Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02881868 2015-02-12
Production of paper, card and board
Description
The present invention relates to a process for production of paper, card and
board
comprising draining a filler-containing paper stock comprising at least one
water-soluble
polymer obtainable by Hofmann degradation of an acrylamide- and/or
methacrylamide-
containing polymer with sheet formation in the wire section and then pressing
the paper in
the press section.
The development of novel processes for production of paper takes place at
various points in
the process. Improved papers are obtained through novel feedstocks or else
modified dosing
processes. But faster and faster papermachines also impose novel requirements
on the
production process.
Initial wet web strength is one limiting factor on the way to any further
increase in
papermachine speed. Initial wet web strength limits the maximum force which
can be exerted
on a sheet which has just been formed in the papermachine, has traveled
through the wire
and press sections of the machine and passed into the dryer section. In the
process, the
sheet has to be pulled off from the press rolls. To be able to ensure
papermachine operation
without broken ends, the pull-off force applied at this point has to be
distinctly less than the
initial wet web strength of the moist paper. Increased initial wet web
strength permits
application of higher pull-off forces and hence faster papermachine operation,
cf. EP-B-0 780
513.
Initial wet web strength is the strength of a never-dried paper. It is the
strength of a wet as-
produced paper after passing through the wire and press sections of the
papermachine.
In the press section, the moist fibrous web is couched by a suction pickup
roll or static
underpressure element onto the press felt. The office of the press felt is to
transport the
fibrous web through press nips in various modified forms. The dry matter
content of the web
is up to not more than 55%, depending on the design of the press section and
the
composition of the paper stock. The dry matter content increases with the
pressure exerted
in the press on the passing paper web. The pressure and hence the dry matter
content of the
paper web can be varied within relatively wide limits in many papermachines.
It is known that initial wet web strength can be increased by increasing the
solids content of
the paper at the point between the press section and the dryer section in the
production
1
process. It is also possible to improve the solids content at this paint in
the process via additives
for increasing drainage. But there are limits to this.
WO 2009/156274 teaches the use of amphoteric copolymers obtainable by
copolymerization of
N-vinylcarboxamide with anionic comonomers and Subsequent hydrolysis of the
vinylcarboxamide as a paper stock additive for enhancing the initial wet web
strength of paper.
The treatment takes place at the thick stuff stage or at the thin stuff stage
in the paper
production process for example.
Prior European Patent Publication EP 11170740 teaches the use of amphoteric
copolymers
based on acrylamide which are obtainable by copolymerization of acrylamide
with anionic
comonomers,, as paper stock additive for enhancing the initial wet web
strength of paper. The
treatment takes place at the thick stuff stage in the paper production
process. It is additionally
necessary for the press section of the papermachine to be adjusted such that
the dry matter
content of the wet paper web leaving the press section exceeds the minimum
value that
depends on the stock composition.
It is further known for example to use polymers obtained by Hofmann
degradation of an
acrylamide- and/or methacrylamide-containing polymer for, strength
enhancement.
It is an object of the present invention to enhance the initial wet web
strength of as-produced
paper prior to transitioning into the dryer section in order to achieve higher
machine speeds in
the paper production process compared with existing processes.
We have found that this object is achieved by a process for production of
paper, card and board
comprising draining a filler-containing paper stock comprising at least one
water-soluble
polymer with sheet formation in the wire section and then pressing the paper
in the press
section, wherein a paper stock having a fibrous concentration in the range
from 20 to 40 g/I has
the at least one water-soluble polymer added to it, then the paper stock is
diluted to a fibrous
concentration in the range from 5 to 15 g/I, the diluted paper stock is
drained to form a sheet
and the sheet is pressed in the press section to a solids content G(x) wt% or
greater and G(x)
computes according to
G(x) = 48 + (x - 15) = 0.4
where xis the numerical value of the filler content of the dry paper, card or
board (in Wt%) and
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CA 02881868 2015-02-12
G(x) is the numerical value of the minimum solids content (in wt%) to which
the sheet is
pressed,
wherein the water-soluble polymer is obtainable by Hofmann degradation of an
acrylamide-
and/or methacrylamide-containing polymer with or without subsequent
postcrosslinking.
The present invention further provides a process for production of paper, card
and board
comprising draining a filler-containing paper stock comprising at least one
water-soluble
polymer with sheet formation in the wire section and then pressing the paper
in the press
section, wherein a paper stock having a fibrous concentration in the range
from 20 to 40 g/I
has the at least one water-soluble polymer added to it, then the paper stock
is diluted to a
fibrous concentration in the range from 5 to 15 g/I, the diluted paper stock
is drained to form
a sheet and the sheet is pressed in the press section to a solids content 48
wt%, wherein
the water-soluble polymer is obtainable by Hofmann degradation of an
acrylamide- and/or
methacrylamide-containing polymer and subsequent postcrosslinking.
Paper stock is hereinbelow to be understood as referring to a mixture of water
and fibrous
material and further comprising, depending on the stage in the paper, card or
board
production process, the water-soluble polymer, filler and optionally paper
auxiliaries.
The dry matter content of paper is to be understood as meaning the solids
content of paper,
card, board and fibrous material as determined using the oven-drying method of
DIN EN ISO 638 DE.
The term pigment herein is used in the same meaning as the term filler, since
pigments are
used as fillers in the production of paper. Filler, as is customary in paper
production, is to be
understood as meaning inorganic pigment.
The process of the present invention is used in the production of paper, card
and board
comprising draining a filler-containing paper stock. The filler content (x) of
the paper, card
and board can be in the range from 5 to 40 wt% based on the paper, card or
board.
One preferable embodiment gives preference to a process for production of
paper having a
filler content in the range from 20 to 30 wt%. Wood-free papers are papers of
this type for
example.
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CA 02881868 2015-02-12
A further preferable embodiment gives preference to a process for production
of paper
having a filler content in the range from 10 to 20 wt%. Papers of this type
are used as
packaging paper in particular.
A further preferable embodiment gives preference to a process for production
of paper
having a filler content in the range from 5 to 15 wt%. Papers of this type are
used as
newsprint in particular.
A further preferable embodiment gives preference to a process for production
of paper
having a filler content in the range from 25 to 40 wt%, for example SC papers.
The aqueous paper stock which, according to the present invention, comprises
at least a
water-soluble amphoteric polymer, fibrous material as well as filler is
drained in the wire
section to form a sheet and the sheet is pressed, i.e., further drained, in
the press section.
Press section drainage is to a minimum solids content, but can also extend
beyond that. This
lower limit to the solids content up to which pressing has to take place is
hereinafter also
referred to as limiting dry matter content or else as minimum solids content
G(x), and is
based on the pressed sheet, which is a mixture of paper stock and water. This
limiting dry
matter content up to which drainage is effected at a minimum is dependent on
filler quantity.
Hence the limiting dry matter content G(x) of a paper having a filler content
of 30 or 15 wt%
computes according to the formula
G(x) = 48 + (x - 15) = 0.4
as G(30) = 48 + (30 - 15) = 0.4 = 54
or, respectively, as G(15) = 48 + (15 - 15) = 0.4 = 48.
In other words, to produce paper having a filler content of 30 wt%, the
present invention
provides for pressing in the press section to a solids content of at least 54
wt% in order that
paper having good initial wet web strength may be obtained.
By contrast, to produce paper having a filler content of 15 wt% or less, the
present invention
provides for pressing in the press section to a solids content of at least 48
wt% in order that
paper having good initial wet web strength may be obtained.
One embodiment of the invention comprises pressing in the press section to at
least a solids
content in the range from 49 to 55 wt% to produce paper, card and board having
a filler
content of 17 to 32 wt%.
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Another embodiment of the invention comprises pressing in the press section to
at least a
solids content of 48 wt% to produce paper, card and board having a filler
content of 15 wt%
or less.
The fibers are treated according to the present invention by adding the water-
soluble polymer
to the paper stock at a fibrous concentration in the range from 20 to 40 g/I.
A fibrous
concentration of 20 to 40 g/I (corresponding to a fibrous concentration of 2
to 4 wt% based
on the aqueous fibrous material) is typically what the thick stuff in paper
production has.
Thick stuff is distinguished from thin stuff, hereinafter to be understood as
meaning a fibrous
concentration in the range from 5 to 15 g/I. Following the treatment with
water-soluble
polymer, the paper stock is diluted with water to a fibrous concentration in
the range from 5
to 15 g/I.
Virgin and/or recovered fibers can be used according to the present invention.
Any softwood
or hardwood fiber typically used in the paper industry can be used, examples
being
mechanical pulp, bleached and unbleached chemical pulp and also fibrous
materials from
any annual plants. Mechanical pulp includes for example groundwood,
thermomechanical
pulp (TMP), chemothermomechanical pulp (CIMP), pressure groundwood,
semichemical
pulp, high-yield pulp and refiner mechanical pulp (RMP). Sulfate, sulfite and
soda chemical
pulps can be used for example. Preference is given to using unbleached
chemical pulp, also
known as unbleached kraft pulp. Suitable annual plants for production of
fibrous materials
include for example rice, wheat, sugar cane and kenaf. Pulps can also be
produced using
wastepaper, used alone or in admixture with other fibrous materials. The
wastepaper can
come from a de-inking process for example. However, it is not necessary to
subject the
wastepaper to be used to such a process. It is further also possible to
proceed from fibrous
mixtures formed from a primary stock and recycled coated broke.
In the case of bleached or unbleached chemical pulp, a fibrous material having
a freeness of
20 to 30 SR can be used. The general rule is to use a fibrous material having
a freeness of
about 30 SR, which is beaten during pulp production. Preference is given to
using fibrous
material having a freeness of SR.
Treating the fibrous material with the water-soluble polymer is done in
aqueous suspension,
preferably in the absence of other process chemicals customarily used in paper
production.
The treatment is effected in the paper production process by adding at least
one water-
soluble polymer to an aqueous paper stock having a fibrous concentration of 20
to 40 g/I.
Particular preference is given to a version wherein a water-soluble polymer is
added to the
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CA 02881868 2015-02-12
aqueous paper stock at a time prior to adding the filler. It is very
particularly preferable for the
addition to take place after adding the dry strength enhancer starch for
example.
The water-soluble polymers are preferably added in an amount of 0.05 to 5.00
wt%, based
on fibrous material (solids).
Typical application rates are for example from 0.5 to 50 kg and preferably
from 0.6 to 10 kg
of at least one water-soluble polymer per metric ton of a dry fibrous
material. It is particularly
preferable for the amounts of water-soluble polymer which are used to be in
the range from
0.6 to 3 kg of polymer (solids), based per metric ton of dry fibrous material.
The time during which the water-soluble polymer acts on a purely fibrous/paper
stock
material from addition to sheet formation is for example in the range from 0.5
seconds to
2 hours, preferably in the range from 1.0 seconds to 15 minutes and more
preferably in the
range from 2 to 20 seconds.
In addition to the water-soluble polymer, inorganic pigment is added to the
fibrous material as
a filler. Useful inorganic pigments include any typical paper industry
pigments based on
metal oxides, silicates and/or carbonates, especially pigments from the group
consisting of
calcium carbonate, which can be used in the form of ground (GCC) lime, chalk,
marble or
precipitated calcium carbonate (PCC), talc, kaolin, bentonite, satin white,
calcium sulfate,
barium sulfate and titanium dioxide. Mixtures of two or more pigments can also
be used.
The present invention utilizes inorganic pigments having an average particle
size (volume
average) 5.10 pm, preferably in the range from 0.3 to 5 pm and especially in
the range from
0.5 to 2 pm. Average particle size (volume average) is generally determined
herein for the
inorganic pigments and also the particles of the pulverulent composition by
the method of
quasi-elastic light scattering (DIN-ISO 13320-1) using a Mastersizer 2000 from
Malvern
Instruments Ltd. for example.
The inorganic pigment is preferably added after the water-soluble copolymer
has been
added. In a preferable embodiment, the addition of the inorganic pigment takes
place at the
stage at which the fibrous material is already in the form of thin stuff,
i.e., at a fibrous
concentration of 5 to 15 g/I.
In a further preferable embodiment, the inorganic pigment is added to thick
stuff as well as
thin stuff, the ratio of the two additions (thick stuff addition/thin stuff
addition) preferably being
in the range from 5/1 to 1/5.
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In addition to the water-soluble polymer, customary paper auxiliaries may
optionally be
added to the paper stock, generally at a fibrous concentration of 5 to 15 g/I.
Conventional
paper auxiliaries include for example sizing agents, wet strength agents,
cationic or anionic
retention aids based on synthetic polymers and also dual systems, drainage
aids, other dry
strength enhancers, optical brighteners, defoamers, biocides and paper dyes.
These
conventional paper additives can be used in the customary amounts.
Useful sizing agents include alkyl ketene dimers (AKDs), alkenylsuccinic
anhydrides (ASAs)
and rosin size.
Useful retention aids include for example anionic microparticles (colloidal
silica, bentonite),
anionic polyacrylamides, cationic polyacrylamides, cationic starch, cationic
polyethyleneimine
or cationic polyvinylamine. In addition, any desired combinations thereof are
conceivable, for
example dual systems consisting of a cationic polymer with an anionic
microparticle or an
anionic polymer with a cationic microparticle. To achieve high filler
retention, it is advisable to
add such retention aids as can be added for example to thin stuff as well as
to thick stuff.
Dry strength enhancers are synthetic dry strength enhancers such as
polyvinylamine,
polyethyleneimine, glyoxylated polyacrylamide (PAM), amphoteric
polyacrylamides or natural
dry strength enhancers such as starch.
In the papermachine, these dry matter contents are set during passage through
the press
section. In the press section, the moist fibrous web is couched by a suction
pickup roll or
static underpressure element onto the press felt. The office of the press felt
is to transport the
fibrous web through press nips in various modified forms. The dry matter
content of the web
is up to not more than 55%, depending on the design of the press section and
the
composition of the paper stock. The dry matter content increases with the
pressure exerted
in the press on the passing paper web. The pressure and hence the dry matter
content of the
paper web can be varied within relatively wide limits in many papermachines.
The water-soluble polymer used according to the present invention is
obtainable by Hofmann
degradation of an acrylamide- and/or methacrylamide-containing polymer with or
without
subsequent postcrosslinking.
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Prepolymer
These acrylamide- and/or methacrylamide-containing polymers, hereinafter also
referred to
as prepolymers, are obtainable by free-radically copolymerizing a monomer
mixture
comprising acrylamide and/or methacrylamide.
The acrylamide and methacrylamide monomers are present in polymerized form,
individually
or as a mixture, in proportions of 10 mol% to 100 mol%, preferably in
proportions of 20 to 90
mol% and more preferably in proportions of 30 to 80 mol%, based on the monomer
composition of the prepolymer.
The monomer mixture preferably has the following composition comprising:
a) acrylamide and/or methacrylamide (monomers a)
b) optionally one or more monoethylenically unsaturated monomers whose
corresponding
structural unit in the polymer is stable under the reaction conditions of
Hofmann
degradation, and/or DADMAC (diallyldimethylammonium chloride) (monomers b),
(c) optionally one or more compounds having two or more ethylenically
unsaturated
moieties, and whose corresponding structural units in the polymer are stable
under the
reaction conditions of Hofmann degradation, except DADMAC is not encompassed
(monomers c).
Examples of monoethylenically unsaturated monomers whose corresponding
structural units
in the polymer are stable under the reaction conditions of Hofmann degradation
are nitriles of
a,3-ethylenically unsaturated mono- and dicarboxylic acids, such as
acrylonitrile and
methacrylonitrile, amides of a,!3-ethylenically unsaturated monocarboxylic
acids and their N-
alkyl and N,N-dialkyl derivatives, N-vinyllactams, nitrogenous heterocycles,
vinylaromatics,
02-C8 monoolefins, a,3-ethylenically unsaturated mono- and dicarboxylic acids
and salts
thereof, anhydrides of a,3-ethylenically unsaturated and dicarboxylic acids,
ethylenically
unsaturated sulfonic acids and salts thereof, ethylenically unsaturated
phosphonic acids and
salts thereof.
Examples of representatives of this group (b) are for instance N-
methyl(meth)acrylamide, N-
ethyl(meth)acrylamide, n-propyl(meth)acrylamide, N-(n-butyl)(meth)acrylamide,
tert-
butyl(meth)acrylamide, n-octyl(meth)acrylamide, 1,1,3,3-
tetramethylbutyl(meth)acrylamide,
ethylhexyl(meth)acrylamide, N, N-dimethylacrylamide, N, N-
dimethylmethacrylamide, N-
vinylformamide, N-methyl-N-vinylacetamide and mixtures thereof. Useful
monomers (b)
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further include N[2-(dimethylamino)ethyl]acrylamide, N-[2-
(dimethylamino)ethyl]nethacrylamide, N-[3-(dimethylamino)propyl]acrylamide, N-
[3-
dimethylamino)propyl]methacrylamide, N-[4-(dimethylamino)butyl]acrylamide, N-
[4-
(dimethylamino)butylynethacrylamide, N[2-(diethylamino)ethyliacrylamide, N-[2-
(diethylamino)ethyl]nethacrylamide and mixtures thereof.
Useful monomers (b) further include N-vinyllactams and their derivatives,
which may include
one or more Cl-C6 alkyl substituents (as defined above) for example. These
include N-
vinylpyrrolidone, N-vinylpiperidone, N-vinylcaprolactam, N-vinyl-5-methyl-2-
pyrrolidone, N-
vinyl-5-ethyl-2-pyrrolidone, N-vinyl-6-methyl-2-piperidone, N-vinyl-6-ethyl-2-
piperidone, N-
viny1-7-methy1-2-caprolactam, N-vinyl-7-ethyl-2-caprolactam and mixtures
thereof.
Useful monomers (b) further include N-vinylimidazoles and
alkylvinylimidazoles, especially
methylvinylimidazoles such as for example 1-vinyl-2-methylimidazole, 3-
vinylimidazole N-
oxide, 2-vinylpyridine N-oxide, 4-vinylpyridine N-oxide and also betainic
derivatives and
quaternization products thereof.
Diallyldimethylammonium chloride (DADMAC) is also suitable.
Useful additional monomers further include ethylene, propylene, isobutylene,
butadiene,
styrene, a-methylstyrene, vinyl acetate, vinyl propionate, vinyl chloride,
vinylidene chloride,
vinyl fluoride, vinylidene fluoride and mixtures thereof.
Also suitable are monomers bearing at least one acid function, i.e., at least
one sulfonic acid
group, phosphonic acid group or carboxylic acid group. The salts of the
aforementioned
compounds are also suitable. Examples are:
vinylsulfonic acid, allylsulfonic acid, methallylsulfonic acid,
styrenesulfonic acid, acryl-
amidomethylenephosphonic acid, 2-acrylamido-2-methylpropanesulfonic acid,
vinyl-
phosphonic acid, CH2=CH-NH-CH2-P03H, monomethyl vinylphosphonate,
allylphosphonic
acid, monomethyl allylphosphonate, acrylamidomethylpropylphosphonic acid.
Also suitable are monoethylenically unsaturated carboxylic acids having 3 to 8
carbon atoms
and also the water-soluble salts such as alkali metal, alkaline earth metal or
ammonium salts
of these carboxylic acids and the monoethylenically unsaturated carboxylic
anhydrides. This
group of monomers includes for example acrylic acid, methacrylic acid,
dimethacrylic acid,
ethacrylic acid, a-chloroacrylic acid, maleic acid, maleic anhydride, fumaric
acid, itaconic
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acid, mesaconic acid, citraconic acid, glutaconic acid, aconitic acid,
methylenemalonic acid,
allylacetic acid, vinylacetic acid and crotonic acid.
Monomers bearing acid groups may be in unneutralized, partially neutralized or
completely
neutralized form, in which case phosphonic acids may have either or both of
the protons
neutralized by suitable bases.
Examples of suitable bases for partially or completely neutralizing the acid
groups of
monomers are alkali metal or alkaline earth metal bases, ammonia, amines
and/or
.. alkanolamines. Examples thereof are sodium hydroxide, potassium hydroxide,
sodium
carbonate, potassium carbonate, sodium bicarbonate, potassium bicarbonate,
magnesium
hydroxide, magnesium oxide, calcium hydroxide, calcium oxide, triethanolamine,
ethanolamine, morpholine.
The monomers of this group (b) can be used singly or mixed.
Examples of preferred monoethylenically unsaturated monomers whose
corresponding
structural units in the polymer are stable reaction conditions of Hofmann
degradation are
nitriles of 00-ethylenically unsaturated mono- and dicarboxylic acids, such as
acrylonitrile
and methacrylonitrile, amides of a,3-ethylenically unsaturated monocarboxylic
acids and their
N-alkyl and N,N-dialkyl derivatives, N-vinyllactams and DADMAC.
The prepolymers preferably comprise not less than 5 mol%, preferably not less
than
10 mol% and preferably not more than 90 mol%, more preferably not more than 70
mol%
and even more preferably not more than 50 mol% of one or more
monoethylenically
unsaturated monomers whose corresponding structural unit in the polymer is
stable under
the reaction conditions of Hofmann degradation (monomer(s) b) in polymerized
form, based
on the total number of moles of monomers (a and b).
In addition, the prepolymers may comprise up to 5 wt%, preferably up to 3 wt%,
more
preferably up to 1 wt% and even more preferably up to 1 wt% and not less than
0.0001 wt%,
especially not less than 0.001 wt% based on the total weight of monomers a and
b used for
the polymerization, of compounds having two or more ethylenically unsaturated
moieties
whose corresponding structural units in the polymer are stable under the
reaction conditions
of Hofmann degradation, in polymerized form, except DADMAC is not encompassed
(monomers c).
Such a modification of the prepolymers by copolymerizing compounds having two
or more
ethylenically unsaturated moieties whose corresponding structural units in the
polymer are
CA 02881868 2015-02-12
stable under the reaction conditions of Hofmann degradation is achieved with
methylenebisacrylamides, triallylamine, tetraallylammonium chloride or N,N1"-
divinylpropyleneurea for example.
It is particularly preferable for the monomer mixture used for preparing the
prepolymer to
have the following composition:
30 to 95 mol% of acrylamide and/or methacrylamide (monomers a),
and
5 to 70 mol% of one or more monoethylenically unsaturated monomers whose
corresponding structural unit in the polymer is stable under the
reaction conditions of Hofmann degradation, and/or
diallyldimethylammonium chloride (monomers b),
and also up to 1.0 wt%, based on the total weight of monomers a and b, of one
or more
compounds having two or more ethylenically unsaturated moieties whose
corresponding
structural units in the polymer are stable under the reaction conditions of
Hofmann
degradation.
In a further preferred embodiment, the monomer mixture used for preparing the
prepolymer
has the following composition:
50 to 90 mol% of acrylamide and/or methacrylamide, and
10 to 50 mol% of one or more monoethylenically unsaturated monomers whose
corresponding structural unit in the polymer is stable under the
reaction conditions of Hofmann degradation, and/or
diallyldimethylammonium chloride (monomers b)
and also up to 1.0 wt%, based on the total weight of monomers a and b, of one
or more
compounds having two or more ethylenically unsaturated moieties whose
corresponding
structural units in the polymer are stable under the reaction conditions of
Hofmann
degradation.
Preference for preparing the prepolymer is given to a monomer mixture of the
following
composition in particular:
60 to 80 mol% of acrylamide and/or methacrylamide (monomer a)
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20 to 40 mol% of diallyldimethylammonium chloride (monomer b)
and also optionally from 0.001 to 0.1 wt%, based on the total amount of
monomer a and
monomer b, of one or more compounds selected from methylenebisacrylamides,
triallylamine, tetraallylammonium chloride, N,1\1"-divinylpropyleneurea.
The prepolymers can be prepared by solution, precipitation, suspension, gel or
emulsion
polymerization. Solution polymerization in aqueous media is preferable. Useful
aqueous
media include water and mixtures of water and at least one water-miscible
solvent, for
example an alcohol, such as methanol, ethanol, n-propanol, isopropanol, etc.
Polymerization temperatures are preferably in a range from about 30 to 200 C
and more
preferably from 40 to 110 C. The polymerization customarily takes place under
atmospheric
pressure, but it can also be carried out under reduced or superatmospheric
pressure. A
suitable pressure range extends from 0.1 to 10 bar.
The acid group-functional monomers (b) are preferably used in salt form.
To prepare the polymers, the monomers can be polymerized using initiators
capable of
forming free radicals.
Useful initiators for free-radical polymerization include the customary peroxo
and/or azo
compounds for this purpose, for example alkali metal or ammonium
peroxydisulfates,
diacetyl peroxide, dibenzoyl,peroxide, succinyl peroxide, di-tert-butyl
peroxide, tert-butyl
perbenzoate, tert-butyl perpivalate, tert-butyl peroxy-2-ethylhexanoate, tert-
butyl permaleate,
cumene hydroperoxide, diisopropyl peroxydicarbamate, bis(o-toluoyl) peroxide,
didecanoyl
peroxide, dioctanoyl peroxide, dilauroyl peroxide, tert-butyl perisobutyrate,
tert-butyl
peracetate, di-tert-amyl peroxide, tert-butyl hydroperoxide,
azobisisobutyronitrile, azobis(2-
amidonopropane) dihydrochloride or 2-2'-azobis(2-methylbutyronitrile). Also
suitable are
initiator mixtures or redox initiator systems, for example ascorbic
acid/iron(II) sulfate/sodium
peroxodisulfate, tert-butyl hydroperoxide/sodium disulfite, tert-butyl
hydroperoxide/sodium
hydroxymethanesulfinate, H202/Cul.
The polymerization can be carried out in the presence of at least one chain
transfer agent to
control the molecular weight. Useful chain transfer agents include the
customary compounds
known to a person skilled in the art, e.g., sulfur compounds, e.g.,
mercaptoethanol, 2-
ethylhexyl thioglycolate, thioglycolic acid, sodium hypophosphite, formic acid
or dodecyl
12
=
mercaptan and also tribromochloromethane or other compounds that have a
controlling effect
on the molecular weight of the polymers obtained.
The molar mass of the water-soluble prepolymer is for example at least 50 000
and 'preferably
at least 100 000 daltons and more particularly at least 500 000 daltons.:The
molar masses Of
_ the prepolymer are then for example in the range from 50 000 to 10
million and preferably in the
range from 100 000 to 5 million (determined by light scattering for example).
This molar mass
range corresponds for example to K values of 50 to 300 and preferably from 70
to 250
(determined by the method of H. Fikentscher in 5% aqueous sodium chloride
solution at 25 C
and a polymer concentration of 0.1 wt%).
=
Hofmann degradation
Hofmann degradation (also known as Hofmann rearrangement) is understood by a
person
skilled in the_art to refer to the degradation of primary amides to amines
with the loss of one
carbon atom (Rompp Online, Version 3.12). In Hofmann degradation, the amide
groups of the
prepolymer are reacted with hypohalides under alkaline conditions and then the
resulting
carbamates are decarboxylated by acidification to obtain amino groups.
Na0C1 NaOH
.4"n
HN/o _______________________________________________ 0-
H211 0 IN 0 -
= -`
cr
=
I
CI CI
NaOH HCI
HN
-CO2 NH2
0 0_
Polymers of this type are known from EP-A-0 377 313 and WO-A-2006/075115 for
example.
The preparation of polymers comprising vinylamine groups is exhaustively
discussed for
= example in WO-A-2006/075115, page 4, line 25 to page 10, line 22 and also
in the examples on
= pages 13 and 14. .
Hofmann degradation is preferably carried out in aqueous solution. From 0.1 to
2.0, preferably =
from 0.8 to 1.1 and more preferably 1.0 mol equivalent of hypohalide is used
per mole
equivalent of amide group. The strong base is used in amounts of 1.0 to 4.0
mol
. 13
CA 2881868 2020-02-06 =
CA 02881868 2015-02-12
equivalents per mole equivalent of amide group, preferably from 1.5 to 3.0 mol
equivalents
and more preferably from 2.0 to 2.5 mol equivalents.
Sodium hypochloride (Na0C1) and sodium hypobromide (Na0Br) are examples of
hypohalogenides used, with Na0Clbeing preferred. Alkali metal hydroxides,
alkaline earth
metal hydroxides and alkaline earth metal oxides are used as strong base.
Hofmann degradation of the polymer is carried out, for example, in the
temperature range
from -15 to 90 C, preferably from -5 to 40 C, in the presence or absence of
quaternary
ammonium salts as a stabilizer to prevent any secondary reaction of the
resulting amino
groups with the amide groups of the starting polymer. On completion of the
reaction with
alkaline base/alkali metal hypochlorite, the aqueous reaction solution is
introduced into a
reactor containing an initially charged acid for decarboxylating the reaction
product. The pH
of the reaction product comprising vinylamine units is adjusted to a value in
the range from 2
to 7.
The water-soluble polymer obtained by Hofmann degradation of an acrylamide-
and/or
methacrylamide-containing polymer can be used in the process of the present
invention.
In a further version, the polymer obtained by Hofmann degradation of an
acrylamide- and/or
methacrylamide-containing polymer is additionally postcrosslinked.
Postcrosslinking
To raise the molecular weight of the Hofmann-degraded polymer and to obtain
branched
polymeric structures, the Hofmann-degraded polymer can additionally be reacted
with
crosslinkers. Crosslinkers in this context are compounds that bear two or more
reactive
groups capable of reacting with the primary amino groups of the Hofmann
product.
Examples of useful crosslinkers include multifunctional epoxides such as
bisglycidyl ethers of
oligo- or polyethylene oxides or other multifunctional alcohols such as
glycerol or sugars,
multifunctional carboxylic esters, multifunctional isocyanates,
multifunctional acrylic or
methacrylic esters, multifunctional acrylic or methacrylic amides,
epichlorohydrin,
multifunctional acyl halides, multifunctional nitriles, a,w-chlorohydrin
ethers of oligo- or
polyethylene oxides or of other multifunctional alcohols such as glycerol or
sugars, divinyl
sulfone, maleic anhydride or w-halocarbonyl chlorides, multifunctional
haloalkanes,
especially a,w-dichloroalkanes and carbonates such as ethylene carbonate or
propylene
carbonate. Further crosslinkers are described in WO-A-97/25367, pages 8 to16.
14
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Preference for use as crosslinkers is given to multifunctional epoxides such
as bisglycidyl
ethers of oligo- or polyethylene oxides or of other multifunctional alcohols
such as glycerol or
sugars.
The crosslinkers are optionally used in amounts up to 5.0 wt% preferably 20
ppm to 2 wt%
based on the polymer obtained by Hofmann degradation.
The process of the present invention provides for papermachine operation with
fewer broken
ends. Paper formed in the process exhibits distinctly enhanced initial wet web
strength.
The examples which follow illustrate the invention. Percentages reported in
the examples are
by weight, unless otherwise stated.
Examples
The polymers are prepared in three consecutive steps:
a) preparing the prepolymer
b) Hofmann degrading the prepolymer
and optionally postcrosslinking.
Preparation of polymer I
a) preparing prepolymer I (70 mol% of acrylamide and 30 mol% of DADMAC
(diallyldimethylammonium chloride) - unbranched)
A 2 I glass apparatus equipped with an anchor stirrer, a reflux condenser, an
internal
thermometer and a nitrogen inlet tube was initially charged with 295.5 g of
distilled water,
189.6 g of a 65 wt% aqueous solution of DADMAC and 1.0 g of 75 wt% phosphoric
acid. The
pH was adjusted to 3 by adding 0.4 g of sodium hydroxide. Nitrogen was
introduced to
remove oxygen from the initial charge while the initial charge was heated to
the
polymerization temperature of 75 C. At the same time, the following feeds were
prepared:
Feed 1: mixture of 253.0 g of a 50 wt% acrylamide solution, 60.0 g
of distilled water
and 0.9 g of sodium hydroxide
CA 02881868 2015-02-12
Feed 2: 100 g of a 0.6% wt% aqeuous bisulfite solution
Feed 3: 100 g of a 0.88 wt% aqueous sodium persulfate solution
The three feeds were started at the same time. Feed 1 was added over a period
of 2 hours,
while feeds 2 and 3 were added over 5 hours. Thereafter, the temperature of
the mixture was
raised to 85 C. On completion of the addition of feeds 2 and 3 the batch was
maintained at
85 C for a further hour before being cooled down.
The prepolymer was obtained as a clear, viscous solution having a solids
content of 25.6
wt% and a viscosity of 50 000 mPas (Brookfield LV viscosity, spindle 4, 6 rpm,
RT).
b) Hofmann degrading the prepolymer
250.0 g of prepolymer I, obtained by a), were initially charged to a three-
neck flask equipped
with an internal thermometer and a blade stirrer and were cooled down to 8 C
with an
ice/sodium chloride mixture under constant agitation.
The following feed was prepared: 234.5 g of a 14.1 wt% aqueous Na0Clsolution
and 20.5 g
of distilled water were initially charged to a glass beaker and cooled down to
5 C with an ice
bath. Under constant agitation, 71.1 g of a 50 wt% aqueous sodium hydroxide
solution were
added dropwise such that the temperature could be maintained below 10 C.
This feed was added dropwise to the cooled initial prepolymer charge from a
cooled dropping
funnel (<10 C) in 80 minutes such that the temperature was maintained in the
range 8-10 C
during the addition. Thereafter, the reaction mixture was warmed to 20 C
within 10 minutes
and maintained at 20 C for 30 minutes. Thereafter, 558.1 g of this mixture
were added
dropwise to 135 g of 37% hydrochloric acid under constant agitation and with
vigorous
evolution of gas.
Finally, the pH of the solution obtained was adjusted to pH 3.5 with 10.0 g of
25 wt%
aqueous sodium hydroxide solution.
Polymer I was obtained as a clear, slightly viscous solution having a polymer
content of 8.6
wt% and a viscosity of 39 mPas (Brookfield LV viscosity, spindle 1, 60 rpm,
RT).
Preparation of polymer II (postcrosslinked)
309.8 g of polymer I were initially charged to a 500 ml three-neck flask
equipped with a blade
stirrer and were adjusted to pH 8.5 by adding 6.8 g of 50 wt% aqueous sodium
hydroxide
16
CA 02881868 2015-02-12
solution. Thereafter, the mixture was heated to 45 C and admixed with 0.9 g of
Grillbond G
1701 (from EMS). After 30 minutes' stirring at 45 C, the temperature was
raised to 55 C and
the batch was maintained at 55 C for 2 hours. During this period, the
viscosity was observed
to increase. After 2 hours, the batch was cooled down to room temperature, and
adjusted to
pH 3.0 by adding 8.0 g of 37% hydrochloric acid.
Polymer II was obtained as a clear, slightly viscous solution having a polymer
content of 8.2
wt% and a viscosity of 190 mPas (Brookfield LV viscosity, spindle 2, 60 rpm,
RT).
.. Preparation of polymer Ill
a) preparing prepolymer III (70 moN/0 of acrylamide and 30 mol% of DADMAC,
triallylamine
as monomer c)
A 2 I glass apparatus equipped with an anchor stirrer, a reflux condenser, an
internal
thermometer and a nitrogen inlet tube was initially charged with 155.8 g of
distilled water,
189.6 g of a 65 wt% aqueous solution of DADMAC and 1.0 g of 75 wt% phosphoric
acid. The
pH was adjusted to 3 by adding 0.4 g of sodium hydroxide. Nitrogen was
introduced to
remove oxygen from the initial charge while the initial charge was heated to
the
polymerization temperature of 75 C.
The following feeds were provided:
Feed 1: 0.5 g of triallylamine was dissolved in 160.0 g of distilled
water by addition
of 0.75 g of 75 wt% phosphoric acid. Thereafter, 253.0 g of a 50 wt%
acrylamide solution were added and the pH was adjusted to 4.0 with 0.4 g
of 25 wt% aqueous sodium hydroxide solution.
Feed 2: 120 g of a 0.6% wt% aqueous bisulfite solution
Feed 3: 120.6 g of a 0.88 wt% aqueous sodium persulfate solution
The 3 feeds were started at the same time. Feed 1 was added over a period of 3
hours, while
feeds 2 and 3 were run in over 6 hours. On completion of the addition of feed
2, the
temperature was raised to 85 C and the batch was maintained at 85 C for a
further hour
before being cooled down.
The prepolymer was obtained as a clear, viscous solution having a solids
content of 25.5
wt% and a viscosity of 15 800 mPas (Brookfield LV viscosity, spindle 4, 6 rpm,
RT).
17
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b) Hofmann degrading the prepolymer III
250.0 g of prepolymer III, obtained by a), were initially charged to a three-
neck flask
equipped with an internal thermometer and a blade stirrer and were cooled down
to 8 C with
an ice/sodium chloride mixture under constant agitation.
The following feed was prepared: 234.5 g of a 14.1 wt% aqueous Na0Clsolution
and 20.5 g
of distilled water were initially charged to a glass beaker and cooled down to
5 C with an ice
bath. Under constant agitation, 71.1 g of a 50 wt% aqueous sodium hydroxide
solution were
added dropwise such that the temperature could be maintained <10 C.
This feed was added dropwise to the initial charge from a cooled dropping
funnel (<10 C) in
80 minutes such that the temperature was maintained in the range 8-10 C during
the
addition. Thereafter, the reaction mixture was warmed to 20 C within 10
minutes and
maintained at 20 C for 60 minutes. Thereafter, 566.2 g of this mixture were
added dropwise
to 135 g of 37% hydrochloric acid under constant agitation and with vigorous
evolution of
gas.
Finally, the pH of the solution obtained was adjusted to pH 3.5 with 12.2 g of
25 wt%
aqueous sodium hydroxide solution.
Polymer III was obtained as a clear, slightly viscous solution having a
polymer content of 8.6
wt% and a viscosity of 23 mPas (Brookfield LV viscosity, spindle 1, 60 rpm,
RT).
Polymer IV (postcrosslinked)
301.8 g of polymer III were initially charged to a 500 ml three-neck flask
equipped with a
blade stirrer and were adjusted to pH 8.5 by adding 6.2 g of 50 wt% aqueous
sodium
hydroxide solution. Thereafter, the mixture was heated to 45 C and admixed
with 0.43 g of
Grillbond G 1701 (from EMS). After 30 minutes' stirring at 45 C, the
temperature was raised
to 55 C and the batch was maintained at 55 C for 3 hours. During this period,
the viscosity
was observed to increase. After 3 hours, the batch was cooled down to room
temperature,
and adjusted to pH 3.0 by adding 7.4 g of 37% hydrochloric acid.
Polymer IV was obtained as a clear, slightly viscous solution having a polymer
content of
8.2% and a viscosity of 419 mPas (Brookfield LV viscosity, spindle 2, 60 rpm,
RT).
Preparation of polymer V
a) preparing prepolymer V (70 mol% of acrylamide and 30 mol /0 of DADMAC,
triallylamine
as monomer c)
18
CA 02881868 2015-02-12
A 2 I glass apparatus equipped with an anchor stirrer, a reflux condenser, an
internal
thermometer and a nitrogen inlet tube was initially charged with 155.8 g of
distilled water,
189.6 g of a 65 wt% aqueous solution of DADMAC and 1.0 g of 75 wt% phosphoric
acid. The
pH was adjusted to 3 by adding 0.4 g of NaOH. Nitrogen was introduced to
remove oxygen
from the initial charge while the initial charge was heated to the
polymerization temperature
of 75 C. At the same time the following feeds were prepared:
Feed 1: 0.25 g of triallylamine was dissolved in 160.0 g of
distilled water by addition
of 0.75 g of 75 wt% phosphoric acid. Thereafter, 253.0 g of a 50 wt%
acrylamide solution were added and the pH was adjusted to 4.0 with 0.6 g
of 25 wt% aqueous sodium hydroxide solution.
Feed 2: 120 g of a 0.6% wt% aqeuous bisulfite solution
Feed 3: 120.6 g of a 0.88 wt% aqueous sodium persulfate solution
The 3 feeds were started at the same time. Feed 1 was added over a period of 3
hours, while
feeds 2 and 3 were run in over 6 hours. On completion of the addition of feed
2, the
temperature was raised to 85 C. On completion of the addition of feeds 2 and
3, the batch
was maintained at 85 C for a further hour before being cooled down.
The prepolymer was obtained as a clear, viscous solution having a solids
content of 25.5
wt% and a viscosity of 12 400 mPas (Brookfield LV viscosity, spindle 4, 6 rpm,
RT).
b) Hofmann degrading the prepolymer
250.0 g of prepolymer V, obtained by a), were initially charged to a three-
neck flask equipped
with an internal thermometer and a blade stirrer and were cooled down to 8 C
with an
ice/sodium chloride mixture under constant agitation.
At the same time the following feed stream was prepared:
234.5 of a 14.1 wt% aqueous Na0Clsolution and 20.5 g of distilled water were
initially
charged to a glass beaker and cooled down to 5 C with an ice bath. Under
constant
agitation, 71.1 g of a 50 wt% NaOH solution were added dropwise such that the
temperature
could be maintained <10 C.
This feed was added dropwise to the initial charge from a cooled dropping
funnel (<10 C) in
80 minutes such that the temperature was maintained in the range 8-10 C during
the
addition. Thereafter, the reaction mixture was warmed to 20 C within 10
minutes and
19
maintained at 20 C for 60 minutes. Thereafter, 566.2 g of this mixture were
added dropwise to
135 g of 37% hydrochloric acid under constant agitation and with vigorous
evolution of gas.
Finally, the pH of the solution obtained was adjusted to pH 3.5 with 16.0 g of
25 wt% aqueous
sodium hydroxide solution.
Polymer V was obtained as a clear, slightly viscous solution having a polymer
content of 8.5%
, and a viscosity of 22 mPas (Brookfield LV viscosity, spindle 1, 60
rpm, RT).
= Polymer VI (postcrosslinked)
314.4 g of polymer V were initially charged to a 500 ml three-neck flask
equipped with a blade
= stirrer and were adjusted to pH 8.5 by adding 6.4 g of 50 wt% aqueous
sodium hydroxide
solution. Thereafter, the mixture was heated to 45 C and admixed with 0.44 g
of Grillbond G
1701 (from EMS). After 30 minutes stirring at 45 C, the temperature was raised
to 55 C and the
batch was maintained at 55 C for 3 hours. During this period, the viscosity
was observed to
increase. After 3 hours, the batch was cooled down to room temperature, and
adjusted to pH
3.0 by adding 7.6 g 37% hydrochloric acid.
Polymer VI was obtained as a clear, slightly viscous solution having a polymer
content of 8.1%
and a viscosity of 190 mPas (Brookfield LV viscosity, spindle 2, 60 rpm, RT).
Polymer VII (85 mol% of acrylamide and 15 mol% of acrylic acid)
In accordance with JP63042998 (see table on page 624), the C-4 Hofmann product
was
emulated.
Polymer VIII (not in accordance with the present invention) (comparative
example corresponds
to polymer I from European Patent Publication EP 11170740).
A 2 I 5-neck flask equipped with an anchor stirrer, a thermometer, a
descending condenser and
= a nitrogen inlet tube was initially charged with 400 g of deionized
water. In addition, the following
feeds were provided: ,=
Feed 1: The following components, were mixed in a glass beaker:
250 g of deionized water
95.6 g of 50 wt% aqueous acrylamide, solution
121.9 g of 80 wt% aqueous solution of acryloyloxyethyltrimethylammonium
chloride =
148.1 g of 32 wt% aqueous sodium acrylate solution
0.2 g of 1 wt% aqueous solution of diethylenetriaminepentaacetic acid.
CA 2881868 2020-02-06
About 32 g of 37% hydrochloric acid were added to set pH 4.1. Feed 2:
60.0 g
of 1 wt% aqueous solution of 2,2"-azobis(2-amidinopropane) dihydrochloride
Feed 3: 16.5 g of 1 wt% aqueous solution of 2,2"-azobis(2-amidinopropane)
dihydrochloride
The initial charge was heated to 63 C and a water jet pump was used to reduce
the pressure
until the water just started to boil. Feeds 1 and 2 were started at the same
time, feed 1 being
added in 2 hours and feed 2 in 3 hours to the initial charge at constant
internal temperature.
Upon completion of feed 2 the reaction was maintained at 63 C for a further
hour and then
heated to 72 C while the vacuum was reduced accordingly. The reaction mixture
was
maintained at 72 C for a further 2 hours, at which point feed 3 was added all
at once to initiate a
2 hour period of secondary polymerization at 72 C. The vacuum was then lifted
and the batch
was diluted with 500 g of deionized water and cooled down to room temperature.
208 g of water
were distilled off during the entire polymerization.
A clear, colorless, viscous solution was obtained of polymer VIII composed of
40 mol%
acrylamide, 30 mol% acryloyloxyethyltrimethylammonium chloride and 30 mol%
sodium
acrylate.
Solids content: 14.5 wt% =
Viscosity: 10 600 mPas (Brookfield, spindle 7, 50 rpm, room
temperature)
K value 120 (0.1% solution of polymer in 5 wt% aqueous sodium
chloride
solution)
Polymer IX (not in accordance with the present invention): (comparative
example corresponds
to polymer II from 'European Patent Publication EP 11170740).
A 2 I 5-neck flask equipped With an anchor stirrer, a thermometer, a
descending condenser and
a nitrogen inlet tube was initially charged with 400 g of deionized water. In
addition, the following
feeds were provided:
Feed 1: The following components were mixed in a glass beaker:
250 g of deionized water
119.5 g of 50 wt% aqueous acrylamide solution
113.8 g of 80 wt% aqueous solution of acryloyloxyethyltrimethylammonium
chloride
108.6 g of 32 wt% aqueous sodium acrylate solution
0.2 g of 1 wt% aqueous solution of diethylenetriaminepentaacetic acid.
About 38 g of 37% hydrochloric acid were added to set pH 4.1.
=
21
CA 2881868 2020-02-06
=
Feed 2: 63.5 g of 1% aqueous solution of 2,2'-azobis(2-amidinopropane)
dihydrochloride
Feed 3: 17.0 g of 1% aqueous solution of 2,2"-azobis(2-amidinopropane)
dihydrochloride.
The initial charge was heated to 66 C and a water jet pump was used to reduce
the pressure
until the water just started to boil. Feeds 1 and 2 were started at the same
time, feed 1 being
added in 2 hours and feed 2 in 3 hours to the initial charge at constant
internal temperature.
Upon completion of feed 2 the reaction was maintained at 66 C for a further
hour and then
heated to 78 C while the vacuum was reduced accordingly. The reaction mixture
was
maintained at 78 C for a further 2 hours, at which point feed 3 was added all
at once to initiate a
2 hour period of secondary polymerization at 78 C. The vacuum was then lifted
and the batch
was diluted with 500 g of deionized water and cooled down to room temperature.
200 g of water
were distilled off during the entire polymerization.
A clear, colorless, viscous solution was obtained of polymer IX composed of 50
mol%
acrylamide, 28 mol% acryloyloxyethyltrimethylammonium chloride and 22 mol%
sodium
acrylate.
Solids content: 14.1 wt%
Viscosity: 42 000 mPas (Brookfield, spindle 7, 50 rpm, room
temperature)
K value 125 (0.1% solution of polymer in 5 wt% aqueous sodium
chloride
solution)
Polymer X (not in accordance with the present invention) (corresponds to
polymer III from
European Patent Publication EP 11170740).
A 2 I 5-neck flask equipped with an anchor stirrer, a thermometer, a
descending condenser and
a nitrogen inlet tube was initially charged with 400 g of deionized water. In
addition, the following
feeds were provided:
Feed 1: The following components were mixed in a glass beaker:
- = 250 g of deionized water
71.7 g of 50 wt% aqueous acrylamide solution
130.1 g of 80 wt% aqueous solution of acryloyloxyethyltrimethylammonium
chloride
187.8 g of 32 wt% aqueous sodium acrylate solution
0.2 g of 1 wt% aqueous solution of diethylenetriaminepentaacetic acid.
About 34 g of 37% hydrochloric acid were added to set pH 4.1.
Feed 2: 60.3 g of 1 wt% aqueous solution of 2,2"-azobis(2-amidinopropane)
dihydrochloride
22
CA 2881868 2020-02-06
CA 02881868 2015-02-12
Feed 3: 16.0 g of 1 wt% aqueous solution of 2,2"-azobis(2-amidinopropane)
dihydrochloride.
The initial charge was heated to 63 C and a water jet pump was used to reduce
the pressure
until the water just started to boil. Feeds 1 and 2 were started at the same
time, feed 1 being
added in 2 hours and feed 2 in 3 hours to the initial charge at constant
internal temperature.
Upon completion of feed 2 the reaction was maintained at 63 C for a further
hour and then
heated to 72 C while the vacuum was reduced accordingly. The reaction mixture
was
maintained at 72 C for a further 2 hours, at which point feed 3 was added all
at once to
initiate a 2 hour period of secondary polymerization at 72 C. The vacuum was
then lifted and
the batch was diluted with 500 g of deionized water and cooled down to room
temperature.
200 g of water were distilled off during the entire polymerization.
A clear, colorless, viscous solution was obtained of polymer X composed of 30
mol%
acrylamide, 32 mol% acryloyloxyethyltrimethylammonium chloride and 38 mol%
sodium
acrylate.
Solids content: 14.8 wt%
Viscosity: 12 000 mPas (Brookfield, spindle 7, 50 rpm, room
temperature)
K value 117 (0.1% solution of polymer in 5 wt% aqueous sodium chloride
solution)
Testing of above-described polymers I to X in enhancing the initial wet web
strength of paper
To simulate the sheet-forming process on the laboratory scale, the thin stuff
in the examples
has to be adjusted to a fibrous concentration of 3.5 g/I.
Pretreatment of fibrous suspension
Bleached birchwood sulfate pulp was beaten in a laboratory pulper at a fibrous
concentration
of 4% until it was free of fiber bundles and had reached a freeness of 30 SR.
The beaten
stuff was subsequently admixed with an optical brightener (Blankophor PSG)
and also with
a fully destructurized cationic starch (HiCat 5163 A) and left exposed to the
action thereof
for 5 minutes. The cationic starch had been destructurized beforehand as a 10%
starch
slurry in a jet cooker at 130 C for 1 minute. The amount of optical brightener
added was 0.5
wt% of commercial product, based on the dry matter content of the fibrous
suspension. The
amount of cationic starch added was 0.8% of starch (solids), based on the dry
matter content
of the fibrous suspension. The fiber content of the fibrous suspension after
starch and optical
brightener had been added was 3.5% (35 g/l).
Examples 1 to 7
23
CA 02881868 2015-02-12
Seven glass beakers were each filled with 50 g of the above-described
pretreated fibrous
suspension. Each of the glass beakers had added to it 1.75 g of a 1 wt%
aqueous solution of
one of the above-described polymers Ito VII under gentle stirring of the
fibrous suspension
(corresponds to 1% of polymer (solids) per fibrous material (solids)). The
fibrous suspensions
were each subsequently reduced to a fibrous concentration of 0.35% by addition
of water.
This was followed by addition of a 20 wt% carbonate pigment slurry (FCC,
Syncarb F474
from Omya). The amount of pigment suspension (corresponds to filler
suspension) added
was adjusted in multiple preliminary tests such that the pigment content of
the laboratory
sheets subsequently formed was about 20%. The fibrous suspension two minutes
after
pigment addition was processed on a Rapid-Kothen sheet-former to ISO 5269/2
into sheets
having a grammage of 100 g/sqm. The wet sheets were subsequently removed from
the wire
frame and placed between two suction felts. The pack consisting of suction
felts and the wet
paper was subsequently pressed in a static press at a press pressure of 6 bar.
In each case,
pressing was done to a 50 wt% solids content of the wet sheets.
Examples 8, 9 and 10 (not according to the invention)
Three glass beakers were each filled with 50 g of the above-described
pretreated fibrous
suspension. Each of the glass beakers had added to it 1.75 g in each case of a
1 wt%
aqueous solution of one of the above-described polymers I ¨ Ill under gentle
stirring of the
fibrous suspension (corresponds to 1% of polymer (solids) per fibrous material
(solids)). The
fibrous suspensions were each subsequently reduced to a fibrous concentration
of 0.35% by
addition of water. This was followed by addition of a 20 wt% carbonate pigment
slurry (FCC,
Syncarb F474 from Omya). The amount of pigment suspension added was adjusted
in
multiple preliminary tests such that the pigment content of the laboratory
sheets
subsequently formed was about 20%. The fibrous suspension two minutes after
pigment
addition was processed on a Rapid-Kothen sheet-former to ISO 5269/2 into
sheets having a
grammage of 100 g/sqm. The wet sheets were subsequently removed from the wire
frame
and placed between two suction felts. The pack consisting of suction felts and
the wet paper
was subsequently pressed in a static press at a press pressure of 6 bar. By
adapting the
residence time within the press arrangement, pressing was in each case carried
on to a
solids content of the wet sheets which is discernible from Table 1.
Examples 11, 12 and 13
Three glass beakers were each filled with 50 g of the above-described
pretreated fibrous
suspension. Each of the glass beakers had added to it 1.75 g of a 1 wt%
aqueous solution of
one of the above-described polymers VIII to X under gentle stirring of the
fibrous suspension
24
CA 02881868 2015-02-12
(corresponds to 1% of polymer (solids) per fibrous material (solids)). The
fibrous suspensions
were each subsequently reduced to a fibrous concentration of 0.35% by addition
of water.
This was followed by addition of a 20 wt% carbonate pigment slurry (FCC,
Syncarb F474
from Omya). The amount of pigment suspension (corresponds to filler
suspension) added
was adjusted in multiple preliminary tests such that the pigment content of
the laboratory
sheets subsequently formed was about 20%. The fibrous suspension two minutes
after
pigment addition was processed on a Rapid-Kothen sheet-former to ISO 5269/2
into sheets
having a grammage of 100 g/sqm. The wet sheets were subsequently removed from
the wire
frame and placed between two suction felts. The pack consisting of suction
felts and the wet
paper was subsequently pressed in a static press at a press pressure of 6 bar.
In each case,
pressing was done to a 50 wt% solids content of the wet sheets.
Examples 14, 15 and 16 (not according to the invention ¨ addition to thin
stuff)
Three glass beakers containing 50 g of the pretreated fibrous suspension
(thick stuff) were
diluted with 450 g of water to a fibrous concentration of 0.35% (corresponds
to 3.5 g/l).
To 500 g in each case of the diluted fibrous suspension (thin stuff) were
added 1.75 g of a 1
wt% aqueous solution of polymer I, II or III (corresponds to 1 wt% of polymer
(solids) based
on fibrous material (solids)).
This was followed by addition of a 20 wt% carbonate pigment slurry (PCC,
Syncarb F474
from Omya) to the mixture. The amount of pigment suspension added was adjusted
in
multiple preliminary tests such that the pigment content of the laboratory
sheets
subsequently formed was about 20%.
The fibrous suspension two minutes after pigment addition was processed on a
Rapid-
Kothen sheet-former to ISO 5269/2 into sheets having a grammage of 100 g/sqm.
The wet
sheets were subsequently removed from the wire frame and placed between two
suction
felts. The pack consisting of suction felts and the wet paper was subsequently
pressed in a
static press at a press pressure of 6 bar. By adapting the residence time of
the papers within
the press arrangement, pressing was in each case carried on to a 50 wt% solids
content of
the wet sheets.
Examples 17 and 18 (reference)
Three glass beakers were each filled with 50 g of the above-described
pretreated fibrous
suspension. The fibrous suspensions were each subsequently reduced to a
fibrous
concentration of 0.35% by addition of water. This was followed by addition of
a 20 wt%
carbonate pigment slurry (FCC, Syncarb F474 from Omya). The amount of pigment
CA 02881868 2015-02-12
suspension (corresponds to filler suspension) added was adjusted in multiple
preliminary
tests such that the pigment content of the laboratory sheets subsequently
formed was about
20%. The fibrous suspension two minutes after pigment addition was processed
on a Rapid-
Kothen sheet-former to ISO 5269/2 into sheets having a grammage of 100 g/sqm.
The wet
sheets were subsequently removed from the wire frame and placed between two
suction
felts. The pack consisting of suction felts and the wet paper was subsequently
pressed in a
static press at a press pressure of 6 bar. The pressing time was varied to
produce not only
sheets of differing dry matter content (see Table 1)
Performance testing: Determination of initial wet web strength
Initial wet web strength must not be confused with a paper's wet strength and
initial wet
strength since both these properties are measured on papers which, after
drying, are
moistened back to a defined water content. Initial wet strength is an
important parameter in
the assessment of papers without permanent wet strength. A dried and
subsequently
remoistened paper has a completely different wet strength than a moist paper
directly after it
has passed through the wire and press sections of a papermachine.
Initial wet web strength is determined on wet paper using the Voith method
(cf. M. Schwarz
and K. Bechtel "Initiale GefOgefestigkeit bei der Blattbildung", in
Wochenblatt fur
Papierfabrikation 131, pages 950 ¨ 957 (2003) No. 16). The wet sheets after
pressing in the
static press were knocked off onto a plastics support and transferred to a
cutting support.
Test strips having a defined length and width were then cut out of the sheet.
They were
pressed under constant pressure until the desired dry matter content was
reached. To
investigate the sheets of paper obtained according to the examples reported
above, four dry
matter contents ranging between 42% and 58% were established in each case.
These
values were used to determine initial wet web strength at 50% dry matter using
a fitting
method described in the abovementioned literature reference. The actual
measurement of
initial wet web strength took place on a vertical tensile tester using a
special clamping device.
The force determined in the tension machine was converted into the grammage-
independent
INF index. For an exact description of the clamping device, the measuring
procedure, the
determination of the dry matter in the paper and the data processing, the
abovementioned
literature reference can be enlisted.
The results of the tests are reproduced in Table 1.
26
CA 02881868 2015-02-12
Table 1: Results of performance testing for production of paper having a
filler content of
20 wt%. According to the computation of the limiting dry matter content G(x) =
G(20), the
invention requires pressing to a solids content of at least 50 wt%:
G(20) = 48 + (20 - 15) - 0.4 = 50
Example Polymer INF index Solids
content
[Nm/g]
pressed [%]
1 I 3.9 50.3
2 Il 3.5 50.5
3 III 3.3 50.2
4 IV 3.4 50.9
5 V 3.5 51.2
6 VI 3.6 50.6
7
VII 3.2 51.3
8
not according to the invention I 1.8 48.6
9
not according to the invention II 1.9 49.1
not according to the invention Ill 2.1 49.2
11
not according to the invention VIII 3.3 50.3
12 IX 3.1 50.5
not according to the invention
13 X 2.9 50.2
not according to the invention
14 (addition to thin stuff)
not according to the invention I 1.8 50.2
(addition to thin stuff)
not according to the invention II 1.5 50.0
27
=
CA 02881868 2015-02-12
16 (addition to thin stuff) UI 1.7 51.2
not according to the invention
17 1.1 48.4
reference
18 1.4 50.6
reference
=
28
