Process for alpha-phase metal phthalocyanine pigments

This invention relates to a process for preparing alpha-phase metal phthalocyanine pigments from crude metal phthalocyanine pigments comprising (a) acid pasting or acid swelling a crude metal phthalocyanine pigment; (b) dry milling the acid-pasted or acid-swelled metal phthalocyanine pigment in the presence of 5 to 50 parts by weight of a stabilizer per 100 parts by weight of the crude metal phthalocyanine pigment until the average particle size is reduced to less than about 0.5 mu m; (c) finishing the milled metal phthalocyanine pigment by thoroughly mixing said milled metal phthalocyanine pigment with a finishing solvent mixture comprising 3 to 6 parts by weight, relative to the crude metal phthalocyanine pigment, of water and 0.4 to 1.0 parts by weight, relative to the crude metal phthalocyanine pigment, of an organic solvent, optionally in the presence of 0 to 45 parts by weight of a stabilizer per 100 parts by weight of the crude metal phthalocyanine pigment, with the proviso that the total amount of stabilizer used in steps (b) and (c) ranges from 5 to 50 parts by weight per 100 parts by weight of the crude metal phthalocyanine pigment; and (d) isolating the alpha-phase metal phthalocyanine pigment.