THE COLLAPSIBLE TUBE moderate order. Apart from a lower degree of chemical resistance, they often fail through the fact that the coating retains its full solubility character- istics. Under alkaline conditions, failure often takes the form of complete stripping of lacquer film from the tube wall. The third group, the microcrystalline waxes, are very old friends and known to everybody. They are very versatile in that they are applicable to any type of tube and are about equal to the Low-Bake lacquers in the degree of protection offered. There is some prejudice against them among users since wax contamination of machine closing jaws can cause hold-ups. They have one hidden virtue in that the coating is itself a good anti-seepage device for the crimped end. Sometimes I am asked: "Why don't you supply internally anodised aluminium tubes ?" The answer is that the cost would be unduly high owing to the nature and number of the articles involved, and people would not like the appearance of the shoulder and nozzle. It has also to be remembered that anodised coatings tend to be both brittle and rigid, and therefore unsuitable for a collapsible tube. SEEPAGE Now- I come to the age-old problem of seepage which must have bedevilled the lives of many of you at some time or other. Since the tube has an opening at both ends the problem is two-fold, and I will deal with the nozzle end first. In practice, there has been more progress in defeating the evil at this end than at the crimp. The complete solution, of course, is the blind end tube which is well known in tin, tin-plated lead, and lead but it so happens that the majority of tubes used are aluminium. The fact that aluminium is so much harder than the other two has placed a formidable obstacle in supplying it with a blind end. Unless one can maintain a uniformly thin membrane across the nozzle (i.e., comparable with the wall thickness) piercing becomes a matter of extreme difficulty. The practical difficulties of this were thought to be unsurmountable and you may well have resigned yourselves to leaving this one out of your schemes. However, I can reveal that such a tube has been made successfully in France, and I hope that it will eventually become available over here. Turning our attention to the open type of nozzle we see that considerable progress has been made in solving this sealing problem, and in every case the solution devolves around the principle of applying the limited force available from the screw thread to make a seal in which the area of contact is kept as low as possible. Consider the following examples: (1) The Plug Cap. In this case, a conical plug is pushed into the orifice of the nozzle and forms its own seating by a slight deformation of its trimmed, inner edge. The area of contact is small and even the softest metal gets outside support from the threaded part of the cap, which prevents excessive '115

JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS distortion. The system is not very good with aluminium because the metal is hard enough to resist everything but the slightest deformation at this edge, and so does not fully compensate for any eccentricity which is often present in the system. (2) The Patented Inner Ring-type Caps. In order that these can function properly the end of the nozzle has to be specially faced off. In one case, an annular ring formed in the top of the cap, adjacent to the threads, has a narrow, flat face leading to a central recess whose vertical walls taper out- wards in the direction of the threads. The tube is extruded to have the normal nozzle, which is subsequently threaded, plus a central extension of smaller diameter which tapers towards its tip. This tapered elongation enters the central recess in the cap and a seal is formed between the two tapers. One can really regard it as a refined version of the plug cap in reverse. A further variation on this theme combines both the inner and outer seal principles. The nozzle end is formed similar to the one just described, whilst the cap has an additional feature in the form of a hollow, central plug. The tapered elongation at the end of the threaded nozzle is forced into the V-shaped annular recess so formed in the cap and a double seal results. In yet another case, the moulded cap is a normal one except for the fact that it has a narrow concentric ring in the form of a V-shaped knife edge where the wad would normally be. The tube nozzle is also normal, but has to be carefully faced off to give a smooth, flat, end surface. When the cap is screwed on, the knife edge bites into the surface of the aluminium to a depth of about 0.003 in., forming a perfect seating. The system is one of extreme simplicity, independent of any location requirements, and takes the principle of applying the available force over the smallest area of contact to its logical conclusion. (3) Wadded Caps. In the majority of cases in which seepage occurs where the ordinary wadded cap is in use, the trouble is due to disintegration of the wad. Shaving creams are particularly bad offenders in this direction. All manner of facing materials have been tried, but the weakness really lies in the compo-cork base. The cap applies pressure between it and a fairly large area of nozzle end surface. Under the effects of prolonged pressure and chemical attack the cork loses its resiliency and eventually seepage must result. The advent of polythene as a liner material was hailed as the answer to this problem of chemical disintegration, but its natural hardness would not permit sufficient compression to ensure that a complete seal was formed. Had human fingers been replaced by a spanner the defect might have disappeared. Only quite recently has the basic principle of applying the available limited force over a minimum area of contact been. called into service. Now we have a heavily chamfered nozzle end whose I16