PROTECTIVE LACQUER SYSTEMS FOR ALUMINIUM CONTAINERS ThE LECTURER: I agree to some extent. The Denison cell is used for noting the behaviour of a known film of lacquer in relation to a particular product and trying to assess corrosivity of the product it is also used for evaluating inhibitors. Using the method outlined by the questioner, it is extremely difficult to distribute a standard amount of electrolyte uniformly. To use a cell of the Denison type is to cut out most of the variables and deal with a couple only. Admittedly, such over-simplification does not give a one hundred per cent insurance. MR. S. F. TOWNSEND: Regarding the film weight test, does one remove epoxy lacquer from a defmite area by scraping and re-weighing ? Does the lecturer know of a better method, or of efficient solvents ? ThE LECTURER: The lacquer is normally softened under reflux with acetone, and rubbed off with a duster. MR. D. F. C. EDE: Adhesion and corrosion resistance can be helped and improved by anodising. To what extent does this add to the price of the finished product ? ThE LECTURER: With an anodised aluminium surface, the price of collapsible tubes is prohibitive. Aerosol containers are anodised quite a lot but principally for subsequent decoration this also helps lacquer adhesion. I wish to make a point here. To obtain good corrosion resistance with a particular corrosive product, you must have good lacquer adhesion, which is extremely important. MR. A. HERZKA: IS there any possibility that the product would penetrate through the lacquer, destroying adhesion ? ThE LECTURER: It is usual to test the product in a lacquered container first of all to determine its suitability for the type of product but one can still get failures. Although a product has already been assessed as satisfactory in a particular container, it can still fail because of a defect in lacquer and adhesion. MR. D. M. BRYCE: Irish Moss and alginates are stated to be very corrosive can you expand on this ? ThE LECTURER: Trials have been carried out with these materials and it has been found that they cause breakdowns, particularly with the Araldites, which are very prone to penetration. DR. •K. G. JOHNSON: In our experiments we have noted severe corrosion with Irish Moss. An extract will give corrosion with an Araldite lacquered aluminium tube, but corrosion becomes much worse when glycerine or a certain amount of inorganic salts are present. MR. A. FOSTER: If adhesion is perfect in the dry state and the container

14 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS is adequately lacquered, does it mean that the lacquer is, in fact, not suitable for the product if the film lifts after filling ? THE LECTURER: Very often the lacquer itself is eminently suitable for the product. Usually it is defective application, e.g. heat treatment of the container, or lubricant residues which cause loss of adhesion. Particularly traces of lubricants, which in the dry state give perfect results, may cause the films to fail very drastically after being in contact with the product for some little time. MR. A. FOSTER: Then the product does have some kind of effect on the lacquer ? THE LECTURER: If everything else had been equal and if some permea- tion had taken place, it would not have happened if there had not been some defect in the processing of the containers. The product does obviously have some effect, but this would have been cancelled out if the processing had been correct. MR. A. SMITH: The lecturer makes the point that in order to overcome the difficulty of lacquering at the nozzle of a collapsible tube, a plastic nozzle may be used. This approach, however, does not seem to have found universal use. Does the elaborate type of plastic nozzle used have a cost effect on the finished tube ? THE LECTURER: There is now a greater tendency to use plastic nozzles and I think they will come into more general use. Polypropylene and high density polythene are often used. I do not consider, particularly with the envisaged usage, that in the long run the cost factor will be important or make much difference. MR. A. SMITH: IS there an additional problem of sealing the nozzle ? THE LECTURER: No. There is a standard test for assessing the tightness of the nozzle. This is an engineering problem and not insuperable. MR. R. CLARK: We have experienced product spoilage arising from corrosion at the neck of the tube. A fresh annealing process did improve the tubes but there was still product spoilage. The metal on the shoulder and body of the tubes differed. Lacquering was resorted to and because of the cost of varnishing, the tubes were more expensive. To cancel out variables, standard lacquering had to be resorted to presumably more and improved efficient production lines reduce the unit cost of the tube, but does it benefit the buyer ? THE LECTURER: I never discuss prices. MR. R. K. WALMSLEY: The degree of lacquer curing is very important. Could you elaborate how we can establish the degree of the curing ?