Principle of Stripping

Stripping is the use of chemical action to destroy the dye on the fiber and make it lose its color.
There are two main types of chemical stripping agents. One is reductive stripping agents, which achieve the purpose of fading or decoloring by destroying the color system in the molecular structure of the dye. For example, dyes with an azo structure have an azo group. It may be reduced to an amino group and lose its color. However, the damage of the reducing agent to the color system of certain dyes is reversible, so the fading can be restored, such as the color system of the anthraquinone structure. Sodium sulfonate and white powder are commonly used reductive peeling agents. The other is oxidative stripping agents, among which the most commonly used are hydrogen peroxide and sodium hypochlorite. Under certain conditions, oxidants can cause damage to certain groups that make up the dye molecular color system, such as decomposition of azo groups, oxidation of amino groups, methylation of hydroxy groups, and separation of complex metal ions. These irreversible structural changes result in the fading or decolorization of the dye, so theoretically, the oxidative stripping agent can be used for complete stripping treatment. This method is particularly effective for dyes with anthraquinone structure.

Common dye stripping

2.1 Stripping of reactive dyes

Any reactive dye containing metal complexes should first be boiled in a solution of metal polyvalent chelating agent (2 g/L EDTA). Then wash thoroughly with water before alkaline reduction or oxidation stripping treatment. The complete stripping is usually treated at high temperature for 30 minutes in alkali and sodium hydroxide. After the peeling is restored, wash thoroughly. Then it is cold bleached in sodium hypochlorite solution. Process example:
Examples of continuous stripping process:
Dyeing cloth → padding reducing solution (caustic soda 20 g/l, soluene 30 g/l) → 703 reduction steamer steaming (100℃) → washing → drying

Example of dyeing vat peeling process:

Color-faulted cloth→reel→2 hot water→2 caustic soda (20g/l)→8 peeling color (sodium sulfide 15g/l, 60℃) 4 hot water→2 cold water scroll→normal sodium hypochlorite level bleaching Process (NaClO 2.5 g/l, stacked for 45 minutes).

2.2 Stripping of sulfur dyes

Sulfur dye-dyed fabrics are usually corrected by treating them 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 fabric before re-dyeing. color. In severe cases, sodium hypochlorite or sodium hypochlorite must be used.
Process example
Light color example:
Into the cloth → more soaking and rolling (sodium hypochlorite 5-6 grams liters, 50 ℃) → 703 steamer (2 minutes) → full water washing → drying.

Dark example:
Color imperfect fabric → rolling oxalic acid (15 g/l at 40°C) → drying → rolling sodium hypochlorite (6 g/l, 30°C for 15 seconds) → fully washing and drying

Examples of batch processes:
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, bath ratio 1:30-40.

2.3 Stripping of acid dyes

Boil for 30 to 45 minutes with ammonia water (2O to 30 g/L) and anionic wetting agent (1 to 2 g/L). Before ammonia treatment, use sodium sulfonate (10 to 20 g/L) at 70°C to help complete peeling. Finally, the oxidation stripping method can also be used.
Under acidic conditions, adding a special surfactant can also have a good peeling effect. There are also those that use alkaline conditions to peel off the color.

Process example:
Examples of real silk peeling process:

Reduction, stripping and bleaching (soda ash 1g/L, flat addition of O 2g/L, sulphur powder 2-3g/L, temperature 60℃, time 30-45min, bath ratio 1:30) → pre-media treatment (ferrous sulfate heptahydrate) 10g/L, 50% hypophosphorous acid 2g/L, formic acid adjust pH 3-3.5, 80°C for 60min)→rinse (80°C wash for 20min)→oxidation stripping and bleaching (35% hydrogen peroxide 10mL/L, pentacrystalline sodium silicate 3-5g/L, temperature 70-8O℃, time 45-90min, pH value 8-10)→clean

Example of wool stripping process:

Nifanidine 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 it.

Example of nylon stripping process:

36°BéNaOH: 1%-3%; flat plus O: 15%-20%; synthetic detergent: 5%-8%; bath ratio: 1:25-1:30; temperature: 98-100°C; time: 20-30min (until all decolorization).

After all the color is peeled off, the temperature is gradually reduced, and it is washed thoroughly with water, and then the alkali remaining on the nylon is fully neutralized with 0.5mL/L acetic acid at 30°C for 10min, and then washed with water.

2.4 Stripping of vat dyes

Generally, in a mixed system of sodium hydroxide and sodium hydroxide, 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.

Examples of continuous stripping process:

Dyeing cloth → padding reducing solution (caustic soda 20 g/l, soluene 30 g/l) → 703 reduction steamer steaming (100℃) → washing → drying

Example of intermittent peeling process:

Pingping plus O: 2-4g/L; 36°BéNaOH: 12-15ml/L; Sodium hydroxide: 5-6g/L;

During the stripping treatment, the temperature is 70-80℃, the time is 30-60 minutes, and the bath 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: Sodium formaldehyde sulfoxylate and carrier, treated at 100°C and pH4-5; the treatment effect is more significant at 130°C.

Method 2: Sodium chlorite and formic acid are processed at 100°C and pH 3.5.

The best result is the first treatment followed by the second treatment. As far as possible over-dye black after treatment.

2.6 Stripping of cationic dyes

The stripping of disperse dyes on polyester usually uses the following methods:

In a bath containing 5 ml/liter monoethanolamine and 5 g/liter sodium chloride, treat at boiling point for 1 hour. Then clean it, and then bleach 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 to 4 to 4.5 with acidic acid. 30 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 of sodium hydroxide at 85°C for 20 to 30 minutes. And finally clean it.

Using detergent (0.5 to 1 g/L) and a boiling solution of acetic acid to treat the dyed fabric at pH 4 for 1-2 hours can also achieve a partial peeling effect.
Process example:
Please refer to 5.1 acrylic knitted fabric color processing example.

2.7 Stripping of insoluble azo dyes

5 to 10 ml/liter of 38°Bé caustic soda, 1 to 2 ml/liter of heat-stable dispersant, and 3 to 5 g/liter of sodium hydroxide, plus 0.5 to 1 g/liter of anthraquinone powder. If there is enough sodium hydroxide and caustic soda, anthraquinone will make the stripping liquid red. If it turns yellow or brown, caustic soda or sodium hydroxide must be added. The stripped fabric should be washed thoroughly.

2.8 Peeling of paint

The paint is difficult to peel off, generally use potassium permanganate to peel off.

Process example:

Dyeing defective cloth → rolling potassium permanganate (18 g/l) → washing with water → rolling oxalic acid (20 g/l, 40°C) → washing with water → drying.

Stripping of commonly used finishing agents

3.1 Stripping of fixing agent

Fixing agent Y can be stripped off with a small amount of soda ash and adding O; polyamine cationic fixing agent can be stripped off by boiling with acetic acid.

3.2 Removal of silicone oil and softener

Generally, softeners can be removed by washing with detergent, and sometimes soda ash and detergent are used; some softeners must be removed by formic acid and surfactant. The removal method and process conditions are subject to sample tests.

Silicone oil is more difficult to remove, but with a special surfactant, under strong alkaline conditions, boiling can be used to remove most of the silicone oil. Of course, these are subject to sample tests.

3.3 Removal of resin finishing agent

The resin finishing agent is generally removed by the method of acid steaming and washing. The typical process is: padding acid solution (hydrochloric acid concentration of 1.6 g/l) → stacking (85 ℃ 10 minutes) → hot water washing → cold water washing → drying dry. With this process, the resin on the fabric can be stripped on the continuous flat track scouring and bleaching machine.

Shade correction principle and technology

4.1 Principle and technology of color light correction
When the shade of the dyed fabric does not meet the requirements, it needs to be corrected. The principle of shading correction is the principle of residual color. The so-called residual color, that is, two colors have the characteristics of mutual subtraction. The remaining color pairs are: red and green, orange and blue, and yellow and purple. For example, if the red light is too heavy, you can add a small amount of green paint to reduce it. However, the residual color is only used to adjust the color light in a small amount. If the amount is too large, it will affect the color depth and vividness, and the general dosage is about lg/L.

Generally speaking, reactive dyes dyed fabrics are more difficult to repair, and vat dyes dyed fabrics are easy to repair; when sulphur dyes are repaired, the shade is difficult to control, generally use vat dyes to add and subtract colors; direct dyes can be used for additive repairs, but the amount should be Less than 1 g/L.

The commonly used methods of shade correction include water washing (suitable for dyeing finished fabrics with darker shades, more floating colors, and repairing fabrics with unsatisfactory washing and soaping fastness), light stripping (refer to dye stripping process, conditions It is lighter than the normal stripping process), padding alkali steaming (applicable to alkali-sensitive dyes, most of which are used for reactive dyes; such as reactive black KNB color-matched dyeing cloth such as blue light, you can roll an appropriate amount of caustic soda , Supplemented by steaming and flat washing to achieve the purpose of lightening blue light), pad whitening agent (applicable to the red light of dyed finished fabrics, especially for finished fabrics dyed with vat dyes, the color is more when the color is medium or light Effective. For normal color fading, re-bleaching can be considered, but hydrogen peroxide bleaching should be the main method to avoid unnecessary color changes.), paint overcoloring, etc.
4.2 Shade correction process example: the subtractive method of reactive dye dyeing

4.2.1 In the first five-grid flat washing tank of the reduction soaping machine, add 1 g/L flat flat and add O to boil, and then carry out flat washing, generally 15% shallow.

4.2.2 In the first five flat washing tanks of the reduction soaping machine, add lg/L flat and flat O, 1mL/L glacial acetic acid, and overrun the machine at room temperature to make the orange light about 10% lighter.

4.2.3 Padding 0.6mL/L of bleaching water in the rolling tank of the reduction machine, and the steaming box at room temperature, the first two compartments of the washing tank do not drain water, the last two compartments are washed with cold water, one compartment with hot water, and then soaped. The bleaching water concentration is different, and the peeling depth is also different, and the bleaching peeling color is slightly faint.

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 to 500L of water, steam it in the reducing machine, and then add O to boil, soap and cook. Shallow 15%.

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

4.2.6 Use 10g/L caustic soda, steam stripping, washing and soaping, it can be 20%-30% lighter, and the color light is slightly dark.

4.2.7 Use sodium perborate 20g/L steam to strip the color, which can be lighter by 10-15%.

4.2.8 Use 27.5% hydrogen peroxide 1-5L in the jig dyeing machine, run 2 passes at 70℃, sample, and control the concentration of hydrogen peroxide and the number of passes according to the color depth. For example, if the dark green passes 2 passes, it can be as shallow as half to half. About 10%, the shade changes little.

4.2.9 Put 250mL of bleaching water in 250L of water in the jig dyeing machine, walk 2 lanes at room temperature, and it can be stripped as shallow as 10-15%.

4.2.1O can be added in the jig dyeing machine, add O and soda ash peeling.

Examples of dyeing defect repair process

5.1 Examples of acrylic fabric color processing

5.1.1 Light-colored flowers

5.1.1.1 Process flow:

Fabric, surfactant 1227, acetic acid → 30 minutes to 100°C, heat preservation for 30 minutes → 60°C hot water washing → cold water washing → warming up to 60°C, putting in dyes and acetic acid for holding for 10 minutes → gradually warming up to 98°C, keeping warm for 40 minutes → gradually Cool down to 60°C to produce cloth.

5.1.1.2 Stripping formula:

Surfactant 1227: 2%; acetic acid 2.5%; bath ratio 1:10

5.1.1.3 Counter-dyeing formula:

Cationic dyes (converted to the original process formula) 2O%; acetic acid 3%; bath ratio 1:20

5.1.2 Dark colored flowers

5.1.2.1 Process route:

Fabric, sodium hypochlorite, acetic acid → heating up to 100°C, 30 minutes → cooling water washing → sodium bisulfite → 60°C, 20 minutes → warm water washing → cold water washing → 60°C, put in dye and acetic acid → gradually raise to 100°C, keep warm for 4O minutes →Gradually lower the temperature to 60°C for the cloth.

5.1.2.2 Stripping formula:

Sodium hypochlorite: 2O%; acetic acid 10%;

Bath ratio 1:20

5.1.2.3 Chlorine formula:

Sodium bisulfite 15%

Bath ratio 1:20

5.1.2.4 Counter-dyeing formula

Cationic dyes (converted to the original process formula) 120%

Acetic acid 3%

Bath ratio 1:20

5.2 Example of dyeing treatment of nylon fabric

5.2.1 Slightly colored flowers

When the difference in color depth is 20%-30% of the depth of dyeing itself, generally 5%-10% of the level plus O can be used, the bath ratio is the same as the dyeing, and the temperature is between 80 ℃ and 85 ℃. When the depth reaches about 20% of the dyeing depth, slowly increase the temperature to 100°C and keep it warm until the dye is absorbed by the fiber as much as possible.

5.2.2 Moderate color flower

For medium shades, partial subtractive methods can be used to add dye to the original depth.

Na2CO3 5%-10%

Add O 1O%-l5% flatly

Bath ratio 1:20-1:25

Temperature 98℃-100℃

Time 90 min-120min

After the color is reduced, the fabric is washed with hot water first, then washed with cold water, and finally dyed.

5.2.3 Serious discoloration

Process:

36°BéNaOH: 1%-3%

Flat plus O: 15% ～20%

Synthetic detergent: 5%-8%

Bath ratio 1:25-1:30

Temperature 98℃-100℃

Time 20min-30min (until all decolorization)
After all the color is peeled off, the temperature is gradually reduced, and then rinsed thoroughly with 0.5 mL of acetic acid at 30°C for 10 minutes to fully neutralize the residual alkali, and then rinsed with water to re-dye. Some colors should not be dyed with primary colors after they are peeled off. Because the fabric base color becomes light yellow after it is peeled off. In this case, the color should be changed. For example: After the camel color is completely stripped, the background color will be light yellow. If the camel color is dyed again, the shade will be gray. If you use Pura Red 10B, adjust it with a small amount of light yellow and change it to a concubine color to keep the shade bright.

image

5.3 Example of dyeing treatment of polyester fabric

5.3.1 Slightly colored flowers,

Strip flower repair agent or high-temperature levelling agent 1-2 g/L, reheat to 135°C for 30 minutes. The additional dye is 10%-20% of the original dosage, and the pH value is 5, which can eliminate the fabric color, stain, shade difference and color depth, and the effect is basically the same as that of the normal production fabric swatch.

5.3.2 Serious blemishes

Sodium chlorite 2-5 g/L, acetic acid 2-3 g/L, methyl naphthalene 1-2 g/L;

Start treatment at 30°C, heat up at 2°C/min to 100°C for 60 min, then wash out the cloth with water.

5.4 Examples of treatment of serious defects in cotton fabric dyeing with reactive dyes

Process flow: stripping → oxidation → counter-dyeing

5.4.1 Color peeling

5.4.1.1 Process prescription:

Insurance powder 5 g／L-6 g／L

Ping Ping with O 2 g／L-4 g／L

38°Bé caustic soda 12 mL／L-15 mL／L

Temperature 60℃-70℃

Bath ratio l: lO

Time 30min

5.4.1.2 Operation method and steps

Add water according to the bath ratio, add the already weighed flat O, caustic soda, sodium hydroxide, and fabric on the machine, turn on the steam and increase the temperature to 70°C, and peel off the color for 30 minutes. After peeling, drain the remaining liquid, wash twice with clean water, and then drain the liquid.

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℃

Bath ratio 1:10

Time 60 min

5.4.2.2 Operation method and steps

Add water according to the bath ratio, add stabilizers, caustic soda, hydrogen peroxide and other additives, turn on the steam and increase the temperature to 95°C, keep it for 60 minutes, then lower the temperature to 75°C, drain the liquid and add water, add 0.2 soda, wash for 20 minutes, drain the liquid; use Wash in hot water at 80°C for 20 minutes; wash in hot water at 60°C for 20 minutes, and wash with cold running water until the cloth is completely cooled.

5.4.3 Counterstaining

5.4.3.1 Process prescription

Reactive dyes: 30% x% of the original process usage

Yuanming powder: 50% Y% of the original process usage

Soda ash: 50% z% of the original process usage

Bath ratio l: lO

Temperature according to the original process

5.4.3.2 Operation method and steps
Follow the normal dyeing method and steps.

Brief introduction of color stripping process of blended fabric

Disperse and acid dyes can be partially peeled from the diacetate/wool blended fabric with 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 on the diacetate/nylon and diacetate/polyacrylonitrile fiber blends. Partial stripping of disperse dyes from polyester/polyacrylonitrile or polyester/wool requires boiling with a 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 peeling of polyester/polyacrylonitrile fibers.

1 g/L anionic detergent; 3 g/L cationic dye retardant; and 4 g/L sodium sulfate treatment at boiling point and pH 10 for 45 minutes. It can partially strip the alkaline and acid dyes on the nylon/alkaline dyeable polyester blended fabric.

1% non-ionic detergent; 2% cationic dye retardant; and 10% to 15% sodium sulfate treatment at boiling point and pH 5 for 90 to 120 minutes. It is often used for stripping wool/polyacrylonitrile fiber.

Use 2 to 5 grams/liter of caustic soda, and 2 to 5 grams/liter of sodium hydroxide, reduction cleaning at 80 to 85°C, or moderate alkaline solution of white powder at 120°C, which can be obtained from polyester/cellulose Many direct and reactive dyes are removed from the blend.

Use 3% to 5% white powder and an anionic detergent to treat for 4O-6O minutes at 80℃ and pH4. Disperse and acid dyes can be stripped from diacetate/polypropylene fiber, diacetate/wool, diacetate/nylon, nylon/polyurethane, and acid dyeable nylon textured yarn.

Use 1-2 g/L sodium chlorite, boil for 1 hour at pH 3.5, to strip disperse, cationic, direct or reactive dyes from the cellulose/polyacrylonitrile fiber blended fabric. When stripping triacetate/polyacrylonitrile, polyester/polyacrylonitrile, and polyester/cellulose blended fabrics, a suitable carrier and non-ionic detergent should be added.

Production considerations

7.1 The fabric must be sample tested before peeling or correcting the shade.
7.2 Washing (cold or hot water) must be strengthened after the fabric is peeled off.
7.3 Stripping should be short-term and should be 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, and chlorine bleaching resistance. To prevent excessive amount of additives or improper temperature control, resulting in excessive peeling or peeling. When necessary, the process must be determined by stakeout.
7.5 When the fabric is partially peeled off, the following situations will occur:
7.5.1 For the color depth treatment of a dye, the shade of the dye will not change much, only the color depth will change. If the color stripping conditions are mastered, it can fully meet the requirements of the color sample;
7.5.2 When the fabric dyed with two or more dyes with the same performance is partially stripped, the shade change is small. Because the dye is only stripped to the same degree, the stripped fabric will only appear Changes in depth.
7.5.3 For the treatment of dyeing fabrics with different dyes in color depth, it is usually necessary to strip the dyes and re-dyed.