Research On Heat Seal Technology And Mechanism Of Plastic Packaging Laminated Materials

Due to the development of sub-packaging and keeping fresh packaging technique, single-layer plastic film often can not meet the application requirements. There is a great growth of the packaging plastic laminated films in food, medication, agriculture and livestock products packaging, and other fields. High heat-seal strength and integrity of the heat sealing part are basic requirements for packaging plastic laminated bags during transport, storage and product distribution process, and other links. Therefore, the performance test of heat seal and further study on the thermal conductivity of the heat seal process, were carried out respectively for two representative packaging plastic laminated films, PET / Al / PE and BOPP / PE. The detailed works are described as follows:Firstly, the heat seal test equipment and universal testing mechanism were used to make heat seal samples and test the heat seal strength. Then main processing parameters of heat seal process were analyzed for the heat seal performance of the two packaging plastic laminated films. The results showed that the sealing temperature, sealing time and sealing pressure were basic conditions to complete a basic heat sealing. After the temperature went up to a certain value, sealing temperature became the most significant factor to heat seal process. If the sealing temperature increased continually, the heat seal strength trend to a stable value.Secondly, apparent judgment was carried out by using transmission electron microscope (TEM) and tension failure models,and thermal analysis of polythene (PE) was carried out by using differential scanning calorimetry (DSC) in the paper. The melting point of PE film was obtained by DSC as the melting peak temperature, and the micrograph showed a good fusion of the laminated film PET/Al/PE can obtained above the melting temperature of PE film. The range of heat sealing temperature of laminated film PET/Al/PE and BOPP / PE were obtained.Whereafter, Taking the actual efficiency and qulity of production into consideration, the three heat seal parameters were optimized by SAS statistical analysis software in order to shorten the sealing time.In the end, according to the unsteady-state heat conduction in the classic heat transfer theory, the heat conduction mechanism in the process of heat seal for PET / Al / PE and BOPP / PE was researched respectively, and the theoretic model of heat conductivity for the film PET / Al / PE was established. The relationship of the temperature in internal and external surface of the laminated film was obtained during the heat seal process. Also, the author established the two-dimensional models for PET / Al / PE and BOPP / PE respectively by the finite element analysis software ANSYS. Also, the heat conduction process was simulated. The thermogram and heat-flux distribution were obtained with different heat load and different time. The differences between the internal and external surface temperature of laminated films were discovered clearly. Finally, the PET / Al / PE theoretical heat conduction model was proved validity by the results.