By Paul Teachout, technical marketing & content specialist, Harper Corporation of America
The anilox roller has played a pivotal role in the flexographic process for nearly a century now. Although it started out as a very primitive and elementary ink transfer roller, it has evolved to be one of the most important and innovative variables in modern-day flexography. From high-definition graphics to decorative embellishments and coatings, anilox engravings now can be tailored to suit almost all packaging design requirements.
In the 1930s, the anilox roller was introduced to the flexo process in the United States, coming from the intaglio gravure process in Europe dating back to the 1800s. It was a simple, mechanically engraved or chemically etched, chrome-plated cylinder produced to transfer an aniline ink chemistry. Aniline inks, made from coal derivatives, were not the most environmentally friendly or cleanest chemistries to work with. The chrome-plated copper rollers were not the ideal solution either. Environmental and more equitable solutions soon followed through the mid- to late-1970s. This would be the era when the flexo process evolved as a major player in the label and packaging markets with the introduction of more innovative technologies. Ink chemistries now were available in solvent, water-based and energy-curable UV inks, rubber plates were replaced by photopolymer, and the old mechanically engraved chrome-plated anilox rollers evolved into laser-engraved ceramic. The flexographic process finally reached a point where it was a repeatable, predictable process run by the numbers and now competes with any other print media available.
Evolution of the anilox roller
In the early 1980s, anilox roller pioneer Ron Harper took the leap to abandon chrome plating as he knew the environmental impact of the process. He developed the first chromium oxide plasma spray process for anilox rollers. Applying ceramic coating to mechanically engraved surfaces proved to be a wise and successful endeavor as it provided a more efficient, safe and environmentally friendly manufacturing process. It also provided packaging printers with a roller surface that had a life expectancy 20-times greater than chrome. The next evolution was the introduction of gas-fired lasers to replace the mechanical engraving, and thus, the 60-degree hexagonal geometry was introduced and remains the most requested anilox engraving geometry to date. Today, anilox manufacturers are utilizing high-energy digital fiber optic lasers (see Figure 1) capable of multi-beam, multi-hit engravings, providing the most innovative geometric solutions.
The role of the anilox roller has evolved much more than an ink-metering roller. It now is a precision instrument used to deliver a measured amount of ink or coating to a flexographic printing plate. Utilizing modern-day laser technology, a much wider range of cell count and volume can be delivered over a variety of geometries tailored to meet any printer’s needs.
Changing geometries and compounds
Through the years, there have been many engraving geometries developed to meet specific application needs. The 60-degree hexagonal engraving has been a proven workhorse for decades as it provides the highest performing engraving for line, combination and process printing, including expanded gamut. Specialty inks and coatings, like opaque whites, fluorescent and embellishment varnishes, require higher-volume, lower-line-screen cell geometry. The common engravings for these applications consisted of 30-degree channel, tri-helical and various other geometries. Many of these engravings were of an open channel design to promote flow and transfer of the higher viscosity inks and coatings. They would deliver heavier coat weights, higher opacities and improved transfer rates to achieve the required results. They also provided improved ink solubility at higher speeds due to the open channel nature of the engraving, allowing ink to flow freely through the channel. This flow also reduced the amount of possible air entrapment of a closed cell, resulting in a decrease in foaming and pin-holing.
Innovations continue to develop in both laser technology and ceramic compounds. These opportunities allow the industry or companies to provide new solutions that can help overcome many of the previous challenges in the inking transfer processes. Close attention is paid to the selection of ceramic compounds that will yield the lowest porosity and provide the most accurate engravings. The lower porosity levels provide a denser ceramic surface, which allows for consistently hitting RA (roughness averages) of below 3, which is smoother than glass. Any porosity level higher than 1% will not allow these results to be achieved and certainly will affect the ability to engrave surfaces at 800 cells per inch (CPI) or higher. This level of repeatable quality allows the industry to innovate new engraving technologies that overcome past transfer challenges. It also has allowed the industry to enter new markets, including security, direct gravure and printed electronics (see Figure 2). These advancements in ceramic compounds, resulting in extremely lower porosity levels, allow for continuous development of new engravings and digitally image high-end graphics directly to the ceramic surface.
The industry also now can offer a single engraving geometry that incorporates all the attributes of past geometries into a single engraving. The ability to engrave a 60-degree hex geometry, with predictable and measurable CPI and volumes that include a channeled application technology, has set a new standard in anilox engraving. This innovation offers the benefits of the traditional 60-degree hexagonal pocket cell with a channeled design to promote ink flow and transfer (see Figure 3). The 60-degree channeled application technology provides proper dot support and dot gain characteristics for screen tone and process images, yet provides efficient ink transfer for high-viscosity inks and coatings. This has proven to be a very effective engraving technology for all applications, including line, spot, combination, process printing and higher-viscosity opacities and embellishments. It works well with all ink systems, including solvent, water-based and UV/LED, with excellent ink release and solubility. This promotes less cell plugging, easier clean-ups and improved production times. Streamlining anilox inventory also is a benefit as users no longer need to manage many different engraving geometries.
These continued innovations also have led to the expansion of the ceramic engraving process to other printing market verticals. The coatings and gravure markets have seen new opportunities with the conversion of traditional chrome rollers to ceramic. The ceramic has a significant lifecycle advantage over chrome that some converters have seen 20:1. The laser engraving process also allows geometries to be optimized to improve transfer efficiencies and coat weight targets. Companies now can offer higher line screens with improved running speeds and consistently maintain color saturation and coating weights throughout press speeds.
Anilox care and maintenance
To achieve the highest performance of an anilox roller, it is required to have a proper cleaning and maintenance process established. A roller simply will not deliver the proper ink or coating volume if it is contaminated or suffers premature wear. There are many variables to consider when deciding which anilox cleaning method is the best for an operation. Anilox rollers come in all shapes and sizes; they can be constructed of mild steel or aluminum bases. The construction of the base materials must be considered when identifying the proper cleaning methods. Aggressive chemical cleaners can attack these base materials, causing corrosion which then can affect the ceramic coating. Ink chemistry can vary among high-PH water-based, solvent or UV, and all require different cleaning methods to break down or dissolve inks. These different chemistries will have a major influence in selecting the optimum cleaning process for each operation. Each chemistry will present its own set of variables that need to be identified to ensure proper cleaning of engraved cells.
The anilox engraving specifications play a critical role in the cleaning process to ensure the proper cleaner is being applied effectively to the engraving geometry. The cleaning process selected for water-based inks running line work on low-line anilox rollers would not be the same as that for UV inks running high-definition process work on very high-line anilox rollers. Identifying all these variables will allow the selection of the most effective cleaning process for the application, from traditional hand cleaners utilizing stainless steel brushes to the more recent laser cleaning systems. They all are very effective when fit to the proper application. They also can destroy a roller if not used in the manufacturer’s suggested operating procedures.
Automation has provided new levels of efficiency now as rollers can be moved to the units and cleaned while operators pursue other activities. To achieve predictable and repeatable results from anilox rollers on press, a proper care and maintenance procedure must be established. Rollers that are not properly cared for will plug, robbing color or coat weight and resulting in quality concerns (see Figure 4). Hand cleaners still are used widely for on-press cleaning, but the automated cleaning systems provide the deep cleaning that the rollers require on a regularly scheduled PM cycle to continue to meet graphic requirements on press. There also are services provided for mobile, in-press cleaning for rollers that spend their life cycle in-press. Regardless of whether it’s manual, media blast, chemical or laser, all technologies have improved over the years, providing safe and effective cleaning options for all applications.
The anilox roller has been on quite a journey. It now is considered the heart of the flexographic process and a critical element to success. Applying the properly specified anilox engraving for each specific application will ensure the production process is not only more efficient and sustainable but also will provide a more predictable and repeatable operation.
Paul Teachout has been in the packaging industry for more than 40 years. Starting out in commercial offset, he moved to flexo press manufacturing with Webtron/Aquaflex in 1986. Teachout has held numerous key positions, including printing management, application engineer, product development manager, director of after sales and vice president of sales/marketing. Teachout currently holds the position of Technical Marketing and Content Specialist at Harper Corporation of America. He also is active on numerous industry committees and college advisory boards, current Chairman of the FTA Board of Directors and is an FTA Level 3 First Implementations Specialist, was honored with the 2014 FTA President’s Award, the 2017 TLMI Supplier of the Year and the 2024 Label Industry Global Achievement Award. For more information, email Paul.Teachout@harpercorporation.com or visit www.harpercorporation.com.