Color stripping methods for various fabrics during dyeing and finishing

1.Principle of color stripping
Stripping uses chemical action to destroy the dye on the fiber, causing it to lose its color.

There are two main types of chemical strippers:

One type is reductive stripping agents, which achieve the purpose of fading or decolorizing by destroying the color system in the molecular structure of dyes. For example, dyes with azo structures, their azo groups may be reduced to amino groups 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 structures.

2. 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 examples:
Example of continuous stripping process:
Dyeing defective cloth → padding reduction solution (caustic soda 20g/L, insurance powder 3Og/L) → steaming in 703 reduction steamer (100℃) → washing → drying

Example of dye vat stripping process:
Fabric with stains → Reel → 2 lanes of hot water → 2 lanes of caustic soda (20 g/L) → 8 lanes of color stripping (15 g/L of insurance powder, 60°C) 4 lanes of hot water → 2 lanes of cold water for rolling → Conventional sodium hypochlorite flat bleaching Process (NaClO2.5 g/L, stacked for 45 minutes).

2.2 Stripping of sulfur dyes

To correct fabrics dyed with sulfur dyes, they are usually treated in a blank solution of reducing agent (6 g/L full-strength sodium sulfide) at the highest possible temperature to achieve partial peeling of the dyed material before heavy dyeing. color. In serious cases, sodium hypochlorite or insurance powder must be used.

Process examples:
Light example:
Input the cloth → dip and roll (5-6 g liters of sodium hypochlorite, 50°C) → 703 steamer (2 minutes) → fully wash with water → dry.

Dark example:
Fabric with color defects → Roll with oxalic acid (15 g/L, 40℃) → Dry → Roll with sodium hypochlorite (6 g/L, 30℃ for 15 seconds) → Fully wash and dry

Examples of batch processes:
55% crystalline sodium sulfide: 5-10 g/L; soda ash: 2-5 g/L (or 36°BéNaOH2-5 ml/L); temperature 80-100, time 15-30, liquor ratio 1:30-40 .

2.3 Stripping of acid dyes

Use ammonia (2O to 30 g/L) and anionic wetting agent (1 to 2 g/L) and 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 also has a good color stripping effect. There are also methods that use alkaline conditions for color stripping.

Process examples:
Example of silk stripping process:
Reduction stripping and bleaching (soda ash 1g/L, O2g/L added, 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, adjust pH to 3-3.5 with formic acid, maintain at 80℃ for 60min) → rinse (clean at 80℃ for 20min) → oxidative stripping and bleaching (35% hydrogen peroxide 10mL/L, pentacrystalline sodium silicate 3 -5g/L, temperature 70-8O℃, time 45-90min, pH value 8-1O)→Cleaning

Example of wool stripping process:
Nilfantine AN: 4; oxalic acid: 2%; raise the temperature to boiling within 30 minutes and keep it at the boiling point for 20-30 minutes; then clean.

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°C for 10 minutes to fully neutralize the alkali remaining on the nylon, and then wash with clean water.

2.4 Stripping of vat dyes

Generally, in a mixed system of sodium hydroxide and insurance powder, the fabric dye is reduced at a relatively high temperature. Sometimes it is necessary to add polyvinylpyrrolidine solution, such as BASF’s AlbigenA.

Example of continuous stripping process:
Dyeing defective cloth → padding reduction solution (caustic soda 20g/L, insurance powder 3Og/L) → steaming in 703 reduction steamer (100℃) → washing → drying

Example of intermittent stripping process:
Add O: 2-4g/L; 36°BéNaOH: 12-15ml/L; insurance powder: 5-6g/L; the temperature during stripping treatment is 70-80℃ and the time is 30-60 minutes. The liquor ratio is 1:30-40.

2.5 Stripping of disperse dyes
The following methods are usually used to strip disperse dyes on polyester:

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 results are achieved through method one, followed by method two. After treatment, overdye as black as possible.

2.6 Stripping of cationic dyes
The following methods are usually used to strip disperse dyes on polyester:
Treat at boiling point for 1 hour in a bath containing 5 ml/l monoethanolamine and 5 g/l sodium chloride. 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.

Partial stripping 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.

Process examples:
See 5.1 Examples of color pattern treatment for acrylic knitted fabrics.

2.7 Stripping of insoluble azo dyes

Treat with 5 to 10 ml/L 38°Bé caustic soda, 1 to 2 ml/L thermally stable dispersant, and 3 to 5 g/L insurance powder, plus 0.5 to 1 g/L 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
The paint is difficult to peel off, so potassium permanganate is usually used to peel off the paint.

Process examples:
Dyeing defective fabric → rolling potassium permanganate (18g/L) → washing → rolling with oxalic acid (20g/L, 40℃) → washing → drying.

3． Removal of commonly used finishing agents
3.1 Removal of color-fixing agent
Fixing agent Y can be removed by adding a small amount of soda ash and O; 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 washing with detergent, and sometimes by using soda ash and detergent; some softeners must be removed by using formic acid and surfactant. The removal methods and process conditions must be tested on small samples.

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 sample testing.

3.3 Removal of resin finishing agent
Resin finishing agents are generally removed by padding acid steaming. The typical process is: padding acid (hydrochloric acid concentration is 1.6 g/L) → stacking (85°C for 10 minutes) → hot water washing → cold water washing → drying Dry. This process can be used to peel off the resin on the fabric on the continuous flat track scouring and bleaching machine.

4. Shade Correction Principles and Technology
4.1 Principles and techniques of color light correction
When the shade of dyed fabric does not meet the requirements, correction is required. The principle of color correction is the residual color principle. The so-called residual color means that two colors have the characteristics of reducing each other. The pairs of complementary colors are: red and green, orange and blue, and yellow and purple. For example, if the red light is too strong, you can add a small amount of green paint to cut it down. 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 difficult to repair, while fabrics dyed with vat dyes are easy to repair; sulfur dyes are difficult to control when repairing, so vat dyes are generally used for additive and subtractive colors; direct dyes can be used for additive color repairs, but the dosage should be Less than 1g/L.

Commonly used methods for color correction include water washing (applicable to dyed finished fabrics with a slightly darker color, more floating colors, and repair fabrics with less than ideal washing and soaping fastness) and shallow stripping (refer to the dye stripping process and conditions Lighter than the normal stripping process), alkali rolling and steaming (suitable for alkali-sensitive dyes, mostly used for reactive dyes; if the color of the dyed cloth using reactive black KNB is bluish, it can be rolled with an appropriate amount of caustic soda , supplemented by the method of steaming and flat washing to achieve the purpose of changing the blue color to light), pad whitening agent (suitable for red light dyeing of finished fabrics, especially for finished fabrics dyed with vat dyes, when the color is medium or light, it is more Effective. If the color fades normally, re-bleaching can be considered, but hydrogen peroxide bleaching should be used to avoid unnecessary discoloration, 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 1g/L O and boil respectively, 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 flat O and 1mL/L glacial acetic acid respectively. After passing through the machine at room temperature, the orange light can be reduced by about 10%.

4.2.3 Dip 0.6mL/L bleach water in the rolling tank of the reduction machine, steam it at room temperature, do not drain the water in the first two compartments of the washing tank, wash the last two compartments with cold water, wash with one compartment with hot water, and then soap it. 20% lighter, the bleaching water concentration is different, the stripping depth is also different, the bleaching water stripping color is slightly faded.

4.2.4 Use 10L of 27.5% hydrogen peroxide, hydrogen peroxideMix 3L of stabilizer, 2L of 36°Bé caustic soda, and 1L of 209 detergent into 500L of water, steam it in a reducing machine, then add O and soap to cook until the mixture is 15% pure.

4.2.5 Use 5-10g/L soda ash, steam to strip the color, wash with water and boil with soap, the color can be 10-20% lighter, and the color will be bluish after stripping.

4.2.6 Use 10g/L caustic soda, steam and strip the color, wash with water and boil with soap, the color 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 lighten the color by 10-15%.

4.2.8 Use 1-5L of 27.5% hydrogen peroxide in the jig dyeing machine, run 2 passes at 70°C, take samples, and control the hydrogen peroxide concentration and number of passes according to the depth of the color. For example, dark green can be lightened by half to light in 2 passes. About 10%, the color and light change little.

4.2.9 Put 250mL of bleaching water into 250L of water in the jigger dyeing machine, and go through 2 channels at room temperature to peel 10-15% of the surface.

4.2.1O can be added in the jigger dyeing machine to add O and soda ash for shallow stripping.

5. 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 → 30 minutes to rise to 100°C, keep warm for 30 minutes → wash with hot water at 60°C → wash with cold water → heat up to 60°C, add dye, acetic acid and keep warm for 10 minutes → gradually heat up to 98°C, keep warm for 40 minutes → gradually Lower the temperature to 60°C to produce the cloth.

5.1.1.2 Stripping formula:
Surfactant 1227:2%; acetic acid 2.5%; liquor ratio 1:10

5.1.1.3 Counterdye formula:
Cationic dye (converted to 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 → heat up to 100°C, 30 minutes → cool down and wash → sodium bisulfite → 60°C, 20 minutes → warm water wash → cold water wash → 6O°C, add dye and acetic acid → gradually rise to 100°C, keep warm for 4O minutes → Gradually lower the temperature to 60°C to release the 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 color pattern treatment on nylon fabric
5.2.1 Lightly colored flowers
When the difference in the depth of the color flower is 20%-30% of the dyeing depth, generally 5%-10% of O2 can be used. The bath ratio is the same as dyeing, and the temperature is kept between 80℃-85℃. When the depth reaches about 20% of the dyeing depth, slowly raise the temperature to 100°C and keep it warm until the dye is absorbed by the fiber as much as possible.

5.2.2 Medium color flowers
Medium-colored flowers can be partially subtracted and then dyed to their original depth.
Na2CO35%-10%
Add O1O%-l5%
Liquor ratio 1:20-1:25
Temperature 98℃-100℃
Time 90min-120min

After color reduction, the fabric is washed out of the vat with hot water, then cold water until clean, and then dyed.

2.3 Severe pornography
Craftsmanship:
36°BéNaOH:1%-3%
Pingping plus O: 15% ~ 20%
Synthetic detergent: 5%-8%
Liquor ratio 1:25-1:30
Temperature 98℃-100℃
Time 20min to 30min (until all discoloration occurs)

After all stripping, gradually cool down, wash thoroughly with water until clean, then use 0.5mL acetic acid at 30°C for 10 minutes to fully neutralize the remaining alkali, then wash with clean water and dye again. 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 color pattern treatment on polyester fabric
5.3.1 Lightly colored flowers,
Apply 1-2g/L of stripe repair agent or high-temperature leveling agent, and reheat the temperature to 135°C for 30 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 Serious pornography
Sodium chlorite 2-5g/L, acetic acid 2-3g/L, methylnaphthalene 1-2g/L;
Start processing at 30℃, raise the temperature to 100℃ at 2℃/min, process for 60min, and then wash the cloth with water.

5.4 Examples of treatment of serious dyeing defects of cotton fabrics dyed with reactive dyes
Process flow: stripping→oxidation→counterdye
5.4.1 Color stripping
5.4.1.1 Process prescription:
Insurance powder 5g/L-6g/L
Add O2g/L-4g/L
38°Bé caustic soda 12mL/L-15mL/L
Temperature 60℃-70℃
Liquor ratio 1:10
Time 30min

5.4.1.2 Operation methods and steps
Add water according to the bath ratio, add the weighed Pingping O, caustic soda, insurance powder, and 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%H2O23mL／L
38°Bé caustic soda lmL/L
Stabilizer 0.2mL/L
Temperature 95℃
Liquor ratio 1:10
Time 60min

5.4.2.2 Operation methods and steps
Add water according to bath ratio, add�� Stabilizer, caustic soda, hydrogen peroxide and other additives, turn on steam and heat up to 95°C, keep warm for 60 minutes, then cool down to 75°C, drain and add water, add 0.2 large soda, wash for 20 minutes, drain; wash with 80°C hot water 20min; wash in 60℃ hot water for 20min, then wash in cold running 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
The temperature is according to the original process

5.4.3.2 Operation methods and steps
Follow normal dyeing methods and procedures.

6. A brief description of the stripping process of blended fabrics
Disperse and acid dyes can be partially stripped from diacetate/wool blends using 3 to 5% alkylamine polyoxyethylene at 80 to 85°C and pH 5 to 6 for 30 to 60 minutes. 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 can usually improve the resulting stripping on polyester/polyacrylonitrile fibers.

1 g/L anionic detergent; 3 g/L cationic retardant; and 4 g/L Yuanming powder at boiling point and pH 10 for 45 minutes. 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 for 90 to 120 minutes. Commonly used for stripping wool/polyacrylic fibers.

Use a moderately alkaline solution of 2 to 5 g/L caustic soda and 2 to 5 g/L sodium silicate powder, reduction cleaning at 😯 to 85°C, or gallbladder powder at 120°C to obtain polyester/cellulose. Removes many direct, reactive dyes from blends.

Use 3% to 5% cartilage powder and an anionic detergent, treat 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.

Disperse, cationic, direct or reactive dyes can be stripped from cellulose/polyacrylonitrile blended fabrics with 1-2 g/L sodium chlorite and boiling at around pH 3.5 for 1 hour. When stripping triacetate/polyacrylonitrile, polyester/polyacrylonitrile, and polyester/cellulose blended fabrics, a suitable carrier and non-ionic detergent must be added.

7. Production Notes

7.1 The fabric must be tested on a sample before stripping or correcting the shade.
7.2 After stripping, the fabric must be washed with water (cold or hot water).
7.3 Stripping should be short-term and repeated if necessary.
7.4 When stripping, the conditions of temperature and additives must be strictly controlled according to the properties of the dye itself, such as oxidation resistance, alkali resistance, chlorine bleaching resistance, etc. 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 may 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 stripped fabric will only appear Changes in shades.