FIELD OF THE INVENTION The present invention relates to a process for reducing the cold flow of a rubber compound blend including compounding at least one hydrogenated nitrile polymer, at least one olefin/vinylacetate and/or olefin/acrylate polymer with at least one precrosslinked olefin/vinyl acetate and/or olefin/acrylate. The present invention also relates to a curable rubber compounds containing the rubber blend having reduced cold flow. Further, the present invention relates to shaped articles containing the rubber blend having reduced cold flow.

BACKGROUND OF THE INVENTION

Hydrogenated nitrile rubbers (HNBR), prepared by the selective hydrogenation of nitrile rubber (NBR, a co-polymer comprising at least one conjugated diene, at least one unsaturated nitrile and optionally further comonomers) are specialty rubbers which have very good heat resistance, excellent ozone and chemical resistance, and excellent oil resistance. Coupled with the high level of mechanical properties of the rubber (in particular the high resistance to abrasion) it is not surprising that HNBR have found widespread use in the automotive (seals, hoses, bearing pads) oil (stators, well head seals, valve plates), electrical (cable sheathing), mechanical engineering (wheels, rollers) and shipbuilding (pipe seals, couplings) industries, amongst others.

EP-A-O 471 250 discloses hydrogenated butadiene/ isoprene/ (meth)- acrylonitrile copolymers, in particular copolymers containing 3.5 to 22% by weight of copolymerized isoprene and 18 to 50% by weight of copolymerized acrylonitrile or methacrylonitrile, and having a degree of hydrogenation, based on the C=C double bonds of the polymer, of at least 85%, that is, an RDB not greater than 15%. There are commercially available HNBR's that have good low temperature properties. Therban ^® LT 2157 is a terpolymer, available from Lanxess, composed

of 21 wt% acrylonitrile, acrylate, and butadiene, that has a residual double bond content (RDB) of 5.5% and a glass transition temperature (Tg) of -38° C. Therban ^® VP KA 8882 is similar, but differs in having an RDB of less than 0.9%, and, again, has a Tg of -38.° C. WO-02/16441-A discloses a hydrogenated copolymer of an unsaturated nitrile, butadiene and isoprene, wherein the molar ratio of butadiene to isoprene is less than 3:1.

EP-A-O 151 691 discloses a blend of 95-5 wt.% of EVA and 5-95 wt.% of HNBR. CA 2,436,742 discloses a polymer blend comprising at least one, preferably statistical, hydrogenated nitrile rubber, at least one, preferably statistical, hydrogenated nitrile terpolymer rubber, at least one, preferably binary, salt of a strong base and a weak acid comprising a group 1 metal, and at least one olefin/vinylacetate or olefin/acrylate rubber.

SUMMARY OF THE INVENTION

The present invention relates to a process for preparing a rubber compound blend having reduced cold flow including compounding

(i) at least one, preferably statistical, hydrogenated nitrile polymer, (ii) at least one olefin/vinyl acetate and/or olefin/acrylate polymers, with

(iii) at least one of the olefin/vinyl acetate and/or olefin/acrylate polymers having a gel content and a swelling index which is adjusted with gamma radiation and wherein the radiation adjusted polymer has a gel content of 40 to 80% based on the total mass of the olefin/vinyl acetate and/or olefin/acrylate polymer and a swelling index of 20 to 80 based on the gel.

The present invention also relates to a process for preparing a rubber blend having reduced cold flow including compounding

(i) at least one, preferably statistical, hydrogenated nitrile terpolymer rubber,

(ii) at least one olefin/vinyl acetate and/or olefin/acrylate polymers, with (iii) at least one of the olefin/vinyl acetate and/or olefin/acrylate polymers having a gel content and a swelling index which is adjusted with gamma radiation and wherein the radiation adjusted polymer has a gel content of 40 to 80% based

on the total mass of the olefin/vinyl acetate and/or olefin/acrylate polymer and a swelling index of 20 to 80 based on the gel.

In addition, the present invention relates to curable rubber compounds containing the rubber blend having reduced cold flow. Further, the present invention relates to a shaped article containing the curable rubber compound having reduced cold flow.

Rubber compound blends prepared according to the present inventive process have reduced cold flow without the deterioration of other physical properties of unvulcanized rubber compounds and vulcanized rubber compounds containing the inventive rubber blends.

BRIEF DESCRIPTION OF THE DRAWING

Figure 1 graphically illustrates the processing improvements in rubber compounds wherein a precrosslinked EVM is incorporated into the compound formulation.

DESCRIPTION OF THE INVENTION

As used throughout this specification, the term "nitrile rubber", "nitrile polymer" or NBR is intended to have a broad meaning and is meant to encompass a copolymer having repeating units derived from at least one conjugated diene, at least one alpha, beta-unsatu rated nitrile and optionally further copolymerizable monomer(s).

As used throughout this specification, the term "nitrile terpolymer rubber" or "LT-NBR" is intended to have a broad meaning and is meant to encompass a copolymer having (a) repeating units derived from at least one conjugated diene, (b) at least one alpha, beta-unsaturated nitrile, (c) repeating units derived from at least one further monomer selected from the group consisting of conjugated dienes, unsaturated carboxylic acids; alkyl esters of unsaturated carboxylic acids, alkoxyalkyl acrylates and ethylenically unsaturated monomers other than dienes and (d) optionally further copolymerizable monomer(s). If (a) and (c) are conjugated dienes, it is understood that the nitrile terpolymer rubber contains repeating units derived from at least two different conjugated dienes.

As used throughout this specification, the term "hydrogenated" or HNBR is intended to have a broad meaning and is meant to encompass a NBR wherein at least 10 % of the residual C-C double bonds (RDB) present in the starting NBR are hydrogenated, preferably more than 50 % of the RDB present are hydrogenated, more preferably more than 90 % of the RDB are hydrogenated, even more preferably more than 95 % of the RDB are hydrogenated and most preferably more than 99 % of the RDB are hydrogenated.

The conjugated diene may be any known conjugated diene preferably a C ₄ - C ₆ conjugated diene. Preferred conjugated dienes include butadiene, isoprene, piperylene, 2,3-dimethyl butadiene and mixtures thereof. Even more preferred C ₄ - C ₆ conjugated dienes include butadiene, isoprene and mixtures thereof. The most preferred C ₄ -C ₆ conjugated diene is butadiene.

The alpha, beta-unsatu rated nitrile may be any known alpha, beta- unsaturated nitrile, preferably a C ₃ -C ₅ alpha, beta-unsatu rated nitrile. Preferred C ₃ - C ₅ alpha, beta-unsaturated nitriles include acrylonitrile, methacrylonitrile, ethacrylonitrile and mixtures thereof. The most preferred C ₃ -C ₅ alpha, beta- unsaturated nitrile is acrylonitrile.

The unsaturated carboxylic acid may be any known unsaturated carboxylic acid copolymerizable with the other monomers, preferably a C ₃ -Ci ₆ alpha, beta- unsaturated carboxylic acid. Preferred unsaturated carboxylic acids include acrylic acid, methacrylic acid, itaconic acid and maleic acid and mixtures thereof.

The alkyl ester of an unsaturated carboxylic acid may be any known alkyl ester of an unsaturated carboxylic acid copolymerizable with the other monomers, preferably an alkyl ester of an C ₃ -C-| ₆ alpha, beta-unsaturated carboxylic acid. Preferred alkyl ester of an unsaturated carboxylic acid include alkyl esters of acrylic acid, methacrylic acid, itaconic acid and maleic acid and mixtures thereof, preferably methyl acrylate, ethylacrylate, butylacrylate, 2-ethylhexyl acrylate and octyl acrylate. Preferred alkyl esters include methyl, ethyl, propyl, butyl and octyl esters. The alkoxyalkyl acrylate may be any known alkoxyalkyl acrylate copolymerizable with the other monomers, preferably methoxyethyl acrylate, ethoxyethyl acrylate and methoxyethoxyethyl acrylate and mixtures thereof

The ethylenically unsaturated monomer may be any known ethylenically unsaturated monomer copolymerizable with the other monomers, preferably allyl glycidyl ether, vinyl chloroacetate, ethylene, butene-1 , isobutylene and mixtures thereof. Preferably, the HNBR according to the present invention contains in the range of from 40 to 85 weight percent of repeating units derived from one or more conjugated dienes and in the range of from 15 to 60 weight percent of repeating units derived from one or more unsaturated nitriles. More preferably, the HNBR contains in the range of from 60 to 75 weight percent of repeating units derived from one or more conjugated dienes and in the range of from 25 to 40 weight percent of repeating units derived from one or more unsaturated nitriles. Most preferably, the HNBR contains in the range of from 60 to 70 weight percent of repeating units derived from one or more conjugated dienes and in the range of from 30 to 40 weight percent of repeating units derived from one or more unsaturated nitriles.

Preferably, the nitrile terpolymer according to the present invention is a hydrogenated alpha, beta-unsaturated nitrile/ butadiene/isoprene rubber. Preferably, the ratio of repeating units derived from butadiene to repeating units derived from isoprene (butadiene:isoprene ratio) is preferably below 3:1 , more preferably below 2:1. The ratio can be as low as 0.1 :1 , but is preferably not less than 0.5:1. Good results are obtained with a ratio of 1 :1 and the preferred range is 0.75:1 to 1 :0.75.

The butadiene plus isoprene usually constitutes in the range of from 50 to 95% of the copolymer, and the nitrile usually constitutes in the range of from 5 to 50% of the copolymer. For the present invention the nitrile content does not normally exceed 36% and is preferably below 30%. The preferred lower limit on the nitrile content is 15%, because copolymers with lower nitrile contents tend to lose their oil resistance. For applications where oil resistance is not of importance, however, lower nitrile contents are acceptable, down to 10% or even 5%. For most purposes a nitrile content of 15 to 25% is preferred.

More preferably, the nitrile terpolymer rubber is a hydrogenated alpha, beta-unsaturated nitrile/butadiene/acrylate rubber. The combined butadiene and

acrylate content constitutes a range of 50 to 95% of the terpolymer, while the nitrile is in the range of 5 to 50%. More preferably, the nitrile range is between 10 and 30%. Commercially available examples of such terpolymers include Therban® LT 2157 (21 % nitrile content, 5.5% residual double bonds) and Therban® LT VP KA 8882 (21 % nitrile content, 0.9 % maximum double bond content).

Optionally, according to the present invention, the hydrogenated nitrile polymer and/or the hydrogenated nitrile terpolymer rubber may further contain repeating units derived from one or more copolymerizable monomers. Repeating units derived from one or more copolymerizable monomers will replace either the nitrile or the diene portion of the nitrile rubber and it will be apparent to the skilled in the art that the above mentioned figures will have to be adjusted to result in 100 weight percent.

The olefin/vinylacetate polymers according to the present invention may be any olefin/vinylacetate rubber known in the art.

The olefin may be any known olefin, preferably ethylene, propylene, butenes, pentenes, hexenes, heptenes, octenes and their higher homologues and mixtures thereof.

The olefin/vinylacetate rubber usually contains in the range of from 10-95 wt.%, preferably 10-80 wt%., of repeating units derived from the olefin monomer(s) and in the range of from 5-90 wt.%, preferably 20-90 wt.%, of repeating units derived from the vinylacetate. Preferred are olefin/vinylacetate rubbers available under the trade-name LEVAPREN ^® from Lanxess Deutschland GmbH. The olefin/acrylate polymer may be any olefin/ acrylate rubber known in the art.

The olefin may be any known olefin, preferably ethylene, propylene, butenes, pentenes, hexenes, heptenes, octenes and their higher homologues and mixtures thereof. The acrylate may be any known acrylate copolymerizable with the olefin, preferably acrylic acid and derivatives such as methacrylic acid and methylmethacrylate.

The olefin/acrylate rubber usually contains in the range of from 5-95 wt.%, preferably 10-80 wt%., of repeating units derived from the olefin monomer(s) and in the range of from 5-95 wt.%, preferably 20-90 wt.%, of repeating units derived from the acrylate(s). Preferred are olefin/acrylate rubbers available under the trade-name VAMAC ^® from DuPont.

According to the present invention, a precrosslinked olefin/vinylacetate and/or a precrosslinked olefin/acrylate polymer is added to a rubber blend to reduce the cold flow of the rubber blend. Suitable precrosslinked olefin/vinylacetate and/or a precrosslinked olefin/acrylate polymers useful in the present invention are prepared according to United States Patent No. 6,399,671 , the contents of which are herein incorporated by reference.

The precrosslinked polymers in the rubber compound blend having reduced cold flow according to the present invention are those synthesized from ethylene and vinyl acetate, from ethylene and the above-stated acrylates. In the precrosslinked polymers, the mixture ratio of the monomers relative to each other is conventionally 0.1%-99.9%, preferably 5%-95%, more preferably 30%-80%.

The gel content and degree of swelling of the precrosslinked polymers according to the present invention is established by ionizing radiation. Treatment with γ radiation is preferably considered as the ionizing radiation.

The precrosslinked polymers useful in the present invention preferably have a gel content of 30 to 80%, more preferably of 40 to 70%. The swelling index is preferably 20 to 80, more preferably 40 to 60.

The gel content and swelling index of the precrosslinked polymers useful in the present invention are determined using the following method:

The sample is placed in methylene chloride, to which 1 g/l of lonol had been added, such that there were 12.5 g of polymer per liter of solvent. The mixture is shaken for 6 hours at 14O ⁰ C, and then centrifuged for 1 hour at 20,000 rpm, wherein the temperature was still maintained at 14O ⁰ C. The sol solution was separated and may optionally be further investigated. The gel is first weighed while moist and the quantity of the dry gel obtained after drying to constant weight in a vacuum drying cabinet is determined.

The percentage gel content and the swelling index are calculated using the following formulae:

~ . . . mass of dry gel . __

Gel content = . . . . ... , — . ' * _r ^• 100 total initial weight of sample _ ... . , mass of moist gel

Swelling index = — mass of dry gel

In order to be able to establish the gel content and degree of swelling of the precrosslinked polymers according to present invention, the treatment with ionizing γ radiation is performed at a radiation dose of 20 to 140, preferably of 60 to 120, more preferably of 70 to 100 kGy (kilogray). Irradiation may be performed using any desired plant suitable for this purpose, for example with a 3.5 MCi ⁶⁰ Co gamma plant (approx. 1.3 MeV). Apart from Co-60 radiation, radiation from the ¹³⁷ Cs isotope is also suitable. The applied radiation dose may, for example, be measured using a photometric system from Far West Technology, USA and the film dosimeter supplied by this company. These film dosimeters contain a radiation-sensitive dye and the radiation dose is calculated on completion of the irradiation process from the change in the absorbance of said dye. These dosimeters are calibrated ex works against an internationally recognized standard. Treatment with γ radiation may be performed in the conventional manner at temperatures of 0° to 130°, preferably of 10° to 120°, more preferably of 20 to 80 ⁰ C. The most favorable temperature range may readily be determined by appropriate preliminary testing. It is essential that the temperature range is selected such that adequate free radical mobility is ensured.

The precrosslinked olefin/vinylacetate and/or olefin/acrylate polymers according to the present invention are preferably produced by initially polymerizing the monomers used in a conventional manner and then treating the resultant polymers with ionizing radiation.

It is possible in this connection to treat the precrosslinked polymers in the most varied forms, ranging from powders to large bales. It must merely be ensured that the γ radiation used sufficiently penetrates the polymers used.

In order to establish desired gel content, it is preferred, once the polymers have been irradiated, to homogenize them in suitable apparatus (internal mixers,

roll mills or co-kneaders). If the precrosslinked polymer is in finely divided form (for example powder or pellets), a powder mixer may also be used for homogenization. By means of this homogenization, it is possible to obtain a product which is entirely uniform with regard to gel content, irrespective of the shape and size of the irradiated container.

The desired average gel content may, of course, also be established by blending with non-irradiated or more or less highly irradiated polymers, i.e. with polymers having different gel contents.

The amount of the individual polymers and/or rubbers present in the present inventive process for preparing a rubber compound blend having reduced cold flow may vary in wide ranges and thus it is possible to tailor the properties of the final compound as well as the properties of the final shaped article. Preferably, the rubber blend contains in the range of from 5 to 50 wt.%, preferably from 10 to 40 wt.%, of at least one, preferably statistical, hydrogenated nitrile rubber and/or in the range of from 5 to 50 wt.%, preferably from 10 to 40wt.%, of at least one, preferably statistical, hydrogenated nitrile terpolymer rubber , and in the range of from 5 to 50 wt.%, preferably from 10to 40 wt.%, of at least one olefin/vinylacetate rubbers and/or one or more olefin/acrylate rubbers and in the range of from 20 to 80 wt.%, preferably from 30 to 70 wt.%, of at least one precrosslinked olefin/vinylacetate rubbers and/or precrosslinked olefin/acrylate rubbers .

The Mooney viscosity of the polymers and/or rubbers in the rubber compound blends having reduced cold flow may vary in wide ranges and thus it is possible to tailor the properties of the final compound as well as the properties of the final shaped article. Preferably, the hydrogenated nitrile polymer and/or hydrogenated nitrile terpolymer may have a Mooney viscosity ML(1+4@ 100 ⁰ C) of in the range of from 20 to 100 MU, preferably 40 to 80 MU. Preferably the olefin/vinyl acetate and/or olefin/acrylate polymer may have a Mooney viscosity ML (1+4@ 100 ⁰ C) of in the range of from 10 to 90 MU, preferably 20 to 70 MU. Preferably the precrosslinked olefin/vinyl acetate and/or olefin/acrylate polymer may have a Mooney viscosity ML (1+4@ 100 ⁰ C) of in the range of from 30 to 90 MU, preferably 40 to 70 MU

The Mooney viscosity of the raw polymers, the rubber compound blend and the cured rubber compound containing the inventive rubber compound blend having reduced cold flow can be determined using ASTM test D1646.

While it may not be preferred, the present inventive rubber compound blend may further contain up to 30 wt% of other polymers such as polyolefins, BR (polybutadiene), ABR (butadiene/acrylic acid-Ci-C^alkylester-copolymers), CR

(polychloroprene), IR (polyisoprene), SBR (styrene/butadiene-copolymers) with styrene contents in the range of 1 to 60 wt%, EPDM (ethylene/propylene/diene- copolymers), FKM (fluoropolymers or fluororubbers), and mixtures of the given polymers. Careful blending with said other polymers often reduce cost of the polymer blend without sacrificing too much of the desired final properties of the compound. The amount of other polymers will depend on the process condition to be applied during manufacture of shaped articles and the targeted final properties and is readily available by few preliminary experiments. According to the present invention is a rubber compound blend having reduced cold flow is prepared by compounding at least one, preferably statistical, hydrogenated nitrile polymer and/or hydrogenated nitrile terpolymer, at least one olefin/vinyl acetate and/or olefin/acrylate polymers with at least one olefin/vinyl acetate and/or olefin/acrylate polymers having a gel content and a swelling index which is adjusted with gamma radiation and wherein the radiation adjusted polymer has a gel content of 40 to 80% based on the total mass of the olefin/vinyl acetate and/or olefin/acrylate polymer and a swelling index of 20 to 80 based on the gel, at a temperature in the range of between 75 to 175°C to form a rubber blend having reduced cold flow. In order to prepare a curable rubber compound containing the present inventive rubber blend having reduced cold flow, preferably at least one filler and vulcanizing agent has to be added to the rubber blend.

Suitable filler(s) may be an active or an inactive filler or a mixture thereof. The filler(s) may be in particular: - highly dispersed silicas, prepared e.g. by the precipitation of silicate solutions or the flame hydrolysis of silicon halides, with specific surface areas of in the range of from 5 to 1000 m ² /g, and with primary particle

sizes of in the range of from 10 to 400 nm; the silicas can optionally also be present as mixed oxides with other metal oxides such as those of AI, Mg, Ca, Ba, Zn, Zr and Ti;

- synthetic silicates, such as aluminum silicate and alkaline earth metal silicate like magnesium silicate or calcium silicate, with BET specific surface areas in the range of from 20 to 400 m ² /g and primary particle diameters in the range of from 10 to 400 nm;

- natural silicates, such as kaolin and other naturally occurring silica;

- glass fibers and glass fiber products (matting, extrudates) or glass microspheres;

- metal oxides, such as zinc oxide, calcium oxide, magnesium oxide and aluminum oxide;

- metal carbonates, such as magnesium carbonate, calcium carbonate and zinc carbonate; - metal hydroxides, e.g. aluminum hydroxide and magnesium hydroxide;

- carbon blacks; the carbon blacks to be used here are prepared by the lamp black, furnace black or gas black process and have preferably BET (DIN 66 131) specific surface areas in the range of from 20 to 200 m ² /g, e.g. SAF, ISAF, HAF, FEF or GPF carbon blacks; - rubber gels, especially those based on polybutadiene, butadiene/styrene copolymers, butadiene/acrylonitrile copolymers and polychloroprene;

- large aspect ratio nanoclays such as Cloisite® or mixtures thereof. Examples of preferred mineral fillers include silica, silicates, clay such as bentonite, gypsum, alumina, titanium dioxide, talc, mixtures of these, and the like. For many purposes, the preferred mineral is silica, especially silica made by carbon dioxide precipitation of sodium silicate. Dried amorphous silica particles suitable for use in accordance with the invention may have a mean agglomerate particle size in the range of from 1 to 100 microns, preferably between 10 and 50 microns and most preferably between 10 and 25 microns. It is preferred that less than 10 percent by volume of the agglomerate particles are below 5 microns or

over 50 microns in size. A suitable amorphous dried silica moreover usually has a BET surface area, measured in accordance with DIN (Deutsche Industrie Norm) 66131 , in the range from 50 and 450 square meters per gram and a DBP absorption, as measured in accordance with DIN 53601 , in the range from 150 and 400 grams per 100 grams of silica, and a drying loss, as measured according to DIN ISO 787/11 , of in the range of from 0 to 10 percent by weight. Suitable silica fillers are available under the trademarks HiSil® 210, HiSil® 233 and HiSil® 243 from PPG Industries Inc. Also suitable are Vulkasil® S and Vulkasil® N, from Bayer AG. Often, use of carbon black as a filler is advantageous. Usually, carbon black is present in the polymer blend in an amount of in the range of from 20 to 200 parts by weight, preferably 30 to 150 parts by weight, more preferably 40 to 100 parts by weight. Further, it might be advantageous to use a combination of carbon black and mineral filler in the inventive rubber compound. In this combination the ratio of mineral fillers to carbon black is usually in the range of from 0.05 to 20, preferably 0.1 to 10.

Optionally, the present curable rubber compound containing the inventive rubber compound blend having reduced cold flow may further contain a carbodiimide, a polycarbodiimide or mixtures thereof. The preferred carbodiimide is available commercially under the tradenames Rhenogran™ PCD-50 and Stabaxol™ P. This ingredient may be used in the present curable rubber compound in an amount in the range of from 0 to about 15 parts by weight, more preferably in the range of from 0 to about 10 parts by weight, even more preferably in the range of from about 2 to about 5 parts by weight. The rubber compound having reduced cold flow may further contain at least one vulcanizing agent or curing system. The present invention is not limited to a special curing system; however, peroxide curing system(s) are preferred. Furthermore, the invention is not limited to a special peroxide curing system. For example, inorganic or organic peroxides are suitable. Preferred peroxides include organic peroxides such as dialkylperoxides, ketalperoxides, aralkylperoxides, peroxide ethers, peroxide esters, such as di-tert.-butylperoxide, bis-(tert.- butylperoxy-isopropyl)-benzene, dicumylperoxide, 2,5-dimethyl-2,5-di(tert.-

butylperoxy)-hexane, 2,5-dimethyl-2,5-di(tert.-butylperoxy)-hexene-(3), 1 ,1-bis- (tert.-butylperoxy)-3,3,5-trimethyl-cyclohexane, benzoylperoxide, tert.-butylcumyl- peroxide and tert.-butylperbenzoate. Usually the amount of neat peroxide in the cured rubber compound containing the rubber blend having reduced cold flow is in the range of from 1 to 6 phr, preferably from 1 to 3 phr. Subsequent curing is usually performed at a temperature in the range of from 100 to 200 ⁰ C, preferably 130 to 180 ⁰ C. Peroxides might be applied advantageously with the aid of a carrier such as polymer or a clay. Suitable systems are commercially available, such as Polydispersion T(VC) D-40 P from Rhein Chemie Rheinau GmbH, D (= polymerbound di-tert.-butylperoxy-isopropylbenzene).

The rubber compound blend having improved cold flow according to the invention can contain further auxiliary products for rubbers, such as reaction accelerators, vulcanizing accelerators, vulcanizing acceleration auxiliaries, antioxidants, foaming agents, anti-aging agents, heat stabilizers, light stabilizers, ozone stabilizers, plasticizers, processing aids, tackifiers, blowing agents, dyestuffs, pigments, waxes, extenders, organic acids, inhibitors, metal oxides, and activators such as triethanolamine, polyethylene glycol, hexanetriol, etc., which are known to the rubber industry. The rubber aids are used in conventional amounts, which depend inter alia on the intended use. Conventional amounts are e.g. from 0.1 to 50 phr. The ingredients of the curable rubber compound (the rubber blend, at least one vulcanizing agent and at least one filler) are often mixed together, suitably at an elevated temperature that may range from 25 ⁰ C to 200 °C.

Normally the mixing time does not exceed one hour and a time in the range from 2 to 30 minutes is usually adequate. The mixing of the rubbers, optionally the filler(s), optionally vulcanization agent, and/or further ingredients is suitably carried out in an internal mixer such as a Banbury mixer, or a Haake or Brabender internal mixer. A two roll mill mixer also provides a good dispersion of the compounds within the final product. An extruder also provides good mixing, and permits shorter mixing times. It is possible to carry out the mixing in two or more stages, and the mixing can be done in different apparatus, for example one stage in an internal mixer and one stage in an extruder. However, it should be taken care that no unwanted pre-crosslinking (= scorch) occurs during the mixing

stage. For compounding and vulcanization see also: Encyclopedia of Polymer Science and Engineering, Vol. 4, p. 66 et seq. (Compounding) and Vol. 17, p. 666 et seq. (Vulcanization).

The rubber compound blend having reduced cold flow and the curable rubber compound according to the present invention are very well suited for the manufacture of a shaped article, such as a seal, hose, bearing pad, stator, well head seal, valve plate, cable sheathing, wheel roller, pipe seal, in place gaskets or footwear component. Furthermore, they are very well suited for wire and cable production.

EXAMPLES

List of Compounding Ingredients

Levapren® 600 HV - ethylene vinyl acetate copolymer containing 60% by weight vinyl acetate available from Lanxess Deutschland GmbH. Levapren® 700 HV - ethylene vinyl acetate copolymer containing 70% by weight vinyl acetate available from Lanxess Deutschland GmbH.

Levapren® VP KA 8815- precrosslinked ethylene vinyl acetate copolymer containing 60% by weight vinyl acetate available from Lanxess Deutschland GmbH. Therban® A 3907 - hydrogenated acrylonitrile butadiene rubber containing

39% acrylonitrile and less than 0.9% residual double bonds. It is available from Lanxess Deutschland GmbH.

Therban® LT VP KA 8882 - hydrogenated acrylonitrile butadiene rubber containing 21% acrylonitrile and less than 0.9% residual double bonds. It is available from Lanxess Deutschland GmbH.

Carbon black N774 and N990 are both available from Cabot Corp..

Elastomag™ 170 Powder is magnesium oxide available from Morton International.

Naugard™ 445 is p-dicumyl diphenylamine and is available through Crompton Corp..

Plasthall™ TOTM is a trioctyl trimellitate from The CP. Hall Co., Inc..

Rhenogran™ PCD-50 is a polycarbodiimide from Rhein Chemie Corp.

Stearic Acid Emersol™ 132 NF is stearic acid available from Acme- Hardesty Co..

TP-759 is an ether/ester based plasticizer available from Morton International. Vulkanox™ ZMB-2/C5 is the zinc salt of 4- and 5-methyl mercaptobenzimidazole (ZMMBI) and is available from Bayer AG.

Zinc Oxide (Kadox™ 920) is available from St. Lawrence Chem. Inc.

TAIC-DLC-A is triallyl isocyanurate (72% by weight) on a silicon dioxide carrier available from Natrochem, Inc.. Vulcup™ 40KE is a bis 2-(t-butyl-peroxy) diisopropylbenzene (40% on

Burgess clay) available from Geo Specialty Chemicals, Inc..

Mixing Procedure

The mixing of the compounds ingredients given in Table 1 was completed in two stages. In the first stage, an internal BR-82 Banbury mixer with tangential rotors turning at 77 rpm was used. The mixing chamber had a volume of 1.6 liters and the water was set for cooling at 30 ⁰ C. At time 0, the Levapren® and Therban® polymers were added to the mixing chamber and allowed to mix for 1 minute. At 1 minute, the carbon black, magnesium oxide, antioxidants (diphenylamine, ZMMBI and polycarbodiimide), TOTM and TP-759 plasticizers, stearic acid and zinc oxide were all added to the mixer. Mixing continued for another 2 minutes.

At 3 minutes a sweep was performed. After 5 minutes, the mix was dumped and final mixing temperatures were recorded. A 10" by 20" two roll mill was used for the second stage of mixing. It was cooled by water set at 3O ⁰ C.

After banding of the compound material, both the TAIC and peroxide were added and incorporated into the mix. The use of 3/4 cuts helped homogenize the ingredients throughout along the mill roll. Finally, 6 endwise passes were carried out to optimize dispersion of all ingredients in the mix.

Description of Tests

Compound Mooney Viscosity and Relaxation

The compound Mooney viscosity was determined at 100 ⁰ C using a large rotor. The sample was preheated within the rotor cavity for one minute and then, subjected to the shearing action of the viscometer disk rotating at 2 rpm for a period of 4 minutes. The torque in Mooney units was immediately recorded at that time. The sample was then allowed to relax for a period of 4 minutes in order to acquire information about the relaxation behavior of the rubber compound. The slope, intercept and area under the relaxation curve were all recorded. The tests were compliant with ASTM D-1646.

Rubber Process Analyzer An RPA 2000 test devise was used to assess the processing behavior of the rubber samples. A frequency sweep was carried out on the unvulcanized rubber samples using a strain of 7% with the platen temperatures set at 100 ⁰ C.

Rheometry

A Moving Die Rheometer (MDR 2000(E)) was used in order to follow the vulcanization behavior of the rubber samples. The platens were set at 180 ⁰ C and a frequency of oscillation of 1.7 Hz coupled with a 1 ° arc were applied to the sample for a time of 30 minutes. This test procedure complies with ASTM D-

5289.

Hardness Hardness measurements were carried out according to ASTM D-2240 using an A-2 type durometer at 23 ⁰ C.

Stress-strain

Tensile slabs were prepared by curing the rubber samples for 12 minutes at

18O ⁰ C. Standard die C dumbbells were died out afterwards for testing. Testing was carried out at 23°C and the procedure complies with ASTM D-412 Method A.

Tear Resistance

Die B and die C geometries were cut out of a tensile sheet which was cured for 12 minutes at 180°C. The test complies with ASTM D-624.

Compression Set Solid compression buttons were prepared by curing the rubber samples 17 minutes at 180°C. Afterwards, the buttons are compressed 25% in a compression

set jig and placed in a hot air oven set at 150 ⁰ C for 168 hours. The test procedure complies with ASTM D-395 (Method B). Stress Strain Hot Air Aging

Hot air aging of the die C cut tensile samples was carried out in a hot air oven set at 150 ⁰ C for a period of 168 hours. Testing was completed in compliance with ASTM D-573.

Stress Strain Liquid Immersion Aging Die C tensile rubber samples were exposed to Service Fluid 105 (SF 105) for a period of 168 hours at 150°C. Testing afterwards was carried out according to ASTM D-471.

Table 1 : Formulations

Table 3: MDR CURE CHARACTERISTICS (1.7 Hz, 180 ⁰ C, 1 ° arc, 30 min

Table 5: TEAR RESISTANCE (test at 23°C)

Property Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6

Tear Strength (kN/m) Die B 49 .64 45. 15 50. 36 59. 68 46.62 55. 22

Tear Strength (kN/m) Die C 22 .17 23 22. 83 24. 03 20.8 23. 16

Table 6: COMPRESSION SET (25% deflection, button sample. 168 hrs at

15O ⁰ C in hot air)

Pro ert Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6

Table 7: STRESS STRAIN (HOT AIR OVEN set at

15O ⁰ C. run 168 hrs)

Property Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6

The RPA results of Figure 1 clearly show the processing improvements of adding a precrosslinked EVM to the compound formulation. It can been seen in the low frequency range that Examples 1 , 3 and 5 possess lower tan deltas compared to corresponding Examples 2, 4 and 6. A lower tan delta at low frequency is indicative of reduced flow behavior which translates into a compound possessing improved cold flow resistance as well as better green strength characteristics.

The compound Mooney viscosity data in Table 2 illustrate higher compound Mooneys for Examples 1 , 3 and 5 versus 2, 4 and 6. The Mooney relaxation data demonstrate slower relaxation times for the rubber compounds containing the precrosslinked EVM. These sets of results support the RPA processability data.

The higher minimum torques values observed in Table 3 for Examples 1 , 3 and 5 over those of 2, 4 and 6 corroborate with compound Mooney viscosity data of Table 2. Addition of the precrosslinked EVM has an effect in reducing the maximum torque and the overall stiffness according to the MH - ML data. The cure data remains for all intents and purposes the same from Example 1 through to 6.

The physical property data in Table 4 illustrates that the hardness does decrease upon replacement of the pre-crosslinked EVM by the standard EVM

(compare Ex. 2 to Ex. 1 , Ex.4 to Ex. 3 and Ex. 6 to Ex. 5). Ultimate tensile and elongation are slightly improved upon using precrosslinked EVM. The moduli values clearly demonstrate a slight loss in overall stiffness in compounds containing the precrosslinked EVM. This fact is supported by the hardness results.

The tear resistance results in Table 5 show a very small variation between compounds containing the precrosslinked EVM and the standard EVM.

Compression set data is similar for all Examples in Table 6. Both the stress strain results after hot air aging (Table 7) and after immersion in SF105 oil (Table 8) show no differentiation between the use of precrosslinked EVM or the standard EVM for this sort of testing.

Although the invention has been described in detail in the foregoing for the purpose of illustration, it is to be understood that such detail is solely for that purpose and that variations can be made therein by those skilled in the art without departing from the spirit and scope of the invention except as it may be limited by the claims.