U.S. patent application number 10/325473 was filed with the patent office on 2004-06-24 for bicomponent strengtheninig system for paper.
This patent application is currently assigned to Kimberly-Clark Worlwide, Inc.. Invention is credited to Branham, Kelly D., Garnier, Gil B.D., Hansen, Lacey, Lindsay, Jeffrey D., Lostocco, Michael R., Shannon, Thomas G., Siderius, Dan.
Application Number | 20040118540 10/325473 |
Document ID | / |
Family ID | 32593778 |
Filed Date | 2004-06-24 |
United States Patent
Application |
20040118540 |
Kind Code |
A1 |
Garnier, Gil B.D. ; et
al. |
June 24, 2004 |
Bicomponent strengtheninig system for paper
Abstract
The present invention is directed to a bicomponent strengthening
system and the paper webs produced with the bicomponent
strengthening system. Through use of the strengthening system,
paper webs may be produced in which the strength characteristics of
the web may be specifically tailored. The first component of the
system comprises a polymer having at least about 1.5 m-eq primary
amine functionality per gram of polymer and a molecular weight of
at least about 10,000 Daltons. The second component may be either a
polymeric anionic compound or a polymeric aldehyde functional
compound. For example, the polyamine polymer component may be a
polyvinylamine or polysaccharide having primary amine
functionality. In one embodiment, the second component may be a
cationic polymeric aldehyde functional compound. For example, the
second component may be a cationic glyoxylated polyacrylamide. In
another embodiment, the second component may be a polymeric anionic
compound comprising carboxy functionality.
Inventors: |
Garnier, Gil B.D.; (Neenah,
WI) ; Lindsay, Jeffrey D.; (Appleton, WI) ;
Shannon, Thomas G.; (Neenah, WI) ; Lostocco, Michael
R.; (Appleton, WI) ; Hansen, Lacey; (Neenah,
WI) ; Branham, Kelly D.; (Winneconne, WI) ;
Siderius, Dan; (Belmont, MI) |
Correspondence
Address: |
DORITY & MANNING, P.A.
POST OFFICE BOX 1449
GREENVILLE
SC
29602-1449
US
|
Assignee: |
Kimberly-Clark Worlwide,
Inc.
|
Family ID: |
32593778 |
Appl. No.: |
10/325473 |
Filed: |
December 20, 2002 |
Current U.S.
Class: |
162/164.1 ;
162/164.6; 162/168.2; 162/168.3 |
Current CPC
Class: |
D21H 17/42 20130101;
D21H 17/37 20130101; D21H 17/56 20130101; D21H 17/71 20130101; D21H
23/04 20130101; D21H 17/20 20130101 |
Class at
Publication: |
162/164.1 ;
162/168.2; 162/164.6; 162/168.3 |
International
Class: |
D21H 021/20; D21H
017/45; D21H 017/47 |
Claims
What is claimed is:
1. A process for forming a paper web comprising: providing a slurry
of pulp fibers; adding a first component comprising a polymer
having at least about 1.5 m-eq primary amine functionality per gram
of polymer and a molecular weight of at least about 10,000 Daltons
to the slurry of pulp fibers; adding a second component to the
slurry of pulp fibers, the second component being selected from the
group consisting of polymeric anionic compounds and polymeric
aldehyde functional compounds, wherein the second component is
added to the slurry of pulp fibers separately from the first
component; depositing the slurry of pulp fibers containing the
first and second components on a forming fabric; and drying the
slurry of pulp fibers to form a paper web, wherein the first and
second components form a bicomponent strengthening system in the
paper web.
2. A process as defined in claim 1, wherein the first and second
components form a polyelectrolyte complex in the slurry of pulp
fibers.
3. A process as defined in claim 1, wherein the first and second
components are bonded to each other in the bicomponent
strengthening system.
4. A process as defined in claim 3, wherein the first and second
components are capable of forming covalent bonds with each
other.
5. A process as defined in claim 1, wherein the first component is
a polyvinylamine.
6. A process as defined in claim 5, wherein the polyvinylamine
comprises vinylformamide units, at least about 50% of which have
been hydrolyzed to offer amine functionality.
7. A process as defined in claim 5, wherein the polyvinylamine
comprises vinylformamide units, at least about 70% of which have
been hydrolyzed to offer amine functionality.
8. A process as defined in claim 1, wherein the first component is
a polysaccharide having primary amine functionality.
9. A process as defined in claim 1, wherein the first component is
added to the slurry of pulp fibers before the second component.
10. A process as defined in claim 1, wherein the first component is
added to the slurry of pulp fibers after the second component.
11. A process as defined in claim 1, wherein the second component
comprises a cationic polymeric aldehyde functional compound.
12. A process as defined in claim 11, wherein the second component
comprises a glyoxylated polyacrylamide.
13. A process as defined in claim 1, further comprising adjusting
the pH of the slurry of pulp fibers to a pH of less than about
6.
14. A process as defined in claim 1, wherein the first component
comprises at least about 11 m-eq primary amine per gram of the
polymer.
15. A process as defined in claim 1, wherein the first component
comprises at least about 15 m-eq primary amine per gram of the
polymer.
16. A process as defined in claim 1, wherein the paper web has less
than about 70% of the initial wet tensile index remaining after
soaking in water for about one hour.
17. A process as defined in claim 1, wherein the paper web has more
than about 70% of the initial wet tensile index remaining after
soaking in water for about one hour.
18. A process as defined in claim 1, wherein the first and second
components are added to the slurry of pulp fibers in a ratio of
between about 5:1 to about 1:5.
19. A process as defined in claim 1, further comprising adjusting
the pH of the slurry of pulp fibers to a pH greater than about
6.
20. A process as defined in claim 1, wherein the second component
comprises a polymeric anionic compound having carboxy
functionality.
21. A process as defined in claim 1, wherein the first component
comprises a polymer having at least about 10 m-eq primary amine
functionality per gram of polymer and a molecular weight of at
least about 20,000 Daltons.
22. A bicomponent strengthening system for a paper web comprising a
first component comprising a polymer having at least about 1.5 m-eq
primary amine functionality per gram of polymer and a molecular
weight of at least about 10,000 Daltons and a second component
selected from the group consisting of polymeric anionic compounds
and polymeric aldehyde functional compounds, wherein the
bicomponent strengthening system develops in a slurry of pulp
fibers after the first component and the second component are
sequentially added to the slurry.
23. A bicomponent strengthening system as defined in claim 22,
wherein the first component comprises a polyvinylamine.
24. A bicomponent strengthening system as defined in claim 22,
wherein the first component comprises a polysaccharide having
primary amine functionality.
25. A bicomponent strengthening system as defined in claim 22,
wherein the first component is added to the slurry of pulp fibers
before the second component.
26. A bicomponent strengthening system as defined in claim 22,
wherein the first component is added to the slurry of pulp fibers
after the second component.
27. A bicomponent strengthening system as defined in claim 22,
wherein the second component comprises a cationic polymeric
aldehyde functional compound.
28. A bicomponent strengthening system as defined in claim 27,
wherein the second component comprises a glyoxylated
polyacrylamide.
29. A bicomponent strengthening system as defined in claim 22,
wherein the bicomponent strengthening system develops in the slurry
of pulp fibers at a pH less than about 6.
30. A bicomponent strengthening system as defined in claim 22,
wherein the first and second components form a polyelectrolyte
complex in the slurry of pulp fibers.
31. A bicomponent strengthening system as defined in claim 22,
wherein the first and second components are bonded to each
other.
32. A bicomponent strengthening system as defined in claim 31,
wherein the first and second components are capable of forming
covalent bonds with each other.
33. A bicomponent strengthening system as defined in claim 22,
wherein the first component has greater than about 11 m-eq primary
amine per gram of polymer.
34. A bicomponent strengthening system as defined in claim 22,
wherein the first component has greater than about 15 m-eq primary
amine per gram of polymer.
35. A bicomponent strengthening system as defined in claim 22,
comprising the first and second components in a ratio to each other
of between about 5:1 and about 1:5.
36. A bicomponent strengthening system as defined in claim 22,
wherein second component comprises a polymeric anionic compound
having carboxy functionality.
37. A bicomponent strengthening system as defined in claim 22,
wherein the second component comprises carboxymethyl cellulose.
38. A bicomponent strengthening system as defined in claim 22,
wherein the bicomponent strengthening system develops in the slurry
of pulp fibers at a pH greater than about 6.
39. A bicomponent strengthening system as defined in claim 22,
wherein the bicomponent strengthening system provides temporary wet
strength to the paper web.
40. A bicomponent strengthening system as defined in claim 22,
wherein the bicomponent strengthening system provides permanent wet
strength to the paper web.
41. A bicomponent strengthening system as defined in claim 22,
wherein the first component comprises a polymer having at least
about 10 m-eq primary amine functionality per gram of polymer and a
molecular weight of at least about 20,000 Daltons.
42. A bicomponent strengthening system as defined in claim 22,
wherein the first component comprises a polyvinylamine polymer
comprising partially hydrolyzed polyvinylformamide.
43. A bicomponent strengthening system as defined in claim 42,
wherein the degree of hydrolyzation of the polyvinylformamide is
about 50% or greater.
44. A bicomponent strengthening system as defined in claim 42,
wherein the degree of hydrolyzation of the polyvinylformamide is
about 70% or greater.
45. A bicomponent strengthening system as defined in claim 42,
wherein the degree of hydrolyzation of the polyvinylformamide is
about 90% or greater.
46. A method for decreasing the amount of low molecular weight
organic chlorinated compounds in the waste stream of a paper
manufacturing process comprising: providing a paper manufacturing
process, wherein said paper manufacturing process comprises the
formation of a slurry of pulp fibers and the addition of a
chlorinated strengthening agent to a paper; eliminating the
addition of said chlorinated strengthening agent from the paper
manufacturing process; adding a first component comprising a
polymer having at least about 1.5 m-eq primary amine functionality
per gram of polymer and a molecular weight of at least about 10,000
Daltons to the slurry of pulp fibers; adding a second component to
the slurry of pulp fibers, the second component being selected from
the group consisting of polymeric anionic compounds and polymeric
aldehyde functional compounds wherein the second component is added
to the slurry of pulp fibers separately from the first component;
depositing the slurry of pulp fibers containing the first and
second components on a forming fabric; and drying the slurry of
pulp fibers to form a paper web, wherein the first and second
components form a bicomponent strengthening system which replaces
the chlorinated strengthening agent in the paper web.
47. A method as defined in claim 46, wherein the chlorinated
strengthening agent comprises a polyamide-epichlorohydrin
strengthening agent.
48. A method as defined in claim 46, wherein the first component
comprises a polyvinylamine.
49. A process as defined in claim 48, wherein the polyvinylamine
has at least about 50 mole % vinylamine per gram of
polyvinylamine.
50. A process as defined in claim 48, wherein the polyvinylamine
has at least about 70 mole % vinylamine per gram of
polyvinylamine.
51. A method as defined in claim 46, wherein the first component
comprises a polysaccharide having primary amine functionality.
52. A method as defined in claim 46, wherein the first component is
added to the slurry of pulp fibers before the second component.
53. A method as defined in claim 46, wherein the first component is
added to the slurry of pulp fibers after the second component.
54. A method as defined in claim 46, wherein the second component
is a cationic polymeric aldehyde functional compound.
55. A method as defined in claim 54, wherein the second component
is a glyoxylated polyacrylamide.
56. A method as defined in claim 46, further comprising adjusting
the pH of the slurry of pulp fibers to a pH less than about 6.
57. A method as defined in claim 46, further comprising adjusting
the pH of the slurry of pulp fibers to a pH greater than about
6.
58. A method as defined in claim 46, wherein the first component
has greater than about 11 m-eq primary amine per gram of
polymer
59. A method as defined in claim 46, wherein the first component
has greater than about 15 m-eq primary amine per gram of
polymer.
60. A method as defined in claim 46, wherein the first and second
components are added to the slurry of pulp fibers in a ratio of
between about 5:1 to about 1:5.
61. A method as defined in claim 46, wherein the second component
comprises a polymeric anionic compound having carboxy
functionality.
62. A paper product comprising: a paper web formed from a slurry of
papermaking fibers; and a bicomponent strengthening system
comprising a first component comprising a polymer having at least
about 1.5 m-eq primary amine functionality per gram of polymer and
a molecular weight of at least about 10,000 Daltons and a second
component selected from the group consisting of polymeric anionic
compounds and polymeric aldehyde functional compounds, wherein the
first component and the second component are sequentially added to
the slurry of papermaking fibers.
63. The paper product of claim 62, wherein the paper web has a bulk
greater than about 2 cc/g.
64. The paper product of claim 62, wherein the first component
comprises a polymer having at least about 10 m-eq primary amine
functionality per gram of polymer and a molecular weight of at
least about 20,000 Daltons.
65. The paper product of claim 62, wherein the paper web has less
than about 70% of the initial wet tensile index remaining after
soaking in water for about one hour.
66. The paper product of claim 65, wherein the paper web has a dry
tensile index greater than about 22 Nm/g.
67. The paper product of claim 65, wherein the paper web has a dry
tensile index greater than about 25 Nm/g.
68. The paper product of claim 65, wherein the paper web has a wet
tensile index less than about 2 Nm/g after soaking in water for
about one hour.
69. The paper product of claim 65, wherein the paper web has less
than about 60% of the initial wet tensile index remaining after
soaking in water for about one hour.
70. The paper product of claim 62, wherein the paper web has more
than about 70% of the initial wet tensile index remaining after
soaking in water for about one hour, wherein the paper web does not
comprise any polyamine epichlorohydrin strengthening agents.
71. The paper product of claim 70, wherein the paper web has a dry
tensile index greater than about 20 Nm/g.
72. The paper product of claim 71, wherein the paper web has a dry
tensile index greater than about 25 Nm/g.
73. The paper product of claim 70, wherein the paper web has more
than about 80% of the initial wet tensile index remaining after
soaking in water for about one hour.
74. The paper product of claim 62, wherein the first component
comprises a polyvinylamine.
75. The paper product of claim 62, wherein the first component
comprises a polysaccharide having primary amine functionality.
76. The paper product of claim 62, wherein the second component
comprises a cationic polymeric aldehyde functional compound
77. The paper product of claim 76, wherein the second component
comprises a glyoxylated polyacrylamide.
78. The paper product of claim 62, wherein the second component
comprises a polymeric anionic compound having carboxy
functionality.
79. The paper product of claim 62, wherein the second component
comprises carboxymethyl cellulose.
80. The paper product of claim 62, wherein the paper product has a
bulk greater than about 5 cc/g.
81. The paper product of claim 62, wherein the paper product has a
basis weight between about 5 and about 200 gsm.
82. The paper product of claim 62, wherein the paper product
comprises a multi-layered paper web, wherein the bicomponent
strengthening system is added to one or more layers of the paper
web.
83. The paper product of claim 82, wherein the multi-layered paper
web comprises a layer comprising soft wood pulp and a layer
comprising hard wood pulp, wherein the bicomponent strengthening
system is added to the layer comprising soft wood pulp.
Description
BACKGROUND OF THE INVENTION
[0001] In the art of tissue making and papermaking in general, many
additives have been proposed for specific purposes, such as
increasing wet strength, improving softness, or control of wetting
properties. For instance, in the past, wet strength agents have
been added to paper products in order to increase the strength or
otherwise control the properties of the product when contacted with
water and/or when used in a wet environment. For example, wet
strength agents are added to paper towels so that the paper towel
may be used to wipe and scrub surfaces after being wetted without
the towel disintegrating. Wet strength agents are also added to
facial tissues to prevent the tissues from tearing when contacting
fluids. In some applications, wet strength agents are also added to
bath tissues to provide strength to the tissues during use. When
added to bath tissues, however, the wet strength agents should not
prevent the bath tissue from disintegrating when dropped in a
commode and flushed into a sewer line. Wet strength agents added to
bath tissues are sometimes referred to as temporary wet strength
agents since they only maintain wet strength in the tissue for a
specific length of time.
[0002] Although great advancements have been made in providing
strength properties to paper products, various needs still exist to
increase strength properties in certain applications, as well as to
allow for variability in the strength characteristics provided to a
paper web by a strength agent.
[0003] In the production of permanent wet strength agents such as
the series of Kymene.RTM. products from Hercules, Inc. (Wilmington,
Del.), chlorinated organic materials are commonly used.
Epichlorohydrin, for example, is commonly used as a raw material,
and the reaction chemistry employed typically generates other
chlorinated organic materials such as 1,3-dichloro-2-propanol (DCP)
and 3-chloro-1,2-propanediol (CPD). Many other wet strength
materials are also chlorinated or comprise chlorine byproducts,
such as the N-chlorinated polymers described in European Patent
Application 289,823, published Nov. 9, 1988; or the
aminopolyamide-epichlorohydrin acid salt resins of U.S. Pat. No.
5,189,142, issued Feb. 23, 1993 to Devore, et al. or U.S. Pat. No.
5,364,927, issued Nov. 15, 1994 to Devore, et al.; or the resins of
U.S. Pat. No. 6,222,006, issued Apr. 24, 2001 to Kokko, et al.,
which are formed by reaction of an epihalohydrin and an end-capped
polyaminamide polymer; or the epichlorohydrin-based resins of U.S.
Pat. No. 5,644,021, issued Jul. 1, 1997 to Maslanka.
[0004] Recently, interest has been growing for methods of removal
of chlorinated residuals from wet-strength paper additives. Methods
under consideration include, for example, using microorganisms and
enzymes, as discussed at a symposium on "The Role of Biotechnology
in Industrial Sustainability," May 16-17, 2002, Antwerp, Belgium.
This presentation described efforts to reduce such chlorinated
byproducts, including the use of bacteria capable of metabolizing
such byproducts to less harmful materials. Others have sought other
means to remove some of the chlorinated organic materials often
found in wet strength resins. However, given the increasing
environmental concerns about halogenated organic compounds, there
is still a need to further reduce or eliminate the use of
chlorinated compounds in wet strength resins or in the production
of wet strength resins.
SUMMARY OF THE INVENTION
[0005] The present invention is directed to a bicomponent
strengthening system and a process for producing paper webs
including the bicomponent strengthening system as well as the webs
produced by the process. In one embodiment, the present invention
is directed to a paper web in which the strength characteristics of
the web may be specifically tailored through use of a bicomponent
strengthening system.
[0006] In general, the process of the present invention includes
providing a slurry of pulp fibers and treating the fibers with a
bicomponent strengthening system prior to forming a web from the
fibers. The first component of the strengthening system comprises a
polymer having at least about 1.5 m-eq primary amine functionality
per gram of polymer and a molecular weight of at least about 10,000
Daltons. The second component may be either a polymeric anionic
compound or a polymeric aldehyde functional compound.
[0007] In one embodiment, the polyamine polymer may have at least
about 11 m-eq primary amine functionality per gram of polymer. In
another embodiment, the polyamine polymer may have at least about
15 m-eq primary amine functionality per gram of polymer. For
example, the polyamine polymer may have at least about 10 m-eq
primary amine functionality and a molecular weight of about 20,000
Daltons or greater.
[0008] In one embodiment, the polyamine polymer component may be a
polyvinylamine. For example, the polyamine polymer may be a
polyvinylamine comprising vinylformamide units, with at least about
50% of the vinylformamide units hydrolyzed to offer amine
functionality. In one embodiment, at least about 70% of the
vinylformamide units may be hydrolyzed to offer amine
functionality. In another embodiment, at least about 90% of the
vinylformamide units may be hydrolyzed to offer amine
functionality.
[0009] In another embodiment, the polyamine polymer component may
be a polysaccharide having primary amine functionality.
[0010] In one embodiment, the second component may be a cationic
polymeric aldehyde functional compound. For example, the second
component may be a cationic glyoxylated polyacrylamide. In another
embodiment, the second component may be a polymeric anionic
compound comprising carboxy functionality. In one embodiment, the
second component may be carboxymethyl cellulose.
[0011] Of importance, the two components are added to the pulp
slurry separately, though depending on desired strength
characteristics of the web, either the first or the second
component may be added to the slurry before the other.
[0012] The pH of the slurry may be adjusted during the process. For
example, the pH of the slurry may be adjusted to an acidic pH, such
as about 6 or less in one embodiment. In another embodiment,
however, the pH may be adjusted to greater than about 6.
[0013] The two components may be added to the slurry in a ratio to
each other anywhere from about a 1:5 ratio to about a 5:1 ratio, as
desired.
[0014] The bicomponent strengthening system of the present
invention may be adjusted so as to provide either temporary or
permanent wet strength to a paper web. For instance, the
bicomponent strengthening system may provide temporary wet strength
to a paper web such that the paper web may have less than about 70%
of the initial wet tensile index remaining after soaking in water
for about one hour. In one embodiment, the paper web may have less
than about 60% of the initial wet tensile index remaining after
soaking in water for about one hour. For example, in one
embodiment, the bicomponent strengthening system of the present
invention can act as a temporary wet strength agent and the paper
web thus produced may have a wet tensile index after soaking in
water for about one hour of less than about 2 Nm/g.
[0015] In an alternative embodiment, the bicomponent strengthening
system may provide permanent wet strength to a paper web such that
the paper web may have more than about 70% of the initial wet
tensile index remaining after soaking in water for about one hour.
In one embodiment, the paper web may have more than about 80% of
the initial wet tensile index remaining after soaking in water for
about one hour.
[0016] In general, the process of the present invention includes
providing a slurry of pulp fibers, sequentially adding the
components of the strengthening system to the slurry of pulp
fibers, depositing the slurry of pulp fibers containing the two
components on a forming fabric, and drying the slurry to form a
paper web.
[0017] In one embodiment, the paper web of the present invention
may have a bulk greater than about 2 cc/g. For example, the paper
web may have a bulk greater than about 5 cc/g.
[0018] The dry tensile index of the paper web can be greater than
about 20 Nm/g in one embodiment. In another embodiment, the dry
tensile index of the paper web can be greater than about 22 Nm/g.
In yet another embodiment, the dry tensile index can be greater
than about 25 Nm/g.
[0019] In general, the basis weight of the paper webs of the
present invention can be any desired basis weight. For instance, in
one embodiment, the paper web may have a basis weight between about
5 and about 200 gsm.
[0020] In one embodiment, the paper web of the present invention
may be a multi-layer paper web, and the bicomponent strengthening
system may be added to one or more layers of the web. For example,
in one embodiment, a multi-layered paper web may be produced having
a layer comprised primarily of soft wood fibers and a layer
comprised primarily of hard wood fibers, wherein the bicomponent
strengthening system is added to the layer comprised primarily of
soft wood fibers.
[0021] The paper webs of the present invention may be converted and
used as is to form a single ply paper product, such as a single ply
bath, facial or towel product or they may be plied together,
converted and used to form a multi-ply paper product, such as a
multi-ply bath, facial or towel product. Any number of plies may be
used.
[0022] In one embodiment, the present invention is directed to a
method for decreasing the amount of low molecular weight organic
chlorinated compounds in the waste stream of a paper manufacturing
process. In this embodiment, the invention includes eliminating the
addition of chlorinated strengthening agents to a paper
manufacturing process, and replacing the chlorinated strengthening
agents with the bicomponent strengthening system of the present
invention. For example, in one embodiment, the bicomponent
strengthening system of the present invention can replace polyamide
epichlorohydrin strengthening agents in a paper manufacturing
process.
Definitions and Test Methods
[0023] As used herein, a material is said to be "absorbent" if it
may retain an amount of water equal to at least about 100% of its
dry weight as measured by the test for Intrinsic Absorbent Capacity
given below (i.e., the material has an Intrinsic Absorbent Capacity
of at about 1 or greater). For example, the absorbent materials
used in the absorbent members of the present invention may have an
Intrinsic Absorbent Capacity of about 2 or greater, more
specifically about 4 or greater, more specifically still about 7 or
greater, and more specifically still about 10 or greater, with
exemplary ranges of from about 3 to about 30 or from about 4 to
about 25 or from about 12 to about 40.
[0024] "Papermaking fibers," as used herein, include all known
cellulosic fibers or fiber mixes comprising cellulosic fibers.
Fibers suitable for making the webs of this invention comprise any
natural or synthetic cellulosic fibers including, but not limited
to non-woody fibers, such as cotton, abaca, kenaf, sabai grass,
flax, esparto grass, straw, jute hemp, bagasse, milkweed floss
fibers, and pineapple leaf fibers; and woody fibers such as those
obtained from deciduous and coniferous trees, including softwood
fibers, such as northern and southern softwood kraft fibers;
hardwood fibers, such as eucalyptus, maple, birch, and aspen. Woody
fibers may be prepared in high-yield or low-yield forms and may be
pulped in any known method, including kraft, sulfite, high-yield
pulping methods and other known pulping methods. Fibers prepared
from organosolv pulping methods may also be used. A portion of the
fibers, such as up to about 50% or less by dry weight, or from
about 5% to about 30% by dry weight, may be synthetic fibers such
as rayon, polyolefin fibers, polyester fibers, bicomponent
sheath-core fibers, multi-component binder fibers, and the like. An
exemplary polyethylene fiber is Pulpex.RTM., available from
Hercules, Inc. (Wilmington, Del.). Any known bleaching method may
be used. Synthetic cellulose fiber types include rayon in all its
varieties and other fibers derived from viscose or chemically
modified cellulose. Chemically treated natural cellulosic fibers
may be used such as mercerized pulps, chemically stiffened or
crosslinked fibers, or sulfonated fibers. For good mechanical
properties in using papermaking fibers, it may be desirable that
the fibers be relatively undamaged and largely unrefined or only
lightly refined. While recycled fibers may be used, virgin fibers
are generally useful for their mechanical properties and lack of
contaminants. Mercerized fibers, regenerated cellulosic fibers,
cellulose produced by microbes, rayon, and other cellulosic
material or cellulosic derivatives may be used. Suitable
papermaking fibers may also include recycled fibers, virgin fibers,
or mixes thereof. In certain embodiments capable of high bulk and
good compressive properties, the fibers may have a Canadian
Standard Freeness of at least about 200, more specifically at least
about 300, more specifically still at least about 400, and most
specifically at least about 500.
[0025] As used herein, "high yield pulp fibers" are those
papermaking fibers of pulps produced by pulping processes providing
a yield of about 65 percent or greater, more specifically about 75
percent or greater, and still more specifically from about 75 to
about 95 percent. Yield is the resulting amount of processed fiber
expressed as a percentage of the initial wood mass. High yield
pulps include bleached chemithermomechanical pulp (BCTMP),
chemithermomechanical pulp (CTMP), pressure/pressure
thermomechanical pulp (PTMP), thermomechanical pulp (TMP),
thermomechanical chemical pulp (TMCP), high yield sulfite pulps,
and high yield Kraft pulps, all of which contain fibers having high
levels of lignin. Characteristic high-yield fibers may have lignin
content by mass of about 1% or greater, more specifically about 3%
or greater, and still more specifically from about 2% to about 25%.
Likewise, high yield fibers may have a kappa number greater than
20, for example. In one embodiment, the high-yield fibers are
predominately softwood, such as northern softwood or, more
specifically, northern softwood BCTMP.
[0026] As used herein, the term "cellulosic" is meant to include
any material having cellulose as a major constituent, and
specifically comprising about 50 percent or more by weight of
cellulose or cellulose derivatives. Thus, the term includes cotton,
typical wood pulps, non-woody cellulosic fibers, cellulose acetate,
cellulose triacetate, rayon, viscose fibers, thermomechanical wood
pulp, chemical wood pulp, debonded chemical wood pulp, lyocell and
other fibers formed from solutions of cellulose in NMMO, milkweed,
or bacterial cellulose. Fibers that have not been spun or
regenerated from solution may be used exclusively, if desired, or
at least about 80% of the web may be free of spun fibers or fibers
generated from a cellulose solution.
[0027] As used herein, "bulk" and "density," unless otherwise
specified, are based on an oven-dry mass of a sample and a
thickness measurement made at a load of 0.34 kPa (0.05 psi) with a
7.62-cm (three-inch) diameter circular platen. Details for
thickness measurements and other forms of bulk are described
hereafter. As used herein, "Debonded Void Thickness" is a measure
of the void volume at a microscopic level along a section of the
web, which may be used to discern the differences between densified
and undensified portions of the tissue or between portions that
have been highly sheared and those that have been less sheared.
[0028] As used herein, the term "hydrophobic" refers to a material
having a contact angle of water in air of at least 90 degrees. In
contrast, as used herein, the term "hydrophilic" refers to a
material having a contact angle of water in air of less than 90
degrees. As used herein, the term "surfactant" includes a single
surfactant or a mixture of two or more surfactants. If a mixture of
two or more surfactants is employed, the surfactants may be
selected from the same or different classes, provided only that the
surfactants present in the mixture are compatible with each other.
In general, the surfactant may be any surfactant known to those
having ordinary skill in the art, including anionic, cationic,
nonionic and amphoteric surfactants. Examples of anionic
surfactants include, among others, linear and branched-chain sodium
alkylbenzenesulfonates; linear and branched-chain alkyl sulfates;
linear and branched-chain alkyl ethoxy sulfates; and silicone
phosphate esters, silicone sulfates, and silicone carboxylates such
as those manufactured by Lambent Technologies, located in Norcross,
Ga. Cationic surfactants include, by way of illustration, tallow
trimethylammonium chloride and, more generally, silicone amides,
silicone amido quaternary amines, and silicone imidazoline
quaternary amines. Examples of nonionic surfactants, include, again
by way of illustration only, alkyl polyethoxylates; polyethoxylated
alkylphenols; fatty acid ethanol amides; dimethicone copolyol
esters, dimethiconol esters, and dimethicone copolyols such as
those manufactured by Lambent Technologies; and complex polymers of
ethylene oxide, propylene oxide, and alcohols. One exemplary class
of amphoteric surfactants is the silicone amphoterics manufactured
by Lambent Technologies (Norcross, Ga.).
[0029] As used herein, "softening agents," sometimes referred to as
"debonders," may be used to enhance the softness of the tissue
product and such softening agents may be incorporated with the
fibers before, during or after disperging. Such agents may also be
sprayed, printed, or coated onto the web after formation, while
wet, or added to the wet end of the tissue machine prior to
formation. Suitable agents include, without limitation, fatty
acids, waxes, quaternary ammonium salts, dimethyl dihydrogenated
tallow ammonium chloride, quaternary ammonium methyl sulfate,
carboxylated polyethylene, cocamide diethanol amine, coco betaine,
sodium lauryl sarcosinate, partly ethoxylated quaternary ammonium
salt, distearyl dimethyl ammonium chloride, polysiloxanes and the
like. Examples of suitable commercially available chemical
softening agents include, without limitation, Berocell 596 and 584
(quaternary ammonium compounds) manufactured by Eka Nobel Inc.,
Adogen 442 (dimethyl dihydrogenated tallow ammonium chloride)
manufactured by Sherex Chemical Company, Quasoft 203 (quaternary
ammonium salt) manufactured by Quaker Chemical Company, and Arquad
2HT-75 (di-hydrogenated tallow) dimethyl ammonium chloride)
manufactured by Akzo Chemical Company. Suitable amounts of
softening agents will vary greatly with the species selected and
the desired results. Such amounts may be, without limitation, from
about 0.05 to about 1 weight percent based on the weight of fiber,
more specifically from about 0.25 to about 0.75 weight percent, and
still more specifically about 0.5 weight percent.
[0030] Unless otherwise specified, tensile strengths are measured
according to Tappi Test Method T 494 om-88 for tissue, modified in
that a tensile tester is used having a 3-inch jaw width, a jaw span
of 4 inches, and a crosshead speed of 10 inches per minute. Wet
strength is measured in the same manner as dry strength except that
the tissue sample is folded without creasing about the midline of
the sample, held at the ends, and dipped in deionized water for
about 0.5 seconds to a depth of about 0.5 cm to wet the central
portion of the sample, whereupon the wetted region is touched for
about 1 second against an absorbent towel to remove excess drops of
fluid, and the sample is unfolded and set into the tensile tester
jaws and immediately tested. The sample is conditioned under TAPPI
conditions (50% RH, 22.7.degree. C.) before testing. Generally 5
samples are combined for wet tensile testing to ensure that the
load cell reading is in an accurate range. Unless otherwise
specified, the dry and wet tensile properties of machine-made webs
are taken in the machine direction of the web.
[0031] Tensile index (TI) is a measure of tensile strength
normalized for basis weight of the web tested in both dry and wet
states. Tensile strength may be converted to tensile index by
converting tensile strength determined in units of grams of force
per 3 inches to units of Newtons per meter and dividing the result
by the basis weight in grams per square meter of the tissue, to
give the tensile index in Newton-meters per gram (Nm/g).
[0032] Wet/Dry TI Ratio (% WeVDry TI) is the wet TI divided by the
dry TI multiplied by 100.
[0033] % Wet TI 1-hr is the ratio of wet TI remaining after 1-hr
soaking versus immediate wet TI. This is a measure of wet strength
permanence. For purposes of this disclosure, temporary wet strength
agents are herein defined as those agents which lose more than
about 30% of the wet TI after 1 hour, i.e. those strength
agents-wherein % wet TI 1-hr is less than about 70%.
[0034] Peak Stretch(%) is the percent elongation in the dry state
at maximum load during the tensile strength test.
[0035] TEA(J/m.sup.2) is the total-energy-absorbed in the dry state
at maximum load during the tensile strength test.
[0036] Elastic Modulus E(kg.sub.f) is the elastic modulus
determined in the dry state and is expressed in units of kilograms
of force. Tappi conditioned samples with a width of 3 inches are
placed in tensile tester jaws with a gauge length (span between
jaws) of 2 inches. The jaws move apart at a crosshead speed of 25.4
cm/min and the slope is taken as the least squares fit of the data
between stress values of 50 grams of force and 100 grams of force,
or the least squares fit of the data between stress values of 100
grams of force and 200 grams of force, whichever is greater. If the
sample is too weak to sustain a stress of at least 200 grams of
force without failure, an additional ply is repeatedly added until
the multi-ply sample may withstand at least 200 grams of force
without failure.
BRIEF DESCRIPTION OF THE FIGURES
[0037] A full and enabling disclosure of the present invention,
including the best mode thereof to one of ordinary skill in the
art, is set forth more particularly in the remainder of the
specification, including reference to the accompanying figure in
which:
[0038] FIG. 1 is a table describing physical characteristics of
exemplary polyvinylamines suitable for the bicomponent
strengthening system of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0039] In general, the present invention is directed to a novel
bicomponent strengthening system for a paper web that may be
particularly tailored to meet the strengthening requirements of a
paper product. More specifically, the first component of the
strengthening system is a polymer containing primary amine
functionality and the second component is one that may complex
and/or react with the first component to form the strengthening
system in a paper web.
[0040] In the process of the present invention, the first and
second components are added separately to a slurry of pulp fibers
in order to improve the strength properties of a web formed from
the pulp fibers. A number of process parameters may be varied in
forming the bicomponent strengthening system such that the strength
characteristics of the formed paper web may be specifically
tailored to design specifications. For instance, the strength
characteristics of the paper web may be varied depending on which
component is added to the pulp slurry first. Strength
characteristics may also be varied depending on pH of the pulp
slurry, the amount of amine functionality contained on the first
component, the molecular weight of the first component, the
specific amine-containing polymer used, the functionality of the
second component, the ionic nature of the second component, the
nature of the association formed between the two components, among
other possible variable parameters.
[0041] The bicomponent strengthening system of the present
invention may be tailored so as to have particular dry strength
characteristics as well as particular wet strength characteristics.
Of particular benefit, the bicomponent strengthening system of the
present invention may be tailored so as to be either a temporary
wet strength agent or a permanent wet strength agent, as desired.
For example in one embodiment, the bicomponent strength system may
be tailored so as to function as a permanent wet strength agent,
thereby rendering unnecessary the use of previously known wet
strength agents. This may be particularly beneficial in those
embodiments wherein the bicomponent strengthening system is used to
replace wet strength agents used in the past which have been known
to increase the levels of pollutants, particularly low molecular
weight organic chlorinated compounds, in the effluent of paper
making processes.
[0042] Various different primary amine polymers and chemical
compounds may be combined in accordance with the present invention.
Examples of suitable primary amine-containing polymers include
various polyvinylamines, polysaccharides having primary amine
functionality, and the like. Examples of suitable agents for use as
the second component in the biocomponent system include polymeric
anionic compounds, polymeric aldehyde functional compounds,
surfactants, mixtures thereof, and the like.
[0043] Cellulosic webs prepared in accordance with the present
invention may be used for a wide variety of applications. For
instance, products made according to the present invention include
tissue products such as facial tissues or bath tissues, paper
towels, wipers, and the like. Webs made according to the present
invention may also be used in diapers, sanitary napkins, wet wipes,
composite materials, molded paper products, paper cups, paper
plates, and the like.
[0044] The present invention will now be discussed in greater
detail. Each of the components used in the present invention will
first be discussed followed by a discussion of the process used to
form the bicomponent strengthening system and paper products in
accordance with the present invention.
[0045] Polymers Having Primary Amine Functionality
[0046] The first component of the present invention may be any
polymer having a suitable amount of primary amine functionality
combined with a suitably high molecular weight. In particular, the
first component of the strengthening system should have at least
about 2 m-eq primary amine per gram of polymer. For example, the
first component may have greater than about 11 m-eq primary amine
per gram of polymer. In one embodiment, the first component may
have at least about 15 m-eq per gram of polymer, such as about 19
m-eq primary amine per gram of polymer, or even greater amounts of
amine functionality.
[0047] In addition, the first component should have a molecule
weight of at least about 10,000 Daltons. For instance, in one
embodiment, the first component may have a molecular weight of at
least about 20,000 Daltons and at least about 10 m-eq primary amine
per gram of polymer. Suitable polyamine compounds can, in certain
embodiments, have a molecular weight range of about 10,000 to
1,000,000 Daltons, though polyamine compounds having any practical
molecular weight range may be used. For example, polyamine polymers
may have a molecular weight range of from about 5,000 to about
5,000,000, more specifically from about 20,000 to about 3,000,000,
and most specifically from about 50,000 to about 500,000 may be
used. For example, polyamines having molecular weights of about
50,000 to about 300,000 having molecular weights of about 40,000 to
about 750,000 may be used.
[0048] Possible primary amine-containing polymers may include
polyvinylamines, polyallylamines, polyethyleneimines, and the like.
In one embodiment, the first component of the present invention may
include polysaccharides having primary amine functionality.
[0049] In general, any suitable polyvinylamine may be used in the
present invention. For instance, the polyvinylamine polymer may be
a homopolymer or may be a copolymer.
[0050] Useful copolymers of polyvinylamine include those prepared
by hydrolyzing polyvinylformamide to various degrees to yield
copolymers of polyvinylformamide and polyvinylamine. Exemplary
materials include the Catiofast.RTM. series sold commercially by
BASF (Ludwigshafen, Germany). FIG. 1 describes the physical
characteristics of several different Catiofast.RTM. polyvinylamines
which may be suitable as the first component of the bicomponent
strengthening system.
[0051] The degree of hydrolysis of polyvinylamines used in the
system formed by hydrolysis of polyvinylformamide, copolymer of
polyvinylformamide, or derivatives thereof, may be about 10% or
greater with exemplary ranges of from about 30% to about 100%, or
from about 50% to about 95%. Characteristics of exemplary
polyvinylamines formed by hydrolysis of polyvinylformamide are
described in the table, below.
1 M-eq primary Mole % Mole % Repeating amine per vinylamine
vinylformamide unit Mw gram polymer 90 10 45.8 19.7 80 20 48.6 16.5
70 30 51.4 13.6 60 40 54.2 11.1 50 50 57 8.8 40 60 59.8 6.7 30 70
62.6 4.8 20 80 65.4 3.1 10 90 68.2 1.5
[0052] Polyvinymine compounds that may be used in the present
invention include copolymers of N-vinylformamide and other groups
such as vinyl acetate or vinyl opionate, where at least a portion
of the vinylformamide groups have been hydrolyzed. Copolymers of
polyvinylamine and polyvinyl alcohol may also be utilized.
[0053] Other polymers having primary amine functionality may also
be utilized. One exemplary polysaccharide having primary amine
functionality that may be used in the first component of the
present invention is Chitosan, which is an amine-containing
polysaccharide developed from Chitin, a naturally occurring
polysaccharide extracted from recycled crab and shrimp shells. As
with many of the other possible components suitable for the present
invention, Chitosan will not add organic chlorinated compounds to
the waste stream of a paper producing facility, and is safely
biodegradable.
[0054] Polymeric Anionic Compounds
[0055] As stated above, according to the present invention, a
polyamine polymer is sequentially combined with a second component
in a pulp furnish and the biocomponent strength system may then
develop. In one embodiment, the polyamine polymer may be combined
with a polymeric anionic compound. When sequentially added to a
pulp furnish, the polyamine and the polymeric anionic compound not
only improve strength such as wet strength, but the process
parameters and particular components may be tailored, offering
increased control over the surface chemistry and wettability of the
web formed from the pulp furnish.
[0056] In the past, polymeric anionic compounds have been used in
wet strength applications. The combination of a polymeric anionic
compound with a polyamine in a pulp furnish, however, has produced
unexpected benefits and advantages. For instance, pulp treated with
a polymeric anionic compound alone may have a slight increase in
wet strength. Likewise, webs treated with a polyamine such as a
polyvinylamine will also show an increase in wet strength. However,
it has been discovered that sequential addition of both
ingredients, a polymeric anionic compound and polyamine polymer to
a pulp furnish, may result not only in enhanced wet and dry
strength, but may also be tailored so as to provide specific
characteristics to the paper web produced by the process. Thus,
according to the present invention, it has been discovered that
specific values for wet strength, dry strength, amount of wet
strength remaining over a period of time (permanence of the wet
strength), and the like may be varied in a paper product by varying
the process parameters while employing the same or different
components in the strengthening system.
[0057] This effect offers additional control over the properties of
the treated web. Thus, wet and dry tensile properties may be
controlled by adjusting parameters such as the relative amounts of
polyamine and polymeric anionic compound, the order of addition of
the polymers to the fiber furnish, the pH of the fiber furnish, the
charge ratio of the polymers, and the like.
[0058] Polymeric anionic compounds, as used herein, are polymers
having repeating units containing two or more anionic functional
groups that may bond to hydroxyl groups of cellulosic fibers. Such
compounds may cause inter-fiber crosslinking between individual
cellulose fibers. In one embodiment, the functional groups are
carboxylic acids, anhydride groups, or the salts thereof. In one
embodiment, the repeating units include two carboxylic acid groups
on adjacent atoms, particularly adjacent carbon atoms, wherein the
carboxylic acid groups are capable of forming cyclic anhydrides and
specifically 5-member ring anhydrides. This cyclic anhydride, in
the presence of a cellulosic hydroxyl group at elevated
temperature, forms ester bonds with the hydroxyl groups of the
cellulose. Polymers, including copolymers, terpolymers, block
copolymers, and homopolymers, of maleic acid represent one
embodiment, including copolymers of acrylic acid and maleic acid.
Polyacrylic acid and associated copolymers may be useful for the
present invention. In one embodiment, carboxy functionality may be
added to a polymer to form the polymeric anionic compound. For
example, acrylic acid functionality may be added to a glyoxylated
polyacrylamide to form a suitable polymeric anionic compound. In
another example, carboxymethylcellulose may be utilized. In one
embodiment, the polymeric anionic compound is a
poly-1,2-diacid.
[0059] Exemplary polymeric anionic compounds include the
ethylene/maleic anhydride copolymers described in U.S. Pat. No.
4,210,489 to Markofsky, herein incorporated by reference.
Vinyl/maleic anhydride copolymers and copolymers of epichlorohydrin
and maleic anhydride or phthalic anhydride are other examples.
Copolymers of maleic anhydride with olefins may also be considered,
including poly(styrene/maleic) anhydride. Copolymers and
terpolymers of maleic anhydride may also be used. Examples of
polymeric anionic compounds include terpolymers of maleic acid,
vinyl acetate, and ethyl acetate known as BELCLENE@ DP80 (Durable
Press 80) and BELCLENE@ DP60 (Durable Press 60), from FMC
Corporation (Philadelphia, Pa.).
[0060] Other polymers of value may include maleic anhydride-vinyl
acetate polymers, polyvinyl methyl ether-maleic anhydride
copolymers, such as the commercially available Gantrez-AN119 from
International Specialty Products (Calvert City, Ky.), isopropenyl
acetate-maleic anhydride copolymers, itaconic acid-vinyl acetate
copolymers, methyl styrene-maleic anhydride copolymers,
styrene-maleic anhydride copolymers, methylmethacrylate-maleic
anhydride copolymers, and the like.
[0061] Other terminal anionic acid groups that may be on the
polymer include sulfonic acid, sulfinic acid, phosphonic acids, and
the like. In addition to anhydrides, as discussed above, acid
halides could be utilized, i.e. R-COX polymers where X is a halogen
including fluorine, chlorine, bromine, or iodine.
[0062] The polymeric anionic compound may have any viscosity
provided that the compound may be added to the pulp furnish. In
some embodiments, the polymeric anionic compound may exhibit low or
not solubility in water. In these particular embodiments, the
polymeric anionic compound may be used in conjunction with a
cosolvent or alternatively may be subjected to a period of
solubilization at a high pH prior to addition to the pulp
furnish.
[0063] In one embodiment, the polymeric anionic compound has a
relatively low molecular weight, though polymeric anionic compounds
according to the present invention may have any suitable molecular
weight. For instance, in one embodiment, a carboxymethyl cellulose
having a molecular weight ranging from about 70,000 Daltons to
about 700,000 Daltons may be utilized. Although other molecular
weight ranges are also encompassed by the second component of the
strengthening system, for example, greater than about 10,000
Daltons. In one embodiment, the second component may have a
molecular weight from about 10,000 Daltons to about 10,000,000
Daltons. As used herein, molecular weight refers to the weight
average molecular weight determined by gel permeation
chromatography (GPC) or an equivalent method.
[0064] The polymeric anionic compound may be a copolymer or
terpolymer to improve flexibility of the molecule relative to the
homopolymer alone. Improved flexibility of the molecule may be
manifest by a reduced glass transition temperature as measured by
differential scanning calorimetry.
[0065] Another useful aspect of the polymeric anionic compounds of
the present invention is that relatively high pH values may be
used, making the compound more suitable for neutral and alkaline
papermaking processes and more suitable for a variety of processes,
machines, and fiber types. In particular, polymeric anionic
compound solutions may have a pH above about 3, more specifically
above about 4, more specifically still above about 6.5, and in one
embodiment, above about 10. In fact, paper webs including
bicomponent strengthening systems formed in alkaline conditions
according to the present invention may have very high wet and dry
tensile indices. For example, a paper web including a
polyvinylamine and a polymeric anionic compound including acrylic
acid functionality bicomponent strengthening system developed at a
pH of about 6.8 or greater may have a dry tensile index of at least
about 18 Nm/g. Moreover, when the polyvinylamine component is added
to the pulp slurry before the polymeric anionic component, the dry
tensile index of the product may be higher yet, in one embodiment
greater than about 20 Nm/g.
[0066] In addition, the bicomponent strengthening system of the
present invention may provide either temporary wet strength or
permanent wet strength to a web by varying the process conditions
while using identical components. For example, in one embodiment, a
polyvinylamine and a polymeric anionic compound including acrylic
acid functionality may be sequentially added to a pulp slurry at
alkaline conditions and may form a bicomponent strengthening system
which may provide permanent wet strength to the paper web, whereas
the same components added to a pulp slurry at acidic conditions may
provide temporary wet strength to the paper web.
[0067] Without wishing to be bound by theory, it is believed that a
polyamine polymer containing amino groups may react in solution
with the polymeric anionic compound, particularly with the carboxyl
groups to yield a polyelectrolyte complex (sometimes termed a
coacervate) that upon heating, may react to form amide bonds that
crosslink the two molecules, leaving a hydrophobic backbone. Other
carboxy groups on the polymeric anionic compound may form ester
cross links with hydroxyl groups on the cellulose, while amino
groups on the polyamine polymer may form hydrogen bonds with
hydroxyl groups on the cellulose or covalent bonds with functional
groups on the cellulose, such as aldehyde groups that may have been
added by enzymatic or chemical treatment, or with carboxyl groups
on the cellulose that may have been provided by chemical treatment
such as certain forms of bleaching or ozonation. The result is a
treated web with added cross linking for wet and dry strength
properties, which may also, in certain embodiments, display a high
degree of hydrophobicity due to depleted hydrophilic groups on the
reacted polymers.
[0068] In one embodiment, the polymeric anionic compound may be
used in conjunction with a catalyst. Examples of suitable catalysts
for use with polymeric anionic compounds include any catalyst that
increases the rate of bond formation between the polymeric anionic
compounds and cellulose fibers. Useful catalysts include alkali
metal salts of phosphorous containing acids such as alkali metal
hypophosphites, alkali metal phosphites, alkali metal
polyphosphonates, alkali metal phosphates, and alkali metal
sulfonates. Particularly desired catalysts include alkali metal
polyphosphonates such as sodium hexametaphosphate, and alkali metal
hypophosphites such as sodium hypophosphite. Several organic
compounds are known to function effectively as catalysts as well,
including imidazole (IMDZ) and triethyl amine (TEA). Inorganic
compounds such as aluminum chloride and organic compounds such as
hydroxyethane diphosphoric acid may also promote crosslinking.
[0069] Other specific examples of effective catalysts are disodium
acid pyrophosphate, tetrasodium pyrophosphate, pentasodium
tripolyphosphate, sodium trimetaphosphate, sodium
tetrametaphosphate, lithium dihydrogen phosphate, sodium dihydrogen
phosphate and potassium dihydrogen phosphate.
[0070] When a catalyst is used to promote bond formation, the
catalyst is typically present in an amount in the range from about
5 to about 100 weight percent of the polymeric anionic compound.
The catalyst is present in an amount of about 25 to about 75% by
weight of the polymeric anionic compound. In one embodiment about
50% by weight of the polymeric anionic compound.
[0071] As will be described in more detail below, the polymeric
anionic compound may be added to the fiber furnish sequentially
with a polyamine polymer using various process techniques depending
upon the particular application. For instance, one or the other of
the components may be added first to the fiber furnish, pH may be
varied, relative concentrations may be varied, charge density of
the polymers may be varied, and the like
[0072] In preparing a web from a fiber furnish comprising a
polyamine compound and polymeric anionic compound bicomponent
strengthening system, any ratio of polyamine compound mass to
polymeric anionic compound mass may be used. For example, the ratio
of polyamine compound to polymeric anionic compound may be from
about 0.01 to about 100, more specifically from about 0.1 to about
10, more specifically still from about 0.2 to about 5, and most
specifically from about 0.5 to about 1.5.
[0073] Polymeric Aldehyde-Functional Compounds
[0074] Besides polymeric anionic compounds, another class of
compounds that may be used with a polyamine in accordance with the
present invention is polymeric aldehyde-functional compounds. By
"aldehyde-functional" it is meant that the aldehyde groups are not
bonded to other functional groups which would render them
unreactive.
[0075] In one embodiment, polyamines may be combined with polymeric
aldehyde-functional compounds in a papermaking furnish to create
improved physical and chemical properties in the resulting web. The
polyaldehyde polymer may be electronically neutral or charged,
e.g., an ionic polymer such as anionic or cationic polyaldehyde
polymer. Without intending to be limited or bound by theory, it is
believed that the cationic polyaldehyde tends to be retained on the
cellulosic fibers, which are anionic in nature. The polymeric
aldehyde-functional compounds may comprise gloxylated
polyacrylamides, aldehyde-functional polysaccharides, and aldehyde
functional cationic, anionic or non-ionic starches. Exemplary
materials include those disclosed by Lovine, et al., in U.S. Pat.
No. 4,129,722, herein incorporated by reference. An example of a
commercially available soluble cationic aldehyde functional starch
is Cobond.RTM. 1000 marketed by National Starch. The polymeric
aldehyde-functional compounds may have a molecular weight of about
10,000 or greater, more specifically about 100,000 or greater, and
more specifically about 500,000 or greater. Alternatively, the
polymeric aldehyde-functional compounds may have a molecular weight
below about 200,000, such as below about 60,000.
[0076] Further examples of aldehyde-functional polymers of use in
the present invention include dialdehyde guar, aldehyde-functional
wet strength additives further comprising carboxylic groups as
disclosed in WO 01/83887, published Nov. 8, 2001 by Thornton, et
al., dialdehyde inulin; and the dialdehyde-modified anionic and
amphoteric polyacrylamides of WO 00/11046, published Mar. 2, 2000,
the U.S. equivalent of which is application Ser. No. 99/18706,
filed Aug. 19, 1998 by Geer and Staib of Hercules, Inc., herein
incorporated by reference. Aldehyde-containing surfactants as
disclosed in U.S. Pat. No. 6,306,249 issued Oct. 23, 2001 to
Galante, et al., may also be used.
[0077] When used in the present invention, the aldehyde-functional
compound may have at least about 5 m-eq of aldehyde per 100 grams
of polymer, more specifically at least about 10 m-eq, more
specifically still about 20 m-eq or greater, and most specifically
about 25 m-eq per 100 grams of polymer or greater.
[0078] In one embodiment, the polymeric aldehyde-functional
compound may be a glyoxylated polyacrylamide, such as a cationic
glyoxylated polyacrylamide. Such compounds include PAREZ 631 NC wet
strength resin available from Cytec Industries of West Patterson,
N.J., and HERCOBOND 1366, manufactured by Hercules, Inc. of
Wilmington, Del. Another example of a glyoxylated polyacrylamide is
PAREZ 745, which is a glyoxylated poly(acrylamide-co-diallyl
dymethyl ammonium chloride). At times it may be advantageous to
utilize a mixture of high and low molecular weight glyoxylated
polyacrylamides to obtain a desired effect.
[0079] The above described cationic glyoxylated polyacrylamides
have been used in the past as wet strength agents. In particular,
the above compounds are known as temporary wet strength additives.
As used herein, a temporary wet strength agent, as opposed to a
permanent wet strength agent, is defined as those resins which,
when incorporated into paper or tissue products, will provide a
product which retains less than about 70% of its original wet
tensile index after exposure to water for a period of about one
hour. Permanent wet strength agents, on the other hand, provide a
product that will retain more than about 70% of its original wet
tensile index after exposure to water for a period of about one
hour. In accordance with the present invention, it has been
discovered that when a glyoxylated polyacrylamide, which is known
to be a temporary wet strength agent, is sequentially combined with
a polyamine polymer in a pulp fiber furnish, the combination of the
two components may result in permanent wet strength
characteristics.
[0080] In this manner, the wet strength characteristics of a paper
product may be carefully controlled by adjusting the relative
amounts of the glyoxylated polyacrylamide and the polyamine polymer
as well as other process parameters, as are discussed further
below.
[0081] As used herein, "wet strength agents" are materials used to
immobilize the bonds between fibers in the wet state. Typically,
the means by which fibers are held together in paper and tissue
products involve hydrogen bonds and sometimes combinations of
hydrogen bonds and covalent and/or ionic bonds. As used herein, the
wet state usually will mean when the product is largely saturated
with water or other aqueous solutions, but could also mean
significant saturation with body fluids such as urine, blood,
mucus, menses, runny bowel movement, lymph and other body
exudates.
[0082] Any material that when added to a paper web or sheet results
in providing the sheet with a mean wet geometric tensile strength:
dry geometric tensile strength ratio in excess of about 0.1 will,
for purposes of this invention, be termed a wet strength agent. As
described above, typically these materials are termed either as
permanent wet strength agents or as temporary wet strength
agents.
[0083] In accordance with the present invention, various wet
strength agents may be used in combination with a polyamine
polymer. In some applications, it has been found that temporary wet
strength agents combined with a polyamine polymer may result in a
composition having permanent wet strength characteristics. In
general, the wet strength agents that may be used in accordance
with the present invention may be cationic, nonionic or anionic. In
one embodiment, the additives are not strongly cationic to decrease
repulsive forces in the presence of cationic polyamine.
[0084] Another class of compounds that may be used with a polyamine
polymer in accordance with the present invention are various
anionic or noncationic (e.g., zwitterionic) surfactants. Such
surfactants may include, for instance, linear and branched-chain
sodium alkylbenzenesulfonates, linear and branched-chain alkyl
sulfates, and linear and branched chain alkyl ethoxy sulfates. Two
or more surfactants may be combined, if desired.
[0085] Process for Forming the Bicomponent Strengthening System
[0086] In one embodiment of the present invention, a polyamine
polymer is added to a pulp furnish in conjunction with a second
component, such as a polymeric anionic compound or a polymeric
aldehyde functional compound in order to provide various benefits
to the web produced from the pulp furnish. Of importance, the
polyamine polymer and the second component are not mixed prior to
being added to the pulp furnish, nor are they added to the pulp
furnish at the same time.
[0087] After the two components have been added to the furnish, the
web may be formed according to any standard web-forming
process.
[0088] By way of example only, addition of either the polyamine
polymer or the second component to the fiber furnish may be by
either of the following methods or combination thereof:
[0089] Direct addition to a fibrous slurry, such as by injection of
the compound into a slurry prior to entry in the headbox. Slurry
consistency may be from about 0.2% to about 25%, specifically from
about 0.2% to about 10%, more specifically from about 0.3% to about
5%, and most specifically from about 1% to about 4%.
[0090] Addition to individualized fibers. For example, comminuted
or flash dried fibers may be entrained in an air stream combined
with an aerosol or spray of the compound to treat individual fibers
prior to incorporation into a web or other fibrous product.
[0091] The addition level may be from about 0.5 to about 10 Kg per
ton of dry fiber for either the polyamine polymer or the second
component of the system. For example, in one embodiment, both
components may be added to the fiber furnish at equal amounts. For
example, up to about 10 kG/ton of the polyamine polymer may be
added to the fiber furnish and an equal addition level of the
second component may be added to the fiber furnish, i.e., up to
about 10 kG/ton. Alternatively, the components may be added in
different amounts. For instance, the ratio of the polyamine to the
second component added to the fiber furnish may be anywhere from
about 0.01 to about 100, for example from about 0.1 to about 10, in
one embodiment from about 0.2 to about 5.
[0092] The polyamine polymer and the second component of the system
may be combined with cellulosic fibers at any pH, and in fact, this
is one of the process parameters which may be adjusted so as to
tailor the affect of the bicomponent strengthening system on the
product web. For example, in certain embodiments, the pulp furnish
may be pH adjusted to acidic levels, such as below about 6, in
order to produce a bicomponent strengthening system in the web that
displays temporary wet strength. In other embodiments, temporary
wet strength may be produced in the web at higher pH levels with
the adjustment of other process parameters, such as, for instance,
the charge density of the polyamine polymer, the relative amounts
of the two components, the polymer concentrations added to the
furnish, the order of addition, and the like.
[0093] While not wishing to be bound by theory, it is believed that
the nature of the association formed between the two components of
the strengthening system and the cellulose fibers of the pulp
furnish may depend in a large part upon the charge ratio of the
bicomponent complex, which, in turn, may depend on the charge
density and molecular weight of the individual components.
[0094] The two components of the strengthening system will be
components which may form some association between each other and
the pulp fibers. For example, the components may form a association
wherein they are capable of bonding or otherwise associating with
each other in the slurry thus forming a composition which may
function in the web as a single strengthening compound, through,
for example, bond formation with the fibers. Alternatively, one or
both of the components may associate preferentially with the fibers
and secondarily with the other component and through this reaction
series, form the bicomponent strengthening system.
[0095] The term "bonding" is herein defined to include any form of
chemical bond, e.g., covalent bond, electrostatic bond, coordinate
bond, hydrogen bond, etc.
[0096] While the components of the strengthening system may
actually form bonds with each other and/or the pulp fibers, they
may alternatively associate due to electrostatic attraction and
form a polyelectrolyte complex, which may, in combination with
interaction with the pulp fibers (either interaction or
electrostatic interaction), form the bicomponent strengthening
system of the present invention. Two mechanisms are believed
possible for this type of association. In the first mechanism, the
first and second components of the system form a polyelectrolyte
complex in the pulp solution which may subsequently interact with
the pulp fibers. The second mechanism is believed to involve
formation of layers of the components on the individual pulp
fibers. According to this mechanism, the component which is added
first to the pulp slurry may adsorb on to the surface of the
cellulose fibers (which have a strong negative charge). This first
association may very likely adopt a flat configuration. The second
component, once added to the slurry, may then adsorb to the fibers
over the first component due to electrostatic attraction to the
first component, the fiber surface, or a combination thereof.
Combination of the various possible associations and interactions
may also be occurring in forming the strengthening system
[0097] While at first glance, it may appear that the polyamine
polymers of the system would not form a polyelectrolyte complex
with cationic or neutral polymers, this is not necessarily the
case. Whether or not complexation occurs can be calculated from
First Principles. The classical DLVO (Derjaguin-Landau and
Vervey-Overbeek) theory states that complexation may occur if the
total potential of interaction between two colloids (or polymer
coils) is negative. The total potential of interaction (V.sub.tot)
is the sum of two main components: the electrostatic potential
(V.sub.el) and the Van der Waals interactions (V.sub.vw). Thus,
V.sub.tot=V.sub.el+V.sub.vw (steric and hydrophobic potential are
sometimes also included in particular applications). V.sub.el may
be positive (i.e. repulsive) or negative (i.e. attractive),
depending on the components, and may be calculated from the
Coulombic equation. V.sub.vw will always be negative and may be
calculated knowing the Hamaker constant. Thus, even in the case of
like charges on the two components, V.sub.tot may be negative and
thus favor formation of a complex when the forces due to the Van
der Waals interaction is greater than the force due to the
electrostatic repulsion.
[0098] The examples following this description more clearly
delineate some of the specific wet strength characteristics which
may be obtained in the product paper webs through a variety of
variations in process parameters. However, generally speaking, the
primary process parameters which appear to affect the wet strength
of the webs are believed to be the ionic nature of the second
component, pH of the slurry at addition of the components, order of
addition of the components, relative ratio of the amounts of the
two components, amount of the components added to the system, and
charge ratio of the components (which may depend on charge density
and molecular weights of the components).
[0099] For instance, when considering a handsheet containing a
bicomponent strengthening system including a polyamine polymer and
a cationic second component, overall tissue strength properties may
decrease with increasing pH of the system, however strength
permanence may increase with increasing pH, thus a desired balance
between strength permanence and overall strength of the paper web
may be obtained. Furthermore, addition of a cationic component to
the fiber slurry prior to addition of the polyamine polymer can
improve both wet and dry strengths over those obtained with the
reverse order of addition. When considering the charge density of
the system, excellent overall strength benefits may be obtained
from a polyamine/cationic bicomponent system wherein the two
components are in about a one to one ratio, and the polyamine has a
high level of charge density (greater than about 15 m-eq/gram of
polymer). This particular system may also provide permanent wet
strength to the paper web.
[0100] In contrast, when the second component of the strengthening
system is anionic rather than cationic, not only may a paper web be
produced with different overall strength characteristics, but
similar variation of the process parameters can produce very
different effects in the paper web. For example, when the second
component of the bicomponent system is anionic, addition of the
polyamine polymer to the fiber slurry prior to addition of the
second component may improve overall strength characteristics of
the product web, which is in contrast to the strength
characteristics of a paper web containing a cationic second
component. This is believed to be due to the inability of the
anionic polymer to adsorb to the surface of the cellulosic fibers.
Thus, when the anionic component is added first, the two components
will associate with the fibers only after the polyamine component
has been added, and will probably associate with the fibers as a
complex, whereas when the polyamine component is added first, it
may associate with the fibers prior to the addition of the second
component, and layers of the components may build up on the fiber
surface. Additionally, when the second component is anionic, the
best overall strength characteristics in the paper web are obtained
when there is a greater amount of polyamine polymer in the system
than there is of the anionic second component, e.g., when the
polyamine polymer-anionic component ratio is between about 2:1 and
about 5:1.
[0101] Clearly, the bicomponent strengthening system of the present
invention may produce quite different strength characteristics in
the paper web produced from the treated fibers depending on process
parameters. This variability in the bicomponent strengthening
system can provide for a strengthening system which may be tailored
to obtain a combination of specific strength characteristics in a
paper web. For example, a paper web may be produced with a desired
dry strength, wet strength, wet strength permanence, and the like
within a very narrow range through variation in the components
forming the strengthening system. More particularly, in contrast to
the rigid, uniform reactivity of strengthening agents used in the
past, which provided limited variability in strength
characteristics of the paper webs incorporating the agents, the
bicomponent strengthening system of the present invention provides
great variability in the reactivity of the system and may be
utilized to produce paper webs with a wide variety of strength
characteristics. For example, if a paper web is desired with
specific set of strength characteristics, routine experimentation
with the bicomponent strengthening system of the present invention
can provide the particular system suitable to obtain the desired
product web.
[0102] Because the bicomponent strengthening system of the present
invention can be specifically tailored to provide a paper product
with desired strength characteristics, it may be used in place of
previously known strength agents, including, for example, strength
agents which may have undesired process effects, such as those
which increase the level of chlorinated organic compounds in the
waste stream of the paper-making process. Through use of the
present invention, levels of these pollutants may be reduced or
even eliminated from the waste stream. To reduce the chlorinated
organic compounds in a waste stream of a papermaking process, one
may consider any paper manufacturing process employing chlorinated
strength agents, such as wet strength agents derived from
epichlorohydrin. Complete or partial elimination of the chlorinated
strength agents may be implemented, either suddenly or phased in
over a period of time such as a day or week, with a substantially
or totally organic-chlorine-free bicomponent strengthening system
of the present invention being used (either suddenly introduced or
phased in over a period of time) to provide at least a portion or
all of the wet or dry strength that was previously contributed by
one or more chlorinated strength agents.
[0103] In one embodiment, the wet or dry strength of the paper
product is maintained at a level at least as great as the level
prior to beginning conversion to the bicomponent strength system.
In another embodiment, the wet strength of the paper is at least
about 90%, at least about 95%, or at least about 98% of the
previous target value prior to conversion to the bicomponent
strength system. In one embodiment, previously employed chlorinated
organic wet strength agents are completely eliminated from the
ingredients combined in the papermaking process, with a bicomponent
system of the present invention being used instead. Any papermaking
process can be considered, such as a papermaking process for a
machine that produces at least 1 metric tonne per day (tpd) of a
wet-laid paper web having a wet:dry tensile strength ratio of at
least about 0.06, more specifically at least about 0.08, and most
specifically at least about 0.1. such as from 0.07 to 0.35, or from
about 0.1 to about 0.4. Production rates for a machine or entire
mill converted to the bicomponent strength system can be much
greater, such as at least about 10 tpd, 50 tpd, 100 tpd, or 300
tpd. Without limitation, the paper web may be tissue, writing
paper, linerboard, packaging paper, paper intended for impregnation
with resins ("prepreg"), photocopy paper, lightweight coated paper,
paperboard, cardstock, and the like. The paper may contain bleached
or unbleached fibers or combinations thereof. In one embodiment,
the paper fibers are substantially free of fibers bleached with
molecular chlorine or chlorine dioxide. In one embodiment, the
paper web produced has an ISO brightness greater than 80 or greater
than 90. The basis weight of the web can be about 10 gsm or
greater, more specifically about 20 gsm or greater, and most
specifically about 40 gsm or greater. The concentration or absolute
mass emitted per 24 hours of chlorinated organic species in an
effluent stream of the production facility may be reduced by 5% or
more, 10% or more, or 50% or more by converting to a bicomponent
system of the presence invention to reach targeted wet or dry
strength levels.
[0104] The bicomponent strengthening system may be selectively
associated with one of a plurality of fiber types in a web, and may
be adsorbed or chemisorbed onto the surface of one or more fiber
types. For example, bleached kraft fibers may have a higher
affinity for the bicomponent strengthening system than synthetic
fibers that may be present.
[0105] Preparation of Paper Webs for Use in the Present
Invention
[0106] The fibrous web to be formed from the fibers treated in
accordance with the present invention may be wet-laid, such as webs
formed with known papermaking techniques wherein the dilute aqueous
fiber slurry is disposed on a moving wire to filter out the fibers
and form an embryonic web which is subsequently dewatered by
combinations of units including suction boxes, wet presses, dryer
units, and the like. Capillary dewatering may also be applied to
remove water from the web.
[0107] Drying operations may include drum drying, through drying,
steam drying such as superheated steam drying, displacement
dewatering, Yankee drying, infrared drying, microwave drying, radio
frequency drying in general, and impulse drying.
[0108] A moist fibrous web may also be formed by foam forming
processes, wherein the treated fibers are entrained or suspended in
a foam prior to dewatering, or wherein foam is applied to an
embryonic web prior to dewatering or drying.
[0109] For tissue webs, both creped and uncreped methods of
manufacture may be used. For either creped or uncreped methods,
embryonic tissue webs may be imprinted against a deflection member
prior to complete drying. Deflection members have deflection
conduits between raised elements, and the web is deflected into the
deflection member by an air pressure differential to create bulky
domes, while the portions of the web residing on the surface of the
raised elements may be pressed against the dryer surface to create
a network of pattern densified areas offering strength.
[0110] The fibrous web is generally a random plurality of
papermaking fibers that can, optionally, be joined together with a
binder. Any papermaking fibers, as herein defined, or mixtures
thereof may be used, such as bleached fibers from a kraft or
sulfite chemical pulping process. Recycled fibers may also be used,
as may cofton linters or papermaking fibers comprising cofton. Both
high-yield and low-yield fibers may be used. In one embodiment, the
fibers may be predominantly hardwood, such as at least 50% hardwood
or about 60% hardwood or greater or about 80% hardwood or greater
or substantially 100% hardwood. In another embodiment, the web is
predominantly softwood, such as at least about 50% softwood or at
least about 80% softwood, or about 100% softwood.
[0111] For many tissue applications, high brightness may be
desired. Thus the papermaking fibers or the resulting paper of the
present invention may have an ISO brightness of about 60 percent or
greater, more specifically about 80 percent or greater, more
specifically about 85 percent or greater, more specifically from
about 75 percent to about 90 percent, more specifically from about
80 percent to about 90 percent, and more specifically still from
about 83 percent to about 88 percent.
[0112] The fibrous web of the present invention may be formed from
a single layer or multiple layers. Both strength and softness are
often achieved through layered tissues, such as stratified webs
wherein at least one layer comprises softwood fibers while another
layer comprises hardwood or other fiber types. Layered structures
produced by any means known in the art are within the scope of the
present invention. In the case of multiple layers, the layers are
generally positioned in a juxtaposed or surface-to-surface
relationship and all or a portion of the layers may be bound to
adjacent layers. The paper web may also be formed from a plurality
of separate paper webs wherein the separate paper webs may be
formed from single or multiple layers.
[0113] In producing such layered structure, the bicomponent
strengthening system of the present invention may be present in one
or more of the layers. For example, the bicomponent strengthening
system may be present in a single layer of a multilayer web or a
single ply of a multi-ply paper product. Alternatively, the
bicomponent strengthening system of the present invention may be
present in all of the layers of a multilayer product. In one
embodiment of the present invention, the strengthening system may
be present in more than one layer of the product, and may be
different in each layer. For example, the same components may be
added to different layers of the product, but the components may be
added under different process conditions, i.e. different order of
addition, different pH, different concentrations, etc. such that
the affect of the strengthening system is different in different
layers of the product. In an alternative embodiment, the
strengthening system of the present invention may be added to more
than one layer of the product, but the components of the system may
vary between layers. For example, polyamine polymers similar but
for different charge density may be added to different layers with
identical second components added to the different layers, so as to
tailor the strength characteristics of the layers. Countless
variations of multi layer paper products are envisioned such that
the strength characteristics of each layer of the product, and thus
the strength characteristics of the product itself, may be
specifically tailored.
[0114] When producing stratified webs, the webs may be made by
employing a single headbox with two or more strata, or by employing
two or more headboxes depositing different furnishes in series on a
single forming fabric, or by employing two or more headboxes each
depositing a furnish on a separate forming fabric to form an
embryonic web followed by joining ("couching") the embryonic webs
together to form a multi-layered web. The distinct furnishes may be
differentiated by at least one of strengthening system components,
consistency, fiber species (e.g., eucalyptus vs. softwood, or
southern pine versus northern pine), fiber length, bleaching method
(e.g., peroxide bleaching vs. chlorine dioxide bleaching), pulping
method (e.g., kraft versus sulfite pulping, or BCTMP vs. kraft),
degree of refining, pH, zeta potential, color, Canadian Standard
Freeness (CSF), fines content, size distribution, synthetic fiber
content (e.g., one layer having 10% polyolefin fibers or
bicomponent fibers of denier less than 6), and the presence of
additives such as fillers (e.g., CaCO.sub.3, talc, zeolites, mica,
kaolin, plastic particles such as ground polyethylene, and the
like), starch, antimicrobial additives, odor control agents,
chelating agents, chemical debonders, quaternary ammonia compounds,
viscosity modifiers (e.g., CMC, polyethylene oxide, guar gum,
xanthan gum, mucilage, okra extract, and the like), silicone
compounds, fluorinated polymers, optical brighteners, and the like.
For example, in one embodiment, the strengthening system of the
present invention may be added to the center layer of a three layer
stratified web, which primarily contains softwood fibers, to
improve the strength characteristics of the multi layer web, while
the outer layers may contain primarily hard wood fibers without the
addition of the strengthening system of the present invention and
may provide desired softness to the multilayer product.
[0115] By way of example, useful stratified headboxes may include a
four-layer Beloit (Beloit, Wis.) Concept III headbox or a Voith
Sulzer (Ravensburg, Germany) ModuleJet.RTM. headbox in multilayer
mode. Principles for stratifying the web are taught by Kearney and
Wells in U.S. Pat. No. 4,225,382, issued Sep. 30, 1980, which
discloses the use of two or more layers to form ply-separable
tissue. In one embodiment, a first and second layer are provided
from slurry streams differing in consistency. In another
embodiment, two well-bonded layers are separated by an interior
barrier layer such as a film of hydrophobic fibers to enhance ply
separability.
[0116] In one embodiment for forming a multi-layer web, an initial
pulp suspension is fractionated into two or more fractions
differing in fiber properties, such as mean fiber length,
percentage of fines, percentage of vessel elements, and the like.
In one embodiment, the complete initial pulp suspension may be
treated according to the present invention prior to fractionation.
In another embodiment, the pulp suspension may be fractionated
first, and then one or more fractions may be treated separately
according to the present invention. Fractionation may be achieved
by any means known in the art, including screens, filters,
centrifuges, hydrocyclones, application of ultrasonic fields,
electrophoresis, passage of a suspension through spiral tubing or
rotating disks, and the like. The fractionated pulp streams may be
treated by combination with additives or other fibers, or
adjustment of the consistency to a level suitable for paper
formation, and then the streams comprising the fractionated fibers
may be directed to separate portions of a stratified headbox to
produce a layered tissue product. The layered sheet may have two,
three, four, or more layers. A two-layered sheet may have splits
based on layer basis weights such that the lighter layer has a mass
of about 5% or more of the basis weight of the overall web, or
about 10% or more, about 20% or more, about 30% or more, about 40%
or more, or about 50%. Exemplary weight percent splits for a
three-layer web include about 20%/20%/60%; about 20%/60%/20%; about
37.5%/25%/37.5%; about 10%/50%/40%; about 40%/20%/40%; and
approximately equal splits for each layer. In one embodiment, the
ratio of the basis weight of an outer layer to an inner layer may
be from about 0.1 to about 5; more specifically from about 0.2 to
about 3, and more specifically still from about 0.5 to about 1.5. A
layered paper web according to the present invention may serve as a
basesheet for a double print creping operation.
[0117] In another embodiment, tissue webs of the present invention
comprise multilayered structures with one or more layers having
over about 20% high yield fibers such as CTMP or BCTMP. In one
embodiment, the tissue web comprises a first strength layer having
cellulosic fibers and the bicomponent strengthening system of the
present invention. The web further comprises a second high yield
layer having at least about 20% by weight high yield fibers and
optional binder material such as synthetic fibers, including
thermally bondable bicomponent binder fibers, resulting in a bulky
multilayered structure having good strength properties.
[0118] The slurry comprising a polyamine polymer and the second
component may also be free of formaldehyde or cross-linking agents
that evolve formaldehyde. In addition, the slurry comprising a
polyamine polymer and the second component may be free of low
molecular weight organic chlorinated compounds, as the use of the
strengthening system of the present invention may render the need
for previously known permanent wet strength agents which include
these compounds, such as polyamide epichlorohydrin strengthening
agents, unnecessary.
[0119] The bicomponent strengthening system of the present
invention may be used in conjunction with any known materials and
chemicals that are not antagonistic to its intended use. For
example, when used in the production of fibrous materials in
absorbent articles or other products, odor control agents may be
present, such as odor absorbents, activated carbon fibers and
particles, baby powder, baking soda, chelating agents, zeolites,
perfumes or other odor-masking agents, cyclodextrin compounds,
oxidizers, and the like. The absorbent article may further comprise
metalphthalocyanine material for odor control, antimicrobial
properties, or other purposes. Suprabsorbent particles, fibers, or
films may be employed. For example, an absorbent fibrous mat of
comminuted fibers treated with the disclosed strengthening system
may be combined with superabsorbent particles to serve as an
absorbent core or intake layer in a disposable absorbent article
such as a diaper. A wide variety of other compounds known in the
art of papermaking and tissue production may be included in the
webs of the present invention.
[0120] Debonders, such as quaternary ammonium compounds with alkyl
or lipid side chains, may be used to provide high wet:dry tensile
strength ratios by lowering the dry strength without a
correspondingly large decrease in the wet strength. Softening
compounds, emollients, silicones, lotions, waxes, and oils may also
have similar benefits in reducing dry strength, while providing
improved tactile properties such as a soft, lubricious feel.
Fillers, fluorescent whitening agents, antimicrobials, ion-exchange
compounds, odor-absorbers, dyes, and the like may also be
added.
[0121] Hydrophobic matter added to selected regions of the web,
especially the uppermost portions of a textured web, may be
valuable in providing improved dry feel in articles intended for
absorbency and removal of liquids next to the skin. Webs formed of
fibers treated with the bicomponent strengthening system may be
further treated with waxes and emollients, typically by a topical
application. Hydrophobic material may also be applied over portions
of the web.
[0122] When debonders are to be applied, any debonding agent (or
softener) known in the art may be utilized. The debonders may
include silicone compounds; mineral oil and other oils or
lubricants, quaternary ammonium compounds with alkyl side chains,
or the like known in the art. Exemplary debonding agents for use
herein are cationic materials such as quaternary ammonium
compounds, imidazolinium compounds, and other such compounds with
aliphatic, saturated or unsaturated carbon chains. The carbon
chains may be unsubstituted or one or more of the chains may be
substituted, e.g. with hydroxyl groups. Non-limiting examples of
quaternary ammonium debonding agents useful herein include
hexamethonium bromide, tetraethylammonium bromide, lauryl
trimethylammonium chloride, and dihydrogenated tallow
dimethylammoniurn methyl sulfate.
[0123] The suitable debonders may include any number of quaternary
ammonium compounds and other softeners known in the art, including
but not limited to, oleylimidazolinium debonders such as C-6001
manufactured by Goldschmidt or Prosoft TQ-1003 from Hercules
(Wilmnington, Del.); Berocell 596 and 584 (quaternary ammonium
compounds) manufactured by Eka Nobel Inc; Adogen 442 (dimethyl
dihydrogenated tallow ammonium chloride) manufactured by Cromtpon;
Quasoft 203 (quaternary ammonium salt) manufactured by Quaker
Chemical Company; Arquad 2HT75 (di(hydrogenated tallow) dimethyl
ammonium chloride) manufactured by Akzo Chemical Company; mixtures
thereof; and the like.
[0124] Other debonders may be tertiary amines and derivatives
thereof; amine oxides; saturated and unsaturated fatty acids and
fatty acid salts; alkenyl succinic anhydrides; alkenyl succinic
acids and corresponding alkenyl succinate salts; sorbitan mono-,
di- and tri-esters, including but not limited to stearate,
palmitate, oleate, myristate, and behenate sorbitan esters; and
particulate debonders such as clay and silicate fillers.
[0125] In one embodiment, a synergistic combination of a quaternary
ammonium surfactant component and a nonionic surfactant may be
used.
[0126] The debonding agent may be added at a level of at least
about 0.1%, specifically at least about 0.2%, more specifically at
least about 0.3%, on a dry fiber basis. Typically, the debonding
agent will be added at a level of from about 0.1 to about 6%, more
typically from about 0.2 to about 3%, active matter on dry fiber
basis. The percentages given for the amount of debonding agent are
given as an amount added to the fibers, not as an amount actually
retained by the fibers.
[0127] Softening agents known in the art of tissue making may also
serve as debonders or hydrophobic matter suitable for the present
invention and may include but not limited to: fatty acids; waxes;
quaternary ammonium salts; dimethyl dihydrogenated tallow ammonium
chloride; quaternary ammonium methyl sulfate; carboxylated
polyethylene; cocamide diethanol amine; coco betaine; sodium
lauroyl sarcosinate; partly ethoxylated quaternary ammonium salt;
distearyl dimethyl ammonium chloride; methyl-1-oleyl
amidoethyl-2-oleyl imidazolinium methylsulfate (Varisoft 3690 from
Witco Corporation, now Crompton in Middlebury, Conn.); mixtures
thereof; and the like known in the art. Topical softening agents
such as functional and non-functional organo polysiloxanes may be
applied to the web to improve the surface feel of the product, such
polysiloxane materials being well known in the art.
[0128] The debonder may be added to the web in the furnish.
However, debonder may also be added to the web after formation of
the wet-laid sheet. In one embodiment, the debonder is added to the
fibers with either the polyamine polymer or the second component of
the system, provided that adverse reactions between the components
and the debonder are avoided by suitable selection of temperatures,
pH values, contact time, and the like. Additives may be applied to
the wet-laid sheet heterogeneously using either a single pattern or
a single means of application, or using separate patterns or means
of application. Heterogeneous application of a chemical additive
may be by gravure printing, spraying, or any method previously
discussed.
[0129] Surfactants may also be used, being mixed with either the
polyamine polymer, the second component, or added separately to the
web or fibers. The surfactants may be anionic, cationic, or
non-ionic, including but not limited to: tallow trimethylammonium
chloride; silicone amides; silicone amido quaternary amines;
silicone imidazoline quaternary amines; alkyl polyethoxylates;
polyethoxylated alkylphenols, fatty acid ethanol amides;
dimethicone copolyol esters; dimethiconol esters; dimethicone
copolyols; mixtures thereof; and the like known in the art.
[0130] In one embodiment, the paper webs of the present invention
may be laminated with additional plies of tissue or layers of
nonwoven materials such as spunbond or meltblown webs, or other
synthetic or natural materials.
[0131] The web may also be calendered, embossed, slit, rewet,
moistened for use as a wet wipe, impregnated with thermoplastic
material or resins, treated with hydrophobic matter, printed,
apertured, perforated, converted to multiply assemblies, or
converted to bath tissue, facial tissue, paper towels, wipers,
absorbent articles, and the like.
[0132] The tissue products of the present invention may be
converted in any known tissue product suitable for consumer use.
Converting may comprise calendering, embossing, slitting, printing,
addition of perfume, addition of lotion or emollients or health
care additives such as menthol, stacking preferably cut sheets for
placement in a carton or production of rolls of finished product,
and final packaging of the product, including wrapping with a poly
film with suitable graphics printed thereon, or incorporation into
other product forms.
[0133] Reference now will be made to various embodiments of the
invention, one or more examples of which are set forth below. Each
example is provided by way of explanation of the invention, not as
a limitation of the invention. In fact, it will be apparent to
those skilled in the art that various modifications and variations
may be made of this invention without departing from the scope or
spirit of the invention.
EXAMPLES
Example 1
Control--the Effect of Catiofast.RTM., Parez.RTM., and Kymene.RTM.
on Wet Strength Development
[0134] Preparation of Pulp Slurry
[0135] To prepare a pulp slurry, 24 grams (oven-dry basis) of pulp
fibers were soaked in 2 liters of deionized water for 5 minutes.
The pulp slurry was disintegrated for 5 minutes in a British
disintegrator. The slurry was then diluted with water to a volume
of 8 liters. The strength agent was then added to the slurry. The
slurry was mixed with a standard mechanical mixer at moderate shear
for 10 minutes after addition of the strength agent.
[0136] Preparation of Handsheets
[0137] Handsheets were made with a basis weight of 60 gsm. During
handsheet formation, the appropriate amount of fiber (0.3%
consistency) slurry required to make a 60 gsm sheet was measured
into a graduated cylinder. The slurry was then poured from the
graduated cylinder into an 8.5-inch by 8.5-inch Valley handsheet
mold (Valley Laboratory Equipment, Voith, Inc.) that had been
pre-filled to the appropriate level with water. After pouring the
slurry into the mold, the mold was then completely filled with
water, including water used to rinse the graduated cylinder. The
slurry was then agitated gently with a standard perforated mixing
plate that was inserted into the slurry and moved up and down seven
times, then removed. The water was then drained from the mold
through a wire assembly at the bottom of the mold that retained the
fibers to form an embryonic web. The forming wire was a 90.times.90
mesh, stainless-steel wire cloth. The web was couched from the mold
wire with two blotter papers placed on top of the web with the
smooth side of the blotter contacting the web. The blotters were
removed and the embryonic web was lifted with the lower blotter
paper, to which it was attached. The lower blotter was separated
from the other blotter, keeping the embryonic web attached to the
lower blotter. The blotter was positioned with the embryonic web
face up, and the blotter was placed on top of two other dry
blotters. Two more dry blotters were also placed on top of the
embryonic web. The stack of blotters with the embryonic web was
placed in a Valley hydraulic press and pressed for one minute with
100 psi applied to the web. The pressed web was removed from the
blotters and placed on a Valley steam dryer containing steam at 2.5
psig pressure and heated for 2 minutes, with the wire-side surface
of the web next to the metal drying surface and a felt under
tension on the opposite side of the web. Felt tension was provided
by a 17.5 lbs of weight pulling downward on an end of the felt that
extends beyond the edge of the curved metal dryer surface. The
dried handsheet was trimmed to 7.5 inches square with a paper
cutter and then weighed in a heated balance with the temperature
maintained at 105.degree. C. to obtain the oven dry weight of the
web. The handsheets were then subjected to dry and wet tensile
testing.
[0138] Three strength agents were compared within this example:
Parez.RTM. 631NC (a cationic glyoxylated polyacrylamide)
manufactured by Cytec Industries; Catiofast.RTM. PR 8106 (a
polyvinylamine from BASF); and Kymene.RTM. 557 LX (a
polyaminoamide-epichlorohydrin from Hercules Inc.). These additives
were each charged to an identical furnish as 1% aqueous solutions
and stirred for 10 minutes. The add-on levels investigated ranged
from 0 to 10-kg/T of dry fiber. pH of the slurry was maintained
neutral (6.8) in each code. No additives were used in the control
sample. The results are reported below in Table 1.
2TABLE 1 Control Data - Effect of Wet strength Type and
Concentration on Handsheet Properties (pH = 6.8) Wet TI % Wet TI
Concentration Dry TI Wet TI 1-hr remain % Wet/Dry Code Polymer
(Kg/T) (Nm/g) (Nm/g) (Nm/g) after 1-hr TI control -- -- 10.7 0.9
0.7 8% 74% 1 PVAm 2.5 10.9 1.6 1.5 94% 15% 2 PVAm 5 18.7 3.9 3.1
79% 21% 3 PVAm 10 15.6 3.8 3.1 81% 24% 4 CParez .RTM. 2.5 14.3 1.9
1.2 63% 13% 5 CParez .RTM. 5 16.5 2.3 1.4 61% 16% 6 CParez .RTM. 10
22.5 4.1 2.7 66% 18% 7 Kymene .RTM. 2.5 14.1 3.4 3.0 88% 24% 8
Kymene .RTM. 5 17.5 5.8 4.7 81% 33% 9 Kymene .RTM. 10 20.6 7.9 6.1
77% 38%
[0139] Several findings may be drawn from this data. First, for
handsheets prepared with Catiofast.RTM. PR 8106, wet handsheet
strength does not change as dosage level is doubled from 5 to 10
kg/T of dry fiber. This effect was not seen with Kymene.RTM. and
Parez.RTM.. While not wishing to be bound by theory, this behavior
may be attributed to high polymer charge which limits its
adsorption capacity. Second, Parez.RTM. is the most efficient dry
strength agent (Code 6), while Kymene.RTM. is the most efficient
wet strength resin (Code 9) as it provides the highest wet strength
and wet-over-dry strength ratio. Third, Kymene.RTM., known as a
permanent wet strength agent develops a wet strength permanency
ranging from 77 to 88% (Codes 7-9); Parez.RTM., largely regarded as
a temporary wet strength resin, develops a wet strength permanency
ranging from 63 to 66% (Codes 4-6). Under the conditions employed,
with a wet strength permanency of 81 to 94%, Catiofast.RTM. PR 8106
has been classified as a permanent wet strength agent with initial
wet strength which is similar to Parez.RTM. 631NC.
Example 2
Effect of pH and Order of Addition on PVAm/cationic Parez
Bicomponent
[0140] A slurry of pulp fibers as described in Example 1 was
prepared. A bicomponent strength system was formed in the slurry
which included the following compounds:
[0141] 1% aqueous solution of CParez.RTM. 631NC (a cationic
glyoxylated polyacrylamide) manufactured by Cytec Industries
[0142] 1% aqueous solution of Catiofast.RTM. PR 8106
polyvinylamine
[0143] Polyvinylamine and CParez.RTM. were added sequentially with
add-on levels constant at 10 Kg/T each. The first polymer was added
to the furnish and stirred for 10 minutes. The second polymer was
then added to the furnish and mixed 2 minutes. Handsheets were
prepared as in Example 1 and tested. Results (average of 5 samples)
are given in Table 2. No additives were used in the control. The pH
of the pulp furnish was adjusted as shown below in Table 2 prior to
the addition of the polymers.
3TABLE 2 Tensile data for handsheets treated with
polyvinylamine/cationic Parez. Effect of pH and order of addition.
(10 Kg/T PVAm with 10 Kg/T Parez.) Dry Wet First TI TI Wet TI % Wet
TI Polymer (Nm/ (Nm/ 1 hour remain % Wet/ Code added pH g) g)
(Nm/g) after 1 hour Dry TI Con- -- 6.9 10.65 0.89 0.66 74.2% 8.36%
trol 10 PVAm 6.8 20.79 5.26 3.98 75.7% 19.1% 11 Parez 631 6.8 30.43
7.85 5.61 71.5% 18.4% 12 PVAm 4 32.78 8.45 5.19 61.4% 15.8% 13
Parez 631 4 35.18 8.93 5.74 64.3% 16.3% 14 PVAm 10 21.13 3.58 2.67
74.6% 12.6% 15 Parez 631 10 29.52 6.48 4.85 74.8% 16.4%
[0144] Several findings may be drawn from this data. First, the
efficiency of the PVAm/CParez system is a function of pH; best wet
and dry strengths were achieved at acidic pH (pH 4). Tissue
strength properties decrease as pH of the system increases. Second,
the efficiency of the PVAm/CParez system is a function of the order
of polymer addition; best wet and dry strengths were achieved with
CParez added first. Third, the wet strength permanency, defined as
the ratio of wet strength after 1 hour soaking to that measured
immediately after soaking, and the wet over dry strength ratio may
both be controlled with pH and the order of polymer addition.
Fourth, PVAm/CParez systems develop temporary wet strength with %
Wet TI remaining after 1 hour ranging from 61% to 76% (Codes
10-15); this contrasts from the behavior of PVAm by itself (Codes
1-3, Example 1)
Example 3
Polyvinylamine/cationic Parez.RTM. Bicomponent Strength
Agents--Effect of Polymer Ratio and Polyvinylamine Charge
Density
[0145] A slurry of pulp fibers as described in Example 1 was
prepared. A bicomponent strength system was formed in the slurry
which included the following compounds:
[0146] 1% aqueous solution of CParez.RTM. 631NC (a cationic
glyoxylated polyacrylamide) manufactured by Cytec Industries
[0147] 1% aqueous solution of polyvinylamine
[0148] Polyvinylamine and CParez.RTM. were added sequentially with
add-on levels constant at 10 Kg/T each. CParez.RTM. was added first
to the furnish and stirred for 10 minutes. The polyvinylamine was
then added to the furnish and mixed 2 minutes. Three types of PVAm
were used: Catiofast.RTM. PR 8106 (90% amine, 21 m-eq amine/g
polymer), Catiofast.RTM. PR 8087 (50% amine, 11 me-q/g), and
Catiofast.RTM. 8104 (10% amine, 2.3 m-eq/g). The total polymer
concentration added to the furnish equaled 10 kg/T of dry fiber.
The weight ratio of PVAm/CParez.RTM. was varied from 0:1,1:5, 1:2,
1:1, 2:1, 5:1, and 1:0. pH of the slurry was maintained at neutral
(6.8) in each code. Handsheets were prepared as in Example 1 and
tested. Results (average of 5 samples) are given in Table 3. No
additives were used in the control.
4TABLE 3 PVAm/CParez .RTM. Bicomponent Strength Agents - Effect of
Polymer Ratio and PVAm Charge Density on Handsheet Properties (pH =
6.8, 10-kg/T polymer concentration) % PVAm PVAm:C Wet TI % Wet TI %
TEA@ Charge Parez .RTM. Dry TI Wet TI 1-hr remain Wet/Dry % Peak
Peak E Code Density Ratio (Nm/g) (Nm/g) (Nm/g) after 1-hr TI
Stretch (J/m2) (kgf) control -- 0.0 10.7 0.9 0.7 8% 74% 0.9% 3.7
319 16 90% 0:1 22.5 4.0 2.7 67% 18% 1.6% 15.0 467 17 90% 1:5 28.3
5.9 3.9 67% 21% 1.8% 21.1 461 18 90% 1:2 27.9 5.8 4.5 77% 21% 2.1%
25.1 429 19 90% 1:1 29.2 6.5 4.7 72% 22% 1.7% 20.5 485 20 90% 2:1
23.1 4.5 3.9 87% 19% 1.5% 14.1 577 21 90% 5:1 24.5 5.1 4.1 80% 21%
1.5% 14.6 336 22 90% 1:0 15.6 3.8 3.1 82% 25% 1.0% 6.3 374 23 50%
0:1 22.5 4.0 2.7 67% 18% 1.6% 15.0 467 24 50% 1:5 22.3 5.0 3.9 78%
22% 1.6% 14.9 436 25 50% 1:2 19.2 4.2 3.3 78% 22% 1.3% 9.8 402 26
50% 1:1 19.7 4.5 3.2 71% 23% 1.3% 10.8 428 27 50% 2:1 18.9 4.5 3.5
78% 24% 1.2% 9.6 429 28 50% 5:1 16.5 3.4 2.9 85% 21% 1.1% 7.0 420
29 50% 1:0 12.8 2.1 1.6 79% 16% 1.0% 5.3 339 30 10% 0:1 22.5 4.0
2.7 67% 18% 1.6% 15.0 467 31 10% 1:5 20.1 3.3 2.1 65% 16% 1.5% 12.5
439 32 10% 1:2 18.9 2.5 1.8 71% 13% 1.5% 12.1 408 33 10% 1:1 17.6
2.6 1.5 58% 15% 1.2% 8.5 410 34 10% 2:1 14.8 1.6 1.1 69% 11% 1.0%
5.7 375 35 10% 5:1 14.7 1.3 0.9 67% 9% 1.1% 6.5 409 36 10% 1:0 13.4
0.8 0.6 67% 6% 1.1% 5.4 269
[0149] Table 3 delineates numerous trends as a consequence of both
polymer ratio and PVAm charge density. First, as the charge density
(% amine) of PVAm increases, dry and wet strength increase. Second,
samples containing PVAm with a 50% or 90% charge density exhibit a
maximum wet strength plateau at a 1:5, 1:2, 1:1, 2:1, and 5:1
PVAm/CParez.RTM. ratio. The samples containing PVAm with a 10%
charge density demonstrate a decrease in wet strength as the
concentration of PVAm increases and the concentration of
CParez.RTM. decreases. The wet strength of samples containing just
PVAm with a 10% charge density (code 36) is equivalent to the wet
strength of control samples containing no additives. Therefore, the
data suggests that adding PVAm with a charge density of 10% lends
little strength benefit to handsheets. Third, wet strength
permanency is greatest as PVAm concentration exceeds CParez.RTM..
However, wet strength after one hour of soaking is most permanent
for the 1:1 PVAm (90% charge)/CParez.RTM. sample (code 19). Wet
strength permanency ranges from 58% to 87%. Fourth, wet/dry ratio
is fairly constant (18-25%) for codes containing PVAm with 50% and
90% charge density. Fifth, peak stretch, TEA, and E decrease, or
remain constant, as the PVAm/CParez.RTM. ratio is increased for
codes containing PVAm with 10% and 50% charge density. For codes
containing PVAm with 90% charge, peak stretch and TEA have a
maximum at a PVAm/CParez.RTM. ratio of 1:2 while modulus peaks at
2:1. Sixth, the PVAm/CParez.RTM. bicomponent system develops dry
strength efficiently. Overall, the 1:1 PVAm (90%
charge)/CParez.RTM. ratio appears as the best combination for both
dry and wet strength properties.
Example 4
Polyvinylamine/CParez.RTM. Bicomponent Strength Agents--Effect of
Total Polymer Concentration
[0150] A slurry of pulp fibers as described in Example 1 was
prepared. A bicomponent strength system was formed in the slurry
which included the following compounds:
[0151] 1% aqueous solution of CParez.RTM. 631NC (a cationic
glyoxylated polyacrylamide) manufactured by Cytec Industries
[0152] 1% aqueous solution of Catiofast.RTM. PR 8106 polyvinylamine
(90% amine)
[0153] The solution of CParez.RTM. was added to the furnish first
and the furnish was mixed for 10 minutes. The solution of
Catiofast.RTM. PR 8106 was added to the furnish second and the
furnish was mixed for 2 minutes. The PVAm/CParez.RTM. ratio added
to the furnish was held constant at 1:1, while the total polymer
concentration was varied, at 0, 2, 4, 6, 10, and 15-kg/T of dry
fiber. pH of the slurry was maintained neutral (6.8) in each code.
Handsheets were prepared as described in Example 1 and tested. The
results are reported in Table 4.
[0154] Table 4 clearly shows that as polymer concentration
increases, dry strength, wet strength and rigidity are enhanced.
Such improvement in said properties is continuous throughout the
defined breadth of polymer concentration.
5TABLE 4 PVAm/CParez .RTM. Bicomponent Strength Agents - Effect of
Polymer Concentration on Handsheet Properties (pH = 6.8, 1:1 90%
charge density PVAm/CParez .RTM. ratio) Polymer Wet TI % Wet TI %
TEA@ Conc Dry TI Wet TI 1-hr remain Wet/Dry % Peak Peak Code (kg/T)
(Nm/g) (Nm/g) (Nm/g) after 1-hr TI Stretch (J/m2) E (kgf) control 0
10.7 0.9 0.7 74% 8% 0.9% 3.7 319 37 2 13.5 1.5 1.0 69% 11% 1.1% 5.8
374 38 4 18.3 3.0 2.3 77% 17% 1.2% 9.1 459 39 6 25.6 5.2 3.7 72%
20% 1.8% 19.1 426 40 10 29.2 6.5 4.7 72% 22% 1.7% 20.5 485 41 15
36.9 7.9 5.8 73% 21% 2.7% 42.2 615
Example 5
Polyvinylamine/CParez.RTM. Bicomponent Strength Agents--Effect of
pH and Polyvinylamine Charge Density
[0155] A slurry of pulp fibers as described in Example 1 was
prepared. A bicomponent strength system was formed in the slurry
which included the following compounds:
[0156] 1% aqueous solution of CParez.RTM. 631NC (a cationic
glyoxylated polyacrylamide) manufactured by Cytec Industries
[0157] 1% aqueous solution of a polyvinylamine
[0158] In this example, the first polymer added to the furnish was
the CParez.RTM. and then the furnish was mixed for 10 minutes. The
polyvinylamine then added was either Catiofast.RTM. PR 8106 (90%
amine, 21 m-eq/g charge density), Catiofast.RTM. PR 8087 (50%
amine, 11 m-eq/g charge density), or Catiofast.RTM. PR 8104(10%
amine, 2.3 m-eq/g charge density). The PVAm/CParez.RTM. ratio and
the total polymer concentration added to the furnish were sustained
at 1:1 and 10 kg/T of dry fiber, respectively. The furnish was
mixed for 2 minutes after the polyvinylamine was added. pH of the
slurry was varied between 3.5 and 10.0. Handsheets were prepared as
in Example 1 and tested. The results are reported in Table 5.
6TABLE 5 PVAm/CParez .RTM. Bicomponent Strength Agents - Effect of
pH and PVAm Charge Density on Handsheet Properties (10-kg/T polymer
concentration, 1:1 PVAm/CParez .RTM. ratio) % PVAm Wet TI % Wet TI
% TEA@ Charge Dry TI Wet TI 1-hr remain Wet/Dry % Peak Peak E Code
Density pH (Nm/g) (Nm/g) (Nm/g) after 1-hr TI Stretch (J/m2) (kgf)
control -- 6.8 10.7 0.9 0.7 74% 8% 0.9% 3.7 319 42 90% 3.5 26.3 5.4
3.2 59% 21% 2.0% 21.8 477 43 90% 3.9 27.9 5.8 3.2 55% 21% 1.8% 21.6
519 44 90% 7.5 29.2 6.5 4.7 72% 22% 1.7% 20.5 485 45 90% 10.0 25.6
5.9 3.9 67% 23% 1.6% 16.7 435 46 50% 3.5 27.0 4.8 3.3 69% 18% 1.8%
19.6 387 47 50% 6.8 19.7 4.5 3.2 71% 23% 1.3% 10.8 428 48 50% 10.0
21.9 4.5 2.7 60% 20% 1.4% 12.4 382 49 10% 3.7 20.1 3.7 2.1 56% 19%
1.4% 11.6 356 50 10% 6.8 17.6 2.6 1.5 58% 15% 1.2% 8.5 410 51 10%
10.0 16.2 1.7 1.1 67% 10% 1.1% 6.7 365
[0159] From Table 5, at 1:1 polymer ratio, a few general statements
may be made regarding the influence of pH upon furnish charge
balance and subsequent wet strength properties:
[0160] i.) Acidic conditions benefit CParez.RTM./Catiofast.RTM. PR
8104 (10% amine) systems.
[0161] ii.) pH does not seem to affect wet handsheet strength of
CParez.RTM./Catiofast.RTM. 8087 (50% amine) systems.
[0162] iii.) Neutral pH significantly influences strength
development of CParez.RTM./Catiofast.RTM. PR 8106 (90% amine)
systems. Under acid conditions, these systems show promise as
bicomponent, temporary wet strength agents.
Example 6
Effect of pH and Order of Addition on PVAm/anionic Parez
Bicomponent
[0163] A slurry of pulp fibers as described in Example 1 was
prepared. A bicomponent strength system was formed in the slurry
which included the following compounds:
[0164] 1% aqueous solution of Anionic Parez (a glyoxylated
polyacrylamide with acrylic acid functionalities)
[0165] 1% aqueous solution of Catiofast.RTM. PR 8106
polyvinylamine
[0166] For all codes, Polyvinylamine was added at 5 Kg/T and AParez
was added at 2.5 Kg/T. The first polymer was stirred for 10 minutes
with the furnish; the second polymer was then added and mixed 2
minutes, prior to handsheet preparation. Handsheets were then
prepared as described in Example 1. After formation, handsheets
were subjected to tensile testing, with results (average of 5
samples) given in Table 6. No additives were used in the
control.
7TABLE 6 Tensile data for handsheets treated with
polyvinylamine/anionic Parez. Effect of pH and order of addition.
The level of addition is 5 Kg/T for PVAm 8106 and 2.5 Kg/T for
anionic Parez. Dry Wet % Wet TI First TI TI Wet TI remain Polymer
(Nm/ (Nm/ 1 hour after 1 % Code added pH g) g) (Nm/g) hour Wet/Dry
TI Con- -- 6.9 10.65 0.89 0.66 74.2% 8.36 trol 52 AParez 6.8 11.65
.89 .72 81 7.7 53 PVAm 6.8 24.2 5.1 4.1 80 21 54 AParez 6.8 18.4
3.2 2.8 88 17 55 PVAm 4 16.6 2.1 1.2 59 13 56 AParez 4 11.7 1.1 .7
65 9 57 PVAm 10 21.0 4.0 3.4 85 19 58 AParez 10 19.4 3.3 2.8 87 17
59 PVAm 6.8 19.2 3.89 -- -- 20 60 PVAm 6.8 19.8 3.1 -- -- 16 61
PVAm 6.8 26.2 5.2 -- -- 20
[0167] Several findings may be drawn from this data. First, the
anionic Parez (AParez) does not improve tissue strength properties
by itself (Code 52). This is because it does not adsorb on pulp
fibers. Second, the efficiency of the PVAm/AParez system is a
function of pH; best wet and dry strengths were achieved at neutral
pH (pH 6.8). Third, the efficiency of the PVAm/AParez system is a
function of the order of polymer addition; best wet and dry
strengths were achieved with PVAm added first. The pH dependency of
the system is a function of the order of polymer addition.
PVAm/AParez might adsorb as a polymer complex when the
non-adsorbing AParez is introduced first to the furnish, whereas,
multilayers might be created by adding the adsorbing PVAm first.
Third, the wet strength permanency, defined as the ratio of wet
strength after 1 hour soaking to that measured immediately after
soaking, and the wet over dry strength ratio may both be controlled
with pH and the order of polymer addition.
Example 7
Effect of Anionic Polymer and Polymer Concentration in PVAm/anionic
Polyelectrolyte Bicomponent Systems
[0168] A slurry of pulp fibers as described in Example 1 was
prepared. A bicomponent strength system was formed in the slurry
which included the following compounds:
[0169] aqueous solution of an anionic polyelectrolyte
[0170] 1% aqueous solution of a polyvinylamine (BASF Catiofast.RTM.
PR 8106)
[0171] Two types of anionic polyelectrolytes were compared: Anionic
Parez (a glyoxylated polyacrylamide with acrylic acid
functionalities) and a low molecular weight (200,000) high charge
poly (acrylamide-co-acrylic acid) (20 wt % acrylamide). BASF
Catiofast.RTM. PR 8106 polyvinylamine was used in conjunction with
the anionic polyelectrolyte in all instances (PVAm). For all codes,
Polyvinylamine was added first as a 1% solution and stirred for 10
minutes with the furnish; the anionic polymer was then added at
various concentrations and mixed 2 minutes, prior to handsheet
preparation as described in Example 1. After formation, handsheets
were subjected to tensile testing, with results (average of 5
samples) given in Table 7.
8TABLE 7 Tensile data for handsheets treated with
polyvinylamine/anionic Parez and polyvinylamine/polyacrylic acid
(PAA). Effect of type of anionic polymer (PAA or AParez) and
polymer concentration. PVAm added first, pH = 6.8. Anionic PVAm
polymer concen- concen- tration Anionic tration Dry Wet TI % Code
(Kg/T) polymer (Kg/T) TI (Nm/g) (Nm/g) Wet/Dry TI Control -- --
10.65 0.89 8.36 62 5 PAA 2.5 19.2 3.89 20 63 5 PAA 5 19.8 3.1 16 64
5 PAA 10 26.2 5.2 20 65 5 AParez 2.5 26.3 5.2 20 66 5 AParez 5 21.8
4.9 22 67 5 AParez 10 19.7 4.2 21 68 2.5 AParez 2.5 17.4 2.9 17 69
2.5 AParez 5 18.7 3.7 20 70 2.5 AParez 10 18 3.4 19
[0172] Several findings may be drawn from this data. First, for
PVAm/PAA systems at neutral pH, handsheet wet strength and dry
strength both increase as increases the concentration of PAA (codes
62, 63 and 64). Code 64 has similar properties to code 65, this
suggests that aldehyde groups are not required on the polymer to
develop strength. Second, for PVAm/AParez systems at neutral pH,
handsheet wet strength and dry strength both decrease as the
concentration of AParez increases (codes 64, 65 and 66). Code 65
provides the highest tissue strength at the lowest polymer
concentration; this suggests that the aldehyde functionalities of
the AParez are involved in the synergetic strength increase.
Example 8
Polyvinylamine/Carboxymethyl Cellulose Bicomponent Strength
Agents--Effect of Polymer Ratio
[0173] A slurry of pulp fibers as described in Example 1 was
prepared. A biocomponent strength system was formed in the slurry
which included the following compounds:
[0174] a carboxy methyl cellulose (CMC) (Mw 250,000 Daltons)
[0175] 1% aqueous solution of a polyvinylamine (BASF Catiofast.RTM.
PR 8106)
[0176] The degree of substitution for CMC was approximately 0.65 to
0.9. For this study, CMC was added first, followed by PVAm. The
total polymer concentration was kept at 10 Kg/T of dry fiber. pH
was held at 6.8. Handsheets were prepared as described in Example
1.
[0177] The effect of polymer ratio on the handsheet properties is
presented in Table 8. At a constant polymer concentration of 10
Kg/T of dry fiber, adjusting the PVAm/CMC ratio affects each
property of interest. Peak strength properties are attained at
PVAm/CMC ratios between 5:1 and 2:1 (codes 72-73). This data
illustrate that strength development does not necessarily require
chemical interaction between amine (PVAm) and aldehyde
(CParez.RTM.) functionalities.
9TABLE 8 PVAm/CMC Bicomponent Strength Agents - Effect of Polymer
Ratio (pH = 6.8, 10-kg/T polymer concentration, CMC added first)
Wet TI % Wet TI % TEA@ PVAm:CMC Dry TI Wet TI 1-hr remain Wet/Dry %
Peak Peak E Code Ratio (Nm/g) (Nm/g) (Nm/g) after 1-hr TI Stretch
(J/m2) (kgf) control -- 10.16 .79 .61 77 8 .82 3.32 338 71 1:0
14.02 3.65 3.01 82 26 .92 5.13 387 72 5:1 19.99 6.2 5.17 83 31 1.52
12.64 416 73 2:1 22.54 5.79 5.03 87 26 1.64 15.26 407 74 1:1 19.69
3.84 2.88 75 20 1.43 11.71 465 75 1:2 12.99 1.37 1.21 88 11 .93
4.82 376 76 1:5 10.90 .72 .66 92 7 .88 3.89 342 77 0:1 11.28 .78
.52 66 7 .78 3.44 370
Example 9
Polyvinylamine/Carboxymethyl Cellulose Bicomponent Strength
Agents--Effect of Polymer Order of Addition
[0178] A slurry of pulp fibers as described in Example 1 was
prepared. A bicomponent strength system was formed in the slurry
which included the following compounds:
[0179] a modest molecular weight (Mw 250,000 Daltons) carboxymethyl
cellulose (CMC)
[0180] 1% aqueous solution of a polyvinylamine (BASF Catiofast.RTM.
PR 8106)
[0181] The components were at a 2:1 PVAm/CMC ratio. The degree of
substitution for CMC was approximately 0.65 to 0.9. For this study,
each polymer served as the initial charge to the furnish. Moreover,
a polyelectrolyte complex was prepared, at the defined ratio, for
single charge application. The total polymer concentration was kept
at 10 Kg/T of dry fiber. pH was held at 6.8. Handsheets were
prepared as described in Example 1 and tested.
[0182] The effect of polymer order of addition on the handsheet
properties is summarized in Table 9. The order of polymer addition
significantly impacts handsheet properties. Best wet strength
results are achieved with the sequential polymer addition and CMC
added first.
10TABLE 9 PVAm/CMC Bicomponent Strength Agents --Effect of order of
Polymer addition (pH = 6.8, 10-kg/T polymer concentration, PVAm/CMC
ratio = 2/1) Polymer Wet TI % Wet TI % TEA@ added Dry TI Wet TI
1-hr remain Wet/Dry % Peak Peak E Code first (Nm/g) (Nm/g) (Nm/g)
after 1-hr TI Stretch (J/m2) (kgf) 78 PVAm 20.83 4.81 3.75 78 23
1.72 15.24 483 79 CMC 21.76 5.69 4.54 80 26 1.62 14.60 505 80
Complex 14.47 2.88 2.7 94 20 1.05 6.03 394
Example 10
Polyvinylamine/Carboxy Methyl Cellulose Bicomponent Strength
Agents--Effect of Polymer Concentration
[0183] A slurry of pulp fibers as described in Example 1 was
prepared except that. A bicomponent strength system was formed in
the slurry which included the following compounds:
[0184] a modest molecular weight (Mw 250,000 Daltons) carboxymethyl
cellulose (CMC)
[0185] aqueous solution of a polyvinylamine (BASF Catiofast.RTM. PR
8106)
[0186] The components were used in combination at a 2:1 PVAm/CMC
ratio. The degree of substitution for CMC was approximately 0.65 to
0.9. For this study, the CMC component was added first to the
furnish, the furnish was mixed for 10 minutes, and then the
polyvinylamine was added to the furnish, and the furnish was mixed
for an additional 2 minutes. pH was held at 6.8, and the total
polymer concentration in the furnish was varied with the different
codes. Handsheets were prepared as described in Example 1 and
tested.
[0187] The effect of total polymer concentration on the handsheet
properties is summarized in Table 10. Wet strength, dry strength,
wet over dry strength ratio, toughness and rigidity increase as a
function of total polymer concentration. Wet strength permanence,
while independent of polymer concentration, mimics the response of
Kymene.RTM..
11TABLE 10 PVAm/CMC Bicomponent Strength Agents --Effect of Polymer
concentration (pH = 6.8, PVAm/CMC ratio = 2/1, CMC added first)
Polymer Wet TI % Wet TI % TEA@ Concentration Dry TI Wet TI 1-hr
remain Wet/Dry % Peak Peak E Code (mg/g) (Nm/g) (Nm/g) (Nm/g) after
1-hr TI Stretch (J/m2) (kgf) control 0 10.14 .85 .69 81 8 .83 3.34
338 81 2 12.65 1.64 1.39 85 13 .87 4.42 422 82 4 15.43 3.10 2.58 83
20 1.12 7.05 440 83 6 17.39 3.63 3.14 87 21 1.33 9.80 456 84 10
22.54 5.79 5.03 86 26 1.64 15.26 407 85 15 23.92 6.66 5.49 82 28
1.64 16.16 488
Example 11
Chitosan/CParez.RTM. Bicomponent Strength Agents
[0188] A slurry of pulp fibers as described in Example 1 was
prepared except that 50 g (oven-dry basis) of pulp fibers were
soaked in 8 liters of deionized water for a fiber furnish used in
the formation of the handsheets having a consistency of 0.625%. A
bicomponent strength system was formed in the slurry which included
the following compounds:
[0189] Chitosan (a natural polysaccharide containing primary amine
functionality)
[0190] 1% aqueous solution of Parez 631NC (a cationic glyoxylated
polyacrylamide) manufactured by Cytec Industries (CParez.RTM.)
[0191] The use of Chitosan as a dry and wet strength additive in
papermaking is documented. The first component was added to the
furnish, the furnish was mixed for 10 minutes, the second component
was added to the furnish, and the furnish was then mixed an
additional 2 minutes. pH was held at neutral. Handsheets were
prepared as described in Example 1 and then tested. When added to
the furnish in conjunction with glyoxylated polyacrylamides
(cationic Parez 631NC) sheet characteristics similar to the
polyvinylamine/cationic Parez system were obtained. That is, a
synergistic strength affect dependent on order of addition of the
two materials. This would suggest that this effect is most likely
to occur with any polymeric amine and aldehyde combination. The
data for Chitosan and glyoxylated polyacrylamide sheets are shown
in Table 11, below.
12TABLE 11 Chitosan/Parez Strength System % % increase increase
over over Parez Chitosan Dry TI control Wet TI control Code (Kg/T)
(Kg/T) (Nm/g) (Dry TI) (Nm/g) (Wet TI) 86 0 0 15.5 0% 0.9 0% 87 5 0
19.9 29% 3.2 239% 88 10 0 24.3 57% 4.9 420% 89 0 5 15.6 1% 1.5 59%
90 0 10 16.9 9% 2.0 116% 91 5 5 19.1 23% 3.3 252% Chitosan added
1.sup.st 92 10 10 26.5 71% 5.0 427% Chitosan added 1.sup.st 93 5 5
27.2 76% 5.4 476% Parez added 1st 94 10 10 34.9 126% 7.7 720% Parez
added 1st
[0192] It will be appreciated that the foregoing examples, given
for purposes of illustration, are not to be construed as limiting
the scope of this invention. Although only a few exemplary
embodiments of this invention have been described in detail above,
those skilled in the art will readily appreciate that many
modifications are possible in the exemplary embodiments without
materially departing from the novel teachings and advantages of
this invention. Accordingly, all such modifications are intended to
be included within the scope of this invention which is defined in
the following claims and all equivalents thereto. Further, it is
recognized that many embodiments may be conceived that do not
achieve all of the advantages of some embodiments, yet the absence
of a particular advantage shall not be construed to necessarily
mean that such an embodiment is outside the scope of the present
invention.
* * * * *