How to Avoid Acrylic Dyeing Streaks

Acrylic (polyacrylonitrile fiber) has its saturation value (SF). Typically, the saturation constant for domestically produced acrylic is between 2.1 and 2.3. Therefore, the total amount of cationic dyes and retarders (cationic charge) used in dyeing should be controlled at around 2.5% (o.w.f). It must be noted that if the retarder used is the surfactant 1227, it is indeed difficult to control the streaking phenomenon. Practical experience has shown that this retarder type has a powerful cationic charge, with high dye uptake competition in the initial dyeing stage, preventing the dye from adhering. Around 95°C, almost instant exchange occurs, where the retarder initially occupying the "seats" is suddenly replaced by the dye waiting outside, leading to streaks. Thus, this retarder is now rarely used.

To overcome dye streaks, the following methods are effective:

• Firstly, choose an appropriate acrylic retarder. It should almost not have the "instant exchange" function and should provide good leveling effects. To ensure proper dyeing, it is unnecessary to add two surfactants as retarders or leveling agents in the same bath. Ideally, one surfactant and one inorganic salt (Glauber's salt, Na2SO4) should be used, as this provides better leveling effects. The former should be used in amounts of 0.5-1% (o.w.f), and the latter in amounts of 5-10 g/L.
• Secondly, it is not advisable to use segmented temperature-rising and holding dyeing methods. Generally, dyeing should start by adding the dye at room temperature, then raising the temperature at a rate of 1.5°C/min to 100°C, and holding the temperature for 40-60 minutes (from light to dark shades). During the holding stage, the temperature should remain relatively stable to avoid fluctuations that could cause ring dyeing, making it difficult for the cationic dyes in the bath to be fully exhausted.
• Finally, at the end of dyeing, the temperature should be lowered at a rate of 1°C/min to 65-70°C. Then, gradually inject cold water while draining the dye solution until cooling is complete. Thoroughly remove residual liquid in the tank and rinse with clean water to remove surface dye and auxiliary residues. This process helps prevent the deformation of fibers or yarns, leaving them soft and fluffy.

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