Note: Descriptions are shown in the official language in which they were submitted.
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A PROCESS FOR THE PRODUCTION OF PAPER
Field of the Invention
The present invention relates to a process for the production of paper and a
composition
comprising anionic components that is suitable for use as an additive in
papermaking.
More specifically, the invention relates to a process for the production of
paper which
comprises adding first, second and third anionic components to a cellulosic
suspension
after all points of high shear and dewatering the obtained suspension to form
paper.
Background of the Invention
In the art of papermaking, an aqueous suspension containing cellulosic fibres,
and
optional fillers and additives, is fed through pumps, screens and cleaners,
which subject
the stock to high shear forces, into a headbox which ejects the suspension
onto a forming
wire. Water is drained from the suspension through the forming wire so that a
wet web of
paper is formed on the wire, and the web is further dewatered and dried in the
drying
section of the paper machine. Drainage and retention aids are conventionally
introduced
at different points in the flow of suspension in order to facilitate drainage
and increase
adsorption of fine particles such as fine fibres, fillers and additives onto
the cellulose
fibres so that they are retained with the fibres on the wire. Examples of
conventionally
used drainage and retention aids include organic polymers, inorganic
materials, and
combinations thereof.
WO 98/56715 discloses aqueous polysilicate microgels, their preparation and
use in
papermaking and water purification. The polysilicate microgels can contain
additional
compounds, e.g. polymers containing carboxylic acid and sulphonic acid groups,
such as
polyacrylic acid.
WO 00/006490 discloses anionic nanocomposites for use as retention and
drainage aids
is papermaking prepared by adding an anionic polyelectrolyte to a sodium
silicate solution
and then combining the sodium silicate and polyelectrolyte solution with
silicic acid.
US 6,103,065 discloses a method for improving the retention and drainage of
papermaking furnish comprising the steps of adding at least one cationic high
charge
density polymer of molecular weight 100,000 to 2,000,000 to said furnish after
the last
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point of high shear; adding at least one polymer having a molecular weight
greater than
2,000,000; and adding a swellable bentonite clay.
WO 01/34910 discloses a process for making paper or paper board in which a
cellulosic
suspension is flocculated by addition of a substantially water soluble polymer
selected
from (a) a polysaccharide or (b) a synthetic polymer of intrinsic viscosity at
least 4 dl/g and
then reflocculated by a subsequent addition of a reflocculating system
comprising (i) a
siliceous material and (ii) a substantially water soluble anionic polymer.
Preferably, the
substantially water soluble polymer is mixed into the cellulosic suspension
causing
flocculation and the flocculated suspension is then sheared, e.g. by passing
it through one
or more shear stages. The water soluble anionic polymeric reflocculating agent
is
preferably added late in the process, preferably after the last point of high
shear, e.g.
subsequent to the centri-screen. The process is claimed to provide
improvements in
retention and drainage.
WO 02/33171 discloses a process for making paper or paper board in which a
cellulosic
suspension is flocculated using a flocculating system comprising a siliceous
material and
organic microparticles which have an unswollen particle diameter of less than
750 nm.
WO 02/101145 discloses an aqueous composition comprising anionic organic
polymeric
particles and colloidal anionic silica-based particles, the anionic organic
polymeric particles
being obtainable by polymerising one or more ethylenically unsaturated
monomers
together with one or more polyfunctional branching agents and/or
polyfunctional
crosslinking agents. The composition is used as a flocculating agent in
dewatering of
suspended soils, in the treatment of water, wastewater and waste sludge, and
as
drainage and retention aid in the production of paper.
It would be advantageous to be able to provide a papermaking process with
further
improvements in drainage, retention and formation.
Summary of the Invention
The present invention is directed to a process for producing paper which
comprises:
(i) providing an aqueous suspension comprising cellulosic fibres,
(ii) adding to the suspension after the last point of high shear:
(a) a first anionic component which is a water-soluble anionic organic
polymer;
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(b) a second anionic component which is a water-dispersible or branched
anionic organic polymer having an unswollen particle size less than 1000
nm; and
(c) a third anionic component which is an anionic siliceous material; and
(iii) dewatering the obtained suspension to form paper.
The present invention is further directed to a process for producing paper
which
comprises:
(i) providing an aqueous suspension comprising cellulosic fibres,
(ii) adding to the suspension after the last point of high shear:
(a) a first anionic component which is a water-soluble anionic organic
polymer;
(b) a second anionic component which is a water-dispersible or branched
anionic organic polymer; and
(c) a third anionic component which is an anionic siliceous material
comprising
anionic silica-based polymer which comprises
(I) aggregated anionic silica-based particles; or
(II) silica-based particles having a specific surface area within the range
of from 100 to 1700 m2/g
(iii) dewatering the obtained suspension to form paper.
The present invention is further directed to a drainage and retention aid
composition which
comprises:
(a) a first anionic component which is a water-soluble anionic organic
polymer;
(b) a second anionic component which is a water-dispersible or branched
anionic organic polymer having an unswollen particle size of less than 1000
nm; and
(c) a third anionic component which is an anionic siliceous material;
wherein the first, second and third anionic components are present in a dry
matter content
of from 0.01 to 50 % by weight.
The present invention is further directed to a drainage and retention aid
composition which
comprises:
(a) a first anionic component which is a water-soluble anionic organic
polymer;
(b) a second anionic component which is a water-dispersible or branched
anionic organic polymer; and
(c) a third anionic component which is an anionic siliceous material
comprising
anionic silica-based polymer which comprises
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(I) aggregated anionic silica-based particles; or
(II) silica-based particles having a specific surface area within the range
of from 100 to 1700 m2/g
wherein the first, second and third anionic components are present in a dry
matter content
of from 0.01 to 50 % by weight.
The present invention further relates to the use of the composition as a
flocculating agent
in the production of pulp and paper and for water purification.
Detailed Description of the Invention
According to the present invention it has been found that drainage and
retention can be
improved without any significant impairment of formation, or even with
improvements in
paper formation, by a process which comprises adding three different anionic
components,
i.e., first, second and third anionic components, to an aqueous cellulosic
suspension after
the last point of high shear. Preferably, after the addition of the first,
second and third
anionic components, the obtained cellulosic suspension is fed into a headbox
and ejected
onto a wire where it is dewatered to form paper. Preferably, the cellulosic
suspension is
pre-treated by addition of a cationic material before addition of the first,
second and third
anionic components.
The present invention provides improvements in drainage and retention in the
production
of paper from all types of cellulosic suspensions, in particular suspensions
containing
mechanical or recycled pulp, and stocks having high contents of salts (high
conductivity)
and colloidal substances, and in papermaking processes with a high degree of
white
water closure, i.e. extensive white water recycling and limited fresh water
supply. Hereby the
present invention makes it possible to increase the speed of the paper machine
and to use
lower dosages of polymers to give corresponding drainage and/or retention
effects, thereby
leading to an improved papermaking process and economic benefits.
First Anionic Component
The first anionic component according to the invention is a water-soluble
anionic organic
polymer. Examples of suitable water-soluble anionic organic polymers include
anionic
polysaccharides and anionic synthetic organic polymers, preferably anionic
synthetic
organic polymers. Examples of suitable water-soluble anionic synthetic organic
polymers
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include anionic aromatic condensation polymers and anionic vinyl addition
polymers.
Preferably, the water-soluble anionic organic polymer is substantially linear.
Examples of suitable water-soluble anionic polysaccharides include anionic
starches, guar
gums, cellulose derivatives, chitins, chitosans, glycans, galactans, glucans,
xanthan gums,
pectins, mannans, dextrins, preferably starches, guar gums and cellulose
derivatives.
Examples of suitable starches include potato, corn, wheat, tapioca, rice, waxy
maize and
barley, preferably potato.
Examples of suitable water-soluble anionic aromatic condensation polymers
include anionic
benzene-based and naphthalene-based condensation polymers, preferably
naphthalene-
sulphonic acid based and naphthalene-sulphonate based condensation polymers.
Examples of suitable water-soluble anionic synthetic organic polymers include
anionic
vinyl addition polymers obtained by polymerization of a water-soluble
ethylenically
unsaturated anionic or potentially anionic monomer or, preferably, a monomer
mixture
comprising one or more water-soluble ethylenically unsaturated anionic or
potentially anionic
monomers and, optionally, one or more other water-soluble ethylenically
unsaturated
monomers. The term "potentially anionic monomer", as used herein, is meant to
include a
monomer bearing a potentially ionisable group which becomes anionic when
included in a
polymer on application to the cellulosic suspension. Examples of suitable
anionic and
potentially anionic monomers include ethylenically unsaturated carboxylic
acids and salts
thereof, and ethylenically unsaturated sulphonic acids and salts thereof, e.g.
(meth)acrylic acid
and salts thereof, suitably sodium (meth)acrylate, ethylenically unsaturated
sulphonic acids
and salts thereof, e.g. 2-acrylamido-2-methyl propanesul phonate, sulphoethyl-
(meth)acrylate,
vinylsulphonic acid and salts thereof, styrenesulphonate, and paravinyl phenol
(hydroxy
styrene) and salts thereof. Preferably, the polymerization is carried out in
the absence or
substantial absence of crosslinking agent, thereby forming substantially
linear anionic
synthetic organic polymers.
The monomer mixture can contain one or more water-soluble ethylenically
unsaturated non-
ionic monomers. Examples of suitable copolymerizable non-ionic monomers
include
acrylamide and acrylamide-based monomers, e.g. methacrylamide, N-alkyl
(meth)acrylamides,
e.g. N-methyl (meth)acrylamide, N-ethyl (meth)acrylamide, N-n-propyl
(meth)acrylamide, N-iso-
propyl (meth)acrylamide, N-n-butyl (meth)acrylamide, N-t-butyl
(meth)acrylamide and N-iso-
butyl (meth)acrylamide; N-alkoxyalkyl (meth)acrylamides, e.g. N-n-butoxymethyl
(meth)acrylamide, and N-isobutoxymethyl (meth)acrylamide; N,N-dialkyl
(meth)acrylamides,
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e.g. N,N-dimethyl (meth)acrylamide; dialkylaminoalkyl (meth) acrylamides;
acrylate-based
monomers like dialkylaminoalkyl (meth)acrylates; and vinyl amines. The monomer
mixture can
also contain one or more water-soluble ethylenically unsaturated cationic or
potentially cationic
monomers, preferably in minor amounts if present. The term "potentially
cationic monomer", as
used herein, is meant to include a monomer bearing a potentially ionisable
group which
becomes cationic when included in a polymer on application to the cellulosic
suspension.
Examples of suitable cationic monomers include those represented by the below-
mentioned
general structural formula (I), and diallyldialkyl ammonium halides, e.g.
diallyldimethyl
ammonium chloride. Examples of preferred copolymerizable monomers include
(meth)acrylamide, and examples of preferred first anionic components include
anionic
acrylamide-based polymer.
The first anionic component according to the invention can have a weight
average molecular
weight of at least about 2,000, suitably at least 10,000. For anionic aromatic
condensation
polymers, the weight average molecular weight is usually at least about 2,000,
suitably at
least 10,000. For anionic vinyl addition polymers, the weight average
molecular weight is
usually at least 500,000, suitably at least about 1 million, preferably at
least about 2 million and
more preferably at least about 5 million. The upper limit is not critical; it
can be about 300
million, usually 50 million and suitably 30 million.
The first anionic component according to the invention usually has a charge
density less
than about 10 meq/g, suitably less than about 6 meq/g, preferably less than
about 4
meq/g, more preferably less than 2 meq/g. Suitably, the charge density is in
the range of
from 0.5 to 10.0, preferably from 1.0 to 4.0 meq/g.
Second Anionic Component
The second anionic component according to the invention is a water-dispersible
or branched
anionic organic polymer. Preferably, the second anionic component is a
synthetic anionic
organic polymer. Examples of suitable water-dispersible anionic organic
polymers include
crosslinked anionic organic polymers and non-crosslinked water-insoluble
anionic organic
polymers. Examples of suitable branched anionic organic polymers include water-
soluble
anionic organic polymers.
Examples of suitable water-dispersible and branched anionic organic polymers
include the
crosslinked and branched polymers obtained by polymerization of a monomer
mixture
comprising one or more ethylenically unsaturated anionic or potentially
anionic monomers and,
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optionally, one or more other ethylenically unsaturated monomers, in the
presence of one or
more polyfunctional crosslinking agents. Preferably, the ethylenically
unsaturated monomers
are water-soluble. The presence of a polyfunctional crosslinking agent in the
monomer mixture
renders possible preparation of branched polymers, slightly crosslinked
polymers and highly
crosslinked polymers that are water-dispersible.
Examples of suitable anionic and potentially anionic monomers include
ethylenically
unsaturated carboxylic acids and salts thereof, ethylenically unsaturated
sulphonic acids and
salts thereof, e.g. any one of those mentioned above. Examples of suitable
polyfunctional
crosslinking agents include compounds having at least two ethylenically
unsaturated bonds,
e.g. N,N-methylene-bis(meth)acrylamide, polyethyleneglycol di(meth)acrylate, N-
vinyl
(meth)acrylamide, divinylbenzene, triallylammonium salts and N-
methylallyl(meth)acrylamide;
compounds having an ethylenically unsaturated bond and a reactive group, e.g.
glycidyl
(meth)acrylate, acrolein and methylol(meth)acrylamide; and compounds having at
least two
reactive groups, e.g. dialdehydes like glyoxal, diepoxy compounds and
epichlorohydrin.
The monomer mixture can contain one or more water-soluble ethylenically
unsaturated non-
ionic monomers. Examples of suitable copolymerizable non-ionic monomers
include
acrylamide and the above-mentioned non-ionic acrylamide-based and acrylate-
based
monomers and vinyl amines. The monomer mixture can also contain one or more
water-
soluble ethylenically unsaturated cationic or potentially cationic monomers,
preferably in minor
amounts if present. Examples of suitable copolymerizable cationic monomers
include the
monomers represented by the above general structural formula (I) and
diallyldialkyl ammonium
halides, e.g. diallyldimethyl ammonium chloride.
Suitable water-dispersible and branched anionic organic polymers can be
prepared using at
least 4 molar parts per million of polyfunctional crosslinking agent based on
monomer present
in the monomer mixture, or based on monomeric units present in the polymer,
preferably from
about 4 to about 6,000 molar parts per million, most preferably from 20 to
4,000.
Examples of preferred water-dispersible or branched anionic organic polymer
include water-
dispersible and branched anionic acrylamide-based polymers.
Examples of suitable non-crosslinked water-insoluble anionic organic polymers
include the
polymers obtained by polymerization of a monomer mixture comprising one or
more water-
insoluble monomers, one or more ethylenically unsaturated anionic or
potentially anionic
monomers and, optionally, one or more other ethylenically unsaturated
monomers. Examples
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of suitable water-insoluble monomers include styrene and styrene-based
monomers, alkenes,
e.g. ethylene, propylene, butylenes, etc. Examples of suitable anionic and
potentially anionic
monomers include ethyleniicafy unsaturated carboxylic adds and salts thereof,
ethylenically
unsaturated suiphonic acids and salts thereof, e.g. any one of those mentioned
above.
Suitable water-dispersible anionic organic polymer have an unswollen particle
size of less
than about 1,500 nm in diameter, suitably less than about 1,000 nm and
preferably less
than about 950 nm. Examples of suitable water-dispersible and branched anionic
organic
polymers include those disclosed in U.S. Patent No. 5,167,766 .
Third Anionic Component
The third anionic component according to the invention is an anionic siliceous
material.
Examples of suitable anionic siliceous materials include anionic inorganic
polymers based
on silicic acid and silicates, i.e., anionic silica-based polymers, and days
of smectite type,
preferably anionic polymers based on silicic acid or silicates.
Suitable anionic silica-based polymers can be prepared by condensation
polymerisation of
siliceous compounds, e.g. silicic adds and silicates, which can be
homopolymerised or co-
polymerised. Preferably, the anionic silica-based polymers comprise anionic
silica-based
particles that are in the colloidal range of particle size. Anionic silica-
based particles are
usually supplied in the form of aqueous colloidal dispersions, so-called
aqueous sots. The
silica-based sole can be modified and contain other elements, e.g. aluminium,
boron, nitrogen,
zirconium, gallium and titanium, which can be present in the aqueous phase
and/or in the
silica-based particles. Examples of suitable anionic silica-based particles
include polysdicic
acids, polysilicic acid microgels, polysilicates, polysilicate microgels,
colloidal silica,
colloidal aluminium-modified silica, polyaluminosilicates, polyaluminosilicate
microgels,
poybonurlicates, etc. Examples of suitable anionic silica-based particles
include those
disclosed in U.S. Patent Nos. 4,388,150; 4,927,498; 4,954,220; 4,961,825;
4,980, 025; 5,127,
994; 5,176, 891; 5,368,833; 5,447,604; 5,470,435; 5,543,014; 5,571,494;
5,573,674;
5,584,966; 5,603,805; 5,688,482; and 5,707,493,.
Examples of suitable anionic slice-based particles include those having an
average particle
size below about 100 nm, preferably below about 20 nm and more preferably in
the range of
from about I to about 10 nm. As conventional in the silica chemistry, the
particle size refers to
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the average size of the primary particles, which may be aggregated or non-
aggregated.
Preferably, the anionic silica-based polymer comprises aggregated anionic
silica-based
particles. The specific surface area of the silica-based particles is suitably
at least 50 m2/g and
preferably at least 100 m2/g. Generally, the specific surface area can be up
to about 1700 m2/g
and preferably up to 1000 m2/g. The specific surface area is measured by means
of titration
with NaOH as described by G.W. Sears in Analytical Chemistry 28(1956):12,1981-
1983 and
in U.S. Patent No. 5,176,891 after appropriate removal of or adjustment for
any compounds
present in the sample that may disturb the titration like aluminium and boron
species. The
given area thus represents the average specific surface area of the particles.
In a preferred embodiment of the invention, the anionic silica-based particles
have a specific
surface area within the range of from 50 to 1000 m2/g, more preferably from
100 to 950 m2/g.
Preferably, the silica-based particles are present in a sol having a S-value
in the range of from
8 to 50 %, preferably from 10 to 400, containing silica-based particles with a
specific surface
area in the range of from 300 to 1000 rrrz/g, suitably from 500 to 950 m2/g,
and preferably from
750 to 950 m2/g, which sols can be modified as mentioned above. The S-value is
measured
and calculated as described by liar & Dalton in J. Phys. Chem. 60(1956), 955-
957. The S-
value indicates the degree of aggregation or microgel formation and a lower S-
value is indica-
tive of a higher degree of aggregation.
In yet another preferred embodiment of the invention, the silica-based
particles have a high
specific surface area, suitably above about 1000 m2/g. The specific surface
area can be in the
range of from 1000 to 1700 m2/g and preferably from 1050 to 1600 m2/g.
Examples of suitable days of smectite type include naturally occurring,
synthetic and
chemically treated materials, e.g. montmorillonite, bentonite, hectorite,
beidelite,
nontronite, saponite, sauconite, hormonite, attapulgite and sepiolite,
preferably bentonite.
Suitable days include those disclosed in U.S. Patent Nos. 4,753,710;
5,071,512; and
5,607,552.
Additional Components
It may be desirable to further include additional components in the process of
the present
invention. Preferably, these components are added to the cellulosic suspension
before it is
passed through the last point of high shear, and these components can be added
to the thick
cellulosic suspension or to the thin cellulosic suspension which can be
obtained by mixing the
thick cellulosic suspension with frech water and/or recirculated white water.
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According to a preferred aspect of the invention, the process comprises adding
a cationic
material to the cellulosic suspension before the last point of high shear.
Examples of suitable
cationic materials include cationic organic polymers and cationic inorganic
materials. Examples
of suitable cationic organic polymers include cationic polysaccharides,
cationic synthetic
polymers and cationic organic flocculants. Examples of suitable cationic
inorganic materials
include cationic inorganic coagulants.
Examples of suitable cationic polysaccharides include cationic starches, guar
gums, cellulose
derivatives, chitins, chitosans, glycans, galactans, glucans, xanthan gums,
pectins, mannans,
dextrins, preferably starches, guar gums and cellulose derivatives. Examples
of suitable
starches include potato, corn, wheat, tapioca, rice, waxy maize and barley,
preferably potato.
Examples of suitable cationic synthetic polymers include water-soluble high
molecular weight
cationic synthetic organic polymers, e.g. cationic acrylamide-based polymers;
poly(diallyl-
dialkyl ammonium halides), e.g. poly(diallyldimethyl ammonium chloride);
polyethylene imines;
polyamidoamines; polyamines; and vinylamine-based polymers. Examples of
suitable water-
soluble high molecular weight cationic synthetic organic polymers include
polymers prepared
by polymerization of a water-soluble ethylenically unsaturated cationic or
potentially cationic
monomer or, preferably, a monomer mixture comprising one or more water-soluble
ethylenically unsaturated cationic or potentially cationic monomers and
optionally one or more
other water-soluble ethylenically unsaturated monomers.
Examples of suitable water-soluble ethylenically unsaturated cationic monomers
include diallyl-
dialkyl ammonium halides, e.g. diallyldimethyl ammonium chloride and cationic
monomers
represented by the general structural formula (I):
CH2 = C - R, R2 (I)
O=C-A-B-N+-R3 X
1
R4
wherein R, is H or CH3; R2 and R3 are each H or, preferably, a hydrocarbon
group, suitably
alkyl, having from 1 to 3 carbon atoms, preferably 1 to 2 carbon atoms; A is 0
or NH; B is an
alkyl or alkylene group having from 2 to 8 carbon atoms, suitably from 2 to 4
carbon atoms, or
a hydroxy propylene group; R4 is H or, preferably, a hydrocarbon group,
suitably alkyl,
having from 1 to 4 carbon atoms, preferably 1 to 2 carbon atoms, or a
substituent containing
an aromatic group, suitably a phenyl or substituted phenyl group, which can be
attached to the
nitrogen by means of an alkylene group usually having from 1 to 3 carbon
atoms, suitably 1 to
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2 carbon atoms, suitable R4 including a benzyl group (-CH2-C6H5); and X is an
anionic counter-
ion, usually a halide like chloride.
Examples of suitable monomers represented by the general structural formula
(I) include
quaternary monomers obtained by treating dialkylaminoalkyl (meth)acrylates,
e.g. dimethyl-
aminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate and
dimethylaminohydroxypropyl
(meth)acrylate, and dial kylaminoalkyl (meth)acrylamides, e.g.
dimethylaminoethyl (meth)acryl-
amide, diethylaminoethyl (meth)acrylamide, dimethylaminopropyl
(meth)acrylamide, and
diethylaminopropyl (meth)acrylamide, with methyl chloride or benzyl chloride.
Preferred
cationic monomers of the general formula (I) include dimethylaminoethyl
acrylate methyl
chloride quaternary salt, dimethylaminoethyl methacrylate methyl chloride
quaternary salt,
dimethylaminoethyl acrylate benzyl chloride quaternary salt and
dimethylaminoethyl
methacrylate benzyl chloride quaternary salt.
The monomer mixture can contain one or more water-soluble ethylenically
unsaturated non-
ionic monomers. Examples of suitable non-ionic monomers include acrylamide and
the above-
mentioned non-ionic acrylamide-based and acrylate-based monomers and vinyl
amines. The
monomer mixture can also contain one or more water-soluble ethylenically
unsaturated anionic
or potentially anionic monomers, preferably in minor amounts if present.
Examples of suitable
copolymerizable anionic and potentially anionic monomers include ethylenically
unsaturated
carboxylic acids and salts thereof, and ethylenically unsaturated sulphonic
acids and salts
thereof, e.g. any one of those mentioned above. Examples of preferred
copolymerizable
monomers include acrylamide and methacrylamide, i.e. (meth)acrylamide, and
examples of
preferred high molecular weight cationic synthetic organic polymers include
cationic
acrylamide-based polymer.
The high molecular weight cationic synthetic organic polymers can have a
weight average
molecular weight of at least 500,000, suitably at least about 1 million and
preferably above
about 2 million. The upper limit is not critical; it can be about 30 million,
usually 20 million.
Examples of suitable cationic organic coagulants include cationic polyamines,
polyamideamines, polyethylene imines, dicyandiamide condensation polymers and
low
molecular weight highly cationic vinyl addition polymers. Examples of suitable
cationic
inorganic coagulants include aluminium compounds like alum and polyaluminium
com-
pounds, e.g. polyaluminium chlorides.
Addition of Components
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According to the present invention, the first, second and third anionic
components are added
to the aqueous cellulosic suspension after it has passed through all stages of
high mechanical
shear and prior to drainage. Examples of high mechanical shear stages include
pumping and
cleaning stages. For instance, such shearing stages are included when the
cellulosic
suspension is passed through fan pumps, pressure screens and centri-screens.
Suitably, the
last point of high shear occurs at a centri-screen and, consequently, the
first, second and third
anionic components are suitably added to the cellulosic suspension subsequent
to the centri-
screen. Preferably, after addition of the first, second and third anionic
components the
cellulosic suspension is fed into the headbox of the paper machine which
ejects the
suspension onto the forming wire for drainage.
The first, second and third anionic components can be separately or
simultaneously added to
the cellulosic suspension. When separately adding the components, they can be
added in any
order. Suitably, the first anionic component is added prior to adding the
second and third
anionic components, the second component can be added prior to, simultaneously
with or
after the third component. Alternatively, the first anionic component is
suitably added to the
cellulosic suspension simultaneously with the second anionic component and
then the third
anionic component is added.
When simultaneously adding the components, the first, second and third anionic
components
can be added separately and/or in the form of a mixture. Examples of suitable
simultaneous
additions include adding the three components separately, and adding one of
the components
separately and two of the components in the form of a mixture. The present
invention further
relates to a composition comprising the above-mentioned first, second and
third components
and the use thereof. Suitably, the composition is used as a flocculating agent
in the
production of pulp and paper and for water purification. Preferably, the
composition is
used as a drainage and retention aid in papermaking, optionally in combination
with a cationic
material, e.g. any one of the cationic materials disclosed herein. Preferably,
the composition is
aqueous and the first, second and third anionic components can be present in a
dry matter
content of from 0.01 to 50 % by weight, suitably from 0.1 to 30 % by weight.
The first (1S),
second (2"d) and third (3rd) anionic components can be present in the
composition in a weight
ratio 1St:2"d:3rd of 0.05-10:0.05-10:1, preferably 0.1-2:0.1-2:1. The
composition according to the
invention can be easily prepared by mixing the first, second and third
components, preferably
under stirring.
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WO 2006/123989 13 PCT/SE2006/050090
The first, second and third anionic components according to the invention can
be added to
the cellulosic suspension to be dewatered in amounts which can vary within
wide limits.
Generally, the first, second and third anionic components are added in amounts
that give
better drainage and retention than is obtained when not adding the polymers.
The first
anionic component is usually added in an amount of at least about 0.001 % by
weight,
often at least about 0.005 % by weight, calculated as dry polymer on dry
cellulosic
suspension, and the upper limit is usually about 2.0 and suitably about 1.5 %
by weight.
Likewise, the second anionic component is usually added in an amount of at
least about
0.001 % by weight, often at least about 0.005 % by weight, calculated as dry
polymer on
dry cellulosic suspension, and the upper limit is usually about 2.0 and
suitably about 1.5 %
by weight. Similarly, the third anionic component is usually added in an
amount of at least
about 0.001 % by weight, often at least about 0.005 % by weight, calculated as
dry
additive (usually drySi02 or dry clay) on dry cellulosic suspension, and the
upper limit is
usually about 2.0 and suitably about 1.5 % by weight. When using the
composition
according to the invention, it is usually added in an amount of at least about
0.003 % by
weight, often at least about 0.005 % by weight, calculated as dry matter on
dry cellulosic
suspension, and the upper limit is usually about 5.0 and suitably about 3.0 %
by weight.
When using a cationic material in the process, such a material can be added in
an amount of
at least about 0.001% by weight, calculated as dry material on dry cellulosic
suspension. Suit-
ably, the amount is in the range of from about 0.05 up to about 3.0%,
preferably in the range
from about 0.1 up to about 2.0%.
The process of this invention is applicable to all papermaking processes and
cellulosic
suspensions, and it is particularly useful in the manufacture of paper from a
stock that has a
high conductivity. In such cases, the conductivity of the stock that is
dewatered on the wire is
usually at least about 1.0 mS/cm, preferably at least 3.0 mS/cm, and more
preferably at least
5.0 mS/cm. Conductivity can be measured by standard equipment such as, for
example, a
WTW LF 539 instrument supplied by Christian Berner.
The present invention further encompasses papermaking processes where white
water is
extensively recycled, or recirculated, i.e. with a high degree of white water
closure, for example
where from 0 to 30 tons of fresh water are used per ton of dry paper produced,
usually less
than 20, preferably less than 15, more preferably less than 10 and notably
less than 5 tons of
fresh water per ton of paper. Fresh water can be introduced in the process at
any stage; for
example, fresh water can be mixed with cellulosic fibres in order to form a
cellulosic
suspension, and fresh water can be mixed with a thick cellulosic suspension to
dilute it so as to
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WO 2006/123989 14 PCT/SE2006/050090
form a thin cellulosic suspension to which the first, second and third anionic
components are
subsequently added.
The process according to the invention is used for the production of paper.
The term "paper",
as used herein, of course include not only paper and the production thereof,
but also other
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
cellulosic fibres, and the suspensions should preferably contain at least 25%
and more
preferably at least 50% by weight of such fibres, based on dry substance. The
suspensions
can be based on fibres from chemical pulp, such as sulphate and sulphite pulp,
thermo-
mechanical pulp, chemo-thermomechanical pulp, organosolv pulp, refiner pulp or
groundwood
pulp from both hardwood and softwood, or fibres derived from one year plants
like elephant
grass, bagasse, flax, straw, etc., and can also be used for suspensions based
on recycled
fibres. The invention is preferably applied to processes for making paper from
wood-containing
suspensions.
The suspension also contain mineral fillers of conventional types, such as,
for example, kaolin,
clay, titanium dioxide, gypsum, talc and both natural and synthetic calcium
carbonates, such
as, for example, chalk, ground marble, ground calcium carbonate, and
precipitated calcium
carbonate. The stock can of course also contain papermaking additives of
conventional types,
such as wet-strength agents, sizing agents, such as those based on rosin,
ketene dimers,
ketene multimers, alkenyl succinic anhydrides, etc.
Preferably the invention is applied on paper machines producing wood-
containing paper
and paper based on recycled fibres, such as SC, LWC and different types of
book and
newsprint papers, and on machines producing wood-free printing and writing
papers, the
term wood-free meaning less than about 15% of wood-containing fibres. Examples
of
preferred applications of the invention include the production of paper and
layer of
multilayered paper from cellulosic suspensions containing at least 50 % by
weight of
mechanical and/or recycled fibres. Preferably the invention is applied on
paper machines
running at a speed of from 300 to 3000 m/min and more preferably from 500 to
2500
m/min.
The invention is further illustrated in the following example which, however,
is not intended
to limit the same. Parts and % relate to parts by weight and % by weight,
respectively,
unless otherwise stated.
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WO 2006/123989 15 PCT/SE2006/050090
Example 1
The following components were used in the examples to illustrate the present
invention:
Al: Water-soluble anionic acrylamide-based polymer prepared by polymerisation
of acrylamide (80 mole%) and acrylic acid (20 mole%), the polymer having a
weight average molecular weight of about 12 million and anionic charge
density of about 2.6 meq/g.
A2: Water-dispersible crosslinked anionic acrylamide-based polymer prepared by
polymerisation of acrylamide (30 mole%), acrylic acid (70 mole%) in he
presence of N,N-methylene-bis(meth)acrylamide as a crosslinking agent (350
ppm), the polymer having an anionic charge density of about 8.5 meq/g.
A3: Anionic inorganic condensation polymer of silicic acid in the form of
colloidal
aluminium-modified silica sol having an S-value of about 21 and containing
silica-based particles with a specific surface area of about 800 m2/g.
Al 23: A mixture of the above Al, A2 and A3 in a dry weight ratio Al :A2:A3 of
0.2:0.2:1.
Cl: Cationic polyaluminium chloride with a cationic charge density of about
8.0
meqv/g.
C2: Cationic acrylamide-based polymer prepared by polymerisation of acrylamide
(90 mole%) and acryloxyethyltrimethyl ammonium chloride (10 mole%), the
polymer having a weight average molecular weight of about 6 million and
cationic charge density of about 1.2 meq/g.
C3: Cationic acrylamide-based polymer prepared by polymerisation of acrylamide
(60 mole%) and acryloxyethyltrimethyl ammonium chloride (40 mole%), the
polymer having a weight average molecular weight of about 3 million and
cationic charge of about 3.3 meq/g.
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WO 2006/123989 16 PCT/SE2006/050090
C4: Cationic starch prepared by treating native starch with 2,3-hydroxypropyl
trimethyl ammonium chloride to achieve D.S. 0.11, the polymer having a
cationic charge density of about 0.6 meq/g.
Example 2
Drainage performance was evaluated by means of a Dynamic Drainage Analyser
(DDA),
available from Akribi, Sweden, which measures the time for draining a set
volume of
cellulosic suspension through a wire when removing a plug and applying vacuum
to that
side of the wire opposite to the side on which the cellulosic suspension is
present.
Retention performance was evaluated by means of a nephelometer, available from
Novasina, Switzerland, by measuring the turbidity of the filtrate, the white
water, obtained
by draining the cellulosic suspension. The turbidity was measured in NTU
(Nephelometric
Turbidity Units).
The cellulosic suspension used in the test was based on 75% TMP and 25% DIP
fibre
material and bleach water from a newsprint mill. Consistency was 0.60%, pH was
7.4 and
conductivity of the cellulosic suspension was 1.5 mS/cm.
In order to simulate additions before and after the last points of high shear,
the cellulosic
suspension was stirred in a baffled jar at different stirrer speeds. The
stirring and creation
of high shear conditions were made according to the following:
(i) stirring at 1000 rpm for 25 seconds;
(ii) stirring at 2000 rpm for 10 seconds;
(iii) stirring at 1000 rpm for 15 seconds; and
(iv) dewatering the stock.
Additions to the cellulosic suspension were made as follows (addition levels
in kg/t):
Additions, if any, were made 45, 25, 15, 10 and 5 seconds prior to dewatering,
corresponding to the additions designated Add. 45, Add. 25, Add. 15, Add. 10
and Add. 5,
respectively, of Table 1. The additions designated Add. 15, Add. 10 and Add. 5
were
accordingly made after the last point of high shear.
Table 1 shows the drainage (dewatering) and retention effect observed. In
Table 1, Drain.
Time means drainage (dewatering) time and Turb. means turbidity. The addition
levels are
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WO 2006/123989 17 PCT/SE2006/050090
given as dry additive (calculated as dry polymer, dry A1203 and dry Si02) on
dry cellulosic
suspension.
Test No. 1 shows the result without any additives. Test Nos. 2 to 4 illustrate
processes
employing additives used for comparison and Test Nos. 5 to 15 illustrate
processes
according to the invention.
Table 1
Test Add. Add. Add. Add. Add. Addition Levels at Drain. Turb.
No. 45 25 15 10 5 Add. 45 / Add. 25 / Time [NTU]
Add. 15 /Add. 10 / [s]
Add. 5 [kg/t]
1 - - - - - -/-/-/-/- 65.1 202
2 C1 A2 Al A3 - 2/0.1 /0.1 /0.5/- 51.3 128
3 C1 A3 Al - A2 2/0.5/0.1 /-/0.1 41.0 110
4 C1 Al - A3 A2 2/0.1 /-/0.5/0.1 43.3 150
5 C1 - Al A3 A2 2/-/0.1 /0.5/0.1 39.7 126
6 - C2 Al A3 A2 -/1.5/0.1/0.5/0.1 36.3 95
7 - C2 Al A3 A2 -/2/0.1 /0.5/0.1 21.8 65
8 - C2 Al A2 A3 -/2/0.1 /0.1 /0.5 18.1 69
9 - C2 A2 Al A3 -/2/0.1 /0.5/0.1 18.3 69
- C2 A2 A3 Al -/2/0.1 /0.5/0.1 33.5 76
11 - C2 A3 Al A2 -/2/0.5/0.1 /0.1 19.9 67
12 - C2 A3 A2 Al -/2/0.5/0.1 /0.1 25.7 67
13 - C2 Al+A2 - - -/2/ 20.5 65
+A3 0.1+0.5+0.1
/ - / -
14 - C2 - Al+A2 - -/2/ 18.5 70
+A3 - / 0.1+0.5+0.1
/ -
- C2 - - Al+A2 -/2/ 17.3 67
+A3 -/-/ 0.1+0.5+0.1
As is evident from Table 1, the processes according to the invention provided
improved
drainage and retention performance in view of the comparative processes.
Example 3
I PCT International Application WISE 2006 / 0 5 0 0 9 Q
= 18 1 4 -03- 2007
Drainage performance was evaluated using the procedure according to Example 2.
The
cellulosic suspension used in the tests was based on 75% TMP and 25% DIP fibre
material
and bleach water from a newsprint mill. Consistency was 0.94%, pH was 7.1. and
conductivity of the cellulosic suspension was 1.4 mS/cm.
Table 2 shows the drainage (dewatering) effect observed. The addition levels
are given as
dry additive (calculated as dry polymer and dry Si02) on dry cellulosic
suspension.
Test No. 1 shows the result without any additives. Test Nos. 2 to 7 illustrate
processes
employing additives used for comparison and Test Nos. 8 to 10 illustrate
processes
according to the invention. In Test No. 9, the components Al, A2 and A3 were
separately
added 10 seconds prior to dewatering. In Test No. 10, the components A2 and A3
were
separately added 5 seconds prior to dewatering.
Table 2
Test Add. Add. Add. Add. Add. Addition Levels at Drain.
No. 45 25 15 10 5 Add. 45 / Add. 25 / Time
Add. 15 / Add. 10 / [s]
Add. 5 [kg/t]
1 - - - - - -/-/ /-/- 71.8
2 - C2 - - - -/ 1 /-/-/ 33.2
3 C3 C2 - - - 0.5/1/-/-/- 26.1
4 C3 C2 - - A3 1 / 1 /-/-/0.1 14.3
5 C3 C2 Al A2 - 1/1/0.1/0.1/- 14.2
6 C3 C2 Al - A3 1/1/0.1/-/0.1 12.5
7 C3 C2 - A2 A3 1 / 1 /-/ 0.1 / 0.1 10.2
8 C3 C2 Al A2 A3 1/1/0.1/0.1/0.1 10.0
9 C3 C2 - Al+A2 - 1 / 1 / 9.5
+A3 - / 0.1+0.1+0.1 / -
10 C3 C2 Al - A2+A3 1 / 1 / 0.1 / - / 0.2+0.1 9.3
As is evident from Table 2 the processes according to the invention provided
improved
drainage and retention performance in view of the comparative processes.
Example 4
CA 02608146 2007-11-08 AMENDED SHEET
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WO 2006/123989 19 PCT/SE2006/050090
Retention performance was evaluated using the procedure of Example 2. The
cellulosic
suspension used in the tests was based on 75% TMP and 25% DIP fibre material
and
bleach water from a newsprint mill. Consistency was 0.61%, pH was 7.7 and
conductivity
of the cellulosic suspension was 1.6 mS/cm.
Table 3 shows the retention effect observed. The addition levels are given as
dry additive
(calculated as dry polymer and drySi02) on dry cellulosic suspension.
Test No. 1 shows the result without any additives. Test Nos. 2 to 11
illustrate processes
employing additives used for comparison and Test Nos. 12 to 15 illustrate
processes
according to the invention. In Test No. 13, the components Al, A2 and A3 were
separately added 10 seconds prior to dewatering. In Test Nos. 14 and 15, the
components Al, A2 and A3 were pre-mixed to form the component A123 which was
added 10 and 5 seconds, respectively, prior to dewatering.
Table 3
Test Add. Add. Add. Add. Add. Addition Levels at Turb.
No. 45 25 15 10 5 Add. 45 / Add. 25 / [NTU]
Add. 15 /Add. 10 /
Add. 5 [kg/t]
1 - - - - - -/-/-/-/- 143
2 C3 C4 - - A3 0.5/5/-/-/1 80
3 C3 C4 Al - - 0.5/5/0.2/-/- 84
4 C3 C4 - A2 - 0.5/5/-/0.2/- 76
5 C3 C4 Al - A3 0.5/5/0.2/-/1 76
6 C3 C4 - A2 A3 0.5/5/-/0.2/1 68
7 C3 C4 Al A2 - 0.5/5/0.2/0.2/- 69
8 C3 C4 Al - - 0.5/5/0.4/-/- 79
9 C3 C4 - A2 - 0.5/5/-/0.4/- 71
10 C3 C4 Al - A3 0.5/5/0.1/-/1 77
11 C3 C4 - A2 A3 0.5/5/-/0.4/1 70
12 C3 C4 Al A2 A3 0.5/5/0.2/0.2/1 64
13 C3 C4 - Al +A2 - 0.5 / 5 / 64
+A3 - / 0.2+0.2+1 / -
14 C3 C4 - A123 - 0.5 / 5 / 64
- / 0.2+0.2+1 / -
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WO 2006/123989 20 PCT/SE2006/050090
15 C3 C4 - - A123 0.5 / 5 / 65
-/-/ 0.2+0.2+1
As is evident from Table 3, the processes according to the invention provided
improved
drainage and retention performance in view of the comparative processes.
