one polymer, on the paper side. The balanced
distribution takes the form of a polymeric matrix
which may include both hydrophobic and hydrophilic
polymer segments. The polymer coating may also
include a particulate filler. The reinforcing base
is designed to inhibit longitudinal and transverse
deformation of the transfer belt, and may be a woven
fabric, and further may be endless or seamable for
closing into endless form during installation on the
paper machine. In addition, the reinforcing base may
contain textile material, and may have one or more
fiber batt layers attached by needling onto its back
side. By textile material is meant fibers and
filaments of natural or synthetic origin, intended
for the manufacturing of textiles. The back side may
also be impregnated and/or coated with polymeric
material.
To date, such sheet transfer belts have been
produced for paper mills in endless form, that is,
having reinforcing bases either woven in endless form
4
215~32~
or joined into endless form prior to being coated
with the polymer material. The installation of an
endless transfer belt on a paper machine, however, is
a time-consuming and technically complicated
endeavor. It goes without saying that paper
production must temporarily cease while the transfer
belt installation, or replacement, proceeds. Because
the installation of an endless belt cannot be
accomplished by snaking or threading the belt through
and around the components of the paper machine, it
must be inserted from the side of the machine. This
necessarily is much more time- and labor-intensive
than the installation of an open-ended belt, as
machine components, such as press rolls, must be
supported while the transfer belt is slipped into the
spaces between them from the side. Needless to say,
the provision of a sheet transfer belt which may be
seamed on the machine would significantly reduce the
time and labor required to install, or replace, one
on a paper machine.
International Publication No. WO 93/17161,
disclosing International Application No.
PCT/SE93/00173, shows a joinable band comprising a
textile web which is provided from at least one side
and through at least part of its thickness with a
quantity of thermoplastic material. When heat-
5
CA 02151329 2005-08-O1
softened, the thermoplastic material will fill out the
fabric structure of the web at least partially. The edges
of respective ends of the band have joining eyelets,
which are formed in the textile web and which coact with
joining eyelets similarly formed in a meeting end of the
band so as to form a detachable join. In order to enable
the band to be fitted easily to a machine and to provide
the region of the band join with the same properties as
the remainder of the band, no plastic filler is applied
to the textile web joining means along a region whose
width extension calculated from end edge and inwardly of
the web corresponds at least to the extension of the
eyelets over that part which coacts with the eyelets of
the meeting web end.
The difficulty associated with the provision of an
open-ended, or seamable, transfer belt is the marking
likely to be left on the paper sheet by the seam region.
Because the sheet transfer belt carries a paper sheet
through a press nip, and is in direct contact with the
paper sheet therein, the slightest difference in caliper,
compressibility and surface hardness of the seam region
of the belt will leave a mark on the sheet.
Summary of the invention
Accordingly, the principal object of the present
invention is to provide a seamable sheet transfer belt,
and a method for making the same, wherein the seam region
thereof has properties substantially identical to those
of the remainder of the sheet transfer belt, so that the
seam region may not mark the paper sheet.
It is also an object of the present invention to
provide a seamable sheet transfer belt, so that the time
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and labor required to install or replace such a belt on a
paper machine may be reduced.
It is a further object of the present invention to
provide a seamable sheet transfer belt, so that existing
paper machines may be more readily modified, or adapted
to incorporate, the sheet transfer belt shown in U.S.
Pat. No. 5,298,124, whereby open draws may be eliminated
therefrom.
Therefore, in accordance with the present
invention, there is provided a method for closing a seam
in a polymeric-resin-coated paper-processing belt
comprising the steps of: providing an open-ended belt
comprising a pin-seamable, papermaker's fabric having
seaming loops at two widthwise edges and having a coating
of a first polymeric resin material thereon, said fabric
having been coated when temporarily joined in endless
form and the resin material subsequently cut at said seam
to enable the belt to be re-opened; installing said open-
ended belt on a paper machine; joining said belt into
endless form with a pintle by directing said pintle
through a passage defined when said seaming loops at said
two widthwise edges of said pin-seamable papermaker's
fabric are interdigitated with one another, whereby said
first polymeric resin material has a slit adjacent to
said seaming loops; and covering said seam on the
uncoated side of said belt with a seam area encapsulating
material, so that said seam has compression properties
substantially identical to those of the remainder of said
belt.
Also in accordance with the present invention,
there is provided a polymeric-resin-coated paper-
processing belt comprising: a pin-seamable papermaker's
fabric, said fabric having seaming loops formed by
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machine-direction yarns at two widthwise edges thereof
and being joined into an endless form having a paper side
and a non-paper side with a pintle directed through a
passage defined by the interdigitation of said seaming
loops, said pintle and seaming loops thereby constituting
a seam for said belt; a coating of a first polymeric
resin material on said paper side of said pin-seamable
papermaker's fabric, said coating having a slit at said
seam; and seam area encapsulating material covering said
seam on said non-paper side of said pin-seamable
papermaker's fabric.
Accordingly, the present invention comprises a
method for closing the seam area of a coated seamed belt
after it has been rejoined into endless form on a paper
machine. The objective of the invention is to totally
seal the seam while providing it with the same
compressive properties as the remainder of the belt under
normal nip loads. The sealing technique also distributes
the bending stress which would otherwise be concentrated
at the coating
7A
2I5132~
join line. This improves the flex fatigue resistance
of the join.
Briefly, in two methods, the prepared seam area
of the belt is filled from the non-paper side using
a foam of a polymeric material. If necessary, the
paper side of the belt may be filled using the same
or a different polymeric material, not necessarily a
foam. In one method, the foam compound is blown and
cured under contact pressure using a heating source
with platens and a suitable release medium. During
the heating operation, the foam compound expands and
fills all voids, including the coating join line.
After curing, the heater is removed and the coated
surface is finish ground, as necessary, to remove
flash. The foam chemistry and the geometry of the
heater platens determines the overall compressibility
of the seam area in the nip.
In another method, the polymeric material is
pre-foamed prior to its application to the seam area,
and is cured by heat as above.
In still other methods, the seam area may be
covered with a solid foam strip of polymeric resin
material, or with a fibrous strip of fibrous batt
material. Either of these may be attached to the
seam area with an adhesive.
8
~~5~.329
In yet another method, the base fabric of the
coated seamed belt may include multiple strand yarns
in its machine direction. During the preparation of
the seam, the multiple strand yarns may be cut and
arranged away from the paper side of the coated
seamed belt to form a fibrous filler underneath the
seam to replace batt missing from the seam region.
Following the seaming operation on the paper machine,
the multiple strand yarns may be held in position
using a spray adhesive, for example.
The coated belt may have a construction
whereby the seam loops may be positioned in the
center of the structure below the coating and above
a back layer, which may include a woven fabric, a
needled web of fibrous batt material, a polymeric
foam, a coating of a polymeric resin material or
other nonwoven structures, a material less
compressible than a needled web of fibrous batt
material, or any combination thereof.
Alternatively, the back layer may be completely
eliminated. The coated surface (paper side) would be
closed using a polymeric material, preferably one not
foamed, curable at room (ambient) temperature or,
more quickly, with the application of heat.
More specifically, the method of the present
invention for closing a seam in a polymeric-resin-
9
2~~~329
coated paper processing belt comprises joining a pin-
seamable papermaker's fabric into endless form with
a pintle, and coating the outer surface (paper side)
of the fabric with a polymeric resin material.
Following the curing of the polymeric resin material,
and optional surface finishing, the pintle is
removed, and the polymeric resin material cut over
the seam to leave the now-coated fabric in open-ended
form. The belt is then shipped to a paper mill where
it is rejoined into endless form with a pintle during
installation on a paper machine . The seam is then
covered on the uncoated side of the belt, that is, on
the inner surface (non-paper side) with a seam area
encapsulating material. The encapsulating material
may be a viscous paste comprising a polymeric
material and a blowing agent. The seam is then
gradually heated to a temperature at which the
blowing agent decomposes to release a gas, producing
a foam from the viscous paste. The foam fills the
voids in the seam, and may pass through the slit
formed when the coating material was cut. The seam
is then heated further to the curing temperature of
the foam. The curing may glue the slit closed, or it
may be glued closed with a separate material.
Alternatively, the encapsulating material may be
a pre-foamed polymeric material, wherein the
2~~~3~9
polymeric material is foamed prior to its application
to the seam area. The pre-foaming may be
accomplished through the use of a blowing agent which
decomposes at or near room temperature. A low-
s density filler, comprising expanded thermoplastic
microspheres, may be used instead of a blowing agent.
Once the pre-foamed polymeric material is applied to
the seam area, it is cured as above with the same
results.
Instead of a liquid encapsulating material, a
solid foam strip of a polymeric material or a fibrous
strip of fibrous batt material may be used as the
encapsulating material. In either case, the strip
may be secured to the seam region by an adhesive, and
the slit may be glued closed with a separate
material.
Alternatively, the base fabric of the coated
seamed belt may include multiple strand yarns in its
machine direction. The multiple strand yarns may be
cut and arranged on the underside of the seam to form
a fibrous filler there to replace missing batt
material. This fibrous filler may be held in
position using, for example, a spray adhesive.
The present invention also includes belts made
in accordance with the methods. While emphasis is
given in the discussion to follow, to the seaming of
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a sheet transfer belt, the invention may also be applied
to the seaming of a long nip press (LNP) belt or of any
other polymer coated belt for the paper industry.
The present invention enables those skilled in the
paper machine clothing arts to control seam
compressibility to eliminate, or, at least, to minimize,
sheet marking in the nip. A further advantage of the
present invention is that distribution of the foam on the
underside of the belt in the seam area reduces the stress
forces at the coating join. Finally, sealing the coating
join may prevent water penetration and possible premature
failure of the belt due to coating delamination. It can
also reduce sheet marking caused by the join line of the
coating.
The present invention will now be described in more
complete detail with reference frequently being made to
the figures identified as set forth below.
Brief description of the drawings
FIG. 1 shows a representative press arrangement
including a transfer belt for eliminating an open draw in
a paper machine, showing an example of a press
arrangement in which the present invention can be used.
FIG. 2 shows a cross-sectional view of a polymeric-
resin-coated paper processing belt according to a
preferred embodiment of the present invention at a point
during its manufacture.
12
~.._
Figure 3 shows a cross-sectional view of the
polymeric-resin-coated paper processing belt at a
subsequent point during its manufacture.
Figure 4 illustrates a method by which the seam
may be closed following the installation of the
polymeric-resin-coated paper processing belt on a
paper machine and is a cross-sectional view of the
belt at that time.
Figure 5 shows a plan view of a seam region of
a transfer belt being closed according to an
alternate embodiment of the present invention.
Figure 6 is a side cross-sectional view taken as
indicated by line 6-6' in Figure 5.
Figure 7 illustrates an alternate method for
closing the seam.
Figure 8 illustrates yet another method by which
the seam may be closed.
Figure 9 shows still another method for closing
the seam.
Figure 10 shows a variation of the method shown
in Figure 9.
Detailed Description of the Preferred Embodiment
A representative press arrangement which
includes a transfer belt for eliminating an open draw
in a paper machine is shown, for purposes of
13
2~~~ ~~
illustration and general background, in Figure 1.
The arrows in Figure 1 indicate the directions of
motion or rotation of the elements shown therein.
In Figure 1, a paper sheet 10, represented by a
dashed line, is being carried toward the right
initially on the underside of a pick-up fabric 12,
which pick-up fabric 12 has previously taken the
paper sheet 10 from a forming fabric, not shown.
The paper sheet 10 and pick-up fabric 12 proceed
toward a first vacuum transfer roll 14, around which
is trained and directed a press fabric 16. There,
suction from within first vacuum transfer roll 14
removes paper sheet 10 from pick-up fabric 12 and
draws it onto press fabric 16. Pick-up fabric 12
then proceeds from this transfer point, toward and
around a first guide roll 18, and back, by means of
additional guide rolls not shown, to the point where
it may again receive the paper sheet 10 from a
forming fabric.
Paper sheet 10 then proceeds, carried by press
fabric 16, toward a press nip 20 formed between a
first press roll 22 and a second press roll 24.
Second press roll 24 may be grooved, as suggested by
the dashed line within the circle representing it in
Figure 1, to provide a receptacle for water removed
in the press nip 20 from the paper sheet 10. A
14
~~~~ l~~
transfer belt 26 is trained around first press roll
22, and is directed through press nip 20 with paper
sheet 10 and press fabric 16. In the press nip 20,
the paper sheet 10 is compressed between the press
fabric 16 and the transfer belt 26.
On exiting press nip 20, paper sheet 10 adheres
to the surface of the transfer belt 26, whose surface
is smoother than that of the press fabric 16.
Proceeding toward the right in the figure from press
nip 20, paper sheet 10 and transfer belt 26 approach
a second vacuum transfer roll 28. Press fabric 16 is
directed by means of second guide roll 30, third
guide roll 32 and fourth guide roll 34, back to first
vacuum transfer roll 14, where it may again receive
paper sheet 10 from pick-up fabric 12.
At second vacuum transfer roll 28, paper sheet
10 is transferred to a dryer fabric 36, which is
trained and directed thereabout. Dryer fabric 36
carries paper sheet 10 toward the first dryer
cylinder 38 of the dryer section.
The transfer belt 26 proceeds onward to the
right in the figure away from second vacuum transfer
roll 28 to a fifth guide roll 40, around which it is
directed to a sixth guide roll 42, a seventh guide
roll 44, an eighth guide roll 46, and a ninth guide
roll 48, which eventually return it to the first
press roll 22 and to the press nip 20, where it may
again accept the paper sheet 10 from the press fabric
16.
As may be observed in Figure 1, the transfer
belt 26 also eliminates open draws in the press
arrangement shown, most particularly, the open draw
often present where the paper sheet 10 is transferred
from the press fabric 16 to the dryer fabric 36.
Paper sheet 10 is supported at all points in its
passage through the press arrangement shown in Figure
1 by a carrier. In addition, it should be noted that
the paper sheet 10 is carried on the underside of the
transfer belt 26 upon exiting from the press nip 20,
because the water film on the transfer belt 26 is
strong enough to hold the paper sheet 10.
To produce the seamed transfer belt of the
present invention, one starts by obtaining a coating
base of the OMS (on-machine-seamable) variety, and by
temporarily joining it into endless form, the inner
surface of the endless loop so formed being the non-
paper side of the transfer belt. A view of the seam
region of such a press fabric is included in Figure
2.
Referring specifically to Figure 2, the seam
region 50 of the seamed OMS coating base 52 comprises
seaming loops 54, formed by machine-direction yarns
16
56 at the widthwise edges of the open-ended press
fabric 52. When such a coating base 52 is to be
closed into endless form, the two ends are brought
together, the seaming loops 54 at the ends are
interdigitated with one another to form a passage 58,
and a pintle 60 is directed through the passage 58 to
interlock seaming loops 54 together. The pintle 60
may be a coarse monofilament as shown in Figure 2.
Alternatively, pintle 60 may be a multifilament
pintle or a plied monofilament pintle.
Figure 2 shows one type of coating base 52 that
may be used. This coating base 52 includes cross-
machine direction yarns 62 and fibrous batt material
64 needled into the base fabric 66 formed by the
interwoven machine-direction yarns 56 and cross-
machine direction yarns 62. Alternatively, instead
of or along with fibrous batt material 64, the back
layer of the coating base 52 may include a woven
fabric, a polymeric foam, a coating of a polymeric
resin material, either the same as or different from
that used on the paper side of the coating base 52,
or other nonwoven structures, a material less
compressible than a needled web of fibrous batt
material, or any combination thereof. The use of a
material less compressible than a needled web of
fibrous batt material is an alternative to making the
17
w 2i5~.~~~
seam more compressible to achieve similar properties
between the seam area and the remainder of the sheet
transfer belt.
Alternatively, the back layer may be completely
eliminated. The coated surface (paper side) would in
such a case be closed using a polymeric material,
preferably one not foamed, which may be curable at
room (ambient) temperature or, more quickly, with the
application of heat, when the coated seamed belt is
installed on the paper machine.
As noted above, the coating base 52 is
temporarily joined into endless form, the outer
surface of the endless loop so formed being the paper
side of the transfer belt, on a suitable apparatus at
the production facility, such that it may be placed
under an amount of longitudinal tension analogous to
that which it supports when running on a paper
machine.
In such a condition, the outside of the closed
loop formed by the coating base 52 is coated with
polymer coating 68, which includes a balanced
distribution with segments of at least one polymer,
forming a polymeric matrix which may include both
hydrophobic and hydrophilic polymer segments. The
polymer coating 68 may also include a particulate
filler 70, as disclosed in U.S. Patent No. 5,298,124.
18
'~ 2~~~~~~
The coating 68 is then cured and subsequently
ground to provide the transfer belt 72, including
seam region 50, with uniform thickness and with a
desired surface topography.
At this point, the transfer belt 72 may be
inverted (turned inside-out) if its length and width
permit this to be done without causing any damage
thereto. Alternatively, the operation to be
described next may be carried out from within the
closed loop formed by the transfer belt 72, so long
as means for disposing the worker to carry out the
operation therewithin without damaging the transfer
belt 72 are provided.
In either case, the pintle 60 is removed, and
the transfer belt 72 folded at the seam region 50 as
shown in Figure 3. That is to say, the transfer belt
72 is folded in such a manner that the coating 68 is
on the inside of the fold. The act of folding
removes the seaming loops 54 from their
interdigitated state, and brings them into a
configuration that may be described as two spaced
parallel rows of upstanding seaming loops 54.
Between the two parallel rows is a portion 74 of the
coating 68. That portion 74 is cut by running a
sharp implement between the two parallel rows of
seaming loops 54 to return the transfer belt 72 to
19
open-ended form, without cutting any of the seaming
loops 54.
In this open-ended form, the transfer belt 72 is
packaged, and shipped to a paper mill for
installation in the paper machine, such as that
illustrated in Figure 1, in the same manner as an OMS
press fabric may be installed. It will be recalled
that in Figure 1, the transfer belt was identified
with reference numeral 26.
Referring back to Figure 1, the seamable
transfer belt 72 is installed on the paper machine
instead of endless transfer belt 26 with the polymer
coating 68 facing outwardly. A yarn more pliable
than coarse monofilament pintle 60 may be used as the
final pintle. It now remains to ensure that the seam
region 50, and, specifically, that portion 74 of the
polymer coating 68 which was cut to make the transfer
belt 72 open-ended, does not mark the paper sheet 10
being manufactured on the paper machine.
With reference to Figure 4, the seam region 50
of seamable transfer belt 72 appears as shown therein
when a pintle 76 is used to rejoin it into endless
form on a paper machine. A slit 78 remains in the
polymer coating 68 more or less directly over the
seaming loops 54, and, less seriously, a break 80
remains in the fibrous batt material 64 directly
2~~~3~~
below the seaming loops 54. The loop/pintle
combination makes the seam region 50 slightly
different from the rest of the seamable transfer belt
72, and raises the possibility that the seam region
50 might mark a paper sheet with which it comes into
contact.
Pintle 76 may be a coarse monofilament pintle,
a multifilament pintle, a plied multifilament pintle,
a plied monofilament pintle, or a composite pintle
including any of these varieties of pintle.
A foam produced by mixing a fluid polymeric
resin material with a blowing agent to form a viscous
paste, and by subsequently heating and curing the
viscous paste, is used to fill and to cement the seam
region 50 and slit 78. A solvent-free urethane
composition, such as Adiprene L-100 from Uniroyal, or
one based on a polyether-type prepolymer, may be used
for this purpose. The following is an example of a
solvent-free urethane composition that may be used
for this purpose.
21
2~5~.~2~
Component Weiaht (%)
Polyether/TDI polyurethane
prepolymer (4.1% NCO) 76.9
Blocked aromatic amine
(equivalent weight - 217) 15.4
Endothermic nucleating agent
(blowing agent) 7.7
Other components such as fillers, plasticizers,
and catalysts may be added as needed. The blowing
agent, typically a solid particulate material which
decomposes to release a gas almost instantaneously
when heated to a characteristic temperature, is mixed
with the liquid polymeric resin material. The
temperature at which the blowing agent activates is
typically less than the temperature at which the
polymeric resin material cures. For example, the
temperature at which the blowing agent decomposes (or
blows) may be 115°C, while the temperature at which
the polymeric resin material cures may be 130°C,
which is the relevant temperature for Adiprene L-100.
The blowing agent causes the viscous paste to foam
and to expand, filling voids in the seam region 50,
and may even pass through the slit 78. In such a
manner, the slit 78 may be glued together, and the
seam region 50 may be left with the same
compressibility and caliper as the rest of the
transfer belt 72.
22
~~~~.~29
The viscous paste producing foam 82 is
preferably applied first to the non-paper side, or
inside, of the seam region 50 of the transfer belt 72
at a point on the paper machine affording ready
access to paper mill personnel. For example, the
area adjacent to seventh guide roll 44 included in
Figure 1 may afford such ready access. The viscosity
of the viscous paste producing foam 82 is preferably
adjusted, so that it may be easy to apply regardless
of the orientation (horizontal, vertical, upside-
down, etc.) of the surface to be coated.
Preferably, the viscous paste may be applied to
the seam region 50 of the non paper side of the
transfer belt 72 for a distance, such as 0.25 inch
(0.64 cm), on both sides of the seam, so that the
bending stress may be distributed across the seam
region 50, rather than concentrated in one place,
such as slit 78.
Once the seam region 50 on the non-paper side of
the seamable transfer belt 72 has been covered with
the viscous paste, it may be covered with a material
84 to which the cured foam 82 (obtained from the
viscous paste) does not stick, such as heat-resistant
release paper, teflon-coated fiberglass tape, and
other materials.
23
2~.~~3~9
The paper-side surface of the seam region 50 of
the seamable transfer belt 72 may also be coated with
the viscous paste which produces foam 82, or may
optionally be coated with another polymeric coating
material, such as that used to provide coating 68, to
fill in any cracks in the slit 78. Similarly, once
the seam region 50 on the paper side of the seamable
transfer belt 72 has been coated in either manner, it
may be covered with a material 84 to which the cured
foam 82 (obtained from the viscous paste) or other
polymeric coating material does not stick.
A heat source may be used to foam the viscous
paste and to cure the foam 82. For example, heat
strips 86 may be fashioned from blocks of aluminum
having a nominally 0.5 inch thickness, and a width
sufficient to completely span the seam region 50 in
the belt-running direction. The heat strips 86
include a heating element by which they may be
brought gradually from ambient temperature up to and
above the temperature at which the foam cures.
The two heat strips 86 are pressed against the
two sides of the seam region 50, so that the caliper
of the seam region 50 may be the same as that of the
rest of the transfer belt 72. In such position, the
heat strips 86 are allowed to rise in temperature
from ambient to the blowing temperature, at which the
24
21513~~
blowing agent included in the viscous paste
decomposes and blows the paste, forcing it into voids
in the seam region 50. The heating of the heat
strips 86 continues above this blowing temperature to
the curing temperature of the polymeric resin
material, which may cure almost instantaneously at
that temperature. Preferably, the curing temperature
is maintained for a time sufficient to ensure that
the curing process is completed.
Instead of using two heat strips 86 as described
above, a heated sled 100 may be pulled across the
seam region 50. Referring to Figure 5, heated sled
100 is drawn across the width of the transfer belt 72
following the seam region 50 at a rate such that the
blowing agent included in the viscous paste
decomposes and blows the paste, forcing it into voids
in the seam region 50; and the curing temperature of
the polymeric resin is reached and maintained for a
time sufficient to ensure that the curing process is
completed. Preferably, the underside of the seam
region 50 is supported during this process, so that
the heated sled 100 may compress the seam region 50,
and ensure that the caliper of the seam region 50 may
be the same as the rest of the transfer belt 72.
Figure 6 is a side cross-sectional view taken as
indicated by line 6-6' in Figure 5. Heated sled 100
2~.~~3~9
is drawn across the transfer belt 72 following the
seam region 50 by cable 102. Support 104 may be
placed beneath the seam region 50 so that heated sled
100 may compress the seam region 50 thereagainst,
although tension on the transfer belt 72 could
provide adequate support for the sled 100.
A viscous paste with a very long pot life at
room temperature may be used, so that one could work
step-by-step across a seam in the case where the seam
is not exactly transverse across the belt . A long
pot life implies that the paste material may be kept
for a long time without its properties changing. If
the paste material has a long pot life, the heat
strips 86 need not be as wide as the transfer belt
72, and, as stated above, one could work step-by-step
across the seam, such as by using heated sled 100, to
seal it in the manner of the present invention.
After curing, any material 84 applied to the
non-paper side and/or paper side of the seam region
50 is removed, and the transfer belt 72 may be moved
so that the seam region 50 is on a roll, such as
seventh guide roll 44 in Figure 1. There, the
surface of polymeric coating 68 may be smoothed by
light sanding to remove any seam filling material
protruding from the seam area.
26
2~~i~29
The slit 78 may alternatively be glued with a
separate material. The following is an example of a
formulation that may be used as the separate
material:
Component Weictht (%)
Polyether/TDI polyurethane
prepolymer (4.1% NCO) 76.9
Blocked aromatic amine
(equivalent weight - 217) 15.4
Kaolin clay 7.7
As an alternative to the use of a viscous paste
obtained by mixing a fluid polymeric resin material
with a blowing agent described above, and the
subsequent production of a foam 82 therefrom
following the application of the viscous paste to the
seam region 50, a pre-foamed fluid polymeric resin
material could be used instead of the viscous paste.
By "pre-foamed" is meant that the foaming is done
prior to the application of the material to the seam
region 50. This could be accomplished through the
use of an endothermic nucleating agent (blowing
agent) which decomposes at or near room temperature.
These are readily available and well-known to those
of ordinary skill in the art.
Instead of such a blowing agent, a low-density
filler could be substituted therefor in the example
of the solvent-free urethane composition used to fill
27
215139
the seam region 50 set forth above. A specific low-
density filler takes the form of a thermoplastic
microsphere containing a hydrocarbon liquid. These
microspheres are expanded by heating and remain in an
expanded state when cooled. Even following
expansion, they remain quite small - on the order of
a micron in diameter - and of extremely low density.
The use of this variety of low-density filler permits
the practitioner to control the density of the foam
to be applied to the seam region accurately. That is
to say, microspheres could be gradually added to the
mixture until a desired density level is reached. An
example of such a low-density filler is Expancel DE
551, which product consists of pre-expanded
thermoplastic hollow microspheres that are added to
"pre-foam" the polymeric material used to cover the
seam.
As a further alternative, a solid foam strip 88
may be applied over the seam region 50, as shown in
Figure 7. The solid foam strip 88 may be
manufactured from the so-called "pre-foamed" fluid
polymeric resin material described above, or from the
fluid polymeric resin material including the low-
density filler (microspheres). The solid foam strip
88 may be either thermoplastic or thermosetting
depending on the manner in which the curing agent
28
215329
included in the fluid polymeric resin material
interacts with the end groups in the polymer chains.
Where the strip 88 is thermoplastic, it may be
secured to the seam region 50 by a heat source, such
a heat strip 86. Alternatively, it may be secured
thereto by an adhesive, such as that set forth above
for securing the slit 78, which may be pre-applied to
the strip 88. Where the strip 88 is thermosetting,
it would be secured to the seam region 50 by an
adhesive, such as that set forth above for securing
the slit 78. Finally, whether thermoplastic or
thermosetting, strip 88 may be provided with a heat-
activated adhesive for attachment to seam region 50.
An example of a heat-activated adhesive that could be
used for this purpose is a thermoplastic polyurethane
(e:g. Estane resin) applied as a solvent cement and
dried.
As yet another alternative, shown in Figure 8,
a fibrous strip 90 of fibrous batt material may be
secured over the seam region 50 instead of a solid
foam strip 88. The adhesive may be that set forth
above for securing the slit 78.
In each of these alternative approaches the slit
78 may be glued with a separate material, such as
that given above by example. The glue formation may
be applied to slit 78 prior to the application of any
29
~~~132~
fluid polymeric resin material 82, pre-foamed solid
strip 88, or fibrous strip 90 to the seam region 50
on the non-paper side of the belt.
A further alternative is illustrated in Figures
9 and 10. In both of these figures multiple strand
yarns are oriented in the machine direction of the
base fabric 66. The multiple strand yarns may be
multifilament, spun staple or textured filament yarns.
It will be noted that there is a gap 106 in the
fibrous batt material 64 at the seam region 50. In
the preparation. of the seam region 50, the multiple
strand yarns 108 are cut and arranged away from the
polymer coating 68 to form a fibrous filler
underneath the seaming loops 54 to replace the
fibrous batt material 64 missing from gap 106. The
multiple strand yarns 108 may come from one or both
sides of the seam region 50 as shown in Figures 9 and
10. Preferably, the multiple strand yarns 108 are
incorporated into the base fabric 66 during the
weaving process, but they may also be inserted after
weaving with a needle, as, for example, in a tufting
process.
After assembly on the paper machine, the
multiple strand yarns 108 can be held in place using,
for example, a spray adhesive, such as a commercially
available acrylic aerosol adhesive. Slit 78 in the
polymer coating 78 may be closed using a polymeric
material and preferably one which has not been
foamed. A polymeric material curable at room
(ambient) temperature may be used for this purpose,
as well as one whose curing may be accelerated by
heating.
In all of the previously described embodiments
of the present invention, non-foaming polymeric
materials cured not by heat or ambient temperature,
but by ultraviolet light and by other means known to
those having ordinary skill in the art may be used.
It should be understood that the object of each
of these alternatives is basically to encapsulate a
looped seam, and to provide the encapsulated seam
with the compression properties of the remainder of
the belt. The method chosen in any given situation
will be that which plant personnel will be able to
carry out in the shortest time, thereby minimizing
the time the papermachine will be down, and not in
use for manufacturing paper.
Modifications to the above would be obvious to
those skilled in the art, and would not bring the
invention so modified beyond the scope of the
appended claims.
31
