Nylon is the trade name of synthetic polyamide fiber, commonly known as nylon. Its basic composition is aliphatic polyamide connected through amide bonds -NHC0. Nylons commonly used in textile fabrics include nylon 6 and nylon 66. Nylon macromolecules are mainly composed of three parts, namely the hydrophobic methylene part, the hydrophilic amide group, and the amino and carboxyl groups at the chain ends.
Although the amino content of nylon is low, its molecular chain has a large number of van der Waals that can form with dyes. Therefore, in addition to combining with anionic dyes through ionic bonds, nylon can also be colored by interacting with dyes through strong van der Waals forces. Although there are some small differences in molecular structure and dyeing properties between nylon 6 and nylon 66, their dyeing and finishing processes are the same.
Nylon fiber has been widely used in clothing fabrics and high-end underwear because of its good strength, excellent wear resistance, better hygroscopicity than polyester fiber, and better wearing comfort than polyester clothing. , sportswear and mountaineering clothing, etc. Due to the development of the market and the advancement of spinning technology, most nylon fabrics currently have elastic fibers (spandex yarns) added to enhance the wear resistance and resilience of nylon fabrics, which makes the dyeing and finishing of nylon fabrics more difficult.
1. Rungs and horizontal bars
Differences in chemical or physical characteristics of nylon fibers on fabrics:
(1) Physical differences in yarns, incl. The difference between the 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 end curl of multiple fibers in the yarn.
(2) The chemical difference comes from 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.
(1) Strengthen the inspection of gray fabrics, and choose light color, original white or whitening if there is any difference.
(2) Choose dyes with good coverage and level dyeing properties. The coverage and leveling properties of disperse dyes are better than those of acid dyes, so you can choose to add some disperse dyes.
2. Color patterns caused by dip dyeing
Nylon The content of the middle terminal amino group is small 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.
Select a dye series with similar dyeing curves and affinity, good compatibility, and suitable for production machines . Understand 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.
(1) Fully consider the compatibility of dyes
When using several dyes for dyeing, you must choose the appropriate dye, and Control the amount of dye used. 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 competing contamination.
(2) Pay attention to the difference in the dyeing performance of large and small samples of dyes
Some dyes are not obvious in the dyeing of small samples. But it was completely exposed in mass production. For example, when producing lake green and peacock blue, if acidic emerald blue and acidic yellow are used to combine, similar problems will arise. 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 acidic blue and acidic green with yellow light are used instead, the problem of competing dyes will be basically solved.
3. Color patterns caused by process conditions
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 technology is prone to defects such as poor level dyeing, color flowers, 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 is related to the temperature. It has a lot to do with the fact that the dyeing temperature must be higher than the glass transition temperature of the fiber (35~50℃). Nylon fiber begins to absorb dye at 40°C. As the temperature rises, the dyeing rate accelerates, and the dyeing process can basically be completed by 100°C. Although dyeing can be basically completed when the temperature is 100°C, continuing to increase the temperature will help the migration of the dye, thereby improving level dyeing. 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; milling resistance The dye uptake rate starts to increase rapidly with the increase of temperature only after the dye bath temperature is higher than 60℃.Especially in the temperature range of 65 to 85°C, controlling the heating rate is the key to the success of nylon dyeing. If not controlled properly, it will cause problems such as fast dyeing, poor dye migration, easy to spend and difficult to repair. If milling-resistant dyes are used to dye nylon, the starting 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, and a stepped heating method should be adopted; then the temperature should be raised to 95 ~98℃, keep warm for 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.
2. Control the pH value well
When dyeing nylon fiber, when the pH value of the dye solution is relatively high, the dye is very Less dyeing; when the pH value of the dye solution drops to a certain value, the dye begins to dye, and soon reaches saturation. If the pH value of the dyeing solution is continued to decrease, the dyeing will not increase significantly; however, when the pH value further drops to 3 , the dye uptake 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, the pH value in the fiber is lower than that in the solution. , hydrolysis is accelerated, more amino groups are produced after hydrolysis, the accessibility of the fiber is increased, and more dyes can be absorbed, making uneven dyeing more likely to occur. Therefore, the pH value can be appropriately raised according to the actual situation 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 to 7 (can be adjusted with dyeing stabilizer M-21 5), and the leveling agent must be increased. Dosage should be used to enhance level dyeing and avoid dyeing flowers, but the pH value should not be too high, otherwise the color will fade; the pH value for dark dyeing is 4 to 6 (can be adjusted with dye stabilizer M-215), and should be kept warm During the process, an appropriate amount of acetic acid is added to lower the pH value and promote dyeing.
3. Pay attention to the selection and dosage of leveling agent
In view of the poor leveling and covering properties of nylon dyeing, both It can be used in the same bath with dyes during dyeing, and can also 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 interaction between the dye and the fiber. Combined with speed, the purpose of leveling is achieved. Non-ionic leveling agents hydrogen bond with dyes in the dye bath, and then gradually decompose during the dyeing process to release the dye, which is adsorbed by the fiber.
The addition of leveling agent can significantly improve the leveling property and covering dyeing ability. However, as the concentration of the additive increases, 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 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 dyeing 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.
Light-colored nylon fabrics often undergo localized slight yellowing during storage and transportation. Affects the appearance and quality of fabrics.
1. There are pollutants and BHT (butylated hydroxyanisole) on the plastic packaging bags that interact with nylon Chemical reactions cause color variation, leading to yellowing.
2. Use anti-phenol yellowing agent for dip dyeing or padding treatment
In summary, the dyeing effect of nylon fiber is affected by many factors. Therefore, in actual operation, appropriate dyes and dyes must be selected according to specific dyeing requirements. Auxiliaries, pre-styling processes, and dyeing conditions such as optimal pH value, temperature, and time. Only by integrating these factors can we obtain good level dyeing results. </p