How does the printing and dyeing factory solve the problem of two colors of cloth? What is the reason for color difference and dyeing defects?
During the dyeing and finishing processing of textile fabrics, there are many factors that have an overall impact on the dyeing and finishing results. Therefore, in actual large-scale production, quality problems of one kind or another are often encountered, among which those related to color and luster are particularly frequent. The biggest problem is the color difference. The following describes how to solve the causes of color differences and dyeing defects.
1. Classification of color differences
Color differences are divided into the following categories:
a. Difference in lofting color (difference between large and small samples);
b. Batch color differences are further divided into color differences between batches, cylinder differences in the same batch, and tube differences in the same cylinder;
C． Other color differences include front and rear color differences, left, middle and right color differences, discoloration color differences (color change after post-processing and finishing), etc.
1.1 Stakeout color differences
At present, the dyeing and finishing process basically needs to be carried out according to the color specified by the customer. The requirements for the color and pattern level are very high, and some customers are almost demanding. The color difference between lofting is the color difference between the small sample and the large sample. This is also a problem that must be faced and solved during mass production. It can be seen that when the sample is more consistent with the coloring mode of the main machine, the difference in color will be smaller. However, the reality is that not many of the two can be highly consistent, and usually can only achieve a certain degree of similarity. There is even a considerable gap in the similarity between the two for some types of coloring (such as curling dyeing). Therefore, the success of a small trial cannot yet be equated to the certainty of success in large-scale production. Especially when developing or trialling new products, new materials, and new processes, the methods and procedures used for small-scale tests in the laboratory may not necessarily be copied to the workshop for large-scale tests, and sometimes there may be a huge gap between the two. For this reason, in addition to matching the appropriate and advanced small prototype machines and other supporting instruments and facilities, when conditions permit, a sample test of one piece of fabric (or 1-2 bobbins) is carried out in the middle, and then the next step is carried out. The big test will undoubtedly be more beneficial and appropriate. Because the effect of the pilot test is much closer to that of the large machine than the small test.
Accurate lofting once has always been the goal pursued in technology. Accurate lofting once is of fundamental significance to the prevention of cylinder errors. This problem is not only inseparable from the advancement of laboratory equipment and facilities, but also involves the level of technology and technical management. There is no doubt that it is also one of the key technologies of printing and dyeing enterprises, and the now widely praised “coloring once” “Success” requires it to be a prerequisite. Transforming the traditional “post-adjustment” to “pre-control and control” is the prerequisite for solving the problem of accurate stakeout. At the same time, a large amount of detailed and detailed basic work is essential to grasp the evolution and regularity of color throughout the entire production process.
1.2 Batch color differences
1.2.1 Color differences between batches
Batch color differences include color differences between different production batches, and color differences with batch properties in the same batch. Batch color difference has always been a long-standing problem in Jie color production, and it involves a wide range of areas. Preventing and overcoming it should be a systematic project.
The factors leading to batch color differences can be summarized as follows:
a. Different origins of fiber raw materials, as well as different batches and batch numbers, have differences in dye absorption rates;
b. Different origins of dyes, auxiliaries, and chemical raw materials, as well as different batches and batch numbers, have differences in the content of their respective active ingredients;
c. The rationality of cylinder allocation and cylinder arrangement in planning and scheduling (different models of coloring machines have differences in color and luster, and improper cylinder configuration and planning arrangements are also related to batch differences and cylinder differences);
d. The standardization of the execution of process conditions (determined by the quality of personnel and the level of management) is not only in the coloring stage, but also in various production links such as pre-processing and finishing.
If there is a problem with any of the above four points, it will affect the production of batch color differences. If the company’s technology and management are deficient, it is very likely that multiple influencing factors will appear concurrently, which will increase the complexity and difficulty of finding the true cause.
1.2.2 Differences between cylinders in the same batch
Cylinder difference is another common problem in batch coloring. First of all, the pre-planning process is the premise for the rationality of the rough blank cylinder configuration, and the biggest source of influence is the collective quality of the workshop line operators, that is, whether the operation execution of the process meets the requirements, and the individual operators, each The machines and each shift are highly unified.
The weighing and measuring of dyeing materials requires accuracy. This is a clear and easy truth. However, in the actual work of the dye and chemical material warehouse, it is easy to make mistakes, so it needs to be equipped with procedures and systems such as review and review to provide sufficient guarantee. Even if it is equipped with a modern automatic weighing and feeding system, it cannot be absolutely foolproof. It is not completely impossible for the system to malfunction or suffer from human control errors after working for a long time. If maintenance and maintenance are neglected, it is not impossible. Inspection and management, especially in continuous production lines, once something goes wrong, the batch size will be very large.
Another thing worth noting is that the lofting work is also closely related to this problem. If you always need to rely on adding dye to correct the color, then the problem of tank difference will definitely increase.
1.2.3 Pipe differences in the same cylinder
Pipe differences occur in coloring machines such as multi-cylinder parallel large-capacity liquid flow and injection machines. The large-capacity coloring machine is designed to reduce or even eliminate the chance of cylinder difference. However, the advantages and disadvantages are that it will also bring about the problem of pipe difference, which is caused by the coloring operation of the equipment. Determined by formal methods. The more cylinders connected in parallel, the larger the single loading capacity of the dyeing machine will naturally be, but the more likely it is that pipe errors will occur. Therefore, in order to pursue the expansion of single coloring capacity, it is not advisable to add too many cylinders for parallel connection. Enough is enough. It can be said that tube difference is essentially another form of cylinder difference in this type of coloring machine.
Summarizing the factors that cause pipe differences, and avoiding differences in the wool natural color cotton cloth matching cylinder in the pre-planning process is the first step to prevent it. Maintaining the normal operation of the equipment is more important than the conventional single-cylinder coloring machine. Strict care and random tracking system in blocking operations are also essential. Because the inspection and identification of tube defects, as well as the color correction and repair, are far more complicated, troublesome and inconvenient than the cylinder defects, especially for polyester, polyester-cotton, viscose and other blended chemical fiber fabrics that need to be overdyed. There is a possibility of secondary coloring errors in the fabric. If you wait until the dyeing process is complete before discovering it, it will be very costly to correct the color and repair it.
1.3 Other color differences
1.3.1 Color difference before and after
The color difference between the front and back easily occurs in the continuous dyeing of long car pad dyeing machines and large package jigger dyeing machines. This is determined by the dyeing mode of these two types of equipment. It is generally not easy to occur on intermittent loose-type exhaust dyeing machines. However, if the coloring operator is blindly seeking speed and quickly heats up while adding dye, then the color difference between the front and rear will also occur on the loose-type exhaust dyeing machine.
When other polyester fiber fabrics are heat-set, the dyes sublimated in the setting machine are not properly removed, resulting in sublimation stains on the subsequent fabrics, especially when dark colors are changed to light colors, or when the production schedule of complementary colors is , often produces what is commonly called setting and color matching, and the dye residue in the setting machine is gradually taken away, resulting in differences in color before and after.
1.3.2 Color difference between left and right
The difference in color between the left and right mainly occurs in pad dyeing and jig dyeing, and is also caused by the coloring mode characteristics of the equipment, so the mechanical factors are often greater than other factors.
In pad dyeing, the main reasons are uneven padding and uneven symmetry due to uneven left and right pressures of the rolls, resulting in uneven padding rates on the left and right; or failure of the replenishing system of the pad dyeing tank, resulting in an increase in the concentration of the left and right dyeing liquors. Uneven.
In jig dyeing, the stretch roller of the jigger dyeing machine is in disrepair and deformed, and the left and right arcs are asymmetrical and uneven, which will lead to inconsistent scraping rates on the fabric. The thinner the dyed fabric and the lower the water absorbency of the fabric, the easier it is for left and right color differences to occur when dyeing some sensitive colors in which the three primary colors are dominant. In addition, irregularities in the feeding of dyeing materials into the machine and improper adjustment of the feeding tension of thin fabrics will also cause uneven dye concentration on the left and right sides of the dye vat, resulting in color differences between the left and right sides.
For loose dyeing, strictly speaking, from the mode and principle of the operation of the coloring machine, there should be no difference between the left and right colors. However, in warp knitted fabrics, color differences in the edges may also occur from time to time. Some types of fabrics are prone to curling. When the curling is too severe, if it cannot open by itself in the coloring machine, This will cause color differences in the edges. This is caused by the variety characteristics of the fabric, and the left and right color differences between pad dyeing and jig dyeing are completely different in nature and reason. Therefore, the solution must start from the weaving and coloring process.
1.3.3 Color change differences
Since some dye varieties will undergo heat-sensitive discoloration to varying degrees, the dyes must be screened first. In terms of additives, they include color-fixing agents, cross-linking agents, softeners, water- and oil-repellent agents, PU coating post-finishing agents, etc. After coloring, the addition and processing of post-processing and finishing additives will have a more or less inevitable color change effect on the color after coloring. The longer the post-processing and finishing process, especially the higher the finishing temperature and the more additives added, the greater the possibility of color change. Even mechanical finishing processes such as raising and sanding that are not directly related to dyes, additives, chemical raw materials, etc. will also affect the apparent color of the fabric and cause color differences. Of course, color differences caused by mechanical finishing are not caused by chemical factors, but are caused by changes in the surface of the fabric that change the basis of light reflection, thereby affecting the color perception of human eyes, resulting in An optical illusion. This color difference is basically unchanged in hue, but the reflection in depth is more obvious, and it also affects the color and light. Although this color difference is due to physical reasons, objectively the color change still occurs, so it is still necessary to control it in advance to avoid it.
In a comprehensive sense, “coloring is complete” should be the end of the final finishing process, the finished product is fully cooled, and can be used for subsequent garment production. Only when the specified color is stably reflected can the coloring task be truly completed. . However, it is unobjective and unrealistic to require post-processing and finishing additives not to affect discoloration at all (at least so far). To be careful, this problem should also fall into the technical work category of “staking out color differences”, and we will also encounter the problem of effect differences between large and small tests (the difference is that the focus is on color). Therefore, this requires technical solutions to the proofing and lofting work. First of all, when making small samples, we must strive to imitate the links, procedures, formats, methods and process conditions of large-scale production, and correct deviations in pilot and large-scale tests to overcome them.
However, what needs to be corrected is that post-processing and finishing additives mainly affect and act on certain intrinsic qualities of textiles (such as various dyeing fastnesses), as well as feel, style, characteristics and special functions. When it comes to color issues, dyes have a greater role and influence than dyes. When it comes to correcting color deviations, dyes undoubtedly play a leading role. Grasping the evolution law of color is the prerequisite for overcoming and solving. Solving it through technology and focusing on prior control is the fundamental solution.
What needs to be mentioned again is the yellowing problem of amino silicone softeners. This type of softener now accounts for a significant proportion of the use of softeners due to its superior feel and good durability. However, there are some problems that must be taken care of in terms of performance of this type of softener. In terms of performance indicators, the higher the amino content, the better the hand feel. However, the higher the ammonia value, the greater the yellowing value. Moreover, the higher the temperature and the longer the finishing time, the greater the degree of oxidation and yellowing.
Although the chemical industry has always been improved and improved through modification and other methods, there are still certain contradictions and conflicts. Therefore, special selection work must be done for extra white and bright light colors (especially purple tones). If necessary, only part of the requirement for softness can be given up to maintain the whiteness value.
2. The relationship and impact of “prevention is better than cure” and “first-time success”
The continuous pursuit and exploration of process technology is one of the important driving forces for the improvement and progress of the industry. However, every new achievement in process technology and other aspects (such as dyes, chemicals, machinery and equipment, etc.) always has a relative retention period, and in time, there is often a certain pattern of duration (also (sometimes more, sometimes less), on the other hand, in order to enable enterprises to maximize production efficiency and benefits, according to the level of technology mastered at the current stage, all types of raw materials, energy, water, etc. must be treated during the entire production process. The consumption of resources must be both necessary, reasonable, appropriate and efficient to the maximum extent, which has become a guiding principle, and “coloring is successful the first time” is the embodiment of this principle in the implementation of the process.
“The coloring is successful the first time” means that during the entire production process, the product does not have any abnormal phenomena such as repairs and re-dying outside the set process. To achieve this level, it is a systematic project that includes extensive and all-round content. In addition to the corresponding comprehensive strength in technology, management, equipment configuration, etc., it also includes the collective quality level of the front-line staff.
There is no doubt that “coloring is successful the first time” can not only fully improve labor production efficiency, but also make full use of raw materials, energy, water and other resources. Therefore, “coloring is successful the first time” is not only a means to improve product quality, but also an important way to save resources, save energy, reduce emissions, and improve corporate efficiency.
The traditional quality management method is to inspect the finished products and then grade them according to the quality grading standards. But at this time, the product has been completed, and the quality status of first-class products, second-class products, and second-class products has been established, and it is objectively difficult to change and effectively remedy it. The epidemic prevention mechanism in the medical community has provided us with great inspiration. “Prevention is better than cure” is not only an important and effective means to control infectious diseases, but also has great significance in keeping production costs and resource consumption at a minimum.
“Prevention is more important than cure” is the guiding principle of the modern quality management system, which adopts a positive and proactive approach, starting from the source, starting from the foundation, and based on the situation reflected in the historical records of the production archives, paying special attention to everything Preventive measures will be taken at all links and places where problems have arisen or may have occurred. In the process and each stage, we strive to prevent the reduction of the required level of semi-finished products, strive to eliminate the occurrence of various defect factors, and strive to achieve the best results by focusing on the perfection of each stage, each part and the process. Full of sex. Therefore, it can also be said that “prevention is better than cure” is also the indispensable philosophical basis for “successful coloring”.
3. Conclusion
There are many factors that influence color differences, including the quality differences of raw and auxiliary materials such as fiber, natural cotton cloth and dyeing materials, the status of dyeing and finishing equipment, technology, technology, management, and personnel quality, etc. Therefore, in the entire production process, from planning and pre-processing to coloring, post-processing, finishing, etc., there is a basis and possibility for color differences, making color differences a common occurrence in dyeing and finishing production. Quality problems have become the first of the three major problems. Although measures such as color correction, repair, and dyeing are still unavoidable in actual large-scale production, these are passive remedies after all, and there are some textiles that do not allow repair. Therefore, for all factors that may lead to color differences, efforts should be made to adopt a prevention-centered strategy. This is the leading concept of dyeing and finishing production management, technical management and quality management.
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