Лако-красочные материалы — производство

The metallic effect is caused by the reflection of light at the plane surfaces of the metal­lic flakes, which is overlaid by the scattering of light at the edges (Figure 5.31). The metal flakes act like tiny mirrors, following the physical principle that the reflection angle is the same as the angle of illumination.

Whereas, from an ideal mirror, 100% of the light is reflected, leading to 100% gloss, the reflection at a metallic effect surface is overlaid by a certain amount of scattered light, resulting in a typical light distribution with a significant maximum in the gloss angle, but visible light around it (Figure 5.32).

This behavior also leads to another typical optical property of the metallic effect: the flop — or two-tone-effect. This effect describes the fact that, at metallic effect coatings,
100% reflection (mirror) -100% gloss

reflection angle = illumination angle no visible light outside the reflection angle

100% (diffuse) scattering — 0% gloss

uniform light distribution in all directions

. * Metallic effect: «somewhere in between”

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Flop-effect: different lightness under different

Tr viewing angles

Fig. 5.32 Physical mechanism of the metallic effect.

the physically experienced lightness depends very much on the viewing angle and varies from extremely light at or close to the gloss angle to rather dark at inclined angles.