1.1 Cause Analysis

There are differences in the chemical or physical characteristics of nylon fibers on fabrics:

(1) Physical differences in yarns, including the number of yarn counts, the number of fibers in a yarn, or the fineness of a fiber, the difference in the end crimp of a single fiber in a yarn, or the crimping of a fiber end.

(2) The chemical difference arises from the difference in the amino group content of the fiber. This difference may occur during the spinning process, during the hot drawing process, or during the simultaneous yarn formation process. For example, the heterogeneity of the supramolecular structure, such as the degree of crystallinity, the degree of orientation, or the inhomogeneity of the structure of the skin-core structure in the fiber, occurs during the processing of the nylon fiber.

1.2 Solution

(1) Strengthen the inspection of grey fabrics, with the choice of light color, white or white.

(2) Select coverage and level dyeing dyes. Disperse dyes have better coverage and leveling than acid dyes, and some disperse dyes can be added.

2 Color flowers caused by competition

2.1 Cause Analysis

The content of the terminal amino group in the nylon is small, and the saturation value is low. When two or more dyes are dyed together, competition occurs for the dyeing position, that is, the so-called competitive dyeing phenomenon. If the dyestuffs used differ greatly in dye uptake and affinity, the coloration of the dyed fibers will be different at different dyeing times, resulting in large sample size and poor reproducibility.

2.2 Solution

Select the dyeing curve and similar affinity, good compatibility, and suitable for the production of dyeing material series. To master the dyeing performance of various dyes, when selecting dyes and dyes, comprehensive consideration should be given to dye uptake rate, dye uptake curve, level dyeing property, color fastness property, and sensitivity to temperature and leveling agent.

(1) Full consideration of the compatibility of dyes

When using several dyes to fight, select the appropriate dye and control the amount of dye. Generally, the same series of dyes from the same company should be selected. Even if dyestuffs from different companies have to be used, try to choose dyestuffs that have similar dyeing curve, similar dyeing temperature, and similar dyes with similar sensitivity to temperature and leveling agent. Avoid competition.

(2) Pay attention to the difference in dye size

Some dyes are not obviously competitive in the dyeing of small samples, but they are fully exposed in large production. For example, in the production of lake green and peacock blue, similar problems arise if acid blue and acid yellow are used. This is due to the large molecular structure of Acid Green Blue, which differs greatly from the acidic yellow dyeing curve, and thus leads to competitive dyeing. If acid blue is used instead of acidic green with yellow light, the problem of competition and competition will be basically solved.

3 Colored flowers caused by process conditions

Nylon dyeing process requirements are extremely high. Process conditions are important factors that affect the shade and leveling properties of dyed products, such as temperature and pH, which can affect the quality of the product.

Unreasonable process is easy to produce poor dyeing, color flower, color, color, poor fastness and other diseases.

3.1 Control the initial dyeing temperature and heating rate

Nylon is a kind of 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 (35-50°C). Nylon fibers began to adsorb dyes at 40°C. As the temperature increased, the dyeing rate accelerated, and the dyeing process was basically completed at 100°C. Although the dyeing can be substantially completed when the temperature is 100° C., the continued increase in temperature contributes to the migration of the dye, thereby increasing the levelness. However, if the heating rate is not good, dyeing unevenness tends to occur.

The effect of temperature on the dye uptake rate varies with the dyes. The dye uptake rate of level dyes increases with increasing temperature; the dye uptake rate of the shrink-resistant dyes is higher than 60 at the dye bath temperature. After °C began to increase rapidly with increasing temperature. Especially in the temperature range of 65-85°C, controlling the heating rate is the key to the success or failure of nylon dyeing. If it is not controlled properly, it will cause problems such as fast coloration, poor transferability, and difficulty in repairing flowers. If nylon dyed with shrink-wool dyes is used, the initial dyeing temperature should be room temperature. In the temperature range of 65-85°C, strictly control the heating rate of 1°C/min or so, and add leveling agent to take the step-up heating method; then raise the temperature to 95°C. ~ 98 °C, heat 45 ~ 60min.

In addition, the dyeing performance of this fiber also varies with the heat treatment condition before dyeing, and the dyeing rate of the fiber after dry heat setting is significantly decreased.

3.2 control the pH value

When the nylon fiber is dyed, when the pH value of the dyeing solution is relatively high, the dye is rarely dyed; when the pH value of the dyeing solution drops to a certain value, the dye begins to dye, soon reaches saturation, and continues to reduce the pH value at night There was no significant increase in dyeing; however, when the pH was further reduced to 3, the amount of dye dyeing increased dramatically and superequivalent adsorption occurred.

When nylon fiber is dyed under low pH conditions, it will be hydrolyzed, especially after super-equivalent adsorption, the pH in the fiber is lower than that in solution, hydrolysis is accelerated, and more amino groups are produced after hydrolysis. The increase in accessibility allows more dye to be adsorbed, making it more prone to uneven dyeing. Therefore, according to the actual situation, appropriate increase in pH to reduce the color phenomenon.

When dyeing nylon with weak acid dyes, the pH value of light-colored dyes is generally controlled at 6 to 7 (adjustable with dyestabilizer M-21 5), and the amount of leveling agent is increased to enhance level dyeing to avoid dyeing, but pH The value should not be too high, otherwise the shade will be dark; the dark-colored pH value is 4-6 (adjustable with the dye stabilizer M-215), and the appropriate amount of acetic acid is added during the incubation process to lower the pH and promote the dye dye.

3.3 Attention levelling agent selection and dosage

For the characteristics of poor leveling and dyeing of nylon dyeing, it can be used together with the dye in the same bath during dyeing, and can also be dyed with nylon before dyeing. The anionic leveling agent dissociates into negative ions in the dye bath and enters the fibers, which firstly occupies the limited dye base on the nylon fibers, and is then gradually replaced by the dye during the dyeing process, lowering the dye-to-fiber ratio. Combine speed to achieve 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 and is adsorbed by the fiber.

Leveling agent can significantly improve the leveling and cover dyeing ability, but with the increase in the concentration of additives, the dyeing rate decreases, resulting in varying degrees of exhaustion rate decreased, so the amount of leveling agent can not be too much. Because the leveling agent in the dyeing process in addition to the leveling effect, there are also blocking effect. Excessive levels of levelling agent will reduce the acid dye uptake and increase the concentration of staining residuals, resulting in large sample size and poor reproducibility. Generally, the leveling agent is used in a larger amount when light-colored and less in a dark-colored.

4 Yellowing

Nylon light-colored fabrics often undergo localized slight yellowing during storage and transportation, affecting the appearance and quality of the fabric.

4.1 Cause Analysis

Contaminants and BHT (butyl hydroxy anisole) on plastic packaging bags react chemically with nylon, causing color variations that lead to yellowing.

4.2 Selection of anti-phenol yellowing agent for impregnation or padding

5 Conclusion

In summary, the dyeing effect of nylon fiber is affected by many factors. Therefore, according to the specific dyeing requirements, the appropriate dyes, auxiliaries, pre-determined processes, and the best pH, temperature, time, etc. should be selected during actual operation. Dyeing conditions, only the integration of these factors in order to get a good leveling effect.