Brown, Roger Francis Graham; (1997) A study of the factors affecting pigment distribution in latex paints. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

The distribution of pigment particles within a decorative gloss paint is of great importance in providing opacity and high gloss. Latex paints differ from solventborne paints in the wet state in a number of ways. One fundamental difference is that the volume occupied by the latex particles cannot be occupied by the pigment particles and the shape of this excluded volume varies as the size ratio of pigment and latex changes. Also, there is competition between latex and pigment surfaces to adsorb surface active species added to provide colloidal stability and rheological control in a latex paint. The geometric effect of varying the particle size ratio was modelled using binary mixtures of chemically similar latices stabilised with the same surfactant. It was found that dispersion of the pigment modelling latex particles was improved in the dry film as the size ratio of latex particles to model pigment particles decreased. Simultaneous computer simulation of binary dispersions using hard sphere potentials generated the same conclusions. There was good numerical agreement between the two sets of results once the effect of volume concentration of the model pigment particles had been mathematically corrected for. Study of systems containing real pigment particles showed that geometric effects predicted by modelling were still valid within the size range studied. Physico-chemical effects associated with varying surface area ratios were not observed. Some chemical effects were also evaluated. Different pigment grades were studied with differing surface treatments. The type and levels of additives were also varied. It was found that pigment distribution changed radically from grade to grade in otherwise similar formulations. The types and levels of additives required to promote good pigment dispersion was very pigment grade specific.

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