| How advisable are large web widths in web offset printing? |
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Just as widths in publication gravure printing have changed, so the trend in the commercial web offset sector is toward web presses that are wider and faster than ever before. Only very moderate improvements in speed are possible, however, making the width a much easier variable to experiment with when it comes to increasing capacity. If web widths in excess of two metres are to be mastered at high speeds while delivering an acceptable quality of print and level of wastage, suitable technical solutions are vital. These might include reducing the cylinder gap, individual drives, new storage techniques, the use of new materials (CFK material), special rubber blankets, precise temperature control where the printing units are located or the use of ink doctoring systems. The trend towards ever wider web widths is not least the result of the tough predatory competition on the market. Printing plants are finding themselves forced to cut costs and streamline production. This is done by boosting the output of printed products while at the same time reducing the investment and labour costs involved. Positive aspects ... The advantages of wide commercial web offset presses are obvious. When utilized to capacity (including the possible web width), they are – for an individual A4 page – fundamentally cheaper to run than 6 or 32-page presses (lower costs per 1000 copies). Of course, such capacity utilisation assumes that there are sufficient jobs to work on. The investment and financing requirement does not rise linearly with the capacity of the web offset press and is lower in terms of the number of pages than for narrower machines. Similarly, the personnel requirement does not normally increase in line with the width of the press, which has a very positive impact on labour costs. In addition, higher page counts in the individual subsections mean fewer stations and correspondingly fewer personnel in the post-press department. Considering total production, a little less wastage is produced, particularly with higher print runs. On top of this come savings in consumables and energy. Furthermore, new reelstands for reel diameters of up to 1500 mm allow further savings in paper due to the reduced need for reel changes. With sections of up to 96 pages, high-volume web offset presses represent serious competition for publication gravure printing where print runs or page counts are high. ... and negative ones too The high print volumes required to make large commercial web offset presses viable to run first have to be acquired in the shape of orders. And, since many such commercial printers have gone wide in the last few years, the price war for suitable bulk print runs is both intense and predatory. Nor does the general trend towards smaller runs always help high-volume presses. Although annual print volumes are still on the rise, run lengths are being reduced due to more and more new special interest titles or regional publications for ever smaller target groups. Low page counts such as 8 and 12-page publications often cannot be produced economically on 64, 80 or even 96-page systems and the flexibility of these commercial web jumbos is similarly restricted. Complexity rises with width As widths increase, so too do the complexity of the production process and the demands on the expertise of the operating personnel. The probability of a tear in the paper web rises, for instance, the ink-water balance requires greater sensitivity, while greater ink misting at high speeds and the build-up of ink on the sides of the rubber blankets when printing on partial webs are among the side-effects noticed by web offset practitioners. More attention also needs to be paid to the choice of inks to use and the conditioning. If all the processes that take place are to be monitored and reliably controlled, a high level of automation is essential – and this increases the number of potential sources of interference and the need for suitable back-up solutions. Pressure to meet deadlines could otherwise cause severe problems. The greater the page count of the product in the folder, the greater also the physical displacement of the individual pages. This causes a deterioration in the accuracy of folding, which can in turn lead to a round spine and creases. Double parallel folds or delta folds are vital from a certain product thickness. The high page count of the sections means that fewer features can be realised in the post-press department, e.g. labels or inserts (CDs or the like). In addition, the enormous productivity of the web presses demands high-performance product disposal systems that must be automated as much as possible. Finally, large widths also mean that the corresponding investment in infrastructure (paper store, fork-lift trucks, underfloor conveyors, plate processing line etc.) has to be factored into the costs. No one-size-fits-all solution High-volume web presses are not the be-all and end-all in every case, nor the panacea for any crisis that a printing plant may already have identified. They only make sense where print lengths and the corresponding page counts require huge capacities. Smaller machines, particularly the flexible 16-page web presses, still have their place, especially if 8 and 12-page production jobs frequently come in as well as 16-page jobs or the printing plant wants to offer additional product finishing as a special feature. Lower page counts, well above-average print qualities, high grammages, sheeter production, special fold variations or inline finishing are the terrain on which narrow presses feel at home – and jumbos find the going hard. Intensive analysis of the job structure is thus essential before any decision on a particular press is made. The one-size-fits-all approach has always been of little help. The most economically viable press – whether large or small – for the particular job structure or existing client base is still the best choice today. |
