Лако-красочные материалы — производство

1.3.1

Fundamental Aspects [1.18-1.22]

When a photon enters a pigmented film, one of three events may occur:

1. It may be absorbed by a pigment particle

2. It may be scattered by a pigment particle

3. It may simply pass through the film (the binder being assumed to be nonab­sorbent)

The important physical-optical properties of pigments are therefore their light — absorption and light-scattering properties. If absorption is very small compared with scattering, the pigment is a white pigment. If absorption is much higher than scat­tering over the entire visible region, the pigment is a black pigment. In a colored pigment, absorption (and usually scattering) is selective (i. e., dependent on wave­length).

Pigments and coatings may be unambiguously characterized by their spectral re­flectance curves p(X) or spectral reflectance factor curves R(X) (Figure 1.3). The re­flectance spectrum p(X) or R(X) and hence the color properties can be almost com­pletely derived from physical quantities [1.21] (Figure 1.4):

1. Colorimetry relates the perceived color quality to the color stimulus, which in turn is based on the reflectance spectrum p(X).

2. The Kubelka-Munk theory relates p(X) to scattering, absorption, and film thick­ness (scattering coefficient S, absorption coefficient K, film thickness h).

3. The theory of multiple scattering (scattering interaction) relates the scattering coefficient S to the pigment volume concentration a and to the scattering diameter Qs of the individual particle. The absorption coefficient K is directly proportional to the absorption diameter QA and the concentration a.

4. In Mie’s theory, the scattering diameter Qs and the absorption diameter Qa are related to the particle size D, the wavelength X, and the optical constants of the material (refractive index n and absorption index к).

1.3.1.1