Note: Descriptions are shown in the official language in which they were submitted.
CA 02310692 2000-05-18
WO 99/34057 PCT/US98/26834
PAPER PRODUCTS AND METHODS FOR APPLYING
CHEMICAL ADDITIVES TO CELLULOSIC FIBERS
Backaround of the Invention
The present invention relates generally to paper products. More particularly,
the
invention concems methods for applying chemical additives to cellulosic fibers
and the
paper products that can be obtained by the methods.
In the manufacture of paper products, it is often desirable to enhance
physical
and/or optical properties by the addition of chemical additives. Examples of
properties
that are developed or enhanced through the addition of chemical additives
include but
are not limited to dry strength, wet strength, softness, absorbency, opacity,
brightness
and color. During the papermaking process, chemical additives are commonly
added to
fiber slurries in the wet end, before the fibers are formed into a web,
dewatered and
dried. Traditionally, wet end additives are added to a fiber slurry that is
between 0.5 and
5 percent consistency. The slurry may then be further diluted in the
papermaking process
before a final dilution at the fan pump to the ultimate forming consistency.
Wet end chemical addition has several advantages over topical spray, printing
or
size press chemical addition methods. For instance, wet end chemical addition
provides
a uniform distribution of chemical additives on the fiber surfaces.
Additionally, wet end
chemical addition allows a selected fiber fraction to be treated with a
specific chemical
additive in order to enhance the performance of the paper and/or the
effectiveness of the
chemical additive. Further, wet end chemical addition enables multiple
chemistries to be
added to a fiber slurry, either simultaneously or sequentially, prior to
formation of the
paper web.
One difficulty associated with wet end chemical addition is that the water
soluble
or water dispersible chemical additives are suspended in water and are not
completely
adsorbed onto the cellulosic fibers. To improve adsorption of wet end
additives, chemical
additives are often modified with functional groups to impart an electrical
charge when in
water. The electrokinetic attraction between charged additives and the
anionically
charged fiber surfaces aids in the deposition and retention of chemical
additives onto the
fibers. Nevertheless, the amount of chemical additive that can be retained in
the wet end
generally follows an adsorption curve exhibiting diminishing effectiveness,
similar to that
described by Langmuir. As a result, the adsorption of water soluble or water
dispersible
chemical additives may be significantly less than 100 percent, particularty
when trying to
achieve high chemical additive loading levels.
--1--
CA 02310692 2000-05-18
WO 99/34057 PCT/US98/26834
Consequently, at any chemical addition level, and particularly at high
addition
levels, only a fraction of the chemical additive is retained on the fiber
surface. The
remaining fraction of the chemical additive remains dissolved or dispersed in
the
suspending water phase. These unadsorbed chemical additives can cause a number
of
problems in the papermaking process. The exact nature of the chemical additive
will
determine the specific problems that may arise, but a partial list of problems
that may
result from unadsorbed chemical additives includes: foam, deposits,
contamination of
other fiber streams, poor fiber retention on the machine, compromised chemical
layer
purity in multilayer products, dissolved solids build-up in the water system,
interactions
with other process chemicals, felt or fabric plugging, excessive adhesion or
release on
dryer surfaces, physical property variability in the finished product, and the
like.
Therefore, what is lacking and needed in the art is a method for applying
adsorbable chemical additives onto cellulosic fiber surfaces in the wet end of
the
papermaking process such that the amount of unadsorbed chemical additives in
the
process water is reduced or eliminated. The method minimizes the associated
manufacturing and finished product quality problems that would othennrise
occur.
Summary of the invention
It has now been discovered that chemical additives can be adsorbed onto
cellulosic papermaking fibers at high levels with a minimal amount of
unadsorbed
chemical additives present In the papermaking process water. This is
accomplished by
treating a fiber slurry with an excess of the chemical additive, allowing
sufficient
residence time for adsorption to occur, filtering the slurry to remove
unadsorbed chemical
additives, and redispersing the filtered pulp with fresh water. Because the
filtrate from the
thickening process contains unadsorbed chemical additive, it is not sent
forward in the
process with the chemically treated fibers. Rather, the filtrate may be sent
to the sewer or
reused in a processing step prior to the filtration step.
Hence in one aspect, the invention resides in a method for applying chemical
additives to cellulosic fibers. The method comprises the steps of: creating a
fiber slurry
comprising water, cellulosic fibers, and an adsorbable chemical additive;
dewatering the
fiber slurry to remove unadsorbed chemical additive; and redispersing the
fibers with
fresh water. This method for processing cellulosic papermaking fibers enables
chemical
additives to be adsorbed by fibers while at the same tirne maintaining
significantly lower
levels of unadsorbed chemical additive in the water phase compared to
traditional wet
end chemical addition. Thus, higher concentrations of the chemical additive on
the fiber
--2 --
CA 02310692 2000-05-18
WO 99/34057 PCT/US98/26834
relative to the process water can be achieved as compared to what has been
possible
with prior methods.
For purposes of the present invention, the term "celluiosic" refers to
papermaking
fibers comprising an amorphous carbohydrate polymer, in contrast to synthetic
fibers.
The term "adsorbable" is used herein to refer to a chemical additive that can
be
assimilated by the surface of a cellulosic fiber, in the absence of any
chemical reaction
invoiving the chemical additive and the cellulosic fiber. The term
"unadsorbed" refers to
any portion of the chemical additive that is not adsorbed by the fiber and
thus remains
suspended in the process water. The term "fresh water" is used herein to refer
to water
that is substantially free of the unadsorbed chemical additive. Most
desirably, the fresh
water is completely free of the chemical additive.
The fiber slurry is desirably dewatered to increase the consistency of the
fiber
slurry to about 20 percent or greater, and particuiarly to about 30 percent or
greater, in
order to remove the majority of the water containing the unadsorbed chemical
additive.
The fibers are thereafter redispersed, desirably to decrease the consistency
of the fiber
slurry to a level suitable for papermaking, to about 20 percent or less, and
more
particularly to about 5 percent or less, such as about 3 to about 5 percent.
The present method allows for the production of fiber fumishes that are useful
for
making paper products, and particuiarly layered paper products. Thus, another
aspect of
the invention resides in a fiber fumish that has a higher chemical additive
loading than
could othennrise be achieved in combination with the reiativeiy low level of
unadsorbed
chemical additive in the water. This is because chemical additive loading via
traditional
wet end addition is often limited by the level of unadsorbed chemical and its
associated
processing difficulties such as foam, deposits, chemical interactions, felt
plugging,
excessive dryer adhesion or release or a variety of paper physical property
control issues
caused by the presence of unadsorbed chemical in the water.
In one embodiment, a fiber fumish of the present invention comprises water,
cellulosic fibers, and an adsorbable chemical additive. The amount of chemical
additive
adsorbed onto the fibers is about 2 kilograms per metric ton or greater, and
the amount
of unadsorbed chemical additive in the water is between 0 and about 20 percent
of the
amount of chemical additive adsorbed onto the fibers. In par6cuiariy desirable
embodiments, the amount of adsorbed chemical additive is about 3 kg/metric ton
or
greater, particularly about 4 kg/metric ton or greater, and more particularly
about 5
kg/metric ton or greater. Moreover, the amount of unadsorbed chemical additive
in the
water is between 0 and about 15 percent, particuiarly between 0 and about 10
percent,
-3-
CA 02310692 2000-05-18
WO 99/34057 PCT/US98/26834
and more particularly between 0 and about 7 percent, of the amount of adsorbed
chemical additive.
Another aspect of the invention resides in a method for making chemically
treated
paper products. The method comprises the steps of: creating a first fiber
slurry
comprising water, cellulosic fibers, and an adsorbable chemical additive;
creating a
second fiber slurry that is substantially free of the adsorbable chemical
additive;
dewatering the first fiber slurry to remove unadsorbed chemical additive;
redispersing the
fibers in the first fiber slurry with fresh water, and forming a paper product
using a layered
headbox, the first fiber slurry supplied to a first headbox layer and the
second fiber slurry
supplied to a second headbox layer.
In another embodiment, a method for making a paper product comprises the steps
of: creating a fiber slurry comprising water, cellulosic fibers and a first
adsorbable
chemical additive; dewatering the fiber slurry to a consistency of about 20
percent or
greater; passing the dewatered fiber slurry through a disperser to
mechanically work the
fibers; diluting the fiber slurry with fresh water that is substantially free
of the first
chemical additive to a consistency of about 5 percent or less; adding a second
adsorbable chemical additive comprising a debonding agent or a softening agent
to the
fiber slurry; dewatering the fiber slurry to a consistency of about 20 percent
or greater,
diluting the fiber slurry with fresh water that is substantially free of the
second chemical
additive to a consistency of about 5 percent or less; and forming a paper
product from
the fiber slurry. The first chemical additive may comprise, for example, a
bonding agent
to decrease the amount of lint from the product.
The present invention is particutarly useful for adding chemical additives
such as
softening agents and debonding agents to the outer layer fumishes in a three
layer paper
product. In particular tissue products, for example, the center layer is
adapted to provide
strength development and control. The present invention allows the softening
agents and
debonding agents to be applied to the outer layers while minimizing
contamination of the
center strength layer.
Hence, another aspect of the invention resides in paper products formed from
fibers that have been chemically treated to minimize the amount of residual,
unadsorbed
chemical additives in the process water. These paper products exhibit high
chemical
"purity on the fiber fraction that has been treated using the present method
and offer the
ability to achieve excellent chemical layer purity when using a stratified
headbox and/or
the ability to achieve fiber specific chemical treatment in papers made from
blends of two
or more fiber types. The term "paper" is used herein to broadly include
writing, printing,
_4 _
CA 02310692 2006-12-08
wrapping, sanitary, and industrial papers, newsprint, linerboard, tissue,
napkins, wipers,
towels, or the like.
The chemical additives that can be used in conjunction with the present
invention
include: dry strength aids, wet strength aids, softening agents, debonding
agents,
absorbency aids, sizing agents, dyes, optical brighteners, chemical tracers,
opacifiers,
dryer adhesive chemicals, and the like. Additional forms of chemical additives
may
include: pigments, emollients, humectants, viricides, bactericides, buffers,
waxes,
fluoropolymers, odor control materials and deodorants, zeolites, perfumes,
debonders,
vegetable and mineral oils, humectants, sizing agents, superabsorbents,
surfactants,
moisturizers, UV blockers, antlbiotic agents, lotions, fungicides,
preservatives, aloe-vera
extract, vitamin E, or the like. Suitable chemical additives are adsorbable by
the cellulosic
papermaking fibers and are water soluble or water dispersible.
The term "softening agent" refers to any chemical additive that can be
incorporated into paper products such as tissue to provide improved tactile
feel. These
chemicals can also act as debonding agents or can act solely to improve the
surface
characteristics of tissue, such as by reducing the coefficient of friction
between the tissue
surface and the hand.
The term 'debonding agent' refers to any chemical that can be incorporated
into
paper products such as tissue to prevent or disrupt inteffiber or intrafiber
hydrogen
bonding. Depending on the nature of the chemical, debonding agents may also
act as
softening agents. In contrast, the term "bonding agent' refers to any chemical
that can be
incorporated into tissue to increase or enhance the level of interfiber or
intrafiber bonding
in the sheet. The increased bonding can be either ionic, Hydrogen or covalent
in nature.
The term "water soluble" refers to solids or liquids that will form a solution
in
water, and the term "water dispersible" refers to solids or liquids of
colloidal size or larger
that can be dispersed into an aqueous medium.
The method for applying chemical additives to papermaking fibers may be used
in
a wide variety of papermaking operations, including wet pressing and creped or
uncreped
throughdrying operations. By way of illustration, various tissue making
processes are
disclosed in U.S. Patent 5,667,636 issued September 16, 1997 to S. A. Engel et
al.; and
U.S. Patent 5,607,551 issued March 4, 1997 to T. E. Farrington, Jr. et al.
The method may also be used in altemative processes, including: chemically pre-
treating pulp in a pulp mill before a dry lap machine or crumb baler, adding
chemical
additives in sequence to reduce interactions; removing chemical additives from
a fiber
-5-
CA 02310692 2000-05-18
WO 99/34057 PCT/US98/26834
slurry (neutralizing anionic components, sizing or softening formulations)
after a chemical
additive has been added to facilitate the removal process; or the like.
Many fiber types may be used for the present invention inciuding hardwood or
softwoods, straw, flax, milkweed seed floss fibers, abaca, hemp, kenaf,
bagasse, cotton,
reed, and the like. All known papermaking fibers may be used, including
bleached and
unbleached fibers, fibers of natural origin (including wood fiber and other
cellulosic fibers,
cellulose derivatives, and chemically stiffened or crosslinked fibers), some
component
portion of synthetic fibers (synthetic papermaking fibers include certain
forms of fibers
made from polypropylene, acrylic, aramids, acetates, and the like), virgin and
recovered
or recycled fibers, hardwood and softwood, and fibers that have been
mechanically
pulped (e.g., groundwood), chemically pulped (including but not limited to the
kraft and
sulfite pulping processes), thermomechanically pulped, chemithermomechanically
pulped, and the like. Mixtures of any subset of the above mentioned or related
fiber
classes may be used. The fibers can be prepared in a multiplicity of ways
known to be
advantageous in the art. Useful methods of preparing fibers include dispersion
to impart
curl and improved drying properties, such as disclosed in U.S. Patents
5,348,620 issued
September 20, 1994 and 5,501,768 issued March 26, 1996, both to M. A. Hermans
et al.
and U.S. Patent 5,656,132 issued August 12, 1997 to Farrington, Jr. et al.
A single headbox or a plurality of headboxes may be used. The headbox or
headboxes may be stratitied to permit production of a multilayered structure
from a single
headbox jet in the formation of a web. In particular embodiments, the web is
produced
with a stratified or layered headbox to preferentially deposit shorter fibers
on one side of
the web for improved softness, with relatively longer fibers on the other side
of the web or
in an interior layer of a web having three or more layers. The web is
desirably formed on
an endless loop of foraminous forming fabric which permits drainage of the
liquid and
partial dewatering of the web. Muitiple embryonic webs from multipie headboxes
may be
couched or mechanically or chemically joined in the moist state to create a
single web
having multiple layers.
Numerous features and advantages of the present invention will appear from the
following description. In the description, reference is made to the
accompanying drawings
which illustrate preferred embodiments of the invention. Such embodiments do
not
represent the full scope of the invention. Reference should therefore be made
to the
claims herein for interpreting the full scope of the invention.
_6 _
CA 02310692 2000-05-18
WO 99/34057 PCT/US98/26834
Brief Descrigtion of the Drawinas
Figure 1 depicts a schematic process flow diagram of a method according to the
present invention for treating papermaking fibers with chemical additives.
Figure 2 depicts a schematic process flow diagram of a method according to the
present invention for both treating papermaking fibers with chemical additives
and
mechanically treating the fibers using a dispemer.
Figure 3 depicts a schematic process flow diagram for a method of making an
uncreped tissue sheet.
Detailed Description of the Dnawings
The invention will now be described in greater detail wfth reference to the
Figures.
For simplicity, the various tensioning rolls schematically used to define the
several fabric
runs are shown but not numbered, and similar elements in different Figures
have been
given the same reference numeral. A variety of conventional papermaking
apparatuses
and operations can be used with respect to the stock preparation, headbox,
forming
fabrics, web transfers, creping and drying. Nevertheless, particular
conventional
components are illustrated for purposes of providing the context in which the
various
embodiments of the invention can be used.
Figure 1 depicts stock preparation equipment used to apply chemical additives
to
papermaking fibers according to one embodiment of the present invention. The
stock
preparation equipment comprises a first stock chest 10, a second stock chest
12, and a
dewatering device 14 operably disposed between the stock chests. Papermaking
fibers
and water are added to the first stock chest 10 to form a fiber slurry 20. The
fiber slurry in
the first stock chest desirably has a consistency of about 20 percent or
lower, and
particularly about 5 percent or lower, such as about 3 to about 5 percent. The
fiber slurry
in the first stock chest is desirably under agitation using a mixing blade,
rotor,
n3cinculation pump, or other suitable device 18 for mixing the fiber slurry.
One or more chemical additives 24 are supplied from a reservoir 26 and added
to
the fiber slurry 20 in the first stock chest 10. The amount of chemical
additive 24 is
suitably about 5 to about 20 kg./metric ton. In particular embodiments, the
chemical
additive comprises an imidazoline-based debonding agent and is added in an
amount
from about 7.5 to about 15 kg./metric ton. The fiber slurry and chemical
additive are
desirably allowed to remain together in the first stock chest under agitation
for a
residence time sufficient to allow the papermaking fibers to adsorb a
substantial portion
-- 7 --
CA 02310692 2000-05-18
WO 99/34057 PCT/US98/26834
of the chemical additive 24. A residence time of about 15 to about 30 minutes,
for
instance, may be sufficient.
The fiber slurry 20 is thereafter transferred through suitable conduits 27 and
a
pump 28 to the dewatering device 14: In the illustrated embodiment, the
dewatering
device comprises a belt press 14, although aitemative dewatering devices such
as a
centrifuge, a nip thickening device or the like may be used. The fiber slurry
is injected
between a pair of foraminous fabrics 30 such that press filtrate 32 is removed
from the
slurry. The press filtrate 32 comprises a portion of the process water along
vrith
unadsorbed chemical additives 24 in the water. The belt press 14 or other
dewatering
device suitably increases the fiber consistency of the slurry to about 20
percent or
greater, and particuiarly about 30 percent or greater. The unadsorbed chemical
additive
can be removed from the process or used as dilution water in prior stock
preparation
steps, but importantiy it is not sent forward with the chemically treated
fumish.
The thickened fiber slurry 20 is then transported through conduits 34 to the
second stock chest 12. The fiber slurry is then re-diluted with fresh water 35
from a
suitable reservoir 36 and optionally agitated using a mixing device 18. The
fiber
consistency of the slurry is suitably decreased to about 20 percent or less,
and
particularly about 5 percent or less, such as about 3 to about 5 percent. The
fiber slurry
may then be removed from the second stock chest through suitable conduits 37
and a
pump 38 for subsequent processing 39. Altemativeiy, the fiber slurry may be
processed
through the foregoing procedure again in an effort to further increase the
chemical
additive retention level.
Figure 2 depicts an aitemative embodiment of the present invention in which
stock preparation equipment is used to apply chemical additives to papermaking
fibers
and to mechanically treat the fibers. In general, the equipment comprises
three stock
chests 10, 12 and 40, two dewatering devices 14 and 42, two diiution water
chests 44
and 46, and a disperser 48 for mechanically treating the papermaking fibers.
Papermaking fibers and water are added to the first stock chest 10 to form a
fiber
slurry 20. The fiber slurry in the first stock chest desirably has a
consistency of about
20 percent or lower, and particuiarly about 5 percent or lower. One or more
chemical
additives 24 are supplied from a reservoir 26 and added to the fiber slurry 20
in the first
stock chest 10 while under agitation 18. The first chemical additive added to
the fiber
slurry is desirably a cationic bonding agent which is used to control lint in
the finished
product. The first chemical additive is desirably not a softening agent or
debonding agent
that would reduce the efficiency of the disperser.
_8_
CA 02310692 2006-12-08
After a sufficient residence time, the fiber slurry is transferred through
suitable
conduits 27 and a pump 28 to a belt press 14 or other suitable dewatering
device.
Unadsorbed chemical additives in the water are removed with the press filtrate
32 during
the pressing operation and stored in the first dilution water chest 44. The
contents of the
first dilution water chest may be used as either pulper make-up water or
dilution water or
may be discarded. The dewatering device 14 suitably increases the fiber
consistency of
the slurry to about 20 percent or greater, and particulariy about 30 percent
or greater.
The thickened fiber slurry 20 is then transported through suitable conduits 34
to
the disperser 48 for mechanical treatment of the fibers. Dispersers suitable
for use in the
present method are disclosed in U.S. Patents 5,348,620 issued September 20,
1994 and
5,501,768 issued March 26, 1996, both to M. A. Hermans et al.
After dispersing, the fiber slurry is transported via conduits 50 to the
second stock
chest 12. A second chemical additive or second group of chemical additives 52
are
supplied from a reservoir 53 and added to the fiber slurry 20 in the second
stock chest 12
while under agitation 18. Additionally, the fiber slurry may optionally be
diluted with filtrate
56 from a source described hereinafter. The fiber consistency of the slurry is
suitably
decreased to about 20 percent or lower, and particularly about 5 percent or
lower, such
as about 3 to about 5 percent. In particular embodiments, the second chemical
additive
52 comprises a softening agent and/or a debonding agent, and the fiber slurry
is not
subjected to high shear refining forces such as those generated in a disperser
once the
softening andJor debonding agent is added to the fiber slurry.
After a sufficient residence time to permit adsorption of the second chemical
additive, the fiber slurry 20 is transferred from the second stock chest 12
through suitable
conduits 58 and a pump 59 to the second dewatering device 42. Unadsorbed
portions of
the second chemical additive 52 in the water are removed with the press
filtrate 56 during
the pressing operation and stored in the second dilution water chest 46. The
contents of
the second dilution water chest may be added to the second stock chest 12 as
described
above or may be discarded. The second dewatering device 42 suitably increases
the
fiber consistency of the slurry to about 20 percent or greater, and
particularly about 30
percent or greater.
The thickened fiber slurry 20 is then transported through conduits 58 to the
third
stock chest 40. The fiber slurry is then re-diluted with fresh water 35 from a
suitable
reservoir 36 and optionally agitated using a mixing device 18. The fiber
consistency of
the slurry is suitably decreased to about 20 percent or lower, and
particulariy about 5
-9--
CA 02310692 2006-12-08
percent or lower, such as about 3 to about 5 percent. The fiber slurry may
then be
removed from the third stock chest through suitable conduits 37 and a pump 38
for
subsequent processing 39. Altematively, the fiber siuny may be retumed to the
second
stock chest 12 for repeated application of the second chemical additive 52.
One suitable process 39 for making paper products from the fiber siurries 20
of
Figures 1 or 2 is the uncreped throughdrying method depicted in Figure 3. The
uncreped
throughdrying method is also disciosed in U.S. Patent 5,656,132 issued August
12, 1997
to Farrington, Jr. et al. A twin wire former
having a layered papermaking headbox 60 injects or deposits a stream from the
fiber
slurry 20 onto the forming fabric 62 to form a cellulosic web 64. The web is
then
transferred to fabric 66, which serves to support and carry the newly-formed
wet web
downstream in the process as the web is partiaiiy dewatered to a consistency
of about 10
dry weight percent. Additional dewatering of the wet web can be carried out,
such as by
vacuum suction, while the wet web is supported by the forming fabric.
The wet web is then transferred from the forming fabric 66 to a transfer
fabric 70
traveling at a siower speed than the forming fabric in order to impart
increased MD
stretch into the web. A kiss transfer is carried out to avoid compression of
the wet web,
preferably with the assistance of a vacuum shoe 72. The transfer fabric can be
a fabric
having impression knuckles or it can be a smoother fabric such as Asten 934,
937, 939,
959 or Albany 94M. If the transfer fabric is of the impression knuckle type
described
herein, it can be utiiized to impart some of the same properties as the
throughdrying
fabric and can enhance the effect when coupled with a throughdrying fabric
also having
the impression knuckles. When a transfer fabric having impression knuckies is
used to
achieve the desired CD stretch properties, it provides the flexibility to
optionaliy use a
different throughdrying fabric, such as one that has a decorative weave
pattem, to
provide additional desirable properties not otherwise attainable.
The web is then transferred from the transfer fabric to a throughdrying fabric
74
with the aid of a vacuum transfer roll 76 or a vacuum transfer shoe. The
throughdrying
fabric can be traveling at about the same speed or a different speed relative
to the
transfer fabric. If desired, the throughdrying fabric can be run at a slower
speed to further
enhance MD stretch. Transfer is preferably carried out with vacuum assistance
to ensure
deformation of the sheet to conform to the throughdrying fabric, thus yielding
desired
bulk, flexibility, CD stretch and appearance. The throughdrying fabric is
preferably of the
impression knuckle type.
-10-
CA 02310692 2006-12-08
The level of vacuum used for the web transfers can be from about 3 to about 15
inches (about 75 to about 380 millimeters) of mercury, preferably about 10 to
about 15
inches (about 254 to about 380 millimeters) of mercury. The vacuum shoe
(negative
pressure) can be supplemented or replaced by the use of positive pressure from
the
opposite side of the web to blow the web onto the next fabric in addition' to
or as a
replacement for sucking it onto the next fabric with vacuum. Also, a vacuum
roll or rolls
can be used to replace the vacuum shoe(s).
Specific embodiments and modes of operation relating to the forming fabric,
transfer fabric, rush transfer, transfer shoes, fabric positioning, and vacuum
levels are
disGosed in U.S. Patent 5,667,636 issued September 16, 1997 to S. A. Engel et
al. and
U.S. Patent 5,607,551 issued March 4, 1997 to T. E. Farrington, Jr. et al.
While supported by the throughdrying fabric, the web is final dried to a
consistency of about 94 percent or greater by the throughdryer 80 and
thereafter
transferred to a carrier fabric 82. The dried basesheet is transported to the
reel 84 using
carrier fabric 82 and an optional carrier fabric 86. An optional pressurized
tuming roll 88
can be used to facilitate transfer of the web from carrier fabric 82 to fabric
86. Suitable
canier fabrics for this purpose are Albany Intemational 84M or 94M and Asten
959 or
937, all of which are relatively smooth fabrics having a fine pattem. The roll
of tissue-may
then be calendered, slit, surface treated with emollient or softening agents,
embossed, or
the like in subsequent operations to produce the final product form.
EXAMPLES
The following examples serve to illustrate possible approaches pertaining to
the
present invention. The particular amounts, proportions, compositions and
parameters are
meant to be exemplary, and are not intended to specifically limit the scope of
the
invention.
Example 1 (Comparative)
For this example, a softening/debonding agent was added during production of a
multi-fiber, three-layer tissue using a conventional, stuffbox chemical
addition method.
The fumish used for the outer two layers comprised 70% Eucalyptus fibers, 29%
tissue
broke and 19'o recycled fiber corestock. The outer layer fumish components
were blended
at the pulper. After repulping, the fumish was transferred to a chest and
treated with a
bonding agent, Parez 631 NC*which is commercially available from Cytec
Industries, Inc.,
* trade-mark
11
CA 02310692 2000-05-18
WO 99/34057 PCT/US98/26834
at a dosage of 1 kg./metric ton. After allowing the slurry to mix for 20
minutes, the fumish
was thickened to greater than 30% consistency using a dewatering press and
treated in
a disperser to impart curl to the fibers. The disperser was operated with a
power input of
80 kilowatts and an exit stock temperature of about 180 F. After dispersing,
the fibers
were stored in a high density chest until needed during tissue manufacturing.
At the time of manufacturing, the outer layer fumish, consisting of the
dispersed
Eucalyptus/broke/corestock blend, was diluted to 3.5% consistency in a chest
using the
filtrate from the earlier thickening process. A softening/debonding agent, C-
6092 which is
commercially available from Witco Corp., was added to this fumish at a rate of
6.5
kg./metric ton at the machine chest stuffbox recirculation loop. This stuffbox
feeds the
fan pumps for both outer layers of a three-layer tissue sheet.
The center layer fumish comprised 100% northem bleached softwood kraft fibers.
This fumish was refined at an energy input of 2 horsepower days/metric ton for
dry
strength development. Parez 631 NC was also added to this fumish at a dosage
of 5.8
kg./metric ton to achieve wet tensile strength control. Dry strength control
was achieved
by varying the ratio of center layer to outer layer fumish.
A one-ply, uncreped through air dried tissue was produced using a pilot tissue
machine. This same tissue machine was used for Examples 1- 4. The machine
contains
a 3 layer headbox, of which the outer layers contained the same fumish (70%
Eucalyptus, 29% broke, 1% corestock), and the center layer was 100% softwood
fiber.
The resulting three-layered sheet structure was formed on a twin-wire, suction
form roll,
former. The speed of the forming fabrics was 2250 feet per minute (fpm). The
newly-
formed web was then dewatered to a consistency of about 20-27 percent using
vacuum
suction from below the forming fabric before being transferred to the transfer
fabric,
which was traveling 1800 feet per minute (25% rush transfer). A vacuum shoe
pulling
about 10 inches of mercury vacuum was used to transfer the web to the transfer
fabric.
The web was then transferred to a throughdrying fabric traveling at a speed of
about
1800 fpm. The web was carried over a pair of Honeycomb throughdryers operating
at
temperatures of about 325 F. and dried to final dryness of about 94-98 percent
consistency.
The air dry basis weight of the sheet was 27.5 gsm. The final fiber ratio in
the
sheet was 32% softwood fiber (in center layer) and 68%
Eucalyptus/broke/corestock
blend (outer layers). The final strength of the tissue was 800 grams per 3
inch width
(geometric mean tensile strength).
-12-
CA 02310692 2006-12-08
Example 2.
For this example, the improved chemical addition method shown in Figure 1 was
used to treat a fumish vvith a softening/debonding agent. The treated fumish
was then
used as the outer layer fumish in a multi-fiber, three-layered tissue
structure. Because
the improved chemical addition method removes most non-retained
softening/debonding
agent from the water phase during tissue forming, the resultant product can be
produced
at equivalent tensile strength, higher softener/debonder content and a lower
softwood
fiber content than a tissue made with the identical softening agent using the
conventional
chemical addition method described in Example 1.
In Example 2, the fumish used for the outer two layers comprised 70%
Eucalyptus
fibers, 29% tissue broke and 1% recyded fiber corestock. During the stock
preparation
phase, the outer layer fumish was blended during repulping and placed in a
stock chest
at 3.5% consistency. The fumish was then treated with a bonding agent, Parez
631 NC
from Cytec Industries, Inc., at a dosage of 1 kg./metric.ton. After allowing
the slurry to mix
for 20 minutes, a softening/debonding agent, C-6092 from Witco Corp., was
added at a
dosage of 7.5 kg. of active chemicaUmetric ton of fiber. After an additional
20 minutes of
mixing time, the slurry was dewatered using a belt press to approximately 32%
consistency. The filtrate from the dewatering process was used as pulper make-
up water
for subsequent batches but not sent forward in the stock preparation or
tissuemaking
process. The thickened pulp was then passed through a disperser with a power
input of
80 kilowatts and a stock temperature of about 180 F to impart curl to the
fibers. After the
dispersing operation, the stock was placed in a high density storage chest
until needed
during tissue manufacturing.
A one-ply, uncreped, through air dried tissue was made using a three layered
headbox, as described in Example 1. The fumish for the outer two layers
comprised the
chemically treated 32% consistency EucalyptusJbroke/corestock fumish blend,
which had
been re-diluted to 3% consistency with fresh water in a chest under agitation.
The center
layer consisted of 100% softwood fibers refined at an energy input of 2
horsepower
days/metric ton, to which 5.8 kg./metric ton of Parez 631 NC was added for wet
strength
control. Finished product dry strength control was achieved by adjusting the
ratio of
center layer and outer layer fumish In the sheet.
The air dry basis weight of the sheet was 27.5 gsm. The final fiber ratio in
the
sheet was 17% softwood fiber (in center layer) and 83%
Eucalyptus/broke/corestock
blend (outer layers). The final strength of the tissue was 802 grams per 3
inch width
(geometric mean tensile strength).
* trade-mark
-13-
CA 02310692 2000-05-18
WO 99/34057 PCT/US98/26834
Exam e 3
For this example, the improved chemical addition method shown in Figure 2 was
used to first treat a fumish with a bonding agent, mechanically modify the
fibers using a
disperser, and then treat the fumish with a softening/debonding agent. The
chemically
treated fumish was used as one fumish in a multi-fiber, three-layered tissue
structure.
Because the improved chemical addition method removes most non-retained
softening/debonding agent from the water phase during tissue forming, the
resultant
product was much stronger (at equal fiber composition) than a tissue made with
similar
softening agent using the conventional chemical addition method described in
Example
1. In addition, because the softener/debonder is not present on the fumish
during the
dispersing operation, there is a more efficient transfer of energy to the
fibers. This results
in a higher level of debonding than demonstrated in Example 2 due to the fiber
curl
properties imparted during dispersing.
In Example 3, the fumish used for the outer two layers comprised 70%
Eucalyptus
fibers, 29% tissue broke and 1% recycled fiber corestock. During the stock
preparation
phase, the outer layer fumish was blended during repulping and placed in a
stock chest
at 3.5% consistency. The fumish was then treated with a bonding agent, Parez
631 NC
from Cytec Industries, Inc., at a dosage of 1 kg./metric ton. After allowing
the slurry to mix
for 20 minutes, the fumish was dewatered using a belt thickening press to
greater than
30% consistency. The thickened pulp was then passed through a disperser with a
power
input of 80 kilowatts and a stock temperature of about 180 F to impart curl
to the fibers.
The high consistency, dispersed pulp was then stored in a chest until
sufficient quantities
could be produced.
In order to treat the fumish with a second chemical additive, the high
consistency
pulp was then diluted to 3.5% consistency with a combination of fresh water
and
thickener filtrate (containing unadsorbed softening/debonding agent, as shown
in Figure
2). The fumish was next treated with 7.5 kg./metric ton of a
softening/debonding agent,
C-6092 from Witco Corp., and allowed to mix for 20 minutes. The fumish was
then
dewatered using a belt press to approximately 32% consistency. The filtrate
from the
dewatering process was used as partial dilution water for the high consistency
stock
dilution step, as previously mentioned. After the second thickening operation,
the stock
was placed in a high density storage chest until needed during tissue
manufacturing.
A one-ply, uncreped, through air dried tissue was made using a three layered
headbox, as described in Example 1. The fumish for the outer two layers
comprised the
chemically treated 32% consistency Eucalyptus/broke/corestock fumish blend,
which had
-- 14 --
CA 02310692 2000-05-18
WO 99/34057 PCT/US98/26834
been re-diluted to 3% consistency with fresh water in a chest under agitation.
The center
layer comprised 100% softwood fibers refined at an energy input of 2
horsepower
days/metric ton, to which 5.8 kg./metric ton of Parez 631 NC was added for wet
strength
control. Finished product dry strength control was achieved by adjusting the
ratio of
center layer and outer layer fumish in the sheet.
The air dry basis weight of the sheet was 27.5 gsm. The final fiber ratio in
the
sheet was 24% softwood fiber (in center layer) and 76%
Eucalyptus/broke/corestock
blend (outer layers). The final strength of the tissue was 806 grams per 3
inch width
(geometric mean tensile strength).
Example 4
This example is similar to Example 3, except that 15 kg./metric ton of C-6092
softener/ debonder was added to the outer layer fumish (instead of 7.5
kg./metric ton in
Example 3). Because the improved chemical addition method has removed most non-
retained softening/debonding agent from the water phase during tissue
formation, the
resultant product contains 55% more softening/debonding agent than the product
described in Example 1, at equivalent tensile strength and fiber composition.
The stock preparation and tissue manufacturing procedures were identical to
Example 3. The air dry basis weight of the sheet was 27.5 gsm. The final fiber
ratio in the
sheet was 31 % softwood fiber (in center layer) and 69%
Eucalyptus/broke/corestock
blend (outer layers). The final strength of the tissue was 795 grams per 3
inch width
(geometric mean tensile strength).
The results shown in Table 1 below indicate that a layered tissue sheet can be
made with a geometric mean tensile strength of about 800 grams per 3 inch
width (795
grams per 3 inch width), under the processing conditions described in Example
4, that
contains 31 % softwood fiber and 5.9 kg./metric ton of retained C-6092
softener/debonder
by using the improved chemical addition method. When using the conventional
chemical
addition method described in Example 1, and othennrise identical manufacturing
conditions, a layered tissue sheet with a geometric mean tensile strength of
800 g./3"
width contains 32% softwood fiber but only 3.8 kg./metric ton of retained C-
6092
softener/ debonder. The reason for this difference in retained C-6092 at
equivalent tissue
strength, it is hypothesized, is because the debonding characteristic of the
unadsorbed
C-6092 in the conventional chemical addition method compromises the strength
development of the softwood fibers in the center layer. As a result, more
softwood fiber is
needed to achieve the same finished product tensile strength.
-15--
CA 02310692 2000-05-18
WO 99/34057 PCT/US98/26834
By using the improved chemical addition method, tissue fiber/chemistry
combinations can be produced at target strength levels that could not
othennrise be made
using conventional chemical additon methods. In Examples 2 - 4, the tissues
were
manufactured with generally constant basis weight and strength by adjusting
the relative
amounts of softwood and hardwood. Of course, various aitematives are possible
such as
maintaining generally constant strength and softwood/hardwood proportion and
adjusting
the basis weight.
TABLE 1
Examnles 1 - 4
Strength Debonder Debonder
Example .(g /3"L % Center Layer % Outer Laver Add-on Retained
1 800 32 68 4.4 3.8
2 802 17 83 6.2 4.6
3 806 24 76 5.7 3.8
4 795 31 69 10.4 5.9
In Table 1, "Strength" refers to the geometric mean tensile strength which is
calculated for purposes of the present invention according to the formula:
[(AIDtensile)(CDterrsile)]. The "MD tensile" strength of a tissue sample is
the
conventional measure, known to those skilled in the art, of load per sample
width at the
point of failure when afissue web is stressed in the machine direction.
Likewise, "CD
tensile" strength is the analogous measure taken in the cross-machine
direction. MD and
CD tensile strength are measured using an Instron tensile tester using a 3-
inch jaw width,
a jaw span of 4, inches, and a crosshead speed of 10 inches per minute. Prior
to testing
the sample is maintained under TAPPI conditions (73 F, 50% relative humidity)
for 4
hours before testing. Tensile strength is reported in units of grams per 3
inch width (at
the failure point).
The % Center Layer and % Outer Layer refer to the weight percent of fibers in
the
appropriate layers.
The Debonder Add-on reflects the chemical additive that is added to the fumish
in
kg./metric ton of the entire sheet. This is calculated based on the add-on
level to the
outer layer fumish and the amount of the outer layer fumish in the final
sheet.
_ 1 g --
CA 02310692 2000-05-18
WO 99/34057 PCT/US98/26834
The Debonder Retained reflects the amount of chemical additive adsorbed onto
the tissue. The Debonder Retained can be determined using the foiiowing
procedure
suitable for imidazoline-based chemical additives such as Witco C-6092 that
are added
to the tissue. The procedure references the percent add-on, which has been
converted to
kg./metric ton (muitipiied by 10) in Table 1. In general, a sample of the
tissue is weighed
and extracted in a sealed container for a given amount time on a flatbed
shaker at
ambient conditions. After the extraction, the tissue is removed and the
extract allowed to
settie. The extract is then analyzed by uftravioiet spectrometer. After the
percent
extracted is calculated, the add-on percent can be determined by reference to
an add-on
correlation curve that is generated as described below.
The following equipment and chemicals are used: pipets, 1, 3, 5, 10 and 100
mL;
volumetric flasks, 100 and 1000 mL; sealed containers, e.g. specimen cups; a
flatbed
shaker, such as an orbital flatbed shaker (Lab Line Orbital Shaker Model No.
3590, Lab
Line Instruments, Inc.); an uitravioiet spectrometer (Hewiett Packard Model
8451A Diode
Array Spectrophotometer, Hewiett Packard); methanol, reagent grade;
imidazoline,
standard such as Witco C-6092; beakers, 30 mL; and control tissues that differ
from the
tissue being tested only by the absence of the chemical additive being tested.
A stock standard imidazoline solution (1000 ppm active) is prepared: Weigh
0.1250 grams of C-6092 (80% active) into a 30mL beaker transfer quantitatively
to a
lOOmL flask with methanol; and dilute to mark with methanol and invert several
times.
Standard imidazoline solutions (10, 30, 50, 100 ppm) are prepared: Into four
100
mL voiumetric flasks, add 1, 3, 5, and 10 mL of the 1000 ppm stock standard
imidazoline
soiution; and dilute to marks with methanol. The standards are 10, 30, 50 and
100 ppm,
respectivefy.
Generate a Standard Solution Curve: With the UV spectrophotometer set at 238
nm wavelength, reference the instrument using a methanol sample. Read the
absorptance of the standard soiutions (10, 30, 50 and 100 ppm), then plot a
curve of the
concentration versus absorptance. Generate a first-order equation fit of the
data.
Spiking solutions (1000 and 5000ppm) are prepared: Weigh out 1.250 and 6.250
grams of C-8092 into 50 ml beakers; transfer quantitatively to a 1000 ml flask
with
distilled water, shake well and allow to dissolve before diluting to mark. If
excessive
foaming occurs, fill to the stem of the flask and add a small amount of
methanol to
eliminate the foam and dilute to mark then invert several times. This makes a
1000 ppm
and 5000 ppm spiking solutions.
-17--
CA 02310692 2000-05-18
WO 99/34057 PCT/US98/26834
Generate an Add-On Correiation Curve: A minimum of three replicates should be
performed for each level of add-on and for blanks. There should be at least
four levels of
add-on to generate a curve. Spiking solutions should be made with distilled
water, so that
the spiked sample can be dried in a 60 degree Celsius oven.
Weigh out 5.00 grams of control tissue into a specimen container. For four
levels,
three replicates, and blanks, prepare 15 samples. A typical curve would be
0.1, 0.3, 0.8,
and 1.0% C-6092 add-on based on the weight of the tissue.
Spike samples with spiking soiution and dry for 48 hours in a 60 degree
Celsius
oven. Use voiumetric pipettes. Example:
Volume of Spiking Solution for
5.00 gram tissue
Add-on Level 1000oam 5000pam
Blank 0 mL 0 mL
0.1% 5 mL -
0.3% 15 mL 0.8% - 8 mL
1.0% - 10mL
Add 100 mL of methanol using a pipet and seai the containers. Place in a
flathed
shaker and extract for % hour. Remove tissue and allow the extract to settle.
With a
transfer pipette, remove supematant and fill a spectrophotometer cuvette.
Measure the
absorptance at 238nm wavelength using the UV spectrometer. A I to 10 dilution
may be
required to stay within the standard curve. Blanks should be read with and
without this
dilution. Subtract the mean absorptance readings from the blanks. Use the 1/10
diiution
blank readings for 1/10 dilution samples and no dilution blank readings for
the no ditution
samples.
The percent extracted is then calculated from the ppm reading from the
standard
curve (imidazoline) as follows:
% Extracted (no dilution) = ppm reading X 0.1 X 100/5000.
% Fxtracted (1/10 dilution) = ppm reading X 0.1 X 10 X 100/5000.
Construct an Add-on Correlation curve with the percent extracted values (y-
axis)
versus the corresponding add-on level (x-axis). Select the best fitting curve
(first or
second order).
-- 18 --
CA 02310692 2000-05-18
WO 99/34057 PCT/US98/26834
Sample Analysis: Weigh out 5.00 grams sample in a specimen container and add
100 mL of methanol. Place on the flatbed shaker and extract for % hour. Remove
the
tissue and allow to settle. Read the extracts at 238nm wavelength and subtract
the mean
blank absorptance reading. Calculate the ppm from the standard curve and then
calculate the percent extracted value. Using the Add-on correlation curve,
calculate the
percent add-on with the percent extracted value.
Imidazoline has a peak absorptance at 238nm wavelength. While blank tissue
extracts do not have this peak absorptance at 238nm, it does have some
absorptance
that interferes with the quantitation. Blanks are quite reproducible and can
be subtracted
for the determination. It is important that the weight of the sample, volume
of methanol,
and the extraction time be kept constant. An add-on correiation curve should
be
generated for different tissue samples, because various chemicals used in the
tissue
process can affect the binding of the imidazoline thus affecting the recovery.
Percent
add-on also affects the percent recovery; using various levels of add-on in
constructing
the correlation curve helps to determine the add-on value.
Example 5
To better illustrate the ability for the improved chemical addition method to
remove unadsorbed chemicals from the fumish of a papermaking process, a
laboratory
scale experiment was conducted. The objective of this experiment was to
demonstrate
how much unadsorbed chemical is present in systems that do not use the
improved
addition method and compare this to systems in which the same amount of
chemical is
added using the improved method. The fumish used in this experiment was 100%
Eucalyptus fibers. The chemical additive used was C-6092, a softener/debonder
commercially available from Witco Corp. The addition levels were 0.5% and 1.0%
active
debonder on dry fiber.
0.5% Addition Experiment: Stea I
During the experiment, 1800 grams of a 2.5% consistency fiber slurry (45 g.
dry
fiber) were agitated using a mechanical mixer. To the fiber sluny under
agitation, the
appropriate amount of C-6092 chemical was added in the form of a 1% active
solution.
The volume of 1% active C-6092 required for a 0.5% loading was 22.5 ml. After
agitation
for 15 minutes, 600 ml of slurry was removed and spread out on a plate to dry
at room
temperature under a hood. This sample will be referred to as 1A.
-- 19 --
CA 02310692 2000-05-18
WO 99/34057 PCT/US98/26834
SteD 2
The remaining 1200 grams of slurry were filtered using a Whatman 4 filter
paper
and Buchner funnel apparatus. This fiitration step simulates the dewatering
step of the
improved chemical addition method shown in Figure 1. The filter pad (at
approximately
25% consistency) was split into two sections of approximately equal mass. One
section
was placed in the hood to dry at room temperature. This sample will be
referred to as 2A.
Step 3
The other half of the filter pad (approximateiy 600 g.) was redispersed to
2.5%
consistency using distilled water. The slurry was mechanically agitated for 15
minutes
and then filtered using a Whatman 4 filter paper and Buchner funnel apparatus.
This
filtration step simulates the dewatering that occurs in the forming and vacuum
dewatering
zones of a tissue machine. The filter pad was placed in a hood to dry at room
temperature. This sample wili be referred to as 3A.
1.0% Addition Ecperiment
Steps 1- 3 were repeated using a 1.0% addition level of C-8092. The
corresponding samples were coded 1 B, 2B and 3B.
All samples were analyzed for C-6092 content using a methanol extraction
followed by UV spectroscopic analysis at 238nm and comparison of the
absorptance to a
known caiibration curve. The results are shown in the table beiow:
Samcie No.
1A 2A 3A 1B 2B 3B
C-6092 Content (%) 0.51 0.30 0.28 1.05 0.73 0.68
The resuits demonstrate the impact of using the improved chemical addition
method on reducing the amount of unadsorbed debonder in the fumish. Comparing
the
C-6092 content of samples 1A and 2A shows that 41% of the chemical is not
retained
sufficiently onto the fibers and is removed during dewatering. If the
conventionai stuffbox
chemical addition method is used this unadsorbed chemical is free in the
fumish to
contaminate other fiber streams and cause the processing problems previously
described. Comparing the C-6092 content of samples 2A and 3A, however, shows
that
only an additional 6% of the retained C-6092 is removed during a second
dewatering
step, which simulates sheet formation on a tissue machine.
-20-
CA 02310692 2000-05-18
WO 99/34057 PCT/US98/26834
When the C-6092 content of the I B, 2B and 3B samples are compared it can be
shown that 30% of the original 1.0% chemical loading is removed during the
first
dewatering step, but only an additional 7% of the retained C-6092 is removed
during the
second dewatering step.
It is believed that this simulation of the improved chemical addition method
demonstrates the ability to significantly reduce the amount of unadsorbed
chemical
additive in the water of a paper manufacturing process while maintaining high
chemical
retention levels on the fiber fraction.
The foregoing detailed description has been for the purpose of illustration.
Thus,
a number of modifications and changes may be made without departing from the
spirit
and scope of the present invention. For instance, altemative or optional
features
described as part of one embodiment can be used to yield another embodiment.
Additionally, two named components could represent portions of the same
structure.
Further, various altemative process and equipment arrangements may be
employed,
paracularly with respect to the stock preparation, headbox, forming fabrics,
web transfers,
creping and drying. Therefore, the invention should not be limited by the
specific
embodiments described, but only by the claims and all equivalents thereto.
_ 21 --
