overview
Acid Dyes are a class of water-soluble dyes with acidic groups on the structure and stained in an acidic medium. Most acid dyes contain sodium sulfonate salts, which are soluble in water, bright in color and complete in color. It is mainly used for dyeing wool, silk and nylon, but can also be used for leather, paper, ink and other aspects. There is generally no coloring power for cellulose fibers.
The acid dye chromatography is complete, the color is bright, and the sun fastness and wet treatment fastness vary greatly with different dye varieties. Compared with direct dyes, acid dyes have a simple structure and lack a longer co-bond and homoplanar structure, so they lack directness to cellulose fibers and cannot be used for the dyeing of cellulose fibers. Different types of acid dyes, due to different molecular structures, so their dyeing performance is also different, the use of different dyeing methods are also different.
apply
It is mainly used for dyeing wool, silk and nylon, but can also be used for leather, paper, ink and other aspects. There is generally no coloring power for cellulose fibers.
classify
(1) Strongly acidic dyes
The earliest development of an acid dye, required to dye in a strong acid dyeing bath, its molecular structure is simple, low molecular weight, containing sulfonic acid groups or carboxyl groups, the affinity for wool is not large, can be evenly shifted on the wool, dyed uniformly, so it is also called acid leveling dye, but the color is not deep, the washing fastness is poor, and there is damage to the wool when dyeing, and the feel of the wool after dyeing is poor. Such as acid red G (i.e., C.I. acid red 1).
(2) Mildly acidic dyes
In strongly acidic dyes, weakly acidic dyes are generated by increasing molecular weight, introducing groups such as aryl sulfone groups, or introducing long carbon chains. The molecular structure is more complex, the affinity for wool is larger, the wool can be dyed in a weak acidic medium, there is no damage to the wool, the color and light are deeper, and the firmness is improved, but it is not leveled. Such as weak acidic brilliant blue RAW (i.e., C.I. acid blue 80).
(3) Acidic medium dyes
An acid dye that forms a metal complex on the fabric after treating with certain metal salts (such as chromium salts, copper salts, etc.) as mordant. The mordant dyeing procedure is more complicated, but you can get dyes with good performance such as sun resistance, washing resistance, friction fastness, etc., such as acidic medium black T (that is, C.I. medium black 11).
(4) Acid complex dye
It is made by the complexion of certain acidic dyes with metals such as chromium and cobalt. Soluble in water, its dyes are sun-resistant and have excellent light resistance. Its dye matrix is similar to the acidic medium dye, but when preparing the dye, the metal atom has been introduced into the azo dye molecule, and the ratio of the metal atom to the dye molecule is 1:1, so it is also called 1:1 metal complex dye. No more mordant treatment is required for staining. Such as acid complex yellow GR (i.e., C.I. acid yellow 99).
Selection Guide
Acid dyes are only suitable for positively charged fibers, such as dyeing polyamide fibers on an acidic bath, but cotton fibers can also be stained with acid dyes after cationization.
When dyeing with two dyes, the dye structure and the structural structure of cationic cotton dominate.
Increasing the number of cationic groups on the cationic cotton can lead to better wash fastness.
In any case, the overall color fastness of cationic cotton dyed on an acid dye is comparable to the 6 color fastness of nylon dyed on the same acid dye.
Precautions
1. Choose dyes carefully
Metal complex dyes containing copper, chromium, and nickel are dyes that are pre-made into metal complexes with dyes of a specific structure and metal complexes. There are 93 acid metal complex dyes. The European Union stipulates that when it is used for fiber dyeing, after dyeing each metal complex dye used, the amount of dyeing solution discharged into the wastewater for treatment should be less than 7%, that is, the coloring rate of metal complex dye should exceed 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 purity.
2. Dyeing water
The staining water hardness of acid dyes is preferably 100-150 mg/kg If the water hardness is high, 0. 5-2s/L chelating agent to improve water quality and ensure staining. However, chelating agents such as phosphates or surfactants will destroy the integration of the dye itself to varying degrees, affecting the vividness and color fastness of color. The test found that the chelating agent 88 provided by ORTHO Chemical Co., Ltd. had less effect on the integration of metal ions in the dye. Therefore, chelating agents must be screened during staining and should not be used blindly.
3. Material transformation method
Due to the inconsistent solubility of acidic complex dyes, they should be treated differently when melting materials. Generally, it is first mixed with cold water into a slurry, and then diluted with hot water or boiling water to dissolve it. Sometimes because the commercial dye is filled with fillers, so that it is difficult to dissolve, if necessary, it is necessary to cook while stirring until it is fully dissolved, and finally slowly injected into the cylinder by sieving to prevent the formation of color spots (spots).
4. Fabric pretreatment
Due to the presence of greases, slurries, impurities and natural colors in the fabric. Sometimes it is not only necessary to remove the slurry, but even to go through a half-drift before dyeing. Practice has proved that the pretreatment of pure textiles is easier, while the blended textiles are more difficult, but they must have good penetration (wetting) before dyeing, depending on the specific variety.
5. The role of acids
Whether sulfuric acid, formic acid (formic acid) or acetic acid, they are all dyeing agents for acidic and acidic complex dyes. Sometimes in order to further dye (suck up) the dye, it is often necessary to add the amount of acid in the middle and late stages of dyeing. However, when adding, it is necessary to dilute in advance, close the steam valve, stop heating, and slowly add people to prevent dyeing.
6. The role of yuanming powder
Sometimes acidic complex dyes need to be stained with a pH below 4, so YuanMing powder can be used as a slow dye. Conversely, if the PH value of the dyeing bath medium is above 4, it is not advisable to use Yuanming powder, because it will increase the tendency of dye aggregation, and nonionic surfactants, such as Pingping plus O and emulsifier OP, should be used as slow dyeing agents. Dosage should be based on color shades and dyeing equipment. Too much consumption will make the wool felt, the feel is rough, affecting the dye in the dyeing liquid to absorb, in the liquid flow machine will also increase the foam, and affect the normal operation of the circulation exchange system; the amount of less is not effective.
7. Neutralize
The alkali agent is mainly used for neutralization treatment after staining of strongly acidic media, with the purpose of returning the ionized amino group to a non-ionized amino group after dyeing, so that the fibers continue to further bind to the dye. The dosage can be determined according to the actual pH of the previously neutralized stain. Generally, the ammonia is lml/L, the soda ash is 2-3S/L, and it is treated for 20-30min at a temperature of 40-50 bar, and then it is fully washed.
8. Dyeing is terminated, the water washing temperature out of the tank should not be too low, generally should be controlled at 50-60 ° C, mainly to prevent the fabric from creases, especially wool and nylon once there is a fold, it will be difficult to repair.
9. Fixing agent treatment
For fabrics with high color fastness requirements, after dyeing, the acid complex dye can be dyed with a positive-loading fixing agent (powder) 2%-6% (owf), the bath ratio is 1:20-30, the temperature is 55 T, and the maceration is 30 min. Especially silk fabrics, through the fixing of color, the general color fastness can be improved by 0. 5-1． Level 5. Tests have shown that nylon fabrics do not require color fixing.
10. Acid metal complex dyes have heat sensitivity to varying degrees, especially red and blue. Therefore, the temperature should not be too high during the drying process to prevent discoloration from recovering.