What is textile sample dyeing in the dyeing lab? Based on the colour requirement and…
How Can You Stand the Color Difference of the Printing and Dyeing Cloth?
In textile printing and dyeing industry, the inspection of the color difference of textile fabric is a very important link in textile quality inspection, which not only is of considerable significance but also one of the main factors affecting the quality of the textile. Especially, the grade of color difference between the product produced in printing and dyeing mill and the standard sample is an important index of quality management.
However, most printing and dyeing mill didn’t use objective color detection methods to achieve accurate control, in the actual production process, the defective percentage is higher than expected out of human factors, resulting in numerous substandard products that fail to meet the requirements. The repairment of such products must be stripped several times before being dyed, which means a great deal of manpower, material and time costs. AS a result, that causes greater environment pollution, wean while loses customers’ trust because of product extension, thus bringing about even greater latent losses.
The color of dyed cloth shall be produced according to the color number or sample specified by the customers. However, in the actual production, the color of the finished product is sometimes inconsistent with the specified standard color and exceeds the allowable color difference standard. So the color difference defect is formed.
So, What are the Reasons for the Color Difference of Printing and Dyeing Cloth?
1 The improperiety of dyeing methods and production process. Before being put into production, there is required the color matching and hand samples to produce bulk samples. But in fact, the different production conditions of hand samples and dyeing result in some differences in dyeing.
2 The disunity of color vision light sources. At present, color-distinguishing light source adapted by most printing and dyeing mills is derived from natural light (northbound daylight) as well as Ordinary fluorescent lamp. The disadvantages of the above light sources in color vision are:
①. Natural light is susceptible to changes in weather.
②. Ordinary fluorescent lamp differs from natural light greatly, whose light generally turns reddish. Therefore, the color effect of the same dyed cloth under different light sources is different. The dyeing standard sample and the dyed cloth are also diverse because of the raw material of dyed fiber, the structure of the grey cloth and the dyeing material used. Rather the color of them are basically similar under one light source, but when observed under the other light source, their color varies a lot.
For example, light green and light orange color dyed at night look like red when watched during daytime, which suggests colors do not match the standard. The failure of color matching leads to the complete disuse of some color positions and had to be redyed; If polyester-cotton blended fabric is double dyed (cotton and polyester fibers are different in color), the colored light obtained under ordinary fluorescent lamp and natural light in daytime are quite different, using which the dyed cloth does not conform to the standard sample.
3 The improper arrangement of the dyeing production schedule. It is not well arranged in line with the order from light to deep, and when the colors with a great difference there lack a transitional color arrangement. What’s worse, the corresponding cleaning work fails to meet the requirements during transformation, which results in the contamination of dyeing solution and the inconformity of dyeing to the standard sample.
4 The poor management of dyes and auxiliaries in batches. Dyes used in dyeing production have a relatively high requirement provided that any dyes with a difference in colored light if mixing within dyes will lead to the inconformity of dyeing cloth color to the standard sample. Affected the differences of raw materials, texture, synthetic routing and the uncertainty of controlling process conditions, the colored light after being dyed of the same producr is diverse as the printing and dyeing mill is in the process of making dyes.
5 The disadvantages of dyeing process conditions and operation. As a result, the reason why the colors of products that do not conform to the standard samples are as follows:
①. The failure of the pre-dyeing products to meet the requirements. The insufficient alkalescent mercerization of these products makes the colored light change. For example, the cloth turns red but not black after being dyed in the use of sulfur black.
②. The improper management in the process of dyeing affecting the effect. For example, when dyed with insoluble azo dyes, the fabric based on the semi-finished product is not colored immediately. Since it is laid aside too long, which causes the color phenol on the backing cloth to be decomposed by the influence of air and become lighter.
③. The strict control of the process conditions in the dyeing process. When the process conditions are poorly mastered, for example, the instability of temperature, humidity, concentration, pressure, pH value, speed and drying conditions, the light of products will be injured.
Six Solutions for the Color Difference Suggested by the Old Master
1 It is necessary to explore and summarize the rules and experience between hand sample’s color matching and bulk samples to strive for achieving a successful dyeing one time. In order to ensure the rationality of large-scale production process, it is required for dyeing workers to understand and master the difference and the relationship between color matching and actual dyeing production, to correctly use the materials and data obtained by matching sample’s color, and to analyze and deal with them for the formulation of more realistic and reasonable dyeing prescription and process.
Take for instance, upon the confirmation of the hand samples, it is imperative to take into consideration the effect of the dye affinity on color difference. The samples used to adapt the discontinuous pad dyeing that makes the residual dye solution unusable, so there is little effect on affinity while the bulk samples use the continuous pad dyeing that allows the reuse of groove dye and its residual. For groove dyes with the large affinity to fibre like Indigosol, leuco vat dye, direct dye, reactive dye, and naphthol dye as well, their concentration will be reduced by fiber in the process of pad dyeing. If the supplement dye is insufficient, the dye concentration of groove dye will be weaker, resulting in the color difference of the fabric in a large amount.
Therefore, in the actual production, the variance of the amount of the dyes used for bulk and hand samples must be determined according to the actual conditions of each dyeing machine. The prescription of the hand samples plus (or minus) the variance of the dyes can tell that of the bulk samples. In this way, the concentration of groove dye always keeps balanced, thus promising the color matching of hand samples is basically consistent with that of bulk samples.
2 Dyes must be screened. Dyes that tend to cause discoloration in the dyeing process are generally not used. If must, it is necessary to adopt the corresponding measures on the basis of understanding and mastering the performance of dyes. For example, when the solubilized vat dye is used for dyeing polyester-cotton blended fabric, there is a must to consider its color change at high temperature. For fabrics that require fastness to ironing, they must stand a high-temperature and hot-expansion procedure after dyeing and consider dyes that do not change color at high temperature.
3 A standard light source for color vision imitating the sunlight is to be used. In order to significantly reduce the difficulty of color identification caused by various light sources, and to ensure that the color of dyed products conforms to the standard sample, the whole process of color matching of hand samples, mass production, and inspection of finished dyeing products should be carried out under the uniform sun-like light source. Generally, the standard color matching cabinet is rather ideal, and the computer color measuring instrument can be used if the conditions permit.
4 The dyeing production plan should be arranged reasonably. In small batch, multi-color dyeing, in order to reduce the parking time of cleaning car and avoid the frequent wrinkles of cloth brought by the car, and for the purpose of improving production efficiency and avoiding string solor and uncleanliness of colors, resulting in non-standard samples, the production phases shall be divided into two categories: light medium color and deep mottled color, each being arranged its own production schedule according to the order of light to deep color. The transition from red to yellow must be made from orange, from yellow to blue from green; from blue to red form purple. Provided that there is no transition color, the cleaning car and vats must be cleaned well. Batch type equipments are required in impregnation and dyeing. At times a machine is responsible for its fixed color positions so as to prevent color differences.
5 The management of dyes and the batch number of auxiliaries should be strengthened. Dyes with the same color but a different place of production should be stacked separately; Those with the same color, the same place of origin but the different batch number should also be so. The best is to dyeing the same batch of cloth with the same batch of dyes following the principle “do not use different batches of dyes” to avoid color differences. Auxiliaries should also be managed in the same way as dyes.
6 Process discipline should be strictly executed. Carefully control the process on the three-level inspection (spinner’s self-inspection, workshop and factory spot inspection). The dyeing process conditions must be controlled to ensure the implementation of the process. Paying careful attention to checking samples per machine by workers, the paste-like system for the convenience for the finding of problems in time and the conformity of the color of dyed products to the standard.
The dyeing and finishing being combined with the spinning, the weaving, and the knitting production forms the whole process of fabric production and processing. The dyeing and finishing is the key to determine the quality of the textile, and also serves as the key technology that can increase the grade and added value of the fiber, the spinning, the weaving, the clothing and the home textiles of the industrial chain. The dyed and finished products not only reflect the technology of dyeing and finishing but also suggests the comprehensive problems existing in the raw materials of the fiber, the spinning, the weaving, the dyeing materials, the auxiliary agents and so on. Therefore, to improve the quality of the dyed and finished products and thus further increase the rate of the finished product, we need to continuously improve the equipment quality, production level, and testing technology of printing, so as to make progress and meet the needs of the market.