Do you find spherical or flat calibration to be better? Why?
BATISTATOS: The flat (roughness plate) calibration was the older calibration method. The concept was to scan a high-precision roughness standard, which had rows of grooves measuring a certain depth. The biggest issue with this method is that the depth of the grooves on the roughness standard varies from spot to spot, by a small amount. These small variations, say only a few tenths of a micron, result in 3 percent to 4 percent in added variation, that of course we want to eliminate from the process.
Spherical calibration is the newer method. The concept is to measure a precision ballbearing with the microscope against a known value. This method provides two main advantages:
- It is very easy to identify when the sphere is centered under the microscope (there is a “bullseye” that can be centered in the crosshairs on the screen). This ensures the sphere is always measured in the same position (top dead center). There is no spot-to-spot variation in this method
- Instead of just confirming the depth (Z direction) measurement against a known value, we create a 3D curve fit of the sphere from the scan to incorporate X, Y and Z direction in the calibration
While the microscope can be calibrated accurately under both methods, the spherical calibration provides better consistency.
HARVEY: Volume measurement is not a simple process. Remember, there is no ISO standard for anilox volume because ISO requires complete process control and repeatability.
There are a few ways to measure volume—liquid ink process and surface area calculation or digital microscopes. Device tolerance, depending on system, can be as much as +/- 0.13 bcm, which means a tolerance of 0.26 bcm.
The calibration of a device requires two key elements:
- The best measurement of a known engraving that has been assessed in laboratory conditions to give a fixed target calibration number
- The validation of the stability of the environment consistency in conjunction with the target number
Calibrations need to be made daily and records kept, to identify the working device tolerance and not just consider a device SOP document as an individual aspect.
WOODARD: While we utilize both technologies, dependent upon what method our customer may be using, our preferred method is spherical, as it is necessary for verifying volume tolerance, while flat calibration is generally used to verify line count.
BEESON: Both are equally important, so we use both. Spherical calibration of a roller measured digitally is more commonplace. Digital volume measurement has moved on greatly. However, flat calibration, such as a drawdown, is a good point of cross reference. A measurement with both; generally, they are very close. A digital system might measure 20 cells in view, where a drawdown system will measure 1.2 million cells. As a manufacturer, we feel it’s important to have both.
It is estimated in flexible packaging that 50 percent of a printer’s ink spend is purely on white ink. What technologies do you have to hit opacity and reduce costs?
BATISTATOS: Ultra Z engraving. We have seen extending the ink, (less viscous) so that it flows through the channels better, can increase opacity. In addition, with advantages I stated earlier for combination printing, you can combine screen and solids into one station.
HARVEY: From my experience, white ink usage is around 35 percent of the total cost of ink spread across multiple designs. Talk related to opacity must address the ink film thickness and the compactness/sizes of the pinholes to understand the dynamics of liquid transfer and the anilox roller’s integral part in the delivery system.
An engraving that eliminates ink aeration will reduce pinholing. An engraving that has the optimum depth-to-opening ratio or an engraving that allows a calm ink transfer will deliver consistency. An engraving that is synchronized to the process parameters—ink, plate, surface pattern, etc.—will optimize the opacity results.
WOODARD: Achieving greater release without increasing volume is critical to obtaining opacity and controlling costs. Open-channel engravings have proven to be most effective, whether it’s a 30-degree hourglass channel cell, or a 70-degree or 75-degree extended or elongated hexagonal cell, as these will always offer much greater release and be less prone to plugging.
POULSON: Harper’s XCAT hybrid channel/cell pocket allows for a better wetout of ink. This has shown on water, solvent and UV inks to work well with a good laydown. Unlike some geometries, where the open channel will allow for extra ink transfer and better opacity, this geometry lays ink down better at standard volumes as well as higher bcm ranges. The XCAT channel, combined with the 60-degree cell pockets, gives better transfer and control as well as a smooth lay of ink.
The 30-degree channel has also helped lay whites down in a way to minimize pinholing. There are many other variables that come into play—ink type, polymer surface technology, polymer durometer—so it’s not just about the anilox with white inks. Adjusting to a variable geometry will help. The less ink used along with less pinholing equates to ink cost savings. I have seen 10 percent to 15 percent ink savings. That’s $100,000 savings for every $1,000,000 of white ink!
I always recommend a correlation roller. This is a banded roll that has all linescreens and volumes used on that roller by that anilox supplier. Once we certify that roller, they use it as a correlation and an everyday calibration roller as well. This should also correlate with their anilox supplier’s incoming rollers. If a different type of scope is used than the manufacturer of the anilox rollers, then you may see variation. Unless using the same scope as the manufacturer, there has to be a benchmark roller (calibration roll) to correlate the volume from interferometer to other theoretical devices.
MIDDLETON: Interflex Laser Engravers recommends the Interrupted channel, which is a semi-open-cell design. The cell works by providing a smooth laydown along with a reduction in pinholing. The Channel Wave works in a similar way, but is an open-cell design. We recommend discussing the situation with technical reps.
RASTETTER: Converters often talk about the fact that 50 percent of their ink spend is on white ink. There are significant opportunities to reduce white ink consumption by choosing the correct anilox specification and cell design. For example, Pamarco’s EZFlo 30-degree channel has the reduced wall height between cells that we spoke of already, yet it still controls the ink. This technology provides a smooth ink lay on the plate which then transfers to the substrate uniformly. Channeling technology also allows the cell to quickly replenish as it rotates through the chamber.
Another cell choice could be EFlo, Pamarco’s 75-degree engraving. This extended cell technology allows a higher line count, while maintaining the volume necessary. By improving the line count, it increases the smoothness of the lay onto the plate and, in turn, onto the substrate.
BEESON: Looking at this issue, Sandon has two distinct solutions
For UV, we offer the HOW series (High Opacity White)—a channeled cell geometry allowing ink to move from cell to cell, letting large particles of titanium oxide transfer to the plate effectively. This is an alternative for screen white application. With a HOW 3, we have seen customers hit 83 percent opacity in one bump.
For solvent- and water-based, Sandon offers the HVP engraving and FLUID FP.