System and method for continuously manufacturing cured membranes
A method of continuously manufacturing a cured membrane includes continuously compounding and mixing a vulcanizable rubber composition in a mixing extruder while continuously removing gasses from the vulcanizable rubber composition during mixing with a vacuum. The vulcanizable rubber composition may be continuously extruded to form an extrudate, which may be continuously calendered to form a green membrane. The green membrane may be continuously cured, such as by a hot air conveyor curing system, to form a cured membrane.
1. A method of continuously manufacturing a partially-cured extrudate, the method comprising:
(i) providing a mixing extruder including a feed throat, a downstream inlet that is downstream of the feed throat, and a material outlet, where the extruder has a length extending from the feed throat to the material outlet, said extruder including a mixing and conveying zone;
(ii) introducing EPDM polymer, filler, and oil into the mixing and conveying zone through the feed throat to thereby form a mixture within the mixing and conveying zone;
(iii) conveying the mixture through the mixing and conveying zone toward the material outlet, where said step of conveying the mixture includes back-mixing the mixture at a location along the length of the extruder;
(iv) introducing a curative into the downstream inlet to thereby introduce the curative into the mixture;
(v) partially curing the EPDM within the mixing and conveying zone to thereby form a partially-cured composition; and
(vi) extruding the partially-cured composition into a partially-cured sheet, where the temperature of the partially-cured composition is between 120° and 160° C. at said step of extruding.
2. The method of claim 1 , wherein the temperature of the mixture at any point along a length of the mixing extruder is within +/−5° C. of a desired temperature.
3. The method of claim 1 , where the temperature of the mixture at all points on a section plane through the mixing extruder is within +/−5° C. of a desired temperature.
4. The method of claim 1 , where said step of conveying the mixture through the mixing and conveying zone is defined by a residence time within the mixing extruder whereby the residence time is the time required for materials to travel between two locations within the mixing extruder, and where said step of conveying is manipulated such that the residence time from the feed throat to the downstream inlet is greater than the residence time from the downstream inlet to the material outlet.
5. The method of claim 1 , further comprising the step of calendaring the partially-cured sheet.
6. The method of claim 1 , further comprising the step of introducing heat to the partially-cured sheet.
7. A partially-cured EPDM sheet formed by a method comprising the steps of:
(i) providing a mixing extruder including a feed throat, a downstream inlet that is downstream of the feed throat, and a material outlet, where the extruder has a length extending from the feed throat to the material outlet, said extruder including a mixing and conveying zone;
(ii) introducing EPDM polymer, filler, and oil into the mixing and conveying zone through the feed throat to thereby form a mixture within the mixing and conveying zone;
(iii) conveying the mixture through the mixing and conveying zone toward the material outlet, where said step of conveying the mixture includes back-mixing the mixture at a location along the length of the extruder;
(iv) introducing a curative into the downstream inlet to thereby introduce the curative into the mixture;
(v) partially curing the EPDM within the mixing and conveying zone to thereby form a partially-cured composition; and
(vi) extruding the partially-cured composition into a partially-cured sheet, where the temperature of the partially-cured composition is between 120° and 160° C. at said step of extruding.
8. The partially-cured EPDM sheet of claim 7 , wherein the temperature of the mixture at any point along a length of the mixing extruder is within +/−5° C. of a desired temperature.
9. The partially-cured EPDM sheet of claim 7 , where the temperature of the mixture at all points on a section plane through the mixing extruder is within +/−5° C. of a desired temperature.
10. The partially-cured EPDM sheet of claim 7 , where said step of conveying the mixture through the mixing and conveying zone is defined by a residence time within the mixing extruder whereby the residence time is the time required for materials to travel between two locations within the mixing extruder, and where said step of conveying is manipulated such that the residence time from the feed throat to the downstream inlet is greater than the residence time from the downstream inlet to the material outlet.
11. The partially-cured EPDM sheet of claim 7 , further comprising the step of calendaring the partially-cured sheet.
12. The partially-cured EPDM sheet of claim 7 , further comprising the step of introducing heat to the partially-cured sheet.