Note: Descriptions are shown in the official language in which they were submitted.
CA 02334744 2007-12-14
METHOD FOR MANUFACTURING PAPER, CARDBOARD AND CORRESPONDING
RETAINING AGENTS
The present invention relates to the technical field
of paper production and the polymers used in this field.
The invention relates to a process for the
manufacture of a paper or paperboard with improved retention.
During the manufacture of paper, paperboard, or the
like, it is well known to introduce into the pulp retention
aids whose function is to retain a maximum of fines and fillers
in the sheet. The beneficial effects that result from the
utilization of a retention aid are essentially:
- increased production and reduction of manufacturing
costs: energy savings, more reliable operation of the machine,
higher yield in terms of fibers, fines, fillers and anionic
finishing products, lower acidity in the circuit linked to a
decrease in the use of aluminum sulfate, and hence a reduction
in corrosion problems;
- an improvement in quality: better formation and
better look-through, an improvement in the moisture content,
the opacity, the gloss, and the absorptive capacity of the
sheet, and a reduction in the porosity of the paper.
Long ago, it was proposed that bentonite be added to
the pulp, possibly together with other mineral products such as
aluminum sulfates or even synthetic polymers, notably
polyethylene imine (see for example the documents
DE-A-2 262 906 and US-A-2 368 635).
In the document US-A-3 052 595, it was proposed to
associate the bentonite with a polyacrylamide of an essentially
linear nature. This process met with competition from systems
that were
i
CA 02334744 2005-02-25
2
easier to use yet performed just as well. Moreover, even with the
current linear polyacrylamides, the retention capacity is still
insufficient.
In the document EP-A-0 017 353, it was proposed, for the
retention of low-filler pulps (less than 5% fillers), to
associate the bentonite with a nonionic or slightly anionic
linear copolyacrylamide. This process has not been very widely
used, since these polymers perform relatively poorly in terms of
retention, especially that of pulps containing fillers, no doubt
as a result of insufficient synergy between these copolymers and
bentonite, which does not have much of a tendency to recoagulate.
Also known in the prior art are systems of retention aids
for the manufacture of a sheet of paper, paperboard or the like,
which comprise a combination of two retention aids, generally a
main retention aid and a secondary retention aid. These are
called "dual" systems.
Thus, in US patent 4,753,710, it is recommended to use of a
linear acrylic polymer of high molecular weight as the main
retention aid, which is added to the fibrous mass, followed by an
intense shearing, particularly in the mixing pump or "fan pump,"
then an addition of bentonite, (which is a swelling clay) as the
secondary retention aid. This document neither suggests nor
describes any shearing of the polymer itself before introduction
into the suspension to be flocculated.
Also known in the prior art are cross-linked retention aids
as described, for example, in European patent 0 202 780,
primarily for the treatment of water, and secondarily for paper.
It is important to note that it uses a cross-linked product,
which is added to the suspension to be flocculated, the flocs
then being sheared during the paper production process, that is,
sheared in and at the same time as the paper pulp. The flocs are
thus transformed into flocs that are smaller and more shear
resistant, therefore more tenacious. This document neither
CA 02334744 2005-02-25
3
suggests nor describes any shearing of the polymer itself before
introduction into the suspension to be flocculated.
Thus, according to the techniques of the prior art related
to papermaking applications, between the flocculating agent and
the fibrous mass of pulp, flocs of fairly large size are formed,
and are then sheared so as to form flocs which, in the documents
cited, are said to be smaller and more tenacious.
In the document EP-A-0 235 893, it was proposed to use
essentially linear cationic polyacrylamides having molecular
weights of greater than one million, of thirty million and
higher. This results in the obtainment of a retention effect that
is satisfactory, but is still deemed inadequate in the
papermaking application; since the use of bentonite causes
problems during water treatment, users select this system only if
there are significant advantages.
US patent 4,753,710 (the commercial product "HYDROCOL"
(TM)), already mentioned above, also describes the addition of a
cationic polymer as the main retention aid, followed by an
intense shearing stage, then an addition of bentonite as the
secondary retention aid. Its drawbacks include the necessity to
optimize the introduction point, which does not present any
particular problem given all of the prior research on this
subject, but which represents a limitation for the user in the
papermaking industry, as well as the risk of an overdosage of the
polymer, and which is necessary to reduce the uncontrolled or
excessive degradation of the flocks by the shearing imposed.
,
In the notes presented at the lecture given in Seattle on
October 11-13, 1989, published under the title "Supercoagulation
in the control of wet end chemistry by synthetic polymer and
activated bentonite," R. Kajasvirta described the mechanism of
supercoagulation of activated bentonite in the presence of a
CA 02334744 2005-02-25
4
cationic polyacrylamide, without specifying its exact nature.
This process has the same drawbacks as those indicated above.
European patent 0 201 237 describes a flocculation process
in which a polymer material is added to water to form an aqueous
composition, and is used to flocculate the solid matter in
suspension in an aqueous suspension, said polymer comprising a
polymer of high molecular weight that is subjected to a shearing,
this shearing being carried out before or during the flocculation
and the polymer being required to have certain intrinsic
properties, which are indicated in this patent.
According to this document, the polymer is a polymer of high
molecular weight, formed from water-soluble monomers or from a
mixture of such monomers, and the polymer is subjected to
shearing. The process described in this patent is characterized
in that it is possible to carry out the shearing before or during
the flocculation. European patent 0 201 237 further indicates
that the polymer used comprises a cross-linked water-swellable
polymer which it is possible to shear to an intrinsic viscosity
of at least 4 dl/g. It is also indicated that the aqueous
composition containing the polymer material can be a stable and
homogenous composition, the shearing in this case causing an
increase in the intrinsic viscosity of at least 1 dl/g.
In this document, "stable and homogenous" designates a
polymer composition that is stable when the polymer is at full
equilibrium with the water, i.e., when it has reached its
ultimate degree of solubility or swelling. The composition is
also homogeneous in the sense that the polymer remains uniformly
dispersed throughout the composition, without having a tendency
to precipitate after several days.
This document specifically describes a number of
applications for water treatment, which is clearly precisely the
main application intended, and coal ore treatment.
This patent also mentions, very briefly and without
providing an exemplary embodiment or even any precise
CA 02334744 2005-02-25
instructions for implementation, an application to paper or
paperboard production; it is merely indicated that the polymer
can be added at an early stage of the pulp (fibrous mass)
circulation line with a shearing along the flow line of the
5 suspension, near the drainage stage or another water removal
stage. The patent indicates that the shearing is carried out by
pumping, hence by means of the "fan pump" or mixing pump
effectively disposed in line in papermaking machines.
For the other applications, and especially for water
treatment, the document also indicates that it is possible to
carry out the shearing on the production line, as the suspension
to be flocculated approaches a centrifuge, a filter press or a
belt press, or another water removal stage. It is also indicated
that the shear can be applied during a water removal stage that
is conducted under a certain shear, preferably in a centrifuge or
even in a filter press or a belt press.
Hence, this document only teaches a shearing of the flocs in
the mixing pump or "fan pump" for the papermaking application.
Moreover, it teaches that very low shear rates can be appropriate
in the other applications, since filter presses and belt presses
induce very low shear.
The invention eliminates the drawbacks mentioned above.
Its object is an improved process of the type in question,
which incorporates operations comprised of adding to the
suspension or fibrous mass to be flocculated, or paper pulp,
8
a) as the main retention aid, a (co)polyacrylamide that is cross-
linked and is prepared in the form of a reverse phase or water-
in-oil emulsion, this reverse-phase emulsion ("inverted" in
water), or even the dried powder obtained from this reverse phase
emulsion and redissolved in water, itself being sheared prior to
introduction or injection into the fibrous mass, and
CA 02334744 2005-02-25
6
b) a second retention aid (a so-called "dual" system of the
"microparticulate" type),
c) without a stage for intense shearing of the pulp between the
additions a) and b), or with an "optional" shearing (as defined
below) of the pulp between the two additions a) and b).
The second retention aid is bentonite, and in thisfield the
reader is referred to the teaching of the above-mentioned US
patent 4,753,710, which can advantageously be replaced by a
kaolin, preferably pre-treated by a polyelectrolyte, according to
the teaching of French patent 95 13 051 filed in the name of the
Applicant; and it would be useful for one skilled in the art to
refer to these documents for the details of implementation, the
usual additives, etc.
The addition of the polymer and that of the bentonite are
not separated according to the invention by any mandatory stage
for intense shearing of the pulp, for example at the level of the
mixing pump known as the "fan pump," contrary to the teaching of
US patent 4,753,710 and contrary to a vast body of prior art
related to the addition point of the retention aid relative to
the shearing stages existing in the machine, including US patent
3,052,595; Unbehend, TAPPI Vol. 59, No. 10, October, 1976; Luner,
1984 Papermakers Conference or TAPPI, April, 1984, pp. 95-99;
Sharpe, Merck and Co., Inc., Rahway, NJ, USA, around 1980,
Chapter 5, "Polyelectrolyte Retention Aids"; Britt, TAPPI Vol.
56, October 1973, p. 46 ff.; Waech, TAPPI, March, 1983, p. 137;
and US patent 4,388,150 (Eka Nobel). According to the invention,
it is in fact entirely preferred that there be no intercalary
shearing of the pulp between the two additions.
This process according to the invention makes it possible to
obtain a distinctly improved retention of fines and fillers
without a reverse effect. An additional characteristic of this
CA 021334744 2005-02-25
7
improvement is that the drainage properties are also improved,
which is unexpected given the improvement of the retention, and
excellent formation is maintained, which is also surprising.
The cross-linked polyacrylamide (or more generally the
cross-linked (co)polymer) is introduced into the suspension or
pulp to be flocculated in the form of the reverse phase water-in-
oil emulsion derived from the synthesis, and itself "inverted" in
water, or in the form of a solution in water, with about 5 g of
polymer/liter, of the powder obtained by drying the reverse phase
water-in-oil emulsion from the synthesis, said emulsion or said
solution being sheared before introduction into the pulp or
suspension to be flocculated, the dosage for the introduction
being established at a rate of 0.03 to one per mill (0.03 to 1
%o, or 30 to 1000 g/t) by weight of active material (polymer)
relative to the dry weight of the fibrous suspension, preferably
0.15 to 0.5 per mill, or 150 to 500 g/t.
In a way that is known to one skilled in the art, when the
emulsion derived from the synthesis of the polymer is used
directly, this water-in-oil polymer emulsion is diluted in water
to obtain a polymer content on the order of 5 to 10 g/l,
preferably close to 5 g/l, and is thus "inverted" by this
dilution to form a solution, which is sheared according to the
invention before its introduction into the pulp.
It is preferred according to the invention to use the
sheared "inverted" emulsion, but Example 3 below shows that the
results of the sheared solution of the powder obtained by drying
the emulsion are equivalent.
According to the techniques of the prior art relative to
papermaking applications, between the flocculating or retention
aid and the fibrous mass of pulp, flocs of fairly large size are
formed, which are then sheared so as to form flocs which, in the
CA 02334744 2005-02-25
8
documents cited, are said to be smaller and more tenacious.
Moreover, the systems of the prior art of the dual system
type require the use of an intense shearing between the addition
of the cationic polymer and the addition of the second retention
aid, the bentonite or a kaolin. Systems of this type can be
classified as microparticulate.
The "dual" systems of the prior art were essentially
composed of linear polymers with an addition of bentonite, or of
a branched polyacrylamide or a starch, with an addition of
colloidal silica, this last component being extremely expensive.
A known improvement of these processes is described in
French patent 95 13 051 in the name of the Applicant, which
relates to a dual system based on a polymer of the linear or
branched polyacrylamide type and kaolin, kaolin being a non-
swelling clay that does not have the drawbacks of bentonite, the
kaolin being pre-treated in a preferred embodiment.
On the other hand, according to the present invention, a
main retention aid is used, which is cross-linked and which is
sheared before its introduction into the pulp, preferably in the
form of a reverse phase water-in-oil emulsion, which leads
directly to microflocs without going through the shearing of
larger flocs involving the fibrous mass.
According to the invention, and without intending to be
limited by any one theory, the Applicant in effect maintains that
a microflocculation occurs directly as a result of the intense
shearing carried out on the polymer itself before its injection
into the fibrous mass of pulp, which is quite a different (and
unexpected) process than reducing the size of large flocs
(involving the fibrous mass) into smaller, more tenacious flocs,
and which results in unforeseen improvements in the properties of
the paper or paperboard sheet.
This selection of the cross-linked form, in a reverse phase
emulsion (or in a solution of the powder obtained by drying the
CA 02334744 2005-02-25
9
emulsion) before introduction into the fibrous mass, in
combination with the subsequent addition of a second retention
aid, but without any intercalary shearing of the pulp, makes it
possible, in the papermaking application for the retention of
fillers and fines, to reach a level of performance unequalled up
to now.
The monomers used for the preparation of the (co)polymer can
be nonionic, but generally at least some of the monomers used to
form the polymer are ionic. The monomers are normally monomers
with monoethylenic unsaturation, sometimes allylic monomers, but
generally vinyl monomers. These are generally acrylic or
methacrylic monomers.
Suitable nonionic monomers are acrylamide, methacrylamide,
N-vinyl methyl acetamide or formamide, vinyl acetate,
vinylpyrrolidone, methyl methacrylate or methacrylates of other
acrylic esters, or of other esters with ethylenic unsaturation,
or even of other vinyl monomers that are insoluble in water such
as styrene or acrylonitrile.
Suitable anionic monomers are for example sodium
acrylate, sodium methacrylate, sodium itaconate, 2-acrylamido-2-
methylpropane sulfonate (AMPS), the sulfopropylacrylates or
sulfopropylmethacrylates, or other water-soluble forms of these
polymerizable sulfonic or carboxylic acids. It is possible to use
a sodium vinylsulfonate or an allylsulfonate, or a sulfomethyl
acrylamide.
Suitable cationic monomers are the dialkylaminoalkyl
acrylates and methacrylates, particularly dialkylaminoethyl
acrylate, as well as their acid salts or their quaternary
products, and even the dialkylaminoalkylalkylacrylamides or -
methacrylamides, as well as their acid salts and the products of
quaternization, for example methacrylamidopropyl trimethyl
ammonium chloride and the Mannich products such as the
quaternized dialkylaminomethylacrylamides. The alkyl groups in
question are generally C1-C4 alkyl groups.
The monomers can contain hydrophobic groups, for example as
CA 02334744 2005-02-25
described in European patent 0 172 723, and in certain cases
allylic ether monomers could be preferred.
For simplicity's sake, the term "(co)polyacrylamide" will be
5 used herein to designate all of the combinations of these
monomers, which are well known to one skilled in the art.
Advantageously, in practice, the cross-linked
(co)polyacrylamide is a cationic copolymer of acrylamide and of
10 an unsaturated cationic ethylenic monomer, chosen from the group
comprising dimethylaminoethyl acrylate (ADAME),
dimethylaminoethyl methacrylate (MADAME), quaternized or salified
by different acids and quaterinizing agents, benzyl chloride,
methyl chloride, alkyl or aryl chloride, dimethyl sulfate,
diallyldimethylammonium chloride (DADMAC),
acrylamidopropyltrimethylammonium chloride (APTAC), and
methacrylamidopropyltrimethylammonium chloride (MAPTAC).
The processes for synthesizing a reverse phase emulsion
(co)polymer are well known to one skilled in the art. In this
field, the reader is referred to the above-mentioned patents.
In a way that is also known, this (co)polymer is cross-
linked by a cross linker constituted by a compound having at
least two reagent groups chosen from the group comprising the
double bonds, the aldehyde bonds or the epoxy bonds. These
compounds are well known and are described, for example, in the
document EP-A-0 374 458 (see also the Applicant's document FR-A-2
589 145).
As is known, a cross-linked polymer is a polymer which, in
the branched chain, has groups or branchings disposed globally in
three dimensions, resulting in practically insoluble products of
infinite molecular weight; cross-linked polymers of this type
having high molecular weights are well known as flocculating
agents, for example as described in European patent 0 202 780 or
CA 02'334744 2005-02-25
11
European patent 0 201 237, whose teachings are equivalent.
The cross-linking can be carried out during or after the
polymerization, for example by reaction of two soluble polymers
having counter-ions, or by reaction on formaldehyde or a
polyvalent metal compound. Often, the cross-linking is carried
out during the polymerization by addition of a cross linker, and
this method is clearly preferred according to the invention.
These processes for polymerization with cross-linking are known.
The cross linkers that can be incorporated comprise ionic
cross linkers such as polyvalent metal salts, formaldehyde,
glyoxal, or preferably, covalent cross linkers that will
copolymerize with the monomers, preferably monomers with
diethylenic unsaturation (like the family of diacrylate esters
such as the diacrylates of polyethylene glycol PEG) or
polyethylenic unsaturation, of the type classically used for the
cross-linking of water-soluble polymers, and particularly
methylenebisacrylamide (MBA), or any of the other known acrylic
cross linkers.
In practice, the cross linker is methylenebisacrylamide
(MBA), introduced at a rate of five to two hundred (5 to 200)
moles per million moles of monomers, preferably 5 to 50,
preferably 10 or 20.
Advantageously, the quantity of cross-linked polyacrylamide
introduced is between 0.03 per mill and one per mill (0.03 %o and
1 %o) or between thirty and one thousand grams of active
polymer/ton of dry pulp (30 and 1000 g/t), preferably between
0.15 and 0.5 per mill (%o) of the quantity of dry pulp~ or from
150 to 500 g/t; it was observed that if the quantity is less than
0.03 %o, no significant retention is obtained; likewise, if this
quantity exceeds 1 %o, no proportional improvement is observed;
however, unlike the linear cationic polyacrylamides, as described
in the documents EP-A-0 017 353 and EP 0 235 893 mentioned in the
CA 02334744 2007-06-27
85750-15
12
preamble, there is no observed reverse dispersion effect by
recirculation in the closed circuits of the excess polymer not
retained in the sheet.
As stated above, it is important that cross-linked polymer
be prepared in the form of a reverse phase emulsion in order to
achieve the improvement of the invention.
This approach was condemned in the above-mentioned patent
574 335, in which it was indicated that if a branched polymer is
used in emulsion, the indispensable presence of surfactants in
these emulsions promotes the formation of foams during the
production of the paper and the appearance of disparities in the
physical properties of the finished paper (modification of the
absorbency in the places where part of the oil phase of the
emulsion is retained in the sheet).
Therefore, it was not obvious to consider, for a papermaking
application, the reverse phase water-in-oil emulsions whose oil
content is clearly high.
Moreover, it was known in the art, on the filing date of the
present application, that it was important to stay within the
field of branched polymers, and not to move into the field of
cross-linked polymers, and cross-linked emulsions were not known
to provide any particular advantage in papermaking.
On the-'filing date of the present patent application, a
cross-linked polymer in reverse phase emulsion or in solution and
sheared before introduction was in fact used, but as the sole
retention aid.
Bentonite, also known as "smectic swelling clay," from the
montmorillonite family, is well known and there is no need to
CA 021334744 2005-02-25
13
describe it in detail here; these compounds, formed of
microcrystallites, comprise surface sites having a high cation
exchange capacity capable of retaining water (see for example the
document US-A-4 305 781, which corresponds to the document EP-A-0
017 353 mentioned above, and FR-A-2 283 102). For the examples
below, a commercial bentonite CPBl, with a density of 900 kg/m3,
a swelling capacity of 40 ml/g, a cation exchange capacity of 85
meq/100 g in the dry state, and an average size of < 75 microns,
was used. The use of this bentonite is not limiting. As indicated
above, it is also possible to use a kaolin as the secondary
retention aid.
Preferably, a semisodic bentonite is used, which is
introduced just upstream from the headbox, at a rate of 0.1 to
0.5 percent (0.1 to 0.5%) of the dry weight of the fibrous
suspension.
As a filler, it is possible to use kaolins, GCC or ground
CaCO3, precipitated CaCO3 or PCC, and the like.
According to the present invention, a cross-linked retention
aid, prepared in the form of a reverse phase emulsion, is either
used directly in the form of the synthetic emulsion ("inverted"
as described above), or in the form of the solution of the powder
obtained by drying said emulsion, the emulsion or the solution
being sheared before its injection or introduction into the pulp
to be flocculated, which leads directly to microflocs without
going through the shearing of larger flocks involving the fibrous
mass.
Without intending to be limited by any one theory; the
Applicant in effect maintains that a microflocculation occurs
directly when the intense shearing is carried out on the polymer
itself before its injection into the fibrous mass of pulp, which
is quite a different process than reducing the size of large
flocs (involving the fibrous mass) into smaller, more tenacious
CA 02334744 2005-02-25
14
flocs, which results in unforeseen improvements in the properties
of the paper or paperboard sheet.
It is noted that, contrary to the teaching of US patent 4,
753,710 ("HYDROCOL" (TM)), a shearing under the flow line
conditions (i.e., a shearing of the pulp) described in this
document absolutely does not lead to the results of the
invention.
For example, a shearing of the pulp in a pump of the "fan
pump" type does not produce the anticipated result.
In this field, the reader is referred to the above examples.
On the other hand, it was discovered according to the
invention that for the application related to the manufacture of
a sheet of paper, paperboard, or the like, it is essential to
carry out an intense shearing before the injection of the cross-
linked polymer into the paper pulp or fibrous mass prior to its
being flocculated, with no intercalary shearing of the pulp
between the injection of the polymer (main retention aid) and the
injection of the bentonite or the kaolin (secondary retention aid
of the dual system).
One skilled in the art will realize, through the examination
of the two series of examples A and B below, that the process
according to the invention enables the paper manufacturer to be
completely free of the constraint of the "intercalary" shearing
of the pulp (i.e., the shearing of the pulp between the addition
of the first and second retention aids). An intercalary shearing
of this type is mandatory in, for example, the "HYDROCOL" (TM)
system, when desiring obtain a compromise between the various
properties of the paper, especially retention, drainage and
formation, some of which are known to have been antagotilistic in
the prior art. However, these same examples show that, if an
intercalary shearing occurs in the tests conducted on a product
sheared before its introduction into the pulp, the properties of
the paper are not appreciably diminished. Therefore, the
invention chiefly relates to a process without intercalary
CA 02334744 2005-02-25
shearing of the pulp, but also to a process comprising such an
intercalary shearing, whether it be deliberate or imposed by the
constraints of the existing equipment. The properties obtained
will be better without this intercalary shearing, but if the
5 injection point of the sheared polymer cannot be chosen freely by
the paper manufacturer because of the existing equipment, the
paper manufacturer can benefit from the excellent set of
properties provided by the invention without having to modify its
machine. Given below are comparative examples A/B which show
10 that, if the shearing of the fibrous mass (i.e., after the
addition of the sheared polymer) is carried out in a paper
application, the results obtained are still entirely acceptable.
This set of possibilities and findings is referred to in this
document as "optional" shearing.
According to a variant of the invention, and as indicated
above, it is possible to use a reverse phase emulsion of the
polymer ("inverted" in water) or even the powder obtained from
the emulsion by means of a known drying technique, such as for
example "spray drying," solvent precipitation, or agglomeration
(PEG) and grinding (on this subject, see also the prior art, such
as USP 5,696,228, WO 97/48 755 (USSN 08/668,288) WO 97/48 750, WO
97/48 732, WO 97/34 945, WO 96/10589, USP 5,346,986, 5,684,107,
EP 0 412 388, EP 0 238 050, USP 4,873,299, EP 0 742 231, WO
90/08789 or EP 0 224 923) which is redissolved in water, sheared,
then used like an emulsion.
This variant of the method is very interesting since the
dried product according to the invention behaves substantially
like the emulsion, and this variant therefore provides a method
~
for using dry products having the advantages of an emuylsion,
which it is not always possible to prepare by direct
polymerization in the aqueous phase, in gel form or in solution.
According to the invention, however, it is preferable to use
the reverse phase emulsion (inverted in water into a solution
with 5-10 g/1) of the cross-linked polymer, with shearing prior
CA 02334744 2005-02-25
16
to the injection into the pulp, of course.
Without intending to be limited by any one theory, the
Applicant maintains that this is due to the fact that the
cationic charge is not released.
According to the invention, laboratory shearing tests can be
conducted, with a concentration on the order of 3-5 to 10-15 g of
active material (i.e., the polymer)/liter of emulsion of the
polymer, preferably between 5 and 10 g/1, in a piece of.equipment
known as an "Ultra Turrax" (TM), for example at 10,000 rpm, or in
a household mixer of the "Moulinex" (TM) type, substantially at
the same magnitude of rotation speed, for a duration that can
last between 15-30 seconds and 2-5 minutes.
In the industry, there is existing equipment suitable for
implementing the invention, for example high-pressure
recirculation pumps or turbines, which are not referred to by the
theoretical example of the document EP 0 201 237.
One skilled in the art will naturally know all the equipment
that makes it possible to carry out an intense shearing of the
polymer emulsion, diluted to an appropriate value as described
below, without being limited to the above examples.
For the generalities of the production of a pulp for paper,
paperboard or the like, as well as a list of the additives,
fillers, etc., that are well known, it would be useful for one
skilled in the art to refer to US patent 4,753,710.
According to the invention, using an optimization within the
scope of one skilled in the art, an ionic regain (IR as defined
in European patent 0 201 237) of 40 to 50% is obtained, which can
reach at least 60 or 70%, and even more, up to values greater or
far greater than 100%.
Moreover, it is possible to adjust the shear so ad to favor,
for the first time in this industry, one property of the paper
over another, for example to promote retention slightly more than
formation or drainage, or vice versa, or any of the various
possible combinations, as will be seen by reading the examples
that follow.
CA 02'334744 2005-02-25
17
A normal dosage of the agent according to the invention is
such that it leads to about 100 to 500 g,of active material
(polymer) per ton of fibrous matter to be treated.
According to the invention, it is possible to use a polymer
having an intrinsic viscosity i.v. as low as 1 to 3, which
becomes an intrinsic viscosity as high as 3-7 or 8 after the
application of the shearing according to the invention.
Moreover, the system according to the invention is not
expensive, and consequently it combines all of the advantages of
the linear or cross-linked single-product systems with floc
shearing and of the "dual" systems with two retention aids and
also with floc shearing.
The cross-linked polymer in reverse phase emulsion (or in a
solution of the redissolved powder), sheared according to the
invention, is injected or introduced into the paper pulp (or
fibrous mass to be flocculated), which is more or less diluted in
accordance with the experience of one skilled in the art, and
generally into the diluted paper pulp or "thin stock," i.e., a
pulp diluted to about 1.5% solid matter such as cellulose fibers,
possible fillers, and the various additives commonly used in
paper production.
The second retention aid, or secondary retention aid, such
as bentonite or a preferably pretreated kaolin, is then added
into said pulp without any intercalary shearing, or with an
"optional" intercalary shearing, for example, in practice,
between 5 and 30 seconds, preferably between about 10-20 s, but
possibly up to 5 minutes, after the introduction into;the pulp of
the pre-sheared polymer in reverse phase emulsion (or in a
solution of the redissolved polymer).
CA 02334744 2007-06-27
85750-15
17a
According to one aspect of the present invention,
there is provided a process for manufacturing a sheet of
paper or paperboard having improved retention and drainage
properties, of the type which uses a dual system of an
acrylic type polymer and bentonite or a possibly treated
kaolin as primary and secondary retention agents,
respectively, wherein it incorporates operations comprised
of adding to the suspension or fibrous mass to be
flocculated, or paper pulp,
(a) as the primary retention agent, a
(co)polyacrylamide that is cross-linked and exists in the
form of a reverse phase or water-in-oil emulsion, or a
solution of the powder obtained by drying said reverse phase
emulsion,
said emulsion or solution being sheared prior to
introduction or injection into the fibrous mass such that
the shearing of the reverse phase emulsion of the polymer or
of the solution obtained by the redissolution in water of
the powder obtained by drying the synthetic reverse phase
emulsion, is carried out before injection into the pulp,
with a concentration in the order of 3-5 to 10-15 g of
active material/liter of emulsion of the polymer, in an
"Ultra Turrax" (TM) machine, or in a household mixer of the
"Moulinex" (TM) type, substantially at the same magnitude of
rotation speed, for a duration that can last between 15-30
seconds and 2-5 minutes, or in that the shearing is carried
out in high pressure recirculation pumps or turbines,
and shearing the reverse phase emulsion "reversed"
in water, or the solution of the dried powder of the
synthetic emulsion, before ejection into the pulp results in
an ion regain IR of 40 to 50%, which can reach at least 60
CA 02334744 2007-06-27
85750-15
17b
or 70% and even more, up to values greater or far greater
than 100%, with:
Ion regain IR = (X-Y) /Y X 100
with X: ionicity after shearing in meg/g
Y: ionicity before shearing in meg/g,
(b) then the second retention agent,
(c) without a stage for intense shearing of the
pulp between the additions a) and b), or with an "optional"
shearing of the pulp between the additions a) and b).
CA 02334744 2005-02-25
18
The following examples illustrate the invention without
limiting its scope. Figs. 1 and 2 represent the histograms
corresponding to Tables (I) and (II).
The abbreviations have the meanings indicated below.
Test Column = type of polymer product used
% = dosage of the retention aid of the test column
in % agent/dry pulp
% Ash = % by weight of ash (filler retention)
DXF = drainage according to the CSF (Canadian Standard Freeness)
standard
X designates a "first pass" measurement.
Formation scale: 1 Excellent (homogeneous)
2 Good (nearly homogeneous)
3 Average (cloudy)
4 Poor (fleecy)
6 Very poor (mottled)
EXAMPLE 1
Production of a cross-linked polymer in reverse phase emulsion
form (PF 455 B)
In a reactor A, the-constituents of the organic phase of the
emulsion to be synthesized are mixed at the ambient temperature.
a) Organic phase
- 252 g of Exxsol D100
- 18 g of Span 80
- 4 g of Hypermer 2296
b) In a beaker B, the aqueous phase of the emulsion to be
produced is prepared by mixing:
- 385 g of acrylamide at 50%
CA 02334744 2005-02-25
19
- 73 g of ethyl acrylate trimethyl ammonium chloride (80%)
- 268 g of water
- 0.5 g of methylenebisacrylamide at 0.25%
- 0.75 ml of sodium bromate at 50 g 1-1
- 0.29 ml of Versenex at 200 g 1-1
The contents of B are mixed into A under agitation. After
the mixture of the phases, the emulsion is sheared in the mixer
for 1 minute in order to create the reverse phase emulsion. The
emulsion is then degassed by means of a nitrogen bubbling; then
after 20 minutes, the gradual addition of the metabisulfite
causes the initiation followed by the polymerization.
Once the reaction is finished, a "burn out" (treatment with
a bisulfite or metabisulfite to eliminate the residual monomer)
is carried out in order to reduce the free monomer content.
The emulsion is then incorporated with its inverting
surfactant in order to subsequently release the polymer in the
aqueous phase. It is necessary to introduce 2 to 2.4% ethoxylated
alcohol. The standard Brookfield viscosity of said polymer is 1.8
cps (viscosity measured at 0.1% in a 1 M NaCl solution at 25 C at
sixty rpm).
The results in terms of UL viscosity are the following:
Table of Example 1:
Test MBA NaHZPO2 UL IR (1) IVR (2) State
ppm ppm Viscosity ( s) (%)
(*)
EM 140 CT 0 10 4.56 0 0 Linear
PF 455 B 10 0 1.80 80 100 Cross-
linked
"HYDROCOL" --- --- 4.10 0 0 Linear
(TM)
CD3 (TM)
(*) sodium hypophosphite, transfer agent
(1) . ionic regain IR in %
CA 02334744 2005-02-25
(2) . intrinsic viscosity regain IVR in %
EM140CT: standard emulsion of very high molecular weight,
containing no cross linker
5 It is noted that the linear products do not develop any
ionic regain RI with shearing, and their intrinsic viscosity IV
decreases (two of the IVR values are null).
The cross-linked product develops a high ionic regain and a
very high IV regain.
Definitions of the ionic regains and intrinsic viscosity regains:
Ionic regain IR - (X-Y)/Y x 100
with X ionicity after shearing in meq/g.
Y , ionicity before shearing in meq/g.
Intrinsic viscosity regain IVR= (Vl-V2)/V2 x 100
with V1 . intrinsic viscosity after shearing in dl/g
V2 intrinsic viscosity before shearing in dl/g
Some of the emulsions cited above will be the subjects of a
study of effectiveness in retention and drainage in an automated
sheet former at the Center for Paper Technology.
Procedure for testina the emulsions
Pulp used-
mixture of 70% bleached hardwood kraft KF
10% bleached softwood kraft KR
20% mechanical pulp PM
20% natural calcium carbonate.
Sizing in a neutral medium with 2% of an alkyl ketene
dimer emulsion.
i
CA 02334744 2005-02-25
21
The pulp used is diluted to a consistency of 1.5%. A sample
of 2.24 dry g of pulp, or 149 g of pulp at 150%, is taken, then
diluted to 0.4% with clear water.
The 560 ml volume is introduced into the plexiglass cylinder
of the (standard) automated sheet former, and the sequence is
begun in accordance with the two procedures A and B.
Procedure A:
(intense shearing of the pulp at 150 rpm for 50 seconds)
- t = 0 s, start of agitation at 1500 rpm (intense shearing).
- t = 10 s, addition of the polymer (in the sheared state
according to the invention when a cross-linked
product is used).
- t = 60 s, automatic reduction to 1000 rpm and, if necessary,
addition of the bentonite.
- t = 75 s, stopping of the agitation, formation of the sheet
with vacuum under the wire, followed by
reclamation of the white water.
Procedure B:
(simple turbulence of the pulp for 10 seconds)
- t = 0 s, start of agitation, imposed at 800 rpm (no intense
shearing).
- t = 10 s, addition of the polymer (in the sheared state
according to the invention when a cross-linked
product is used).
- t = 20 s, addition of bentonite, if necessary, still at 800
rpm.
- t = 30 s, stopping of the agitation, formation of the sheet
with vacuum under the wire, followed by
reclamation of the white water.
The following operations are then carried out:
CA 02334744 2005-02-25
22
- measurement of the turbidity of the water under the wire.
- dilution of a beaker of thick stock for a new sheet with the
reclaimed water under the wire.
- drying of the so-called lst pass sheet.
- start of a new sequence for producing the so-called 2nd pass
sheet.
After 3 passes, the products to be tested are changed.
The following analyses are then performed:
- measurement of the matter in suspension in the water under the
wire (TAPPI standard T 656 cm/83)
- measurement of the ash in the sheets (TAPPI standard: T 211 om-
93)
- measurement of turbidity 30' after the fibers are deposited in
order to learn the state of neutralization of the colloidal
matter.
- measurement of the degree of drainability of the pulp with a
Canadian Standard Freeness (CSF; TAPPI standard T 227 om - 94).
Comments on the results: see the comparative Table (I) below
relative to Example 1
In Table (I), tests were conducted on various products in
accordance with the two procedures (A) and (B).
Example 3 corresponds to a linear polymer similar to the
"HYDROCOL" (TM) technique of the above-mentioned US patent '710
(a linear polymer). The results are therefore similar to test 7,
which corresponds to the technique of US patent '710. likewise,
tests 2 and 6 are comparable (a linear polymer, but without
bentonite).
An examination of tests 3, 7 and 2, 6 confirms that
bentonite provides advantageous performance levels.
CA 02334744 2005-02-25
23
Test 5 corresponds to a cross-linked polymer emulsion,
sheared before injection into the pulp, and hence according to
the invention, which leads to a extremely advantageous
performance in terms of drainage (CSF Canadian Standard Freeness)
while having excellent formation (an index of 1 as opposed to 2
for the other comparable tests).
This is quite surprising, since one skilled in the art knows
that when drainage is successfully increased, formation is
affected negatively. According to the invention, on the other
hand, the formation is not affected.
Moreover, the clarity of the water under the wire is
distinctly improved -- note the very low turbidity of 122 as
opposed to 134-159 ("HYDROCOL" (TM)).
Thus, surprisingly, the use of a cross-linked (rather than
linear) polymer, sheared before its injection, results in a
distinct improvement in comparison with the "HYDROCOL" (TM)
system, while freeing the paper manufacturer from the constraint
of shearing the pulp between the two additions of polymer and of
bentonite.
Tests 8 through 13 verified the effect obtained when
attempting to eliminate the shearing of the pulp between the two
additions, in contrast to US patent '710. It may be seen that, in
a "HYDROCOL" (TM) context, it is important to shear the pulp. In
effect, it is possible to obtain a very high flocculation if the
pulp is not sheared, but the formation suffers (indexes of 4 or
5), making it unusable.
If test 5 (A) (shearing of the pulp) is compared to test
11(B) (same test without shearing of the pulp), it may be seen
that the invention (11) improves the drainage properties and
provides good turbidity, while the formation remains excellent
CA 02334744 2005-02-25
24
(an index of 2 rather than 1).
Lastly, if test 11 (the invention, strongly cross-linked) is
compared to test 7 ("HYDROCOL" (TM), linear) it may be seen that
the process according to the invention distinctly improves
drainage (512 vs. 458), or +34%, with equal formation (an index
of 2) -- which is completely surprising, since this formation
would have been expected to decrease sharply -- improves
turbidity (104 vs. 175) and improves filler retention (% ash X=
% ash in the first pass) (100 vs. 90.4).
EXAMPLE 2
Production of a cross-linked ethyl acrylate trimethyl ammonium
chloride-based in the form of an emulsion of the EM 240 BD tyue:
In a reactor A, the constituents of the organic phase of the
emulsion to be synthesized are mixed at the ambient temperature.
a) Organic phase:
- 266 g of "Exxsol D 100" (TM)
- 18 g of "Span 80" (TM)
- 6 g of "Hypermer 2296" (TM)
b) In a beaker B, the phase of the emulsion to be produced is
prepared by mixing:
- 438 g of acrylamide at 50%
- 186.5 g of ethyl acrylate trimethyl ammonium chloride (80%)
- 85 g of water
- 0.31 ml of methylenebisacrylamide at 6 g/1
- 1.50 ml of sodium bromate at 50 g/1
- 0.24 ml of Versenex at 200 g/l
- pH: 4
The contents of B are mixed into A under agitation. After
CA 02334744 2005-02-25
the mixture of the phases, the emulsion is sheared in the mixer
for 1 minute in order to create the reverse phase emulsion.
The emulsion is then degassed by means of a nitrogen
5 bubbling; then after 20 minutes, the gradual addition of the
metabisulfite causes the initiation followed by the
polymerization.
Once the reaction is finished, a "burn" out is performed in
10 order to reduce the free monomer content.
The emulsion is then incorporated with its inverting
surfactant in order to release the polymer in the aqueous phase.
15 Table of Example 2:
Test MBA NaH2PO2 UL IR (1) IVR (2) State
ppm ppm (*) Viscosity (%) ( o)
EM 240 CT 0 10 4.20 0 0 Linear
EM 240 BD 10 0 1.6 58 55 Cross-
linked
Procedure for testing the emulsions
(procedure identical to that of Example 1)
Comments on the results: see the comparative table (II) below
relative to Example 2
Example 2 leads to the same types of conclusions as Example
1.
According to the invention, the formation is maintained at
an excellent level of 2. The drainage, filler retention and
first pass retention are improved considerably.
CA 02334744 2005-02-25
26
If the series A and series B tests on a linear product of
the "HYDROCOL" (TM) type with bentonite (15) are compared, it may
be seen that without a shearing of the pulp, the formation drops
from 2 to a disastrous value of 5; on the other hand, with a
shearing of the pulp, the formation remains at the index 2.
Consequently, for a linear product comparable to the "HYDROCOL"
(TM) type, the shearing of the pulp is essential.
On the other hand, with a cross-linked product according to
the invention, if the tests 17 and 21 are compared, it may be
seen that, without a shearing of the pulp, the drainage is
improved, and moreover, the filler retention on the wire (% ash)
and the first pass retention (o Ret. X) are maintained. With a
shearing of the pulp, the drainage (CSF) is admittedly slightly
diminished, as are the retention and the turbidity, but the
formation remains at a very good level (index 2). According to
the invention, it is therefore entirely preferable not to shear
the pulp between the addition of the sheared cross-linked polymer
and the addition of the bentonite, but an intercalary shearing
still results in a good combination of properties.
The invention is therefore compatible with all the existing
papermaking equipment, including the equipment in which the
injection point of the polymer cannot be chosen freely.
Moreover, the invention provides another important advantage
relative to a very good formation of the sheet. As is known,
formation indicates qualities of the sheet such as homogeneity
and the like.
This advantage is attributable to the microflocculation
produced by the agents sheared according to the invention.
EXAMPLE 3
Production of a polymer in the form of a redissolved powder (SD
455 B .
CA 021334744 2005-02-25
27
Example 1 is repeated in order to prepare the product PF 455
G in reverse phase emulsion.
This reverse phase emulsion is dried by means of a known
spray drying technique; a white powder is obtained which is
redissolved in water, to 5 g of polymer per liter.
This solution is then sheared in the "Ultra Turrax" (TM) as
described above, under the same conditions as for the shearing of
the reverse phase emulsion PF 455 B in Example 1 (inverted in
water before shearing, of course).
Table of Example 3:
Test MBA NaH2PO2 UL IR (1) IVR (2) State
ppm ppm (*) Viscosity (%) (%)
EM140 CT 0 10 4.56 0 0 Linear
PF 455 B 10 0 1.80 80 100 Cross-
linked
SD 455 B 10 0 1.85 85 100 Cross-
linked
SD 455 B = a solution of the powder obtained by drying the
reverse phase emulsion PF 455 B.
EM140CT = a standard emulsion of very high molecular weight,
containing no cross linker.
Comments on the results see the comparative Table (III) relative
to Example 3.
An examination of Table (III) shows that the solution
sheared before injection, SD 455 B, obtained by dissolution in
water of 5 g of polymer/liter of the powder obtained by spray
drying the emulsion PF 455 G, behaves substantially like the
sheared emulsion itself.
The invention also relates to the novel retention aids
CA 02334744 2005-02-25
28
described above, which consist of or comprise a sheared cross-
linked polyacrylamide (or more generally a cross-linked acrylic
(co)polymer) in reverse phase (or water-in-oil) emulsion
(inverted in water), or in the form of the sheared solution of
the powder obtained by drying said emulsion, as well as the
processes for producing sheets of paper, paperboard or the like
that use the agents according to the invention or the process
according to the invention described above, and the sheets thus
obtained.
.$
