Introduction to pearlescent pigments

▲ Pearlescent pigments are widely used in cosmetics, plastics, printing inks and automotive coatings. The main types of pearlescent pigments are: natural fish scale pearlescent pigments, bismuth oxychloride crystal pearlescent pigments, and mica coated pearlescent pigments. They are mica flakes covered with thin titanium dioxide or iron, or other metal oxides. The mica has a size of from 4 μm to 200 μm and a thickness of about 0.5 μm.

▲ Metal oxide coated mica sheets are very smooth, so they have good light reflection properties, and transparency, which means that only a part of the light is reflected, and the transmitted part of the light passes through the mica sheet to another layer, which can continue to be Shots resulted in multiple reflections at many levels. It is difficult for the eye to focus on a certain layer and thereby establish the depth of the light. So you can see a wonderfully deep, shiny sheen, which we call "Pearl."

▲ The pearlescent effect can be determined by the thickness of the titanium dioxide coating. White pearlescence is formed by the reflection of the thinnest layer of titanium dioxide. As the thickness of the coating increases, the reflected light is white, yellow, gold, red, blue, and green, respectively.

▲ The iron oxide coating has the above properties in addition to its own color. The bronze color is formed by the absorption of yellow color by ferric oxide. The same principle can be used to obtain reddish brown, burgundy, and the like.

▲ The color of the pearlescent pigment is related to the substrate color. On a white substrate, transmitted light can be seen at any angle, and the coloration is not obvious. If the transmitted light is absorbed by the substrate on a black or dark substrate, the interference color is strong at the angle of reflection.

▲The pearlescent pigment reflects light according to the specular effect, so the interference color can be seen at the reflection angle, and in the direction of the scattering angle, since the light is transmitted through the thin layer, the complementary color of the interference color can still be seen. For example, an interference red pearlescent pigment coating can see red at the reflection angle and green at the scattering angle. The white pearlescent pigment is white at the reflection angle, and the scattering angle will reveal the color of the substrate or the color of the colorant.

▲ The color has a layered three-dimensional effect and different color effects due to different angles, making the pearlescent pigment different from other metallic pigments. Commonly used metallic pigments such as aluminum silver powder are opaque. The light is not transmissive, and all the light is reflected on the surface like a mirror surface, so it does not have the stereoscopic depth effect of the multilayer reflection of the pearlescent pigment. When a certain light absorbing pigment is added to the pearlescent pigment, since the pearlescent pigment itself is transparent, allowing light to penetrate and reach the light absorbing pigment, and then being reflected, the color of the light absorbing pigment is thereby enhanced and brighter. If a light-absorbing pigment is added to a metallic pigment, since the metallic pigment itself is opaque, light cannot pass through the metal sheet to reach the pigment, and thus the color is weakened. For example, aluminum powder, which is itself gray, the color of the light absorbing pigment thus becomes a dull gray, like a mud.

▲ Metallic pigments are similar in shape and size to pearlescent pigments. The light is reflected by the specular principle, that is, the light is incident from a 45 degree angle and then reflected at a 45 degree angle. As the viewing angle increases, the reflected light is dimmed and the color is darkened. When you look at the metallic pigment coating from different angles, the color changes only in shades and does not have the same color change as pearlescent pigments.