Surface and Adhesion Characteristics of Current and Next Generation Steel Packaging Materials

Abstract

Steel packaging remains an important mean by which foodstuffs and other products can be stored safely for a prolonged period of time. The industry is being challenged by the dual legislative pressures which require the elimination of Chrome (VI) from the manufacturing process and the elimination of bisphenol A as a component from the lacquer system. Initial indications suggest lower adhesive performance, and it has been postulated that thermal treatment may be a mean of improving adhesion. Three substrates (two current and one future) were physically and chemically characterized prior and post treatment and the resultant impact of adhesion was quantified. The net impact of the thermal treatment is that it increases the adhesion of the lacquer on the surface. As there is minimal change in the physical characteristics of the surface, the authors propose that this is a result of changes in the chemical surface species, particularly the increase in the oxidic nature of each of the substrates which provides additional bonding sites for the organic species in the lacquer. These trends are observed for current substrate materials as well as next generation Chrome VI free substrate. Next generation replacement substrate materials perform better than current materials for dry adhesion while next generation bisphenol A non-intent lacquer materials perform poorer than the current epoxy phenolic materials.

Food packaging simulant failure mechanisms in next generation steel packaging

“…The effect of citric acid, demonstrated in Figure 7, is more pronounced on 294269M than the ECCS, and this attributed to the higher chromium level which is applied which allows greater conversion to chromium oxide and thus an increased number of lacquer bonding sites. 33 This mechanism also results in higher substrate/lacquer adhe- may be associated with the corrosion of the substrate surface. The increase in failure force is initially rapid and, in most instances, reached 90% of its final value within 50 hours.…”

Identifying interlayer surface adhesion failure mechanisms in tinplate packaging steels

“…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 …”

“…Any passivation technology which replaces Cr (VI) will need to prevent the growth of oxide with performance at least comparable with the incumbent Cr (VI). Thermal history and prolonged storage have been shown to be contributory factors to tin oxide growth, and this imposes additional requirements on passivation. The dataset provided by this paper provides a measure against which the future passivation technologies can be compared in terms of the adhesion.…”

“…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.…”

Continuous In-Line Chromium Coating Thickness Measurement Methodologies: An Investigation of Current and Potential Technology

“…High concentrations of Cr (VI) have been found in US tap water, which may be resultant from the discharge of steel, pulp, metal-plating, and leather-tanning facilities, as well as through erosion of soil and rock [ 23 , 24 , 25 ]. REACH (Registration, Evaluation, Authorization and Restriction of Chemicals) legislation require the withdrawal of the use of chromium (VI) compounds due to safety concerns [ 18 ], which requires the steel packaging industry to develop new substrate variants [ 20 ]. One of the most recent developments in this area is Trivalent Chromium Coating Technology (TCCT), which is based on a chromium (III) process [ 6 , 26 ].…”