U.S. patent application number 10/158717 was filed with the patent office on 2003-02-27 for paper products and a method for applying a dye to cellulosic fibers.
Invention is credited to Gentile, Victor Michael, Georger, Jill A., Goulet, Mike Thomas, Polderman, Denise Alice, Wyatt, Maurice Alan.
Application Number | 20030037896 10/158717 |
Document ID | / |
Family ID | 23171658 |
Filed Date | 2003-02-27 |
United States Patent
Application |
20030037896 |
Kind Code |
A1 |
Goulet, Mike Thomas ; et
al. |
February 27, 2003 |
Paper products and a method for applying a dye to cellulosic
fibers
Abstract
Chemical additives can be adsorbed on cellulosic papermaking
fibers at high levels with a minimal amount of unadsorbed chemical
additives present in the papermaking process water. A method
includes 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.
Filtrate from the thickening process contains unadsorbed chemical
additive and it is not sent forward in the process with the
chemically treated fibers. The method can be employed to make
improved paper products.
Inventors: |
Goulet, Mike Thomas;
(Appleton, WI) ; Georger, Jill A.; (Neenah,
WI) ; Polderman, Denise Alice; (Martinez, GA)
; Wyatt, Maurice Alan; (Evans, GA) ; Gentile,
Victor Michael; (Appleton, WI) |
Correspondence
Address: |
KIMBERLY-CLARK WORLDWIDE, INC.
401 NORTH LAKE STREET
NEENAH
WI
54956
|
Family ID: |
23171658 |
Appl. No.: |
10/158717 |
Filed: |
May 29, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10158717 |
May 29, 2002 |
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09303344 |
Apr 30, 1999 |
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6423183 |
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09303344 |
Apr 30, 1999 |
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09010675 |
Jan 22, 1998 |
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Current U.S.
Class: |
162/182 ;
162/123; 162/126; 162/127; 162/132; 162/134; 162/158; 162/162;
162/181.1; 162/181.2; 162/189; 162/190; 162/9 |
Current CPC
Class: |
D21H 21/22 20130101;
D21H 23/765 20130101; D21H 27/38 20130101; D21C 9/002 20130101;
D21H 21/285 20130101; D21H 27/30 20130101; D21H 21/28 20130101;
D21H 21/20 20130101; D21H 23/04 20130101 |
Class at
Publication: |
162/182 ; 162/9;
162/158; 162/162; 162/181.2; 162/189; 162/190; 162/181.1; 162/123;
162/126; 162/127; 162/132; 162/134 |
International
Class: |
D21H 011/00 |
Claims
We claim:
1. A method comprising: 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.
2. A method comprising: 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.
3. The method of claim 1, wherein creating a fiber slurry comprises
adding the adsorbable chemical additive to an aqueous solution
comprising the water and cellulosic fibers.
4. The method of claim 1 or 2, wherein the chemical additive is
added to a slurry of water and cellulosic fibers in an amount of
about 5 kilograms per metric ton or greater.
5. The method of claim 1 or 2, wherein dewatering increases the
consistency of the fiber slurry to about 30 percent or greater.
6. The method of claim 1 or 2, wherein redispersing the fibers
decreases the consistency of the fiber slurry to about 5 percent or
lower.
7. The method of claim 1 or 2, further comprising maintaining the
removed unadsorbed chemical additive separate from the fiber
slurry.
8. The method of claim 1 or 2, wherein the fresh water is
completely free of unadsorbed chemical additive.
9. The method of claim 1 or 2, wherein sufficient residence time is
provided after the chemical additive is added to allow for
adsorption.
10. The method of claim 1 or 2, wherein the removed unadsorbed
chemical additive is reused in a processing step prior to
dewatering the fiber slurry.
11. The method of claim 1 or 2, wherein the adsorbable chemical
additive comprises a debonding agent.
12. The method of claim 1 or 2, wherein the adsorbable chemical
additive comprises a softening agent.
13. The method of claim 1 or 2, wherein the chemical additive
comprises a debonding agent or softening agent and the fiber slurry
is not subjected to high shear refining forces once the chemical
additive is added to the fiber slurry.
14. The method of claim 1 or 2, wherein the redispersed fiber
slurry is treated with a second adsorbable chemical additive,
dewatered a second time to remove unadsorbed chemical additives and
redispersed a second time.
15. The method of claim 14, wherein the second chemical additive
comprises a softening agent.
16. The method of claim 14, wherein the second chemical additive
comprises a debonding agent.
17. The method of claim 1, further comprising forming a paper
product comprising a plurality of layers, with one but not all of
the layers being formed from the fiber slurry containing the
adsorbable chemical additive.
18. A method comprising: 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.
19. The method of claim 18, wherein the first chemical additive
comprises a bonding agent.
20. A fiber furnish produced using the method described in claim 1,
wherein 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.
21. A fiber furnish comprising water, cellulosic fibers, and an
adsorbable chemical additive, wherein 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.
22. The fiber furnish of claim 20 or 21, wherein the amount of
chemical additive adsorbed onto the fibers is about 3 kilograms per
metric ton or greater.
23. The fiber furnish of claim 22, wherein the amount of chemical
additive adsorbed onto the fibers is about 4 kilograms per metric
ton or greater.
24. The fiber furnish of claim 22, wherein the amount of chemical
additive adsorbed onto the fibers is about 5 kilograms per metric
ton or greater.
25. The fiber furnish of claim 20 or 21, wherein the amount of
unadsorbed chemical additive in the water is between 0 and about 15
percent of the amount of chemical additive adsorbed onto the
fibers.
26. The fiber furnish of claim 25, wherein the amount of unadsorbed
chemical additive in the water is between 0 and about 10 percent of
the amount of chemical additive adsorbed onto the fibers.
27. The fiber furnish of claim 25, wherein the amount of unadsorbed
chemical additive in the water is between 0 and about 7 percent of
the amount of chemical additive adsorbed onto the fibers.
28. The furnish of claim 20 or 21, wherein the chemical additive is
selected from the group comprising softening agents, debonding
agents, dry strength agents, wet strength agents and opacifying
agents.
29. A paper product made from the furnish of claim 21.
30. A paper product made using the method of claim 1.
31. A paper product comprising a plurality of unitary layers, the
paper product made using the method of claim 2.
32. The paper product of claim 29 or 30, having a chemical additive
retention of about 4 kilograms per metric ton or greater.
33. The paper product of claim 32, having a chemical additive
retention of about 5 kilograms per metric ton or greater.
34. The paper product of claim 31, comprising a center layer
consisting essentially of softwood fibers and two outer layers
comprising about 70 percent or greater hardwood fibers.
35. The paper product of claim 29 or 30, wherein the paper product
is a layered tissue.
36. A method for applying a dye to cellulosic fibers, said method
comprising the steps of: a) creating a fiber slurry of water,
cellulosic fibers, and an adsorbable dye, said dye being adsorbed
onto said cellulosic fibers in an amount ranging from between about
0.01 to about 20 kilograms per metric ton; b) dewatering said fiber
slurry to remove said dye which was unadsorbed; and c) redispersing
said cellulosic fibers in said fiber slurry with fresh water.
37. The method of claim 36 wherein said dye is an acid dye.
38. The method of claim 36 wherein said dye is a basic dye.
39. The method of claim 36 wherein said dye is a direct dye.
40. The method of claim 36 wherein said dye is a cellulose reactive
dye.
41. The method of claim 36 wherein said dye is a pigment.
42. The method of claim 36 wherein said dye is applied to said
cellulosic fibers to alter the color of said fibers.
43. The method of claim 36 wherein said dye is added to said water
and said cellulosic fibers in an amount of about 0.01 kilograms per
metric ton or greater.
44. The method of claim 36 wherein said dewatering increases the
consistency of said fiber slurry to about 30 percent or
greater.
45. A method for applying a dye to cellulosic fibers, said method
comprising the steps of: a) creating a first fiber slurry of
cellulosic fibers, water and an adsorbable dye, said dye being
adsorbed onto said cellulosic fibers in an amount ranging from
between about 0.01 to about 20 kilograms per metric ton; b)
creating a second fiber slurry that is substantially free of any
adsorbable dye; c) dewatering said first fiber slurry to remove
said dye which was unadsorbed; d) redispersing said cellulose
fibers in said first fiber slurry with fresh water; and e) forming
a paper product using a layered headbox having a first layer and a
second layer, said first fiber slurry being directed to said first
layer and said second fiber slurry being directed to said second
layer.
46. The method of claim 45 wherein said dye is applied to said
cellulosic fibers to alter the color of said fibers.
47. The method of claim 45 further comprising forming a paper
product having a plurality of layers, with one of said layers being
formed from said first fiber slurry.
48. The method of claim 45 wherein said dye is a direct dye.
49. The method of claim 45 wherein said dye is a basic dye.
50. The method of claim 45 wherein said dye is a pigment.
51. A method for applying a dye to cellulosic fibers, said method
comprising the steps of: a) creating a fiber slurry containing
water, cellulosic fibers and a first adsorbable dye; b) dewatering
said fiber slurry to remove said dye which was unadsorbed, said
fiber slurry having a consistency of about 20 percent or greater;
c) passing said dewatered fiber slurry through a disperser to
mechanically work said cellulosic fibers; d) diluting said fiber
slurry with fresh water to a consistency of about 5 percent or
less; e) adding a second adsorbable chemical additive to said fiber
slurry; f) dewatering said fiber slurry to a consistency of about
20 percent or greater; g) diluting said fiber slurry with fresh
water to a consistency of about 5 percent or less; and h) forming a
paper product from said fiber slurry.
52. The method of claim 51 wherein said second adsorbable chemical
is a debonding agent.
53. The method of claim 51 wherein said second adsorbable chemical
is a softening agent.
54. The method of claim 51 wherein said dye is a direct dye.
55. The method of claim 51 wherein said dye is a basic dye.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates generally to paper products.
More particularly, the invention concerns methods for applying
chemical additives to cellulosic fibers and the paper products that
can be obtained by the methods.
[0002] 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.
[0003] 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.
[0004] 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
[0005] 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, particularly
when trying to achieve high chemical additive loading levels.
[0006] 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.
[0007] Therefore, what is lacking and needed in the art is a method
for applying adsorbable chemical additives, particularly a dye,
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 otherwise occur.
SUMMARY OF THE INVENTION
[0008] 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.
[0009] 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 time 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
relative to the process water can be achieved as compared to what
has been possible with prior methods.
[0010] For purposes of the present invention, the term "cellulosic"
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 involving 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.
[0011] The fiber slurry is desirably dewatered to increase the
consistency of the fiber slurry to about 20 percent or greater, and
particularly 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.
[0012] The present method allows for the production of fiber
furnishes that are useful for making paper products, and
particularly layered paper products. Thus, another aspect of the
invention resides in a fiber furnish that has a higher chemical
additive loading than could otherwise be achieved in combination
with the relatively 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.
[0013] In one embodiment, a fiber furnish 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 particularly 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, particularly between 0 and about 10 percent, and more
particularly between 0 and about 7 percent, of the amount of
adsorbed chemical additive.
[0014] When the chemical additive is a dye, the amount of dye
adsorbed onto the fibers can vary from between about 0.01 to about
20 kg per metric ton. Preferably, the amount of dye adsorbed onto
the fibers is from between about 0.05 to about 15 kg per metric
ton. More preferably, the amount of dye adsorbed onto the fibers is
from between about 0.05 to about 7.5 kg per metric ton. Even more
preferably, the amount of dye adsorbed onto the fibers is from
between about 0.05 to about 10 kg per metric ton. Most preferably,
the amount of dye adsorbed onto the fibers is from between about
0.05 to about 2.0 kg per metric ton.
[0015] The amount of unadsorbed dye in the water can vary from
between 0 and about 20 percent of the amount of dye adsorbed onto
the fibers. More preferably, the amount of unadsorbed dye in the
water can vary from between about 5 to about 20 percent of the
amount of dye adsorbed onto the fibers. Moreover, the amount of
unadsorbed dye in the water is from between 0 and about 15 percent,
particularly from between 0 and about 10, percent, and more
particularly, from between 0 and about 7 percent of the amount of
unadsorbed dye.
[0016] Another aspect of the invention resides in a method for
making chemically treated paper products. The method includes the
steps of: creating a first fiber slurry containing water,
cellulosic fibers, and an adsorbable dye, and creating a second
fiber slurry that is substantially free of the adsorbable dye. The
first fiber slurry is dewatered to remove unadsorbed dye before the
fibers in the first fiber slurry are redispersed with fresh water.
The first and second fiber slurries are then used to form a paper
product using a layered headbox. The first fiber slurry is supplied
to a first layer of the headbox and the second fiber slurry is
supplied to a second layer of the headbox.
[0017] 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.
[0018] 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.
[0019] The present invention is particularly useful for adding
chemical additives such as softening agents and debonding agents to
the outer layer furnishes 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.
[0020] 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, wrapping, sanitary, and
industrial papers, newsprint, linerboard, tissue, napkins, wipers,
towels, or the like.
[0021] 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, antibiotic
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.
[0022] 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.
[0023] The term "debonding agent" refers to any chemical that can
be incorporated into paper products such as tissue to prevent or
disrupt interfiber 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.
[0024] The term "dye" refers to any chemical that can be
incorporated into paper products, such as bathroom tissue, facial
tissue, paper towels and napkins, to impart a color. Depending on
the nature of the chemical, dyes may be classified as acid dyes,
basic dyes, direct dyes, cellulose reactive dyes or pigments. All
classifications are suitable for use in conjunction with the
present invention.
[0025] 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.
[0026] 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. Pat. No. 5,667,636 issued Sep. 16, 1997 to S.
A. Engel et al.; and U.S. Pat. No. 5,607,551 issued Mar. 4, 1997 to
T. E. Farrington, Jr. et al.; which are incorporated herein by
reference.
[0027] The method may also be used in alternative 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
slurry (neutralizing anionic components, sizing or softening
formulations) after a chemical additive has been added to
facilitate the removal process; or the like.
[0028] Many fiber types may be used for the present invention
including 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. Pat. Nos.
5,348,620 issued Sep. 20, 1994 and 5,501,768 issued Mar. 26, 1996,
both to M. A. Hermans et al. and U.S. Pat. No. 5,656,132 issued
Aug. 12, 1997 to Farrington, Jr. et al.
[0029] Drying should be considered a means of further improving the
substantivity of the chemical treatment. The two generally accepted
methods of drying include flash drying and can drying. Flash drying
is most common with bleached, chemi-thermo-mechanical pulp
(BCTMP).
[0030] A single headbox or a plurality of headboxes may be used.
The headbox or headboxes may be stratified 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. Multiple embryonic webs from multiple headboxes may be couched
or mechanically or chemically joined in the moist state to create a
single web having multiple layers.
[0031] 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.
[0032] The general object of this invention is to provide paper
products and a method for applying chemical additives to cellulosic
fibers. More particularly, this invention relates to a method for
applying chemical additives to cellulosic fibers used to make
bathroom tissue.
[0033] Another object of this invention if to provide a method of
adding a dye to cellulosic fibers at a location separate and
distinct from the paper making equipment.
[0034] A further object of this invention is to provide a method
for applying one or more chemical additives to cellulosic fibers at
a location where the unadsorbed chemical additives can be removed
without contaminating process water.
[0035] Still another object of this invention is to provide a
method of dying cellulosic fibers to alter the color of the fibers
before they are directed to a paper making machine.
[0036] Still further, an object of this invention is to provide a
method for applying a chemical additive to cellulosic fibers which
is economical and efficient.
[0037] Others objects and advantages of the present invention will
become more apparent to those skilled in the art in view of the
following description and the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0038] FIG. 1 depicts a schematic process flow diagram of a method
according to the present invention for treating papermaking fibers
with chemical additives.
[0039] FIG. 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 disperser.
[0040] FIG. 3 depicts a schematic process flow diagram for a method
of making an uncreped tissue sheet.
DETAILED DESCRIPTION OF THE DRAWINGS
[0041] The invention will now be described in greater detail with
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.
[0042] FIG. 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,
recirculation pump, or other suitable device 18 for mixing the
fiber slurry.
[0043] 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 of the chemical additive 24. A residence time
of about 15 to about 30 minutes, for instance, may be
sufficient.
[0044] The chemical additive can be an imidazoline-based debonding
agent that is added in an amount of from between about 2.0 to about
15 kg metric ton. The chemical additive 24 can also be a dye which
is applied to the cellulosic fibers to alter the color of the
fibers. In particular, the dye can be used in the treatment of
mechanical pulps to reduce and/or eliminate the yellow color
associated with pulp having a high lignin content. Violet dyes from
the direct dye classification are particularly useful. A particular
dye which works well on cellulosic fibers is Pergasol Violet BN and
is available from Ciba-Geigy. For this particular dye, the amount
adsorbed onto the fibers can vary from between about 0.01 to about
0.5 kilograms per metric ton. However, if one desires, the fibers
could adsorb a larger amount of the dye, for example from between
about 0.5 to about 20 kg per metric ton.
[0045] It should be noted that through mixing is required when
adding an adsorbable chemical additive, for example, a dye. The
time period required can be very short and only require a few
seconds in many cases.
[0046] 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 alternative 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 with
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 particularly 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 importantly it is not sent forward with the
chemically treated furnish.
[0047] 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. Alternatively, the fiber slurry may be
processed through the foregoing procedure again in an effort to
further increase the chemical additive retention level.
[0048] In some instances, the treated fibers may not be used
directly in a paper or tissue making process but instead can be
dried and baled for later use. In this case, the chemically
treated, thickened fiber slurry 20 can be pressed to a consistency
of about 40 percent. The higher the consistency, the less free
chemical and water is available to evaporate during drying. For
practically reason, the minimum consistency of the fiber slurry 20
should not fall below 30 percent and the maximum consistency of the
fiber slurry 20 should not exceed 50 percent when using a twin roll
press. Other types of presses which could be used include: a screw
press, a twin-wire press, as well as various other types of press
machines used in pulp sheeting machines. After the fiber slurry 20
has been pressed, it can be dispersed using a fluffier device to
separate clumps of fiber and then be dried using a flash drier
before being baled.
[0049] FIG. 2 depicts an alternative 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 dilution water
chests 44 and 46, and a disperser 48 for mechanically treating the
papermaking fibers.
[0050] 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. 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.
[0051] 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
particularly about 30 percent or greater.
[0052] 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. Pat. Nos. 5,348,620 issued Sep. 20, 1994 and
5,501,768 issued Mar. 26, 1996, both to M. A. Hermans et al., which
are incorporated herein by reference.
[0053] 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 and/or debonding agent is added to
the fiber slurry.
[0054] 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.
[0055] 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 particularly about 5 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. Alternatively, the fiber slurry may be
returned to the second stock chest 12 for repeated application of
the second chemical additive 52.
[0056] One suitable process 39 for making paper products from the
fiber slurries 20 of FIG. 1 or 2 is the uncreped throughdrying
method depicted in FIG. 3. The uncreped throughdrying method is
also disclosed in U.S. Pat. No. 5,656,132 issued Aug. 12, 1997 to
Farrington, Jr. et al., which is incorporated herein by reference.
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 partially dewatered
to a consistency of about 10 dry weight percent. Additional
dewatering of the wet web can be carried out, such as by vacuum
suction, while the wet web is supported by the forming fabric.
[0057] The wet web is then transferred from the forming fabric 66
to a transfer fabric 70 traveling at a slower 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 utilized 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 knuckles is used
to achieve the desired CD stretch properties, it provides the
flexibility to optionally use a different throughdrying fabric,
such as one that has a decorative weave pattern, to provide
additional desirable properties not otherwise attainable.
[0058] 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.
[0059] 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).
[0060] Specific embodiments and modes of operation relating to the
forming fabric, transfer fabric, rush transfer, transfer shoes,
fabric positioning, and vacuum levels are disclosed in U.S. Pat.
No. 5,667,636 issued Sep. 16, 1997 to S. A. Engel et al. and U.S.
Pat. No. 5,607,551 issued Mar. 4, 1997 to T. E. Farrington, Jr. et
al., which are incorporated herein by reference.
[0061] 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 turning roll 88 can be used to facilitate transfer of
the web from carrier fabric 82 to fabric 86. Suitable carrier
fabrics for this purpose are Albany International 84M or 94M and
Asten 959 or 937, all of which are relatively smooth fabrics having
a fine pattern. 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
[0062] 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
[0063] 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 furnish used
for the outer two layers comprised 70% Eucalyptus fibers, 29%
tissue broke and 1% recycled fiber corestock. The outer layer
furnish components were blended at the pulper. After repulping, the
furnish was transferred to a chest and treated with a bonding
agent, Parez 631NC which is commercially available from Cytec
Industries, Inc., at a dosage of 1 kg./metric ton. After allowing
the slurry to mix for 20 minutes, the furnish 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.degree. F. After dispersing, the fibers
were stored in a high density chest until needed during tissue
manufacturing.
[0064] At the time of manufacturing, the outer layer furnish,
consisting of the dispersed Eucalyptus/brokelcorestock 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
furnish 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.
[0065] The center layer furnish comprised 100% northern bleached
softwood kraft fibers. This furnish was refined at an energy input
of 2 horsepower days/metric ton for dry strength development. Parez
631NC was also added to this furnish 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
furnish.
[0066] 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 furnish (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.degree. F. and
dried to final dryness of about 94-98 percent consistency.
[0067] 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).
Example 2
[0068] For this example, the improved chemical addition method
shown in FIG. 1 was used to treat a furnish with a
softening/debonding agent. The treated furnish was then used as the
outer layer furnish 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.
[0069] In Example 2, the furnish 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 furnish was blended during repulping and placed in a stock
chest at 3.5% consistency. The furnish was then treated with a
bonding agent, Parez 631NC 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 chemical/metric 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.degree. 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.
[0070] A one-ply, uncreped, through air dried tissue was made using
a three layered headbox, as described in Example 1. The furnish for
the outer two layers comprised the chemically treated 32%
consistency Eucalyptus/broke/corestock furnish 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 631NC was added for wet strength
control. Finished product dry strength control was achieved by
adjusting the ratio of center layer and outer layer furnish in the
sheet.
[0071] 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).
Example 3
[0072] For this example, the improved chemical addition method
shown in FIG. 2 was used to first treat a furnish with a bonding
agent, mechanically modify the fibers using a disperser, and then
treat the furnish with a softening/debonding agent. The chemically
treated furnish was used as one furnish 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 furnish 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 cud properties imparted
during dispersing.
[0073] In Example 3, the furnish 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 furnish was blended during repulping and placed in a stock
chest at 3.5% consistency. The furnish was then treated with a
bonding agent, Parez 631NC from Cytec Industries, Inc., at a dosage
of 1 kg./metric ton. After allowing the slurry to mix for 20
minutes, the furnish 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.degree. F. to impart curl to the fibers.
The high consistency, dispersed pulp was then stored in a chest
until sufficient quantities could be produced.
[0074] In order to treat the furnish 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 FIG. 2). The furnish 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 furnish 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.
[0075] A one-ply, uncreped, through air dried tissue was made using
a three layered headbox, as described in Example 1. The furnish for
the outer two layers comprised the chemically treated 32%
consistency Eucalyptus/broke/corestock furnish blend, which had
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 631NC was added for wet strength control.
Finished product dry strength control was achieved by adjusting the
ratio of center layer and outer layer furnish in the sheet.
[0076] 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
[0077] This example is similar to Example 3, except that 15
kg./metric ton of C-6092 softener/debonder was added to the outer
layer furnish (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.
[0078] 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).
[0079] 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 otherwise 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.
[0080] By using the improved chemical addition method, tissue
fiber/chemistry combinations can be produced at target strength
levels that could not otherwise be made using conventional chemical
addition 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
alternatives are possible such as maintaining generally constant
strength and softwood/hardwood proportion and adjusting the basis
weight.
1TABLE 1 Examples 1-4 Strength % Center Debonder Debonder Example
(g./3") Layer % Outer Layer 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
[0081] In Table 1, "Strength" refers to the geometric mean tensile
strength which is calculated for purposes of the present invention
according to the formula: {square root}{square root over
([(MDtensile)(CDtensile)])}. 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 a tissue
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.degree. 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).
[0082] The % Center Layer and % Outer Layer refer to the weight
percent of fibers in the appropriate layers.
[0083] The Debonder Add-on reflects the chemical additive that is
added to the furnish in kg./metric ton of the entire sheet. This is
calculated based on the add-on level to the outer layer furnish and
the amount of the outer layer furnish in the final sheet.
[0084] The Debonder Retained reflects the amount of chemical
additive adsorbed onto the tissue. The Debonder Retained can be
determined using the following 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 (multiplied 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 settle. The extract is
then analyzed by ultraviolet 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.
[0085] 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 ultraviolet spectrometer (Hewlett
Packard Model 8451A Diode Array Spectrophotometer, Hewlett
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.
[0086] A stock standard imidazoline solution (1000 ppm active) is
prepared: Weigh 0.1250 grams of C-6092 (80% active) into a 30 mL
beaker; transfer quantitatively to a 100 mL flask with methanol;
and dilute to mark with methanol and invert several times.
[0087] Standard imidazoline solutions (10, 30, 50, 100 ppm) are
prepared: Into four 100 mL volumetric flasks, add 1, 3, 5, and 10
mL of the 1000 ppm stock standard imidazoline solution; and dilute
to marks with methanol. The standards are 10, 30, 50 and 100 ppm,
respectively.
[0088] 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 solutions (10, 30, 50 and 100 ppm), then plot a curve of
the concentration versus absorptance. Generate a first-order
equation fit of the data.
[0089] Spiking solutions (1000 and 5000 ppm) are prepared: Weigh
out 1.250 and 6.250 grams of C-6092 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.
[0090] Generate an Add-On Correlation 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.
[0091] 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.
[0092] Spike samples with spiking solution and dry for 48 hours in
a 60 degree Celsius oven. Use volumetric pipettes. Example:
2 Volume of Spiking Solution for 5.00 gram tissue Add-on Level 1000
ppm 5000 ppm Blank 0 mL 0 mL 0.1% 5 mL -- 0.3% 15 mL -- 0.8% -- 8
mL 1.0% -- 10 mL
[0093] Add 100 mL of methanol using a pipet and seal the
containers. Place in a flatbed shaker and extract for 1/2 hour.
Remove tissue and allow the extract to settle. With a transfer
pipette, remove supernatant and fill a spectrophotometer cuvette.
Measure the absorptance at 238 nm wavelength using the UV
spectrometer. A 1 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 {fraction (1/10)} dilution blank readings for {fraction
(1/10)} dilution samples and no dilution blank readings for the no
dilution samples.
[0094] The percent extracted is then calculated from the ppm
reading from the standard curve (imidazoline) as follows:
% Extracted (no dilution)=ppm reading.times.0.1.times.100/5000.
% Extracted ({fraction (1/10)} dilution)=ppm
reading.times.0.1.times.10.ti- mes.100/5000.
[0095] 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).
[0096] 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 1/26 hour. Remove the tissue and allow to settle.
Read the extracts at 238 nm 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.
[0097] Imidazoline has a peak absorptance at 238 nm wavelength.
While blank tissue extracts do not have this peak absorptance at
238 nm, 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 correlation 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
[0098] To better illustrate the ability for the improved chemical
addition method to remove unadsorbed chemicals from the furnish 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
furnish 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.
[0099] 0.5% Addition Experiment: Step 1
[0100] 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 slurry 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.
[0101] Step 2
[0102] The remaining 1200 grams of slurry were filtered using a
Whatman 4 filter paper and Buchner funnel apparatus. This
filtration step simulates the dewatering step of the improved
chemical addition method shown in FIG. 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.
[0103] Step 3
[0104] The other half of the filter pad (approximately 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 will be
referred to as 3A.
[0105] 1.0% Addition Experiment
[0106] Steps 1-3 were repeated using a 1.0% addition level of
C-6092. The corresponding samples were coded 1B, 2B and 3B.
[0107] All samples were analyzed for C-6092 content using a
methanol extraction followed by UV spectroscopic analysis at 238 nm
and comparison of the absorptance to a known calibration curve. The
results are shown in the table below:
3 Sample No. 1A 2A 3A 1B 2B 3B C-6092 Content (%) 0.51 0.30 0.28
1.05 0.73 0.68
[0108] The results demonstrate the impact of using the improved
chemical addition method on reducing the amount of unadsorbed
debonder in the furnish. 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
conventional stuffbox chemical addition method is used this
unadsorbed chemical is free in the furnish 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.
[0109] When the C-6092 content of the 1B, 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.
[0110] 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.
[0111] 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, alternative 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 alternative process and equipment
arrangements may be employed, particularly 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.
* * * * *