Why is the color fastness to light so poor?

Reason: The photofading mechanism of dyes is very complicated, but the main reason is that the dyes are excited after absorbing photons, and a series of photochemical reactions occur to destroy the structure, resulting in discoloration and fading. The light fastness of textiles mainly depends on the chemical structure of the dye, as well as its aggregation state, bonding state and mixed color combination.

Reasonable selection of dyes is very important

First, dyes are selected according to fiber properties and textile applications.

For cellulose fiber textiles, dyes with better oxidation resistance should be selected; for protein fibers, dyes with better reduction resistance or containing weak oxidative additives should be selected; other fibers should be selected according to the effect on fading.

In order to enhance the photo-oxidative stability of the azo group in the dye molecular structure, some strong electron-withdrawing groups are usually introduced at the ortho position of the azo group during the dye synthesis process, thereby reducing the electron cloud density of the azo gas atom. In addition, hydroxyl groups can also be introduced at the two ortho positions of the azo group, and its coordination ability can be used to complex with heavy metals, thereby reducing the electron cloud density of the hydrogen atom of the azo group, and shielding the azo group. Color fastness to light of dyes.

Choose dyes based on color depth

The color fastness to light of reactive dyes on cellulose fibers is proportional to the depth of the dyed luster, that is, the darker the color and luster, the better the color fastness to light. This is because the higher the concentration of the dye on the fiber, the greater the aggregation of the dye molecules, the smaller the surface area of the same amount of dye exposed to air, moisture and light, and the lower the probability of the dye being oxidized by light. On the contrary, the lighter the color, the more highly dispersed the dyes are on the fiber, the higher the probability of being exposed to light, and the final color fastness to light is significantly reduced. Therefore, when dyeing light-colored varieties, dyes with higher light fastness should be selected. In addition, many post-finishing agents such as softeners and anti-wrinkle finishing agents are added to the fabric, which will also reduce the light fastness of the product. Therefore, dyes that are not sensitive to these finishes should be selected.

Use dyes with good light resistance stability and compatibility for color matching

Different dyes have different fading properties and even different photofading mechanisms. Sometimes the presence of one dye sensitizes the fading of another dye.

When color matching, dyes that will not sensitize each other and can even improve light stability should be selected, which is especially important when dyeing dark varieties such as black. If one of the three primary colors fades too quickly, the dyed fiber or fabric will soon be discolored, and the faded dye residue will also affect the light stability of the other two dyes that are not faded. Reasonable control of the dyeing process, the full combination of dyes and fibers, and the avoidance of hydrolyzed dyes and unfixed dyes remaining on the fibers are an important way to obtain higher color fastness to light.