U.S. patent application number 12/751551 was filed with the patent office on 2010-07-29 for structured forming fabric, papermaking machine and method.
Invention is credited to Scott D. Quigley.
Application Number | 20100186921 12/751551 |
Document ID | / |
Family ID | 44009847 |
Filed Date | 2010-07-29 |
United States Patent
Application |
20100186921 |
Kind Code |
A1 |
Quigley; Scott D. |
July 29, 2010 |
STRUCTURED FORMING FABRIC, PAPERMAKING MACHINE AND METHOD
Abstract
A fabric for a papermaking machine, the fabric including a
machine facing side and a web facing side having pockets formed by
warp and weft yarns. Each pocket is defined by four sides on the
web facing side, two of the four sides each formed by a warp
knuckle of a single warp yarn that passes over three consecutive
weft yarns to define the warp knuckle, the other two of the four
sides each formed by a weft knuckle of a single weft yarn that
passes over three consecutive warp yarns to define the weft
knuckle, a lower surface of each pocket being formed by first and
second lower warps yarns and first and second lower weft yarns, a
first warp knuckle being of the first warp yarn passed over by a
first weft knuckle and the first lower warp yarn being of the
second warp yarn passed over by the first weft knuckle and the
second lower warp yarn being of the third warp yarn passed over the
first weft knuckle, a second weft knuckle being of the first weft
yarn passed over by the first warp knuckle and the second lower
weft yarn being of the second weft yarn passed over by the first
warp knuckle and the first lower weft yarn being of the third weft
yarn passed over by the first warp knuckle, the first lower warp
yarn passing over the first lower weft yarn and under the second
lower weft yarn, and the second lower warp yarn passing over the
first and second lower weft yarns.
Inventors: |
Quigley; Scott D.; (Bossier
City, LA) |
Correspondence
Address: |
TAYLOR & AUST, P.C.
P.O. Box 560, 142. S Main Street
Avilla
IN
46710
US
|
Family ID: |
44009847 |
Appl. No.: |
12/751551 |
Filed: |
March 31, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12167890 |
Jul 3, 2008 |
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12751551 |
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Current U.S.
Class: |
162/358.1 ;
162/289 |
Current CPC
Class: |
D21F 3/0281 20130101;
D21F 11/006 20130101; D21F 1/0027 20130101; D21F 3/0272
20130101 |
Class at
Publication: |
162/358.1 ;
162/289 |
International
Class: |
D21F 3/00 20060101
D21F003/00; D21G 9/00 20060101 D21G009/00 |
Claims
1. A fabric for a papermaking machine, the fabric comprising: a
machine facing side; and a web facing side comprising pockets
formed by warp and weft yarns; wherein each pocket is defined by
four sides on the web facing side, two of the four sides each
formed by a warp knuckle of a single warp yarn that passes over
three consecutive weft yarns to define the warp knuckle, the other
two of the four sides each formed by a weft knuckle of a single
weft yarn that passes over three consecutive warp yarns to define
the weft knuckle, a lower surface of each pocket being formed by
first and second lower warps yarns and first and second lower weft
yarns, a first warp knuckle being of the first warp yarn passed
over by a first weft knuckle and the first lower warp yarn being of
the second warp yarn passed over by the first weft knuckle and the
second lower warp yarn being of the third warp yarn passed over the
first weft knuckle, a second weft knuckle being of the first weft
yarn passed over by the first warp knuckle and the second lower
weft yarn being of the second weft yarn passed over by the first
warp knuckle and the first lower weft yarn being of the third weft
yarn passed over by the first warp knuckle, the first lower warp
yarn passing over the first lower weft yarn and under the second
lower weft yarn, and the second lower warp yarn passing over the
first and second lower weft yarns.
2. The fabric of claim 1, wherein the warp yarns and the weft yarns
form a repeating weave pattern with a pattern square, each of the
warp yarns weaving with the weft yarns in an identical pattern in
the pattern square, and the two warp knuckles that define sides of
each pocket have similar portions that are offset from each other
by one weft yarn.
3. The fabric of claim 1, wherein the warp yarns and the weft yarns
form a repeating weave pattern with a pattern square, each of the
warp yarns weaving with the weft yarns in an identical pattern in
the pattern square, and the two weft knuckles that define sides of
each pocket have similar portions that are offset from each other
by one warp yarn.
4. The fabric of claim 1, wherein each of the warp and weft
knuckles forms one of the four sides of a first pocket and one of
the four sides of a second pocket.
5. The fabric of claim 1, wherein the warp yarns are non-circular
yarns.
6. The fabric of claim 1, wherein the warp yarns and the weft yarns
form a repeating weave pattern with a pattern square including ten
weft yarns and ten warp yarns, each of the ten warp yarns having a
pattern of passing over two consecutive weft yarns, passing under
one weft yarn, passing over three consecutive weft yarns, passing
under two consecutive weft yarns, passing over one weft yarn and
passing under one weft yarn.
7. The fabric of claim 1, wherein the pockets are arranged in an
uninterrupted series that extends diagonally relative to the
direction of the warp and weft yarns.
8. The fabric of claim 1, wherein the fabric is configured for use
in conjunction with at least one of a convention through air dryer
(TAD), an ATMOS.TM. machine, an E-TAD and a Metso machine as a part
of the papermaking machine.
9. A papermaking machine, comprising: a vacuum roll having an
exterior surface; a dewatering fabric having first and second
sides, the dewatering fabric being guided over a portion of the
exterior surface of the vacuum roll, the first side being in at
least partial contact with the exterior surface of the vacuum roll;
and a structured fabric including: a machine facing side; and a web
facing side comprising pockets formed by warp and weft yarns;
wherein each pocket is defined by four sides on the web facing
side, two of the four sides each formed by a warp knuckle of a
single warp yarn that passes over three consecutive weft yarns to
define the warp knuckle, the other two of the four sides each
formed by a weft knuckle of a single weft yarn that passes over
three consecutive warp yarns to define the weft knuckle, a lower
surface of each pocket being formed by first and second lower warps
yarns and first and second lower weft yarns, a first warp knuckle
being of the first warp yarn passed over by a first weft knuckle
and the first lower warp yarn being of the second warp yarn passed
over by the first weft knuckle and the second lower warp yarn being
of the third warp yarn passed over the first weft knuckle, a second
weft knuckle being of the first weft yarn passed over by the first
warp knuckle and the second lower weft yarn being of the second
weft yarn passed over by the first warp knuckle and the first lower
weft yarn being of the third weft yarn passed over by the first
warp knuckle, the first lower warp yarn passing over the first
lower weft yarn and under the second lower weft yarn, and the
second lower warp yarn passing over the first and second lower weft
yarns.
10. The papermaking machine of claim 9, wherein the warp yarns and
the weft yarns form a repeating weave pattern with a pattern
square, each of the warp yarns weaving with the weft yarns in an
identical pattern in the pattern square, and the two warp knuckles
that define sides of each pocket have similar portions that are
offset from each other by one weft yarn.
11. The papermaking machine of claim 9, wherein the warp yarns and
the weft yarns form a repeating weave pattern with a pattern
square, each of the warp yarns weaving with the weft yarns in an
identical pattern in the pattern square, and the two weft knuckles
that define sides of each pocket have similar portions that are
offset from each other by one warp yarn.
12. The papermaking machine of claim 9, wherein each of the warp
and weft knuckles forms one of the four sides of a first pocket and
one of the four sides of a second pocket.
13. The papermaking machine of claim 9, wherein the warp yarns are
non-circular yarns.
14. The papermaking machine of claim 9, wherein the warp yarns and
the weft yarns form a repeating weave pattern with a pattern square
including ten weft yarns and ten warp yarns, each of the ten warp
yarns having a pattern of passing over two consecutive weft yarns,
passing under one weft yarn, passing over three consecutive weft
yarns, passing under two consecutive weft yarns, passing over one
weft yarn and passing under one weft yarn.
15. The papermaking machine of claim 9, wherein the pockets are
arranged in an uninterrupted series that extends diagonally
relative to the direction of the warp and weft yarns.
16. A papermaking machine, comprising: a Yankee dryer; and at least
one structured fabric including: a machine facing side; and a web
facing side comprising pockets formed by warp and weft yarns;
wherein each pocket is defined by four sides on the web facing
side, two of the four sides each formed by a warp knuckle of a
single warp yarn that passes over three consecutive weft yarns to
define the warp knuckle, the other two of the four sides each
formed by a weft knuckle of a single weft yarn that passes over
three consecutive warp yarns to define the weft knuckle, a lower
surface of each pocket being formed by first and second lower warps
yarns and first and second lower weft yarns, a first warp knuckle
being of the first warp yarn passed over by a first weft knuckle
and the first lower warp yarn being of the second warp yarn passed
over by the first weft knuckle and the second lower warp yarn being
of the third warp yarn passed over the first weft knuckle, a second
weft knuckle being of the first weft yarn passed over by the first
warp knuckle and the second lower weft yarn being of the second
weft yarn passed over by the first warp knuckle and the first lower
weft yarn being of the third weft yarn passed over by the first
warp knuckle, the first lower warp yarn passing over the first
lower weft yarn and under the second lower weft yarn, and the
second lower warp yarn passing over the first and second lower weft
yarns.
17. The papermaking machine of claim 16, wherein the warp yarns and
the weft yarns form a repeating weave pattern with a pattern
square, each of the warp yarns weaving with the weft yarns in an
identical pattern in the pattern square, and the two warp knuckles
that define sides of each pocket have similar portions that are
offset from each other by one weft yarn.
18. The papermaking machine of claim 16, wherein the warp yarns and
the weft yarns form a repeating weave pattern with a pattern
square, each of the warp yarns weaving with the weft yarns in an
identical pattern in the pattern square, and the two weft knuckles
that define sides of each pocket have similar portions that are
offset from each other by one warp yarn.
19. The papermaking machine of claim 16, wherein the warp yarns and
the weft yarns form a repeating weave pattern with a pattern square
including ten weft yarns and ten warp yarns, each of the ten warp
yarns having a pattern of passing over two consecutive weft yarns,
passing under one weft yarn, passing over three consecutive weft
yarns, passing under two consecutive weft yarns, passing over one
weft yarn and passing under one weft yarn.
20. The fabric of claim 16, wherein the fabric is configured for
use in conjunction with at least one of a convention through air
dryer (TAD), an ATMOS.TM. machine, an E-TAD and a Metso machine as
a part of the papermaking machine.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This is a continuation-in-part of U.S. patent application
Ser. No. 12/167,890 entitled "STRUCTURED FORMING FABRIC,
PAPERMAKING MACHINE AND METHOD", filed Jul. 3, 2008, which is
incorporated herein by reference.
FIELD OF THE INVENTION
[0002] The present invention relates generally to papermaking, and
relates more specifically to a structured forming fabric employed
in papermaking. The invention also relates to a structured forming
fabric having deep pockets.
[0003] In the conventional Fourdrinier papermaking process, a water
slurry, or suspension, of cellulosic fibers (known as the paper
"stock") is fed onto the top of the upper run of an endless belt of
woven wire and/or synthetic material that travels between two or
more rolls. The belt, often referred to as a "forming fabric,"
provides a papermaking surface on the upper surface of its upper
run which operates as a filter to separate the cellulosic fibers of
the paper stock from the aqueous medium, thereby forming a wet
paper web. The aqueous medium drains through mesh openings of the
forming fabric, known as drainage holes, by gravity or vacuum
located on the lower surface of the upper run (i.e., the "machine
side") of the fabric.
[0004] After leaving the forming section, the paper web is
transferred to a press section of the paper machine, where it is
passed through the nips of one or more pairs of pressure rollers
covered with another fabric, typically referred to as a "press
felt." Pressure from the rollers removes additional moisture from
the web; the moisture removal is often enhanced by the presence of
a "batt" layer of the press felt. The paper is then transferred to
a dryer section for further moisture removal. After drying, the
paper is ready for secondary processing and packaging.
[0005] Typically, papermakers' fabrics are manufactured as endless
belts by one of two basic weaving techniques. In the first of these
techniques, fabrics are flat woven by a flat weaving process, with
their ends being joined to form an endless belt by any one of a
number of well-known joining methods, such as dismantling and
reweaving the ends together (commonly known as splicing), or sewing
on a pin-seamable flap or a special foldback on each end, then
reweaving these into pin-seamable loops. A number of auto-joining
machines are available, which for certain fabrics may be used to
automate at least part of the joining process. In a flat woven
papermakers' fabric, the warp yarns extend in the machine direction
and the filling yarns extend in the cross machine direction.
[0006] In the second basic weaving technique, fabrics are woven
directly in the form of a continuous belt with an endless weaving
process. In the endless weaving process, the warp yarns extend in
the cross machine direction and the filling yarns extend in the
machine direction. Both weaving methods described hereinabove are
well known in the art, and the term "endless belt" as used herein
refers to belts made by either method.
[0007] Effective sheet and fiber support are important
considerations in papermaking, especially for the forming section
of the papermaking machine, where the wet web is initially formed.
Additionally, the forming fabrics should exhibit good stability
when they are run at high speeds on the papermaking machines, and
preferably are highly permeable to reduce the amount of water
retained in the web when it is transferred to the press section of
the paper machine. In both tissue and fine paper applications
(i.e., paper for use in quality printing, carbonizing, cigarettes,
electrical condensers, and the like) the papermaking surface
comprises a very finely woven or fine wire mesh structure.
[0008] In a conventional tissue forming machine, the sheet is
formed flat. At the press section, 100% of the sheet is pressed and
compacted to reach the necessary dryness and the sheet is further
dried on a Yankee and hood section. This, however, destroys the
sheet quality. The sheet is then creped and wound-up, thereby
producing a flat sheet.
[0009] In an ATMOS.TM. system, a sheet is formed on a structured or
molding fabric and the sheet is further sandwiched between the
structured or molding fabric and a dewatering fabric. The sheet is
dewatered through the dewatering fabric and opposite the molding
fabric. The dewatering takes place with air flow and mechanical
pressure. The mechanical pressure is created by a permeable belt
and the direction of air flow is from the permeable belt to the
dewatering fabric. This can occur when the sandwich passes through
an extended pressure nip formed by a vacuum roll and the permeable
belt. The sheet is then transferred to a Yankee by a press nip.
Only about 25% of the sheet is slightly pressed by the Yankee while
approximately 75% of the sheet remains unpressed for quality. The
sheet is dried by a Yankee/Hood dryer arrangement and then dry
creped. In the ATMOS.TM. system, one and the same structured fabric
is used to carry the sheet from the headbox to the Yankee dryer.
Using the ATMOS.TM. system, the sheet reaches between about 35 to
38% dryness after the ATMOS.TM. roll, which is almost the same
dryness as a conventional press section. However, this
advantageously occurs with almost 40 times lower nip pressure and
without compacting and destroying sheet quality. Furthermore, a big
advantage of the ATMOS.TM. system is that it utilizes a permeable
belt which is highly tensioned, e.g., about 60 kN/m. This belt
enhances the contact points and intimacy for maximum vacuum
dewatering. Additionally, the belt nip is more than 20 times longer
than a conventional press and utilizes air flow through the nip,
which is not the case on a conventional press system.
[0010] Actual results from trials using an ATMOS.TM. system have
shown that the caliper and bulk of the sheet is 30% higher than the
conventional through-air drying (TAD) formed towel fabrics.
Absorbency capacity is also 30% higher than with conventional TAD
formed towel fabrics. The results are the same whether one uses
100% virgin pulp up to 100% recycled pulp. Sheets can be produced
with basis weight ratios of between 14 to 40 g/m.sup.2. The
ATMOS.TM. system also provides excellent sheet transfer to the
Yankee working at 33 to 37% dryness. There is essentially no
dryness loss with the ATMOS.TM. system since the fabric has square
valleys and not square knuckles (peaks). As such, there is no loss
of intimacy between the dewatering fabric, the sheet, the molding
fabric, and the belt. A key aspect of the ATMOS.TM. system is that
it forms the sheet on the molding fabric and the same molding
fabric carries the sheet from the headbox to the Yankee dryer. This
produces a sheet with a uniform and defined pore size for maximum
absorbency capacity.
[0011] U.S. patent application Ser. No. 11/753,435 filed on May 24,
2007, the disclosure of which is hereby expressly incorporated by
reference in its entirety, discloses a structured forming fabric
for an ATMOS.TM. system. The fabric utilizes an at least three
float warp and weft structure which, like the prior art fabrics, is
symmetrical in form.
[0012] U.S. Pat. No. 5,429,686 to CHIU et al., the disclosure of
which is hereby expressly incorporated by reference in its
entirety, discloses structured forming fabrics which utilize a
load-bearing layer and a sculptured layer. The fabrics utilize
impression knuckles to imprint the sheet and increase its surface
contour. This document, however, does not create pillows in the
sheet for effective dewatering of TAD applications, nor does it
teach using the disclosed fabrics on an ATMOS.TM. system and/or
forming the pillows in the sheet while the sheet is relatively wet
and utilizing a hi-tension press nip.
[0013] U.S. Pat. No. 6,237,644 to HAY et al., the disclosure of
which is hereby expressly incorporated by reference in its
entirety, discloses structured forming fabrics which utilize a
lattice weave pattern of at least three yarns oriented in both warp
and weft directions. The fabric essentially produces shallow
craters in distinct patterns. This document, however, does not
create deep pockets which have a three-dimensional pattern, nor
does it teach using the disclosed fabrics on an ATMOS.TM. system
and/or forming the pillows in the sheet while the sheet is
relatively wet and utilizing a hi-tension press nip.
[0014] International Publication No. WO 2005/035867 to LAFOND et
al., the disclosure of which is hereby expressly incorporated by
reference in its entirety, discloses structured forming fabrics
which utilize at least two different diameter yarns to impart bulk
into a tissue sheet. This document, however, does not create deep
pockets which have a three-dimensional pattern. Nor does it teach
using the disclosed fabrics on an ATMOS.TM. system and/or forming
the pillows in the sheet while the sheet is relatively wet and
utilizing a hi-tension press nip.
[0015] U.S. Pat. No. 6,592,714 to LAMB, the disclosure of which is
hereby expressly incorporated by reference in its entirety,
discloses structured forming fabrics which utilize deep pockets and
a measurement system. However, it is not apparent that the
disclosed measurement system is replicatable. Furthermore, LAMB
relies on the aspect ratio of the weave design to achieve the deep
pockets. This document also does not teach using the disclosed
fabrics on an ATMOS.TM. system and/or forming the pillows in the
sheet while the sheet is relatively wet and utilizing a hi-tension
press nip.
[0016] U.S. Pat. No. 6,649,026 to LAMB, the disclosure of which is
hereby expressly incorporated by reference in its entirety,
discloses structured forming fabrics which utilize pockets based on
five-shaft designs and with a float of three yarns in both warp and
weft directions (or variations thereof). The fabric is then sanded.
However, LAMB does not teach an asymmetrical weave pattern. This
document also does not teach using the disclosed fabrics on an
ATMOS.TM. system and/or forming the pillows in the sheet while the
sheet is relatively wet and utilizing a hi-tension press nip.
[0017] International Publication No. WO 2006/113818 to KROLL et
al., the disclosure of which is hereby expressly incorporated by
reference in its entirety, discloses structured forming fabrics
which utilize a series of two alternating deep pockets for TAD
applications. However, KROLL does not teach to utilize one
consistent sized pocket in order to provide effective and
consistent dewatering and would not produce a regular sheet finish
on the finished product. KROLL also does not teach an asymmetrical
weave pattern. This document also does not teach using the
disclosed fabrics on an ATMOS.TM. system and/or forming the pillows
in the sheet while the sheet is relatively wet and utilizing a
hi-tension press nip.
[0018] International Publication No. WO 2005/075737 to HERMAN et
al. and U.S. patent application Ser. No. 11/380,826 filed on Apr.
28, 2006, the disclosures of which are hereby expressly
incorporated by reference in their entireties, disclose structured
molding fabrics for an ATMOS.TM. system which can create a more
three-dimensionally oriented sheet. These documents, however, do
not teach, among other things, the deep pocket weaves according to
the invention.
[0019] International Publication No. WO 2005/075732 to SCHERB et
al., the disclosure of which is hereby expressly incorporated by
reference in its entirety, discloses a belt press utilizing a
permeable belt in a paper machine which manufactures tissue or
toweling. According to this document, the web is dried in a more
efficient manner than has been the case in prior art machines such
as TAD machines. The formed web is passed through similarly open
fabrics and hot air is blown from one side of the sheet through the
web to the other side of the sheet. A dewatering fabric is also
utilized. Such an arrangement places great demands on the forming
fabric because of the pressure applied by the belt press and hot
air is blown through the web in the belt press. However, this
document does not teach, among other things, the deep pocket weaves
according to the invention.
[0020] The above-noted conventional fabrics limit the amount of
bulk that can be built into the sheet being formed due to the fact
that they have shallow depth pockets compared to the present
invention. Furthermore, the pockets of the conventional fabrics are
merely extensions of the contact areas on the warp and weft
yarns.
[0021] What is needed in the art is an efficient effective fabric
weave pattern to be used in a papermaking machine.
SUMMARY OF THE INVENTION
[0022] In one aspect, the invention provides a fabric for a
papermaking machine; the fabric including a machine facing side and
a web facing side having pockets formed by warp and weft yarns.
Each pocket is defined by four sides on the web facing side, two of
the four sides each formed by a warp knuckle of a single warp yarn
that passes over three consecutive weft yarns to define the warp
knuckle, the other two of the four sides each formed by a weft
knuckle of a single weft yarn that passes over three consecutive
warp yarns to define the weft knuckle, a lower surface of each
pocket being formed by first and second lower warps yarns and first
and second lower weft yarns, a first warp knuckle being of the
first warp yarn passed over by a first weft knuckle and the first
lower warp yarn being of the second warp yarn passed over by the
first weft knuckle and the second lower warp yarn being of the
third warp yarn passed over the first weft knuckle, a second weft
knuckle being of the first weft yarn passed over by the first warp
knuckle and the second lower weft yarn being of the second weft
yarn passed over by the first warp knuckle and the first lower weft
yarn being of the third weft yarn passed over by the first warp
knuckle, the first lower warp yarn passing over the first lower
weft yarn and under the second lower weft yarn, and the second
lower warp yarn passing over the first and second lower weft
yarns.
[0023] In another aspect, the invention provides methods of using a
structured forming fabric of the invention in TAD, ATMOS.TM., Metso
and E-TAD papermaking systems.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] The above-mentioned and other features and advantages of
this invention, and the manner of attaining them, will become more
apparent and the invention will be better understood by reference
to the following description of embodiments of the invention taken
in conjunction with the accompanying drawings, wherein:
[0025] FIG. 1 shows a weave pattern of a top side or paper facing
side of an embodiment of a structured fabric of the present
invention;
[0026] FIG. 2 shows the repeating pattern square of the structured
fabric of FIG. 1. Each `X` indicates a location where a warp yarn
passes over a weft yarn;
[0027] FIG. 3 is a schematic representation of the weave pattern of
the structured fabric shown in FIGS. 1 and 2, and illustrates how
each of the ten warp yarns weaves with the ten weft yarns in one
repeat;
[0028] FIG. 4 is a cross-sectional diagram illustrating the
formation of a structured web using an embodiment of the present
invention;
[0029] FIG. 5 is a cross-sectional view of a portion of a
structured web of a prior art method;
[0030] FIG. 6 is a cross-sectional view of a portion of the
structured web of an embodiment of the present invention as made on
the machine of FIG. 4;
[0031] FIG. 7 illustrates the web portion of FIG. 5 having
subsequently gone through a press drying operation;
[0032] FIG. 8 illustrates a portion of the fiber web of the present
invention of FIG. 6 having subsequently gone through a press drying
operation;
[0033] FIG. 9 illustrates a resulting fiber web of the forming
section of the present invention;
[0034] FIG. 10 illustrates the resulting fiber web of the forming
section of a prior art method;
[0035] FIG. 11 illustrates the moisture removal of the fiber web of
the present invention;
[0036] FIG. 12 illustrates the moisture removal of the fiber web of
a prior art structured web;
[0037] FIG. 13 illustrates the pressing points on a fiber web of
the present invention;
[0038] FIG. 14 illustrates pressing point of prior art structured
web;
[0039] FIG. 15 illustrates a schematic cross-sectional view of an
embodiment of an ATMOS.TM. papermaking machine;
[0040] FIG. 16 illustrates a schematic cross-sectional view of
another embodiment of an ATMOS.TM. papermaking machine;
[0041] FIG. 17 illustrates a schematic cross-sectional view of
another embodiment of an ATMOS.TM. papermaking machine;
[0042] FIG. 18 illustrates a schematic cross-sectional view of
another embodiment of an ATMOS.TM. papermaking machine;
[0043] FIG. 19 illustrates a schematic cross-sectional view of
another embodiment of an ATMOS.TM. papermaking machine;
[0044] FIG. 20 illustrates a schematic cross-sectional view of
another embodiment of an ATMOS.TM. papermaking machine;
[0045] FIG. 21 illustrates a schematic cross-sectional view of
another embodiment of an ATMOS.TM. papermaking machine; and
[0046] FIG. 22 is illustrates a schematic cross-sectional view of
an E-TAD papermaking machine.
[0047] Corresponding reference characters indicate corresponding
parts throughout the several views. The exemplification set out
herein illustrates one embodiment of the invention, in one form,
and such exemplification is not to be construed as limiting the
scope of the invention in any manner.
DETAILED DESCRIPTION OF THE INVENTION
[0048] The particulars shown herein are by way of example and for
purposes of illustrative discussion of the embodiments of the
present invention only and are presented in the cause of providing
what is believed to be the most useful and readily understood
description of the principles and conceptual aspects of the present
invention. In this regard, no attempt is made to show structural
details of the present invention in more detail than is necessary
for the fundamental understanding of the present invention, and the
description is taken with the drawings making apparent to those
skilled in the art how the forms of the present invention may be
embodied in practice.
[0049] The present invention relates to a structured fabric for a
papermaking machine, a former for manufacturing premium tissue and
toweling, and also to a former which utilizes the structured
fabric, and in some embodiments a belt press, in a papermaking
machine. The present invention relates to a twin wire former for
manufacturing premium tissue and toweling which utilizes the
structured fabric and a belt press in a papermaking machine. The
system of the invention is capable of producing premium tissue or
toweling with a quality similar to a through-air drying (TAD) but
with a significant cost savings.
[0050] The present invention also relates to a twin wire former
ATMOS.TM. system which utilizes the structured fabric which has
good resistance to pressure and excessive tensile strain forces,
and which can withstand wear/hydrolysis effects that are
experienced in an ATMOS.TM. system. The system may also include a
permeable belt for use in a high tension extended nip around a
rotating roll or a stationary shoe and a dewatering fabric for the
manufacture of premium tissue or towel grades. The fabric has key
parameters which include permeability, weight, caliper, and certain
compressibility.
[0051] The structured fabric of the present invention is
illustrated in FIGS. 1-3. FIG. 1 depicts a top pattern view of the
web facing side of the fabric (i.e., a view of the papermaking
surface). The numbers 1-10 shown on the bottom of the pattern
identify the warp (machine direction) yarns while the left side
numbers 1-10 show the weft (cross-direction) yarns. In FIG. 2,
symbol X illustrates a location where a warp yarn passes over a
weft yarn and an empty box illustrates a location where a warp yarn
passes under a weft yarn. As shown in FIG. 1, the areas formed
between warp yarn 6 and warp yarn 9, and between weft yarn 4 and
weft yarn 7 define a representative pocket area P that is
instrumental in forming a pillow in a web or sheet. The shaded area
indicates the location of one of the pockets of the pattern. The
sides of each pocket are defined by two warp knuckles and two weft
knuckles.
[0052] The embodiment shown in FIGS. 1-3 results in deep pockets
formed in the fabric whose bottom surface is formed by two warp
yarns (e.g., warp yarns 7 and 8 for pocket P) and two weft yarns
(e.g., weft yarns 5 and 6 for pocket P) and the four spaces
adjacent to the intersections of these two warp yarns with these
two weft yarns. As shown in FIG. 1, the repeating pattern square of
the fabric includes an upper plane having warp and weft knuckles
that define sides for the numerous pockets of the pattern
square.
[0053] The fabric of FIG. 1 shows a single repeating pattern square
of the fabric that encompasses ten warp yarns (yarns 1-10 that
extend vertically in FIG. 1) and ten weft yarns (yarns 1-10 that
extend horizontally in FIG. 1). FIG. 3 depicts the paths of warp
yarns 1-10 as they weave with weft yarns 1-10. While FIGS. 1-3 only
show a single section of the fabric, those of skill in the art will
appreciate that in commercial applications the pattern shown in
FIGS. 1-3 would be repeated many times, in both the warp and weft
directions, to form a large fabric suitable for use on a
papermaking machine.
[0054] As seen in FIG. 3, warp yarn 1 weaves with weft yarns 1-10
by passing over weft yarn 1, under weft yarns 2 and 3, over weft
yarn 4, under weft yarn 5, over weft yarns 6 and 7, under weft yarn
8 and over weft yarns 9 and 10. As can be understood from the
repeating pattern, in the area where warp yarn 1 weaves with weft
yarn 1 and where warp yarn weaves with weft yarns 9 and 10 pockets
are formed on each side of warp yarn 1. Furthermore, weft knuckles
are formed in the areas where the weft yarns pass over 3 warp
yarns.
[0055] Warp yarn 2 weaves with weft yarns 1-10 by passing under
weft yarns 2, 5, 9 and 10 and passing over weft yarns 1, 3, 4 and
6-8. That is, warp yarn 2 passes over weft yarn 1, then under weft
yarn 2, then over weft yarns 3 and 4, then under weft yarn 5, then
over weft yarns 6-8 and then under weft yarns 9 and 10.
[0056] As can be seen this weave pattern of the warp yarns is
repeated for the ten weft yarns with an offset of 7 for each
subsequent weft yarn. For example, warp yarn 1 has a distinctive
position with weft yarn 4, where warp yarn 1 is above weft yarn 4
and is below the two adjacent weft yarns. This similar occurrence
for warp yarn 2 is positioned seven positions to the right as the
pattern repeats, or rolls around, placing it at weft yarn 1. This
formula repeats placing the similar occurrence at weft yarns, 8, 5,
2, 9, 6, 3, 10 and 7, for warp yarns 3-10 in respective
sequence.
[0057] Each warp yarn weaves with the weft yarns in an identical
pattern; that is, each warp yarn passes over two consecutive weft
yarns, passes under one weft yarn, passes over three consecutive
weft yarns, passes under two consecutive weft yarns, passes over
one weft yarn and passes under one weft yarn. As discussed above
this pattern between adjacent warp yarns is offset by seven weft
yarns.
[0058] As discussed above, the yarns define areas in which pockets
are formed. Due to the offset of the weave pattern between warp
yarns as discussed previously, the pockets defined by the warp and
weft yarns are offset from each other by one yarn. This causes each
adjacent pocket in the cross machine direction to be located an
offset of one weft yarn in the machine direction of the fabric. In
a similar fashion, each adjacent pocket in the machine direction is
located an offset of one warp yarn in the cross-machine direction
of the fabric.
[0059] Each pocket is defined by four sides. Two sides are defined
by warp knuckles, each of which crosses three weft yarns, and two
sides are defined by weft knuckles, each of which crosses three
warp yarns. In addition, each warp knuckle and each weft knuckle
defines a side for two adjacent pockets.
[0060] Each of the warp knuckles and weft knuckles that define a
single pocket passes over an end of one of the other knuckles and
has an end that passes under one of the other knuckles.
[0061] By way of non-limiting example, the parameters of the
structured fabric shown in FIGS. 1-3 can have a mesh (number of
warp yarns per inch) of 42 and a count (number of weft yarns per
inch) of 36. The fabric can have a caliper of about 0.045 inches.
The number of pockets per square inch is preferably in the range of
100-200. The depth of pockets, which is the distance between the
upper plane and the lower plane of the fabric, is preferably
between 0.07 mm and 0.60 mm. The fabric has an upper plane contact
area of 10% or higher, preferably 15% or higher, and more
preferably 20% depending upon the particular product being made.
The top surface may also be hot calendered to increase the flatness
of the fabric and the upper plane contact area. In addition, the
single or multi-layered fabric should have a permeability value of
between approximately 400 cfm and approximately 600 cfm, and is
preferably between approximately 450 cfm and approximately 550
cfm.
[0062] Regarding yarn dimensions, the particular size of the yarns
is typically governed by the mesh of the papermaking surface. In a
typical embodiment of the fabric disclosed herein, the diameter of
the warp and weft yarns can be between about 0.30 mm and 0.50 mm.
The diameter of the warp yarns can be about 0.45 mm, is preferably
about 0.40 mm, and is most preferably about 0.35 mm. The diameter
of the weft yarns can be about 0.50 mm, is preferably about 0.45
mm, and is most preferably about 0.41 mm. Those of skill in the art
will appreciate that yarns having diameters outside the above
ranges may be used in certain applications. In one embodiment of
the present invention, the warp and weft yarns can have diameters
of between about 0.30 mm and 0.50 mm. Fabrics employing these yarn
sizes may be implemented with polyester yarns or with a combination
of polyester and nylon yarns.
[0063] The woven single or multi-layered fabric may utilize
hydrolysis and/or heat resistant materials. Hydrolysis resistant
materials should preferably include a PET monofilament having an
intrinsic viscosity value normally associated with dryer and TAD
fabrics in the range of between 0.72 IV (Intrinsic Velocity, i.e.,
a dimensionless number used to correlate the molecular weight of a
polymer; the higher the number the higher the molecular weight) and
approximately 1.0 IV. Hydrolysis resistant materials should also
preferably have a suitable "stabilization package" which including
carboxyl end group equivalents, as the acid groups catalyze
hydrolysis and residual DEG or di-ethylene glycol as this too can
increase the rate of hydrolysis. These two factors separate the
resin which can be used from the typical PET bottle resin. For
hydrolysis, it has been found that the carboxyl equivalent should
be as low as possible to begin with, and should be less than
approximately 12. Even at this low level of carboxyl end groups an
end capping agent may be added, and may utilize a carbodiimide
during extrusion to ensure that at the end of the process there are
no free carboxyl groups. There are several chemical classes that
can be used to cap the end groups such as epoxies, ortho-esters,
and isocyanates, but in practice monomeric and combinations of
monomeric and polymeric carbodiimides are preferred.
[0064] Heat resistant materials such as PPS can be utilized in the
structured fabric. Other materials such as PEN, PST, PEEK and PA
can also be used to improve properties of the fabric such as
stability, cleanliness and life. Both single polymer yarns and
copolymer yarns can be used. The yarns for the fabric need not
necessarily be monofilament yarns and can be a multi-filament
yarns, twisted multi-filament yarns, twisted monofilament yarns,
spun yarns, core and sheath yarns, or any combination thereof, and
could also be a non-plastic material, i.e., a metallic material.
Similarly, the fabric may not necessarily be made of a single
material and can be made of two, three or more different materials.
Shaped yarns, i.e., non-circular yarns such as round, oval or flat
yarns, can also be utilized to enhance or control the topography or
properties of the paper sheet. Shaped yarns can also be utilized to
improve or control fabric characteristics or properties such as
stability, caliper, surface contact area, surface planarity,
permeability and wearability. In addition, the yarns may be of any
color.
[0065] The structured fabric can also be treated and/or coated with
an additional polymeric material that is applied by, e.g.,
deposition. The material can be added cross-linked during
processing in order to enhance fabric stability, contamination
resistance, drainage, wearability, improve heat and/or hydrolysis
resistance and in order to reduce fabric surface tension. This aids
in sheet release and/or reduced drive loads. The treatment/coating
can be applied to impart/improve one or several of these properties
of the fabric. As indicated previously, the topographical pattern
in the paper web can be changed and manipulated by use of different
single and multi-layer weaves. Further enhancement of the pattern
can be attained by adjustments to the specific fabric weave by
changes to the yarn diameter, yarn counts, yarn types, yarn shapes,
permeability, caliper and the addition of a treatment or coating
etc. In addition, a printed design, such as a screen printed
design, of polymeric material can be applied to the fabric to
enhance its ability to impart an aesthetic pattern into the web or
to enhance the quality of the web. Finally, one or more surfaces of
the fabric or molding belt can be subjected to sanding and/or
abrading in order to enhance surface characteristics. Referring to
FIG. 1, the upper plane of the fabric may be sanded, ground, or
abraded in such a manner, resulting in flat oval shaped areas on
the warp knuckles and the weft knuckles.
[0066] The characteristics of the individual yarns utilized in the
fabric of the present invention can vary depending upon the desired
properties of the final papermakers' fabric. For example, the
materials comprising yarns employed in the fabric of the present
invention may be those commonly used in papermakers' fabric. As
such, the yarns may be formed of polypropylene, polyester, nylon,
or the like. The skilled artisan should select a yarn material
according to the particular application of the final fabric.
[0067] By way of non-limiting example, the structured fabric can be
a single or multi-layered woven fabric which can withstand high
pressures, heat, moisture concentrations, and which can achieve a
high level of water removal and also mold or emboss the paper web.
These characteristics provide a structured fabric appropriate for
the Voith ATMOS.TM. papermaking process. The fabric preferably has
a width stability and a suitable high permeability and preferably
utilizes hydrolysis and/or temperature resistant materials, as
discussed above. The fabric is preferably a woven fabric that can
be installed on an ATMOS.TM. machine as a pre-joined and/or seamed
continuous and/or endless belt. Alternatively, the forming fabric
can be joined in the ATMOS.TM. machine using, e.g., a pin-seam
arrangement or can otherwise be seamed on the machine.
[0068] The invention also provides for utilizing the structured
fabric disclosed herein on a machine for making a fibrous web,
e.g., tissue or hygiene paper web, etc., which can be, e.g., a twin
wire ATMOS.TM. system. Referring again to the drawings, and more
particularly to FIG. 4, there is a fibrous web machine 20 including
a headbox 22 that discharges a fibrous slurry 24 between a forming
fabric 26 and structured fabric 28. It should be understood that
structured fabric 28 is an embodiment of the structured fabric
discussed above in connection with FIGS. 1-3. Rollers 30 and 32
direct fabric 26 in such a manner that tension is applied thereto,
against slurry 24 and structured fabric 28. Structured fabric 28 is
supported by forming roll 34 which rotates with a surface speed
that matches the speed of structured fabric 28 and forming fabric
26. Structured fabric 28 has peaks 28a and valleys 28b, which give
a corresponding structure to web 38 formed thereon. Peaks 28a and
valleys 28b generally represent the shape of the fabric due to the
upper plane, the lower plane, and the pockets of the structured
fabric as discussed above. Structured fabric 28 travels in
direction W, and as moisture M is driven from fibrous slurry 24,
structured fibrous web 38 takes form. Moisture M that leaves slurry
24 travels through forming fabric 26 and is collected in save-all
36. Fibers in fibrous slurry 24 collect predominately in valleys
28b as web 38 takes form.
[0069] Forming roll 34 is preferably solid. Moisture travels
through forming fabric 26 but not through structured fabric 28.
This advantageously forms structured fibrous web 38 into a more
bulky or absorbent web than the prior art.
[0070] In prior art methods of moisture removal, moisture is
removed through a structured fabric by way of negative pressure.
This results in a cross-sectional view of a fibrous web 40 as seen
in FIG. 5. Prior art fibrous web 40 has a pocket depth D which
corresponds to the dimensional difference between a valley and a
peak. The valley is located at the point where measurement C is
located and the peak is located at the point where measurement A is
located. A top surface thickness A is formed in the prior art
method. Sidewall dimension B and pillow thickness C of the prior
art result from moisture drawn through a structured fabric.
Dimension B is less than dimension A and dimension C is less than
dimension B in the prior art web.
[0071] In contrast, structured fibrous web 38, as illustrated in
FIGS. 6 and 8, have for discussion purposes, a pocket depth D that
is similar to the prior art. However, sidewall thickness B' and
pillow thickness C' exceed the comparable dimensions of web 40.
This advantageously results from the forming of structured fibrous
web 38 on structured fabric 28 at low consistency and the removal
of moisture is an opposite direction from the prior art. This
results in a thicker pillow dimension C'. Even after structured
fibrous web 38 goes through a drying press operation, as
illustrated in FIG. 8, dimension C' is substantially greater than
A.sub.P'. As illustrated in FIG. 7, this is in contrast to the
dimension C of the prior art. Advantageously, the fiber web
resulting from the present invention has a higher basis weight in
the pillow areas as compared to the prior art. Also, the
fiber-to-fiber bonds are not broken as they can be in impression
operations, which expand the web into the valleys.
[0072] According to the prior art, an already formed web is vacuum
transferred into a structured fabric. The sheet must then expand to
fill the contour of the structured fabric. In doing so, fibers must
move apart. Thus the basis weight is lower in these pillow areas
and therefore the thickness is less than the sheet at point A.
[0073] Now, referring to FIGS. 9 to 14 the process will be
explained by simplified schematic drawings. As shown in FIG. 9,
fibrous slurry 24 is formed into a web 38 with a structure that
matches the shape of structured fabric 28. Forming fabric 26 is
porous and allows moisture to escape during forming. Further, water
is removed as shown in FIG. 11, through dewatering fabric 82. The
removal of moisture through fabric 82 does not cause compression of
pillow areas C' in the web, since pillow areas C' reside in valleys
28b of structured fabric 28.
[0074] The prior art web shown in FIG. 10 is formed between two
conventional forming fabrics in a twin wire former and is
characterized by a flat uniform surface. It is this fiber web that
is given a three-dimensional structure by a wet shaping stage,
which results in the fiber web that is shown in FIG. 5. A
conventional tissue machine that employs a conventional press
fabric will have a contact area approaching 100%. Normal contact
area of the structured fibrous web, as in this present invention,
or as on a TAD machine, is typically much lower than that of a
conventional machine; it is in the range of 15 to 35% depending on
the particular pattern of the product being made.
[0075] In FIGS. 12 and 14 a prior art web structure is shown where
moisture is drawn through a structured fabric 33 causing the web,
as shown in FIG. 5, to be shaped and causing pillow area C to have
a low basis weight as the fibers in the web are drawn into the
structure. The shaping can be done by performing pressure or
underpressure to the web 40 forcing the web to follow the structure
of the structured fabric 33. This additionally causes fiber tearing
as they are moved into pillow area C. Subsequent pressing at the
Yankee dryer 52, as shown in FIG. 14, further reduces the basis
weight in area C. In contrast, water is drawn through dewatering
fabric 82 in the present invention, as shown in FIG. 11, preserving
pillow areas C'. Pillow areas C' of FIG. 13 are unpressed zones
which are supported on structured fabric 28 while pressed against
Yankee dryer 52. Pressed zone A' is the area through which most of
the pressure is applied. Pillow area C' has a higher basis weight
than that of the illustrated prior art structures.
[0076] The increased mass ratio of the present invention,
particularly the higher basis weight in the pillow areas carries
more water than the compressed areas, resulting in at least two
positive aspects of the present invention over the prior art, as
illustrated in FIGS. 11 and 12. First, it allows for a good
transfer of the web 38 to the Yankee surface 52, since the web 38
has a relatively lower basis weight in the portion that comes in
contact with the Yankee surface 52, at a lower overall sheet solid
content than had been previously attainable, because of the lower
mass of fibers that comes in contact with the Yankee dryer 52. The
lower basis weight means that less water is carried to the contact
points with the Yankee dryer 52. The compressed areas are dryer
than the pillow areas, thereby allowing an overall transfer of the
web to another surface, such as a Yankee dryer 52, with a lower
overall web solids content. Secondly, the construct allows for the
use of higher temperatures in the Yankee hood 54 without scorching
or burning of the pillow areas, which occurs in the prior art
pillow areas. The Yankee hood 54 temperatures are often greater
than 350.degree. C., preferably greater than 450.degree. C., and
even more preferably greater than 550.degree. C. As a result the
present invention can operate at lower average pre-Yankee press
solids than the prior art, making more full use of the capacity of
the Yankee hood drying system. The present invention allows the
solids content of web 38 prior to the Yankee dryer 52 to run at
less than 40%, less than 35% and even as low as 25%.
[0077] Due to the formation of the web 38 with the structured
fabric 28 the pockets of the fabric 28 are fully filled with
fibers. Therefore, at the Yankee surface 52 the web 38 has a much
higher contact area, up to approximately 100%, as compared to the
prior art because the web 38 on the side contacting the Yankee
surface 52 is almost flat. At the same time the pillow areas C' of
the web 38 are maintained unpressed, because they are protected by
the valleys of the structured fabric 28 (FIG. 13). Good results in
drying efficiency were obtained only pressing 25% of the web.
[0078] As can be seen in FIG. 14 the contact area of the prior art
web 40 to the Yankee surface 52 is much lower as compared to the
one of the web 38 manufactured according to the invention. The
lower contact area of the prior art web 40 results from shaping the
web 40 by drawing water out of the web 40 through structured fabric
33. Drying efficiency of the prior art web 40 is less than that of
the web 38 of the present invention because the area of the prior
art web 40 is in less contact with the Yankee surface 52.
[0079] Referring to FIG. 15, there is shown an embodiment of the
process where a structured fibrous web 38 is formed. Structured
fabric 28 carries a three dimensional structured fibrous web 38 to
an advanced dewatering system 50, past vacuum box 67 and then to a
position where the web is transferred to Yankee dryer 52 and hood
section 54 for additional drying and creping before winding up on a
reel (not shown).
[0080] A shoe press 56 is placed adjacent to structured fabric 28,
holding fabric 28 in a position proximate Yankee dryer 52.
Structured fibrous web 38 comes into contact with Yankee dryer 52
and transfers to a surface thereof, for further drying and
subsequent creping.
[0081] A vacuum box 58 is placed adjacent to structured fabric 28
to achieve a solids level of 15-25% on a nominal 20 gsm web running
at -0.2 to -0.8 bar vacuum with a preferred operating level of -0.4
to -0.6 bar. Web 38, which is carried by structured fabric 28,
contacts dewatering fabric 82 and proceeds toward vacuum roll 60.
Vacuum roll 60 operates at a vacuum level of -0.2 to -0.8 bar with
a preferred operating level of at least -0.4 bar. Hot air hood 62
is optionally fit over vacuum roll 60 to improve dewatering. If,
for example, a commercial Yankee drying cylinder with 44 mm steel
thickness and a conventional hood with an air blowing speed of 145
m/s is used, production speeds of 1400 m/min or more for towel
paper and 1700 m/min or more for toilet paper are used.
[0082] Optionally a steam box can be installed instead of the hood
62 supplying steam to the web 38. The steam box preferably has a
sectionalized design to influence the moisture re-dryness cross
profile of the web 38. The length of the vacuum zone inside the
vacuum roll 60 can be from 200 mm to 2,500 mm, with a preferable
length of 300 mm to 1,200 mm and an even more preferable length of
between 400 mm to 800 mm. The solids level of web 38 leaving
suction roll 60 is 25% to 55% depending on installed options. A
vacuum box 67 and hot air supply 65 can be used to increase web 38
solids after vacuum roll 60 and prior to Yankee dryer 52. Wire
turning roll 69 can also be a suction roll with a hot air supply
hood. As discussed above, roll 56 includes a shoe press with a shoe
width of 80 mm or higher, preferably 120 mm or higher, with a
maximum peak pressure of less than 2.5 MPa. To create an even
longer nip to facilitate the transfer of web 38 to Yankee dryer 52,
web 38 carried on structured fabric 28 can be brought into contact
with the surface of Yankee dryer 52 prior to the press nip
associated with shoe press 56. Further, the contact can be
maintained after structured fabric 28 travels beyond press 56.
[0083] Dewatering fabric 82 may have a permeable woven base fabric
connected to a batt layer. The base fabric includes machine
direction yarns and cross-direction yarns. The machine direction
yarn is a three-ply multi-filament twisted yarn. The
cross-direction yarn is a monofilament yarn. The machine direction
yarn can also be a monofilament yarn and the construction can be of
a typical multilayer design. In either case, the base fabric is
needled with a fine batt fiber having a weight of less than or
equal to 700 gsm, preferably less than or equal to 150 gsm, and
more preferably less than or equal to 135 gsm. The batt fiber
encapsulates the base structure giving it sufficient stability. The
sheet contacting surface is heated to improve its surface
smoothness. The cross-sectional area of the machine direction yarns
is larger than the cross-sectional area of the cross-direction
yarns. The machine direction yarn is a multi-filament yarn that may
include thousands of fibers. The base fabric is connected to a batt
layer by a needling process that results in straight through
drainage channels.
[0084] In another embodiment of dewatering fabric 82, there is
included a fabric layer, at least two batt layers, an
anti-rewetting layer, and an adhesive. The base fabric is
substantially similar to the previous description. At least one of
the batt layers includes a low melt bi-compound fiber to supplement
fiber-to-fiber bonding upon heating. On one side of the base
fabric, there is attached an anti-rewetting layer, which may be
attached to the base fabric by an adhesive, a melting process, or
needling wherein the material contained in the anti-rewetting layer
is connected to the base fabric layer and a batt layer. The
anti-rewetting layer is made of an elastomeric material thereby
forming an elastomeric membrane, which has openings there
through.
[0085] The batt layers are needled to thereby hold dewatering
fabric 82 together. This advantageously leaves the batt layers with
many needled holes there through. The anti-rewetting layer is
porous having water channels or straight through pores there
through.
[0086] In yet another embodiment of dewatering fabric 82, there is
a construct substantially similar to that previously discussed with
an addition of a hydrophobic layer to at least one side of
dewatering fabric 82. The hydrophobic layer does not absorb water,
but it does direct water through pores therein.
[0087] In yet another embodiment of dewatering fabric 82, the base
fabric has attached thereto a lattice grid made of a polymer, such
as polyurethane, that is put on top of the base fabric. The grid
may be put on to the base fabric by utilizing various known
procedures, such as, for example, an extrusion technique or a
screen-printing technique. The lattice grid may be put on the base
fabric with an angular orientation relative to the machine
direction yarns and the cross-direction yarns. Although this
orientation is such that no part of the lattice is aligned with the
machine direction yarns, other orientations can also be utilized.
The lattice can have a uniform grid pattern, which can be
discontinuous in part. Further, the material between the
interconnections of the lattice structure may take a circuitous
path rather than being substantially straight. The lattice grid is
made of a synthetic, such as a polymer or specifically a
polyurethane, which attaches itself to the base fabric by its
natural adhesion properties.
[0088] In yet another embodiment of dewatering fabric 82, there is
included a permeable base fabric having machine direction yarns and
cross-direction yarns that are adhered to a grid. The grid is made
of a composite material the may be the same as that discussed
relative to a previous embodiment of dewatering fabric 82. The grid
includes machine direction yarns with a composite material formed
there around. The grid is a composite structure formed of composite
material and machine direction yarns. The machine direction yarns
may be pre-coated with a composite before being placed in rows that
are substantially parallel in a mold that is used to reheat the
composite material causing it to re-flow into a pattern. Additional
composite material may be put into the mold as well. The grid
structure, also known as a composite layer, is then connected to
the base fabric by one of many techniques including laminating the
grid to the permeable fabric, melting the composite coated yarn as
it is held in position against the permeable fabric or by
re-melting the grid onto the base fabric. Additionally, an adhesive
may be utilized to attach the grid to the permeable fabric.
[0089] The batt layer may include two layers, an upper and a lower
layer. The batt layer is needled into the base fabric and the
composite layer, thereby forming a dewatering fabric 82 having at
least one outer batt layer surface. Batt material is porous by its
nature, and additionally the needling process not only connects the
layers together, but it also creates numerous small porous cavities
extending into or completely through the structure of dewatering
fabric 82.
[0090] Dewatering fabric 82 has an air permeability of from 5 to
100 cfm, preferably 19 cfm or higher, and more preferably 35 cfm or
higher. Mean pore diameters in dewatering fabric 82 are from 5 to
75 microns, preferably 25 microns or higher, and more preferably 35
microns or higher. The hydrophobic layers can be made from a
synthetic polymeric material, a wool or a polyamide, for example,
nylon 6. The anti-rewetting layer and the composite layer may be
made of a thin elastomeric permeable membrane made from a synthetic
polymeric material or a polyamide that is laminated to the base
fabric.
[0091] The batt fiber layers are made from fibers ranging from 0.5
d-tex to 22 d-tex and may contain a low melt bi-compound fiber to
supplement fiber-to-fiber bonding in each of the layers upon
heating. The bonding may result from the use of a low temperature
meltable fiber, particles and/or resin. The dewatering fabric can
be less than 2.0 mm thick.
[0092] Preferred embodiments of the dewatering fabric 82 are also
described in the PCT/EP2004/053688 and PCT/EP2005/050198 which are
herewith incorporated by reference.
[0093] Now, additionally referring to FIG. 16, there is shown yet
another embodiment of the present invention, which is substantially
similar to the invention illustrated in FIG. 15, except that
instead of hot air hood 62, there is a belt press 64. Belt press 64
includes a permeable belt 66 capable of applying pressure to the
machine side of structured fabric 28 that carries web 38 around
vacuum roll 60. Fabric 66 of belt press 64 is also known as an
extended nip press belt or a link fabric, which can run at 60 KN/m
fabric tension with a pressing length that is longer than the
suction zone of roll 60.
[0094] Preferred embodiments of the fabric 66 and the required
operation conditions are also described in PCT/EP2004/053688 and
PCT/EP2005/050198 which are herewith incorporated by reference.
[0095] The above mentioned references are also fully applicable for
dewatering fabrics 82 and press fabrics 66 described in the further
embodiments.
[0096] While pressure is applied to structured fabric 28 by belt
press 64, the high fiber density pillow areas in web 38 are
protected from that pressure as they are contained within the body
of structured fabric 28, as they are in the Yankee nip.
[0097] Belt 66 is a specially designed extended nip press belt 66,
made of, for example reinforced polyurethane and/or a spiral link
fabric. Belt 66 also can have a woven construction. Such a woven
construction is disclosed, e.g., in EP 1837439. Belt 66 is
permeable thereby allowing air to flow there through to enhance the
moisture removing capability of belt press 64. Moisture is drawn
from web 38 through dewatering fabric 82 and into vacuum roll
60.
[0098] Belt 66 provides a low level of pressing in the range of
50-300 KPa and preferably greater than 100 KPa. This allows a
suction roll with a 1.2 m diameter to have a fabric tension of
greater than 30 KN/m and preferably greater than 60 KN/m. The
pressing length of permeable belt 66 against fabric 28, which is
indirectly supported by vacuum roll 60, is at least as long as a
suction zone in roll 60. However, the contact portion of belt 66
can be shorter than the suction zone.
[0099] Permeable belt 66 has a pattern of holes there through,
which may, for example, be drilled, laser cut, etched formed or
woven therein. Permeable belt 66 may be monoplanar without grooves.
In one embodiment, the surface of belt 66 has grooves and is placed
in contact with fabric 28 along a portion of the travel of
permeable belt 66 in belt press 64. Each groove connects with a set
of the holes to allow the passage and distribution of air in belt
66. Air is distributed along the grooves, which constitutes an open
area adjacent to contact areas, where the surface of belt 66
applies pressure against web 38. Air enters permeable belt 66
through the holes and then migrates along the grooves, passing
through fabric 28, web 38 and fabric 82. The diameter of the holes
may be larger than the width of the grooves. The grooves may have a
cross-section contour that is generally rectangular, triangular,
trapezoidal, semi-circular or semi-elliptical. The combination of
permeable belt 66, associated with vacuum roll 60, is a combination
that has been shown to increase sheet solids by at least 15%.
[0100] An example of another structure of belt 66 is that of a thin
spiral link fabric, which can be a reinforcing structure within
belt 66 or the spiral link fabric will itself serve as belt 66.
Within fabric 28 there is a three dimensional structure that is
reflected in web 38. Web 38 has thicker pillow areas, which are
protected during pressing as they are within the body of structured
fabric 28. As such the pressing imparted by belt press 64 upon web
38 does not negatively impact web quality, while it increases the
dewatering rate of vacuum roll 60.
[0101] Referring to FIG. 17, there is shown another embodiment of
the present invention which is substantially similar to the
embodiment shown in FIG. 16 with the addition of hot air hood 68
placed inside of belt press 64 to enhance the dewatering capability
of belt press 64 in conjunction with vacuum roll 60.
[0102] Referring to FIG. 18, there is shown yet another embodiment
of the present invention, which is substantially similar to the
embodiment shown in FIG. 16, but including a boost dryer 70 which
encounters structured fabric 28. Web 38 is subjected to a hot
surface of boost dryer 70, and structured web 38 rides around boost
dryer 70 with another woven fabric 72 riding on top of structured
fabric 28. On top of woven fabric 72 is a thermally conductive
fabric 74, which is in contact with both woven fabric 72 and a
cooling jacket 76 that applies cooling and pressure to all fabrics
and web 38. Here again, the higher fiber density pillow areas in
web 38 are protected from the pressure as they are contained within
the body of structured fabric 28. As such, the pressing process
does not negatively impact web quality. The drying rate of boost
dryer 70 is above 400 kg/hr m.sup.2 and preferably above 500 kg/hr
m.sup.2. The concept of boost dryer 70 is to provide sufficient
pressure to hold web 38 against the hot surface of the dryer thus
preventing blistering. Steam that is formed at the knuckle points
of fabric 28 passes through fabric 28 and is condensed on fabric
72. Fabric 72 is cooled by fabric 74 that is in contact with
cooling jacket 76, which reduces its temperature to well below that
of the steam. Thus the steam is condensed to avoid a pressure build
up to thereby avoid blistering of web 38. The condensed water is
captured in woven fabric 72, which is dewatered by dewatering
device 75. It has been shown that depending on the size of boost
dryer 70, the need for vacuum roll 60 can be eliminated. Further,
depending on the size of boost dryer 70, web 38 may be creped on
the surface of boost dryer 70, thereby eliminating the need for
Yankee dryer 52.
[0103] Referring to FIG. 19, there is shown yet another embodiment
of the present invention substantially similar to the invention
disclosed in FIG. 16 but with an addition of an air press 78, which
is a four roll cluster press that is used with high temperature air
and is referred to as an HPTAD for additional web drying prior to
the transfer of web 38 to Yankee dryer 52. Four roll cluster press
78 includes a main roll, a vented roll, and two cap rolls. The
purpose of this cluster press is to provide a sealed chamber that
is capable of being pressurized. The pressure chamber contains high
temperature air, for example, 150.degree. C. or higher and is at a
significantly higher pressure than conventional TAD technology, for
example, greater than 1.5 psi resulting in a much higher drying
rate than a conventional TAD. The high pressure hot air passes
through an optional air dispersion fabric, through web 38 and
fabric structured 28 into a vent roll. The air dispersion fabric
may prevent web 38 from following one of the cap rolls. The air
dispersion fabric is very open, having a permeability that equals
or exceeds that of fabric structured 28. The drying rate of the
HPTAD depends on the solids content of web 38 as it enters the
HPTAD. The preferred drying rate is at least 500 kg/hr m.sup.2,
which is a rate of at least twice that of conventional TAD
machines.
[0104] Advantages of the HPTAD process are in the areas of improved
sheet dewatering without a significant loss in sheet quality and
compactness in size and energy efficiency. Additionally, it enables
higher pre-Yankee solids, which increase the speed potential of the
invention. Further, the compact size of the HPTAD allows for easy
retrofitting to an existing machine. The compact size of the HPTAD
and the fact that it is a closed system means that it can be easily
insulated and optimized as a unit to increase energy
efficiency.
[0105] Referring to FIG. 20, there is shown another embodiment of
the present invention. This is significantly similar to the
embodiments shown in FIGS. 16 and 19 except for the addition of a
two-pass HPTAD 80. In this case, two vented rolls are used to
double the dwell time of structured web 38 relative to the design
shown in FIG. 19. An optional coarse mesh fabric may used as in the
previous embodiment. Hot pressurized air passes through web 38
carried on structured fabric 28 and onto the two vent rolls. It has
been shown that depending on the configuration and size of the
HPTAD, more than one HPTAD can be placed in series, which can
eliminate the need for roll 60.
[0106] Referring to FIG. 21, a conventional twin wire former 90 may
be used to replace the crescent former shown in previous examples.
The forming roll can be either a solid or open roll. If an open
roll is used, care must be taken to prevent significant dewatering
through the structured fabric to avoid losing basis weight in the
pillow areas. The outer forming fabric 93 can be either a standard
forming fabric or one such as that disclosed in U.S. Pat. No.
6,237,644. The inner fabric 91 should be a structured fabric that
is much coarser than the outer forming fabric 90. For example,
inner fabric 91 may be similar to structured fabric 28. A vacuum
roll 92 may be needed to ensure that the web stays with structured
fabric 91 and does not go with outer wire 90. Web 38 is transferred
to structured fabric 28 using a vacuum device. The transfer can be
a stationary vacuum shoe or a vacuum assisted rotating pick-up roll
94. The second structured fabric 28 is at least the same coarseness
and preferably coarser than first structured fabric 91. The process
from this point is the same as the process previously discussed in
conjunction with FIG. 16. The registration of the web from the
first structured fabric to the second structured fabric is not
perfect, and as such some pillows will lose some basis weight
during the expansion process, thereby losing some of the benefit of
the present invention. However, this process option allows for
running a differential speed transfer, which has been shown to
improve some sheet properties. Any of the arrangements for removing
water discussed above as may be used with the twin wire former
arrangement and a conventional TAD.
[0107] Referring to FIG. 22, the components shown in previous
examples may be replaced by a machine in which the web is not
directly transferred between fabrics. This system is referred to as
an E-TAD and includes a press felt 102 that originally carries a
structured fibrous web. The web is transferred to a backing roll
104 at a shoe press 106. Backing roll 104 is preferably a dryer
that carries the web without the assistance of a fabric over part
of its surface. Backing roll 104 transfers the web to a transfer
fabric 108 that is an embodiment of the structured fabric discussed
above in connection with FIGS. 1-3. This process allows for running
a differential speed transfer between backing roll 104 and transfer
fabric 108. Transfer fabric 108 subsequently transfers the web to
Yankee dryer 52. Additional components may be added to the E-TAD
system, such as other drying components as discussed with previous
embodiments of the invention.
[0108] Although the structured fabric of the present invention is
preferably used with a papermaking machine according to the
previous discussion, the structured fabric may be used with a
conventional TAD machine. TAD machines, as well as their operating
characteristics and associated components, are well known in the
art as for example from U.S. Pat. No. 4,191,609, hereby
incorporated by reference in its entirety.
[0109] The fiber distribution of web 38 in this invention is
opposite that of the prior art, which is a result of removing
moisture through the forming fabric and not through the structured
fabric. The low density pillow areas are of relatively high basis
weight compared to the surrounding compressed zones, which is
opposite of conventional TAD paper. This allows a high percentage
of the fibers to remain uncompressed during the process. The sheet
absorbency capacity as measured by the basket method, for a nominal
20 gsm web is equal to or greater than 12 grams water per gram of
fiber and often exceeds 15 grams of water per gram fiber. The sheet
bulk is equal to or greater than 10 cm.sup.3/gm and preferably
greater than 13 cm.sup.3 /gm. The sheet bulk of toilet tissue is
expected to be equal to or greater than 13 cm.sup.3/gm before
calendering.
[0110] With the basket method of measuring absorbency, 5 grams of
paper are placed into a basket. The basket containing the paper is
then weighed and introduced into a small vessel of water at
20.degree. C. for 60 seconds. After 60 seconds of soak time, the
basket is removed from the water and allowed to drain for 60
seconds and then weighed again. The weight difference is then
divided by the paper weight to yield the grams of water held per
gram of fibers being absorbed and held in the paper.
[0111] As discussed above, web 38 is formed from fibrous slurry 24
that headbox 22 discharges between forming fabric 26 and structured
fabric 28. Roll 34 rotates and supports fabrics 26 and 28 as web 38
forms. Moisture M flows through fabric 26 and is captured in
save-all 36. It is the removal of moisture in this manner that
serves to allow pillow areas of web 38 to retain a greater basis
weight and therefore thickness than if the moisture was removed
through structured fabric 28. Sufficient moisture is removed from
web 38 to allow fabric 26 to be removed from web 38 to allow web 38
to proceed to a drying stage. As discussed above, web 38 retains
the pattern of structured fabric 28 and, in addition, any zonal
permeability effects from fabric 26 that may be present.
[0112] As slurry 24 comes from headbox 22 it has a very low
consistency of approximately 0.1 to 0.5%. The consistency of web 38
increases to approximately 7% at the end of the forming section
outlet. In some of the embodiments described above, structured
fabric 28 carries web 38 from where it is first placed there by
headbox 22 all the way to a Yankee dryer to thereby provide a well
defined paper structure for maximum bulk and absorbency. Web 38 has
exceptional caliper, bulk and absorbency, those parameters being
about 30% higher than with a conventional TAD fabric used for
producing paper towels. Excellent transfer of web 38 to the Yankee
dryer takes place with the ATMOS.TM. system working at 33% to 37%
dryness, which is a higher moisture content than the TAD of 60% to
75%. There is no dryness loss running in the ATMOST configuration
since structured fabric 28 has pockets (valleys 28b), and there is
no loss of intimacy between a dewatering fabric, web 38, structured
fabric 28 and the belt.
[0113] As explained above, the structured fabric imparts a
topographical pattern into the paper sheet or web. To accomplish
this, high pressures can be imparted to the fabric via the high
tension belt. The topography of the sheet pattern can be
manipulated by varying the specifications of the fabric, i.e., by
regulating parameters such as, yarn diameter, yarn shape, yarn
density, and yarn type. Different topographical patterns can be
imparted in the sheet by different surface weaves. Similarly, the
intensity of the sheet pattern can be varied by altering the
pressure imparted by the high tension belt and by varying the
specification of the fabric. Other factors which can influence the
nature and intensity of the topographical pattern of the sheet
include air temperature, air speed, air pressure, belt dwell time
in the extended nip, and nip length.
[0114] The creative weave pattern of the present invention can be
utilized, for example, in each of the following papermaking
machines: [0115] conventional TAD (known from: U.S. Pat. No.
6,953,516 B2 and WO 2009/069046 A1) [0116] molding position on
ATMOS (known from: U.S. Pat. No. 7,351,307 B2) [0117] transfer
position on E-TAD (known from: U.S. Pat. No. 7,608,164 B2) and
[0118] appropriate position on METSO concept (known from: US Patent
No. 2010/0065234 A1 and WO 2010/030298 A1).
[0119] While this invention has been described with respect to at
least one embodiment, the present invention can be further modified
within the spirit and scope of this disclosure. This application is
therefore intended to cover any variations, uses, or adaptations of
the invention using its general principles. Further, this
application is intended to cover such departures from the present
disclosure as come within known or customary practice in the art to
which this invention pertains and which fall within the limits of
the appended claims.
* * * * *