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FLEXO Magazine : November 2009
www.flexography.org NOVEMBER 2009 FLEXO 29 time and other factors. I've run everything from 30,000ft. to 100,000ft. The largest I've ever done was a 700,000ft. run. When you do a run that long, you have to add ink to the press while you are running. In that case, you have to go through this process of weighing the inks and viscosity reducer, so that you always know how much of each you are adding --- throughout the entire run. Shorter runs do tend to have more variation than longer ones. Try to keep the operators consistent throughout---don't go over shifts. Watch everything. Don't allow operators to add ink or viscosity reducer/pH adjuster when it isn't needed. That will throw off the ink chemistry or viscosity. If additions are made, document their weight and include it in the calculations. CALCULATIONS Once the printrun is complete, weigh everything left over. Empty the doctor blade chamber or pan and include that in the final weight. Make sure you don't do a wash up and contaminate the mixture with cleaning chemicals. Calculate how much of the press return is heavy ink and how much is viscosity reducer or pH adjuster. This lets you know how much ink you used and how much viscosity reducer you used, which is important to calculate the cost of the applied ink. Determine exactly how much material you printed and determine your square footage using a spreadsheet like the one in Table 1. Using this information you can calculate how much substrate you can print with a pound of ink, or, if you like, how much ink it takes to print 1 million square inches. Table 2 shows an example financial analysis. This includes the cost of the ink per pound. Remember: Just because you are going to a less costly ink doesn't always mean you are going to save money. In that example, Ink 2 is $1.95 per pound, as op- posed to Ink 1, which is $2.10. But the mileage is so much better with Ink 1 that it shows much greater savings. Not to mention, the solvent cost of Ink 1 is lower, adding to the savings. SOME POINTERS I prefer to do multiple runs using different aniloxes with the same line screen and volume. One data point is just that---one data point. Recently I conducted a study using three different presses. The anilox rolls were all, theoreti- cally, engraved to the same line-screen and audited to have about the same volume. In reality, as you run rolls in the shop, you have different levels of wear that affects ink volume and transfer. Each press produced a different result. That's why, the more trials you can run, and the more data you collect, the more accurate your average mileage will be. I do recommend conducting at least three mileage runs. I prefer to do five when I have the time. For example, I evaluated a mileage study conducted com- paring two competing white ink formulations. After the first run, the new ink showed a 23 percent increase in mileage---every- one was ecstatic! Then we did the second test on another press and it was only a 12 percent increase. After a few additional tests we determined the average was somewhere in between. All the things that cause variability in flexo printing in the first place can cause variation in the mileage study: the anilox line screen, the plate to substrate impression, the plate to anilox impression, the type of plate. The dyne level of the substrate can pull more or less ink off the plate too. This is why it is important to run these studies on the substrates you run the most and take all variables into consideration. They weigh into financial decisions. Finally, if you are actively looking to improve mileage and save money on your ink costs, one way is to go to a finer anilox roll. This works well if your current inks have excellent color strength and you find that you often need to extend them out, as there is a recurring cost associated with that. Of course, you have to make sure you are still getting the same L*a*b* values. Slight changes to ink color formulations may be needed when apply- ing a thinner ink film. This is especially true if you're changing to a completely new ink system. Adding to or changing your anilox inventory isn't cheap, so the numbers have to show a return on your investment. Running a series of mileage studies will help you determine if this is the right move for you. ABOUT THE AUTHOR: John Paine has been involved in the flexographic printing industry since 1992. He is an R&D engineer working with C-P Flexible Packaging in York, PA. He is council leader of FTA's Wide Web Leadership Council and a member of FLEXO Magazine's Editorial Advisory Committee. He can be reached at firstname.lastname@example.org. Table 2. Ink Usage Comparison Ink 1 Ink 2 Average sq. inches/pound of ink (1) 278,411 229,077 Pounds of ink per million sq. inches 3.59 4.37 Cost per pound of ink $2.10 $1.95 Heavy ink cost per million sq. inches $7.54 $8.51 Pounds of cut solvent added per million sq. inches 0.84 1.09 Cost per gallon (2) $5.00 $5.00 lbs/gallon (3) 6.75 6.75 Cost per pound $0.74 $0.74 Solvent cost per million sq. inches $0.62 $0.81 Total cost of cut ink per million sq. inches $8.17 $9.32 MSI Printed per Year 200000 200000 Annual Ink Cost $1,633,301.82 $1,863,965.80 Annual Ink Savings $230,663.97 $230,663.97 NOTES: (1) Average of three mileage studies performed as of June 29, 2009 (2) Price from March 2009 (3) Calculated based on the solvent ratio and the specific gravity of each solvent in the blend TECHNOLOGIES & TECHNIQUES
Sustainable Fall 2009