Лако-красочные материалы — производство

Lightness. The white pigment powder is compressed in a suitable powder press to give an even, matt surface. The CIE tristimulus value Yis measured with color measuring

equipment. For standards, see Table 1.1 (“Lightness”). Apparatus: spectrophotome­ter, powder press, white standard.

Full Shade. Full-shade systems are media that contain only a single pigment. The color of the full-shade system in an optically infinitely thick (opaque) coating is re­ferred to as full shade. The mass tone denotes the color obtained when the pigmented medium is applied as a layer that does not hide the substrate completely (e. g., on a white substrate). Evaluation can be carried out visually or by color measurement. For standards, see Table 1.1 (“Color in full-shade systems”). Apparatus: spectropho­tometer.

Color Difference. Figure 1.11 shows the CIELAB color positions of a reference pigment and a test sample: the color difference ДЕ*ab, and the derived differences (Section 1.3.1), i. e., lightness difference ДЕ*, chroma difference ДC*„ь, and hue difference ДН*ab. The color difference of colored pigments in reduction can be similarly de­termined, including the “color difference after color reduction” which arises when tinting strength matching is carried out (see Section 1.3.3). A number of color dif­ference formulas have been published recently. They typically introduce weighting factors giving the lightness, chroma and hue difference values depending on the location in color space:

— CIE 94, chroma and hue difference depend on the chroma values [1.22].

— CMC (British Standard BS 6923) additionally take into account the dependence on the hue angle.

— CIEDE 2000, (CIE-report 142), extending the color difference formulas by in­troducing a fourth factor [1.48, 1.49].

— DIN99, trying a different approach: In contrast to the formulas stated above this formula tries to keep the calculation of the color difference as simple as in the CIELAB system while changing the color space to give a better conformance to the visual impression.

The future will tell the acceptance of the new formulas. All formulas can be transformed to give equivalent values in a Euclidean color space [1.50].

Undertone of Near-White Samples and Gray Undertones. The undertone of an almost uncolored sample is the small amount of color by which the color of a sample differs from ideal white or achromatic material. It is described by hue and chroma. The distance and direction of the CIELAB color position of the test sample (aT*, bT*) from the achromatic position (0, 0) are used to characterize the hue. The relative undertone is expressed by the distance and direction between the CIELAB color position of the test sample (aT*, bT*) and that of the reference pigment (aR*, bR*). In both cases, the distance is expressed by a figure and the direction by a color name. For standards, see Table 1.1 (“Hue relative to near white specimens”). Apparatus: spectrophotometer for determining the CIE tristimulus values X, Y and Z with standard illuminants D 65 or C. If a computer is available, the color name can be printed out instead of the number of the octant (for example, see Figure 1.12).

1.3.3