PREFLOCCULATION OF FILLERS USED IN PAPERMAKING
Background of the Invention
This invention relates to the preflocculation of fillers used in
papermaking, particularly, the production of shear resistant filler floes with a
defined and controllable size distribution at high filler solids is disclosed.
Increasing the filler content in printing and writing papers is of great
interest for improving product quality as well as reducing raw material and energy
costs. However, the substitution of cellulose fibers with fillers like calcium
carbonate and clay reduces the strength of the finished sheet. Another problem
when the filler content is increased is an increased difficulty of maintaining an even
distribution of fillers across the three-dimensional sheet structure. An approach to
reduce these negative effects of increasing filler content is to preflocculate fillers
prior to their addition to the wet end approach system of the paper machine.
The definition of the term "preflocculation" is the modification of
filler particles into agglomerates through treatment with coagulants and/or
flocculants prior their flocculation and addition to the paper stock. The flocculation
treatment and shear forces of the process determine the size distribution and stability
of the floes prior to addition to the paper stock. The chemical environment and high
fluid shear rates present in modern high-speed papermaking require filler floes to be
stable and shear resistant. The floe size distribution provided by a preflocculation
treatment should minimize the reduction of sheet strength with increased filler
content, minimize the loss of optical efficiency from the filler particles, and
minimize negative impacts on sheet uniformity and printability. Furthermore, the
entire system must be economically feasible.
Therefore, the combination of high shear stability and sharp particle
size distribution is vital to the success of filler preflocculation technology.
However, filler floes formed by a low molecular weight coagulant alone, including
commonly used starch, tend to have a relatively small particle size that breaks down
under the high shear forces of a paper machine. Filler floes formed by a single high
molecular weight flocculant tend to have a broad particle size distribution that is
difficult to control, and the particle size distribution gets worse at higher filler solids
levels, primarily due to the poor mixing of viscous flocculant solution into the
slurry. Accordingly, there is an ongoing need for improved preflocculation
technologies.
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. In
addition, this section should not be construed to mean that a search has been made or
that no other pertinent information as defined in 37 C.F.R. § 1.56(a) exists.
Brief Summary of the Invention
At least one embodiment is directed towards a method of preparing
stable dispersion of flocculated filler particles having a specific particle size
distribution for use in papermaking processes. The method comprises the steps of:
a) providing an aqueous dispersion of filler particles; b) adding a first flocculating
agent to the dispersion in an amount sufficient to mix uniformly in the dispersion
without causing significant flocculation of the filler particles, and the first
flocculating agent being amphoteric; c) adding a microparticle to the dispersion in
an amount insufficient cause significant flocculation of the filler particles before,
simultaneous to, and/or after adding the first flocculating agent, and prior to adding
a second flocculating agent; d) adding the second flocculating agent to the
dispersion in an amount sufficient to initiate flocculation of the filler particles in the
presence of the first flocculating agent wherein the second flocculating agent has
opposite charge to the net charge of the first amphoteric flocculating agent; e)
shearing the flocculated dispersion to provide a dispersion of filler floes having the
desired particle size; and
f flocculating the filler particles prior to adding them to a paper stock and wherein
no paper stock is present during the flocculation.
The filler floes may have a median particle size of 10-100 mih. The
filler may be selected from the group consisting of precipitated calcium carbonate,
ground calcium carbonate, kaolin clay, talc, titanium dioxide, alumina trihydrate,
barium sulfate and magnesium hydroxide, and mixtures thereof. The first
flocculating agent may have a net anionic charge. The second flocculating agent
may be cationic, and/or may be selected from the group consisting of copolymers
and terpolymers of (meth) acrylamide with dimethylaminoethyl methacrylate
(DMAEM), dimethylaminoethyl acrylate (DMAEA), diethylaminoethyl acrylate
(DEAEA), diethylaminoethyl methacrylate (DEAEM) or their quaternary
ammonium forms made with dimethyl sulfate, methyl chloride or benzyl chloride,
and mixtures thereof. The second flocculating agent may be acrylamidedimethylaminoethyl
acrylate methyl chloride quaternary copolymer having a
cationic charge of 10-50 mole percent and a RSV of at least 15 dL/g and/or may be a
homopolymer of diallyl dimethyl ammonium chloride having an RSV of 0.1-2 dL/g.
The method may further comprise adding one or more microparticles to the
flocculated dispersion after addition of the second flocculating agent. The filler may
be anionically 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 or microparticle. Swollen starch may also be added to
the dispersion of filler particles. The swollen starch may be cationic, anionic,
amphoteric or noionic and/or may be a swollen-starch-latex composition. The
microparticle may be one item selected from the list consisting of: siliceous
materials, silica based particles, silica microgels, colloidal silica, silica sols, silica
gels, polysilicates, cationic silica, aluminosilicates, polyaluminosilicates,
borosilicates, polyborosilicates, zeolites, and synthetic or naturally occurring
swelling clays, anionic polymeric microparticles, cationic polymeric microparticles,
amphoteric organic polymeric microparticles, and any combination thereof.
At least one embodiment is directed towards a paper product
incorporating the filler floes prepared as described herein.
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 be construed. The
organization of the definitions is for convenience only and is not intended to limit
any of the definitions to any particular category. For purposes of this application the
definition of these terms is as follows:
"Coagulant" means a composition of matter having a higher charge
density and lower molecular weight than a flocculant, which when added to a liquid
containing finely divided suspended particles, destabilizes and aggregates the solids
through the mechanism of ionic charge neutralization.
"Flocculant" 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 finely divided suspended particles, destabilizes and aggregates the
solids through the mechanism of interparticle bridging.
"Flocculating Agent" means a composition of matter which when
added to a liquid destabilizes, and aggregates colloidal and finely divided suspended
particles in the liquid, flocculants and coagulants can be flocculating agents.
"GCC" means ground calcium carbonate, which is manufactured by
grinding naturally occurring calcium carbonate rock
"FCC" means precipitated calcium carbonate which is synthetically
produced.
"Microparticle" means a particle of between 0.1 mih and 100 mih in
size, it can compose a number of materials including silicon, ceramics, glass,
polymers, and metals, because microparticles have a much larger surface-to-volume
ratio than similar macroscale sized materials their behavior can be quite different.
In 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-Othmer 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 is directed towards a method of preparing a
stable dispersion of flocculated filler particles having a specific particle size
distribution for use in a papermaking processes. A first flocculating agent is added
to an aqueous dispersion of filler particles in an amount and under conditions such
that it mixes uniformly with the dispersion but does not cause any significant
flocculation of the filler particles. Either: before, during, or after the addition of the
first flocculating agent, a microparticle is added to the dispersion. After both the
first flocculating agent and the microparticle have been added a second flocculating
agent is added to the dispersion in an amount and under conditions sufficient to
initiate flocculation of the filler particles in the presence of the first flocculating
agent. In at least one embodiment the types of first and second agents and the
methods of their use, and/or addition are according to any and all of the methods and
procedures described in US Patent 8,088,213.
Optionally the flocculated dispersion can be sheared to provide a
dispersion of filler floes having an optimal particle size.
While microparticles have previously been used in papermaking
processes, their use in this manner is quite novel. In some prior art processes,
microparticles were added in the wet end to prevent the loss of material from the
fiber-filler mixture. In this invention however the microparticles are added to the
dispersion of filler prior to the dispersion coming into contact with the fibers used to
make the paper.
This invention is also different than previous microparticle using
methods of preparing filler dispersions aiming to have optimal degrees of high shear
stability simultaneous to sharp particle size have used microparticles (such as that of
US Published Patent Application 2009/0267258). Those previous methods used the
microparticles after the second (flocculation initiating) flocculating agent. In this
invention the microparticle is added to the dispersion before flocculation is initiated.
This is because the invention makes use of a previously unknown property of these
microparticles.
Microparticles are known to facilitate flocculation by strongly
interacting with the flocculating agents to strengthening the resulting particle
agglomeration. Thus it was previously known that they assisted only one (shear
strength) of the two prerogatives of concern (shear strength and particle size).
The invention however makes use of the newly discovered fact that
microparticles can positively interact with the filler particles in the absence of any
flocculation occurring. Without being limited by theory or design it is believed that
the microparticles form very hard "anchor sites" on the surface of the filler
particles.. Because these anchor sites are much harder that the flocculating
polymers, they resist bending and more firmly hold polymer agglomerations onto
the filler particles than agglomerations anchored in place by flocculating agents.
Thus the inventive method uses microparticles to facilitate the other of the two
prerogatives, increasing agglomeration size.
In at least one embodiment the microparticles include siliceous
materials and polymeric microparticles. Representative siliceous materials include
silica based particles, silica microgels, colloidal silica, silica sols, silica gels,
polysilicates, cationic silica, aluminosilicates, polyaluminosilicates, borosilicates,
polyborosilicates, zeolites, and synthetic or naturally occurring swelling clays. The
swelling clays may be bentonite, hectorite, smectite, montmorillonite, nontronite,
saponite, sauconite, mormite, attapulgite, and sepiolite. A suitable representative
microparticle is product PosiTEK 8699 (produced by Nalco Company, Naperville
IL).
Polymeric microparticles useful in this invention include anionic,
cationic, or amphoteric organic microparticles. These microparticles typically have
limited solubility in water, may be crosslinked, and have an unswollen particle size
of less than 750 nm.
Anionic organic microparticles include those described in US
6,524,439 and made by hydrolyzing acrylamide polymer microparticles or by
polymerizing anionic monomers as (meth)acrylic acid and its salts, 2-acrylamido-2-
methylpropane sulfonate, sulfoethyl-(meth)acrylate, vinylsulfonic acid, styrene
sulfonic acid, maleic or other dibasic acids or their salts or mixtures thereof. These
anionic monomers may also be copolymerized with nonionic monomers such as
(meth)acrylamide, N-alkylacrylamides, N,N-dialkylacrylamides, methyl
(meth)acrylate, acrylonitrile, N-vinyl methylacetamide, N-vinyl methyl formamide,
vinyl acetate, N-vinyl pyrrolidone, and mixtures thereof.
Cationic organic microparticles include those described in US
6,524,439 and made by polymerizing such monomers as diallyldialkylammonium
halides, acryloxyalkyltrimethylammonium chloride, (meth)acrylates of
dialkylaminoalkyl compounds, and salts and quaternaries thereof and, monomers of
N,N-dialkylaminoalkyl(meth)acrylamides,
(meth)acrylamidopropyltrimethylammonium chloride and the acid or quaternary
salts of N,N-dimethylaminoethylacrylate and the like. These cationic monomers
may also be copolymerized with nonionic monomers such as (meth)acrylamide, Nalkylacrylamides,
N,N-dialkylacrylamides, methyl (meth)acrylate, acrylonitrile, Nvinyl
methylacetamide, N-vinyl methyl formamide, vinyl acetate, N-vinyl
pyrrolidone, and mixtures thereof.
Amphoteric organic microparticles are made by polymerizing
combinations of at least one of the anionic monomers listed above, at least one of
the cationic monomers listed above, and, optionally, at least one of the nonionic
monomers listed above.
Polymerization of the monomers in an organic microparticle typically
is done in the presence of a polyfunctional crosslinking agent. These crosslinking
agents are described in US 6,524,439 as having at least two double bonds, a double
bond and a reactive group, or two reactive groups. Examples of these agents are
N,N-methylenebis(meth)acrylamide, polyethyleneglycol di(meth)acrylate, N-vinyl
acrylamide, divinylbenzene, triallylammonium salts, N-methylallylacrylamide
glycidyl (meth)acrylate, acrolein, methylolacrylamide, dialdehydes like glyoxal,
diepoxy compounds, and epichlorohydrin.
In an embodiment, the microparticle dose is between 0.2 and 8 lb/ton
of filler treated. In an embodiment, the microparticle dose is between 0.5 and 4.0
lb/ton of filler treated. These dosages refer to the active pounds of microparticle per
2000 pounds of dry filler.
In at least one embodiment the method also involves contacting the
filler particles with swollen starch. As described in US Patents 2,805,966,
2,1 13,034, 2,328,537, and 5,620,510 when starch slurry is cooked in a steam cooker
under controlled temperature (and optionally controlled pH) condition, the starch
can absorb large amounts of water without rupturing. The addition of such swollen
starches can also increase the size of the filler floes used in this invention. In at least
one embodiment the swollen starch is a cross-linked starch such as one or more of
those described in US Patent 8,298,508 and International Patent Application
WO/97/46591.
In at least one embodiment the swollen starch added to the filler
particles and/or the method of its use is according to any one of the swollen starchlatex
compositions and methods described in US Patent Application 2010/0078138.
As an example, the swollen starch-latex composition, in the presence
or absence of co-additives, is suitably prepared in batch or jet cookers or by mixing
the suspension of starch and latex with hot water. For a given starch, the swelling is
done under controlled conditions of temperature, pH, mixing and mixing time, in
order to avoid rupture of the swollen starch granules. The composition is rapidly
added to the filler suspension, which is then introduced to the paper furnish, at a
point prior to or at the headbox of the paper machine. During the drying operation
the retained swollen starch granules with filler particles will rupture, thereby
liberating amylopectin and amylose macromolecules to bond the solid components
of the sheet.
The combination of swollen starch and latex can be used in filler
treatments under acid, neutral or alkaline environments. In at least one embodiment
the filler is treated with a swollen starch-latex composition, made with or without
co-additives, and is then added to paper slurry. The filler particles agglomerate and
the agglomerated filler particles adsorb on the surfaces of the fines and fibers
causing their rapid flocculation in the furnish.
In at least one embodiment the swollen starch-latex composition is
made by adding latex to uncooked starch and is followed by partial cooking at
temperatures slightly below the gel point to produce swollen starch.
In at least one embodiment one or more swollen starch compositions
(including swollen starch-latex compositions) is added to the filler dispersion before
or simultaneous to when the microparticle is added, before or simultaneous to when
the first flocculating agent is added, before or simultaneous to when the second
flocculating agent is added, after the second flocculating agent is added, and any
combination thereof.
The fillers useful in this invention are well known and commercially
available. They typically would include any inorganic or organic particle or
pigment used to increase the opacity or brightness, increase the smoothness, or
reduce the cost of the paper or paperboard sheet. Representative fillers include
calcium carbonate, kaolin clay, talc, titanium dioxide, alumina trihydrate, barium
sulfate, magnesium hydroxide, and the like. Calcium carbonate includes GCC in a
dry or dispersed slurry form, chalk, PCC of any morphology, and PCC in a
dispersed slurry form. Some examples of GCC and PCC slurries are provided in co
pending US Patent Application Serial Number 12/323,976. The dispersed slurry
forms of GCC or PCC are typically produced using polyacrylic acid polymer
dispersants or sodium polyphosphate dispersants. Each of these dispersants imparts
a significant anionic charge to the calcium carbonate particles. Kaolin clay slurries
may also be dispersed using polyacrylic acid polymers or sodium polyphosphate.
In an embodiment, the fillers are selected from calcium carbonate and
kaolin clay and combinations thereof.
In an embodiment, the fillers are selected from precipitated calcium
carbonate, ground calcium carbonate and kaolin clay, and mixtures thereof.
The first flocculating agent is preferably a cationic polymeric
flocculant when used with cationically charged fillers and anionic when used with
anionically charged fillers. However, it can be anionic, nonionic, zwitterionic, or
amphoteric as long as it will mix uniformly into a high solids slurry without causing
significant flocculation.
The definition of "without causing significant flocculation" is no
flocculation of the filler in the presence of the first flocculating agent or the
formation of floes which are smaller than those produced upon addition of the
second flocculating agent and unstable under conditions of moderate shear.
Moderate shear is defined as the shear provided by mixing a 300 ml sample in a 600
ml beaker using an IKA RE16 stirring motor at 800 rpm with a 5 cm diameter, fourbladed,
turbine impeller. This shear should be similar to that present in the approach
system of a modern paper machine.
Suitable flocculants 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 or 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
flocculants generally have a charge content of less than 80 mole percent and often
less than 40 mole percent.
While cationic polymer flocculants may be formed using cationic
monomers, it is also possible to react certain nonionic vinyl addition polymers to
produce cationically charged polymers. Polymers of this type include those
prepared through the reaction of polyacrylamide with dimethylamine and
formaldehyde to produce a Mannich derivative.
Similarly, while anionic polymer flocculants may be formed using
anionic monomers, it is also possible to modify certain nonionic vinyl addition
polymers to form anionically charged polymers. Polymers of this type include, for
example, those prepared by the hydrolysis of polyacrylamide.
The flocculant 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 (meth)acrylamide with
dimethylaminoethyl methacrylate (DMAEM), dimethylaminoethyl acrylate
(DMAEA), diethylaminoethyl acrylate (DEAEA), diethylaminoethyl methacrylate
(DEAEM) or their quaternary ammonium forms made with dimethyl sulfate, methyl
chloride or benzyl chloride. Representative anionic polymers include copolymers of
acrylamide with sodium acrylate and/or 2-acrylamido 2-methylpropane sulfonic acid
(AMPS) or an acrylamide homopolymer that has been hydrolyzed to convert a
portion of the acrylamide groups to acrylic acid.
In an embodiment, the flocculants have a RSV of at least 3 dL/g.
In an embodiment, the flocculants have a RSV of at least 10 dL/g.
In an embodiment, the flocculants have a RSV of at least 15 dL/g.
As used herein, "RSV" stands for reduced specific viscosity. Within
a series of polymer homologs which are substantially linear and well solvated,
"reduced specific viscosity (RSV)" measurements for dilute polymer solutions are
an indication of polymer chain length and average molecular weight according to
Determination of Molecular Weights, by Paul J . Flory, pages 266-316, Principles of
Polymer Chemistry , Cornell University Press, Ithaca, NY, Chapter VII (1953). The
RSV is measured at a given polymer concentration and temperature and calculated
as follows:
RSV = [( |/ |o)- l ]/c where h = viscosity of polymer solution, h 0 = viscosity of
solvent at the same temperature and c = concentration of polymer in solution.
The units of concentration "c" are (grams/100 ml or g/deciliter).
Therefore, the units of RSV are dL/g. Unless otherwise specified, a 1.0 molar
sodium nitrate solution is used for measuring RSV. The polymer concentration in
this solvent is 0.045 g/dL. The RSV is measured at 30°C. The viscosities h and h0
are measured using a Cannon Ubbelohde semi-micro dilution viscometer, size 75.
The viscometer is mounted in a perfectly vertical position in a constant temperature
bath adjusted to 30 + 0.02°C. The typical error inherent in the calculation of RSV
for the polymers described herein is about 0.2 dL/g. When two polymer homologs
within a series have similar RSV's that is an indication that they have similar
molecular weights.
As discussed above, the first flocculating agent is added in an amount
sufficient to mix uniformly in the dispersion without causing significant flocculation
of the filler particles. In an embodiment, the first flocculating agent dose is between
0.2 and 6.0 lb/ton of filler treated. In an embodiment, the flocculant dose is between
0.4 and 3.0 lb/ton of filler treated. For purposes of this invention, "lb/ton" is a unit
of dosage that means pounds of active polymer (coagulant or flocculant) per 2,000
pounds of filler.
The second flocculating agent can be any material that can initiate the
flocculation of filler in the presence of the first flocculating agent. In an
embodiment, the second flocculating agent is selected from microparticles,
coagulants, flocculants and mixtures thereof.
Suitable coagulants generally have lower molecular weight than
flocculants and have a high density of cationic charge groups. The coagulants useful
in this invention are well known and commercially available. They may be
inorganic or organic. Representative inorganic coagulants include alum, sodium
aluminate, polyaluminum chlorides or PACs (which also may be under the names
aluminum chlorohydroxide, aluminum hydroxide chloride, and polyaluminum
hydroxychloride), sulfated polyaluminum chlorides, polyaluminum silica sulfate,
ferric sulfate, ferric chloride, and the like and blends thereof.
Many organic coagulants are formed by condensation
polymerization. Examples of polymers of this type include epichlorohydrindimethylamine
(EPI-DMA) copolymers, and EPI-DMA copolymers crosslinked
with ammonia.
Additional coagulants include polymers of ethylene dichloride and
ammonia, or ethylene dichloride and dimethylamine, with or without the addition of
ammonia, condensation polymers of multifunctional amines such as
diethylenetriamine, tetraethylenepentamine, hexamethylenediamine and the like
with ethylenedichloride or polyfunctional acids like adipic acid and polymers made
by condensation reactions such as melamine formaldehyde resins.
Additional coagulants include cationically charged vinyl addition
polymers such as polymers, copolymers, and terpolymers of (meth)acrylamide,
diallyl-N,N-disubstituted ammonium halide, dimethylaminoethyl methacrylate and
its quaternary ammonium salts, dimethylaminoethyl acrylate and its quaternary
ammonium salts, methacrylamidopropyltrimethylammonium chloride,
diallylmethyl(beta-propionamido)ammonium chloride, (betamethacryloyloxyethyl)
trimethyl ammonium methylsulfate, quaternized
polyvinyllactam, vinylamine, and acrylamide or methacrylamide that has been
reacted to produce the Mannich or quaternary Mannich derivatives. Suitable
quaternary ammonium salts may be produced using methyl chloride, dimethyl
sulfate, or benzyl chloride. The terpolymers may include anionic monomers such as
acrylic acid or 2-acrylamido 2-methylpropane sulfonic acid as long as the overall
charge on the polymer is cationic. The molecular weights of these polymers, both
vinyl addition and condensation, range from as low as several hundred to as high as
several million.
Other polymers useful as the second flocculating agent include
cationic, anionic, or amphoteric polymers whose chemistry is described above as a
flocculant. The distinction between these polymers and flocculants is primarily
molecular weight.
The second flocculating agent may be used alone or in combination
with one or more additional second flocculating agents. In an embodiment, one or
more microparticles are added to the flocculated filler slurry subsequent to addition
of the second flocculating agent.
The second flocculating agent is added to the dispersion in an amount
sufficient to initiate flocculation of the filler particles in the presence of the first
flocculating agent. In an embodiment, the second flocculating agent dose is between
0.2 and 8.0 lb/ton of filler treated. In an embodiment, the second component dose is
between 0.5 and 6.0 lb/ton of filler treated.
In an embodiment, one or more microparticles may be added to the
flocculated dispersion prior to shearing to provide additional flocculation and/or
narrow the particle size distribution.
In an embodiment, the second flocculating agent and first
flocculating agent are oppositely charged.
In an embodiment, the first flocculating agent is cationic and the
second flocculating agent is anionic.
In an embodiment, the first flocculating agent is selected from
copolymers of acrylamide with dimethylaminoethyl methacrylate (DMAEM) or
dimethylaminoethyl acrylate (DMAEA) and mixtures thereof.
In an embodiment, the first flocculating agent is an acrylamide and
dimethylaminoethyl acrylate (DMAEA) copolymer with a cationic charge content of
5-50 mole % and an RSV of > 15 dL/g.
In an embodiment, the second flocculating agent is selected from the
group consisting of partially hydrolyzed acrylamide and copolymers of acrylamide
and sodium acrylate.
In an embodiment, the second flocculating agent is acrylamidesodium
acrylate copolymer having an anionic charge of 5-40 mole percent and a
RSV of 0.3-5 dL/g.
In an embodiment, the first flocculating agent is anionic and the
second flocculating agent is cationic.
In an embodiment, the first flocculating agent is selected from the
group consisting of partially hydrolyzed acrylamide and copolymers of acrylamide
and sodium acrylate.
In an embodiment, the first flocculating agent is a copolymer of
acrylamide and sodium acrylate having an anionic charge of 5-75 mole percent and
an RSV of at least 15 dL/g.
In an embodiment, the second flocculating agent is selected from the
group consisting of epichlorohydrin-dimethylamine (EPI-DMA) copolymers, EPIDMA
copolymers crosslinked with ammonia, and homopolymers of diallyl-N,Ndisubstituted
ammonium halides.
In an embodiment, the second flocculating agent is a homopolymer
of diallyl dimethyl ammonium chloride having an RSV of 0.1-2 dL/g.
In an embodiment, the second flocculating agent is selected from
copolymers of acrylamide with dimethylaminoethyl methacrylate (DMAEM) or
dimethylaminoethyl acrylate (DMAEA) and mixtures thereof.
In an embodiment, the second flocculating agent is an acrylamide and
dimethylaminoethyl acrylate (DMAEA) copolymer with a cationic charge content of
5-50 mole % and an RSV of > 15 dL/g.
Dispersions of filler floes according to this invention are prepared
prior to their addition to the papermaking furnish. This can be done in a batch-wise
or continuous fashion. The filler concentration in these slurries is typically less than
80% by mass. It is more typically between 5 and 65% by mass.
A batch process can consist of a large mixing tank with an overhead,
propeller mixer. The filler slurry is charged to the mix tank, and the desired amount
of first flocculating agent is fed to the slurry under continuous mixing. The slurry
and flocculant are mixed for an amount of time sufficient to distribute the first
flocculating agent uniformly throughout the system, typically for about 10 to 60
seconds, depending on the mixing energy used. The desired amount of second
flocculating agent is then added while stirring at a mixing speed sufficient to break
down the filler floes with increasing mixing time typically from several seconds to
several minutes, depending on the mixing energy used. Microparticle is added to
the filler slurry before, simultaneous to, and/or after adding the first flocculating
agent, and prior to the second flocculant agent. Optionally, a microparticle is added
after the second flocculating agent. The addition of microparticle increases the
shear stability of filler floes and narrow down the particle size distribution of floes.
When the appropriate size distribution of the filler floes is obtained, the mixing
speed is lowered to a level at which the floes are stable. This batch of flocculated
filler is then transferred to a larger mixing tank with sufficient mixing to keep the
filler floes uniformly suspended in the dispersion. The flocculated filler is pumped
from this mixing tank into the papermaking furnish.
In a continuous process the desired amount of first flocculating agent
is pumped into the pipe containing the filler and mixed with an in-line static mixer,
if necessary. A length of pipe or a mixing vessel sufficient to permit adequate
mixing of filler and flocculant may be included prior to the injection of the
appropriate amount of second flocculating agent. The second flocculating agent is
then pumped into the pipe containing the filler and mixed with an in-line static
mixer, if necessary. Microparticle is pumped into the pipe containing the filler
slurry and mixed with an in-line static mixer, if necessary. The addition point is
before, simultaneous to, and/or after pumping the first flocculating agent, and prior
to addition of the second flocculant agent. Optionally, a microparticle is pumped
after the second flocculating agent. Addition of microparticle increases the shear
stability of filler floes and narrow down the particle size distribution of floes. High
speed mixing is then required to obtain the desired size distribution of the filler
floes. Adjusting either the shear rate of the mixing device or the mixing time can
control the floe size distribution. A continuous process would lend itself to the use
of an adjustable shear rate in a fixed volume device. One such device is described in
US Patent 4,799,964. This device is an adjustable speed centrifugal pump that,
when operated at a back pressure exceeding its shut off pressure, works as a
mechanical shearing device with no pumping capacity. Other suitable shearing
devices include a nozzle with an adjustable pressure drop, a turbine-type
emulsification device, or an adjustable speed, high intensity mixer in a fixed volume
vessel. After shearing, the flocculated filler slurry is fed directly into the
papermaking furnish.
In both the batch and continuous processes described above, the use
of a filter or screen to remove oversize filler floes can be used. This eliminates
potential machine runnability and paper quality problems resulting from the
inclusion of large filler floes in the paper or board.
In an embodiment, the median particle size of the filler floes is at
least 10 mih. In an embodiment, the median particle size of the filler floes is
between 10 and 100 mih. In an embodiment, the median particle size of the filler
floes is between 10 and 70 mih.
In at least one embodiment the invention is practiced using at least
one of the compositions and/or methods described in US Patent Application
12/975,596. In at least one embodiment the invention is practiced using at least one
of the compositions and/or methods described in US Patent 8,088,213. In at least
one embodiment the invention is practiced using at least one of the compositions
and/or methods described in US Patent 8,172,983.
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.
Experimental Methods
In the filler flocculation experiments, the filler slurry was diluted to
10% solids with tap water and 300 mL of this diluted slurry was placed in a 500 mL
glass beaker. Stirring was conducted for at least 30 seconds prior to the addition of
any chemical additives. The stirrer was an IKA® EUROSTAR Digital overhead
mixer with a R1342, 50 mm, four-blade propeller (both available from IKA® Works,
Inc., Wilmington, NC USA). The final floe size distribution was characterized by
laser light scattering using the Malvern Mastersizer Micro from Malvern
Instruments Ltd., Southborough, MA USA. The analysis was conducted using a
polydisperse model and presentation 4PAD. This presentation assumes a 1.60 real
component and a 0 imaginary component for the refractive index of the filler and a
refractive index of 1.33 for water as the continuous phase. The quality of the
distribution was indicated by the volume-weighted median floe size, D(V,0.5) and
the span of the distribution, which is defined as:
D(y ,o.9) - D(y ,o .i)
span =
D(V,0.5)
Here D(V,0 ), D(V,0.5), and D(V,0.9) are defined as the diameters
that are equal or larger than 10%, 50%, and 90% in volume of filler floes,
respectively. Smaller span values indicate more uniform particle size distributions
that are believed to have better performance in papermaking. The values of
D(V,0.5) and span for each example were listed in Table I and II.
Example 1
The filler used was scalenohedral, precipitated calcium carbonate
(PCC) dry powder (available as Albacar HO from Specialty Minerals Inc.,
Bethlehem, PA, USA). This PCC powder was dispersed in tap water at 10% solid.
The slurry was stirred under 800 rpm, and a small amount of the sample was taken
to measure the particle size distribution using Malvern Mastersizer. The
experiments made use of: a) flocculating agent DEVI 15 (which is a commercially
available anionic sodium acrylate-acrylamide copolymer with an RSV of about
32dL/g and a charge content of 29 mole percent, available from Nalco Company,
Naperville, 111., USA), b) flocculating agent DEV125 (which is a commercially
available cationic acrylamide-dimethylaminoethyl acrylate-methyl chloride
quaternary salt copolymer with an RSV of about 25 dL/g and a charge content of 10
mole percent, available from Nalco Company, Naperville, 111., USA..), and c)
microparticle Nalco-8699 which is a commercially available colloidal silica
dispersion available from Nalco Company, Naperville, 111., USA.).
The results in Table 1 show that the untreated PCC had a monomodal
particle size distribution with a median particle size of 3.75 mih and a span of 1.283.
After 30s mixing of the 10% PCC slurry under 800 rpm, 1.5 lb/ton Nalco DEVI 15
was added slowly into the slurry using a syringe, followed by slow addition of 1.0
lb/ton Nalco DEV125 using another syringe. After addition of DEV125, one filler
sample was taken for particle size measurement (time = 0 minutes), then the stirring
rate was increased to 1500 rpm and kept for 8 minutes. Samples were taken in every
two minutes interval to measure the particle size distribution (time =2, 4 , 6 and 8
minutes). This shearing was done for the purpose of evaluating the stability of the
filler floes. The results are shown in Table 1.
Example 2
Experiment 1 was repeated with microparticle as one of the
component in the treatment program. 0.5 lb/ton Nalco-8699 was added before the
addition of DEVI 15.
Example 3
Experiment 1 was repeated with microparticle as one of the
component in the treatment program. 1.0 lb/ton Nalco-8699 was added before the
addition of DEVI 15.
Example 4
Experiment 1 was repeated with microparticle as one of the
component in the treatment program. 1.5 lb/ton Nalco-8699 was added before the
addition of DEVI 15.
Example 5
Experiment 1 was repeated with microparticle as one of the
component in the treatment program. 1.0 lb/ton Nalco-8699 was added after the
addition of DEVI 15 but before DEV125.
Example 6
Experiment 1 was repeated with microparticle as one of the
component in the treatment program. 1.0 lb/ton Nalco-8699 was added after the
addition of DEV125.
Example 7
Experiment 1 was repeated with microparticle as one of the
component in the treatment program. 1.0 lb/ton Nalco-8699 and 1.5 lb/ton DEVI 15
were premixed before adding into the filler slurry, followed by the addition of
DEV125.
The particle size distribution characteristics of PCC (precipitated
calcium carbonate) floes formed by different chemical programs and
sheared under 1500 rpm for various times.
4 1.944 20.1 59.87 136.48
6 1.942 15.77 48.19 109.36
8 1.974 14.01 42.6 98.1
5 0 0.995 82.66 163.61 245.52
2 1.808 22.98 60.79 132.91
4 1.838 16.45 43.4 96.2
6 1.862 13.71 35.96 80.65
8 1.859 12.23 3 1.73 7 1 .22
6 0 0.748 119.7 216.05 281 .41
2 1.824 28.38 77.75 170.22
4 1.863 18.62 5 1 .98 115.44
6 1.863 15.4 42.34 94.27
8 1.834 13.68 37.07 8 1 .65
7 0 0.855 102.72 196.83 270.95
2 1.81 5 27.65 7 1 .58 157.55
4 1.806 17.97 48.93 106.34
6 1.823 15.6 40.28 89.04
8 1.823 13.91 35.53 78.69
The results in Table I show that with Nalco-8699 microparticle in the
flocculation program, no matter if it is added before the anionic flocculating agent,
after anionic flocculating agent, pre-mixed with anionic flocculating agent or after
cationic flocculating agent, both filler flocculation and shear stability of the resulted
filler floes improved significantly.
Example 8
The filler used was ground calcium carbonate (GCC) slurry as 70%
solids. This slurry was diluted to 10% solids with tap water. The slurry was stirred
under 800 rpm, and a small amount of the sample was taken to measure the particle
size distribution using Malvern Mastersizer. The results in Table II show that the
untreated GCC had a monomodal particle size distribution with a median particle
size of 1.51 mih and a span of 2.029.
After 30s mixing of the 10% GCC slurry under 800 rpm, 1.5 lb/ton
Nalco DEV120 was added to the slurry, followed by slow addition of 0.75 lb/ton
Nalco DEVI 15 into the slurry using a syringe, and finally slow addition of 0.60
lb/ton Nalco DEV125 using another syringe. After addition of DEV125, one filler
sample was taken for particle size measurement (time = 0 minutes), then the stirring
rate was increased to 1500 rpm and kept for 8 minutes. Samples were taken in every
two minutes interval to measure the particle size distribution (time =2, 4, 6 and 8
minutes). The results were shown in Table II.
Example 9
Experiment 8 was repeated with microparticle as one of the
component in the treatment program. 0.5 lb/ton Nalco-8699 was added before the
addition of DEVI 15.
Example 10
Experiment 8 was repeated with microparticle as one of the
component in the treatment program. 1.0 lb/ton Nalco-8699 was added before the
addition of DEVI 15.
Example 1 1
Experiment 8 was repeated with microparticle as one of the
component in the treatment program. 1.0 lb/ton Nalco-8699 was added after the
addition of DEVI 15 but before DEV125.
Example 12
Experiment 8 was repeated with microparticle as one of the
component in the treatment program. 1.0 lb/ton Nalco-8699 was added after the
addition of DEV125.
Example 13
Experiment 8 was repeated with microparticle as one of the
component in the treatment program. 1.0 lb/ton Nalco-8699 and 0.75 lb/ton DEVI 15
were premixed before adding into the filler slurry, followed by the addition of
DEV125.
The particle size distribution characteristics of GCC (ground calcium
carbonate) floes formed by different chemical programs and sheared
under 1500 rpm for various times.
time D(v, 0 .1) D(v, 0.5) D(v, 0.9)
Experiment (min) span (m h ) (m h ) m)
GCC,
untreated 0 2.029 0.59 1.51 3.66
8 0 1.421 49.54 117.71 2 16.78
2 1.851 23.36 59.89 134.24
4 1.903 17.45 45.71 104.43
6 1.983 14.70 38.82 9 1 .68
8 2.066 13.03 34.67 84.69
9 0 1. 1 94 66.24 14 1.62 235.37
2 1.862 27.07 70.07 157.53
4 1.994 19.23 5 1 .69 122.29
6 2.039 15.43 42.88 102.85
8 2.086 13.33 37.92 92.41
10 0 9.935 84.92 169.81 253.62
2 1.87 28.30 78.39 174.88
4 2.1 04 18.56 57.97 140.51
6 2.208 14.50 47.87 120. 18
8 2.272 12.04 4 1.38 106.04
11 0 1.003 84.93 167.75 253.25
2 1.802 30.94 79.63 174.45
4 1.847 23.1 8 59.74 133.54
6 1.91 1 19.82 5 1 .1 6 117.78
8 1.874 17.61 45.47 102.84
12 0 1.09 77.99 143.99 234.88
2 1.385 53.53 114.17 2 11.62
4 1.612 38.48 94.83 191 .38
6 1.728 29.81 82.46 172.33
8 1.864 24.06 74.69 163.22
13 0 7.599 116.61 218.64 218.24
2 1.558 40.47 112.51 215.72
4 1.899 25.81 83.24 183.87
6 2.06 19.94 68.76 161 .58
8 2.12 16.97 60.81 145.90
The results in Table II show that with Nalco-8699 microparticle in
the flocculation program, no matter if it is added before the anionic flocculating
agent, after anionic flocculating agent, pre-mixed with anionic flocculating agent or
after cationic flocculating agent, both filler flocculation and shear stability of the
resulted filler floes improved significantly.
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 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 that also specifically excludes any one or some of the
various embodiments described herein and/or incorporated herein.
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 art. 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 10" should be considered to include
any and all subranges between (and inclusive of) the minimum value of 1 and the
maximum value of 10; that 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 to
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. All percentages and ratios are by weight unless
otherwise stated.
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 preparing a stable dispersion of flocculated filler particles
having a specific particle size distribution for use in papermaking processes
comprising:
a) providing an aqueous dispersion of filler particles;
b) adding a first flocculating agent to the dispersion in an amount sufficient
to mix uniformly in the dispersion without causing significant flocculation of the
filler particles, and the first flocculating agent being amphoteric;
c) adding a microparticle to the dispersion in an amount insufficient cause
significant flocculation of the filler particles before, simultaneous to, and/or after
adding the first flocculating agent, and prior to adding a second flocculating agent;
d) adding the second flocculating agent to the dispersion in an amount
sufficient to initiate flocculation of the filler particles in the presence of the first
flocculating agent wherein the second flocculating agent has opposite charge to the
net charge of the first amphoteric flocculating agent;
e) shearing the flocculated dispersion to provide a dispersion of filler floes
having the desired particle size; and
f flocculating the filler particles prior to adding them to a paper stock and
wherein no paper stock is present during the flocculation.
2. The method of claim 1 wherein the filler floes have a median particle size of
10-100 m i.
3. The method of claim 1 wherein the filler is selected from the group
consisting of precipitated calcium carbonate, ground calcium carbonate, kaolin clay,
talc, titanium dioxide, alumina trihydrate, barium sulfate and magnesium hydroxide,
and mixtures thereof.
4. The method of claim 1 wherein the first flocculating agent has net anionic
charge.
5. The method of claim 4 wherein the second flocculating agent is cationic,
selected from the group consisting of copolymers and terpolymers of (meth)
acrylamide with dimethylaminoethyl methacrylate (DMAEM), dimethylaminoethyl
acrylate (DMAEA), diethylaminoethyl acrylate (DEAEA), diethylaminoethyl
methacrylate (DEAEM) or their quaternary ammonium forms made with dimethyl
sulfate, methyl chloride or benzyl chloride,
and mixtures thereof.
6. The method of claim 5 wherein the second flocculating agent is acrylamidedimethylaminoethyl
acrylate methyl chloride quaternary copolymer having a
cationic charge of 10-50 mole percent and a RSV of at least 15 dL/g.
7. The method of claim 4 wherein the second flocculating agent is a
homopolymer of diallyl dimethyl ammonium chloride having an RSV of 0.1-2 dL/g.
8. The method of claim 1 further comprising adding one or more microparticles
to the flocculated dispersion after addition of the second flocculating agent.
9. The method of claim 1 wherein the filler is anionically 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 or
microparticle.
10. The method of claim 8 wherein the filler is anionically 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 or
microparticle.
11. The method of claim 1 further comprising adding a swollen starch to
dispersion of filler particles.
12. The method of claim 11 wherein the swollen starch is added before, and/or
after adding the first flocculating agent, and prior to adding a second flocculating
agent;
13. The method of claim 1lwherein the swollen starch is cationic, anionic,
amphoteric or noionic.
14. The method of claim 10 wherein the swollen starch is a swollen-starch-latex
composition.
15. The method of claim 1 in which the microparticle is one selected from the
list consisting of: siliceous materials, silica based particles, silica microgels,
colloidal silica, silica sols, silica gels, polysilicates, cationic silica, aluminosilicates,
polyaluminosilicates, borosilicates, polyborosilicates, zeolites, and synthetic or
naturally occurring swelling clays, anionic polymeric microparticles, cationic
polymeric microparticles, amphoteric organic polymeric microparticles, and any
combination thereof.