Note: Descriptions are shown in the official language in which they were submitted.
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Process for manufacturing paper
The present invention refers to a process for manufacturing paper and board
comprising the addition of two different polymers to an aqueous cellulose-
containing
suspension one being an aromatic-containing cationic vinyl addition polymer
and the
other an anionic polymer having a weight average molecular weight in the range
of from
about 6,000 up to about 100,000 selected from the group consisting of vinyl
addition
polymers and condensation polymers.
Background
Internal sizing agents are usually added to the .wet end of the paper making
process whereby the adsorption capability of the paper of liquids is
decreased.
Commonly used internal sizing agents are sizing agents based on rosin
derivatives and
cellulose-reactive sizing agents, notably ketene. dimers and acid anhydrides.
Multipurpose office paper need to be rather heavily sized in order to function
properly in
today's high speed reproducing machines. ~'une way of at~ctinii ig paper vvh
ich is fully
sized, i.e. having a cobbso number below 30 or measuring the contact angle of
a water
droplet on the paper where angles larger the 80 degrees after 10 seconds
indicate good
sizing, is to add more sizing agent to the suspension. However, the likelihood
of ending
up with runability problems in the paper mill increases as well as the
production costs.
Apart from the addition of sizing agents to the pulp suspension, dewatering
and
retention agents are also added to the suspension. As the name indicates, the
latter
agents enhance both dewatering and retention of the pulp suspension. According
to the
present invention it has surprisingly been found that sizing efficiency is
improved by the
addition of at least two different types of polymers to the pulp suspension
which polymers
simultaneously function as dewatering and retention agents. Thus, by applying
the
present process both sizing, dewatering and retention are positively
influenced. The
effect is also observed on suspensions having high conductivities.
According to the present invention it has been found that specifically
improved .
sizing can be obtained by a process for manufacturing paper and board
comprising
providing a suspension comprising cellulose and at least a sizing agent,
dewatering said
suspension thereby forming °a paper-web, whereby an aromatic-containing
cationic vinyl
addition polymer, and an anionic polymer having a weight average molecular
weight in
the range of from about 6,000 up to about 100,000 selected from the group
consisting of
vinyl addition polymers and condensation polymers vinyl addition polymer are
added to
the suspension.
Detailed description of the invention
The present invention is not restricted to specific types of cellulose
suspensions,
but can be applied on cellulose suspensions confiaining virgin or recycled
pulp and
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different fillers such as calcium carbonate. The pH of the suspension may also
vary from
being acidic, which is the case if sizing agents derived from rosins are used,
to being
neutral or alkaline. If cellulose-reactive sizing agents are used the pH of
the cellulose
suspension is neutral to alkaline, i.e. in the range from about 5 up to about
10, which also
makes it possible to include inorganic filler materials in the suspension,
e.g. precipitated
calcium carbonate and clays. The two different polymers are suitable added to
a fairly
diluted lignocellulose-containing suspension commonly referred to as the thin
stock
having a concentration of from 0.1 up to 3.0 % by weight based on dry fibres.
The process is furthermore not dependent on the type of sizing agent added,
thus, any sizing agent or mixture of sizing agents may be present in the
cellulose
suspension. Preferably, the cellulose suspension contains cellulose-reactive
sizing .
agents, normally present in an amount of from 0.01 to 5 % by weight based on
dry fibres,
and has a pH value where the cellulose-reactive sizing agent still functions
properly, i.e. a
pH in the range from 5 up to 10. Suitable cellulose-reactive sizing agents ar
a ketel a
dimers, ketene multimers, acid anhydrides, organic isocyanates, carbamoyl
chlorides and
mixtures thereof, where ketene dimers and acid anhydrides are preferred.
According to the present process an aromatic-containing cationic vinyl
addition
polymer and an anionic vinyl addition polymer having a weight average
molecular weight
in the range of from about 6,000 up to about 100,000 is added to the cellulose
suspension. Usually, the cationic polymer is added to the suspension prior to
the addition
of the anionic polymer. Suitably, the addition of the cationic polymer is
followed by a
shear stage or stages, whereas the anionic polymer is added after any stage
providing
significant shear but before the formation of the paper web.
Aromatic-containing cationic vinyl addition polymer
. The aromatic-containing cationic vinyl addition polymer may be linear or
branched and contain monomers having anionic or potentially anionic groups as
long as
the overall charge of the polymer is cationic. However, the cationic polymer
is preferably
obtained by polymerising a reaction mixture essentially free from monomers
having
anionic groups or groups which can be rendered anionic in aqueous
compositions. The
cationic polymer can be a homo polymer or a copolymer containing cationic
aromatic
monomers, cationic non-aromatic monomers and non-ionic monomers, the latter
also
being non-aromatic. Suitably, the cationic vinyl addition polymer contains
cationic
aromatic monomers selected from the group consisting of acrylamide,
(meth)acrylamide,
acrylate and (meth)acrylate, whereby said cationic monomers preferably have at
least
one aromatic group covalently linked to a nitrogen atom either direct or via
hydrocarbon
groups which can have heteroatoms. Preferably, the aromatic-containing
cationic vinyl
addition polymer contains aromatic (meth)acrylamide and/or (meth)acrylate
monomers
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which are present in the polymer in an amount from about 2 molar % up to about
97
molar %. The aromatic-containing cationic vinyl addition polymer is suitably
obtained by
polymerising a cationic monomer or a reaction mixture containing a monomer
mixture
comprising a cationic monomer represented by the general formula (I):
CHZ = C - Ri R2 (I)
O=C-Aa-B~-N+-Q X
l
Rs
wherein R~ is H or CH3; R2 and R3 are independently from another a hydrogen or
an alkyl
group having from 1 to 3 carbon atoms, usually 1 to 2 carbon atoms; A~ is O or
NH; B~ is an
alkylene group having fr om 2 to 3 carbon atoms, suitably from 2 to 4 carbon
atoms, a
hydroxy propylene group or a hydroxy ethylene group; Q is a substituent
containing an
aromaiic group, suitably a pi5e~lyi UP :ii.ibstltuiGd p henyi gr uup, v~i'iivl
i ~'c~n b~ attached ~o ~he
nitrogen by means of an alkylene group usually having from 1 to 3 carbon
atoms, suitably 1
to 2 carbon atoms, and preferably Q is a benzyl group (- CHZ- C6H5); and X is
an anionic
counterion, usually a halide like chloride. Examples of suitable monomers
represented by
the general formula (1) include quaternary monomers obtained by treating
dialkylaminoalkyl
(meth)acrylates, e.g. dimethyiaminoethyl (meth)acrylate, diethylaminoethyl
(meth)acrylate
and dimethylaminohydroxypropyl (meth)acrylate, and dialky(aminoalkyl
(meth)acrylamides,
e.g. dimethylaminoethyl (meth)acrylamide, diethylaminoethyl (meth)acrylamide,
dimethylaminopropyl (meth)acrylamide, and diethylaminopropyl (meth)acrylamide,
with
benzyl chloride. Preferred cationic monomers of the general formula (I)
include dimethyl-
aminoethylacryiate benzyl chloride quaternary salt,
dimethylaminoethylmethacrylate benzyl
chloride quaternary salt and dimethylaminopropyl(meth)acrylamide benzyl
chloride
quaternary salt.
The cationic vinyl addition polymer can be a homopolymer prepared from a
cationic
monomer having an aromatic group or a copolymer prepared from a monomer
mixture
comprising a cationic monomer having an aromatic group and one or more
copolymerizable
monomers. Suitable copolymerizable non-ionic monomers include monomers
represented
by the general formula (II):
CH2 = C - R4 R5 (I I)
O=C-A2-B2-N
Rs
wherein R4 is H or CH3; R5 and Rs are each H or a hydrocarbon group, suitably
alkyl, having
from 1 to 6, suitably from 1 to 4 and usually from 1 to 2 carbon atoms; AZ is
O or NH; B2 is
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an alkylene group of from 2 to 8 carbon atoms, suitably from 2 to 4 carbon
atoms, or a
hydroxy propylene group or, alternatively, A and B are both nothing whereby
there is a
single bond between C and N (O=C - NR~R6). Examples of suitable
copolymerizable
monomers of this type include (meth)acrylamide; acrylamide-based monomers like
N-alkyl
(meth)acrylamides and N,N-dialkyl (meth)acrylamides, e.g. N-n-
propylacrylamide, N-
isopropyl (meth)acrylamide, N-n-butyl (meth)acrylamide, N-isobutyl
(meth)acrylamide and N-
t-butyl (meth)acrylamide; and dialkylaminoalkyl (meth)acrylamides, e.g.
dimethylaminoethyl
(i~neth)acrylamide, diethylaminoethyl (meth)acrylamide, dimethylaminopropyl
(meth)acryl-
amide and diethylaminopropyl (meth)acrylamide; acrylate-based monomers like
dialkyl-
aminoalkyl (meth)acrylates, e.g. dimethylaminoethyl (meth)acrylate,
diethylaminoethy(
(meth)acrylate, t-butylaminoethyl (meth)acrylate and
dimethylaminohydroxypropyl acrylate;
and vinylamides, e.g. N-vinylformamide and N-vinylacetamide. Preferred
copoiymerizable
non-ionic monomers include acrylamide and methacrylamide, i.e.
(meth)acrylamide, and the
main polymer is preferably an acrylamide-based polymer.
Suitable copolymerizable cationic monomers include the monomers represented by
the general formula (III):
CH2 = C - R~ R$ . (I II)
O=G-A3-B3-N+-Rio X
Rs
wherein R~ is H or CH3; R$ and R9 are preferably a hydrocarbon group, suitably
an alkyl
group having from 1 to 3 carbon atoms; Rio can be a hydrogen or preferably a
hydrocarbon
group, suitably an alkyl group having from 1 to S carbon atoms, usually 1 to 2
carbon atoms;
A3 is O or NH; B3 is an alkylene group of from 2 to 4 carbon atoms, suitably
from 2 to 4
carbon atoms, or a hydroxy propylene group, and X is an anionic counterion,
usually
methylsulphate or a halide like chloride. Examples of suitable cationic
copolymerizable
monomers include acid addition salts and quaternary ammonium salts of the
dialkyi-
aminoalkyl (meth)acrylates and dialkylaminoalkyl (meth)acrylamides mentioned
above,
usually prepared using acids like HCI, H~S04, etc., or quaternizing agents
like methyl
chloride, dimethyl sulphate, etc.; and diallyldimethylammonium chloride.
Preferred
copolymerizable cationic monomers include dimethylaminoethyl (meth)acrylate
methyl
chloride quaternary salt, diallyldimethylammonium chloride and and
dimethylaminopropyl(meth)acrylamide benzyl chloride quartenary salt.
Copolymerizable
anionic monomers Like acrylic acid, methacryiic. acid, itaconic acid, various
sulfonated vinyl
addition monomers, etc. can also be employed and, preferably, in minor
amounts.
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The cationic vinyl addition polymer can be prepared from a monomer mixture
generally comprising from 1 to 99 mole%, suitably from 2 to 50 mole% and
preferably from 5
to 20 mole% of cationic monomer having an aromatic group, preferably
represented by the
general formula (I), and from 99 to 1 mole°fo, suitably from 98 to 50
mole%, and preferably
5 from 95 to 65 mole% of other copolymerizable monomers which preferably
comprises
acrylamide or methacrylamide ((meth)acrylamide), the monomer mixture suitably
comprising
from 98 to 50 mole% and preferably from 95 to 80 mole% of (meth)acrylamide,
the rest up to
100% preferably of compounds according to formula I and II.
Alternatively the cationic polymer can be a polymer subjected to aromatic
modification using an agent containing an aromatic group. Suitable modifying
agents of this
type include benzy! chloride, benzyl bromide, N-(3-chloro-2-hydroxypropyl)-N-
benzyl-N,N
dimethyiammonium chloride, and N-(3-chioro-2-hydroxypropyi) pyridinium
chloride. Suitable
polymers for such an aromatic modification include vinyl addition polymers. If
the polymer
contains a tertiary nitrogen which can be quaternized by the modifying agent,
the use of
such agents usually results in that the polymer is rendered cationic.
Alternatively, the
polymer to be subjected to aromatic modification can be cationic, for example
a cationic vinyl
addition polymer.
Usually the charge density of the cationic polymer is within the range of from
0.1
to 6.0 meqv/g of dry polymer, suitably from 0.2 to 4.0 and preferably from 0.5
to 3Ø The
weight average molecular weight of the cationic polymer is usually at least
about
500,000, suitably above about 1,000,000 and preferably above about 2,000,000.
The
upper limit is not critical; it can be about 30,000,000, usually 20,000,000
and suitably
10, 000, 000.
The cationic vinyl addition polymer can be added into the suspension in
amounts
which can vary within wide limits depending on, inter alia, type of
suspension, salt content,
type of salts, filler content, type of filler, point of addition, etc.
Generally the cationic vinyl
addition polymer is added in an amount that give better sizing, dewatering and
retention
than is obtained when not adding it provided the anionic vinyl addition
polymer is added.
The cationic polymer is usually added in an amount of at least 0.002%, often
at least
0.005% by weight, based on dry pulp, whereas the upper limit is usually 1.0%
and suitably
0.5% by weight.
Anionic vinyl additionpolymer
Further to the above described aromatic-containing cationic vinyl addition
polymer, an anionic polymer having a weight average molecular weight in the
range of
from about 6,000 up to about 100,000 selected from the group consisting of
vinyl addition
polymers and condensation polymers is added to the cellulose suspension. The
anionic
polymer can be linear, branched or cross-linked, yet suitably essentially
linear, and usually
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water-soluble or water-dispersable. The anionic polymer may furthermore be a
homopolymer or a copolymer containing at least two different types of
monomers.
Preferably, the anionic polymer is a vinyl addition polymer having a weight
average
molecular weight in the range of from about 6,000 up to about 100,000.
Suitable anionic
vinyl addition polymers are polymers obtained from a reaction mixture
comprising vinylic
unsaturated monomers, preferably vinylic unsaturated aromatic containing
monomers,
having one or more anionic groups or groups rendered anionic in aqueous
solutions,
suitably at least one sulphonate group. Examples of anionic groups attached to
vinylic
unsaturated monomers are phosphate groups, phosphonate groups, sulphate
groups,
sulphonic acid groups, sulphonate groups, carboxylic acid groups, carboxylate
groups
such as acrylic acid, methacrylic acid, ethyl acrylic acid, crotonic acid,
itaconic acid,
malefic acid or salts thereof, aikoxide groups, malefic acid groups and
phenolic groups, i.e.
hydroxy-substituted phenyls and naphthyls. Groups carrying an anionic charge
are usually
salts of an alkali metal, alkaline earth or ammonia. -I he anionic vinyl
addition polymer i=r~ay
also in some extent contain cationic groups such as monomers having cationic
groups,
though, preferable the only ionic groups present in the vinyl addition polymer
are anionic.
Preferably, the anionic groups are linked to aromatic vinylic (ethylenically)
unsaturated
monomers such as styrene, i.e. styrene sulphonate. If the anionic vinyl
addition polymer is a
copolymer, said polymer can be obtained from a reaction mixture comprising non-
ionic
vinylic unsaturated monomers, e.g. acrylamide, (meth)acrylamide. The anionic
vinyl addition
polymer may comprise from about 20 mole % up to about 100 mole % of anionic
monomers
containing at least one anionic charge.
Suitable anionic condensation polymers having a weight average molecular
weight in the range of from about 6,000 up to about 100,000 are 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
polymerization such as urea and melamine. Examples of suitable aromatic
compounds
containing anionic groups comprises benzene and naphthalene-based compounds
containing anionic groups such as phenolic and naphtholic compounds, e.g.
phenol,
naphthol, resorcinol and derivatives thereof, aromatic acids and salts
thereof, e.g.
phenylic, phenolic, naphthylic and naphtholic acids and salts, usually
sulphonic acids and
sulphonates, e.g. benzene sulphonic acid and sulphonate, xylen sulphonic acid
and
sulphonates, naphthalene sulphonic acid and sulphonate, phenol sulphonic acid
and
sulphonate. Examples of suitable anionic condensation polymers include anionic
benzene-
based and naphthalene-based condensation polymers, preferably naphthalene-
sulphonic
acid based and naphthalene-sulphonate based condensation polymers.
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The weight average molecular weight of the anionic vinyl addition polymer and
the condensation polymer is in the range of from about 6,000 up to about
100,000. The
lower limit is suitably from about 7,000, preferably from about 8,000,
preferably from
about 15,000, preferably from about 25,000, whereas he upper limit is suitably
up to
about 80,000, preferably up to about 75,000, preferably up to 45,000,
preferably up to
about 40,000. Any combination of lower and higher limit can be a preferred
range. If the
anionic polymer is a vinyl addition polymer, the preferred ranges of the
weight average
molecular weight is from about 10,000 up to about 100,000, more preferably
from about'
15,000 up to about 75,000, most preferably from about 25,000 up to about
45,000.
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
1.0, 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
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 density of the anionic
polymer is within
the range of from 0.1 to 6.0 meqv/g of dry polymer, suitably from 0.5 to 5.0
and preferably
from 1.0 to 5Ø
The anionic polymer can be added to the suspension in amounts which can vary
within wide limits depending on, inter alia, type of stock, salt content, type
of salts, filler
content, type of filler, point of addition, etc. Generally the anionic polymer
is added in an
amount that give better sizing, dewatering and retention than is obtained when
not adding
the anionic polymer provided the cationic vinyl addition polymer is added. The
anionic
polymer is usually added in an amount of at least 0.001%, often at least
0.005% by weight,
. based on dry pulp, whereas the upper limit is usually 3.0% and suitably 1.0%
by weight.
According to one preferred embodiment of the present invention the aromatic-
containing cationic vinyl addition polymer can be provided as an aqueous
composition,
suitably aqueous solution, preferably comprising further cationic polymers,
for example
synthetic cationic polymers and naturally occurring polymers. Suitable
synthetic cationic
polymers cationic are vinyl addition polymers such as acrylamide based
polymers or
acrylate based polymers. Other synthetic cationic polymers include cationic
condensation
polymers like epihalohydrin polymers, e.g. polymers formed by reacting
aliphatic amines
and epichlorohydrine, polyamideamine polymers, polyethyleneimine polymers.
Preferred
naturally occurring cationic polymers as cationic polysaccharides,
particularly cationic
starch and aromatic substituted cationic starch. The aqueous solution
preferably contains
the aromatic-containing cationic vinyl addition polymer in a predominant
amount, i.e. ~at
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least 50 % by weight, even though effects are present at considerably lesser
amounts,
down to amount at least 10 % by weight. The further cationic polymers
referred. to in this
paragraph may also be added separately.
According to yet another preferred embodiment of the present invention
inorganic anionic microparticulate materials like anionic silica-based
particles, polysilicic
acid and clays of the smectite type are added to the suspension. The inorganic
anionic
microparticulate material can be added separately to the suspension or is
preferably
comprised in an aqueous composition also comprising the anionic polymer.
Furthermore, the process can also be useful in the manufacture of paper and
board
from cellulosic suspensions having high conductivity. In such cases, the
conductivity of the
suspension that is dewatered on the wire is usually at least 1.0 mS/cm,
suitably at least 2.0
mS/cm, and preferably at least 3.5 mSlcm. Conductivity can be measured by
standar d
equipment such as, for example, a vV'IW ~.F 539 instrument supplied by
Christian earner.
The values referred to above are suitably determined by measuring the
conductivity of
the cellulosic suspension that is fed into or present in the head box 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) which can be
derived from the materials used to form the stock, from various additives
introduced into the
stock, from the fresh water supplied to the process, 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 based
on dry fibres, respectively, unless otherwise stated. All compound added to
the furnish are
calculated as dry material, if not otherwise indicated. In the examples, a
good retention is
shown by a low turbidity value in the white water, i.e. more fines and filler
are retained in the
formed sheet. A turbidity value under 120 is acceptable and a value under 90
is in this set of
experiment excellent. The dewatering figure should also be low. The sizing of
the paper
was measured by the contact angle of a water droplet on the paper. Contact
angles
larger the 80 degrees after 10 seconds are indicating a good sizing.
Example 1
The pulp (at 3%) used was a 80120 mixture of hardwood/softwood kraft. Ground
calcium carbonate filler (GCC) was added to the pulp, to a filler
concentration of 40% on dry
solids. The resulting furnish was diluted to 0.3% before additional chemicals
were added.
The chemical additions are expressed as % on dry solids in the furnish.
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In this example two furnishes were used one having a low conductivity of 500
p,S/cm (furnish I), the other having a high conductivity of 4.0 p,S/cm
(furnish II). The
conductivity was adjusted by addition of sodium sulphate. A dispersion
containing a
conventional ketene dimer sizing agent and 1 % cationic starch were added to
fihe furnishes.
Subsepuent to these additions, either 0.1% of an aromatic cationic
polyacrylamide having
benzyldimethyiammonium groups (A-PAM) or 0.1 % of a conventional non-aromatic
cationic
polyacrylamide (C-PAM) was added prior to the addition of either 0.1 % of a
silica sol or
0.1 % of an anionic polystyrene sulphonate having a weight average molecular
weight of
70,000 (PSS). The added amounts of compounds are indicated in table I and II.
The
retention and dewatering properties of the formed furnishes were evaluated by
measuring
the dewatering time using a Dynamic Drainage Analyser (DDA-unit). A lower
value in this
test means better dewatering efficiency. The retention was evaluated by
measuring the
turbidity of the white water with a Nephelometer 156 from f~9ovasine. A lower
turbidity value
signifies higher retention of solids in the DDA-unit. Moreover, the sizing of
the formed, dried
and cured paper was evaluated by measuring the contact angle of water after 10
seconds
utilising a Dynamic Absoption and contact angle tester from Fibro Systems
(DAT). A
higher value of the contact angle means better sizing efficiency.
Table I, Furnish II (high conductivity)
test Amount of Type Type of TurbidityDewateringContact
added keteneof anionic /[sec.J angle
dimer/[kg/t cationiccompound , (10
dry polyacryla sec./[degre
pulp] mide es]
blank*0.2 none none 390 7.8 below
10
1 0.2 C-PAM silica 91 6.92 29.6
sol
2 0.2 A-PAM PSS 47 4.54 44.6
3 0.3 C-PAM silica 90 6.64 80.8
sol
4 0.3 A-PAM PSS 43 4.47 84.6
5 0.4 C-PAM silica 90 6.77 89.9
sol
6 0.4 A-PAM PSS 47 4.47 94.4
As shown by table I, the addition of an aromatic-moditied cationic vinyl
aaaition polymer
and an anionic vinyl addition polymer significantly increases not only
dewatering and
retention but also the sizing efficiency.
* No addition of neither cationic polyacrylamide nor anionic compound,
otherwise
conditions were the same as for tests 1 and 2.
Table II, Furnish I (low conductivity)
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1 f1
test Amount Type of Type of TurbidityDewateringContact
.of
added cationic anionic /[sec.] angle
(10
ketene polyacrylacompound sec./[degre
dimer/(kgltmide es]
dry pulp]
blank* 0.3 none none . 420 5.6 35
1 0,3 C-PAM silica-sol100 4.8 83.3
2 0.3 A-PAM PSS 76 3.5 87.8
._ J .. ..7 ..tln....-..~in.~f
..
* In this test neither cationic poiyacryam~ae ~m ammm ~~~~~N~u~~u ~~G~ u~~..,
~~.........._
conditions were the same as for tests 1 and 2.
Example 2
The furnish used was the same as used in example 1, however, in this example
the furnish was adjusted to a conductivity of 400 p.S/cm
The sizing dispersion as used in example 1 was added to the furnish followed
by the
addition of cationic starch. The dosage for the size was 0.03% (calculated as
active ketene
dimer on dry furnish) and for the cationic starch 1.0%. Subsequent to these
additions, 0.1
of an aromatic cationic polyacrylamide having benzyldimethylammonium groups
was added
prior to the addition of 0.07% of an anionic polystyrene sulphonate having
different weight
average molecular weights as indicated in table III and an anionic naphthalene
sulphonate,
respectively. The added amounts of compounds are indicated in table III. The
retention and
dewatering properties of the formed furnishes were evaluated by measuring the
dewatering
time using a DDA-unit. The retention was evaluated by measuring the turbidity
of the white
water with a Nephelometer 156 from Novasine. Moreover, the sizing of the
formed, dried
and cured paper was evaluated by measuring the contact angle of water after 10
seconds
utilising a DAT equipment.
25
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Table Ill
test Weight averageTurbidity Dewatering/[sec.]Contact angle
molecular (10
weight of sec./(degrees]
the
anionic polymer
blank* none 125 5.4 below 30
1 8,000 78 5.05 91
2 20, 000 75 4.95 94
3 35,000' 56 4.89 ~ 92.7
q. 75,000 50 4.03 88
100,000 47 3.82 85
780,000 30 3.17 69.2
1:polystyrene sulpnonate, ~:napninaiene suipnona~e
Tests 1 to 5 are according to the present invention, i.e. the anionic polymer
having a
5 weight average molecular weight in the range of from about 6,000 up to about
100,000.
As can be seen in table lll, the sizing efficiency is significantly increased
while at the
same time the turbidity and dewatering performance are high with regard to
tests 1 to 5
compared to the blank. In addition, comparing test 6 with tests 1 to 5 (the
latter five
according to the invention), the sizing efficiency is much higher, while
simultaneously the
turbidity value still indicates good retention. What is more, a contacting
angle of 69.2 as
obtained in test 6 is not an acceptable sizing degree. Thus, the overall
performance of
tests 1 to 5 in respect of retention, dewatering and not least sizing clearly
outperform test
6.
* No addition of neither cationic polyacrylamide nor anionic compound,
otherwise
conditions were the same as for tests 1 to 6.
