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Flexo Sustainable : Fall 2008
Figure 4: Flexo/Gravure Average Printed Substrate Comparison. (Source: DuPont Life Cycle Assessment Flexography & Rotogravure Printing Public Report, September 2008) compared to flexographic printing. Rotogravure requires a lower viscosity/higher solvent content ink mixture to allow for transfer to the etched recesses in the imaged cylinder and transfer to the substrate. Rotogravure printing is also set up with a different station for each color, with complete drying required between stations. This requires increased electricity for the larger overall press and higher energy for drying than a comparable flexographic printing press. The increased air for drying also leads to higher fuel use in the thermal oxidizers for rotogravure. Using an Aligned Plastics Model1 to account for the inherent technology differences between flexographic and rotogravure printing, aligned models were developed based on printers only using film (plastic) substrate. Only printers using 95 percent or more film substrate were aligned to avoid any differences due to printing paper. The UCTE average European electricity grid and the average European heat, natural gas, at industrial furnace Ecoinvent™ models were selected for the aligned models. Figure 5 shows the GHG emissions and non-renewable energy consumption for the weighted average aligned models. Using the aligned models, the study reveals that flexographic printing has 51 percent lower GHG emissions and 48 percent lower nonrenewable energy consumption than gravure printing when comparing them for film substrates. Solvent vS. thermal Platemaking2 It’s evident from the previous graphs that the environmental impact of image carriers on the printing process is dwarfed by the other printing input burdens. Substrates, inks and the processes associated with them at the print stage, dominate the environmental footprint for converters. But, this does not mean that there aren’t 10 savings upstream at platemaking. Clearly, all responsible participants in the value chain are looking for multiple ways, however small, to improve their environmental footprint. In order to study the impact of different solvent recycling practices, participating tradeshops provided data on their yearly consumption of fresh solvent and surrogate solvent and their yearly still bottom production and consistency (residual solvent content). Electricity consumption data were derived from characteristics of their stills (installed power) and their distillation practices (e.g. number of cook-downs and warm-ups). Based on the tradeshop inputs and their yearly plate throughput by plate type, a model was developed to allocate all inputs and outputs to specific plate thickness taking typical target reliefs into account. The burden of the manufacture of the solvents is important in determining the overall burden of plate preparation. This along with surrogate solvents—typically a high boiling hydrocarbon that stays in the still bottom allowing for more complete recovery of a solvent—were considered in this study. For the solvent platemaking processes, drying and solvent recycle are the major contributors to non-renewable energy and greenhouse gas emissions. Typical industrial residual solvent contents in the still bottoms discharged range between 5 and 20 percent by weight. The participating tradeshops are a representative subset of the industry covering the typical range. The processing step, including manufacture and combustion of the developer roll, dominates energy and greenhouse gas emissions in thermal platemaking process. Figure 6 details the non-renewable energy consumption and greenhouse gases for digital solvent and digital thermal systems at imaging. The average digital thermal process has 60 percent lower nonrenewable energy consumption and 51 percent lower greenhouse gas emissions compared to the average digital solvent plate imaging processes for a 0.067in. plate. LCA insights reveal Figure 5: Aligned Plastic Substrate Flexo/Gravure Comparison of Cradle-to-Gate Impact Contribution by Input. (Source: DuPont Life Cycle Assessment Flexography & Rotogravure Printing Public Report, September 2008) Sustainable FLEXO FALL 2008 www. f le xomag.com that recovering as much solvent as possible (5 percent residual), actually results in a higher environmental impact due to the increased electricity
End of Year 2008