Inter-layer Adhesion Performance of Steel Packaging Materials for Food Cans Under Retort Conditions

Abstract

The steel packaging industry faces the dual challenge imposed by legislation to eradicate the use of Chrome(VI) from substrate manufacture and the removal of Bisphenol-A (BPA) from the organic lacquer at the point of food contact. The paper reports on an experimental investigation into the quality of adhesion between the coatings and substrates as a result of the retort process, typically the harshest conditions to which the materials will be exposed. In terms of adhesion, the novel Chrome(III) substrates show promise when compared with current Chrome(VI) substrate. There is a significant reduction in the adhesion of the polyester-based Bisphenol-A non-intent lacquers compared to the incumbent epoxy-phenolic lacquers. Adhesion performance is lower with an increase in retort temperature and time of exposure. The adhesion further reduces in mild acidic and saline conditions. The reduction in adhesion post-retort is attributed to the sensitivity of the polyester-based BPANI lacquers to water vapour absorption. The process reversible nature of the adhesion loss indicates that, at short timescales, the adhesion loss is a result of polyester hydrolysis. Acidic and saline solutions also lead to a reduction in adhesion as a result of metal surface corrosion. The paper has impact on producers, fillers and consumers of steel packaging foodstuffs.

Food packaging simulant failure mechanisms in next generation steel packaging

“…A novel developmental substrate, combined with next generation coatings (bisphenol-A non-intent) that comply with legislative moves in some European territories, presents the metal packaging industry with a system that has been shown to be less robust than the wellestablished ECCS/epoxyphenolic coating system. 11 The adhesion of an organic coating to a metallic surface occurs through a variety of bonding mechanisms, including electrostatic interactions, dispersion forces, and covalent bonds, 12,13 all of which are susceptible to modification through the interaction with a simulant solution and by extension, foodstuff. Work has previously been conducted studying the effects of the sterilisation process on the quality of adhesion that is observed, a phenomenon that had not been quantified before.…”

“…Work has previously been conducted studying the effects of the sterilisation process on the quality of adhesion that is observed, a phenomenon that had not been quantified before. 11 This study focussed on the quality of adhesion varied with adjusting retort parameters, establishing relationships and highlighting strengths and failures within novel substrate/coating systems. Previous work has begun the examination process of the changing chemistry of both the coatings and the substrate, an area that is to be more fully explored here.…”

Identifying interlayer surface adhesion failure mechanisms in tinplate packaging steels

“…It has been validated in other studies 7,8 and was repeated for five samples, and repeated measurements were shown to be +/− 0.25 g in terms of adhesion force. 8 3 | RESULTS…”

“…This adhesion measurement method provides a physical stress on the surface which is akin to that produced during can forming which can be a primary source of can defects and provides a single nonsubjective numerical value for adhesion. It has been validated in other studies and was repeated for five samples, and repeated measurements were shown to be +/− 0.25 g in terms of adhesion force …”

“…Legislative pressures, which see the ban of the use of epoxy phenolic lacquers 6 and chrome VI 6 passivation in Europe, are restarting the interest in the area as the combined performance of these materials have been shown to perform less robustly in terms of lacquer/substrate adhesion than the incumbent technology. 7,8 These changes potentially have significant implications for the European steel packaging industry. Alternatives to chrome (VI) passivation systems have been studied including cerium, 9 TiO 2 , 10,11 sol-gel derived silanes, 12 polymers, and fluorozirconic acid.…”