Permeation through defects in transparent barrier-coated plastic films

摘要

Transparent barrier coatings may decrease permeation of gases through polymeric materials by several orders of magnitude. We have shown earlier that permeation of gases through silica-coated plastic films is a defect-controlled phenomenon. The number density, sizes and shapes of defects, along with thickness of the plastic substrate film, are important parameters that determine permeation through single-side coated films. Transparent barrier coatings show many advantages over conventional permeation barriers (such as PVDC- or EVOH-containing laminates, or aluminized films); namely, they are fully recyclable, microwave-compatible, sterilizable, insensitive to humidity, chemically inert, impermeable to plastic additives, and they are deposited in a solvent-free, environmentally friendly process. For large-scale food packaging applications, barrier-coated films are typically laminated to other plastic materials to provide necessary mechanical properties, sealability, etc., as well as to protect ultrathin (tens of nanometers) ceramic coatings from mechanical damage. Transparent barrier coatings may also be used in flexible (foldable) flat panel displays, as encapsulating materials. Multilayer barrier coatings are often deposited on plastic substrate films for this application, where extremely low OTR and WVTR values are required. Also in this case, single- or multilayer coatings may be used in combination with a few layers of polymeric films, such as "smoothing layers" or "protective topcoats" etc. In this paper, we describe a method of permeation evaluation through multilayer structures comprising one or more barrier coatings with defect-controlled permeation. Using our simple model for gas permeation through transparent barrier coatings, presented earlier, we show why double-side coated films display nearly the same barrier improvement factor (BIF) as their single-side coated counterparts. We also describe permeation calculations through very thick coated substrates, where low BIF values may be expected, in principle. Brief discussions on defect-, material-, and porosity-controlled permeation are also presented.