How to choose and use acid dyes

Acid dyes are only suitable for positively charged fibers, such as polyamide fibers in an acid bath, but cotton fibers can also be dyed with acid dyes after cationization.

When dyeing with two dyes, the structure of the dye and the structure of the cationic cotton dominate.

Better wash fastness can be obtained by increasing the number of cationic groups on the cationic cotton.

In any case, the overall color fastness of cationic cotton dyed with acid dyes is comparable to the color fastness of nylon 6 dyed with the same acid dyes.

Precautions

1. Choose dyes carefully

Metal complex dyes containing copper, chromium and nickel are dyes prepared in advance of metal complexes with dyes with specific structures and metal complexing agents. There are 93 acid metal complex dyes. EU regulations: When it is used for dyeing related fibers, after each metal complex dye used is dyed, the amount of dye liquor discharged into wastewater for treatment should be less than 7%, that is, the coloring rate of metal complex dyes should be less than 7%. More than 93%; at the same time, copper or nickel should not exceed 75ms/ks fiber, and chromium should not exceed 50m ore ks fiber. Therefore, the selected dye requires a certain degree of purity.

2. Dyeing water

The hardness of the water used for dyeing acid dyes is preferably 100-150 mg/kg. If the water hardness is too high, 0.5-2s/L chelating agent can be added to improve the water quality and ensure dyeing. However, chelating agents such as phosphates or surfactants will destroy the integration of dyes to varying degrees, affecting the brightness and color fastness of color. The test found that the chelating agent 88 provided by ORTHO Chemical Co., Ltd. had little effect on the integration of metal ions in the dye. Therefore, chelating agents must be screened during dyeing, and should not be used blindly.

3. Chemical method

Due to the inconsistent solubility of acid complex dyes, they should be treated differently when compounding. Generally, it is made into a slurry with cold water first, and then diluted with hot water or boiling water to dissolve it. Sometimes it is difficult to dissolve due to the addition of fillers in commercial dyes. If necessary, it is necessary to cook and stir until fully dissolved. Finally, it is slowly injected into the tank after sieving to prevent the formation of color spots (spots).

4. Fabric pretreatment

Due to the presence of grease, pulp, impurities and natural pigments in the fabric. Sometimes it is necessary not only to remove the pulp, but even to go through half-bleaching before dyeing. Practice has proved that the pretreatment of pure textiles is easier, while blended textiles are difficult, but must have good penetration (wetting) before dyeing, depending on the specific variety.

5. The role of acid

Regardless of sulfuric acid, formic acid (formic acid) and acetic acid, they are all dye accelerators for acid and acid complex dyes. Sometimes in order to further dye the dye (exhaustion), it is often necessary to add the amount of acid in the middle and later stages of dyeing. However, when adding, it needs to be diluted in advance, close the steam valve, stop heating, and add people slowly to prevent dyeing.

6. The role of Yuanmingfen

Sometimes acid complex dyes need to be dyed with a pH value below 4, so Yuanming powder can be used as a retarder. On the contrary, if the PH value of the dye bath medium is above 4, it is not suitable to use Yuanming powder, because it will increase the tendency of dyes to aggregate, and non-ionic surfactants, such as peregrine and emulsifier OP, should be used as retarders. . The dosage should be determined according to the color depth and dyeing equipment. Too much dosage will make the wool felt and feel rough, which will affect the dye absorption in the dye liquor. On the liquid machine, the foam will increase, which will affect the normal operation of the circulation exchange system; if the dosage is too small, the effect will not be good.

7. Neutralize

Alkaline agent is mainly used for neutralization treatment after dyeing with strong acid medium, the purpose is to restore the ionized amino group to non-ionized amino group after dyeing, so that the fiber can be further combined with the dye. The amount can be determined according to the actual pH value of the dye before neutralization. Generally, ammonia water is 1mL/L, soda ash is 2-3S/L, and it is treated at a temperature of 40-50 bar for 20-30min. After neutralization, it is fully washed.

8. After the dyeing is terminated, the washing temperature should not be too low. Generally, it should be controlled at 50-60 ℃, mainly to prevent the fabric from wrinkling, especially wool and nylon, once wrinkled, it will be difficult to repair.

9. Fixing agent treatment

For fabrics with high color fastness requirements, after dyeing with acid complex dyes, positive fixative (powder) 2%-6% (owf) can be used, bath ratio 1:20-30, temperature 55 T, immersion 30 min. Especially for silk fabrics, the general color fastness can be improved by 0.5-1.5 grades by fixing the color. Experiments show that nylon fabrics do not require color-fixing treatment.

10. Acid metal complex dyes have different degrees of heat sensitivity, especially red and blue. Therefore, the temperature should not be too high during the drying process, in order to prevent the color change from being restored.