Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2000-07-03
2002-06-04
Lipman, Bernard (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S193000, C525S194000, C525S196000, C525S197000, C525S198000, C525S211000, C525S237000
Reexamination Certificate
active
06399710
ABSTRACT:
FIELD OF INVENTION
Thermoplastic random copolymers of ethylene can be used to increase the elongation to break and toughness of thermoplastic vulcanizates made from a thermoplastic polypropylene phase and a crosslinkable rubber. The thermoplastic random copolymers of ethylene are available from several suppliers as polymers from single site catalyst, often referred to as metallocene catalyst polymerized polymers. They differ from other ethylene copolymers in that the comonomer is rather uniformly distributed in substantially all of the polymer chains, while in prior art thermoplastic ethylene copolymers the comonomer was disproportionately increased in a portion of the polymer chains and the comonomer was disproportionately reduced in a portion of the polymer chains resulting in a broad compositional distribution for the polymer.
BACKGROUND OF INVENTION
Thermoplastic vulcanizates from polypropylene and a rubber have gained wide acceptance as a substitute for thermoset rubbers in a variety of applications. It would be desirable for many of these applications to increase the elongation to break of said thermoplastic vulcanizates and to increase the total toughness (as measured by the area under the stress strain curve) when a thermoplastic vulcanizate is measured in a tensile test.
Polyethylene and copolymers of polyethylene are very interesting polymers because they can have both amorphous regions and crystalline regions. Amorphous regions of polyethylene are rubbery at room temperatures having a glass transition temperature well below 0° C. Crystalline regions of polyethylene are more rigid materials having a melting point generally between about 80° C. and 135° C. depending on the characteristics of the crystals and the density of the polyethylene. The crystalline regions of polyethylene are more dense, i.e., have higher densities than the amorphous region of the polymer. High density polyethylene has higher relative proportions of crystalline polymer versus amorphous polymer than its low-density counterparts. Generally polymer chain branching and the incorporation of comonomers decrease the crystallinity in polyethylene due to the fact that the crystal structure cannot accommodate many comonomers or large chain branches. The amorphous regions of semi-crystalline polyethylene adds to the toughness of the material as it can undergo elastic and plastic deformation to accommodate stresses or strains thus avoiding fracture of the crystalline regions.
Ethylene-propylene-diene polymers (EPDM) also known as ethylene-propylene-diene-polymethylene rubber with weight ratios of ethylene to propylene of from 25:75 to about 75:25 have sufficient incorporation of both ethylene and propylene in the polymer chain such that these materials are rubbery at room temperature rather than solid, such as polyethylene or polypropylene.
Copolymers from polyethylene have been made in the past with catalysts other than single site catalysts. Various polymerization techniques have been used so that a specified portion of comonomer is present in the copolymer. However, few polymerization catalysts or polymerization systems are known which truly randomly polymerize ethylene with comonomers into a thermoplastic copolymer. Linear low density polyethylene involves the polymerization with an ethylene feed and a second olefin feed, generally 4-8 carbon atoms, keeping a relatively constant feed ratio. The catalysts have several different active sites such that some sites incorporate the second olefin more efficiently than others. The different sites also can result in different polymer chain lengths. This results in a broad molecular weight distribution and a broad compositional distribution in the resulting polymer. Another method of making low-density polyethylene involves using polymerization conditions that encourage branching in the polyethylene chain, said branching disrupting the crystallinity of the polyethylene and causing a reduced amount of crystallinity and consequently a reduced density.
SUMMARY OF INVENTION
Thermoplastic vulcanizates from polypropylene, a rubber, and a thermoplastic random copolymer of ethylene can be prepared by blending a thermoplastic random copolymer of ethylene with the components of a thermoplastic vulcanizate or by mixing a thermoplastic random copolymer of ethylene with a preformed thermoplastic vulcanizate from polypropylene and a rubber. The thermoplastic random copolymers of ethylene are commercially available as a result of the development of single site catalysts including metallocene catalysts. The thermoplastic random copolymers of ethylene currently have rather narrow molecular weight distributions and rather narrow compositional distributions. The average comonomer concentration is from about 5 to about 30 weight percent based on the weight of the ethylene copolymer. As is known to the art, thermoplastic vulcanizates usually comprise from about 15 to about 75 parts of the thermoplastic phase and from about 25 to about 85 parts by weight of the rubber phase. They can further comprise various amounts of curatives, plasticizers, fillers, etc. The thermoplastic random copolymer of ethylene is desirably present in amounts of from about 5 to about 150 parts per 100 parts of polypropylene in the thermoplastic vulcanizate. The rubber can be any hydrocarbon rubber such as butyl rubbers, halobutyl rubbers, halogenated (e.g., brominated) copolymers of paramethyl styrene and iso-butylene, EPDM rubber, and natural rubber or diene-based homo or copolymer rubber.
DETAILED DESCRIPTION OF THE INVENTION
The thermoplastic random copolymer of ethylene used to modify thermoplastic vulcanizates in this invention is different from other ethylene copolymers used in thermoplastic vulcanizates in the past: it is much more random in terms of the incorporation of comonomer(s) in the copolymer. In the past, copolymers with more than 2, 5, or 10 weight percent comonomer were either rubbers or were a physical blend of copolymers low in ethylene repeat units and other copolymers significantly richer in ethylene repeat units, which blend would have a relative weight percent of comonomer and ethylene cited in the product literature. The thermoplastic random copolymer of ethylene used in this invention can have very narrow molecular weight distributions (Mw/Mn) of from about 1.5 or 1.7 to 3.5, more desirably from about 1.8 to about 3.0 and preferably from about 1.5 or 1.9 to 2.8 due to the single site catalyst, also referred to as metallocene catalyst, currently used to prepare such polymers. This disclosure is not limited to thermoplastic random copolymers of ethylene made with metallocene catalysts, but rather uses those commercially available polymers as illustrative of a polymerization method capable of making random copolymers operable in this disclosure. Further, the molecular weight distributions are recited as a method of identifying these polymers, but are not a requirement for operativeness of the copolymer in a thermoplastic vulcanizate.
The thermoplastic random copolymer of ethylene can have varying amounts of one or more comonomers therein. In the examples, the thermoplastic random copolymer of ethylene is often referred to as a plastomer indicating that it has some properties of both a plastic and an elastomer. Desirably the amount of repeat units from one or more comonomers is from about 5, 10, 15 or 20 to about 30 or 35 weight percent of the thermoplastic random copolymer of ethylene. More desirably, the amount of repeat units from said one or more comonomers is from about 10 to about 25 weight percent. The amount of ethylene in said thermoplastic random copolymer of ethylene is desirably from about 65 or 70 to about 80, 85, 90 or 95 weight percent, and more desirably from about 65, 70 or 75 to about 80, 85 or 90 weight percent. The one or more comonomers can be any ethylenically unsaturated compound copolymerizable with ethylene using a single site catalyst. The one or more ethylenically unsaturated monomers desirably have from about 3 or 4 to about 12 carbon atoms, more desirably
Abdou-Sabet Sabet
Ellul Maria D.
Finerman Terry M.
Advanced Elastomer Systems L.P.
Laferty Samuel B.
Lipman Bernard
Skinner William A.
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