Thermoplastic vulcanizates and processes for making the same

1. A process for producing a thermoplastic vulcanizate, the process comprising:

(i) dynamically vulcanizing a rubber with a curative in a first stage, where the rubber is within a blend that includes the rubber, a propylene homopolymer, oil and the curative, where said step of dynamically vulcanizing occurs at a temperature at or above the melting point of the propylene homopolymer, where said rubber is a terpolymer having units derived from ethylene, one or more α-olefins, and 0.1 to 3.0 mole % polymeric units deriving from 5-vinyl-2-norbornene, wherein said propylene homopolymer has an MFR of less than 1 g/10 min, where said curative is a peroxide curative present in the first stage in an amount of from 0.5 to 6 parts by weight per 100 parts by weight of the rubber, and where the weight ratio of the propylene homopolymer to the rubber is from 0.1:1 to 0.4:1, and where the oil is present in the first stage in an amount of from 50 to 200 parts by weight per 100 parts by weight of the rubber;

(ii) continuing said step of dynamically vulcanizing to cause phase inversion of the blend to thereby convert the propylene homopolymer into a continuous phase;

(iii) maintaining the blend at or above the melting point of the propylene homopolymer after the phase inversion; and

(iv) introducing molten thermoplastic resin into the blend in a second stage, where the thermoplastic resin introduced into the blend in the second stage is a propylene homopolymer, propylene copolymer with ethylene, reactor propylene copolymer, or impact propylene copolymer, where said step of introducing molten thermoplastic resin occurs after phase inversion but before the blend is cooled to a temperature below the melting point of the propylene homopolymer;

wherein the thermoplastic vulcanizate has the following properties (a)-(d):

(a) Ultimate tensile strength of 5.77 to 7.52 MPa, as determined in accordance with ASTM D-412 at 23° C. using an Instron testing machine;

(b) Compression set of 26% to 31%, as determined at 25% compression, 22 hours, and 100° C. according to ASTM D-395;

(c) Compression set of 32% to 35%, as determined at 25% compression, 168 hours, and 100° C. according to ASTM D-395; and

(d) Tension set of 10 to 12.5%, as determined according to ASTM D-142;

and further wherein the thermoplastic vulcanizate comprises 60 to 80 wt % of the rubber, based on the total weight of the rubber, the polypropylene homopolymer from the first stage, and the thermoplastic resin from the second stage, and where the thermoplastic vulcanizate comprises from 30 to 35 wt % of the polypropylene homopolymer from the first stage and the thermoplastic resin from the second stage, based on the total weight of the rubber, the polypropylene homopolymer from the first stage, and the thermoplastic resin from the second stage; provided that the total amount of thermoplastic vulcanizate, polypropylene homopolymer from the first stage, and the thermoplastic resin from the second stage does not exceed 100% based on the total weight of the rubber, the polypropylene homopolymer from the first stage, and the thermoplastic resin from the second stage.

2. The process of claim 1 , where the rubber is a terpolymer including polymeric units deriving from ethylene, propylene, and 5-vinyl-2-norbornene.

3. The process of claim 1 , where the terpolymer includes from about 5 to about 75 mole % units deriving from ethylene.

4. The process of claim 1 , where oil is added during the second stage in an amount of from about 5 to about 100 parts by weight per 100 parts of the rubber.

5. The process of claim 1 , wherein the peroxide curative includes 2,5-dimethyl-2,5-di-(t-butyl peroxy)hexane.

6. A molded, extruded, or foamed article prepared with a thermoplastic vulcanizate prepared by the process of claim 1 .

7. The process of claim 1 , wherein the thermoplastic vulcanizate has a hardness of at least 60 Shore A.

8. The process of claim 1 , wherein the first and second stages takes place in a single mixer.

9. The process of claim 1 , wherein carbon black filler is added in the first stage, second stage, or both stages of the process.

10. The process of claim 1 , wherein the thermoplastic resin introduced in the second stage is a propylene homopolymer having a MFR of less than 1 g/10 min.

11. A process for preparing a thermoplastic vulcanizate, the process comprising:

(i) preparing a blend in a first stage comprising a rubber, a propylene homopolymer and a curative, where the weight ratio of the propylene homopolymer to the rubber is from 0.1:1 to 0.4:1, where said rubber is a terpolymer having units derived from ethylene, and 0.1 to 3.0 wt % polymeric units deriving from 5-vinyl-2-norbornene, and wherein said propylene homopolymer has an MFR of less than 1 g/10 min,

(ii) dynamically vulcanizing the rubber at a temperature above the melting temperature of the propylene homopolymer, where said step of dynamically vulcanizing employs a peroxide curative present in an amount of from 0.5 to 6 parts by weight per 100 parts by weight of the rubber; and

(iii) adding from about 10 to 300 parts molten thermoplastic resin per 100 parts of the rubber to the blend in a second stage, where the thermoplastic resin introduced into the blend in the second stage is a propylene homopolymer, propylene copolymer with ethylene, reactor propylene copolymer, or impact propylene copolymer, where said step of adding additional thermoplastic resin occurs after said step of dynamically vulcanizing causes phase inversion of the blend, and where said step of adding additional thermoplastic resin occurs before the blend is permitted to cool below the melting temperature of the propylene homopolymer;

wherein the thermoplastic vulcanizate has the following properties (a)-(d):

(a) Ultimate tensile strength of 5.77 to 7.52 MPa, as determined in accordance with ASTM D-412 at 23° C. using an Instron testing machine;

(b) Compression set of 26% to 31%, as determined at 25% compression, 22 hours, and 100° C. according to ASTM D-395;

(c) Compression set of 32% to 35%, as determined at 25% compression, 168 hours, and 100° C. according to ASTM D-395; and

(d) Tension set of 10 to 12.5%, as determined according to ASTM D-142;

and further wherein the thermoplastic vulcanizate comprises 60 to 80 wt % of the rubber, based on the total weight of the rubber, the polypropylene homopolymer from the first stage, and the thermoplastic resin from the second stage, and where the thermoplastic vulcanizate comprises from 30 to 35 wt % of the polypropylene homopolymer from the first stage and the thermoplastic resin from the second stage, based on the total weight of the rubber, the polypropylene homopolymer from the first stage, and the thermoplastic resin from the second stage; provided that the total amount of thermoplastic vulcanizate, polypropylene homopolymer from the first stage, and the thermoplastic resin from the second stage does not exceed 100% based on the total weight of the rubber, the polypropylene homopolymer from the first stage, and the thermoplastic resin from the second stage.

12. The process of claim 11 , where the process includes introducing a processing oil during the first stage in an amount of from about 50 to about 300 parts by weight oil per 100 parts by weight of the rubber.

13. The process of claim 11 , wherein the thermoplastic vulcanizate has a hardness of at least 60 Shore A.

14. The process of claim 11 , wherein the first and second stages takes place in a single mixer.

15. The process of claim 11 , wherein carbon black filler is added in the first stage, second stage, or both stages of the process.

16. The process of claim 11 , wherein the thermoplastic resin added in the second stage is a propylene homopolymer having a MFR of less than 1 g/10 min.