Process of producing a particle having a core-shell structure

A process for producing a particle having a core-shell structure and comprising an organic solid component (A) containing a thermoplastic polymer (A1) and a thermoplastic hydrophilic polymer (A2), which comprises

• kneading the organic solid component (A) with a water-soluble auxiliary component (B) containing at least an oligosaccharide (B1) to provide a composition which has a disperse system and comprises a matrix comprising the water-soluble auxiliary component (B) and a particulate dispersed phase comprising the organic solid component (A) and dispersed in the matrix, wherein the particulate dispersed phase corresponds to the particle having a core-shell structure, and
• eluting the auxiliary component (B) from the composition;
• and
• wherein the core of the particle contains the polymer (A1) and the shell of the particle contains the hydrophilic polymer (A2) which has a hydrophilicity higher than the polymer (A1),
• wherein the particle is spherical and has an average particle size of 0.1 to 100 μm, a coefficient of variation of the average particle size of not more than 60.