Pigment particle

The state of the art of paints and coatings, including pigments and extenders, has been reviewed (7). 

Detailed lists of pigments that are available on the market and their properties have been compiled (8). The tables contain 7,184 pigments, dyestuffs and fillers. Besides the name and manufacturer, specific properties are also given, as collected in Table 4.1. 

Name Manufacturer Color index American abbreviations are used there 

DBF value Bulk density suitable, therefore the surface area is given DIN 53193 (10) 

Lightfastness Post treatment Base pigment Type of preparation Based on the blue wool scale (11) As disclosed by the manufacturer 

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Other. A large variety of additives are used in paper-coatiag colors primarily to modify the physical properties of the colors (102). At high soHds concentrations in water, mineral pigment particles tend to associate and form viscous pastes. Dispersants (qv) are used to prevent this and to provide low viscosity slurries. Common dispersants include polyphosphates and sodium polyacrylate [9003-04-7]. Various water-soluble polymers are added to coatiag colors and act as water-retention agents and as rheology modifiers. 

Pigments Aftertreatments. The surfaces of pigment particles can have different properties and composition than the particle centers. This disparity can be caused by the absorption of ions during wet milling, eg, the —OH groups, on the surface. In some cases, surfaces are modified intentionaHy to improve the pigments appHcation properties, interaction with the organic matrix, and weather resistance. 

In some cases, a pigment s thermal and chemical resistance can be improved by the encapsulation of the pigment particles by an iasoluble, colorless layer of metal oxide or oxide—hydroxide, eg, siUca, Si02. The function of such a shell is to prevent direct contact and reaction between the pigment surface and the organic matrix ia which the pigment is dispersed (11). 

The energy required to initiate an explosion and the maximum explosive pressure developed by a number of polyester—epoxy powder coatings has been studied in some detail (89). The variables studied included composition, level and type of pigmentation, particle size, and concentration in air. The lowest MEG for unfilled and unpigmented powders was 33—35 g/m. ... 

Colorant Mixing. A colorant, whether a dye dissolved in a medium or pigment particles dispersed in it, produces color by absorbing and/or scattering part of the transmitted light. If only absorption is present, the Beer-Lambert law appHes ... 

Fig. 12. A, the schematic variation of scattering, and B, color strength for pigment particles of various sizes (5).

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