Interlayer Adhesion Between Acrylic Acid Copolymers and Low Density Polyethylene: Test Method Development and Impact of..., 1993 Polymers, Laminations & Coatings Conference Proceedings

In flexible packaging applications, ethylene-acid copolymers (EAA) are often coextruded with low density polyethylene (LDPE) as a tie layer to aluminum foil.

A common challenge in LDPE/EAA coextrusions is to optimize adhesion of the EAA to the foil and to the LDPE simultaneously. Another challenge is to obtain meaningful data through LDPE/acid copolymer interlayer adhesion testing. It is important to interpret the measured force in terms of its components: delamination (interlayer adhesion) and stretching of the polymeric sealant.

Measuring techniques used to obtain meaningful interlayer adhesion values were developed. Using these techniques, resin properties and extrusion variables which potentially impact interlayer adhesion were analyzed.

Interlayer adhesion between LDPE and EAA copolymers was found to be good (>2.5 lb/in.) in all structures tested. Incremental improvements were made by 1) increasing the LDPE melt temperature, 2) increasing the EAA melt temperature 3) coextruding to copolymers with 6.5% acrylic acid verses 9.5% acrylic acid content, 4) increasing the LDPE melt index, 5) using a higher density LDPE resin, 6) increasing the air gap, and 7) increasing the total thickness of the polymer coating.

Interlayer adhesion was not affected by 1) increasing chill roll temperature, 2) changing EAA feed zone temperatures, nor 3) changing LDPE feed zone temperatures.