Note: Descriptions are shown in the official language in which they were submitted.
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Preparation of an emulsifier-free polymer dis~ersion
The present invention relates to a process for
the preparation of an emulsifier-free po'ymer dispersion
by polymerization of ethylenically unsaturated monomers
S~A), which can be sub]ected to free radical polymeriza- i
tion, with the aid of free radical initiators in an
aqueous medium which contains a polymer (B). The present
invention also rela~es to the polymer dispersions
prepared in this manner and to their use as an agueous
10coating material or paper lacquer.
Aqueous polymer dispersions or latices are
usually prepared by processes in which emulsifiers
stabili~e the polymer particles. However, these
emulsifiers give rise to certain disadvantages with
15regard to the preparation and use of such dispersions.
For example, undesirable foam formation occurs both
during preparation and during processing of the
dispersions. Furthermore, the emulsifiers frequently
cause troublesome tack of ~he polymer film obtained from
20the dispersions and are often also responsible for the
low water resistance of the film. Toxicological and
ecological criteria likewise make it necessary to find
aqueous dispersions which manage without such assistants.
In coating and lacquer formulations, the
25stabilizing effect of the emulsifiers is frequently
reduced by undesirable interactions with the formulating
agents (film-forming assistants, fillers, pigments, ionic
resins and waxes), which may lead to a substantial
deterioration in the performance characteristics ( for
30example gloss, shelf life and leveling). These stability
problems occur in particular in the case of very finely
divided dispersions having a correspondingly large total
particle surface, where considerable amounts of
emulsifier have to be added in order to achieve a
35coverage of the particle surface with emulsifier which is
sufficient to effect stabilization.
To circumvent these problems, various attempts
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have been made with the aim of preparing emulsifier-free
aqueous polymer dispersions.
For example, US-A-4 151 143 describes a two-stage
preparation process for emulsifier-free dispersions, in
which, in the first step, an anionic polymer is prepared
by solution or mass polymerization. After this polymer
has been dispersed in water rendered alkaline, mixtures
of certain monomers which can be subjected to free
radical polymerization are then added in a second stage,
after which the mixture is polymerized as a batch in the
presence of the pol~mer from stage 1. The dispersions
prepared in this manner are intended to be used as
components for coatings.
DE-A-31 23 598 describes emulsifier-free aqueous
latices which are used for anodic electrocoating
finishes. These polymer dispersions, too, are prepared
by a method in which a batch is first prepared :Erom
monomers and a carboxylated polymer. This batch is then
polymerized. This is effected, inter alia, by a
procedure in which the batch o~ monomers and carboxylated
polymer is passed in the form of emulsion int.o heated
water, the pol~meriza~ion initiator being introduced
simultaneously.
Such latices prepared by the batch process can
not be used for aqueous paper lacquers since in many
cases the lacquers obtained do not have a sufficiently
long shelf life or the gloss is insufficient. Moreover,
the latices frequently exhibit a very large number of
specks and have a high coagulum content.
US-A 4 465 803 describes a similar batch process
for the preparation of emulsifier-free latices. There,
monomers which can be subjected to free radical
pol~merization are added, in an aqueous medium, to
polymers functionalized in a specific manner. The batch
is then polymerized. The latices ob~ained have the
disadvantage that there are certain restrictions with
regard to their use. For example, paper lacquers
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obtained from such emulsifier-free latices frequently
have disadvantageous gloss values.
It is an object of the present invention to
provide a process for the preparation of aqueous,
emulsifier-free polymer dispersions which do not have the
disadvantages of the prior art and can be used for
coatings and paper lac~uers of high quality.
We have found that this object is achieved by the
process defined above, wherein the monomers (A) are
metered into the aqueous medium during the
polymerization.
We have also found the pol~mer dispersions
prepared in this manner and their use as aqueous coating
matarials or paper lacquer.
Preferred embodiments of the invention are
described in the subclaims.
Emulsifiers are known to be amphiphilic
molecules, ie. surfactants, which essentially consist of
a hydrophilic moiety and a hydrophobic moiety. Suitable
hydrophilic moieties are polyethylene oxide chains having
not less than 5 ethylene oxide units, amines, ammonium
groups, -COOR-, -S03R and -OS03R, where R is one
equivalent of a cation or hydrogen. A hyrophobic moiety
is, for example, a long-chain alkyl group, an alkaryl or
aralkyl group of 8 to 30 carbon atoms or aryl. In rare
cases, emulsifiers may have up to 3 hydrophilic and/or up
to 3 hydrophobic moieties. For the purposes of the
present invention, emulsifier-free means that no
emulsifiers are added before or during the polymerization
of monomers (A). This of course does not rule out the
possibility that traces of emulsifiers, usually less than
O.01% by weightr based on the sum of (A) and (B), are
introduced by other ~tarting materials. However,
emulsifiers in these small amounts have no adverse
effects.
Suitable componen~s tA) of the novel polymer
dispersions are in principle all ethylenically
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unsaturated monomers which can ~e subjected to free
radical polymerization.
Particularly suitable monomers are those having
a water solubility of up to 50 g/l at 25C, and
combinations thereof.
Examples of suitable monomers are the esters of
unsaturated monocarboxylic acids of 3 to 5 carbon
atoms with alcohols of l to 20 carbon atoms, such as the
acrylates, methacrylates and crotonates of, in
particular, aliphatic or cycloaliphatic alcohols of 1 to
carbon atoms, such as methyl, ethyl, n-propyl,
isopropyl, n-butyl, isobutyl, tert-butyl, hexyl, 2-ethyl-
hexyl, octyl, stearyl, cyclohexyl and methylcyclohexyl
alcohol. However, the esters of the abovementioned acids
with benzyl alcohol or phenol are also suitable for this
purpose.
The monoesters of k ~ B-monoolefinically
unsaturated monocarboxylic acids of 3 to 4 carbon atoms
with satura~ed dihydric alcohols of 3 to 6 carbon atoms,
for example 2-hydroxypropyl methacrylate, 4-hydroxybutyl
methacrylate or 4-hydroxybutyl acrylate, are also
suitable.
Glycidyl esters of acrylic and methacrylic acid,
eg. glycidyl methacrylate, or the aminoalkyl esters of
the two acids stated, for example N,N-diethylaminoethyl
acrylate, N,N-dimethylaminoneopentyl acrylate or N,N-
dimethylaminoethyl methacrylate, are also suitable.
Vinyl and allyl esters of carboxylic acids of 1
to 20 carbon atoms, such as allyl acetate, allyl
propionate, vinyl formate, vinyl laurate, vinyl stearate
and especially vinyl propionate and vinyl acetate, are
also useful.
Vinyl ethers of alcohols of 1 to 8 carbon atoms
are, for example, vinyl methyl ether, vinyl ethyl e~her,
vinyl isopropyl ether and vinyl butyl ether.
Suitable vinylaromatic monomers of not more than
carbon atoms are vinyltoluene, ~- and
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paramethylstyrene, ~-butylstyrene, 4-n-butylstyrene, 4-
n-decylstyrene and preferably styrene.
The vinyl halides are chlorine , fluorine- o~
bromine-substituted ethylenically unsaturated compounds,
preferably vinyl chloride and vinylidene chloride.
Examples of nitriles are acrylonitrile and meth-
acrylonitrile. ~crylamide and mekhacrylamide are
examples of amides.
Hydrocarbons having a polymerizable olefinic
double bond are butadiene, isoprene, ethylene, propylene
and isobukylene.
Monomers capable of crosslinking, such as butane-
diol diacrylate, hexanediol diacrylate, tripropylene
glycol diacrylate and trimethylolpropane triacrylate and
trLmethacrylate, may also be used in minor amounts, for
example from 1 to 10% by weight, based on the monomers
used.
Minor amounts, for example not more than 5% by
weight, based on the monomers used, of other auxiliary
monomers, such as acrylic acid, methacrylic acid, maleic
anhydride, vinylcarbazole, 1-(methacryloyloxyethyl)-
imidazolidin-2-oneandl-(acry~oyloxyethyl)-imidazolidin-
2-one (also referred to as ureido(meth)acrylake), may
sometimes be used to impart certain proper-ties to the
polymers.
Preferred monomers are methyl methacrylate, ethyl
methacrylate, n-butyl, isobutyl and tert-butyl acrylate,
n-butyl and tert-butyl methacrylate, n-hexyl acrylate, 2-
ethylhexyl acrylate, n-lauryl acrylate, styrene and a
mixture of two or more of these monomers, such as
mixtures of from 20 to 80% by weight of methyl meth-
acrylate and from 20 to 80% by weight of n-butyl
acr~late, based in each case on the mixture, and in
particular styrene ikself.
The component ~B) of khe polymer dispersion is
pre~erably used as an aqueous solution. This is
therefore preferably a convenkional water-soluble
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polymer. In contrast to polymer dispersions, polymer
solutions have an LT value of more than 99% at 25C. The
LT value, a measure of the light transmittance of an
aqueous phase, is determined at a dil~tion to a solids
content of 0.01% by weight, using a commercial photometer
(at a wavelength of 0.54b ~m) for a path length of 25 mm
relative to water, to which an LT value of 100% is
assigned.
Random copolymers of from 5 to 70% by weight, in
particular from 40 to 70~ by weight of styrene and from
30 to 95, in particular from 30 to 60, % by weight of
(meth)acrylic acid, usually having a weight average
molecular weight of from 1,000 to 100,000, preferably
from 1,000 to 20,000, are suitable. In order to ensure
adequate water solubility, these compounds are partially
or completely neutralized with bases, such as ammonia,
amines or alkali metal or alkaline earth metal
hydroxides.
Copolymers of from 40 to 60% by weight of maleic
acid and from 60 to 40% by weight of diisobutene and
copolymers of from 5 to g5~ by weight of maleic acid and
from 5 to 95% by weight of (meth)acrylic acid or of from
50 to 90% by weight of maleic acid and from 10 to 50~ by
weight of methyl. vinyl ether can also be used to
advantage. The average molecular weights of these
copolymers are in general from 1,000 to 20~,000.
Copolymers of from 10 to 50% by weight of
(meth)acrylamide and from 50 to 90% by weight of
vinylpyrrolidone, whose molecular weight may be from
5,000 to 200,000, are also suitable. To obtain
advantageous water solubility, these compounds too can be
partially or completely neutralized with the above-
mentioned bases.
Poly(meth)acrylic acids or poly-2-acrylamido-2
methylpropanesulfonic acids, which may contain up to 60%
by weight, based on the polymer, of acrylates and
methacrylates of alcohols of 1 to 4 carbon atoms,
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acrylamide or methacrylamide as polymerized units and
generally have an average molecular weight of from 2,000
to 500,000, are also suitable. To obtain sufficient
water solubility, these polymers too may be partially or
completely neutralized with the abovementioned bases.
Other suitable polymers B are water-soluble
polyvinylpyrrolidones having average molecular weights
of, usually, from 1,000 to 350,000, polyethylene oxides
having average molecular weights of in general from 2,000
to 100,000, poly(meth)acrylamides having average
molecular weights of, usually, from 20,000 to 200,000,
polyvinyl acetates which have been partly hydrolyzed to
polyvinyl alcohol and have average molecular weights of,
usually, from 2,000 to 100,000 and, if desired,
lS ethoxylated hydroxyalkylcellulose where the alkyl radical
is of 1 to 3 carbon atoms and which has a degree of
ethoxylation of not more than 4 ethylene oxide units per
anhydroglucose unit. Examples of these are NatrosolV 250
LR or 250 L from Hercules GmbH, Hamburg. The viscosity
of 2P6 strength aqueous solutions of such polymers at
20C ~s-tandard viscosity) is in general less than 350
mPas.
Preferred polymers are the stated polyvinyl-
pyrrolidones, polyethylene oxides, poly-2-acrylamido-2-
methylpropanesulfonic acids with not more than 5 r
preferably 0, % by weight of polymerized comonomers,
polyacrylamides and in particular the copolymers of
styrene and acrylic acidr particularly successful results
being obtained with copolymers which are composed of from
55 to 65~ by weight of styrene and 35 to 45% by weight of
acrylic acid and have an average molecular weight of from
1,000 to 5,000.
These polymers are well known ~o the skilled
worker and are commercially available and therefore need
not be described further.
The novel polymerization process is carried out
in an aqueous medium, preferably without the addition of
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organic solvents, by a feed procedure. Organic solvents
are understood as meaning those which are inert in the
polymerization of the monomers A. From 10 to 95,
preferably from 45 to 90, % by weight of monomers A and
from 5 to ~, preferably from 10 to 55, % by weight of
the polymer B are used, the percentages in each case
being based on the total amount of A and B.
The monomers are generally subjected to free
radical polymerization at a pH of from 3 to 11 and at a
reaction temperature of from 20 to 95C, preferably from
40 to 90C. In general, from 0.1 to 5% by weight, based
on the monomers used, of conventional, water-soluble
initiators for the emulsion polymerization are used as
free radical ini~iators for the free radical polymeriza-
tion. The initiators, for example hydrogen peroxide,sodium peroxodisulfate or ammonium peroxodisulfate, may
be used alone or in a known manner with small amounts,
such as from 0.001 to 0.1% by weight, based on the
monomers used, of reducing agents, such as ascorbic acid,
sodium pyrosulfite, Rongalit~ from B~SF AG, thiourea or
hydrazine, or hea~y metal salts, such as sulfates or
halides of iron, of cobalt, of nickel, of titanium or of
vanadium.
Conventionally used regulators, such as n-dodecyl
~5 mercaptan, tert-dodecyl mercaptan, thioglycol and thio-
glycerol, may furthermore be used for regulating the
molecular weight. These substances are generally in
added in amounts of from 0.1 to 2% by weight, based on
the monomers used.
In the novel feed process, the polymer B,
preferably as an aqueous ~olution, and usually not more
than 60, preferably from 1 to 50, in particular from 20
to 40, % by weight of the total amoullt of the free
radical initiator used are added to the initially taken
aqueous medium. If necessary, other known assistants,
such as buffer substances or regulators, may be added in
conventional amounts. The reducing agent which may be
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used can be metered in.
After heating to the desired reaction
temperature, the remaining amount of free radical
initiator and the monomers A are metered in in a
S conventional manner in separate feeds. From 30 to 300,
preferably from 30 to 180, minutes are required for the
component A and from 10 to 60, preferably from 15 to 40,
minutes or longer are required for the residual amount of
the free radical initiator. After the end of the
addition of the polymerization initiator, polymerization
is allowed to continue for a further 30-150 minutes at
the reaction temperature.
The free radical initiator can be metered in or
some of the free radical initiator can be initially taken
in a preerred manner. The amount of initially taken
initiator and the feed rate of the initiator and monomers
are advantageously chosen so that there is no
accumulation of unconverted monomers in the reaction
vessel, for example more than 1% by weight, based on the
total amount of the monomers used. This can be
determined by the skilled worker in a simple manner, for
example by sampling or in preliminary experiments. The
polymerization process has the advantage that the heat of
reaction is evolved not in surges but uniformly in a
controlled manner and can be readily removed. Only small
heat exchangers are required for this purpose.
The polymer dispersions having a solids content
of from 15 to 55, in particular from 30 to 50~ % by
weight, measured according to DIN 53,189, are obtained.
With the abovementioned inorganic bases, such as the
alkali metal and alkaline earth metal hydroxides, ammonia
or organic bases, such as amines, the aqueous emulsifier-
free polymer dispersions can be brought to the desired
pH.
The main particle diameter of the polymer
dispersions, determined by the method of dynamic light
scattering ~accordlng to B.J. Berne, R. Pecora, Dynamic
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Light Scattering, John Wiley & Sons~ New York, 1976), may
be from 20 to 1,000 nm, in particular from 40 to 1,000
nm .
The aqueous emulsifier-free polymer dispersions
obtainable by the novel process have a long shelf life
and are ready for shipment and use without further
treatment. They can be prepared without organic
solvents. They are particularly suitable for aqueous
coating materials and in particular as high quality
aqueous paper lacquers. In the paper lacquers, they
result in a very long shelf lie and extremely high gloss
of the applied and dried paper lacquers.
Aqueous coating materials frequently contain
further conventional components, in general from 15 to
25% by weight of pigments, such as TiO2, from 5 to 25% by
weight of fillers, such as cha~k or silicates, from 0.1
~o 1~ by weight of pigmant distributors, from 0.2 to 1%
by weight of antifoams, from 0.05 to 0.2% by weight of
preservatives and not more than about 10% by w~ight o~
film-forming assistants, plasticizers and thickeners, in
addition to the polymer dispersions as binders, which are
generally present in amounts of from 25 to 60% by weight,
based on the aqueous coating material.
Aqueous paper lacquers contain further conven-
tional components in addition to the polymer dispersions.Examples are film-forming assistants, such as propylene
glycol and butylglycol, plasticizers, such as di-n-butyl
phthalate, surface tension regulators, such as
isopropanol, and waxes, in each case in amounts of,
usually, from 1 to 10% by weight, based on the aqueous
paper lacquer. Furthermora, from 10 to 50% strength by
weight aqueous solutions of the abovementioned polymers
B, such as the stated styrene/acrylic acid copolymers,
may be present in amounts o~ from 10 to 50% by weight in
the aqueous paper lacquer.
In the Examples which follow, percentages, parts
and ratios are by weight, unless stated otherwise. The
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following abbreviations are used:
n-BA: n-Butyl acrylate
i-BA: Isobutyl acrylate
t-BA: tert-Butyl acrylate
n-HA: n-Hexyl acrylate
2-EHA: 2-Ethylhexyl acryla-te
n-LA: n-Lauryl acrylate
MMA: Methyl methacrylate
EMA: Ethyl methacrylate
n-BMA: n-Butyl methacrylate
t-BMAo tert-Butyl methacrylate
S: Styrene
SC. Solids content
M: Weight average molecular weight
General preparation method for Examples 1 to 20
In a 3 l four-necked flask which was equipped
with a reflux condenser, 2 feed vessels, a thermometer,
a pilot stirrer and a gas inlet and outlet, the amount,
stated in Table 2, of a 22.5% strength ammoniacal
solution (pH lO) of a copolymer B of 60~ by weight of
styrene and 40% by weight of acrylic acid and having an
average molecular weight of 1,200 was initially taken
and, after the reaction vessel had heen flushed with
nitrogen, was heated to 85C. 54 g of 1.5% strength
aqueous ammonium peroxodisulfate solution were added and
220 g of the monomer or monomer mixture A were then run
in at 85C in the course of 1 hour while stirring. At
the same time, in a separate~ feed, 126 g of a 1.5%
strength ammonium peroxodisulfate solution were added
dropwise, but in this case the time for the dropwise
addition was increased by 30 minutes to a total o~ 1.5
hours. A~ter the end o the two feeds, the reaction was
allowed to continue for a further 1 hour at 85C, after
which the mixture was cooled to room temperature.
The polymer dispersions obtained by this
preparation method are coagulum-free and have the
following data:
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T ~ LE 2
Example Monomer A Solution of pH SC (%) Parti~le
copolymer Bdiamete~
g (nm)
1 n-BA 802 9.0 39.0 143
2 i~BA 391 8.7 38.7 113
3 t-BA 391 9.0 40.0 110
4 n-HA 391 8.9 39.6 127
2-E~A 391 9.1 39.7 136
6 n-LA 391 9.0 39.9 193
7 ~MA 802 9.6 39.7 96
8 MMA 978 9.6 41.6 75 -`
9 EMA 391 9.0 39.4 77
lS 10 n-B~ 802 8.6 39.6 78
11 t- 'JMA 391 9.2 39.9 Sl
12 50% S, 50% n-BA 802 9.2 39.4 116
13 5~% NMA, 50% n-BA 802 9.1 39.6 131
14 50X ~MA, 50% n-BA 978 9.3 41.0 98
50% NMA, 50X n-BA 182 9.2 42.9 140
16 S 978 9 1 45 7 97
; 17 S 802 9.0 45.3 100
18 S 684 9.0 45.4 105
19 S 489 8.9 44.9 111
S 400 8.9 40.6 135
General preparation methods for Examples 21 to 33
; In a 3 1 four-necked flask which was equipped
with a reflux condenser~, 2 feed vessels, a thermometer,
:a pilot stirrer and a gas inlet and outlet, the amount,
stated in Table 3, of the aqueous solution of polymex B
was initially taken and, after the reaction vessel had
been flushed with nitrogen, was heated to 85C. 54 g of
a 1.5% strength a~ueous ammonium peroxodisulfate solution
were added and 220 g of styrene were then run in at 85C
: 35 in the course of 1 hour while stirring. At the same
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time, in a separate feed, 126 g of a 1.5% strength
ammonium peroxodisulfate solution were added dropwise,
but in this case the time for the dropwise addition was
increased by 30 minutes to a total of 1.5 hours. After
the end of the two feeds, the reaction was allowed to
continue for a further hour at o5C, after which the
mixture was cooled to room temperature.
The polymer dispersions obtained by this
preparation method are coagulum-free and have the
following data:
TABLE 3
Example Monomer B Solution of Dispersion obtained
polymer B used SC Particle
Amount (g) (%)1) (%) diameter (~m)
_.___ _
21 Copolymer 293 30 43.3 103
50% of methyl meth-
acrylate
35X of methyl acrylate
15% of acrylic acid
22 Polyethylene oxide 601 30 39.1 177
M ~ 9,000
23 Polyvinylpyrrolidone 733 30 40.0 130
M ~ 40,000
: 25 24 Poly-2-acrylamido- 495 20 35.2 400
2-methanesulfonic
acid, Na salt
M ~ 42,000
Copolymer of 600 30 39.1 250
50% of maleic acid :
50% of diisobutylene
Na salt
M ~ 1,200
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Concentration of the solution
TA13LE 3 ( continued)
Example Monomer BSolution of Dispersion obtained
polymer B used SC Particle
A~ount (g) (%)1) (X) diameter (~m)
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26 Copolymer of lO00 11 23.9 1000
88% of polyvinyl alcohol
12% of polyvinyl acetate
M ~ 26,000
(Mowiol~ 4/88 from Hoechst AG, Frankfurt)
27 Cellulose hydroxy 2000 5.5 13.9 183
ethyl ether containing
2.5 ethylene oxide units
lS per anhydroglucose unit
(Natrosol 250 LR)
28 Polyacrylamide S18 20 35.3 405
M ~ 120,000
.
29 Copolymer of 1100 10 21.3 395
70% of vinylpyrrolidone
30% of methacrylamide
M ~ 100,000
:'
Copolymer of 440 25 39.5 420
: 50% of maleic acid and
50% of acrylic acid :
M ~ 3,000
31 Copolymer of 30% oE 470 23.5 32.0 465
: maleic acid and 70%
: of acrylic acid
Na salt
M - 70,000
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Concentration oE the solution
TABLE 3 (continued)
~xample Monomer B Solution of Dispersion obtained
- polymer B used SCParticle
Amount (g) (%)1) (%) diameter (~)
32 Copolymer of 440 25 39.01000
67% of maleic acid and
33% of methyl vinyl ether
M = 70,000
33 Polyethylene oxide 601 3038.3 81
= 6,800
Concentration oE the solutiorl
~eneral method for Examples 34 to 36
The procedure described for Examples 21 to 33 is
followed, but using a mixture of 802 g of a 22.5%
strength by weight aqueous solution of the ammonium salt
of a copolymer of 60% hy weight of styrene and 40% by
weight of acrylic acid (M = 1,200) and 15 g of a 30%
strength by weight aqueous solution of a polyethylene
oxide (M - 9,OOO) as polymer B and 220 g of the monomer
A stated in Table 4 of the monomer mixture A.
Example Monomer A Dispersion obtained
:: SCParticle diameter
(%)(~m)
34 ~MA 40.678
50% MMA/50% n-BA 40.9102
36 S 46.5~06
COMPARATIVE EXAMPLE 1
In the prior art batch preparation process, 220
g of a random copolymer of 60% of styrene and 40% of
acrylic acid, having an average molecular weight of
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1,200, wexe dissolved in 758 g of a 3% strength aqueous
ammonia solution. 220 g of styrene were emulsified in
this resin solution at 85C. 180 g of a 1.5~ streng-th
ammonium peroxodisulfate solution were then added
dropwise to the emulsion at 85C in the course of 1 hour
while stirring. The batch coagulated completely during
the addition of ~he initiator.
COMPARATIVE EXAMPLE 2
Example 15 in Table 2 was carried out by the
batch procedure ~cf. Comparative Exa~ple 1~.
40.3 g of the copolymer of 60% of styrene and 40%
of acrylic acid in 141 g of a 3~ strength aqueou~ ammonia
solution formed the initially taken mixture in which 220
g of monomers, consisting of 110 g of n-BA and 110 g of
MMA, were emulsified.
The batch coagulated during the addition of the
initiator.
COMPARATIVE EXAMPLE 3
In the feed preparation process described in DE-
A-31 23 598, 90 g of a random copolymer of 60% of styrene
and 40% of acrylic acid, having an average molecular
weight of 1,200, ware dissolved in 210 g of a 4% strength
aqueous ammonia solution. 220 g of styrene were
emulsified in this solution at room temperature, after
which the emulsion obtained was passed, while stirring,
into 160 g of water which had been initially taken and
heated to 85C. At the same time, 100 g of a 1.5%
strength ammonium peroxodisulfate solution were added
dropwise in the course of 1.5 hours to the initially
taken mixture at 85C. After the end of ~he feeds,
polymerization was allowed to continue for a further 1
hour at 85C, and a finely divided, bluish white
dispersion having a solids conten~ of 40% was obtained.
The dispersion contained 1.3% of coagulum (based on the
total solids content) and, in the form of a film applied
to a glass sheet, exhibited many specks.
Determination of the speck content:
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The aqueous dispersion was spread over a glass
sheet in a layer thickness of 200 ~m and dried for 24
hours at room tempera-ture. Thereafterr the specks
visible with the naked eye were visually e~aluated in an
area of 6 x 20 cm and were assigned to a scale of ratings
which ranged from 0 (speck-free) to 3 (very large number
of specks). The Table below shows the results:
Example No. Ratinq
16 0
17
18 1-2
19
Comp. Example 3 3
The Examples which follow describe the
formulations for aqueous paper lacquers in which the
emulsifier-free polymer dispersions are present as
binders.
A water-soluble pol~mer can be used as a cobinder
for paper lacquers. A copolymer of from 55 to 65% by
weight of styrene and from 35 to 45% by weight of acrylic
acid, having a molecular weight of from lrOOO to 5,000,
proved to be particularly suitable, and in some cases up
to 50% by weight of the styrene may be replaced with ~-
methylstyrene. The abovementioned water-soluble poly-
acrylic and polymethacrylic acids are also suitable.
General method for formulation I:
Parts by weight Component
56a) Aqueous solution of a copolymer (35%
strength by weight)
27 Polymer dispersion (SC = 45%)
9 Aqueous polyethylene wax emulsion, 35%
strength, as assistant for increasing
the scratch-resistance
7b) Water
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- 18 ~ O.Z. 0050~42377
~): Solution consisting of
Parts by weight Component
Copolymer of 60% of styrene
and 40% of acrylic acid
(M = 1,200)
13 Concentrated NH3
3 Butylglycol as film-forming
assistant
49 Water
o b~: Where the polymer content of th~ dispersion
fluctuated, the amount was ad~usted accordingly.
The individual components were mixed with one
another with continuous stirring. It was advantageous to
prepare the polymer dispersion and wax emulsion together
beforehand and to avoid coagulation of the wax particles.
The formulation II used a novel dispersion as the
sole binder. Only a few commercial aqueous dispersions
could be processed in this manner to give an acceptable
paper lacquer.
General method for formulation II:
Parts by weight Component
74 Polymer disparsion, SC = 45
4 Isopropanol as assistant for reducing
the sur~ace tension
2 Propylene glycol as film-forming
assistant
8 Di-n-butyl phthalate as plasticizer
2 Polyethylene wa~ emulsion, 35%
strength, as assistant for higher
scratch-resistance
10~ Water
Testing the paper lacquers
1. Viscosity: Measured according to DIN 53,211 using
a DIN 4 mm cup at 23C, stated in seconds.
2. Shelf life: The lacquer was stored at 50C in a
closed vessel in a drying oven. A test was carried
out to determine whether the lacquer thickened or
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~ 19 - O.ZO 0050/42377
whether its viscosity increased greatly.
Testing of the paper coating
The lacquer was applied with a 6 ~m knife coater
to white and black contrast paper and cardboard and was
dried at room temperature. The gloss was measured using
a multi-gloss reflectometer at an angle of 60C.
The results are shown in Tables 5 and 6.
It is clear that tha dispersions prepared
according to the invention have a wide range of uses.
Thus, when used as paper lacquers in many formulations on
many papers, they have a balanced property profile
between the shelf life of the aqueous lacquer and surface
properties of the dry coating, such as gloss, on various
substrates.
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- 20 - O. Z . 0050/42377
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COMPARATIVE EXAMPLE 4
Example 5 of US-~ 4 465 803 was repeated. With
this dispersion as a binder, an aqueous paper lacquer was
prepared as described abo~e using formulation I. The
gloss is shown in Table 7.
EXAMPLE 37
Example 5 of US-A 4 465 803 was repeated.
However, 207 g of n-butyl methacrylate and 0.5 g of
ammonium persulfate were not added before heating ~o
lQ 80C, and 100 g of water were also retained. After the
initially taken mixture had been heated, 207 g of n-butyl
methacrylate were metered in continuously in the course
of 60 minutes and 0.5 g of ammonium persulfate, dissol~ed
in 100 g of water, were metered in continuously in the
course of 90 minutes, and the mixture was then kept at
this temperature for 1.5 hours.
With this dispersion as a binder, an aqueous
paper lacquer was prepared as described above using
formulation I. The gloss values in Table 7 show the
clear superiority of the novel dispersion o~er the
dispersion prepared by the prior art batch process.
TABLE 7
Paper lacquer formulations according to formulation I
Comparative Example 4 Dispersion 37
Gloss Cardboard 23 31
60C Paper (white) 43 54
6 ~m Paper (black) 51 59
, ~ . ~ . .. .
.. . . ~ .
. .
