A METHOD TO INCREASE DEWATERING, SHEET WET WEB STRENGTH AND WET
STRENGTH ΪN FA E MA ING
Cross-Referenee to Related Applications
This is a continuation in part application of US Patent Application 12/727,299
filed on March 19, 2010
Statement Regarding Federally Sponsored Research or Development
Not Applicable
Background of the Invention
This invention relates to a method of improving dewatering efficiency, increasing
sheet wet web strength, increasing sheet wet strength and enhancing filler retention in a
paperaaaking process. Typically in a papermaking process chemicals are added in the wet end to
assist in the dewatering of the slurry and improving wet or dry sheet strength. The wet end of the
papermaking process refers to the stage in the papermaking process where the fiber is dispersed
in the water in the slurry form. The fiber-water slurry then goes through drainage and dewatering
process to form a wet web. The solid content after this wet formation process is about 50%. The
wet web is further dried and forms a dry sheet of paper mat. Paper mat comprises water and
solids and commonly 4 to 8% water. The solid portion of the paper mat includes fibers (typically
cellulose based fibers) and can also include filler.
Fillers are mineral particles that are added to paper at during the papermaking
process to enhance the resulting paper's opacity and light reflecting properties. Some examples
of fillers are described in US Patent Number 7,21 1,608. Fillers include morganic and organic
particles or pigments used to increase the opacity or brightness, or reduce the cost of the paper or
paperboard sheet. Some examples of fillers include one or more of: kaolin clay, talc, titanium
dioxide, alumina trihydrate, barium sulfate, magnesium hydroxide, pigments such as calcium
carbonate, and the like.
Calcium carbonate filler comes in two forms, GCC (ground calcium carbonate)
and PCC (precipitated calcium carbonate) GCC is naturally occurring calcium carbonate rock
and PCC is synthetically produced calcium carbonate. Because it has a greater specific surface
area, PCC l as greater light scattering abilities and provides better optical properties to the
resulting paper. For the same reason however, PCC filled paper is weaker than GCC filled paper
in dry strength, wet strength and wet web strength. Filler is generally much smaller than fiber,
therefore, filler has much larger specific surface area than fiber. One of the challenges people
found to increase filler content in the sheet is that high filler content decreases the efficiency of
wet end chemicals, such as dewatering aids. This invention is to provide novel filler
preflocculation, so that it reduced the adsorption of wet end chemicals onto filler surface,
therefore, increased the efficiency of we end chemicals such as dewatering aids.
Paper wet web strength is the tensile strength of a never dried sheet. Paper wet
web strength is very critical for paper producers because increased paper wet we strength would
increase machine runnability and reduce sheet breaks and machine down time. Paper wet web
strength is a function of the number and the strength of the bonds formed between interweaved
fibers of the paper mat. Filler particles with greater surface area are more like y to become
engaged to those fibers and interfere with the number and strength of those bonds. Because of its
greater surface area, PCC filler interferes with those bonds more than GCC.
Paper dewatering efficiency is also very critical for paper producers because
decreased dewatering efficiency in wet end would increase steam demand for drying operation,
reduce machine speed and production efficiency. Dewatering aids are widely used to improve
dewatering efficiency for reducing energy consumption, increasing machine speed and production
efficiency.
Paper wet strength is the tensile strength of the sheet when it is re-wet. Paper wet
strength is not only one of importani sheet properties, but also important for machine runnabiliiy
for fine papermaehine with a size press. Sheet gets re-wet after size press, and tends to break if
the sheet wet web strength is low Same as paper dry strength and wet web strength paper wet
strength decreases with the filler content in the sheet due to filler interference with f er- iber
bonding.
Thus there is clear need and utility in methods and compositions for improving
dewatering efficiency, increasing sheet wet web strength, increasing sheet wet strength and
enhancing filler retention in a papennaking process. The art described in this section is not
intended to constitute an admission that any patent, publication or other information referred to
herein is "prior art" with respect to this invention, unless specifically designated as such. n
addition, bis section should not be construed to mean that a search has been made or that no
other pertinent information as defined in 37 CFR § 1.56(a) exists.
Brief Summary of the
At least one embodiment of the invention is directed towards a method of
papermaking having improved sheet wet strength or wet web strength or increased drainage
through combining filler prefloceulation and dewatering aid. The method comprises the steps of:
adding a first flocculating agent to an aqueous dispersion in an amount sufficient to mix
uniformly in the dispersion without causing significant floeculation of the filler particles, adding
a second flocculating agent to the dispersion after adding the first flocculating agent in an amount
sufficient to initiate flocculation of the filler particles in the presence of he first flocculating
agent the second flocculating agent being of opposite charge to the first flocculant, combining
the filler particles with the paper fiber stock, treating the combination w h at least one
dewaiering aid, and forming a paper mat by removing some of the water from the combination.
The cellulose fiber stock comprises a plurality of cellulose fibers and water. The second
flocculating agent inhibits dewaiering aid from adhering to the filler particles.
At least one embodiment of the invention is directed towards a method in which
the dewaiering of the paper made by the papermaking process is increased by an amount greater
than the sum of the dewaiering enhancement provided by the preflocculation process using the
first and second flocculation agents and the dewaiering agent if they were added separately.
At least one embodiment of the invention is directed towards a method in which
filler particles further comprises one item selected from the list consisting of: calcium carbonate,
organic pigment, inorganic pigment, clay, talc, titanium dioxide, alumina trihydrate. barium
sulfate, magnesium hydroxide and any combination thereof. The method may farther comprise
the step of shearing the dispersion to obtain a predetermined loe size. The filler floes may have a
median particle size of -200mh . The first flocculating agent may be anionic and amphoteric.
The dewaiering agent may be glyoxylated Aerylamide / Diailyl-Dimethyi-Animomum-Chloride
(AcAm/DADMAC) copolymer or Diallylamine/ Aerylamide (DAA/AcAm) copolymer or
polyviny a i e (PVAM) resin. The ratio of dewatering aid relative to the solid portion of the
paper mat can be 0.3 to 10 kg of additive per ton of paper mat. The first flocculation agent may
be a copolymer of aerylamide and sodium acrylate. The dewatering aid and the second
flocculating agent may carry the same charge.
The second flocculating agent may be selected from the list consisting of
consisting of copolymers of aerylamide with DMAEM, DMAEA, DEAEA, DEAEM. The second
A
flocculating agent may be in quaternary ammonium salt fo n made with a salt selected from the
list consisting of dimethyl sulfate, methyl chloride, benzyl chloride and any combination thereof.
The filler may be a oni a y dispersed and a low molecular weight, cationic coagulant is added
to the dispersion to at least partially neutralize its anionic charge prior to the addition of the first
flocculating agent. The second flocculating agent may have a charge, which is opposite to the
charge of the first flocculating agent. The filler floes may have a median particle size of 0-
200mh . The blend of filler particles further comprises one item selected from the list consisting
of: calcium carbonate, organic pigment, inorganic pigment, clay talc, titanium dioxide, alumina
txihydrate, barium sulfate, magnesium hydroxide, and any combination thereof. The low
molecular weight composition may be a cationic coagulant, the first flocculating agent may be an
anionic floe uIen the second flocculating agent may be a cationic flo cu ent, and both
flocculants may have a molecular weight of at. least 1,000,000.
Brief Description of the Drawing
A detailed description of the invention is hereafter described with specific
reference being made to the drawings in which:
FIG. 1 is a graph showing the improved wet strength of paper made according to
the invention,
Detailed Description of the Invention
The following definitions are provided to determine how terms used in this
application, and in particular how the claims, are to he construed. The organization of the
definitions is for convenience only and is not intended to limit any of the definitions to any
particular category.
g l means a composition of matter having a higher charge density and
lower molecular weight than a fiocc ant, which when added to a liquid containing finely divided
suspended particles, destabilizes and aggregates the solids through the mechanism of ionic charge
neutralization.
De ter g Aid means chemical additives that will improve the dewaiering of
the paper web, at any point in the process. This means that a material might not affect free
drainage, but have a significant effect on vacuum drainage or pressing response.
"BAA" means dial ylamine
ADMA means diallyl dimethyl ammonium chloride,
"DMAEM' means dimethylaminoethylmeihaciyiate as described and defined in
US Patent 5,338,816.
"DMAEA" means dimethyiaminoethylacrylate as described and defined in US
Patent 5,338,816.
"DEAEA" means diethylaminoethyl acrylate as described and defined in S
Patent 6,733,674.
"DEAEM" means diethylaminoethyl methacrylate as described and defined in
US Patent 6,733,674.
& ί means a composition of matter having a low charge density and a
high molecular weight (in excess of 1,000,000) which when added to a liquid containing finelydivided
suspended particles, destabilizes and aggregates the solids through the mechanism of
interparticie bridging,
"Flocculating Agent means composition of matter that when added to a liquid,
destabilizes and aggregates coliotdal and finely divided suspended particles in liquid into floes.
Floecuiants suitable for the invention generally have molecular weights in excess
of 1,000,000 and often in excess of 5,000,000.
The polymeric flocculant is typically prepared by vinyl addition polymerization of
one or more cationic, anionic o nonionic monomers, by copolymerization of one or more
cationic monomers with one or more nonionic monomers, by copolymerization of one or more
anionic monomers with one or more nonionic monomers, by copolymerization of one or more
cationic monomers with one or more anionic monomers and optionally one or more nonionic
monomers to produce an amphoteric polymer or by polymerization of one or more zwitterionic
monomers and optionally one or more nonionic monomers to form a zwitterionic polymer. One
or more zwitterionic. monomers and optionally one or more nonionic monomers may also be
copolymerized with one or more anionic or cationic monomers to impart cationic or anionic
charge to the zwitterionic polymer. Suitable floecuiants generally have a charge content of less
than 80 mole percent and often less than 40 mole percent.
While cationic polymer floecuiants may be formed using cationic monomers, it is
also possible to react certain nonionic vinyl addition polymers to produce cattonicaily charged
polymers. Polymers of this type include those prepared through the reaction of polyacrylamide
with dirnethylamine and formaldehyde to produce a Mannich derivative.
Similarly, while anionic polymer floecuiants may be formed using anionic
monomers, it is also possible to modify certain nonionic vinyl addition polymers to form
amonically charged polymers. Polymers of this type include, for example, those prepared by the
hydrolysis of polyacrylamide.
The ilocculant may be prepared in the solid form, as an aqueous solution, as a
water-in-oil emulsion or as a dispersion in water. Representative cationic polymers include
copolymers and terpolymers of ( eth acryiamide with dimethylaminoethyl methaerylate
(DMAEM), dimeihylaminoeihy] acrylate (DMAEA), diethylaminoethyl acrylate (DEAEA),
diethyla inoe y methacrylate (DEAEM) or their quaternary ammonium forms made with
dimethyl sulfate, methyl chloride or benzyl chloride. Representative anionic polymers include
copolymers of acrvlamide with sodium acrylate and/or 2-acrylamido 2-methylpropane sulfonic
acid (AMPS) or an acrvlamide homopolymer that has been hydrolyzed to convert a portion of the
acrvlamide groups to acrylic acid.
" C means ground calcium carbonate, which is manufactured by grinding
naturally occurring calcium carbonate rock
"Papermaking Process"' means a method of making paper and paperboard
products from pulp comprising mixing the pulp with water which forms an aqueous celluiosic
paper t, draining the mat to form a sheet, and drying the sheet. It should be appreciated that
any suitable paper mat may be used. Representative paper mats include, for example, an aqueous
celluiosic slurry containing virgin pulp recycled pulp, kraft pulp (bleached and unbleached),
sulfite pulp, mechanical pu p, polymeric plastic fibers, the like, and any combination of the
foregoing pulps. The steps of forming the paper mat draining and drying may be carried out in
any manner generally known to those skilled in the art.
means precipitated calcium carbonate which is synthetically produced.
Prefl i cc iion means the modification of filler particles into agglomerates
through treatment with a particular floccuiating agent prior to the addition of those filler particles
into the paper mat, the floccuiating agent is selected o the basis of the size distribution and
stability of the floe thai the flocculating agent will form.
' VA means polyvmyiarnme resins.
nn bilii mea s the degree to which a sheet of paper or paper precursor
passes trouble free through the various stages and pieces of equipment in a papermaking process,
such troubles include but is not limited to jamming, clogging, or fouling equipment, damaging
equipment, and/or requiring more energy to pass the sheet of paper or paper precursor through he
equipment.
h the event that the above definitions or a description stated elsewhere in this
application is inconsistent with a meaning (explicit or implicit) which is commonly used, in a
dictionary, or stated in a source incorporated by reference into this application, the application
and the claim terms in particular are understood to be construed according to the definition or
description in this application, and not according to the common definition, dictionary definition,
or the definition that was incorporated by reference. In light of the above in the event that a term
can only be -understood if it is construed by a dictionary, if the term is defined by the Kirk-
Otlimer Encyclopedia of Chemical Technology, 5th Edition, (2005), (Published by Wiley, John &
Sons, Inc.) this definition shall control how the term is to be defined in the claims.
At least one embodiment of the invention is a method of making paper, which is
strong, has a high filler content, and has superior optical properties. n at least one embodiment
of the invention the method of papermaking comprises the steps of: providing filler material, pretreating
at least some of the filler material by preflocculation leading to a decrease in the
adsorption of a dewatering aid on the filler material, and adding both the prefloeculated filler
blend and the dewatering aid to the paper mat.
Preflocculation is a process in which, material is treated by two flocculating
agents in a maimer that optimizes the size distribution and stability of the floes under a particular
shear force prior to its addition to the paper stock. The particular chemical environment and high
fluid shear rates present in modern high-speed papermaking require filler lo s to be stable and
shear resistant. Examples of preflocculation methods applicable to this invention are described in
US Published Applicaiion 2009/0065162 A and US Application 12/431356.
t has been known for some time that adding d a eri ng aid to paper mat
increases the wet web strength of the resulting paper or enhances drainage or improves machine
speed and runnability or enhance sheet wet strength. Some examples of wet strength aids wet
web strength additives and drainage aids are described in US Patents 7,125,469» 7,615,135 and
7,641,776.
Unfortimately it is not practical to add large amounts of dewatermg aid to
compensate for the weakness that results from using large amounts of filler in paper mat. One
reason is because dewatering aids are expensive and using large amounts of additives would
result m production costs that are commercially non-viable. n addition, adding too much
dewatering aid negatively affects the process of papermaking and inhibits the operabihty of
various forms of papermaking equipment. Furthermore cellulose fibers can only adsorb a limited
amoun of dewatering aid. This imposes a limit on how much additive can be used. One reason
why this is because dewatering aid tends to neutralize the anionic fiber filler charges and when
these charges are neutralized further adsorption of those additives is inhibited.
Adding filler to the paper mat reduces the effectiveness of the dewatering aid.
Because filler has a much higher specific surface area than fiber, most of the dewatering aid
added into the papermaking slurry goes to filler surfaces, and therefore there is less dewatering
aid available to bind the cellulose fibers together. This effect is more acute with PCC compared
to GCC because PCC has a much higher surface area and is able to adsorb more dewatering aid.
n at least one embodiment the dewatering efficiency, sheet wet web strength,
sheet wet strength and filler retention is increased y the following method: An aqueous
dispersion of filler materials is formed and the filler materials are preflocculated before being
added to a paper fiber stock. A first flocculating agent is added to the dispersion i an amount
sufficient to mix uniformly in the dispersion without causing significant flocculation of the filler
particles. A second flocculating agent is then added following the first flocculating agent, in an
amount sufficient to initiate flocculation of the filler material in the presence of the first
flocculating agent, the second flocculating agent being of opposite charge to the first flocculating
agent. A paper mat is formed by combining the preflocculated filler material with the fiber stock
and treating this combination with the dewatenng aid. The preflocculation of the filler material
enhances the performance of the dewatering aid. The fiber stock comprises fibers, fillers, and
water.
n at least one embodiment, the fibers are predominantly cellulose based. In a
least one e bodi e t the flocculated dispersion is sheared to obtain a particularly desired
particle size.
While pre-treating filler particles is known in the art, prior art methods of pretreating
filler particles are not directed towards affecting the adhesion of the dewatering aid to the
filler particles with two floecuiants. In fact, many prior art pre-treatnients increase the adhesion
of the strength additive to the filler particles. For example, US Patent Number 7, 1,608
describes a method of pre-treating filler particles w th hydrophobic polymers. This pre-treatenent
however does nothing to the adhesion between the dewatering aid and the filler particles and
merely repels water to counterbalance an excess of water absorbed by the dewatering aid. n
contrast, the invention decreases the interactions between the dewatering aid and the filler
particles and results in an unexpectedly huge increase in the dewatering efficiency, sheet wet web
strength, sheet wet strength and filler retention, sheet dewatering and machine ninnability. This
can best be appreciated by reference to FIG .
FIG. 1 illustrates that a paper produced from a paper mate that includes PCC
filler tends to become weaker as more PCC filler is added. When a large amount of PCC is added
(over 20%), the addition of a dewatering aid adds little wet strength to the paper. Paper mads
from prefioceukted PCC filler combined with a dewatering additive however increases the wet
strength to a degree that it is stronger than paper having 10% ss PCC that is not prefioceukted.
As a result at least two conclusions can he reached, 1) the dewatering aid is more effective in
increasing sheet wet strength or wet web strength or increased drainage with prefloccislated filler
than with untreated filler and 2) there is a synergistic effect from the combination of dewatering
aid and filler prefloccuiation which makes it superior to the additive effects of the sum of the
dewatering aid alone plus the filler prefloccuiation alone. As a result, prefloccuiation of the PCC
filler material leads to improvement of efficiency of dewatering aids.
At least some of the fillers encompassed by this invention are well known and
commercially available. They include any inorganic or organic particle or pigment used to
increase the opacity or brightness, reduce the porosity or reduce the cost of the paper or
paperboard sheet. The most common fillers are calcium carbonate and clay. However, talc,
titanium dioxide, alumina trihydrate, barium sulfate, and magnesium hydroxide are also suitable
fillers. Calcium carbonate includes ground calcium carbonate (GCC) in a dry or dispersed slurry
form, chalk, precipitated calcium carbonate (PCC) of any morphology, and precipitated calcium
carbonate in a dispersed slurry form. The dispersed slurry forms of GCC or PCC are typically
produced using po ya rylic acid polymer dispersants or sodium polyphosphate dispersants Each
of these dispersants imparts a significant anionic charge to the calcium carbonate particles.
Kaolin clay slurries also are dispersed using polyaerylic acid polymers or sodium polyphosphate.
In at least one embodiment the mrmability issues caused by the high filler content
is ameliora ted by the addition of a dewatering aid to the paper mat. t is known in general that
dewatering aids assist in addressing rannability issues. However in the prior art dewatering aids
were not typically used in conjunction with high levels of filler because fillers also reduce the
effectiveness of dewatering aids.
Without limitation to theory and in particular the scope of the claims it is
believed that the reason why filler impairs dewatering aids is because the filler particles absorb
dewatering agent leaving less of such agents available to assist the papermaking process. In at
least one embodiment the pre-f oc u a ion of the filler particles is done in conjunction with the
use of a de-watering aid without unduly (or at all) reducing the effectiveness of the de-watering
aid. The pre-fiocculation reduces the available surface area of the filler particles available to
interact with the de-watering aids and thereby leaves the de-watering aid available to assist in the
papermaking process. This allows the high levels of filler particles to be used in the papermaking
process but it also allows the de-watering aid to improve process runnability.
at least one embodiment, the dewatering aid carries the same charge as the
second flocculating agent for treating the filler particles. When the two ca y the same charge,
the filler additive is less likely to adsorb wet strength aid, wet web strength additive or drainage
aid on its surface. Dewatering aids encompassed by the inven tion include any one of the
compositions of matter described i US Patent 4,605,702 and US Patent Application
2005/0 .181 A and in particular the various glyoxylated Acrylamide/DADMAC copolymer
compositions described therein. An example of a glyoxylated Acrylamide/DADMAC copolymer
composition is Na co 63700 (available from Nalco Company, Naperville, Illinois, 60563). Other
examples are amine-containing polymers including Daliyiamine/aerylamide (DA A/Ac Am)
copolymers and polyvinylamines (PVAM).
n at least one embodiment, the fillers used are PCC, GCC. and/or kaolin lay
n at least one embodiment, the fillers used are PCC, GCC, and/or kaolin clay with polyacrylic
acid polymer dispersants or their blends. The ratio of dewatering aid relative to solid paper mat
can be 3kg of additive per ton of paper mat.
EXAMPLES
The foregoing may be better understood by reference to the following examples
which are presented for purposes of illustration and are not intended to limit the scope of the
invention.
A Paper mat was prepared y disintegrating commercial bleached
hardwood dry lap The filler material preflocculation was performed with the dual floeculants
approach described in example 4 of U.S. application Ser. No 12/431,356. PCC was added to the
paper mat to achieve different filler content in the sheet. 200 pp of a commercial flocculant
(Nalco 61067) was used as a retention aid. During handsheet preparation, 3kg/ton dewatering aid
(Nalco 63700) was added. The wet strength as then measured. As shown in FIG. 1, the absence
of the dewatering aid resulted in various process/runnability issues that caused the paper to have
impaired wet strength. Filler preflocculation caused some improvement but preflocculation
combined with dewatering caused significant improvements in wet strength.
While this invention may be embodied in many different forms, there described
in detail herein specific preferred embodiments of the invention. The present disclosure is an
exemplification of the principles of the invention and is not intended to limit the invention to the
particular embodiments illustrated. All patents, patent applications, scientific papers, and any
other referenced materials mentioned herein or mentioned within any mentioned reierence, are
incorporated by reference in their entirety. Furthermore, the invention encompasses any possible
combination of some or all of the various embodiments described herein and/or incorporated
herein. In addition the invention encompasses any possible combination tha also specifically
excludes any one or some of the various embodiments described herein and/or incorporated
herei
The above disclosure is intended to be illustrative and not exhaustive. This
description will suggest many variations and alternatives to one of ordinary skill in this ar All
these alternatives and variations are intended to be included within the scope of the claims where
the term "comprising" means "including, but not limited to". Those familiar with the art may
recognize other equivalents to the specific embodiments described herein which equivalents are
also intended to be encompassed by the claims.
All ranges and parameters disclosed herein are understood to encompass any and all
subranges subsumed therein, and every number between the endpoints. For example, a stated
range of " 1 to 0" should be considered to include any and all subranges between (and inclusive
of) the minimum value of 1 and the maximum value of 10; tha is, all subranges beginning with a
minimum value of 1 or more, (e.g. 1 to 6.1), and ending with a maximum value of 10 or less, (e.g.
2.3 io 9.4, 3 to 8, 4 to 7), and finally to each number 1, 2, 3, 4, 5, 6, 7, 8, 9, and 10 contained
within the range.
This completes the description of the preferred and alternate embodiments of the
invention. Those skilled in the art may recognize other equivalents to the specific embodiment
described herein which equivalents are intended to be encompassed by the claims attached hereto.
Claims
1. A method of papermaking comprising filler, the method comprising the steps of:
providing a aqueous dispersion of filler particles, at least one dewaiering aid and
cellulose fiber stock,
adding a first flocculating agent to an aqueous dispersion of filler particles in an amount
sufficient to mix uniformly in the dispersion without causing significant flocculation of the filler
particles,
adding a second flocculating agent to the dispersion after adding the first flocculating
agent in an amount sufficient to initiate flocculation of the filler particles in the presence of the
first flocculating agent, the second flocculating agent being of opposite charge to the first
flocculant,
combining the filler particles w h the paper fiber stock,
treating the combination with at least one dewaiering aid selected from the group
consisting of synthetic dewaiering additives, and
forming a paper mat from the combination,
the paper fiber stock comprises a plurality of fibers and water, and
the filler pre fio c ation enhances the performance of the dewaiering aid in the paper mat.
2. The method of claim 1 in which the dewaiering efficiency, sheet wet web strength, sheet
wet strength and filler retention is increased by an amount greater than the sum of: the
dewaiering efficiency, sheet wet web strength, sheet wet strength and filler retention
enhancement provided by the preflocculaiion process and the dewaiering aids, if they were
applied separately.
3. The method of claim 1 wherein the filler is selected from the group consisting of calcium
carbonate, kaolin clay, talc, titanium dioxide, alumina trihydrate, barium sulfate, and
magnesium hydroxide
4. The method of claim 1 in which paper fiber is cellulose fiber
5. The method of claim 1 further comprising the step of shearing the dispersion to obtain a
predetermined floe size of between 10 and 200 microns.
6, The method of claim 1 wherein the first flocculating agent is anionic or amphoteric.
7. The method of claim 1 wherein the first flocculating agent is a copolymer of acrylamide
and sodium acrylate.
8. The method of claim 1 in which the second flocculating agent has a charge which is
opposite to the charge of the first flocculating agent.
9. The method of claim 1 wherein the second flocculating agent is selected from the list
consisting of copolymers of acrylamide with DMAEM, DMAEA, DEAEA, DEAEM.
10. The method of claim 9 in which the second flocculating agent is in quaternary ammonium
salt form made with a sal selected from the list consisting of dimethyl sulfate, methyl
chloride benzyl chloride, and any combination thereof.
The method of claim 1 wherein the ratio of the first flocculating agent to the filler is
between 0.2 and 4kg flocculating agent per ton filler and the ratio of the second flocculating
agent to the filler is between 0.2 and 4 kg flocculating agent per ton filler
12. The method of claim 1 in which the dewatering aid and the second flocculating agent
ca y the same charge.
13. The method of claim 1 in which the dewatering aid is one selected from the list consisting
of: DAA/AcAm copolymer, PVAM, Aldehyde-mnctionalized polymers based on
polyacrylamide, and any combination thereof.
The method of claim 1 in which the ratio of dewatering aid relative to the solid portion of
the paper mat s 0.3 to 1 kg of dewatering additive per ton of paper mat.
'The method of claim 1 wherein the iiller is anionically dispersed and a low molecular
weight, catiomc coagulant is added to the dispersion to at least partially neuiraiize its anionic
charge prior to the addition of the first flocculating agent.
The method of claim wherein the ow molecular weight composition is a cationie
coagulant, the first flocculating agent is an anionic floccxilant , the second flocculating age t
is a cationie flcce n , and both flocculating agents have a molecular weight of at least
1,000,000.