Until now, coating application on the surface of a molded article has been widely carried out in order to give an additional value such as decoration properties or the like to resin molded articles used for automobiles, electrical appliances or building materials, or to prolong the lifetime of products by enhancing weathering resistance.
As such a coating method, it is general to employ a spray coating method. Recently, the environmental problems have been strongly concerned, so that the urgent development of a technique in place of spray coating has been desired. This is because there is a tendency to set a strict limit to release of hazardous organic substances discharged from various factories to the atmosphere, and is from the standpoint of making much of the health care for employees. Under the circumstances, noted is a method of coating and molding in the mold such that a paint is injected into between the surface of a resin molded product molded in a mold and the mold cavity surface, this paint is cured in the mold, and thereby a monolithic molded article wherein the coating is adhered on the surface of the resin molded product is prepared (in-mold coating, hereinafter referred to as “IMC”). It is expected that this IMC method not only improve the quality of the molded article's surface by adhering a coating on the surface but also decrease costs by decreasing the coating steps.
By reason that the paint used for in-mold coating molding of a thermoplastic resin is desired to have curing properties capable of curing at a temperature lower than the curing temperature of a paint for thermosetting resins, it is generally difficult to develop a paint having both of coating appearance and adhesion. Therefore, paints which have been already developed as a paint used for the in-mold coating molding method are limited to paints used for thermosetting resins and paints used for some thermoplastic resins such as nylon, ABS resins and the like. On this account, the kind of synthetic resins applicable to the in-mold coating molding method is limited to the thermosetting resins or some thermoplastic resins such as nylon, ABS resins and the like at present. Further, it has been considered that it is technically difficult in the structure of the resins to develop paints having sufficient adhesion to olefin resins such as polypropylene resin or polyethylene resin.
Furthermore, it is also difficult in the structure of olefin resins such as polypropylene resin or polyethylene resin to adhere the paint to the olefin resins even by the general spray coating method. Therefore, for the olefin resins, a method of coating the resin surface with an intermediate layer such as primer or the like and then coating the coated primer surface with a paint is employed.
Accordingly, it has been considered that it is technically very difficult to develop a polypropylene resin composition having sufficient coating adhesion in an in-mold one-component coating molding method such as IMC.
As a method of applying the in-mold coating molding method to the polyolefin resin, JP-A-2001-170964 discloses a method such that on the polyolefin resin surface, a skin material having good adhesion with a paint is molded with lamination, the paint is injected into between the surface of the skin material and the mold cavity surface to thereby prepare a molded article with a coating monolithically formed on the polyolefin resin surface through the skin material.
Under the circumstances, the present inventors have earnestly been studied and found that using a paint for in-mold coating prepared by adding in a specific ratio acryl modified chlorinated polyolefin containing a specific amount of chlorine, an organic peroxide and polyisocyanate to a vehicle component comprising an oligomer having a (meth)acrylate group and an ethylenically unsaturated monomer capable of copolymerizing with the oligomer, and a hydroxyl group-containing polypropylene resin composition having a specific hydroxyl value and containing a specific amount of rubber components, there can be obtained an in-mold coating molded article that the above paint for coating is monolithically formed on the surface of the resin molded product of the polypropylene resin composition, which is a polyolefin resin, in such a state as to have good adhesion. Accordingly, the present invention has been accomplished.