The dyeing principle of reactive dyes (reactiondye): also called reactive dyes. The molecules contain chemically active groups that can react with cotton, wool and other fibers in aqueous solution to form co-bonded dyes. Reactive dyes are composed of parent dyes, connecting groups and reactive groups, which enable them to form strong covalent bonds with fibers when used.
Reactive dyes
Reactive dyes have extremely good solubility in water state, reactive dyes mainly rely on the sulfonic acid groups on the dye molecules to dissolve in water. For medium-temperature reactive dyes containing vinyl sulfone groups, in addition to the sulfonic acid groups, their β-ethyl sulfone sulfate radicals are also extremely Good dissolving group.
In aqueous solution, the sodium ions on the sulfonic acid group and the -ethylsulfonyl sulfate group undergo a hydration reaction, causing the dye to form negative ions and dissolve in the water. The dyeing of reactive dyes relies on the negative ions of the dye. to the fiber.
The solubility of reactive dyes exceeds 100 g/L. The solubility of most dyes is between 200 and 400 g/L, and some dyes can even reach 450 g/L. However, during the dyeing process, the solubility of the dye will decrease (or even become completely insoluble) due to various reasons. When the solubility of the dye decreases, some dyes will transform from single free negative ions into particles. Due to the great charge repulsion between particles, Decrease, particles will attract each other to produce agglomeration. This agglomeration first assembles the dye particles into agglomerates, then transforms into agglomerates, and finally transforms into flocs. Although the flocs are a relaxed collection, due to the The surrounding double electric layer formed by positive and negative charges is difficult to decompose due to the shear force during the circulation of the dye liquor. The flocs can easily precipitate on the fabric, causing surface staining or staining.
Once the dyes produce such agglomeration, the dye fastness will be significantly reduced, and different degrees of color flowers, stains, and stains will be caused. For some dyes, their flocs will further accelerate their aggregation under the shear force of the dye liquor, causing dehydration and salting out. Once salting out occurs, the dyed color will become very light or even uncolored. Even if it is dyed, it will cause serious stains and stains.
The reason why dyes agglomerate
The main reason is caused by electrolytes. In the dyeing process, the main electrolytes are dye accelerators (Yuanming powder and salt), the dye accelerator contains sodium ions, and the sodium ion equivalents in the dye molecules are much lower than the sodium ion equivalents of the dye accelerator. In the normal dyeing process, the normal dye accelerator concentration has no effect on the solubility of the dye in the dye bath. It would have too big an impact.
However, when the amount of dye accelerator increases, the concentration of sodium ions in the solution also increases accordingly. Excess sodium ions will inhibit the ionization of sodium ions on the dissolving groups of the dye molecules, thus reducing the dye properties. Solubility. When the dye accelerator concentration exceeds 200 g/L, most dyes will agglomerate to varying degrees. When the dye accelerator concentration exceeds 250 g/L, the degree of aggregation will intensify and aggregates will be formed first. Then aggregates and flocculations are quickly formed under the shear force of the dye liquor. Some dyes with low solubility are partially salted out or even dehydrated. Dyes with different molecular structures also have different anti-aggregation and salting-out resistance. The higher the solubility, the higher the solubility. The lower the value, the worse the anti-coagulation and salting-out resistance.
The solubility of the dye is mainly determined by the number of sulfonic acid-containing groups and the number of β-ethyl sulfonyl sulfate in the dye molecule. At the same time, the greater the hydrophilicity of the dye molecule, the higher the solubility. , the smaller the hydrophilicity, the lower the solubility. (For example, dyes with azo structures are more hydrophilic than dyes with heterocyclic structures.) In addition, the larger the molecular structure of the dye, the lower the solubility, and the smaller the molecular structure, the higher the solubility.
The solubility of reactive dyes
can be roughly divided into four categories:
Category A, containing bisethyl sulfone sulfate (i.e. vinyl sulfone) and three reactive groups (monochloro-s-triazine + divinyl sulfone) dyes have the highest solubility, such as Yuanqing B, Navy Blue GG, Navy Blue RGB, Golden Yellow: RNL and all reactive dyes made from Yuanqing B. Black, three-reactive dyes such as ED type, Ciba S type, etc. The solubility of this type of dye is mostly around 400 g/L.
Class B, dyes containing heterobi-reactive groups (monochloro-s-triazine + vinyl sulfone), such as yellow 3RS, red 3BS, red 6B, red GWF, RR type three primary colors , RGB three primary colors, etc., their solubility is based on about 200 to 300 grams/liter, among which the solubility of meta-ester is higher than that of para-ester.
Category C: Navy blue with heterobivalent reactive groups: BF, navy blue 3GF, dark blue 2GFN, red RBN, red F2B, etc., due to fewer sulfonic acid groups or larger molecular weight , its solubility is also low, only 100-200 g/L.
Class D: Dyes containing monovinyl sulfone groups and heterocyclic structures, with the lowest solubility, such as brilliant blue KN-R, turquoise blue G, bright yellow 4GL, purple 5R, blue BRF, bright orange F2R, bright red F2G, etc. The solubility of this type of dye is only about 100 g/L. This type of dye is particularly sensitive to electrolytes. Once this type of dye agglomerates, it does not even need to go through the flocculation process and will directly salt out.
In the normal dyeing process, the maximum dosage of dye accelerator is 80 grams/liter. Only dark colors require such a high concentration of dye accelerator. When the dye concentration in the dyeing bath is below 10 g/L, most reactive dyes still have good solubility at this concentration and will not agglomerate. But the problem is in the material vat. According to the normal dyeing process, the dye is added first. After the dye is fully diluted to uniformity in the dye bath, the dye accelerator is added. The dye accelerator is basically…℃ dyeing is 12.0, 80℃ dyeing is 11.0).
Powdered light soda ash is commonly used, 5~25g/L, pH=10.65~10.99, and its pH buffering capacity is very large. Therefore, depending on the depth of dyeing, a dosage of 5 to 20g/L of soda ash is sufficient. If the dosage is too much, the color depth will not be significantly improved, but it will reduce the dissolution stability of the dye in the salt-alkali fixation bath and harm the dyeing quality.
How to apply soda ash. Practice has proved that the application of alkali agents must follow the following two principles:
First, the addition of soda ash must be based on “balanced and uniform color absorption”. That is to say, the alkali agent can be added only after the color absorption balance is truly reached in the neutral salt bath (color absorption bath) and the color absorption is uniform through dye transfer. This is because after reaching the color absorption equilibrium, the residual dye liquor concentration is the lowest. The lower the dye liquor concentration, the smaller the tendency of dye aggregation after the addition of alkali agent, the milder the secondary color absorption rate, and the smaller the probability of dyeing defects. After the alkali agent is added, the dye on the fiber will lose its dye migration ability due to fixation. This can turn the unevenness created during the absorption phase into permanent blemishes.
Second, the application of alkali agent must be “less at first, then more, and added in batches.” Because the faster the alkali agent (soda ash) is added, the stronger the alkalinity of the fixation bath will be, the higher the salt-alkali mixing concentration will be, the more intense the aggregation and coloring behavior of the dye will be, and the easier it will be to produce dyeing quality problems. Practice has proved that the alkalinity of the fixation bath increases from weak to strong, the concentration of the salt-alkali mixture increases from low to high, and the concentration of the dye solution changes from thick to light, which can effectively alleviate the excessive behavior of the dye caused by the addition of alkali agents, thereby ensuring the dyeing quality. Achieve stability.
The soaping process must be correct
The soaping effect is a key factor in determining the color fastness of reactive dyes. Therefore, we must pay attention to the soaping process and overcome the wrong concept of focusing on dyeing and neglecting soaping.
The key points of the soaping process are: soaping must be carried out on the basis of sufficient cleaning. That is, after dyeing, it must be washed with warm or hot water to remove the residual salt, alkali, dye liquor and some floating dyes on the fabric to improve the freshness of the soaping solution and reduce the “re-staining” rate of the dye.
When using ordinary soaping agents for soaping, the key is that the soaping temperature must be kept above 90°C. Never use medium temperature (60-70℃) soaping in order to reduce fading and color correction. When using a low-temperature (60°C) soaping agent for soaping, the key is to choose a soaping agent with good wetting, penetration, solubilization (solubilization), and diffusion (dispersion) effects under low-temperature conditions to ensure good soaping. washing effect.
Attached is a test for the anti-aggregation and salting-out resistance of dyes: Measurement 1: Weigh 0.5 grams of dye, 25 grams of Yuanming powder or salt, and dissolve them in 100 ml of clean water at about 25°C for about 5 minutes. , use a dropper to draw the solution and drop 2 drops continuously on the same position on the filter paper. Determination 2: Weigh 0.5 grams of dye, 8 grams of sodium chloride powder or salt and 8 grams of soda ash, dissolve it in 100 ml of purified water at about 25°C, wait for about 5 minutes, and use a dropper to draw the solution continuously at the same position on the filter paper. Add 2 drops. The above method can be used to simply judge the anti-aggregation and salting-out resistance of the dye, and basically determine which dyeing process should be used. </p
