METHODS FOR INCREASING THE COLOR STABILITY OF POLYETHYLENE RESINS Russian patent published in 2022 - IPC C08L23/04 C08K5/98 C08K5/13 C08K5/51 

FIELD: polymer compositions.

SUBSTANCE: inventions relates to a polymer composition having improved long-term color fastness or lower levels of discoloration upon aging, as well as methods for improving long-term color fastness or reducing discoloration upon aging of a polymer composition. The method for obtaining a polymer composition with long-term color fastness includes the following steps: (a) contacting the 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 containing zinc stearate and/or calcium stearate, a phenolic antioxidant and a diphosphite antioxidant, a monophosphite antioxidant, to form a polymer composition comprising: from 150 ppm by weight to 350 ppm by weight of zinc stearate and/or calcium stearate; from 50 hours/million by weight to 5000 hours/million by weight of the phenolic antioxidant; from 200 ppm by weight to 3000 ppm by weight diphosphite antioxidant, from about 200 ppm by weight to about 3000 ppm by weight of monophosphite antioxidant. The mass ratio of diphosphite antioxidant and monophosphite antioxidant in the polymer composition varies in the range from 5:1 to 1:5. At the same time, the method for improving the long-term color stability of the polymer composition includes the steps of combining an ethylene polymer with an additive system containing zinc stearate and/or calcium stearate, a phenolic antioxidant and a diphosphite antioxidant, a monophosphite antioxidant, to form a polymer composition. Also described are industrial products containing a polymer composition with long-term color fastness.

EFFECT: resulting polymer composition has a PE color index of at least 200 after storage for 4 weeks at 80°C.

15 cl, 1 tbl, 5 dwg, 6 ex