Coating processes – Coating pavement or the earth
Reexamination Certificate
2000-12-27
2003-03-11
Cameron, Erma (Department: 1762)
Coating processes
Coating pavement or the earth
C427S393600, C427S421100, C427S358000, C427S359000
Reexamination Certificate
active
06531179
ABSTRACT:
The present invention relates to a method of coating concrete moldings with a plastic mineral coating composition which is modified with polymer dispersions having a glass transition temperature of from −20 to +80° C., in which the polymer has been built up from ethylenically unsaturated monomers.
Concrete moldings are moldings or construction components made from concrete and obtainable by molding a flowable concrete mixture and then bringing about setting of the molded mixture. Examples of concrete moldings are concrete pipes, e.g. those for waste water, kerbstones, floor slabs, base slabs, stair treads, walling components and concrete roof tiles.
Concrete roof tiles are concrete moldings in the shape of roof tiles, and in recent times have been increasingly preferred over the clay roof tiles used hitherto for covering roofs.
Concrete moldings, in particular concrete roof tiles, are generally produced by extrusion processes from plastic concrete compositions which have not yet set. For coloring, these concrete compositions generally comprise an inorganic color pigment, such as iron oxide red pigments or iron-oxide black pigments. The advantage of concrete roof tiles over conventional clay roof tiles is their much lower production cost and their relatively high mechanical strength, for example that shown in adverse weather conditions, e.g. in hail showers. However, a disadvantage of concrete moldings, in particular concrete roof tiles, is that on weathering some of the calcium present in these migrates to the surface, where it causes unsightly efflorescence. In addition, concrete moldings have a rough surface as a result of their method of production, and this promotes erosion and in particular facilitates infestation with plant life, such as algae, lichens or mosses.
While in recent times the problem of weathering-related efflorescence has been substantially solved by treating the surface with coating materials based on aqueous polymer dispersions, there are no cost-effective solutions to the problem of producing concrete moldings, in particular concrete roof tiles, with smooth surfaces.
GB-A 2,030,890 has proposed providing extruded concrete roof tiles with a cement-bonded mineral coating in which the substantive materials present are cement, water and pigments. The coating is generally applied, by extrusion or roller-application, to the freshly extruded and as yet unset green concrete roof tile. The coatings give a smoother surface on the concrete roof tile. However, a disadvantage of the coatings is that they flake readily. In addition, their high cement content makes them uneconomic. While the criterion of economy can be met by adding very fine sands to the mineral coating material, the problem of flaking remains.
DE-A 3932573 describes concrete roof tiles provided with a mineral coating which comprises a cement-compatible polymer, besides cement as binder, very fine sand as aggregate and inorganic pigments. Concrete roof tiles thus coated are substantially free from pores and have better chemical and physical resistance to the effects of weathering.
However, the aqueous polymer dispersions usually used for modifying cement-bound mineral compositions retard the setting of the mineral compositions. This produces problems in their subsequent use. For example, even after a period of 24 h, for example, the strength of the coating is only modest, and it is therefore very easily damaged during the packaging of the concrete moldings or during their shipping.
In the case of concrete roof tiles, retarded setting causes problems during subsequent coating of the roof tiles with water-based paints. The problem of flaking of the mineral coating on exposure to frost/thaw cycles is moreover not satisfactorily solved by the polymeric additives generally used.
It is an object of the present invention to provide an aqueous polymer dispersion which gives mineral coatings which do not flake and which at the same time do not impair the process of setting of the mineral composition.
We have found that this object is achieved, surprisingly, by eans of aqueous polymer dispersions based on styrene-acrylate polymers, styrene-butadiene polymers or straight acrylate polymers, if these comprise not more than 2% by weight of copolymerized monomers bearing acid groups and, to stabilize the polymer particles in the dispersion, comprise an emulsifier system which embraces a mixture made from a salt a selected among sulfuric half-esters of ethoxylated alcohols having at least one C
4
-C
20
-alkyl group and neutral compounds b selected among ethoxylated alcohols having a C
4
-C
20
-alkyl group.
The present invention therefore provides a method of coating a concrete molding which comprises:
a) the application of at least one plastic, cement-bound mineral composition to an uncoated concrete molding, wherein said plastic composition comprises very fine sand, cement, at least one aqueous polymer dispersion and water in amounts ensuring that said plastic composition has plastic deformability, and
b) bringing about the setting of the plastic composition;
wherein the aqueous polymer dispersion is selected from
A at least one polymer P in the form of dispersed polymer particles with a glass transition temperature within the range from −20 to +80° C., the polymer having been built up from ethylenically unsaturated monomers M, embracing:
i) from 90 to 99.9% by weight of at least one hydrophobic, monoethylenically unsaturated monomer M1, selected among styrene, butadiene, the C
1
-C
4
-alkyl esters of methacrylic acid and the C
2
-C
12
-alkyl esters of acrylic acid, and
ii) from 0.1 to 10% by weight of at least one hydrophilic, monoethylenically unsaturated monomer M2 embracing up to 2% by weight, based on the total amount of monomer, of one or more monoethylenically unsaturated monomers having at least one acid group (monomers M2a), and/or embracing up to 10% by weight of other hydrophilic monomers M2b, and
B at least one emulsifier system for stabilizing the polymer particles and comprising:
a) at least one salt of a sulfuric half-ester of an alkoxylated alcohol which has at least one C
4
-C
20
-alkyl chain (salt a), and
b) at least one alkoxylated alcohol which has at least one C
4
-C
20
-alkyl chain (neutral compound b).
The present invention also provides a process for producing concrete roof tiles with a mineral coating, and also the concrete roof tiles obtainable by this process.
All data in % by weight are based on 100% by weight, i.e. on the entire amount of monomers.
For the purposes of the present invention, the general term concrete roof tiles includes, of course, pantiles and verge tiles, ridge tiles, step tiles, ventilation tiles and other concrete roofing components used in the covering of roofs.
According to the invention, the emulsifier system used to stabilize the particles of the polymer P comprises at least one anionic emulsifier (salt a) which has a sulfated oligoalkylene oxide unit as hydrophilic structural element and has a C
4
-C
20
-alkyl chain as hydrophobic structural element. Examples of salts a are the salts of sulfuric half-esters of alkoxylated alkylphenols having a C
4
-C
20
-alkyl chain, preferably a C
6
-C
16
-alkyl chain and in particular a C
8
-C
12
-alkyl chain, and also the salts of sulfuric half-esters of alkoxylated alkanols, preferably those derived from linear or branched C
8
-C
16
-alkanols. The last-mentioned class of emulsifiers is preferred according to the invention. The alcohol component in this last-mentioned class of emulsifiers generally derives from little-branched fatty alcohols obtainable, for example, by reducing naturally occurring fatty acids, or from oxo alcohols obtainable by oxo synthesis and generally having a somewhat greater degree of branching, or from primary, linear Ziegler alcohols. It is, of course, also possible to use mixtures of the salts a with different alcohol components. Particularly preferred alcohol component in emulsifiers of this type is lauryl alcohol.
Among the salts a, particular preference is given to the alkali
Bechert Bertold
Denu Hans-Jürgen
Schwartz Manfred
Wistuba Eckehardt
BASF - Aktiengesellschaft
Cameron Erma
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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