The effect of pearlescent pigments

The effect of pearlescent pigments

　　The color of general pigments is derived from the selective absorption (or reflection) of specific wavelengths of light, while the brilliance of pearlescent pigments comes from the interference of light.

　　If the object fully reflects the illuminated white light, it will appear white; if part of it is reflected and partially absorbed, it will be gray; when it is almost completely absorbed, it will appear black. If the object appears red, it is because of the incident white light, only the red wavelength is reflected, and the rest of the colored light is completely absorbed. Generally, pigments are added to the vehicle of plastics, coatings, and inks, and the combined effects of light absorption, diffusion, and penetration of the pigments show different effects such as the color, gloss, or transparency of the object. Pearlescent pigments, color changing pigments, fluorescent pigments

　　The pearly luster effect produced by the interference of light can be understood from the example of oil floating on water. The occurrence of this rainbow-like color is caused by the interference and enhancement of specific wavelengths of visible light reflected from the air/oil interface at the top of the film and the oil/water interface at the bottom at the same time.

The pearl luster of pearlescent pigments is derived from the titanium dioxide layer deposited on the mica flakes and the film thickness is strictly controlled. There are many paths when light hits the flakes of pearlescent pigments. Some light passes through the interface with low refractive index near the air or pearlescent pigment (such as the resin of the coating film), and it is reflected when it hits the surface of the titanium dioxide layer. This is caused by the high refractive index of titanium dioxide and the difference in refractive index between the resin and the titanium dioxide interface. . Part of the light passes through the titanium dioxide layer and is reflected again at the interface between the titanium dioxide layer and the mica. Only through repeated reflections and refractions can pearl luster be produced.

The color caused by 　　 depends on whether the light reflected from two different interfaces is the result of strengthening or interfering with each other. The change of the thickness of the titanium dioxide film will cause the change of the color light. The optical thickness of the transparent film (the product of the geometric thickness and the refractive index) is a prerequisite for the occurrence of light interference. Since the interference color changes with the light and the angle of observation, the iridescence appears.

　　The optical properties of pearlescent pigments are different from those of ordinary pigments. They have regular multiple reflection and refraction effects. Therefore, when the surface of the pearlescent pigment particles are arranged in parallel, they can show a more beautiful effect.