Paul Teachout, Technical Marketing & Content Specialist, Harper Corporation of America05.15.23
Since the first mechanically engraved rotogravure cylinders invented in France back in the late 19th century, we have been on an endless pursuit to develop the most efficient ink transfer process for flexography. Douglas Tuttle here in the USA was instrumental in introducing this mechanical engraving technology to the flexographic aniline printing process back in the mid 1930s.
From then on, we have gone through countless innovations and improvements to our ink transfer process and the technology that provides it. Through the early years mechanically engraved cylinders covered in copper and chrome were the norm, the 45-degree quadrangle geometries were simple to mechanically engrave and could reach line screens of 360 LPI. In the 1970s Ron Harper pioneered the 60-degree hexagonal honeycomb cell geometry into our process, and in 1990 Harper introduced the first laser engraved 60-degree ceramic engraving. It remains the predominant and most efficient engraving geometry to date.
Advancements in laser engraving technology continued over the next few decades. The predominant was the CO2 gas fired lasers that were later adapted to YAG engravings that could provide higher line screens of 1200 LPI and beyond, and now continued innovations in Digital Fiber Optics offer the most advanced and accurate laser engraving technology available. Harper's process has evolved from a 2 roller, open bath inking system with mechanically engraved cylinders to enclosed doctor blade chambers with laser engraved ceramic rollers now competing with every print process on the planet.
Where we are now
Through the years there have been many engraving geometries developed to meet specific application needs. The 60-degree hexagonal engraving has been the 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 would require higher volume, lower line screen cell geometries.
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.
For UV/LED inks, which tend to be much higher in viscosity, the open channels often helped with UV ink spitting. This is an issue where the higher viscosity UV/LED inks would create pressure behind the blade forcing it through the shear point, resulting in the accumulation of ink on the face of the blade that would then “spit” off onto to the printed image.
The open channel geometries often reduced this pressure allowing inks to flow freely reducing this concern. The downside of these engravings is that they could not provide the adequate dot support or ink film tolerances required for screen tones and process printing like the 60-degree closed cell hex could. This required the converter to have many different engraving technologies to achieve the optimum production results.
As advancements in flexo printing continued the ink transfer process has been met with many variables to manage. Working with many ink systems including solvent, water based and UV/LED, each provided their own set of characteristics that needed to be managed. No two-ink systems perform the same and all are utilized for specific market verticals from wide web flexible packaging to narrow web tag and label. Each application requires anilox characterization within its environment to determine optimum engraving geometry, cell volume and line screen to meet the graphic requirements and the ink system being run.
Other considerations also include the type of blade metering and cleaning practices. As each ink system, transfer process and production environments vary it is critical to optimize this process for consistent, repeatable cost-effective operations.
The anilox cell geometry also plays a crucial role in plate imaging. It is possible for a screen angle conflict between the anilox and the plate file that could result in a moire affect in the printed image. Many open cell geometries utilize nontraditional cell angles that could cause this problem when printing screen tone or process work. The 60-degree hex is still the optimum engraving angle to avoid this concern. The traditional 60-degree hex also responds well with specialty software for plate imaging, such as micro screening, FM screening, and other such specialty graphic enhancements.
Utilizing the 60-degree angle will allow you to maintain the traditional ratio of six times your plate screen DPI would be your minimum anilox line screen. For instance, if you are running a 200 DPI image then a 1200 LPI engraving would provide the optimum dot support and dot gain tolerances desired.
Where we're going
Innovations continue to develop in both laser technology and ceramic compounds. These opportunities allow us to provide new offerings that can help overcome many of the previous challenges in the 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 us to consistently hit RA (roughness averages) of below 3, which is smoother than glass. Any porosity level higher than 1% will not allow you to achieve these results and will certainly affect the ability to engrave cells at 800 dpi or higher. This level of repeatable quality allows us to innovate new engraving technologies that overcome past transfer challenges. We can now offer a single engraving 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 line screens and volumes that includes a channeled application technology has set a new standard in anilox engraving. This new technology offers the benefits of the traditional 60-degree hexagonal pocket cell with a channeled design to promote ink flow and transfer.
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 inks 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 your anilox inventory is also a benefit as you will no longer need to manage many different engraving geometries.
We are here
At last year’s 2022 FTA Fall Conference in Columbus, OH, USA, the agenda focus was on the newly released Optimal Method. The Optimal Method is a groundbreaking print calibration technique that utilizes tone curves to match an ICC profile. A new way of managing the flexographic printing process with the right methodology to improve color accuracy and consistency. Each attendee received a printed sample of this groundbreaking new prepress technique that they could review and follow along during the presentation.
This sample was produced utilizing the new channeled application technology and the results clearly spoke for themselves. This engraving technique can be dropped into an existing operation with virtually no compensation utilizing existing profiles. Minor adjustments were made to achieve Solid Ink Densities (SID) and the sample was executed to near perfection.
After two years of development and trialing this engraving technology is available and being widely used. It has been tagged as “Groundbreaking anilox innovation." Entire press inventories have been converted and multiple new press installations have displayed improved performance and increased uptime.
After decades of the revolutionary 60-degree hexagonal geometry there seems to be a proven alternative. The 60-degree channeled application technology has provided a new path forward in anilox innovation and performance.
About the author: 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 specialists, sales support, engineering support, marketing, product development manager, VP sales and marketing, and more.
From then on, we have gone through countless innovations and improvements to our ink transfer process and the technology that provides it. Through the early years mechanically engraved cylinders covered in copper and chrome were the norm, the 45-degree quadrangle geometries were simple to mechanically engrave and could reach line screens of 360 LPI. In the 1970s Ron Harper pioneered the 60-degree hexagonal honeycomb cell geometry into our process, and in 1990 Harper introduced the first laser engraved 60-degree ceramic engraving. It remains the predominant and most efficient engraving geometry to date.
Advancements in laser engraving technology continued over the next few decades. The predominant was the CO2 gas fired lasers that were later adapted to YAG engravings that could provide higher line screens of 1200 LPI and beyond, and now continued innovations in Digital Fiber Optics offer the most advanced and accurate laser engraving technology available. Harper's process has evolved from a 2 roller, open bath inking system with mechanically engraved cylinders to enclosed doctor blade chambers with laser engraved ceramic rollers now competing with every print process on the planet.
Where we are now
Through the years there have been many engraving geometries developed to meet specific application needs. The 60-degree hexagonal engraving has been the 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 would require higher volume, lower line screen cell geometries.
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.
For UV/LED inks, which tend to be much higher in viscosity, the open channels often helped with UV ink spitting. This is an issue where the higher viscosity UV/LED inks would create pressure behind the blade forcing it through the shear point, resulting in the accumulation of ink on the face of the blade that would then “spit” off onto to the printed image.
The open channel geometries often reduced this pressure allowing inks to flow freely reducing this concern. The downside of these engravings is that they could not provide the adequate dot support or ink film tolerances required for screen tones and process printing like the 60-degree closed cell hex could. This required the converter to have many different engraving technologies to achieve the optimum production results.
As advancements in flexo printing continued the ink transfer process has been met with many variables to manage. Working with many ink systems including solvent, water based and UV/LED, each provided their own set of characteristics that needed to be managed. No two-ink systems perform the same and all are utilized for specific market verticals from wide web flexible packaging to narrow web tag and label. Each application requires anilox characterization within its environment to determine optimum engraving geometry, cell volume and line screen to meet the graphic requirements and the ink system being run.
Other considerations also include the type of blade metering and cleaning practices. As each ink system, transfer process and production environments vary it is critical to optimize this process for consistent, repeatable cost-effective operations.
The anilox cell geometry also plays a crucial role in plate imaging. It is possible for a screen angle conflict between the anilox and the plate file that could result in a moire affect in the printed image. Many open cell geometries utilize nontraditional cell angles that could cause this problem when printing screen tone or process work. The 60-degree hex is still the optimum engraving angle to avoid this concern. The traditional 60-degree hex also responds well with specialty software for plate imaging, such as micro screening, FM screening, and other such specialty graphic enhancements.
Utilizing the 60-degree angle will allow you to maintain the traditional ratio of six times your plate screen DPI would be your minimum anilox line screen. For instance, if you are running a 200 DPI image then a 1200 LPI engraving would provide the optimum dot support and dot gain tolerances desired.
Where we're going
Innovations continue to develop in both laser technology and ceramic compounds. These opportunities allow us to provide new offerings that can help overcome many of the previous challenges in the 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 us to consistently hit RA (roughness averages) of below 3, which is smoother than glass. Any porosity level higher than 1% will not allow you to achieve these results and will certainly affect the ability to engrave cells at 800 dpi or higher. This level of repeatable quality allows us to innovate new engraving technologies that overcome past transfer challenges. We can now offer a single engraving 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 line screens and volumes that includes a channeled application technology has set a new standard in anilox engraving. This new technology offers the benefits of the traditional 60-degree hexagonal pocket cell with a channeled design to promote ink flow and transfer.
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 inks 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 your anilox inventory is also a benefit as you will no longer need to manage many different engraving geometries.
We are here
At last year’s 2022 FTA Fall Conference in Columbus, OH, USA, the agenda focus was on the newly released Optimal Method. The Optimal Method is a groundbreaking print calibration technique that utilizes tone curves to match an ICC profile. A new way of managing the flexographic printing process with the right methodology to improve color accuracy and consistency. Each attendee received a printed sample of this groundbreaking new prepress technique that they could review and follow along during the presentation.
This sample was produced utilizing the new channeled application technology and the results clearly spoke for themselves. This engraving technique can be dropped into an existing operation with virtually no compensation utilizing existing profiles. Minor adjustments were made to achieve Solid Ink Densities (SID) and the sample was executed to near perfection.
After two years of development and trialing this engraving technology is available and being widely used. It has been tagged as “Groundbreaking anilox innovation." Entire press inventories have been converted and multiple new press installations have displayed improved performance and increased uptime.
After decades of the revolutionary 60-degree hexagonal geometry there seems to be a proven alternative. The 60-degree channeled application technology has provided a new path forward in anilox innovation and performance.
About the author: 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 specialists, sales support, engineering support, marketing, product development manager, VP sales and marketing, and more.