Лако-красочные материалы — производство

The Kubelka-Munk theory [1.25, 1.27, 1.28] is based on the fact that the optical prop­erties of a film which absorbs and scatters light may be described by two constants: the absorption coefficient K and the scattering coefficient S. In a simplification, the flux of the diffuse incident light is represented by a single beam L+, and the flux of the light scattered in the opposite direction by a beam L-. Each beam is attenuated by absorption and scattering losses, but is reinforced by the scattering losses of the respectively opposite beam. The absorption and scattering losses are determined quantitatively by the two coefficients K and S. A simple system of two linked dif­ferential equations can be written. These can be integrated for the valid boundary conditions at the incident light side, and at the opposite side. Solutions for the trans­mittance t and the reflectance p are obtained from these integrals as a function of the absorption coefficient K, the scattering coefficient S, the film thickness h, and in special cases of the reflectance po of a given substrate.

The most important and widely used quantity derived from the Kubelka-Munk theory is the reflectance of an opaque (infinitely thick) film that is described by a very simple equation:

K/S = (1 — pco) 7 (2px)

From this expression (Kubelka-Munk function) it follows that, within the range of validity of the theory, p depends only on the ratio of the absorption coefficient to the scattering coefficient, and not on their individual values. The equation has been most useful where reflectance measurements are used to obtain information about absorption and scattering (e. g., in textile dyeing, thin layer chromatography, and IR spectroscopy).

This theory is especially useful for computer color matching of pigmented systems [1.25,1.29-1.31]: absorption and scattering coefficients are combined additively using the specific coefficients of the components multiplied by their concentrations.

1.3.1.3