Influence of pore spacing in barrier coatings on the mass transport through plastics—a simulative and experimental approach

Abstract

In many applications, the use of plastics is only made possible by functionalizing them with coatings for barrier against gases or flavors. These coatings are often produced in low-pressure processes such as plasma enhanced chemical vapor deposition or physical vapor deposition processes. Mass transport through these systems takes place mainly through pores in the nano- and micrometer range. A lot of research has been done to describe the mechanisms of permeation through these thin films under consideration of pores and their influence to each other on the permeation. Until now, all investigations to describe the influence of neighboring pores have been mathematical or simulative. In this work the barrier coating is substituted by a stainless steel foils with 10 000 micro pores (d = 1.5 µm) at different spacings. The micro drillings by means of ultrashort lasers proved to be extremely reproducible and well suited for the application. Real transmission rates are compared and correlated with simulated data to gain a better understanding of the permeation processes. The comparison shows a good agreement of the data regarding the curve progression but most simulation models underestimate the influence of adjacent pores. Real measurements of oxygen transmission through polyethylene terephthalate with porous barrier coatings show an influence up to a pore spacing of 100 µm or 133 times the pore radius, which results in a 66%–100% larger spacings than stated in other simulations in literature.