Reactive dyes and disperse dyes

Disperse dyes Disperse dyes are nonionic dyes with strong hydrophobicity and low water solubility. There are no water-soluble groups in their structures, but they contain many polar groups, such as -NO2, -NH2, -CN and -OG. The dye uptake of disperse dyes varies with different dyes. When matching colors, we should try to choose dyes with similar dye uptake or good compatibility, such as disperse dyes mixed with weak matching dyes or neutral dyes, in order to adjust the color shade, improve the levelness and learn from each other's strong points. The dye uptake of disperse dyes is very dependent on temperature, so special attention should be paid to the control of temperature when dyeing. With the increase of temperature, the adsorption of dyes by dispersants will decrease, and the chances of collision and coagulation between dye particles will increase. On the other hand, with the increase of temperature, the solubility of small particles increases, and the growth of large particles will reduce the stability of dispersion. Therefore, the temperature of the prepared dye solution should be low, and heating the dye solution for a long time should be avoided before dyeing. Generally, dyes are dyed at 40~50℃ and heated to boiling at a rate of about 0.5℃/min. According to the levelness and exhaustion of dyes, keep warm and wash with water. Disperse dyes can dye nylon and polyurethane at the same time. The reactive groups in the dye are dyed and fixed with a large number of amide groups and amino groups at the end of PA6 molecules through hydrogen bonds, van der Waals forces and dipole forces. In addition, PA6 molecules contain a large number of nonpolar hydrocarbon hydrophobic chains, which is also the reason why hydrophobic disperse dyes can dye brocade. Disperse dyes have small molecular weight, good diffusion performance, simple dyeing method, good levelness, good light fastness and good coverage, which can avoid uneven dyeing of nylon due to different component sizes during polymerization and different stretching degrees during spinning. However, the saturation value of PA6 is low, so it is difficult to dye with disperse dyes. Disperse dyes have a good coloring effect on polyurethane, which is related to its own molecular structure and relatively compact foaming structure. Polyurethane forms an incomplete polymer film on the surface and inside of synthetic leather base fabric, and its structure consists of soft segment and hard segment. Some soft segments are loose in structure, which is the main position of disperse dyes dyeing. Polyurethane has a large adsorption capacity for disperse dyes and less dye residue in dyeing residue, so it is necessary to use high-strength disperse dyes to dye dark varieties. In a certain range, with the increase of dyeing temperature, the color yield is larger. In addition, the color fastness of disperse dyes on polyurethane is also good. Disperse dyes are the main dyes for polyurethane dyeing in sea-island superfine fiber synthetic leather dyeing. In contrast, some other types of dyes color polyurethane badly, on the contrary, they color nylon; Although some dyes polyurethane well, they dye nylon at the same time, which is very unfavorable for the dyed finished products to have uniform light and no color difference. Even if disperse dyes are used, the dosage should be controlled, because the coloring of nylon will not only affect its color light, but also affect the dyeing fastness of nylon. Acid dyes Acid dyes are important dyes for nylon dyeing, and fibers and dyes are mainly bonded through ionic bonds. If the PH value during dyeing is low (pH < 3 =), the imino group in the molecular chain can also be positively ionized (-N+H2-) to combine with the dye anion. In addition, hydrogen bonding and van der Waals force also play an important role in weak acid or neutral bath dyeing of acid dyes, and the dyeing saturation value often exceeds the saturation value calculated by amino content. Because the content of amino group at the end of nylon is lighter than that of nylon, when two or more dyes match colors, the problem of competitive dyeing often occurs. Therefore, attention should be paid to choosing dyes with good compatibility when matching colors. The molecule of nylon is a linear molecule, and there are no branched chains and large side groups in the molecular chain, but there are many groups that can form hydrogen bonds. Dye molecules are easy to interfere with fiber molecules, and fiber molecules have large van der Waals force, so hydrogen bonds are easy to form between dyes and fibers. Therefore, the affinity of acid dyes for nylon is generally higher than that of wool. The saturation value of nylon dyed with strong acid dyes is 2.3%, and the weak acid dyes are 5%~5.2%. Therefore, weak acid dyes are generally used to dye nylon, and the dye uptake is improved by van der Waals force and hydrogen bonding. Polyamide dyed with strong acid dyes is generally not deep, because the proportion of amphoteric groups is different (acetic acid or benzoic acid is often used to adjust the molecular weight in polyamide synthesis, and the amino group at the end of some macromolecules is acylated, and the amino group content is lower than that of carboxyl group, and there are also cyclic amide groups in PA6). Therefore, it is difficult to dye with typical level-dyeing acid dyes, that is, it is difficult to dye deep colors only with coulomb force. Acid dyes can also dye polyurethane, because there are amide groups, urea groups and carbamate groups in the molecular bonds of polyurethane, and the binding forms are van der Waals force, hydrogen bonds and ionic bonds, but the dyeing effect is not ideal. Especially for strong acid dyes, almost all dyes are fixed on the fiber surface and rarely penetrate into the fiber, which leads to serious fading and poor color fastness in soaping. The dye uptake percentage of weakly mixed dyes is slightly higher than that of strong acid dyes, and the washing fastness is the same, but the soaping fastness is still not ideal, and the dye can not penetrate into the fiber, so the light fastness is poor. Neutral Dyeing Neutral dyes are 1: 2 acid mordants. Metal atoms and dye molecules are combined in the ratio of 1: 2. Dye molecules do not contain water-soluble groups such as sulfonic acid groups, but only hydrophilic groups with low water solubility, such as sulfonamide group (-SO2NHR) and sulfone group (-SO2CH3), which are usually dyed in neutral or weakly acidic media, hence the name. Nylon has a large number of amino carboxyl end groups in its molecule, so neutral dyes can be used.