As shown in Table 1, untreated vitamin C ester is not so stable in both a weakly basic O/W type emulsion emulsified with a soap and a nonionic surface active agent (Base I) and a weakly acidic O/W type emulsion 45 emulsified with a nonionic surface active agent (Base II). However, when using the oil-treated vitamin C, stability is improved. Particularly, when the oil-treated vitamin C or the ester thereof is formulated in Base II, stability thereof is remarkably improved. Further, as 50 shown in Table 2, the oil used for the treatment of vitamin C is not limited a specific kind of oils, but a nonpolar oil is preferred.
Thus, the emulsion cosmetic of the present invention is prepared by homogeneously dispersing and mixing a 55 mixture of L-ascorbic acid or a fatty acid ester thereof and an oil in an emulsion, preferably, in an O/W type emulsion emulsified with a nonionic surface active agent, more preferably, in a weakly acidic O/W type emulsion.
The L-ascorbic acid used may be in the form of either a free acid or a fatty acid ester. Examples of the fatty acid ester include mono-, di- or triesters of fatty acids having 10 or more carbon atoms such as monopalmitate, dipalmitate, monostearate and distearate thereof.
As mentioned above, the oil used for preparation of the above mixture is not limited to a specific one. Although oils having relatively higher polarity such as