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
2000-12-29
2002-09-17
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...
C525S203000, C525S216000, C525S232000, C525S240000, C525S241000
Reexamination Certificate
active
06451915
ABSTRACT:
TECHNICAL FIELD
The present invention is generally directed toward thermoplastic elastomers and processes for making the same. These thermoplastic elastomers have improved processing properties. Specifically, the thermoplastic elastomers include a rubber that is at least partially cured, a thermoplastic resin, and a polymeric processing additive. The polymeric processing additive is a thermoplastic resin that has a very high melt flow index.
BACKGROUND OF THE INVENTION
Thermoplastic elastomers are known. They have many of the properties of thermoset elastomers, yet they are processable as thermoplastics. One type of thermoplastic elastomer is a thermoplastic vulcanizate, which maybe characterized by finely-divided rubber particles dispersed within a plastic. These rubber particles are crosslinked to promote elasticity. Thermoplastic vulcanizates are conventionally produced by dynamic vulcanization, which is a process whereby a rubber is cured or vulcanized within a blend with at least one non-vulcanizing polymer while the polymers are undergoing mixing or masticating at some elevated temperature, preferably above the melt temperature of the non-vulcanizing polymer.
The presence of the rubber, however, makes these thermoplastic vulcanizates difficult to process after dynamic vulcanization. As a result, heavier demands are placed upon processing machinery, especially as the amount of rubber within the thermoplastic vulcanizate is increased, which it desirably is in order to maximize the elastomeric behavior.
Conventionally, these processing problems have been alleviated by reducing the amount of cure, by using lower molecular weight thermoplastic resins, or by using processing oils such as paraffinic oils and waxes, processing aids such as metal stearates or fatty acid amides, or surfactants such as sulfate and sulfonate salts.
Because conventional approaches to alleviating processing difficulties can deleteriously impact the mechanical properties of thermoplastic elastomers, there is a need for thermoplastic elastomers that have improved processability without inferior mechanical properties.
SUMMARY OF INVENTION
In general the present invention provides a thermoplastic elastomer formed by a process comprising the steps of dynamically vulcanizing a rubber within a mixture that includes the rubber, from about 10 to about 80 percent by weight of a thermoplastic resin based upon the total weight of the rubber and the thermoplastic combined, and from about 1 to about 25 percent by weight of a polymeric processing additive based upon the total weight of the rubber and the thermoplastic combined, where the polymeric processing additive is a linear polyolefin resin that has an melt flow rate that is greater than about 1,000 dg/min, a diene-modified polyolefin polymer that has an melt flow rate that is greater than about 1,000 dg/min, from about 0.005 to about 2.00 mole percent polymeric units deriving from dienes, and a viscosity average branching index that is from about 0.4 to about 0.95, or a mixture of the linear polyolefin resin and the diene-modified polyolefin polymer, where the step of dynamically vulcanizing the rubber results in vulcanized rubber having a crosslink density of about 40 to about 180 mole per milliliter of rubber.
The present invention also includes a composition comprising a vulcanized rubber a thermoplastic resin, and a polymeric processing additive that has a melt flow rate that is greater than about 500 dg/min.
The present invention further includes a process for forming a thermoplastic elastomer comprising of the step of dynamically vulcanizing a rubber within a mixture that includes the rubber, a thermoplastic resin, and a polymeric processing additive, where said polymeric processing additive includes a linear polyolefin having a melt flow rate that is greater than about 500 dg/min, branched molecules characterized by a viscosity average branching index of less than about 0.85 and melt flow rate that is greater than about 500 dg/min, or a mixture of both the linear polyolefin and the branched molecules.
The thermoplastic elastomers of the present invention advantageously demonstrate an improved processability and surface appearance. Surprisingly, this result has been achieved without deleteriously sacrificing mechanical properties. It has been found that by using relatively small amounts of polymeric processing additives having a very high melt flow rate, the processability of the thermoplastic elastomers can be improved without significantly reducing mechanical properties.
PREFERRED EMBODIMENT FOR CARRYING OUT THE INVENTION
The thermoplastic elastomers of this invention include at least one rubber, at least one thermoplastic resin, and at least one polymeric processing additive. The polymeric processing additive is a resin that has a very high melt flow rate.
Any rubber or mixture thereof that is capable of being crosslinked or cured can be used as the rubber component of the thermoplastic elastomers of this invention. Reference to a rubber may include mixtures of more than one rubber. Some non-limiting examples of these rubbers include elastomeric copolymers, butyl rubber, natural rubber, styrene-butadiene copolymer rubber, butadiene rubber, acrylonitrile rubber, halogenated rubber such as brominated and chlorinated isobutylene-isoprene copolymer rubber, butadiene-styrene-vinyl pyridine rubber, urethane rubber, polyisoprene rubber, epichlolorohydrine terpolymer rubber, and polychloroprene. The preferred rubbers are elastomeric copolymers and butyl rubber.
The term elastomeric copolymer refers to rubbery copolymers polymerized from ethylene, at least one &agr;-olefin monomer, and optionally at least one diene monomer. The &agr;-olefins may include, but are not limited to, propylene, 1-butene, 1-hexene, 4-methyl-1 pentene, 1-octene, 1-decene, or combinations thereof. The preferred &agr;-olefins are propylene, 1-hexene, 1-octene or combinations thereof. The diene monomers may include, but are not limited to, 5-ethylidene-2-norbornene; 1,4-hexadiene; 5-methylene-2-norbornene; 1,6-octadiene; 5-methyl-1,4-hexadiene; 3,7-dimethyl-1,6-octadiene; 1,3-cyclopentadiene; 1,4-cyclohexadiene; dicyclopentadiene; 5-vinyl-2-norbornene and the like, or a combination thereof. The preferred diene monomers are 5-ethylidene-2-norbornene and 5-vinyl-2-norbornene. In the event that the copolymer is prepared from ethylene, &agr;-olefin, and diene monomers, the copolymer may be referred to as a terpolymer or even a tetrapolymer in the event that multiple &agr;-olefins or dienes are used. The preferred elastomeric copolymers include terpolymers of ethylene, propylene, and 5-ethylidene-2-norbornene.
Elastomeric copolymers are commercially available under the tradenames Vistalon™(Exxon Mobil Chemical Co.; Houston, Tex.), Keltan™ (DSM Copolymers; Baton Rouge, La.), Nordel™ IP (DuPont Dow Elastomers; Wilmington, Del.), BUNA EP™ (Bayer; Germany) and ElastoFlo™ (Union Carbide; Danbury, Conn.).
The term butyl rubber refers to rubbery amorphous copolymers of isobutylene and isoprene or an amorphous terpolymer of isobutylene, isoprene, and a divinyl aromatic monomer. These copolymers and terpolymers should preferably contain from about 0.5 to about 10 percent by weight, or more preferably from about 1 to about 4 percent by weight, isoprene. The term butyl rubber also includes copolymers and terpolymers that are halogenated with from about 0.1 to about 10 weight percent, or preferably from about 0.5 to about 3.0 weight percent, chlorine or bromine. This chlorinated copolymer is commonly called chlorinated butyl rubber. While butyl rubber is satisfactory for the practice of this invention, halogen-free butyl rubber containing from about 0.6 to about 3.0 percent unsaturation is preferred, with butyl rubber having a polydispersity of about 2.5 or below being especially preferred. Butyl rubbers are commercially prepared by polymerization at low temperature in the presence of a Friedel-Crafts catalyst as disclosed within U.S. Pat. Nos. 2,356,128 and 2,944,576. Butyl rubber is commercially avail
Brant Patrick
Cheng Jianya
Dekmezian Armenag H.
Ellul Maria D.
McDaniel Paul E.
Advanced Elastomer Systems L.P.
Nutter Nathan M.
Reginelli Arthur M.
Skinner William A.
LandOfFree
Thermoplastic elastomers having improved processing and... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Thermoplastic elastomers having improved processing and..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Thermoplastic elastomers having improved processing and... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2839867