Food packaging is divided into ordinary packaging and high-performance packaging. The corresponding polyurethane adhesives can be divided into four categories: (1) general use, (2) boiling, (3) transparent cooking, and (4) aluminum foil cooking.
Composite film polyurethane adhesives for general packaging generally include dry food packaging adhesives and plastic food packaging adhesives that resist 70 to 100° C. boiling sterilization. Usually such adhesives are two-component solvent-based polyurethane adhesives.
Its main agent is a hydroxyl group-containing polyurethane polyol modified by aromatic isocyanate (polypropylene), and a curing agent is an adduct of aromatic isocyanate and trimethylolpropane (a ) When using, mix the A component and the B component in a certain proportion, and then dilute to a certain concentration with ethyl acetate and then sizing and coating.
At present, this kind of glue has been produced in China. Polyadipate polyester polyols are mainly used as raw materials, while propylene oxide polyethers are mostly used abroad as raw materials, and the cost is low. Composite film polyurethane adhesives for transparent cooking bags and aluminum foil cooking bags generally include composite film adhesives resistant to retort sterilization at 121°C and composite film adhesives resistant to high temperature retort sterilization at 135°C.
The so-called high-temperature cooking refers to a process of sterilizing food at a high temperature of 121 to 145° C. and a steam pressure of 0.18 to O.40 MPa. This requires not only that a variety of substrates withstand the high temperatures, but also that the adhesives used should be able to withstand high temperatures. Polyurethane adhesives for ordinary packaging are easily hydrolyzed at this high temperature, and the adhesive strength is reduced, which also easily causes the film to fall off.
In order to improve the retort resistance of polyurethane adhesives, it is usually to change the molecular structure of the soft segment polyester and the hard segment, introduce moisture- and heat-resistant high-temperature segments, change the type of cross-linker, adjust the density of the cross-linking agent, and even use a total of polymer Mixed to form an interpenetrating polymer network (IPN) approach to solve.
