Solublized Vat Dyes (Indigosol Dyes)
Vat dyes are are insoluble in water and leuco vat is not a stable product , however leuco esters of vat dyes are stable and readily soluble in water, leuco ester of vat dyes are available in powder form known as Indigosol Dyes or solubilized vat dyes.Being water soluble these dyes are readily applied to cellulosic fibers and are subsequently converted to parent vat dye by oxidation treatment.
Properties of Soluble Vat colors
The stability of leuco esters is good and varies with different types . The decomposition may occur by action of light , moisture and acid fumes, Which results into auto decomposition. The auto decomposition may be prevented by adding alkaline salts during dye standardization , which acts as buffer during storage.
The leuco ester powders are readily soluble in water , but boiling must be avoided , which may result into premature oxidation of the dye.
3.Principles of application
The application process of soluble vat colors consists of two steps
a.The exhaustion of color from alkaline , neutral or acidic conditions.
b.The oxidation or development of exhausted leuco ester in the presence of an acid and oxidizing agent , changing the color into original dyestuff.
The affinity for cellulosic materials is low , but the dye exhaustion is assisted by addition of electrolytes , however the affinity for animal fibers such as wool is good and can be increased by temperature.
5.Sensitivity to Light
Most of the soluble vats are sensitive to light before development and exposure to light can affect the leucoester in powder or paste , dye stuff solution , on dyeing machine before development, during dyeing and after dyeing and drying. In order to avoid all difficulties which may occur through the action of light , it is advisable to reduce the exposure to minimum.
6.Development or Oxidation
The ease of regeneration of leucoesters to original vat dye is most important .The potential of oxidizing medium depends upon ,
- Choice of Oxidizing agent.
- pH of the developing bath.
However over oxidation must be avoided , because excess oxidizing agent may result into over oxidation and may attack the developed dye.
Due to the higher cost and low substantivity towards cellulosics , these dyes are used only for light and pale shades or on the substrates such as mercerized cotton where penetration of normal vat dye is a problem.
Exhaust dyeing method for dyeing of hanks with soluble vat dyes
(cotton yarn in hank form)Advantages of Soluble vat dyes
1.They offer extremely good coverage of yarn irregularities .
2.They are especially suitable for cotton and viscose rayon for pale shades.
3.Since no alkali is being used in the dyeing process these can be used for over dyeing of shirting materials dyed with vat or naphthol dyes, without affecting them. These dyes can be used for wool and silk dyeing also.
4.Soluble vat dyes can be easily used for mercerized sewing threads , viscose rayon and cotton embroidery threads for hank dyeing.
5.These can be applied knitted goods on winch machines and suitable for piece goods by padding and jigger dyeing.