No abstract

The heat-seal performance of a flexible plastic package depends on the sealing bar temperature, packaging line speed, film thickness and properties of the sealant resin. For a given sealant, thinner films reach their maximum seal strength at lower bar temperatures and faster line speeds than thicker films. A model is developed that relates these factors to the amount of molecular penetration that develops at the heat-seal interface of ionomer films. A critical value of the penetration is found that corresponds to the ultimate heatseal strength in laboratory heat-seal data. The results point to how laboratory data may be used to predict the sealing performance of ionomers on high-speed packaging lines.

Excessive pressure and temperature during hot bar sealing of flexible packaging films can result in seal failure due to squeezing out of the sealant from the seal area. A model is developed that shows the amount of squeeze-out increases with increasing seal bar pressure, seal temperature (by lowering the viscosity of the sealant), sealing dwell time, film thickness, and decreasing seal bar width. Validation experiments qualitatively agree with the model predictions. Both the model and experimental results show that the rheology of the sealant plays a significant role in preventing squeeze-out; high viscosity at low shear rates favor less squeeze-out. The work shows that under normal sealing conditions, squeeze-out is not substantial. Avoiding excessive temperature or pressure is critical to minimizing squeeze out to ensure good sealing performance.