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FLEXO Magazine : November 2009
28 FLEXO NOVEMBER 2009 www.flexography.org Flexographic printers/converters must continue to look for every possible area in which to save some money without compromising quality. One option is to try to improve the ink mileage---the amount of area you can print with a given amount of ink. The fact is, not all inks are created equal. Perhaps a new or existing ink vendor is claiming it has a new formulation that can improve mileage and save you money. Performing a mile- age test is a great way to evaluate these claims. When conducting such a test, it is essential to establish a constant. In the case of comparing inks from multiple vendors, the constant would be the same opacity/density and viscosity as you hope to run. START FRESH & MEASURE The first step is to make sure you are starting fresh. That means having a clean anilox in the press, and ensuring the press and the ink pump are clean. Then you need to weigh all your inks. You should also weigh the viscosity reducer. Whether you are running water-based, solvent-based or UV inks, be sure to always cut your inks with a manufacturer- recommended viscosity reducer or pH adjuster. Once you cut the viscosity down to what you intend to run at, weigh the remaining reducer again to determine how much was needed. If you want to do a good mileage study, you need to calculate the cost of the viscosity reducer. Differ- ent inks have different rheologies. Sometimes you need twice as much reducer to cut a particular ink. At a first glance, you may think that's great, but when you calculate your reducer costs, it could turn out to be more expensive. You also need to know what the percent coverage is of the inks you're testing. I prefer to use 100-percent ink coverage to keep it simple. This works well for whites, varnishes and other coatings. Try to perform these tests on live jobs. Just pump up the press with your pre-weighed inks and run. The length that you choose to run will vary depending on available press Conducting an Ink Mileage Study A Step-by-Step Approach By John Paine • Measure starting weight of ink/viscosity reducer. • Run to the desired length. 3 -- 5 pressruns optimal. • Measure the remaining ink and viscosity reducer. • Calculate total ink usage based on coverage, total length and total amount of ink consumed. Table 1. Ink Mileage Study Date: October 20, 2009 Press: 12 Job: 484746 - Snack Food Bag Anilox: A300 Plate: Rubber Roller cut to 36.25 inches print width Film: Matte OPP Vendor 1 Vendor 2 Calculations Ink A Ink B Cut ink viscosity (seconds): #2 Zahn Cup 22 23 Opacity: X-Rite 58 59 Ink before solvent add (lbs): A weighed on scale 38.5 42.0 Solvent before add to ink (lbs): B weighed on scale 17.5 17.2 Solvent after add to ink (lbs): C weighed on scale 8.5 7.5 Solvent added to ink (lbs): D B-C 9.0 9.7 Total ink + solvent start of run (lbs): E A+D 47.5 51.7 % heavy ink to start: F (A/E)*100% 81% 81% % solvent added to start: G (D/E)*100% 19% 19% Total ink + solvent end of run (lbs): H weighed on scale 25.2 22.5 Total ink + solvent used (lbs): J E-H 22.3 29.2 Calculated ink used (lbs): K I*F 18.1 23.7 Calculaled solvent used (lbs): L I*G 4.2 5.5 Run length (LF): M press reading 12,924 13,146 Area printed (sq. inches) N (M*12)*36.25 5,621,940 5,718,510 Sq. inches/pound of heavy ink: N/K 311,039 241,069 TECHNOLOGIES & TECHNIQUES
Sustainable Fall 2009