Preparation of O/I₁-type Emulsions and S/I₁-type Dispersions Encapsulating UV-Absorbing Agents

抄録

Oil-in-cubic phase (O/I₁) emulsions encapsulating the cosmetic UV absorbing agents 2-ethylhexyl 4-methoxycinnamate (EHMC), 2-ethylhexyl 2-cyano-3,3-diphenylacrylate (octocrylene, OCR) and 1-(4-tertbutylphenyl)-3-(4-methoxyphenyl)-1,3-propanedione (Avobenzone, TBMP) were prepared by vortex mixing accompanied by a heating-cooling process. A ternary phase diagram in a water/C₁₂EO₂₅/EHMC system at 25°C was constructed and the two-phase equilibrium of an oil phase and an I₁ phase, which is necessary to prepare the O/I₁-type emulsions, was confirmed. Also, the melting of the I₁ phase into a fluid micellar solution phase was confirmed, allowing emulsification by a heating-cooling process. The O/I₁-type emulsions were formulated in the ternary system as well as a quaternary system. The four-component system contained an additional cosolvent, isopropyl myristate (IPM). The use of the cosolvent allows the use of reduced amounts of EHMC, which is desirable because EHMC can cause temporary skin irritation. Formulation of the O/I₁-type emulsions with other UV absorbing agents (OCR and TBMP) was also possible using the same emulsification method. When IPM was changed to tripalmitin, which has a melting point greater than room temperature, a solid-oil dispersion in I₁ phase was formed. We have termed this a “solidin-cubic phase (S/I₁) type dispersion”. These novel emulsions have not been reported previously. The UV absorbability of the O/I₁-type emulsions and S/I₁-type dispersions that encapsulate the UV absorbing agents was confirmed by measurement of UV absorption spectra.