A decorative resin-molded article decorated by laminating a decorative sheet provided on the surface of a molded article is used in various applications such as automotive interior parts. The method of forming such a decorative resin-molded article includes insert molding in which a decorative sheet is previously three-dimensionally formed with a vacuum forming mold, and then the molded sheet is inserted in an injection mold and then a fluidized resin is injected in the injection mold to integrate this resin with the molded sheet (for example, Patent document 1); and simultaneous injection-molding and decorating in which a decorative sheet inserted in a mold is integrated with a melted resin injected in a cavity during injection molding to decorate the surface of the resin compact (for example, Patent documents 2 and 3).
The above-mentioned decorative resin-molded article is provided with a surface protection layer in order to improve the damage resistance on the surface. However, the above-mentioned method of forming such a decorative resin-molded article has a problem in the process of three-dimensionally forming a decorative previously sheet with a vacuum forming mold in insert molding and in the process of drawing and firmly attaching a decorative sheet along the inner periphery of the cavity during preforming or during injecting a melted resin in simultaneous injection-molding and decorating. Specifically, the decorative sheet will be drawn more than minimum requirement to fit the shape of the mold due to the effect of vacuum or compressed air or due to the tension or the like generated by the pressure and the shear stress of the melted resin, resulting in a crack generated on the surface protection layer of the curved surface of a molded article.
To approach the above-mentioned problem, an ionizing radiation curable resin such as an ultraviolet curable resin has been used as the surface protection layer for increase the cross-link density of the resin forming the surface protection layer of a decorative sheet so as to attempt to improve the abrasion resistance and the damage resistance of the surface of a decorative molded article. However, the problem of a crack generated on the curved surface of a molded article during the forming still exists.
Alternatively, an ionizing radiation curable resin such as an ultraviolet curable resin used as the surface protection layer has been attempted to be half-cured at the stage of a decorative sheet and then fully cured after decorative molding (Patent document 4). However, problems are created, in which the surface protection layer containing an uncured resin component is easily damaged and hardly handled and in which the mold is contaminated due to the uncured resin component adhering to the mold. To solve these problems, a protection film may be provided on a half-cured surface protection layer. However, this complicates the manufacturing process and causes the cost increases.
USPTO Backgrounds
USPTO Backgrounds