Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
1999-03-26
2001-02-13
Nutter, Nathan M. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S227000, C525S230000, C525S232000, C525S233000, C525S238000, C525S240000, C525S222000
Reexamination Certificate
active
06187867
ABSTRACT:
The present invention relates to hydrogenated nitrile rubber compositions containing thermoplastic olefins, which retain substantially the desirable resistance to heat and chemicals and the mechanical properties characteristic of hydrogenated nitrile rubbers when vulcanized, and further have other improved mechanical properties. The invention also relates to processes for preparing the compositions, and articles made therefrom.
BACKGROUND OF THE INVENTION
Aside from being used in tires, rubber is used in a variety of other parts for automobiles, and other motorized vehicles and machines. In those environments, the components made from rubber have to withstand exposure to different chemical environments, such as oil, water, air or ozone, without losing the mechanical properties required for their intended use over a wide range of operating temperatures.
Hydrogenated nitrile rubbers, which have good heat-aging resistance and resistance to chemicals as well as suitable mechanical properties, are used in mechanical parts for performance in physical environments such as automobiles. However, the use of hydrogenated nitrile rubbers in some applications is limited by their relatively high cost.
Blends with other elastomers such as NBR, ECO, EPDM, CR, CPE, and the like have been considered. For example, U.S. Pat. No. 5,612,418 describes blends of a partially hydrogenated nitrile rubber and a polyacrylate elastomer. In general, some compromise of physical properties, especially heat resistance, must be made in such elastomeric blends. An important requirement for those blends is occuring between the elastomers to maintain key thermoset type properties, e.g., elevated temperature compression set resistance.
Also, in the prior art, attempts to combine the use of thermoplastic resins with rubbers have focused on using the rubbers as modifiers for the thermoplastic resins, in proportions such that the rubbers are dispersed as discrete particles, which may be partially vulcanized, in a matrix of the elastomers. For example, thermoplastic resins thus modified with hydrogenated nitrile rubbers are known. However, those compositions are not suitable for applications for which rubbers are usually used. In other words, such rubber-modified elastomers do not have sufficient rubber-like properties.
SUMMARY OF THE INVENTION
One aspect of the present invention is to provide hydrogenated nitrile rubber compositions containing thermoplastic polyolefins, e.g. polyethylene, which retain the desirable resistance to heat and chemicals and the mechanical properties characteristic of hydrogenated nitrile rubbers, and further have other improved mechanical properties.
Another aspect of the invention is to provide processes for preparing the hydrogenated nitrile rubber compositions containing thermoplastic polyolefins.
Yet another aspect of the invention is to provide articles made from the hydrogenated nitrile rubber compositions containing thermoplastic olefins.
DETAILED DESCRIPTION OF THE INVENTION
Hydrogenated nitrile rubbers are prepared by hydrogenating the conjugated diene units of an unsaturated nitrile-conjugated diene copolymer rubber or an unsaturated nitrile-conjugated diene-ethylenically unsaturated monomer terpolymer by known methods. The unsaturated nitrile-conjugated diene copolymer rubber or the unsaturated nitrile-conjugated diene-ethylenically unsaturated monomer terpolymer is prepared, for example, by emulsion polymerization or solution polymerization.
Examples of the unsaturated nitrile monomer for preparing nitrile rubbers are: acrylonitrile and methacrylonitrile.
Examples of the conjugated diene monomer for preparing nitrile rubbers are: 1,3-butadiene, 2,3-dimethylbutadiene, isoprene and 1,3-pentadiene.
Examples of the ethylenically unsaturated monomers which are copolymerizable with the nitrile monomers and the conjugated diene monomers are: unsaturated carboxylic acids such as acrylic acid, methacrylic acid, itaconic acid and maleic acid and salts thereof, alkyl esters of unsaturated carboxylic acids such as methyl acrylate and butyl acrylate; alkoxyalkyl esters of unsaturated carboxylic acids such as methoxy acrylate, ethoxyethyl acrylate, methoxyethyl acrylate, acrylamide, methacrylamide; N-substituted acrylamides such as N-methylolacrylamide, N,N′-dimethylolacrylamide and N-ethoxymethylolacrylamide; N-substituted methacrylamides such as N-methylolmethacrylamide, N,N′-dimethylolmethacrylamide and N-ethoxymethylmethacrylamide.
In lieu of the copolymerizable ethylenically unsaturated monomer a non-conjugated diene such as vinylnorbomene, dicyclopentadiene or 1,4-hexadiene may be used as a comonomer in the nitrile rubber.
Examples of the hydrogenated nitrile rubber used in the invention are the hydrogenated products of a butadiene-acrylonitrile copolymer rubber (“NBR”), an isoprene-acrylonitrile copolymer rubber, an isoprene-butadiene-acrylonitrile copolymer rubber, and a butadiene-acrylic acid-acrylonitrile copolymer rubber.
A commonly used hydrogenated nitrile rubber is HNBR made of 15 to 50% by weight of acrylonitrile and 85 to 50% by weight of butadiene by the free-radical initiated solution or emulsion copolymerization of these monomers. The unsaturated units derived from butadiene in the obtained NBR rubber are hydrogenated so that the remaining degree of unsaturation is from 0.1 to 20%. Hydrogenated nitrile rubbers having a degree of unsaturation lower than 0.1% are not readily peroxide curable, and those having a degree of unsaturation above 20% are less resistant to heat aging and to attack by ozone.
The hydrogenated nitrile rubber in the composition of the present invention can be a single hydrogenated nitrile rubber or a mixture of two or more hydrogenated nitrile rubbers selected to give the desired balance of properties.
Thermoplastic polyolefins are thermoplastic resins which are not rubbers, i.e., they exhibit some degree of crystallinity, have melting temperatures above room temperature, and are typically not rubbery in their intended range of usage temperature. They are widely used, typically in applications where they are cast, molded or extruded into articles such as containers, various consumer articles, pipes, films, insulating covers material for cables, etc. Thermoplastic polyolefins are versatile because of their low cost, their chemical resistance, their useful range of mechanical properties and the fact that they can be cross-linked, for example with peroxides.
The thermoplastic polyolefins suitable for use in the present invention are polymers of unsaturated aliphatic hydrocarbons containing one double bond per molecule, the most common monomers being ethylene and propylene. Isobutene, but-1-ene and 4-methylpent-1-ene are examples of other suitable monomers. The thermoplastic polyolefins may be homopolymers of the unsaturated aliphatic hydrocarbons, copolymers of an unsaturated aliphatic hydrocarbon with another unsaturated aliphatic hydrocarbon, or copolymers of an unsaturated aliphatic hydrocarbon with another monomer such as vinyl acetate, ethyl acrylate, unsaturated carboxylic acids (e.g.,methacrylic acid).
For use in the rubber composition of the invention, the thermoplastic polyolefin is not particularly limited, and may be selected according to the desired properties for a particular application. The polyolefin used in the composition of the present invention can be a single polyolefin or a mixture of two or more polyolefins selected to give the desired balance of properties, in particular mechanical properties. Curing is required to achieve the desirable properties characteristics of the present invention, and peroxide curing agents are particularly suitable because they serve as crosslinking agents for most polyolefins, in particular polyethylenes, as well as for the hydrogenated nitrile rubber. In other words, in the rubber composition of the invention the thermoplastic polyolefin is at least partially cross-linked after curing of the composition.
Further description of polyolefin polymers is provided in the Encyclopedia of Chemical Tec
Milazzo Philippe
Rau Paul
Armstrong, Westerman Hattori, McLeland & Naughton
Nutter Nathan M.
Zeon Chemicals L.P.
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