01 Reproducibility problem of yarn dyeing
Under the same process prescription, process dyeing materials, etc., 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) means that during intermittent dyeing, the same dyed objects (yarns) are dyed with the same dyeing materials, prescriptions and processes. However, there are color differences (different shades, different shades, or both) between 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.
02 Reasons for poor dyeing reproducibility
There are many reasons for poor color reproducibility. The reasons for color difference in yarn package dyeing include: 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.
Objective factors
1. Yarn
Some certain factors in the growth process of cotton fiber Differences 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 yarns 7S and 40S are dyed, the appearance of 7S will be 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).
2. Dyeing materials
Dye production is mostly organic synthesis reaction, with long process and complex reaction. Fluctuation of any process parameters during production will cause The composition and quality of the product deviate. Dyes with the same structure have different dye quality 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, which will also affect the dyeing performance and the quality of the dyed objects. Differences in color, light and shade. In addition, 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 easy to deteriorate if stored for improper time or conditions. Most dyes will absorb moisture and deliquesce, thus directly affecting the quality of the dye. 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.
3. Instruments and equipment
Dyeing bobbins, beam coils and scales. Different types of bobbins have different sealing conditions, 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 flow rate circulating in the yarn Different amounts of dye liquor lead to different amounts of dye carried on the yarn, 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. Different dyeing machines have different bottom discs, top discs, and top locks with different seals and leaks, so the effective flow rate is different, and the cylinder difference cannot be controlled. There must also be strict selection of scales for weighing dyes. Scales with different precisions should be used for different weighing ranges. Do not use large scales to weigh small amounts. The general weighing tolerance range is as follows:
Weighing tolerance range table
Therefore, dyes are equipped with different measuring ranges when weighing and related measuring instruments are very necessaryOperators have to do their own thing according to strict operating methods. What’s more, process changes often occur on manual or semi-automatic equipment. The non-reproducibility of the process will lead to poor dyeing reproducibility.
6. Management issues
Dyeing reproducibility not only involves the dyeing process, but also involves the entire production process. It is a system Engineering, 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 it is replaced, the sample must be repeated. Achieve “practice before use”, “practice before 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 the management Failure to pay attention to this can easily lead to poor reproducibility between batches in the dyeing of package yarns.
7. Laboratory tracking of large-scale production
First of all, the laboratory’s support for production is not to separate processes and prescriptions. Instead of transferring it to large-scale production, it simulates large-scale production in the laboratory to achieve high reproducibility of large-scale production-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.
03 Solutions and measures
Poor reproducibility of yarn dyeing is often encountered in yarn production. Based on the dyeing situation of yarn in our factory and my partial understanding of production operations, I feel that management should be strengthened in the following aspects to ensure the reproduction of yarn dyeing from the basic level:
1. Selection of equipment
The 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
In order to ensure dyeing through, the density of the package yarn is average Control it 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 types of dyes carefully, pay attention to the inspection between dye batches, and ensure the cleanliness of the dye room Ventilate and dry, and protect the dye from moisture.
4. Process parameters
The formulation and control of process parameters are the key to dyeing. A good dyeing process must have a set of Supported by scientific and reasonable parameters. For example, the amount of 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 reproducibility of dyeing;
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, 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 dye properties, the process is appropriately adjusted to arrive at the process for putting the large sample into production; the yarn used for the small sample and the production should be consistent, and the pre- and post-processing processes should 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. Operational 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. Use soft water as much as possible. The pH value of soft water should be controlled at around 7.0 to ensure the stability of the pH value of dyeing; strengthen the quality testing of additives; different For the use of raw cotton and cotton blends between 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. If the pre-treatment is not good and the foundation is not laid firmly, dyeing will also have heavy problems. The performance is poor, so attention should be paid to the pre-treatment of the yarn. </p
