CONTROLLABLE FILLER PREFLOCULATION
USING A DUAL POLYMER SYSTEM
Cross-Reference to Related Applications
This Application is a Continuation-in-part of pending US Patent Application serial
number 1/854,044 filed on September 12, 2007
Statement Regarding Federally Sponsored Research or Development
Not Applicable
Background of he n
This invention relates to the prefioceulation of fillers used in papermakmg,
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 lay reduces the strengtli of
the finished sheet. Another problem when the filler content is increased is an increased difficulty
of maintaining an even clistributioii of fillers across the three-dimensional sheet stracture. An
approach to reduce these negative effects of increasing filler content is to prefiocculate fillers
prior to their addition to the wet end approach system of the paper machine.
The definition of the term "prefioceulation" is the modification of filler particles
into agglomerates through treatment with coagulants and/or flocculants prior their 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 modem high-speed papermaking require filler
floes to be stable and shear resistant. The floe size distribution provided by a prefioceulation
ireatraent should minimize the reduciiors of sheet strength with increased filler content minimize
the loss of optical efficiency from ihe filler particles, and minimize negative impacts on sheet
uniformity and printahility. Furthermore, he 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 preilocculation 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 preilocculation 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 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; e) adding a 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; and d) optionally shearing the flocculated
dispersion to provide a dispersion of filler floes having the desired particle size.
At least one embodiment is directed towards a method of making paper products
from pulp comprising forming an aqueous cellulosie papermaking furnish adding an aqueous
dispersion of filler floes prepared as described herein to the furnish, draining the furnish to form
a sheet a d drying the sheet. The steps of forming the papermaking furnish, draining and drying
may be canied out in any conventional manner generally known to those skilled in the art.
At least one embodiment is directed towards a paper product incorporating the
filler floes prepared as described herein.
Brief Description of the Drawings
A detailed description of the invention is hereafter described with specific
reference being made to the drawings in which:
FIG. I is an illustration of an MCL time resolution of a flocculating reaction.
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 a y
particular category. For purposes of this application the definition of these terms is as follows:
C g means a composition of matter having a higher charge density and
lower molecular weight than a flocculani, which when added to a liquid containing finely divided
suspended particles, destabilizes and aggregates the solids through the mechanism of ionic
charge neutralization.
F cc l n 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
mterpariicle bridging.
"Flocculating Agen means a composition of matter which when added to a
liquid destabilizes, and aggregates colloidal and fineiy divided suspended particles in d e liquid,
flocculants and coagulants can be flocculating agents.
"GCC means ground calcium carbonate, which is manufactured by grinding
naturally occurring calcium carbonate rock
"PCC means precipitated calcium carbonate which is synthetically produced.
In the event tha 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 n 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.
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, tale, titanium dioxide,
alumina irihydrate, 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 rising polyacryiic acid polymer dispersants or sodium polyphosphate
dispersants. Each of these dispersants imparts a significant anionic charge to the calcium
carbonate particles. Kaolin clay slumes may also be dispersed using polyacryJic acid polymers
or sodium polyphosphate.
In an embodiment, the fillers are selected from calcium carbonate and kaolin clay
and combinations thereof
n 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 cationieally charged fillers and anionic when used with anionically charged fillers.
However it can be anionic nonionic, zwitterionic, or amphoteric as lo g as it will uniformly
into a high solids slurry without causing significant fiocculation.
The definition of "without causing significant fiocculation" is no fiocculation 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 RE 16 stirring motor at 800 rp with a 5 cm diameter, fourb
aded turbine impeller. This shear should be similar to that present in the approach system of a
modem paper machine.
Suitable fiocculants generally have molecular weights in excess of ,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 nonionie monomers to form a zwitterionic polymer. One
o more zwitterionic monomers and optionally one or more nomonie monomers may also be
eopolymerized with one or more anionic or catiomc monomers to impart cationic or anionic
charge to the zwitterionic polymer. Suitable flocculants generally have a charg content of less
than 80 mole percent and often less tha 40 mole percent.
While cationic polymer flocculants ay be formed using catiomc monomers, it is
also possible to react certain nonionie viny 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 nonionie vinyl addition polymers to form
anionieally 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 (raeth)acrylamide with dimethylaminoethyl methacrylate
(DMAEM), dimethylaminoethyl aerylate (DMAEA), diethylaminoethyl aerylate (DEAEA),
diethylaminoethyl methacrylate (DEAEM) or their quaternary ammonium forms made with
dimethyl sulfate, methyl chloride or benzyl chloride. Representative anionic polymers include
copolymers of acryiamide with sodium aerylate and/or 2-acrylamido 2-methylpropane sulfonic
acid (AMPS) or an acryiamide homopolymer that has been hydrolyzed to convert a portion of the
acryiamide groups to acrylic acid
n an embodiment, the flocculants have a RSV of at least 3 dL/g.
n an embodiment, the flocculants have a RSV of at least dL/g.
In an embodiment the flocculants have a RSV of at least 5 dL/g.
As used herein, "RSV" stands for reduced specific viscosity. Within a series of
polymer horaologs 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 moieciilar weight according to Determination of Molecular Weights by Paul J . Flory,
pages 266-3 , 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:
RS = [(n/rj )-l]/e where h = viscosity of polymer solution, h 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/decihter). 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 are measured using a Cannon Ubbeiohde semi-micro
dilution viscometer, size 75. The viscometer is mounted in a perfectly vertical position in a
constant temperature hath 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 homoiogs
within a series have similar RSV's that is an indication that they have similar molecular wesghts.
As discussed above, the first flocculating agent is added in a 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 s 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 micro-particles include siliceous materials and polymeric microparticles.
Representative siliceous materials include silica based particles, silica microgels, colloidal silica,
silica sols, silica gels, polysilicates, cationic silica, aluniinosilicates, polyaiuminosiiicates,
borosiiieates, polyborosiiicates, zeolites, and synthetic or naturally occurring swelling clays. The
swelling clays may be bentonite, hectorite, smectite, montmorillonite, nonironiie, saponiie,
sauconite, monnite, attapulgite, and sepiolite.
Polymeric microparticles useful in this invention include anionic, cationic, or
amphoteric organic microparticles. These microparticles typically have limited solubility in
water, may be erosslinked, and have an unswollen particle size of less than 750 n .
Anionic organic microparticles include those described in US 6,524,439 and made
by hydrolyzing aerylamide polymer microparticies or by polymerizing anionic monomers as
(meth)aerylic acid and its salts, 2-acrylamido-2-methylpropane sulfonate, sul ethy!
(meth)acrylate, vinyisulfonic acid, styrene sulfonic acid, maieic or other dibasic acids or their
salts or mixtures thereof These anionic monomers may also be copolymerized with nonionic
monomers such as (meih)acrylamide, N-alkylaerylamides, N, -dialkylaerylamides, methyl
(meth)acrylate, acrylonitrile, N-vinyl methylacetamide, N-vinyl methyl formamide, vinyl acetate,
-vinyl pyrrolidone, and mixtures thereof.
Cationic organic microparticles include those described in US 6,524,439 and
made by polymerizing such monomers as diaiiyldialkyiammonium hafides,
acryioxyaikyltrimethylammonium chloride, (meth)aciylates of dialkyiarninoaikyl compounds,
and salts and quaternaries thereof and, monomers of ,N dialkylaminoalkyl(meth)acrv'lamides,
(meth)aciylamidopropyltrimethyiaimnonium chloride and the acid or quaternary salts of N, ~
dimethylaminoethylacrylate and the like. These cationic monomers may also be copolymerized
with nonionic monomers such as (meth)acrylamide, N-alkylacrylamides, N, -
dialkylacrylatnides, methyl (meth)acrylate, acrylonitrile, N-vinyl methylacetamide, N-vinyl
methyl formamide, vinyl acetate, N-vinyl pyrrolidone, and mixtures thereof.
Amphoteric organic niieroparticles are made by polymerizing combinations of at
least one of the anionic monomers listed above, at least one of the eationie 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 polyfunctions! cross!inking 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,
polyethyleneglyeol di(meth)aerylate, N-vinyl acrylamide, divinylbenzeiie, ri allylam or m
salts, N-methyla y ac amide glycidyl (meth)aerylate, acrolein, methylolacryiamide,
dialdehydes like g!yoxal, diepoxy compounds, and epiehlorohydrm.
In an embodiment, the microparticle dose is between 0.5 and 8 lb/ton of filler
treated n an embodiment, the microparticle dose is between .0 and 4.0 lb/ton of filler treated.
Suitable coagulants generally have lower molecular weight than flocculants and
have a high density of eationie 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 hydroxyehloride), 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 epichlorohydrin-dimethylamine (EPI-DMA) copolymers, and
EPI-DMA copolymers crosslinked with ammonia.
Additional coagulants include polymers of ethylene dichioride and ammonia, or
ethylene dichioride and dimethylamine, with or without the addition of ammonia, condensation
polymers of multifunctional amines such as diethylenetriamine. tetraethylenepeniamine,
hexarnethylenediamine and the like with ethylenedichioride or polyfunctions! 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)aerylanride diallyl-N,N~disubstituted
ammonium halide, dimethylammoethyl methacrylate and its quaternary ammonium salts,
dimethyiaminoethyl acrylate and its quaternary ammonium salts,
methacrylainidopropyltrimethyiamnionium chloride. diailylmethyl(betapropionamido)
axrmioniutn chloride, (beta-methacryloyloxyethyl)irimethyi ammonium
methvlsulfate, quatetmzed polvvinyllactam, vinylamine, and acrylamide or methaerylamide that
has been reacted to produce the Maxmieh or quatemaiy 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 floceulant The distinction
between these polymers and floccuianis is primarily molecular weight.
The second flocculating agent may be used alone or i combination with one or
more additional second flocculating agents in an embodiment, one or more roparticles 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 floccu!ation of the filler particles in the presence of the first flocculating agent an
embodiment, the second flocculating agent dose is between 0.2 and 8.0 lb/ton of filler treated n
an embodiment the second component dose is between 0.5 and 6.0 lb/ton of filler treated.
n an embodiment, one or more microparticies 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 fro copolymers of
acryiamide with dmiethylaminoethyl metbacrylaie (DMAEM) or diraethyiarainoethyl acrylate
(DMAEA) and mixtures thereof
In an embodiment, the first flocculating agent is an acryiamide and
dimethylaminoethyl acrylate (DMAEA) copolymer with a cationic charge content of 5-50 mole
% and an RSV of > dL/g.
In an embodiment, the second flocculating agent is selected from the group
consisting of partially hydrolyzed acryiamide and copolymers of acryiamide and sodium acrylate.
In an embodiment, the second flocculating agent is acrylamide-sodium 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 acryiamide and copolymers of acryiamide and sodium acrylate.
n an embodiment, the first flocculating agent is a copolymer of acryiamide 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 (ERΪ-DMA) copolymers, EPI-DMA copolymers
crossiinked with ammonia, and homopolymers of dia y -NJS-disubslituted ammonium halides.
In an embodiment, he second flocculating agent is a homopolyrner of dialiyi
dimethyl ammonium chloride having an RSV of 0.1-2 dL/g.
In an embodiment, the second flocculating agent is selected from copolymers of
aerylamide with dimethylaimnoethyi raethacrylate (DMAEM) or diinethylaminoethyl acrylate
(DMAEA) and mixtures thereof.
in an embodiment, the second flocculating agent is an aerylamide and
diinethylaminoethyl acrylate (DMAEA) copolymer with a cationic charge content of 5-50 mole
% and an RSV of > 5 dL/g.
Dispersions of filler f o s 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 floeculant are mixed for an
amount of time sufficient to distribute the first flocculating agent un ormly 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 o s with increasing mixing time typically from several seconds to several
minutes, depending on the mixing energy used. Optionally, a microparticle is added as a third
component to cause reflocculation and narrow the floe size distribution. When the appropriate
size distribution of d e filler floes is obtained, the mixing speed is lowered to 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.
n a continuous process the desired amount of first flocculating agent is pumped
into the pipe containing the filler a d 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 i
line static mixer, f necessary. Optionally, a niicroparticle is added as a third component to cause
refloceuiation and narrow the floe size distribution. 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. Qu such device s
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 paperrnaking 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 i the paper or board.
In an embodiment, the median particle size of the filler floes is at least 1 mh . In
an embodiment, the median particle size of the filler ilocs is between 0 and 100 m . In an
embodiment, the median particle size of the filler ilocs is between and 70 nm.
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.
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;
Examples 1-7
The filler used for each example was either undispersed or dispersed,
scalenohedral PCC (available as Albacar HO from Specialty Minerals Inc., Bethlehem, PA
USA). When undispersed PCC is used, the dry product was diluted to 1 % solids using tap
water. When dispersed PCC was used, it was obtained as 40% solids slurry and is diluted to 10%
solids using tap water. The size distribution of the PCC was measured at three second intervals
during floeculation using a Lasentec^ S400 FBRM (Focused Beam Reflectance Measurement)
probe, manufactured by Lasentec, Redmond, WA. A description of the theory behind the
operation of the FBRM can be found in US Patent 4,87 251. The mean chord length (MCI.) of
the PCC fiocs is used as an overall measure of the extent of floeculation. The laser probe is
inserted in a 600 m beaker containing 300 L of the 10% PCC slimy. The solution is stirred
using an KA RE16 stirring motor at 800 rpm for at least 30 seconds prior to the addition of
flocculating agents.
The first flocculating agent s added slowly over the course of 30 seconds to 60
seconds using a syringe. When a second flocculating agent is used t is added in a similar
manner to the first flocculating agent after waiting seconds for the first flocculating agent to
mix. Finally, when a micropartiele is added, it is added in a similar manner to the flocculating
agents after waiting 0 seconds for the second flocculating agent to mix. Floccu!ants are diluted
to a concentration of 0.3% based on solids, coagulants are diluted to a concentration of 0 7%
based on solids, starch is diluted to a concentration of 5% based on solids, and microparticles are
diluted to a concentration of 0 5% based on solids prior to use. A typical MCL time resolution
profile is shown in FIG. 1.
The MCL ti e resolution profile of FIG. 1 was recorded by Lasentec^ S400
FBRM. At point one, the first flocculating agent is introduced into the slurry and the MCL
increases then quickly decreases under 800 rpm mixing speed, indicating that the filler floes are
not stable under the shear. At point two, the second flocculating agent is introduced, and the
MCL also increases the decreases slightly under 800 rpm mixing. At point three, a
microparticle is introduced and the MCL increases sharply then reaches a plateau, indicating that
the filler floes are stable under 800 rpm mixing. Once the shear is raised to 00 rpm, MCL
starts to decrease.
For every filler flocculation experiment, the maximum MCL after addition of the
flocculating agent is recorded and listed i Table P. The maximum MCL indicates the extent of
flocculation. The slurry is then stirred at 1500 rpm for 8 minutes to test the stability of the filler
floes under high shear conditions. The MCL values at 4 minutes and 8 minutes are recorded and
listed in Tables III and IV, respectively.
The particle size distribution of the filler floes is also characterized by laser light
scattering using the Mastersizer Micro from Malvern Instruments Ltd., Southborough, MA USA.
The analysis is conducted using a polydisperse model and presentation 4PAD. This presentation
assumes a .60 refractive index of t filler and a refractive index of i .33 for water as the
continuous phase. The quality of the distribution is indicated by the volume-weighted median
iloc size, D(V,9.5), the span of the distribution, and the uniformity of the distribution. The span
and uniformity are defined as:
·-·-
/ V
Here D(v, 0.1) Div.0.5) and D(v, 0.9} are defined as the diameters thai are equal or larger tha
0%, 50% and 90% by volume of filler particles, respectively. Vj and D are the volume fraction
and diameter of particles in size group i . Smaller span and uniformity values indicate a more
uniform particle size distribution thai is generally believed to have better performance
papermaking. These characteristics of filler floes at maximum MCI,, 4 minutes and minutes
under 00 rpm shear are listed in Tables li, 1 and IV for each example The PCC type,
flocculating agents, and doses of flocculating agents used in each example are listed in Table I,
Example 8
This experiment demonstrates the feasibility of using a continuous process to
flocculate the PCC slurry. A batch of 18 liters of 0% solids undispersed PCC (available as
Albacar HO from Specialty Minerals Inc., Bethlehem, PA USA) in tap water was pumped using
a centrifugal pump at 7.6 L/mi into a five gallon bucket. A .0 lb/ton active dose of 0.3% solids
flocculant A solution was fed into the PCC slurry at the centrifugal pump inlet using a
progressive cavity pump. The PCC was then fed into a static mixer together with 1.0 lb/ton
active dose of a 0.7% solids solution of coagulant A. The size distribution of the filler floes was
measured using the Mastersizer Micro and reported in Table II. 300 ml, of the resultant slurry
was stirred in a beaker at 1500 rpm for 8 minutes in the same manner as in Examples 1-7. The
characteristics of the filler floes at 4 minutes and 8 minutes are listed i Tables III and IV,
respectively.
Example 9
The filler slurry and experimental procedure was the same as in Example 8, except
that coagulant A v/as fed into the centrifugal pump and flocculant A was fed into the static mixer.
The size characteristics of the filler floes are listed in Tables P, PI and IV.
Table I, PCC type flocculating agent descriptions, and flocculating agent doses for
examples 1 through 9
Napervilie, IL USA.
Table II. Characteristics of filler floca at maximum MCL or 0 miri under 1 00 rp shear.
Table Characteristics of filler floes after 4 minutes under 00 rpm shear.
Table IV. Characteristics of filler floes after 8 minutes under 00 rp shear.
As shown in Tables - V, filler floes formed in Example 1, where only calionic
starch was used, are not shear stable. On the other hand, filler floes formed by multiple polymers
exhibit enhanced shear stability, as demonstrated in Examples 2 to 9. Examples 2, 4, 6 and 8
show filler floes prepared according to this invention and Examples 3, 5, 7 and 9 show filler floes
prepared using existing methods. The filler floes prepared according to the invention generally
have narrower particle size distributions after being sheared down as shown by the smaller
values of span and uniformity in Tables 111 and V) compared with those formed by existing
methods.
xa le
The purpose of this example was to evaluate the effects of different sizes of PCC
floes on the physical properties of handsheets. The PCC samples were obtained using the
procedure described in Example 2 , except that the PCC solids level was 2%. Four samples of
prefloceulated filler f oes -A, -B, 10-C and 10-D) were prepared with different particle
sizes by shearing at 1 00 rpm for different times The shear times and resulting particle size
characteristics are listed in Table V.
Thick stock with a consistency of 2.5% was prepared from 80% hardwood dry lap
pulp and 20% recycled fibers obtained from American Fiber Resources (AFR) LLC. Fairmont,
WV The hardwood was refined to a freeness of 300 L Canadian Standard Freeness (TAPPI
Test Method T 227 om-94) in a Valley Beater (from Voith Sulzer, Appleton, WI). The thick
stock is diluted with tap water to 0.5% consistency.
Handsheets were prepared by mixing 650 mL of 0.5% consistency furnish at 800
rp in a Dynamic Drainage Jar with the bottom screen covered by a solid sheet of plastic to
prevent drainage. The Dynamic Drainage Jar and rnixer are available from Paper Chemistry
Consulting Laboratory, inc., Carmei, NY. Mixing was started and 1 g of one of the PCC samples
was added after seconds, followed by 6 lb/ton (product based) of GC7503 polyaluminum
chloride solution (available from Gulbrandsen Technologies, Clinton, NJ, USA) at 30 seconds, 1
lb/ton (product based) of a sodium acrylate-acrylarnide copolymer floccuiant with an RSV of
about 32 dL/g and a charge content of 29 mole % (available from Nalco Company, Naperville, L
USA) at 45 seconds and 3 5 lb/ton (active) of a borosilicate micioparticle (available from Nalco
Company, Naperville, IL USA) at 60 seconds.
Mixing was stopped at 75 seconds and the furnish was transferred into the deckle
box of Noble & Wood handsheet mold. The 8"x 8" handsheet was formed by drainage through
a 100 mesh forming wire. The handsheet was couched from the sheet mold wire by placing two
blotters and a metal plate on the wet handsheet and roll-pressing with six passes of a 25 lb metal
roller. The forming wire and one blotter were removed and the handsheet was placed between
two new blotters and the press felt and pressed at 50 psig using a roll press. All of the blotters
were removed and the handsheet is dried for 60 seconds (top side facing the dryer surface) using
a rotary drum drier set at 220°F. The average basis weight of a handsheet was 84 g/m The
handsheet mold, roll press, and rotary drum dryer are available from Adirondack Machine
Company, Queensbury. NY. Five replicate handsheets are produced for each PCC sample tested.
T e finished handsheeis we e stored overnight at TAPPI standard conditions of
50% relative humidit - and 23 °C. For each sheet the basis weight was determined using TAPPI
Test Method T 4 om-9 the ash content was determined using TAPPI Test Method T 2 om~
93, brightness is determined using ISO Test Method 2470:1999, and opacity was determined
using ISO Test Method 247 1;1998. Sheet formation, a measure of basis weight uniformity, was
determined using a Kajaani* Formation Analyzer from Metso Automation, Helsinki, FX The
results from these measurements are listed in Table V . The tensile strength of the sheets
measured using TAPPI Test Method T 494 om-01, Scott Bond was measured using TAPPI Test-
Method T 569 pm 00 and z-directional tensile strength (ZDT) was measured using TAPPI Test
Method T 541 om-89. These results are listed in Table VII.
z
Table V. Filler floe size characteristics for samples 10-A through -E. The 10-E sample is
an untreated PCC slurry.
Table VI. The optical properties of sheets with different size filler floes.
Table VII. Mechanical strength properties of sheets with different size filler floes.
[Mechanical Strength Improvement (%)
[FCC fro ZDT cot B n 3 en$ !e dexjTEA Sc tt Tensile
|EX. NO, kPa) p i) (N /g) N.cm/c 2) |ZDT [Bond index TEA
[ -L [733.2 [226.3 82 .9 [2.6 I4 [26 3.8 44
|10-B [709.7 [254.8 pi. 7 2.2 [10 [52 2.3 20
- [675.9 [217.2 [83.0 [2,5 .8 j 3.9
lO-D 81.4 1219.6 185.5 [2.3 [5.7 7.0 30
m o-E 644.9 1 79 0 [79.9 [1.8 j J) 0 0
As shown in Table V, the size of the filler floes decreases as the time under 00
rp shear increases, demonstrating the feasibility of controlling the size of filler floes by the ti e
under high shear. Handsheets prepared from each of the four preflocculated fillers (10-A through
I0-D) and the untreated filler (10-E) have roughly equivalent ash contents and basis weight, as
listed in Table VI. Increasing the floe size did not hurt brightness, but decreased the formation
a d opacity of the sheets slightly. The mechanical strength of the sheets, as measured by zdireciional
tensile strength, Scott Bond, tensile index, and tensile energy absorption (TEA)
increased significantly with increasing filler floe size. This is shown in Table VII. In general,
higher median PCC floe size lead to increased sheet strength. In practice, the slight loss of
opacity could be compensated for by increasing the PCC content of the sheet at constant to
improved sheet strength.
In at least one embodiment, a method of preflocculating filler particles for use in
papermaking processes comprises: a) providing an aqueous slimy of filler particles; h) adding a
first flocculating agent to the dispersion under conditions of high mixing; d) adding a second
flocculating agent under conditions of high mixing in an amount sufficient to initiate flocculation
of the filler particles in the presence of the first flocculating agent; and e) optionally shearing the
flocculated dispersion to provide a dispersion of filler floes having the desired particle size.
Preferably, the first flocculating agent is one of the previously described anionic flocculants.
Preferably, the second flocculating agent is one of the previously described cationic flocculants.
The two flocculants may each have a high molecular weight and low to medium charge density.
Without being limited by theory or design it is believed that the first high
molecular weight flocculating agent forms an evenly distributed mixture through the slurry
before absorption. This evenly distributed mixture aids the cationic second flocculating agent in
efficiently pulling together the mass to form the floe particles. As the following examples
demonstrate this embodiment's novel use of two high molecular weight flocculating agents to
control the particle size distribution through the slurry produces unexpectedly efficient floe
production. This embodiment can best be understood with reference to Examples 16.
Sealenohedral FCC (available as Syncarb S NY from Omya) was diluted to 10%
solids using tap water. The size distribution of the filler was measured at three second intervals
during floeculation using a Lasentec® S400 B M. The laser probe was inserted in a 600 mL
beaker containing 300 mL of the 0% FCC slurry. The solution was stirred using an IKA RE16
stirring motor at 800 rpm for at least 30 seconds prior to the addition of flocculating agents.
The first flocculating agent was added, as a dilute solution, slowly over the course
of several minutes using a syringe. When a second flocculating agent is used, it was added in a
similar manner to the first flocculating agent after waiting seconds for the first flocculating
agent to mix. The slum' is then stirred at 00 rpm for 2-4 minutes to test the stability of the
filler floes under high shear conditions. The PCC type, flocculating agents, and doses of
flocculating agents used in these examples are listed in Table VIII and the resulting
characterization of the particles is given in Table X.
This experiment demonstrated the feasibility of using a continuous process to
flocculate the PCC slurry A batch of liters of % solids undispersed PCC (available as
Albacar HO from Specialty Minerals Inc., Bethlehem. PA USA) in tap water is pumped using a
centrifugal pump at 7.2 kg PCC/min into a five gallon bucket. The appropriate dosage of the first
flocculating agent solution is fed into the PCC slurry at the centrifugal pump inlet using a
progressive cavity pump. The PCC is then fed into a static mixer together with the appropriate
dosage of the second flocculating agent. The size distribution of the filler floes is measured
using the Mastersizer Micro and reported in Table X. The resulting sample is exposed to
additional shear by circulating the sample through a centrifugal pump; the results are also given
in Table X.
The results shown in Tables ΪC C highlight the advantages of the dual l ec lan
treatment. Examples . 4- demonstrate improved shear stability as indicated by a lower
volume percent of pariicles with size less than micron These samples were found to he
superior to Examples and 3,
Table VIII. Calcium carbonate type, flocculating agent descriptions, and flocculating agent
doses for examples.
Table C Characteristics of flocculated calcium carbonate samples in Examples 11-12 as
prepared at 800 pm and upon subsequent shear under 1 00
Table X. Characteristics of flocculated calcium carbonate samples in Exampl
At least one embodiment is a method of pr oc ulating filler that has been
dispersed using a high charge, low molecular weight, anionic dispersing agent. The method
consists of a) providing an aqueous slurry of anionically dispersed filler particles; b) adding a low
molecular weight coagulant to the dispersion in order to completely or partially neutralize the
charge in the system; c) adding a first flocculating agent to the dispersion under conditions of high
mixing; d) adding a second flocculating agent (can he a coagulant or floceulant) to the dispersion
under conditions of high mixing; and e) optionally shearing the flocculated dispersion to provide a
dispersion of filler floes having the desired particle size.
Preferably, the low molecular weight, charge-neutralizing component is a
coagulant as previously described. Preferably, the first flocculating agent is an anionic or
atio ie floceulant, as previously described. Preferably, the second flocculating agent is either a
coagulant or a floceulant w th the opposite charge of the first flocculating agent. This can best be
understood with reference to the following Examples -20:
Examples -20
The dispersed ground calcium carbonate (GCC) used in the examples is either
Hydrocarb HO G-ME or Omyaf'ii 90 from Oroya. The dispersed GCC, obtained as a 65% solids
slurry, s diluted to 10% solids using tap water. The size distribution of the filler is measured at
three second intervals during fiocculation using a Lasentee® S400 FBRM (Focused Beam
Reflectance Measurement) probe, as described in Examples -7. The laser probe is inserted in a
600 mL beaker containing 300 m , of the 10% PCC slurry. The solution is stirred using an KA
RE16 stirring motor at 800 rpm for at least 30 seconds prior to the addition of flocculating agents.
The neutralizing polymer is added slowly over the course of approximately a few
minutes. The first flocculating agent is then added slowly over the course of several minutes
using a syringe. When a second flocculating agent is used, it is added in a similar manner to the
first flocculating agent after waiting 10 seconds for the first flocculating agent to mix. The
sluny is then stirred at 1500 rpm for 2-4 minutes to test the stability of the filler floes under high
shear conditions.
Table XI. Ground calcium carbonate source flocculating agent descriptions, and flocculating
agent doses for examples 17-20.
Table XII. Characteristics of flocculated ground calcium carbonate samples in Example 17-20,
as prepared at 800 rpm and upon subsequent shear under 00 rpm.
As shown in Table XI, Examples 18 and 20 demonstrate the invention disclosed,
namely, an initial treatment with a charge-neutralizing polymer followed by two flocculating
polymers. Examples 17 and represent the use of a coagulant followed by a floceulani As
shown in Table XII, the preflocculated GCC in Examples 1 and 20 sho improved shear
stability indicated by larger median particle size D(v,0.5) at the same amount of shear. Examples
8 and 20 also have an iraproved particle size distribution, indicated by smaller span and lower
percent by volume less than microns.
Example 2
The purpose of these examples was to evaluate the impact of the preflocculated
ground calcium carbonate on the physical properties of paper sheets. The preflocculated sample
from Example 20 was used for this purpose, and compared against untreated Omyafil 90.
Thick stock with a consistency of 2.3% was prepared from 75% hardwood dry lap
pulp and 25% softwood dry lap pulp. Both woods were refined to a freeness of 400 ml. Canadian
Standard Freeness (TAPPI Test Method T 227 om-94) in a Valley Beater (from Voith Sulzer,
Appleton, W ) The thick stock was diluted with tap water to 0.5% consistency.
Handsheets were prepared by mixing 650 mL of 0.5% consistency furnish at 800
rpm in a Dynamic Drainage Jar with the bottom screen covered by a solid sheet of plastic to
prevent drainage. The Dynamic Drainage Jar and mixer are available from Paper Chemistry
Consulting Laboratory, inc., Carmel, NY. Mixing was started and the GCC sample was added,
followed by lb/ton cationic starch and 3 lb/ton of a co 7542 sizing agent at 15 seconds, and
finally 0.6 lb/ton (product based) of a sodium aciyiate-acrylamide copolymer fiocculant with an
RSV of about 32 dL/g and a charge content of 29 mole % (available from Nalco Company,
Naperville, L).
Mixing was stopped at 45 seconds and the furnish was transferred into the deckle
box of a Noble & Wood handsheet mold. The 8"x handsheet was formed by drainage through
a 00 mesh forming wire. The handsheet was couched from the sheet mold wire by placing two
blotters and a metal plate on the wet handsheet and roll-pressing with six passes of a 25 lb metal
roller. The forming wire and one blotter were removed and the handsheet was placed between
two new blotters and the press fel and pressed at 50 psig using a fiat press. All of the blotters
were removed and the handsheet was dried for 60 seconds (top side facing the dryer surface)
usi g a rotary drum drier set at 220°F. The handsheet mold, roll press, and rotary dram dryer are
available from Adirondack Machine Company, Glens Falls, NY. Five replicate handsheets were
produced for each CC sample tested.
The finished handsheets were stored overnight at TAPPI standard conditions of
50% relative humidity and 23°C. The basis weight (TAPPI Test Method T 4 om-98), ash
content (TAPPI Test Method T 2 om-93) for determination of PCC content, brightness (ISO
Test Method 2470:1999), opacity (ISO Test Method 2471:1998), formation, tensile strength
(TAPPI Test Method T 494 om-01), Scott Bond (TAPPI Test Method T 569 pm-00), and z -
directional tensile strength. (ZDT, TAPPI Test Method T 541 om-89) of the handsheets were
tested. The formation, a measure of basis weight uniformity, was determined using a Kajaaniw
Formation Analyzer from Metso Automation, Helsinki, FI.
Table XII. Properties of sheets containing untreated ground calcium carbonate or
a prefloceulated sample as described in Example 20
The mechanical strength data in Table XII indicates a 20% increase in tensile
index and 0% increase in internal bond strength at a level % ash for the sheets containing the
prefloceulated filler produced in Example 20, compared to the sheets containing untreated GCC.
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 ordinaiy 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 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: 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.
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 floccuiating agent to the dispersion in an amount sufficient to ix
imiformly in the dispersion without causing significant flocculation of the filler particles, and the
first flocculating agent being amphoteric;
c adding a second floccuiating 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;
d) shearing the flocculated dispersion to provide a dispersion of filler floes having the
desired particle size; an
e) 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 .
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
dimethylaminoeihyl rnethacrylate (DMAEM), dimethylaniinoetliyl aerylate (DMAEA),
diethylaminoethyi acrvlate (DEAEA), diethylaminoethyl rnethacrylate (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 acrylamidedimethylaminoeihyl
aerylate methyl chloride quaternary copolymer having a cationic charge of
10-50 mole percent and a RSV of a least 1 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
q. A method of papermaking comprising the use of filler, the method comprising the steps
of:
providing an aqueous dispersion of filler part icles at least one dry strength aid, and
cellulose fiber stock,
treating the filler particles with a composition of matter,
combining the filler particles with the cellulose fiber stock,
treating the combination with at least one dry strength aid, and
forming a paper mat from the combination,
wherein at least 0% of the filler particles are in a dispersed form using a high anionically
charged dispersant,
the cellulose fiber stock comprises a plurality of cellulose fibers and water, and
the composition of matter enhances the performance of the dry strength aid in the paper
mat.