U.S. patent application number 10/025192 was filed with the patent office on 2003-06-19 for tissue products and methods for manufacturing tissue products.
This patent application is currently assigned to Kimberly-Clark Worldwide, Inc.. Invention is credited to Hu, Sheng-hsin.
Application Number | 20030111196 10/025192 |
Document ID | / |
Family ID | 21824569 |
Filed Date | 2003-06-19 |
United States Patent
Application |
20030111196 |
Kind Code |
A1 |
Hu, Sheng-hsin |
June 19, 2003 |
Tissue products and methods for manufacturing tissue products
Abstract
In the practice of the invention, a multi-ply paper product or
tissue having hardwood layers on the outside and on the inside
provides reduced amounts of undesirable sloughing. The multi-ply
product includes at least two plies, with three layers in each ply.
Hardwood layers, such as for example eucalyptus-containing fiber
layers, are provided on the outside surfaces of each ply and also
on the interface of one or more plies. The resulting paper product
may exhibit reduced sloughing, with little or no sacrifice in
softness. A product having two, three, four, or more plies is
shown.
Inventors: |
Hu, Sheng-hsin; (Appleton,
WI) |
Correspondence
Address: |
John E. Vick, Jr.
Dorithy & Manning, Attorney at Law, P.A.
P.O. Box 1449
Greenville
SC
29602
US
|
Assignee: |
Kimberly-Clark Worldwide,
Inc.
|
Family ID: |
21824569 |
Appl. No.: |
10/025192 |
Filed: |
December 19, 2001 |
Current U.S.
Class: |
162/129 ;
162/179 |
Current CPC
Class: |
B32B 29/00 20130101;
D21H 27/38 20130101; D21H 27/30 20130101 |
Class at
Publication: |
162/129 ;
162/179 |
International
Class: |
D21H 021/22; D21H
027/30 |
Claims
What is claimed is:
1. A multi-ply tissue product, comprising: (a) a first ply, the
first ply comprising: a first hardwood layer, a second hardwood
layer, and a softwood layer positioned between the first and second
hardwood layers; and (b) a second ply mated to the first ply, the
second ply comprising: a first hardwood layer, a second hardwood
layer, and a softwood layer positioned between the first and second
hardwood layers.
2. The product of claim 1 in which the total percentage by weight
of hardwood in the product is between about 50 and about 80
percent.
3. The product of claim 1 in which the total percentage by weight
of softwood in the product is between about 20 and about 50
percent.
4. The product of claim 1 in which the slough is less than about
7.3 mg at a GMT of between about 500-800 at a softness of between
about 8-9.
5. The product of claim 1 in which the slough is less than about 6
mg.
6. The product of claim 1 in which a debonding agent is applied in
the product.
7. The product of claim 6 in which debonding agent is applied in at
least one hardwood layer.
8. The product of claim 6 in which the debonding agent is an
imidazoline-containing composition.
9. The product of claim 1 in which the softwood fiber is
refined.
10. The product of claim 1 in which the total amount of hardwood
fiber in the product is between about 60 and about 70 percent, and
the total amount of softwood fiber in the product is between about
30 and about 40 percent.
11. The product of claim 1 in which the total amount of hardwood
fiber in the product is about 65%.
12. The product of claim 1 in which the hardwood fiber comprises
eucalyptus fiber.
13. The product of claim 1 in which the softwood fiber comprises
northern softwood kraft fiber.
14. The product of claim 1, further comprising: (c) a third ply,
the third ply comprising: a first hardwood layer, a second hardwood
layer, and a softwood layer positioned between the first and second
hardwood layers.
15. The product of claim 14 further comprising: (d) a fourth ply,
the fourth ply comprising: a first hardwood layer, a second
hardwood layer, and a softwood layer positioned between the first
and second hardwood layers.
16. A multi-ply tissue, comprising: (a) a first ply, the first ply
comprising: a first hardwood layer, a second hardwood layer, and a
softwood layer positioned between the first and second hardwood
layers; and (b) a second ply mated to the first ply, the second ply
comprising: a first hardwood layer, a second hardwood layer, and a
softwood layer positioned between the first and second hardwood
layers; wherein the total hardwood content of the tissue is between
about 50 and about 80 percent by weight.
17. The tissue of claim 16 in which the total hardwood content of
the tissue is between about 60 and about 70 percent.
18. The tissue of claim 17 further comprising a third ply.
19. The tissue of claim 18 further comprising a fourth ply.
20. The tissue of claim 16 in which the total softwood content of
the tissue is between about 30 and about 40 percent.
21. The tissue of claim 16 in which a debonding agent is employed
in the tissue.
22. The tissue of claim 21 in which the debonding agent is employed
in one or more of the hardwood layers.
Description
BACKGROUND OF THE INVENTION
[0001] Strength and softness are important attributes in consumer
paper products such as facial tissue, bathroom tissue, towels, and
napkins. Strength and softness are strongly influenced by the sheet
structure of a paper product. Mechanical treatment of fibers and
fiber slurries in the manufacture of paper products is an important
factor in determining the strength and softness of products which
are produced thereby.
[0002] Strength and softness usually are inversely related. That
is, the stronger a given sheet, the less softness that sheet is
likely to provide. Likewise, a softer sheet is usually not as
strong. Thus, an inverse relationship that exists between the
properties of strength and softness results in consistent efforts
in the industry to produce sheets or webs having strength levels
which are at least as great as conventional sheets, but with
improved softness. Also, a sheet or web that is at least as soft as
previously known sheets, but with improved strength, also is
desirable.
[0003] As a general rule, fibers having superior softness are
provided in outer layers of paper products--i.e. those layers which
routinely contact the skin of consumers. This is true for bath
tissue, for example. The inner layers of such products often
comprise coarser fibers which are less desirable in their
properties of softness, absorbency, or strength.
[0004] Sloughing of tissue products, such as facial tissue, and
bath tissue, may be an important factor in tissue usage and
manufacture. Sloughing is the loss of paper particles from the
surface of the paper due to surface abrasion. Sloughing is
undesirable. Unfortunately, sloughing sometimes is increased by the
use of debonding agents. Debonding agents are used to soften paper
products. Many consumers react negatively to paper that exhibits a
high degree of sloughing. Therefore, efforts are made to provide a
paper product that exhibits a minimal amount of sloughing. Many
changes that are made to paper manufacture to decrease sloughing
have the undesirable side effect of stiffening the tissue (i.e.
reducing softness). Thus, in the manufacture of paper products it
is a constant struggle to reduce sloughing of such products without
adverse effects upon softness levels.
[0005] Many currently known premium facial tissue and bath tissues
are two-ply products, in which the plies are separately
manufactured from a slurry, and then mated or crimped together. The
term "tissue" is generally used to describe multi-ply paper
product. Each ply may comprise two layers. In these two-ply
products having two layers per ply, each ply may consist of a
hardwood layer that is facing outward (towards the consumer) with
an inner layer of softwood. Thus, the inner softwood layers of each
ply may be in contact with each other, and may be (pressed)
together when the two-ply product is formed.
[0006] In other products, a single ply product having three layers
may be formed. The outer layers may be hardwood, while the inner
layer comprises softwood. The hardwood layers are exposed to the
outside, because they usually contain shorter, softer fibers.
However, hardwood may provide high levels of sloughing, which is
undesirable.
[0007] In conventional papermaking processes, the softer hardwood
layers (such as eucalyptus, for example) usually are provided on
the outside of the product, while the stronger softwood layers are
usually employed on the inside of the product (i.e. the strength
layer). This arrangement applies whether it is a one ply or two ply
product under construction.
[0008] It would be desirable to provide a process, system and
product that is capable of providing a high degree of softness and
strength, with reduced amounts of sloughing. Furthermore, a layered
paper product that reveals reduced sloughing with a minimal or
negligible effect upon softness levels would be desirable.
SUMMARY OF THE INVENTION
[0009] A multi-ply tissue or paper product is provided having
hardwood layers on the outside and on the inside. The multi-ply
product of the invention includes at least two plies, with at least
three layers in each ply. Hardwood layers are provided on the
outside surfaces of each ply and at the inner interface of one or
more plies. The resulting paper product may exhibit reduced
sloughing, with little or no sacrifice in softness. A product
having two, three, four, or more plies is provided.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] A full and enabling disclosure of this invention, including
the best mode shown to one of ordinary skill in the art, is set
forth in this specification.
[0011] FIG. 1 is a schematic flow diagram of one embodiment of a
papermaking process that can be used in the present invention;
[0012] FIG. 2 is a schematic flow diagram of another embodiment of
a papermaking process that can be used in the present
invention;
[0013] FIG. 3 is a schematic flow diagram of still another
embodiment of a papermaking process that can be used in the present
invention;
[0014] FIG. 4A is a representation of the a two ply tissue
assembled according to the invention;
[0015] FIG. 4B is a representation of the a two ply tissue
assembled according to the invention;
[0016] FIG. 4C is a representation of the a two ply tissue
assembled according to the invention; and
[0017] FIG. 5 is a perspective view of a machine used to measure
slough of a paper sample.
DETAILED DESCRIPTION OF THE INVENTION
[0018] Reference now will be made to the 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 as
a 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 this 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 cover such modifications and
variations as come within the scope of the appended claims and
their equivalents. Other objects, features and aspects of the
present invention are disclosed in or are obvious from the
following detailed description. 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, which
broader aspects are embodied in the exemplary constructions.
[0019] Surprisingly, in the practice of this invention it has been
discovered that a tissue product with hardwood provided at the
inner layer interface provides superior sloughing and softness
characteristics. It is shown herein that a multi-ply product
consisting of at least two plies, with three layers in each ply,
having hardwood layers on both the outside surfaces and on the
interface (i.e. in the middle) may exhibit reduced sloughing, with
little or no sacrifice in softness.
[0020] A wide variety of cellulosic fibers may be employed in the
process of the present invention. In many embodiments of the
invention, a first furnish comprising a strength layer is employed.
This first furnish may be a softwood, for example. The average
fiber length of a softwood fiber typically is about two to four
times longer than a hardwood fiber. Softwood sources include trees
sources, such as pines, spruces, and firs and the like.
[0021] Hardwood sources such as oaks, eucalyptuses, poplars,
beeches, and aspens, may be used, but this list is by no means
exhaustive of all the hardwood sources that may be employed in the
practice of the invention. Fibers from different sources of wood
exhibit different properties. Hardwood fibers, for example, tend to
show high degrees of "fuzziness" or softness when placed on the
exterior surface of a paper product, such as a bathroom tissue.
[0022] Hardwood fiber sources generally contain fibers of a shorter
length than softwood sources. Many times, sloughing occurs when
shorter fibers flake or fall from the outer hardwood layers of
multi-layered tissues.
[0023] Illustrative cellulosic fibers that may be employed in the
practice of the invention include, but are not limited to, wood and
wood products, such as wood pulp fibers; non-woody paper-making
fibers from cotton, from straws and grasses, such as rice and
esparto, from canes and reeds, such as bagasse, from bamboos, form
stalks with bast fibers, such as jute, flax, kenaf, cannabis, linen
and ramie, and from leaf fibers, such as abaca and sisal. It is
also possible to use mixtures of one or more cellulosic fibers.
[0024] As used herein, the term "fiber" or "fibrous" is meant to
refer to a particulate material wherein the length to diameter
ratio (aspect ratio) of such particulate material is greater than
about 10. Conversely, a "nonfiber" or "nonfibrous" material is
meant to refer to a particulate material wherein the length to
diameter ratio of such particulate material is about 10 or less. It
is generally desired that the cellulosic fibers used herein be
wettable. Suitable cellulosic fibers include those which are
naturally wettable. However, naturally non-wettable fibers can also
be used.
[0025] In the practice of the present invention, it is desired that
the cellulosic fibers be used in a form wherein the cellulosic
fibers have already been prepared into a pulp. As such, the
cellulosic fibers will be presented substantially in the form of
individual cellulosic fibers, although such individual cellulosic
fibers may be in an aggregate form such as a pulp sheet. This is in
contrast with untreated cellulosic forms such as wood chips or the
like. Thus, the current process is generally a post-pulping,
cellulosic fiber separation process as compared to other processes
that may be used for high-yield pulp manufacturing processes.
[0026] The preparation of cellulosic fibers from most cellulosic
sources results in a heterogeneous mixture of cellulosic fibers.
The individual cellulosic fibers in the mixture exhibit a broad
spectrum of values for a variety of properties such as length,
coarseness, diameter, curl, color, chemical modification, cell wall
thickness, fiber flexibility, and hemicellulose and/or lignin
content. As such, seemingly similar mixtures of cellulosic fibers
prepared from the same cellulosic source may exhibit different
mixture properties, such as freeness, water retention, and fines
content because of the difference in actual cellulosic fiber
make-up of each mixture or slurry.
[0027] In general, the cellulosic fibers may be used in the process
of the present invention in either a dry or a wet state. However,
it may be desirable to prepare an aqueous mixture comprising the
cellulosic fibers wherein the aqueous mixture is agitated, stirred,
or blended to effectively disperse the cellulosic fibers throughout
the water.
[0028] The cellulosic fibers are typically mixed with an aqueous
solution wherein the aqueous solution beneficially comprises at
least about 30 weight percent water, suitably about 50 weight
percent water, more suitably about 75 weight percent water, and
most suitably about 100 weight percent water. When another liquid
is employed with the water, such other suitable liquids include
methanol, ethanol, isopropanol, and acetone. However, the use or
presence of such other non-aqueous liquids may impede the formation
of an essentially homogeneous mixture such that the cellulosic
fibers do not effectively disperse into the aqueous solution and
effectively or uniformly mix with the water. Such a mixture should
generally be prepared under conditions that are sufficient for the
cellulosic fibers and water to be effectively mixed together.
Generally, such conditions will include using a temperature that is
between about 10 degrees C. and about 100 degrees C.
[0029] In general, cellulosic fibers are prepared by pulping or
other preparation processes in which the cellulosic fibers are
present in an aqueous solution. The cellulosic fibers treated
according to the process of the present invention are suited for
use in disposable paper products such as facial or bathroom tissue,
paper towels, wipes, napkins, and disposable paper products.
Furthermore, other applications of the invention may be directed to
products including: diapers, adult incontinent products, bed pads,
sanitary napkins, tampons, other wipes, bibs, wound dressings,
surgical capes or drapes.
Papermaking Processes
[0030] A papermaking process can be utilized to form a
multi-layered paper web, such as described and disclosed in U.S.
Pat. No. 5,129,988 to Farrington, Jr.; U.S. Pat. No. 5,494,554 to
Edwards, et al.; and U.S. Pat. No. 5,529,665 to Kaun, which are
incorporated herein in their entirety by reference thereto for all
purposes.
[0031] In this regard, various embodiments of a method for forming
a multi-layered paper web will now be described in more detail.
Referring to FIG. 1, a method of making a wet-pressed tissue in
accordance with one embodiment of the present invention is shown,
commonly referred to as couch forming, wherein two wet web layers
are independently formed and thereafter combined into a unitary
web. To form the first web layer, a specified fiber (either
hardwood or softwood) is prepared in a manner well known in the
papermaking arts and delivered to the first stock chest 1, in which
the fiber is kept in an aqueous suspension. A stock pump 2 supplies
the required amount of suspension to the suction side of the fan
pump 4. If desired, a metering pump 5 can supply an additive (e.g.,
latex, reactive composition, etc.) into the fiber suspension.
Additional dilution water also is mixed with the fiber
suspension.
[0032] The entire mixture of fibers is then pressurized and
delivered to the headbox 6. The aqueous suspension leaves the
headbox 6 and is deposited on an endless papermaking fabric 7 over
the suction box 8. The suction box is under vacuum that draws water
out of the suspension, thus forming the first layer. In this
example, the stock issuing from the headbox 6 would be referred to
as the "air side" layer, that layer eventually being positioned
away from the dryer surface during drying.
[0033] The forming fabric can be any forming fabric, such as
fabrics having a fiber support index of about 150 or greater. Some
suitable forming fabrics include, but are not limited to, single
layer fabrics, such as the Appleton Wire 94M available from Albany
International Corporation, Appleton Wire Division, Menasha, Wis.;
double layer fabrics, such as the Asten 866 available from Asten
Group, Appleton, Wis.; and triple layer fabrics, such as the
Lindsay 3080, available from Lindsay Wire, Florence, Miss.
[0034] The consistency of the aqueous suspension of papermaking
fibers leaving the headbox can be from about 0.05 to about 2%, and
in one embodiment, about 0.2%. The first headbox 6 can be a layered
headbox with two or more layering chambers which delivers a
stratified first wet web layer, or it can be a monolayered headbox
which delivers a blended or homogeneous first wet web layer.
[0035] To form the second web layer, a specified fiber (either
hardwood or softwood) is prepared in a manner well known in the
papermaking arts and delivered to the second stock chest 11, in
which the fiber is kept in an aqueous suspension. A stock pump 12
supplies the required amount of suspension to the suction side of
the fan pump 14. A metering pump 5 can supply additives (e.g.,
latex, reactive composition, etc.) into the fiber suspension as
described above. Additional dilution water 13 is also mixed with
the fiber suspension. The entire mixture is then pressurized and
delivered to the headbox 16. The aqueous suspension leaves the
headbox 16 and is deposited onto an endless papermaking fabric 17
over the suction box 18. The suction box is under vacuum which
draws water out of the suspension, thus forming the second wet web.
In this example, the stock issuing from the headbox 16 is referred
to as the "dryer side" layer as that layer will be in eventual
contact with the dryer surface. Suitable forming fabrics for the
forming fabric 17 of the second headbox include those forming
fabrics previously mentioned with respect to the first headbox
forming fabric.
[0036] After initial formation of the first and second wet web
layers, the two web layers are brought together in contacting
relationship (couched) while at a consistency of from about 10 to
about 30%. Whatever consistency is selected, it is typically
desired that the consistencies of the two wet webs be substantially
the same. Couching is achieved by bringing the first wet web layer
into contact with the second wet web layer at roll 19.
[0037] After the consolidated web has been transferred to the felt
22 at vacuum box 20, dewatering, drying and creping of the
consolidated web is achieved in the conventional manner. More
specifically, the couched web is further dewatered and transferred
to a dryer 30 (e.g., Yankee dryer) using a pressure roll 31, which
serves to express water from the web, which is absorbed by the
felt, and causes the web to adhere to the surface of the dryer. The
web is then dried, optionally creped and wound into a roll 32 for
subsequent converting into the final creped product.
[0038] FIG. 2 is a schematic flow diagram of another embodiment of
a papermaking process that can be used in the present invention.
For instance, a layered headbox 41, a forming fabric 42, a forming
roll 43, a papermaking felt 44, a press roll 45, a Yankee dryer 46,
and a creping blade 47 are shown. Also shown, but not numbered, are
various idler or tension rolls used for defining the fabric runs in
the schematic diagram, which may differ in practice. In operation,
a layered headbox 41 continuously deposits a layered stock jet
between the forming fabric 42 and the felt 44, which is partially
wrapped around the forming roll 43. Water is removed from the
aqueous stock suspension through the forming fabric 42 by
centrifugal force as the newly-formed web traverses the arc of the
forming roll. As the forming fabric 42 and felt 44 separate, the
wet web stays with the felt 44 and is transported to the Yankee
dryer 46.
[0039] At the Yankee dryer 46, the creping chemicals are
continuously applied on top of the existing adhesive in the form of
an aqueous solution. The solution is applied by any convenient
means, such as using a spray boom that evenly sprays the surface of
the dryer with the creping adhesive solution. The point of
application on the surface of the dryer 46 is immediately following
the creping doctor blade 47, permitting sufficient time for the
spreading and drying of the film of fresh adhesive.
[0040] In some instances reactive compositions may be applied to
the web as it is being dried, such as through the use of the spray
boom. For example, the spray boom can apply the additives to the
surface of the drum 46 separately and/or in combination with the
creping adhesives such that such additives are applied to an outer
layer of the web as it passes over the drum 46. In some
embodiments, the point of application on the surface of the dryer
46 is the point immediately following the creping blade 47, thereby
permitting sufficient time for the spreading and drying of the film
of fresh adhesive before contacting the web in the press roll nip.
Methods and techniques for applying an additive to a dryer drum are
described in more detail in U.S. Pat. No. 5,853,539 to Smith, et
al. and U.S. Pat. No. 5,993,602 to Smith, et al., which are
incorporated herein in their entirety by reference thereto for all
purposes.
[0041] The wet web is applied to the surface of the dryer 46 by a
press roll 45 with an application force of, in one embodiment,
about 200 pounds per square inch (psi). Following the pressing or
dewatering step, the consistency of the web is typically at or
above about 30%. Sufficient Yankee dryer steam power and hood
drying capability are applied to this web to reach a final
consistency of about 95% or greater, and particularly 97% or
greater. The sheet or web temperature immediately preceding the
creping blade 47, as measured, for example, by an infrared
temperature sensor, is typically about 235.degree. F.
[0042] The web can also be dried using non-compressive drying
techniques, such as through-air drying. A through-air dryer
accomplishes the removal of moisture from the web by passing air
through the web without applying any mechanical pressure.
Through-air drying can increase the bulk and softness of the web.
Examples of such a technique are disclosed in U.S. Pat. No.
5,048,589 to Cook, et al.; U.S. Pat. No. 5,399,412 to Sudall, et
al.; U.S. Pat. No. 5,510,001 to Hermans, et al.; U.S. Pat. No.
5,591,309 to Rugowski, et al.; and U.S. Pat. No. 6,017,417 to
Wendt, et al., which are incorporated herein in their entirety by
reference thereto for all purposes.
[0043] For example, referring to FIG. 3, one embodiment of a
papermaking machine that can be used in forming an uncreped
through-dried tissue product 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 110 can be used to inject or deposit a stream of an aqueous
suspension of papermaking fibers onto an upper forming fabric 112.
The aqueous suspension of fibers is then transferred to a lower
forming fabric 113, which serves to support and carry the
newly-formed wet web 111 downstream in the process. If desired,
dewatering of the wet web 111 can be carried out, such as by vacuum
suction, while the wet web 111 is supported by the forming fabric
113.
[0044] The wet web 111 is then transferred from the forming fabric
113 to a transfer fabric 117 while at a solids consistency of
between about 10% to about 35%, and particularly, between about 20%
to about 30%. As used herein, a "transfer fabric" is a fabric that
is positioned between the forming section and the drying section of
the web manufacturing process. In this embodiment, the transfer
fabric 117 is a patterned fabric having protrusions or impression
knuckles, such as described in U.S. Pat. No. 6,017,417 to Wendt et
al. Typically, the transfer fabric 117 travels at a slower speed
than the forming fabric 113 to enhance the "MD stretch" of the web,
which generally refers to the stretch of a web in its machine or
length direction (expressed as percent elongation at sample
failure). For example, the relative speed difference between the
two fabrics can be from 0% to about 80%, in some embodiments
greater than about 10%, in some embodiments from about 10% to about
60%, and in some embodiments, from about 15% to about 30%. 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., which is incorporated herein in its entirety by
reference thereto for all purposes.
[0045] Transfer to the fabric 117 may be carried out with the
assistance of positive and/or negative pressure. For example, in
one embodiment, a vacuum shoe 118 can apply negative pressure such
that the forming fabric 113 and the transfer fabric 117
simultaneously converge and diverge at the leading edge of the
vacuum slot. Typically, the vacuum shoe 118 supplies pressure at
levels between about 10 to about 25 inches of mercury. As stated
above, the vacuum transfer shoe 118 (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 can also be used to assist in
drawing the fibrous web 111 onto the surface of the transfer fabric
117.
[0046] From the transfer fabric 117, the fibrous web 111 is then
transferred to the through-drying fabric 119. When the wet web 111
is transferred to the fabric 119. While supported by the
through-drying fabric 119, the web 111 is then dried by a
through-dryer 121 to a solids consistency of about 95% or greater.
The through-dryer 121 accomplishes the removal of moisture from the
web 111 by passing air therethrough without applying any mechanical
pressure. Through-drying can also increase the bulk and softness of
the web 111. In one embodiment, for example, the through-dryer 121
can contain a rotatable, perforated cylinder and a hood for
receiving hot air blown through perforations of the cylinder as the
through-drying fabric 119 carries the web 111 over the upper
portion of the cylinder. The heated air is forced through the
perforations in the cylinder of the through-dryer 121 and removes
the remaining water from the web 111. The temperature of the air
forced through the web 111 by the through-dryer 121 can vary, but
is typically from about 250.degree. F. to about 500.degree. F. It
should also be understood that other non-compressive drying
methods, such as microwave or infrared heating, can be used.
[0047] In the invention, a three-layer tissue sheet may be plied
with the hardwood on the outsides (i.e. top and bottom) to form a
three-layered, two-ply tissue. The three-layered tissue may contain
about 50-80% hardwood fibers, and about 20-50% softwood fibers.
More preferably, the total amount of hardwood fibers may be about
60-70% (i.e. 30-35% in each outer layer), and a total softwood
fiber amount of about 30-40%.
[0048] The hardwood fibers generally may be selected from any known
type of hardwood fiber, and the softwood likewise may be selected
from any known softwood fiber.
[0049] In some embodiments of the invention, a three-layer
structure having: about 32-22% fiber in the outer hardwood layer,
about 35% softwood fiber in the interface (i.e.: middle layer), and
about 32-33% hardwood fiber in the second outer hardwood layer may
be employed. Of course, this describes one-ply, and it is
understood that the layered structure would be mated with at least
one other layer structure to form a two or more ply structure. In
some embodiments of the invention, a three-ply, four-ply, or more
ply product can be manufactured and employed.
[0050] Turning to FIG. 4A, a two-ply paper product 210 is shown. A
first hardwood layer 212, a second hardwood layer 216, and a
softwood layer 214 are shown in the first ply. The softwood layer
214 is positioned between the first hardwood layer 212 and the
second hardwood layer 216. Likewise, the second ply comprises a
first hardwood layer 218, a second hardwood layer 222, and a
softwood layer 220 in between. The first ply and second ply are
mated or pressed together in the final two-ply paper product
210.
[0051] In FIG. 4B, a three-ply paper product 340 is shown. The
first ply comprises a first hardwood layer 342, a second hardwood
layer 346, and a softwood layer 344 therebetween. A second ply
likewise includes a first hardwood layer 348, a second hardwood
layer 352, and a softwood layer 350. A third play includes a first
hardwood layer 354, a second hardwood layer 358, and a softwood
layer 356.
[0052] FIG. 4C reveals a four ply paper product 400. This
embodiment of the invention includes four plies, with hardwood
layers 470, 474, 476, 480, 482, 486, 488 and 492. Softwood layers
472, 478, 484, and 490 also are shown. Each ply provides a
respective softwood layer between two other hardwood layers, as
shown in the FIG. 4C.
Tensile (GMT) Strength Test Method
[0053] Geometric mean tensile (GMT) strength values shown in the
examples below were obtained on a MTS/Sintech tensile tester,
available from the MTS Systems Corp. Eden Prairie, Minn. Tissue
samples measuring 3 inches wide were cut in both the machine and
cross-machine directions. For each test, a sample strip was placed
in the jaws of the tester, set at a 4 inch gauge length (for facial
tissue) and 2 inch gauge length (for bath tissue). The crosshead
speed during the test was 10 in./minute. The tester was connected
with a computer loaded with data acquisition system; eg. MTS
TestWork for windows software. Readings were taken directly from a
computer screen readout at the point of rupture to obtain the
tensile strength of an individual sample. GMT (grams per 3 inch of
sample)=(square root of product of MD tensile strength).times.(CD
tensile strength).
Handfeel (Softness) Testing and Stiffness
[0054] Stiffness (or softness) was ranked on a scale from 0
(described as pliable/flexible) to 16 (described as stiff/rigid).
Twelve (12) panelists were asked to consider the amount of pointed,
rippled or cracked edges or peaks felt from the sample while
turning in your hand. The panelists were instructed to place two
tissue samples flat on a smooth tabletop. The tissue samples
overlapped one another by 0.5 inches (1.27 centimeters) and were
flipped so that opposite sides of the tissue samples were
represented during testing. With forearms/elbows of each panelist
resting on the table, they placed their open hand, palm down, on
the samples. Each was instructed to position their hand so their
fingers were pointing toward the top of the samples, approximately
1.5 inches (approximately 3.81 centimeters) from the edge. Each
panelist moved their fingers toward their palm with little or no
downward pressure to gather the tissue samples. They gently moved
the gathered samples around in the palm of their hand approximately
2 to 3 turns. The rank assigned by each panelist for a given tissue
sample was then averaged and recorded.
Refining of Fiber
[0055] Refining or beating of chemical pulps is the mechanical
treatment and modification of fibers so that they can be formed
into paper or board having desirable properties. It is used when
preparing papermaking fibers for high-quality papers or
paperboards, and in the past has not been widely employed for
bathroom tissue or similar soft paper products.
[0056] Refining improves the bonding ability of fibers so that they
form a strong and smooth paper sheet with good printing properties.
Sometimes refining shortens fibers that are too long for a good
sheet formation, or to develop other pulp properties such as
absorbency, porosity, or optical properties specifically for a
given paper grade.
[0057] A common refining or beating method is to treat fibers in
the presence of water with metallic bars. The plates or fillings
are grooved so that the bars that treat fibers and the grooves
between bars allow fiber transportation through the refining
machine. Such machines are known in the papermaking art.
Slough Measurement Methods and Apparatus
[0058] To determine the abrasion resistance or tendency of fibers
to be rubbed from the web, samples were measured by abrading the
tissue specimens by way of the following method. This test measures
the resistance of tissue material to abrasive action when the
material is subjected to a horizontally reciprocating surface
abrader. All samples were conditioned at about 23.degree. C. and
about 50% relative humidity for a minimum of 4 hours.
[0059] FIG. 5 shows a diagram of the test equipment that may be
employed to abrade a sheet. In FIG. 5, a machine 541 having a
mandrel 543 receives a tissue sample 542. A sliding magnetic clamp
548 with guide pins (not shown) is positioned opposite a stationary
magnetic clamp 549, also having guide pins (550-551). A cycle speed
control 547 is provided, with start/stop controls 545 located on
the upper panel, near the upper left portion of FIG. 5. A counter
546 is shown on the left side of machine 541, which displays counts
or cycles.
[0060] In FIG. 5, the mandrel 543 used for abrasion may consist of
a stainless steel rod, about 0.5" in diameter with the abrasive
portion consisting of a 0.005" deep diamond pattern extending 4.25"
in length around the entire circumference of the rod. The mandrel
543 is mounted perpendicular to the face of the machine 541 such
that the abrasive portion of the mandrel 543 extends out from the
front face of the machine 541. On each side of the mandrel 543 are
located guide pins 550-551 for interaction with sliding magnetic
clamp 548 and stationary magnetic clamp 549, respectively. These
sliding magnetic clamp 548 and stationary magnetic clamp 549 are
spaced about 4" apart and centered about the mandrel 543. The
sliding magnetic clamp 548 and stationary magnetic clamp 549 are
configured to slide freely in the vertical direction.
[0061] Using a die press with a die cutter, specimens are cut into
3" wide.times.8" long strips with two holes at each end of the
sample. For tissue samples, the Machine Direction (MD) corresponds
to the longer dimension. Each test strip is weighed to the nearest
0.1 mg. Each end of the sample 542 is applied upon the guide pins
550-551 and sliding magnetic clamp 548 and stationary magnetic
clamp 549 to hold the sample 542 in place.
[0062] The mandrel 543 is then moved back and forth at an
approximate 15 degree angle from the centered vertical centerline
in a reciprocal horizontal motion against the test strip for 20
cycles (each cycle is a back and forth stroke), at a speed of about
80 cycles per minute, removing loose fibers from the web surface.
Additionally the spindle 543 rotates counter clockwise (when
looking at the front of the instrument) at an approximate speed of
5 revolutions per minute (rpm). The sliding magnetic clamp 548 and
stationary magnetic clamp 549 then are removed from the sample 542.
Sample 542 is removed by blowing compressed air (approximately 5-10
psi) upon the sample 542.
[0063] The sample 542 is weighed to the nearest 0.1 mg and the
weight loss calculated. Ten test samples per tissue sample may be
tested and the average weight loss value in milligrams is recorded.
The result for each example was compared with a control sample
containing no hairspray.
[0064] As used herein, "softener or debonder or debonding agent" is
a chemical compound that serves to soften the final paper product.
These compounds may be selected from the group of compounds
consisting of: quaternary ammonium compounds, quaternary protein
compounds, phospholipids, silicone quaternaries, quaternized,
hydrolyzed wheat protein/dimethicone phosphocopolyol copolymer,
organoreactive polysiloxanes, and silicone glycols. Other debonding
agents also could be used.
[0065] For example, compounds and procedures similar to that
disclosed in U.S. Pat. No. 6,156,157 could be employed. A
quaternary ammonium compound softener/debonder (methyl-1-oleyl
amidoethyl-2-oleyl imidazolinium methyl sulfate identified as
Varisoft 3690 available from Witco Corporation could be employed,
for example. Furthermore, as set forth in one or more examples
below, an imidazoline-based debonding agent such as Kimberly Clark
Designation No. DC-83 manufactured by McIntyre Corporation of
University Park, Ill., can be employed. In some applications, this
debonding agent is added to the hardwood layers in an amount
equivalent to about 6 lbs/Ton (i.e. to the two eucalyptus stock
chests).
Procedures Employed in the Examples
[0066] To demonstrate the use fractionated softwood fibers for
making soft tissue with less slough, several tissue prototypes were
produced (Examples 1-3) on a small scale continuous pilot machine.
This machine formed two separate tissue sheets and mated them
together into a single sheet that was then pressed, dried and
creped. The bottom sheets were formed by way of a headbox having
two layers. This configuration allowed simulation of a
three-layered tissue sheet. Each layer had its own stock system
including stock chest, metering pump, fan pump and white water
handling. This allowed each layer to have its own fiber blend and
independent chemical treatment. The chemicals could be added to the
chest to create a single batch at one concentration or metered into
the stock line to allow periodic adjustment.
EXAMPLE 1
Two-Layered, Two Ply Tissue as Control
[0067] In this example, two layered tissue was made by using the
same fiber furnish in the two layer of the bottom former (headbox).
Permanent wet strength agent (Kymene, available from Hercules, Inc)
was added in an amount equivalent to about 4 lbs/(i.e. about 0.2%)
to the dryer side stock chest containing eucalyptus fiber (fiber
obtained from Bahil Su, Inc.).
[0068] The air side stock chest contained a northern softwood Kraft
fiber (LL-19, from Kimberly-Clark Corporation). Permanent wet
strength agent (Kymene, from Hercules, Inc) was also added in an
amount equivalent to about 4 lbs/(i.e. about 0.2%) to the LL-19
fiber. The LL-19 fiber was subjected to about 4 minutes refining
with a refiner located below the stock chest. A dry strength agent
(Parez from Cytec) was added to the softwood side stock pump to
adjust tensile strength. In the converting, the tissue sheet was
plied up with the hardwood on the outside. The tissue sheets
contained about 35% LL-19 softwood fibers and about 65% eucalyptus
fibers, in total. The tensile strength, slough of the tissue sheets
was tested. The softness properties of the tissue sheets were
evaluated with panel tester as shown in Table 1 below.
EXAMPLE 2
Three Layered, Two Ply Tissue
[0069] In this example of one embodiment of the invention, a three
layered, two ply tissue was manufactured with the three layered
tissue having hardwood eucalyptus on the outer sides of each layer.
The two layers were meshed together into a two ply tissue.
[0070] Eucalyptus fiber was applied in the top former (headbox).
Also, eucalyptus fiber was employed in the lower layer of the
bottom former (headbox); and the LL-19 fiber was employed in the
top layer of the bottom former (headbox).
[0071] Permanent wet strength (Kymene, available from Hercules,
Inc) was added in an amount equivalent to about 4 lbs/(about 0.2%)
to a three layer stock chest. The LL-19 fiber was subjected to
about 4 minutes refining with a refiner located below the stock
chest. A dry strength agent (Parez from Cytec) was added to the
softwood side stock pump to adjust tensile strength.
[0072] In the converting, the three-layer tissue sheet was plied up
with the hardwood on the outsides (i.e. top and bottom) to form a
three-layered, two ply tissue. The three-layered tissue contained
32.5% eucalyptus fiber, 35% LL-19 fiber, and 32.5% eucalyptus
fiber. Overall the tissue still contained 35% LL-19 softwood fibers
and 65% eucalyptus fibers, in total, as in the control example 1
above. The tensile strength and slough of the tissue sheets were
tested, and reported below in Table 1. The softness properties of
the tissue sheets were evaluated with panel tester as shown in
Table 1.
EXAMPLE 3
Three Layered, Two Ply Tissue with Debonding Agent in the Hardwood
Layer
[0073] The tissue was prepared as in example 2 above, with two
three layered structures having hardwood on the outside and
softwood on the inside of each three layered structure. The three
layered structures were combined to form a two ply tissue. A
difference in this example is that an imidazoline-based debonding
agent (Kimberly Clark Designation No. DC-83) was added to the
hardwood layers in an amount equivalent to about 6 lbs/Ton (i.e. to
the two eucalyptus stock chests). Furthermore, the LL-19 fiber was
subjected to about 10 minutes refining with a refiner located
beneath the stock chest.
[0074] The tensile strength and slough of the tissue sheets were
tested. The softness properties of the tissue sheets also were
evaluated with panel tester as shown in the Table 1 below.
1 TABLE 1 GMT Slough, Panel g/3 in. mg Softness Example 1 Two 777
7.38 8.21 Layered Two Ply (Control) Example 2 Three 559 5.26 8.37
Layered Two Ply Example 3 Three- 726 4.97 8.6 Layered With Debonder
in the Hardwood Layer
EXAMPLE 4
Three Layered, Three Ply Product
[0075] A product was manufactured as above in Example 2 except that
a three ply product was produced.
EXAMPLE 5
Three Layered, Three Ply Product with Debonding Agent in Hardwood
Layer
[0076] A product was manufactured as above in Example 3 above
except that a three ply product was produced.
EXAMPLE 6
Three Layered, Four Ply Product
[0077] A product was manufactured as above in Example 2 except that
a four ply product was produced.
EXAMPLE 7
Three Layered, Four Ply Product with Debonding Agent in Hardwood
Layer
[0078] A product was manufactured as above in Example 3 above
except that a four ply product was produced.
[0079] It is 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, which broader aspects are embodied in the
exemplary constructions. The invention is shown by example in the
appended claims.
* * * * *