Coating processes – Applying superposed diverse coating or coating a coated base – Synthetic resin coating
Reexamination Certificate
2001-02-26
2003-04-01
Beck, Shrive P. (Department: 1762)
Coating processes
Applying superposed diverse coating or coating a coated base
Synthetic resin coating
C427S372200, C524S556000, C524S558000, C524S832000
Reexamination Certificate
active
06541070
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method of forming a composite coating film on car bodies and so on and a composite coating film obtained by the method.
PRIOR ART
From environmental considerations, efforts have been made in recent years to develop water-based coating systems for reducing the levels of organic solvents in coatings. In automotive coating where it is common practice to apply a base coating and, then, a clear coating, attempts have been made to apply a water-based system to the base coating.
As a water-based base coat composition suited to automotive use, Japanese Kokai Publication Sho-63-193968 discloses a water-based coating composition comprising a water-dispersible film-forming acrylic emulsion polymer, a hydrophobic melamine resin and a pigment and Japanese Kokai Publication Sho-63-265974 discloses a water-based paint comprising a resin emulsion having a core component comprised of a C
4-12
alkyl-containing monomer and a shell component containing an acrylamide or methacrylic acid.
However, with any of the water-based base coat compositions heretofore available generally, inclusive of those mentioned above, it has been found difficult to attain both coat appearance and workability, particularly workability under highly humid conditions.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a method of forming a composite coating film which makes it possible to attain both appearance and workability, particularly attain workability, in a high-humidity environment.
The method of forming a composite coating film according to the present invention comprises applying a water-based base coat composition on a substrate, and then applying a clear coat thereonto,
wherein said water-based base coat composition comprises a pigment and a resin emulsion obtained by emulsion polymerization of an &agr;,&bgr;-ethylenically unsaturated monomer mixture,
said &agr;,&bgr;-ethylenically unsaturated monomer mixture having an acid value of 3 to 50 and containing at least 65% by weight of a (meth)acrylic ester whose ester moiety contains 1 or 2 carbon atoms.
It is to be understood that the hydroxyl value of said &agr;,&bgr;-ethylenically unsaturated monomer mixture may be within the range of 10 to 150.
Furthermore, the emulsion polymerization may be carried out in two stages.
In addition, said pigment may be a luster pigment.
Furthermore, the water-based base coat composition may comprise a curing agent and/or a water-soluble acrylic resin.
The water-soluble acrylic resin may for example be obtainable by solution polymerization of a component containing not less than 65 weight % of a (meth)acrylic ester whose ester moiety contains 1 or 2 carbon atoms.
The composite coating film of the invention is obtainable by the above method of forming a composite coating film.
DETAILED DESCRIPTION OF THE INVENTION
The method of forming a composite coating film according to the invention comprises applying a water-based base coat composition to a substrate and, then applying a clear coat composition thereon, in which said water-based base coat composition comprises a pigment and a resin emulsion obtained by emulsion polymerization of an &agr;,&bgr;-ethylenically unsaturated monomer mixture, said &agr;,&bgr;-ethylenically unsaturated monomer mixture having an acid value of 3 to 50 and containing at least 65% by weight of a (meth)acrylic ester whose ester moiety contains 1 or 2 carbon atoms.
Water-Based Base Coat Composition
The water-based base coat composition for use in the method of forming a composite coating film in accordance with the invention contains a pigment and a resin emulsion obtained by emulsion polymerization of an &agr;,&bgr;-ethylenically unsaturated monomer mixture.
The amount of the (meth)acrylate ester whose ester moiety contains 1 or 2 carbon atoms as contained in the &agr;,&bgr;-ethylenically unsaturated monomer mixture is not less than 65% by weight. If the proportion is less than 65%, the coating film obtained will be poor in appearance. The (meth)acrylate ester whose ester moiety contains 1 or 2 carbon atoms includes methyl (meth)acrylate and ethyl (meth)acrylate. In the context of the present invention, “(meth)acrylic ester” includes, within the meaning thereof, both of “acrylic ester and methacrylic ester”.
The &agr;,&bgr;-ethylenically unsaturated monomer mixture has an acid value of 3 to 50, preferably 7 to 40. Any acid value less than 3 will not contribute to improved workability and an acid value exceeding 50 will lead to decreased water resistance of the coating film. When, on the other hand, the water-based base coat composition is required to have curability, the &agr;, &bgr;-ethylenically unsaturated monomer mixture should have a hydroxyl value of 10 to 150, preferably 20 to 100. A hydroxyl value less than 10 will fail to provide sufficient curability while a hydroxyl value exceeding 150 will lead to decreased water resistance of the coating film. From the viewpoint of physical properties of the coating film, it is preferred that the polymer obtained by copolymerization of the above &agr;,&bgr;-ethylenically unsaturated monomer mixture have a glass transition temperature between −20° C. and 80° C.
The &agr;,&bgr;-ethylenically unsaturated monomer mixture can have such an acid value and/or hydroxyl value as mentioned above by containing an acid group- or hydroxyl group-containing &agr;, &bgr;-ethylenically unsaturated monomer or monomers therein.
As the acid group-containing &agr;,&bgr;-ethylenically unsaturated monomer, there may be mentioned acrylic acid, methacrylic acid, acrylic acid dimer, crotonic acid, 2-acryloyloxyethyl phthalate, 2-acryloyloxyethyl succinate, &ohgr;-carboxypolycaprolactone mono(meth)acrylate, isocrotonic acid, &agr;-hydroxy-&ohgr;-((1-oxo-2-propenyl)oxy)poly(oxy(1-oxo-1,6-hexanediyl)), maleic acid, fumaric acid, itaconic acid, 3-vinylsalicylic acid, 3-vinylacetylsalicylic acid, 2-acryloyloxyethyl acid phosphate, 2-acrylamido-2-methylpropanesulfonic acid and the like. Among these, acrylic acid, methacrylic acid and acrylic acid dimer are preferred.
As the hydroxyl group-containing &agr;,&bgr;-ethylenically unsaturated monomer, there may be mentioned hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, hydroxybutyl (meth)acrylate, allyl alcohol, methacryl alcohol, hydroxyethyl (meth)acrylate-&egr;-caprolactone adducts and the like. Preferred among these are hydroxyethyl (meth)acrylate, hydroxybutyl (meth)acrylate, and hydroxyethyl (meth)acrylate-&egr;-caprolactone adducts.
The &agr;,&bgr;-ethylenically unsaturated monomer mixture may contain one or more other &agr;,&bgr;-ethylenically unsaturated monomers. Such other &agr;,&bgr;-ethylenically unsaturated monomers include (meth)acrylate esters whose ester moiety contains 3 or more carbon atoms (e.g. n-butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, lauryl (meth)acrylate, phenyl (meth)acrylate, isobornyl (meth)acrylate, cyclohexyl (meth)acrylate, tert-butylcyclohexyl (meth)acrylate, dicyclopentadienyl (meth)acrylate, dihydrodicyclopentadienyl (meth)acrylate, etc.), polymerizable amide compounds (e.g. (meth)acrylamide, N-methylol (meth)acrylamide, N-butoxymethyl (meth)acrylamide, N,N-dimethyl(meth)acrylamide, N,N-dibutyl(meth)acrylamide, N,N-dioctyl(meth)acrylamide, N-monobutyl(meth)acrylamide, N-monooctyl(meth)acrylamide, 2,4-dihydroxy-4′-vinylbenzophenone, N-(2-hydroxyethyl)acrylamide, N-(2-hydroxyethyl)methacrylamide, etc.), polymerizable aromatic compounds (e.g. styrene, &agr;-methylstyrene, vinyl ketones, tert-butylstyrene, p-chlorostyrene, vinylnaphthalene, etc.), polymerizable nitriles (e.g. acrylonitrile, methacrylonitrile, etc.), &agr;-olefins (e.g. ethylene, propylene, etc.), vinyl esters (e.g. vinyl acetate, vinyl propionate, etc.), dienes (e.g. butadiene, isoprene, etc.), and so forth. One or more of these monomers may be selected according to the intended application. For assuring hydrophilicity with ease, the use of (meth)acrylamide is preferred.
The proportio
Hayashi Kouki
Kuwajima Teruaki
Magoshi Atsuo
Ohsugi Hiroharu
Beck Shrive P.
Connolly Bove & Lodge & Hutz LLP
Fletcher, III William Phillip
Nippon Paint Co. Ltd.
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