CA1113629A - Injection moldable composition - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

An injection-moldable, peroxide crosslinkable elastomeric composition comprises a mixture of a crystalline interpolymer comprising ethylene and propylene; a low density polyethylene; one or more multi-functional vinylic or allylic monomers; a medium to high structure form of carbon; and an organic peroxide.
The composition is particularly useful for the fabrication of injection molded structures which are required to flex on impact and return to their original shape when the distorting force is released.
Typical structures are automotive fender extensions, grilles and front and rear fascia.

Description

z~'~
- I -1 Thi 5 inven-tion relatDs to an ela 9 tomeric composi-

2 tion and a process fox itq production. More particularly,

3 this invention is concerne~ with an injection~moldable elas

4 tomeric COmpQSitiOn compris~ng a mlxt~re of a crystalline interpolymer comprising e~hylene and propylene~ a low den-6 sity polyethylene; one or more multifuncticnal vinylic or 7 allylic monomers whieh ccpolymerizes ln the presence o~
8 peroxide and w~ich functions as a co-curing agent3 an am~unt 9 of caxbon sufflcienL tD re~der the composition, when cross- -linked, ele~trostatically conductive, an~ ~ pero~lda cross-11 linking agent. Mo~t partlcularly9 this invention relates 12 to the sai~ composition3 a method ~or it~ productio~ and 13 cross-linked str~ctures ma~e f~om ~he compcsit~enO
14 Recently the ne2d ~cr impr~ed fuel ecc~omy in th~
operat~on o~ Automobiles has led tc smaller cars and aut~
16 mo~ive manufa~ rPrs lowering the weigh~ 3f automobiles by 17 r~placing s~eel, particularly in t~e body3 with llght metal 18 alloys and pol~meric ~o~posltions, ~rrently automct~v~
19 companies are developing elastomeric structures ~asci~
for the front and rear ends o~ aut~mobll~s to r~place the 21 present steel fen~er extPnsions, radiat~r grilles and the 22 like. These structures are required to flex on impact in 23 concert with energy ~bsorbing d~v~c~s and return, undamaged~
24 to their original shape when the distcrting forces are re leasedO In additicn, the structure must rea~ily accep~ pal~t 26 and the finished surface must have ~dequate weather resist~
27 ance and show a minim~m of marking ~r marring on impact and 28 recovery.

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6~9 1 S~ltable and commercially acceptable compositicn~
2 for the fabric~tion of these str~ctures ~lSt not only be 3 capable of being amenable to mass production methods, às by 4 conventional injection molding ~echniques, but the finished product must possess the necessary physical properties of 6 high flexural stiffness, high tensile strength, hardness, 7 ability to recover rapidly to its ori~inal state when de-8 formed and to be mar and tear resistant. In addition, since 9 fascia structur~s are usually painted electrostatically and the paint cured in an oven, the structurs must be electrical 11 ly conductive and must not undergo deformation when passing 12 through the paint oven.
13 Currently two types of polymeric compositions are 14 being used for the fabrication of fascia structuresO In the one, disclosed in U.S~ Patent 3,915,928, the composition 16 comprises an injection moldable mixture of a crystalline co-17 polymer o~ ethylene and propylene or a terpolymer o~ ethyl-18 ene, propylene and a non-conjugated diene~ carbon, from 5 to 19 30 weight percent of chopped glass fibers and sulfur based vulcanizing agents. Parts injection molded from this com-21 position show "trail" lines d~e to alignment of the glass 22 fibers and the parts must be routinely sanded prior to pain~
?3 ing in order to produce acceptable automotive f~scia.
24 In the other, in which the end product is a micro cellular polyurethane, described in a paper by Prepelka and 26 Wharton, "Reaction Injection Mo~ding in the Automotive In-27 dustry," Journal of Cellular Plastics, po87~ March/April 28 1975, the cost o~ the components comprising the composition .
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1 is higher than the cost of hydrocarbon based elastomers and 2 production of the pclyurethane structures requires special-3 ized meterlng and mixing equipment and presses~
4 A variety of compositions and processes have been described in the patent literature for the post vulcanization 6 of preformed elastomers.
7 U. S0 Patent 3,1~8,868 discloses a process for vul-8 canizing preshaped articles formesl from vulcanizing materials g comprising blends of amorphous copol7mers of ethylene and higher~ -olefins with polyethylene wherein the shaped ~1 article is impregnated with a solution of an organic per-12 oxide, dried and vulcanized by the application of heatO
13 U S. Patent 3,256,366 discloses a process for the 14 preparation and vulcanization of a mixture of a copolymer of ethylane and propylene containing 40 to 60 mol percent of lS ethylene (30.8 to 5000 weight percent of ethylene~ with 17 either low density or high density polyethylene comprisingo 18 mixing the polymers at a temperature above 125Co 9 adding 19 a peroxide to the mixture at a temperature in the range of about 60C. to about 90C ; shaping the mixture to a con-21 formation; and heating the shaped article to vulcanize lt 22 at a temperature in the range of about 150C~ t9 180C
23 British patent 1,294,665 discloses cross-linked, 24 electrically conductive9 heat-shrinkable polymer composi-tions having volume resistivities below 1000 ohms-centimeter 26 which comprise mix~ures of at least 40 parts of an elec-27 trlcally conductive filler; àt least 20 parts of a natural 28 or synthetic rubber, and at least 10 parts of a normally , ~

' . " , ., ~' . ; , 2~3 1 qolid ~eat-flot~able hvmo- ~r co~ol~mer cf ethylene 2 This invention is concerned with a method or the 3 preparation and the cross-linked product of a co~position 4 comprising a mixture of S (a) an elastomeric polymer selected from the group 6 consisting of copolymers of ethylene and propylene contain-7 ing 62 to 80 we~ght percen~ e~hyleme and possessing a cry~-8 ~alline content in the r~e of about 10 to about 25 weigh~
9 percent, and terpolymer~ of ethylene, propylene and a C~-Clo non-conjugated diolefin containing from about 72 to 11 a~out 80 weight percent o~ ethylene and possessing a crystal-12 line content in the range of about 15 to a~out 25 weight per 13 cen~;
14 (b) 50 to 150 parts per hundred parts by weight of elastomeric polymerj preferably 80 to 120 parts, of a 16 low~density polyethylene havlng a melt index in the range 17 of 2 to 40, preferably 12 to 20;
18 (c) 50 to 150 parts per hundred parts by weight 19 of elastomeric polymer, preferably 80 to 120 parts, of a medium to high s~ructure form of carbon, such as carbon 21 black;
22 (d) 0.5 to 5 parts per hundred parts by weight of 23 elastomeric polymer,preferably 1 to 3 parts, of one or more 24 polyfu~ctional vinylic or allylic monomers; and ~e) 1 to 10 parts per hundred parts by weight of 26 elastomeric polymer, preferably 2 to 6 parts of an organic 27 peroxide comprising one or more peroxide moieties 1n the 28 molecule having the following structure:

- . . .. ...

~ ~J~ 3 2 ~ --~--C-~~~~~~~~
3 OOR' 4 wherein R and R' are independently selected from the group consisting of Cl to C8 alkyl radicals and provided said per-6 oxide has a half -lif~ at 130C. in excess of 5 hours and 7 less than 1 minute at 230C. when tested in low-densit~ poly 8 ethylene.
9 The above composition when compounded by the method of this invention possesses a rheology which permits the 11 unvulcanized compound to flow through narrow orifices over 12 relatively large distan~es at temperatures and under pres-13 sures that will not prematurely vulcanize the compound when 14 large structures are fabricated by injection molding. The inclusion of carbon in an amount sufficient to give the vul-16 canized composition a volume resistivity in the range of 103 17 to 108 ohm-cm permits the vulcanized composition to be 18 painted electrostatically. The presence of carbon black 19 is considered essential for reinforcement purposes--all~w~ng~
the product to be removed from the hot mold without tearing, 21 The physical properties of the cross-linked com-22 po9ition makes the composition particularly useful in the ~3 automotive field for the ~abrication of fascia, fender ex-24 tensions and grilles.
A. Polymers 26 Copolymers of ethylene and ~ropylene containing 27 from about 62 to 8bout 80 weight percent of ethylene, pre-28 ferably 65 to 76 weight percent of ethylene and possess~ng ,- ;

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1 a crystalline content in ~he range of about 10 to about 25 2 weight percen~; and terpolymers of ethylene, propylene and 3 a C6 to Clo non-conjugated diolefin containing from about 4 72 to about 80 weight percent o~ ethylene and a crystalline content in the range of about 15 to about 25 weight percent, 6 having a range of molecular weights and Mooney viscosities 7 suitable for the practice of this invention m~y be readily 8 prepared using soluble Ziegler-Natta catalyst combinations 9 well known in the art.
Suitable copolymers have a Mooney Viscosity, 11 ML(1~8) at 127C. in the range of about 10 to about 40, pre-12 ferably 13 to ~7.
13 Suitable terpolymers have from about 0.5 to 5 14 weight percent of a C6 to Clo non-conjuga~ed diolein, non-limiting examples of which include: 5-ethylidene-2~norborn-16 ene, 1~4-hexadiene, ~nd dicyclopentadiene~ These terpolymers 17 have Mooney viscosities, ML(1~8~ at 127C, in the range of 18 10 to 40O
19 Ethylene content of the polymers m~y be readily detesmined by the method o &ardner, Cozewith and VerStrate:
21 Rubber Chem. & Te~h. 44~ 1015 (1971~o Cry~tallinity of the 22 polymers may be determined by the method of VerStrate &
23 Wilchinsky: JO Polymer Sci. A-2, 9, 127 ~1971).
24 ~ow-density polyethylene having a density o 0.93 g/cm3 or less and a melt index in the range of about 2 to 26 about 40, preferably 1~ to 20 is preferred for mixing with 27 the polymers co~rising ethylene and propyleneO
28 All of the above polymers are produced commercially 29 and are available in tonnage quantitiesO

1 B. Carbon Blaclc ~ Carbon blacks suitable for the practice o~ this 3 inYention include medium to high structure bl~cks which not 4 only add reinforcement to the cross-linked structure but when used in an amount equal to aibout 20 to 40 weight percent 6 based on the total composition yileld a cross-linked struc~ure 7 having adequate electrical conductivity for painting by elec-8 trostatic means.
9 The carbon blacks msy be further defined as those having a nitrogen surface area of about 30 to 100 square 11 meters per gram and a DBP absorption tASTM D-2414) of about 12 60-1250 Specific examples are the ASTM D-2516 grades of 13 carbon black such as N-326~ N-330, N-339, N-347, N-351, 14 N-440, N-539, N-550, N-660, N-650, N-762 and N-7650 C0 Polyfunctional Vinylic and Allylic Monomers 16 Polyfunctional vinyl and allylic monomers have 17 been found to be a critical ingretient in the compositions 18 of the present inventionO The presencP of these monomers in 19 the compo~ition is essential to provide curing of the com-position so that the injection molded article prepared in 2~ accordance with the present invention passes the Heat Sag 22 test which is an indicatlon of the extent of cro~slinking 23 that has been achieved~
24 The monomers useful in the present invantion are those polyfunctional vinylic and allylic monomers containing 26 two or more polymerizable groupings, at least one of which 27 is a vinyl or allyl functional group~
28 Illustrations of such vinylic and allylic mono-. , ~
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~3 1 mers useful in the present invention are polyfunctional 2 monomers con~aining ~wo or more vinyl groups such as divinyl-3 benzene, trivlnylbenzene, 2~3-divinylpyridine, divinyl sul-4 fone and 2,5-divinyl-6-methylpyridine) polyfunctional acry-late monomers such as ethylene glycol dimethacrylate, tri-6 methylol propane trimethacrylste, 19 2-propanediol dimeth-7 acrylate, polyfunctional ~llyl momomers surh as diallyl 8 cyanurate, triallyl cyanurate~ diaLlyl maleate9 diallyl 9 phthalateO
Particularly preferred monomers for use in the 11 present invention ~re ethylene glycol dimethacryl~t~, tri-12 methylol propane trimethacrylate, divinylbenzene and tri 13 allyl cyanurate, with the latter being especially effectiveO
14 D. Peroxides The choice of the peroxide is critical to both 16 the physical properties and the paintability of structures 17 molded from the composition In order or a particular per-18 oxide to be suitable for the practice of this invention i~
19 must not undergo appreciable decomposition with attendant.
free-radical formation at the temper~ture at which it is 21 blended into the composition and at t~e temperature a~ which 2~ the composition ls injection molded, bu~ the decomposition 23 end-products of the peroxide must be compatible with the 24 crosslinked elastomeric structureO Preferably, the peroxide should decompose at the lowest possible temperature above 26 the flux te~perature of the compound.
27 Acceptable peroxides for use in the present inven-28 tion are defined in terms of hal-life at two temperature ~s~ 3 1 ranges. It has been determined in accordance with the pre~-2 ent invention that the peroxite must have a half-life, when 3 measured in low density polyethyle.ne, which i5 greater than 4 5 hours at 130Co and less than 1 minute at 230C, An organ-ic peroxide curing agent which exhibits this half-life will 6 provide the proper balance of inhibition of curing during 7 processing temp~rature and the desirable crosslinking promo-8 tion under in~ection molding conditions and produce articles 9 which do not exhibit "bloom."
102,5-dimethyl-2,5-di(t-butyl peroxy~hexaneo 11 CH3, CH3 12 CH3-Çoc~2 ~H2-~ cH3 15 CH3-CDC~3 CH3-~ ~H3 16 CH3 ~3 17 meets the half-life requirements noted hereinabove, has the 18 required stability at blending temperatures and effects a 19 cure of the molded struc~ure at a temperature and time which 20 is acceptable u~der current production schedules and can pro-21 du~e bloom-free articles and therefore rPpresents a pre-22 ferred pProxide curi~g agent. Its precise half-life measure-23 ments are reported in Table I.
24 It has been common practice to rate peroxides in 25 terms of half-life time ~50% decomposition) at a particular 26 temperature, Nearly all of the data reported in thP liter-27 sture have been based on determinations made in solution in 28 benzene with results which differ materially when the da~a - , , . :
. - . . ~ :. - . : ., ~- . . :
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1 are obtained or example for the c~se wheee the peroxide ha~
2 been blended with a thermoplastic such as low~density poly-3 ethylene (LDPE).
4 Table I giYes the results obtained with "Luperco 101-XL," a commercial grade of 2,5-dimethyl-2,5-di(t-butyl 6 peroxy) hexane containing 45% active ingredient, the 55%
7 inactive portion being an inert silica support3 when tested 8 in benzene and LDPE.
9 TABLE~I

11Tem~ersture for 50% De~2 , . . _ _ .
12 Medium 1 Minute 10 ho~rs 13 In Benzene, ~. 175 119 14 In LDPE, C~ 192 131 Peroxides such as ter-butyl peroxypivalate, di-16 cumyl peroxide and ~,4-dichlorobenzoyl peroxide have been 17 evaluated but have been found not to have the requisite cur~
18 ing char~cteristics to produce products in accordance with 19 the present invention Eo rocess 21 The process for producing an injection moldable 22 ~omposition, which, when crosslinked, meets the requirements 23 for automotive fascia, namelyo process rheology, physical 24 properties and amenability to electrostatic painting com-prises: (a) mixing the copolymer or terpolymer interpolymer 26 comprising ethylene and propylene with the low-density 27 polye~hylene and carbon in an internal mixer, such as a 28 Banbury mixer at a ~mperature above the crystalline melting ~3~

1 point of the polyethylene, (b) cooling the mixture to a 2 temperature below 130C.; ~c) adding the peroxide and the 3 polyfunctional vinylic or allylic co-curing agent and thor-4 oughly mixing the composition while maintaining the temper-ature below about 130C For ease in subsequent injection 6 molding the blended composition may be pelletized.
7 F. Properties 8 Compositions suitable or the production of auto-g motive fascia by injection molding techniques must possess a rheology which will permit the fabrication of structures 11 which may be as large as 170 cm by 80 cm by 1 cmO When 12 attempts are made to injection mold elastomers, very high 13 pressures must be used, as contrasted to thermoplastics, 14 since as a general rule elastomers have a much higher viscos-ity than thermoplastics at the same temperature. The dif-16 ficulties in the use o~ elastomers for the production of 17 fascia are made more severe since fascia structures are re-18 quired to have high flexural modulusO To achieve high flex-19 ural modu~us with most elastomers usually requires that the elastomers be compounded with large amounts of reinforcing 21 fillersO The addition of fillers increasas the viscosity of 22 the compounded elastomer so that the use of injection molding 23 for fabrication requires impractically high injection pres-24 suresO Use of fillers which do not ~ppr~ciably increase the viscosity of the compounded stock, yields structures which 26 do not meet the required physical properties. Attemp~s to 27 obtain the necessary stif~ness 'Dy the insorporation of a sub-28 stantial quantity of glass fiber has not been too satisfactory ., 1 since the molded parts usually show the ~low pattern o the 2 glass fiber on its surface and the part requires extensive 3 ~anding and buffing be~ore painting. Also, glass ibers can 4 advercely affec~ the mold ltself by causing abrasion of the mold sur~ace.
6 A maJor object o~ thi~ invention is ~he production 7 of an elastomeric compo~ on, and a process for it~ prepara-8 tion, which po~se~ses a rheology suitable for the fabrlcatlon g of automotive fascia by injection molding and aftPr cross-linking ha~ a flexural modulus in the range of about 20,000 11 to 30,000 psi at room temperature and a con~uctivity suit-12 able for painting by electrostatic means.
13 We hsve now found that homogeneous blends of elas~
14 tomeric polymers comprising ethylene and propylene; low-density polyethylene, carbon black, a multi-functional 16 vinylic or allyllc monomer~ and a pero~ide possess a viscos-17 ity which permits the compound to be injection molded through 18 small orifices into a mold csvity at reasonable temperatures 19 and pressures, and when crosslinked by the application of heat yields smooth structures requiring no prefinishing be-21 fore painting, possesses ade~uate flexural strength and is 22 readily pain~ed by eleetrostatic meansO
23 The choice of the olefinic homopolymer thermoplas-24 tic that i~ blended with the ethylane-propylene copolymer or terpolymer is criticsl The homopolymer must be compatible 26 with the elastomer while at the same time flux at a ~empera-27 ture below about 130Co which is the maximum safe processing 28 temperature that can be maintained in the barrel of the in-3~9 1 jection molding machin~ Both high density polyethylene and 2 polypropylene are not suitable since both require hi~her 3 processing temperatures which could cause serious scorching 4 probl~ms in the barrelO When scorching occurs, the compound undergoes a significant increase in viscosity and loses its 6 ability to flow through the mold. In addition, polypropylene, 7 unlike low-density polyethylene, undergoes chain scission 8 ~n the presence o peroxides~ rst:her than forming cro~s-9 links. Other non-olefinic thermoplastics do not h~ve ~ufi-cient compatibility with ~PM or F.PD~ elsstomers and are 11 therefore not suitable for blending.
12 While the physical properties desired in automotive 13 fascia have not been finalized by the manufacturer3, the 14 best estimate of the property requirements from published in-formation is as follows:

18 Property Re uirement q 19 Tensile at Failure, psi (ASTM D-638)1,500 Minimum Ultimate Elongation, % (ASTM D-638)150 Mlnimum 21 Tear Strength, ppi (ASTM D-624)300 Minimum 22 Flexural Modulus, psi ~ASTM D-790) 23 at -28C. 1003000 Maximum 24 at 23C. 20-30,000 at 70C. 7,000 Minimum 26 Flexural Set, Chevrolet CTZ-Z2003(a)15 Maximum 27 Degree aft,er 5 minu~es 28 Heat Sag, Chevrolet CTZ-ZZ006(b) 4 Maximum ~ Cm at 121DC.

3~;2' 1 Notes: (a) The Chevrolet Flexural Recovery of Elastomeric 2 Materials Test CTZ-ZZ003 measures th~ ability of an elasto-3 meric macerial tO recover after bein~ bent 180 degrees ~ around a 0 50" mandrel at room ternperature. Good recovery of fascia structures after impact is essentialO An injec 6 tion molded sample measuring 5" x 1/2" x 1/8" is bent 180 7 degrees and the angle of recovery measured after 5 minutesO
8 A specimen that returns to its original po~ition has a flex-9 ural set of 0 degrees, whlle a specimen that recovers only half-way has a flexural set of 9Q degrees.
11 (b) The Chevrolet High TemF~erature Sag of Elastomeric 12 Materials Test measures the 8ag of an injection molded specl-13 men measuring 6" x 1'l x 1/8" clamped with a 4 inch overhang 14 and heated at a speci~ied temperature in a circulating hot-air oven for 1 hour.
16 This invention will be further understood by refer-17 ence to the ~ollowing examples. Parts reported are by weight.
18 EXAMPLE 1.
19 Fifty parts of an ethylene-propylene copolymer which camprised 65 percent by weight of ethylene, had a 21 crystalline content o~ ll.S weight percent, a Mn of 35,000 2~ and a Mooney Viscosity, ML (l+B) of 27 at 127C. was master-23 bstched in a Banbury mixer at 180C. for 5 minutes wi~h 50 24 psrts of a low-density polyethylene having a melt index of 21 and 50 parts of a general purpose furnace black N-660 and 26 0.2 parts of zinc stearate as a lubricant. The mixture was 27 cooled and fluxed at a temperature of about 100C~ with 5 28 parts of a 45 percent active 2,5 dimethyl-295-di(t-butyl 29 peroxy) h~ane and 2 parts of a 75 percent active triallyl cyanurate.
31 Using the above compound, test specimens were in-32 jection mo~ded in an injection molding machine equipped with 33 8 reciprocating screw, a 5 ounce capacity and a 100 ton 34 clamp. Conditions during molding were as follows z~

1 Cylinder Temperature:
2 Rear 90C~
3 , Center 100C.
4 Front 110C.
Nozzle Temperature110C.
6 Mold Temperature 205C.
7 ~he injection molded specimens were retained in the mold for 8 105 seconds following the termination of the in;ection in 9 order to effect crosslinking or vulcaniza~ion, ~he physlca~.
properties of the w lcanized compound were as follows:

12 PROPERTIES_OF VULCANIZED COMPQSITION
13 Shore D Hardnes~
14 Initial 49 ~-15 Seconds Reading 43 16 Tensile Strength, psi 2,630 -.
17 Ult~mate Elongation, % 230 18 Tear Strength, Die C, ppi410 ~ 5 Minutes Flexural Set, Degrees 12 Droop at 121C. cm 3.5 21 Secant Flexural Modulus, psi 20,000 23 The procedure of Example 1 was repeated except 24 that the 50 parts of the EPM copolymer was replaced with 55 parts of an EPM copolymer containing 76 weight percent of 26 ethylene having a Mooney Visco~ity ML (lt~) of 13 at 127Co 27 The physical properties of the molded co~po~ition af~er 28 curing for 5 mi~utes ~t 180C~ were as follows: : ' ~, ~: :

: , : . : ~ : : :

.
2 PROPE~TIES OF VULCANIZED COMPOUND
3 Shore D ~ardness 4 Iniitial 48 15 Seconds Reading 42 6 Tensile Strength, psi3,000 7 Ultimate Elongatlon3 % 280 8 Tear Strength, Die C, ppi400 9 5 Minutes Flexural Set,Degrees 14 Droop st 121C~ cm 3 05 11 Secant Flexu~al Modulus, psi 12 a~ -29Co 100 000 13 at 23G. 28,000 14 at 70Co 8,000 ExAMpLE 3 16 The procedure of Example 1 was repea~ed with a 17 composition which had the followinæ proportions in parts by 18 weight:
19 EP~I(a) 80 Low Density PE (Melt Index-21) 50 21 N-660 Carbon Blac~ 60 22 Zinc S earate 0.2 23 Triallyl Cyanurate tTAC) 75% 2 24 Active 225 Luperico )Ol-XL Peroxide (45% 6.5 27 (a) Ethylene--propylene copol~mer, 76 wt. % ethv-28 le~e, Moone~ viscosity, ML (1~8) of 13 at ~27C.
29 Physical properties of test specimens molded ~rom the above compositlon and cured for 5 minutes at 180C were as ~ollows:

.
. -. - , .. . . , .. , , -: , : .:: .

3 Shore D Hardness 4 Initial 47 15 Seconds Reading 42 6 Tensile Strength7 psi 3100 7 Ultimate Elongation, % 310 8 Tear Strength, Die C, ppi 420 9 5 Minutes Fle~ural Set, Degrees 12 Droop at 121C. cm 3.0 11 Secant Flexural Modulus, psi 12 at -29C. 100,000 13 at 23Co 27,000 14 ~t 70C. 7,000 ExAMpLE 4 16 Example 3 was repeated with the same polymers but 17 with the following proportions3 19 Low Density PE 50 ~-660 Carbon Black 40 21 Zinc Stearate ~.2 22 TAC ~75%) 2.0 23 Luperco 101-XL ~4570~ 5.0 24 Physical propertie~ a~ter molding and curing for 5 minutes at 5 minutes at 180C. were ~ follows:

28 Shore D Ha~ess 29 Initial 49 15 Seconds Reading 43 ~;
. " .

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~3 1 Tensile Strength, psi 3,000 2 U~imate Elongation 310 3 Tear Strength, Die C, ppi 400 4 5 Mlnutes Flexural Set, Degree~ 13 Droop at 121Co cm 400 6 Secant Flexural Modulus, psi 7 at -29C~ 100,000 8 at 23Co 25~000 9 at 70Co ;7~000 A11 of the test spec~men~ molded from the abcve 11 compositions had smoo~h surfaces free from bloom and had 12 conductivities in ~he range c~ 103 to 108 ohm-cmO The re 13 sults also show that the compositions meet the current cri 14 teria ~or automotive fasciaO

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Claims (13)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. An injection moldable composition comprising a mixture of (a) an elastomeric interpolymer selected from the group consisting of copolymers of ethylene and propylene containing from about 62 wt. % to 80 wt. % of ethylene and having a crystalline content in the range of about 10 wt. %
to 25 wt. % and terpolymers of ethylene, propylene and a C6 to C10 non-conjugated diolefin containing from about 72 wt.
% to about 80 wt. % ethylene and having a crystalline con-tent in the range of about 15 wt. % to 25 wt. %;
(b) 50 to 150 parts by weight, per hundred parts by weight of elastomeric interpolymer, of low density poly-ethylene having a melt index in range of 2 to 40;
(c) 50 to 150 parts by weight, per hundred parts by weight of elastomeric interpolymer, of a reinforcing carbon black having a nitrogen surface area of about 30 to 100 square meters per gram;
(d) 0.5 to 5 parts, per hundred parts of elas-tomeric interpolymer of a polyfunctional vinyl or allylic monomer co-curing agent; and (e) 1 to 10 parts, per hundred parts of elas-tomeric interpolymer of an organic peroxide crosslinking agent having one or more peroxide moieties with the struc-ture R -- OOR' where R and R' are independently selected from the group consisting of C1 to C8 alkyl radicals and said peroxide having a half-life when measured in low den-sity polyethylene in excess of 5 hours at 130°C. and less than 1 minute at 230°C.

2. A composition according to claim 1 wherein said polyfunctional monomer is triallyl cyanurate.

3. A composition according to claim 1 wherein said polyfunctional monomer is selected from the group con-sisting of ethylene glycol dimethacrylate, trimethylolpro-pane trimethacrylate, and divinylbenzene.

4. A composition according to claim 1 wherein said peroxide is 2,5-dimethyl-2,5-di(t-butyl peroxy) hexane.

5. The crosslinked composition of claim 1.

6. The crosslinked composition of claim 1 where-in the electrical conductivity is in the range of about 103 to 108 ohms-cm.

7. The composition according to claim 1 wherein said interpolymer is a copolymer of ethylene and propylene having an ethylene content in the range of about 65 to about 76 weight percent of ethylene and a Mooney Viscosity, ML(1 + 8) at 127°C. in the range of about 13 to 27.

8. A composition according to claim 1 wherein said interpolymer is a terpolymer of ethylene, propylene and a non-conjugated diene selected from the group consist-ing of 1,4-hexadiene, 5-ethylidene-2-norbornene and dicyclo-pentadiene, said interpolymer having an ethylene content in the range of about 72 to about 80 weight percent and a Mooney viscosity ML(1 + 8) at 127°C. in the range of about 10 to 40.

9. A process for preparing an injection-moldable elastomeric composition which comprises:
(a) mixing an interpolymer comprising ethylene and propylene, said interpolymer having an ethylene content in the range of about 62 to about 80 weight percent of ethyl-ene and a crystalline content in the range of about 10 to 25 weight percent with from 50 to 150 parts by weight, per hundred parts by weight of interpolymer, of a low density polyethylene having a melt index in the range of 2 to 40 and 50 to 150 parts by weight, per hundred parts by weight of interpolymer, of a reinforcing carbon black having a nitro-gen surface area of about 30 to 100 M2/gram at a temperature above the crystalline melting temperature of the polyethyl-ene thereby preparing a first mixture;
(b) cooling said first mixture to a temperature below 130°C.;
(c) adding to said first mixture from 0.5 to 5 parts by weight, per hundred parts by weight of interpoly-mer, of one or more polyfunctional vinylic or allylic monomer and from 1 to 10 parts by weight, per hundred parts by weight of interpolymer, of an organic peroxide comprising one or more peroxide moieties in the molecule having the following structure:
R - ? - OOR' wherein R and R' are independently selected from the group consisting of C1 to C8 alkyl radicals said peroxide having a half-life when measured in low density polyethylene in ex-cess of 5 hours at 130°C. and less than 1 minute at 230°C.;
and (d) admixing said first mixture and said addi-tives to a composition while maintaining the temperature below 130°C.

10. A process according to claim 9 wherein said interpolymer is a copolymer of ethylene and propylene hav-ing an ethylene content in the range of about 65 to 76 weight percent, a crystalline content in the range of about 10 to 25 weight percent and a Mooney Viscosity ML(1 + 8) at at 127°C. in the range of about 13 to 27.

11. A process according to claim 9 wherein said interpolymer is a copolymer of ethylene and propylene having an ethylene content in the range of about 65 to 76 weight percent, a crystalline content in the range of about 15 to 25 weight percent and a Mooney Viscosity ML(1 + 8) at 127°C.
in the range of about 10 to 40.

12. A process according to claim 9 wherein said interpolymer is a terpolymer of ethylene, propylene and a non-conjugated diene selected from the group consisting of 1,4-hexadiene, 5-ethylidene-2-norbornene and dicyclopentadi-ene, said interpolymer having an ethylene content in the range of about 72 to about 80 weight percent and a Mooney Viscosity ML(1 + 8) at 127°C. in the range of about 10 to 40.

13. The crosslinked composition of claim 9.