The bonding construction matters of polyurethane adhesives
2026,03,27
1.Gluing: The methods of applying glue include spraying, brushing, dipping, and roller coating, etc. The choice depends on the type of glue, its viscosity, and production requirements. The key is to ensure that the glue layer is uniform, free of bubbles, and without any missing areas.
2. Air-drying: For solvent-based polyurethane adhesives, after applying the adhesive, it is necessary to let it air-dry for several minutes to several tens of minutes to allow most of the solvents in the adhesive to evaporate. This is beneficial for enhancing the initial adhesion. If necessary, heating and forced air drying (such as in the laminating process of composite films) should be carried out. Otherwise, due to the presence of a large amount of solvents remaining in the adhesive, bubbles are likely to form during the curing process in the adhesive layer, thereby affecting the bonding quality. For solvent-free polyurethane adhesives, the adherend can be directly attached after application of the adhesive.
3. Bonding: This step involves aligning the bonding surfaces of the objects that have been coated with adhesive. Adhesive fixtures can also be used to secure the bonding components, ensuring that the bonding surfaces are perfectly aligned and positioned. If necessary, a certain amount of pressure can be applied to facilitate better plastic flow of the adhesive, allowing it to penetrate the surface of the object and achieve maximum contact with the base material surface.
4. Curing: Most polyurethane adhesives do not have high bonding strength immediately upon bonding; they need to undergo curing. Curing refers to the process where the liquid adhesive turns into a solid. The curing process also includes post-curing, which is the further reaction of the reactive groups in the adhesive or the formation of crystals after the initial curing, to achieve the final curing strength. For polyurethane adhesives, the curing process is the process that ensures the complete reaction of the NCO groups in the adhesive, or the complete evaporation of the solvent, the crystallization of the polyurethane molecular chains, and the generation of sufficient bonding strength between the adhesive and the substrate.
