Note: Descriptions are shown in the official language in which they were submitted.
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Sizing of Paper
The present invention relates to sizing of paper and more specifically to
dispersions of cellulose-reactive sizing agents, their preparation and use.
Back4round
Cellulose-reactive sizing agents, such as those based on alkyl ketene dimer
(AKD) and alkenyl succinic anhydride (ASA), are widely used in papermaking at
neutral or
slightly alkaline stock pH's in order to give paper and paper board some
degree of resistance
to wetting and penetratie~n by aqueous liquids. Paper sizes based on cellulose-
reactive sizing
agents are generally provided in the form of dispersions containing ati
aqueous phase and
finely divided particles or droplets of the sizing agent dispersed therein.
The dispersions are
usually prepared with the: aid of a dispersant system consisting of an anionic
compound, e.g.
sodium lignosuffonate, in combination with a high molecular weight amphoteric
or cationic
polymer, e.g. cationic starch, polyamine, polyamideamine or a vinyl addition
polymer.
Depending on the overall charge of the compounds of the dispersant system, the
size
dispersions will be cationic or anionic in nature. However, dispersions of
these types usually
exhibit rather poor stability and high viscosity, even at relatively low
solids contents, which
evidently lead to difficulties in handling the dispersions, for example on
storage and in use. A
further drawback is that the products have to be supplied as low concentration
dispersions
which further increases the costs of transportation of the active sizing
agent.
Cellulose-reactive sizing agents generally provide good sizing with low
dosages
of the sizing agent. However, it has been experienced that the efficiency of
conventional
cellulose-reactive sizing agents is deteriorated when they are used with
stocks having a high
cationic demand and containing substantial amounts of lipophiiic wood
extractives, such as,
for example, resin acids, fatty acids, fatty esters, triglycerides, etc. Due
to the anionic
character of lipophilic substances containing carboxylate or carboxylic acid
groups, stocks
containing substantial amounts of lipophilic extractives usually have a rather
high cationic
demand. It has been found that the lipophilic substances can be detrimental to
the adsorption
of sizing agents onto thE: fibres which may cause the poor sizing results. In
order to improve
sizing with such stocks the papermaker has had to increase the dosage of
sizing agent,
which of course is less favourable economically and can increase the
accumulation of sizing
agent in the white water recirculating in the papermaking process. These
problems are even
more pronounced in paper mills where white water is extensively recirculated
with the
. introduction of only low amounts of fresh water into the process, thereby
increasing the
cationic demand and the accumulation of lipophilic extractives and non-
retained sizing agent
in the white water and the stock to be dewatered.
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- 1a -
Summary of the Invention
In accordance with the invention there is provided aqueous
dispersion of a sizing agent, characterized in that it contains a cellulose-
reactive sizing agent and a dispersant system comprising a low molecular
weight cationic organic compound having a molecular weight less than 10,000
and an anionic stabilizer which is an anionic polyelectrolyte.
In accordance with another aspect of the invention there is
provided a method for the preparation of an aqueous dispersion of a
cellulose-reactive sizing agent, characterized in that the cellulose-reactive
sizing agent is homogenized in the presence of an aqueous phase and a
dispersant systern comprising a low molecular weight cationic organic
compound having a molecular weight less than 10,000 and an anionic
stabilizer which is an anionic polyelectrolyte.
In accordance with still another aspect of the invention there is
provided the use of an aqueous dispersion of the invention as a stock sizing
agent or surface sizing agent in the production of paper.
In accordance with still another aspect of the invention there is
provided a process for the production of paper by addition of an aqueous
dispersion of a sizing agent to a stock containing cellulosic fibres and
optional fillers, and dewatering the stock on a wire to obtain paper and white
water, wherein the dispersion is a dispersion of the invention as defined
above.
In still another aspect of the invention there is provided a
substantially water-free composition containing a cellulose-reactive sizing
agent, a low molecular weight cationic organic compound having a molecular
weight less than 10,000 and an anionic stabilizer which is an anionic
polyelectrolyte, arnd use of such composition in the preparation of an aqueous
dispersion of a celllulose-reactive sizing agent of the invention.
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The Invention
In accordance with the present invention it has been found that improved
stability and sizing characteristics can be obtained with aqueous dispersions
of cellulose-
reactive sizing agents in which the sizing agent is dispersed in the aqueous
phase by means
of a dispersant system comprising a low molecular weight cationic compound and
an anionic
stabilizer. The size dispersions of this invention exhibit excellent stability
and low viscosity
and they are particularly useful with papermaking stocks having a high
cationic demand
andlor containing high levels of lipophilic substances. It has also been found
that improved
sizing can be obtained by using such dispersions in papermaking processes
where white
water is extensively recirculated. More specifically, the present invention
relates to an
aqueous dispersion containing a cellulose-reactive sizing agent and a
dispersant system
comprising a low molecular weight cationic organic compound and an anionic
stabilizer, its
preparation and use, as further defined in the claims.
The present size dispersions makes it possible to produce paper with improved
sizing over conventional size dispersions at a corresponding dosage of
cellulose-reactive
sizing agent and to use a lower dosage of cellulose-reactive sizing agent to
attain a
corresponding level of sizing. The possibility of using lower amounts of
sizing agent to attain
in-specification sizing reduces the risk of accumulation of non-adsorbed
sizing agents in the
white water recirculating in the process, thereby reducing the risk of
aggregation and
deposition of the sizing agent on the paper machine. The present invention
thus offers
substantial economic and technical benefits.
The cellulose-reactive sizing agent according to the invention can be selected
from any of the cellulose-reactive sizing agents known in the art. Suitably
the sizing agent is
selected from the group consisting of hydrophobic ketene dimers, ketene
multimers, acid
anhydrides, organic isocyanates, carbamoyl chlorides and mixtures thereof,
preferably
ketene dimers and acid anhydrides, most preferably ketene dimers. Suitable
ketene dimers
have the general formula (t) below, wherein R~ and RZ represent saturated or
unsaturated
hydrocarbon groups, usually saturated hydrocarbons, the hydrocarbon groups
suitably
having from 8 to 36 carbon atoms, usually being straight or branched chain
alkyl groups
having 12 to 20 carbon atoms, such as hexadecyl and octadecyl groups. Suitable
acid
anhydrides can be characterized by the general formula (II) below, wherein R3
and R4 can be
identical or different and represent saturated or unsaturated hydrocarbon
groups suitably
containing from 8 to 30 carbon atoms, or R3 and R4 together with the -C-O-C-
moiety can
form a 5 to 6 membered ring, optionally being further substituted with
hydrocarbon groups
containing up to 30 carbon atoms. Examples of acid anhydrides which are used
commercially
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3
include alkyl and alkenyl succinic anhydrides and particularly isooctadecenyl
succinic
anhydride.
(1) R'-CH=C-CH-R2 (II) O O
I I ~ p
O-C ~O R~-C-O-C-R4
Suitable ketene dimers, acid anhydrides and organic isocyanates include the
compounds disclosed in U.S. Pat. No. 4,522,686.
Examples of suitable carbamoyi chlorides include those disGosed in U.S. Pat.
No.
3,887,427.
In addition to the cellulose-reactive sizing agent, the size dispersions may
also
contain a non-cellulose-reactive sizing agent. Examples of suitable sizing
agents of this type
include rosins, e.g. fortfied and/or ester~fied rosin, waxes, fatty acid and
resin acid
derivatives, e.g. fatty amides and fatty esters, e.g, glycerol triesters of
natural fatty acids.
The dispersions of this invention contain a dispersant, or dispersant system,
comprising a cationic organic compound and an anionic stabilizer. The
compounds are
preferably bound together by the force of electrostatic attraction, thereby
representing a
coacervate dispersant. When used in combination, these compounds are effective
as a
dispersant for the sizing agent although the cationic compound and/or the
anionic compound
do not have to be effecive as a dispersant when used singly. Particularly
preferred
dispersions of this invention include those containing a cationic surfactant
and an anionic
stabilizer, as defined hereinafter. In a preferred embodiment of the
invention, the dispersion
is anionic, i.e. the dispersant system has an overall anionic charge.
The cationic compound contains one or more cationic groups of the same or
different types and include cationic compounds having one cationic group and
cationic.
compounds having two or more cationic groups, i.e. cationic polyelectrolytes.
Examples of
suitable cationic groups include suifonium groups, phosphonium groups, acid
addition salts of
primary, secondary and tertiary amines or amino groups and quaternary ammonium
groups,
for example where the nitrogen has been quatemized with methyl chloride,
dimethyl sulfate
or benzyl chloride, preferably acid addition salts of amines/amino groups and
quaternary
ammonium groups. Cationic polyelectrolytes can have a degree of substitutio~~
varying over a
wide range; the degree of cationic substitution (DSc) can be from 0.01 to 1.0,
suitably from
0.1 to 0.8 and preferably from 0.2 to 0.6.
Suitable cationic organic compounds for use in this invention include cationic
compounds capable of functioning as a surfactant and/or dispersing agent
andlor coupling
agent between the particle or droplet of sizing agent and the anionic
stabilizer. Preferably the
cationic compound is a surfactant. Preferred cationic surfactants include
compounds having
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the general formula R4N+ X , wherein each R group is independently selected
from (i)
hydrogen; (ii) hydrocarbon groups, suitably aliphatic and preferably alkyl
groups, having from
1 to about 30 carbon atoms, preferably from 1 to 22 carbon atoms; and (iii)
hydrocarbon
groups, suitably aliphatic and preferably alkyl groups, having up to about 30
carbon atoms,
preferably from 4 to 22 carbon atoms, and being interrupted by one or more
heteroatoms,
e.g. oxygen or nitrogen, and/or groups containing a heteroatom, e.g. carbonyl
and acyloxy
groups; where at (east one, suitably at least three and preferably all of said
R groups contain
carbon atoms; suitably at least one and preferably at least two of said R
groups containing at
feast 7 carbon atoms, preferably at least 9 carbon atoms and most~preferably
at least 92
carbon atoms; and wherein X- is an anion, typically a halide like chloride, or
an anionic group
present in the anionic compound of the dispersant, e.g. where the surfactant
is a protonated
amine of the formula RAN wherein R and N are as defined above. Examples of
suitable
surfactants include dioctyldimethylammonium chloride, didecyldimethylammonium
chloride,
dicocodimethyfammonium chloride, cocobenzyldimethylammonium chloride,
coco(fractiona-
ted)benzyldimethylammonium chloride, octadecyl trimethylammonium chloride,
dioctadecyl
dimethylammonium chloride, dihexadecyl dimethylammonium chloride,
di(hydrogenated
tallow)dimethyiammonium chloride, di(hydrogenated tallow)benzylmethylammonium
chloride,
(hydrogenated tallow)benzyidimethylammonium chloride, dioleyfdimethylammonium
chloride,
and di(ethyiene hexadecanecarboxylate)dimethylammonium chloride. Particularly
preferred
cationic surfactants thus include those containing at least one hydrocarbon
group with from 9
to 30 carbon atoms and notably quaternary ammonium compounds.
Further prefer-ed cationic surfactants include quaternary di- and poly-
ammonium compounds containing at least one hydrocarbon group, suitably
aliphatic and
preferably alkyl, with from 9 to 30 carbon atoms, preferably from 12 to 22
carbon atoms.
Examples of suitable surfactants of this type include N-octadecyl-N-dimethyl-
N'-trimethyl-
propylene-diammonium dichloride.
Preferred cationic poiyelectrolytes further include low molecular weight
cationic
organic pclymers, optionally degraded, e.g. those derived from polysaccharides
like starches
and guar gums, cationic condensation products like cationic polyurethanes,
polyamide-
amines, e.g. polyamideamine-epichlorohydrin copolymers, poiyamines, e.g.
dimethylamine-
epichlorohydrin copolymers, dimethylamine-ethylenediamine-epichlorohydrin
copolymers,
ammonia-ethylenendichloride copolymers, vinyl addition polymers formed from
monomers
with cationic groups, e.g. homopolymers and copolymers of
diallyldimethylammonium
chloride, dialkylaminoalkyl acrylates, methacrylates and acrylamides (e.g.
dimethylaminoethyl
acryfates and methacrylates) which usually are present as acid addition salts
or quaternary
ammonium salts, optionally copolymerized with non-ionic monomers including
acrylamide,
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alkyl acrylates, styrene wand acryionitrile and derivatives of such monomers,
vinyl esters, and
the like.
The molecular weight of the cationic organic compound generally can be up to
about 10,000, usually up to about 5,000, suitably up to about 3,000 and
preferably up to
5 about 800. The moiecular weight is usually at least about 200. Suitable
cationic surtactants
may have a molecular weigtht up to about 3,000 and preferred cationic
surfactants have a
molecular weight between about 200 and about 800.
Suitable anionic stabilizers for use in this invention include anionic
compounds
functioning as stabilizer', andlor being effective in combination with the
cationic compound to
stabilize the sizing agent in an aqueous phase as well as anionic compounds
known as
useful as dispersants in the preparation of size dispersions. Preferably the
anionic compound
is water-soluble or water-dispersabte. The anionic stabilizer can be can be
selected from
organic or inorganic compounds and it can be derived from natural or synthetic
sources. The
anionic stabilizer of the dispersant system contains one or more anionic
groups of the same
or different types and include anionic compounds having one anionic group and
anionic
compounds having two or more anionic groups, herein referred to as an anionic
poiyelectrolyte. The term anionic polyelectraiyte is meant to include also
anionic compounds
acting as a polyelectrolyte, e.g. through chemical non-ionic interaction or
attraction. In a
preferred embodiment, the anionic stabilizer is an anionic poiyelectrolyte.
Examples of
suitable anionic groups, i.e. groups that are anionic or rendered anionic in
water, include
phosphate, phosphonat~s, sulphate, sulphonate, suiphonic acid and carboxylic
acid groups
and salts thereof, usually ammonium or alkali metal (generally sodium) salts.
The anionic
groups can be native or introduced by means of chemical modification in known
manner. The
anionic stabilizer can have a degree of anionic substitution (DS,~ varying
over a wide range;
the DSA can be from 0.01 to 1.4, suitably from 0.1 to 1.2 and preferably from
0.2 to 1Ø
Anionic polyelectrolytes may contain one or more cationic groups as long as it
has an overall
anionic charge.
In a preferred embodiment, the anionic stabilizer is selected from organic
compounds. Suitable anionic stabilizers of this type include polymeric
compounds such as
those based on polysaccharides like starches, guar gums, celluloses, chitins,
chitosans,
glycans, galactans, giucans, xanthan gums, mannans, dextrins, etc., preferably
phosphated,
sulphonated and carboxylated polysaccharides, as well as synthethic organic
polymers like
condensation products, e.g. anionic polyurethanes and polymeric anionic
compounds based
on naphthalene, e.g. condensated naphthalene sulfonates, and further vinyl
addition
polymers formed from monomers with anionic groups, e.g. acrylic acid,
methacylic acid,
maieic acid, itaconic acid, crotonic acid, vinyisulfonic acid, sulfonated
styrene and
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phosphates of hydroxyalkyl aaylates and methacrylates, optionally
copolymerized with non-
ionic monomers including acrylamide, alkyl acrylates, styrene and
acrylonitrils as well as
derivatives of such monomers, vinyl esters, and the like. Particularly
preferred organic
anionic stabilizers include anionic polysaccharides, e.g. cellulose-
derivatives like carboxy-
methyl celluloses, condensated naphthalene sulfonates, anionic acryiamide-
based polymers
and polymers based on acrylic acid and similar acid monomers.
in a preferred embodiment of the invention, the anionic stabilizer is
hydrophobe-modified and contains one or more hydrophobic groups, suitably
being a hydro-
phobically modified polysaccharide, preferably carboxymethyl cellulose:
F~camples of suitable
groups include hydrophobic substituents containing from 4 to about 30 carbon
atoms, notably
hydrophobic amide, ester and ether substituents comprising a saturated or
unsaturated
hydrocarbon chain of at least 4 and preferably from 8 to 30 carbon atoms,
optionally being
interrupted by one or more heteroatoms, e.g. oxygen or nitrogen, andlor groups
containing a
heteroatom, e.g. carbonyl or acyloxy. Suitable anionic polysaccharides,
anionic hydro-
phobicaHy modified polysaccharides and methods of introducing hydrophobic
substituents
into polysaccharides are for example disclosed in U.S. Pat. No. 4,687,519 and
International
Pat. Publ. No. WO 94/24169.
In another preferred embodiment, the anionic stabilizer is selected from
inorganic anionic materials, preferably anionic inorganic polyelectrolytes
such as, for
example, compounds containing silicon atoms, e.g. various forms of condensated
or
polymerized silicic acid which have negative hydroxyl groups, e.g. oligomeric
silicic acid,
polysilicic acid, poiysilicates and polyaluminiumsilicates.
The anionic stabilizer can also be selected from microparticuiate material
where
both organic and inorganic anionic materials are encompassed. Suitable
particulate materials
of this type include highly cross-linked anionic vinyl addition polymers, e.g.
acrylamide-based
and acryiate-based polymers, anionic condensation polymers, e.g. melamine-
sulfonic acid
sots, inorganic silica-based materials, e.g. materials of the type present in
aqueous silica-
based sots like silica sots, aluminated silica sots, aluminiumsilicate sots,
polysilicate microgels
and polyaluminiumsilicate microgels, as weU as silica gels and precipitated
silica. The
microparticulate material preferably is colloidal, i.e. in the colloidal range
of particle size. The
colloidal particles suitably have a particle size from about 1 nm to about 80
nm, preferably
from 2 to 35 nm and most preferably from 2 to 10 nm.
The molecular weight of the anionic compound can be varied over a broad
range from a few hundreds or thousands to several millions. Usually the
molecular weight is
above 200 and suitably above 500, whereas the upper limit is usually 10
million and
preferably 2 million. In a preferred embodiment, the molecular weight is up to
about 50,000.
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The amount of cationic and anionic compounds present in the dispersion
according to the invention can be varied over a broad range depending on,
among other
things, type and charges density of the cationic and anionic materials, type
of sizing agent,
desired anionicitylcationicity and solids content of the resulting dispersion.
The present
dispersion is suitably anionic and hereby is meant that the anionic charge of
the anionic
stabilizer is greater that the cationic charge of the cationic compound. In
the dispersion, the
cationic compound can be present in an amount of up to 100% by weight, usually
from 0.1 to
20% by weight, suitably from 1 to 10% by weight and preferably from 2 to 7% by
weight,
based on the sizing agE:nt, and the anionic stabilizer can be present ~in an
amount of up to
100% by weight, usually from 0.1 to 20% by weight, suitably from 0.2 to 10% by
weight and
preferably from 0.3 to 6% by weight, based on the sizing agent, where the
overall charge of
the cationic compound and the anionic stabilizer which are present in the
dispersions
preferably is anionic or negative.
It has been found that the present dispersions can be prepared in high solids
contents and yet exhibit very good stability on storage and low viscosity.
Accordingly, this
invention provides size dispersions with improved storage stability, higher
solids content
andlor lower viscosity. ,A further benefit observed with the present
dispersions is improved
dilute stability which means less aggregation of the particles or droplets of
sizing agent,
thereby forming lower levels of bigger aggregates having lower sizing
efficiency, as well as
less deposition of the hydrophobic sizing agent on the paper machine and less
wire
contamination, thereby reducing the need for maintenance of the paper machine.
The
present dispersions generally can have sizing agent contents of from about 0.1
to about 50°,'0
by weight and suitably above 20% by weight. Dispersions containing a ketene
dimer sizing
agent according to the invention may have ketene dimer contents within the
range of from 5
to about 50% by weight and preferably from about 10 to about 35% by weight.
Dispersions,
or emulsions, containing an acid anhydride sizing agent according to the
invention may have
acid anhydride contents within the range from 0.1 to about 30% by weight and
usually from
about 1 to about 20% by weight.
The sizing dispersions according to the invention can be produced by mixing an
aqueous phase with the anionic stabilizer, the cationic compound and the
sizing agent,
preferably at a temperature where the sizing agent is liquid, and homogenizing
the mixture so
obtained, suitably under pressure. Suitable temperatures for ketene dimer
sizing agents are
from about 55°C to 95°C whereas lower temperatures can be
employed for acid anhydrides.
The obtained emulsion, which contains droplets of sizing agent normally having
a size of
from 0.1 to 3.5 ~,m in diameter, is then cooled. In addition to the above-
mentioned
components other materials can also be incorporated into the size dispersions,
such as, for
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example, anionic and non-ionic dispersing agents and stabilizers, extenders,
e.g. urea and
urea derivatives, and preservative agents. It will be appreciated that the
negative and positive
charges of the compounds of the dispersant system can be formed in situ, for
example by
contacting the compounds with one another and/or by mixing the compounds with
an
aqueous phase and/or by lowering pH of the aqueous phase. For instance, the
loss of a
hydrogen from an acid group will form an anionic charge, and a basic amine or
an amino
group can be rendered cationic by protonation or abstraction of a hydrogen.
Accordingly, it is
possible to start with uncharged compounds in preparing the dispersion. For
example, an
organic compound with basic amino groups or a basic amine of thG formula R3N
can be
used, where the corresponding ammonium moiety R4N+ X be formed in the
preparation
process, where R, N and X can be as defined above.
ft has further been found that the components of the present dispersions can
be easily homogenized in the presence of an aqueous phase. Usually less energy
and tower
shear forces are required in this process compared to processes for preparing
conventional
dispersions and hereby simplified equipment can be employed. Therefore, a
further method
of preparing the present dispersions comprises (i) mixing the cellulose-
reactive sizing agent
with the dispersant system comprising the anionic stabilizer and the cationic
compound, as
defined above, to obtain an intermediate composition, and (ii) homogenizing
the intermediate
composition in the presence of an aqueous phase, as described above. it is
preferred that
the components are homogeneously mixed in stage (i). The sizing agent used in
stage (i)
may be solid although it is preferced that it is liquid in order to simplify
homogeneous mixing.
If desired, the intermediate composition can be removed after the mixing stage
(i), and
optionally be cooled for solidification, to form a substantially water-free
intermediate size
composition which enables simplified shipping in an economically attractive
manner. At the
location of intended use, or elsewhere, the size composition can be
homogenized in the
presence of water in conventional manner. This method is especially attractive
when
preparing dispersions of ketene dimers and acid anhydrides, the latter of
which are usually
prepared in the paper mill in direct connection to its use as a sizing agent
in the production of
paper. The provision of a storage-stable water free size composition thus
offers considerable
economic and technical benefits. The present invention thus also relates to a
substantially
water-free size composition comprising a cellulose-reactive sizing agent, a
cationic organic
compound and an anionic stabilizer, where the cationic and anionic compounds
when used in
combination are effective as a dispersant system for the sizing agent in an
aqueous phase,
its preparation and use, as further defined in the claims.
The components that are present in the composition according to the invention,
i.e., the cellulose-reactive sizing agent, the cationic compound and the
anionic stabilizer,
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9
preferably are as defined above. The present composition is substantially
water-free and
hereby is meant that a small amount of water can be present; the water content
can be from
0 up to 10% by weight, suitably less than 5% by weight and preferably less
than 2%. Most
preferably it contains no water. The composition preferably contains the
cellulose-reactive
sizing agent in a predominant amount, based on weight, i.e. at least 50% by
weight, and
suitably the composition has sizing agent content within the range of from 80
to 99.8% by
weight and preferably from 90 to 99.7% by weight. The cationic compound,
preferably a
surfactant, and the anionic stabilizer can be present in the size composition
in amounts
defined above with respect to the dispersions where the percentages are based
on the
weight of sizing agent. In the composition, the anionic stabilizer can be
present in an amount
of up to 100% by weight, usually from 0.1 to 20% by weight, suitably from 0.2
to 10% by
weight and preferably from 0.3 to 6% by weight, based on the sizing agent, and
the cationic
compound, e.g. a surfanant, can be present in an amount of up to 100% by
weight, usually
from 0.1 to 20% by weight, suitably from 1 to 10% by weight and preferably
from 2 to 7% by
weight, based on the sizing agent, where the overall charge of the cationic
compound and
the anionic stabilizer that are present in the composition preferably is
negative or anionic.
The dispersions according to the invention can be used in conventional manner
in the production of paper using any type of cellulosic fibres and they can be
used both for
surface sizing and internal or stock sizing. The term "paper", as used herein,
is meant to
include not only paper but all types of cellulose-based products in sheet and
web form,
including, for example, board and paperboard. The stock contains cellulosic
fibres, optionally
in combination with mineral fillers, and usually the content of ceflulosic
fibres is at least 50%
by weight, based on dry stock. Examples of mineral fillers of conventional
types include
kaolin, china clay, titanium dioxide, gypsum, talc and natural and synthetic
calcium
carbonates such as chalk, ground marble and precipitated calcium carbonate.
The present
invention also relates to a method for the production of paper in which an
aqueous
dispersion, as defined above, is used as a surface or stock size. Suitably the
amount of
cellulose-reactive sizing agent either added to the stock containing
cellulosic fibres, and
optional fillers, to be drained on a wire to form paper, or applied on the
paper surface as a
surface size, usually at the size press, is from 0.01 to 1.0% by weight, based
on the dry
weight of cellulosic fibres and optional fillers, preferably from 0.05 to 0.5%
by weight, where
the dosage is mainly dependent on the quality of the pulp or paper to be
sized, the cellulose-
reactive sizing agent used and the level of sizing desired.
The dispersions of this invention, notably the anionic dispersions, are
particularly useful in stock sizing of pulp having a high cationic demand
and/or containing
substantial amounts of lipophilic substances, for example stacks prepared from
wood-
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containing and recycled pulps, for example where recirculation of white water
is extensive.
Examples of lipophilic substances commonly found in paper pulp include anionic
and non-
ionic iipophilic substances, such as, for example, resin acids, fatty acids,
fatty esters,
triglycerides, etc. The amount of lipophilic substances may be at least 10 ppm
and up to
5 about 100 ppm, usually at least 20 ppm, suitably at least 30 ppm and
preferably at least 50
ppm, measured as ppm DCM by means of extraction using DCM (dichloromethane) in
known
manner. The cationic demand can be at least 50, suitably at least 100 and
preferably at least
150 peq/litre stock filtrate. The cationic demand can be measured in
conventional manner,
for example by means of a Mutek Particle Charge Detector using a'_stock
filtrate obtained
10 from a raw stock filtered through a 1.6 p.m filter and
poly(diallyidimethyiammonium chloride)
as a titrant. Further, the present dispersions are preferably used in
papermaking processes.
where white water is extensively 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. Recircuiation of white water in the
process preferably
takes place by mixing the white water with ceifulosic fibres, preferably in
the form of a stock
or suspension, before or after the addition of the sizing dispersion, e.g. to
form the stock to
be dewatered. Fresh water can be introduced in the process at any stage; for
example, it can
be mixed with cellulosic fibres in order to form the stock, and it can be
mixed with a stock
containing cellulosic fibres to dilute it so as to form the stock to be
dewatered, before or after
mixing the stock with white water and before or after the addition of the
sizing dispersion.
Chemicals conventionally added to the stock in papermaking such as retention
aids, aluminium compounds, dyes, wet-strength resins, optical brightening
agents, etc., can
of course be used in conjunction with the present dispersions. Examples of
aluminium
compounds include alum, aluminates and polyaluminium compounds, e.g.
polyaluminium
chlorides and sulphates. Examples of suitable retention aids include cationic
polymers,
anionic inorganic materials in combination with organic polymers, e.g,
bentonite in
combination with cationic polymers, silica-based sots in combination with
cationic polymers or
cationic and anionic polymers. Particularly good stock sizing can be obtained
when using the
dispersions of the invention in combination with retention aids comprising
cationic polymers.
Suitable cationic polymers include cationic starch, guar gum, acrylate-based
and acrylamide-
based polymers, poiyethyleneimine, dicyandiamide-formaldehyde resins,
polyamines,
polyamidoamines and poly(diallyldimethyl ammoniumchloride) and combinations
thereof.
Cationic starch and cationic acrylamide-based polymers are preferably used,
either alone or
in combination with each other or with other materials. In a preferred
embodiment of the
invention, the dispersions are used in combination with a retention system
comprising at least
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11
one cationic polymer and anionic silica-based particles. The present
dispersions can be
added before, between, after or simultaneously with the addition of the
cationic polymer ar
polymers. It is also possible to pre-mix the size dispersion with a retention
aid, e.g. a cationic
polymer like cationic starch or a cationic acrylamide-based polymer, or an
anionic silica-
based material, prior to~ introducing the mixture thus obtained into the
stock. Accordingly, the
dispersion can be prepared just prior to introducing it into the stock by
bringing into contact a
size dispersion containing the cationic compound, preferably a cationic
surfactant, with an
anionic silica-based material, for example as defined above.
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
Anionic alkyl ketene dimer (AKD) dispersions according to the invention were
prepared by mixing di(hydrogenated tallow) dimethylammonium chloride, which is
a cationic
surfactant commercially available under the trade name Querton 442, Akzo
Nobel, with
molten AKD at 70°C, passing the mixture through a homogenizer in the
presence of an
aqueous solution of an anionic stabilizer and then cooling the dispersion so
obtained. The pH
of the dispersion was adjusted to about 5 by addition of acid. The anionic
stabilizer used in
this Example was an anionic fatty amide-modified carboxymethyl cellulose
(FACMC)
containing a hydrophobic substituent derived from N-hydrogenated tallow-1,3-
diaminopropan
prepared according to the disclosure of WO 94124169. The FACMC had a degree of
carboxylic substitution of 0.6 and a degree of hydrophobic substitution of
0.1. The dispersions
contained AKD particles with an average particle size of about 1 ~m which were
anionicafly
charged, as shown by a negative zeta potential determined by means of a
ZetaMaster S
Version PCS. The AKC> content of the dispersions were 30%. Dispersion No. 1
contained 3%
of cationic surfactant and 1 % of anionic stabilizer, both based on the weight
of AKD.
Dispersion No. 2 contained 7% of cationic surfactant and 1 % of anionic
stabilizer, both based
on the weight of AKD.
Example 2
The general procedure of Example 1 was repeated except that a condensated
sodium naphthalenesulphonate commercially availably under the trade name
OrotanT"" SN,
Rohm & Haas Company, was used as the anionic stabilizer and different
proportions of the
compounds of the dispersion was employed. Dispersion No. 3 obtained in this
Example had
an AKD content of 30°,io and contained 6% of anionic stabilizer and 4%
of cationic surfactant,
both based on the weight of AKD. The dispersion contained AKD particles with
an average
particle size of about 1 ~m which were anionically charged, determined as
above.
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Example 3
Stability of the anionic dispersions according to Examples 1 and 2 was tested
as follows: The dispersion was diluted with water to give a dispersion
containing 40 ppm of
AKD. In some of the tests 10 ppm of stearic acid was added in order to raise
the content of
lipophilic substances and the cationic demand. The dilute dispersion was
placed in a jar
equipped with a device for turbidity measurements, a loop, circulation means
and heating
and cooling means. A set volume of the dilute dispersion was circulated in the
loop while
automatically recording the turbidity and subjecting the dispersion to a
heating and cooling
cycle for a set time period of 45 minutes. The temperature of the dispersion
was raised
from 20°C to 62°C and then lowered again to 20°C.
Turbidity is affected by particle size and
the difference in turbidity of the dispersion before and after a temperature
cycle is a mea-
sure of the ability of the dispersed particles to withstand growth by
agglomeration and thus
a measure of the stability of the dispersion. The difference in turbidity (OT)
is calculated as
follows: ~T=(final turbidity I initial turbidity) x 100. The higher the DT the
better the stability.
Two standard dispersions were also tested for comparison purposes; Ref. 1
is an anionic AKD dispersion containing a dispersant system comprising sodium
ligno-
sulphonate and cationic starch where the lignosulphonate is present in ionic
excess; Ref. 2
is a cationic AKD dispersion also containing sodium fignosulphonate and
cationic starch
but where the cationic starch is present in ionic excess. Table 1 gives the
results obtained.
Table 1
Dispersion No. Stearic acid fopml ~T
1 - 53
1 10 40
2 - 79
2 10 66
3 - 72
3 10 55
Ref. 1 - 45
Ref. 1 10 32
Ref. 2 - 35
Ref. 2 10 6
As is shown in Table 1 the OT values of the dispersions of this invention were
considerably higher than those of the standard dispersions which accordingly
are indicative
of better dilute stability.
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Example 4
Sizing effic;iency of size dispersions according to Example 3 was evaluated
irr
this Example. Paper sheets were prepared according to the standard method SCAN-
C23X
for laboratory scale. T'he papermaking stock used contained 80% of 60:40
bleached
birchlpine sulphate and 20% of chalk to which 0.3 g/I of NaZS0410H20 was
added. Stock
consistency was 0.5% and pH 8Ø The size dispersions were used in conjunction
with a
commercial retention and dewatering system, CompozifT"", comprising cationic
starch and
an anionic aluminium-modified silica sol which were added to the stock
separately; the
cationic starch was added in an amount of 8 kg/ton, based on dry stock, and
the silica sol
was added in an amount of 0.8 kg/ton, calculated as Si02 and based on dry
stock
Cobb values, measured according to TAPPI standard T 441 OS-63, obtained
in the tests are set forth in Table 2. The dosage of AKD is based on dry
stock.
Table 2
Dispersion No. AKD dosage fk-/~ton~ Cobb 60 f4lmzl
1 0.45 54
__ 1 0.60 27
Ref. 1 0.45 80
Ref. 1 0.60 30
Ref. 2 0.45 68
Ref. 2 0.60 31
Table 2 dE:monstrates the improvement in paper sizing obtained with the size
dispersion according to the invention.
Example 5
Sizing efficiency was evaluated according to the procedure of Example 4
except that the stock contained precipitated calcium carbonate as a filler
instead of chalk,
and the dosage of cationic starch was 12 kglton, based on dry stock. In some
of the tests
10 ppm of stearic acid was added to the stock in order to raise the the
cationic demand
and the fiphophific sub:;tance content of the stock. The results are set forth
in Table 3.
Table 3
Dispersion No. AKD dosaoe fkgltonj Stearic acid (ppm] Cobb 60 fo/m21
1 0.45 - 32
1 0.60 - 28
1 0.75 - 26
1 0.45 10 62
1 0.60 10 36
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14
1 0.75 10 27
Ref. 1 0.45 - 50 -
Ref. 1 0.60 - 32
Ref. 1 0.75 - 30
Ref. 1 0.45 10 103
Ref. 1 0.60 10 76
Ref. 1 0.75 10 35
As is evident from Table 3, Dispersion No. 1 according to the invention
generally gave much better sizing than the dispersion Ref. 1 used for
comparison, and
considerably improved sizing effect was obtained when the stock contained a
substantial
amount of lipophilic substances.
Example 6
A water-free size composition according to the invention was prepared by dry
mixing 93 parts of AKD pellets with 3 parts of cationic surfactant according
to Example 1
and 4 parts of anionic stabilizer according to Example 2. This dry mixture was
later added
to hot water and the aqueous mixture so obtained was heated to 80°C,
pumped through a
high shear pump and then cooled to room temperature. The resulting anionic
dispersion,
Dispersion No. 4, had an AKD content of 20% and an average particle size of
about 1 um.
Sizing efficiency was evaluated as in Example 4, except that the cationic
starch addition
amounted to 12 kg/ton, based on dry stock. The results are given in Table 4.
Table 4
Dispersion No. AKD dosage fkaltonl Cobb 60 ~g/m?1
4 0.30 58
4 0.40 30
Ref. 1 0.30 84
Ref. 1 0.40 65
Ref. 2 0.30 66
Ref. 2 0.40 40
Table 4 demonstrates the improvement in paper sizing obtained with the size
dispersion according to the invention.
Example 7
An AKD dispersion according to the invention having a dispersant system
comprising a cationic surfactant and an anionic stabilizer in the form of an
inorganic
microparticulate material was evaluated in this test series.
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WO 98/33979 PCT/SE98/00192
The dispersion was prepared by pre-blending at 75°C 0.2 g of
cocoamine
commercially availably under the trade name Armeen CT"", which is a mixture of
amines of
the formula RNH2 wherein R is C~2-C~8 hydrocarbons, and 1.0 g, calculated as
Si02, of an
aqueous sol of aluminiium-modified silica of the type disclosed in U.S. Pat.
No. 5,368,833,
5 and then adding 25 g of AKD and acid to adjust pH to 4Ø The aqueous
mixture was
homogenized using an Ultra Turrax and then cooled. The dispersion obtained,
Dispersion
No. 5, had an AKD content of 25% by weight and contained a dispersant system
which
was anionic in nature.
Sizing efficiency of the dispersion was evaluated according to the procedure
10 of Example 4 using a similar stock at pH 8.1 and using the standard AKD
dispersion Ref. 2
for comparison. The results are set forth in Table 5 where the dosage of AKD
is based on
dry stock.
Table 5
Dispersion No. AKD dosa4e jk41ton1 Cobb 60 (q/mzl
5 0.3 58
5 0.5 30
5 0.6 28
Ref. 2 0.3 73
Ref. 2. 0.5 33
Ref. 2 0.6 30
15 Example 8
An AKD dispersion according to the invention was prepared and evaluated in
a similar manner to Ea;ample 7 except that the anionic stabilizer used in this
Example was
a melamine-suffonic acid sol, prepared in accordance with the teachings of
Int. Pat. Appl.
Publ. No. WO 961340;?7. Dispersion No. 6 was prepared from 0.4 g of cocoamine,
2 g of
melamine-suffonic acid, 30 g of AKD and water up to 100 g. The results of the
sizing tests
are shown in Table 6 where the dosage of AKD is based on dry stock.
Table 6
Dispersion No. AKD dosa4e (k4/tonl Cobb 60 (ctlm2l
6 0.4 39
6 0.5 28
6 0.6 22
Ref. 2 0.4 50
Ref. 2 0.5 35
Ref. 2 0.6 25
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Example 9
Ease of manufacture of dispersions according to the invention was evaluated
by preparing anionic AKD dispersions at different AKD contents. Dispersions of
the inven-
tion were prepared by homogenising a mixture of 0.8% by weight of
di(hydrogenated
tallow)dimethylammonium chloride, 1.6% by weight of condensated sodium
naphthalene-
sulphonate, 77.6% by weight of water and 20% by weight of AKO for a set time
using an
Ultra Turrax mixer at 15.000 rpm and then cooling the dispersion so obtained
for 2 hours.
Similar dispersions were prepared in the same manner at different AKD contents
in order to
provide dispersions with AKD contents of 10, 20, 30 and 40% by weight. The
dispersions are
denoted Inv. followed by the AKD content in % by weight.
Standard AKD dispersions were manufactured for comparison purposes in
the same manner and under the same conditions by homogenising a mixture of
1.0% by
weight of cationic starch, 0.25% by weight of sodium lignosulfonate, 89% by
weight of
water and 10% by weight of AKD. Similar dispersions were prepared at different
AKD
contents in order to provide standard dispersions with AKD contents of 10, 20,
30 and 40%
by weight. The dispersions are denoted Ref. 3 followed by the AKD content in %
by weight.
Partic;e size and viscosity were assessed in conventional manner. Table 7
shows the results obtained.
Table 7
AKD Dispersion Particle size Viscosity
No. (um) (cps)
Inv. - 10% 2.98 10
Inv. - 20% 3.12 20
Inv. - 30% 3.50 20
lnv. - 40% 3.50 25
Ref. 3 - 10% 4.31 15
Ref. 3 - 20% 4.52 20
Ref. 3 - 30% 5.20 25
Ref. 3 - 40% 5.57 40
Table 3 demonstrates that the dispersions according to the invention were
easier to manufacture; a lower viscosity was obtained at corresponding AKD
contents and a
smaller particle size was obtained using the same amount of energy to set
surfaces free.
Compared to the standard dispersion, less energy and lower shear forces are
thus required
according to this invention in order to manufacture dispersions with equal
particle size. fn
addition, an increase in stirrer speed to 25.000 rpm considerably reduced the
particle size of
the dispersions according to the invention to be within the range of from 1 to
2 Vim.
