01 Reasons for color deviation
1. Different batches of pre-processed semi-finished fabrics, Due to differences in fiber performance, whiteness, wool effect, etc., color and light deviations of dyed fabrics are caused.
2. There are differences between dyeing materials from different manufacturers or different batches of the same manufacturer, causing color differences.
3. Improper selection of color matching dyes and failure to follow the principles of same color matching, close color matching, and less color matching. The synchronization of dyeing is poor, which reduces the color reproducibility and causes dyeing shade deviation.
4. Improper control of dyeing process conditions is the main cause of color deviation.
① Dyeing temperature is a key factor that affects the color light. For example, reactive dyes are very sensitive to dyeing temperature. If the dyeing temperature is high, the balance of X-GN and X-BR will be affected. Compared with other dyes, the dyeing percentage is relatively increased, while X-3B and X-2B are relatively reduced, resulting in a deviation in the color light.
② Fluctuations in the pH value of the dye bath mainly affect the fixation rate of reactive dyes, and the color light of some disperse dyes containing ester groups, amide groups, cyano groups, etc. when dyed at high temperatures.
③The fluctuation of liquor ratio in dip dyeing affects the reproducibility of color and light. Reactive dye dyeing is more obvious. Generally, the smaller the liquor ratio, the higher the color yield.
④Influence of post-dyeing treatment: The processes such as peracid oxidation, soaping, whitening, and resin finishing after fabric dyeing have an impact on the color and light of dyed fabrics. In addition, the storage time of dyeing materials and auxiliaries for too long or being affected by water vapor, acidity and alkalinity, oxidation and reducing gases in the air may lead to color difference in dyeing; weighing errors, poor cleaning of dyeing equipment and pipes, etc. It will also cause a certain color difference.
When the shade of dyed fabrics does not meet the requirements, the shade needs to be repaired to improve product quality and reduce production costs. There are two main categories of shade restoration methods: non-dye shade restoration and dye overlay restoration.
02 Non-dye color light repair
This method is easy to operate, low in cost and good in quality.
1. Water washing is the simplest method for repairing dyed fabrics that are slightly darker in color, have more floating colors, and have poor water and soap washing fastness. Floating colors can be removed by washing with water to achieve the purpose of correcting the seemingly light color.
To determine whether this method is applicable, you should generally check whether the soaping fastness in the physical test and the color change after soaping are consistent with the color correction direction before color correction. If they are consistent, this method can be used.
In addition, master the color change characteristics of individual dyes during washing and soaping, which can be used in color correction. For example: when reactive yellow and blue dyes are mixed with green dyes, in view of the characteristics of reactive emerald blue KNG and reactive emerald blue KGL that are easy to fade when washed and soaped, the color light deviation after green dyeing can be improved by water washing to improve the yellow light of the dyed finished fabric. The purpose of color correction can be achieved.
2. Alkaline washing. This method is suitable for alkali-sensitive dyes to be used for repair of chromatic light. More reactive dyes can be used, such as dyeing cloth with reactive black KN-B color matching such as chromatic light. If it is bluish, you can use an appropriate amount of caustic soda to wash it flat to achieve the purpose of removing the blue light and making it lighter.
Not all stains can be repaired using this method. For those dyed fabrics that are dark in color, dull in color or still do not meet the standard after being lightened, they can only be repaired by over-dying, stripping and re-dying, or changing to a darker color.
03 Dye registration and back-dye repair
When applying this method for repair, you should try to choose a process that is easy to operate, low-cost, and of good quality.
① When the dyed cloth sample is much lighter in color, 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 lightness ratio. And use the original process for color registration.
② There are fewer light shades, so you can use the direct dye process for color registration. ③When the color depth is close but the hue is wrong, use the principle of matching what is missing. ④ If the shade is darker, but within the color correction range, the color should be stripped first and then overdyed and repaired.
Examples of common stripping processes and techniques are as follows:
Sulfur dye dyeing fabrics can achieve satisfactory results through the sodium hypochlorite method, while reactive dye dyeing fabrics can use the insurance value method or the sodium chlorate method. Stripping, but the insurance powder method is not very satisfactory for stripping phthalocyanine structural dyes such as turquoise blue KN-G. If you use two methods one after another, you can achieve satisfactory results. The two methods are as follows:
①Insulin method: 5g/L insulating powder, 15Ml/L caustic soda (360Cbe’), liquor ratio 1:20~30, temperature T=40~900C, time = 40min.
②Sodium hypochlorite method: available chlorine 5g/L, pH value 11, liquor ratio 1:20~30, temperature T = room temperature, time = 30min, then secondary water washing – pickling (acetic acid) Dechlorination.
③If the color is dark and cannot be repaired, it can only be changed to a darker color.
04 Precautions for color light repair
1. When using direct dye for repair, the dosage should generally be controlled below 1g/L to avoid affecting the return. The dye fastness of the finished fabric after repair.
2. When repairing the color, you should not only consider that the color conforms to the standard sample, but also pay attention to the strength, width, brightness of the color and dye fastness of the fabric after repair, which must all meet the standards.
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