Propylene homopolymer and propylene copolymer

Details Propylene homopolymer and propylene copolymer Propylene homopolymer and propylene copolymer

2002-03-19

2004-09-21

Cheung, William (Department: 1713)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Polymers from only ethylenic monomers or processes of...

C526S348200, C526S348400, C526S348600, C525S416000

Reexamination Certificate

active

06794476

ABSTRACT:

BACKGRAOUND OF THE INVENTION
The present invention relates to a propylene polymer, more specifically to a propylene polymer which has physical properties equivalent to or not lower than those of conventional propylene copolymers and is excellent in melt-processing characteristics, molding processability and a recycling property and which is suitably used particularly for large size blow molding, extrusion foaming molding and sheet molding and can be used for a raise in the performances of polyolefin composite materials and elastomers.
RELATED ART
Polypropylene is used in a wide range in a lot of the fields making the best use of the excellent characteristics thereof.
In conventional polypropylenes, however, the melt tension and the melt viscoelasticity are short, and the stability in parison in large size blow molding is inferior. Accordingly, the phenomenon of drawdown is liable to take place, and it used to be difficult to mold large-sized parts. Further, when the molecular weight is increased in order to elevate the melt tension, brought about is the problem that it is reduced in a melt fluidity and therefore can not be applied to molding of complicated shapes.
Further, in the field of foamed molded articles, requirements to foamed molded articles having a heat resistance as well as a reduction in weight, a heat insulating property and a damping property grow large, and polypropylene foamed molded articles are expected. However, the existing situation is that conventional polypropylenes are short of a melt tension, and sufficiently satisfactory foamed molded articles are less liable to be obtained.
The extrusion molding processability has to be improved in order to further expand the application field of this polypropylene. A melt processability of polyolefin has so far been tried to be improved in various ways, and there have been tried, for example, a method in which a polymerization catalyst and a polymerization procedure in producing polyolefin are improved to expand the molecular weight distribution thereof to thereby improve the melt processability and a method in which polyolefin is partially cross-linked to improve the melt processability.
On the other hand, in ethylene polymers, proposed in recent years is an ethylene polymer improved in a melt tension by a catalyst system in which a metallocene catalyst is combined with aluminoxane while the molecular weight distribution is narrow (Japanese Patent Application Laid-Open No. 213306/1992). Further, in respect to ethylene polymers produced with an constrained geometry catalyst, it is disclosed that the melt tension is improved though the molecular weight distribution is narrow as well (Japanese Patent Application Laid-Open No. 163088/1991), and the presence of a long branched chain is indicated. In the formation of this long branched chain, proposed is a mechanism in which an ethylene polymer in which a vinyl group is present at a molecular chain end is produced in polymerization and in which this is polymerized again in the form of a macro monomer. Further, disclosed as well is branched polyolefin comprising a homopolymer or a copolymer of &agr;-olefin having 2 to 30 carbon atoms as a principal chain and a homopolymer or a copolymer of &agr;-olefin having 250 or more carbon atoms as a side chain (Japanese Patent Application (through PCT) Laid-Open No. 502303/1996), and a method of passing through the production of a macro monomer of a terminal vinyl type is shown as a method for forming a side chain of the above branched polyolefin. However, (1) it is shown that the macro monomer is produced by &bgr; hydrogen transfer, but when propylene is used, an internal olefin or a vinylidene structure is formed by &bgr; hydrogen transfer, and a macro monomer having terminal vinyl is not produced; (2) it is shown as a method for obtaining a macro monomer other than ethylene that ethylene is added at the ┌end┘ stage of the polymerization reaction to ┌cap┘ it with ethylene to thereby produce the macro monomer, and it is apparent that ethylene is essential for producing the macro monomer; and (3) because of very quick chain reaction at a polymerization reaction stage in the methods of (1) and (2), a macro monomer of a block type is not produced by &bgr; hydrogen transfer after a block copolymer with ethylene is produced even if introducing ethylene, and it is apparent that as a matter of fact, the macro monomer of ethylene alone is produced, so that the above method is a technique limited to an ethylene polymer. Thus, a technique for producing branches by &agr;-olefin higher than propylene is neither disclosed nor indicated.
In general, the introduction of a long chain branch into a polymer chain elevates the melt processing characteristics by the branch. A branched polymer in which a branched chain is constituted by a monomer different from a monomer constituting a principal chain polymer lowers an interfacial tension between different kinds of polymers in the field of a so-called composite material comprising different kinds of polymers to elevate the dispersibility of the polymers and makes it possible to effectively provide such incompatible physical properties as an impact strength and a rigidity. Further, it has a micro phase separation structure and therefore can be applied to various elastomers. In the polyolefin field, however, there is restriction in introducing branches, and therefore there have been limits in developing the applications thereof. If this becomes possible, the application fields thereof are expected to be expanded to a large extent by virtue of excellent mechanical properties and environmental compatibility represented by a recycling property which are intrinsically endowed to polyolefins.
On the other hand, there have so far been tried as a method for improving a melt tension of polypropylene and elevating melt processing characteristics thereof, (1) a method in which blended is high density polyethylene having a high melt tension and a high molecular weight (Japanese Patent Publication 55868/1994), (2) a method in which blended is high density polyethylene having a high melt tension produced with a chromium catalyst (Japanese Patent Application Laid-Open No. 92438/1996), (3) a method in which blended is low density polyethylene produced by a conventional high pressure radical polymerization method, (4) a method in which conventional polypropylene is irradiated with light to thereby elevate the melt tension, (5) a method in which conventional polypropylene is irradiated with light in the presence of a cross-linking agent and peroxide to thereby elevate the melt tension, (6) a method in which conventional polypropylene is grafted with a radically polymerizable monomer such as styrene and (7) a method in which propylene is copolymerized with polyene (Japanese Patent Application Laid-Open No. 194778/1993 and Japanese Patent Application Laid-Open No. 194779/1993).
In the methods of (1) to (3), however, the components for elevating the melt tension are short of an elastic modulus, a strength and a heat resistance, and therefore the intrinsic characteristics of polypropylene can not be prevented from being damaged. Further, involved in the methods of (4) and (5) are the problems that it is difficult to control a cross-linking reaction which takes place as a side reaction to bring about the inferior appearance by the production of gel and exert an adverse effect on the mechanical characteristics and that in addition thereto, there is a limit in optionally controlling the molding processability and the controlling range is narrow. Further, not only the heat stability is low, and the melt tension is reduced in melt molding processing to bring about a problem on the moldability but also recycling of the resin is hindered to a large extent. Further, in the method of (6), a chemical stability of polypropylene is damaged, and a problem is caused on a recycling property of a resin in a graft polymer of a styrene. Also, in the method of (7), not only an effect for improving the melt tension is

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