Reactive dyes, also known as reactive dyes. A dye that chemically reacts with fibers during the dyeing process. This dye molecule contains a group capable of chemically reacting with the fiber, and the dye reacts with the fiber during the dyeing process to form a covalent bond between the two to form a whole, which improves washing and rubbing fastness. Reactive dyes are a new class of dyes. In 1956, the first production of Procion grade reactive dyes in the UK. The reactive dye molecules include the two main components of the parent dye and the reactive group, and the groups reactive with the fiber are referred to as reactive groups.
The properties of reactive dyes are as follows:
First, solubility
Excellent water solubility is used in the quality of reactive dyes. The solubility and concentration of the prepared dye is related to the size of the selected tank, the amount of electrolyte added, the dyeing temperature, and the amount of urea used. The solubility of reactive dyes varies widely. See each theory. The solubility listed is the range allowed when using the dye. For reactive dyes used for printing or dyeing, a variety having a solubility of about 100 g/l should be selected. The dye should be completely dissolved, not turbid, and not painted. Hot water can accelerate the dissolution, and urea has the function of melting, salt, yuanming powder and other electrolytes, which will reduce the solubility of the dye. The reactive dye is not dissolved with an alkaline agent to prevent hydrolysis of the dye.
Methods for determining the solubility of reactive dyes include vacuum filtration, spectrometry, and filter paper spotting. The filter paper spot method is easy to operate and is suitable for practical use in the factory. During the measurement, a series of dye solutions of different concentrations were prepared and stirred at room temperature (20 ° C) for 10 min to completely dissolve the dye. Use a 1 ml scaly pipette to enter the middle of the test solution and stir and release three times while aspirating. Then absorb 0.5 ml of the test solution and place it vertically on the beaker filter paper and repeat. After drying, the solubility of the dye on the filter paper was measured with the previous concentration, and there was no obvious spot, which was expressed as g/L. Some solutions of reactive dyes, after cooling, are turbid colloidal solution, which can be evenly permeated on the filter paper without speckle precipitation, which does not hinder normal use.
Second, diffusivity
The diffusivity refers to the ability of the dye to move inside the fiber and the temperature dependent diffusion of the dye molecules. For dyes with high diffusion coefficient, the reaction rate is high, the fixing efficiency is high, the leveling property is good, and the light transmittance is good. The diffusion rate depends on the structure and size of the dye. The larger the molecule, the more difficult it is to diffuse. High affinity dyes are difficult to adsorb by fibers, usually by increasing the temperature to accelerate diffusion. When the electrolyte is added to the dye solution, the diffusion coefficient of the dye is reduced.
The membrane process is typically determined by measuring the diffusion properties of the dye. The adhesive film (cellophane) was immersed in distilled water to a thickness of 2.4 filaments before immersion, and after immersion for 24 hours, the thickness was 4.5 filaments. During the measurement, the film was laminated to a certain thickness as needed and pressed under a glass plate to remove air bubbles. It is then sandwiched between two splints with rubber washers in the middle, one of which has a round hole in the middle of the splint. The dye solution can only diffuse through the pores into the film layer, and the splint film is immersed in the dye solution at 20 ° C for 1 hour. Then, it was taken out and rinsed with water, and the number of layers of the transparent film of the dye and the color of the dye of each layer were observed. There is a certain correlation between the number of diffusion layers and the half-staining time, the half-staining time is short, and the number of diffusion layers is large.
Third, directness
Directness refers to the ability of a reactive dye to be absorbed by a fiber in a dyeing solution. Highly soluble reactive dyes tend to have poor directionality, and continuous padding should use poor directionality. For dyeing equipment with large bath ratios, such as dyeing and hank dyeing, direct dyes should be preferred. In the dyeing (cold pile) dyeing, the dye solution is transferred to the fiber by dipping and filling, the direct dye is small, the color difference is small before and after dyeing, and the leveling is easy to be achieved, and the hydrolysis dye is easy to wash.
The directness of the reactive dye is represented by the equilibrium dye uptake (i.e., coloration rate) or rf value of the chromatographic analysis.
Determination method (1): 2 g of bleached mercerized 40X40 cotton poplin for fiber material. The dyeing solution has a concentration of 0.2 g/L, a bath ratio of 20 ≤ 1, and a dyeing temperature of 30 ° C and 80 ° C. During the measurement, 2 grams of the cut fabric was placed in a three-necked flask (to avoid evaporation of water) to the specified dyeing temperature, and 2 ml of the dye solution was absorbed while stirring regularly (while adding 2 ml of water). The optical density of the dye solution was measured. As the dyeing time is extended, the adsorption reaches equilibrium and the optical density of the dye solution no longer changes. The dye uptake rate at this point indicates the directness of the dye.
Measurement method (2): Paper surface analysis (Xinhua No. 3 filter paper), and the height at which each color spot rises is different, that is, the Rf value is different. The higher the Rf value, the smaller the directness of the dye and cellulosic material; the smaller the Rf value, the greater the directness. A 0.2 g/L dye solution was prepared, and the sample was fixed on a filter paper with a capillary tube. After drying, the dye solution was saturated in a closed column packed with distilled water for 30 minutes, and one end of the filter paper was contacted with water to start chromatography. When the front end of the toner rises to 20 cm, the Rf value of the dye spot is calculated. Paper chromatography is a convenient method for determining the directness of dyes, but the Rf value is not completely consistent with the actual properties of the dye.
Fourth, the reaction is lively
The reactivity of a reactive dye generally refers to the ability of a dye to react with a cellulose hydroxyl group. Reactive dyes can be fixed at room temperature and under weak conditions, but the dye stability in this reaction is relatively poor and easy. It is hydrolyzed to lose its ability to stain. The weakly reactive dye needs to be bound to the cellulose under relatively temperature conditions, or the strong hydroxyl reagent is used to activate the hydroxyl groups of the fiber yarn to cause the dye reaction to adhere to the fiber.
The reactivity of the same type of reactive dye is approximately the same. The reactivity depends on the chemical structure of the active group, followed by the linking group between the dye body and the active group, which also has a certain influence on the reactivity of the dye. In addition, due to the pH value, the total pH increases and the reaction rate increases. Temperature is also a factor influencing the rate of reaction. As the temperature increases, the reaction speed increases. As the temperature increases, the reaction rate can be increased by 2 to 3 times, so that the dye can react with the fiber after printing, drying or cooking.
