Surface Treated CaCO3 (Stearic Acid Coated)

Stearic acid-coated calcium carbonate is a functionally enhanced filler where the particle surface has been uniformly treated with stearic acid (typically 1–2 wt%) to convert the hydrophilic inorganic surface to an organophilic surface. This modification fundamentally changes the filler-resin interaction, resulting in markedly improved dispersibility, reduced moisture uptake, and better compatibility with hydrophobic polymer matrices.

The coating reduces the tendency of CaCO3 particles to absorb moisture from the atmosphere, a critical benefit in regions with high humidity or in applications where residual moisture in the filler could cause foam, voids, or adhesion failure in the cured laminate. The organophilic surface also dramatically improves wetting by non-polar resin systems, reducing mix time and energy requirements.

In UPR and epoxy systems, stearic acid-coated CaCO3 typically produces 20–35% lower compound viscosity compared to uncoated grades at equal loading, allowing either higher filler loading for cost reduction or easier processing at equal loading. The coating acts as an internal lubricant, improving flow in injection and RTM processes. Mechanical properties are generally comparable to or slightly inferior to silane-treated grades, but at significantly lower cost.