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The blackness is directly related to the particle size of carbon black. The smaller the particle size, the larger the specific surface area, and the higher the blackness of carbon black. This is because even though the primary particles have been fused into primary aggregates, the ratio of the primary particles can still work. If the primary particles are finer, the greater the specific surface area of ​​the aggregates. The displayed color is darker, and the effect of UV protection is better. Since fine particle carbon black has a higher light absorption rate than coarse particle carbon black, the coloring power is stronger. However, when the particle size decreases, the blue light is preferentially absorbed, so the hue becomes brown.
　　The fine primary particles give carbon black a larger specific surface area, and at the same time increase the difficulty of dispersion. Generally, surface treatment can adjust the wettability and improve the dispersibility.