Method of producing nanoparticle-in-oil dispersion

A method for producing a nanoparticle-in-oil dispersion in which fine particles made up of a solid component, an aqueous liquid component or a mixture thereof are dispersed in an oil phase, the method comprising:

• (1) a step of preparing a W/O emulsion-type precursor in which an aqueous phase in the form of droplets of an aqueous solution containing a water-soluble substance dissolved therein is dispersed in an oil phase containing an oil and a surfactant having a concentration of the surfactant within a range of 5 to 50 wt % in 100 wt % of the oil phase;
• and
• (2) a step of obtaining a nanoparticle-in-oil dispersion in which the fine particles having an average particle diameter of 30 to 195 nm are dispersed in the oil phase by boiling the aqueous phase of the W/O emulsion-type precursor.