Tinctorial Efficacy of Dyes in Polyester Fibers

Tinctorial efficacy of a dye, at any given concentration, is defined as the perceptual color intensity per unit dye concentration (g/m ² ) in the fabric. Color intensity is expressed by the Kubelka-Munk ΔK/S values calculated from reflectances measured as lightness-darkness with a green tristimulus filter. A plot of ΔK/S versus dye con centration in the fabric is linear on logarithmic scales and yields two parameters that describe the tinctorial efficacy of the dyeing process. The tinctorial efficacy of dyes in polyester fabric is shown to depend on dyeing conditions. Padding with an aqueous dye dispersion containing a migration inhibitor produces a higher tinctorial efficacy than padding with a solution of the dye in a volatile solvent. The tinctorial efficacy depends also on the dye fixation conditions and increases in the following order: heating in tetrachloroethylene vapor at 160°C for 120 seconds << immersion in an aqueous surfactant solution at 130°C for 60 minutes ≤ heating in air at 213°C for 90 seconds. A lower tinctorial efficacy of dyes in continuous solvent dyeing in tetrachloroethylene is related to microscopically uneven dye distribution in fibers. The tinctorial efficacy increases when a fabric, padded with a dye solution and dried, is immersed in a hot aqueous surfactant solution to redistribute the dye before it diffuses into the fibers.