2. Vat dyes dyeing process

    Vat dyes do not dissolve in water, while when reduced to be leuco salt by reducing agent under alkaline conditions, they can dissolve in water and get feature of immediacy with cellulose fibers, which is the way to achieve the purpose of dyeing. Then stable shade and good color fastness would come out via oxidation and soaping.

    2.1 Reduction of dyes

    Insoluble reducing dye will change into soluble leuco.

    .Different levels of the best staining methods are brought out according to the reduction dyes' reduction potential and level of its immediacy to fibers.

    2.2 Dye-uptake of leuco

      The leuco is adsorbed by fiber and then it is diffusing into the fiber.

        It is necessary to use soft water or softened water in dyeing process. Hereby it is suggested to add the water softener for 1g/L to some poor quality cotton fabric. The water softener would not only absorb calcium, magnesium ions, but also the iron, copper ions which are absorbed by the pipe into the dye bath, and finally keep the solubility of leuco.

 The sodium sulfate could increase the dyeing absorption rate, and surely it is also a good promoter. So it can be added into the dye bathes with medium or low immediacy according to the demand.Referring to 3.13. 

    2.3  Leuco Oxidizing

        The leuco absorbed by fiber is oxygenated and changed into the former insoluble vat dyes,  then it colors.

        Scour them in 2-3 baths with soft ware before oxygenation, avoiding to be oxygenated with alkali.

        Hydrogen  peroxide is most suitable for  suspension padding, while after oxygenation, it should be in soap boiling immediately without washing.

        The sodium perborate is mild in very widely use. It can be bathed with the next procedure (referring to soap boiling).

2.4  Soaping treatment

        The stable shade and good color fastness would come out via soap boiling.

        Through high-temperature soap boiling, the floating color can be removed and the crystallization of vat dyes on fabric would be enhanced, so the fastness is increased, the stable and full color is achieved.