New models for calculation of the permeability of structures
At Norner we continuously strive to improve our services and have been working on development of new features for the barrier calculator for a while.
We have recently added new models for calculation of the permeability of structures containing:
Cavitated and metallised OPP
We have developed separate empirical models for these are based on research results, scientific articles and reference data which again has been integrated into the calculator to enable calculation of these in multilayer structures with plastic materials.
These empiric models come with somewhat less accuracy than the physical models of polymers which you might be used to. The models consider the typical pin holes present in metallised layers and Alu foils which typically are a function of optical density and thickness.
For metallised films, thickness is not a relevant value because it is very thin. This is therefore normally expressed in optical density. This value must be known and inputted for calculation. The metallised layer is basically impenetrable, but it will always be pin holes present where gas transmission can occur. The number of pin holes is correlated to the thickness and therefore to the optical density.
For Aluminium foil, the gas transmission will also take place through pin holes and the number is normally correlated to the thickness. Aluminium foil is rolled to achieve a specific thickness and the rolling will for instance create pin holes at locations or particles with different morphology like grains.
Our models for calculating take into account the typical levels of pinholes of metallised films and aluminium foils as is from the production line. Such materials will however be sensitive to any crimping or stretching of the web during converting, printing and lamination processes as well as the mechanical handling of the final bags and pouches. The pin holes or such cracks formed after production are random and not possible to account for in a standard model.
The barrier calculator makes design and process simulations more efficient in the development phase and the prototyping phase will be more efficient and predictable. Prototypes and samples from upscaling to production should however be tested on reliable OTR, WVTR or CO2TR test instruments.
Norner is testing OTR and WVTR with test instruments from Mocon.