Low temperature reactive dyes are vinyl sulfone dyes. Compared with medium-temperature reactive dyes, there are two major differences in the requirements for dyeing conditions.
Two dyeing condition requirements
1. Low requirements for dyeing temperature. Low-temperature reactive dyes have relatively strong reactivity in dye baths with high alkalinity and are suitable for dyeing at 40°C. If the dyeing temperature is too high or too low, the color yield will decrease (table)
2. For fixation alkalinity High standard. Low-temperature reactive dyes have a different dye matrix than medium-temperature reactive dyes, and the combination between the sulfate ester group and the vinyl sulfone group in the active group is relatively stable. Therefore, the alkalinity required for the “elimination reaction” to occur is relatively high. After testing, low-temperature reactive dye dyeing is suitable for using compound alkali (soda ash and caustic soda) as a color-fixing alkali agent. Optimum fixation alkalinity pH=12. 21 ~ 12. 40
[Testing conditions: dye 1.25% (owf), salt 50g/L, liquor ratio 1:3, Absorb color at 40°C for 30 minutes, fix color for 50 minutes, and wash with soap]. Note: Soda ash is weakly alkaline and has a low pH value (soda ash 20g/L, pH=ll). Obviously it is not suitable for low-temperature reactive dyes to be used as color-fixing alkali agents. After testing, when using soda ash to fix color, even if the fixing temperature is raised to 50°C (the color yield is relatively the highest), the color depth still cannot reach the level of compound alkali fixing at 40°C.
Two major advantages in the performance of low-temperature reactive dyes
Low-temperature type Compared with medium-temperature reactive dyes, reactive dyes have two major advantages in dyeing performance:
1. They have less cohesion in the fixation bath. As we all know, when dyeing medium-temperature vinyl sulfone dyes (such as reactive brilliant blue, etc.), due to the high electrolyte concentration in the fixation bath (soda ash is also an electrolyte), the salting out of the dye is greater.
In addition, the B-hydroxyethyl sulfone sulfate active group in the dye is sensitive to alkali agents, and will undergo a rapid elimination reaction when exposed to alkali, making the originally water-soluble active group become hydrophobic. This results in a sharp drop in the solubility of the dye itself.
ß-hydroxyethyl sulfone sulfate active group
Vinyl sulfone active group
Therefore, in the fixation bath where salt and soda ash coexist, the aggregation of the dye is significant or even serious.
When dyeing with low-temperature reactive dyes, due to the use of compound alkali (soda ash 5g/L + caustic soda 1~1.5g/L) as the alkali agent, the mixing concentration of the electrolyte is low, which is harmful to the dye. The salting out effect is small. In addition, the active group of low-temperature reactive dyes causes the elimination reaction to occur relatively slowly, and the impact on the solubility of the dye itself is relatively mild. Therefore, there is no obvious aggregation phenomenon in the fixation bath, and there are almost no quality problems caused by excessive dye aggregation.
2. The sudden dyeing is small in the early stage of fixation.
For medium-temperature reactive dyes, in the early stages of color fixation by adding alkali, there is a common problem of “flash dyeing” to varying degrees. Especially for vinyl sulfone dyes, the phenomenon of sudden dyeing is becoming more and more serious. For example, when adding alkali to fix the color within 10 minutes, reactive brilliant blue KN-R can increase the relative color absorption by 59.96%; reactive black KN-B can increase by 68.95%.
The reason is: after adding alkali, the dye liquor changes from neutral to alkaline, and the D-hydroxyethyl sulfone sulfate active group in the dye will undergo an elimination reaction quickly and become Vinyl sulfone group with double bond.
Firstly, the directness of the dye is immediately improved, which greatly accelerates the color absorption; secondly, the reactivity of the dye is immediately strengthened, and the fixation reaction between the dye and the fiber occurs quickly, thus making The original color absorption balance of the dye is broken, prompting the dye to be dyed for a second time quickly. Of course, the addition of alkali agent will suddenly increase the mixed concentration of electrolytes in the dye solution, increase the dyeing effect, and also play a certain role in promoting the “flash dyeing” of dyes.
Low-temperature reactive dyes are different from medium-temperature reactive dyes. In the early stage of color fixation by adding alkali, the degree of sudden dyeing of the dye is very small.
The SERF value curve of the dye shows that the secondary color absorption rate of low-temperature reactive dyes in the fixation stage is relatively stable, and the sudden coloring phenomenon is not prominent. For example, the relative color absorption (S 7 value) within 10 minutes of adding alkali for color fixation only increases by about 30% (medium-temperature reactive dyes generally have a net increase of more than 40%).
The main reason is: low-temperature reactive dyes have a different dye matrix from other vinyl sulfone dyes. The structural characteristics of the matrix improve the reactive group of B-hydroxyethyl sulfone thioester. The bonding stability between the sulfone group and the sulfate ester group is stable. In the alkaline bath, the elimination reaction of the sulfate ester group proceeds relatively slowly. Therefore, the instantaneous coloring phenomenon caused by the large amount of active sulfone groups being generated in a short period of time is eliminated.
From the above analysis, we can know:
1. Low-temperature reactive dyes are suitable for low-temperature dyeing at 40°C using complex alkali as alkali agent. , compared with medium-temperature reactive dyes, it has outstanding advantages in “energy saving, emission reduction, and efficiency improvement”.
2. Low-temperature reactive dyes have less cohesiveness and flash dyeing properties during the fixation stage (secondary color absorption). Compared with medium-temperature reactive dyes, low-temperature reactive dyes are less uniform.�Excellent dyeing effect.
3. The dyeing process of low-temperature reactive dyes is different from that of medium-temperature reactive dyes. The representative dyeing processes are as follows:
A-low temperature reactive dye x
B-water softener 1 ~2g/L
D-Soda ash 5g/L
E-caustic soda (100%) 1～1.5g/L
1 Ordinary staining method. This method is more suitable for dyeing medium to light colors.
2 Pre-alkali staining method. This method is more suitable for dyeing medium to dark colors.