U.S. patent application number 16/612177 was filed with the patent office on 2020-08-27 for structured papermaking fabric.
The applicant listed for this patent is Kimberly-Clark Worldwide, Inc.. Invention is credited to Mark Alan Burazin, Mike Thomas Goulet, Jeffrey Dean Holz, Mark William Sachs, Kevin Joseph Vogt, Kenneth John Zwick.
Application Number | 20200270812 16/612177 |
Document ID | / |
Family ID | 1000004859475 |
Filed Date | 2020-08-27 |
United States Patent
Application |
20200270812 |
Kind Code |
A1 |
Holz; Jeffrey Dean ; et
al. |
August 27, 2020 |
STRUCTURED PAPERMAKING FABRIC
Abstract
Disclosed are papermaking fabrics comprising a plurality of
structuring elements disposed on a carrier structure. The fabrics
are useful in the manufacture of tissue products having good
caliper and smoothness without negatively affecting drying of the
tissue product. The fabrics have structuring elements having a
polygonal cross-sectional shape and a perimeter less than 3.6 mm,
such as from about 1.4 to 3.6 mm. In certain instances the
structuring elements may cover more than about 28 percent, such as
from about 28 to about 35 percent, of the surface area of the web
contacting surface of the carrier structure without adversely
affecting drying. In this manner the amount of the nascent web that
contacts the structuring elements and is molded into a smooth
surface is maximized without exacerbating the negative affect to
drying commonly associated with occluding a large portion of the
surface area of the papermaking fabric.
Inventors: |
Holz; Jeffrey Dean;
(Sherwood, WI) ; Zwick; Kenneth John; (Neenah,
WI) ; Sachs; Mark William; (Neenah, WI) ;
Vogt; Kevin Joseph; (Neenah, WI) ; Goulet; Mike
Thomas; (Neenah, WI) ; Burazin; Mark Alan;
(Oshkosh, WI) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Kimberly-Clark Worldwide, Inc. |
Neenah |
WI |
US |
|
|
Family ID: |
1000004859475 |
Appl. No.: |
16/612177 |
Filed: |
May 21, 2018 |
PCT Filed: |
May 21, 2018 |
PCT NO: |
PCT/US18/33611 |
371 Date: |
November 8, 2019 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62509310 |
May 22, 2017 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
D03D 2700/0162 20130101;
D21H 27/02 20130101; D21F 7/086 20130101; D03D 2700/02 20130101;
D21F 11/006 20130101; D03D 3/08 20130101; D03D 1/0094 20130101 |
International
Class: |
D21F 7/08 20060101
D21F007/08; D21F 11/00 20060101 D21F011/00; D21H 27/02 20060101
D21H027/02; D03D 1/00 20060101 D03D001/00; D03D 3/08 20060101
D03D003/08 |
Claims
1. A papermaking fabric comprising a woven carrier structure having
a machine and a cross-machine direction and a first side with a
plurality of continuous, substantially machine direction oriented
structuring elements disposed thereon, the structuring elements
having a cross-sectional height and width, wherein the width is 0.7
mm or less and the aspect ratio is from about 2:1 to about 2:3.
2. The papermaking fabric of claim 1 wherein the structuring
elements have a polygonal cross-sectional shape.
3. The papermaking fabric of claim 2 wherein the structuring
elements have a cross-sectional shape selected from the group
consisting of a trapezoid, a parallelogram, a rectangle, a rhombus,
and a square.
4. The papermaking fabric of claim 1 wherein the structuring
elements have a height from about 0.4 to 0.7 mm.
5. The papermaking fabric of claim 1 wherein the structuring
elements have a cross-sectional perimeter from about 1.6 to about
2.4 mm.
6. The papermaking fabric of claim 1 wherein the structuring
elements are impermeable to air and water and comprise silicone or
polyurethane.
7. The papermaking fabric of claim 1 wherein the structuring
elements cover from about 28 to about 32 percent of the surface
area of the first side of the carrier structure.
8. The papermaking fabric of claim 1 wherein the structuring
elements have a rectangular cross section, a height from about 0.4
to 0.7 mm and a width from 0.4 to less than 0.7 mm and are spaced
apart from one another at least about 1.0 mm.
9. The papermaking fabric of claim 1 wherein the structuring
elements have a substantially similar cross-sectional shape, height
and width and are disposed substantially parallel to one another
and cover from about 28 to about 35 percent of the first side of
the carrier structure.
10. A papermaking fabric comprising a woven carrier structure
having a machine and a cross-machine direction and a first side
with a plurality of continuous, substantially machine direction
oriented air impermeable polymeric structuring elements disposed
thereon, the structuring elements having a trapezoidal, square or
rectangular cross-sectional shape, a height less than 0.7 mm and a
width less than 0.7 mm.
11. The papermaking fabric of claim 10 wherein the structuring
elements have a height from about 0.4 to 0.7 mm.
12. The papermaking fabric of claim 10 wherein the structuring
elements have a cross-sectional perimeter from about 1.6 to about
2.4 mm.
13. The papermaking fabric of claim 10 wherein the structuring
elements cover from about 28 to about 35 percent of the surface
area of the first side of the carrier structure.
14. The papermaking fabric of claim 10 wherein the structuring
elements have a substantially similar cross-sectional shape, height
and width and are disposed substantially parallel to one another
and cover from about 28 to about 35 percent of the first side of
the carrier structure.
15. A papermaking fabric comprising a woven carrier structure
having a machine and a cross-machine direction and a first side
with a plurality of continuous, substantially machine direction
oriented air impermeable polymeric structuring elements disposed
thereon and covering from about 28 to about 35 percent of the first
side of the carrier structure, wherein the plurality of structuring
elements are substantially similarly shaped, each having a
polygonal cross-sectional shape, an aspect ratio from about 1.5:1
to about 1:1 and a width less than 0.7 mm.
16. The papermaking fabric of claim 15 wherein the structuring
elements have a height from about 0.4 to about 0.7 mm.
17. The papermaking fabric of claim 15 wherein the structuring
elements have a cross-sectional perimeter from about 1.6 to about
2.4 mm.
18. The papermaking fabric of claim 15 wherein the structuring
elements cover from about 28 to about 32 percent of the surface
area of the first side of the carrier structure.
19. The papermaking fabric of claim 15 wherein the structuring
elements have a substantially planar top surface and the elements
have substantially similar heights ranging from about 0.4 to about
0.7 mm.
20. The papermaking fabric of claim 15 wherein the structuring
elements have a width from about 0.4 to less than 0.7 mm.
Description
BACKGROUND
[0001] In the manufacture of tissue products, particularly
absorbent tissue products, there is a continuing need to improve
the physical properties and final product appearance. It is
generally known in the manufacture of tissue products that there is
an opportunity to mold a partially dewatered cellulosic web on a
papermaking belt specifically designed to enhance the finished
paper product's physical properties. Such molding can be applied by
fabrics in an uncreped through-air dried process as disclosed in
U.S. Pat. No. 5,672,248 or in a wet pressed tissue manufacturing
process as disclosed U.S. Pat. No. 4,637,859. Wet molding typically
imparts desirable physical properties independent of whether the
tissue web is subsequently creped, or an uncreped tissue product is
produced.
[0002] However, absorbent tissue products are frequently embossed
in a subsequent operation after their manufacture on the paper
machine, while the dried tissue web has a low moisture content, to
impart consumer preferred visually appealing textures or decorative
lines. Thus, absorbent tissue products having both desirable
physical properties and pleasing visual appearances often require
two manufacturing steps on two separate machines. Hence, there is a
need for a single step paper manufacturing process that can provide
the desired visual appearance and product properties. There is also
a need to develop a paper manufacturing process that not only
imparts visually discernable pattern and product properties, but
which does not affect machine efficiency and productivity.
[0003] Previous attempts to combine the above needs, such as those
disclosed in International Application Nos. PCT/US13/72220,
PCT/US13/72231 and PCT/US13/72238, have utilized through-air drying
fabrics having a pattern extruded as a line element onto the
fabric. The extruded line element may form either discrete or
continuous patterns. While such a method can produce textures,
extrusion techniques are limited in the types of lines that may be
formed resulting in reduced permeability of the through-air drying
fabric. The reduced permeability in-turn decreases drying
efficiency and negatively affects tissue machine efficiency and
productivity.
[0004] As such, there remains a need for articles of manufacture
and methods of producing tissue products having visually
discernable patterns with improved physical properties without
losses to tissue machine efficiency and productivity.
SUMMARY
[0005] The present inventors have now discovered a means of
improving tissue web drying by supporting the nascent web on a
papermaking fabric comprising a plurality of structuring elements
disposed on a carrier structure. More specifically the present
inventors have discovered that certain desirable tissue product
properties such as caliper and smoothness may be optimized without
negatively affecting drying of the tissue product by providing a
papermaking fabric having structuring elements having a perimeter
less than 3.6 mm, such as less than about 3.0 mm, such as from
about 1.4 to 3.6 mm, such as from about 1.6 to about 2.4 mm,
wherein the structuring elements cover more than about 28 percent,
such as from about 28 to about 35 percent, of the surface area of
the web contacting surface of the fabric. In this manner the amount
of the nascent web that contacts the structuring elements and is
molded into a smooth surface is maximized without exacerbating the
negative affect to drying commonly associated with occluding a
large portion of the surface area of the papermaking fabric.
[0006] Accordingly, it has now been discovered that relatively
narrow structuring elements, such as elements having a width of 0.7
mm or less, such as from 0.3 to 0.7 mm, have limited negative
affect on drying, particularly the normalized drying rate, even
when the elements cover a relatively large percentage of the
papermaking surface area, such as more than 28 percent and in some
instances more than 30 percent. This is counter to what was
previously believed. Previously, it was believed that an increase
in the percentage of fabric covered by structuring elements
resulted in a commensurate reduction in heat transfer, based on the
theoretical drying rate:
DR=q/.phi.=hA(T.sub.supply-T.sub.sheet)
Where q is the heat transfer in W/m.sup.2, .phi. is the latent heat
of the water dried in j/g, DR is the drying rate in g/s m.sup.2, h
is the heat transfer coefficient in W/m.sup.2 C, A is the area open
to the flow in m.sup.2/m.sup.2, and T is temperature. In view of
the foregoing, it was believed that when the coverage area (A) is
reduced the drying rate should be reduced by the same amount. It
has now been discovered, however, that the dominant factor
affecting drying rate is the relative size of the structuring
member, and that the coverage area may be increased so long as the
size of the structuring element is optimized.
[0007] Thus, in certain embodiments the present invention provides
a papermaking belt comprising a woven carrier structure having a
machine contacting surface and an opposite web contacting surface
and a plurality of structuring elements, which may be formed from a
liquid and air impervious material such as silicone or
polyurethane, disposed on the web contacting surface. The
structuring elements are preferably shaped and sized to enable
molding of the nascent web and to minimize negative impacts to
drying and as such generally have a cross-sectional perimeter less
than 3.6 mm, such as less than about 3.0 mm, such as less than
about 2.4 mm, such as less than about 2.0 mm, such as from about
1.4 to 3.6 mm, such as from about 1.6 to about 3.0 mm.
[0008] When viewed in the cross-section perpendicular to the X-Y
plane of the papermaking belt the structuring elements may have any
number of different cross-sectional shapes such as, for example,
polygonal, semicircular or elliptical. In certain preferred
embodiments the structuring member has a polygonal cross-sectional
shape such as, for example, a trapezoid, a parallelogram, a
rectangle, a rhombus, or a square. Regardless of the
cross-sectional shape, the structuring elements generally have a
cross-sectional perimeter less than 3.6 mm, such as less than about
3.0 mm, such as less than about 2.4 mm, such as less than about 2.0
mm, such as from about 1.4 to 3.6 mm, such as from about 1.6 to
about 3.0 mm.
[0009] Structuring elements can provide a means for deflecting
papermaking fibers in the Z-direction as the nascent web is molded
and dried while supported by the fabric. The amount of fiber
deflection and the physical properties of the resulting tissue web
such as caliper, density and surface topography may be affected to
some extent by the size and shape of the structuring elements.
Thus, in certain embodiments, it may be preferred that the
structuring member have a Z-directional height greater than about
0.4 mm, such as greater than about 0.5 mm, and more preferably
greater than about 0.6 mm, such as from about 0.4 to about 1.2 mm
and more preferably from about 0.4 to about 0.8 mm. In other
embodiments the structuring member have width, generally measured
in the cross-machine direction (CD) across the widest portion of
the element and parallel to the upper surface plane of the carrier
structure, of 0.7 mm or less, such as less than about 0.6 mm, such
as less than about 0.5 mm, such as from about 0.4 to 0.7 mm.
[0010] In other instances fiber deflection and the physical
properties of the resulting tissue web such as caliper, density and
surface topography, as well as the effective drying of the web may
be affected by the aspect ratio of the structuring member, or the
ratio of the width to Z-directional height. For optimal drying and
physical properties the aspect ratio, which is generally the ratio
of the element height to the element width, may be from about 2:1
to 2:3, such as from 1.5:1 to about 1:1.
[0011] In addition to the size and the shape of the structuring
member the physical properties of the resulting tissue web, as well
as the drying of the web, may be influenced by the relative
percentage of the carrier structure that is covered by the
structuring elements. For example, it may be desirable to provide
the finished tissue web with a plurality of relatively smooth,
elevated portions that are brought in contact with a user's skin
in-use, yet at the same time minimize the amount of the web that is
contacted by the structuring elements, which are generally
impermeable to air and water, so as not to impede drying. By
providing a structuring member having a cross-sectional perimeter
less than 3.6 mm, such as from about 1.4 to 3.6 mm, such as from
about 1.6 to about 2.4 mm, it has been discovered that the relative
area of the carrier structure that may be covered by structuring
elements may be relatively high such as greater than about 28
percent, such as greater than about 30 percent and more preferably
greater than about 32 percent, such as from about 28 to about 35
percent and more preferably from about 30 to about 32 percent,
without negatively affecting drying of the nascent web. As such a
finished tissue web having a relatively high degree of relatively
smooth, elevated portions may be produced without negatively
affecting drying of the nascent web.
DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 is a perspective view of a papermaking fabric useful
in the manufacture of tissue webs according to one embodiment of
the present invention;
[0013] FIG. 2 is top view of a papermaking fabric useful in the
manufacture of tissue webs according to one embodiment of the
present invention;
[0014] FIG. 3 is a cross section view of a papermaking fabric taken
through line 3-3 of FIG. 2;
[0015] FIG. 4 is a cross-sectional image of a papermaking fabric
taken using a Keyence VHX-5000 Digital Microscope (Keyence
Corporation, Osaka, Japan) at a magnification of 20.times.;
[0016] FIG. 5 is a top view of a papermaking fabric taken using a
Keyence VHX-5000 Digital Microscope (Keyence Corporation, Osaka,
Japan) at a magnification of 20.times.;
[0017] FIG. 6 is an image of the papermaking fabric of FIG. 5 that
has been processed to calculate the element coverage area as
described in the Test Method section;
[0018] FIG. 7 is a plot of the heat transfer coefficient (drying
rate normalized by the through-air dryer supply temperature) versus
element coverage area (x-axis) at a through-air dryer supply
temperature of 300.degree. F. for through-air drying fabrics having
structuring elements having widths of 0.9 mm (.circle-solid.), 0.8
mm (x), 0.7 mm (.tangle-solidup.), and 0.6 mm (.box-solid.);
[0019] FIG. 8 is a plot of the heat transfer coefficient (drying
rate normalized by the through-air dryer supply temperature) versus
element perimeter (x-axis) at a through-air dryer supply
temperature of 300.degree. F. for through-air drying fabrics having
structuring elements having widths of 0.9 mm (.circle-solid.), 0.8
mm (x), 0.7 mm (.tangle-solidup.), and 0.6 mm (.box-solid.);
and
[0020] FIG. 9 is a plot of the drying loss factor (y-axis) versus
element coverage area (x-axis) at a through-air dryer supply
temperature of 300.degree. F. for through-air drying fabrics having
structuring elements having widths of 0.9 mm (.circle-solid.), 0.8
mm (x), 0.7 mm (.tangle-solidup.), and 0.6 mm (.box-solid.).
DEFINITIONS
[0021] As used herein, the term "papermaking fabric" means any
woven fabric used for making a cellulosic web such as a tissue
sheet, either by a wet-laid process or an air-laid process.
Specific papermaking fabrics within the scope of this invention
include forming fabrics; transfer fabrics conveying a wet web from
one papermaking step to another, such as described in U.S. Pat. No.
5,672,248; molding, shaping, or impression fabrics where the web is
conformed to the structure through pressure assistance and conveyed
to another process step, as described in U.S. Pat. No. 6,287,426;
creping fabrics as described in U.S. Pat. No. 8,394,236; embossing
fabrics as described in U.S. Pat. No. 4,849,054; structured fabric
adjacent a wet web in a nip as described in U.S. Pat. No.
7,476,293; or through-air drying fabric as described in U.S. Pat.
Nos. 5,429,686, 6,808,599 B2 and 6,039,838. The fabrics of the
invention are also suitable for use as molding or air-laid forming
fabrics used in the manufacture of non-woven, non-cellulosic webs,
such as baby wipes.
[0022] As used herein the term "machine direction," designated MD,
is the direction parallel to the flow of the fibrous web through
the web-making equipment.
[0023] As used herein the term "cross machine direction,"
designated CD, is the direction perpendicular to the machine
direction in the X-Y plane.
[0024] As used herein the term "width" when referring to a
structuring member generally refers to the widest portion of a
cross-sectional portion of the element in the cross-machine
direction (CD). Generally width is measured at the widest point of
the element and parallel to the upper surface plane of the carrier
structure.
[0025] As used therein the term "height" when referring to a
structuring member is the Z-direction height of a member extending
from the carrier structure and is generally measured between the
upper surface plane of the carrier structure and the upper surface
plane of the element.
[0026] As used herein the term "aspect ratio" when referring to a
structuring member is the ratio of the element height to the
element width.
[0027] As used herein the terms "effective perimeter" and
"perimeter" when referring to a structuring member is the total
perimeter of a cross-sectional portion of the element. Generally
the perimeter of a cross-sectional portion of the element is a
continuous line forming the boundary of a closed geometric
figure.
[0028] As used herein the term "coverage area" generally refers to
percentage of the carrier structure's upper surface area that is
covered by structural elements as measured using a Keyence VHX-5000
Digital Microscope (Keyence Corporation, Osaka, Japan) and
described in the Test Methods section below.
[0029] As used herein the term "line element" refers to structuring
elements in the shape of a line, which may be a continuous,
discrete, interrupted, and/or partial line with respect to the
carrier structure on which it is present. The line element may be
of any suitable shape such as straight, bent, kinked, curled,
curvilinear, serpentine, sinusoidal, and mixtures thereof that may
form regular or irregular periodic or non-periodic lattice work of
structures wherein the line element exhibits a length along its
path of at least 10 mm. In one example, the line element may
comprise a plurality of discrete elements, such as dots and/or
dashes for example, that are oriented together to form a line
element.
[0030] As used herein the term "continuous" when referring to a
structuring member generally refers to an element disposed on a
carrier structure useful in forming a tissue web that extends
without interruption throughout one dimension of the carrier
structure.
[0031] As used herein the term "discrete element" when referring to
a structuring member generally refers to separate, unconnected
elements disposed on a carrier structure useful in forming a tissue
web that do not extend continuously in any dimension of the support
structure or the tissue web as the case maybe.
[0032] As used herein the term "curvilinear element" when referring
to a structuring member generally refers to any structuring member
that contains either straight sections, curved sections, or both
that are substantially connected visually. Curvilinear structuring
elements may appear as undulating lines, substantially connected
visually, forming signatures or patterns.
[0033] As used herein "decorative pattern" refers to any non-random
repeating design, figure, or motif. It is not necessary that the
curvilinear structuring elements form recognizable shapes, and a
repeating design of the curvilinear structuring elements is
considered to constitute a decorative pattern.
DETAILED DESCRIPTION
[0034] With reference now to FIGS. 1-3 a papermaking fabric 10
according to the present invention is illustrated. The papermaking
fabric 10 comprises a carrier structure 30 having a web contacting
surface 64 and a machine contacting surface 62. In use, web
contacting surface 64 is generally the side of the fabric 10 on
which fibers, such as papermaking fibers, are deposited. The web
contacting surface forms an X-Y plane, where X and Y can correspond
generally to the cross-machine direction (CD) and machine direction
(MD), respectively, when using the belt in the manufacturing of
tissue webs. One skilled in the art will appreciate that the
symbols "X," "Y," and "Z" designate a system of Cartesian
coordinates, wherein mutually perpendicular "X" and "Y" define a
reference plane formed by the web contacting surface 64 of the
papermaking fabric 10 when disposed on a flat surface, and "Z"
defines a direction orthogonal to the X-Y plane. The person skilled
in the art will appreciate that the use of the term "plane" does
not require absolute flatness or smoothness of any portion or
feature described as planar. In fact, a portion of the web
contacting surface of the fabric may consist of a woven fabric
having a textured upper surface, which may be useful in imparting
patterns or physical properties to a tissue web, yet be defined as
being generally planar or as having a surface plane.
[0035] As used herein, the term "Z-direction" designates any
direction perpendicular to the X-Y plane. Analogously, the term
"Z-dimension" means a dimension, distance, or parameter measured
parallel to the Z-direction and can be used to refer to dimensions
such as the height of discrete primary elements or the thickness
(or height or caliper), of the secondary elements. It should be
carefully noted, however, that an element that "extends" in the
Z-direction does not need itself to be oriented strictly parallel
to the Z-direction; the term "extends in the Z-direction" in this
context merely indicates that the element extends in a direction
which is not parallel to the X-Y plane. Analogously, an element
that "extends in a direction parallel to the X-Y plane" does not
need, as a whole, to be parallel to the X-Y plane; such an element
can be oriented in the direction that is not parallel to the
Z-direction.
[0036] One skilled in the art will also appreciate that any given
structuring member may not necessarily have an upper surface that
is substantially flat throughout its entire length, yet the upper
most portion of the member may generally define a plane.
Irregularities in the upper surface of structuring elements may
result from the elements being manufactured by depositing a
polymeric material, which may be flowable to a certain extent, onto
a woven carrier structure having an upper surface of which is not
entirely flat, but has a degree of texture. Nonetheless, as
illustrated in FIG. 1 and discussed herein, the structuring member
40 being disposed on a carrier structure 30 having a substantially
flat upper surface 48 and the macroscopic "X-Y" plane is
conventionally used herein for the purpose of describing relative
geometry of several elements of the structuring member 40.
[0037] As shown in FIG. 1, the structuring elements 40 are provided
in the form of substantially similarly shaped continuous line
elements. Each structuring element 40 extends in the Z-direction on
the web contacting side 64 of the carrier structure 30. The
structuring elements 40 have a generally square cross-sectional
shape with spaced apart relatively straight, parallel sidewalls 45,
47. While the illustrated structuring elements have a generally
square cross-sectional shape, the invention is not so limited and
the elements may have a variety of shapes such as, for example,
polygonal, semicircular or elliptical. In certain preferred
embodiments the line elements have a polygonal cross-sectional
shape such as, for example, a trapezoid, a parallelogram, a
rectangle, a rhombus, or a square. Further, the structuring element
sidewalls 45, 47 and top surfaces 48 can be relatively straight and
planar, such as illustrated in FIG. 1, or they may be curved,
partially straight and partially curved, or irregular when viewed
in cross-section. It should be noted that the drawings
schematically show the sidewalls 45, 47 and top surface 48 as
straight lines for ease of illustration only.
[0038] Although each of the structuring elements 40 have similar
shapes and dimensions, the invention is not so limited, and a
variety of different shapes and sizes may be employed. For example,
each of the line elements can be individually sized, shaped, and
spaced. The illustrated structuring elements 40 are continuous line
elements, each having a generally flat distal portion 48 (portion
distal from the carrier structure 30) providing the papermaking
fabric 10 with a relatively uniform second upper surface plane 74
(as illustrated in FIG. 3). In this manner each of the structuring
elements 40 have a Z-direction height (h), measured from the upper
surface plane 72 of the web contacting surface 64 of the carrier
structure 30. Although not illustrated in FIGS. 1-3, the
structuring elements may also vary in relation to one another in
terms of height or width. Further, the height and width of a given
line element need not be uniform along its entire length, but can
vary depending on the method of manufacturing the element or
according to the desired physical properties of the finished tissue
web.
[0039] There are virtually an infinite number of shapes, sizes,
spacing and orientations that may be chosen for the structuring
elements. The actual shapes, sizes, orientations, and spacing can
be specified and manufactured by additive manufacturing processes
based on the desired properties of the finished tissue web such as
caliper, sheet bulk, surface smoothness and aesthetic appearance.
The improvement of the present invention is that the shapes, sizes,
spacing, and orientations of the structuring element are such that
they provide the finished tissue web with desirable physical
properties, such as caliper, sheet bulk and surface smoothness,
without negatively affecting drying of the tissue web. As such the
structuring elements are generally designed such that a sufficient
amount of the nascent web is contacted by and molded into the
elements, but the amount of the web that is effectively rendered
impermeable because of its contact with the elements is
minimized.
[0040] For optimal molding of the web and minimal negative impact
to drying, the shape of the elements may be modified such that the
cross-sectional perimeter is less than 3.6 mm, such as less than
about 3.0 mm, such as less than about 2.4 mm, such as less than
about 2.0 mm, such as from about 1.4 to 3.6 mm, such as from about
1.6 to about 3.0 mm. In other embodiments the aspect ratio may be
modified to promote drying and impart the resulting web with the
desired physical properties and aesthetic appearance. For example,
optimal drying and physical properties of the tissue product may be
obtained by using a through-air drying fabric having structuring
elements with an aspect ratio, which is generally the ratio of the
element height to the element width, from about 2:1 to 2:3, such as
from 1.5:1 to about 1:1.
[0041] With continued reference to FIGS. 1-3, the carrier structure
30 comprises a pair of opposed major surfaces--a web contacting
surface 64 from which the structuring elements 40 extend and a
machine contacting surface 62. Machinery employed in a typical
papermaking operation is well known in the art and may include, for
example, vacuum pickup shoes, rollers, and drying cylinders. In one
embodiment the belt comprises a through-air drying fabric useful
for transporting an embryonic tissue web across drying cylinders
during the tissue manufacturing process. In such embodiments the
web contacting surface 64 supports the embryonic tissue web, while
the opposite surface, the machine contacting surface 62, contacts
the through-air dryer.
[0042] Generally the structuring element 40 is disposed on the
web-contacting surface 64 for cooperating with, and structuring of,
the wet fibrous web during manufacturing. In a particularly
preferred embodiment the web contacting surface 64 comprises a
plurality of spaced apart three-dimensional elements 40 distributed
across the web-contacting surface 64 of the carrier structure 30
such that the relative area of the carrier structure covered by the
elements may be relatively high such as greater than about 28
percent, such as greater than about 30 percent and more preferably
greater than about 32 percent, such as from about 28 to about 35
percent and more preferably from about 30 to about 32 percent,
without negatively affecting drying of the nascent web. As such a
finished tissue web having a relatively high degree of relatively
smooth, elevated portions may be produced without negatively
affecting drying of the nascent web.
[0043] In addition to structuring elements 40 the web-contacting
surface 64 preferably comprises a plurality of continuous landing
areas 60. The landing areas 60 are generally bounded by the
elements 40 and coextensive with the upper surface plane 72 of the
web contacting surface 64. Landing areas 60 are generally permeable
to liquids and allow water to be removed from the cellulosic tissue
web by the application of differential fluid pressure, by
evaporative mechanisms, or both when drying air passes through the
embryonic tissue web while on the papermaking belt 10 or a vacuum
is applied through the belt 10. Without being bound by any
particularly theory, it is believed that the arrangement of
elements and landing areas allow the molding of the embryonic web
causing fibers to deflect in the z-direction and generate the
caliper of, and patterns on the resulting tissue web.
[0044] The carrier structure 30 has two principle dimensions--a
machine direction ("MD"), which is the direction within the plane
of the belt 10 parallel to the principal direction of travel of the
tissue web during manufacture and a cross-machine direction ("CD"),
which is generally orthogonal to the machine direction. The carrier
structure 30 is generally permeable to liquids and air. In one
particularly preferred embodiment the carrier structure is a woven
fabric. The carrier structure may be substantially planar or may
have a three dimensional surface defined by ridges. In one
embodiment the carrier structure is a substantially planar woven
fabric such as a multi-layered plain-woven fabric 30 having base
warp yarns 32 interwoven with shute yarns 34 in a 1.times.1 plain
weave pattern. One example of a suitable substantially planar woven
fabric is disclosed in U.S. Pat. No. 8,141,595, the contents of
which are incorporated herein in a manner consistent with the
present invention. In a particularly preferred embodiment, the
carrier structure comprises a substantially planar woven fabric
wherein the plain-weave load-bearing layer is constructed so that
the highest points of both the load-bearing shutes 34 and the
load-bearing warps 32 are coplanar and coincident with the upper
surface plane 72 of the web contacting surface 64.
[0045] A plurality of structuring elements 40 that may, such as in
the embodiments illustrated in FIGS. 1-3, comprise a plurality of
continuous line elements having a substantially rectangular
cross-section, are disposed on the web-contacting surface 64 of the
carrier structure 30. Each structuring element 40 has a first
dimension in a first direction (x) in the plane of the top surface
area, a second dimension in a second direction (y) in the plane of
the top surface area, the first and second directions (x, y) being
at right angles to each other. The extent of the element 40 in the
first direction (x) generally defines the element width (w). The
continuous element 40 further comprises a top surface 48 extending
substantially along the second direction (y) and a pair of opposed
sidewalls 45, 47 extending in the z-direction and having a mean
height (h). These dimensions being defined when the belt is in an
uncompressed state.
[0046] The structuring elements 40 generally extend in the
z-direction (generally orthogonal to both the machine direction and
cross-machine direction) above the upper surface plane 72 of the
web contacting surface 64. As noted previously, in certain
embodiments, the elements 40 may have straight, parallel sidewalls
45, 47 providing the structuring elements 40 with a width (w), and
a height (h) and the elements 40 may be similarly sized.
[0047] In certain embodiments the elements may have a Z-directional
height greater than about 0.4 mm, such as greater than about 0.5
mm, and more preferably greater than about 0.6 mm, such as from
about 0.4 to about 1.2 mm and more preferably from about 0.4 to
about 0.8 mm. In a particularly preferred embodiment the height of
the elements is substantially similar and ranges from about 0.4 to
about 1.2 mm and more preferably from about 0.4 to about 0.8
mm.
[0048] Further, the structuring elements 40 may have a width (w),
generally measured in the cross-machine direction (CD) across the
widest portion of the element and parallel to the upper surface
plane of the carrier structure, of 0.7 mm or less, such as less
than about 0.6 mm, such as less than about 0.5 mm, such as from
about 0.4 to 0.7 mm.
[0049] While the height (h) and width (w) of the elements may be
varied, it is generally preferred that the elements have a
cross-sectional perimeter less than 3.6 mm, such as less than about
3.0 mm, such as less than about 2.4 mm, such as less than about 2.0
mm, such as from about 1.4 to 3.6 mm, such as from about 1.6 to
about 3.0 mm. In other instances the elements have a height (h) and
width (w) such that the aspect ratio is from about 2:1 to 2:3, such
as from 1.5:1 to about 1:1.
[0050] In a particularly preferred embodiment the structuring
elements 40 have planar sidewalls 45, 47 such that the
cross-section of the element has an overall square or rectangular
shape. However, it is to be understood that the design element may
have other cross-sectional shapes, such as a trapezoid or a
parallelogram, which may also be useful in producing high bulk
tissue products according to the present invention. Accordingly, in
a particularly preferred embodiment the structuring elements 40
preferably have planar sidewalls 45, 47 and a square cross-section
where the width (w) and height (h) are equal and are 0.7 mm or
less, such as less than about 0.6 mm, such as less than about 0.5
mm, such as from about 0.4 to 0.7 mm.
[0051] The spacing and arrangement of the structuring elements
relative to one another may vary depending on the desired tissue
product properties and appearance. In one embodiment a plurality of
elements extend continuously throughout one dimension of the belt
and each element in the plurality is spaced apart from the adjacent
element. Thus, the elements may be spaced apart across the entire
cross-machine direction of the belt, may endlessly encircle the
belt in the machine direction, or may run diagonally relative to
the machine and cross-machine directions. Of course, the directions
of the elements alignments (machine direction, cross-machine
direction, or diagonal) discussed above refer to the principal
alignment of the elements. Within each alignment, the elements may
have segments aligned at other directions, but aggregate to yield
the particular alignment of the entire elements.
[0052] Generally the elements are spaced apart from one another so
as to define a landing area there-between. In use, as the embryonic
tissue web is formed fibers are deflected in the z-direction by the
continuous elements, however, the spacing of elements is such that
the web maintains a relatively uniform density. This arrangement
provides the benefits of improved web extensibility, increased
sheet bulk, better softness, and a more pleasing texture.
[0053] If the individual elements are too high, or the landing area
is too small, the resulting sheet may have excessive pinholes and
insufficient compression resistance and cross-machine direction
physical properties, such as stretch, and be of poor quality.
Further, tensile strength may be degraded if the span between
elements greatly exceeds the fiber length. Conversely, if the
spacing between adjacent elements is too small the tissue will not
mold into the landing areas without rupturing the sheet, causing
excessive sheet holes, poor strength, and poor paper quality.
[0054] In addition to varying the spacing and arrangement of the
elements along the carrier structure, the shape of the element may
also be varied. For example, in one embodiment, the elements are
substantially sinusoidal and are arranged substantially parallel to
one another such that none of the elements intersect one another.
As such, in the illustrated embodiment, the adjacent sidewalls of
individual elements are equally spaced apart from one another. In
such embodiments, the center-to-center spacing of design elements
(also referred to herein as pitch or simply as p) may be greater
than about 1.0 mm apart, such as from about 1.0 to about 20 mm
apart and more preferably from about 2.0 to about 10 mm apart. In
one particularly preferred embodiment the continuous elements are
spaced apart from one-another from about 2.5 to about 4.0 mm apart.
This spacing will result in a tissue web which generates maximum
caliper when made of conventional cellulosic fibers. Further, this
arrangement provides a tissue web having three dimensional surface
topography, yet relatively uniform density.
[0055] In other embodiments the continuous elements may occur as
wave-like patterns that are arranged in-phase with one another such
that the pitch (p) is approximately constant. In other embodiments
elements may form a wave pattern where adjacent elements are offset
from one another. Regardless of the particular element pattern, or
whether adjacent patterns are in or out of phase with one another,
the elements are separated from one another by some minimal
distance. Preferably the distance between continuous elements is
greater than 0.5 mm and in a particularly preferred embodiment
greater than about 1.0 mm and still more preferably greater than
about 2.0 mm such as from about 2.0 to about 6.0 mm and still more
preferably from about 2.5 to about 4.0 mm.
[0056] Where the continuous elements are wave-like, the elements
have an amplitude (A) and a wavelength (L). The amplitude may range
from about 2.0 to about 200 mm, in a particularly preferred
embodiment from about 10 to about 40 mm and still more preferably
from about 18 to about 22 mm. Similarly, the wavelength may range
from about 20 to about 500 mm, in a particularly preferred
embodiment from about 50 to about 200 mm and still more preferably
from about 80 to about 120 mm.
[0057] While in certain embodiments the structuring elements are
continuous the invention is not so limited. In other embodiments
the elements may be discrete. For clarity, the discrete elements
will be referred to herein as protuberances. Generally the
protuberances are discrete and spaced apart from one another. Each
protuberance is joined to a carrier structure and extends outwardly
from the web contracting plane of thereof. In this manner the
protuberances contact the tissue web during manufacture.
[0058] The protuberances may have a square horizontal and lateral
(relative to the plane of the carrier structure) cross-sectional
shape, however, the shape is not so limited. The protuberance may
have any number of different horizontal and lateral cross-sectional
shapes. For example, the horizontal cross-section may have a
rectangular, circular, oval, polygonal or hexagonal shape. A
particularly preferred protuberance has planar sidewalls which are
generally perpendicular to the plane of the carrier structure.
Alternatively, the protuberances may have a tapered lateral
cross-section formed by sides that converge to yield a protuberance
having a base that is wider than the distal end.
[0059] The individual protuberances may be arranged in any number
of different manners to create a decorative pattern. In one
particular embodiment protuberances are spaced and arranged in a
non-random pattern so as to create a wave-like design. In the
illustrated embodiment spaced between the decorative patterns are
landing areas that provide a visually distinctive interruption to
the decorative pattern formed by the individual spaced apart
protuberances. In this manner, despite being discrete elements, the
protuberances are spaced apart so as to form a visually distinctive
curvilinear decorative element that extends substantially in the
machine direction. Taken as a whole the discrete elements form a
wave-like pattern.
[0060] In other embodiments the protuberances may be spaced and
arranged so as to form a decorative figure, icon or shape such as a
flower, heart, puppy, logo, trademark, word(s), and the like.
Generally the design elements are spaced about the support
structure and can be equally spaced or may be varied such that the
density and the spacing distance may be varied amongst the design
elements. For example, the density of the design elements can be
varied to provide a relatively large or relatively small number of
design elements on the web. In a particularly preferred embodiment
the design element density, measured as the percentage of
background surface covered by a design element, is from about 10 to
about 35 percent and more preferably from about 20 to about 30
percent. Similarly the spacing of the design elements can also be
varied, for example, the design elements can be arranged in spaced
apart rows. In addition, the distance between spaced apart rows
and/or between the design elements within a single row can also be
varied.
[0061] In certain embodiments the plurality of protuberances
defining a given design element may be spaced apart from one
another so as to define landing areas there between. The landing
areas are generally bounded by the designs and coextensive with the
top surface plane of the carrier structure. Landing areas are
generally permeable to liquids and allow water to be removed from
the cellulosic tissue web by the application of differential fluid
pressure, by evaporative mechanisms, or both when drying air passes
through the embryonic tissue web while on the papermaking belt or a
vacuum is applied through the belt.
[0062] The elements may be formed from a polymeric material, or
other material, applied and joined to the carrier structure in any
suitable manner. Thus in certain embodiments elements are formed by
extruding, such as that disclosed in U.S. Pat. No. 5,939,008, the
contents of which are incorporated herein by reference in a manner
consistent with the present invention, or printing, such as that
disclosed in U.S. Pat. No. 5,204,055, the contents of which are
incorporated herein by reference in a manner consistent with the
present invention, a polymeric material onto the carrier structure.
In other embodiments the design element may be produced, at least
in some regions, by extruding or printing two or more polymeric
materials. In certain instances the polymeric material may be
silicone or polyurethane, or a combination thereof.
[0063] The papermaking fabrics of the present invention are
particularly useful in making through-air dried tissue webs and
products. Through-air drying manufacturing processes are well known
in the art and may be either creped through-air drying (CTAD) or
uncreped through-air drying (UCTAD) processes. In one embodiment
the fabrics are useful in an UCTAD manufacturing process such as
that described in U.S. Pat. No. 5,607,551. In that process a twin
wire former having a papermaking headbox, such as a layered
headbox, injects or deposits a stream of an aqueous suspension of
papermaking fibers onto a forming fabric positioned on a forming
roll. The forming fabric serves to support and carry the
newly-formed wet web downstream in the process as the web is
partially dewatered to a consistency of about 10 dry weight
percent. Additional dewatering of the wet web can be carried out,
such as by vacuum suction, while the wet web is supported by the
forming fabric.
[0064] The wet web is then transferred from the forming fabric to a
transfer fabric. In one embodiment, the transfer fabric can be
traveling at a slower speed than the forming fabric in order to
impart increased stretch into the web. This is commonly referred to
as a "rush" transfer. Preferably the transfer fabric can have a
void volume that is equal to or less than that of the forming
fabric. The relative speed difference between the two fabrics can
be from 0 to 60 percent, more specifically from about 15 to 45
percent. Transfer is preferably carried out with the assistance of
a vacuum shoe such that the forming fabric and the transfer fabric
simultaneously converge and diverge at the leading edge of the
vacuum slot.
[0065] The web is then transferred from the transfer fabric to the
through-air drying fabric with the aid of a vacuum transfer roll or
a vacuum transfer shoe, optionally again using a fixed gap transfer
as previously described. The through-air drying fabric can be
traveling at about the same speed or a different speed relative to
the transfer fabric. If desired, the through-air drying fabric can
be run at a slower speed to further enhance stretch. Transfer can
be carried out with vacuum assistance to ensure deformation of the
sheet to conform to the through-air drying fabric, thus yielding
desired bulk and texture.
[0066] The side of the web contacting the through-air drying fabric
is typically referred to as the "fabric side" of the paper web. The
fabric side of the paper web, as described above, may have a shape
that conforms to the surface of the through-air drying fabric after
the paper web is dried in the throughdryer. The opposite side of
the paper web, on the other hand, is typically referred to as the
"air side."
[0067] The level of vacuum used for the web transfers can be from
about 3 to about 15 inches of mercury (75 to about 380 millimeters
of mercury), preferably about 5 inches (125 millimeters) of
mercury. The vacuum shoe (negative pressure) can be supplemented or
replaced by the use of positive pressure from the opposite side of
the web to blow the web onto the next fabric in addition to or as a
replacement for sucking it onto the next fabric with vacuum. Also,
a vacuum roll or rolls can be used to replace the vacuum
shoe(s).
[0068] While supported by the through-air drying fabric, the web is
dried to a consistency of about 94 percent or greater by the
throughdryer and thereafter transferred to a carrier fabric. The
dried basesheet is transported to the reel using the carrier
fabric. Suitable carrier fabrics for this purpose are Albany
International 84M or 94M and Asten 959 or 937, all of which are
relatively smooth fabrics having a fine pattern. Optionally the
base sheet may be subjected to additional converting steps such as
reel calendering, off-line calendering or embossing.
TEST METHODS
Fabric Image Analysis
[0069] Fabric images were acquired and analyzed using a Keyence
VHX-5000 Digital Microscope (Keyence Corporation, Osaka, Japan)
equipped with VHX-5000 Communication Software Ver. 1.5.1.1. The
lens is an ultra-small, high performance zoom lens,
VH-Z20R/Z20T.
[0070] Structuring element dimensions were measured using the
Keyence software. For example, element height was measured by first
drawing a line approximately along the top surface plane of the
carrier structure with the line tangent to at least two filaments
forming the web contacting surface of the carrier structure. A
second parallel line has been drawn approximately along the top
surface plane of the structuring element with the line tangent to
the top surface of the element. With the two lines drawn, each
corresponding to a surface plane of the fabric, the digital
microscope software was instructed to calculate the distances
between the planes.
[0071] Element width was measured by determining the widest portion
of the element and using the software to draw a first line through
the widest point, the line being substantially parallel to the web
contacting surface plane of the carrier structure. A pair of lines
were then drawn perpendicular to the first line tangent to the
point that the first line intersected the element, the digital
microscope software was instructed to calculate the distances
between the pair of lines.
[0072] The surface area of the carrier structure covered by the
structuring elements was measured using a Keyence Microscope and
image analysis software described above. The sample of carrier
structure for measurement should be an undamaged, flat fabric
swatch approximately 3.times.3 inches in size.
[0073] An image of the fabric was acquired at a magnification of
20.times. and from the on-screen menu "Measure" was selected,
followed by selection of "Auto" area measurement, then the "Color"
option was selected and a measurement was taken. Once a measurement
was taken the structuring elements were filled using the "Fill" and
"Eliminate Small Grains" features, followed by selecting a Shaping
step. If there are areas of the structuring elements that needed to
be filled in, or otherwise edited to create an accurate 2-D
highlight of the structuring elements, an accurate area
representation was created by selecting "Edit", "Fill." The results
were than tabulated by selecting the "Next" to proceed to the
Result Display step where "Measure Result" was selected and the
calculated Area Ratio Percent was displayed. FIG. 6 illustrates the
output of the foregoing measurement method. The measurement was
repeated for 3 distinct areas of the fabric sample and an
arithmetic average Area Ratio Percent of the measurements was
reported as the Area Ratio Percent.
EXAMPLES
[0074] To evaluate the effect of structuring element size and
coverage area on the drying of tissue webs several different
through-air drying fabrics were used to manufacture a single ply
uncreped through-air dried ("UCTAD") tissue web as generally
described in U.S. Pat. No. 5,607,551, the contents of which are
incorporated herein in a manner consistent with the present
invention. Tissue webs having a target bone dry basis weight of
about 40 grams per square meter (gsm).
[0075] In all cases the base sheets were produced from a furnish
comprising northern softwood kraft and eucalyptus kraft using a
layered headbox fed by three stock chests such that the webs having
three layers (two outer layers and a middle layer) were formed. The
two outer layers comprised eucalyptus (each layer comprising 30
percent weight by total weight of the web) and the middle layer
comprised softwood and eucalyptus. The amount of softwood and
eucalyptus kraft in the middle layer was maintained for all
inventive samples--the middle layer comprised 29 percent (by total
weight of the web) softwood and 11 percent (by total weight of the
web) eucalyptus. Strength was controlled via the addition of starch
and/or by refining the softwood furnish.
[0076] The tissue web was formed on a Voith Fabrics TissueForm V
forming fabric, vacuum dewatered to a consistency ranging from
about 30 to about 33 percent and then subjected to rush transfer
when transferred to the transfer fabric. The transfer fabric was
the fabric described as "Fred" in U.S. Pat. No. 7,611,607
(commercially available from Voith Fabrics, Appleton, Wis.).
[0077] The web was then transferred to a through-air drying fabric
comprising a printed silicone pattern disposed on the sheet
contacting side. The silicone formed a wave-like pattern on the
sheet contacting side of the fabric. Inventive papermaking fabrics
are shown in FIGS. 4 and 5. The pattern properties of the various
fabrics are summarized in Table 1, below.
TABLE-US-00001 TABLE 1 Element Element Element Element Coverage
Height Width Perimeter Aspect Area Fabric (mm) (mm) (mm) Ratio (%)
1 0.9 0.9 3.6 1:1 24 2 0.8 0.8 3.2 1:1 31 3 0.7 0.7 2.7 1:1 30 4
0.6 0.6 2.4 1:1 31 5 0.6 0.6 2.4 1:1 25
[0078] The tissue web was dried to a final consistency of about 98
percent by passing the web over first and second through-air dryers
while supported by the through-air drying fabric. The exhaust
temperature of the first through-air dryer was controlled to about
300.degree. F. It was discovered that through-air drying fabrics
having narrower structuring elements, which are impermeable to air
and water, were able to produce tissue webs having a sufficient
degree of smooth flat surfaces without negatively affecting drying.
The plot shown in FIGS. 7 and 8 shows the heat transfer coefficient
(shown in the equation below) calculated over the first through-air
dryer for each fabric of the present example.
h = Drying Rate ( T supply - T sheet ) ##EQU00001##
In addition to varying the width of the elements the percent of
coverage area was varied by altering the spacing of the elements
relative to one another. In each case the structuring elements had
a substantially square cross-sectional shape and an aspect ratio of
1:1. It was expected that the main factor affecting heat transfer
coefficient would be the relative area of the fabric occluded by
the elements and that for every one percent increase in coverage
there would be a one percent reduction in heat transfer. It was
surprisingly discovered however, that the dimensions of the
elements was a dominant factor affecting drying rate, and that
using elements having a width of 0.7 mm or less the coverage area
could be increased with very little adverse effect on drying
rate.
[0079] The drying benefit may also be determined by calculating the
Drying Loss Factor that compares the loss in drying rate measured
for a given fabric having impermeable structuring elements
(DR.sub.occluded) to the drying rate of a fabric devoid of such
elements (DR.sub.open):
Drying Loss Factor = 1 - DR occluded DR open Coverage Area
##EQU00002##
Assuming that the area of the web in contact with the structuring
elements are not drying at all, then the Drying Loss Factor will
equal 1, if it is drying just as well as the rest of the web then
the Drying Loss Factor will be 0. FIG. 9 shows the Drying loss
factor measured for the fabrics of the present example compared to
commercially available through-air drying fabric that is void of
structuring elements (designated as T-1205-2 and described
previously in U.S. Pat. No. 8,500,955). The Drying Loss Factor
increases as the width of the structuring element increases,
however, for elements having a width of 0.8 Drying Loss Factor
increases more rapidly compared to elements having a width of 0.7
mm or less.
[0080] Accordingly, in a first embodiment the present invention
provides a papermaking fabric comprising a woven carrier structure
having a machine and a cross-machine direction and a first side
with a plurality of substantially machine direction oriented
structuring elements disposed thereon, the structuring elements
having a cross-sectional height and width, wherein the width is 0.7
mm or less and the aspect ratio is from about 2:1 to about 2:3
[0081] In a second embodiment the present invention provides the
papermaking fabric of the first embodiment wherein the structuring
elements are continuous line elements and have a polygonal
cross-sectional shape.
[0082] In a third embodiment the present invention provides the
papermaking fabric of the first or the second embodiments wherein
the structuring elements have a cross-sectional shape selected from
the group consisting of a trapezoid, a parallelogram, a rectangle,
a rhombus, and a square.
[0083] In a fourth embodiment the present invention provides the
papermaking fabric of the first through the third embodiments
wherein the structuring elements have a height from about 0.4 to
0.7 mm.
[0084] In a fifth embodiment the present invention provides the
papermaking fabric of the first through the fourth embodiments
wherein the structuring elements have a perimeter from about 1.6 to
about 2.4 mm.
[0085] In a sixth embodiment the present invention provides the
papermaking fabric of the first through the fifth embodiments
wherein the structuring elements are impermeable to air and water
and comprise silicone or polyurethane.
[0086] In a seventh embodiment the present invention provides the
papermaking fabric of the first through the sixth embodiments
wherein the structuring elements cover from about 28 to about 32
percent of the surface area of the first side of the carrier
structure.
* * * * *