Methods for improving color stability in polyethylene resins
AssigneeChevron Phillips Chemical Comany LP
InventorsJustin Wade Kamplain, Elizabeth Mary Lanier
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Abstract
Polymer compositions containing a titanated chromium-based ethylene polymer, 150-350 ppm of zinc stearate and/or calcium stearate, 50-5000 ppm of a phenolic antioxidant, 200-3000 ppm of a diphosphite antioxidant, and optionally, 200-3000 ppm of a monophosphite antioxidant, are described. These polymer compositions have improved long-term color stability, as well as lower levels of color formation after aging.
Claims20
A process for producing a polymer composition with long-term color stability, the process comprising:
- (a) contacting a chromium-based catalyst system with ethylene and an optional olefin comonomer under polymerization conditions in a polymerization reactor system to produce an ethylene polymer;
- and
- (b) combining the ethylene polymer with an additive system comprising zinc stearate and/or calcium stearate, a phenolic antioxidant, a monophosphite antioxidant, and a diphosphite antioxidant, to form the polymer composition, wherein the polymer composition comprises:
- from about 150 ppm to about 350 ppm of zinc stearate and/or calcium stearate;
- from about 50 ppm to about 5000 ppm of the phenolic antioxidant;
- from about 200 ppm to about 3000 ppm of the monophosphite antioxidant;
- and
- from about 200 ppm to about 3000 ppm of the diphosphite antioxidant;
- wherein the polymer composition has a PE color number of at least 200 after storage for 4 weeks at a temperature of 80° C.;
- and wherein the polymer composition has a Δcolor/Δtime of less than 40.
A method for improving the long-term color stability of a polymer composition, the method comprising:
- combining an ethylene polymer with an additive system comprising zinc stearate and/or calcium stearate, a phenolic antioxidant, a monophosphite antioxidant, and a diphosphite antioxidant, to form the polymer composition, wherein the polymer composition comprises:
- from about 150 ppm to about 350 ppm of zinc stearate and/or calcium stearate;
- from about 50 ppm to about 5000 ppm of the phenolic antioxidant;
- from about 200 ppm to about 3000 ppm of the monophosphite antioxidant;
- and
- from about 200 ppm to about 3000 ppm of the diphosphite antioxidant;
- wherein the polymer composition has a PE color number of at least 200 after storage for 4 weeks at a temperature of 80° C.;
- and wherein the polymer composition has a Δcolor/Δtime of less than 40.
A polymer composition comprising:
- (i) a titanated chromium-based ethylene polymer;
- (ii) from about 150 ppm to about 350 ppm of zinc stearate and/or calcium stearate;
- (iii) from about 50 ppm to about 5000 ppm of a phenolic antioxidant;
- (iv) from about 200 ppm to about 3000 ppm of a monophosphite antioxidant;
- and
- (v) from about 200 ppm to about 3000 ppm of a diphosphite antioxidant;
- wherein the polymer composition has a PE color number of at least 200 after storage for 4 weeks at a temperature of 80° C.;
- and wherein the polymer composition has a Δcolor/Δtime of less than 40.
Dependencies are inferred from the claim text.