With the vigorous development of the national economy and the improvement of national production levels, consumers’ recognition of the richness and brightness of textiles’ colors continues to expand, and demand is rising day by day. With the characteristics of high emission intensity, bright colors and strong fluorescence, fluorescent dyes are widely used in the dyeing and printing of fabrics in addition to the clothing of traffic police and road maintenance personnel to meet the daily needs of consumers.
Fluorescent dye
Fluorescent dyes: dyes that can strongly absorb and radiate fluorescence in the visible light range.
The fluorescence reflectance of fluorescent dyes on fabrics depends on the intensity of the ultraviolet light source, the amount of fluorescent substances dyed on the fabric and the fluorescence of the fluorescent substances Quantum efficiency. Different fluorescent dyes have different fluorescence quantum efficiencies and different dyeing dosages. Generally, the concentration of fluorescent dye dyeing is around medium color, not too dark and not too light. When the fluorescent dye solution is dilute, the fluorescence intensity is proportional to the concentration. If the solution concentration is too high, the fluorescent substance will undergo a “self-extinguishing” reaction and the fluorescence intensity will decrease. The concentration of the solution is too small, the fluorescence is not obvious, and the brightness is not enough.
Different fabrics give fluorescent dyes different fluorescent properties. For example, when dyed with dispersed fluorescent yellow 8GFF, polyester, acid ester fiber, and cotton fiber show bright fluorescent yellow with green light, but when dyeing acrylic fiber, they will appear bright yellow light, less green light, and no fluorescence.
PH value has an impact on fluorescence reflectance. Generally speaking, dyeing in acidic and weakly acidic dye baths (pH value between 4-6) is beneficial to improving fluorescence reflectivity. Adding fluorescent additives to fluorescent dyes helps to increase the fluorescence reflectance; when fluorescent dyes and non-fluorescent dyes are mixed, the fluorescence reflectance decreases, the proportion of non-fluorescent dyes increases, and the fluorescence reflectance decreases rapidly.
Fluorescent pigments have heterocyclic rings in their molecular structure. Common ones include azocyanines, xanthenes, coumarins, hemicyanine structures, etc. Fluorescent dyes are mainly yellow, orange and red, such as dispersed fluorescent yellow 10GN, dispersed fluorescent yellow 8GFF, dispersed fluorescent red G, dispersed fluorescent pink BG, dispersed fluorescent pink FBS, dispersed fluorescent orange 2GFL, etc.
Principle of fluorescence generation
Fluorescence is a photoluminescence phenomenon. When ultraviolet light, or some kind of light, shines on a fluorescent substance, the substance absorbs energy consistent with its characteristic frequency and transitions from the ground state to an excited state with higher energy.
Molecules in an unstable excited state will transfer and relax to the lowest vibration energy level of the excited state in a short period of time, balancing the excited state , and then fall back to the higher vibrational energy level of the ground state. During the fall-back process, the energy is attenuated in the form of fluorescence, and the fluorescence disappears when the irradiation is stopped.
Fluorescent dyes for textiles:
1. Fluorescent whitening agent
2. Dispersed fluorescent dye
3. Fluorescent paint
01
Fluorescent whitening agents
Fluorescent whitening agents have been widely used in textiles, papermaking, washing powder, soap, rubber, plastics, and pigments and paint, etc.
In the textile industry, the whiteness of the fiber itself often fails to meet people’s aesthetic requirements. Especially for natural fibers, their whiteness varies greatly due to different growth environments and growth cycles. White substances generally slightly absorb the blue light of 450-480nm in visible light, resulting in a lack of blue, making it slightly yellow and giving people an old feeling.
Fluorescent whitening agents can absorb higher-energy near-ultraviolet light, causing their molecules to enter an excited state, and then the excited molecules transition to a lower-energy ground state and emit fluorescence. .
Due to the energy loss, the fluorescence wavelength of the radiation becomes longer (about 450nm blue light), and the yellow color of yellowed items can be compensated by the blue light reflected by the fluorescent whitening agent , thereby increasing the apparent whiteness of the item. Since the intensity of the emitted light exceeds the intensity of the original visible light projected on the treated fabric, a slightly colored whitening effect is produced. Fluorescent whitening agents with practical value, in addition to absorbing ultraviolet light and emitting purple-blue fluorescence and having high fluorescence efficiency, must also be close to colorless or slightly yellow and have the characteristics of ordinary dyes. If the fiber has good affinity, good solubility or dispersion properties and…Excellent fastness properties such as washing, light fastness and ironing resistance.
02
Dispersed fluorescence Dye
Dispersed fluorescent dyes have small molecules and no water-soluble groups in their structure. They are uniformly dispersed into the fibers in the dye liquor with the help of the dispersant. . After padding in the dyeing solution, it is dried and then hot-melted. Under the action of high temperature, the dye deposited on the fabric can diffuse into the fiber in the form of single molecules, completing the dyeing of the chemical fiber in a very short time.
Because the small molecules of fluorescent dyes are fused with the fibers, the color fastness to rubbing and washing of the fabric is Both are very good, but the color fastness to light is poor
03
Fluorescent paint
1. Fluorescent paint is a slurry composed of fluorescent pigments, dispersants and wetting agents. It is insoluble in water. It has no affinity for fibers and cannot be dyed according to the dyeing conditions of conventional dyes
2. If the fluorescent pigment particles are large, the coloring rate is low, the color is dim, the fastness is poor, and the color is not easy to be accurate; if the particles are small, the coloring rate is high and the fastness is good, but the brightness is affected.
3. The fluorescent coating is attached to the fiber surface through padding, and then through the adhesive The resin component helps the coating to fix on the fiber surface and achieve a certain color fastness. The fabric will feel stiff due to the influence of the resin contained in the adhesive.
Fluorescent fabric
Fluorescent
Fabric
Fluorescent fabric refers to Fabrics with strong reflective effects after ordinary fabrics are fluorescently dyed or coated.
The use of fluorescent fabrics can strongly reflect light to extremely distant targets or targets in the dark, thus serving as a good warning and safety precaution.
Fluorescent fabrics are mainly made of chemical fibers, and dispersed fluorescent dyes are used to dye the fibers. They have good color fastness to washing and bright colors.
If you want to make fluorescent colors on cotton, linen, silk, and wool fabrics, you basically use fluorescent paint to bond the paint to the fiber through an adhesive to achieve dyeing. the goal of. The color of fabrics varies due to factors such as surface mechanism, paint concentration, dye uptake rate, and PH value. The fluorescence effect may not even occur, resulting in fluorescent colors having no effect.
Problems and misunderstandings about the use of fluorescent fabrics
Color disadvantages:
1. The color fastness of fluorescent fabrics to light is very poor.
2. Fluorescent paint has poor color fastness to rubbing and fades badly when washed.
3. The fluorescent colors of fabrics made of cotton, linen, wool, and silk have problems such as difficulty in color accuracy, dim color, and low fluorescence reflectivity.
Production issues:
1 . The minimum packaging of dyes commonly used in the industry is generally 25 kilograms. Many factories do not prepare fluorescent dyes. In the case of multi-color matching, the quantity is too small to produce.
2. Many natural material fabric factories lack experience in making fluorescent fabrics, resulting in many color fastness and color light problems.
3. Some factories add fluorescent whitening agents to ordinary dyes to pretend to be dyed with fluorescent dyes
