9 сентября, 2015 
Pokraskin 1.5.1
Fundamental Aspects [1.77, 1.78]
A pigment-binder dispersion is a suspension before it is dried; after drying it is a solid sol. In pigment-binder systems, the concepts and laws of colloid chemistry therefore apply. The dispersing of pigments and extenders in binders is an extremely complex process consisting of a series of steps that can be interlinked [1.77]. Dispersing involves the following steps:
1. Wetting. Removal of the air from the surface of the pigment particles and formation of a solvate layer [1.79, 1.80].
2. Disintegration. Breaking up of pigment agglomerates with external energy (e. g., by dispersing equipment).
3. Stabilization. Maintenance of the disperse state by creating repulsive forces between the particles (e. g., by coating them with solvate layers). These forces must be greater than the van der Waals attraction forces [1.81] that cause flocculation [1.82, 1.83].
The degree of dispersing usually has a large influence on the properties of the coating system [1.84, 1.85]. Some of these properties depend strongly on the degree of dispersing, and are therefore used to measure dispersibility. For standards, see Table 1.1 (“Ease of dispersion”). Examples are viscosity (pigment-binder dispersions always show non-Newtonian behavior properties before drying) and color properties, especially hue, tinting strength, gloss, and gloss haze [1.86] (see Sections 1.3 and 1.4).
In many systems, tinting strength depends so highly on the degree of dispersing that the rate of tinting strength development can be taken as a direct measure of dispersibility [1.87-1.90] (see Section 1.5.2.2). The numerical values of the half-life times (characterizing the dispersibility) and of the increases in strength (characterizing the strength potential) depend on the binder and the dispersing equipment used.
In systems where different pigments are combined (e. g., white and colored pigments), segregation effects can occur which change the optical appearance (flooding
[1.91] ). Flooding can be counteracted by preflocculation of the pigments with suitable gelling agents, and in some cases by addition of extenders. In solvent-containing systems with several pigments, but also in full-shade systems, color changes (rub-out effect) can take place due to flocculation, especially if the systems are subjected to mechanical stress during application and drying. The flocculation tendency can be determined by means of the “rub-out test”.
1.5.2
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