352 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Table I Comparison between Occlusive Effect of O/W and W/O Type Emulsions Emulsion Type o/w w/o Time required to begin showing occlusivity after application (min) Time required to reach to the maximum occlusivity after application (rain) Maximum occlusivity (%) Occlusivity at 135 minutes after application (%) 50 65 90 120 28 33 19 30 film was formed in the case of the o/w emulsion due to the coalescence of the droplets. A similar oil film was also formed by the w/o emulsion upon the evaporation of water and the occlusive effect of both types of the emulsions observed was almost the same in spite of the opposite emulsion type. An occlusive film formed from o/w emulsions tends to re-emulsify by the skin moisture because the oil film contains a small amount of hydrophilic emulsifier. However, those oil films formed from w/o emulsions containing a hydrophobic emulsifier seldom re-emulsify. The HLB number of the emulsifier may affect • the destruction of oil films by re-emulsification. Our data in Table I indicated the possibility that the occlusive effect of w/o type emulsion would last for a long period of time. The effect of the droplet diameter of emulsions on the occlusivity was determined and Figure 5 shows the results. As seen from the figure, the occlusivity of solid paraffin in the emulsion form decreased markedly with the increase in the particle size, while that of liquid paraffin in the emulsion form did not depend on the droplet diameter. It was observed that the particles of solid paraffin in a fine emulsion packed closely, forming lOO 5o u •= LP(120M] • LP(60MIN) SP(120MIN) SP(90MIN) SP(60MIN) 0 I I , i I I I I, 20 40 60 80 MEAN DROPLET DIAMETER(MiCRONS) Figure 5. Effect of droplet diameter of emulsions composed of oils on occlusivity.

OCCLUSIVITY OF OIL FILMS 353 SOLID PARAFFIN EARLY STAGE FINAL STAGE o_ooo COARSE . ._ ..(J...• ,0: ..• ...,, .:..• EMULS ION "' ::': :'" '" ' ' "" ":' :': i:."'•:.": :."':?"'•"".". ::...:....':.... ..:....'.....:.'...•.. 0 0 0 000 o o 0 o oo0o•ooooo FINE o o o ..' ...• EMULSION ':.'•3:'",:.!!":•:'?:)':i ' ?.•.' :',:') :':.'": :':: :: '-"-'".':: ' 1::': LIQUID PARAFFIN EARLY STAGE FINAL STAGE COARSE EMULSION i 0 0 0 0 0 O0 i i o o o .=, FINE o. o:• • . '.•:...x :' "':" -"'" ' "'" '" : i "'.'5 '"':-": ? :=:5 ( 7.'.:. ':.:..":".".5'.':':.-,.4._ EMULSION .: :":':". ! 7.".' 5.".".-': '.' ::.....- ..... ... Figure 6. Schematic illustration of residual states of solid paraffin and liquid paraffin emulsions of different particle size on skin surface. a firm and flexible film, whereas the film formed by solid paraffin in a coarse emulsion had a high porosity. The changes of the states of oil films on the skin surface respecting time are schematically shown in Figure 6. The formation of a continuous oil film was also observed with liquid paraffin in both fine and coarse emulsions. Although there existed a time lag until the continuous film was formed because the rate of coalescence depended on the droplet size, the final state of the oil films was the same both for fine and coarse emulsions. This is also illustrated in Figure 6. Since rubbing is the general technique used to apply cosmetic creams to the skin, the effect of rubbing on the occlusive effect was also investigated. Table II summarizes the