U.S. patent application number 10/327701 was filed with the patent office on 2003-07-24 for method for increasing filler retention of cellulosic fiber sheets.
This patent application is currently assigned to Weyerhaeuser Company. Invention is credited to Jewell, Richard A., Neogi, Amar N., White, Steven J..
Application Number | 20030136532 10/327701 |
Document ID | / |
Family ID | 23041629 |
Filed Date | 2003-07-24 |
United States Patent
Application |
20030136532 |
Kind Code |
A1 |
Jewell, Richard A. ; et
al. |
July 24, 2003 |
Method for increasing filler retention of cellulosic fiber
sheets
Abstract
A method for increasing filler retention of cellulosic fiber
sheets is disclosed. In the method, cellulosic fibers with
increased anionic sites are treated with either positively charged
filler particles and/or amphoteric filler particles or a cationic
retention aid and negatively charged filler particles and/or
amphoteric filler particles. Cellulosic fiber sheets with retained
filler particles are also disclosed.
Inventors: |
Jewell, Richard A.;
(Bellevue, WA) ; Neogi, Amar N.; (Seattle, WA)
; White, Steven J.; (Gig Harbor, WA) |
Correspondence
Address: |
WEYERHAEUSER COMPANY
INTELLECTUAL PROPERTY DEPT., CH 1J27
P.O. BOX 9777
FEDERAL WAY
WA
98063
US
|
Assignee: |
Weyerhaeuser Company
|
Family ID: |
23041629 |
Appl. No.: |
10/327701 |
Filed: |
December 20, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10327701 |
Dec 20, 2002 |
|
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09272865 |
Mar 19, 1999 |
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6514384 |
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Current U.S.
Class: |
162/157.6 ;
162/158; 162/164.3; 162/168.3; 162/175; 162/181.2; 162/181.8 |
Current CPC
Class: |
D21H 17/455 20130101;
D21H 17/675 20130101; D21H 23/765 20130101; D21H 17/375 20130101;
D21H 17/29 20130101; D21H 17/55 20130101; D21H 17/68 20130101; D21H
21/10 20130101; D21H 11/20 20130101 |
Class at
Publication: |
162/157.6 ;
162/158; 162/181.2; 162/168.3; 162/175; 162/181.8; 162/164.3 |
International
Class: |
D21H 013/06; D21H
017/28; D21H 017/54; D21H 017/67; D21H 017/68; D21H 017/52 |
Claims
The embodiments of the invention in which an exclusive property or
privilege is claimed are defined as follows:
1. A method for preparing a cellulosic fiber sheet having retained
filler particles, comprising treating fibers having increased
anionic sites with positively charged filler particles to provide a
cellulosic fiber sheet having retained positively charged filler
particles.
2. The method of claim 1 wherein fibers having increased anionic
sites comprise carboxylated cellulosic fibers.
3. The method of claim 1 wherein the positively charged filler
particles comprise calcium carbonate particles.
4. A method for preparing a cellulosic fiber sheet having retained
filler particles, comprising: treating fibers having increased
anionic sites with a cationic retention aid to provide cellulosic
fibers having bonded cationic retention aid; and treating the
fibers having bonded cationic retention aid with negatively charged
filler particles to provide a cellulosic fiber sheet having
retained negatively charged filler particles.
5. The method of claim 4 wherein fibers having increased anionic
sites comprise carboxylated cellulosic fibers.
6. The method of claim 4 wherein the cationic retention aid is
selected from the group consisting of cationic polyacrylamides and
cationic starches.
7. The method of claim 4 wherein the negatively charged filler
particles are selected from the group consisting of ground
limestone and clay particles.
8. A method for preparing a cellulosic fiber sheet having retained
filler particles, comprising: combining a cationic retention aid
with negatively charged filler particles; and treating fibers
having increased anionic sites with the combination of a cationic
retention aid and negatively charged filler particles to provide a
cellulosic fiber sheet having retained negatively charged filler
particles.
9. A cellulosic fiber sheet having retained filler particles,
wherein the filler particles are bonded to fibers having increased
anionic sites, wherein the filler particles are bonded to the
fibers through the anionic sites, and wherein the filler particles
are selected from the group consisting of positively charged filler
particles, negatively charged filler particles, and amphoteric
filler particles.
10. A cellulosic fiber sheet having retained positively charged
filler particles, wherein the filler particles are bonded to the
fibers through anionic sites incorporated into the fibers.
11. The sheet of claim 10 wherein the anionic sites are carboxyl
groups.
12. The sheet of claim 10 wherein the positively charged filler
particles comprise calcium carbonate particles.
13. A cellulosic fiber sheet having retained negatively charged
filler particles, wherein the filler particles are bonded to the
fibers through a cationic retention aid bonded to anionic sites
incorporated into the fibers.
14. The sheet of claim 13 wherein the anionic sites are carboxyl
groups.
15. The sheet of claim 13 wherein the cationic retention aid is
selected from the group consisting of cationic polyacrylamides and
cationic starches.
16. The sheet of claim 13 wherein the negatively charged filler
particles are selected from the group consisting of ground
limestone and clay particles.
17. A cellulosic fiber sheet having retained negatively charged
filler particles, wherein the filler particles are bonded to the
fibers through a cationic retention aid bonded to the anionic sites
incorporated into the fibers, wherein the fixed anionic sites
comprise carboxyl groups, wherein the cationic retention aid
comprises cationic polyacylamide, and wherein the negatively
charged filler particles are selected from the group consisting of
ground limestone and clay particles.
18. A papermaking furnish comprising cellulosic fibers having
increased anionic sites and positively charged filler particles,
wherein the filler particles are bonded to the fibers through fixed
anionic sites incorporated into the fibers.
19. The furnish of claim 18 wherein the fixed anionic sites are
carboxyl groups.
20. The furnish of claim 18 wherein the positively charged filler
particles comprise calcium carbonate particles.
21. A papermaking furnish comprising cellulosic fibers having
increased anionic sites and negatively charged filler particles,
wherein the filler particles are bonded to the fibers through a
cationic retention aid bonded to anionic sites incorporated into
the fibers.
22. The furnish of claim 21 wherein the anionic sites are carboxyl
groups.
23. The furnish of claim 21 wherein the cationic retention aid is
selected from the group consisting of cationic polyacrylamides and
cationic starches.
24. The furnish of claim 21 wherein the negatively charged filler
particles are selected from the group consisting of ground
limestone and clay particles.
25. A method for increasing the drainage of water from a fibrous
furnish deposited onto the forming wire of a papermaking machine,
comprising incorporating into a fibrous furnish cellulosic fibers
having increased anionic sites and positively charged filler
particles, wherein the filler particles are bonded to the fibers
through anionic sites incorporated into the fibers.
26. A method for increasing the drainage of water from a fibrous
furnish deposited onto the forming wire of a papermaking machine,
comprising incorporating into a fibrous furnish cellulosic fibers
having increased anionic sites and negatively charged filler
particles, wherein the filler particles are bonded to the fibers
through a cationic retention aid bonded to fixed anionic sites
incorporated into the fibers.
27. A method for increasing the drainage of water from a fibrous
furnish deposited onto the forming wire of a papermaking machine,
comprising incorporating into a fibrous furnish cellulosic fibers
having increased anionic sites and a cationic material.
28. The method of claim 27 wherein the cellulosic fibers having
increased anionic sites comprise carboxylated fibers.
29. The method of claim 27 wherein the cationic material comprises
polyamide epichlorohydrin.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a method for increasing
filler retention of cellulosic fiber sheets and, more particularly,
to a method for increasing filler retention for cellulosic fiber
sheets by incorporating cellulosic fibers having increased anionic
sites into the sheet.
BACKGROUND OF THE INVENTION
[0002] Fillers are often incorporated into cellulosic fiber sheets
to provide paper products having enhanced printability and
increased strength properties. However, the improvement provided by
filler retained fibers is limited by the amount of filler that can
be retained by the fiber sheets and the retention of filler by the
fiber sheet. Accordingly, there exist a need for methods for
increasing fiber capacity for filler and for increasing the filler
retention of fiber sheets. The present invention seeks to fulfill
these needs and provides further related advantages.
SUMMARY OF THE INVENTION
[0003] In one aspect, the present invention provides a method for
increasing filler retention of cellulosic fiber sheets. In the
method, cellulosic fibers with increased anionic sites are treated
with either positively charged and/or amphoteric filler particles
or a cationic retention aid and negatively charged and/or
amphoteric filler particles to provide sheets having increased
filler retention.
[0004] In another aspect of the invention, cellulosic fiber sheets
with retained filler particles are provided. In one embodiment,
fiber sheets with retained positively charged and/or amphoteric
filler particles are provided and, in another embodiment, the fiber
sheets with retained negatively charged and/or amphoteric filler
particles are provided.
[0005] In a further aspect, a method for increasing drainage from a
papermaking furnish is provided. In the method, cellulosic fibers
having increased anionic sites are incorporated into the
furnish.
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] The foregoing aspects and many of the attendant advantages
of this invention will become more readily appreciated by reference
to the following detailed description, when taken in conjunction
with the accompanying drawings, wherein:
[0007] FIG. 1 is a graph illustrating the change in sizing as a
function of added cationic starch for fibrous sheets formed in
accordance with the present invention;
[0008] FIG. 2 is a graph illustrating change in sizing as a
function of added sizing agent for fibrous sheets formed in
accordance with the present invention;
[0009] FIG. 3 is a graph illustrating percent filler retained as a
function of added cationic starch for fibrous sheets formed in
accordance with the present invention;
[0010] FIG. 4 is a graph illustrating percent ash in sheet as a
function of added cationic starch for fibrous sheets formed in
accordance with the present invention;
[0011] FIG. 5 is a graph illustrating drain time as a function of
percent ash in sheet for fibrous sheets formed in accordance with
the present invention;
[0012] FIG. 6 is a graph illustrating specific extensional
stiffness as a function of percent ash in sheet for fibrous sheets
formed in accordance with the present invention; and
[0013] FIG. 7 is a graph illustrating tensile index as a function
of percent ash in sheet for fibrous sheets formed in accordance
with the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0014] The present invention provides a method for increasing
filler retention in cellulosic fiber sheets. The method provides a
cellulosic fiber sheet having retained filler particles. When
fibers having increased anionic sites and filler particles are
incorporated into a papermaking furnish, and the furnish is
deposited onto the papermachine's forming wire, the resulting
furnish can be drained at an increased rate relative to comparable
furnishes lacking cellulosic fibers having increased anionic
sites.
[0015] As used herein, the term "filler particle" refers to
positively charged filler particles, negatively charged filler
particles, and amphoteric filler particles. Amphoteric particles
can be either formally charged (i.e., positively or negatively
charged) or lack formal charge. Filler particles useful in the
present invention are retained to cellulosic fibers through
electrostatic bonding and association. Filler particles are
generally noncellulosic particle additives combined with cellulosic
fibers in the papermaking process to provide paper products having
improved properties compared to paper products containing solely
cellulosic fibers.
[0016] In general, the method of the invention includes applying
either (1) positively charged and/or amphoteric filler particles or
(2) cationic retention aid and negatively charged and/or amphoteric
filler particles to cellulosic fibers having an increased number of
fixed anionic sites. The terms "cellulosic fibers having an
increased number of fixed anionic sites" and "cellulosic fibers
having increased anionic sites" refer to cellulosic fibers that
have been modified such that the number of available anionic sites
in the fibers is increased relative to corresponding fibers that
have not been so modified.
[0017] By virtue of its hydroxyl groups, cellulose is a polar
molecule that can form hydrogen bonds with other polar molecules,
such as other cellulose molecules, to form fibers. Wood pulp fibers
contain cellulose and hemicelluloses. Hemicelluloses contain a
small number of carboxyl groups, providing the fibers with an
overall negative charge. Accordingly, cellulose has some natural
tendency to retain certain other materials. To increase cellulose's
capacity to form bonds with and retention of certain materials, the
method of the present invention provides for increasing the number
of sites on the fiber to which bonding can occur. Accordingly, the
addition of fixed anionic sites (e.g., carboxyl groups) to
cellulose fibers provides the fibers with additional sites or
positions through which bonding to cationic species can occur. In
the practice of the invention, the number of carboxyl groups added
to a fiber is not particularly critical and can be controlled to
provide fibers having the desired capacity for and retention of
certain materials. Generally, the greater the number of fixed
anionic sites for a cellulosic fiber, the greater the filler
retention of fiber sheets incorporating these fibers. In general,
increasing the number of carboxyl groups for a cellulosic fiber
will increase its capacity to bond to cationic materials and its
ability to retain those materials. As used herein, the term "bond"
refers to the electrostatic attractive force between oppositely
charged materials, such as the anionic sites of a cellulose fiber
and a cationic retention aid or positively charged filler particle.
The term "charged" refers to materials and particles having formal
positive and negative charges as well as to materials lacking
formal charge but that are capable of electrostatic bonding and
association through dipolar interactions.
[0018] Anionic sites can be introduced into a cellulosic fiber by,
for example, chemically modifying the fiber to increase the fiber's
carboxyl content. Suitable methods for increasing a fiber's
carboxyl content include any method that results in carboxyl group
incorporation. Preferably carboxyl group introduction into
cellulosic pulp is without substantial crosslinking and without
substantially reducing the degree of polymerization of the pulp.
Suitable methods are known in the art and include carboxylating
cellulosic fibers such as described in U.S. Pat. No. 5,667,637,
issued to Jewell et al., relating to cellulose carboxyethylation;
U.S. Pat. No. 5,755,828, issued to Westland, relating to
polyacrylic acid carboxylation of cellulosic fibers; and U.S.
patent application Ser. No. 09/222,372, filed Dec. 29, 1998,
relating to cellulose succinylation; each assigned to Weyerhaeuser
Co. and expressly incorporated herein by reference. Other
carboxylated cellulosic fibers and methods for their formation are
known and are suitable in the practice of the present invention.
For example, carboxymethylated cellulose (CMC) is a suitable
carboxylated cellulosic fiber. Carboxylated cellulose fibers
prepared by TEMPO catalyzed oxidation of cellulose is another
suitable method for increasing the number of cellulose carboxyl
groups. In this method, the cellulose carboxyl groups formed are
glucuronic acid groups. These fibers and methods for their
formation are described in U.S. patent application Ser. No. ______,
entitled "Method of Making Carboxylated Cellulose Fibers and
Products of the Method," filed Mar. 19, 1999, and assigned to
Weyerhaeuser Company, expressly incorporated herein by
reference.
[0019] To prepare a product that includes a cationic filler
particle from cellulosic fibers that have been modified to include
an increased number of fixed anionic sites (e.g., a carboxylated
fiber), the fiber having increased anionic sites is treated with a
positively charged filler particle. For example, fibers with
increased anionic sites can be combined with positively charged
filler particles in an aqueous slurry and then deposited onto a
foraminous support to form a wet composite. Once deposited,
drainage of the slurry's dispersion medium from the wet composite
occurs and, on subsequent drying, a sheet composed of cellulosic
fibers with retained positively charged filler particles is
produced. Alternatively, a mixture comprising a cationic filler and
an anionic retention aid can be prepared and then added to a
mixture of cellulosic fibers and a cationic retention aid. For
example, a positively charged filler such as cationic calcium
carbonate (PCC) can be mixed with anionic polyacrylamide (i.e.,
anionic retention aid) and then added to a mixture of cellulosic
fibers and a cationic retention aid (e.g., cationic starch).
[0020] Positively charged filler particles useful in the present
invention include calcium carbonate, such as chalk and precipitated
calcium carbonate (PCC); and aluminum trihydrate. Precipitated
calcium carbonate is a preferred positively charged filler
particle.
[0021] Because cellulosic fibers modified to have increased anionic
sites are anionic in nature, negatively charged filler particles
cannot be directly combined with such fibers to provide fibers
having retained negatively charged filler particles. In the method
of the invention, negatively charged filler particles are bonded to
cellulosic fibers having increased anionic sites through an
intermediate cationic retention aid. The cationic retention aid
serves to bond to the cellulosic fibers through its anionic sites
to provide fibers effectively having a cationic surface. Through
the retention aid, negatively charged filler particles are bonded
to the fibers' cationic surface to provide cellulosic fibers with
retained negatively charged filler particles.
[0022] Cellulosic fiber sheets with retained negatively charged
filler particles can be formed sequentially by first treating
fibers having increased anionic sites with a cationic retention aid
and then treating the resulting fibers with negatively charged
filler particles. For example, the cationic retention aid can be
combined with the anionic cellulosic fibers in an aqueous slurry.
To the resulting slurry are added negatively charged filler
particles. However, the presence of excessive amounts of cationic
retention aid can render both the filler and fiber cationic,
thereby reducing filler retention. The slurry can then be then
deposited on a foraminous support and the wet composite dried to
provide a sheet composed of cellulosic fibers having retained
negatively charged filler particles. Alternatively, a mixture of
cationic retention aid and negatively charged filler particles can
be added to fibers having increased anionic sites.
[0023] Cationic retention aids useful in the present invention
include resins such as polyamide epichlorohydrin (commercially
available under the tradename KYMENE from Hercules, Inc.,
Wilmington, Del., e.g., KYMENE 557H), polyethyleneimine, and
polyacrylamide (commercially available under the tradename PAREZ
from American Cyanamid Co., Stanford, Conn., e.g., PAREZ 631 NC and
PAREZ 750B; CYPRO 514 and ACCOSTRENGTH 711 from American Cyanamid
Co., Wayne, N.J.); cationic urea formaldehyde and melamine
formaldehyde resins; cationic starch (commercially available under
the designation WESCAT EF cationic starch from Western Polymer Co.,
Moses Lake, Wash.); cationic dialdehyde starch-based resin
(commercially available under the designation CALDAS from Japan
Carlet; National Starch 78-0080; COBOND 1000 from National Starch
and Chemical Corp., New York, N.Y.). Other useful retention aids
include cationic polymers such as chitosan and cationic siloxanes.
Preferred cationic retention aids include cationic polyacrylamide
and cationic starches.
[0024] Negatively charged filler particles useful in the present
invention include ground limestone or marble (calcium carbonate,
supplied in strongly anionic form due to polyanionic dispersants),
clay (mildly anionic), titanium dioxide (supplied with anionic
dispersant), silicas, sodium aluminosilicates, and calcinated clay.
Preferred negatively charged filler particles include clay and
ground limestone particles.
[0025] Cellulosic fibers are the basic, component of the product of
the present invention. Suitable fibers include any cellulosic fiber
that can be modified to increase the fibers' fixed anionic sites.
Suitable fibers include cellulosic fibers that can be modified to
include carboxyl groups. Although available from other sources,
cellulosic fibers are derived primarily from wood pulp. Suitable
wood pulp fibers for use with the invention can be obtained from
well-known chemical processes such as the Kraft and sulfite
processes, with or without subsequent bleaching. The pulp fibers
may also be processed by thermomechanical, chemithermomechanical
methods, or combinations thereof. The preferred pulp fiber is
produced by chemical methods. Ground wood fibers, recycled or
secondary wood pulp fibers, and bleached and unbleached wood pulp
fibers can be used. The preferred starting material is prepared
from long fiber coniferous wood species, such as southern pine,
Douglas fir, spruce, and hemlock. Details of the production of wood
pulp fibers are well-known to those skilled in the art. These
fibers are commercially available from a number of companies,
including Weyerhaeuser Company. For example, suitable cellulose
fibers produced from southern pine that are usable with the present
invention are available from Weyerhaeuser Company under the
designations CF416, NF405, PL416, FR516, and NB416. Other suitable
cellulose fibers can be obtained from northern softwood bleached
kraft including Grand Prairie softwood and Prince Albert NBK;
Douglas fir bleached kraft including Kamloops kraft; hardwood
bleached kraft and sulfite pulps; and softwood bleached sulfite
pulps. Other preferred pulps include bleached hardwood chemical
pulps commonly used in the manufacture of fine papers.
[0026] The wood pulp fibers useful in the present invention can
also be pretreated prior to use with the present invention. This
pretreatment may include physical treatment, such as subjecting the
fibers to steam, or chemical treatment.
[0027] Although not to be construed as a limitation, examples of
pretreating fibers include the application of fire retardants to
the fibers, and surfactants or other liquids, such as water or
solvents, which modify the surface chemistry of the fibers. Other
pretreatments include incorporation of antimicrobials, pigments,
and densification or softening agents. Fibers pretreated with other
chemicals, such as thermoplastic and thermosetting resins also may
be used. Combinations of pretreatments also may be employed.
[0028] In another aspect, the present invention provides cellulosic
fiber sheets with retained filler particles. In one embodiment of
the invention, the filler particles are positively charged. For
these fibers, positively charged filler particles are bonded to the
fibers through the fibers' anionic sites or through a combination
of anionic and cationic retention aids. In another embodiment, the
filler particles are negatively charged. For these fibers,
negatively charged filler particles are bonded to the fibers
through a cationic retention aid that is bonded to the fibers
through the fibers' anionic sites. In a further embodiment,
amphoteric particles are bonded to the fibers having fixed anionic
sites through cationic and/or anionic retention aids. In a
preferred embodiment, the fixed anionic sites include carboxyl
groups that have been incorporated into the cellulosic fiber.
[0029] Preferably, the fiber sheets include carboxylated fibers to
which have been retained ground limestone and/or clay particles
through cationic polyacrylamide as the retention aid.
[0030] In another aspect of the present invention, a method for
increasing the drainage rate for a papermaking machine is provided.
In the method, cellulosic fibers having increased anionic sites are
incorporated into a conventional papermaking furnish. By virtue of
the presence of fibers having increased anionic sites in the
furnish, water drainage from the furnish deposited on the forming
wire of a papermachine is greatly increased compared to a similar
furnish lacking fibers having retained filler particles. The fibers
having increased anionic sites retain filler particles in the
sheet, thereby reducing the amount of filler in the papermaking
machine whitewater. Accordingly, a papermachine having its
production speed limited by drainage can increase its production by
incorporating fibers having increased anionic sites in accordance
with the method of the invention. Similarly, a furnish including
fibers having increased anionic sites allows for the incorporation
of highly refined fibers with relatively low freeness to provide a
sheet with increased sheet strength and that can be formed with an
acceptable drainage/production rate.
[0031] The increased carboxyl content of cellulosic fibers provides
the fibers with a great number of fixed anionic sites and results
in increased filler capacity and retention for the fiber sheet
incorporating these fibers. For paper products, sizing is increased
by increasing the retention of cationic sizing emulsion particles
further resulting in improved printability. With regard to sheet
formation, wet end drainage from papermaking machines and machine
speed can be increased by partial flocculation of the highly
carboxylated fibers and fines with cationic wet end additives.
Sheet strength can also be increased by enhancing the bonding of
recycled furnishes with highly carboxylated fiber addition, by
increasing cationic starch retention, or by increased retention of
other cationic polymer dry and wet strength additives.
[0032] The following examples are for the purpose of illustrating,
not limiting, the present invention.
EXAMPLES
Example 1
Comparison of Characteristics and Properties of Handsheets Prepared
from Cellulosic Fibers Having Retained Filler
[0033] In this example, the characteristics and properties of
handsheets prepared from cellulosic fibers having increased anionic
sites is compared. The handsheets were prepared from a stock
mixture containing 70 percent by weight hardwood (i.e., Prince
Albert hardwood pulp refined to 500 CSF in a Valley beater) and 30
percent by weight softwood. The softwood was Grand Prairie softwood
pulp refined to 300 CSF. To illustrate the advantages of the
present invention, handsheets were prepared from two types of
softwood pulp: (1) softwood pulp as described above without further
treatment and having about 3.5 milliequivalents (meq) carboxyl
groups/100 g pulp (designated GP in the FIGURES) and
(2).carboxyethylated softwood prepared from the above softwood and
having about 23 meq carboxyl groups/100 g pulp (designated CW in
the FIGURES), pulp containing cellulosic fibers having increased
anionic sites.
[0034] Fine paper handsheets were formed with the following
additives applied in order to a fibrous slurry (0.5 percent
consistency) while stirring at 750 rpm in a Britt Jar:
[0035] (1) cationic starch added at 0.5, 1, 2, or 4 percent by
weight based on the weight of total solids, followed by 1 minute of
stirring;
[0036] (2) a sizing agent (ASA, alkyl succinic anhydride) added at
either 2.7 or 4.0 pounds per ton fiber, followed by 15 seconds of
stirring;
[0037] (3) scalenohedral precipitated calcium carbonate (sPCC)
added at 25, 35, or 45 percent by weight based on the weight of
total solids, followed by 15 seconds of stirring; and
[0038] (4) an anionic retention aid (ACCURAC 171) added at 0.5
pounds per ton fiber, followed by 1 minute of stirring.
[0039] Sufficient stock was added to provide a sheet having a basis
weight of about 75 g/m2, however unretained materials caused the
sheet basis weights to be lower.
[0040] The sizing of the comparative sheets was determined by the
Hercules Sizing Test (HST), which measured the number of seconds
that ink is held on the paper's surface before soaking in and
wetting the sheet. The results for handsheets incorporating GP (3.5
meq carboxyl groups/100 g pulp) and CW (23 meq carboxyl groups/100
g pulp) having 0.5, 1, 2, and 4 percent by weight cationic starch
based on the total weight of solids and either 25, 35, and 45
percent by weight filler (PCC) based on the total weight of solids
is shown in FIG. 1.
[0041] Referring to FIG. 1, HST increases with decreasing filler
and generally decreases with increasing cationic starch. Handsheets
prepared from CW softwood generally showed significantly increased
sizing, greater than about 50 percent or more, compared to GP
softwood containing sheets.
[0042] Handsheet sizing as a function of sizing agent for CW- and
GP-containing handsheets is illustrated in FIG. 2. Referring to
FIG. 2, sizing generally increases with increasing sizing agent and
handsheets prepared from CW softwood generally showed significantly
increased sizing, greater than about 50 percent or more, compared
to GP-containing sheets.
[0043] The amount of filler retained for CW- and GP-containing
handsheets as a function of percent cationic starch for 25, 35, and
45 percent filler added is illustrated in FIG. 3. Referring to FIG.
3, filler retention generally decreases with increasing cationic
starch and handsheets prepared from CW softwood generally showed
significantly increased filler retention, greater than about 5
percent or more, compared to GP-containing sheets.
[0044] The amount of retained filler in a handsheet can be
determined by ashing the handsheet. FIG. 4 compares the percent ash
in handsheet for CW- and GP-containing handsheets as a function of
percent cationic starch for 25, 35, and 45 percent filler added.
Referring to FIG. 4, ash content generally decreases with
increasing cationic starch and handsheets prepared from CW softwood
generally showed increased ash content compared to GP-containing
sheets. These results are consistent with those noted above
relating to filler retention.
[0045] Drainage time during sheet formation in a sheet mold was
determined for CW- and GP-containing handsheets. Handsheet drain
time as a function of ash content in the sheet was determined and
the results presented in FIG. 5. As shown in FIG. 5, drain time
generally decreases with increasing filler retained and handsheets
containing CW softwood had significantly decreased drain times,
about 5 percent, compared to the GP handsheets. The time required
for drainage for sheets formed in accordance with the present
invention is less than for comparable sheets that do not include
such filler retained fibers.
[0046] The strength of handsheets containing CW softwood with
increased retained filler was comparable to GP-containing
handsheets having a lower amount of retained filler. Specific
Extensional Stiffness (measured in meters) as a function of percent
cationic starch for CW- and GP-containing handsheets at 25, 35, and
45 percent added filler is shown in FIG. 6. Referring to FIG. 6,
stiffness generally increases with increasing starch and decreasing
retained filler. The stiffness of the CW-containing sheets was
slightly less but comparable to the GP-containing sheets.
[0047] The tensile index (measured in NM/g) as a function of
percent ash in the sheet is illustrated in FIG. 7. Referring to
FIG. 7, tensile strength generally decreases with increasing ash
content and increasing retained filler. The tensile index for
handsheets containing CW softwood was slightly lower but comparable
to GP-containing handsheets.
[0048] The results above demonstrate that cellulosic fiber sheets
formed in accordance with the present invention exhibit
advantageous properties including increased filler retention,
decreased drainage times, and increased sizing compared to
comparable sheets lacking fibers having increased anionic sites.
Furthermore, the sheets of the invention do not suffer from a
decrease in strength as a result of their increased filler
retention.
Example 2
Measurement of Drainage Rate and Preparation of Low Basis Weight
Low Density Tissue Handsheets
[0049] About 30-31 g of pulp was refined in a PFI Refiner to 570+5
mL Canadian Standard Freeness. Nineteen grams (dry basis) of the
refined pulp in a total of 2000 mL of water was placed in a British
disintegrator, 2.28 g of 12.5% Kymene 557H solution was added, and
the slurry was disintegrated for 10 minutes. The resulting
disintegrated pulp slurry was diluted to 19 L to form a 0.1%
consistency slurry. The drainage rate of this slurry was measured
by the amount of time taken to pass 300 mL of filtrate water, using
a liquid slurry head height of 36 inches, through a 1.0 inch
diameter circular handsheet forming wire containing 84.times.76
wires per inch. The forming wire was obtained from Albany
International, 435 Sixth St., Menasha, Wis., 54952.
[0050] A 12 inch.times.12 inch deckle box was used to form
handsheets of approximately 26 g/m.sup.2 basis weight and
approximately 240 kg/m.sup.3 density on the forming wire described
above. Five sheets were formed for each pulp. The sheets were not
wet pressed. Dewatering of the handsheets was accomplished by
passing the sheets still on the forming wire over a vacuum slit.
The sheets were dried on a steam-heated drum dryer and cured in an
oven for one hour at 105.degree. C. Wet burst strength of the
sheets was measured on a Thwing Albert Model 1300-177 Wet Burst
Tester manufactured by Thwing Albert Instrument Co., Philadelphia,
Pa., 19154. Eight measurements were made for each pulp and the
average calculated and taken as the wet burst strength.
Example 3
Wet Burst Strength and Drainage Rate of Highly Carboxylated
Fibers
[0051] Pulp Sample SC was washed with 1% CaCl.sub.2 solution
followed by water to produce a highly carboxylated pulp with the
cations substantially all calcium, and is designated Sample 5C1.
Sample 5C1 was blended with Grande Prairie Softwood northern
bleached kraft in a ratio of 10% Sample 5C1 and 90% northern
bleached kraft. This blend was used in the evaluations described in
Example A, and was compared to a pulp consisting of 100% Grande
Prairie Softwood. The pulp blend containing 10% highly carboxylated
fibers showed a 17% decrease in drain time and slightly improved
wet burst strength in comparison to the 100% Grande Prairie pulp at
equal freeness. The results are summarized in Table 1.
1TABLE 1 Drain Time and Wet Burst Comparison. Pulp Drain Time
(seconds) Wet Burst (g) Blend 166 1152 100% Grande Prairie Softwood
201 1136
Example 4
Preparation of Highly Carboxylated Fibers
[0052] In the examples shown to the present time, maximum carboxyl
content of the product has been about 25 meq/100 g. It is readily
possible to prepare a fibrous product having much higher
substitution. This may be done most readily by increasing the
amount of hypohalite used and/or by extending the reaction time. To
illustrate this, three samples were prepared according to the
following procedures. For example 5A, a buffer solution was
prepared using 10.1 g NaHCO.sub.3 and 8.48 g Na.sub.2CO.sub.3
dissolved in 2.6 L of deionized water. In this was dispersed 100 g
dry basis of northern softwood kraft pulp followed by the addition
of 1.4 kg ice. The pH was about 9.7. An oxidizing mixture was
prepared by first mixing 200 mg TEMPO with 2.00 g NaBr then adding
5 mL of a total 40 mL 5.25% NaOCl solution and mixing well until
the oily material was dissolved. This was added to the buffered
pulp slurry. The remaining 35 mL of NaOCl solution was added slowly
over the next 22 minutes. The slurry was then drained, washed, and
redispersed in water with 2.13 g NaBH.sub.4 to make a total weight
of 1336 g. After two hours the pulp from the reducing treatment was
again drained and washed. Total carboxyl content was measured as 11
meq/100 g.
[0053] For Example 5B, 190 mL of 5.25% NaOCl solution was used and
the oxidation time was 2.8 hours during oxidation the pH dropped
from 9.7 to 9.3. After washing the pulp was again slurried in water
with 3.2 g NaBH.sub.4 to make a total slurry weight of 2000 g.
After one hour the pulp was drained and washed. Total carboxyl
content was measured as 49 meq/100 g.
[0054] For Example 5C the oxidizing mixture was made up of 427 mg
TEMPO, 2.1 g NaBR and a total of 390 mL 5.25% NaOCl solution. At
2.8 hours after initiation of oxidation pH had dropped to 9.5 and 3
g Na.sub.2CO.sub.3 was added. After five hours the temperature had
risen to 60.degree. C. and pH had dropped to 9.0. At that time 250
g of ice and 4 g Na.sub.2CO.sub.3 were added. Again, at 7.5 hours
after the start of oxidation an additional 4 g of Na.sub.2CO.sub.3
was added. At 8.5 hours the slurry was drained and washed. The
oxidized pulp was treated with NaBH.sub.4 as in Example 4B. Total
carboxyl content was 97 meq/100 g.
[0055] Water retention values are an important property of
cellulose papermaking fibers. Higher values often indicate higher
surface areas or relatively higher fiber saturation points. In
general, higher water retention values will correlate with
increased strength properties of sheeted products. Water retention
as reported herein has been determined by TAPPI. Briefly, a sample
of known dry weight is slurried in water, centrifuged, and
reweighed. Water retention values, carboxyl content, and D.P. for
the three products of the present example are summarized in Table
2.
2TABLE 2 Carboxyl Content, Degree or Polymerization, and Water
Retention Comparison. Water Retention Carboxyl Value Sample No.
meq/100 g D.P. g/g 5A 11 1620 1.80 5B 49 1140 2.55 5C 97 860 4.21
Untreated 4 1700 1.35
[0056] The improvement in water retention values in all samples is
immediately evident.
[0057] While the preferred embodiment of the invention has been
illustrated and described, it will be appreciated that various
changes can be made therein without departing from the spirit and
scope of the invention.
* * * * *