U.S. patent application number 14/330839 was filed with the patent office on 2017-09-07 for anionic preflocculation of fillers used in papermaking.
The applicant listed for this patent is Nalco Company. Invention is credited to Katherine M. Broadus, Weiguo Cheng, Dorota Smoron, Shawnee M. Wilson.
Application Number | 20170254022 14/330839 |
Document ID | / |
Family ID | 53367730 |
Filed Date | 2017-09-07 |
United States Patent
Application |
20170254022 |
Kind Code |
A9 |
Cheng; Weiguo ; et
al. |
September 7, 2017 |
ANIONIC PREFLOCCULATION OF FILLERS USED IN PAPERMAKING
Abstract
A method of preparing a stable dispersion of flocculated filler
particles for use in papermaking processes comprises use of an
anionic first flocculating agent to an aqueous dispersion of filler
particles, followed by addition of a second anionic flocculating
agent to the dispersion and further optional shearing of the
resultant filler flocs to the desired particle size resulting in
shear resistant filler flocs with a defined and controllable size
distribution.
Inventors: |
Cheng; Weiguo; (Naperville,
IL) ; Broadus; Katherine M.; (Aurora, IL) ;
Smoron; Dorota; (Hoffman Estates, IL) ; Wilson;
Shawnee M.; (Downers Grove, IL) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Nalco Company |
Naperville |
IL |
US |
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Prior
Publication: |
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Document Identifier |
Publication Date |
|
US 20150167245 A1 |
June 18, 2015 |
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|
Family ID: |
53367730 |
Appl. No.: |
14/330839 |
Filed: |
July 14, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13665963 |
Nov 1, 2012 |
8778140 |
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14330839 |
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11854044 |
Sep 12, 2007 |
8172983 |
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13665963 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
D21H 17/74 20130101;
D21H 17/675 20130101; D21H 21/18 20130101; D21H 17/375 20130101;
D21H 17/69 20130101; D21H 17/68 20130101; D21H 17/67 20130101 |
International
Class: |
D21H 17/00 20060101
D21H017/00; D21H 17/37 20060101 D21H017/37; D21H 17/67 20060101
D21H017/67 |
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) adding a first flocculating
agent to an aqueous dispersion of filler particles, the dispersion
in an amount sufficient to mix uniformly in the dispersion without
causing significant flocculation of the filler particles the first
flocculating agent being anionic and having an RSV of at least 3
dL/g; b) 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 wherein the second
flocculating agent is anionic; c) shearing the flocculated
dispersion to provide a dispersion of filler flocs having the
desired particle size; and d) causing or allowing flocculation of
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 flocs have a median
particle size of 10-100 .mu.m.
3. The method of claim 1 wherein the filler is selected from the
group consisting of calcium carbonate, kaolin clay, talc, titanium
dioxide, alumina trihydrate, barium sulfate and magnesium
hydroxide.
4. The method of claim 1 wherein the first flocculating agent is
selected from the group consisting of partially hydrolyzed
acrylamide and copolymers of acrylamide and sodium acrylate.
5. The method of claim 9 wherein 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.
6. The method of claim 1 wherein the filler particles are selected
from the group consisting of precipitated calcium carbonate, ground
calcium carbonate and kaolin clay, and mixtures thereof.
7. The method of claim 13 wherein the filler flocs have a median
particle size of 10-70 .mu.m.
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. A method of making paper products from pulp comprising forming
an aqueous cellulosic papermaking furnish, adding an aqueous
dispersion of filler flocs prepared according to the method of
claim 1 to the furnish, draining the furnish to form a sheet and
drying the sheet.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a Continuation of application Ser. No.
13/665,963 filed on Nov. 1, 2012 which in turn was a
Continuation-in-part of pending U.S. patent application Ser. No.
13/449,888 filed on Apr. 18 2012 and issued as U.S. Pat. No.
8,747,617, which in turn is a continuation in part application
claiming priority from U.S. patent application Ser. No. 11/854,044
filed on Sep. 12, 2007 and which has issued as U.S. Pat. No.
8,172,983.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0002] Not Applicable.
BACKGROUND OF THE INVENTION
[0003] This invention relates to the preflocculation of fillers
used in papermaking, particularly, the production of shear
resistant filler flocs with a defined and controllable size
distribution at high filler solids is disclosed.
[0004] 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.
[0005] 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 flocs prior to addition to the
paper stock. The chemical environment and high fluid shear rates
present in modern high-speed papermaking require filler flocs to be
stable and shear resistant. The floc 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.
[0006] Therefore, the combination of high shear stability and sharp
particle size distribution is vital to the success of filler
preflocculation technology. However, filler flocs 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 flocs 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.
[0007] 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.
.sctn.1.56(a) exists.
BRIEF SUMMARY OF THE INVENTION
[0008] 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. 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 flocs
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.
[0009] The filler flocs may have a median particle size of 10-100
.mu.m. 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 acrylamide-dimethylaminoethyl 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.
[0010] At least one embodiment is directed towards a paper product
incorporating the filler flocs prepared as described herein.
DETAILED DESCRIPTION OF THE INVENTION
[0011] 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:
[0012] "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.
[0013] "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.
[0014] "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.
[0015] "GCC" means ground calcium carbonate, which is manufactured
by grinding naturally occurring calcium carbonate rock
[0016] "PCC" means precipitated calcium carbonate which is
synthetically produced.
[0017] "Microparticle" means a particle of between 0.1 .mu.m and
100 .mu.m 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.
[0018] 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.
[0019] 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 U.S. Pat. No. 8,088,213.
[0020] Optionally the flocculated dispersion can be sheared to
provide a dispersion of filler flocs having an optimal particle
size.
[0021] 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.
[0022] 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.
[0023] 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).
[0024] 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.
[0025] 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 Ill.).
[0026] 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.
[0027] Anionic organic microparticles include those described in
U.S. Pat. No. 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.
[0028] Cationic organic microparticles include those described in
U.S. Pat. No. 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, N-alkylacrylamides,
N,N-dialkylacrylamides, methyl (meth)acrylate, acrylonitrile,
N-vinyl methylacetamide, N-vinyl methyl formamide, vinyl acetate,
N-vinyl pyrrolidone, and mixtures thereof.
[0029] 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.
[0030] 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 U.S. Pat. No.
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.
[0031] 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.
[0032] In at least one embodiment the method also involves
contacting the filler particles with swollen starch. As described
in U.S. Pat. Nos. 2,805,966, 2,113,034, 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
flocs 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 U.S. Pat. No. 8,298,508 and International Patent
Application WO/97/46591.
[0033] 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 starch-latex compositions and methods described
in US Patent Application 2010/0078138.
[0034] 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.
[0035] 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.
[0036] 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.
[0037] 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.
[0038] 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 U.S.
patent application Ser. No. 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.
[0039] In an embodiment, the fillers are selected from calcium
carbonate and kaolin clay and combinations thereof.
[0040] In an embodiment, the fillers are selected from precipitated
calcium carbonate, ground calcium carbonate and kaolin clay, and
mixtures thereof.
[0041] 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.
[0042] 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 flocs 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 stifling motor at 800 rpm with a 5 cm
diameter, four-bladed, turbine impeller. This shear should be
similar to that present in the approach system of a modern paper
machine.
[0043] Suitable flocculants generally have molecular weights in
excess of 1,000,000 and often in excess of 5,000,000.
[0044] 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.
[0045] 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.
[0046] 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.
[0047] 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.
[0048] In an embodiment, the flocculants have a RSV of at least 3
dL/g.
[0049] In an embodiment, the flocculants have a RSV of at least 10
dL/g.
[0050] In an embodiment, the flocculants have a RSV of at least 15
dL/g.
[0051] 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, N.Y., Chapter
VII (1953). The RSV is measured at a given polymer concentration
and temperature and calculated as follows:
RSV=[(.eta./.eta..sub.o)-1]/c where .eta.=viscosity of polymer
solution, .eta..sub.o=viscosity of solvent at the same temperature
and c=concentration of polymer in solution.
[0052] 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.degree. C. The viscosities
.eta. and .eta..sub.o 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.degree. 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.
[0053] 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.
[0054] 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.
[0055] 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.
[0056] 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.
[0057] 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.
[0058] 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,
(beta-methacryloyloxyethyl)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.
[0059] 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.
[0060] 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.
[0061] 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.
[0062] 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.
[0063] In an embodiment, the second flocculating agent and first
flocculating agent are oppositely charged.
[0064] In an embodiment, the first flocculating agent is cationic
and the second flocculating agent is anionic.
[0065] In an embodiment, the first flocculating agent is selected
from copolymers of acrylamide with dimethylaminoethyl methacrylate
(DMAEM) or dimethylaminoethyl acrylate (DMAEA) and mixtures
thereof.
[0066] 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.
[0067] In an embodiment, the second flocculating agent is selected
from the group consisting of partially hydrolyzed acrylamide and
copolymers of acrylamide and sodium acrylate.
[0068] 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.
[0069] In an embodiment, the first flocculating agent is anionic
and the second flocculating agent is cationic.
[0070] In an embodiment, the first flocculating agent is selected
from the group consisting of partially hydrolyzed acrylamide and
copolymers of acrylamide and sodium acrylate.
[0071] 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.
[0072] In an embodiment, the second flocculating agent is selected
from the group consisting of epichlorohydrin-dimethylamine
(EPI-DMA) copolymers, EPI-DMA copolymers crosslinked with ammonia,
and homopolymers of diallyl-N,N-disubstituted ammonium halides.
[0073] In an embodiment, the second flocculating agent is a
homopolymer of diallyl dimethyl ammonium chloride having an RSV of
0.1-2 dL/g.
[0074] In an embodiment, the second flocculating agent is selected
from copolymers of acrylamide with dimethylaminoethyl methacrylate
(DMAEM) or dimethylaminoethyl acrylate (DMAEA) and mixtures
thereof.
[0075] 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.
[0076] Dispersions of filler flocs 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.
[0077] 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
stifling at a mixing speed sufficient to break down the filler
flocs 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 flocs and narrow down the particle
size distribution of flocs. When the appropriate size distribution
of the filler flocs is obtained, the mixing speed is lowered to a
level at which the flocs are stable. This batch of flocculated
filler is then transferred to a larger mixing tank with sufficient
mixing to keep the filler flocs uniformly suspended in the
dispersion. The flocculated filler is pumped from this mixing tank
into the papermaking furnish.
[0078] 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 flocs and narrow down the particle size
distribution of flocs. High speed mixing is then required to obtain
the desired size distribution of the filler flocs. Adjusting either
the shear rate of the mixing device or the mixing time can control
the floc 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 U.S. Pat. No. 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.
[0079] In both the batch and continuous processes described above,
the use of a filter or screen to remove oversize filler flocs can
be used. This eliminates potential machine runnability and paper
quality problems resulting from the inclusion of large filler flocs
in the paper or board.
[0080] In an embodiment, the median particle size of the filler
flocs is at least 10 .mu.m. In an embodiment, the median particle
size of the filler flocs is between 10 and 100 .mu.m. In an
embodiment, the median particle size of the filler flocs is between
10 and 70 .mu.m.
[0081] In at least one embodiment the invention is practiced using
at least one of the compositions and/or methods described in U.S.
patent application Ser. No. 12/975,596. In at least one embodiment
the invention is practiced using at least one of the compositions
and/or methods described in U.S. Pat. No. 8,088,213. In at least
one embodiment the invention is practiced using at least one of the
compositions and/or methods described in U.S. Pat. No.
8,172,983.
EXAMPLES
[0082] 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
[0083] 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.RTM. EUROSTAR Digital overhead
mixer with a R1342, 50 mm, four-blade propeller (both available
from IKA.RTM. Works, Inc., Wilmington, N.C. USA). The final floc
size distribution was characterized by laser light scattering using
the Malvern Mastersizer Micro from Malvern Instruments Ltd.,
Southborough, Mass. 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 floc size, D(V,0.5) and the
span of the distribution, which is defined as:
span = D ( V , 0.9 ) - D ( V , 0.1 ) D ( V , 0.5 ) ##EQU00001##
[0084] Here D(V,0.1), 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 flocs, 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
[0085] 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 DEV115 (which is a commercially
available anionic sodium acrylate-acrylamide copolymer with an RSV
of about 32 dL/g and a charge content of 29 mole percent, available
from Nalco Company, Naperville, Ill., 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, Ill.,
USA.), and c) microparticle Nalco-8699 which is a commercially
available colloidal silica dispersion available from Nalco Company,
Naperville, Ill., USA.).
[0086] The results in Table 1 show that the untreated PCC had a
monomodal particle size distribution with a median particle size of
3.75 .mu.m and a span of 1.283. After 30 s mixing of the 10% PCC
slurry under 800 rpm, 1.5 lb/ton Nalco DEV115 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 flocs. The results are shown in Table
1.
Example 2
[0087] 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 DEV115.
Example 3
[0088] 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 DEV115.
Example 4
[0089] 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 DEV115.
Example 5
[0090] 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 DEV115 but before DEV125.
Example 6
[0091] 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
[0092] 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 DEV115 were premixed before adding into the filler slurry,
followed by the addition of DEV125.
TABLE-US-00001 TABLE I The particle size distribution
characteristics of PCC (precipitated calcium carbonate) flocs
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 (.mu.m) (.mu.m) (.mu.m) PCC, 0 1.283 1.97 3.75 6.78
untreated 1 0 0.916 95.26 188.13 267.59 2 1.803 21.26 58.14 126.06
4 1.849 14.94 41.5 91.69 6 1.882 12.49 34.76 77.91 8 1.890 11.08
30.71 69.12 2 0 0.946 92.69 169.24 252.87 2 1.617 24.7 57.99 118.49
4 1.655 17.91 41.92 87.29 6 1.688 14.9 34.64 73.36 8 1.695 13.06
30.36 64.53 3 0 0.837 104.51 197.7 269.9 2 1.663 27.74 66.15 137.74
4 1.678 19.69 46.96 98.49 6 1.693 16.42 38.98 82.43 8 1.694 14.55
34.39 72.8 4 0 0.831 102.98 196.94 266.56 2 1.758 30.99 86.86
183.69 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 31.73 71.22 6 0 0.748 119.7 216.05 281.41 2 1.824 28.38 77.75
170.22 4 1.863 18.62 51.98 115.44 6 1.863 15.4 42.34 94.27 8 1.834
13.68 37.07 81.65 7 0 0.855 102.72 196.83 270.95 2 1.815 27.65
71.58 157.55 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
[0093] 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 flocs improved significantly.
Example 8
[0094] 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 .mu.m and a span of 2.029.
[0095] After 30 s 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 DEV115 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
[0096] 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 DEV115.
Example 10
[0097] 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 DEV115.
Example 11
[0098] 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 DEV115 but before DEV125.
Example 12
[0099] 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
[0100] 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 DEV115 were premixed before adding into the filler slurry,
followed by the addition of DEV125.
TABLE-US-00002 TABLE II The particle size distribution
characteristics of GCC (ground calcium carbonate) flocs 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
(.mu.m) (.mu.m) (.mu.m) GCC, 0 2.029 0.59 1.51 3.66 untreated 8 0
1.421 49.54 117.71 216.78 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 91.68 8 2.066 13.03 34.67 84.69 9
0 1.194 66.24 141.62 235.37 2 1.862 27.07 70.07 157.53 4 1.994
19.23 51.69 122.29 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
2.104 18.56 57.97 140.51 6 2.208 14.50 47.87 120.18 8 2.272 12.04
41.38 106.04 11 0 1.003 84.93 167.75 253.25 2 1.802 30.94 79.63
174.45 4 1.847 23.18 59.74 133.54 6 1.911 19.82 51.16 117.78 8
1.874 17.61 45.47 102.84 12 0 1.09 77.99 143.99 234.88 2 1.385
53.53 114.17 211.62 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
[0101] 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 flocs improved significantly.
[0102] 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.
[0103] 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.
[0104] 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.
[0105] 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.
* * * * *