Printing blankets are a vital, yet often overlooked component in the print process. Trelleborg product area director Thomas Linkenheil provides insight into the importance of selecting the right blanket for the right application
Printing blankets provide the essential link between the image on the plate and the substrate, whether it’s paper, board or even plastics, impacting on everything from print quality, cost, wastage, efficiency and even carbon footprint. Considerable development goes into developing blankets for different print processes, and it can mean the difference between a good return on investment, or working at a loss.
One of the greatest false economies in the industry is the use of blankets that reduce press productivity. The capability to recuperate from a ‘smash’ (a blanket becoming debossed or compressed, due to excessive pressure being applied) varies hugely, depending upon the manufacturer and product.
Printers need to be aware that cheaper, easily damaged blankets inevitably need replacing more frequently, causing more downtime. The blanket is the medium by which the image is transferred – if you falsely economise on the blanket, you also economise on finish and productivity.
If a blanket is damaged as a result of a smash it can take 30min to change, which can cost the business hundreds of pounds and missed deadlines.
An increasing problem for printers is the lack of knowledge of the variety of blankets available, and their capabilities. This generally means print buyers can find themselves needlessly compromising on quality, and occasionally even over-specifying. Blanket technology is constantly evolving, and the optimum solution, which could improve all-round process, might already be available.
There are many blanket characteristics that can influence the type of blanket specified and subsequently improve the print process; it is impossible to find a ‘one size fits all’ solution across the whole range of substrates and press conditions.
Some degree of compressibility is a feature of virtually all blankets, with widely different characteristics and performance. The wrong blanket, chosen on price rather than performance, can quickly lead to higher operational costs.
The compressibility, carcass construction and top rubber compound of a printing blanket all affect paper feeding and release, as well as paper wastage, web breakage and print registration problems, all of which will reduce productivity.
The properties of the compressible layer and the carcass structure of the blanket allow for optimum pressure absorbance and better smash resistance. The ability of the blanket to rebound over time influences its life expectancy.
For sheetfed processes, widely used in packaging, the thicker and more complex substrates can damage an incorrectly specified blanket. A higher flexibility blanket with greater compressibility – that will adapt to changes in substrate format without the need for frequent replacement – is often required.
The chemical composition of the top surface compound influences the dot reproduction and quality of ink transfer, as well as providing the best combination of grip and release to suit a specific process. It also affects the frequency of the wash cycle through reduced ink and paper build-up on the top surface; high frequency wash cycles waste energy, paper and machine time.
The impact the choice of blanket can have on energy consumption and press overheating is often underestimated. The polarity of the top surface compound, the carcass design and top surface finish of the blanket are also significant. By choosing a blanket with the correct dynamic and feeding characteristics for a specific press installation, the power absorption and temperature of the press and cylinders can be controlled. This is particularly important in web offset presses.
Changing between positive feed and negative feed blankets, and making the correct tension point adjustments within the printing units, feeds, chill rolls and the folders, allows the printer to optimise energy consumption. This also helps obtain high quality results, with minimum wastage and reduced web breaks.
Printing blankets clearly have an important role in the quality and efficiency of printing in the packaging industry. The characteristics of the blanket composition, compressibility and surface characteristics directly affect the print process. However, by specifying the right blanket for the print requirements, the highest quality results with reduced operating costs can easily be achieved.
Printing blankets is a product area within Trelleborg Engineered Systems, part of the Trelleborg Group, based in Sweden. With its Vulcan and Rollin brands, the company provides offset printing blankets for the web, sheetfed, newspaper, business forms, metal decorating and packaging markets in 60 countries.
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