Process flow of dyeing cloth in printing and dyeing factory

Dyeing cloth-scouring and bleaching in dyeing and finishing process to remove impurities contained in natural fibers, and adding various sizes, grease and polluted dirt in textile processing. The existence of these impurities not only hinders the smooth progress of dyeing and finishing, but also affects the wearability of fabrics. The purpose of scouring and bleaching is to remove impurities from the fabric by chemical and physical and mechanical actions, so that the fabric is white, soft and breathable, which meets the wearing requirements and provides qualified semi-finished products for dyeing, printing and finishing. The main processes of scouring and bleaching of pure cotton fabric are: grey cloth preparation, singeing, desizing, scouring, bleaching and mercerizing. 1) Grey cloth preparation: Grey cloth preparation includes grey cloth inspection, cloth turning (batch, packing and printing) and sewing. The purpose of raw cloth inspection is to check the quality of grey cloth and solve problems in time. The inspection contents include physical indicators and appearance defects. The former includes the length, amplitude, weight, warp and weft density and strength of the original cloth, while the latter includes spinning defects, weaving defects, various stains and damages. Usually, about 10% of the total amount is randomly selected. After the original cloth is inspected, it must be divided into batches and boxes, and printed on the cloth head, indicating the variety, processing technology, batch number, box number, release date and code of the cloth turning machine for easy management. In order to ensure continuous batch processing, the original cloth must be stitched. 2) singeing: the purpose of singeing is to burn the fluff on the cloth surface, make the cloth surface smooth and beautiful, and prevent the uneven printing and dyeing defects caused by fluff during printing and dyeing. Fabric singeing means that the fabric quickly passes through a high-temperature flame or rubs a hot metal surface on the open width. At this time, the fluff on the surface of the fabric quickly heats up and burns, while the fabric body is relatively dense and the temperature rises slowly. Before it reaches the ignition point, it leaves the flame or hot metal surface, so as to burn the fluff without operating the fabric. 3) Desizing: In order to weave smoothly, textile mills often size warp yarns to improve strength and wear resistance. The size on grey cloth not only affects the water absorption of fabric, but also affects the quality of dyeing and finishing products and increases the consumption of dyeing chemicals. Therefore, the pulp should be removed before cooking. This process is called desizing. The size on cotton fabric can be removed by alkali desizing, enzyme desizing, acid desizing and oxidant desizing. Alkaline desizing makes the size expand, and the adhesion to the fiber decreases, and it is removed from the fabric after washing. Enzymes, acids and oxidants degrade starch, increase its solubility in water and remove it after washing. Because of the great damage to cotton fiber, acid and oxidant are rarely used alone, and they are often used in combination with enzyme desizing and alkali desizing. 4) scouring: when cotton fiber grows, there are natural impurities (pectin, waxy substances, nitrogen-containing substances, etc. After desizing, most of the size and some natural impurities have been removed, but a small amount of size and most natural impurities remain on the fabric. The existence of these impurities makes the surface of cotton woven fabric yellow and has poor air permeability. At the same time, the existence of cottonseed hull has a great influence on the appearance quality of cotton cloth. Therefore, it is necessary to scour the fabric in high-temperature concentrated alkali solution for a long time to remove residual impurities. Scouring refers to the chemical degradation, emulsification, expansion and other reactions between scouring AIDS such as caustic soda and pectin, waxy substances, nitrogen-containing substances and cottonseed hulls. And impurities are removed from the fabric after washing. 5) Bleaching: The appearance of cotton fabric is not white enough after scouring because there are natural pigments on the fiber, which will affect the brightness of color when used for dyeing or printing. The purpose of bleaching is to remove the pigment and give the fabric the necessary and stable whiteness without obvious damage to the fiber itself. The common bleaching methods of cotton fabric are sodium nitrite method, hydrogen peroxide method and sodium chlorite method. The PH value of sodium hypochlorite bleaching solution is about 10, and it is carried out at room temperature. The equipment is simple, the operation is convenient and the cost is low, but the strength of the fabric is damaged greatly and the whiteness is low. The PH value of hydrogen peroxide bleaching solution is 10. When bleached at high temperature, the bleached fabric has high whiteness and stability, good hand feeling, and can also remove size and natural impurities. Disadvantages are high requirements for equipment and high cost. Under appropriate conditions, desizing, scouring and bleaching can be completed at one time with caustic soda. The PH value of sodium chlorite bleaching solution is 4 ~ 4.5, and it is carried out at high temperature, which has the advantages of good whiteness and little damage to fiber. However, it is easy to produce toxic gas during bleaching, which pollutes the environment and corrodes equipment, and requires special metal materials, so its application is limited. Both sodium hypochlorite and sodium chlorite should be dechlorinated after bleaching to prevent the fabric from being damaged by residual chlorine. 6) Dyeing and dyeing is a complicated process, and different fabrics have different dyeing processes. Used for cotton, polyester cotton, linen cotton, wool products, silk products, chemical fiber products, blended products, etc. Some can be pad-dyed and jig-dyed, some must be dyed at high temperature and high pressure, some must be dyed once, and some must be colored many times. Different dyes have different processes. Take the basic cotton fabric as an example: although dyeing can be done by a roller, it is also the most difficult process, because besides the known color control of dyeing, there are many unknown things in it, such as the stability of dyes at different temperatures, the control of steam, the control of roller pressure and so on. These are very delicate tasks. The long dyeing car is divided into two parts: front dyeing and rear fixing. Dyeing methods vary with dyes. Dyes are generally active, such as stone forest, vulcanization and coating. They have their own advantages and disadvantages, generally depending on the desired color, and cannot be substituted for each other. Among them, Shilin has the best color fastness, but it is expensive, not suitable for dyeing dark colors, and light colors are not bright enough. Except for dark dyeing, it will increase. In addition, dark dyeing is more difficult to control than reactive dyes, and it is prone to the cloth flower and other phenomena. The color fastness to activity is worse than that of Shilin, but the light color dyeing is more gorgeous, the dark color is easy to control and the cost is correspondingly less. Vulcanization is the worst, the color fastness is not very good, and the banned azo is not up to standard, but now there is liquid vulcanization (also called water vulcanization) that can meet the standard, but the price is close to Shilin, and the dyeing is not easy to control and cannot be popularized. Only a few people pursue its fading effect and adopt it. Paint is not comparable and the color fading is very serious, so the pursuit of color fading effect after washing is the best choice for clothing. It can be flexibly applied with Shilin to obtain different washing effects (common Shilin or reactive primer, coloring, can solve the white spot problem of single-dyed paint, and the cost will increase accordingly). The activity of Shilin is basically the same as that of vulcanized dyeing, but the difference is infrared pre-drying. The two groups are either not open. The back car is completely different. The active ones are fixed with salt and soda ash, the Shilin ones are reduced with hydrogen peroxide (so Shilin is also called vat dye), and the vulcanized ones need high-temperature cooking to fix the color. The water temperature must be above 95 degrees. After the paint is dyed, it is decided whether to bake and fix the color according to the fading requirements of color fastness. The baking temperature is about 195-2 10 degrees. Dyeing is impossible 100% good. 7) Mercerization: Mercerization refers to the process of treating cotton fabric with concentrated caustic soda solution at room temperature or low temperature under the condition of tension in both warp and weft directions to improve fabric properties. After mercerizing, the natural twist in the longitudinal direction of the mercerized cotton fabric disappears due to the bulkiness of the fiber, the cross section is oval, and the reverse direction of light is more regular, thus improving the luster. With the increase of invisible area of fiber, the dye uptake of dye increases. With the improvement of orientation, the strength of the fabric increases, and it also has the function of setting. After mercerizing, the alkali should be fully removed by washing, steaming or washing until the fabric is neutral. Dyeing is a process of combining dyes with fibers physically or chemically, or generating pigments on fibers by chemical methods, so that the whole textile has a certain color. Dyeing is carried out under certain conditions, such as temperature, time, PH value and necessary dyeing auxiliaries. Dyed products should have uniform color and good color fastness. The dyeing methods of fabrics are mainly divided into dip dyeing and pad dyeing. Dip dyeing is a method of dipping the fabric into dye solution to make the dye gradually penetrate the fabric. Suitable for small batch and multi-variety dyeing. Rope dyeing and jigging belong to this category. Pad dyeing is a dyeing method in which the fabric is soaked in dye solution, then the fabric passes through a roller, and the dye solution is evenly rolled into the fabric, and then steamed or hot-melted. It is suitable for dyeing a large number of fabrics. 8) Finishing after finishing is a textile technology project that endows clothing fabrics with wearability and aesthetics. The following are the common textile finishing types at present: the main equipment includes singeing machine, desizing machine, mercerizing machine, liquid ammonia machine, setting machine, pre-shrinking machine, calender, washing machine, sanding machine, wool grabbing machine, coating machine and so on. Main functions: 1, sanding 2, calendering 3, embossing 4, flocking and transfer hot stamping. 5. coating (a, dry coating; B, wet coating; C, transfer coating is also called centrifugal paper coating) 6, PVC calendering and embossing treatment 7, composite (a, TPU film PTFE film; B, fabric composite) 8, washing water, stone grinding, ink jet, fixing color treatment. 9. Waterproof, windproof and lint-proof treatment. 10, antistatic treatment 1 1, flame retardant treatment 12, anti-ultraviolet treatment 13, napping, sanding, anti-pilling treatment 14, wrinkling and foaming treatment/kloc-. With the development of technology, new finishing processes and materials will appear constantly. Dyed cloth-color fastness Dyeing fastness is the most important index of dyed cloth. The ability of printing and dyeing textiles to keep their original colors under the external action, also known as color fastness. After dyeing and printing, textiles sometimes go through other processes, such as felting of wool fabrics and heat setting of synthetic fiber textiles. Pay attention to the atmosphere, sweat stains, washing, rubbing and ironing during taking. All these will make the printing and dyeing textiles fade and change color in different degrees. The main processes that affect the dyeing fastness of printed and dyed textiles are felting, carbonization, chlorine bleaching and sublimation. The dyeing fastness of dyes or pigments on textiles is related to their chemical structure, concentration and state on fibers and the properties of fibers. The test method of dyeing fastness is formulated by simulating various wearing or technological conditions. The International Organization for Standardization (ISO) has successively formulated various international standards and testing and evaluation methods for color fastness with reference to the standards formulated by the British and American Dyeing Associations (SDC and AATCC) and the European Continental Association for Color Fastness (ECE). There are also national standards for various main dyeing fastnesses in China, such as: ① lightfastness, also known as lightfastness, which is divided into eight grades, with 1 being the least lightfastness and 8 being the best. At all levels, there is a blue wool fabric reference sample dyed with a specified dye with a specified concentration, which is called a blue standard sample. During the test, the sample and eight blue standard samples were exposed to the sun for a certain period of time according to the specified conditions, and then compared with the blue standard samples to evaluate the light fastness level of the samples. Due to the long sun exposure test time and the limitation of climate change, artificial light sources, such as xenon lamps and carbon arc lamps, are generally used, and the spectral energy distribution of xenon lamps is close to that of sunlight. (2) The washing fastness is divided into fading and staining, which are divided into five grades according to the regulations of gray standard samples respectively, and the color difference step by step becomes geometric series. During the test, the sample and the white cloth are sewn together, washed under specified conditions, and dried after washing. Separate the sample from the white cloth, and compare and evaluate the fading fastness with the gray fading sample card according to the color difference before and after washing the sample. 1 grade has the largest chromatic aberration, and there is no chromatic aberration at grade 5 by visual inspection. Compare the stained white cloth with the stained gray sample card to evaluate the color fastness of the sample to the white cloth. 1 grade staining is the most serious, and there is no staining at grade 5 by visual inspection. There are four test temperatures for washing fastness: 95℃, 60℃, 50℃ and 40℃, which depend on the requirements of printing and dyeing textiles. ③ Friction fastness is also divided into five grades. During the test, the samples were rubbed with dry and wet white cloth according to the specified conditions, and then the staining degree on the white cloth was compared with the gray staining sample card. The result obtained by rubbing dry white cloth is dry rubbing fastness; The result of wet white cloth rubbing is wet rubbing fastness. Other dyeing fastnesses can be tested according to the specified conditions, and the test results can be compared with gray faded sample cards or gray dyed sample cards to evaluate the series.