Overview of polyurethane laminated adhesive used in food packaging analysis

Food packaging can be divided into ordinary packaging and high-performance packaging. The corresponding polyurethane laminating adhesives can be divided into four categories: (1) general use, (2) steaming use, (3) transparent cooking use, (4) aluminum foil cooking use.

 

Polyurethane laminated adhesive with composite film for general packaging generally includes adhesive for dry food packaging and adhesive for boiling sterilization at 70 ~ 100℃. Usually, such adhesives are two-component solvent-based polyurethane adhesives. The main agent is hydroxyl-containing polyurethane polyol modified by polyether or polyester polyol with aromatic isocyanate (called component A), and the curing agent is the adduct of aromatic isocyanate and trimethylolpropane (called component B). When in use, the component A and component B are mixed in a certain proportion, and then diluted to a certain concentration with ethyl acetate for sizing and coating. At present, this kind of glue has been produced in most places. It is mainly made of polyester polyol of polyadipic acid.

 

Composite film polyurethane laminating adhesives for transparent retort pouch and aluminum foil retort pouch generally include composite film adhesives resistant to 121℃ cooking and sterilization and composite film adhesives resistant to 135℃ high temperature cooking and sterilization. The so-called high-temperature cooking refers to the processing technology of food sterilization at high temperature of 121 ~ 145℃ and steam pressure of 0.18 ~ 0.40 MPa. This requires not only a variety of substrates to withstand the test of high temperature, but also the adhesives used to withstand high temperature. Polyurethane laminating adhesive for ordinary packaging is easy to hydrolyze at this high temperature, and the adhesive strength is reduced, which also easily causes the film to fall off. In order to improve the cooking resistance of polyurethane laminating adhesive, it is usually solved by changing the molecular structure of soft segment polyester and hard segment, introducing moisture-heat resistant and high-temperature segment, changing the variety of crosslinking agent, adjusting the density of crosslinking agent, and even forming interpenetrating polymer network (IPN) by blending high polymers.