Wind mark definition
Generally refers to a dyeing defect produced during the drying and storage process of textiles after printing and dyeing. Compared with the normal dyed light base, the wind mark will show white or dull gray long strips in the latitudinal direction of almost the entire door width. This defect is not visible before setting, but will appear after setting.
Reactive dye wind marks
The problem of wind marks generally refers to textiles dyed and processed by printing and dyeing manufacturers. During drying and storage A phenomenon of partial discoloration or defects caused by the process.
The cause of wind marks on textiles is mainly related to the dye itself and the dyeing process or the added auxiliaries. Usually, most direct dyes and some azo types (including heterocyclic azo types) are reactive. Dyes, a few vat dyes, and naftol dyes may produce wind marks due to the poor fastness of the dyes to sunlight and oxidation. Some vinyl sulfone reactive dyes (such as reactive emerald blue KN-G, reactive brilliant orange G, etc.) are highly sensitive to alkali. If the alkali agent is not removed from the cloth surface after dyeing and fixation, it may cause stains. Produce wind marks.
As we all know, reactive dyes rely on the reactive groups on the dye to react with the hydroxyl groups on the cotton fiber to form covalent bonds. This is a very strong bond between the dye and the fiber. This reaction is generally carried out under alkaline conditions. At present, academic circles believe that the more suitable pH value range for the reaction between reactive dyes and cotton fibers is around 11. The commonly used alkali agent is soda ash. Currently, alkali substitute powder is also used as an alkali agent. of.
When reactive dyes are fixed under alkaline conditions, on the one hand, the reactive groups on the dye react with the hydroxyl groups on the cotton fiber to form covalent bonds; on the other hand, Dyes that have not reacted with cotton fibers will also undergo hydrolysis and bond breaking – the reactive groups will separate from the dye matrix, resulting in floating colors; at the same time, dyes that have reacted with cotton fibers to form covalent bonds may also undergo hydrolysis and bond breaking. Bond–the separation of the dye matrix from the cotton fibers, resulting in floating colors. These floating, bond-breaking dyes have lost the ability to recombine with cotton fibers and can only be removed during the washing and soaping process.
Light discoloration generally only affects those reactive dyes with poor light fastness. The light fastness of reactive dyes mainly depends on the parent structure of the reactive dye, that is, Color conjugated system. According to the chemical structure of the dye parent, reactive dyes can be divided into azo-type (including heterocyclic azo-type) reactive dyes, quinone-type reactive dyes, metal complex-type reactive dyes, phthalocyanine-type 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 bonds in the parent structure of reactive dyes are easily broken under the influence of light or other conditions. The most common ones are 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 agents in the air is generally very low, especially at room temperature. Very low concentrations of reducing agents can break the azo bonds in the parent structure of reactive dyes. The impact is relatively small.
It is very possible and common for alkali agents to break the bonds of reactive dyes. This is mainly due to various factors in the dyeing process such as operating factors, equipment factors, process factors, etc. For example, the alkali agent is not completely dissolved, and some undissolved alkali agent remains in the equipment; after the color fixation is completed, the alkali agent on the color cloth is not cleaned in time, is not in place, and the neutralization is not complete, etc. These alkali agents remaining on the colored cloth are likely to hydrolyze and break the bonds of the dyes that have reacted with the cotton fibers to form covalent bonds
Produced during the dyeing process of cotton cloth Among reactive dyes that have a problem of wind printing, if the alkali agent on the colored cloth is not removed after fixation, the problem of wind printing will easily occur when the pH value is greater than 9. After the fixation is completed, vinyl sulfone reactive dyes, which have reacted with cotton fibers to form covalent bonds, are still sensitive to alkali. Hydrolysis and bond breaking may still occur under alkaline conditions. This is caused by vinyl sulfone. The fundamental reason why reactive dyes produce wind marks during cotton dyeing and processing.
In the process of reactive dye dyeing, an alkali agent is generally added for color fixation. The alkali agent used is generally soda ash, and alkali substitute powder is also used. The use of these alkali agents requires Dissolve fully. After the color fixation is completed, these alkali agents will make the color cloth more alkaline, and those undissolved solid alkali agents may make the color cloth more alkaline, which requires the printing and dyeing manufacturers to After the color fixation is completed, wash it thoroughly with a large amount of water in a timely manner, and even add dilute acetic acid solution to neutralize it to remove these excess alkali agents.
However, during actual production operations, printing and dyeing manufacturers are unable to remove excess alkali on colored cloths in time due to various practical conditions, which may cause dyed cotton cloths to produce Wind seal problem.
Printing and dyeing manufacturers use vinyl sulfone reactive dyes to cause wind marks during the dyeing process of cotton fabrics. The main reasons are as follows:
1. Currently, printing and dyeing manufacturers use reactive dyes to fix the color of cotton fabrics. After completion, the colored cloth often needs to wait because the equipment cannot be arranged. The waiting time can be as short as a few hours or as long as more than ten hours. During this period of stacking and waiting, the colored cloth contains strong alkali because the alkali agent is not cleaned in time. sex. Especially the part of the colored cloth that is exposed to the outside often causes alkaline corrosion on the colored cloth due to the evaporation of water on the cloth.The dye is stronger and is still unevenly distributed. At this time, vinyl sulfone reactive dyes are prone to bond breaking, including dyes that have reacted with cotton fibers to form covalent bonds. Partial bond breaking may also occur, thus Wind seal problems arise.
2. After the reactive dye has finished fixing the color of the cotton cloth, if there is too much floating color on the cloth, the alkali concentration is too concentrated, or even undissolved solid alkali agent remains, the color will The cloth may also continue to contain strong alkalinity due to insufficient alkali cleaning and incomplete neutralization, and it is still unevenly distributed. At this time, vinyl sulfone reactive dyes are prone to bond breaking, including those that have been combined with cotton fibers. Dyes that react to form covalent bonds may also undergo partial bond breakage, causing wind-marking problems.
3. After the reactive dyes on the cotton cloth are fixed and cleaned, they are not dried in time or the cooling is uneven after drying (such as piled in the air duct after drying and blowing Cold wind) may also cause wind mark problems.
Polyester fabric wind print
Polyester fabric in continuous production (Long car production line) is not prone to wind marks, while intermittent production (during high temperature and high pressure overflow dyeing) is prone to wind marks.
Most of the wind marks on polyester fabrics occur after the fabric is dehydrated and opened and before it is set, and appear in the reciprocating folding marks when the fabric is stored in the stacker. In severe cases, dozens of strips will appear in the weft direction, and their spacing is exactly the spacing of the reciprocating folding of the gray fabric.
Compared with the normal dyed light base, the wind-stamped area will show red, white or dull gray long strips in the latitudinal direction of almost the entire door width.
For example, for pulp-free polyester woven fabrics or polyester knitted fabrics, the process flow is: dyeing → post-processing → dehydration → opening → shaping → cloth inspection. The placement of such fabrics after opening is to be determined. During the shaping process, the reciprocating folds are exposed to the air, and the flow of air causes the moisture in these parts to evaporate and dry first. Due to the capillary effect, free water in other parts will rush to the reciprocating folds. However, the antistatic agents, lubricants added during spinning and weaving, and the leveling agents and detergents added during dyeing post-processing will still have a small amount of residue in the fabric and the free water carried by the fabric, and most of these additives are Nonionic additives. Similar to the principle of dye migration, when free water flows to the reciprocating folds that are first evaporated and air-dried, the residual additives dissolved in the free water also flow to the reciprocating folds. As the water evaporates further, the concentration of additives at the reciprocating folds is bound to be much greater than in other parts.
If the fabric can be dehydrated, opened, and shaped in time after coming out of the vat, it will generally not produce wind marks. If left for a period of time (about 30 hours) before shaping, it is easy to produce wind marks. In order to fundamentally solve the problem of wind marks, we must start from the mechanism of wind marks and reduce the factors that cause wind marks to a minimum.
It is found that there are wind marks after setting, and the high concentration of additives or OH-ions in the reciprocating folds of the remaining unshaped fabric are only physically adsorbed on the fiber surface and cannot be dissolved without high-temperature setting aids. For dyes in the fiber region, OH- ions cannot enter the amorphous region of the fiber to react with disperse dyes. Therefore, after water washing or pickling, the high concentration of additives and OH-ion ions in the reciprocating folds have been diluted, and re-shaping in time can avoid wind marks.
The specific methods to solve the wind mark are as follows:
1. Try to strengthen the washing process after dyeing to reduce the residual amount of additives.
2. Arrange the process reasonably, and give priority to styling after dyeing for colors and varieties that are prone to wind marks. The time should not exceed 3 hours.
3. If it cannot be transferred to the shaping stage in time, it can be wrapped with plastic film or dried and placed.
Editor’s note:
For a long time, the problem of wind marks is almost likely to occur in many printing and dyeing manufacturers and has always been a problem for printing and dyeing. The industry believes that it is something that comes and goes without a trace, and it is also a headache that has always plagued printing and dyeing manufacturers in terms of product quality. In fact, in the production process, many problems can be avoided by being more careful and taking more responsibility. </p
