Lightfastness to color

The photofading mechanism of dyes is very complex, but mainly it is that after dyes absorb photons, they are excited and undergo a series of photochemical reactions that destroy their 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 the situation of mixed color matching. Therefore, it is very important to select dyes reasonably.

1. Select dyes based on the properties of the fibers and the uses of the textiles. For cellulose fiber textiles, dyes with better antioxidant properties should be selected. For protein fibers, dyes with better resistance to reduction or containing weakly oxidizing additives should be selected. Dyes for other fibers should be selected based on their impact on fading. To enhance the photo-oxidation 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 adjacent position of the azo group, thereby reducing the electron cloud density of the azo nitrogen atom.

In addition, hydroxyl groups can be introduced at the two adjacent positions of the azo group. By taking advantage of their coordination ability, they can complex with heavy metals, thereby reducing the electron cloud density of the azo hydrogen atom and shielding the azo group, ultimately enhancing the light fastness of the dye.

2. Dyes should be selected based on the depth of the color. A large number of experiments have proved that the light fastness of reactive dyes on cellulose fibers is directly 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 aggregation degree of the dye molecules. The same amount of dye has a smaller surface area in contact with air, moisture and light, and the lower the probability of the dye being photo-oxidized. Conversely, the lighter the color, the more highly dispersed the dye is on the fiber, and the higher the probability of being exposed to light, ultimately resulting in a significant decrease in light fastness. Therefore, when dyeing light-colored varieties, dyes with higher light fastness should be selected.

In addition, the addition of many post-treatment agents such as softeners and anti-wrinkle finishing agents to fabrics can also reduce the light fastness of the products. Therefore, dyes that are not sensitive to these finishing agents should be selected.

3. Dyes with good light stability and compatibility should be selected for color matching. The fading properties of different dyes vary, and even the photo-fading mechanisms are different. Sometimes, the presence of one dye can sensitize the fading of another dye.

When matching colors, dyes that do not sensitize each other and can even improve light stability should be selected. This is particularly important when dyeing dark varieties such as black. If one of the three primary colors fades too quickly, it will soon cause the dyed fibers or fabrics to change color, and the residue of the faded dye will also affect the light stability of the other two dyes that have not faded.

Reasonable control of the dyeing process to ensure that dyes are fully combined with fibers and to minimize the residue of hydrolyzed dyes and unfixed dyes on the fibers is an important way to achieve high light fastness.

Color fastness to water

The most important way to enhance the water and sweat fastness of fabrics is to rationally select dyes, especially those with high fixation rates and good stability.

Reasonable formulation and control of dyeing processes, strengthening of color fixation conditions, and formation of highly stable covalent bonds can ensure that dyes are fully fixed. For instance, when dyeing with less reactive dyes, catalysts can be selected, or appropriate fixatives can be chosen, or fixation can be carried out at a higher temperature.