Acid Dyes Basics

Traditional acid dyes refer to water-soluble dyes containing acid groups in the dye structure, and are usually dyed under acidic conditions.

I. Overview of acid dyes

1. History of acid dyes:

In 1868, the earliest acid dye triarylmethane acid dye appeared, which had strong dyeing ability but poor fastness;

In 1877, Acid Red A, the first acid dye used for wool dyeing, was synthesized, and its basic structure was determined;

After 1890, acid dyes with anthraquinone structure were invented, and their chromatograms became more and more complete;

So far, there are nearly hundreds of acid dyes, which are widely used in the dyeing of wool, silk, nylon and other fibers.

2. Characteristics of acid dyes:

The acid groups in acid dyes are generally sulfonic acid groups (-SO3H), which exist on the dye molecule in the form of sulfonic acid sodium salt (-SO3Na), and some dyes are acidic with carboxylic acid sodium salt (-COONa). group.

It is characterized by good water solubility, bright color, complete chromatogram, simpler molecular structure than other dyes, lack of longer conjugated coherent systems in dye molecules, and low directness of dyes.

3. The reaction mechanism of acid dyes:

II. Classification of acid dyes

1. Classified according to the molecular structure of the dye matrix:

Azos (60%, broad spectrum)

Anthraquinones (accounting for 20%, mainly blue and green)

Triaryl methanes (accounting for 10%, purple and green)

Heterocyclics (accounting for 10%, red and purple)

2. Classification according to the pH of dyeing:

Strong acid bath acid dye: dyeing pH value 2.5-4, good light fastness, but poor wet fastness, bright color, good level dyeing;

Weak acid bath acid dye: the dyeing pH value is 4-5, the proportion of sulfonic acid groups in the molecular structure of the dye is slightly lower, so the water solubility is slightly worse, the wet treatment fastness is better than that of strong acid bath dye, and the level dyeing property is slightly worse.

Neutral bath acid dye: the dyeing pH value is 6-7, the proportion of sulfonic acid groups in the molecular structure of the dye is lower, the dye solubility is low, the level dyeing property is poor, the color is not bright enough, but the wet fastness is high.

III. Terms related to acid dyes

1. Color fastness:

The color of textiles is related to its resistance to various physical, chemical and biochemical effects in the dyeing and finishing process or in the process of use and consumption.

2. Standard depth:

Recognized depth standard series, which defines medium depth as 1/1 standard depth. Colors of the same standard depth are equal in psychological perception, so that color fastness can be compared on the same basis. At present, it has developed to 2/1, 1/1, 1/3, 1/6, 1/12 and 1/25, a total of six standard depths.

3. Dyeing depth:

It is expressed as the percentage of dye mass to fiber mass (ie O.M.F), and the dye concentration varies according to different shades.

4. Discoloration:

After a certain treatment, the color of the dyed fabric changes in shade, depth or brilliance, or the comprehensive result of these changes.

5. Staining:

After a certain treatment, the color of the dyed fabric is transferred to the adjacent lining fabric, which will stain the lining fabric.

6. Gray sample card for evaluating discoloration:

In the color fastness test, the standard gray sample card used to evaluate the degree of discoloration of the dyed matter is generally called the color change sample card.

7. Gray sample card for assessing staining:

In the color fastness test, the standard gray sample card used to evaluate the staining degree of the dyed matter on the adjacent fabric is generally called the staining sample card.

8. Color fastness rating:

The color fastness properties of textiles are rated on the basis of color fastness tests, the degree of discoloration of dyed fabrics and the degree of staining of adjacent fabrics. Except that the light fastness is grade 8 (except AATCC standard light fastness), the rest are five grades, the higher the grade, the better the fastness.

9. Lining fabric:

In the color fastness test, in order to judge the degree of staining of dyed fabrics on other fibers, undyed white fabrics are treated together with dyed fabrics.

IV. Common color fastness of acid dyes

1. Sunlight fastness:

Also known as color fastness to light, the color of textiles is resistant to artificial light, and the general inspection standard is ISO105 B02;

2. Color fastness to washing (water immersion):

The resistance of the color of textiles to washing under different conditions, such as ISO105 C01\C03\E01, etc.;

3. Color fastness to rubbing:

The color resistance of textiles against rubbing can be divided into dry and wet rubbing fastness.

4. Color fastness to chlorine water:

Also known as chlorine pool fastness, it is generally tested by imitating the concentration of chlorine in swimming pools to test the degree of chlorine discoloration resistance of fabrics. For example, it is suitable for nylon swimwear. The test method is ISO105 E03 (available chlorine content 50ppm);

5. Color fastness to perspiration:

The resistance of the color of textiles to human sweat can be divided into acid and alkali perspiration fastness according to the acidity and alkalinity of the test sweat. Fabrics dyed with acid dyes generally need to be tested for alkaline perspiration fastness.

Summary:

Acid dyes are mainly used on wool and silk. Because the wool silk amino group is positively charged under acidic conditions, it combines with the sulfocarboxylic acid group of the acid dye through electrostatic attraction.

The more sulfonic acid groups of the dye, the stronger the acidic conditions required, the stronger the hydrolysis of the dye, and therefore the worse the washing fastness.