The surface acidity of carbon black is related to the occurrence of chemisorbed oxygen. The surface acidity is attributed to surface oxygen and its contained groups, such as carboxyl, ruthenium, and internal, and also forms chemically similar carbon dioxide on the surface of carbon black. a complex of CO2). In the presence of air, when the carbon black is heated, it causes an increase in acidity and an increase in the adsorption capacity.
The darker the carbon black, the higher the acidity, and the pH of the mouth is between about 2.5 and 4.5. The lower carbon black has a pH that is almost neutral. Therefore, its adsorption capacity is not obvious. Since the adsorption capacity of carbon black has a special influence on the drying property of the coating, the drying rate of the coating film is often reduced due to the adsorption of the drier in the color paint.
When the pH of the black is 4 or less, the greater the acidity, the greater the adsorption capacity of the drier, and the more obvious the effect against dryness. The anti-drying effect of carbon black is not manifested immediately after painting, but is reflected in some time after storage in whole or in part after adsorption of the drier. Therefore, when designing a paint formulation, it is necessary to consider an appropriate increase in the amount of drier.