CA2112173A1 - Thermoplastic elastomers having improved low temperature properties - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
Thermoplastic elastomers having improved low temperature properties are provided by incorporating suitable low molecular weight ester plasticizer into blends of crystalline polyolefin homopolymer or copolymer and olefinic rubber. The rubber component of the composition is at least partially cured.

Description

-~ 2 i 12~73 , THERMOPLASTIC ELASTOMERS HAVING IMPROVED
LOw TEMPERATURE PROPERTIES
~-, ~, BACKGROUND OF THE ~VENTION
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 . ~hermoplasuc material. ye~ has properties and performance similar to that of vulcanized -. 10 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 applicauons.
Description of the Related Art Polymer blends which have a combination of both thermoplastic and elastic properties 15 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 vulcanizauon as well as the technique of dynarnic vulcanization wherein a vulcanizable r,* 20 elastomer is dispersed into a resinous thermoplastic polymer and the elastomer is cured while continuously mixing and shearing the polymer blend. The resulting composiuion is a micro-3 gel dispersion of cured elastomer, such as butyl rubber, chlorinated butyl rubber, ., ~ . ,, , .. . ~ . ~ !, . , ., ` , ,, . . . " , ....

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2i~L73 -r polybutadiene or polyisobutene in an uncured matrix of thermoplastic polymer such as ~, polypropylene. This patent descnbes the use of oii additives derived from coal tar. pine tar or petroleum in the composition.
In U.S. Pat. No. Re. 3~,028 polymer blends comprising an olefin thermoplastic resin 5 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 composi~ions.
U.S. Pat. Nos. 4.130.53~ and 4.130.535 disclose thermoplastic elastomer 10 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 15 type of plastickers. 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 matrDc of polyolefinic resin Rubber process oils derived from petroleum fractions may be ~0 included, and a general suggestion is made that organic esters and other synthetic plasticizers can be used.

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; The present invention is based on the discovery that a thermoplastic elastomer ',7, composition having improved low temperature properties is provided by incorporating certain types of low molecular weight ester plasticizers into a blend of crystalline polyolefin 5 homopolymer or copolymer and olefinic rubber. The rubber component of the composition is usually present as very small, i.e. micro-siu, 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 10 the rubber and polyolefin phases, improved impact strength at low temperatures and i ~
improved abrasion resistance, 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 IS which need to be serviceable at low temperatures, e.g. -40 C.
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DESCRIPIION OF T~E PREFERRED EMBODIMENTS
, ~ POLYOLEFIN
Polyolefins suitable for use in the compositions of the invention include thermoplastic, crystalline polyolefin homopolymas and copolymers. They are desirably prepared from ~- t0 monoolefin monomers having 3 to 6 carbon atoms, such as propylene, l-butene, isobutylene, l-pentene and the like, with propylene being preferred. As used in the specification and ~:~A claims the term polypropylene includes homopolymers of propylene as well as reactor ~ ,. ~

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l 7 3 copolvmers of polypropylene which can contain about 1 tO about 20 wt% of ethylene or an ~-olefin comonomer ot 4 to 16 c~rbon atoms, and mixtures thereof. The polypropylene can be highly crystalline isotactic or svndiotactic polypropylene. usually having a narrow range of glass transition temperature (T.). Commercially available polyolefins may be used in the 5 practice of the invention.
The amount of polyolefin found to provide useful compositions is generally from $ about 10 to about 90 weight percent~ b~sed on the weight of the rubber and polyolefin.
, Preferably, the polyolefin conlent will range trom about 60 to about 90 percent by weight.
,, OLEFINlC RUBBER
Suitable monoolefin copolvmer rubbers comprise non-polar, essentially non-crystailine, rubbery copolymers ot two or more x-monoolefins, preferably copolymerized with at least one polyene, usually a diene. Saturated monoolefin copolymer rubber, for e1~ample ethylene-propylene copolymer rubber (EPM) can be used. However, unsaturated monoolefin rubber such as EPDM rubber is more suitable. EPDM is a terpolymer of 15 ethylene, propylene and a non-conjuga~ed diene. Satisfactory non-conjugated dienes include 5-ethylidene-2-norbornene (ENB); I,~-hexadiene; 5-methylene-2-norbornene (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 20 specification and claims, the term "butyl rubber" includes copolymers of an isoolefin and a conjugated monaolefin, terpolymers of an isooolefin, a conjugated monoolefin and divinyl aromatic monomers, and the halogenated deriviatives of such copolymers and terpolymers.
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v wli21 73 The useful butyl rubber copolvmers comprise a major portion of isoolefin and a minor , amount, usually less than 30 Wt%, or a conjugated multiolefin. The preferred copolymers comprise about 85-99.5 wt~o ot a C, 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 ~"i the descripdon in U.S. Pat. No. ~.916.180, which is fully incorporated herein by this reference.
Another suitable copolvmer ~nhin the scope of the olefinic rubber of the present , 10 invention is a copolymer ot a C,, isomonoolefin and a para-alkylstyrene, and preferably a ?.
halogenated derivadve thereot. The amount of halogen in the copolymer, predominantly in ~,, the para-alky}styrene, 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 invendon is natural rubber. The main consdtuent of natural rubber is the linear polymer cis-1,4-polyisoprene. It is normally commercially available in the form of smolted sheets and crepe. Synthetic polyisoprene can also be used.
Blends of any of the above olefinic rubbers can be employed, rather than a single olefinic rubber.
In preparing the compositions of the invention, the amount of olefinic rubber S

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~112~ 73 -generally ranges from about 90 tO about 10 weight percent, based on the weight of the rubber and polyolefin. Preferablv. ~he ole~`inic rubber content will be in the ranve of from -..;.
about 40 to about 10 weight percent.
ESTER PLASTICIZE~
The addition of cenain low to medium molecular weight (< lO,000) organic esters and alkyl ether esters to the compositions of the invention dramatically lowers the T, of the polyolefin and rubber componen~s. and o~ the overall composition, and improves the low temperature properties, particularly tlexibility and strength. It is believed that these effects `f. are achieved by the partitioning ol the ester into both the polyolefin and rubber components ~ 10 of the compositions. Particularly suitable esters include monomeric and oligomeric materials f~ ~ having an average molecular weight below about 2000, and preferably below about 600. It .~
,' is important that the ester be compatible. or miscible, with both the polyo}efin and rubber components of the compositions, i.e. that it mix with the other components to form a single phase. The esters found to be most suitable were either aliphatic mono- or diesters or alten~atively oligomeric aliphatic esters or alkyl ether esters. Polymeric aliphatic esters and . aromatic esters were found to be significantly less effective, and phosphate esters were for the most part ineffective.
Esters may be screened for suitability by a simple test of their ability to swell a polyolefin such as polypropylene. For the purposes of this invention, polypropylene samples (2.0 x 20 x 50 mm) were immersed in various ester plasticizers or non-ester diluents such as mineral oils, and were swollen at 125 C to constant weight (norma}ly about 24 hours). ~f the total change in weight was greater than 40%. the diluent was considered significantly !' ~ ~

~2~73 compatible with the polypropylene and theretore suitable for preparing compositions with enhanced low temperature performance.
Examples of esters which have been t^ound satisfactory for use in the present invention include isooctyltallate, isooc~vlolea~e. n-butvltallate, n-butyloleate, butoxyethyloleate.
dioctylsebacate, di 2-ethylhexyisebacate, dioctylazelate, diisooctyldodecanedioate, alkylalkylether diester glutarate and oligomers thereof. Other analogues expected to be '~ useful in the present invention include alkvl alkylether mono- and di-adipates, mono- and ;, .
diallcyl àdipates, glutarates. sebacates. azelates, ester deriviatives of castor oil or tall oil and oligomeric mono- and diesters or mono- and dialkvl ether esters therefrom. Isooctyltallate and n-butyltallate are parucularly preterred. These esters may be used alone in the compositions, or as mixtures ot different esters, or they may be used in combination with conventional hydrocarbon oil diluents or process oils, e.g. paraffin oil. The amount of ester plasticizer in the composition will generally be less than about 250 phr, and preferably less than about 175 phr.
ADDITIVES
In addition to the polyoletm. rubber and ester components, the compositions of the invention include curatives and may also include reinforcing and non-reinforcing fillers, antioxidants, stabilizers, rubber processing oil, extender oils, lubricants, antiblocking agents, antistatic agents, waxes, foaming agents, pigments, flame retardants and other processing aids known in the rubber compounding art. Such additives can comprise up to about 50 wt%
of the total composition. Fillers and extenders which can be utilized include conventional inorganics such as calcium carbonate. clays, silica, talc, titanium dioxide, carbon black and '~

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-~-l i2173 the like. The rubber processing oiis generally are paraffinic, naphthenic or aromatic oils ~3! derived from petroleum trac~ions. The tvpe will be that ordinarily used in conjunction with the specific rubber or rubbers present in (he composition, and the quantity based on the total rubber content may range trom zero to a few hundred phr. However, it is an important aspect of the present invention that processing oil need not be present, and in fact it may be totally replaced by the ester plasticizer component of the composition. In other word, depending upon the properties desired in the thermoplastic elastomers of the invention, the composition may be ~ree ot processing oil or it may contain a combination of processing oil and ester.
PROCESSING
The olefin rubber component or the thermoplastic elastomer is generally present as small, i.e. micro-size, particles within a continuous polyolefin matrix, although a co-continuous morphology or a phase inversion is also possible depending on the amount of rubber relative to plastic, and the cure system or degree of cure of the rubber. The rubber is desirably at least partially crosslinked, and preferably is completely or fully crosslinked.
The partial or complete crosslinking can be achieved by adding an appropriate rubber curative to the blend of polyolefin and rubber and vulcanizing the rubber to the desired degree under conventional vulcanizing conditions. However, it is preferred that the rubber be crosslinked by the process of dynamic vulcanization. As used in the specification and claims, the term "dynamic vulcanization" means a vulcanization or curing process for a rubber contained in a thermoplastic elastomer composition, wherein the rubber is vulcanized under conditions of high shear at a temperature above the melting point of the polyolefin ~, ' . ~ ",,~,~, .. .

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component. The rubber is thus simultaneouslv crosslinked and dispersed as fine particles - within the polyolefin matrix. 31though as noted above other morphologies may also exist.
- Dynarnic vulcanization is etfected by mixing the thermoplastic elastomer components at ,, elevated temperature in conventional mixing equipment such as roll mills, Banbury mixers, 5 Brabender mixers, continuous mixers. mixing extruders and the like. The uniquecharac~eristic of dynamically cured compositions is that, notwithstanding the fact that the rubber component is partially or fully cured, the compositions can be processed and 'i reprocessed by conventional plaslic processing techniques such as extrusion, injection ~s molding and compression molding. Scrap or flashing can be salvaged and reprocessed.
~10 Those ordinarily skilled in the art will appreciate the appropriate quantities! types of cure systems and vulcanization conditions required to carry out the vulcanization of ~he rubber. The rubber can be vulcanized using varying amounts of curative, varying temperatures and varying time of cure in order to obtain the optimum crosslinking desired.
Any known cure system for the rubber can be used, so long as it is suitable under the vulcanization conditions with the specific olefinic rubber or combination of rubbers being used and with the polyolefin, These curatives include sulfur, sulfur donors, metal oxides, resin systems, peroxide-based systems and the like, both with and without accelerators and co-agents. Such cure systems are well known in the art and literature of vulcanization of elastomers.
The terrns "fully vulcanized" and "completely vulcanized" as used in the specification and claims means that the rubber component to be vulcanized has been cured to a state in which the elastomeric properties of the crosslinked rubber are similar to those of the rubber ~'' ' ' ,'~ ~

~ ~ i2173 in its conventional vulcanized sr~te. apart rrom ~he thermoplastic elastomer composition. The ' degree or cure can be descnbed in lerms or gel content or, conversely, extractable components. Alternatively the degree of cure mav be expressed in terrns of crosslink density. All of these descriptions are well known in ~he art, for example in U.S. Pat. Nos.
5,100,947 and 5,157,081, both or which are fullv incorporated herein by this reference.
The following general procedure was used in the preparation of thermoplastic elas~omers of the inven~ion as se~ tor~h in ~he examples. The polyolefin and rubber were '~ placed in a heated internal mixer. ~-ith ~n appropriate portion of the ester and other desired additives. The mixture was hea~ed to a temperature sufficient to melt the polyolefin 10 component, the mixture was masticated and curati-e was added while mastication continued.
After a maximum of mixing lorque indicated that ulcanization had occured, additional ester was added as indicated, and mixing was continued until the desired degree of vulcanization was achieved. The order of addition of the various components may vary. The compositions were then removed from the mixer, molded and tested for their physical 15 properlies.
The invention will be better understood by reference to the following examples which serve to illustrate but not limit the present invention.
Example I
After screening diluents with the swelling test described earlier, compositions were 20 prepared to demonstrate the effect of including certain organic esters in thermoplastic elastomers, as compared to mineral oils. The rubber, plastic, a phenolic curing agent and additives were blended in an elec~rically heated Brabender mixer of 65-80 cml capacity, at a ~ii2173 - mixin_ speea of 100 rpm and a semoerature of 120 to 190 C. Before melting of the polvolefin component~ a Lewis acid ~ as added to the blend and mixing was continued. The mixing temperature as a funcuon os time was obser~edt and the onset of vulcaniza~ion was .- accompanied by a rapid increase in mixin torque at around 185 C. Mixing was stopped 5 when the torque became relatively constant. The compositions were removed from the mixer and sheets were molded at 190C and used for measurement of physical properties.
The key property for determining ~he etficacy ot a plasticizer in improving the low temperature behavior ot a lhermopiastic elastomer is the glass transition temperature of both the rubber and plastic components. , he ~lass transition temperatures (T~) were measured using a Rheometncs RDA II d~namic mechanical spectrometer, using the torsional mode.
The dynamic strain was 0.5%: ~he autostran feature was used; the frequency was 10 Hz.
Control blend "A" contained no ester plasticizer, and had the following composition:
Ingredient % PHR
EPDM (Vistalon 8600) 25.71 100 lS Isotactic Polypropylene 56.34 219.10 Fillers:
Active black (40%) 4.96 19.28 Clay 10.29 40.00 Curatives 2.70 lO.50 ~ ~ .

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21 ~ ~173 The remaining blends conr~ined es~er plasticizer or conventional processing oil, and had the following composition "B":
Ingredient ~ P~R
S EPDM (Vistalon 86û0) 19.28 100 lsotactic Polypropylene 42.22 219.10 Fillers:
Active black (~0%) 3.72 19.28 Clay 7.71 40.00 Curatives . 2.03 10.50 ~ -Oil/Ester plasticizer 25.05 130 The glass transition lemperatures ot the compositions are set forth in Table 1. The oils asld plasticizers were selected using the swelling screening test described earlier.

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Blend OillEster Rubber T~ C Plastic Tg C
A None -~1 +10 B1 Amoco Rycon~ Grease -17 -1 j 5 B2 SunpaP 150M Paratfinic Oil ~6 -5 B3 Parapol~ 750 Polvbutene -~7 -5 B4 Cyclolube~D 213 Naphthenic Oil -18 -5 ~ .
BS Cyclolube 4053 Naphthenic Oil -j0 -5 B6 Cyclolube 410 Naph~henic Oil -51 -5 B7 Amoco 9012 Polvpropene a5 -10 B8 Alkylalkvlether diester glutarate -55 -11 (Plasthall0 7041) B9 Diisooctyldodecanedioate (Plasthall DlODD) -56 -14 B10 Dioctylazelate (Plasthall DOZ) -60 -22 Bll Diocty}sebacate (Plasthall DOS) -60 -18 B12 Butoxyethyloleate (Plasthall 325) -66 -20 B13 n-Butyloleate (Plasthall 914) -71 -24 814 n-Butyltallate (Plasthall 503) -70 -24 B15 ~sooctyltallate (Plasthall 100) -75 -26 As is apparent from the foregoing, the inclusion of organic alkyl and alkyl ether esters in dynamically vulcanized thermoplastic elastomer substantially reduces the T, of both the rubber and plastic components, in comparison to the conventional processing oils and grease.

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Example 2 Compositions containing hivn molecular weight (polymeric) ester plasticizers were compared with a composition ot the invemion to demonstrate that the polymeric materials are S not very effective in reducing To~ ~lends were prepared as in Exarnple I, using the sarne proportions of components as composition "B", except that the amount of ester plasticizer was 70 phr in all cases.

Blend Ester Plasticizer~v~u .~1 W. Rubber Tg ~C Plastic Ts C
B16 n-Butyltallate ~ ~00 -65 -15 B11 Polyester adipate 6000 -41 +5 (Paraplex~ G-~0) A None - -41 + 10 It is apparent that the polymenc ester did not have the same effect of lowering the T~
of both the rubber and plastic components of the thermoplastic elastomer, compared to monomeric esters such as n-butyltall~te. This phenomenon is related to the increase in combinatorial entropy of mi%ing which is large for monomeric esters. This in turn results in a large and negative free energy ot mixing which favors miscibility in the case of the 20 monomeric esters but not as much for the polymeric esters. This example therefore illustrates the importance of diluent molecular weight and miscibility for maximum effect of the plasticizer.

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2 i 1~73 E.~ample 3 Blends were prepared wherein combinations of low molecular weight ester and paraffin oil were added to a thermoplastic elastomer. Blends were prepared as in Example 1, based on composition "B" plus the indicated additives, and T8 was determined~

Blend Paraffin Oil (phr) n-Butvl tallate (phr) Rubber T3 C Plastic TQ C
A 0 0 -41 +10 For a fixed amount of total diluent added (plasticizer and/or oil - 130 phr in this exa nple) the depression of Ts in the thermoplastic elastomers can be controlled by combinadon of the ester plasticizer with appropriate amounts of rubber process oil. Mixtures of different esters toge~her with oil may also be used.

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-' ,.,' ',' .' ~ ' 2~12~ 73 !' EYample 4 Ihe effect of addition o~ low moiecular weight esters on the impact strength of thermoplastic elastomers was studied and compared with the effect of conventional process oil. Blends were prepared as in E~ample 1. using a 1300 cm3 Banbury mixer, based on composition "A", plus the indicaled additives (in phr). The notched Izod impact resistance at -40C was deterrnined for each composi~ion following the procedure set forth in ASTM
D256-84, using specimens cu~ trom compression molded plaques 3.17 mm in thich~ess.
Blend - A I A2 A3 A4 A5 A6 A7 Carbon black (N326) 0 100 0 0 100 0 0 Silica (Hisil 233) 0 0 100 0 0 100 0 n-Butyltallate 0 0 0 130 130 130 0 Paraffinic oil (Sunpar 150M) 130 130 130 0 0 0 0 isooctyltallate 0 0 0 0 0 0 100 Hardness (Shore D) 38 38 36 37 37 36 35 Notched Izod Impact 82 76 93 414 489 424 427 Strength (I/m +a) +48 +35 +52 +48 +40 +32 +47 It was observed that the inclusion of an alkyl monoester in place of paraffinic oil resulted in a marked improvement in toughness at -40 C, by at least a factof of 5. Such 20 compositions are much more ductile than those prepared with hydrocarbon process oils, and have enhanced resistance to cracking at low temperatures.

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E~ample 5 Compositions were prepared following the procedure of E~arnple I, wherein the point Ot addition of the es~er plasticizer was varied. Composition "A" was utilized, and n-butvltallate plasticizer (130 phr) was added as follows.
Composition "Cn - All plasticizer was added before dynamic vulcanization of the EPDM rubber in the presence or the polypropylene.
Composition "D" - One h~lf (65 phr) of the plasticizer was added to the formulation prior to dynamic vulcanization, and one half was added after dynamic vulcanization.
Composition "E" - All plasticizer ~.vas added after dynamic vulcanization.

Both T and physical properties were determined for the composiuons, and are set forth below.
TABLE S
C D E
T, EPDM phase, C -76 - -71 T, Polypropylene phase, C -20 - -25 Densily, gm/cm3(ASl~I D297) 0.952 0.952 0.953 Stress ~ break, MPa (ASTM D412) 13.40 13.24 11.64 Strain ~ break, % (ASTM D412) 372 316 249 Compress~on set, 22hr/100C, % 72 - 66 (ASTM D395B) Weight change, 24hr/125C, ASTM 3, æ 59 - 51 (ASTM D471) ACR viscosity, poise 1389 1286 872 It can be seen from the foregoing that the properties of the thermoplastic elastomer can be varied by changing the point of addition of the ester plasticizer in relation to the curing step.

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2~i2173 Example 6 Therrnoplastic elas;omers 3ased on bulvl rubber and polypropylene were prepared following the technique or E.Ya.~.?le 1. using two different ester plasticizers, a conventiona rubber process oil and a b.end c ester ~nd process oil. About 90% of the diluents were 5 added before the cure in each c_se. Formulations (in phrl and physical properties are set forth in Table 6.
In addition to reduced T~ _nd improved low temper~ture characteristics, it should be noted that the compositions or ~ inven~ion have improved (lowered) damping characteristics, as rneasurea b~ ieit~ ~t '3 C. In contrast, the use of paraffinic oil 10 increased the loss tangent a~

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21 ~ 3 :i ~, TABLE 6 Composition l~ G H 1 J
Butvl rubber 100 100 100 100 100 3 (Polysar~ Butvl 301) Polypropvlene (Aristech FP200F) '0 '0 20 20 20 Polypropylene (Rexene 51S07A) 180 180 180 180 180 Isooctyltallate (Plasthall P100) lOO O so O , O
n-Butyltallate (Plas~hall P503) ù () O 100 0 P~ramnic oil ~) 100 50 0 o (Sunpar 150M) Cure system' l l 11 11 11 11 Stearic acid Active carbon black 40% '0 '0 20 20 20 T, Butyl rubber phase, C -,6 -52 -57 -75 -56 T, Polypropylene, C -22 0 - 16 -25 + 10 Tan Delta ~ 23C 0.0537 0.0800 0.0581 0.0386 0.0638 Hardness (Shore D)2 36 37 35 34 51 Stress ~ break, MPa 10.0 l 1 11.4 9.6 16.6 Strain ~ break, %3 '16 308 282 258 593 Tear strength, kJ/sq m ~ 51 66 60 54 Compression set (22hr/100C) 7' 60 61 79 78 Weight change, %
(ASTAI 3, 24hr/125C) 62 l6 51 58 91 'Phenolic resin (5 phr). SnCI, (I phr), Zinc oxide (5 phr) 'ASl~M D624 ' ,. . . ., ., . . . . ~ .
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~1 2 i 1~ ~ 7 3 EYam~le 7 llle efrect or ester concentra~ion ievels on the ~ and physical properlies of an EPDM
.~bber - polypropylene thermoplastic elaslomer was studied. Composition "A" was utilized, and the technique of EYample 1 ~as followed. The concentration of n-butyltallate in the formulation was varied from 0 to 219 phr, and the results are set forth in Table 7.

Conl~Q~ition A A8 A9 A10 ~ A13 n-Butyltallate (phr) () 15 30 ,0 100 130 219 T, Rubber phase. "C --I I -S0 -S5 -65 -70 -74 -75 T~ Polypropylene, ~C - lO -~ 6 -~.8 -15 -16 -24 -25 Hardness (Shore D) ~8 ~0 ~9 12 38 37 27 100% Modulus, MPa 16.2 16.2 15.0 11.7 15.5 11.6 6.5 Stress a? break. MPa _.3 '2.9 17.7 18.5 21.1 14.3 6.6 Strain~break, % ~67 ~2 334 493 452 345 110 Weight gain, %
(24hr/125C, ASTM 3) 61 S8 55 55 47 45 27 Compression set, %
(22hr/100C) - 6~ 63 64 66 63 59 It can be seen that the lowering ot T~ is effective across most of the range of ester ~20 plasucizer added to ~he tormulrtions.

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E.Yample 8 Soft (low modulus) thermopiastic elastomer composi~ions containing natural rubber or EPDM rubber or oil-e.Ytended EPDM rubber were prepared following the technique described in Example 1. mixed in a '0 liter Banburv-tvpe mixer. The effects of ester S piasticizer on T,, friction coet'ficien~ and physical properties were determined. The results are set forth in Table 8A. The concentrations of ingredients are expressed as phr.

Composition K L M N Q P Q
Oil-extended EPDM' '00 '00 0 0 0 0 0 .~'atural rubber2 0 0 0 O 100 100 100 EPDM rubber3 0 0 100 100 0 0 0 Clay 13,16 '3.46 43.46 43.46 0 0 0 .lineral filler O O O 0 50 50 50 Z.nc Oxide 1.98 !.98 1.98 1.98 5 5 5 1 15 Stearic acid O () O O
Polypropylene AJ ~1 ~1 10 lO O O O
Polypropylene B5 7 7 7 7 0 0 0 Polypropylene c6 0 O O 0 46.8 46.8 46.8 Paraffinic oil7 ~o O O 0 97.5 0 0 i 20 Isooctyltallate O ~0 150 0 0 97.5 0 Color concentrate8 3.25 3.25 3.25 3.25 3.25 3.25 3.25 Curadve A9 ~ 1 4 4 0 O O
Cura~ive B~ O O O 0 11.7 11.7 11.7 SnCl. 1.68 1.68 1.68 1.68 0 0 0 Antioxidant~' O () O O
'Epsyn P597 rubber, e,Ytended with 100 pans paraMn oil (Copolymer Rubber & Chemical Co.) 2CV60 natur,al rubber, Mooney 60 (Golden Hope Plantations) 3VistalonD 8600 (Exxon Chemical Co.) 'Rexene~ polypropylene (Rexene Corp.) 5Arislech FP2OOF (Aristech Corp.) 6Aristech D008M (Aristech Corp.) 'Sunpar 150 (Sun Chemical) 135 8Americhem 21065 R-l 9SP-1045 (Schenectady Intemational Inc.) 'HRJ 10518 (Schenectady Intemational Inc.) "Irganox3l' 1010 (General Electric Co.) IE ~; :c~ ~: , ~ ~ - -- -s . ,.,.. -~, " ~ , ,, ~ ,. ; . ' '' . ' l ~
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Composition ~ O P Q
TgRubberphase, C -~0 -60 -,6 -35 -55 --77 -51 Hardness (Shore A) ~ ~3 53 85 67 64 85 Stress ~? 100% strain. ~Pil 1.8 1.7 L.5 5.9 2.7 2.5 4.5 Stress ~ break, MPa I 89 '.17 1.90 7.33 4.86 4.50 1.46 Striain@~break, % 317 317 ~70 184 257 219 178 Weight gain, %
(24hr/125C, ASTM 3) ~7 109 - 204 123 121 00 Friction coefficient against polypropylene Static 1 .80 : .51 1 .07 I.S3 1 .00 1 . 131 .40 Kinetic !.6' ;.66 1.19 1.55 1.08 1.33 1.22 As apparent from EYamDle ~. the thermoplastic elastomers of the present invention have significantly reduced T, ;-nile re~ining good physical properties.
While the best mode and preterred embodiment of the invention have been set forth in 0 accord with the Patent Statutes. lhe scope of the invention is not limited thereto, but rather is defined by the attached claims.

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Claims (12)

1. A composition comprising (a) from 10 to 90 weight percent of a thermoplastic, crystalline polyolefin homopolymer or copolymer, (b) from 90 to 10 weight percent of an olefinic rubber, and (c) from 1 to 250 parts per hundred parts of rubber of a low molecular weight ester or ether ester plasticizer which is compatible with both the polyolefin and rubber, wherein said rubber is at least partially crosslinked.

2. The composition of claim 1 wherein the polyolefin is a polymer of a C2-6 monomer or comonomers thereof.

3. The composition of claim 1 wherein the rubber is selected from the group consisting of EPDM rubber, EPM rubber, butyl rubber, halogenated butyl rubber, copolymers of isomonoolefin and para-alkylstyrene, natural rubber, polyisoprene and mixtures thereof.

4. The composition of claim 1 wherein the ester plasticizer has a molecular weight of 2000 or less.

5. The composition of claim 1 wherein the plasticizer is selected from the group consisting of monomeric or oligomeric alkyl mono- and diesters, and monomeric or oligomeric alkylether mono- and diesters.

6. The composition of claim 1 wherein the rubber is fully crosslinked.

7. A method for the preparation of thermoplastic elastomers comprising the steps of (a) blending 90 to 10 weight percent of an olefinic rubber with 10 to 90 weight percent of a thermoplastic, crystalline polyolefin homopolymer or copolymer at a temperature above the melting point of the polyolefin, (b) adding to the blend from 1 to 250 parts per hundred parts of rubber of a low molecular weight ester or ether ester plasticizer which is compatible with both the rubber and the polyolefin, and (c) crosslinking the rubber in the resulting mixture.

8. The method of claim 7 wherein the polyolefin is a polymer of a C2-6 monomer or comonomers thereof.

9. The method of claim 9 wherein the rubber is selected from the group consisting of EPDM rubber, EPM rubber, butyl rubber, halogenated butyl rubber, copolymers of isomooolefin and para-alkylstyrene, natural rubber, polyisoprene and mixtures thereof.

10. The method of claim 7 wherein the plasticizer has a molecular weight of 2000 or less.

11. The composition of claim 7 wherein the plasticizer is selected from the group consisting of monomeric or oligomeric alkyl mono- and diesters, and monomeric or oligomericalkylether mono- and diesters.

12. The method of claim 7 wherein the rubber is fully crosslinked in step (c).