Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
2002-02-26
2004-05-18
Sanders, Kriellion A. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C524S426000, C524S427000, C524S451000, C474S191000, C474S264000, C474S271000
Reexamination Certificate
active
06737461
ABSTRACT:
FIELD OF THE INVENTION
This invention is related to articles which are to be subjected to dynamic loading. Examples of such applications include belts, including accessory drive and power transmission belts, as well as flat belts and other shaped articles useful in dynamic applications, such as vehicle brake parts and engine mounts, for example. More particularly, the invention relates to belting and other shaped articles useful in dynamic applications whose compositions exhibit superior heat aging properties.
BACKGROUND OF THE INVENTION
Polychloroprene rubber (CR) has been the most popular material of choice for the manufacture of power transmission belts for the past half century, due to its unique combination of properties, namely oil resistance; toughness; dynamic flex life; good adhesion to other materials and heat resistance up to 100° C. In the past, CR belt technology has kept pace with the needs of the automotive industry but, in recent years, the combination of decreased vehicle size and more aerodynamic design has resulted in smaller engine compartments. This has resulted in higher under-the-hood temperatures (>150° C.), placing additional stresses on parts in the engine compartment. Thus, the need for new materials having improved heat and ozone resistance for belting applications has emerged.
New materials such as alkylated chorosulfonated polyethylene and hydrogenated acrylonitrile rubber have been introduced, but these polymers bring significant increase in the cost of a belt.
The use of blends of ethylene-propylene copolymer (EPM), ethylene-propylene non-conjugated diene terpolymer (EPDM), ethylene vinyl acetate copolymer (EVM) or ethylene acrylate copolymer (EAM) with other elastomers exhibiting more favorable mechanical properties has also been explored for use in dynamic applications, such elastomers including polychloroprene, nitrile-diene rubbers, organopolysiloxane resins and poly ethyl vinyl acetate. In such cases, the EPM, EPDM, EVM or EAM is added to improve the ozone- or oxygen-resistance of the composition, or in order to reduce the cost thereof. The amount of ethylene polymer added, however, has been estimated to be limited to less than about 40% by weight of the final elastomeric composition in order to maintain satisfactory mechanical properties.
U.S. Pat. No. 5,610,217 (the '217 patent) reports that ethylene-propylene non-conjugated diene terpolymer (EPDM) and ethylene vinyl acetate (EVM) elastomers could serve as the primary elastomer in polymer compositions for belting. The '217 patent further discloses that using a metal salt of an alpha-beta-unsaturated organic acid (in amounts of about 1-30 phr) helps maintain abrasion and pilling resistance, tensile strength, cut-growth resistance, modulus and adhesion to reinforcement materials under high and low temperature dynamic loading.
European Patent Application EP 0 605 843 A1 claims the use of zinc diacrylate (at a level of about 5-35 phr) in an ethylene-vinyl acetate composition, or in a blend with ethylene alpha olefin polymer.
European Patent Application EP 0 940 429 A1 discloses a vulcanizate having improved hot-air aging characteristics. The composition comprises a nitrile polymer; a filler; an additive and a vulcanization system. The additive may be a strong base, a salt of a strong base and a weak acid, a salt of a weak acid, a polycarbodiimide, or mixtures thereof.
Bayer's unpublished Canadian patent application 2,281,274 (the disclosure of which is hereby incorporated by reference) discloses that compositions comprising a polymer, such as an ethylene-alpha-olefin polymer, and a Group I metal salt of a strong base and a weak acid have improved hot-air aging characteristics.
SUMMARY OF THE INVENTION
We have found that compositions comprising an elastomer having a main polymer chain derived from: (i) at least about 30% by weight of a first monomer which introduces at least one of a secondary carbon and a tertiary carbon to the main polymer chain, and (ii) from 0 to about 70% by weight of at least one other monomer, a Group I metal salt of a strong base and a weak acid, and an antioxidant have excellent hot-air aging characteristics, and so are useful for the manufacture of articles to be subjected to dynamic loading, such as power transmission belts, shaft seals, rubber roll covers and vehicle brake parts, as well as applications such as engine mounts and pulley torsion dampeners. It is also envisaged that such compositions would be useful for hose applications, particularly in non-aqueous environments where the improved properties would be of benefit.
DESCRIPTION OF THE INVENTION
The first component of the present polymer composition is a polymer having a main polymer chain derived from: (i) at least about 30% by weight of a first monomer which introduces at least one of a secondary carbon and a tertiary carbon to the main polymer chain, and (ii) from 0 to about 70% by weight of at least one other monomer.
As used throughout this specification, the term “polymer” is intended to have a broad meaning and is meant to encompass any polymer having a main polymer chain which comprises at least one secondary or tertiary carbon. Those of skill in the art will understand that a secondary carbon is a carbon atom having two hydrogen atoms bonded to it while a tertiary carbon is a carbon atom having one hydrogen atom bonded to it. The polymer may be a homopolymer, a copolymer, a terpolymer and the like. Also, it is possible to use a mixture of polymers provided at least one polymer in the mixture has the polymer main chain properties described above.
The polymer suitable for use herein may be an elastomer (e.g., a hydrocarbon rubber), a graft polymer or block polymer of monomers having at least one ethylenically unsaturated bond and polymerizable through this unsaturation, and the like.
Elastomers are well known to those of skill in the art. Non-limiting examples of suitable elastomers may be selected from the group comprising natural rubber (NR), cis-1,4-polyisoprene rubber (IR), polybutadiene rubber (BR), styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber (NBR), hydrogenated acrylonitrile-butadiene rubber (HNBR), other HNBR copolymers, HNBR terpolymers (including hydrogenated acrylonitrile, butadiene, unsaturated carboxylic acid ester terpolymers), ethylene-propylene monomer rubber (EPM), ethylene-propylene-diene monomer rubber (EPDM), ethylene-vinyl acetate rubber (EVM) and the like.
Of course, subject to compatibility, mixtures of two or more of any of the foregoing polymers may be used herein.
Preferably, the polymer used in the present polymer composition is an elastomer. More preferably, it is an ethylene-alpha-olefin-based elastomer such as an ethylene-propylene copolymer (e.g. EPM), an ethylene-propylene non-conjugated diene terpolymer (e.g. EPDM), an ethylene-vinyl acetate copolymer (e.g. EVM) or an ethylene acrylate copolymer (e.g. EAM). Further examples of such polymers include, but are not limited to, copolymers of ethylene with conjugated dienes such as 1,3-Butadiene, Isoprene, 1,3-Pentadiene, as well as non-conjugated dienes such as 1,4-Hexadiene, 1,5-Heptadiene, 5,7-Dimethyl-1,6-octadiene, 7-Methyl-1,6-octadiene, 4-Vinyl-1-cyclohexene, 5-Ethylidene-2-norbornene, 5-Vinyl-2-norbornene and Dicyclopentadiene. Preferably, the ethylene-containing polymer has from about 10% to about 90% ethylene, or in the case of EPDM, up to about 20% 5-ethylidene-2-norbornene.
The second component of the present polymer composition is a Group I metal salt of a strong base and a weak acid. Non-limiting examples of the weak acids useful in the production of the above-mentioned salt may be selected from the group comprising carbonic acid, C
1
-C
50
fatty acids, ethylene diamine tetra(acetic acid), phosphoric acid and mixtures thereof. The preferred salt for use in the present polymer composition may be selected from the group comprising sodium carbonate, potassium carbonate, sodium stearate, potassium stearate and mixtures thereof. The most preferred salt for use in the present p
Bender Harald
Hannay Judy
Bayer Inc.
Cheung Noland J.
Gil Joseph C.
Sanders Kriellion A.
Seng Jennifer R.
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