Acid dye is a water-soluble dye with acid group in structure, which is dyed in acid medium. Most acid dyes contain sodium sulfonate, which is soluble in water, bright in color and complete in chromatography. It is mainly used for dyeing wool, silk and nylon, and also for leather, paper and ink. Generally, there is no coloring force on cellulose fiber.
Acid dyes have complete chromatography and bright color, and the fastness of different dyes to sun and wet treatment is very different. Compared with direct dyes, acid dyes have simple structure and lack of long coplanarity and coplanarity structure, so they are lack of direct properties and cannot be used in dyeing cellulose fibers. Different types of acid dyes have different dyeing properties and different dyeing methods due to different molecular structure.
apply.
It is mainly used for dyeing wool, silk and nylon, and also for leather, paper and ink. Generally, there is no coloring force on cellulose fiber.
Classification.
(1) Strong acid dye.
The first acid dyes developed need to be dyed in strong acid dyeing bath. It has simple molecular structure, low molecular weight, and contains sulfonic or carboxyl groups, and has a small affinity to wool. It can move evenly on wool and dye evenly, so it is also called acid leveler. But the color is not deep, the fastness of washing is poor, and it is harmful to wool when dyeing, and the hand feeling of the dyed wool is poor. For example, acid red g (i.e. C.I. Acid Red 1).
(2) Weak acid dye.
Weak acid dyes can be produced by increasing molecular weight, introducing aromatic sulfone group or long carbon chain in strong acid dyes. The molecular structure is complex and has strong affinity to wool. It can dye wool in weak acid medium, without damage to wool, deep color and better fastness, but uneven dyeing. For example, the light blue raw with weak acid (i.e. C.I. Acid Blue 80).
(3) Acid media dye.
Some metal salts (such as chromium salt, copper salt, etc.) It is used as mordant to form acid dye with metal complex on fabric. Mordant dyeing procedure is complex, but dyes with better performance such as sun fastness, washing fastness and friction fastness can be obtained, such as acid mordant black T (i.e. C.I. mordant black 11).
(4) Acid complex dye.
It is made up of some acid dyes that are complexed with chromium, cobalt and other metals. It is easy to dissolve in water, and its dyeing products have excellent sun and light resistance. The dye matrix is similar to that of acid mordant dye, but when preparing dyes, metal atoms have been introduced into azo dye molecules. The ratio of metal atoms to dye molecules is 1:1, so it is also called 1:1 metal complex dye. Dyeing does not require mordant treatment. For example, the acid complex yellow gr (i.e. C.I. Acid Yellow 99).
Select the guide.
Acid dyes are only suitable for fibers with positive charge, such as polyamide fibers dyed in acid bath, but cotton fibers can also be dyed with acid dyes after cation.
When dyeing with two dyes, dye structure and cationic cotton structure play a leading role.
By increasing the number of cation groups on cationic cotton, the better washing fastness can be obtained.
However, the overall color fastness of cationic cotton dyed with acid dye is equivalent to that of nylon 6 with the same acid dye.
matters needing attention.
1. carefully select dye.
The metal complex dyes containing copper, chromium and nickel are the dyes prepared by the metal complex with the dye of specific structure and metal complexing agent. There are 93 kinds of acid metal complex dyes. EU stipulates that when used for dyeing related fibers, the dye solution discharged into wastewater treatment shall be less than 7% after each metal complex dye is dyed, that is, the dye rate of metal complex dyes shall exceed 93%; Meanwhile, copper or nickel shall not exceed 75ms/ks fiber, and chromium shall not exceed 50m ore KS fiber. So the dye you choose needs a certain purity.
2. dyed water.
The hardness of dyeing water for acid dyes shall be 100-150 mg / kg. If the hardness of water is high, 0.5-2s/l chelating agent can be added to improve the water quality and ensure dyeing. However, chelating agents such as phosphate or surfactant will destroy the integrity of dyes to varying degrees, affecting brightness and color fastness. It was found that chelating agent 88 provided by ortho Chemical Co., Ltd. had little effect on the integration of metal ions in dyes. Therefore, chelating agents must be screened during dyeing, and can not be used blindly.
3. chemical methods.
Because of the different solubility of acid complex dyes, it is necessary to treat them differently. Generally, it is first to be slurry with cold water, and then dilute and dissolve with hot water or boiling water. Sometimes, because commercial dyes are filled with fillers, it is difficult to dissolve. If necessary, boil and stir to full dissolution. Finally, filter and slowly inject it into the cylinder to prevent the formation of color spots (spots).
4. fabric pretreatment.
Because of the existence of grease, slurry, impurities and natural pigment in the fabric. Sometimes, not only the pulp is removed, but also semi bleached to dye. The practice shows that the pretreatment of pure textiles is easy and the pretreatment of blended textiles is difficult. But it must have good permeability (wettability) before dyeing, which depends on the specific varieties.
5. the effect of acid.
Sulfuric acid, formic acid and acetic acid are dye promoters of acid and acid complex dyes. Sometimes, in order to further dye (exhaust), acid is often added in the middle and later period of dyeing. But dilute in advance, close the steam valve, stop heating, add people slowly, and prevent flower dyeing.
6. the function of sodium sulfate.
Sometimes acid complex dyes need to be dyed at pH less than 4, so sodium sulfate can be used as retarder. On the contrary, if the pH value of the dye bath medium is above 4, sodium sulfate should not be used, because it will increase the aggregation tendency of dyes. The non-ionic surfactant such as adding O and emulsifier OP should be used as the dye retarder. The dosage shall be determined according to the color depth and dyeing equipment. The excessive use of wool will make woollen felt and handle rough, affect the exhaustion of dye in dye solution, and also affect the normal operation of circulating exchange system due to the increase of foam on the liquid flow machine. The effect is not good if the dosage is low.
7. neutralization.
Alkali agent is mainly used for neutralization treatment after dyeing in strong acid medium, so as to reduce the ionized amino group to non ionized amino group, so that the fiber can continue to combine with dye. The dosage can be determined according to the actual pH value of the dye before neutralization. Generally, the ammonia water is lml/l, and the soda ash is 2-3s/l. It is treated at 40-50bar for 20-30min. Wash with water after neutralization.
8. when dyeing is terminated, the washing temperature should not be too low, but it should be controlled at 50-60 ℃ in general, mainly to prevent the fabric from wrinkling, especially when wool and nylon wrinkle, it is difficult to repair.
9. fixing agent treatment.
For fabrics with high color fastness, the cationic fixing agent (powder) 2% - 6% (OWF), bath ratio 1:20-30, temperature 55T, immersion for 30 minutes can be used after dyeing with acid composite dyes. Especially for silk fabrics, the general color fastness can be improved by 0.5-1.5 by fixing color. The experiment shows that the nylon fabric does not need fixing color treatment.
10. the acid metal complex dyes have different degrees of thermal sensitivity, especially red and blue. Therefore, in the drying process, the temperature should not be too high, so as to avoid discoloration and recovery.
