Polyamide resin can express not only high rigidity and high tenacity but also high deflectability under loading when it is reinforced with glass fiber. Therefore, a polyamide resin composition reinforced with glass fiber is widely used as interior and exterior equipments in the fields of electronic/electric devices and automobiles. In recent years, required level of anti-vibration property is becoming high due to a demand for making thickness of the product thin particularly in the field of electronic/electric devices and due to a demand for making size of the vehicle part small. Accordingly, there has been a demand for a thermoplastic resin composition having specific elastic modulus expressed by elastic modulus/specific gravity. In addition, since a molded product of polyamide resin is inferior in weather resistance as compared with a molded product of poly(methyl methacrylate) resin (PMMA), there are many cases wherein weather resistance is imparted to the product during the process after the molding such as coating with paint. Moreover, when the filling amount of glass is 60% by weight or more, weather resistance is significantly deteriorated and it cannot be used particularly as interior and exterior parts for vehicles.
In the Patent Document 1, Nylon 66 base is copolymerized with isophthalamide component which lowers the crystallinity followed by compounding with 60% or more of a reinforcing material such as glass fiber to give a resin composition having an anti-vibration property with high resonance frequency. However, an increase in elastic modulus is not sufficient due to the component which lowers the crystallinity and no good balance between bending elastic modulus and specific gravity for giving the resonance frequency of 200 Hz or more is achieved in a test sample shape. There is also another problem of deterioration of elongation and impact resistance as a result of addition of mica.
In Patent Document 2, there is disclosed a long-fiber polyamide molding material in which polyamide resin is combined with glass roving fibers having a non-circular cross section. However, in Examples of this patent document, glass fibers are not compounded in an amount of 60% or more. Therefore, the ratio of (elastic modulus)/(specific gravity) which is in a proportional relation with resonance frequency is not sufficiently high. As a result, although it is a molding material having high level properties in terms of strength and impact resistance, no sufficient property is expressed so far as anti-vibration property is concerned.
In Patent Document 3, plural resins such as polyamide 6, polyamide 66 and non-crystalline polyamide are used not by means of copolymerization but by means of a blended base, then a reinforcing material is highly filled while the crystallinity is still kept and, further, polypropylene is added thereto in an optimum amount whereupon high resonance frequency is achieved and, at the same time, attenuation property is also imparted. However, as to the current demand for the anti-vibration, resonance frequency of 230 Hz or more is required in the test method of Patent Document 3. When a resin expressing low elastic modulus such as polypropylene is used as a component, it is absolutely impossible to reach the requirement. Accordingly, there has been a demand for a combination of glass fibers with thermoplastic resin which can express higher specific elastic modulus.
In Patent Document 4, there is disclosed a composition showing good weather resistance by addition of inorganic filler, stabilizer and carbon black to a mixed base of aliphatic polyamide with semi-aromatic polyamide. However, adding amount of the inorganic filler is still limited to an extent of 60% by weight and, in Examples, adding amount of the inorganic filler is also in about 50% by weight. Accordingly, in the composition of the Patent Document 4, high anti-vibration property and weather resistance are not compatible.