U.S. patent number RE46,649 [Application Number 15/142,252] was granted by the patent office on 2017-12-26 for method for improving rheological properties of an aqueous pigment slurry and a dispersion agent.
This patent grant is currently assigned to KEMIRA OYJ. The grantee listed for this patent is Kemira Oyj. Invention is credited to Esko Aarni, Perttu Heiska, Kimmo Huhtala.
United States Patent |
RE46,649 |
Aarni , et al. |
December 26, 2017 |
Method for improving rheological properties of an aqueous pigment
slurry and a dispersion agent
Abstract
The invention relates to a method for improving rheological
properties of an aqueous pigment slurry. In the method dispersion
agent is added to an aqueous phase of a slurry comprising pigment
particles or to the aqueous phase into which the pigment particles
are to be added. The dispersion agent comprises styrene acrylate
copolymer. The invention also relates to a dispersion agent for a
pigment slurry comprising a first component comprising styrene
acrylate copolymer and a second component comprising a conventional
dispersion agent, such as a straight-chain polyacrylate.
Inventors: |
Aarni; Esko (Espoo,
FI), Heiska; Perttu (Espoo, FI), Huhtala;
Kimmo (Turku, FI) |
Applicant: |
Name |
City |
State |
Country |
Type |
Kemira Oyj |
Helsinki |
N/A |
FI |
|
|
Assignee: |
KEMIRA OYJ (Helsinki,
FI)
|
Family
ID: |
40240610 |
Appl.
No.: |
15/142,252 |
Filed: |
April 29, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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Reissue of: |
12493660 |
Jun 29, 2009 |
8785550 |
Jul 22, 2014 |
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Foreign Application Priority Data
|
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Dec 18, 2008 [FI] |
|
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20086214 |
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C09D
17/004 (20130101); C09D 17/001 (20130101); D21H
19/58 (20130101); C09D 7/45 (20180101); D21H
19/58 (20130101); C09D 7/45 (20180101); C09D
17/004 (20130101); C09D 17/001 (20130101); C08K
2003/265 (20130101); C08K 2003/265 (20130101) |
Current International
Class: |
C04B
24/26 (20060101); B60C 1/00 (20060101); C08L
3/00 (20060101); C08L 1/00 (20060101); C08L
3/02 (20060101); C08L 5/16 (20060101); D21H
19/58 (20060101); C09D 7/02 (20060101); C09D
17/00 (20060101); C08K 3/26 (20060101) |
References Cited
[Referenced By]
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2245952 |
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02/084028 |
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WO |
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Other References
Japanese Office Action dated Aug. 20, 2013; Prepared by Tsutomu
Nishina; English Translation included. cited by applicant .
Chinese Office Action dated Mar. 18, 2013. cited by applicant .
JP 58115196 Abstract, 5 pages. cited by applicant .
International Search Report; International Application No.
PCT/FI2009/051013; International Filing Date Dec. 18, 2009; 4
pages. cited by applicant .
European Office Action dated Apr. 11, 2012; Application No. 09 796
406.8-1217. cited by applicant .
Russian Office Action dated Dec. 17, 2013; 5 pages; Russian Patent
Office. cited by applicant.
|
Primary Examiner: Kugel; Timothy J.
Attorney, Agent or Firm: Thomas Horstemeyer, LLP
Claims
The invention claimed is:
1. A method for improving .Iadd.the .Iaddend.rheological high shear
properties of an aqueous pigment slurry comprising calcium
carbonate, kaolin, calcinated kaolin, talc, titanium dioxide,
gypsum, chalk, satine white, barium sulphate, sodium aluminium
silicate, aluminium hydroxide or any of their mixture, the aqueous
pigment slurry having a solids content .Iadd.of .Iaddend.about 68%,
the method comprising adding a dispersion agent to an aqueous phase
of a slurry comprising pigment particles or to the aqueous phase
into which the pigment particles are to be added, the dispersion
agent comprising styrene acrylate copolymer, wherein the styrene
acrylate copolymer comprises starch, wherein the dispersion agent
improves the rheological properties of the slurry, and wherein the
dispersion agent decreases the high shear viscosity of the slurry,
and further comprising adding also a conventional dispersion agent
comprising straight-chain polyacrylate to the aqueous phase.
2. The method according to claim 1, comprising adding at least 0.1
parts dispersion agent comprising styrene acrylate copolymer per
100 parts pigment in the slurry.
3. The method according to claim 1, wherein the dispersion agent
comprising the styrene acrylate copolymer is used in the form of an
aqueous polymer dispersion having a solids content of 10-50%.
4. The method according to claim 1, wherein the proportion .[.first
component: second component.]. .Iadd.of the dispersion agent:the
conventional dispersion agent .Iaddend.is in the range .Iadd.of
.Iaddend.50:50-99:1.
5. A dispersion agent for a pigment slurry, where the pigment
slurry comprises calcium carbonate, kaolin, calcinated kaolin,
talc, titanium dioxide, gypsum, chalk, satine white, barium
sulphate, sodium aluminium silicate, aluminium hydroxide or any of
their mixture, comprising a first component comprising styrene
acrylate copolymer wherein the styrene acrylate copolymer decreases
the high shear viscosity of the slurry, wherein the styrene
acrylate copolymer comprises starch, the aqueous pigment slurry
having a solids content of about 68%, a second component comprising
.Iadd.a .Iaddend.conventional dispersion agent comprising
straight-chain polyacrylate.
6. The dispersion agent according to claim 5, wherein the
proportion .Iadd.of .Iaddend.first component:second component is in
the range .Iadd.of .Iaddend.50:50-99:1.
7. The dispersion agent according to claim 5, wherein the mean
particle size of the styrene acrylate copolymer is 20-300 nm.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
This application claims priority to Finnish Patent Application No.
20086214 filed on Dec. 18, 2008, the disclosure of which is also
incorporated herein by reference.
The present invention relates to a method for improving rheological
properties of aqueous pigment slurry according to the preamble of
the enclosed independent claim. The invention relates also to
dispersion agent and to use of styrene acrylate copolymer.
Paper and paperboard are coated with different coating colors in
order to improve, among other things, the strength, printability
and appearance of the paper, e.g., smoothness and gloss. During the
coating process an aqueous solution of coating composition is
applied to one or both sides of paper. Conventional coating
compositions comprise mainly pigment and binder, and possible other
additives, such as co-binders, preservatives, dispersion agents,
defoaming agents, lubricants, hardeners and optical brighteners.
The main ingredient of the coating color is pigment particles.
There exist a number of different pigments. Usually they are
various minerals by their origin, kaolin clay and calcium carbonate
being the most common.
Some of the pigments must be subjected to so-called grinding
operation, where the size of the pigment particles is reduced via
an input of energy, in order to adapt the particle size
distribution of the particles to the intended application. For
example calcium carbonate and gypsum are subjected to grinding
before they are used in the paper coating compositions. Usually the
grinding is performed as wet grinding, and one or several grinding
agents are added during the process. In most of the grinding
processes, in the last process step the size of the pigment
particles does not essentially change, but a dispersion agent is
added to the pigment slurry in order to stabilize it.
Some of the pigments do not require grinding as they are readily
obtained with suitable particle size for paper coating
compositions. Examples of such pigments are precipitated calcium
carbonate and kaolin. These pigments are directly slurried with
water, into which is usually added dispersion agent.
Some dispersion agents can be used in both processes. Dispersion
agents may have an impact on rheological properties of the obtained
slurry. The rheological properties of the pigment slurries and
coating compositions are important for their usability. For
handling of the slurries, e.g. during pumping and mixing, the
low-shear properties are important, while the high shear properties
of coating compositions are important for good coating runnability
during application of the coating to the paper. The high shear
properties of a coating composition are directly comparable with
the high shear properties of the pigment slurry that is used for
preparing it. It would be a great advantage to be able to modify
the rheological properties of the pigment slurries in order to
optimize the rheological properties of coating compositions used in
coating processes of paper and/or board.
When conventional dispersion agents are used, the rheological
properties of the pigment slurries are not improved by increasing
the dosage of the dispersion agent over the normal dispersion
dosage levels. In other words, increasing the dosage of a
conventional dispersion agent over the amount that is needed for
dispersing of the pigment particles does not notably affect the
rheological properties of the obtained slurry.
An object of this invention is to minimize or possibly even
eliminate the disadvantages existing in the prior art.
An object is also to provide a method for improving the rheological
properties of pigment slurry.
A further object of this invention is also to provide a dispersion
agent with which rheological properties of a pigment slurry can be
improved.
These objects are attained with a method and an arrangement having
the characteristics presented below in the characterizing parts of
the independent claims.
In a typical method according to the present invention for
improving rheological properties of an aqueous pigment slurry a
dispersion agent is added to an aqueous phase of a slurry
comprising pigment particles or to the aqueous phase into which the
pigment particles are to be added, the dispersion agent comprising
styrene acrylate copolymer.
A typical dispersion agent according to the present invention for a
pigment slurry comprises
a first component comprising styrene acrylate copolymer, and
a second component comprising a conventional dispersion agent, such
as a straight-chain polyacrylate.
A typical use of styrene acrylate copolymer according to the
present invention is as a dispersion agent in a pigment slurry for
improving its rheological properties.
Now it has been surprisingly found out that by adding a dispersion
agent comprising styrene acrylate copolymer to a pigment slurry the
rheological properties of the slurry are unexpectedly improved at
the same time as the other properties of the slurry are kept at
least at the conventional level. Especially the addition of
dispersion agent comprising styrene acrylate copolymer improves the
high shear properties of the slurry, which consequently improves
behavior of the slurry in paper coating compositions. It has also
been found out that the increased dosage of such a dispersion agent
has a positive impact on rheological properties of the slurry, i.e.
the high shear viscosity of the slurry is decreased, compared to
slurries with similar solids content without addition of dispersion
agent comprising styrene acrylate copolymer.
Typical pigments that may be used in the present invention for
preparation of a pigment slurry are calcium carbonate, kaolin,
calcinated kaolin, talc, titanium dioxide, gypsum, chalk, satine
white, barium sulfate, sodium aluminum silicate, aluminum hydroxide
or any of their mixture. Calcium carbonate may be ground calcium
carbonate (GCC) or precipitated calcium carbonate (PCC) or their
mixture. Preferably the pigment is calcium carbonate.
Typically the dispersion agent that is employed in the present
invention comprises as a first component styrene acrylate copolymer
that has been obtained by polymerizing styrene and acrylate
monomers in presence of starch, as described later in the
application. The dispersion agent may also comprise small amount of
other constituents, such as unpolymerized monomers or other
substances. The amount of other constituents is typically less than
5 weight-%, more typically less than 3 weight-%.
According to one embodiment of the present invention the dispersion
agent comprising styrene acrylate copolymer may be added during the
final stages of wet grinding of a pigment when the pigment
particles have already obtained the desired particle size. The
dispersion agent is added to the pigment slurry coming from the
preceding process steps. The pigment slurry may comprise grinding
agents that have been added under grinding steps preceding this
last process step. Typical examples of such grinding agents are
polyacrylates, such as Na- or K-polyacrylate, polyacrylate
copolymers or mixtures thereof. Polyacrylate copolymers may be
branched or straight chained. This process is especially useful
when preparing pigment slurries of ground calcium carbonate (GCC),
titanium dioxide or gypsum.
According to another embodiment of the present invention the
dispersion agent comprising styrene acrylate copolymer may be added
to the aqueous phase into which any suitable pigment in powder,
paste or cake form, such as precipitated calcium carbonate or
titanium dioxide, is added with suitable means, e.g. screw
conveyor, and the final pigment slurry is obtained by mixing of the
aqueous phase and pigment powder. This process is used for example
when preparing pigment slurry from kaolin, titanium dioxide or
pigments having needle-like particles.
The dispersion agent is usually added in such amount that the
pigment slurry comprises at least 0.1 parts thereof per 100 parts
pigment. Typically the dispersion agent is added in such amount
that the pigment slurry comprises 0.1-3.5, preferably 0.25-3.0,
more preferably 0.05-2.5, most preferably 1.0-2.0 parts dispersion
agent per 100 parts pigment. These amounts refer to the total
amount of dispersion agent, the dispersion agent comprising only
co-polymer or a mixture of co-polymer with other agents.
Also a conventional dispersion agent, such as straight-chain
polyacrylate, may be added to the aqueous phase. According to one
preferred embodiment of the invention the dispersion agent
comprises a second component. The second component may be a
conventional dispersion agent, such as polyacrylate, polyacrylate
copolymer or their mixtures. In these cases the dispersion agent
comprises a first component comprising styrene acrylate copolymer
and a second component comprising conventional dispersion agent as
described above. In this way the dispersion of the pigment
particles in the slurry may be optimized and at the same time
achieve improved rheological properties for the slurry. It is also
possible to add a conventional dispersion agent as a separate input
flow to the aqueous pigment slurry in addition to another separate
input flow comprising styrene acrylate copolymer. This embodiment
is suitable for processes where the dispersion agent is directly
added to the aqueous phase into which the pigment is added in
powder form.
When the dispersion agent comprises a second component comprising a
conventional dispersion agent as described above, such as
polyacrylate, the proportion first component to the second
component is typically in the range 55:45-95:5, more typically
50:50-92.5:7.5, even 70:30-90:10. In some cases the proportion
first component to the second component may be 99:1. According to
one embodiment the proportion first component:second component is
in the range 50:50-99:1, preferably 50:50-90:10.
According to one embodiment of the invention styrene acrylate
copolymer is used as the sole dispersion agent. In other words, it
is not necessary to use other dispersion agents except styrene
acrylate copolymer, for obtaining the desired stability for pigment
slurry. If other dispersion agents are used, their dosage may be
reduced from the conventional and still the stability of the slurry
is kept at the desired level.
The styrene acrylate copolymer that is used as the dispersion agent
in the present invention may be obtained by copolymerization of
ethylenically unsaturated monomers. Suitable styrene monomers are
styrene and substituted styrenes, such as a-methylstyrene or
vinyltoluene or their mixtures, and suitable acrylate monomers are
C1-C4-alkyl acrylates, C1-C4-alkyl methacrylates or their mixtures,
e.g. n-butyl, iso-butyl, tert-butyl or 2-butyl acrylate and the
corresponding butyl methacrylates; methyl acrylate, methyl
methacrylate, ethyl acrylate, ethyl methacrylate, propyl acrylate
or propyl methacrylate, mixture of at least two isomeric butyl
acrylates being preferred, mixtures of n-butyl acrylate and methyl
methacrylate being particularly preferred. According to one most
preferred embodiment of the invention the mixtures of n-butyl
acrylate and tert-butyl acrylate are used in polymerization. For
mixtures of two monomers the mixing ratio may be 10:90 to
90:10.
According to one preferred embodiment of the invention the styrene
acrylate copolymer comprises starch. Preferably the styrene
acrylate copolymer is obtained as described in U.S. Pat. No.
6,426,381, i.e. by free radical emulsion copolymerization of
ethylenically unsaturated monomers in the presence of starch.
Starch may be any suitable native starch, such as potato, rice,
corn, waxy corn, wheat, barley or tapioca starch, potato starch
being preferred. Starches having an amylopectin content >80%,
preferably >95% are advantageous. Starch may be also modified,
for example, anionized, cationized or degraded. Anionized starch
comprises anionic groups, such as carboxylate or phosphate groups,
whereas cationized starch comprises cationic groups, such as
quaternized ammonium groups. Degree of substitution (DS),
indicating the number of anionic/cationic groups in the starch on
average per glucose unit, is typically 0.01-0.20. Amphoteric
starches, comprising both anionic and cationic groups, may also be
used in the preparation of the styrene acrylate copolymer. Degraded
starch is obtained by subjecting the starch to oxidative, thermal,
acidic or enzymatic degradation, oxidative degradation being
preferred. Hypochlorite, peroxodisulfate, hydrogen peroxide or
their mixtures may be used as oxidizing agents. Degraded starch has
typically an average molecular weight (Mn) 500-10 000, which can be
determined by known gel chromatography methods. The intrinsic
viscosity is typically 0.05 to 0.12 dl/g, determined, for example,
by known viscosimetric methods.
According to one embodiment of the invention it is possible to use,
instead of starch any other polysaccharide, which contains a free
hydroxyl group, such as amylose, amylopectine, carrageen,
cellulose, chitosan, chitin, dextrines, guar gum (guarane) and
other galactomannans, arabic gum, hemi-cellulose components, and
pullulan, for obtaining styrene acrylate copolymer used in the
present invention. Dextrin is more preferred of the polysaccharides
listed, i.e. the styrene acrylate copolymer comprises dextrin.
The dispersion agent comprising styrene acrylate copolymer may be
used in form of aqueous polymer dispersion having a solids content
of 10-50%, preferably 20-50%, more preferably 25-45%, most
preferably 30-40%.
According to one embodiment of the invention the mean particle size
of the styrene acrylate copolymer is 20-300 nm, preferably less
than 150 nm when it is used as dispersion agent. According to one
embodiment of the invention the mean particle size of the
dispersion agent in the aqueous dispersion is in the range 20-150
nm, preferably 40-100 nm, more preferably 50-90 nm. The particle
size of the dispersion agent may be determined by using a Malvern
Zetamaster. It is speculated, without being bound by the theory,
that the small particle size of the styrene acrylate copolymer
might be beneficial for attaining the improved high shear viscosity
values.
In this application and in the example the composition of the
pigment slurry is given, if not otherwise stated, as conventional
in the art, by giving the total amount of pigments value 100, and
calculating the amounts of other components relative to the amount
of the total pigment. Proportions of all components are given as
dry parts.
EXAMPLE
100 parts of dried undispersed PCC (precipitated calcium carbonate,
95%<1 .mu.m) is added into water with 0.55 pph (parts per 100)
conventional Na-polyacrylate dispersant, Colloid 220 (trademark) by
Kemira, to the solid content of the slurry 68%. The pH is adjusted
to the value 9.9 or 9.5 (sample 4) using 10% sodium hydroxide. The
slurry is mixed 10 minutes at ambient temperature in Diaf-mixer at
3000 rpm, after which 1 pph of dispersion agent according to the
present invention is added for formulations 2 to 4. The mixing of
the slurry is continued for further 5 minutes. From the prepared
slurries viscosities are measured using Brookfield viscometer, type
DV-II, with speeds 100 and 50 rpm and using spindle 3. The sample
size was 500 g of dry pigment, solid content of the slurry ca 68%.
High shear viscosity at shear blocking is measured using Hercules
Hi-Shear DV-10 rotational viscometer. The test procedure of
evaluating the viscosity of slurry pigments is as outlined by TAPPI
(Technical Association of the Pulp and Paper Industry) test method
T-648 (valid in September 2008). Results are shown in table 1.
Dispersion agent in the samples is as follows:
Reference: pigment slurry with 0.55 pph Na-polyacrylate
Sample 2: pigment slurry with 0.55 pph Na-polyacrylate+1 pph
styrene acrylate copolymer
Sample 3: pigment slurry with 0.55 pph Na-polyacrylate+1 pph 90/10
styrene acrylate copolymer/Na-polyacrylate
Sample 4: pigment slurry with 0.55 pph Na-polyacrylate+1 pph
Na-polyacrylate
In other words, samples 2 and 3 are according to the present
invention, in reference sample and sample 4 employ conventional
dispersion agent in different amounts.
TABLE-US-00001 TABLE 1 Results of viscosity measurements Sample
Measured Property Unit Reference Sample 2 Sample 3 4 Viscosity,
mPas 115 103 124 131 Brookfield 100 rpm Viscosity, mPas 132 141 164
173 Brookfield 50 rpm High shear viscosity mPas 95 85 63 101 at
shear blocking Solids content % 68.2 68.1 68.1 68.3 pH 9.9 9.9 9.9
9.5 Temperature .degree. C. 24 24 24 24 Density g/cm.sup.3 1.84
1.84 1.84 1.84
From the results it can be seen that when a dispersion agent
according to the present invention comprising styrene acrylate
copolymer is used, the high shear viscosity at shear blocking
decreases compared to slurries with conventional Na-polyacrylate
dispersant.
Even if the invention was described with reference to what at
present seems to be the most practical and preferred embodiments,
it is appreciated that the invention shall not be limited to the
embodiments described above, but the invention is intended to cover
also different modifications and equivalent technical solutions
within the scope of the enclosed claims.
* * * * *