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
2001-06-01
2003-05-13
Seidleck, James J. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S063000, C525S09200D
Reexamination Certificate
active
06562903
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a clear coating for top coating of automotive bodies which has weathering resistance, acid resistance and car wash-free excellent stain resistance and is also excellent in stain resistance in polished surface sections, to a method of forming a multilayer coating film on automotive bodies using the same and to an automotive body.
PRIOR ART
A clear coating for top coating for automobiles is required to have decorativeness, weathering resistance and like qualities as key performance characteristics in addition to the minimum requirement to be met by any coating, namely storage stability, since that composition constitutes the outermost layer of coating films on automotive bodies. In recent years, it has been found that the melamine resin curing agent occurring in such coating films is causative of etching by acid rain and, for providing acid resistance to prevent such etching, the development of curing systems other than the melamine curing system has been awaited.
In Japanese Kokai Publication Hei-02-45577, Japanese Kokai Publication Hei-03-287650, Japanese Kokoku Publication Hei-06-41576 and Japanese Kokai Publication Hei-08-259667, there are disclosed coating compositions in which no melamine resin curing agents are used. These coating compositions make use of ester linkages formed by the reaction between an acid group and an epoxy group as crosslinking sites and therefore provide good acid resistance. In these curing systems (hereinafter referred to as “acid-epoxy curing systems”), hard and fragile coating films are readily formed when the crosslink density is increased to thereby provide coating films with sufficient weathering resistance and, further, the problem concerning stain resistance, namely the ease of stains being washed off, when causing deposits of contaminants such as soot and dust, has not been studied or solved.
In Japanese Kokai Publication Hei-10-140077, there is disclosed a top coating for automobiles which comprises an acid/epoxy-curable coating with a low condensate (low silicate condensate), with a degree of condensation of 2 to 10, of tetramethyl silicate and/or tetraethyl silicate as incorporated therein. This technology is to solve the problems mentioned above about stain resistance. This technology contrives to retain the reactivity with water by restricting the number of carbon atoms in the alkoxyl group and thus using a low condensate of tetramethyl silicate and/or tetraethyl silicate. And, the basic principle thereof is to cause coating films obtained from this coating to show high hydrophilicity resulting from the hydroxyl groups formed by the reaction of methoxy or ethoxy groups of the low silicate condensate as occurring in large amounts in the vicinity of the surface of the coating films with water upon exposure or treatment with an acid and thus show stain resistance.
In an automobile coating line, however, there is a finishing step in which the coated surface after top coating is polished with a #2400 and/or #4000 sandpaper, following removal of dust, grains, when such or other grains are found on that surface.
Those sections of the coating films polished in the above manner show decreased stain resistance due to the disappearance of hydrophilicity resulting from polishing off of the silicate-rich layer in the vicinity of the coating film surface. Therefore, when the whole automotive coating is viewed, there occur sections differing in hydrophilicity level, hence markedly differing in stain resistance level. Thus, there arises the problem of black and white spotted pattern formation upon exposure.
Further, automotive coatings are washed with water by the user to remove stains and, where necessary, further treated with wax. In the case of luxury cars, there is a tendency toward preference for waxing from the decorativeness viewpoint or for the purpose of polishing. In the case of cars of practical use, for example cars for commercial use, if coating films having sufficient hydrophilicity to provide the so-called car wash-freeness, namely a property such that surface stains can be washed off by rainwater or the like without particularly removing stains by washing with water, can be formed, the user will be no more required to waste time and labor for car washing.
SUMMARY OF THE INVENTION
In view of the above-mentioned state of the art, it is an object of the present invention to provide a clear coating for top coating of automobiles which has basic performance characteristics such as weathering resistance, acid resistance and car wash-free stain resistance as well as good stain resistance in polished surface sections, a method of forming a multilayer coating film on automotive bodies, and an automotive body having such a coating.
The present invention provides a clear coating for top coating of automobiles
which comprises a half-esterified acid group-containing acrylic copolymer (I) and a silicate-grafted acrylic copolymer (II) as resin constituents,
said half-esterified acid group-containing acrylic copolymer (I) being obtainable by:
preparing a copolymer from an acid anhydride group-containing, radical-polymerizable monomer (I-a) and another radical-polymerizable monomer (I-b) and then half-esterifying said acid anhydride group with a low-molecular alcohol compound,
said silicate-grafted copolymer (II) being obtainable by grafting a silicate compound (II-B) onto a hydrolyzable silyl-containing copolymer (II-A),
said silicate compound (II-B) being represented by the general formula (1):
wherein n represents an integer of 1 to 50 and the R
1
groups may represent different groups and each represents a substituted or unsubstituted organic group containing 1 to 20 carbon atoms, and
the amount of said silicate compound (II-B) grafted being 5 to 50% by mass (on solids basis) relative to the total amount of the above resin constituents.
The invention also provides a clear coating for top coating of automobiles
wherein the above hydrolyzable silyl-containing copolymer (II-A) is an acrylic copolymer obtainable by copolymerizing a hydrolyzable silyl-containing, radical-polymerizable monomer (II-A-a) and a hydroxyl-containing, radical-polymerizable monomer (II-A-b).
The invention further provides a process for forming a multilayer coating film on automotive bodies
which comprises forming an undercoat film layer on an automotive panel,
then applying a base coating containing a color pigment and/or a luster pigment
and applying a clear coating for top coating thereonto by the wet-on-wet technique, followed by heating for curing,
said clear coating for top coating being the above-mentioned clear coating for top coating of automobiles.
The invention further provides a method of forming a multilayer coating film on automotive bodies
which comprises:
forming an undercoat film layer on an automotive panel,
applying thereonto a solid color coating containing a color pigment, heating the same for curing , or applying to the outside panel a base coating and a clear coating by the wet-on-wet technique, heating the same for curing,
applying thereonto a clear coating for top coating by the dry-on-wet technique
and heating the same for curing,
said clear coating for top coating being the above-mentioned clear coating for top coating of automobiles.
The invention still further provides an automotive body coated with a multilayer coating film,
the outermost layer of said multilayer coating film being formed from the above-mentioned clear coating for top coating of automotive bodies.
In the following, the invention is described in detail.
DETAILED DESCRIPTION OF THE INVENTION
The clear coating of the invention for top coating of automobiles comprises the half-esterified acid group-containing acrylic copolymer (I) and the silicate-grafted polymer (II) as resin constituents. The half-esterified acid group-containing acrylic copolymer (I) is obtainable by preparing a copolymer from an acid anhydride group-containing, radical-polymerizable monomer (I-a) and another radical-polymerizable monomer (I-b) and the
Kubota Hiroshi
Sudo Nobuhisa
Tanabe Hisaki
Toui Teruzo
Yamane Takakazu
Asinovsky Olga
Nippon Paint Co. Ltd.
Seidleck James J.
Sughrue & Mion, PLLC
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