Note: Descriptions are shown in the official language in which they were submitted.
CA 02323636 2000-09-14
WO 99/49132 PCT/SE99/00382
1
0
The present invention relates to a paper machine for
manufacturing a fibrous soft paper web, including:
- a wet section having a headbox; a forming roll; and
inner an outer clothings running around the forming roll,
between which clothings the fibrous web is formed;
- a press section having at least one shoe press having a
shoe press roll and a counter roll, said rolls forming an
extended press nip, a substantially impermeable belt and
a press felt, the substantially impermeable belt and the
press felt running through the extended press nip with
the fibrous web enclosed therebetween; and
- a drying section having a drying cylinder and a
transfer member which, together with the drying cylinder,
forms a transfer nip for transfer of the fibrous web to
the drying cylinder.
The invention also relates to a method of manufacturing a
fibrous soft paper web in a paper machine, said machine
including:
- a wet section having a headbox; a forming roll; and
inner and outer clothings running around the forming
roll, between which clothings the fibrous web is formed;
- a press section having a least one shoe press having a
shoe press roll and a counter roll, said rolls forming an
extended press nip, a substantially impermeable belt and
a press felt, the substantially impermeable belt and the
press felt running through the extended press nip with
the fibrous web enclosed therebetween; and
- a drying section having a drying cylinder and a
transfer member which, together with the drying cylinder,
CA 02323636 2000-09-14
WO 99/49132 PCT/SE99/00382
2
forms a transfer nip for transfer of the fibrous web to
the drying cylinder.
A paper machine of the type described above is disclosed
in US-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
conducted directly to the press nip, where it runs
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 '384 patent, 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 in question 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 the belt,
press felt and paper web pass together through a press
nip and that, 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
US-4,483,745. Since, however, both the impermeable belt
and the drying cylinder in the paper machine according to
US-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
CA 02323636 2000-09-14
WO 99/49132 PCT/SE99/00382
3
to the smooth surface of the impermeable belt after it is
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.
DE-195 48 747 describes 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 r:ip
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 for dewatering the
felt 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 at the entry to the
second press nip. One drawback with such a paper machine
is that the paper web is exposed to rewetting by the wet
felt before it reaches the Yankee dryer.
US-5,298,124 describes a compressible transfer belt for
use in a paper or board machine in order to eliminate
open draws of 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
CA 02323636 2000-09-14
WO 99/49132 PCT/SE99100382
4
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 designed so that a liquid film
formed in the 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 proposal or suggestion to having
the transfer belt to carry the paper web to a drying
cylinder in a tissue machine.
US-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 described in patent specifications US-A-4,483,745,
4,976,821, 4,500,588, 5,002,638, 4,529,643 and
CA-A-1,188,556. According to US-A-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 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 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 described in US-5,298,124 has
a web-contacting surface which is substantially
impermeable to water and air and has 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
CA 02323636 2000-09-14
WO 99149132 PCT/SE99/00382
smoother and allows the formation of a thin, continuous
film of water thereon.
It has surprisingly been found that a belt of the type
described in US-5,298,124 is also well suited for use in
5 a paper machine according to the invention, for
transferring a soft paper web in closed draw from a shoe
press nip in the press section to a Yankee dryer in the
drying section of the soft paper machine. As is known, a
shoe press nip results in a high degree of dewatering.
The object of the present invention is to provide an
improved paper machine and an improved method of
manufacturing soft paper, said paper machine and said
method enabling the manufacture of a fibrous web with
high dry solids content before the drying cylinder in
order to enable a high production rate to be achieved at
reasonable cost, and to reliably transfer the fibrous web
to the drying cylinder although the fibrous web is
carried to the drying cylinder by an impermeable belt.
The paper machine according to the invention is
characterized in that
a) the substantially impermeable belt comprises a
carrier with a compressible polymer coating on the side
facing the paper web, having a hardness in the range from
50 to 97 Shore A, which polymer coating has a
web-contacting surface with a pressure-responsive,
recoverable degree of roughness, the web-contacting
surface having a degree of roughness in unloaded state of
Rz=2-80 m, measured in accordance with ISO 4287, Part I,
and a lower degree of roughness of Rz=0-20 m when the
polymer coating is compressed by linear load of
20-220 kN/m on the substantially impermeable belt as
measured in a non-extended press nip;
CA 02323636 2000-09-14
WO 99/49132 PCT/SE99/00382
6
b) the press felt is arranged to carry the fibrous web
to the press section from the forming roll or from a
point situated downstream of the forming roll and
upstream of the press section;
c) the substantially impermeable belt and the
web-carrying press felt are arranged to run together not
until they enter the press section to enclose the fibrous
web between them, the substantially impermeable belt
being arranged to run directly to the press section;
d) the substantially impermeable belt is arranged to run
from the shoe press to the drying cylinder to carry the
fibrous web to said transfer nip;
e) the press felt is arranged to run in a direction away
from the substantially impermeable belt at a point
immediately after the extended press nip and before a
water film formed in the extended press nip on the
substantially impermeable belt breaks up; and
f) 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
fibrous web.
The method according to the invention is characterized by
a) performing the pressing with the aid of a
substantially impermeable belt that includes a carrier
and a compressible polymer coating on the side facing the
paper web, said polymer coating having a hardness in the
range from 50 to 97 Shore A and a web-contacting surface
with a pressure responsive, recoverable degree of
roughness, the web-contacting surface having a degree of
roughness in unloaded state of Rz=2-80 m, measured in
accordance with ISO 4287, Part I, and a lower degree of
roughness of Rz=0-20 m when the polymer coating is
compressed by linear load of 20-220 kN/m on the
CA 02323636 2000-09-14
WO 99/49132 PCT/SE99/00382
7
substantially impermeable belt as measured in a
non-extended press nip;
b) using the press felt to carry the fibrous web to the
press section from the forming roll or from a point
situated downstream of the forming roll and upstream of
the press section;
c) running the substantially impermeable belt and the
web-carrying press felt together not until they enter the
press section to enclose the fibrous web between them,
and running the substantially impermeable belt directly
to the press section;
d) running the substantially impermeable belt from the
shoe press to the drying cylinder to carry the fibrous
web to said transfer nip;
e) running the press felt in a direction away from the
substantially impermeable belt at a point immediately
after the extended press nip and before a water film that
is formed on the substantially impermeable belt in the
extended press nip breaks up; and
f) applying a continuous adhesive layer on the envelope
surface of the drying cylinder and/or on the fibrous web
by means of an adhesive applying device at a point before
said transfer nip.
It is surprising that a transfer belt according to
US-A-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, is useful with
advantage for transferring a soft paper web from a shoe
press nip directly to a Yankee dryer or other drying
cylinder. As is well known, the conditions at a Yankee
dryer are completely different from those in a press nip.
With a Yankee dryer no pressing of the soft paper web
occurs for direct dewatering. Rather it is a question of
CA 02323636 2000-09-14
WO 99/49132 PCT/SE99/00382
8
supporting the soft paper web to the envelope surface of
the Yankee dryer so that the fibers of the soft paper web
adhere 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 in the paper machine according to the
invention and which is not achieved with a press felt as
described in DE-195 48 747 due to rewetting of the paper
web 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 US-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
results in 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 efficiency in the
process. The increased efficiency can either be used to
increase machine speed or to reduce energy consumption
while maintaining the same production volume.
The invention is described in more detail in the
following with reference to the 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.
CA 02323636 2000-09-14
WO 99/49132 PCT/SE99/00382
9
Figures 1-3 show schematically parts of a paper machine
for manufacturing a fibrous web 1 of soft paper such as
tissue and other sanitary paper products. Each of the
paper machines comprises a wet section 2, a press section
3 and a drying section 4.
The wet section 2 comprises 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 and 10 run, each
in its own loop, around a plurality of guide rolls 11 and
12, respectively.
The drying section 4 comprises 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 arranged to crepe the fibrous web 1
off the Yankee dryer 5. An application device 31 is
provided for applying of a suitable adhesive on the
envelope surface of the Yankee dryer 5 immediately before
the transfer nip.
The press section 3 comprises 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 comprises an endless press felt 15
which runs in a loop around guide rolls 6, and an
endless, substantially impermeable transfer belt 16. The
substantially impermeable 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 pressure,
i.e. about 30-60 kN, through which transfer nip the
substantially impermeable belt 16 thus passes.
In the embodiments shown in Figures 1 and 2 the press
section 3 also includes a roll press, the rolls of which
consisting of a suction press roll 13 and said counter
CA 02323636 2000-09-14
WO 99/49132 PCT/SE99/00382
roll 19 to form a press nip through which the
substantially impermeable 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
5 fibrous web 1 and the substantially impermeable 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 1 and the substantially impermeable belt 16
immediately before the extended press nip. If desired,
10 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 conveyed to the
press section 3 to be also used 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 fabric, in which case the press
felt 15 runs around a pick-up roll 20 arranged close to
the loop of the 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 and suction shoe may be
replaced by a pick-up suction box.
Figure 4 shows schematically parts of a paper machine
according to a further 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 belt 16 and the
press felt 1S. This embodiment can be used when there is
little risk of rewetting of the fibrous web.
CA 02323636 2000-09-14
WO 99/49132 PCT/SE99/00382
11
In the embodiments according to Figures 1-4 the counter
roll 19 is a smooth roll and is arranged in a loop of the
substantially impermeable belt 16. In an alternative
embodiment (not shown) of the press section according to
Figure 3, the positions of rolls 14 and l9 are reversed,
i.e. the shoe press roll 14 is arranged in a loop of the
substantially impermeable belt 16 and the counter roll 19
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 and elastically
compressible transfer belt 16 is of the type described in
US-5,298,124, for instance. The substantially
impermeable belt 16 used in the paper machines according
to the invention is compressible under the influence of
the press forces prevailing in the press nips. The
substantially impermeable belt 16 thus assumes an
uncompressed state upstream and downstream of a press nip
and a compressed state when it passes a 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 belt and a lower
degree of roughness in the compressed state of the
substantially impermeable belt so that the web-carrying
surface in the compressed state of the substantially
impermeable belt is sufficiently smooth for a continuous
liquid film to be formed on the web-carrying surface when
the substantially impermeable belt, together with press
felt and fibrous web, passes through the press nip and so
that the web-carrying surface in the uncompressed state
of the substantially impermeable belt is sufficiently
rough to permit the continuous liquid film to break up
after the substantially impermeable belt has expended in
thickness direction. More specifically, the
substantially impermeable and elastically compressible
transfer belt consists of an endless carrier,
CA 02323636 2000-09-14
WO 99/49132 PCT/SE99/00382
12
alternatively including a joinable seam, with a polymer
coating on its web-contacting surface having a hardness
of 50-97 Shore A, the polymer coating having a degree of
roughness in uncompressed state of RZ = 2-80 m, measured
in accordance with ISO 4287, Part I, and being
compressible to a lower degree of roughness of RZ = 0-20
m when a linear load of 20-220 kN/m is applied on the
substantially impermeable belt, and also has the ability
to be recovered to its uncompressed degree of roughness
when the pressure exerted on the substantially
impermeable belt ceases. The RZ-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 volleys in the
reference length measured from a line parallel to the
mean line and not crossing the surface profile. The
substantially impermeable transfer belt preferably has an
air permeability of less than 6 m3/m2/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".
As stated in said US-5,298,124, the polymer coating of
the substantially impermeable belt may advantageously
comprise a polymer composition such as acrylic polymer
resin, polyurethane polymer resin and
polyurethane/polycarbonate polymer resin composition.
The polymer coating may also contain particles of filler
with a different hardness from the polymer material and
which may consist of kaolin clay, polymer material or
metal, preferably stainless steel.
The transfer belt included in the paper machine according
to the invention is manufactured in the manner also
described in US-5,298,124. Thanks to the use of the
above polymer composition, a surface layer is achieved on
the belt which is elastically compressible. After the
CA 02323636 2000-09-14
WO 99/49132 PCT/SE99/00382
13
actual surface working in the manufacturing process a
surface is obtained which gives a controlled topography.
The compressibility and topography of the surface layer
are not noticeably affected by possible wear during
operation. The dense polymer surface is easy to keep
clean and can stand being cleaned with a doctor blade
directly on the belt surface. To ensure that the belt
will not age at the edge portions running against the
Yankee dryer outside.the paper web, this must be taken
into consideration when selecting material and the
combinations which withstand heat best must be chosen.
Otherwise edge cooling must be effected by spraying water
on the edge, for instance, immediately before or after
passage of the Yankee dryer.
The carrier in the transfer belt is endless and includes
also types of base elements which can in some way be made
endless. The term also particularly covers an openable
base element provided with a seam, which element is made
endless first when it is installed in the paper machine
with the aid of a suitable seam. The carrier may
consist, for instance, of a multi-layered woven fabric
produced from polymer monofilaments such as polyester,
polyamide and the like. The base element may also
consist of a fibrous web (non-woven) held together by
binder, combined wound yarns, polymer foil/film, warp
knitting or the like. The requirement is that the
carrier is form-stable both in machine direction and
transverse thereto, so that it contributes to stability
of the belt upon mechanical stress in these directions.
If the carrier is to be completely enclosed in the
polymer coating, this can either be applied on one side
with complete bleeding through to the reverse side, or it
may be applied first on one side and then on the other.
Configurations may occur requiring particularly thin
belts, in which case it may be advisable to apply the
coating only from one side with restricted
CA 02323636 2000-09-14
WO 99/49132 PCT/SE99/00382
14
through-bleeding. In this case it is essential that the
non-coated surface of the base element is wear-resistant
and easy to keep clean.
The paper machine according to the invention, with
single-felted press nip(s), produces a fibrous web with a
high dry solids content before the drying section, i.e.
up to 55~, which should be compared with the dry solids
contents of up to 45~ achieved with paper machines in use
today. This improvement can be utilized either to run
the paper machine at a higher production or to reduce the
energy consumption in the drying section. It also
enables a reduction in 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 belt 16 immediately before the transfer
roll 17.
With the embodiments shown and described a transfer
member is used consisting of the transfer roll 17.
According to an alternative embodiment (not shown), the
transfer roll is replaced by the substantially
impermeable belt itself which is allowed to run around a
predetermined part of the drying cylinder, e.g. within a
sector angle of 30-60, to form an extended transfer nip
with the drying cylinder.
