The solution to the cause of color spot in the dyeing process of Yadong reactive dyes

The solution to the cause of color spot in the dyeing process of Yadong reactive dyes

(Summary description)

The characteristic values of reactive dyes are s, e, R and F. the reaction process of salt and alkali resistance of reactive dyes with cellulose fiber and water. The main causes of color spot and flower are analyzed. The method to solve the problem of color spot and color flower in dyeing was put forward.
Reactive dyes play an important role in the dyeing of cellulose fibers. They are widely used in dip dyeing, pad dyeing, overflow dyeing and cold pad batch dyeing. They have bright color, good color fastness, simple process, and meet the environmental protection requirements of oeko-textl00 of the European Union. They are deeply loved by the majority of dyeing workers, especially the role of reactive brilliant blue and turquoise blue in some colors. However, in the process of dyeing, these two dyes often appear color spot phenomenon, so that when they are used, some dyeing workers are still worried. In fact, as long as we recognize the structural characteristics of these two dyes, make a reasonable process, and strictly follow the process operation, the color spot can be completely avoided.
1. Alkali resistance test
Up to now, there is no unified standard for salt and alkali resistance test of reactive dyes. Different customers have different requirements on dye concentration, alkali agent type, alkali agent concentration, salt content in the test and the time required for stability, which is difficult to be unified and confidential. Therefore, different customers are required to formulate various enterprise standards for alkali resistance test. During the test, reactive brilliant blue KN-R and reactive turquoise blue KN-G were dissolved in the specified volume of nas0 aqueous solution under stirring according to the enterprise standard. The 5olna: CO solution was added at 50% and stirred for a specified time to evaluate the residual spots of filter paper. The less the residue, the less easy it is to color. And the salt resistance test can also be used as one of the detection methods for selecting dyes.
2. The process of forming color spots
"D" is the parent material of dye. In the process of alkali resistance stability test, it can be judged according to the observation of residual spots on filter paper: when alkali agent is added, the dye molecules react about 5 minutes, and the solubility decreases a lot. For example, under the influence of external factors (electrolyte, poor water quality, some auxiliaries, etc.), it is easy to form color spots in the dye solution, and the phenomenon of color spots and flowers will occur on the fabric; Reactive turquoise blue KN-G, the parent of the dye is copper phthalocyanine structure, the whole molecular structure has good coplanarity. In general, dyes in the "aggregation" state exist in the dye solution, and these dyes in the aggregation state are difficult to penetrate in the fiber, because the amorphous area of cotton fiber only allows the penetration and diffusion of single molecule dyes, so the dye molecules of the upper dyed fabric are less, a large number of dyes exist in the dye solution, such as in case of external factors (high hardness of water, some auxiliaries, etc.), it is easy to gather more and more It's easy to see color spots on the fabric.
3. Characteristic values of reactive dyes s, e, R, f
S value is direct, which is expressed by the adsorption value after adding salt;
E is the absorption value, which is expressed by the final absorption value after adding alkali agent;
F value is the fixation value, which is expressed by the fixation value after soap cooking;
R value is the fixation rate, which is expressed by the ratio of fixation value after adding alkali agent for 10 minutes to the final fixation value.
S value and the difference between s value and F value are the main factors that determine the level dyeing. The difference between E value and F value indicates the floating color dye and determines the difficulty of washing.
Generally speaking, the direct property of reactive dyes is low, the adsorption value after alkali addition is large, and the alkali agent has a great influence on dye uptake, which is the main influencing factor of color spot and flower; the direct property of reactive turquoise blue KN-G is large, the temperature has a great influence on dye uptake, and the E-F difference is large, which indicates that there are many floating colors after dyeing, so it is necessary to strengthen soap washing and water washing.
4. Solution of active color spot and flower in dip dyeing process
Reactive brilliant blue and turquoise blue are inevitable to be used in some colors (such as brilliant blue, bright green, green, etc.). Because of the special structure of these two dyes, they are sensitive to process conditions (water quality, electrolyte, alkali agent, temperature, additives, etc.).
The s value of reactive turquoise blue KN-G is large. At room temperature, dye molecules exist in the dye solution in the state of "aggregation", which makes it difficult to enter the amorphous area of cotton fiber. There are few dyes on the dyed fabric (the dyeing rate of reactive turquoise blue at room temperature is significantly slower than that of other dyes in overflow machine and spray dyeing). If the water quality is not good or some auxiliaries have influence, the dye is easy to form a suspension, which can be seen as a color spot on the fabric. Even if the temperature of the dye solution is increased, the dye suspension is difficult to dissolve in water. When the temperature of dye solution rises to the process temperature, there is enough energy between dye molecules, which changes from "aggregation" state to single molecule state. At this time, the s value becomes larger. The turquoise blue in single molecule state is easy to enter into the amorphous area of human cotton fiber, and the dyeing rate becomes faster. At this time, the phenomenon of dyeing flowers should be prevented. Therefore, strictly control the heating rate and increase the transfer time. Light or thin fabrics and elastic fabrics can increase dyeing temperature. Use clear water to dissolve the alkali agent. The alkali agent is added slowly first and then quickly.
It needs to be emphasized here: for some fabrics, such as cotton elastic knitted fabric, the process conditions (such as temperature, pH value, etc.) of the auxiliaries (such as emulsified degreaser) used in the pretreatment must be clear, and demulsification cannot be caused by improper use conditions. Once demulsification occurs, it is difficult to clean, and color stains and stains are easy to appear during dyeing.
5. Solution to active brilliant blue and emerald blue spots in rolling, drying, rolling and steaming process
In the rolling, drying, rolling and steaming process, dye and alkali agent are separated. In the absence of alkali, the solubility of these two dyes is relatively large. As long as the dye is fully dissolved, it will not be excellent in the bottoming part. Strictly control the pre drying and drying temperature, so as to avoid streaking on the cloth due to dye migration. The color spots are mainly produced after steaming. This is because when the fabric passes through the color fixing solution of the soaking tank, some dyes are resolved in the color fixing solution. In addition, some supplementary dyes are added in the soaking tank. In the high concentration salt alkali solution, if the temperature of the soaking tank is low, the water quality and some auxiliaries affect the solubility of the dyes, and the dyes appear in the color fixing solution in the state of "aggregation", which is easy to combine with calcium and magnesium ions and suspended floccules in the water It is easy to form floccules when the temperature is low in the high concentration salt alkali solution. Solution: reduce the hardness of water to less than 70ppm, increase the temperature of high level tank solid solution (above 80 ℃), ensure that the temperature of dip rolling tank solid solution is not less than 50%, accelerate the movement of dye molecules, make dye molecules not easy to gather, which can effectively solve the problem of color spots.
Application Department of Yadong company
Wang Liping

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