The Conditioning of Perylene Diimide Pigments

Acid pasting is a pigmentation process in which perylene cmde is dissolved in concentrated ( 90%) sulfuric acid, and then reconstituted by precipitation under precisely controlled conditions, to produce a pigment with the desired physical characteristics. Acid sweUing is a similar process, except that 75-85% sulfuric add is used to partially solubilize the cmde to achieve an equUibration between the smallest and 

Vatting is a process where the perylene crude is chemically reduced in an aqueous alkaline dithionite solution to a (colorless) leuco form, then filtered and washed to remove impurities. It is then oxidized by air or peroxide to give purified and recrystaUized perylene pigment [40]. Since this type of processing purifies the pigment, higher chroma and specific hue shifts can often be obtained as a result. 

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