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
2001-10-19
2003-05-27
Moore, Margaret G. (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C524S862000, C524S751000, C524S754000, C525S904000
Reexamination Certificate
active
06569958
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a thermoplastic elastomer composition wherein a silicone base is blended with a polyester resin and a glycidyl ester compatibilizer. The silicone gum contained in the base is then dynamically vulcanized during the mixing process to produce the thermoplastic elastomer composition.
BACKGROUND OF THE INVENTION
Thermoplastic elastomers (TPEs) are polymeric materials which possess both plastic and rubbery properties. They have elastomeric mechanical properties but, unlike conventional thermoset rubbers, they can be re-processed at elevated temperatures. This re-processability is a major advantage of TPEs over chemically crosslinked rubbers since it allows recycling of fabricated parts and results in a considerable reduction of scrap.
In general, two main types of thermoplastic elastomers are known. Block copolymer thermoplastic elastomers contain “hard” plastic segments which have a melting point or glass transition temperature above ambient as well as “soft” polymeric segments which have a glass transition or melt point considerably below room temperature. In these systems, the hard segments aggregate to form distinct microphases and act as physical crosslinks for the soft phase, thereby imparting a rubbery character at room temperature. At elevated temperatures, the hard segments melt or soften and allow the copolymer to flow and to be processed like an ordinary thermoplastic resin.
Alternatively, a thermoplastic elastomer referred to as a simple blend, or physical blend, can be obtained by uniformly mixing an elastomeric component with a thermoplastic resin. When the elastomeric component is also cross-linked during mixing, a thermoplastic elastomer known in the art as a thermoplastic vulcanizate (TPV) results. Since the crosslinked elastomeric phase of a TPV is insoluble and non-flowable at elevated temperature, TPVs generally exhibit improved oil and solvent resistance as well as reduced compression set relative to the simple blends.
Typically, a TPV is formed by a process known as dynamic vulcanization, wherein the elastomer and the thermoplastic matrix are mixed and the elastomer is cured with the aid of a crosslinking agent and/or catalyst during the mixing process. A number of such TPVs are known in the art, including some wherein the crosslinked elastomeric component can be a silicone polymer while the thermoplastic component is an organic, non-silicone polymer (i.e., a thermoplastic silicone vulcanizate or TPSiV). In such a material, the elastomeric component can be cured by various mechanisms including radical, condensation and hydrosilylation method, but each method has its limitations.
Arkles, in U.S. Pat. No. 4,500,688, discloses semi-interpenetrating networks (semi-IPNs) wherein a vinyl-containing silicone fluid having a viscosity of 500 to 100,000 cS is dispersed in a conventional thermoplastic resin. Arkles only illustrates these IPNs at relatively low levels of silicone. 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 polyesters, 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 IPN.
Ward et al., in U.S. Pat. No. 4,831,071, disclose 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, after which the resulting composition is extruded and melt-drawn.
U.S. Pat. No. 6,013,715 to Gornowicz et al. teaches the preparation of TPSiV elastomers wherein a silicone gum (or filled silicone gum) is dispersed in either a polyolefin or a poly(butylene terephthalate) resin 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).
U.S. Pat. No. 6,281,286 to Chorvath et.al. discloses that the impact resistance of polyester and polyamide resins can be greatly augmented by preparing a thermoplastic silicone vulcanizate therefrom wherein the elastomeric component is a silicone rubber base which comprises a silicone gum and a silica filler and the weight ratio of the base to the resin ranges from 10:90 to 35:65. Although the resulting thermoplastic materials have improved impact resistance, they do not exhibit sufficiently low modulus to be useful as elastomers.
Copending application Ser. No. 09/535,556, filed on Mar. 27, 2000, discloses the incorporation of a hindered phenol compound in a TPSiV based on specific nylons wherein the phenol compound imparts improved mechanical properties relative to an unmodified composition.
Copending U.S. patent applications Ser. No. 09/843,906 and Ser. No. 09/845,971 discloses methods for making TPSiV using peroxide cure techniques. Ser. No. 09/843,906 teaches polyolefin TPSiV's whereas Ser. No. 09/845,971 teaches polyamide and polyester based TPSiV's.
Copending U.S. patent application Ser. No. 09/616,625, filed on Jul. 26, 2000, discloses the incorporation of a compatibilizer selected from (i) a coupling agent, (ii) a functional diorganopolysiloxane or (iii) a copolymer comprising at least one diorganopolysiloxane block and at least one block selected from polyamide, polyether, polyurethane, polyurea, polycarbonate or polyacrylate, in a TPSiV elastomer based on specific nylons wherein that inclusion the selected compatibilizer in the formulation improves either tensile strength or elongation over a similar TPSiV elastomer which does not contain the compatibilizer.
Copending U.S. patent application Ser. No. 09/728,920, filed on Dec. 4, 2000, discloses thermoplastic elastomer compositions wherein a silicone gum and a stabilizer are dispersed in a polyester resin and the silicone gum is dynamically vulcanized in the resulting mixture.
While copending U.S. patent application Ser. No. 09/728,920 represents advances in the technology of polyester based TPSiV elastomers, there is still a need for improvements in the processing of these formulations. In particular, there is a need to provide comparable or enhanced elastomeric properties with lower costs formulations, or alternatively formulations having greater latitude. For example, a TPSiV elastomer having reduced levels of expensive Pt catalysts, silicone crosslinker, or silicone base, yet comparable performance to previously reported polyester TPSiV's would of commercial interest. Furthermore, there is a need to provide polyester based TPSiV formulations having excellent tensile and elongation properties, yet having improved flex modulus properties. Such materials are desirable for fabricating blow-molded and extruded articles of manufacturing.
SUMMARY OF T
Gross Craig Steven
Lee Michael Kang-Jen
Liao Jun
Dow Corning Corporation
Moore Margaret G.
Zombeck Alan
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