Coating processes – Direct application of electrical – magnetic – wave – or... – Electrostatic charge – field – or force utilized
Reexamination Certificate
1999-05-07
2001-05-29
Cameron, Erma (Department: 1762)
Coating processes
Direct application of electrical, magnetic, wave, or...
Electrostatic charge, field, or force utilized
C427S380000, C427S407100, C427S409000
Reexamination Certificate
active
06238748
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a process of forming a multilayer coating film with excellent smoothness and with thinner intermediate coating film without deteriorating the coating film properties by using an intermediate paint with a specific pigment composition and by coating a topcoat paint after curing of the coating film of said intermediate paint, when a multilayer coating film is formed by successive coatings by an undercoat paint, an intermediate paint and a topcoat paint.
BACKGROUND TECHNOLOGY
A process of forming a multilayer coating film by successively coating with an undercoat paint (such as an electrodeposition paint), an intermediate paint and a topcoat paint is known. Concerning the intermediate paint, however, it is necessary to coat to a thick coating film of usually more than 30 &mgr;m (as a cured coating film) in order to hide the undercoat layer and to maintain the coating film properties. Therefore, it is desired to lower the coating cost of the whole multilayer coating film by making the intermediate coating film thinner without deteriorating the hiding properties and the coating film properties.
The present inventors had been conducting an intensive research to solve these problems and as a result they found that in a process of successive coatings by an undercoat paint, an intermediate paint and a topcoat paint it is possible to make the intermediate coating film thinner with improved undercoat hiding properties and chipping resistance of the intermediate coating film and, in addition, with improved smoothness of the topcoat surface by using a thermocurable paint containing both components of aluminium powder and titanium oxide pigment as the intermediate paint and by coating a topcoat paint after curing of the intermediate coating film, and completed the present invention.
DISCLOSURE OF THE INVENTION
Thus the present invention provides a process of forming a multilayer coating film characterized by that in a process of forming a multilayer coating film by successively coating a substrate with an undercoat paint (A), an intermediate paint (B) and a topcoat paint
(1) to use a liquid thermocurable paint containing (C), 0.1-30 parts by weight of aluminium powder and 1-200 parts by weight of titanium oxide pigment per 100 parts by weight of a thermosetting resin composition and the hiding film thickness of its coating film being less than 25 &mgr;m as said intermediate paint (B),
(2) to use a solid color paint, a metallic paint or an interference pattern paint as said topcoat paint (C), and
(3) to coat said topcoat paint (C) after curing by heating of the coating film of said intermediate paint (B).
The process of forming a multilayer coating film of the present invention (hereinafter referred to as “the process”) is described more specifically hereinbelow.
Undercoat paint (A):
Undercoat paint (A) is used to give anticorrosivity, adhesivity etc. by directly coating a substrate made of metal or plastics. In the process any usual undercoat paint can be used without special restriction, only if it suits to these purposes. As a substrate applicable to said undercoat paint outer panels of automobile are particularly preferable. It is usually desirable to suitably conduct rust removal, washing and chemical treatments of the substrate previously.
If a substrate is metalbacked or has an electroconductive surface, a cationic electrodeposition paint is preferable as an undercoat paint. As a cationic electrodeposition paint there can be used a per se known one comprising an aqueous solution or aqueous dispersion of a salt of cationic high polymer compound, compounded, as necessary, with crossliking agent, pigment and various additives and its sort is not specially restricted. As a cationic high polymer compound there can be mentioned, for example, acrylic resin or epoxy resin having crosslinking functional groups in which cationic groups such as amino groups are introduced. They can be made water-soluble or water-dispersible through neutralization with an organic acid or an inorganic acid. As a crosslinking agent to cure these high polymer compounds block polyisocyanate compounds, alicyclic epoxy resins etc. can be preferably used.
Electrodeposition coating can be conducted by dipping metallic substrates such as outer panels of automobile or bumpers as a negative electrode in a bath of said cationic electrodeposition paint and by depositing the paint on said substrate by sending an electric current between it and a positive electrode under the usual conditions. The thickness of the formed electrodeposition coating film is preferable usually in a range of 10-40 &mgr;m based upon a cured coating film, and a coating film can be cured by crosslinking through heating at about 140 to about 220° C. for about 10 to about 40 minutes. In the process it is preferable to coat an intermediate paint after curing said electrodeposition coating film. Optionally, however, an intermediate paint can be coated during the latter is in the uncured state.
Intermediate Paint (B):
In the process a liquid thermocurable paint containing 0.1-30 parts by weight of aluminium powder and 1-200 parts by weight of titanium oxide pigment per 100 parts by weight of a thermosetting resin composition and the hiding film thickness of its coating film being less than 25 &mgr;m as the intermediate paint (B),
Using both aluminium powder and titanium oxide pigment in the intermediate paint (B) increases the hiding power of the coating film and make it possible to sufficiently hide the undercoat surface with a cured coating film of less than 25 &mgr;m, especially with a thin film of 10-25 &mgr;m and thus can achieve making the intermediate coating film thinner.
Thermosetting resin composition which is used as a vehicle component in such an intermediate paint (B) consists fundamentally of a base resin and a cross-linking agent or a self-crosslinking type resin. As a base resin there can be mentioned, for example, acrylic resin, polyester resin, alkyl resin etc. having more than 2 crosslinking functional groups such as hydroxyl group, epoxy group, isocyanate group, carboxyl group etc. in the molecule. As a crosslinking agent there can be used, for example, amino resins such as melamine resin, urea resin etc., polyisocyanate compounds which may be blocked, compounds containing carboxyl groups etc. As the above-mentioned self-crosslinking type resin there can be mentioned, for example, resins containing more than 2 alkoxysilane groups in the molecule, resins containing a carboxyl group(s) and a hydroxyl group (s) in the molecule, resins containing a hydroxyl group (s) and an isocyanate group(s) which may be blocked etc. These resins are based upon, for example, vinyl resin, acrylic resin, polyester resin, urethane resin etc.
As aluminium powder to be compounded in the intermediate paint (B) aluminium powder whose average particle diameter is generally less than 40 &mgr;m, preferably less than 10 &mgr;m, and more preferably in a range of 3-7 &mgr;m is suitable. Particularly, if fine powder of an average particle diameter of less than 10 &mgr;m is used, the formed intermediate coating film itself has no brilliance. “Average diameter” here means a median diameter measured by laser diffraction scattering (LA-500). The main component of this aluminium powder is metallic aluminium, whose surface may be treated with a silane coupling agent or the like.
As titanium oxide pigment to be compounded in the intermediate paint (B) according to the process those which are per se known as pigments for paint can be used. Their average particle diameter is preferable to be generally 5 &mgr;m. Moreover, the surface of said titanium oxide pigment may be treated with alumina, silica etc.
Concerning compounding amount of aluminium powder and titanium oxide pigment per 100 parts by weight of a thermosetting resin composition (as solid content) aluminium powder can be in a range of 0.1-30 parts by weight, preferably 0.5-20 parts by weight and more preferably 1-7 parts by weight and titanium oxide pigment can be in a ra
Nakamura Shigeru
Ueno Naruhito
Cameron Erma
Kansai Paint Co. Ltd.
Wenderoth , Lind & Ponack, L.L.P.
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