Crystal polymorphs of C.I. Pigment Yellow 191 and their preparation

C.I. Pigment Yellow 191 in the form of a crystal lattice of the formula (1) or a tautomeric, cis/trans-isomeric or tautomeric cis/trans-isomeric form thereof

• wherein the C.I. Pigment Yellow 191 exhibits the following reflections in a X-ray powder diffractogram, measured with Cu-Kαradiation:
• beta-polymorph:
• 2Θ d rel. intensity 4.90 18.03 100 8.44 10.47 9 9.49 9.31 10 10.04 8.80 19 12.53 7.05 8 14.73 6.01 12 15.21 5.81 20 15.79 5.60 12 16.93 5.23 9 17.74 4.99 17 18.50 4.79 13 19.79 4.48 13 20.11 4.41 17 21.77 4.07 7 23.01 3.86 8 25.44 3.49 32 25.85 3.44 19 26.89 3.31 10 29.11 3.06 7 29.71 3.00 5 30.40 2.93 7 or gamma polymorph 2Θ d rel. intensity 4.77 18.49 100 10.08 8.76 27 11.79 7.50 29 13.39 6.60 20 14.34 6.17 21 16.71 5.30 22 18.23 4.86 30 21.22 4.18 29 22.67 3.91 21 23.10 3.84 20 25.79 3.45 36 or delta polymorph 2Θ d rel. intensity 4.69 18.82 46.6 8.14 10.85 28.1 8.67 10.19 23.8 10.09 8.76 24.7 11.37 7.78 25.1 13.50 6.55 18.8 15.83 5.60 19.9 16.27 5.44 22.9 17.03 5.20 29.2 17.70 5.01 20.7 19.13 4.63 20.4 19.39 4.57 26.1 20.27 4.38 22.0 21.41 4.15 39.6 22.96 3.87 32.4 24.16 3.68 100.0 24.79 3.59 26.1 26.30 3.39 21.2 27.14 3.28 11.3 27.67 3.22 12.8 30.99 2.88 10.5 31.59 2.83 10.6 33.13 2.70 10.6 or epsilon polymorph 2Θ d rel. intensity 5.34 16.54 66 7.81 11.31 100 12.20 7.25 35 18.49 4.79 45 23.22 3.83 63 25.04 3.55 57 29.58 3.01 29 or a mixture of these polymorphs.

A C.I. Pigment Yellow 191 mixture comprising at least 10%, of the beta, gamma, delta or epsilon polymorphs:

• beta-polymorph:
• beta-polymorph:
• 2Θ d rel. intensity 4.90 18.03 100 8.44 10.47 9 9.49 9.31 10 10.04 8.80 19 12.53 7.05 8 14.73 6.01 12 15.21 5.81 20 15.79 5.60 12 16.93 5.23 9 17.74 4.99 17 18.50 4.79 13 19.79 4.48 13 20.11 4.41 17 21.77 4.07 7 23.01 3.86 8 25.44 3.49 32 25.85 3.44 19 26.89 3.31 10 29.11 3.06 7 29.71 3.00 5 30.40 2.93 7 or gamma polymorph 2Θ d rel. intensity 4.77 18.49 100 10.08 8.76 27 11.79 7.50 29 13.39 6.60 20 14.34 6.17 21 16.71 5.30 22 18.23 4.86 30 21.22 4.18 29 22.67 3.91 21 23.10 3.84 20 25.79 3.45 36 or delta polymorph 2Θ d rel. intensity 4.69 18.82 46.6 8.14 10.85 28.1 8.67 10.19 23.8 10.09 8.76 24.7 11.37 7.78 25.1 13.50 6.55 18.8 15.83 5.60 19.9 16.27 5.44 22.9 17.03 5.20 29.2 17.70 5.01 20.7 19.13 4.63 20.4 19.39 4.57 26.1 20.27 4.38 22.0 21.41 4.15 39.6 22.96 3.87 32.4 24.16 3.68 100.0 24.79 3.59 26.1 26.30 3.39 21.2 27.14 3.28 11.3 27.67 3.22 12.8 30.99 2.88 10.5 31.59 2.83 10.6 33.13 2.70 10.6 or epsilon polymorph 2Θ d rel. intensity 5.34 16.54 66 7.81 11.31 100 12.20 7.25 35 18.49 4.79 45 23.22 3.83 63 25.04 3.55 57 29.58 3.01 29 or a mixture of two, three or four of these polymorphs.