The present invention relates to a polymer compound comprising at least one carboxylated nitrile rubber polymer, that is optionally hydrogenated, at least one epoxidized compound having one or more epoxide functions, at least one cross-linking agent and at least one filler, a method of method of improving the fluid aging and/or reducing the viscosity of a compound comprising at least one carboxylated nitrile rubber polymer, that is optionally hydrogenated, at least one cross-linking agent and at least one filler, by addition of at least one epoxidized compound having one or more epoxide functions.

Background of the Invention Carboxylated hydrogenated nitrile rubber (HXNBR), prepared by the selective hydrogenation of carboxylated acrylonitrile-butadiene rubber (nitrile rubber; XNBR, a co-polymer comprising at least one conjugated diene, at least one unsaturated nitrile, at least one carboxylated monomer and optionally further comonomers), is a specialty rubber which has 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 XNBR and HXNBR have found widespread use in the automotive (seals, hoses, bearing pads) oil (stators, well head seals, valve plates), electrical (cable sheating), mechanical engineering (wheels, rollers) and shipbuilding (pipe seals, couplings) industries, amongst others.

Summary of the Invention In one of it's aspects, the present invention relates to a polymer compound comprising at least one carboxylated nitrile rubber polymer, that is optionally hydrogenated, at least one epoxidized compound having one or more epoxide functions and at least one filler. It is preferred that the XNBR is

fully or partially hydrogenated ("HXNBR"). In particular, the invention relates to a polymer compound comprising at least one carboxylated nitrile rubber polymer, that is optionally hydrogenated, at least one epoxidized compound having one or more epoxide functions and at least one filler and at least one cross-linking agent, such as peroxides, sulphur, sulphur compounds, and the like. In another one of it's aspects, the present invention relates to a method of reducing the viscosity of a polymer compound comprising at least one, optionally hydrogenated, carboxylated nitrile rubber polymer in the presence of at least one cross-linking agent, such as peroxides, sulphur, sulphur compounds, and the like, by addition of at least one epoxidized compound having one or more epoxide functions.

In still another one of it's aspects, the present invention relates to a method of improving the fluid aging of a composition comprising at least one carboxylated nitrile rubber polymer, that is optionally hydrogenated, at least one filler and at least one cross-linking agent, by co-vulcanising at least one epoxidized compound having one or more epoxide functions..

Description of the Invention As used throughout this specification, the term"carboxylated nitrile polymer"or XNBR is intended to have a broad meaning and is meant to encompass an elastomer having repeating units derived from at least one conjugated diene, at least one alpha-beta-unsaturated nitrile, at least one monomer having a carboxylic group and optionally further one or more copolymerizable monomers.

The conjugated diene may be any known conjugated diene, in particular a C4-C6 conjugated diene. Preferred conjugated dienes are butadiene, isoprene, piperylene, 2, 3-dimethyl butadiene and mixtures thereof. Even more preferred C4-C6 conjugated dienes are butadiene, isoprene and mixtures thereof. The most preferred C4-C6 conjugated diene is butadiene.

The alpha-beta-unsaturated nitrile may be any known alpha-beta- unsaturated nitrile, in particular a C3-C5 alpha-beta-unsaturated nitrile.

Preferred C3-C5 alpha-beta-unsaturated nitriles are acrylonitrile,

methacrylonitrile, ethacrylonitrile and mixtures thereof. The most preferred C3- C5 alpha-beta-unsaturated nitrile is acrylonitrile.

The monomer having at least one carboxylic group may be any known monomer having at least one carboxylic group being copolymerizable with the nitrile and the diene.

Preferred monomers having at least one carboxylic group are unsaturated carboxylic acids. Non-limiting examples of suitable unsaturated carboxylic acids are fumaric acid, maleic acid, acrylic acid, methacrylic acid and mixtures thereof.

Preferably, the copolymer comprises in the range of from 40 to 85 weight percent of repeating units derived from one or more conjugated dienes, in the range of from 15 to 60 weight percent of repeating units derived from one or more unsaturated nitriles and in the range of from 0.1 to 15 weight percent of repeating units derived from one or more monomers having at least one carboxylic group. More preferably, the copolymer comprises in the range of from 55 to 75 weight percent of repeating units derived from one or more conjugated dienes, in the range of from 25 to 40 weight percent of repeating units derived from one or more unsaturated nitriles and in the range of from 1 to 7 weight percent of repeating units derived from one or more monomers having at least one carboxylic group.

Optionally, the copolymer may further comprise repeating units derived from one or more copolymerizable monomers, such as alkylacrylate, styrene.

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.

Hydrogenated in this invention is preferably understood by more than 50 % of the residual double bonds (RDB) present in the starting nitrile polymer/NBR being hydrogenated, preferably more than 90 % of the RDB are hydrogenated, more preferably more than 95 % of the RDB are hydrogenated and most preferably more than 99 % of the RDB are hydrogenated.

The present invention is not restricted to a special process for preparing the hydrogenated carboxylated NBR. However, the HXNBR preferred in this

the invention is readily available as disclosed in WO-01/77185-A1. For jurisdictions allowing for this procedure, WO-01/77185-A1 is incorporated herein by reference.

The XNBR as well as the HXNBR which forms a preferred component of the polymer compound of the invention can be characterized by standard techniques known in the art. For example, the molecular weight distribution of the polymer was determined by gel permeation chromatography (GPC) using a Waters 2690 Separation Module and a Waters 410 Differential Refractometer running Waters Millennium software version 3.05. 01. Samples were dissolved in tetrahydrofuran (THF) stabilized with 0.025% BHT. The columns used for the determination were three sequential mixed-B gel columns from Polymer Labs. Reference Standards used were polystyrene standards from American Polymer Standards Corp.

The inventive polymer compound further comprises at least epoxidized compound having one or more epoxide functions. The epoxidized compound having one or more epoxide functions is not restricted and any known epoxidized compound having two or more epoxide functions that has a molecular weight of at least 250 is suitable. It is beneficial to use an epoxidized plasticizer with a molecular weight of greater than 3000. Non- limiting examples are epoxidized mineral oils, epoxidized fatty acids, epoxidized oils from natural sources, epoxidized derivatives of fatty acid glycerides which are prepared from the corresponding oils and fats by methods known in the art. Suitable epoxidized fatty acid glycerides include epoxidized soy bean oil (ESBO), epoxidized linseed oil, epoxidized corn oil, epoxidized coconut oil, epoxidized cottonseed oil, epoxidized olive oil, epoxidized palm oil, epoxidized palm kernel oil, epoxidized peanut oil, epoxidized codliver oil, epoxidized tung oil, epoxidized beef tallow oil, epoxidized butter and mixtures thereof. Preferred is epoxidized soy bean oil (ESBO).

The epoxidized plasticizer should be present in the rubber composition in an amount of from 2 to 30 phr. Preferably, it is present at 5 to 20 phr.

The inventive polymer compound further comprises at least one filler.

The filler may be an active or an inactive filler or a mixture thereof. The filler 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 m2/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 Al, 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 m2/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; - 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 m2/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 ; 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. These mineral particles have hydroxyl groups on their surface, rendering them hydrophilic and oleophobic. This exacerbates the difficulty of achieving good interaction between the filler particles and the rubber. 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, of in the range of from 50 and 450 square meters per gram and a DBP absorption, as measured in accordance with DIN 53601, of in the range of 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 (D 210, HiSil 233 and HiSilO 243 from PPG Industries Inc. Also suitable are Vulkasil0 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 composite 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 polymer composite. 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.

The inventive polymer compound further comprises at least cross-linking agent (curative). The curative is not restricted and any known curative that under the conditions typically used for rubber curing is capable of creating cross-linking of the polymer chains is suitable such as peroxides, sulphur, sulphur compounds, and the like. However, peroxide curing systems are preferred. For example, inorganic or organic peroxides are suitable. Preferred were organic peroxides such as dialkylperoxides, ketalperoxides, aralkylperoxides, peroxide ethers, peroxide esters, such as di-tert.- butylperoxide, bis- (tert.-butylperoxyisopropyl)-benzene, dicumylperoxide, 2,5- dimethyl-2, 5-di (tert.-butylperoxy)-hexane, 2, 5-dimethyl-2, 5-di (tert.-butylperoxy)- hexyne- (3), 1, 1-bis- (tert.-butylperoxy)-3, 3, 5-trimethyl-cyclohexane, benzoylperoxide, tert.-butylcumylperoxide and tert.-butylperbenzoate. Usually the amount of peroxide in the polymer compound (composite) is in the range of from 1 to 10 phr (= per hundred rubber), preferably from 4 to 8 phr.

Subsequent curing is usually performed at a temperature in the range of from 100 to 200 °C, preferably 130 to 180 °C. Peroxides might be applied advantageously in a polymer-bound form. 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 polymer composite may advantageously further comprise other natural or synthetic rubbers such as BR (polybutadiene), ABR (butadiene/acrylic acid-C1-C4-alkylester-copolymers), CR (polychloroprene), IR (polyisoprene), SBR (styrene/butadiene-copolymers) with styrene contents in the range of 1 to 60 wt%, NBR (butadiene/acrylonitrile-copolymers with acrylonitrile contents of 5 to 60 wt%, HNBR with a Mooney viscosity (ML 1+4 @ 100°C according to ASTM test D1646) of at least 30 (partially or totally hydrogenated NBR-rubber), EPDM (ethylene/propylene/diene-copolymers), FKM (fluoropolymers or fluororubbers), olefin-vinylacetate-copolymers (e. g.

LEVAPREN), olefin-vinylacrylate-copolymers (e. g. VAMACO) and mixtures of the given polymers. Careful blending with conventional HNBR often reduces cost of the polymer composite without sacrificing the processability. The amount of conventional HNBR and/or other natural or synthetic rubbers will depend on the process condition to be applied during manufacture of shaped articles and is readily available by few preliminary experiments.

The rubber composition 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, processing aids, plasticizers, 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 wt. %, based on rubber. Preferably the composition comprises in the range of 0.1 to 20 phr of an organic fatty acid as an auxiliary product, preferably a unsaturated fatty acid having one, two or more carbon double bonds in the molecule which more preferably includes 10% by weight or more of a conjugated diene acid having at least one conjugated carbon-carbon double bond in its molecule. Preferably those fatty acids have in the range of from 8-22 carbon atoms, more preferably 12-18. Examples include stearic

acid, palmitic acid and oleic acid and their calcium-, zinc-, magnesium-, potassium-and ammonium salts.

The ingredients of the final polymer composite are mixed together, suitably at an elevated temperature that may range from 25 °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 is suitably carried out in an internal mixer such as a Banbury mixer, or a Haake or Brabender miniature internal mixer. A two roll mill mixer also provides a good dispersion of the additives within the elastomer. 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, but that the conditions are suitable for the reaction between epoxidized compound and carboxylic groups. 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).

Thus, the inventive polymer compound may be used in the manufacture of a shaped article comprising said inventive polymer compound. Preferred shaped articles are a seal, hose, bearing pad, stator, well head seal, valve plate, cable sheating, wheel roller, pipe seal, in place gaskets or footwear component prepared by injection molding technology. Furthermore, the inventive polymer composite is very well suited for wire and cable production.

EXAMPLES Examples 1-4 Polymer composites were mixed in a brabender internal mixer (8min/30°C/50 rpm). The curatives were added on a cold mill in a separate mixing step. The formulations used in this assessment are based on a recipe according to Table 1. Example 1 is used for comparison.

Table 1. Compounding Recipe.

Comp. Ex. 2 Ex. 3 Ex. 4 Ex. 1 Armeen 18D 0. 5 0. 5 0. 5 0. 5 THERBAN XT 8889 100 100 100 100 Carbon Black N 660 Sterling-V 50 50 50 50 Naugard 445 1 1 1 1 Maglite D 5 5 5 5 Plasthall TOTM 5 DIAK #7 2 2 2 2 Paraplex G-62 5 10 20 Struktol ZP 1014 7 7 7 7 Vulcup 40KE 7 7 7 7 Armen 18D is an octadecylamine available from AkzoNobel and is used to reduce compound stickiness to metal. THERBAN XT 8889 is HXNBR from Bayer AG.

Naugardw 445 (p-dicumyl diphenyl amine) is a stabilizer from Uniroyal.

Plasthall TOTMTM (Trioctyl Trimellitate) is a plasticizer from C. P. Hall.

Maglite D is Magnesium Oxide from C. P. Hall.

Paraplex G-62 is Epoxidized Soy Bean Oil from C. P. Hall.

Diak 7 (Triallyl isocyanurate) is a coagent from DuPont.

StruktolT" ZP 1014 (zinc peroxide 50% on inert carrier).

Vulcup 40 KE (a, a-bis (t-butylperoxy) diisopropylbenzene), 40% peroxide.

Polymer Composites Properties Table 2 shows a summary of the properties of polymer composites of Ex. 1-4. MDR Cure Properties (ASTM D5289, 180°C, 1° arc, 1. 7 Hz, 60 minutes), Mooney (ASTM D1646), Stress-Strain (ASTM D412), Fluid aging (ASTM D471).

Table 2. Polymer Composites Properties.

Comp. Ex. 2 Ex. 3 Ex. 4 Ex. 1 MDR Cure Properties Maximum Torque (MH, dN. m) 46.8 62.0 67.0 75.1 Minimum Torque (ML, dN. m) 2.8 2.9 2.4 1.5 Delta MH-ML (dN. m) 44.0 59.2 64.6 73.6 Mooney ML (1+4 @ 100°C) 98.1 100.5 84.4 61.1 Stress-Strain Hardness (Shore A) 81 81 79 75 Elongation @ Break (%) 135 119 120 117 Ultimate Tensile (MPa) ) 27.5 24.8 23.6 22.6 Modulus @ 100% (Mpa 20.2 20.2 19.5 18.6 Fluid Aging ASTM oil #1 (168 hours @ 150°C) Weight Change %-3.5-1. 5-1.6-1. 7 IRM 903 (168 hours @ 150°C) Weight Change % 7.6 10.1 10.4 11.0 The Delta MH-ML gives an indication of the crosslinking density and it increases as a function of epoxidized compound (ESBO) content. The processability of the composite, as measured by Mooney viscosity, decreases with the epoxidized compound level. The epoxidized (ESBO) plasticizer is co- vulcanised, thus is not extracted during fluid aging leading to a better retention of properties upon aging. As a result, the plasticizer level can be increased to

meet processability requirements without loosing fluid aging performance due to plasticizer being extracted from the composite.

Examples 5-7 Polymer composites were mixed in a brabender internal mixer (8min/30°C/50 rpm). The curatives were added on a cold mill in a separate mixing step. The formulations used in this assessment are based on a recipe according to Table 3. Example 5 is used for comparison.

Table 3. Compounding Recipe.

Comp. Ex. 6 Ex. 7 Ex. 5 Armeen 18D 0. 5 0. 5 0. 5 THERBAN LT 8882 70 70 70 THERBANXT8889 30 30 30 Carbon Black N 660 Sterling-V 50 50 50 Naugard 445 1 1 1 Maglite D 5 5 5 Plasthall TOTM 5 DIAK #7 2 2 2 Paraplex G-62 5 10 <BR> <BR> Struktol ZP 1014 7 7 7<BR> Vulcup40KE 7 7 7 Polymer Composites Properties Table 4 shows a summary of the properties of polymer composites of Ex. 5-7. MDR Cure Properties (ASTM D5289, 180°C, 1° arc, 1. 7 Hz, 60 minutes), Mooney (ASTM D1646), Stress-Strain (ASTM D412), Fluid aging (ASTM D471).

Table 4. Polymer Composites Properties.

Comp. Ex. 6 Ex. 7 Ex. 5 MDR Cure Properties Maximum Torque (MH, dN. m) 36.1 41.4 40.6 Minimum Torque (ML, dN. m) 2.5 2.5 2.1 Delta MH-ML (dN. m) 33.5 38.9 38.5 Mooney ML (1+4 @ 100°C) 65.8 65.8 54.9 Stress-Strain Hardness (Shore A) 70 70 67 Elongation @ Break (%) 191 179 184 Ultimate Tensile (MPa)) 20.7 19.6 17.6 Modulus @ 100% (Mpa 10.3 10.3 9.4 Fluid Aging ASTM oil #1 (168 hours @ 150°C) Weight Change %-1.3 0.5 0.0 IRM 903 (168 hours @ 150°C) Weight Change % 20.6 22.3 22.3 The processability of the composite, as measured by Mooney viscosity, decreases with the epoxidized compound level. The epoxidized (ESBO) plasticizer is co-vulcanised, thus is not extracted during fluid aging leading to a better retention of properties upon aging. As a result, the plasticizer level can be increased to meet processability requirements without loosing fluid aging performance due to plasticizer being extracted from the composite.