After bag making, there are wrinkles in the heat-sealed edges.
Material combination: Aluminum foil cooking bag (PET/AL/PA/RCPP); the issue arises when heat sealing, with the sealing edge wrinkling when the sealing blade temperature is too high, and it fails to seal properly when the temperature is too low. The pressure and cooling system have been adjusted, and silicone pad and raw materials have been replaced, but the problem persists. Why?
You should consider two aspects: one is the issue of wrinkling in the sealed edges, sometimes resulting in delamination; the other is the problem of inadequate sealing or poor sealing. For the wrinkling issue, the typical reasons are:
Insufficient temperature resistance of the material, causing wrinkling when exposed to high heat during sealing.
Insufficient heat resistance of adhesives and inks, meaning their temperature resistance is lower than the sealing temperature (if there are no imprints on the edge, focus on the adhesive only).
Excessive residual solvents in adhesives and inks, leading to the formation of bubbles and wrinkles as they evaporate during the sealing process.
Lack of parallelism in the sealing blade of the bag-making machine, inadequate hardness, smoothness of the silicone pad, and the presence of foreign substances on the sealing blade.
Inadequate cooling temperature after sealing.
For the issue of poor sealing, the usual reasons are:
Quality issues with the heat-sealing material, where the temperature resistance is too high, resulting in a sealing temperature that is too low, or the heat-sealing performance is unstable.
The sealing blade temperature is too low, and the pressure is too low.
Floating additives in the heat-sealing material and excessive corona treatment, leading to breakdown and hindrance to the adhesion of the heat-sealing layer.
Therefore, it is recommended to thoroughly check these points and find countermeasures from the listed reasons. Pay special attention to the source of the RCPP material for the inner layer and perform physical property testing. Additionally, you can use a laboratory heat-sealing instrument to conduct a heat-sealing curve test on the material to prove that the material is not the issue. This will help determine whether the problem lies with the material or the bag-making machine equipment.