Thermoplastic vulcanizate and membrane for covering a roof made therefrom

1. A thermoplastic vulcanizate comprising:

a reaction product of a blend of

at least one polypropylene random copolymer;

at least one polyethylene copolymer containing at least 70% ethylene monomer units and at least 10 percent α-olefin co-monomer units by weight;

at least one compatibilizing rubber selected from the group consisting of ethylene vinyl acetate, ethyl methyl acrylate, and methyl acrylic rubber; and

at least one peroxide-based cross-linking agent, wherein the compatibilizing rubber is simultaneously dispersed throughout the polymer matrix and cross-linked.

2. The thermoplastic vulcanizate of claim 1 wherein said polypropylene random copolymer comprises:

from about 50 to about 99 percent by weight of repeating propylene monomer units; and

from about 1 to about 50 percent by weight of repeating ethylene co-monomer units;

wherein the repeating propylene monomer units and the repeating ethylene co-monomer units are randomly polymerized throughout the copolymer.

3. The thermoplastic vulcanizate of claim 1 wherein said polyethylene copolymer comprises:

from 70 to about 90 percent by weight of repeating ethylene monomer units; and

from 10 to about 35 percent by weight of repeating α-olefin co-monomer units having from 4 to 8 carbon atoms.

4. The thermoplastic vulcanizate of claim 1 wherein said polyethylene copolymer comprises:

from about 78 to about 82 percent by weight of repeating ethylene monomer units; and

from about 18 to about 22 percent by weight of repeating α-olefin co-monomer units having from 4 to 8 carbon atoms.

5. The thermoplastic vulcanizate of claim 1 wherein said polyethylene copolymer has high melt flow.

6. The thermoplastic vulcanizate of claim 1 wherein said repeating α-olefin co-monomer unit is butene, hexene or octene.

7. The thermoplastic vulcanizate of claim 1 wherein said polyethylene copolymer comprises a metallocene-catalyzed polyethylene copolymer.

8. The thermoplastic vulcanizate of claim 7 wherein said metallocene-catalyzed polyethylene copolymer comprises:

from 70 to about 90 percent by weight of repeating ethylene monomer units; and

from 10 to about 35 percent by weight of repeating α-octene co-monomer units,

wherein the repeating ethylene monomers units and repeating α-octene co-monomer units are randomly polymerized throughout the copolymer.

9. The thermoplastic vulcanizate of claim 1 wherein said peroxide-based cross-linking agent comprises 40 percent by weight dicumyl peroxide supported on calcium tricarbonate.

10. The thermoplastic vulcanizate of claim 1 further comprising a dynamic vulcanization catalyzing agent.

11. The thermoplastic vulcanizate of claim 1 , comprising:

from about 1 to about 40 parts by weight of at least one polypropylene random copolymer having an ethylene co-monomer content of from about 1 to about 10 percent;

from about 20 to about 90 parts by weight of at least one polyethylene copolymer having a α-olefin co-monomer content of from 10 to about 30 percent by weight; and

from about 10 to about 50 parts by weight of at least one compatibilizing rubber, so as to provide 100 parts by weight rubber to the thermoplastic vulcanizate.

12. The thermoplastic vulcanizate of claim 11 , further comprising from about 0.5 to about 1.5 parts by weight crossing linking agent per 100 parts rubber.

13. The thermoplastic vulcanizate of claim 11 , further comprising from about to about 90 parts by weight filler per 100 parts rubber.

14. The thermoplastic vulcanizate of claim 13 , wherein said filler includes from about 5 to about 70 parts by weight flame retardants per 100 parts rubber.

15. The thermoplastic vulcanizate of claim 14 , wherein said flame retardants include both aluminum trihydrate and magnesium hydroxide, and wherein the decomposition temperature of said aluminum trihydrate is increased in the vulcanizate as compared to other vulcanizates not including a compatibilizing rubber.

16. A roofing membrane comprising at least one ply of material comprising a thermoplastic vulcanizate, said thermoplastic vulcanizate comprising:

a reaction product of a melt blend of

at least one polypropylene random copolymer;

at least one polyethylene copolymer containing from about 10 to about 30 percent by weight of repeating α-olefin co-monomer units;

at least one compatibilizing rubber selected from the group consisting of ethylene vinyl acetate, ethyl methyl acrylate, and methyl acrylic rubber;

at least one peroxide-based cross-linking agent;

at least one filler; and

optionally, one or more additives selected from the group consisting of oils, pigments, thermal stabilizers, antioxidants, imidazole-type inhibitors, and UV or light stabilizers;

wherein the compatibilizing rubber is simultaneously dispersed throughout the polymer matrix and cross-linked.

17. The roofing membrane of claim 16 , wherein the thermoplastic vulcanizate comprises

from about 1 to about 40 parts by weight of at least one polypropylene random copolymer having an ethylene co-monomer content of from about 1 to about 10 percent;

from about 20 to about 90 parts by weight of at least one polyethylene copolymer having a α-olefin co-monomer content of from about 10 to about 35 percent by weight; and

from about 10 to about 50 parts by weight of at least one compatibilizing rubber, so as to provide 100 parts by weight rubber to the thermoplastic vulcanizate.

18. The roofing membrane of claim 17 , further comprising from about 0.5 to about 1.5 parts by weight crossing linking agent per 100 parts rubber, and from about 5 to about 90 parts by weight filler per 100 parts rubber.

19. The roofing membrane of claim 18 , wherein said filler includes from about 5 to about 70 parts by weight flame retardants per 100 parts rubber.

20. A method for making a roofing membrane comprising:

preparing a thermoplastic vulcanizate by melt blending at least one polypropylene random copolymer; at least one polyethylene copolymer containing from about 10 to about 35 percent by weight of repeating α-olefin co-monomer units; at least one compatibilizing rubber selected from the group consisting of ethylene vinyl acetate, ethyl methyl acrylate, and methyl acrylic rubber;

at least one peroxide-based cross-linking agent; and at least one filler; and

extending or calendering the thermoplastic vulcanizate into thin sheets.

21. A bilaminate roofing membrane comprising:

a first layer of a non-black sheeting comprising a thermoplastic vulcanizate formed from the reaction product of a melt blend comprising:

at least one polypropylene random copolymer;

at least one polyethylene copolymer containing from about 10 to about 35 percent by weight of repeating α-olefin co-monomer units;

at least one compatibilizing rubber;

at least one peroxide-based cross-linking agent;

at least one non-black filler; and

optionally, one or more additives selected from the group consisting of oils, thermal stabilizers, antioxidants, and UV or light stabilizers, wherein the compatibilizing rubber is simultaneously dispersed throughout the copolymer matrix and cross-linked; and

a second layer of a black sheeting comprising a thermoplastic vulcanizate formed from the reaction product of a melt blend comprising:

at least one polypropylene random copolymer;

at least one polyethylene copolymer containing from about 10 to about 35 percent by weight of repeating α-olefin co-monomer units;

at least one compatibilizing rubber;

at least one peroxide-based cross-linking agent;

at least one black filler; and

optionally, one or more additives selected from the group consisting of oils, thermal stabilizers, antioxidants, and UV or light stabilizers; wherein the compatibilizing rubber is simultaneously dispersed throughout the copolymer matrix and cross-linked; and wherein said first and second layers are attached together.

22. A thermoplastic vulcanizate comprising:

a reaction product of a blend of

at least one polypropylene random copolymer;

at least one polyethylene copolymer containing from about 10 to about 30 percent by weight α-olefin co-monomer units;

at least one compatibilizing rubber; and

at least one peroxide-based cross-linking agent,

wherein the compatibilizing rubber is selected from the group consisting of ethylene vinyl acetate, ethyl methyl acrylate, and methyl acrylic rubber.

23. The thermoplastic vulcanizate of claim 22 wherein said polyethylene copolymer comprises a metallocene-catalyzed polyethylene copolymer.

24. The thermoplastic vulcanizate of claim 22 wherein said compatibilizing rubber is selected from the group consisting of ethylene vinyl acetate, ethyl methyl acrylate, and methyl acrylic rubber.

25. The thermoplastic vulcanizate of claim 1 wherein said polyethylene copolymer comprises a metallocene-catalyzed polyethylene copolymer.

26. The method of claim 20 wherein said polyethylene copolymer comprises a metallocene-catalyzed polyethylene copolymer.