Note: Descriptions are shown in the official language in which they were submitted.
' CA 02403966 2002-09-24
Pulverulent Polymers Crosslinked on the Surface
The present invention relates to a pulverulent polymer
post-crosslinked on the surface that absorbs water or
aqueous liquids, synthesised from polymerised, optionally
pre-crosslinked, partially neutralised monomers containing
carboxyl groups. The present invention also relates to a
process for the post-treatment of the aforementioned
polymers and the use of a solution of at least one
trivalent cation for the restoration of the gel
permeability of the aforementioned polymers that have been
damaged by mechanical action.
Polymers that absorb aqueous liquids, so-called
superabsorbers, are known from numerous publications.
Modified natural polymers as well as partially or
completely synthetic polymers may be used for this purpose.
The fully synthetic polymers are as a rule produced by
free-radical polymerisatio n of various h~.~droph:~lic mor~cmers
in aqueous solution according to different methods. In
general crosslinking agents are incorporated by
polymerisation, ~~hereby the polymer obtained is nc longer
water-soluble but is only water-swella_ble. For example,
polymers based on (meth)acrylic acid that are present in
partially neutralised form as alkali metal salt may be used
as superabsorbers.
The superabsorber polymer is as a rule mechanically
comminuted, dried and ground after the polymerisation. In
this connection the pulverulent water-swellable polymer
falls in a more or less broad grain spectrum depending on
the production process, which is typically in a range from
10 to 1000 Vim, of which normally the grain fraction from
150 to 850 ~.m is used for practical purposes, above all in
the hygiene sector, as absorption material. Fine fractions
of < 150 ~.m are undesirable on account of their dust-
forming behaviour and their toxic properties when inhaled.
CA 02403966 2002-09-24
2
The development of more recent nappy constructions is
highlighted by the tendency to replace increasingly larger
proportions of the voluminous cellulose fluff by
superabsorbers. This is happening on grounds of volume
reduction and above all on grounds of an improved property
profile. Due to the increased concentration of
superabsorbers there is increased contact of the swollen
absorber particles with one another after absorption of
liquid has taken place. By means of the surface post-
crosslinking methods described in the prior art the so-
called gel blocking, in which only the surfaces of the
absorber particles swell and the liquid does not penetrate
into the inner regions and swollen absorber particles that
have clumped together build up to form a barrier layer for
subsequent liquid, can be suppressed.
The superabsorbers are therefore post-crosslinked on the
surface after the comminution, drying, grinding and
grading.
Such surface post-crosslinking processes are described for
example in patent specifications DE 40 20 780 C1 and
US 4,043,952. In DE 40 20 780 C1 the polymers are
crosslinked on the particle surface by low molecular weight
organic compounds. Not only is the absorptive capacity
under pressure thereby raised, but also the behaviour of
the absorbers known as ~~gel blocking' is suppressed.
US 4,043,952 discloses a treatment of the surface of the
absorber particles with at least divalent metal ions
(column 8, line 51) in organic solvents in order to improve
the dispersibility in aqueous media and effect a more rapid
absorption of the liquid. EP 233 067 B1 and US 4,558,091
describe the surface post-crosslinking of superabsorbers
based on polyacrylic acid and/or hydrolysed starch/
acrylonitrile graft polymers with aluminium compounds in
combination with polyhydroxyalcohols in order to improve
the absorption properties.
CA 02403966 2002-09-24
3
During and after the surface post-crosslinking the polymer
powders are changed by mixing and transportation processes
as regards their grain spectrum, due to the formation of
finely particulate abraded material, with the result that a
renewed screening of the fine fractions is necessary in
order to restore the previous state. This results in
additional production costs and material losses since the
fine fractions can now no longer be used at all, or at best
only to a limited extent. In addition to the formation of
the abraded material there is also a deterioration of the
absorption properties that had previously been improved by
the surface post-crosslinking, i.e. in particular the
ability of the swollen absorber gel to transport further
liquid (gel permeability) is also impaired. This problem
occurs not only in the production of the superabsorber
pn~,yers, but ultimately also in their subsequent further
processing for the production of hygiene products. In this
case it is frequently found that the absorption properties
of the superabsorbers are impaired due to abrasion during
their conveyance, and undesirable dust: is formed.
In EP 691 995 A1 according to the prior art measures are
described for example for reducing the proportion of dust
by addition of polyglycols, which however only prevent the
dust but do not deal with the problem of the deteriorated
absorption properties. US 5,002,986 describes a process
for improving the absorption rate of superabsorbers that
consist only of fine fractions that ar_e agglomerated in
intensive mixers in the presence of ionic crosslinking
agents to form larger particles. DE :196 46 484 A1.
describes superabsorbers consisting of a combination of
special crosslinking agents and monomers that suffer only a
slight deterioration in properties under mechanical stress.
A significant suppression of the property loss cannot
however be achieved in this way.
In the prior art no superabsorbing polymer is known whose
properties are not impaired by mechanical stress during
conveyance in production and nappy manufacture. The prior
CA 02403966 2002-09-24
n
4
art also does not disclose any process that solves the
problem of impairment of the properties of the
superabsorber powders due to the mechanical stress during
the surface modification and subsequent conveyance in
production and nappy manufacture. In any case, a screening
of fine fractions is carried out at the expense of product
yield.
The object of the present invention is accordingly to
provide polymers whose properties deteriorate only
insignificantly during nappy manufacture, that do not form
dust or only small amounts of dust, and that have a lesser
tendency to form clumps in environments with a high
atmospheric moisture content than products of the prior
art. The object of the present invention is also to
provide a process for the production of the aforementioned
polymers, by means of which the screening of the fine
fractions after the surface post-crosslinking is largely
avoided without the properties of the polymer being
substantially impaired. A further object of the present
invention is to provide a substance by means of which the
gel permeability of surface-crosslinked superabsorber
powders containing fine fractions and that have been
damaged by abrasion processes is restored..
This object is achieved according to the invention by a
pulverulent polymer post-crosslinked on the surface that
absorbs water or aqueous liquids, and that is synthesised
from polymerised, optionally pre-crosslinked monomers
containing partially neutralised carboxyl groups, wherein
the pulverulent polymer has after the post--crosslinking
been reacted with the preferably aqueous solution. of at
least one salt of an at least trivalent cation.
The polymers according to the invention have, compared to
superabsorbers according to the prior art, improved gel
permeabilities that correspond roughly to those of
mechanically unstressed polymers. The retention behaviour
is~not reduced in the polymer according to the invention
CA 02403966 2002-09-24
G
J
dnd the swellability under pressure is not impaired or only
slightly so. Furthermore it has been .found that the
polymers according to the invention have a good flowability
and exhibit an improvement in the so-called anticaking
behaviour, i.e. in a moist ambient atmosphere they have
only a slight tendency to agglomerate and moreover exhibit.
a reduced dust formation. Accordingly the treatment steps
that are normally envisaged for the dust removal and
anticaking treatment can be reduced or dispensed with
entirely. The pulverulent polymers according to the
invention permit a reliable further processing for example
into nappies without dust formation and loss of properties
during mechanical or pneumatic conveyance.
As salt component in the solution there may be used
according to the invention chlorides, bromides, sulfates,
carbonates, nitrates, phosphates as well as salts of
organic acids, such as for example acetates and lactates,
and other salts of at least trivalent cations. Examples of
cations that may be used according to the invention include
aluminium as well as iron, chromium, manganese, titanium,
zirconium and other transition metals as weld as double
salts of two cations or also mixtures of several salts.
Aluminium salts and alums and their various hydrates are
preferred, such as for example AlCl3 x 6 H20, NaAl (S04) 2 x 12
HZO, KAl ( S04 ) Z x 12 HZO or A12 ( S09 ) 3 x 18 H20 . A12 ( S04 ) 3 and l is
hydrates are particularly preferably used. The salt
components are preferably used, calculated on the basis of
the cation according to the invention, in amounts of 0.001-
1.0 wt. o, preferably 0.002-0.5 wt.~ and particularly
preferably 0.005-0.2 wt.o, in each ca:>e referred to the
polymer. The added amount is preferably calculated so that
the absorption of the polymer powder under pressure is not,
or only slightly, impaired.
The salts of at least trivalent cations to be used
according to the invention are preferably applied in the
form of a solution. Suitable solvents are water or polar,
water-miscible organic solvents such as for example
CA 02403966 2002-09-24
O
acetone, methanol, ethanol or 2-propanol or their mixtures;
water is preferably used. The term aqueous solution within
the context of the invention means in relation to the
solvent component that the solution may contain, apart from
water, also other organic solvents. The concentration of
the salts (calculated in anhydrous form) in the solvent may
vary within wide limits and is generally in the range from
1 to 80 wt.~, preferably in a range from 1 to 60 wt.o and
most particularly preferably in a range from 5 to 35 wt. o.
The preferred solvent for the salt component is water,
which is used in an amount of 0.05-10 wt.%, preferably
0.1-5 wt.~ and particularly preferably 0.1-3 wt. o, referred
to the polymer. The amount of water is preferably adjusted
in the lower range so that sufficient liquid is available
to distribute the salt solution. In the upper range the
amount of water must on the other hand be optimised so that
the formation of agglomerates, which may occur temporarily
when using relatively large amounts of water, remains
within acceptable limits. It is generally the case that,
with increasing amount of salt of at least trivalent
cations, increasing amounts of water m.ay also be used
without resulting in a temporary agglomerate formation.
Natural, partially synthetic and fully synthetic substances
are suitable as water-swellable hydrophilic polymers.
Partially synthetic and fully synthetic substances are
preferred, in particular anionic polymers based on
(meth)acrylic acid that are present ire partially
neutralised form as alkali metal salts, in particular
sodium and/or potassium salts. The degree of
neutralisation of the acid monomer components may vary, but
is preferably between 25 and 85 mol o. These components
may be homopolymers and copolymers that can be obtained
from acrylic acid and/or methacrylic acid alone, from these
monomers together with one or more other monomers, or
simply from one or more other monomers, but for example may
also be grafted-on anionic polymers, for example based on
(meth)acrylic acid, present in partially neutralised form
as alkali metal salt, for example may comprise graft
CA 02403966 2002-09-24
7
polymers on polyvinyl alcohols, on polysaccharides such as
for example starch or cellulose or derivatives thereof, or
on polyalkylene oxides such as polyethylene oxides or
polypropylene oxides.
As examples of monomers that may be used in addition to
(meth)acrylic acid in the production of the polymers, there
may be mentioned methyl, ethyl and (poly)hydroxyalkyl
esters of (meth)acrylic acid, (meth)acrylamide, crotonic
acid, malefic and fumaric acids, itaconic acid,
2-acrylamido-2-methylpropanesulfonic acid, vinylsulfonic
acid and vinylphosphonic acid and the methyl, ethyl and
(poly)hydroxyalkyl esters and amides of these acids, amino
group-containing and ammonium group-containing esters and
amides of all the aforementioned acids and water-soluble
N-vinylamides, but also the polymer may contain structural
units derived from all further monomers conventionally used
in the production of superabsorber polymers. The polymer
is preferably crosslinked. As examples of suitable
crosslinking substances containing two or more reactive
groups that may be used in the production of the
superabsorber polymers, whose structural units may then be
contained in the polymer, there may be mentioned
polyglycidyl ethers, methylene bis(meth)acrylamide,
bisacrylamidoacetic acid, esters of unsaturated acids of
polyols and/or alkoxylated polyols, for example ethylene
glycol di(meth)acrylate or trimethylolpropane triacrylate
or allyl compounds, such as for example allyl
(meth)acrylate, polyallyl esters, tetraallyloxyethane,
triallylamine, tetraallyl ethylenediamine or allyl esters
of phosphoric acid as well as vinylphosphonic acid
derivatives. The proportion of crosslinkir_g agents that
are already added in the production of the superabsorber
polymers is preferably 0.01 to 20 wt.~, particularly
preferably 0.1 to 3 wt.~, referred to the total monomers
used.
The production of the polymer is otherwise carried out
according to methods known per se, such as are described
CA 02403966 2002-09-24
for example in DE 40 20 780 C1, which is hereby included by
way of reference and thus forms part of the disclosure,
preferably by polymerisation in aqueous solution according
to the so-called gel polymerisation process.
The polymer powders are formed by comminution, drying and
grinding of the polymer gels followed by surface post-
crosslinking and may have a broad grain spectrum. Suitable
substances for such a surface post-crosslinking are for
example compounds containing two or more groups that can
form covalent bonds with the carboxyl groups of the
hydrophilic polymer. Suitable compounds are for example
diols and polyols, diglycidyl compounds and polyglyci.dyl
compounds such as phosphonic acid diglycidyl esters,
alkylene carbonates such as ethylene carbonate, alkoxysilyl
compounds, polyaziri.dines, polyamines or polyamidoamines,
in which connection the aforementioned compounds may also
be used in the form of mixtures with one another.
The surface post-crosslinking agent is used in an amount of
0.01 to 30 wt.~, preferably 0.1 to 10 wt.o, referred to the
polymer to be post-crosslinked.
Before the surface post-crosslinking the polymer is
preferably dried, ground and screened to the grain fraction
appropriate for the respective application technology, and
is then added to the surface post-crosslinking reaction.
In many cases it has however also proved convenient to add
the surface post-crosslinking agents already before the
drying of the polymer gel and/or before the comminution of
the partially or largely dried polymer. A surface post-
crosslinking to be carried out accordir_g to the invention
is described for example in US 4,666,983 and in
DE 40 20 780. These specifications are hereby introduced
by way of reference and thus form part of the disclosure.
The addition of the surface post-crosslinking agents often
advantageously also takes place in the form of a solution
in water, organic solvents or mixtures thereof, especially
if minor amounts of surface post-crosslinking agents are
' CA 02403966 2002-09-24
J
used. Suitable mixing units for applying the surface post-
crosslinking agent are for example Patterson-Kelley mixers,
DRAIS turbulence mixers, Lodige mixers, Ruberg mixers,
screw mixers, pan mixers and fluidised bed mixers, as well
as continuously operating vertical mixers in which the
powder is mixed at high speed by means of rotating blades
(Schugi mixers). After the surface post-crosslinking agent
has been mixed with the pre-crosslinked polymer, the
reaction mixture is heated to temperatures of 60° to 250°C,
preferably to 135° to 200°C and particularly preferably to
150° to 185°C in order to carry out the surface post-
crosslinking reaction. The duration o~ the post-heating is
limited by the point at which the desired property profile
of the polymer is destroyed again as a result of heat
damage.
After the surface post-crosslinking the pulverulent polymer
is reacted according to the invention with the solution of
at least one salt of an at least trivalent cation. The
moisture content of the polymer powder before the reaction
may fluctuate, and is typically less than 10 wt. o,
preferably less than 8 wt.o and particularly preferably
less than 5 wt.~.
The polymer powder may contain fine fractions before the
reaction. This fine fraction may be formed during the
drying, grinding and/or post-crosslink:ing or may be added
to the polymer powder, so that the polymer according to the
invention may also contain recycled fine fractions.
Preferably the fine dust fraction with a mean grain
diameter of less than 150 dun is up to 15 wt. o, particularly
preferably up to 10 wt.o and most particularly preferably
up to 5 wt.~. In order for the polymer powders to be used
in the hygiene industry, an upper grain limit of 1000 ~tm,
preferably of 850 Vim, has proved suitable.
The powder and the solution of at least one salt of the at
least trivalent cation are preferably :intimately and as
~
CA 02403966 2002-09-24
homogeneously as possible mixed with one another and
thereby reacted.
The pulverulent water-swellable hydrophilic polymers
5 according to the invention may be used for all purposes for
which such superabsorbers are normally employed, in
particular therefore for the absorption of water and
aqueous solutions. They are preferably used in the
absorption of body fluids, in particular blood and urine.
10 For this they are incorporated in particular in absorbing
single-use disposable hygiene articles, for example in
nappies, tampons or sanitary towels, or also for other
medicinal purposes. Other possible uses include for
example as water-storing floor improvement agents or as
moisture binding agents for cable sheathing or as support
material for active constituents and their controlled
release.
The present invention also provides a process for the
production of the polymers according to the invention, in
which a solution of at least one salt of an at least
trivalent cation is added to the pulveruient polymer after
the post-crosslinking and the said pulverulent polymer and
the solution are preferably homogeneously thoroughly mixed.
By means of the process according to the invention it is
possible to restore the gel permeability of polymer powders
that have suffered high abrasion damage. The stage
involving the screening of the fine fractions after the
post-crosslinking is omitted. The process products have,
compared to superabsorbers according to the prior art,
improved gel permeabilities that correspond approximately
to those of mechanically unstressed polymers. The
retention behaviour is not adversely affected by the
process according to the invention and the swellability
under pressure is not reduced or only slightly so.
Furthermore it has been found that the pulverulent process
products have a good flowability, an improvement in the so-
called anticaking behaviour, i.e. only a slight tendency to
CA 02403966 2002-09-24
1 1
11
agglomerate in a moist ambient atmosphere, and furthermore
have a reduced tendency to form dust. The treatment steps
that are normally envisaged for dust removal and anticaking
behaviour may be reduced or dispensed with altogether. The
polymer powders according to the invention permit a
reliable further processing without formation of dust and
loss of properties during mechanical or pneumatic
conveyance. A further advantage of the process according
to the invention is the fact that the solvent fraction
introduced via the salt solution does not have to be
distilled off, especially if it consists only of water,
with the result that the polymer powder can be used without
further working-up.
According to the invention a solution of at least one salt
of an at least trivalent cation is added to the polymer
powder after the post-crosslinking. The pulverulent
polymer and the solution are preferably homogeneously
thoroughly mixed during or after the addition of the
solution.
The moisture content of the polymer powder after the post-
crosslinking and before the addition of the solution may
vary, and is typically less than 10 wt. o, preferably less
than 8 wt.~ and particularly preferably less than 5 wt. o.
The pulverulent polymer may contain very fine dust
fractions before the addition of the solution, which are
formed either in the post-crosslinking or are added to the
polymer powder, with the result that t:he process according
to the invention is also suitable for the recycling of fine
fractions. Preferably the grain fraction <150 ~tm accounts
for up to 15 wt.~, particularly preferably up to 10 wt.~
and most particularly preferably up to 5 wt.~. An upper
grain boundary of 1000 Etm, preferably 850 dun, has proved
suitable for the use of the polymer powders in the hygiene
industry.
CA 02403966 2002-09-24
12
According to the invention the powder must be mixed
intimately and as homogeneously as possible with the
solution of the salt of the at least trivalent cation. The
mixing may be carried out in a continuous or discontinuous
procedure in any apparatus suitable for mixing pulverulent
products with liquid additives. The mixing is preferably
carried out using a stirrer mixer that is preferably
operated at a rotational speed of 700-1000 r.p.m. In
particular renewed damage to the process products is
thereby avoided. The intensive mixers with a high energy
input of for example 1000 to 5000 Wh/m3 that are otherwise
described in the prior art (DE 41 31 045 C1) for the
surface treatment of superabsorbing polymer powders should
preferably not be used for the process according to the
invention.
The mixing times are generally between 1 and 120 minutes,
but preferably less than 1 hour. Temporary agglomerates,
such as may be formed by the addition of relatively large
amounts of water, are broken down again by the gentle
mixing movement of the mixer, but can :however prolong the
mixing time.
The addition of the solution to the pulverulent polymers
takes place preferably in the temperature range from 0°C to
100°C, particularly preferably in the range from 10°C to
80°C, most particularly preferably in the range from 20°C
to 50°C.
The present invention furthermore provides the polymers
that are formed by the process according to the invention.
The pulverulent water-swellable hydrophilic polymers
according to the invention may be used for all purposes for
which such superabsorbers are normally employed, in
particular therefore for the absorption of water and
aqueous solutions. They are preferably used in the
absorption of body fluids, in particular blood and urine.
CA 02403966 2002-09-24
13
rFor this they are incorporated in particular in absorbing
single-use disposable hygiene articles, for example in
nappies, tampons or sanitary towels, or also for other
medicinal purposes. Other possible uses include for
example as water-storing floor improvement agents or as
moisture binding agents for cable sheathing or as support
material for active constituents and their controlled
release.
The present invention furthermore provides for the use of a
solution of at least one salt of an at least trivalent
cation for the restoration of the gel permeability of
pulverulent polymers absorbing water or aqueous liquids
that have been damaged by mechanical action, synthesised
from polymerised, optionally pre-cross:linked, partially
neutralised monomers containing carboxyl groups, in which
the solution of the salt is added to t-~ze pulverulent
polymer after the post-crosslinking and the pulverulent
polymer and the solution are thoroughly mixed.
By means of the use according to the invention it is
possible to restore the gel permeability of polymer powders
that have suffered high abrasion damage and with large fine
fractions. The stage involving the screening of the fine
fractions after the post-crosslinking is omitted. The
process products have, compared to superabsorbers according
to the prior art, improved gel permeabilities that
correspond approximately to those of. mechanically
unstressed polymers. The retention behaviour is not
adversely affected by the process according to the
invention and the swellability under pressure is not
reduced or only slightly so. Furthermore it has been found
that the pulverulent process products :have a good .
flowability, an improvement in the so-called anticaking
behaviour, i.e. only a slight tendency to agglomerate in a
moist ambient atmosphere, and furthermore have a reduced
tendency to form dust. The treatment steps that are
normally envisaged for dust removal and anticaking
behaviour may therefore be reduced or dispensed with
CA 02403966 2002-09-24
1~
altogether. The polymer powders according to the invention
permit a reliable further processing, for example into
nappies, without formation of dust and loss of properties
during mechanical or pneumatic conveyance. A further
advantage of the process according to t:he invention is the
fact that the solvent fraction introduced via the salt
solution does not have to be distilled off, especially if
it consists only of water, with the result that the polymer
powder can be used without further working-up.
As salt component in the solution there may be used
according to the invention chlorides, bromides, sulfates,
carbonates, nitrates, phosphates as well as salts of
organic acids, such as for example acetates and lactates,
and other salts of at least trivalent rations. Examples of
rations that may be used according to -he invention include
aluminium as well as iron, chromium, manganese, titanium,
zirconium and other transition metals as well as double
salts of two rations or also mixtures of several salts.
Aluminium salts and alums and their various hydrates are
preferred, such as for example A1C13 x 6 HZO, NaAl (S04) z x 12
Hz0 , KAl ( SO9 ) ? X 12 H20 Or Aiz ( SOQ ) 3 X 18 HZG . AiZ ( Sv4 ) 3 and l
tS
hydrates are particularly preferably used. The salt
components are preferably used, calculated on the basis of
the ration according to the invention, in amounts of 0.001-
1.0 wt. o, preferably 0.002-0.5 wt.o and particularly
preferably 0.005-0.2 wt.~, in each case referred to the
polymer. The added amount is preferably calculated so that
the absorption of the polymer powder under pressure is not,
or only slightly, impaired.
The salts of at least trivalent rations to be used
according to the invention are preferably applied in the
form of a solution. Suitable solvents are water or polar,
water-miscible organic solvents such as for example
acetone, methanol, ethanol or 2-propanol or their mixtures;
water is preferably used. The term aqueous solution within
the context of the invention means in relation to the
solvent component that the solution may contain, apart from
CA 02403966 2002-09-24
mater, also other organic solvents. The concentration of
the salts (calculated in anhydrous form) in the solvent may
vary within wide limits and is generally in the range from
1 to 80 wt.~, preferably in a range from 1 to 60 wt.~ and
5 most particularly preferably in a range from 5 to 35 wt. o.
The preferred solvent for the salt component is water,
which is used in an amount of 0.05-10 wt. o, preferably 0.1-
5 wt.~ and particularly preferably 0.1-3 wt.~, referred to
the polymer. The amount of water is preferably adjusted in
10 the lower range so that sufficient liquid is available to
distribute the salt solution. In the upper range the
amount of water must on the other hand be optimised so that
the formation of agglomerates, which may occur temporarily
when using relatively large amounts of water, remains
15 within acceptable limits. It is generally the case that,
with increasing amount of salt of at least trivalent
canons, increasing amounts of water may also be used
without resulting in a temporary agglomerate formation.
Natural, partially synthetic and fully synthetic substances
are suitable as water-swellable hydrophilic polymers.
Partially synthetic and fully synthetic substances are
preferred, in particular anionic polymers based on
(meth)acrylic acid that are present in partially
neutralised form as alkali metal salts, in particular
sodium and/or potassium salts. The degree of
neutralisation of the acid monomer components may vary, but
is preferably between 25 and 85 mol o. These components
may be homopolymers and copolymers that can be obtained
from acrylic acid and/or methacrylic acid alone, from these
monomers together with one or more other monomers, or
simply from one or more other monomers, but for example may
. also be grafted-on anionic polymers, for example based on
(meth)acrylic acid, present in partially neutralised form
as alkali metal salt, for example may comprise graft
polymers on polyvinyl alcohols, on polysaccharides such as
for example starch or cellulose or derivatives thereof, or
on polyalkylene oxides such as polyethylene oxides or
polypropylene oxides.
CA 02403966 2002-09-24
iG
As examples of monomers that may be used in addition to
(meth)acrylic acid in the production of the polymers, there
may be mentioned methyl, ethyl and (poly)hydroxyalkyl
esters of (meth)acrylic acid, (meth)acrylamide, crotonic
acid, malefic and fumaric acids, itaconic acid,
2-acrylamido-2-methylpropanesulfonic acid, vinylsulfonic
acid and vinylphosphonic acid and the methyl, ethyl and
(poly)hydroxyalkyl esters and amides of these acids, amino
group-containing and ammonium group-containing esters and.
amides of all the aforementioned acids and water-soluble
N-vinylamides, but also the polymer may contain structural
units derived from all further monomers conventionally used
in the production of superabsorber polymers. The polymer
is preferably crosslinked. As examples of suitable
crosslinking substances containing two or more reactive
groups that may be used in the production of the
superabsorber polymers, whose structural units may then be
contained in the polymer, there may be mentioned
polyglycidyl ethers, methylene bis(met:h.)acrylamide,
bisacrylamidoacetic acid, esters of unsaturated acids of
polyols and/or alkoxylated poiyois, for example ethylene
glycol di(meth)acrylate or trimethylol.propane triacrylate
or allyl compounds, such as for example allyl
(meth)acrylate, polyallyl esters, tetraallyoxyethane,
triallylamine, tetraallyl ethylenediamine or allyl esters
of phosphoric acid as well as vinylphosphonic acid
derivatives. The proportion of crosslinking agents that
are already added in the production of. the superabsorber
polymers is preferably 0.01 to 20 wt.~, particularly
preferably 0.1 to 3 wt. o, referred to the total monomers
used.
The production of the polymer is otherwise carried out
according to methods known per se, such as are described
for example in DE 40 20 780 C1, which is hereby included by
way of reference and thus forms part of the disclosure,
preferably by polymerisation in aqueous solution according
to the so-called gel polymerisation process.
CA 02403966 2002-09-24
i r
The polymer powders are formed by comminution, drying and
grinding of the polymer gels followed by surface post-
crosslinking and may have a broad grain spectrum. Suitable
substances for such a surface post-crosslinking are for
example compounds containing two or more groups that can
form covalent bonds with the carboxyl groups of the
hydrophilic polymer. Suitable compounds are for example
diols and polyols, diglycidyl compounds and polyglycidyl
compounds such as phosphonic acid diglycidyl esters,
alkylene carbonates such as ethylene carbonate, alkoxysilyl
compounds, polyaziridines, polyamines or polyamidoamines,
wherein the aforementioned compounds may also be used in
the form of mixtures with one another.
Before the surface post-crosslinking the polymex is
preferably dried, ground and screened to the grain fraction
appropriate for the respective application technology, and
is then added to the surface post-crop>siinking reaction.
In some cases it has however also proved convenient to add
the surface post-crosslinking agents already before the
drying of the polymer gei and/or before the comminution of
the partially or largely dried polymer. A surface
post-crosslinking to be carried out according to the
invention is described for example in US 4,666,983 and in
DE 40 20 780. These specifications are hereby introduced
by way of reference and thus form part of the disclosure.
The addition of the surface post-crosslinking agents often
advantageously also takes place in the form of a solution
in water, organic solvents or mixtures thereof, especially
if minor amounts of surface post-crosslinking agents are
used. Suitable mixing units for applying the surface post-
crosslinking agent are for example Patterson-Kelley mixers,
DRAIS turbulence mixers, Lodige mixers, Ruberg mixers,
screw mixers, pan mixers and fluidised bed mixers, as well
as continuously operating vertical mixers in which the
powder is mixed at high speed by means of rotating blades
(Schugi mixers). After the surface post-crosslinking agent
has been mixed with~the pre-crosslinked polymer, the
CA 02403966 2002-09-24
18
'reaction mixture is heated to temperatures of 60° to 250°C,
preferably to 135° to 200°C and particularly preferably to
150° to 185°C in order to carry out the surface post-
crosslinking reaction. The duration of the post-heating is
limited by the point at which the desired property profile
of the polymer is destroyed again as a result of heat
damage.
After the surface post-crosslinking, according to the
invention the solution of at least one salt of an at least
trivalent cation is added to the pulverulent polymer and
intimately mixed therewith. The moisture content of the
polymer powder before the addition of the solution may
fluctuate, and is typically less than 10 wt. o, preferably
less than 8 wt.o and particularly preferably less than
5 wt, o.
The polymer powder may contain fine fractions before the
addition. This fine fraction may be formed during the
drying, grinding and/or post-crosslinking, or may be added
to the polymer powder, so that the polymer according to the
invention may also contain recycled fine fractions.
Preferably the fine dust fraction with a mean grain
diameter of less than 150 um is up to 15 wt. o, particularly
preferably up to 10 wt.o and most particularly preferably
up to 5 wt.~. In order for the polymer powders t.o be used
in the hygiene industry, an upper grain limit of 1000 Vim,
preferably of 850 ~tm, has proved suitable.
According to the invention a solution of at least one salt
of an at least trivalent cation is added to the polymer
powder after the post-crosslinking. The pulverul.ent
polymer and the solution are preferably homogeneously
thoroughly mixed during or after the addition of the
solution.
The moisture content of the polymer powder after the post-
crosslinking.and before the addition of the solution may
CA 02403966 2002-09-24
19
vary, and is typically less than 10 wt.~, preferably less
than 8 wt.~ and particularly preferabl~~ less than 5 wt. o.
The pulverulent polymer may contain very fine dust
fractions before the addition of the solution, which are
formed either in the post-crosslinking or are added to the
polymer powder, with the result that the process according
to the invention is also suitable for the recycling of fine
dust fractions. Preferably the grain fraction <150 (gym
accounts for up to 15 wt.~, particularly preferably up to
10 wt.o and most particularly preferably up to 5 wt.o. An
upper grain boundary of 1000 ~tm, preferably 850 ~~n, has
proved suitable for the use of the polymer powders in the
hygiene industry.
According to the invention the powder must be mixed
intimately and as homogeneously as possible with the
solution of the salt of the at least trivalent ration. The
mixing may be carried out in a continuous or discontinuous
procedure in any apparatus suitable for mixing pulverulent
products with liquid additives. The mixing is preferably
carried out using a stirrer mixer that. is preferably
operated at a rotational speed of 700-1000 r.p.m. In
particular renewed damage to the process products is
thereby avoided. The intensive mixers. with a high energy
input of for example 1000 to 5000 Wh/m3 that are otherwise
described in the prior art (DE 41 31 045 C1) for the
surface treatment of superabsorbing polymer powders should
preferably not be used for the process according to the
invention.
The mixing times are generally between 1 and 120 minutes,
but~preferably less than 1 hour. Temporary agglomerates,
such as may be formed by the addition of relatively large
amounts of water, are broken down again by the gentle
mixing movement of the mixer, but can however prolong the
mixing time.
CA 02403966 2002-09-24
The addition of the solution to the pulverulent polymer
takes place in the temperature range from 0°C to 100°C,
particularly preferably in the range from 10°C to 80°C,
most particularly preferably in the range from 20°C to
5 50°C. Temperatures above 100°C and/or subsequent
temperature treatments are undesirable since they either do
not produce any improvement of the properties or may even
lead to a deterioration of the properties.
10 The polymers according to the invention as well as the
superabsorbers occurring as a result of the process
according to the invention or the use according to the
invention are preferably employed in liquid-absorbing
hygiene products such as for example baby nappies,
15 incontinence products and sanitary towels.
Liquid-absorbing hygiene products as a rule are generally
constructed of a liquid-permeable covering facing the body,
a liquid-absorbing suction layer as well as a substantially
20 liquid-impermeable outer layer facing away from the body.
Optionally further structures are also used for the rapid
absorption and distribution of body fluid ir~ the sucticr~
core. These structures are frequently but however not
necessarily used between the liquid-permeable covering
facing the body and the liquid-absorbing suction layer.
The liquid-permeable covering consists as a rule of a non-
woven fibre-like fleece or another porous structure.
Suitable materials for this covering include for example
synthetic polymers such as polyvinyl chloride or fluoride,
polytetrafluoroethylene (PTFE), polyvinyl alcoho:is and
derivatives, polyacrylates, polyamides, polyesters,
polyurethanes, polystyrene, polysiloxanes or polyolefins
(e.g. polyethylene (PE) or polypropylene (PP)) as well as
natural fibre materials and also arbitrary combinations of
the aforementioned materials in the sense of mixed
materials or composite materials or copolymers.
CA 02403966 2002-09-24
21
the liquid-permeable covering has a hydrophilic character.
It may furthermore consist of a combination of hydrophilic
and hydrophobic constituents. As a rule the liquid-
permeable covering is preferably rendered hydrophilic in
order to ensure that body fluids are rapidly soaked up into
the liquid-absorbing suction layer, although partially
hydrophobised coverings are also employed.
Liouid-absorbing suction layer
The liquid-absorbing suction layer contains the
superabsorbing powders and/or granules and further
components of for example fibrous materials, foam-like
materials, film-forming materials or porous materials, as
well as combinations or two or more of these materials.
Each of these materials may either be of natural or
synthetic origin or may have been produced. by chemical or
physical modification of natural materials. The materials
may be hydrophilic or hydrophobic, hydrophilic materials
being preferred. This applies in part.icuiar to those
compositions that are intended efficiently to absorb
excreted body fluids and transport the latter in the
direction of regions of the absorbing core more remote from
the entry point of the body fluid.
Suitable hydrophilic fibre materials include for example
cellulose fibres, modified cellulose fibres (e. g. stiffened
cellulose fibres), polyester fibres (e. g. Dacron),
hydrophilic nylon but also hydrophilised hydrophobic fibres
such as for example polyolefins (PE, 7?P), polyesters,
polyacrylates, pol.yamides, polystyrene, polyurethanes,
etc., that have been hydrophilised with surfactants.
Cellulose fibres and modified cellulose fibres are
preferably used. Combinations of cellulose fibres and/or
modified cellulose fibres with synthetic fibres such as for
example PE/PP composite materials, so-called bicomponent
fibres, such as are used for example for the thermobonding
of airlaid materials or other materials are also commonly
used. The fibre materials~may be present in various w
CA 02403966 2002-09-24
22
application forms, for example as loose cellulose fibres
precipitated from an airstream or from an aqueous phase, or
laid cellulose fibres, as non-woven fleece or as tissue.
Combinations of various application forms are possible.
In addition to the superabsorbers according to the
invention there may optionally be used further pulverulent
substances, such as for example deodorising substances such
as cyclodextrines, zeolites, inorganic or organic salts,
7_0 and similar materials.
As porous materials and foam-like materials there may for
example be used polymer foams such as are described in the
specifications DE 44 18 319 A1 and DE :195 05 709 A1, which
are hereby introduced by way of reference and thus form
part of the disclosure.
Thermoplastic fibres (e. g. two-component fibres formed from
polyoiefins, polyoiefin granules, latex dispersions or hot
melt adhesives) may be used for the mechanical
stabilisation of the liquid-absorbing suction layer.
Optionally one or more tissue plies are used for the
stabilisation.
The liquid-absorbing suction layer may be a single-ply
layer or may consist of several layers. Preferably
structures are used that consist of hydrophilic fibres,
preferably cellulose fibres, optionally having a structure
for the rapid absorption and distribution of body fluids,
such as for example chemically stiffened (modified)
cellulose fibres or highloft fleeces of hydrophilic or
hydrophilised fibres as well as superabsorbing polymers.
The superabsorbing polymer according to the invention may
be distributed homogeneously in the cellulose fibres or the
stiffened cellulose fibres, may be incorporated in the form
of plies between the cellulose fibres or the stiffened
cellulose fibres, or the concentration. of the
superabsorbing polymer may exhibit a gradient within the"
CA 02403966 2002-09-24
23
cellulose fibres or stiffened cellulose fibres. The ratio
of the total amount of superabsorbing polymer to the total
amount of cellulose fibres or stiffened cellulose fibres in
the absorbing suction core may vary between 0 to 1000 and
80 to 20~, wherein in one embodiment concentrations of up
to 100 of superabsorber may be achieved locally, for
example with a gradient-type or layer-type incorporation.
Such structures with regions of high concentrations of
absorbing polymer, in which the proportion of superabsorber
in specific regions is between 60o and 100 and most
preferably between 90o and 100, are also described for
example in US patent specification 5,669,894, which is
hereby introduced by way of reference and thus forms part
of the disclosure.
Optionally several different superabsorbers differing for
example in suction rate, permeability, storage capacity,
absorption under pressure, grain distribution or also
chemical composition, may also be used simultanecusly~. The
various superabsorbers may be introduced, mixed with one
another, into the suction cushion or alternatively may be
distribution in a locally differer~tiat:ed manner in the
absorbent core. Such a differentiated distribution may
take place over the thickness of the suction cushion or
over the length or width of the suction cushion.
The liquid-absorbing suction layer accommodates one or more
of the aforedescribed plies of cellulose fibres or
stiffened cellulose fibres containing superabsorbing
polymers. In a preferred embodiment structures are used
consisting of combinations of plies with a homogeneous
introduction of superabsorber and in addition a layer-type
incorporation.
Optionally these aforementioned structures are also
complemented by further plies of pure cellulose fibres or
stiffened cellulose fibres on the side facing the body
and/or also on the side facing away from the body.
CA 02403966 2002-09-24
24
~~he aforedescribed structures may also be multiply
repeated, which may involve a layer formation of two or
more identical layers on top of one another or
alternatively a layer formation of two or more different
structures on top of one another. In this connection the
differences are in turn of a purely structural nature or
may also relate to the type of material used, such as for
example the use of absorbing polymers or different types of
cellulose differing as regards their properties.
Optionally the whole suction cushion or also individual
plies of the liquid-absorbing suction layer are separated
by plies of tissue of other components, or are in direct
contact with other plies or components.
For example, the structure for the rapid absorption and
distribution of body fluids and the liquid-absorbing
suction layer may be separated from one another by tissue
or may however be in direct contact with one another.
Provided there is no separate structure for the rapid
absorption and distribution of body fluids between the
liquid-absorbing suction layer and the liquid-permeable
covering facing the body, but instead the liquid
distribution effect is to be achieved for example by the
use of a special liquid-permeable covering facing the body,
then the said liquid-absorbing suction layer may likewise
optionally be separated from the liquid-permeable covering
facing the body by a tissue.
Instead of tissue, non-woven fleece may optionally also be
incorporated into the liquid-absorbing suction layer. Both
components lead to the desired secondary effect of
stabilising and securing the absorption core in the moist
state.
CA 02403966 2002-09-24
Process for producing the liquid-absorbing suction layer
Fibre-containing and superabsorber-containing layers that
distribute and store liquid can be made by a large number
5 of production processes.
Apart from the established conventional processes, such as
are generally known to the person skilled in the art,
involving drum forming with the aid of moulded wheels,
10 pockets and product moulds and correspondingly adapted
metering devices for the raw materials, there may also be
used modern established processes such as the airlaid
process (e. g. EP 850 615, column 4 line 39 to column 5 line
29, US 4,640,810) with all forms of metering, laying of the
15 fibres and compaction such as hydrogen bonding (e.g. DE 197
50 890, column 1 line 45 to column 3 line 50,
thermobonding, latex bonding (e.g. EP 850 615, column 8
line 33 to column 9 line 17 and hybrid bonding, the wetlaid
process (e.g. PCT CVO 99149905, column 4 lire 14 t.o column 7
20 line 16), carding, meltblown, spunblown processes as well
as similar processes for the production of superabsorber-
containing nor-wover~s (within th a mearair~g of the EDANA
definition, Brussels), also in combinations of these
processes with conventional methods for the production of
25 the aforementioned liquid storage media. The
aforementioned specifications are introduced by way of
reference and thus farm part of the disclosure.
Further suitable processes include the production of
laminates in the broadest sense, as well as the production
of extruded and co-extruded, wet-compacted and dry-
compacted and also subsequently compacted structures.
Combinations of these processes with one another is also
possible.
Structures for the raid absorption and distribution of
body fluid
CA 02403966 2002-09-24
26
A structure for the rapid absorption and distribution of
body fluid consists for example of chemically stiffened
(modified) cellulose fibres or highloft= fleeces of
hydrophilic or hydrophilised fibres or a combination of the
two.
Chemically stiffened, modified cellulose fibres may be
produced for example from cellulose fibres that have been
converted in a chemical reaction by means of crosslinking
1.0 agents such as for example Cz-Cg dialdehydes, CZ-CB
monoaldehydes with an additional acid function, or CZ-Ce
polycarboxylic acids. Particular examples include
glutaraldehyde, glyoxal, glyoxalic acid or citric acid.
Also known are cationically modified starch or polyamide-
epichlorohydrin resins (e. g. KYMENE 557H from Hercules
Inc., Wilmington, Delaware). A twisted crumpled structure
is produced and stabilised by the crosslinking, which acts
advantageously on the rate of liquid absorption.
Weight per unit area and density of liquid-absorbing
articles
The absorbing hygiene products may differ as regards their
weight per unit area and thickness and accordingly the
density may vary greatly. Typically the densities of the
regions of the absorption cores are between 0.08 and 0.25
g/cm3. The weights per unit areas are between 10 and 1000
g/m2, preferred weights per unit area being between 100 and
600 g/mz (see also US 5,669,894, which is introduced here by
way of reference and thus forms part of the disclosure).
The density varies as a rule over the length of the
absorbing core, as a result of a selective metering of the
amount of cellulose fibres or stiffened cellulose fibres or
of the amount of the superabsorbing polymer, since these
components in preferred embodiments are incorporated more
strongly into the front region of the absorbing disposable
article.
This selective increase in the absorbing material in
specific regions of the absorbing core may also be achieved w
2?
'in another way by for example producing an appropriately
large two-dimensional structure by means of an airlaid or
wetlaid process, the said structure consisting of
hydrophilic cellulose fibres, optionally of stiffened
cellulose fibres, optionally of synthetic fibres (e. g.
polyolefins) as well as of superabsorbing polymers, which
are then folded or laid on top of one another.
Test methods
Test method 1: Retention (TB)
The retention is measured by the teabag method and is given
as the mean value of three measurements. About 200 mg of
polymer are welded into a teabag and immersed for 30
minutes in 0.9o NaCl solution. The teabag is then
centrifuged for 3 minutes in a centrifuge (23 cm diameter,
1,400 r.p.m.) and weighed. A teabag without water-
absorbing polymer is also centrifuged to provide a blank
value.
Retention = final weight - blank value/initial weight [g/g]
Test method 2: Anticaking test and moisture absorption
This test is intended to serve for the evaluation of the
caking behaviour and to determine the moisture absorption.
For this, 5 g of superabsorber are weighed out into a dish
and uniformly distributed, and stored for more than 3 hours
at 38°C and 80o relative atmospheric humidity in a climatic
test cafiinet. The dish is then reweighed in order to
determine the moisture uptake. The caking behaviour is
determined from the percentage screenings of the
superabsorber sample through a screen of 1.68 mm mesh width
shaken three times. Superabsorbers with a good anticaking
behaviour exhibit only a slight tendency to agglomerate
when stored under moist conditions and pass almost
completely through the screen.
Test method 3: Gel permeability (SFC)
CA 02403966 2002-09-24
CA 02403966 2002-09-24
28
The test is carried out according to a method published in
WO 95/22356, which is hereby introduced by way of reference
and thus forms part of the disclosure. About 0.9 g of
superabsorber material is weighed out :into a cylinder with
a screen plate and carefully distributE=d over the screen
surface. The superabsorber material is allowed to swell in
JAYCO synthetic urine for 1 hour against a pressure of
20 g/cmz. After measuring the swelling height of the
superabsorber 0.118 M NaCl solution is allowed to flow at
constant hydrostatic pressure from a levelled storage
vessel through the swollen gel layer. The swollen gel
layer is covered with a special screen cylinder during the
measurement, which ensures a uniform distribution of the
0.118 M NaCl solution above the gel and constant conditions
(measurement temperature 20°-25°C) as regards the state of
the gel bed during the measurement. T~~e pressure acting on
the swollen superabsorber is 20 g/cm2. With the aid of a
computer and a weighing machine the amount of liquid
passing through the gel layer as a furu~tion of time is
measured at 20-second intervals over a period of 10
minutes. The flow rate (in g/sec) through the swollen gel.
layer is determined by means of regressicr~ analysis by
extrapolation of the gradient and determination of the
midpoint at time t=0 of the amount of flow within the
period 2-10 minutes. The SFC value (K) is calculated as
follows:
F.(t = 0) ~ Lo F=(t = 0) ~ Lo
r ~ A - 0 P 139506
where: FS(t=0) is the flow rate in g/sec
Lo is the thickness of the gel layer in cm
r is the density of the NaCl solution (1.003 g/cm')
A is the area of the surface of the gel layer in
the measurement cylinder (28.27 cmz)
0P is the hydrostatic pressure acting on the gel
layer (4920 dynes/cmz),
CA 02403966 2002-09-24
29
and K is the SFC value [ cm3 ~ s ~ g-'
Test method 4: Liquid absorption under pressure (AAP test)
The absorption under pressure (pressure load 50 g/cm2) is
determined according to a method described in EP 0339461,
page 7. About 0.9 g of superabsorber is weighed out into a
cylinder with a screen plate. The uniformly scattered
layer of superabsorber i.s tamped with a pestle, which
exerts a pressure of 50 g/cmz. The previously weighed
cylinder is then placed on a glass filter plate arranged in
a dish containing 0.9o NaCl solution whose liquid level
corresponds exactly to the height of the filter plate.
After the cylinder unit has absorbed the 0.9o NaC:L solution
for one hour, the cylinder unit is reweighed and the AAP is
calculated as follows:
AAP = final weight (cyl.inder unit + fully soaked
superabsorber) - initial weight (cylinder unit +
superabsorber)/weighed out amount of superabsorber
CA 02403966 2002-09-24
best method 5: Flowability (FFC value)
The flowability of the superabsorbing polymer powders is
determined with the RST-1.01 annular shear device from
Dr.-Ing Dietmar Schulze Schuttgutme~technik. The FFC value
5 provides information on the flow properties of a bulk
material in a silo. In the measurement the bulk material
is subjected to various loads in an annular shear cell
(initial shear load 500,000 Pa, shearing off loads 100,000
Pa, 250,000 Pa, 400,000 Pa and 100,000 Pa) and the FFC
10 value is calculated from the determined measurement values.
The flow behaviour can be characterised as follows:
FFC Flowabilitv
>10 free flowing
15 4-10 slightly flowing
2-4 cohesive
1-2 very cohesive
<1 non-flowing
CA 02403966 2002-09-24
31
Examples
The invention is described in more detail hereinafter with
the aid of examples. These explanations are given simply
by way of example and do not restrict the general scope of
the invention. Unless otherwise specified, all polymer
powders have a moisture content of less than 5 wt.o, and
the treatments with the salt solutions were carried out at
room temperature.
Examples 1 - 5
Comparison examples 1 - 4
Powder of a superabsorbing, partially neutralised acrylic
acid polymer post-crosslinked on the surface was taken from
an industrial production batch and, without prior screening
of the fine fractions (3 wt.~ below 150 ~.tm), aqueous
solutions of aluminium sulfate, iron(III) chloride and.
magnesium chloride were added thereto while stirring with a
Krups domestic mixer, and the whole was slowly thoroughly
mixed on a bank of rollers to break down agglomerates. The
quantitative ratio of salt to water as well as the
properties of the powders treated with the salt solutions
and also the properties of the original powder without
screening (V1) and after screening (V2) of the fine
fractions under 150 ~m are given in Table 1.
35 Table 1:
Amounts of salt and water in wt.~ added to polymer powder
Example A12(S04)3i/Hz0 FeCl3+/H20 MgClz~~HzO AAP TB SFC
32
. ExampleAla ( S04 FeCl3'/H~O MgClZ~/H20 AAP TB SFC
) 3*/H20
V1 23.2 24 52
V2 23.5 24 69
B1 0.1/0.5 22.5 24 53
B2 0.1/3.0 21.6 23 60
B3 1.0/1.0 21.1 24 105
B4 0.25/0.5 21.6 23 98
B5 0.75/3.0 20.6 23 120
V3 0.25/3.0 22.1 23 48
V4 0.25/1..0 22.3 23 37
*: as hydrate with 18 H20, . as hydrate with 6 HzO,
as hydrate with 6 Hz0
Comparison Example 5:
The same procedure as in V3 is employed except that CaCl~ is
used instead of MgCl2. The polymer powder had a teabag
retention of TB = 23 g/g, an absorption under pressure of
AAP = 21.9 g/g and a gel permeability of SFC = 42
[ cm3 ° s ~ g-' ] .
Example 6:
A surface-crosslinked polymer powder according to Example 8
treated with an aluminium sulfate solution is stored under
the conditions of the anticaking test for 3 hours at 83°C
and 80~ relative atmospheric humidity and then subjected to
the screening test. In contrast to an untreated sample,
the polymer powder according to the invention passes almost
quantitatively through the test screen whereas the
untreated sample remains for the most part on the test
screen on account of its tendency to agglomerate.
Table 2
Product Moisture Absorption Screenings
Treatment
10.2 33.0
CA 02403966 2002-09-24
33
Product Moisture Absorption Screenings
Treatment [%~ [%]
wi thout A12 ( S04 ) 3
8.1 99.8
wi th A1z ( S04 ) 3
Example 7:
The powder of a Favor° SXM 91001 type superabsorber post-
s crosslinked on the surface, with 3.9 wt.o of fine fractions
below 150 ~tm and a gel permeability of SFC = 19
[ cm3 ~ s ~ g-1 ] was homogeneous 1y mixed wi th 1 wt . o o f a 5 0 ~
Al2 (S09) j x 14 H20 solution in a Ruberg mixer. Following
this the polymer powder contained only 2.0 wt.~ of fine
fractions and the gel permeability SFC had increased to 50
[ cm3 . s . g_1 ] .
If the fine fractions below 150 ~.m are separated from the
starting powder not treated with Al2(S09)3 solution, then a
powder is obtained with an SFC = 43 [crn3 ~ s ~ g-1] .
1. Surface-crosslinked superabsorber powder of pre-
crosslinked, partially neutralised pol~racrylic acid from
Stockhausen GmbH & Co., KG, Krefeld, Germany.
25 Example 8:
Corresponding to the procedure of Example 7, various
amounts of 50 wt . ~ A12 ( SO9 ) 3 x 14 HZO soI_ution are added to
Favor° SXM 65652 type superabsorber powder post-crosslinked
on the surface, containing 3.1 wt.o of fine fractions below
15 0 ~tm .
CA 02403966 2002-09-24
CA 02403966 2002-09-24
34
In order to evaluate the abrasion stability the
permeability was measured after grinding a sample not
treated according to the invention, and one treated
according to the invention. The grinding test was carried
out with 10 g of product over 6 minutes in a ball mill at
95 r.p.m. The permeability is measured after the grinding
test without separating any fine fractions.
Table 3
Wt . % A12 ( SOa ) 3 Solution 0 0 . 4 1. 0 2 . 0 4 . 0
SFC without separation of the 44 52 67 89 87
fine fractions below 150 ~.~m
SFC with separation of the fine 71
fractions below 150 [tm
SFC after ball mill treatment 20 79
2 Surface-crosslinked superabsorber powder of pre-
crosslinked, partially neutralised polyacrylic arid from
Stockhausen GmbH & Co., KG, Krefeld, Germany.
Example 9:
A superabsorber powder post-crosslinked on the surface and
containing 3 wt.~ of fine fractions (<:150 dim) obtained from
pre-crosslinked polyacrylic acid partially neutralised to
an amount of 70 mol o and grafted onto polyvinyl alcohol
(Mowiol 5-88, 1.9 wt.~ dry substance) was treated according
to the invention with 1 wt.o of a 50~ aqueous solution of
A12 ( SOQ ) 3 x 18 H20 by mixing on a bank of rollers . The
product had a retention of 25.5 g/g, an absorption under
pressure of AAP = 21 g/g and a gel permeability of SFC = 75
[ cm3 ~ s ~ g-1 ] .
CA 02403966 2002-09-24
Untreated, the superabsorber including 3 wt.o of fine
fractions (<150 ~.m) had a teabag retention of TB = 25 g/g,
an absorption under pressure of AAP = 22 g/g and a gel
5 permeability of SFC = 45 [cm3 ~ s ~ g-i] . After the screening
of the fine fractions the untreated absorber had, under
constant retention, an absorption under pressure of AAP =
22.5 g/g and a gel permeability of SFC = 75 [cm3 ~ s
g 1] .
Examples 10 - 13
Comparison Examples 6 - 7
A superabsorber powder according to Example 1 containing
3 wt.~ of fine fractions of <150 ~.(m is treated as in
Example 1. The properties of the absorber powders with
fine fractions (V6), without fine fractions (V7) and post-
treated according to the invention are shown in Table 4.
Table 4:
Amounts of salt or water in wt.o added to polymer powder
Example A1z ( S04 ) 3t/H20 FeCl3'/H20 AAP TB SFC
V6 23 24 45
v7 23.5 23.7 69
B10 0.5/0.5 21.5 24.5 93
B11 1.0/3.0 22 24 72
812 0.25/0.5 21 24 76
B13 0.5/3.0 21 23.5 60
* :. as hydrate with 18 HzO, +: as hydrate with 6 H20,
CA 02403966 2002-09-24
36
.Examples 14 - 19
Comparison Examples 8 - 10
A superabsorber powder according to Example 1 containing 5,
10 and 15 wt.o of fine fractions of <150~.m is treated as in
Example 1. The properties of the absorber powders with
fine fractions (V8-V10) and post-treated according to the
invention are shown in Table 5.
Table 5:
Amounts of salt and water in wt.~ added to polymer powder
ExampleFine Ala ( S04 AAP TB SEC Fine
) 3~/H20
Fractions Fractions
Before After
Treatment Treatment
V8 5 22 24 26
B14 5 0.5/0.5 21.3 24.7 52
B15 5 0.5/3.0 20.2 24.4 45 2.5
V9 10 21.4 24.3 29
B16 10 0.5/0.5 20.8 24.3 53
B17 10 0.5/3.0 20 23.7 45 3.5
V10 15 21.5 23.2 25
B18 15 0.5/0.5 19.6 23.7 53
B19 15 0.5/3.0 19.8 23.8 40 4.5
*: as hydrate with 18 H20
Examples 20 - 24
Comparison examples 11 - 15
Variously concentrated aqueous solutions of aluminium
sulfate were~added to powders of a pol_yacrylic acid polymer
partially neutralised to 70 mol o with sodium hydroxide and
post-crosslinked on the surface and containing a fine dust
fraction <150 ~m of 1.1 wt.~, in an MTI mixer (blade mixer)
and thoroughly mixed at 750 r.p.m.
Table 6:
Amounts of salt and water in wt.~added to polymer powder
Example Ala ( S04 FFC AAP TB SFC
) 3~/Hz0
B20 0.15/0.15 14 22.5 27 47
Vli without 5.7 23 26.5 44
B21 0.15/0.5 11 22.8 26 41
V12 without 6.2 23.3 26.'7 37
B22 0.15/1.0 10.4 22.8 26.5 48
V13 without 6.2 23.5 27 37
B23 0.15/2.0 8.6 22.3 26.8 45
V14 without 6.2 24 26.3 38
B24 0.15/3.0 8.3 22 26 63
V15 without 6.8 23.8 26.5 46 '
* : as hydrate wi th 18 HzJ
The products exhibited a good to extremely good
flowability, which in the case of Examples 20 - 22 was
manifested immediately after brief mixing, whereas the
products according to Examples 23 and 24 that had been
treated with salt solutions of lower concentration required
a longer standing and/or mixing time o:f up to 1 hour.
CA 02403966 2002-09-24
