Why don't make money: since the 21st century, the knitting dyeing and finishing industry in our country has come into the fastest growing period in its history with the growing demand for knitwear in domestic and foreign market, the annual processing capacity exceed ten million tons and is in the first place of the world. Due to the introduction of advanced equipment and technology, dyeing and finishing process and technology level has been improved significantly compared with the past, but in the face of more intense competition in the market and the increasingly stringent environmental requirements, there are some obvious aspects in the existing dyeing and finishing technical level that does not adapt to the development of the situation, but compared with international advanced level, there still exists big difference.Dyeing and finishing technological level is the key link of the knitted product quality and grades, it is also the most important mark for the energy conservation and emissions reduction, the only way forward for the sustainable development of the entire knitting industry will be the research and improvement of the total dyeing and finishing process.
The present situation of dyeing and finishing technology of knitted fabric in China
1.1 Pre-treatment processes(1) Sub oxygen bleaching process
At present there is only a dozen dyeing factories in Shandong province that are still using sodium chlorite bleaching technology, processing cotton elastic rib, cotton wool (double-sided tissue) underwear products. Products of the sodium chlorite peroxide bleach looks white, has a good elasticity, the grey fabric has less weight loss, in recent years, the equipment has changed from the tank to the titanium plate overflow machine, with type 0, and type L, compared with the tank type machines, the grey fabric and bleaching liquid have a high ratio of exchange, short bleaching time, this reduce the occurrence of crease due to pile pressure on the interior of the tank.
But since the Cl02 in the sodium chlorite bleaching process is toxic, corrosion to equipment, has air pollution, harmful to human health, unable to process the product containing spandex and other issues, this do not belongs to the clean production and thus has long been eliminated at abroad, its production has also been shrinking year after year at home.
Normal temperature overflow bleaching machine technology has a history of more than 30 years, because oxygen bleaching is in the boiling point, dyeing machine is not sealed, a large amount of heat and H202 decomposition is fading away in the workshop in the form of heat of vaporization, huge steam heat loss, long process time, leading to large energy consumption. The process use the unification of caustic soda, scouring and bleaching, caustic soda can remove grease and wax from cotton fibers, make the fabric feel thick and hard, and with a high rate of weightlessness rate, which is generally between 5% and 8%. Calculate yearly with a 8 million t cotton fabric processing, the weight loss is between 400,000 and 640,000 t, which is huge waste. Therefore controlling the loss rate of bleaching is the urgent task of process improvement, and it will have a great social benefit.
At the same time, caustic soda can play the catalyst role in the oxygen's damage to the fiber strength, to bring down the grey fabric's strength. When oxygen bleaching, the unevenness absorption of the alkali will lead to the dyeing defect in the next process. In addition, caustic soda bleaching is difficult to wash, washing more times, causing large water consumption, with high COD in the waste water, the sewage treatment is difficult, the fabrics containing spandex, viscose and other fiber should not be treated with caustic soda. Therefore, the pretreatment process of knitted fabric should be improved to the oxygen-free process without caustic soda.
(3) Rapid oxygen bleaching process without caustic soda
In the end of the 20th century, a foreign auxiliary enterprises in Shandong province introduced a compound rapid oxygen bleaching agent that containing no caustic soda from European head office, in the application of the oxygen bleaching technology such as knitted fabric, bobbin, etc. It's good in whiteness, less weight loss (2.5% ~ 3.6%), easy to clean, even dye ability, suitable for high temperature drift and a variety of fiber oxygen bleaching. This reagent has been widely used and promoted for several years, from the Pearl River delta, the Southeast Coast, the Yangtze River delta to the knitting dyeing factory and bobbin mills of the Shandong Peninsula, Liaoning Peninsula, it is in heavy use.
The use of biological enzymes mainly refers to the cooking process of pectinase, which has been promoted. Using pectinase under the condition of 50-60 ℃, pH 4.5 ~ 5.5 to process cotton can remove the pectin substance, improve the capillary effect, and it will cause low potential damage to cotton. After enzyme scouring and then to oxygen bleaching, the weightlessness rate is less than the alkali oxygen process, some dark products such as navy blue, black can be directly dyed after scoured with pectinase, the fabrics feels soft, thick and with small shrinkage. Compared with the alkali oxygen process, the pretreatment process of biological enzyme can reduce the water and steam consumption, which is a clean production process that is been vigorously promoted.
The continuous pretreatment process has the three forms of processing type, they are rope, cylinder and slitting open width. The cylinder open width introduced by a manufacturer in Zhejiang from German ERBATECH GMBH company has been put into production and the slitting open width is also put into production in Guangdong province, and the same kind of equipment has been produced in China as experiment. Cloth made by continuous pretreatment process is good in quality and cloth is very flat without fine wrinkles, sanding, bias filling, etc., the enrire machine is equipped with automatic feeding, process parameters online monitoring equipment, with good reproducibility craft, less water consumption (water consumption of per ton cloth is 1:8 - 1:10), (steam consumption of per ton cloth is 1:0.8), high production efficiency (shift production per capita can reach 6 ~ 8 t).
At present, there's only a few companies is still using this production line in domestic, but with the constant improvement of equipment and the reducing of the cost, it will be the trend of future development of pretreatment process, particularly when it is used together with open-width singeing, mercerizing, open-width cold heap, open-width printing, open-width dyeing finishing, the product and enterprise's competitiveness can be significantly improved.
1.2 Dyeing process
The dyeing process of cotton and its blended and interwoven knitted fabrics is mainly impregnated, and adopt reactive dyeing process by dye overflow machine, the pad dyeing process is still in the initial stage.
Reactive dyes overflow dyeing machine, in order to promote dyeing, a lot of salt (sodium sulfate, table salt) is needed, a lot of sodium carbonate is needed for the sake of fixation, dyeing dark varieties such as black, navy blue, etc. the usage of sodium sulfate is up to 90% - l00 % (o.w.f), the usage of sodium carbonate is up to 20% to 25% (o.w.f) salt, alkali consumption amount is huge, if the amount of dark color product is about 20% at home, and calculate by 2 million tons of production per year, the salt consumption would be 2 million tons, the consumption of sodium carbonate would be a half million tons, add 80% dyeing products, the total consumption of salt, alkali are a surprising bigness, after dyeing a lot of water is needed for flushing, per ton cloth’s water consumption is l: 7-1:10, dyeing degree of reactive dyes is only 70% - 85%, large amount of sewage and high colority increased the difficulty and fees of sewage disposal.
The improvement of reactive dyes dyeing process that is been pushed at present, one is to use the substitution alkali (compound with high concentration of mixed alkali) instead of sodium carbonate, the amount is 1/5-1/6, it is easy cleaning after dyeing, the second is to use acid bifunctional soap detergent, combined the acid neutralization with soaping of the original process, after dyeing and three times washes, using acid neutralization and soaping directly, eliminating the separate acid neutralization, this process improvement can reduce 80% sodium carbonate, saving 10% water, saving electricity and time and is worth promoting and is worth of being generalized.
After the short liquor dyeing machine with excellent performance is been introduced, the liquor ratio of reactive dyes dyeing process can reach 1:4-1:5, which obviously reduces the consumption of dye and energy. The knitted fabric reactive dyes dyeing process and cold pad-batch dyeing which use no salt at all has already put into production in some factories in Guangdong province.
The present situation of the knitted fabric dyeing process is there exist differences between regions, and enterprises, some powerful dye house from the Pearl River Delta, Yangtze River Delta, Shandong province are well equipped with dyeing machine, advanced testing instruments, they use high quality dyestuff, the process design is reasonable, the success rate of one-off dyeing can reach more than 98%, some foreign knitting brand products are made orders processing production in those factories.
Some small and medium scale knitting dye houses in the north, Midwest are relatively backward due to the shortage of hardware and software, re-work rate is high, bath ratio is high up to1: 10, process time is long, the water consumption of per ton cloth can reach up to 1:150 -1:200, the products processed are low in grade, every year, there are some companies loss out.
1.3 After finishing process
The after finishing process of knitted fabric is generally of two kinds, they are cylinder and slitting open-width.
The cylinder process mainly deal with the rib of the small round machine, cotton wool, sweat cloth and underwear products, and adopts the overfeeding humid size enlarging, the round net drying, the non-tension loose drying and the overfeed rolling light. Using the tapered preshrinking machine of separated supporting plate imported from FERRARO or SANTEX, the radial reduction rate can be controlled within 5%. However, there's a huge extrusion pressure exist between the cylinder tapered preshrinking machine's supporting plate and overfeeding wheel, dark color varieties of grey fabrics are more likely to get calendering marks, large diameter circular knitting machine product's skewing is difficult to deal with, etc., this aircraft can't satisfy the large diameter circular knitting machine grey fabric's quality requirements.
The after finishing process of the slitting stentering is more commonly applied at present, the grey fabric of the single and double-sided large diameter circular knitting machine, especially the grey fabric with the spandex fiber is arranged by the stentering setting process. Some factories in Zhejiang and Shandong province have already introduced the stentering tapered preshrinking machine, which can effectively solve the reduction rate of pure cotton knitted fabric and the problem of smooth surface. After stentering setting, the high quality effect of the medium and high-grade knitted fabrics can e shown off through the stentering overfeeding steaming blanket preshrinking, the hand feeling will be soft and glossy, the shrink rate can be controlled within 2%.
The Gap of Knitting Dyeing and Finishing Technology at Home and Abroad
Compared with the foreign advanced knitting dyeing and finishing technology, the entire technology level of our country's knitting dyeing and finishing process is still far away to achieve the balance, it can be embodied in the dyeing and finishing equipment, process technology, modern management, information, product innovation, the quality of technicians and operators, etc.
2.1 The overall equipment level is lagged behind and the update speed is slow
Except from foreign owned enterprise, stock listed enterprises, some large or very large enterprises, most of the medium and small businesses existing in domestic are still using equipment of 10 years, 20 years ago, not much new equipment, equipment update speed is slow.
Some automatic control machine has just started, such as online process parameter monitoring instrument, computer color matching, airflow dyeing machine, small liquor ratio double-flow dyeing machine, open-width pretreatment production line, etc.
The initial capital accumulation of enterprises is slow and working fund is not abundant, while the dyeing factories in developed countries have already formed capital intensive and technology-intensive enterprises.
2.2 Lack of R & D ability
In knitting dyeing and finishing enterprises, most enterprises are processing materials, as long as they can meet the quality requirements of the order, enterprises generally do not have researching and developing capability departments. To complete an order and ensure the quality of delivery, quantity and on schedule have had done a very big job, there's no more manpower, material and energy to process technology research, develop new products, also lack of competent technical personnel, the enterprises working for foreign merchant.
2.3 Poor product quality and is low in grade
As companies are constantly developing and lack of technology and person with ability, technology update speed is slow, enterprise is in a deal with situation in production and can only meet the downline of customer's demand quality, and product quality control is not strict. Due to lack of key equipment and technical research and development personnel, product level is low.
2.4 High energy consumption and serious pollution
Most of the dyeing factory's water consumption per ton cloth is above 1:150, if processing 50t's cloth then the sewage would be 7500 t. Most enterprises adopt dyeing machine from pretreatment to the batch production of softening finishes, bath ratio is about 1:10, due to the backward technology, especially without strictly process design and process control, one-off accurate dyeing is impossible, re-work quantity is big, and the water consumption will be more; Use more caustic soda, sewage with high COD, and the sewage treatment cannot meet the discharge standard. Due to the force price down phenomenon, the export tax rebate is reduced, the exchange rate is changed, the cost of labor is increased, and the profit space is getting smaller and smaller.
The cost of sewage treatment is difficult to pay and the sewage treatment is also half open, to cope with a check, so there is still a distance from the cleaner production. However, in recent years, the situation has improved somewhat due to the increased management of environmental work by the government at all levels. For instance, there's a large enterprise in Zhejiang province control the water usage for bleaching at 1:6 0, not only does the wastewater reached the discharging standard, and there are 60% treated water can recycled by membrane filtration, it has obtained good effect, it is definitely worth promoting.
Due to the relatively poor working conditions in the dyeing factory, it is very rare for the technical secondary graduates of dyeing and finishing majors to get to work at the factory directly in recent years, lack of talents and brain drain is impressing. Enterprises not only lack of qualified management personnel and technical personnel, but also lack of high-quality talents, especially the chief engineer with comprehensive technology, meanwhile, enterprises lack of technical training to the staff, all these factors have restricted the enterprise to develop in the direction of high level.
In conclusion, what the dyeing factory lack is a sense of belonging of the technician, the centripetal force and a series of perfect employment mechanism alike.
Growing trends of knitted fabric dyeing and process of finishing agent
China has been joining WT0 for six years, and the textile quota has been cancelled, the main obstacle of the current export of textile clothing is technical barriers such as green and environmental protection. In order to strengthen the protection of human health and environment and reduce the harm of chemicals, the European Union has introduced the REACH regulation, which makes the world textile trade competition fiercer. Our knitting dyeing and finishing industry will be unable to continue if it is to stay in the low labor cost advantage and price advantage, to accelerate the improvement level of science and technology is urgent, we should relying on technology, research on new technology, to improve product technical content and added value continuously through innovation, enhancing the grade of the product and its competitiveness in the international market.
3.1 cleaning production is the principle of dyeing and finishing process design
The state environmental protection administration made it clear that by 2010, all printing and dyeing enterprises in China should adopt environment-friendly raw materials and implement cleaner production. The process of knitting dyeing and finishing must meet the requirements of cleaner production, and make clean production the principle of the design of dyeing and finishing technology is the inevitable trend of dyeing and finishing process. Knitting dyeing and finishing enterprise should pass the certification of the IS014000 and establish the guarantee system of enterprises environmental protection, to improve environmental control ability of the product quality, create conditions to apply for the "environmental protection and ecological" label of Oek0-Tex standard series, in order to increase consumers' trust of our products and competitiveness in the international market, bring long-term benefits for the enterprises.
To conduct clean production of dyeing and finishing process design, should improve the utilization rate of resources at first, reduce the generation of pollutants and emissions, water saving, energy saving, use less or no toxic dyes, auxiliaries and use less waste or no waste technology. To achieve energy conservation, emission reduction and choose to use efficient equipment and perfect management system from the source of the process design, therefore to produce environmental friendly a knitting products.
3.2 Knitting dyeing and finishing technology should grow in the direction of one-off success
Modern control technology based with computers has been widely used in knitting dyeing and finishing apparatus, equipment, production and management, from the laboratory, computer color matching, the dyeing machine computer process control, etc.
In order to reduce the time of delivery, dyeing and finishing process design of small batch and multi-variety should be one-off success in order to reduce the cost and enhance the competitiveness of the product. The process test of the laboratory must be refined, all the technological parameters, the accuracy and reproducibility of small sample tests should be measured. An accurate process can be achieved after small, medium and large sample test, a one-off success can be achieved according to process production.
3.3 Pretreatment technology process grows to short process, high speed, high efficiency and clean production direction
(1) Application of enzyme
Using pectin, hydrogen peroxide to remove enzymes and cellulase in the pretreatment process, reduce water consumption, save energy, and reduce the burden of waste water treatment.
(2) High temperature speed drift
As mentioned before, non-caustic rapid oxygen bleaching process is a kind of clean production process. This process use rapid oxygen bleaching agent and hydrogen peroxide only, keep warm at ll0 ℃ in high temperature overflow machine about l5 ~ 20 mins.
When the dosage of oxygen bleaching agent is 2．5～3 g/L, PH value can stabilize at 10.5 ~ 10, make H202 linear decomposition by the increase of temperature and the extension of time, the decomposition rate can thus reach more than 85%. Rapid oxygen bleaching agent have function as scouring, emulsification, degreasing, integrate detergent washing, adjust pH value, etc. it can replace caustic soda, penetrating agent, stabilizer, degreaser and several other auxiliaries fundamentally in oxygen bleaching process. Compared with caustic soda process, this process has less fiber weightlessness, the fabric is soft (can reduce 1/3-1/2 softener dosage) and easy to clean after bleaching, just wash once with warm water is enough, the sewage of bleached water has a PH value less than 9, COD value is half less than caustic soda process, which is easy for wastewater treatment and has a good reproducibility.
(3) Continuously evaporating and evaporating knitted fabric
Continuous oxygen bleaching based on cylinder open width and slitting open width, compared with overflow machine oxygen bleaching, the bleaching quality has been greatly improved, cloth is bright and clean, no sanding, no fine wrinkles, water consumption is 1:10, per ton fabric's water consumption is 1-0. 8, it has high production efficiency. Continuous pretreatment of slitting open width can matching the open-width mercerizing, open-width tie-dye, open-width reactive dyes printing, to realize the high grade knitting fabric production line.
3.4. The mercerizing process of the open width knitted fabric
High quality knitted fabrics such as high - level yarn products, usually need to go through the mercerization. Some domestic bleaching and dyeing house with strong economic strength should develop open-width knitted fabric mercerizing, the color of knitted fabric processed by open-width mercerizing dyeing is gorgeous, cloth cover is luster, with more size stability and low shrinkage, it can save 30%-40% dyes and can matching open width scouring and bleaching, open-width dyeing, open-width printing, the process route is more reasonable.
3.5 airflow dyeing technology promotion
Airflow dyeing machine is using the principle of aerodynamics, using pressure air to optimize the dyeing effect of overflow dyeing machine, this can make the dyed cotton's bath ratio to l: 4, compared with the conventional dyeing, reduce about 50% water consumption.Due to the small bath ratio, it can reduce the dosage of 10% or l5 % dye material, reduce 30% steam consumption; Besides, the fabric has low tension, this reduces creases, uneven dye and improves the fabric's hand feeling at the same time.
The dyeing quality can be improved by airflow dyeing technology, a one-off successful dyeing is achievable. The technology of airflow dyeing has been continuously improved. For example, intelligent injection system is adopted to simplify dyeing procedures and significantly reduced the dyeing time. The whole function vertical equipment cylinder is set up, the cleaning water can be programmed according to the requirement, and the automatic cleaning filtration system is configured. The storage tank is changed into variable load storage tank, and each tube can be completely independently controlled, which is worth spreading.
3.6 Open width knitted fabric cold pad-batch dyeing process
Knitted fabric open-width cold pad-batch dyeing process technology is advancing day after day, it adapt to the small batch with many varieties’ production and does not need to add salt, saving dyes, auxiliaries, water, steam, less energy consumption, reducing the drawbacks, such as fabric wrinkle, grinding, etc.
After open-width pretreatment of cellulose fiber fabric, firstly, padding the reactive dyes by uniform padder, and send it to the stacking system by feed preparation unit roller, coiling with constant tension in the whole piling project, so as to avoid any squeeze on the knitted fabric, after fabric rolled up to a predetermined time, then wash it in the drum type open width washing machine.
The open width cold pile dyeing equipment is equipped with the optimized anti-rolling edge device. Open width processed knitted fabric does not bring any wrinkle on the fabric. Dyes and auxiliaries are added in different proportions, and the amount of liquid can be reproduced to maintain the dynamic balance and high accuracy. Using a PLC error compensation roller to adjust the rolling pressure effect, make the process control be datamation, bring down the fabric tension. Special temperature control system can measure the temperature online to guarantee the constant reproducing temperature. In this way, the dyeing process parameters can be controlled to ensure the one-off dyeing success. At present, there is only one factory in Guangdong province that has introduced the open width knitting fabric dyeing equipment and has put it into production.
3.7 Finishing process
The finishing process technology level is an important process to improve the level of knitting products. Through the advanced finishing processing, make the fabric's hand feeling good, the elasticity high, cloth surface clean, the grain clear and straight, and the reduction rate low. According to the customer's requirement, some products also carry out special function finishing, such as anti-ultraviolet finishing, antibacterial finishing, far-infrared finishing, anti-static finishing, anti-fouling, moisture absorption and quick drying etc.
The back finishing of knitted fabrics has two technological routes: one is the circular cylinder, the second is the coexistence of cylinder and slitting open width, these two kinds of processing forms all has its own characteristics. The cylinder processed fabric is suitable for underwear products. It should be used for overfeeding strong size enlarging, loose tension-free drying and separated supporting plate overfeeding tapered preshrinking machine. It is best to go by tentering felt preshrinking process after the slitting products went through tenter setting, this can effectively solve the problems such as shrinkage rate, fabric surface finish and hand feeling.
To sum up, the development trend of knitted fabric dyeing and finishing technology must head for the direction of cleaning, effective short process, one-off success and open width processing. Facilitated by dyeing and finishing machinery, electronic automatic control, fine chemical engineering, personnel education training and the development of information engineering, The new technology of knitting dyeing and finishing in our country will certain to walk in the forefront of the world.