A Study On The Application Of Vat Dyes For Spun-Dyed Viscose

Spun-dyed technology has more superiorities than the traditional dyeing technology, just like saving human resource, reducing the cost of materials, saving energy sources and good properties of spun-dyed fibre. Now, in our country, the dyed-reagent for spun-dyed viscose is pigment, but it is only suitable for short-fibre in that the particles of dyed-reagent are big and irregulary, they can assemble easily ; the color of dyed-reagent will change during spinning viscose; the dyed-reagent is not good at resisting to acid or alkail, and it will congulutinate on the pipes and the spinneret easily. Comparing to the pigment, the dye has more advantages with fresh color, better transparence, uniformity of the color and it can dissolve in the solution of polymer but not wall up the spinneret. Consequently, it is so valuable as to study the application of the dye as a reagent for the spun-dyed viscose.Usually, most of dyes will be hydrolyzed or isomerized on the conditions of high concentration of acid and alkali during spinning viscose. Consequently, they can not be suitable for spun-dyed viscose as dyed-reagents. But when they are applied for dyeing, vat dyes should be reduced to leuco-sodium, which can be dissolved in water and get into the fibers, and then rivet on the fibers after being oxidized by oxidant. It shows that vat dyes are able to resist to acid and alkail, which provides the theoretical possibility of spinning viscose with vat dyes as dyed-reagents.At first, the color stability of different vat dyestuffs as dyed-reagents for viscose was studied. According to the results of experiments, we get to know that the conditions all will influence the color stability of vat dyes, such as the alkali with high concentration, oxidizing with alkali, and soap-washing. And we also get the fact that many vat dyestuffs can not be suitable for spun-dyed for viscose as dyed-reagents with the way of "reducing-oxidizing", such as C.I. Vat Blue 6, C.I. Vat Red 29, C.I. Vat Black 29, C.I. Vat Orange 1, C.I. Vat Brown 3 and so on. But some vat dyestuffs have a stable color, such as C.I. Vat Green 3, C.I. Vat Black 8 and so on. So, it is necessary to choose a suitable dyestuff as a dyed-reagent for spun-dyed viscose.Secondly, this paper studied the feasibility of dyeing neutral color with two of eight vat dyestuffs which can be suitable for spun-dyed viscose as dyed-reagents, dyeing as the way of viscose's spinning. According to the results, when the central colors are brown, gray and olive and the subsidiary colors are red, orange, yellow, blue and purple, it is feasible to dye neutral color with two vat dyestuffs.At last, the pigmentation of vat dyes was studied because some vat dyestuffs can not be suitable for spun-dyed viscose with the way of" reducing -oxidizing", such as C.I. Vat Blue 4. We also investigated the facts that can influence the effect of pigmentation, such as different dispersants, different concentrations of dispersant, different times of rubbing and oxidizing and so on. According to the results of experiments, we get to know that the diameters of particles of C.I. Vat Blue 4 are about 0.5μm, which meets the requirement of spun-dyed viscose as a dyed-reagent. The choice range of color will be increased when pigmental dye is used as a dyed-reagent for spun-dyed viscose.