CA2558900A1 - Blends of hxnbr and low mooney hnbr - Google Patents

Abstract

The present invention relates to polymer blends of low Mooney hydrogenated nitrite butadiene rubber and hydrogenated carboxylated nitrite butadiene rubber. The present invention further relates to rubber compounds containing polymer blends of low Mooney hydrogenated nitrite butadiene rubber and hydrogenated carboxylated nitrite butadiene rubber. In addition the present invention relates to shaped articles containing rubber compounds based on polymer blends of low Mooney hydrogenated nitrite butadiene rubber and hydrogenated carboxylated nitrite butadiene rubber.

Description

BLENDS OF HXNBR AND LOW MOONEY HNBR
FIELD OF THE INVENTION
The present invention relates to polymer blends of low Mooney hydrogenated nitrite butadiene rubber and hydrogenated carboxylated nitrite butadiene rubber. The present invention also relates to a process to prepare blends of low Mooney hydrogenated nitrite butadiene rubber and hydrogenated carboxylated nitrite butadiene rubber.
The present invention further relates to rubber compounds containing polymer blends of low Mooney hydrogenated nitrite butadiene rubber and hydrogenated carboxylated nitrite butadiene rubber. In addition the present invention relates to shaped articles containing rubber compounds based on polymer blends of low Mooney hydrogenated nitrite butadiene rubber and hydrogenated carboxylated nitrite butadiene rubber.
The polymer blends according to the present invention have improved processability characteristics and the compounds containing the polymer blends have excellent mechanical strength retention at elevated temperatures, improved low temperature properties and enhanced hot air/chemical resistance.
BACKGROUND OF THE INVENTION
Hydrogenated nitrite rubber (HNBR), prepared by the selective hydrogenation of acrylonitrile-butadiene rubber (nitrite rubber; NBR, a co-polymer containing at least one conjugated diene, at least one unsaturated nitrite and optionally further co-monomers), 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 NBR and HNBR has 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.
Commercially available NBR and HNBR have a Mooney viscosity in the range of from 55 to 105, a molecular weight in the range of from 200,000 to 500,000 g/mol, and for the HNBR a polydispersity greater than 3.0 and a residual double bond (RDB) content in the range of from 1 to 18% (by IR spectroscopy).
One limitation in processing NBR and HNBR is the relatively high Mooney viscosity. In principle, NBR and HNBR having a lower molecular weight and lower Mooney viscosity would have better processability. Attempts have been made to reduce the molecular weight of the polymer by mastication (mechanical breakdown) and by chemical means (for example, using strong acid), but such methods have the disadvantages that they result in the introduction of functional groups (such as carboxylic acid and ester groups) into the polymer, and the altering of the micro-structure of the polymer. This results in disadvantageous changes in the properties of the polymer. In addition, these types of approaches, by their very nature, produce polymers having a broad molecular weight distribution.
A, optionally hydrogenated, nitrite rubber having a low Mooney (<55) and improved processability, but which has the same microstructure as those rubbers which are currently available, is difficult to manufacture using current technologies. The hydrogenation of NBR to produce HNBR results in an even bigger increase in the Mooney viscosity of the raw polymer. This Mooney Increase Ratio (MIR) is generally around 2, depending upon the polymer grade, hydrogenation level and nature of the feedstock. Furthermore, limitations associated with the production of NBR
itself dictate the low viscosity range for the HNBR feedstock.
Karl Ziegler's discovery of the high effectiveness of certain metal salts, in combination with main group alkylating agents, to promote olefin polymerization under mild conditions has had a significant impact on chemical research and production to date. It was discovered early on that some "Ziegler-type" catalysts not only promote the coordination-insertion mechanism but also affect an entirely different chemical process that is the mutual exchange (or metathesis) reaction of alkenes.
Acyclic diene metathesis (or ADMET) is catalyzed by a great variety of transition metal complexes as well as non-metallic systems. Heterogeneous catalyst systems based on metal oxides, sulfides or metal salts were originally used for the metathesis of olefins. However, the limited stability (especially towards hetero-substituents) and the lack of selectivity resulting from the numerous active sites and side reactions are major drawbacks of the heterogeneous systems.
Homogeneous systems have also been devised and used to effect olefin metathesis. These systems offer significant activity and control advantages over the heterogeneous catalyst systems. For example, certain Rhodium based complexes are effective catalysts for the metathesis of electron-rich olefins.
The discovery that certain metal-alkylidene complexes are capable of catalyzing the metathesis of olefins triggered the development of a new generation of well-defined, highly active, single-site catalysts. Amongst these, Bis-(tricyclohexylphosphine) benzylidene ruthenium dichloride (commonly know as Grubb's catalyst) has been widely used, due to its remarkable insensitivity to air and moisture and high tolerance towards various functional groups. Unlike the molybdenum-based metathesis catalysts, this ruthenium carbene catalyst is stable to acids, alcohols, aldehydes and quaternary amine salts and can be used in a variety of solvents (C6H6, CH2CI2, THF, t BuOH).
The use of transition-metal catalyzed alkene metathesis has since enjoyed increasing attention as a synthetic method. The most commonly-used catalysts are based on Mo, W and Ru. Research efforts have been mainly focused on the synthesis of small molecules, but the application of olefin metathesis to polymer synthesis has allowed the preparation of new polymeric material with unprecedented properties (such as highly stereoregular poly-norbornadiene).
The utilization of olefin metathesis as a means to produce low molecular weight compounds from unsaturated elastomers has received growing interest. The use of an appropriate catalyst allows the cross-metathesis of the unsaturation of the polymer with the co-olefin. The end result is the cleavage of the polymer chain at the unsaturation sites and the generation of polymer fragments having lower molecular weights.
In addition, another effect of this process is the "homogenizing" of the polymer chain lengths, resulting in a reduction of the polydispersity. From an application and processing stand point, a narrow molecular weight distribution of the raw polymer results in improved physical properties of the vulcanized rubber, while the lower molecular weight provides good processing behavior.
The so-called "depolymerization" of copolymers of 1,3-butadiene with a variety of co-monomers (styrene, propene, divinylbenzene and ethylvinylbenzene, acrylonitrile, vinyltrimethylsilane and divinyldimethyl- silane) in the presence of classical Mo and W
catalyst system has been investigated. Similarly, the degradation of a nitrite rubber using WC16 and SnMe4 or PhC=CH co-catalyst was reported in 1988. However, the focus of such research was to produce only low molecular fragments which could be characterized by conventional chemical means and contains no teaching with respect to the preparation of low molecular weight nitrite rubber polymers. Furthermore, such processes are non-controlled and produce a wide range of products.
The catalytic depolymerization of 1,4-polybutadiene in the presence of substituted olefins or ethylene (as chain transfer agents) in the presence of well-defined Grubb's or Schrock's catalysts is also possible. The use of Molybdenum or Tungsten compounds of the general structural formula {M(=NR~)(OR2)2(=CHR); M = Mo, W}
to produce low molecular weight polymers or oligomers from gelled polymers containing internal unsaturation along the polymer backbone was claimed in U.S. Patent No.
5,446,102. Again, however, the process disclosed is non-controlled, and there is no teaching with respect to the preparation of low molecular weight nitrite rubber polymers.
International Applications PCT/CA02/00966, PCT/CA02/00965, and WO-03/002613-A1 and Co-pending Canadian Patent Application. No.2,462,011 disclose that hydrogenated and non-hydrogenated nitrite rubber having lower molecular weights and narrower molecular weight distributions than those known in the art can be prepared by the olefin metathesis of nitrite butadiene rubber, optionally followed by hydrogenation of the resulting metathesized NBR. Currently, some of the lowest Mooney viscosity products are currently available from LANXESS Corporation.
Hydrogenated carboxylated acrylonitrile-butadiene rubber (HXNBR) is known to provide vulcanizates possessing outstanding mechanical properties (tensile, elongation and tear) combined with excellent property retention at high temperatures. In addition, vulcanizates containing HXNBR exhibit excellent abrasion resistance, adhesive strength as well as improved hot air aging resistance over carboxylated nitrite. HXNBR
thrives in severe end use environments such as oil well (packer and drill bit seals) and roll (printing and paper-making) applications.
SUMMARY OF THE INVENTION
The present invention relates to polymer blends of low Mooney hydrogenated nitrite butadiene rubber and hydrogenated carboxylated nitrite butadiene rubber. The present invention also relates to a process to prepare blends of low Mooney hydrogenated nitrite butadiene rubber and hydrogenated carboxylated nitrite butadiene rubber.
The present invention further relates to rubber compounds containing polymer blends of low Mooney hydrogenated nitrite butadiene rubber and hydrogenated carboxylated nitrite butadiene rubber. In addition the present invention relates to shaped articles containing rubber compounds based on polymer blends of low Mooney hydrogenated nitrite butadiene rubber and hydrogenated carboxylated nitrite butadiene rubber.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 illustrates the compound Mooney viscosity of blended compounds of low Mooney HNBR and HNXBR.
Figure 2 illustrates the Mooney scorch of blended compounds of low Mooney HNBR
and HNXBR.
Figure 3 illustrates the injection moldability of blended compounds of low Mooney HNBR and HNXBR.
Figure 4 illustrates the hardness of blended compounds of low Mooney HNBR and HNXBR.
Figure 5 illustrates the stress as 100% elongation of blended compounds of low Mooney HNBR and HNXBR.
Figure 6 illustrates the elongation at break of blended compounds of low Mooney HNBR
and HNXBR.
Figure 7 illustrates the tensile strength of blended compounds of low Mooney HNBR
and HNXBR.
Figure 8 illustrates the tear resistance of blended compounds of low Mooney HNBR and HNXBR.
Figure 9 illustrates the temperature retraction of blended compounds of low Mooney HNBR and HNXBR.
Figure 10 illustrates the hardness and stress strain changes of blended compounds of low Mooney HNBR and HNXBR.
Figure 11 illustrates the hot air heat resistance under compression of blended compounds of low Mooney HNBR and HNXBR.
Figure 12 illustrates the immersion aging resistance to lithium grease of blended compounds of low Mooney HNBR and HNXBR.

DETAILED DESCRIPTION OF THE INVENTION
The present invention will now be described for purposes of illustration and not limitation. Except in the operating examples, or where otherwise indicated, all numbers expressing quantities, percentages, and so forth in the specification are to be understood as being modified in all instances by the term "about." Also, all ranges include any combination of the maximum and minimum points disclosed and include any intermediate ranges therein, which may or may not be specifically enumerated herein.
The low Mooney hydrogenated nitrite rubbers useful in the present invention and processes for making them are known in the art and are the subject of U.S.
Patent Nos.

6,673,881, 6,780,939 and 6,841,623 the disclosure of which is incorporated by reference for the purpose of Jurisdictions allowing for this feature. Such rubbers are formed by the olefin metathesis of nitrite butadiene rubber with a Ru metathesis catalyst, such as a Grubb's catalyst, followed optionally by hydrogenation of the resulting metathesized NBR.
Low Mooney hydrogenated nitrite rubbers useful in the present invention have a Mooney viscosity (ML(1 +4) @ 100°C) of between 1 and 55, preferably between 5 and 50, more preferably between 20 and 45 and most preferably between 15-40.
As used throughout this specification, the term "nitrite rubber" 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 nitrite and optionally (c) repeating units derived from at least one further monomer.
As used throughout this specification, term, hydrogenated carboxylated nitrite rubber is intended to have a broad meaning and is meant to encompass a hydrogenated copolymer having (a) repeating units derived from at least one conjugated diene, (b) at least one alpha, beta-unsaturated nitrite and (c) repeating unites derived from monomers selected from the group consisting of conjugated dienes, unsaturated carboxylic acids and alkyl esters of unsaturated carboxylic acids.
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 nitrite may be any known alpha,beta-unsaturated nitrite, in particular a C3-C5 alpha,beta-unsaturated nitrite. Preferred C3-CS
alpha,beta-unsaturated nitrites are acrylonitrile, methacrylonitrile, ethacrylonitrile and mixtures thereof. The most preferred C3-C5 alpha,beta-unsaturated nitrite is acrylonitrile.
The unsaturated carboxylic acid may be any known unsaturated carboxylic acid copolymerizable with the other monomers, in particular a C3-C~6 alpha,beta-unsaturated carboxylic acid. Preferred unsaturated carboxylic acids are acrylic acid, methacrylic acid, itaconic acid and malefic 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, in particular an alkyl ester of an C3-C~6 alpha,beta-unsaturated carboxylic acid. Preferred alkyl ester of an unsaturated carboxylic acid are alkyl esters of acrylic acid, methacrylic acid, itaconic acid and malefic acid and mixtures thereof, in particular butyl acrylate, methyl acrylate, 2-ethylhexyl acrylate and octyl acrylate. Preferred alkyl esters include methyl, ethyl, propyl, and butyl esters.
Hydrogenated in this invention is preferably understood by more than 50 % of the residual double bonds (RDB) present in the starting nitrite 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.
An antioxidant may be useful in the preparation of polymers blends and compounds containing polymer blends according to the present invention.
Examples of suitable antioxidants include p-dicumyl diphenylamine (Naugard~ 445), Vulkanox~ DDA
(a diphenylamine derivative), Vulkanox~ ZMB2 (zinc salt of methylmercapto benzimidazole), Vulkanox~ HS (polymerized 1,2-dihydro-2,2,4-trimethyl quinoline) and Irganox~ 1035 (thiodiethylene bis(3,5-di-tert.-butyl-4-hydroxy) hydrocinnamate or thiodiethylene bis(3-(3,5-di-tert.-butyl-4-hydroxyphenyl)propionate supplied by Ciba-Geigy.
Suitable peroxide curatives useful in the preparation of polymer blends and compounds containing polymer blends according to the present invention include dicumyl peroxide, di-tert.-butyl peroxide, benzoyl peroxide, 2,2'-bis (tert.-butylperoxy diisopropylbenzene (Vulcup 40KE), benzoyl peroxide, 2,5-dimethyl-2,5-di(tert-butylperoxy)-hexyne-3, 2,5-dimethyl-2,5-di(benzoylperoxy)hexane, (2,5-bis(tert.-butylperoxy)-2,5-dimethyl hexane and the like can be used. The high temperature of the polyamide melt influences the selection, however. The best suited curing agents are readily accessible by means of few preliminary experiments. A preferred peroxide curing agent is commercially available under the trademark Vulcup 40KE. The peroxide curing agent is suitably used in an amount of 0.2 to 7 parts per hundred parts of rubber (phr), preferably 1 to 3 phr. Too much peroxide may lead to undesirably violent reaction. Sulphur, sulphur-containing compounds and resins can also be used as curatives.
Vulcanizing co-agents can also be used in the preparation of compounds according to the present invention. Mention is made of triallyl isocyanurate (TAIC), commercially available under the trademark DIAK 7 from DuPont or N,N'-m-phenylene dimaleimide know as HVA-2 (DuPont Dow), triallyl cyanurate (TAC) or liquid polybutadiene known as Ricon~ D 153 (supplied by Ricon Resins). Amounts can be equivalent to the peroxide curative or less, preferably equal.
Crosslinking density can further be increased by the addition of an activator such as zinc peroxide (50% on an inert carrier) using Struktol~ ZP 1014 in combination with the peroxide. Amounts can be between 0.2 to 7 phr, preferably 1 to 3 phr.
It is possible to achieve further crosslinking by using curatives used with carboxylated polymers such as: amines, epoxies, isocyanates, carbodiimides, aziridines, or any other additive that can form a derivative of a carboxyl group.
The ratio of hydrogenated carboxylated nitrite rubber to low Mooney hydrogenated nitrite rubber can vary between wide limits, preferably 95 parts to 5 parts by weight (phr) to 5 parts to 95 parts by weight. More preferably. 75 parts to 25 parts by weight to 25 parts to 75 parts by weight. The ratio of HXNBR to low Mooney HNBR
can vary and can be optimized by simple experimentation by one skilled in the art.
It is possible to include processing oils and extenders or plasticizers in the compound according to the present invention. Suitable plasticizers include those well known for use with nitrite polymers such as the phthalate compounds, the phosphate compounds, the adipate compounds, the alkyl carbitol formal compounds, the coumarone-indene resins and the like. An example is the plasticizer commercially available under the trademark Plasthall~ 810, or Plasthall~ TOTM (trioctyl trimellitate) or TP-95 (di-(butoxy-ethoxy-ethyl) adipate supplied by Morton International. The plasticizer should be a material that is stable at high temperature and will not exude from the compound.
It is also possible to use a mixture of another elastomer in the compound of the present invention, for example, a carboxylated nitrite rubber (XNBR), a hydrogenated nitrite rubber (HNBR) or a nitrite rubber (NBR), a vinyl acetate rubber (EVM) or a ethylene/acrylate rubber (AEM). Suitable XNBR's are commercially available from Lanxess Deutschland GmbH under the trademark Krynac~ and suitable HNBR's are commercially available from Lanxess Deutschland GmbH under the trademark Therban~ and suitable NBR's are available from Lanxess Deutschland GmbH under the trademark Perbunan~. EVM is commercially available from Lanxess Deutschland GmbH
under the trademark Levapren~. Vamac~ D an ethylene acrylic elastomer is commercially available from DuPont.
The present inventive compound can also contain at least one filler. The filler may be an active or inactive filler or a mixture thereof. The filler may be added to the compound in an amount from 1 to 200 phr, preferably 10 - 120 phr, most preferably 20 -80 phr. Suitable fillers include:
- 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 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 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~ 210, HiSil~ 233 and HISiI~ 243 from PPG
Industries Inc. Also suitable are Vulkasil S and Vulkasil N, from Lanxess Deutschland GmbH.
The compound according to the present invention can contain further auxiliary products suitable for use with 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 include from 0.1 to 50 wt.%, based on rubber. Preferably the compound contains 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. Preferably the compound includes in the range of 5 to 50 phr of an acrylate as an auxiliary product.
Suitable acrylates are known from EP-A1-0 319 320, U.S. Patent Nos. 5,208,294 and 4,983,678. Reference is made to zinc acrylate, zinc diacrylate or zinc dimethacrylate or a liquid acrylate, such as trimethylolpropanetrimethacrylate (TRIM), butanedioldi-methacrylate (BDMA) and ethylenglycoldimethacrylate (EDMA). It might be advantageous to use a combination of different acrylates and/or metal salts thereof. Of particular advantage is often to use metal acrylates in combination with a Scorch-retarder such as sterically hindered phenols (e.g. methyl-substituted aminoalkylphenols, in particular 2,6-di-tert.-butyl-4-dimethylaminomethylphenol). It is possible to incorporate other known additives or compounding agents in the compound according to the present invention.
The ingredients of the final polymer blend can be 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. If the polymer blend is prepared without solvent or was recovered from the solution, the mixing can be 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. 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 invention is further illustrated but is not intended to be limited by the following examples in which all parts and percentages are by weight unless otherwise specified.
EXAMPLES
The peroxide cured HXNBR and/or HXNBR and low Mooney HNBR blend recipes used for this investigation is tabulated in Table I. The control formulation contains 100%
HXNBR. HNBR-AT (34% ACN, < 0.9% RDB, 39 MU) is then blended into HXNBR at three different levels: 25/75, 50/50 and 75/25.
Table I: Standard HXNBR formulation used with the blend ratios INGREDIENT PHRS

Exam 1e 9 2 3 4 ODA 0.5 ODPA 1.5 ZINC PEROXIDE 50% 7 TAIC 1.5 PEROXIDE 40% 7.5 List of compound ingredients and testing fluids HXNBR = Therban XT VP KA 8889 (33% ACN, 3.5% RDB, 5% carboxylic acid and 77 MU (100°C)) available from LANXESS Deutschland GmbH.
HNBR-AT = Low Mooney HNBR Therban AT VP KA 8966 (34% ACN, < 0.9% RDB and 39 MU (100°C)) available from LANXESS Deutschland GmbH.
ODA = Octadecyl amine = Armeen 18D from Akzo Nobel ODPA = p-dicumyl diphenylamine = Naugard 445 from Chemtura.
CARBON BLACK = N660 from Cabot.
TOTM = trioctyl trimellitate (Plasthall) from C.P. Hall.
ZINC PEROXIDE (Zn02) = 50% active zinc peroxide preparation, Struktol ZP 1014, available from Struktol.

TAIC = triallyl isocyanurate (Disk#7) from DuPont.
PEROXIDE = bis (t-butyl-peroxy) diisopropylbenzene (40% on Burgess clay) =
Vulcup 40KE from Geo Chemicals.
Lithium grease = Motomaster constant velocity joint grease (meets GM
specification 7843867).
A laboratory BR-82 internal mixer (1.6 L capacity) was used for first stage mixing.
The rotor speed was set at 55 rpm and cooling carryied out at 30°C. All ingredients except the peroxide were added to the mixer. At time 0 min, HXNBR and HNBR
were added to the mixer and allowed to mix for 1 minute. At this time, the carbon black, ODA, ODPA and zinc peroxide were added to the mix. Mixing continued for an additional 1 minute at which time a sweep was performed. After an additional one minute of mixing, the TAIC and TOTM were added and the whole batch was allowed to mix for an extra 2 minutes then discharged from the mixer. The peroxide was added and incorporated during the second stage on a 10" by 20" two roll mill cooled at 30°C.
The processability and final compound properties of the HNBR blends were measured in accordance with the ensuing list of ASTM procedures:
Mooney Viscosity and Scorch - ASTM D1646-81 Capillary Rheometer - ASTM D5099-93 A (except barrel inside diameter = 19 mm and barrel length = 25.4 mm).
Hardness - ASTM D2240 Stress Strain - ASTM D412 A
Tear Resistance - ASTM D624 Temperature Retraction - ASTM D1329 Hot air aging resistance - ASTM D573 Compression Set - ASTM D395 B
Fluid Resistance - ASTM D471 Figure 1 clearly shows that the systematic and progressive blending of low Mooney HNBR-AT into HXNBR brings about a substantial lowering of the compound Mooney viscosity. Compound Mooney values decrease by up to 20 MU in the cases where the blend ratio is 25/75. Compound Mooney viscosities in the range of 50 to 60 are desirable for injection moldable products.

Mooney scorch is often an issue with carboxylated elastomers. The use of a slow release dispersion of zinc peroxide alleviates this issue in 100% HXNBR, however, as can be seen from the data in Figure 2, low Mooney HNBR-AT addition will help to prolong the safety period before vulcanization. Longer scorch safety is advantageous in injection molding in the case of long channels and intricate die designs which require good flow for complete mold filling.
A capillary rheometer (Monsanto Processability Tester) possessing a barrel LlD
of 30 and a die diameter of 0.0754 cm was employed to explore the injection moldability of the compounds in the higher shear rate zone. In Figure 3, the barrel pressure is plotted as a function of shear rate. It is observed that increasing the concentration of low Mooney HNBR-AT in the blend will help in decreasing barrel pressure, meaning that for the same barrel pressure, a low Mooney HNBR-AT blend will flow quicker through the capillary compared to the HXNBR compound alone. Barrel pressures became unreliable in the 3000 s-1 range of the rheometer as the 1000 bar range limit of the apparatus was attained. Nevertheless, the trends observed in the lower shear rate range of the rheometer are favourable towards the use of low Mooney HNBR-AT
rich blends for lower barrel pressures and/or quicker flow behavior.
Hardnesses (A-2 type) were measured at 23, 100 and 150°C (Figure 4). The highest hardnesses were obtained on the HXNBR compounds as low Mooney HNBR-AT addition progressively lowered hardness values. Improved retention of hardness at elevated temperature testing was observed with the low Mooney HNBR-AT rich compounds compared with the control compound (ex. 1 ).
In Figure 5, stress at 100% elongation data are presented at 23, 100 and 150°C.
The stress data in figure 5 mirror the trends observed in the hardness values of Figure 4. Low Mooney HNBR-AT addition to HXNBR causes a decrease in stiffness values at room temperature. The low Mooney HNBR-AT rich compounds display the least change in stiffness upon elevated temperature testing.
In Figure 6, elongation to break values increase with low Mooney HNBR-AT
addition. Here it is observed that the best elongation at higher temperatures is seen with the HXNBR rich blends.
In Figure 7, it is illustrated that extraordinary high tensile strengths of over 25 MPa are possible using HXNBR (ex. 1 ). Blending in low Mooney HNBR-AT brings about a slight decrease in tensile strength, but only by about 1 - 3 MPa. A
drop in tensile strength is noted during the elevated temperature testing, however values of 8 -13 MPa are possible at 150°C. Excellent mechanical property retention at elevated temperatures is crucial for proper functioning of parts which provide good sealing behavior.
Tear resistance by using die B or die C cut specimens was measured at room temperature in Figure 8. The excellent tear strength of HXNBR is observed.
Blending in low Mooney HNBR-AT has only a moderate effect in decreasing the tear strength as excellent values are retained up to the 25/75 blend ratio.
As shown by the temperature retraction data in Figure 9, the low temperature resistance slightly improves upon HNBR-AT addition. HXNBR contains 33% ACN
whereas low Mooney HNBR-AT contains 34% ACN. As its level predominantly determines the low temperature behavior in HNBRs (low ACN levels provide improved low temperature characteristics), it is a clear advantage that low Mooney HNBR-AT rich blends display improved low temperature properties.
The hardness and stress strain data changes upon exposing die C dumbbell samples to hot air at 135°C for 504 hours are depicted in Figure 10. In all cases, hardening and stiffening takes place with corresponding loss of elongation. It is clear however, that elongation loss can be lessened by adding more low Mooney HNBR-AT.
The hot air heat resistance under compression at 135°C and for 70, 168 and 504 hours is presented in Figure 11. The trends are readily apparent. Progressive low Mooney HNBR-AT addition causes a lowering of unwanted set due to compression.
Immersion aging resistance to lithium grease (Figure 12) was carried out on specimens aged for 168 hrs at 135°C. Property change in terms of hardness, tensile, elongation and volume swell is reported. Lithium based constant velocity joint grease resistance is improved in the low Mooney HNBR-AT rich blends as witnessed by the lower tensile and hardness changes as well as better elongation retention as a function of immersion aging.
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.

Claims (11)

1. A polymer blend comprising a low Mooney hydrogenated nitrite polymer and a hydrogenated carboxylated nitrite polymer, wherein the low Mooney hydrogenated polymer has a Mooney viscosity (ML(1 +4) @ 100°C) of between 1 and 55.

2. A polymer blend according to Claim 1, wherein the low Mooney hydrogenated nitrite rubber is a hydrogenated copolymer of acrylonitrile, and butadiene having a Mooney viscosity of between 5 and 50.

3. A polymer blend according to Claim 2, wherein the low Mooney hydrogenated nitrite rubber is a hydrogenated copolymer of acrylonitrile, and butadiene having a Mooney viscosity of between 20 and 45.

4. A polymer blend according to Claim 3, wherein the low Mooney hydrogenated nitrite rubber is a hydrogenated copolymer of acrylonitrile, and butadiene having a Mooney viscosity of between 15 and 40.

5. A polymer blend according to Claim 1, wherein the ratio of hydrogenated carboxylated nitrite rubber to low Mooney hydrogenated nitrite rubber is 95 parts to 5 to 5 parts to 95 parts by weight per hundred parts rubber.

6. A polymer blend according to Claim 5, wherein the ratio of 75 parts to 25 parts by weight to 25 parts to 75 parts by weight.

7. A polymer blend according to Claim 1, further comprising an elastomer selected from carboxylated nitrite rubber (XNBR), nitrite rubber (NBR), ethylene vinyl acetate rubber (EVM) and ethylene/acrylate rubber (AEM).

8. A compound comprising the polymer blend according to Claim 1 and a curative.

9. A compound according to Claim 8, wherein the curative is a peroxide selected from dicumyl peroxide, di-tert-butyl peroxide, benzoyl peroxide, 2,2'-bis(tert-butylperoxy diisopropylbenzene, benzoyl peroxide, 2,5-dimethyl-2-5-di(tert-bytylperoxy)22,5-dimethyl hexane or mixtures thereof.

10.A shaped article comprising the compound according to Claim 8.

11. A shaped article according to Claim 10, wherein the shaped article is in the form a seal, a hose, a bearing pad, an oil stator, an oil well head seal, a oil valve plate, a cable sheathing, a wheel, a roller, a pipe seal, a coupling.