The main process of the cotton fabric bleaching and processing are: preparation of the original cloth, singeing, desizing, scouring, bleaching, mercerizing.
1) the original cloth preparation: the original cloth preparation, including the original cloth inspection, flip (in batches, sub-boxes, printing) and sewing head. The purpose of the original fabric inspection is to check the quality of fabric, found that the problem can be resolved in time. Inspection includes physical indicators and appearance defects two. The former includes the length of the original cloth, amplitude, weight, warp and weft yarn density and density, strength, etc., which such as spinning defects, weaving defects, a variety of class stains and damage. Usually about 10% of the total sample. After the original inspection, must be the original cloth in batches, sub-boxes, and printed on the cloth head, indicating the variety, processing technology, batch number, box number, release date and the cloth code to facilitate management. In order to ensure continuous batch processing, the original cloth must be stitched.
2) singeing: singeing purpose is to burn the cloth on the villi, so that the surface smooth and beautiful, and to prevent the dyeing, printing due to the presence of villi dyeing uneven and printing defects. Fabric singeing is the fabric width quickly through the high-temperature flame, or rubbed over the red metal surface, then the existence of the fabric on the rapid rise in temperature, and burning, and cloth closer, warming is slow, Rose to the ignition point, that has left the flame or red hot metal surface, so as to burn down the villi, do not operate the purpose of the fabric.
3) desizing: textile mills in order to smooth weaving, often sizing the warp to improve strength and wear resistance. The fabric on the fabric that affects the water absorption properties, but also affect the quality of dyeing and finishing products, and will increase the consumption of dyed drugs, it should be removed before scouring the pulp, this process is called desizing. The slurry on the cotton fabric can be removed from the fabric by alkali desizing, enzyme desizing, acid desizing and oxidizing agent desizing. Alkaline desizing causes the slurry to expand and decrease its adhesion to the fiber, and is removed from the fabric by washing. Enzymes, acids, oxidants to starch degradation, increased solubility in water, washed away. As the acid, oxidant damage to cotton fibers, rarely used alone, often with the enzyme desizing, combined use of alkaline desizing.
4) scouring: cotton fiber growth, there are natural impurities (pectin, waxy material, nitrogenous substances, etc.) associated with. After desizing the cotton fabric, most of the slurry and some natural impurities have been removed, but there are a small amount of slurry and most of the natural impurities also remain in the fabric. The presence of these impurities, the cotton fabric of yellow cloth, poor permeability. At the same time, due to the existence of cottonseed hull, greatly affected the appearance of cotton quality. It is necessary to the fabric in high temperature concentrated alkali for a long time scouring to remove residual impurities. Scouring is the use of caustic soda and other scouring auxiliaries and pectin, waxy material, nitrogen substances, cotton seed hull chemical degradation reaction or emulsification, puffing, washed by the impurity from the fabric after the withdrawal.
5) bleaching: After scouring the cotton fabric, there are natural pigments on the fiber there, its appearance is not enough white, for dyeing or printing, will affect the color of the bright degree. The purpose of bleaching is to remove the pigment, imparting the necessary and stable whiteness of the fabric, while the fiber itself is not significantly damaged. Cotton fabrics commonly used bleaching methods are sodium nitrite method, hydrogen peroxide and sodium chlorite method. Sodium hypochlorite bleach bleaching solution PH value of about 10, at room temperature, simple equipment, easy operation, low cost, but the fabric strength damage, low brightness. Hydrogen peroxide bleaching bleaching solution PH value of 10, at high temperature for bleaching, bleaching fabric white high and stable, feel good, but also remove the slurry and natural impurities. Drawback is the equipment requirements, high cost. In the appropriate conditions, combined with caustic soda, can desizing, scouring, bleaching once completed. Sodium chlorite bleaching bleach PH value of 4 ~ 4.5, at high temperatures, with good whiteness, the advantages of small fiber damage, but bleaching easy to produce toxic gases, pollution of the environment, corrosion equipment, equipment needs special Metal materials, it is subject to certain restrictions on the application. Sodium hypochlorite and sodium chlorite bleaching should be carried out after the dechlorination to prevent the presence of fabric in the presence of residual chlorine damage.
6) mercerization: mercerized cotton fabric at room temperature or low temperature, in the warp and weft direction are subject to tension, with concentrated caustic soda solution treatment to improve the fabric properties of the processing process. Cotton after mercerization, due to fiber puffing, fiber vertical natural reverse disappear, cross-section into an oval, reverse the light more regular, thus enhancing the gloss. The increase of the fiber invisibility area increases the dye uptake rate of the dye during dyeing. The degree of orientation increases, so that the fabric strength increases, as well as shaping effect. Mercerizing, be sure to use the red suction alkali or steam box to alkali, or flat to wash the alkali and other methods to fully alkali, until the fabric was neutral.
