What is Reactive Dye Windprint?

The windmark problem generally refers to the phenomenon of partial discoloration or defects in the dyeing and processing of textiles by printing and dyeing manufacturers during the drying and storage process.

The reason for the windmark of textiles is mainly related to the dye itself and the dyeing process or the added auxiliaries, usually the vast majority of direct dyes, some azo (including heterocyclic azo) reactive dyes, a few vat dyes and nano. Futo dyes, due to the poor fastness of the dye itself to sunlight and oxidation, may produce windmarks. Some vinyl sulfone reactive dyes (such as reactive turquoise blue KN-G, reactive bright orange G, etc.), due to their strong sensitivity to alkali, may also be damaged if the alkali agent on the cloth is not removed after dyeing and color fixing. generate windmarks.

As we all know, reactive dyes rely on reactive groups on dyes to react with hydroxyl groups on cotton fibers to form covalent bonds, which are very strong bonding methods between dyes and fibers. This reaction is generally carried out under alkaline conditions. At present, the academic circles believe that the more suitable pH value range for the reaction of reactive dyes and cotton fibers is about 11. The commonly used alkali agent is generally soda ash, and there is also a useful alkali powder as an alkali agent. .

When the reactive dyes are fixed under alkaline conditions, on the one hand, the reactive groups on the dyes react with the hydroxyl groups on the cotton fibers to form covalent bonds; on the other hand, the dyes that have not reacted with the cotton fibers will also undergo hydrolysis. Bond - the reactive group is separated from the dye matrix, resulting in floating color; at the same time, the dye that has reacted with the cotton fiber to form a covalent bond may also hydrolyze the bond - the dye matrix is separated from the cotton fiber, resulting in a floating color . These floating color or bond-breaking dyes have lost the ability to recombine with cotton fibers and can only be removed in the process of washing and soaping.

Light color loss generally only works on reactive dyes with poor light fastness. The light fastness of reactive dyes mainly depends on the parent structure of reactive dyes, that is, chromophoric conjugated system. According to the chemical structure of the dye parent, reactive dyes can be divided into azo (including heterocyclic azo) reactive dyes, quinone reactive dyes, metal complex reactive dyes, phthalocyanine reactive dyes, etc., of which more than 70% It is an azo reactive dye. The color fastness of azo reactive dyes to sunlight is generally poor. The main reason is that the azo bond on the parent structure of reactive dyes is easily broken under the influence of light or other conditions. The common ones are mainly reactive red series, such as reactive dyes. Red 3BS, etc., while anthraquinone reactive dyes, metal complex reactive dyes, and phthalocyanine reactive dyes generally have better light fastness.

The concentration of reducing agent in the air is generally very low, especially at room temperature, the effect of a very low concentration of reducing agent on the azo bond breaking on the reactive dye parent structure is relatively small.

The cleavage of reactive dyes by alkaline agents is very possible and common. This is mainly due to various factors in the dyeing process, such as operational factors, equipment factors, process factors and so on. For example, the alkaline agent is not completely dissolved, and some undissolved alkaline agent remains in the equipment; after the color fixing is completed, the alkaline agent on the color cloth is not cleaned in time, not in place, and incompletely neutralized. These alkaline agents remaining on the colored cloth are likely to hydrolyze and break the bonds of the dyes that have reacted with cotton fibers to form covalent bonds.

Among the reactive dyes that cause windmark problems in the cotton dyeing process, if the alkali agent on the dyed cloth is not removed cleanly after fixing, the windmark problem is likely to occur when the pH value is greater than 9. After the fixation is completed, vinylsulfone reactive dyes, which have reacted with cotton fibers to form covalent bonds, are still sensitive to alkalis, and may still undergo hydrolysis and bond breakage under alkaline conditions, which is the cause of vinylsulfone. The root cause of windmarks produced by reactive dyes in cotton cloth dyeing process.

In the dyeing process of reactive dyes, an alkali agent is generally added to fix the color. The alkali agent used is generally soda ash, and there is also a substitute for alkali powder. The use of these alkali agents needs to be fully dissolved. After the color fixing is completed, these alkaline agents will make the color cloth more alkaline, and those undissolved solid alkaline agents may make the color cloth more alkaline, which requires the printing and dyeing manufacturers to After the fixation is completed, it should be washed with a large amount of water in time, and even add dilute acetic acid solution to neutralize to remove these excess alkali agents.

However, in the actual production and operation process of printing and dyeing manufacturers, due to various actual situations, the excess alkali agent on the colored cloth cannot be removed in time, resulting in the possibility of windmarking of dyed cotton cloth.