Warp Dyeing of Indigo

Continuous Warp Dyeing of Indigo:

The principles of dyeing ball warps, warp beams or piece goods with the leuco-indigo anion are easy to understand, and the present processed result from the low substantivity of the anion for cellulose.

The dyeing equipement cosists essentially of a series of open width wash boxes equipped with multiple upper and lower rolls, around which the goods are led in a serpantine path, wich squeeze rolls between the boxes. Above the middle set of four to six boxes (vats), skying rolls are provided. The process is carried out at ambient temperature.

After wetting out the goods in first boxes, they pass at about 25 meters per minute to the middle set of boxes and are immersed in leuco-indigo dye liquors for 10 to 30 seconds, sqeezed to about 100% wet pickup, and skyed for about 2 minutes. These three steps are repeated in successive boxes, as many time as desired, up to about six. In each box some more leuco-indigo is imbibed, followed by air oxidation, and the indigo pigment is gradually built up, primarily on the fiber surfaces.

The indigo is usually dissolved in a stock vat which contains indigo (100%), caustic soda and hydrosufite at concentrations of about 80, 70 and 60 grams per liter. The stock vat os used to supply the boxes which are preset with caustic and hydrosulfite, to maintain a level of: indigo (100%), Caustic soda and hysrosulfite, at concentrations of about 5, 2, 1.5 grams per liter. The heart of the process is in the circulating of the liquor in the vats and metering-in stock dye and chemicals to maintian constant, uniform dyeing conditions. The dyeing is concluded by carrying the goods several boxes of counterflowing water.

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Further Reading on Indigo Manufacturing...