1. The choice of dye or paint
The light-fading 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, leading to 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, choose dyes according to fiber properties and textile applications. For cellulose fiber textiles, dyes with good oxidation resistance should be selected; for protein fibers, dyes with good reduction resistance or containing weak oxidizing additives should be selected; for other fibers, dyes should be selected according to the effect on fading. In order to enhance the photooxidation resistance of the azo group in the dye molecular structure, in the dye synthesis process, some strong electron withdrawing groups are usually introduced at the ortho position of the azo group to reduce the electron cloud density of the azo nitrogen atom. In addition, it is also possible to introduce hydroxyl groups at the two ortho positions of the azo group, and use its coordination ability to complex with heavy metals, thereby reducing the electron cloud density of the azo group hydrogen atoms, and shielding the azo group, and ultimately improving the dye Fastness to light.
Second, the dye should be selected according to the color depth. A large number of tests have proved that the light fastness of reactive dyes on cellulose fibers is directly proportional to the depth of the dyed luster, 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 degree of aggregation of dye molecules, the smaller the surface area of the same amount of dye in contact with air, moisture and light, and the lower the probability of the dye being oxidized by light. On the contrary, the lighter the color, the dye is mostly in a highly dispersed state on the fiber, the probability of exposure to light is higher, and the light fastness will eventually decrease significantly. Therefore, for 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 selected.
Third, dyes with good light resistance stability and compatibility should be used for color matching. The fading properties of different dyes are different, and even the light fading mechanism is also different. Sometimes, the presence of one dye sensitizes the fading of another dye. When matching colors, you should choose dyes that do not sensitize each other and can even improve the stability of light resistance. This is especially important when dyeing dark colors such as black. One of the three primary colors fades too fast, which will quickly cause the dyed fiber or fabric to change color, 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, fully combining the dye and fiber, and avoiding hydrolyzed dyes and unfixed dyes remaining on the fiber as much as possible is an important way to obtain higher light fastness.
2. Improvement of soaping process
During the dyeing process, a reasonable dyeing process should be formulated, fully soaping, washing, and reducing the amount of hydrolyzed dyes and floating colors to improve the light fastness of the fabric; at the same time, improving the color fastness of washing, water perspiration, rubbing, etc. .
3. Choice of fixing agent and softener
Most fixing agents are quaternary ammonium salts, sulfonium salts or phosphate salts. Such fixing agents and dyes form lakes on the fibers. Although the washing fastness is good, they tend to reduce the original light fastness of the dyes. Therefore, when the light fastness requirements are high, try to avoid using this type of fixing agent. Some cationic softeners and amino-modified silicone softeners give the fabric a plump feel, but also have the disadvantages of yellowing, discoloration of dyes, and suppression of fluorescent brighteners.
4. Ultraviolet absorber and light fastness improver
If the processing conditions of the colored fabric have been fixed, such as dyeing, fixing, softening and other steps have been completed, under these conditions to improve the light fastness of the colored fabric, you can choose a light fastness enhancer or ultraviolet absorber. Such additives can directly absorb the ultraviolet rays irradiated on the fabric and prevent the dyes from being damaged by photooxidation.
5. Light fastness enhancer
Can significantly improve the anti-ultraviolet grade, sunlight and perspiration light fastness of reactive, direct, dispersive, acid, vat dyes and other dyed fabrics. It is suitable for improving the anti-ultraviolet finishing of dyed fabrics such as reactive, direct, dispersive, acid, and vat dyes.