Note: Descriptions are shown in the official language in which they were submitted.
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A process for the production of paper
This invention relates to papermaking and more specifically to a process for
the
production of paper in which cationic and anionic polymers having aromatic
groups are
added to a papermaking stock. The process provides improved drainage and
retention.
Background
In the papermaking art, an aqueous suspension containing cellulosic fibres,
and
optional fillers and additives, referred to as stock, is fed 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. The obtained water, usually
referred to
as white water and containing fine particles such as fine fibres, fillers and
additives, is
usually recycled in the papermaking process. Drainage and retention aids are
conventionally introduced into the stock in order to facilitate drainage and
increase
adsorption of fine particles onto the cellulose fibres so that they are
retained with the
fibres. A wide variety of drainage and retention aids are known in the art,
for example
anionic, non-ionic, cationic and amphoteric organic polymers, anionic and
cationic
inorganic materials, and many combinations thereof.
International Patent Application Publication Nos. WO 99/55964 and WO 99/55965
disclose the use of drainage and retention aids comprising cationic organic
polymers
having aromatic groups. The cationic organic polymers can be used alone or in
combination with various anionic materials such as, for example, anionic
organic and
inorganic condensation polymers, e.g. sulphonated melamine-formaidehyde and
silica-
based particles.
It would be advantageous to be able to provide a papermaking process with
improved drainage and retention. It would also be advantageous to be able to
provide
drainage and retention aids comprising cationic organic polymers and anionic
polymers
with improved drainage and retention performance.
The Invention
According to the present invention it has been found that improved drainage
and/or retention can be obtained by using drainage and retention aids
comprising a
cationic organic polymer having an aromatic group and an anionic polymer
having an
aromatic group. More specifically, the present invention relates to a process
for the
production of paper from an aqueous suspension containing cellulosic fibres,
and
optional fillers, which comprises separately adding to the suspension a
cationic organic
polymer having an aromatic group and an anionic polymer having an aromatic
group, the
anionic polymer being selected from step-growth polymers, polysaccharides, and
naturally
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occurring aromatic polymers and modifications thereof; forming and draining
the
suspension on a wire, with the proviso that if the anionic polymer is selected
from step-
growth polymers, it is not an anionic melamine-sulphonic acid condensation
polymer. The
invention further relates to a process for the production of paper from an
aqueous suspen-
sion containing cellulosic fibres, and optional fillers, which comprises
separately adding to
the suspension a cationic organic polymer having an aromatic group and an
anionic
polymer having an aromatic group, forming and draining the suspension on a
wire, with the
proviso that the anionic polymer is not an anionic polystyrene sulphonate or
anionic
melamine-sulphonic acid condensation polymer.
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/or retention than is obtained when not adding the said two or
more
components.
The present invention results in improved drainage and/or retention in the
production of paper from all types of stocks, in particular stocks having high
contents of
salts (high conductivity) and colloidal substances, and/or 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 a lower dosage of additives to give a corresponding
drainage
and/or retention effect, thereby leading to an improved papermaking process
and economic
benefits. The present invention also provides paper with improved dry
strength.
The cationic organic polymer having an aromatic group according to the present
invention can be derived from natural or synthetic sources, and it can be
linear, branched
or cross-linked. Preferably the cationic polymer is water-soluble or water-
dispersable.
Examples of suitable cationic polymers include cationic polysaccharides, e.g.
starches,
guar gums, celluloses, chitins, chitosans, glycans, galactans, glucans,
xanthan gums,
pectins, mannans, dextrins, preferably starches and guar gums, suitable
starches including
potato, com, wheat, tapioca, rice, waxy maize, barley, etc.; cationic
synthetic organic
polymers such as cationic chain-growth polymers, e.g. cationic vinyl addition
polymers like
acrylate-, acrylamide-, vinylamine- and vinylamide-based polymers, and
cationic step-
growth polymers, e.g. cationic polyurethanes. Cationic starches and cationic
acrylamide-
based polymers having an aromatic group are particularly preferred cationic
polymers.
The cationic organic polymer according to the invention has one or more
aromatic groups and the aromatic groups can be of the same or different types.
The
aromatic group of the cationic organic polymer can be present in the polymer
backbone
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(main chain) or in a substituent group that is attached to the polymer
backbone, preferably
in a substituent group. Examples of suitable aromatic groups include aryl,
aralkyl and
alkaryl groups, e.g. phenyl, phenylene, naphthyl, phenylene, xylyiene, benzyl
and
phenylethyl; nitrogen-containing aromatic (aryl) groups, e.g. pyridinium and
quinolinium, as
well as derivatives of these groups, preferably benzyl. Examples of
cationically charged
groups that can be present in the cationic polymer as well as in monomers used
for
preparing the cationic polymer include quaternary ammonium groups, tertiary
amino groups
and acid addition salts thereof.
According to a preferred embodiment of this invention, the cationic organic
polymer having an aromatic group is a polysaccharide represented by the
general
structural formula (I):
R, (I)
I X-
P-(-A, -N+-Q)n
1
RZ
wherein P is a residue of a polysaccharide; A, is a group attaching N to the
polysaccharide
residue, suitably a chain of atoms comprising C and H atoms, and optionally 0
and/or N
atoms, usually an alkylene group with from 2 to 18 and suitably 2 to 8 carbon
atoms,
optionally interrupted or substituted by one or more heteroatoms, e.g. 0 or N,
e.g. an
alkyleneoxy group or hydroxy propylene group (-CH2-CH(OH)-CH2-); R, and R2 are
each H.-
or, preferably, a hydrocarbon group, suitably alkyl, having from 1 to 3 carbon
atoms,
preferably 1 to 2 carbon atoms; 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 (-CH2-C6H5); n is an integer, usually from
about 2 to about
300,000, suitably from 5 to 200,000 and preferably from 6 to 125,000 or,
alternatively, R,,
R2 and Q together with N form a aromatic group containing from 5 to 12 carbon
atoms; and
X- is an anionic counterion, usually a halide like chloride. Suitable
polysaccharides
represented by the general formula (I) include those mentioned above. Cationic
polysaccharides according to the invention may also contain anionic groups,
preferably in
a minor amount. Such anionic groups may be introduced in the polysaccharide by
means
of chemical treatment or be present in the native polysaccharide.
According to another preferred embodiment of this invention, the cationic
organic
polymer having an aromatic group is a chain-growth polymer. The term "chain-
growth
polymer", as used herein, refers to a polymer obtained by chain-growth
polymerization,
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also being referred to as chain reaction polymer and chain reaction
polymerization,
respectively. Examples of suitable chain-growth polymers include vinyl
addition polymers
prepared by polymerization of one or more monomers having a vinyl group or
ethylenically
unsaturated bond, for example a polymer obtained by polymerizing a cationic
monomer or
a monomer mixture comprising a cationic monomer represented by the general
structural
formula (II):
CH2 = C - R3 R, (II)
I I
O=C-A2-B2-N+-Q X'
(
RZ
wherein R3 is H or CH3; R, and R2 are each H or, preferably, a hydrocarbon
group, suitably
alkyl, having from I to 3 carbon atoms, preferably 1 to 2 carbon atoms; A2 is
0 or NH; B2 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; 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 (-CH2-C6H5); and X- is an anionic
counterion,
usually a halide like chloride.
Examples of suitable monomers represented by the general formula (II) include
quaternary monomers obtained by treating dialkylaminoalkyl (meth)acrylates,
e.g. dimethyl-
aminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate and
dimethylaminohydroxy-
propyl (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 (1) include
dimethylaminoethylacrylate benzyl
chloride quaternary salt and dimethylaminoethylmethacrylate benzyl chloride
quaternary
salt. The monomer of formula (II) can be copolymerized with one or more non-
ionic,
cationic and/or anionic monomers. Suitable copolymerizable non-ionic monomers
include
(meth)acrylamide; acrylamide-based monomers like N-alkyl (meth)acrylamides,
N,N-dialkyl
(meth)acrylamides and dialkylaminoalkyl (meth)acrylamides, acrylate-based
monomers like
dialkylaminoalkyl (meth)acrylates, and vinylamides. Suitable copolymerizable
cationic
monomers include acid addition salts and quaternary salts of
dimethylaminoethyl
(meth)acrylate and diallyldimethylammonium chloride. The cationic organic
polymer may
also contain anionic groups, preferably in a minor amount. Suitable
copolymerizable anionic
monomers include acrylic acid, methacrylic acid and various sulphonated
vinylic monomers
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such as styrenesulphonate. Preferred copolymerizable monomers include
acrylamide and
methacrylamide, i.e. (meth)acrylamide, and the cationic or amphoteric organic
polymer is
preferably an acrylamide-based polymer.
Cationic vinyl addition polymers according to this invention can be prepared
from
5 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
and from
99 to I mole%, suitably from 98 to 50 mole%, and preferably from 95 to 80
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 sum of percentages
being 100.
Examples of suitable cationic step-growth polymers according to the invention
include cationic polyurethanes which can be prepared from a monomer mixture
comprising
aromatic isocyanates and/or aromatic alcohols. Examples of suitable aromatic
isocyanates
include diisocyanates, e.g. toluene-2,4- and 2,6-diisocyanates and
diphenylmethane-4,4'-
diisocyanate. Examples of suitable aromatic alcohols include dihydric
alcohols, i.e. diols,
e.g. bisphenol A, phenyl diethanol amine, glycerol monoterephthalate and
trimethylol-
propane monoterephthalate. Monohydric aromatic alcohols such as phenol and
derivaties
thereof may also be employed. The monomer mixture can also contain non-
aromatic
isocyanates and/or alcohols, usually diisocyanates and diols, for example any
of those
known to be useful in the preparation of polyurethanes. Examples of suitable
monomers
containing cationic groups include cationic diols such as acid addition salts
and
quaternization products of N-alkandiol dialkylamines and N-alkyl
dialkanolamines like 1,2-
propanediol-3-dimethylamine, N-methyl diethanolamine, N-ethyl diethanolamine,
N-propyl
diethanolamine, N-n-butyl diethanolamine and N-t-butyl diethanolamine, N-
stearyl di-
ethanolamine and N-methyl dipropanolamine. The quaternization products can be
derived
from alkylating agents like methyl chloride, dimethyl sulphate, benzyl
chloride and
epichlorohydrin.
The weight average molecular weight of the cationic polymer can vary within
wide limits dependent on, inter alia, the type of polymer used, and usually it
is at least
about 5,000 and often at least 10,000. More often, it is above 150,000,
normally above
500,000, suitably above about 700,000, preferably above about 1,000,000 and
most
preferably above about 2,000,000. The upper limit is not critical; it can be
about
200,000,000, usually 150,000,000 and suitably 100,000,000.
The cationic organic polymer can have a degree of cationic substitution (DSc)
varying over a wide range dependent on, inter alia, the type of polymer used;
DSc can be
from 0.005 to 1.0, usually from 0.01 to 0.5, suitably from 0.02 to 0.3,
preferably from
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0.025 to 0.2; and the degree of aromatic substitution (DSQ) can be from 0.001
to 0.5,
usually from 0.01 to 0.5, suitably from 0.02 to 0.3 and preferably from 0.025
to 0.2. In
case the cationic organic polymer contains anionic groups, the degree of
anionic
substitution (DSA) can be from 0 to 0.2, suitably from 0 to 0.1 and preferably
from 0 to
0.05, the cationic polymer having an overall cationic charge. 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 5.0 and preferably from 0.5 to 4:0.
Examples of suitable cationic organic polymers having an aromatic group that
can
be used according to the present invention include those described in
Intemational Patent
Publication Nos. WO 99/55964, WO 99/55965 and WO 99/67310.
Anionic polymers having an aromatic group according to the invention can be
selected from step-growth polymers, chain-growth polymers, polysaccharides,
naturally
occurring aromatic polymers and modifications thereof. The term step-growth
polymer", as
used herein, refers to a polymer obtained by step-growth polymerization, also
being
referred to as step-reaction polymer and step-reaction polymerization,
respectively.
Preferably the anionic polymer is selected from step-growth polymers,
polysaccharides
and naturally occurring aromatic polymers and modifications thereof, most
preferably step-
growth polymers. The anionic polymers according to the invention can be
linear, branched
or cross-linked. Preferably the anionic polymer is water-soluble or water-
dispersable. The
anionic polymer is preferably organic.
The anionic polymer according to the invention has one or more aromatic
groups and the aromatic groups can be of the same or different types. The
aromatic
group of the anionic polymer can be present in the polymer backbone or in a
substituent
group that is attached to the polymer backbone (main chain). Examples of
suitable
aromatic groups include aryl, aralkyl and alkaryl groups and derivatives
thereof, e.g. phenyl,
tolyl, naphthyl, phenylene, xylylene, benzyl, phenylethyl and derivatives of
these groups.
Examples of anionically charged groups that can be present in the anionic
polymer as well
as in the monomers used for preparing the anionic polymer include groups
carrying an
anionic charge and acid groups carrying an anionic charge when dissolved or
dispersed in
water, the groups herein collectively being referred to as anionic groups,
such as
phosphate, phosphonate, sulphate, sulphonic acid, sulphonate, carboxylic acid,
carboxylate, alkoxide 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.
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Examples of suitable anionic step-growth polymers according to the present
invention include condensation polymers, i.e. polymers obtained by step-growth
condensa-
tion polymerization, e.g. 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, xylene sulphonic acid and sulphonates, naphthalene sulphonic acid
and
sulphonate, phenol sulphonic acid and sulphonate. Examples of suitable anionic
step-
growth polymers according to the invention include anionic benzene-based and
naphthalene-based condensation polymers, preferably naphthalene-sulphonic acid
based
and naphthalene-sulphonate based condensation polymers.
Examples of further suitable anionic step-growth polymers according to the
present invention include addition polymers, i.e. polymers obtained by step-
growth addition
polymerization, e.g. anionic polyurethanes which can be prepared from a
monomer mixture
comprising aromatic isocyanates and/or aromatic alcohols. Examples of suitable
aromatic
isocyanates include diisocyanates, e.g. toluene-2,4- and 2,6-diisocyanates and
diphenyl-
methane-4,4'-diisocyanate. Examples of suitable aromatic alcohols include
dihydric
alcohols, i.e. diols, e.g. bisphenol A, phenyl diethanol amine, glycerol
monoterephthalate
and trimethylolpropane monoterephthalate. Monohydric aromatic alcohols such as
phenol
and derivaties thereof may also be employed. The monomer mixture can also
contain non-
aromatic isocyanates and/or alcohols, usually diisocyanates and diols, for
example any of
those known to be useful in the preparation of polyurethanes. Examples of
suitable
monomers containing anionic groups include the monoester reaction products of
triols, e.g.
trimethylolethane, trimethylolpropane and glycerol, with dicarboxylic acids or
anhydrides
thereof, e.g. succinic acid and anhydride, terephthalic acid and anhydride,
such as
glycerol monosuccinate, glycerol monoterephthalate, trimethylolpropane
monosuccinate,
trimethylolpropane monoterephthalate, N,N-bis-(hydroxyethyl)-glycine, di-
(hydroxy-
methyl)propionic acid, N,N-bis-(hydroxyethyl)-2-aminoethanesulphonic acid, and
the like,
optionally and usually in combination with reaction with a base, such as
alkali metal and
alkaline earth hydroxides, e.g. sodium hydroxide, ammonia or an amine, e.g.
triethylamine, thereby forming an alkali metal, alkaline earth or ammonium
counter-ion.
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Examples of suitable anionic chain-growth polymers according to the invention
include anionic vinyl addition polymers obtained from a mixture of vinylic or
ethylenically
unsaturated monomers comprising at least one monomer having an aromatic group
and at
least one monomer having an anionic group, usually co-polymerized with non-
ionic
monomers such as acrylate- and acrylamide-based monomers. Examples of suitable
anionic monomers include (meth)acrylic acid and paravinyl phenol (hydroxy
styrene).
Examples of suitable anionic polysaccharides include starches, guar gums,
celluloses, chitins, chitosans, glycans, galactans, glucans, xanthan gums,
pectins,
mannans, dextrins, preferably starches, guar gums and cellulose derivatives,
suitable
starches including potato, corn, wheat, tapioca, rice, waxy maize and barley,
preferably
potato. The anionic groups in the polysaccharide can be native and/or
introduced by
chemical treatment. The aromatic groups in the polysaccharide can be
introduced by
chemical methods known in the art.
Naturally occurring aromatic anionic polymers and modifications thereof, i.e.
modified naturally occurring aromatic anionic polymers, according to the
invention include
naturally occuring polyphenolic substances that are present in wood and
organic extracts of
bark of some wood species and chemical modifications thereof, usually
sulphonated
modifications thereof. The modified polymers can be obtained by chemical
processes such
as, for example, sulphite pulping and kraft pulping. Examples of suitable
anionic polymers
of this type include lignin-based polymers, preferably sulphonated lignins,
e.g. ligno-
sulphonates, kraft lignin, suiphonated kraft lignin, and tannin extracts.
The weight average molecular weight of the anionic polymer can vary within
wide limits dependent on, inter alia, the type of polymer used, and usually it
is at least
about 500, suitably above about 2,000 and preferably above about 5,000. The
upper limit
is not critical; it can be about 200,000,000, usually 150,000,000, suitably
100,000,000
and preferably 10,000,000.
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
0.8, 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 (DSc) 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 4Ø
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Examples of suitable anionic aromatic polymers that can be used according to
the
present invention include those described in U.S. Patent Nos. 4,070,236 and
5,755,930;
and Intemational Patent Application Publication Nos. WO 95/21295, WO 95/21296,
WO
99/67310 and WO 00/49227.
Examples of particularly preferred combinations of anionic and cationic
polymers
having aromatic groups, as defined above, according to the present invention
include
(i) cationic polysaccharides, preferably cationic starch, and anionic step-
growth polymers,
suitably anionic benzene-based and naphthalene-based condensation polymers and
anionic polyurethanes, preferably anionic naphthalene-based condensation
polymers;
(ii) cationic polysaccharides, preferably cationic starch, and naturally
occurring aromatic
anionic polymers and modifiations thereof, suitably anionic lignin-based
polymers,
preferably sulphonated lignins;
(iii) cationic chain-growth polymers, suitably cationic vinyl addition
polymers, preferably
cationic acrylamide-based polymers, and anionic step-growth polymers, suitably
anionic
benzene-based and naphthalene-based condensation polymers and anionic
polyurethanes,
preferably anionic naphthalene-based condensation polymers; and
(iv) cationic chain-growth polymers, suitabiy cationic vinyl addition
polymers, preferably
cationic acrylamide-based polymers, and naturally occurring aromatic anionic
polymers and
modifiations thereof, suitably anionic lignin-based polymers, preferably
sulphonated lignins.
The cationic and anionic polymers according to the invention are preferably
separately added to the aqueous suspension containing cellulosic fibres, or
stock, and not
as a mixture containing said polymers. Preferably the cationic and anionic
polymers are
added to the stock at different points. The polymers can be added in any
order. Usually the
cationic polymer is firstly added to the stock and the anionic polymer is
subsequently
added, although the reverse order of addition may also be used. The polymers
can be
added to the stock to be dewatered 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 polymers are added in an amount that give better
drainage
and/or retention than is obtained when not adding them and usually the
cationic polymer
is added to the stock prior to adding the anionic polymer. The cationic
polymer is usually
added in an amount of at least 0.001%, often at least 0.005% by weight, based
on dry
stock substance, whereas the upper limit is usually 3% and suitably 2.0% by
weight. The
anionic polymer is usually added in an amount of at least 0.001%, often at
least 0.005% by
weight, based on dry stock substance, whereas the upper limit is usually 3%
and suitably
1.5% by weight.
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The polymers having aromatic groups according to the invention can be used in
conjunction with additional additive(s) that are beneficial to the overall
drainage and/or
retention performance, thereby forming drainage and retention aids comprising
three or
more components. Examples of suitable stock additives of this type include
anionic
5 microparticulate materials, e.g., silica-based particles and clays of
smectite type, low
molecular weight cationic organic polymers, aluminium compounds, anionic vinyl
addition
polymers and combinations thereof, including the compounds and the use thereof
disclosed in Intemational Patent Application Publication Nos. WO 99/55964 and
WO
99/55965.
10 Low molecular weight (hereinafter LMW) cationic organic polymers that can
be
used according to the invention include those commonly referred to as anionic
trash
catchers (ATC). The LMW cationic organic polymer can be derived from natural
or
synthetic sources, and preferably it is an LMW synthetic polymer. Suitable
organic
polymers of this type include LMW highly charged cationic organic polymers
such as poly-
amines, polyamidoamines, polyethyleneimines, homo- and copolymers based on
diallyi-
dimethy( ammonium chloride, (meth)acrylamides and (meth)acrylates. In relation
to the
molecular weight of the cationic organic polymer having an aromatic group of
this invention,
the molecular weight of the LMW cationic organic polymer is preferably lower;
it is suitably
at least 2,000 and preferably at least 10,000. The upper limit of the
molecular weight is
usually about 700,000, suitably about 500,000 and usually about 200,000.
Aluminium compounds that can be used according to the invention include alum,
aluminates, aluminium chforide, aluminium nitrate and polyaluminium compounds,
such as
polyaluminium chlorides, polyaluminium suiphates, polyaluminium compounds
containing
both chloride and sulphate ions, polyaluminium silicate-sulphates, and
mixtures thereof.
The polyaluminium compounds may also contain other anions than chloride ions,
for
example anions from sulphuric acid, phosphoric acid, organic acids such as
citric acid and
oxalic acid.
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 2.0 mS/cm, suitably at least 3.5 mS/cm, and
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 Bemer. The values
referred to
above are suitably determined by measuring the conductivity of the cellulosic
suspension
that is fed into or present in the headbox of the paper machine or,
alternativefy, by
measuring the conductivity of white water obtained by dewatering the
suspension. High
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conductivity levels mean high contents of salts (electrolytes) which can be
derived from the
materials used to form the stock, from various additives introduced into the
stock, from the
fresh water supplied to the process, etc. Further, the content of salts is
usually higher in
processes where white water is extensively recirculated, which may lead to
considerable
accumulation of salts in the water circulating in the process.
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, suitably less than 15, preferably less than 10 and
notably less than 5
tons of fresh water per ton of paper. Recycling of white water obtained in the
process
suitably comprises mixing the white water with cellulosic fibres and/or
optional fillers to form
a suspension to be dewatered; preferably it comprises mixing the white water
with a
suspension containing cellulosic fibres, and optional fillers, before the
suspension enters
the forming wire for dewatering. The white water can be mixed with the
suspension before,
between, simultaneous with or after introducing the drainage and retention
aids of this
invention. Fresh water can be introduced in the process at any stage; for
example, it can be
mixed with cellulosic fibres in order to form a suspension, and it can be
mixed with a thick
suspension containing cellulosic fibres to dilute it so as to form a thin
suspension to be
dewatered, before, simultaneous with or after mixing the suspension with white
water.
Further additives which are conventional in papermaking can of course be used
in
combination with the polymers according to the invention, such as, for
example, dry
strength agents, wet strength agents, optical brightening agents, dyes, sizing
agents like
rosin-based sizing agents and cellulose-reactive sizing agents, e.g. alkyl and
alkenyl ketene
dimers, alkyl and alkenyl ketene multimers, and succinic anhydrides, etc. The
cellulosic
suspension, or stock, can also contain mineral fillers of conventional types
such as, for
example, kaolin, china clay, titanium dioxide, gypsum, talc and natural and
synthetic
calcium carbonates such as chalk, ground marble and precipitated calcium
carbonate.
The process of this 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 cellulosic fibre-containing sheet or web-like products, such as for
example board
and paperboard, and the production thereof. The process can be used in the
production of
paper from different types of suspensions of cellulose-containing fibres and
the
suspensions should suitably contain at least 25% by weight and preferably at
least 50% by
weight of such fibres, based on dry substance. The suspension can be based on
fibres
from chemical pulp such as sulphate, sulphite and organosolv pulps, mechanical
pulp such
as thermomechanical pulp, chemo-thermomechanical pulp, refiner pulp and
groundwood
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pulp, from both hardwood and softwood, and can also be based on recycled
fibres,
optionally from de-inked pulps, and mixtures thereof.
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,
respectively, unless otherwise stated.
Example 1
Cationic polymers used in the tests were purchased on the market or prepared
by
generally known procedures. The cationic polysaccharides used in the tests
were prepared
by reacting native potato starch with a quaternising agent according to the
general
procedure described in EP-A 0 189 935 and WO 99/55964. The cationic polymers
used in
the tests, hereinafter also collectively referred to as cationic polymer, Cl
to C3 according to
the invention and Cl-ref to C3-ref intended for comparison purposes, were the
following:
Cl: Cationic starch obtained by quarternisation of native potato starch with 3-
chloro-
2-hydroxypropyl dimethyl benzyl ammonium chloride to 0.5% N.
C2: Cationic starch obtained by quarternisation of native potato starch with 3-
chloro-
2-hydroxypropyl dimethyl benzyl ammonium chloride to 0.7% N.
C3: Cationic vinyl addition polymer prepared by polymerisation of acrylamide
(90
mole%) and acryloxyethyldimethylbenzylammonium chloride (10 mole%),
molecular weight about 6,000,000.
C1-ref: Cationic starch obtained by quarternization of native potato starch
with 2,3-
epoxypropyl trimethyl ammonium chloride to 0.8% N.
C2-ref: Cationic starch obtained by quarternization of native potato starch
with 2,3-
epoxypropyl trimethyl ammonium chloride to 0.5% N.
C3-ref: Cationic vinyl addition polymer prepared by polymerisation of
acrylamide (90
mole%) and acryloxyethyltrimethylammonium chloride (10 mole%), molecular
weight about 6,000,000.
Anionic polymers used in the tests were purchased on the market or prepared by
generally known procedures. The anionic polymers used in the tests,
hereinafter also
collectively referred to as anionic polymer, Al to A8 according to the
invention and A1-ref to
A2-ref intended for comparison purposes, were the following:
Al: Anionic polycondensate of formaldehyde with naphthalene sulphonate,
molecular weight about 20,000.
A2: Anionic polycondensate of formaldehyde with naphthalene sulphonate,
molecular weight about 110,000.
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A3: Anionic polycondensate of formaldehyde with naphthalene sulphonate,
molecular weight about 40,000.
A4: Anionic polycondensate of formaldehyde with naphthalene sulphonate,
molecular weight about 210,000.
A5: Anionic polyurethane obtained by reacting glycerol flnonostearate with
toluene
diisocyanate to form a pre-polymer containing terminal isocyanate groups which
is then reacted with dimethylol propionic acid.
A6: Anionic polyurethane obtained by reacting phenyl diethanol amine with
toluene
diisocyanate to form a pre-polymer containing terminal isocyanate groups which
is
then reacted with dimethylol propionic acid and N-methyl diethanol amine.
A7: Anionic sulphonated kraft lignin.
A8: Anionic lignosulphonate.
A1-ref: Anionic melamine-formaldehyde-sulphonate polycondensate.
A2-ref: Anionic inorganic condensation polymer of silicic acid in the form of
colloidal
silica particles with a particle size of 5 nm.
A low molecular weight cationic organic polymer, also referred to as ATC,
which
was used in some of the tests, was available on the market and producible by
generally
known procedures. The ATC was the following:
ATC: Cationic copolymer of dimethylamine, epichlorohydrin and ethylene diamine
with a
molecular weight of about 50,000.
All polymers were used in the form of dilute aqueous polymer solutions.
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 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.
A standard stock was prepared from a furnish based on 56% by weight of
peroxide bleached TMP/SGW pulp (80/20), 14% by weight of bleached birch/pine
sulphate pulp (60/40) refined to 200 CSF and 30% by weight of china clay. To
the stock
was added 25 g/I of a colloidal fraction, bleach water from a paper mill.
Stock volume was
800 ml and pH about 7. Calcium chloride was added to the stock to adjust the
conductivity to 0.5 mS/cm. The obtained stock is referred to as standard
stock. Additional
amounts of calcium chloride were added to the standard stock in order to
prepare a
medium conductivity stock (2.0 mS/cm) and a high conductivity stock (5.0
mS/cm).
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The stock was stirred in a baffled jar at a speed of 1500 rpm throughout the
test
and chemicals additions were conducted as follows: i) adding cationic polymer
to the
stock following by stirring for 30 seconds, ii) adding anionic polymer to the
stock followed
by stirring for 15 seconds, iii) draining the stock while automatically
recording the
drainage time. If used, the ATC was added to the stock followed by stirring
for 30
seconds prior to i) adding cationic polymer and ii) adding anionic polymer
according to
the procedure described above.
Table 1 shows the dewatering (drainage) effect at various dosages of the
cationic polymer Cl, calculated as dry polymer on dry stock system, and
various
dosages of the anionic polymers Al-ref, Al and A2, calculated as dry polymer
on dry
stock system. The standard stock was used in Test Nos. 1-5 and the high
conductivity
stock was used in Test Nos. 6-9.
Table 1
Test C1 A Dewatering time
No. Dosage Dosage [s]
[kglt] [kg/t] A1-ref Al A2
1 30 0 19.0 19.0 19.0
2 30 0.5 17.5 17.0 15.5
3 30 1.0 14.6 12.6 12.1
4 30 2.0 12.8 9.0 8.4
5 30 3.0 9.8 8.7 7.2
6 20 0 26.4 26.4 26.4
7 20 2.0 21.5 15.7 15.6
8 20 3.0 17.6 14.6 13.7
9 20 4.0 15.7 14.5 13.4
Example 3
First pass retention was evaluated by means of a nephelometer by measuring
the turbidity of the filtrate from the Dynamic Drainage Analyser (DDA), the
white water,
obtained by draining the stock obtained in Example 2. The results are shown in
Table 2.
Table 2
Test C1 A Turbidity
No. Dosage Dosage [NTU]
[kglt] [kg/t] A1-ref Al A2
1 30 0.5 56 49 55
2 30 1.0 55 50 50
3 30 2.0 52 47 48
4 30 3.0 50 43 45
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Example 4
Drainage performance was evaluated using the cationic and anionic polymers
5 according to Example 1 and the standard stock and procedure according to
Example 2.
The results are shown in Table 3.
Table 3
Test C1 A Dewatering time
No. Dosage Dosage [s]
[kg/t] [kg/t] Al A3 A4
1 0 0 18.0 18.0 18.0
2 20 0 12.5 12.5 12.5
3 20 1.0 10.9 10.0 10.2
4 20 2.0 10.3 9.0 8.9
5 20 4.0 10.0 8.7 8.0
Example 5
Drainage performance was evaluated using the cationic and anionic polymers
according to Example 1 and the medium conductivity stock and procedure
according to
Example 2. The results are shown in Table 4.
Table 4
Test C Al Dewatering time
No. Dosage Dosage [s]
[kg/t] [kg/t] C1-ref C1 C2
1 10 0 13.8 14.6 11.5
2 10 0.75 12.6 10.6 7.4
3 10 1.5 12.8 9.5 6.6
4 10 3.0 14.1 10.1 7.2
Example 6
Drainage performance was evaluated using the cationic and anionic polymers
according to Example 1 and the high conductivity stock and procedure according
to
Example 2. The results are shown in Table 5.
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Table 5
Test C1 A Dewatering time
No. Dosage Dosage [s]
[kg/t] [kg/t] A2-ref A5 A6
1 20 0 31.8 31.8 31.8
2 20 1.0 31.0 27.5 28.8
3 20 2.0 28.0 22.0 24.4
4 20 4.0 23.8 16.5 19.5
20 6.0 23.0 14.0 18.3
5
Example 7
Drainage performance was evaluated using the cationic and anionic polymers
according to Example 1 and the high conductivity stock and procedure according
to
Example 2. The results are shown in Table 6.
Table 6
Test C3 A Dewatering time
No. Dosage Dosage [s]
[kg/t] [kglt] A5 A6
1 2 0 15.8 15.8
2 2 0.25 13.8 13.3
3 2 0.5 13.2 12.9
4 2 0.75 13.4 13.1
5 2 1.0 13.5 13.3
Example 8
Drainage and retention performance was evaluated using the cationic and
anionic
polymers according to Example 1 and the standard conductivity stock and
procedures
according to Examples 2 and 3. The results are shown in Table 7.
Table 7
Test C A7 Dewatering time / Turbidity
No. Dosage Dosage [s] / NTU
[kglt] [kg/t] C2-ref C1
1 25 0 22.0 / 49 23.4 / 43
2 25 2 22.1 / 50 16.3 / 40
3 25 4 21.2 / 46 14.3 / 40
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Example 9
Drainage performance was evaluated using the cationic and anionic polymers
and ATC according to Example 1 and the medium conductivity stock and procedure
according to Example 2. The results are shown in Table 8.
Table 8
Test ATC C A7 Dewatering time
No. Dosage Dosage Dosage [s]
[kg/t] [kg/t] [kg/t] C3-ref C3
1 3 3 1 20.8 11.0
2 3 3 1.5 17.9 9.3
3 3 3 2 14.7 7.9
Example 10
Drainage and retention performance was evaluated using the cationic and
anionic
polymers and ATC according to Example 1 and the medium conductivity stock and
procedures according to Examples 2 and 3. The results are shown in Table 9.
Table 9
Test ATC C A8 Dewatering time I Turbidity
No. Dosage Dosage Dosage [s] / NTU
[kg/t] [kg/t] [kglt] C3-ref C3
1 3 3 2 21.4/49 11.1/40
2 3 3 3 17.4/46 9.3/40
3 3 3 4 15.6/48 8.9/45
Example 11
Drainage performance was evaluated using the cationic and anionic polymers
according to Example 1 and the standard conductivity stock and procedures
according to
Example 2. The results are shown in Table 10.
Table 10
Test C A8 Dewatering time / Turbidity
No. Dosage Dosage [s] I NTU
[kglt] [kg/t] C2-ref C1
1 25 1 23.0 / 47 20.8/44
2 25 2 22.6 / 50 19.0 / 43
3 25 4 22.8 / 49 18.8 / 45
4 25 6 22.6 / 49 16.3 / 40
5 25 8 22.1 / 50 15.5 / 42
