Preparation of multimodal, high density, ethylene homopolymer barrier resins and films
View Patent ↗Disclosed is a multimodal, high density, homopolyethylene barrier resin. The resin is preferably made by a multistage process. The process comprises a first stage in which ethylene is homopolymerized in the presence of a Ziegler-Natta catalyst, organoaluminum cocatalyst, alkoxysilane modifier, and hydrogen. The reaction mixture from the first stage is devolatilized to remove all or substantially all of the hydrogen. The polymerization continues in a second stage wherein ethylene is added to the devolatilized reaction mixture to produce the barrier resin. The barrier resin provides films with improved barrier properties.
1. A multimodal, high density, homopolyethylene barrier resin having a density greater than or equal to 0.955 g/cm 3 , an melt index MI 2 less than or equal to 2.5 dg/min, and a melt flow ratio MFR less than or equal to 50; said barrier resin providing a film with a water vapor transmission rate less than 0.4 g-mil/100 in 2 /day, wherein the barrier resin is made by a process comprising (a) polymerizing ethylene in the presence of a Ziegler-Natta catalyst selected from the group consisting of titanium halides, titanium alkoxides, vanadium halides, and mixtures thereof, an organoaluminum cocatalyst, hydrogen, and an alkoxysilane modifier in a hydrogen to ethylene molar ratio in vapor space within the range of 1 to 6, to produce a homopolyethylene having a density greater than or equal to 0.96 g/cm 3 and a melt index MI 2 greater than or equal to 5 dg/min; (b) devolatilizing the reaction mixture to remove hydrogen; and (c) continuing the polymerization by adding ethylene and hydrogen to the devolatilized reaction mixture in a hydrogen to ethylene molar ratio in vapor space less than or equal to 0.8 to form the barrier resin.
2. The barrier resin of claim 1 , having an MI 2 less than or equal to 1 dg/min.
3. The barrier resin of claim 1 , having a density within the range of 0.955 g/cm 3 to 0.960 g/cm 3 .
4. The barrier resin of claim 1 , having an MI 2 less than or equal to 1.5 dg/min.
5. The barrier resin of claim 1 , wherein step (a) is performed in the presence of an antistatic agent.
6. The barrier resin of claim 1 , wherein the alkoxysilane has the general formula R 4-y Si(OR) y where y is 2 or 3 and R is independently an alkyl or cycloalkyl group.
7. The barrier resin of claim 6 , wherein the alkoxysilane is selected from the group consisting of cyclohexylmethyldimethoxysilane, methyltriethoxysilane, and mixtures thereof.
8. The barrier resin of claim 7 , wherein the alkoxysilane is cyclohexylmethyldimethoxysilane.
9. The barrier resin of claim 1 , comprising from 40 wt % to 60 wt % of the homopolyethylene made in step (a).
10. The barrier resin of claim 1 , wherein the homopolyethylene made in step (a) has a melt index MI 2 within the range of 5 dg/min to 200 dg/min.
11. The barrier resin of claim 1 , wherein steps (a) to (b) are performed in slurry phase.
12. A film made from the barrier resin of claim 1 .
13. The film of claim 12 having a water vapor transmission rate less than 0.4 g-mil/100 in 2 /day.
14. A multilayer film comprising a layer of the film of claim 12 .