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
2000-07-18
2001-12-11
Short, Patricia A. (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...
C525S132000, C525S146000, C525S173000, C525S176000
Reexamination Certificate
active
06329463
ABSTRACT:
FIELD OF INVENTION
The present invention relates to thermoplastic vulcanizates (TPVs) containing high melting point thermoplastics such as aromatic/aliphatic polyesters and a vulcanized polar rubber interdispersed therein or dispersed therein. The use of preferred curatives, e.g. bisoxazolines, have the advantage of selectively crosslinking the rubber phase without affecting the thermoplastic and without causing the evolution of volatile organics.
BACKGROUND OF THE INVENTION
Heretofore, crystalline polyolefins such as polyethylene and polypropylene when utilized as the thermoplastic component in thermoplastic vulcanizates have an upper continuous use temperature below 130° C. due to the relatively low melting point of the crystalline thermoplastic phase (e.g. commercially available polypropylene has a melting temperature of 165° C.). Accordingly, these hydrocarbon based compositions have limited use in under the hood applications of a vehicle where high temperatures are encountered and where low hydrocarbon oil swell is desirable. Blends of polar thermoplastics and polar rubbers in uncrosslinked form tend to have undesirable high compression set and poor mechanical strength. Conventional curatives for the polar rubbers generally have undesirable effects on a thermoplastic vulcanizate formed from a polyester and an acrylate rubber, such as degrading the thermoplastic or the release of undesirable volatile components during the curing process.
SUMMARY OF THE INVENTION
The thermoplastic vulcanizate compositions of the present invention contain a polar thermoplastic and a crosslinked polar rubber. Preferred polar thermoplastics include polyesters, polycarbonates, polyphenylene oxide, or combinations thereof Preferred rubbers include acrylate (acrylic) rubbers, and ethylene-acrylate rubbers with pendant or terminal carboxylic acid or carboxylic anhydride functionality. Preferred curatives include multi-functional oxazolines and oxazine compounds.
DETAILED DESCRIPTION
Polyesters are preferred as the thermoplastic phase of a thermoplastic vulcanizate (TPV). The polyesters of the thermoplastic defined herein are condensation polymers as contrasted to the acrylate rubbers which are formed by addition polymerization. The various polyesters can be either aromatic or aliphatic or combinations thereof and are generally directly or indirectly derived from the reactions of diols such as glycols (including aliphatic, cycloaliphatic and aryl or combinations thereof) having a total of from 2 to 10, 12 or 15 carbon atoms and desirably from about 2 to about 4 or 6 carbon atoms with either aliphatic acids having a total of from about 3 to about 20 carbon atoms and desirably from about 3 to about 15 or aromatic acids having a total of from about 8 to about 15 carbon atoms or combinations thereof. The use of aromatic diacids generally result in desirable higher softening temperatures. Acids generally refer to dicarboxylic acids, their anhydrides, or their dialkyl esters. Generally, aromatic polyesters are preferred such as poly(ethylene terephthalate) (PET). poly(propylene terephthalate) (PPT), poly(trimethylene terephthalate) (PTT), poly(butylene terephthalate) (PBT), poly(ethylene isophthalate), poly(butylene naphthalate) and the like, as well as an end-capped epoxy derivative thereof e.g., a monofunctional epoxy poly(butyleneterephthalate). Desirably at least 70 or 80, more desirably at least 90 mole percent of the polyester, based on the dicarboxylic acid component, is terephthalic acid radicals. Desirably at least 70 or 80, more desirably at least 90 mole percent of the polyester, based on the diol component, is derived from ethylene glycol, 1,3-propylene glycol or 1,4-butylene glycol or combinations thereof. Trifunctional and higher functionality acids and polyols desirably can be in the polyester in small amounts, such as less than 1, 5, or 10 mole percent of the acid or polyol component. U.S. Pat. No. 3,692,744 discloses such polyesters.
Various polycarbonates can also be utilized as the thermoplastic and the same are esters of carbonic acid and the above diols. A suitable polycarbonate is the ester of carbonic acid and bisphenol A, i.e., poly(carbonyldioxy-1,4-phenyleneisopropylidene-1,4-phenylene). The various ester polymers can also include polyester block copolymers such as those containing at least one block of a polyester with a softening temperatures above 100° C. and at least one rubbery block with a softening temperature below 100° C. and desirably below 75° C. Such rubbery blocks include a polyether derived from at least one glycol having from 2 to 6 carbon atoms, e.g., polyethylene glycol, or from at least one alkylene oxide having from 2 to 6 carbon atoms. The rubbery block can also be another polyester that has a softening point below 100° C. or more desirably below 75° C. A preferred block polyester is poly(butylene terephthalate)-b-(tetramethylene glycol) which is available as Hytrel™ from DuPont. A preferred polyester block copolymer described in U.S. Pat. No. 4,981,908 is herein incorporated by reference. That block copolymer has polyester blocks with a softening temperature above 100° C. and polyester blocks with a softening temperature of less than 100 or less than 75° C. in the weight ratios of from 1:4 to 1:0.1 respectively. Coupling species including ester linkages and others, e.g. urethane, epoxy, etc. The block copolymers desirably have a number average molecular weight of at least 5000. The dicarboxylic acids desirably have molecular weights of 300 or less for the molecule less the carboxylic acid groups. The glycols of the ester desirably have a molecular weight of 300 or less for the molecule less the hydroxyl groups.
The molecular weight of the various polyesters is such that it is a suitable engineering plastic. Accordingly, the weight average molecular weight of the various polyesters desirably range from about 40,000 to about 100,000 with from about 90,000 to about 100,000 being preferred.
Polyphenylene oxides can be used as part or all of the thermoplastic phase. They are commercially available and generally have a molecular weight such that they also have a glass transition temperature of at least 150° C., desirably at least 1 75° C., and preferably 210° C.
The acrylic rubbers (acrylate) useful as the rubber phase of the thermoplastic vulcanizate are polymerized from monomers comprising alkyl acrylates wherein the alkyl portion of the ester has from 1 to 10 or 12 carbon atoms, with from 1 to 4 carbon atoms being preferred. The total carbon atoms of each alkyl acrylate may range from 4 to 13 or 15 carbon atoms and include alkyl substituted, e.g. alkyl alkylacrylates such as methyl methacrylate in small amounts, i.e., desirably less than 5, 10 or 15 mole percent. Desirably the monomers include unsaturated mono or polycarboxylic acids or anhydrides thereof having from about 2 to about 15 carbon atoms. Monomers such as methyl methacrylate form thermoplastic rather than rubbery polymers when present in high amounts. Specific examples of rubbery acrylic polymers include polymers of methyl acrylate, butyl acrylate, butyl acrylate, ethylhexyl acrylate, and the like. The acrylic polymers generally include repeat units with pendant or terminal functionality (e.g., pendant carboxylic groups to facilitate crosslinking with oxazoline curatives). These polymers desirably have from about 1 or 2 to about 10 mole percent, more desirably from about 2 or 3 to about 8 mole percent repeat units with at least one carboxylic acid or anhydride of a dicarboxylic acid. If the polymers are only copolymers of acrylate and acid or anhydride monomers they desirably have from about 90 to about 98 mole percent repeat units from acrylates, more desirably from about 92 to about 97 or 98 mole percent.
The carboxylic acid cure site in the rubber may alternatively be generated by heat during the rubber and plastic melt blending process. For example, tert-butyl acrylate or tert-butoxycarbonyl acrylate that is copolymerized into the ethylene-acrylate or acrylate rubber can decompose to a repeat u
Abdou-Sabet Sabet
Abraham Tonson
Advanced Elastomer Systems L.P.
Laferty Samuel B.
Short Patricia A.
Skinner William A.
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