With growing concern for the environment and the emergence of eco-friendly alternatives across all industries, there is a need to perform research on more sustainable solutions within the packaging industry.
The use of environmentally friendly substrates and inks should be explored as an alternative to petrochemical-based inks that have detrimental effects on the environment. The definition of a sustainable or environmentally friendly ink may differ between print companies and ink manufacturers.
For the purposes of this study, biorenewable inks are used as the eco-friendly ink set. The National Association of Printing Ink Manufacturers (NAPIM) defines a biorenewable ink as being derived from tree, plant, insect and/or animal materials (Sun Chemical, 2018). Along with being derived from natural materials, biorenewable inks should not have more than trace levels of heavy metals and reduce volatile organic compounds (VOCs) that are released into the atmosphere (Sun Chemical, 2018). These inks do not have the same negative impacts on the environment as petrochemical-based inks.
Table 1. The target L*a*b* values for the two Clemson brand colors and the anilox roller specifications used for each print trial
In addition to their environmental impact, it is important to consider the impact eco-friendly inks have on color reproduction. Consumer brands place importance on color as a way to build brand awareness and help shoppers recognize their products against competitors. The ability to produce packaging that retains brand color accuracy and desired aesthetic properties, while providing benefits to the environment, opens new opportunities for the future of the packaging industry. This study analyzes color accuracy and durability properties of eco-friendly inks compared to petrochemical-based inks printed on biodegradable paperboard.
Two Clemson brand colors were referenced as color standards for the experiment: Clemson Orange, Pantone 1595 C and Calhoun Fields, Pantone 583 C. The eco-friendly ink is hypothesized to be able to obtain a Delta E 2000 color difference of 2.0 or less, as this is commonly accepted as the threshold for the human eye’s ability to perceive color difference.
On press, adjustments were made to impression, press speed and anilox roller configurations to achieve the printed color target. A test target and package design pressrun were completed. Samples were collected from each test run to analyze solid ink density and Delta E 2000 values. Averages were calculated of the measured samples to confirm consistent ink density on the operator and gear sides of the press as well as the average Delta E 2000 values achieved on press.
Objective
The purpose of this study is to answer the following questions:
- Can brand color accuracy be achieved by obtaining a Delta E 2000 color difference of 2.0 or below using currently available eco-friendly inks and biodegradable substrates?
- If the eco-friendly inks fail to match, what drawbacks could keep these materials from being widely accepted?
Table 3.1. Average solid ink density operator and gear side for the test target pressrun. PMA = petrochemical-based ink and DPA = eco-friendly ink.
Inks
Flexographic water-based inks were used to conduct this experiment. Sun Chemical provided two ink formulations: CHROMAFINE, which served as the petrochemical-based ink, and AquaGreen, which served as the eco-friendly ink. The Pantone colors, along with the L*a*b* values, were provided for color matching with a tolerance of Delta E 2000 difference of 2.0 or less. Each of the inks was color matched within tolerance by Sun Chemical prior to the press trials.
The pigments used for both formulations remained constant and the essential difference between the petrochemical-based inks and eco-friendly inks was the ink vehicle. The ink vehicle is an essential component of the ink, as it holds the pigment and binds it to the surface of the substrate. The type of vehicle used in an ink affects how it dries and the overall quality of the ink on the printed surface. Within this report, the CHROMAFINE (PMA) formulation contains a petrochemical-based ink vehicle and the AquaGreen (DPA) formulation contains a bio-based ink vehicle in which the contents are biorenewable.
Table 3.2: The target Delta E 2000 L*a*b* values
Table 1 displays the target L*a*b* values for the two Clemson Brand colors and the anilox roller specifications used for each print trial. The values in parentheses represent the number of anilox rollers with this configuration that were used during the pressrun.
Substrate
WestRock 14 pt. PrintKote coated paperboard was used for both pressruns. Paperboard is often manufactured using recycled materials, but certain substrate additives may cause the product to no longer be considered biodegradable or compostable after its initial use. The PrintKote substrate is recyclable and does not contain optical brightening agents (OBAs).
A fluorescence test using a Judge QC X-Rite light booth confirmed there were no OBAs present in the substrate. Optical brighteners contain harmful organic chemicals that have been found to contaminate aquatic bodies, as they are not easily degradable by wastewater treatment (Ginebreda et al., 2011). The paperboard also contains elemental chlorine free (ECF) bleached fibers. The ECF bleaching process serves as an environmentally friendly alternative to traditional fiber bleaching. This process substitutes the use of molecular chlorine for chlorine dioxide, reducing water usage and toxic waste (Bajpai, 2018).
Table 3.3: Average Delta E 2000 values – Pressrun 1
Methodology
DuPont DFR 0.067-in. photopolymer plates were exposed on a DuPont Cyrel Fast exposure unit and imaged using an Esko CDI Spark 2530. The plates were thermally processed on a Cyrel Fast thermal processor. All plates had a 0.020-in. plate relief within Flexographic Image Reproduction Specifications & Tolerances (FIRST) guidelines. The plates were then mounted on plate cylinders with a 15-in. repeat using 3M E1315 mounting tape. Two pressruns were completed for each type of ink, the first being a test target run and the second being a graphics pressrun for a paperboard package.
Table 4.1: Average solid ink density operator and gear side for the graphics pressrun
Prior to each pressrun, the viscosity and pH of the inks were recorded using a #3 Zahn cup and a pH meter. Flexographic inks typically have between an 8.5 and 9.5 pH range. The viscosity and pH measurements are shown in Table 2.
This study was conducted on a Comco Captain Series 10-in. narrow web inline flexographic press with six print stations. Four stations were used for both the test target and graphics run. The graphics run consisted of a design that was converted into a paperboard package. On press, adjustments were made to press speed, impression settings and anilox roller configurations.
Test Target Pressrun
The initial test target pressrun was completed using four water-based inks, two Clemson brand colors and two auxiliary colors for the graphic elements (see Figure 1). After either of the ink sets—petrochemical-based or bio-based—were run on press, the plates, ink chambers and anilox rollers were cleaned thoroughly to avoid contamination.
Table 4.3: Average Delta E 2000 values – Pressrun 2
All four stations contained an 800 cpi, 2.0 bcm anilox roller and the press ran at 100 fpm. A marker was placed in the rewind roller, the press speed was increased to 110 fpm and additional markers were placed in the rewind roller after each minute for five minutes. Four print samples were pulled after each minute. Solid ink density and Delta E 2000 measurements were taken from 20 samples and the average values for each ink are shown in Table 3.1 and Table 3.3. The target Delta E 2000 L*a*b* values are shown in Table 3.2.