THE COLLAPSIBLE TUBE ALUMINIUM (99'7 per cent purity) It is only since the end of the second world war that aluminium has been used in any quantity. It now constitutes well over 50 per cent of the total output, and this phenomenal rise is due to four factors. First, th• production of this metal increased enormously under the impetus of war, and the cessation of hostilities left the world with abundant supplies at comparatively low prices. Secondly, the war had adversely affected the supply of tin, with the result that its market price rocketed upwards to a peak exceeding •1,600 per ton. It has since fallen appreciably, but even now it is only just below oe740. Thirdly, advances in the chemistry of surface- coating resins had produced internal lacquers with excellent chemical resistance, good adhesion to aluminium, and a high degree of flexibility. Fourthly, chemists have shown considerable skill in finding corrosion inhibitors and in making modifications in product formulae. The tube manufacturer had his own difficulties in this change-over to aluminium, but they were eventually overcome. You, as the packer, are only interested in the service which each type will give you. Physically, the aluminium tube looks almost as good as the tin tube and far better than a lead tube. In use, it inevitably feels somewhat harsher than the familiar tin tube. Vickers Pyramid Diamond Hardness measurements reveal that it has a V.P.N. of 20 compared with 14 for tin and about 10 for lead, as used in tubes. Nothing can be done about this, and even when the manufacturer takes the utmost precaution to see that his tubes are fully annealed, there is a further effect which tends to emphasise this fundamental difference. As all of you know, collapsible tubes are impact-extruded from a slug of metal. The forces involved are very high and the whole operation is over in a fraction of a second. Where a metal work-hardens, as does aluminium, considerable heat is evolved, and a cold slug becomes a very rigid tube too hot to hold in the hand. Because of this behaviour it requires a larger press for a given size of tube than does tin or lead. The wear on the extrusion tools is likewise proportionately greater. Now a set of extrusion tools can cost from •15 to •20 to make, and one has to get the best possible life out of them. As the tools wear, and the edge of the punch is more susceptible than the wall of the die, the wall thickness of the tube increases steadily, since the annular gap between punch and die is enlarged. One thus starts at 4 thou., which is the minimum satisfactory wall thickness, and works up to the maximum limit of 6 thou., before replacing the nose end of the punch. After several such replacements the wall of the die requires attention but if it has been made to give a tube with an overall diameter on the minimum limit, it is possible to resurface the wall of the die, thereby increasing its diameter slightly, and work it again with correspondingly larger punches over the 4 to 6 thou. range. Assuming that the overall diameter tolerance is q- 4 109

JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS thou. and that each resurfacing involves the removal of 1 thou. of metal (2 thou. increase in diameter) it is theoretically possible to achieve a total of 5 runs over the 4 to 6 thou. wall thickness range. In practice, this is seldom achieved, since an unusually deep score may be made by a foreign particle on the surface of the dump, necessitating the removal of more than 1 thou. of die surface to clear it, or an accidental smash may prematurely terminate the life of the tools. I have gone into this detail because of the repeated 4 to 6 thou. wall thickness cycle and its effect upon the so-called hardness of the tube. Hardness in the true sense is independent of wall thickness, but a customer uses the term loosely to describe a combination of true hardness and the effect of thickness, a quality which I prefer to call "rigidity." This characteristic is very dependent upon thickness being proportional to the 3rd power. While the wall thickness has increased by 50 per cent it has gone up by 238 per cent. Thus the expert responsible for the working of a filling machine is quite right when he says that the tubes he is using to-day are stiffer or more rigid than those going through earlier in the week. He will only be justified in blaming inadequate annealing if there is also evidence of residual spring in the metal. So far so good you have liked the cost and the appearance and have resigned yourself to the necessity of accepting a tube of a slightly stiffer character. There are no difficulties so far as decoration is concerned and you are left with the question of possible corrosion. With aluminium it is particu- larly necessary to proceed with caution, as quite a large number of compounds are reactive towards it. Since I have been asked to speak particularly on corrosion and seepage I shall deal with these general subjects after completing the review of the metals. TIN It is no exaggeration to say that tin is the ideal metal for making a collapsible tube. It has an excellent surface appearance which does not tarnish with the passage of time. It is not subject to work-hardening and has perfect manipulation characteristics while the product is being e:kpelled from the tube. Only a very limited range of products are unsuitable from the corrosion angle, and toxic effects are absent. Cost alone has allowed alumin- ium to supplant it on such a wide scale, but there are still certain types, such as the familiar eye ointment tube, for which it is essential, since elongated nozzles are not practicable in the harder metal. LEAD This metal in its natural state is rather too soft for making satisfactory tubes and is often hardened by small additions of other metals. It is still by a narrow margin the cheapest tube available, but its appearance leaves 11o