Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Patent
1996-03-13
1998-04-07
Delmendo, Romulo H.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
525247, 525270, 525323, C08F29708
Patent
active
057366136
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a highly rigid propylenic resin and a blow molded article made therefrom. More particularly, it pertains to a highly rigid propylenic resin which has favorable resistance to drawdown and can produce a large sized and lightweight blow molded part being excellent in rigidity, dimensional stability and heat resistance and to a blow molded article obtained therefrom which is particularly favorably usable for bumpers such as bumpers and bumper beams for automobiles.
BACKGROUND ART
Polypropylene as a resin for general purpose has heretofore been molded into a product with a desirable form and shape by any of various molding methods including extrusion molding, injection molding and blow molding. Of the above-mentioned molding methods, blow molding method has found its extensive use in molding large-sized structural materials typified by car parts because of its advantages in that molds therefor are inexpensive and that the production process can be simplified by integral molding methods. In this case, propylenic resin is frequently and extensively employed as raw materials from the viewpoint of specific gravity, rigidity, dimensional stability, heat resistance and the like.
However, the propylenic resin for general purpose is not necessarily sufficient in satisfying rigidity or resistance to drawdown which is required in blow molding and thus, various attemps have been made to improve such properties. There is proposed for example, in Japanese Patent Publication No. 36609/1988 (corresponding to U.S. Pat. No. 4,550,145), a process for producing propylenic resin improved in drawdown property by constituting a combination of propylene homopolymer and propylene/ethylene copolymer at a specific intrinsic viscosity and a specific compositional ratio. However, such propylenic resin is not sufficient in rigidity when made into a molding, and thus further improvement has been desired. There are also disclosed a technique of improving the rigidity thereof by means of multistage polymerization and a nucleating agent (refer to Japanese Patent Publication No. 74264/1991), a technique of improving the resistance to drawdown thereof by means of specific multistage polymerization and a specific nucleating agent (refer to Japanese Patent Application Laid-Open No. 213547/1988) and the like technique.
However, although these techniques improve the rigidity and resistance to drawdown of propylenic resin to some extent, the problems still remain unsolved in that when an attempt is made to form a so-called large-sized blow molded part, that is, weighing about 5 kg or more, insufficiency in resistance to drawdown makes molding itself impossible or makes the thickness distribution ununiform, thus resulting in failure to produce a satisfactory molded product. Such being the case, the actual state is that in forming a large-sized blow molded article weighing 5 kg or more, propylenic resin is blended with polyethylene such as high density polyethylene to contrive to solve the problem of drawdown. Nevertheless, the blending of high density polyethylene greatly lowers the rigidity of the blended resin, and therefore, an inorganic filler such as talc is actually added to the resin.
At any rate, the characteristics inherent in propylenic resin are lost by blending polyethylene, talc or the like and in particular, the disadvantage that the pinch-off strength in blow molding is extremely lowered is caused thereby. Accordingly, it is desired to realize a specific propylenic resin capable of forming a large-sized blow molded article and coping with increase in weight due to the blending of talc. The above-mentioned problems should be solved in view of not only the technical aspect but also the social circumstances including the recycle of molded articles.
DISCLOSURE OF THE INVENTION
Under such circumstances, it is an object of the present invention to develop a highly rigid propylenic resin which has favorable resistance to drawdown and can produce a large sized, lightweight blow-molded part
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patent: 5077341 (1991-12-01), Saito et al.
patent: 5218052 (1993-06-01), Cohen et al.
Kunststoffe Europe, Oct. 1989, pp. 108-109, 111-112, 114-115, "Blow Moulding Technical Parts From Polypropylene", by W. Low Francfort.
Hirano Koki
Kijima Masato
Shinohara Masayuki
Sugawara Minoru
Delmendo Romulo H.
Idemitsu Petrochemical Co. Ltd.
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