Abstract:

Objective The color matching of dyes is prone to fail in obtaining the desired color in practical production. In the process of continuous pad dyeing, it is necessary to adjust constantly the liquid replenishment to ensure stable dye concentration in the dye bath to avoid color difference between the head and tail in the dyeing process. However, the goal of precise control of the dyeing process cannot be achieved by relying on the experience of dyeing and finishing masters, and replenishment modelling in pad dyeing becomes necessary.
Method In order to explore the digital control method of the replenishment system of mixed dye in the pad dyeing process, the replenishment model was established based on the real-time monitoring of the dyeing process with mixed dyes using Raman spectroscopy. Firstly, the quantitative analysis model of mixed dye concentration with C.I. Reactive Red 195 (RR195) and C.I. Reactive Blue 194 (RB194) was established based on Raman spectroscopy monitoring and partial least square method (PLS). Then, the initial dye uptake rate of RR195 and RB194 were obtained under different dyeing processing conditions. Finally, the replenishment model of the combination pad dyeing was established to calculate the amount of each dye to be added in real-time according to the conservation of mass with dye solution and dyes before and after replenishment, and compared with the replenishment system through the concentration of the original dye solution.
Results The results showed that the correlation coefficients of RR195 and RB194 dyes in the correction set and prediction set in the quantitative analysis model were greater than 0.990 0 (Fig.4), and the root mean square error of cross validation (RMSECV) and the root mean squared errors of prediction (RMSEP) were 0.279 0 and 0.129 0, 0.115 0 and 0.054 5, respectively. The fitting curves of the correction set and prediction set of the two dyes demonstrated a high coincidence. This suggested that the established quantitative analysis model had a high prediction capability. The real-time monitoring of the dyeing process of RR195 and RB194 were achieved by using the quantitative analysis model, according to which the color matching dyeing process of RR195 and RB194 (at a mass ratio 1:1) were obtained in real time. It is assumed that the soaking time of the fabric in the pad dye solution is 6 s, and the initial dye-uptake rate of RR195 and RB194 were calculated as 28.10 and 36.63 mg/(g·min) respectively according to the dye-uptake curves. By using the formula of the replenishment model, it was found that the volume of dye solution to be replenished after dyeing each fabric (3.0 g) was 2.15 mL, and the mass of RR195 and RB194 dyes to be replenished were 13.80 and 16.36 mg, respectively. The color difference of 25 fabrics after the pad dyeing through the replenishment system is maintained at 0.5, and the concentration of RR195 and RB194 in the dye solution remains unchanged. However, the color difference of 25 fabrics after the pad dyeing with original replenishment model is about 7, and the dye concentration of RR195 and RB194 was reduced by more than 50%, which verifies the accuracy of the replenishment model.
Conclusion The experimental results of RR195 and RB194 with color matching dyeing verifies the accuracy of the quantitative analysis model and replenishment model. The developed replenishment model helps control the replenishment system digitally without relying on the human experience, and it minimizes the color difference between the head and tail in the pad dyeing process of color matching. The quantitative analysis model of mixed dye concentration established by Raman spectroscopy and PLS can be used for mixing most dyes without decomposition spectrum. This approach is applicable to further explorations on the influencing factors and mechanism of color matching dyes, and on studying the quantitative evaluation method of color matching dyes.

Key words: mixed dyes, replenishment model, pad dyeing, quantitative analysis, Raman spectroscopy