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. More
specifically,
the invention relates to a process for the production of paper which comprises
adding first,
second and third polymers to an aqueous 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, referred to as stock, is fed through pumps, screens and
cleaners,
which subject the stock to high shear forces, into a headbox which ejects the
stock onto a
forming wire. Water is drained from the stock 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 stock 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.
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 point of
high shear;
adding at least one polymer having a molecular weight greater than 2,000,000;
and adding
a swellable bentonite clay.
EP 1 238 161 BI discloses a process for making paper or paper board in which a
cellulosic
suspension is flocculated by addition to a thin stock stream of the cellulosic
suspension of
a substantially water-soluble cationic synthetic polymer of intrinsic
viscosity of at least 4
dl/g, wherein the flocculated cellulosic suspension is subjected to mechanical
shearing and
then reflocculated by addition subsequent to the centri-screen of a
reflocculating system
comprising (i) a siliceous material and (ii) a substantially water soluble
anionic polymer of
intrinsic viscosity of at least 4 dl/g. The process is claimed to provide
improvements in
retention and drainage.
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WO 20041015200 discloses a method for producing paper and board by shearing
the
paper material, adding a microparticle system made of cationic polymers and a
fine-
particle inorganic component to the paper material following the last shearing
step before
agglomerating the material, dewatering the paper material so as to form
sheets, and drying
said sheets. The method is claimed to provide improvements in retention and
drainage.
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 all points of high shear:
a first polymer being a cationic polymer having a charge density above 4.0
meq/g;
a second polymer having a molecular weight above 500,000; and
a third polymer being an anionic polymer; and
(iii) dewatering the obtained suspension to form paper.
The present invention is also directed to a process for producing paper which
comprises:
(i) providing an aqueous suspension comprising cellulosic fibres,
(ii) adding to the suspension after all points of high shear:
a first polymer being a cationic, acrylamide-based polymer having a charge
density above 2.5 meq/g;
a second polymer being an acrylamide-based polymer having a molecular
weight above 500,000; and
a third polymer being an anionic polymer; 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 all points of high shear:
a first polymer being a cationic polymer having a charge density above 2.5
meq/g;
a second polymer being a water-dispersible polymer; and
a third polymer being an anionic polymer; and
(iii) dewatering the obtained suspension to form paper.
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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 drainage and retention
aids
comprising first, second and third polymers to a cellulosic suspension after
all points of high
shear and then dewatering the obtained suspension to form paper. The present
invention
provides improvements in drainage and retention in the production of paper
from all types
of stocks, in particular stocks 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.
The term "drainage and retention aids", as used herein, refers to two or more
components
which, when added to an aqueous cellulosic suspension, give better drainage
and
retention than is obtained when not adding the said two or more components.
The first polymer according to the present invention is a cationic polymer
having a charge
density of at least 2.5 meq/g, suitably at least 3.0 meq/g, preferably at
least 4.0 meq/g.
Suitably, the charge density is in the range of from 2.5 to 10.0, preferably
from 3.0 to 8.5
meq/g.
The first polymer can be selected from inorganic and organic cationic
polymers. Preferably,
the first polymer is water-soluble. Examples of suitable first polymers
include
polyaluminium compounds, e.g. polyaluminium chlorides, polyaluminium
sulphates, polyalu-
minium compounds containing both chloride and sulphate ions, polyaluminium
silicate-
sulphates, and mixtures thereof.
Further examples of suitable first polymers include cationic organic polymers,
e.g. cationic
acrylamide-based polymers; poly(diallyldialkyl ammonium halides), e.g.
poly(diallyldimethyl
ammonium chloride); polyethylene imines; polyamidoamines; polyamines; and
vinylamine-
based polymers. Examples of suitable cationic organic polymers include
polymers prepared
by polymerization of a water-soluble ethylenically unsaturated cationic
monomer or,
preferably, a monomer mixture comprising one or more water-soluble'
ethylenically
unsaturated cationic monomers and' optionally one or more other water-soluble
ethylenically
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unsaturated monomers. Examples of suitable water-soluble ethylenically
unsaturated cationic
monomers include diallyldialkyl ammonium halides, e.g. diallyldimethyl
ammonium chloride
and cationic monomers represented by the general structural formula (I):
CH2 = C - R1 R2 (I)
1
O=C-A-B-N+-R3 X
R4
wherein R1 is H or CH3; R2 and R3 are each H or, preferably, a hydrocarbon
group, suitably
alkyl, having from I 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 I 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 I to 3 carbon
atoms, suitably
1 to 2 carbon atoms, suitable R4 including a benzyl group (-CH2-C6H5); and X
is an anionic
counterion, 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 dialkylaminoalkyl (meth)acrylamides, e.g.
dimethylaminoethyl (meth)-
acrylamide, 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 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-isopropyl (meth)acrylamide, N-n-butyl (meth)acrylamide, N-
t-butyl
(meth)acrylamide and N-isobutyl (meth)acrylamide; N-alkoxyalkyl
(meth)acrylamides, e.g. N-
n-butoxymethyl (meth)acrylamide, and N-isobutoxymethyl (meth)acrylamide; N,N-
dialkyl
(meth)acrylamides, e.g. N,N-dimethyl (meth)acrylamide; dialkylaminoalkyl
(meth)
acrylamides; acrylate-based monomers like dialkylaminoalkyl (meth)acrylates;
and
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vinylamines. The monomer mixture can also contain one or more water-soluble
ethylenically
unsaturated anionic or potentially anionic monomers, preferably in minor
amounts. 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
5 to the cellulosic suspension. Examples of suitable copolymerizable anionic
and potentially
anionic monomers include ethylenically unsaturated carboxylic 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-
methylpropanesulphonate,
sulphoethyl-(meth)acrylate, vinylsulphonic acid and salts thereof,
styrenesuiphonate, and
paravinyl phenol (hydroxy styrene) and salts thereof. Examples of preferred
copolymerizable
monomers include acrylamide and methacrylamide, i.e. (meth)acrylamide, and
examples of
preferred cationic organic polymers include cationic acrylamide-based polymer,
ie. a cationic
polymer prepared. from a monomer mixture comprising one or more of acrylamide
and
acrylamide-based monomers
The first polymer in the form of a cationic organic polymer can have a weight
average
molecular weight of at least 10,000, often at least 50,000. More often, it is
at least 100,000
and usually at least about 500,000, suitably at least about I million and
preferably above
about 2 million. The upper limit is not critical; it can be about 30 million,
usually 20 million.
The second polymer according to the present invention is preferably an organic
polymer
which can be selected from non-ionic, cationic, anionic and amphoteric
polymers. The
second polymer can be water-soluble or water-dispersible. Suitably, the second
polymer is
prepared by polymerization of one or more ethylenically unsaturated monomers,
preferably
one or more water-soluble ethylenically unsaturated monomers. Examples of
preferred
second polymers include acrylamide-based polymers.
Examples of suitable second polymers include water-soluble and water-
dispersible non-ionic
organic polymers obtained by polymerizing 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 vinylamines. Examples of preferred non-ionic monomers include,
acrylamide
and methacrylamide, i.e., (meth)acrylamide, and examples of preferred second
polymers
include non-ionic acrylamide-based polymer.
Further examples of suitable second polymers include cationic organic polymers
obtained by
polymerizing a water-soluble ethylenically unsaturated cationic monomer or,
preferably, a
monomer mixture comprising one or more water-soluble ethylenically unsaturated
cationic
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monomers and optionally one or more other water-soluble ethylenically
unsaturated
monomers. Examples of suitable cationic monomers include those represented by
the
above-mentioned general structural formula (I), wherein R1, R2, R3, R4, A, B
and X are as
defined above, and diallyldialkyl ammonium halides, e.g. diallyldimethyl
ammonium chloride.
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 vinylamines. The monomer mixture can also contain one or more
water-
soluble ethylenically unsaturated anionic or potentially anionic monomers,
preferably in minor
amounts. 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,,
Le.' (meth)acrylamide, and examples of preferred second polymers include
cationic
acrylamide-based polymer.
Further examples of suitable second polymers include anionic organic polymers
obtained by
polymerizing 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. 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. any one of
those mentioned
above. 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 vinylamines. The monomer mixture can also contain one or more
water-
soluble ethylenically unsaturated cationic and potentially cationic monomers,
preferably in
minor amounts. 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
copolymerizable
cationic and potentially cationic monomers include the monomers represented by
the above
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 second polymers include anionic
acrylamide-
based polymer.
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Further examples of suitable second polymers include amphoteric organic
polymers obtained
by polymerizing a monomer mixture comprising one or more water-soluble
ethylenically
unsaturated anionic or potentially anionic monomers and 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 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 suitable cationic and potentially cationic
monomers include
the monomers represented by the above general structural formula (I) and
diallyidialkyl
ammonium halides, e.g. diallyldimethyl ammonium chloride. 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
vinylamines.
Examples of preferred copolymerizable monomers include (meth)acrylamide, and
examples
of preferred second polymers include amphoteric acrylamide-based polymer.
In preparing suitable second polymers, the monomer mixture can also contain
one or more
polyfunctional crosslinking agents in addition to the above-mentioned
ethylenically
unsaturated monomers. The presence of a polyfunctional crosslinking agent in
the monomer
mixture renders possible preparation of second polymers that are water-
dispersible. The
polyfunctional crosslinking agents can be non-ionic, cationic, anionic or
amphoteric.
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. Suitable
water-dispersible
second 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 suitable water-
dispersible organic
polymers include those disclosed in U.S. Patent No. 5,167,766, which is hereby
incorporated
herein by reference. Further examples of suitable second polymers include
water-dispersible
anionic, cationic and amphoteric organic polymers, and preferred second
polymers include
water-dispersible anionic organic polymers, preferably water-dispersible
anionic acrylamide-
based polymers.
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The second polymers according to the invention, preferably second polymers
that are water-
soluble, can have a weight average molecular weight of at least about 500,000.
Usually, the
weight average molecular weight is at least about 1 million, suitably at least
about 2 million
and preferably at least about 5 million. The upper limit is not critical; it
can be about 50
million, usually 30 million.
The second polymer according to the invention can have a charge density less
than about
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
1'D 10.0, preferably from 1.0 to 4.0 meqIg. Suitable second polymers include
anionic organic
polymers having a charge density less than 10.0 meq/g, suitably less than 6.0
meq/g,
preferably less than 4.0 meq/g. Suitable second polymers further include
cationic organic
polymers having a charge density less than 6.0 meq/g, suitably less than 4.0
meq/g,
preferably less than 2.0 meq/g.
The third polymer according to the present invention is an anionic polymer
which can be
selected from inorganic and organic anionic polymers. Examples of suitable the
third
polymers include water-soluble and water-dispersible inorganic and organic
anionic
polymers.
Examples of suitable third polymers include inorganic anionic polymers based
on silicic acid
and silicate, i.e., anionic silica-based polymers. Suitable anionic silica-
based polymers can
be prepared by condensation polymerisation of siliceous compounds, e.g.
silicic acids 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 sols. The silica-based sols 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 polysilicic acids, polysilicic acid
microgels,
polysilicates, polysilicate microgels, colloidal silica, colloidal aluminium-
modified silica,
polyaluminosilicates, polyaluminosilicate microgels, polyborosilicates, 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.
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Examples of suitable anionic silica-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 1 to about 10 nm. As conventional in the silica chemistry, the
particle size refers
to 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 40%, containing silica-based particles
with a specific
surface area in the range of from 300 to 1000 m2/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 Her & 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 indicative 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.
Further examples of suitable third polymers include water-soluble and water-
dispersible
organic anionic polymers obtained by polymerizing an ethylenically unsaturated
anionic or
potentially anionic monomer or, preferably, a monomer mixture comprising one
or more
ethylenically unsaturated anionic or potentially anionic monomers, and
optionally one or more
other ethylenically unsaturated. monomers. Preferably, the ethylenically
unsaturated
monomers are water-soluble. Examples of suitable anionic and potentially
anionic monomers
include ethylenically unsaturated carboxylic acids and salts thereof,
ethylenically unsaturated
sulphonicacids and salts thereof, e.g. any one of those mentioned above. 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
CA 02592314 2010-03-30
vinylamines. The monomer mixture can also contain one or more water-soluble
ethylenically
unsaturated cationic and potentially cationic monomers, preferably in minor
amounts:
Examples of suitable copolymerizable'cationic monomers include the monomers
represented
by the above general structural formula (1) and diallyldialkyl ammonium
halides, e.g. diallyl-
5 dimethyl ammonium chloride. The Monomer mixture can' also contain one or
more
polyfunctional crosslinking agents. The presence of a polyfunctional
crosslinking agent in the
monomer mixture renders possible preparation of third polymers that are water-
dispersible.
Examples of suitable polyfunctional crosslinking agents including the above-
mentioned
polyfunctional crosslinking agents. These agents can be used in the. above-
mentioned
10 amounts. Examples, of suitable water-dispersible organic anionic polymers
include those
disclosed in U.S. Patent No. 5,167,766. Examples of preferred copolymerizable
monomers include (meth)acrylamide, and examples of preferred third polymers
include water-soluble and water-dispersible anionic acrylamide-based polymers.
The third polymer being an organic anionic polymer according to the invention,
preferably an
organic anionic polymer that is water-soluble, has a weight average molecular
weight of at
- least about 500,000. Usually, the weight average molecular weight is at
least about I million,
suitably at least about 2 million and preferably at least about 5 million. The
upper limit is not
critical; it can be about 50 million, usually 30 million.
The third polymer being an organic anionic polymer can have a charge density
less than
about 14 meq/g, suitably less than about 10 meq/g, preferably less than about
4 meq/g.
Suitably, the charge density is in the range of from 1.0 to 14.0, preferably
from 2.0 to 10.0
meq/g.
Examples of preferred drainage and retention aids according to the invention
include:
(i) first polymer being cationic acrylamide-based polymer, second polymer
being
cationic acrylamide-based polymer, and third polymer being anionic silica-
based
particles;
(ii) first polymer being cationic polyaluminium compound, second polymer being
cationic acrylamide-based polymer, and third polymer being anionic silica-
based
particles;
(iii) first polymer being cationic acrylamide-based polymer, second polymer
being
water-soluble or water-dispersible anionic acrylamide-based polymer, and third
polymer being anionic silica-based particles:
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(iv) first polymer being cationic polyaluminium compound, second polymer being
water-
soluble or water-dispersible anionic acrylamide-based polymer, and third
polymer
being anionic silica-based particles;
(v) first polymer being cationic acrylamide-based polymer, second polymer
being
cationic acrylamide-based polymer, and third polymer being water-soluble or
water-
dispersible anionic acrylamide-based polymer; and
(vi) first polymer being cationic polyaluminium compound, second polymer being
cationic acrylamide-based polymer, and third polymer being water-soluble or
water-
dispersible anionic acrylamide-based polymer.
According to the present invention, the first, second and third polymers 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 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 polymers
are suitably added subsequent to the centri-screen. Preferably, after addition
of the first,
second and third polymers the cellulosic suspension is fed into the headbox
which ejects the
suspension onto the forming wire for drainage,
It may be desirable to further include additional materials in the process of
the present
invention. Preferably, these materials are added to the cellulosic suspension
before it is
passed through the last point of high shear. Examples of such additional
materials include
starches, e.g. cationic, anionic and amphoteric starch, preferably cationic
starch; water-
soluble organic polymeric coagulants, e.g. cationic polyamines,
polyamideamines,
polyethylene imines, dicyandiamide condensation polymers and low molecular
weight highly
cationic vinyl addition polymers; and inorganic coagulants, e.g. aluminium
compounds, e.g.
alum and polyaluminium compounds.
The first, second and third polymers can be separately added to the cellulosic
suspension.
Suitably, the first polymer is added to the cellulosic suspension prior to
adding the second
and third polymers. The second polymer can be added prior to, simultaneously
with or after
adding the third polymer. Alternatively, the first polymer is suitably added
to the cellulosic
suspension simultaneously with the second polymer and then the third polymer
is added.
The first, second and third polymers 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 polymers are added in amounts that give
better
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12
drainage and retention than is obtained when not adding the polymers. The
first polymer 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
polymer 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
polymer 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 or dry Si02 on dry cellulosic suspension,
and the upper
limit is usually about 2.0 and suitably about 1.5 % by weight.
When using starch and/or cationic coagulant in the process, such additives can
be added in
an amount of at least about 0.001% by weight, calculated as dry additive on
dry cellulosic
suspension. Suitably, the amount is in the range of from about 0.05 up to
about 3.0%, prefer-
ably 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 1.5 mS/cm, preferably at least 3.5 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 fibers in
order to form a
cellulosic suspension, and fresh water can be mixed with a thick cellulosic
suspension to
dilute it so as to form a thin cellulosic suspension to which the first,
second and third
polymers are 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 fibers, and the suspensions should preferably contain at least 25%
and more
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13
preferably at least 50% by weight of such fibers, based on dry substance. The
suspensions
can be based on fibers 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 fibers derived from one
year plants
like elephant grass, bagasse, flax, straw, etc., and can also be used for
suspensions based
on recycled fibers. 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 fibers, 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 fibers. 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.
Examples
The following additives were used in the examples:
C-PAM 1: Cationic acrylamide-based polymer prepared by polymerisation of
acrylamide
(40 mole%) and acryloxyethyltrimethyl ammonium chloride (60 mole%), the
polymer having a weight average molecular weight of about 3 million and
cationic charge density of about 4.2 meq/g.
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C-PAM 2: 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.
C-PAM 3: Cationic acrylamide-based polymer prepared by polymerisation of
acrylamide
(88 mole%), acryloxyethyltrimethyl ammonium chloride (10 mole%) and
dimethyl acrylamide (2 mole%), the polymer having a weight average
molecular weight of about 6 million and cationic charge density of about 1.2
meq/g.
C-PAM 4: 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.
PAC: Cationic polyaluminium chloride with a cationic charge density of about
8.0
meq/g
C-PAI 1: Cationic polyamine having a weight average molecular weight of about
200,000 and cationic charge density of about 7 meq/g.
C-PAI 2: Cationic polyamine having a weight average molecular weight of about
400,000 and cationic charge density of about 7 meq/g.
A-PAM: 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.
A-X-PAM: Anionic crosslinked acrylamide-based polymer prepared by
polymerisation of
acrylamide (30 mole%) and acrylic acid (70 mole%), the polymer having a
weight average molecular weight of about 100,000 and anionic charge
density of about 8.0 meq/g.
Silica: 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.
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Bentonite: Bentonite
Example 1
5
Drainage (dewatering) 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 stock through a wire when removing a plug and applying vacuum to
that side of
the wire opposite to the side on which the stock is present.
The stock used in the tests was based on 75% TMP and 25% DIP fibre material
and
sedimented white water from a newsprint mill. Stock consistency was 0.78%.
Conductivity
of the stock was 1.5 mS/cm and pH was 6.8.
In order to simulate additions after all points of high shear, the stock was
stirred in a
baffled jar at different stirrer speeds. Stirring and additions were made
according to the
following:
(i) stirring at 1000 rpm for 20 seconds,
(ii) stirring at 2000 rpm for 10 seconds,
(iii) stirring at 1000 rpm for 15 seconds while making additions, and
(iv) dewatering the stock while automatically recording the dewatering time.
Additions to the stock were made as follows: The first addition (addition
level of 5kg/t) was
made 15 seconds prior to dewatering, the second addition (addition level of
0.8 kg/t) was
made 10 seconds prior to dewatering and the third addition (addition level of
0.5 kg/t) was
made 5 seconds prior to dewatering.
Table I shows the dewatering times at different modes of addition. The polymer
and
bentonite addition levels were calculated as dry product on dry stock system,
and the sol of
silica-based particles were calculated as Si02 and based on dry stock system.
Test No. I shows the result without any additives. Test Nos. 2 to 4 illustrate
processes
used for comparison and Test Nos. 5 to 7 illustrate processes according to the
invention.
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Table 1
Test First Second Third Dewatering
No. Addition Addition Addition Time [s]
1 - - - 60.6
2 C-PAI 1 C-PAM 4 Bentonite 24.5
3 C-PAI 1 C-PAM 4 Bentonite 24.4
C-PAI 2
(1:1)
4 - C-PAM 4 Bentonite 32.4
C-PAM I C-PAM 3 Silica 22,4
6 C-PAM 2 C-PAM 4 Silica 21.2
7 C-PAM 2 C-PAM 3 Silica 19.0
Table I shows that the process according to the present invention resulted in
improved
5 dewatering.
Example 2
Drainage performance was evaluated using the DDA according to Example 1.
The stock used in the test was based on 75% TMP and 25% DIP fibre material and
bleach
water from a paper mill. Stock consistency was 0.77%. Conductivity of the
stock was 1.6
mS/cm and pH was 7.2.
In order to simulate additions prior to and after all points of high shear,
the stock was
stirred in a baffled jar at different stirrer speeds. Stirring and additions
were made
according to the following:
(i) stirring at 1000 rpm for 25 seconds while making from 0 to 2 additions,
(ii) stirring at 2000 rpm for 10 seconds,
(iii) stirring at 1000 rpm for 15 seconds while making from 0 to 3 additions,
and
(iv) dewatering the stock while automatically recording the dewatering time.
Additions to the stock were made as follows: The first addition, if any, was
made 45 or 15
seconds prior to dewatering, the second addition, if any, was made 25 or 10
seconds prior
to dewatering and the third addition, if any, was made 5 seconds prior to
dewatering.
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Table 2 shows the dewatering times at different modes of addition. Addition
times are
given in seconds prior to dewatering and addition levels are given in kg/t for
the first,
second and third additions (1st / 2nd / 3rd) respectively. The polymer
addition levels were
calculated as dry product on dry stock system, and the silica-based particles
were
calculated as SiO2 and based on dry stock system.
Test No. I shows the result without any additives. Test Nos. 2 to 7 illustrate
processes
used for comparison and Test Nos. 8 to 10 illustrate processes according to
the invention.
Table 2
Test First Second Third Addition Addition Dewatering
No. Addition Addition Addition Times [s] Levels [kglt] Time [s]
1st / 2nd /3 rd 1st / 2nd 13 rd
I - - - - - 84.0
2 C-PAM 2 C-PAM 4 Silica 45 / 25 / 5 0.1 / 0.2 / 0.5 61.8
3 C-PAM 2 C-PAM 4 Silica 45/25/5 0.2/0.2/0.5 50.2
4 C-PAM 2 C-PAM 4 Silica 45/25/5 0.1 /0.5/0.5 39.0
5 C-PAM 2 C-PAM 4 Silica 45 / 10 / 5 0.1 /-0.2 / 0.5 56.0
6 C-PAM 2 C-PAM 4 Silica 45 / 10 / 5 0.2 / 0.2 / 0.5 46.0
7 C-PAM 2 C-PAM 4 Silica 45/10/5 0.1 /0.5/0.5 32.1
8 C-PAM 2 C-PAM 4 Silica 15/10/5 0.1 /0.2/0.5 48.2
9 C-PAM 2 C-PAM 4 Silica 15/10/5 0.2/0.2/0.5 43.8
10 C-PAM2 C-PAM4 Silica 15/10/5 0.1 /0.5/0.5 31.0
It is evident from Table 2 that the process according to the present invention
resulted in
improved dewatering.
Example 3
Drainage performance was evaluated according to the procedure of Example 2.
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 stock. The turbidity was measured in NTU (Nephelometric
Turbidity Units).
The stock and modes of stirring and addition used in Example 2 were similarly
used in this
example.
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Table 3 shows the dewatering effect at different modes of addition. Test No. I
shows the
result without any additives. Test Nos. 2 and 3 illustrate processes used for
comparison
and Test No. 4 illustrates the process according to the invention.
Table 3
Test First Second Third Addition Addition Dewatering Turbidity
No. Addition Addition Addition Times [s] Levels [kg/t] Time [s] [NTU]
1st / 2nd / 3rd 1st / 2nd / 3rd
1 - - 84.0 100
2 C-PAM 2 A-PAM Silica 45 / 25 / 5 0.8 / 0.210.5 66.0 31
3 C-PAM 2 A-PAM Silica 45 / 10 / 5 0.8 / 0.2 / 0.5 61.9 32
4 C-PAM 2 A-PAM Silica 15/1015 0.810.210.5 53.2 26
Table 3 shows that process of the present invention resulted in improved
drainage
performance.
Example 4
Drainage and retention performance was evaluated according to the procedure of
Example
3. The stock and modes of stirring and addition used in Example 2 were
similarly used in
this example.
Table 4 shows the dewatering effect at different modes of addition. Test No. I
shows the
result without any additives. Test Nos. 2 to 7 illustrate processes used for
comparison and
Test Nos. 8-9 illustrate processes according to the invention.
Table 4
Test First Second Third Addition Addition Dewatering Turbidity
No. Addition Addition Addition Times [s] Levels [kg/t] Time [s] [NTU]
1st12nd/ 3rd 1st/ 2nd/3rd
84.0 100
2 C-PAM 2 - A-PAM 451-15 0.21-10.3 148.0 76
3 C-PAM 2 - A-PAM 15/45 0.2/-10.3 162.4 58
4 - C-PAM 4 A-PAM - /25/,' - / 0.8 / 0.3 101.0 18
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19
- C-PAM4 A-PAM -/10/5 -/0.8/0.3 82.2 26
6 C-PAM 2 C-PAM 4 A-PAM 45 / 25 / 5 0.210.8 / 0.2 77.4 20
7 C-PAM 2 C-PAM 4 A-PAM 45/10/5 0.2/0.8/0.3 60.0 22
8 C-PAM 2 C-PAM 4 A-PAM 15/1015 0.2 / 0.8 / 0.2 49.0 17
9 C-PAM 2 C-PAM 4 A-PAM 15 / 10 / 5 0.2 / 0.810.31 52.5 20
Table 4 shows that the process according to the present invention resulted in
improved
drainage (dewatering) and retention performance.
5 Example 5
Drainage and retention performance was evaluated according to the procedure of
Example
3. The modes of stirring and addition used in Example 2 were similarly used in
this
example.
The stock used in this example was based on 75% TMP and 25% DIP fibre material
and
bleach water from a newsprint mill. Stock consistency was 0.82%. Conductivity
of the stock
was 1.7 mS/cm and pH was 7.2.
Table 5 shows the dewatering effect at different modes of addition. Test No. 1
shows the
result without any additives. Test Nos. 2 to 8 illustrate processes used for
comparison and
Test No. 9 illustrates the process according to the invention.
Table 5
Test First Second Third Addition Addition Dewatering Turbidity
No. Addition Addition Addition Time [s] Levels [kg/t] Time [s] [NTU]
1st/ 2nd/ 3rd 1st/ 2nd/ 3rd
1 - - - - - 93.9 82
2 - C-PAM 4 Silica - 1 25 / 5 -/0.2/0.5 67.7 58
3 - C-PAM 4 Silica - / 10 / 5 -/0.2/0.5 60.7 68
4 PAC - Silica 45/45 21-10.5 88.5 62
5 PAC - Silica 151-/5 2/-/0.5 83.5 73
6 PAC C-PAM 4 - 45/25/- 2/0.2/- 51.8 52
7 PAC C-PAM 4 - .45/10/- 2/0.21- 54.5 56
8 PAC C-PAM 4 Silica 451 10 / 5 2/0.2/0.5 54.6 51
9 PAC C-PAM 4 Silica 15110/5 2/0.2/0.5 51.2 48
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Table 5 shows that the process according to the present invention resulted in
improved
drainage (dewatering) and retention performance.
5 Example 6
Drainage performance was evaluated according to the procedure of Example 2.
The stock
and modes of stirring and addition used in Example 5 were similarly used in
this example.
10 Table 6 shows the dewatering effect at different modes of addition. Test
No. 1 shows the
result without any additives. Test Nos. 2 to 6 illustrate processes employing
additives used
for comparison (Ref.) and Test No. 7 illustrates the process according to the
invention.
Table 6
Test First Second Third Addition Addition Dewatering
No. Addition Addition Addition Time [s] Levels [kg/t] Time [s]
1st / 2nd /3 rd 1st, 2nd 13rd
1 - - - - - 93.9
2 PAC C-PAM 4 - 45 / 25 / - 2 / 0.2 / - 51.8
3 PAC C-PAM4 - 45/10/- 2/0.2/- 54.5
4 PAC C-PAM 4 - 15 / 10 / - 210.2 / - 48.7
5 PAC C-PAM 4 A-X-PAM 45 / 25 / 5 210.2/0.1 44.8
6 PAC C-PAM 4 A-X-PAM 45 / 10 / 5 210.2/0.1 43.9
7 PAC C-PAM 4 A-X-PAM 15 / 10 / 5 210.2/0.1 42.9
Table 6 shows that the process according to the invention resulted in improved
dewatering
performance.
Example 7
Drainage performance was evaluated according to the procedure of Example 2.
The stock
and modes of stirring and addition used in Example 5 were similarly used in
this example.
Table 7 shows the dewatering effect at different modes of addition. Test No. I
shows the
result without any additives. Test Nos. 2 to 7 illustrate processes used for
comparison and
Test No. 8 illustrates the process according to the invention.
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Table 7
Test First Second Third Addition Addition Dewatering
No. Addition Addition Addition Time [s] Levels [kg/t] Time [s]
1st12nd/ 3rd 1st/ 2nd/ 3rd
1 - - - - 93.9
2 PAC - A-PAM 45145 0.21-10.1 185.0
3 PAC - A-PAM 15/45 0.2/-10.1 96.8
4 - C-PAM 4 A-PAM - / 25 / 5 -/0.8/0.1 76.5
- C-PAM4 A-PAM -/10/5 -/0.810.1 55.1
6 PAC C-PAM 4 A-PAM 45 / 25 / 5 0.210.8 10.1 107.0
7 PAC C-PAM 4 A-PAM 45 / 10 / 5 0.210.8 / 0.1 61.5
8 PAC C-PAM 4 A-PAM 15/1015 0.2 / 0.8 / 0.1 39.8
Table 7 shows that the process according to the invention resulted in improved
dewatering
5 performance.
