Urea-Modified Polyamide Thixotrope (BYK-R 605 Type)

Urea-Modified Polyamide Thixotrope (BYK-R 605 type) is a high-efficiency rheology modifier for unsaturated polyester resin (UPR), vinyl ester (VER), and epoxy resin systems, providing strong thixotropic behavior with low additive loading and excellent compatibility with most thermoset resin formulations. Unlike fumed silica which builds viscosity through hydrogen bonding networks that are sensitive to polar solvents, urea-modified polyamide thixotropes build viscosity through a combined hydrogen bonding and physical entanglement mechanism that is more temperature-stable and less affected by water or polar additives.

The urea-modified polyamide structure (UMAP) forms a semi-crystalline network in liquid resin through hydrogen bonding between urea groups, creating a three-dimensional thixotropic structure. This structure breaks down under shear (during mixing or application) and reforms rapidly at rest. The thixotropic gel structure provides anti-sagging in vertical applications (gelcoat spray, putty, flow coatings), prevents filler settling in stored compounds, and maintains paste consistency in SMC/BMC formulations without the excessive thickening effect at low shear that fumed silica can produce.

BYK-R 605 type is supplied as a viscous paste in styrene or in an active diluent, and must be activated by high-shear mixing into the base resin system for full thixotropic development. It is particularly valued in gelcoat formulations where very smooth, bead-free spray application is required without sag — UMAP thixotropes allow higher solid content gelcoat spraying without the orange peel artifacts that poorly activated fumed silica can produce.