The flexible packaging polyurethane laminating adhesives are classified into three types based on production line speed: low-speed, medium-speed, and high-speed composite. They are suitable for different production capacities, adhesive types, and production requirements, and have significant differences in process characteristics.
The low-speed lamination line speed is generally ≤ 80m/min, mostly for small dry lamination machines, suitable for general-purpose solvent-based PU adhesive. The glue liquid has a long opening time and a relatively high viscosity, with a large tolerance margin. The requirements for equipment temperature control and tension accuracy are low, making it suitable for small-batch, multi-specification orders. It is often used for lamination of aluminum foil, thick PE and other difficult-to-adhere substrates. The coating amount is relatively high. A gradual temperature increase during drying is sufficient. It needs to be aged for 24–48 hours. The disadvantages are low production capacity and high pressure for solvent residue control. It is only suitable for small-scale processing factories.
Medium-speed lamination zone: 80–200m/min. This is the mainstream model in the industry. Both solvent-based and conventional non-solvent PU adhesives can be used. The adhesive fluid combines leveling and initial adhesion, is suitable for conventional packaging structures of plastic-plastic and aluminum-coated, and the drying and tension control systems of the equipment are mature. The coating is uniform and stable, balancing production capacity and product quality rate. It is applicable to regular packaging bags for food and daily chemicals, taking into account production costs and efficiency. The curing period is moderate, and the ink compatibility is wide. This process is widely adopted by medium-sized and large packaging factories.
High-speed lamination line speed: 200–450m/min. Mainly uses solvent-free quick-drying PU laminating adhesive, and a few quick-drying solvent adhesives can be adapted. The adhesive has low viscosity, rapid leveling, and instantaneous wetting of the substrate. After mixing, the stability of the coating is stable, and it is suitable for high-precision metering coating equipment. The entire process is temperature-controlled for glue application, with a lower coating amount, and the curing time is shortened to 12–24 hours, significantly improving production efficiency. The requirements for the fluidity of the glue, anti-bubble resistance, and thermal stability are strict. It is suitable for large-scale standardized food packaging. The VOC emissions are lower, and it is the mainstream solution for upgrading large-scale factories.
The core differences among the three types of processes lie in the activity of the adhesive solution, the control of coating, and the efficiency of curing. Enterprises select the corresponding lamination system based on the order quantity, environmental protection requirements, and other factors.
