Reactive dyes

  For the continuous process, the materials must be carefully pretreated to guarantee rapid wetting and uniform absorption of liquor [5, pp. 254±264]. The padding liquor should contain an antimigration agent After dye application, the fabric is uniformly and gently dried to minimize migration of the insoluble dye, and the disperse dye is fixed in the PES component by the thermosol process .  Subsequently,  the vat  dyes  on  the  CEL  portion  is developed either continuously according to the pad steam process or batchwise by the pad jig method. The most elegant method is pad steam development, which frequently follows the thermosol process in one pass. In pad steam development, the fabric is padded with reducing agent and alkali, and the vat dye is fixed by steaming in saturated steam (103±105 DC dry thermometer). Finely dispersed vat dyes must be used in this process because of the short vatting time.

  Disperse and Reactive Dyes . Reactive dyes are often used to dye the cellulose portion of PES±CEL blends because the coloring possibilities of  reactive  dyes  are  especially  diverse,  and  a  large  number  of relatively  easy application processes produce dyeings that are sufficiently fast for the clothing sector and, frequently, for household textiles. In the two-bath  batch method  the  PES component is predyed with  disperse dyes, and the CEL portion is topped with reactive dyes after reductive intermediate clearing, if necessary. In a one-bath two-stage batch process, the bath contains all the dyes from the start. After the PES component is dyed at 130 DC, the bath is cooled to ca. 80DC, and alkali is added to fix the reactive dyes to the CEL component. Careful selection of dyes is required because the reactive dyes must be stable at pH 4±5 and 130 DC.

  In a reverse process, the CEL component is predyed at alkaline pH, the pH is then lowered, and the PES component is dyed at 130 DC. In this case, alkali-stable disperse dyes must be chosen if the disperse dye is added at the start. In addition, large amounts of salt in the bath can interfere with dispersion stability. Hence, especially fast exhausting disperse dyes are used.