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 vinyl sulfone-containing For medium-temperature reactive dyes based on sulfonic acid groups, their β-ethyl sulfonyl sulfate groups are also very good dissolving groups.
In aqueous solution, the sodium ions on the sulfonic acid group and -ethylsulfonyl sulfate group undergo a hydration reaction, causing the dye to form negative ions and dissolve in water.
The dyeing of reactive dyes relies on the negative ions of dyes to be dyed onto the fiber. The solubility of reactive dyes exceeds 100 grams/liter; the solubility of most dyes The solubility 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 due to various reasons (or even become completely insoluble); when the solubility of the dye decreases, some dyes will It will transform from a single free negative ion into a particle, because the charge repulsion between particles is greatly reduced.
Particles will attract each other to produce agglomeration
This agglomeration First, the dye particles aggregate into aggregates, then transform into aggregates, and finally transform into flocs. Although the flocs are a relaxed collection, due to the double electric layer formed by positive and negative charges around them, it is difficult to decompose them due to the shear force during the circulation of the dye liquor, and the flocs are easy to form on the fabric. Precipitate on the surface, 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.
The reason why reactive 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 accelerators contain sodium ions, and the sodium ion equivalent in the dye molecules is much lower than that of the dye accelerators. The normal dye accelerator concentration will not have much impact on the 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. , thereby 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, the degree of aggregation will intensify, forming agglomerates first, and then quickly forming agglomerations under the shear force of the dye liquor. Some dyes with low solubility are partially salted out or even dehydrated.
Dye dyes with different molecular structures also have different anti-aggregation and salting-out resistance. The lower the solubility, the worse the anti-aggregation and salting-out resistance.
The solubility of dyes is mainly determined by the number of sulfonic acid-containing groups and the number of β-ethyl sulfonyl sulfate in the dye molecules.
At the same time, the greater the hydrophilicity of the dye molecule, the higher the solubility, and 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.
Active solubility
can be roughly divided into Category 4: Category 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 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. Category D: dyes containing monovinyl sulfone groups and heterocyclic structures, with the lowest solubility, such as brilliant blue KN-R, emerald blue G, bright yellow 4GL, purple 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 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 are still available at this concentration.��, the reaction rate is higher. In order to prevent color spots and step differences from instantaneous color fixation, 1/4 of the alkali agent can be pre-added at low temperature.
The only thing that needs to be controlled during the transfer dyeing process is the alkali agent
The transfer dyeing process is not only suitable for the heating method, but also for the constant temperature method. The constant temperature method can improve the solubility of the dye and accelerate the diffusion and penetration of the dye. The expansion rate of the amorphous zone of the fiber at 60°C is about twice as high as that at 30°C. Therefore, the constant temperature method is more suitable for yarns such as cheese and skein. The warp beam includes dyeing methods such as jig dyeing that require high penetration and diffusion or have a relatively high dye concentration and a small liquor ratio.
Note that the Yuanming powder currently available on the market is sometimes highly alkaline, and its pH value can reach 9 to 10. This is very dangerous. If we compare pure Yuanming powder with pure salt, the effect of salt on dye aggregation is higher than that of Yuanming powder. This is because the sodium ion equivalent in table salt is higher than the sodium ion equivalent in Yuanming powder under the same weight.
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.
Dye anti-aggregation and salting-out resistance test and determination 1: Weigh 0.5 grams of dye, 25 grams of Yuanming powder or salt, and dissolve them at about 25°C 100 ml of purified water for about 5 minutes, use a dropper to draw 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, we can simply judge the dye’s anti-aggregation and salting-out resistance, and basically determine which dyeing process should be used. </p
