Note: Descriptions are shown in the official language in which they were submitted.
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DISPERSION
The present invention relates to an aqueous dispersion comprising a cellulose
reactive sizing agent, a cellulose non-reactive sizing agent and an
emulsifier, its
preparation, and use thereof in paper making.
Cellulose reactive sizes, such as those based on alkyl ketene dimer (AKD) and
alkenyl succinic anhydride (ASA), are widely used for internal sizing in
papermaking. They
generally provide good internal sizing even in low dosages. However, it has
been
experienced that under some circumstances the efficiency of conventional
cellulose reactive
sizing agents is not fully satisfactory, for example when used with stocks
having a high cat-
ionic demand and containing substantial amounts of lipophilic wood
extractives, such as
resin acids, fatty acids, fatty esters, triglycerides, etc.
It has also been suggested to use cellulose reactive sizing agents for surface
sizing, but it has been found that they may cause problems with size
reversion, toner
adhesion and high speed paper converting.
Cellulose non-reactive sizes have so far mainly been used for surface sizing.
Examples of such materials are starch and other polymeric sizes such as
copolymers of
styrene with vinyl monomers such as maleic anhydride, acrylic acid and its
alkyl esters,
acrylamide, etc. Cellulose non-reactive sizes generally exhibit improved toner
adhesion,
little or no effect on coefficient of friction, no effect, or an improved
effect on high speed
converting, and no size reversion when compared to reactive sizes. However,
they are
less efficient at sizing than the cellulose reactive sizes.
Cellulose reactive sizes are generally provided in the form of dispersions
containing
an 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 lignosulfonate, in combination with a high
molecular
weight amphoteric or cationic polymer, e.g. cationic starch, polyamine,
polyamide amine 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.
US Patent 5969011 discloses an improved aqueous dispersion of a cellulose-
reactive sizing agent dispersed in the aqueous phase by means of a dispersant
system
comprising a low molecular weight cationic organic compound and an anionic
stabiiiser.
WO 02/090653 discloses a sizing composition comprising a sizing agent, a non-
ionic surfactant, an anionic surfactant and a monohydric alcohol.
US Patent 4529447 discloses a sizing composition comprising a carboxylic acid
anhydride and a polyoxyalkylene non-ionic surfactant blocked with a lower
alkyl, acyl or
carbamoyl group and/or an alkaline earth metal salt of a sulfur-containing
anionic surfactant.
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EP-A1-151646 discloses a sizing agent composition based on alkyl-succinic
anhydride.
US Patent 5498648 discloses a paper size mixture prepared by mixing a
suspension of cationic starch with a polymer dispersion and emulsifying a
alkyldiketene in
this mixture. However, such formulations are predominantly cationic and have
been found to
interfere with anionic components used in paper making, particularly optical
brightening
agents.
US Patent 6162328 discloses a process for the production of paper in which
cellulose reactive size that is not solid at 25 C and a cellulose non-reactive
size that is a
polymer of weight average molecular weight greater than about 1500 are applied
to paper
obtained by sheeting and drying an aqueous pulp suspension. However, it has
been
found difficult to provide dispersions of high stability comprising both a
cellulose reactive
size and a cellulose non-reactive size, particularly for anionic dispersions.
It is an object of the invention to provide a dispersion of high stability
comprising a
cellulose reactive sizing agent.
It is another object of the invention to provide a dispersion comprising a
cellulose
reactive sizing agent and a cellulose non-reactive sizing agent.
It is still another object of the invention to provide a size of high
efficiency for
internal sizing.
It is a further object of the invention to provide a size of high efficiency
for surface
sizing.
It has surprisingly been found possible to obtain stable dispersions of
cellulose
reactive and cellulose non-reactive sizing agents by using a certain kind of
emulsifier. Thus,
the invention concerns an aqueous dispersion useful for internal sizing or
surface sizing in
the production of paper, comprising at least one cellulose reactive sizing
agent selected from
the group consisting of ketene dimers and multimers, at least one cellulose
non-reactive
sizing agent, and at least one emulsifier selected from the group consisting
of oxyalkylene
phosphate and sulfate esters (the latter also being called oxyalkylene
sulfonates), and salts
thereof, of which oxyalkylene phosphate esters and salts thereof are most
preferred.
The weight ratio between the cellulose reactive sizing agent and the cellulose
non-
reactive sizing agent is preferably from about 1:99 to about 99:1, most
preferably from about
1:9 to about 9:1. In a dispersion for internal sizing, suitable for being
added to a stock
containing cellulosic fibres, the weight ratio preferably is from about. 0,4:1
to about 99:1,
most preferably from about 1:1 to about 9:1, while in a dispersion for surface
sizing, suitable
for being added to a paper web, the weight ratio preferably is from about 1:99
to about 1:1,
most preferably from about 1:9 to about 1:1.5.
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Preferably, the dispersion also comprises at least one cationic organic
compound
having a weight average molecular weight less than about 10000 or at least one
anionic
stabiiiser, or both, which is most preferred.
In the most preferred embodiment the dispersion thus comprises a cellulose
reactive sizing agent selected from the group consisting of ketene dimers and
multimers, a
cellulose non-reactive sizing agent and a dispersing system comprising an
emulsifier
selected from the group consisting of oxyalkylene phosphate and sulfate esters
and salts
thereof, a cationic organic compound having a weight average molecuiar weight
less than
about 10000 and an anionic stabiliser.
The amount of ketene dimers. and multimers in the dispersion is preferably
from
about 0.1 to about 50 wt%, most preferably from about 0.5 to about 50 wt%.
Preferably at
least one hydrophobic ketene dimer is present. Preferred ketene dimers have
the general
formula:
R'-CH= C-CH-RZ
I I
o-c=o
where R' and R2 represent the same or different saturated or unsaturated
hydrocarbon
groups such as alkyl, alkenyl, cycloalkyl, aryl or aralkyl. The hydrocarbon
groups preferably
have from 6 to 36 carbon atoms, most preferably from 12 to 20 carbon atoms.
Examples of
hydrocarbon groups include octyl, decyl, dodecyl, tetradecyl, hexadecyl,
octadecyl,
eicosyl, docosyl, tetracosyl, phenyl, benzyl, beta-naphthyl, cyclohexyl and
hexadecyl
groups. Preferred hydrocarbon groups are straight or branched chain alkyl
groups, such as
hexadecyl and octadecyl groups. Useful ketene dimers also include those
prepared from
organic acids such as montanic acid, naphthenic acid, 9,10-decylenic acid,
9,10-
dodecylenic acid, paimitoleic acid, oleic acid, ricinoleic acid, linoleic
acid, eleostearic acid,
naturally occurring mixtures of fatty acids found in coconut oil, babassu oil,
palm kernel
oil, palm oil, olive oil, peanut oil, rape oil, beef tallow, lard, whale
blubber, and mixtures of
any of the above named fatty acids with each other.
The amount of emuisifier selected from oxyalkylene phosphate and sulfate
esters
and salts thereof in the dispersion is preferably from about 0.01 to about 10
wt%, most
preferably from about 0.1 to about 5 wt%. Preferred phosphate and sulfate
esters fall under
the formula:
R3 - A' - O- Q- R4
where R4 is - OH or - O- AZ - R5;
A' and A2, independently of each others, are oxyalkylene chains, preferably
with from 2 to
100 oxyalkylene units, most preferably with from 3 to 50 oxyalkylene units,
particulariy most
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preferably with from 5 to 20 oxyalkylene units;
Q is PO(OH) or SO2, of which PO(OH) is preferred; and,
R3 and R5, independently of each others, are hydrocarbon groups, preferably
having from 3
to 50 carbon atoms, most preferably from 8 to 20 carbon atoms.
The hydrocarbon groups may, for example, be alkyl, alkenyl, cycloalkyl, aryl
or
aralkyl, of which aliphatic groups and particularly alkyl groups are
preferred. The oxyalkylene
chains preferably consist of oxyethylene units, oxypropylene units or a
mixture thereof, of
which pure oxyethylene chains are most preferred. The most preferred
emulsifiers belong to
the group of aliphatic mono and di (polyoxyethylene alkyl) phosphate esters
having one or
two oxyethylene chains each comprising from 5 to 15 moles ethylene oxide and
where
the alkyl group(s) have from 10 to 15 carbon atoms. Examples of such
polyoxyethylene
alkyl phosphate esters include ethoxylated tridecyl phosphate esters. Most
preferably a
mixture of mono and di (polyoxyalkylene alkyl) esters of phosphate is used.
As already stated, the emulsifier may also be one or more salt of compounds as
described above, preferably ammonium or alkali metal salts, such as sodium or
potassium
salts, but also salts of other metals such as magnesium or calcium are
possible.
If a cationic organic compound having a weight average molecular weight less
than
about 10000 is present, the amount thereof in the dispersion is preferably
from about 0.01 to
about 5 wt / , most preferably from about 0.1 to about 2 wt%. The cationic
organic
compound preferably contains one or more cationic groups of the same or
different types
and most preferably 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 sulfonium 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 quaternized 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
substitution
(DSc) varying over a wide range, for example from about 0.01 to about 1.0,
preferably from
about 0.1 to about 0.8 and most preferably from about 0.2 to about 0.6.
Suitable cationic organic compounds for use in this invention include cationic
com-
pounds capable of functioning as a surfactant and/or dispersing agent and/or
coupling agent
between particles or droplets of a sizing agent and/or an anionic stabiliser.
Preferably the
cationic organic compound is a surfactant. Preferred cationic surfactants
include compounds
having the general formula R4N+ X, wherein each R group, independently of each
other, is
hydrogen or a hydrocarbon group having from 1 to 30 carbon atoms, preferably
from 1 to 22
carbon atoms. The hydrocarbon groups are suitably aliphatic and preferably
alkyl groups,
and may be interrupted by one or more heteroatoms, e.g. oxygen or nitrogen,
and/or groups
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containing a heteroatom, e.g. carbonyl and acyloxy groups. At least 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 least 7 carbon atoms,
preferably at
least 9 carbon atoms and most preferably at least 12 carbon atoms. X- is an
anion, suitably
5 a halide like chloride, or an anionic group present in an anionic compound
of the dispersion,
e.g. where the surfactant is a protonated amine of the formula R3NH+ where R
is as defined
above. Examples of suitable surfactants include dioctyldimethylammonium
chloride, didecyl-
dimethylammonium chloride, dicocodimethylammonium chloride,
cocobenzyidimethylammo-
nium chloride, coco(fractionated)benzyldimethylammonium chloride, octadecyl
trimethyl-
ammonium chloride, dioctadecyl dimethylammonium chloride, dihexadecyl
dimethylammo-
nium chloride, di(hydrogenated tallow)dimethylammonium chloride,
di(hydrogenated tallow)-
benzylmethylammonium chloride, (hydrogenated tallow)benzyldimethylammonium
chloride,
dioleyidimethylammonium chloride, and di(ethylene
hexadecanecarboxylate)dimethyl-
ammonium 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.
Useful cationic polyelectrolytes also include low molecular weight cationic
organic
polymers, optionally degraded, e.g. those derived from polysaccharides like
starches and
guar gums, cationic condensation products like cationic polyurethanes,
polyamideamines,
e.g. polyamideamine-epichlorohydrin copolymers, polyamines, e.g. dimethylamine-
epichlo-
rohydrin copolymers, dimethylamine-ethylenediamine-epichiorohydrin 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 acrylates and methacrylates) which usually are present as
acid addition
salts or quaternary ammonium salts, optionally copolymerized with non-ionic
monomers
including acrylamide, alkyl acrylates, styrene and acrylonitrile and
derivatives of such
monomers, vinyl esters, and the like.
The weight average molecular weight of the cationic organic compound generally
can be up to about 10000, usually up to about 5000, suitably up to about 3000
and
preferably up to about 800, and most preferably at least about 200. Suitable
cationic
surfactants preferably have a weight average molecular weight up to about
3000, most
preferably from about 200 to about 800.
If an anionic stabiliser is present, the amount thereof in the dispersion is
preferably
from about 0.01 to about 5 wt%, most preferably from about 0.1 to about 3 wt%.
Suitable
anionic stabilisers for use in this invention include anionic compounds
functioning as
stabilisers and/or being effective in combination with a cationic organic
compound as
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described above to stabilise 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-dispersable. The
anionic
stabiliser can be can be selected from organic or inorganic compounds and can
be derived
from natural or synthetic sources. The anionic stabiliser of the dispersant
system contains
one or more anionic groups of the same or different types and include anionic
compounds
having one anionic grbup and anionic compounds having two or more anionic
groups,
herein referred to as an anionic polyelectrolyte. The term anionic
polyelectrolyte 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 stabiliser
is an anionic
polyelectroiyte. Examples of suitable anionic groups, i.e. groups that are
anionic or rendered
anionic in water, include phosphate, phosphonate, sulfate, sulforiate,
sulphonic 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 stabiliser can have a degree of
anionic
substitution (DSA) 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 stabiliser is selected from organic
compounds. Suitable anionic stabilisers of this type include polymeric
compounds such as
those based on lignin or polysaccharides like starches, guar gums, celluloses,
chitins,
chitosans, glycans, galactans, glucans, xanthan gums, mannans, dextrins, etc.,
preferably
phosphated, sulphonated and carboxylated lignin or 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, maleic acid, itaconic acid, crotonic acid, vinylsulfonic
acid, sulfonated
styrene and phosphates of hydroxyalkyl acrylates and methacrylates, optionally
copoly-
merized with non-ionic monomers including acrylamide, alkyl acrylates, styrene
and acrylo-
nitrile as well as derivatives of such monomers, vinyl esters, and the like.
Particularly
preferred organic anionic stabilisers include anionic polysaccharides, e.g.
cellulose-
derivatives like carboxymethyl celluloses, condensated naphthalene or lignin
sulfonates,
anionic acrylamide-based polymers and polymers based on acrylic acid and
similar acid
monomers.
In one embodiment of the invention, the anionic stabiliser is hydrophobically-
modified and contains one or more hydrophobic groups, suitably being a
hydrophobically
modified polysaccharide, preferably carboxymethyl cellulose. Examples of
suitable groups
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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, and/or groups
containing a
heteroatom, e.g. carbonyl or acyloxy.
In the case the anionic stabiliser is an organic compound or polymer, its
weight
average molecular weight is preferably above about 200 most preferably above
500, but is
preferably below 50000.
In another embodiment, the anionic stabiliser 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,
polysilicates and
polyaluminiumsilicates.
The anionic stabiliser can also be selected from microparticulate 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 acrylate-based polymers, anionic condensation polymers,
e.g.
melamine-sulfonic acid sols, inorganic silica-based materials, e.g. materials
of the type
present in aqueous silica-based sols like silica sols, aluminated silica sols,
aluminiumsilicate
sols, polysilicate microgels and polyaluminiumsilicate microgels, as well as
silica gels and
precipitated silica. The microparticulate material preferably is colloidal,
i.e. in the colloidal
range of parkicle size. The colloidal particles suitably have a particle size
from about 1 nm to
about 40 nm, preferably from 2 to 35 nm and most preferably from 2 to 10 nm.
A cellulose non-reactive sizing agent is preferably present in the dispersion
in an
amount from about 0.1 to about 50 wt%, most preferably from about 0.5 to about
50 wt%.
Suitable cellulose non-reactive sizing agents are polymeric materials
preferably having a
weight average molecular weight greater than 50000, most preferably from 50000
up to
about 1000000. Preferably the polymeric material is made from ethylenically
unsaturated
monomers.
Particularly suitable polymers include copolymers of styrene or substituted
styrenes with at least one other kind of ethylenically unsaturated monomers,
preferably
comprising monomers containing one or more carboxyl groups. Examples of such
monomers include maleic anhydride, acrylic acid, methacrylic acid and itaconic
acid, as
well as esters, amides and nitrile thereof, of which esters are particularly
preferred.
Preferred esters are alkyl esters where the alkyl group preferably have from I
to 12
carbon atoms, most preferably from I to 5 carbon atoms. Particularly preferred
are esters
of acrylic acid or methacrylic acid. Examples of suitable alkyl groups are
methyl, ethyl,
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propyl, n-butyl, iso-butyl, tert-butyl and 2-butyl. A mixture at least two
isomeric butyl
acrylates or methacrylates, such as n-butyl- and t-butyl acrylate or
methacrylate, is
particularly preferred. The monomers as described above may also be co-
polymerised
with other ethylenically unsaturated monomers.
In a preferred embodiment the cellulose non-reactive sizing agent is a co-
polymer obtained from ethylenically unsaturated monomers comprising from about
20 to
about 80 wt%, preferably from about 30 to about 70 wt% of styrene or
substituted
styrene, from about 20 to about 80 wt%, preferably from about 30 to about 70
wt% of
alkyl acrylate or methacrylate, and from 0 to about 15 wt%, preferably from 0
to about 10
wt% of other ethylenically unsaturated monomers.
The dispersion of the invention may also comprise other components, such as
one or more of biocides, defoamers, inorganic compounds like aluminium or
zirconium
compounds, etc.
The dispersion of the invention is preferably predominantly anionic, which
reduces the risk for interference with anionic components used in paper
making. The pH
is preferably from about 2 to about 6, most preferably from about 3 to about
5, which
improves the stability of e.g. ketene dimers. The viscosity is preferably from
about 1 to
about 300 mPas, most preferably from about 5 to about 100 mPas.The dry content
is
preferably from about I to about 50 wt 6 , most preferably from about 5 to
about 40 wt / .
It has been found possible to provide a dispersion of the invention with low
viscosity and where both the static storage stability and the thermal
stability are excellent.
Furthermore, the dispersion of the invention has been found very efficient
both for internal
sizing and surface sizing at paper making.
The term "paper", as used herein, is meant to include not only ordinary paper
but all
types of cellulose-based products in sheet or web form, including, for
example, board and
paperboard. However, the invention is particularly advantageous for
preparation of graphic
paper to be used in all kinds of printing processes, such as ink-jet printing,
laser printing,
copying, etc.
The invention also concerns a process for the preparation of a dispersion as
3.0 described above. The process comprises the steps of bringing together at
least one
cellulose reactive sizing agent selected from the group consisting of ketene
dimers, and
multimers, at least one cellulose non-reactive sizing agent, and at least one
emulsifier
selected from the group consisting of oxyalkylene phosphate and sulfate esters
and salts
thereof, in the presence of water to obtain a mixture, and homogenising the
mixture to
obtain an aqueous dispersion. The temperature during the homogenisation is
preferably
sufficiently high for the cellulose reactive sizing agent to be liquid, and is
in most case
preferably from about 20 to about 1 00 C, most preferably from about 50 to
about 95 C.
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Preferably the cellulose non-reactive sizing agent is added in the form of an
aqueous
dispersion, for example a commercially available cellulose non-reactive size
such as
dispersions of poly (styrene/acrylate) marketed under the trademarks Jetsize
AE 27, AE
35 and AE 76 (Eka Chemicals AB), Basoplast 400 DS (BASF), Perglutin A 281
(Giulini), or a dispersion as described in US Patent 6426381. Further, it is
preferred to,
before the homogenisation, also add a cationic organic compound having a
weight average
molecular weight less than about 10000 or an anionic stabiliser, or both,
which is most
preferred. Regarding suitable and preferred variants of the components and
amounts
thereof, the above description of the dispersion as such is referred to.
The invention further concerns use of a dispersion according to the invention
as
described above for surface sizing of paper and a process for the production
of paper
comprising the steps of forming a paper web from a stock containing cellulosic
fibres and
applying to the surface of the paper web an aqueous dispersion according to
the
invention as described above. The dispersion may be applied to the paper web
by all
known methods in a size press or other suitable equipment and is preferably
included in
the size press liquor. Preferably a dispersion of the invention is supplied to
the paper in
an amount from about 0.05 to about 20 wt%, preferably from about 0.1 to about
10 wt / ,
based on amount of paper produced. It is further possible to supply with the
size press
liquor one or more of the following components: optical brightening agents,
preferably in
an amount from about 0 to about 2 wt% of amount of paper produced, pigments
(e.g.
chalk, precipitated calcium carbonate, kaolin, titanium dioxide, barium
sulphate or
gypsum), preferably in an amount from about 0 to about 15 g/m2 paper produced,
starch,
preferably in an amount from about 0 to about 5 g/mz paper produce,
crosslinkers such
as zirconium compounds, insolubilisers, defoamers, etc.
The invention furthermore concerns use of a dispersion according to the
invention as described above for internal sizing at production of paper and a
process for
the production of paper comprising the steps of adding a dispersion according
to the
invention as described above to a stock containing cellulosic fibres, and
dewatering the
stock on a wire to obtain paper and white water. The dispersion may be added
separately
or be premixed with one or more other additive, such as a retention aid.
The stock preferably contains from about 50 to about 100 wt%, most preferably
from about 70 to about 100 wt% of cellulosic fibres, based on dry stock.
Preferably the stock
also contains one or more fillers, e.g. mineral fillers like kaolin, china
clay, titanium dioxide,
gypsum, talc, chalk, ground marble or precipitated calcium carbonate, and
optionally other
commonly used additives, such as retention aids, aluminium compounds, dyes,
wet-strength
resins, optical brightening agents, etc. Examples of aluminium compounds
include alum,
aluminates and polyaluminium compounds, e.g. polyaluminium chlorides and
sulphates.
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Examples of retention aids include cationic polymers, anionic inorganic
materials in
combination with organic polymers, e.g. bentonite in combination with cationic
polymers,
silica-based sols in combination with cationic polymers or cationic and
anionic polymers.
A dispersion of the invention is preferably added to the stock and/or the
paper web
5 in an amount so the total amount of cellulose reactive sizing agent added is
from about 0.01
to about 10 wt%, most preferably from about 0.03 to about 5 wt% of the paper
produced,
while the total amount of cellulose non-reactive sizing agent added preferably
is from about
0.01 to about 10 wt%, most preferably from about 0.03 to about 5 wt% of the
paper
produced. The exact amounts depend on the quality of the pulp and the level of
sizing
10 desired.
It has been found that by using the dispersion of the invention the sizing
effect
compared to use of conventional sizes is improved at a corresponding doses of
cellulose
reactive sizing agent. The possibility of using lower amounts of sizing agent
to achieve a
desired level of 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 agents on the paper machine. Thus, the invention is
particularly
advantageous in processes with high degree of white water closure, for example
where
from 0 to 30 tonnes, usually less than 20 tonnes, suitably less than 15
tonnes, preferably
less than 10 tonnes and most preferably less than 5 tonnes of fresh water are
used per ton
of dry paper produced. Besides, the invention gives a fast on-machine sizing
and a very
uniform sizing. Furthermore, the dispersion does not interfere significantly
with strong
anionic components present in the papermaking process, and does therefore not
reduce
the efficiency of, for example, optical brightening agents.
The invention will now be further described in connections with the following
Examples which, however, do not intend to limit the scope thereof. Unless
otherwise stated,
all parts and percentages refer to parts and percent by weight.
Example 1: An anionic aqueous sizing dispersion according to the invention was
prepared from the following formulation for 1 kg dispersion:
60 g AKD (alkyl ketene dimer) (Keywax SF100, Eka Chemicals)
115 g aqueous dispersion of poly (styrene/acrylic ester) (Jetsize AE 76, Eka
Chemicals)
2.75 g ditallow dimethyl ammonium chloride (ArquadT"' 2HT-75PG, Akzo Nobel)
4.5 g polyoxyethylene phosphate ester (RhodafacTM RS-710, Rhodia)
3.6 g condensated sodium naphthalene sulfonate formaldehyde condensate
(OrotanTMSN
Rohm & Haas Company)
balance up to 1000 g: water
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The ditallow dimethyl ammoniumchloride was mixed with molten alkyl ketene
dimer at
70 C and the mixture was passed through a homogenizer in the presence of the
dispersion of poly (styrene/acrylic ester), which was pre-blended with the
polyoxyethylene
phosphate ester and the condensated sodium naphthalene sulfonate.
The dispersion was used for internal sizing in a pilot plant paper machine
producing paper from fine paper furnish with 15% ground calcium carbonate
(HydrocarbT"" 50BG GCC, Omya) and 0.6% optical brightening agent. The
retention
system used was 0.5% cationic potato starch (Hi-CatTM 142, Roquette) and 0.3%
anionic
silica sol (EkaTM NP 442, Eka Chemicals). For comparison, paper was produced
under
the same conditions but sized with a standard AKD dispersion Keydime C (Eka
Chemicals). The papers were tested in respect of water absorption according to
Cobb 60
(Tappi test method T 441 om-90) and ink resistance according to HST 80 (Tappi
test
method T 530 pm-89). The results are shown in the table below:
Product Keydime C Invention Example I
AKD 0.5 0.7 0.9 0.5 0.7 0.9
dosage
k/t paper)
Cobb 60 33 24 22 26 22 21
/m7-
HST 80 104 302 378 192 348 470
(seconds)
It appears that the dispersion of the invention gives considerably improved
sizing than the
conventional AKD based size.
Example 2: A dispersion of the invention was prepared in the same way as in
Example I from 30 g Keywax SF100, 200 g Jetsize AE 76, 4.8 g ArquadT"" 2HT-
75PG,
6.3 g RhodafacTM RS-710, 6.3 g OrotanTMSN and water to 1000 g. The dispersion
was
used for surface sizing of an internally pre-sized paper (Cobb 60 = 37g/m2)
produced
from fine paper furnish containing 18% ground calcium carbonate (HydrocarbT"'
50 BG;
GCC Omya) and with ASA (Lasar 220, Eka Chemicals) as internal sizing agent in
an
amount of 0.75 kg per tonne paper. The basis weight was 80 g/m2. The retention
system
was 0.5% cationic potato starch (Hi-CatTM 142, Roquette) and 0.5% anionic
silica sol
(EkaTM NP 780, Eka Chemicals). Additionally 0.6% optical brightening agent was
added
to the stock. The dispersion of the invention was added in the size press
together with
oxidised potato starch (PerfectamylT"" P 255 SH, Avebe) at 5 % solids content.
For
comparison, the same kind of paper was surface sized under the same conditions
with a
standard surface size based on a styrene acrylate co-polymer dispersion
(Jetsize AE 76,
Eka Chemicals). The caoers were tested in respect of water absorption
according to
CA 02520642 2005-09-27
WO 2004/088036 PCT/SE2004/000306
12
Cobb 60 and ink resistance according to HST 80. The results are shown in the
table
below:
Product Jetsize AE 76 Invention Example 2
Dosage 0.025 0.035 0.05 0.085 0.01 0.02 0.03 0.04
(% active components* of
produced a er
Cobb 60 /m2 33 32.1 30.4 24.8 36.2 25 22.8 22.1
HST 80 (seconds) 89 91 119 161 67 148 171 208
* Active components refer to the total amount of alkyl ketene dimers and
styrene acrylate
co-polymer
It appears that the dispersion of the invention gives considerably improved
sizing than the
conventional surface size.
Example 3: Dispersion were prepared in the same way as in Example 1 and the
static storage stability was tested by storing the samples in bottles for five
weeks and
then measuring the dry content at the top and the bottom of the bottles. The
formulations
(for 1 kg dispersion) and the results are shown in the table below:
Formulation (a) (b) (c) (d)
Ke wax SF 100 60 60 60 60
Jetsize AE 76 86 86 86 86
Ar uadT"' 2HT-75PG 2.75 2.75 2.75 2.75
RhodafacTM RS-710 - 0.7 3.6 6.7
rotanTM SN 3.6 3.6 3.6 3.6
water balance balance balance balance
Dry content on top after 5 weeks Separated into 10.3 10.8 11.2
% two phases
Dry content at bottom after 5 Separated into 6.0 10.3 11.1
weeks (%) two phases
It appears that the sample without the polyoxyethylene phosphate ester had
separated into
two phases already after five weeks of storage.
Example 4: Dispersions were prepared in the same way as in Example 1 and the
thermal stability was tested by shaking the samples 10 days at 250 rpm and 30
C and
measuring the particle size distribution. The formulations (for 1 kg
dispersion) and the
results are shown in the table below. The figures for particle size refer the
particle size
50% and 90% by volume , respectively, of the particles in each sample are
smaller than.
Thus, in Formulation (1) after 10 days 50% of the particles were smaller than
0.59 pm
and 90% smaller than 0.92 pm.
CA 02520642 2005-09-27
WO 2004/088036 PCT/SE2004/000306
13
Formulation (1) (2) (3) (4) (5)
Ke wax SF 100 60 60 60 60 60
Jetsize AE 76 115 115 115 115 115
Ar uadT"' 2HT-75PG 2.75 5.5 1.375 2.75 2.75
RhodafacTM RS-710 3.6 3.6 3.6 3.6 3.6
OrotanTM SN 3.6 3.6 3.6 7.2 1.85
water balance balance balance balance balance
Initial Particle size 50% / 0.56/0.85 0.64/1.47 0.53/0.86 0.58/0.95 0.61/1.05
90% (pm)
Particle size after 7 days 0.59/0.97 14.8/27.0 0.51/0.71 0.71/3.62 13.8/25.5
50% / 90% (pm)
Particle size after 10 days 0.59/0.92 14.7/25.0 0.68/16.1 0.72/16.9 14.2/24.4
50% / 90% m
