PVOH COATED POLYESTER BARRIER FILMS
G. Met-ton CumberbatchPackaging & Industrial Polymers
Chestnut Run Plaza
Robert R. ReitzPolyester Films
Experimental Station
DuPont Co., Inc.Wilmington, Delaware 19898
Polyvinyl alcohol (PVOH) coated polyester films are excellent barrier films for packaging applications at low tomoderate humidity conditions. They are a viable, non-chlorine containing alternative for PVDC coated films inmany applications. When metallised with aluminum, this film exhibits oxygen barrier at least 5 times better thanconventional 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. ThePVOH surface is printable with non aqueous inks.
INTRODUCTION
In some countries, the use of chlorine containing films is becoming environmentally unacceptable. This hasencouraged the development of alternative materials. DuPont now offers a PVOH coated polyester film, which canbe 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 heatsealable layer provides moisture protection.
PROPERTIES
Films
Polyester (PET) film with thin coatings of PVOH has excellent optical properties, Table 1. Barrier properties aregiven in Table 2. Oxygen Transmission Rate (OTR) is quite low compared to uncoated PET or even commerciallyavailable PVDC coated PET. Moisture Vapor Transmission Rates (MVTR), however, are much like uncoated PETdue to PVOH’s moisture sensitivity. Oxygen permeation rate is sensitive to relative humidity (RI-I). This detail isshown in Figure 1 which plots OTR as RH increases. Figure 2 shows a similar plot but compared to PVDC coatedfilm. PVDC is generally not sensitive to humidity change, but importantly, this plot shows that at 70% RI-I theoxygen barrier of PVOH coated film is better than PVDC coated film, and at 50% RH the improvement is almosttwo orders of magnitude.
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