JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS (b) The "Low Bake" lacquers, which are resins applied in solution from which the solvents are then driven off at moderate temperatures to leave a protective film which retains its full solubility characteristics. These are re- presented by the vinyl, Vinylitc, ethyl cellulose and even nitrocellulose types. (c) The micro-crystalline waxes. Which do you select ? It is a rough approximation to say that the list is in order of cost and effectiveness. Given a new product, my approach is to try it against a wide range of coatings and leave the customer to make the final choice if two or more are equally suitable. Those in group (a) have the highest chemical resistance and very few products affect them. They fail in contact with such things as dimethyl phthalate, which softens the film, mixtures of menthol and oil of wintergreen which cause stripping, and in the presence of products which are naturally vicious pin-holing agents containing high proportions of wetting agent (e.g., shampoo/conditioning creams). The latter concentrate on the inevit- able weak spots which exist in a proportion of such coatings and cause penetration at isolated points. Of the three types mentioned, Araldite is outstandingly good for its combination of high chemical resistance with good flexibility and adhesion. Epikote-based lacquers, with a chemical constitution that has much in common with Araldite, also have high chemical resistance and are less subject to application troubles. There has been some difficulty in getting a modification which could provide the exact balance in physical. characteristics needed for the collapsible tube, and this has delayed their general introduc- tion into this field. Improvements during the last year have given us lacquers which are now on trial and are showing very good results. The phenolic types are rather weak in respect of flexibihty, and efforts to improve. this inevitably lead to a reduction in actual chemical resistance. Before" leaving this group, two other points are worth mentioning. There is a tendency with certain products for these coatings to have their flexibility :'. decreased although the coating may be otherwise unaffected. Generally, the'.:.': decrease is small and only shows up on severe bending or stretching of the.::.: tube wall and can be ignored. More serious in its effect is the power which these coatings retain of causing slight discoloration of certain types of product. Fortunately, the effect appears limited to a few transparent,? colourless gels, which take on a faint brown tint, and to some of those! modern oxidation dyestuff systems which seem to have their oxidation! ' process very slightly catalysed so that a partial--unfortunately often.:i variable--premature colour development results. Normally, these lacquers/ are brownish straw-coloured, but a type of Araldite in a pigmented off-white. shade is also available with a somewhat reduced chemical resistance. The Low-Bake lacquers, of which the white-pigmented Vinylitc is easilY::i i the best known, are useful where the degree of protection desired is 114

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