Flexographic Aqueous Latex Barrier Coating Viscosity Measurement Fundamentals
Flexographic aqueous latex barrier coating viscosity requires multi-shear rotational measurement to ensure accurate anilox transfer and barrier film continuity.
Zahn Cup
Flow Instrument
A portable, U-shaped viscosity cup suspended by a long handle is a standard tool used to measure the flow characteristics of paints, varnishes, and inks in industrial settings. Press operators utilize the zahn cup to make quick, on-site measurements of fluid consistency directly from the ink reservoir of a printing press. It is designed to provide rapid results without requiring laboratory conditions, making it ideal for high-speed packaging plants.
Measurement Method
The test begins by dipping the cup into the liquid until it is completely filled and then lifting it out, starting a stopwatch the moment the top of the cup breaks the surface. The operator watches the stream of liquid draining through the calibrated orifice at the bottom and stops the timer when the continuous flow first breaks. This total time in seconds represents the viscosity of the liquid, which can be converted to kinematic viscosity using standard tables.
There are five different orifice sizes, labeled one through five, to measure liquids of varying thickness from thin inks to heavy coatings.
Pressroom Control
Maintaining the correct ink thickness prevents printing issues such as ink splattering or poor color density on the paperboard. If the drainage time is too long, the ink is too thick and may not transfer properly, requiring the addition of a solvent to dilute the mixture. Conversely, thin ink will drain too quickly and produce a weak, washed-out print.
This simple dip-and-drain test allows operators to maintain consistent ink quality throughout a long production run.