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PVOH COATED POLYESTER BARRIER FILMS G. Met-ton Cumberbatch Packaging & Industrial Polymers Chestnut Run Plaza Robert R. Reitz Polyester Films Experimental Station DuPont Co., Inc. Wilmington, Delaware 19898 Polyvinyl alcohol (PVOH) coated polyester films are excellent barrier films for packaging applications at low to moderate humidity conditions. They are a viable, non-chlorine containing alternative for PVDC coated films in many applications. When metallised with aluminum, this film exhibits oxygen barrier at least 5 times better than conventional metallised uncoated polyester; with improvements also in metal adhesion and flex crack resistance. PVOH coated PET is not heat sealable, and must thus be combined with a sealant layer; such as polyolefins. The PVOH surface is printable with non aqueous inks. INTRODUCTION In some countries, the use of chlorine containing films is becoming environmentally unacceptable. This has encouraged the development of alternative materials. DuPont now offers a PVOH coated polyester film, which can be substituted for PVDC coated polyester in many applications. The PVOH is inherently a polymeric barrier to gas permeation. It is moisture sensitive, but combination with a heat sealable layer provides moisture protection. PROPERTIES Films Polyester (PET) film with thin coatings of PVOH has excellent optical properties, Table 1. Barrier properties are given in Table 2. Oxygen Transmission Rate (OTR) is quite low compared to uncoated PET or even commercially available PVDC coated PET. Moisture Vapor Transmission Rates (MVTR), however, are much like uncoated PET due to PVOH’s moisture sensitivity. Oxygen permeation rate is sensitive to relative humidity (RI-I). This detail is shown in Figure 1 which plots OTR as RH increases. Figure 2 shows a similar plot but compared to PVDC coated film. PVDC is generally not sensitive to humidity change, but importantly, this plot shows that at 70% RI-I the oxygen barrier of PVOH coated film is better than PVDC coated film, and at 50% RH the improvement is almost two orders of magnitude. 913
