1 Defect form
The color of the dyed cloth must be produced according to the color number or sample specified by the customer. However, in actual production, sometimes the color of the dyed finished product does not match the specified standard color and exceeds the allowable color difference standard. The defect of color not conforming to the standard is essentially a defect of color difference. But the difference from the aforementioned color difference is that the former does not necessarily need to be compared with the dyeing standard sample to identify color difference defects. You can see whether there are different shades of color on the same cloth by directly looking at the cloth surface of the dyed product, and whether there are different shades of color on the same cloth. The identification of defects that do not match the color and luster of the standard sample must be compared with the dyeing standard sample. The color and luster on the dyed cloth may be uniform, but the shade and color depth are different from the standard sample.
The manifestations of color that does not conform to the standard sample include:
(1) Does not match similar fabric samples (similar fabric samples refer to color samples in which the actual production sample and the original sample have the same fibers and the same structure).
(2) Does not conform to the reference sample (the reference sample refers to the color of different raw materials and different tissues).
(3) Does not conform to foreign samples (samples refer to fabric samples, pattern samples, designated color samples, and digital samples of the measurement and matching system).
(4) Does not conform to the transaction sample (the transaction sample refers to the dyeing sample cards and pattern samples provided in China and confirmed by both parties during the foreign trade transaction).
2 Causes
(1) The dyeing prescription and process are improperly formulated. Before dyeing products are put into production, they must undergo color matching and make samples. But in fact, the actual conditions of the sample and the dyeing production are different, and the dyed colors are generally different. Therefore, this requires dyeing workers to understand and master the gap and relationship between the color matching sample and the actual dyeing production, correctly use the information and data obtained from the color matching sample, analyze and process it, and formulate a more realistic and reasonable solution. Dyeing recipes and processes. If not mastered properly and adjusted many times during dyeing production, the color of the dyed cloth produced will inevitably be inconsistent with the standard sample.
(2) Color identification of light sources is not uniform. At present, most color discrimination light sources in printing and dyeing factories use natural light (northern daylight) and ordinary fluorescent lamps. The disadvantages of the above light sources in color discrimination are:
a) Natural light is susceptible to differences due to weather changes;
b) Ordinary fluorescent lamps are quite different from natural light, and the color is generally reddish. Therefore, the color effect of the same piece of dyed cloth when viewed under different light sources is different. Dyeing standards and dyeing fabrics are often different due to the dyeing fiber raw materials, fabric structure, and dyeing materials used. As a result, the color is basically similar when viewed under a certain light source, while the color is basically similar when viewed under another light source. , the gap between the two is quite large.
For example, light jade and light orange dyed at night tend to have a reddish color when viewed during the day, causing the color to be inconsistent with the standard, resulting in certain color positions being “annihilated” and having to be re-dyed; another example is polyester-cotton blended fabrics. Fabrics are dyed with two colors (cotton and polyester fibers have different hues). As a result, certain colors obtained under ordinary fluorescent lamps and under natural light during the day are completely different, and the dyed fabric does not conform to the standard sample.
(3) The dyeing production plan is not well arranged. The dyeing production plan is not arranged in order from light to dark, and there is no transitional color arrangement when changing colors with large hue differences. The cleaning work when changing colors is not done well, resulting in contamination of the dye solution and the dyeing color will not meet the standard sample. .
(4) Improper batch management of dyes and auxiliaries. Dyeing production has relatively high requirements on the color and light of the dyes used. If any dye with a different color and light is mixed in, the color of the dyed cloth will not match the standard sample. When dye factories manufacture dyes, due to the differences in raw materials, textures, synthesis process routes, and uneven control of process conditions, the color and lightness of dyes with the same product name produced by different origins and factories may vary. Differences. Even dyes with different production batch numbers from the same place of origin, the same factory, and the same product name will have differences in color and light. If a dyeing factory mixes materials and uses them regardless of origin or batch, the dyed color will definitely not match the standard sample. A similar situation exists for additives.
(5) The dyeing process conditions and operations are not well controlled. The situations where the color does not match the standard sample due to this reason are roughly as follows:
a) The semi-finished product before dyeing does not meet the requirements. If the dyed semi-finished product has insufficient mercerization, the mercerization will contain alkali, causing the color to change. For example, after dyeing with sulfide, the cloth surface will be reddish but not black.
b) Use hard water for dyeing. Dyes that are sensitive to hard water can easily cause dyeing defects. For example, Direct Pink 12B, Direct Lightfast Blue RGL, etc. will become lighter in color when exposed to hard water and do not match the color standard.
c) Improper management during dyeing affects the dyeing effect. For example, when dyeing with insoluble azo dyes, the semi-finished fabric does not develop color immediately after priming. If it is left for too long, the color phenol on the priming fabric will be decomposed by the influence of air, causing the color to become lighter.
d) The dyeing materials were weighed incorrectly, the dosage was inaccurate, and the dyeing process was not discovered in time, so the dyed color did not match the standard sample.
e) The process conditions must be strictly controlled during the dyeing process. If the process conditions are not well controlled, such as temperature, humidity, concentration, pressure pH, vehicle speed, and drying conditions that are unstable and fluctuate, the color of the product will be affected.
3 ways to overcome
(1) Explore the rules and sum up experience. We should pay attention to exploring and summarizing the rules and experiences between the color matching samples and the actual production of large samples, and strive to ensure that the dyeing is successful the first time. ��To ensure the rationality of large-scale production processes, the following points must be achieved:
a) The tissue specifications of the large and small fabrics should be the same, and the process conditions of the semi-finished products before dyeing should be consistent. It is better to use the same batch of semi-finished products.
b) During pad dyeing, the padding car for making small samples should control a certain pressure. The pressure of the large padding car and the small padding car should be relatively fixed and should not be changed arbitrarily, so that the large and small samples can be easily consistent. The liquor ratio should be kept consistent during dip dyeing.
c) The title, color name, suffix and batch number of the dye used when making small samples must be the same as those used in large-scale production, as well as the additives used. The conditions for dyeing small samples should be consistent with those of large samples.
d) When color matching, the main color dye should be relatively fixed, and the dye should be used to adjust the color and light for proofing, so as to facilitate the consistency of color and light for large and small samples.
e) After the small sample is tested, the influence of the dye’s affinity and adhesion to the fiber on the color difference between the small sample and the large sample must also be considered. Since the pad dyeing of the sample is discontinuous and the residual dye liquor is not reused, the impact on the affinity is minimal. The pad dyeing of large samples is continuous, and the pad dyeing liquid and pad residual liquid are continuously reused. If the affinity of the dye to the fiber is relatively large, such as indicol, vat dye leuco body, direct, reactive, and nanof If the dyes are properly equalized, the dye concentration of the pad bath dye solution taken away from the fabric during pad dyeing will be greater than the dye concentration of the remaining dye solution in the pad bath. If the replenishing solution is insufficient, the concentration of the pad bath dye solution will become lighter as the fabric is pad-dyed. The concentration of the dye taken away from the dye liquor will also gradually decrease until the reduction in the concentration of the padding solution reaches a balance with the concentration of the replenishing solution. However, this has caused a large number of differences in the color of the fabric.
Therefore, in actual production, it is necessary to calculate the difference in the amount of each dye used in the large sample and small sample prescriptions of the machine based on the actual conditions of each machine, so as to calculate the amount of each dye used in the large sample production of this machine and this process condition. Only the percentage difference in dye usage. The small sample prescription plus (or minus) the difference percentage of the dye is the large sample prescription. In this way, the dye concentration of the pad bath dye solution can be kept in a balanced state from the beginning to the end, and the color difference between the color matching sample and the large sample can be basically consistent.
(2) Dyes need to be screened. Dyes that are prone to discoloration during the dyeing process are generally not used. If it must be used, corresponding measures must be taken after understanding and mastering the properties of the dye. For example, when soluble vat dyes are used to dye polyester-cotton blended fabrics, the discoloration of such dyes at high temperatures must be considered. Some acid dyes will change color at a certain temperature, such as weak acid black GR, which will change color when the temperature is higher than 96°C. All fabrics that require ironing fastness must go through a high-temperature heat drawing process after dyeing. When color matching, consider using dyes that do not change color at high temperatures. Otherwise, the dye will change color and the color will not match the standard sample.
(3) Use a daylight-like color discrimination standard light source. The entire process of dyeing production, including color matching sampling, mass production, and inspection of dyed finished products, is conducted under a unified imitation daylight light source to greatly reduce the difficulties in color identification caused by different light sources and ensure that the color of the dyed products conforms to the standard sample. Generally, it is ideal to use a standard light source box, and computer color measuring instruments can be used if conditions permit.
(4) Arrange the dyeing production plan reasonably. When dyeing small batches and multi-color positions, in order to reduce the parking time for wiping and cleaning and avoid the shortcomings of frequent wiping that easily causes wrinkles in the fabric, we can improve production efficiency and avoid cross-color stains that may cause non-compliance with standards. For this purpose, the color positions that need to be produced in the near future should be divided into two categories: light, medium color and dark variegated color. The production schedule of each category should be arranged in order from light to dark color spectrum. The transition from red to yellow must be from orange, from yellow to blue must be from green; from blue to red must be the transition from green lotus. If there is no transition color, the car must be wiped or the dye vat must be cleaned, and the cleaning work must be done. If dip dyeing uses intermittent equipment, sometimes different color positions can be fixed relatively to the machine to prevent color difference.
(5) Strengthen the management of batch numbers of dyes and auxiliaries. Dyes of the same color and from different origins should be stacked separately; dyes of the same color and origin from the same manufacturer but with different batch numbers should also be stacked separately. It is best to use the same batch of dyes when dyeing the same batch of cloth. In principle, do not use dyes with different batch numbers to avoid color differences. The management of auxiliaries should also adopt the same management methods as dyes.
(6) Strict process discipline. Carefully carry out the three-level inspection of process onboard vehicles (self-inspection by stopper, spot inspection in section workshop and factory). Master the dyeing process conditions and ensure that the dyeing process is carried out according to the process. It is necessary to carefully implement the system of sample checking and pasting for each truck by fabric workers, so as to facilitate inspection and verification, solve problems in a timely manner, and ensure that the color of dyed products conforms to the standard sample.
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