Traditional acid dyes refer to water-soluble dyes containing acidic groups in the dye structure, which are usually dyed under acidic conditions.
Overview of Acid Dyes
1.The history of acid dyes
In 1868, there appeared the earliest acid dyes, as triaromatic methane acid dyes, which had strong dyeing ability but poor fastness.
In 1877, there synthesized the first acid dye for dyeing wool, as red A. It basic structure was determined.
After 1890, acid dye with anthraquinone structure has been invented. And it has more and more complete chromatography.
So far, there are nearly hundreds of varieties of acid dyes, which are widely applied in dyeing wool, silk and nylon, etc.
2.The features of acid dyes
The acidic group in acid dyes is generally based on sulfonic acid group (-SO3H) and exists in the form of sodium sulfonic acid salt (-SO3NA) on the dye molecule. And also some is based on sodium carboxylate (-COONa).
Acid dyes have good water solubility, bright color shade, complete chromatography and more simple molecular structure than other dyes. Also for the lack of long conjugate coherent system in the dye molecules, the directness of acid dyes is low.
3.The reaction mechanism of acid dyes
Wool — NH3+ + -O3S — Dye → Wool — NH3+·-O3S — Dye
Silk — NH3+ + -O3S — Dye → Silk — NH3+·-O3S — Dye
Nylon — NH3+ + -O3S — Dye → Nylon — NH3+·-O3S — Dye
Classifications of Acid Dyes
1.Classification by molecular structure of dye parent
■ Azo dyes (Account for 60%. Broad spectrum)
■ Anthraquinone dyes (Account for 20%. Mainly are blue and green series)
■ Triaromatic methane dyes (Account for 10%. Purple and green series)
■ Heterocyclic dyes (Account for 10%. Red and purple series.)
2.Classification by pH of dyes
■ Acid dyes in strong acid bath: Dyeing pH value is 2.5~4. The light fastness is good, but wet handling fastness is poor. The color shade is bright and leveling property is good.
■ Acid dyes in weak acid bath: Dyeing pH value is 4~5. The rate of sulfonic acid group in the molecular structure of dye is low. So the water solubility is slightly poor. The wet handling fastness is better than acid dyes in strong acid bath, but leveling property is a little poorer.
■ Acid dyes in neutral acid bath: Dyeing pH value is 6~7. The rate of sulfonic acid group in the molecular structure of dye is lower. The solubility of dyes is low and the leveling property is poor. The color shade is not bright enough, but the wet handling fastness is high.
The Common Color Fastness of Acid Dyes
1.Light fastness
It is the resistance of color of textile to artificial light. Generally it is tested according to ISO105 B02.
2.Color fastness to washing
It is the resistance of color of textile to washing under different conditions, as ISO105 C01\C03\E01, etc.
3.Color fastness to rubbing
It is the resistance of color of textile to rubbing action. It can be divided into fastness to dry rubbing and fastness to wet rubbing.
4.Color fastness to chlorine water
It is also called colorfastness to chlorine pool water. Generally it is to mimic the concentration of chlorine in a swimming pool to test the resistance of fabric to chlorine discoloration. For example, the testing method ISO105 E03 (The effective chlorine content is 50ppm.) is suitable for nylon swimwear.
5.Color fastness to perspiration
It is the resistance of color of textile to human sweat. According to the acid and alkali of the sweat, it can be divided into color fastness to acid perspiration and color fastness to alkali perspiration. Fabrics dyed by acid dyes generally are tested for color fastness to alkali perspiration.
Post time: Aug-16-2022