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Acid Dye Dyeing Nylon Common Problems

Views: 5 Author: Site Editor Publish Time: 2024-01-02 Origin: Site

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Rungs and bars

1. Cause analysis

The nylon fibers in the fabric differ in their chemical or physical characteristics.

Physical differences in yarns, including differences in yarn count, the number of fibers in the yarn or the fineness of the fibers, the end curl of a single fiber in the yarn or the difference between the end curls of multiple fibers in the yarn;

The chemical difference in the yarn is the difference in the amino content of the fiber. This difference may be produced during the spinning process, the heat drawing process, or the doubling process. For example, the inhomogeneity of the supramolecular structure produced during the processing of nylon fiber, such as the difference in crystallinity and orientation in the fiber or the inhomogeneity of the sheath-core structure.

2. Solution

Strengthen the inspection of gray fabrics, and make different choices for light color, original white or whitening.

Choose dyes with good coverage and leveling properties. Because the coverage and leveling properties of disperse dyes are better than those of acid dyes, you can choose to add some disperse dyes.

Color flowers caused by competitive dyeing

1. Cause analysis

The content of terminal amino groups in nylon is low and the saturation value is low. When two or more dyes are dyed together, competition for the dyeing position will occur, which is the so-called competitive dyeing phenomenon.

If the dyes selected have large differences in dye uptake and affinity, the fiber dyed colors will be very different at different dyeing times, resulting in color differences between large and small samples and poor reproducibility.

2. Solution

Choose a dyeing material series that has similar dyeing curves and affinity, good compatibility, and is suitable for production machines. Master the dyeing properties of various dyes. When selecting dyeing chemicals, factors such as dye uptake, dye uptake curve, leveling properties, color fastness performance, and sensitivity to temperature and leveling agents must be comprehensively considered.

Fully consider the compatibility of dyes. When using several dyes for dyeing, choose appropriate dyes and control the amount of dyes. Generally, you should try to choose the same series of dyes from the same company. Even if you have to use dyes from different companies, you should try to choose dyes with similar dyeing curves, similar starting dyeing temperatures, and similar sensitivity to temperature and leveling agents. Try to avoid race contamination.

Pay attention to the differences in the dyeing of large and small samples. Some dyes are not obvious when dyeing small samples, but they are completely exposed in large-scale production. For example, when producing lake green and peacock blue, if acidic turquoise blue and acidic yellow are used to combine, similar problems will occur. This is because the molecular structure of acidic emerald blue is large and the dyeing curve of acidic yellow is very different, thus causing competitive dyeing. If the acid green basket is used instead of acid green with yellow light, the problem of competing dyes will be basically solved.

Color bloom caused by process conditions

1. Cause analysis

Nylon dyeing has extremely high process requirements. Process conditions are important factors that affect the color and levelness of dyed products, such as temperature, pH value, etc., which will affect the quality of the product.

Unreasonable craftsmanship is prone to defects such as poor level dyeing, color flowers, color willow, color difference, and poor fastness.

2. Solution

Control the initial dyeing temperature and heating rate.

Effect of temperature Nylon is a thermoplastic fiber. Therefore, the dyeing rate of the fiber has a great relationship with the temperature. The dyeing temperature must be higher than the glass transition temperature of the fiber (35~50°C). Nylon fiber begins to absorb dyes at 40°C. As the temperature rises, the dyeing rate accelerates. The dyeing process can be basically completed by 100C. Although the dyeing can be basically completed when the temperature is 100C, continuing to increase the temperature will help the dye to dissolve. migration, thereby improving levelness. However, if the heating rate is not well controlled, uneven dyeing may easily occur.

The effect of temperature on the dye uptake rate also varies with different dyes. The dye uptake rate of level dyeing dyes gradually increases as the temperature increases; the dye uptake rate of milling-resistant dyes must be maintained when the dye bath temperature is higher than 60°C. It starts to increase rapidly with the increase of temperature after °C. Especially in the temperature range of 65~85°C, controlling the heating rate is the key to the success of nylon dyeing. If it is not controlled properly, it will cause problems such as fast color development, poor dye migration, easy to spend and difficult to repair. If milling-resistant dyes are used to dye nylon, the initial dyeing temperature should be room temperature. In the temperature range of 65~85°C, the heating rate should be strictly controlled at about 1 C/min, and a leveling agent should be added, and a step heating method should be adopted; then the temperature is raised to 95~98C, heat preservation 45~60min.

In addition, the dyeing performance of this fiber also changes with the heat treatment conditions before dyeing. The dyeing rate of the fiber after dry heat setting decreases significantly.

Control the pH value.

When dyeing nylon fiber, when the pH value of the dye solution is relatively high, the dye rarely dyes; when the pH value of the dye solution drops to a certain value, the dye begins to dye, and soon reaches saturation, continuing to reduce the pH value during the dyeing night. , there was no significant increase in dye uptake. However, when the pH value further dropped to 3, the dye uptake amount increased sharply, and super-equivalent adsorption occurred.

When nylon fiber is dyed under very low pH conditions, it will also be hydrolyzed. Especially after super-equivalent adsorption occurs, the pH value in the fiber is lower than that in the solution, and the hydrolysis is accelerated. After hydrolysis, more amino groups are produced, and the fiber The increased accessibility can absorb more dyes, making uneven dyeing more likely to occur. Therefore, according to the actual situation, you can adjust the pH value according to the light to reduce the phenomenon of colored flowers.

When dyeing nylon with weakly acidic dyes, the pH value of light colors is generally controlled at 6~7 (commonly used for adjustment with ammonium acetate), and the amount of leveling agent is increased to enhance leveling and avoid dyeing, but the pH value should not be excessive. High, otherwise the color will be dark; the pH value for dark dyeing is 4 to 6 (commonly used for adjustment with acetic acid and ammonium acetate), and an appropriate amount of acetic acid should be added during the heat preservation process to reduce the pH value and promote dyeing.

Pay attention to the selection and dosage of leveling agent.

In view of the poor leveling and covering properties of nylon dyeing, a small amount of anionic or nonionic leveling agents should be added to the dye bath, with anionic surfactants being the main ones. It can be used in the same bath with dyes during dyeing, or it can be used to pre-dye nylon with a leveling agent. The anionic leveling agent dissociates into negative ions in the dye bath, enters the fiber, and first occupies a limited dye seat on the nylon fiber. Then it is gradually replaced by the dye as the temperature increases during the dyeing process, reducing the bond between the dye and the fiber. Speed, to achieve the purpose of leveling; non-ionic leveling agent hydrogen bonds with the dye in the dye bath, and then gradually decomposes to release the dye during the dyeing process, and is adsorbed by the fiber.

The addition of leveling agent can significantly improve the leveling properties and covering ability. However, as the concentration of the additive increases, the dyeing rate decreases, resulting in a decrease in exhaustion rate to varying degrees. Therefore, the amount of leveling agent should not be too much. Because leveling agents not only have a leveling effect during the dyeing process, they also have a dye-blocking effect. Excessive dosage of leveling agent will reduce the dye uptake rate of acid dyes, increase the concentration of dyeing residue, and cause 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 smaller.

Yellowing

1. Cause analysis:

There are pollutants and BHT (butylated hydroxyanisole) on the plastic packaging bags that react chemically with the nylon, causing color variation and yellowing.

2. Solution:

Use anti-phenol yellowing agent for dip dyeing or padding treatment.

acid dye dyeing nylon common