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The Printing Efficiency of Vat Dyes
Author(s) -
Michie A. G. H.,
Thornton R.
Publication year - 1953
Publication title -
journal of the society of dyers and colourists
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.297
H-Index - 49
eISSN - 1478-4408
pISSN - 0037-9859
DOI - 10.1111/j.1478-4408.1953.tb02806.x
Subject(s) - steaming , chemistry , potassium carbonate , fixation (population genetics) , pulp and paper industry , materials science , organic chemistry , food science , biochemistry , engineering , gene
A method of assessing vat‐dye prints has been established involving determination of the amount of dye applied to a cotton fabric by a roller printing technique, and the amount fixed at various stages during the afterprinting processes. By extracting the vat dye from the fabric and determining optically the amount present in a given area it is possible to calculate the percentage dye fixation under a variety of conditions. This method of assessment was used initially to study a range of seventeen vat dyes, applied by the potassium carbonate‐Formosul process under conditions of varying Formosul concentration in the print paste, varying steaming times, and varying depths of shade. Later the effect of using different alkalis at various concentrations was studied, and also the effect of the addition of glycerol and of different thickening agents. The predominant feature which emerged was the marked difference between the dyes in sensitivity to the Formosul concentration in the print paste. The dyes varied from those showing little change in percentage fixation, despite large variations in the amount of Formosul present, to those requiring a “threshold” concentration for adequate fixation, while a final group showed the threshold effect and was also susceptible to over‐reduction at still higher concentrations. It is apparent, therefore, that the instability of Formosul gives rise to the bulk of troubles experienced in printing vat dyes, since, provided the required amount of Formosul was added to the print paste and remained on the print up to the time of steaming, all vat dyes could be satisfactorily printed. Varying the thickening agent did not affect the amount of print paste applied to the fabric nor the percentage dye fixation, though marked visual differences were apparent. Caustic soda was shown to be a more efficient alkali than potassium or sodium carbonate, giving both increased percentage fixation and increased rate of fixation. The addition of glycerol had the greatest effect when the steaming times were short. A preliminary study of the pad‐steam prooess showed a general decrease in the sensitivity of the dyes to the amount of Formosul present on the prints. The basic underlying principles were the same, however, since the order of “printability” was the same for both the pad‐steam and the potassium carbonate‐Formosul process.