Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
1999-08-03
2001-12-11
Moore, Margaret G. (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C524S806000, C524S811000, C524S833000, C524S832000, C524S836000
Reexamination Certificate
active
06329461
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method of producing aqueous coating compositions excellent in shelf stability of emulsion and in weather resistance, stain resistance, water resistance and solvent resistance of coatings and, more particularly, to a method of producing aqueous coating compositions useful as building material coating compositions, adhesives or paper coating compositions.
PRIOR ART
Polyalkoxypolysiloxanes or tetraalkoxysilanes and resins comprising an alkoxysilyl (hydrolyzable silyl)-containing monomer, in particular acrylsilicone resins, have ordinary curing properties and form highly hard coatings excellent in performance characteristics such as weather resistance and stain resistance. Therefore, they have been used as adhesives, binders for coatings and paper coating compositions.
In Japanese Kokai Tokkyo Koho H06-145453, for example, there are disclosed hydrophilic curable compositions comprising an alkoxysilyl-containing acrylic copolymer, a tetraalkyl silicate (tetraalkoxysilane) and/or a condensate derived therefrom and a curing catalyst and it is described that since the coating surface becomes hydrophilic, contaminants can be washed away by rainwater or the like, hence effective stain resistance can result.
In recent years, however, attempts have been made, in the fields of paints and adhesives, to change over the resins from those for which organic solvents are used to aqueous or water-dispersible resins from the viewpoints of antipollution policy or saving of resources. The technology disclosed in the above-cited publication, however, mainly consists in polymerization in organic solvent systems and, in aqueous systems, it hardly allows stable polymerization and requires fairly advanced techniques for the production of desired emulsions
Various attempts have been made with respect to polymerization in such aqueous systems. As examples of emulsion polymerization using alkoxysilyl-containing monomers, emulsions resulting from emulsion polymerization of an alkyl methacrylate, an alkoxysilane group-containing monomer, acrylamide, etc. are disclosed in Japanese Kokai Tokkyo Koho H03-227312 and reactive type resin emulsions comprising a resin containing at least one hydrolyzable silyl group and at least one amine imide group in each molecule are disclosed in Japanese Kokai Tokkyo Koho H05-25354. Although these technologies disclosed can indeed improve the weather resistance and solvent resistance, further improvements are required, however. In particular, emulsions satisfactory in stain resistance have not been obtained as yet with such technologies. Therefore, for making improvements in these aspects, the present inventors made various investigations based on the finding that the use of polyalkoxypolysiloxanes is essential.
However, in the polymerization of polyalkoxypolysiloxanes in aqueous systems, the polyalkoxypolysiloxanes can hardly be stable in aqueous media, as mentioned above, and the emulsion polymerization process in general use, namely the process comprising dispersing by emulsification a polyalkoxypolysiloxane and a polymerizable monomer in an emulsifier-containing aqueous medium and carrying out the polymerization with heating in the presence of an initiator while charging said emulsified dispersion, is disadvantageous in that the polyalkoxypolysiloxane cannot be stably introduced into emulsion particles, hence the desired emulsions can hardly be obtained. Therefore, it was revealed that further studies are required for the development of a method of producing silicone-containing aqueous emulsions having good shelf stability and giving coatings excellent in weather resistance, water resistance, solvent resistance and stain resistance.
SUMMARY OF THE INVENTION
As a result of intensive investigations made by the present inventors in an attempt to solve such problems, it was found that the above problems can be solved by the silicone-containing aqueous coating composition (hereinafter briefly referred to as coating composition) obtained by subjecting an aqueous emulsion prepared in advance by emulsification in an aqueous medium containing a polyalkoxypolysiloxane (A), an unsaturated monomer (B) and an emulsifier (C) so as to attain an oil droplet diameter not more than 1,000 nm to polymerization in the presence of a polymerization initiator (D). It was also found that the combined use, in the aqueous medium, of an unsaturated monomer (E) containing at least one functional group, which is a hydrolyzable silyl group, a hydroxyl group or an epoxy group, results in further improvements in weather resistance, water resistance and solvent resistance and, further, that the use (in lieu of the polyalkoxypolysiloxane (A)) of a partial condensate of a polyalkoxypolysiloxane (A) or a tetraalkoxysilane (A′) and an unsaturated monomer (E) containing at least one functional group, which is a hydrolyzable silyl group, a hydroxyl group or an epoxy group, results in marked improvements in stain resistance and improvements in the odor of emulsions. Based on these findings, the present invention has now been completed.
DETAILED DESCRIPTION OF THE INVENTION
In the following, the present invention is described more specifically.
First, the materials to be used in the practice of the present are described. The polyalkoxypolysiloxane (A) to be used in the present invention includes those represented by the general formula (1) given below, without any particular restriction.
In the above formula, n represents the mean degree of condensation and is a value of 2 or more and it may be such that the above compound have fluidity at ordinary temperature. R represents an alkyl, aryl or aralkyl group (preferably an alkyl group). The R groups may be the same or different in the number of carbon atoms and may be straight or branched. The number of carbon atoms is preferably 1 to 10 (more preferably 1 to 5).
As specific examples of the above (A), there may be mentioned polymethoxypolysiloxane, polyethoxypolysiloxane, polypropoxypolysiloxane, polybutoxypolysiloxane and the like. In view of the fact that stain resistance, water resistance and solvent resistance are manifested in a short time, polymethoxypolysiloxane and polyethoxypolysiloxane are preferred.
The tetraalkoxysilane (A′) to be used in the present invention specifically includes tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, tetrabutoxysilane and the like. In view of the fact that stain resistance, water resistance and solvent resistance are manifested in a short time, tetramethoxysilane and tetraethoxysilane are preferred.
The method of producing the above (A) is not critical. It can be obtained by hydrolyzing (condensing) a tetraalkoxysilane such as tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane or tetrabutoxysilane and the value n in the above general formula (1) can be adjusted by controlling the degree of hydrolysis.
The hydrolysis reaction itself can be carried out in a per se known manner. For example, it is possible, after addition of a predetermined amount of water to such tetraalkoxysilane, to carry out the reaction in the presence of an acid catalyst at about room temperature to 100° C. while distilling off the byproduct alcohol. The degree of hydrolysis can be adjusted by means of the amount of water used to an extent such that the condensate has fluidity and is soluble in the unsaturated monomer (B) to be mentioned later herein.
The unsaturated monomer (B) to be used in the present invention may be any one capable of radical polymerization, without any particular restriction. As specific examples, there may be mentioned styrene, methyl (meth)acrylate, ethyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, 2-ethylhexyl acrylate, n-hexyl methacrylate, lauryl methacrylate, vinyl acetate, vinyl tert-decanoate, tridecyl (meth)acrylate, stearyl (meth)acrylate, hexyl (meth)acrylate, cyclohexyl (meth)acrylate, octyl (meth)acrylate, isobornyl (meth)acrylate, dicyclopentadienyl (meth)acrylate, vinyltoluene, (meth)acr
Akiyama Mamoru
Kitagawa Akio
Kyogoku Masayuki
Ogawa Teruhiko
Armstrong Westerman Hattori McLeland & Naughton LLP
Moore Margaret G.
Nippon Gohsei Kagaku Kogyo Kabushiki Kaisha
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