Polyurethane laminating adhesives are the core materials in the flexible packaging laminating process. According to the formulation system, they can be divided into solvent-based and solvent-free types. These two types differ significantly in composition, process, environmental friendliness, performance during use, and cost, and are suitable for different requirements of flexible packaging production.
In terms of composition and solid content, solvent-based adhesives use ethyl acetate as the diluent. The solid content is usually not 100%, relying on the solvent to reduce the viscosity of the glue and facilitate uniform coating. Non-solvent adhesives have a 100% solid content and do not contain any volatile organic solvents. They regulate the viscosity through the ratio of raw materials and temperature control, and do not require solvent dilution.
The production process and energy consumption are significantly different. Solvent-based lamination requires a long drying tunnel, where the solvent is evaporated through high-temperature drying. This process involves high equipment investment and high energy consumption. It generates a large amount of VOCs waste gas during the production process, and the finished product is prone to solvent residue issues, posing potential food safety hazards. Non-solvent-based lamination does not require a drying process. The equipment structure is simple, and the coating and compounding can be completed at room temperature. The energy consumption is significantly reduced, and there is no exhaust gas emission throughout the process. The product has no solvent residue.
The adhesive properties and applicable scenarios have their own advantages and disadvantages. Solvent-based adhesives have excellent wetting performance, strong initial bonding strength, outstanding resistance to boiling and low temperatures, and are suitable for high-demand packaging such as high-temperature boiling bags and aluminum foil composites. Non-solvent adhesives have a slower curing speed, are sensitive to production environment humidity, have slightly weaker temperature resistance, but have higher production efficiency and are suitable for common snacks, daily chemical products, and other regular flexible packaging.
At present, environmental protection policies are continuously tightening. Non-solvent adhesives, due to their green and low-carbon advantages, have gradually become the mainstream in the industry. However, solvent-based adhesives still play an irreplaceable role in the high-end, high-temperature-resistant flexible packaging field.
