Global Graphics Software has a long history in screening innovation dating back to its patented FM or stochastic screening technology of the 1990s. With the advent of inkjet printing Global Graphics has developed new screening technologies in response to press manufacturers’ concerns about image quality.
The development of PrintFlat began when several inkjet press vendors asked Global Graphics Software for help. They had exhausted possible mechanical improvements and were still dissatisfied with the results. Working with more than a dozen vendors gave us plenty of press time to test different screening algorithms.
Irregular drop positioning leads to drops ‘randomly’ coalescing on the media
Our group of vendors shared common problems due to the physics of jetting ink onto moving substrates. We noticed that there was more streaking when a press ran faster because the ink drops form a teardrop shape when they hit the substrate. We created a vertical bias control to correct for this.
Another common artifact that we observed is sometimes called “mottle” or “orange peel” caused by an interaction of ink and the drying process.
To mitigate orange peel we experimented using a screening tool that we developed in-house, trying different screening algorithms and based on our earlier breakthroughs with dispersed screens. We introduced an error diffusion screen into a dispersed screen. This showed more benefit in plastic films than on paper. So, we redesigned our dispersed screens entirely, aligning the structure horizontally, reworking the dot structure and screen angle for inkjet to create a micro structured screen.
Mirror, one of two Advanced Inkjet Screens, avoids orange peel mottle on poorly wettable substrates.
Pearl, one of two Advanced Inkjet Screens, counteracts streaking on output from inkjet presses.
We evaluated our new screens on a variety of different technologies, from UV inks to aqueous, using a variety of print heads as well as different substrates, from absorbent corrugated board to metal cans. We concluded that absorbent substrates respond best to the dispersed screen (Pearl) and non-absorbent to the microstructured screen (Mirror).
With Mirror and Pearl more ink can be used to increase the colour gamut without triggering mottle. In 2017 Global Graphics introduced its Advanced Inkjet Screens for use with the high-speed screening engine, ScreenPro. In 2018 ScreenPro received a PIA InterTech™ Technology Award.
With streaking and mottling resolved the next challenge we were tasked with was to work out how to mitigate non-uniformity across the web. We created a method by which custom calibrations could be generated based on measurements taken from the press. We called these PrintFlat because they mask the banding, creating a “flat” uniform appearance on areas that are particularly difficult to print using the inkjet process, namely areas of flat colors.
PrintFlat calibrations are installed into the ScreenPro screening engine which applies the correction to the press. PrintFlat adjusts the density within ScreenPro to produce uniformity across a print bar. The process can be automated for closed-loop correction and, unlike correction by adjustment of voltages, there is no effect on jetting stability or head lifetime, nor ink pressure and timing/drop speed variation. It greatly reduces the time and cost both of building a press and of maintaining it.
PrintFlat gave us another “Eureka” moment. And because it is applied by ScreenPro you also can achieve excellent print quality at high speeds on any workflow.
ScreenPro can be supplied as a development component, a fully branded user interface that allows input and output folders to be configured, or, as a high-speed pipeline driving print electronics directly.