Non-Sagging Polyurethane Compositions

Non-sagging behavior is an essential property for polyurethane paint and adhesive formulations that are applied onto vertical surfaces. Traditionally, the non-sag property is achieved through additives that control rheological properties of a paint or adhesive. For waterborne polymers such as latex paints, rheology modifiers include hydroxyethyl-cellulose, hydrophobically modified alkali-soluble emulsions, and hydrophobically modified ethylene oxide urethanes (associative thickeners). Solvent-based polymers, such as alkyd paints, typically use castor oil derivatives, attapulgite or bentonite clays, or fumed silica. Bayer Corporation has developed a non-sagging polyurethane technology that overcomes disadvantages associated with these filled systems. This technology involves the reaction of a liquid polyisocyanate with polyhydroxy compounds and an aliphatic or aromatic amine. The amines may be added to the reaction in an amount sufficient to produce adequate resistance to flow/sag upon mixing of the reactants. Hence, when a bead of polyurethane is applied to a vertical surface, it does not run, drip or sag. Due to the almost immediate reaction of the amine component with the isocyanate, an initial buildup in molecular weight produces the desired non-sagging behavior. The system remains in this “B-stage” for a controllable amount of time before the hydroxy/isocyanate reaction takes place and the system cures to a solid polyurethane. This paper describes the basic principles of non-sagging polyurethane compositions as well as a wide variety of applications for this technology. Applications for non-sagging polyurethanes include: structural adhesives for SMC, expandable caulkings and sealants, furniture edging, carpet seam sealants, and flexible, sandable patching compounds.