Coating processes – Restoring or repairing – Metal article
Reexamination Certificate
1999-06-15
2001-10-02
Beck, Shrive (Department: 1762)
Coating processes
Restoring or repairing
Metal article
C427S140000, C427S409000, C427S458000, C427S521000, C427S578000
Reexamination Certificate
active
06296899
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a repair coating process in order to form multilayer coating films with excellent highly white pearl luster effect, color stability etc.
2. Description of the Related Art
It is already known to form multilayer coating films on an outer panel of a car body etc. by coating with an electrodeposition paint and an intermediate paint and, after curing them, by wet-on-wet coating on the intermediate coating surface with topcoat paints such as a white type water base coat capable of forming a coating film adjusted in the range of Munsell Color Chart N7-N9 with titanium white pigment and aluminium flake, a pearly base coat formed by compounding flake-like mica powder coated with titanium oxide and a clear coat etc., and then by curing by crosslinking these 3-layer coating films simultaneously through heating (for example, U.S. Pat. No. 5,718,950).
In a coating line to form these multilayer coating films on an outer panel of a car body etc., dust may adhere or seediness like projection etc. may generate on the intermediate coating surface and if a topcoat paint is coated as such, finished appearance like smoothness etc. declines which is undesirable. Therefore, it is necessary to previously remove such dust, seediness etc.
Concretely speaking, on the cured intermediate coating film, a part of the coating surface around the point, on which dust, seediness etc. is adhered, is ground spot-wise to remove them. By the grinding usually 20 &mgr;m or more depth of the intermediate coating film (and sometimes a part of the electrodeposition coating film, too) is removed. To the ground part then a repair coating is performed.
As a repair coating process of the ground part there can be mentioned, for example, i) a process to coat a white type water base coat, which would be used at the next step, to the ground part and, leaving it at an uncured state without heat-curing, to coat the same white type water base coat on the whole surface to be coated, ii) a process to coat the intermediate paint, which was used at the previous step, to the ground part and, after curing it by heating, to coat a white type water base coat on the whole surface to be coated, and others.
However, the above-mentioned process i) has a drawback of being prone to generate blistering and/or popping, because the total film thickness of the white type water base coat at the ground part is thicker than that at other unground parts, although a heating step of the repair coating film can be saved. The above-mentioned process ii) does not have such a drawback as mentioned above, but is not favorable in view of shortening process steps, because it contains a heating step.
The main aim of the present invention is to provide a repair coating process, which does not require a heating step and does not generate blistering and/or popping, at the ground part of an intermediate coating film, on which dust, seediness etc. adhered during a process of forming multilayer coating films by coating a topcoat paint such as a white type water base coat, a pearly base coat, a clear coat etc. on a heat-cured intermediate coating surface by a 3-coat-1-bake process, and its characteristic exists in performing a repair coating to the ground part of an intermediate coating film using a specific hydrophilic organic solvent type paint.
SUMMARY OF THE INVENTION
Namely, the present invention provides a repair coating process of multilayer coating films characterized by grinding the part of an intermediate coating surface to be repaired and then performing a repair coating of the ground part with a thermocurable organic solvent type repair paint (F) containing a neutralized product of a hydroxyl group-containing resin having an acid value of 5-100 mgKOH/g and a crosslinking agent in forming multilayer coating films by coating an electro-deposition paint (A) and an intermediate paint (B) and curing them by heating, then, after performing a repair coating on the intermediate coating surface, by successively coating wet-on-wet a white type water base coat (C) capable of forming a coating film adjusted the Munsell Color Chart to be in the range of N7-N9 with titanium white pigment and aluminium flake, a pearly base coat (D) formed by compounding flake-like mica powder coated with titanium oxide and a clear coat (E), and then by curing by crosslinking the films of the above-mentioned coats (C), (D) and (E) simultaneously through heating.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The repair coating process of multilayer coating films of the present invention (hereinafter referred to as “the present repair coating process”) is described in more detail herein below.
Electrodeposition paint (A):
As the electrodeposition paint (A) usually a cationic electrodeposition paint is used. As the cationic electrodeposition paint there can be used generally those, which are known per se, obtained by compounding an aqueous solution or an aqueous dispersion of a salt of a cationic polymer compound with a crosslinking agent and, as necessary, pigments and various additives, and their kinds are not particularly restricted. As the cationic polymer compound, there can be mentioned, for example, those obtained by introducing an amino group(s) in an acrylic resin or an epoxy resin having a cross-linking functional group(s), for example, hydroxyl group, carboxyl group etc., which will be made water-soluble or water-dispersible by neutralization with an organic acid or an inorganic acid. As a crosslinking agent to be used together in order to cure these resins, for example, a blocked polyisocyanate, an alicyclic epoxy resin etc. are preferable.
Electrodeposition coating can be performed by immersing as a negative electrode metallic materials (substrates) such as an outer panel or colored bumper of a car in a bath of the cationic electrodeposition paint and by depositing the above-mentioned resins on these materials by passing current from a positive electrode under the usual conditions. The thickness of an electrodeposition coating film is preferable in the range of usually 10-40 &mgr;m and particularly 15-30 &mgr;m as the cured film. The coating film can be cured by crosslinking through heating generally at 140-220° C. for 10-40 minutes. In the present repair coating process, it is possible to coat an intermediate paint without curing the electrodeposition coating film, but generally it is preferable to coat the intermediate paint after curing the electrodeposition coating film.
Intermediate Paint (B):
Intermediate paint (B) to be coated on the coating surface of the electrodeposition paint (A) comprises a resin component and a solvent as main components, and, as necessary, color pigments, fillers, other additives for paint etc., and contributes to improve the smoothness, image sharpness, gloss etc. of the multilayer coating films to be formed.
Preferable resin component in the intermediate paint (B) is a thermocurable resin composition and specifically includes base resins such as acrylic resin, polyester resin, alkyd resin etc. having a crosslinking functional group(s) (for example, hydroxyl group etc.) in combination with a crosslinking agent such as melamine resin, urea resin, polyisocyanate compound (including blocked product) etc. As the above-mentioned solvent an organic solvent or water can be used.
Intermediate paint (B) can be coated on a crosslink-cured or uncured electrodeposition coating surface by such a method as electrostatic coating, air spray, airless spray etc. Its film thickness is preferable generally in the range of 10-50 &mgr;m, particularly 15-40 &mgr;m as the cured film. The coating film can be cured by crosslinking through heating usually at 100-170° C.
Grinding of the Part to be Repaired:
According to the present repair coating process, after coating and curing of an electrodeposition paint (A) and an intermediate paint (B), a defect in the coating by dust, seediness etc. on the intermediate coating surface is removed by grinding and the part is repaired by coating with a the
Beck Shrive
Kansai Paint Co. Ltd.
Kolb Jennifer
Wenderoth , Lind & Ponack, L.L.P.
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