Thermoplastic blend of partially cured monoolefin copolymer rubber and polyolefin plastic

Abstract

Thermoplastic blends of partially cured monoolefin copolymer rubber (such as EPM or EPDM rubber) with a polyolefin resin (such as polypropylene) exhibit good physical properties and are reprocessable. The partial cure of the rubber is effected by heating the rubber with a curative such as a peroxide. The blends are used to make molded or extruded articles which have good physical properties without requiring vulcanization; preferred blends have the characteristics of thermoplastic elastomers.

Having thus described our invention what we claim and desire to protect by Letters Patent is: 
     
       1. A thermoplastic reprocessable blend of (A) a rubbery copolymer of ethylene and at least one other copolymerizable monoolefin of the formula CH 2  ═CHR where R is an alkyl radical having from one to 12 carbon atoms, with or without at least one copolymerizable polyene, said copolymer being partially cross-linked, prior to blending to a gel content of at least 30 percent but less than 90 percent by weight measured by immersion in cyclohexane for 48 hours at 73° F., and (B) an uncross-linked resinous polyolefin, the weight ratio of (A) to (B) being from 10:90 to 90:10.Iadd., said partial cross-linking having been accomplished by the action of a curative, the action of the curative being substantially exhausted so that there is little or no tendency for further cure to take place subsequently.Iaddend.. 
     
     
       2. A blend as in claim 1 in which the said mono-olefin is propylene. 
     
     
       3. A blend as in claim 1 in which (A) is a saturated ethylene-propylene binary copolymer. 
     
     
       4. A blend as in claim 1 in which (A) is an unsaturated terpolymer of ethylene, propylene, and a non-conjugated diene. 
     
     
       5. A blend as in claim 4 in which the diene is dicyclopentadiene. 
     
     
       6. A blend as in claim 4 in which the diene is 5-ethylidene-2-norbornene. 
     
     
       7. A blend as in claim 1 in which the said gel content of (A) is from 40 to 85 percent. 
     
     
       8. A blend as in claim 1 in which the said gel content of (A) is from 55 to 85 percent. 
     
     
       9. A blend as in claim 1 in which (B) is selected from the group consisting of polyethylene and polypropylene. 
     
     
       10. A blend as in claim 1 in which (B) is polyethylene. 
     
     
       11. A blend as in claim 10 in which the polyethylene has a density of 0.910 to 0.925 g/cc. 
     
     
       12. A blend as in claim 10 in which the polyethylene has a density of 0.926 to 0.940 g/cc. 
     
     
       13. A blend as in claim 10 in which the polyethylene has a density of 0.941 to 0.965 g/cc. 
     
     
       14. A blend as in claim 1 in which (B) is polypropylene. 
     
     
       15. A blend as in claim 14 in which the polypropylene is isotactic. 
     
     
       16. A blend as in claim 1 in which the weight ratio of (A) to (B) is from 50:50 to 90:10. 
     
     
       17. A blend as in claim 1 in which the weight ratio of (A) to (B) is from 60:40 to 80:20. 
     
     
       18. A blend as in claim 1 in which (A) is semi-cured with a peroxide curative. 
     
     
       19. A blend as in claim 18 in which (A) is saturated ethylene-propylene binary copolymer. 
     
     
       20. A blend as in claim 18 in which (A) is an unsaturated ethylene-propylene-non-conjugated diene terpolymer. 
     
     
       21. A blend as in claim 18 in which the peroxide curative is 2,5-bis(tert.-butylperoxy)-2,5-dimethylhexane. 
     
     
       22. A blend as in claim 18 in which the peroxide curative is benzoyl peroxide. 
     
     
       23. A blend as in claim 1 in which (A) is semi-cured with an azide curative. 
     
     
       24. A blend as in claim 23 in which the azide curative is p,p'-oxybis(benzenesulfonylazide). 
     
     
       25. A blend as in claim 1 in which (A) is unsaturated ethylene-propylene-non-conjugated diene terpolymer semi-cured with a sulfur curative. 
     
     
       26. A thermoplastic reprocessable blend of A. a monoolefin copolymer rubber selected from the group consisting of saturated ethylene-propylene binary copolymer rubber and unsaturated ethylene-propylene-non-conjugated diene terpolymer rubber, partially cross-linked, prior to blending, to a gel content of from 40 to 85 percent, measured by immersion in cyclohexane for 48 hours at 73° F., the percent swell of the said partially cross-linked rubber being 10 to 70 percent less than the percent swell prior to cross-linking of the rubber, said partially cross-linked rubber being capable of forming a coherent band on a roll mill, and   B. an uncross-linked resinous polyolefin selected from the group consisting of polyethylene and polypropylene, the weight ratio of (A) to (B) being from 60:40 to 80:20, the said blend, when formed into a molded test specimen without further cross-linking, having a performance factor (defined as the value obtained by multiplying the tensile strength in psi by the ultimate elongation in percent and dividing by the elongation set in percent) being at least 20 percent in excess of the performance factor of an otherwise identical blend containing the same rubber without partial cross-linking, whereby the said blend containing the partially cross-linked rubber has the characteristics of a thermoplastic elastomer.Iadd., said partial cross-linking having been accomplished by the action of a curative, the action of the curative being substantially exhausted so that there is little or no tendency for further cure to take place subsequently.Iaddend..   
     
     
       27. A method of making a thermoplastic reprocessable blend comprising in combination the steps of a. providing (A) a rubbery copolymer of ethylene and at least one other copolymerizable monoolefin of the formula CH 2  ═CHR where R is an alkyl radical having from one to 12 carbon atoms, with or without at least one copolymerizable polyene,   b. semi-curing the said rubbery copolymer until it has a gel content, measured by immersion in cyclohexane for 48 hours at 73° F., at least 10 percent higher than the gel content of the said rubbery copolymer prior to said semi-cure, but less than 90%,   c. providing (B) an uncross-linked resinous polyolefin, and   d. uniformly blending (A) and (B) at a temperature in excess of the softening temperature of (B), the weight ratio of (A) to (B) being from 10:90 to 90:10.Iadd., said semi-curing being accomplished by the action of a curative, the action of the curative being substantially exhausted so that little or no further cure takes place subsequently.Iaddend..  .[.28. A method as in claim 27 in which the action of the curative in step (b) is   
     
     
        substantially exhausted..]. 29. A method as in claim 27 in which the said semi-curing step (b) is carried out by heating the said rubbery copolymer (A) at curing temperature in admixture with a curative for said rubbery copolymer until the said gel content is at least 20 percent higher than 
     
     
        the gel content of the starting rubbery copolymer. 30. A method as in claim 27 in which the said semi-curing step (b) is carried out by heating the said rubbery copolymer (A) at curing temperature in admixture with a curative for said rubbery copolymer until the said gel content is at least 30 percent higher than the gel content of the starting rubbery copolymer. 
     
     
         1. A method as in claim 30 in which the said gel content after the 
     
     
        semi-curing step (b) is within the range of from 40 to 85 percent. 32. A method as in claim 30 in which the said rubbery copolymer (A) after the semi-curing step (b) has percent swell at least 8% less than the percent 
     
     
        swell prior to the semi-cure. 33. A method as in claim 32 in which the 
     
     
        curative is a peroxide curative. 34. A method as in claim 33 in which the 
     
     
        peroxide curative is 2,5-bis(tert.-butylperoxy)-2,5-dimethylhexane. 35. A method as in claim 33 in which the peroxide curative is benzoyl peroxide. 
     
     
         6. A method as in claim 32 in which the curative is an azide curative. 
     
     
            A method as in claim 36 in which the azide curative is 
     
     
        p,p'-oxybis(benzenesulfonylazide). 38. A method as in claim 32 in which (A) is an unsaturated ethylene-propylene-non-conjugated diene terpolymer 
     
     
        rubber and the said curative is a sulfur curative. 39. A method as in claim 32 in which the semi-curing step (b) is carried out under dynamic conditions while masticating the mixture of rubbery copolymer and 
     
     
        curative. 40. A method as in claim 32 in which the semi-curing step (b) is 
     
     
        carried out under static conditions. 41. A method of making a thermoplastic reprocessable blend comprising in combination the steps of a. providing (A) a monoolefin copolymer rubber selected from the group consisting of saturated ethylene propylene binary copolymer rubber and unsaturated ethylene-propylene-non-conjugated diene terpolymer rubber,   b. heating the said rubbery copolymer at curing temperature in admixture with a curative for said rubbery copolymer until the gel content of the copolymer, measured by immersion in cyclohexane at 73° F. is within the range of from 40 to 85 percent, the percent swell after said heating being 10 percent to 70 percent less than prior to said heating, the thus-treated rubbery copolymer being in a semi-cured thermoplastic state and capable of being formed into a coherent band on a roll mill,   c. providing (B) an uncross-linked resinous polyolefin, and   d. uniformly blending (A) and (B) by masticating at a temperature in excess of the softening temperature of (B), the weight ratio of (A) to (B) being from 60:40 to 80:20, the resulting blend being a thermoplastic elastomeric composition.Iadd., the action of the curative being substantially exhausted so that little or no further cure takes place   
     
     
        subsequently.Iaddend.. 42. A method as in claim 41 in which the action of the curative in step (b) is substantially exhausted and thereafter an 
     
     
        antioxidant is added to scavenge any residual free radicals. 43. A method as in claim 42 in which step (b) is carried out while masticating the 
     
     
        mixture of rubbery copolymer and curative in a heated internal mixer. 44. A method as in claim 42 in which step (b) is carried out statically in 
     
     
        a heated autoclave. 45. A method of making a thermoplastic elastomeric shaped article comprising carrying out the steps of claim 42, and thereafter shaping the blend into a desired shape without further cure, whereby the shaped blend can be reprocessed.