Old VAT dye VAT dye, insoluble in water, in the alkaline solution by sodium dithionite reduction processing powder (insurance), and make the fiber dyeing dye. Its fast and washing fastness especially, can be used for cotton, linen, viscose, whalen fiber dyeing and printing, etc.
In the molecular structure of VAT dye excluding sulfonic group, carboxylic acid base, such as water soluble groups, insoluble in water, therefore, cannot be directly dyed; The molecular conjugated double bond systems containing at least two carbonyl, interaction with insurance powder in the alkaline solution, carbonyl reduction into hydroxyl, become water soluble compounds ─ ─ the leuco body. Is leuco body has affinity to fiber, fiber after adsorption, oxidized by air or other oxidants, leuco body back for VAT dye fixation on fiber staining. Leuco body staining method shortcoming is dye into the fibers not easily, if the suspension pad dyeing, the reduction of the outstanding dye made from suspension solution, borrow machine rolling pressure make dye fine, evenly distributed on the dyed fabric treated with insurance powder and make dye reduction by fiber adsorption, good is thicker and uniform can be obtained by the oxidation dyeing effect.
Its chromatographic is full, bright color, soaping, tanning fastness are high, but because the price is more expensive, some yellow, orange and other color with photosensitivity brittle damage phenomenon, make its application is limited by certain.
Because Vat Dyes does not dissolve in water, so the side effects of it on the human body easy to control, more safe and convenient for environmental protection, but its cost is generally high.
