Note: Descriptions are shown in the official language in which they were submitted.
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COMPOSITI~ON ~MD PROCESS FOR
NEUTRAL SIZING
The present invention relates to a sizing
composition for paper, cardboard ancl other cellulose-containing
materials in the neutral range as well as to a one-step
process of sizing pulp with this composition.
Aluminum sulfate is known to be an important
additive for sizing which has been used for a long time in
the paper industry. Aluminum sulfate causes the precipitation
and fixation of the sizing component, for example rosin, on
the cellulose fiber. Due to hydrolytic splitting the
resulting pH-value is between about 4.2 and 4.8, rlepending
on the aluminum sulfate concentration, and thus clearly in
the acidic range. This can lead to corrosion of screens and
machine parts. In addition, the paper so produced exhibits
litt]e resistance to aging and reduced mechanical strength.
The acidic pH-range is particularly disadvantageous in the
production of paper which contains calcium carbonate in the
coating or in the pulp, for example due to input of used
paper stock. The reason for this is that the composition
of the calcium carbonate starts, though to a small extent,
already close to the neutral point ~pH 6.5). Carbon
dioxide generation as well as the calcium ions in solution can
lead to considerable disturbances in the paper production and
can impair paper sizing.
For this reason numerous atkempts ha~e been made to
eliminate the disadvantages and difficulties encountered in
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the sizing of paper when aluminum sulfate is used as flocculation
and fixation agent. Attempts to raise the PH such as by
reducing the amount of aluminum sulfate and to substltute
the thus "saved" aluminum sulfate with a cationic retention
agent did not have the expected success. The pH-value of the
fiber suspension could only be raised to about 5, since a
minimum amount of aluminum sulfat:e is essential for achieving
good sizing.
It is known that according to U.S. Patent 3,540,980
aluminum sulfate can be substituted wholly or partially with
water-soluble aluminate. To this effect the aqueous fiber
suspension which is to be sized is first mixed with sufficient
aluminate solution to reach a pH-value of at least about 9.
Following this the pH is lowered to a value no~ lower than 4.5
with an inorganic acid or an acidic salt, for
example sulfuric acid or aluminum sulfate. After addition
of the resin siziny the aluminum hydroxide formed during
neutrali~ation causes the precipitation of aluminum resinate
and the aluminum ions fix the resinate on the fiber. Under
these conditions the partial or complete substitution of the
aluminum sulfate with sodium aluminate leads to the desired
increase in the pH-value without any observed impairment of
the sizing. Accordingly, aluminum sulfate is no longer
required for precipitation of resin sizing and its fixation
on the cellulose fibers. Aluminum sulfate can be replaced
by sodium aluminate and subsequent adjustment of the pH-value.
The disadvantagç of the above process is the fact
that it is a tw~-step process and both steps have to take place
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in highly diluted suspensions. Secondary reactions and
disturbances in operation are unavoidable when the process
parameters are varied.
It is the objeet of the present invention to seek
to overcome these and other disaclvantages of the known methods
by providing a eomposition and a process for neutral sizing
of paper, eardboard and other cellulose-containing materials.
The present invention is based on the discovery
that the known sizing processes can be improved and, in
partieular, ean be performed more eost effeetively, if the
sizing is earried out with a eomposition whieh contains the
aluminate as well as the resin sizing and in such a way that
precipitation of the resin sizing is avoided. The precipitation
should only take place after mixing of the sizing and the
cationic retention agent with the fiber suspension.
According to one aspect of the invention there is
provided a sizing composition for neutral sizing of paper,
cardboard and other cellulose-containing materials which
comprises water, an organic solvent which is infinitely
miscible with water, a haSic reacting compound, an alkali aluminate
and a sizing component. As organie solvent water-~olllh]e alcohols
sueh as methan~l, ethanol and isopropanol are suitable, but
water soluble ketones sueh as aeetone and the like may also
be used. The weight ratio of organic solvent to sizing c~n~nt may
fall between lO:l and 0.5:l, preferably however between 5:l
and 0.5:l. The amount o organie solvent is dependent on the
solubility and quantiky o~ the organic sizing component which,
aceording to the invention, must be eompletely dissolved in
the sizing composition.
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Thus the present invention pro~ides a sizing agent
composition of matter for the neutral sizing of paper,
paperboard, cardboard and other cellulose-containing
materials, comprising water, an organic solvent that is
infinitely miscible with water, a water soluble alkali
compound, an alkali aluminate and a sizing c~mponent,
wherein the alkali compound is present in a sufficient
amount to maintain a pH of about 12 in the c~nposition
and to completely saponify any fatty acids present, and
the alkali aluminate and sizing component are present in
amounts of at least 10 percent by weight and ~0 percent
by weight, respectively, based on the weight of total
solids in said composition; and wherein the organic
solvent is selected such that the sizing component is
completely dissolved, and the sizing component is one or
more compounds selected from the group consisting of
rosins, modified rosins, natural resins, modified natural
resins and fatty acids having 12 to 23 carbon atoms, said
sizing agent composition being a clear solution.
In another embodiment the present in~ention pro-
vides a method for neutral sizing of paper) cardboard or
other cellulose-containing materials comprising (a) adding
to an aquéous suspension of cellulose fibers 0.1 to 10~
by weight, based on the fiber content of the suspension
and calculated as solids content, of a sizing composition
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comprising water, an organic solvent infinitely miscible
with water, a basic reacting compound, an alkali aluminate
and a sizing component; (b) activating said sizing compo
sition by neutralization; and (c) adding a cation-active
retention agent, wherein the alkali compound is present
in a sufficient amount to maintain a pH of about 12 in
the composition and to completely saponify any fatty acids
present, and the alkali aluminate and sizing component
are present in amounts of at least 10 percent by weight
and 40 percent by weight, respectively/ based on the weight
of total solids in said composition.
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As b~sic reacting compound it is advantageous to
use sodium or potassium hydroxide in such an amount that the
pH-value of the sizing composition is about 12 so that the
precipitation of aluminum hydroxide can be avoided. If
appropriate, the basic compound may also serve to
saponify the sizing component, for example to
saponify a saturated or unsaturated fatty acid
with 12 to 24 carbon atoms. Such saponification should
be effected 100 percent.
The sizing component may be a rosin. a tall oil, a
resin soap or a drying oil. Fatty acids with 12 to 24 carbon
atoms are also suitable. Rosin and tall oil may, o course,
also be present as adduct of maleic or fumaric acid
(Diels-Alder diene synthesis).
The ~roduction of the sizi~q composition according
to the invention can be effected in a relatively simple
manner by mixing the components at room temperature in such
a way that solid alkali aluminate or an aqueous alkali
aluminate solution is added to the water which is softened
or stabilized Sodium hydroxide is added in solid or
dissolved form to avoid precipitation and, if appropriate,
to saponify the sizing component. ~inally an alcohol and sizing
component are added with stirring. The stirring i9 continued
until the sizing component is completely dissol~ed. Based
on the total amount of active ingredients in the sizing
composition the proportion of basic compound amounts to
between about 5 and 30 percent by weight, the proportion of
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sodium aluminate to between about 10 and 50 percent by weight
and t~e proportion of sizing component to between about 40
and 85 percent by weight.
Softening or stabilization of the water is
neeessary to avoid precipitation and is efected according to
known ~rocedures (for example with ethylenediamine tetra-
acetic acid and nitrilotriacetic acid).
In a further aspect of the invention there is
provided a method for neutral sizing of paper, cardboard or
other cellulose-containing materials comprising
a) adding to an aqueous suspension of cellulose
fibers 0.1 to 10% by weight, based on the fiber content of
the suspensi~n and calculated as solids content, of a
sizing composition comprising water, an organic solvent
infinitely miscible with water, a basic reacting compound,
an alkali aluminate and a sizing component;
b) activating said sizing composition by neutralization
and
c) adding a cation-active retention agent.
The novel sizing composition can be introduced
direetly into the fiber suspension which is to be sized.
After mixing in the pulper or in the refiner,
;the sizing composition is activated with acids and/or aeidic
salts/ whereby the quantity of acid and/or salt is
adjusted such t:hat a pH-value of about 7 is reached.
Suitable activating agents include all organic and
inorganic aeids which form neither insoluble salts nor eomplexes
with the aluminum ions. With the new sizing composition
neut~alization to a pH-value of about 6.8 to 7.2 has yielded
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excellent results. Besides sulfuric acid and aluminum sulfate,
formic and acetic acid have proven very useful in the tests
performed. Cationic retention agents considerably improve
the fixation of fiber and filler material as well as of the
sizing composition. The quantitv is dependent on the kind of
retention agent. However, about 0.02 to 0.5 percent by weight, preferably 0.02
to 0.2 percent by weight, based on the starting material should be sufficient.
According to an alternat:e embodiment of the
inventive method the sizing composition can be added to the
aqueous suspension of cellulose fibers until a pH of maximum
9 is reached. ~ollowing this, a cation-active retention
agent, preferably a cation-active polymer retention agent,
is added and homogenously distributed, and the sizing composition
is activated by adjusting the pH to about 7.2 to 7.5.
Advantageously, the sizing ~ oq;tion is added to the aqueous
suspension in an amount sufficient to reach a pH of about
7.5 to 8 or 7.6 to 8.
As in the previously described embodiment of the
inventive method, suitable cation-active retention agents
which can be added to the a~ueous suspension include poly-
ethyleneimine, cationic starch derivatives, polyacrylamide
and polymethacrylamide. Quaternary nitrogen compounds and
cation-active polymers may also be used. Quantities of
about 0.1 to 0.5 percent by weight, based on the fiber content
of the aqueous suspension, are generally sufficient to achieve a good
sizing of the pulp. The sizing composition is introduced
in an amount of about 0.1 to 10 percent by weight based on
the fiber content of the suspension and calculated as solids c~l-L~Ilt.
1 357
In some cases amounts of retention agents of
from 0.02 percent by weight based on the starting material may
be sufficient.
As in the previously described embodiment of the
inventive method activation of the sizing composition can be
effected with acids and/or acidic salts. Organic
and inorganic acids which form neither insoluble.salts nor
complexes which aluminum ions are suitable. Besides sulfuric acid
and alurninum sulfate, formic and acetic acid have proven
very useful.
It has also been found that the novel method can
be carried out in such a way that the aqueous suspension of
cellulose fibers having a pH of less than 7, in particular of between
6.5 to 6.9, is mixed with a cation-active polymer retention
agent and then homogenously distributed. Following this,
sizing composition is added until a pH of greater than 7
is reached. Desirably sufficient sizing composition should
be introduced into the aqueous suspension to reach a pH of
7.5 to 8. ~he pH of the suspension of cellulose fibers
should not be below 6.
As cation--active retention agent the abo~e mentioned
agents may be employed in amounts of between about 0.02 and
0.5 percent by weight based on the fiber content of the
aqueous suspension.
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The following exa~ples describe se~eral embodiments
of the invention in more detail, but are not to be construed
as limiting.
Preparation of Sizing Composition
Example 1:
570 parts by weight of softened water were introduced
into a stirring vessel. To this were added 145 parts by
weight of sodium aluminate solution having an A12O3-contenk
of 19% and 25 parts by weiyht of sodium hydro~xide. As soon as
these components were dissolved 135 parts by weight of isopropanol
and then 125 parts by weight of a mixture o~ fatty acids
were added, the titer of the fatty acid mixture was 19, the
acid nu~ber 200, the saponification number 290 and the
iodine number 105. The mixture was stirred until a clear
solution was obtained. The active ingredients of the neutral
sizing composition amounted to 20% by weight.
Example 2:
As in example 1, 645 parts by weight of water were
introduced into a stirring vessel. After addition of 50
parts by weight of a 50% sodium hydroxide solution and ~5
parts by weight of solid sodium aluminate in powder form the
mixture was stirred until complete solution was obtainedO
Following this,135 parts by weight of i~ ol were added and
125 parts by weight of fortiied powdered resin sizing were
distributed in the mixture. A~ter complete solution of the
powdered sizing a light yellow solution was obtained and was
stabilized by adding 1 part by weight of sorbitol. The actiYe
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ingredients of the sizing composition amounted to about 20%
by weight.
Example 3:
630 parts by weight of softened water were introduced
into a stirring vessel. Then 100 parts by weight of sodium
aluminate solution having an A12O3 content of 19~ and 25
parts by weight of solid sodium hyclroxide were added. After
the components were dissolved and distributed, 160 parts by
weight of isopropanol were added. Following this a mixture
of 100 parts by weight of gum rosin and 10 parts by weight of a
rosin reacted with maleic acid were introduced into the
vessel. Stirring was continued until all components were
dissolved.
Example 4:
75 parts by weight of ethanol were introduced into a
stirring vessel. Then 50 parts by weight of comminuted rosin
and 5 parts by weight of a rosin reacted with maleic acid
were added and stirring was continued until the solid components
were completely dissolved. Following this, 50 parts by weight of
sodium aluminate solution having an A12O3-content of 19%
and 25 parts b~ weight of a 50~ sodium hydroxide solution
were introduced with stirring. Lastly 101 parts by weight of
softened water were added. A reddish brown solution with a
solids content of 27.4% was obtained.
Example 5:
365 parts by weight Of tap water containing about
25 mg CaO/100 ml water were pumped into a stirring
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vessel and 1 part by weight of ethylene diamine tetraacetic
acid or nitrilotriacetic acid were added. ~hile stirring
200 parts by weight of sodium aluminate solution having an
A12O3 ~ L of 19% by weight, 35 parts by weight of flake-shaped sodium
hydroxide and 200 parts by weight of ethanol
were added. Stirring was continued until a clear solution
was obtained. Following this, 160 parts by weight of ground
rosin and 40 parts by weight of ground rosin reacted with
maleic acid were added and stirred until all solids were
dissolved. As final product are reddish brown clear solution
with a solids content of 30% was obtained.
~xample 6:
365 parts by weight of stabilized tap water were
introduced into a stirring vessel and 200 parts by weight of
sodium aluminate solution (19~ A1~03-content) were added.
Then 35 parts by weight of flake-shaped sodium hydroxide
were introduced. To this solution a mixture of alcohols
consisting of 160 parts by weight of ethanol and 40 parts of
weight of methanol were added and stirred until a clear solution
was obtained. Then 200 parts by weight of ground rosin
containing about 10% maleic acid were added. The final
product was a reddish brown transparent liquid with a solids
content of 30%.
Pulp Sizing
~xample 7:
The fiber starting material used in the process of
this example consisted of ~5% by w~ight of pulp (50% spruce
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sulfite pulp, 50% bleached pine sulfate pulp), 10~ by weight of
chalk (filler) and 5% by weiyht of ~ater-soluble starch. The
degree of comminution was about 30 SR.
The sizing process was effected with a charge having
3% fiber content. To this charge sizing composition
according to example 1 was added until an effective amount
of sizing composition of 2.5% by weight, based on the fiber
content, was reached. After mixing the suspension was
pumped into the mixing tank and the pH was adjusted to 6.8
with sulfuric acid (50%). Following this a cationic retention
agent was added in the known manner.
After sheet formation and drying a fully sized
paper was obtained which had an ink resistance of over 8
minutes and a Cobb(60)-value of less than 30. The weight
of the sized paper was between about 110 and 120 g/m2.
Example 8:
A wood containing starting material was converted to
half-sized printing paper. To this effect the pulp was first
treated in a pulper, then comminuted and introduced into a
mixing tank. In the mixing tank a 3.5~ starting material was
mixed with the sizing composition according to example 2 while
being continuously stirred. More particularly, 5 parts by weight
of the 20~ sizing composition were âdded for each 100 parts by
weight of the starting material. After thorough mixing the
suspension was pumped into an intermediate tank and was activated
with 10~ hydrochloric acid. When a pH of 6.8 was reached, the
activation was t:erminated. As in example 7, a cationic retention
agent was added to improve fixation of fiber and filler material
as well as of the sizing composition.
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The sized pulp was converted to paper which had an
ash content of 15% by weight ~kaolin content) and a weight of
70 g/cm . The Cobb(60)-value was 45.
Example 9:
In a used paper stock processing operation which had
a tightly controlled water circulation, wrapping paper was
produced. The amount of dirt and the degree of hardness were
therefore high (the degree of hardness was more than 100 mg CaO/100
ml water).
In a mixing tank sizing composition according to
example 2 was mixed with the used paper stock. 2.25~ by weight
of active ingredients of the sizing composition were added to
each 100 g used paper stock. The activation was performed in
an intermediate tank with diluted sulfuric acid (50%) or aluminum
sulfate. The pH at activation was 6.7 and 6.8, respectively,and
the density was 3.0%. A cationic retention agent was also added.
The fully sized wrapping paper had a weight of 110 and 120
g/m2, respectively.
~xample 10: `
In a mi~ing tank with a 25 m3 holding capacity a
suspension with a 4% density was placed. In this case the
suspension was a dissolved fiber material consisting of 55
mixed waste paper, 25% corrugated waste paper and 20Po
cardboard waste. The pH of the suspension was 6.9. 125 kg
of the 20% sizing composition according to example 3
were added. At the same time -the pH increased to a value
o~ 8.35. After the sizing com~osition was well mixed with
the fiber suspension, 1.5 kg polyethylene imine were introduced
and evenly distributed. ~he pH-value o~ the suspension did
not change. Following this, the activating agent (diluted
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sulfuric acid) was slowly added until the pH became adjusted
to about 7.3. The subsequent treatmen-t on the machine was
effected in the usual way and a cardboard material having
a Cobb(60)~value of between 50 and 75 was obtained.
Example 11:
Neutral pulp sizing was effected with a charge
which consisted of 50% bleached spruce sulfite pulp and 50%
partially bleached mechanical wood pulp. This charge which
had a density of 4% and a pH of 6.5 was mixed in a mixing
tank with 0.2% by weight, based on the fiber content, of a
strongly cationic retention agent (a polyethylene imine which
is commercially available under the trademark POLYMIN SK).
After thorough mixing 2% of the sizing composition (130%),
produced according to example 3 were added. Subsequently,
the mixture was circulated in the tank and thereby
diluted with about 5 times the amount of water ~volume)
and adjusted to the desired consistency of about 0.8%. After
draining and drying of the paper very well sized paper was
obtained.
Example 12:
The pulp sizing was performed as described in
example 7 except that no starch was added. With the sizing
composition according to example 4 a fully sized paper having
a Cobb(60)-value of less than 30 and a weight of 70 g/m2 was
obtained.
