A superior-quality, process-free printing plate—or at the minimum, an aqueous process plate—has been a goal for printers since the days of hand-engraved plates. Their hope: streamline the plate making process.
High-performance aqueous plate processing finds its roots in a 1948 Kodak patent, which serves as the foundation of photopolymer imaging. While offset plates have progressed, until recently, flexo plate making had trouble matching that achievement.
Development took some time, but market availability and adoption of aqueous-processed plates began, in earnest, after drupa 2004. Now, 15 years later, with the increasing pressures of environmental sustainability, it has finally become the primary method of offset plate processing. The unique challenges of flexo plate making have added complexity to achieving that goal.
All photos courtesy of Miraclon Corp
Challenges of Flexo
The earliest of flexo relief plates were composed of rubber and the resultant print was not of the highest quality. Introduction of photopolymer flexo plates helped increase the quality, but not by that much, in comparison to offset or gravure, two of the primary packaging print technologies. Subsequent introduction of CTP- (computer-to-plate) imaged photopolymer flexo plates, in the mid 1990s, provided much higher resolution and tighter controls to the plate making process, but still didn’t achieve the quality of offset or gravure.
One of the challenges of flexographic printing is that the flexo plates image directly on the substrate, creating plate wear and therefore impeding run longevity, as well as print quality. The flexo plate, unlike offset, is without an aluminum backing, thereby making it a comparatively soft surface. That makes it harder to achieve a small minimum printing dot or maintain a durable dot structure over the course of a pressrun. In order to mitigate these issues, flexo plate manufacturers have developed different plate materials, exposure and processing solutions.
The most widely used method of flexo digital plate making today involves a plate that has a laser ablative mask system (LAMS), which is a black carbon mask layer, manufactured directly on the plate. The LAMS is then exposed with a digital laser imaging device that blasts away the non-image areas.
Flexo plate and laser imaging technology has continued to improve over time, along with image quality. However, the LAMS process still doesn’t offer the level of control or detailed reproduction we would typically find in offset or gravure plate making.
At drupa 2008, things started changing. Kodak refined its process to use a thermal imaging layer (TIL) mask, which in essence is exposed film laminated by a unique process that provides a 1:1 reproduction to the polymer flexo plate material. The plate is then developed in a solvent-based solution to wash away the non-imaged areas.
The TIL can yield a much cleaner image mask and the plate can be produced with smaller flat top halftone dots with broad shoulders to help stand up to the direct imaging on the media. The plate can also carry ink more consistently and requires three-to-four-times less energy to image the TIL, compared to LAMS.
Ridding Residual Matter
Efficiently and completely removing residual material from the exposed and processed plate has proven to be a challenge over the years for many plate manufacturers. Additionally, since the flexo plate dot structure and process requires a tall dot, in order to create a shoulder to maintain the dot under the pressure of compacting it against the media, there is a good deal of residual non-print plate media that needs to be removed, or washed off. If not washed out properly, developed plate debris ultimately redeposits on the plate, causing print defects.
This issue can be further compounded if the surface of the plate is textured, where it can act as an additional trap for debris. (Note: The most sophisticated plate systems use imaged micro texturization patterns to control both ink transfer and ink flow and can be quite successful in achieving high density and smooth ink laydowns while minimizing actual ink usage.)
Solvents initially proved to be more efficient than water for plate processing and washing off the residue, but brought solution handling and waste disposal issues. That changed at Labelexpo Americas 2018, which saw introduction of a new “ultra clean,” aqueous-based development process that is solvent and VOC (volatile organic compound) free. It uses a specially designed plate processor and a specially designed processing solution with a dispersing agent.
The plate processor develops the latent image into a relief image by removing the unexposed photopolymer from the photosensitive flexographic printing plate, using this unique aqueous processing solution, while the plate is being mechanically cleaned. The unique patented process uses natural-based agents to prevent the buildup of unexposed polymer on the plate and the plate processor itself, ensuring both the quality of the plate and a minimal amount of maintenance and cleaning for the operator. The system is fast—only seven minutes to process a plate—and with the rapid drying times possible thanks to an aqueous-processed plate, a printer can be press-ready, from beginning to end, in less than one hour.
And as for waste products, the spent solution is drained out of the processor as a combination of reclaimed water and inert byproduct for treatment and municipal disposal. The combination creates a level of quality, efficiency and sustainability not seen before in flexo plate making.
“The plate can also carry ink more consistently and requires three-to-four-times less energy to image the thermal image layer, compared to a laser ablative mask system.”
Excited Customers
The benefits are apparent to the European and US early adopters. Krzysztof Malengowski, Fleksograf owner, comments: “Sustainability is at the forefront of many of our customers’ and brands’ requirements, and we are setting a new standard with our aqueous, solvent-free flexo plate solution. Sustainability can now start with the plate.”
“In the 21st century packaging industry, eco-friendly printing begins with the flexo plate,” says Stefan Schneider, sales coordinator at U. Günther. “Tests and initial production runs have confirmed that the plates deliver excellent print quality with high edge definition. There is much less ink buildup during print production, so printers benefit from longer cleaning intervals and less downtime. Print production speeds can also be substantially increased.”
“We have a green initiative in our facility,” explains Rob Anderson, director, production and planning, IGT, a major lottery ticket printer based in Florida. “Operators see the difference in the dots and how they print, as well as how vignettes, fine screens, everything looks so much cleaner. Essentially, it has made their job much easier.”
Problem Solved
High-performance flexo plate making and processing have come a long way since the invention of photopolymer imaging. With the addition of aqueous alternatives to solvent processing, flexo print providers can support high-quality print, increased productivity and lower costs for years to come.
About the Author
