1. Field of the Invention
The present invention relates to a composite plate material of a thermoplastic resin and reinforcing fibers (hereinafter referred to as FRTP plate) suitable in use for molding various products constructed from a composite material of the thermoplastic resin and reinforcing fibers (fiber reinforced thermoplastics, hereinafter referred to as FRTP) by stamping or press flow molding method etc., and relates to products molded out of the composite plate material or materials (hereinafter referred to as FRTP products).
2. Description of the Prior Art
Various FRTP plates are known. There are two types of FRTP plates, using excessively long reinforcing fibers and using excessively short reinforcing fibers. Typical FRTP plate of the former type comprises unidirectionally oriented reinforcing fibers, or reinforcing fibers formed as a fabric or a swirl mat. Typical FRTP plate of the latter type comprises reinforcing fibers formed as a chopped strand mat formation. Although both types of FRTP plates have respective characteristics, recently the former having higher mechanical properties has been more noted than the latter from the viewpoint of use of FRTP material for various mechanical parts which has been broadly developed.
The former type of FRTP plates, which use excessively long reinforcing fibers, are disclosed in, for example, JP-B-63-37694 and JP-A-60-36136. The FRTP plates disclosed in these publications are composites of thermoplastic resins and reinforcing fibers orientated in one direction parallel to one another in the form of a sheet. Since the reinforcing fibers are unidirectionally orientated in these FRTP plates, they are very suitable in the case where a product to be molded requires a directivity in its mechanical properties. However, in the case where a quasi isotropy is required for the mechanical properties of a product to be molded, it is required that a plurality of the FRTP plates must be laminated and arranged so as to gradually shift the directions of the reinforcing fibers of the laminated plates when the product is molded. In this molding, if the lamination structure of the FRTP plates is not adequately determined, the anisotropic properties of the molded product increase.
The FRTP plates of reinforcing fibers formed as a fabric or a swirl mat are disclosed in, for example, the above-described JP-B-63-37694, JP-B-48-8468 and JP-B-48-9958. The FRTP plates having these formations in reinforcing fibers have anisotropies smaller than those of the FRTP plates using unidirectionally orientated reinforcing fibers. However, the FRTP plate of reinforcing fibers formed as a fabric is not suitable for molding an FRTP product having a complicated shape such as a shape having many curved surfaces and/or many corners even if an FRTP product having a simple shape such as a plane plate can be easily molded, because the structural stability of a fabric, wherein warp fibers and weft fibers cross crimp each other, is high, and therefore, the fittability of the FRTP plate in molding to a complicated shape is not good. Also in the FRTP plate of reinforcing fibers formed as a swirl mat, the fittability thereof is not good though the anisotropic properties thereof are smaller than those of the FRTP plate of a reinforcing fiber fabric. Therefore, it is difficult to uniformly distribute the reinforcing fibers in a molded FRTP product because the reinforcing fibers of the FRTP plate lack in fluidity during molding.
On the other hand, the FRTP plate of excessively short reinforcing fibers formed as a chopped strand mat has an excellent fittability higher than that of any above-described FRTP plate, and can be relatively easily served to mold an FRTP product having a complicated shape. However, since the reinforcing fibers are short and it is difficult to increase the volume content of the reinforcing fibers in the FRTP plate or the FRTP product, the reinforcement effect due to the reinforcing fibers cannot be greatly increased, and therefore, the mechanical properties of the molded FRTP product are not high.
To solve such a problem, JP-A-59-62112 proposes that, after a thermoplastic resin is impregnated into or applied on the bundle of reinforcing fibers, the bundle including the thermoplastic resin is cut to many bundle pieces each of which has an excessively long length comparing to its width, the bundle pieces are disposed in a required form and the disposed bundle pieces are heated and pressed. According to this process, the thermoplastic resin is impregnated into the reinforcing fibers more completely and the volume content of the reinforcing fibers can be increased to some extent. Therefore, the mechanical properties of the molded FRTP product using the bundle pieces also can be increased to some extent. However, the degree of the increase is not sufficient to satisfy the objects of the present invention at all.
Moreover, the common problem in FRTP materials or FRTP products comprising relatively short reinforcing fibers is that the impact resistance thereof is relatively low.