Analysis on factors affecting color fastness of textiles to sunlight and improve
Sunlight color fastness is to determine the sunlight resistance of dyes and materials. The test method can be either sunlight exposure or sunlight aging machine exposure. The fading degree of the sample after exposure is compared with the standard color sample. The rating standards are wool blue label and gray card. For this reason, it can be concluded whether it meets the standard requirements and what can be improved. Shanghai Qianshi Precision Electromechanical Technology Co., Ltd. is a manufacturer of textile testing instruments. It can provide domestic and imported sunlight aging machines. Customers with needs are welcome to call for inquiries in time. In addition, the factors affecting the color fastness of textiles to sunlight and the improvement methods are described below.
Factors affecting the color fastness of textiles to sunlight:
1. Influence of dye and coating structure
The light fading mechanism of dyes is very complicated, but it is mainly that the dye is excited after absorbing photons, and a series of photochemical reactions occur to destroy the structure, resulting in discoloration and fading. The light color 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, it is very important to choose dyes reasonably.
2. Influence of dyeing depth and floating color
The light fastness of dyed fabrics is related to the depth of dyeing. The greater the depth of dyeing, the larger the particles of dye aggregate on the fabric, the smaller the proportion of dye per unit weight exposed to the air, and the higher the light fastness. For light-colored fabrics, the proportion of dye aggregates on the fiber is small, and the light fastness tends to decrease accordingly. The light fastness grade in the factory that cannot meet the requirements is generally medium and light colors. In some light coffee-colored fabrics, after the light fastness test, the red light is almost completely lost, and the color change is more obvious. Whether the dyeing process is properly selected and whether the washing and soaping after dyeing are thorough will affect the amount of unfixed dyes and hydrolyzed dyes, i.e. floating colors, on the fabric. The light fastness of floating colors is significantly lower than that of fixed reactive dyes. Therefore, improper post-dyeing treatment will also affect the light fastness of fabrics.
3. The influence of fixing agents and softeners
The use of fixing agents greatly improves the friction fastness, washing fastness, and staining fastness of reactive dyes. Generally, the washing fastness of fabrics treated with cationic low molecular weight or polyamine color fixing agents is 4~5, but the light fastness of fabrics fixed with such color fixing agents is reduced. Softening cotton fabrics with cationic softeners will reduce the light fastness of reactive dyes, mainly because the softener turns yellow after exposure to the sun, which changes the color of the fabric.
Methods to improve the light fastness of textiles:
1. Selection of dyes or coatings
In terms of improving light fastness, the selection of dyes or coatings is the key. For single colors, try to select dyes with higher light fastness. For colored fabrics that need to be matched, the light-fastness grades of the dyes of each component should be equivalent. If the light fastness of one component is poor, it will affect the light fastness of the entire mixed color. Dyes with relatively small content in the mixed color component can be selected with dyes with high light fastness grades, to ensure the light fastness grade of the overall color fastness of the fabric.
2. Improvement of the soaping process
During the dyeing process, a reasonable dyeing process should be formulated, and sufficient soaping and washing should be performed to minimize the amount of hydrolyzed dyes and floating colors to improve the light fastness of the fabric; at the same time, various color fastnesses such as washing, water sweat stains, and friction should also be improved.
3. Selection of fixing agents and softeners
Most fixing agents are quaternary ammonium salts, sulfonium salts, or phosphate salts. Such fixing agents and dyes form lakes on the fibers. Although they have good water fastness, they often reduce the original light fastness of the dyes. Therefore, when the light fastness requirement is high, try to avoid using such fixing agents. Some cationic softeners and amino-modified silicone softeners give the fabric a full feel, but they also have the disadvantages of yellowing, discoloring the dye, and inhibiting fluorescent brighteners.
4. UV absorbers and light fastness enhancers
If the processing conditions of colored fabrics have been fixed, such as dyeing, fixing, softening and finishing, etc., to improve the light fastness of colored fabrics under these conditions, you can choose light fastness enhancers or UV absorbers. These additives can directly absorb ultraviolet rays irradiating the fabric to prevent the dye from being damaged by photooxidation.