Coating processes – Applying superposed diverse coating or coating a coated base – Synthetic resin coating
Reexamination Certificate
2000-07-19
2003-02-04
Beck, Shrive P. (Department: 1762)
Coating processes
Applying superposed diverse coating or coating a coated base
Synthetic resin coating
C427S409000, C427S410000
Reexamination Certificate
active
06514568
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a novel method of forming a multilayered topcoat film.
BACKGROUND ART
A 3-coat 2-bake method of forming a multilayered topcoat film on an automotive outer plate or the like is known, which comprises applying a first coating composition and a second coating composition to a substrate usually coated with an undercoat, such as a cationic electrodeposition coat, and an intermediate coat, thermally curing the first and second coating compositions, and applying and thermally curing a clear coating composition.
The clear coating composition used for the above method is usually an organic solvent-based coating composition comprising a hydroxyl-containing acrylic resin and a melamine resin, a powder coating composition, an organic solvent-based coating composition to be cured by crosslinking between a carboxyl group and an epoxy group.
However, it was found that when the 3-coat 2-bake method employs, as the clear coating composition, a powder coating composition or an organic solvent-based coating composition to be cured by crosslinking between a carboxyl group and an epoxy group, the method has the drawback that, if the coating surface of the second coating composition is not sanded before application of the clear coating composition, the intercoat adhesion between the second coating composition and the clear coating composition becomes insufficient.
DISCLOSURE OF THE INVENTION
An object of the present invention is to provide a novel method of forming a multilayered topcoat film free from the above drawback of the prior art.
Another object of the present invention is to provide a novel method of forming a multilayered topcoat film excellent in intercoat adhesion, finish properties such as film appearance and gloss, and film performance properties such as solvent resistance, weather resistance and water resistance.
Other objects and features of the present invention will be apparent from the following description.
The present invention provides a 3-coat 2-bake method of forming a multilayered topcoat film, comprising applying a first coating composition (A) and a second coating composition (B) to a substrate, thermally curing the two compositions, and applying and thermally curing a clear coating composition (C);
the first coating composition (A) being an organic solvent-based colored coating composition;
the second coating composition (B) being an organic solvent-based coating composition comprising an acrylic resin (b-1) whose main chain has, bonded thereto, at least two side chains of different lengths each having at least one hydroxyl group, a polyepoxide (b-2) and a crosslinking agent (b-3); and
the clear coating composition (C) being a powder coating composition (C-1) or an organic solvent-based coating composition (C-2) comprising a hydroxyl- and carboxyl-containing resin (c-2
a
) and a polyepoxide (c-2
b
).
The present inventors conducted extensive research to develop a 3-coat 2-bake method of forming a multilayered topcoat film having improved intercoat adhesion between the second coating composition and the clear coating composition (which is a powder coating composition or an organic solvent-based coating composition to be cured by crosslinking between a carboxyl group and an epoxy group), without impairing finish properties and film performance of the multilayered topcoat film. As a result, they found that when the above specified organic solvent-based coating composition is used as the second coating composition, the intercoat adhesion between the second coating composition and the clear coating composition can be improved, without impairing the excellent finish properties and high film performance of the multilayered topcoat film and without necessitating sanding of the coating surface of the second coating composition.
The present invention has been accomplished based on these findings.
The method of forming a multilayered topcoat film of the present invention will be described below in further detail.
Substrate
Substrates usable in the method of the invention include metallic or plastic materials for automobiles, electric appliances, etc.; these materials as coated with an undercoat such as a cationic electrodeposition coat; and these materials as coated with the undercoat and an intermediate coat.
First Coating Composition (A)
In the method of the invention, the first coating composition (A) to be applied to the substrate is an organic solvent-based colored coating composition.
Usable as the composition (A) are known thermosetting coating compositions comprising a base resin, a crosslinking agent, a coloring pigment and an organic solvent.
Examples of base resins include acrylic resins, vinyl resins, polyester resins, alkyl resins and urethane resins, each having hydroxyl, epoxy, carboxyl, alkoxysilane or like crosslinkable functional group. These base resins may be used either singly or in combination.
Examples of crosslinking agents include alkyl-etherified melamine resins, urea resins, guanamine resins, polyisocyanate compounds, blocked polyisocyanate compounds, epoxy compounds and carboxyl-containing compounds. These crosslinking agents may be used either singly or in combination.
The proportions of the base resin and the crosslinking agent are usually about 50 to 90 wt. % of the base resin and about 50 to 10 wt. % of the crosslinking agent, based on the total amount of the two components.
Usable coloring pigments include titanium oxide, zinc oxide, carbon black, cadmium red, molybdenum red, chrome yellow, chrome oxide, Prussian blue, cobalt blue and like inorganic solid coloring pigments; azo pigments, phthalocyanine pigments, quinacridone pigments, isoindorine pigments, vat pigments, perylene pigments and like organic solid coloring pigments; flaky aluminum and like metallic pigments; and mica, metal oxide-coated mica, micaceous iron oxide and like light-interference coloring pigments. These pigments may be used either singly or in combination.
These coloring pigments are suitably selected to obtain a solid color coating composition, a metallic coating composition, a light-interference color coating composition or a coating composition having a combination of color characteristics of these coating compositions. The amount of the coloring pigment to be added can be determined in consideration of the hiding power described hereinafter.
Usable organic solvents include ordinary solvents for use in coating compositions, such as hexane, heptane, xylene, toluene, cyclohexane and like hydrocarbon solvents; methyl acetate, ethyl acetate, ethylene glycol monomethyl ether acetate, diethylene glycol monomethyl ether acetate and like ester solvents; isopropyl ether, ethylene glycol monomethyl ether, diethylene glycol monobutyl ether and like ether solvents; ethyl alcohol, butyl alcohol, hexyl alcohol and like alcohol solvents; and methyl isobutyl ketone, methyl ethyl ketone, isophorone, acetophenone and like ketone solvents.
The first coating composition (A) may further contain, where necessary, an extender pigment, a UV absorber, a photostabilizer, a flow modifier, an anti-cissing agent or like ordinary coating additive.
It is preferable that the composition (A) has a solid content of about 20 to 70 wt. %, preferably about 30 to 70 wt. %, at the time of application. The viscosity of the composition (A) is adjusted preferably to about 10 to 60 second (Ford Cup #4/20° C.) for application.
The single-layer coating of the composition (A) preferably has a hiding power sufficient to mask the color of the coating surface below the coating. Specifically stated, the composition (A) has such a hiding power that a 15 &mgr;m thick cured coating of the composition (A) has a light transmittance of 3% or less in the wavelength range of 400 to 700 nm.
The composition (A) can be applied by airless spraying, air spraying, electrostatic coating or like coating technique, to such a thickness as to form a cured coating of about 10 to 50 &mgr;m. The applied composition is allowed to stand, where necessary, for several minutes at room temperatu
Nagano Hiroyuki
Okumura Yasumasa
Sugai Hideo
Armstrong Westerman & Hattori, LLP
Beck Shrive P.
Fletcher, III William Phillip
Kansai Paint Co. Ltd.
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