The solubility of reactive dyes can be roughly divided into four categories:
Class A, dyes containing diethylsulfone sulfate (ie vinylsulfone) and three reactive groups (monochloro-s-triazine + divinylsulfone) have the highest solubility, such as Yuanqing B, Tibetan blue GG, Tibetan blue RGB, golden yellow: RNL As well as all active blacks made by mixing Yuanqing B, dyes with three reactive groups such as ED type, Ciba s type, etc. The solubility of such dyes 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 200 ~ 300 grams /L or so, wherein, the solubility of meta-ester is higher than that of para-ester.
Class C: The same is the navy blue of the hetero-double reactive group: BF, navy blue 3GF, dark blue 2GFN, red RBN, red F2B, etc., due to less sulfonic acid groups or large molecular weight, its solubility is also low, only 100 ~ 200 g/ Rise. Class D: dyes containing monovinylsulfone group and heterocyclic structure with the lowest solubility, such as brilliant blue KN-R, turquoise blue G, bright yellow 4GL, violet 5R, blue BRF, brilliant orange F2R, brilliant 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 coagulates, it does not even need to go through the flocculation process, and it will salt out directly.
In the normal dyeing process, the maximum amount of dye accelerator is 80 g/L, only dark colors need 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 tank. According to the normal dyeing process, the dyestuff is added first, and after the dyestuff is fully diluted in the dye bath to uniformity, the dye accelerator is added. The dye accelerator basically completes the dissolution process in the material tank.
Operate according to the following process, assuming: the dyeing concentration is 5%, the liquor ratio is 1:10, the cloth weight is 350Kg (double-pipe liquid flow), the water level is 3.5T, the Yuanming powder is 60 grams/liter, and the total amount of Yuanming powder is 200Kg (50Kg A total of 4 bags per bag) (the capacity of the material tank is generally about 450 liters).
In the operation to dissolve Yuan Ming powder, the reflux liquid of the dye vat is often used. The reflux liquid contains the dyes added before. Generally, 300L of the reflux liquid is put into the material tank first, and then two packets of Yuan Ming powder (100 kg) are poured.
The problem is here, most dyes will agglomerate to varying degrees under this concentration of Yuanming powder. Among them, the C-type dyes will be seriously agglomerated, and the D-type dyes will not only agglomerate, but even salt out.
Although the general operator will slowly replenish the Yuanming powder solution in the material tank into the dyeing tank through the main circulating pump according to the program. But the dyes in the 300-liter Yuanming powder solution have already formed flocs, and even salted out.
When all the solution in the material tank is replenished into the dye tank, it can be seen that there is a layer of greasy dye particles on the tank wall and the bottom of the tank. If these dye particles are scraped off and put into clean water, it is generally difficult to dissolve them again. In fact, this is the case for the 300 liters of solution that go into the dye vat.
Remember that there are two packets of Yuan Mingfen that will also be dissolved and replenished into the dye vat in this way. When this happens, color flowers, stains, and stains will inevitably occur, and the color fastness will be seriously reduced due to surface dyeing.
Even without significant flocculation or salting out. Dye agglomeration also occurs for the A and B types with higher solubility. Although such dyes have not yet formed flocs, at least some dyes have formed aggregates.
These aggregates are difficult to penetrate in the fibers. Because the amorphous region of cotton fibers allows only single-ion dyes to penetrate and diffuse. Any agglomerates cannot enter the amorphous regions of the fibers. It can only be adsorbed on the surface of the fiber. The color fastness will also be significantly reduced, and serious color flowers and stains will also occur.
The solution degree of reactive dyes is related to the alkali agent. When the alkali agent is added, the β-ethylsulfone sulfate of the reactive dyes will undergo elimination reaction to form its real vinyl sulfone. Vinyl sulfone is a very soluble gene. Since the alkali reagent required for the elimination reaction is very small, (often only accounts for less than 1/10 of the process dosage,) the more alkali doses are added, the more dyes the elimination reaction occurs. Once the elimination reaction occurs, the solubility of the dye will also decrease.
The same alkaline agent is also a strong electrolyte, containing sodium ions. Therefore, excessive alkali concentration will also cause the dyes that have formed vinyl sulfone to agglomerate or even salt out.
The same problem occurs in the material tank. When dissolving the alkali agent (take soda ash as an example), if the reflux liquid is used. At this time, the reflux liquid already contains the dye accelerator and dye of normal process concentration. Although some of the dyes may have been absorbed by the fibers, at least more than 40% of the remaining dyes are still in the dye liquor. Assuming that a bag of soda ash is poured in during operation, the concentration of soda ash in the material tank exceeds 80 g/L. Even if the dye accelerator in the reflux liquid is 80 g/L, the dye in the material tank will also agglomerate. C-type and D-type dyes even salt out, especially for D-type dyes, even if the concentration of soda ash is reduced to 20 g/L, local salting-out will occur. Among them, brilliant blue KN.R, turquoise blue G, and monitoring BRF are the most sensitive.
Coagulation of the dye, or even salting out, does not mean that the dye has been completely hydrolyzed. If coagulation or salting out is caused by a dye accelerator, it can still be dyed as long as it can be redissolved. But to make it re-dissolved, a sufficient amount of dyeing auxiliaries (such as urea above 20 g/L) must be added, and the temperature should be raised to above 90 °C with sufficient stirring. Obviously, it is very difficult in actual process operation.
In order to prevent the dyes from agglomerating or salting out in the material tank, the dye migration method must be used when making deep colors for the C and D dyes with low solubility, as well as the A and B dyes.