Sulfur dye yarn dyeing
The colored yarns used in dark varieties of yarn-dyed cotton fabrics, such as denim and Yuangong, are mostly colored with sulfur dyes. Sulfur dyes are cheap, have full color after coloring, and have good washing fastness. They are one of the commonly used dyes for coloring spinning yarns. Sulfur dyes contain a large amount of sulfur in their molecular structure and are insoluble in water. They must be reduced and dissolved with sodium sulfide when coloring. In recent years, water-soluble sulfur dyes and anti-brittle sulfur black have emerged, giving new prospects for the application of sulfur dyes.
Key points of coloring process
— The pre-dyeing treatment of spinning yarn is the key to ensuring the coloring quality of spinning yarn. The coloring of sulfur dyes can be divided into unfinished and unfinished. Some light-colored spun yarns need to be dyed. Bleached.
If the scouring is poor, the wool efficiency of the spinning yarn will be poor, or the concentration of the alkali solution after the yarn is different, and the bleached yarn will contain more chlorine, etc., which will directly affect the coloring quality. Therefore, the white yarn must be carefully inspected before dyeing, and the whiteness must be uniform and free of yellow spots, black spots, alkali spots, rust spots, stains, and chlorine, etc. The dehydrated white yarn must be covered with a damp cloth to prevent the surface from drying out. White yarn that has been stacked for too long must be washed again before dyeing, otherwise local white stripes or shallow stripes of color defects will occur after dyeing.
For unfinished yarn that has not been boiled with alkali but only scoured with water, the cotton grease and wax grease have not been completely removed, so the stacking time should not be too long. Especially in high temperature seasons, it is easy to deteriorate. It needs to be dyed before dyeing. Re-treat with hot soda lye at 80-70°C. In severe cases, pickling is required, otherwise the dyed yarn will easily appear light in color and whitish.
Since sulfur dyes are dyed slowly, it is suitable to use high temperature for coloring, which is conducive to the continuous melting and thinning of the dye particles and rapid incorporation into the fiber. It can penetrate and diffuse the fiber layer, and can make the fiber yarn expand and loosen when heated, and obtain better level dyeing effect. Generally, the coloring temperature of sulfur dyes is roughly 75-80°C. It is inconvenient to operate at high temperatures when hand-dyed yarn is operated, so the temperature is controlled at 60-70°C. If the temperature is too low, it will affect the dyeing process, make the color lighter, and cause the dye concentration in the residual liquid to gradually increase, resulting in color differences between vats. However, some dyes are suitable for coloring at low temperatures. If the temperature is too high, the color will be lighter. This is mainly because the directness of the dye to the fiber is reduced when the temperature rises.
Generally, light-colored yarns are dyed at low temperature. For example, the weft threads of labor cloth dyed with sulfur bleaching can be dyed at room temperature. In addition, the coloring temperature is closely related to the finish or unfinishedness of cotton yarn, yarn dyeing machinery, etc. Generally, the coloring temperature of unfinished yarn is high, while that of silk-finished yarn is lower. High-temperature and high-pressure dyeing yarns have a sealed device, and the coloring temperature can be increased to above 100°C. However, if the temperature of the reciprocating dyeing machine is too high, the spinning yarn will easily float, causing yarn chaos and yarn breakage, so the coloring temperature is mostly 70°C. ~80℃.
When sulfur dyes are dyed in dark colors, due to the high dye concentration in the dye bath and the fast oxidation rate, after dyeing, the unfixed dye on the spinning yarn comes into contact with the air to produce lakes and is adsorbed on the The surface of colored yarn can easily cause defects such as red stripes, gold and copper colors, which will reduce the color fastness. In order to obtain better level dyeing effect and color fastness, the general dyeing method is to immediately immerse the spun yarn taken out from the dye bath into another reducing solution for re-reduction, and gradually reduce the temperature and temperature of the dyed yarn itself. The concentration of the adsorbed dye liquor slows down the oxidation rate to achieve uniform color and stable quality, or removes part of the floating color on the surface of the colored yarn through the reducing solution. This process is often called a stuffy vat.
When dyeing cotton yarn with sulfur dyes, the leuco body coloring method is commonly used, among which black and navy blue are the most common. The dye uptake rate is generally 25% to 30%, so the dye residue remains in the dye. There is a lot of dye in the bath, so the residual liquid after coloring with sulfur dye is usually used continuously. The ratio between the input amount of dye in the first cylinder and the replenishment amount of dye in the continuation cylinder is often called the bonus number of the dye in the first cylinder. If the bonus number is wrong, it will affect the color depth of the first cylinder and the continuation cylinder.
When dyeing light-colored yarn, the bonus number of the head cylinder can be appropriately reduced, while when dyeing dark-colored yarn, it should be increased. When the dye uptake rate is 25.4%, the bonus of the dye in the first tank is about 2.5 to 4 times that of the dye in the continuation tank. There are many factors that affect the coloring of sulfur dyes. In addition to the amount of dye and alkali sulfide, the cotton blending, scouring quality, water hardness, and alkali sulfide content of the spinning yarn directly affect the dye uptake rate of the yarn.
AAAVBJYTUJGHNH
Disclaimer:
Disclaimer: Published on this site��Some text, pictures, audio, and videos in some articles come from the Internet and do not represent the views of this website. The copyright belongs to the original author. If you find that the information reproduced on this website infringes upon your rights, please contact us and we will change or delete it as soon as possible.
AA
