Note: Descriptions are shown in the official language in which they were submitted.
CA 02419143 2009-04-16
1
TISSUE WITH SURFACES HAVING ELEVATED REGIONS
Background of the Invention
Consumers use paper wiping products, such as tissues, for a wide
variety of applications. For example, various types of tissues can be used
for applications, such as for nose care, cosmetics, eyeglass cleaning, etc.
Typically, a user of such tissues requires that the tissues possess a
relatively soft feel. Moreover, a user often desires that the tissue be
capable of absorbing a certain amount of a liquid without substantially
wetting the user's hand during use. In the past, various mechanisms
have been utilized to produce tissues having a soft feel. For example, in
many cases, a tissue is softened through the application of a chemical
additive (i.e., softener) that is capable of enhancing the soft feel of the
tissue product. Moreover, in other instances, a side of the tissue is
imparted with domes to provide a softer feel.
In the past, domes were typically imparted onto a tissue surface by
the application of pressure. For instance, one prior art tissue forming
process is described in U.S. Patent No. 5,556,509 to Trokhan, et al. Trokhan
describes a process for forming a web by adhering the web to a surface of
a heated dryer drum and pressing it between the drum and a roller at a nip
to form a web surface with different elevations. Thereafter, the web is
creped from the dryer and wound up at a reel. However, one problem with
such conventional tissues is that they typically have a "two-sided" feel.
Moreover, such conventional tissues also generally have relatively poor
absorption properties. For example, a conventional tissue, such as
described above, is generally characterized as having relatively high
density regions and relatively low regions. Accordingly, these
conventional tissues possess a substantial fiber density gradient in the x-y
plane (or the plane formed by the machine direction and cross-machine
CA 02419143 2003-02-11
WO 02/14605 PCT/US01/41701
2
direction), while possessing a relatively low fiber density gradient in the -z
direction so that a higher density gradient exists in the x-y plane than in
the -z direction.
As a result of such density gradients, the conventional tissues
discussed above also have a substantial pore size distribution gradient in
the x-y plane and a relatively low pore size distribution gradient in the -z
direction so that a higher pore size distribution gradient exists in the x-y
plane than in the -z direction. For example, a conventional tissue has
larger pores formed by the regions and smaller pores formed by the
regions. However, because liquids normally flow at a faster rate through
larger pores than smaller pores, a user's hand can be easily wetted when.
using the prior art tissues. Specifically, water can flow readily flow through
the pores of the regions onto a user's hand.
As such, a need currently exists for an improved tissue that
possesses a soft feel and has good absorption properties.
Summary of the Invention
The present invention is generally directed to a tissue with surfaces
having elevated regions. In particular, a tissue of the present invention
includes one surface with one topography and another surface with a
different topography.
In general, the present invention is directed to a tissue having
"elevated regions" on two surfaces. As used herein, "elevated regions"
generally refer to any type of shape imparted onto a tissue surface
including, but not limited to, dome, parabola, hyperbola, inverted cone,
multiples or combinations thereof or variable contour shapes. In particular,
a tissue of the present invention can be provided with two surfaces having
elevated regions so that the surfaces have at least one different
topographical characteristic, such as a different pitch depth, number (i.e.,
number of elevated regions in a given area), pitch width, direction, shape,
etc.
CA 02419143 2003-02-11
WO 02/14605 PCT/US01/41701
3
To form elevated regions onto each tissue surface, a variety of well-
known papermaking techniques and devices can be utilized. In particular,
devices containing protrusions, such as patterned fabrics, patterned rolls,
wire-mesh, etc., can be provided to form elevated regions on the surface
of a tissue when contacted therewith. Moreover, various papermaking
techniques, such as through-air drying, creping, embossing, calendering,
etc., can be utilized when forming the tissue.
In one particular embodiment, for example, the tissue can be
formed utilizing a technique known as uncreped through-air drying. In this
embodiment, a fibrous web is first deposited onto a forming fabric. From
the forming fabric, the web is then transferred to a transfer fabric with the
assistance of a vacuum box or shoe, if desired. During this transfer stage
(i.e., "rush transfer"), the consistency of the web is typically less than
about 35% dry weight, and particularly between about 15% to about 30%
dry weight.
In one embodiment, the transfer fabric can also be provided with
protrusions, as stated above, to impart elevated regions onto one surface
of the tissue. The protrusions of the transfer fabric can generally vary as
desired. For example, the transfer fabric can have protrusions of a pitch
depth greater than about 0.010 mm, particularly between about 0.025 to
about 2 mm, and more particularly between about 1 to about 1.8 mm; and
a pitch width greater than about 0.001 mm, particularly between about
0.005 to about 5 mm, and more particularly between about 0.25 mm to
about 2.5 mm. In addition, the transfer fabric can also have differing
protrusion directions, number per unit area, shapes, etc.
From the transfer fabric, the fibrous web is then transferred to a
through-air dryer to substantially dry the web, although other dryers are
equally suitable. In some embodiments, for example, the web can be
transferred from the transfer fabric to the through-air dryer at a consistency
CA 02419143 2003-02-11
WO 02/14605 PCT/US01/41701
4
less than about 60% by weight, and particularly between about 25% to
about 50% dry weight.
The through-air dryer, in some instances, can also contain a device
for imparting elevated regions onto a surface of the tissue. For example,
the device can be a wire-mesh surface or a patterned fabric wrapped
around the through-air dryer. In one embodiment, a through-air drying
fabric can be utilized that has certain protrusions of a pitch depth greater
than about 0.010 mm, particularly between about 0.025 to about 2 mm,
and more particularly between about 1 to about 1.8 mm; and a pitch width
greater than about 0.001 mm, particularly between about 0.005 to about 5
mm, and more particularly between about 0.25 to about 2.5 mm. In
addition, the through-air drying fabric can also have differing protrusion
directions, number per unit area, shapes, etc.
As stated, in another embodiment, the through-air dryer can contain
wire-mesh that also has spaces defined by certain wire protrusions. For
instance, in most embodiments, the wire-mesh is formed such that the
spaces make up at least about 20% of the overall area of the total wire-
mesh surface area. In one embodiment, for example, the wire-mesh
surface can contain wire protrusions having a diameter of about 0.029 mm
and also spaces defined by the protrusions having an area of about 0.005
mm2.
In some embodiments, other devices, such as a pressure roll, can
also be utilized to apply pressure to one or more surfaces of the tissue.
For instance, in one embodiment, a pressure roll can press the tissue
against the through-air dryer as the tissue travels through a nip. The
pressure roll can have a smooth or patterned surface, or can have a
smooth or patterned fabric wrapped around the roll. Moreover, in some
embodiments, the pressure roll can apply a pressure less than about 60
pounds per square inch (psi), and particularly between about 35 to about
40 psi, to one or more surfaces of the tissue.
CA 02419143 2003-02-11
WO 02/14605 PCT/US01/41701
As stated, the tissue of the present invention is generally formed
with two surfaces having elevated regions. In particular, each surface
includes elevated regions having at least one different topographical
characteristic, such as, pitch depth, pitch width, number per unit area,
5 direction, etc. For instance, in some embodiments, one surface of the
tissue has at least about 50% more elevated regions per square inch than
the other surface of the tissue, and particularly between about 50% to
about 300%. Further, the pitch depth of the elevated regions of one
surface of the tissue, in some embodiments, is between about 20% to
about 100% greater than the pitch depth of the elevated regions of the
other surface of the tissue.
Moreover, a tissue of the present invention has a substantial fiber
density gradient in the -z direction. Further, a tissue of the present
invention can also have a relatively low fiber density gradient in the x-y
plane so that a higher density gradient exists in the -z direction than in the
x-y plane. By providing a tissue with such a fiber density gradient(s), the
resulting tissues can have a variety of improved characteristics, such as
improved absorbency. In particular, tissues of the present invention can
also have a substantial pore size distribution gradient in the -z direction
and a relatively low pore size distribution gradient in the x-y plane so that
a
higher pore size distribution gradient exists in the -z direction than in the
x-
y plane. For instance, by having a substantial pore size distribution
gradient in the -z direction, the tissue can absorb liquids at a slower rate.
Further, as a result of having a relatively low pore size distribution density
gradient in the x-y plane, the tissue can also act as a liquid transfer
barrier
for liquid flowing through the tissue.
Other features and aspects of the present invention are discussed
in greater detail below.
CA 02419143 2009-04-16
6
Brief Description of the Drawings
A full and enabling disclosure of the present invention, including the
best mode thereof, directed to one of ordinary skill in the art, is set forth
more particularly in the remainder of the specification, which makes
reference to the appended figures in which:
Figure 1 is schematic diagram of one embodiment for forming
elevated regions onto the surfaces of a tissue of the present invention;
Figure 2 is a cross-sectional view of one embodiment for forming
elevated regions onto a surface of a tissue of the present invention;
Figure 3 is a cross-sectional view of another embodiment for
forming elevated regions onto a surface of a tissue of the present
invention;
Figure 4 is another cross-sectional view of the embodiment
illustrated in Figure 3;
Figure 5A is a perspective view of a patterned fabric that can be
used to form one embodiment of a tissue of the present invention;
Figure 5B is a perspective view of wire-mesh that can be used to
form one embodiment of a tissue of the present invention;
Figure 6A is a cross-sectional view of the fiber densities of regions 80,
90 of a prior art tissue 100;
Figure 6B is a cross-sectional view of the pore size distributions of
various regions of the prior art tissue illustrated in Figure 6A;
Figure 7A is a cross-sectional view of the fiber densities of various
regions of one embodiment of a tissue of the present invention; and
Figure 7B is a cross-sectional view of the pore size distributions of
various regions of one embodiment of a tissue made of the present
invention.
Repeat use of reference characters in the present specification and
drawings is intended to represent same or analogous features or elements
of the invention.
CA 02419143 2003-02-11
WO 02/14605 PCT/USO1/41701
7
Detailed Description of Representative Embodiments
Reference now will be made in detail to various embodiments of the
invention, one or more examples of which are set forth below. Each
example is provided by way of explanation of the invention, not limitation
of the invention. In fact, it will be apparent to those skilled in the art
that
various modifications and variations can be made in the present invention
without departing from the scope or spirit of the invention. For instance,
features illustrated or described as part of one embodiment, can be used
on another embodiment to yield a still further embodiment. Thus, it is
intended that the present invention covers such modifications and
variations as come within the scope of the appended claims and their
equivalents.
In general, the present invention is directed to a tissue having
"elevated regions" onto two surfaces. For example, a tissue of the present
invention can include two surfaces having elevated regions with
topographies that differ with respect to at one topographical characteristic,
such as pitch depth, number (i.e., number of elevated regions in a given
area), pitch width, direction, etc.
In general, any of a variety of tissues or other types of paper webs
can be formed with elevated regions in accordance with the present
invention. For example, the tissue can be a single or multi-ply tissue.
Normally, the basis weight of a tissue of the present invention is less than
about 120 grams per square meter (gsm), particularly less than about 60
gsm, particularly from about 10 to about 50 gsm, and more particularly
between about 15 to about 35 gsm.
Moreover, a tissue of the present invention can generally be formed
from any of a variety of materials. In particular, a variety of natural and/or
synthetic fibers can be used. For example, some suitable natural fibers
can include, but are not limited to, nonwoody fibers, such as abaca, sabai
grass, milkweed floss fibers, pineapple leaf fibers; softwood fibers, such as
CA 02419143 2009-04-16
8
northern and southern softwood kraft fibers; and hardwood fibers, such as
eucalyptus, maple, birch, aspen, and the like. Illustrative examples of
other suitable pulps include southern pines, red cedar, hemlock, and black
spruce. Exemplary commercially available long pulp fibers suitable for the
present invention include those available from Kimberly-Clark Corporation
under the trade designations "Longlac-19". In addition, furnishes including
recycled fibers may also be utilized. Moreover, some suitable synthetic
fibers can include, but are not limited to, hydrophilic synthetic fibers, such
as rayon fibers and ethylene vinyl alcohol copolymer fibers, as well as
hydrophobic synthetic fibers, such as polyolefin fibers.
In addition, a tissue of the present invention can generally be
formed utilizing any of a variety of papermaking processes. In particular, it
should be understood that the present invention is not limited to any
particular papermaking process. In fact, any process capable of forming a
paper web can be utilized in the present invention. For example, a
papermaking process of the present invention can utilize creping,
embossing, wet-pressing, through-air-drying, creped through-air-drying,
uncreped through-air-drying, single recreping, double recreping,
calendering, as well as other steps in forming the tissue.
In this regard, one particular embodiment for forming a tissue of the
present invention will now be described. Specifically, the embodiment
described below relates to one method for forming the tissue of the
present invention with elevated regions utilizing a papermaking technique
known as uncreped through-drying. Examples of such a technique are
disclosed in U.S. Patent Nos. 5,048,589 to Cook, et al.; 5,399,412 to
Sudall, et al.; 5,510,001 to Hermans, et at.; 5,591,309 to Rugowski, et al.;
and 6,017,417 to Wendt, et al. Uncreped through-air drying generally
involves the steps of: (1) forming a furnish of cellulosic fibers, water, and
optionally, other additives; (2) depositing the furnish on a traveling
CA 02419143 2009-04-16
9
foraminous belt, thereby forming a fibrous web on top of the traveling
foraminous belt; (3) subjecting the fibrous web to through-drying to remove
the water from the fibrous web; and (4) removing the dried fibrous web
from the traveling foraminous belt.
For example, referring to Figure 1, one embodiment of a
papermaking machine that can be used in the present invention is
illustrated. For simplicity, the various tensioning rolls schematically used
to define the several fabric runs are shown but not numbered. As shown,
a papermaking headbox 10 can be used to inject or deposit a stream of an
aqueous suspension of papermaking fibers onto a forming fabric 13, which
serves to support and carry the newly-formed wet web 11 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. The headbox 10 may be a conventional headbox or may
be a stratified headbox capable of producing a multilayered unitary web.
Further, multiple headboxes may be used to create a layered structure, as
is known in the art.
Forming fabric 13 can generally be made from any suitable porous
material, such as metal wires or polymeric filaments. Suitable fabrics can
include, but are not limited to, Albany 84M and 94M available from Albany
International of Albany, N.Y.; Asten 856, 866, 892, 959, 937 and Asten
Synweve Design 274, available from Asten Forming Fabrics, Inc. of
Appleton, Wis. The fabric can also be a woven fabric as taught in U.S.
Patent No. 4,529,480 to Trokhan. Forming fabrics or felts comprising
nonwoven base layers may also be useful, including those of Scapa
Corporation made with extruded polyurethane foam such as the Spectra
Series. Relatively smooth forming fabrics can be used, as well as textured
fabrics suitable for imparting texture and basis weight variations to the
CA 02419143 2009-04-16
web. Other suitable fabrics may include Asten 934 and 939, or Lindsey
952-S05 and 2164 fabric from Appleton Mills, Wis.
The wet web 11 is then transferred from the forming fabric 13 to a
transfer fabric 17. As used herein, a "transfer fabric" is a fabric which is
5 positioned between the forming section and the drying section of the web
manufacturing process. The transfer fabric 17 typically travels at a slower
speed than the forming fabric 13 in order to impart increased stretch into
the web. The relative speed difference between the two fabrics can be
from 0% to about 80%, particularly greater than about 10%, more
10 particularly from about 10% to about 60%, and most particularly from
about 10% to about 40%. This is commonly referred to as "rush" transfer.
One useful method of performing rush transfer is taught in U.S. Pat. No.
5,667,636 to Engel et al.
Transfer may be carried out with the assistance of a vacuum shoe
18 such that the forming fabric 13 and the transfer fabric 17
simultaneously converge and diverge at the leading edge of the vacuum
slot. For instance, the vacuum shoe 18 can supply pressure at levels
between about 10 to about 25 inches of mercury. The vacuum transfer
shoe 18 (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 some embodiments, other vacuum shoes, such as
a vacuum shoe 20, can also be utilized to assist in drawing the fibrous web
11 onto the surface of the transfer fabric 17. During rush transfer, the
consistency of the fibrous web 11 can vary. For instance, when assisted
by the vacuum shoe 18 at vacuum level of about 10 to about 25 inches of
mercury, the consistency of the web 11 may be up to about 35% dry
weight, and particularly between about 15% to about 30% dry weight.
Although not required, in some embodiments, the transfer fabric 17
is a patterned fabric having protrusions or impression knuckles, such as
CA 02419143 2009-04-16
11
described in U.S. Patent No. 6,017,417 to Wendt et al. For instance,
referring to Figures 2 and 5A, a patterned transfer fabric 17 can have
protrusions 37 that allows the fibrous web 11 to be imparted with elevated
regions as it is pressed into contact with the transfer fabric 17. Thus, one
surface of the fibrous web can be imparted with elevated regions, such as
shown in Figures 7A-7B.
When utilized, a patterned transfer fabric 17 can generally have any
pattern desired. For instance, a pattern for the transfer fabric 17 may
imprint the fibrous web 11 with between about 5 to about 300 elevated
regions per square inch. Moreover, the protrusions 37 may have a pitch
depth "a" greater than about 0.010 mm, particularly between about 0.025
to about 2 mm, and more particularly between about 1 to about 1.8 mm;
and a pitch width "b" greater than about 0.001 mm, particularly between
about 0.005 to about 5 mm, and more particularly between about 0.25 to
about 2.5 mm. In some embodiments, the transfer fabric can have a wire-
mesh surface, as is well known in the art. For example, in one
embodiment, the transfer fabric has a wire-mesh surface where the wire
has a diameter of 1.14 millimeters and a "mesh-count" of 8 x 13. As used
herein, the mesh-count refers to the number of open spaces formed per
inch by the wire-mesh in a certain direction. Thus, a mesh-count of 8 x 13,
for example, can refer to a wire-mesh with 8 spaces in length and 13
spaces in width. The transfer fabric 17 can also have protrusions 37 in
more than one plane, if desired, to provide elevated regions having
differing pitch depths. However, it should be understood that the method
of the present invention is not limited to any particular spacing, amount, or
size of protrusions 37. In addition, the transfer fabric 17 can also possess
protrusions 37 positioned at any desired angle. For instance, the pitch
direction of the protrusions can be in the machine direction, or at an angle
up to about 45 from the machine direction. However, other angles can be
CA 02419143 2003-02-11
WO 02/14605 PCT/US01/41701
12
utilized, particularly when forming a tissue having a more complex or
irregular surface topology. Moreover, the pitch direction of different
protrusions 37 of the transfer fabric 17 can also be positioned at different
angles as well.
From the transfer fabric 17, the fibrous web 11 is then transferred to
the through-air dryer 21, optionally with the aid of a vacuum transfer shoe
42 or roll. The vacuum transfer roll or shoe 42 (negative pressure) can
also 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. The web 11
is typically transferred from the transfer fabric 17 to the through-air dryer
21 at the nip 40 at a consistency less than about 60% by weight, and
particularly between about 25% to about 50% dry weight.
In some embodiments, as shown in Figure 1, a pressure roll 45 can
be utilized to press the web 11 against the through-air dryer 21 at a nip 40.
The roll 45 can be of made any of a variety of materials, such as of steel,
aluminum, magnesium, brass, or hard urethane.
In general, the surface of the pressure roll 45 can vary depending
on the characteristics of the papermaking process. In particular, when the
"roll side" of the fibrous web 11 is previously imparted with domes by a
patterned transfer fabric 17, it may be more desirable that the pressure roll
45 have a smooth surface. As used herein, the "roll side" of the fibrous
web refers to the side of the web 11 facing the pressure roll 45 at the nip
40. When utilized, a smooth-surfaced pressure roll 45 can be
accomplished in a variety of well-known ways. For example, the pressure
roll 45 itself can have a relatively smooth surface. Moreover, in some
instances, a relatively smooth fabric can be wrapped around the pressure
roll 45.
On the other hand, in some embodiments, the pressure roll 45 can
have a patterned surface or be wrapped with a patterned fabric, as is well
known in the art. For example, a patterned pressure roll 45 may be
CA 02419143 2009-04-16
13
utilized to impart elevated regions onto the "roll side" of the fibrous web
when the transfer fabric 17 has a smooth surface. However, it should be
understood that a patterned pressure roll 45 is not necessarily required.
As stated, the surface of the pressure roll 45, whether smooth or
patterned, generally presses the fibrous web 11 against the through-dryer
21 at the nip 40. In general, the pressure roll 45 can press the web 11
against the dryer 21 at a variety of pressures. For instance, in some
embodiments, a roll pressure less than about 60 pounds per square inch
(psi), and particularly between about 35 to about 40 psi, can be utilized.
In most embodiments, the through-air dryer 21 is provided with a
patterned surface 47 to impart domes onto the "dryer side" of the web 11. As
opposed to the "roll side", the "dryer side" of the web 11 generally refers to
the side of the fibrous web 11 facing the dryer 21 at the nip 40. To impart
elevated regions onto the dryer side of the web 11, a patterned surface 47 for
the through-air dryer 21 can be provided in a variety of ways. For
instance, in some embodiments, the through-air dryer 21 can be formed
with a wire-mesh surface, such as well known in the art, to impart a
surface with elevated regions onto the "dryer side" of the web. In one
particular embodiment, for example, as shown in Figure 5B, the through-
air dryer 21 has a wire-mesh surface in which the wire 47a has a diameter
of about 0.029 mm and the spaces 49 defined by the wire have an area of
about 0.005 mm2. In'another embodiment, the wire 47a has a diameter of
about 1 mm and a mesh-count of 4 x 4. Moreover, in most embodiments,
the wire-mesh is formed such that the open spaces 49 make up at least
about 20% of the overall area of the total wire-mesh surface area. It
should be understood, however, that wire-mesh surfaces of a variety of
sizes may be suitable for use in the present invention.
In other embodiments, the through-air dryer 21 may also be
provided with a through-air drying fabric 19, such as depicted in Figures 1
and 3-4. The through-air drying fabric 19 can travel at about the same
CA 02419143 2009-04-16
14
speed or a different speed relative to the transfer fabric 17. For example,
if desired, the through-air drying fabric 19 can run at a slower speed to
further enhance stretch.
As stated, when utilized, the through-air drying fabric 19 is typically
provided with various protrusions or impression knuckles to impart a
surface with elevated regions onto the "dryer side" of the fibrous web.
Some examples of such fabrics are described in U.S. Patent No.
6,017,417 to Wendt et al.. The through-air drying fabric 19 may be woven
or nonwoven. In general, the patterned through-air drying fabric 19 can
have any pattern desired. For instance, protrusions 47b of the through-air
drying fabric 19 may imprint the fibrous web 11 with between about 5 to
about 300 elevated regions per square inch. Moreover, the protrusions 47b
may have a pitch depth "a" greater than about 0.010 mm, particularly
between about 0.025 to about 2 mm, and more particularly between about
1 to about 1.8 mm; and a pitch width "b" greater than about 0.001 mm,
particularly between about 0.005 to about 5 mm, and more particularly
between about 0.25 to about 2.5 mm. The through-air drying fabric 19 can
also have protrusions 47b in more then one plane, if desired, to provide
elevated regions having differing pitch depths. However, it should be
understood that the method of the present invention is not limited to any
particular number or size of protrusions 47b.
In addition, the through-air drying fabricl9 can also possess
protrusions 47b positioned at any desired angle. For instance, the pitch
direction of the protrusions 47b can be in the machine direction, or at an
angle up to about 45 from the machine direction. However, other angles
can be utilized, particularly when forming a tissue having a more complex
or irregular surface topography. Moreover, the pitch direction of different
protrusions 47b of the through-air drying fabric 19 can also be positioned at
different angles as well.
CA 02419143 2009-04-16
Regardless of the mechanism utilized, the "dryer side" of the fibrous
web 11 is generally provided with a different pattern of elevated regions
than the "roll side". Thus, for example, in one embodiment of the present
invention, the pressure roll 45 simultaneously presses the fibrous web 11
5 into contact with the transfer fabric 17 and the through-air drying fabric
19
at the nip 40. The transfer fabric 17 has a first pattern of protrusions 37
and imparts the "roll side" of the web 11 with a first pattern of elevated
regions, while the through-air drying fabric 19 has a second pattern of
protrusions 47b and imparts the "dryer side" of the web 11 with a second
10 pattern of elevated regions.
Once the pressure roll 45 impresses the fibrous web 11 against the
through-air dryer 21, the through-air dryer 21 can then accomplish the
removal of moisture from the web 11 by passing air through the web
without applying any mechanical pressure. Through-air drying can also
15 increase the bulk and softness of the web. In one embodiment, for
example, the through-dryer can contain a rotatable, perforated cylinder
and a hood 50 for receiving hot air blown through perforations of the
cylinder as the through-air drying fabric 19 carries the fibrous web 11 over
the upper portion of the cylinder. The heated air is forced through the
perforations in the cylinder of the through-air dryer 21 and removes the
remaining water from the fibrous web 11. The temperature of the air
forced through the fibrous web 11 by the through-air dryer 21 can vary, but
is typically from about 250 F to about 500 F. It should also be understood
that other non-compressive drying methods, such as microwave or
infrared heating, can be used. Moreover, if desired, certain compressive
heating methods, such as Yankee dryers, may be used as well.
While supported by the through-air drying fabric 19, the web can
then be dried to a consistency of about 95 percent or greater by the
through-air dryer 21 and thereafter transferred to a carrier fabric 22. The
dried basesheet 23 having two sides with elevated regions is then
CA 02419143 2003-02-11
WO 02/14605 PCT/US01/41701
16
transported to from the carrier fabric 22 to a reel 24, where it is wound. An
optional turning roll 26 can be used to facilitate transfer of the web from
the carrier fabric 22 to the reel 24.
It should be understood that the process described above is but one
method for forming a tissue having elevated regions in accordance with
the present invention. As stated, other well-known papermaking steps,
such as creping, etc., may also be utilized in the present invention.
Moreover, the process of forming the tissue of the present invention is also
not limited to the employment of the above-mentioned devices for
imparting elevated regions onto a surface of a tissue (e.g., transfer fabrics,
pressure rolls, through-air drying fabrics, etc.). In fact, other devices,
such
as other fabrics, rolls, and the like, may be employed to impart the desired
elevated regions.
By providing each surface of a tissue with elevated regions, it has
been discovered that the tissue can have a variety of improved
characteristics, such as improved softness and absorbency. For instance,
because the tissue has relatively lightly bonded elevated regions on each
surface, each side of the tissue typically has a soft feel.
Furthermore, a tissue of the present invention also possesses a
variety of other advantageous properties. For instance, the surfaces of the
tissue can increase the absorption rate of a liquid and/or act as a barrier to
liquid transfer through the tissue. In particular, a tissue of the present
invention can generally have a relatively low fiber density gradient in the x-
y (or machine direction) plane, while also having a substantial fiber density
gradient in the -z direction so that a higher density gradient exists in the -
z
direction than in the x-y plane. In particular, each tissue surface is
imparted with elevated regions having different topographical
characteristics, such as different depths, widths, direction, number of
elevated regions per unit area, etc. For instance, in some embodiments,
one surface of the tissue has at least about 50% more elevated regions
CA 02419143 2009-04-16
17
per square inch than the other surface of the tissue, and particularly
between about 50% to about 300%. Further, the pitch depth of the
elevated regions of one surface of the tissue, in some embodiments, is
between about 20% to about 100% greater than the pitch depth of the
elevated regions of the other surface of the tissue.
Referring to Figures 7A-7B, for example, one embodiment of a
single ply tissue 60 of the present invention is illustrated. As shown, the
tissue 60 has a first surface 62 with elevated regions 63 and a second
surface 72 with elevated regions 73 such that the first surface 62 has at
least one different topographical characteristic than the second surface 72.
Specifically, in this embodiment, the number (i.e., elevated regions per
square inch) of elevated regions 73 is less than the number of elevations
63, while the elevated regions 73 have a greater pitch width and depth
than the elevated regions 63. Due to their smaller number per square inch
and greater size, the elevated regions 73 typically contain fibers 75 that
maintain a relatively larger distance from each other. As a result, less
hydrogen bonds are likely to form between the fibers, and consequently,
the elevated regions 73 tend to have a relatively lower fiber density. On
the other hand, the elevated regions 63 typically contain fibers that tend to
maintain a relatively shorter distance from each other. Thus, the elevated
regions 63 of the first surface 62 tend to have a higher fiber density than
the elevated regions 73 of the second surface 72. Accordingly, tissues
made in accordance with the present invention have a substantial fiber
density gradient in the -z direction.
In addition, as stated above, the tissues of the present invention
also have a relatively low fiber density gradient in the x-y plane. For
example, referring again to Figure 7A, the fiber densities of the first
surface 62 and the second surface 72 do not substantially change in the x-
y plane. In particular, it is believed that the use of elevated regions on
each surface of the tissue causes much of the fiber compression to occur
CA 02419143 2003-02-11
WO 02/14605 PCT/US01/41701
18
near the smaller elevated regions 63 of the first surface 62, rather than the
larger elevated regions 73 of the second surface 72. Thus, although the
fiber densities in the x-y plane may vary somewhat for one surface (i.e.,
vary from the portions of the surface impressed between protrusions and
portions of the surface forming the elevated regions), the fiber densities in
the x-y plane do not substantially change, such as in conventional tissues.
By providing a substantial fiber density gradient in the -z direction
and a relatively low fiber density gradient in the x-y plane, the resulting
tissue can have a variety of improved characteristics, such as improved
absorbency. In particular, an elevated region with less hydrogen bonding
between fibers generally possesses a greater pore size distribution than
an elevated region with more hydrogen bonding between fibers. For
example, referring to Figure 7B, the larger elevated regions 73 of the
second surface 72 have pores 74 with a certain area. In contrast, the
smaller elevated regions 63 of the first surface 62 have pores 64 that are
generally smaller in area than the pores 74. As a result, tissues of the
present invention typically have a substantial pore size distribution
gradient in the -z direction and a relatively low pore size distribution
gradient in the x-y plane so that a higher pore size distribution gradient
exists in the -z direction than in the x-y plane. Because tissues of the
present invention have such a pore size distribution gradient in the -z
direction, for example, it is believed that a capillary affect can occur that
causes a liquid traveling therethrough to flow more readily through the
larger pores than the smaller pores. The smaller pores act as a "vacuum"
to attract liquid from the larger pores, which thus increases the rate of
absorption of the liquid from the tissue surface. Moreover, because the
liquid flows at a slower rate through the smaller pores, the liquid tends to
reside in the smaller pores for a longer period of time. Further, as a result
of having a relatively low pore size distribution density gradient in the x-y
plane, the liquid can disperse from certain smaller pores to other smaller
CA 02419143 2003-02-11
WO 02/14605 PCT/US01/41701
19
pores in the x-y plane. As a result, the smaller pores can often act as a
liquid transfer barrier for liquid flowing through the tissue.
For instance, referring to Figure 7B, a tissue of the present
invention can have larger pores 74 and smaller pores 64. As a liquid
contacts the second surface having larger pores 74, it quickly flows
therethrough. Once the liquid flows through the larger pores, it then
contacts the smaller pores 64 and is dispersed in the x-y plane. As a
result, the absorption rate of the liquid is increased by one tissue surface,
while a liquid transfer barrier for keeping the hands of a user relatively dry
is provided by the other tissue surface. In other embodiments, the liquid
may also first contact the first surface 62 having smaller pores 64. In such
instances, the first surface 62 can still act as a liquid transfer barrier for
keeping the hands of a user relatively dry.
It should be understood that a tissue of the present invention can be
a single- or multi-ply tissue. When utilizing multi-ply tissues, one or more
of the plies may be formed in accordance with the present invention.
Moreover, in some instances, only the outer surfaces of the multi-ply
tissue may be imparted with elevated regions. For instance, in one
embodiment, a two-ply tissue can be formed. The first ply can have one
surface with elevated regions and another surface with non-elevated
regions. The second ply can also have one surface with elevated regions
and another surface with non-elevated regions. The non-elevated surface
of the first ply can then be placed adjacent to the non-elevated surface of
the second ply to form a multi-ply tissue having two surfaces with elevated
regions.
In an alternative embodiment, both surfaces of a single ply can
have elevated regions, but of differing size. The first ply, for example, can
have one surface with larger (e.g., depth, width, etc.) elevated regions and
another surface with smaller elevated regions. The second ply can also
have one surface with larger elevated regions and another surface with
CA 02419143 2003-02-11
WO 02/14605 PCT/US01/41701
smaller elevated regions. The smaller elevated surface of the first ply can
then be placed adjacent to the smaller elevated surface of the second ply
to form a multi-ply tissue with certain beneficial properties. In particular,
a
liquid be quickly absorbed into the center of the multi-ply tissue, and
5 dispersed in the x-y plane by the surfaces having smaller elevated regions.
In some instances, a multi-ply tissue made according to the present
invention can be particularly useful to consumers. In particular,
consumers often use more than one tissue at once. Thus, when the outer
surface of each outer ply is formed with elevated regions in accordance
10 with the present invention, the liquid tends to flow along the x-y instead
of
in the z-direction. As a result, the time required for liquid transfer through
the tissue is increased. This provides a unique benefit in that a
consumer's hand can be protected without loosing the tissue liquid
absorbent capability.
15 In addition to the benefits and advantages discussed above, a
tissue of the present invention can also have a variety of other benefits as
well. For instance, a tissue having elevated regions on each surface can
increase the caliper of the tissue, which allows for the use of smaller
elevated regions (e.g., smaller pitch depth or width) to provide a desired
20 sheet thickness. Moreover, because each surface of the tissue possesses
some hydrogen bonding, lint and slough may also be reduced.
While the invention has been described in detail with respect to the
specific embodiments thereof, it will be appreciated that those skilled in the
art, upon attaining an understanding of the foregoing, may readily
conceive of alterations to, variations of, and equivalents to these
embodiments. Accordingly, the scope of the present invention should be
assessed as that of the appended claims and any equivalents thereto.
