Acid dyes are Na- salt of sulphonic acid. But there are a few containing carboxyl groups. Acid dyes are applied in acid medium. That’s why these dyes are called Acid Dye.
Acid dye have a direct affinity towards protein fiber and the main class are used in Wool Dyeing. Polyamide fibers have an affinity for acid dye.
Properties of Acid Dye
- Acid dye contains Na-salt of sulphonic Acid
- Dyeing is performed in acidic medium.
- Natural protein fiber (Wool, Silk) and Nylon can be dyed easily.
- No affinity to cotton and cellulosic fiber
- Light fastness is good.
- Wash fastness is poor.
- Soluble in water and forms colloidal solution.
Classification of Acid Dye
According to the chemical construction Acid Dye can be classified into three groups.
- Azo Group
- Nitro Group
- Antra-Quinine group
According to the Characteristics Acid dyes are three types
- Strong Acid Dye
- Weak Acid dye
- Neutral Acid Dye.
Comparative Study on Strong, Weak and Neutral Acid Dye
|Sl||Criteria||Strong Acid Dye||Weak Acid Dye||Neutral Acid Dye|
|1||Fastness to Wet||Poor||Good||Very Good|
|2||Dyeing Method||Sulfuric Acid||Acetic Acid||Ammonium Acetate|
|3||PH of Dyeing||2 to 4||4-6||Neutral|
|4||Leveling condition||Good||Moderate poor||Very Poor|
|5||Dye Characteristics||Low Molecular weight and high solubility||High molecular weight and low solubility||High molecular weight and low solubility|
|6||Affinity of Anion||Low||High||Very Low|