U.S. patent application number 11/772332 was filed with the patent office on 2007-12-13 for nonwovens having reduced poisson ratio.
Invention is credited to Ralph L. Anderson, Mark Burazin, Charles J. Garneski, Douglas W. Stage, Maurizio Tirimacco, Eugenio G. Varona, Kenneth J. Zwick.
Application Number | 20070286987 11/772332 |
Document ID | / |
Family ID | 34701058 |
Filed Date | 2007-12-13 |
United States Patent
Application |
20070286987 |
Kind Code |
A1 |
Anderson; Ralph L. ; et
al. |
December 13, 2007 |
Nonwovens Having Reduced Poisson Ratio
Abstract
Nonwoven materials having a pattern incorporated into the
materials are disclosed. The nonwoven materials may be, for
instance, tissue webs, meltspun webs such as meltblown webs or
spunbond webs, bonded carded webs, hydroentangled webs, and the
like. The pattern may be incorporated into the webs using various
techniques. For instance, the pattern may be formed into the web by
topically applying a bonding material. In an alternative
embodiment, the pattern may be formed according to a thermal
bonding process. The pattern contains individual cells that include
two spaced apart expanded regions separated by a constricted
region. By incorporating the pattern into the web, a material is
produced having a relatively low Poisson ratio.
Inventors: |
Anderson; Ralph L.;
(Marietta, GA) ; Varona; Eugenio G.; (Marietta,
GA) ; Garneski; Charles J.; (Kenmore, WA) ;
Tirimacco; Maurizio; (Appleton, WI) ; Stage; Douglas
W.; (Appleton, WI) ; Burazin; Mark; (Oshkosh,
WI) ; Zwick; Kenneth J.; (Neenah, WI) |
Correspondence
Address: |
DORITY & MANNING, P.A.
POST OFFICE BOX 1449
GREENVILLE
SC
29602-1449
US
|
Family ID: |
34701058 |
Appl. No.: |
11/772332 |
Filed: |
July 2, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10749475 |
Dec 31, 2003 |
7252870 |
|
|
11772332 |
Jul 2, 2007 |
|
|
|
Current U.S.
Class: |
428/152 ;
428/174; 428/411.1 |
Current CPC
Class: |
B32B 5/26 20130101; Y10T
428/2481 20150115; Y10T 428/24802 20150115; B31F 1/126 20130101;
D04H 1/66 20130101; Y10T 428/31504 20150401; A61F 13/513 20130101;
B31F 2201/0733 20130101; D21H 27/005 20130101; Y10T 428/24455
20150115; B31F 1/07 20130101; Y10T 428/24628 20150115; D04H 1/425
20130101; Y10T 428/24463 20150115; D04H 1/76 20130101; Y10T
428/24446 20150115; D21H 27/008 20130101; B32B 2307/54 20130101;
B32B 3/06 20130101; B32B 2555/02 20130101; Y10T 428/24826 20150115;
B32B 2317/00 20130101; A61F 13/51104 20130101; D21H 25/005
20130101 |
Class at
Publication: |
428/152 ;
428/174; 428/411.1 |
International
Class: |
D06N 7/04 20060101
D06N007/04; B32B 1/00 20060101 B32B001/00; B32B 9/00 20060101
B32B009/00 |
Claims
1. A web having a reduced Poisson ratio comprising: a nonwoven web
comprising fibers, the nonwoven web having a first side and a
second side; and a pattern formed into the nonwoven web, the
pattern comprising a plurality of interconnected individual cells,
each cell comprising first and second expanded regions connected
together by a constricted region.
2. A web as defined in claim 1, wherein the nonwoven web comprises
a meltspun web and wherein the pattern is thermally bonded into the
web.
3. A web as defined in claim 1, wherein the nonwoven web comprises
a tissue web containing pulp fibers, the pattern being formed into
the nonwoven web by applying a bonding material to at least one
side of the web.
4. A web as defined in claim 1, wherein the nonwoven web comprises
a tissue web, and wherein the tissue web is formed on a forming
fabric having a 3-dimensional topography, the pattern being
contained in the 3-dimensional topography and being incorporated
into the tissue web during formation.
5. A web as defined in claim 3, wherein the tissue web has been
creped after application of the bonding material.
6. A web as defined in claim 1, wherein the nonwoven web comprises
a hydroentangled web.
7. A web as defined in claim 1 wherein the nonwoven web comprises
an elastic web containing an elastomeric material.
8. A laminated web comprising a patterned layer of material,
wherein the patterned layer is arranged in a pattern comprising a
plurality of individual cells, each cell comprising first and
second expanded regions connected together by a constricted
region.
9. A laminated web as defined in claim 8 wherein the patterned
layer is chosen from a scrim or a film.
10. A laminated web as defined in claim 9 further comprising a
tissue web containing pulp fibers, wherein the tissue web is
laminated to the patterned layer.
11. A laminated web as defined in claim 9 further comprising a
meltspun web, wherein the meltspun web is laminated to the
patterned layer.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application claims priority to and is a
continuation application of Application Ser. No. 10/749,475, filed
on Dec. 31, 2003, which is incorporated herein by reference in its
entirety.
BACKGROUND OF THE INVENTION
[0002] Many nonwoven sheet materials, such as tissue webs, meltspun
webs, hydroentangled webs, bonded carded webs, and the like are
designed to include several important properties. For example,
tissue products should have good bulk, a soft feel and should be
highly absorbent. Tissue products should also have good strength
even while wet and should resist tearing. Unfortunately, it is very
difficult to produce a high strength tissue product that is also
soft and highly absorbent. Usually, when steps are taken to
increase one property of the product, other characteristics of the
product are adversely affected. For instance, softness is typically
increased by decreasing or reducing fiber bonding within the tissue
product. Inhibiting or reducing fiber bonding, however, adversely
affects the strength of the tissue web.
[0003] In the past, various methods have been used in order to
increase the strength of nonwoven webs. For instance, many tissue
webs and meltspun webs, such as meltblown webs and spunbond webs,
undergo embossing or thermal bonding after being formed in order to
increase the strength and integrity of the webs. In many
applications, the web is thermally bonded according to a particular
pattern. Nonwoven webs are also treated with latex materials to
increase strength. The latex materials may be applied topically to
the web in a pattern.
[0004] One particular process that has proved to be very successful
in increasing the strength of tissue products, such as paper towels
and wipers, without significantly adversely affecting other
properties of the web is disclosed in U.S. Pat. No. 3,879,257 to
Gentile, et al., which is incorporated herein by reference. In
Gentile, et al., a process is disclosed in which a bonding material
is applied in a fine, spaced apart pattern to one side of a fibrous
web. The web is then adhered to a heated creping surface and creped
from the surface. A bonding material is applied to the opposite
side of the web and the web is similarly creped. The process
disclosed in Gentile, et al. produces tissue products having
exceptional bulk, outstanding softness and good absorbency. The
surface regions of the web also provide excellent strength,
abrasion resistance, and wipe-dry properties.
[0005] One problem that still persists, however, is the ability to
produce a web that has properties in the cross-machine direction
that are comparable to the properties of the web in the machine
direction. For instance, many of the bonding patterns that are
applied to webs typically greatly enhance the strength and stretch
properties of the web in the machine direction without similarly
increasing the same properties of the web in the cross-machine
direction.
[0006] One particular problem encountered in the manufacture of
nonwoven sheet materials is that most materials exhibit relatively
high Poisson ratios in that when the material is pulled in the
machine direction, the width of the material in the cross-machine
direction significantly decreases. Since nonwoven materials are
typically pulled in the machine direction during formation of the
materials and during incorporation of the materials into a product,
the above effect must be compensated for when processing the
nonwoven materials. In some applications, the machine width is
overdesigned or process conditions are compromised in order to
control the width loss. This problem also extends into finishing
operations causing issues of sheet control and overcompensating
machine conditions or product dimensions.
[0007] As such, a need currently exists for a method of improving
the overall properties of nonwoven sheet materials. In particular,
a need currently exists for nonwoven sheet materials having a
bonding pattern that reduces the Poisson ratio of the material such
that the material has less tendency to shrink in the cross-machine
direction when pulled in the machine direction.
[0008] A need also exists for an improved tissue product that
possesses a negative Poisson ratio. When having a negative Poisson
ratio, the web actually increases in width when the material is
pulled in the lengthwise direction. It is believed that by creating
a tissue product with a negative Poisson ratio, the product will
also exhibit an increase in stretch in the cross-machine direction,
with increased energy absorption in the cross direction.
SUMMARY OF THE INVENTION
[0009] In general, the present invention is directed to a method
for producing nonwoven sheet materials and to sheet materials made
from the method. In one particular embodiment of the present
invention, for instance, a tissue product is formed similar to the
process disclosed in Gentile, et al. as described above. For
instance, in this embodiment, a bonding material is applied to the
first side of a tissue web according to a preselected pattern. The
pattern comprises a plurality of individual cells. Each cell
comprises first and second expanded regions connected together by a
constricted region. The individual cells may be interconnected
along at least two sides to adjacent cells. For instance, in one
embodiment, every side of each cell is interconnected with an
adjacent cell. After the bonding material is applied to the first
side of the tissue web, the first side of the tissue web is creped.
For example, the tissue web may be adhered to a creping surface and
then creped from the surface.
[0010] If desired, a second bonding material may be applied to the
second side of the tissue web according to a similar pattern. The
second side of the tissue web may also be optionally creped,
depending upon the particular application. The bonding materials
may be, for instance, an ethylene vinyl acetate copolymer.
[0011] The pattern by which the bonding material is applied as
described above reduces the Poisson ratio of the tissue web. In one
embodiment, for instance, it is believed that the tissue web may
actually have a negative Poisson ratio. In other embodiments, the
tissue web may have a Poisson ratio of less than about 0.3, such as
less than about 0.25, less than about 0.2, or less than about
0.1.
[0012] The individual cells that make up the pattern may have a
variety of shapes. For instance, the expanded regions may have a
square, triangular, hexagonal, elliptical or curvilinear shape. The
constricted region may have a width of less than about 2 mm, such
as less than about 1.5 mm. For instance, in one embodiment, the
constricted region has a width of from about 0.5 mm to about 1.5
mm, such as about 0.75 mm.
[0013] The tissue web may have a basis weight of from about 10 gsm
to about 120 gsm, such as from about 20 gsm to about 80 gsm. In
general, however, lowering the basis weight of the tissue web may
lead to much lower Poisson ratios, such as negative Poisson ratios,
particularly, when the internal fiber bonding is disrupted by use
of a cellulose debonder, e.g. Arosurf PA801 (available from
Degussa-Goldschmidt Chem. Corp.). When producing tissue webs having
a negative Poisson ratio, for instance, the tissue web may have a
basis weight of less than about 40 gsm, such as less than about 30
gsm.
[0014] The tissue web after being creped may have a bulk greater
than about 2 cc/g, such as greater than about 5 cc/g. In other
embodiments, the bulk of the tissue web may be greater than about 9
cc/g, such as greater than about 10 cc/g, such as greater than
about 11 cc/g. For instance, in one embodiment, the tissue web may
have a bulk of from about 9 cc/g to about 12 cc/g.
[0015] The tissue web as described above may be incorporated into
various tissue products. For instance, the tissue web may be used
to produce paper towels, industrial wipers, facial tissues, bath
tissues, napkins, and the like.
[0016] In addition to forming tissue products according to a print
creping process, patterns as described above may be incorporated
into various nonwoven sheet materials using various techniques for
reducing Poisson ratios. The nonwoven sheet materials may be, in
addition to tissue webs, meltspun webs such as meltblown webs or
spunbond webs, hydroentangled webs, bonded carded webs, and the
like. Once formed, the nonwoven sheet materials may be incorporated
into laminates or may be used in a single ply product. Almost an
infinite variety of products may be formed from the sheet materials
in addition to the tissue products described above. For instance,
nonwoven sheet materials made according to the present invention
can be used to produce absorbent articles such as diapers, feminine
hygiene products, adult incontinence products, absorbent swimwear,
surgical drapes, bandages, and the like.
[0017] Patterns as described above may be formed into the nonwoven
sheet materials using various methods in addition to print creping
processes. For instance, the pattern may be thermally bonded into
the web. In this embodiment, for instance, the web may be fed
through a heated embossing roll which forms the pattern.
[0018] In another embodiment, the pattern may be formed into the
nonwoven web by forming the web on a forming surface having a
3-dimensional topography that contains a pattern as described
above. When formed on the forming surface, the pattern becomes
incorporated into the web. The forming surface may be, for
instance, a fabric where water drainage occurs or a drying fabric
should the nonwoven web comprise a tissue web. Alternatively, the
nonwoven web may be formed on a forming fabric having differential
drainage to impart a pattern of high and low basis weights
corresponding to a pattern as described above. In still another
embodiment, the nonwoven web may be a tissue web that is molded
into a drying fabric imparting a 3-dimensional topography to the
tissue web that contains a pattern as described above, optionally
drying the web to final dryness while the tissue web is held in the
3-dimensional state.
[0019] In another embodiment of the present invention, a laminated
structure may be produced having a relatively low Poisson ratio.
The laminated structure may comprise one or more auxetic layers in
accordance with the present invention. The auxetic layer, for
instance, may comprise a scrim or apertured film in which the
openings in the material comprise an auxetic pattern.
[0020] Various other features and aspects of the present invention
are discussed in greater detail below.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] A full and enabling disclosure of the present invention,
including the best mode thereof to one skilled in the art, is set
forth more particularly in the remainder of the specification,
including reference to the accompanying figures, in which:
[0022] FIG. 1 is a schematic diagram of one embodiment of a process
for forming uncreped through-dried tissue webs for use in the
present invention;
[0023] FIG. 2 is a schematic diagram of one embodiment of a process
for forming wet creped tissue webs for use in the present
invention;
[0024] FIG. 3 is a schematic diagram of one embodiment of a process
for applying bonding materials to each side of a tissue web and
creping of the web in accordance with the present invention;
[0025] FIG. 4 is a schematic diagram of an alternative embodiment
of a process for applying a bonding material to one side of a
tissue web and creping one side of the web in accordance with the
present invention;
[0026] FIG. 5 is a plan view of one embodiment of a bonding pattern
made in accordance with the present invention;
[0027] FIG. 6 is a plan view of one embodiment of an enlarged cell
that may be contained in a bonding pattern made in accordance with
the present invention;
[0028] FIG. 7 is a plan view of another embodiment of a bonding
pattern in accordance with the present invention;
[0029] FIG. 8 is a plan view of still another embodiment of a
bonding pattern in accordance with the present invention;
[0030] FIG. 9 is a plan view of another embodiment of a bonding
pattern in accordance with the present invention;
[0031] FIG. 10 is a plan view of still another embodiment of a
bonding pattern in accordance with the present invention;
[0032] FIG. 11 is a plan view of another embodiment of a bonding
pattern in accordance with the present invention;
[0033] FIGS. 12 through 14 are the graphical results obtained in
Example 1 below; and
[0034] FIG. 15 is a graphical depiction of an incremental
deformation of a fiber segment in a web.
[0035] Repeat use of reference characters in the present
specification and drawings is intended to represent the same or
analogous features or elements of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0036] It is to be understood by one of ordinary skill in the art
that the present discussion is a description of exemplary
embodiments only, and is not intended as limiting the broader
aspects of the present invention.
[0037] In general, the present invention is directed to various
nonwoven sheet materials that have improved properties due to the
incorporation of a pattern into the materials. The pattern may
comprise a plurality of individual cells. The cells may be
interconnected. Each cell includes first and second expanded
regions connected together by a constricted region. Examples of
patterns according to the present invention, for instance, are
shown in FIGS. 5, 7, 8, 9, 10, and 11.
[0038] In accordance with the present invention, the pattern
incorporated into the nonwoven material significantly lowers the
Poisson ratio of the material. The Poisson ratio of a material is
the ratio of transverse contraction strain to longitudinal
extension strain in the direction of a stretching force. Tensile
deformation is considered positive and compressive deformation is
considered negative. The mathematical expression of a Poisson ratio
for a material contains a minus sign so that normal materials have
a positive ratio. In other words, since most common materials
decrease in width when stretched in a lengthwise direction, the
Poisson ratio for these materials is positive.
[0039] When a pattern of the present invention is incorporated into
a nonwoven material, the Poisson ratio of the material is
significantly reduced. The pattern causes the material to resist
deformation and shrinkage of the width of the material when the
material is pulled in the lengthwise direction. Specifically, with
a negative Poisson ratio, the constricted regions of the individual
cells contained in the pattern expand when the material is pulled
in an opposite direction. In this manner, the cells may be
considered to be auxetic (growing), since the cells expand when
subjected to strain.
[0040] In certain embodiments of the present invention, especially
when processing tissue webs according to a print creping process,
the auxetic pattern may in fact create a tissue web having a
negative Poisson ratio. When the material has a negative Poisson
ratio, the material actually increases in width when stretched in
the lengthwise direction. Tissue webs exhibiting a negative Poisson
ratio may display increased cross-direction stretch and increased
energy absorption in the cross direction.
[0041] During a print creping process, a first bonding material is
applied to a first side of a base sheet or tissue web. The first
side of the tissue web is then adhered to a creping surface and
creped from the surface. Optionally, a second bonding material,
which can be the same or different from the first bonding material,
may be applied according to a preselected pattern to the second
side of the tissue web. The second side of the tissue web may then
be creped if desired.
[0042] In accordance with the present invention, the bonding
materials are applied to the tissue web in preselected patterns
that create a product having a relatively low Poisson ratio such as
a negative Poisson ratio, provided the fiber to fiber bonding is
reduced enough to allow the pattern bonding to be predominant.
Creping the web causes delamination and increases the sheet caliper
and cross-directional stretch of the web. By increasing caliper,
creping also increases the bulk of the sheet making the tissue web
feel softer.
[0043] Exemplary embodiments of print creping processes will now be
described in detail. It should be understood, however, that a print
creping process is merely one exemplary embodiment for use of the
patterns of the present invention. In no way is the following
description intended to limit the invention.
[0044] Tissue webs processed according to the present invention can
be made in different manners and can contain various different
types of fibers. In general, however, the tissue web contains
papermaking fibers, such as softwood fibers. In addition to
softwood fibers, the tissue web can also contain hardwood fibers
such as eucalyptus fibers and/or high-yield pulp fibers. In a
preferred embodiment, the tissue web is produced from northern
softwood fibers of a coarseness of 11-15, with a fiber length of
2-3 mm.
[0045] As used herein, "high-yield pulp fibers" are those
papermaking fibers produced by pulping processes providing a yield
of about 65 percent or greater, more specifically about 75 percent
or greater, and still more specifically from about 75 to about 95
percent. Yield is the resulting amount of processed fiber expressed
as a percentage of the initial wood mass. Such pulping processes
include bleached chemithermomechanical pulp (BCTMP),
chemithermomechanical pulp (CTMP) pressure/pressure
thermomechanical pulp (PTMP), thermomechanical pulp (TMP),
thermomechanical chemical pulp (TMCP), high-yield sulfite pulps,
and high-yield kraft pulps, all of which leave the resulting fibers
with high levels of lignin. High-yield fibers are well known for
their stiffness (in both dry and wet states) relative to typical
chemically pulped fibers. The cell wall of kraft and other
non-high-yield fibers tends to be more flexible because lignin, the
"mortar" or "glue" on and in part of the cell wall, has been
largely removed. Lignin is also nonswelling in water and
hydrophobic, and resists the softening effect of water on the
fiber, maintaining the stiffness of the cell wall in wetted
high-yield fibers relative to kraft fibers. The preferred
high-yield pulp fibers can also be characterized by being comprised
of comparatively whole, relatively undamaged fibers, high freeness
(250 Canadian Standard Freeness (CSF) or greater, more specifically
350 CFS or greater, and still more specifically 400 CFS or
greater), and low fines content (less than 25 percent, more
specifically less than 20 percent, still more specifically less
that 15 percent, and still more specifically less than 10 percent
by the Britt jar test).
[0046] In one embodiment of the present invention, the tissue web
contains softwood fibers in combination with high-yield pulp
fibers, particularly BCTMP fibers. BCTMP fibers can be added to the
web in order to increase the bulk and caliper of the web, while
also reducing the cost of the web.
[0047] The amount of high-yield pulp fibers present in the sheet
can vary depending upon the particular application. For instance,
the high-yield pulp fibers can be present in an amount of about 2
dry weight percent or greater, particularly about 15 dry weight
percent or greater, and more particularly from about 5 dry weight
percent to about 40 dry weight percent, based upon the total weight
of fibers present within the web.
[0048] In one embodiment, the tissue web can be formed from
multiple layers of a fiber furnish. The tissue web can be produced,
for instance, from a stratified headbox. Layered structures
produced by any means known in the art are within the scope of the
present invention, including those disclosed in U. S. Pat. No.
5,494,554 to Edwards, et al. and U.S. Pat. No. 5,129,988 to
Farrington, which are incorporated herein by reference.
[0049] In one embodiment, for instance, a layered or stratified web
is formed that contains high-yield pulp fibers in the center.
Because high-yield pulp fibers are generally less soft than other
papermaking fibers, in some applications, it is advantageous to
incorporate them into the middle of the tissue web, such as by
being placed in the center of a 3-layered sheet. The outer layers
of the sheet can then be made from softwood fibers and/or hardwood
fibers.
[0050] For example, in one particular embodiment of the present
invention, the tissue web contains outer layers made from softwood
fibers. Each outer layer can comprise from about 15% to about 40%
by weight of the web and particularly can comprise about 25% by
weight of the web. The middle layer, however, can comprise from
about 40% to about 60% by weight of the web, and particularly about
50% by weight of the web. The middle layer can contain a mixture of
softwood fibers and BCTMP fibers. The BCTMP fibers can be present
in the middle layer in an amount from about 40% to about 60% by
weight of the middle layer, and particularly in an amount of about
50% by weight of the middle layer.
[0051] In another embodiment of the present invention, the tissue
web can be made containing two layers of fibers. The first layer
can contain the high-yield pulp fibers. The second layer, on the
other hand, can comprise softwood fibers. This particular
embodiment is well suited for creating two-ply products. In
particular, the layer of fibers containing the high-yield fibers
can be laminated to a second nonwoven web in forming the multi-ply
product. The layer of fibers containing the softwood fibers, on the
other hand, may be treated with a bonding material and creped from
a creping surface.
[0052] The tissue web of the present invention can also be formed
without a substantial amount of inner layer fiber-to-fiber bond
strength. In this regard, the fiber furnish used to form the base
web can be treated with a chemical debonding agent. The debonding
agent can be added to the fiber slurry during the pulping process
or can be added directly into the head box. Suitable debonding
agents that may be used in the present invention include cationic
debonding agents such as fatty dialkyl quaternary amine salts, mono
fatty alkyl tertiary amine salts, primary amine salts, imidazoline
quaternary salts, silicone quaternary salt and unsaturated fatty
alkyl amine salts. Other suitable debonding agents are disclosed in
U.S. Pat. No. 5,529,665 to Kaun which is incorporated herein by
reference. In particular, Kaun discloses the use of cationic
silicone compositions as debonding agents.
[0053] In one embodiment, the debonding agent used in the process
of the present invention is an organic quaternary ammonium chloride
and particularly a silicone based amine salt of a quaternary
ammonium chloride. For example, the debonding agent can be PROSOFT
TQ1003 marketed by the Hercules Corporation. The debonding agent
can be added to the fiber slurry in an amount of from about 1 kg
per metric tonne to about 10 kg per metric tonne of fibers present
within the slurry.
[0054] In an alternative embodiment, the debonding agent can be an
imidazoline-based agent. The imidazoline-based debonding agent can
be obtained, for instance, from the Witco Corp. of Middlebury,
Conn. The imidazoline-based debonding agent can be added in an
amount of between 2.0 to about 15 kg per metric tonne.
[0055] In one embodiment, the debonding agent can be added to the
fiber furnish according to a process as disclosed in PCT
Application having an International Publication No. WO 99/34057
filed on Dec. 17, 1998 or in PCT Published Application having an
International Publication No. WO 00/66835 filed on Apr. 28, 2000,
which are both incorporated herein by reference. In the above
publications, a process is disclosed in which a chemical additive,
such as a debonding agent, is adsorbed onto cellulosic papermaking
fibers at high levels. The process includes the steps of treating a
fiber slurry with an excess of the chemical additive, allowing
sufficient residence time for adsorption to occur, filtering the
slurry to remove unadsorbed chemical additives, and redispersing
the filtered pulp with fresh water prior to forming a nonwoven
web.
[0056] The basis weight of tissue webs used in the process of the
present invention can vary depending upon the final product. For
example, the process of the present invention can be used to
produce bath or facial tissue webs, paper towels, industrial
wipers, and the like. For these products, the basis weight of the
tissue web can vary from about 10 gsm to about 120 gsm, and
particularly from about 20 gsm to about 80 gsm.
[0057] In multiple ply products, the basis weight of each tissue
web present in the product can also vary. In general, the total
basis weight of a multiple ply product will generally be the same
as indicated above, such as from about 10 gsm to about 120 gsm.
Thus, the basis weight of each ply can be from about 10 gsm to
about 60 gsm, such as from about 15 gsm to about 40 gsm.
[0058] As stated above, the manner in which the tissue web is
formed can also vary depending upon the particular application. In
general, the tissue web can be formed by any of a variety of
papermaking processes known in the art. For example, the tissue web
can be a wet-creped web, a calendered web, an embossed web, a
through-air dried web, a creped through-air dried web, an uncreped
through-air dried web, as well as various combinations of the
above. In one particular embodiment of the present invention,
however, the tissue web is made in an uncreped through-air dried
process.
[0059] For example, referring to FIG. 1, shown is a method for
making throughdried paper sheets in accordance with this invention.
(For simplicity, the various tensioning rolls schematically used to
define the several fabric runs are shown but not numbered. It will
be appreciated that variations from the apparatus and method
illustrated in FIG. 1 can be made without departing from the scope
of the invention.) Shown is a twin wire former having a papermaking
headbox 34, such as a layered headbox, which injects or deposits a
stream 36 of an aqueous suspension of papermaking fibers onto the
forming fabric 38 positioned on a forming roll 39. 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.
[0060] The wet web is then transferred from the forming fabric to a
transfer fabric 40. 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. 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 0-60
percent, more specifically from about 15-45 percent. Transfer is
preferably carried out with the assistance of a vacuum shoe 42 such
that the forming fabric and the transfer fabric simultaneously
converge and diverge at the leading edge of the vacuum slot.
[0061] The web is then transferred from the transfer fabric to the
throughdrying fabric 44 with the aid of a vacuum transfer roll 46
or a vacuum transfer shoe, optionally again using a fixed gap point
contact transfer as previously described. The throughdrying fabric
can be traveling at about the same speed or a different speed
relative to the transfer fabric. If desired, the throughdrying
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 throughdrying fabric,
thus yielding desired bulk and appearance if desired. Suitable
throughdrying fabrics are described in U.S. Pat. No. 5,429,686
issued to Kai F. Chiu et al. and U.S. Pat. No. 5,672,248 to Wendt,
et al. which are incorporated by reference.
[0062] In one embodiment, the throughdrying fabric contains high
and long impression knuckles. For example, the throughdrying fabric
can have about from about 5 to about 300 machine direction
impression knuckles per square inch which are raised at least about
0.005 inches above the plane of the fabric. During drying, the web
can be macroscopically arranged to conform to the surface of the
throughdrying fabric and form a three-dimensional surface. Flat
surfaces, however, can also be used in the present invention.
[0063] The side of the web contacting the throughdrying fabric is
typically referred to as the "fabric side" of the tissue web. The
fabric side of the tissue web, as described above, may have a shape
that conforms to the surface of the throughdrying fabric after the
fabric is dried in the throughdryer. The opposite side of the
tissue web, on the other hand, is typically referred to as the "air
side". The air side of the web is typically smoother than the
fabric side during normal throughdrying processes.
[0064] The level of vacuum used for the web transfers can be from
about 3 to about 15 inches of mercury (about 75 to about 380
millimeters of mercury), preferably about 5 inches (about 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).
[0065] While supported by the throughdrying fabric, the web is
final dried to a consistency of about 94 percent or greater by the
throughdryer 48 and thereafter transferred to a carrier fabric 50.
The dried basesheet 52 is transported to the reel 54 using carrier
fabric 50 and an optional carrier fabric 56. An optional
pressurized turning roll 58 can be used to facilitate transfer of
the web from carrier fabric 50 to fabric 56. 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. Although not shown, reel calendering or subsequent
off-line calendering can be used to improve the smoothness and
softness of the basesheet.
[0066] In one embodiment, the tissue web 52 is a textured web which
has been dried in a three-dimensional state such that the hydrogen
bonds joining fibers were substantially formed while the web was
not in a flat, planar state. For instance, the web can be formed
while the web is on a highly textured throughdrying fabric or other
three-dimensional substrate. Processes for producing uncreped
throughdried fabrics are, for instance, disclosed in U.S. Pat. No.
5,672,248 to Wendt, et al.; U.S. Pat. No. 5,656,132 to Farrington,
et al.; U.S. Pat. No. 6,120,642 to Lindsay and Burazin; U.S. Pat.
No. 6,096,169 to Hermans, et al.; U.S. Pat. No. 6,197,154 to Chen,
et al.; and U.S. Pat. No. 6,143,135 to Hada, et al., all of which
are herein incorporated by reference in their entireties.
[0067] Uncreped through-air dried tissue webs made according to the
process illustrated in FIG. 1 may provide various advantages in the
process of the present invention. It should be understood, however,
that other types of tissue webs can be used in the present
invention. For example, in an alternative embodiment, a wet creped
tissue web can be utilized.
[0068] For example, referring to FIG. 2, one embodiment of a
papermaking machine is illustrated capable of forming a tissue web
for use in the process of the present invention. As shown, in this
embodiment, a head box 60 emits an aqueous suspension of fibers
onto a forming fabric 62 which is supported and driven by a
plurality of guide rolls 64. A vacuum box 66 is disposed beneath
forming fabric 62 and is adapted to remove water from the fiber
furnish to assist in forming a web. From forming fabric 62, a
formed web 68 is transferred to a second fabric 70, which may be
either a wire or a felt. Fabric 70 is supported for movement around
a continuous path by a plurality of guide rolls 72. Also included
is a pick up roll 74 designed to facilitate transfer of web 68 from
fabric 62 to fabric 70.
[0069] From fabric 70, web 68, in this embodiment, is transferred
to the surface of a rotatable heated dryer drum 76, such as a
Yankee dryer. Web 68 is lightly pressed into engagement with the
surface of dryer drum 76 to which it adheres, due to its moisture
content and its preference for the smoother of the two surfaces. In
some cases, however, an adhesive can be applied over the web
surface or drum surface for facilitating attachment of the web to
the drum.
[0070] As web 68 is carried through a portion of the rotational
path of the dryer surface, heat is imparted to the web causing most
of the moisture contained within the web to be evaporated. Web 68
is then removed from dryer drum 76 by a creping blade 78. Although
optional, creping web 68 as it is formed further reduces internal
bonding within the web and increases softness.
[0071] Once the tissue web is formed, a bonding material is applied
to at least one side of the web according to a pattern of the
present invention and at least one side of the web is then creped.
Referring to FIG. 3, one embodiment of a system that may be used to
apply bonding materials to each side of the tissue web and to crepe
each side of the web is illustrated. The embodiment shown in FIG. 3
can be an in-line or off-line process. As shown, tissue web 80 made
according to the process illustrated in FIG. 1 or FIG. 2 or
according to a similar process, is passed through a first bonding
agent application station generally 82. Station 82 includes a nip
formed by a smooth rubber press roll 84 and a patterned rotogravure
roll 86. Rotogravure roll 86 is in communication with a reservoir
88 containing a first bonding material 90. Rotogravure roll 86
applies the bonding material 90 to one side of web 80 in a
preselected pattern according to the present invention.
[0072] Web 80 is then contacted with a heated creping roll 92 by a
press roll 94. The tissue web 80 is carried on the surface of the
creping roll 92 for a distance and then removed therefrom by the
action of a creping blade 93. The creping blade 93 performs a
controlled pattern creping operation on the first side of the
tissue web.
[0073] From the creping roll 92, the web 80 can be advanced by pull
rolls 96 to a second bonding material application station generally
98. Station 98 includes a transfer roll 100 in contact with a
rotogravure roll 102, which is in communication with a reservoir
104 containing a second bonding material 106. Similar to station
82, second bonding material 106 is applied to the opposite side of
web 80 in a preselected pattern according to the present invention.
Once the second bonding material is applied, web 80 is adhered to a
heated creping roll 108 by a press roll 110. Web 80 is carried on
the surface of the creping drum 108 for a distance and then removed
therefrom by the action of a creping blade 112. The creping blade
112 performs a controlled pattern creping operation on the second
side of the tissue web.
[0074] Once creped, tissue web 80, in this embodiment, is pulled
through a drying station 114. Drying station 114 can include any
form of a heating unit, such as an oven energized by infrared heat,
microwave energy, hot air or the like. Drying station 114 may be
necessary in some applications to dry the web and/or cure the
bonding materials. Depending upon the bonding materials selected,
however, in other applications drying station 114 may not be
needed.
[0075] Once passed through drying station 114, web 80 can be wound
into a roll of material 116.
[0076] The bonding materials applied to each side of the tissue web
are selected for not only assisting in creping the web but also for
adding dry strength, wet strength, stretchability, and tear
resistance to the paper. Particular bonding materials that may be
used in the present invention include latex compositions, such as
acrylates, vinyl acetates, vinyl chlorides and methacrylates. Some
water-soluble bonding materials may also be used including
carboxylated vinyl acetate-ethylene terpolymers, polyacrylamides,
polyvinyl alcohols and cellulose derivatives such as carboxymethyl
cellulose. In one embodiment, the bonding materials used in the
process of the present invention comprise an ethylene vinyl acetate
copolymer. In particular, the ethylene vinyl acetate copolymer can
be cross-linked with N-methyl acrylamide groups using an acid
catalyst. Suitable acid catalysts include ammonium chloride, citric
acid and maleic acid. Examples of such bonding materials are
produced by Air Products Corporation.
[0077] In general, the first bonding material and the second
bonding material can be different bonding materials or the same
bonding material.
[0078] The bonding materials are applied to the base web as
described above in preselected patterns. The patterns of the
present invention create a tissue web having a significantly
reduced Poisson ratio. In particular, once a pattern according to
the present invention is applied to a tissue web, the pattern
counteracts the natural tendency of the web to shrink during
creping, drying or pulling.
[0079] For example, referring to FIG. 5, one embodiment of a
pattern 200 in accordance with the present invention is shown. As
illustrated, the pattern 200 includes a plurality of individual
cells 210. Each cell 210 includes expanded regions 212 and 214 and
a constricted region 216. The constricted region 216 is positioned
in between the expanded regions 212 and 214. When a tissue web
containing the bonding pattern 200 as shown in FIG. 5 is pulled in
the machine direction as indicated by arrow 218, the constricted
regions 216 of the individual cells 210 have a tendency to expand
thus lowering the Poisson ratio. More specifically, each cell 210
includes a pair of ribs 220 and 222 which have a tendency to move
in an outward direction from each cell when the tissue web is
placed under a strain.
[0080] Referring to FIG. 6, an individual cell 210 from the pattern
shown in FIG. 5 is illustrated. As shown, the cell 210 includes a
total length LT, a total width WT, an expanded region length LE,
and a constricted region width Wc. For many applications, the total
length LT is at least about twice the total width WT of each
cell.
[0081] The width Wc of the constricted area may vary depending upon
various factors. In general, the width of the constricted area is
less than about 2 mm, such as less than about 1.5 mm, such as from
about 0.3 mm to about 1 mm. In one particular embodiment, for
instance, the width of the constricted area may be from about 0.4
mm to about 0.8 mm. In one embodiment, the width of the constricted
region 216 may be no less than the average length of the fibers
used to form the nonwoven material, such as the tissue web.
[0082] In an alternative embodiment, however, the constricted
region may be no greater than the average length of the fibers in
the web. By having the width of the constricted region less than
the average length of the fibers used to form the web, strength in
the cross direction may be maximized. In fact, the material may
exhibit a secondary yield point when stretched in the cross
direction.
[0083] The expanded regions 212 and 214 of each cell 210 may come
in a variety of shapes. The expanded regions, for instance, may
have a square, curvilinear, hexagonal, or elliptical shape. In FIG.
5, the expanded regions 212 and 214 have a triangular shape.
[0084] The patterns of the present invention may also be
interconnected. By interconnected is meant that each cell 210 may
share a common border with an adjacent cell. For example, in one
embodiment, at least two sides of each cell may be interconnected
with adjacent cells. In FIG. 5, for instance, every side of the
cells 210 are interconnected with adjacent cells. As shown, FIG. 5
comprises a plurality of rows of cells. The cells in adjacent rows
are in a staggered or alternating configuration allowing the cells
to be interlocked together.
[0085] Referring to FIG. 7, another embodiment of a pattern 300 in
accordance with the present invention is shown. As illustrated, the
pattern 300 is comprised of individual cells 310. Each cell 310
includes a pair of expanded regions 312 and 314 separated by a
constricted region 316. In this embodiment, the expanded regions
312 and 314 have a hexagon-like shape. The cells are also shown in
an interconnected arrangement.
[0086] Referring to FIG. 8, still another embodiment of a bonding
pattern made in accordance with the present invention is shown. In
this embodiment, the bonding pattern 400 includes individual cells
410 comprised of a pair of expanded regions 412 and 414 separated
by a constricted region 416. In this embodiment, the expanded
regions 412 and 414 are in the shape of a rectangle. Again, the
cells 410 are in an interconnected and alternating arrangement.
[0087] In FIGS. 9 and 10, alternative embodiments of bonding
patterns generally 500 made in accordance with the present
invention are shown. As illustrated, each bonding pattern 500
includes individual cells 510 comprised of expanded regions 512 and
514 separated by constricted regions 516. In this embodiment, the
expanded regions have a curvilinear shape.
[0088] Referring to FIG. 11, still another embodiment of a bonding
pattern generally 600 made in accordance with the present invention
is shown. The bonding pattern shown in FIG. 11 is somewhat similar
to the bonding pattern shown in FIG. 5. In FIG. 11, the individual
cells 610 include two constricted regions 516A and 516B. The
constricted regions 516A and 516B are surrounded by expanded
regions. For instance, constricted region 516A may be considered to
be bordered by expanded regions 512A and 514A, while constricted
region 516B may be considered to be bordered by expanded region
512B and 514B. As shown, expanded region 514A and expanded region
512B may also be considered to form a single expanded region.
[0089] According to the present invention, the bonding materials
are applied to each side of the tissue web so as to cover from
about 5% to about 90% of the surface area of the web, such as from
about 30% to about 80% of the surface area of the web. In general,
the amount of surface area covered by the bonding material is
determined by the particular pattern used, the size of the
individual cells, and the width of the bond lines. In many
applications, the bonding material may cover from about 40% to
about 60% of the surface area of each side of the web. The total
amount of bonding material applied to each side of the web can be
in the range of from about 2% to about 20% by weight, based upon
the total weight of the web, such as from about 4% to about 10% by
weight.
[0090] At the above amounts, the bonding materials can penetrate
the tissue web from about 10% to about 70% of the total thickness
of the web. In most applications, the bonding materials should at
least penetrate from about 10% to about 15% of the thickness of the
web.
[0091] Once a bonding material is applied to each side of the
tissue web as shown in FIG. 3, the Poisson ratio of the tissue web
is substantially reduced when the web is stressed in the machine
direction. The amount the Poisson ratio is reduced may depend on
various factors. For instance, the degree to which the Poisson
ratio is reduced may depend upon the actual pattern selected, the
size of the individual cells contained in the pattern including the
size of the constricted region, the basis weight of the tissue web,
besides various other factors. In some embodiments, it is believed
that a tissue web may be produced actually having a negative
Poisson ratio such that the width of the web does not shrink and
may even expand when the web is pulled in the lengthwise
direction.
[0092] To achieve a negative Poisson ratio, it is believed that in
addition to the particular pattern chosen, the basis weight of the
tissue web and the amount the fibers have been debonded within the
tissue web may play an important role. For instance, it is believed
that the lowest Poisson ratios are achieved when treating a tissue
web that has been highly debonded and that has a basis weight of
less than about 45 gsm, such as less than about 40 gsm, such as
less than about 35 gsm, such as less than about 30 gsm.
[0093] In other embodiments, it may not be desirable or necessary
to produce a tissue web having a negative Poisson ratio in order to
receive various benefits and advantages. For instance, in other
embodiments, the Poisson ratio may be reduced by greater than about
30%, such as greater than about 40%, or such as greater than about
50% when the bonding materials are applied. For instance, the
Poisson ratio of the tissue web may be less than about 0.3, such as
less than about 0.2, such as less than about 0.1.
[0094] In addition to significantly decreasing the Poisson ratio of
tissue webs, the process of the present invention may also be used
to increase total energy absorption and increase cross-direction
stretch.
[0095] According to the process of the current invention, numerous
and different paper products can be formed. For instance, the paper
products may be single-ply wiper products. The products can be, for
instance, facial tissues, bath tissues, paper towels, napkins,
industrial wipers, and the like.
[0096] In an alternative embodiment, tissue webs made according to
the present invention can be incorporated into multiple ply
products. For instance, in one embodiment, a tissue web made
according to the present invention can be attached to one or more
other tissue webs for forming a wiping product having desired
characteristics. The other webs laminated to the tissue web of the
present invention can be, for instance, a wet-creped web, a
calendered web, an embossed web, a through-air dried web, a creped
through-air dried web, an uncreped through-air dried web, an
airlaid web, and the like.
[0097] In one embodiment, when incorporating a tissue web made
according to the present invention into a multiple ply product, it
may be desirable to only apply a bonding material to one side of
the tissue web and to thereafter crepe the treated side of the web.
The creped side of the web may then be used to form an exterior
surface of a multiple ply product. The untreated and uncreped side
of the web, on the other hand, may be attached by any suitable
means to one or more plies.
[0098] For example, referring to FIG. 4, one embodiment of a
process for applying a bonding material to only one side of a
tissue web in accordance with the present invention is shown. The
process illustrated in FIG. 4 is similar to the process shown in
FIG. 3. In this regard, like reference numerals have been used to
indicate similar elements.
[0099] As shown, a web 80 is advanced to a bonding material
application station generally 98. Station 98 includes a transfer
roll 100 in contact with a rotogravure roll 102, which is in
communication with a reservoir 104 containing a bonding material
106. At station 98, the bonding material 106 is applied to one side
of the web 80 in a preselected pattern, such as those shown in
FIGS. 5, 7, 8, 9, 10 or 11.
[0100] Once the bonding material is applied, web 80 is adhered to a
creping roll 108 by a press roll 110. Web 80 is carried on the
surface of the creping drum 108 for a distance and then removed
therefrom by the action of a creping blade 112. The creping blade
112 performs a controlled pattern creping operation on the treated
side of the web.
[0101] From the creping drum 108, the tissue web 80 is fed through
a drying station 114 which dries and/or cures the bonding material
106. The web 80 is then wound into a roll 116 for use in forming
multiple ply products.
[0102] In addition to print creping processes, it should be
understood that the patterns of the present invention may be
incorporated into tissue webs using other methods. Further, it
should also be understood that the patterns of the present
invention may be incorporated into other nonwoven materials.
[0103] For instance, the nonwoven materials may comprise in
addition to tissue webs, meltspun webs such as meltblown webs and
spunbond webs, bonded carded webs, hydroentangled webs, and the
like. The nonwoven webs may also be elastic and may contain, for
instance, an elastomeric material.
[0104] The manner in which the pattern is incorporated into the
nonwoven materials may vary depending upon the particular
circumstances. For instance, the pattern may be incorporated into
the web by topically applying a bonding material to one or both
sides of the web such as shown in FIG. 3 but without creping.
Alternatively, the web may be formed on a 3-dimensional
topographical forming surface. The forming surface may have a
pattern of the present invention incorporated into it which is
transferred to the web upon formation. For instance, the pattern
may be incorporated into a tissue web during a throughdrying
process. In one particular embodiment, once the pattern is
incorporated into the web, the raised portions of the pattern may
be printed with a bonding material. After being printed with a
bonding material, the web may be pressed against a creping drum and
creped from the drum.
[0105] The pattern may also be incorporated into the web through
thermal bonding. For instance, the web may be a meltblown web, a
spunbond web, a bonded carded web, a coform web, a tissue web, or a
hydroentangled web containing, for instance, synthetic fibers. In
this embodiment, the web may be fed through a nip being formed from
a heated embossing roll which embosses the pattern into the
web.
[0106] As used herein, a "meltblown web" refers to a web made from
fibers formed by extruding a molten thermoplastic material through
a plurality of fine, usually circular, die capillaries as molten
fibers into converging high velocity gas (e.g. air) streams that
attenuate the fibers of molten thermoplastic material to reduce
their diameter, which may be to microfiber diameter. Thereafter,
the meltblown fibers are carried by the high velocity gas stream
and are deposited on a collecting surface to form a web of randomly
disbursed meltblown fibers. Such a process is disclosed, for
example, in U.S. Pat. No. 3,849,241 to Butin, et al., which is
incorporated herein in its entirety by reference thereto for all
purposes. Generally speaking, meltblown fibers may be microfibers
that may be continuous or discontinuous, are generally smaller than
10 microns in diameter, and are generally tacky when deposited onto
a collecting surface.
[0107] As used herein, the term "spunbond web" refers to a web made
from small diameter substantially continuous fibers that are formed
by extruding a molten thermoplastic material from a plurality of
fine, usually circular, capillaries of a spinnerette with the
diameter of the extruded fibers then being rapidly reduced as by,
for example, eductive drawing and/or other well-known spunbonding
mechanisms. The production of spun-bonded nonwoven webs is
described and illustrated, for example, in U.S. Pat. No. 4,340,563
to Appel, et al., U.S. Pat. No. 3,692,618 to Dorschner, et al.,
U.S. Pat. No. 3,802,817 to Matsuki, et al., U.S. Pat. No. 3,338,992
to Kinney, U.S. Pat. No. 3,341,394 to Kinney, U.S. Pat. No.
3,502,763 to Hartman, U.S. Pat. No. 3,502,538 to Levv, U.S. Pat.
No. 3,542,615 to Dobo, et al., and U.S. Pat. No. 5,382,400 to Pike,
et al., which are incorporated herein in their entirety by
reference thereto for all purposes. Spunbond fibers are generally
not tacky when they are deposited onto a collecting surface.
Spunbond fibers can sometimes have diameters less than about 40
microns, and are often between about 5 to about 20 microns.
[0108] As described above, the wiper may also be formed from a
hydroentangled nonwoven fabric. Hydroentangling processes and
hydroentangled composite webs containing various combinations of
different fibers are known in the art. A typical hydroentangling
process utilizes high pressure jet streams of water to entangle
fibers and/or filaments to form a highly entangled consolidated
fibrous structure, e.g., a nonwoven fabric. Hydroentangled nonwoven
fabrics of staple length fibers and continuous filaments are
disclosed, for example, in U.S. Pat. No. 3,494,821 to Evans and
U.S. Pat. No. 4,144,370 to Bouolton, which are incorporated herein
in their entirety by reference thereto for all purposes.
Hydroentangled composite nonwoven fabrics of a continuous filament
nonwoven web and a pulp layer are disclosed, for example, in U.S.
Pat. No. 5,284,703 to Everhart, et al. and U.S. Pat. No. 6,315,864
to Anderson, et al., which are incorporated herein in their
entirety by reference thereto for all purposes.
[0109] The wiper may also be formed from a coform material. The
term "coform material" generally refers to composite materials
comprising a mixture or stabilized matrix of thermoplastic fibers
and a second non-thermoplastic material. As an example, coform
materials may be made by a process in which at least one meltblown
die head is arranged near a chute through which other materials are
added to the web while it is forming. Such other materials may
include, but are not limited to, fibrous organic materials such as
woody or non-woody pulp such as cotton, rayon, recycled paper, pulp
fluff and also superabsorbent particles, inorganic absorbent
materials, treated polymeric staple fibers and the like. Some
examples of such coform materials are disclosed in U.S. Pat. No.
4,100,324 to Anderson, et al.; U.S. Pat. No. 5,284,703 to Everhart,
et al.; and U.S. Pat. No. 5,350,624 to Georger, et al.; which are
incorporated herein in their entirety by reference thereto for all
purposes.
[0110] The pattern of the present invention may be incorporated
into the above nonwoven materials containing thermoplastic fibers
using methods known in the art. For instance, bonding techniques
for thermally bonding webs or adhesively bonding webs are disclosed
in U.S. Pat. No. 3,855,046, U.S. Pat. No. 5,620,779, U.S. Pat. No.
5,962,112, U.S. Pat. No. 6,093,665, U.S. Pat. No. 5,284,703, U.S.
Pat. No. 6,103,061, and U.S. Pat. No. 6,197,404, which are all
incorporated herein by reference.
[0111] Once the pattern is incorporated into a nonwoven material,
various benefits and advantages are realized. For instance, by
reducing the Poisson ratio of the material, the material may be
more easily processed. Specifically, since the pattern counteracts
the natural tendency of the material to shrink while being pulled,
processing equipment does not have to compensate for width loss.
Thus, the material may be easier to form, to combine with other
materials, and/or to form into a product.
[0112] In some applications, incorporating a pattern according to
the present invention into a nonwoven material also increases the
cross-machine direction stretch characteristics of the material. In
fact, in some embodiments, the cross direction stretch
characteristics will increase approximately to that of the machine
direction stretch characteristics. The pattern has also been found
to improve the drape of some materials and to improve tear
resistance in the cross-machine direction. When applying the
pattern using a latex, latex consumption may also be reduced in
comparison to other patterns used in the past. The pattern may also
further increase total energy absorption (TEA) when the material is
stressed.
[0113] In some applications, incorporating a pattern according to
the present invention into a nonwoven web may actually serve to
increase process capacity. For example, in some embodiments,
nonwoven materials are formed that have a width of about 100
inches. The 100-inch parent rolls are then converted into
individual rolls having a width of approximately 11 inches. In the
past, however, during converting operations the web has a tendency
to shrink in width such that a 100-inch parent roll may only
produce eight product rolls or less. By controlling shrinkage in
the width direction according to the present invention, however, it
is possible to produce nine product rolls from a parent roll that
is 100 inches wide. In particular, shrinkage can be controlled to
be less than 1.5%, such as less than 1% during the process. In this
manner, capacity of the process is increased.
[0114] Nonwoven materials made in accordance with the present
invention may be used in single ply applications or may be combined
with other plies to form laminates. Laminates made according to the
present invention can be made by any suitable technique or
process.
[0115] In one embodiment, for instance, a nonwoven web may be
molded with an impression device in order to form a raised auxetic
pattern in accordance with the present invention. A bonding
material may then be printed onto the raised portions of the
pattern and the web may then be adhered to another web for forming
a laminate. In this embodiment, the raised pattern may be created
into the web during formation of the web using a 3-dimensional
forming fabric or may be embossed into the web. In one particular
embodiment, a first web with a first raised auxetic pattern may be
bonded to a second web with a second raised auxetic pattern,
wherein the second raised pattern is a mirror image of the first
raised auxetic pattern. When joining the webs together, the
patterns may be registered together.
[0116] As stated above, nonwoven webs, such as tissue webs
containing a pattern according to the present invention have a
relatively low Poisson ratio in the cross-machine direction when
stressed in the machine direction. The actual resulting Poisson
ratio of the material depends on various factors including the
manner in which the pattern is incorporated into the web and the
material used to form the web. In many applications, for instance,
the Poisson ratio of the web may be less than about 0.3, such as
less than about 0.25, such as less than about 0.2, or such as less
than about 0.15. For instance, in one embodiment, the Poisson ratio
of the resulting material may be less than 0.1. Further, it is
believed that in some embodiments, the Poisson ratio may even be
negative meaning that the material actually increases in width when
pulled in the lengthwise direction.
[0117] The present invention may be better understood with
reference to the following examples.
EXAMPLE 1
[0118] Computer modeling of different print-creped tissue products
was completed to demonstrate the ability of the present invention
to significantly lower Poisson ratios.
[0119] Specifically, two bonding patterns made in accordance with
the present invention were compared with a control. The first
bonding pattern was similar to the one shown in FIG. 5 wherein the
expanded regions had a triangular shape. The second bonding pattern
was similar to the bonding pattern illustrated in FIG. 7, wherein
the expanded regions were shaped like hexagons. The control was a
bonding pattern as shown in FIG. 7 except all sides of the hexagons
were enclosed. The pattern thus appeared to be honeycomb-like. Each
hexagon had a length of 3 mm and a width of 3 mm.
[0120] During computer simulations, the computer was programmed to
predict transverse (cross direction) strain versus longitudinal
(machine direction) strain for a print-creped, print-creped web
containing the patterns on each side of the web.
[0121] The computer model was based on the incremental deformation
principle. Referring to FIG. 15, a fiber segment of original length
lo, oriented at an angle .theta. relative to the machine direction
(MD) is graphically depicted. Both ends of this fiber segment are
anchored at two different bond sites, shown as diamonds on FIG. 15.
As the web is deformed, the fiber segment is extended to a length
(I.sub.0+.delta.I) such that:
(I.sub.0+.DELTA.I).sup.2=(y.sub.0+.DELTA.y).sup.2+(x.sub.0+.DELTA.x+tan
.delta..gamma. ((y.sub.0+.DELTA.y))).sup.2
[0122] where [0123] .DELTA.I is the elongation of the fiber [0124]
.DELTA.x is the elongation component in the machine direction
[0125] .DELTA.y is the elongation component in the cross direction,
and [0126] .delta..gamma. is the shear strain of the web.
[0127] In the case of very small increments of strain at each
deformation step, the incremental strain,
.delta..epsilon..sub..theta., and the incremental specific stress,
.DELTA.f.sub..theta., in the bridging fiber are respectively,
.delta..epsilon..sub..theta.=(I.sub.x/I.sub.0).delta..epsilon..sub.x
cos .theta.+(I.sub.y/I.sub.0).delta..epsilon..sub.y sin
.theta.+.delta..gamma. sin .theta. cos .theta. and
.DELTA.f.sub..theta.=E(.epsilon.)[I.sub.x/I.sub.0).delta..epsilon..sub.x
cos .theta.+(I.sub.y/I.sub.0).delta..epsilon..sub.y sin
.theta.+.delta..gamma. sin .theta. cos .theta.]
[0128] The global coordinates system (MD and CD direction) were
obtained from the local coordinate system (fiber direction) by the
rotation angle of .theta. at which the fiber is oriented. As the
model employed the input generated from the image simulation, the
contribution of all fibers to the global coordinates could be
obtained by simply summing the contributions of each fiber without
the need for considering specific structural parameters of the web
such as the web areal density and fiber linear density.
[0129] The incremental forces .DELTA.F.sub.x and .DELTA.F.sub.y in
MD and CD, respectively, and the incremental shear force
.DELTA.F.sub.xy acting on the circumscribed rectangle are given in
the matrix form as: { .DELTA. .times. .times. F x .DELTA. .times.
.times. F y .DELTA. .times. .times. F xy } = ( Q 11 Q 12 Q 13 Q 21
Q 22 Q 23 Q 31 Q 32 Q 33 ) { .delta. .times. .times. x .delta.
.times. .times. y .delta. .times. .times. xy } ##EQU1## where
.times. : ##EQU1.2## Q 11 = n = 1 N .times. .times. E .function. (
n ) .times. cos 3 .times. .theta. n .function. ( l nx / l n .times.
.times. 0 ) ##EQU1.3## Q 12 = n = 1 N .times. .times. E .function.
( n ) .times. sin .times. .times. .theta. n .times. cos 2 .times.
.theta. n .function. ( l ny / l n .times. .times. 0 ) ##EQU1.4## Q
13 = n = 1 N .times. .times. E .function. ( n ) .times. sin .times.
.times. .theta. n .times. cos 3 .times. .theta. n ##EQU1.5## Q 21 =
n = 1 N .times. .times. E .function. ( n ) .times. sin 2 .times.
.times. .theta. n .times. cos .times. .times. .theta. n .function.
( l nx / l n .times. .times. 0 ) ##EQU1.6## Q 22 = n = 1 N .times.
.times. E .function. ( n ) .times. sin 3 .times. .times. .theta. n
.function. ( l ny / l n .times. .times. 0 ) ##EQU1.7## Q 23 = n = 1
N .times. .times. E .function. ( n ) .times. sin 3 .times. .times.
.theta. n .times. cos .times. .times. .theta. n ##EQU1.8## Q 31 = n
= 1 N .times. .times. E .function. ( n ) .times. sin .times.
.times. .theta. n .times. cos 2 .times. .theta. n .function. ( l nx
/ l n .times. .times. 0 ) ##EQU1.9## Q 32 = n = 1 N .times. .times.
E .function. ( n ) .times. sin 2 .times. .times. .theta. n .times.
cos .times. .times. .theta. n .function. ( l ny / l n .times.
.times. 0 ) ##EQU1.10## Q 33 = n = 1 N .times. .times. E .function.
( n ) .times. sin 2 .times. .times. .theta. n .times. cos 2 .times.
.times. .theta. n ##EQU1.11## where, [0130] I.sub.x is the relative
distance between the two bond sites in the global MD, [0131]
I.sub.y is the relative distance between the two bond sites in the
global CD, [0132] E(.epsilon..sub.n) is the local modulus of the
nth fiber, obtained from the load-strain curve of the fiber (in
general, E(.epsilon..sub.n) varies with extension if the fiber
load-extension behavior is nonlinear), [0133]
.delta..epsilon..sub.x is the incremental tensile strain of the web
in MD, [0134] .delta..epsilon..sub.y is the incremental tensile
strain of the web in CD, and [0135] .delta..gamma. is the shear
strain of the web.
[0136] Assuming a rectangular area circumscribing the bond site,
oriented parallel to the MD and CD, the incremental linear tensile
forces and shear forces were defined as the forces acting on the
unit width and height of the rectangular region.
[0137] The program modeled the stress/strain behavior by
incrementally straining the fabric and computing the linear stress
components at each strain level. The program calculated the fiber
strain from the original fiber length and the elongated fiber
length. To form the global constitution equation, the fiber strain
component was transformed at the global x-y coordinate using the
delta(x), delta(y), shear angle, and their original values. At each
incremental strain level, the resulting force components were
determined. The model was programmed such to ensure that the force
balance was maintained. That is, the summation of all force
components must equal zero. If the force balance was not
maintained, the force brought about by the changes in strain was
re-calculated until convergence was achieved. Once convergence was
met, the total force was checked against the amount of force
required to fail the fibers. The bonding strength was assumed to
exceed the rupture strength of the fibers. If the force required to
fail the fibers in the computational model were higher than the
corresponding experimental data, those elements were eliminated and
the force balance convergence was reevaluated. If the model met web
failure condition, the resulting data was automatically saved and
displayed for review.
[0138] The simulation parameters were based on pulp fiber
dimensions of 2.5 mm by 20 microns and a basis weight range of 10
to 30 gsm. The incremental strain parameter was set at 0.01, and
the debonding force was assumed to be 0.05 N. The CD strain
interval was 0.02.
[0139] The results are shown in FIGS. 12-14. In particular, FIG. 12
is the strain versus strain curve for the first pattern according
to the present invention similar to the one shown in FIG. 5, FIG.
13 is the strain versus strain curve for the second pattern
according to the present invention as shown in FIG. 7, while FIG.
14 is the strain versus strain curve for the control in which the
pattern was comprised of enclosed hexagons. As shown, the slope of
the graph for the two tissue products made according to the present
invention is opposite to the slope of the graph for the control.
Thus, tissue webs made according to the present invention exhibited
a negative Poisson ratio.
EXAMPLE 2
[0140] In order to demonstrate that the bonding patterns of the
present invention are capable of significantly reducing the Poisson
ratio of a tissue web, an uncreped through-air dried (UCTAD) base
web was treated with a bonding material according to the teachings
of the present invention and the web was then subjected to various
standardized tests. During this example, the tissue webs were
treated with a bonding material in accordance with the present
invention but were not creped from a creping surface. Further, none
of the products were optimized in the example. This example was
completed merely to show that applying a bonding material to a
tissue web according to an auxetic pattern will significantly lower
Poisson ratios.
[0141] The UCTAD based web was formed in a process similar to the
method shown in FIG. 1. In this particular example, the base web
was made from a stratified fiber furnish containing a center layer
of fibers positioned between two outer layers of fibers. Both outer
layers of the UCTAD base web contained 100% LL19, a northern
softwood Kraft pulp and up to 6 kg/MT of TQ1003 debonder obtained
from the Hercules Corporation. The center layer contained 50% BCTMP
pulp obtained from Miller Western Pulp Ltd. and 50% of the
aforementioned softwood Kraft pulp with up to 6 kg/MT of TQ1003
debonder.
[0142] This example had 3 separate runs, each with a different test
material. All three runs used the same basesheet and all bonding
material used was from the same batch. The bonding material
contained the bonding agent AirFlex 426, a carboxylated vinyl
acetate-ethylene terpolymer, obtained from Air Products, Inc. of
Allentown, Pa. The bonding agent was mixed with Nalco 7565
defoamer, water, sodium hydroxide, and KYMENE 2064, an epoxy
functional polymer.
[0143] The bonding material was applied to the basesheet using a
flexographic printing procedure in which the pattern was printed on
both sides of the sheet. The samples were not creped after the
bonding material was applied. For Run 1, a photopolymer plate was
used to print a diamond pattern made to match the direct gravure
pattern used on Kleenex.RTM. Viva.RTM. paper towels. For Run 2, the
Auxetic pattern shown in FIG. 5 was used instead of the Viva.RTM.
diamond pattern, and once again, a photopolymer plate was employed
for the printing. Run 3 printed the same pattern of Run 2 from FIG.
5, but used a natural rubber plate.
[0144] Approximately 15 to 20 feet of material was printed for each
run. The samples were placed in the temperature and humidity
controlled lab for at least four (4) hours. The lab maintained a
constant temperature of 23.+-.2.degree. C. and relative humidity of
50.+-.5%. Machine direction (MD) samples having a width of three
inches (3'') were then cut out of the center of each sample. Ten
(10) samples were prepared for each run and these samples were used
for all further testing.
[0145] The samples were first used to determine a Poisson Ratio
using a simple elongation test. The term "elongation" refers to the
increase in length of a sample during testing. To elongate the
samples a Synergie Tensile Frame available from MTS Systems, Corp.
located in Eden Prairie, Minn., was used. During the test, each end
of a sample was placed in an opposing clamp. The clamps held the
material in the same plane, and then the clamps were moved apart
until the sample had a MD length of 4.5'', resulting in an
elongation of 0.5''. The width in the cross-machine direction (CD)
was measured for the sample before and after elongation, and the
two values were used to calculate the Poisson Ratio. As defined in
the detailed description, the Poisson Ratio is the ratio of the
transverse contraction strain to the longitudinal extension strain
in the direction of the stretching force. The mathematical
expression for the ratio contains a leading negative sign so that
normal materials, which decrease in width as they are stretched
lengthwise, will have a positive ratio. Therefore, for the current
example, the Poisson Ratio was calculated as the negative ratio of
the change in width in the CD direction to the change in length in
the MD direction as shown below. The average Poisson Ratio for each
of the three runs is given in Table 1 below. TABLE-US-00001 TABLE 1
PoissonRatio = - [ ( CDwidth .times. : .times. elongated ) - (
CDwidth .times. : .times. relaxed ) ( MDlength .times. : .times.
elongated ) - ( MDlength .times. : .times. relaxed ) ] ##EQU2##
Poisson Ratio Results Run Pattern Average Poisson Ratio 1 Diamond
0.4316 2 Auxetic Photopolymer (PP) 0.2316 3 Auxetic Natural Rubber
NR 0.2316
[0146] The samples were then subjected to standardized tests for
tensile strength and stretch. The tensile strength and the percent
stretch of samples were determined in both the machine direction
and in the cross-machine direction. The results are expressed in
grams to break per mm width of at rest sample (in the stretched
dimension) and percent stretch before breakage.
[0147] Once again a Synergie Tensile Frame was used to elongate the
samples in order to determine the tensile strengths. The samples
were once again placed in opposing clamps and then the clamps were
moved apart at a constant rate. The clamps moved apart until
breakage occurred in order to measure the tensile strength. Percent
elongation was calculated as the positive change in the length of
the sample divided by the length of the sample at rest. The results
of these tests are shown in Table 2 below: TABLE-US-00002 TABLE 2
Tensile Test Results MD CD MD Strength Stretch CD Strength Stretch
Run Pattern (grams/76 mm) (%) (grams/76 mm) (%) 1 Diamond 2261.7
17.14 1603.7 12.92 2 Auxetic PP 1529.6 20.97 1054.7 10.93 3 Auxetic
NR 1680.3 21.48 1072.6 11.07
[0148] As shown above, simply applying a pattern of the present
invention to a tissue web without optimization may significantly
decrease the Poisson ratio of the material.
[0149] These and other modifications and variations to the present
invention may be practiced by those of ordinary skill in the art,
without departing from the spirit and scope of the present
invention, which is more particularly set forth in the appended
claims. In addition, it should be understood that aspects of the
various embodiments may be interchanged both in whole or in part.
Furthermore, those of ordinary skill in the art will appreciate
that the foregoing description is by way of example only, and is
not intended to limit the invention so further described in such
appended claims.
* * * * *