Coating processes – Coating pavement or the earth
Reexamination Certificate
2000-09-11
2002-04-16
Cameron, Erma (Department: 1762)
Coating processes
Coating pavement or the earth
C427S393600, C427S407100
Reexamination Certificate
active
06372287
ABSTRACT:
Use of aqueous film-forming preparations based on copolymers of methacrylic acid alkyl esters for coating mineral shaped bodies
The present invention relates to the use of film-forming aqueous formulations which comprise at least one copolymer P in disperse form for coating mineral moldings.
For the purposes of the invention mineral moldings here and below are shaped articles which comprise a mineral binder and mineral aggregates. The formulations comprising mineral binder and the aggregates can be shaped in the wet state and undergo stonelike solidification over time in the air or else under water, with or without exposure to elevated temperature, to form the desired mineral molding. Mineral binders are general knowledge. They are finely divided inorganic substances such as lime, gypsum, clay and/or cement. Mineral aggregates are generally granular or fibrous, natural or synthetic rock materials (gravel, sand, mineral fibers) with particle sizes or fiber lengths adapted conventionally to the respective end use. In addition, in special cases the mineral moldings also include metals or organic adjuvants. For the purpose of coloration, color pigments are frequently also used as adjuvants.
Examples of mineral moldings to be coated in accordance with the invention are concrete pipes, such as those for wastewater, concrete roofing (cf. e.g. DE-A 39 01 073) or edging stones, steps, floor slabs, pedestal slabs and fiber cement slabs, i.e. flat mineral moldings filled with inorganic or organic fibers, such as polyester fibers or nylon fibers, for example.
A disadvantage of mineral moldings is that under the influence of weathering (especially exposure to water) they lose their strength, since the cationic constituents, such as Ca
2+
, are leached out over time. A further disadvantageous property of mineral moldings is the occurrence of efflorescence phenomena. These are probably attributable to the fact that the mineral binders contain cations with a valence of two or more, such as Ca
2+
, in an alkaline environment. Reaction with the carbon dioxide from the air can therefore cause the formation, on the surface of the mineral moldings, of white spots of lime which are unsightly and relatively insoluble in water. The phenomenon of efflorescence may appear either during the hardening of freshly prepared mineral moldings or on exposure to weathering of mineral moldings which have already hardened.
In order to avoid these disadvantageous properties, the mineral moldings are often provided with a coating. For this purpose use is generally made of aqueous coating systems whose film-forming constituent comprises an aqueous polymer dispersion. Customary film-forming constituents include styrene-acrylate copolymers, vinyl acetate homo- and copolymers, pure acrylates and the like. Coating gives the mineral moldings a lustrous appearance which is desirable for numerous applications, especially in the case of concrete roof tiles.
DE-A-38 27 975 and DE-A-40 03 909 disclose coatings for concrete slabs that are based on aqueous polymer dispersions comprising at least one aromatic ketone as photosensitizer. The photosensitizer causes superficial crosslinking of the coating. Although this largely prevents the unwanted efflorescence, the coatings are unstable to long-term weathering. In addition, EP-A 279 069 discloses transparent coating materials which comprise highly crosslinked polymers based on alkyl methacrylates. Coatings of this kind lose their luster on weathering and become brittle over time.
The protection of mineral moldings against the above-described efflorescence has also been improved by coating compositions based on styrene-acrylate dispersions or all-acrylate dispersions of EP-A-469 295 and DE-A-195 14 266. For this purpose EP-A-469 295 recommends the use of a specific anionic emulsifier and DE-A-195 14 266 the use of polymers comprising, in copolymerized form, specific monomers having sulfonate groups.
The prior art coatings all have the disadvantages that they lose their luster on prolonged weathering and that their mechanical strength and elasticity decline.
It is an object of the present invention to provide coatings for mineral moldings which are suitable for long-term outdoor use and which do not lose their luster or elasticity even after a long period. In addition, the coatings should effectively prevent efflorescence and should adhere well to the mineral substrates.
We have found that this object is achieved by aqueous formulations whose film-forming constituent comprises substantially or fully uncrosslinked copolymers P that are composed essentially of alkyl esters of methacrylic acid, the majority of the monomers being other than methyl methacrylate, and which lead to coatings having high long-term stability in respect of their luster. In addition, the coatings have good adhesion to mineral substrates and afford good protection against efflorescence.
The present invention therefore provides for the use of aqueous film-forming formulations comprising at least one copolymer P as film-forming constituent which is present in disperse form in the formulation and is composed of ethylenically unsaturated monomers M, the monomers M comprising
i. from 70 to 99.9% by weight of at least one ester of methacrylic acid with a C
1
-C
10
-alkanol and
ii. from 0.1 to 30% by weight of at least one different monoethylenically unsaturated monomer
and at least 50% by weight of the monomers M being other than methyl methacrylate and not more than 1% by weight of the monomers M having two or more ethylenically unsaturated double bonds, for coating mineral moldings.
Examples of suitable esters of methacrylic acid with C
1
-C
10
-alkanols are methyl, ethyl, n-propyl, isopropyl, n-butyl, 2-butyl, isobutyl, tert-butyl, 1-methylbutyl, 2-methylbutyl, 3-methylbutyl, 1,1-dimethylbutyl, 2,2-dimethylbutyl, n-pentyl, 1-methylpentyl, 2-methylpentyl, 2-ethylpentyl, n-hexyl, 1-methylhexyl, 2-methylhexyl, 2-ethylhexyl, n-heptyl, 1-methylheptyl, 2-methylheptyl, 2-propylheptyl, n-octyl, 1-methyloctyl, 2-methyloctyl and n-decyl methacrylate. Preference is given to the esters of methacrylic acid with n-alkanols having 2 to 6 carbon atoms, i.e. ethyl, n-propyl, n-butyl, n-pentyl and n-hexyl methacrylate. Of these, n-butyl methacrylate is particularly preferred.
In accordance with the invention, from 70.0 to 99.9% by weight, preferably from 90.0 to 99.8% by weight, in particular from 95.0 to 99.5% by weight and, with very particular preference, from 97.0 to 99.0% by weight of the monomers M in the copolymers P are selected from the abovementioned esters of methacrylic acid. At the same time, preferably at least 80% by weight, in particular at least 90% by weight and, with very particular preference, all of the monomers M are other than methyl methacrylate.
The advantages of the coatings of the invention are manifested in particular when the copolymers P comprise n-butyl methacrylate as sole ester of methacrylic acid in copolymerized form.
In addition to the esters of methacrylic acid the copolymers P comprise from 0.1 to 30% by weight, in particular from 0.2 to 10% by weight, with very particular preference from 0.5 to 5% by weight and, specifically, from 1.0 to 3.0% by weight of copolymerized monomers which are different from but copolymerizable with the alkyl methacrylates.
The monomers different from the alkyl methacrylates include firstly those monomers which are normally employed as principal monomers in coating compositions based on aqueous polymer dispersions. Examples of such monomers, referred to below as monomers MH, are vinylaromatic monomers, such as styrene, &agr;-methylstyrene, o-chlorostyrene or vinyltoluenes, vinyl esters of aliphatic C
1
-C
18
-monocarboxylic acids, such as vinyl acetate, propionate, butyrate, valerate, hexanoate, 2-ethylhexanoate, decanoate, pivalate, laurate and stearate and commercial monomers VEOVA® 5-11 (VEOVA® X is a trade name of Shell and stands for vinyl esters of a-branched aliphatic carboxylic acids having X carbon atoms, which are also known as Versatic® X acids
Bechert Bertold
Hümmer Wolfgang
Reck Bernd
Schwartz Manfred
Wiese Harm
BASF - Aktiengesellschaft
Cameron Erma
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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