Hiding power values

The authors determined pigment particle size using Green s photographic method (9) which could not have been too precise, but it was claimed that good correlation had been obtained with the relative hiding power values of Hallet (11) when calculated for film thicknesses, providing a residual contrast of 2% over their black substrate (see Table III). 

In the same year (1926) Hallet (16) reappraised his hiding power values and discovered that they could be related to carefully determined tinting strength values by the equation... 

According to ASTM D 2805-70, the hiding power of a layer is characterized by the ratio of the Y values (as defined in the CIE color system) over a black and a white patch of substrate. If this ratio is larger than 0.98, the layer is referred to as hiding. This criterion occasionally fails if applied to brightly colored pigments. 

Refraction, R0, which is related to the hiding power of a pigment, is equal to the square of the differences in the n values of the pigment and the polymer, as shown by Fresnel s law where , and nt are the refractive indices of the pigment and the polymer. 

Prime pigments are used for their ability to hide or cover the surface. The term hiding power is used to describe the relative abihty of fixed amounts of different pigments to cover a surface and depends on the difference in refractive indices between the pigment and the binder thus primary pigments usually have high values in refractive index. 

Hiding power of pigment in paint can be measured by refiectometry without the use of standard. It is calculated from the determined values of reflectivity and the scattering coefficient. 

Accepted methods of the first type comprise the hide-power method [77], the refrac-tometric method, and various visible, ultraviolet, and infrared spectrometric methods. Accepted methods of the second type include comparative methods such as the Stiasny-Orth method [78,79] and its modifications, all these being gravimetric methods largely obsolete today due to the lack of reliability consequent to coprecipitation of some carbohydrates together with the phenolic material of the tannin extract and to the results being expressed in an absolute value which is never reportable to a percentage of useful material in the extract, the Lemme [80] sodium bisulfite backtitration method, the ultraviolet spectrophotometric molybdate ion method [77,81], and infrared spectrophotometric methods [82]. 

The properties of paints, such as water permeability, corrosion resistance, gloss, hiding power, or the tendency to blister, are dependent on the PVC. There is a critical value of this parameter, called the critical pigment value concentration, at which the practical properties of the paint undergo important changes. 

Prime pigments n. Pigments which possess colorant value and hiding power. The refractive index of these pigments is 2.0 or higher in contrast to extended pigments. 

Hiding Power Chart n (1) A paper chart, partially black and partially white. A paint film applied over such a chart gives a visual evaluation of the degree of hiding. If a measurement of the reflectance of the film over the black portion is divided by the measurement of the reflectance over the white portion, the contrast ratio (opacity) is obtained. (2) A chart prepared calculation of the Kubelka-Munk equation for a white substrate of specified reflectance for various reflectances at complete hiding (Roo) and for various reflectances over black, various contrast ratios, scattering-thickness values (SX). From such a chart, using measurements of reflectances over black and white, or measurements over black and... 

The particles with higher refractive index give higher luminance values for the same hiding power. This trend was also observed experimentally when we incorporated three different particles with the same... 

---