Note: Descriptions are shown in the official language in which they were submitted.
a
2~~"~~~-i~ 0.~. 0050/41956
Engine sizing of caper, board and cardboard
The present invention relates to a process for
the engine sizing of paper, board and cardboard using
d a cationic polymer which contains polymer-
i
ze an
resin s
ized vinylamine units as a fixing agent.
;., U.S. Patent 4,421,602 discloses partially hydro-
"'
lyzed homopolymers of N-vinylformamide which contain N-
vinylformamide and vinylamine units. They are used as .
retention and drainage aids and flocculants in paper-
making.
EP-A-0 216 387 discloses that copolymers of from
95 to 10 mol % of N-vinylformamide and from 5 to 90 mol %
of an ethylenically unsaturated monomer from the group
consisting of vinyl acetate, vinyl propionate, the C1-C4-
alkyl vinyl ethers, N-vinylpyrrolidone, the esters,
nitriles and amides of acrylic acid and methacrylic acid
in partially or completely hydrolyzed form, in which up
100 mol % of the formyl groups have been eliminated
to
from the copolymer, are added in amounts of from 0.1 to
. 20 5% by weight, based on dry fibers, to the paper stock
prior to sheet formation, as wet strength and dry
strength agents for paper.
> German Laid-Open Application DOS 3,203,189
.;..i
. discloses sizes based on hydrophobic, cellulose-reactive
sizing materials and fixing and sizing accelerators
consisting of polymers which contain primary, secondary
or tertiary amino groups and/or quaternary ammonium
groups bonded directly or via side chains. These cationic
polymers include hydrolyzed polymers of N-vinylformamide
and partially hydrolyzed copolymers of N-vinylacetamide
and vinyl acetate. According to the German Laid-Open
Application, hydrophobic, cellulose-reactive sizing
~~~ materials are preferably alkylketene dimers, anhydrides,.
such as rosin anhydride, and isocyanates.
The most well known engine size based on natural
products is resin size. This is a compound which is not
reactive toward cellulose fibers and is precipitated onto
CA 02085348 2002-~04-29 I
- 2 -
the- cellulose fibers in the paper stock with the addition
of fixing agents. Examples of suitable fixing agents are
aluminum sulfate or, according to German Published
Application DAS 1,070,916 and European Patent 0,187,666,
cationic dicyanodiamide resins. While the efficiency of
the cationic dicyanodiamide resins is unsatisfactory,
aluminum sulfate and alum have the disadvantage that
calcium carbonate cannot be used as a filler in their
presence and the papers obtainable in this manner are not
sufficiently resistant to aging owing to the fact that
the process is carried out at acidic pH.
The present invention
provides a process for the engine sizing of paper, board
and cardboard with resin size, in which sizing can be
carried out at neutral pH and in which papers resistant
to aging are obtained.
According to the invention, there is provided
a process for the engine
sizing of paper, board and cardboard using resin size and
a fixing agent for fixing the resin size to the cellulose
fibers, if the fixing agent used is a cationic polymer
which contains polymerized vinylamine units.
In the present context, resin sizes are the
products conventionally used for the engine sizing of
paper and based on natural substances, for example resin
sizes consisting of hydrogenated rosin, tallow resin
sizes, reinforced resin sizes, dry resin sizes or emul-
sions rich in free resin. These products are nonreactive
resin sizes which result in virtually no sizing of paper
when used alone for engine sizing but always have to be
used together with a fixing agent. Suitable resin sizes
are described in, for example, Papier 43 (5), (1989),
188-192. As in known processes for the engine sizing of
paper, in the present process too resin size is used in
an amount of from about 1 to 4, preferably from 1.5 to 3,
~ by weight, based on dry paper stock.
According to the invention, the engine sizing of
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paper is carried out in the presence of small amounts of
aluminum sulfate and/or alum, using a cationic polymer
which contains polymerized vinylamine units. Aluminum
sulfate and alum are used in amounts of < 5, preferably
from 2 to 3, ~ by weight, as a precipitating agent for
resin size. The cationic polymers surprisingly act as
fixing agents for nonreactive resin size. Polymers of
this type are disclosed, for example, in U.S. Patent
4,421,602 and EP-A-0 216 387, which were mentioned in
connection with the prior art. They are prepared by
hydrolyzing homo- and copolymers containing polymerized
N-vinylamides.
Such polymers contain the following typical
structures:
_CH 2_ I H_
N 0
R/ \C\ ( Z )
R1
where R and R1 are each H or C1-C6-alkyl.
For the preparation of compounds which contain
' exclusively structural units of the formula I, for
example, N-vinylformamide, N-vinylacetamide, N-vinyl-N
methylformamide, N-vinylpropionamide or N-vinylbutyramide
is polymerized. The structure
-CH 2-CH--
N (ZZ)
/\
R H
where R is H or C1-Cfi-alkyl is formed from the compounds
containing structural elements of the formula Z by
hydrolysis using an acid, eg. hydrochloric acid, sulfuric
. acid or phosphoric acid, or in the presence of a base,
such as sodiumhydroxide solution or potassium hydroxide
solution, with elimination of the group -CO-R1.
Zn the case of 100% hydrolysis of all units of
the structure Z in the polymer, polyvinylamines are
-. - 4 - O.Z. 0050/41956
obtained. If only partial hydrolysis is carried out, the
polymers prepared from the N-vinylamides contain units of
the structures I and II. The compound of the formula
CHO
/ (III)
CH = CH-H\
H
ie. N-vinylformamide, is preferably used as the N-vinyl-
amide. Partially hydrolyzed homopolymers of the compound
III are disclosed in the abovementioned U.S. Patent
4,421,602. The degree of hydrolysis may be from 0.1 to
100%. The preferred polymers captaining polymerized
vinylamine units include compounds which are obtainable
by copolymerization of
(a) from 1 to 99, preferably from 10 to 90, mol % of N-
vinylformamide and
(b) from 99 to 1 mol % of monoethylenically unsaturated
monomers from the group consisting of vinyl acetate,
vinyl propionate, the C1-C,-alkyl vinyl ethers, N
vinylpyrrolidone, the esters, nitriles, amides, N
alkylamides and sulfo-carrying N-alkylamides of
acrylic acid and methacrylic acid and mixtures of
these monomers
and subsequent hydrolysis of the amide groups of the
structural units I of the polymers to form amino groups
of the structure II. The degree of hydrolysis of the
polymerized N-vinylformamide units is from Ø1 to 100%,
preferably not less than 10%.
Such copolymers are described in EP-A-0 216 387.
In addition to N-vinylformamide, for example, N-vinyl-N-
methylformamide, N-vinylacetamide, N-vinyl-N-methylacet-
amide, N-vinylpropionamide or N-vinylbutyramide can be
used as a monomer of component (a). In the hydrolysis of
copolymers of N-vinylformamide and vinyl acetate or vinyl
propionate, it is also possible, depending on the reac-
tion conditions, to hydrolyze the polymerized monomer
units (b), so that, in the case of the last-mentioned
2n~~~;~9 ~
.,.
- 5 - O.Z. 0050/41956
comonomers, the copolymers then additionally contain, for
example, polymerized vinyl alcohol units. The degree of
hydrolysis of the acetyl and/or propionyl groups in the
polymerized units (b) of the copolymers may be from 0.1
to I00~.
The homo- and copolymers containing polymerized
vinylamine units have K values of from 5 to 300, prefer-
ably from 15 to 150. Polyvinylamines and hydrolyzed
copolymers of N-vinylformamide having K values of from 20
to 115 are particularly preferred.
The cationic polymers containing polymerized
vinylamine units are water-soluble. For engine sizing,
they are added directly to the paper stock or can be
added to the paper stock in the form of a mixture with
the resin size. In the case of separate metering of the
polymer and resin size, it is unimportant whether the
resin size or the cationic polymer is added first to the
paper stock because adequate mixing of the components
always takes place in the paper stock. From 1 to 100,
preferably from 5 to 30, parts by weight of one or more
cationic polymers which contain polymerized vinylamine
units are used per 100 parts by weight of resin size.
Suitable fibers for the preparation of the pulps
are all conventional qualities, for example mechanical
pulp, bleached and unbleached chemical pulp and paper
stocks obtained from all annual plants. Mechanical pulp
includes, for example, groundwood, thermomechanical pulp
(TMP), chemothermomechanical pulp (CTMP), pressure-ground.
pulp, semi-chemical pulp, high-yield chemical pulp and
refiner mechanical pulp (RMP). Examples of suitable
chemical pulps are sulfate, sulfite and soda pulps. The
unbleached chemical pulps, which are also referred to as
unbleached kraft pulps, are preferably used. Suitable
annual plants for the preparation of paper stocks are,
for example, rice, wheat, sugar cane and kenaf. Waste
paper, either alone or as a mixture with other fibers, is
also used for the preparation of the pulps. For the
--~ - 6 - 0. Z . 0050/41956
production of paper, board and cardboard, the pulps'
are
mixed with resin size and, as fixing agents, one
or more
polymers to be used according to the invention,
and are
drained on a wire.of a paper machine in a known
manner.
The consistency of the pulps is from 0.1 to 1.5%
by
weight and their pH is not snore than 8, preferably
from
6 to 7.5.
In the Examples which follow, parts and per-
centages are by weight. The K values were determined
according to H. Fikentscher, Cellulose-Chemie 18
(1932),
48-64 and 71-74, in 5% strength aqueous sodium chloride
solution at 25C and at a polymer concentration of
1% by
Weight. The .quality'of sizing was determined with
the
aid of the Cobb value according to DIN 53,132 and
the ink
flotation test (50% strike-through). To characterize
the
sizing, the preparation take-up was also determined.
For
this purpose, a paper strip ( 80 cm x 10 cm) was
drawn
through a laboratory size press to constant contact
pressure and a speed of 10 m/min. The test liquid
used
was tap water. The preparation take-up was calculated
;a from the weight increase as follows:
(Weight after size press -
Weight before size press ) x 100
Preparation take-up = -
Weight of absolutely dry sample
The following starting materials were used:
Size 1
50% strength low-viscosity resin soap prepared
from chemically reinforced natural~resins having a total
resin acid number of 170, a free resin content of about
2% and a Brookfield viscosity of 1,000 mPa.s at 20°C and
20 rpm.
Fixing agent 1
lI% strength aqueous solution of a copolymer
which contained 98% of vinylaanine units and 2% of N
vinylformamide units and had a K value of 87. The pH of
the aqueous solution was 3.5.
2~t~~'~~,~~8
O.Z. 0050/41956
Fixing agent 2
12% strength aqueous solution (pH 3.5) of a
copolymer which contained 68% of vinylamine units, 2% of
N-vinylformamide units, 25% of vinyl alcohol units and 5%
of vinyl acetate units and had a K value of 105.
Fixing agent 3
17% strength aqueous solution of a copolymer
which contained 4S% of vinylamine units and 55% of N-
vinylformamide units and had a K value,of 87. The pH of
the aqueous solution was 3.5.
EXAMPLES
A paper stock was prepared from 100% bleached
birch sulfate pulg with the addition of 40% of chalk.
The freeness was 35°SR (Schopper-Riegler) . 1.5% by weight
of the size, 3% by weight of alum and then 0.1% by weight
of one of the fixing agents stated in Tables 1 and 2 were
added to the paper stock, the percentages being based on
the solids content. The pH of the stock ;remained un-
changed at 7. In all Examples, 0.3% of a commercial
weakly cationic polyacrylamide having a K value of 130
was also added as a retention aid to the paper stock,
after which sheets having a basis weight of 100 g/m2 were
formed on a Rapid-Kathen sheet former. The sheets were
each dried on a steam-heated drying cylinder at 90°C to a
residual moisture content of from 6 to 10%.
In all Examples, the preparation take-up, the
Cobb value and the ink flotation time were determined
immediately after drying. These results are summarized
in Table 1. The sheets were then stored for one day at
23°C and' at a relative humidity of 50%. The preparation
take-up, the Cobb value and the ink flotation time were
then determined. The results obtained are shown in Table
2.
COMPARATIVE EXAMPLE
Example 1 was repeated, with the sole exception
that, instead of 0.1% by weight of fixing agent 1, only
3% by weight of alum were used as a fixing agent and
2~?~~~~'.8
- 8 - O.Z. 0050/41956
precipitating agent. The pH of the pulp was 7. ~ The
results obtained are shown in Tables 1 and 2.
TABLE 1
Immediate sizing
S Example Fixing Preparation Cobb value Ink flotation
agent take-up ($) 60 " time (min}
1 1 21.1 31 >60
2 2 22.S 51 30
3 3 21.2 41 >60
Comparative
Example
,1 ~ alum 30.3 46 5
TABLE 2
Sizing afteraging
Example Fixing Preparation Cobb valueInk flotation
agent take-up (~) , 60 " time (min)
1 1 18.5 46 >60
2 2 21.5 49 >30
3 3 17.9 41 >60
Comparative
Example
1 1 31.2 64 1
r
