Note: Descriptions are shown in the official language in which they were submitted.
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1
Sizing of Paaer
This invention relates to sizing of paper and more specifically to aqueous
dispersions containing a cellulose-reactive sizing agent and a hydrophobically
modified
dispersing agent, their preparation and use.
Backoround
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 penetration by aqueous liquids. Paper sizes based on cellulose-
reactive sizing
agents 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 cationic or
amphoteric
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.
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 a substantial amount of lipophilic 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 a substantial amount 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 stock:; 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 recircufated
with the
introduction of only love amounts of fresh water into the process, thereby
further 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.
' It is accordingly an object of this invention to provide improved
dispersions of
cellulose-reactive sizing agent and processes resulting in improved sizing
where dispersions
of cellulose-reactive ~;izing agent are used with ceilulosic stocks having a
high cationic
CA 02280136 1999-08-04
_2_
demand and/or a high content of lipophilic extractives and/or in processes
with extensive white water recirculation
Summary of the Invention
In accordance with one aspect of the invention there is provided
use of an aqueous sizing dispersion containing a cellulose-reactive sizing
agent and a hydrophobically modified dispersing agent containing one or
more anionic groups for sizing cellulosic fibres by addition of the sizing
dispersion to a stock containing cellulosic fibres, dewatering the stock on a
wire to obtain a web containing cellulosic fibres, wherein the stock has a
cationic demand of at least 50 peq/litre stock filtrate.
In accordance with another aspect of the invention there is
provided an aqueous dispersion of a sizing agent, characterized in that it
contains a cellulose-relative sizing agent and an anionic hydrophobically
modified cellulose-derivative.
In accordance with still another aspect of the invention there is
provided a procesa for stock sizing cellulosic fibres which comprises addition
of the dispersion of the invention, as described above, to a stock containing
cellulosic fibres.
In accordance with yet another aspect of the invention there is
provided a method for preparing a dispersion of the invention, which
comprises homogenizing the cellulose-reactive sizing agent in the presence
of an aqueous phase and the anionic hydrophobically modified cellulose-
derivative.
In still another aspect of the invention there is provided a
substantially water-free composition containing a cellulose-reactive sizing
agent and an anionic hydrophobically modified cellulose-derivative.
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The Invention
According to the present invention it has been found that improved sizing can
be obtained by using aqueous dispersions of cellulose-reactive sizing agent
having a
hydrophobe-modified dispersing agent in the internal sizing of stocks having a
high cationic
demand and/or containing high levels of lipophiiic 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, thereby creating conditions of, high
cationic demand
and/or high contents of lipophilic extractives. Accordingly, the invention
generally relates to
the use of an aqueous sizing dispersion containing a cellulose-reactive sizing
agent and a
hydrophobically modified dispersing agent in the internal sizing of difficult-
to-size stocks by
addition of the sizing dispersion to a stock containing cellulosic fibres, and
optional fillers,
dewatering the stock on a wire to obtain a web containing cellulosic fibres,
or paper. In a first
aspect of the invention, the stock has a cationic demand of at least 50
~eqllitre stock filtrate.
In a second aspect of the invention, the stock has a content of lipophilic
substances of at
least 10 ppm. A third .aspect of the invention comprises dewatering the stock
on a wire to
obtain white water and a web containing celluiiosic fibres, recirculating the
white water, and
optionally introducing fresh water, to ferm a stock containing cellulosic
fibres to be dewatered,
wherein the amount of fresh water introduced is less than 30 tons per ton of
dry cellulosic
product produced. ThE: invention thus relates to the use of an aqueous sizing
dispersion
containing a cellulose-reactive sizing agent and a hydrophobically modified
dispersing agent
in a process for sizing cellulosic fibres .
In a prefE:rred embodiment of this invention, the aqueous dispersion contains
a
cellulose-reactive sizing agent and an anionic hydrophobe-modified dispersing
agent, notably
an anionic hydrophobically modified cellulose-derivative, and this invention
further relates to
such a dispersion and its preparation, as further defined in the claims. The
dispersion
provides improved si:ability and sizing characteristics and it is particularly
useful with
papermaking stocks having a high cationic demand and containing lipophilic
substancev
notably with a high degree of white water closure.
The invention makes it possible to produce paper with improved sizing o: =:::
conventional sizing dispersions at a corresponcJing 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 agent in the white
water recirculating
CA 02280136 1999-08-04
3
in the process, thereby reducing the risk of aggregation and deposition of the
sizing agent on
the paper machine. The: invention thus offers substantial economic and
technical benefits.
The cellulose-reactive sizing agent according to the invention can be selected
from any of the ceilulo:ce-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 i:;ocyanates, carbamoyl chlorides and mixtures thereof,
preferably
ketene dimers and acid anhydrides, most preferably ketene dimers. Suitable
ketene dimers
have the general formula (I) 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
include alkyl and alkE:nyl succinic anhydrides and particularly isooctadecenyl
succinic
anhydride.
(I) R'-C;H~C-CH-RZ (II) O O
O-C~O R3-C-O-C-R°
Suitable ketene dimers, acid anhydrides and organic
isocyanates include the compounds 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 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. fortified andlor esterified rosin, waxes, fatty acid and
resin acid
derivatives, e.g. fatty amides and fatty esters, e.g. glycerol triesters of
natural fatty acids.
The dispersion used according to the invention contains a hydrophobically
modified dispersing agent, i.e. a dispersing agent having one or more
hydrophobic groups.
Preferably the hydrophobic group is pendent, i.e. being attached to the
dispersing agent in
the form of a hydrophobic side-chain. Examples of suitable groups include
hydrophobic
substituents containing at least 4, suitably at least 6 and preferably from
about 8 to about 30
carbon atoms, notably hydrophobic amide, ester and ether substituents
comprising a
saturated or unsaturated hydrocarbon chain of at least 4, suitably at least 6
and preferably
from 8 to 30 carbon .atoms, optionally being interrupted by a heteroatom, e.g.
oxygen or
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4
nitrogen, andlor a group containing a heteoratom, e.g. carbonyl or acyloxy.
The dispersing
agent can have a degree of hydrophobic substitution (DSH) of from 0.01 to 0.8,
suitably from
0.02 to 0.5 and preferably from 0.03 to 0.4.
The hydrophobically modified dispersing agent may be charged or uncharged,
preferably it is charged and contains one or more ionic groups of the same or
different types.
The ionic groups can be cationic and/or anionic. Accordingly, the dispersing
agent can be
anionic, amphoteric or cationic in nature, preferably amphoteric or anionic,
most preferably
anionic. 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.
The dispersing agent can have a degree of ionic 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 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 dispersing agent can be derived from synthetic and natural sources and it
is preferably water-soluble or water-dispersable. Examples of suitable
dispersing agents
include hydrophobically modified polysaccharides such as, for example,
starches, guar gums,
celluloses, chitins, chitesans, glycans, galactans, glucans, xanthan gums,
mannans, dextrins,
etc., preferably starches, guar gums and cellulose derivatives, suitably
anionic and cationic
derivatives and preferably anionic derivatives like phosphated, sulfonated and
carboxylated
polysaccharides, hydrophobically modified polymeric condensation products such
as, for
example, anionic and, cationic polyurethanes, cationic polyamidoamines;
hydrophobe-
modified anionic and cationic vinyl addition polymers such as, for example,
polymers based
on (meth)acrylamide, (meth)acrylates, vinyl carboxyates, and the like. The
hydrophobically
modified synthetic polymers can easily be prepared by employing in the
polymerization
monomers having a hydrophobic substituent, e.g. hydrophobic chain alkyl
(meth)acrylamides
and (meth)acrylates, vinyl stearate, etc., and optional anionic and/or
cationic monomers.
Examples of suitable hydrophobically modified and charged
dispersing agents :include those disclosed in U.S. Pat. Nos. 4,228,277;
4,239,592 and 4,687,519; European Pat. Appl. Nos. 512 319 and 551 817;
and International Pat. Appl. Publ. No. WO 94/24169. The dispersions used
according to this in~rention can be prepared in conventional manner with the
exception that the dispersing agent is hydrophobically modified.
The amount of hydrophobically-modified dispersing agent present in the
dispersion can be variied over a broad range depending on, among other things,
type of
material and its DSH and, if charged, the DSA, the DSc, type of sizing agent,
desired
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WO 98/33982 PCT/SE98/00191
anionicity, cationicity and solids content of the resulting dispersion. The
hydrophobicaily
modified dispersing agent can be present in the dispersion 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.
5 In a preferred embodiment of this invention, the size dispersion contains a
hydrophobe-modified dispersing agent, as described above, and a surfactant.
This
surfactant, when employed, may be anionic, non-ionic or cationic in nature.
Surfactants to be
employed should suitat~ly have I-ILB values ranging from about 8 to about 30
or higher, and
preferably from about 8-25.
Suitable cationic surfactants include any cationic compound which is capable
of
functioning as a surfactant and~or as a coupling agent between the particle or
droplet of
sizing agent and the hydrophobe-modified cellulose-derivative. Preferred
surfactants include
ammonium compounds having the general formula RgN+ 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, andlor groups
containing a
heteroatom, e.g. carbonyl and acyloxy groups; suitably at least three and
preferably all of
said R groups containing carbon atoms; suitably at least one and preferably at
least two of
said R groups containing at least 9 carbon atoms and preferably at least 12
carbon atoms;
and wherein X- is an anion, typically a halide, e.g. chloride. Examples of
suitable surfactants
include dioctyldimethylammonium chloride, didecyfdimethylammonium chloride,
dicoco-
dimethylammonium chloride, cocobenzyidimethylammonium chloride,
coco(fractionated)-
benzyidimethylammonium chloride, octadecyl trimethylammonium chloride,
dioctadecyl
dimethylammonium chloride, dihexadecyl dimethylammonium chloride,
di(hydrogenated
tallow)dimethylammonium chloride, di(hydrogenated tallow)benzylmethylammonium
chloride,
(hydrogenated tallow)t~enzyldimethylammonium chloride, dioleyldimethylammonium
chloride,
and di(ethylene 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
preferred
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.
Suitably the
cationic surfactant ha.s a molecular weight between about 200 and about 800.
Suitable
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anionic surfactants include alkyl, aryl and alkylaryl sulfates and
ethersulfates, alkyl, aryl and
alkylaryl carboxylates, alkyl, aryl and alkylaryi 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
alkylaryi groups
having from from 7 to 30 carbon atoms. Suitable anionic surtactants include
sodium lauryl
sulfate, sodium lauryl sulfonate and sodium dodecylbenzenesulfonate.
When being used, the surfactant can be present in the dispersion in an amount
of 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. In a preferred embodiment, the size
dispersion
contains an anionic hydrophobe-modified dispersing agent and a cationic
surfactant.
Preferably this size dispersion is anionic in nature, i.e. the anionic
dispersing agent is present
in ionic excess. In another preferred embodiment, the size dispersion contains
a cationic
hydrophobe-modified dispersing agent and an anionic surfactant. Preferably
this size
dispersion is cationic, i.e. the cationic dispersing agent is present in ionic
excess.
The sizing dispersions can be added to the paper making stock in conventional
manner. The term "paper", as used herein, is meant to include not oily paper
but all types ef
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 cellulosic 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. Suitably the amount of cellulose-reactive
sizing agent added
to the stock is from 0.01 to 1.0% by ~.veight, based on the dry weight of
celluiosic 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 sizing agent
used and the level
of sizing desired.
The size dispersions are used in stock sizing of cellulosic pulp where the
stock
has a high cationic demand and/or contains substantial amounts of lipophilic
substances, e.g.
stocks prepared from certain grades of wood-containing and recycled pulps, for
example
where recircu(ation of white water is extensive. Usually the cationic demand
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
Cetector using a stock filtrate obtained from a raw stock filtered through a
1.6 um filter and
poly(diallyldimethylammonium chloride) as a titrant. The amount of lipophilic
substances 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
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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 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 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 cellulosic fibres in order to form tha
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.
Chemicaho 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 size dispersions. Examples
of aluminium
compounds include alum, aluminates and polyafuminium compounds, e.g.
polyaiuminium
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 and
acryiamide-based
polymers, polyethyleneimine, dicyandiamide-formaldehyde, poiyamines,
poiyamidoamines
and poly(diallyldimethyl~ ammoniumchloride) and combinations thereof. Cationic
starch and
cationic acrylamide-bared 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 simultaneously with the addition of the cationic polymer or
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.
In a preferred embodiment of this invention, the aqueous dispersion contains a
cellulose-reactive sizing agent, as defined above, and an anionic
hydrophobically modified
cellulose-derivative, and the invention also relates to such a dispersion and
its preparation,
as further defined in th,e claims.. These dispersions are preferably anionic.
Suitable cellulose-
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8
derivatives include any compound derived from cellulose that is anionic and
hydrophobically
modified and capable of functioning as a dispersing agent or stabilizer. The
cellulose-
derivative preferably is water-soluble or water-dispersable. The cellulose-
derivative contains
one or more hydrophobic groups. Examples 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,
suitably a least 6 and preferably from 8 to 30 carbon atoms, optionally being
intemrpted by
one or more heteroatoms, e.g. oxygen or nitrogen, andlor groups containing a
heteoratom,
e.g. carbonyl or acyloxy. Fatty amide-mod~ed celluloses are preferred. The
cellulose-
derivative can have a degree of hydrophobic substitution (DSH) of from 0.01 to
0.8, suitably
from 0.02 to 0.5 and preferably from 0.03 to 0.4. The hydrophobe-modified
cellulose-
derivative is anionic and contains one or more anionic groups of the same or
different type,
preferably it is polyanionic. Suitable anionic groups, i.e. groups that are
anionic or rendered
anionic in water, include sulfate groups and carboxylic, sulfonic, phosphoric
and phosphonic
acid groups which may be present as free aad or as water-soluble ammonium or
alkali metal
(generally sodium) salts. Anionic groups can be introduced by means of
chemical
modification in known manner. The cellulose-derivative can have a degree of
anionic
substitution (DSA) of from 0.1 to 1.4, suitably from 0.4 to 0.9 and preferably
from 0.5 to 0.8.
The cellulose-derivatives suitably contain carboxyalkyl and preferably
carboxymethyl groups.
Examples of suitable cellulose-derivatives according to the invention include
hydrophobically modified and optionally charged, preferably anionic, cellulose-
derivatives
selected from carboxymethyi cellulose (CMC), mixed cellulose ethers of CMC,
e.g. hydroxy-
ethyl carboxymethyl cellulose (HECMC), hydroxypropyl carboxymethyl cellulose
(HPCMC),
dihydroxypropyl carboxymethyl cellulose (DHPCMC), quaternary nitrogen-
containing
carboxymethyl cellulose (QNCMC), e.g. CMC etherifted with glyadyl trialkyl
ammonium
chloride, carboxymethyl ethylsulphonate cellulose. (CMESC), methyl
carboxymethyl cellulose
(MCMC), etc. Fatty amide-modified carboxyl-containing celfufoses are
particularly preferred,
e.g. fatty amide-modified carboxymethyl celtuloses (FACMC). Suitable
hydrophobically
modified cellulose-derivatives and methods of introducing hydrophobic
substituents into
anionic cellulose-derivatives are for example disclosed in International Pat.
Appl. Publ. No.
WO 94/24169.
The hydrophobically modified cellulose-derivative can be present in the
dispersion 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 cellulose-
reactive sizing agent.
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9
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. This invention
provides sizing dispersions with improved storage stability and/or high solids
content. The
present dispersions generally can have sizing agent contents of from about 0.1
to about 45%
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 45% 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 preferably from about 5 to about 20%
by weight.
The dispersions of this invention can be produced by mixing an aqueous phase
with the dispersing agent and the sizing agent, and optionally the surfactant,
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 pm 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
example, dispersing
agents and stabilizers, extenders, e.g. urea and urea derivatives, and
preservative agents.
It has further been found that the components of the dispersions can be easily
homogenized in the presence of an aqueous phase. Therefore, a further method
of preparing
the dispersions comprises (i) mixing the cellulose-reactive sizing agent with
the anionic
cellulose-derivative, and optionally the surfactant, to obtain an intermediate
composition, and
(ii) homogenizing the untermediate 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 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 size composition which enables simplified shipping in
an
economically attractivE~ manner. At the location of intended use, or
elsewhere, the
intermediate size composition can be homogenized in the presence of water in
conventional
' manner, optionally at ellevated temperature so as to render the intermediate
size composition
liquid. This methed is easpecially 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 size composition thus offers considerable
economic and
technical benefits. The present invention thus also relates to a substantially
water-free size
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WO 98/33982 PCT/SE98100191
composition comprising a cellulose-reactive sizing agent and an anionic
hydrophobically
modified cellulose-derivative, and optionally a surfactant, its preparation
and use, as further
defined in the claims.
The components that are present in the composition according to the invention,
5 i.e., the cellulose-reactive sizing agent and the anionic hydrophobically
modified cellulose-
derivative, and optionally the surfactant, 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
10 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 a sizing agent content
within the range
of from 80 to 99.9% by weight and preferably from 90 to 99.7% by weight. The
cellulose-
derivative can be present in the size composition in amounts defined above
with respect to
the dispersions where the percentages are based on the sizing agent. The
anionic cellulose-
derivative can thus be present in the composition 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. If being used, the surfactant,
which suitably
is a cationic surfactant, can be present in the composition in an amount of
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, wherein the overall charge of the surfactant and the anionic
cellulose-
derivative being present in the composition preferably is anionic or negative.
The sizing dispersions according to the invention can be used in conventional
manner in the production of paper using any type of cellulosic fibres and it
can be used both
for surface sizing and internal or stock sizing. 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, 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 are particularly useful in stock sizing of
cellulosic pulp where the stock has a high cationic demand andlor contains
substantial
amounts of lipophilic substances. Suitable levels of the cationic demand,
contents of lipophilic
extractives and levels of fresh water introduced into the process are
described above.
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11
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
Alkyl ketene dimer (AKD) dispersions according to the invention were prepared
by mixing an aqueous solution of an anionic hydrophobe-modified cellulose-
derivative with
molten AKD at 70°C, passing the mixture through a homogenizer and then
cooling the
dispersion so obtained. The pH .of the dispersion was adjusted to about 5 by
addition of acid.
Dispersion No. 1 was prepared using 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
94/24169. The FACMC had a degree of carboxylic substitution of 0.6 and a
degree of
hydrophobic substitution of 0.1. The dispersion contained AKD particles with
an average
particle size of about 1 Vim, had an AKD content of 30% and contained 1.5% by
weight of
FACMC, based on the ,AKD.
Dispersion No. 2 was prepared as above except that a cationic surfactant,
di(hydrogenated tallow) dimethylammonium chloride, commercially available
under the trade
name Querton 442, Akzo Nobel" was also present during the homogenization. The
dispersion
contained AKD particles with an average particle size of about 1 um which were
anionically
charged, as shown by a negative zeta potential determined by means of a
ZetaMaster S
Version PCS. The AKD content was 30%. Dispersion No. 2 contained 3% by weight
of
cationic surfactant and 1 % by weight of FACMC, both based on the AKD.
Example 2
Sizing efficiency of Dispersion No. 1 according to Example 1 was evaluated in
this Example. An anionic AKD dispersion was also prepared by using
carboxymethyl cellu
lose as a dispersing agent (5% by weight of CMC, based on the AKD) and tested
for
comparison purposes. This dispersion, Ref. 1, showed poor stability and was
therefore
used immediately after its preparation.
Paper sheets were prepared according to the standard method SCAN-C23X
for laboratory scale. The papermaking stock used contained 80% of 60:40
bleached
birchlpine sulphate and 20% of chalk to which 0.3 g/l of NazS04'10H20 was
added. Stock
consistency was 0.5°/r. and pH 8Ø The size dispersions were used in
conjunction with a
commercial retention .and dewatering system, CompozilT"', comprising cationic
starch and
an anionic aluminium-modified silica sol which were added to the stock
separately; the
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WO 98/33982 PCTISE98/00191
12
cationic starch was added in an amount of 8 kglton, based on dry stock, and
the silica sol
was added in an amount of 0.8 kg/ton, calculated as SiOz 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 1
Dispersion No. AKD dosage fk4/tonl Cobb 60 f4lmz~
1 0.4 67
1 0.6 28.
1 0.8 24
Ref. 1 0.4 80
Ref. 1 0.6 62
Ref. 1 0.8 50
Table 1 demonstrates the improvement in paper sizing obtained with the
anionic size dispersion according to the invention.
Example 3
Sizing efficiency of Dispersion No. 2 according to Example 1 was evaluated
and compared to a conventional anionic AKD dispersion, Ref. 2, containing a
dispersant
system consisting of sodium lignosulphonate and cationic starch where the
lignosulpho
pate is present in ionic excess.
The procedure of Example 2 was repeated except that the stock contained
precipitated calcium carbonate as a filler instead of chalk, and the dosage of
cationic starch
was 12 kg/ton, based on dry stock. In some of the tests 10 ppm of stearic acid
was added
to the stock in order to raise the cationic demand and the lipophilic
substance content of
the stock and to create conditions similar to those obtained with extensive
white water
recirculation. The results are set forth in Table 2.
Table 2
Dispersion No. AKD dosage fk4/tonl Stearic acid fppml Cobb 60 fc~lmzl
2 0.45 - 32
2 0.60 - 28
2 0.75 - 26
2 0.45 10 62
2 0.60 10 36
2 0.75 10 27
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WO 98/33982 PCT/SE98/00191
'! 3
Ref. 2 0.45 - 50
Ref. 2 0.60 - 32
Ref. 2 0.75 - 30
Ref. 2 0.45 10 103
Ref. 2 0.60 10 76
Ref. 2 0.75 10 35
As is evident from Table 2, Dispersion No. 2 according to the invention
generally gave much beater sizing than the anionic dispersion Ref. 2used for
comparison,
and considerably improved sizing effect was obtained when the stock had a
higher cationic
demand and contained a substantial amount of lipophilic substances.
