Note: Descriptions are shown in the official language in which they were submitted.
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SOFT TISSUE HAVING TEMPORARY WET STRENGTH
Field of the Invention
The invention relates to paper products having temporary wet strength. The
invention
especially relates to paper products having temporary wet strength that are
desirably soft
while possessing the ability to rapidly disperse when exposed to conventional
sewage
systems.
Background of the Invention
Paper webs or sheets, sometimes called tissue or paper tissue webs or sheets,
find
extensive use in modern society. These include such staple items as paper
towels, facial
tissues and sanitary (or toilet) tissues. These paper products can have
various desirable
properties, including wet and dry strength, softness, and lint resistance.
Strength is the ability of the product, and its constituent webs, to maintain
physical
integrity and to resist tearing, bursting, and shredding under use conditions,
particularly
when wet.
Softness is the tactile sensation perceived by the consumer as he/she holds a
particular product, rubs it across his/her skin, or crumples it within his/her
hand. This
tactile sensation is provided by a combination of several physical properties.
Important
physical properties related to softness are generally considered by those
skilled in the art to
be the stiffness, the surface smoothness and lubricity of the paper web from
which the
product is made. Stiffness, in turn, is usually considered to be directly
dependent on the
dry strength of the web and the stiffness of the fibers which make up the web.
In
particular, as dry strength increases, softness decreases.
Lint resistance is the ability of the fibrous product, and its constituent
webs, to bind
together under use conditions, including when wet. In other words, the higher
the lint
resistance is, the lower the propensity of the web to lint will be.
The dry strength of paper products should be sufficient to enable manufacture
of the
product and use of the product in a relatively dry condition. Increases in dry
strength can
be achieved either by mechanical processes to insure adequate formation of
hydrogen
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bonding between the hydroxyl groups of adjacent papermaking fibers, or by the
inclusion_
of certain dry strength additives. Such dry strength additives are typically
natural or
synthetic polymers. Exemplary dry strength additives include: starch and
starch
derivatives, polyvinyl alcohol, and polyacrylamide.
Wet strength is a desirable attribute of many disposable paper products that
come
into contact with aqueous fluids in use, such as napkins, paper towels,
household tissues,
disposable hospital wear, etc. In particular, it is often desirable that such
paper products
have sufficient wet strength to enable their use in a moistened or wet
condition. For
example, a moistened tissue or towel may be used for body or other cleaning.
Unfortunately, an untreated cellulose fiber assemblage will typically lose 95%
to 97% of
its strength when saturated with water such that it cannot usually be used in
the moistened
or wet condition.
Historically, one approach to providing wet strength to paper products is to
incorporate additives in the paper product which contribute toward the
formation of
interfiber bonds which are not broken or, for temporary wet strength, which
resist being
broken, by water. A water soluble wet strength resin may be added to the pulp,
generally
before the paper product is formed (wet-end addition). The resin generally
contains
cationic functionalities so that it can be easily retained by the cellulose
fibers, which are
naturally anionic.
A number of resins have been used or disclosed as being particularly usefiil
for
providing wet strength to paper products. Certain of these wet strength
additives have
resulted in paper products with permanent wet strength, i.e., paper which when
placed in
an aqueous medium retains a substantial portion of its initial wet strength
over time.
Exemplary resins of this type include urea-formaldehyde resins, melamine-
formaldehyde
resins and polyamide-epichlorohydrin resins. Such resins have limited wet
strength decay.
Permanent wet strength in paper products is often an unnecessary and
undesirable
property. Paper products such as toilet tissues, etc., are generally disposed
of after brief
periods of use into sewage systems and the like. Clogging of these systems can
result if the
paper product permanently retains its wet strength properties. Therefore,
manufacturers
have more recently added temporary wet strength additives to paper products
for which
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3
wet strength is sufficient for the intended use, but which then decays upon
soaking in
water. Decay of the wet strength facilitates flow of the paper product through
septic
systems. Numerous approaches for providing paper products claimed as having
good
initial wet strength which decays significantly over time have been suggested.
One type of temporary wet strength additive are aldehyde containing resins
exemplified by COBONDTM 1000, and aldehyde functionalized cationic starch
commercially available from the National Starch & Chemical Corp. of
Bloomfield, NJ,
and PAREZTM 631 NC and PAREZT" 750A, aldehyde funtionalized cationic
polyacrylamides commercially available from Cytec Industries, Inc. of West
Paterson, NJ.
Exemplary patents describing paper products having temporary wet strength
include:
U.S. Patent 4,981,557, issued to Bjorkquist on January 1, 1991; U.S. Patent
5,690,790,
issued to Hedlam, et al. on November 25, 1997; and U.S. Patent 5,723,022,
issued to
Dauplaise, et al. on March 3, 1998. While all of these patents describe paper
products
having a decay in strength with time after exposure to water or an aqueous
solution, none
of them describes low density paper products having a combination of short
term
maintenance of strength after exposure to water, decay in strength with time
after exposure
. to water and softness as would be particularly desirable for paper products
that are used for
toweling, sanitary tissue, and the like. In particular, the paper products
described by the
above-identified patents have dry tensile properties that would suggest a need
for
improved softness or, in the absence of any disclosure of dry tensile
properties, a need for
improved short term maintenance of dry strength properties on exposure to
water.
Thus, there is a continuing need for improvements in paper products that are
used for
toweling, sanitary tissue, and the like. In particular, there is a need for
paper products that
maintain a greater percentage of their dry strength when they are first
wetted, while, on
further exposure to water or an aqueous solution, showing a substantial decay
from their
initial wet strength. There is a further need for paper products having such
desirable wet
strength properties that are also soft and lint resistant.
Summarv of the Invention
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The soft, low density paper products of the present invention comprise
papermaking fibers and a cationic temporary wet strength resin. Such paper
products
have a density less than about 0.6 grams per cubic centimeter, a basis weight
is
between about 10 and about 65 grams per square meter, a dry strength less than
about
500 grams per inch (197 grams per centimeter), a ratio of an initial wet
strength to the
dry strength greater than about 0.15:1, and a ratio of a thirty minute wet
strength to
the initial wet strength less than about 0.4. The paper products of the
present
invention may be produced either as homogeneous structures or as multi-layered
structures and may be either creped or uncreped.
According to an aspect of the present invention, there is provided a low
density paper product with temporary wet strength, said paper product having a
density, a basis weight, a wet burst strength, an initial wet strength, a
thirty minute
wet strength, and a dry strength, said paper product comprising:
papermaking fibers; and
a chemical strength additive comprising a temporary wet strength
resin;
wherein the amount of temporary wet strength resin used is at least about 4
pounds per ton, said density is less than about 0.6 grams per cubic
centimeter, said
basis weight is between about 10 and about 65 grams per square meter, said dry
strength is less than about 500 grams per inch (197 grams per centimeter), and
said
wet burst strength is at least about 35 grams, wherein the ratio of said
initial wet
strength to said dry strength is greater than about 0.15:1, and the ratio of
said thirty
minute wet strength to said initial wet strength is less than about 0.4.
According to another aspect of the present invention, there is provided a
method of preparing a low density paper product with temporary wet strength,
the
method comprising:
a) providing an aqueous slurry comprising long papermaking fibers, the slurry
having
a first pH;
b) providing a first pH adjustment means to adjust the first pH and adjusting
the first
pH to a first controlled pH range that is between about 5.0 and about 6.5;
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4a
c) providing a second pH adjustment means to adjust the first controlled pH
range to a
second, more narrowly controlled pH range that is between about 4.8 and about
5.4;
d) providing a temporary wet strength resin solution;
e) mixing the slurry, the second pH adjustment means, and the temporary wet
strength
resin solution so as to provide an initially conditioned, resin treated, long
papermaking fiber slurry;
f) providing a third pH adjustment means to adjust the second controlled pH
range so
as to control the pH of the papermaking slurry to a range that is between
about 4.8
and about 5.4;
g) providing dilution water;
h) mixing the initially conditioned, resin treated, long papermaking fiber
slurry, the
third pH adjustment means, and the dilution water to form a papermaking
furnish; and
i) directing the furnish to a headbox.
Brief Description of the Drawings
Figure 1 is a schematic representation illustrating the steps for preparing an
aqueous papermaking furnish for a papermaking process suitable for producing
the
paper product of the present invention.
Figure 2 is a schematic representation illustrating a papermaking process for
producing the paper product of the present invention wherein the product is
creped
after drying.
Figure 3 is a schematic representation of an alternative drying process
wherein
the paper product is uncreped.
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4b
Detailed Description of the Invention
While this specification concludes with claims particularly pointing out and
distinctly claiming the subject matter regarded as the invention, it is
believed that the
invention can be better understood from a reading of the following detailed
description in conjunction with the accompanying figures and of the appended
examples.
As used herein, the term "lint resistance" is the ability of the fibrous
product,
and its constituent webs, to bind together under use conditions, including
when wet.
In other words, the higher the lint resistance is, the lower the propensity of
the web to
lint will be.
As used herein, the term "binder" refers to the various wet and dry strength
resins and retention aid resins known in the papermaking art
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As used herein, the term "water soluble" refers to materials that are soluble
in water
to at least 3% at 25 C.
As used herein, the terms "tissue paper web, paper web, web, paper sheet and
paper
product" all refer to sheets of paper made by a process comprising the steps
of forming an
aqueous papermaking furnish, depositing this furnish on a foraminous surface,
such as a
Fourdrinier wire, and removing the water from the furnish as by gravity or
vacuum-
assisted drainage, with or without pressing, and by evaporation.
As used herein, an "aqueous papermaking furnish" is an aqueous slurry of
papermaking fibers and the chemicals described hereinafter.
As used herein, the term "multi-layered tissue paper web, multi-layered paper
web,
multi-layered web, multi-layered paper sheet and multi-layered paper product"
all refer to
sheets of paper prepared from two or more layers of aqueous papermaking
furnish which
are preferably comprised of different fiber types, the fibers typically being
relatively long
softwood and relatively short hardwood fibers as used in tissue papermaking.
The layers
are preferably formed from the deposition of separate streams of dilute fiber
slurries, upon
one or more endless foraminous screens. If the individual layers are initially
formed on
separate wires, the layers are subsequently combined (while wet) to form a
layered
composite web.
As used herein the term " multi-ply tissue paper product" refers to a tissue
paper
consisting of at least two plies. Each individual ply in turn can consist of
single-layered or
multi-layered tissue paper webs. The multi-ply structures are forrned by
bonding together
two or more tissue webs such as by gluing or embossing.
As used herein the term "through air drying" technique refers to a technique
of
drying the web by hot air.
As used herein the term "mechanical dewatering" technique refers to a
technique of
drying the web by mechanical pressing with a dewatering felt.
General Description of the Paper of the Present Invention
Paper according to the present invention has a desirable combination of
initial wet
strength, wet strength decay, softness and lint resistance. While the prior
art typically uses
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chemical strength additives (dry strength additives, wet strength resins, and
the like) to
enhance the strength properties of papermaking fibers, the Applicants have
found that,
when papermaking fibers and a temporary wet strength resin are formed into a
paper
structure according to the method of the present invention, the resulting low
density tissue
paper has a unique combination of dry strength, high initial wet strength,
rapid wet
strength decay, softness, and lint resistance. Each of these properties will
be discussed in
greater detail below.
Initial Wet StrenZh
As noted above, the initial wet strength of a paper product is important in
maximizing its utility in many use situations. For example, maintaining
product integrity
during wiping tasks with paper toweling, providing hand protection during post
urination
cleanup for sanitary tissue, and providing protection against mucus for facial
tissue. In
other words, maintenance of as much as possible of the dry strength of a paper
product
after the paper product has become wetted with water or an aqueous solution is
highly
desirable.
A common measure of such dry strength maintenance is the ratio of initial wet
strength (W;) to dry strength (DS). As used herein, this ratio is identified
as the wet to dry
strength ratio. Wet strength and dry strength can be measured according to the
methods
described in the TEST METHODS section below. While the prior art has described
paper
products having a wet to dry strength ratio of about 0.2:1, or even somewhat
higher, such
products also have a dry strength that is great enough that the paper product
would be
undesirable for use as toweling, sanitary tissue or facial tissue because it
was insufficiently
soft. As is well known and will be discussed in the Softness Section below,
there is a clear
relationship between dry strength and perceived softness that says increasing
dry strength
decreases perceived softness. In other words, to date. the only way the art
has been able to
achieve substantial dry strength maintenance is by taking dry strength to
levels which
cause an unacceptable degradation in perceived softness for products such as
toweling,
sanitary tissue, and facial tissue. Typically, the art has been able to
achieve wet to dry
strength ratios on the order of 0.1:1 or, perhaps, 0.12:1 while, at the same
time maintaining
an acceptable level of softness.
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On the other hand, the paper products of the present invention are able to
achieve a
wet to dry ratio of at least about 0.15:1 or, preferably, at least about 0.2:1
or, more
preferably, 0.25:1. Without being bound by theory, the Applicants believe such
ratios are
achievable because the Applicants have identified certain furnish
compositions,
papermaking conditions, and finished paper composition that use the temporary
wet
strength resin, typically a component of low density tissue paper, to provide
a greater
portion of the dry strength. It is known that increasing the level of
temporary wet strength
resin also causes an increase in dry strength. However, in the past the art
has considered
this increase a limitation, if softness is to be maintained, rather than an
opportunity. For
example, the art, as in U.S. Patent 3,755,220, issued to Freimark, et al. on
August 28,
1973, has provided chemical debonders to off-set this perceived undesirable
dry strength
so as to provide a softer, less harsh sheet of paper. The following details
the specific
furnish, papermaking, and paper composition parameters that the Applicant has
identified
as being of importance to achieving the present invention.
Temporary Wet Strength Resin
As noted above, the temporary wet strength resin not only provides temporary
wet
strength but also contributes to dry strength. A key element of the present
invention is a
substantial increase in the level of temporary wet strength resin. For
example, a
commercially successful sanitary tissue uses a temporary wet strength resin at
a level of
about 1 pound per ton (0.05%). In recognizing that the temporary wet strength
resin can
also provide the bulk of the dry strength for low density paper products
prepared under the
proper conditions, the Applicants have found that for the low density paper of
the present
invention the paper should comprise between about 4 pounds of temporary wet
strength
resin per ton of papermaking fibers (0.2%) and about 16 pounds per ton (0.8%).
Preferably, the paper comprises between about 6 pounds per ton (0.3%) and
about 12
pounds per ton (0.6%). In the particularly preferred layered paper products of
the present
invention the temporary wet strength resin is distributed between the inner
layer and the
outer layer such that the inner layer comprises between about 3 and 12 pounds
per ton
(0.15%-0.6%) and the outer layer comprises between about 1 and 4 pounds per
ton
(0.05%-0.2%). Preferably, the inner layer of the preferred layered paper
products
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comprises between about 4 pounds per ton (0.2%) and about 8 pounds per ton
(0.4%) and _
the outer layer comprises between about 2 pounds per ton (0.1 %) and about 4
pounds per
ton (0.2%). A particularly preferred layered paper product comprises about 8
pounds of
temporary wet strength resin per ton of papermaking fibers (0.4%) in the inner
layer and
about 3 pounds per ton in the outer layers (0.15%). All percentages are based
on the total
weight of papermaking fibers (i.e. the combined weight of any short
papermaking fibers
and any long papermaking fibers that may be used).
Headbox pH
The Applicants have found that controlling headbox pH to be between about 4.5
and
about 5.5, preferably between about 4.8 and about 5.4 contributes to an
increased wet to
dry strength ratio. Without being bound by theory, the Applicants believe that
a more acid
pH encourages more efficient crosslink formation by the temporary wet strength
resin.
While headbox pH for tissue products of the prior art may vary between about 4
and about
6 depending on the particular furnish composition, the art preferred to
operate at a pH
close to 6 due to a perceived increased risk of deposition of insoluble
materials (stickies)
onto the Fourdrinier wire as pH decreased. Stickies prevent proper formation
by blocking
portions of the Fourdrinier wire. However, as will be discussed in greater
detail below, the
Applicants have found that a sequential reduction in pH, combined with control
of pH as
discussed above, prevents undue formation of stickies when operating in a more
acid
range. Given this novel path to controlled pH, the Applicants have been able
to achieve a
papermaking process that produces low density tissue having a desirable wet to
dry
strength ratio.
Long Fiber Reduction
As is well known in the art, paper produced using longer papermaking fibers
has a
higher dry strength than paper produced using shorter fibers. For example,
paper produced
using Northern Sulfite Kraft (NSK) fibers has a greater dry strength than
paper produced
by shorter Eucalyptus fibers. Conversely, the paper produced using Eucalyptus
fibers is
softer than the paper produced using NSK fibers. Using layered structures, the
art has
taken advantage of these properties to produce paper structures having a
center layer of
longer fibers for dry strength and outer layers of shorter fibers for
softness.
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The Applicants have been able to take advantage of the contribution of the
temporary
wet strength resin to the dry strength of the low density paper by reducing
the amount of
long fiber in the paper structure. Specifically, paper structures according to
the present
invention having a papermaking fiber composition comprising between about 13%
and
about 25% long fibers have a desirable increase in wet to dry strength ratio.
Preferably, the
papermaking fiber composition comprises between about 14% and about 16% long
fibers.
More preferably, these long fibers are concentrated in the center layer of a
three layered
paper structure and the short fibers are concentrated in the outer layers of
the structure.
Refining
The art also uses refining to increase the dry strength of paper products. As
is known,
refining is a mechanical process that fibrillates the papermaking fibers and
encourages the
formation of interfiber hydrogen bonds. One measure of refining is the Pulp
filtration
Resistance.(PFR) test as is described in the TEST METHODS section below.
Typically,
the long papermaking fibers are refined to increase their dry strength
contribution. Passing
a typical long papermaking fiber, such as NSK, through a refining step
typically causes a
change in PFR of between about I second and about 3 seconds, more typically
between
about 2 and about 3 seconds. The low density tissue products of the present
invention are
able to achieve their desirable wet to dry strength ratios using substantially
less refining.
Suitably, the change in PFR for paper products of the present invention is
between about
0.5 and about 1.5 seconds. Preferably, the change is between about 0.5 seconds
and about
1 second.
Dry Strength Additive
As noted above, the art typically uses both a dry strength additive and one or
more
wet strength resins in producing tissue products. Perhaps, a debonding agent
is also
provided to overcome some of the negative softness effect of the dry strength
additive. By
taking advantage of the dry strength contribution of the temporary wet
strength resin, the
low density tissue products of the present invention substantially eliminate
the need for
adding a debonding agent to the furnish and substantially reduce the need for
a dry
strength additive. Suitably, the low density paper products of the present
invention have a
center layer comprising between about 0 and about 2 pounds of dry strength
additive per
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ton of long papermaking fibers (0-0.1 %). More preferably, the low density
tissue products _
of the present invention comprise between 0 and about 1 pound per ton (0-
0.05%). A
particularly preferred low density tissue product of the present invention is
dry strength
additive free.
Wet Strength Decay
As used herein, the term "wet strength decay" is defined as the ratio of wet
strength
after thirty minutes (W30) to initial wet strength (W;). As noted above, wet
strength decay
is important so as to enable passage through sewer systems and septic tanks.
In particular,
wet strength decay allows such paper products to break up into small enough
pieces that
piping in such systems does not become clogged. It can be recognized that, the
more
quickly wet strength decays, the lower the risk of clogging. Typically, prior
art paper
products having temporary wet strength lose about thirty percent to one half
of their initial
wet strength after thirty minutes exposure to water. Certain high dry strength
paper
products lose as much as 80% of their initial wet strength (W30/W;-0.2). The
paper
products of the present invention lose at least about 60% (W,o/W;<0.4),
preferably at least
about 70% of their initial wet strength(W30/W;<0.3).
As noted above, the low density tissue products of the present invention use
an
increased level of the temporary wet strength resin to provide both dry
strength and
temporary wet strength. As is known, temporary wet strength resins function by
providing
labile crosslinks between papermaking fibers. On exposure to water, these
crosslinks begin
to decay so there is a substantially reduced risk of problems on disposal of
the tissue (eg
sewer clogging). The Applicants have found that, as long as W30 is less than
about 3 5
grams per inch (14 grams/cm) disposal problems are minimized. PreferabIy W30
is less
than 30 grams per inch (12 grams/cm). The Applicants believe that the low
density tissue
products of the present invention are able to achieve such acceptable levels
of decay, even
though they have substantially increased initial wet strengths, because wet
strength decays
at a relatively constant rate versus time. That is, after a given time, wet
strength will decay
by a given percentage so, while the higher initial wet strengths decay to a
higher absolute
value of W30, this value is still sufficiently low so as not to pose a
substantial risk of
disposal problems.
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Softness
The paper products according to the present invention are desirably soft. _ In
particular, the paper products of the present invention have softness that is
at least
comparable to prior art paper products. As used herein, softness of one paper
product is at
least comparable to the softness of another paper product if the relative
softness value
when the two products are compared according to the Panel Softness Method
described in
the TEST METHODS section is greater than about -0.2PSU. To achieve this
desirable
softness the Applicants have looked at several of the contributors to softness
and defined
product and process conditions so as to provide such softness along with the
other aspects
of the present invention. Such contributors are discussed individually below.
Dry Strength
As noted above, there is an inverse relationship between softness and dry
strength.
Softness is typically measured by comparing a test paper to a control paper. A
method for
conducting such measurements is described in the TEST METHODS section below.
For
paper products having utility as toweling, sanitary tissue, or facial tissue
softness is highly
desirable. Given the relationship between softness and dry strength, such
desired softness
effectively places an upper limit on dry strength. The Applicants have found
that paper
products having a total dry tensile strength of less than about 500 grams per
inch (197
grams per centimeter) have softness that is at least comparable to prior art
paper products.
Preferably the total dry tensile strength is less than about 450 grams per
inch (177 grams
per centimeter), more preferably less than about 425 grams per inch (167 grams
per
centimeter), still more preferably, less than about 375 grams per inch (148
grams per
centimeter).
The art has used various means to achieve dry strength. Exemplary means
include:
refining whereby the surface area of the papermaking fibers is increased bv
fibrillation so
as to increase hydrogen bonding between the papermaking fibers; the
aforementioned dry
strength additives; and the dry strength contribution of any wet strength
resins (either
permanent wet strength resins or temporary wet strength resins) that may be
provided. As
noted above, the Applicants have found that desirable levels of dry strength
can be
achieved for the paper products of the present invention, while minimizing the
use of
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extraneous means, such as refining or a specially added dry strength additive.
Without _
being bound by theory, the Applicants believe that, this achievement of a
desirable level of
dry strength is due to a more efficient use of the temporary wet strength
resin. That is, a
contribution of interfiber hydrogen bonding and the temporary wet strength
resin of the
present invention provides sufficient dry strength to meet the process and
performance
needs of the paper product without being so great so as to cause a negative
softness profile.
Modulus
As is well known, stiffer products are perceived as being less soft. One
measure of
stiffness is modulus (i.e. the slope of a stress/strain curve). A method for
measuring
modulus is provided in the TEST METHODS section below. The Applicants believe
that
one reason that softness of the present invention is at least comparable to
the to the
softness of the prior art, while providing higher temporary wet strength, is
that the low
density paper of the present invention has a modulus that is comparable to,
preferably
lower than, the modulus of low density paper of the prior art. Low density
tissue paper
having a modulus less than about 12 grams/cm% has satisfactory softness.
Preferably, the
modulus is less than about 10 grams/cm%. A particularly preferred embodiment
of the
present invention has a modulus between about 6 grams/cm% and about 10
grams/cm%.
A particularly preferred low modulus tissue paper is pattern densified tissue
paper.
Pattern densified tissue paper is characterized by having a relatively high
bulk field of
relatively low fiber density and an array of densified zones of relatively
high fiber density.
The high bulk field is alternatively characterized as a field of pillow
regions. The densified
zones are alternatively referred to as knuckle regions. The densified zones
may be
discretely spaced within the high bulk field or may be interconnected, either
fully or
partially, within the high bulk field. Because of their lower density, the
pillow regions
provide regions are believed to provide relatively higher stretch causing
pattern densified
tissue to have an overall lower modulus than a web having a substantially
uniform density.
Preferred processes for making pattem densified tissue webs are disclosed in
U.S.
Patent No. 3,301,746, issued to Sanford and Sisson on January 31, 1967, U.S.
Patent No.
3,974,025, issued to Peter G. Ayers on August 10, 1976, and U.S. Patent No.
4,191,609,
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13
issued to Paul D. Trokhan on March 4, 1980, and U.S. Patent No. 4,637,859, and
issued to
Paul D. Trokhan on January 20, 1987.
In general, pattern densified webs = are preferably prepared by depositing a
paper
making furnish on a foraminous forming wire such as a Fourdrinier wire to form
a wet
web and then juxtaposing the web against an array of supports. The web is
pressed against
the array of supports, thereby resulting in densified zones in the web at the
locations
geographically corresponding to the points of contact between the array of
supports and
the wet web. The remainder of the web not compressed during this operation is
referred to
as the high bulk field. The web is dewatered, and optionally predried, in such
a manner so
as to substantially avoid compression of the high bulk field. This is
preferably
accomplished by fluid pressure, such as with a vacuum type device or blow-
through dryer,
or alternately by mechanically pressing the web against an array of supports
wherein the
high bulk field is not compressed. The operations of dewatering, optional
predrying and
formation of the densified zones may be integrated or partially integrated to
reduce the
total number of processing steps performed. Subsequent to formation of the
densified
zones, dewatering, and optional predrying, the web is dried to completion,
preferably still
avoiding mechanical pressing. Preferably, from about 8% to about 55% of the
multi-
layered tissue paper surface comprises densified knuckles having a relative
density of at
least 125% of the density of the high bulk field.
The array of supports is preferably an imprinting carrier fabric having a
patterned
displacement of knuckles which operate as the array of supports which
facilitate the
formation of the densified zones upon application of pressure. The pattern of
knuckles
constitutes the array of supports previously referred to. Imprinting carrier
fabrics are
disclosed in U.S. Patent No. 3,301,746, Sanford and Sisson, issued January 31,
1967, U.S.
Patent No. 3,821,068, Salvucci, Jr. et al., issued May 21, 1974, U.S. Patent
No. 3,974,025,
Ayers, issued August 10, 1976, U.S. Patent No. 3,573,164, Friedberg et al.,
issued March
30, 1971, U.S. Patent No. 3,473,576, Amneus, issued October 21, 1969, U.S.
Patent No.
4,239,065, Trokhan, issued December 16, 1980, and U.S. Patent No. 4,528,239,
Trokhan,
issued July 9, 1985.
A particularly preferred pattern densified, low density tissue according to
the present
invention is made according to the aforementioned U.S. Patent 4,637,859 using
a
CA 02331178 2004-03-02
14
deflection member as described in the aforementioned U.S. Patent 4,528,239.
Such paper _
has an interconnected pattem of higher density corresponding to the knuckles
of_ the
deflection member. The densified zones surround and isolate a plurality of
lower density
pillows which are distributed in a non-random repeating pattern. That is, each
pillow is in
the form of a closed figure having a shape (in plan view) which includes, but
is not limited
to, circles, ovals, polygons of six and fewer sides, bow tie shaped figures,
and weave-like
patterns, bow tie shaped figures being particularly preferred. Such patterns
are discussed in
greater detail in U.S. Patent 5,679,222, issued in the name of Rasch, et al.
on October 21,
1997.
As is also discussed in the aforementioned U.S. Patent 5,679,222, overburden
can
significantly affect the properties of any paper made using the belt. Such
properties
include: degree of pinholing, caliper generation, and modulus. In addition to
the teachings
of U.S. Patent 5,679,222, the Applicants have found that an overburden between
about 2.0
mils (0.05 mm) and about 8 mils (0.2 mm) provides an acceptable balance
between caliper
generation, modulus, and prevention of pinholing. A particularly preferred
overburden is
between about 5.5 mils (0.14 mm) and about 6.5 mils (0.17 mm). As noted above,
the
Applicants believe that the pillow regions provide relatively higher stretch
resulting in an
overall lower modulus for pattern densified tissue when compared to a non-
pattern
densified tissue having a comparable basis weight.
Wet Burst Strength
The combination of improved temporary wet strength and lower modulus combine
to
provide improved temporary wet burst strength when compared to low density
tissue
products of the prior art. Wet burst strength is particularly important for
sanitary tissue
products because it is a measure of the protection such products provide
during use ("poke
through" resistance). That is, paper products having insufficient wet burst
strength are seen
as being very undesirable. The low density tissue products of the present
invention have an
initial wet burst strength of at least about 35 grams, preferably the wet
burst strength is
between about 35 grams and about 70 grams. More, preferably, the wet burst
stre~,:,,-th is
between about 45 grams and about 60 grams. A method for measuring wet burst
strenLyth is
given in the TEST METHODS section below.
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Lint Resistance
Lint resistance is an important property for many of the uses of low density
tissue
products. For example, sanitary tissue products with a propensity to lint can
cause dusting
as such a product is unrolled and high linting facial tissue products can
leave unsightly lint
on surfaces (eg glasses) after wiping. The Applicants have found that, when a
paper
product has a lint value of less than about 8 when measured according to the
Lint Test
described in the TEST METHODS section, negative linting comments are
substantially
reduced. Preferably, the lint value is less than about 7.
The low density tissue products of the present invention have such desirable
low lint
values because of the increased level of the temporary wet strength resin. For
example, by
providing the particularly preferred layered products of the present invention
with a low
level of a temporary wet strength resin (typically strength additives are not
provided to the
outer layers of low density tissue products because of reductions in
softness), lint
resistance is substantially increased.
Composition of the Paper Product
Papermakin Fibers
It is anticipated that wood pulp in all its varieties will normally comprise
the
papermaking fibers used in this invention. However, other cellulose fibrous
puips, such as
cotton liners, bagasse, rayon, etc., can be used and none are disclaimed. Wood
pulps useful
herein include chemical pulps such as Kraft, sulfite and sulfate pulps as well
as mechanical
pulps including for example, ground wood, thermomechanical pulps and Chemi-
ThermoMechanical Pulp (CTMP). Pulps derived from both deciduous and coniferous
trees
can be used.
Synthetic fibers such as rayon, polyethylene and polypropylene fibers, may
also be
utilized in combination with the above-identified natural cellulose fibers.
One exemplary
polyethylene fiber which may be utilized is Pulpex , available from Hercules,
Inc.
(Wilmington, Del.).
Both hardwood pulps and softwood pulps as well as blends of the two may be
employed. The terms hardwood pulps as used herein refers to fibrous pulp
derived from
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16
the woody substance of deciduous trees (angiosperms): wherein softwood pulps
are fibrous
pulps derived from the woody substance of coniferous trees (gymnosperms).
Hardwood
pulps such as eucalyptus are particularly suitable for the outer layers of the
multi-layered
tissue webs described hereinafter, whereas northern softwood Kraft (NSK) pulps
are
preferred for the inner layer(s) or ply(s). Also applicable to the present
invention are low
cost fibers derived from recycled paper, which may contain any or all of the
above
categories as well as other non-fibrous materials such as fillers and
adhesives used to
facilitate the original paper making.
Temporary Wet Strength Resin
The paper products of the present invention also contain as an essential
ingredient a
temporary wet strength resin. Preferably, the temporary wet strength resin is
a cationic,
polyaldehyde polymer having free aldehyde groups. By "free aldehyde groups" it
is meant
that the aldehyde groups are not bonded to other functional groups which would
render
them unreactive with the cellulosic fibers. For example, an aldehyde group may
form
interfiber chemical bonds, typically covalent bonds, with a cellulosic
hydroxyl group when
the paper product is dried (chemical bonds joining different cellulosic fibers
are formed).
Preferred polyaldehydes are those which impart a temporary, rather than
permanent, wet
strength to paper products when they are incorporated as a sole strength
additive in
comparable paper products.
Preferred polyaldehydes are water soluble in order to facilitate a water based
process.
As used herein, "water soluble" includes the ability of a material to be
dissolved,
dispersed, swollen, hydrated or similarly admixed in water. Similarly, as used
herein,
reference to the phrase "substantially dissolved," "substantially dissolving"
and the like
refers to the dissolution, dispersion, swelling, hydration and the like
admixture of a
material in a liquid medium (e.g., water). The mixture typically forms a
generally uniform
liquid mixture having, to the naked eye, one physical phase.
Suitable polyaldehyde polymers include natural and synthetic polymers prepared
or
modified to contain aldehyde groups. Suitable polyaldehyde polymers include,
but are not
limited to, aldehyde modified starches and polyacrylamides, and acrolein
copolymers.
CA 02331178 2004-03-02
17
The polyaldehyde polymer may be electronically neutral or charged, e.g., an
ionic _
polymer such as anionic or cationic polyaldehyde polymers. Cationic
polyaldehYde
polymers are preferred. Without intending to be limited or bound -by theory,
it is believed
that. the cationic polyaldehyde tends to be retained on the cellulosic fibers,
which are
anionic in nature. Exemplary cationic polyaldehyde polymers include cationic,
aldehyde
functionalized starches and cationic, aldehyde functionalized polyacrylamides,
the
polyacrylamides being preferred. Cationic, aldehyde-functionalized starches
suitable for
use herein include that which is commercially available from National Starch &
Chemical
Co. of Bloomfield, NJ under the trademark COBONDT"' 1000. Cationic, aldehyde-
"
f~tianalized polyacrylamdes suitable for use herein include those commercially
available from Cytec Industries Inc. West Paterson, NJ under the trademark
PAREZTM.
Suitable resins of this type include: 631 NC and PAREZT"' 750A. Particularly
preferred
cationic, aldehyde-functionalized polyacrylamides are: PAREZTM 750B and PAREZ
EXPNT"'
3683.
Aldehyde-functionalized polymers suitable for use herein also include other
temporary wet strength resins described in U.S. Patent 4,954,538, Dauplaise et
al., issued
September 1990; U.S. Patent No. 4,981,557, Bjorkquist, issued January 1, 1991;
and U.S.
Patent No. 5,320,711, Dauplaise, et al., issued June 14, 1994; U.S. Patent
5,723,022,
Dauplaise, et al., issued March 3, 1998.
The PanermakingyProcess
Figures 1-3 are schematic representations of various portions of papermaking
processes incorporating the preferred embodiments of the present invention.
These
preferred embodiments are described in the following discussion, wherein
reference is
made to Figure 1 which is a schematic representation illustrating the steps
for preparing an
aqueous papermaking furnish for a papermaking process suitable for producing
the paper
product of the present and Figures 2 and 3 are side elevational views of
papermachines
suitable for producing the low density tissue of the present invention.
The papermaking process begins with the preparation of the one or more
papermaking furnishes. Depending on the desired structure of the finished
paper product
CA 02331178 2004-03-02
18
and the design of a particular papermachine, one or more furnishes is
prepared. For _
homogeneous paper structures only one fiunish is necessary. For layered
structures two or
more furnishes are necessary. Referring to Figure 1, a process for preparing
the furnishes
necessary to. produce the paper according to the present invention having a
particularly
preferred layered structure is described hereinafter.
Referring to Figure 2, which is a side elevational view of a preferred
papermachine
80 for manufacturing paper according to the present invention, the furriishes
is (are)
delivered to the papermachine 80. Papermachines producing homogeneous paper
structures may have one or more chambers 82-83 (One of skill in the art will
recognize
that the same fumish can be directed to more than one chamber). Papermachines
producing layered structures require at least two chambers 82-83. Such layered
papermachines 80 comprise, for example, a layered headbox 81 having a top
chamber 82 a
center chamber 82b, and a bottom chamber 83, a slice roof 84, and a
Fourdrinier wire 85
which is looped over and about breast roll 86, deflector 90, vacuum suction
boxes 91,
couch ro1192, and a plurality of turning rolls 94.
While the paper product of the present invention can have either a homogeneous
or a
layered structure, a particularly preferred embodiment is multi-layered with
three layers.
The two outer layers are produced by a first furnish 22 pumped to chambers 82
and 83 as
shown in Figure 2 and the center layer is produced by a second furnish 21
pumped to
center chamber 82b. The following discusses a particularly preferred
composition for each
of the fumishes.
Referring to Figure 1 a storage vessel 1 is provided for staging an aqueous
slurry
of relatively long papermaking fibers. The slurry is made up by dispersing the
fibers in
water using a conventional repulper (not shown). A caustic solution (e.g.
sodium
hydroxide in water) may also be added during repulping to adjust the pH of the
slurry so it
is between about 5.0 and about 6.5 as it enters pump 2. The slurry is conveyed
by pump 2
and, optionally, through refiner 3 to mixer 4 (provided for the optional
addition of other
sources of fiber, such as broke). First long fiber additive pipe 5 is provided
to add ar acid
solution to initially condition the pH of the furnish toward the desired
range. Second long
fiber additive pipe 6 is provided to introduce a water solution of a temporary
wet strength
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WO 99/63158 PCT/US98/10966
19
resin to the papermaking fiber slurry. Pump 7 mixes the papermaking fiber
slurry, the acid,
and the temporary wet strength resin. The slurry pH after mixing is controlled
to be
between about 4.8 and about 5.4. Pump 7 also conveys the initially
conditioned, resin
treated long papermaking fiber slurry toward third long fiber additive pipe 8
where a
second portion of acid is added to control the pH of the slurry, compensating
for
whitewater alkalinity. Fan pump 10 mixes the slurry and the additional acid
with diluting
whitewater from pipe 9. The fully conditioned slurry 21 (pH remains between
about 4.8
and about 5.4) is then conveyed to the middle chamber 82b of headbox 81 (shown
in
Figure 2).
Still referring to Figure 1, a storage vessel 11 is provided for a slurry of
short
papermaking fibers. The slurry is made up by dispersing the short papermaking
fibers in
water using a conventional repulper (not shown). A caustic solution (e. g.
sodium
hydroxide in water) may also be added during repulping to adjust the pH of the
slurry so it
is between about 5.0 and about 6.5 as it enters pump 12. The slurry is
conveyed by pump
12 to mixer 14 (provided for the optional addition of other sources of fiber,
such as broke).
First short fiber additive pipe 15 is provided to add acid to initially
condition the pH of the
furnish toward the desired range. Second short fiber additive pipe 16 is
provided to
introduce a water solution of a temporary wet strength resin to the
papermaking fiber
slurry. Pump 17 mixes the papermaking fiber slurry, the acid, and the
temporary wet
strength resin. The slurry pH after mixing is controlled to be between about
4.8 and about
5.4. Pump 17 also conveys the initially conditioned, resin treated short
papermaking fiber
slurry toward third short fiber additive pipe 18 where a second portion of
acid is added to
control the pH of the slurry, compensating for whitewater alkalinity. Fan pump
20 mixes
the slurry and the additional acid with diluting whitewater from pipe 19. The
fully
conditioned slurry 22 (pH remains between about 4.8 and about 5.4) is then
divided into
two portions one of which is conveyed to top chamber 82 of headbox 81 and the
other of
which is conveyed to bottom chamber 83 of headbox 81 (as shown in Figure 2).
Again referring to Figure 2, the first papermaking furnish 22 is pumped
through top
chamber 82 and bottom chamber 83 and the second papennaking furnish 21 is
pumped
through center chamber 82b and thence out of the slice roof 84 in over and
under relation
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WO 99/63158 PCTIUS98/10966
onto Fourdrinier wire 85 to form thereon an embryonic web 88 comprising layers
88a, and
88b, and 88c. Dewatering occurs through the Fourdrinier wire 85 and is
assisted by
deflector 90 and vacuum boxes 91. As the Fourdrinier wire makes its return run
in the
direction shown by the arrow, showers 95 clean it prior to its commencing
another pass
over breast roll 86. At web transfer zone 93, the embryonic web 88 is
transferred to a
foraminous carrier fabric 96 by the action of vacuum transfer box 97. Carrier
fabric 96
carries the web from the transfer zone 93 past vacuum dewatering box 98,
through blow-
through predryers 100 and past two turning rolls 101, forming semi-dry
embryonic tissue
paper web, 106, still supported by the foraminous carrier fabric, 96.
The semi-dry tissue paper web is secured to the cylindrical surface of Yankee
dryer
109 aided by adhesive applied by spray boom 107 and 108. Adhesion of the web
is
promoted by use of the opposing cylindrical steel drum, 102. Drying is
completed on the
steam heated Yankee dryer 109 and by hot air which is heated and circulated
through
drying hood 110 by means not shown. The web is then dry creped from the Yankee
dryer
109 by doctor blade 111, also-called a creping blade, after which it is
designated paper
sheet 70 comprising a Yankee-side layer 71 a center layer 77, and an off-
Yankee-side layer
75. Paper sheet 70 then passes between calender rolls 112 and 113, about a
circumferential
portion of reel 115, and thence is wound into a roll 116 on a core 117
disposed on shaft
118.
After the web is transferred to Yankee dryer 109, the carrier fabric 96 is
then cleaned
and dewatered as it completes its loop by passing over and around additional
turning rolls
101, showers 103, and vacuum dewatering box 105.
In an alternative drying scheme, shown in Figure 3, the embryonic web 88
supported
by Fourdrinier wire 85 is transferred to a foraminous transfer (i.e. carrier)
fabric 186 by the
action of vacuum transfer box 187 and turning roll 189. Carrier fabric 186
travels at a
slower speed than Fourdrinier wire 85. The purpose of carrier fabric 186 is
therefore to
shorten the embryonic web 88 relative to its length while being supported on
Fourdrinier
wire 85. A further purpose of carrier fabric 186 is to transport the embryonic
web to a
blow through dryer fabric 190. During this travel, the embryonic web can
optionally be
further dewatered by means of vacuum boxes not shown. The path of carrier
fabric 186 is
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WO 99/63158 PCTIUS98/10966
21
controlled by a plurality of turning rolls shown but not numbered for
simplicity. The
transfer to the blow through dryer fabric 190 is effected by means of a vacuum
box 191.
Carrier fabric 186 is preferably showered by means not shown prior to its
return to the web
transfer zone promoted by vacuum box 187. After transfer to the blow through
dryer fabric
190, the wet web is transported through blow through dryer 192, whereupon, hot
air
generated by means not shown is propelled through the dryer fabric and
consequently the
embryonic web which resides thereupon. The dried web 193 is dislodged from the
dryer
fabric 190 at the exit of the predryer. At this point, dried web 193 can
optionally be
directed between two, relatively smooth, dry end carrying fabrics, an upper
fabric 196 and
a lower fabric 194. While secured between fabrics 196 and 194, the dried web
193 can be
calendered by a series of fixed gap calendering nips formed between opposing
pairs of
rollers 195. These nips smooth the surface and control the thickness of the
tissue paper.
Still referring to Figure 3, the finished calendered web 171 emerges from the
space
between opposing carrier fabrics 196 and 194 still supported by carrier fabric
94 after
which it is wound upon reel 198.
The present invention is particularly adapted for paper products which are to
be
disposed into sewer systems, such as toilet tissue. However, it is to be
understood that the
present invention is applicable to a variety of paper products including, but
not limited to
disposable absorbent paper products such as those used for household, body, or
other
cleaning applications and those used for the absorption of body fluids such as
urine and
menses. Exemplary paper products thus include tissue paper including toilet
tissue and
facial tissue, paper towels, absorbent materials for diapers, feminine hygiene
articles
including sanitary napkins, pantiliners and tampons, adult incontinent
articles and the like,
and writing paper.
Tissue paper of the present invention can be homogeneous or multi-layered
construction; and tissue paper products made therefrom can be of a single-ply
or multi-ply
construction. The tissue paper preferably has a basis weight of between about
10 g/m2 and
about 65 g/m2, and density of about 0.6 g/cm3 or less. More preferably, the
basis weight
will be about 40 g/m2 or less and the density will be about 0.3 g/cm3 or less.
Most
preferably, the density will be between about 0.04 g/cm3 and about 0.2 g/cm3.
See
CA 02331178 2004-03-02
22
Column 13, lines 61 - 67, of U.S. Patent 5,059,282 (Ampulski et al), issued
October 22,
1991, which describes how the density of tissue paper is measured. (Unless
otherwise
specified, all amounts and weights relative to the paper are on a dry basis.)
The tissue
paper may be pattern densified tissue paper, and uncompacted, nonpattern-
densified tissue
paper. These types of tissue paper and methods for making such paper are well
known in
the art and are described, for example, in U.S. Patent 5,334,286, issued on
August 2, 1994
in the names of Dean V. Phan and Paul D. Trokhan.
TEST METHODS
A. Strength Tests
The paper products are aged prior to tensile testing a minimum of 24 hours in
a
conditioned room where the temperature is 73 F + 4 F (22.8 C + 2.2 C) and
the relative
humidity is 50% + 10%.
1. Total Drv Tensile Strength (DS)
This test is performed on one inch by five inch (about 2.5 cm X 12.7 cm)
strips of paper
(including handsheets as described below, as well as other paper sheets) in a
conditioned
room where the temperature is 73 F + 4 F (about 28 C + 2.2 C) and the relative
humidity
is 50% + 10%. An electronic tensile tester (Model 1122T"', Instron Corp.,
Canton, Mass.) is
used and operated at a crosshead speed of 2.0 inches per minute (about 5.1 cm
per min.)
and a gauge length of 4.0 inches (about 10.2 cm). Reference to a machine
direction means
that the sample being tested is prepared such that the 5" dimension
corresponds to that
direction. Thus, for a machine direction (MD) DS, the strips are cut such that
the 5"
dimension is parallel to the machine direction of manufacture of the paper
product. For a
cross machine direction (CD) DS, the strips are cut such that the 5" dimension
is parallel
to the cross-machine direction of manufacture of the paper product. Machine-
direction and
cross-machine directions of manufacture are well known terms in the art of
paper-making.
The MD and CD tensile strengths are determined using the above equipment and
calculations in the conventional manner. The reported value is the arithmetic
average of at
CA 02331178 2004-03-02
23
least six strips tested for each directional strength. The DS is the
arithmetic total of the
MD and CD tensile strengths.
2. Wet Tensile
An electronic tensile tester (Model 1122, Instron Corp.) is used and operated
at a
crosshead speed of 1.0 inch (about 2.5 cm) per minute and a gauge length of
1.0 inch
(about 2.5 cm), using the same size strips as for DS. The two ends of the
strip are placed in
the upper jaws of the machine, and the center of the strip is placed around a
stainless steel
peg. The strip is soaked in distilled water at about 20 C for the desired soak
time, and then
measured for tensile strength. One half the measured wet tensile is taken as
the single strip
wet strength. As in the case of the DS, reference to a machine direction means
that the
sample being tested is prepared such that the 5" dimension corresponds to that
direction.
The MD and CD wet tensile strengths are determined using the above equipment
and
calculations in the conventional manner. The reported value is the arithmetic
average of at
least six strips tested for each directional strength. The total wet tensile
strength for a given
soak time is the arithmetic total of the MD and CD tensile strengths for that
soak time.
Initial total wet tensile strength (W;) is measured when the paper has been
saturated for 5
0.5 seconds. 30 minute total wet tensile (W30) is measured when the paper has
been
saturated for 30 0.5 minutes.
3. Tensile Modulus
Tensile Modulus of tissue samples is obtained at the same time as the tensile
strength
of the sample is determined. In this method a single ply 10.16 cm wide sample
is placed in
a tensile tester (Thwing AlbertTM QCII interfaced to an LMS data system) with
a gauge
length of 5.08 cm. The sample is elongated at a rate of 2.54 cm/minute. The
sample
elongation is recorded when the load reaches 10 g/cm (F 10), 15 g/cm (F 15),
and 20 g/cm
(F20). A tangent slope is then calculated with the mid-point being the
elongation at 15
g/cm (F15).
The Tangent slope is calculated in the following manner:
Tangent slope (TenModl5) = (delta force) / (delta elongation)
CA 02331178 2004-03-02
24
_ (F20-F10)
(%elongation@ F20 - %elongation@ F 10)
Another exemplary method for obtaining the tangent slope at 15 g/cm is to use
a Thwing-
Albert STD tensile tester and set the load trap to 152.4 grams in the tangent
slope
calculation program. This is equivalent to 15 g/cm when using the 10.16 cm
width sample.
Total Tensile Modulus is obtained by measuring the Tensile Modulus in the
machine
direction at 15 g/cm and cross machine direction at 15 g/cm and then
calculating the
geometric mean. Mathematically, this is the square root of the product of the
machine
direction Tensile Modulus (TenMod 15MD) and the cross direction Tensile
Modulus
(TenMod 15CD).
TotalTensileModulus = TenMod 15 MD x TenMod 15CD
High values for Total Tensile Modulus indicate that the sample is stiff and
rigid.
4. Burst Strength
Overview
The test specimen, held between annular clamps, is subjected to increasing
force that
is applied by a 0.625 inch diameter, polished stainless steel ball. The burst
strength is that
force that causes *the sample to fail. Burst strength may be measured on wet
or dry
samples.
Annaratus
Burst Tester Intelect-II-STDT"t Tensile Test Instrument, Cat. No. 1451-24PGB
or
the Thwing-Albert Burst TesterTM are both suitable. Both instrument
are available from Thwing-Albert Instrument Co., Philadelphia, PA.
The instruments must be equipped with a 2000 g load cell and, if
wet burst measurements are to be made, the instruments must be
equipped with a load cell shield and a front panel water shield.
Conditioned Room Temperature and humidity should be controlled to remain
within the
following limits:
Temperature: 73t3 F (23 Cf2 C)
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WO 99/63158 PCT/US98/10966
Humidity: 50 2% Relative Humidity
Paper Cutter Scissors or other equivalent may be used
Pan For soaking wet burst samples, suitable to sample size
Solution Water for soaking wet burst samples should be equilibrated to the
temperature of the conditioned room.
Timer Appropriate for measuring soak time
Sample preparation
1) Cut the sample to a size appropriate for testing (minimum sample size 4.5
in x 4.5
in). Prepare a minimum of five samples for each condition to be tested.
2) If wet burst measurements are to be made, place an appropriate number of
cut
samples into a pan filled with temperature-equilibrated
EQuipment Setup
1) Set the burst tester up according to the manufacturer's instructions. If an
Intelect-Il-
STD Tensile Test Instrument is to be used the following are appropriate:
Speed: 12.7 centimeters per minute
Break Sensitivity: 20 grams
Peak Load: 2000 grams
2) Calibrate the load cell according to the expected burst strength.
Measurement and Reportin~
1) Operate the burst tester according to the manufacturer's instructions to
obtain a burst
strength measurement for each sample.
2) Record the burst strength for each sample and calculate an average and a
standard
deviation for the burst strength for each condition.
3) Report the average and standard deviation for each condition to the nearest
gram.
B. Densi
CA 02331178 2004-03-02
26
The density of multi-layered tissue paper, as that term is used herein, is the
average _
density calculated as the basis weight of that paper divided by the caliper,
with the
appropriate unit conversions incorporated therein. Caliper of the multi-
layered tissue
paper, as used herein, is the thickness of the paper when subjected to a
compressive load of
95 g/in2 (15.5 g/cm2).
C. Measurement of Panel Softness of Tissue Papers
Ideally, prior to softness testing, the paper samples to be tested should be
conditioned
according to TAPPI Method #T402OM-88. Here, samples are preconditioned for 24
hours
at a relative humidity level of 10 to 35% and within a temperature range of 22
to 40 C.
After this preconditioning step, samples should be conditioned for 24 hours at
a relative
humidity of 48 to 52% and within a temperature range of 22 to 24 C.
Ideally, the softness panel testing should take place within the confines of a
constant
temperature and humidity room. If this is not feasible, all samples, including
the controls,
should experience identical environmental exposure conditions.
Softness testing is performed as a paired comparison in a form similar to that
described in "Manual on Sensory Testing Methods", ASTM Special Technical
Publication
434, published by the American Society For Testing and Materials 1968.
Softness is evaluated by subjective testing using what is referred to as a
Paired Difference
Test. The method employs a standard external to the test material itself. For
tactile perceived
softness two samples are presented such that the subject cannot see the
samples, and the
subject is required to choose one of them on the basis of tactile softness.
The result of the test
is reported in what is referred to as Panel Score Unit (PSU). With respect to
softness testing
to obtain the softness data reported herein in PSU, a number of softness panel
tests are
performed. In each test ten practiced softness judges are asked to rate the
relative softness of
three sets of paired samples. The pairs of sample are judged one pair at a
time by each judge
one sample of each being designated X and the other Y. Briefly, each X sample
is graded
against its paired Y sample as follows:
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1. a grade of plus one is given if X is judged to may be a little softer than
Y, and a
grade of minus one is given if Y is judged to may be a little softer than X;
2. a grade of plus two is given if X is judged to surely be a little softer
than Y, and
a grade of minus two is given if Y is judged to surely be a little softer than
X;
3. a grade of plus three is given to X if it is judged to be a lot softer than
Y, and a
grade of minus three is given if Y is judged to be a lot softer than X; and,
lastly:
4. a grade of plus four is given to X if it is judged to be a whole lot softer
than Y,
and a grade of minus 4 is given if Y is judged to be a whole lot softer than
X.
The grades are averaged and the resultant value is in units of PSU. The
resulting data are
considered the results of one panel test. If more than one sample pair is
evaluated then all
sample pairs are rank ordered according to their grades by paired statistical
analysis. Then,
the rank is shifted up or down in value as required to give a zero PSU value
to which ever
sample is chosen to be the zero-base standard. The other samples then have
plus or minus
values as determined by their relative grades with respect to the zero base
standard. The
number of panel tests performed and averaged is such that about 0.2 PSU
represents a
significant difference in subjectively perceived softness.
D. Measurement of Tissue Paper Lint
The amount of lint generated from a tissue product is determined with a
Sutherland
Rub Tester. This tester uses a motor to rub a weighted felt 5 times over the
stationary toilet
tissue. The Hunter Color L value is measured before and after the rub test.
The difference
between these two Hunter Color L values is calculated as lint.
Sample Preparation:
Prior to the lint rub testing, the paper samples to be tested should be
conditioned
according to TAPPI Method #T4020M-88. Here, samples are preconditioned for 24
hours
at a relative humidity level of 10 to 35% and within a temperature range of 22
to 40 C.
After this preconditioning step, samples should be conditioned for 24 hours at
a relative
humidity of 48 to 52% and within a temperature range of 22 to 24 C. This rub
testing
should also take place within the confines of the constant temperature and
humidity room.
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The SutherlandT'" Rub Tester may be obtained from Testing Machines, Inc.
(Amityville, NY, 11701). The tissue is first prepared by removing and
discarding_ any
product which might have been abraded in handling, e.g. on the outside of the
roll. For
multi-ply finished product, three sections with each containing two sheets of
multi-ply
product are removed and set on the bench-top. For single-ply product, six
sections with
each containing two sheets of single-ply product are removed and set on the
bench-top.
Each sample is then folded in half such that the crease is running along the
cross direction
(CD) of the tissue sample. For the multi-ply product, make sure one of the
sides facing out
is the same side facing out after the sample is folded. In other words, do not
tear the plies
apart from one another and rub test the sides facing one another on the inside
of the
product. For the single-ply product, make up 3 samples with the wire side out
and 3 with
the non-wire side out. Keep track of which samples are wire side out and which
are non-
wire side out.
Obtain a 30" X 40" piece of Crescent #300 cardboard from Cordage Inc. (800 E.
Ross Road, Cincinnati, Ohio, 45217). Using a paper cutter, cut out six pieces
ofcardboard
of dimensions of 2.5" X 6". Puncture two holes into each of the six cards by
forcing the
cardboard onto the hold down pins of the Sutherland Rub tester.
If working with single-ply finished product, center and carefully place each
of the
2.5" X 6" cardboard pieces on top of the six previously folded samples. Make
sure the 6"
dimension of the cardboard is running parallel to the machine direction (MD)
of each of
the tissue samples. If working with multi-ply finished product, only three
pieces of the
2.5" X 6" cardboard will be required. Center and carefully place each of the
cardboard
pieces on top of the three previously folded samples. Once agairi, make sure
the 6"
dimension of the cardboard is running parallel to the machine direction (MD)
of each of
the tissue samples.
Fold one edge of the exposed portion of tissue sample onto the back of the
cardboard. Secure this edge to the cardboard with adhesive tape obtained from
3MT" Inc.
(3/4" wide Scotch Brand, St. Paul, MN). Carefully grasp the other over-hanging
tissue
edge and snugly fold i: over onto the back of the cardboard. While maintaining
a snug tit
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of the paper onto the board, tape this second edge to the back of the
cardboard. Repeat this _
procedure for each sample.
Turn over each sample and tape the cross direction edge of the tissue paper to
the
cardboard. One half of the adhesive tape should contact the tissue paper while
the other
half is adhering to the cardboard. Repeat this procedure for each of the
samples. If the
tissue sample breaks, tears, or becomes frayed at any time during the course
of this sample
preparation procedure, discard and make up a new sample with a new tissue
sample strip.
If working with multi-ply converted product, there will now be 3 samples on
the
cardboard. For single-ply finished product, there will now be 3 wire side out
samples on
cardboard and 3 non-wire side out samples on cardboard.
Felt Preparation
Obtain a 30" X 40" piece of Crescent #300 cardboard from Cordage Inc. (800 E.
Ross Road, Cincinnati, Ohio, 45217). Using a paper cutter, cut out six pieces
of cardboard
of dimensions of 2.25" X 7.25". Draw two lines parallel to the short dimension
and down
1.125" from the top and bottom most edges on the white side of the cardboard.
Carefully
score the length of the line with a razor blade using a straight edge as a
guide. Score it to a
depth about half way through the thickness of the sheet. This scoring allows
the
cardboard/felt combination to fit tightly around the weight of the Sutherland
Rub tester.
Draw an arrow running parallel to the long dimension of the cardboard on this
scored side
of the cardboard.
Cut the six pieces of black felt (F-55 or equivalent having a coefficient of
friction
between 0.5 and 0.58 against low density tissue paper. Suitable felt is
available from New
England Gasket of Bristol, CT) to the dimensions of 2.25" X 8.5" X 0.0625."
Place the felt
on top of the unscored, green side of the cardboard such that the long edges
of both the felt
and cardboard are parallel and in alignment. Make sure the fluffy side of the
felt is facing
up. Also allow about 0.5" to overhang the top and bottom most edges of the
cardboard.
.Snugly, fold over both overhanging felt edges onto the backside of the
cardboard with
ScotchT" brand tape. Prepare a total of six of these felt/cardboard
combinations.
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For best reproducibility, all samples should be run with the same lot of felt.
Obviously, there are occasions where a single lot of felt becomes completely
depleted. In
those cases where a new lot of felt must be obtained, a correction factor
should be
determined for the new lot of felt. To determine the correction factor, obtain
a
representative single tissue sample of interest, and enough felt to make up 24
cardboard/felt samples for the new and old lots.
As described below and before any rubbing has taken place, obtain Hunter color
L
readings for each of the 24 cardboard/felt samples of the new and old lots of
felt. Calculate
the averages for both the 24 cardboard/felt samples of the old lot and the 24
cardboard/felt
samples of the new lot.
Next, rub test the 24 cardboard/felt boards of the new lot and the 24
cardboard/felt
boards of the old lot as described below. Make sure the same tissue lot number
is used for
each of the 24 samples for the old and new lots. In addition, sampling of the
paper in the
preparation of the cardboard/tissue samples must be done so the new lot of
felt and the old
lot of felt are exposed to as representative as possible of a tissue sample.
For the case of 1-
ply tissue product, discard any product which might have been damaged or
abraded. Next,
obtain 48 strips of tissue each two usable units (also termed sheets) long.
Place the first
two usable unit strip on the far left of the lab bench and the last of the 48
samples on the
far right of the bench. Mark the sample to the far left with the number "1" in
a 1 cm by I
cm area of the corner of the sample. Continue to mark the samples
consecutively up to 48
such that the last sample to the far right is numbered 48.
Use the 24 odd numbered samples for the new felt and the 24 even numbered
samples for the old felt. Order the odd number samples from lowest to highest.
Order the
even numbered samples from lowest to highest. Now, mark the lowest number for
each set
with a letter "W." Mark the next highest number with the letter "N." Continue
marking the
samples in this alternating "W"/"N" pattern. Use the "W" samples for wire side
out lint-
analyses and the "N" samples for non-wire side lint analyses. For 1-ply
product, there are
now a total of 24 samples for the new lot of felt and the old lot of felt. Of
this 24, twelve
are for wire side out iint analvsis and 12 are for non-wire side lint
analysis.
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Rub and measure the Hunter Color L values for all 24 samples of the old felt
as
described below. Record the 12 wire side Hunter Color L values for the old
felt. Average
the 12 values. Record the 12 non-wire side Hunter Color L values for the old
felt. Average
the 12 values. Subtract the average initial un-rubbed Hunter Color L felt
reading from the
average Hunter Color L reading for the wire side rubbed samples. This is the
delta average
difference for the wire side samples. Subtract the average initial un-rubbed
Hunter Color L
felt reading from the average Hunter Color L reading for the non-wire side
rubbed
samples. This is the delta average difference for the non-wire side samples.
Calculate the
sum of the delta average difference for the wire side and the delta average
difference for
the non-wire side and divide this sum by 2. This is the uncorrected lint value
for the old
felt. If there is a current felt correction factor for the old felt, add it to
the uncorrected lint
value for the old felt. This value is the corrected Lint Value for the old
felt.
Rub and measure the Hunter Color L values for all 24 samples of the new felt
as
described below. Record the 12 wire side Hunter Color L values for the new
felt. Average
the 12 values. Record the 12 non-wire side Hunter Color L values for the new
felt.
Average the 12 values. Subtract the average initial un-rubbed Hunter Color L
felt reading
from the average Hunter Color L reading for the wire side rubbed samples. This
is the
delta average difference for the wire side samples. Subtract the average
initial un-rubbed
Hunter Color L felt reading from the average Hunter Color L reading for the
non-wire side
rubbed samples. This is the delta average difference for the non-wire side
samples.
Calculate the sum of the delta average difference for the wire side and the
delta average
difference for the non-wire side and divide this sum by 2. This is the
uncorrected lint value
for the new felt.
Take the difference between the corrected Lint Value from the old felt and the
uncorrected lint value for the new felt. This difference is the felt
correction factor for the
new lot of felt.
Adding this felt correction factor to the uncorrected lint value for the new
felt should
be identical to the corrected Lint Value for the old felt.
The same type procedure is applied to two-ply tissue product with 24 samples
run for
the old felt and 24 run for the new felt. But, only the consumer used outside
layers of the
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plies are rub tested. As noted above, make sure the samples are prepared such
that a
representative sample is obtained for the old and new felts.
Care of Four Pound Weights
The four pound weight has four square inches of effective contact area
providing a
contact pressure of one pound per square inch. Since the contact pressure can
be changed
by alteration of the rubber pads mounted on the face of the weight, it is
important to use
only the rubber pads supplied by the manufacturer (Brown Inc., Mechanical
Services
Department, Kalamazoo, MI). These pads must be replaced if they become hard,
abraded
or chipped off.
When not in use, the weight must be positioned such that the pads are not
supporting
the full weight of the weight. It is best to store the weight on its side.
Rub Tester Instrument Calibration
The Sutherland Rub Tester must first be calibrated prior to use. First, turn
on the
Sutherland Rub Tester by moving the tester switch to the "cont" position. When
the tester
arm is in its position closest to the user, turn the tester's switch to the
"auto" position. Set
the tester to run 5 strokes by moving the pointer arm on the large dial to the
"five" position
setting. One stroke is a single and complete forward and reverse motion of the
weight. The
end of the rubbing block should be in the position closest to the operator at
the beginning
and at the end of each test.
Prepare a tissue paper on cardboard sample as described above. In addition,
prepare a
felt on cardboard sample as described above. Both of these samples will be
used for
calibration of the instrument and will not be used in the acquisition of data
for the actual
samples.
Place this calibration tissue sample on the base plate of the tester by
slipping the
holes in the board over the hold-down pins. The hold-down pins prevent the
sample from
moving during the test. Clip the calibration felt/cardboard sample onto the
four pound
weight with the cardboard side contacting the pads of the weight. Make sure
the
cardboard/felt combination is resting flat against the weight. Hook this
weight onto the
tester arm and gently place the tissue sample underneath the weight/felt
combination. The
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end of the weight closest to the operator must be over the cardboard of the
tissue sample
and not the tissue sample itself. The felt must rest flat on the tissue sample
and must be in
100% contact with the tissue surface. Activate the tester by depressing the
"push" button.
Keep a count of the number of strokes and observe and make a mental note of
the
starting and stopping position of the felt covered weight in relationship to
the sample. If
the total number of strokes is five and if the end of the felt covered weight
closest to the
operator is over the cardboard of the tissue sample at the beginning and end
of this test, the
tester is calibrated and ready to use. If the total number of strokes is not
five or if the end
of the felt covered weight closest to the operator is over the actual paper
tissue sample
either at the beginning or end of the test, repeat this calibration procedure
until 5 strokes
are counted the end of the felt covered weight closest to the operator is
situated over the
cardboard at the both the start and end of the test.
During the actual testing of samples, monitor and observe the stroke count and
the
starting and stopping point of the felt covered weight. Recalibrate when
necessary.
Hunter Color Meter Calibration
Adjust the Hunter Color Difference Meter for the black and white standard
plates
according to the procedures outlined in the operation manual of the
instrument. Also run
the stability check for standardization as well as the daily color stability
check if this has
not been done during the past eight hours. In addition, the zero reflectance
must be
checked and readjusted if necessary.
Place the white standard plate on the sample stage under the instrument port.
Release
the sample stage and allow the sample plate to be raised beneath the sample
port.
Using the "L-Y", "a-X", and "b-Z" standardizing knobs, adjust the instrument
to read
the Standard White Plate Values of "L", "a", and "b" when the "L", "a", and
"b" push
buttons are depressed in turn.
Measurement of Samples
The first step in the measurement of lint is to measure the Hunter color
values of the
black felt/cardboard samples prior to being rubbed on the tissue. The first
step in this
measurement is to lower the standard white plate from under the instrument
port of the
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Hunter color instrument. Center a felt covered cardboard, with the arrow
pointing to the
back of the color meter, on top of the standard plate. Release the sample
stage, allowing
the felt covered cardboard to be raised under the sample port.
Since the felt width is only slightly larger than the viewing area diameter,
make sure
the felt completely covers the viewing area. After confirming complete
coverage, depress
the L push button and wait for the reading to stabilize. Read and record this
L value to the
nearest 0.1 unit.
If a D25D2A head is in use, lower the felt covered cardboard and plate, rotate
the felt
covered cardboard 90 degrees so the arrow points to the right side of the
meter. Next,
release the sample stage and check once more to make sure the viewing area is
completely
covered with felt. Depress the L push button. Read and record this value to
the nearest 0.1
unit. For the D25D2M unit, the recorded value is the Hunter Color L value. For
the
D25D2A head where a rotated sample reading is also recorded, the Hunter Color
L value
is the average of the two recorded values.
Measure the Hunter Color L values for all of the felt covered cardboards using
this
technique. If the Hunter Color L values are all within 0.3 units of one
another, take the
average to obtain the initial L reading. If the Hunter Color L values are not
within the 0.3
units, discard those felt/cardboard combinations outside the limit. Prepare
new samples
and repeat the Hunter Color L measurement until all samples are within 0.3
units of one
another.
For the measurement of the actual tissue paper/cardboard combinations, place
the
tissue sample/cardboard combination on the base plate of the tester by
slipping the holes in
the board over the hold-down pins. The hold-down pins prevent the sample from
moving
during the test. Clip the calibration felt/cardboard sample onto the four
pound weight with
the cardboard side contacting the pads of the weight. Make sure the
cardboard/felt
combination is resting flat against the weight. Hook this weight onto the
tester arm and
gently place the tissue sample underneath the weight/felt combination. The end
of the
weight closest to the operator must be over the cardboard of the tissue sample
and not the
tissue sample itself. The felt must rest flat on the tissue sample and must be
in 100%
contact with the tissue surface.
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Next, activate the tester by depressing the "push" button. At the end of the
five
strokes the tester will automatically stop. Note the stopping position of the
felt covered
weight in relation to the sample. If the end of the felt covered weight toward
the operator
is over cardboard, the tester is operating properly. If the end of the felt
covered weight
toward the operator is over sample, disregard this measurement and recalibrate
as directed
above in the Sutherland Rub Tester Calibration section.
Remove the weight with the felt covered cardboard. Inspect the tissue sample.
If
torn, discard the felt and tissue and start over. If the tissue sample is
intact, remove the felt
covered cardboard from the weight. Determine the Hunter Color L value on the
felt
covered cardboard as described above for the blank felts. Record the Hunter
Color L
readings for the felt after rubbing. Rub, measure, and record the Hunter Color
L values for
all remaining samples.
After all tissues have been measured, remove and discard all felt. Felts
strips are not
used again. Cardboards are used until they are bent, torn, limp, or no longer
have a smooth
surface.
Calculations
Determine the delta L values by subtracting the average initial L reading
found for
the unused felts from each of the measured values for the wire side and the
non-wire side
of the sample. Recall, multi-ply-ply product will only rub one side of the
paper. Thus,
three delta L values will be obtained for the multi-ply product. Average the
three delta L
values and subtract the felt factor from this final average. This final result
is termed the lint
for the 2-ply product.
For the single-ply product where both wire side and non-wire side measurements
are
obtained, subtract the average initial L reading found for the unused felts
from each of the
three wire side L readings and each of the three non-wire side L readings.
Calculate the
average delta for the three wire side values. Calculate the average delta for
the three non-
wire side values. Subtract the felt factor from each of these averages. The
final results are
termed a lint for the non-wire side and a lint for the wire side of the single-
ply product. By
CA 02331178 2004-03-02
36
taking the average of these two values, an ultimate lint is obtained for the
entire single-ply
product. .
E. Pulp Filtration Resistance (PFR)
The PFR is, like the Canadian Standard Freeness (CSF), a method for measuring
the
drainage rate of pulp slurries. It is believed that the PFR is a superior
method for
characterizing fibers with respect to their drainage characteristics. For
purposes of
estimation, the CSF may be related to the PFR by the following formula:
PFR=11270/CSF-10.77,
where the PFR is in units of seconds and the CSF is in seconds of milliliters.
Because this
relationship is subject to error it should be used for estimation purposes
only. A more
accurate method of measuring the PFR is as follows.
The PFR is measured by discharging three successive aliquots of a 0.1 %
consistency
slurry from a proportioner and filtering through a screen connected to the
proportioner
discharge. The time required to collect each aliquot is recorded and the
screen is not
removed or cleaned between filtrations.
The proportioner (obtained from Special Machinery Corporation, 546 Este
Avenue,
Cincinnati, OH 45232, Drawing #C-PP-318) is equipped with a PFR attachment
(also
obtained from Special Machinery Corporation, Drawing #4A-PP-103, part #8). The
PFR
attachment is loaded with a clean screen (a 1'/8 inch (2.9 cm) die cut circle
of the same
type of screen used for handsheeting, Appleton WireTM 84X76M, is used and it
is loaded
with the sheet side "up" in the tester).
A 0.10% consistency slurry of disintegrated pulp is prepared in the
proportioner at a
volume of 19 liters, with the PFR attachment in position. A 100 ml volumetric
flask is
positioned under the outiet of the PFR attachment. T'ne proportioner outlet
valve is opened
and a timer started, the valve is closed and timer stopped the instant 100 ml
is collected in
the volumetric flask (additional liquid will probably drain into the flask
after the valve is
closed). The time is recorded to the nearest 0.10 seconds. noted as "A".
The filtrate is discarded, the flask repositioned, and another 100 ml aliquot
is
collected by the same procedure without removing or cleaning the screen
between
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filtrations. This time interval is recorded as "B". Again, the filtrate is
discarded, the flask _
repositioned, and another 100 ml aliquot is collected by the same procedure
without
removing or cleaning the screen between filtrations. This time interval is
recorded as "C".
PFR is then calculated using the following equation:
PFR- j(E)x(B+C_(2x A))
1.5
where A, B, and C are the recorded time intervals, and E is a function of
temperature used
to correct the PFR to the value that would be observed at 75 F (24 C)
E=1+(0.013×(T-75))
where T is the slurry temperature measured to the nearest degree F in the
proportioner
after taking the last aliquot.
EXAMPLES
The following nonlimiting examples are provided to illustrate the preparation
of paper
products according to the present invention. The scope of the invention is to
be determined
by the claims which follow.
Example I
This example is intended to demonstrate preparation of low density tissue
having
temporary wet strength according to the prior art.
A commercial Fourdrinier papermaking machine is used in the practice of the
present invention.
An aqueous slurry of Northern Softwood Kraft (NSK) of about 3.5% consistency
is
made up using a conventional repulper. Sufficient sodium hydroxide is added
during
repulping to adjust the pH to about 6 and the slurry is passed through a stock
pipe toward
the headbox of the Fourdrinier.
The slurry is passed through a refiner which fibrillates the NSK causing the
pulp
filtration resistance to increase by about 2.5seconds.
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In order to impart dry strength to the finished product, a 1.5% dispersion of
_
RediBOND 5330 (a cationic starch available from National Starch and Chemical
Company, (Bridgewater, NJ) is prepared and is added to the NSK stock pipe at a
rate
sufficient to deliver 0.17% RediBOND 53300 based on the dry weight of the NSK
fibers.
The absorption of the dry strength resin is enhanced by passing the treated
slurry through
an in-line mixer.
In order to impart a temporary wet strength to the finished product, a 1.5%
dispersion
of Parez 750B is prepared and is added to the NSK stock pipe at a rate
sufficient to
deliver 0.42% Parez 750B('~ based on the dry weight of the NSK fibers. The
absorption of
the temporary wet strength resin is enhanced by passing the treated slurry
through an in-
line mixer.
An aqueous slurry of Eucalyptus Hardwood Kraft fibers of about 3.5%
consistency is
made up using a conventional repulper. Sufficient sodium hydroxide is added
during
repulping to adjust the pH to about 6 and the slurry is passed through a stock
pipe toward
the headbox of the Fourdrinier.
The NSK fibers are diluted with white water at the inlet of a fan pump to a
consistency of about 0.15% based on the total weight of the NSK fiber slurry.
The
eucalyptus fibers, likewise, are diluted with white water at the inlet of a
fan pump to a
consistency of about 0.15% based on the total weight of the eucalyptus fiber
slurry. The
eucalyptus slurry and the NSK slurry are both directed to a layered headbox
capable of
maintaining the slurries as separate streams until they are deposited onto a
forminD fabric
on the Fourdrinier.
The paper machine has a layered headbox having a top chamber, a center
chamber,
and a bottom chamber. The eucalyptus fiber slurry is pumped through the top
and bottom
headbox chambers and, simultaneously, the NSK fiber slurry is pumped through
the center
headbox chamber and delivered in superposed relation onto the Fourdrinier wire
to form
thereon a three-layer embryonic web, of which about 70% is made up of the
eucalyptus
fibers and 30% is made up of the NSK fibers. Dewatering occurs through the
Fourdrinier
wire and is assisted by a deflector and vacuum boxes. The Fourdrinier wire is
of a 5-shed,
satin weave configuration having 87 machine-direction and 76 cross-machine-
direction
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direction monofilaments per inch, respectively. The embryonic web is
transferred from the _
Fourdrinier wire, at a fiber consistency of about 22% at the point of
transfer, to a patterned
drying fabric.
The drying fabric is designed to yield a pattern-densified tissue and has a 5
shed satin
weave configuration having 44 machine-direction and 33 cross-machine-direction
direction monofilaments per inch. The filament crossovers are sanded to
provide a knuckle
area of about 38%.
The web is carried on the drying fabric past the vacuum dewatering box,
through the
blow-through predryers after which the web is transferred onto a Yankee dryer.
The fiber
consistency is about 27% after the vacuum dewatering box and, by the action of
the
predryers, about 65% prior to transfer onto the Yankee dryer; creping adhesive
comprising
a 0.25% aqueous solution of polyvinyl alcohol is spray-applied to the Yankee
dryer
surface; the fiber consistency is increased to an estimated 98% before dry
creping the web
with a doctor blade. The doctor blade has a bevel angle of 26 degrees and is
positioned
with respect to the Yankee dryer to provide an impact angle of about 81
degrees; the
Yankee dryer is operated at about 340 F (171 C); the Yankee dryer is operated
at about
3800 feet per minute (180 meters per minute). The web is then passed between
two
calender rolls and wound on a reel.
The resulting paper was evaluated according to the methods described herein
with
the results being provided in Table 1.
Table 1
Test Parameter Result
Density 0.26 grams/cm'
Basis Weight 11 grams/m'
Total Dry Strength 411 grams/inch (162 grams/cm)
Total Initial Wet Strength 44 grams/inch (17 grams/cm)
Total Thirty Minute Wet 15.2 grams/inch (6 grams/cm)
Strength 13.0 grams/cm%
Total Dry Tensile Modulus 21 grams
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Wet Burst 7
Lint Resistance
The ratio of initial wet strength to dry strength for the paper made according
to Example 1
is 0.11:1 and the ratio of thirty minute wet strength to initial wet strength
for the paper
made according to Example 1 is 0.35:1
Example 2
This example is intended to demonstrate preparation of low density tissue
having
temporary wet strength according to one aspect of the present invention.
A commercial Fourdrinier papermaking machine is used in the practice of the
present invention.
An aqueous slurry of Northern Softwood Kraft (NSK) of about 3.5% consistency
is
made up using a conventional repulper Sufficient sodium hydroxide is added
during
repulping to adjust the pH to about 6 and the slurry is passed through a stock
pipe toward
the headbox of the Fourdrinier.
Sulfuric acid at a concentration of 1% is added to the NSK stock pipe in a
controlled
manner so as to control the pH of the slurry to about 5.1 0.2.
In order to impart a temporary wet strength to the finished product, a 1.5%
dispersion
of Parez 750B is prepared and is added to the NSK stock pipe at a rate
sufficient to
deliver 1.4% Parez 750B based on the dry weight of the NSK fibers. The
absorption of
the temporary wet strength resin is enhanced by passing the treated slurry
through an in-
line mixer.
Additional sulfuric acid at a concentration of 1% is added to the treated NSK
slurry
in order to control the headbox pH to 5.1 0.2
An aqueous slurry of Eucalyptus Hardwood Kraft fibers of about 3.5%
consistency is
made up using a conventional repulper Sufficient sodium hydroxide is added
during
repulping to adjust the pH to about 5.7 and the slurry is passed through a
stock pipe toward
the headbox of the Fourdrinier.
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41
Sulfuric acid at a concentration of 1% is added to the Eucalyptus stock pipe
in a
controlled manner so as to control the pH of the Eucalyptus slurry to 5.1 0.2
In order to impart a temporary wet strength to the finished product, a 1.5%
dispersion
of Parez 750B is prepared and is added to the Eucalyptus stock pipe at a rate
sufficient to
deliver 0.12% Parez 750 based on the dry weight of the Eucalyptus fibers. The
absorption of the temporary wet strength resin is enhanced by passing the
treated slurry
through an in-line mixer.
Additional sulfuric acid at a concentration of 1% is added to the treated
Eucalyptus
slurry in order to control the headbox pH to 5.1 0.2
The NSK fibers are diluted with white water at the inlet of a fan pump to a
consistency of about 0.15% based on the total weight of the NSK fiber slurry
forming a
portion of the headbox furnish. The eucalyptus fibers, likewise, are diluted
with white
water at the inlet of a fan pump to a consistency of about 0.15% based on the
total weight
of the eucalyptus fiber slurry forming a second portion of the headbox
furnish. The
eucalyptus slurry and the NSK slurry are both directed to a layered headbox
capable of
maintaining the slurries as separate streams until they are deposited onto a
forming fabric
on the Fourdrinier.
The paper machine has a layered headbox having a top chamber, a center
chamber,
and a bottom chamber. The eucalyptus fiber slurry is pumped through the top
and bottom
headbox chambers and, simultaneously, the NSK fiber slurry is pumped through
the center
headbox chamber and delivered in superposed relation onto the Fourdrinier wire
to form
thereon a three-layer embryonic web, of which about 78% is made up of the
eucalyptus
fibers and 22% is made up of the NSK fibers. Dewatering occurs through the
Fourdrinier
wire and is assisted by a deflector and vacuum boxes. The Fourdrinier wire is
of a 5-shed,
satin weave configuration having 87 machine-direction and 76 cross-machine-
direction
direction monofilaments per inch, respectively. The embryonic web is
transferred from the
Fourdrinier wire, at a fiber consistency of about 22% at the point of
transfer, to a patterned
drying fabric.
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42
The drying fabric is designed to yield a pattern-densified tissue with
discontinuous
low-density deflected areas arranged within a continuous network of high
density
(knuckle) areas. This drying fabric is formed by casting an impervious resin
surface onto a
fiber mesh supporting fabric. The supporting fabric is a 48 x 52 filament,
dual layer mesh.
The thickness of the resin cast above the surface of the secondary is about
5.5 mils. The
knuckle area is about 36% and the open cells are present at a frequency of
about 575 per
square inch.
The web is carried on the drying fabric past the vacuum dewatering box,
through the
blow-through predryers after which the web is transferred onto a Yankee dryer.
The fiber
consistency is about 27% after the vacuum dewatering box and, by the action of
the
predryers, about 65% prior to transfer onto the Yankee dryer; creping adhesive
comprising
a 0.25% aqueous solution of polyvinyl alcohol is spray-applied to the Yankee
dryer
surface by applicators; the fiber consistency is increased to an estimated 98%
before dry
creping the web with a doctor blade. The doctor blade has a bevel angle of 26
degrees and
is positioned with respect to the Yankee dryer to provide an impact angle of
about 81
degrees; the Yankee dryer is operated at about 340 F (171 C); the Yankee
dryer is
operated at about 3400 feet per minute (161 meters per minute). The web is
then passed
between two calender rolls and wound on a reel.
The resulting paper was evaluated according to the methods described herein
with
the results being provided in Table 2.
Table 2
Test Parameter Result
Density 0.21 grams/cm3
Basis Weight 13.5 grams/m'
Total Dry Strength 380 grams/inch (150 grams/cm)
Total Initial Wet Strength 85 grams/inch (33 grams/cm)
Total Thirty Minute Wet 32 grams/inch (13 grams/cm)
Strength 7.9 grams/cm%
Total Dry Tensile Modulus 46 grams
Wet Burst 7
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Lint Resistance
The ratio of initial wet strength to dry strength for the paper made according
to Example 2
is 0.22:1 and the ratio of thirty minute wet strength to initial wet strength
for the paper
made according to Example 2 is 0.38:1.
Example 3
This example is intended to demonstrate preparation of low density tissue
having
temporary wet strength according to a second aspect of the present invention.
A commercial Fourdrinier papermaking machine is used in the practice of the
present invention.
An aqueous slurry of Northern Softwood Kraft (NSK) of about 3.5% consistency
is
made up using a conventional repulper. Sufficient sodium hydroxide is added
during
repulping to adjust the pH to about 6 and the slurry is passed through a stock
pipe toward
the headbox of the Fourdrinier.
Sulfuric acid at a concentration of 1% is added to the NSK stock pipe in a
controlled
manner so as to control the pH of the slurry to 5.1 0.2
In order to impart a temporary wet strength to the finished product, a 1.5%
dispersion
of Parez EXPN 3683 is prepared and is added to the NSK stock pipe at a rate
sufficient to
deliver 0.91% Parez EXPN 3683 based on the dry weight of the NSK fibers. The
absorption of the temporary wet strength resin is enhanced by passing the
treated slurry
through an in-line mixer.
Additional sulfuric acid at a concentration of 1% is added to the treated NSK
slurry
to control the pH to 5.1 0.2.
An aqueous slurry of Eucalyptus Hardwood Kraft fibers of about 3.5%
consistency is
made up using a conventional repulper Sufficient sodium hydroxide is added
during
repulping to adjust the pH to about 6 and the slurry is passed through a stock
pipe toward
the headbox of the Fourdrinier.
Sulfuric acid at a concentration of 1% is added to the Eucalyptus stock pipe
in a
controlled manner so as to control the pH of the Eucalyptus slurry to5.1 0.2.
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In order to impart a temporary wet strength to the finished product, a 1.5%
dispersion _
of Parez EXPN 3683 is prepared and is added to the Eucalyptus stock pipe at a
rate
sufficient to deliver 0.12% Parez EXPN 3683 based on the dry weight of the
Eucalyptus
fibers. The absorption of the temporary wet strength resin is enhanced by
passing the
treated slurry through an in-line mixer.
Additional sulfuric acid at a concentration of 1% is added to the treated
Eucalyptus
slurry in order to control the headbox pH to 5.1 0.2
The NSK fibers are diluted with white water at the inlet of a fan pump to a
consistency of about 0.15% based on the total weight of the NSK fiber slurry
forming a
portion of the headbox furnish. The eucalyptus fibers, likewise, are diluted
with white
water at the inlet of a fan pump to a consistency of about 0.15% based on the
total weight
of the eucalyptus fiber slurry forming a second portion of the headbox
furnish. The
eucalyptus slurry and the NSK slurry are both directed to a layered headbox
capable of
maintaining the slurries as separate streams until they are deposited onto a
forming fabric
on the Fourdrinier.
The paper machine has a layered headbox having a top chamber, a center
chamber,
and a bottom chamber. The eucalyptus fiber slurry is pumped through the top
and bottom
headbox chambers and, simultaneously, the NSK fiber slurry is pumped through
the center
headbox chamber and delivered in superposed relation onto the Fourdrinier wire
to form
thereon a three-layer embryonic web, of which about 78% is made up of the
eucalyptus
fibers and 22% is made up of the NSK fibers. Dewatering occurs through the
Fourdrinier
wire and is assisted by a deflector and vacuum boxes. The Fourdrinier wire is
of a 5-shed,
satin weave configuration having 87 machine-direction and 76 cross-machine-
direction
direction monofilaments per inch, respectively. The embryonic web is
transferred from the
Fourdrinier wire, at a fiber consistency of about 22% at the point of
transfer, to a pattemed
drying fabric.
The drying fabric is designed to yield a pattern-densified tissue with
discontinuous
low-density deflected areas arranged within a continuous network of high
density
(knuckle) areas. This drying fabric is formed by casting an impervious resin
surface onto a
fiber mesh supporting fabric. The supporting fabric is a 48 x 52 filament,
dual layer mesh.
CA 02331178 2000-11-02
WO 99/63158 PCTIUS98/10966
The thickness of the resin cast above the surface of the secondary is about
5.5 mils. The
knuckle area is about 36% and the open cells are present at a frequency of
about 562 per
square inch.
The web is carried on the drying fabric past the vacuum dewatering box,
through the
blow-through predryers after which the web is transferred onto a Yankee dryer.
The fiber
consistency is about 27% after the vacuum dewatering box and, by the action of
the
predryers, about 65% prior to transfer onto the Yankee dryer; creping adhesive
comprising
a 0.25% aqueous solution of polyvinyl alcohol is spray-applied to the Yankee
dryer
surface by applicators; the fiber consistency is increased to an estimated 98%
before dry
creping the web with a doctor blade. The doctor blade has a bevel angle of 26
degrees and
is positioned with respect to the Yankee dryer to provide an impact angle of
about 81
degrees; the Yankee dryer is operated at about 340 F (171 C); the Yankee
dryer is
operated at about 3400 feet per minute (161 meters per minute). The web is
then passed
between two calender rolls and wound on a reel.
The resulting paper was evaluated according to the methods described herein
with
the results being provided in Table 3.
Table 3
Test Parameter Result
Density 0.20 grams/cm'
Basis Weight 13.5 grams/m'-
TotaI Dry Strength 407 grams/inch (160 grams/cm)
Total Initial Wet Strength 89 grams/inch (35 grams/cm)
Total Thirty Minute Wet 29 grams/inch (11 grams/cm)
Strength 7.7 grams/cm%
Total Dry Tensile Modulus 46 grams
Wet Burst 7
Lint Resistance
The ratio of initial wet strength to dry strength for the paper made according
to Example 3
is 0.22:1 and the ratio of thirty minute wet strength to initial wet strength
for the paper
made according to Example 3 is 0.33:1
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46
Examvle 4
This example is intended to demonstrate that low density tissue prepared
accortling
to the present invention has softness that is comparable to low density tissue
prepared
according to the prior art.
Tissue prepared according to Examples 2 and 3 were evaluated for panel
softness
according to the method described in the TEST METHODS section. Tissue prepared
according to Example 1 is used as the control tissue. The results of this
evaluation are
given in Table 4
Table 4
Sample Softness
(PSU)
Tissue According to Example 2 -0.09
Tissue According to Example 3 +0.02
As can be seen, tissue prepared according to the present invention has
softness that is
comparable to tissue prepared according to the prior art.
While particular embodiments of the present invention have been illustrated
and
described, it would be obvious to those skilled in the art that various other
changes and
modifications can be made without departing from the spirit and scope of the
invention. It
is therefore intended to cover in the appended claims all such changes and
modifications
that are within the scope of this invention.
