It was found that the level dyeing property and covering capacity could be improved obviously by adding leveling agent. However, with the increase of auxiliary concentration, the dyeing rate decreased, resulting in the decrease of exhaustion rate. Therefore, the dosage of leveling agent should not be too much.

In addition to leveling effect, leveling agent can also inhibit dyeing. Too much leveling agent is used. It will reduce the dye uptake of acid dyes, increase the concentration of dyeing residue, and cause color difference and poor reproducibility of large and small samples. In general, the amount of leveling agent is large when dyeing light color, and less when dyeing dark color. For a long time, it has been considered that the control of pH value is the key to the success or failure of nylon dyeing. After years of production experience, we found that the selection and dosage of leveling agent play a decisive role in controlling the color difference of large and small samples after the introduction of buffer system. Leveling agent should be used with the corresponding dye category, but the dosage must be adjusted according to the actual situation. In large-scale production, it can be corrected according to the amount of small samples, which can achieve good results.