Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2002-05-16
2004-05-25
Sanders, Kriellion A. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
Reexamination Certificate
active
06740692
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to coating compositions for producing soiling-resistant coatings which can be prepared in the absence of organic solvents, to processes for preparing such compositions, and to their use. The coatings are especially useful for building facades.
2. Background Art
It is common to use film-forming polymers in dispersion or powder form as binders for preparing polymer-modified facade coatings or plasters. These binders raise the mechanical stability of the coating and increase the wet abrasion resistance. A disadvantage in many cases, is an increased soiling tendency of the facade as a result of the polymer modification.
Common techniques for avoiding or at least reducing the tendency toward soiling include the use of harder polymers with a higher Tg. This, however, necessitates the use of volatile organic film-forming auxiliaries, and is no longer acceptable from an environmental standpoint. In many cases, photochemically crosslinkable binders are used as well. Such binders, however, have the disadvantage that the photoinitiator, which has poor solubility in water, can only be introduced into the composition by using solvents.
DE-A 19918052 relates to pigmented coating compositions having good wet abrasion resistance and a low soiling tendency, based on (meth)acrylate polymers and containing a small fraction of nonpolymerizable photoinitiator. DE-A 4318083 discloses coating compositions based on (meth)acrylate copolymers with increased UV sensitivity due to use of a mixture of hydrophilic and hydrophobic photoinitiators. U.S. Pat. No. 3,320,198 discloses a process for preparing coating compositions for exterior paints by adding a benzophenone solution to an acrylic latex. A disadvantage here is that solvents are always introduced into the coating composition with the water-insoluble photoinitiator. EP-A 599676 describes UV-crosslinkable coating compositions based on acrylic copolymers with a copolymerizable photoinitiator. Although the latter process avoids the introduction of solvents into the coating composition, it also entails high costs for the polymerizable photoinitiator.
It would be desirable to provide a coating composition for producing soiling-resistant facades which avoids the known disadvantages of the prior art and leads to facades which are less susceptible to soiling.
SUMMARY OF THE INVENTION
It has surprisingly been found that, by employing a photoinitiator and/or fungicide complexed with cyclodextrin, coating compositions may be obtained which impart markedly improved weathering characteristics to the facades coated or plastered with them. The coating compositions may be prepared without adding solvent.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)
The invention provides coating compositions for producing soiling-resistant coatings which may be prepared in the absence of organic solvents, comprising a) at least one film-forming polymer of one or more vinyl ester monomers, (meth)acrylate monomers, vinylaromatic monomers, olefin monomers, 1,3-diene monomers, and vinyl halide monomers, and optionally, further monomers copolymerizable therewith, in the form of its aqueous dispersion or water-redispersible powder, b) one or more photoinitiators and/or fungicides, c) at least one pigment, d) one or more fillers, and optionally, e) further additives, wherein the photoinitiator(s) and/or fungicide(s) b) are in the form of complexes with cyclodextrin or a cyclodextrin derivative.
By “solventlessly preparable” is meant that photoinitiator and fungicide can be added without adding solvent, so that solvent-free and low-emission coating compositions are obtainable whose fraction of volatile nonaqueous constituents is less than 1% by weight, based on the overall weight of the coating composition.
Suitable vinyl esters are those of carboxylic acids having from 1 to 12 carbon atoms. Preference is given to vinyl acetate, vinyl propionate, vinyl butyrate, vinyl 2-ethylhexanoate, vinyl laurate, 1-methylvinyl acetate, vinyl pivalate, and vinyl esters of &agr;-branched monocarboxylic acids having from 9 to 11 carbon atoms, an example being VeoVa9® or VeoVa10® (trade names of Shell). Vinyl acetate is particularly preferred.
Suitable monomers from the group of acrylates or methacrylates are esters of unbranched or branched alcohols having from 1 to 15 carbon atoms. Preferred methacrylates and acrylates are methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, propyl acrylate, propyl methacrylate, n-butyl acrylate, n-butyl methacrylate, t-butyl acrylate, t-butyl methacrylate, and 2-ethylhexyl acrylate. Particular preference is given to methyl acrylate, methyl methacrylate, n-butyl acrylate, t-butyl acrylate, and 2-ethylhexyl acrylate.
Preferred vinylaromatics are styrene, methylstyrene, and vinyltoluene. A preferred vinyl halide is vinyl chloride. The preferred olefins are ethylene and propylene and the preferred dienes are 1,3-butadiene and isoprene.
If desired, it is also possible for from 0.1 to 5% by weight, based on the overall weight of the monomer mixture, of auxiliary monomers to be copolymerized. It is preferred to use from 0.5 to 2.5% by weight of auxiliary monomers. Examples of auxiliary monomers are ethylenically unsaturated monocarboxylic and dicarboxylic acids, preferably acrylic acid, methacrylic acid, fumaric acid, and maleic acid; ethylenically unsaturated carboxamides and carbonitriles, preferably acrylamide and acrylonitrile; monoesters and diesters of fumaric acid and maleic acid such as the diethyl and diisopropyl esters and also maleic anhydride; ethylenically unsaturated sulfonic acids and their salts, preferably vinylsulfonic acid and 2-acrylamido-2-methylpropanesulfonic acid. Further examples are precrosslinking comonomers such as polyethylenically unsaturated comonomers, examples being divinyl adipate, diallyl maleate, allyl methacrylate, and triallyl cyanurate, or postcrosslinking comonomers, examples being acrylamidoglycolic acid (AGA), methacrylamidoglycolic acid methyl ester (MAGME), N-methylolacrylamide (NMA), N-methylolmethacrylamide, -methylolallylcarbamate, alkyl ethers or esters such as the isobutoxy ethers or esters of N-methylolacrylamide, of N-methylolmethacrylamide and of N-methylolallylcarbamate. Also suitable are epoxy-functional comonomers such as glycidyl methacrylate and glycidyl acrylate. Further examples are silicon-functional comonomers, such as acryloyloxypropyltri(alkoxy)silanes and methacryloyloxypropyltri(alkoxy)silanes, vinyltrialkoxysilanes, and vinylmethyldialkoxysilanes, in which the alkoxy groups may, for example, include ethoxy and ethoxypropylene glycol ether radicals. Mention may also be made of monomers containing hydroxyl or CO groups, examples being hydroxyalkyl methacrylates and acrylates such as hydroxyethyl, hydroxypropyl or hydroxybutyl acrylate or methacrylate, and also compounds such as diacetone-acrylamide and acetylacetoxyethyl acrylate or methacrylate.
The monomers and the weight fractions of the comonomers are selected so as to give, in general, a glass transition temperature, Tg, of from −30° C. to +40° C., preferably from −10° C. to +25° C. The glass transition temperature Tg of the polymers may be determined in a known manner by means of differential scanning calorimetry (DSC). The Tgs may also be calculated approximately in advance using the Fox equation. According to T. G. Fox, BULL. AM. PHYSICS SOC. 1, 3, page 123 (1956): 1/Tg=x
1
/Tg
1
+x
2
/Tg
2
+. . . +x
n
/Tg
n
, x
n
being the mass fraction (% by weight/100) of the monomer n and Tg
n
being the glass transition temperature, in Kelvin, of the homopolymer of the monomer n. Tgs for homopolymers are listed in Polymer Handbook, 2
nd
Edition, J. Wiley & Sons, New York (1975).
Preference is given to homopolymers or copolymers containing one or more monomers from the group consisting of vinyl acetate, vinyl esters of a-branched monocarboxylic acids having from 9 to 11 carbon atoms, vinyl chloride, ethylene, methyl acr
Weitzel Hans-Peter
Zeh Harald
Wacker Polymer Systems GmbH & Co. KG
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