High stiffness high impact propylene impact copolymers
View Patent ↗The present invention relates to polypropylene impact copolymer compositions which exhibit improved stiffness without degrading the impact resistance performance. The polypropylene impact copolymer comprises a matrix and a dispersed phase. The matrix comprises a polypropylene homopolymer or a propylene/alpha-olefin random copolymer which comprises more than 50 wt. % of units derived from propylene monomer. The matrix should have a relatively high crystallinity, preferably 50% or greater. The polypropylene homopolymer or a propylene/alpha-olefin random copolymer preferably has a MWD between 4 and 8, such as typically obtained using Ziegler-Natta catalysts. The dispersed phase in the impact copolymer comprises an ethylene-propylene copolymer which comprises from 45 to 70 wt. % of units derived from an ethylene monomer. Preferably the dispersed phase comprises from 20 to 50 percent by weight of the polypropylene impact copolymer.
1. A polypropylene impact copolymer comprising:
(a) a matrix comprising a polypropylene homopolymer or a propylene/alpha-olefin random copolymer which comprises more than 50 wt. % of units derived from propylene monomer, the polypropylene homopolymer or a propylene/alpha-olefin random copolymer having an MWD between 4 and 8; wherein said matrix has a crystallinity of at least 50%;
(b) a dispersed phase comprising an ethylene-propylene copolymer which comprises from 45 to 70 wt. % of units derived from an ethylene monomer;
wherein the dispersed phase comprises from 20 to 50 percent by weight of the polypropylene impact copolymer;
wherein the alpha-olefin of the propylene/alpha-olefin random copolymer is selected from the group consisting of ethylene, butene, 1-hexene and 1-octene; and
wherein the overall alpha-olefin content of the impact copolymer is in the range of from about 10% to about 35% by weight.
2. The propylene impact copolymer of claim 1 wherein the dispersed phase comprises from 30 to 40 percent by weight of the polypropylene impact copolymer.
3. The propylene impact copolymer of claim 1 wherein the matrix comprises a polypropylene homopolymer.
4. The propylene impact copolymer of claim 1 wherein the matrix has an MWD between 4 and 6.
5. The propylene impact copolymer of claim 1 wherein the matrix is a propylene/alpha-olefin random copolymer which comprises more than 90 wt. % of units derived from propylene monomer.
6. The propylene impact copolymer of claim 1 wherein the matrix is a propylene/alpha-olefin random copolymer in which the alpha-olefin is ethylene.
7. The propylene impact copolymer of claim 1 wherein the matrix has a crystallinity greater than 60%.
8. The propylene impact copolymer of claim 1 wherein the dispersed polymer comprises at least 50 wt. % of ethylene.
9. The propylene impact copolymer of claim 1 having a melt flow rate of from 1 to 50 g/10 min (230° C./2.16 kg).
10. The propylene impact copolymer of claim 1 which has been vis-broken and the vis-breaking ratio is greater than or equal to 2.
11. The propylene impact copolymer of claim 10 in which the vis-breaking ratio is greater than or equal to 4.