How Each Step of FIRST Was Followed & Special Considerations Taken During the Project
As explained in the introductory “FIRST in Motion” article by Dr. Mark R. Mazur and Dr. Malcolm G. Keif in the August issue of FLEXO Magazine, the purpose of the project at the center of that session was to print a “real” job under live production conditions using FIRST (Flexographic Image Reproduction Specifications & Tolerances) guidelines and the latest technology, and then view and measure the final print to assess results.
This is a project involving multiple partners performing different types of work at multiple locations. By definition, a project is a set of tasks performed between a predefined beginning and end. This article is less about the “project” and more about the specific “print job.” The final products resulting from that print job were six stand-up pouches. These six comprised three items (which we’ll refer to as “coffee,” “dog” and “kebab”) reproduced two different ways: CMYK plus spot, and expanded gamut (EG).
This was not an EG promo project—We were not trying to make one look better than another. On the contrary, we wanted to show that FIRST specifications apply equally to CMYK, spot colors and EG. We also wanted to show that all of this could be printed in a single 10-color pressrun on a large, wide web film, central impression (CI) press.
FIRST 6.0 & ANSI CGATS TR 012
One of the principles of FIRST is to not create new specifications if existing specifications meet the needs of the flexo community. With respect to the steps to objectively define tone and color reproduction capabilities and to apply quality control principles to flexo printing, FIRST defers to the principles described in the Committee for Graphic Arts Technical Standards (CGATS) TR 012 specification. This specification outlines five steps in the following order:
- Fingerprint (curves pressrun)
- Process control
- Characterize (profile pressrun)
- Process improvement
The end product of “FIRST in Motion” was six stand-up pouches printed to FIRST specifications. Each item was printed CMYK plus spot as well as 7-color EG.
Above images courtesy of The ALC Group; all other images courtesy of Mark Samworth
The subject of flexo print optimization can be indefinitely long and consume an entire book in and of itself. In a forthcoming article in this series, Sean Teufler will go into greater detail on FIRST optimization as it applies to this project. For now, it’s worth pointing out that optimization must occur before all other steps. If you change a variable in the middle of the process, you will have to return to the fingerprint and redo all subsequent steps.
For this project, we felt that starting with an existing set of optimized conditions would have been “cheating.” As such, we intentionally started anew with a plate that Plastic Packaging Technologies LLC (PPT) had not optimized. We then ran the single-color test target (see Figure 1) and selected the image screening parameters which produced the best fade to zero and the ink transfer screen parameters which produced the smoothest coverage with the highest density.
Fingerprint (the Curves Pressrun)
The purpose of the fingerprint is to settle on final solid color values for all 10 colors to be printed on the final production run—as well as to derive the curves required to match the print at PPT to the specification at which we are aiming. Steve Smiley will be dedicating an entire article to color specifications as they applied to this project. In summary, he will describe how the P2P51 targets were used to match CMYK to CRPC-6, and how all other colors were matched to linear SCTV with corresponding test targets. He will also describe the roll of CxF 4 for the quantification of spot color data for proofing.
In most simple terms, “process control” is the implementation of tools and methods to assure consistent print results. An interesting debate could be had as to where the step should be located in the five-step CGATS 012 sequence. While you absolutely must have process control in place between the characterization run and the production run (the goal of the production run is to match the press profile obtained in the characterization run), process control truly starts during and after the fingerprint.
Characterize (The Profile Pressrun)
The purpose of the profile pressrun is to quantify the true color characteristics of the specific set of printing conditions. This information is used to convert spot colors into CMYK or CMYKOGV as well as to produce proofs in which 4-color, 7-color and spot colors match what will be printed on press. Richard Black will dedicate a forthcoming article to press characterization, as well as to how process control was applied in the curves pressrun, the profile pressrun and the final production run to assure predictable results between the three.
By listing “process improvement” as the last step in the five-step process, the CGATS committee is reminding us that quality is an ongoing process in which the goal is continuous improvement. And while this is certainly a true statement, it should be understood that no improvement should be made that changes the color characteristics obtained in profile pressrun.
An example of a process improvement step that was applied in this project after the characterization run and before the production run was related to ink transfer screening. High cell count (1,400 cell per inch) ink transfer screening was used for the solids during the profile run. This resulted in solids with higher densities and smoother ink laydown than were achieved with a “normal” solid. However, the laydown in the shadow areas (e.g. at 95 percent) was far from optimal and even showed a reversal (the 95 percent was lighter than the 90 percent). It was clear that ink transfer screens were needed not just in the solids, but also in the dots. However, the profiles were made based on transfer screens in solids only.
Observing that the highest tint patch in the profile chart was at 85 percent, we chose to apply ink transfer screening to the halftone dots from 100 percent down to 85 percent. The results in the final production run were near perfect! This process improvement actually assisted the production run to match the profile pressrun and the proof more closely because the profile charts with shadow values between 85 percent and 100 percent did not contain the reversals, but a nice smooth transition from lighter to darker.