Online optical inspection of air permeability of packaging materials during laser perforation

Laser perforations are formed in packaging to control the rate of gas exchange and maintain a balance between the respiration of the product and the permeation of the package. The air permeability of the packaging materials is typically measured using air-driven methods, but these do not allow for online measurement during the rapid production of perforations. The required permeability is generally obtained through trial and error. This paper describes the simulation of air-driven methods through computational fluid dynamics to study the effects of turbulence on the rate of air flow through perforations. A mathematical model is developed to quantify the influence of the microperforated size, the total area of exchange, and the thickness of the material on air permeability under certain temperature and pressure differences. The numerical results are in good agreement with the experimental results. An optical system based on the model is designed for the online inspection of packaging materials during the rapid production of laser perforations. Air permeability is precisely determined by analyzing continuous images of the perforations. Perforation characteristics such as shape, quantity, and density can also be measured to allow for feedback control of the perforation process according to the features of the packaged products. The validity and accuracy of the developed system are experimentally verified.