JPS59169579A - Manufacture of metal formed body for vehicle - Google Patents

Abstract

PURPOSE:To obtain the titled plastic metal body for a vehicle which does not deteriorate in external appearance, while inhibiting the formation of bubbles, by forming an epoxy resin coating film on the surface of a metal formed body by a cation electrodeposition method, and baking it above the baking temp. of polyamide resin to be applied thereon but below a specified temp. CONSTITUTION:An undercoat film of 10-50mum in thickness, for instance, is formed on the surface of a plastic metal body by a cation electrodeposition method using epoxy resin paint. Then, said undercoat film is baked at a temp. above the baking temp. of polyamide resin in the following step but below 250 deg.C. Thereafter, a powdery polyamide resin body is applied onto the baked coating film by an electrostatic coating method, for instance. Then, the applied powdery polyamide resin body is baked and melted above its melting point by the same method as that in a conventional manner, to form a coating film. The baking temp. at this time is above the melting point of the polyamide resin but below 250 deg.C, pref. 215+ or -5 deg.C. As a result, the obtd. finished product being free from bubbles exhibits excellent external appearance.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a metal molded article for a vehicle, and more particularly to a method for manufacturing a metal molded article having a molten coating of powder resin formed on its surface.

BACKGROUND OF THE INVENTION Some metal molded products for vehicles, such as outer panels and exterior parts of automobiles, have a molten coating of powder resin formed on their surfaces in order to provide anti-corrosion properties and decorative properties.

Polyamide resin is used as the powder resin, and this resin is directly melted and baked on a metal plate such as iron to form a film, which is used for coating and undercoating.

Conventional undercoating uses a polypucdiene paint to form a coating film by an anionic electrodeposition coating method, but the rust-preventing power of the coating film is not high. In recent years, particularly high rust prevention power has been required, so instead of the conventional anionic electrodeposition coating, undercoating is performed by a cationic electrodeposition coating method using an epoxy resin paint.

The conventional method of using epoxy resin paint is to form an epoxy resin coating film by cationic electrodeposition coating method, and then
The optimum curing temperature for epoxy resin is 170-180℃
The polyamide resin powder is baked on the baked coating film at a temperature higher than the melting temperature of the polyamide resin at 20°C.
It was baked at 0 to 215°C to form a molten polyamide resin film.

However, in such conventional manufacturing methods,
When the thickness of the polyamide resin film was increased, many minute bubbles were generated on the outer surface, which caused a problem in that the appearance was significantly impaired.

This invention was made by focusing on the conventional problems such as σ mentioned above, and after forming an epoxy resin coating film, baking is performed at a temperature higher than the firing temperature of polyamide resin and lower than 250°C, thereby solving the above problems. It aims to solve the problem.

This invention involves forming an epoxy resin coating on the surface of a metal molded product using a cationic electrodeposition coating method, and then baking it.
In a method in which polyamide resin powder is attached to a coating film and baked at a temperature higher than the melting temperature of the polyamide, the epoxy resin is baked at a temperature higher than the baking temperature of the polyamide resin.
This is a method for manufacturing metal molded products for vehicles, which is characterized in that it is carried out at a temperature of 50°C or lower.

An investigation into the cause of air bubbles occurring on the outer surface of molded products using conventional methods revealed that when polyamide resin is baked, the epoxy resin in the undercoat decomposes and is baked with water, but then the polyamide resin is heated to a higher temperature. In order to bake the resin, the epoxy resin decomposes and the generated hydrogen collects at the interface with the polyamide resin layer, forming bubbles.

Therefore, we investigated a method to prevent the generation of bubbles, and found that if the undercoat film is baked at a temperature higher than the baking temperature of the polyamide resin, the epoxy resin will not decompose even if the polyamide resin is baked as a post-process. I understand. The optimal hardening wet layer of epoxy resin is 170 to 180°C, and baking is generally performed at a temperature within this range.
Baking at temperatures higher than this range will cause deterioration of the coating.

However, it has been found that as long as the molded product is used as a molded product for vehicles, it can be used as long as baking is performed at a temperature of 250° C. or lower, as it has good adhesion to molecules and anti-corrosion properties.

Therefore, in the present invention, the baking temperature of polyamide resin is 25°C or higher.
The undercoat film is baked at a temperature below 0°C.

The undercoat film is formed by a cationic coating method using an epoxy resin paint, as in the conventional method. It is also the same as the conventional method that degreasing, washing with water, chemical conversion coating treatment, etc. are carried out prior to forming the undercoat film. The thickness of the undercoat film is not particularly limited, and may be, for example, 10 to 50 μm.

The undercoat film thus formed is baked at a temperature above the baking temperature of the polyamide resin in the subsequent process and below 250°C, but the temperature is higher than the baking temperature of the polyamide resin.

It is preferable to carry out baking at a temperature higher than 10°C, and in this case, a temperature higher than the baking temperature of the polyamide resin by 10°C or more is desirable. The baking time is the same as in the conventional method, and is approximately 20 to 40 minutes.

Next, the method for attaching polyamide resin powder onto the baked coating film may be the same as the conventional method, for example, by electrostatic coating method,
Electrostatically deposit polyamide resin powder. The particle size of the polyamide resin powder can be, for example, 80 to 160 μm.

The attached polyamide resin powder can be melted and formed into a film by baking at a temperature higher than its melting temperature as in the conventional method. The baking temperature at this time is the basis for determining the baking temperature of the undercoat film, and is the melting temperature of the polyamide resin or higher and 250°C or lower, and is 215±
It's 5 degrees Celsius.

The baking time is about 60 to 50 minutes. The finished product has a foam seal and an excellent appearance.

The molded product to which the present invention is applied is a metal molded product for vehicles, and is particularly suitable for manufacturing outer panels and exterior parts of vehicle bodies where corrosion resistance is a problem. In addition, epoxy-based paints are mainly made of epoxy resin, and in addition to the epoxy resin alone, they may also contain other resin components such as phenol-fit, alicyclic, etc., and harden amines, polyamides, etc. Those conventionally used, such as those used as agents, can be used. As the polyamide dark resin, conventionally used materials such as nylon 6.11.12.66 can be used.

As explained above, according to the present invention, after forming an epoxy dark fat coating on a metal molded product, baking is performed at a temperature higher than the baking temperature of the polyamide resin and lower than 250°C, and then the polyamide Since the resin powder is attached and baked, the epoxy resin does not decompose when the polyamide resin is baked, and there is no deterioration in appearance due to the generation of bubbles.

Next, embodiments of this invention will be described.

Example After a steel plate garnish was subjected to a degreasing process, a water washing process, a zinc phosphate chemical conversion coating process, a water washing process, a pure water washing process and a drying process, an epoxy resin paint (Kansai Paint K
Nireclone 9200 (manufactured by K) and Powercoat U60 (manufactured by Nippon Paint KK) were coated with 20% by cationic electrodeposition coating method.
A µm primer coating film is formed, baked for 60 minutes at various temperatures, and then a polyamide resin (nylon 11) with a particle size of 80 to 160 µm is attached by electrostatic coating.
Baking was performed at 215° C. for 40 minutes to form a melted and baked film, which was then air-dried to obtain a finished product.

The following table shows the appearance of the finished product depending on the baking temperature of the undercoat film. In the table, × indicates that the surface of the finished product has a large number of bubbles and the appearance is poor, O indicates that the surface of the finished product is homogeneous and has no bubbles and has a good appearance, and Δ indicates that the appearance is intermediate between the two.

From the above results, it can be seen that the baking temperature of the undercoat film is preferably higher than the baking temperature of the polyamide resin and 250° C. or less.

Agent: Patent attorney Sei Yanagi Hara

Claims (1)

[Claims] (1) An epoxy resin coating film is formed on the surface of a metal molded product by a cationic electrolyte coating method, and after baking, polyamide resin powder is attached on the coating film, and polyamide resin powder is attached on the coating film. In the method of baking the epoxy resin at a temperature higher than the melting temperature of polyamide resin,
A method for manufacturing a metal molded product for a vehicle, characterized in that the manufacturing method is carried out at a temperature of 50°C or lower. (2) The degree of burnout of the epoxy resin coating is 225 to 2.
The method for manufacturing a metal molded article for a vehicle according to claim 1, wherein the temperature is 50°C. (6) Baking temperature of epoxy resin coating is 200±5
The method for manufacturing a metal molded article for a vehicle according to claim 1, wherein the temperature is .degree. (4) Baking temperature of polyamide resin powder is 215±5
The method for manufacturing a metal molded article for a vehicle according to any one of claims 1 to 6, wherein the temperature is .degree.