PROPELLENTS IN PRESSURIZED PACKAGING 349 130 Typical Temperature.pressure relationship in pressure dispensed packages. 120 • 110 • 100 '"" 90 8o 7o 6o j_ 1_0"_ i NITROUS OXIDE and CARBON DIOXIDE 185:15%1 8 Fl. Oz. FILL 3 PSIG I 50 60 70 NITROGEN 8 Fl. Oz. FILL / / / / VAPOR PRESSURE • OF PROPEL 12 114 (50 501 ß ß / VAPOR PRESSURE • OF PROPELLENT • 12 11 (50 501 ß / ß I I . 80 90 o o o CENTER TEMPERATURE DEGREES F. Figure 5. nonfood field utilizing nitrogen as a propellent was toothpaste. Since pressurized toothpaste occupies the unique position of being a first in the industry, it is of some historic interest and warrants an exposition that should be of value to a wide variety of products. The basic problem presented by toothpaste involves its consistency. In toothpaste of fairly high viscosity, the type traditional with the consumer, a phenomenon occurs known as cavitation. This cavitation effect is illus- trated in Fig. 7. It was therefore necessary to eliminate or minimize the adherence of the fill to the internal container walls caused by cavitation. To deal with the problem, Prussin et aL applied for a patent involving the quantitative exhaustion of bulk substances characterized as relatively vis- cous materials through application of a lubricating system to the internal container. For a toothpaste this was accomplished with a binary system consisting of a microcrystalline wax--polyisobutylene resin substrate and an oil overlay. The application of the oil system minimizes cavitation and results in a surface configuration graphically represented in Fig. 7. Of course, many factors are involved in toothpaste. It is possible to

350 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS SOLUBILITY OF GASES IN H• 0 ml(STP) Solubility Coefiqcient oc Alm-ml TEMPERATURE 'C Gas P ,atm 0 15 20 25 30 40 50 60 1.0 0.0235 0.0168 0.0154 0.0143 0.0134 0.0118 0.0109 0.0102 Nitrogen 20.0 0.01235 1.0 1.0954( :'•) 0.7778 0.6700 0.5961 N:•O 6.6 O.55 1.0 1.713 1.019 0.878 0.759 0.665 0.530 0.436 0.359 CO? 5.0 1.73 10.0 1.60 1.0 0.056 0.0336 0.0310 0.0288 0.0252 0.0223 A 25 0.0516 5O O.O5O4 Figure 6. CAVITATION ILLUSTRATED t B' B C' C D' D E' Figure 7.