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
2002-07-15
2004-09-21
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...
C525S196000, C525S216000, C525S222000, C525S238000, C525S239000, C525S240000
Reexamination Certificate
active
06794452
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the covulcanization of polymeric materials. The present invention also relates to compositions comprising covulcanized polymeric materials.
BACKGROUND OF THE INVENTION
Many polymeric materials find applications that impose multiple performance requirements on physical properties such as, for instance, tensile strength, elasticity and abrasion resistance. Also, these applications require the material to be effective over a wide temperature range. It is known in the art to blend different polymers in an attempt to form a polymeric material having these desired properties. This is not always easy, especially if the two polymers will not mix and bond with each other. When this occurs, the resultant material has large domains of one polymer distributed in a continuous phase of the other polymer. In the absence of bonding between the two polymers, or if bonding occurs to only a limited extent, the discontinuous polymer does not contribute to the properties of the blend, and a product is formed that has low modulus and low tensile strength.
For example, ethylene/propylene rubber (EPR) is a copolymer of ethylene and propylene usually containing 50 to 75 parts of ethylene and the balance propylene. EPDM is a terpolymer of ethylene, propylene and a diene monomer, the diene monomer being hexadiene, dicyclopentadiene or, more commonly, ethylidene norbornene. EPR and EPDM both have good heat resistance, good cold resistance, good ozone resistance and good weather resistance. However, both have poor physical, abrasive and adhesive properties. Attempts have been made in the past to blend EPR or EPDM with other polymers, seeking to obtain a composition that has the good weather and temperature properties of EPR or EPDM and also good physical properties of the other polymer. Difficulty has been encountered in blending the EPR or EPDM and other polymers, resulting in compositions that display no useful enhancement of physical properties.
SUMMARY OF THE INVENTION
The present invention provides a method for covulcanizing two or more polymeric materials, which involves admixing the two or more polymeric materials with a hydrogenated carboxylated nitrile rubber (HXNBR), a multivalent salt of an organic acid and a vulcanizing agent.
The present invention also provides a composition containing two or more different polymeric materials that have been admixed with a hydrogenated carboxylated nitrile rubber, a multivalent salt of an organic acid and a vulcanizing agent.
DETAILED DESCRIPTION OF THE INVENTION
Different polymers have different solubility parameters. Solubility parameters correlate with polarity, and are measured in units of (cal.cm
3
)
1/2
. According to “The Elements of Polymer Science and Engineering”, Academic Press Inc. 1982, by Alfred Rudin, Chapter 12 Polymer Mixtures, pages 428 to 445, nitrile rubber having a 43% acrylonitrile content, for example, has a solubility parameter of 10.53. Hydrogenated nitrile rubber having a 43% acrylonitrile content has a solubility parameter of 10.71. These polymers can be readily blended. EPR has a solubility parameter of about 8.1 and EPDM has a solubility parameter of about 8.0. These polymers do not blend readily with nitrile rubber or hydrogenated nitrile rubber. The compatibility between polymers reduces as the difference in the solubility parameters of the respective polymers approaches a value of 0.5 or greater, especially 2 or greater. Accordingly, the present invention relates to a method of blending polymers, which differ in solubility parameter by the value of 0.5 or more and in some instances by 2 or greater.
Because EPR and EPDM display good weather resistance, heat resistance and cold resistance, it is desirable to blend them with polymers that have good physical properties but whose weather resistance, heat resistance and cold resistance are not as good as desired. For example, accessory drive belts in automobiles and trucks, such as alternator belts and the like may be made from nitrile rubber or hydrogenated nitrile rubber. These display good physical properties for these applications. It is desired to increase the temperature range over which these can be used, so that the high temperature demands imposed by summer in Arizona, Nevada and New Mexico, and the low temperature demands imposed by winter in Alaska and Northern Alberta can be satisfied by the same material. In accordance with the present invention EPR or EPDM polymers can be covulcanized with nitrile rubbers or hydrogenated nitrile rubbers.
EPR's are well known. They are commercially available from Bayer under the trademark Buna and include examples bearing the designations EP T 2070 and EP G 5050. EP T 2070 is a copolymer of ethylene and propylene with an ethylene content of 70%, the balance propylene, a Mooney viscosity of 20 and contains no processing oil. EP G 5050 is a copolymer of ethylene and propylene with an ethylene content of 50%, and the balance propylene, a Mooney viscosity of 50 and contains no processing oil. EPR's with or without processing oil can be used in the present invention. However, EPR's without processing oil are preferred.
Terpolymers of ethylene, propylene and ethylidene norbornene are commercially available, for example under the designations EP T 3950, EP T 6470 and EP T 2450. EP T 3950 has a viscosity in Mooney units of 30, a content of ethylidene norbornene of 9%, an ethylene content of 50% and contains no processing oil. EP T 6470 has a Mooney Viscosity of 60, a content of ethylidene norbornene of 4%, an ethylene content of 70% and contains no processing oil. EP T 2450 has a Mooney viscosity of 20, a content of ethylidene norbornene of 4%, an ethylene content of 50% and contains no processing oil. EPDM's with or without processing oil can be used in the present invention however EPDM's without processing oil are preferred. EPDM's with oil contents of 30, 50 and 100 per hundred parts by weight of rubber (phr) are also commercially available.
Nitrile rubbers (NBR's) are copolymers of a conjugated diene and a nitrile. Many conjugated dienes are used in nitrile rubbers and these may all be used in the present invention. Suitable conjugated dienes include 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, 1,3-pentadiene and piperylene, of which 1,3-butadiene is preferred.
The nitrile is normally acrylonitrile or methacrylonitrile or &agr;-chloroacrylonitrile, of which acrylonitrile is preferred.
The conjugated diene usually constitutes about 50 to about 85 wt. % of the copolymer and the nitrile usually constitutes about 15 to 50 wt. % of the copolymer. The polymer may also contain an amount, usually not exceeding about 10 wt. %, of one or more other copolymerizable monomers, for example, an ester of an unsaturated acid, such as, ethyl, propyl or butyl acrylate or methacrylate, or a vinyl compound, for example, styrene, &agr;-methylstyrene or a corresponding compound bearing an alkyl substituent on the phenyl ring, for instance, a p-alkylstyrene such as p-methylstyrene. Suitable nitrile rubbers are commercially available under the trademarks PERBUNAN® (Bayer AG) and KRYNAC® (Bayer AG).
Hydrogenated nitrile rubbers (HNBR's) are formed by hydrogenating nitrile rubbers. When a conjugated diene and a nitrile copolymerize, the product of the copolymerization contains carbon-carbon double bonds. These can be hydrogenated in any known manner. Hydrogenation is not always complete, however, and the degree of remaining unsaturation is expressed in terms of residual double bonds, or “RDB”, being the number of carbon-carbon double bonds that remain in the copolymer after hydrogenation. The “RDB” is expressed as a percentage of the carbon-carbon double bonds present in the copolymer prior to hydrogenation. Hydrogenated nitrile rubbers are available from Bayer under the trademark THERBAN®, with acrylonitrile contents of 34%, 39% and 43% and with RDB's of 18, 5.5, 3.5 and less than 0.9.
Past attempts to covulcanize an EPR or an EPDM and a nitrile rubber or a
Bayer Inc.
Gil Joseph C.
Nutter Nathan M.
Seng Jennifer R.
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