Observing the effect of pressure and temperature on the seal integrity of critical seal regions of various flexible bag designs

Abstract

Folding geometry and the design of a flexible package cause pressure differences along sealing region during heat sealing. These differences might be one of the main reasons behind microchannels and leak formation at the seal area making it difficult to create hermetic packaging. In this article, the influence of changing pressure at different critical sealing regions such as folded corners, layer jumps, and seal intersections was examined via seal characterization methods and image analysis of the cross-section. According to the results, at the 2 layers folded corners pressure and temperature combinations above 2 bar and 130ºC do not cause insufficient sealing. However, at the layer jump points of 3 layers (lap seal) regions and 4 layers (gusset) regions, gaps inside the seal interphase persists at low temperature and low-pressure combinations below 140ºC and 4 bar. Additionally, when the temperature and pressure combination exceeds 160ºC and 4 bars some seal damages and squeeze-out problem is clearly observed in this seal regions. The optimum levels of temperature and pressure to minimize the interphase gap are different at each critical seal region for BOPP/metBOPET/CPP based multilayer packaging. Pressure increase positively influences the integrity of the seal for mentioned critical regions. However, it is discovered that above 150ºC, high-pressure levels (4–5 bars and higher) create a transition in the sealing characteristic from peel seal to lock seal. Additionally, squeeze out of the sealant polymer starts to occur at 3 bars for 150ºC sealing temperature. Squeeze-out problems can increase due to changing pressure distribution along the layer jumps and cause wrinkles as confirmed via visual observation of the sample packages from the industry. To sum up, it has been shown that pressure optimization based on the package design can improve seal integrity and help to prevent seal defects that lead to food quality and safety issues.