JPS629405B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for surface modification of plastics, more specifically a method for surface roughening or oxidation of the surface of plastic molded products, and improves secondary processability such as paintability, plating performance, and adhesion to the surface of plastic molded products. The purpose is to Conventionally, when performing secondary processing such as painting, plating, and adhesion on plastic molded products, where the plastic itself has polar groups, a simple pretreatment such as degreasing the surface with a solvent etc. was used. Although sufficient adhesion can be obtained, in order to obtain even more sufficient adhesion, the surface is roughened to provide anchoring properties. On the other hand, for non-polar plastics such as polyolefin, (1) flame treatment, corona treatment,
A method in which polar groups are introduced to the surface by plasma treatment, sulfuric acid-chromic acid mixture treatment, surface grafting using ultraviolet radiation, etc.; (2) a method in which easily eluted substances are blended in advance and the surface layer is formed by etching after molding; (3) A method of physically roughening the surface layer using methods such as sanding to impart anchoring properties. Method (1) has the advantage that the introduced polar group improves the wettability of the surface and at the same time chemically bonds strongly with the paint film, plating film, adhesive, etc., resulting in sufficient adhesion. However, this method requires a large amount of capital investment and increases the number of steps, resulting in an increase in the price of the product. Method (2) has the advantage of obtaining sufficient adhesion due to its excellent anchoring properties, but on the other hand, since the substance to be eluted (e.g. ethylene propylene rubber) is homogeneously dispersed throughout the molded product, the inherent physical properties of the molded product are For example, this method has disadvantages in that it causes a decrease in the bending elastic modulus) and increases the number of steps. Although method (3) is a simple method, it cannot be applied to molded products with complex shapes, has insufficient anchoring properties, and has the drawbacks of requiring additional steps. As described above, conventional surface modification of molded products has been performed after molding, and each method has its advantages and disadvantages. In contrast, the present invention uses an organic peroxide between the surface of a molded product finally formed from plastic (hereinafter referred to as the molded product surface) and the surface of the mold that is in contact with it (hereinafter referred to as the mold surface). It is characterized in that the surface of the plastic molded product is modified at the same time as the molding by interposing the molded product. In other words, by interposing an organic peroxide, which is generally used as a polymerization initiator, crosslinking agent, or oxidizing agent, between the surface of the molded product and the mold surface, the surface of the molded product will be roughened. This brings us to the heading of the present invention. The reason why the molded product surface becomes rough is not clear, but the organic peroxide applied to the mold surface for the purpose of interposing it between the molded product surface and the mold surface is caused by the heat accumulated when the plastic melts, or by heat. It is thought that the heat from the disc causes it to decompose, and the resulting gas oxidizes and roughens the surface of the molded product. The state of surface roughening is shown in FIGS. 1 and 2 as photographs substituted for drawings. FIG. 1 shows the surface of a molded product to which the present invention is applied, and there is a clear difference from the surface of a molded product produced by the conventional method shown in FIG. As the organic peroxide used in the present invention, commonly available ones such as Kent peroxide type, hydroperoxide type, dialkyl peroxide type, diacyl peroxide type, and peroxy ester type can be used. Of course, these organic peroxides can be diluted with an appropriate solvent as necessary, or
Alternatively, even if a chemical that promotes thermal decomposition of the organic peroxide is used in combination, the effect obtained remains the same. The molds used in the present invention include metal molds, wooden molds,
It can be applied to plaster molds and resin molds, commonly called molding molds, and those whose purpose is to form a flat surface, such as a mirror plate. As a method for interposing the organic peroxide between the surface of the molded product and the mold surface, for example, a method of diluting the organic peroxide with an organic solvent and applying it to the mold surface by spraying, brushing, etc. can be applied. . The invention will now be explained in more detail with reference to examples. Example 1 A very thin layer of liquid t-butylperoxy 2-ethylhexanoate was applied to the surface of an injection mold.
A molded article was manufactured using polypropylene (J802H manufactured by Ube Industries). A thick film of acrylic urethane paint (Origin Denki Planet PA) was applied to this molded product.
I spray painted it to a thickness of 20-25μ. After baking the paint film at 80℃ for 30 minutes, leave it at room temperature for 24 hours.
Next, adhesion and moisture resistance tests were conducted. Example 2 Same as Example 1, except that dicumyl peroxide dissolved in toluene at a concentration of 10% is used as the organic peroxide. Comparative Example 1 The same operation as in Example was carried out without applying organic peroxide to the injection mold. Comparative Example 2 After producing a molded article in the same manner as in Comparative Example 1, an organic peroxide was applied to the surface of the molded article, and the operations after application were performed in the same manner as in Example 1. The test results are shown in Table 1.

[Table] Primary adhesion test Cut 10 mm x 10 mm gongs at 1 mm intervals by penetrating the paint film, being careful not to bulge up the underlying polypropylene, and place 25 mm wide cellophane adhesive tape over the goblets. Immediately after applying it, pull it upwards. The results are expressed as a fraction, with the number of closely connected gobans as the numerator and the number before the test as the denominator. Humidity test: The test piece was exposed to a constant temperature and humidity chamber adjusted to 50°C - 98% RH and 70°C - 98% RH, and after a specified period of time.
The sample was taken out at 20+2°C and 65±5%RH, and after 24 hours, the same test as the primary adhesion test was conducted. As mentioned above, most of the conventional surface modification methods only have the effect of introducing polar groups or roughening the surface, and they are carried out in a separate process after molding. By interposing an organic peroxide between the surface of the molded product and the mold surface, it is possible to have both the effects of introducing polar groups and roughening the surface of the molded product through surface oxidation. Now they can be given at the same time. Therefore, it has become possible to significantly shorten the time conventionally spent on surface modification, even to zero in some cases.

[Brief explanation of the drawing]

FIG. 1 is an electron micrograph of the surface of an injection molded product obtained according to the present invention, which is a substitute for a drawing, and FIG. 2 is an electron micrograph of the surface of a conventional general injection molded product, which is a substitute for a drawing.

Claims (1)

[Scope of Claims] 1. A surface of a plastic product characterized in that it is molded with an organic peroxide interposed between the surface of a molded product finally formed from the plastic and the surface of a mold that is in contact with the surface of the molded product. Modification method. 2. The method for surface modification of plastic according to claim 1, wherein the plastic is a polyolefin resin. 3. The method for surface modification of plastics according to claim 1 or 2, wherein the organic peroxide is t-butyl peroxy 2-ethylhexanoate. 4. The method for surface modification of plastics according to claim 1 or 2, wherein the organic peroxide is dicumyl peroxide.