Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
2003-04-17
2004-10-05
Cheung, William K. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
C526S348300, C526S348400, C526S348500, C526S348600, C526S351000
Reexamination Certificate
active
06800711
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a propylene-based polymer, especially to a branched propylene-based polymer. More precisely, it relates to a propylene-based polymer, of which the properties are comparable to or better than those of conventional propylene-based polymers, and which has good melt workability and is favorably used for large-size blow molding, extrusion foaming and the like.
In addition, the invention also relates to a propylene-based polymer which, in a composite material comprising the propylene-based polymer and some other propylene-based block copolymer and/or random copolymer, functions as a miscibility improver for those polyolefin-based resins and is effective for improving the properties of the composite material and for elastomerizing it.
BACKGROUND OF THE INVENTION
Polypropylene has heretofore been widely used in various fields, as being characterized in that (1) it has high mechanical strength such as stiffness, and has good physical balance, (2) it is chemically stable, while having good weather resistance, and is hardly corroded by chemicals, (3) it has a high melting point and has good heat resistance, and (4) it is lightweight and low-priced. In addition, as having good melt workability, various melt molding methods of, for example, extrusion molding, blow molding, injection molding and inflation molding are applicable to polypropylene.
To produce thermoplastic resin foams, amorphous resins such as polystyrene have heretofore been much used, as being relatively easily subjected to extrusion foaming. In these days, however, there is increasing a great demand for high-quality lightweight foams with good heat-insulating ability and good damping ability, especially those having good heat resistance and good impact resistance, for which polypropylene-based resin foams are being required.
However, polypropylene is problematic in that the suitable temperature range for its foaming is extremely narrow, since it has a relatively high degree of crystallization and its visco-elasticity greatly is greatly varied by minor temperature variation. Another problem is that bubbles in polypropylene foams could not be kept well therein but are easily broken, since the melt viscosity of polypropylene is extremely low at temperatures higher than its crystal melting point and the melt tension thereof is low. For these reasons, therefore, it is difficult to obtain polypropylene foams having closed cells therein and having good mechanical properties and heat resistance. In order to produce polypropylene-based resin foams through extrusion foaming, like polystyrene-based resin foams, propylene-based resin must be so modified that it is foamable within a broadened temperature range and that its melt has a high visco-elasticity at temperatures higher than its melting point.
As having excellent characteristics such as those mentioned above, polypropylene-based resin is actively used in car parts, etc., and it is much desired to further improve the properties of the resin and to lower the production costs for the resin moldings, for example, by simplifying the process of molding the resin. For this, if large-sized products of the resin, which have heretofore been produced through injection molding, could be produced through blow molding, the production costs could be greatly reduced.
However, the conventional polypropylene has a low melt tension and a low melt visco-elasticity, and if it is subjected to large-size blow molding, the stability of its parison is poor, thereby often causing a phenomenon of drawing down. For these reasons, therefore, it is difficult to produce large-sized products of the polymer through blow molding. If the polymer is modified to have an increased molecular weight in order to increase its melt tension, the melt fluidity of the polymer is lowered, thereby causing another problem that the polymer could no more apply to moldings having a complicated shape.
As so mentioned hereinabove, extrusion moldability of polypropylene must be improved in order to further enlarge the field where the polymer is usable. For this, heretofore, various attempts have been made for improving the melt workability of polyolefins, for example, by increasing the melt visco-elasticity thereof.
In general, introducing long-chain branches into polymer chains improves the melt workability of the resulting polymers due to the branches introduced. In the field of so-called composite materials comprising different types of polymers, branched polymers of which the monomers for the branched chains are different from those for the main polymer chain act to lower the surface tension between those different types of polymers to thereby improve the dispersibility of the polymers in the composite materials, and are effective for making the composite materials have contradictory properties of impact resistance and stiffness. In addition, as having a microscopic phase-separation structure, the branched polymers are applicable to various elastomers. However, in the field of polyolefins, the introduction of branched chains into the polymers is limited, and the applications of the polymers are limited. If the limitation on the introduction of branched chains into polyolefins could be removed, it is expected that the applications of polyolefins could be greatly expanded because of the intrinsic good mechanical properties and environmental affinity, such as typically recyclability, of the polymers.
For this, various proposals have heretofore been made, including, for example, (1) a method of mixing a high-molecular weight, high-density polyethylene having a high melt tension with polypropylene (see Japanese Patent Publication (JP-A) Hei-6-55868); (2) a method of mixing a high-density polyethylene having a high melt tension, which is prepared in the presence of a chromium catalyst, with polypropylene (see Japanese Patent Application (JP-A) Hei-8-92438); (3) a method of mixing a low-density polyethylene to be prepared through ordinary high-pressure radical polymerization, with polypropylene; (4) a method of exposing ordinary polypropylene to light to thereby make it have an increased melt tension; (5) a method of exposing ordinary polypropylene to light in the presence of a crosslinking agent or a peroxide to thereby make it have an increased melt tension; (6) a method of grafting ordinary polypropylene with a radical-polymerizing monomer such as styrene; and (7) a method of copolymerizing propylene and polyenes (see JP-A Hei-5-194778 and Hei-5-194779).
However, in the methods (1) to (3), since the elasticity, the strength and the heat resistance of the melt tension-improving component added are low, the component inevitably interferes with the intrinsic characteristics of polypropylene and also with the properties of the foams to be formed from the polymer mixture. In the methods (4) and (5), it is difficult to control the side reaction, crosslinking to give gel, which shall have negative influences of the outer appearance and the mechanical properties of the foams to be formed. In addition, in those, it is difficult to freely control the degree of crosslinking between the molecules that influence on the moldability of the polymer mixture, through polymer reaction, and the controllable range for the degree of crosslinking in question is problematically narrow. The method (6) is problematic in that it detracts from the chemical stability of polypropylene, and that styrene-based graft polymers formed therein are not recyclable. The method (7) is problematic in that it is not so much effective for increasing the melt tension of the copolymer formed and that the copolymerization may give gel.
On the other hand, for impact-resistant polypropylene compositions, used are mixtures of a relatively low-molecular, high-stereospecific propylene homopolymer and a relatively high-molecular ethylene/propylene random copolymer. In wrapping films, used are mixtures of a propylene homopolymer and a propylene-based random copolymer as prepared by copolymerizing propylene and ethylene or any ot
Goto Yasuhiro
Kanzawa Mitsugu
Kijima Masato
Machida Shuji
Minami Yutaka
Cheung William K.
Idemitsu Petrochemical Co. Ltd.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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