SULPHUR DYES

Sulphur dyes are one of the most widely used dyes for cotton. The output of sulphur dyes in the world reaches hundreds of thousands of tons, and the most important variety is SULPHUR BLACK. The color blackness of sulphur black dyed cotton textiles is special and irreplaceable, especially on mercerized cotton textiles. Practice has proved that if the whole dyeing process of direct black, reactive black and even vat black, which are commonly used at present, is not in place, the color fastness and color blackness are also difficult to reach the level of sulphur black. Sulphur black is simple in synthesis, low in cost, good in fastness and non carcinogenic. It is favored by various printing and dyeing manufacturers and is widely used in the dyeing of cotton and other cellulose fibers.

In 1893, R Vikal fused p-aminophenol with sodium sulfide and sulfur to make sulphur black. He also found that a variety of black dyes can be made by fusing some benzene and naphthalene derivatives with sulfur and sodium sulfide. Since then, people have developed blue, red and green sulphur dyes on this basis. At the same time, the preparation method and dyeing process have been greatly improved. The emergence of water-soluble sulphur dyes, liquid sulphur dyes and environmental friendly sulphur dyes has made sulphur dyes flourish.

There are two industrial production methods for sulphur dyes.

1. Baking method.The amine, phenol or nitro compounds of raw aromatic hydrocarbons are baked with sulfur or sodium polysulfide at high temperature to prepare yellow, orange and brown sulfide dyes.
2. Boiling method: the amine, phenol or nitro compound of raw aromatic hydrocarbon and sodium polysulfide are heated and boiled in water or organic solvent to prepare black, blue and green sulfide dyes.

Classification of sulphur dyes.

1. Powder sulphur dye.Generally, it needs sodium sulfide to boil and apply after dissolution. This kind of dye is insoluble in water. The dye can be reduced to cryptochrome by alkaline reducing agent and dissolved in water. The sodium salt of cryptochrome can be absorbed by the fiber.
2. Water soluble sulphur dye.These dyes are characterized by water-soluble groups in their molecular structure, good solubility and good levelness. Ordinary sulphur dyes are reacted with sodium sulfide or sodium bisulfite to form thiosulfate of the dye, which has a solubility of 150g / L at 20 ℃ and is used for continuous dyeing. The water-soluble sulphur dye dissolves quickly at room temperature, there is no insoluble matter, and the saturated dissolved amount is sufficient to meet all the dissolution requirements of the dye dyeing amount. Water soluble sulphur dyes have excellent high temperature resistance. However, there is no reducing agent in the dye and it has no affinity for the fiber. Alkali sulfide needs to be added during dyeing, and it is converted into a state with affinity for cellulose fiber through nucleophilic reaction and reduction reaction. Suspension pad dyeing is generally applied to textiles.
3. Liquid sulphur dye.Containing a certain amount of sodium sulfide reductant, the dye is pre reduced to water-soluble leuco. Common sulfide dyes are reduced to water-soluble leucosomes with reducing agents, and excess reducing agents are added as antioxidants. The liquid dyes made by adding penetrants, inorganic salts and soft water agents are also called pre reducing dyes. When used, it can be directly applied after being diluted with water. This kind of dye contains sulfur, such as sodium sulfide, but also does not contain or contains a small amount of sulfur. There is no sulfur-containing wastewater during dyeing.
4. Environmental friendly sulphur dye.In the production process, it is refined into dyeing cryptochrome, but the sulfur content and polysulfide content are far lower than that of ordinary sulfide dyes. This dye has high purity, stable reducibility and good permeability. At the same time, glucose and insurance powder are used as binary reducing agents in the dyeing bath, which can not only reduce sulfide dyes, but also play an environmental role.
5. Sulphur vat dye.It is often made into powder, fine, ultra-fine powder or liquid dye. It is suitable for the dyeing of polyester cotton blended fabrics with disperse dyes in the same bath. It can be used for the reduction of caustic soda, insurance powder (or sulfur dioxide urea) instead of the reduction and dissolution of sodium sulfide.
6. Disperse sulphur dye.Disperse sulphur dyes are made on the basis of sulphur dyes and sulphur vat dyes according to the commercial processing method of disperse dyes. They are mainly used for pad dyeing of polyester viscose or polyester cotton blended fabrics with disperse dyes in the same bath.