In the printing process of self-adhesive bags, the adhesive layer, as the core component for achieving the sealing function, directly affects the product's sealing performance and user experience. During the printing process, factors such as ink, solvents, and mechanical pressure can erode or physically damage the adhesive layer, requiring a balance through process optimization and material selection.
The choice of ink system is paramount. Traditional solvent-based inks contain organic components that may dissolve the polymers in the adhesive layer, leading to a decrease in viscosity. Currently, the industry commonly uses water-based inks or UV-cured inks. The former uses water as a solvent, reducing the risk of chemical corrosion; the latter cures through ultraviolet light, eliminating the need for volatile solvents. For example, in the printing of food packaging self-adhesive bags, water-based polyurethane inks ensure color saturation while avoiding reactions with acrylate substances in the adhesive layer. Furthermore, the pH value of the ink must be strictly controlled within the weakly acidic to neutral range to prevent alkaline components from damaging the molecular structure of the adhesive layer.
Adjusting the printing equipment and process parameters is equally crucial. In traditional gravure printing, excessive contact pressure between the doctor blade and the printing roller can cause the adhesive layer to be squeezed and deformed. Modern processes often use flexographic printing, whose light-pressure contact characteristics reduce physical impact on the adhesive layer. Simultaneously, the printing speed must be matched with the curing time of the adhesive layer; printing too fast may cause the ink to come into contact with the adhesive layer before it is fully dry, leading to adhesion or solvent residue. For example, in the production of self-adhesive bags for clothing packaging, reducing the printing speed to 80 meters per minute, combined with an infrared drying device, ensures that the ink is fully cured before subsequent lamination processes.
Improving the lamination process is crucial for protecting the adhesive layer. In traditional dry lamination, excessive adhesive coating can penetrate into the adhesive layer, altering its tackiness. Current mainstream co-extrusion lamination processes use multi-layer co-extrusion technology to simultaneously form the adhesive layer and the printed layer, avoiding interference from secondary lamination on the adhesive layer. For example, in the production of self-adhesive bags for medical devices, a five-layer co-extrusion structure is used, placing the adhesive layer in the middle layer, with the outer layers being the printing layer and barrier layer. This ensures printing quality while preventing ink solvents from contacting the adhesive layer.
Optimizing the adhesive layer's formulation is also crucial. Adding fillers such as nano-silica can improve the adhesive layer's abrasion resistance and solvent resistance. Some high-end products use a two-component adhesive system, pre-curing the adhesive layer before printing to form a protective surface layer, and then restoring its tackiness through heat activation after printing. For example, in self-adhesive bags for electronic product packaging, this process ensures that the adhesive layer is unaffected by the printing process during transportation and maintains its initial tackiness during use.
Management during storage and transportation is equally important. Printed self-adhesive bags need to be left to stand for 24 hours in an environment of 25°C and 50% humidity to allow the ink and adhesive layer to fully stabilize. When stacking, pallets should be used to separate the layers, avoiding direct stacking that could cause the adhesive layers to stick together. For example, in the production of export-oriented self-adhesive bags, the introduction of automated storage and retrieval systems (AS/RS) allows for independent storage of individual boxes, reducing potential damage to the adhesive layer from human contact.
From material innovation to process upgrades, the printing process for self-adhesive bags has developed into a systematic solution for protecting the adhesive layer. Through the comprehensive application of technologies such as water-based inks, flexographic printing, and co-extrusion lamination, combined with strict storage management, it is possible to ensure that self-adhesive bags maintain excellent sealing performance while meeting personalized printing needs.
