Note: Descriptions are shown in the official language in which they were submitted.
CA 02418416 2003-02-05
WO 02/12624 PCT/SE01/01700
1
Sizing dispersion
The present invention refers to an aqueous dispersion of a sizing agent
comprising starch having aromatic groups containing less than 95 weight % of
amylopectine and condensed sulfonate. The invention further encompasses a
method for
the preparation of an aqueous dispersion and the use of an aqueous dispersion
as a
stock or surface size.
Back rq oud
Aqueous dispersions or emulsions of sizing agents are used in papermaking in
order to give paper and paper board improved resistance to wetting and
penetration by
various liquids.
Dispersions of sizing agents generally contain an aqueous phase and finely
divided
particles or droplets of the sizing agent dispersed therein. The dispersions
are usually
prepared by homogenizing the sizing.agent, water insoluble material in an
aqueous phase in
the presence of a dispersant using high shear forces and fairly high
temperatures.
Dispersants conventionally used include anionic, amphoteric and cationic high
molecular
weight polymers e.g. lignosulfonates, starches, polyamines, 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
com-
ponents of the dispersant system, the size dispersions will be anionic or
cationic in nature.
The sizing dispersions are usually added to an aqueous suspension containing
cellulosic
fibres, optional fillers and various additives.
The cellulosic suspension contains a certain amount of non-fibrous material,
for
example fillers, colloidal substances, charged polymers and various charged
Contaminants, i.e. anionic trash, electrolytes, charged polymers etc.. The
charged
contaminants has an influence on the sizing efficiency and commonly impairs
the sizing
performance. High amounts of charged contaminants such as high contents of
salts in
the suspension renders a suspension which is increasingly difficult to size,
i.e. to obtain a
paper with satisfactory sizing properties. Other compounds contained in the
suspension
which deteriorates sizing are various lipophilic wood extractives which may
come from
recycled fibres and mechanical pulps. An increased amount of added sizing
agent often
improve sizing, however, leading to higher costs as well an increased
accumulation of
sizing agents in the white water. The accumulation of non-fibrous material as
well as any
other components present in the suspension will be even more pronounced in
mills where
white water is extensively recirculated with the introduction of only low
amounts of fresh
water into the papermaking process. Thus, it is an objective of the present
invention to
further improve sizing. Another objective of the present invention is to
improve sizing
when applying sizes on cellulosic suspensions having high conductivities.
Still another
CA 02418416 2003-02-05
WO 02/12624 PCT/SE01/01700
2
objective of the present invention is that the stability of the dispersions
are improved. Yet
further objectives will appear hereinafter.
Invention
In accordance with the invention it has been surprisingly been found that
improved sizing can be obtained with an aqueous dispersion according to the
claims.
More specifically, the present invention refers to an aqueous dispersion of a
sizing agent
comprising starch having aromatic groups containing less than 95 weight % of
amylopectine and a condensation product of aromatic sulfonic acids and
aldehyde. The
present invention further also encompasses a method for the preparation of an
aqueous
dispersion as well the use of the dispersion as a stock size and surface size.
The sizing agent of the dispersion according to the present invention is
suitably
any sizing agent known, such as non-cellulose-reactive agents including rosin,
e.g.
disproportionated rosin, hydrogenated rosin, polymerized rosin, formaldehyde-
treated rosin,
esterified rosin, fortified rosin and mixtures of such treatments and so
treated rosins, fatty
acids and derivatives thereof, e.g. fatty acid esters and amides like bis-
stearamide, resin and
derivatives thereof, e.g. hydrocarbon resins, resin acids, resin acid esters
and amides,
waxes, e.g. crude and refined paraffin waxes, synthetic waxes, naturally
occuring waxes,
etc, and/or cellulose-reactive agents. Preferably, the sizing agent is a
cellulose-reactive
sizing agent. The cellulose-reactive sizing agents comprised in the sizing
dispersion can
be selected from any cellulose-reactive agents known in the art. Suitably, the
sizing agent
is selected from the group consisting of hydrophobic ketene dimers, ketene
multimers, acid
anhydrides, organic isocyanates, carbamoyl chlorides and mixtures thereof,
preferably
ketene dimers and acid anhydrides, most preferably ketene dimers. Suitable
ketene dimers
have the general formula (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. The
ketene dimers
may be liquid at ambient temperature, i.e. at 25 °C, suitably at 20
°C. Suitable acid
anhydrides can be characterised 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
comrP~er-
cially include alkyl and alkenyl succinic anhydrides and particularly
isooctadecenyl succinic
anhydride.
(I) R' - CH = C - CH - Ra (II) O O
CA 02418416 2003-02-05
WO 02/12624 PCT/SE01/01700
~ ~~
3
O-C=O 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, which is hereby incorporated
herein by
reference. Examples of suitable carbamoyl chlorides include those disclosed in
U.S. Pat.
No. 3,887,427 which is also incorporated herein by reference.
The starch comprised in the dispersion according to the invention has aromatic
groups and contains less than 95 weight % of amylopectin. Starch contains
primarily two
components namely amylos and amylopectin. Amylos is a linear polymer whereas
amylopectin is a branched polymer having a molecular weight considerably
higher than
the molecular weight of amylos. Preferably, the aromatic starch has an
amylopectin
content less than 92 weight %, more preferably less than 90 weight %, and even
more
preferably less than 85 weight %. The starch comprised in the dispersion of
the present
invention is suitably a cationic starch having an aromatic group, i.e. the
cationic starch
has at least one aromatic group and at least one cationic group, the cationic
group suitably
being tertiary amino groups or, preferably, quaternary ammonium groups. The
starch may
also contain one or more anionic groups which can be, for example, phosphate,
phosphonate, sulphate, sulphonate or carboxylic acid groups and they are
preferably
phosphate groups. If present, the anionic groups can be native or introduced
by means of
chemical treatment in conventional manner; native potato starch contains a
substantial
amount of covalently bound phosphate monoester groups. In amphoteric starches,
cationic
groups are preferably present in a predominant amount.
The aromatic group of the starch can be attached to a heteroatom, e.g.
nitrogen or
oxygen, the heteroatom optionally being charged, for example when it is a
nitrogen. The
aromatic group can also be attached to a group comprising a heteroatom, e.g.
amide, ester
or ether, which groups can be attached to the polysaccharide backbone(main-
chain) of the
starch, for example via a chain of atoms. Example of suitable aromatic groups
and groups
comprising an aromatic group include aryl and aralkyl groups, e.g. phenyl,
phenylene,
naphthyl, phenylene, xylylene, benzyl and phenylethyl; nitrogen-containing
aromatic (aryl)
groups, e.g. pyridinium and quinolinium, as well as derivatives of these
groups where one or
more substituents attached to said aromatic groups can be selected from
hydroxyl, halides,
3.
e.g. chloride, nitro, and hydrocarbon groups having from 1 to 4 carbon atoms.
Particularly suitable starches comprised in the sizing dispersion include hose
comprising the general structural formula (I):
Ri (I)
X
P-(-A-N+-Rz)n
CA 02418416 2003-02-05
WO 02/12624 PCT/SE01/01700
4
R3
wherein P is a residue of the starch polysaccharide; A is a group attaching N
to the
polysaccharide residue, suitably a chain of atoms comprising C and H atoms,
and optionally
O and/or N atoms, usually an alkylene group with from 2 to 18 and suitably 2
to 8 carbon
atoms, optionally interrupted or substituted by one or more heteroatoms, e.g.
O or N, e.g. an
alkyleneoxy group or hydroxy propylene group (- CHZ- CH(OH) - CH2 - ); R~ and
RZ
are each H or, preferably, a hydrocarbon group, suitably alkyl, having from 1
to 3 carbon
atoms, suitably 1 or 2 carbon atoms; R3 is an aromatic hydrocarbon group
including
aralkyl groups, e.g. benzyl and phenylethyl groups; n is an integer from about
2 to about
300,000, suitably from 5 to 200,000 and preferably from 6 to 125,000 or,
alternatively, R~,
R2 and R3 together with N form a aromatic group containing from 5 to 12 carbon
atoms; and
X is an anionic counterion, usually a halide like chloride.
The aromatic group modified cationic or amphoteric starch can have a degree of
substitution varying over a wide range; the degree of cationic substitution
(DSc) can be from
0,01 to 0,5, suitably from 0,02 to 0,3, preferably from 0,025 to 0,2, the
degree of aromatic
substitution (DSH) can be from from 0,01 to 0,5, suitably from 0,02 to 0,3,
preferably from
0,025 to 0,2, and the degree of anionic substitution (DSA) can be from 0 to
0,2, suitably from
0 to 0,1, preferably from 0 to 0, 05.
The starches can be prepared by subjecting a starch to cationic and aromatic
modification in known manner using one or more agents containing a cationic
group
and/or a aromatic group, for example by reacting the agent with the starch in
the
presence of an alkaline substance such as an alkali metal or alkaline earth
metal
hydroxide. The starch to be subjected to cationic and aromatic modification
can be non-
ionic, anionic, amphoteric or cationic. Suitable modifying agents include non-
ionic agents
such as, for example, aromatic substituted succinic anhydrides; aralkyl
halides, e.g.
benzyl chloride and benzyl bromide; the reaction products of epichlorohydrin
and
dialkylamines having at least one substituent comprising an aromatic group as
defined
above, including 3-dialkylamino-1,2-epoxypropanes; and cationic agents such
as, for
example, the reaction product of epichlorohydrin and tertiary amines having at
least one
substituent comprising an aromatic group as defined above, including
trialkylamines,
alkaryldialkylamines, e.g. dimethylbenzylamine; arylamines, e.g. pyridine and
quinoline.
3
Suitable cationic agents of this type include 2,3-epoxypropyl trialkylammonium
halides
and halohydroxypropyl trialkylammonium halides, e.g. N-(3-chloro-2-
hydroxypropyl)-N
(hydrophobic alkyl)-N,N-di(lower alkyl)ammonium chloride and N-glycidyl-N-
(hydrophobic
alkyl)-N,N-di(lower alkyl)ammonium chloride where the aromatic group is as
defined
above, notably octyl, decyl and dodecyl, and the lower alkyl is methyl or
ethyl; and halo
CA 02418416 2003-02-05
WO 02/12624 PCT/SE01/01700
hydroxypropyl-N,N-dialkyl-N-alkarylammonium halides and N-glycidyl-N-(alkaryl)-
N,N-
dialkylammonium chloride, e.g. N-(3-chloro-2-hydroxypropyl)-N-(alkaryl)-N,N-
di(lower
alkyl)ammonium chloride where the alkaryl and lower alkyl groups are as
defined above,
particularly N-(3-chloro-2-hydroxypropyl)-N-benzyl-N,N-dimethylammonium
chloride; and
5 N-(3-chloro-2-hydroxypropyl) pyridinium chloride. Generally, when using a
non-ionic
aromatic agent, the starch is suitably rendered cationic by using any of the
cationic
agents known in the art before or after the hydrophobic modification. Examples
of
suitable cationic and/or aromatic modifying agents, aromatic group modified
starches and
methods for their preparation include those described in U.S. Patent Nos.
4,687,519 and
5,463,127; International Patent Application WO 94/24169, European Patent
Application
No. 189 935; and S.P. Patel, R.G. Patel and V.S. Patel, Starch/Starke, 41
(1989), No. 5,
pp. 192-196, the teachings of which are hereby incorporated herein by
reference.
The starch, suitably cationic or amphoteric can be present in the dispersion
in
amounts varying within wide limits depending on, inter alia, 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.
The starch can
be present in an amount of up to 100% by weight, suitably from 0.1 to 35% by
weight and
preferably from 1 to 30% by weight, based on the hydrophobic material.
The dispersion according to the invention further comprises condensed
sulfonates
such as the condensation product of aromatic sulfonic acids and aldehyde. By
condensed
sulfonate is meant a sulfonate, suitably a polymeric sulfonate, obtained by a
condensation
reaction. Suitably, the dispersion comprises a condensation product of
aromatic sulfonic
acids and formaldehyde. The condensation products are generally
polyelectrolytes and
readily soluble in water. A wide variety of aromatic sulfonic acids can be
used such as
aromatic sulfonic acids containing one aromatic ring, usually having six
carbon atoms, and
aromatic sulfonic acids containing two or more aromatic rings having six
carbon atoms as
well as fused aromatic sulfonic acids. Suitably, the aromatic sulfonic acid is
selected from
naphthalene, naphthalene reacted with cresol, diphenyl ether, toluene,
isopropylbenzene,
cresol, phenol,. Commonly, the condensation products are formed by reacting
the aromatic
compound with sulfuric acid thereby forming sulfonic acid and thereafter
adding the
aldehyde whereby the condensation product is obtained. Occasionally, sodium
sulfite may
be present during the reaction. According to a prefer-ed embodiment of the
present
invention the aqueous dispersion comprises a condensation product of
naphthalene sulfbnic
acid and formaldehyde, a condensation polymer commonly referred to as
condensated
naphthalene sulfonate.
The amount of condensed sulfonates present iri the dispersion can vary within
wide
limits depending on, inter alia, the type of stock, and other compounds
present in the
CA 02418416 2003-02-05
WO 02/12624 PCT/SE01/01700
6
aqueous dispersion like stabilisers, dispersion agent and sizing agents.
Usually, the
dispersion contains from about 1 up to about 20 % by weight based on the
sizing agent of
condensed sulfonate, suitably from about 1 up to about 15 % by weight,
preferably from
about 2 up to about 10 % by weight based on the sizing agent.
The dispersions according to the present invention can be anionic or cationic
depending on the amount of starch and/or further additives such as
dispersing/stabilising
agents and protecting compounds contained in the dispersions. By anionic or
cationic
dispersions is understood that the dispersant is anionic or cationic, i.e. has
an overall anionic
or cationic charge. The dispersant (system) refers to any compounds present in
the
dispersion which facilitate the formation of a dispersionlemulsion such as
charged polymers
(polyelectrolytes) and surfactants. Suitable additives can be any
dispersing/stabilising
agents and protecting agent known in the art such as non-ionic polymers;
cationic, anionic
and amphoteric polymers derived from natural sources, i.e. polysaccharides
like starch, guar
gum, cellulose, chitins, chitosans, glycans, galactans, glucans, xanthan gums,
mannans,
dextrins, etc., and synthetic 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, malefic acid, itaconic
acid, crotonic acid,
vinyisulfonic acid, sulfonated styrene and phosphates of hydroxyalkyl
acrylates and
methacrylates, optionally copolymerized with non-ionic monomers including
acrylamide,
alkyl acrylates, styrene and acrylonitrile as well as derivatives of such
monomers, vinyl
esters, and the like.
Suitably, the dispersion comprises cellulose-reactive sizing agents having a
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.
By the "term" dispersion" is meant both dispersion and emulsion depending on
the
physical state of the sizing agent.
The dispersions according to the invention can be prepared by a method
comprising homogenising a sizing agent, suitably under pressure, in the
presence of an
aqueous phase and a starch preferably at a temperature where the sizing agent
is liquid.
The obtained aqueous emulsion, which contains droplets of the sizing agent,
normally
CA 02418416 2003-02-05
WO 02/12624 PCT/SE01/01700
7
having a size of from 0.1 to 3.5 wm in diameter, is then cooled. 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 dispersions of the present invention can be used as sizing agents 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 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 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.
The amount of 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 optio
nal 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.
Furthermore, the dispersions of the present invention are preferably used in
the
manufacture of paper from a stock containing cellulosic fibers, and optional
fillers, having a
high conductivity. Usually, the conductivity of the stock is at least 0.20
mS/cm, suitably at
least 0.5 mS/cm, preferably at least 3.5 mS/cm. Very good sizing results have
been
observed at conductivity levels above 5.0 mSlcm and even above 7.5 mSlcm.
Conductivity
can be measured by standard equipment such as, for example a VVfUl1 l-F 539
instrument
supplied by Christian Berner. The values referred to above are suitably
determined by
measuring the conductivity of the cellulosic suspension that is fed into or
present in the
headbox of the paper machine or, alternatively, by measuring the conductivity
of white water
obtained by dewatering the suspension. High conductivity levels mean high
contents of salts
(electrolytes), where the various salts can be based on mono-, di- and
multivalent cations
like alkali metals, e.g. Na+ and K+, alkaline earths, e.g. Ca2+ and Mgr+,
aluminium ions, e.g.
AI3+, AI(OH)2+ and polyaluminium ions, and mono-, di- and multivalent anions
like halides,
e.g., Cf, sulfates, e.g. S042' and HS04 , carbonates, e.g. C032' and HC03 ,
silicates and
lower organic acids. The dispersion is particularly useful in the manufacture
of paper from
stocks having high contents of salts of di- and multivalent cations, and
usually the ca'tion
content is at least 200 ppm, suitably at least 300 ppm and preferably at least
400 ppm. The
salts can be derived from the cellulosic fibres and fillers used to form the
stock, in particular
in integrated mills where a concentrated aqueous fibre suspension from the
pulp mill
normally is mixed with water to form a dilute suspension suitable for paper
manufacture in
CA 02418416 2003-02-05
WO 02/12624 PCT/SE01/01700
8
the paper mill. The salt may also be derived from various additives introduced
into the stock,
from the fresh water supplied to the process, or be added deliberately, etc.
Further, the
content of salts is usually higher in processes where white water is
extensively recirculated,
which may lead to considerable accumulation of salts in the water circulating
in the process.
The 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
An anionic sizing dispersion was prepared containing 8,9 % of a commercial
alkyl ketene
dimer, 0,89 % of an aromat substituted cationic starch having a DS of 0,065
containing
benzyl groups, and 0,22 % of condensated naphthalene sulphonate available
under the
trade name Tamol ~. The anionic dispersion was added in an amount of 0,0125%
(test 1)
and 0,0140 (test 2) as indicated by table 1 to (dry base) based on the ketene
dimer to a
cellulosic suspension (dry base) containing 30% Pine, 30% Bee, 40% Eucaluptus,
and
15% of precipitated CaC03. The conductivity of the suspension was 500 NS/cm.
To the
suspension was also added a sizing promoter containing benzyl substituted
starch having
a DS of 0.065 (5 kg/tonne dry stock) and condensated naphtalene sulphonate
(0,120
kg/tonne dry stock) available under the trade name Tamol ~.
Table 1
Test anionic cobb
no.
sizing 601[g/m~]
dispersion/
[kg sizing
agent/tonne
dry stock]
test 0.125 27.0
1
test 0.140 25.5
2
Example 2
In this example the same anionic sizing dispersion was used as in example 1.
Furthermore, the same sizing promoter was also used as in example 1 containing
benzyl
substituted starch having a DS of 0.065 (5 kg/tonne dry stock) and condensated
naphtalene sulphonate (0,120 kg/tonne dry stock) available under the trade
name
Tamol~. The anionic sizing dispersion was added to the same cellulosic
suspension,
however, the conductivity of the suspension was 5000 NS/cm instead of 500
pS/cm.
CA 02418416 2003-02-05
WO 02/12624 PCT/SE01/01700
9
Table 2
Test anionic cobb 60/jg/m']
no.
sizing
dispersion/
jkg sizing
agentltonne
dry stock]
test 0.125 33
1
test 0.140 25
2
Example 3
The sizing performance of a cationic sizing according to prior art was
evaluated using the
cobb 60 test. The sizing dispersion was prepared by mixing cationic starch
having no
aromatic groups and lignosulphonate with molten AKD having an AKD content of
15
weight % based on total dispersion. The papermaking stock contained 85% of
30:30:40
pine:birch:eucaluptus sulphate pulp and 15 % of precipitated calcium to which
CaCl2 was
added. Stock consistency was 2.5 g// having a pH of 8.1 and a conductivity of
500 ~s.
The dispersion was used in conjunction with a retention and dewatering system
comprising a cationic aromatic modified starch having a DS~ of 0,065
containing bezene
groups and condensated naphtalene sulphonate which were added to the stock
separately. The cationic aromatic modified starch was added in an amount of 5
kg/ tonne,
based on dry stock and the condensated naphtalene sulphonate was added in an
amount
of 0.5 kg/tonne, repectively.
Table 3
Sizing dispersion cobb 60/jg/m']
added/jkg
AKD/tonne dry stock]
0,122 42
Example 4
In this example the conditions, i.e. sizing dispersion, dewatering and
retention system,
etc. were the same as for example 3, however, the conductivity of the stock
was 5000 its
by the addition of CaClz.
CA 02418416 2003-02-05
WO 02/12624 PCT/SE01/01700
Table 4
Sizing dispersion Cobb
added/[kg
AKD/tonne dry stock]
0,122 95
