Dyebath initial stage

Class B direct dyes have poor leveling power and exhaustion must be brought about by controlled salt addition. If these dyes are not taken up uniformly in the initial stages it is extremely difficult to correct the urdevelness. They are dyes that have medium—high affinity and poor diffusion. In their apphcation the cellulose is entered into a dyebath containing ordy dye. The salt is added gradually and portionwise as the temperature is increased and possibly the final additions made after the dyebath has come to the bod. 

Simulation resnlts indicate that in the case of integration dyeing, in which dyes and auxiliaries are continuously dosed into the dyebath over a period of time, the quadratic dosing method will be the preferred method during the initial stage of dyeing, since the rate of dye injection starts slowly. After 7 time units the rate increase may be too rapid for a level distribntion of dye (as shown in Fig. 6.36, dashed line), and an exponential dosing method may be the preferred method... 

Liquids. Some Hquid dyes are made directly from the thionation melt by additions of caustic soda and sodium hydrosulfide. Hydrotropic substances are sometimes added, either at the initial thionation stage or after the polysulfide melt is finished in order to keep the reduced dye in solution. Pardy reduced Hquids are also available. They are usually more concentrated than fully reduced Hquids, thus saving packaging and transportation costs. However, they require a further addition of reducing agent to the dyebath in order to obtain full color value. On the other hand, fully reduced Hquids are... 

The initial reuse research dealt with dyeing of 100% cotton knit underwear fabrics. The approach was to dye 100% cotton with a single reactive dye (low-temperature) in order to determine the initial problems in adapting reuse to reactive dye systems. The analysis of the reactive dyebath was similar to that described for disperse dyes in the general discussion section of this chapter. Since the reactive dye was water soluble, no organic extraction was necessary before analysis. The problems encountered and the solutions derived in this stage were ... 

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