The following five points for you to solve the common problems of cotton fabric dyeing!

The use of sulphur dyes for dyeing cotton textiles is indeed very economical, and the color fastness is also good, but it often produces erythema and red strips that require rework, affecting production and costs. To solve this problem, we must pay attention to the following points:

1. Use sodium sulfide (Na2S). Sulfuric alkali is an indispensable main additive for the dyeing of sulphur dyes. Sulfur dyes must be dyed according to specific products with different proportions of sulfurized alkali (50%), generally with the dye (folded into 100%) is 1:1, like sulfide can also be formulated into 1:1.5. Its role is mainly to promote the dissolution and reduction of dyes. Sometimes the sulfide base used is not a reddish-brown, grayish-white powder that is also added to the bath. In fact, the sulfuric alkali has been weathered as grayish white powder. Adding it to the dyeing bath not only does not dissolve or reduce the dye, but it causes the dye to oxidize prematurely into lake. If the washing is not clean, it will inevitably produce erythema and red strips. And other staining rickets.

2, control the dyeing process conditions. Practice has proved that the dyeing of sulphur dyes cannot be dyed theoretically at the so-called 80-85°C, in particular vulcanized blue or vulcanized black. After the addition of dyes and sulfuric acid, the temperature should be gradually increased to 98 °C, heat and dyeing 15-20min, and then stop heating; while dyeing, let the temperature in the cylinder drop to 80-85 °C, continue staining for about 20min, and then drain Into the cold water wash oxidation. Regardless of the residue (heat) and the addition of cold water, the speed should be slow, not too fast. This kind of hot dyeing method, after the first heat, not only facilitates even dyeing, but also facilitates the full dissolution and reduction of dyes, and can overcome dyeing defects.

3, the dye should be slowly cleaned. As already mentioned above, the dyed fabric cannot be cleaned in a cold water bath all at once. Especially like vulcanized blue, it should transition from the dye bath to mild after dyeing, even in the water containing a certain reducing agent, the term is called "foot cylinder". This will not only be beneficial to the full cleaning of the alkali and reducing agent on the fabric, but also to the full color (oxidation) of the dye on the fabric. Of course, for some difficult-to-oxidize dyes, such as Cyan Blue CV/3G, Red Brown GN, Dark Brown, etc., 1-2 g/L of sodium perborate and hydrogen peroxide should be added to the 2-3 cylinder water bath to promote the dye. Oxidation hair color.

4, pay attention to the stability of the dye bath, solve the problem before the cylinder. Sulphur dye is a kind of dye with more sulfur content, especially like black, there are many factors that are unstable during application. When the dyeing starts, the leucosome of the dyeing bath is dark green or ginger (according to the different types of dyes, the leucosome is not the same). Before the dyeing is stopped, the leuco body in the dyeing bath is changed. Now. Then, it is impossible to produce cylinders. In general, add 1⁄2 or 1/3 of the original amount of sulfurized alkali, and then continue dyeing at about 85°C for 10-15 minutes. The leucosome of the dye bath is similar to the initial one. At that time, it will go out again. Otherwise, there will be problems after the cylinder is out, causing rework. Practice has proved that, when dyeing, if adding 2-3g/L baking soda, soda ash, glucose (technical grade) or 0.5-1g/L of insurance powder and 1-2g/L urea, it can promote dye dissolution and stabilize the dye bath. , significantly reduce the risk of erythema and red stripes.

5, repair of erythema, redness and other rickets. Usually with a dilute solution of alkali sulfide (about 5-10g / L) at 85-90 °C for 20min, rickets can be eliminated. When the rickets are severe, the amount of sulfurized alkali must be increased accordingly. When the amount of sulfurized alkali is more than 10g/L, proper amount of dye should be added in the treatment bath, otherwise rickets such as erythema may be repaired but the color may become light. The specific amount and method of repair depends on the actual situation.

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