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
1999-10-29
2001-06-26
Nutter, Nathan M. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S194000, C525S195000, C525S210000, C525S232000, C525S240000, C525S241000
Reexamination Certificate
active
06251998
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to thermoplastic elastomer compositions prepared using hydrosilylation crosslinking of the elastomer component of the composition. A thermoplastic elastomer is generally defined as a polymer or blend of polymers that can be processed and recycled in the same way as a conventional thermoplastic material, yet has properties and functional performance similar to that of vulcanized rubber at service temperatures. Blends or alloys of plastic and elastomeric rubber have become increasingly important in the production of high performance thermoplastic elastomers, particularly for the replacement of thermoset rubbers in various applications. High performance thermoplastic elastomers in which a highly vulcanized rubbery polymer is intimately dispersed in a thermoplastic matrix are generally known as thermoplastic vulcanizates.
2. Description of the Related Art
Polymer blends which have a combination of both thermoplastic and elastic properties are generally obtained by combining a thermoplastic resin with an elastomeric composition in a way such that the elastomer component is intimately and uniformly dispersed as a discrete particulate phase within a continuous phase of the thermoplastic. Early work with vulcanized rubber components is found in U.S. Pat. No. 3,037,954 which discloses both static vulcanization of the rubber, as well as the technique of dynamic vulcanization wherein a vulcanizable elastomer is dispersed into a molten resinous thermoplastic polymer and the elastomer is cured while continuously mixing and shearing the blend. The resulting composition is a micro-gel dispersion of cured elastomer in an uncured matrix of thermoplastic polymer.
In U.S. Pat. No. 32,028 polymer blends comprising an olefin thermoplastic resin and an olefin copolymer are described, wherein the rubber is dynamically vulcanized to a state of partial cure. The resulting compositions are reprocessible. U.S. Pat. Nos. 4,130,534 and 4,130,535 further disclose thermoplastic vulcanizates comprising butyl rubber and polyolefin resin, and olefin rubber and polyolefin resin, respectively. The compositions are prepared by dynamic vulcanization and the rubber component is cured to the extent that it is essentially insoluble in conventional solvents. A range of crosslinking, or curing, agents for the vulcanization of the rubber are described in the early art, including peroxides, sulfurs, phenolic resins, radiation, and the like.
U.S. Pat. No. 4,803,244 generally discusses the use of multifunctional organosilicon compounds in conjunction with a catalyst as an agent for crosslinking the rubber component of a thermoplastic elastomer by hydrosilylation. Hydrosilylation involves the addition of a silicon hydride across a multiple bond, often with a transition metal catalyst. This patent describes a rhodium catalyzed hydrosilylation of EPDM rubber in a blend with polypropylene to produce thermoplastic elastomers having a gel content of up to 34% (after correction for the plastic phase). This degree of vulcanization was achieved only with a high level of catalyst.
A further discussion of hydrosilylation crosslinking of the rubber in a thermoplastic elastomer composition is found in U.S. Pat. No. 5,672,660. The platinum catalyzed hydrosilylation of EPDM rubber containing 5-vinyl-2-norbornene as a diene monomer is described.
SUMMARY OF THE INVENTION
The present invention is based on the discovery that the process for hydrosilylation crosslinking of the rubber is a thermoplastic elastomer can be improved by employing as the rubber an ethylene, &agr;-olefin, non-conjugated diene elastomeric polymer containing vinyl norbornene as a diene component. More particularly, it has been discovered that when the Mooney viscosity, ethylene content and diene content of this rubber are within defined ranges, unexpectedly low concentrations of hydrosilylation agent and catalyst will fully crosslink the rubber in the dynamic vulcanization process and provide a thermoplastic elastomer product with excellent physical properties and oil resistance. Additionally the ethylene, &agr;-olefin, non-conjugated diene elastomeric polymer of the invention on which the blends with thermoplastic resins are based will generally have lower levels of diene to achieve similar or improved properties, when compared to blends made from previously available ethylene, &agr;-olefin, non-conjugated diene elastomeric polymers. The previously available elastomers contained a diene selected from 5-ethylidene-2-norbornene, 1.4-hexadiene, dicyclopentadiene, or combinations thereof and compounds derived from them. The combination of lower diene content and lower catalyst required lead to even better properties for heat aging, UV stability and colorability.
The compositions produced by the improved process have utility as replacements for thermoset rubber compounds in a variety of applications, particularly where molding or extrusion is involved and the combination of thermoplastic and elastomeric properties provides an advantage. Typical uses include molded articles for automobile underhood parts, engineering and construction materials, mechanical rubber goods, industrial parts such as hose, tubing and gaskets, electrical applications and household goods.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Thermoplastic elastomer compositions may generally be prepared by blending a thermoplastic resin and a rubber, then melting the thermoplastic component and mixing the melt until the blend is homogeneous. If a composition of vulcanized rubber in a thermoplastic matrix is desired, crosslinking agents (also referred to as curatives or vulcanizing agents) are added to the blend and crosslinking occurs during the mixing under conditions of heat and shear. This latter process is described as dynamic vulcanization.
Thermoplastic Resins
A wide range of thermoplastic resins and/or their mixtures have been used in the preparation of thermoplastic elastomers, including polypropylene, polypropylene copolymers, HDPE, LDPE, VLDPE, LLDPE, polyethylene copolymers, cyclic olefin homopolymers or copolymers as well as olefinic block copolymers, polystyrene, polyphenylene sulfide, polyphenylene oxide and ethylene propylene copolymer (EP) thermoplastics.
Thermoplastic resins useful in the compositions produced by the invention include crystalline and semi-crystalline polyolefin homopolymers and copolymers. They are desirably prepared from monoolefin monomers having 2 to 20 carbon atoms, such as ethylene, propylene, 1-butene, 1-pentene and the like, as well as copolymers derived from linear and cyclic olefins, with propylene being preferred. As used in the specification and claims the term polypropylene includes homopolymers of propylene as well as reactor copolymers of polypropylene which can contain about 1 to about 20 wt % of ethylene or an &agr;-olefin comonomer of 4 to 20 carbon atoms, and mixtures thereof. The polypropylene can be atactic, isotactic or syndiotactic, made with Ziegler-Natta or metallocene catalysts. Commercially available polyolefins may be used in the practice of the invention. Other thermoplastic resins which are substantially inert to the rubber, the silicon hydride and the hydrosilylation catalyst would also be suitable. Blends of thermoplastic resins may also be used.
The amount of thermoplastic resin found to provide useful compositions is generally from about 5 to about 90 weight percent, based on the weight of the rubber and resin. Preferably, the thermoplastic resin content will range from about 20 to about 80 percent by weight of the total polymer.
Rubber
In the present invention an ethylene, &agr;-olefin, non-conjugated diene elastomeric polymer containing vinyl norbornene as a diene component is used as the rubber component. It contains from about 40 to about 85 weight percent ethylene, preferably about 45 to about 80 weight percent, and more preferably in the range of from about 50 to about 75 weight percent. The rubber component contains in the range of from about 0.25 to about 5 weig
Abdou-Sabet Sabet
Gilbertson Gary W.
Hazelton Donald R.
Hazelton Ronald L.
Medsker Robert E.
Advanced Elastomer Systems L.P.
Nutter Nathan M.
Skinner William A.
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