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Research progress of pad dyeing equipment with reactive dyes

Time:2020-11-30 17:13:46 Source:

1. Preface Reactive dyes are the most important dyes for dyeing cellulose fiber textiles, and the continuous pad dyeing of reactive dyes is one of the most important dyeing processes. However, it is necessary to dry the fabric in the middle after dip rolling, so as to improve the processing speed and reduce the hydrolysis of dyes during subsequent steaming or baking fixation, so as to obtain high fixation rate and color fastness. However, there are many problems in intermediate drying. First of all, when drying, the dye is easy to migrate, resulting in color difference and color fastness reduction, and the reproducibility of dyeing is also poor. In addition, when wet fabrics are dried, the evaporation of water will consume a lot of energy. In addition, drying will make the water on the fabric evaporate first, and then dip rolling or fabric steaming will make the dye and chemicals re absorb water and dissolve, and dry fabrics will release heat when they absorb moisture The phenomenon of overheating is unfavorable to the rapid dye uptake and fixation, and this kind of repetition makes the fabric absorb water and lose water, which is also very unreasonable in energy utilization. Therefore, wet steam dyeing is the long-term goal of printing and dyeing industry. 2. Dyeing process of several common reactive dyes The pad dyeing processes of cellulose fiber with reactive dyes are mainly as follows: ① Rolling drying steaming process ② Rolling drying rolling steaming process ③ Rolling baking baking process ④ Cold rolling and coil stacking process Among the four processes mentioned above, processes (1-3) are all continuous pad dyeing processes, and intermediate drying is required after pad dyeing solution is dipped in these three processes, so as to reduce the hydrolysis of dyes on the fabric and improve the heating rate and fixation rate during steaming or baking. Process 1 is mainly suitable for dyes with high stability, but it has low dye uptake, light color gain and poor color fastness. In the second dip rolling, a large amount of electrolyte, i.e. salt or sodium sulfate, must be added to prevent the dye from being desorbed, and the fabric is dried first and then absorbed water, which not only prolongs the process, but also consumes more energy. Process 3 needs to consume a lot of urea as fixation and penetrant. High temperature curing process not only consumes a lot of energy, but also has a dark color. When the temperature reaches 150-180 ℃, urea will decompose to produce toxic flue gas and reduce the fixation rate of dyes. It can be seen that the above three processes have the problems of long process, high energy consumption, poor fixation rate and color fastness, and heavy environmental pollution. Process 4 is a semi continuous pad dyeing process, suitable for reactive dyes with high reactivity and diffusion properties. However, the production cycle of this process is long, it is not easy to set out, and a large amount of caustic soda and sodium silicate (sodium silicate) are needed as color fixing agent, which makes it difficult to wash, the finished fabric feels hard, and the dirt around the machine is serious. Therefore, the use of this process in printing and dyeing enterprises is greatly limited. Because there are many problems in the production practice of the above processes, the wet short steaming pad dyeing process, which has the advantages of energy saving, environmental friendly, and improving the dyeing quality, has attracted more and more attention. 3. Theoretical basis of wet short steam dyeing process Wet short steaming dyeing process is to use special steaming equipment to raise the temperature of the fabric as soon as possible under the premise of selecting appropriate dyes and fixing alkali agent, so that the moisture content of the fabric from 60% to 70% during rolling can be quickly reduced to an appropriate level, and then wet steaming or baking can be carried out to fix the dyes quickly. The wet short steaming dyeing process uses wet fabrics for direct steaming fixation, and the heating carrier also contains a certain amount of humidity. Therefore, the process has the advantages of fast steaming fixation speed, high fixation rate, difficult migration of dyes, low alkali dosage, or the use of weak alkali agent with less pollution. Generally, urea is not needed, and the reproducibility, levelness and penetration are better. In particular, the wet fabric is directly steamed (baked) without intermediate drying, which has obvious energy-saving effect. There are many factors affecting wet short steam dyeing process, including the structure and properties of dyes, fiber properties and fabric structure, alkali agent properties, fixation temperature and time, auxiliaries and salts, etc.; different from conventional pad dyeing process, it is also affected by moisture content of fabric, composition of heating carrier, moisture content and temperature of gas medium, etc. Due to the joint influence of so many factors, the appearance of fixed color is often different from that of conventional rolling drying rolling steaming process by using wet short steaming fixation process, whether superheated steam or air steam mixture as heat carrier. This is also the most difficult place for the technical personnel of dyeing and finishing enterprises. Therefore, it is necessary to study the special wet short steaming process equipment through continuous process test, and establish the special technical conditions of wet short steaming, so as to better promote the popularization and application of wet short steaming dyeing process. 4. Research progress of domestic wet short steam process equipment 4.1 overview of wet short steaming dyeing technology abroad Since the application of reactive dyes in the 1950s, countries all over the world have focused on the research of the structure of reactive dyes and the development of new process equipment. In the 1980s, Hoechst (Hurst) and Bruckner (Bruckner) Co developed eco steam system (economic steam method); in 1995, monforts (Fuji) and Zeneca (Jericho) Co developed econtrol process (wet steam dyeing method); Babcock (bakok) and BASF (BASF) Co., Ltd. in 1998 Babco heat dryer, developed in, has completed the new process of easy fixation and color development. The above new wet steaming process opens a new era of reactive dye wet steaming dyeing technology, and provides a good experience basis for our research on wet short steaming dyeing technology. 4.2. Recent development of wet short steam dyeing technology in China In 2002, on the basis of digesting and absorbing the eco steam system wet steaming process, Shanghai No.2 printing and dyeing Co., Ltd. changed the domestic baking equipment into high temperature wet short steaming process equipment to carry out the wet short steaming process of domestic kn, m and K reactive dyes; after the introduction of an econtrol process equipment in 2002, the former Handan printing and dyeing factory made a lot of process contrast tests, taking the more difficult coffee, dark blue and carbon black as examples The above two companies have made positive contributions to the promotion and application of wet short steaming dyeing process in China. As the temperature and humidity control requirements of wet short steaming process are very strict, and the temperature and humidity are closely related, the moisture content of fabric and the relative humidity of heat carrier are also related to the temperature rise rate of fabric and the temperature in the platform area of the temperature rise curve, and affect the dye uptake and fixation. Therefore, the successful application of reactive dye wet short steaming dyeing process, in addition to the research and development of new reactive dyes and auxiliaries, research and development of special process and technical conditions, research and development of new wet short steaming pad dyeing process equipment, to achieve accurate control of temperature and humidity, is a very important content. Over the past period of time, some domestic dyeing and finishing equipment enterprises have tried to demonstrate the wet short steaming process equipment and manufactured the prototype. However, due to the lack of research and development in many aspects, such as process adaptability, equipment structure setting, temperature and humidity control system, it failed in the production test. As early as 1997, Jiangdu printing and Dyeing Machinery Co., Ltd. and the former Yangzhou printing and dyeing factory jointly tested the X-type reactive dye continuous pad dyeing and low-temperature baking fixation process, and developed the reactive dye short process wet steaming equipment in 2003. In the following years, the process test and equipment improvement were continuously carried out. Last year, the textile industry association clearly put forward in the "Twelfth Five Year Plan" outline of scientific and technological progress of textile industry that the wet short steaming dyeing technology of reactive dyes should break through the industrialization technology in 2015, and strive to reach 30% in 2020, which provides a good opportunity for the application and rapid development of warm short steaming dyeing technology in China. Jiangdu printing machine is the foundation of continuous research on wet short steaming process equipment for more than ten years. It adapts to the technical research and industrialization requirements of "progress outline". Through joint research and development with relevant equipment and process experts in the industry, it is now solemnly launching the company's latest product intelligent wet short steaming pad dyeing machine to the industry. 4.3 main features of intelligent wet short steaming pad dyeing machine 4.3.1 process flow of the equipment: as shown in Figure 1 (only the wet steam fixation part of the front section is listed) Flat cloth feeding in the middle → uniform rolling → infrared pre drying → humidification device → hot air pre drying (20m) → wet steaming fixation (40m + 40m) → high temperature water washing → soaping → water washing 4.3.2 configuration and characteristics of each unit Uniform rolling: ① On the premise of keeping the soaking time unchanged, the volume of the rolling groove was reduced to less than 30L, so that the dye solution could be renewed in time and kept fresh all the time. ② The dye and alkali are accurately mixed and supplied by 1:4 proportional pump, and then evenly mixed through the mixing pipe, and then supplied to the rolling tank, so as to improve the stability of the process dye solution, prevent the hydrolysis of the dye, save the dye, and reduce the chroma of the process sewage. ③ There are liquid level automatic control and gate width correction devices in the rolling groove, which can adjust the liquid supply according to the change of liquid level and gate width. ④ The rolling mill is equipped with an automatic cleaning device. When a batch of fabric is dyed and the guide runs, the automatic spray cleaning is immediately carried out on the rolling mill to realize color change without stopping the machine and shorten the batch change time. Infrared pre drying: innovative design of infrared pre drying device, in the same radiation sermon fabric through three times, make full use of thermal radiation, thermal convection effect, improve the process speed, reduce the comprehensive energy consumption; at the same time, the infrared pre drying machine exhaust fan exhaust hot and humid air into the wet steaming drying room, play the double effect of humidifying and heating the drying room. Moisture supply device: the special moisture supply device is used to wet the cloth and then lead it into the drying room. During the heating process of the equipment, the moisture of the cloth staying in the drying room evaporates. Before the process production, the humidity and temperature in the drying room tend to be stable, creating conditions for the formal process production. Hot air pre drying (20m): in front of the wet steamer, there is a room of hot air pre drying oven with a cloth capacity of about 20m, which can quickly dry the dipped and rolled fabric with infrared pre drying, so as to ensure that the moisture content of the fabric is below the critical moisture content before entering the wet steamer, and meet the process conditions of wet steaming fixation. Wet steam fixation (40m + 40m) ① The patented multi guide roll resistance torque compensation control ensures the fabric to run with low uniform tension and no wrinkling. ② The mixing of hot air and steam is controlled by computer PID fuzzy control, and the temperature control accuracy of wet steamer is less than ± 1 ℃. ③ According to the technical conditions of different wet short steaming processes, an intelligent "expert control system" is established to solve the key "wet balance" control difficulty of wet short steaming process. The non-contact moisture content control of home-made fabric and on-line measurement and control of relative humidity of atmosphere are adopted to ensure the "true process", good process reproducibility and save energy consumption. In addition, the new liquid flow high-efficiency soaping machine innovatively designed in the soaping unit can improve the wet rubbing fastness of soaping, which is 50% lower than the standard water. The drying condensate can be reused through the direct drainage washing machine without the steam trap, which can reuse 3000t of condensate throughout the year, save 300t of steam, and reduce 150t of steam leakage from the steam trap. 6t / h self-cleaning drum water-water heat exchanger is used for waste heat recovery of the whole unit. At least 60kg steam of 0.1MPa (gauge pressure) can be recovered per ton of hot sewage, and 2200t steam can be saved throughout the year. 4.3.3. The intelligent wet short steaming pad dyeing machine is used for wet short steaming continuous pad dyeing process without adding urea, sodium silicate (sodium silicate), caustic soda, inorganic salt and other chemicals and various additives, which is environmentally friendly and reduces production cost. According to the experimental calculation, for every 1kg cotton fabric, the chemical emission of the continuous pad dyeing process with reactive dyes is 214G, while that of the wet short steaming process is only 8.1G. The water consumption is reduced by 50%, and the comprehensive energy consumption is reduced by 30% ~ 50%. It can be seen that the wet short steaming process equipment fully shows the advantages of salt free, less water and short process dyeing in the application of one bath one-step process for cotton fabric and polyester cotton fabric. 5. Conclusion Due to the above unique advantages of wet short steam dyeing, it is of great practical significance to develop this dyeing process under the current situation of vigorously developing cleaner production and ecological processing. However, the wet short steaming dyeing technology is still in the experimental and initial stage in China, so the further development and application of wet short steaming technology still need to be further studied in the following aspects ① Continuously improve and improve the performance of wet short steaming processing equipment, make the equipment temperature and humidity, moisture content of fabric and other parameters control more intelligent and accurate. ② Strengthen the basic theoretical research of wet short steaming dyeing, including the research on the heating, moisture absorption and swelling properties of different fiber fabrics in different wet short steaming equipment. ③ Research new dyeing process, especially low alkali or neutral fixation process and controlled dyeing process; develop special auxiliaries to further improve the fixation rate, save dyes and reduce sewage. ④ We should strengthen the research and screening of reactive dyes, produce a series of matching dyes, and test their properties under the condition of wet short steaming, so as to improve their compatibility. ⑤ It can be used not only in reactive dyeing, but also in one bath one-step dyeing of other dyes and various dyes, especially in dyeing of some new fibers and multi-component fiber textiles, and even in pretreatment, printing and finishing.

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