Key Considerations for Lamination in Paperboard Box Packaging
Lamination in paperboard packaging is a result of the physical effects of heat pressing, where lamination temperature, pressure, and speed are critical for achieving quality. Proper management of these factors is key to ensuring lamination quality and providing a good interface for subsequent processes.
1.Temperature Control in Lamination
The temperature in the coating tunnel should neither be too high nor too low, typically maintained between 122°F to 140°F. If the temperature is too low, the solvent in the adhesive will not function effectively, leading to weak adhesion and potential delamination and bubbling. Overheating can cause wrinkling on the surface after lamination.
During heat pressing, the adhesive layer melts, and molecular bonding increases, maximizing the adhesive force between the plastic film, the print, and the adhesive interface. Optimal lamination temperatures help enhance adhesive strength but should be kept within a reasonable range. Generally, the temperature for direct lamination films is controlled around 176°F to 194°F, and for pre-coated films, it’s about 176°F to 212°F. Excessively high temperatures can cause the plastic film to shrink and deform, leading to wrinkles, curling, and localized bubbling in the final product.
Temperature control during lamination also affects the thermal resistance of hot melt adhesives and their ability to withstand additional heat during subsequent processes like hot stamping.
2.Pressure Control in Lamination
Despite appearing smooth, the surfaces of printed papers are not perfectly flat. Ideal pressure is necessary to expel air from the surface during lamination, allowing the molten adhesive to wet the print surface thoroughly. This promotes diffusion and displacement of adhesive molecules between the ink and paper, achieving a strong bond and complete coverage, resulting in a glossy, clear, and crease-free surface.
Excessive pressure can deform the film, causing wrinkles, and can also deform the rubber rollers. Insufficient pressure leads to poor adhesion. Adjusting the pressure appropriately can enhance internal and surface harmony of the printed paper without causing wrinkles.
In production, lamination pressure should be adjusted based on the texture and porosity of the paper. For papers with a rough surface and loose texture, higher pressure may be necessary. Typically, the lamination pressure for dense, smooth paper should be controlled between 396 lbs to 440 lbs; for loose, rough paper, it should be between 418 lbs to 484 lbs.
3.Speed Control in Lamination
Lamination of printed paper with plastic film (BOPP) occurs on a conveyor belt. The speed of the lamination machine determines the dwell time of the paper and film at the heat pressing interface. When temperature and pressure are fixed, changes in conveyor speed can affect the lamination outcome.
Too fast a speed can result in weak adhesion between the paper and film, potentially causing a foggy appearance. Too slow a speed reduces efficiency and increases the likelihood of bubbling. Based on practical experience, lamination speed is generally kept between 20 to 39 feet per minute, roughly equivalent to about 20 sheets of paper.