Note: Descriptions are shown in the official language in which they were submitted.
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PAPER MACHINE, PAPER MACHINE BELT FOR AND METHOD OF MANUFACTURING TEXTURED
SOFT PAPER
FIELD OF THE INVENTION
The present invention relates to papermaking
machines and methods of making paper, and more
particularly relates to machines and methods for making
textured soft paper, such as tissue.
BACKGROUND OF THE INVENTION
A paper machine for the production of tissue
paper is disclosed in U.S. Patent No. 5,393,384, see
particularly Figure 6. The paper machine shown therein
has a belt impermeable to water, which runs in a loop
through an extended press nip formed by a shoe press
roll and a counter roll. A press felt is conveyed
directly to the press nip, where it is brought together
with the impermeable belt and the paper web. The paper
web is transferred from a forming fabric to the
impermeable belt which is to carry the paper web on its
under side up to the press nip and thence to the drying
cylinder. The impermeable belt thus carries the paper
web a relatively long distance after the paper web has
been transferred from the forming fabric to the
impermeable belt. There is therefore a risk of the
paper web not adhering sufficiently strongly along the
entire distance and thus becoming detached from the
impermeable belt. According to the patent
specification the adhesion force between the
impermeable belt and the paper web is greater than that
between the press felt and the paper web. The
impermeable belt under discussion here is not
compressible and has a smooth, web-carrying surface.
It is generally known that such a smooth,
impermeable belt obtains a film of liquid on its
smooth, web-carrying surface when belt, press felt and
paper web pass together through a press nip and that,
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after the press nip, the paper web therefore adheres to
the impermeable belt instead of to the press felt which
does not have a smooth surface, when the press felt and
the impermeable belt run away from each other. This
situation is also utilized in U.S. Patent No.
4,483,745. Since, however, both the impermeable belt
and the drying cylinder in the paper machine according
to U.S. Patent No. 5,393,384 have smooth surfaces with
which the paper web is intended to come into contact,
there is considerable risk of the paper web continuing
to adhere to the smooth surface of the impermeable belt
after it has passed.the nip at the drying cylinder
instead of being transferred to the smooth surface of
the drying cylinder as desired. Probably not even the
application of large quantities of adhesive on the
envelope surface of the drying cylinder would ensure
adhesion of the paper web to the drying cylinder. U.S.
Patent No. 5,393,384 mentions nothing about texturing
the paper web before the drying cylinder.
DE-195 48 747 discloses a paper machine for
manufacturing creped tissue paper which is provided
with a press comprising a shoe press roll, a counter
roll and a suction roll, the counter roll forming a
first press nip with the suction roll and a second
extended press nip with the shoe press roll. A felt
passes through the two press nips together with the
paper web and then carries the paper web with it to a
Yankee dryer, to which the paper web is transferred
when the felt and the paper web pass around a transfer
roll forming a non-compressing nip with the Yankee
dryer. Suction zones are provided before and after the
first press nip, the suction zone before the press nip
being situated within the suction roll whereas the
suction zone after the press nip is in a side loop in
which the felt runs alone and joins the paper web again
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at the entry to the second press nip. One drawback
with such a paper machine is that the paper web is
exposed to re-wetting by the wet felt before it reaches
the Yankee dryer. The paper machine has no impermeable
belt, nor does the patent specification mention
anything about texturing the paper web.
U.S. Patent No. 5,298,124 discloses a
compressible transfer belt for use in a paper or board
making machine in order to eliminate open draws in the
paper web and to easily release the paper web so that
it can be transferred to a fabric or belt. The
transfer belt carries the paper web through the press
section, which comprises one or more press nips, and on
to the drying section which comprises a plurality of
drying cylinders and a belt passing in a loop around a
transfer roll which forms a nip with the transfer belt.
Each press is also provided with a felt passing through
its press nip and enclosing the paper web between it
and the transfer belt. The impermeable transfer belt
is also so designed that a liquid film formed in a
press nip between the transfer belt and the paper web
breaks up when the pressure on the transfer belt ceases
after the press nip so that its release properties
increase and the paper web can thus more easily be
transferred to a fabric or another belt running in a
loop. There is no suggestion or intimation in the
patent specification that the transfer belt should be
allowed to carry the paper web to a drying cylinder in
a tissue machine. Nor is there any mention of
texturing the paper web.
U.S. Patent No. 5,298,124 offers an excellent
description of the tasks a transfer belt cooperating
with a press felt shall perform in a satisfactory
manner, and also of the properties and design of such
transfer belts which then were disclosed in patent
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specifications U.S. Patent Nos. 4,483,745, 4,976,821,
4,500,588, 5,002,638, 4,529,643 and CA-A-1,188,556.
According to U.S. Patent No. 5,298,124, for a transfer
belt intended for cooperation with a press felt the
critical tasks are a) to remove the paper web from the
press felt without causing instability problems; b) to
cooperate with the press felt in one or more press nips
to ensure optimal dewatering and high quality of the
paper web, and c) to transfer the paper web in a closed
draw from a press in the press section to a paper web
receiving fabric or belt in the following press or
presses of the press section or to a pick-up fabric in
the drying section.
As mentioned, the transfer belt for the press
section of a paper machine disclosed in U.S. Patent No.
5,298,124 has a web-contacting surface which is
substantially impermeable to water and air and has a
pressure-responsive microscale topography. Under
influence of the pressure in a press nip in the press
section, the transfer belt is compressed so that the
microscale roughness of said surface is decreased,
whereupon the surface becomes much smoother and allows
the formation of a thin, continuous film of water
thereon.
Paper machines for manufacturing soft paper
with high bulk are known=through a plurality of patent
specifications. An imprinting fabric or felt is
generally used which passes, together with the paper
web formed, through a press nip in which the paper web
is pressed into the imprinting fabric, thus acquiring a
texture pattern on one side. Paper machines having
such texturing fabrics and press nips are disclosed in
U.S. Patent Nos. 3,301,746, 3,537,954, 4,309,246,
4,533,437, 5,569,358, 5,591,305 and WO 91/16493. The
drawback with the paper machines disclosed in these
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publications is that dewatering in the press nip is
relatively low and the dry solids content of the paper
web is therefore low when the paper is transferred to
the drying cylinder. The production rate of the paper
machine is thus relatively low.
U.S. Patent No. 4,849,054 discloses a machine
for manufacturing an imprinted fabric web with high
bulk without the use of a press nip. A roll, e.g., a
transfer roll or felt-carrying roll, forms a nip with
an imprinting fabric at a transfer point for the web
where the imprinting fabric passes around a suction
tube with a slit opening facing the transfer point.
The nip is so wide that the web is not compressed when
it passes through. The suction effect from the suction
tube via the narrow slit opening is sufficient to
ensure that the web is not only transferred to the
imprinting belt but is also shaped in compliance with
the surface of the imprinting belt facing the web, this
belt having a three-dimensional pattern. Prior to the
transfer point the speed of the fabric web is greater
than that of the imprinting fabric. The roll carrying
the web to the non-compressing nip has a smooth surface
and it is generally known that in practice considerable
problems are entailed in transferring a fabric web from
a smooth surface to a fabric, which fabric web has been
pre-pressed to a dry solids content of 30-50%.
U.S. Patent No. 5,411,636 discloses
manufacture of soft paper where the paper web is formed
on a forming fabric, pre-pressed in a double-felted
press nip and transferred to a coarse-meshed fabric.
When the paper web is carried by the coarse-meshed
fabric it is subjected to a vacuum in a suction zone so
that the paper web is sucked into the openings and
depressions in the fabric and thereby acquires
increased thickness and thus increased bulk. The
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coarse-meshed fabric then carries the paper web to the
drying cylinder. The double-felted press nip ensures
that the dry solids content of the paper web is
relatively low, i.e., 25-30%. Since no dewatering can
be performed in the nip at the drying cylinder, the dry
solids content of the paper web upon transfer to the
drying cylinder is correspondingly low. Furthermore,
it is extremely difficult to transfer the paper web
from the felt to the coarse-meshed fabric.
Accordingly, an improved paper machine and
method of manufacturing textured soft paper would
enable the manufacture of a textured fibrous web with
high bulk and high dry solids content before the drying
cylinder to enable a high production rate to be
achieved at a reasonable cost. Further, it would be
desirable to reliably transfer the textured fibrous web
to the drying cylinder although the fibrous web is
carried to the drying cylinder by an impermeable
texturing belt.
SUMMARY OF THE INVENTION
The paper machine according to the invention
is characterized in that
a) the substantially impermeable belt is a
texturing belt including a back layer and a web-
contacting layer having a multitude of uniformly
distributed depressions with surface portions located
between them to form an equivalent relief pattern in
the fibrous web during its passage through the press
nip;
b) the substantially impermeable texturing
belt is arranged to run from the press to the drying
cylinder in order to carry the textured fibrous web to
said transfer nip;
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c) the press felt is arranged to run in a
direction away from the impermeable texturing belt at a
point immediately after said press nip and before a
water film formed in the press nip on the substantially
impermeable texturing belt breaks up; and
d) a device for applying adhesive is
arranged before said transfer nip to apply a continuous
adhesive layer on the envelope surface of the drying
cylinder and/or on the textured fibrous web.
The method according to the invention is
characterized by
a) texturing the fibrous web by means of
the substantially impermeable belt, which is a
texturing belt including a carrier and a web-contacting
layer having a multitude of uniformly distributed
depressions with surface portions located between them
to form an equivalent pattern in the fibrous web during
its passage through said press nip;
b) running the substantially impermeable
texturing belt from the press to the drying cylinder in
order to carry the textured fibrous web to said
transfer nip;
c) running the press felt in a direction
away from the impermeable texturing belt at a point
immediately after said press nip and before a water
film formed in the press nip on the substantially
impermeable texturing belt breaks up; and
d) applying a continuous layer of adhesive
on the envelope surface of the drying cylinder and/or
on the textured fibrous web with the aid of a device
for applying adhesive at a point before said transfer
nip.
According to the invention it has
surprisingly been found that impermeability or
substantial impermeability is an extremely favorable
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property in a texturing belt, that is included in the
paper machine according to the invention if the
impermeable texturing belt is also used to transport a
pressed paper web,to the transfer nip at a Yankee dryer
in the drying section of the paper machine. The
property allows steam which, as a result of heating the
Yankee dryer is formed in the depressions or pits in
the texturing pattern by the water present in the pits
or depressions, to be pressurized, thus pressing the
paper fibers also present in the pits or depressions as
a result of the press effect in the press section, so
that these in the Yankee dryer nip are pressed into the
pits or depressions at the same time as the parts of
the paper fiber web present between the raised parts of
the texturing pattern and the Yankee dryer become
thinner. The desired texturing effect and high bulk of
the paper web is thus achieved.
The texturing effect and the productivity can
be increased if the texturing belt or a layer of the
texturing belt intended for contact with the paper web
is also given the feature of reversible compressibility
so that the texturing belt is compressed in the
transfer nip at the Yankee dryer. When the texturing
belt then leaves the transfer nip and resumes its
uncompressed state, a vacuum is created, which
contributes to the formation of steam, which in turn
facilitates separation of the texturing belt and paper
web after the transfer nip and also quicker drying of
the paper web on the Yankee dryer, i.e., higher paper
production capacity. The vacuum-forming effect
increases the quicker the belt resumes its uncompressed
state, i.e., the more resilient the reversible
compressibility is.
The texturing effect of the texturing belt
that is included in the paper machine according to the
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invention is, of course, selected taking into
consideration the desired texture pattern in the paper
to be manufactured. The texture pattern is regular
across the texturing belt or, if the texture pattern in
the paper web is to include a particularly prominent
additional pattern, e.g., a picture, logotype, etc., it
has a regular basic pattern of depressions or pits and
raised portions, onto which pattern the additional
pattern is superimposed. "Regular" does not
necessarily imply that the pattern appears regularly in
all directions of the texturing belt. For instance, if
the paper is soft paper that is to be creped, a tighter
dominant transverse pattern (across the machine
direction) as compared with a longitudinal pattern of
elevations and pits, will give an increased creping
effect. Thus, the pattern can be used for altering the
properties of the paper in a desired direction.
Taking into consideration the material in the
texturing belt or its surface layer that is intended to
come into contact with the paper web, the texturing
pattern can be achieved in some manner, known per se,
such as etching, calendering, laser processing or
embossing.
The density of the texturing pattern can also
be used to influence the effect of the drying of the
paper web on the Yankee dryer. Fewer contact points
between the Yankee dryer and the paper web thus results
in reduced drying effect from the Yankee dryer but
increased drying effect from the hot air hood around
the Yankee dryer on the fluffier parts of the paper web
located between the thinner contact points.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be described in more
detail in the following with reference to the attached
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drawings.
Figure 1 shows a paper machine according to a
first embodiment of the invention.
Figure 2 shows a paper machine according to a
second embodiment of the invention.
Figure 3 shows a paper machine according to a
third embodiment of the invention.
Figure 4 shows a paper machine according to a
fourth embodiment of the invention.
Figure 5 shows a paper machine according to a
fifth embodiment of the invention.
Figure 6 shows in perspective a part of a
substantially impermeable texturing belt constructed of
a back layer in the form of a tight polymer layer and a
web-contacting layer in the form of a polymer-coated
fabric.
Figure 7 shows from above a part of a
substantially impermeable texturing belt constructed of
a back layer in the form of a carrier and a web-
contacting layer supported by the carrier, in the form
of a resilient, compressible polymer layer, which
polymer layer is provided with longitudinal grooves.
Figure 8 shows a section through the
texturing belt according to Figure 7.
Figure 9 shows from above a part of a
substantially impermeable texturing belt of the same
type as that according to Figure 7, but provided with
diagonally intersecting grooves.
DETAILED DESCRIPTION OF THE INVENTION
The present invention now will be described
more fully hereinafter with reference to the
accompanying drawings, in which preferred embodiments
of the invention are shown. This invention may,
however, be embodied in many different forms and should
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not be construed as limited to the embodiments set
forth herein; rather, these embodiments are provided so
that this disclosure will be thorough and complete, and
will fully convey the scope of the invention to those
skilled in the art. Like numbers refer to like
elements throughout.
Figures 1-3 show schematically parts of paper
machines for manufacturing a textured web 1 of soft
paper, such as tissue and other paper products with low
density. Each of the paper machines comprises a wet
section 2, a press section 3 and a drying section 4.
The wet section 2 includes a headbox 7 a
forming roll 8, an endless, carrying, inner clothing 9
and an endless, covering outer clothing 10 consisting
of a forming fabric. The inner and outer clothings 9,
10 run, each in its own loop, around a plurality of
guide rolls 11 and 12, respectively.
The drying section 4 includes a drying
cylinder 5 covered by a hood 30. The drying cylinder
is suitably a Yankee dryer. At the outlet side of the
drying section a creping doctor is arranged to crepe
the fibrous web 1 off the Yankee dryer. An application
device 31 is also provided for applying a suitable
adhesive on the envelope surface of the Yankee dryer 5
immediately before the transfer nip.
The press section 3 includes a shoe press
with a shoe press roll 14 and a counter roll 19, these
rolls 14 and 19 forming an extended press nip with each
other. The press section also has an endless press
felt 15 which runs in a loop around guide rolls 6, and
an endless, substantially impermeable belt 16, which
according to the invention is a texturing belt. The
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substantially impermeable texturing belt 16 runs in a
loop around the counter roll 19, a transfer roll 17 and
a plurality of guide rolls 18. The transfer roll 17
forms a transfer nip with the Yankee dryer 5 with low
linear load, i.e., about 30 to 60 kN (kiloNewtons),
through which transfer nip the substantially
impermeable texturing belt 16 thus passes.
In the embodiments shown in Figures 1 and 2
the press section 3 also includes a roll press,
constituted by a suction press roll 13 and said counter
roll 19 to form a press nip, through which the
substantially impermeable texturing belt 16 and the
press felt 15 pass together with the fibrous web 1.
After this initial press nip, the press felt 15 is
conducted away from the fibrous web 1 and the
substantially impermeable texturing belt 16 in a side
loop around the suction press roll 13 and two guide
rolls 32. The press felt 15 rejoins the fibrous web
and the substantially impermeable texturing belt 16
immediately before the extended press nip. If desired,
suction devices may be arranged within this side loop
of the press felt 15 in order to increase the capacity
of the press felt to absorb water at the entrance to
the extended press nip.
In the embodiments shown in Figures 1 and 3,
the inner clothing 9 of the wet section 2 is a felt
guided to the press section 3 to be also utilized as
press felt 15, and which thus runs in a loop back to
the forming roll 8.
In the embodiment shown in Figure 2, the
inner clothing 9 of the wet section 2 is a forming
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fabric, the press felt running around a pick-up roll 20
arranged close to the loop of fabric 9, so that press
felt 15 and fabric 9 run in contact with each other to
transfer the fibrous web from the fabric 9 to the press
felt 15. The pick-up roll 20 may be provided with a
suction shoe (not shown). Alternatively, the pick-up
roll with suction shoe may be replaced by a pick-up
suction box.
Figure 4 shows schematically parts of a paper
machine according to another embodiment of the
invention. It is similar to that shown in Figure 1
with the exception that the press felt 15 is not led in
a side loop between the two press nips, but instead
accompanies the counter roll 19, so that the fibrous
web 1 is held enclosed between the substantially
impermeable texturing belt 16 and the press felt 15.
This embodiment can be used when there is little risk
of rewetting of the fibrous web.
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Figure 5 shows schematically parts of a paper
machine according to yet another embodiment of the
invention for manufacturing a textured web of soft
paper, such as tissue and other sanitary paper
products. The paper machine comprises a wet section 2,
a press section 3 and a drying section 4. The wet
section 2 includes a headbox 7, a forming roll 8, an
endless, carrying inner clothing 9 and an endless,
covering, outer clothing 10 constituted by a forming
fabric. The inner and outer clothings 9 and 10 run in
individual loops around a plurality of guide rolls 11
and 12, respectively. The drying section 4 includes a
drying cylinder 5 covered by a hood 30. The drying
cylinder is suitably a Yankee dryer. At the outlet
side of the drying section a creping doctor 21 is
provided to crepe the fibrous web off the Yankee dryer
5. An application device 31 is also provided for
applying a suitable adhesive on the envelope surface of
the Yankee dryer 5 immediately before the transfer nip.
The press section 3 includes a shoe press with a shoe
press roll 14 and a counter roll 19, these rolls 14 and
19 forming an extended press nip with each other. The
press section also has an endless press felt 15 which
runs in a loop around guide rolls 6, and an endless,
substantially impermeable belt 16, which according to
the invention is a texturing belt. The substantially
impermeable texturing belt 16 runs in a loop around the
counter roll 19, a transfer roll 17 and a plurality of
guide rolls 18. The transfer roll 17 forms a transfer
nip with the Yankee dryer 5 with low linear load,
through which transfer nip the substantially
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impermeable texturing belt 16 thus passes. In this
embodiment the substantially impermeable texturing belt
16 is also used as the inner clothing 9 in the wet
section 2, its loop being extended to the forming roll
8. The substantially impermeable texturing belt 16
thus runs in a loop between the wet section 2 and the
drying section, around the transfer roll 17, guide
rolls 18 and 11 and forming roll 8. The substantially
impermeable texturing belt carries the fibrous web on
its under side from the forming roll to the drying
cylinder.
In the embodiments shown in Figures 1 to 5,
the counter roll 19 is a smooth roll and is arranged in
a loop of the substantially impermeable texturing belt
16. In an alternative embodiment (not shown) of the
press section according to Figures 3 and 5, the
positions of the rolls 14 and 19 are reversed, i.e.,
the shoe press roll 14 is arranged in the loop of the
substantially impermeable texturing belt 16, and the
counter roll is in the loop of the press felt 15. In
such a configuration the counter roll may be a suction
roll, a grooved roll or a blind-drilled roll.
The substantially impermeable texturing belt
used in the embodiments above of the paper machine
according to the invention comprises a back layer 33
and a web-contacting layer 34 having a multitude of
uniformly distributed depressions 35 with flat or
arched surface portions 36 situated therebetween, see
Figures 6 to 9. According to the first embodiment,
shown in Figure 6, the substantially impermeable
texturing belt 16 consists of a tight layer 33 forming
said back layer and a fabric forming said web-
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contacting layer 34. The fabric 34 is coated with a
polymer enclosing the threads of the fabric without
altering the structure of the fabric, which is formed
of depressions and arched or convex surface portions 36
situated between the depressions. The depressions 35
and surface portions 36 are in turn formed by the
threads of the fabric extending in the machine
direction (as indicated by the arrow) and transverse to
this. The depressions 35 are sealed by the tight back
layer 33 formed by coating polymer on the surface of
the fabric not coming in contact with the web. Said
arched surface portions 36,comprise both oblong
arc-shaped ridges 36a of the longitudinally running
fabric threads, and also knuckles 36b of the
transversely running threads, which knuckles produce
small bowl-shaped pits in the fibrous web in the
texturing phase. In the embodiment shown in Figure 6,
the substantially impermeable texturing belt has 100
knuckles 36b per cm2. In general it may have 25 to 150
knuckles/cm2, preferably 50 to 100 knuckles/cmz. This
structure of depressions, ridges and knuckles produces
a corresponding texture pattern in the fibrous web when
it runs through the extended press nip together with
the texturing belt 16 and press felt 15. The polymer
coating on the fabric ensures that the fibrous web is
reliably adhered to the substantially impermeable
texturing belt as it runs out from the extended press
nip. This ensures that the fibrous web accompanies the
substantially impermeable texturing belt 16 and not the
press felt 15. The structure of the web-contacting
layer of the impermeable texturing belt, i.e., the
polymer-coated fabric 34, combined with the envelope
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surface of the drying cylinder 5 being coated with a
continuous adhesive layer, also ensures that the
fibrous web is safely transferred to the drying
cylinder 5 when it passes through and out of the
transfer nip.
What is generally termed a coarse, single-
layered fabric, having 100 knuckles/cm' may be used in
the first embodiment of the substantially impermeable
texturing belt described above. The back layer, which
is substantially impermeable, may consist of a suitable
polymer resin material, e.g., the polymers described
below for the polymer layer in the second embodiment of
the substantially impermeable texturing belt. The
polymer for coating the fabric threads may be selected
in the same way.
According to a second embodiment, the
substantially impermeable texturing belt 16 consists of
a carrier 33, which forms said back layer 33, and a
polymer layer 34 on its web-contacting side having a
hardness of 50 to 97 Shore A, the polymer coating
having a degree of roughness in uncompressed state of RZ
= 2 to 80 m, measured in accordance with ISO 4287,
Part I, and being compressible to a lower degree of
roughness of R. = 0 to 20 m when a linear load of 20 to
200 kN/m is applied in the substantially impermeable
texturing belt, and also has the ability to be
recovered to its uncompressed degree of roughness when
the pressure exerted on the substantially impermeable
texturing belt ceases. The R_-value is more
specifically the ten-point height, which is defined in
said ISO norm as the average distance between the five
highest peaks and the five deepest valleys in the
reference length measured from a line parallel to the
mid-line and not crossing the surface profile. The
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substantially impermeable texturing belt preferably has
an air permeability of less than 6 m'/m'/minute,
measured in accordance with the procedure described in
"Standard Test Method for Air Permeability of Textile
Fabrics, ASTM D 737-75, American Society of Testing and
Materials".
The substantially impermeable texturing belt
16 is thus compressible under the influence of the
pressure forces prevailing in the extended press nip.
The substantially impermeable texturing belt 16
therefore assumes an uncompressed state upstream and
downstream of the extended press nip, the surface, the
web-carrying surface facing the fibrous web, having a
high degree of roughness in the uncompressed state of
the substantially impermeable texturing belt and a
lower degree of roughness in the compressed state of
the substantially impermeable texturing belt, so that
the web-carrying surface in the compressed state of the
substantially impermeable texturing belt is
sufficiently smooth for a continuous liquid film to be
formed on the web-carrying surface, when the
substantially impermeable texturing belt, together with
press felt 15 and fibrous web 1, passes through the
extended press nip, and so that the web-carrying
surface in the uncompressed state of the substantially
impermeable texturing belt is sufficiently rough to
permit the continuous liquid film to be broken up after
the substantially impermeable texturing belt has
expanded in thickness.
The compressible polymer layer 34 is provided
with said multitude of uniformly distributed
depressions 35, in order to take up a large share of
the web-contacting surface, viz. from 20% up to 50%.
The depressions can be formed in many ways to achieve
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the desired effect of texturing a relief pattern in the
fibrous web in order to increase its bulk. The
depressions may consist of continuous grooves in the
polymer layer 33, see Figure 7, which extend in machine
direction. According to another embodiment, the
grooves extend diagonally from one edge to the other,
forming an angle of 10 to 80 to the machine direction.
According to another embodiment, see Figure 8, the
depressions consist of diagonally intersecting grooves
which extend in one group from the first edge to the
second edge, and in a second group from the second edge
to the first edge, intersecting grooves forming an
angle a of 10 to 170 . The grooves in the various
embodiments may be straight, as shown, or wave shaped
or the like, e.g., sinus shaped or zigzag shaped. The
distance a between two grooves 35 running in the same
direction may be within the interval 1 to 3 mm. The
width b of the groove is within the interval 0.5 to 1.0
mm and its depth c within the interval 0.1 to 1.0 mm.
According to another embodiment (not shown)
the depressions comprise hollows of the same or similar
shapes. These hollows may be circular, elliptical or
polygon in shape, e.g., triangular, rectangular or
hexagonal, the largest dimension lying within the
interval 0.5 to 3.0 mm and the depth within the
interval 0.5 to 1.0 mm.
All or some of the depressions, individually
or in groups, may be constituted by hollows of special
symbol shapes, e.g., numbers, letters, trade or company
symbols repeated at regular intervals within a length
unit of the belt.
The substantially impermeable texturing belt
according to said second embodiment may be built up in
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accordance with the recipes described in U.S. Patent
No. 5,298,124, discussed in the introduction. The
polymer coating 34 comprises a polymer composition such
as acrylic polymer resin, polyurethane polymer resin
and polyurethane/polycarbonate resin composition. The
polymer coating also contains particles of a filler,
which have a different hardness from the polymer
material and may consist of kaolin, clay, polymer
material or metal, preferably stainless steel. The
carrier constituting the back layer 33 includes all
types of base elements that can in some way be made
endless. The term also covers base elements provided
with seams. The carrier may consist, for instance, of
a single-layered or multi-layered fabric produced from
monofilaments such as polyester, polyamide, and the
like. The base element may even consist of a fiber web
(non-woven) held together by adhesive, combined wound
yarns, polymer foil/film, warp knitting, or the like.
The carrier may be coated on the rear side with a
polymer material of the same type as that used for the
polymer layer 34.
It is surprising that a transfer belt as
described in U.S. Patent No. 5,298,124, which is
intended for pressing in a press section and usable for
transferring a paper web from the press section to a
drying fabric, can be used with great advantage for
texturing and transferring a soft paper web from a shoe
press nip directly to a Yankee dryer or some other
drying cylinder. As is well known, the conditions at a
Yankee dryer are completely different from those in a
conventional press nip. With a Yankee dryer, no
pressing of the soft paper occurs for direct
dewatering. Rather it is a question of supporting the
soft paper web to the envelope surface of the Yankee
dryer, so that the fibers of the soft paper web adhere
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efficiently to the surface of the Yankee dryer, thereby
achieving good heat transfer to the paper web. This is
exactly the effect which is achieved with the transfer
belt included in one embodiment of the paper machine
according to the present invention, but cannot be
achieved with a press felt as described in DE-195 48
747 due to the paper being exposed to rewetting after
the last press nip in the press section, which prevents
satisfactory adhesion. Neither can it be achieved, or
only to a minor extent, with a transfer belt as
described in U.S. Patent No. 5,393,384 for the reason
stated above. The compressibility of the transfer belt
used in the paper machine according to the invention
results in lower specific pressure at the adhesion
point, which in turn offers increased rate of
operation, i.e., higher production rate. This property
also results in increased vaporization of water from
the soft paper web, i.e., quicker drying of the soft
paper web on the Yankee dryer, which also contributes
to higher production rates.
The paper machine according to the invention,
the press nips of which being single-felted, produces a
textured fibrous web with a high dry solids content
before the drying section, viz. up to 55k, which should
be compared with the dry solids contents of up to 45t
achieved with paper machines in practical use today.
This improvement can be utilized either to run the
paper machine at a higher production rate or to reduce
the energy consumption in the drying section. It is
also then possible to reduce the diameter of the drying
cylinder.
With the embodiments shown and described, a
guide roll may be arranged, if desired, in the loop of
the substantially impermeable texturing belt 16
immediately before the transfer roll 17.
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With the embodiments shown and described, a
transfer member is used constituted by the transfer
roll 17. According to an alternative embodiment (not
shown), the transfer roll is replaced by the
substantially impermeable texturing'belt itself, which
is allowed to run around a predetermined part of the
drying cylinder, e.g., within a sector angle of 30 to
60 , to form an extended transfer nip with the drying
cylinder.
Although the embodiments of the paper machine
described above all have press sections comprising a
shoe press, the invention is also applicable when the
press section lacks a shoe press and instead has at
least one press with two press rolls, of which the
press roll around which the press felt runs is a
suction roll, a grooved roll or a blind-drilled roll.
Many modifications and other embodiments of
the invention will come to mind to one skilled in the
art to which this invention pertains having the benefit
of the teachings presented in the foregoing
descriptions and the associated drawings. Therefore,
it is to be understood that the invention is not to be
limited to the specific embodiments disclosed and that
modifications and other embodiments are intended to be
included within the scope of the appended claims.
Although specific terms are employed herein, they are
used in a generic and descriptive sense only and not
for purposes of limitation.
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