Basic Dyes

Basic dyes are called so since they are salts of organic bases. Basic dyes are also called  cationic  dyes because  in  solution  the  basic  dye  molecule  ionizes,  causing  its colored component to become an action of positively charged radical. Basic dyes are used for dyeing wool, silk, and acrylic and mod-acrylic fibres.

Properties of Basic Dyes

1. The outstanding characteristics of the basic are brilliance and intensity of their colors.
2. The bright colors achieved from basic dyes do not usually occur with other dye classes.
3. Many of the basic dyes are sparingly soluble in water.
4. The addition of glacial acetic acid helps to dissolve the basic dye quickly in water.
5. Basic dyes are readily soluble in alcohol or mentholated spirit.
6. The basic dyes are poor fastness to light and vary with regard to washing fastness from poor to moderate.

Preparation of Dye Solution

Owing to the relative insolubility special precautions are necessary when dissolving basic dyes. The dyestuff is first made into a paste with about its own weight of 30% acetic acid. Sufficient boiling water is then added with constant stirring to dissolve the dye. The basic dyes have such a great affinity for wool fibres the presence of a retarding agent is often desirable. The Acetic acid acts as a retarding agent.

The excess of hydrogen ions in the liquor counter acts the attracting of the electro negative sites in the fibre and slows down the rate of absorption. When acid has been used, the addition of a small amount alkali may be necessary towards the end of the dyeing to complete exhaustion.

Dyeing

The dye bath is made up containing 1 to 3 % of 40% acetic on the weight of the wool, the dye solution, after being strained through a filter is added, and the goods, which have previously been scoured, are entered. The dye bath temperature is slowly raised to the boil and dyeing is continued for ½ to ¾ hour. After dyeing the goods are rinsed, hydro-extracted and dried.