Heat-resistant resins, such as polyether sulfone (hereinafter abbreviated as PES), polyether imide (hereinafter abbreviated as PEI), polysulfone (hereinafter abbreviated as PSF), polyamide imide (hereinafter abbreviated as PAI), polyimide (hereinafter abbreviated as PI), polyphenylene sulfide (hereinafter abbreviated as PPS), polyether ether ketone (hereinafter abbreviated as PEEK), aromatic polyester (hereinafter abbreviated as PER) and polyether ketone (hereinafter abbreviated as PEK), are much superior in heat resistance and mechanical strength to engineering plastics of the general purpose grade, and hence are named super engineering plastics. They find a variety of applications in the field of electric and electonic equipment, machines, automobiles, etc.
Recent progress of technology has however been urging these heat-resistant resins to improve further their properties, particularly mechanical strength.
Thus, it has been practiced to improve the mechanical strength and heat resistance of the heat-resistant resins by blending them with a fibrous reinforcing material, particularly a carbon fiber.
Carbon fibers are being used in large amounts in carbon fiber-reinforced plastics whose matrices are epoxy resins. Hence, epoxy resins are used as binders of carbon fibers. However, although the epoxy resin binders are effective when thermosetting resins such as epoxy resins are used as matrices, their adherence is so poor to the aforesaid heat resistant resins that they hardly produce resin compositions excellent in mechanical strength. For this reason, it has been attempted in the case of thermoplastic resins to use polyamide resins as a binder of carbon fibers, as seen in Japanese Patent Laid-Open No. 106752/1978. Further, a disclosure is made in Japanese Patent Laid-Open No. 120730/1981 to use carbon fibers bound with aromatic polysulfone resins.
As conventional internal combustion engine parts, for example, impellers made of fiber-reinforced resins, there are those described in Japanese Patent Publication No. 48684/1977 and Japanese Patent Laid-Open No. 119105/1982. The resin materials composing the impellers are characterized by incorporating carbon fibers as reinforcing materials of the resins. Particularly, in Japanese Patent Laid-Open No. 119105/1982, it is disclosed that impellers can be prepared from a carbon fiber-reinforced resin in which a heat-resistant thermoplastic or thermosetting resin is used as the matrix resin.
When the above-described carbon fiber bound with an epoxy or polyamide resin is applied to the aforementioned heat-resistant resin, the binder dissociates thermally during molding to form voids or to decrease the strength of the weld part, because the molding temperature of the heat-resistant resin is required to be as high as at least 300.degree. C.
To overcome this problem, carbon fibers bound with aromatic polysulfone resins are used so as to eliminate the formation of voids and the decrease of the strength of the weld part, as seen in Japanese Patent Laid-Open No. 120730/1981. However, the resulting resin compositions show only a small improvement in mechanical strength, and therefore a further improvement in the mechanical strength is desired.
The service conditions of existing internal combustion engine parts, e.g., impellers of centrifugal compressors are in the range of from -50.degree. C. to 200.degree. C. (the highest temperature in usual service: 150.degree. C.) and 13.times.10.sup.4 rpm as the maximum number of revolution. Moreover, the maximum stress generated at the maximum number of revolution amounts to about 20 kg/mm.sup.2 for existing impellers (made of aluminum alloys; with an outer diameter of about 60 mm) and about 10 kg/mm.sup.2 at their blade roots.
It is hence preferable to use a fiber-reinforced resin that has a small specific gravity, because it allows the maximum stress during revolution to decrease to about one half. However, when an impeller material is selected in view of its heat resistance, strength, modulus of elasticity, durability, tension and compression creep characteristics, etc. under such existing service conditions, the thermoplastic or thermosetting resins disclosed in Japanese Patent Laid-Open No. 119105/1982 may not be used as the material unless modified.
As fiber-reinforced resin compositions meeting these conditions, it may be thought of to compound heat-resistant resins including PES, PEI, PEEK, PAI, etc. with carbon fibers, glass fibers, wiskers, etc. However, the aforesaid resins have high glass transition temperatures or melting temperatures so that it is necessary to mold them by melting at temperatures as high as 360.degree. C.-420.degree. C.
As for the carbon fiber in particular, existing commercially available carbon fibers for resin reinforcement employ primarily a thermoplastic polyamide resin (dissociation temperature: 280.degree. C.) and a thermosetting epoxy resin (dissociation temperature: 300.degree. C.) as the surface treating agent (binder). Therefore, at the aforesaid resin melting temperatures (360.degree. C.-420.degree. C.) upon molding, these resins are liable to dissociate, resulting in the reduction of the boundary strength between the carbon fiber and the matrix resin due to insufficient wetting. Further, the resulting molded products are apt to have dispersed strengths. Therefore, when these fiber-reinforced resins are used as an impeller material for centrifugal compressors, the resulting impellers may not effectively be reinforced and cured by the carbon fiber and hence their strength will be low.