Process for forming thermoplastic vulcanizates
Provided are methods for producing a thermoplastic vulcanizate. One method includes charging vulcanizable rubber to a reactor; charging a masterbatch of thermoplastic resin and a catalyst for a phenolic resin curative to the reactor; charging a phenolic resin curative to the reactor; and dynamically vulcanizing the rubber with the phenolic resin curative in the presence of the catalyst. Also provided are thermoplastic vulcanizates made by the methods of the invention.
1. A method for making a thermoplastic vulcanizate, the method comprising the steps of:
charging vulcanizable rubber and a first thermoplastic resin to a reactor to form a molten mass, wherein the first thermoplastic resin is substantially devoid of a catalyst for the phenolic resin;
charging a masterbatch consisting essentially of a second thermoplastic resin and a catalyst for a phenolic resin curative to the molten mass in the reactor, wherein the masterbatch contains ≧10 wt% and ≦90 wt% of the catalyst based on the total weight of the masterbatch and wherein the masterbatch contains less than 1 wt% of material other than the catalyst or the second thermoplastic resin based on the weight of the masterbatch;
charging a phenolic resin curative to the molten mass reactor; and
dynamically vulcanizing the rubber with the phenolic resin curative in the presence of the catalyst.
2. The method of claim 1 , further comprising the step of mixing the vulcanizable rubber and the masterbatch above the melt temperature of the first thermoplastic resin.
3. The method of claim 1 , where the catalyst is stannous chloride.
4. The method of claim 1 , where the catalyst is anhydrous stannous chloride.
5. The method of claim 1 , where the masterbatch includes ≧ 20 wt% and 70 wt% stannous chloride based on the total weight of the masterbatch.
6. The method of claim 1 , where the masterbatch is charged to the reactor in the form of pellets.
7. The method of claim 1 , where the first thermoplastic resin includes polypropylene.
8. A method for making a thermoplastic vulcanizate, the method comprising the steps of:
a. mixing a vulcanizable rubber and a first thermoplastic resin above the melt temperature of the thermoplastic resin to form a molten mass;
b. adding a masterbatch consisting of a second thermoplastic resin and catalyst to the molten mass;
c. melting the second thermoplastic resin of the masterbatch to thereby disperse the catalyst within the molten mass;
d. adding a phenolic curative to the molten mass; and
e. dynamically vulcanizing the rubber with the phenolic resin in the presence of the catalyst.
9. The method of claim 8 , where the vulcanizable rubber is a poly(ethylene-propylene-diene)copolymer, the first thermoplastic resin is polypropylene, and the second thermoplastic resin is polypropylene.
10. The method of claim 8 , where the catalyst is anhydrous stannous chloride.
11. The method of claim 8 , where said dynamic vulcanization is effected in the presence of ≧10 wt% and ≦70 wt% stannous chloride based on the total weight of the masterbatch.
12. A method for making a thermoplastic vulcanizate, the method comprising the steps of: charging a poly(ethylene-propylene-diene)copolymer to a twin-screw extruder through the feed throat of the extruder; charging polypropylene to the twin-screw extruder through the feed throat of the extruder; mixing, within an initial mix zone, the poly(ethylene-propylene-diene)copolymer and the polypropylene at a temperature above the melt temperature of the polypropylene to form a molten mass; charging pellets that include a blend of polypropylene and anhydrous stannous chloride to the twin-screw extruder through an inlet in a barrel downstream of the initial mix zone, wherein the pellets include less than 1% of material other than the stannous chloride or the polypropylene based on the weight of the pellet; heating the pellets above the melt temperature of the polypropylene and mixing the molten polypropylene with the molten mass; charging a phenolic resin curative to the twin-extruder through an inlet in a barrel downstream of the barrel where the pellets are charged; mixing the phenolic resin with the molten mass while transferring the molten mass through a cure zone where dynamic vulcanization of the rubber takes place to thereby form a thermoplastic vulcanizate; removing the thermoplastic vulcanizate from the twin-screw extruder; cooling the thermoplastic vulcanizate; and pelletizing the thermoplastic vulcanizate.
13. A thermoplastic vulcanizate made by the method of claim 1 .
14. A thermoplastic vulcanizate made by the method of claim 8 .
15. A thermoplastic vulcanizate made by the method of claim 13 .