Continuous Pretreatment Process And Application Technology Of Woven Cotton And Cotton Blended Yarn

The selection of fabric dyeing and finishing process is mainly based on fabric specification, finished product requirements, etc., which can be divided into scouring, bleaching, dyeing and finishing. At present, many factories have a semi continuous production of scouring and bleaching. Singeing, desizing, using cold pad batch or desizing bleaching alone, and cold pad batch have some protective effects on fabric strength, but stacking for 24 hours will affect production efficiency. Therefore, the combined pretreatment of bleaching and bleaching is superior to intermittent treatment in environmental protection, energy saving and high efficiency. It can save labor and improve production efficiency. A three person can be controlled at 90 to 110m/min, which is much higher than intermittent efficiency. This paper focuses on continuous pre-processing and process.

Author: Ding Shiquan, Bachelor of dyeing and finishing, Qiingdao University, Shandong, master of management science and engineering, Qiingdao University.

Natural fibers contain impurities. In the process of textile processing, various sizes, oil and contaminants are added. The existence of these impurities not only hinders the smooth operation of dyeing and finishing, but also affects the performance of fabrics.

The purpose of scouring and bleaching is to remove impurities from fabric by chemical action, so that the fabric is white and soft, and has good penetrability and preparation for dyeing and finishing.

1. introduction of continuous pretreatment equipment

The device is composed of a cloth stacking device, a bristle box, a singeing machine, a water washing box, a chemical treatment tank (automatic control system for chemicals), a steam steaming box, a water washing box, a drying device, a cloth discharging device, a cloth rolling device, a mercerizing machine and a heat setting machine (for example, for reference only, the factories can add washing boxes in front of the two steamboxes according to their own needs to meet their own production needs).

　　 2. process introduction

The raw cloth is ready to go into the cloth, then the singeing, desizing, boiling, bleaching, drying, drying and rolling.

2.1 raw cloth preparation

The original cloth preparation includes cloth inspection, cloth turning and sewing head. The purpose of the original cloth inspection is to check the quality of the grey cloth and find out the problem in time. The inspection includes two items: physical index and appearance defect. The former includes the length, amplitude and weight of the original cloth, density and density of warp and weft yarns, and so on, such as spinning defects, weaving defects, various class stains and breakage. After the original cloth inspection, the original cloth must be distributed in batches, and the varieties should be printed and printed on the cloth heads so as to facilitate the management. If the factory produces, the embryo cloth examination can be omitted, and the weaving factory will inspect the above items.

In order to ensure continuous batch processing, the original cloth must be suture joint. The stitch should not be too dense or too thin. It is too tight to cause the joint mark to be too thin and easy to break.

2.2 bristles and singeing

The purpose of singeing is to burn down the fuzz on the cloth so as to make the cloth clean and beautiful, and prevent uneven dyeing and printing defects due to fuzz in dyeing and printing. Fabric singeing is to quickly pass the fabric through the high temperature flame. There are usually two positive two oppositely in the singeing process. According to the thickness of the fabric, it is usually chosen to make two sheets of fire. The thick cloth needs two of the fire and two sides.

At that time, the floss on the cloth quickly heated up and burned, and the cloth itself was more compact, and the heating rate was slower. When it did not reach the ignition point, it left the flame, so as to achieve the purpose of burning fluff and not burning the fabric.

2.3 Desizing

In order to smooth weaving, textile mills often use warp sizing to improve their strength and wear resistance. The size of the fabric on the grey cloth affects the water absorption of the fabric, and also affects the quality of the dyeing and finishing products, and increases the consumption of dyeing chemicals. Therefore, the slurry should be removed before scouring, which is called desizing.

The size of the fabric is usually PVA starch slurry, which is characterized by easily dissolved in hot water above 80 degrees. Therefore, most of the slurry can be removed before scouring. PVA slurry is difficult to degrade and is easy to cause environmental pollution. The slurry returned from hot water can be collected and collected for recycling. The recovered PVA can continue to be used in the weaving factory, and the PVA recovery device can be reduced. The pressure of sewage treatment can save cost.

2.4 scouring

When cotton fibers grow, they are accompanied by natural impurities (pectin, waxy substances, nitrogenous substances, etc.). After desizing, most of the pulp and some of the natural impurities have been removed, but a small amount of slurry and most of the natural impurities remain on the fabric. The presence of these impurities makes cotton fabrics more yellow and less permeable. At the same time, the appearance quality of cotton cloth is greatly affected.

Therefore, the fabric needs to be scoured under the action of high temperature concentrated lye and some auxiliary aids to remove residual impurities. Scouring is to use caustic soda and other scouring agents to react with pectin, waxy substances, nitrogenous substances and cottonseed husks to produce chemical degradation or emulsification and expansion. After washing, impurities can be removed from the fabric.

2.4.1 scouring process

　　 Steam for 102 minutes at 30 minutes and rinse into bleaching process.

Matters needing attention in 2.4.2 process

The concentration control of scouring chemicals is relatively strict. The concentration control of caustic soda, sodium persulfate, penetrating agent and chelating agent is accurate. It is necessary to select a high performance chemical central control system (CCCMETER).

Penetrant must select products with high alkali resistance and strong penetrability (screened according to factory inspection requirements).

Chelating agents should choose strong chelating properties, and defoamer should be selected for defoaming, anti foaming and alkali resistance.

Sodium persulfate is a strong oxidant. The amount of scouring must be controlled accurately. The actual amount is determined by chemical titration every half an hour during the production. Too high will cause the fabric strength to drop, and too low will result in inadequate cooking.

2.5 bleach

After being scoured, the fabric's appearance is not white enough because of its natural pigments. Dyeing and printing will affect the brightness of the fabric. The purpose of bleaching is to remove pigment, give fabric the necessary and stable whiteness, and fiber itself is not subject to significant damage. The common bleaching methods for cotton fabrics are double oxygen water method and sodium subchlorite method.

Usually, hydrogen peroxide is used in factories to bleach. The pH value of the chemical solution is about 10, which is bleached at high temperature. The bleached fabric has high whiteness and stability, good handle, and can remove slurry and natural impurities. The drawback is that the equipment requirements are high and the cost is high. Under suitable conditions, combined with caustic soda, desizing, scouring and bleaching can be completed at one time. The bleached cloth gives a uniform whiteness and water absorption to the subsequent process to better control the levelling effect of dyeing or white cloth.

2.5.1 bleaching process

　　 Matters needing attention in 2.5.2 process

Steam at 25 degrees for 102 minutes and wash into the drying and rolling process. The overflow water can be recycled to the water washing process after scouring, energy saving and emission reduction.

Chemical concentration control also needs central control system to achieve. During the production process, the concentration of chemicals in each process should be checked. The error of machine setting and manual titration has met the requirements of the process. Chemical distribution can be carried out before production, and the concentration changes will be checked according to the frequency of every half hour to grasp the law of machine control.

Sampling must be done to check whether the water absorption of cloth contains PVA, PH, whiteness, strength and so on.

3. mercerizing

　　 Mercerization refers to the processing of cotton fabric under tension at room temperature or low temperature in the direction of warp and weft, which is treated with concentrated caustic soda or liquid ammonia to improve the fabric properties. After the mercerization of cotton fabric, the fiber is expanded and the longitudinal natural torsion of the fiber vanishes, and the cross section is elliptical. The reverse direction of the light is more regular, which enhances the luster. The increase of fiber stability increased the dye uptake of dyes. The improvement of orientation improves the strength of fabrics, as well as the shaping effect.

Mercerizing usually consists of alkali mercerizing or liquid ammonia mercerization. After alkali mercerizing, the caustic soda must be rinsed to remove alkali or wash away the alkali. The 8 sets of washing boxes are the best. Rinse seventh and eighth boxes with water, and add acetic acid to neutralize. After neutralization, the pH value is controlled at 5.5 to 7. It can be tested with a wide range of indicators.

Liquid ammonia mercerizing is carried out by mercerizing with ammonia. Compared with alkali mercerizing, liquid ammonia can instantly expand into the inside of cotton fibers, and the effect is uniform and easy to be eliminated. Liquid ammonia mercerization does not damage the fibers. On the contrary, it can also improve wear resistance and tear strength, while alkali mercerizing has serious damage to cotton strength. The dyeing rate of liquid ammonia mercerizing is less than that of alkali mercerizing, but its levelness is good, Hikaruzawa Youwa is soft.

Because of the high cost of liquid ammonia and highly volatile characteristics, it requires high environmental protection equipment and has environmental protection problems. At present, the application is not too extensive. If we can improve the recycling problem of volatile waste gas, it will be widely used in production in the future.

The role of mercerization is mainly to improve the cellular structure of cotton fibers by making use of strong alkali or liquid ammonia, so as to make them swelling rules, so as to better absorb dyes and finishing auxiliaries in dyeing and finishing. In addition, it can also improve fabric shrinkage properties and strength.

4. heat setting

Heat setting is an important process in dyeing and finishing of polyester and polyester / cotton blended fabrics. The main purpose is to eliminate wrinkles on the fabric, improve the thermal stability and shape stability of fabric size, and ensure that products are not easy to produce wrinkles which are difficult to eliminate in use and subsequent processing. Heat setting can also improve or alter the feel, strength, pilling and dyeing properties of fabrics to a certain extent.

Dacron belongs to thermoplastic fiber. When heat treatment is applied under the action of tension, the thermal movement of macromolecule chain is aggravated and rearranged in the direction of the force, melting small crystals with poor integrity inside the fiber, forming larger size crystals, thus improving the integrity and orientation degree, thus obtaining structural stability. Under the condition of certain tension, the setting effect of polyester is mainly affected by temperature and time.

The thermal stability of polyester and polyester / cotton blended fabrics is improved after heat setting. The setting effect of the fibers can be measured by determining the shrinkage of the fabric under certain heating conditions. In order to reduce wrinkles, pure cotton fabrics can also be qualitatively determined by wet stretching. The cotton strength is greatly affected by temperature. Therefore, the temperature control of the drawing type is 140~160 C, and the time is 30s. Because the number of baking machines in different factory setting machines is different (there are 10 groups in 8 groups), the ultimate drying time of the final cloth is the standard.

5. conclusion

To sum up, the continuous production of pre-processing is easy to achieve highly automated control. Product quality stability can greatly improve production efficiency and save energy. Continuous production requires high control of production conditions and chemicals. As long as proper selection of relevant auxiliary facilities (centralized control system), enhanced management and waste reduction can be achieved, efficient production can be achieved.