Special considerations about multi-layer packaging and chemical migration

3 Special considerations about multi-layer packaging and chemical migration 

Most laminators use solventless polyurethanes. The composition and comparative properties of typical products are summarised in Table 16.3. 

First-generation solventless polyurethane adhesives are one-component isocyanate terminated prepolymers formed by the reaction of MDI (4,4 methylene bis (phenyl isocyanate)), or other isocyanates with polyether and/ or polyester polyols. One-component 100% solids adhesives rely on moisture from the air or substrates or from induced moisture misting during the converting process, to cure the adhesive via an isocyanate/water reaction and subsequent polyurea-polyurethane polymer formation. Typically the high viscosity of the adhesive is such as to require adhesive delivery equipment and application rollers heated from 65-80 °C for use. They have a high level 

Property One-part moisture cure adhesive Two-part isocyanate (higher monomer)/ polyol Two-part isocyanate prepolymer (low monomer )/polyol 

General First-generation Second-generation Third- and fourth- 

---