The amount of waste the US generates is one of the largest issues we face in ensuring the health and enjoyment of future generations.
Sustainable practices remain a critical focus for both flexographic printers and CPCs. Multi-tiered approaches are embraced by CPCs for improving sustainability including reducing and lightweighting current packaging materials, looking for alternate compostable materials, as well as improving the recycling of existing materials.
To combat current waste volumes, we need a more efficient recycling system, so that more material can be recovered, sorted and reused. Procter & Gamble (P&G) founded—and now is a leading participant of—the HolyGrail 2.0 Project, which aims to implement a new auto-identification system for package recycling. This technology makes it so that different plastic materials can be sorted based on composition, at higher and faster rates.
The flexographic industry in the US produces the vast majority of single-use plastic packaging. With such a large market share, the industry needs to be forward-looking to keep up with current and future sustainability practices.
The flexographic industry has a huge opportunity to transform the end-of-life of single-use plastics. This project aims to show how flexographic printing can be used to implement this new auto-identification system with optimum techniques for brand color management. Many recyclable plastics are sent to a landfill because they cannot be sorted by Materials Recovery Facilities in a cost-efficient way. HolyGrail 2.0 addresses this by encoding labels, packages, films and containers with Digimarc Barcode to identify the core material and its product use case, thus making it machine readable and sortable, optimizing the recycling process.
This project investigates challenges CPCs face to minimize the color difference (CIE Delta E 2000) on brand spot colors when integrating Digimarc Barcode enhancements. By exploring how different enhancement techniques affect the Delta E 2000 of common brand spot colors, it can be shown how this technology can be best implemented into a CPC’s existing workflow.
History & Robustness
There has already been a variety of studies published on the effective creation of Digimarc Barcodes or watermarks. One such study, titled, “Using Watermark Visibility Measurements to Select an Optimized Pair of Spot Colors for Use in a Binary Watermark” (Reed, Kitanovski, Falkenstern, Digimarc Corp, Norwegian University of Science and Technology), explores the selection of a complementary spot color to print within another spot color to optimize scanning.
This selection is important because the complementary spot color should be imperceptible at viewing distance but scannable by a point of sale (POS) bar code scanner used in retail grocery stores. POS scanners typically use red illumination at a wavelength of 670-nm. Specifically, green and black spot colors reflect very little red light. This creates the challenge of creating a watermark with low visibility for some spot colors. The findings of this study were a method in which a complementary fill color can be chosen for a binary watermark of a base color with low reflectivity at 670-nm. This is dependent upon whether or not the spot color has low reflectivity at 670-nm., therefore it will not interfere with the watermark signal.
Another study involving Digimarc’s Barcode technology is titled, “Selecting Best Ink Color for Sparse Watermark” (Reed, Falkenstern, Hattenberger, Digimarc Corp, USA X-Rite Inc). This study is also involved in the ink color selection for the creation of a robust watermark. Specifically, this study looks at a binary watermark that is encoded into a single ink color. The findings of this study were that a color could be accurately predicted for best use in a binary watermark in white areas of a design.
While the thousands of POS scanners in use in grocery stores are deeply rooted in red-light scanning, newer scanners developed for recycling are not limited to 670-nm. Recycling scanners are typically considered white-light scanners. The studies discussed here point to the differences between white light scanning and POS red-light scanning, as well as how to create a robust watermark based on a brand’s specific spot color palette. A white-light scanner has three strobing colors of light—red, blue and green—at three unique wavelengths. This means that the bar codes created for this project need to be robust using this type of scanner.
Robustness is a measurement of how scannable a bar code is. This number is calculated from two readings: linear grid strength and the message strength.
The linear grid strength is how the bar code is recognized and scaled, and the message strength is the payload of the bar code. While the Delta E 2000 value is the primary data to be analyzed, the robustness of each target printed was also examined to inform how these bar codes will work for the needs of a recycling system. A recycling system requires a bar code to be robust enough to be read at high speeds and from a package that may be damaged. The robustness will also be used to inform on future projects to see how these targets can be further improved specifically for the recycling application.
Design of Experiment
Six inks were chosen to represent common brand spot colors. Then, based upon the qualities of each spot color, a variety of enhancement methods was chosen. These techniques were chosen in consultation with Digimarc color scientists with the expectation of producing the least variation in Delta E 2000 values. Pantone 123, Pantone 185, Pantone 286 and Pantone Orange were enhanced by a Black Overprint, Spot Direct and a Positive Binary Overprint, while Pantone Green and Pantone Black were enhanced with Spot Direct and a Negative Binary Overprint. This difference in techniques is due to the difference in how much light green and black reflect back to the scanner.
Each method of enhancement works differently but accomplishes the same goal of making the printed area responsive to a scanner. First, the Spot Direct technique modulates pixels within the file and thus does not add any additional ink colors. This creates a change in value that is mostly imperceptible to the eye but can be picked up by a white-light scanner. This method does not require additional inks to be used on press, but it does require additional file setup and, depending on the color, does not always produce robust codes.
Second, the Black Overprint is an added separation consisting of different strength dots dependent upon the spot color being printed. This requires an additional black plate to be used on press.
Third, the Positive Binary method is where an additional non-black ink is printed on top of the spot color. In this study, Pantone 9520 and Pantone 9120—both pastels—were used. This is much like the Black Overprint in that it requires an additional separation and ink to be used. The fourth method chosen was Negative Binary. This is similar to Positive Binary in that it calls for an additional ink color, however, this ink is to be printed as a flood behind the spot color. “Holes” are poked in the spot color separation so the flood behind can be seen through those areas and scanned. The additional inks used for this were Pantone 2747 and Pantone 7467.
Upon evaluation of the enhancement methods being used, four hypotheses were formed. These hypotheses are as follows:
- Hypothesis One: Each test target will produce a Delta E 2000 within 3
- Hypothesis Two: The Spot Direct Digimarc technique will produce a lower Delta E 2000 value than the Positive Binary and Negative Binary Digimarc techniques
- Hypothesis Three: The Black Overprint Digimarc technique will produce a lower Delta E 2000 value than the Positive Binary and Negative Binary Digimarc techniques
- Hypothesis Four: All enhancement methods will produce a robustness score greater than 60
A test target was created to be put on press. The components required for the test target were a 25 percent dot density patch, a 50 percent dot density patch, a 75 percent dot density patch, a 100 percent dot density patch, bearer bars and examples of a variety of applications. These examples were a logo, a photo and an illustration. These components make it so the Delta E 2000 can be measured at different densities to see how the Digimarc method performs, as well as show how the bar code method would look in different instances.
Upon completion of these test target files, 11 unique plates were made to be used in the pressrun. The plates used were LUX ITP60 067 with a 133 lpi. The test targets for each spot color were printed on white polypropylene substrate. In total, eight test targets—each comprised of three to four encoding methods—were printed for evaluation. Each test target also included a control, which served as the standard for measuring Delta E 2000. A sample set was printed for each of the six spot colors, with two additional sets printed for black with different anilox rolls. This allowed us to see how the change in black ink density affects the Delta E 2000 of the Negative Binary enhancement.
Analysis, Findings, Takeaways
With all samples printed, the Delta E 2000 for each target was measured. The Delta E 2000 value was measured using a Techkon SpectroDens. Four readings were taken from each section (for each enhancement) of the test target per spot color. The readings were taken from the 100 percent patch, 75 percent patch, 50 percent patch and 25 percent patch in comparison to the corresponding patch on the control section of the test target. This determined the effectiveness of the treatment overall by allowing the comparison of how the Delta E 2000 value changes as patch density decreases.
The test targets were also sent to Digimarc to be analyzed for robustness. Each enhancement per spot color was given a robustness score that was calculated using Verify Report. The robustness calculations use a Digimarc proprietary calculation but incorporate both linear grid strength and message strength (a higher number is better).
Based upon the collected results, one can see that from a Delta E 2000 value perspective, some of the enhancement methods were much more effective than others. As for the robustness, there is room for improvement across all spot colors before these enhancements can be practically applied for recycling scanning.