Popular Science | When polyester or nylon is dyed dark, how does the dyeing factory deal with it?

Disperse dyeing is an important dyeing method in dyeing factory processing and production. In actual production, the color may be too dark or the shade may not match. Once the dyed polyester or nylon fabric is If the color is too deep, too dark, or too bright, you must first subtract the color (lighten it), and then proofing and re-dying (color correction).

Color reduction of polyester fabric

1. Color reduction of polyester fabric

Disperse dyes dye polyester. There are multiple molecular forces between the dye and the polyester. (mainly hydrogen bonds and van der Waals forces). Therefore, to reduce the color of dyed polyester, general physical methods can be used, that is, high-temperature migration dyeing method to reduce the color.

2. Color subtraction mechanism

The color reduction of dyed polyester is a comprehensive reflection of multiple effects.

Therefore, in a high-temperature (130~135℃) treatment bath in the presence of color corrector, disperse dyes dyed on polyester will produce larger dye migration behavior, some of the dye will fall back from the polyester into the water, making the color of the polyester lighter.

3. Subtractive color method

Polyester color corrector: 3~5g/L ( as needed)

Glacial acetic acid: 0.5m/L (pH=4~4.5)

Processing temperature: 130℃

Processing time: high-temperature and high-pressure jigger dyeing machine, processing 6~8 passes; high-temperature and high-pressure dyeing machine, processing 30~50min.

Craftsmanship tips:

The color subtraction rate of this subtractive color method is generally 15%~25%. The color reduction rate is closely related to the molecular structure of the dye, the color reduction ability of the additive, processing temperature, processing time and other factors.

4. Subtractive color effect

①Polyester dyed fabrics, when the processing temperature is high (130℃), the amount of color correction agent Under the condition of more (4~5g/L), the color reduction effect is relatively good, and the color reduction rate can generally reach about 25%. The color reduction rate will decrease accordingly when the processing temperature is reduced or the amount of color corrector is reduced. .

② High-temperature leveling agents have poor color reduction effect and should not be used.

The subtractive color of nylon fabric

1. Nylon Usually dyed with disperse dyes, neutral dyes and acid dyes

Disperse dyes mainly rely on the molecular attraction between the dye and nylon, so they are easier to lose color. Neutral dyes and acid dyes can be dyed by the molecular attraction between the dye and nylon, and can also be dyed by ionic bonding with NH2 in the nylon. Therefore, the bonding fastness between neutral dyes, acid dyes and nylon is relatively good, and color reduction is relatively difficult.

2. Nylon has poor stability to oxidants

The available chlorine in sodium hypochlorite can replace the amide The hydrogen on the bond will hydrolyze the nylon and reduce the strength; hydrogen peroxide can also degrade the nylon macromolecules and reduce the strength.

3. Nylon has high stability to alkali

According to actual experience, 100% caustic soda 50g/L, treated at 100℃ for 2 hours, the strength decreases very little. Therefore, nylon dyeing can only undergo alkali color reduction.

Notes on color reduction

1. When dyeing nylon with disperse dyes, it is easier to use alkali agents to reduce the color, but the color light changes greatly and the color darkens seriously.

2. Neutral dyes dye nylon. Soda ash treatment has almost no color reduction ability, and the color light changes. Caustic soda has color reduction ability, and the higher the concentration, the greater the color reduction ability. Larger, and the color change is greater.

3. When dyeing nylon with acid dyes, soda ash has almost no color reduction ability, but the color change is small; caustic soda has a slight color reduction ability, but the color change is serious.

It can be seen that the dyeing of nylon uses alkali agent to reduce the color. Either the color reduction rate is low, or it isThe color becomes serious (especially darkened). This brings great difficulties to the next level of color cultivation, and it is even impossible to achieve the original color light.

Therefore, when the dyed nylon material must be subtracted (lightened), it can only be stripped to an appropriate extent by using the stripper-caustic soda method as needed. Process, and then proof and counter-dye (color correction).

Basic knowledge of disperse dyeing

At room temperature

1. Dye liquid

The role of dye liquor composition auxiliaries

1) Composition: glacial acetic acid, leveling agent SE (or dispersing agent N), disperse dye

2) Help Agent effect:

① Glacial acid: glacial acetic acid, leveling agent SE (or dispersant N), disperse dyes

② Dispersant N (leveling agent SE)

Make disperse dyes evenly dispersed in the dye liquor, maintain the stability of the dye in the dye liquor, and prevent dye aggregation.

2. Why do disperse dyes need to be slightly acidic (PH=5-6) Dyeing under conditions.

① If the PH value is too low (PH-<4= → dye color = light will change and the dye uptake rate will decrease.

② If the pH is too high (such as alkaline), the dye will be decomposed and destroyed under high-temperature alkaline conditions, the color will be dark, and the polyester will be damaged under alkaline high-temperature conditions.

3. How to mix and add materials for disperse dye dyeing?

1) Material mixing method:

Cold water beating: warm water (<50℃ = stir thoroughly and evenly, dilute and filter before adding to the dye vat for use.

①Add glacial acid first (add after dilution) to adjust the pH value (can be measured with pH test paper).

② Add the dissolved leveling agent and dispersant.

③ Finally, add the dye that is evenly dispersed.

That is: glacial acid → dispersant (leveling agent) → dye

Note:

Check whether the filter of the feeding bucket is intact before adding materials.

4. Why is the maximum dyeing temperature 130℃?

Because at 130℃, disperse dyes have the highest dyeing percentage, bright colors, level dyeing, and less floating colors.

1) If the temperature is too high, the dye is easy to decompose and the fiber is easily damaged.

2) If the temperature is too low, the dye uptake rate will be low and the dyeing through will be poor. Therefore, the maximum suitable temperature for disperse dyes is 130°C.

5. What are the requirements for rising and cooling during dyeing, and why?

1) Heating requirements:

Control the temperature rise, otherwise the temperature rises too fast, which will cause the dye to dye too quickly , and color difference occurs.

① Color flower: refers to uneven dyeing.

② The purpose of heat preservation in the middle (90℃*5′) is to make the dye evenly absorbed by the fiber and then heat up to prevent color blooming.

③ Heating rate: should be slow, generally controlled at 1~2℃/min

2) Cooling requirements:

① Requirement: Natural cooling below 80℃ after dyeing (generally controlled at 1~2℃/min)

② if Sudden cooling after dyeing can easily cause chicken paw prints (wrinkles) or make the fabric feel rough.

③ General operations:

Cool the temperature to 80℃ at 2℃/min and then wash it with water. It is strictly forbidden to open the cover and wash it above 80℃, otherwise Security issues are prone to occur.

6. What is the purpose of 130℃ insulation (30~45min)?

1) Purpose: to dye the fiber thoroughly and evenly.

Light color: short holding time.

Dark color: long heat preservation time.

2) If the holding time is shorter, it will not be conducive to the uniform diffusion of the dye, and it will easily cause color blooming and light color.

Key points of coloring operations

1. When dyeing and washing the vat, pay attention to cleaning the high-temperature vat conveying pipe.

2. Materials and dyes should be mixed in advance 20-30 minutes in advance, stirred and dispersed evenly for use.

3. The temperature of the chemical material should not exceed 50℃, otherwise the dye will condense.

4. Before opening materials, check whether the filter of the chemical barrel is intact.

5. It is forbidden to add dye while heating up. After adding dye, the fabric should wait for a certain period of time (such as 5 minutes) before it can heat up.

6. The heating and cooling speeds must be strictly in accordance with the process curve to prevent quality problems caused by excessive heating or cooling.

7. After dyeing, the temperature should be naturally cooled to 80°C before the dye vat working door can be opened to avoid burns.