Sulfur dyes are dyes that must be dissolved in alkali sulfide. They are mainly used for dyeing cotton fibers, but also for cotton/dimensional blended fabrics. The cost is low, and the dyed products are generally washable and light-resistant, but the color is not bright enough. Commonly used varieties are sulfur black, sulfur blue and so on.
Sulfur dyes are one of the most widely used dyes. According to reports, the world's output of sulphur dyes reaches hundreds of thousands of tons, and the most important variety is sulphur black dyes. The output of sulphur black accounts for 75%-85% of the total output of sulphur dyes. Because of its simple synthesis, low cost, good fastness, and non-carcinogenicity, it is favored by various printing and dyeing manufacturers. It is widely used in the dyeing of cotton and other cellulose fibers, with black and blue series being the most widely used.
There are two industrial production methods for sulfur dyes:
(1) Baking method, baking amines, phenols or nitro compounds of raw materials aromatic hydrocarbons and sulfur or sodium polysulfide at high temperature to prepare yellow, orange and brown sulfur dyes.
(2) Boiling method, heating and boiling the amines, phenols or nitro compounds of raw aromatic hydrocarbons and sodium polysulfide in water or organic solvents to prepare black, blue and green sulfur dyes.
Sulfur dyes are a type of sulfur-containing dyes. The molecules contain sulfur bonds composed of two or more sulfur atoms. When used, they are reduced to leuco body, dissolved in water, and dyed fibers. The dyeing characteristics of sulfur dyes vary depending on the type of dye. Sulfur dyes have high washing fastness and strong applicability. Although the rubbing fastness and vividness are not as good as reactive dyes, their color fastness and light fastness are better than reactive dyes. Sulfur dyes use less salt and consume less water. less. Sulfur dyes are organic compounds containing nitro and amino groups, most of which are formed by reacting with sulfur and sodium sulfide at high temperatures. Many sulfur dyes do not have a certain chemical formula. The dyeing principle of sulfur dyes is similar to that of vat dyes. They form a water-soluble leuco body dyeing fiber with affinity through chemical reduction reaction, and then bind tightly to the fiber through an oxidation process.
Sulfur dyes are insoluble in water. Sodium sulfide or other reducing agents are needed to reduce the dyes to soluble leucos. It has affinity for fibers and dyes the fibers, and then restores its insoluble state after oxidation and color development and is fixed on the fibers. So sulfur dye is also a kind of vat dye. Sulfur dyes can be used for dyeing cotton, linen, viscose and other fibers. Its manufacturing process is simple and low in cost. It can dye single colors and can also match colors. It has good light fastness and poor abrasion fastness. The color spectrum lacks red and purple, and the color is dark, suitable for dyeing deep colors.