| 摘要 |
PROBLEM TO BE SOLVED: To provide a method for producing aδtype indanthron blue pigment having a more reddish hue and a higher chroma than those of an a type indanthron blue pigment, a less dichromatic property (a flip-flop property) than that of the a type indanthron blue pigment as a coating material, especially as a mica and aluminum metallic coating material and a weather resistance practically fitting for use, without using a large amount of a reducing agent or an oxidizing agent such as hydrosulfite or hydrogen peroxide. SOLUTION: This method for producing aδtype indanthron blue pigment is to dissolve or disperse a crude indanthron blue with sulfuric acid or an aqueous solution thereof to obtain a solution containing a reduced indanthron blue, then adjusting the concentration of sulfuric acid at 79-86 wt.%, putting the solution into water for obtaining a crudeδtype indanthron blue pigment and then treating for making a pigment. It is desirable that the treatment for making the pigment of theδtype indanthron blue pigment is to mix the crudeδtype indanthron blue pigment with water and/or an organic solvent and wet pulverizing in the presence of a crushing medium by using a crusher.
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