Stock material or miscellaneous articles – Composite – Of epoxy ether
Patent
1995-11-21
1997-06-24
Beck, Shrive
Stock material or miscellaneous articles
Composite
Of epoxy ether
427410, 4274121, B05D 136
Patent
active
056415745
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a novel overcoating process wherein a base coat and a clear coat are formed by the two-coat one-bake method.
BACKGROUND ART
Motor vehicle outer panels and the like are overcoated often by the so-called two-coat one-bake method wherein a base coat composition and a clear coat composition are applied to the substrate wet-on-wet and then cured at the same time by heating.
As clear coat compositions for use in the two-coat one-bake method, thermosetting coating compositions are generally used which consist primarily of an acrylic resin or like hydroxyl-containing resin and a melamine resin.
However, air pollution due to sulfur oxides, nitrogen oxides, etc. has become aggravated on a global scale in recent years to produce an acid rain, which has developed a new drawback in the overcoat formed on motor vehicle outer panels by the two-coat one-bake method using the clear coat composition, i.e., susceptibility to etching, whitening or staining. It is urgently required to obviate this drawback. The overcoat has another drawback in that the surface thereof is subject to scratches, for example, when the motor vehicle is washed.
On the other hand, a two-coat one-bake coating process is also proposed with use of a clear coat composition which comprises an epoxy- and hydroxyl-containing resin and a cyclic anhydride serving as a crosslinking agent (U.S. Pat. Nos. 4,732,790 and 4,732,791). This coating process gives coatings that have inferior scratch resistance and do not always have satisfactory acid resistance.
The present invention provides a novel two-coat one-bake coating process for forming overcoats that are free of the foregoing deficiencies of the prior art and form overcoats that have excellent acid and scratch resistance.
SUMMARY OF THE INVENTION
The present invention provides a process for forming an overcoat by the two-coat one-bake method wherein a base coat composition and a clear coat composition are applied to a substrate wet-on-wet and thereafter cured at the same time by heating, the process being characterized in that the base coat composition is an aqueous coating composition consisting primarily of:
(I) an aqueous dispersion or solution of a polymer containing a crosslinkable functional group,
(II) a crosslinking agent,
(III) a coloring pigment, and
(IV) water, having at least one epoxy group and at least one hydroxyl group in the molecule, (ii) a resin mixture of (ii-1) a resin having at least two epoxy groups in the molecule and (ii-2) a resin having at least two hydroxyl groups in the molecule, (iii) a resin having at least two epoxy groups in the molecule, and (iv) an any mixture thereof, noncyclic acid anhydride groups and represented by the formula ##STR2## wherein R is a monovalent hydrocarbon group having 2 to 50 carbon atoms, R' is a bivalent hydrocarbon group having 2 to 50 carbon atoms, the hydrocarbon groups R and R' containing or not containing an ether linkage, urethane linkage or ester linkage, and n is an integer of 1 to 500, and
DETAILED DESCRIPTION OF THE INVENTION
Intensive research has been conducted to overcome the deficiencies of the prior art and it has been found that cured coatings which have excellent acid and scratch resistance are obtained by conducting the two-coat one-bake method using as a clear coat composition a coating composition comprising an epoxy- or epoxy- and hydroxyl-containing resin, a crosslinking agent which is a compound having noncyclic acid anhydride groups and represented by the formula (1), and a curing catalyst.
The substrates to be overcoated by the process of the invention include those of various metals and plastics. Preferably, the substrate has its surface treated by a usual chemical conversion process before coating. Examples of such substrates are outer panels of motor vehicles, outer panels of household electric devices, outer panels of office machines, building materials, etc.
Further preferably, the substrate is coated with a primer coating composition, or with a primer coating com
REFERENCES:
patent: 4650718 (1987-03-01), Simpson et al.
patent: 4681811 (1987-07-01), Simpson et al.
patent: 4699814 (1987-10-01), Ambrose et al.
patent: 4703101 (1987-10-01), Singer et al.
patent: 4732790 (1988-03-01), Blackburn et al.
patent: 4732791 (1988-03-01), Blackburn et al.
patent: 4749743 (1988-06-01), Ambrose et al.
patent: 4764430 (1988-08-01), Blackburn et al.
Ikushima Satoshi
Isozaki Osamu
Kasari Akira
Matsumoto Naoji
Nordstrom John David
Beck Shrive
Cameron Erma
E. I. Du Pont de Nemours and Company
Fricke Hilmar L.
Kansai Paint Company Limited
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