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The invention relates to low-emission dispersion paints, coating materials
and synthetic resin dispersion plasters in the form of aqueous
preparations based on aqueous synthetic resin dispersions having a pigment
volume concentration (PVC) of at least 60% which are free from organic
solvents and volatile organic film-forming auxiliaries and low-molecular
weight plasticizers, and which are free from readily volatile non-aqueous
constituents and from malodorous by-products, furthermore to processes for
the preparation thereof and to the use thereof as construction protective
materials and as structural materials, especially in spaces that are
inadequately ventilated and are inhabitated.
In order to reduce pollution by noxious substances it is often desirable
for aqueous dispersion paints, coating materials and synthetic resin
dispersion plasters, when used in the open or especially in enclosed
spaces, to be unable to liberate, apart from water, any non-aqueous
volatile organic or inorganic constituents.
However, according to the state of the art, construction protective
materials such as, for example dispersion paints, plasters, mastics, and
liquid adhesives, contain more or less large amounts of solvents. The
readily volatile or the moderately to slightly volatile additives here
used as solvents or film-consolidating or film-forming auxiliaries or also
as plasticizers, are generally indispensable for achieving the required
application properties of the construction protective materials. In order
to attain high wet abrasion resistance, mechanical strength, low tendency
to soiling and to blocking of the used materials, it has not been hitherto
possible to employ dispersion polymers whose aqueous dispersions possess a
freezing or glass temperature (Tg) or a minimum film-forming temperature
(MFT) in the neighborhood of 0.degree. C. These application properties
could accordingly only be achieved by the use of polymer dispersions
having a Tg or MFT distinctly above 0.degree. C. in conjunction with
film-forming auxiliaries which reduce the Tg or MFT, with the result that
it was possible to employ them even at, or, if desired, below 5.degree. C.
Film-forming auxiliaries and temporary-plasticizers, however, migrate into
the atmosphere on drying, which may be toxicologically hazardous
especially with indoor paints, for example through unpleasant odor or
through inhalation by sensitive persons.
Permanent plasticizers have also been used in the past. This can lead to
shortcomings due to increased tackiness, plasticizer migration as well as
to possible volatility.
Experiments were also undertaken into using vinyl acetate dispersion
copolymers, especially vinyl acetate/ethylene copolymer dispersions which
possess a Tg or a MFT in the neighborhood of 0.degree. C.
It was found, however, that the pigment binding power of such dispersions
is limited compared with systems having binders obtained from harder
dispersion copolymers with additions of film-consolidating auxiliaries.
Thus the object forming the basis of the present invention has been to make
available such aqueous dispersion paints, coating materials and plasters
which contain no significant proportions of non-aqueous volatile compounds
apart from water and which contain as binders synthetic resin dispersions
which are free from film-forming auxiliaries, and which have a high
pigment binding power per se and moreover whose films possess low tendency
to soiling and to blocking even at a low Tg or low MFT of the dispersion.
It has now been found, surprisingly, that the foregoing difficulties may be
overcome by using dispersions of such synthetic resin dispersion
copolymers whose copolymer macromolecules contain small amounts of
monomeric units derived from unsaturated hydrolyzable organic silicon
compounds and possess the required Tg and MFT values, and furthermore the
dispersions are virtually free from volatile non-aqueous organic and/or
inorganic constituents.
Accordingly, the subject matter of the invention are low-emission
dispersion paints, coating materials and synthetic resin dispersion
plasters in the form of aqueous preparations based on aqueous synthetic
resin dispersion polymers derived from olefinically unsaturated monomers
having a pigment volume concentration (PVC) of at least 60% and containing
water, fillers, pigments, synthetic resin dispersion polymers and
auxiliaries selected from the group wetting agents, dispersants,
emulsifiers, protective colloids, thickeners, antifoams, dyes and
preservatives, wherein the non-volatile part of the aqueous preparations
contains
35 to 94% by weight of a filler,
2 to 30% by Weight of a pigment,
0.1 to 10% by weight of an auxiliary and
4 to 35% by weight of a synthetic resin dispersion copolymer, based on the
total non-volatile part, the aqueous dispersion of which copolymer
possesses a minimum film-forming temperature (MFT) of <10.degree. C.,
preferably <5.degree. C., particularly <2.degree. C., and the synthetic
resin dispersion copolymer has a content of 0.05 to 2% by weight,
preferably 0.1 to 0.4% by weight, particularly 0.05 to 0.2% by weight,
based on the synthetic resin dispersion copolymer, of monomeric units
derived from unsaturated hydrolyzable organic silicon compounds of the
formula I,
##STR1##
in which R denotes an organic radical olefinically unsaturated in the
.omega.-position and R.sup.1 R.sup.2 and R.sup.3 which may be identical or
different, denote halogen, preferably chlorine, or the group -OZ, Z
denoting primary or secondary alkyl or acyl radicals optionally
substituted by alkoxy groups, or hydrogen, the content of volatile
non-aqueous constituents of the aqueous preparations being <0.1% by
weight, preferably <0.05% by weight, based on the total non-volatile part,
and the pH of the aqueous preparations being in the range from 5.5 to 10,
preferably 7 to 9, particularly 8 to 9.
A preferred embodiment of the invention comprises the synthetic resin
dispersion copolymer used containing monomeric units selected from the
group vinyl esters, vinyl esters/ethylene, vinyl esters/vinyl
chloride/ethylene, vinyl esters/vinyl versatates, vinyl esters/acrylic
esters and acrylic esters/vinyl versatates/ethylene, in addition to
monomeric units derived from compounds of the formula I.
Preferred compounds of the formula I are, for example,
.gamma.-acryloxypropyltrimethoxysilane,
.gamma.-methacryloxypropyltrimethoxysilane, vinyltrimethoxysilane,
vinyltriethoxysilane, vinyltrimethylglycol silane, vinyltriacetoxysilane,
vinyltrichlorosilane, vinylmethyldichlorosilane and
.gamma.-methacryloxypropyltris(2-methoxyethoxy)silane.
A particular variant of the invention is for the synthetic resin dispersion
copolymer used to comprise mixtures of dispersion copolymers, a part of
which contains no monomeric units of the formula I and another part of
which contains monomeric units of the formula I in such an amount that the
mean content of monomeric units of the formula I in the total dispersion
copolymer mixture is 0.05 to 2% by weight, preferably 0.1 to 0.4% by
weight, particularly 0.05 to 0.2% by weight, based on the total synthetic
resin dispersion copolymer mixture.
Furthermore, a particular feature according to the invention is that the
aqueous preparations according to the invention are free from readily
volatile residual monomers, from low alcohols and from ammonia and/or
volatile amines or from components which give rise by cleavage to H.sub.2
S or mercaptans, if appropriate, and the total content of volatile
non-aqueous constituents of the aqueous preparations is <0.05% by weight,
based on the total non-volatile part.
The preparation of synthetic resin copolymer dispersions, where the
monomers are copolymerized with hydrolyzable, unsaturated organic silicon
compounds of the formula I, is known.
Synthetic resin dispersions based on vinyl acetate with 0.5. to .1% by
weight, based on the total amount of monomers, of a copolymerizable
silane, such as, for example, vinyltrimethoxysilane,
.gamma.-methacryloxypropyltrimethoxysilane and vinyl
tris(2-methoxyethoxy)silane, are known from U.S. Pat. No. 3,729,438. The
polymer crosslinks on drying, giving rise to a clear, high-gloss film.
U.S. Pat. No. 3,814,716 describes synthetic resin dispersions based on
vinyl acetate, acrylic esters, maleic and fumaric esters with 0.5 to 5% by
weight of a copolymerizable silane. On drying the synthetic resin
dispersion yields clear, high-gloss and crosslinked films with excellent
water and solvent resistance.
The use of polymeric binders in aqueous dispersion for the preparation of
structural coating materials are known from DE-PS 2,148,457, where the
synthetic resin dispersions contain polymers from vinyl esters, acrylic
esters or butadienestyrene copolymers into which the silanol groups have
been introduced by polymerization.
The preparation of aqueous synthetic resin dispersions based on vinyl
esters of carboxylic acids of 2 to 18 carbon atoms, ethylene, optionally
up to 25% by weight of other olefinically unsaturated monomers and 0.3 to
5% by weight, based on the total amount of monomers, of an unsaturated
hydrolyzable organic silicon compound, is known from DE-PS 2,148,458.
Films prepared from the synthetic resin dispersions described exhibit with
copolymers containing 1 to 2% by weight of the silicon compounds named
above, high drying and wet peeling strengths on glass and asbestos cement.
However, the synthetic resin dispersion prepared according to Example 1 of
the above DE-PS possesses a 0.2% by weight content of unreacted monomeric
vinyl acetate and the synthetic resin dispersions prepared according to
Examples 6 and 10 contain, respectively, 3.8 and 4.8% by weight of
methanol, in each case based on the polymeric part.
It cannot be simply assumed or deduced from the above state of the art that
synthetic resin dispersions containing silanol groups may also give rise,
in addition to a high pigment binding power in dispersion paints, to an
improvement of the pull-off resistance of the coatings produced by the
paints and, in addition, to a low tendency to soiling and blocking of the
films or coatings produced therefrom, despite a low Tg and a low MFT.
It was therefore the more surprising to find that with binders based on
synthetic resin dispersions having a low MFT, in the absence of volatile
organic film-forming auxiliaries, a marked improvement of the binder
properties is achieved if the dispersion copolymers contain only very
small amounts of monomeric units with silanol groups formed from compounds
of the formula I, amounts from 0.1 to 0.4% by weight, based on the total
amount of monomer, being preferred.
A preferred embodiment of the present invention further is that the
synthetic resin dispersion copolymer contained in the aqueous preparations
and carrying silicon radicals in the monomeric units of the formula I was
prepared by radically initiated copolymerization of the finely divided
monomers having an amount of 0.05 to 2% by weight, preferably 0.1 to 0.4%
by weight, particularly 0.05 to 0.2% by weight, based on the total amount
of monomer, of monomers of the formula I in aqueous medium with the
simultaneous use of hydroxyethylcellulose, non-ionic emulsifiers and
monomeric sodium vinylsulfonate as emulsifier/protective colloid system,
and the volatile alcohol components which may have formed by hydrolysis
from the monomeric units of the formula I in the aqueous dispersion and
any volatile amounts of residual monomers which may be present after the
terminated polymerization reaction have been removed by physical methods,
preferably by distillation under reduced pressure.
In the preparation of the synthetic resin dispersion copolymers, for
example by emulsion polymerization, the alkoxy, acyloxy and halogen
radicals of the silicon compounds of the formula I used hydrolyze at least
partially to give silicon compounds containing hydroxyl groups (silanol
groups) which are then contained in the copolymer and may lead to
crosslinking between the macromolecules.
Suitable hydrolyzable unsaturated organic silicon compounds of the formula
I are preferably those in which the radical R in the formula I represents
an .omega.-unsaturated alkenyl of 2 to 10 carbon atoms, particularly of 2
to 4 carbon atoms, or an .omega.-unsaturated carboxylic acid ester formed
from unsaturated carboxylic acids of up to 4 carbon atoms and alcohols
carrying the Si group of up to 6 carbon atoms. Suitable radicals R.sup.1,
R.sup.2, R.sup.3 are preferably halogen, particularly chlorine, and the
group -OZ, Z representing primary and/or secondary alkyl radicals of up to
10 carbon atoms, preferably up to 4 carbon atoms, or alkyl radicals
substituted by alkoxy groups, preferably of up to 3 carbon atoms, or acyl
radicals of up to 6 carbon atoms, preferably of up to 3 carbon atoms, or
hydrogen.
Examples of such compounds of the formula I are vinyltrichlorosilane,
vinylmethyldichlorosilane,
.gamma.-methacryloxypropyltris(2-methoxyethoxy)silane, vinylmethoxysilane,
vinyltriethoxysilane, vinyldiethoxysilanol, vinylethoxysilanediol,
allyltriethoxysilane, vinyltripropoxysilane, vinyltriisopropoxysilane,
vinyltributoxysilane, vinyltriacetoxysilane, trimethylglycolvinylsilane,
.gamma.-methacryloxypropyltrimethylglycolsilane,
.gamma.-acryloxypropyltriethoxysilane and
.gamma.-methacryloxypropyltrimethoxysilane.
The removal of residual monomers in the synthetic resin copolymer
dispersions used according to the invention may also be carried out by
resorting to known chemical methods such as, for example, by radically
initiated, preferably using redox catalysts, secondary polymerization.
Should subsequently traces of volatile monomers be still present in the
dispersion, these can be readily removed by other methods, preferably by
physical methods, particularly by distillation, preferably under reduced
pressure and, if desired, by passing inert carrier gases such as, for
example, air, nitrogen, CO.sub.2 or steam, through or over the reaction
mixture.
A particular feature of the present invention is also the fact that the
synthetic resin copolymer dispersions used according to the invention are
not only free from volatile residual monomers, but also that any volatile
alcohols forming or formed in the hydrolysis of the used comonomers of the
formula I, such as, for example, methanol, methoxyethanol or isopropanol,
have been removed by the aftertreatment referred to above using chemical
and/or physical methods. This may be of considerable significance when,
for example, vinyltrimethoxysilane is used as comonomer, since the
methanol formed by hydrolysis and present in the resultant dispersion may
prevent the use of the dispersion on toxicological grounds, if the
methanol has not been eliminated beforehand.
The aqueous preparations according to the invention comprise in their final
composition to be used as construction protective materials or structural
materials, if appropriate, preferably also the following components as
further auxiliaries in addition to the constituents from the synthetic
resin copolymer dispersion:
0.1 to 0.6% by weight of a wetting agent or dispersant for filler and
pigment,
0.1 to 1% by weight of a thickener,
0.01 to 2% by weight of a preservative and
0.001 to 0.5% by weight of an anti-foam,
each based on the total weight of the aqueous preparations.
The aqueous preparations according to the invention in the form of
dispersion paints, coating materials and synthetic resin dispersion
plasters, using synthetic resin dispersion copolymer latices according to
the invention, which preparations are free from residual monomers and
other volatile constituents, may be prepared by application of known
techniques, such as they are used in the preparation of conventional
products of this type using conventional synthetic polymer latices.
However, it is important that in the choice of the usual starting
materials attention is paid particularly to their freedom from ammonia,
amines, ammonium compounds, alkyl ammonium compounds, solvents, H.sub.2 S,
SO.sub.2 and formaldehyde as well as freedom from other volatile organic
substances.
Preferred fillers used are, for example, calcium carbonate, magnesite,
dolomite, kaolin, mica, talc, silica, calcium sulfate, feldspar, barium
sulfate and plastic beads.
Examples of white pigments used are zinc oxide, zinc sulfide, basic lead
carbonate, antimony trioxide, lithopone (zinc sulfide+barium sulfate) and,
preferably, titanium dioxide.
Examples of inorganic colored pigments which may preferably be used are
iron oxides, carbon black, graphite, luminescent pigments, zinc yellow,
zinc green, Paris blue, ultramarine, manganese black, antimony black,
manganese violet or Schweinfurt green.
Suitable organic colored pigments preferably are, for example, sepia,
gamboge, Cassel brown, toluidine red, para red, Hansa yellow, indigo, azo
dyes, anthraquinone and indigo dyes as well as dioxazine, quinacridone,
phthalocyanin, isoindolinone and metal complex pigments of the azomethine
series.
The fillers may be used as individual components. Mixtures of fillers such
as, for example, calcium carbonate/kaolin and calcium
carbonate/kaolin/talc have been found to be particularly useful in
practice. To increase the hiding power and to save on titanium dioxide,
finely divided fillers such as, for example, finely divided calcium
carbonate and mixtures of various calcium carbonates with different
particle size distribution are frequently used.
To adjust the hiding power, the shade and the depth of color the fillers
are mixed with appropriate amounts of white pigment and inorganic and/or
organic colored pigments.
To disperse the fillers and pigments in water, 0.1 to 0.6% by weight, based
on the total weight of the aqueous preparation, of auxiliaries based on
anionic or non-ionic wetting agents, such as preferably, for example,
sodium pyrophosphate, sodium polyphosphate, naphthalenesulfonate, sodium
polyacrylate, sodium polymaleinates and polyphosphonates such as sodium
1-hydroxyethane-1,1-diphosphonate and sodium
nitrilotris(methylenephosphonate), may be added.
Thickeners which may be used, are inter alia preferably cellulose derivates
such as methylcellulose, hydroxyethylcellulose and carboxymethylcellulose.
Other thickeners which may be used, are casein, gum arabic, gum
tragacanth, starch, sodium alginate, polyvinyl alcohol,
polyvinylpyrrolidone, sodium polyacrylate and water-soluble copolymers
based on acrylic and methacrylic acid, such as acrylic acid/acrylamide and
methacrylic acid/acrylic ester copolymers.
Inorganic thickeners, such as, for example, bentonites or hectorite, may
also be used.
Such thickeners are generally employed in amounts from 0.1 to 3% by weight,
preferably 0.1 to 1% by weight, based on the total weight of the aqueous
preparations.
The thickener may be incorporated already during the dispersion of the
fillers and pigments in water with the addition of a dispersant and, if
desired, an antifoam, for example using a dissolver; however, the
thickener may also be added to the finished preparation, provided that the
water balance of the finished construction protective material permits
this to be done.
The synthetic resin copolymer dispersion used as binder according to the
invention may already be present during the dispersion of the pigment and
filler, but in most cases it is advantageously added to the filler/pigment
paste which is still hot or also cooled, under rapid or also slower
stirring. In order to maintain a pigment volume concentration of >60%, 4
to 35 parts by weight of synthetic resin dispersion copolymer are used per
65 to 95.9 parts by weight of filler+pigment.
The preparation of the copolymer dispersions for the aqueous construction
protective material preparations low in noxious substances emission
according to the invention is carried out in known manner, preferably by
emulsion polymerization in the presence of a radically initiated catalyst
and at least one emulsifier at a pH of 2 to 6. The various known catalysts
forming free radicals or also redox systems may be used as catalysts. The
concentration range of the total amount of emulsifiers is preferably
between 0.5 and 5% by weight, based on the total amount of monomer, where
the emulsifiers may be anionic, non-ionic or, if appropriate, cationic
emulsifiers. It is also possible to use latex stabilizers, such as, for
example, water-soluble polymers selected from the group
carboxymethylcellulose, hydroxyethylcellulose, polyvinylpyrrolidone,
poly-N-vinylacetamide, polyvinyl alcohol as well as combinations of
emulsifiers and latex stabilizers, and also the known stabilizing
comonomers based on monocarboxylic and dicarboxylic acids and the
half-esters and amides thereof as well as vinylsulfonic acid and its
salts.
Examples of monomers which are suitable for the preparation of the
synthetic resin dispersion, are vinyl esters, in particular vinyl esters
of aliphatic monocarboxylic acids of 1 to 12 carbon atoms, for example
vinyl esters of lower (C.sub.1 -C.sub.6)carboxylic acids such as vinyl
acetate, vinyl propionate, vinyl butyrate, vinyl caproate, furthermore
vinyl laurate, vinyl decanate and vinyl versatate, furthermore, for
example, olefinically unsaturated compounds of the formula II,
##STR2##
in which R.sup.1 denotes hydrogen, an alkyl radical of 1 to 4 carbon
atoms, an alkoxy radical of 1 to 4 carbon atoms, a nitrile group, a
halogen atom, preferably chlorine, or an alkoxycarbonyl radical of 2 to
12, preferably 2 to 9, carbon atoms, and R.sup.2 represents hydrogen, a
methyl or a vinyl group.
Examples of suitable monomers of the formula II are in particular olefins,
for example ethylene and isobutylene, vinyl ethers, for example vinyl
methyl ether, vinyl ethyl ether and vinyl n-butyl ether, furthermore
acrylonitrile, methacrylonitrile, vinyl chloride, acrylic acid esters of
monohydric alcohols, for example methyl acrylate, ethyl acrylate, butyl
acrylate and 2-ethylhexyl acrylate, as well as methacrylic acid esters of
monohydric alkanols, for example methyl methacrylate, ethyl methacrylate,
butyl methacrylate and 2-ethylhexyl methacrylate. Equally suitable are
maleic acid diesters, in particular of monohydric aliphatic alcohols of 2
to 10, preferably 3 to 8 carbon atoms, for example dibutyl maleate,
dihexyl maleate and dioctyl maleate.
The monomers or monomer mixtures are chosen in such a manner that
homopolymer-based, copolymer-based or terpolymer-based synthetic resin
dispersions having an MFT of .ltoreq.10.degree. C., preferably
.ltoreq.5.degree. C., particularly .ltoreq.0.degree. C., are produced. Any
person skilled in the art knows on the basis of the Tg of the polymers and
the polymerization parameters which monomers or mixtures of monomers must
be employed for this purpose. Since the MFT below 0.degree. C. can no
longer be measured, the lower limit of the MFT can only be specified by
the Tg. In this connection the Tg should not be below -20.degree. C.
preferably below -10.degree. C. Suitable copolymers are, for example,
vinyl acetate/ethylene in the ratio 86/14 to 75/25, such as may be
prepared at an ethylene pressure in the region from 25 to 60 bar. Other
suitable copolymers are vinyl acetate/vinyl chloride/ethylene terpolymers
in the ratio 58.8/25.2/16, prepared at an ethylene pressure of 40 bar and
having an MFT of 10.degree. C., or 60.8/15.2/24 and 45 6/30 4/24, such as
may be obtained at an ethylene pressure of 50 bar and having an MFT of
<0.degree. C. and a Tg of -0.5 and +5.5.degree. C. respectively. With
vinyl acetate/butyl acrylate copolymer dispersions the suitable MFT range
is obtained when the monomers are used in the ratio 80/20 to 50/50.
The main monomers are copolymerized with small amounts, particularly
preferably with 0.05 to 0.3% by weight, based on the total amount of
monomer, of olefinically unsaturated silicon compounds of the formula I
containing hydrolyzable groups, the radical R in the formula I preferably
denoting vinyl, allyl, .gamma.-acryloxypropyl and
.gamma.-methacryloxypropyl, and R.sup.1, R.sup.2, R.sup.3 preferably
denoting alkoxy of 1 to 8 carbon atoms or alkoxyalkoxy of 2 to 10 carbon
atoms, acetoxy or halogen, in particular chlorine.
Examples of particularly preferred compounds of the formula I are
vinyltrimethoxysilane, vinyltriethoxysilane, vinyltrimethylglycolsilane,
vinyltriacetoxysilane, .gamma.-acryloxypropyltrimethoxysilane,
.gamma.-methacryloxypropyltrimethoxysilane,
.gamma.-methacryloxypropyltris-(2-methoxyethoxy)silane,
vinyltrichlorosilane, vinylmethyldichlorosilane and allyltrimethoxysilane.
The silanes of the formula I may be added in the emulsion copolymerization
either mixed with the main monomers or separately. They may be metered in
uniformly with the other monomers in the course of the polymerization or
either in the first or the second half of the monomer amount. Only
relatively small amounts of the above silanes are required to improve the
properties of the synthetic resin dispersion according to the invention,
preferably up to a maximum of 2% by weight, based on the total amount of
monomers, preferably 0.1 to 0.4% by weight, particularly 0.05 to 0.2% by
weight.
Removal of the unreacted monomers from the synthetic resin dispersion may
be carried out chemically, i.e. for example by polymerization to
completion. For this purpose catalysts forming free radicals are employed.
Examples of such catalysts are peroxide and azo compounds, such as, for
example, azobis(isobutyramidine hydrochloride). Equally particularly
suitable are the combination types of catalysts in which both reducing
agents and oxidation agents are used. When combination catalysts of this
type are used, the reducing agent is generally termed activator and the
oxidation agent initiator. Examples of suitable activators are bisulfites,
sulfoxylates or compounds having reducing properties, such as, for
example, ascorbic acid and ferrous salts. Examples of initiators are inter
alia, hydrogen peroxide, persulfates such as sodium and potassium
persulfate, perborates and also other pers compounds. Examples of special
combination catalysts or redox systems which may be employed for the
removal of the residual monomers by polymerization, are inter alia
hydrogen peroxide and zinc formaldehyde sulfoxylate, hydrogen peroxide and
sodium metabisulfite, sodium persulfate and sodium metabisulfite, hydrogen
peroxide and sodium sulfite, hydrogen peroxide and rongalite, sodium or
potassium persulfate and sodium sulfite, sodium or potassium persulfate
and rongalite, hydrogen peroxide and ascorbic- acid,
tert-butylhydroperoxide and sodium sulfite, tert-butylhydroperoxide and
rongalite, sodium persulfate and sodium thiosulfate. Metal salts, used in
traces, such as, for example, 1 to 100 ppm per monomer equivalent of iron
or copper salts, such as, for example, Mohr's salt, may further activate
the redox system. Examples are tert-butylhydroperoxide/Mohr's
salt/rongalite or sodium persulfate/sodium sulfite/sodium
thiosulfate/copper sulfate.
The redox catalyst is typically used in an amount between about 0.1 and
about 2% by weight, preferably between about 0.25 and about 0.75% by
weight, based on the amount of monomers. The activator is normally added
in aqueous solution and the amount of activator generally is 0.25 to 1
times of the amount of initiator.
Physical methods, such as, for example, distillation, may also be used for
the removal of residual monomers from the synthetic resin dispersion.
Furthermore it is possible to combine chemical and physical methods. The
removal of the residual monomers by distillation may take place under
elevated, but preferably also under reduced pressure. In the removal of
the residual monomers by distillation at 760 Torr or a lower pressure, the
demonomerization may be speeded up by passing steam or a carrier gas, such
as, for example, air, nitrogen or carbon dioxide, across the surface of
the synthetic resin dispersion. However, the carrier gas is preferably
passed in the demonomerization apparatus from the bottom through the
synthetic resin dispersion. The residual monomers removed by physical
methods from the synthetic resin dispersion are recovered by being
condensed in a condenser. If a carrier gas is used in the
demonomerization, coolants having a lower temperature than water from
0.degree. to 30.degree. C., for example cooling brine or acetone/dry ice,
are employed if appropriate in the condenser. Furthermore, the residual
monomers may be removed in vacuo and recovered from the synthetic resin
dispersion by the use of pumps with rotary slide valves. The content of
residual monomers and other volatile organic substances possibly
originating from the starting materials or of volatile organic
constituents formed in the polymerization, and of the alcohol which is
formed in the hydrolysis of the copolymerized silicon compound of the
formula I in the synthetic resin copolymer dispersion to be used according
to the invention is less than 0.1% by weight, preferably 0.05 to 0.001% by
weight, based on the dispersion copolymer.
Surprisingly in the case of binders having a low MFT, the copolymerization
with tracers of copolymerizable silanes of the formula I gives rise to
dispersion copolymers of a pigment binding power as great as that normally
only achievable with dispersion (co)polymers having a high MFT, such as,
for example, styrene/acrylate, when large amounts of solvent are added to
the synthetic resin dispersion or to a dispersion paint prepared from it.
Synthetic resin copolymer dispersions based on vinyl acetate/ethylene and
vinyl acetate/vinyl chloride/ethylene are preferably used for the
odourless aqueous preparations, low in noxious substances emission, of
construction protective materials, in addition to water, filler, pigment,
dispersant, thickener, antifoam and preservative. To attain a low MFT, the
ethylene pressure chosen must be higher in the case of vinyl acetate/vinyl
chloride/ethylene than in the case of vinyl acetate/ethylene because of
the higher freezing temperature of polyvinyl chloride. The resultant
dispersion copolymers or the aqueous dispersions thereof have the
advantage that copolymer dispersions may be made available which possess
the low MFT required according to the invention.
Furthermore, because of the low boiling points of the monomers used, the
synthetic resin dispersions prepared in this manner possess great
advantages over styrene/acrylate and styrene/butadiene copolymers with
their unpleasant by-products which may form, for example, by a Diels-Alder
reaction.
The vinyl acetate/ethylene dispersion copolymers and the corresponding
terpolymers with vinyl chloride may be advantageously prepared by
copolymerization in water with the aid of anionic, non-ionic or cationic
emulsifiers in the form of aqueous dispersions. Water-soluble, stabilizing
polymers such as carboxymethylcellulose, hydroxyethylcellulose,
polyvinylpyrrolidone, poly-N-vinylmethylacetamide and polyvinyl alcohol
can be used for this purpose, as well as the known stabilizing comonomers
based on monocarboxylic and dicarboxylic acids and their half-esters and
amides. Furthermore, known initiator systems such as, for example
persulfates, sodium persulfate/sulfite and
tert-butylhydroperoxide/Fe.sup.2+ /rongalite may be advantageously used
for the polymerization.
If the appropriate autoclaves are not available, such as are normally
required for the copolymerization with ethylene and/or vinyl chloride, it
is also possible to obtain dispersion copolymers according to the
invention having the required MFT by copolymerization of customary
monomers with those monomers that can strongly lower the MFT, such as, for
example, 2-ethylhexyl acrylate, dioctyl maleate, vinyl versatate or
butadiene. However, the copolymers and terpolymers based on vinyl
acetate/ethylene and vinyl acetate/vinyl chloride/ethylene possess the
quite considerable advantage that because of their low boiling points
their starting monomers are readily freed from the residual monomer part
which has not reacted in the polymerization.
By choosing appropriate technical measures, it is furthermore possible to
use the recovered residual monomers for further polymerizations.
The above dispersion copolymers based on vinyl acetate/ethylene and vinyl
acetate/vinyl chloride/ethylene with comonomers of the formula I are
particularly preferred according to the invention.
By the combination of redox and strip processes or by the strip process
alone for removing the residual monomers, the proposition is made here for
the first time in connection with the preparation of low-emission
construction protective materials according to the invention and the use
of hydrolyzable and copolymerizable silanes of the formula I for the
removal of mostly readily volatile alcohols formed in the hydrolysis of
silanes. A special and preferred embodiment of the invention of
unexpectedly great technical advance is based on the following mode of
operation. Synthetic resin copolymer dispersions are prepared which
contain, for example hydroxyethylcellulose or poly-N-vinylmethylacetamide
as protective colloids and which contain in addition to these protective
colloids preferably non-ionic emulsifiers and in addition to non-ionic
emulsifiers only small amounts of ionic such as anionic or cationic
emulsifiers. It is advantageous in this connection for further
stabilization of the copolymer dispersion to use at the same time
unsaturated hydrophilic comonomers capable of copolymerization, such as,
for example, unsaturated monocarboxylic and dicarboxylic acids and their
half-esters and amides as well as sodium
methacrylamido-2-methyl-2-propanesulfonate or sodium vinylsulfonate.
Synthetic resin copolymer dispersions are thus obtained with not very
small particle sizes, such as, for example, .ltoreq.0.1 .mu.m, but with
mean particle sizes of at least 0.1 .mu.m, preferably .gtoreq.0.15 .mu.m,
particularly .gtoreq.0.2 .mu.m. They are distinguished by outstanding
application properties, such as, for example, in that the synthetic resin
dispersions are readily miscible with dry fillers and pigments and the
construction protective materials prepared therefrom are highly resistant
over the usual extended storage period.
For many years vain attempts were made by experts to prepare these
dispersions, as advantageous on account of their application properties as
those based on vinyl acetate/ethylene and vinyl acetate/vinyl
chloride/ethylene and also possessing very high pigment binding power.
This object has now been achieved in an unexpectedly advantageous manner
by the present invention by the use of dispersion copolymers which contain
comonomeric units derived from silicon compounds of the formula I, which
units carry small amounts of hydrolyzable silicon-containing radicals or
which form Si(OH).sub.x groups (x=1 to 3), and whose aqueous dispersions
have an MFT of <10.degree. C. When these dispersion copolymers are used as
binders in the aqueous preparations of construction protective materials
under discussion, the so-called crazing of the dried coating and of the
dried coating even after only a brief drying period of the preparation, as
assessed by the resistance to washing and shearing of coatings according
to DIN 53,778, surprisingly does not occur, despite the absence of
solvents and film-consolidating auxiliaries, i.e the coating does not
possess inadequate mechanical strength after a brief drying period, as can
be frequently observed with paints derived from polymer dispersions.
Those aqueous preparations of construction protective materials according
to the invention are particularly suitable and preferred which contain
solvent-free synthetic resin copolymer dispersions having a low MFT as
binders and whose copolymers contain in toto only small amounts of
monomeric units derived from silicon compounds of the formula I, which
units are capable of copolymerization and carry hydrolyzable
silicon-containing radicals or form Si(OH).sub.x groups (x=1 to 3), viz.
preferably 0.05 to 2% by weight, particularly 0.1 to 0.4, particularly
preferably 0.05 to 0.2% by weight, based on the copolymer, and the
copolymers were prepared by emulsion copolymerization from combinations of
comonomers which result in the required low MFT values, in the presence of
hydroxyethylcellulose, a non-ionic emulsifier, small amounts of monomeric
vinyl sulfonate, with the addition in toto of only small amounts of
comonomers of the formula I.
In order to tint dispersion paints and dispersion plasters, commercially
available pigment pastes are frequently used. These pigment pastes
generally contain solvents for reasons of stability or their
preparability. A novel path has also been taken according to the invention
for overcoming the resultant difficulties. Because of the high stability
of the synthetic resin copolymer dispersion used according to the
invention and its compatability with dry pigments, the preparation and use
of pigment pastes containing solvents is unnecessary, since the pigment
may be admixed with the synthetic resin dispersion or the white dispersion
paint or the dispersion plaster in the dry state, if desired.
The advance in properties achievable in dispersion copolymers having MFT
values of their aqueous dispersions of <10.degree. C | | |
