Note: Descriptions are shown in the official language in which they were submitted.
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IMPROVED RETENTION AND DRAINAGE IN THE MANUFACTURE OF PAPER
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Provisional Application
No. 60/640,164, filed December 29, 2004, the entire content of which is herein
incorporated by reference.
FIELD OF THE INVENTION
[0002] This invention relates to the process of making paper and
paperboard from a cellulosic stock, employing a flocculating system.
BACKGROUND
[0003] Retention and drainage is an important aspect of papermaking. It is
known that certain materials can provide improved retention and/or drainage
properties in the production of paper and paperboard.
[0004] The making of cellulosic fiber sheets, particularly paper and
paperboard, includes the following: 1) producing an aqueous slurry of
cellulosic
fiber which may also contain inorganic mineral extenders or pigments; 2)
depositing this slurry on a moving papermaking wire or fabric; and 3) forming
a
sheet from the solid components of the slurry by draining the water.
[0005] The foregoing is followed by pressing and drying the sheet to further
remove water. Organic and inorganic chemicals are often added to the slurry
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prior to the sheet-forming step to make the papermaking method less costly,
more rapid, and/or to attain specific properties in the final paper product.
[0006] The paper industry continuously strives to improve paper quality,
increase productivity, and reduce manufacturing costs. Chemicals are often
added to the fibrous slurry before it reaches the papermaking wire or fabric
to
improve drainage/dewatering and solids retention; these chemicals are called
retention and/or drainage aids.
[0007] Drainage or dewatering of the fibrous slurry on the papermaking wire
or fabric is often the limiting step in achieving faster paper machine speeds.
Improved dewatering can also result in a drier sheet in the press and dryer
sections, resulting in reduced energy consumption. In addition, as this is the
stage in the papermaking method that determines many of the sheet final
properties, the retention and/or drainage aid can impact performance
attributes of
the final paper sheet.
[0008] With respect to solids, papermaking retention aids are used to
increase the retention of fine furnish solids in the web during the turbulent
method
of draining and forming the paper web. Without adequate retention of the fine
solids, they are either lost to the mill effluent or accumulate to high levels
in the
recirculating white water loop, potentially causing deposit buildup.
Additionally,
insufficient retention increases the papermakers' cost due to loss of
additives
intended to be adsorbed on the fiber. Additives can provide opacity, strength,
sizing or other desirable properties to the paper.
[0009] High molecular weight (MW) water-soluble polymers with either
cationic or anionic charge have traditionally been used as retention and
drainage
aids. Recent development of inorganic microparticles, when used as retention
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and drainage aids, in combination with high MW water-soluble polymers, have
shown superior retention and drainage efficacy compared to conventional high
MW water-soluble polymers. U.S. Patent Nos. 4,294,885 and 4,388,150 teach
the use of.starch polymers with colloidal silica. U.S. Patent Nos. 4,643,801
and
4,750,974 teach the use of a coacervate binder of cationic starch, colloidal
silica,
and anionic polymer. U.S. Patent No. 4,753,710 teaches flocculating the pulp
furnish with a high MW cationic flocculant, inducing shear to the flocculated
furnish, and then introducing bentonite clay to the furnish. U.S. Patent Nos.
5,274,055 and 5,167,766 disclose using chemically cross-linked organic
micropolymers as retention and drainage aids in the papermaking process.
[0010] The efficacy of the polymers or copolymers used will vary depending
upon the type of monomers from which they are composed, the arrangement of
the monomers in the polymer matrix, the molecular weight of the synthesized
molecule, and the method of preparation.
[0011] It had been found recently that water-soluble copolymers when
prepared under certain conditions exhibit unique physical characteristics.
These
polymers are prepared without chemical cross linking agents. Additionally, the
copolymers provide unanticipated activity in certain applications including
papermaking applications such as retention and drainage aids. The anionic
copolymers which exhibit the unique characteristics were disclosed in WO
03/050152 Al, the entire content of which is herein incorporated by reference.
The cationic and amphoteric copolymers which exhibit the unique
characteristics
were disclosed in U.S. serial number 10/728,145, the entire content of which
is
herein incorporated by reference.
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[0012] The use of inorganic particles with linear copolymers of acrylamide,
is known in the art. Recent patents teach the use of these inorganic particles
with water-soluble anionic polymers (US 6,454,902) or specific crosslinked
materials (US 6,454,902, US 6,524,439 and US 6,616,806).
[0013] However, there still exists a need to improve drainage and retention
performance.
SUMMARY OF THE INVENTION
[0014] A method of improving retention and drainage in a papermaking
process is disclosed. The method provides for the addition of an associative
polymer and an organic microparticle to a papermaking slurry.
[0015] Additionally, a composition comprising an associative polymer and
an organic microparticle and optionally further comprising cellulose fiber is
disclosed.
[0016] Additionally, a composition comprising an associative polymer, an
organic microparticle, a siliceous material and optionally further comprising
cellulose fiber is disclosed.
DETAILED DESCRIPTION OF THE INVENTION
[0017] The present invention provides for a synergistic combination
comprising a water soluble copolymer prepared under certain conditions
(Hereinafter referred to as "associative polymer") and an organic
microparticle. It
has surprising been found that this synergistic combination results in
retention
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and drainage performance superior to that of the individual components.
Synergistic effects occur when the combination of components are used
together.
[0018] It has been found, unexpectedly, that the use of microparticles in
combination with associative polymers, such as the copolymers disclosed in WO
03/050152 Al or US 2004/0143039 Al, results in enhanced retention and
drainage.
[0019] The present invention also provides for a novel composition
comprising an associative polymer and an organic microparticle.
[0020] The present invention also provides for a novel composition
comprising an associative polymer, an organic microparticle and a siliceous
material.
[0021] The present invention also provides for a novel composition
comprising an associative polymer, an organic microparticle, and cellulose
fiber.
[0022] The present invention also provides for a novel composition
comprising an associative polymer, an organic microparticle, a siliceous
material
and cellulose fiber.
[0023] The use of multi-component systems in the manufacture of paper
and paperboard provides the opportunity to enhance performance by utilizing
materials that have different effects on the process and/or product. Moreover,
the combinations may provide properties unobtainable with the components
individually. Synergistic effects occur in the multi component systems of the
present invention.
[0024] It is also observed that the use of the associative polymer as a
retention and drainage aid has an impact on the performance of other additives
in
the papermaking system. Improved retention and/or drainage can have both a
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direct and indirect impact. A direct impact refers to the retention and
drainage aid
acting to retain the additive. An indirect impact refers to the efficacy of
the
retention and drainage aid to retain filler and fines onto which the additive
is
attached by either physical or chemical means. Thus, by increasing the amount
of filler or fines retained in the sheet, the amount of additive retained is
increased
in a concomitant manner. The term filler refers to particulate materials,
typically
inorganic in nature, that are added to the cellulosic pulp slurry to provide
certain
attributes or be a lower cost substitute of a portion of the cellulose fiber.
Their
relatively small size, on the order of 0.2 to 10 microns, low aspect ratio and
chemical nature results in their not being adsorbed onto the large fibers yet
too
small to be entrapped in the fiber network that is the paper sheet. The term
"fines" refers to small cellulose fibers or fibrils, typically less than 0.2
mm in length
and /or ability to pass through a 200 mesh screen.
[0025] As the use level of the retention and drainage aid increases the
amount of additive retained in the sheet increases. This can provide either an
enhancement of the property, providing a sheet with increased performance
attribute, or allows the papermaker to reduce the amount of additive added to
the
system, reducing the cost of the product. Moreover, the amount of these
materials in the recirculating water, or whitewater, used in the papermaking
system is reduced. This reduced level of material, that under some conditions
can be considered to be an undesirable contaminant, can provide a more
efficient
papermaking process or reduce the need for scavengers or other materials
added to control the level of undesirable material.
[0026] The term additive, as used herein, refers to materials added to the
paper slurry to provide specific attributes to the paper and/or improve the
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efficiency of the papermaking process. These materials include, but are not
limited to, sizing agents, wet strength resins, dry strength resins, starch
and
starch derivatives, dyes, contaminant control agents, antifoams, and biocides.
[0027] The associative polymer useful in the present invention can be
described as follows:
[0028] A water-soluble copolymer composition comprising the formula:
~B-co-F+ (I)
wherein B is a nonionic polymer segment formed from the polymerization of one
or more ethylenically unsaturated nonionic monomers; F is an anionic, cationic
or
a combination of anionic and cationic polymer segment(s) formed from
polymerization of one or more ethylenically unsaturated anionic and/or
cationic
monomers; the molar % ratio of B:F is from 95:5 to 5:95; and the water-soluble
copolymer is prepared via a water-in-oil emulsion polymerization technique
that
employs at least one emulsification surfactant consisting of at least one
diblock or
triblock polymeric surfactant wherein the ratio of the at least one diblock or
triblock surfactant to monomer is at least about 3:100 and wherein; the water-
in-
oil emulsion polymerization technique comprises the steps of: (a) preparing an
aqueous solution of monomers, (b) contacting the aqueous solution with a
hydrocarbon liquid containing surfactant or surfactant mixture to form an
inverse
emulsion, (c) causing the monomer in the emulsion to polymerize by free
radical
polymerization at a pH range of from about 2 to less than 7.
[0029] The associative polymer can be an anionic copolymer. The anionic
copolymer is characterized in that the Huggins' constant (k') determined
between
0.0025 wt. % to 0.025 wt. % of the copolymer in 0.01 M NaCi is greater than
0.75
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and the storage modulus (G') for a 1.5 wt. % actives copolymer solution at 4.6
Hz
greater than 175 Pa.
[0030] The associative polymer can be a cationic copolymer. The cationic
copolymer is characterized in that its Huggins' constant (k') determined
between
0.0025 wt. % to 0.025 wt. % of the copolymer in 0.01 M NaCI is greater than
0.5;
and it has a storage modulus (G') for a 1.5 wt. % actives copolymer solution
at
6.3 Hz greater than 50 Pa.
[0031] The associative polymer can be an amphoteric copolymer. The
amphoteric copolymer is characterized in that its Huggins' constant (k')
determined between 0.0025 wt. % to 0.025 wt. % of the copolymer in 0.01 M NaCI
is greater than 0.5; and the copolymer has a storage modulus (G') for a 1.5
wt. %
actives copolymer solution at 6.3 Hz greater than 50 Pa.
[0032] Inverse emulsion polymerization is a standard chemical process for
preparing high molecular weight water-soluble polymers or copolymers. In
general, an inverse emulsion polymerization process is conducted by 1)
preparing an aqueous solution of the monomers, 2) contacting the aqueous
solution with a hydrocarbon liquid containing appropriate emulsification
surfactant(s) or surfactant mixture to form an inverse monomer emulsion, 3)
subjecting the monomer emulsion to free radical polymerization, and,
optionally,
4) adding a breaker surfactant to enhance the inversion of the emulsion when
added to water.
[0033] Inverse emulsions polymers are typically water-soluble polymers
based upon ionic or non-ionic monomers. Polymers containing two or more
monomers, also referred to as copolymers, can be prepared by the same
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process. These co-monomers can be anionic, cationic, zwitterionic, nonionic,
or
a combination thereof.
[0034] Typical nonionic monomers, include, but are not limited to,
acrylamide; methacrylamide; N-alkylacrylamides, such as N-methylacrylamide;
N,N-dialkylacrylamides, such as N,N-dimethylacrylamide; methyl acrylate;
methyl
methacrylate; acrylonitrile; N-vinyl methylacetamide; N-vinyl formamide; N-
vinyl
methyl formamide; vinyl acetate; N-vinyl pyrrolidone;
hydroxyalky(meth)acrylates
such as hydroxyethyl(meth)acrylate or hydroxypropyl(meth)acrylate; mixtures of
any of the foregoing and the like.
[0035] Nonionic monomers of a more hydrophobic nature can also be used
in the preparation of the associative polymer. The term 'more hydrophobic' is
used here to indicate that these monomers have reduced solubility in aqueous
solutions; this reduction can be to essentially zero, meaning that the monomer
is
not soluble in water. It is noted that the monomers of interest are also
referred to
as polymerizable surfactants or surfmers. These monomers include, but are not
limited to, alkylacryamides; ethylenically unsaturated monomers that have
pendant aromatic and alkyl groups, and ethers of the formula CH2=CR'CH2OAmR
where R' is hydrogen or methyl; A is a polymer of one or more cyclic ethers
such as ethyleneoxide, propylene oxide and/or butylene oxide; and R is a
hydrophobic group; vinylalkoxylates; allyl alkoxylates; and allyl phenyl
polyolether
sulfates. Exemplary materials include, but are not limited to,
methylmethacrylate,
styrene, t-octyl acrylamide, and an allyl 'phenyl polyol ether sulfate
marketed by
Clariant as Emulsogen APG 2019.
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[0036] Exemplary anionic monomers include, but are not limited to, the free
acids and salts of: acrylic acid; methacrylic acid; maleic acid; itaconic
acid;
acrylamidoglycolic acid; 2-acrylamido-2-methyl-l-propanesulfonic acid; 3-
allyloxy-2-hydroxy-l-propanesulfonic acid; styrenesulfonic acid; vinylsulfonic
acid;
vinylphosphonic acid; 2-acrylamido-2-methylpropane phosphonic acid; mixtures
of any of the foregoing and the like.
[0037] Exemplary cationic monomers include, but are not limited to, cationic
ethylenically unsaturated monomers such as the free base or salt of:
diallyldialkylammonium halides, such as diallyldimethylammonium chloride; the
(meth)acrylates of dialkylaminoalkyl compounds, such as dimethylaminoethyl
(meth)acrylate, diethylaminoethyl (meth)acrylate, dimethyl aminopropyl
(meth)acrylate, 2-hydroxydimethyl aminopropyl (meth)acrylate, aminoethyl
(meth)acrylate, and the salts and quaternaries thereof; the N,N-
dialkylaminoalkyl(meth)acrylamides, such as N,N-dimethylaminoethylacrylamide,
and the salts and quaternaries thereof and mixture of the foregoing and the
like.
[0038] The co-monomers may be present in any ratio. The resultant
associative polymer can be non-ionic, cationic, anionic, or amphoteric
(contains
both cationic and anionic charge).
[0039] The molar ratio of nonionic monomer to anionic monomer (B:F or
Formula I) may fall within the range of 95:5 to 5:95, preferably the range is
from
about 75:25 to about 25:75 and even more preferably the range is from about
65:35 to about 35:65 and most preferably from about 60:40 to about 40:60. In
this regard, the molar percentages of B and F must add up to 100%. It is to be
understood that more than one kind of nonionic monomer may be present in the
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Formula I. It is also to be understood that more than one kind of anionic
monomer
may be present in the Formula I.
[0040] In one preferred embodiment of the invention the associative
polymer, when it is an anionic copolymer, is defined by Formula I where B, the
nonionic polymer segment, is the repeat unit formed after polymerization of
acrylamide; and F, the anionic polymer segment, is the repeat unit formed
after
polymerization of a salt or free acid of acrylic acid and the molar percent
ratio of
B:F is from about 75:25 to about 25:75
[0041] The physical characteristics of the associative polymer, when it is an
anionic copolymer, are unique in that their Huggins' constant (k') as
determined in
0.01 M NaCI is greater than 0.75 and the storage modulus (G') for a 1.5 wt. %
actives polymer solution at 4.6 Hz is greater than 175 Pa, preferably greater
than
190 and even more preferably greater than 205. The Huggins' constant is
greater than 0.75, preferably greater than 0.9 and even more preferably
greater
than 1.0
[0042] The molar ratio of nonionic monomer to cationic monomer (B:F of
Formula I) may fall within the range of 99:1 to 50:50, or 95:5 to 50:50, or
95:5 to
75:25, or 90:10 to 60:45, preferably the range is from about 85:15 to about
60:40
and even more preferably the range is from about 80:20 to about 50:50. In this
regard, the molar percentages of B and F must add up to 100%. It is to be
understood that more than one kind of nonionic monomer may be present in the
Formula I. It is also to be understood that more than one Knd of cationic
monomer may be present in the Formula I.
[0043] With respect to the molar percentages of the amphoteric copolymers
of Formula I, the minimum amount of each of the anionic, cationic and non-
ionic
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monomer is 1% of the total amount of monomer used to form the copolymer. The
maximum amount of the non-ionic, anionic or cationic is 98% of the total
amount
of monomer used to form the copolymer. Preferably the minimum amount of any
of anionic, cationic and non-ionic monomer is 5%, more preferably the minimum
amount of any of anionic, cationic and non-ionic monomer is 7% and even more
preferably the minimum amount of any of anionic, cationic and non-ionic
monomer is 10% of the total amount of monomer used to form the copolymer. In
this regard, the molar percentages of anionic, cationic and non-ionic monomer
must add up to 100%. It is to be understood that more than one kind of
nonionic
monomer may be present in the Formula I, more than one kind of cationic
monomer may be present in the Formula I, and that more than one kind of
anionic monomer may be present in the Formula I.
[0044] The physical characteristics of the associative polymer, when it is a
cationic or amphoteric copolymer, are unique in that their Huggins' constant
(k')
as determined in 0.01 M NaCI is greater than 0.5 and the storage modulus (G')
for
a 1.5 wt. % actives polymer solution at 6.3 Hz is greater than 50 Pa,
preferably
greater than 10 and even more preferably greater than 25, or greater than 50,
or
greater than 100, or greater than 175, or greater than 200. The Huggins'
constant is greater than 0.5, preferably greater than 0.6, or greater than
0.75, or
greater than 0.9 or greater than 1Ø
[0045] The emulsification surfactant or surfactant mixture used in an
inverse emulsion polymerization system have an important effect on both the
manufacturing process and the resultant product. Surfactants used in emulsion
polymerization systems are known to those skilled in the art. These
surfactants
typically have a range of HLB (Hydrophilic Lipophilic Balance) values that is
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dependent on the overall composition. One or more emulsification surfactants
can be used. The emulsification surfactant(s) of the polymerization products
that
are used to produce the associative polymer include at least one diblock or
triblock polymeric surfactant. It is known that these surfactants are highly
effective emulsion stabilizers. The choice and amount of the emulsification
surfactant(s) are selected in order to yield an inverse monomer emulsion for
polymerization. Preferably, one or more surfactants are selected in order to
obtain a specific HLB value.
[0046] Diblock and triblock polymeric emulsification surfactants are used to
provide unique materials. When the diblock and triblock polymeric
emulsification
surfactants are used in the necessary quantity, unique polymers exhibiting
unique
characteristic result, as described in WO 03/050152 Al and US 2004/0143039
Al, the entire contents of each is herein incorporated by reference. Exemplary
diblock and triblock polymeric surfactants include, but are not limited to,
diblock
and triblock copolymers based on polyester derivatives of fatty acids and'
poly[ethyleneoxide] (e.g., Hypermer(D B246SF, Uniqema, New Castle, DE),
diblock and triblock copolymers based on polyisobutylene succinic anhydride
and
poly[ethyleneoxide], reaction products of ethylene oxide and propylene oxide
with
ethylenediamine, mixtures of any of the foregoing and the like. Preferably the
diblock and triblock copolymers are based on polyester derivatives of fatty
acids
and poly[ethyleneoxide]. When a triblock surfactant is used, it is preferable
that
the triblock contains two hydrophobic regions and one hydrophilic region,
i.e.,
hydrophobe-hydrophile-hydrophobe.
[0047] The amount (based on weight percent) of diblock or triblock
surfactant is dependent on the amount of monomer used to form the associative
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polymer. The ratio of diblock or triblock surfactant to monomer is at least
about 3
to 100. The amount of diblock or triblock surfactant to monomer can be greater
than 3 to 100 and preferably is at least about 4 to 100 and more preferably 5
to
100 and even more preferably about 6 to 100. The diblock or triblock
surfactant
is the primary surfactant of the emulsification system.
[0048] A secondary emulsification surfactant can be added to ease
handling and processing, to improve emulsion stability, and/or to alter the
emulsion viscosity. Examples of secondary emulsification surfactants include,
but are not limited to, sorbitan fatty acid esters, such as sorbitan
monooleate
(e.g., Atlas G-946, Uniqema, New Castle, DE), ethoxylated sorbitan fatty acid
esters, polyethoxylated sorbitan fatty acid esters, the ethylene oxide and/or
propylene oxide adducts of alkylphenols, the ethylene oxide and/or propylene
oxide adducts of long chain alcohols or fatty acids, mixed ethylene
oxide/propylene oxide block copolymers, alkanolamides, sulfosuccinates and
mixtures thereof and the like.
[0049] Polymerization of the inverse emulsion may be carried out in any
manner known to those skilled in the art. Examples can be found in many
references, including, for example, Allcock and Lampe, Contemporary Polymer
Chemistry, (Englewood Cliffs, New Jersey, PRENTICE-HALL, 1981), chapters 3-
5.
[0050] A representative inverse emulsion polymerization is prepared as
follows. To a suitable reaction flask equipped with an overhead mechanical
stirrer, thermometer, nitrogen sparge tube, and condenser is charged an oil
phase of paraffin oil (135.0g, Exxsol D80 oil, Exxon - Houston, TX) and
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surfactants (4.5g Atlas G-946 and 9.Og Hypermer B246SF). The temperature
of the oil phase is then adjusted to 37 C.
[0051] An aqueous phase is prepared separately which comprised 53-wt. %
acrylamide solution in water (126.5g), acrylic acid (68.7g), deionized water
(70.0g), and Versenex@ 80 (Dow Chemical) chelant solution (0.7g). The
aqueous phase is then adjusted to pH 5.4 with the addition of ammonium
hydroxide solution in water (33.1g, 29.4 wt. % as NH3). The temperature of the
aqueous phase after neutralization is 39 C.
[0052] The aqueous phase is then charged to the oil phase while
simultaneously mixing with a homogenizer to obtain a stable water-in-oil
emulsion. This emulsion is then mixed with a 4-blade glass stirrer while being
sparged with nitrogen for 60 minutes. During the nitrogen sparge the
temperature of the emulsion is adjusted to 50 1 C. Afterwards, the sparge is
discontinued and a nitrogen blanket implemented.
[0053] The polymerization is initiated by feeding a 3-wt. % solution of 2,2'-
azobisisobutyronitrile (AIBN) in toluene (0.213g). This corresponds to an
initial
AIBN charge, as AIBN, of 250 ppm on a total monomer basis. During the course
of the feed the batch temperature was allowed to exotherm to 62 C (-50
minutes), after which the batch was maintained at 62 1 C. After the feed the
batch was held at 62+1 C for 1 hour. Afterwards 3-wt. % AIBN solution in
toluene (0.085g) is then charged in under one minute. This corresponds to a
second AIBN charge of 100 ppm on a total monomer basis. Then the batch is
held at 62 1 C for 2 hours. Then batch is then cooled to room temperature,
and
breaker surfactant(s) is added.
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[0054] The associative polymer emulsion is typically inverted at the
application site resulting in an aqueous solution of 0.1 to 1% active
copolymer.
This dilute solution of the associative polymer is then added to the paper
process
to affect retention and drainage. The associative polymer may be added to the
thick stock or thin stock, preferably the thin stock. The associative polymer
may
be added at one feed point, or may be split fed such that the associative
polymer
is fed simultaneously to two or more separate feed points. Typical stock
addition
points include feed point(s) before the fan pump, after the fan pump and
before
the pressure screen, or after the pressure screen.
[0055] The associative polymer may be added in any effective amount to
achieve flocculation. The amount of copolymer could be more than 0.5 Kg per
metric ton of cellulosic pulp (dry basis). Preferably, the associative polymer
is
employed in an amount of at least about 0.03 lb. to about 0.5 Kg. of active
copolymer per metric ton of cellulosic pulp, based on the dry weight of the
pulp.
The concentration of copolymer is preferably from about 0.05 to about 0.5 Kg
of
active copolymer per metric ton of dried cellulosic pulp. More preferably the
copolymer is added in an amount of from about 0.05 to 0.4 Kg per metric ton
cellulose pulp and, most preferably, about 0.1 to about 0.3 Kg per metric ton
based on dry weight of the cellulosic pulp.
[0056] The second component of the retention and drainage system can be
an organic microparticle (also know as a micropolymer or a microbead) For the
purpose of this invention the words microparticle, micropolymer or microbead
will
be used interchangably. Organic microparticies are crosslinked, ionic, organic
polymeric materials. They are copolymers of a nonionic monomer, an ionic
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monomer and a crosslinking agent. Further, the ionic monomer may be anionic
or cationic. Use of both anionic and cationic monomers in the same polymer
results in an amphoteric material. The microparticles are typically formed by
the
polymerization of ethylenically unsaturated monomers that can be anionic,
cationic or non-ionic. Inverse emulsion polymerization is typically used to
prepare these materials although other polymerization methods known to those
skilled in the art can be used.
[0057] The preferred ethylenically unsaturated non-ionic monomers in
preparing the organic microparticle are selected from acrylamide;
methacrylamide; N,N-dialkylacrylamides; N-alkylacrylamides; N-vinyl
methacetamide; N-vinyl formamide, N-vinyl methylformamide; N-vinyl
pyrrolidone; and mixtures thereof.
[0058] Exemplary anionic monomers used in preparing the organic
microparticle include, but are not limited to, the salts and free acid of:
acrylic
acid, methacrylic acid, ethylacrylic acid, 2-acrylamido-2-alkylsulfonic acids
where
the alkyl group contains 1 to 6 carbon atoms, such as 2-acrylamido-2-propane-
sulfonic acid or mixtures of any of the foregoing and the like; and their
alkaline
salts. Especially preferred are the salts or acids of acrylic acid,
methacrylic acid,
and 2-acrylamido-2-methylpropane sulfonic acid. The preferred salts have
sodium as the cation
[0059] Exemplary cationic monomers used in preparing the organic
microparticle include, but are not limited to , ethylenically unsaturated
monomers
selected from the free base or salts of: acryloxyethyltrimethylammonium
chloride;
diallydimethylammonium chloride; 3-(meth)acrylamido-propyltrimethylammonium
chloride; 3-acrylam id o-p ropyltrimethyla m m on i u m-2-hyd roxyp ropylacryl
ate
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methosulfate; trimethylammoniumethyl methacrylate methosulfate; 1-
tri methyla m m on i um-2-hyd roxyp ropyl-m ethacryl ate methosulfate;
methacryloxyethyltri-methylammonium chloride; and mixtures of any of the
foregoing and the like.
[0060] These ethylenically unsaturated anionic, cationic and nonionic
monomers that make up the organic microparticle may be polymerized to form
anionic, cationic or amphoteric copolymers, with the three types of monomer
present in any ratio. Acrylamide is the preferred nonionic monomer.
[0061] Polymerization of the monomers is conducted in the presence of a
polyfunctional crosslinking agent to form the crosslinked composition. The
polyfunctional crosslinking agent comprises molecules that have at least two
double bonds, or a double bond and reactive group, or two reactive groups.
Examples of the polyfunctional cross-linking agent containing at least two
double
bonds include, but are not limited to N,N-methylenebisacrylamide, N,N-
methylenebismethacrylamide, polyethyleneglycol diacrylate, polyethyleneglycol
dimethacrylate, N-vinyl acrylamide, divinylbenzene, triallylammonium salts, N-
methyallylacrylamide and the like. Examples of the polyfunctional cross-
linking
or branching agent containing at least one double bond and at least one
reactive
group include, but are not limited to, glycidyl acrylate, acrolein,
methylolacrylamide and the like. Examples of the polyfunctional branching
agents containing at least two reactive groups include, but are not limited
to,
aldehydes such as glyoxal, diepoxy compounds, epichlorohydrin and the like.
Crosslinking agents are to be used in sufficient quantities to assure a
crosslinked
composition.
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[0062] An example of an organic microparticle is disclosed in US
5,171,808. Microparticles are commercially available under the trade name
Polyflex CP.3 (Ciba, Tarrytown, NY).
[0063] The second component of the retention and drainage system can be
added at amounts up to 0.5 Kg of active material per metric ton of cellulose
pulp
based on dry weight of the pulp, with the ratio of the associative polymer to
second component being 1:100 to 100:1. It is contemplated that more than one
second component can be used in the papermaking system.
[0064] Optionally siliceous materials can be used as an additional
component of a retention and drainage aid used in making paper and
paperboard. The siliceous material may be any of the materials selected from
the group consisting of silica based particles, silica microgels, amorphous
silica,
colloidal silica, anionic colloidal silica, silica sols, silica gels,
polysilicates,
polysilicic acid, and the like. These materials are characterized by the high
surface area, high charge density and submicron particle size.
[0065] This group includes stable colloidal dispersion of spherical
amorphous silica particles, referred to in the art as silica sols. The term
sol refers
to a stable colloidal dispersion of spherical amorphous particles. Silica gels
are
three dimensional silica aggregate chains, each comprising several amorphous
silica sol particles, that can also be used in retention and drainage aid
systems;
the chains may be linear or branched. Silica sols and gels are prepared by
polymerizing monomeric silicic acid into a cyclic structure that result in
discrete
amorphous silica sols of polysilicic acid. These silica sols can be reacted
further
to produce a three dimensional gell network. The various silica particles
(sols,
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gels, etc.) can have an overall size of 5-50 nm. Anionic colloidal silica can
also
be used.
[0066] The siliceous material can be added to the cellulosic suspension in
an amount of at least 0.005 Kg per metric ton based on dry weight of the
cellulosic suspension. The amount of siliceous material may be as high at 50
Kg
per metric ton. Preferably, the amount of siliceous material is from about
0.05 to
about 25 Kg per metric ton. Even more preferably, the amount of siliceous
material is from about 0.25 to about 5 Kg per metric ton based on the dry
weight
of the cellullosic suspension.
[0067] Optionally, an additional component of the retention and drainage
aid system can be a conventional flocculant. A conventional flocculant is
generally a linear cationic or anionic copolymer of acrylamide. The additional
component of the retention and drainage system is added in conjunction with
the
aluminum compound and the associative polymer to provide a multi-component
system which improves retention and drainage.
[0068] The conventional flocculant can be an anionic, cationic or non-ionic
polymer. The ionic monomers are most often used to make copolymers with a
non-ionic monomer such as acrylamide. These polymers can be provided by a
variety of synthetic processes including, but not limited to, suspension,
dispersion
and inverse emulsion polymerization. For the last process, a microemulsion may
also be used.
[0069] The co-monomers of the conventional flocculant may be present in
any ratio. The resultant copolymer can be non-ionic, cationic, anionic, or
amphoteric (contains both cationic and anionic charge).
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[0070] Yet other additional components that can be part of the inventive
system are aluminum sources, such as alum (aluminum sulfate), polyaluminum
sulfate, polyaluminum chloride and aluminum chlorohydrate.
[0071] The components of a retention and drainage system may be added
substantially simultaneously to the cellulosic suspension. The term retention
and
drainage system is used here to encompass two or more distinct materials added
to the papermaking slurry to provide improved retention and drainage. For
instance, the components may be added to the cellulosic suspension separately
either at the same stage or dosing point or at different stages or dosing
points.
When the components of the inventive system are added simultaneously any two
of more of the materials may be added as a blend. The mixture may be formed
in-situ by combining the materials at the dosing point or in the feed line to
the
dosing point. Alternatively the inventive system comprises a preformed blend
of
the materials. In an alternative form of the invention the components of the
inventive system are added sequentially. A shear point may or may not be
present between the addition points of the components. The components can be
added in any order.
[0072] The inventive system is typically added to the paper process to
affect retention and drainage. The inventive system may be added to the thick
stock or thin stock, preferably the thin stock. The system may be added at one
feed point, or may be split fed such that the inventive system is fed
simultaneously to two or more separate feed points. Typical stock addition
points
include feed points(s) before the fan pump, after the fan pump and before the
pressure screen, or after the pressure screen.
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EXAMPLES
[0073] To evaluate the performance of the present invention, a series of
drainage tests were conducted utilizing a synthetic alkaline furnish. This
furnish
is prepared from hardwood and softwood dried market lap puips, and from water
and further materials. First, the hardwood and softwood dried market lap pulp
are refined separately. These pulps are then combined at a ratio of about 70
percent by weight of hardwood to about 30 percent by weight of soft wood. in
an
aqueous medium. The aqueous medium utilized in preparing the furnish
comprises a mixture of local hard water and deionized water to a
representative
hardness. Inorganic salts are added in amounts so as to provide this medium
with a total alkalinity of 75 ppm as CaCO3 and hardness of 100 ppm as CaCO3..
Precipitated calcium carbonate (PCC) is introduced into the pulp furnish at a
representative weight percent to provide a final furnish containing 80% fiber
and
20% PCC filler. The drainage tests were conducted by mixing the furnish with a
mechanical mixer at a specified mixer speed, and introducing the various
chemical components into the furnish and allowing the individual components to
mix for a specified time prior to the addition of the next component. The
specific
chemical components and dosage levels are described in the data tables. The
drainage activity of the invention was determined utilizing the Canadian
Standard
Freeness (CSF) . The CSF test, a commercially available device (Lorentzen &
Wetfire, Stockholm, Sweden), can be utilized to determine relative drainage
rate
or dewatering rate is also known in the art; standard test method (TAPPI Test
Procedure T-227) is typical. The CSF device consists of a drainage chamber and
a rate measuring funnel, both mounted on a suitable support. The drainage
chamber is cylindrical, fitted with a perforated screen plat and a hinged
plate on
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the bottom, and with a vacuum tight hinged lid on the top. The rate-measuring
funnel is equipped with a bottom orifice and a side, overflow orifice.
[0074] The CSF drainage tests are conducted with 1 liter of the furnish.
The furnish is prepared for the described treatment externally from the CSF
device in a square beaker to provide turbulent mixing. Upon completion of the
addition of the additives and the mixing sequence, the treated furnish is
poured
into the drainage chamber, closing the top lid, and them immediately opening
the
bottom plate. The water is allowed to drain freely into the rate-measuring
funnel;
water flow that exceeds that determined by the bottom orifice will overflow
through the side orifice and is collected in a graduated cylinder. The values
generated are described in milliliters (ml) of filtrate; higher quantitative
values
represent higher levels of drainage or dewatering.
[0075] Table 1 (below) illustrates the utility of the invention. The test
samples were prepared as follows: the furnish prepared as described above, is
added, first, 5 Kg of cationic starch (Stalo{c 400, AE., Staley, Decatur, IL)
per
metric ton of furnish (dry basis). Next, 2.5 Kg of alum (aluminum sulfate
octadecahydrate obtained from Delta Chemical Corporation, Baltimore, MD as a
50% solution) per metric ton of furnish (dry basis) is added, followed by 0.25
Kg
of PerForm@ PC8138 cationic polymer (Hercules Incorporated, Wilmington, DE)
per metric ton of furnish (dry basis).
[0076] The additive(s) of interest, as noted in table 1 were then added in
the examples provided in table 1. SP9232 is PerForm SP9232, a retention and
drainage aid associative polymer (see PCT WO 03/050152 A), is a product of
Hercules Incorporated, Wilmington, DE; Polyflex is Polyflex CP.3,. an organic
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microparticle marketed by Ciba Specialty Chemicals, Tarrytown, NY; and silica
is
NP780, a colloidal silica product of Eka Chemicals, Marietta, GA.
Table 1
Additive s) Addition CSF Freeness
Example of Interest(a) Scheme(b) (ml)
1 None - 430
2 SP9232 - 654
3 Silica - 606
4 Polyflex - 634
Pol flex/SP9232 SIM 677
6 Polyflex/Silica/SP9232 SIM 698
7 Pol flex/SP9232 SEQ 660
8 Pol flex/Silica/SP9232 SEQ 688
(a) Additives used at 0.25 Kg per metric ton of furnish
(b3 SIM indicates simultaneous addition; SEQ indicates sequential addition
[0077] These data indicate there is a synergistic effect when any two, or all
three, of the materials, are used relative to the individual material. A
simultaneous addition sequence is preferred, although the data from the
sequential addition experiments also show an improvement over the use of a
single material.
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