US Patent 7192477 Process for producing pigment nanoparticle

The process for producing highly concentrated nanometer-size fine particles of an organic pigment, which comprises dissolving the organic pigment in an amide solvent, especially an organic solvent comprising at least 50 vol % 1-methyl-2-pyrrodinone, and pouring the resultant organic pigment solution with stirring into a poor solvent which is not compatible with the organic pigment. The pigment may be a quinacridone pigment, phthalocyanine pigment etc. Any atmospheric pressure to a sub-critical and/or supercritical state can be employed as the production conditions.