Nylon fiber is a polycondensation fiber, and the main varieties are nylon 6 and nylon 66. As a thermoplastic fiber, temperature differences during manufacturing and processing have a great impact on the physical properties and dyeing properties of nylon. Special fiber properties and processing procedures will affect the final leveling effect.
Factors affecting level dyeing of nylon
1. Fabrics and Influence of fiber structure
From the perspective of the entire dyeing and finishing process, the most direct reasons affecting the uniformity of nylon dyeing are uneven warp and weft density of the fabric, different yarn counts, and The production batches of nylon fiber used on fabrics are different. These factors may affect the dyeing performance of nylon, resulting in uneven dyeing.
From a fiber perspective, the chemical structure of nylon fiber is polyamide. There is a certain amount of amino groups at the end of the fiber molecular chain. The dyeing properties of nylon are affected by the chemical and physical differences of the fiber. , these differences may arise from the manufacturing process or processing of the fiber, which directly affect the dyeing performance of the dye. The chemical difference comes from the difference in the amino content of the fiber, which may be produced during the spinning process, the heat drawing process, or the doubling process.
Differences in amino content will lead to differences in the dyeing rate, especially the final adsorption amount of anionic dyes. This difference can only be minimized through careful control of the production process.
The difference in physical structure of yarn mainly includes two aspects: on the one hand, it comes from the overall physical difference of yarn, including yarn count, number of fibers or fibers in yarn Different fineness, the difference between the end curl of a single fiber in the yarn or the end curl of multiple fibers; on the other hand, it comes from the inhomogeneity of the supramolecular structure produced during the processing of nylon fiber, such as crystallization in the fiber Differences in degree and orientation or uneven skin-core structure. When fabrics made of chemically or physically different nylon fibers are dyed, a characteristic weft color stripe is easily produced.
2. Influence of pre-treatment conditions
Pre-processing of nylon fabric Improper selection of conditions during processing is also an important factor causing uneven dyeing. Improper fabric pre-treatment mainly includes: uneven fabric treatment, which causes great differences in the adsorption properties of the fibers, causing dyeing to bloom; rapid temperature rise during the pre-treatment process of the jigger dyeing machine, causing the nylon yarn to shrink suddenly, or the temperature during heat setting Non-uniformity will cause structural differences in the nylon fibers, and uneven dyeing will occur during the dyeing process.
3. Influence of dyeing conditions
①Influence 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 (35~5O℃). Nylon fiber begins to absorb dye at 40°C. As the temperature rises, the dyeing rate accelerates. The dyeing process can be basically completed by 100°C. Although the dyeing can be basically completed when the temperature is 100°C, continuing to increase the temperature will help Due to the migration of dyes, it improves level dyeing. Some researchers believe that the dye uptake rate of nylon fibers dyed with acid dyes is related to temperature. When the temperature is higher than the glass transition temperature, the mobility of the macromolecular chains in the fiber is enhanced and the fiber opens, allowing the dye to penetrate into the fiber and react with the terminal amino cations. However, if the heating rate is not well controlled, uneven dyeing is likely to occur. Phenomenon.
②The influence of pH value
When dyeing nylon fiber, when dyeing When the pH value of the dye solution is relatively high, the dye rarely stains; when the pH value of the dye solution drops to a certain value, the dye begins to stain, and it quickly reaches saturation. If the pH value of the dyeing solution is continued to decrease, there will be no significant increase in dyeing; However, when the pH value further dropped to 3, the amount of 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 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 dye, making it easier to produce uneven dyeing. Therefore, according to the actual situation, the pH value can be adjusted to the photopic level to reduce the phenomenon of colored flowers.
③The influence of auxiliaries
Nylon fiber is mostly dyed with acid dyes , and there are three main types of leveling agents for acid dyes: anionic, cationic and nonionic. Anionic leveling agents have a certain affinity for fibers in acidic media and compete with dye anions for dyeing fibers. Their affinity is lower than dye anions but their diffusion rate is faster than dye anions. At the beginning of dyeing, anionic leveling agents compete with dyes for dye seats. Due to their fast diffusion rate, they dye the fiber before the dye anions, combine with NH on the fiber, and then are gradually replaced by dye anions with greater affinity for the fiber. Down, thus reducing the initial dyeing rate of the dye and achieving a leveling effect.
Cationic and nonionic leveling agents combine with dye anions to reduce the effective concentration of dye anions, and gradually release dye anions during the dyeing process to cause leveling. effect. In addition, factors such as dyeing time, dye compatibility, dye liquor concentration, liquor ratio, and dye liquor circulation rate will also affect the leveling effect of nylon dyeing.
Methods to improve the levelness of nylon dyeing
1. Dyes of��Selection
First of all, the correct selection of dyes is a key factor in improving the level dyeing properties of nylon. There is a wide range of dyes that can be used to dye nylon fibers. Among the many dyes suitable for dyeing nylon fibers, disperse dyes, anionic dyes such as acid dyes, 1:2 metal complex dyes, and preferred direct dyes are the most important.
Disperse dyes with simple molecular structures can cover the physical and chemical differences in nylon fibers due to their non-ionic nature and low molecular weight, but only moderate color fastness can be obtained with this dye . Disperse dyes with more complex structures can have better wet fastness when dyeing nylon fibers, but due to their high molecular weight, they can only cover chemical differences but not physical differences. The preferred direct dyes bring superior wet processing fastness to nylon dyeing and are economical for producing dark products. Compared with disperse dyes, dyeing with the most vivid dyes can obtain relatively brighter dyed products ( The color is better than disperse dyes).
Acid dyes are often used for nylon dyeing. Their biggest advantages are that they are easy to color and can obtain darker colors. The dyeing procedures and requirements are relatively simple, and the wet fastness of the dyes is good. But the level dyeing property is worse than that of disperse dyes. The leveling ability of various dyes on nylon fibers is generally: disperse dyes>acid dyes>reactive dyes>neutral dyes>direct dyes. At present, dyes for nylon with good dyeing effects and high dye fastness include acid dyes such as Tectilon, ErionylA, LanaSet and low-temperature disperse dyes.
2. Selection of pre-shaping process
To improve level dyeing The pretreatment, dyeing and heat setting of nylon fibers or fabrics must have strict requirements. In actual production, tenter pre-shaping can be carried out before pre-treatment, generally controlled at 140~150℃x30s, and moderate overfeeding is required. In particular, nylon filament fabrics are prone to wrinkles during high-temperature treatments such as dyeing. Once formed, wrinkles are difficult to eliminate, resulting in uneven dyeing and affecting the appearance. Therefore, shaping before dyeing can fix the shape of the fabric, stabilize the size, and prevent defects during the entire processing process.
3. Selection of dyeing conditions
①Selection of pH value
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Controlling the pH value of dyeing is also the key to improving level dyeing. As mentioned before, the dyeing effect of nylon fiber has a great relationship with the pH value of the dye bath. Although a lower pH value is beneficial to the dyeing process, the faster the dyeing process, the lower the levelness. Therefore, it is important to control the pH value of the dye bath. Generally, when dyeing nylon with acid dyes, the pH value of the dye bath can be divided into strong, weak or neutral.
②Auxiliary selection
The selection of dyeing auxiliaries often It is related to the success or failure of dyeing. According to research by dyeing and finishing experts, when acid dyes are used to dye nylon, anionic additives have the best leveling effect. Their function is to block the terminal amino groups and thereby control the initial dyeing.
③Temperature selection
The temperature of the dye bath depends on the acidic dye The dyeing rate is directly proportional. The higher the temperature, the faster the dyeing rate. Especially when the temperature reaches above 80°C, the dyeing rate will be faster and it is easy to produce color flowers. In order to obtain as uniform a dyeing effect as possible, some experts have proposed that a gradual temperature rise dyeing process can be used when dyeing nylon. Dyeing starts at 40°C, then gradually raises the temperature to boiling (about 45 minutes), and continues dyeing for 45 minutes. When the temperature is low, the dyeing rate is slow. When the temperature exceeds 80°C, the dyeing rate accelerates rapidly and the temperature needs to be raised slowly. In addition, controlling the dyeing liquor ratio, dye liquor circulation rate, dye liquor concentration and other factors will also help improve the leveling effect of nylon.
④Selection of other conditions
Selection of feeding sequence before dyeing . Since nylon can be dyed at 40℃ (close to normal temperature), the temperature of the dye solution should be kept as low as possible before adding dye. There are also certain requirements for the order of adding materials before dyeing.
The general order of adding materials is: after adding the cloth and water, adjust the liquor ratio, add the leveling agent and mix evenly, and finally add the dye. It is recommended that the dye be added in multiple times. Since the dye uptake rate is the fastest when the dye is first added to the bath, do not rush to heat up after adding the dye. Instead, keep it at room temperature for 15 minutes and then heat up according to the process. The influence of color correction, because the color after dyeing is wrong, when the color needs to be corrected, it is recommended to drain the water and dye it again. Because the dye solution still has a certain temperature after dyeing (usually about 60 degrees), and this temperature can easily cause the dye to stain, so when the dye is replenished, color flowers may occur.
Afterword
In summary, the properties of nylon fiber The dyeing effect is affected by many factors. Therefore, in actual operation, the combination of dyes, auxiliaries, pre-forming processes, and optimal pH value, temperature, time and other dyeing conditions must be selected according to the specific dyeing requirements. Only by integrating these factors, can the dyeing effect be achieved. In order to obtain good level dyeing. </p
