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What should we pay attention to when checking the color after dyeing?

Date:Nov 11, 2020

What should we pay attention to when checking the color after dyeing?


1. Causes of color deviation

1.1. Different batches of pre-treated semi-finished fabrics have differences in fiber properties, whiteness and wool effect, which cause color deviation of dyed fabrics.

1.2. There are differences between the dyestuffs of different manufacturers or different batches of the same manufacturer, causing color difference.

1.3. Improper selection of color matching dyes, failure to follow the principle of same color matching, close color matching, and less color matching. The dyeing synchronization is poor, which reduces the reproducibility of color and causes the deviation of dyeing shade.

1.4. Improper control of dyeing process conditions is the main cause of color deviation.

①Dyeing temperature is a key factor affecting shade. For example, reactive dyes are very sensitive to dyeing temperature. For example, when the dyeing temperature is too high, the equilibrium dyeing percentage of X-GN and X-BR will increase relative to other dyes, X-3B, X -2B is relatively reduced, so that the color light deviation occurs. 

②The fluctuation of pH value of the dyeing bath mainly affects the fixation rate of reactive dyes, and the shade of some disperse dyes containing ester groups, amide groups, cyano groups, etc. during high temperature dyeing.

③The fluctuation of bath ratio in dip dyeing affects the reproducibility of shade. The dyeing with reactive dyes is more obvious. Generally, the smaller the bath ratio, the higher the color yield.

④The effect of post-dyeing treatment: After the fabric is dyed, peracid oxidation, soaping, whitening, resin finishing and other processes have an impact on the shade of the dyed fabric. In addition, the storage time of dyes and auxiliaries is too long, or they are affected by water vapor, acidity and alkalinity in the air, and oxidizing and reducing gases. It is worthwhile to cause color difference in dyeing; weighing errors, dyeing utensils, poor pipeline cleaning, etc. It will also cause a certain color difference. When the shade of the dyed fabric does not meet the requirements, the shade needs to be repaired to improve product quality and reduce production costs. There are two main types of shading restoration methods, non-dye shading restoration and dye overdyeing restoration.


2. Non-dye shade restoration methods are easy to operate, low cost, and good quality.

① Wash with water. This method is suitable for dyeing fabrics with slightly darker shades, more floating colors and poor water and soaping fastness. It is the easiest way to repair. The floating color can be removed by washing with water to achieve the purpose of correcting the seemingly light shade. Whether this method can be applied, it is generally necessary to check whether the soaping fastness in the physical test and the color change after soaping in the physical test conform to the color correction direction before the color repair. If they do, this method can be used. In addition, grasp the characteristics of individual dyes' color change during washing and soaping, which can be used in color correction. For example: when reactive yellow and blue dyes are combined with green dyes, the reactive turquoise blue KNG and reactive turquoise blue KGL soaps are easy to fade after being boiled. The color deviation after dyeing can be washed with water to improve the yellow light of the finished fabric. It can achieve the purpose of color repair.

②Alkaline water washing. This method is suitable for dyes that are sensitive to alkali for shade restoration. More reactive dyes can be applied. For example, dyed cloth with reactive black KN-B color matching, such as blue shade, can be washed flat by rolling an appropriate amount of caustic soda. The method achieves the purpose of repairing the blue light and changing the light level. Not all stains can be repaired with this method. For those dyed fabrics that are dark in color, faint in color, or not in compliance with the standard sample after being changed to light, only over-dyeing, stripping and re-dyeing, and changing to darker colors can be used for repair.

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two. When applying this type of method to repair the dye overprinting, the process of simple operation, low cost and good quality should be selected as far as possible.


① When the color of the dyed cloth sample is too light, but the hue is basically the same, the original prescription can be used, and the dosage of the prescription can be determined according to the number of light colors. And use the original process for color registration.


②The color light is less, and the direct dye process can be used for color registration.


③When the shade depth is close, but the hue is wrong, the principle of what is missing is used.


④The shade is darker, but within the repairable color range, the color should be stripped first and then over-dyed for repair. Examples of common stripping processes and processes are as follows: Sulfur dye dyeing fabrics can achieve satisfactory results through the sodium hypochlorite method, and reactive dyes dyeing fabrics can be stripped using the safe value method or sodium chlorate method, but the sodium cyanide dyes such as phthalocyanine Blue KN-G peeling is not satisfactory. If you use two methods one after another, you can achieve satisfactory results. The two methods are as follows:


①Solsing powder method: Singoling powder 5g/L, caustic soda (360Cbe’) 15Ml/L, bath ratio 1:20~30, temperature T=40~900C, time input=40min.


②Sodium hypochlorite method: effective chlorine 5g/L, pH value 11, bath ratio 1:20~30, temperature T=room temperature, time input=30min, and then two water washing-pickling (acetic acid) dechlorination.


③For the deep shade and cannot be repaired, only dark color can be changed.

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3. precautions for shade repair


3.1. When repairing with direct dyes, the dosage should generally be controlled below 1g/L, so as not to affect the dye fastness of the finished fabric after repairing.


3.2. When reworking the shade, not only consider that the color meets the standard sample, but also pay attention to the strength, width, color brightness and color fastness of the fabric after the refurbishment to meet the standards.