Fundamental investigation of induction sealing of paper/foil aseptic food packages

Sealing is a critical step in the manufacture of paper/foil aseptic food packages because it directly affects the production rate and the product quality. Three sealing systems incorporated with data acquisition system were built, then the effects of the sealing parameters on the process time and quality were studied. Ultrasonic sealing provides a short process time and consistent seal quality with peel strength being limited by failure in the paper cardboard. But breakage of the aluminum foil along the joint interface always occurs during ultrasonic sealing due to both dynamic compression and tensile force from the squeeze flow of molten polyethylene layer. This may break the barrier between the air and the food and create a potential problem in food protection. Induction sealing also provides a short process time with consistent quality and no breakage in the foil. IR sealing was able to produce same quality seal as in the induction and ultrasonic sealing but the process time required is longer. Therefore induction sealing was chosen for further in-depth study.;Induction sealing of paper/foil aseptic food package was studied theoretically and experimentally. The modeling of induction heating of the package was divided into heat generation and heat transfer processes. For heat generation modeling, a FEM 3-D time harmonic electromagnetic analysis was conducted to predict the power dissipation in the aluminum foil. Then the power dissipation in the aluminum foil was used as an input for heat transfer analysis. For heat transfer modeling, a FEM 3-D transient thermal analysis was conducted to predict the temperature distribution and temperature history at the polyethylene layer during sealing. The resulting tensile stress was then compared with the tensile strength of the aluminum foil. Under the optimal sealing pressures the resulting stresses are always smaller than the tensile strength of the aluminum foil. The predicted results were also verified by microscopic examination of the joint interface. Among the sealing parameters, the heating time is the most important parameter to affect the peel strength and process time. Longer heating time is beneficial to the peel strength until the surface gets overheated. Under the optimal sealing conditions, the failure always occurs at the paperboard and not at the joint interface. No noticeable effects of electron beam radiation sterilization on the sealing time and quality were observed during the experiments. (Abstract shortened by UMI.).