High Speed Ink Liquid Interface Dynamics in Ultra Light Coated Virgin Hardwood Graphic Papers
Ultra-light coated virgin hardwood papers demand sub-50nm coat pore radii to balance high-speed inkjet solvent absorption against hardwood fiber swelling.
Dynamic Impact Pressure
Droplet Collision
Kinetic energy transfer occurs when a high velocity ink droplet strikes a paper or board surface during digital printing. The term dynamic impact pressure defines the brief mechanical force exerted by the liquid drop at the moment of contact. This transient force drives the liquid into the surface pores before capillary forces begin to act.
Penetration Mechanism
The initial stage of drop contact occurs within microsecond time scales and involves a rapid conversion of kinetic energy into fluid flow. In dynamic impact pressure studies, the force depends on drop velocity, fluid density, and the deceleration rate upon striking the substrate. Higher speeds generate greater initial pressure, which can force the liquid into smaller pores that would normally resist passive capillary absorption.
This action dominates the wetting phase and dictates the starting diameter of the printed dot on the coated board.
Print Quality
Coating designers control the surface porosity and compressibility of the sheet to manage this rapid energy transfer. When dynamic impact pressure is too high relative to the substrate absorption rate, the droplet can splash or splatter, creating ragged edges around the dot. Controlled pressure dissipation ensures sharp print definition and prevents unwanted lateral spread of the ink on high speed presses.