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 chromatic aberration, color deviation, etc., you need to add additional dyes and counter-dyes; sometimes After solid removal, silicon removal and color 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 is generally easier to repair and re-dye them. After color and soft finishing, especially pure cotton knitted fabrics after baking or heat setting, the difficulty of repairing is greatly increased.
Characteristics of fixing agents and softening agents
1. Fixing agents
In order to improve the color fastness of pure cotton fabrics to soaping, the fabrics need to be fixed and finished after dyeing, especially deep-colored fabrics dyed with direct dyes and reactive dyes.
The fixing agents currently used are basically formaldehyde-free cationic fixing agents, which have stable performance in weak acid baths and can combine with dyes through ionic bonds to form insoluble lake deposits. On the fiber, it reduces its water solubility and improves the soaping color fastness of the fabric.
If the fixing agent remaining on the fiber and its products with the dye are not fully removed before repair, the dye will be dyed very quickly during counter-dying. If the dye transfer property is poor, it will inevitably lead to color flowers and stains. 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 and non-ionic type and hermaphroditism. 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.
At present, the silicone softeners on the market mainly include amino polysiloxane, epoxy polysiloxane, polyether polysiloxane, and polyether epoxy polysiloxane. Oxane and polyether aminopolysiloxane, 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 tank → hot water washing (80℃×10 rain) → overflow water washing (10 min) → solid removal and silicon removal → overflow water washing (10 min) → color stripping, solid removal and silicon removal →Bath→Overflow washing (10 min)→Net washing→Overflow washing (10 min)→Oxygen bleaching→Overflow washing (10 min)→Chlorine bleaching→Dechlorination→Overflow washing (10 min)→Second dehydration Chlorine→overflow water washing (20 min)→hot water washing (80℃×10 min)→counterstaining
2. Process parameters
2.1 Entering the cylinder
When repairing, because the fabric needs to run for a long time in the dyeing machine, in order to reduce the wear and tear of the fabric, weft-knitted pure cotton Knitted fabrics should be turned over before loading into the pot, with the back of the fabric facing out.
2.2 Solid and silicon removal
(1) Prescription for solid and silicon removal/( g／L)
(2) Solid removal and silicon removal heating curve
The solid remover is a special polymer that is a non-ionic powerful dispersant and can effectively Remove the fixing agent on the pure cotton fabric, break the ionic bond formed by the cationic group in the fixing agent molecule and the anionic group of the anionic dye, thereby removing the fixing agent on the fiber and its reaction with the dye. The products 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 on 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 of color stripping, solid removal and silicon removal
(1) Color stripping , solid and silicon removal one-bath prescription/(g/L)
(2 ) Temperature rising curve of one-bath stripping, solid removal and silicon removal method
Commonly used color stripping Agents include reducing agents, oxidants, surfactants with strong cleaning functions, and alkaline agents.
Among them, the most effective additive is�The original agent is 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 into 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 to maximize the removal of color fixing agents, softeners and their combinations on the surface and inside of the fiber. Products and residues of fiber reactions.
Before stripping, a solid and silicon removal treatment at 100°C When staining, the unreacted softener on the fabric will break emulsions, bleach oil, and form a dark brown sticky paste, causing secondary staining of the fabric. 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 12 g/L when stripping.
2.4 Cleansing
(1) Cleansing prescription/(g/L)
(2) Washing temperature rise curve
Powerful degreaser is a compound of anionic, nonionic surfactants and aromatic solvents. It is effective for all types of mineral oils and vegetable oils. It has high emulsifying, dispersing and dissolving abilities, 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, oxygen bleaching and chlorine bleaching are not required. It can be washed directly in hot water at 80°C
2.5 Oxygen Bleaching
Oxygen Bleaching Process Conditions
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 Chlorine bleaching
For fabrics with serious stains and stains, reducing agents should be used , Insurance powder stripping, local color stains are serious and stripping is difficult, it is necessary to use sodium hypochlorite for bleaching.
Chlorine bleaching process conditions
2.7 Dechlorination
After chlorine bleaching, dechlorination must be carried out. Otherwise, the fabric contains sodium hypochlorite, which will affect the dyeing color yield and damage the fabric. Strong, affects the feel.
Dechlorination process conditions
2.8 Secondary dechlorination
The prescription and process parameters of secondary dechlorination 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
Conduct 80℃ on the fabric before counterdyeing X 10 min hot water washing can effectively remove various additives remaining on the fabric and 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.
Attention
(1) Heat at 80℃×10 rain before solid and silicon removal Washing with water can effectively remove the softening agent and color-fixing agent on the surface of the fabric that have not reacted with the fiber.
(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 solids on the fabric that have not reacted with the fibers. Color agent is used to prevent the softener from demulsifying and oil drifting when peeling at 130°C for 40 minutes.
(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) Cleaning and oxygen bleaching are performed after removing solids, silicone and color from the fabric, 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 stripping, 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 repeated solid removal, silicon removal, color stripping and bleaching, a very small amount of additives will inevitably remain on the fabric. During re-dying, 5 more additives should be added simultaneously according to the original prescription. About % dye.
Solution failed.
(4) Cleaning and oxygen bleaching are performed after removing solids, silicone and color from the fabric, 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 stripping, 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 repeated solid removal, silicon removal, color stripping and bleaching, a very small amount of additives will inevitably remain on the fabric. During re-dying, 5 more additives should be added simultaneously according to the original prescription. About % dye. </p
