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How to dye yarn with vat dyes?

Date:Nov 23, 2020

Vat dyes are one of the main dyes for dyeing cotton yarns of current colored fabrics. The dyed yarn is not only bright in color, but also has excellent fastness. Most of the light fastnesses are above level 6, and some varieties are as high as level 8. Therefore, all yarn-dyed fabrics that need finishing such as scouring, bleaching, mercerizing and heat setting can be dyed with vat dyes. There are many varieties of vat dyes, which can be divided into indigo and anthraquinones according to their chemical structure. The vat dyes used in yarn dyeing are mostly anthraquinones.

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Basic dyeing method


The total color body sodium salt of anthraquinone vat dyes is easily absorbed by cotton yarn, and the dyeing rate is fast, so level dyeing is poor, and the dye bath requires higher caustic soda and sodium hydroxide. In the yarn dyeing process, 1g of anthraquinone vat dyes often consume 5~6g of caustic soda and sodium hydroxide in the dyeing bath. In addition, the dyeing bath also needs to add bone glue, leveling 0 and other retarding agents to reduce the amount of dye. Dyeing rate is conducive to the diffusion of the dye liquor into the fiber and improves the leveling effect. The dosage is 0.2~0.5g/L. In daily dyeing, the dyeing time is generally 15~20min. In order to improve the levelness and color fastness of colored yarn, the dyeing time can be extended to 20~30min. For a small amount of vat dyes that need to be dyed at a lower temperature, after the leuco sodium salt is adsorbed by the yarn, it is not easy to oxidize in the air. You can choose an appropriate oxidation method and oxidant to promote the conversion and color development of the dye leuco , And then washed with water or treated with dilute acid solution to remove residual alkali and impurities, and finally soaped and washed to complete yarn dyeing. Since different vat dyes have different dyeing properties, when dyeing yarns, you can choose the appropriate reduction method and dyeing method according to the amount of caustic soda, sodium hydroxide, auxiliaries, dyeing temperature, time and other conditions required for yarn dyeing. .



Dyeing process and operation


(1) Manual yarn dyeing

When manual yarn dyeing is used, the white yarn needs to be continuously lifted up and down for 7 to 9 times (about 5 minutes) after it is lowered, but the interval is required to be uniform.


(2) Dyeing with reciprocating yarn dyeing machine

The reciprocating yarn dyeing machine is used for yarn dyeing. When lowering the vat, two people will lift the yarn sequentially. The machine should be in a state of only swinging and not rotating, and the white yarn should be completely saturated with the dyeing solution (equivalent to the time of reciprocating swing 3 times). Roll the yarn rod. Some high level dyeing and mercerized yarns need to be combined with manual operation when the white yarn is lowered into the cylinder, and the yarn is swayed from side to side, and the yarn is continuously rolled back and forth for 4~5min, and then stopped, but the oscillation still needs to continue. Carry out, afterwards, change direction every 1min and go back once. After dyeing for 10 minutes, change the direction and turn the head every 2 to 3 minutes. When turning the head, about 1/3 of the colored yarn exposed to the liquid surface must be immersed in the dyeing solution again to prevent early oxidation and dark and shallow heads.


(3) Dyeing on high temperature and high pressure yarn dyeing machine

For cheese dyeing, the dye solution can be driven by the circulation pump in the forward and reverse directions, and the flow direction is changed at regular intervals. First, spray the liquid from the center to the surroundings (that is, the positive circulation), the time is 0.5~1.5min, and then spray the liquid from the surroundings to the center (Ie reverse circulation), the time is 4.5~3.5min. If it is hank dyeing, it can always be dyed with forward circulating liquid flow, which is not suitable for reverse circulation. When the dyeing liquid circulates from the periphery to the center, the density of the upper layer of the skein will inevitably decrease, while the density of the lower layer will increase. The larger it is, the short circuit of liquid flow is formed, and the yarn core is impermeable to dyeing, causing white core, white spot and light spot.

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Before dyeing the yarn, the quality of the white yarn should be inspected. It is required that the appearance of the white yarn is clean, free of stains, and neutral. The stacking time should not exceed 8 hours, and it should be covered with a damp cloth. When the yarn dyeing machine is installed, it should be filled according to the requirements of different yarn dyeing equipment to prevent dyeing defects caused by improper yarn filling.