Today's Anilox Roller Can Provide a Bright Future for PackagingApril 2011 By Paul Teachout, Harper Corp.
All these opportunities have allowed today’s anilox roller technology to compete with and share in the market with other processes that are much more costly. Even the advancements of high definition flexographic digital plates are incorporating this tool to create graphics that were once thought of as unobtainable.
Having the ability to take advantage of all these processes on a flexographic printing press has allowed converters to offer many cost-effective solutions to their customers. We no longer require expensive rotary screen and hot foil units to compete in today’s competitive markets. It is very common now to see packaging that is printed 300 LPI with opaque white, tactile varnish, and cold foil accents—all on one package, all flexo, and all printed in-line with no added investment in ancillary equipment. This is all being done, in part, with special care in anilox roller selection and use.
High definition flexography
The latest in digital plate technologies is taking great advantage of today’s anilox roller. As plate screens continue to climb, it is up to the anilox supplier to deliver an engraved roller that supports the plate structure and graphic design. It is critical for the plate and anilox roller to work together to maintain the crisp highlights and mid-tones that are required from today’s CPGs and converters. Current screen rulings are approaching 300 LPI and beyond.
This requires that the dot structure be uniformly supported by anilox cell structure to reduce over inking, bridging, and other print-related defects. The tried-and-true 60 degree hexagonal engraving is still proving best for this task. Nothing to date beats the honeycomb pattern for strength, rigidity, wear characteristics, and all-around dot support.
Having as many cells as possible under the highlight dots is what will lead to clean and crisp reproduction. To properly support the graphics, a rule of thumb for the required anilox cells per inch (CPI) is five to six times the plate screen. This means that a 300 LPI image will require a 1,500 to 1,800 CPI engraving to properly support the graphic reproduction of a one percent dot.
If this guideline is not followed there is a distinct possibility of some dots being supported and others not. This will lead to inconsistent ink transfer and variations in the highlight and mid-tone reproduction. You will have a very challenging time trying to meet these objectives with engravings that do not offer the uniform construction of one of Mother Nature’s best inventions, the 60 degree hexagonal honeycomb.
High opacity in flexo whites
Mid-volume anilox roller engravings are widely used in both the flexible packaging and UV printing segments to maximize opacity in flexo whites. There are many other variables that contribute to their success like substrate treatment, drying capacity, and plate and tape combinations. But these engravings offer a very cost-effective solution when compared to other forms of printing formats.
In conducting many banded roller trials with numerous geometries and ink suppliers, it has been determined that the 30 degree channeled engraving pattern is most cost-effective with high opacity whites. The opacity readings that were obtained rival any other geometry available. Unlike the standard 60 degree honeycomb geometry, the 30 degree geometry is positioned so the flat is at the top of the cell. Similar to the orientation of a stop sign.
This circumvential alignment of the cells allows us to (somewhat) drag the laser over the top and bottom cell walls to create an hour-glass design of the cell instead of a closed hexagon. This channeling effect allows high-viscosity inks and coatings to flow more freely through the metering blade to reduce the hydraulic force behind the blade and not trap excessive air into the system. This increase in transfer efficiency allows for the ink to wet-out more uniformly thus reducing the effect of mottling or pin-holing. This geometry is very effective for heavy inks and coatings that require mid to higher volumes.
Cold foil made simple
One of the most appealing decorative technologies in flexo is the use of foil on a variety of packaging substrates. In the past, a downside of the common hot foil process was the need for expensive tooling and equipment to produce the application, in addition to some limits on what substrates could be run.
The cold foil process has offered a very cost-effective alternative to add decorative design characteristics to the package. It is as easy to setup as a print station with a photopolymer plate and a roll of lamination.
Identifying the proper CPI and volume of the anilox roller is a key factor. Too much volume and it will be a challenge to hold small type and fine lines. Too little volume results in the possibility of flaking around the edges. The best results for this application are found when the proper volume anilox roller is used for the specific adhesive.
It is also most critical to have the rest of the process in control as well. Having a hard durometer nipping roller will insure an efficient transfer of the adhesive. To maintain the crisp edges, it is recommended to have a one inch stripping roller removing the foil film at a sharp 90 degree angle directly after the UV curing unit and before any other web wrap. Following these guidelines will lead to a very cost-effective decorative application that is very appealing to the eye and very satisfying to business margins.
Achieving tactile feel
A more recent flexo enhancement is the effect of tactile coatings. These coatings provide a two-dimensional feel to the package without the use of embossing or expensive tooling. This application has traditionally been done with the use of a rotary screen unit. Advancements in anilox and coating technologies have now opened the door for this application to be run flexo. This application can be used to enhance the package by having raised water drops or having the veins on a leaf have a texture. It will also allow us to feel the dimples on a golf ball, or the scales on a fish for a very unique packaging design.
The anilox roller selection in this process is very critical as there are many different perceptions of feel. Some packaging buyers will want a subtle feel, while others will want a more textured appearance. This will have a drastic effect on the coat weight of the application.
The objective is to apply the ideal amount of coating to meet the requirement. If the proper volume for the application is not accurately identified it could cause thousands of dollars in wasted coating annually. This application will require very high volume rollers that will transfer large amounts of coating. Calculations are critical to be cost effective. Much testing has been done to determine a low-, mid-, and high-volume range for tactile feel and perception. Working with the anilox supplier will help optimize this process.
The science of selection
As with any new flexo endeavor, we have the opportunity to test and predict the outcome. Taking a scientific approach to the way anilox roller engravings are selected for the above applications is critical to their success.
The best way to go about this is to perform banded-roll analysis to identify the optimum cells per inch and volume required to optimize the target application. The information gathered during these profiles will allow us to maximize efficiencies and standardize the process. Standardizing the process for high-definition process printing, spot colors, high opacity whites, and decorative technologies is what allows a printer to take full advantage of the flexo process. Producing award-winning packaging that meets both design and purpose requirements, as well as a strong appeal to the consumer is the ultimate goal.
Conducting the proper research and testing will allow effective use of today’s anilox roller technology that is at the heart of the flexographic process. It will take a once known craft and turn it into a manufacturing process that will be consistent, repeatable, and most important, profitable.
Author—Paul Teachout has been in the packaging industry for more than 25 years. Starting out in offset, he moved to flexo press manufacturing with Webtron/Aquaflex in 1986. In 2008, he became southeast technical graphics advisor for Harper Corporation of America.