Лако-красочные материалы — производство

Within certain limits, relative tinting strength can be interpreted as the ratio of the ab­sorption coefficients of equal masses of test and reference pigments. This procedure avoids visual matching of the test and reference pigments employed in a previously used method (tinting strength matching). For standards, see Table 1.1 (“Tinting strength, relative”). Materials and apparatus: white paste, spectrophotometer.

In the determination ofthe tinting strength, specification ofthe matching between the test and the reference pigments is extremely important [1.51]. Since the criterion used for matching greatly influences the value of the tinting strength, it is not per­missible to speak of tinting strength purely and simply. There are as many tinting strength values as there are matching criteria. In the German Standard, the following criteria are permitted:

1. The lowest of the three CIE tristimulus values X, Y and Z.

2. The CIE tristimulus value Y.

3. The depth of shade (see Section 1.4.2.1).

When using commercial colorimeter software it has to be ascertained which for­mula is used to calculate the tinting strength. As there is no universally accepted defi­nition and the formulas in use result in divergent results under certain circumstances only values with a known tinting strength criteria can be applied. When determin­ing the tinting strength of inorganic pigments, the tristimulus value Y (lightness) is usually used [1.51].

Another standard method uses depth of shade as the matching criterion, but it is employed almost exclusively for testing organic pigments. This method can be applied by means of the “principle of spectral evaluation” (see Section 1.3.4 [1.52], which uses the wavelength-dependent Kubelka-Munk coefficients S(A), K (Я) to cal­culate the match [1.53]. The tinting strength for all other matching criteria can be determined by applying the principle of spectral evaluation. (For tinting strength in cement, see Section 1.5.2.3; for change in tinting strength, see Section 1.5.2.2).

1.3.3.2