This article systematically elaborates on the accuracy and stability of color light duplication of the process. It analyzes the factors that affect color light from three aspects: making small samples, enlarging samples, and mass production, and puts forward operational precautions based on practice. How to improve the accuracy and stability of the color light of dyed fabrics and adapt to customer requirements is not only related to the economic benefits of the company, but also related to the company’s reputation.
The accuracy and stability of color light are the soul of dyeing in a dyeing factory
1 , Proofing and imitation: The new color list issued by the business planning department must first be carefully reviewed, such as: the standard sample must be complete, the light source must be clear, the fabric weave specifications must be clear, and the dye fastness requirements (soaping, rubbing, and sun exposure , chlorine resistance, dry cleaning, etc.) and post-finishing requirements (softness, waterproof, antibacterial, flame retardant, UV protection, etc.) must be accurate, the sample delivery time must be reasonable, and if any problems are found, they must be understood in a timely manner with the business planning department.
Before sampling, the quality of semi-finished products must be determined with the production planning department, such as mercerized cloth or unmercerized cloth, sanded cloth or unsanded cloth, original white cloth or bleached cloth, pre-set cloth or post-set cloth, Whether it is pre-shrunk fabric or non-shrunk fabric, etc., the principle is: the fabric used for proofing must be consistent with the fabric used for mass production in the future, so as to unify the process flow and process conditions, and it should not be changed midway after being determined.
Before proofing, first identify the production method with the production planning department, such as whether it will be liquid jet dyeing or flat vat jig dyeing for large-scale production. Once determined, it should not be changed during the process. Because the proofing conditions of liquid flow dyeing and jig dyeing are different, the dyes and auxiliaries used are also different; if they are changed, the proofing can only be done again, and the proofing prescriptions must not be used interchangeably.
Carefully select dyes based on the customer’s color list requirements for dyeing depth, color brightness and color fastness. For example, if you want to dye a deep color, use dyes with high strength, high darkening properties, and high wet rubbing fastness; if you want to dye light colors, use dyes with high leveling properties and high light fastness; if they are fast to chlorine bleaching, If the fastness to dry cleaning is required, chlorine-resistant dyes should be used; if dry cleaning fastness is required, dyes that are resistant to organic solvents should be used; when dyeing cotton nylon or cotton-polyester interwoven fabrics, especially when dyeing flash white or flash colors, it is necessary to Choose dyes that are less likely to contaminate each other. If it is nylon-cotton or cotton-nylon elastic fabric, when dyeing nylon, disperse dyes and neutral dyes or acid dyes must be well matched to ensure brightness, color fastness and surface uniformity to meet customer requirements. What should be pointed out here is that nylon and spandex have very different color absorption properties (shades and shades) of disperse dyes. Dying nylon with disperse dyes alone has good level dyeing properties, but spandex often appears “different colors” on the cloth surface. The silk “jumps out”, affecting the uniformity and color of the cloth surface.
Before printing the approval sample, the original sample provided by the customer must be re-certified. The original samples provided by customers usually have the following situations:
(1) The tissue specifications of the original samples are different from those specified in the color list. In this case, it is often difficult to match the color of the sample with the original sample due to the different light absorption, reflection and light transmission of the fabric. At this time, you should make a few more samples with different shades and colors for customers to choose from, so as to increase customer recognition rate.
(2) The original sample is not fabric, but printed cardboard. In this case, due to factors such as the smooth surface of the paper pattern, strong gloss, and the fact that the paper pattern is printed with printing paint instead of dye, the color of the dyed sample is generally difficult to match the original sample under the prescribed light source. At this time, we can only print a few more samples with different shades and colors for customers to choose from.
(3) When dyeing cotton-nylon or cotton-polyester interwoven fabrics, if the color depth and color uniformity of the bicomponent fiber in the original sample provided by the customer are poor, there is a two-color phenomenon; at this time, there are usually two This situation: the first is to retain this two-color effect; the second is not to have a two-color effect, but to uniform one color. Therefore, the shades of bicomponent fibers should be evened out (in the original sample, the shades of bicomponent fibers were different, which was due to poor dyeing uniformity). In this case, be sure to ask the customer clearly to avoid the sample not being confirmed.
(4) The original sample has a certain fluorescence under the light source. In this case, be extra careful. There are generally two possibilities: first, the fabric is required to have a fluorescent effect under a specific light source; second, the fabric itself is not required to be fluorescent, but during dyeing, in order to enhance the brightness, a fluorescent whitening agent is added. At this time, the customer’s true requirements must be clarified first, and then samples can be produced according to the requirements.
(5) The original sample is made of silk fabric or acrylic fabric (or acrylic yarn), but the small sample needs to be made of pure cotton, or cotton polyester or cotton nylon. This situation often occurs because the original sample is made of Dyeing with acidic dyes or cationic dyes has very good brightness, so the sample cannot meet the brightness requirements of the original sample. In this case, a similar sample must be made first for customer reference, and the reason must be explained to the customer. If fluorescent whitening agents are added for brightening, the customer’s consent must be obtained.
(6) Customers’ color lists often include “white” color numbers. For example: natural white, ivory white, pearl white, etc., but there is no physical standard sample. In this case, you must clarify in advance whether the so-called “shade” in the color list refers to original white, bleaching or whitening. If customers are confused about this and find it difficult to identify, they must firstChromatographic analysis is represented by the Rf value.
Determination method (1): The fiber material is 2 grams of bleached and mercerized 40X40 cotton poplin products. The dye liquor concentration is 0.2 g/L, the liquor ratio is 20:1, and the dyeing temperature is divided into two levels: 30°C and 80°C. When measuring, cut 2 grams of fabric into pieces and put it into a three-neck bottle that has reached the specified dyeing temperature (to avoid evaporation of water). At certain intervals, absorb 2 ml of dye solution while stirring (while adding 2 ml of water), determine the optical density of the dye solution. As the dyeing time increases, the adsorption reaches equilibrium and the optical density value of the dye solution no longer changes. The dyeing percentage at this time indicates the directness of the dye.
Measurement method (2): Chromatography on paper (Xinhua #3 filter paper), observe the different rising heights of each dye spot, that is, the different Rf values. The larger the Rf value, the smaller the directivity between the dye and the cellulose material; the smaller the Rf value, the greater the directivity.
Prepare a 0.2 g/L dye solution, use a capillary tube to spot a sample on the filter paper, dry it in the sun and hang it in a closed chromatography jar filled with distilled water to saturate for 30 minutes, and then connect the sampled end of the filter paper to Chromatography starts when water comes into contact. When the developing agent front rises to 20 cm, calculate the Rf value of the dye spot. Paper chromatography is a simple method to determine the substantivity of dyes, but the Rf value is not completely consistent with the actual performance of the dye.
03 Diffusivity
Diffusivity refers to the ability of dyes to move into the fiber. The temperature affects the diffusion of dye molecules. Dyes with large diffusion coefficients have high reaction rates and fixation efficiency, as well as good level dyeing and through-dying. The quality of diffusion performance depends on the structure and size of the dye. The larger the molecule, the more difficult it is to diffuse. Dyes with a high affinity for fibers are strongly adsorbed by the fibers and have difficulty in diffusion. Dye diffusion is usually accelerated by increasing the temperature. When electrolyte is added to the dye liquor, the diffusion coefficient of the dye decreases.
The thin film method is usually used to measure the diffusion properties of dyes. Dip the adhesive film (cellophane) into distilled water. The thickness before immersion is 2.4 strands, and the thickness after 24 hours of immersion is 4.5 strands. During measurement, fold the film to a certain thickness as needed and press it under the glass plate to remove air bubbles. Then sandwich it between two plywood with rubber gaskets in the middle. One of the plywood has a round hole in the middle. The dye solution can only diffuse into the film layer through this hole. Immerse the plywood film in the dye solution at 20°C and let it stand for 1 hour. , then take it out and rinse it with water, and observe the number of layers of the dyeing film and the color of each layer of dye. There is a certain correlation between the number of diffusion layers and the half-dying time. The shorter the half-dying time, the greater the number of diffusion layers.
04 Reactivity
The reactivity of reactive dyes usually refers to the ability of the dye to react with the hydroxyl group of cellulose. Highly reactive dyes can be fixed at room temperature and under weak alkali conditions, but the stability of the dyes in this reaction is relatively poor and they are easily hydrolyzed and lose their dyeing ability. Weakly reactive dyes need to be bonded to cellulose under relatively high temperature conditions, or a strong alkali agent must be used to activate the hydroxyl groups of the fiber yarn to promote the dye reaction and fixation on the fiber.
Reactive dyes of the same model have roughly the same reactivity. The reactivity depends on the chemical structure of the dye’s active group, followed by the connecting group between the dye body and the active group. , also has a certain impact on the reactivity of dyes. In addition, it is also affected by pH value. Generally, as the pH value increases, the reaction speed increases. As for temperature, it is also a factor that affects the reaction speed. As the temperature increases, the reaction speed becomes faster. For every 10°C increase in temperature, the reaction speed can be increased by 2 to 3 times. Therefore, after printing, drying or steaming can promote the reaction between the dye and the fiber.
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