Case Against Oxidation as a Primary Factor for Bonding Acid Copolymers to Foil, 2000 Polymers, Laminations & Coatings Conference Proceedings

Barry A. Morris, Naozumi Suzuki--Oxidation is often used in the extrusion-coating industry to enhance the adhesion of LDPE to polar substrates such as aluminum foil. Previous investigators have suggested that oxidation plays a key role in the adhesion of acid copolymers to foil; the most direct evidence for this is the observed increase in peel strength with increasing time in the air gap (TIAG). The results of new experiments, however, suggest that oxidation may not be responsible for this behavior. Acid copolymers that have been ozone treated, loaded with antioxidants or processed at temperatures well below the expected onset of oxidation still show the characteristic increase in adhesion with increasing TIAG. Measurement of peel strength in the MD and TD show that the TD peel strength is not influenced by TIAG and peel strength correlates with % elongation of the coating. This suggests that stress and orientation may play a role in the observed behavior. A practical implication of this work is that acid copolymers will generally adhere more strongly to foil than LDPE, even when the acid copolymer is processed at lower temperatures. This reduces the potential for taste/odor, processing and other problems associated with high-temperature processing.