Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
1999-04-30
2001-07-03
Dawson, Robert (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S100000, C525S105000, C525S106000, C525S132000, C525S146000, C525S326500, C525S342000
Reexamination Certificate
active
06255392
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a curable composition for top coating which is suitably applied to, for example, automobiles, industrial equipments, steel furnitures, building interior and exterior, household electric appliances and plastic products, and an article coated with a clear top coat comprising the curable composition as a main component. More particularly, the invention relates to a curable composition for top coating which exhibits excellent acid resistance, scratch resistance, appearance and thermosetting property and which can be suitably used particularly as a top coat for automobiles, and a coated article using it.
BACKGROUND ART
Paints composed mainly of a melamine resin such as alkyd-melamine resin or acrylic melamine resin have been conventionally used for coating automobiles, industrial equipments, steel furnitures, interior and exterior of buildings, household electric appliances, plastic products and the like.
However, such paints composed mainly of a melamine resin has problems that harmful formaline is generated at the time of curing, and that the cured coating films are attacked by acid rain because they are poor in acid resistance. In particular, the problem of acid rain resulting from air pollution assumes a serious aspect in recent years, and there is observed a phenomenon that etching, whitening or spotting occurs in the coating films.
In order to solve the problems, it is proposed to use, in paints, a blend of a vinyl copolymer having a hydrolyzable silyl group and an acrylic polyol, or a copolymer of a vinyl monomer having a hydrolyzable silyl group and a vinyl monomer having an alcoholic hydroxyl group.
The use of a blend of a vinyl copolymer having a hydrolyzable silyl group and an acrylic polyol, or the use of a copolymer of a vinyl monomer having a hydrolyzable silyl group and a vinyl monomer having an alcoholic hydroxyl group has the advantage that coating films formed therefrom are superior in acid resistance and weatherability as compared with paints composed mainly of a melamine resin such as acrylic melamine or alkyd-melamine resin, since the hydrolyzable silyl group and the alcoholic hydroxyl group form stable siloxane bonds or siloxy bonds to cure.
However, in case of using a blend of a vinyl copolymer having a hydrolyzable silyl group and an acrylic polyol, or a copolymer of a vinyl monomer having a hydrolyzable silyl group and a vinyl monomer having an alcoholic hydroxyl group, the scratch resistance is not always sufficient. It is proposed to introduce a flexible component having a polyester structure in order to impart a scratch resistance. However, there is a case that the introduction rather lowers the acid resistance and hardness, so this proposal is not satisfactory in this respect.
For example, in case of top coat finishing of automobiles, metallic color finishing and solid color finishing have been generally adopted. In case of the solid color finishing, an alkyd-melamine resin paint has been conventionally used and generally cured in a one coat-one bake manner. Recently, in compliance with strict demands of properties such as appearance of finishing, weatherability, acid resistance and scratch resistance, it is proposed to coat on the solid color finishing a clear paint, e.g., an acrylic-melamine resin paint, a paint containing the above-mentioned blend system of a hydrolyzable silyl group-containing vinyl copolymer and an acrylic polyol, or a paint containing a vinyl copolymer having both a hydrolyzable silyl group and an alcoholic hydroxyl group in the same molecule. In this case, it is also proposed to introduce a flexible component having a polyester structure into the clear paint resin in order to raise the scratch resistance, but it is known that the acid resistance and hardness are not always satisfactory.
Thus, it is an object of the present invention to provide a curable topcoat composition which not only exhibits excellent acid resistance and scratch resistance, but also is excellent in balance of physical properties of coating films such as weatherability, appearance and hardness.
Another object of the present invention is to provide articles coated with the curable composition.
DISCLOSURE OF THE INVENTION
The present invention provides a curable topcoat composition comprising:
(A) 100 to 30 parts by weight of a vinyl copolymer the main chain of which consists essentially of a vinyl copolymer, and which has in its molecule at the main chain end and/or the side chain both at least one of alcoholic hydroxyl group and phenolic hydroxyl group and at least one hydrolyzable silyl group of the formula (I):
wherein R
1
and R
2
are hydrogen atom or a monovalent hydrocarbon group selected from the group consisting of an alkyl group having 1 to 10 carbon atoms, an aryl group and an aralkyl group, and a is 0, 1 or 2, and which has a carbonato structure of the formula (II):
in the main chain and/or the side chain,
(B) 0.001 to 70 parts by weight of a hydroxyl group-containing compound having no hydrolyzable silyl group, and
(C) a solvent, the total amount of the components (A) and (B) being 100 parts by weight.
Further, the present invention provides a coated article wherein a clear top coat comprising as a main component the above-mentioned curable topcoat composition is coated onto the surface coated with a paint containing a metallic powder and/or a color pigment.
The term “vinyl” as used herein denotes that a substance is derived from a compound having a polymerizable C═C bond, such as vinyl group or vinylidene group.
BEST MODE FOR CARRYING OUT THE INVENTION
Component (A)
In the present invention used is a vinyl copolymer (A) the main chain of which consists essentially of a vinyl copolymer, and which has in its molecule at the main chain end and/or the side chain both at least one hydroxyl group of an alcoholic hydroxyl group and a phenolic hydroxyl group (hereinafter referred to as “alcoholic hydroxyl group and the like”) and at least one hydrolyzable silyl group (including silanol group) of the formula (I):
wherein R
1
and R
2
are a hydrogen atom or a monovalent hydrocarbon group selected from the group consisting of an alkyl group having 1 to 10 carbon atoms, an aryl group and an aralkyl group, and a is 0, 1 or 2, and if a plurality of R
1
or R
2
groups are present, they may be the same or different, and which has a carbonato structure of the formula (II):
in the main chain and/or the side chain. Since the main chain of the vinyl copolymer (A) is substantially composed of a vinyl copolymer chain, coating films formed from the obtained curable composition have good properties such as weatherability and chemical resistance. Also, since the vinyl copolymer (A) has at least one hydrolyzable silyl group (I) in its molecule, it has a curability. Further, since the vinyl copolymer (A) has both at least one hydrolyzable silyl group (I) and at least one alcoholic hydroxyl group and the like in its molecule, it is excellent in curability under heat curing conditions, thus raising the crosslinking density of cured products. Further, because of having a carbonate structure, a scratch resistance is imparted without lowering the acid resistance.
It is sufficient that at least one hydrolyzable silyl group (I) is present in a molecule of the vinyl copolymer (A), but it is preferable that the vinyl copolymer (A) has 2 to 10 silyl groups (I) per one molecule, since the coating films formed from the obtained curable composition is superior in solvent resistance.
In the formula (I), R
1
is a hydrogen atom or a monovalent hydrocarbon group selected from an alkyl group having 1 to 10 carbon atoms (preferably an alkyl group having 1 to 4 carbon atoms such as methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group or t-butyl group), an aryl group (e.g., a group having 6 to 25 carbon atoms such as phenyl group) and an aralkyl group (e.g., a group having 7 to 12 carbon atoms such as benzyl group). Of these, alkyl groups having 1 to 10 carbon atoms, especially alkyl
Inoue Masaharu
Kono Yoshiyuki
Nakamura Seigo
Nanbu Toshiro
Dawson Robert
Kaneka Corporation
Leydig , Voit & Mayer, Ltd.
Robertson Jeffrey B.
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