Over the years, flexographic printing has faced a wide variety of challenges.
In fact, today’s combined set of trial-laden tasks and tribulations is focused on maintaining high print quality expectations while controlling costs, in the midst of a growing skills shortage that is driving a need to simplify on-press production.
The team at Miraclon has been focused on addressing these fundamental challenges since the introduction of FLEXCEL NX Technology in 2008, starting with 1:1 imaging improving on-press consistency and solid ink density laydown.
One of the first industry-wide challenges to be solved in terms of the plate and its performance in printing were the traditional issues with poor solid ink laydown and resultant image density capabilities. The anilox cell structure, particularly the anilox wall transferring the pattern of ink to the plate (and this pattern being transferred to the final substrate), needed to be addressed—and has been—in several different ways, by many different minds.
At Miraclon, this led to the 2010 introduction of DIGICAP NX Patterning for process inks to break up the pattern from the anilox cells on the plate surface, and Advanced DIGICAP NX Patterning (NX Advantage) in 2016 that covered all liquid ink types—process, spot color, whites and specialty applications (see Figure 1).
All graphics courtesy of Miraclon Corp
Once ink laydown is addressed and greatly improved—normally with better density without using more ink—it does not mean that all is perfect. Instead, it helps to highlight other problems that were always present, but hidden or ignored because of the bigger ink laydown issue.
Over the past 25 years, the flexographic industry accepted that with a raised print surface covered with ink, excess ink would be pushed off when the plate is compressed, causing high dot gain. It was seen as a necessary evil of the flexographic printing process, despite advances in all components and equipment.
I describe this effect (see Figure 2 and Figure 3) as unwanted ink spread and relate it to the image areas of the digital file (each pixel) versus the final print achieved on the substrate.
Patented Structure
Within the plate surface engineering and technology applied today, there are single- and multi-structure solutions. In the past, these solutions were optimized for ink transfer. In the case of NX Advantage, Miraclon applied a secondary smaller pattern around the outer edge of the feature (dot, line, solid, etc.) called Advanced Edge Definition (AED), to help retain the ink and slow it from flowing out, while still helping the air escape (see the middle image in Figure 4).
The plate reproduction capabilities of FLEXCEL NX technology, a unique flexographic plate characteristic that gives it the capability to consistently reproduce and hold such precision plate surface structures, enables even further, more complex multi-functional plate surface patterning, like PureFlexo Printing.
PureFlexo Printing is a patented, multi-functional plate surface patterning solution that utilizes the same main surface engineering options for improved ink transfer and laydown as NX Advantage, but changes the AED structure into two parts. The very outer row of pixels forming the outer wall remains, and inside that a micro-channel is formed, which is significantly higher in volume than main surface structure volume, but only 30 percent the width of a human hair, indicated in the right image of Figure 4.
The way PureFlexo Printing reduces unwanted ink spread is quite straightforward and is illustrated in Figure 5. First, for a traditional single-pattern structure, the ink on the plate surface (shown as a dot) becomes compressed and transfers to the substrate, but any excess ink is pushed backward and off the back and side edges of the dot, which results in unwanted ink spread.
But when the PureFlexo Printing dot is compressed, it transfers ink to the substrate and any excess ink is pushed backward. Instead of the ink all pushed off the dot surface, it first flows into the microchannel to fill the inside edge of the structure, reducing unwanted ink spread. (Some will still escape to cause a lower level of physical dot gain.)
Reducing Defects
Utilizing existing plate surface texturization technologies, PureFlexo Printing does not affect ink laydown in the middle of large solids. Its effectiveness is restricted to the edges of print, where the dot gain and many defects occur.
The No. 1 benefit PureFlexo Printing delivers is the physical reduction of unwanted ink spread, which reduces dot gain and ink buildup at the edges, and prevents defects like dot bridging from occurring. This is illustrated by the dot gain curves from the technology options applied to surface technologies and printed side by side under identical conditions.
Figure 6 shows the original DIGICAP NX Patterning producing an ink density of 1.76 and the highest dot gain characteristics (blue line), the NX Advantage Technology with better ink laydown and a higher ink density of 1.89, and slightly lower dot gain characteristics (green line), compared to PureFlexo Printing with matching laydown and ink density (as expected) of 1.88 but significantly reduced dot gain characteristics (orange line).
PureFlexo Printing also assists in reducing a common defect: dot bridging. Unwanted ink spread builds up between the dots and features over time, causing the ink to bridge and dots to join, often resulting in a jump or visual defect in tonal reproduction. These traditional shifts in tonal values, due to ink buildup, can also cause a drift in the color achieved; diminishing color accuracy against the target values. See the improvement in dot bridging in Figure 7.
Another flexographic printing challenge that is addressed and significantly reduced is trail edge voids (TEV). Voids are where air is trapped in the excess ink during compression, forming a bubble that bursts as the plate and substrate start to separate, leaving a void near the trailing edge of a feature or solid. The microchannel of PureFlexo Printing, in most cases, allows this air to escape instead of bursting; leaving excellent print all the way to the trail edge of the dot.
Color Stability
Lower dot gain characteristics delivered are highly valuable to grow the use of process printing in flexography, including the support of not having to use spot colors with their additional costs in inks and press time. By reducing the gain characteristics significantly, it enables more colors to be successfully built out of process inks, with greater predictability and stability.
This translates into a greater number of colors achievable within the existing color gamut. Whether you’re printing CMYK or expanded gamut (EG), more colors are addressable in normal production, leading to a trend of using higher process densities, akin to gravure in an X-CMYK format.
Control of the dot gain characteristics also assists in increasing the perceived contrast from the process printing by increasing the range of tone available in the shadow range. Traditionally this is an area that challenges many flexographic printers, making images look dull and less attractive to consumers on the shelf.
An additional benefit seen with PureFlexo Printing is that it functions really well on lower linescreen prints; the reduced dot gain makes it seem like a higher LPI print and capitalizes on the benefits of ease of use on-press and stability. For example, using a 133 LPI screen with PureFlexo Printing, instead of a 150 LPI without the technology, delivers the added benefit of having visual parity on shelf to the consumer.
When it comes to making life easier on press, the prior improvement in ink laydown, combined with the resistance of unwanted ink spread, reducing the gain, print defects and need to print higher LPI values, all combine to make it simpler to implement on press than prior solutions.
PureFlexo Printing technology has addressed several industry challenges including pinholes, TEV, dot gain, the use of harder mounting tapes which lead to even more unwanted ink spread, dot bridging and dot gain through the run. Printers using PureFlexo Printing can regularly use softer tapes—one or two levels softer—while keeping excellent ink laydown, which further helps to reduce dot gain, especially in the highlights. It also helps bounce and chatter.
Globally Proven
By the close of 2022, well over 50,000 commercial flexible packaging jobs had been produced using PureFlexo Printing, making it a globally proven solution. Printers like it and see the value and impact it has on improving efficiency.
Originally created for solvent-based inks in flexible packaging, further testing proved PureFlexo Printing to be applicable to many forms of water-based and EB inks with flexible and shrink film packaging. Customers are proving successful in utilizing PureFlexo Printing with water-based inks, after correct pattern selection evaluations, on films, foils, coated papers, uncoated papers, disposables and even postprint corrugated board.
The benefits of addressing underlying industry challenges makes PureFlexo Printing a highly innovative solution that will help a vast range of flexographic applications to be printed more efficiently, making it a tool to help transform packaging printing globally.
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