Revo partners mark flexo progress

Revo is a hugely ambitious flexo industry initiative which aims to ‘digitally’ standardize and automate the flexo process from pre-press to print delivery. A recent Revo masterclass at Bobst Firenze gave converters a chance to assess the technology’s progress and future prospects.

The ‘Digital Flexo’ Revo project brings together Bobst, DuPont, AVT, Flint Group, Esko, X-Rite, Apex, UPM Raflatac and converter Amerik Packaging. Set up in December 2013, the Revo group’s aim is to develop an ‘off-the-shelf’ turnkey solution consisting of the following key elements: a ‘digitally’ automated press; Extended Color Gamut (ECG) implementation with in-line color measurement; and standardization of all print elements including plate, anilox, inks, pre-press, substrates and inspection. The group is also committed to the development of new Revo-compliant products.

Matteo Cardinotti, general manager at Bobst Firenze, explained that Revo targets the ‘profitability gap’ between digital printing (up to 500 meters) and ‘standard’ flexo (greater than 5,000 meters). ‘Digital is trying to move that curve in order to increase the number of meters where it is more profitable and fill the profitability gap. This will be possible only with inkjet as dry and liquid toner have already achieved their maximum performance. Inkjet can obtain these higher speeds but it has not the same quality as today’s dry and liquid toner.’ 

Cardinotti said non-stop production was the key to moving flexo into the profitability gap. ‘We aim to remove the constraints that stop flexo being profitable. So with just seven plates there is one set up for multiple jobs. Every time you stop the press there are 40 meters of waste in the press, so non-stop production is key – to prepare the new job while the press is running. Color matching is at the software level, like digital, using a profile of the substrate. It is a digital workflow, where we start from the file and go to closed loop print adjustment to make sure you are hitting the color target.’

Press automation

The masterclass featured a 670mm-wide Bobst Revo M6 Digital Flexo press, optimized for non-stop flexible packaging production. Jobs were changed over in less than one minute and with less than 20 sheets waste, made possible by a range of automation and workflow features including automatic change of plate sleeve cylinders, automated pressure and register setting, and no need to change of inks or anilox between jobs.

A new feature is the tight integration of a bespoke AVT Helios/ SpectraLab workflow developed especially for the Revo program, which controls each point of the production cycle. During press start and make-ready AVT analyzes the printed images and sets optimal pressure on all print units; as the press accelerates to working speed, the system carries out job verification against the master PDF and starts 100 percent print inspection; and during production the system gives live print quality feedback and sends in-line spectral measurements back to production, ensuring target colors are matched.

The latter is a particularly important feature, because Revo is designed to work only with a fixed ECG ink set. Dan Pulling, business development manager flexo and color management at Esko, explained the importance of measuring color targets throughout the workflow. Pulling said Revo with four fixed colors is now achieving 65 percent of the Pantone color gamut within a DeltaE of two, and 7-color ECG is achieving 85 percent of the Pantone gamut. Revo customers have access to substrate profiles to match a range of standards including G7 and ISO.

Flexo platemaking has traditionally been a weak link in the flexo workflow, taking up to three hours to make a new plate. But Jan Scharfenberg, DuPont’s global technical manager for packaging graphics, explained how the company’s thermal processing workflow brings this down to 40 minutes, demonstrated using a DuPont Cyrel 1000ECL exposure unit and a Cyrel Fast 1001TD thermal plate processor. The company’s new Easy plate material combines a structured flat top dot with 1 percent digital dot, yielding less than two percent dots on the final material.

Dan Pullen noted that while Revo uses the same anilox for all materials, converters are able to adjust the amount of ink transfer for different substrates by changing the surface pattern on the Easy Plate material.

Food safe UV

Demonstrated on this Bobst M6 press for the first time since Labelexpo Americas was a certified food-safe UV flexible packaging workflow. Introducing the system, Federico d’Annunzio, strategic products and marketing director, flexible materials, at Bobst, explained: ‘We and our partners have engineered groundbreaking technologies that make this the safest press available – even safer than a solvent-based press. It meets and exceeds the most demanding packaging safety regulations throughout Europe and around the world.’

The key breakthrough is Bobst’s new in-line UV output monitoring system, with two sensors continuously measuring the exact UV dose on the substrate for every meter of printed roll. The press was using Flint’s low migration/low odor Flexocure Ancora ink series. Niklas Olsson, Flint Group Narrow Web global brand manager, said the ink meets 10ppb migration standards on non-evaluated substances, with optimized adhesion to a wide range of labels and flexible packaging films. ‘Revo inks are compliant to the highest level of migration testing,’ said Olsson.

Olsson went on to explain the complexity of current legislation concerning migration, which applies equally to solvent, water-based and UV ink systems: ‘There is no single European Union law about what is allowed, and the potential migration risk has to be assessed on a pack by pack basis. It depends on a complex interaction of factors including substrate type and thickness, whether there is a functional barrier, and the properties of the product to be packed. Another factor is the ink density compared to the size of the printed area, and the Revo process helps here because it requires less ink coverage per shade compared to a solid ink.’

Olsson said conventional UV inks are suitable for packs with absolute barriers – glass, metal and evaluated plastic materials – but for all other substrates low migration UV inks should be selected. ‘Note though, that low migration does not mean no migration, just as a low odor product will not necessarily show low migration.’

The Revo team aims to measure and control all factors which affect the UV curing process, including power output, reflector geometry, spectral output, UV light absorption of ink pigments, the amount and reactivity of the photo-initiator and film weight/ink thickness, and press speed and anilox configuration.

‘We also need to know the storage conditions of the printed roll and of the finished pack, the type of food or liquid, the time it is in contact with the food packaging, and the heating, cooling, sterilization and pasteurization processes to which the pack is exposed.’

Good Manufacturing Practice needs to be strictly adhered to, including quality assurance and control and traceability.

Olsson advised converters to attain a Declaration of Conformity for their flexible packaging products on behalf of the brand owner. ‘Although the ultimate responsibility is with the “person placing the pack on the market”, we all have to work together. The responsibility for compliance does not lie with only one individual member of the packaging supply chain.’

Flint has been a major pioneer of UV-LED and is currently fine tuning its LED inks for the Revo 7-color process. Olsson suggested that LED should make quality assurance easier: ‘lamp output is more easily measured, allowing superior process control in low migration/food packaging applications.’ 

Olsson went on to describe Flint’s positive experience of UV-LED in production environments: up to 30 percent higher press speeds – since LED is particularly effective on whites, dense blacks and multiple film layers; energy savings of between 50-80 percent; installation, maintenance and health and safety benefits – lamps don’t get hot, are lightweight and compact, eliminate toxic mercury, ozone and noise, and LED light is not harmful to the eyes. Lack of heat output means better performance on heat sensitive films – a particular advantage for flexible packaging and shrink films – and easier registration control for better dot quality. 

Converter experience

Having a converter as part of the Revo team to test new the technology in a commercial production environment has been key to its success. Daragh Whelan, technical director at Americk Packaging Group, has been a strong advocate of Revo since the project started, and gave delegates an insight into his experience over the last three years.

Americk Haverhill in the UK specializes in short run, fast lead time production of flexible packaging and labels for the food and cosmetics sector, with a customer base that reads like a Who’s Who of global brands. The company runs two Revo presses – a Bobst M5 530mm cylinder press and a Bobst M5 630mm-wide sleeve press. Close to 70 percent of the site’s production is now converted to Revo. 

‘Before Revo we were looking for a quick make-ready solution, and color matching was contributing to a large section of downtime.’

Whelan had already tried to implement 4-color process ‘but it returned a very poor gamut – 65 percent using seven colors. Paper substrate was mottled and a lot of pantones could not be converted. The blame game started between suppliers and it was evident that the suppliers did not understand each process, which was a surprise to me. At that point, digital printing seemed like a better option.

‘Revo was formed to tackle these issues. We spent months testing and improving the flexo print process. Today we can hit 65 percent of pantones using four colors and nearly 90 percent with seven color, and paper now prints to a similar quality to polypropylene. And this all happens by a simple press of a button.’

Americk Haverhill is now achieving make-readies of less than 20 minutes, with all jobs printed at 223 lpi/90 lcm. ‘We are seeing reduced ink coverage and an average of 0.05 deltaE from start to finish of a print run. The AVT 100 percent inspection system is recording 99 percent good production, so waste is minimal. Because we are printing less ink, adhesion is better as well.’

Revo has allowed the company to reduce lead times from two weeks to four days: ‘We can be printing within hours of receiving a file,’ said Whelan. ‘We now call Revo “a different kind of digital”.’

Revo allows Whelan to print multiple special colors in the same job, as well as printing multiple designs in one pass. ‘We actually find that Revo is more consistent than spot color. The repeatability is there. In three years, we have had no complaints and our customers are only getting charged for one set of plates.’

The consistency of the Revo process allows Haverhill to move work seamlessly between presses. ‘We can move work from one Revo press to the other without compromise,’ said Whelan. ‘We have profiled machine in the UK and put the same plates on the Bobst press here in Florence and it matched the jobs to under 1 deltaE.’

Asked to give advice to converters considering a move to the Revo system, Whelan said: ‘Get used to the machine first. It took us six months to get used to cameras controlling register and pressure and the operators saying they could do it better. Now operators won’t use the machine without cameras. So don’t get the pre-press in-house before you understand the press.’ He added that in-line lamination had been added seamlessly and with no need to take on extra staff.