Patent No. U.S. 7,115,164 B2
Sun Chemical Company has obtained a patent for a process for the manufacture of a transparent Pigment Yellow 155 or transparent Pigment Yellow 180. The process is comprised of grinding particles of the pigment in the presence of a grinding agent until the particles achieve a surface area of at least 40 m2/g; and isolating the pigment by a process comprised of preparing an aqueous slurry of the ground pigment; filtering the slurry resulting in a filter cake containing particles of transparent pigment; and either flushing the pigment from the filter cake; or drying the filter cake optionally followed by grinding.