Direct dyes copper after-treatment

The present practice of copper after-treatment owes its origin to the discovery in 1915 that some of the oo dihydroxy direct dyes would form complexes with copper. The hue of the new derivative was usually somewhat duller, but boA the light- and the wet-fastnesses w ere improved. An example is Sirius Super Green BTL in which the ethoxy and hydroxyl groups are in the oo positions as shown below ... 

A single-bath method can be used if desired. The dyes are dissolved separately and added to the dyebath which already contains an ethylene oxide condensate which acts as an anti-precipitant. The dyebath is adjusted to pH 5 to 5-5 with acetic acid and sodium acetate and the goods are entered at 40 to 45°C (104 to 113°F). A period of 45 minutes is taken to raise the temperature to the boil, at which it is maintained for one hour. Alternatively, the acrylic fibre may be dyed first and then the same liquor is neutralized and the cellulosic fibre is dyed. Application of a cationic fixing agent improves wet fastness of direct dyes but copper after-treatment should be avoided because this can have an adverse effect on the light fastness of the cationic dye. Very good fastness is obtained if, after the acrylic component has been dyed, the cellulosic fibre is brought to shade with vat dyes. 

There are many direct dyes of which the wet-fastness is improved by after-treatment with a copper salt such as copper sulphate or, alternatively, spedally prepared mixtures of copper salts and cationic resin-fixing scents. Some of the dyes which have been specifically developed for this treatment are the Cuprofix, the Cuprophenyl, and the Coprantine colours, as well as many others not necessarily classified in distinctive groups. Examples of mixtures of copper salts and cationic products for after-treatment are Resofix C and Ct rantex B. 

There are direct dyes the wash-fastnesses of which are improved by after-treatment with potassium bichromate in the following maimer. Immerse for 20 to 30 minutes at 60° to 80°C (140° to 180°F) in a solution containing 1 to 3 per cent of potassium or sodium bichromate and 1 to 2 per cent of acetic acid (30 per cent). Fastness to light as well as washing is sometimes improved by substituting 1 to 2 per cent of bichromate, 1-2 per cent of copper sulphate, and 2-4 per cent of 30 per cent acetic acid. 

---