Shear Thinning Rheology

Fluid Dynamics

Viscosity in a coating or ink formulation decreases as the rate of applied mechanical force increases. Behavior of this type, known as shear thinning rheology, is essential for high speed application methods where the liquid must flow easily through small gaps or nozzles. Once the stress is removed, the material regains its original thickness.

Quick recovery prevents the coating from dripping or sagging before it has a chance to dry or cure on the substrate.

Application Mechanism

Metering rods and blade coaters rely on the thinning effect to spread a uniform layer of pigment across the paper surface. When the coating head moves at several hundred metres per minute, the high shear environment allows for a low resistance application. If the liquid did not exhibit shear thinning rheology, the energy required to pump and spread it would be prohibitively high.

The degree of thinning is controlled by adding rheology modifiers such as carboxymethyl cellulose or synthetic thickeners. Excessive thinning can lead to the coating penetrating too deeply into the base paper, which reduces surface gloss and increases drying time.