High shrink polyethylene films
View Patent ↗A homogeneous blend of a low density polyethylene with a metallocene-catalysed polyethylene having a density of from 0.906 g/cm 3 and a Dow Rheology Index of at least 5/MI 2 ,MI 2 being the melt index measured according to ASTMD-1238 condition 190° C./2.16 kg and the Dow Rheology Index being determined by a dynamic rheological analysis performed at 190°.
1. A polyethylene composition comprising a homogenous blend of a low density polyethylene with a metallocene-catalyzed polyethylene having a density of at least 0.906 g/cm 3 and a Dow Rheology Index of at least 5/MI 2 , wherein MI 2 is the melt index measured according to ASTMD-1238 condition 190° C./2.16 kg and the Dow Rheology Index being determined by a dynamic rheological analysis performed at 190°, said metallocene-catalyzed polyethylene being catalyzed with a catalyst system comprising a metallocene component and an activating agent selected from the group consisting of an alumoxane or an aluminum alkyl providing a mole ratio of aluminum to the transition metal of said metallocene component within the range of 50:1-300:1.
2. The composition of claim 1 wherein the metallocene-catalyzed polyethylene has a Dow Rheology Index of at least 10/MI 2 .
3. The composition of claim 1 wherein the metallocene-catalyzed polyethylene has a Dow Rheology Index of at least 20/MI 2 .
4. The composition of claim 1 wherein the metallocene-catalyzed polyethylene has a density of from 0.925 g/cm 3 to less than 0.965 g/cm 3 .
5. The composition of claim 4 wherein the metallocene-catalyzed polyethylene has a Dow Rheology Index of at least 10/MI 2 .
6. The composition of claim 4 wherein the metallocene-catalyzed polyethylene has a Dow Rheology Index of at least 20/MI 2 .
7. The composition of claim 1 wherein the metallocene-catalyzed polyethylene has a density of from 0.906 g/cm 3 to less than 0.925 g/cm 3 .
8. The composition of claim 7 wherein the metallocene-catalyzed polyethylene has a Dow Rheology Index of at least 10/MI 2 .
9. The composition of claim 7 wherein the metallocene-catalyzed polyethylene has a Dow Rheology Index of at least 20/M 2 .
10. A blown film comprising at least one layer formed of a polyethylene composition comprising a homogenous blend of a low density polyethylene with a metallocene-catalyzed polyethylene having a density of at least 0.906 g/cm 3 and a Dow Rheology Index of at least 5/MI 2 , wherein MI 2 is the melt index measured according to ASTMD-1238 condition 190° C./2.16 kg and the Dow Rheology Index being determined by a dynamic rheological analysis performed at 190°, said metallocene-catalyzed polyethylene being catalyzed with a catalyst system comprising a metallocene component and an activating agent selected from the group consisting of an alumoxane or an aluminum alkyl providing a mole ratio of aluminum to the transition metal of said metallocene component within the range of 50:1-300:1.
11. The film of claim 10 wherein said layer is a monolayer blown film.
12. The film of claim 10 wherein said layer comprises at least one layer of a multilayer blown film.
13. A process for the preparation of a blown film, forming said film in a blown film line from a polyethylene composition comprising a homogenous blend of a low density polyethylene with a metallocene-catalyzed polyethylene having a density of at least 0.906 g/cm 3 and a Dow Rheology Index of at least 5/MI 2 , wherein MI 2 is the melt index measured according to ASTMD-1238 condition 190° C./2.16 kg and the Dow Rheology Index being determined by a dynamic rheological analysis performed at 190°, said metallocene-catalyzed polyethylene being catalyzed with a catalyst system comprising a metallocene component and an activating agent selected from the group consisting of an alumoxane or an aluminum alkyl providing a mole ratio of aluminum to the transition metal of said metallocene component within the range of 50:1-300:1, said film being characterized by:
a cohesion force in the transverse direction at room temperature of at least 5% greater than the cohesion force in the transverse direction of a corresponding biaxially-oriented film formed of said low density polyethylene in a pure form; and
a gloss at an angle of 45° of at least 60 and a haze of less than 10% while keeping a good rigidity.
14. A biaxially-oriented film which has been oriented in the machine direction and the transverse direction, formed from a homogenous blend of a polyethylene composition comprising a homogenous blend of a low density polyethylene with a metallocene-catalyzed polyethylene having a density of at least 0.906 g/cm 3 and a Dow Rheology Index of at least 5/MI 2 , wherein MI 2 is the melt index measured according to ASTMD-1238 condition 190° C./2.16 kg and the Dow Rheology Index being determined by a dynamic rheological analysis performed at 190°, said metallocene-catalyzed polyethylene being catalyzed with a catalyst system comprising a metallocene component and an activating agent selected from the group consisting of an alumoxane or an aluminum alkyl providing a mole ratio of aluminum to the transition metal of said metallocene component within the range of 50:1-300:1, said film having a cohesion force in the transverse direction which is greater than the cohesion force in the transverse direction of a corresponding biaxially-oriented film formed of said low density polyethylene in a pure form.
15. The biaxially-oriented film of claim 14 , wherein said film has a cohesion force in the machine direction which is greater than the cohesion force in the machine direction of the corresponding film formed of said low density polyethylene in a pure form.
16. The film of claim 15 , having a gloss at an angle of 45° of at least 60, and a haze which is less than 10%.
17. A blown film comprising at least one layer of the polyethylene composition of claim 4 .
18. The blown film of claim 17 wherein the metallocene catalyzed polyethylene has Dow Rheology Index of at least 10/MI 2 .
19. A biaxially oriented film which has been oriented in the machine direction and the transverse direction, formed from the polyethylene composition of claim 4 wherein said film has a cohesion force in the transverse direction which is greater than the cohesion force in the transverse direction of a corresponding biaxially-oriented film formed of said low density polyethylene in a pure form.
20. THe biaxially-oriented film of calim 19 , wherein said film has a cohesion force in the machine direction which is greater than the cohesion force in the machine direction of the corresponding film formed of said low density polyethylene in a pure form.