In the dyeing and finishing process of pure cotton knitted fabrics, after the fabrics are dyed, fixed and softened, they often need to be repaired due to dyeing defects. Before the fabric is repaired, it needs to be solidified, siliconed, and even stripped.
Sometimes after solid removal, silicon removal, and cleaning, if you encounter downward color deviation, color deviation, etc., you need to add additional dyes and counterdyes; sometimes after solid removal, silicon removal, etc. After stripping, if you encounter partial color difference, color flowers, stains, etc., you need to re-dye.
For fabrics with downward bias and color deviation that have not been fixed and softened, it generally only needs to be repaired and re-dyed, which is relatively easy; after being fixed and softened, Especially for pure cotton knitted fabrics that have been baked or heat-set, the difficulty of repair is greatly increased.
Characteristics of fixing agents and softening agents
1. In order to improve the color fastness of pure cotton fabrics to soaping, the fixing agents need to be fixed after dyeing. Color finishing, especially deep color fabrics dyed with direct dyes and reactive dyes. The color fixing agents currently used are basically formaldehyde-free cationic color fixing agents. They have stable performance in weak acid baths and can combine with dyes through ionic bonds to form insoluble lakes that are deposited on the fibers to reduce their water solubility and improve the quality of the fabric. color fastness to soaping.
Before repair, if the fixing agent remaining on the fiber and its products with the dye are not fully removed, the dye will absorb very quickly during counter-dying. If the dye has poor migration properties, It will inevitably lead to color flowers and stains, and even adding a leveling agent will not help. If the dyed fabric is baked, the color flowers and stains will become more serious.
2. Softeners Softeners can be divided into cationic, anionic, nonionic and amphoteric types. Among them, amino silicone oil cationic softeners have excellent lubrication effects. They mainly generate elastic network structure polymers on the fiber surface through self-crosslinking and condensation, which can give the fabric a soft feel and high washability. However, if the dyeing fastness needs to be repaired, it will be more difficult to re-dye.
The commercially available silicone softeners mainly include amino polysiloxane, epoxy polysiloxane, polyether polysiloxane, polyether epoxy polysiloxane and polyether amino polysiloxane. Oxane etc. If it is a fatty acid derivative softener, it can be removed from the fabric by washing with hot water or adding a small amount of alkali.
Repair process and process parameters
1. Process flow into the cylinder → hot water washing (80℃×10 rain) → overflow water washing (10 min) → solid removal, silicon removal → overflow water washing (10 min) → color stripping, solid removal, silicon removal → bath → overflow water washing (10 min) → clean washing → overflow water washing (10 min) → oxygen bleaching → Overflow washing (10 min)→chlorine bleaching→dechlorination→overflow washing (10 min)→secondary dechlorination→overflow washing (20 min)→hot water washing (80℃×10 min)→counterdyeing
2. Process parameters 2.1 When entering the vat for repair, since the fabric needs to run in the dyeing machine for a long time, in order to reduce the wear and tear of the fabric, the weft-knitted cotton knitted fabric should be turned over and loaded into the pot, with the back of the fabric facing outward.
2.2 Solid and silicon removal
Recipe for solid and silicon removal/(g/L)
Heatingcurveofsolidremovalandsiliconremoval
The solid remover is a special polymer that is a non-toxic Ionic strong dispersant can effectively remove the fixing agent on pure cotton fabrics, breaking the ionic bond formed by the cationic group in the fixing agent molecule and the anionic group of the anionic dye, thereby breaking the fixing agent on the fiber. Colorants and their reaction products with dyes are fully removed. Therefore, the solid remover itself also has a certain color stripping effect. Silicone remover has high emulsification and foaming properties, and has outstanding decontamination ability. It can effectively destroy the chemical bonds formed by the amino groups in the amino silicone softener and the hydroxyl and carboxyl groups on the cellulose fibers.
In addition to having a certain color stripping effect, soda ash can mainly remove oil from fabrics and reduce the staining of fabrics by stripped softener residues. When the temperature is lowered to 80°C after each process, the liquid is not drained directly, but is washed with overflow water to 30°C and then drained. This is because most of the stripped softener residue and oil are floating in the working fluid foam and need to be effectively removed by overflow water washing. Chelating dispersants can chelate metal ions, soften water quality, and correspondingly improve the effects of solid removers and color-correcting silicone removers.
2.3 One-bath method for color stripping, solid removal and silicon removal
Prescription for one-bath color stripping, solid removal and silicon removal method/(g/L )
Temperature rising curve of one-bath stripping, solid removal, and silicon removal
Commonly used stripping agents include reducing agents, oxidizing agents, surfactants with strong cleaning functions, and alkali agents.
Among them, the most effective additive is the reducing agent sodium dithionite (insurance powder). It has strong color stripping ability under alkaline conditions, can destroy the chromogenic group of the dye, make the color of the fiber disappear completely or mostly, and can also destroy the fixing agent. Insurance powder is unstable in aqueous solution and easily decomposes.�Sulfur dioxide and releases a lot of heat. When the temperature is raised to 80°C, insurance powder is added cyclically to prevent part of the insurance powder from decomposing and failing during the heating process.
Carry out silicone and solid removal treatment before stripping, which can remove the softener, solid remover and some residual substances on the fiber surface that have not chemically reacted with the fiber. When stripping, use one bath of color stripping, secondary solid removal, and silicon removal, which can remove the fixing agent, softener, and the products and residues of the reaction with the fiber on the surface and inside of the fiber to the maximum extent.
Before stripping, a 100°C The reacting softener will break emulsions, bleach oil, and form a dark brown sticky paste, causing secondary contamination of fabrics. For fabrics that do not require color stripping such as downward chromatic aberration and chromatic light deviation discoloration, the heating curve listed in this section can be carried out according to the solid and silicon removal prescription, and the temperature can be quickly raised to 130°C × 40 minutes; for deep and dense colors For fabrics with serious stains and flowers, the dosage of insurance powder and soda ash can be increased to 12g/L when stripping.
2.4 Cleansing
Cleaning prescription/(g/L)
Cleaning temperature rise curve
Powerful degreaser is a compound of anionic, nonionic surfactants and aromatic solvents. It has high emulsifying, dispersing and dissolving abilities for various mineral oils and vegetable oils, and has good ability to remove silicone softeners and silicon plaque.
For fabrics that do not require color stripping such as downward chromatic aberration and chromatic light deviation discoloration, after clean washing and overflow water washing, they do not require oxygen bleaching or chlorine bleaching, but can be directly washed at 80 ℃ Wash with hot water for 10 minutes, then wash with overflow water for 20 minutes, and then counterstain after proofing in the laboratory, or directly adjust the color and counterstain.
2.5 Oxygen Bleaching
Oxygen Bleaching Heating Curve
After the fabric is stripped, it needs to be oxygenated. Hydrogen peroxide has a strong impurity and decontamination effect. It can effectively remove impurities and oil stains on the fiber, make the fiber obtain a good whiteness, and increase the brightness of the counter-dyed fabric. The pH value of oxygen bleaching working solution is 11~11.5.
2.6 Oxygen bleaching
For fabrics with serious color stains and stains, reducing agents and insurance powder should be used to peel off the color. Difficult to color areas need to be bleached with sodium hypochlorite.
Chlorine bleaching process conditions
2.7 Dechlorination
Chlorine bleaching Finally, dechlorination treatment must be carried out, otherwise the fabric contains sodium hypochlorite, which will affect the color yield of the dyeing, damage the strength of the fabric, and affect the feel.
Dechlorination process conditions
2.8 Secondary dechlorination
The prescription and The process parameters are the same as the former. After the second chlorine bleaching, sufficient overflow water washing should be carried out to lay a good foundation for the next step of counter-dying.
2.9 Counterdyeing
Before counterdying, wash the fabric with hot water at 80℃ Avoid low color yield of dyed fabrics, resulting in secondary replenishment and repair. After the above-mentioned solid removal, silicon removal, color stripping, oxygen bleaching, and chlorine bleaching, the whiteness of the fabric has reached the whiteness before the initial dyeing, and it can be counter-dyed according to the original color number. However, because the fabric has been desolidified, siliconized, stripped, and bleached many times, a very small amount of additives will inevitably remain on the fabric. Therefore, when redying, about 5% more dye should be added simultaneously according to the original dyeing recipe.
Note
1. Wash with hot water at 80°C × 10 rain before solid and silicon removal, which can effectively remove the surface part of the fabric that has not reacted with the fibers. Softeners and fixatives.
2. After the fabric is treated at 100°C × 30 minutes to remove solids and silicon, then wash with overflow water to completely remove the softener and color-fixing agent on the fabric that have not reacted with the fiber to prevent 130°C When peeling for 40 minutes, the softener will break emulsification and oil will drift out.
3. Because insurance powder is unstable in aqueous solution, it decomposes into sulfur dioxide and releases a lot of heat. When the peeling temperature rises to 80°C, cyclic addition of insurance powder can prevent part of the insurance powder from decomposing and failing during the heating process.
4. The fabric is cleaned and oxygen bleached after solid removal, silicon removal and color stripping, which can remove residual impurities and oil stains on the fabric and improve the whiteness of the fabric.
5. For fabrics with serious local color stains and difficult peeling, sodium hypochlorite bleaching is required to remove local pigments on the fabric. Dechlorination must be completed after chlorine bleaching to prevent low color yield of the fabric and damage to the fiber by sodium hypochlorite during counter-dying.
6. After many times of solid removal, silicon removal, color stripping, and bleaching, a very small amount of additives will inevitably remain on the fabric. When redying, about 5% more dye should be added simultaneously according to the original prescription.
Add about 5% more dye.
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