How To Deal with Polyester Or Nylon Dyed Too Dark?

Disperse dyeing is an important dyeing method in dyeing factory processing and production. In actual production, the color may be too dark or the color may not match. Once the dyed polyester or nylon fabric is too dark, too dark or too bright, it must be treated with color reduction (lightening) first, and then proof-dyeing (color correction).

Color reduction of polyester fabric

1. Color reduction of polyester fabric. 

When disperse dyes are used to dye polyester, the dye and polyester are combined by multiple molecular forces (mainly hydrogen bonds and van der Waals forces). Therefore, general physical methods, i.e. high-temperature transfer dyeing method, can be used to reduce the color of dyed polyester.

2. Color reduction mechanism.

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

a. Under high temperature (above 100°), the dense structure of polyester becomes loose, the instantaneous gaps in the microstructure increase, and the dye is easy to pass through.

b. Under high temperature (above 100 degrees), the activation energy of the dye increases, the vibration intensifies, the distance between dye molecules and between dye and fiber molecules increases, the binding force weakens, and the dye is easy to move.

c. The applied color-correcting agent can produce a strong swelling effect and a large stripping effect on polyester.

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

3. Color reduction method.

Polyester color-correcting agent: 3~5g/L (as needed);

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

Treatment temperature: 130℃;

Treatment time: high temperature and high pressure roller dyeing machine, 6~8 treatments; high temperature and high pressure spray dyeing machine, 30~50min treatment;

Process tips: The color reduction rate of this color reduction 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 auxiliary agent, the processing temperature, the processing time and other factors.

4. Color reduction effect.

1. For polyester dyed fabrics, the color reduction effect is relatively good under the conditions of high processing temperature (130℃) and large amount of color correcting agent (4~5g/L). Its color reduction rate can generally reach about 25%. The color reduction rate will decrease with the decrease of processing temperature or the decrease of color correcting agent.

2. The color reduction effect of high-temperature leveling agent is poor and should not be used.

Color reduction of nylon fabric

1. Nylon is usually dyed with disperse dyes, neutral dyes and acid dyes.

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

2. Nylon has poor stability to oxidants. The effective chlorine in sodium hypochlorite can replace the hydrogen on the amide bond, thereby hydrolyzing nylon and reducing its strength; hydrogen peroxide can also degrade nylon macromolecules and reduce its strength.

3. Nylon has high stability to alkali. According to practical experience, 100% caustic soda 50g/L, 100℃ treatment for 2h, the strength decreases very little. Therefore, nylon dyeing can only be reduced by alkali.

Method of alkali color reduction:

Light powdered soda ash 20g/L;

Or 30% caustic soda 12~50mL/L (as needed;

Chelating dispersant 2g/L

Boiling temperature alkali boiling treatment, the treatment time is as needed.

If you want to know more about dyeing solutions, please contact: info@tiankunchemical.com