Organoclay Rheology Modifier (Bentone Type)

Organoclay Rheology Modifier (Bentone type) is a quaternary ammonium-modified smectite clay used as a thixotropic agent and anti-settling additive in solvent-borne and non-polar resin systems including unsaturated polyester, alkyd, and epoxy resin formulations. The surface modification of the base hectorite or bentonite clay with quaternary ammonium compounds transforms the inherently hydrophilic clay into an organophilic material compatible with organic resin matrices.

Organoclay functions by forming a card-house gel structure through edge-to-face electrostatic attraction between clay platelets in the resin medium. This structure imparts strong thixotropy and anti-sagging behavior at rest, while the structure breaks down under shear to allow normal processing and application. The characteristic of organoclay thixotropy is its very pronounced pseudoplastic behavior — high viscosity at rest, low viscosity under high shear — making it effective in spray and brush applications for anti-sag in vertical work.

In polyester and alkyd coatings, organoclay provides thixotropic anti-sag and anti-settling at loadings of 0.5–2.0% by weight. It requires activation (polar activator such as 95% ethanol or propylene carbonate, typically 20–40% of clay weight) to fully develop the gel network in most resin systems. Without activation, the clay platelets may not fully exfoliate and the thixotropic efficiency is significantly reduced. Organoclay is particularly valuable in systems where fumed silica gives insufficient thixotropy at low shear, or where moisture-sensitivity of amine-based thixotropes is a concern.