Note: Descriptions are shown in the official language in which they were submitted.
2 ~ ~/J ~
O.Z. 0050/40946
Polymer powders which are L-edispersible in water and
can be prepared by atomizinq aqueous ~olymer
dispersions, and their use as additives in hydraulic
binders
The present invention relates to polymer powders
which are redispersible in water and are obtainable by
atomizing aqueous polymer dispersions to which from 3 to
50% by weight, based on the polymer, of a water-soluble
alkali metal salt or alkaline earth metal sal~ of a
phenolsulfonic acid/formaldehyde condensate has been
added, and their use as additives in hydraulic binders.
It is known that redispersible dispersion powders
can be prepared by atomizing aqueous polymer dispersions
in a stream of hot air. In the case of dispersions whose
polymers have glass transition temperatures below about
50C, it is necessary to add assi~tants to prevent the
polymer particles from forming a film in the drier with
formation of wall deposits and lumps, and to achieve
adequate blocking resistance of the powders.
In addition to water-insoluble inert additives,
such as finely divided silica, other possible additives
are dispersions of polymers having a high s~yrene content
~c~: ~7/O~ (DE-A 2 238 903~ or aqueous copolymer solutions based on
vinylpyrrolidone and vinyl acetate tDE-A 3 143 071) and
water-soluble sulfonat~-containing condensates of mela-
mine and formaldehyde tDE-A 2 049 114). ~
For the preparation of polymer powders which are
redispersible in water and have particularly high block-
ing re~istance, DE-A 3 143 070 recommends the addition of
a water-soluble naphthalene ulfonic acid/formaldehyde
con-densate in the form of the alkali metal salt or
alkaline earth metal salt. In this proce g, free-flowing
powders which are readily redispersible in water can be
obtained, even from contact adhesive copolymer disper-
sions. Such redisper~ible polymer powders are suitahle,
for example, a~ additive~ in hydraulic binder3 which have
a viscosity-reducing effect and impart ela~tic properties
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to the et mortar.
~ he advantages of the concrete or mortar which
are achievable by this process are, however, offset by
the fact that the flow is restricted, which is disadvan~
tageous, for example in self-leveling filling compounds.
It is an object of the present invention to pro-
vide redispPrsible polymer powders which guar~n~ee good
flow when used as additives in hydraulic binders.
We have found that this object is achieved by the
polymer powders mentioned at the ou~set and their use as
additives in hydraulic binders.
Preferred embodiments of the invention are des-
cribed in the subclaims.
The polymer dispersions for the preparation of
redispersible polymer powders can be obtained in a con-
ventional manner by emulsion polymerization of olefinic-
ally unsaturated monomer~ in the presence of the usual
polymerization initiators, emulsifiers and diYpersant~ at
elevated temperatures, for example up to about 95C. The
mean particle size can be adjusted by conventional
measures, for example via the type and amount of the
emulsifiers: for the preparation of coarse-particled
polymer dispersions, a small amount of emulsifier and
nonionic or highly ethoxylated ionic emulsifiers are
generally advantageou Protective colloids, for example
polyvinyl alcohol, frequently have an advantageous
effect. Polymerization in the presence of a seed latex
can al~o be advantageous, particularly if the formation
of new particles is suppressed. Finally, coarse
particled dispersions can also be produced by controlled
agglomeration of finely divided latic~s.
Preferred polymer di~persions have a mean par-
ticle diameter (weight average) of from 400 to 5,000 nm,
in particular from 650 to 5,000 nm. ~he measurement of
the mean particle sizes of polymer dispersions, for
example with the aid of an ultracentrifuge, i~ ~amiliar
to the skilled worker. The LT value, ie. the light
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transmittance of the aqueous dispersion diluted to 0.01%
by weight, a standard parameter which is readily obtain-
able experimentally, can also be used as a measure of the
mean particle size of a polymer dispersion of similar
5 monomer composition.
In the preparation of the polymer powders, the
polymer content of the dispersion may vary from 30 to 65,
in particular from 45 to 60, % by weight. The polymers
generally have glass transition temperatures of from +50
to -60C, polymers having a glass transition temperature
of less than +25C preferably being used. Examples of
olefinically unsaturated monomers from which the polymers
may be derived are vinylaromatic monomers, such as
styrene, monoolefinically unsatura~ed carboxylates of, in
general, 4 to 14 carbon atoms, in particular acryla~es
and me~hacrylates of alkanols of l to 8 car~on atoms, and
vinyl esters, in particular of acetic and propionic acid,
as well a~ vinyl laurate and vinyl esters of versatic
acids. Other suitable polymers are those which are
derived from vinyl chloride and/or vinylidene chloride or
from diolefins, in particular butadiene. In addition,
the polymers may contain, as polymerized units, acrylo-
nitrile and/or mono- and/or dicarboxylic acids of, in
general, 3 to 5 carbon atoms and/or their amides which
may be substituted at the nitrogen atom, in particular
acrylic acid, methacrylic acid, itaconic acid, acryl-
amide, methacrylamide, N-methylolacrylamide and -meth-
acrylamide and N-metho~ymethylacrylamide and -methacryl-
amide. The amount of such monomers can be varied within
wide ranges. It i~ from 0 to 40, frequently from 10 to
30, % by weight in the case of acrylonitrile, and fre-
quently from 0.5 to 5, in particular from 1 to 4, % by
weight in the case of monoolefinically unsaturated mono-
mers having polar groups, such as acrylic acid or N-
methylolmethacrylamids. The polymers may also contain,
as polymerized units, small amounts of olefinically un-
saturated e~ters of alkanediol~, such as ethylene glycol
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monoacrylate and diacrylate and the corresponding meth-
acrylates and butane-1,4-diol monoacrylate and diacrylate
and the corresponding methacrylates. Finally, polymer
dispersions which contain, as polymerized units, ethylene
and vinyl acetate in a molar ratio of, in general, from
15 : 85 to 85 : 15 are also suitable.
Preferably used copolymers are those of acrylates
and methacrylates of alkenols of 1 to 8 carbon atoms,
which may contain, as polymerized unit~, not more than
65, in particular from 15 to 60, % by weight of styrene
or a mixture of styrene and not more than 40~ by weight,
based on the styrene/acrylonitrile mixture, of acrylo-
nitrile. For such acrylate/styrenecopolymer dispersions
the LT value is in general less thatn 20~, frequently
less than 10%.
In the preparation of the polymer powders, water-
soluble alkali metal and/or alkaline earth metal salts of
phenolsulfonic acid/formaldehyde condensates are added to
the polymer dispersions prior to atomization, in an
amount of from 3 to 50, preferably from 3 to 15, in par-
ticular from S to 10, % by weight, based on the polymer
content of the aqueous polymer dispersion~. The conden-
sates contain in general 1 or 2 formaldehyde radicals, in
particular 1 formaldehyde radical, per phenol radical and
in particular 1 sulfo group per molecule. They are
preferably used in the form of the Na salt~. The alka-
line earth metal salts and in particular the Ca salt~ are
particularly preferred since they give a nonhygroscopic
powder. Such salts of phenol~ulfonic acid/formaldehyde
conden3ates are commercially available.
In addition to the condensates, water-insoluble
finely divided solids, for example finely divided ~ilica
or water-soluble proteckive colloids, for example poly-
vinyl alcohols or vinylpyrrolidone (co)polymers, may also
have been added to the polymer dispersions in the prep-
aration of the polymer powder~.
Atomization of the aqueous polymer disper~ion~
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which contain the salts of the phenolsulfonic acid/form-
aldehyde condensates can be carried out in a conventional
manner, in particular using one-material or multi-
material nozzles or atomizer disks. The dispersions are
generally atomized in a warm air stream, in which the
water evaporates. Atomization can be carried out under
atmospheric or reduced pressure. In general, the temp-
erature of the warm air stream used for spray d~ying is
from 100 to 200C, in particular from 120 to 170C. The
dry redispersible polymer powders can be separated off in
a conventional manner, in particular using cyclones or
filter separators.
Polymer powders having high blocking resistance
are obtained in a high yield even using comparatively
small amounts of phenolsulfonic acid/formaldehyde conden-
sates and can be readily stored at room temperature,
without caking. The polymer powders are readily redi~-
persible in water. After stirring in water, they can be
cast into films which are ~imilar in their tensile
strength and elongation at break to films obtained from
the primary dispersions.
~ hen used for modifying hy~raulic binders, the
polymer powders are mixed with, for example, cement, from
5 to 30% by weight, based on cement, of polymer powder
preferably being used, and further proce~sing by mixing
with water and if necessary mineral additives gives
mortars having good flow and high flexibility.
Furthermore, the flexural strength and adhesive
strength o~ such mortars are generally higher than in the
ca~e o~ plastic-free comparative samples. In addition to
the mechanical properties, processing is also advantage-
ously effec~ed by the novel polymer powders: the polymer
powders impart to the mortar a more fluid consistency,
which changes only slightly during processing. Because
they also harden rapidly, the polymer powders are there-
fore particularly suitable for flow mortars, for example
self-leveling flooring plasters or filling compounds.
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In the Examples which follow, parts and percent-
ages are by weight. The mean particle size (weigh~
average) of the polymer dispersions was determined with
the aid of an analytical ultracentrifuge. The glass
5 transition temperatures of the polymers were determined
by the method of differential thermal analysis.
Preparation of the polymer powder
The amount, stated in Table 2, of the calcium
salt of a phenolsulfonic acid/~ormaldehyde condensate or
of the calcium salt of a naphthalenesulfonic acid/formal-
dehyde condensate was added to the aqueous dispersions of
the polymers stated in Table 1 below. The mixture was
atomized via a two-material nozzle of an IWK drier at
25C at a rate of 80 kg~hour. Precipitated hydrophobic
silica was metered in an amount of 3~ by weight, based on
the dispersion, by means of a screw and via a further
nozzle. The IWK drier was simultaneously fed with 2300
m3 (S.T.P.)/hour of warm air at 120C, and the product
obtained was separated off in a cyclone.
The compositions and characteri~tics of the poly-
mer dispersions used are listed in Table 1.
TABLE 1
Dis- Polymer Poly- Glass LT Mean
per- composition mer transi- value particle
sion con- tion weight
tent ~ Temp. C ~ average
nm
A 46 parts of styrene 50 16 7 832
54 parts of butyl
acrylate
0.8 part of acryl-
amide
0.8 part of meth-
acrylamide
B 29 parts of styrene 55 -7 36 234
69 parts of butyl
acrylate
2 parts of acryl-
amide
~ ~ S~ C)
_ 7 _ o.z. 0050/40946
~he polymer powders obtained using the various
amounts, stated in Table 2, of the phanolsulfonic acid/
formaldehyde condensate showed little or no tendency to
block (testing of blocking resis~ance under a pressure of
5 0.785 N/cm2 at 23C for 24 hours) and could if necessary
readily be milled and easily redispersed in water.
Properties of mortar modified with the polymer powders
The solidification time was characterized using
mortars having a plastic/cement ratio of 0.1, on the
1~ basis of the Vicat solidification time (DIN 1164, Part
S) .
The flow was determined using a mortar of the
following composition:
137.0 g of cement PZ 55
71.4 g of quartz powder W 4
141.6 g of quartz sand 0.15-0.6
13.7 g of polymer powder
75.35 g of water
Some of the mortar was placed in a ring of 7 cm
diameter and 4 cm height, and the ring was pulled upward.
The diameter of the spread-out mortar cake in cm indi-
cates the flow of the mortar.
The value~ obtained in the mea~urements using the
novel polymer powders are listed in Table 2. For com-
parison, the flow of the mortar without the addition of
polymer powder (Example N) or with only 1.37 g of the
calcium salt of the phenolsulfonic acid/formaldehyde con-
densate (Example NI) is also mentioned.
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- 8 - O . Z . 0050/40946
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- 9 - O.Z. 0050/40946
For comparison, Table 3 states the corresponding
values obtained when the calcium salt of the naphthalene-
sulfonic acid/formaldehyde condensate is used instead of
the calcium salt of the phenolsulfonic acidJformaldehyde
S condensate.
For Example NII, 1.37 g of this product were
accordingly used instead of the polymer powder.
~ `J: J ~
- 10 - O. Z . 0050/40946
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