Principle of color stripping
Color stripping is to use chemical action to destroy the dye on the fiber and lose it. color.
There are two main types of chemical stripping agents. One is reductive stripping agents, which achieve fading by destroying the color system in the molecular structure of the dye. Or for achromatic purposes, such as azo-structured dyes, the azo group may be reduced to an amino group and lose color. However, the damage caused by reducing agents to dye color systems with certain structures is reversible, so their fading can be restored, such as the color system with anthraquinone structure. Insurance powder and white powder are commonly used reducing stripping agents. The other type is oxidative stripping agents, of which hydrogen peroxide and sodium hypochlorite are commonly used. Under certain conditions, oxidants can cause damage to certain groups that make up the color system of dye molecules, such as azo group decomposition, amination oxidation, hydroxymethylation, and detachment of complex metal ions. These irreversible structural changes lead to fading or decolorization of the dye, so theoretically speaking, oxidative stripping agents can be used for complete color stripping. This method is particularly effective for dyes with anthraquinone structure.
Stripping of commonly used dyes
2.1 Stripping of reactive dyes
Any reactive dye containing metal complexes should first be boiled in a solution of metal sequestering agent (2 g/L EDTA). Then rinse thoroughly before alkaline reduction or oxidation stripping treatment. Complete color stripping is usually done at high temperature in alkali and insurance powder for 30 minutes. After restoration and stripping, rinse thoroughly. Then cold bleach in sodium hypochlorite solution. Process example:
Continuous stripping process example:
Dyeing defective cloth → padding Original solution (caustic soda 20g/L, insurance powder 3Og/L)→703 reduction steamer steaming (100℃)→wash→dry
Example of dyeing vat stripping process:
Defected cloth → Scroll → 2 channels of hot water → 2 channels of caustic soda (20 g/L) → Stripping 8 lanes (15 g/L of insurance powder, 60°C) 4 lanes of hot water → 2 lanes of cold water rolling → conventional sodium hypochlorite flat bleaching process (NaClO 2.5 g/L, stacking for 45 minutes).
2.2 Stripping of sulfur dyes
To correct fabrics dyed with sulfur dyes, they are usually soaked in a blank solution of reducing agent (6 g/L full strength) Sodium sulfide), treat it at the highest possible temperature to partially strip the dyed material before re-dying it. In serious cases, sodium hypochlorite or insurance powder must be used.
Process example
Light color example:
Input the cloth → Dip and roll (5-6g liters of sodium hypochlorite, 50℃) → 703 steamer (2 minutes) → Fully wash with water → Dry.
Dark color example:
Fabric with color defects → Rolled oxalic acid (1 5g/L 40℃)→dry→roll sodium hypochlorite (6 g/L, 30℃ for 15 seconds)→fully wash and dry
Intermittent process example:
55% crystalline sodium sulfide: 5-10 g/L; soda ash: 2-5 g/L (or 36°BéNaOH 2-5 ml/L);
Temperature 80-100, time 15-30, liquor ratio 1:30-40.
2.3 Stripping of acid dyes
Use ammonia (2O to 30g/ L), and anionic wetting agent (1 to 2 g/L), boil for 30 to 45 minutes. Before ammonia treatment, use insurance powder (10 to 20 g/L) at 70°C to help complete color stripping. Finally, oxidation stripping method can also be used.
Under acidic conditions, adding special surfactants can also have a good color stripping effect. There are also methods that use alkaline conditions for color stripping.
Process example:
Silk stripping process example:
Reduction stripping and bleaching (soda ash 1g/L, O 2g/L, insurance powder 2-3g/L, temperature 60℃, time 30-45min, liquor ratio 1:30) → pre-media treatment (ferrous sulfate heptahydrate 10g/L, 50% hypophosphorous acid 2g/L, formic acid to adjust pH 3-3.5, maintained at 80℃ for 60min) → rinse ( 80℃ Cleaning 20min)→Oxidative stripping and bleaching (35% hydrogen peroxide 10mL/L, pentahydrate sodium silicate 3-5g/L, temperature 70-8O℃, time 45-90min, pH value 8-1O)→cleaning
Example of wool stripping process:
Nifandine AN: 4; oxalic acid: 2%; within 30 minutes Raise the temperature to boiling point and keep it at the boiling point for 20-30 minutes; then clean it.
Nylon stripping process example:
36°BéNaOH: 1%-3%; Pingping O: 15%-20%; Synthetic detergent: 5%-8%; Liquor ratio: 1:25-1:30; Temperature: 98-100 ℃; time: 20-30min (until all discoloration occurs).
After all stripping, gradually cool down, wash thoroughly with water until clean, then use 0.5mL/L acetic acid at 30℃ for 10 minutes to fully neutralize the alkali remaining on the nylon. , then rinse with clean water.
2.4 Stripping of vat dyes
Usually in a mixed system of sodium hydroxide and insurance powder In the process, the fabric dye is reduced again at a relatively high temperature. Sometimes it is necessary to add polyvinylpyrrolidine solution, such as BASF’s Albigen A.
Example of continuous stripping process:
Dyeing defective cloth → padding reduction solution (caustic soda 20g/L, insurance powder 3Og/L)→703 reduction steamer steaming (100℃)→wash→dry
Example of intermittent stripping process:
Add O: 2-4g/L; 36°BéNaOH: 12-15ml/L; Insurance Powder: 5-6 g/L;
During stripping treatment, the temperature is 70-80°C, the time is 30-60 minutes, and the liquor ratio is 1:30-40.
2.5 Stripping of disperse dyes
Stripping of disperse dyes on polyester The following methods are usually used:
Method 1: Treat sodium formaldehyde sulfoxylate (carbohydrate) and carrier at 100°C and pH 4-5; the treatment effect is more significant at 130°C.
Method 2: Sodium chlorite and formic acid are treated at 100°C and pH 3.5.
The best result is to handle it through method one, and then through method two. After treatment, overdye as black as possible.
2.6 Stripping of cationic dyes
Stripping of disperse dyes on polyester The following method is usually used:
In a bath containing 5 ml/L monoethanolamine and 5 g/L sodium chloride, treat at boiling point for 1 hour. Then clean it, and then bleach it for 30 seconds in a bath containing 5 ml/L sodium hypochlorite (150 g/L available chlorine), 5 g/L sodium nitrate (corrosion inhibitor), and adjust the pH value to 4 to 4.5 with acid. minute. Finally, the fabric is treated with sodium chloride sulfite (3 g/L) at 60°C for 15 minutes, or 1-1.5 g/L sodium chloride powder at 85°C for 20 to 30 minutes. And then clean it.
It can also be achieved by using a boiling solution of detergent (0.5 to 1 g/L) and acetic acid to treat dyed fabrics at pH 4 for 1-2 hours. Partial peeling effect.
2.7 Stripping of insoluble azo dyes
5 to 10 ml/L Treat with 38°Bé caustic soda, 1 to 2 ml/L of thermally stable dispersant, and 3 to 5 g/L of insurance powder, plus 0.5 to 1 g/L of anthraquinone powder. If there is enough insurance powder and caustic soda, anthraquinone will turn the stripping liquid red. If it turns yellow or brown, further caustic soda or insurance powder must be added. Fabrics after stripping should be thoroughly washed.
2.8 Stripping of paint
Paint is difficult to peel off, so potassium permanganate is usually used to peel it off.
Process example:
Dyeing defective cloth → rolling with potassium permanganate (18g/L) → washing → rolling with oxalic acid (20g/L, 40℃) → washing → drying.
Removal of commonly used finishing agents
3.1 Removal of fixing agents
The fixing agent Y can be removed by adding a small amount of soda ash and O; the polyamine cationic fixing agent can be removed by boiling with acetic acid.
3.2 Removal of silicone oil and softener
Generally, softeners can be removed by cleaning with detergent, sometimes using soda ash and detergent. Method; Some softeners must be removed by using formic acid plus surfactant. The removal method and process conditions must be tested on a small sample.
Silicone oil is difficult to remove, but most silicone oil can be removed by boiling under strong alkaline conditions using special surfactants. Of course, these are subject to small sample testing.
3.3 Stripping of resin finishing agent
Resin finishing agents are generally removed by padding acid steam washing. The typical process is: padding acid solution (hydrochloric acid concentration is 1.6 g/L) → stacking (85°C for 10 minutes) → hot water washing → Wash in cold water → dry. Use this process to peel off the resin on the fabric on a continuous flat track scouring and bleaching machine.
Color light correction principle and technology
4.1 Color light correction principle and technology
When the color and light of the dyed fabric does not meet the requirements, it needs to be corrected. The principle of color and light correction is the principle of residual color. The so-called residual color means that two colors have the property of attenuating each other. The pairs of colors that are residual colors are: For example, red and green, orange and blue, yellow and purple, if the red light is too strong, you can add a small amount.Green paint to cut. However, the residual color is only used to adjust the color slightly. If the amount is too large, it will affect the color depth and brightness. The general dosage is about lg/L.
Generally speaking, fabrics dyed with reactive dyes are more difficult to repair, while fabrics dyed with vat dyes are easier to repair; sulfur dyes are difficult to control when repairing, so vat dyes are generally used. Dyes add and subtract colors; direct dyes can be used for additive color repair, but the dosage should be less than 1 g/L.
Commonly used methods for color correction include water washing (applicable to color correction of finished dyed fabrics that are slightly darker in color, have more floating colors, and repair fabrics with less than ideal washing and soaping fastness), and shallow peeling (refer to the peeling of dyes) color process, the conditions are lighter than the normal stripping process), alkali padding and steaming (suitable for alkali-sensitive dyes, mostly used for reactive dyes; such as dyeing with reactive black KNB color matching If the color of the cloth is bluish, you can use an appropriate amount of caustic soda, supplemented by steaming and flat washing to achieve the purpose of changing the blue light) and whitening agent (applicable to the red light of dyed finished fabrics, especially for those dyed with vat dyes) The finished fabric is more effective when the color is medium or light. If the color is normal and dark, re-bleaching can be considered, but hydrogen peroxide bleaching should be used to avoid unnecessary color change, paint color transfer, etc.
4.2 Example of color correction process: subtractive color method of reactive dye dyeing
4 ．2.1 In the first five flat washing tanks of the reduction soaping machine, add 1 g/L O and boil, and then perform flat washing. Generally, it can be 15% lighter.
4.2.2 In the first five flat washing tanks of the reduction soaping machine, add 1g/L O and 1mL/L glacial acetic acid respectively. After passing through the machine at room temperature, the orange light can be made about 10% lighter.
4.2.3 Pad and roll 0.6mL/L bleach water in the rolling tank of the reduction machine, oversteam the box at room temperature, and do not drain the water in the first two wash tanks. , then wash with cold water in two compartments, wash with hot water in one compartment, and then soap and boil, it can be 20% lighter. Different bleaching water concentrations will lead to different peeling depths. The bleaching water will fade slightly.
4.2.4 Use 10L of 27.5% hydrogen peroxide, 3L of hydrogen peroxide stabilizer, 2L of 36°Bé caustic soda, 1L of 209 detergent, and 500L of water. Steam with a reducing machine, then add O and soap to cook on five grids, and it will be reduced to 15%.
4.2.5 Use 5-10g/L soda soda, steam and peel, wash with water and boil with soap, it can be 10-20% lighter, peel the color The back color is bluish.
4.2.6 Use 10g/L caustic soda, steam and strip the color, wash with water and boil with soap, it can be 20%-30% lighter, and the color is slightly darker.
4.2.7 Use 20g/L sodium perborate to steam and strip the color, which can make it 10-15% lighter.
4.2.8 Use 1-5L of 27.5% hydrogen peroxide in the jigger dyeing machine, run 2 passes at 70℃, take samples, and control according to the color depth. The concentration and number of channels of hydrogen peroxide, for example, dark green can be lightened by half to about 10% in 2 channels, and the color and light will not change much.
4.2.9 Put 250mL of bleaching water into 250L of water in the jigger dyeing machine, and run 2 channels at room temperature to peel 10-15% of the color.
4.2.1O You can add flat O and soda ash in the jigger dyeing machine.
Examples of dyeing defect repair process
5.1 Examples of color pattern treatment on acrylic fabric
5.1.1 Light-colored flowers
5.1.1.1 Process flow:
Fabric, surfactant 1227, acetic acid → rise to 100℃ for 30 minutes, keep warm for 30 minutes → Wash in hot water at 60°C → Wash in cold water → Raise the temperature to 60°C, add dye and acetic acid to keep it warm for 10 minutes → Gradually raise the temperature to 98°C, keep it warm for 40 minutes → Gradually lower the temperature to 60°C to release the cloth.
5.1.1.2 Stripping formula:
Surfactant 1227: 2%; acetic acid 2.5%; liquor ratio 1:10
5.1.1.3 Countersyeing formula:
Cationic dye (converted to the original process formula) 2O%; acetic acid 3%; liquor ratio 1:20
5. 1.2 Dark colored flowers
5.1.2.1 Process route:
Fabric, sodium hypochlorite, acetic acid → heating to 100°C, 30 minutes → cooling water washing → sodium bisulfite → 60°C, 20 minutes → warm water washing → cold water washing → 6O°C, adding dye, Acetic acid → Gradually raise to 100℃, keep warm for 4O minutes → Gradually lower the temperature to 60℃ to produce cloth.
5.1.2.2 Stripping formula:
Sodium hypochlorite: 2O%; Acetic acid 10%;
Liquor ratio 1:20
5.1.2.3 Chlorine release formula:
Sodium bisulfite 15%
Liquor ratio 1:20
5.1.2.4 Counterdye formula
Cationic dye (converted to original process formula) 120%
Acetic acid 3%
Liquor ratio 1:20
5.2 Examples of nylon fabric color pattern processing
5.2.1 Mild staining
When the difference in the depth of the stain is 20%-3O% of the depth of the dyeing itself, it can generally be Use 5%-10% flat plus O, the liquor ratio is the same as dyeing, and keep the temperature between 80℃-85℃. When the depth of the dye solution reaches about 20% of the dyeing depth, slowly raise the temperature to 100℃ , keep warm until the dye is absorbed by the fibers as much as possible.
5.2.2 Medium color flowers
Part of the medium color flowers can be used The method of subtracting color and then adding dye to the original depth.
Na2CO3 5 %-10 %
MediocreAdd O 1O%-15%
Liquor ratio 1:20-1:25
Temperature 98℃-100℃
Time 90 min-120min
After color reduction, the fabric is washed out of the vat with hot water, then cold water until clean, and then dyed.
5.2.3 Severe color flowers
Craftsmanship:
36°BéNaOH:1%-3%
Bingping plus O: 15% ~20%
Synthetic detergent: 5%-8%
Liquor ratio 1: 25-1：30
Temperature 98℃-100℃
Time 20min to 30min (until all decolorization)
After all stripping, gradually cool down, wash thoroughly with water until clean, then use 0.5mL acetic acid, 30℃, 10min Neutralize the remaining alkali, then rinse with water and re-dye. Some colors should not be dyed in their original color after stripping. Because the background color of the fabric turns light yellow after stripping. In this case, the color should be changed. For example: after the camel is fully stripped, the background color will be light yellow. If it is dyed with camel again, the color will be dark. If you use Pula Red 10B, add a small amount of bright yellow and dye it into a princess color, the color can be kept bright.
5.3 Examples of polyester fabric color patterns
5.3.1 Lightly colored flowers,
Stripe repair agent or high temperature uniform Dye l-2 g/L, reheat to 135℃ and keep warm30 minutes. Adding 10%-20% of the original amount of dye and a pH value of 5 can eliminate the color flowers, stains, color differences and color depth on the cloth surface. The effect is basically the same as that of normal production cloth samples.
5.3.2 Severe color flowers
Sodium chlorite 2-5 g /L, acetic acid 2-3 g/L, methylnaphthalene 1-2 g/L;
Start treatment at 30℃, and heat up to 100 at 2℃/min ℃ treatment 60 min, then wash the cloth with water.
5.4 Examples of treatment of serious dyeing defects in cotton fabrics dyed with reactive dyes
Process flow: Stripping → Oxidation → Counterstaining
5.4.1 Stripping
5.4.1.1 Process prescription:
Insurance powder 5 g/L-6 g/L
Add O 2 g/L-4 g/L
38°Bé caustic soda 12 mL/L-15 mL／L
Temperature 60℃-70℃
Liquor ratio l: lO
p>
Time 30min
5.4.1.2 Operation methods and steps
Add water according to the liquor ratio, add the weighed Pingping O, caustic soda, insurance powder, put the fabric on the machine, turn on the steam and raise the temperature to 70°C, and peel the color for 30 minutes. After stripping, drain off the remaining liquid, rinse twice with clean water, and then drain.
5.4.2 Oxidation
5.4.2.1 Process prescription
3O%H2O2 3 mL／L
38°Bé caustic soda l mL／L
Stabilizer 0.2mL/L
Temperature 95℃
Liquor ratio 1:10
Time 60 min
5.4. 2.2 Operation methods and steps
Add water according to the bath ratio, add stabilizer, caustic soda, hydrogen peroxide and other additives, turn on the steam and raise the temperature to 95°C, keep it warm for 60 minutes, then cool it down to 75°C, drain the liquid and add water, add 0.2 large soda, and wash for 20 minutes. Drain the liquid; wash with 80℃ hot water for 20 minutes; wash with 60℃ hot water for 20 minutes, and wash with cold water until the cloth cools down completely.
5.4.3 Counterstaining
5.4.3.1 Process prescription
Reactive dyes: 30% x% of the original process dosage
Yuanming powder: 5O% Y% of the original process dosage
Soda ash: 50% z% of the original process dosage
Liquor ratio l: lO
Temperature is according to the original process
5.4.3.2 Operation methods and steps
Proceed according to normal dyeing methods and steps
A brief description of the stripping process of blended fabrics
Disperse and acid dyes can be obtained from diacetate/wool blends using 3 to 5% alkylamine polyoxyethylene at 80 to 85°C. , and pH 5 to 6, complete after 3O to 60 minutesSeparate colors. This treatment can also partially remove disperse dyes from the acetate component of diacetate/nylon and diacetate/polyacrylic blends. Partial stripping of disperse dye from polyester/polyacrylonitrile or polyester/wool requires boiling with carrier for up to 2 hours. Adding 5 to 10 grams/liter of non-ionic detergent and 1 to 2 grams/liter of white powder will usually improve the resulting stripping on polyester/polyacrylonitrile fibers.
1g/L anionic detergent; 3g/L cationic retarder; and 4g/L Yuanming powder at boiling point and pH 10 after 45 minutes to process. Partially strips alkaline and acid dyes from nylon/alkali-dyeable polyester blends.
1% non-ionic detergent; 2% cationic retardant; and 10% to 15% Yuanming powder at boiling point and pH 5, 90 to 120 minute. Commonly used for stripping wool/polyacrylic fibers.
Use 2 to 5 g/L caustic soda and 2 to 5 g/L insurance powder for reduction cleaning at 😯 to 85℃, or at 120℃ A moderately alkaline solution of gallbladder powder can remove many direct, reactive dyes from polyester/cellulose blends.
Use 3% to 5% cartilage powder and an anionic detergent, and treat it at 80°C and pH 4 for 40-60 minutes. Can strip disperse and acid dyes from diacetate/polyacrylic fiber, diacetate/wool, diacetate/nylon, nylon/polyurethane, and acid-dyeable nylon textured yarn.
Use 1-2 g/L sodium chlorite and boil for 1 hour at around pH 3.5 to remove cellulose/polyacrylonitrile fiber blended fabrics. Strips disperse, cationic, direct or reactive dyes. When stripping triacetate/polyacrylonitrile, polyester/polyacrylonitrile, and polyester/cellulose blended fabrics, a suitable carrier and non-ionic detergent must be added.
Production precautions
7.1 Fabrics must be stripped or corrected before coloring Nice sample test.
7.2 After stripping, the fabric must be washed with cold or hot water.
7.3 Stripping should be short-term and repeated if necessary.
7.4 When stripping, the properties of the dye itself must beProperties such as oxidation resistance, alkali resistance, chlorine bleaching resistance, temperature, and additive conditions need to be strictly controlled. Prevent excessive peeling or peeling caused by excessive dosage of additives or improper temperature control. If necessary, the process must be determined through stakeout.
7.5 When partially stripping fabrics, the following situations will occur:
7.5.1 For the color depth treatment of a dye, the color light of the dye will not change much, only the color depth will change. If the stripping conditions are mastered, the requirements of the color sample can be fully met;
7.5.2 When partial stripping is performed on fabrics dyed with two or more dyes with the same properties, the color change will be very small, because the dyes are only stripped to the same extent. The fabric will only appear in shades.
7.5.3 For the treatment of dark fabrics dyed with several dyes with different properties, it is usually necessary to strip the dye to a lighter color and then dye it again.
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