Thermoporosimetry for Characterizing the Porosity of Pigmented Coatings of Paper, 2002 Coating Conference Proceedings

E. Lehtinen, J. E. Laine and H. Paulapuro

This paper describes the results of applying thermoporosimetry for characterizing the porosity of paper pigment coatings. Thermoporosimetry is based on the decrease in the melting temperature of a probe liquid in small pores, with a certain melting temperature corresponding to a certain pore diameter. The amount of pores with a certain pore diameter can be calculated from the melting enthalpy at a particular temperature in a calorimeter measurement. Using cyclohexane (chex) as the probe liquid, the measurable pore diameter range is 5 - 590 nm. Chex swells latexes so porosities measured with chex from latex-containing coatings are biased. Chex does not swell starch. The pigments used in the experiments were an engineered CaCO3, a conventional CaCO3, and an engineered primary kaolin clay. Coatings were made using these pigments as such and blending carbonates with kaolin using starch as a binder. Pore volume development with increasing pore diameter is reported up to 590 nm. The porosities of these coating layers decreased in the order: engineered CaCO3 > engineered kaolin > conventional CaCO3. Mixing conventional CaCO3 with engineered kaolin produced a small increase in the porosity of kaolin alone, while mixing engineered CaCO3 with engineered kaolin increased the porosities of these pigments alone.