The choice of fabric dyeing and finishing process is mainly based on the variety, specifications and finished product requirements of the fabric, which can be divided into bleaching, dyeing, finishing, etc. At present, the scouring and bleaching production in many factories is still in a semi-continuous state, with singeing alone and desizing using a cold pad batch or desizing and bleaching alone. The cold pad batch protects the strength of the fabric, but stacking it for 24 hours affects production efficiency. , there are also problems such as difficulty in cleaning up pollution on the stacking ground. Therefore, combined decoction and bleaching pre-treatment is better than intermittent processing in terms of environmental protection, energy saving and high efficiency. It can not only save labor but also improve production efficiency. One combined decoction and bleaching machine only requires three workers, and the production speed can be controlled between 90 and 90 110m/min, the efficiency is greatly improved compared to the intermittent type. This article focuses on the continuous pre-treatment process and technology.
Natural fibers contain impurities, and various slurries and oils are added during the textile processing process and contaminated dirt, etc. The existence of these impurities not only hinders the smooth progress of dyeing and finishing processing, but also affects the clothing performance of the fabric.
The purpose of scouring and bleaching is to use chemical action to remove impurities on the fabric, making the fabric white, soft, with good permeability, and to prepare for dyeing and finishing.
1． Introduction to continuous pre-treatment equipment
Fabric feeding and stacking device→Brush box→Singeing machine→Washing box→Chemical tank (chemical automatic control system)→Steaming box→Washing box→Drying device → Cloth stacking device → Cloth rolling device → Mercerizing machine → Heat setting machine (the picture is for reference only. Each factory can add washing boxes before and after the two steaming boxes according to its own needs to meet its own production needs).
2. Process introduction
Original cloth preparation → cloth feeding → singeing → desizing → scouring → bleaching → drying → rolling.
2.1 Original fabric preparation
Original fabric preparation includes original fabric inspection, turning and sewing. The purpose of the original fabric inspection is to check the quality of the gray fabric and solve the problems in a timely manner. The inspection content includes physical indicators and appearance defects. The former includes the length, width, weight, warp and weft yarn density, strength, etc. of the original cloth, while the latter includes spinning defects, weaving defects, various stains and damage, etc. After the original cloth is inspected, the original cloth must be divided into batches, and the variety should be printed on the cloth head to facilitate management. If you produce it in your own factory, you can omit the inspection of the gray cloth, and the weaving factory will inspect the above items.
In order to ensure continuous batch processing, the original fabric must be seamed. The stitches at the joint should not be too dense or too thin. Too dense will easily cause joint marks during rolling, and too thin will easily break the fabric.
2.2 Brushing and singeing
The purpose of singeing is to burn off the fluff on the cloth surface to make the cloth surface smooth and beautiful, and to prevent dyeing and printing Uneven dyeing and printing defects may occur due to the presence of fluff. Fabric singeing is to quickly pass the flat width of the fabric through a high-temperature flame. The singeing openings usually have two forward and two reverse burners, which are selected according to the thickness of the fabric. Usually, two burners, one front and one reverse, are enough for thin fabrics, and two burners are required for thick fabrics. opposite.
At this time, the fluff on the cloth surface heats up quickly and burns, while the cloth itself is relatively dense and heats up slowly. Before it reaches the ignition point, it has left the flame, thus achieving the goal of burning. The purpose is to reduce fluff and not burn the fabric.
2.3 Desizing
In order to weave smoothly, textile mills often sizing the warp yarns to improve strength and wear resistance. The sizing on the gray fabric affects the water absorption performance of the fabric, and also affects the quality of the dyeing and finishing products, and increases the consumption of dyeing chemicals. Therefore, the sizing should be removed before scouring. This process is called desizing.
The slurry on the fabric is usually PVA starch slurry, which is easily soluble in hot water above 80°C, so most of the slurry can be removed before scouring. PVA slurry is It is difficult to degrade and easily causes environmental pollution. The slurry removed by hot water can be collected and recycled. The recycled PVA can continue to be used in weaving factories. The PVA recovery device can reduce the pressure of sewage treatment and save costs. .
2.4 Scouring
When cotton fiber grows, it is accompanied by natural impurities (pectin, waxy substances, nitrogen-containing substances, etc.). After desizing the cotton fabric, most of the sizing and some natural impurities have been removed, but a small amount of sizing and most of the natural impurities remain on the fabric. The presence of these impurities makes the cotton fabric surface yellower and has poor permeability. At the same time, it greatly affects the appearance quality of cotton cloth.
Therefore, the fabric needs to be scoured under the action of high-temperature concentrated alkali solution and some auxiliary additives to remove residual impurities. Scouring is the use of caustic soda and other scouring aids to react chemically with pectin, waxy substances, nitrogen-containing substances, cottonseed hulls, emulsification, puffing, etc., to remove impurities from the fabric after washing with water.
2.4.1 Cooking process
Steam at 102℃ for 30 minutes, wash with water and enter the bleaching process.
2.4.2 Process Precautions
Concentration control of scouring chemicals is relatively strict, such as caustic soda and persulfuric acid To accurately control the concentration of sodium, penetrant, and chelating agent, a high-performance chemical central control system (CCCMETER) needs to be selected to achieve this.
Penetrating agentProducts with high alkali resistance and strong permeability must be selected (selected according to the factory’s testing requirements).
The chelating agent should be selected with strong chelating properties, and the defoaming agent should be selected with good defoaming and foam suppression and strong alkali resistance.
Sodium persulfate is a strong oxidant. The amount of scouring must be controlled accurately. During production, chemical titration is used to determine the actual amount every half hour. If it is too high, it will cause The strength of the cloth decreases, and if it is too low, it will cause insufficient cooking.
2.5 Bleaching
After scouring the fabric, due to the presence of natural pigments on the fiber, its appearance is not white enough. Dyeing or printing will affect the brightness of the color. The purpose of bleaching is to remove pigments and give the fabric the necessary and stable whiteness without causing significant damage to the fiber itself. Commonly used bleaching methods for cotton fabrics include hydrogen peroxide method and sodium hypochlorite method.
Usually factories use hydrogen peroxide for bleaching. The chemical solution has a pH value of about 10 and is bleached at high temperatures. The bleached fabric has high and stable whiteness, good hand feel, and can also remove slurry and natural impurities. The disadvantage is that it requires high equipment and the cost is high. Under appropriate conditions, combined with caustic soda, desizing, scouring and bleaching can be completed at one time. Bleaching fabrics gives a uniform whiteness and water absorption properties to subsequent processes, allowing for better control of the leveling effect of dyeing or whitening fabrics.
2.5.1 Bleaching process
2.5.2 Process Precautions
Steam at 102℃ for 25 minutes and then wash with water to enter the drying and rolling process (the washing overflow water here can be recycled into the washing process after scouring to save energy and reduce emissions).
Chemical concentration control also requires a central control system; during the production process, the chemical concentration in each process must be spot-checked to check that the error between machine settings and manual titration has reached the process limit. According to the requirements, chemicals can be prepared before production, and concentration changes can be checked every half hour to grasp the rules of machine control.
When rolling, you must take samples to check the water absorption of the fabric and whether it contains PVA, PH, whiteness, strength, etc.
3. Mercerized
Mercerization refers to the treatment of cotton fabrics with concentrated caustic soda or liquid ammonia to improve the performance of the fabric at room temperature or low temperature, under tension in both the warp and weft directions. processing process. After the cotton fabric is mercerized, due to the expansion of the fibers and the disappearance of the natural longitudinal twist of the fibers, the cross-section becomes elliptical, and the reverse direction of the light is more regular, thus increasing the luster. The increase in fiber stability increases the dye uptake rate during dyeing. The increase in orientation increases the strength of the fabric and also has a shaping effect.
Mercerization usually includes alkali mercerization or liquid ammonia mercerization. After alkali mercerization, be sure to use light alkali washing to remove alkali or flat washing to remove alkali. The best is to use 8 sets of water washing boxes. First rinse the seventh and eighth boxes with water, and add acetic acid for neutralization. After mixing, the pH value is controlled between 5.5 and 7, and can be tested with a wide range of indicators.
Liquid ammonia mercerization uses ammonia water for mercerization treatment. Compared with alkali mercerization, liquid ammonia can instantly penetrate into the interior of cotton fibers and expand. The effect is uniform and easy to eliminate. Liquid ammonia mercerization not only does not damage the fibers, but on the contrary It can also improve wear resistance and tear strength, while alkali mercerization seriously damages cotton strength. The dye uptake rate of liquid ammonia mercerization is not as good as that of alkali mercerization, but it has good level dyeing, soft luster and soft hand feel.
Due to the high cost of liquid ammonia and its high volatility, it requires high environmental protection equipment and has environmental problems. It is not widely used at present. If the problem of recycling of volatile waste gas can be improved, it can be widely used in the future. in production. The main function of mercerization is to improve the cell structure of cotton fiber through the action of concentrated alkali or liquid ammonia, making it swell regularly so that it can better absorb dyes and finishing auxiliaries during dyeing and finishing; in addition, it can also improve the shrinkage performance of the fabric. and powerful.
4. Heat setting
Heat setting is an important process in the dyeing and finishing of polyester and polyester/cotton blended fabrics. Its main purpose is to eliminate existing creases on the fabric and improve the thermal stability and shape stability of the fabric. It ensures that the product will not easily produce wrinkles that are difficult to eliminate during use and subsequent processing. Heat setting can also improve or change the fabric’s feel, strength, pilling and dyeing properties to a certain extent.
Polyester is a thermoplastic fiber. When heat treated under tension, the thermal movement of the macromolecular segments intensifies and rearranges in the direction of the force, causing smaller crystals with poor integrity inside the fiber to melt and form The larger the size of the crystals, the greater the integrity and orientation, thereby achieving structural stability. Under certain tension conditions, the shaping effect of polyester is mainly affected by temperature and time.
The dimensional thermal stability of polyester and polyester/cotton blended fabrics is improved after heat setting. By measuring the shrinkage of the fabric under certain heating conditions, the shaping effect of the fiber can be reflected. In order to reduce wrinkles, pure cotton fabrics can also be characterized by wet tentering. Cotton strength is greatly affected by temperature, so the temperature for tentering and shaping is preferably controlled at 140~160℃ and the time is 30 seconds. Because the number of ovens in the setting machine is different in different factories (some have 8 groups and some have 10 groups), the final drying time of the fabric shall prevail.
5. Conclusion
In summary, the continuous production of pre-treatment can easily achieve a high degree of automated control. Stable product quality can greatly improve production efficiency and save energy. Continuous production has very high requirements on production process conditions and chemical control. High, as long as the relevant auxiliary equipment (central chemical control system) is correctly selected, management is strengthened, and waste is reduced, efficient production can be achieved.
��The time it takes for the fabric to dry completely shall prevail.
5. Conclusion
In summary, the continuous production of pre-treatment can easily achieve a high degree of automated control. Stable product quality can greatly improve production efficiency and save energy. Continuous production has very high requirements on production process conditions and chemical control. High, as long as the relevant auxiliary equipment (central chemical control system) is correctly selected, management is strengthened, and waste is reduced, efficient production can be achieved. </p
