Dynamic Surface Tension Measurement in Liquid Curtain Coating Systems
Dynamic surface tension at millisecond surface ages dictates liquid curtain stability and dynamic wetting limits in paperboard coating operations.
Capillary Dead Time
Flow Delay
Temporal intervals required for a fluid to travel through the internal plumbing of a rheometer before reaching the sensor define the latency of a measurement. In high-speed coating analysis, capillary dead time represents the gap between the start of pressure application and the appearance of the sample at the capillary exit. This offset must be subtracted from the total test time to isolate the actual shear behavior of the fluid.
Viscosity Correction
Accounting for the volume of the capillary tube and the delivery lines is necessary to calculate the true shear rate. If the fluid is highly compressible or contains entrapped air, the delay increases as the system pressurizes. Laboratory technicians use calibration fluids of known density to map this response across different pressure ranges.
This calibration ensures that the data reflects the properties of the coating rather than the mechanics of the machine. Accurate timing is needed to capture the transient flow properties of modern high-solids formulations.
Test Accuracy
Error margins in viscosity readings grow if the lag is ignored during rapid testing cycles. Small volumes of fluid remaining in the capillary from previous tests can also skew the results. A precise correction factor improves the repeatability of measurements between different batches of ink.