Note: Descriptions are shown in the official language in which they were submitted.
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Aaueous silica-containing composition and process for production of paper
The present invention relates to an aqueous silica-containing composition
comprising an anionic organic polymer having at least one aromatic group and
anionic
silica-based particles. The invention further relates to a method for the
preparation of the
aqueous silica-containing composition, uses of the aqueous silica-containing
composition
and a papermaking process.
Background of the Invention
In the papermaking art, an aqueous suspension containing cellulosic fibres,
and
optionally fillers and additives, referred to as stock, is fed into a headbox
which ejects the
stock onto a forming wire. Water is drained from the stock through the forming
wire so
that a ~r~et ~Neb of paper is formed on the v!~ire. The formed paper web is
dewatered and
dried in the drying section of the paper machine. Drainage and retention aids
are
CiU11Ve11tIVllally IIILIUUI.IGed IIItV t le jtoOk III Vrdel tV Ia1r111tatC dl
alllage atld tV IIIUlease
adsorption of fine particles onto the cellulosic fibres in such a way that the
fine particles
are retained with the fibres on the wire.
US 4,388,150 discloses a binder in papermaking comprising a complex of
cationic starch and colloidal silicic acid to produce a paper having increased
strength and
improved levels of retention of added minerals and papermaking fines.
US 4,750,974 discloses a coarcervate binder for use in papermaking comprising
a tertiary combination of a cationic starch, an anionic high molecular weight
polymer and
a dispersed silica.
US 5,368,833 discloses silica sots containing aluminium modified silica
particles
with high specific surface area and a high content of microgel.
US 5,567,277 discloses a composition comprising an aqueous cellulosic furnish,
a high molecular weight cationic polymer and an anionic polymer comprising
modified
lignin.
US 6,022,449 discloses the use of water-dispersible polyisocyanates with
anionic and/or potentially anionic groups and cationic and/or potentially
cationic
, compounds in paper finishing.
EP 0 418 015 A1 discloses an active sizing composition containing an aqueous
emulsion in combination with an anionic dispersant or emulsifier. By using
anionic
polyacrylamide, anionic starch or colloidal silica the anionic charge density
in the sizing
composition can be extended.
US 5,670,021 refers to a process for the production of paper by forming and
dewatering a suspension of cellulose, wherein the dewatering takes place in
the
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presence of an alkali metal silicate and a phenolic resin added at the same
point into the
suspension.
US 6,033,524 discloses a method for increasing retention and drainage of
filling
components in a paper making furnish in a paper making process comprising
adding to
the furnish a slurry of filling components, also containing a phenolic
enhances.
US 6,315,824 pertains to a dispersed composition comprising a hydrophobic
phase and an aqueous phase, the composition being stabilised by a cationic
colloidal
coacervate stabilising agent, the coacervate stabilising agent comprising an
anionic
component and a cationic component.
EP 0,953,680 A1 refers to a process for the production of paper from s
suspension comprising adding to the suspension a cationic organic polymer.
US 5,185,062 discloses a papermaking process including the steps of adding to
the papermaking slurry a high molecular weight cationic polymer and then a
medium
i'noieci.ilar weig hi aiiioiiii. poiyiier.
US 4,313,790 refers to a process for the production of paper which consists of
the addition to the papermaking furnish of kraft lignin or modified kraft
lignin and
poly(oxyethylene).
US 6,165,259 relates to an aqueous dispersion containing a dispersant and a
disperse phase containing a hydrophobic material, the dispersant comprising an
anionic
compound and a cationic compound.
It would be advantageous to be able to provide drainage and retention aids
with
improved performance. It would also be advantageous to be able to provide
retention and
drainage aids with good storage stability. It would further be advantageous to
be able to
provide a papermaking process with improved drainage and/or retention
performance.
The Invention
According to the present invention it has unexpectedly been found that an
improved drainage and/or retention effect of a cellulosic suspension on a wire
can be
obtained by using an aqueous silica-containing composition comprising at least
one
anionic organic polymer with at least one aromatic group and anionic
aggregated or
microgel formed silica-based particles. The aqueous silica-containing
composition is
useful in processes for production of paper from all types of stocks, in
particular stocks
having high contents of salts (high conductivity) and colloidal substances.
The aqueous
silica-containing composition is also useful in papermaking processes with a
high degree
of white water closure, i.e. extensive white water recycling and limited fresh
water supply.
Hereby the present invention makes it possible to increase the speed of the
paper machine
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and to use a lower dosage of additives to give a corresponding drainage and/or
retention
effect, thereby leading to an improved papermaking process and economic
benefits.
The terms "drainage and retention aid", as used herein, refer to one or more
components, which when added to an aqueous cellulosic suspension, give better
drainage andlor retention than is obtained when not .adding the said one or
more
components. All types of stocks, in particular stocks having high contents of
salts (high
conductivity) and colloidal substances will obtain better drainage and
retention
performances by the addition of the composition according to the present
invention. This
is important in papermaking processes with a high degree of white water
closure, i.e.
extensive white water recycling and limited fresh water supply.
In accordance with the present invention there is provided an aqueous silica-
containing composition comprising an anionic organic polymer having at least
one
aromatic group and anionic silica-based particles comprising aggregated or
microgel
r__.r_r 'I:~.. 1.........,I .-a;..l.... T4... 'li..., n~.,ininn nr,mr~n i~inn
rnnf inc fHc
IUI II ICU JIIII.G-LJCIJGU pal LIt.IGJ. 1 I IG aqueous jlllvGt-VVl I1C7111111~
vvi ~ ~Nv"v'mn ~ vm Wwn w a w
anionic organic polymer having at least one aromatic group and the anionic
silica-based
particles, calculated as Si02, in an amount of at least 0.01 % by weight based
on the total
weight of the aqueous silica-containing composition. The composition contains
substantially no cellulose-reactive sizing agent and the said anionic organic
polymer is
not an anionic naphthalene sulphonate formaldehyde condensate.
There is further provided an aqueous silica-containing composition obtainable
by mixing an anionic organic polymer having at least one aromatic group with
an aqueous
alkali stabilised silica-based sol having an S-value in the range of from
about 5 up to
about 50% containing-anionic aggregated or microgel formed silica-based
particles . The
obtained aqueous silica-containing composition contains the anionic organic
polymer
having at least one aromatic group and the silica-based particles, calculated
as SiOz, in
an amount of at least 0.01 % by weight based on the total weight of the
aqueous silica-
containing composition. The composition contains substantially no cellulose-
reactive
sizing agent and that said anionic organic polymer is not anionic naphthalene
sulphonate
formaldehyde condensate.
There is further provided a method for preparation of an aqueous silica-
containing composition which comprises mixing in the presence of substantially
no
cellulose-reactive sizing agent an anionic organic polymer having at least one
aromatic
group with silica-based particles comprising anionic aggregated or microgel
formed silica-
based paricles to provide an aqueous silica-containing composition containing
the anionic
organic polymer having at least one aromatic group and the silica-based
particles,
calculated as SiO~, in an amount of at least 0.01 % by weight, based on the
total weight
of the aqueous silica-containing composition with the proviso that the anionic
organic
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polymer having at least one aromatic group is not an anionic naphthalene
sulphonate
formaldehyde condensate.
There is further provided a method for preparation of an aqueous silica
containing composition which comprises mixing an anionic organic polymer
having at
least one aromatic group and a charge density of at least 0.1 meq/g of dry
polymer, with
silica-based particles comprisng anionic aggregated or microgel formed to
provide an
aqueous silica-containing composition containing the anionic organic polymer
having at
least one aromatic group and the silica-based particles, calculated as Si02,
in an amount
of at least 0.01 % by weight, based on the total weight of the aqueous silica-
containing
composition, with the proviso that the anionic organic polymer having at least
one
aromatic group is not an anionic naphthalene sulphonate formaldehyde
condensate.
There is further provided a method for preparation of an aqueous silica-
containing composition which comprises desalinating an aqueous solution of an
anionic
organic pOly~Tl~r Il~vl~lc~.- at ledst VI Ie ar W i ~aiii~ gr vup, ~ i ~ixii g
in ti i° dW~'.iin~ted ~: ~io:~:~
organic polymer having at least one aromatic group with silica-based particles
comprisng
anionic .aggregated or microgel formed siluca-based particles to provide an
aqueous
silica-containing composition containing the anionic organic polymer having at
least one
aromatic group and the aggregated or microgel formed silica-based particles,
calculated
as Si02, in an amount of at least 0.01 % by weight, based on the total weight
of the
aqueous silica-containing composition with the proviso that the anionic
organic polymer
having at least one aromatic group is not an anionic naphthalene sulphonate
formaldehyde condensate.
There is further provided an -aqueous silica-containing composition obtainable
by the methods according to the invention.
The invention further relates to the use of the aqueous silica-containing
composition of the invention, as flocculating agent in combination with at
least one
cationic organic polymer in the production of pulp and paper and for water
purification.
According to the invention there is further provided a process for the
production
of paper from a suspension containing cellulosic fibres, and optionally
fillers, comprising
adding to the suspension at least one cationic organic polymer and an aqueous
silica
containing composition according to the invention.
The aqueous silica-containing composition comprises at least one anionic
organic polymer with at least one aromatic group, which is not an anionic
naphthalene
sulfonate formaldehyde condensate. The aromatic group of the anionic polymer
can be
present in the polymer backbone or in a substituent group that is attached to
the polymer
backbone (main chain). Examples of suitable aromatic groups include aryl,
aralkyl and
alkaryl groups and derivatives thereof, e.g. phenyl, tolyl, naphthyl,
phenylene, xylylene,
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benzyl, phenylethyl and derivatives of these groups. The anionically charged
groups can
be present either in the anionic polymer or in the monomers used for preparing
the
anionic polymer. The anionically charged groups can either be groups carrying
an anionic
charge or acid groups carrying an anionic charge when dissolved or dispersed
in water.
5 These groups are herein collectively being referred to as anionic groups,
such as
phosphate, phosphonate, sulphate, sulphonic acid, sulphonate; carboxylic acid,
carboxylate, alkoxide and phenolic groups, i.e. hydroxy-substituted phenyls
and
naphthyls. Groups carrying an anionic charge are usually salts of an alkali,
alkaline earth
metals or ammonia.
Anionic polymers containing one or more aromatic groups according to the
invention can suitably be selected from the group consisting of step-growth
polymers, chain-
gr owt h polymers, polysaccharides and naturally occurring aromatic polymers.
The term
"step-growth polymer", as used herein, refers to a polymer obtained by step-
growth
polymerisation, aiSO ISein~ rife?ed tv a~ ~t8p-r eaCtioi ii pviy i 'cr ai ~d
step-r ~a~t~~vn
polymerisation, respectively. Preferably the anionic polymer is a step-growth
polymer. The
anionic polymers according to the invention can be linear, branched or cross-
linked.
Preferably the anionic polymer is water-soluble or water-dispersible.
Examples of suitable anionic step-growth polymers according to the present
invention include condensation polymers, i.e. polymers obtained by step-growth
condensa
tion polymerisation, e.g. condensates of an aldehyde such as formaldehyde with
one or
more aromatic compounds containing one or more anionic groups, and optional
other co-
monomers useful in the condensation polymerisation such as urea and melamine.
Examples of suitable aromatic compounds containing anionic groups comprises
compounds containing anionic groups such as phenolic compounds, e.g. phenol,
resorcinol and derivatives thereof, aromatic acids and salts thereof.
Examples of suitable anionic step-growth polymers according to the present
invention include addition polymers, i.e. polymers obtained by step-growth
addition
polymerisation, e.g. anionic polyurethanes prepared from a monomer mixture
comprising
aromatic isocyanates andlor aromatic alcohols. Examples of suitable aromatic
isocyanates
include diisocyanates, e.g. toluene-2,4- and 2,6-diisocyanates and
diphenylmethane-4,4'-
diisocyanate. Examples of suitable aromatic alcohols include dihydric
alcohols, i.e. diols, e.g.
bisphenol A, phenyl diethanol amine', glycerol monoterephthalate and
trimethylolpropane
monoterephthalate. Monohydric aromatic alcohols such as phenol and derivatives
thereof
may also be employed. The monomer mixture can also contain non-aromatic
isocyanates
and/or alcohols, usually diisocyanates and diols, for example any of those
known to be
useful in the preparation of polyurethanes. Examples of suitable monomers
containing
anionic groups include the monoester reaction products of triols, e.g.
trimethylolethane, tri-
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methylolpropane and glycerol, with dicarboxylic acids or anhydrides thereof,
e.g. succinic
acid and anhydride, terephthalic acid and anhydride, such as glycerol
monosuccinate,
glycerol monoterephthalate, trimethylolpropane monosuccinate,
trimethylolpropane
monoterephthalate, N,N-bis-(hydroxyethyl)-glycine, di-(hydroxymethyl)propionic
acid,
N,N-bis-(hydroxyethyl)-2-aminoethanesulfonic acid, and the like, optionally
and usually in
combination with reaction with a base, such as alkali and alkaline earth metal
hydroxides,
e.g. sodium hydroxide, ammonia or an amine, e.g. triethylamine, thereby
forming an
alkali, alkaline earth metals or ammonium counter-ion.
Examples of suitable anionic chain-growth polymers according to the invention
include anionic vinyl addition polymers obtained from a mixture of vinylic or
ethylenically
unsaturated monomers. The mixture of vinylic or ethylenically unsaturated
monomers
comprises at least one monomer having an aromatic group and at least one
monomer
having an anionic group. Usually the monomers are co-polymerised with non-
ionic
_ _ ~ L.t.. .d L......~.J.~ h..o .-I r.~nr,nmcrc Ev~mr~le~ of ctNlaHhle
t~tort~W er 5 Si.iW i aS aci ~%IQIG- al IU al.i yal I Iltrcw.ra~eu ~ ~ m ~m ~
m.~.~. nw ~ y
anionic monomers include (meth)acrylic acid and paravinyl phenol (hydroxy
styrene).
Examples of suitable anionic polysaccharides with at least one aromatic group
include starches, guar gums, cellulose derivatives, chitins, chitosans,
glycans, galactans,
glucans, xanthan gums, pectins, mannans, dextrins, preferably starches, and
guar gums,
suitable starches including potato, corn, wheat, tapioca, rice, waxy maize and
barley,
preferably potato. The anionic groups in the polysaccharide can be native
and/or introduced
by chemical treatment. The aromatic groups in the polysaccharide can be
introduced by
chemical methods known in the art.
Examples of-suitable-(modified) naturally occurring aromatic_anionic polymers
of
this invention include lignosulphonates, Kraft lignins, oxylignins, and tannin
extracts i.e.
naturally occurring polyphenolic substances that are obtained from the
sulphite or sulphate
pulp processes or from extracts of bark.
The weight average molecular weight of the anionic polymer can vary within
wide limits dependent on, inter alia, the type of polymer used, and usually it
is at least
about 500, suitably above about 800 and preferably above about 1,000. The
upper limit is
not critical; it can be about 10,000,000, usually 1,000,000, suitably 500,000,
preferably
200,000 and most preferably 100,000.
The anionic polymer can have a degree of anionic substitution (DSA) varying
over a wide range dependent on, inter alia, the type of polymer used. DSA is
usually from
0.01 to 2.0, suitably from 0.02 to 1.8 and preferably from 0.025 to 1.5; and
the degree of
aromatic substitution (DSQ) can be from 0.001 to 1.0, usually from 0.01 to
0.8, suitably
from 0.02 to 0.7 and preferably from 0.025 to 0.5. In case the anionic polymer
contains
cationic groups, the degree of cationic substitution (DSO) can be, for
example, from 0 to
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0.2, suitably from 0 to 0.1 and preferably from 0 to 0.05, the anionic polymer
having an
overall anionic charge. Usually the anionic charge of the anionic polymer is
within the
range of from 0.1 to 10.0 meq/g of dry polymer, suitably from 0.2 to 6.0
meq/g, and
preferably from 0.5 to 4.0 meq/g.
The aqueous silica-containing composition according to the invention also
comprises anionic aggregated or microgel formed silica-based particles i.e.
particles
based on Si02, preferably formed by polymerising silicic acid, encompassing
both
homopolymers and copolymers. Optionally the silica-based particles can be
modified and
contain other elements, e.g. amine, aluminium and/or boron, which can be
present in the
aqueous phase and/or in the silica-based particles.
Examples of suitable aggregated or microgel formed silica-based particles
include
colloids! silica, colloidal aluminium-modified silica or aluminium silicate,
and different types of
polysilicic acid and mixtures thereof, either alone or in combination with
other types of
a~lllA IJ 1 V IGrIW IltrV tV aJ i./VIyl11V11V Iv
al Ilol lIlr s111Ca-based par iIt;IGJ. li I ii IG ar i, ~.rvlyjiiiviir ~i~ is
~InSn re?forrc~ fn c r~nlvmorir ~~livlr
acid, polysilicic acid microgel, polysilicate and polysilicate microgel, which
are all
encompassed by the term polysilicic acid used herein. Aluminium-containing
compounds of
this type are commonly referred to as polyaluminosilicate and
polyaluminosilicate microgel
including colloidal aluminium-modified silica and aluminium silicate.
The anionic silica-based particles are in the colloidal range of particle
size. This
state comprises particles sufficiently small not to be affected by
gravitational forces but
sufficiently large not to show mar4eed deviation from the properties of
typical solutions, i.e.
average particle size significantly less than 1 Vim. The anionic silica-based
particles have
an average particle size suitably below about 50 nm, preferably below about 20
nm and
more preferably in the range of from about 1 to about 50 nm, most preferably
from about 1
up to about 10 nm. As conventional in silica chemistry, the particle size
refers to the average
size of the primary particles, which may be aggregated or non-aggregated.
Suitably, the
silica-based particles present in the aqueous silica-containing composition of
the invention
comprise aggregated or microgel formed silica-based particles, optionally and
usually in
combination with non-aggregated, or monodisperse, silica-based particles.
Suitably, the silica-based particles have a specific surface area larger than
50 m2/g,
preferably larger than 100 m2lg. The specific area can be up to 1700 m2lg,
preferably up to
1300 m2/g and usually in the range from 300 to 1300 m2/g, preferably from 500
to 1050
m2/g. The specific surface area can be measured by means of titration with
NaOH according
to the method described by Sears, Analytical Chemistry 28(1956), 12, 1981-1983
or in U.S.
Patent No. 5,176,891. The given area thus represents the average specific
surface area of
the particles.
The total weight of the anionic organic polymer having at least one aromatic
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group and anionic silica-based particles, calculated as Si02, contained in the
aqueous
silica-containing composition is at least 0.01 % by weight, calculated on the
total weight of
the aqueous silica-containing composition, preferably at least 0.05 % by
weight, more
preferably at feast 0.1 % by weight. Suitably the concentration of the anionic
organic
polymer having at least one aromatic group and the anionic silica-based
particles,
calculated as Si02, is within the range of 1 to 45% by weight, preferably
within the range
of 2 to 35 % by weight, most preferably 5 to 30% by weight.
The aqueous silica-containing composition can have an anionic charge density
of at least 0.1 meq/g, usually the charge is within the range of from 0.1 to
10 meq/g,
suitably within the range of from 0.1 to 8 meq/g, preferably within the range
of from 0.1 to
6 meq/g, and most preferably within the range of from 0.2 to 4 meq/g.
The aqueous silica-containing composition according to the invention contains
substantially no cellulose-reactive sizing agent. By substantially no means
that less than
n~ n m ~W n.. i..-~-, W....... c0/ .C...,...4.h~ L~.~.~. l.h.,n ~0/_ hw woinh~
of
or equal to l U %° I5y Vllelgf ll, siii~amy IGaa LI lal 1 J 70, pr elc~
amy ~co~ « ~a~ ~ ~ ~~ Ny VYV,~y is .m
cellulose-reactive sizing agent is present in the aqueous silica-containing
composition.
Most preferably there is no cellulose-reactive sizing agent in the aqueous
silica-
containing composition. Even more preferably, the aqueous silica-containing
composition
according to the invention contains substantially no sizing agent, suitably,
contains no
sizing agent.
The present invention relates further to a method for preparation of an
aqueous
silica-containing composition. The two components are preferably stirred
together. The
anionic organic polymer having at least one aromatic group can be added to an
aqueous
sol containing the silica-based particles or the silica-based particles can be
added to an
aqueous solution of anionic organic polymer having at least one aromatic
group. The
aqueous solution of anionic organic polymer having at least one aromatic group
may be
desalinated or deionisated. The desalination or deionisation can be carried
out with
dialysis, membrane filtration, ultrafiltration, reversed osmosis or ion
exchange or the like. It is
preferred that the desalination or deionisation is carried out by the use of
ultra-filtration or
dialysis. The pH of an aqueous solution of anionic organic polymer may be
adjusted to the
pH of the silica-based particles, prior to or after mixing the aqueous
solution with the silica-
based particles. The pH can be adjusted to at least pH 8.0, suitably at least
9.0, preferably at
least 9.5, preferably within the range of 9.0 to 11Ø
The anionic organic polymer having at least one aromatic group to be mixed
with
the silica-based particles can have an anionic charge density of at least 0.1
meq/g, usually
within the range of from 0.1 to 10.0 meq/g of dry polymer, suitably within the
range of
from 0.2 to 6.0 and preferably within the range of from 0.5 to 4Ø
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The silica-based particles, preferably anionic, to be mixed with the anionic
organic
polymer can have the previous mentioned properties. Suitably the silica-based
particles
are contained in a sol. The sol may have an S-value in the range of from 5 to
80%, suitably
from 5 to 50%, preferably from 8 to 45%, and most preferably from 10 to 30%.
Calculation
and measuring of the S-value can be performed as described by Iler & Dalton in
J. Phys.
Chem. 60(1956), 955-957. The S-value indicates the degree of aggregate or
microgel
formation and a lower S-value is indicative of a higher degree of aggregation.
Suitably, the silica-based particles comprise aggregated or microgel formed
silica
based particles, optionally and usually in combination with non-aggregated, or
monodispers,
silica-based particles.
Suitably the silica-based particles have a molar ratio Si20:Na20 less than 60,
usually within the range 5 to 60, and preferably ~n~ithin the range from 8 to
55.
The aqueous silica-containing composition obtained by any of the methods
according to the invention, contains suitably a total ~~eigh t of th~ anionic
organic p.~.lymer
having at least one aromatic group and anionic silica-based of at least 0.01 %
by weight,
calculated on the total weight of the aqueous silica-containing composition,
preferably at
least 0.05 % by weight, more preferably at least 0.1 % by weight. Suitably the
concentration of anionic organic polymer having at least one aromatic group
and anionic
silica-based particles is within the range of 1 to 45% by weight, preferably
within the
range of 2 to 35 % by weight, most preferably 5 to 30% by weight.
The products prepared by any of these methods shows improved drainage and
retention properties, and also a better storage stability and therefore a
better drainage and
retention aid performance when stored because it has a longer shelf life.
The mixing procedure of above mention methods is suitably carried out in the
presence of substantially no cellulose-reactive sizing agent. By substantially
no means
that less or equal to 10% by weight, suitably less than 5%, preferably less
than 1 % by
weight of cellulose-reactive sizing agent is present. Most preferably there is
no cellulose
reactive sizing agent present. The mixing procedure may also be carried out in
the
presence of substantially no sizing agent, or in the presence of no sizing
agent.
The present invention further relates to a process for the production of paper
from an aqueous suspension containing cellulosic fibres. The process comprises
adding
to the suspension a cationic organic polymer and the aqueous silica-containing
composition of the invention. The cationic organic polymer according to the
invention can
be linear, branched or cross-linked. Preferably the cationic polymer is water-
soluble or
water-dispersible.
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Examples of suitable cationic polymers include synthetic organic polymers,
e.g.
step-growth polymers and chain-growth polymers, and polymers derived from
natural
sources, e.g. polysaccharides.
Examples of suitable cationic synthetic organic polymers include vinyl
addition
5 polymers such as acrylate- and acrylamide-based polymers, as well as
cationic
poly(diallyl dimethyl ammonium chloride), cationic polyethylene imines,
cationic
polyamines, polyamidoamines and vinylamide-based polymers, melamine-
formaldehyde
and urea-formaldehyde resins.
Examples of suitable polysaccharides include starches, guar gums, cellulose
10 derivatives, chitins, chitosans, glycans, galactans, glucans, xanthan gums,
pectins,
mannans, dextrins, preferably starches and guar gums. Examples of suitable
starches
include potato, corn, wheat, tapioca, rice, waxy maize, barley, etc.
Cationic starches and cationic acrylamide-based polymers are preferred
,_._____ .~;-,.- +.. +~,.. ' +inr, .~nrl +hcv r'n ho wyerJ gingly~ together
with each
po~yU m ~ a~;V~r uu y w a is ii vci iuv, ~, a, ,u c, m.y.u~
other or together with other polymers, particularly preferred are cationic
starches and
cationic acrylamide-based polymers having at least one aromatic group.
The cationic organic polymers can have one or more hydrophobic groups
attached to them. The hydrophobic groups can be aromatic groups, groups
comprising
aromatic groups or non-aromatic groups, preferably the hydrophobic groups
comprise
aromatic groups. The hydrophobic group can be attached to a heteroatom, e.g.
nitrogen or
oxygen, the nitrogen optionally being charged, which heteroatom, it can be
attached to the
polymer backbone, for example via a chain of atoms. The hydrophobic group may
have at
least 2 and usually at least 3 carbon atoms, suitably from_3 to_12 and
preferably from 4 to
8 carbon atoms. The hydrophobic group is suitably a hydrocarbon chain.
Suitable dosages counted as dry substance based on dry pulp and optional
filler,
of the cationic polymer in the system is from 0.01 to 50 kg/t (kg/tonne,
"metric ton") of,
preferably from 0.1 to 30 kg/t and most preferably from 1 to 15 kg/t.
Suitable dosages counted as dry substances based on dry pulp and optional
filler, of the aqueous silica-containing composition defined above in the
system are from
0.01 to 15 kg/t, preferably from 0.01 to 10 kg/t calculated as an anionic
organic polymer
having at least one aromatic group and anionic silica-based particles, and
most
preferably from 0.05 to 5 kg/t.
Suitable mineral fillers of conventional types may be added to the aqueous
cellulosic suspension according to the invention. Examples of suitable fillers
include
kaolin, china clay, titanium dioxide, gypsum, talc and natural and synthetic
calcium
carbonates such as chalk, ground marble and precipitated calcium carbonate
(PCC).
Further additives that are conventional in papermaking can of course be used
in
combination with the chemicals according to the invention, for example anionic
trash
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11
catchers (ATC), wet strength agents, dry strength agents, optical brightening
agents,
dyes, aluminium compounds, etc. Examples of suitable aluminium compounds
include
alum, aluminates, aluminium chloride, aluminium nitrate, and polyaluminium
compounds,
such as polyaluminium chlorides, polyaluminium sulphates, polyaluminium
compounds
containing chloride and/or sulphate ions, polyaluminium silicate sulphates,
and mixtures
thereof. The polyaluminium compounds may also contain other anions than
chloride ions,
for example anions from sulfuric acid, phosphoric acid, or organic acids such
as citric acid
and oxalic acid. When employing an aluminium compound in the present process,
it is
usually preferably to add it to the stock prior to the polymer component and
micro- or
nano-particulate material. Suitable addition levels of aluminium containing
compounds is
at least 0.001 kg/t, preferably from 0.01 toy kglt and more preferably from
0.05 to 1 kg/t,
calculated as Ah03 based on dry pulp and optional filler.
Examples of suitable anionic trash catchers include cationic poiyamines,
polymers or copolymers of quaternary amines, or aluminum containing compounds.
The process of this invention is used for the production of paper . I s le ler
l l l
"paper", as used herein, include not only paper and the production thereof,
but also other
web-like products, such as for example board and paperboard, and the
production
thereof. The invention is particularly useful in the manufacture of paper
having
grammages below 150 g/m2, preferably below 100 g/m2, for example fine paper,
newspaper, light weight coated paper, super calendered paper and tissue.
The process can be used in the production of paper from all types of stocks,
both
wood containing and woodfree. The different types of suspensions of cellulose-
containing
fibres and the suspensions should suitably contain at least 25% by weight and
preferably
at least 50% of weight of such fibres, based on dry substance. The suspensions
comprise
fibres from chemical pulp such as sulphate, sulphite and organosolv pulps wood
containing or mechanical pulp such as thermomechanical pulp, chemo-
thermomechanical
pulp, refiner pulp and groundwood pulp, from both hardwood and softwood, and
can also
be based on recycled fibres, optionally from de-inked pulps, and mixtures
thereof.
Preferably the stock is a wood containing stock, which have high contents of
salts (high
conductivity).
The chemicals according to the present invention can be added to the
aqueous cellulosic suspension, or stock, in conventional manner and in any
order. It is
usually preferably to add the cationic polymer to the stock before adding the
aqueous
silica-containing composition, even if the opposite order of addition may be
used. It is
further preferred to add the cationic polymer before a shear stage, which can
be selected
from pumping, mixing, cleaning, etc., and to add the aqueous silica-containing
composition after that shear stage.
The aqueous silica-containing composition can be used as a flocculation agent
in
the treatment of water for the production of drinking water or as an
environmental treatment
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12
of waters for instance in lakes. The composition can also be used as
flocculation agent in
the treatment of wastewater or waste sludges.
The invention is further illustrated in the following examples, which are not
intended
to limit the scope thereof. Parts and % relate to parts by weight and % by
weight, respec
tively, and all solutions are aqueous, unless otherwise stated. The units are
metric.
Example 1
Drainage performance was evaluated by means of a Dynamic Drainage
Analyser (DDA), available from Akribi, Sweden. The drainage time was measured
on a
set volume of stock through a wire when removing a plug and applying vacuum to
that
side of the wire opposite to the side on which the stock is present.
Retention performance was evaluated by means of a nephelometer by
measuring the turbidity of the filtrate, the white water, obtained by draining
the stock. The
trurbidity was measure in NTU (Nephelometric Turbidity Units).
TI.~. t....t 1....1. .J 1..~.1.~.7.~~.. '+1., V 7 '7 +ho ~."nrlm.tiwi+v of fho
c~nr~
I I IC ICJI .7lUt,A V1%QJ vVVVU VVI IICtII 111 l~ w1u 1 a pl 1 l .c., me
vvmuvuvny m a w uwvm
was 5.0 mSlcm, and the consistency was 1.42 g/I. The stock was stirred in a
baffled jar at
a speed of 1500 rpm throughout the test.
In the example a cationic polymer was added to the stock before the aqueous
compositions according to the invention or the anionic reference. The cationic
polymer
was a cationic starch (C1) obtained by quarternisation of native potato starch
with 3-
chloro-2-hydroxypropyl dimethyl benzyl ammonium chloride to 0.5% N was added
followed by 45 seconds of stirring, and then the anionic aqueous composition
was added,
followed by 15 seconds stirring before drainage.
Aqueous compositions according _ to the invention containing . anionic
polyurethane and colloidal silica were measured to evaluate their drainage and
retention
performance. All samples were diluted to 0.5% of solids before the evaluation
of drainage
properties. The anionic polyurethane (P1) is based on an anionic polyurethane
of 15%
solids, produced from glyceryl monostearate (GMS) and toluolyl diisocyanate
(TDI), which
forms a pre-polymer, which is reacted with dimethylol propionic acid (DMPA),
with 30
mol% of GMS is replaced by DPMA l N-methyl diethanol amine (N-MDEA). The
colloidal
silica sol (S1) is of the type described in US 5,447,604 having a molar ratio
Si02:Na20 of
10, specific surface area of 870 m2/g, S-value of 35% and silica content of
10.0% by
weight. The drainage time measured on the stock with addition of 20 kg/t of C1
was 29
seconds and the turbidity was measured to 44 NTU. All additions are calculated
as dry on
dry stock. The drainage times derived from the different additions to the
stock of the
aqueous composition of the invention are summarised in Table 1.
Table 1
Sample I Ratio Drainage time (sec) I Turbidity (NTU) at dosage of
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13
4 k /t 6 k /t 8 k /t 10 k /t
S1 19.7/35 16.9/31 15.6/30 16.0/29
P 1 17.7 I 15.3 I 33 14.0 / 13.9 / 32
34 32
S1/P1 ~ 4:1 17.3/33 14.0/30 13.5/28 14.0/27
S 1 /P 1 1:1 16.4 l 13.6 / 30 13.0 / 13.1 / 28
34 28
S1/P1 1:4 16.5/33 13.9/31 13.3/29 12.9/29
raw rr~w _~_...,..4.....,
1L...J~ +Hr, +wn,
The drainage rimes aria mrom~y IUI LIIG lrVlll'.IVJIIIVIr v rrr r mrv~~ w.w.
........ .~.- ----
components (S1 and P1) are added as a composition they have a synergistic
improvement on the drainage and retention performance.
Example 2
The aqueous compositio~.s according to the invention containing anionic
polyurethane (P2) based on an anionic polyurethane of 19% solids, produced
from TDI
and phenyl dlethan0l amine PDEA, which f(7~i' 5 the pre-poiy~rier, w iiCii i~
reacted vvit h a
mixture of DMPA and N-MDEA and of which 30 mol% of PDEA is replaced by DPMA/N
MDEA, and a colloidal silica (S2) having a molar ratio Si02:Na20 of 20,
specific surface
area of 700 m2/g, S-value of 32% and silica content of 15.0%, were evaluated
for
drainage and retention performance. All the samples were diluted to 0.5%
solids before
the drainage and retention evaluation, which was performed exactly in the same
manner
as in Example 1 and with the same cationic starch in the same stock. The
drainage time
measured on the stock with addition of 20 kg/t of C1 was 27 seconds and the
turbidity
was measured to 45 NTU. All additions are calculated as dry on dry stock. The
drainage
times derived from the different additions to the stock of the aqueous
composition of the
invention are summarised in Table 2.
Table 2
Sample Ratio Draina a
time sec
/ Turbidit
NTU at
dosa a
of
2 k /t 4 k /t 6 k /t 8 k /t
S2 21.01- 15.7/- 12.4/- 12.9/-
P2 21.8/44 18.0/39 12.9/31 12.0/29
S2 I P2 4:1 21.0 / 40 15.5 / 12.0 /.28 10.4 I 27
31
S2/P2 1:1 - 13.8/30 11.0/27 9.8/27
S2/P2 1:4 - 13.3/32 11.0/29 10.3/27
Example 3
In this example the test stock was SC-furnish (furnish for Super Calandered
paper) with a pH 7.6, the conductivity of the stock was 0.5 mS/cm, and the
consistency
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14
was 1,49 g/l. The stock was stirred in a baffled jar at a speed of 1500 rpm
throughout the
test. C1 was added to the stock in an amount of 20kg/t (kgltonne) in each
test. The
drainage time measured on the stock without any additives was 30 seconds and
the
turbidity was 98 NTU, the drainage time on the stock with addition of C1 only
was 14.8
seconds and the turbidity was measured to 52 NTU. The anionic polyurethane
used in
this example was an anionic polyurethane (P3) of 15% solids, produced from GMS
and
TDI, which forms a pre-polymer, which is reacted DMPA and the colloidal silica
(S3)
described in US 5,368,833 was a silica sol having a molar ratio SiO2:Na20 of
45, specific
surface area of 850 m~/g, S-value of 20% and a silica content of 8.0%, and was
modified
with aluminium to 0.3% AI203.
The performance of the aqueous composition, according to the invention was
co~~~pared to the performance of the components added separately. In all tests
C1 was
added to the stock followed by 45 seconds of stirring, then the composition
S3/P3 was
added foiiowed by 15 seGOnQS Uf 5tlr r if lg. vvh ei ~ th a CW i iipoi ci iS
Yvcr c added ~u°par at°ly
the first component was added followed by 30 seconds of stirring and the
second
components was added followed by 15 seconds of stirring. All additions are
calculated as
dry on dry stock. The drainage times derived from the different additions to
the stock are
summarised in Table 3.
Sample Ratio Draina bidit NTU
a time at dos.
sec / age of
Tur
1 k /t 2 k /t 3 k /t 4 k /t
C1 +S3 - . - _ 10.2/56
C1+P3 13.9/54 13.0/55 12.0/56 13.0/55
C1+ S3 I P3 1:1 12.6 / 11.4/ 51 10.0 I 58 10.0 I
52 55
C1+S3/P3 3:1 12.2/52 11.1 /54 10.7/55 10.4/55
C1+S3/P3 1:3 12.9/52 12.1 /55 11.6/54 -
C1+S3+P3 1:1 - - - 12.4 /
53
C1+P3+S3 1:1 - - - 12.4 /
55
Example 4
The aqueous compositions according to the invention containing a 10% solution
of an anionic lignosulphonate (LS1), which is the sodium salt of sulphonated
and
carboxylated Kraft lignin derived from soft wood, having a dry matter of 89.0%
by weight,
pH of 10.5, a sodium content of 9.5%, and a total sulphur content of 5.4%,
wherein
sulphur is bound to 4.2%, or a 10% solution anionic lignosulphonate (LS2),
which is a
Table 3
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WO 03/056099 PCT/SE02/02444
sodium oxylignin derived from fermented spruce wood sulphite liquor, having a
dry matter
of 93.0% by weight, pH of 8.5, a sodium content of 8%, and sulphur content of
3%, and
colloidal silica S1., were evaluated for drainage and retention performance.
All the
samples were diluted to 0.5% solids before the drainage evaluation. The
drainage time
5 measured on the stock with addition of 20 kg/t of C1 was 29 seconds and the
turbidity
was measured to 44 NTU. All additions are calculated as dry on dry stock. The
drainage
times derived from the different additions to the stock of the aqueous
composition of the
invention are summarised in Table 4.
15
Table 4
Sample Ratio Drain a a sec bidit U at a of
time / Tur NT doss
2k /t 4k /t 6k /t 8k /t 10k 12k
/t It
S1 23.5/3819.7/3516.9/3115.6/3016.0/29-
- LS1 - 21.9/3518.8/34-17.5/3317.2/32- -
LS2 - 22.51- 19.9/3617.9/3517.8/3418.5/
-
S 1 / LS 1 4:1 - 18.5/ 15.3/2914.4/2614.5/25-
-
S 1 / LS 1 1:1 - 18.8/ 15.5/3013.1 12.8/31-
- /30
S 1 / LS2 4:1 - 18.4/ 15.1 13.2/2812.5/2712.4/25
- /31
S 1 / LS2 1:1 - 19.2/ 15.8/3313.8/2812. 12.1
- 8/25 /26
