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FLEXO Magazine : January 2008
-- - - - -- -- -- for the inclusion of many features that require separate passes in offset, such as hot- and cold-foil stamping, rotary screen and ro- togravure print stations, backside printing and multiple emboss- ing, scoring and diecutting operations. Rotary die cutting deserves a special mention. Long thrown up as an objection by offset printers, due to the higher price of rotary dies (when compared to steel rule dies typically used in platen diecutters), it is in-line rotary diecutting that unlocks much of the economy of the web-fed process. However, when addressing the quality aspect of folding carton production, it is die cutting that accounts for the most important physical feature of a carton-a consistent score. Inconsistent scores are the chief cause of down- stream processing problems, since folder-gluers and filling lines depend on the score's consistency to operate reliably at high speeds. A rotary diecutter delivers more consistent scores than a flat- bed diecutter, period. This is because steel is more precise than wood. Also, from the engineer's point of view, imagine the diffi- culty of holding an exact dimension across the entire surface of a flat die, compared to holding it across a single line (the tangency of two precision-ground cylinders, concentric within +/- .0003 of an inch). Then, take that flat die and bang it up and down 200 or so times a minute, while you smoothly roll the two cylinders together in precision bearings. Try to think of a single precision thing made of wood; now look at an airplane, a watch, or an au- tomobile. So, it stands to reason that the quality of the die-cut carton, equally important as the graphics, will be superior when done with the rotary die. At this point, if you accept this argument, we have printed quality which is by and large Uoffset-equal" and, better-quality converted cartons. Now, on to the business case. FLEXO ECONOMICS While we in the printing business like to pat ourselves on the back for producing Van Goghs on a daily basis, and our customers demand it as such, the stark reality is that we are in a commod- ity business. Service and flexibility are important to consumer product companies (CPCs), but in the end cash is king and price is perhaps the single most important factor in a print buyer's world. So, it is imperative that we produce our products with a minimum of capital, labor and material consumption if we want to prosper. In-line flexo printing delivers exactly that-high-quality cartons, produced in the most efficient manner possible. Productivity, paper savings and labor savings give the converter a means to compete and thrive, meeting customer demands while generating a profit for himself. Productivity. As an engine of economic growth, productivity is hard to beat. Every economic expansion since the industrial revolution can be traced, in some degree, to increases in worker productivity. This is the essence of making more with less. When we apply this concept to printing and die cutting folding cartons, it takes the form of throughput speeds, minimal work-in-process inventory, and single-pass production. These are the three main supporting characteristics of the web-fed process. First, consider throughput speeds. Modern flexo presses typi- cally print and diecut cartons from a web at 500 to 1,000fpm. Sheetfed offset presses, by contrast, can print upwards of 12,000sph, but diecutting is still limited to 6,000 sheets or so for many boxes. Thus, the net throughput is held to the speed achiev- able by the diecutter, irrespective of printing speed. It is difficult, at first glance, to equate lineal feet per minute to sheets per hour since the units of measurement differ. In order to properly compare the two, one must convert to a common measurement. Square inches of board is a convenient way to do this. So, for example, we can compare a 26-in. wide in-line flexo system to a 28-in. x 40-in. sheetfed system, it appears as follows: 6,000 sph 13,440 11,700,000 672,000 NOTES: 1.) 6,000 SHEETS/HOUR ASSUMED TO BE DIECUTTER SPEED. 2.) BOTH CALCULATIONS USE A 50-MINUTE HOUR. Clearly, other measures could be used to increase sheetfed's output. A second diecutter would increase throughput to 12,000sph, but would require additional capital and labor, or addi- tional shifts could be added. Either way, the converter must spend more to achieve the same output. This represents a net loss of profits, and/or increases the price the converter must charge for his products to stay in business. Work-in-process inventory and single pass production are closely related, and have a pronounced impact on productivity. Simply stated, a single machine that produces gluer-ready blanks results in less WIP, as products do not have to be transferred from machine to machine. This enhances productivity and thus profits. Paper Savings. Substrate costs, whether a converter is indepen- dent or affiliated with a paper mill, represent the biggest single chunk of cost in the making of a folding carton. This inescapable fact makes paper savings an extremely important part of contin- ued profitable operations. A flat sheet imposes limitations that simply do not exist in the web world. Firstly, the sheetfed process requires gripper edges to transport the paper through the process. Gripper edges are unnecessary in a webfed press, since the web, once fed into the machine, pulls itself through. Second, a web offers opportunities for tighter nesting of cartons than often don't exist, or don't exist to the same degree, in a sheet plant. The dia- grams on page 48 illustrate this point. It has been estimated that webfed folding carton converting has the potential to save between 8 percent and 11 percent on substrate usage, across a wide range of sizes and styles. This sav- ings drops directly to a converter's bottom line, without any other measures being necessary. Labor Savings. With most cartons produced in a single pass, flexo printing affords a considerable labor savings. In an age where we North Americans are competing with very low labor www.flexog ra phy.org JANUARY 2008 - FLEXO