Note: Descriptions are shown in the official language in which they were submitted.
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PROCESS FOR PREPARING A POLYMER DISPERSION AND A POLYMER
DISPERSION
The present invention relates to a process for preparing a polymer dispersion.
It
also relates to a polymer dispersion, the use of the polymer dispersion and a
process for
producing paper.
Background of the invention
An important use of aqueous dispersions of anionic charged polymers is
retention and dewatering aid in paper manufacturing industry. Further uses of
such
polymer dispersions are as aids in various processes where they act as, for
example,
flocculants when treating wastewater or aids in other solid-liquid separation
processes in,
for example, the metal-, ceramic-, printing-, biotechnological-, and
pharmaceutical
industries. They can also be used as thickeners in, e.g., chemical-
biotechnological-,
pharmaceutical-, and cosmetic industries and soil improving agents.
Generally, these polymer dispersions comprise a dispersed polymer and a
dispersant in which the dispersant usually is a polymeric dispersant.
Anionic polymer dispersions are generally prepared by polymerising a reaction
mixture of water-soluble anionic and non-ionic monomers in the presence of a
salt.
Finished polymer will precipitate from the aqueous salt solution and, by using
a suitable
dispersant, form a stable polymer dispersion. WO 01/18063, US 5,837,776 and US
5,605,970 disclose processes for preparing a dispersion of a water-soluble
polymer
comprising polymerising water-soluble monomers in an aqueous reaction mixture
containing a salt.
Factors to consider are, for example, the process viscosity, active content,
stability, good retention properties, and easiness of preparing the polymer
dispersion
sometimes including preparing the stabiliser. Also, criteria such as
environmental and
safety aspects are of importance.
There are a number of criteria that the polymer dispersion should fulfil to
give good
results in the final application and be of commercial interest. Such criteria
are for example
low-cost production, rapid performance, effective flocculation or dewatering,
and long
shelf life.
Prior art anionic polymer dispersions described contain significant amounts of
salt which makes up a great part of the weight of the polymer dispersion.
There is
presently a desire to reduce, or completely avoid, the use of salt in polymer
dispersions
due to environmental and economical reasons.
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The viscosity of the reaction mixture when producing the polymer dispersion,
"the process viscosity", should be kept low and viscosity peaks should be
avoided, or at
least reduced as much as possible, during the production of the polymer
dispersion.
The shelf life of the dispersion, i.e., the stability of the polymer
dispersion over
time, is an important property. An efficient dispersant is needed for keeping
the polymer
particles stable in dispersion without settling as sediment.
A further factor to consider is the active content, i.e., the amount of
dispersed
polymer in the polymer dispersion. A high active content minimises
transportation costs
and gives easier handling at the end-application. By using an efficient
dispersant,
dispersions with a high active content can be obtained at the same time the
viscosity can
be kept low. However, an increase of the active content above a certain level
may not
always give improved performance in retention and dewatering in a papermaking
process.
During preparation of a polymer dispersion, deposits of polymer may form and
stick to the reaction vessel and stirrer. This leads to time consuming
cleaning procedures
of the reaction equipment.
It is an object of the present invention to provide a, preferably salt-free,
water
soluble anionic polymer dispersion having high stability and high active
content. The
polymer dispersion should also give good retention and dewatering results when
used in
papermaking processes, act as a good flocculant in other processes such as
waste water
treatment, act as a good thickener in various applications such as cosmetic
formulations
and also be possible to use in soil improvement processes. It is further an
object of the
present invention to provide a process for preparing a, preferably salt-free,
water soluble
anionic polymer dispersion in which the process viscosity is kept low and
smooth during
preparation without any large viscosity peaks, and which gives no deposits.
Finally, it is
an object of the present invention to provide a process for producing paper in
which the
polymer dispersion is used.
The invention
By "stabiliser" is herein meant a polymer which function is to keep dispersed
polymer particles/droplets in dispersion.
By "co-stabiliser" is herein meant a polymer which function is to make a
polymer
formed from polymerisation of one or more monomers to precipitate out from
solution into
solid particles or liquid droplets.
According to the invention it has surprisingly been found that a highly stable
polymer dispersion having high active content of a dispersed polymer and low
process
viscosity can be achieved by a process for preparing a polymer dispersion
comprising
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polymerising one or more anionic monomers (m,) and one or more non-ionic vinyl
monomers (m2) present in a reaction mixture further comprising a polymeric
stabiliser (B)
and a polymeric co-stabilisers (C).
The invention further comprises a polymer dispersion comprising a dispersed
polymer (A) of one or more anionic monomers (m,) and one or more non-ionic
vinyl
monomers (m2), a polymeric stabiliser (B), and a polymeric co-stabiliser (C).
The reaction medium is suitably an aqueous medium. The polymer dispersion is
suitably an aqueous polymer dispersion. The polymer dispersion is suitably
water-
soluble. The polymer particles/droplets suitably has an average size
(thickness) of up to
about 25 pm, also suitably from about 0.01 to about 25 pm, preferably from
about 0.05 to
about 15 pm, most preferably from about 0.2 to about 10 pm.
The polymeric stabiliser (B) is suitably an organic polymer. Preferably the
polymeric stabiliser (B) is a polymer of one or more monomers belonging to the
group of
acrylic acid, methacrylic acid, itaconic acid, 2-acrylamido-2-methyl-1-propane
sulphonic
acid (AMPS), 2-acrylamido-2-methyl-1-butane sulphonic acid (AMBS),
acryloyloxyethyl
sulphonic acid, methacryloyloxyethyl sulphonic acid, acryloyloxypropyl
sulphonic acid,
methacryloyloxypropyl sulphonic acid, vinyl sulphonic acid, allyl sulphonic
acid, methallyl
sulphonic acid, styrene sulphonic acid, maleic acid, maleamidic acid, and/or
vinyl
phosphonic acid. Other suitable polymeric stabilizers are copolymers of maleic
acid or
maleamidic acid, respectively, with styrene or vinyl ethers, or alpha-olefins
which may
contain additional comonomers. Preferably, the polymeric stabiliser (B) is a
copolymer of
acrylic acid or methacrylic acid with a further of the listed monomers,
preferably 2-
acrylamido-2-methyl-1 -propane sulphonic acid (AMPS).
The weight average molecular weight of the polymeric stabiliser (B) is
suitably
from about 5.000 to about 5.000.000 g/mole, preferably from about 10.000 to
about
1.000.000 g/mole, more preferably from about 20.000 to about 1000.000 g/mole,
most
preferably from about 35.000 to about 500.000 g/mole.
The polymer dispersion suitably comprises from about 0.2 to about 5 weight %
of
the polymeric stabiliser (B) based on the total weight of the dispersion or
reaction mixture,
preferably from about 0.5 to about 3 weight %, most preferably from about 0.8
to about
1.5 weight %.
The polymeric co-stabiliser (C) is suitably an organic polymer. Preferably,
the
polymeric co-stabiliser (C) is a polymer of one or more monomers belonging to
the group
of acrylic acid, methacrylic acid, vinyl sulphonate, styrene sulphonic acid,
itaconic acid,
vinylphosphonic acid, 2-acrylamido-2-methyl-1-propane sulphonic acid (AMPS), 2-
acrylamido-2-methyl-1-butane sulphonic acid (AMBS), acryloyloxyethyl sulphonic
acid,
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methacryloyloxyethyl sulphonic acid, acryloyloxypropyl sulphonic acid, and
methacryloyloxypropyl sulphonic acid.
Preferably, two or more co-stabilisers (C) are present in the reaction mixture
and
polymer dispersion.
The weight average molecular weight of the polymeric co-stabiliser (C) is
suitably from about 100 to about 50.000 g/mol, preferably from about 500 to
about 30.000
g/mol, more preferably from about 1.000 to about 20.000 g/mol, even more
preferably
from about 1.000 to about 15.000 g/mol, most preferably from about 1.000 to
about
10.000 g/mol.
The polymer dispersion suitably comprises from about 2 to about 50 weight % of
one or more polymeric co-stabilisers (C) based on the total weight of the
dispersion or
reaction mixture, preferably from about 3 to about 25 weight %, most
preferably from
about 5 to about 15 weight %.
The polymeric stabiliser (B) and the polymeric co-stabiliser (C) in the
reaction
mixture or polymer dispersion are preferably made up from different monomers
or, if they
are made up from the same monomers, contain different monomer ratios.
The polymeric stabiliser (B) or polymeric co-stabiliser (C) is suitably not a
dextrin
or dextrin derivative.
The one or more anionic monomers (m,) suitably belong to the group of acrylic
acid, methacrylic acid, (styrene sulphonic acid), 2-acrylamido-2-methyl-1-
propane
sulphonic acid (AMPS), 2-acrylamido-2-methyl-1-butane sulphonic acid (AMBS),
acryloyloxyethyl sulphonic acid, methacryloyloxyethyl sulphonic acid,
acryloyloxypropyl
sulphonic acid, methacryloyloxypropyl sulphonic acid, vinyl sulphonic acid,
and their
alkali, earth alkali or ammonium salts.
The one or more non-ionic monomers (m2) suitably belong to the group of
acrylamide, methacrylamide, N-methylacrylamide, N-methylmethacrylamide, N-
ethylacrylamide, N-ethylmethacrylamide, N-isopropylacrylamide, N-
isopropylmethacrylamide, N,N-dimethylacrylamide, N-t-butylacrylamide, N-t-
butylmethacrylamide, N-hydroxyethylacrylamide, N-(tris-(hydroxymethyl)-methyl)-
acrylamide, N-vinyl formamide, N-vinyl acetamide, hydroxyalkylacrylate or
hydroxyalkylmethacrylate with C2-C4 alkyl, alkylacrylate or alkylmethacrylate
with C1-C4
alkyl, benzylacrylate or benzylmethacrylate, esters of acrylic or methacrylic
acid with
dihydroxy-(polyethylene oxide) having 1-20 ethylene oxide units, or esters of
acrylic or
methacrylic acid with monomethoxyhydroxy-(polyethylene oxide) having 1-20
ethylene
oxide units. Preferably, the one or more non-ionic monomers (m2) belong to the
group of
acrylamide, acrylate or methacrylate esters.
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The molar ratio between the anionic monomer (m,) and the non-ionic monomer
(m2) is suitably from about 1:99 to about 25:75, preferably from about 3:97 to
about
20:80, most preferably from about 5:95 to about 15:85.
The weight average molecular weight of the dispersed polymer (A) is suitably
5 from about 1.000.000 to about 15.000.000 g/mole, preferably from about
1.500.000 to
about 10.000.000 g/mole, most preferably from about 2.000.000 to about
8.000.000
g/mole.
The polymerisation is suitably a free-radical polymerisation. The initiator is
suitably a radical former, preferably a water-soluble azo-initiator, a water-
soluble
peroxide, or a water-soluble redox initiator. Preferred initiators include
2,2'-azobis-
(amid in propane) hydrochloride, 2,2'-azobis-(2-methyl-N-(2-hydroxyethyl)-
propionamide,
4,4'-azobis-(4-cyanovaleric acid) and its alkali and ammonium salts, t-
butylhydroperoxide,
perhydrol, peroxydisulphate, or the before mentioned peroxides in combination
with a
reducing agent such as sodium metabisulphite or ferrous salts.
The polymer dispersion suitably comprises from about 5 to about 40 weight % of
the dispersed polymer (A) based on the total weight of the dispersion,
preferably from
about 10 to about 30 weight %, most preferably from about 12 to about 25
weight %.
The amount of one or more inorganic salts in the polymer dispersion is
suitably
from 0 to about 1.9 weight % based on the total weight of the dispersion or
reaction
mixture, preferably from 0 to about 1 weight %, more preferably from 0 to
about 0.5
weight %, most preferably from 0 to about 0.1 weight %, or substantially salt-
free.
By "inorganic salts" is herein suitably meant any inorganic salt, preferably
salts
belonging to the group of inorganic alkali metal, alkali earth metal or
ammonium halides,
sulphates and phosphates.
The polymer dispersion may also comprise additional substances, such as
cross-linkers and branching agents.
The polymerisation temperature when may vary depending on, e.g., which
monomers and polymerisation initiator are being used. Suitably, the
polymerisation
temperature is from about 30 to about 90 C, preferably from about 35 to about
70 C. The
process is suitably a semi-batch process, i.e., the monomers m, and m2 are
both present
at the beginning of the polymerisation process and further added at a later
stage, either in
one or more portions or continuously over a period of time during the
reaction. The
reaction mixture is suitably stirred during the polymerisation process at a
stirring rate
suitable for the process. Suitably, the stirring rate is from about 100 to
about 1000 rpm.
The invention further comprises use of a polymer dispersion as retention and
dewatering aid for paper manufacturing, as thickening agent, as soil
improvement agent
and/or as an additive for increasing the dry strength of paper. The polymer
dispersion of
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the present invention can more specifically be used as aid in various
processes as, for
example, flocculants when treating wastewater or aids in other solid-liquid
separation
processes in, for example, the metal-, ceramic-, printing-, biotechnological-,
and
pharmaceutical industries. The polymer dispersion can also be used as
thickener in, e.g.,
chemical- biotechnological-, pharmaceutical-, and cosmetic industries.
Finally, the present invention comprises a process for the production of paper
from an aqueous suspension containing cellulosic fibres, and optional fillers,
which
comprises adding to the suspension an aqueous polymer dispersion according to
the
invention, forming and draining the suspension on a wire.
When using the polymer dispersion, according to the invention, in papermaking
processes, the dispersion is added to the suspension of cellulosic fibres, and
optional fillers,
to be dewatered in amounts which can vary within wide limits depending on,
inter alia, type
and number of components, type of furnish, filler content, type of filler,
point of addition, etc.
The dispersed polymer is usually added in an amount of at least 0.001%, often
at least
0.005% by weight, based on dry substance in the stock to be dewatered, and the
upper limit
is usually 3% and suitably 1.5% by weight. The polymer dispersion according to
the
invention is suitably diluted before adding it to the cellulosic suspension.
Further additives
which are conventional in papermaking can of course be used in combination
with the
polymer dispersion according to the invention, such as, for example, silica-
based sols, dry
strength agents, wet strength agents, optical brightening agents, dyes, sizing
agents like
rosin-based sizing agents and cellulose-reactive sizing agents, e.g. alkyl and
alkenyl ketene
dimers, alkyl and alkenyl ketene multimers, and succinic anhydrides, etc. The
cellulosic
suspension, or stock, can also contain mineral fillers of conventional types
such as, for
example, kaolin, china clay, titanium dioxide, gypsum, talc and natural and
synthetic calcium
carbonates such as chalk, ground marble and precipitated calcium carbonate.
The term
"paper", as used herein, include not only paper and the production thereof,
but also other
cellulosic fibre-containing sheet or web-like products, such as for example
board and
paperboard, and the production thereof. The process can be used in the
production of paper
from different types of suspensions of cellulose-containing fibres and the
suspensions
should suitably contain at least 25 % by weight and preferably at least 50 %
by weight of
such fibres, based on dry substance. The suspension can be based on fibres
from chemical
pulp such as sulphate, sulphite and organosolv pulps, mechanical pulp such as
thermome-
chanical pulp, chemo-thermomechanical pulp, refiner pulp and groundwood pulp,
from both
hardwood and softwood, and can also be based on recycled fibres, optionally
from de-inked
pulps, and mixtures thereof.
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The invention will now further be described in connection with the following
examples which, however, not should be interpreted as limiting the scope of
the
invention.
Examples
Example 1:
A stabiliser made of methacrylic acid (MAA) and 2-acrylamido-2-methyl-1-
propane sulphonic acid (AMPS) in a mole ratio of 80:20 was prepared: A mixture
of 85g
ultra-pure water, 8.24g AMPS (solid), 16.62g MAA and 11.5g NaOH (50%) was
adjusted
to pH 7 by means of NaOH (50%). 0.028 EDTA (solid) was given into the mixture.
Further
ultra-pure water was added to reach a total mass of 127g. This was filled into
a double-
wall 150m1 glass reactor with anchor stirrer, nitrogen inlet, reflux condenser
and bottom
valve. The mixture was stirred with 150/min and purged with nitrogen. The
reactor content
TM
was heated up to 45 C. 0.05g V-50 (2,2'-Azobis-(2-amidinopropane)
dihydrochloride)
were added. After 60min, temperature was increased up to 50 C. The mixture was
polymerised over 72 h at 50 C and 150/min. The stabiliser was purified and
isolated by
ultrafiltration and freeze-drying. The weight average molecular weight was
about 15.000
g/mole.
Examples 2-7:
A polymer dispersion was prepared by polymerising a monomer mixture
comprising acrylamide and acrylic acid in the presence of a polymeric
stabiliser and a
polymeric co-stabiliser.
A mixture of 30 g water, 24.3 g co-stabiliser polyacrylic acid (45%, Sigma-
Aldrich, Mw 1.200), 1.2 g stabiliser poly (MAA-co-AMPS) (80:20) copolymer
(according to
example 1, Mw 15.000), 28.1 g acrylamide (50 wt%), 1.07 g acrylic acid, 0.04 g
sodium
formiate, 0.03 g EDTA, and 1.17 g NaOH (50 wt%) was stirred and the pH was
adjusted
TM
to 7. Water was added up to 100 g and during 8 hours azo-initiator VA-044 (4%)
(2,2'-
azobis-(N,N'-dimethyleneisobutyramidine) dihydrochloride, Wako) was added (0.5
g in
steps). The temperature was kept at 35 C. After 16 hours, the stirring was
stopped.
Five further polymer dispersions were prepared using the same procedure as
described above but changing the ratio non-ionic monomer and anionic monomer,
using
a second non-ionic monomer in the dispersed polymer, and also using as co-
stabiliser in
some cases a combination of polyacrylic acid and polymethacrylic acid. As
stabiliser 1.2
weight % poly-(MMA-co-AMPS) in a mole ratio of 80:20 was used. The active
contents
(polymer content) in the stabiliser was around 15 weight%. 11 weight % of co-
stabiliser
was used.
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In Table 1, the following abbreviations are used:
AAm = acrylamide
AA = acrylic acid
MMA = methylmethacrylate
t-BuA = t-butyl acrylate
n-BuA = n-butyl acrylate
PAA = polyacrylic acid
PMAA = polymethacrylic acid
Table 1.
Dispersion anionic monomer non-ionic co-stabiliser stabiliser
monomer
Example 2 AA (10 mol-%) AAm PAA (Mw 1.200) poly-(MMA-co-AMPS)
(90 mol-%) (Mw 15.000)
Example 3 AA (15 mole-%) AAm PAA (Mw 1.200) poly-(MMA-co-AMPS)
(85 mole-%) (Mw 20.000)
Example 4 AA (15 mole-%) AAm PAA (Mw 1.200) poly- (MMA-co-AMPS)
(85 mole-%) PMAA (Mw 9.500) (Mw 20.000)
(1:1 ratio)
Example 5 MMA (10 mole-%) AAm PAA poly-(MMA-co-AMPS)
AA (10 mole-%) (80 mole-%) (Mw 1.200) (Mw 20.000)
Example 6 MMA (10 mole-%) AAm PAA poly-(MMA-co-AMPS)
t-BuA (10 mole-%) (80 mole-%) (Mw 1.200) (Mw 20.000)
Example 7 MMA (10 mole-%) AAm PAA (Mw 1.200) poly-(MMA-co-AMPS)
n-BuA (10 mole-%) (80 mole-%) PMAA (Mw 9.500) (Mw 20.000)
(1:1 ratio)
The process viscosity was low (lower than -2000 mPas) for all dispersions.
Example 8:
The polymer dispersions prepared in Examples 2-4 were tested for retention and
dewatering performance in papermaking processes by means of a Dynamic Drainage
Analyser (DDA) available from Akribi, Sweden. The furnish used was based on 60
% by
weight of bleached 80/20 birch-pine pulp and 40 % by weight of calcium
carbonate. The
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stock volume was 800 ml, the pulp concentration 5 g/L and the conductivity 1.5
mS/cm.
The stock was stirred at a speed of 1500 rpm while the following was added to
the stock:
an anionic trash catcher (0.5 kg/t), polymer dispersion (1.0 kg/t) and finally
anionic
inorganic particles (0.5 kg/t). The temperature was 22.5 C. A vacuum of 0.35
bar was
used for the analysis. The retention time (s) and turbidity (NTU) was
measured.
Table 2. Polymer dispersions and application tests
Polymer Application tests
dispersion Polymer load Retention time Turbidity
(kg/t) (s) (NTU)
Example 2 1.0 15.2 198
Example 3 1.0 14.6 220
Example 4 1.0 13.2 214
It is concluded that the dispersions according to the invention function well
in
retention and dewatering aids.
Example 9:
The shelf life, measured as sedimentation stability, was tested for the
dispersions according to Examples 2-7. A 10 g sample of each dispersion was
centrifuged for 30 minutes at 3000 rpm. The amount of polymer sediment was
determined for each sample. No sample gave any polymer sediment
Thus, it is concluded that polymer dispersions with long shelf life can be
obtained
by the present invention, also at high active contents.
