AEROSOL EMULSION SYSTEMS :279 emulsions that occurs as the proportion of water is increased. ]'his point will be discussed in more detail later. Emulsions of "12"/"11" generally exhibit slight bubbling when sprayed on a surface. For some uses, this may be undesirable. The bubbling probably results from vaporization of the "11" that is retained in the spray. Emulsions with dluxiliary Solvents The use of auxiliary solvents, such as odorless mineral spirits, has a number of advantages in formulating aerosol water-in-oil emulsions. As shown later, the solvents may increase emulsion stability, particularly with emulsions formulated with "12" alone or "12"/"114" solutions as the propellents. As previously noted, "12"/"1 l"/water emulsions tend to cause bubbling when sprayed on a surface. The addition of an auxiliary solvent may minimize or eliminate the bubbling entirely. The ease of preparation of the emulsions is increased considerably by the use of solvents. For example, the solvent may be used to dissolve the water-insoluble surface-active agent. A water-in-oil emulsion is then prepared from the solvent by adding the water to the solvent. This emulsion is used to fill the aerosol container. The propellent is pressure loaded after capping the container. In this case, the addition ofpropellent to the previously formed emulsion can be considered merely as extending the continuous oil phase. Under the present ICC regulations, "12"/water emulsions would not be permissible in the standard aerosol containers as a result of pressure limitations. Auxiliary solvents serve as pressure depressants for "IT' and permit the formulation of emulsions using "12" alone as the propellent. Propellent "12"/ Solvent/tl/ater Systems Emulsion systems of "iT'/odorless mineral spirits/water produce non- foaming sprays. The spray characteristics themselves may be varied over a wide range from very fine to very coarse by changing the "12"/solvent ratio. Examples of this are listed in Table 4. TASLE 4--Pv. oPEL•E•v "12"/OooR•SS M•ERAL Sm•vs/WxvE• EMuLsions Propellent "12"/OMS*/H20 .---•Separation Times--• Spray Ratio, Wt. % Without "12" With "12" Characteristics 60/20/20 1 hr. 1-5 min. Fine 40/20/40 l hr. 1 hr. Medium 20/20/60 1 hr. 1 hr. Wet 60/30/10 5-15 min. 1-5 min. Fine 60/10/30 1 hr. 1-5 min. Fine 4 parts Emcol 14/104 parts of finished emulsion * OMS = Odorless mineral spirits.

280 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS As discussed previously, "12"/water emulsions of satisfactory stability were not obtained. As shown by the data in Table 4, the effect of the odorless mineral spirits is to increase the emulsion stability considerably. A comparison of the stability of the odorless mineral spirits/water emul- sions before and after the addition of "12" is also shown in order to indicate the effect of the "12" upon the emulsion stability. Propellent "12" decreases the emulsion stability but in most cases the stability is still sufficient for practical purposes. Odorless mineral spirits is one of the best solvents for obtaining non- foaming sprays. For certain applications, other solvents such as cotton- seed oil may be more desirable. These solvents form fairly good emulsions but in some cases there appears to be a tendency to promote slight bubbling or foaming. Propellent "Z2"/"ZZ¾"/Odorless Mineral Spirits/1/Fater Emulsions Pressures of 25 psig. or less at 70øF., are generally considered desirable for aerosols to be packaged in glass. In "12"/odorless mineral spirits/ water systems pressures below 25 psig. may be achieved by the proper ratio of propellent to solvent. As discussed later, however, the extent to which this can be done is limited by flammability considerations. In order to obtain pressures below 25 psig. it may be necessary to have such a low propellent/solvent ratio that the product is flammable. It is also found that emulsions with sufficiently low "IT'/odorless mineral spirits ratios to satisfy the pressure requirements generally give excessively wet sprays. The above difficulties may be eliminated by formulating with "IT'/ "114" solutions as the propellent. Emulsion systems producing sprays ranging from very wet to fine may be obtained by varying the ratio of "iT' to "114." The propellent solutions with a low concentration of "12," TABLE 5--PROPELLENTS "12"/"114"/OooRLESS MINERAL SPIRITs/WATER EMULSION Propellen ts Propellen ts "12"/"114" Spray "12"/" 114" Spray Ratio, Separation Charac- Ratio, Separation Charac- Wt. % Times teristics Wt. % Times teristics Propellent/Solvent/Water Ratio 60/20/20 0/100 1-5 min. Soft-- medium wet 15/85 1-5 min. Soft-- medium wet 40/60 1-5 min. Medium 57/43 1-5 min. Medium fine 100/0 1-5 min. Fine Propellent/Solvent/Water Ratio•'tO/20/40 0/100 15-30 min. Very wet 15/85 15-30 min. Medium wet 40/60 15-30 min. Medium 57/43 l hr. Medit, m 100/0 1 hr. Medium fine 2 parts Eracol 14/102 parts finished emulsion