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
1995-01-13
2001-12-04
Mums, Jeffrey (Department: 1711)
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...
C524S274000, C524S306000, C524S308000, C524S314000, C524S315000, C524S317000
Reexamination Certificate
active
06326426
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to thermoplastic elastomers having improved low temperature performance characteristics. 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 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 rubber in various applications.
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 polyolefin with an elastomeric composition in a way such that the elastomer is intimately and uniformly dispersed as a discrete particulate phase within a continuous phase of the thermoplastic. Early work with vulcanized compositions is found in U.S. Pat. No. 3,037,954 which discloses static vulcanization as well as the technique of dynamic vulcanization wherein a vulcanizable elastomer is dispersed into a resinous thermoplastic polymer and the elastomer is cured while continuously mixing and shearing the polymer blend. The resulting composition is a micro-gel dispersion of cured elastomer, such as butyl rubber, chlorinated butyl rubber, polybutadiene or polyisobutene in an uncured matrix of thermoplastic polymer such as polypropylene. This patent describes the use of oil additives derived from coal tar, pine tar or petroleum in the composition.
In U.S. Pat. No. Re. 32,028 polymer blends comprising an olefin thermoplastic resin and an olefin copolymer rubber are described, wherein the rubber is dynamically vulcanized to a state of partial cure. The resulting compositions are reprocessible. The addition of various lubricants to the cured blend at about one phr is taught to be useful for improving extrusion quality of the compositions.
U.S. Pat. Nos. 4,130,534 and 4,130,535 disclose thermoplastic elastomer compositions 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. The addition of plasticizers and aromatic, naphthenic and paraffinic extender oils to the blend is suggested. No details are given regarding the choice or suitability of any particular class or type of plasticizers. It is well known that different rubbers are compatible with certain types of plasticizers and that not all plasticizers are suitable with all rubbers.
In U.S. Pat. No. 5,157,081 a dynamically vulcanized blend is described comprising a first butyl rubber based elastomer and a second ethylene-propylene polymer elastomer in a matrix of polyolefinic resin. Rubber process oils derived from petroleum fractions may be included, and a general suggestion is made that organic esters and other synthetic plasticizers can be used.
SUMMARY OF THE INVENTION
The present invention is based on the discovery that a thermoplastic elastomer composition having improved low temperature properties is provided by incorporating certain types of low molecular weight ester plasticizers into a blend of crystalline polyolefin homopolymer or copolymer and olefinic rubber. The rubber component of the composition is usually present as very small, i.e. micro-size, particles in the thermoplastic matrix, and it is preferably at least partially cured. Co-continuous morphologies are also possible. Unexpectedly, the inclusion of these organic esters in the composition provides a thermoplastic elastomer which has a significantly lowered glass transition temperature of both the rubber and polyolefin phases and improved impact strength at low temperatures, while maintaining the desirable properties of low compression set, high tear strength and good dynamic properties over a broad temperature range. The compositions have utility as constant velocity joint boots, rack and pinion boots, automotive elastoplastic components and mechanical rubber-plastic (thermoplastic elastomer) goods which need to be serviceable at low temperatures, e.g. −40° C.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
POLYOLEFIN
Polyolefins suitable for use in the compositions of the invention include thermoplastic, crystalline polyolefin homopolymers and copolymers. They are desirably prepared from monoolefin monomers having 3 to 6 carbon atoms, such as propylene, 1-butene, isobutylene, 1-pentene and the like, 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 ∝-olefin comonomer of 4 to 16 carbon atoms, and mixtures thereof. The polypropylene can be highly crystalline isotactic or syndiotactic polypropylene, usually having a narrow range of glass transition temperature (T
g
). Commercially available polyolefins may be used in the practice of the invention.
The amount of polyolefin found to provide useful compositions is generally from about 10 to about 90 weight percent, based on the weight of the rubber and polyolefin. Preferably, the polyolefin content will range from about 60 to about 90 percent by weight.
OLEFINIC RUBBER
Suitable monoolefin copolymer rubbers comprise non-polar, essentially non-crystalline, rubbery copolymers of two or more ∝-monoolefins, preferably copolymerized with at least one polyene, usually a diene. Saturated monoolefin copolymer rubber, for example ethylene-propylene copolymer rubber (EPM) can be used. However, unsaturated monoolefin rubber such as EPDM rubber is more suitable. EPDM is a terpolymer of ethylene, propylene and a non-conjugated diene. Satisfactory non-conjugated dienes include 5-ethylidene-2-norbornene (ENB); 1,4-hexadiene; 5-methylene-2-norbomene (MNB); 1,6-octadiene; 5-methyl-1,4-hexadiene; 3,7-dimethyl- 1,6-octadiene; 1,3-cyclopentadiene; 1,4-cyclohexadiene; dicyclopentadiene (DCPD); and the like.
Butyl rubbers are also useful in the compositions of the invention. As used in the specification and claims, the term “butyl rubber” includes copolymers of an isoolefin and a conjugated monoolefin, terpolymers of an isooolefin, a conjugated monoolefin and divinyl aromatic monomers, and the halogenated derivatives of such copolymers and terpolymers. The useful butyl rubber copolymers comprise a major portion of isoolefin and a minor amount, usually less than 30 wt %, of a conjugated multiolefin. The preferred copolymers comprise about 85-99.5 wt % of a C
4-7
isoolefin such as isobutylene and about 15-0.5 wt % of a multiolefin of 4-14 carbon atoms, such as isoprene, butadiene, dimethyl butadiene and piperylene. Commercial butyl rubber, useful in the invention, is a copolymer of isobutylene and minor amounts of isoprene. Other butyl co- and terpolymer rubbers are illustrated by the description in U.S. Pat. No. 4,916,180, which is fully incorporated herein by this reference.
Another suitable copolymer within the scope of the olefinic rubber of the present invention is a copolymer of a C
4-7
isomonoolefin and a para-alkylstyrene, and preferably a halogenated derivative thereof. The amount of halogen in the copolymer, predominantly in the para-alkylstyrene, is from about 0.1 to about 10 wt %. A preferred example is the brominated copolymer of isobutylene and para-methylstyrene. These copolymers are more fully described in U.S. Pat. No. 5,162,445, which is fully incorporated herein by this reference.
A further olefinic rubber suitable in the invention is natural rubber. The main constituent of natural rubber is the linear polymer cis-1,4-polyisoprene. It is normally commercially available in the form of smoked sheets and crepe. Synthetic polyisoprene can also be used.
Blends of any of the above olefinic rubbers can be
Advanced Elastomer Systems L.P.
Mums Jeffrey
Skinner William A.
LandOfFree
Thermoplastic elastomers having improved low temperature... 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 low temperature..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Thermoplastic elastomers having improved low temperature... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2570831