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Coatings Ingredients

Quantitative Determination of Particle Dispersion in a Paint Film

SpecialChem / Nov 16, 2005

Degree of particle dispersion in a liquid paint or dry paint film affects practically every important property of these systems, including viscosity, touch-up, rub-up, scrub resistance, porosity, gloss, appearance of defects, and, for opacifying particles like TiO2, hiding power and tinting strength. Numerous methods have been devised to quantify degree of dispersion, but most are comparative rather than absolute, especially those that pertain to dispersion in the dry film (e.g., comparing hiding power to a standard). We detail a technique, based on electron microscopy and image analysis, of quantifying degree of TiO2 dispersion in a paint film. Results clearly indicate flocculation in some paints and, more importantly, put an upper limit on the potential for improvement of pigment dispersion. Pigmentary titanium dioxide is found in virtually all modern coatings, except those that are clear or extremely dark, because of its high opacity. Efficient use of TiO2 requires the particles be well dispersed in the final paint film, since close particle-particle interactions decrease the scattering efficiency of TiO2 and, thereby, its opacity.

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