Rheology Agents Used in Paints and Their Effects

The rheological behavior of paint—its deformation, shape change and flow—is defined as rheology. Although often confused conceptually with viscosity, rheology is a critically important parameter for paint. This is because the rheological properties of paint determine not only its behavior in the container, but also its applicability, spreadability, and production and storage characteristics. The profiles used to describe flow behavior in liquids are Newtonian, pseudoplastic and thixotropic profiles. Fluids that undergo deformation (flow) in direct proportion to applied force are classified as Newtonian. In pseudoplastic and thixotropic liquids, which exhibit behavior corresponding to applied force and resulting shear stress, viscosity decreases. In pseudoplastic flow, viscosity decreases with applied force and remains unchanged. However, in thixotropic behavior, viscosity decreases with applied force and returns to its original state when the force is removed. Application properties of paints are determined according to their flow behavior. Rheology agents are auxiliary additives that provide the required consistency in paints and coatings and facilitate application. They are also called thickeners or viscosity adjusters. These additives give wet paint low viscosity or thixotropic properties through shear force.

Rheology agents are used in water-based systems to improve many properties of the product and to tailor it according to its intended use. The principal ones impart many properties such as good spreadability, no splashing during application, good loading and smooth application with application equipment, scrub resistance, and stabilization in pigmented systems.

Rheology agents for water-based systems are examined in two groups: associative and non-associative. Non-associative rheology agents include acrylic (ASE – Alkali Swellable Emulsion) and hydroxyethyl cellulose (HEC) thickeners. These types of agents interact only with water within the system and begin to thicken upon contact with water. The associative ones are polyurethane HEUR (Hydrophobically modified ethylene oxide urethane), HASE (Hydrophobically modified Alkali Soluble Emulsion) and polyether-based HMPE (Hydrophobically modified etoxylated polyether). These hydrophobically modified rheology agents are named as such because they interact with all hydrophobic surfaces within the formulation. They interact primarily with binders, as well as with wetting agents, pigments and fillers. PU rheology agents work over a wide pH range. This enables them to provide excellent application ease (roller loading and wall application), spreadability, flow resistance and similar properties. HASE, on the other hand, is associative and consists of modified acrylic thickener (ASE) chains. ASE chain molecules are as follows: For HASE thickener to function, the pH value of the system must be in the range of 8.5-9.0. In light of all this information, the correct rheology agent must be selected to impart the desired properties to the correct system. BASF, whose products we distribute, offers rheology agents for water-based systems called "RHEOVIS® (PU-PE-AS-HS)"; a broad environmentally friendly product portfolio that is nonionic associative (HEUR/HMPE), anionic associative (HASE) and non-associative (ASE), synthetic, low-VOC and heavy metal-free. At the same time, BASF's newly designed rheology agents for solvent-based systems, the "polyamide wax" types in liquid form EFKA® RM 1463, EFKA® RM 1469 and EFKA® RM 1506, also demonstrate excellent performance in automotive, furniture and industrial coatings. As Boysan San. ve Tic. A.Ş., we are pleased to offer these products, manufactured by BASF whose representative we are in Turkey and the Turkic republics, at your service. Tuğba Sadıç / Technical Director / Boysan A.Ş.