Fluorescent and phosphorescent printing

Phosphorescence and fluorescence have long been known. As early as the year AD 450, there was a record of “night light” and the nighttime pearls of folklore in China’s Later Han Dynasty. In fact, “Nightlight” is an imaginary surface, and the night jewels should contain phosphorus. They heat in friction and they glow in the dark.

Luminescence is the process by which an object converts absorbed energy into light radiation in some way. The phenomenon in which a light body emits light due to an external action is called "excitation" in optics. The difference between fluorescence and phosphorescence is that the path from which the excited molecule drops from the excited state to the ground state is different, and the length of time from the excitation to the light emission is different. Therefore, when the incident light source is cut off, the presence of phosphorescence can also be seen, and the fluorescence will soon disappear. Luminescent substances are divided into organic and inorganic categories. Inorganic phosphors include red (yttrium oxide), yellow-green (zinc sulfide), and blue (silver sulfide). This kind of phosphor is expensive and is mainly used for coating color picture tubes. The inorganic phosphor particles with lower price are rougher, and after being ground, the light-emitting crystals are destroyed and the luminance decreases. The ink made with this kind of phosphor has poor transparency, strong hiding power, easy to paste and print, but it has strong moisture resistance. Synthetic organic phosphors, containing both carriers and stimulants. The stimulant function can stimulate the specific carrier to emit light that does not emit light or emit light. The different types of stimuli can also change the wavelength and color of the originally emitted light. This organic phosphor powder has a simple manufacturing process, a low price, fine grains, and a small loss of brightness after mechanical grinding. The ink made with it has high transparency and low hiding power.

Phosphorescence and fluorescence printing are currently produced using two processes. One is to use light powder as a coating material and produce phosphorescent and fluorescent papers before ink printing. The other is the direct printing of light powder made into ink. There are two methods for ink preparation: one is to add binder and solvent to the light powder, and the ink is made after ball milling; the other is to directly synthesize a colorless transparent phosphorescent liquid, which is naturally dried or cured by Uv light after printing. dry. It should be particularly pointed out that phosphorescent and fluorescent inks should be on the top layer of the print, that is, the last layer of the print, to prevent the general ink color from covering the phosphor color. Because the phosphorescent color is printed on other ink colors, black, deep purple and other colors will absorb phosphorescence, so that the luminous intensity decreases; white and light colors can improve the luminous brightness. Therefore, try to use light, light tone or reduce the printing level.

Source: China Washing & Dyeing Industry Information Center