Why does the dye fade under the sun?

Factors affecting the light fastness of dyes

1. The wavelength of the light source and the irradiated light;

2. Environmental factors;

3. The chemical properties and organizational structure of the fiber;

4. Bonding strength between dye and fiber;

5. The chemical structure of the dye;

6. Dye concentration and aggregation state;

7. The influence of artificial sweat on the light fading of the dye;

8. The influence of additives.

Methods to improve the light fastness of dyes      

1. Improve the structure of the dye so that it can consume light energy while minimizing the impact on the dye color system, thereby maintaining the original color; that is, the high light fastness dye is often said. The price of such dyes is generally higher than that of ordinary dyes. For fabrics with high solar requirements, we should first start with the selection of dyes.       

2. If the fabric has been dyed and the light fastness is not up to the requirement, it can also be improved by additives. In the dyeing process or after dyeing, add suitable auxiliary agents to make the light react before the dye when it is exposed to light, and consume the light energy, so as to protect the dye molecules. Generally divided into ultraviolet absorbers and anti-ultraviolet agents, collectively referred to as light fastness enhancers.

Light fastness of light-colored fabrics dyed with reactive dyes     

The light fading of reactive dyes is a very complex photooxychlorination reaction. After knowing the light fading mechanism, the molecular structure of the dye is designed to consciously create some obstacles to the photooxidation reaction to delay the light fading. For example, yellow dyes containing Dole sulfonic acid group and pyrazolone, blue dyes containing methane phthalocyanine and bis-azo trichelate ring, and red dyes containing metal complexes, but still lack the bright red color and resistance to sunlight. Reactive dyes for light fastness.       

The light fastness of dyed products varies with the change of dyeing concentration. For fabrics dyed with the same dye on the same fiber, the light fastness increases with the increase of dyeing concentration. Light-colored fabrics have low dyeing concentration and are fast to the sun. The degree drops accordingly. However, the light fastness of common dyes on the printed dye color card is measured under the standard depth of 1/1 (that is, 1% owf or 20-30g/l dye concentration). If the dyeing concentration is 1/ In the case of 6, 1/12 or 1/25, the light fastness will be greatly reduced.      

Some people have proposed using ultraviolet absorbers to improve the fastness to light. This is not a desirable method. Ultraviolet rays need to be used a lot, and it can only be improved by half a level, and the cost must be improved a lot. Therefore, only fair selection of dyes can solve the light fastness.