Deep‐colour vat dyeing of cotton knit fabric on a modified jet dyeing machine

Abstract

To improve the vat dyeing of cotton knit fabric with Indanthren Black RB Coll. (CI Vat Black 9), the basic parameters of dyeing, including the concentrations of chemicals, the dyeing temperature and duration, and the apparent diffusion coefficient of the dye, were obtained by test dyeing with a stoppered Erlenmeyer flask and the cellophane film roll method. A stable vat dyeing process has been developed on a modified jet dyeing machine for the first time without using nitrogen to purge oxygen. Modifications were made to improve the airtightness of the machine and the equipment in the liquor circulating system, with a water inlet and outlet for the gentle oxidation of dyed fabric, and with monitoring by means of a sensor inserted in the liquor circulating system for in situ measurements of the redox potential and the pH of the dyeing liquors. These measurements made it possible to follow to their completion the process of dyeing and the process of gentle oxidation by overflow washing with water and final oxidation. Optimal conditions with regard to the amount of reducing agent, the dyeing temperature (80 °C), and oxidising processes were established with this machine. It was found that, by using the modified machine and process conditions, dyeing proceeded stably and reproducibly (at 80 °C) to yield grade A dyed fabric. Visual inspection confirmed that faultless deep‐colour dyeing of the fabric was attained. Production has been proceeding successfully for the past 2 years. Owing to its insolubility, complete removal of the dye from the wastewater has been possible.