Reactive dyes, also known as reactive dyes. A type of dye that reacts chemically with fibers during dyeing. This kind of dye molecules contain groups that can chemically react with fibers, and when dyeing, the dye reacts with the fibers, forming a covalent bond between the two and becoming a whole, which improves the washing resistance and friction fastness. Reactive dyes are a new type of dyes. In 1956, the United Kingdom first produced the reactive dye Procion. 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.
The properties of reactive dyes are as follows:
First, solubility
The quality of reactive dyes used in commercial applications is good for water solubility. The solubility and the concentration of the dye solution are related to the selected bath ratio, the amount of electrolyte added, the dyeing temperature and the amount of urea. The solubility of reactive dyes varies widely, see monographs, and the solubility listed refers to the permissible range of application of the dye. The reactive dyes applied to printing or pad dyeing should be selected with a solubility of about 100 g/l, requiring the dyes to dissolve completely, without turbidity and without color spots. Hot water can accelerate the dissolution, urea has a solubilization effect, salt, sodium powder and other electrolytes will reduce the solubility of dyes. Alkali agent should not be added at the same time when the reactive dye is dissolved to prevent hydrolysis of the dye.
The methods for determining the solubility of reactive dyes include vacuum filtration, spectrophotometry and filter paper spot method. The filter paper spot method is easy to operate and suitable for practical use in factories. In the determination, a series of dye solutions with different concentrations were prepared and stirred at room temperature (20 ° C) for 10 minutes to fully dissolve the dye. Use a 1ml scale suction tube to reach into the middle of the test liquid, and suck and discharge three times while stirring. Then take 0.5 ml of the test solution, drop it vertically on the filter paper flat on the mouth of the beaker, and repeat. After drying, the eye tests the liquid infiltration circle, and the concentration of the first step without obvious spots in the filter paper is used as the solubility of the dye, expressed in grams/liter. The solution of some reactive dyes, after cooling, presents a cloudy colloidal solution, and drops on the filter paper can permeate evenly, without spots, and does not hinder normal use.
Second, diffusivity
Diffusivity refers to the ability of the dye to move into the interior of the fiber, the diffusion of the dye molecules at a temperature. The dye with large diffusion coefficient has high reaction rate and fixing efficiency, and the degree of evenness and penetration is good. The diffusion performance depends on the structure and size of the dye, and the larger the molecule, the more difficult it is to diffuse. The dye with a large affinity for the fiber is strongly adsorbed by the fiber, and diffusion is difficult, usually by increasing the temperature to accelerate the diffusion of the dye. The diffusion coefficient of dye decreased when electrolyte was added to dye solution.
The diffusion property of dyes is usually determined by thin film method. Soak the viscose film (cellophane) in distilled water with a thickness of 2.4 silk before immersion and 4.5 silk after 24 hours of immersion. When measuring, the film is stacked into a certain thickness according to the need, and pressed under the glass plate to remove bubbles. Then sandwiched in the middle of the two splints with rubber gaskets, one of which has a round hole in the middle of the splints can only be diffused to the film layer through this hole, the splints film immersed in 20 ° C dye solution stand for 1 hour, and then take out the water to rinse, observe the number of layers of the film and each layer of dye color wheat. There is a certain correlation between the number of diffusion layers and the half-dyeing time. The half-dyeing time is short and the number of diffusion layers is large.
Third, directness
Directness refers to the ability of reactive dyes to be absorbed by fibers in the dye solution. Reactive dyes with high solubility often have low directness, and varieties with low directness should be selected for continuous pad dyeing and printing. Dyeing equipment with large bath ratio, such as rope dyeing and Hank dyeing, should preferentially use dyes with high directness. Rolling (cold rolling pile) dyeing method, the dye is transferred to the fiber by dipping, and it is easy to get even dyeing with dyes with slightly lower directness, less color difference before and after, and hydrolyzed dyes are easy to wash.
The directness of the reactive dye is expressed by the equilibrium dye percentage (that is, the color rate) or the Rf value of the chromatographic analysis.
Determination method (1) : Fiber material with bleached mercerized 40X40 cotton poplin packing 2 grams. The dyeing solution concentration is 0.2g/l, the bath ratio is 20:1, and the dyeing temperature is divided into 30℃ and 80℃. During the determination, the 2 grams of fabric cut into pieces are put into a three-neck bottle that has reached the specified dyeing temperature (to avoid water evaporation), and at certain intervals, 2 ml of the dyeing solution is absorbed in the stirring (at the same time, 2 ml of water is added) to determine the optical density of the dyeing solution. With the extension of dyeing time, the adsorption reached equilibrium, and the optical density of the dyeing solution did not change. At this time, the dyeing percentage indicates the directness of the dye.
Determination method (2) : paper chromatography (Xinhua #3 filter paper), observe the different height of each dye spot rise, that is, the Rf value is different. The larger the Rf value is, the less direct the dyestuff is with the cellulose material. The smaller the Rf value, the greater the directness. A 0.2g/l dye solution was prepared, and samples were taken on filter paper with capillary tubes. After drying, it was saturated in a closed chromatographic cylinder containing distilled water for 30 minutes. Then, one end of the filter paper sample was made in contact with water to start chromatographic analysis. Paper chromatography is a simple method to determine the directness of dyes, but the Rf value is not completely consistent with the actual properties of dyes.
Fourth, reaction activity
The reactivity of reactive dyes usually refers to the strength of the reaction ability of dyes and cellulose hydroxyl groups, reactive dyes can complete fixation at room temperature and weak base conditions, but the stability of the dyes in this reaction is relatively poor, easy to be hydrolyzed to lose the dyeing ability. Weak reactive dyes need to bond with cellulose at a higher temperature, or use a strong alkali to activate the hydroxyl group of the fiber yarn, prompting the dye reaction fixed on the fiber.
The reactivity of the same type of reactive dyes is roughly the same, and the strength of the reactivity depends on the chemical structure of the reactive group of the dye, followed by the linking group between the dye body and the active group, which also has a certain impact on the reactivity of the dye. In addition, it is also affected by the pH value, and the general pH value increases, and the reaction speed increases. As for temperature, it is also a factor that affects the reaction speed, and the reaction speed is faster when the temperature increases. Every 10℃ increase in temperature, the reaction speed can be increased by 2 to 3 times. Therefore, after printing, after drying or steaming, it can promote the reaction between the dye and the fiber.