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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.
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- Azo Group
- Nitro Group
- Antra-Quinine group
According to the Characteristics Acid dyes are three types
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- 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 |
