Dye Basics: Acid Dyes

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

An overview of acid dyes

1. History of acid dyes:

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

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

**0 years later, acid dyes with anthraquinone structure were invented, and their chromatograms became more and more complete;

Up to now, acid dyes have nearly hundreds of dye varieties, which are widely used in the dyeing of wool, silk, nylon and other fibers.

2. Characteristics of acid dyes:

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

It is characterized by good water solubility, bright color, complete chromatogram, simpler molecular structure than other dyes, lack of a long conjugated coherent system in the dye molecule, and low directivity of the dye.

3. The reaction mechanism of acid dyes:

Classification of acid dyes

1. Classification according to the molecular structure of the dye parent:

Azos (60%, broad spectrum) Anthraquinones (20%, mainly blue and green) Triarylmethanes (10%, purple, green) Heterocycles (10%, red, green) purple)
2. Classification by pH of dyeing:

Strong acid bath acid dye: pH 2.5-4 for dyeing, good light fastness, but poor wet fastness, bright color, good levelness; Weak acid bath acid dye: pH 4-5 for dyeing, molecular structure of dye The proportion of sulfonic acid groups in the medium is slightly lower, so the water solubility is slightly worse, the wet treatment fastness is better than that of strong acid bath dyes, and the levelness is slightly worse. Neutral bath acid dyes: The pH value of dyeing is 6-7, the proportion of sulfonic acid groups in the dye molecular structure is lower, the dye solubility is low, the levelness is poor, the color is not bright enough, but the wet fastness is high.

Terms related to acid dyes

1. Color fastness:

The color of textiles is resistant to various physical, chemical and biochemical effects in the dyeing and finishing process or in the process of use and consumption. 2. Standard depth:

A series of recognized depth standards that define medium depth as 1/1 standard depth. Colors of the same standard depth are psychologically equivalent, so that color fastness can be compared on the same basis. At present, it has developed to a total of six standard depths of 2/1, 1/1, 1/3, 1/6, 1/12 and 1/25. 3. Dyeing depth:

Expressed as the percentage of dye mass to fiber mass (ie O.M.F), dye concentration varies according to different shades. 4. Discoloration:

The change in shade, depth or brilliance of the color of a dyed fabric after a certain treatment, or the combined result of these changes. 5. Stain:

After a certain treatment, the color of the dyed fabric is transferred to the adjacent lining fabric, and the lining fabric is stained. 6. Gray sample card for assessing discoloration:

In the color fastness test, the standard gray sample card used to evaluate the degree of discoloration of the dyed object is generally called the discoloration sample card. 7. Gray sample card for evaluating staining:

In the color fastness test, the standard gray sample card used to evaluate the degree of staining of the dyed object to the lining fabric is generally called the staining sample card. 8. Color fastness rating:

According to the color fastness test, the degree of discoloration of dyed fabrics and the degree of staining to the backing fabrics, the color fastness properties of textiles are rated. In addition to the light fastness of eight (except AATCC standard light fastness), the rest are five-level system, the higher the level, the better the fastness. 9. Lining fabric:

In the color fastness test, in order to judge the degree of staining of the dyed fabric to other fibers, the undyed white fabric is treated with the dyed fabric.

Fourth, the common color fastness of acid dyes

1. Fastness to sunlight:

Also known as color fastness to light, the ability of the color of textiles to resist artificial light exposure, 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 C01C03E01, etc.; 3. Color fastness to rubbing:

The color resistance of textiles to 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 performed by imitating the concentration of chlorine in swimming pools. The degree of chlorine discoloration of the fabric, such as suitable for nylon swimwear, the detection method is ISO105 E03 (effective 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. The fabric dyed with acid dyes is generally tested for alkaline perspiration fastness.

Post time: Jul-21-2022