PLASTIC COATED PUSH BUTTON CONTAINERS 391 number of variables no definite pressure can be stated as maximum safe pressure. Glass pressure packaging is still new. The Interstate Commerce Com- mission has not as yet provided regulations dealing specifically with glass aerosols. In order to remain in this non-regulated category, we, at Whea- ton, have recommended that no package be formulated at a pressure over 24 lb. at 70 ø F. However, a blanket statement that 24 lb. at 70 ø F. constitutes a safe pack- age cannot be made. A 10-cc. pharmaceutical vial may be perfectly safe at over 24 lb., whereas a 4 oz. hair spray container with a large proportion of propellent may not be safe at a pressure of 18 lb. Because the glass aerosol is a non-regulated package, there is no necessity for following the prescribed hot water test method to bring the contents to 130 ø F. This is significant in that components which can be unstable at such temperatures need not be subjected to this heat. It is advisable to use a water test for the determination of leaking packages but the temper- atures need not reach 130 ø F., within the container. This is fortunate because the heat transfer through the plastic jacket and the glass is very slow in comparison to heat transfer in metal containers. The temperatures reached in a bath will not permanently affect the quality of the plastic jacket. Elevated temperatures will affect any plastic ma terial merely through increase in entropy but there is no permanent effect. Please bear in mind that none of these packages are dangerous at normal room temperatures. Expansion and pressure increases created by increased temperatures (100 ø F.) can cause fracture of the plastic jacket under cer- tain conditions where the jacket thickness is insufficient to resist elongation past its plastic limit. As has been mentioned before, the proportion of propellent to product is of considerable importance. A rapid computation of expanded volumes of propellents at 100 ø F., using basic gas laws will show that expanded volumes of propellent are proportional to the liquid mass. Pressure, per se, enters into this computation as an acceleration factor. The thickness of the plastic jacket enters the computation as a resistance to tearing, elongation, abrasion and cutting. The bottle shape enters the computation as a factor upon which the fragmentation pattern is based. The fragmentation pattern determines the possibility of long silver-like particles piercing and, upon being pierced, rupture of the jacket depends upon its proximity to the elongation limit. The case of a toy balloon can be used as an illustration. When the balloon is only partially blown up, with only little pressure in it, piercing the balloon will result in pressure release without violent rupture of the rubber. On the other hand a balloon freely distended will tear itself to pieces upon being pierced because it is close to the elongation limit of the rubber upon full dis-

392 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS tension and contains a volume of gas which is seeking to expand further. The same thing happens to a tire when a blowout occurs, but the possibility of the same thing happening with a tubeless tire is considerably smaller be- cause the wall thicknesses of a tubeless tire are considerably greater than the wall thickness of the tube and the walls are less close to their elongation limit. The larger size containers, generally hair sprays, tend to be formulated with higher propellent proportions than colognes. For this reason pres- ß sures should be lowered, and the plastic jacket should be of sufficient thick- ness to insure elongation without rupture. The venting of these heavy jackets is of primary importance. Experi- mentally it has been found that excessive venting causes rocketing effects. Insufficient venting, on the other hand, may result in rupture of the jacket and allow glass fragments to escape. We have experimented with many different venting systems and have found that large holes in the bottom of the container provide a positive venting area, and if they are of sufficient area the jacket will not approach the elongation limit. In addition to the obvious advantage of a large vent- ing area the vents do not deface the jacket which is again an important item in packaging. Slit vents, though relatively inconspicuous, do not have the positive ac- tion of round holes unless they are quite long. When slit venting is used, it has been found that expansion of the jacket is accompanied by actual tearing of the slits, which is undesirable. Therefore, it is preferable to use round holes. High cost propellents are not necessary to obtain the desired spray pat- terns in hair lacquers. However 30:70 ratios require high coating weights. There should be only one reason for using high cost propellents in hair lacquers. The low cost propellents are considerably more active in de- grading essential oils than the high cost propellents, even though there are many that are resistant to change. For the house which would like to carry out the family theme in odorants, it cannot be too strongly empha- sized that there is no adequate substitute for shelf testing to determine possibility and degree of degradation under normal storage conditions. Glass has long been recognized as one of the most resistant materials for packaging purposes. Chemical changes will take place even in glass, but the changes for the most part are on a micro scale and are difficult to detect even with advanced analytical techniques. There may possibly be in- stances which might present special formulating problems due to container attack but these should be rare compared with problems encountered in metal packaging. Why should we consider aerosol packaging? There are several advan- tages, both real and apparent, which offer the merchandiser an opportunity