U.S. patent application number 10/066077 was filed with the patent office on 2002-11-14 for process for manufacturing paper.
Invention is credited to Andersson, Kjell, Frolich, Sten, Johansson-Vestin, Hans, Lindgren, Erik, Solhage, Fredrik.
Application Number | 20020166648 10/066077 |
Document ID | / |
Family ID | 43706171 |
Filed Date | 2002-11-14 |
United States Patent
Application |
20020166648 |
Kind Code |
A1 |
Frolich, Sten ; et
al. |
November 14, 2002 |
Process for manufacturing paper
Abstract
The invention relates to a process for manufacturing paper and
board comprising providing a suspension comprising cellulosic
fibres and at least a sizing agent, dewatering said suspension
thereby forming a paper-web, whereby an aromatic-containing
cationic vinyl addition polymer, and an anionic polymer having a
weight average molecular weight of up to about 500,000 selected
from the group consisting of vinyl addition polymers and
condensation polymers is added separately to the suspension.
Inventors: |
Frolich, Sten; (Askim,
SE) ; Solhage, Fredrik; (Kode, SE) ; Lindgren,
Erik; (Bohus, SE) ; Johansson-Vestin, Hans;
(Kungalv, SE) ; Andersson, Kjell; (Goteborg,
SE) |
Correspondence
Address: |
LAINIE E. PARKER
AKZO NOBEL INC.
7 LIVINGSTONE AVENUE
DOBBS FERRY
NY
10522-3408
US
|
Family ID: |
43706171 |
Appl. No.: |
10/066077 |
Filed: |
January 31, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10066077 |
Jan 31, 2002 |
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09923096 |
Aug 6, 2001 |
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60249365 |
Nov 16, 2000 |
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60223367 |
Aug 7, 2000 |
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60223368 |
Aug 7, 2000 |
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60223369 |
Aug 7, 2000 |
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Current U.S.
Class: |
162/168.2 ;
162/158; 162/164.5; 162/168.3; 162/183 |
Current CPC
Class: |
D21H 23/10 20130101;
D21H 23/00 20130101; D21H 17/45 20130101; D21H 27/42 20130101 |
Class at
Publication: |
162/168.2 ;
162/168.3; 162/183; 162/164.5; 162/158 |
International
Class: |
D21H 017/45; D21H
027/42; D21H 023/00; D21H 023/10 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 16, 2000 |
EP |
00850195.9 |
Aug 7, 2000 |
EP |
00850135.5 |
Aug 7, 2000 |
EP |
00850136.3 |
Aug 7, 2000 |
EP |
00850137.1 |
Claims
1. A process for manufacturing paper and board comprising providing
a suspension comprising cellulosic fibres and at least a sizing
agent, dewatering said suspension thereby forming a paper-web,
wherein i) an aromatic-containing cationic vinyl addition polymer
is added to the suspension in an amount of from about 0.005% by
weight up to about 1.0% by weight based on dry pulp, and ii) an
anionic polymer having a weight average molecular weight of up to
about 500,000 selected from the group consisting of vinyl addition
polymers and condensation polymers is added to the suspension in an
amount of from about 0.001% by weight up to about 3.0% by weight
based on dry pulp, whereby the aromatic-containing cationic vinyl
addition polymer and the anionic polymer are added separately to
the suspension.
2. A process according to claim 1, wherein the anionic polymer has
a weight average molecular weight in the range from about 10,000 up
to about 100,000.
3. A process according to claim 2, wherein the weight average
molecular weight is in the range from about 15,000 up to about
75,000.
4. A process according to claim 1, wherein the anionic polymer
comprises aromatic monomers having sulphonate groups.
5. A process according to claim 1, wherein the anionic polymer is a
vinyl addition polymer having a weight average molecular weight of
up to about 500,000.
6. A process according to claim 5, wherein the anionic vinyl
addition polymer comprises aromatic monomers.
7. A process according to claim 6, wherein the aromatic monomers
have at least one sulphonate group.
8. A process according to claim 5, wherein the anionic vinyl
addition polymer is polystyrene sulphonate.
9. A process according to claim 1, wherein the aromatic-containing
cationic vinyl addition polymer has a weight average molecular
weight of at least about 500,000.
10. A process according to claim 1, wherein the cationic vinyl
addition polymer is prepared from a reaction mixture comprising
from about 1 up to 99 mole % of a cationic monomer having an
aromatic group.
11. A process according to claim 11, wherein the cationic monomer
having an aromatic group is represented by formula (I) 4wherein
R.sub.1 is H or CH.sub.3; R.sub.2 and R.sub.3 are independently
from another a hydrogen or an alkyl group having from 1 to 3 carbon
atoms; A.sub.1 is 0 or NH; B.sub.1 is an alkylene group having from
2 to 8 carbon atoms; Q is a substituent containing an aromatic
group; and X is an anionic counterion.
Description
[0001] This application is a continuation of application Ser. No.
09/923,096, filed Aug. 6, 2001, which claims priority of EPO
Application Nos. 00850195.9, filed Nov. 16, 2000, 00850135.5, filed
Aug. 7, 2000, 00850136.3, filed Aug. 7, 2000, and 00850137.1, filed
Aug. 7, 2000, and U.S. Provisional Application No. 60/249,365,
filed Nov. 16, 2000, No. 60/223,367, filed Aug. 7, 2000, No.
60/223,368, filed Aug. 7, 2000, and No. 60/223,369, filed Aug. 7,
2000.
[0002] The present invention refers to a process for manufacturing
paper and board comprising the addition of two different polymers
to an aqueous cellulose-containing suspension one being an
aromatic-containing cationic vinyl addition polymer and the other
an anionic vinyl addition polymer having a weight average molecular
weight of up to 500,000.
BACKGROUND
[0003] Internal sizing agents are usually added to the wet end of
the paper making process whereby the adsorption capability of the
paper of liquids is decreased. Commonly used internal sizing agents
are sizing agents based on rosin derivatives and cellulose-reactive
sizing agents, notably ketene dimers and acid anhydrides.
Multipurpose office paper need to be rather heavily sized in order
to function properly in today's high speed reproducing machines.
One way of attaining paper which is fully sized, i.e. having a
cobb.sub.60 number below 30 or measuring the contact angle of a
water droplet on the paper where angles larger the 80 degrees after
10 seconds indicate good sizing, is to add more sizing agent to the
suspension. However, the likelihood of ending up with runability
problems in the paper mill increases as well as the production
costs.
[0004] Apart from the addition of sizing agents to the pulp
suspension, dewatering and retention agents are also added to the
suspension. As the name indicates, the latter agents enhance both
dewatering and retention of the pulp suspension. According to the
present invention it has surprisingly been found that sizing
efficiency is improved by the addition of at least two different
types of polymers to the pulp suspension which polymers
simultaneously function as dewatering and retention agents.
[0005] According to the present invention it has been found that
specifically improved sizing can be obtained by a process for
manufacturing paper and board comprising providing a suspension
comprising cellulose and at least a sizing agent, dewatering said
suspension thereby forming a paper-web, whereby an
aromatic-containing cationic vinyl addition polymer, and an anionic
polymer having a weight average molecular weight of up to 500,000
selected from the group consisting of vinyl addition polymers and
condensation polymers vinyl addition polymer are added separately
to the suspension.
DETAILED DESCRIPTION OF THE INVENTION
[0006] The present invention is not restricted to specific types of
cellulose suspensions, but can be applied on cellulose suspensions
containing virgin or recycled pulp and different fillers such as
calcium carbonate. The pH of the suspension may also vary from
being acidic, which is the case if sizing agents derived from
rosins are used, to being neutral or alkaline. If
cellulose-reactive sizing agents are used the pH of the cellulose
suspension is neutral to alkaline, i.e. in the range from about 5
up to about 10, which also makes it possible to include inorganic
filler materials in the suspension, e.g. precipitated calcium
carbonate and clays. The two different polymers are suitable added
to a fairly diluted lignocellulose-containing suspension commonly
referred to as the thin stock having a concentration of from 0.1 up
to 3.0% by weight based on dry fibres.
[0007] The process is furthermore not dependent on the type of
sizing agent added, thus, any sizing agent or mixture of sizing
agents may be present in the cellulose suspension. Preferably, the
cellulose suspension contains cellulose-reactive sizing agents,
normally present in an amount of from 0.01 to 5% by weight based on
dry fibres, and has a pH value where the cellulose-reactive sizing
agent still functions properly, i.e. a pH in the range from 5 up to
10. Suitable cellulose-reactive sizing agents are ketene dimers,
ketene multimers, acid anhydrides, organic isocyanates, carbamoyl
chlorides and mixtures thereof, where ketene dimers and acid
anhydrides are preferred.
[0008] According to the present process an aromatic-containing
cationic vinyl addition polymer and an anionic vinyl addition
polymer having a weight average molecular weight of up to 500,000
is added to the cellulose suspension. Usually, the cationic polymer
is added to the suspension prior to the addition of the anionic
polymer. Suitably, the addition of the cationic polymer is followed
by a shear stage or stages, whereas the anionic polymer is added
after any stage providing significant shear but before the
formation of the paper web.
[0009] Aromatic-Containing Cationic Vinyl Addition Polymer
[0010] The aromatic-containing cationic vinyl addition polymer may
be linear or branched and contain monomers having anionic or
potentially anionic groups as long as the overall charge of the
polymer is cationic. However, the cationic polymer is preferably
obtained by polymerising a reaction mixture essentially free from
monomers having anionic groups or groups which can be rendered
anionic in aqueous compositions. The cationic polymer can be a homo
polymer or a copolymer containing cationic aromatic monomers,
cationic non-aromatic monomers and non-ionic monomers, the latter
also being non-aromatic. Suitably, the cationic vinyl addition
polymer contains cationic aromatic monomers selected from the group
consisting of acrylamide, (meth)acrylamide, acrylate and
(meth)acrylate, whereby said cationic monomers preferably have at
least one aromatic group covalently linked to a nitrogen atom
either direct or via hydrocarbon groups which can have heteroatoms.
Preferably, the aromatic-containing cationic vinyl addition polymer
contains aromatic (meth)acrylamide and/or (meth)acrylate monomers
which are present in the polymer in an amount from about 2 molar %
up to about 97 molar %. The aromatic-containing cationic vinyl
addition polymer is suitably obtained by polymerising a cationic
monomer or a reaction mixture containing a monomer mixture
comprising a cationic monomer represented by the general formula
(I): 1
[0011] wherein R.sub.1 is H or CH.sub.3; R.sub.2 and R.sub.3 are
independently from another a hydrogen or an alkyl group having from
1 to 3 carbon atoms, usually 1 to 2 carbon atoms; A.sub.1 is 0 or
NH; B.sub.1 is an alkylene group having from 2 to 8 carbon atoms,
suitably from 2 to 4 carbon atoms, a hydroxy propylene group or a
hydroxy ethylene group; Q is 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 2 carbon atoms, and
preferably Q is a benzyl group (--CH.sub.2--C.sub.6H.sub.5); and X
is an anionic counterion, usually a halide like chloride. Examples
of suitable monomers represented by the general formula (I) include
quaternary monomers obtained by treating dialkylaminoalkyl
(meth)acrylates, e.g. dimethylaminoethyl (meth)acrylate,
diethylaminoethyl (meth)acrylate and dimethylamino-hydroxypropyl
(meth)acrylate, and dialkylaminoalkyl (meth)acrylamides, e.g.
dimethylaminoethyl (meth)acrylamide, diethylaminoethyl
(meth)acrylamide, dimethylaminopropyl (meth)-acrylamide, and
diethylaminopropyl (meth)acrylamide, with benzyl chloride.
Preferred cationic monomers of the general formula (I) include
dimethylaminoethylacrylate benzyl chloride quaternary salt,
dimethylaminoethylmethacrylate benzyl chloride quaternary salt and
dimethylaminopropyl(meth)acrylamide benzyl chloride quaternary
salt.
[0012] The cationic vinyl addition polymer can be a homopolymer
prepared from a cationic monomer having an aromatic group or a
copolymer prepared from a monomer mixture comprising a cationic
monomer having an aromatic group and one or more copolymerizable
monomers. Suitable copolymerizable non-ionic monomers include
monomers represented by the general formula (II): 2
[0013] wherein R.sub.4 is H or CH.sub.3; R.sub.5 and R.sub.6 are
each H or a hydrocarbon group, suitably alkyl, having from 1 to 6,
suitably from 1 to 4 and usually from 1 to 2 carbon atoms; A.sub.2
is 0 or NH; B.sub.2 is an alkylene group of from 2 to 8 carbon
atoms, suitably from 2 to 4 carbon atoms, or a hydroxy propylene
group or, alternatively, A and B are both nothing whereby there is
a single bond between C and N (O.dbd.C--NR.sub.5R.sub.6). Examples
of suitable copolymerizable monomers of this type include
(meth)acrylamide; acrylamide-based monomers like N-alkyl
(meth)acrylamides and N,N-dialkyl (meth)acrylamides, e.g.
N-n-propylacrylamide, N-isopropyl (meth)acrylamide, N-n-butyl
(meth)acrylamide, N-isobutyl (meth)acrylamide and N-t-butyl
(meth)acrylamide; and dialkylaminoalkyl (meth)acrylamides, e.g.
dimethylaminoethyl (meth)acrylamide, diethylaminoethyl
(meth)acrylamide, dimethylaminopropyl (meth)acrylamide and
diethylaminopropyl (meth)acrylamide; acrylate-based monomers like
dialkylaminoalkyl (meth)acrylates, e.g. dimethylaminoethyl
(meth)acrylate, diethylaminoethyl (meth)acrylate, t-butylaminoethyl
(meth)acrylate and dimethylaminohydroxypropyl acrylate; and
vinylamides, e.g. N-vinylformamide and N-vinylacetamide. Preferred
copolymerizable non-ionic monomers include acrylamide and
methacrylamide, i.e. (meth)acrylamide, and the main polymer is
preferably an acrylamide-based polymer.
[0014] Suitable copolymerizable cationic monomers include the
monomers represented by the general formula (III): 3
[0015] wherein R.sub.7 is H or CH.sub.3; R.sub.8 and R.sub.9 are
preferably a hydrocarbon group, suitably an alkyl group having from
1 to 3 carbon atoms; R.sub.10 can be a hydrogen or preferably a
hydrocarbon group, suitably an alkyl group having from 1 to 8
carbon atoms, usually 1 to 2 carbon atoms; A.sub.3 is 0 or NH; B3
is an alkylene group of from 2 to 4 carbon atoms, suitably from 2
to 4 carbon atoms, or a hydroxy propylene group, and X is an
anionic counterion, usually methylsulphate or a halide like
chloride. Examples of suitable cationic copolymerizable monomers
include acid addition salts and quaternary ammonium salts of the
dialkylaminoalkyl (meth)acrylates and dialkylaminoalkyl
(meth)acrylamides mentioned above, usually prepared using acids
like HCl, H.sub.2SO.sub.4, etc., or quaternizing agents like methyl
chloride, dimethyl sulphate, etc.; and diallyldimethylammonium
chloride. Preferred copolymerizable cationic monomers include
dimethylaminoethyl (meth)acrylate methyl chloride quaternary salt,
diallyldimethylammonium chloride and and
dimethylaminopropyl(meth)acrylamide benzyl chloride quartenary
salt. Copolymerizable anionic monomers like acrylic acid,
methacrylic acid, itaconic acid, various sulfonated vinyl addition
monomers, etc. can also be employed and, preferably, in minor
amounts.
[0016] The cationic vinyl addition polymer can be prepared from a
monomer mixture generally comprising from 1 to 99 mole %, suitably
from 2 to 50 mole % and preferably from 5 to 20 mole % of cationic
monomer having an aromatic group, preferably represented by the
general formula (I), and from 99 to 1 mole %, suitably from 98 to
50 mole %, and preferably from 95 to 65 mole % of other
copolymerizable monomers which preferably comprises acrylamide or
methacrylamide ((meth)acrylamide), the monomer mixture suitably
comprising from 98 to 50 mole % and preferably from 95 to 80 mole %
of (meth)acrylamide, the rest up to 100% preferably of compounds
according to formula I and II.
[0017] Alternatively the cationic polymer can be a polymer
subjected to aromatic modification using an agent containing an
aromatic group. Suitable modifying agents of this type include
benzyl chloride, benzyl bromide,
N-(3-chloro-2-hydroxypropyl)-N-benzyl-N,N-dimethylammonium
chloride, and N-(3-chloro-2-hydroxypropyl) pyridinium chloride.
Suitable polymers for such an aromatic modification include vinyl
addition polymers. If the polymer contains a tertiary nitrogen
which can be quaternized by the modifying agent, the use of such
agents usually results in that the polymer is rendered cationic.
Alternatively, the polymer to be subjected to aromatic modification
can be cationic, for example a cationic vinyl addition polymer.
[0018] Usually the charge density of the cationic polymer is within
the range of from 0.1 to 6.0 meqv/g of dry polymer, suitably from
0.2 to 4.0 and preferably from 0.5 to 3.0. The weight average
molecular weight of the cationic polymer is usually at least about
500,000, suitably above about 1,000,000 and preferably above about
2,000,000. The upper limit is not critical; it can be about
30,000,000, usually 20,000,000 and suitably 10,000,000.
[0019] The cationic vinyl addition polymer can be added into the
suspension in amounts which can vary within wide limits depending
on, inter alia, type of suspension, salt content, type of salts,
filler content, type of filler, point of addition, etc. Generally
the cationic vinyl addition polymer is added in an amount that give
better sizing, dewatering and retention than is obtained when not
adding it provided the anionic vinyl addition polymer is added. The
cationic polymer is usually added in an amount of at least 0.002%,
often at least 0.005% by weight, based on dry pulp, whereas the
upper limit is usually 1.0% and suitably 0.5% by weight.
[0020] Anionic Vinyl Addition Polymer
[0021] Further to the above described aromatic-containing cationic
vinyl addition polymer, an anionic polymer having a weight average
molecular weight of up to 500,000 selected from the group
consisting of vinyl addition polymers and condensation polymers is
added to the cellulose suspension. The anionic polymer can be
linear, branched or cross-linked, yet suitably essentially linear,
and usually water-soluble or water-dispersable. The anionic polymer
may furthermore be a homopolymer or a copolymer containing at least
two different types of monomers. Preferably, the anionic polymer is
a vinyl addition polymer having a weight average molecular weight
of up to 500,000. Suitable anionic vinyl addition polymers are
polymers obtained from a reaction mixture comprising vinylic
unsaturated monomers, preferably vinylic unsaturated aromatic
containing monomers, having one or more anionic groups or groups
rendered anionic in aqueous solutions, suitably at least one
sulphonate group. Examples of anionic groups attached to vinylic
unsaturated monomers are phosphate groups, phosphonate groups,
sulphate groups, sulphonic acid groups, sulphonate groups,
carboxylic acid groups, carboxylate groups such as acrylic acid,
methacrylic acid, ethyl acrylic acid, crotonic acid, itaconic acid,
maleic acid or salts thereof, alkoxide groups, maleic acid groups
and phenolic groups, i.e. hydroxy-substituted phenyls and
naphthyls. Groups carrying an anionic charge are usually salts of
an alkali metal, alkaline earth or ammonia. The anionic vinyl
addition polymer may also in some extent contain cationic groups
such as monomers having cationic groups, though, preferable the
only ionic groups present in the vinyl addition polymer are
anionic. Preferably, the anionic groups are linked to aromatic
vinylic (ethylenically) unsaturated monomers such as styrene, i.e.
styrene sulphonate. If the anionic vinyl addition polymer is a
copolymer, said polymer can be obtained from a reaction mixture
comprising non-ionic vinylic unsaturated monomers, e.g. acrylamide,
(meth)acrylamide. The anionic vinyl addition polymer may comprise
from about 20 mole % up to about 100 mole % of anionic monomers
containing at least one anionic charge.
[0022] Suitable anionic condensation polymers having a weight
average molecular weight of up to 500,000 are condensates of an
aldehyde such as formaldehyde with one or more aromatic compounds
containing one or more anionic groups, and optional other
co-monomers useful in the condensation polymerization such as urea
and melamine. Examples of suitable aromatic compounds containing
anionic groups comprises benzene and naphthalene-based compounds
containing anionic groups such as phenolic and naphtholic
compounds, e.g. phenol, naphthol, resorcinol and derivatives
thereof, aromatic acids and salts thereof, e.g. phenylic, phenolic,
naphthylic and naphtholic acids and salts, usually sulphonic acids
and sulphonates, e.g. benzene sulphonic acid and sulphonate, xylen
sulphonic acid and sulphonates, naphthalene sulphonic acid and
sulphonate, phenol sulphonic acid and sulphonate. Examples of
suitable anionic condensation polymers include anionic
benzene-based and naphthalene-based condensation polymers,
preferably naphthalene-sulphonic acid based and
naphthalene-sulphonate based condensation polymers.
[0023] The weight average molecular weight of the anionic polymer
is up to 500,000, suitably up to 250,000. Preferred ranges of the
weight average molecular weight are from about 10,000 up to about
100,000, preferably from about 15,000 up to about 75,000, suitably
from about 15,000 up to about 45,000, and most preferably from
about 25,000 up to about 40,000.
[0024] The anionic polymer can have a degree of anionic
substitution (DSA) varying over a wide range dependent on, inter
alia, the type of polymer used; DSA is usually from 0.01 to 2.0,
suitably from 0.02 to 1.8 and preferably from 0.025 to 1.5; and the
degree of aromatic substitution (DSQ) can be from 0.001 to 1.0,
usually from 0.01 to 1.0, suitably from 0.02 to 0.7 and preferably
from 0.025 to 0.5. In case the anionic polymer contains cationic
groups, the degree of cationic substitution (DS.sub.c) can be, for
example, from 0 to 0.2, suitably from 0 to 0.1 and preferably from
0 to 0.05, the anionic polymer having an overall anionic charge.
Usually the anionic charge density of the anionic polymer is within
the range of from 0.1 to 6.0 meqv/g of dry polymer, suitably from
0.5 to 5.0 and preferably from 1.0 to 5.0.
[0025] The anionic polymer can be added to the suspension in
amounts which can vary within wide limits depending on, inter alia,
type of stock, salt content, type of salts, filler content, type of
filler, point of addition, etc. Generally the anionic polymer is
added in an amount that give better sizing, dewatering and
retention than is obtained when not adding the anionic polymer
provided the cationic vinyl addition polymer is added. The anionic
polymer is usually added in an amount of at least 0.001%, often at
least 0.005% by weight, based on dry pulp, whereas the upper limit
is usually 3.0% and suitably 1.0% by weight.
[0026] According to one preferred embodiment of the present
invention the aromatic-containing cationic vinyl addition polymer
can be provided as an aqueous composition, suitably aqueous
solution, preferably comprising further cationic polymers, for
example synthetic cationic polymers and naturally occurring
polymers. Suitable synthetic cationic polymers cationic are vinyl
addition polymers such as acrylamide based polymers or acrylate
based polymers. Other synthetic cationic polymers include cationic
condensation polymers like epihalohydrin polymers, e.g. polymers
formed by reacting aliphatic amines and epichlorohydrine,
polyamideamine polymers, polyethyleneimine polymers. Preferred
naturally occurring cationic polymers as cationic polysaccharides,
particularly cationic starch and aromatic substituted cationic
starch. The aqueous solution preferably contains the
aromatic-containing cationic vinyl addition polymer in a
predominant amount, i.e. at least 50% by weight, even though
effects are present at considerably lesser amounts, down to amount
at least 10% by weight. The further cationic polymers referred to
in this paragraph may also be added separately.
[0027] According to yet another preferred embodiment of the present
invention inorganic anionic microparticulate materials like anionic
silica-based particles, polysilicic acid and clays of the smectite
type are added to the suspension. The inorganic anionic
microparticulate material can be added separately to the suspension
or is preferably comprised in an aqueous composition also
comprising the anionic polymer.
[0028] The invention is further illustrated in the following
examples which, however, are not intended to limit the same. Parts
and % relate to parts by weight and % by weight based on dry
fibres, respectively, unless otherwise stated. All compound added
to the furnish are calculated as dry material, if not otherwise
indicated. In the examples, a good retention is shown by a low
turbidity value in the white water, i.e. more fines and filler are
retained in the formed sheet. A turbidity value under 120 is
acceptable and a value under 90 is in this set of experiment
excellent. The dewatering figure should also be low. The sizing of
the paper was measured by the contact angle of a water droplet on
the paper. Contact angles larger the 80 degrees after 10 seconds
are indicating a good sizing.
EXAMPLE 1
[0029] The pulp (at 3%) used was a 80/20 mixture of
hardwood/softwood kraft. Ground calcium carbonate filler (GCC) was
added to the pulp, to a filler concentration of 40% on dry solids.
The resulting furnish was diluted to 0.3% before additional
chemicals were added. The chemical additions are expressed as % on
dry solids in the furnish.
[0030] In this example two furnishes was used one having a low
conductivity of 500 .mu.S/cm (furnish I), the other having a high
conductivity of 4.0 RS/cm (furnish II). The conductivity was
adjusted by addition of sodium sulphate. A dispersion containing a
conventional ketene dimer sizing agent and 1% cationic starch were
added to the furnishes. Subsequent to these additions, either 0.1%
of an aromatic cationic polyacrylamide having
benzyldimethylammonium groups (A-PAM) or 0.1% of a conventional
non-aromatic cationic polyacrylamide (C-PAM) was added prior to the
addition of either 0.1% of a silica sol or 0.1% of an anionic
polystyrene sulphonate having a weight average molecular weight of
70,000 (PSS). The added amounts of compounds are indicated in table
I and II. The retention and dewatering properties of the formed
furnishes were evaluated by measuring the dewatering time using a
Dynamic Drainage Analyser (DDA-unit). A lower value in this test
means better dewatering efficiency. The retention was evaluated by
measuring the turbidity of the white water with a Nephelometer 156
from Novasine. A lower turbidity value signifies higher retention
of solids in the DDA-unit. Moreover, the sizing of the formed,
dried and cured paper was evaluated by measuring the contact angle
of water after 10 seconds utilising a Dynamic Absoption and contact
angle tester from Fibro Systems (DAT). A higher value of the
contact angle means better sizing efficiency.
1TABLE I Furnish II (high conductivity) Amount of Type of Contact
added ketene cationic Type of angel (10 dimer/[kg/t dry polyacryla-
anionic Dewatering/ sec./[de- test pulp] mide compound Turbidity
[sec.] grees] blank* 0.2 none none 390 7.8 below 10 1 0.2 C-PAM
silica sol 91 6.92 29.6 2 0.2 A-PAM PSS 47 4.54 44.6 3 0.3 C-PAM
silica sol 90 6.64 80.8 4 0.3 A-PAM PSS 43 4.47 84.6 5 0.4 C-PAM
silica sol 90 6.77 89.9 6 0.4 A-PAM PSS 47 4.47 94.4
[0031] As shown by table I, the addition of an aromatic-modified
cationic vinyl addition polymer and an anionic vinyl addition
polymer with a weight average molecular weight of up to 500,000
significantly increases not only dewatering and retention but also
the sizing efficiency.
2TABLE II Furnish I (low conductivity) Amount of added Type of
Contact ketene cationic Type of angle (10 dimer/[kg/t polyacryla-
anionic Dewatering/ sec./[de- test dry pulp] mide compound
Turbidity [sec.] grees] blank* 0.3 none none 420 5.6 35 1 0.3 C-PAM
silica-sol 100 4.8 83.3 2 0.3 A-PAM PSS 76 3.5 87.8 *In this test
neither cationic polyacrylamide nor anionic compound was used,
otherwise conditions were the same as for tests 1 and 2. *No
addition of neither cationic polyacrylamide nor anionic compound,
otherwise conditions were the same as for tests 1 and 2.
EXAMPLE 2
[0032] The furnish used was the same as used in example 1, however,
in this example the furnish was adjusted to a conductivity of 400
.mu.S/cm
[0033] The sizing dispersion as used in example 1 was added to the
furnish followed by the addition of cationic starch. The dosage for
the size was 0.03% (calculated as active ketene dimer on dry
furnish) and for the cationic starch 1.0%. Subsequent to these
additions, 0.1% of an aromatic cationic polyacrylamide having
benzyldimethylammonium groups was added prior to the addition of
0.07% of an anionic polystyrene sulphonate having different weight
average molecular weights as indicated in table III. The added
amounts of compounds are indicated in table III. The retention and
dewatering properties of the formed furnishes were evaluated by
measuring the dewatering time using a DDA-unit. The retention was
evaluated by measuring the turbidity of the white water with a
Nephelometer 156 from Novasine. Moreover, the sizing of the formed,
dried and cured paper was evaluated by measuring the contact angle
of water after 10 seconds utilising a DAT equipment.
3TABLE III Weight average molecular Contact angle weight of the (10
test PSS Turbidity Dewatering/[sec.] sec./[degrees] blank* none 125
5.4 below 30 1 35,000 56 4.89 92.7 2 220,000 39 3.49 82.1 3 780,000
30 3.17 69.2 *No addition of neither cationic polyacrylamide nor
anionic compound, otherwise conditions were the same as for tests 1
to 3.
[0034] Tests 1 and 2 are according to the present invention, i.e.
the anionic vinyl addition polymer having a weight average
molecular weight of up to 500,000. As can be seen in table III, the
sizing efficiency is significantly increased while the turbidity
and dewatering performance are high with regard to tests 1 and 2
compared to the blank. In addition, comparing test 3 with tests 1
and 2 (the latter two according to the invention), the sizing
efficiency is much higher, while the turbidity value still
indicates excellent retention. What is more, a contacting angle of
69.2 as obtained in test 3 is not an acceptable sizing degree.
Thus, the overall performance of test 1 and 2 in respect of
retention, dewatering and not least sizing clearly outperform test
3.
* * * * *