Converters struggle with rising costs and an increasing awareness for food safety. Of all available lamination technologies, solventless polyurethane (PU) adhesives are the most cost-effective.

With adhesive coat weights typically ranging from 1–1.15 lb/ream, these adhesives offer good adhesion to a wide variety of substrates. Printed, metalized, or otherwise coated materials and a myriad of sealant layers are no problem. These systems are convenient to use with near-room-temperature application and long potlives.

Conventional solventless systems, however, require long storage times in order to comply with food safety regulations. With unique curing technology offered in a new line of solventless PU adhesives, bond development and food safety compliance are both achieved in a very short time.

Compliance testing performed using 3% acetic acid is the most stringent, worst case scenario to meet the FDA regulations. These new technology adhesives meet the dual needs of physical performance and regulatory compliance for food safety in less than three days for the majority of structures, compared to the many weeks required by conventional systems.

A recent study compared the relationship across a range of variables including substrates, coating weight, cure conditions, moisture, etc. Special attention was paid to the filling good used as the food simulant in the migration test. In a time of increased environmental awareness and food safety, these new adhesives offer fast cure without compromising food safety.

Rapid Compliance
A laminate manufactured with the ideal adhesive would be in compliance with food safety legislation at the same time it reaches its full physical performance. Flexible packaging suppliers must allow a certain storage time for the PU adhesive to cure prior to further processing, e.g., slitting, pouchmaking, etc. It is the obligation of the flexible packaging manufacturer to ensure that the packaging material introduced into the market complies with all relevant food safety regulations.

With conventional two-component room-temperature adhesive systems, the storage time eventually can take weeks. Due to a special curing mechanism, new laminating adhesives cure fully and reach legal compliance in only a few days.

Migration of Primary Aromatic Amines
If the laminating adhesive is not fully cured and still contains unreacted monomeric diisocyanates, these substances may migrate through the sealant film and into the food.

Once migrated, they will react with most ubiquitous moisture and form the corresponding primary aromatic amines. Primary aromatic amines have been classified as carcinogenic.