Note: Descriptions are shown in the official language in which they were submitted.
1~53~40
This invention relates to a process for the
production of emulsifier-free rubber latices of (meth)
acrylic acid and acyclic conjugated dienes together with
arylvinyl monomers and/or (meth)acrylonitrile.
In conventional emulsion polymerisation processes,
the monomers are normally polymerised in the presence
of an initiator which releases free radicals and an
emulsifier which keeps the polymer particles formed in
dispersion. However, the presence of emulsifiers
frequently leads to difficulties in the processing of
the latices owing to inadequate mechanical stability or
to foam formation and results in a reduction in the wet
strength of the coatings produced with dispersions such
as these or of the substrates treated with them and in
reduced adhesion of the binder to the substrates.
It i8 known that the stability of rubber latices
can be increased and the sensitivity of the $ilms to
water can be reduced by carrying out the emulsion
polymerisation reaction in the presence of emulsifiers
which are incorporated into the polymer, such as for
example semiesters of maleic acid and fatty alcohols
(German Auslegeschrift No. 1,011,548) or 4-styrene
undecanoic acid (US Patent No. 2,868,755). This internal
binding of the surface-active substances considerably
reduces the sensitivity of the latices to shear forces
by co~parison with latices of the type in which the
polymer particles are stabilised by the adsorption of
emulsifier molecules.
The incorporation o~ monomers containing strongly
3o dissociating groups also gives rubber latices which
show considerably greater stability than rubber latices
containing adsorbed surface-active substances. Stable
emulsifier-free rubber latices of this type are obtained
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by copolymerising monomers containing sulphonic acid
groups in aqueous emulsion, for example by the incorporation
o~ 4-styrene sulphonic acid (US Patents Nos. 2,913,429 and
3,306,871~ or by means oi esters o~ acrylic or methacrylic
acid and 2-hydroxyethane sulphonic acid, such as for
example 2-sulphoethyl acrylate (US Patent No. 2,914,499).
In this way, the latex particles are stabilised by
sulphonate groups which provide ~or an adequate charge
on the suriace oi the particles.
It is known irom US Patent No. 3,784,498 that
emulsi~ier-free carboxylated rubber latices can be
obtained by initially preparing a latex ~rom the total
quantity o~ the ethylenically unsaturated carboxylic
acid and part of the water-insoluble monomers at a pH-
value o~ irom about 2 to 4, adding the rest of the
monomers after the pH-value has been adjusted to between
7 and 10 and continuing polymerisation until a complete
conversion is obtained. This measure drastically increases
the dissociation o~ the carboxyl groups so that the polymer
particle9 are adequately stabilised by the carboxylate
groups during the second polymerisation stage, thus
avoiding coagulation. ~owever, the necessary increase
in the pH-value from 2-4 to 7-10, ior which aqueous
ammonia ispre~erably used, complicates the process
because the ammo~nia has to be added slowly and carefully
and, in many cases, leads to considerable coagulate
~ormation.
It has now been found that emulsi~ier-free
carboxylated latices can be obtained from (meth)acrylic
acid, dienes and arylvinyl monomers and/or (meth)acrylo-
nitrile using a peroxodisulphate as radical initiator,
providing at least part of the (meth)acrylic acid, part
- of the diene and other monomers are polymerised at a
pH-value oi irom 3.5 to 7, the rest of the monomers
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are added in one or more stages and the polymerisation
reaction is continued at this pH-value until at least
50 % of the monomers have been polymerised and, in the
final stage, until from 85 to lO0 % of the monomers
have been polymerised. The process according to the
invention enables corresponding rubber latices to be
produced without using emulsifiers.
~ he process is generally carried out by initially
introducing water and at least part of the (meth)acrylic
acid, part of the conjugated diene and arylvinyl monomers
and/or (meth)acrylonitrile into a reactor and initiating
the polymerisation reaction at a temperature above 70C
and preierably at a temperature of from 75 to ~5C by
the addition of an aqueous, preferably ammoniacal
peroxodisulphate solution, the ammonia content of which
is measured in such a way that polymerisation takes place
at a pH-value of ~rom 3.5 to 7. Polymerisation is
continued up to a conversion oi at least 50 % and,
depending on the pressure conditions in the reactorand
the required final concentration, more monomer and,
optionally, (meth)acrylic acid and more aqueous, preferably
ammoniacal, peroxodisulphate solution are added in batches
so that the polymerisation reaction is continued at a
pH-value of from 3.5 to 7.
In general, two or three stages are su~iicient Yor
this polymerisation reaction, although more polymerisation
stages are also possible. In each polymerisation stage,
polymerisation is continued up to a conversion of at least
50 /0. In the ~inal stage, polymerisation is continued
up to a con~ersion of from ~5 to lO0 /0 o$ the monomers.
A latex having a solids content o~ from 30 to 65 /0 by
weight and preierably from 40 to 60 % by weight is obtained.
Both organic and also inorganic bases, for example
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NaHC03, ammonia or triethylamine, are suitable for
adjusting the pH to a value of from 3.5 to 7 during
the polymerisation reaction. It is preferred to use
aliphatic amines and ammonia, ammonia being particularly
preferred.
The total quantity of the peroxodisulphate used as
initiator in the process according to the invention
amounts to between 0.5 and 3.0 parts by weight, based
on the total quantity of monomers. Suitable initiators
are salts of peroxodisulphuric acid, such as sodium,
potassium or, pre~erably, ammonium peroxodisulphate.
In one preferred embodiment, the individual poly-
merisation stages are initiated by the addition of an
aqueous ammoniacal peroxodisulphate solution which
simultaneously adjusts the pH to a value of 3.5 - 7.
Surprisingly, the process according to the invention
can be applied so universally that the ratio of conjugated
diene to arylvinyl monomer and/or (meth)acrylonitrile
can be varied within very wide limits. Accordingly, it
is possible in accordance with the invention to produce
from the above-mentioned monomers rubber latices which
contain from lO to 90 parts by weight of one or more
acyclic conjugated dienes containing from 4 to 9 carbon
atoms, from 0 to 90 parts by weight of one or more
arylvinyl monomers containing from 8 to 12 carbon atoms
and/or ~rom 0 to 50 parts by weight of (meth)acrylonitrile,
the sum of the last two components amounting to between
lO and 90 parts by weight.
Accordingly, the present invention provides a process
for the production of an emulsifier-free rubber latex from
l to 6 parts by weight oi ~meth)acrylic acid and 94 to 99
; parts by weight o~ a mixture of lO to 90 parts by weight
; of one or more acyclic conjugated dienes containing ~rom
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4 to 9 carbon atoms and 10 to 90 parts by weight of one
or more arylvinyl monomers containing from 8 to 12
carbon atoms and/or (meth)acrylonitrile, the quantity
oi (meth)acrylonitrile amounting to at most 50 parts
by weight, characterised in that
a) an aqueous emulsion i9 prepared by adding at
least part of the (meth)acrylic acid, part of the
diene and other monomers to water,
b) the polymerisation reaction is initiated by the
addition of an aqueous ~olution of a peroxodi-
sulphate,
c) polymerisation is carried out in a first stage at
a pH-value of from 3.5 to 7 and at a temperature
above 70C until at least 50 /0 of the monomers
have been polymerised,
d) the rest o~ the monomers and more aqueous peroxo-
di~ulphate solution are added in one or more
; ~urther stages, and
e) polymerisation is continued at a pH-value oi from
3.5 to 7 and at a temperature above 70C until at
least 50 % of the monomers have been converted and,
in the ~inal stage, until irom 85 to 100 /0 of the
monomers have been converted.
Suitable acyclic conjugated dienes containing from
4 to 9 carbon atoms are, ~or example, 1,3-butadiene,
2-methyl-1,3-butadiene (isoprene), 2,3-dimethyl-1,3-
butadiene, piperylene, 2-neopentyl-1,3-butadiene and
other substituted dienes, such as ior example 2-chloro-
1,3-butadiene (chloroprene), 2-cyano-1,3-butadiene and
substituted straight-chain conjugated pentadienes and
straight-chain or branched chain hexadienes. Its ability
to copolymerise particularly well with arylvinyl monomers
makes 1,3-butadiene the preferred monomer.
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Suitable arylvinyl monomers are those in which the
vinyl group, optionally alkyl-substituted in the ~-
position, i9 directly attached to an aromatic nucleus
consisting of from 6 to lO carbon atoms3 for example
styrene and substituted styrenes, such as 4-methyl
styrene, 3-methyl styrene, 2,4-dimethyl styrene, 2,4-
diethyl styrene, 4-isopropyl styrene, 4-chlorostyrene,
2,4-dichlorostyrene, divinyl benzene, ~-methyl styrene
and vinyl naphthalene. For reasons o$ availability
and by virtue o$ its ability to copolymerise ef$ectively,
particularly with l,3-butadiene, styrene is the preferred
monomer.
Up to 25 parts by weight o$ the non-dissociating
monomers may be replaced by one or more monomers which
can be copolymerised with the above-mentioned monomers.
Monomers such as these are acrylic and/or methacrylic
acid esters o$ alcohols containing up to 8 carbon atoms
and also diesters oY alkane diols and ~,~-monoethylenically
unsaturated monocarboxylic acids, such as ethylene glycol
diacrylate and l,4-butane diol diacrylate, and amides of
~,~-monoethylenically unsaturated mono- and di-carboxylic
acids, such as acrylamide and methacrylamide. Further
comonomers ~hich may be used for the purposes o$ the
invention include vinyl esters o$ carboxylic acids
containing $rom l to 18 carbon atoms, particularly
vinyl acetate and vinyl propionate, vinyl chloride and
vinylidene chloride, vinyl ethers, such as vinyl
methyl ether, vinyl ketones, such as vinyl ethyl ketone,
and heterocyclic monovinyl compounds, such as vinyl
pyridine.
In addition to the a~ove-mentioned monomers, known
chain-transfér agents may be used ior in$1uencing the
properties of the copolymers. Suitable chain-trans$er
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agents are long-chain alkyl mercaptans such as, for
example, tert.-dodecyl mercaptan, mercaptocarboxylic
acids, such as thioglycolic acid, lower dialkyl di-
xanthogenates, carbon tetrabromide and bromoethyl
benzene. The quantity in which the chain transfer
agent is used is determined inter alia by its effectiveness
and also by the quantity in which the diene is used and
may readily be selected by the expert.
As already mentioned, the process according to
the invention is a polymerisation process which i8
carried out in two or more stages, the number of stages
being determined by the pressure conditions in the
reactor and by the required final concentration of the
latex. Depending on the number of polymerisation stages,
about hal~ the total of non-dissociating monomers is
initially introduced in a two-stage operation, about a
third in a three-stage operation, and so on. Accordingly,
the monomers are added in substantially equal portions
commensurate with the number of stages. ~his also
applies to the (meth)acrylic acid, although it is also
possible for the methacrylic acid to be completely
introduced in the first stage alone.
In the first stage, the polymerisation reaction
is carried out until a conversion of at least 50 /0 is
obtained. In the majority of cases, complete poly-
merisation in the first stage i9 unadvisable because,
in many cases, this measure leads to the formation of
deposits and microcoagulate. In the first stage,
polymerisation is preferably carried out up to a
conversion of from 70 to 85 /0 by weight, after which
a second batch of the non-dissociating monomers is
~- added, more aqueous peroxodisulphate solution is intro-
duced and polymerisation is continued at a pH-value of
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from ~.5 to 7. The addition of more acrylic and/or
methacrylic acid is governed by the total quantity of
the acid which may amount to between l and 6 parts by
weight, based on the monomer total. Where only l part
by weight is used, the total quantity of (meth)acrylic
acid i9 introduced in the first stage, although where a
larger quantity is used, it is generally more favourable
to distribute the acid between the individual polymeris-
ation stages. In the second polymerisation stage and in
each following polymerisation stage, polymerisation is
continued until all the monomers then present have been
polymerised up to a conversion of at least 50 %. Finally,
in the last stage, polymerisation is continued until
from 85 to lO0 /0 oi' the monomers have been converted.
In many cases, it is su~ficient to carry out the process
in only two stages, in the first of which polymerisation
is carried out up to a conversion of at least 50 /0 and
in the second of which polymerisation is continued up to
a conversion of from 85 to lO0 %. The late~ may then
be freed from residual monomers in known manner at a
pH-value of from 6 to 8 and, to increase its mechanical
stability, may be adjusted to a pH-value of from about 8
to lO.
The process according to the invention gives
emulsifier-free rubber latices which have extremely
high stability with respect to chemical and mechanical
influences, show very little foam formation during
processing, are compatible with other emulsifier-free
or emulsifier-containing latices and with liquid
phenolic resins, and may readily be concentrated by the
removal of water. The polymer films produced from these
latices and articles produced with these dispersions
show considerably improved resistance to water, dry and
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harden more quickly, adhere much more firmly to the
particular substrates and show far less discolouration
by comparison with articles produced from dispersions
containing even small quantities of emulsifiers. Polymer
films and products wi*h improved resistance to water
are obtained in particular from alkali-metal-free
latices in the production of which ammonia is used for
adjusting the pH-value and ammonium peroxodisulphate as
initiator. ~he latices produced in accordance with the
invention are surprisingly distinguished by their
versatility in terms of practical application and may
be used, for example, as a leather finish, for bonding
non-woven fabrics, for impregnating and coating textile
materials and papers, and for the production oi adhesives,
printing inks and aqueous paint binder formulations.
The process according to the invention is illustrated
by the ~ollowing Examples.
EXAMPLE 1
In a 40 litre stainless steel reactor equipped with
a crossed-arms paddle stirrer, a solution of 120 g of
ammonium peroxodisulphate and 30 ml of a 25 % aqueous
ammonia solution in 500 g of water is added at 80C
to a mixture of 2500 g of 1,3-butadiene, 2400 g of
styrene and lll g of 90 /0 methacrylic acid in 8750 g of
water, followed by polymerisation at 80C until a solids
concentration of approximately 20 % by weight is reached
tafter 4 hours). In the meantime, the pH-value of the
emulsion remains between 4.3 and 4.l. 2500 g of l,3-
butadiene, 2400 g of styrene and lll g of 90 ~0 meth-
acrylic acid are then added, followed by the additionof another 30 g of ammonium peroxodisulphate and 30 ml
of a 25 % aqueous ammonia solution in 500 g of water to
the emulsion, after which polymerisation is continued to
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10.5 hours at a temperature of 80C. During this
second polymerisation phase, the pH-value of the
emulsion remains between 4.~ and 4.6.
After a solids concentration of 50.5 % by weight
has been reached, the polymerisation mixture is cooled
to room temperature, 280 g of a 7 ~ diethyl hydroxylamine
solution are added, and the latex i9 substantially
neutralised with an aqueous ammonia solution and then
freed from residual monomers. The pH is then adjusted
to a value of 9.2 with aqueous ammonia solution. Deposits
which only amount to 130 g (weighed moist) are then
filtered off, leaving a latex having a solids content o~
49.6 ~, a particle diameter of from 320 to 340 nm and
a surface tension of 47.2 mN/m.
This latex is suitable for the production of needle
felt floor coverings and as a first-coat latex for
stabilising tufted fabrics.
The following Comparison Examples illustrate the
influence on polymerisation of the pH-value and the
methacrylic acid.
COMPARISON EXAMPLE 1 (without ammonia)
The procedure is as in Example 1, except that the
aqueous ammonia solutions are not added in either of
the two polymerisation phases. As a result, the first
polymerisation phase is carried out at a pH-value of
from 2.1 to 1.6 and a solids concentratio~ of 20 ~0 by
weight is reached after akout 3.5 hours. In the second
phase, the polymerisation time amounts to 11 hours for
a pH value o~ from 1.5 to 1.4.
; 30 After a concentration of 49.7 /0 by weight has
been reached, the polymerisation mixture is cooled,
the polymerisation reaction is stopped, the lateæ is
substantially neutralised with ammonia and then freed
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~rom residual monomers in the same way as in Example 1.
Adjustment of the pH-value to 9.0 with dilute aqueous
ammonia solution gives a latex having a solids concen-
tration o~ 47.5 /0 by weight and containing considerable
quantities of coagulate. The filtered latex has
particle diameters oi irom about 280 to 310 nm and a
suriace tension oi 48.3 mN/m.
COMPARISON EXAMPLE 2 (without m_thacrylic acid)
In a 40 litre stainless steel autoclave equipped
with a crossed-arms paddle stirrer, a mixture of 2500 g
oi 1,3-butadiene and 2500 g of styrene in 11250 g of
water is polymerised at 80C with a solution of 150 g o~
ammonium peroxodisulphate and 30 ml o~ a 25 % aqueous
ammonia solution until a solids concentration o~
appro~imately 20 /0 by weight is reached (after 6.5 hours).
During this first polymerisation phase, the pH-value
o$ the emulsion ialls ~rom 8.2 to 2.3. Another 2500 g
oi 1,3-butadiene and 2500 g of styrene and an aqueous
solution o$ 100 g oi ammonium peroxodisulphate and 30 ml
oi 25 % aqueous ammonia solution are then added, after
which polymerisation is continued for 20 hours at a pH-
value falling from 8.0 to 1.7 until a solids concentrationo~ 44 /0 by weight is reached. Stopping oi the poly-
merisation reaction and working up in the same way as
in Example 1 leave a latex which has to be iiltered
o~f irom a large quantity of coagulate.
COMPARISON EXAMPLE 3 (without ammonia and methacr~lic acid)
~ he procedure is as in Comparison Example 2, e~cept
that no ammonia is added in either the first or the
second polymerisation phase. As a result, the poly-
merisation velocity decreases with a reduction in pH
- ~rom 2.4 to 1 4, so that a solids concentration o$ 19 /0
by weight is only reached a~ter 10 hours and a final
concentration of 43.7 /0 by weight is only reached a~ter
another 25 hours at a pH-value oi 1.0 despite reactivation
with 20 g of ammonium peroxodisulphate in 100 g oi water
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at a solids content of 40 /0 by weight. An unstable
latex is obtained, coagulating spontaneously on
completion of polymerisation.
COMPARISON EXAMPLE 4 (with methacrylic a _d)
2500 g of 1,3-butadiene~ 2400 g of styrene and
111 g of 90 % methacrylic acid in 250 g of water are
added to 10,000 g of water, and polymerisation is
initiated by the addition at 80C of a solution of 150 g
of ammonium peroxodisulphate in 500 g of water. A solids
concentration of 20 % by weight is reached after only
3.5 hours. The pH-value during the first polymerisation
phase remains between 2.4 and 1.6. 2400 g of styrene,
2500 g Or 1,3-butadiene, 111 g of 90 /0 methacrylic acid
and a solution of 100 g of ammonium peroxodisulphate
in 500 g of water are then added. A solids concentration
of 43.7 % by weight is reached after another 10 hours at
a pH-value of 1~3. Stopping of the polymerisation
reaction and working up in the same way as in Example 1
leaves a latex which, although stable, contains
considerable quantities of coagulate.
EXAMPLE 2
In a 40 litre stainless steel reactor equipped with
a crossed-arms paddle stirrer, a mi~ture of 1200 g of
styrene and 1200 g of acrylonitrile, 2500 g of 1,3-
butadiene and 111 g of 90 /0 methacrylic acid in 250 g
Of water and 100 g of methacrylamide are polymerised
at 75C in 12500 g of water with a solution of 50 g of
ammonium peroxodisulphate in 500 g of water and 3~ ml of
25 oh aqueous ammonia solution. A solids concentration of
25.3 /0 by weight is reached after polymerisation rOr
4.5 hours at 75C. In the meantime, the pH-value increases
from 4.6 to 5.3. A mixture of 1200 g of acrylonitrile,
1200 g of styrene and 2500 g of 1,3-butadiene is then
added, followed by the introduction of a solution of
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100 g of ammonium peroxodisulphate and 30 ml of 25 ~
aqueous ammonia solution in 500 g of water. A solids
concentration of 43.2 /0 by weight is reached after
ano~her 8 hours, and the contents of the reactor are
then cooled and the polymerisation reaction stopped by
the addition of 280 g of 7 /0 diethyl hydroxylamine
solution. During the second polymerisation phase, the
pH-value falls from 6.8 to 6.5. The latex is freed
from residual monomers and adjusted to pH 9.0 with
aqueous ammonia solution. After 300 g (weighed moist)
of deposits have been iiltered o$f, the solids
concentration amounts to 42.0 % by weight and the surface
tension to 50.5 mN/m. With particle diameters between
360 and 670 nm, the latex has a wide particle size
distribution.
This product may be satisfactorily mixed with
large quantities of liquid phenol-formaldehyde resins.
It is therefore suitable as an elasticising agent for
articles produced with phenol-formaldehyde resins, for
example separator plates.
EXAMPLE 3
In a 40 litre stainless steel reactor equipped with
a crossed-arms paddle stirrer, 12500 g of water, 1100 g
of acrylonitrile, 10 g of tert.-dodecyl mercaptan and
222 g of 90 % methacrylic acid in 500 g of water are
mixed and polymerised at 75C with a solution of 50 g
of ammonium peroxodisulphate and 30 ml of 25 ~ aqueous
ammonia solution in 500 g of water. After polymerisation
for 5 hours, during which the pH-value rises from 4.0
3o to 4.5, a solids concentration of 16.3 /0 by weight is
reached. A mixture of 2200 g of 1,3-butadiene, 1000 g
of acrylonitrile and 40 g of tert.-dodecyl mercaptan
and a solution of 50 g of ammonium peroxodisulphate and
15 ml of 25 % aqueous ammonia solution in 250 g of water
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are added and polymerisation is continued at pH 6.Q to
6.4 until the second polymerisation phase is terminated
at a solids concentration of around 28 /0 by weight (total
polymerisation time 7.5 hours). The third polymerisation
phase is initiated by the addition of the same solutions
as at the beginning of the second polymerisation phase.
Polymerisation is completed up to a solids concentration
of 40.9 /0 by weight and, shortly beiore the final
concentration is reached, is reactivated by the addition
of another 20 g of ammonium peroxodisulphate in 100 g
of water. In the third polymerisation phase, the pH-
value remains substantially constant at 6.o. After the
polymerisation reaction has been stopped by the addition
of 280 g of 7 % diethyl hydroxylamine solution, the late~
is degassed in vacuo at 40C. The latex is substantially
~ree from coagulate, has a final concentration of 41.4 /0
by weight, a pH-value of 6.4 and a surface tension of
56.3 mN/m. It has a particle size distribution of from
about 170 to 460 nm.
This late~ is suitable for the production of
hydrophobic solver.t-resistant special papers.
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