Disperse dyes are poured into water and then dispersed into fine particles. The particle size distribution is expanded according to the binomial formula, with an average value of 0.5 to 1 micron. The particle size of high-quality commercial dyes is very close, and there is a high percentage, which can be indicated by the particle size distribution curve. Dyes with poor particle size distribution have coarse particles of different sizes and poor dispersion stability. If the particle size greatly exceeds the average range, recrystallization of tiny particles may occur. Due to the increase of large recrystallized particles, the dyes are precipitated and deposited on the walls of the dyeing machine or on the fibers.
In order to make the fine particles of dye into a stable water dispersion, there must be a sufficient concentration of boiling dye dispersant in the water. The dye particles are surrounded by the dispersant, which prevents the dyes from getting close to each other, preventing mutual aggregation or agglomeration. The charge repulsion of the anion contributes to the stability of the dispersion. Commonly used anionic dispersants include natural lignosulfonates or synthetic naphthalene sulfonic acid dispersants: there are also non-ionic dispersants, most of which are alkylphenol polyoxyethylene derivatives, which are specially used for synthetic paste printing.