Лако-красочные материалы — производство

The hiding criterion is an agreed color difference between two contrasting areas of a coated contrast substrate. The hiding power can be determined and expressed as Dv (m2 L-1) or Dm (m2 kg-1), which give the area (m2) of the contrasting substrate that can be coated with 1 L or 1 kg, respectively, of the pigmented medium when the hiding criterion is satisfied. Layers of various thicknesses or mass-to-area ratios of the test material are applied to the contrast background. The color difference AE * ab between the two contrasting areas is determined by color measurement on each of the layers. The color difference is plotted against the reciprocal of the film thickness (mm-1) or the reciprocal of the mass to area ratio (m2 kg-1). The hiding power Dv (m2 L-1) or Dm (m2 kg-1) at the hiding criterion (e. g., AE* ab = 1) is then obtained from the diagram (Figure 1.11). For standards, see Table 1.1 (“Hiding power”). Apparatus: spectrophotometer, film thickness measuring equipment.

Fig. 1.11 Determination of the hiding power of a yellow iron oxide pigment.

A modern well-equipped color measurement laboratory can use the “principle of spectral evaluation” described above [1.52] to simulate this procedure with a computer. The thickness of the hiding film can then be calculated in advance from the reflectance curves of a single film on a black/white substrate at a known film thickness.

Hiding Power of Achromatic Coatings. Equally thick coatings of the pigmented coating material are applied to a black and white background, and their reflectance measured with a photometer after drying. The hiding power is then calculated from the reflection on black and white substrates and the film thickness. The hiding criterion is AL* = 1, in analogy with that for colored pigments [1.19]. The use of hiding power as a basis for assessing the economy and effectiveness of pigments is described in [1.59]. Apparatus: spectrophotometer, black and white glass plates.

1.3.4.2