Methods for improving color stability in polyethylene resins
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.
1. A polymer composition comprising:
a titanated chromium-based ethylene polymer comprising an ethylene homopolymer and/or an ethylene/α-olefin copolymer;
(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; and
(iv) from about 200 ppm to about 3000 ppm of a diphosphite antioxidant; and
wherein the polymer composition has a Δcolor/Δtime of less than 45.
2. An article of manufacture comprising the polymer composition of claim 1 .
3. The composition of claim 1 , wherein the polymer composition contains:
from about 150 ppm to about 300 ppm of zinc stearate and/or calcium stearate;
from about 200 ppm to about 2500 ppm of the phenolic antioxidant; and
from about 750 ppm to about 3000 ppm of the diphosphite antioxidant; and
wherein the Δcolor/Δtime is less than 40.
4. The composition of claim 3 , wherein:
the polymer composition is in the form of pellets; and
the polymer composition further comprises at least one other additive selected from an antiblock additive, a slip additive, a colorant, a filler, a UV additive, or any combination thereof.
5. The composition of claim 3 , wherein:
the Δcolor/Δtime is less than 35; and
the polymer composition has a PE color number of at least 200 after storage for 4 weeks at a temperature of 80° C.
6. The composition of claim 1 , wherein the ethylene polymer comprises the ethylene homopolymer, an ethylene/1-butene copolymer, an ethylene/1-hexene copolymer, and/or an ethylene/1-octene copolymer.
7. The composition of claim 6 , wherein the ethylene polymer is characterized by:
a density in a range from about 0.92 to about 0.96 g/cm 3 ;
a Mw in a range from about 150,000 to about 750,000 g/mol;
a ratio of Mw/Mn in a range from about 5 to about 40;
a melt index (MI) in a range from 0 to about 0.5 g/10 min; and
a high load melt index (HLMI) in a range from about 0.5 to about 25 g/10 min.
8. The composition of claim 6 , wherein the ethylene polymer contains:
less than 0.2 ppm of zirconium;
less than 0.2 ppm of hafnium; and
less than 5 ppm of magnesium.
9. The composition of claim 6 , wherein the ethylene polymer contains:
from about 0.5 to about 15 ppm of chromium; and
from about 0.5 to about 15 ppm of titanium.
10. The composition of claim 6 , wherein:
the polymer composition comprises calcium stearate; and
the Δcolor/Δtime is less than 40.
11. The composition of claim 6 , wherein:
the polymer composition comprises zinc stearate; and
the Δcolor/Δtime is less than 40.
12. A polymer composition comprising:
(i) a titanated chromium-based ethylene polymer comprising an ethylene homopolymer and/or an ethylene/α-olefin copolymer;
(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; and
wherein the polymer composition has a Δcolor/Δtime of less than 45.
13. An article of manufacture comprising the polymer composition of claim 12 .
14. The composition of claim 12 , wherein the polymer composition contains:
from about 150 ppm to about 300 ppm of zinc stearate and/or calcium stearate;
from about 200 ppm to about 2500 ppm of the phenolic antioxidant;
from about 500 ppm to about 2000 ppm of the monophosphite antioxidant; and
from about 750 ppm to about 3000 ppm of the diphosphite antioxidant; and
wherein the Δcolor/Δtime is less than 40.
15. The composition of claim 14 , wherein:
the polymer composition is in the form of pellets; and
the polymer composition further comprises at least one other additive selected from an antiblock additive, a slip additive, a colorant, a filler, a UV additive, or any combination thereof.
16. The composition of claim 14 , wherein:
the Δcolor/Δtime is less than 35; and
the polymer composition has a PE color number of at least 200 after storage for 4 weeks at a temperature of 80° C.
17. The composition of claim 12 , wherein the ethylene polymer comprises the ethylene homopolymer, an ethylene/1-butene copolymer, an ethylene/1-hexene copolymer, and/or an ethylene/1-octene copolymer.
18. The composition of claim 17 , wherein the ethylene polymer is characterized by:
a density in a range from about 0.92 to about 0.96 g/cm 3 ;
a Mw in a range from about 150,000 to about 750,000 g/mol;
a ratio of Mw/Mn in a range from about 5 to about 40;
a melt index (MI) in a range from 0 to about 0.5 g/10 min; and
a high load melt index (HLMI) in a range from about 0.5 to about 25 g/10 min.
19. The composition of claim 17 , wherein the ethylene polymer contains:
less than 0.2 ppm of zirconium;
less than 0.2 ppm of hafnium; and
less than 5 ppm of magnesium.
20. The composition of claim 17 , wherein the ethylene polymer contains:
from about 0.5 to about 15 ppm of chromium; and
from about 0.5 to about 15 ppm of titanium.
21. The composition of claim 17 , wherein:
the polymer composition comprises calcium stearate; and
the Δcolor/Δtime is less than 40.
22. The composition of claim 17 , wherein:
the polymer composition comprises zinc stearate; and
the Δcolor/Δtime is less than 40.