Unreasonable craftsmanship is easy to produce defects such as level dyeing difference, color flower, color willow, color difference, and poor fastness.
1. Control the initial dyeing temperature and heating rate
Nylon is a thermoplastic fiber, so the dyeing rate of the fiber has a great relationship with the temperature, and the dyeing temperature must be higher than the glass transition temperature of the fiber (35 ~ 50 ℃). Nylon fibers begin to absorb dyes at 40°C, and as the temperature increases, the dyeing rate accelerates, and the dyeing process can be basically completed at 100°C. Although when the temperature is 100°C, the dyeing can be basically completed, but continuing to raise the temperature will help the migration of the dye, so that the levelness is improved. However, if the heating rate is not well controlled, uneven dyeing is likely to occur.
The effect of temperature on the dyeing rate of dyes also varies with different dyes. The dyeing rate of level dyeing dyes gradually increases with the increase of temperature; the dyeing rate of mill-resistant dyes should be higher than 60°C in the dyebath. After ℃, it began to increase rapidly with the increase of temperature. Especially in the temperature range of 65 ~ 85 ℃, controlling the heating rate is the key to the success or failure of nylon dyeing. If you use mill-resistant dyes to dye nylon, the initial dyeing temperature should be room temperature. In the temperature range of 65 to 85 °C, the heating rate should be strictly controlled at about 1 °C/min, and a leveling agent should be added to adopt a step heating method; ～98℃, keep warm for 45～60min.
In addition, the dyeing properties of this fiber also changed with the heat treatment conditions before dyeing, and the dyeing rate of the fibers after dry heat setting decreased significantly.
2. Control the pH value
When dyeing nylon fibers, when the pH value of the dye solution is relatively high, the dye is rarely dyed; when the pH value of the dye solution drops to a certain value, the dye begins to dye, and soon reaches saturation, and continues to reduce the pH value of the dyeing night. , the dye uptake did not increase significantly; however, when the pH value was further reduced to 3, the dye uptake increased sharply again, and superequivalent adsorption occurred.
When nylon fiber is dyed under the condition of very low pH value, it will also be hydrolyzed, especially after super-equivalent adsorption, the pH value in the fiber is lower than that in the solution, the hydrolysis is accelerated, and more amino groups are produced after hydrolysis, and the fiber The increased availability of dyes can adsorb more dyes, making it easier to produce uneven dyeing. Therefore, according to the actual situation, the pH value can be appropriately adjusted to reduce the phenomenon of colored flowers.
When dyeing nylon with weak acid dyes, the pH value of dyeing light color is generally controlled at 6 to 7 (adjustable by dyeing stabilizer M-21 5), and the amount of leveling agent is increased to strengthen leveling and avoid dyeing, but pH The value should not be too high, otherwise the shade will fade; the pH value of dyed dark color is 4 to 6 (adjustable with dye stabilizer M-215), and an appropriate amount of acetic acid is added during the heat preservation process to reduce the pH value and promote the dyeing process. dye.
3. Pay attention to the selection and dosage of leveling agent
In view of the characteristics of poor levelness and coverage of nylon dyeing, it can be used in the same bath with the dye during dyeing, or it can be used for pre-dyeing treatment of nylon with a leveling agent. The anionic leveling agent dissociates into negative ions in the dyeing bath, enters the fiber, first occupies the limited dye seat on the nylon fiber, and then is gradually replaced by the dye as the temperature rises during the dyeing process, reducing the difference between the dye and the fiber. Combine speed to achieve the purpose of leveling. The non-ionic leveling agent is hydrogen-bonded with the dye in the dye bath, and then gradually decomposes during the dyeing process to release the dye, which is adsorbed by the fiber.
The addition of leveling agent can significantly improve the leveling and cap dyeing ability, but with the increase of the concentration of the auxiliary, the dyeing rate decreases, resulting in a decrease in the exhaustion rate to varying degrees. Therefore, the amount of leveling agent should not be too much. Because the leveling agent in the dyeing process in addition to the leveling effect, but also has the effect of blocking. Excessive amount of leveling agent will reduce the dyeing rate of acid dyes and increase the concentration of dyeing residue, resulting in color difference between large and small samples and poor reproducibility. Generally, when dyeing light colors, the amount of leveling agent is larger; when dyeing dark colors, the amount of leveling agent is less.