JPS60217243A - Coating of articles of polyolefinic synthetic resin - Google Patents

Abstract

PURPOSE:Resin articles are treated with cold plasma on their surfaces, cleaned with solvent vapor, and coated with paint to form coating films of markedly increased adhesion. CONSTITUTION:Resin articles of polyolefin are subjected to low-temperature plasma treatment on their surfaces (plasma power, up to several KW; vacuum, several Torr; treating gas, air; treating time, less than 10sec) to activate the surfaces and cleaned with solvent vapor, then coated. The synthetic resin of polyolefin may include fine particles of synthetic rubber powder. The cleaning solvent is trichlorethane. The coating used is a thermosetting type polyurethane.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a method for coating polyolefin synthetic resin products,
More specifically, the present invention relates to an improved method for applying various coatings on the surface of such resin products after activating them by so-called low-temperature plasma treatment.

Polyolefin synthetic resin is lightweight, strong, stable,
In addition to its properties such as durability and ease of processing, it is also cheap and available in large quantities, so it has recently come to be used as a variety of structural materials. However, a disadvantage of polyolefin synthetic resins is that they require pretreatment if they are to be coated with paints of appropriate colors for applications requiring a decorative appearance. Polyolefin synthetic resins generally have poor paint adhesion because they do not have polar groups in their molecular structure, but in order to overcome this drawback, various types of surface coatings have been used in the past for polyolefin synthetic resin products. This method is used to activate and introduce polar groups, and then paint on top of that.

A so-called low-temperature plasma treatment is employed as one of such surface activation treatments before painting.

This method generates excited radicals, ions, and free electrons in the gas by causing a discharge under relatively low processing gas pressure, and when these collide with the surface of the workpiece, the impact occurs. A polar group is introduced by activating the point and causing a direct reaction with, for example, radically excited oxygen in the processing gas.

As one of the above-mentioned uses as a structural material, polyolefin-based synthetic resins, especially polypropylene resin products, are used to replace various parts of automobiles for the purpose of weight reduction. Synthetic resin products are often painted with a suitable paint for reasons of appearance. Conventionally, when applying this coating, the surface of the polyolefin synthetic resin product is first subjected to a surface cleaning treatment by exposing it to vapor of a solvent such as trichloroethane or trichlene, and then subjected to a low-temperature plasma treatment, and then subjected to a painting process. It is being done.

The purpose of the present invention is to further improve the adhesion of the coating film in such a coating method, and in order to achieve this objective, unlike conventional coating methods, the polyolefin synthetic resin product to be coated is first treated with plasma. This is based on the discovery that the adhesion of the coating film is significantly improved when the coating is applied after a surface cleaning treatment using solvent vapor.

That is, according to the present invention, the process order of the coating method is changed from the conventional method, and the plasma treatment is performed first, and then the surface cleaning treatment is performed with solvent vapor such as trichloroethane, and then the painting is applied. It was confirmed that an adhesive strength of about 120 to 140% could be obtained compared to the adhesive strength of the coating film obtained in the above method.

The reason why surface cleaning using solvent vapor after plasma treatment improves the adhesion strength is that if the surface had not been cleaned, contaminants on the surface would have reduced the effectiveness of plasma treatment. This is extremely surprising.

Although the reason why the adhesion strength of the coating film is improved by adopting the pretreatment process sequence according to the present invention is not yet fully clear, it can be considered as follows. That is, in the case of the conventional method, by first cleaning the surface with solvent vapor, the relatively low molecular weight part of the polyolefin synthetic resin absorbs the solvent molecules and becomes 111 wet, and the solvent molecules are removed during plasma treatment. In contrast, with this method, the surface is cleaned with solvent vapor after plasma treatment, so the coating is maintained in a swollen state, creating an anchoring effect and increasing the adhesive strength of the coating. It is thought that it will improve. Another reason is that in the case of conventional methods, the absorbed solvent is released from the inside during plasma treatment, and these solvent molecules shield and prevent the surface activation effect of plasma treatment. It is also possible.

The plasma processing used in the present invention uses, for example, dry air as a processing gas, a vacuum pressure of up to several Torr, a plasma processing time of several tens of seconds, and a plasma output of about several kilowatts.
For example, a conventional plasma processing apparatus using a microwave oscillator can be used as is. Surface cleaning with solvent vapor is also carried out in accordance with the prior art, for example by exposing the article to be coated in trichloroethane vapor for several minutes and washing the surface with the condensed liquid.

The thus pretreated polyolefin synthetic resin product is then coated with various paints, such as thermosetting urethane paint, to a dry coating thickness of several IQgm, and then dried in a drying oven for several tens of minutes. A coated product is obtained by heat treatment.

The adhesion strength of the coating film of the coated product thus obtained showed an improvement of about 20 to 40% compared to the coated product using conventional methods.

The present invention will be explained in detail below using Examples and Comparative Examples.

"Seshibashi" A polypropylene resin flat plate molded product (contains 10% ethylene propylene rubber crushed to a particle size of several gm) for use in passenger cars is subjected to surface cleaning by exposing it to trichloroethane vapor for 2 minutes, and then outputted with ( 1. Low-temperature plasma treatment was performed under the conditions of OKW, vacuum degree of 1.0T..., treatment time of 30 seconds, and dry air as the treatment gas.The thus pretreated molded product was treated with thermosetting urethane. Paint to a dry film thickness of approximately 60p, m,
The painted product was dried for 30 minutes at 120°C. A 50 x 10 mm test piece was cut out from the center of this painted product, a portion of the paint film was peeled off from the longitudinal ends of the test piece, and this paint film was sandwiched with cellophane tape. The peeled portion of the polypropylene base material was fixed to the upper chuck of a tensile tester, and the sellotape with the coating film sandwiched therebetween was fixed to the lower chuck. This corresponds to an improvement in strength at a tensile speed of 50 mm/win.

A paint film peeling test was conducted. An average peel strength of 930 g/cm was obtained.

The same conditions as in the comparative example were adopted, except that the plasma treatment was carried out first and the surface cleaning with trichloroethane vapor was carried out afterwards. The results of the paint film peeling test for products coated under the same coating conditions were an average of 1120 g/Cm. This corresponds to an improvement in peel strength of about 20% compared to Comparative Example 1.

In the plasma treatment of Comparative Example 1, only the degree of vacuum was set to 0.
The same procedure as in Comparative Example 1 was conducted except that the pressure was changed to 2 Torr. The paint film peeling test result of the obtained painted product was 9 on average.
It was 50g/Cm.

Case 1 A coated product was made using exactly the same conditions as in Comparative Example 2 above, except that the plasma treatment was performed first and the trichloroethane treatment was performed afterwards. The resulting product had an average peeling test result of 1350 g/cm.

This is about 42% of the peeling agent compared to Comparative Example 2.

Claims (5)

[Claims] (1) In a painting method in which the surface of a polyolefin synthetic resin product is surface activated by low-temperature plasma treatment and then painted with various paints, pre-painting treatment (surface grating and no-glue caused by solvent vapor during the treatment process) is used. A coating method characterized in that it is carried out after the low-temperature plasma treatment. (2) The coating method according to claim 1, characterized in that the polyolefin synthetic resin contains a mixture of atomized synthetic rubber powder. (3) Low temperature plasma processing with plasma output up to KW, vacuum degree up to Torr, processing gas dry air, processing time 1
2. The method of painting according to claim 1 or 2, characterized in that the painting process is carried out within 0 seconds. (4) The coating method according to any one of claims 1 to 3, characterized in that trichloroethane is used as a surface cleaning solvent. (5) The coating method according to any one of claims 1 to 4, characterized in that a thermosetting polyurethane paint is used for coating.