For the evaluation of dye-dispersing power of surface active agents, semimicro azopigment method has been developed. The method consists of coupling diazonized base with naphthol (mole ratio 1 : 1) in presence of dispersing agent under definite condition at pH 4.5, and measuring an amount of dispersing agent just suffcient to prevent the precipitation of azopigment. Dispersion value is defined as follows;
Dispersion value=An amout of dispersing agent enough to prevent precipitation (g) /An amount of azopigment (g) (calcd.)
It has been confirmed that the suitable diazo components are : Red KB Base, Red TR Base and p-nitroaniline, and the coupling components : Naphthol AS and Naphthol AS-SW.
Among the various dispersing agents examined, sodium alkyl naphthalene sulfonate and sodium naphthalene sulfonate formaldehyde condensate showed most excellent azopigment dispersing power (Dispersion Value 2).
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