Note: Descriptions are shown in the official language in which they were submitted.
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o.z. 0050/41719
Precast concrete coated with copolvmer films
The present invention relates to precast concrete
which is coated on at least one of its surfaces with a
film, with or without fillers, of a copolymer of
S a) from 65 to 100% by weight of Cl-C3-alkyl acrylates,
C~-Ca-alkyl methacrylates and/or vinylaromatic
monomers and
b) from 0 to 35% by weight of other copolymerizable
monomers
with a glas~ transition temperature of from -25 to +30C,
where the film contains from 0.5 to 10% by weight, based
on the copolymer, of a compound of the formula I
Rl R2
(I)
SO3X So3~
where R1 and R2 are each hydrogen or C4-C24-alkyl but not
more than one i8 hydrogen, and X and Y are each alkali
metal ions or ammonium ions.
Precast concrete, especially concrete roofing
tile~, is manufactured from mortar whose consistency
makes the final molding possible. The shape of the
roofi~g tile is retained even during hardening, which
usually take~ place at from 40 to 100C. Concrete roofing
tile~ are prone to efflorescence of lime; this is pro-
duced by reactlon of calcium hydroxide on the surface of
the tiles with the carbon dioxide from the air. Calcium
hydroxide may reach the ~urface of the tiles during
curing or else on weathering. The results are spotted,
unsightly roofs.
Polymer dispersions are used a~ coatings (cf. DE-
A 21 64 256). However, the results achieved with the
copolymer coating~ to date are still unsatisfactory.
Moreover, the tiles become heavily soiled.
DE-A 39 01 073 describes a concrete roofLng tile
which i8 coated with a copolymer which contains an
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organotin compound as copolymerized unit. The emulsifier
I is not mentioned in this publication.
German Patent Application P 40 03 909.9 and DE-A
38 27 975 disclose processe~ for preventing efflorescence
on mineral substrates, in which copolymers with a glass
tran~ition temperature of from -25 to +30C are used.
However, the process requires the addition of special
substances, namely aromatic ketones and, as additional
process step, irradiation of the coating with ultraviolet
light.
It is an ob~ect of the present invention to find
precast concrete which is coated in a straightforward
manner, shows virtually no efflorescence and becomes
soiled to only a small extent, especially at elevated
temperature. Moreover, the coating should display its
action as quickly as possible.
We have found that this ob~ect is achieved by the
precast concrete defined in the first paragraph.
We have also found a process for producing
preca~t concrete of this type.
Preferred embodiments of the invention are to be
found in the ~ubclaims.
The copolymer i~ composed of a) from 65 to 100,
preferably 80 to 100 and e~peclally 90 to 99, ~ by
weight, based on the copolymer, of Cl-C~-alkyl acrylates,
Cl-C~-alkyl methw rylates and/or vinylaromatic monomers.
At lea~t two monomer~ are preferably employed. The alkyl
group~ ln the acrylate~ and methacrylates can be linear,
branched or cyclic. They are, in general, methyl, ethyl,
propyl, n~ o- and t-butyl, n-pentyl, n-hexyl, ethyl-
hexyl, n-octyl, cyclohexyl and, preferably, methyl, n-
butyl and ethylhexyl.
Vlnylarom~tic monomers with, norm~lly, up to 20
carbon atom~ are, in gener~l, styrenes which are sub~ti-
tuted on the nucleus by C~-C~-~lkyl, chlorine or bromine,
such as ~-methylstyrene, para-methylstyrene, p~ra-chloro-
styrene or para-bromostyrene, especi~lly ~tyrene it~elf.
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Other monomers b) which are copolymerizable with
the abovementioned monomers are used in amounts of up to
35, preferably up to 20, especially from 1 to 10, % of
the weight of the copolymer. Possible examples of these
are: acrylonitrile, methacrylonitrile, ~-olefins such as
ethylene, propene or isobutene, diene~ such as butadiene
and isoprene, vinyl chloride, vinylidene chloride,
acrylic acid, methacrylic acid, itaconic acid, maleic
acid, fumaric acid, amides of these acids, tetrahydrofur-
furyl acrylate and methacrylate, alkoxyalkyl acrylatesand methacrylates with from 1 to 4 carbon atoms in the
alkoxy andJor alkyl, such as 2- or 3-methoxy-n-butyl
acrylate and methacrylate. Acrylic acid, methacrylic
acid, the amide~ thereof, acrylonitrile and methacrylo-
nitrile are preferred. In some cases, good results areachieved with copolymers which contain no monomers b.
It is essential to the in~ention that the copoly-
mer has a glas~ tran~ition temperature of from -25 to
+30C, in particular from -12 to +22C.
The glass transition temperature can be deter-
mined by conventional methods, eg. by measurement of the
modulus of ela~ticity a~ a func~ion of the temperature in
a creep te~t or by differential thermal anslysis ~DTA)
(see A. Zosel, P~rbe und Lack 82 (1976) 125-134)~
Typlcal comblnation~ of monomer~ a whose gla~s
transltlon temperature i~ in the range according to the
inventlon are, for example, (in % by weight)s
- 65% 2-ethylhexyl acrylate, 35% styrene,
- 55% 2-ethylhexyl acrylate, 45% styrene,
- 60% 2-ethyl~exyl acrylate, 20% methyl methacrylate,
20% ~tyrene,
- 55% 2-ethylhexyl acrylate, 35% n-butyl meth-
acrylate, 10% ~tyrene,
- 25% n-butyl acrylate, 25% 2-ethylhexyl acrylate,
50% styrene,
- 60% n-butyl acrylate, 40% ~tyrene,
50% n-butyl acrylate, 50% ~tyrene,
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- 30~ n-butyl acrylate, 30% 2-ethylhexyl acrylate,
20% styrene, 20% methyl methacrylate,
- 35% n-butyl acrylate, 30% methyl methacrylate,
35% n-butyl methacrylate.
Additional incorporation of monomers b likewise
has an effect on the glass transition temperatures of the
copolymers. This iq why the ratios of the amounts of
monomers a indicated above may need adjustment.
Compound I is preferably employed in amounts of
from 0.5 to 4, in particular 0.5 to 3 and e~pecially 1 to
2, % of the weight of the copolymer.
In formula I, R1 and R2 are preferably linear or
branched alkyls of from 6 to 18 carbon atoms or hydrogen,
especially of 6, 12 or 16 carbon atoms, with R1 and R2 not
both being hydrogen. X and Y are preferably ~odium,
potas~ium or ammonium ion~ and especially sodium. It is
particularly preferred for X and Y to be sodium, R1 to be
a branched alkyl of 12 carbon atoms and R2 to be hydrogen
or R1. Mixtures which contain from 50 to 90~ by weight of
the monoalkylated product are often uset in industry, for
example Dowfax 2A1 (proprietary name of Dow Chemical
Company)~
These compounds are generally known as emulsi-
fiers, for example from US-A 4 269 749 of the Dow Chemi-
cal Company, and are commercially available.
The emulsifler I is preferably added to the
copolymer during the preparation thereof. However, it can
al~o be added in whole or in p rt to the copolymer after
the polymerization. The copolymer can be prepared in a
conventional manner by free radical copolymerization of
monomers a and b in aqueous emulsion. It is possible to
use batch processes or feed processes in which the
initiator and/or monomer~, which may be emulsified in
water, are added a little at a time or continuously
during the polymerization (see, for example, Encyclopedia
of Polymer Science and Engineering, Vol. 6 tl986) 1-52)~
The resulting aqueou~ polymer dispersions usually have a
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copolymer concentration of from 40 to 60% by weight. From
0.5 to 4, in particular 0.5 to 3 and especially 1 to 2,
~ by weight, based on the copolymer, of compound I are
preferred as emulsifier. It i~ possible additionally to
use conventional emulsifiers such as anionic and/or
nonionic emulsifiers, for example sodium dialkyl sulfo-
succinates, sodium salts of sulfated oils, sodium alkyl-
sulfonates, sodium, potassium and ammonium alkyl sul-
fates, alkali metal salts of sulfonic acids, alkoxylated
Cl2-C24-fatty alcohols and alkoxylated alkylphenols, as
well as ethoxylated fatty acids, fatty alcohols and/or
fatty amides, ethoxylated alkylphenols, furthermore
sodium salts of fatty acids such as sodium stearate and
sodium oleate or fatty alcohol sulfate~ and fatty alcohol
ethoxylates.
The aqueous copolymer di~persion~ form at room
temperature films which are shiny, clear and tough but
flexible and which absorb only little water, less than
10, usually le~s than 5, % by weight being measured after
storage in water for 24 hours. They are generally free of
plasticizers and of film-formers.
The coating compositlons are prepared in a
conventional manner by incorporating inorganic fillers
and colored pigments into the aqueou~ copolymer disper-
sions and ad~usting to the required viscosity with water.
Examples of suitable inorganic fillers ares chalk, silica
flour and/or barytes. The amount of pigments and/or
fillers is generally from 50 to 450 parts by weight based
on the copolymer as 100 parts by weight.
Exsmples of ~uitable precast concrete are shaped
articles made of concrete ~nd expanded concrete, eg.
slabs, pipes and, especially, roofing tiles, it also
being possible to apply the coating to uncured products
of this type, e~pecia~ly roofing tiles, called green
tiles. The precast concrete is produced in a conventional
manner from ready-mixed concrete by an extrusion proce~s
during which it is given it~ final shape. The coating
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composition is applied in a conventional manner by spray,
trowel, knife or by pouring, the amounts applied u~ually
being from sO to 400, in particular 100 to 250, g/mZ~
measured in the dry state. It i9 of particular interest
to apply such coatings to concrete roofing tile~ which
have not set. The coating or coating~ can be dried in a
conventional manner, at room temperature or at a ~lightly
elevated temperature. For thi , the coated tile is
generally placed in a chamber where the concrete sets in
a process lasting from 6 to 12 hours at from 40 to 65C,
and the copolymer in the coating composition form3 a
film.
After this proce~s, the tile is preferably
sprayed with the coating composition a second time. It is
dried in a drying tunnel with air circulating at 100C.
The drying tunnel and the subsequent cooling section are
designed so that complete film formation takes place.
The tiles are thus well protected against lime
efflorescence. In addition, the surface of the coatings
is not tacky even at elevated temperatures, so that the
tiles pick up hardly any dirt.
Unle~s otherwise indicated, parts and percentages
are by welght in the followlng Examples.
COMPARATIVE EXANPLE lC
An emulsion of 45 parts of styrene (S), 55 part~
of 2-ethylhexyl acrylste (EHA), 2.5 parts of acrylic acid
(AA), 105 parts of water and 1.5 parts of the sodium salt
of a sulfuric acid hemiester of an isononylphenol ethoxy-
late with an average of 25 ethylene oxide units and
0.5 part of an isononylphenol ethoxylate with an average
of 25 ethylene oxide units as emul~ifiers wa~ polymerized
using 0.5 part of ~odium peroxodisulfate in a feed
process at 90C.
EXAMP~E 1
~he process of Comparative Example lC was carried
out but with the difference that the emulslfier used was
not the mixture from Comparative Example lC but 1.5 parts
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of a technical mixture of abou~ 80% of a compound I where
X and Y are sodium, R1 is a branched alkyl of 12 carbon
atoms and R2 is hydrogen, and about 20% of a compound I
where X and Y are sodium and Rl and R2 are branched alkyls
of 12 carbon atoms. The resulting copolymer dispersion
had a copolymer content of 4g% measured in the conven-
tional manner by evaporation of the water.
A3 a measure of the soilability, the energy to
separate a sample specimen from a polymer film dried at
room temperature for 2 weeks was measured at 70C by the
method of A. Zosel, J. Adhesion 30 (1989) 135-139. The
results in Table 1 clearly show the superiority of the
claimed emulsifier. All the Examples and Comparative
Experiments were tested in the same way.
COMPARATIVE BXANPLE 2C
An emulsion of 35 parts of n-butyl acrylate (BA),
35 parts of n-butyl methacrylate (BMA), 30 parts of
methyl methacrylate (MMA), 2.5 part~ of acrylic acid,
105 parts of water and 1.5 parts of the sodium ~alt of a
sulfuric acid hemiester of an isononylphenol ethoxylate
with an average of 25 ethylene oxide units and 0.5 part
of an isononylphenol ethoxylate with an average of 25
ethylene oxide units as emulsifiers was polymerized using
0.5 part of sodium peroxodisulfate in a feed process at
90C.
EXAMPLE 2
The process of Comparative Example 2C was carried
out but with the difference that the emulsifier used was
not the mixture from Comparative Example 2C but 1.5 parts
ef a technical mixture of about 80% of a compound I where
X and Y are sodium, Rl is a branch0d alkyl of 12 carbon
atom~ and R2 is hydrogen, and about 20% of a compound I
where X and Y are sodium and Rl and R2 are branched alkyls
of 12 carbon atoms.
COMPARATIVE EXAMPLE 3C
An emulslon of 20 parts of methyl methacrylate,
60 parts of 2-ethylhexyl acrylate, 20 parts of styrene,
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2.5 part3 of acrylic acid, 105 parts of water and
1.5 parts of the sodium ~alt of a sulfuric acid hemiester
of an isononylphenolethoxylate with an average of 25
ethylene oxide unit4 and 0.5 part of an isononylphenol-
ethoxylate with an average of 25 ethylene oxide units as
emulsifier~ wa~ polymerized u~ing 0.5 part of sodium
peroxodisulfate in a feed process at 90C.
EXAMPLE 3
The process of Comparative Example 3C was carried
out but with the difference that the emulsifier used was
not the mixture from Comparative Example 3C but 1~.5 parts
of a technical mixture of about 80% of a compound I where
X and Y are sodium, R1 i8 a branched alkyl of 12 carbon
atoms and R2 i8 hydrogen, and about 20% of a compound I
where X and Y are ~odium and Rl and R2 are branched alkyls
of 12 carbon atoms.
COMPARATIVE EXAMPLE 4C
An emulsion of 35 part~ of n-butyl methacrylate,
10 parts of styrene, 55 part~ of 2-ethylhexyl acrylate,
2.5 parts of acrylic acid, 105 parts of water and 1.5
parts of the sodium salt of a sulfuric acid hemiester of
an i~ononylphenolethoxylate with an average of 25 ethy-
lene oxide units and 0.5 part of an isononylphenol
ethoxylate with an average of 25 ethylene oxide units as
emulsifiers wa~ polymerized using 0.5 part of sodium
peroxodisulfate in a feed process at 90-C.
EXAMPLE 4
The process of Comparative Example 4C was carried
out but with the difference that the emulsifier used was
not the mixture from Comparative Example 4C but 1.5 parts
of a technical mixture of about 80~ of a compound I where
X and Y are sodium, Rl is a branched alkyl of 12 csrbon
atoms and R2 is hydrogen, and bout 20~ of a compound I
where X and Y are sodium and R~ and R2 are branched alkyls
of 12 carbon atoms.
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~ABLE 1
Monomers Separation energy
[parts] in J/ma at 70C
. . _ . . .
lC 45 S 55 EHA 2.5 AA 4.6
1 45 S 55 EHA 2.5 AA 2.0
2C 35 ~A 35 BMA 30 MMA 2.5 AA 4.5
2 35 BA 35 BMA 30 MMA 2.5 AA 1.0
3C 60 EHA 20 MMA 20 S 2.5 A~ 8.3
3 60 EHA 20 MMA 20 S 2.5 AA 1.5
4C 55 EHA 35 BMA 10 S 2.5 AA 4.0
4 55 EHA 35 BM~ 10 S 2.5 AA 3.7
