Coatings are materials in liquid form, and their rheological and flow properties directly affect their behavior during preparation, processing and application. The rheological properties of a coating, that is, its flow law under the action of external forces, are usually determined by the interaction between particles.

In the rheology of coatings, there are many basic flow types. Plastic fluid is a kind of flow characteristic, under the action of external force, only when the shear stress exceeds a certain limit can destroy the internal structure and produce flow. The minimum shear stress required at the beginning of the flow is called the yield point, the viscosity after the flow is called the plastic viscosity, and the viscosity shown before the flow is the structural viscosity of the suspension system.

Paint rheology – Understand the basic properties of paint flow

With the increase of shear force, the internal structure of pseudoplastic fluid is constantly destroyed, resulting in a gradual decrease in viscosity. The plastic thixotropic fluid has a yield point, and after the flow begins, the viscosity decreases with the destruction of the internal structure, which is called the apparent viscosity. Different from pseudoplastic fluids, thixotropic fluids require a certain amount of time to reach a new equilibrium when the internal structure of the fluid is destroyed and rebuilt under shear stress. When the shear stress is withdrawn, the reconstruction of the internal structure is also a time function, so that the thixotropic fluid produces a change curve during the shear process, and the area of the closed loop can represent the size of its thixotropy.

The viscosity of dilatant fluid increases with the increase of shear stress, which can be explained by geometric effects and particle condensation. When at rest, the suspended particles are interleaved with each other, and the external force destroys this state, so that the edges and corners of the particles touch, the gap increases, and the volume expands, thereby increasing the friction and resulting in an increase in viscosity.

Rheological properties of coatings are affected by many factors, such as solid volume, temperature, pigment type, adhesive type and dosage, particle condensation degree, etc. Coatings with high solid content usually have a higher viscosity and yield point. Different types of pigments and solvents will also affect the flow characteristics of the coating, for example, casein type coatings show different rheological types under different solid content, and the size and content of particles in China clay coatings will also affect its rheological properties, ranging from swelling to thixotropy.

Paint rheology – Understand the basic properties of paint flow

For the study of coatings, it is very important to understand their rheological properties. By understanding the internal structure of the coating and the interactions between the particles, it is possible to better regulate its flow behavior, optimize the preparation process, and ensure that it exhibits better performance and stability during application. The research and exploration of rheology of coatings in the coating industry will provide an important reference for the development of coating technology and bring more innovation and application potential.