Peroxide-cured blends of polyacrylates and partially hydrogenated nitrile rubbers

Abstract

Blends of a polyacrylate elastomer with a partially hydrogenated rubber, when peroxide-cured, provide a product which is excellent in resistance to degradation by heat or contact with oil, and which is particularly suitable for making belts, hoses, gaskets and the like for use in automobile engines.

Description

This invention relates to peroxide-curable blends of acrylate elastomers and partially hydrogenated nitrile rubbers, and to the blends which have been peroxide-cured. The cured blends exhibit excellent resistance to the degrading effects of oil and heat and are particularly useful as belts, hoses, seals, gaskets and the like in automobile engines.

BACKGROUND OF THE INVENTION

Polyacrylates are elastomeric polymers or copolymers of acrylic acid esters having a saturated main chain with the ester groups constituting side chains on the main chain. Polyacrylates are resistant to ozone and to aging in air at moderately elevated temperatures up to about 200.degree. C., and resist swelling, hardening, and other changes that take place when contacted with hot oils in an automobile engine.

Partially hydrogenated nitrile rubbers have excellent resistance to degradation when contacted by hot oils but are not as resistant to high temperatures as are polyacrylates. Unlike polyacrylates made by polymerizing mixtures of alkyl acrylate esters, partially hydrogenated nitrile rubbers contain carbon-carbon unsaturation and are readily peroxide-curable. Peroxide curing is advantageous in that a good cure is obtained with a minimum of scorch (premature crosslinking during cure), and the cured product, where the polymer chains are crosslinked by carbon-carbon linkages, is generally more stable than a product obtained by vulcanization with nitrogen- or sulfur-containing compounds.

It is, therefore, an object of the present invention to provide a blend of elastomers which can be peroxide-cured to yield a cured product which is resistant to deterioration caused by exposure to both heat and oil.

BRIEF SUMMARY OF THE INVENTION

It has now been discovered that the desirable properties of oil-resistance and high service temperature in a blend of elastomers can be realized in a peroxide-cured composition which comprises from 10 to 90 parts by weight of a particular polyacrylate elastomer and 90 to 10 parts by weight of a partially hydrogenated nitrile rubber.

BRIEF DESCRIPTION OF THE INVENTION

In one composition aspect, the present invention is a peroxide-cured blend comprising:

10 to 90 parts by weight of a polyacrylate elastomer comprising at least 10 mole % of the structural unit ##STR1## wherein R.sup.1 is a C.sub.4-8 alkyl group; up to 30 mole % and preferably 20 to 30 mole % of the structural unit ##STR2## wherein R.sup.2 is an alkoxyalkyl group containing 2-12 carbon atoms; and the balance to a total of 100 mole % of the structural unit ##STR3## wherein R.sup.3 is a C.sub.1-3 alkyl group; and

90 to 10 parts by weight of a partially hydrogenated nitrile rubber having a degree of unsaturation of from 0.1 to 20%.

Particularly preferred are blends wherein the polyacrylate elastomer additionally contains 1 to 10% of structural units derived from acrylonitrile. Such polyacrylate elastomers comprise at least 10 mole % of the structural unit ##STR4## wherein R.sup.1 is a C.sub.4-8 alkyl group; up to 30 mole % and preferably 20 to 30 mole % of the structural unit ##STR5## wherein R.sup.2 is an alkoxylakyl group containing 2-12 carbon atoms; 1 to 20 mole % of the structural unit ##STR6## and the balance to a total of 100 mole % of the structural unit ##STR7## wherein R.sup.3 is a C.sub.1-3 alkyl group.

The present invention also contemplates curable compositions comprising the above-described blends and containing a peroxide curing system, particularly a peroxide curing system comprising an organic peroxide and m-phenylenediamine bis-maleimide.

DETAILED DESCRIPTION OF THE INVENTION

The polyacrylate elastomers utilized in practicing the method of the present invention are copolymers formed by copolymerizing a mixture containing two alkyl acrylates and containing at least 10 mole % of a C.sub.4-8 acrylate, wherein the alkyl groups may be straight-chain or branched-chain alkyl groups such as isobutyl, n-pentyl, isoamyl, n-hexyl, 2-ethylhexyl and n-octyl, with n-butyl acrylate being preferred. The other alkyl acrylate monomer may be a C.sub.1-3 acrylate, such as methyl, ethyl or propyl acrylate, where the alkyl groups may be straight-chain or branched-chain alkyl groups; and/or an alkoxyalkyl group containing 2-12 carbon atoms, such as methoxyethyl, methoxymethyl, ethoxyethyl, butoxyethyl and ethoxypropyl and with methoxyethyl being preferred. Preferably, the mixture may contain 1 to 20 mole %, of structural units derived from acrylonitrile. These polyacrylates do not contain reactive sites, such as chlorine or an epoxy group in their side chains, characteristic of sulfur and nitrogen-vulcanizable polyacrylates.

Polyacrylate elastomers or rubbers are prepared by emulsion, suspension, solution or bulk polymerization. Emulsion and suspension polymerization are more commonly employed, and polymerization is generally initiated by free-radical generating agents. Methods for making polyacrylates are well known to those skilled in the art and are not part of the present invention.

The nitrile rubbers blended with the polyacrylate elastomers are partially hydrogenated copolymers of 75-25 parts of 1,3-butadiene and 25-50 parts acrylonitrile having a degree of unsaturation of from 0.1 to 20%. Partially hydrogenated nitrile rubbers having a degree of unsaturation lower than 0.1% are not readily peroxide curable. And those having a degree of unsaturation above 20% are less resistant to heat aging and to attack by ozone.

The curable blends of the present invention are cured by heating at 140.degree.-220.degree. C. for up to 30 minutes, preferably 4-10 minutes, with a peroxide-curing system containing a dialkyl peroxide such as di-1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane as the peroxide curing agent and m-phenylenediamine bis-maleimide as the coagent or promoter. A polyacrylate elastomer and hydrogenated nitrile rubber masterbatch is prepared in the customary manner and admixed with the curing system using conventional equipment, such as blenders, mixers, extruders or the like. The curable or vulcanizable composition, may contain, in addition to the curing system, a conventional lubricant such as stearic acid, a carbon black filler and an antioxidant. As is well known to those skilled in the art, compression set is an art-recognized measure of the extent of curing and is determined by compressing an article between flat plates for a specified time at the test temperature, after which the compressing force is released and the article allowed to recover for a specified period of time. The amount of unrecovered height, calculated as a percentage, is compression set.

Articles made from acrylic elastomer and hydrogenated nitrile rubber blends are processed in the same general manner as articles made from other elastomers, and can be shaped by compression, transfer or injection molding, with the latter being preferred. Articles made from conventionally vulcanized or cured polyacrylate parts are usually post-cured after primary curing because of the stringent requirements for articles to be used in automotive applications. As shown by their compression set values, articles made from the peroxide-cured polyacrylates of the present invention do not require post-curing.

Our invention is further illustrated by means of the following non-limiting examples:

EXAMPLE 1

This example illustrates compositions comprising a variety of polyacrylate elastomers admixed with the same partially hydrogenated nitrile rubber. (Example 1A does not contain a polyacrylate rubber and is not a composition according to the present invention).

The curable compositions were prepared by mixing all components, except for the curing system, in a Banbury mixer. The curing system, 1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane and m-phenylenediamine bis-maleimide, and antioxidant when utilized, were added, and the compositions uniformly blended using the Banbury mixer. The components of the curable compositions, the times and temperatures of curing, processing properties during curing and the properties of the cured product, including the results of tests on aged products, are summarized below.

______________________________________ 1A 1B 1C 1D 1E 1F______________________________________Nitrile rubber 100.0 80.0 80.0 80.0 80.0 80.0Polyacylate I 20.0Polyacylate II 20.0Polyacylate III 20.0Polyacylate IV 20.0Polyacylate V 20.0Carbon black 50.0 50.0 50.0 50.0 50.0 50.0Magnesium oxide 5.0 5.0 5.0 5.0 5.0 5.0Plasticizer 5.0 5.0 5.0 5.0 5.0 5.0Amine antioxidant 1.5 1.5 1.5 1.5 1.5 1.52-mercaptolimidazone 0.5 0.5 0.5 0.5 0.5 0.5Peroxide 8.0 8.0 8.0 8.0 8.0 8.0Bis-maleimide 2.0 2.0 2.0 2.0 2.0 2.0 172.0 172.0 172.0 172.0 172.0 172.0______________________________________

The nitrile rubber is a partially hydrogenated nitrile rubber containing about 36% of acrylonitrile having a degree of unsaturation of about 4%. Polyacrylate I contains about 55% by weight of structural units derived from ethyl acrylate and 45% by weight of structural units derived from n-butyl acrylate. Polyacrylates II-V contain about 6-23% by weight of structural units derived from ethyl acrylate, 47-62% by weight of structural units derived from butyl acrylate, about 26-30% by weight of structural units derived from methoxyethyl acrylate and 4-9% by weight of structural units derived from acrylonitrile.

The processess properties of the curable compositions were measured using a Mooney Viscometer, large rotor, at 125.degree. C., and a rheometer oscillating disc using a microdie at 100 cpm, 3.degree. arc at 190.degree. C.

______________________________________ 1A 1B 1C 1D 1E 1F______________________________________MOONEYVISCOMETER:VISC. MINIMUM 58 45 47 47 47 45T5, minutes 12.2 10.7 9.7 9.6 9.5 8.9REHEOMETER,MICRODIEML,1bf*in 17.9 14.8 15.1 14.9 14.8 14.1ML,N*m 2.0 1.6 1.7 1.6 1.6 1.6MH,1bf*in 121.0 91.7 98.2 98.2 100.0 96.0MH,N*m 13.4 10.2 10.9 10.9 11.1 10.7Ts2, minutes 1.2 1.1 1.1 1.1 1.1 1.0T90, minutes 13.0 11.9 11.5 11.3 11.6 11.8CURE RATE 11.8 10.8 10.2 10.5 10.5 10.8______________________________________

Properties of the cured composition, 20 minutes cure time at 170.degree. C. with no post-cure, are as follows:

__________________________________________________________________________ 1A 1B 1C 1D 1E 1F__________________________________________________________________________STRESS 100%, psi 1175 945 1010 1060 1065 1045STRESS 100%, MPa 8.1 6.5 7.0 7.3 7.3 7.2TENSILE, psl 3990 3150 3240 3435 3490 3200TENSILE, MPa 27.5 21.7 22.4 23.7 24.1 22.1ELONGATION, % 255 240 235 250 260 230HARDNESS, A pts 75 72 73 71 70 74COMPRESSION SET,METHOD B, BUTTONS70 hrs @ 150.degree. C. 19 23 25 24 27 23168 hrs @ 150.degree. C. 21 30 34 34 37 34GEHMAN LOW TEMPERATURETORISON TEST, ASTM D1053ORIGINAL ANGLE TWISTT2, .degree.C. -20 -16 -16 -16 -15 -15T5, .degree.C. -30 -32 -33 -32 -32 -32LOW TEMPERATURE BRITTLENESS,ASTM D 2137Tp, .degree.C. -33 -27 -30 -30 -26 -36__________________________________________________________________________

Stability of the peroxide cured acrylates to oxidation was measured using accelerated aging tests in which dumbbells cut from the material to be tested were exposed to circulating hot air in an oven. Their stability, when exposed to hot oil, a particularly important property from articles intended for automotive applications, was also measured. The results of aging the cured composition are summarized below:

__________________________________________________________________________HEATING IN AIR OVEN 1A 1B 1C 1D 1E 1F__________________________________________________________________________70 hours at 150.degree. C.TENSILE, psi 4195 3195 3615 3465 3265 3365TENSILE, MPa 28.9 22.0 24.9 23.9 22.5 23.2TENSILE CHANGE, % 5 1 12 1 -6 5ELONGATION, % 220 215 230 220 200 205ELONG, CHANGE, % -14 -10 -2 -12 -23 -11HARDNESS A, pt's 81 79 79 80 79 80HARD CHANGE, pt's 6 7 6 9 9 6168 hours at 150.degree. C.TENSILE, psi 3905 2895 3155 3135 3290 2825TENSILE, MPa 26.9 20.0 21.8 21.6 22.7 19.5TENSILE CHANGE, % -2 -8 -3 .9 -6 -12ELONGATION, % 205 195 185 200 195 165ELONG, CHANGE % -20 -19 -21 -20 -25 -28HARDNESS A, pt's 79 77 81 82 81 80HARD CHANGE, pt's 4 5 8 11 11 6504 hours at 150.degree. C.TENSILE, psi 3420 2705 3005 2980 3080 2875TENSILE, MPa 22.4 18.7 20.7 20.6 21.3 19.8TENSILE CHANGE, % -19 -14 -7 -13 -12 -10ELONGATION, % 120 120 120 120 130 110ELONG, CHANGE % -53 -50 -49 -52 -50 -52HARDNESS A, pt's 84 80 84 87 87 85HARD CHANGE, pt's 9 8 11 16 17 111008 hours at 150.degree. C.TENSILE, psi 3420 2560 2775 2920 2720 2540TENSILE, MFs 23.6 17.7 19.1 20.1 18.8 17.5TENSILE CHANGE, % -14 -19 -14 -15 -22 -21ELONGATION, % 75 55 55 65 60 50ELONG CHANGE, % -71 -77 -77 -74 -77 -78HARDNESS A, pt's 91 90 87 92 92 87HARD CHANGE, pt's 16 18 14 21 22 13ASTM 903 OIL70 hours at 150.degree. C.TENSILE, psi 3540 2750 3130 3095 3415 2875TENSILE, MPa 25.1 19.0 21.6 21.4 23.6 19.8TENSILE CHANGE, % -9 -13 -3 -10 -2 -10ELONGATION, % 220 200 215 220 230 205ELONG, CHANGE, % -14 -17 -9 -12 -12 -11HARDNESS A, pt's 69 64 67 67 67 64HARD CHANGE, pt's -6 -8 -6 -4 -3 -10VOLUME CHANGE, % 14 15 14 12 12 15168 hours at 150.degree. C.TENSILE, psi 3640 2040 3165 2775 3265 2840TENSILE, MPa 25.1 14.1 21.8 19.1 22.5 19.6TENSILE CHANGE, % -9 -35 -2 -19 -6 -11ELONGATION, % 250 160 215 195 215 205ELONG CHANGE, % -2 -33 -9 -22 -17 -11HARDNESS A, pt's 63 62 67 65 66 64HARD CHANGE, pt's -12 -10 -6 -6 -4 -10VOLUME CHANGE, %__________________________________________________________________________

EXAMPLE 2

This example illustrates compositions comprising a variety of partially hydrogenated nitrile rubbers admixed with the same polyacrylate elastomer. The experimental and test procedures utilized were the same as those of Example 1. The polyacrylate contains about 55% by weight of structural units derived from ethyl acrylate and about 45% by weight of structural units derived from n-butyl acrylate. The nitrile rubbers are partially hydrogenated nitrile rubbers containing from about 17 to 50% by weight of acrylonitrile and having a degree of unsaturation in the range of about 91-99%. Those partially hydrogenated rubbers containing about 17-25% of acrylonitrile also contain units derived from a third monomer, such as an alkyl ester or a dialkyl ester of an unsaturated carboxylic acid. The components of the curable compositions, the times and temperatures of curing, processing properties during curing, and the properties of the cured product, including the results of tests on aged products, are summarized below:

__________________________________________________________________________ 2A 2B 2C 2D 2E 2F 2G 2H 2I 2J 2K 2L__________________________________________________________________________Polyacralyte 80.0 80.0 80.0 80.0 80.0 80.0 80.0 80.0 80.0 80.0 80.0 80.0Nitrile Rubber I 20.0Nitrile Rubber II 20.0Nitrile Rubber III 20.0Nitrile Rubber IV 20.0Nitrile Rubber V 20.0Nitrile Rubber VI 20.0Nitrile Rubber VII 20.0Nitrile Rubber VIII 20.0Nitrile Rubber IX 20.0Nitrile Rubber X 20.0Nitrile Rubber XI 20.0Nitrile Rubber XII 20.0Carbon black 60.0 60.0 60.0 60.0 60.0 60.0 60.0 60.0 60.0 60.0 60.0 60.0Stearic Acid 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0Amine antioxidant 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0Peroxide 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0Bis-maleimide 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0TOTAL 170.0 170.0 170.0 170.0 170.0 170.0 170.0 170.0 170.0 170.0 170.00 170.0PROCESSINGPROPERTIESMOONEY VISCOMETER:Large Rotor, 125.degree. C.VISC. MINIMUM 46 45 45 45 45 44 44 44 42 42 42 42T5, minutes 30 30 30 30 30 30 30 30 30 30 30 30RHEOMETER, MICRODIE,100 cpm, 3.degree. ARCML,lbf*in 11.7 11.3 11.7 11.7 11.3 11.0 11.3 11.3 10.9 11.1 10.9 10.9ML,N*m 1.3 1.3 1.3 1.3 1.3 1.2 1.3 1.3 1.2 1.2 1.2 1.2MH,lbf*in 30.3 33.7 31.0 34.8 28.6 30.6 32.4 38.6 30.1 31.3 30.5 31.1MH,N*m 3.4 3.7 3.4 3.9 3.2 3.4 3.6 4.3 3.3 3.5 3.4 3.5Ts2, minutes 1.2 1.2 1.2 1.1 1.3 1.1 1.1 1.1 1.3 1.3 1.4 1.3T.sup.1 90, minutes 2.6 2.9 2.7 2.8 2.7 2.6 2.8 3.3 2.6 2.7 2.7 2.7VULCANIZEDPROPERTIES4 minutes at 190.degree. C.STRESS 100%, psi 835 920 1045 925 770 810 520 865 765 735 595 645STRESS 100%, MPa 5.8 6.3 7.2 6.4 5.3 5.6 3.6 6.0 5.3 5.1 4.1 4.5TENSILE, psi 1430 1250 1375 1355 1440 1360 1125 1335 1375 1285 1220 1235TENSILE, MPa 9.9 8.6 9.5 9.3 9.9 9.4 7.8 9.2 9.5 8.9 8.4 8.5ELONGATION, % 190 155 145 60 200 190 210 170 200 185 205 200HARDNESS, A pts 72 77 75 72 70 72 70 73 66 70 67 68COMPRESSION SET,METHOD B, BUTTONS,cure time 6 minutes at 190.degree. C.70 h @ 150.degree. C. 45 49 54 48 41 46 45 46 39 39 41 41168 h @ 150.degree. C. 55 57 56 51 50 52 54 55 41 48 43 41GEHMAN LOW TEMPER-ATURE TORSION TESTT2, .degree.C. 4 11 8 6 5 6 10 9 9 0 4 9T5, .degree.C. -12 -3 -7 -8 -11 -9 -9 -9 -9 -16 -13 -8T10, .degree.C. -20 -10 -15 -15 -20 -19 -17 -18 -17 -22 -21 -18T100, .degree.C. -32 -29 -31 -32 -32 -31 -30 -31 -32 -35 -34 -34FREEZE PT, .degree.C. -30 -20 -27 -28 -34 -33 -33 -33 -34 -35 -37 -37AGING: ENVIRON-MENAIR OVEN70 hours at 150.degree. C.Tensile, psi 1135 1410 1415 1300 1480 1320 1065 1335 1095 1110 985 830Tensile, MPa 9.2 9.7 9.8 9.0 10.2 9.1 7.3 9.2 7.6 7.7 6.8 5.7Tensile change, % -7 13 3 -4 3 -3 -5 0 -20 -14 -19 -33Elongation, % 160 95 120 115 175 155 165 95 205 185 235 260Elong. Change, % -16 -39 -17 -28 -13 -18 -21 -44 3 0 15 30Hardness A, pt's 81 87 84 88 80 83 83 83 78 79 75 77Hard change, pt's 9 10 9 16 10 11 13 10 12 9 8 9180.degree. Bend Pass Pass Pass Pass Pass Pass Pass Pass Pass Pass Pass PassAGING: ENVIRON-MENAIR OVEN168 hours at 150.degree. C.TENSILE, psi 1355 1315 1580 1425 1315 1340 1340 1495 1005 1015 885 745TENSILE, MPa 9.3 9.1 10.9 9.8 9.1 9.2 9.2 10.3 6.9 7.0 6.1 5.1TENSILE CHANGE, % -5 5 15 5 -9 -1 19 12 -27 -21 -27 -40ELONGATION, % 145 76 110 80 165 115 95 60 205 170 250 255ELONG. CHANGE, % -24 -51 -24 -50 -18 -39 -55 -65 3 -8 22 28HARDNESS A, pt's 82 90 87 91 82 86 86 90 81 83 81 80HARD CHANGE, pt's 10 13 12 19 12 14 16 17 15 13 14 12180.degree. BEND Pass Pass Pass Pass Pass Pass Pass FAIL Pass Pass Pass PassAGING: ENVIRON-MENAIR OVEN1008 hours at 150.degree. C.TENSILE, psi 1430 2330 1840 2230 1460 1900 2030 2485 1370 1665 1195 1350TENSILE, MPa 9.9 16.1 12.7 15.4 10.1 13.1 14.0 17.1 9.5 11.5 8.2 9.3TENSILE CHANGE, % 0 86 34 65 1 40 80 86 0 30 -2 9ELONGATION, % 35 8 15 8 45 20 10 10 40 20 47 30ELONG. CHANGE -82 -95 -90 -95 -78 -89 -95 -94 -80 -89 -77 -85HARDNESS A, pt's 95 92 88 94 93 86 96 96 93 90 93 94HARD CHANGE, pt's 20 15 13 22 23 14 26 23 27 20 26 26180.degree. BEND Fail Fail Fail Fail Pass Fail Fail Fail Fail Fail Pass FailAGING: ASTM 903 OIL70 hours at 150.degree. C.TENSILE, psi 980 945 1070 975 1005 910 950 1020 975 890 750 715TENSILE, MPa 6.8 6.5 7.4 6.7 6.9 6.3 6.6 7.0 6.7 6.1 5.2 4.9TENSILE CHANGE, % -31 -24 -22 -28 -30 -33 -16 -24 -29 -31 -39 -42ELONGATION, % 180 120 135 125 185 165 165 125 185 155 170 165ELONG. CHANGE, % -5 -23 -7 -22 -8 -13 -21 -26 -8 -16 -17 -18HARDNESS A, pt's 40 54 49 54 40 45 46 51 39 40 34 34HARD CHANGE, pt's -32 -23 -26 -18 -30 -27 -24 -22 -27 -30 -33 -34VOLUME CHANGE, % 32 27 27 27 30 30 31 29 33 34 43 43180.degree. BEND Pass Pass Pass Pass Pass Pass Pass Pass Pass Pass Pass PassAGING: ASTM 903 OIL168 hours at 150.degree. C.TENSILE, psi 875 855 875 890 955 890 875 905 740 880 685 670TENSILE, MPa 6.0 5.9 6.0 6.1 6.6 6.1 6.0 6.2 5.1 6.1 4.7 4.6TENSILE CHANGE, % -39 -32 -36 -34 -34 -35 -22 -32 -46 -32 -44 -46ELONGATION, % 170 115 115 125 190 150 150 115 180 165 175 165ELONG. CHANGE, % -11 -26 -21 -22 -5 -21 -29 -32 -10 -11 -15 -18HARDNESS A, pt's 43 5 51 53 41 46 47 51 39 40 34 35HARDNESS CHANGE, pt's -29 -22 -24 -19 -29 -26 -23 -22 -27 -30 -33 -33VOLUME CHANGE, % 32 27 27 27 30 30 31 29 33 34 43 43180.degree. BEND Pass Pass Pass Pass Pass Pass Pass Pass Pass Pass Pass PassAGING: 10W40 OIL70 hours at 150.degree. C.TENSILE, psi 1135 1225 1440 1345 1285 1140 1215 1005 1270 1210 1145 1150TENSILE, MPa 7.8 8.5 9.9 9.3 8.9 7.9 8.4 6.9 8.8 8.3 7.9 7.9TENSILE CHANGE, % -21 -2 5 -1 -11 -16 8 -25 -8 -6 -6 -7ELONGATION, % 85 155 110 80 170 125 100 140 150 115 175 155ELONG. CHANGE, % -55 0 -24 -50 -15 -34 -52 394 -25 -38 -15 -23HARDNESS A, pt's 69 69 74 77 65 70 71 75 65 67 61 63HARD CHANGE, pt's -3 -8 -1 5 -5 -2 1 3 -1 -3 -6 -5VOLUME CHANGE, % 7 5 5 6 7 6 6 6 8 8 11 11180.degree. BEND Pass Pass Pass Pass Pass Pass Pass Pass Pass Pass Pass PassAGING: 10W40 OIL168 hours at 150.degree. C.TENSILE, psi 1230 1135 1335 1200 1265 1315 1325 1000 1165 1150 1125 1040TENSILE, MPa 7.8 8.5 9.9 9.3 8.9 7.9 8.4 6.9 8.8 8.3 7.9 7.9TENSILE CHANGE, % -21 -2 5 -1 -11 -16 8 -25 -8 -6 -6 -7ELONGATION, % 150 70 90 65 155 105 95 55 130 115 165 135ELONG. CHANGE, % -55 0 -24 -50 -15 -34 -52 394 -25 -38 -15 -23HARDNESS A, pt's 70 81 75 78 70 73 74 78 67 67 61 63HARD CHANGE, pt's -3 -8 -1 6 -5 -2 1 2 -1 -3 -6 -5VOLUME CHANGE, % 6 5 5 6 6 6 6 6 8 7 11 10180.degree. BEND Pass Pass Pass Pass Pass Pass Pass Pass Pass Pass Pass Pass__________________________________________________________________________

EXAMPLE 3

This example illustrates the effect of varying the relative proportions of the polyacrylate elastomer and the partially hydrogenated nitrile rubber in the mixture being peroxide-cured. Examples 3A and 3B are for comparative purposes and do not represent compositions within the scope of the present invention. The experimental and testing procedures utilized were the same as those of Example 1. The components of the curable compositions, the times and temperatures of curing, processing properties during curing and the properties of the cured product, including the results of aging tests, are summarized below:

__________________________________________________________________________ 3A 3B 3C 3D 3E 3F 3G 3H 3I__________________________________________________________________________Polyacrylate 100.0 95.0 90.0 85.0 80.0 70.0 70.0 60.0 60.0Nitrile rubber 5.0 10.0 15.0 20.0 30.0 30.0 40.0 40.0Carbon 60.0 60.0 60.0 60.0 60.0 60.0 60.0 60.0 60.0Stearic Acid 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0Amine antioxidant 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0Peroxide 2.0 2.0 2.0 2.0 2.0 2.0 3.0 2.0 3.0Bis-maleimide 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0TOTAL 169.0 169.0 169.0 169.0 169.0 169.0 170.0 169.0 170.0PROCESSING PROPERTIESMOONEY VISCOMETER:VISC. MINIMUM 36 42 44 45 46 49 49 51 51T5, minutes 30 30 30 30 30 30 30 30 30RHEOMETER, MICRODIE,100 cpm, 3.degree. ARC at 190.degree. C.ML,lbf*in 8.2 10.7 11.5 11.5 11.5 11.9 11.7 11.9 12.0ML,N + m 0.9 1.2 1.3 1.3 1.3 1.3 1.3 1.3 1.3MH,lbf*in 20.0 24.0 25.0 25.0 25.0 29.0 29.0 30.0 31.0MH,N*m 2.2 2.7 2.8 2.8 2.8 3.2 3.2 3.3 3.4Ts2, minutes 1.6 1.5 1.5 1.5 1.5 1.6 1.5 1.5 1.5T.sup.1 90, minutes 5.1 3.7 3.3 3.6 3.5 4.4 4.3 4.5 4.3VULCANIZED PROPERTIESCURE TIME 4 minutes at 190.degree. C.STRESS 100%, psi 250 420 545 625 610 680 675 725 675STRESS 100%, MPa 1.7 2.9 3.8 4.3 4.2 4.7 4.7 5.0 4.7TENSILE, psi 980 1015 1170 1270 1365 1640 1660 1910 1920TENSILE, MPa 6.8 7.0 8.1 8.8 9.4 11.3 11.5 13.2 13.2ELONGATION, % 325 270 265 240 255 240 250 280 280HARDNESS, A pts 54 67 69 68 70 71 73 76 75COMPRESSION SET, METHOD B,CURE TIME 6 minutes at 190.degree. C.BUTTONS 70 hrs @ 150.degree. C. 39 34 37 40 40 46 49 53 55AGING: ENVIRONMENT AIR OVEN70 hours at 175.degree. C.TENSILE, psi 770 835 935 1105 1320 1460 1525 1810 1775TENSILE, MPa 6.1 5.8 6.5 7.6 9.1 10.1 10.5 12.5 12.2TENSILE CHANGE, % -21 -18 -20 -13 -3 -11 -8 -5 -8ELONGATION, % 285 235 175 150 140 130 140 145 135ELONG. CHANGE, % -12 -13 -34 -38 -45 -46 -44 -48 -52HARDNESS A, pt's 72 84 86 86 88 88 89 88 89HARD CHANGE, pt's -81 -17 -17 -18 -18 -17 -16 -12 -14180.degree. BEND Pass Pass Pass Pass Pass Pass Pass Pass PassAGING: ASTM 902 Oil70 hours at 150.degree. C.TENSILE, psi 975 1005 1125 1250 1370 1635 1625 1955 1920TENSILE, MPa 6.7 6.9 7.8 8.6 9.5 11.3 11.2 13.5 13.2TENSILE CHANGE, % -1 -1 -4 -2 0 0 -2 2 0ELONGATION, % 355 315 255 255 245 250 230 255 265ELONG. CHANGE, % 9 17 -4 6 -4 4 -8 -9 -5HARDNESS A, pt's 46 53 59 60 62 65 64 68 68HARD CHANGE, pt's -8 -14 -10 -8 -8 -6 -9 -8 -7VOLUME CHANGE, % 12 10 10 10 9 10 9.5 9 9180.degree. BEND Pass Pass Pass Pass Pass Pass Pass Pass PassAGING: ENVIRONMENT ASTM 903 OIL70 hours at 150.degree. C.TENSILE, psi 700 730 820 875 100 1235 1225 1565 1345TENSILE, MPa 4.8 5.0 5.7 6.0 6.9 8.5 8.5 10.8 9.3TENSILE CHANGE, % -29 -28 -30 -31 -27 -25 -26 -18 -30ELONGATION, % 265 230 230 225 215 215 235 250 225ELONG. CHANGE, % -18 -15 -13 -6 -16 -10 -6 -11 -20HARDNESS A, pt's 26 33 36 38 40 44 45 49 49HARD CHANGE, pt's -28 -34 -33 -30 -30 -27 -28 -27 -26VOLUME CHANGE, % 43 39 38 36 34 32 32 28 29180.degree. BEND Pass Pass Pass Pass Pass Pass Pass Pass Pass__________________________________________________________________________

EXAMPLE 4

This example, like the previous example, illustrates the effect, in a somewhat different formulation, of varying the proportions of the polyacrylate elastomer and the partially hydrogenated nitrile rubber in the mixture being peroxide-cured. Examples 4A and 4B are for comparative purposes and do not represent compositions within the scope of the present invention. The experimental and test procedures utlized were the same as those of Example 1. The components of the curable composition, the times and temperatures of curing, processing conditions during curing and the properties of the cured product, including the results of testing of the aged products, are summarized below:

__________________________________________________________________________ 4A 4B 4C 4D 4E 4F 4G__________________________________________________________________________Nitrile Rubber 100.0 100.0 90.0 80.0 80.0 70.0 70.0Polyacylate 5.0 10.0 20.0 20.0 30.0 30.0Carbon black 50.0 50.0 50.0 50.0 50.0 50.0 50.0Magnesium Oxide 5.0 5.0 5.0 5.0 5.0 5.0 5.0Stearic acid 0.5 0.5 0.5 0.5 0.5 0.5 0.5Plasticizer 5.0Amine antioxidant 1.5 1.5 1.5 1.5 1.5 1.5 1.5Vanox MTI 0.5 0.5 0.5 0.5 0.5 0.5 0.5Peroxide 8.0 8.0 8.0 8.0 8.0 8.0 8.0Bis-Maleimide 2.0 2.0 2.0 2.0 2.0 2.0 2.0TOTAL: 172.5 172.5 167.5 167.5 167.5 167.5 167.5PROCESSING PROPERTIESMOONEY VISCOMETER:Large Rotor, 125.degree. C.VISC. MINIMUM 48 54 52 48 48 42 42T5, minutes 21 18.5 19.8 18.4 19 18.4 17.6RHEOMETER, MICRODIE,100 cpm, 3.degree. ARC at 170.degree. C.ML,lbf*IN 14.8 17.5 16.5 14.4 15.1 13.4 14.5ML,N*m 1.6 1.9 1.8 1.6 1.7 1.5 1.6MH,lbf*in 115.0 118.0 115.0 102.0 102.0 91.0 87.5MH,N*m 12.8 13.1 12.8 11.3 11.3 10.1 9.7Ts2, minutes 1.3 1.3 1.3 1.2 1.2 1.2 1.2T.sup.1 90, minutes 12.5 13.0 13.1 13.5 13.5 13.0 12.5VULCANIZED PROPERTIESCURE TIME 20 minutes at 170.degree. C.STRESS 100%, psi 1060 1075 1235 1175 1145 1120 1105STRESS 100%, MPa 7.3 7.4 8.5 8.1 7.9 7.7 7.6TENSILE, psi 3940 3780 3670 3265 2465 3085 2870TENSILE, MPa 27.2 26.1 25.3 22.5 17.0 21.3 19.8ELONGATION, % 265 260 235 225 170 225 220HARDNESS, A pts 73 75 77 75 75 73 73COMPRESSION SET, METHOD B,BUTTONS 70 hrs @ 150.degree. C. % 21 22 23 26 24 27 26GEHMAN LOW TEMPERATURE TORSIONT2, .degree.C. -18 -17 -17 -15 -15 -13 -18T5, .degree.C. -23 -22 -22 -21 -22 -22 -23T10, .degree.C. -26 -24 -24 -23 -24 -24 -25T100, .degree.C. -32 -30 -30 -30 -30 -30 -35FREEZE PT, .degree.C. -31 -29 -30 -27 -29 -30 -30AGING: ENVIRONMENTAIR OVEN 70 hours at 150.degree. C.TENSILE, psi 4135 4055 3565 3375 3280 2805 2860TENSILE, MPa 28.5 28.0 24.6 23.3 22.6 19.4 19.7TENSILE CHANGE, % 5 7 -3 3 33 -9 0ELONGATION, % 240 230 200 205 190 175 185ELONG. CHANGE, % -9 -12 -15 -9 12 -22 -16HARDNESS A, pt's 80 80 81 81 81 78 79HARD CHANGE, pt's 7 5 4 6 6 5 6180.degree. BEND Pass Pass Pass Pass Pass Pass PassAGING: ENVIRONMENTASTM 903 OIL 70 hours at 150.degree. C.TENSILE, psi 3085 3475 3225 2985 2405 2345 2320TENSILE, MPa 21.3 24.0 22.3 20.6 16.6 16.2 16.0TENSILE CHANGE, % -22 -8 -12 -9 -2 -24 -19ELONGATION, % 215 235 225 215 235 185 180ELONG. CHANGE, % -19 -10 -4 -4 38 -18 -18HARDNESS A, pt's 65 66 68 65 68 61 62HARD CHANGE, pt's -8 -9 -9 -10 -7 -12 -11VOLUME CHANGE, % 13 17 17 19 19 20 20180.degree. BEND Pass Pass Pass Pass Pass Pass Pass__________________________________________________________________________

Our invention has been described in terms of specific embodiments and non-limiting examples. Various modifications in the compositions of the present invention will be apparent to those skilled in the art and are included within the scope of the invention.

Claims

1. A peroxide-cured blend consisting essentially of:

10 to 90 parts by weight of a polyacrylate elastomer comprising at least 10 mole % of the structural unit ##STR8## wherein R.sup.1 is a C.sub.4-8 alkyl group; up to 30 mole % of the structural unit ##STR9## wherein R.sup.2 is an alkoxyalkyl group containing 2-12 carbon atoms; and the balance to a total of 100 mole % of the structural unit ##STR10## wherein R.sup.3 is a C.sub.1-3 alkyl group; and 9- 10parts by weight of a partially hydrogenated nitrile rubber having a degree of unsaturation of from 0.1 to 20%.

2. A peroxide-cured blend according to claim 1, comprising 20 to 30 mole % of the structural unit ##STR11##

3. A peroxide-cured blend according to claim 1, wherein R.sup.1 is n-butyl, R.sup.2 is methoxyethyl and R.sup.3 is ethyl.

4. A peroxide-cured blend consisting essentially of:

10 to 90 parts by weight of a polyacrylate elastomer comprising at least 10 mole % of the structural unit ##STR12## wherein R.sup.1 is a C.sub.4-8 alkyl group; up to 30 mole % of the structural unit ##STR13## wherein R.sup.2 is an alkoxylakyl group containing 2-12 carbon atoms; 1to 10 mole % of the structural unit ##STR14## and the balance to a total of 100 mole % of the structural unit ##STR15## wherein R.sup.3 is a C.sub.1-3 alkyl group; and 10to 90 parts by weight of a hydrogenated nitrile rubber having a degree of unsaturation of 1 to 20%.

5. A peroxide-cured blend according to claim 4, comprising 20 to 30 mole % of the structural unit ##STR16##

6. A peroxide-cured blend according to claim 4, wherein R.sup.1 is n-butyl, R.sup.2 is methoxyethyl and R.sup.3 is ethyl.

7. A peroxide-curable composition consisting essentially of a blend of:

10 to 90 parts by weight of a polyacrylate elastomer comprising at least 10 mole % of the structural unit ##STR17## wherein R.sup.1 is a C.sub.4-8 alkyl group; up to 30 mole % of the structural unit ##STR18## wherein R.sup.2 is an alkoxyalkyl group containing 2-12 carbon atoms; and the balance to a total of 100 mole % of the structural unit ##STR19## wherein R.sup.3 is a C.sub.1-3 alkyl group; 90to 10 parts by weight of a hydrogenated nitrile rubber having a degree of unsaturation of from 0.1 to 20%; and a peroxide curing system.

8. A peroxide-curable composition according to claim 7 wherein the peroxide curing system comprises di-1,1-bis (t-butylperoxy)-3,3,4-trimethylcyclohexane and m-phenylenediamine bis-maleimide.

9. A peroxide curable composition blend according to claim 7, consisting essentially of 20 to 30 mole % of the structural unit ##STR20##

10. A peroxide-curable composition which comprises a blend of:

10 to 90 parts by weight of a polyacrylate elastomer comprising at least 10 mole % of the structural unit ##STR21## wherein R.sup.1 is a C.sub.4-8 alkyl group; up to 30 mole % of the structural unit ##STR22## wherein R.sup.2 is an alkoxylalkyl group containing 2-12 carbon atoms; 1 to 10 mole % of the structural unit ##STR23## and the balance to a total of 100 mole % of the structural unit ##STR24## wherein R.sup.3 is a C.sub.1-3 alkyl group; 90to 10 parts by weight of a hydrogenated nitrile rubber having a degree of unsaturation of from 0.1 to 20%; and

a peroxide curing system.

11. A peroxide-curable composition according to claim 10, wherein the peroxide curing system comprises an organic peroxide and m-phenylenediamine bis-maleimide.

12. A peroxide-cured blend according to claim 10, consisting essentially of 20 to 30 mole % of the structural unit ##STR25##