Reason: The mechanism of light fading of dyes is very complex, but mainly the dye is stimulated after absorbing photons, and a series of photochemical reactions occur to destroy the structure, resulting in discoloration and fading. The light fastness of textile mainly depends on the chemical structure of the dye, as well as its aggregation state, binding state and mixed color.
Reasonable selection of dyes is very important
First, dyes are selected according to fiber properties and textile uses.
For cellulose fiber textiles, dyes with better antioxidant properties should be selected. For protein fibers, dyes with better resistance to reduction or containing weak oxidizing additives should be selected; Other fibers should be selected according to the impact on fading.
In order to enhance the photooxidation stability of the azo group in the dye molecular structure, some strong electron-absorbing groups are usually introduced in the ortho-position of the azo group during the dye synthesis, so as to reduce the electron cloud density of the azo group gas atom. In addition, the two adjacent hydroxyl groups of the azo group can also be introduced, using its coordination ability to complex with heavy metals, thereby reducing the electron cloud density of the azo hydrogen atom, and playing a shielding effect on the azo group, and finally improving the color fastness of the dye to light.
Choose dyes according to color depth
The light fastness of reactive dyes on cellulose fibers is proportional to the depth of the dyed color, 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 concentration of the dye molecules, the smaller the surface area of the same amount of dye in contact with air, water and light, and the lower the probability of the dye being photooxidized. On the contrary, the lighter the color, the dye is mostly in a highly dispersed state on the fiber, and the probability of being exposed to light is higher, and the color fastness to light is ultimately significantly decreased. Therefore, dyeing light-colored varieties should choose dyes with high light fastness. 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 selected.
Choose dyes with good light stability and compatibility
The fading properties of different dyes are different, and even the mechanism of light fading is different. Sometimes, the presence of one dye sensitizes the fading of another.
When matching colors, dyes that will not sensitize each other and can even improve light stability should be selected, which is particularly important when dyeing dark varieties such as black. The rapid fading of one of the three primary colors will quickly cause discoloration of the dyed fiber or fabric, and the faded dye residue will also affect the light stability of the other two dyes that are not faded. It is an important way to obtain high color fastness to light by controlling dyeing process, making dye-fiber fully combined and avoiding hydrolyzed dye-unfixed dye-residue on fiber.