Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
2001-04-30
2002-11-12
Moore, Margaret G. (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C524S866000, C524S860000, C524S291000, C524S343000, C524S342000
Reexamination Certificate
active
06479580
ABSTRACT:
FIELD OF THE INVENTION
This invention provides a method of preparing a thermoplastic elastomer composition comprising mixing a silicone gum, with or without filler, and a thermoplastic resin containing more than 50% by volume of a polyolefin resin having a softening point of 23° C. to 300° C., and dynamically vulcanizing the silicone gum via a radical initiator.
BACKGROUND OF THE INVENTION
Thermoplastic elastomer vulcanizates (TPV), represent a known class of thermoplastic elastomers. These materials are prepared by a process known as dynamic vulcanization wherein an elastomer is dispersed in a thermoplastic resin and the elastomer is subsequently cured with the aid of a crosslinking agent and/or catalyst during the mixing process. A number of such TPV systems are known in the art, including some wherein the crosslinked elastomeric component can be a silicone polymer while the thermoplastic component is an organic (i.e., non-silicone) polymer. For example, Arkles, in U.S. Pat. No. 4,500,688, discloses semi-interpenetrating networks (semi-IPN) wherein a vinyl-containing silicone fluid having a viscosity of 500 to 100,000 cS is dispersed in a conventional thermoplastic resin. The vinyl-containing silicone is vulcanized in the thermoplastic during melt mixing according to a chain extension or crosslinking mechanism, which employs a silicon hydride-containing silicone component. Typical thermoplastics mentioned include polyamides, polyurethanes, styrenics, polyacetals and polycarbonates. This disclosure is expanded by Arkles in U.S. Pat. No. 4,714,739 to include the use of hybrid silicones which contain unsaturated groups and are prepared by reacting a hydride-containing silicone with an organic polymer having unsaturated functionality. Although Arkles discloses a silicone fluid content ranging from 1 to 40 weight percent (1 to 60% in the case of the '739 patent), there is no suggestion of any criticality as to these proportions or to the specific nature of the organic resin.
Crosby et al., in U.S. Pat. No. 4,695,602, teach composites wherein a silicone semi-IPN vulcanized via a hydrosilation reaction is dispersed in a fiber-reinforced thermoplastic resin having a high flexural modulus. The silicones employed are of the type taught by Arkles, cited supra, and the composites are said to exhibit improved shrinkage and warpage characteristics relative to systems, which omit the semi-IPN.
Ward et al., in U.S. Pat. No. 4,831,071, discloses a method for improving the melt integrity and strength of a high modulus thermoplastic resin to provide smooth-surfaced, high tolerance profiles when the modified resin is melt-drawn. As in the case of the disclosures to Arkles et al., cited supra, a silicone mixture is cured via a hydrosilation reaction after being dispersed in the resin to form a semi-IPN, and the resulting composition is subsequently extruded and melt-drawn.
U.S. Pat. No. 6,013,715 to Gornowicz et al. teaches the preparation of thermoplastic silicone vulcanizates (TPSiV) wherein a silicone gum (or filled silicone gum) is dispersed in either a polyolefin or a poly(butylene terephthalate) resins and the gum is subsequently dynamically vulcanized therein via a hydrosilation cure system. The resulting elastomers exhibit an ultimate elongation at break of at least 25% and have significantly improved mechanical properties over the corresponding simple blends of resin and silicone gum in which the gum is not cured (i.e., physical blends).
EP 651,009A1 to Sumitomo Bakelite Co., published May 3,1995, discloses a thermoplastic elastomer composition which is prepared by dynamically vulcanizing a mixture comprising an unsaturated organic (i.e., non-silicone) rubber, a thermoplastic resin, an SiH-containing crosslinker, a hydrosilating catalyst and a compatibilizing agent.
U.S. Pat. No.6,153,691, discloses the preparation of TPSiVs by a condensation cure mechanism. The silicone component employed contains silanol (—SiOH) functionality and is cured with an organohydrido functional crosslinker in the presence of, e.g., an organotin condensation catalyst.
EP 506,465 A2 to Japan Synthetic Rubber Co. discloses thermoplastic elastomers having improved mechanical properties, resistance to heat and oil, and compression set. These systems are prepared by mixing a thermoplastic polyester elastomer with a rubber and dynamically vulcanizing the rubber as these components are mixed. Various stabilizers and compatibilizers may be incorporated in the compositions, but no criticality is ascribed to these optional ingredients. Further, this publication only teaches the preparation of a thermoplastic elastomer from another thermoplastic.
Thus, although the above cited publications disclose the preparation of thermoplastic elastomer compositions using various thermoplastic resins as the matrix and a silicone phase which is dynamically vulcanized therein, neither these publications teach polyolefin TPSiV compositions cured by a radical reaction.
SUMMARY OF THE INVENTION
The present invention is a method for preparing thermoplastic elastomers by
(I) mixing
(A) a thermoplastic resin comprising more than 50 percent by volume of a polyolefin resin, said thermoplastic resin having a softening point of 23° C. to 300° C.;
(B) a silicone base comprising
(B′) 100 parts by weight of a diorganopolysiloxane gum having a plasticity of at least 30 and having an average of at least 2 alkenyl groups per molecule, and optionally,
(B″) up to 200 parts by weight of a reinforcing filler,
wherein the weight ratio of said silicone base to said thermoplastic resin is from 35:65 to 85:15;
(C) a radical initiator, in an amount sufficient to cure said diorganopolysiloxane gum (B′); and
(II) dynamically vulcanizing said diorganopolysiloxane gum,
wherein said thermoplastic elastomers have an elongation of at least 25% and at least one property of said thermoplastic elastomers selected from tensile strength or elongation is at least 25% greater than the respective property for a corresponding simple blend wherein said diorganopolysiloxanes gum is not cured.
The invention further relates to thermoplastic elastomers prepared by the above method.
DETAILED DESCRIPTION OF THE INVENTION
Component (A) of the present invention is a thermoplastic resin comprising more than 50% by volume of a polyolefin resin having a softening point of 23° C. to 300° C. As used herein, “softening point” corresponds to the respective melting point of the thermoplastic resin if the resin is at least partially crystalline, or corresponds to the glass transition temperature when the thermoplastic resin is completely amorphous. Preferably, the softening point is between 50° C. and 300° C. and most preferably between 100° C. and 250° C.
The polyolefin resins may be selected from polyethylene, polypropylene, or styrenic block copolymers. The polyolefin resins may be selected from homopolymers of olefins as well as random graft or block copolymers of one or more olefins with each other and/or up to about 40 mole percent of one or more monomers, which are copolymerizable with the olefins. Examples of suitable polyolefin resins include homopolymers of ethylene, propylene, butene-1, isobutylene, hexene, 1,4-methylpentene-1, pentene-1, octene-1 , nonene-1 and decene-1, inter alia. These polyolefins can be prepared using peroxide, Ziegler-Natta or metallocene catalysts, as well known in the art. Copolymers of two or more of the above mentioned olefins may also be employed as Component (A) and they may also be copolymerized with, e.g., vinyl or diene compounds or other such compounds which can be copolymerized with the olefins.
Specific examples of suitable copolymers are ethylene-based copolymers, such as ethylene-propylene copolymers, ethylene-butene-1 copolymers, ethylene-hexene-1 copolymers, ethylene-octene-1 copolymers, ethylene-butene-1 copolymers and copolymers of ethylene with two or more of the above mentioned olefins.
The polyolefin resin may also be a blend of two or more of the above-mentioned homopolymers or copolymers. For example, the blend c
Chorvath Igor
Gray Dean Curtis
Lee Michal Kang-Jen
Tangney Thomas John
Dow Corning Corporation
Moore Margaret G.
Zombeck Alan
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