Control of Curing, Printing, and Residual Solvents:
Solventless lamination cannot reduce the residual solvents caused by printing, so there is a higher demand for controlling residual solvents from printing. Solventless adhesives do not contain organic solvents, which do not increase residual solvents, but at the same time, they do not reduce the solvent residues caused by printing. Only by minimizing the residual solvents from printing can we truly eliminate the odor in the final product. Typically, for gravure printing on nylon films, the ink type is polyurethane resin-based ink. When using polyurethane-based ink for high-temperature retort pouches, ink curing agents should be added as solvents for dissolving the ink. The amount of added true solvents must be sufficient and replenished promptly. Without timely replenishment, the ink in the inkwell swells due to poor solubility of the resin, resulting in an increase in viscosity, which affects the ink's adhesion to the film. Therefore, a sufficient amount of true solvents must be maintained to meet the needs of dissolving the resin. Polyurethane resin inks have a faster increase in viscosity when printed in the summer, and dilution solvents should be continuously replenished in a timely manner during operation to keep the ink in the inkwell at a relatively low viscosity, ensuring stable print quality and preventing quality issues such as missing printing, color differences, plate blocking, and ink adhesion problems during the printing process. Various types of inks use different true solvents based on the ink resin. It is necessary to first determine the type of resin ink being used to match the appropriate true solvent. The introduction of moisture into adhesive systems containing isocyanate (NCO) groups can cause gelling and whitening, resulting in bubbles and pinholes, gradually accumulating waste. Residual solvents must be removed during the printing process because solventless lamination does not use organic solvents, and there is no solvent residue in the lamination process. Therefore, the addition of slow-drying solvents during the printing process should be approached with special caution and control.