How Surface Tension and Engraving Geometry Shape Liquid Transfer

The performance of an anilox roll is not determined by the powders & coating process alone. While surface tension is often discussed as a property of the liquid itself, real-world coating performance is strongly influenced by the ceramic anilox surface and, more importantly, the engraving geometry.

Surface tension describes a liquid’s resistance to spreading. On a ceramic anilox roll, this resistance directly affects how effectively ink or coating wets the surface, fills the engraving, releases from the roll, and ultimately forms a uniform film on the substrate.

Ceramic as a material naturally exhibits high surface energy, which promotes wetting. However, the microscopic shape and structure of the engraving determine whether this wetting occurs smoothly or is disrupted by turbulence and resistance.

This is where the fundamental difference between 60° Hex and other cell-based engravings and the Apex GTT engraving becomes critical.

60° Hex and Cell-Based Engravings: Interrupted Flow and Air Resistance

Traditional 60° hex and other cell-based anilox engravings are made up of many small, enclosed cells separated by ceramic walls. Each cell acts like a tiny container that must be filled with ink or coating and then emptied again during the transfer process.

Because these cells are fully surrounded by walls, the ink or coating comes into contact with a large amount of ceramic surface area as it fills the cell. As the liquid contacts more ceramic surface area, adhesive and capillary forces increase, strengthening the tendency of surface tension effects to retain ink within the engraving. This natural attraction causes the ink to cling to the cell walls, making it more difficult for the liquid to release cleanly and completely.

As ink enters the enclosed cells, the air inside must escape through the small opening at the top. This restricted air escape, combined with the strong surface tension holding the ink against the ceramic, can limit how efficiently the cells fill and empty—especially with higher-viscosity inks or coatings.

As the anilox rotates in the doctor blade chamber, the ink is repeatedly pushed into and pulled out of each individual cell. The sharp edges and walls between cells force the ink to change direction constantly. These interruptions in flow, together with the surface tension holding the ink to the ceramic walls, can disturb smooth ink movement and contribute to uneven or inconsistent ink release during transfer.

To overcome these limitations, printers are often forced to:

• • • Increase coating volume

    • Increase pressure

    • Accept higher shear conditions

These adjustments promote micro-foaming and aeration, which can manifest as:

• • • Mottling

    • Pinholing

    • Uneven gloss

    • Inconsistent tactile or visual appearance

In practical terms, cell-based engravings behave like thousands of miniature reservoirs that resist smooth flow and encourage air entrapment.

Attempts to Mimic GTT Flow in Cell-Based Engravings:

A Short-Term Compromise

Recognizing the inherent flow limitations of traditional cell-based engravings, some alternative engravings attempt to improve liquid behavior by modifying the cell structure itself. These efforts aim to replicate the smoother transfer characteristics of GTT while retaining a fundamentally cell-based geometry.

The most common approaches include:

• • • Breaking or weakening selected cell walls to create partial flow paths

    • Applying ultra-light polishing to provide raised pins in the corners of the hexagon and promote better flow and easier release

While these methods can deliver short-term improvements, they introduce structural weaknesses that ultimately work against long-term performance.

Weakening cell walls compromises the integrity of the ceramic surface. Light polishing often leaves raised cell corners and uneven contact points, creating localized stress concentrations.

In the short term, these raised edges may appear to improve ink flow. However, this effect can be unstable and introduces two significant drawbacks.

Short-Lived Performance Gains

The lightly polished and structurally weaker surface area that is in direct contact with the doctor blade can wear rapidly under normal press conditions. As raised corners degrade, coating performance declines, often reverting to original flow limitations of a standard 60° hex engraving.

Increased Risk of Scorelines and Premature Damage

Raised corners create high-stress contact points against the doctor blade. This increases the likelihood of micro-scoring and deeper scorelines. Once scoring occurs, coating uniformity is permanently affected, often requiring costly repair or early roll replacement.

These outcomes result in:

• • • • • Reduced roll lifespan

        • Increased maintenance and rework

        • Inconsistent coating quality over time

        • Higher total cost of ownership

These modified cell-based approaches address symptoms rather than solving the underlying structural limitation.

GTT Engraving: Continuous Flow and Controlled Wetting

Apex’s GTT engraving replaces closed cells with directional channels and significantly fewer walls. This fundamentally changes how liquid interacts with the ceramic surface.

Instead of being forced into isolated pockets, ink or coating moves through open, continuous pathways. Air has a direct and uninterrupted escape route, dramatically reducing micro-aeration.

This geometry promotes a calmer and more controlled flow profile, requiring less pressure for full wetting and release. The coating spreads more evenly and forms a stable, uniform film.

While the intrinsic surface tension of the liquid and the ceramic surface does not change, the engraving
geometry reduces the effects of surface tension during operation. By minimizing flow resistance, sharp
directional changes, and trapped air, the liquid can wet and release more easily. As a result, the coating behaves as if it has improved wetting characteristics, even though the material surface tension itself remains unchanged.

Where cell-based engravings introduce resistance at every boundary, GTT provides a continuous flow landscape that supports stable transfer throughout the life of the roll.

Engraving Geometry and Its Impact on Aeration

Aeration is one of the most critical yet underestimated factors in coating performance. Entrapped air reduces visual quality and often forces operators to apply excess coating volume to mask defects.

The influence of engraving style on aeration is clear:

These differences translate directly into measurable pressroom results. Contact us for more information.

Efficiency, Quality, and Cost Implications

Because 60° hex and other cell-based engravings introduce turbulence and air entrapment, printers often apply excess ink or coating to achieve acceptable visual results. This increases material usage, energy consumption, and process variability.

GTT achieves higher transfer efficiency through controlled flow and reduced air interference. The coating lays down more uniformly, delivers color and gloss more efficiently, and dries more predictably.

Typical results include:

• • • 10–20% reduction in ink or coating consumption

    • Improved gloss consistency or soft-touch performance

    • Reduced drying energy requirements

    • Lower defect rates and rework

    • More stable long-term press performance

Conclusion

Surface tension on a ceramic anilox roll is not governed solely by the chemistry of the ink and ceramic surface. Its practical effect during printing is strongly influenced by the geometric and mechanical interaction between the liquid, the ceramic surface, and the engraving design.

60° hex and other cell-based engravings introduce disruptive flow patterns that increase turbulence and aeration, leading to inconsistent coating performance. Attempts to modify these systems through broken walls and light polishing offer only short-term improvements while accelerating wear and increasing the risk of scorelines.

GTT engraving delivers superior liquid transfer through fundamental design optimization, not structural compromise. The result is smoother flow, reduced air entrapment, improved coating stability, and consistent performance throughout the roll’s lifecycle.

By combining enhanced transfer efficiency with controlled flow, GTT provides not only a quality advantage but a measurable cost-saving solution, delivering improved visual results with less ink or coating and greater long-term process stability. If you would like to see how GTT could improve your process, contact us to discuss your application.