Use a computer to measure color matching and test the performance of reactive dyes —– S, E, R, F values.
1. Solubility
High-quality reactive dye products have good water solubility. The solubility and concentration of the prepared dye solution are related to the selected liquor ratio, the amount of electrolyte added, the dyeing temperature and the amount of urea and other factors. The solubility of reactive dyes varies greatly. Please refer to the individual monographs. The solubility listed refers to the allowable range of the dye when used. For reactive dyes used in printing or pad dyeing, varieties with a solubility of about 100 g/L should be selected. The dyes are required to be completely dissolved without turbidity or color spots. Hot water can accelerate the dissolution, urea has a solubilizing effect, and electrolytes such as salt and Yuanming powder will reduce the solubility of the dye. When dissolving reactive dyes, alkalis should not be added at the same time to prevent hydrolysis of the dyes.
The methods for measuring the solubility of reactive dyes include vacuum filtration method, spectrophotometry and filter paper spot method. The filter paper spot method is easy to operate and suitable for actual use in factories. When measuring, first prepare a series of dye solutions with different concentrations and stir them at room temperature (20°C) for 10 minutes to fully dissolve the dye. Use a pipette with a 1 ml graduation to insert into the middle of the test solution and suck it up three times while stirring. Then draw 0.5 ml of the test solution, drop it vertically onto the filter paper placed flat on the mouth of the beaker, and repeat once. After drying, visually test the liquid penetration circle, and use the previous concentration without obvious spots in the filter paper as the solubility of the dye, expressed in grams/liter. Some reactive dye solutions will turn into a turbid colloidal solution after cooling. When dropped on the filter paper, it will spread out evenly without spots, which does not hinder normal use.
2. Directness
Directness means that reactive dyes are The ability of dye liquor to be absorbed by fibers. Reactive dyes with high solubility tend to have low directness, so continuous pad dyeing and printing should use varieties with low directness. Dyeing equipment with a large liquor ratio, such as rope piece dyeing and skein dyeing, should give priority to dyes with high substantivity. In the pad coil (cold pad batch) dyeing method, the dye liquor is transferred to the fiber through padding. It is also easy to get level dyeing with dyes with slightly lower directness. The color difference between the front and back is small, and the hydrolyzed dye is easy to wash.
The substantivity of reactive dyes is expressed by the equilibrium dyeing percentage (i.e. color loading rate) or the Rf value of chromatographic analysis.
Measurement method (1): The fiber material is 2 grams of bleached and mercerized 40X40 cotton poplin products. The dye liquor concentration is 0.2 g/L, the liquor ratio is 20:1, and the dyeing temperature is divided into two levels: 30°C and 80°C. When measuring, cut 2 grams of fabric into pieces and put it into a three-necked bottle that has reached the specified dyeing temperature (to avoid evaporation of water). At certain intervals, absorb 2 ml of dye solution while stirring (and add 2 ml of dye solution at the same time). water), measure the optical density of the dye liquor. As the dyeing time increases, the adsorption reaches equilibrium and the optical density value of the dye solution no longer changes. The dyeing percentage at this time indicates the directness of the dye.
Measurement method (2): Paper chromatography (Xinhua #3 filter paper), observe the different rising heights of each dye spot, that is, the different Rf values. The larger the Rf value, the smaller the directivity between the dye and the cellulose material; the smaller the Rf value, the greater the directivity.
Prepare a 0.2 g/L dye solution, use a capillary tube to spot the sample on the filter paper, dry it in the sun and hang it in a closed chromatography jar filled with distilled water to saturate it for 30 minutes, and then let it saturate for 30 minutes. The spotted end of the filter paper comes into contact with water to start chromatography. When the front edge of the developing agent rises to 20 cm, calculate the Rf value of the dye spot. Paper chromatography is a simple method to determine the substantivity of dyes, but the Rf value is not completely consistent with the actual performance of the dye.
3. Diffusion
Diffusivity refers to the diffusion of dye into fibers The ability to move internally, temperature has the effect of grounding the diffusion of dye molecules. Dyes with large diffusion coefficients have high reaction rates and fixation efficiency, as well as good level dyeing and through-dying. The quality of diffusion performance depends on the structure and size of the dye. The larger the molecule, the more difficult it is to diffuse. Dyes with a high affinity for fibers are strongly adsorbed by the fibers and have difficulty in diffusion. Dye diffusion is usually accelerated by increasing the temperature. When electrolyte is added to the dye liquor, the diffusion coefficient of the dye decreases.
The thin film method is usually used to measure the diffusion properties of dyes. Dip the adhesive film (cellophane) into distilled water. The thickness before immersion is 2.4 strands, and the thickness after 24 hours of immersion is 4.5 strands. During measurement, fold the film to a certain thickness as needed and press it under the glass plate to remove air bubbles. Then sandwich it between two plywood with rubber gaskets in the middle. One of the plywood has a round hole in the middle. The dye solution can only diffuse into the film layer through this hole. Immerse the plywood film in the dye solution at 20°C and let it stand for 1 hour. , then take it out and rinse it with water, and observe the number of layers of the dyeing film and the color of each layer of dye. There is a certain correlation between the number of diffusion layers and the half-dying time. The shorter the half-dying time, the greater the number of diffusion layers.
4. Reactivity
The reactivity of reactive dyes is usually It refers to the strength of the reaction ability between dyes and cellulose hydroxyl groups. Highly reactive dyes can be fixed at room temperature and under weak alkali conditions. However, the stability of dyes in this reaction is relatively poor and they are easily hydrolyzed and lose their dyeing ability. Weakly reactive dyes need to be bonded to cellulose under relatively high temperature conditions, or a strong alkali agent must be used to activate the hydroxyl groups of the fiber yarn to promote the dye reaction and fixation on the fiber.
Reactive dyes of the same model have roughly the same reactivity.�Depends on the chemical structure of the active 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 pH value. Generally, as the pH value increases, the reaction speed increases. As for temperature, it is also a factor that affects the reaction speed. As the temperature increases, the reaction speed becomes faster. For every 10°C increase in temperature, the reaction speed can be increased by 2 to 3 times. Therefore, after printing, drying or steaming can promote the reaction between the dye and the fiber. </p
