Package wrapping including PLA film with moisture barrier by atomic layer deposition
Provided herein is a moisture barrier film for packaging, such as tobacco or cigarette packaging. The film comprises polylactic acid (“PLA”) that is both biodegradable and transparent. The film includes multiple layers of PLA, with a base layer having a relatively high melting point compared to two outer layers, which have a relatively low melting point. The outer layers provide heat sealing capabilities to the film. The film is coated with a metal oxide layer comprised of aluminum oxide, titanium oxide, and/or aluminum-titanium oxide using an atomic layer deposition (“ALD”) coating method. The ALD coating to the PLA film results in a moisture transmission rate of less than 4 g/m2/day after the film has been subjected to creasing, which induces cracking of the ALD metal oxide layer.
1 . A method of making a film having a moisture barrier coating, the method comprising:
forming a base layer consisting essentially of a first poly(lactic acid) (PLA) or polypropylene material having a first melting point;
forming an outer layer comprising a second material comprising PLA having a second melting point, the second melting point is lower than the first melting point;
a first side of the outer layer bonded to a first side of the base layer;
forming an inner layer comprising the second material, a first side of the inner layer bonded to a second side of the base layer, the second side of the base layer opposite the first side of the base layer; and
coating each of a second side of the outer layer and a second side of the inner layer with a moisture barrier coating comprising a metal-oxide via atomic layer deposition, the second side of the outer layer opposite the first side of the outer layer and the second side of the inner layer opposite the first side of the inner layer, wherein the moisture barrier coating has a thickness in the range of 2-10 nm.
2 . The method of claim 1 , further comprising wrapping the film around a core to form a roll of the film.
3 . The method of claim 1 , wherein the atomic layer deposition process occurs under vacuum.
4 . The method of claim 1 , wherein the base layer and the outer layer are formed through an extrusion process.
5 . The method of claim 1 , wherein the first material is a first polylactic acid material, and the second material is a second polylactic acid material.
6 . The method of claim 5 , wherein at least one of the first polylactic acid material or the second polylactic acid material are corn-based.
7 . The method of claim 1 , wherein the first material is a bio-based polypropylene.
8 . The method of claim 1 , wherein the moisture barrier coating is transparent.
9 . The method of claim 1 , wherein the moisture barrier coating is at least one of an aluminum oxide, a titanium oxide, or an aluminum-titanium oxide.
10 . The method of claim 1 , wherein the film has a moisture transmission rate of less than 4 grams per meter squared per day.
11 . The method of claim 10 , wherein the film has a moisture transmission rate of less than 2 grams per meter squared per day.
12 . The method of claim 1 , wherein the film is between 15 and 30 microns in thickness.