Bemis Company, Inc.,
Keywords: fluorophosphate, Glass, Tg, Barrier, Multilayer, Packaging
Summary:Current food and pharmaceutical product packaging frequently comprise complex layered assemblies of different polymeric materials that are selected to maintain the microbiological, organoleptic and compositional qualities of the packaged contents. To preserve product safety and efficacy, it is common to dedicate multilayer sub-assemblies to limiting the diffusion rates of small molecules like oxygen and water through the package wall. Polymers with low permeability to specific molecules are often favored for industrial production because of the ability to easily melt and shape the materials through established extrusion processes. However, the most demanding applications rely upon inorganic materials with extremely low free volume to control diffusion. Techniques such as chemical vapor deposition and atomic layer deposition enable the creation of organic/inorganic composites, but several manufacturing steps are needed to convert the coated structures into a package, and the ability to use those techniques for creating complex geometries is limited. To address these shortcomings, a family of low Tg (80-150 °C) fluorophosphate glasses with rheologically similar melt behavior to commercial polymer resins was designed. Polymer/glass layered composites having outstanding diffusion barrier were produced with conventional thermoplastic processing equipment, e.g. extrusion and injection molding. Thin film coextrusions that alternated sub-micron-thick glass and thermoplastic polymer layers displayed good layer continuity and thickness uniformity. Additionally, the glass layers showed exceptional resiliency, as no damage was apparent following bending at radii as small as 3 mm. Similarly, multilayer injection molded articles made with a single, discrete glass layer yielded excellent glass and thermoplastic polymer layer distribution while delivering a water vapor transmission rate of 9·10-3 g/(m2·d) @ 38°C and 90% RH. The ability to leverage the scale and design flexibility of thermoplastic extrusion processes for the production of glass/polymer composites offers a new set of possibilities for barrier product design for food, pharmaceutical and electronics packaging.