Note: Descriptions are shown in the official language in which they were submitted.
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WO 98133980 1 PGT/SE98/00193
Aaueous dispersions of hydrophobic material
The present invention relates to aqueous dispersions of hydrophobic material -
and more specifically to dispersions having a dispersant system containing two
oppositely
charged compounds, their preparation and use.
Background
Aqueous dispersions of hydrophobic material are well-known and used in
numerous applications. For instance, in papermaking, aqueous dispersions of
hydrophobic
material are used as sizing agents in order to give paper and paper board some
degree of
resistance to wetting and penetration by aqueous liquids. Examples
ofhydrophobic materials
widely used for sizing include cellulose-reactive sizing agents, e.g. alkyl
ketene dimers and
substituted succinic anhydrides, and non-cellulose-reactive sizing agents,
e.g. rosin-based
and resin-based sizing agents.
Dispersions of hydrophobic material generally contain an aqueous phase and
finely divided particles or droplets of the hydrophobic material dispersed
therein. The
dispersions are usually prepared by homogenizing the hydrophobic, water
insoluble material
in an aqueous phase in the presence of a dispersant using high shear forces
and fairly high
temperatures. Dispersants conventionally used ir~cfude anionic, amphoteric and
cationic high
molecular weight polymers, e.g. iignosulfonates, starches, pclyamines,
polyamideamines,
and vinyl addition polymers. The polymers can be used singly, together or in
combination
with other compounds to form a dispersant system. Depending on the overall
charge of the
components of the dispersant system, the size dispersions will be anionic or
cationic in
nature.
Dispersions of hydrophobic material 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 hydrophobic material.
It is accordingly an object of this invention to provide aqueous dispersions
of
hydrophobic material with improved stability and viscosity properties. It is
another object of
this invention to provide improved aqueous dispersions of sizing agent,
notably cellulose-
reactive sizing agents. Further objects will appear hereinafter.
The Invention
In accordance with the present invention it has been found that improved
stability and viscosity properties can be obtained with aqueous dispersions of
hydrophobic
material in which the hydrophobic material is dispersed in the aqueous phase
by means of a
dispersant comprising two oppositely charged compounds having relatively low
molecutar
CA 02280094 1999-08-04
_t;_
weights. More specifically, the invention relates to an aqueous dispersion
containing a disperse phase comprising a hydrophobic material and a
dispersant comprising an anionic compound having a molecular weight less
than 50,000 and being selected from organic compounds and silicon-containing
compounds, and a cationic organic compound having a molecular weight less
than 50,000.
In particular at least one oiF the anionic and cationic compounds is
a polyelectrolyte.
In another aspect of the invention there is provided a method for
the preparation of an aqueous disper~;ion by homogenizing a hydrophobic
sizing agent in the presence of an aqueous phase and a dispersant comprising
an anionic compound having a molecular weight less than 50,000 and being
selected from carbon-containing compounds and silicon-containing
compounds, and a cationic organic compound having a molecular weight less
than 50,000, wherein at least one of thc; anionic and cationic compounds is a
polyelectrolyte.
In still another aspect of the invention there is provided the use of
an aqueous dispersion of the invention., as defined above, as a stock size or
surface size in the production of paper.
In yet another aspect o1~ the invention there is provided a
substantially water-free sizing composition containing a hydrophobic sizing
agent, an anionic compound having a molecular weight less than 50,000 and
being selected from carbon-containing compounds and silicon-containing
compounds, and a cationic organic compound having a molecular weight less
than 50,000 wherein at least one of the anionic and cationic compounds is a
polyelectrolyte; as well as the use of such composition for the preparation of
an
aqueous dispersion of the invention, as defined above.
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The present invention makes it possible to provide dispersions of hydrophobic
material with improved storage stability, higher solids content andlor lower
viscosity. In
addition, when using the dispersions in applications involving very high
dilution of the initially
high concentration dispersion, it has been found that the disperse phase is
more stable, i.e.
the dispersions exhibit improved dilute stability,. Examples of applications
with extremely high
dilution include papermaking wet-end conditions and stock or intemaf sizing
which involves
addition of a dispersion of hydrophobic material to an aqueous suspension
containing
cellulosic fibres and optional filler. In this c.~ntext, improved dilute
stability means less
aggregation of the particles or droplets of hydrophobic sizing agent, thereby
forming lower
levels of bigger aggregates with lower sizing efficiency, as well as less
deposition of the
hydrophobic sizing agent on the paper ma~;tiine and less wire contamination,
thereby
reducing the need for maintenance of the paper machine. Further benefits
observed with the
present dispersions include improved stability 'in the presence of disturbing
substances, e.g.
anionic trash derived from impure pulps and/or recycled fibres, and less
accumulation of the
hydrophobic material in white water recirculatcng in the papermaking process.
Accordingly,
dispersions of this invention are particularly useful in processes where white
water is
extensively recirculated and where the cellulosic suspension contains a
substantial amount of
trash. Furthermore, the dispersions of this invention also makes it possible
to obtain
improved sizing over conventional size dispersions at a corresponding dosage
of sizing agent
and to use a lower dosage of sizing agent to attain a corresponding level of
sizing. The
possibility of using lower amounts of sizing agent to attain in-specifiication
sizing further
reduces the risk of accumulation of non-adsorbed hydrophobic sizing agents in
the white
water recircuiating in the process, thereby further reducing the risk of
aggregation and
deposition of the hydrophobic material on the' paper machine. The present
invention thus
offers substantial economic and technical benefits.
The hydrophobic material present in the dispersion preferably is substantially
insoluble in water. Examples of suitable hydrophobic materials include
compounds useful as ,
sizing agents in papermaking which can be derived from both natural and
synthetic sources,
e.g. cellulose-reactive hydrophobes and non-cellulose-reactive hydrophobes. In
a preferred
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embodiment, the hydrophobic material has a melting point below about
100°C and notably
below about 75°C.
In a preferred embodiment of this invention, the hydrophobic material is a
cellulose-reactive sizing agents which 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 proferably ketene dimers. Suitable ketene dimers have the general formula
(I) below,
wherein R' and R2 represent saturated or unsaturated hydrocarbon gr6ups,
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 (!I) below, wherein R3 and R' 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 'include alkyl and
alkenyl succinic
anhydrides and particularly isooctadecenyl succinic anhydride.
(I) R'-CH~C-CH-RZ (II) O O
O-Cs~0 R3-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
carbamoyl
chlorides include those disclosed in U.S. Pat. No. 3,887,427.
In another preferred embodiment of this invention, the hydrophobic material is
a
non-cellulose-reactive hydrophobe which can be selected from any of the non-
cellulose-
reactive sizing agents knovm in the art. Suitably the non-cellulose-reactive
sizing agent is
selected from the group consisting of hydrophobes based on rosin, e.g. rosin,
disproportionated rosin, hydrogenated rosin, polymerized rosin, formaldehyde-
treated rosin,
esterified rosin, fortfied rosin and mixtures of such treatments and so
treated rosins, fatty
adds and derivatives thereof, e.g. fatty aad esters and amides like bis-
stearamide, resin and
derivatives thereof, e.g. hydrocarbon resins, resin aads, resin acid esters
and amides,
waxes, e.g. crude and refined paraffin waxes, synthetic waxes, naturally
occuring waxes, etc.
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Dispersions according to this invention contain a dispersant, or dispersant
system, comprising at least one anionic compound and at least one cationic
compound, both_
having a low molecular weight (hereinafter LMW). The LMW compounds are
preferably
bound together by the force of electrostatic attraction, thereby representing
a coacervate
dispersant. When used in combination, the LMW compounds are effective as a
dispersant for
the hydrophobic material, although the anionic and cationic compounds do not
have to be,
and ususally are not, effective as a dispersant when used singly. In a
preferred embodiment,
at least one of the anionic and cationic compounds is a polyelectrolyte.. The
term
"polyelectroiyte", as used herein, refers to a compound having tvvo or more
charged
(anioniclcationic) groups and charged (anioniclcationic) compounds acting as a
poly-
electrolyte, e.g. through chemical non-ionic interaction or attraction.
The anionic compound of the dispersant 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
polyelectrolyte. Anionic polyelectrolytes may contain one or more cationic
groups as long as it
has an overall anionic charge. Examples of suitable anionic groups include
sulfate groups
and carboxylic, sulfonic, phosphoric and phosphonic acid groups which may be
present as
free acid or as water-soluble ammonium or alkali metal (generally sodium)
salts, e.g. sodium
carboxylates and sulfonates. Anionic polyelectroiytes can have a degree of
substitution
varying over a wide range; the degree of anionic substitution (DSA) can be
from 0.01 to 1.4,
suitably from 0.1 to 1.2 and preferably from 0.2 to 1Ø
The anionic compound of the dispersant can be derived from synthetic and
natural sources and preferably it is water-soluble or water-dispersable. In a
preferred
embodiment, the anionic compound is an organic compound, i.e. containing
carbon atoms.
Suitable anionic compounds include anionic surfactants like alkyl, aryl and
alkylaryl sulfates
and ethersulfates, alkyl, aryl and alkylaryl carboxyiates, alkyl, aryl and
alkylaryl sulfonates,
alkyl, aryl and alkylaryl phosphates and etherphosphates, and dialkyl
sulfosuccinates, the
alkyl groups having from 1 to 18 carbon atoms, the aryl groups having from 6
to 12 carbon
atoms, and the alkylaryl groups having from 7 to 30 carbon atoms. Examples of
suitable
anionic surfactants include sodium lauryl sulfate, sodium fauryl sulfonate and
sodium
dodecylbenzenesulfonate. Further examples of suitable anionic compounds
include anionic
polyeiectroiytes such as anionic organic LMW polymers, optionally degraded,
e.g. those
derived from phosphated, sulphonated and carboxylated polysaccharides like
starches, guar
gums and celluioses, preferably cellulose derivatives and notably
carboxymethyi celluloses,
as well as condensation products, e.g. anionic polyurethanes and condensated
naphthalene
sulfonates, and further vinyl addition polymers formed from monomers with
anionic groups,
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e.g. acrylic acid, methacytic acid, malefic acid, itaconic acid, crotonic
acid, vinylsulfonic acid,
sulfonated styrene and phosphates of hydroxyalkyl acryiates and methacrylates,
optionally
copolymerized with non-ionic monomers including acrytamide, alkyl acrylates,
styrene and
acryionitrile as well as derivatives of such monomers, vinyl esters, and the
like. The anionic
5 compound can also be selected from LMW inorganic compounds containing
silicon atoms
such as, for example, silicates and various forms of condensateded or
polymerized siticic
acid, e.g. oligomeric sitiac acid, polysilicic acids, polysilicates,
polyaluminiumsilicates,
pofysilicate microgels, polyaluminiumsilicate mtcrogets and silica-based
material, e.g. in the
form of silica sots, which have negative hydroxyl groups.
The cationic compound of the dispersant 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, herein referred to as a
cationic
polyelectrotyte. Cationic polyelectrolytes may contain one or more anionic
groups as long as
it has an overall cationic charge. 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 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 substitution 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.
The cationic compound of the dispersant can be derived from synthetic and
natural sources and preferably it is water-soluble or water-dispersable. The
cationic
compound preferbly is an organic compound. Examples of suitable cationic
compounds
include cationic surfactants, e.g. compounds of the type 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
intemrpted by one or more heteroatoms, e.g. oxygen or nitrogen, andlor groups
containing a
heteroatom, e.g. carbonyl and acyloxy groups; where 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; 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 R3N wherein R
and N are as
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defined above. Examples of suitable surfactants include
dioctyldimethylammonium chloride, -
didecyldimethylammonium chloride, dicocodimethylammonium chloride,
cocobenzyldimethyl-__
ammonium chloride, coco(fractionated)benzyldimethyfammonium chloride,
octadecyl
trimethyiammonium chloride, dioctadecyl dimethylammonium chloride, dihexadecyl
dimethyl-
ammonium chloride, di(hydrogenated tallow)dimethyiammonium chloride,
di(hydrogenated
tallow)benzylmethylammonium chloride, (hydrogenated
tallow)benzyldimethylammonium
chloride, dioleyidimethylammonium chloride, and di(ethylene
hexadecanecarboxylate)-
dimethyiammonium 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 suitable cationic surfactants include
quaternary
di- and polyammonium 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. Further examples of suitable
cationic
compounds include cationic polyelectrolytes such as cationic organic LMW
polymers,
optionally degraded, e.g. those derived from polysaccharides like starches and
guar gums,
cationic condensation products like polyurethanes, polyamideamines, e.g.
polyamideamine-
epichlorohydrins, polyamines, e.g. dimethylamine-epichlorohydrin copolymers,
dimethyl-
amine-ethylenendiamine-epichlorohydrin-copolymers, ammonia-ethylenen
dichloride co-
polymers, vinyl addition polymers formed from monomers with cationic groups,
e.g. homo-
polymers 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
acrylonitriie and derivatives of such monomers, vinyl esters, and the like.
Both the anionic LMW compound and the cationic LMW compound for use in
this invention have a molecular weight (hereinafter MW) less than 50,000,
suitably less than
30,000 and preferably less than 20,000. Further benefits can be seen where the
MW of the
anionic compound andlor the cationic compound of the dispersant is even lower,
for example
less than 15,000 and notably less than 10,000. Normally the anionic and
cationic compounds
have an MW above 200 and suitably above 500. Usually the anionic and cationic
surfactants
have a lower MW than the anionic and cationic polyelectrolytes; preferred
surfactants have
an MW from 200 to 800. When one of the compounds of the dispersant is a
surfactant,
another compound of the dispersant should preferably be a polyelectrolyte,
which may have
an MW as defined above.
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Preferred dispersions of this invention contain a dispersant selected from the
group consisting of a dispersant (i) comprising a cationic surfactant and an
anionic
polyelectralyte where the dispersant has an overall anionic charge; a
dispersant (ii)
comprising a cationic polyelectrolyte and an anionic polyelectrolyte where the
dispersant has
an overall anionic charge; a dispersant (iii) comprising an anionic surfactant
and a cationic
poiyelectrolyte where the dispersant has an overall cationic charge; and a
dispersant (iv)
comprising an anionic polyelectrolyte and a cationic polyelectrolyte where the
dispersant has
an overall cationic charge; the anionic and cationic surfactants, the anionic
and cationic
polyelectrolytes and their molecular weights being as defined above.
The anionic and cationic compounds of the dispersant can be present in the
dispersion in amounts varying within wide limits depending on, inter olio, the
molecular weight
of the compounds, the degree of ionic substitution of the compounds, i.e. the
charge density,
the desired overall charge of the dispersion and the hydrophobic material
used. Both the
anionic compound and the cationic compound can be present in an amount of up
to 100% by
weight, suitably from 0.1 to 20% by weight and preferably from 1 to 10% by
weight, based on
the hydrophobic material.
It has been found that the dispersions according to the invention can be
prepared in high solids contents and yet exhibit very good stability on
storage and low
viscosity. This invention provides dispersions of hydrophobic material with
improved storage
stability andlor high solids content. Partcularly preferred dispersions in
this regard include
dispersions of cellulose-reactive sizing agent, notably dispersions having a
dispersant with an
overall anionic charge. Dispersions of cellulose-reactive sizing agents
according to the
invention generally can have sizing agent contents of from about 0.1 to about
50% by weight,
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
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 of from about 0.1 to about 30% by weight and usually from
about 1 to about
20% by weight. Dispersions of non-cellulose-reactive sizing agents generally
can have sizing
agent contents of from 5 to 50% by weight and preferably from 10 to 35% by
weight.
The dispersions according to the invention can be produced by mixing an
aqueous phase with the dispersant system and the hydrophobic material,
preferably at a
temperature where the hydrophobic material is liquid, and homogenizing the
mixture so
obtained, suitably under pressure. The obtained aqueous emulsion, which
contains droplets
of the hydrophabe, normally having a size of from 0.1 to 3.5 wm in diameter,
is then cooled.
In addition to the above-mentioned components other materials can also be
incorporated into
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8
the size dispersions, such as, for example, additional dispersants and
stabilizers, e.g. non-
ionic dispersants, 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
can be formed in situ, for example by contacting the compounds with one
another andlor 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
the 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.
It has been found that the components of the present dispersions can be easily
homogenized in the presence of an aqueous phase, in particular where the LMW
compounds
of the dispersant are used in combination with hydrophobic materials having a
melting point
5 below about 100°C and notably below about 75°C. Usually less
energy and lower 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 dispersions comprises (i) mixing the hydrophobic material
with the anionic
and cationic compounds of the dispersant 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 hydrophobe used in stage (i) may be solid although it is preferred 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 composition containing the dispersant and the
hydrophobic material
which enables simplified shipping in an economically attractive manner. At the
location of
intended use, or elsewhere, the intermediate hydrophobe composition can be
homogenized
in the presence of water in conventional or simpified manner, optionally at
elevated
temperature so as to render the intermediate composition liquid. This method
is especially
attractive when preparing dispersions of ketene dimers and acid anhydrides,
the latter of
which usually being 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 substantially
water-free
composition thus offers considerable economic and technical benefits. The
present invention
thus also relates to a substantially water-free concentrate composition
comprising a
hydrophobic material, an anionic LMW compound selected from carbon-containing
compounds and silicon-containing compounds, and a cationic organic LMW
compound,
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9
where the anionic and cationic compounds when used in combination are
effective as a
dispersant system for the hydrophobic material in an aqueous phase, its
preparation and
use, as further defined in the claims.
The components that are present in the concentrate composition according to
the invention, i.e., the hydrophobic material and the anionic and cationic
compounds,
preferably are as defined above. The 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 hydrbphobic
material in a
predominant amount, based on weight, i.e. at least 50% by weight, and suitably
the
composition has a hydrophobe content within the range of from 80 to 99.9% by
weight and
preferably from 90 to 99.7% by weight. The anionic and cationic compounds can
be present
in the composition in amounts defined above with respect to the dispersions
where the
percentages ace based on hydrophobic material. Accordingly, both the anionic
compound
and the cationic compound can be present in the composition in an amount of up
to 100% by
weight, suitably from 0.1 to 20% by weight and preferably from 1 to 10% by
weight, based on
the hydrophobic material.
The dispersions of this invention can be used as sizing agents in conventional
manner in the production of paper using any type of ceilulosic fibres and it
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 celluiosic
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 amount of
hydrophobic sizing agent added to the stock can be from 0.01 to 5% by weight
suitably from
0.05 to 1.0% by weight, based on the dry weight of cellulosic fibres and
optional fillers, where
the dosage is mainly dependent on the quality of the pulp or paper to be
sized, the sizing
agent used and the level of sizing desired.
In a preferred embodiment, the dispersions are used in stock sizing of
cellulosic
pulp where the stock has a high cationic demand andlor contains substantial
amounts of
lipophilic substances, e.g. stocks prepared from certain grades of wood-
containing and
recycled pulps, for example where recirculation of white water is extensive.
Particularly
preferred dispersions in such uses include dispersions of cellulose-reactive
sizing agent and
dispersions having a dispersant with an overall anionic charge. Usually the
cationic demand
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is at least 50, suitably at least 100 and preferably at least 150 ~eqllitre
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 from a raw
stock filtered
through a 1.6 p.m filter and poly(diallyldimethylammonium chloride) as a
titrant. The amount
5 of lipophilic extractives may be at least 10 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. 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 o'~ fresh
water are used
10 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.
Recirculation of white
water in the process preferably takes place by mixing the white water with
cellulosic 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 ceilufosic fibres in
order to form the
stock, and it can be mixed with a stock containing ceilulosic 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 sizing dispersions. Non-
cellulose-reactive
sizing agents are usually used with an aluminium compound for fixing the
sizing agent to the
cellulosic fibre. Examples of aluminium compounds include alum, aluminates end
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 sols 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 pciymers. Suitable cationic polymers
include cationic
starch, guar gum, acrylate and acrylamide-based polymers, polyethyleneimine,
dicyandiamide-formaldehyde, 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 one cationic polymer
and anionic
silica-based particles. The present dispersions can be added before, between,
after or
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11
simultaneously with the addition of the cationic polymer or polymers. It is
also possible to
premix 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
A dispersion of hydrophobic alkyl ketene dimer (AKD) according to the
invention was prepared by mixing di(hydrogenated tallow)dimethylammonium
chloride, which
is a cationic surfactant with an MW of 340, 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 a condensated sodium
naphthalene-
sulphonate with an estimated MW of about 6,000, commercially availably under
the trade
name Orotann'" SN, Rohm & Haas Company, and then cooling the dispersion so
obtained.
The pH of the dispersion was adjusted to about 5 by addition of acid. The
dispersion,
denoted Dispersion No. 1, had an AKD content of 30% and contained 6% of the
anionic
compound and 4% of the cationic compound, both based on the weight of AKD. The
dispersions contained particles of the cellulose-reactive hydrophobe with an
average particle
size of about 1 wm which were anionically charged, as shown by a negative zeta
potential
determined by means of a ZetaMaster S Version PCS.
Examale 2
Stability of the dispersion of Example 1 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 evaluate the stability in the
presence of a
~ liphophilic, anionic trash substance. 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
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turbidity of the dispersion before and after a temperature cycle is a measure
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 (DT) is calculated as
follows: OT=(final
turbidity I initial turbidity) x 100. The higher the OT the better the
stability.
Two standard dispersions were also tested for comparison purposes; Ref. 1
is an anionic AKD dispersion containing a dispersant system consisting of
sodium
lignosuiphonate and a high molecular weight (HMW) cationic starch where the
anionic
lignosulphonate is present in ionic excess; Ref. 2 is a cationic AKD
dispersion also
containing sodium lignosulphonate and HMW cationic starch but where the
cationic starch
is present in ionic excess. Table 1 gives the results obtained.
Table 1
Dispersion No. Stearic acid fpoml ~1T
- 72
1 10 55
Ref. 1 - 45
Ref. 1 10 32
Ref. 2 - 35
Ref. 2 10 6
As is shown in Table 1 the 0T values of the dispersion of this invention were
considerably higher than those of the standard dispersions which accordingly
are indicative
of better dilute stability.
Example 3
A water-free concentrate composition according to the invention was
prepared by dry mixing 93 parts of AKD pellets with 3 parts of the cationic
surfactant and 4
parts of the anionic compound used in Example 1. 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. 2, had an AKD content of 20% and an average particle size of
about 1 p.m.
Sizing efficiency was evaluated by preparing paper sheets according to the
standard method SCAN-C23X for laboratory scale, and using a papermaking stock
containing 80% of 60:40 bleached birchlpine sulphate and 20% of chalk to which
0.3 g/i of
Na2S0410H20 had been added. Stock consistency was 0.5% and pH 8Ø The
dispersions
were used in conjunction with a commercial retention and dewatering system,
CompoziiT"",
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comprising cationic starch and an anionic aluminium-modified silica sof which
were added
to the stock separately; the cationic starch was added in an amount of 12
kg/ton, based on-
dry stock, and the silica sol was added in an amount of 0.8 kglton, 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 dosacre Ik41ton1 Cobb 60'.fa/m?1
2 0.30 58
2 0.40 30
Ref. 1 0.30 84
Ref. 1 0.40 65
Ref. 2 0.30 66
Ref. 2 0.40 40
Table 2 demonstrates the improvement in paper sizing obtained with the
dispersion according to the invention.
Examgle 4
Ease of manufacture of dispersions according to the invention was evaluated
by preparing anionic AKD dispersions at different AKD contents. Dispersions of
the
invention 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°ro by weight of AKD 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.
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Particle size and viscosity were assessed in conventional manner. Table 3
shows the results obtained. _
Table 3
AKD Dispersion Particle size Viscosity
No. (um) (cps)
Inv. - 10% 2.98 10
I nv. - 20% 3.12 20
Inv. - 30% 3.50 20
Inv. - 40% 3.50 2y
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 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. In
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.
