12 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS •)ISCUSSiON MR. A. HERZKA: (1) What do you consider a sufficient number for shelf tests ? (2) What is your real opinion of vinyl lacquers ? When describing types of lacquers available, you refer to vinyls as excellent, yet when dis- cussing drawbacks you state that "spray coating in the case of vinyls leaves much to be desired". THE LECTURER: (1) One gross tubes, two dozen aerosols. ' (2) Vinyl lacquers are very good, particularly with light applications. The point made in my paper was that it does not matter how good the lacquer is, if it has not been put on in a proper manner it is of no use. The solids content achievable is lower with vinyl lacquers. DR. H. W. HIBBOTT: In reading your paper I felt that in view of all the difficulties of vertical scratching and transverse scratching of flexible containers, no metal tubes get out of the manufacturer's premises at all! Could you let us have more detail of the methods used to inspect and examine vertical and transverse scratching in subsequent screening opera- tions. It does seem that every aluminium tube is suffering from scratches in one direction or another. THE LECTURER ' A lot depends on the product, whether tube or aerosol can. It is extremely important that basic machinery, spindles, and extrud- ing tools are made to a very high engineering standard. Bad tooling and rough edges are to be avoided and a great amount of money and time have to be spent on tool work on the actual machinery itself. This is a matter of precision engineering. DR. H. W. Hm•OTT: On your production plant, when an item is being inspected and a flaw discovered, is it possible that several thousand such items with flaws have passed through your machinery since this item was manufactured, because of the siting of your inspectors and the speed of your machinery ? THE LECTURER: If any defects are found on inspection, the whole of the previous ha!f-hour's production is scrapped. QUESTION: Using the Denison type cell there can be misleading results. In an aluminium collapsible tube one uses a very small proportion of the tube surface and in the case of a lacquered tube, one normally cuts a speci- men from somewhere in the middle of the tube for the test, but in the case of the finished tube, shoulder and nozzle portions are not so well lacquered as the middle, and in addition the bottom of the tube cotfid be damaged in the folding operation. Is not the complete tube necessary and more useful for evaluating products than the straightforward Denison type cell ?

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