In actual production, when encountering bright green and brilliant blue color combinations, a large amount of emerald blue dyes will be used. Due to the particularity of the molecular structure of emerald blue reactive dyes, quality problems such as color spots and color differences often occur during the dyeing process. Especially when the amount of dye reaches 2.0 or more, the probability of quality problems is greater. , therefore, is called a sensitive color. Based on actual production conditions, the author introduces measures to prevent color spots from emerald blue dye dyeing.
01Promote dye dissolution
1.1Appropriately increase the dissolution temperature of the dye
Uneven dissolution of dye is one of the important factors leading to color spots in dyeing. The temperature of the chemical material should be appropriately increased. For example, using hot water of 70-80℃ to dissolve the dye can improve the solubility of the dye to a certain extent. Stir and shake the hot water bath thoroughly for 10-20 minutes and then slowly pour it into the dyeing machine, usually 15-20 minutes It is more appropriate to finish adding inside.
1.2Use co-solvent
Urea can not only promote the dissolution of dyes, but also swell the fibers in the dye bath, which facilitates the penetration of dye molecules into the fibers, thereby achieving the purpose of leveling and through-dying. Moreover, some liquid leveling agents can also play a certain role in dissolving emerald blue reactive dyes.
When dyeing with reactive dyes, in order to overcome the charge repulsion between the negative charges on the cotton fiber and the dye anions, it is necessary to use a large amount of electrolytes, that is, dye accelerators, during the dyeing process. The main dye accelerators are Yuanming powder and table salt. Among them, the purity of industrial salt is not high and contains more calcium, magnesium, iron and other ions. The phthalate structure of turquoise dye molecules is greatly affected by iron ions. Excessive iron ions will make the original bright color dark. Therefore, when dyeing with such reactive dyes, Yuanming powder with higher purity should be used as the dye-accelerating salt.
02Choose high-purity dye accelerator
When dyeing with reactive dyes, in order to overcome the charge repulsion between the negative charges on the cotton fiber and the dye anions, it is necessary to use a large amount of electrolytes, that is, dye accelerators, during the dyeing process. The main dye accelerators are Yuanming powder and table salt. Among them, the purity of industrial salt is not high and contains more calcium, magnesium, iron and other ions. The phthalate structure of turquoise dye molecules is greatly affected by iron ions. Excessive iron ions will make the original bright color dark. Therefore, when dyeing with such reactive dyes, Yuanming powder with higher purity should be used as the dye-accelerating salt.
03Add dyeing salt in the correct way
When adding, the Yuanming powder should be dissolved in clean water instead of the return water (Flow back from the dyeing machine to the feeding barrel). Facts have shown that too much electrolyte in the dye bath is an important factor leading to the aggregation of dye molecules, but during the dyeing process, it is necessary to use a large amount of dye-promoting salt. If return water is used to dissolve Yuanming powder, the concentration of Yuanming powder will be too high, and the salting out effect will be strengthened, which will cause a large number of dye molecules to precipitate from the dye bath, aggregate, and form color spots on the dyed fabrics.
It is worth noting that before adding Yuanming powder, it should be fully dissolved and stirred in the mixing barrel, and then added slowly, the time is 10-15 min It is advisable to ensure that each tube of rope-shaped fabric circulates for more than four times in the dyeing machine. Considering that the maximum solubility of Yuanming powder is 500 g/L (30℃), and the volume of the chemical barrel is limited(Generally no more than 800 L), so when using a larger amount of starch powder, you should add it in batches. This allows Yuanming powder to be diluted quickly and evenly in the dye bath without causing the local electrolyte concentration in the dye bath to be too high.
The soda ash fixative used in reactive dye dyeing is also an electrolyte, but its salting out effect on dyes is not as obvious as that of Yuanming powder, and it has little effect on the formation of color spots. All are injected with return water. The method of feeding is completely feasible.
04Develop a reasonable dyeing heating and feeding curve
Usually the time interval between each feeding is 15-20min. Appropriately extending the time interval for feeding can prolong the adsorption and diffusion process of the dye. The dye molecules in the dye bath can more fully diffuse and adsorb into the fiber, thereby effectively reducing the dye concentration in the dye bath and greatly increasing the tendency of dye molecules to agglomerate. reduce. In addition, for turquoise dyes with low directivity, appropriately increasing the initial dyeing temperature can also increase the amount of adsorption on cotton fibers to a certain extent, thereby reducing the dye concentration before adding electrolyte.
ΔDyeing, feeding and heating process curves
Nowadays, dyeing and finishing manufacturers basically have computer numerical control feeding equipment. The curve No. 0 in Figure 1 represents constant rate feeding, that is, the same amount of people added per minute; 1 Curve No. is the feeding method of fast first and then slow feeding; curve No. 2 is the feeding method of slow feeding first and then fast. In practice, it has been found that for most reactive dye dyeing, the 0 curve feeding method can achieve ideal results.
05Choose appropriate leveling agent
For dyeing with emerald blue reactive dyes, a leveling agent with dual functions of dispersing and leveling should be used. Leveling agent with strong dispersing ability is very effective in preventing dye aggregation. A good leveling agent should meet the following requirements:
1. It has good dyeing retarding ability and has little impact on the dyeing color. The color change caused by it is generally 5%–10%, or no impact;
2, has good chelation and dispersion ability, and has a certain dissolving effect on dyes;
3, stable to electrolytes, acids and alkalis in the dye bath, and compatible with other anionic additives;
4, low foaming or has certain anti-foaming effect.
06Use dyeing auxiliaries with caution
Silicon-containing defoaming agents must not be used during dyeing with emerald blue dyes. Because the HLB value of defoaming agents is generally 1-3, it is difficult for this type of additive to disperse in water, and it is easy to form “Microdroplets“, while the emerald blue dye molecules with larger molecular weight are easy to “Micro droplets“ gather around them to form dye molecule clusters. Once they stain the cloth, they will form color spots or stains. In the dyeing process of sensitive colors, the use of anti-wrinkle agents or softeners in the dye bath should also be cautious, because the compatibility of such additives with dyes, electrolytes and alkalis in the dye bath is also a problem that cannot be ignored.
07Ensure the hardness index of the dye bath
The hardness of the dye bath refers to the calcium and magnesium content in the dye bath. In the dyeing process of pure cotton fabrics, its sources mainly come from the following three aspects:
1, Ca2+, Mg2+ in dyeing water, Although dyeing water is mostly softened , but affected by factors such as equipment operation stability, the hardness of soft water is not stable and sometimes exceeds the standard;
2, Ca2+, Mg2+ brought in by natural fibers during the natural growth process, This part of the hardness value cannot be ignored when dyeing sensitive colors. For dyeing with emerald blue dyes, Ca2+ and Mg2+Once aggregation occurs, it will further cause the aggregation of dye molecules, thereby forming color spots and stains on the cloth surface;
3. When fabric pre-treatment, the pre-treatment additives used will bring in Mg2+, such as those generally contained in oxygen bleaching stabilizers span>Mg2+. Mg2+For improving the decomposition stability and control of H2O2H2O2 The decomposition rate of plays an important role but affects dyeing uniformity.
Theoretically, when the Ca2+, M g 2+ content is lower than20mg/kg can be called soft water and can meet the requirements for general reactive dye dyeing, but the dyeing of turquoise dyes has higher requirements for the hardness of the dye bath. In practice, it has been found that ultra-soft water with a hardness value lower than 15mg/kg or approaching 0 is more susceptible to sensitive Color dyeing is more advantageous. Therefore, it is necessary to select a suitable chelating dispersant during dyeing, which can effectively improve the hardness produced in the above three aspects and provide ideal dye bath conditions for emerald blue dyes. However, the chelating ability of the chelating dispersant should not be too strong, otherwise it will pull out the metal ions in the molecular structure of some dyes“ ”, destroy the molecular structure of the dye, thereby affecting the dyeing performance of the dye.
��ContainsMg2+. Mg2+For improving the decomposition stability and control of H2O2H2O2 The decomposition rate of plays an important role but affects dyeing uniformity.
Theoretically, when the Ca2+, M g 2+ content is lower than20mg/kg can be called soft water and can meet the requirements for general reactive dye dyeing, but the dyeing of turquoise dyes has higher requirements for the hardness of the dye bath. In practice, it has been found that ultra-soft water with a hardness value lower than 15mg/kg or approaching 0 is more susceptible to sensitive Color dyeing is more advantageous. Therefore, it is necessary to select a suitable chelating dispersant during dyeing, which can effectively improve the hardness produced in the above three aspects and provide ideal dye bath conditions for emerald blue dyes. However, the chelating ability of the chelating dispersant should not be too strong, otherwise it will pull out the metal ions in the molecular structure of some dyes“ ”, destroy the molecular structure of the dye, thereby affecting the dyeing performance of the dye.
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