Scouring and bleaching removes impurities contained in natural fibers, as well as various sizes, oils and contaminants added during textile processing. The existence of these impurities not only hinders the smooth progress of the dyeing and finishing process, but also affects the wearing performance of the fabric. The purpose of scouring and bleaching is to apply chemical and physical mechanical action to remove impurities on the fabric, so that the fabric is white, soft, and has good permeability to meet the requirements of wearing, and to provide qualified semi-finished products for dyeing, printing and finishing. The main processes of scouring and bleaching of pure cotton fabrics are: original fabric preparation, singeing, desizing, scouring, bleaching, and mercerizing.

1) Original cloth preparation: The original cloth preparation includes original cloth inspection, cloth turning (batch, box, printing) and sewing head. The purpose of the original fabric inspection is to check the quality of the grey fabric, and find problems that can be solved in time. The inspection contents include physical indicators and appearance defects. The former includes the length, width, weight, warp and weft yarn density and strength, strength, etc. of the original cloth, while the latter includes spinning defects, weaving defects, various class stains and damages. Usually about 10% of the total number of random inspections. After the original cloth inspection, the original cloth 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 the code of the person who turned the cloth, so as to facilitate management. To ensure continuous batch processing, the original fabric must be sewn.

2) Singeing: The purpose of singeing is to burn off the fluff on the cloth surface, make the cloth surface smooth and beautiful, and prevent uneven dyeing and printing defects due to the existence of fluff during dyeing and printing. Fabric singeing is to quickly pass the fabric through a high-temperature flame, or wipe the red-hot metal surface. At this time, the fluff on the fabric quickly heats up and burns. When it rises to the ignition point, it has left the flame or the red hot metal surface, so as to achieve the purpose of burning off the fluff without manipulating the fabric.

3) Desizing: For smooth weaving, textile mills often sizing warp to improve strength and abrasion resistance. The slurry on the grey fabric not only affects the water absorption performance of the fabric, but also affects the quality of dyeing and finishing products, and will increase the consumption of dyeing chemicals. Therefore, the slurry should be removed before scouring. This process is called desizing. The size of the cotton fabric can be removed from the fabric by methods such as alkali desizing, enzymatic desizing, acid desizing and oxidizing desizing. Alkali desizing causes the pulp to expand, and the adhesion to the fiber decreases, and is removed from the fabric by washing. Enzymes, acids and oxidants degrade starch, increase its solubility in water, and remove it by washing. Because acid and oxidant damage cotton fibers, they are rarely used alone, but are often used in combination with enzyme desizing and alkali desizing.

 4) Scouring: When cotton fibers grow, natural impurities (pectin, waxy substances, nitrogenous substances, etc.) are accompanied together. After the cotton fabric is desizing, most of the pulp and some natural impurities have been removed, but a small amount of pulp and most of the natural impurities still remain on the fabric. The presence of these impurities makes the surface of cotton woven cloth yellower and has poor permeability. At the same time, due to the existence of cottonseed husks, the appearance quality of cotton cloth is greatly affected. Therefore, it is necessary to scour the fabric in high temperature concentrated lye solution for a long time to remove residual impurities. Scouring is the use of caustic soda and other scouring aids and pectin, waxy substances, nitrogen-containing substances, cottonseed husks to undergo chemical degradation reaction or emulsification, puffing, etc., and the impurities are removed from the fabric after washing.

5) Bleaching: After the cotton fabric is scouring, due to the existence of natural pigments on the fibers, its appearance is not white enough. It will affect the brightness of the color when it is used for dyeing or printing. The purpose of bleaching is to remove pigments and impart the necessary and stable whiteness to the fabric without causing significant damage to the fibers themselves. Commonly used bleaching methods for cotton fabrics include sodium nitrite, hydrogen peroxide and sodium chlorite. The pH value of the bleaching solution for sodium hypochlorite bleaching is about 10, and it is carried out at room temperature. The equipment is simple, the operation is convenient, and the cost is low. However, it has great damage to the fabric strength and low whiteness. The PH value of the bleaching solution for hydrogen peroxide bleaching is 10. Bleaching is carried out at high temperature. The bleached fabric has high and stable whiteness, good hand feeling, and can also remove pulp and natural impurities. The disadvantage is that the equipment requirements are high and the cost is high. Under appropriate conditions, combined with caustic soda, desizing, scouring and bleaching can be completed at one time. The pH value of the bleaching solution for sodium chlorite bleaching is 4 to 4.5. It is carried out at high temperature and has the advantages of good whiteness and little damage to fibers, but it is easy to generate toxic gas during bleaching, pollute the environment, and corrode equipment. The equipment requires special It is made of metal material, so it is limited in application. Both sodium hypochlorite and sodium chlorite are dechlorinated after bleaching to prevent the fabric from being damaged by the presence of residual chlorine during its existence.

 6) Dyeing and dyeing is a relatively complicated process, and the dyeing process of different qualities of cloth is different. Cotton, polyester-cotton, linen cotton, woolen woolen, silk products, chemical fiber products, blended products, etc. some use pad dyeing, rolling It is enough to dye, some must be dyed with high temperature and high pressure, some only dye once, and some need to be dyed multiple times.

There are also different processes using different dyes, just take the basic cotton fabric as an example: Although dyeing can be done through a paddle, it is also the most difficult process, because the color control of dyeing is known, there are many There are unknown things in it, such as the stability of dyes at different temperatures, the control of steam, the control of rolling car pressure, etc., all of which are very delicate activities. .

 The dyed long car is divided into two parts, the front car is dyed, and the rear car is fixed. The dyeing method varies according to the variety of dyes used. The dyes are generally active, Shilin, vulcanization, and paint. They have their own advantages and disadvantages, generally It depends on the required color and cannot be replaced with each other. Among them, Shihlin has the best color fastness, but the price is expensive, and it is not suitable for dyeing dark colors, and the colors of light colors are not bright enough. Except that dyeing dark colors will increase the cost , and dyeing dark colors are difficult to control compared to reactive dyes, and are prone to fabric flowers and other phenomena. The color fastness of reactive dyes is worse than that of Shilin, but dyeing light colors is more gorgeous, dark colors are easy to control, and the cost is correspondingly less. .The vulcanization is the worst, the color fastness is not very good, and the ban on AZO is not up to the standard, but now there is a liquid vulcanization (also called water vulcanization) that bans AZO can reach the standard, but the price is close to that of Shilin, the dyeing is not easy to control and cannot be popularized, only A small number of people pursue its fading effect and use it. The paint is not comparable, and its color fading is very serious. It is the best choice for the pursuit of fading effect after clothing is washed. It can be used flexibly with Shilin and active to obtain different washing effects ( Generally, Shilin or reactive primers, and the paint covers the complexion, can solve the white spot problem of single-dyed paints, and the cost will increase accordingly. The dyeing fronts of reactive, shilin and vulcanization are basically the same, and the difference is that the infrared pre-bake one The rear car is completely different. The active one uses salt and soda ash to fix the color, the Shilin one uses hydrogen peroxide to fix the color (so Shilin is also called vat dye), and the vulcanized one needs to be cooked at high temperature to fix the color. The water temperature must be above 95 degrees. After the paint is dyed, it is determined whether to cure the color according to the fading requirements of the color fastness. The curing temperature is about 195-210 degrees. .Slight adjustments such as lightening the paint, darkening with soda ash.

 7) Mercerizing: Mercerizing refers to the process of treating cotton fabrics with concentrated caustic soda solution at room temperature or low temperature under tension in the warp and weft directions to improve the properties of the fabrics. After the cotton fabric is mercerized, due to the puffing of the fiber, the natural twist of the fiber in the longitudinal direction disappears, the cross section is oval, and the reverse of the light is more regular, thus enhancing the luster. The increase of the amorphous fixed area of ​​the fiber increases the dye uptake rate during dyeing. The improvement of the degree of orientation increases the strength of the fabric, and also has a setting effect.

After mercerizing, it is necessary to fully remove the alkali by flushing to remove the alkali or steaming the alkali, or to remove the alkali by flat washing, etc., until the fabric is neutral. Dyeing Dyeing is a process in which the physical or chemical combination of dyes and fibers, or chemical methods are used to generate pigments on fibers, so that the entire textile has a certain color. Dyeing is carried out under certain conditions of temperature, time, pH value and required dyeing auxiliaries. Dyeing products should be uniform in color and luster, and also need to have good color fastness. Fabric dyeing methods are mainly divided into dip dyeing and pad dyeing. Dip-dyeing is a method in which the fabric is immersed in the dye solution and the dye is gradually applied to the fabric. It is 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 first immersed in the dye liquor, and then the fabric is passed through the rollers, the dye liquor is evenly rolled into the fabric, and then the dyeing method is processed by steaming or hot melting. It is suitable for dyeing large batches of fabrics.

 8) Finishing Finishing is a textile technology project that endows clothing fabrics with wearability and aesthetics. The following are the common types of textile finishing:, the main equipment are: singeing machine, desizing machine, mercerizing machine, liquid ammonia machine, setting machine, pre-shrinking machine, calendering machine, washing machine, sanding machine, scratching machine wool machine, coating machine, etc.