Extended Engravings
Coupled with the ability to alter the cell cavity shape, today’s laser technology enables the cell structure or geometry to be changed as well. For this, I’ll use the general term “extended engravings.” As evidenced in the images that make up Figure 3a & Figure 3b, these cells have the six sided hexagonal shape, but are elongated in the north/south and web direction. They also have a different cavity shape compared to the standard hexagonal and extended volume cells.
It’s better to more efficiently use the volume that we have than to engrave deeper. More is not always better.
It’s important to understand that any linescreen specified is what the user will receive. For example, should a 600 linescreen be specified, there will be 600 cells per linear inch along the horizontal axis of the engraving, but not on the axis of engraving (60 degrees) as it is with the traditional hexagonal engraving. The extension or elongation of the cells during engraving removes many of the angular cell walls around the circumference of the roll.
From a printing perspective, the cell geometry and cavity shape yields several benefits:
- Fewer cell walls equates to more ink carrying capacity in the engraved cells. These engravings can be used as a “higher volume” solution for the same difficult to print applications as the extended volume engravings
- A more important benefit is the cells have more “open area” at the surface. More ink at the surface equates to better transfer through a more efficient engraving
- Extended engravings are well suited to improve opacity and laydown with opaque white and metallic inks, because the larger open area of the cells can accept and transfer more pigment particles, an important need in effectively printing them
- Having fewer angular cell walls also reduces blade and roll surface wear, improving consistency over long or multiple runs; particularly with aggressive pigments like those found in whites and metallics
These engravings can be also used for printing line work and screen jobs in “normal” or not so difficult to print applications, even if more volume is not needed. Should the same volume be needed/specified for a particular color, the extended engraving would be produced with shallower cell depths to achieve the same volume as a standard 60 degree hex engraving. Shallower cells equate to more efficient delivery of ink and also make the engraving easier to clean and keep clean; allowing for better consistency of print.
The extended engravings are also a viable option to consider in overprint varnish and laminating adhesive applications, where a lot material needs to be laid down to achieve the desired effect or required bond strength. These are typically applied with low linescreen/high volume traditional 60 degree rolls which aren’t as efficient in transferring thicker, more viscous materials. In many cases, a higher linescreen, slightly lower volume, more efficient extended engraving can yield better results with respect to smoothness and consistency of laydown.
The cell cavity shape associated with the extended engravings has a flatter bottom, which makes for a higher vertical cell wall. Whether the application be an opaque white, metallic, pastel, standard PMS color, varnish or adhesive, the higher vertical wall means even less volume loss as a function of roll wear as compared to the standard 60 degree hex and extended volume engravings.
The traditional 60 degree hex engraving is the tried and true “standard” for flexo applications, and if specified properly is efficient in delivering inks, varnishes and adhesives. It is not, however, the “silver bullet” for all volume requirements and applications.
More ≠ Better
Reality has taught us there are some instances where more ink, varnish or adhesive—and hence, more anilox roll volume—is necessary to meet a requirement. In all other situations, delivering the least amount of material required to achieve the color target, image quality or end use characteristic is what is desired.
When the time comes to specify an anilox roll, think first in terms of what volume is needed, then consider a linescreen that matches up with that volume, and then which cell geometry and cavity profile is best suited to deliver the material. If you are “close” to what’s needed with the existing roll; don’t specify a new one at the same linescreen and more volume. To do so means the new engraving will be deeper, which we know from experience is less efficient and can create other unintended consequences. Consider instead specifying the roll at the same volume with either an extended volume or extended cell engraving. It’s better to more efficiently use the volume that we have than to engrave deeper. More is not always better.
About the Author: Tom is the technical manager for ARC International, based in Charlotte, NC. He has served in many manufacturing, technical and management capacities on both the anilox roll and printing plate side of the flexo industry over his 27-year career.