In production practice, some clients have found that packaging bags produced using solvent-free lamination sometimes require higher heat seal temperatures to achieve proper sealing. This issue is more common in structures where PE is used as the heat seal layer. To help industry partners better understand this phenomenon, Haide Packaging combines experimental data and production experience to analyze the issue and propose practical solutions.
I. Problem Description and Cause Analysis
The heat sealing process is mainly influenced by three factors: temperature, pressure, and time. In actual production, it has been observed that under the same pressure and sealing time, some solvent-free laminated products require higher heat seal temperatures compared to traditional solvent-based dry laminated products, sometimes even needing an increase of 15–20°C. This phenomenon occurs noticeably more frequently in winter than in summer.
Through comparative experiments, the following was found:
Products with abnormal heat seal temperatures have a layer of substance on the heat seal surface that can be wiped off with a solvent.
After removing this substance, the heat seal temperature returns to normal.
Under microscopic observation, the PE layers fully fuse during normal heat sealing, whereas problematic samples show incomplete fusion of the PE layers at the same temperature.
Combining theory with production practice, we believe the root cause of the issue may be as follows:
PE film inherently has tiny molecular gaps, which expand particularly during temperature changes. Certain small molecules in solvent-free adhesives may permeate through these gaps to the PE surface. When environmental temperature differences cause an imperceptibly thin film of condensation to form on the film surface, these components react with water, forming an extremely thin layer of polyurea.
This polyurea layer acts like a layer of microscopic "dust," preventing the direct fusion of the PE layers at normal temperatures. A higher temperature is required to fully melt the PE, allowing this substance to "sink" into the molten PE and achieve proper sealing.
II. Haide Packaging's Solutions
Based on the above analysis, Haide Packaging recommends the following three approaches for prevention and resolution:
Preventive Measures
Material Selection: Choose PE materials with denser molecular structures to reduce the possibility of small molecule penetration.
Environmental Control: Pay special attention to temperature differences between the workshop and the curing room during seasonal transitions to avoid condensation on the film surface.
Process Optimization: Ensure the adhesive is fully cured to minimize the residue of small molecular components.
On-Site Solutions
If products already produced exhibit increased heat seal temperatures, the following remedial methods can be applied:
Gently wipe the heat seal surface with a solvent to remove the surface substance.
Adjust the heat sealing process parameters, moderately increasing the temperature while ensuring sealing quality.
For batch issues, perform surface cleaning treatment using equipment.
III. Summary and Recommendations
The phenomenon of increased heat seal temperatures in solvent-free laminated products is primarily caused by the combined effects of material characteristics, environmental factors, and process conditions, and is not an inherent flaw of the solvent-free process itself.
Through years of practical experience, Haide Packaging has established a comprehensive system for prevention and response. We recommend:
Implementing a material inspection system upon receipt, with particular attention to the molecular structure characteristics of PE materials.
Strengthening control of the production environment, especially during seasons with significant temperature and humidity changes.
Maintaining technical communication with adhesive suppliers to select adhesive types suitable for seasonal variations.
Through systematic prevention and refined process control, the impact of this issue can be effectively avoided or minimized. Haide Packaging is committed to sharing more practical experience with industry partners to collectively enhance the quality stability of solvent-free laminated products.