In
this study, heat transfer in a heat sealing process was simulated
using COMSOL Multiphysics software. Variations of thermal conductivity,
specific heat, and density of polymers with temperature were measured
in a wide temperature range. The temperature profile at the interface
between two sealing films was measured using a fine thermocouple.
Comparing experimental and simulation results indicated the high accuracy
of the simulation and the significant role of considering thermal
contact resistance as the boundary condition between the jaws and
films. These results showed that the present simulation, for the first
time, can successfully predict heat transfer and interface temperature
in a heat sealing process without any fitting parameter. Moreover,
the obtained results showed that the simulation can predict the effect
of jaw temperature, sealing time, film thickness, and polymer crystallinity
in a wide range of temperatures from below melting point to much higher
temperatures than the melting point of the sealant.
In this work, effects of sealing temperature, time, pressure, as well as sealant thickness and viscosity on squeeze out flow (SOF) in heat sealing were examined. A new image analysis approach is presented to quantify SOF in heat sealing. It was found that increasing temperature or pressure could improve SOF but only in thick 130 μm sealants and reducing the sealant thickness to 50 μm suppressed SOF. Reducing viscosity in 50 μm sealant films was also found to improve SOF only at high-sealing pressure and long sealing times. Three approaches were used to model SOF: analytical one-dimensional model, numerical one-dimensional model using finite difference method (FDM), (iii) Numerical two-dimensional model using finite element analysis. Heat transfer was modeled, and it was shown that heat transfer induces a delay in SOF. When the FDM and the heat transfer models were combined, a good agreement between experimental and model prediction could be obtained. In addition, modeling results showed that SOF occurred in shear rates within the transition region between the Newtonian and Power-law regions. This indicates the importance of considering the Carreau-Yasuda fluid behavior in modeling of SOF.
This work studies effects of back‐layer materials, thickness of sealant layer, and sealing condition on seal performance of multilayer polyethylene‐based films. Multilayer films with back‐layers of high‐density polyethylene (HDPE), or low‐density polyethylene (LDPE), or linear low‐density polyethylene (LLDPE) were produced with different thicknesses of the metallocene layer. It was found that increasing the thickness of the metallocene layer improved hot tack properties. In addition, films with back‐layers of LLDPE or LDPE showed higher hot tack strength compared to those with HDPE back‐layer. Increasing sealing temperature reduced significantly the hot tack strength and its dependency on metallocene layer thickness. It was found that increasing delay time after sealing, before peeling test, increased hot tack strength, but the rate of hot tack evolution and the type of peeling behavior were considerably affected by the type of back‐layer material. The effect of dwell time was also examined, and it was observed that increasing dwell time in the studied range did not affect the hot tack evolution. The mechanisms involved in the development of hot tack evolution were discussed, and it was shown that the back‐layer effects can be explained by bulk viscoelastic energy dissipation theory.
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