Nylon fiber is a condensation polymer 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.
Impact Factors of level dyeing of nylon
1. The influence of fabric and fiber structure
From the perspective of the entire dyeing and finishing process, the most direct reason affecting the uniformity of nylon dyeing is the warp and weft density of the fabric Unevenness, different yarn counts, and different production batches of nylon fibers used on fabrics. 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. process, they 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 group 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 differences in the physical structure of the yarn mainly include two aspects: on the one hand, it comes from the overall physical difference of the yarn, including the yarn count, the number of fibers in the yarn or the fiber fineness, and the end of a single fiber in the yarn. The difference between crimps or curls at the ends of multiple fibers; on the other hand, it comes from the inhomogeneity of the supramolecular structure produced during the processing of nylon fibers, such as differences in crystallinity and orientation in the fibers or sheath-core structures. Uneven etc. When fabrics made of chemically or physically different nylon fibers are dyed, a characteristic weft color stripe is easily produced.
2. Influence of pre-processing conditions
Improper selection of conditions during pre-treatment of nylon fabrics 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
①The influence 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 the pH value of the dye liquor is relatively high, the dye is rarely dyed; when the pH value of the dye liquor drops to a certain value, the dye is dyed.text-align: left;”>Controlling the pH value of dyeing is also the key to improving level dyeing. As mentioned above, The dyeing effect of nylon fiber has a great relationship with the pH value of the dye bath. Although a lower pH value is conducive to dyeing, the faster the dyeing speed, the levelness will also decrease accordingly. Therefore, the dye bath must be The pH value is well controlled. 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 choice of dyeing auxiliaries is often related to dyeing Success or failure. 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 is directly proportional to the dyeing rate of acid dyes. 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 try as much as possible To obtain a uniform dyeing effect, some experts have suggested that a gradual temperature rise dyeing process can be used when dyeing nylon. Dyeing starts at 40°C, then gradually heats up to boiling (about 45 minutes), and continues dyeing for 45 minutes. When the temperature is low, the dyeing rate is slower, exceeding 80 ℃, the dyeing rate accelerates rapidly and the temperature needs to be raised slowly. In addition, controlling the dyeing bath ratio, dye liquor circulation rate, dye liquor concentration and other factors will also help to improve the leveling effect of nylon.
④Selection of other conditions
Selection of the order of adding materials before dyeing. Since nylon can be dyed at 40°C (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 bath ratio, add the leveling agent and mix evenly, and finally add the dye. It is recommended that the dye be added in multiple times, because the dye uptake rate when the dye is first added to the bath is The fastest, so don’t rush to heat up after adding the dye, but 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.
Postscript
To sum up, the dyeing effect of nylon fiber is affected by many factors. Therefore, in actual operation, it is necessary to select synthetic dyes, auxiliaries, pre-forming processes, and the best pH value, temperature, etc. according to the specific dyeing requirements. Time and other dyeing conditions, only by combining these factors can good uniformity be obtained.
