Views: 0 Author: Site Editor Publish Time: 2020-12-23 Origin: Site
The basic principles of photochemistry of dye fading
During the sun exposure, the effect of light on dyes can be explained in two ways.
First of all, as far as the structure of the dye is concerned, under the action of ultraviolet light, the chemical bond in the dye changes or even breaks, causing the structure of the chromophore and auxochrome group in the dye to be destroyed, thereby losing the color; Under irradiation, the three-dimensional structure of the dye changes, causing the color to change, which is the color change.
On the other hand, it is explained from the changes in the electronic structure and energy of the dye molecule. Under the irradiation of a large amount of higher energy ultraviolet light, some of the bonded electrons obtain higher energy and transition to higher energy level anti-bonding orbitals, or electrons in lower energy level bonding orbitals transition to anti-bonding orbitals . When these electrons return to the original orbit, they release different energy and show a different color from the original, thus showing different light fastness.
Measures to improve light fastness
①The effect of dye floating color, incomplete soaping after dyeing, unfixed dyes and hydrolyzed dyes remaining on the cloth surface will also affect the light fastness of dyed products, their light fastness is significantly lower than the fixed reactive dyes. The more thoroughly the soaping is done, the better the light fastness;
② The application of cationic low-molecular-weight or polyamine-condensed resin-type fixing agent and cationic softener to the finishing of fabrics will significantly reduce the light fastness of the dyed material. Therefore, when choosing fixing agents and softeners, attention must be paid to their influence on the light fastness of dyed products;
③Ultraviolet absorbers are often used in light-colored dyed fabrics to improve light fastness, but they must be used in a large amount to have some effect, which not only increases the cost, but also causes yellowing and strong damage to the fabric, so it is not a good measure.