1 Reactive dyes
Reactive dyes have a very good solubility in water. Reactive dyes mainly rely on the sulfonic acid groups on the dye molecules to dissolve in water. For those containing ethylene For sulfone-based medium-temperature reactive dyes, in addition to the sulfonic acid group, its β-ethyl sulfone sulfate group is also an 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 is It relies on the negative ions of the dye to be dyed onto the fiber.
The solubility of reactive dyes exceeds 100 g/L. The solubility of most dyes is 200-400 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 dye has 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.
2 The reason for dye aggregation
The main reason is caused by electrolyte In the dyeing process, the main electrolyte is the dye accelerator (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. Normal dye accelerator concentration will not have much impact on dye solubility in the dye bath during normal dyeing.
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 solubility of the dye. 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, this degree of aggregation will intensify. , first form agglomerates, and then quickly form aggregates and flocculates 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 are resistant to aggregation and salting out. The properties are also different. The lower the solubility, the worse the anti-coagulation and salting-out resistance.
3 The solubility of reactive dyes
can be roughly divided into four categories:
Type A, dyes containing bisethyl sulfone sulfate (i.e. vinyl sulfone) and three reactive groups (monochloro-s-triazine + bis vinyl sulfone) have the highest solubility, such as Yuanqing B, Navy Blue GG, Navy Blue RGB, Golden Yellow: RNL and all reactive blacks made by mixing Yuanqing B, three-reactive base 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 lies 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 then added. The dye accelerator basically completes the dissolution process in the material vat.
Follow the following process, assuming:
The dyeing concentration is 5%, the liquor ratio is 1:10, and the cloth weight is 350Kg (double tube liquid flow), the water level is 3.5T, Yuanming powder is 60g/L, and the total amount of Yuanming powder is 200Kg (50Kg/bag, 4 bags in total) (the capacity of the material tank is generally about 450 liters).
When operating and dissolving Yuanming powder, the reflux liquid from the dye vat is often used. The reflux liquid contains the dye added previously. Generally, 300L of reflux liquid is put into the material vat first, and then poured Add two packages of Yuanming powder (100kg).
The problem is here, most dyes are concentrated here.In comparison, the effect of salt on the aggregation of dyes is higher than that of Yuanming powder. This is because under the same weight, the sodium ion equivalent in salt is higher than the sodium ion equivalent in Yuanming powder.
The aggregation of dyes is closely related to the water quality. Generally, calcium and magnesium ions below 150ppm will not have much impact on the aggregation of dyes, but heavy metal ions in the water, such as ferric iron, Ions and aluminum ions, including some algae and microorganisms, will accelerate the aggregation of dyes. For example, if the concentration of ferric ions in water exceeds 20 ppm, it can significantly reduce the anti-aggregation ability of dyes, and the impact of algae is even more serious.
Attached is a test for the anti-aggregation and salting-out resistance of dyes:
Measurement 1: Weigh 0.5 grams of dye and 25 grams of Yuanming Powder or salt, dissolve it in 100 ml of clean water at about 25°C, wait for about 5 minutes, use a drop tube to absorb the solution, and drop 2 drops continuously on the same position on the filter paper.
Measurement 2: Weigh 0.5g of dye, 8g of Yuanming powder or salt and 8g of soda ash, dissolve them in 100 ml of purified water at around 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.
Using the above method, the dye’s resistance to aggregation and salting-out resistance can be simply judged, and basically what kind of dyeing process should be used. </p
