1. Comparison of light fastness test methods:
The light fastness test refers to placing the textile sample and a set of blue wool standard samples under artificial light under the conditions of exposure, and then comparing the two to change the color fastness to evaluate the color fastness.
2. Ways to improve light fastness:
The photofading mechanism of dyes is very complicated, but mainly because 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, binding state and mixed fight color. Therefore, the rational selection of dyes is very important.
3. Choose dyes 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 resistance to reduction or containing weakly oxidizing additives should be selected; for other fibers, dyes should be selected based on the effect on fading. In order to enhance the photooxidation stability of the azo group in the molecular structure of the dye, 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 azo group gas atoms. In addition, it can also attract hydroxyl groups at the two adjacent positions of the azo group, and use its coordination ability to complex with the heavy metal, thereby reducing the electron cloud density of the azo hydrogen atom, and shielding the azo group, and ultimately improving Dye fastness to light.
4. 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 proportional to the shade of the dyeing, 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 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 oxidized by light. On the contrary, the lighter the color, the more the dyes are in a highly dispersed state on the fiber, and the probability of being exposed to light is higher, which ultimately reduces the color fastness to light. Therefore, for light-colored varieties, dyes with high light fastness should be used. In addition, adding a lot of finishing agents such as softeners and anti-wrinkle finishing agents to the fabric will also reduce the light fastness of the product. Therefore, dyes that are not sensitive to these finishing agents should be selected.
5. Dyes should be selected for light stability and good compatibility:
Different dyes have different fading properties, and even the mechanism of light fading is different. Sometimes, the presence of one dye sensitizes the fading of another dye. When mixing colors, you should choose dyes that do not sensitize each other and can even improve light stability. This is especially important when dyeing dark varieties such as black. One of the three primary colors fades too quickly, which will soon cause the dyed fiber or fabric to change color, and the faded dye residue will also affect the photostability of the other two dyes that have not faded. Reasonable control of the dyeing process to fully combine the dye and the fiber, and try to avoid the hydrolysis dye and unfixed dye remaining on the fiber, is an important way to obtain higher light fastness.
