Phthalocyanine pigments acid pasting

Less widely used methods include acid pasting, i.e., dissolving the material in a medium such as chlorosulfonic acid and precipitating it in water, or milling the crude pigment. These methods gain importance whenever phthalocyanine is to be chlorinated by a route other than with aluminum chloride or acids. 

Another method, used particularly with phthalocyanine blues and greens, involves dissolving the pigment in a strong sulfuric acid (acid-pasting) and then controlling the particle size during precipitation into water. 

Acid Pasting. The crude pigment is dissolved in a massive excess of concentrated sulfuric acid, from which it is then reprecipitated in a controlled manner by drowning out the acid solution into iced water to obtain the red-shade, crystallizing-grade, alpha copper phthalocyanine blue. 

Phthalocyanines are extremely difficult to purify and characterize beeause most are only sparingly soluble in common solvents. The typical purification procedure, aeid pasting, entails dissolving the pigment in coneentrated sulfuric acid followed by precipitation into ice water. It has been found that both the synthetie route and the... 

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