Coating processes – With post-treatment of coating or coating material – Heating or drying
Reexamination Certificate
2003-02-25
2004-03-23
Cameron, Erma (Department: 1762)
Coating processes
With post-treatment of coating or coating material
Heating or drying
C427S407100
Reexamination Certificate
active
06709710
ABSTRACT:
The invention relates to a process for producing coated mineral moldings, which comprises using, for the coating process, aqueous coating compositions which comprise at least one styrene-maleic anhydride copolymer. The resultant coated moldings have improved efflorescence behavior. The process is particularly suitable for the coating of roofing tiles and of fiber-filled cement panels.
In producing concrete roofing tiles, an appropriately molded mortar mass is generally coated, prior to setting, with an emulsion paint to impart a color. The subsequent setting is then carried out together with the drying of the paint at temperatures of from 40 to 100° C. After the setting process, there may be a second coating process with an emulsion paint or with a clear lacquer. The task of the emulsion paint, besides coloring, is to prevent lime efflorescence during the setting of the concrete roofing tiles.
In order that the paint does not coagulate on the unset concrete, which is termed green concrete, a certain degree of cement-compatibility and salt resistance is required from the binder present in the paint. This is generally achieved by using ionic and/or nonionic emulsifiers, and also by using functional monomers, e.g. methacrylic acid, acrylic acid, maleic acid, acrylamide, methacrylamide, ethenesulfonate, sulfoxyalkyl methacrylate, or acrylamidoalkylsulfonic acids.
Another task for the emulsion paint is to prevent or reduce soiling, and in particular algal growth, on the finished roofing tiles.
EP-A-0 894 780 describes radiation-cured coatings for mineral moldings with improved resistance to efflorescence, but their production requires relatively high levels of technical resource and is relatively costly.
EP-A-0 754 663 describes the coating of cement-like substrates, the efflorescence behavior being improved by foaming the coatings onto the substrates, using aliphatic (C
12
-C
24
) carboxylic acids as foaming agents.
EP-A-0 469 295 describes coatings whose efflorescence behavior is improved by the use of emulsifiers based on sulfonated diaryl ethers.
WO 99/48841 describes the use of carboxymethylcellulose as protective colloid to prepare dispersions with good resistance to efflorescence and adequate stability.
WO 97/15604 describes styrene-acrylate latices which are prepared by emulsion polymerization of styrene and acrylates in the presence of a styrene-maleic anhydride copolymer, and are suitable for preparing solvent-free paints.
Surprisingly, it has now been found that when mineral moldings are coated with an aqueous coating composition comprising a polymer dispersion as binder, the efflorescence behavior of the coated moldings is improved if the polymer dispersion comprises at least one styrene-maleic anhydride copolymer solution which is added to the polymer dispersion after conclusion of the polymerization.
The present application therefore provides a process for preparing an at least partially coated mineral molding, by applying an aqueous coating composition comprising a polymer dispersion as binder and comprising at least one aqueous styrene-maleic anhydride copolymer solution to at least part of the surface of the molding, followed by setting of the molding and drying of the coating composition, which comprises adding the at least one aqueous styrene-maleic anhydride copolymer solution to the polymer dispersion after conclusion of the polymerization.
For the purposes of the present invention, examples of these moldings are stones, tiles, concrete blocks, roofing tiles, panels, pipes, and sculptures.
The coating composition may be applied by any of the techniques familiar to the skilled worker.
The setting of the molding and drying of the coating composition preferably takes place at temperatures of from 40 to 100° C.
Based on solids content, the polymer dispersions preferably comprise from 0.5 to 5% by weight, particularly preferably from 1 to 3% by weight, of styrene-maleic anhydride copolymers.
The styrene-maleic anhydride copolymer solutions here are preferably prepared by stirring the styrene-maleic anhydride copolymers into water, and dissolving these by adding a solution of an alkali, e.g. ammonia, monoethanolamine, sodium hydroxide, and/or potassium hydroxide, at temperatures of from 20 to 100° C. The pH of the finished solution is preferably >8.
Suitable styrene-maleic anhydride copolymer solutions also include commercially available solutions, e.g. SMA 1000 HNa®, SMA 2000 HNa®, SMA 3000 HNa® and SMA 4000 HNa® (Elf Atochem).
The polymer dispersions are preferably based on polymers which contain
a) from 85 to 100% by weight, particularly preferably from 85 to 99.8% by weight, of esters of acrylic acid with C
1
-C
12
alkanols, e.g. ethyl acrylate, butyl acrylate, n-octyl acrylate, and 2-ethylhexyl acrylate, esters of methacrylic acid with C
1
-C
12
alkanols, e.g. methyl methacrylate, butyl methacrylate, cyclohexyl methacrylate, and isobornyl methacrylate, and/or vinylaromatic monomers, such as styrene and vinyltoluene,
b) from 0 to 5% by weight, particularly preferably from 0.2 to 5% by weight, of stabilizing monomers, and
c) from 0 to 10% by weight of other monomers.
Preference is given here to those combinations of softening monomers, e.g. butyl acrylate and 2-ethylhexyl acrylate, and of hardening monomers, e.g. methyl methacrylate and styrene, which give the polymers a glass transition temperature which is preferably in the range from −10 to 60° C., particularly preferably in the range from −5 to 45° C., and in particular in the range from 0 to 30° C.
Preferred monomers a) are esters of acrylic acid with C
1
-C
12
alkanols and/or styrene.
Preferred stabilizing monomers b) are carboxylic acids, e g. acrylic acid, methacrylic acid, and itaconic acid, carboxamides, e.g. acrylamide, methacrylamide, phosphates, e.g. (meth)acryloyloxyalkyl phosphates, phosphonates, sulfates, sulfonates, e.g. sodium ethenesulfonate, sulfoalkyl (meth)acrylates, e.g. the potassium salt of sulfopropyl methacrylate (SPM®, from the company Raschig), and/or sulfoalkyl(meth)acrylamides, e.g. the sodium salt of acrylamido-2-methylpropanesulfonic acid (AMPS®, from the company Lubrizol).
Preferred monomers c) are keto-group-containing monomers, e.g. acetoacetoxy-group-containing monomers, copolymerizable derivatives of diacetone, e.g. diacetoneacrylamide and diacetonemethacrylamide, copolymerizable silanes, e.g. alkoxyvinylsilanes, and (meth)acryloyloxyalkylsilanes, copolymerizable ethyleneurea derivatives, e.g. N-((meth)acryloxyethyl)-N,N′-ethyleneurea and N-(acrylamidoethyl)-N, N′-ethyleneurea, hydroxyl-group-functionality monomers, e.g. hydroxyalkyl (meth)acrylates, and/or epoxy-functionality monomers, e.g. glycidyl methacrylate.
Particularly preferred monomers c) are the acetoacetoxy-group-containing monomers acetoacetoxyethyl methacrylate, acetoacetoxybutyl methacrylate, acrylamidomethylacetylacetone, vinyl acetoacetate, diacetoneacrylamide, and diacetonemethacrylamide.
To improve soiling behaviour, polymer dispersions which, as other monomers c), contain keto-group-containing monomers advantageously also contain polyfunctional carboxylic hydrazides which have at least two hydrazide groups. It is preferable for the ratio of hydrazide groups to keto groups used to be equimolar. Particularly suitable polyfunctional carboxylic hydrazides are adipic dihydrazide, oxalic dihydrazide, isophthalic dihydrazide, and/or polyacrylic polyhydrazide.
Other suitable polymer dispersions are commercially available straight acrylate dispersions and styrene-acrylate dispersions, e.g. Mowilith®DM 611, Mowilith® DM 777, Mowilith® LDM 7412 and Mowilith® 771 (Clariant GmbH).
The polymer dispersions may be prepared by the customery processes of emulsion polymerization, where the monomers are emulsified in the aqueous phase in the presence of emulsifiers, initiators, and protective colloids, and are advantageously polymerized at temperatures of from 60 to 95° C.
The emulsion polymerization may be carried out by the familiar processes known to the skilled worker, e.g. batch processes, me
Grau Angelika
Krieger Stephan
Cameron Erma
Celanese Emulsions GmbH
Muserlian Lucas and Mercanti
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