1. Field of the Invention
The present invention relates to polycarbonate molded articles and a process for the preparation thereof. More particularly, the invention relates to polycarbonate molded article having excellent weather resistance and excellent abrasion resistance, which are prepared by forming a protective layer on the surface of a polycarbonate molded object with an ultraviolet ray setting paint applied through a primer layer, and a process for the preparation of them.
2. Description of the prior art
In general, polycarbonates are superior in their transparency, molding characteristic, impact resistance and other respects, and so they are widely used in various fields. However, their big problem is their inferior weather resistance and poor abrasion resistance of surface compared with other materials.
To solve such problem, various proposals have been made. For example, processes for improving weather resistance are disclosed in Japanese Patent Publication No. Sho 44(1969)-29756, Japanese Patent Laid-open Nos. Sho 53(1978)-119985 and Sho 54(1979)-87774, etc. and processes for improving abrasion resisting property are disclosed in Japanese Patent Laid-open Nos. Sho 57(1982)-162728, Sho 57(1982)-42737 and Sho 54(1979)-11833, Japanese Patent Publication Nos. Sho 54(1979)-28429, Sho 54(1979)-28430, Sho 55(1980)-427 and Sho 54(1979)-37828, etc. In these processes an alkoxyl silane or an acrylic resin was used as the primer and the surface was further treated with an alkoxyl silane of thermosetting type, to make the surface hardness higher and improve the abrasion resisting property.
Further, a process using a product of an ultraviolet ray setting reaction as primer and forming a surface layer thereon with an organosiloxane of thermosetting type is disclosed in Japanese Patent Laid-open No. Sho 55(1980)-148158.
These processes, however, had a defect that a high setting temperature and a long time were required as conditions for curing the surface layer. When an organosiloxane of thermosetting type was used, an unfavorable phenomenon such as flushing was apt to occur depending on the conditions of painting because the organosiloxane easily absorbed the moisture in the air and, accordingly, it was necessary to perform the working under controlling the moisture, which induced a problem of high cost of equipments.
Besides the above-mentioned processes using a paint of thermosetting type, processes for improving the abrasion resistance of polycarbonate molded articles by applying an ultraviolet ray setting paint comprising, for example, a polyfunctional acrylic resin to the polycarbonate molding directly have been also proposed. For instance, a process of hardening by application of heat after the ultraviolet ray irradiation treatment has been proposed in Japanese Patent Laid-open No. Sho 57(1982)-61043 and a process for obtaining polycarbonate moldings having good abrasion resisting property by hardening by cross-linking a resin by means of a special reflection plate in Japanese Patent Publication No. Sho 58(1983)-12295, and materials for the ultraviolet ray setting paints have been disclosed by Japanese Patent Laid-open Nos. Sho 54(1979)-25941, Sho 54(1979)-60390 and Sho 56(1981)-82802, etc.
These ultraviolet ray setting type paints had the merits that the temperature for their curing by cross-linking was lower and the time for their curing by cross-linking was significantly shorter as compared with those necessary for the aforementioned thermosetting type paints.
However, the ultraviolet ray setting type paints had an inconvenience that, when they were applied to plastics, especially to polycarbonate resins, they were inferior in the weather resistance and could not withstand an outdoor use extending for a long time.
One of the purposes of the present invention resides in obtaining polycarbonate moldings having excellent weather resistance as well as excellent abrasion resistance by using such ultraviolet ray setting type paints.
In the case of thermosetting type paints, processes by forming a primer layer containing an ultraviolet ray absorbing agent were hitherto employed in order to improve their weather resistance, and the ultraviolet ray absorbing agent was used in an amount of 10-20% by weight of the resin forming the primer layer. Therefore, it could be thought of theoretically that, also in the case of ultraviolet ray setting type paints, the weather resistance would be improved by forming the same primer layer as used for the thermosetting type paints. This, however, was difficult in practice. That is, when a primer layer containing a relatively large amount as mentioned above of an ultraviolet ray absorbing agent was formed and an ultraviolet ray setting type paint having a good abrasion resistance was applied on the primer layer, the ultraviolet ray absorbing agent contained in the primer bleeded out in the surface layer (the layer of the ultraviolet ray setting type paint) and the interface of the primer and the surface layer in the course or process of drying or the like prior to the curing, and accordingly the curing could not be effected satisfactorily even by irradiation of strong ultraviolet ray on the surface. This would result from some inconvenience such as deterioration of the tight adhesion in the surface layer portion.
Under the circumstances, the inventors have made various investigations and found a process for obtaining polycarbonate molded articles having excellent weather resistance and excellent abrasion resistance economically, by forming on the surface of a polycarbonate molding a protective layer which does not injure the transparency and has an excellent tightly adhesive property.