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.

10 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS In addition, with aluminium collapsible tubes the annealing conditions should be such that there is maximum lubricant removal as well as the formation of the optimum oxide film for lacquer adhesion. This involves something of a compromise, as cleaning of the surface is more efficient at higher temperatures, whilst the type of oxide film formed at these tempera- tures is not the one that gives maximum adhesion. Dealing with our second conclusion, it is very obvious that one of the main drawbacks to present one-lacquer systems is the fact that the lacquer is applied at an early stage of the container's production, i.e., following annealing or degreasing, and that no matter how many coats are applied, or how good the film build, damage and possibly contamination must occur during subsequent operations. Secondly, there is a limit to the film thickness which can be applied without brittleness. Finally, high speed automatic spray- ing leaves something to be desired in the way of continuity. Recent systems overcome these defects by utilizing two coats of dissimilar matehals, the second coat being applied at the final stage of the container's production. This type of system gives very good protection, for apart from compensating for flaws in the first lacquer coat, the barrier provided by a laminate of dissimilar organic materials has very high resistance to penetration. Flush coated wax and spray coated vinyl-based lacquers are at present in production use as final coats for use with corrosive products, although wax itself, and spray coating in the case of the vinyls leave much to be desired. Development work in this connection is mainly directed at substituting thermoplastic polymers for wax, and flush coating plastisols or organosols based on high molecular weight vinyl resins, in place of spray coated vinyl lacquers. In this way, very thick films of inert solids can be built up as a final coat. TESTING The only effective way of determining the suitability or otherwise, of lacquered aluminium containers is by subjecting a sufficient number of filled specimens to shelf life tests at varying temperatures, and by extracting specimens at regular periods and examining the product and product/lacquer contact areas visually and by means of a surface microscope. Care should be taken to ensure that the specimens are representative of bulk production, and that the specimen containers have been through all the stages of pro- duction, otherwise, as has been mentioned earlier, a more favourable result may be obtained than with bulk production containers. ELECTRO-CHEMICAL TESTS Two standard types of test are in use for determining the standard of lacquer coverage on aluminium containers. The first consists basically of