Study On The Performance Regulation And Dyeing Factors Of Liquid Indigoid Dyes

Indigoid dyes are very common and important in the dye industry.It is often used for dyeing and printing cotton fabrics of which indigo is popular and has become the most widely used Indigoid dyes.However,indigo has large particle,slow reduction rate and low dyeing rate,and the indigo dyeings have problems such as poor color fullness and brightness.Based on this,liquid indigoid dyes were prepared using synthetic indigo and dibromoindigo as colorants,respectively.By adjusting the structure and dosage of dispersant to control the particle size and crystallization property of the dyestuff,the relationship between particle size and crystallinity with the reduction rate of the dyestuff and the K/S value of the dyeings was investigated.The reduction time was shortened and the color performance of the dyeings was improved by optimizing the dyeing process.Finally,the brightness of liquid indigo dyeings was promoted by dye composition with natural indigo as the imitation.The research content was as follows:Firstly,four dispersants with different structure were used to disperse synthetic indigo and dibromoindigo.The relationship between the structure and dosage of dispersant and the particle size,crystallinity and dispersion stability of the dyestuff was studied.The results show that when the concentration of anionic dispersant DM-1501 in liquid indigo is 1.5% and that of anionic dispersant DM-1501 in liquid dibromoindigo is 9%,the particle size of the dyestuff is in the range of 280 ～ 300 nm,the crystallinity is enhanced to 75%,and the particle size change rates of storage,thermal stability and centrifugal stability are reduced to 10% and below,and high dispersion stability is obtained.Then,the relationship between particle size and crystallinity of liquid indigoid and K/S values of dyeings was analyzed,the dyeing process of cotton fabrics was optimized,and the thermodynamics and kinetics of two dyes on cotton fabrics were investigated.The result shows that when the particle size of liquid indigo and liquid dibromoindigo are in the range of 280～300 nm and the crystallinity of the dye is about 75%,a better dyeing performance can be obtained.And the better dyeing process for liquid indigo is 6 g/L sodium dithionite,reduction temperature 70 ℃,p H value is 11,20 g/L urea,100 g/L dyeing promoter DM-1522,and the dyeings is oxidized by air for 20 min,then 100 g/L deepening agent is used for deepening processing.Compare with the unprocessed dye filter cake,the K/S value of liquid indigo dyeings is increased from 7.72 to 19.32.The better dyeing process for liquid dibromoindigo is3 g/L sodium dithionite,reduction temperature 80 °C,p H value is 11,20 g/L urea and the dyeings is oxidized by air for 20 min,then 80 g/L deepening agent is used for deepening process.Compare with the unprocessed dye filter cake,the K/S value of liquid dibromoindigo dyeings is increased from 13.08 to 29.80.In addition,the thermodynamic and kinetic studies of liquid indigo and liquid dibromoindigo show that the dyeing rate curves of both dyestuffs are in accordance with the quasi-secondary model,the adsorption process is in accordance with the Freindlich adsorption model,the addition of dyeing promoter can reduce the absolute value of dyeing heat and improve the affinity between dyestuff and cotton fabrics,thus increasing the dyeing rate.Finally,natural indigo was used as the imitation to improve the color brightness of liquid indigo.The composition of natural indigo was analyzed,and the formulation of liquid natural indigo imitation was discussed.The results show that the main colored components of natural indigo are indigo and indirubin.The best dyeing performance can be seen when indirubin is used to compound with synthetic indigo.While indirubin is expensive,dibromoindigo,C.I.Vat Red 1 and C.I.Vat Red 41 are compounded with synthetic indigo in order to reduce the cost.When synthetic indigo and C.I.Vat Red 41 are compounded with a mass ratio of 21:1 and the total mass concentration of dye is 4.5 g/L,the color,brightness and K/S value of the dyeings are similar to those of the dyeings with 200 g/L natural indigo.Compared with liquid indigo dyeings,the C* value of liquid natural indigo imitation dyeings is increased from 19.91 to 21.21,meeting the requirement of color brightness improvement of liquid indigo dyeings.