MDO multilayer polyethylene film
View Patent ↗A multilayer film and a method of making the film are disclosed. In the method a multilayer film is post-oriented uniaxially in the machine direction resulting in a film that has a water vapor transmission rate of less than 2.5 g-mil/m 2 -day and an oxygen transmission rate of less than 1.5 cm 2 -mil/m 2 -day. The film of this invention is ideal for applications requiring low water vapor and oxygen transmission rates.
1. A multilayer film comprising:
(a) an ethylene-vinyl alcohol copolymer (EVOH) layer having a first surface and a second surface,
(b) a first tie-layer adhesive bonded to the first surface and a second tie-layer adhesive bonded to the second surface of the EVOH layer,
(c) at least one high density polyethylene (HDPE) layer bonded to the first tie-layer and at least one polyethylene layer selected from the group consisting of linear low density polyethylene (LLDPE) and high density polyethylene (HDPE) bonded to the second tie-layer,
wherein the multilayer film is post-oriented uniaxially in the machine-direction with a draw down ratio of greater than about 5 and wherein the post-oriented film has a water vapor transmission rate less than about 3.5 g-mil/m 2 -day and an oxygen transmission rate of less than about 2.5 cm 2 -mil/m 2 -day.
2. The multilayer film of claim 1 wherein the HDPE is prepared with a Ziegler catalyst.
3. The multilayer film of claim 1 wherein the HDPE is prepared with a single-site catalyst.
4. The multilayer film of claim 1 wherein the HDPE is multimodal.
5. The multilayer film of claim 1 wherein the drawdown ratio is greater than about 6.
6. The multilayer film of claim 1 wherein the water vapor transmission rate is less than about 3.0 g-mil/m 2 -day and the oxygen transmission rate is less than about 2.0 cm 2 -mil/m 2 -day.
7. The multilayer film of claim 1 wherein the water vapor transmission rate is less than about 2.5 g-mil/m 2 -day and an oxygen transmission rate of less than about 1.5 cm 2 -mil/m 2 -day.
8. The multilayer film of claim 1 wherein the first and second tie layers are a maleic anhydride grafted polyolefin.
9. The multilayer film of claim 1 wherein the post-oriented film has a thickness within the range of about 0.75 to about 1.5 mil.
10. The multilayer film of claim 1 wherein the film is seven-layers comprising the following layers, in order, as follows: LLDPE/HDPE/tie-layer/EVOH/tie-layer/HDPE/LLDPE.
11. The multilayer film of claim 10 wherein the thickness of each individual layer as a percentage of total film thickness before the machine direction orientation is about 15% LLDPE/20% HDPE/5% tie-layer/20% EVOH/5% tie-layer/20% HDPE/15% LLDPE.
12. The multilayer film of claim 10 wherein the HDPE layers have a density, the same or different, within the range of about 0.945 to about 0.970 g/cm 3 and the LLDPE layers have a density, the same or different, of about 0.865 to about 0.925 g/cm 3 .
13. A method of modifying a multilayer film comprising post-orienting the film uniaxially in the machine-direction with a drawdown ratio greater than about 5, wherein the resulted post-oriented film has a water vapor transmission rate of less than about 3.5 g-mil/m 2 -day and an oxygen transmission rate of less than about 2.5 cm 2 -mil/m 2 -day.
14. The method of claim 13 wherein the multilayer film is seven layers comprising the following layers, in order, as follows: LLDPE/HDPE/tie-layer/EVOH/tie-layer/HDPE/LLDPE.
15. The method of claim 14 wherein the water vapor transmission rate is less than about 3.0 g-mil/m 2 -day and the oxygen transmission rate is less than about 2.0 cm 2 -mil/m 2 -day.
16. The method of claim 14 wherein the water vapor transmission rate is less than about 2.5 g-mil/m 2 -day and the oxygen transmission rate is less than about 1.5 cm 2 -mil/m 2 -day.
17. The method of claim 14 wherein the drawdown ratio is greater than about 6.
18. The method of claim 14 wherein the drawdown ratio is greater than about 7.