There are many and complex factors that cause color difference in dyed finished fabrics. To strictly control the color difference within the standard range and keep it stable for a long time, all aspects of the production and processing process are involved, and various elements and influencing factors must be comprehensively analyzed. Analyze, formulate corresponding preventive measures, strictly standardize implementation methods, and control the color difference of dyed fabrics.
Based on production practice, the following briefly analyzes the causes of these four types of color differences, and proposes prevention and control measures.
1 The main factors causing color difference
1. Pre-treatment
With the advancement and development of printing and dyeing production and processing technology, the processing capacity, processing quality and processing effect of pre-treatment have an increasingly prominent impact on the quality of printing and dyeing finished products. Industry experts believe that about 70% of product quality should be controlled in the pre-processing process.
1.1 Semi-finished products have uneven desizing and impurity removal and are not clean
After the fabric has been scoured and bleached, the pigment has been removed. It is difficult to detect the quality problems of uneven desizing and impurity removal and uncleanness from the fabric surface alone. Using this kind of semi-finished product to produce bleached and light-colored varieties is prone to problems such as yellowing, discoloration, unstable hue (wilting, darkening), and poor brightness. In addition, it will also affect the mercerization and dyeing effects of the fabric, causing the surface of the fabric to be damaged. Defects such as mercerization and dyed white core.
When mercerizing, if the fabric comes out of the first concentrated alkali tank of the mercerizing machine and before entering the first rolling point, if there are spots on the cloth, it means that the fabric absorbs alkali unevenly during mercerization. This is The desizing and impurity removal of semi-finished products are uneven and unclean. When such semi-finished products are pad-dyed in the base machine, uneven color absorption may occur.
1.2 Semi-finished product wool effect and whiteness
What we usually emphasize The good pre-treatment effect of semi-finished fabrics is not just about desizing and removing impurities, high wool efficiency and good whiteness, but also emphasizing “evenness”, that is, the consistency and stability of the quality of semi-finished products.
During the pre-processing process, fluctuations in equipment status, process conditions, parameters and other factors will affect the quality consistency of semi-finished fabrics. For example, if the pressure difference between the left and right sides of the water washing pad is large or the roller concavity is serious, the washing effect on both sides and the middle of the fabric will be greatly different. During dyeing, the fabric’s wool effect and whiteness will be inconsistent, resulting in color differences between the left, middle and right sides of the fabric. .
Similarly, the left and right pressure difference or concave center of the padding car will cause inconsistent padding rates on both sides and in the middle of the fabric, causing color difference in the fabric after dyeing.
In addition, the unstable addition of chemicals and auxiliaries, the high and low washing temperature, and the high and slow speed of the machine will lead to inconsistent roughness and whiteness of the pre-processed semi-finished products, thereby causing the fabric to be inconsistent. Color difference before and after. Especially dyes with high substantivity, such as reactive, indicosin, naftol and other dyes, can easily produce color differences. Even reducing suspensions and disperse dyes that are not very direct will have obvious color differences. . This is mainly because semi-finished products with high wool efficiency have better hygroscopicity, higher dye uptake rate and darker color; conversely, semi-finished products with low wool efficiency have poor hygroscopicity, low dye uptake rate and light color yield, resulting in poor dyeing of fabrics during dyeing. uniform. It needs to be emphasized that the inconsistent whiteness of semi-finished products to be dyed will also have a great impact on the shade of the fabric, especially when producing bleached and light-colored dyeing varieties.
1.3 Semi-finished product mercerization process
Mercerization effect on cotton fiber dyeing rate has a greater impact.
The instability of mercerizing process conditions and parameters has a very obvious impact on fabric dyeing, such as large fluctuations in the concentration of alkali solution in the concentrated alkali tank, and sudden and sudden changes in vehicle speed during production and processing. If it is too slow, it will affect the mercerization effect of cotton fibers and cause color difference in fabric dyeing.
In addition, the unstable pH value of mercerized fabrics, that is, poor or unstable de-alkali removal and washing effects of mercerized fabrics, will also have a negative impact on fabric dyeing. Especially when producing polyester-cotton dyed fabrics and dyeing with dyes that are sensitive to alkali, the pH value is too high or unstable, which will cause the color of the fabric to change greatly after dyeing, resulting in dull color, unstable hue, and poor brightness. Make the fabric produce the original color difference.
2. Dyeing
The dyeing process is the dyeing and finishing process of fabrics. One of the key processes is also the process where the color difference of the fabric is concentrated. This process has many factors that affect the color difference of the fabric and is also complex. According to production practice, it can be roughly divided into four main influencing factors: dye performance, dye liquor preparation, process conditions and equipment performance.
2.1 Dye properties
Some dyes have thermal denaturation, that is, high temperature Will cause discoloration or shade change of dyed fabrics. Reactive dyes and Shilin dyes are more obviously denatured by heat, and it takes a long time to return to normal color light. Some dyes may even take more than ten hours or longer. For example, general green dyes emit blue light when heated and yellow light when cooled; while Shilinlian IR emits red light when heated and blue light when cooled. This will cause the fabric to become stained after dyeing.When brushing the car, it is necessary to clean the dust-proof screens of the left and right heating plates in time to ensure that the dust-proof screens are clean so as not to affect the air volume of the left and right circulating fans.
In addition, during the high-temperature hot-melt dyeing process of polyester-cotton blended fabrics, the temperature difference between the edges in the hot-melt box will also cause color differences in the edges of the fabric. When the hot melt dyeing machine is empty, the hot air nozzle sprays air evenly inward. Whether it is a pre-drying oven or a hot melt box, the middle temperature is generally higher than the temperature on both sides. The reason is that the two walls of the box and the two ends of the guide roller have heat dissipation in the air. When the dyeing and priming machine is operating normally, because the wet cloth enters the pre-drying oven, it consumes a lot of heat. The hot air exchange on both sides is fast, and the fabric is easy to dry. Therefore, the temperature of the entire box will become high on both sides and low in the middle. While the hot-melt dyeing machine feeds dry cloth, the temperature of the baking oven is the opposite. Dry cloth consumes less heat, so the temperature of the entire box remains higher in the middle than on both sides. Some equipment due to symmetry If it is not enough, or the cloth feeding deviation is large, there will be color difference between the left, middle and right.
The temperature difference between the left, middle and right parts of the hot melt box will lead to inconsistent fixation rates and sublimation degrees of disperse dyes or reactive dyes on the cloth. If the fabric contains a lot of impurities or has a large amount of alkali, there will be different degrees of yellowing on the left, middle, and right sides, resulting in color difference in single-color varieties; in multi-color varieties, if the heat sensitivities of the dyes are different, the fabric will also appear on the left. The center and right have different hues. Therefore, the color difference problem can be solved only by completely eliminating the temperature difference in the box.
In terms of technology, dyes with flat hot melt curves can be used, because under the same dyeing processing conditions, the dye properties are different, showing color difference in the edge or left, center and right color difference. is different. For example, after dyeing with Disperse Red 3B, color differences between edge depth, medium and light color often occur. Low-temperature disperse dyes can be fixed at lower temperatures, but high temperatures will cause sublimation of the dye, affecting the dye fixation and causing color differences in the edges. The color fixation of high-temperature disperse dyes requires a higher temperature. If the temperature is not reached, the fixation of the dye will be affected and the color will be lighter. Therefore, the dyeing of high-temperature disperse dyes often shows differences between light edges, medium colors and dark colors.
The color difference caused by inconsistent baking temperatures is generally more obvious for high-temperature disperse dyes than for lower-temperature disperse dyes. This is mainly because the hot solution solid color curve of the former is mostly not very flat. More sensitive to temperature.
The width of the product during production should be lower than the width of the air nozzle, so that there is sufficient space on both sides of the baking chamber and the hot air can circulate more in the baking chamber. and room for mixing. In addition, a movable valve can be installed on the equipment to adjust the air inlet volume in the middle; or the middle 60cm of the air nozzle can be blocked to reduce the middle temperature. Through the above measures, the left, center and right color difference of the fabric can be effectively solved.
4. Prevention and control of color difference between front and back sides
Front and back sides Color difference is more obvious when dyeing plain weave fabrics. The main reason for the color difference between the front and back is that the front and back sides of the fabric are heated inconsistently during the dyeing and finishing process. This is generally caused by dye migration or dye fixation during the drying process. Therefore, to solve this kind of color difference, you can install an infrared pre-drying device on the base machine, check the distance between the air nozzle in the pre-drying room and the cloth surface, and control the air volume of the fan in the pre-drying room.
Color difference is a quality problem that often occurs in fabric dyeing and finishing. Corresponding measures need to be taken continuously and according to different situations over a long period of time. Since color difference occurs during production and processing, various factors should be comprehensively analyzed and effective prevention and control measures should be formulated based on the conditions at the production site to achieve better results. </p
