Chemistry: electrical and wave energy – Processes and products – Electrophoresis or electro-osmosis processes and electrolyte...
Reexamination Certificate
2001-01-29
2002-11-05
Mayekar, Kishor (Department: 1741)
Chemistry: electrical and wave energy
Processes and products
Electrophoresis or electro-osmosis processes and electrolyte...
C204S486000, C204S505000, C029S460000
Reexamination Certificate
active
06475365
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a car body coating process wherein the metal-exposed portion of shell body of a car body, a part or whole of which has been made of plastics-covered metal plates, is electrocoated with use of an electrodeposition paint which contains no coloring pigment and has a bath solid content of at most 10% by weight and which is capable of forming a clear coating film.
In the body of passenger car or of small passenger car, the portion which is mainly constituted of sheet metal and which is free of riggings such as engine or wheels is called shell body. Shell body is usually constituted of a main body, which consists of underbody, side member, roof, cowl, upper back, lower back, etc., and outer cover parts such as hood, front balance, front fender, cowl louver, door, luggage (back door), etc.
Up to the present, metal plates which have been cut and molded in the size and shape of each component part have been assembled to form main body and outer cover parts, which in turn are combined to make a shell body, which is dipped into a cationic electrodeposition paint bath so that the surface, backside, edge surface portion, etc., of the metal plates may be electrocoated, and, thus, the shell body is coated with a primer film.
Usually, after conducting this electrodeposition, water-washing is carried out several times with use of ultrafiltration filtrate, deionized water, tap water, etc., so as to remove superfluous electropaint which has adhered to the electrocoated surface or electropaint which has collected in the interior of bag-like portion. Then, heating is conducted so that thus formed coating film may be cured. Outside portions of shell body are coated with intermediate paint and topcoat paint.
In car body coating, however, cutting down of effluent from the process of water-washing of electrocoating film has recently been strongly desired for the sake of step saving, energy saving and CO
2
reduction in the coating line, and for the preservation of environment. Moreover, there has further been desired improvement not only in throwing power of electrodeposition paint to edge surface portion, but also in chipping resistance, corrosion resistance, etc., of total coating film including intermediate coating and top coating.
In the coating of a car body, on the other hand, there is proposed an inverse method (for example, Japanese Pre-grant Patent Publication No. 41317/1980), in which a substrate is powder-coated and the resulting coating film is cured, and, thereafter, the uncoated portion is electrocoated, for the purpose of the reduction of organic solvent discharged and the improvement of edge surface coatability of electrodeposition paint. This method has, however, such problems that powder coating facilities need to be newly provided, and that the corrosion resistance of the boundary portion between powder coating film and electrodeposition coating film is not sufficient.
The chief objective of the present invention is to provide a car body coating method which satisfies the above-mentioned requirements in car body coating and which ls free of the above-mentioned defects.
BRIEF SUMMARY OF THE INVENTION
As a result of assiduous study, the inventors of this invention have found that the above-mentioned objective can be attained by making a part or whole of shell body by using previously prepared metal plates covered with plastics layer, and then electrocoating the metal exposed portion of thus made shell body with an electrodeposition paint which contains no coloring pigment and has a bath solid content of at most 10% by weight and which is capable of forming a clear coating film, and, thus, have completed this invention.
Thus, according to the present invention, there is provided a car body coating process (hereinafter referred to as Process I) which is characterized in that main outer parts of a car body is made of plastics-covered metal plates to form a shell body, and that the metal exposed portion of the shell body is electrocoated with an electrodeposition paint which contains no coloring pigment and has a bath solid content of at most 10% by Weight and which is capable of forming a clear coating film.
According to the present invention, there is also provided a car body coating process (hereinafter referred to as Process II) which is characterized in that car parts which have been made by cutting, molding and joining plastics-covered metal plates are attached to the main outer portions of main body of a car body which has previously been assembled, and that the metal exposed portion of thus formed shell body is electrocoated with an electrodeposition paint which contains no coloring pigment and has a bath solid content of at most 10% by weight and which is capable of forming a clear coating film.
The car body coating processes of the present invention are described in more detail in the following.
DETAILED DESCRIPTION OF THE INVENTION
The processes of the present invention can be applied mainly to normal and small passenger car, but can also be applied to truck, bus, motorcycle, and specially equipped vehicles in the same manner.
As a metal plate to be covered with plastics, metals which have heretofore been used for car body can be similarly used. As the material of metal, there may be mentioned, for example, iron, steel, stainless steel, aluminium, copper, and alloys containing these metals, and, furthermore, plate of these metals whose surface is plated with zinc, zinc
ickel, iron, etc. For use, they can be processed into coils or cut plates. The thickness of these metal plates is suitably in the range of 0.3 to 2.0 mm, particularly 0.5 to 1.0 mm. The surface of these metal plates is preferably subjected to suitable treatment such as grinding treatment, degreasing treatment or phosphate treatment with a view to improvement in adhesivity with plastics layer, corrosion resistance, etc.
As plastic materials to cover the above-mentioned metal plates, there can be used known thermoplastic resins, for example, polyolefin resin such as polyethylene and polypropylene; polyester resin such as polyethylene terephthal ate (PET); polycarbonate resin; epoxy resin; vinyl acetate resin; vinyl chloride resin; fluorine-containing resin; polyvinyl acetal resin; polyvinyl alcohol resin; polyamide resin; polystyrene resin; acrylic resin; polyurethane resin; phenolic resin; polyether resin; cellulose type resin; etc. These plastic materials may contain color pigment, extender pigment, etc.
Covering of a metal plate with these plastics materials can be performed by known methods, which include sticking, onto metal plate, film- or sheet-like plastics formed by such a method as extrusion molding, injection molding, calender molding or compression molding; sticking with pressure, onto metal plate, molten plastics extruded into film or sheet; adhering plastics in powder form onto metal plate by methods such as fluidized immersion, electrostatic coating, etc. and then melting by heating. Particularly preferable is the process of sticking plastics in film er sheet form onto metal plate. Covering of a metal plate with plastics is performed at least on the surface of a metal plate located at outer side of a car body. However, it is possible to cover both surfaces, if desired. The thickness of the plastics layer covering a metal plate is preferably in the range of usually 1 to 100 &mgr;m, particularly 3 to 75 &mgr;m, more desirably 5 to 50 &mgr;m. Moreover, it is possible to treat the surface of these plastics by corona discharge, plasma, flame, etc., before or after the covering onto the metal plate.
When a metal plate is to be covered with plastics by means of sticking film-like or sheet-like plastics onto the metal plate, it is preferable to previously apply an adhesive to the metal plate and/or to plastics film or sheet in order to increase adhesivity between the two. As such an adhesive there may be mentioned thermosetting or thermoplastic adhesives containing one or more kinds of resins selected from, for example, bisphenol type epoxy resin
Hiraki Tadayoshi
Tominaga Akira
Watanabe Tadashi
Yawata Takeshi
Kansai Paint Co. Ltd.
Mayekar Kishor
Wenderoth , Lind & Ponack, L.L.P.
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