Not all colored organic compounds can be used as dyes. As a dye generally, four conditions must be met:
1. Color. That is, a certain concentration of color that must be dyed (with a certain dyeing promotion rate);
Second, the ability to color. That is, it has a certain binding force with the textile material, that is, affinity or directness;
3. Solubility. That is, it can be dissolved in water directly or by chemical action;
Fourth, color fastness. That is, the color dyed on the textile material has a certain durability and is not easy to fade or change color.
Some colored substances are insoluble in water, have no affinity for fibers, and cannot enter the interior of fibers, but can be mechanically fixed on the fabric by the action of adhesives. This substance is called pigment. Pigments and dispersants, hygroscopic agents, water, etc. are ground to obtain coatings, and coatings can also be used for dyeing, but they are not widely used in printing.
Classification of Dyes
1. Classification according to the chemical structure of dyes or their characteristic groups, called chemical classification
Divided into: azo dyes, anthraquinone dyes, arylmethane dyes, indigo dyes, sulfur dyes, phthalocyanine dyes, nitro and nitroso dyes, in addition to other structural types of dyes, such as methine and polymethine dyes , stilbene dyes and various heterocyclic dyes.
2. Classification according to the properties and application methods of dyes, called application classification
Divided into: direct dyes, acid dyes, cationic dyes, reactive dyes, insoluble azo dyes, disperse dyes, vat dyes, sulfur dyes, polycondensation dyes, optical brighteners, in addition, there are oxidation dyes for textiles (such as nigrosine) ), solvent dyes, polypropylene dyes, and food colorings for food.
Dyeing objects and methods
Direct dyes are a class of water-soluble anionic dyes. Most of the dye molecules contain sulfonic acid groups, and some have carboxyl groups. The dye molecules and cellulose molecules are combined by van der Waals forces and hydrogen bonds.
Direct dyes are mainly used for the dyeing of cellulose fibers, but also for the dyeing of silk, paper and leather. During dyeing, the dye is directly dyed on the fiber in the dye solution, and is adsorbed on the fiber through van der Waals force and hydrogen bonding.
Acid dyes are a class of water-soluble anionic dyes. The dye molecules contain acidic groups such as sulfonic acid groups and carboxyl groups, which usually exist in the form of sodium salts. In the acid dye bath, they can be combined with the amino groups in the protein fiber molecules by ionic bonds, so they are called acid dyes.
Often used for silk, wool and polyamide fibers and leather dyeing. Acid dyes dye fibers by their own affinity and bind to fibers with ionic bonds; acid mordant dyes, whose dyeing conditions are similar to those of acid dyes, but require the action of certain metal salts to form chelates on fibers to obtain good results Excellent washing resistance; acid mordant dyes, some acid dyes have chelated metal ions in their molecules, which have a small hydrolysis tendency and good color fastness.
Cationic dyes are soluble in water and are in a cationic state. The early dye molecules have basic groups such as amino groups, which often exist in the form of acid salts.
It is mainly used for the dyeing of polyacrylonitrile fibers. When dyeing, it can be combined with the carboxyl anions in the protein fiber molecules such as silk in the form of salt bonds.
Reactive dyes are also called reactive dyes. This type of dye contains reactive groups in its molecular structure, which can be covalently bonded to the hydroxyl and amino groups in the fiber molecule during dyeing to firmly dye the fiber.
Reactive dyes are mainly used in the dyeing and printing of cellulose fiber textiles, and can also be used in the dyeing of wool and nylon fibers. The dye dyes the fiber by its own affinity, and then binds firmly to the fiber through covalent bonds under the action of the alkali agent.
Insoluble azo dyes
In the dyeing process, this type of dye is dyed by the direct reaction of the diazo component (chromophore) and the coupling component (chromophore) on the fiber to generate an insoluble lake. This dye is called an insoluble azo dye.
Such dyes are mainly used for dyeing and printing of cellulose fibers. The chromophore is first diazotized, and then dyed to the chromophore-based fiber fabric by affinity, and then coupled to form an insoluble lake, which is firmly stored on the fabric.
Disperse dyes are a kind of non-ionic dyes with simple structure and extremely low water solubility, which mainly exist as dispersions of tiny particles in the dye bath. The chemical structure of disperse dyes is mainly azo and anthraquinone, and there are also heterocyclic disperse dyes.
Disperse dyes are mainly used in the dyeing and printing of polyester fibers, but also in the dyeing of acetate fibers and polyamide fibers. When dyeing, the dye must be evenly dispersed in the dye liquor with the help of a dispersant, and then various types of synthetic fibers are dyed.
Most of vat dyes belong to polycyclic aromatic compounds, and their molecular structures do not contain water-soluble groups such as sulfonic acid groups and carboxylic acid groups. Their basic feature is that in the conjugated double bond system of the molecule, there are two or more carbonyl groups, so under the action of hydrosulfite, the carbonyl group can be reduced to a hydroxyl group and become soluble in alkaline aqueous solution. Chromosomal sodium salt.
Vat dyes are mainly used for dyeing cellulose fibers. When dyeing, they are reduced to water-soluble leuco sodium salts in an alkaline solution containing a reducing agent (such as Na2S2O4, sodium dithionite, commonly known as hydrosulfite), and then dyed fibers, and then re-oxidized to become insoluble dyes. anchored to the fibers.
Sulfur dyes are a class of water-insoluble dyes, which are generally prepared by mixing and heating aromatic amines or phenolic compounds with sulfur or sodium polysulfide. This process is called vulcanization.
Sulfur dyes are mainly used for dyeing cellulose fibers. During dyeing, they are reduced to a soluble state in an alkali sulfide solution, and after dyeing the fiber, they are oxidized and fixed on the fiber in an insoluble state.
Polycondensation dyes are a kind of dyes that can be covalently bonded between the molecules of the dye itself or with compounds other than fibers during or after the dyeing process, thereby increasing the molecular weight. Polycondensation dye molecules contain thiosulfuric acid groups (-SSO3Na), which can remove sulfite radicals from thiosulfuric acid groups under the action of sodium sulfide, sodium polysulfide, etc., and form -S-S between dye molecules - bond, which binds two or more dye molecules into an insoluble state and is fixed on the fiber.
Polycondensation dyes are soluble in water, they can remove water-soluble groups on the fibers and undergo intermolecular polycondensation reaction, becoming insoluble dyes with relatively large molecular weights and fixed on the fibers. At present, such dyes are mainly used in the dyeing and printing of cellulose fibers, and can also be used in the dyeing of vinylon.
Fluorescent whitening agent
Fluorescent whitening agents can be regarded as a class of colorless dyes. After they are dyed on substrates such as fibers and paper, they can absorb ultraviolet rays and emit blue light, thereby offsetting the yellow feeling caused by excessive yellow light reflection on the fabric. Visually produce a white, dazzling effect
Different types of optical brighteners can be used to brighten various fibers. They are processed directly onto the fabric, anchored to the fibers by their own affinity or cross-linking agents.
nomenclature of dyes
There are many kinds of dyes. In order to meet the requirements of production and application, the color and application performance of the correct reaction dye must be given a special name for the dye.
Now, according to the "Draft Nomenclature of Dyestuff Products" piloted by the former Ministry of Chemical Industry of my country since January 1965, the nomenclature of my country's dyestuffs - three-segment nomenclature is introduced as follows. The name of dyestuff consists of three parts, namely "crown name" , "color name" and "suffix".
The crown part - indicates the application category of the dye. Internationally, the trade name or application category of the dye indicates the crown name of the dye. In China, the application classification or nature of the dye is used as the crown name.
Color part - indicates the color of the dye on the fiber, which is basically the same at home and abroad.
Suffix - that is, to use certain symbols and numbers to describe shades, shapes, special properties and other dyeing properties.