Method of forming multi-layered coating film

Abstract

This invention provides a method for forming multi-layered coating film excelling in appearance, corrosion resistance and chipping resistance, which comprises applying a first coloring paint (B), second coloring paint (C) and clear paint (D) onto cured coating film of a specific electrodeposition paint (A) of low weight loss under heating, wet-on-wet by the order stated; and heat-curing the three-layered coating film simultaneously.

Description

TECHNICAL FIELD [0001] This invention relates to a method for forming multi-layered coating film excelling in appearance, corrosion resistance and chipping resistance, which comprises applying a first coloring paint, second coloring paint and clear paint onto cured coating film of an electrodeposition paint, wet-on-wet by the order stated; and heat-curing the three-layered coating film simultaneously. BACKGROUND ART [0002] Coating of metallic shaped articles such as automobile bodies, metallic parts of two-wheeled vehicles, house electric appliances, steel furnitures and the like is normally conducted by the steps of applying an electrodeposition paint, baking the resulting coating film, applying an intermediate coat thereon and baking the same, and then applying a top coat and baking the same to form a multi-layered coating film. However, when baking is performed after application of each of those paints, not only high energy costs are incurred for the baking but also great labor a...

AI Technical Summary

Benefits of technology

[0007] The object of the present invention is to provide a method of forming multi-layered coating film excelling in appearance, corrosion resistance, chipping resistance and so on, while coping with environ mental problems by reducing generation of volatile organic compound in coating metallic objects.

[0008] We have engaged in concentrative studies to now discover that the above object can be accomplished by successively applying a first coloring paint, second coloring paint and clear paint onto cured coating film surface of specific electrodeposition paint of little weight loss under heating, and curing the three-layered coating film by single baking (which procedures may hereafter be referred to as 3-coat-1-bake or 3C1B) and completed the present invention.

[0012] According to the method of the present invention, coated articles with little generation of volatile organic compound and exhibiting excellent appearance, corrosion resistance, chipping resistance and so on can be obtained. Still in addition, because the method of the invention adopts 3C1B system, it can contribute to energy saving and space reduction.

Problems solved by technology

However, when baking is performed after application of each of those paints, not only high energy costs are incurred for the baking but also great labor and costs are required for operation and maintenance of the baking facilities.

This method, however, is subject to a problem that once finishing quality of the electrocoated film which is the undercoat applied before the three layers are formed thereon degrades, that of the multi-layered coating film surface also degrades as influenced thereby.

This method, however, is subject to a problem that costly laser-treated dull steel plate-made shaped articles must be used to secure good finishing quality of perpendicular and horizontal parts, for forming a high quality three-layered coating film by single baking.

While this method can provide multi-layered coating film of good appearance and free of foaming or pinholing, there remains a problem that the multi-layered coating film surface becomes uneven, as affected by unevenness on the electrocoated film surface.

However, because the method as described in the Official Patent Gazette uses, as the cationic electrodeposition paint, a paint containing cationic epoxy resin and blocked isocyanate curing agent, undulation or unevenness result on the electrocoated surface due to volatilization of the blocking agent during the baking for curing the electrocoated film, and when the multi-layered coating film is formed on such an electrocoated film surface by 3-coat-1-bake system of the first coloring paint, second coloring paint and clear paint, the finally formed multi-layered coating film shows degraded appearance, as affected by the unevenness of the electrocoated film.

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