Light fastness refers to the degree of discoloration of colored fabrics by sunlight.
Influencing factors of light fastness
1. Related to the dye structure: Generally speaking, the light fastness of anthraquinone dyes, phthalocyanine dyes, vulcanized sulfur blue and metal complex dyes are relatively good; most of the insoluble azo dyes also have relatively good light fastness. High; but benzidine type azo dyes have low light fastness; triarylmethane dyes are not light fast.
2. Related to fiber types: ①Indigo has a low light fastness on wool but low light fastness on cellulose; ②Van Laming Blue Salt B has a higher light fastness on viscose than cotton Many.
3. It is related to the influence of external conditions: the humidity of the air and the temperature have a great influence on the light fastness. Generally, the light fastness is low when the moisture content is high. For example: Vanlamin blue is easier to reddish and fade in the south than in the north.
4. Related to additives: There are many additives that can effectively improve the light fastness.
Measures to improve light fastness
Dye selection (the most important factor)
①High light fastness of yellow spectrum: reactive dyes are based on pyrazolone and naphthalene trisulfonic acid;
②High light fastness of blue spectrum: reactive dyes use anthraquinone, phthalocyanine and methyl ester as the matrix structure;
③The light fastness of red spectrum reactive dyes is generally low, especially for light colors. Only some azo groups contain coordinating hydroxyl groups in two adjacent positions, which form a stable chelating ring with copper, which can improve the light fastness. degree;
④When selecting dyes for color matching, make sure that the light fastness level of each component dye selected is equivalent, as long as any one of the components, especially the component with the least amount, can not reach the light fastness of light color dyeing. The requirements of the material will make the light fastness of the final dyed material fail to meet the standard.
①The effect of dye floating color, incomplete soaping after dyeing, unfixed dyes and hydrolyzed dyes remaining on the cloth will also affect the light fastness of dyed products, and their light fastness is significantly lower than that of 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 post-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 dyeings to improve the 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.