． When jig dyeing vulcanized indigo, the finished product often has bronze streaks. Why? How to solve it?
Answer Sulfide cyanide is a simple oxidizing dye that can oxidize naturally in the air. When the reducing power of the dye liquor is insufficient, the dye on the cloth roll will gradually oxidize, changing from the reducing form to the oxidizing form, and gradually attach to the surface of the fabric, forming a floating color (bronze color), commonly known as “red rib” defect. Here’s how to overcome it.
① The dosage of alkali sulfide should be sufficient, generally 100% sulfide black: 60% alkali sulfide = 1:1. However, it should be noted that the strength of domestic sulfur black dyes varies from high to low (100% to 150%), and the active ingredients of alkali sulfide are also different (containing 50% to 62% sodium sulfide). The strength of the dye and alkali sulfide should be determined according to the different strength of the dye and alkali sulfide. And the increase or decrease ratio. After being unpacked, alkali sulfide is easily oxidized into gray-white powder when exposed to air, reducing or even losing its reducing ability. For this reason, testing should be strengthened before use. The amount of alkali sulfide should not be too much, otherwise, the dye uptake rate will be reduced.
② When sulfide black and sulfide blue are rolled and dyed, the edges of the cloth will oxidize and develop color prematurely due to contact with air. If necessary, the edges of the cloth roll can be poured with dye solution at intervals to keep both ends of the cloth roll in good condition. Restore the state, which can prevent the occurrence of “red edge” defects.
③ During the jig dyeing process, a complete cover should be added to cover the cloth roll in reducing gas to reduce the contact between the dye solution and the air.
④After coloring, the water should be discharged completely to shorten the natural oxidation time of the cloth roll. The water discharge volume should be large (flowing water) so that the residual liquid on the fabric can be quickly removed before it is oxidized, so as to reduce the occurrence of floating color on the cloth surface. . Or treat it with dilute alkali sulfide after coloring, wash it twice at a temperature of 40 to 50°C, and then rinse with plenty of water.
⑤ The sulfide cyanine dye must be evenly dispersed during mixing. If the dye is not dissolved properly, a large amount of dye will adhere to the surface of the fabric, resulting in bronze stripes after dyeing. The reasonable chemical method is: first beat the dye with an appropriate amount of hot water and add an appropriate amount of ancient oil to blend, then pour it into the foot water of the jigger dyeing machine (containing a full amount of alkali sulfide and 2g/L soda ash), and heat it to boiling while stirring. Boil for 10 minutes to dissolve the dye thoroughly, then rinse with water to the specified amount and adjust to the specified temperature.
⑥ The cloth roll should not be too large (too long), and the coloring time for each pass should not exceed 10 minutes to prevent the cloth roll from being exposed to the air for too long, and part of the dye will be oxidized, which will promote the occurrence of “red veins” defects.
⑦The quality of natural cotton cloth used for coloring has a certain impact on leveling dyeing. The natural color cotton cloth boiled in clean water should not be stored for too long and should be used as soon as it is boiled.
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