3.2.4. Modified full backtan after treatment
The colorimetric data (Table 4) show that, for C.I. Acid Blue 284,
After treatment with the modified full backtan process reduced the chroma and imparted a reddish hue to the dyeings. These findings were expected on the basis of the well-known shade changes that can be observed for the tannic acid component of this after treatment [1]; however, in the case of C.I. Acid Blue 193, after treatment
had little effect upon the hue and colour of the dyeing. The application of the after treatment resulted in a reduction in colour strength (Fig. 8) and an increase in L* value for both dyes used prior to wash testing, which can be attributed to dye having been desorbed from the dyed substrate during the two-stage modified full backtan process. In terms of the fastness of the dyeings, Fig. 8 shows that the colour strength of the backtanned dyeings was higher than that obtained for the syntan + cation process in the cases of the last four wash tests and was similar to that achieved
for the syntan after treatment for the final wash test. Thus, the fk data (Fig. 8) show that after treatment with the modified full backtan improved the fastness of both dyes to repeated washing. This finding gained support from the staining results obtained
(Table 3), which show that the backtanned dyeings displayed highest fastness after five washes. Furthermore, in terms of the extent to which the depth of shade of the dyeings was reduced during repeated wash fastness testing, the % colour loss values
(Fig. 9) clearly show that the modified full backtan after treatment was more effective than either the syntan or the syntan + cation after treatments for both dyes.
3.2.4. Modified full backtan after treatmentThe colorimetric data (Table 4) show that, for C.I. Acid Blue 284,After treatment with the modified full backtan process reduced the chroma and imparted a reddish hue to the dyeings. These findings were expected on the basis of the well-known shade changes that can be observed for the tannic acid component of this after treatment [1]; however, in the case of C.I. Acid Blue 193, after treatmenthad little effect upon the hue and colour of the dyeing. The application of the after treatment resulted in a reduction in colour strength (Fig. 8) and an increase in L* value for both dyes used prior to wash testing, which can be attributed to dye having been desorbed from the dyed substrate during the two-stage modified full backtan process. In terms of the fastness of the dyeings, Fig. 8 shows that the colour strength of the backtanned dyeings was higher than that obtained for the syntan + cation process in the cases of the last four wash tests and was similar to that achievedfor the syntan after treatment for the final wash test. Thus, the fk data (Fig. 8) show that after treatment with the modified full backtan improved the fastness of both dyes to repeated washing. This finding gained support from the staining results obtained(Table 3), which show that the backtanned dyeings displayed highest fastness after five washes. Furthermore, in terms of the extent to which the depth of shade of the dyeings was reduced during repeated wash fastness testing, the % colour loss values(Fig. 9) clearly show that the modified full backtan after treatment was more effective than either the syntan or the syntan + cation after treatments for both dyes.
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