Talk about the effect and mechanism of pearlescent pigment
1. Basic characteristics of pearlescent pigments
Pearlescent pigments include natural pearlescent pigments and constituent pearlescent pigments. When used in coatings, pearl luster, rainbow effect and metallic luster effect can be obtained.
Pearlescent pigment is a translucent flake-like structure, and the diameter of the flake is much larger than the thickness. The thin films are placed in parallel layers in the coating film, and the incident light is partially reflected and partially transmitted, resulting in a common optical performance, namely, multi-angle color. When viewed from different angles, the color is different, sometimes the reflected color is seen, sometimes the transmission color is seen, resulting in a three-dimensional luster.
2. Mechanism of optical properties of mica titanium pearlescent pigment
① Pearlescent effect
It refers to the pearly soft color of pearly pigment, which is caused by the multiple reflection and transmission of the incident light by the titanium dioxide polycrystalline film coated on the mica substrate, that is, the interference of light.
For pearlescent pigments with small particle size, because the titanium dioxide coating film coated on the mica sheet is divided into many tiny layers like natural pearls, when the incident light shines on its surface, there will be a silk-like soft light (pearlescent). This optical property of the mica titanium pearlescent pigment is called the pearlescent effect.
② Metallic flash effect
The flickering visual sensation caused by the specular reflection of light on the metal surface is called "metal flash effect".
Mica-titanium pearlescent pigment can obtain a series of metallic luster after being treated with other metal oxide films or colorants.
Mica-titanium pearlescent pigment, which only uses titanium dioxide as the coating material, can show the silver-white metallic luster, and is called silver-white pearlescent pigment;
Silver white pearlescent pigment is colored with carbon black, with deep color, similar to lead powder;
The color of silver-white pearlescent pigment painted with chromium oxide is similar to that of bronze;
The yellow disturbing pearlescent pigment colored with iron oxide has a strong golden luster.
③ Visual flicker effect
Mica-titanium pearlescent pigment is composed of a layer of transparent metal oxide with a refractive index much higher than that of the base material mica deposited on the surface of the transparent mica sheet. When the light refracts, reflects, partially absorbs and penetrates at the interface of the transparent layer with different refractive index, the light interference phenomenon will occur between the parallel reflected light, so the pearly luster and color will occur. When you are at the reflection angle of light, you can see the strong reflection color of Z; When you deviate from the reflection angle, you can only see pearl white and other colors. This phenomenon of seeing different interference colors with different investigation angles is called "angle flicker effect".
④ Color transfer effect
The continuous coating film made of interference color mica titanium pearlescent pigment can display two colors together. This color change is called color transfer effect. For example, for pearlescent coating made of mica titanium pearlescent pigment with interference color, the color of the coating film will change with the curvature of the coating film surface. The color transfer effect changes from blue to orange, from yellow to purple, that is, from the reflection color of pearlescent pigment to its complementary color. Because of the unique "color transfer effect" of mica titanium pearlescence, various wonderful decorative effects can be designed according to needs.
⑤ Additional color effect
Mica-titanium pearlescent pigments can be mixed with bright inorganic or organic pigments, and the pearlescent pigments can be directly colored with these pigments, resulting in more attractive colors. If copper phthalocyanine blue or copper phthalocyanine green is used to color pearlescent pigment, its color will not be weakened, but will be enhanced. This is the unique "additional color effect" of pearlescent pigment, also known as "color enhancement effect".
⑥ Stereoscopic space effect
Pearlescent pigment is always a transparent or translucent sheet. When the light shines on its surface, it always reflects most of the incident light, and projects the remaining light onto the next layer of pearlescent pigment chip, repeating the reflection and refraction of light. This is repeated several times until the base layer is completely reflected and absorbed. This optical property makes pearlescent pigment have a profound three-dimensional texture in transparent film. When the vision is perpendicular to a certain point of the coating film, it will be found that the pigment chips are embedded at different thickness of the coating film. Even though the film is thin, it feels thick.