Лако-красочные материалы — производство

The definition of hiding power is based on a black and white contrasting support upon which the film of coating is applied. The thickness h of the applied film is determined at the point at which the contrasting surface just disappears, as judged by eye. The film thickness (mm), which fulfills this condition, is called the hiding thickness. Its reciprocal, the hiding power (mm-1 = m2 L-1) is, like tinting strength, an indicator of yield because it gives the area (m2) that can be covered with 1 L of applied paint. This traditional visual testing method has been improved by the use of a photometer and a colorimetric criterion to evaluate the hiding film thickness, e. g., AE*ab = 1 for equally thick films applied to black and white backgrounds. The method can, however, be further rationalized. In this method only a single coating has to be prepared. The total reflectance spectrum is measured and after measuring the film thickness, the spectral scattering and absorption coefficients S(A) and K(A) are calculated at selected wavelengths (e. g., at intervals of 20 nm) by the Kubelka — Munk method. Once these values are known, the expected reflectance over black and white at the chosen wavelengths of the spectrum can be calculated for a given film thickness. Using the CIE and CIELAB systems, the CIELAB position of a color, which would have this spectrum, is calculated. This provides an iteration method for determining the film thickness at which the hiding power criterion AE*ab = 1 is satisfied [1.52, 1.56, 1.57]. This principle of spectral evaluation [1.52] is the key to handling test methods based on the visual matching of two color samples (see also “Transparency” and “Tinting Strength”, Section 1.3.3).

The transparency of a pigmented system denotes its ability to scatter light as little as possible. The color change of a transparent pigmented system when applied to a black substrate has to be very small; the lower the color change, the higher is

the transparency [1.58]. Measurement of transparency is important for assessing transparent varnishes and printing inks.

1.3.4.1