Epsilon copper phthalocyanine

It may be not so easy to develop such pigments, but blue pigments with a more reddish shade may be affected by consideration of crystal forms, substituents, and central metal ions. It has been found that copper phthalocyanine, synthesized from a mixture of phthalic anhydride and a small portion of trimellitic anhydride and pyr-omellitic anhydride in sulfolane as solvent under pressure, exhibits the pi form, with a more reddish shade than that of epsilon copper phthalocyanine. ... 

Copper phthalocyanine is available as two major commercial forms, the alpha and the beta crystal. Other crystal variations such as the epsilon crystal PB 15 6 are available commercially but on a very limited basis. The alpha crystal is described as Cl pigment blue 15 1 and 15 2 and is a clean, bright-red-shade blue. The beta crystal is described as Cl pigment blue 15 3 and 15 4 and is a clean green-shade blue. The beta form is the most stable crystal form and readily resists crystallization. The alpha form, conversely, is the least stable, or meta, form and readily converts to the more stable, green-shade beta crystal. As such, the alpha crystal requires special, proprietary treatments to produce a red-shade product offering stability to both crystallization and flocculation. 

The epsilon form of copper phthalocyanine blue (C.I. Pigment Blue 15 6) and bro-minated copper phthalocyanine green (C.I. Pigment Green 36) are used respectively as the basic colorants for blue and green pixels in color filters. But these two pigments are not satisfactory as the primary colors in the system. 

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