Various dyes classification, dyeing mechanism introduction 7 friends together to add!
Introduction
Dyes are colored substances that dye cotton, linen, silk, wool, viscose, nylon, vinyls and many other textiles through their own or certain chemical reactions. According to the nature and application method, dyestuff can be divided into direct dyes, reactive dyes, sulfur dyes, disperse dyes, acid dyes, basic dyes, reduction dyes, phthalocyanine dyes and many other types. Today, Seven introduces the main classification and characteristics of various dyestuffs, hoping to bring some help to you.
Direct dyes
Definition
Direct dyes are dyes that are directly soluble in water and have a high degree of directness to cellulose fibers and do not require chemical methods to color fibers and other materials. Direct dyes can color protein fibers (such as wool and silk) in weakly acidic or neutral solutions and are also used in cotton, hemp, human silk and human cotton dyeing. Complete color spectrum, low price, easy to operate. The disadvantage is that the washing and sun fastness are not ideal.
Dyeing mechanism
Direct dyes have water-soluble groups such as sulfonic acid group (-SO H) or carboxyl group (-COOH) molecular structure arranged in a linear pattern. The aromatic ring structure is in the same plane, so direct dyes have a greater affinity for cellulose fibers and can be dyed directly in neutral media by dissolving the dyes in dry water.
The dyes are adsorbed to the surface by the fibers in solution and then continuously diffuse to the amorphous regions of the fibers, forming hydrogen bonds and van der Waals force bonds with the fiber macromolecules. Its derivatives are direct sunlight resistant dyes and direct copper salt dyes.
Commonly used pigments
Reactive dyes
Definition
Reactive dyes are also called reactive dyes. Dyes that contain chemically active groups in their molecules and can react with cotton, wool and other fibers in aqueous solution to form a common bond.
Dyeing mechanism
Reactive dyes, also known as reactive dyes. They are dyes that react chemically with fibers during dyeing. The molecules of these dyes contain groups that react chemically with fibers, and the dyes react with fibers during dyeing, forming covalent bonds between them and making them whole, which improves the fastness to washing and rubbing. Reactive dyes are a new type of dyestuff, and the Procion brand of reactive dyes was first produced in the UK in 1956. The reactive dye molecule consists of two main components: the parent dye and the reactive group, and the group that can react with the fiber is called the reactive group.
Commonly used dyes
X type: The dyestuff molecule contains dichlorotriazine reactive group, with higher activity and lower dyeing and color fixing temperature (20~40℃), which is common type or low temperature type. Its characteristics are better uniformity, poor stability, not acid hydrolysis, not suitable for dyeing dark colors, fixing rate of about 60%. Example: reactive red X-3B.
K type: the dye molecule contains a chlorine even triazine reactive group, because of the two chlorine atoms in the melamine chlorine replaced by other groups, the activity is lower than X type, dyeing color fixing temperature is higher (80 ~ 100 ℃), also known as “heat-set” dyes. It has high affinity with fibers and can dye dark colors, with a fixation rate of about 60~90%.
M type: Dyestuff molecule contains a chlorine homotriazine and β-hydroxyethyl sulfone sulfate double reactive dyestuff, strong reaction activity, acid resistance and alkali stability than K and KN type, high fixation rate. KN type: the reactive group of the dye is ethylene sulfone group (-SO2CH=CH2), generated by -SO2CH2CH2OSO3Na during dyeing, its reactivity is between X type and K type, the fixing temperature is about 60 ℃, very stable in solution, will not occur hydrolysis. Example: Reactive black KN-B (C.I.20505).
KD type: the parent is a direct dye, the reactive group is two monochlorotriazine group, this dye and fiber affinity, dyeing temperature is above 70 ℃, suitable for dyeing dark colors. Example: Reactive brilliant red KD-8B.
P type: The dyestuff contains phosphonic acid type reactive group, successfully developed by ICI Company 70, it can fix color under weak acidic (pH6.0) condition, it can be used with disperse dyestuff, there is no hydrolysis reaction, it has high fixing rate.
Sulfide dyes
Definition
Sulfide dyes are dyes produced by the reaction of amines, phenols or nitro substances of aromatic hydrocarbons with sulfur or sodium polysulfide by sulfidation, and were first synthesized by French chemists Crucian and Bretonnier.
Dyeing mechanism
In simple terms, it is a sulfur-containing dye, a kind of sulfur-containing dye formed by certain sulfurization of organic matter, which is able to dissolve the sulfur in some way when dyeing, and finally finish dyeing.
Sulfur dyes are insoluble in water and require the use of sodium sulfide or other reducing agents to reduce the dye to a soluble cryptochrome when dyeing. It has an affinity for fibers and stains the fibers, and then reverts to its insoluble state after oxidation and color development and is fixed on the fibers. Therefore, sulfide dyes are also a kind of reducing dyes.
Commonly used dyes
Sulfide black
Vulcanized blue CV
Disperse dyes
Definition
Disperse dyes are a class of non-ionic dyes with low water solubility. They were first used for dyeing vinyl acetate fiber and were called vinyl dyes. With the development of synthetic fibers, nylon and polyester appeared one after another, especially polyester, because of its properties such as high neatness, few fiber voids and strong hydrophobicity, it is necessary to expand the fiber with a carrier or under high temperature and heat solubility in order for the dye to enter the fiber and be dyed. Therefore, new requirements for dyestuff, namely, the requirement for better hydrophobicity and certain dispersion and resistance to sublimation dyestuff, etc., printing and dyeing process for polyester fabric dyeing disperse dyestuff basically has these properties, but because of the variety, the use must also be selected according to the processing requirements line selection. These dyestuffs require a high level of post-processing and are usually ground by a mill in the presence of dispersant to become highly dispersed and crystallographically stable particles before they can be used.
Dyeing mechanism
Disperse dyes have small molecules and do not contain water-soluble groups in their structure, and they are uniformly dispersed in the dyeing solution by the action of dispersants. It can dye polyester fiber, acetate fiber and polyester amine fiber, and has become a special dye for polyester.
Main classification
One is classified by chemical structure, which can be mainly divided into azo, anthraquinone and heterocyclic types, among which the azo type is mainly used, and the azo type is divided into single azo type and double azo type.
Another kind of classification by application performance, can be divided into high temperature type, medium temperature type and low temperature type three categories, detailed classification see the following table:
Acid dyes
Definition
AcidDyes are a class of water-soluble dyes with acidic groups in their structure, which are used for dyeing in acidic media. Most acid dyes contain sodium sulfonate salts, are soluble in water, and have a bright color and complete chromatography. They are mainly used for dyeing wool, silk and nylon, but also for leather, paper, ink, etc. It has no coloring power for cellulose fiber in general.
Dyeing mechanism
The acidic group in acid dyes is generally dominated by sulfonic acid group (-SO3H), which exists on the dye molecule in the form of sodium salt of sulfonic acid (-SO3Na), and there are also individual dyes with sodium salt of carboxylic acid (-COONa) as the acidic group.
They are characterized by good water solubility, bright color, full chromatography, relatively simple molecular structure compared to other dyes, lack of a longer conjugated coherent system in the dye molecule, and low directivity of the dye.
Main classification
Classified by the molecular structure of the parent dyestuff:
1、Azo class (60% of the total, extensive chromatography)
Azo dyes (a class of organic compounds with aromatic groups attached to both ends of the azo group) is the most widely used class of synthetic dyes for textile garments in the printing and dyeing process, used in the dyeing and printing of a variety of natural and synthetic fibers, also used in the coloring of paints, plastics, rubber, etc.. Under special conditions, it can decompose and produce more than 20 kinds of carcinogenic aromatic amines, which can cause lesions and induce cancer by changing the DNA structure of human body through activation.
2, anthraquinones (accounting for 20%, mainly blue, green system)
Triarylmethane class (accounting for 10%, purple, blue, green system)
Triaryl methane dyes are substituted triaryl methane derivatives and substituted anthracenes oxide compounds, with different precipitating agents to generate dyes.
4、heterocyclic class (10%, red, purple system)
Heterocyclic pigments (heterocyclic pigments) contain heterocyclic structure in organic pigment molecules, mainly oxygen heterocyclic ring or nitrogen heterocyclic ring as the color-emitting system. Heterocyclic pigment chromatography includes yellow, orange, red, purple, a few are blue, and have molecular symmetry and planarity, many varieties show excellent heat resistance, migration resistance and weather resistance similar to phthalocyanines.
2、Classification according to the pH of dyeing:
Strong acid bath acidic dyes: dyeing pH 2.5-4, good sun fastness, but poor wet treatment fastness, bright color, good uniformity;
Weak acid bath acid dyes: dyeing pH 4-5, the proportion of sulfonic acid groups in the dye molecular structure is slightly lower, so the water solubility is slightly worse, wet treatment fastness is better than strong acid bath dyes, leveling is slightly worse.
Neutral bath acidic dyes: dyeing pH 6-7, the proportion of sulfonic acid group in the molecular structure of dyestuff is even lower, so the solubility of dyestuff is low, the leveling is poor, the color is not bright enough, but the wet treatment fastness is high.
Basic dyestuff
Definition
Basic dyes, also known as salt-based dyes, are salts generated by aromatic bases and acids (organic acids, inorganic acids), i.e. salts of colored organic bases. The basic group is usually an amino group, which becomes salt as -NH2-HCl salt group and dissolves in water to form dye cations and acid anions. Also known as cationic dyes.
Dyeing principle
Dyes that dissociate in aqueous solution to form cationic pigments, so they are classified as cationic dyes. Because of the poor color fastness to light and washing after dyeing fibers, basic dyes are rarely used for dyeing fabrics, but are mainly used for educational materials and paper.
