The reproducibility problem of yarn dyeing is that under the same process prescription, process dyeing materials and other conditions, the result is that there is always color difference between different batches.
The reproducibility problem of yarn dyeing is that under the same process prescription, process dyeing materials and other conditions, the result is that there is always color difference between different batches. Textile enterprises, especially yarn dyeing, have problems with the reproducibility of yarn dyeing.
Under the same process prescription, process dyeing materials and other conditions, the result is that there is always color difference between different batches. The competitiveness of textile companies, especially yarn dyeing factories, lies in just-in-time production and first-time success, and the two are inseparable. Just-in-time production can quickly respond to the market and produce products in the shortest time. First-time success means that the product should meet quality requirements.
Product quality generally includes two aspects: intrinsic quality and appearance quality, which mainly require reproducibility. The color and light reproducibility of dyed yarn is poor. The essence is that the dyes used in different batches of dyeing have poor reproducibility. To achieve reproducible yarn dyeing, all factors in the dyeing process must be controlled.
Generally, poor reproducibility (i.e. vat difference) refers to the same dyed object (yarn) during intermittent dyeing The same dyeing materials, recipes, and processes are used for dyeing, but there are color differences (different shades, different shades, or both) between the dyed objects in different dyeing batches.
The situations where poor reproducibility often occurs are generally: between small samples, between small samples and medium samples, between medium samples and large samples, between small samples and large samples; between different dyeing machines, or The capacity of two dyeing machines is different, or the capacity is the same but the manufacturer is different, or even the dyeing machine with the same capacity of the manufacturer; the same dyeing machine and different dyeing batches.
Causes for poor dyeing reproducibility
There are many reasons for poor color reproducibility. Color difference occurs in yarn package dyeing. The reasons are roughly: yarn, dyeing materials, process design and control, operation, equipment, water quality, etc. Generally speaking, they are divided into external objective factors and human subjective factors.
1. Objective factors
1.1 Yarn
At some point during the growth process of cotton fiber This difference will produce differences in fiber quality. Therefore, the quality of yarns produced by different manufacturers is different, resulting in different dye absorption properties of the yarns, and the reproducibility after dyeing will be different. In addition, the thickness (linear density) of cotton fibers is different, and the apparent depth after dyeing is also different.
For example, after cotton yarn 7S and 40S are dyed, the appearance of 7S will appear darker, the thicker ones will be darker, and the thinner ones will be lighter. The twist, cotton mix, and moisture regain of the yarn will also affect the reproducibility of the shade. Even fibers with the same components and specifications will have different dyeing properties due to fluctuations in the production process. As for fibers re-spun from recycled waste, the dyeing properties are also different from conventional fibers.
For dyed yarn, when the fiber batch changes, small sample testing should be carried out, and the prescription should be adjusted if necessary before it can be officially put into production. (If it is a blended yarn of two or more fibers, if the blending ratio fluctuates and the dyeing prescription is different, vat differences will also occur in batch dyeing).
1.2 Dyestuffs
Dye production is mostly organic synthesis reactions, with long processes and complex reactions. Any process in the production Fluctuations in parameters will cause deviations in the composition and quality of the product.
The quality of dyes with the same structure is also different due to differences in technology, equipment, management, operation, and control levels; the same dyes in different batches of the same company also have reproducibility problems, and will also Causes differences in dyeing performance and color and depth of dyed objects.
Also, the sensitivity (dependence) of various process conditions for dyeing with different dye degrees is different. The more sensitive the dye (the greater the dependence), the worse the reproducibility. In addition, the different blending recipes of dyes provided by dye factories will also have a great impact on the dyeing performance and shade. At the same time, the blending of dyes also has problems with reproducibility and blending uniformity.
Another point is that dyes also have their own storage cycles. Some dyes (such as reactive and soluble vat dyes) are easily deteriorated due to improper storage time or conditions. Most dyes will absorb moisture and deliquesce, thus directly affecting the quality of the dyes. Strength points. Sometimes there will be differences in shade and strength between the upper, middle and lower layers of the same dye (shade differences often occur in blended dyes). This may be due to the delamination of dyes and additives with different particles and specific gravity during transportation. Of course, we do not rule out blending quality issues caused by individual middlemen.
1.3 Instruments and Equipment
(1) Different types of dyeing bobbins, beam coils and weighing bobbins. The sealing conditions are different, so the effective flow rate is also different. Even if the main pump discharges the same flow rate, the difference can reach 10% to 40%. The degree of dye liquor leakage is different, so that the actual amount of dye liquor circulating in the yarn is different, causing the yarn to be damaged. The amount of dye carried on the thread is different, resulting in poor reproduction of shades. Different forms and designs of bobbin penetration rates change, which will also cause the flow rate to change, and the cycle frequency and number of cycles will also change, resulting in poor filament dyeing vats.
The bottom disc, top disc, and top lock of different dyeing machines have different seals and leaks, so the effective flow rate is different, and the cylinder difference cannot be controlled. The scales used for weighing dyes must also be strictly selected. Different weighing ranges should be used with different precisions.�Just wipe with a dry rag; place each prescription dye in the same container, weigh it, and pour it into the bucket.
Also, the operator did not operate carefully. For example, if the seal between the bobbins is not corrected when loading, the winding weight is not handled if the winding weight exceeds the standard, the barrel is not carefully cleaned when mixing materials, the additives are not weighed correctly, and because the management personnel do not formulate correct and strict operating methods, the operator will You have to do your own thing, not to mention that process changes often occur on manual or semi-automatic equipment. The non-reproducibility of the process will lead to poor dyeing reproducibility.
2.6 Management Issues
Dyeing reproducibility not only involves the dyeing process, but also involves the entire production process. It is a systematic project , which is also closely related to management, such as gray yarn and semi-finished products management, dye management, measurement management, technical management and laboratory management: the same batch of gray yarn should be used for the same color number. If you want to replace it, you must re-sample, and you should do To “practice first, use first”, “practice later, use”, “same color and same batch”; dyes produced by different manufacturers, even dyes from different batches in the same factory, will have reproducibility problems, etc. due to management issues. If you do not pay attention to it, it is easy to cause poor reproducibility between batches in the dyeing of package yarns.
2.7 Laboratory tracking of large-scale production
First of all, the laboratory’s support for production is not to transfer processes and prescriptions Instead of moving to large-scale production, we simulate large-scale production in the laboratory to achieve a high degree of reproducibility between large-scale production and the laboratory. When there is a hue discrepancy in large-scale production and color correction is required, the laboratory should work together to complete the process. The laboratory should analyze and test the information provided by large-scale production (color and light differences between large and small samples) to find out the differences between the large and small sample production of each dye. Correlation to reduce color correction.
In addition, in order to achieve large-scale production – attaching great importance to the laboratory, we must first achieve reproducibility from laboratory to laboratory, and reproducibility from large-scale production to large-scale production, otherwise large-scale production The reproducibility with the laboratory is poor.
Solutions
Poor reproducibility of yarn dyeing is often encountered in yarn production. The dyeing situation of the yarn and the partial understanding of the production operation should be strengthened in the following aspects to ensure the reproduction of yarn dyeing from the basic level:
1. The selection of equipment
Should be selected to ensure the dyeing quality of the product and shorten the dyeing time. It should adopt a self-drop top lock device and use the internal flow of the equipment to naturally compress the package yarn. Equipment to provide basic conditions for reproducibility on the equipment;
2. Winding quality
To ensure dyeing penetration , the density of the package yarn is generally controlled between 0.35 and 0.40, and the density after compression should be controlled between 0.41 and 0.46;
3. Dyeing materials
Select the variety of dyes carefully, pay attention to the inspection between dye batches, ensure that the dye room is clean, ventilated and dry, and the dyes are moisture-proof;
4. Process parameters
The formulation and control of process parameters are the key to dyeing. A good dyeing process must be supported by a set of scientific and reasonable parameters. For example, when using salt and alkali, we should pay attention to the way and time of adding materials. We can use the salt prepared in advance to reduce the aggregation and precipitation of dyes caused by insufficient salt dissolution, resulting in poor dyeing reproducibility;
5. Proofing and setting out
The laboratory samples should imitate the actual situation of large-scale production to the greatest extent, including cycle time, heating rate, salt The addition of alkali and alkali, post-dyeing treatment, color matching light source, etc.; therefore, mid-sample experiments must be done before large sample production, and laboratory technicians must keep track and record as a reference for large-scale production; when large samples are put into production, technicians must Based on the difference between the small sample and the large sample, past experience and the mastery of the dye properties, the process is appropriately adjusted to obtain the process for the large sample to be put into production; the yarn used for the small sample and the put into production must be consistent, and the pre- and post-processing processes must be consistent. , it is necessary to duplicate the sample when changing the yarn, and the dye mother liquor for making small samples should not be stored for too long to avoid changes in dye concentration and strength;
6. Operation factors
Sampling personnel must standardize their operations, use dyes scientifically, increase operator training, reduce the types of additives used, and use accurate measuring instruments;
7. Other factors
The water used for small samples should be consistent with that of large-scale production. Try to use soft water. The PH value of soft water should be controlled at around 7.0 to ensure that the dyeing is of PH value. Stability; strengthen the quality testing of auxiliaries; when using raw cotton and cotton blends from different batches, the laboratory must repeat the sample before dyeing. If the color light changes, it must be adjusted in time; pre-treatment is the basis of dyeing, and pre-treatment is not necessary. Well, if the foundation is not laid firmly, the dyeing will still have poor reproducibility, so attention should be paid to the pre-treatment of the yarn.
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