The fabric after finishing treat, why does the shade change? How to deal with it?

1 cause

After the fabric is dyed and finished, its shade will change to a certain extent. This is a common phenomenon of dyeing. After analysis, the following factors are closely related to the fluctuation of color and light.

①After dyeing, many dyes are not stable on the fiber, but metastable (the most prominent of vat dyes). After the subsequent wet and heat treatment, the following changes may occur:

a. The dye molecules in a highly dispersed state in the fiber will further aggregate, which will change the crystalline state of the dye to a certain extent.

b. The dye molecules in the fiber will change from the parallel state of the fiber molecular chain to the vertical state, which will change the existing orientation of the dye.

c. Dyes with a tendency for molecular isomerization (cis-trans) will undergo configuration changes.

Once the dyes dyed in fibers change in crystallization, orientation, configuration, etc., it will inevitably lead to changes in the light absorption properties of the dyes, thereby causing fluctuations in color and light.

②Commonly used finishing agents (softeners, water repellants, antibacterial agents, anti-ultraviolet agents, etc.) will cause the following problems in the process of humidity and heat treatment:

a. Some complex chemical reactions will occur between cationic additives and cationic dyes.

b. The auxiliary film on the fiber will have a certain degree of "yellowing".

c: The pH (mainly acidity) of the finishing solution will cause the color and light of the dye to change.

d. The post-finishing agent will cause the disperse dyes to produce different degrees of "thermal migration" and "thermal sublimation" under high temperature conditions. This complex relationship between finishing agents and dyes will inevitably affect dyeing shades.

③ The color of the dyed cloth after finishing may also change during the placement process. The main influencing factors are as follows:

a. Commonly used dyes generally have different "three-sensitivity" (humidity, heat, and photosensitivity) phenomena. That is to say, the dyeing shade will vary with the moisture content of the fiber, the temperature, and the intensity of the light. Therefore, once the moisture content, temperature, and light of the fabric change, its color and light will be different.

b. Minerals and heavy metal compounds (mainly from water and finishing agents) remaining on the fabric will slowly undergo complex chemical interactions with dyes during the placement of the dyed cloth, resulting in changes in shade.

c. During the placement of the color cloth, the acid, alkaline gas or oxidizing and reducing gas in the surrounding environment will also cause the stability of the dye to decrease, and then the color and light change will occur.

2 The countermeasures are as follows

①Be sure to thoroughly wash (soap) after dyeing. There are two reasons: one is that sufficient washing (soaping) can promote the dyes in the fibers to achieve a stable state in terms of crystallization, orientation, configuration, etc.; , heat, light, acid, alkali, and chemicals are more sensitive and more likely to cause changes in color and light. Fully washing (soaping) to remove floating color and various dyeing chemicals as much as possible will undoubtedly improve the stability of shade.

②The dye should be optimized. To choose "three sensitive" phenomenon is not obvious, the color light by the finishing agent and acid, alkali little influence. Disperse dyes should be selected with good fastness of "thermal migration" and "sublimation".

③ To use the finishing agent selectively. It is necessary to choose the one with less yellowing and slight influence on the color light. To this end, a pioneer experiment must be done in advance.

④The production workshop should strengthen ventilation and improve the cleanliness of the air. Moreover, the cloth box should be covered, and the finished product should be timely.

The implementation of the above comprehensive measures can significantly improve the color and light stability of dyed cloth.