Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Cellular products or processes of preparing a cellular...
Reexamination Certificate
2001-02-16
2003-02-04
Foelak, Morton (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Cellular products or processes of preparing a cellular...
C521S142000, C521S150000, C526S160000, C526S335000, C526S351000, C526S943000
Reexamination Certificate
active
06515037
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a polypropylene base resin composition for foam-molding which uses a propylene•&agr;,&ohgr;-diene base copolymer containing a small amount of &agr;,&ohgr;-diene and obtained by copolymerizing propylene with a specific amount of &agr;,&ohgr;-diene in the presence of a catalyst system for polymerizing olefin comprising a metallocene supported catalyst or a pre-activated metallocene supported catalyst and an organic aluminum compound and which provides a foamed article having uniform and fine foamed cells (bubbles) and a high foaming magnification, a foamable polypropylene base resin composition comprising the propylene•&agr;,&ohgr;-diene base copolymer and a specific amount of a foaming agent, a foamed article obtained by foam-molding the above composition, a production process for the above foamed article and a foam-molded product prepared by heat-molding the above foamed article.
BACKGROUND ART
Polypropylene is excellent in a mechanical property and a chemical resistance and very useful in terms of balance with profitability, so that it is widely used in the various molding fields.
A foamable thermoplastic resin composition obtained by adding azodicarbonamide and zinc hydroxycarbonate to a thermoplastic resin containing a polypropylene resin is disclosed in Japanese Patent Application Laid-Open No. 45656/1985 as a method for obtaining such formed article of polypropylene or a composition (particle) which provides a formed article of polypropylene; disclosed in Japanese Patent Publication No. 46532/1989 is a foamable polypropylene base resin composition comprising 70 to 99.8% by weight of a polypropylene base resin which comprises propylene, &agr;-olefin of hexene-1 or 4-methylpentene-1 and, if necessary, ethylene or butene-1 and in which at least one of melting peaks based on differential scanning calorimetric analysis is present at 130° C. or higher when the &agr;-olefin described above is hexene-1 and at 145° C. or higher when the &agr;-olefin described above is 4-methylpentene-1 and a density is 0.887 g/cm
3
or less after annealing at 105° C. for 90 minutes based on JIS-K6758 and 0.2 to 30% by weight of a foaming agent; disclosed in Japanese Patent Application Laid-Open No. 103944/1986 are polypropylene foamed particles which are substantially non-cross-linked polypropylene foamed particles having a density of 8 to 100 g/liter and a particle diameter of 1 to 5 mm and contain organic sodium phosphate; and disclosed in Japanese Patent Application Laid-Open No. 31538/1985 is a production process for a polyolefin copolymer-foamed article characterized by introducing a solvent or gas into a mixture of a propylene polymer or a propylene-ethylene block copolymer having an ethylene content of 1 to 20% by weight and a propylene-&agr;-olefin copolymer by using an extruder and foam it.
However, a polypropylene base resin has a large temperature dependency of a melt viscosity, and a reduction in the melt viscosity suddenly grows large as the melting temperature is elevated. Accordingly, it becomes difficult to maintain a strength of a bubble wall in foaming, so that it has been difficult to obtain a foamed article having a high independent cell ratio.
Disclosed as a method for improving such performances of the foamed articles of the polypropylene base resins are a method in which a cross-linking agent is reacted with polypropylene in a melting state in the presence of an organic peroxide to produce a partial cross-linked structure in the molten resin to thereby inhibit a reduction in a melt viscosity (Japanese Patent Application Laid-Open No. 93711/1984 and Japanese Paten Application Laid-Open No. 15275/1986) and a method in which a low decomposition temperature-peroxide is reacted with semi-crystalline polypropylene in the absence of oxygen to obtain polypropylene having a free end-long chain branch and containing no gel (Japanese Patent Application Laid-Open No. 298536/1990).
Further, disclosed as other methods for improving a temperature dependency of a melt visco-elasticity of a polypropylene base resin are compositions in which polyethylene or polypropylene having a different intrinsic viscosity or molecular weight is blended to expand a molecular weight distribution and a production process in which such compositions as described above are produced by multistage polymerization to thereby produce polypropylene having a high melt strength.
Disclosed are, for example, a method in which ultra high molecular weight polypropylene is added in a proportion 2 to 30 parts by weight per 100 parts by weight of conventional polypropylene and the mixture is extrusion-molded to thereby improve a melt visco-elasticity (Japanese Patent Publication No. 28694/1986) and an extruded sheet comprising polypropylene comprising two components produced by a multistage polymerization process which have a limiting viscosity ratio of 2 or more and different molecular weights (Japanese Patent Publication No. 12770/1989).
Further, proposed are a production process in which a pre-polymerization catalyst prepared by pre-polymerizing ethylene and a polyene compound on a supported titanium-containing catalyst component and an organic aluminum compound catalyst component is used to polymerize propylene to thereby produce polypropylene having a high melt strength (Japanese Patent Application Laid-Open 222122/1993) and a production process in which the same catalyst components are used to pre-polymerize ethylene alone and an ethylene-containing pre-polymerization catalyst containing polyethylene having a limiting viscosity of 20 dl/g or more is used to thereby produce an ethylene.&agr;-olefin copolymer having a high melt strength (Japanese Patent Application Laid-Open 55410/1992).
In various polypropylene base compositions and production processes for them, a melt strength of propylene can be elevated to some extent but is not yet satisfactory, and there still remain such points to be improved that gas generated from a foaming agent can not sufficiently be incorporated into a molten resin and therefore it is very difficult to elevate the foaming magnification.
Further, in a multistage polymerization process in which a production step for polyolefin of a high molecular weight is incorporated into a conventional propylene (co)polymerization step in the present polymerization, it is difficult to control an olefin (co)polymerization amount for producing a trace amount of polyolefin having a high molecular weight, and a low polymerization temperature for producing polyolefin having a sufficiently high molecular weight is required. Accordingly, the process has to be modified, and further involved is the problem that the finished polypropylene resin is reduced in a productivity.
Further, in a process in which a polyene compound is used to carry out pre-polymerization, the polyene compound has to be separately prepared.
SUMMARY OF THE INVENTION
The present inventors repeated intensive investigations in order to obtain a polypropylene base resin composition which provides a foamed article having uniform and fine foamed cells (bubbles) and a high foaming magnification. As a result thereof, they have found that a propylene•&agr;, &ohgr;-diene base copolymer containing a small amount of &agr;, &ohgr;-diene and obtained by copolymerizing propylene with &agr;, &ohgr;-diene in the presence of a catalyst system for (co)polymerizing olefin comprising a specific metallocene supported catalyst or a pre-activated metallocene supported catalyst obtained by supporting the above metallocene supported catalyst into contact with olefin to pre-(co)polymerize the olefin and further supported the above pre-(co)polymerized olefin polymer and an organic aluminum compound is used to carry out foam-molding to thereby obtain a foamed article having uniform and fine foamed cells (bubbles) and a high foaming magnification. Thus, they have completed the present invention based on this finding.
As apparent from the above descriptions, an object of the present invention is to provide a po
Hatada Kouichi
Maehara Hiroyuki
Tsutsui Mototake
Ushioda Tsutomu
Chisso Corporation
Foelak Morton
McDermott & Will & Emery
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