At what wear percentage from original engraving do you recommend re-engraving the anilox surface and why?
BATISTATOS: Sometimes 10 percent; sometimes 20 percent. It depends on the converter and their requirements.
HARVEY: Qualify and monitor use, speed, color requirements, meters produced, doctor blade pressure and the number of times the anilox roller runs dry or out of ink for each anilox—All these affect anilox lifespan. There is no magic wand a supplier can effectively stand behind without such data points.
As a supplier of ceramic coated anilox rollers, you have two choices:
- Make the ceramic as compact as possible with minimum porosity and then slow the engraving process down to weld and melt the small holes of porosity closed
- Simply add a sealant to the ceramic after plasma spraying to fill in the porosity holes
A combination of ceramic and sealant is by nature a weaker structure than a compact ceramic coating. How do I know this? I love science and facts, and what I can tell you is that all the suppliers on stage at FORUM 2022 use the same Applied Laser Engineering laser-engraving systems (see sidebar); some have older versions for sure, but the manufacturer of the laser equipment is the same.
We at Apex have tested multiple versions of sealant in the past which gave the results as follows:
- You can engrave deeper and more volume in an anilox that has sealant applied! This, by nature, means the surface and structure is weaker (basic science)
- You can engrave quicker, due to the fact that you don’t need to weld the tiny holes of porosity closed
So, without the details of the use/environment of the anilox, I can say with all confidence that the optimum anilox volume for lpi, with the optimum polishing that is engraved in a ceramic coating that is compact and without sealant, will have the longest life and the minimum cleaning/maintenance costs.
WOODARD: Aside from plugged cells, which can often be saved with effective cleaning procedures—preferably laser cleaning—we believe when the engraving has 10 percent of cell wall wear, dependent upon the line count and the application, it’s time to replace or resurface the roller.
POULSON: At 15 percent to 18 percent cell wear, depending on the application, substrate and ink type. By doing yearly audits, we gain the information needed to make these decisions.
MIDDLETON: We feel 15 percent loss on volume, particularly for high line counts (900 lpi). Lower line counts being used for line work or spot color may find this number more forgiving. It is crucial to understand why there is a loss of volume. A review of the audit along with our customers can help identify the issue.
RASTETTER: It’s a great question because it varies, but let’s keep in mind that wear is not what typically causes the anilox to be returned for resurfacing. The typical issue is damage. An operator dings or damages the surface when removing the roller or sleeve from the press, or the roller is improperly cared for and becomes plugged, or the client hasn’t utilized best practices for ink management—they didn’t use rare earth magnets and filters in conjunction with steel doctor blades—which created an atmosphere of metal fragments in the inking system that cause scoring.
These problems, in turn, provide inconsistent print results and are the real reasons the majority of anilox rollers get resurfaced. If you provide the proper care and handling, the maximum life is much longer. Most printers consider re-engraving at 7 percent to 15 percent volume reduction. This percent range is when hitting your Delta E targets becomes difficult.
BEESON: This is customer specific. Regular cleaning and checking of anilox is the only way to benchmark a specific customer’s requirements. Every customer has a different opinion on when they should change an anilox based upon end-user requirements, in-house standard operating procedures, and ink, blade, plate and tape combinations.
We work with our customers to offer audits and follow-up meetings to analyze the results, gauging at what point a specific drop in volume is creating print related issues on press. Once this work is complete, we are able to set a datum point, where wear is becoming an issue, and proactively remove worn anilox from a customer’s inventory before it becomes an issue on press.
Specialized enhancements like glitter, pearlescent and soft touch are popular in printing. What engravings are most suitable for particle coatings and why?
BATISTATOS: The best engraving for these types of application is the Ultra X (pins up) technology. There are no cells for the particles to get trapped in, and it offers optimal release that is free of pinholing and roughness (orange peel).
HARVEY: Again, you need to understand the particle size, shape and rheology of the coatings in order to be able to advise effectively. From the anilox roller perspective, we can all give you coarse anilox engravings—either cell-based/open structure or trihelical, up to a volume of 90 bcm (depending on supplier and sealant).
What does that mean for the performance? What percentage of the volume is offered to the plate or substate if direct coating? What capacity does the plate have to receive and transfer the coating? What drying capacity does the machine have to dry or cure the coating? What impact does the huge amount of potential coating have on the press speed?
The anilox is said to be the heart of the flexographic printing process. In answering these questions, hopefully we demonstrate that the anilox has a critical role to play in that process. The need to understand the full process, the customer’s goals and our co-suppliers’ expert capabilities is critical to be able to support and advise effectively.
WOODARD: We’ve invested in new laser technology which is referred to as Twin Track engraving technique (see sidebar). This provides control of the focused laser beam in two ways:
- By controlling the laser power
- By controlling the position of the focus beam within each anilox cell
Defocusing the laser in order to fill out a cell is no longer necessary. All parts of the cell can be reached by the focused laser beam and power can be controlled. Thus, the energy density ceiling is no longer an issue, as with single-track technology. Higher cell volumes can be obtained with a lower depth of engraving and flatter cell bottom—clearly better for transferring added enhancements.
POULSON: My go-to on these products is usually an open-cell technology. Why? It’s not just the geometry; it’s about the cell opening. This is where I apply lower linescreens to allow for a higher percent of particle transfer. Using a lower linescreen allows for a larger cell opening. This can support more particle transfer. For example, 360 linescreen/6.0 = 65-micron opening. Another option: use a 180 linescreen/6.0 = 133-micron opening—that’s twice the area, which means more particulants!
How about 2.0 bcm? A 550 linescreen and up at +/- 0.1 bcm; or 6.0 bcm? At Harper, we publish those tolerances. From 550 linescreen to 2,000 linescreen, we hold a +/- 0.1 bcm. From 500 linscreen down to 200 linescreen, we can hold a +/- 5 percent tolerance. And from 180 linescreen down to 120 linescreen, our tolerance is +/- 6 percent. These are listed on our volume chart for 60, 30 and XCAT volumes.
MIDDLETON: Diamond and Interrupted channel engravings work well for particle coatings. The engraving patterns provide a more consistent flow. This is because the high volume and large cell size maximizes the transfer of coating and provides a superior release in a controlled fashion.
RASTETTER: In these cases, the biggest thing we need to consider is particle size. There are a couple of different types of engravings that can be recommended, depending on the particle size. Typically, a channel or pins-up engraving becomes preferential, so you’re able to apply the proper level of coating and run clean. Examples of these engravings would be a trihelical or 30-degree channel.
BEESON: Large particle coatings are always going to be an issue with conventional engravings. The cell-to-depth opening ratio is vital here.
GMX is a patented technology to Sandon Global, designed for large particle applications such as haptic, glitter or pearlescent, applied at large coating volumes. Its unique geometry stops cell blocking, allowing easier cleaning. The volume is made up from the cell area with a shallow engraving. This shallow engraving allows large particles to easily be collected and transferred to the printing plate. A conventional cell will plug and will only print the suspension fluid. GMX technology was created to overcome this issue.