This article introduces the stripping principle and stripping process of cotton spandex fabric, combined with the characteristics of spandex fiber that is not resistant to alkali at high temperatures; the process of using soda ash instead of caustic soda and oxygen bleaching after stripping, and briefly describes the principle and complex color correction dyeing process and points out production precautions.
At present, the quality requirements for clothing fabrics are getting higher and higher, especially the requirements for appearance quality (shade, color difference, pattern) are more stringent. During the dyeing and finishing process, various reasons often lead to excessive dyeing depth, incorrect shades, and color spots and defects that cannot be directly corrected. Therefore, it is necessary to strip and counter-dye the dyed fabrics.
Cotton and spandex fabrics are mostly dyed with reactive dyes, and the color stripping is more thorough for light-colored series. However, it is relatively difficult for dark-colored fabrics because there are more residual pigments, the fabric is not white enough after peeling, and the strength loss is too large. In addition, spandex is sensitive to alkaline conditions, so stripping is technically difficult. To this end, the author combined the chemical processing characteristics of spandex fibers in fabrics and used the insurance powder stripping-hydrogen peroxide bleaching method to study the stripping process of reactive dye-dyed spandex fabrics, and proposed a set of reasonable stripping and counter-dyeing processes.
Principle and process of stripping
1. Principle of stripping
Color stripping, that is, using chemical action to destroy the dye on the fiber so that it cannot develop color. Various stripping methods take advantage of the limited oxidation resistance, alkali resistance, chlorine bleaching resistance and other properties of the covalent bond formed between the dye and the fiber. The chemical bonds are broken and the dye falls off the fibers, thus making the surface of the fabric lighter.
Commonly used chemical stripping agents include insurance powder and white powder, which achieve the purpose of fading or decolorizing by destroying the color system in the molecular structure of the dye. Cotton spandex fabrics are often stripped with sodium hydroxide soda ash, which can achieve the stripping effect without damaging the strength of the fabric and meet the needs of dyeing and finishing.
2. Stripping prescription
The insurance powder-caustic soda method is generally used to strip cotton fabrics, while for cotton and spandex fabrics Said that because it contains 3% to 5% spandex fiber, spandex is not resistant to strong alkali. Especially under high temperature conditions, caustic soda decomposes spandex. Therefore, the concentration of caustic soda must be reduced as much as possible during the finishing and processing of cotton spandex fabrics, and the temperature should not be too high. . Soda ash is often used instead of caustic soda in production. Due to its weak alkalinity, it has a mild effect on spandex.
Oxygen bleaching prescription and process
1. Oxygen bleaching prescription
After stripping, fabrics are often not white enough and fail to meet dyeing requirements. When the light color is re-dyed after stripping, the whiteness of the fabric is required to be higher. Therefore, bleaching the fabric after stripping will result in better whiteness. Because the fabric contains spandex, the spandex fiber will combine with nitrogen and chlorine in the hypochlorite solution, causing the fiber to become damaged and turn yellow, causing serious damage. Therefore, chlorine-containing bleach cannot be used for bleaching fabrics containing spandex. Spandex has good stability to oxygen-containing bleach, but the peroxide concentration in the solution should not be too high. Similarly, considering that caustic soda will cause great damage to spandex fibers, soda ash is used when bleaching, which has a gentle effect and will not have a significant impact on the elasticity of the fabric.
Recipe for bleaching cotton and spandex fabrics
H2024%
Scouring agent 2%
Na2C033%
Liquor ratio 1:10
2. Oxygen bleaching process
Hydrogen peroxide bleaching: After the cotton spandex elastic fabric is treated by the above-mentioned stripping and bleaching process, because the fabric itself has greater elasticity, and soda ash is used instead of caustic soda during stripping and bleaching, the effect is relatively gentle and the fabric elasticity is reduced. and strong force had no significant effect.
In addition, using the insurance powder stripping-hydrogen peroxide bleaching method, cotton and spandex fabrics will not turn yellow after decolorization, and the processing effect is better. After bleaching treatment, the hydrogen peroxide on the surface of the fabric must be completely removed, otherwise it may cause light colors and stains during counterdyeing. For residual hydrogen peroxide and soda ash on the fabric, first treat it with 90°C hot water, then treat it with 2% deoxygenase at 60°C for 5 minutes: then treat it with 0.5% acetic acid solution at 70°C for 5 minutes, and then wash it thoroughly with water to completely remove the fabric surface. of residues.
Counter-dyeing process
Dyeing usually uses an overflow dyeing machine or For the jet overflow dyeing machine, when counter-dying, the dye is increased by 15% according to the original recipe, and the dosage of other additives and process conditions remain unchanged. Fabrics that have been stripped and bleached are whiter than undyed, unstripped semi-finished products, so counterdying requires an increase in dye concentration.
1. Color correction and precautions
Principles of color correction
If the color of the dyed fabric does not meet the requirements, color correction is required. Color light correction is based on the principle of residual colors. The so-called residual colors refer to the characteristics of two colors that subtract from each other. For example: red and green, yellow and purple. If the fabric is too reddish, you can add a small amount of green dye such as emerald blue to cut it down. However, the residual color principle is only used to adjust the color slightly. If the amount is too large, it will affect the depth and brightness of the color. Generally, the maximum amount is about 0.3%.
Color correction methods. Common color correction methods are as follows:
a. Water washing: used for dyeing finished fabrics, because the color is slightly darker, there are more floating colors, and the soaping fastness is not ideal for repairing the color of the repaired fabrics.
b. Shallow peeling: used for semi-finished fabrics that are 10% darker in color.�30%; refer to the dye stripping process, but the conditions are milder than the normal stripping process, and the dosage of each stripping agent and auxiliary agent is smaller.
c. Normal stripping: used for semi-finished products and dyed fabrics that are much darker or have spots that cannot be directly repaired.
d. Pad whitening agent: It is suitable for dyeing finished fabrics with a heavy red light, especially for finished fabrics dyed with vat dyes. The color correction effect is more obvious in medium and light colors. .
e. Turquoise blue method: It is suitable for bleaching fabrics with excessive red light. 0.01% ~ 0.1% emerald blue dye is often used to eliminate part of the red light and make the color Pure color and light.
Conclusion
The stripping, re-dying or color correction of fabrics is a problem often encountered in dyeing and finishing factories. This article combines the characteristics of spandex fabrics that are not resistant to high temperatures and alkali, using soda ash instead of caustic soda and oxygenating after stripping. Beautiful craftsmanship. Through the above process, the problems of color stripping and counter-dying during the processing in the dyeing factory are effectively solved. In actual production, it has good stripping and counter-dyeing effects, and at the same time, it will not cause great damage to the spandex yarn and fabric strength, meeting the production and processing needs. </p
