The development of composite flexible packaging to today, reducing and removing organic solvents in the composite has become the direction of the industry's joint efforts. At present, the composite method capable of completely eliminating the solvent is a water-based composite and a solvent-free composite. Solvent-free recombination is still in its infancy due to factors such as cost technology. Since the water-based adhesive can be directly used on the existing dry laminating machine, it is welcomed by the domestic soft packaging manufacturers, and has achieved rapid development abroad.
Water-based composite is divided into dry composite and wet composite. Wet composite is mainly used in the composite of paper and paper and paper aluminum. White latex is popular in this field. In the plastic composite and plastic aluminum composite, mainly water-based polyurethane and water-based acrylic polymer. Waterborne adhesives have the following main advantages:
（1） The composite strength is large. The water-based adhesive has a large molecular weight, which is several times that of the polyurethane adhesive. Its adhesive force is mainly based on van der Waals force and belongs to physical adsorption, so a small amount of sizing can achieve a relatively high composite strength. For example, compared with a two-component polyurethane adhesive, in the process of compounding an aluminized film, a composite strength of 2.6 g/m2 of a two-component polyurethane adhesive can be achieved by applying a dry glue amount of 1.8 g/m2.
（2） Soft, more suitable for the composite of aluminized film. One-component aqueous adhesives are softer than two-component polyurethane adhesives. When they are fully solidified, the polyurethane adhesive is very rigid and the aqueous adhesive is very soft. Therefore, the softness and elasticity of the water-based adhesive are more suitable for the composite of the aluminized film, and it is not easy to cause the transfer of the aluminized film.
（3） No need to mature, it can be cut after the machine is off. The one-component water-based adhesive composite does not need to be matured, and the subsequent processes such as slitting and bag making can be carried out after the machine is removed. This is because the initial adhesive strength of the water-based adhesive, especially the high shear strength, ensures that the product does not cause problems such as “tunneling” and wrinkles during the compounding and slitting process. Moreover, the film composited with the aqueous adhesive can be increased in strength by 50% after being left for 4 hours. This is not a concept of ripening. The colloid itself does not crosslink, mainly due to the leveling of the glue, and the composite strength is also increased.
（4） The rubber layer is thin and the transparency is good. Since the amount of sizing of the water-based adhesive is small and the concentration at the time of sizing is higher than that of the solvent-based adhesive, the amount of moisture required to be dried and discharged is much less than that of the solvent-based adhesive. After the moisture is completely dried, the film becomes very transparent. Because the rubber layer is thin, the transparency of the composite is better than that of the solvent-based adhesive.
（5） Environmental protection, harmless to people. Water-based adhesives have no solvent residue after drying. Many manufacturers use water-based adhesives to avoid residual solvents caused by compounding. Therefore, the use of water-based adhesives is safe to produce and does not damage the health of operators.