Solids System
Liquid systems consisting of 100 percent reactive solids allow for the joining of two or more webs without the use of volatile organic compounds. A solvent-free laminating adhesive typically relies on a two-component polyurethane chemistry that cures at room temperature or slightly above. Because there is no carrier fluid to evaporate, the process does not require drying tunnels, which substantially reduces the energy consumption of the converting line.
This technology has become the standard for food packaging due to the reduced risk of odor or flavor contamination. Choosing this method allows converters to produce high-quality laminates without the environmental burden of thermal oxidizers.
Coating Application
Laminating machines for these adhesives use a multi-roll coating head to apply a very thin, consistent layer of the liquid across the substrate. The amount of adhesive applied is usually between 1.5 and 2.5 grams per square meter, depending on the surface roughness of the paper or film. If the application weight is too low, the bond will be weak and show optical defects known as orange peel.
Higher weights may cause the adhesive to squeeze out of the edges or lead to tunneling in the film.
Safety Regulation
Migration of unreacted monomers remains a primary concern for the safety of food-contact materials. Proper mixing ratios and sufficient curing time are necessary to ensure that all isocyanate groups are consumed before the package is filled. Regulatory bodies set strict limits on the amount of primary aromatic amines that can migrate from these adhesives into the food.
