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Discussion on color difference control of dyeing
Dec 04, 2018

First, the pretreatment of the grey fabric

 

   The pre-treatment of the grey cloth is very important, the pre-treatment is well controlled, and the dyeing is completed halfway successfully, so we need to align the grey cloth with the large-produced grey cloth. Nowadays, many proofing fabrics are generally refined on small prototypes. The pre-treatment effect is often different from the large production results, which will affect the accuracy of proofing. Especially nowadays, many fabrics have to undergo pre-shrinking, predetermined type, and alkali reduction. When pre-treatment, the temperature of the predetermined type and the amount of alkali reduction directly affect the depth of the dyeing. The same formula, the higher the alkali rate, the lighter the color. The proofer should use the large amount of raw cloth with a good amount of alkali in the workshop to re-sample the previous formula, which should be paid attention to in actual production.

Second, the dye selection must be appropriate

 

    Through careful review of customer samples, we can understand the fiber composition, color fastness grade requirements, color light source, appearance quality requirements and post-processing requirements (such as coating, white coating, silver coating, bright PU). , oil surface calendering, etc.) to select the most suitable dye. The principle of dye selection is to use dyes with high one-time success rate and low cost as much as possible on the basis of satisfying customer requirements.

 

1. Different fibers are dyed with different dyes. Generally, polyester fabrics are dyed with disperse dyes, nylon fabrics are dyed with acid dyes, cotton fabrics are dyed with reactive dyes or direct dyes, etc., so we must understand before proofing. The fiber composition is sampled to select the most reasonable dye.

 

2. There is an implementation standard for dye fastness. Each country has its own standards: GB is the Chinese national standard, ISO is the international organization standard, CEN is the European Standardization Committee standard, AATCC is the American chemist and dyer association standard, ATTS It is the standard of the Japan Fiber Products Technology Association. Different standards have different detection methods and representation methods, and the results are naturally different, even larger. Therefore, the customer's fastness standards and grade requirements must be clear and clear. We need to choose different dyes according to different fastness requirements. When customers ask for sun exposure, we use high-sun dye combination. When customers require high-washing, we use high-wash dye combination.

3. Consider whether the color is different: choose a formula for a jumper, the color will be different under different light sources or different time periods, the customer is difficult to confirm, so we have to choose to synchronize with the customer as it is to meet the customer's requirements. The color formula is the best.

 

  4. The dye used in the laboratory to test the sample must be consistent with the dye used in the production of large samples in the workshop. The dye strength of each batch will be slightly different. If the dye is left for a long time, it will cause a change in weight. Therefore, the laboratory must use the dye used in the production to proof the sample to improve its accuracy. , reduce the difference in size.

 

  5. In terms of color matching, light colors such as light gray, light apricot, khaki, etc., mostly use light-colored three primary colors for color matching, while dark colors mostly use the same color as the customer's closest color, and then use other colors. The dye adjusts the shade. In order to reduce the deviation of color and light in large sample production, dyes with similar dyeing rates and good compatibility should be selected for color matching. Moreover, the fewer the number of dyes used, the better, and the more the number of dyes, the greater the error.

6. For customers who require post-processing orders (such as coating, white coating, silver coating, bright PU, oil surface calendering, etc.), the post-processing should be carried out after the sample is applied, and then the color is applied. Otherwise, it is easy to return to the cylinder when the sample is placed. Color, affecting the success rate of stakeout.

 Third, the use of additives should be appropriate

 

It is well known that the addition of the most suitable dyeing auxiliaries in the dyebath can effectively improve the dyeing quality. For example, when dyeing a nylon fabric, adding 1-1.5 g/L of a nylon leveling agent to the dyebath can significantly improve the neutral dye or acid dye pair. The covering ability of nylon enamel prevents the generation of latitude and longitude. The leveling agent, acid, fixing agent and other additives used in the large sample production must also use the same additives. Because these additives, such as leveling agent, have an effect on the color light, so the simulation should be simulated simultaneously. The temperature, pressure and other conditions in the production of large samples, at the same time use leveling agent, and scale down, the amount should be the same to ensure the consistency of the sample and the large dye bath components.

 

It is worth noting that the amount of leveling agent should not be too much, because the leveling agent has the effect of leveling and dyeing during dyeing. When the leveling agent is used in an appropriate amount, the leveling agent inhibits the dyeing speed of the dye, so that the dye does not cause the coloring phenomenon due to excessive dyeing; however, if the leveling agent is used in an excessively large amount, the dye dyeing rate is lowered, so that the dyeing rate is lowered. The dye residue concentration is increased, the dye is wasted, and the cost is increased. In general, the leveling agent is used in a large amount when dyeing light color; when the color is dark, the leveling agent is used in a small amount. Each leveling is different in its concentration and composition, so it is necessary to determine the amount of each leveling agent based on actual experimental comparisons.

 

    Considering that the amount of sample is very small, it is easy to cause weighing error, so the auxiliary agent should be dissolved in advance to a standard solution with a concentration of 20g/L and then added.

 Fourth, the control of the operation process

 

     When producing large samples, select the appropriate dyeing method according to the type and color of the fabric. The production practice proves that the compatibility of the dyes and the reasonable formulation of the process are the prerequisites for the successful dyeing. Dye with non-rigid structure, dyeing performance is different, dyeing

 

The art should be adapted to the practical properties of the dye to achieve the best dyeing effect.

1. Dyeing temperature

 

     Dyeing temperature is one of the key factors affecting the dyeing results, whether it is to test the dyeing temperature in small samples or large cylinder production.

 

The system must be extraordinarily serious. Different dyes have different dyeing temperatures, such as disperse dyes for high temperature and high pressure dyeing, and acidity.

 

The dye should be colored 100 degrees, while the medium temperature reactive dye can be colored as long as 60 degrees, so we have to determine the different color temperature according to the different fiber components of the grey fabric. In addition, the temperature when the sample is used should be consistent with the temperature produced by the large cylinder. The dyeing temperature actually refers to the temperature of the dyeing solution. The temperature displayed on the meter and the large cylinder temperature meter sometimes cannot accurately reflect the actual dyeing temperature. Therefore, we need to perform regular temperature detection and correction on the small prototype and the large cylinder. The effect of the dyeing temperature on the dyeing result is fundamentally eliminated, so that the chromatic aberration between the large and small cylinders and the cylinder difference between the large cylinder and the cylinder can be effectively reduced.

 2. Dye bath pH

 

    The effect of the pH value of the dyeing bath on the dyeing result is sometimes greater than the influence of the dyeing temperature. Each dye has a pH range when dyeing, and the pH of the dyeing bath is controlled within the optimal range to make the dye fully color. Thereby achieving good reproducibility.

 

For example, the best fixing color PH value of medium-temperature reactive dyes is 10.5-11 (except for active Cuilan, which is 10.5-12). When disperse dyes are dyed with polyester, it must be carried out under weakly acidic conditions. -6 or so is the safest, the color is the most pure, the color is the deepest, the PH value is high, the safety factor is low, especially the dyes with poor alkali stability, such as: the dispersion of bauxite 200% deep blue HGL, Deshida XF Navy, etc., but when the dye bath is too low <4, many dyes will also have a tendency to be shallow and dark.

 

    On-site inspection found that the pH value of the residual liquid after dyeing is the basis for detecting and controlling the PH value of the dye bath, which is safer and more

 

reliable. This is because the pH of the residual liquid is different after the dye bath is not dyed. The factors that cause the pH of the dye bath to move, mainly

 

There are three: (1) The dyeing water is alkaline: the river water in many areas is alkaline water, that is, the pH value is close to neutral before heat treatment.

 

After cooling by heat treatment at 100 ° C or higher, it becomes alkaline. (2) Semi-products to be dyed with alkali: Generally, the raw fabrics must be pre-alkaline before being dyed, and the alkali chemicals in the fabrics are difficult to remove even after neutralization. Therefore, alkali release occurs during the dyeing process. (3) The pH value of the dye solution is unstable: the pH of different dyes is different at different concentrations. For example, the acid yellow M-2R has a pH of 7.8 at 2 g/L, and at 5 g/L. Its pH is 8.5.

The alkaline substances brought into the dye bath by the outside, when the pH buffering capacity of the dye bath is weak, the PH value of the dye bath will exceed the safe range set by the process, resulting in a significant decrease in the reproducibility of dyeing, rework and repair. The rate has risen significantly. Therefore, increasing the buffering capacity of the dye bath pH is a key point for stabilizing the dyeing quality. It must be pointed out here that the practical ratio and concentration of the PH buffer system determine the pH value of the dye bath and the buffering capacity, so it must be used correctly and must not be added at will. The pH regulator used in the lab's sample and large cylinder production must be unified, which is one of the main factors controlling the color difference.

3. Bath ratio control

 

  The bath ratio of the sample and the large cylinder must be uniform. For water-soluble dyes such as reactive dyes, acid dyes and direct dyes, since the dye will be hydrolyzed in water, the bath ratio is quite large, even if it is not water-soluble. Sexual disperse dyes, the effect of bath ratio is more obvious when playing dark samples. Therefore, before the sample is sampled, the bath ratio at the time of production of the large cylinder should be calculated according to the meter and the weight of the gray cloth that the customer has thrown. Then, according to the bath ratio, the solution amount of the dye and the auxiliary agent is first added according to the formula. Add up, calculate the amount of water that needs to be replenished, then take the water from the measuring cylinder, add it to the dyeing cup, reach the formula bath ratio, and then dye the proof. At present, most of our factories use automatic drip system. The instrument will automatically add the required water according to the amount of dye or auxiliary added to reach the set total bath volume. The precision is high, the error is small, and there is no operation between different operators. error.

 

When the bath is smaller than the design or the fabric area of the sample is large, the fabric is immersed in the dyeing liquid to be even enough, and it is easy to appear the coloring flower. Once the color flower is printed, it is difficult to formulate the dyeing formula, and the success rate of dyeing is decreased. , so as to ensure the uniformity of the sample,

 

Cut the sample into small pieces and add the dye cup to improve the proofing uniformity.

4. Heating rate and holding time

 

    The heating rate is preferably 1 to 2 ° C / min. If the speed is too fast, the temperature gradient in the cylinder will be too large, resulting in uneven dyeing on the dye, which will cause coloration; too low will affect production efficiency. The holding time is divided according to the color depth, the light color is generally kept for 30 minutes, and the medium dark color is generally kept for 45-60 minutes. After the completion of the heat preservation, the temperature is lowered to normal temperature, and the first water washing is performed after the dyeing, and the residual liquid remaining on the cloth surface and the floating color are sufficiently washed away. If the temperature rises and falls too fast, it will easily cause color flowers, and the symptoms such as sputum printing will directly affect the success rate from the face of repair. When holding a sample, the holding time should be the same as that of the workshop. The dyes with the best compatibility have different dyeing temperatures and time. The dyeing time will be slightly different after different holding time. For example, we use the most commonly used light. The three primary colors of 2BLN blue, E-GL yellow, and 3B red, the shorter the holding time, the worse the coloring of 3B red, so the uniformity of controlling the heating rate and holding time is also a key point to reduce the size and color difference.

 

    In addition to the above points, the degree of automation and accuracy of the dyeing and finishing equipment, the accuracy of the metering meter, the correctness of the proofing operation, the speed of the vehicle during the post-processing and setting, and the sample cloth The drying method, the color light source, etc. will cause color differences, so we must implement standardization and refined management, formulate detailed and perfect operating standards, strictly check the standardization operation, and continuously introduce advanced automation equipment (computer Color measurement and color matching system, automatic feeding system, small sample automatic dropping system, etc.) ensure that our first process is correct, to reduce the color difference between the size and sample, and improve the one-time success rate of dyeing.


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