What are fluorescent dyes

Fluorescent Dyes: Dyes that strongly absorb and radiate fluorescence in the visible light range.

The fluorescent reflectance of fluorescent dyes on fabrics depends on the intensity of the ultraviolet light source, the amount of fluorescent substances dyed on the fabrics and the fluorescent quantum efficiency of the fluorescent substances. Different fluorescent dyes have different fluorescence quantum efficiencies and different dyeing dosages. Generally, the concentration of fluorescent dye dyeing is about medium color, not too dark and not too light. When the fluorescent dye solution is diluted, the fluorescence intensity is proportional to the concentration. If the concentration of the solution is too large, the fluorescent substance will appear "self-extinguishing" reaction, and the fluorescence intensity will decrease. The solution concentration is too small, the fluorescence is not obvious, and the vividness is not enough. 

Different fabrics make fluorescent dyes exhibit different fluorescent properties. For example, dispersed fluorescent yellow 8GFF, when polyester, ester fiber and cotton fiber show bright fluorescent yellow with green light, but when acrylic fiber is dyed, it will appear bright yellow light, less green light, and no fluorescence.

The pH value has an effect on the fluorescence reflectance. Generally speaking, acid and weak acid dye baths (pH value between 4-6) are beneficial to improve the fluorescence reflectance. Adding a fluorescent enhancer to the fluorescent dye helps to improve the fluorescent reflectance; when the fluorescent dye is mixed with the non-fluorescent dye, the fluorescent reflectance decreases, the proportion of the non-fluorescent dye increases, and the fluorescent reflectance decreases rapidly.

Fluorescent pigments have heterocycles in their molecular structure. Common ones are azacyanines, xanthenes, coumarins, semicyanines, etc. Fluorescent dyes are mainly yellow, orange and red, such as Disperse Fluorescent Yellow 10GN, Disperse Fluorescent Yellow 8GFF, Disperse Fluorescent Red G, Disperse Fluorescent Pink BG, Disperse Fluorescent Pink FBS, Disperse Fluorescent Orange 2GFL, etc.

Fluorescent dyes for textiles:

1. Fluorescent whitening agent

Optical brighteners have been widely used in textiles, papermaking, washing powder, soap, rubber, plastics, pigments and paints.

In the textile industry, the whiteness of the fiber itself often fails to meet people's aesthetic requirements. Especially natural fibers, due to the different growth environment and growth cycle, their whiteness varies greatly. The white substance generally slightly absorbs the blue light of 450-480nm in the visible light, resulting in insufficient blue color, making it slightly yellowish and giving people a sense of staleness.

Fluorescent whitening agents can absorb near-ultraviolet light with high energy to make the molecules enter the excited state, and then the excited molecules transition to the ground state with lower energy, and emit fluorescence.

Due to the loss of energy, the fluorescent wavelength of the radiation becomes longer (about 450nm blue light), and the yellow color of the yellowed article can be compensated by the blue light reflected by the fluorescent whitening agent, thereby increasing the apparent whiteness of the article. Since the intensity of the emitted light exceeds the intensity of the original visible light projected on the treated fabric, a slightly tinted whitening effect is produced. The fluorescent whitening agent with practical value, in addition to absorbing ultraviolet light and emitting violet-blue fluorescence and having high fluorescence efficiency, must also be close to colorless or slightly yellow, and have the characteristics of ordinary dyes. For example, the fiber has good affinity, good solubility or dispersion properties, and good fastness properties such as washing, light and ironing.

2. Disperse fluorescent dyes

Disperse fluorescent dyes have small molecules and do not contain water-soluble groups in structure. They are uniformly dispersed into the fiber in the dye liquor with the help of the dispersant. After the pad dyeing solution, it is dried, and then hot-melt treatment is carried out. Under the action of high temperature, the dye deposited on the fabric can diffuse into the fiber in the form of single molecule, and complete the dyeing of chemical fiber in a very short time.

Because the small molecules of fluorescent dyes are fused together with the fibers, the color fastness to rubbing and washing of the fabric are good, but the color fastness to light is poor

3. Fluorescent paint

1. Fluorescent paint is a slurry composed of fluorescent pigments, dispersants and wetting agents. It is insoluble in water and has no affinity for fibers. It cannot be dyed according to the dyeing conditions of conventional dyes.

2. If the particles of fluorescent pigments are large, the coloring rate is low, the color light is dim, the fastness is poor, and the color light is not easy to be accurate; the particles are small, the coloring rate is high, and the fastness is good, but the vividness is affected.

3. The fluorescent coating is attached to the surface of the fiber by padding, and then the resin component of the binder helps the coating to be fixed on the surface of the fiber to achieve a certain color fastness. Due to the influence of the resin contained in the adhesive, the hand of the fabric will become stiff.