In the printing and dyeing industry, the concept of continuous pad dyeing difference is very wide, including sample color difference, inter-batch color difference, bottom surface color difference, left, middle and right color difference, intra-batch color difference, etc. This is a complex quality problem that printing and dyeing workers have encountered for a long time and is difficult to completely solve. As my country’s textile exports expand, international competition becomes more intense, and quality requirements become more stringent. At present, the standard requirements for left, center, and right color difference and intra-batch color difference among export dyeing products are above level 4.5, which is much higher than my country’s national standards.
At the same time, the assessment of color difference has also shifted from traditional visual rating to computer color measurement and identification. That is to say, the traditional craftsmanship has been upgraded to science and technology, and the color transmission has begun to transition from physical color plates to digitalization to computer color matching. The CMC and DE values are controlled within 0.6, and the color difference within the batch is within 0.9. (General brands such as Walmart require DEcmc to be within 1.2, but for samples, the requirements are often stricter to 0.6~0.9, and even to 0.5 for black. Some brands will be loose with DEcmc but will control DH)
And the color matching light source has also developed from ordinary office lights D65, CWF, TL84, D75 to U3O, HORIZON, INCA and other light sources, and the color matching has been increased from one lamp to two lights. , the three lights are required to match the color respectively and the color and light are required to remain unchanged. In order to meet the quality requirements of customers and improve the export competitiveness of enterprises, controlling, reducing or even overcoming dyeing color differences has become an important issue for printing and dyeing workers.
The author of this article mainly focuses on how to control and reduce the left, center and right color difference (commonly known as edge color) and intra-batch color difference (commonly known as LOT color).
1. The stability and reliability of raw materials are the basis for controlling color difference
The raw materials for dyeing products mainly refer to gray fabrics and dyeing materials. Regardless of the batch size, the requirement for consistent quality of raw materials before and after is an important condition to ensure that the LOT color is overcome. Even if the quality of raw materials is objectively different, we must be aware of it, handle it differently, and strictly control the LOT color within the minimum range.
The specific methods are as follows:
l. For gray fabrics of the same color number, the purchasing department is required to try to purchase them from the same cotton mill and the same batch of origin. Cotton gray fabric.
2. If a middleman supplies gray fabrics, the products of different cotton weaving factories must be distinguished. If there are gray fabrics from two factories, they must be put into production separately according to batch numbers when they are put into production. When necessary, the materials used in the pre-treatment and dyeing processes must be appropriately adjusted to overcome the intra-batch color difference of the batch of products.
3. For some special products, such as linen, linen cotton and other semi-bleached blanks, although they have been pre-processed, it is still difficult to control the LOT color change of sensitive colors. The control method can be to first take a sample of 1 meter from each piece (roll), record the number of each piece (roll) and the sample, and try dyeing the more sensitive colors. Then according to the results of the LOT color of the sample, each piece (roll) will be put into production in batches. Adjusting in batches during dyeing can reduce the generation of LOT color.
4. For products with the same color number, the supply department must notify the technical department when there are changes in raw materials (including the origin of gray fabrics, dyes, and finishing agents), classify and stack them, and strictly compare and test them to ensure reasonable process and technology. Adjustment cannot keep things unchanged in response to ever-changing changes.
5. Dyeing materials must be prepared in sufficient quantities according to the batch requirements. Regardless of the size of a color, the first requirement is that it is a dye from the same origin, the same batch, the same color, light, and concentration. It is best to use a full test method for dyes. If any differences are found, they should be used separately and re-sampled to avoid LOT color due to different shades and strengths of the dyes.
6. Don’t ignore the influence of finishing agents such as softeners on the shade, depth and edge color. For a large batch of color, it is best to use the same batch of products during the soft finishing process. Produced on the same machine. At the same time, it is also necessary to cut samples and track and control the color, otherwise it will be difficult to control the lot color and edge color within the batch.
7. Whether the dye selection is correct is another key to controlling the LOT color and edge color.
Many companies submit samples to laboratories for proofing after receiving samples from customers. The compatibility of dyes is determined by the proofing personnel. The problem is that some samplers lack practical production experience. They only focus on small samples and samples from customers, but it is difficult to grasp the dyeing rate, the speed of color and light changes, the stability of compatibility, and the changes in metamerism of different color samples. Often small samples are sent to customers for confirmation, and problems are discovered only during production. At this time, changing the dye compatibility is very passive due to the constraints of color and light changes.
For this reason, we use computer color matching. Based on the usually selected dye combinations, we select the compatibility with the best DE value, six in one, and then send it to the dyeing supervisor according to the Based on the principles of good quality, strong stability (the dyeing curve is roughly the same), and low cost, a group of compatibility is selected and then submitted to the laboratory for proofing. Such a sample not only meets the customer’s requirements, but also ensures that the color difference can be controlled to the most stable level during production.
8. Although there are thousands of variations of the three primary colors, they are not omnipotent.
Practice has proved that you cannot rely entirely on the matching of the three primary colors. When facing any color, the best way is to choose a similar color dye as the main color, and then fine-tune it with other dyes according to the color light. At the same time, the compatibility of dyes should adhere to the principle of less rather than more, and the less the better. (The brighter the three primary colors, the more difficult they are to use in actual color applications, and color differences are likely to occur.)
2. Reform and strengthening of internal management of enterprises are the guarantee for reducing color difference
(There are more reasons for color difference.Property.
②Weighing materials:
Due to errors in weighing materials, intra-batch color differences are the most unworthy mistakes for printing and dyeing factories. The reliable method is : Weigh the materials according to the colors, have a designated person review it, and strictly implement the regulations on the use of weighing instruments according to the amount of dye. In order to achieve the heap accuracy.
③ Material opening:
The capacity of each material barrel is preferably 800-1000 liters, and each pad dyeing machine is equipped with three (live injection baking The solid method can only open 300-500 liters per barrel). If the activated vapor solid method and Shilin dry reduction method, vulcanization and paint dyeing are used, when a large batch of color is encountered, 2-3 barrels of dye liquor can be opened and connected at the same time. Use to reduce color differences caused by dye or operation errors. In addition, after each barrel of dye solution is opened, you can use filter paper to spot-check and analyze the changes in diffusion and color depth as a final check before dyeing.
④Sample:
The sample cloth of the pad dyeing sample is generally controlled to be about 20 meters each time, so as to achieve the effect of accuracy and no waste. The process and technical conditions of the sample (including pressure, speed, temperature, concentration) must be the same as normal production. In this way, the sample is accurate and the color difference will be reduced. When testing samples, in addition to adjusting the square and color, the color difference between the left, center and right should also be adjusted to the ideal level, so that accurate color alignment and good edge color can be achieved when it is officially put into production.
⑤Pre-baking:
Whether it is infrared pre-baking or transverse guide roller pre-baking, the heating temperature of the fabric surface must be kept even and consistent, otherwise the dye will The migration of water causes color difference. In particular, whether the wind power in the pre-drying oven is evenly distributed, a system must be developed to strengthen inspections to prevent errors. In addition, qualified enterprises can install an online moisture meter in the pre-drying machine to check whether the dry humidity of the fabric in the pre-drying machine is consistent to prevent front-to-back color difference caused by uneven drying and wetness.
⑥Steamer:
The speed, temperature and concentration of the reduction steamer must be consistent. In particular, caustic soda is indispensable for both active vapor solid liquid and Shilin reducing liquid. Practice has proved that the color light is very sensitive to the concentration of caustic soda in the vapor solid or reducing liquid. In order to reduce the impact of caustic soda concentration errors, the amount of caustic soda required for each color can be prepared at one time and titrated accurately before use. The control of the temperature and pressure of the steamer can be specified to control the pressure of steam entering the steamer and monitor the temperature gauge. In addition, a steamer pressure U-shaped pipe can be installed on the wall of the steamer, and there is a prescribed control point for the height of the U-shaped pipe (that is, the pressure in the steamer). Since the U-shaped pipe reacts more favorably than the thermometer, the pressure gauge The reaction is faster and more sensitive, so the temperature and pressure in the steamer can be controlled more accurately with the U-shaped tube, and the front and rear color lights are more consistent.
⑦Monitoring:
With the continuous development of technology, monitoring instruments for edge color and LOT color are also developing day by day. For example: the uniform padding car is equipped with a computer to automatically regulate the left, middle and right rolling liquid rates, as well as online color difference measurement and portable colorimeter, automatic temperature control, automatic control of PH value, etc. Enterprises that have the conditions to gradually purchase some advanced and practical scientific and technological instruments will undoubtedly be of great help in reducing chromatic aberration. At present, the dyeing of most enterprises still relies on the strict control of employees and careful inspection to control it. Each box of fabric must be cut and tested at least three times to check the change in color difference before and after. Before dyeing, you need to cut strips of fabric (usually 20cm wide), and then use a sewing machine to connect the left, middle and right sides together to check the edge color. Take timely measures to resolve problems if they are discovered.
⑧Finishing:
The finishing of printed and dyed fabrics will be affected by finishing additives and cause color difference. This must be taken seriously and prevented. Specifically, the following measures can be taken: When pad-dying samples, they should be based on the finishing requirements of the variety, such as softness, sizing, waterproofing, antifouling, coating, resin, etc. Before cutting the sample and color matching, it should be sorted according to the finishing requirements. Go to the color. This can avoid the disadvantages of color alignment in the pad dyeing machine and color changes in the final machine. Therefore, the selection and formula of finishing auxiliaries should be formulated by the pad dyeing supervisor. After dyeing and finishing, the products coming off the machine also need to cut samples and check the color (the color samples are provided by the dyeing supervisor), and check the changes in color difference between the left, middle and right sides of each box of fabric to prevent micro-delays.
⑨Finished product inspection:
At present, the operating procedures for finished product inspection in our factory are: roll inspection → color separation → packaging. The main purpose of inspection is to check the appearance defects of the cloth and distinguish between cloth A and cloth B. Each roll is required to cut the first two 10cm fabric samples (one to be given to the customer and one to be retained by the factory for future reference). A designated person is responsible for color separation, mainly distinguishing the LOT color and checking the edge color based on the cloth strip color swatch. Only qualified products can be released. The packaging should be packed and stacked according to the color-separated LOT colors. There should be clearly distinguishable color labels in Chinese and English, which is conducive to color separation and cutting by the garment factory.
The above is the author’s superficial experience of controlling and reducing color difference in dyeing, pretending to be a “shallow talk”. </p
