Aqueous polymer dispersion

An aqueous polymer dispersion having a solids volume concentration of 50% by volume or more is obtainable by polymerizing radical polymerizable monomers other than vinyl or vinylidene halides by the method of free radical aqueous emulsion polymerization with the addition of an aqueous starting polymer dispersion having a certain diameter distribution of the starting polymer particles present therein by the stream addition process.

The present invention relates to a final aqueous polymer dispersion which 
has a solids volume concentration (solids volume=solids mass divided by 
solids density) of at least 50% by volume and is obtainable by 
polymerizing at least one radical polymerizable monomer other than a vinyl 
or vinylidene halide with the addition of at least one aqueous starting 
polymer dispersion I in a polymerization vessel by the method of free 
radical aqueous emulsion polymerization in the presence of dispersants and 
free radical polymerization initiators with the proviso that 
A) the mass of polymer contained in the at least one aqueous starting 
polymer dispersion I added relative to the total mass comprising the mass 
of the at least one radical polymerizable monomer and the mass of polymer 
added in the form of the aqueous starting polymer dispersion I is from 1 
to 10%, preferably from 1 to 5%, 
B) the at least one aqueous starting polymer dispersion I added is 
constituted like an aqueous polymer dispersion obtained by adding together 
n aqueous starting polymer dispersions II with the proviso that 
a) n is an integer .gtoreq.2, 
b) the weight average particle diameter of the starting polymer particles 
present in dispersion in the respective aqueous starting polymer 
dispersions II is for every aqueous starting polymer dispersion II within 
the range &gt;0 to 400 nm, 
c) the weight average particle diameter of the starting polymer particles 
of at least one aqueous starting polymer dispersion II is within the range 
&gt;0 to 100 run, 
d) the aqueous starting polymer dispersions II have a monomodal 
distribution of the diameters of the starting polymer particles they 
contain such that, if d.sub.x defines the diameter below which is the 
particle diameter of X % by weight of all the starting polymer 
particles-present in the particular aqueous starting dispersion II, the 
ratio (d.sub.90 -d.sub.10)/d.sub.50 is from 0.1 to 0.6, 
e) the relation between the volume V.sub.i, obtainable by dividing the mass 
of the i-th starting polymer II present in the i-th aqueous starting 
polymer dispersion II by the mass density of the i-th starting polymer II, 
and the similarly determined volume V.sub.j, providing that not only the 
weight average particle diameter (d.sub.w,i) of the starting polymer 
particles present in the i-th aqueous starting polymer dispersion II but 
also d.sub.w,j is above 100 nm, satisfies equation 1 
##EQU1## 
where k is from 1/1.5 to 1.5, f) the relation between the weight average 
particle diameter (d.sub.w,.ltoreq.100) of the starting polymer particles 
determined over the total amount of all the aqueous starting polymer 
dispersions II that have a weight average particle diameter of the 
starting polymer particles they contain 
within the range &gt;0 to .ltoreq.100 nm, and the weight average particle 
diameter (d.sub.w,i) of the starting polymer particles present in the i-th 
aqueous starting polymer dispersion II, providing that d.sub.w,i is &gt;100 
nm, satisfies equation 2 
##EQU2## 
where k' is from 0.5 to 5, V.sub.i is the mass of the starting polymer 
present in the i-th aqueous starting polymer dispersion II divided by the 
mass density of the starting polymer, 
V.sub..ltoreq.100 is the mass of the starting polymer present in the total 
amount of all aqueous starting polymer dispersions II that have a weight 
average particle diameter of the starting polymer particles they contain 
within the range &gt;0 to .ltoreq.100 run, divided by the mass density of the 
starting polymer, 
g) V.sub..ltoreq.100 is from 0.3 to 10% by volume, based on the sum of all 
V.sub.i, and 
h) the difference between the smallest and the largest weight average 
particle diameter d.sub.w,i of the aqueous starting polymer dispersions II 
present in the aqueous starting polymer dispersion I is at least 150 run, 
c) the total amount of the at least one aqueous starting polymer dispersion 
I to be added is introduced into the polymerization vessel as initial 
charge prior to the start of the free radical aqueous emulsion 
polymerization, and 
D) the free radical aqueous emulsion polymerization of the at least one 
radical polymerizable monomer is effected by the stream addition method 
with the proviso that 
from the start of the free radical aqueous emulsion polymerization the 
addition of the at least one radical polymerizable monomer to the 
polymerization vessel is effected in such a way that at any time of the 
addition the polymerization conversion of the total monomers already added 
previously to the polymerization vessel is at least 80 mol %, and the 
amount of dispersant present in the polymerization vessel is at any time 
from the start of the free radical aqueous emulsion polymerization from 
0.5 to 5% by weight, based on the sum of the masses of starting polymer I 
and the monomers to be polymerized already added to the polymerization 
vessel. 
The present invention further relates to the process for preparing such 
final aqueous polymer dispersions and to the use thereof as binders and as 
materials for preparing coatings and adhesive Joints. 
Aqueous polymer dispersions are systems comprising polymer particles 
dispersed as disperse phase in an aqueous dispersion medium. 
Polymer solutions form polymer films as the solvent evaporates. Aqueous 
polymer dispersions behave the same way on evaporation of the aqueous 
dispersion medium, which is why aqueous polymer dispersions find varied 
use as binders, for example for paints or for leather coatings. 
Aqueous polymer dispersions having a high polymer content are of particular 
advantage in that, on the one hand, their relatively lower proportion of 
aqueous dispersion medium reduces the energy required for evaporating it, 
for example for film formation or for preparing polymer powders, and, on 
the other, the useful polymer can be stored and transported using a 
relatively smaller amount of aqueous phase as carrier medium. 
However, there is a disadvantage in that, as the volume concentration of 
the polymer increases (U.S. Pat. NO. 4,130,523), there are problems with 
the preparation of aqueous polymer dispersions. For instance, the flow 
resistance (viscosity) increases and this increased viscosity makes it 
difficult not only to remove the heat of reaction but also to process the 
aqueous dispersion; secondly, there is an increasing tendency for the 
dispersed polymer particles to aggregate for reasons of thermodynamic 
stability. The resulting flocs [a) microflocs or specks; not normally 
removable by conventional filtration; b) macroflocs or coagulum; normally 
removable by conventional filtration] interfere in particular with the 
film forming of the aqueous polymer dispersions and are therefore 
generally undesirable. 
According to studies about the flow resistance of aqueous polymer 
dispersions, those having a broad size distribution (polydispersity) of 
the dispersed polymer particles for the same solids content generally have 
a lower flow resistance than those with a narrow size distribution (which 
are in the extreme case monodispersed). Furthermore, coarse aqueous 
polymer dispersions have a lower flow resistance than fine aqueous polymer 
dispersions, given the same solids content. 
EP-A-129 699 discloses a process for preparing an aqueous polymer 
dispersion wherein unsaturated monomers are polymerized in a conventional 
manner in a polymerization vessel by the method of free radical aqueous 
emulsion polymerization with the addition of an aqueous dispersion of a 
starting polymer such that the addition of the aqueous dispersion of the 
starting polymer must be concluded before 40% by weight of the total 
monomers to be polymerized have copolymerized and must not start before 
the average particle size of the emulsion polymer formed in the course of 
the polymerization of the monomers is twice that of the aqueous dispersion 
of the starting polymer. In fact, the aqueous dispersion of the starting 
polymer is preferably not added over a prolonged period but all at once. 
The disadvantages of the aqueous polymer dispersions thus obtainable are 
that their flow resistance is not fully satisfactory above a solids volume 
concentration of 50% by volume and that, according to the embodiment 
examples, the solids volume concentration is limited to values below 65% 
by volume. 
U.S. Pat. No. 4,130,523 concerns a process for preparing aqueous polymer 
dispersions wherein aqueous polymer dispersion already formed in the 
course of the polymerization process is continuously removed from the 
reaction zone, stored and later reintroduced into the reaction zone as a 
kind of starting polymer dispersion. A disadvantage of this process is 
that it is unsuitable for industrial implementation. 
U.S. Pat. No. 3,424,706 concerns a process for preparing aqueous 
dispersions of polymers containing at least 70-97% by weight of vinylidene 
chloride as copolymerized units, wherein the polymerization of the 
monomers is effected with the addition of an aqueous dispersion of a 
starting polymer. The said reference teaches inter alia mixing the 
monomers to be polymerized and the aqueous dispersion of the starting 
polymer with one another and adding this mixture to the initial charge 
comprising part of the polymerization batch. 
The disadvantage with this process is that it is restricted to monomer 
mixtures consisting chiefly of vinylidene chloride. Moreover, according to 
the illustrative embodiments, the aqueous polymer dispersions obtainable 
by this process are unsatisfactory not only as regards the flow resistance 
above a solids volume concentration of 50% by volume but also as regards 
the upper limit for the solids volume concentration attainable in a still 
satisfactorily flowable state. 
It is an object of the present invention to make available aqueous polymer 
dispersions that are obtainable in a simple, industrially suitable, 
reproducible manner not restricted to specific monomers with an increased 
solids volume concentration but a reduced flow resistance and reduced floc 
content. 
We have found that this object is achieved by the final aqueous polymer 
dispersions defined at the beginning. 
Remarkably, the subject-matter of the invention is not restricted to the 
free radical aqueous emulsion polymerization of monomer mixtures composed 
chiefly or exclusively of vinyl and/or vinylidene halides, despite the 
generally known fact that the development of the disperse phase in the 
case of monomers other than vinyl and/or vinylidene halides is a 
significantly more complex phenomenon. 
Suitable radical polymerizable monomers for the process of the invention 
are therefore in particular, inter alia, monoethylenically unsaturated 
monomers such as olefins, for example ethylene, aromatic vinyl monomers 
such as styrene, .alpha.-methystyrene, o-chlorostyrene or vinyltoluenes, 
esters of vinyl alcohol and monocarboxylic acids having from 1 to 18 
carbon atoms, such as vinyl acetate, vinyl propionate, vinyl-n-butyrate, 
vinyl laurate and vinyl stearate, esters of 
.alpha.,.beta.-monoethylenically unsaturated mono- and dicarboxylic acids 
preferably of from 3 to 6 carbon atoms, such as, in particular, acrylic 
acid, methacrylic acid, maleic acid, fumaric acid and iraconic acid, with 
alkanols in general of from 1 to 12, preferably of from 1 to 8, in 
particular of from 1 to 4, carbon atoms, such as, in particular, methyl, 
ethyl, n-butyl, isobutyl and 2-ethylhexyl acrylate and methacrylate, 
dimethyl maleate or n-butyl maleate, nitriles of 
.alpha.,.beta.-monoethylenically unsaturated carboxylic acids such as 
acrylonitrile and also C.sub.4-8 -conjugated dienes such as 1,3-butadiene 
and isoprene. The monomers mentioned generally form the principal monomers 
which, based on the total amount of the monomers to be polymerized by the 
method of free radical aqueous emulsion polymerization, normally account 
for a proportion of more than 50% by weight. Monomers which polymerized by 
themselves normally form homopolymers that possess enhanced water 
solubility are normally included in the polymer only as modifying 
monomers, in amounts, based on the total amount of monomers to be 
polymerized, of less than 50% by weight, in general from 0.5 to 20, 
preferably from 1 to 10, % by weight. 
Examples of monomers of this type are .alpha.,.beta.-monoethylenically 
unsaturated mono- and dicarboxylic acids of from 3 to 6 carbon atoms and 
amides thereof, eg. acrylic acid, methacrylic acid, maleic acid, fumaric 
acid, itaconic acid, acrylamide and methacrylamide, also vinylsulfonic 
acid and water-soluble salts thereof, and also N-vinylpyrrolidone. 
Monomers which customarily enhance the internal strength of the films 
formed from the final aqueous polymer dispersion are in general likewise 
included in the polymer only in minor amounts, usually from 0.5 to 10% by 
weight, based on the total amount of monomers to be polymerized. Monomers 
of this type normally have an epoxy, hydroxyl, N-methylol, carbonyl or at 
least two nonconjugated ethylenically unsaturated double bonds. Examples 
thereof are N-alkylolamides of .alpha.,.beta.-monoethylenically 
unsaturated carboxylic acids of from 3 to 10 carbon atoms and esters 
thereof with alcohols of from 1 to 4 carbon atoms, of which 
N-methylolacrylamide and N-methylolmethacrylamide are very particularly 
preferred, divinyl monomers, divinylidene monomers and also dialkenyl 
monomers. Particularly suitable instances of these are the diesters of 
dihydric alcohols with .alpha.,.beta.-monoethylenically unsaturated 
monocarboxylic acids, of which in turn acrylic and methacrylic acid are 
preferred. Examples of such monomers having two nonconjugated 
ethylenically unsaturated double bonds are alkylene glycol diacrylates and 
dimethacrylates such as ethylene glycol diacrylate, 1,3-butylene glycol 
diacrylate, 1,4-butylene glycol diacrylate, propylene glycol diacrylate, 
divinylbenzene, vinyl methacrylate, vinyl acrylate, allyl methacrylate, 
allyl acrylate, diallyl maleate, diallyl fumarate, methylenebisacrylamide, 
cyclopentadienyl, acrylate and triallyl cyanurate. In this connection of 
particular importance are also C.sub.1 -C.sub.8 -hydroxyalkyl 
methacrylates and acrylates, such as n-hydroxyethyl, n-hydroxypropyl or 
n-hydroxybutyl acrylate and methacrylate, and also compounds such as 
diacetoneacrylamide and acetylacetoxyethyl acrylate or methacrylate. As 
well as monomers having unsaturated double bonds it is possible for minor 
amounts, customarily from 0.01 to 2% by weight, based on the monomers to 
be polymerized, of molecular weight regulators, such as tert-dodecyl 
mercaptan and 3-mercaptopropyltrimethoxysilane to be included in the 
polymer. It is preferable to add such substances to the polymerization 
zone mixed with the monomers to be polymerized. 
Suitable dispersants include not only the protective colloids customarily 
used for carrying out free radical aqueous emulsion polymerizations but 
also emulsifiers. Examples of suitable protective colloids are polyvinyl 
alcohols, cellulose derivatives and vinylpyrrolidone-containing 
copolymers. A detailed description of further suitable protective colloids 
may be found in Houben-Weyl, Methoden der organischen Chemie, Volume 
XIV/1, Makromolekulare Stoffe, Georg Thieme Verlag, Stuttgart, 1961, pages 
411 to 420. It is of course also possible to use mixtures of emulsifiers 
and/or protective colloids. Preferably, the dispersants used are 
exclusively emulsifiers whose relative molecular weights are customarily 
below 1000, in contradistinction to the protective colloids. They can be 
anionic, cationic or nonionic in nature. Of course, if mixtures of surface 
active substances are used, the individual components must be compatible 
with one another, which can be verified beforehand by means of a few 
preliminary experiments if there is any doubt. In general, anionic 
emulsifiers are compatible with one another and with nonionic emulsifiers. 
The same is true of cationic emulsifiers, while anionic and cationic 
emulsifiers are usually incompatible with one another. Examples of 
customary emulsifiers are ethoxylated mono-, di- and trialkylphenols (EO 
degree: 3-50, alkyl radical: C.sub.4 -C.sub.9), ethoxylated fatty alcohols 
(EO degree: 3-50, alkyl radical: C.sub.8 -C.sub.36), and also alkali metal 
and ammonium salts of alkyl sulfates (alkyl radical: C.sub.8 -C.sub.12), 
of sulfuric monoesters of ethoxylated alkanols (EO degree: 4-30, alkyl 
radical: C.sub.12 -C.sub.18), and ethoxylated alkylphenols (EO degree: 
3-50, alkyl radical: C.sub.4 -C.sub.9), of alkylsulfonic acids (alkyl 
radical: C.sub.12 -C.sub.18) and of alkylarylsulfonic acids (alkyl 
radical: C.sub.9 -C.sub.18). Further suitable emulsifiers may be found in 
Houben-Weyl, Methoden der organischen Chemie, Volume XIV/1, 
Makromolekulare Stoffe, Georg Thieme Verlag, Stuttgart, 1961, pages 192 to 
208. 
Particularly suitable surface active substances are compounds of the 
general formula I 
##STR1## 
where R.sup.1 and R.sup.2 are each hydrogen or C.sub.4 -C.sub.24 -alkyl 
but are not both hydrogen, and X and Y are each an alkali metal or 
ammonium ion In the formula I, R.sup.1 and R.sup.2 are each preferably 
linear or branched alkyl radicals of from 6 to 18 carbon atoms or 
hydrogen, in particular of 6, 12 and 16 carbon atoms, but R.sup.1 and 
R.sup.2 must not both be hydrogen. X and Y are each preferably sodium, 
potassium or ammonia ions, of which sodium is particularly preferred. Of 
particular advantage are compounds I in which X and Y are each sodium, 
R.sup.1 is a branched alkyl radical of 12 carbon atoms and R.sup.2 is 
hydrogen or R.sup.1. It is common to employ technical grade mixtures 
containing from 50 to 90% by weight of the monoalkylated product, for 
example Dowfax.sup.500 2A1 (trademark of the Dow Chemical Company). In 
the process of the invention compounds I are preferably used as the sole 
dispersants and particularly preferably in mixture with ethoxylated fatty 
alcohols (EO degree: 3-50, alkyl radical: C.sub.8 -C.sub.36). Compounds I 
are generally known, for example from U.S. Pat. No. 4,269,749, and are 
commercially available. It is advantageous for the final aqueous polymer 
dispersion of the invention to contain from 1 to 3% by weight of surface 
active substances, based on the mass of the final polymer. 
Suitable free radical polymerization initiators are all those which are 
capable of initiating a free radical aqueous emulsion polymerization. This 
includes not only peroxides, for example alkali metal peroxodisulfates, 
but also azo compounds. Preference is given to using combined systems 
composed of at least one organic reducing agent and at least one peroxide 
and/or hydroperoxide, eg. tert-butyl hydroperoxide and the sodium salt of 
hydroxymethanesulfinic acid or hydrogen peroxide and ascorbic acid, and 
very particular preference is given to combined systems which in addition 
contain a small amount of a metal compound that is soluble in the 
polymerization medium and whose metallic component can exist in a 
plurality of valence states, for example ascorbic acid/iron(II) 
sulfate/hydrogen peroxide, although instead of ascorbic acid it is also 
common to employ the sodium salt of hydroxymethanesulfinic acid, sodium 
sulfite, sodium bisulfite or sodium metabisulfite and instead of hydrogen 
peroxide it is common to employ tert-butyl hydroperoxide or alkali metal 
peroxodisulfates and/or ammonium peroxodisulfate. Instead of a 
water-soluble iron(II) salt it is common to employ a combination of 
water-soluble Fe/V salts. The amount of free radical initiator system used 
is preferably from 0.1 to 2% by weight, based on the total amount of 
monomers to be polymerized. 
The manner of addition of the free radical initiator system to the 
polymerization vessel in the course of the free radical aqueous emulsion 
polymerization of the invention is rather of minor importance for the 
success of the process of the invention. The initiator system can not only 
be introduced into the polymerization vessel in its entirety as part of 
the initial charge but also be added continuously or stepwise in the 
course of the free radical aqueous emulsion polymerization at the rate of 
its consumption. The choice in a particular case depends in the usual 
fashion not only on the chemical nature of the initiator system but also 
on the polymerization temperature. 
The polymerization pressure and the polymerization temperature are likewise 
of rather minor importance. In general, the temperature employed will be 
between room temperature and 100.degree. C., preferably within the range 
from 50 to 95.degree. C. The employment of superatmospheric or reduced 
pressure is possible, so that the polymerization temperature may also 
exceed 100.degree. C. and may in fact be as high as 130.degree. C. 
Volatile monomers such as ethylene, butadiene or vinyl chloride are 
preferably polymerized under superatmospheric pressure. To control the pH 
of the polymerization medium ammonia, for example, may be added during the 
free radical aqueous emulsion polymerization of the invention. 
The radical polymerizable monomers mentioned by way of example as suitable 
for the free radical aqueous emulsion polymerization of the invention are 
suitable not only for use as constituents of the monomer mixture to be 
polymerized according to the invention, but also, in the same way as the 
polymerization initiators, molecular weight regulators and pH regulators 
recommended for the free radical aqueous emulsion polymerization of the 
invention, for use as constituents of the starting polymers I, II and of 
the starting polymer dispersions containing these, although the monomer, 
regulator and initiator composition for the preparation of the aqueous 
starting polymer dispersions I, II can be not only congruent with but also 
different from that for the process of the invention. This applies mutatis 
mutandis necessarily also to the surface active substances to be used for 
preparing the aqueous starting polymer dispersions I, II. 
Aqueous starting polymer dispersions I are obtainable in a simple manner by 
adding together in the manner defined n aqueous starting polymer 
dispersions II whose particle diameter distribution functions preferably 
essentially do not overlap. From an application point of view n is 
preferably within the range from 2 to 10, preferably within the range from 
2 to 5. The preparation of aqueous starting polymer dispersions II is 
known per se. Appropriate teaching may be found for example in 
Houben-Weyl, Methoden der organischen Chemie, Volume E 20, part I, 
Makromolekulare Stoffe, Georg Thieme Verlag, Stuttgart, 1987, pages 248 to 
268. If the solids content used is to be a preferred 20-40% by weight and 
the desired weight average particle diameter is within the range &gt;0 to 
.ltoreq.50 nm, the aqueous starting polymer dispersions II are obtainable 
in a particularly simple manner, for example by mixing together the 
aqueous phase, the monomers, the free radical initiators (normally from 
0.1 to 5% by weight, based on the amount of starting monomers to be 
polymerized), and dispersants (customarily from 10 to 50% by weight, based 
on the amount of starting monomers to be polymerized) at a low temperature 
and heating the mixture to the polymerization temperature and polymerizing 
it (the particle diameter generally decreases with increasing amount of 
dispersant). In another version, the initial charge comprises essentially 
all the components, but the polymerization initiator is added continuously 
after the charge has been heated to the reaction temperature and while it 
is maintained at that temperature. As regards polymerization temperature 
and pressure, the statements concerning the process of the invention 
apply. 
Starting with thus obtainable relatively finely divided aqueous starting 
polymer dispersions II, coarsely divided aqueous starting polymer 
dispersions II are obtainable for example by introducing a finely divided 
aqueous starting polymer dispersion II into a polymerization vessel as 
initial charge, heating to the polymerization temperature and then adding 
further monomers, customarily preemulsified in aqueous medium, and 
polymerization initiator while the polymerization temperature is 
maintained. The amount of emulsifier added as part of the aqueous monomer 
emulsion is determined in such a way that the total amount of dispersant 
present in the resulting more coarsely divided aqueous starting polymer 
dispersion II is from 0.5 to 5, preferably from 0.5 to 3,% by weight, 
based on the resulting coarsely divided starting polymer II. The particle 
enlargement to be obtained is essentially determined by the ratio of 
initially charged finely divided starting polymer II particles and added 
monomers. Of course, there can be a smooth transition from the process of 
preparing a relatively finely divided aqueous starting polymer dispersion 
II to the process of particle size enlargement. The statements about 
weight average polymer particle diameters and ratios (d.sub.90 
-d.sub.10)/d.sub.50 of the aqueous starting polymer dispersions here 
always relate to determinations by means of an analytical ultracentrifuge 
(W. Machtle, Makromolekulare Chemie 185 (1984), 1025-1039). The 
determinations of the polymer particle size distribution of the final 
aqueous polymer dispersions were carried out in an analytical 
ultracentrifuge using the coupling PSD technique (cf. W. Me,uml/a/ chtle, 
Angewandte Makromolekulare Chemie 162 (1988), 35-42 (no. 2735)). 
For the purposes of the present invention it is preferable to use those 
aqueous starting polymer dispersions I which, of aqueous starting polymer 
dispersions II where e,ovs/d/ .sub.w,i .ltoreq.100 nm, contain only those 
whose d.sub.w,i is exclusively within the range .ltoreq.20 nm to 
.ltoreq.100 nm, particularly preferably exclusively within the range 
.ltoreq.30 to .ltoreq.60 nm. It is also advantageous to use those aqueous 
starting polymer dispersions I which contain only such aqueous starting 
polymer dispersions II that the difference between d.sub.w, .ltoreq.100 
and d.sub.w,i , where d.sub.w,i here is the weight average particle 
diameter of that aqueous starting polymer dispersion II contained in the 
aqueous starting polymer dispersion I whose above 100 nm value is closest 
to 100 nm, is at least 60, preferably at least 100, rim. 
Furthermore, preference is given to using those aqueous starting polymer 
dispersions I for which all the k values are within the range from 0.9 to 
1.1 and all the k' values within the range from 0.75 to 3, preferably 
within the range from 0.9 to 1.5. It is particularly advantageous for all 
the values k and k' of the at least one aqueous starting polymer 
dispersion I used to be about 1. 
Furthermore, V.sub..ltoreq.100 of the at least one aqueous starting polymer 
dispersion I to be added is advantageously from 0.5 to 5% by volume, based 
on the sum of all the V.sub.i it contains. The dispersant content of the 
at least one aqueous starting polymer dispersion I is normally from 0.5 to 
5% by weight, based on the amount of starting polymer I present therein. 
As defined, the final aqueous polymer dispersions of the invention are 
obtainable when the total amount of the at least one aqueous starting 
polymer dispersion I to be added is introduced into the polymerization 
vessel as initial charge prior to the start of the free radical aqueous 
emulsion polymerization of the invention, and the free radical aqueous 
emulsion polymerization of the at least one monomer to be subjected to a 
free radical polymerization is effected by the stream addition process. 
If final polymer dispersions having a particularly high solids volume 
concentration are desired, it is advantageous to add the monomers to the 
polymerization vessel by themselves. Otherwise the monomers to be 
subjected to a free radical polymerization are preferably added 
preemulsified in an aqueous phase, in which case the amount of emulsifier 
used for this purpose is advantageously from 0.5 to 3% by weight, based on 
the amount of emulsified monomer. 
It is technically advantageous for the initial charge introduced into the 
polymerization vessel to comprise not only the at least one aqueous 
starting polymer dispersion I to be added but also some polymerization 
initiator and a small proportion of the at least one monomer to be 
polymerized (typically from 1 to 5% by weight based on the total amount of 
the at least one monomer to be polymerized), the mixture to be heated to 
the polymerization temperature and then, while the poly-merization is 
maintained, for the remaining monomer and further polymerization initiator 
to be added synchronously to the polymerization vessel in such a way that 
from the start of the free radical aqueous emulsion polymerization the 
addition of the at least one radical polymerizable monomer into the 
polymerization vessel is effected in such a way that at any time of the 
addition the polymerization conversion of the total monomers already added 
previously to the polymerization vessel is at least 80, preferably at 
least 90, mol %, in which case the initiator addition period preferably 
extends somewhat beyond the duration of the monomer addition period. 
However, the free radical aqueous emulsion polymerization of the invention 
can also be carried out by including in the initial charge only the 
aqueous starting polymer dispersion I, heating to the polymerization 
temperature and then initiating the polymerization by starting the 
addition of polymerization initiator and the addition of monomer at the 
same time. of course, in the course of the addition stream process the 
polymerization vessel can be supplied with additional dispersant, for 
example as a spatially separate stream or as part of the monomer emulsion. 
If this is the case, then the procedure according to the invention is such 
that the amount of dispersant present in the polymerization vessel is at 
any time from the start of the free radical aqueous emulsion 
polymerization of the invention from 0.5 to 5% by weight, based on the sum 
of the masses of starting polymer I and the monomers to be polymerized 
already added to the polymerization vessel. 
Of course, in the course of the aqueous free radical emulsion 
polymerization of the invention it is possible for the composition of the 
monomers to be added to be changed during the stream addition process. 
Furthermore, the addition can take place not only stepwise but also 
continuously or by the gradient method. Preferably, the monomer addition 
takes place continuously. 
On completion of the actual polymerization process of the invention the 
mixture is preferably stirred for some additional hours while the 
polymerization temperature is maintained. This may be followed by 
customary measures for residual monomer removal, for setting a different 
pH or other methods of post-stabilization, including the subsequent 
addition of dispersants. Of course, the various possible, generally 
spatially separate, feed streams can be mixed with one another immediately 
before entry into the polymerization vessel. 
Preferred classes of final polymers are those composed 
to an extent of from 70 to 100% by weight of esters of acrylic and/or 
methacrylic acid with alkanols of from 1 to 12 carbon atoms and/or styrene 
or 
to an extent of from 70 to 100% by weight of styrene and/or butadiene of 
which the class of the acrylates is particularly preferred and preferably 
comprises the following monomer compositions: 
70-99% by weight of at least one ester of acrylic and/or methacrylic acid 
with alkanols of from 1 to 8 carbon atoms, 
1-5% by weight of acrylic acid, methacrylic acid or a mixture thereof, and 
0-25% by weight of vinyl acetate, styrene or a mixture thereof. 
The free radical aqueous emulsion polymerization of the invention makes it 
possible to produce in a simple manner final aqueous polymer dispersions 
which have a very wide final polymer particle size distribution which 
typically forms part of the following two particle size distribution 
specifications and has all of one of the following sets of particle size 
distributions: 
2-25% by weight of final polymer .ltoreq.200 nm 
0-50% by weight of final polymer .ltoreq.300 nm 
0-75% by weight of final polymer .ltoreq.400 nm 
5-85% by weight of final polymer .ltoreq.500 nm 
100% by weight of final polymer .ltoreq.700 nm or 
2-5% by weight of final polymer .ltoreq.200 nm 
8-15% by weight of final polymer .ltoreq.300 run 
8-45% by weight of final polymer .ltoreq.400 nm 
0-50% by weight of final polymer .ltoreq.500 nm 
2-65% by weight of final polymer .ltoreq.600 nm 
0-85% by weight of final polymer .ltoreq.700 nm 
5-98% by weight of final polymer .ltoreq.800 run 
100% by weight of final polymer .ltoreq.1200 nm 
It is presumably this specific particle size distribution which is 
responsible for the reduced flow resistance of the final aqueous polymer 
dispersions of the invention, which normally have Newtonian flow 
characteristics. Below a solids volume concentration of 50% by volume the 
effect of the particle size distribution on the flow resistance decreases 
progressively. The final aqueous polymer dispersions of the invention are 
generally obtained as described in an industrially readily implementable 
manner with solids volume concentrations of up to 75% by volume with fully 
satisfactory reproducibility and no flocs. 
The final aqueous polymer dispersions of the invention show their 
advantageous properties particularly markedly at solids volume 
concentrations above 65% by volume, which is why such final polymer 
dispersions are preferred. They are generally suitable for use as binders 
and as materials for preparing coatings and adhesive joints, for which 
purpose they may have additionally mixed into them in a conventional 
manner assistants such as film forming aids, fillers or plasticizers.

EXAMPLES 
EXAMPLE 1 
Preparation of aqueous starting polymer dispersions II 
(SDII(1) to SDII(8)) of starting polymers II (SPII(1) to SPII(8)) 
SDII(1): A mixture of 
1.44 kg of n-butyl acrylate, 
16.28 kg of water, 
1.27 kg of a 45% strength by weight solution of the surface active 
substance corresponding to 
Dowfax 2A1, and 
0.52 kg of a 30% strength by weight aqueous hydrogen peroxide solution 
was admixed all at once with 25% by weight of stream II at 25.degree. C. 
After the onset of the exothermic polymerization had heated the mixture to 
50.degree. C. (which took about 10 min), the remainder of stream II and 
the entire amount of the stream I were added continuously, starting at the 
same time, in the course of respectively 3 h and 2 h while the 50.degree. 
C. were maintained. This was followed by an additional hour of stirring at 
60.degree. C. 
Stream I: 
47.0 kg of water, 
14.7 kg of n-butyl acrylate, 
14.7 kg of methyl methacrylate, 
0.60 kg of methacrylic acid, 
0.664 kg of a 45% strength by weight aqueous solution of the surface active 
substance corresponding to Dowfax 2A1 
Stream II: 
10 kg of water, 
0.156 kg of ascorbic acid, 
0.004 kg of iron(II) sulfate. 
The result was an aqueous dispersion SDII(1), characterised as follows: 
Solids content: 30% by weight 
d.sub.w,1 : 40 nm 
##EQU3## 
SDII(2): A mixture of 521 g of water, 12 g of a 30% strength by weight 
aqueous hydrogen peroxide solution, and 
600 g of aqueous dispersion SDII(1) 
was heated to 60.degree. C. and, while this temperature was maintained, 
continuously admixed, starting at the same time, with stream I (in the 
course of 2.5 h) and stream II (in the course of 3 h). This was followed 
by an additional hour of stirring at 60.degree. C. 
Stream I: 
1176 g of n-butyl acrylate, 
24 g of methacrylic acid, 
30 g of a 20% strength by weight aqueous solution of an ethoxylated fatty 
alcohol (C.sub.18, EO degree:18), and 
60 g of a 45% strength by weight aqueous solution of the surface active 
substance corresponding to Dowfax 2A1 
Stream II: 
3.6 g of ascorbic acid, 
0.12 g of iron(II) sulfate, 
400 g of water. 
The result was an aqueous dispersion SDII(2), characterised as follows: 
Solids content: 40.8% by weight 
d.sub.w,2 : 84 nm 
##EQU4## 
SDII(3): As for SDII(2), except that the initial charge comprised 602 g of 
water, 
12 g of a 30% strength by weight aqueous hydrogen peroxide solution, and 
300 g of aqueous dispersion SDII(1). 
The resulting aqueous dispersion SDII(3) had the following characteristics: 
Solids content: 40.8% by weight 
d.sub.w,3 : 95 nm 
##EQU5## 
SDII(4): As for SDII(2), except that the initial charge comprised 639 g of 
water, 
12 g of a 30% strength by weight aqueous hydrogen peroxide solution, and 
160 g of aqueous dispersion SDII(1). 
SDII(4) had the following characteristics: 
Solids content: 40.3% by weight 
d.sub.w,4 : 122 nm 
##EQU6## 
SDII(5): As for SDII(2), except that the initial charge comprised 661 g of 
water, 
12 g of a 30% strength by weight aqueous hydrogen peroxide solution, and 
80 g of aqueous dispersion SDII(1). 
SDII(5) had the following characteristics: 
Solids content: 40.7% by weight 
d.sub.w,5 : 150 nm 
##EQU7## 
SDII (6 ): As for SDII (2 ), except that the initial charge comprised 672 
g of water, 
12 g of a 30% strength by weight aqueous hydrogen peroxide solution, and 
40 g of aqueous dispersion SDII(1). 
SDII(6) had the following characteristics: 
Solids content: 40.8% by weight 
d.sub.w,6 : 198 nm 
##EQU8## 
SDII(7): As for SDII(2), except that the initial charge comprised 677 g of 
water, 
12 g of a 30% strength by weight aqueous hydrogen peroxide solution, and 
20 g of aqueous dispersion SDII(1). 
SDII(7) had the following characteristics: 
Solids content: 41.0% by weight 
d.sub.w,7 : 233 nm 
##EQU9## 
SDII(8): As for SDII(2), except that the initial charge comprised 680 g of 
water, 
12 g of a 30% strength by weight aqueous hydrogen peroxide solution, and 
10 g of aqueous dispersion SDII(1). 
SDII(8) had the following characteristics: 
Solids content: 40.7% by weight 
d.sub.w,8 : 283 nm 
##EQU10## 
EXAMPLE 2 
Preparation of aqueous starting polymer dispersions I (SDI(1) to SDI(9)) 
They were prepared by simply adding together those different dispersions 
SDII obtained in Example 1 in amounts determined in such a way that the 
resulting dispersions SDI contained the starting polymers SPII in the 
volume contents shown below in Table 1 (% by volume, based on the total 
volume of all the starting polymers SPII contained in the respective 
dispersion SDI). Accordingly, the solids content of the SDIs was in all 
cases about 40% by weight. 
TABLE 1 
__________________________________________________________________________ 
% by volume 
SPII (1) 
SPII (2) 
SPII (3) 
SPII (4) 
SPII (5) 
SPII (6) 
SPII (7) 
SPII (8) 
__________________________________________________________________________ 
SDI (1) 
0.7 3.1 3.9 6.5 10.0 17.1 23.7 35.0 
SDI (2) 
0.8 -- -- -- -- -- 44.8 54.4 
SDI (3) 
0.6 -- -- -- 22.4 -- 34.8 42.2 
SDI (4) 
-- 1.24 -- -- 22.26 
-- 34.6 41.9 
SDI (5) 
0.81 -- -- -- -- 22.4 30.96 
45.73 
SDI (6) 
2.0 -- -- -- -- 22.2 30.6 45.2 
SDI (7) 
3.0 -- -- -- -- 21.9 30.3 44.8 
SDI (8) 
1.9 -- -- -- -- -- -- 98.1 
SDI (9) 
4.5 -- -- -- -- 21.7 33.7 40.1 
__________________________________________________________________________ 
EXAMPLE 3 
Preparation of final aqueous polymer dispersions FD(1) to FD(13 ) according 
to the invention 
A mixture of water, of a 30% strength by weight aqueous hydrogen peroxide 
solution, of a starting polymer dispersion I of Example 2 and of part of 
stream I was heated to 70.degree. C. and then admixed continuously, 
starting at the same time, with the remainder of stream I (in the course 
of 3 h) and stream II (the first 10% by weight within 20 min, the 
remaining 90% by .weight within 220 min) while the polymerization 
temperature was maintained. This was followed by additional stirring for 1 
h at 70.degree. C. 
The composition of stream I for FD(1) to FD(10) was as follows: 
1960 g of n-butyl acrylate, 
40 g of methacrylic acid, 
100 g of a 20% strength by weight aqueous solution of the surface active 
substance corresponding to Dowfax 2A1, 
50 g of a 20% strength by weight aqueous solution of an ethoxylated fatty 
alcohol (C.sub.18, EO degree: 18 ) and 
W g of water, 
where W had been determined in such a way as to produce the Table 2 solids 
contents for the respective final aqueous polymer dispersion according to 
the invention. 
The composition of stream I for FD(11 ) to FD(13 ) was similar, except that 
the 1960 g of n-butyl acrylate had been replaced by 
FD(11) 
1560 g of n-butyl acrylate and 
400 g of methyl methacrylate 
FD(12) 
1560 g of n-butyl acrylate and 
400 g of methyl acrylate 
FD(13): 
1560 g of n-butyl acrylate 
400 g of vinyl acetate. 
The composition of stream II was in all cases: 
300 g of water, 
6 g of ascorbic acid, and 
0.2 g of iron(II) sulfate. 
Table 2 indicates the respective composition of the initial charge 
(quantities in grams), the solids content and the volume concentration of 
the final dispersion (% by weight and % by volume respectively) and also 
the dynamic viscosities .eta..sub.60 and .eta..sub.60.9 in mPa.s of final 
aqueous polymer dispersions diluted to a standard 60% by weight or 60.9% 
by volume respectively, the .eta. determinations having been carried out 
in accordance with DIN 53019 at 23.degree. C. and at a shear gradient of 
487 s.sup.-1 . 
Table 3 additionally indicates the final polymer particle size distribution 
(% by weight of the particles of the final polymer whose particle diameter 
is .ltoreq. X nm, where X is an element of the set {200, 300, 400, 500, 
600, 700, 800, 900, 1000, 1200}). 
TABLE 2 
__________________________________________________________________________ 
Final dispersions FD 
(1) (2) (3) (4) (5) (6) (7) (8) (9) (10) 
(11) 
(12) 
(13) 
__________________________________________________________________________ 
Water 251 224 169 169 169 169 246 246 246 246 169 169 169 
Peroxide 
13.33 
13.33 
13.33 
13.33 
13.33 
13.33 
13.33 
13.33 
13.33 
13.33 
13.33 
13.33 
13.33 
solution 
SDI ( ) 
62.5 
125 250 250 250 250 75 75 75 75 250 250 250 
(1) (1) (1) (2) (3) (4) (5) (6) (7) (8) (9) (9) (9) 
Proportion 
45.5 
45.5 
45.5 
45.5 
45.5 
-- 45.5 
45.5 
45.5 
45.5 
45.5 
45.5 
45.5 
of stream I 
Solids 
68.0 
67.1 
65.8 
68.0 
66.6 
66.8 
70.6 
67.8 
67.5 
70.3 
65.9 
67.1 
64.7 
content 
Volume 
concen- 
64.8 
63.9 
62.7 
64.8 
63.4 
63.6 
67.2 
64.6 
64.3 
67.0 
60.0 
60.6 
58.9 
tration 
.eta..sub.60 
21 44 56 29 43 45 -- -- -- -- 50 37 33 
.eta..sub.60.9 
100 170 200 89 140 160 48 88 100 59 -- -- 
__________________________________________________________________________ 
TABLE 3 
__________________________________________________________________________ 
ED ( ) 
200 
300 400 
500 600 
700 800 
900 1000 
1200 
__________________________________________________________________________ 
(1) 4 38 63 78 98 100 -- -- -- -- 
(2) 3 12 22 43 65 83 95 100 -- -- 
(3) 4 15 47 74 92 100 -- -- -- -- 
(4) 4 11 18 21 22 72 98 100 -- -- 
(5) 3 11 33 48 97 100 -- -- -- -- 
(6) 4 11 46 74 98 100 -- -- -- -- 
(7) 2 14 24 35 36 50 78 98 98 
100 
(8) 4 8 40 43 46 68 86 -- -- -- 
(9) 4 10 44 46 50 78 95 -- -- -- 
(10) 4 8 30 50 52 54 56 100 100 
-- 
(11) 24 47 75 82 100 
-- -- -- -- -- 
(12) 12 42 64 74 95 100 -- -- -- -- 
(13) 20 40 61 75 98 100 -- -- -- -- 
__________________________________________________________________________