Color fastness of textiles to sunlight

The photofading mechanism of dyes is very complex, but the main reason is that the dye is 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, combination state and mixed color matching. Therefore, the rational selection of dyes is very important.

First,Select dyesaccording to fiber properties and textile uses. For cellulose fiber textiles, dyes with better oxidation resistance should be selected; for protein fibers, dyes with better resistance to reduction or containing weak oxidizing additives should be used; for other fibers, dyes should be selected based on their impact on fading. In order to enhance the photooxidation stability of the azo group in the dye molecular structure, during the dye synthesis process, some strong electron-withdrawing groups are usually introduced at the ortho-position of the azo group, thereby reducing the electron cloud density of the nitrogen atom of the azo group. In addition, hydroxyl groups can also be introduced into the two ortho-positions of the azo group, and their coordination ability can be used to complex with heavy metals, thereby reducing the electron cloud density of the hydrogen atoms of the azo group and shielding the azo group, ultimately improving the dye quality light fastness.

The second should be selected according to the color depth Dyes. A large number of tests have proven that the light fastness of reactive dyes on cellulose fibers is directly proportional to the depth of the dye, that is, the darker the color, the better the light fastness. 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 chance of the dye being photo-oxidized. On the contrary, the lighter the color, the dye is mostly highly dispersed on the fiber, and the probability of being exposed to light is higher, resulting in a significant decrease in light fastness. Therefore, when dyeing light-colored varieties, dyes with higher light fastness should be used. In addition, many 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 finishing agents should be used.

Third,Dye color matching with good light stability and compatibility should be selected. Different dyes have different fading properties and even different photofading mechanisms. Sometimes, the presence of one dye can sensitize the fading of another dye. When color matching, you should choose dyes that will not sensitize each other and can even improve light resistance. This is especially important when dyeing dark colors such as black. If one of the three primary colors of dye fades too quickly, it will quickly cause the dyed fiber or fabric to discolor, and the faded dye residue will also affect the light stability of the other two dyes that have not faded. Reasonable control of the dyeing process to fully combine the dye with the fiber and try to avoid hydrolyzed dyes and unfixed dyes remaining on the fiber is an important way to obtain higher light fastness.