Ritu Dye Chem

DESCRIPTION:

Acid dyes are highly water-soluble and have better lightfastness than basic dyes. The textile acid dyes are effective for protein fibers such as silk, wool, nylon, and modified acrylics. They contain sulphonic acid groups, which are usually present as sodium sulphonate salts. These increase solubility in water and give the dye molecules a negative charge. In an acidic solution, the -NH2 functionalities of the fibres are protonated to give a positive charge: -NH3+. This charge interacts with the negative dye charge, allowing the formation of ionic interactions. As well as this, Van-der-Waals bonds, dipolar bonds and hydrogen bonds are formed between dye and fibre. As a group, acid dyes can be divided into two sub-groups: acid-leveling or acid-milling. Chemical structure of acid dyes These dyes are normally very complex in structure but have large aromatic molecules, having a sulphonyl or amino group which makes them soluble in water. Most of the acid dyes belong to following three main structural molecules 1. Anthraquinon type 2. Azo dye type 3. Triphenylmethane type. Different types of acid dyes 1. Neutral acid dyes :- These are supra milling or fast acid dyes, having medium to good wet fastness properties, some of the dyes have poor lightfastness in pale shades. many of the dyes are used as self shades only. These are applied to the fiber in a weakly acid or neutral pH. 2. Weak acid dyes These dyes belong to the milling class of dyes. These dyes have good fastness properties but lightfastness is moderate to poor. 3. Strong acid dyes These dyes are applied in a strongly acidic medium and also called leveling dyes, however there wet fastness properties are a limitation. These dyes are very good to produce the combination shades. Classification according to dyeing characteristics The original classification of this type, based on their behaviour in wool dyeing, is as follows: 1. Level dyeing or equalising acid dyes; 2. Fast acid dyes; 3. Milling acid dyes; 4. Super-milling acid dyes. Properties of acid dyes 1. These dyes are anionic in nature. 2. These dyes are suitable for wool, silk, polyamide and modified acrylics. 3. These are applied from a strongly acidic to neutral pH bath. 4. These dyes have no affinity for cotton cellulose’s, hence not suitable for cellulosics. 5. These dyes combine with the fiber by hydrogen bonds, vander waals forces or through ionic linkages.