In the paints and coatings industry, flow properties of the final formulation hold a prime importance. The manufacturing & storage of coatings, the process of application and film formation require a high degree of control on flow to achieve success and desired finish. The study of flow or deformation of materials when subjected to stress is called “Rheology”.
Viscosity and rheology are often confused, and they are significantly different concepts. While rheology is the study of flow, viscosity, a part of rheology, can be obtained from rheological measurements. Viscosity is merely a measurement of the fluid’s resistance to flow.
Rheology measurements, on the other hand, are useful to stimulate flow behaviours of paints and coatings under different processing and application conditions. For example, a coating must be stable during storage, easy to apply and result in a smooth and defect-free surface finish. These aspects are connected closely with rheology resulting in desired product performance.
Why does rheology matter for paints & coatings?
It is important because in paints and coatings, rheology examines the behaviour of flow and deformation properties during:
· Manufacturing (pigment dispersion, mill base preparation)
· Storage (pigment/particle settling, in-can properties)
· Application (brush, spray, roller), and
· Film formation (leveling, adhesion, texture).
It influences key characteristics such as vertical flow, levelling, gloss, adhesion, film thickness, covering power, spattering tendency, brush and roll resistance, sedimentation tendency and pigment stabilisation of a formulation. During the coating production, rheology is useful to obtain optimal flow behaviour.
There are several thickening technologies that influence the rheology profile of paints and coatings. From a broader perspective, rheology modifiers can be divided into inorganic and organic:
Further, rheological additive technologies can also be divided into thickeners suitable for waterborne and solvent-based systems.
The commercial viability of paints and coatings formulation largely depends on having the correct rheology at every stage. When formulating a high-performance paint or coating system, it is therefore essential to understand the background of rheology and role of functional additives to achieve complete process efficiency.
Chemgrit Coatings supplies a variety of paint additives including rheology modifiers from leading suppliers around the world. For more information contact Chemgrit Coatings on www.chemgrit.co.za or athol@chemgritsa.co.za.
[Information sourced: www.specialchem.com]