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Denim Fabric Shade Variation
Sample development and bulk production is totally different as sample is developed with very short quantity. But in case of bulk production as the order quantity increased quality variation intensity also increased due to some technical limitation and some uncontrollable limitation. Every retailer tries to provide best quality product to customer by maintaining proper required quality system. From the entire quality visual shade match is one of the major issues. In case of bulk production shade variation is common problem for both knit and woven fabric.
Open Bath Slasher Dyeing Close Bath Knit Dyeing
The common factor for both knit & woven fabric shade variation is tone variation of lot to lot dyes chemical. There are some common technical issues also like water hardness controlling; proper natural impurities removal by scouring and bleaching; material and liquor ratio; dyes, chemical and water ratio; maintaining proper timing and temperature. But for woven fabric there are some different issues for shading. Because woven fabric dyeing proceeds in open bath dyeing machine and knit dyeing proceeds in close bath dyeing machine. As a result room temperature, humidity affects woven fabric shade what changes simultaneously from morning to noon to evening to night and season to season. Besides this, maximum dyeing machine is developed with dosing system rather developing with injecting system. Dosing is consecutive process and injecting is continuous process. As a result in continuous process of woven dyeing material and liquor ratio varies frequently. What causes running shading on fabric. For improper mixing and temperature maintaining there is also coagulation of dyes chemical causes side to side or side to centre shading. In woven dyeing there is no way to proceed striping or topping to achieve required shade. In following writing why sulphur dye or vat dye is used in denim slasher or rope dyeing and reason of its shade variation, is discussed.
Denim dyeing basically proceeds with Vat dye and sulphur dyes for their outstanding wash effect on final garments.
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Oxidation in Indigo (Vat) Dyeing
Vat dye is water insoluble dye. Dyes are dissolved in water in presence of reducing agent in dye bath. In this process yarn passes through dye bath and absorbs dyes, chemical and oxidizing agent. In the presence of oxidizing agent yarn surface is oxidized in air. As a result gradual color change of yarn from right to left (as per figure) is visible in air. But dyes don’t penetrate inside the yarn. As a result how much the depth of indigo color on fabric, inside the yarn it remains white. For that reason it brings huge wash range in washing effect by different wash process.
Oxidation in Sulphur Dyeing
Sulphur dye is water insoluble dye with big molecular bond. In the presence of reducing agent this bond gets broken and dissolved in water. In dyeing bath yarn picks dyes chemical and gets oxidized in air by treating with Per Oxide (H2O2) in further bath. After getting oxidized dyes molecules get back to insoluble big molecular structure and can’t penetrate in yarn in huge range as other dyes can. As a result in garments washing this also brings huge wash range.
In both vat dyeing and sulphur dyeing yarn has to be oxidized in air. As oxidizing is proceeded in air, there is huge scope of shade variation for room temperature and moisture content variation from morning to noon to evening to night and season to season. Besides this, warping speed variation is also another considering factor. This can be maintained by standardizing article wise machine speed. But maintaining room temperature and moisture content is out of control. But where there is limitation there is scope of new innovation of technology by research. Now this is to achieve conditioning room temperature and moisture content in dyeing floor to avoid shade variation issue as this can be maintained in lab.
