Process for the preparation of polymer dispersions and their application

A process for the preparation of aqueous dispersions, also emulsion (co)polymerization of vinyl halides and/or vinyl esters and, if needed, additional monomers in the absence of emulsifying agents are described. Protective colloid is added after the initiation of the polymerization to stabilize the forming dispersion. The dispersions are characterized by low viscosity, even with high solids contents, and low structural viscosity, and they are suitable a.o. especially for the preparation of redispersible powders.

The present invention concerns an improved process for the preparation of 
aqueous polymer dispersions stabilized by a protective colloid, especially 
by polyvinyl alcohol (PVAL), by one-step radical polymerization of vinyl 
halides and/or vinyl alkanoates, if needed with other compounds with 
unsaturated ethylene bonds copolymerizable with the former in amounts of 
up to 50 percent by weight. 
The preparation of aqueous dispersions of polymers of the type mentioned 
above by emulsion polymerization is known in principle. The dispersing 
agent needed for the stabilization of the dispersions, namely an 
emulsifying agent, if needed in combination with a protective colloid, is 
generally included in the batch for this purpose. (cf. EP-B-No. 
590,DE-B-No. 11 80 133 and DE-A-No. 17 70 395). 
To achieve special effects (e.g. coarser consistency or bimodal particle 
size distribution), it has been suggested that the polymerization be 
started without the emulsifying agent and to add the latter, or the 
starting materials for its formation, only during the course of the 
polymerization (cf. DE-B-No. 15 20 849 and DE-A-No. 28 37 992). 
There existed the need to develop a process by which dispersions can be 
prepared which are suitable a.o. for use in the preparation of adhesives, 
for the coating of paper, textiles, fiber fleeces and similar products, as 
additive to mortar and concrete mixes and as film-forming components in 
paints, which are also characterized by low structural viscosity and low 
viscosity despite high solids contents. 
The last-mentioned property is especially advantageous if the preparation 
of a redispersible powder is intended, since, in this case, even 
dispersions with a high solids content can be sprayed through jets without 
any problem. Usually, conventionally prepared dispersions, in which 
additional protective colloids are included to produce redispersible 
powders, have a higher structural viscosity because of this addition. 
The problems mentioned above can be solved in a surprising manner by the 
present invention. Furthermore, this new process can also be used to 
produce dispersions of polymers containing ethylene, which still have a 
high initial grabbing rate despite contents of ethylene units in the 
polymer exceeding 10 wt%, even exceeding 15 wt% and also even exceeding 20 
wt%, and are therefore still highly suitable as adhesives. 
The subject of the invention is a process for the preparation of aqueous 
polymer dispersions stabilized by a protective colloid, preferably only by 
protective colloid during the preparation, with solids contents of 20 to 
75, preferably 20 to 70, especially 30 to 60 wt%, calculated with respect 
to the total weight, by one-step polymerization of vinyl halides, 
preferably of vinyl/chloride and/or of vinyl alkanoates, preferably of 
vinyl acetate, if needed together with not more than 50 percent by weight, 
with respect to the monomers that are liquid under the reaction 
conditions, other compounds with unsaturated ethylene bonds 
copolymerizable with the former monomers at temperatures of 0.degree. to 
120.degree. C., preferably 20.degree. to 100.degree. C., and pressures of 
up to 200 bar, with the aid of at least partially water-soluble initiator 
systems and, if needed, in the presence of conventional additives. The 
process is characterized by the fact that the addition of protective 
colloid, preferably at least one PVAL with a degree of hydrolysis of 70 to 
99.8 mol% and a mean degree of polymerization P.sub..eta. of 200 to 3,000, 
as first dispersing agent, begins only after the conversion of 1 to 60 
wt%, preferably 2 to 25 wt%, calculated with respect to the total weight, 
of the monomers liquid under the reaction conditions. 
In a preferred embodiment, 1 to 40 wt%, especially 5 to 30 wt%, of the 
monomers liquid at under the reaction conditions are initially placed in 
the reaction vessel. The remaining amounts of these monomers, i.e. 60 to 
99 wt%, or especially 70 to 95 wt%, are added during the course of the 
polymerization, preferably at the rate of their consumption. Here, it was 
often found advantageous to keep the concentration of these monomers in 
the reaction mixture, until the completion of the addition, at approx. the 
same level existing in the initial batch, e.g. 0.2 and 30, preferably 1 to 
21, especially 1.5 to 18 wt% (calculated with respect to the total weight 
of the reaction mixture). But a deviation from this is obviously possible, 
e.g. when special effects shall be produced. 
Included in the "monomers liquid under the reaction conditions" within the 
scope of this application, are those polymerizable compounds with 
unsaturated ethylene bonds that can be liquified in the range from 
0.degree. to 120.degree. C. and up to 200 bar, or are already liquid. 
Examples are primarily the vinyl halides such as vinyl fluoride, vinyl 
bromide, preferably vinyl chloride, as well as the vinyl alkanoates (vinyl 
esters of saturated straight-chain or branched carboxylic acids, 
preferably with up to 20 C-atoms) such as vinyl formate, propionate, 
butyrate, ethylhexanoate, laurate, stearate, isotridecanoate, vinyl esters 
of Versatic.RTM. acids and preferably vinyl acetate. The sum of these 
monomers, especially of vinyl chloride and vinyl acetate is at least 50 
wt%, preferably at least 80 wt%, of the total amount of the monomers 
liquid under the given reaction conditions. Also suitable as such monomers 
besides the mentioned vinyl chloride and vinyl acetate, as well as besides 
individual, or mixtures of the other vinyl halides and/or alkanoates, are, 
especially preferably, in amounts of up to 20 wt%: 
mono and dialkyl, glycidyl and hydroxyalkyl esters of mono- and 
dicarboxylic acids with unsaturated ethylene bonds, e.g. esters of 
(meth)acrylic acid, maleic acid, fumaric acid, crotonic acid and itaconic 
acid with (un)branched C.sub.1 - to C.sub.20 -alkanols such as methanol, 
ethanol, n- and iso-propanol, n-, sec- and tert-butanol, 2-ethylhexanol, 
octanol, dodecanol, Alfol.RTM.-alcohols, polyalcohols such as ethylene, 
propylene and butylene glycol and pentaerythritol; 
allyl and vinyl esters of (meth)acrylic acid (di)acetoacetic acid; 
vinyl and allyl compounds of silanes, glycideyl alcohol, amino alcohols, 
.alpha.-chloroalkyl carboxylic acids, dichlorotriazines; 
vinylidene halides such as vinylidene chloride; 
acryltrialkoxysilanes; 
mono- and dicarboxylic acids with unsaturated ethylene bonds, their 
anhydrides, their amides and their N-methylolamides, which are, 
optionally, etherified with (poly)alkoxyl groups (ethoxyl or propoxyl 
groups), such as (meth)acrylic acid, (meth)acrylamide, N-methylol 
(meth)-acrylamide, maleic acid anhydride, crotonic acid, crotonic acid 
amide; 
vinyl ether; 
vinyl derivatives of heterocyclic compounds, e.g. N-vinylpyridine, and 
N-vinyl-pyrrolidone; 
vinyl sulfonic acid and its salts; 
.alpha.-olefins, e.g. prolypene, butylene, octene, dodecene. 
Monomers with strongly polar groups, e.g. vinyl sulfonate, the carboxylic 
acids, amides and anhydrides, should be used preferably in the amounts of 
only up to 5 wt%, especially up to 2 wt%, calculated with respect to the 
liquid monomers under the reaction conditions. 
Di- and polyvinyl and allyl compounds of di- and polycarboxylic acids and 
phenols as well as vinyl and allyl (meth)acrylate and/or crotonate can be 
copolymerized in amounts of 0 to 2, preferably up to 0.5, wt%, calculated 
with respect to the liquid monomers. The monomers from the mentioned 
groups can be placed separately or as premixes, after the beginning of the 
addition of protective colloid also as preemulsion, into the reaction 
vessel, or metered into it. It is possible to place the total or partial 
amounts of individual monomers from this group in the reaction vessel and 
to meter the remainder. But the premixing of the desired monomers from the 
mentioned group and its use as premix, and thus keeping the composition of 
this monomer phase largely constant for a relatively long time during the 
reaction, is often preferred for the sake of simplicity. 
In addition to the mentioned monomers, ethylene is also used as comonomer 
in another preferred embodiment of the process according to the invention. 
For this purpose, a partial pressure of up to 200 bar, preferably up to 80 
bar of ethylene is applied to the reaction vessel either before or also 
during the reaction. The pressure is applied preferably before the 
reaction, in order that the liquid reaction mixture can dissolve part of 
the ethylene until the equilibrium between the gas volume and the liquid 
phase has been established. The ethylene can be added in one operation, or 
its partial pressure can be kept largely constant over a relatively long 
time, partially to the end of the metering of the monomers that are liquid 
under the reaction conditions. 
The process according to the invention allows the incorporation of larger 
amounts of ethylene in the polymer than previously possible with the 
existing processes, even in the presence of higher concentrations of 
monomers that are liquid under the reaction conditions, i.e. more than 15 
or even more than 25 wt%, calculated with respect to the total weight of 
the reaction mixture. For example, preferred polymers with a content of 
units that are not derived from vinyl chloride, vinyl acetate and/or 
ethylene of not more than 20 wt% can be produced. The content of ethylene 
units in these may amount to up to 45 wt%, preferably 5 to 30 wt%, 
calculated with respect to the polymer. The monomers that are liquid under 
the reaction conditions react practically quantitatively. Furthermore, the 
particle size distribution of the forming dispersions can be controlled in 
a simple way through the time and amount of the first addition of 
protective colloid. Also, the polymerization rate can be accelerated since 
a faster removal of the heat of reaction is possible due to the lower 
viscosity. 
This lower viscosity of dispersions prepared according to the invention, 
even at high solids contents, is especially surprising since it is known 
that the viscosity of aqueous dispersions can be increased by the addition 
of protective colloids. Another advantage of the process according to the 
invention is the fact that when preferably using the dispersions prepared 
according to the invention for the production of redispersible powders, 
e.g. for use in the building sector as adhesive or additive for 
hydraulically setting masses, more free protective colloid is present at 
the end of the polymerization because of the lower rate of grafting of the 
protective colloid, especially of the polyvinyl alcohol (PVAL). This 
eliminates, at least partially, the need for the further addition of 
protective colloid, especially PVAL, during or after drying. 
Used as protective colloids are those generally suitable for 
polymerization, e.g. cellulose derivatives or water-soluble polymers such 
as partially saponified polyvinyl acetate or vinyl pyrrolidone polymers. 
Preferred is at least one polyvinyl alcohol with a degree of hydrolysis of 
70 to 99.8 mol% (corresponding to a saponification number of approx 10 to 
approx. 257), preferably 74 to 99.5 mol% (corresponding to a 
saponification number of approx. 20 to approx. 240) and with a mean degree 
of polymerization of 200 to 3,000 (corresponding to a Hoppler viscosity of 
approx. 3 to approx. 50 m.Pas of a 4 wt% aqueous solution at 20.degree. 
C.). The protective colloid, especially the PVAL, is added in total 
amounts of 0.5 to 15 wt%, preferably of 3 to 10 wt%, calculated with 
respect to the monomers that are liquid under the reaction conditions. 
When additional comonomers are used that are known to stabilize the 
dispersion (e.g. vinyl sulfonate), even the addition of approx. 1 to 3 
wt/% of protective colloid can produce very good results. 
Of course, the use of mixtures of various different protective colloids is 
possible, e.g. mixture of PVAL's of higher and lower viscosity, or higher 
or lower degrees of saponification. It is also possible to add one (or 
several) of these protective colloids earlier and (one) several other(s) 
later. It should also be mentioned that polymers generally have a certain 
range of composition, e.g. a given PVAL, characterized by the properties 
above, does not consist of a single species of molecules only. 
The polymerization is performed preferably with so-called redox initiator 
systems, which generally consist of a combination of at least one peroxide 
compound and at least one reducing agent. One of these components can be 
placed in the reaction vessel in its entirety or partly, the other 
component and, optionally, the rest of the components, part of which has 
been initially placed or, if needed, both components, are then metered 
during the course of the polymerization. For example, the oxidation 
component can be placed in the reaction vessel, and the polymerization is 
controlled by the metering of the reducing component. This is generally 
the preferred practical application. 
Approximately 0.01 to approx. 0.5 wt%, preferably 0.03 wt%, of reducing 
component and approx. 0.01 to approx. 2 wt%, preferably 0.03 to 0.8 wt%, 
of oxidizing component are generally needed, and particularly good results 
are often obtained when the molar ratio of oxidizing to reducing component 
is 0.5 to 4. The percentages given above are calculated with respect to 
the total weight of the monomers that are liquid under the reaction 
conditions. 
Preferred examples of the oxidizing component are the following peroxide 
compounds: 
Ammonium and potassium persulfate and peroxodisulfate, hydrogen peroxide, 
alkyl hydroperoxides such as tert-butyl hydroperoxide, peroxodiphosphates 
such as potassium-, sodium- and ammonium peroxodiphosphate as well as 
their mixtures. 
To be mentioned as preferred examples of the reducing component are 
compounds of sulfur in which the sulfur is not present in its formal 
degree of oxidation of +6. Especially mentioned are: water-soluble 
sulfites and sulfoxylates such as alkali (Na, K) or ammonium sulfite or 
hydrogen sulfite or alkali (Na, K) or zinc formaldehyde sulfoxylate. 
Equally suitable are hydrogen/precious metal catalyst components with the 
concurrent use of small amounts of salts of heavy metals as activators. 
Suitable initiator systems are described, a.o., in "Fundamental Principles 
of Polymerization" by G. F. Alelio, John Wiley and Sons Inc. New York, 
1952, pages 333 ff and in the DE-B-No. 11 33 130. 
The use of radical initiators, e.g. the persulfates or peroxodiphosphates, 
is principally possible in the absence of a reducing agent. In this system 
as well as in those previously mentioned, traces of salts of suitable 
heavy metals e.g. iron or copper, preferably, are added by a well-known 
method. 
After the polymerization, possibly (at the most) also at the end of the 
polymerization, e.g. for the post polymerization, anionic and/or 
nonionogenic emulsifying agents can be added, if wanted, in amounts of 0 
to 4 wt%, preferably up to 2 wt%, calculated with respect to the solids 
content of the dispersion. 
Mentioned as examples are: alkaline or alkaline earth salts of alkylated 
benzene- and naphthalinesulfonic acids such as sodium benzylsulfonate, 
alkali alkyl sulfonates such as sodium lauryl sulfonate, sodium dodecyl 
sulfonate, salts of the alkyl sulfuric acids such as sodium lauryl 
sulfate, also sodium alkyl sulfosuccinate or mono- and diesters of sodium 
alkyl sulfosuccinate, sodium or ammonium salts of sulfate esters of alkyl 
phenoxipoly (ethoxylene) ethanols, such as octyl- or iso-nonyl phenoxipoly 
(ethoxylene) ethanols, as well as their ethoxylated products, ethylene 
oxide adducts of alkyl glycols and alkyl phenols, block copolymers of 
ethylene oxide and propylene oxide as well as sulfonated fatty acid 
amides, and ethylene oxide addition products with fatty alcohols or fatty 
amines. 
The process according to the invention is performed preferably at a pH of 
2.5 to 7. But this range may be extended, if necessary. The usual buffer 
substances, e.g. bicarbonates, borates, acetates, citrates, mixtures of 
primary and secondary phosphates of the alkali metals, may also be added 
to stabilize the pH. 
The process according to the invention is performed preferably by the 
metering method, but the entire amount of monomers can be placed in the 
reaction vessel. When using the metering method, at least one monomer may 
be placed in the reaction vessel, either in its entirety or partly, while 
the others are metered in their entirety, including, if needed, the 
remainder of the partially batched monomers. 
Since conversions are frequently difficult to measure in practice, 
preferably the addition of protective colloid begins at the earliest at a 
solids content of 2 wt%, preferably 5 wt%, for the dispersion (which is 
easily determined), and at the latest at a solids content of 40 wt%, 
better 30 wt%, especially 20 wt%. 
The dispersions prepared by the process according to the invention are 
suitable as adhesives, for the coating of paper, cloth and fleeces of 
natural or synthetic fibers, fiberglass, wood fibers etc., as additive or 
as binder in concrete and mortar mixes. 
The following examples serve to explain the invention. The results of the 
examples and comparison tests are compiled in the added tables. Unless 
otherwise stated, the percentages are always percent by weight and are 
calculated with respect to 
(a) the total weight of the monomers that are liquid under the reaction 
conditions 
(b) the solids content 
(c) the total weight of the dispersion. 
The viscosities of the PVAL's in m.Pas were determined according to 
Hoppler, as mentioned above; those of the dispersions, with the Epprecht 
rheometer, with the measuring unit always given in ( ). 
Pressures were recorded only when the initial pressure was greater than the 
pressure of the surrounding atmosphere.