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Methods for Testing The Quality of Disperse Dyes

Views: 2 Author: Site Editor Publish Time: 2023-12-11 Origin: Site

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Disperse dye

Textile dyes

Dyeing

Disperse dye definition

Disperse dyes are a type of dye with smaller molecules (molecular weight 200-500) and relatively simple structure. It does not contain strong hydrophilic groups such as sulfonic acid group so3- and carboxyl COOH. It only contains some weak polar groups such as carboxyl groups, amino groups, and nitro groups, and is a non-ionic dye with very low water activity.

The five major dyeing properties of disperse dyes are listed below.

Diffusion testing

Accurately weigh 1g of dye, add 100mL of 30°C water, and stir evenly with a glass rod. Use a pipette to drop 4-5 drops of the dye suspension on the filter paper. Observe its natural seepage circle. The larger the area with better diffusivity.

Some dye solutions have 1 to 2 layers of fuzzy seepage circles at the place where they are dropped. The area is not large. Outside the dye solution seepage circles is the aqueous solution. When using this kind of dye, it is best to add 20% to 30% of the dye dosage as a diffusing agent. Or add 2g/L disperse dye repair agent to improve dye diffusion and dye migration.

Dispersion testing

Place the remaining dye solution from the previous step on a constant-temperature electric furnace and heat it to 70°C to 72°C. Remove the heat source, stir with a glass rod, and observe whether the dye on the beaker wall and the glass rod is sticky. If the fluidity of the dye solution is very good and there is almost no stain on the glassware, it means that the dye has good dispersion and can be dyed at 100°C or high temperature and high pressure.

High temperature dispersion stability testing

Pour the above yibuzhou dye solution into a glass dyeing cup, place it in the dyeing machine, and process it for 30 minutes at 130°C and 0.18MPa. After taking it out, observe whether the solution thickens and slowly pour it on the filter paper (the filter paper can generally be placed in 50mL beaker), the shorter the filtration time, the better. If it is observed that the dye solution thickens after heating and feels mushy when touched with fingers, it indicates that the dye has poor high-temperature dispersion stability. When using this dye, measures should also be taken to supplement the dye dosage with 20% to 30% of the diffusing agent. If the water hardness used in production is too high, disperse dyes added to the dye bath will cause secondary agglomeration. To prevent this situation, first of all, the pH value of the dye bath should be stabilized with ammonium sulfate; secondly, 1~2g/L dispersing additive can be added to improve it. Do not add sodium hexametaphosphate as a water softener, because sodium hexametaphosphate will lose its ability to complex calcium and magnesium ions under high temperature and high pressure conditions, and to a certain extent, it can also increase the pH value of the dye bath and destroy the dye bath. stability. In mild cases, the floating color on the fiber surface will increase and the color fastness will decrease. In severe cases, dark discoloration will occur. In actual production, once the above phenomenon occurs, the color clarity can be improved through reduction cleaning, or adding a dispersing chelating agent to the reduction bath will achieve better results.

Tar content testing

Most of the diffusing agents produced today use crude methylnaphthalene, which contains high impurity content, including not only tar but also other compounds. Generally, after the above-mentioned heated and unheated dye solutions are poured onto filter paper and dried, if there are small irregular black spots on the filter paper, it can be regarded as tar and other impurities. If the impurity content is small, you only need to add some leveling agents with good dispersing and emulsifying capabilities to the prescription, and dyeing medium or dark colors will not be a big problem. If the tar content is high, a bright golden layer like oil flowers will appear on the surface of the dye solution. 2g/L dispersant can be added during dyeing, and a small amount of foam suppressor can be added before adding dye.

Thermal migration testing

After polyester products are dyed with disperse dyes, during heat treatment such as heat setting and ironing, the dyes inside the fibers migrate out of the fibers and contaminate other fibers. It is different from sublimation fastness, but the test method of sublimation/iron fastness can be used to conduct simulation tests. That is, a piece of dyed polyester is used, and a piece of nylon and acetate fabric is attached to both sides. After hot pressing at 180°C for 30 seconds, the degree of thermal migration performance is judged based on the color of the attached fabric. Generally speaking, it is better to have a gray card with level 3 or above, and vice versa. For products with high color fastness requirements or yarn-dyed products, dyes with poor thermal migration cannot be used.

Methods for Testing the Quality of Disperse Dyes