JPH022893B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for coating polyamide molded articles. In particular, the present invention relates to a method for forming a coating film with high adhesion on a polyamide molded article containing an ionomer.

In recent years, there has been rapid progress in replacing metal automotive exterior parts with plastic molded products, particularly polyamide molded products, which are engineering plastics. Polyamide molded products for automobile exterior panels are required to have impact resistance, and as a means to meet this requirement, it has been proposed to blend polyamide with an impact resistance improver, ionomer, or even ethylene-propylene rubber. . However, polyamide molded products containing ionomers have poor adhesion to paint films formed by melamine alkyd, acrylic melamine, or acrylic urethane paints, which are widely used as paints for automobile exterior panels. The drawback is that it is not sufficient.

Japanese Patent Publication No. 58-1689 describes a method of applying a paint containing metal powder to the surface of a plastic molded product containing polyamide, and then applying a topcoat to give the plastic molded product permanent antistatic properties. is listed. However, this publication does not describe a polyamide composition containing an ionomer or a method for forming a coating film with high adhesion using this composition. Although there is no direct description of the mixing ratio of metal powder in the above publication, in column 4, lines 31 to 36, it is stated that metal powder is added so that the surface resistivity after topcoating is 10 ¹² Ω or less. There is a statement that it is necessary to incorporate it into paints. As described later, the surface resistivity of the coated product obtained by the present invention is 10 ¹³ Ω or more.

An object of the present invention is to provide a method for forming a coating film with high adhesion on the surface of a polyamide molded article containing an ionomer.

The present invention is a method for coating a polyamide molded product, which is characterized in that a paint containing 1 to 7% by weight of metal powder based on the resin content in the paint is applied to the surface of a polyamide molded product containing an ionomer. be.

As used herein, "paint" includes both primers and top coats.

Specific examples of polyamides include polylactams such as nylon 6, nylon 11, and nylon 12, polyamides obtained from dicarboxylic acids and diamines such as nylon 66, nylon 610, and nylon 612, nylon 6/66, and nylon 6/610. , nylon 6/
12, copolymerized polyamides such as nylon 6/612,
Mixtures of these may be mentioned.

The ionomer used in the present invention is a thermoplastic resin in which molecules consisting of long chains are linked by ionic bonds, and the carboxyl group of each molecule is usually cross-linked with monovalent or polyvalent metal ions. Has a structure. Typical ionomers include copolymers of unsaturated hydrocarbons such as ethylene, propylene, and butylene and unsaturated carboxylic acids such as maleic acid, acrylic acid, and methacrylic acid; Copolymers of saturated carboxylic acids and alkyl esters of unsaturated carboxylic acids can form monovalent metal ions such as sodium and potassium, or polyvalent metal ions such as calcium, magnesium, barium, zinc, iron, copper, and silver. Mention may therefore be made of thermoplastic resins which are crosslinked. Specific examples include Surlyn (registered trademark) manufactured by DuPont, Himilan (registered trademark) manufactured by Mitsui Polychemicals, and Corporen (registered trademark) manufactured by Asahi Kasei.

The amount of ionomer used is preferably 1 to 400 parts by weight, particularly 10 to 100 parts by weight, per 100 parts by weight of polyamide.

In addition to the above-mentioned ionomer, the polyamide molded article of the present invention can contain ethylene-propylene rubber and an inorganic filler.

As the ethylene-propylene rubber, various conventionally known ethylene-propylene rubbers can be used, but those with a propylene content of 20 to 30
% by weight is preferably used. Further, the ethylene-propylene rubber may contain other copolymer components, such as ethylene-propylene-diene rubber. When ethylene-propylene rubber is used in combination with an ionomer, it is preferred to use 1 to 400 parts by weight of the ionomer and 1 to 15 parts by weight of ethylene-propylene rubber per 100 parts by weight of polyamide.

Specific examples of inorganic fillers include natural silicon compounds such as quartz, asbestos, diatomaceous earth, and mica, metal oxides such as titanium oxide, zinc white, and alumina, barium sulfate, calcium sulfate, calcium carbonate, and calcium silicate ( wollastonite), metal salts such as magnesium carbonate, magnesium silicate (talc), and white lead, inorganic mixtures such as kaolin, clay, and glass, metal fibers such as iron, aluminum, and brass, other carbon fibers, and potassium titanate fibers. , glass fiber, etc. Among these, talc, kaolin, calcium silicate, etc. are conveniently used. The amount of inorganic filler used is
It is preferably 150 parts by weight or less, particularly 10 to 100 parts by weight, per 100 parts by weight.

The polyamide molded article used in the present invention may further contain known additives, such as heat-resistant agents, ultraviolet absorbers, flame retardants, lubricants, plasticizers, nucleating agents, coupling agents, stabilizers, and pigments.

As the paint, a wide variety of what are generally called synthetic resin paints can be used, but among them, melamine alkyd paints, acrylic melamine paints, and acrylic urethane paints, which are often used as paints for automobile exterior panels, are preferably used. Ru.

Specific examples of metal powder include aluminum, silver,
Examples include fine powders of copper, zinc, brass, iron, etc. The particle size of the metal powder is preferably 10 to 50μ.

The amount of metal powder mixed is based on the resin content in the paint.
It is 1 to 7% by weight, preferably 2 to 5% by weight.
If the blending amount is less than the lower limit, it will not be possible to form a coating film with strong adhesion on the surface of the polyamide molded product, and even if the blending amount is larger than the upper limit, the adhesion of the coating film will not be further improved. This is industrially disadvantageous, as the price of paint increases. As mentioned above, the surface resistivity of the coating film obtained by the present invention is 10 ¹³ Ω or more.

As a method for applying the paint to the surface of the polyamide molded article, known methods such as brush coating, spray coating, dip coating, flow coating, etc. can be employed.

Examples are shown below. The adhesion between the polyamide molded product and the paint film is determined by cutting lines on the paint film at intervals of approximately 1 mm in both the vertical and horizontal directions to form a checkerboard pattern, adhering the adhesive tape onto the cut lines, and then peeling off the adhesive tape. Evaluation was made based on the peeling state of the coating film. The evaluation criteria are as follows.

A: The paint film does not peel easily.

B: Part of the coating film peels off along the incision line.

C: Part of the coating film was completely peeled off.

D: The entire surface of the coating peels off.

In the following description, all "parts" are "parts by weight"
shows.

Example 1 65 parts of nylon 6 (relative viscosity: 2.9), ionomer [manufactured by Mitsui Polychemical Co., Ltd., Himilan 1855] 28
and 7 parts of ethylene-propylene rubber (propylene content: 26% by weight) was melt-kneaded using a twin-screw extruder at a cylinder temperature of 260°C, pelletized, and then dried under reduced pressure at 110°C for 24 hours. . The obtained pellets were molded using an injection molding machine at a cylinder temperature of 260°C to obtain test pieces of 75 x 125 x 3 mm.

An acrylic melamine paint (Belcoat, produced by NOF Corporation) containing approximately 4% by weight of aluminum powder based on the resin content in the paint was applied to an absolutely dry test piece to a film thickness of 25 to 30 μm. Apply at room temperature for 10 minutes, then heat at 140℃.
Baking was carried out for 30 minutes.

The adhesion of the resulting coating film was "A".

Comparative Example 1 Example 1 was repeated except that an acrylic melamine paint containing no aluminum powder (Belcoat Clear, manufactured by NOF Corporation) was used.

The adhesion of the resulting coating film was "C".

Example 22 A test piece was prepared in the same manner as in Example 1, except that the amount of nylon 6 used was changed to 45 parts, and 20 parts of short glass fibers were used.

Apply acrylic melamine paint [Super Rack, manufactured by Nippon Paint Co., Ltd.] containing approximately 3% by weight of aluminum powder to the resin content to a film thickness of 25 to 30μ on an absolutely dry test piece. Apply and set at room temperature for 10 minutes, then heat to 140℃.
Baking was carried out for 30 minutes.

The adhesion of the resulting coating film was "A".

Comparative Example 2 Example 2 was repeated except that an acrylic melamine paint (Belcoat Clear, manufactured by NOF Corporation) containing no aluminum powder was used.

The adhesion of the resulting coating film was "C".

Example 3 Example 1 was repeated except that the amount of nylon 6 used was changed to 40.5 parts, and 4.5 parts of wollastonite were used.

The adhesion of the resulting coating film was "A".

Example 4 A test piece obtained in the same manner as in Example 2 was coated with an acrylic melamine paint containing about 4% by weight of aluminum powder as a primer based on the resin content [Belcoat, manufactured by NOF Corporation]. ] was applied to a film thickness of 20 to 30 μm, set at room temperature for 10 minutes, and then baked at 140° C. for 30 minutes. Then, as a top coat, the above-mentioned acrylic melamine paint or melamine alkyd paint containing no metal powder [Melami, manufactured by Nippon Oil & Fats Co., Ltd.]
was applied to a film thickness of 25 to 30μ and left at room temperature.
After setting for 10 minutes, baking was performed at 140°C for 30 minutes.

The adhesion of the resulting coating films was rated "A" in all cases.

Claims (1)

[Claims] 1. A method for coating a polyamide molded product, which comprises applying a paint containing 1 to 7% by weight of metal powder based on the resin content of the paint onto the surface of a polyamide molded product containing an ionomer.