PURIFICATION PROCESS FOR VANADYL PHTHALOCYANINE
Original Publication Date: 1978-Dec-31
Included in the Prior Art Database: 2004-Mar-31
Xerox Disclosure Journal
Disclosed is a process for purifying crude vanadyl phthalo-cyanine using the strong solvating power of sulfuric acid in such a manner that the organic as well as inorganic impuri-ties, for example, vanadium salts or acids can be extracted and washed away from the pigment. This purification can occur even though the vanadyl phthalocyanine is completely soluble in concentrated sulfuric acid in that it forms an insoluble entity in acid concentrations from 75 to 85% with water, thereby allowing the isolation and washing of this inter-mediate with such strong acid solutions In a specific embodiment, the method involves complete solution of the crude pigment in concentrated sulfuric acid prior to dilution of the acid concentrations to 75 to 80% with water at which point the green crystalline pigment-sulfate intermediate is isolated and washed with the same acid medium. It is only after washing with the strong acids that the free pigment is generated by quenching into large amounts of water, In this manner, impurities that may be occluded in the synthesis are freed by the dissolution and filtration of the pigment sulfate which will remove those impurities which would precipitate or re-absorb in a simple acid-pasting procedure.