Diketopyrrolopyrrole cocrystals with high transparency
View Patent ↗The present invention relates to a pigment composition composed of compounds of the formula (I), (II) and (III) with a novel crystal modification, to their preparation and to the use of this novel product as a pigment. For many applications of organic pigments, for example the coloring of metallic lacquers or the use thereof in color filters, a very high transparency is required. To produce color filters, for example, particularly fine pigments are used, in order to substantially rule out the particle scattering which leads to a lowering of the contrast ratio. The commercially available products, however, do not always meet all requirements of the art. More particularly, there was a need for improvement with regard to the transparency and the associated fineness of the pigment crystals, and also the color purity (chroma).
1. A mixed crystal comprising compounds of formula (I), (II), (III),
obtained by reacting a succinic diester with a nitrile mixture comprising 95 to 83 mol % of 3-chlorobenzonitrile and 5 to 17 mol % of 4-X-benzonitrile,
wherein X=chlorine, methyl or nitrile and the molar fractions of said 3-chloro- and 4-X-benzonitriles summing to 100 mol %, and
wherein the mixed crystal has a BET surface area of 90 to 150 m 2 /g.
2. The mixed crystal as claimed in claim 1 , wherein X is chlorine.
3. The mixed crystal as claimed in claim 1 , wherein the mixed crystal has a characteristic line in a x-ray diffraction diagram at 2 theta 18.5°+/−0.2, measured with Cu—K α radiation.
4. The mixed crystal as claimed in claim 1 , wherein the main signals in a x-ray powder diagram:
2 theta:
relative intensity:
5.8
s
13.2
s
14.9
w
16.3
w
18.5
m
20.9
w
24.1
m
25.7
s
27.4
s
29.7
m
wherein the x-ray powder diagram is Cu—K α , radiation, 2 theta values in degrees, measuring accuracy +/−0.2°, intensities: s=strong, m=medium, w=weak).
5. A process for preparing a mixed crystal as claimed in claim 1 , comprising the steps of reacting a succinic diester with 95 to 83 mol % of 3-chlorobenzonitrile and 5 to 17 mol % of 4-X-benzonitrile in an organic solvent in the presence of a strong base and at elevated temperature to form a pigment alkali salt, hydrolyzing the pigment alkali salt in water, alcohol or both to obtain the mixed crystal and optionally solvent finishing the hydrolyzed pigment alkali salt, wherein X=chlorine, methyl or nitrile.
6. A macromolecular organic material of natural or synthetic origin pigmented by a mixed crystal as claimed in claim 1 .
7. A composition pigmented by a mixed crystal as claimed in claim 1 , wherein the composition is in a form selected from the group consisting of plastics, resins, coatings, paints, printing inks, electrophotographic toners, electrophotographic developers, color filters and liquid inks.
8. A color filter, metallic coating or inkjet ink pigmented by the mixed crystal as claimed in claim 1 .