By Sean Smyth, Print and Packaging Analyst
When I was approached by Contiweb to write about their Thallo litho press technology being a competitive option to flexo to print flexibles, I was a little surprised. While offset lithography is by far the most widely used printing process in use across the world today, it is not widely used for flexible packaging. It dominates newspapers, magazines, books and commercial print, while in packaging it is widely used to print cartons, litholam and microflute corrugated, metal sheets and labels (not just offset units in a flexo pressline). But it is not on the radar of many flexible packaging converters, perhaps this should change.
Litho is a more complex process than flexo, particularly in terms of ink control involving a train of rollers that accurately meters the ink film weight allowing adjustment across the web. Litho ink is a viscous paste, it is pumped into the ink duct and it is transferred down a chain of distribution rollers onto the ink receptive areas on a plate (that is right-reading by the way, so easy to check before mounting). There is no anilox to deliver a constant amount of ink to the plate, instead there is a flexible doctor blade held in tension against the metal fountain roller. The pressure can be reduced by an ink key to allow more ink across a particular segment and this profile is adjusted to match the image coverage on the plate. In make-ready there is automatic ink key adjustment and plate loading taking a matter of just a few minutes to change over. The fast change over, with no waste ink (spot colour ink can be scooped back into a bucket and stored) making litho well suited for short and medium runs.
This fast set-up is probably the main strength of web offset litho, together with fast running speeds to print very high-quality graphics with razor sharp text and linework. Litho prepress is much simpler than for flexo or gravure, with new plates a fraction of the cost of flexo or a gravure cylinder. They are recycled after use (for cash), new ones made for a reprint that means changes are very easy, including promotional messages.
Web offset presses used in graphics are aimed at paper products. These machines feature precision plate and blanket cylinders arranged to allow double sided printing at very high speed. This limits the flexibility of size, which is not usually a problem for books, magazines or newspapers as the size is fixed. But a fixed cut-off (repeat) is useless in flexible packaging where pack sizes vary and customers will not pay for any waste, with extra laminate which cannot easily be removed during subsequent conversion of form-filling. So, litho was not in use as flexible packaging demand exploded, because the presses could only produce a fixed size. In business forms there were single sided web presses, usually less than 500mm wide, and the plate and blanket cylinders could be swapped out to change the cut off for different form drops (again the repeat – yet another example of different terminology being used to describe the same technical feature in print). For a six or eight colour press this would take hours, with much adjustment needed to set up the correct pressures, so print companies would plan to only change the drop every couple of weeks or so. Then a new press was developed for the continuous stationery and forms market from Drent Goebel, the VSOP (variable sleeve offset press). This did not change out the whole cylinder mechanism but used a series of sleeves to change the length of the image as needed. So, the drawback to litho was removed. But at the same time demand for forms and stationery plunged as the world went digital, and the press manufacturers looked for new market opportunities and sold several machines into flexible packaging manufacturers.
Counting existing VSOP systems as well as Contiweb’s Thallo, there are almost a hundred web offset presses with variable sleeve technology in the field today for flexible packaging. They are typically 7 colours and may feature a flexo reverse white postprint unit with UV or electron beam curing inks that work in the same way as flexo and gravure alternatives. The Contiweb Thallo now sells in three widths, with a growing list of flexible packaging companies making money and improving their service to customers.
As a consultant my objective is simple. I help companies (throughout the supply chain) make money. While using litho may not be the solution for every company, the flexible packaging market is changing with customers demanding shorter runs and faster turnrounds. This results in having to handle many more jobs per shift and the utilisation of presses falls with more downtime and waste, making the plant less efficient. To succeed, you can’t continue in the same way when market demands change. The strengths of litho will be useful to many flexible converters looking to be more responsive to their customers while making more money. Thallo is well worth taking a good look at.
Dr. Sean Smyth is a print and packaging consultant, both independently and on behalf of Smithers Pira. He is also a trade journalist in the UK and North America. With over 30 years industrial experience, he provides hands-on consultancy, helping companies make money through implementing the appropriate technology for their business. After completing his doctorate in Chemistry he joined the industry as an ink chemist before moving into printing and packaging companies where he held a series of senior technical and managerial roles. He has owned and managed printing and packaging businesses in the UK and been involved in many investment decisions over the years. He regularly speaks and acts as Chair at conferences on printing markets and technology, including Smithers Pira Digital Print for Packaging in the USA and Europe. He edited Digital Labels & Packaging magazine from Whitmar Publications, for whom he acts as Group Technical Editor. Beside his Ph.D. Sean also holds an MBA and is used to providing strategic advice to publishers, packaging and print companies together with suppliers (equipment, consumables and software) across the print, packaging and publishing supply chains.