What is acid dye and what is the function of acid dye?

The biggest performance defect of acid dye dip dyeing nylon is its dependence on the pH value of the dyeing bath, that is, its dyeing rate and amount will change significantly with the fluctuation of the pH value of the dyeing bath. According to inspections, when acid dyes are commonly used to dye nylon, the optimal pH range of the dye bath is 4.5-5.5. Because in this range, the dye yield is the highest and the color stability is the best. When the pH of the dyeing bath is greater than 6, the dyeing rate becomes significantly slower and the color depth becomes significantly shallower.

When the pH of the dyeing bath is<3, the dyeing rate will increase rapidly, and the color depth will increase rapidly. This is because the imino group (–NH–) in the amide group on the long molecular chain of nylon also absorbs H+ at this time. Ionization (–N+H2–), resulting in super-equivalent adsorption of dyes. This is not only easy to cause uneven color absorption (color flowers), but also severely decrease the fastness to washing and soaping.

The problem here is that the pH of the dye bath is affected by the content of the pH regulator (acid agent), the accuracy of the measurement, and the stability of the bath ratio. It is also affected by the amount of acid-base substances contained in the dyeing water, semi-finished products to be dyed, and dye auxiliaries used. In other words, the pH value of the actual dyeing bath is prone to fluctuations. The fluctuation of the pH value of the dyeing bath can easily affect the stability of the color, that is, it is easy to produce the color difference of the size and the color difference between the tank and the tank.

Points for attention when applying acid metal complex dyes:

1. Choose dyes carefully

Metal complex dyes containing copper, chromium and nickel are dyes that are pre-made into metal complexes with dyes with specific structures and metal complexing agents. There are 93 acid metal complex dyes.

2. Dyeing water

The best water hardness for acid dyeing is 100-150 mg/kg. If the water hardness is too high, 0.5-2s/L chelating agent can be added to improve water quality and ensure dyeing. However, chelating agents such as phosphates or surfactants will destroy the integration of the dye itself to varying degrees and affect the vividness and fastness of colors.

3. Chemical method

Because the solubility of acid complex dyes is inconsistent, it is necessary to treat differently when compounding. Generally, it is first adjusted into a slurry with cold water, and then diluted with hot or boiling water to dissolve it.

4. The role of acid

Regardless of sulfuric acid, formic acid (formic acid) and acetic acid, they are all accelerants for acid and acid complex dyes. Sometimes in order to further dye up (exhaust) the dye, the amount of acid is often added in the middle and later stages of dyeing.

5. Fabric pretreatment

Because there are grease, slurry, impurities and natural pigments in the fabric. Sometimes it is not only necessary to remove the slurry, but even after half-bleaching before dyeing.