Single polymer film structures for use in stand-up-pouches
The present invention relates to film structure suitable for use in stand up pouches comprising all polyethylene material. The film structure can be a monolayer film or a multilayer film structure having specific requirements for each layer. The combination results in a film structure having adequate stiffness to function as a stand-up pouch while also providing acceptable water vapor transmission rates and good tear resistance. Such films have improved sustainability characteristics as they should permit down-gauging of the films and, can more easily be recycled, at least for the preferred embodiment comprising only polyethylene resins.
1. A laminated film structure suitable for use in stand up pouches comprising:
a) a first film comprising:
i) at least one surface layer (A) comprising from 70 to 100 percent by weight of the layer (A) of a linear low density polyethylene having a density from 0.89 to 0.91 g/cm 3 and a melt index of less than 1.3 dg/min, and a peak melting point in the range of from 85° C. to 100° C., and a molecular weight distribution, Mw/Mn, in the range of from 2.0 to 3.0; and
ii) at least one additional layer (B) comprising from 70 to 100 percent by weight of the layer (B) of a first multimodal polyethylene polymer having a multimodal distribution in terms of molecular weight, wherein said first multimodal polyethylene comprises units derived from ethylene and at least one C 3 -C 10 alpha-olefin, and wherein the first multimodal polyethylene polymer has a density in the range of from 0.950 to 0.965 g/cm 3 , a melt index in the range of from 0.8 to 1.2 dg/min, a peak melting point in the range of from 120° C. to 135° C. as measured by a differential scanning calorimeter, and a molecular weight distribution, Mw/Mn ratio greater than 5.0;
b) at least a second film comprising:
i) a first surface layer (C) comprising from 60 to 100 percent by weight of the layer (C) of a second multimodal polyethylene polymer having a multimodal distribution in terms of molecular weight, wherein said second multimodal polyethylene comprises units derived from ethylene and at least one C 3 -C 10 alpha-olefin, and wherein the second multimodal polyethylene polymer has a density in the range of from 0.910 to 0.930 g/cm 3 , a melt index in the range of from 0.8 to 1.2 dg/min, a peak melting point in the range of from 110° C. to 130° C., and a molecular weight distribution, Mw/Mn ratio in the range of from 3.0 to 4.0;
ii) at least one core layer (D) comprising from 70 to 100 percent by weight of the layer (D) of a third multimodal polyethylene polymer having a multimodal distribution in terms of molecular weight, wherein said first multimodal polyethylene comprises units derived from ethylene and at least one C 3 -C 10 alpha-olefin, and wherein the first multimodal polyethylene polymer has a density in the range of from 0.950 to 0.965 g/cm 3 , a melt index in the range of from 0.8 to 1.2 dg/min, a peak melting point in the range of from 120° C. to 135° C. as measured by a differential scanning calorimeter, and a molecular weight distribution, Mw/Mn ratio greater than 5.0; and
iii) a second surface layer (E) comprising from 60 to 100 percent by weight of the layer (E) of a copolymer comprising units derived from ethylene and at least one alpha-olefin in the range of C 3 -C 10 wherein said copolymer has a density from 0.91 to 0.93 g/cm 3 , a melt index in the range of from 0.8 to 1.2 dg/min, a peak melting point in the range of from 110° C. to 130° C. and a molecular weight distribution, Mw/Mn ratio in the range of from 3.0 to 4.5;
wherein the first film is laminated to the second film such that the additional layer (B) of the first film is adjacent to the first surface layer (C) of the second film; and
wherein the laminated film structure is characterized by the substantial absence of polymers other than polyethylene homopolymers and copolymers.
2. The laminated film structure of claim 1 wherein the surface layer (A) is further characterized as having a heat seal strength of at least 34 N/25 mm at 90° C.
3. The laminated film structure of claim 1 wherein the first multimodal polyethylene and the third multimodal polyethylene are the same material.
4. The laminated film structure of claim 1 wherein the first film has a thickness of 60 microns or less and is characterized by having a water vapor transmission rate (WVTR) of less than 2.5 g·60 μm/m 2 ·day based on ASTM E 96/E 96 M-05 and a dart impact of 140 g or more, based on ASTM D 1709 method A.
5. The laminated film structure of claim 1 wherein the second film has a thickness of 60 microns or less, and is characterized by having a WVTR of less than 3.5 g·60 μm/m 2 ·day based on ASTM E 96/E 96 M-05 and a dart impact of 245 g or more, based on ASTM D 1709 method A.
6. The laminated film structure of claim 1 wherein the overall film structure has a thickness of 120 microns or less and is characterized by having a WVTR of less than 1.5 g·120 μm/m 2 ·day based on ASTM E 96/E 96 M-05 and a dart impact of 300 g or more, based on ASTM D 1709 method A.
7. The laminated film structure of claim 1 wherein the surface layer (A) of the first film has a thickness range of from 10 to 15 microns.