8 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS coating material is not at fault in this respect, and that optimum stoving conditions have been observed: 1. L,•bricant Residues remaining under the dried lacquer .film. It is very easy to be misled, as tests on newly applied coatings which have not been in contact with product invariably give equal results to those obtained with specimens free from lubricant residues. It is only after ageing in contact with the product, that adhesion losses become apparent. Much controversy has raged about the part played by the lubricant itself, bearing in mind that the best lubricants for impact extrusion are, quite frequently, those which are the most difficnlt to remove, and in the case of collapsible tubes, no actual degreasing is used--the lubricant is intended to be removed by annealing. Further, that whatever lubricant is used is very strongly attached to the metal surface, and if any appreciable time elapses before annealing in the case of collapsible tubes, or degreasing in the case of rigid containers, it becomes almost impossible to guarantee complete lubricant removal. Many instances are known of adhesion failures in service of containers which have been subjected to, and passed, stringent coating tests when newly produced. There is little doubt that these are due to the fairly long term effects of lubricant residues. 2. Film •Penetrators in the product. Certain ingredients used in many pro- ducts packed in tubes and containers are known to rapidly penetrate the lacquer fihns, particularly epoxy based lacquers. These materials rapidly destroy the adhesive forces at the metal/lacquer interface. Chief among these are the following :-- Irish moss and associated gums. Sodium alginate under certain conditions. Menthol. Methyl salicylate and similar esters. Usually this particular difficulty can be overcome by slight reformulation of the product. With the gums, by substituting tragacanth, karaya, locust bean, sodium carboxymethyl cellulose or methyl cellulose, all of which are innocuous. 3. Oxide Films on the metal. The type of oxide film formed on aluminium containers is dependent on the annealing process in the case of collapsible tubes, the type of degreasing used, and on subsequent drying in the case of rigid containers, and in both cases on the length of time the containers are exposed to atmosphere before application of the lacquer. All these condi- tions should be controlled to give the optimum oxide film for maximum

PROTECTIVE LACQUER SYSTEMS FOR ALUMINIUM CONTAINERS adhesion. Rigid aluminium containers may be anodized to give maximum corrosion resistance and lacquer adhesion. The point should also be made in connection with collapsible tubes concerning the difficulty in obtaining adequate coatings in the nozzle owing to the restricted diameter, and it should be noted in connection with very aggressive products that lacquer films in the nozzle area are invariably much weaker than on the remainder of the tube. From the foregoing general outlines, two main conclusions can be drawn. 1. It is possible to draw up a code of good practice for producing containers P•using a one lacquer system, i.e., one lacquer irrespective of the number of • coats employed. N, 2. It is possible to develop further systems for dealing with corrosive products to overcome the defects inevitable with system (1). Dealing with system (1), the following simple rules should be observed :-- 2} (b) (c) (d) (f) The lacquer itself must be suitable chemically. The minimum optimum film Weight must be determined and the degree of cure of the film. These must be controlled to fine limits by a properly designed inspection scheme. The lubricant used for impact extrusion should be purely organic. Metallic soaps, such as zinc stearate should be avoided, and if water soluble compounds, e.g., ethoxylated lanolines can be used, so much the better, as subsequent degreasing is going to be more effective. There must be minimum delay between extruding and annealing or degreasing. With rigid containers, solvent degreasing should be avoided. Aqueous treatments giving a chemically clean surface and slight etch should be used, and there should be no delay between final rinse and drying. The containers themselves should be free from deep extrusion lines and torn metal. (g) Cross scoring should be absent. (h) Knur! marks should be absent from the nozzles of collapsible tubes. (i) The containers should be processed on plastic covered spindles for operations subsequent to lacquering. (j) There should be minimum delay between annealing or degreasing and internal lacquering. (k) The nozzle diameter of a collapsible tube should be as large as possible to permit effective lacquering, or alternatively, a plastic nozzle may be used.