Prevention and Control of Color Difference in Large and Small Samples of Reactive Dyestuff Package Yarn Dyeing

Precautions for sample dithering

1. Weighing of yarn when copying samples. If the yarn is not weighed accurately, even if the color is adjusted accurately, the color will be different during mass production. To accurately weigh yarn, you must first control the moisture regain of the sample yarn. The moisture regain directly affects the weight of the yarn. Secondly, the yarn weighing for sample must be accurate to 0.001g and cannot be measured by the traditional number of turns. Because yarns of the same yarn count produced by different manufacturers and yarns from different batches of the same manufacturer have greatly different weights even if the number of turns is the same. Thirdly, the imitation color sample must use the same batch of yarn base as the actual production, because the yarn base cotton from different manufacturers or the yarn base cotton that is not shipped from the same batch is very different, and the color yield is also very different.

2. Measurement of dyes. It is necessary to compare samples of each batch of dyes and obtain detailed information of each batch of dyes; weighing materials should be accurate; imitation dyes should be kept fresh, and the same batch of dyes used in large-scale production should be used for imitation colors to eliminate differences in batches. Differences in strength and color between secondary dyes.

3. The color imitation process for small samples should be unified with mass production. During the production process, it was found that if Yuanming powder and soda ash were added at the same time, the sampling rate would be low, and the deviation of individual varieties would be very obvious. Using the method of adding Yuanming powder for 20 minutes and then adding soda ash, the sampling rate is greatly improved, but the sample yield rate is slightly affected. Taking into account the sample operation efficiency, the constant temperature sample dithering process can be used:

4． Liquor ratio. Most of the large-scale production dyeing of cheese yarn adopts a small liquor ratio, as low as 1:5 to 1:6. However, due to equipment limitations, the minimum liquor ratio of the normal temperature oscillating dithering machine is 1:15, and the glycerin dithering machine is small. The liquor ratio is 1:10, and the low liquor ratio infrared dithering machine can reach a minimum liquor ratio of 1:5. Appropriate equipment must be selected for color imitation to ensure that the sample imitation color bath ratio is as consistent as possible with actual production.

5. Compatibility and process dependencies. Choose dyes with good compatibility and little dependence on the process.

Precautions for dyeing production

1. Boil the yarn. The boiled yarn must be even and transparent, and the wool effect must reach 8 to 10min/30min. Otherwise, it will cause the dyeing color of the cheese and the color difference between the inner and outer layers, which will affect the one-time pattern rate; after boiling, the yarn must be pickled and neutralized to neutral, and then used The deoxidizing enzyme removes the residual hydrogen peroxide. If the hydrogen peroxide is not completely removed, it will cause light color and blooming.

2. Chemical materials. The chemical material must be uniform. If the chemical material is uneven or not melted, the dye particles will be adsorbed on the surface of the cheese, which will not only affect the dye uptake and color fastness of the dye, but also directly affect the sampling rate of the large sample. The temperature of the chemical material should not be too high and the time should not be too long, otherwise some dyes will be hydrolyzed, resulting in light color and inconsistent color and light, which will affect the one-time matching rate.

3. water quality. The water quality requirements for cheese dyeing are relatively high. Generally, soft water is used in the whole process of pre-treatment, dyeing and finishing, and the hardness of the water should be less than 50mg/L. Before adding alkali, since there is no bonding reaction between the dye and the fiber, it generally does not affect the level dyeing. However, after adding the alkali, the pH value of the dye liquor increases, and the bonding reaction between the dye and the fiber occurs, which can easily cause color flowers and affect the primary pattern. Rate. Therefore, the first time you add alkali, you need to add it slowly.

4. Post-dyeing treatment. Post-dyeing treatment needs to be adjusted according to the dye dosage and dye variety.

① Soaping is usually performed at 90-95°C. Before soaping, the yarn needs to be washed and neutralized to make the yarn PH value reach 7±0.5 to reduce color blooming caused by hydrolysis of the dye during soaping.
②Dark varieties and varieties with large amounts of reactive emerald blue KN-G and brilliant blue KN-R need to be fixed with a color fixing agent to improve the color fastness after soaping. Reasonable consideration must be given to the color change and color fixation of the color fixing agent. The problem of fastness. At present, the fixing agents on the market have good color fastness and large color change, but small color change and unsatisfactory fixing fastness. Therefore, it is necessary to select a suitable fixing agent based on the difference between the color light before the yarn is fixed and the original color light.
③Choose softener reasonably. The cheese yarn needs to be adapted to its yarn feel according to its use. For example, knitting yarn requires the finished yarn to be soft and smooth, so as to facilitate weaving on circular knitting machines and flat knitting machines, and does not require high yarn strength; weaving yarn requires the finished yarn to be smooth, so as to facilitate finishing and weft feeding. Strong requirements are high. There are three main types of softeners used for cheese yarn: anionic, nonionic and weak cationic. Weak cationic softeners have good hand feel and smoothness, but the color change is large, so they need to be selected according to the color and purpose of the yarn.
④Dyeing auxiliaries. Some auxiliaries have a great impact on water quality, especially when dyeing uses a large amount of Yuanming powder and soda ash (salt is not suitable for cheese dyeing because it contains too many impurities and is corrosive to the dye vat). Their purity directly affects the water quality. Therefore, the purity of Yuanming powder and soda ash for cheese dyeing should be high. It is best to choose Yuanming powder with a content of more than 99%. Even so, Yuanming powder can still increase the hardness of the dye liquor. When the amount of Yuanming powder is large, the hardness can increase by about 50 mg/L, and it will introduce some heavy metal ions and calcium and magnesium ions into the yarn semi-finished products. These ions will also affect the dyeing. Effect. Therefore, chelating agents need to be added during the dyeing process to eliminate their impact on dyeing. But it is not advisable to add sodium hexametaphosphate.

⑤Dyeing process. Comprehensive considerations should be taken into consideration when formulating the dyeing processConsidering quality and production efficiency, generally medium-temperature dyes should be fixed at 60-65°C. There are usually three processes:

▊Most factories use process A. The B process is more suitable for some dyes with poor level dyeing properties and dyes that are easy to dye flowers.

Ⅰ: Some commonly used varieties of medium-temperature reactive dyes, such as black KN-B and brilliant blue KN-R, have the characteristics of instant dyeing with alkali fixation. Within 10-15 minutes of alkali fixation, the color absorption rate increases by 30% to 50% %, it is easy to cause color flowers or differences between the inner and outer layers. For these dyes, the “pre-alkali heating method” (B process) is used to make the dye liquor almost alkaline at low temperature. By slowly heating up (1℃/min) and maintaining heat, the level dyeing property can be effectively improved and the inner and outer layers can be reduced. Color difference, improve sample rate.

Ⅱ: Mixed dyes such as reactive black KN-G2RC and reactive black B-ED are made from medium-temperature black KN-B and a low-temperature reactive orange. Because low-temperature active orange is sensitive to alkali and temperature, it only needs to be dyed and fixed at 40°C; while medium-temperature black KN-B requires a fixing temperature of 60 to 65°C. Since the fixation temperature of the two dyes is quite different, the “pre-alkali heating method” (B process) is used for this type of dye, and the difference between the inner and outer layers is greatly improved. When using emerald blue KN-G and bright yellow BF-4G for color matching, the C process is used. Because this type of dye has a larger molecular structure, greater affinity for fibers, faster dyeing speed, and slower fixation reaction. This type of dye needs to be added with alkali in batches at 60°C, and then heated to 85-90°C to fix the color, which can ensure both level dyeing and color yield.