Known as synthetic resins having well-balanced properties between rigidity and impact strength are polycarbonates, ABS (acrylonitrile-butadiene-styrene compositions), etc. For instance, polycarbonates are resins which are excellent in rigidity as well as in heat resistance, heat ageing characteristics and impact strength. However, polycarbonates involve such a problem that they are poor in chemical resistance as they are easily attacked by strong alkali. Further, they have high water absorption. Though ABS are excellent in mechanical properties, they have such problems that they are poor in chemical resistance and further, because of double bonds in their molecular structure they are poor in weather resistance and heat resistance.
On one hand, polyolefins which are widely used as general-purpose resins are excellent in chemical resistance and solvent resistance. However, many of polyolefins are poor in heat resistance, insufficient in crystallizability and poor in rigidity. In general, to improve polyolefins in rigidity and heat resistance, there is employed a procedure in which nucleating agents are incorporated into polyolefins to expedite the growth of crystal, or a procedure in which polyolefins are gradually cooled to accelerate the growth of crystal. However, it is hard to say that the alleged effects obtained by these procedures are sufficient. The procedure of incorporating into polyolefins a third component such as nucleating agents rather involves the risk of marring various excellent properties inherent in polyolefins, and the gradually cooling procedure is low in production efficiency and involves the risk of lowering impact strength as the non-crystalline part of polyolefins decreases.
A copolymer of ethylene and 2,3-dihydroxydicyclopentadiene has been disclosed as an example of copolymers of ethylene and bulky comonomers, for example, in U.S. Pat. No. 2,883,372. However, this copolymer is poor in heat resistance as it has a glass transition temperature in the vicinity of 100.degree. C., though said copolymer is well balanced between rigidity and transparency. Similar drawback is also observed in copolymers of ethylene and 5-ethylidene-2-norbornene.
Japanese Patent Publn. No. 14910/1971 proposes a homopolymer of 1,4,5,8-dimethano-1,2,3,4,4a,5,8,8a-octahydronaphthalene. The proposed polymer, however, is poor in heat resistance and heat ageing characteristics. Japanese Patent L-O-P Publn. No. 127728/1983 further proposes a homopolymer of 1,4,5,8-dimethano-1,2,3,4,4a,5,8,8a-octahydronaphthalene or copolymers of said cycloolefin and norbornene type comonomers, which are apparently those obtained by ring opening polymerization (ring opening polymers) in light of the disclosure in said publication. These ring opening polymers which have unsaturated bonds in the polymer main chains, however, have such a drawback that they are poor in heat resistance and heat ageing characteristics.
In the course of these researches, we found that cycloolefin type random copolymers of ethylene and bulky cycloolefins are synthetic resins which are excellent in heat resistance as well as in heat ageing characteristics, chemical resistance, solvent resistance, dielectric characteristics and rigidity. On the basis of the above findings, we have already made various technical proposals as disclosed in Japanese Patent L-O-P Publn. No. 168708/1985 and Japanese Patent Appln. Nos. 220550/1984, 236828/1984, 236829/1984, 242336/1984 and 95906/1986. In spite of their being olefin type polymers, the cycloolefin type random copolymers as proposed are excellent in heat resistance and rigidity. However, they involve such problems that they are brittle and poor in impact resistance.
We have made studies to improve the rigidity and impact resistance of cycloolefin type random copolymers without detriment to their excellent heat resistance, heat ageing characteristics, chemical resistance, solvent resistance and dielectric characteristics. As a result, we have found that compositions consisting of a cycloolefin type random copolymer having a specific softening temperature (TMA) and at least one specific non-rigid copolymer or compositions obtained by blending inorganic filler and/or organic filler with said composition consisting of said random copolymer and said non-rigid copolymer have the above-described excellent characteristics. This invention has been performed on the basis of the above findings.