MODIFIED LABEL PRESS LAUNCHES OFFSET CARTON PRINTER INTO UV FLEXO

The versatility of today’s narrow web press lines is well demonstrated by the development by Omet of successful prototype carton packaging press based around its established label press technology.

Omet has unveiled its first UV flexo carton press at French carton printer TPG, based in Malville. Initially installed as a prototype machine last year, the 8-station press can also be used to print a range of substrates from self adhesive labels to foils.

TPG was a ‘traditional’ offset carton house running two Roland Record machines and a range of off-line sheet finishing equipment including Bobst die cutters, embossers and hot stamping units. The company’s primary market is for chocolate wraps. It services some of Europe’s biggest confectionery groups with jobs which require dense blacks, browns and reds, as well as fine golds and delicate reversed out text.

The move from offset sheet production to a complete UV flexo in-line process including die cutting, embossing and stacking, is a bold move in the confectionery market, where offset is regarded as the quality benchmark for carton work.

Chairman and managing director at TPG, Alain Bouche, concedes that selling the UV flexo process to packaging print buyers has been one of the most challenging aspects of moving to the new workflow. ‘The change from offset board printing to flexographic has raised eye-browns and possibly even caused concern among customers. We need clearly to explain our strategy since these reactions are the limited information widely available at present on flexographic printing.’

But a focused sales effort aimed at brand managers added to the TPG team’s huge enthusiasm for the new print process, has already paid handsome dividends. Today more than 40 different products printed on the Multiboard are on the shelves of stores. Some were switched from offset to UV flexo and others were produced from the outset UV flexo.

At the open day when the press was shown to selected journalists, Angelo Bartseaghi, president and chairman of Omet, predicted ‘new horizons’ for the folding carton industry. ‘I am predicting today that UV flexo technology and in-line board converting will deeply modify this market within the next ten years. Printers will discover new approaches to get back to better production profits and this with even less investment than for traditional sheetfed offset equipment. Today’s presentation of a UV flexo press inside an offset printing company is consequently a major event.’ Bartseaghi also emphasised the critical importance of close collaboration with the team at TPG in developing the prototype Multiboard into a fully production ready machine.

Working fully rotary and in-line with the print stations allows TPG to produce completed cartons in a fully integrated process from blank stock to finished product, with no work in progress, presenting the company with the opportunity to completely rethink its workflow, as Daniel Beillevert, production manager at TPG explains:

‘On-line production of labels or folding cartons required a vast staff retraining exercise. To learn a new trade, to learn not to intervene for the least think, to just verify the correct operation of the line and then not to worry – all this is a far reach from the habitual role of the offset printer. Indeed, once the setting check list is complete, production boils down to simple parameter verification.’

This process consistency has allowed TPG to focus much more heavily on QA at the pre-press level, according to Roselyne Rocherioux, quality manager at TPG. ‘Quality in flexography – the global quality of a product from the Multiboard chain – is achieved before production, since flexo line production offers immediate quality control of the finished product. This allows us to act further upstream and preventively.’

Once the press is running at its full 120 m/min production speed, it will produce 60,000 cases of finished cartons at the exit stacker an hour, supervised by just three operators. TPG can produce one million 20 x 25cm cartons a day, 8-colour, complete with varnishing print-registered embossing and cutting. Vincent Cahier, manufacturing planning manager, says this has led to a ‘spectacular’ change. ‘In the morning I draw up the material exit form for the flexo machine and plan for delivery departure that afternoon.’ This has had significant staffing implications, allowing TPG to reduce the number of hours worked by the staff operating the Multiboard to 32 hours a week while the press is running 24 hours a day, six days a week.

What is the cutoff point between offset and flexo jobs at TPG? At first, the company transferred short runs of offset jobs onto the Omet just to prove to themselves and their customers that offset quality could be matched acceptably.

But with the consistency of the UV flexo process combined with the ability to produce finished products in one pass, TPG is opening up new markets where on-demand, repeat production is called for. ‘The Omet press is most effective where you need longer runs but delivered in a series of smaller quantities, just-in-time,’ says Alain Bouche. So it is the shorter run, one-off jobs which tend to go to offset.

TPG is not talking about the death of offset. On the contrary, it believes the two systems will continue to run side by side, and it is important to recognise the limitations of flexography. ‘The quality we are achieving is very similar to offset printing,’ says Alain Bouche. ‘But if you want to go from 100 per cent to nothing you still need offset.’ A ‘safe’ lower dot range for TPG using analogue plates and manual mounting is around four per cent.

Flexo also has some clear advantages over offset in terms both of speed of make-ready. With no ink/water balance to set, UV inks are up to correct density within a couple of cylinder rotations and the process is inherently stable thereafter. The ink is maintained at a constant temperature by pre-heating the ink pans to 38-40oC. This is important, as temperature changes can affect UV ink viscosity and print consistency. The printing units are mounted on water-cooled drums to aid temperature control.

The UV lamps on the press – supplied by GEW – are rated at 240 w/cm to ensure consistent cure, particularly on the heavy whites and blacks. (To obtain a ‘luxury’ feel on the chocolate wraps an all-over white is often used as an ‘undercoat’.)

The density of UV flexo inks – supplied here by Sicpa – was the second important factor, since the chocolate wrap market demands heavy blacks, browns and reds. To obtain sufficient density on an offset press, it is often necessary to run two black towers. TPG’s existing offset presses are three- and four-colour Roland Records, so jobs with seven or eight colours had to be run through the press twice.

Specification

The Omet Multiboard 520 installed at TPG is an eight-unit press with UV dryers on the first six units and combination hot air/UV on the last two.

The Multiboard shares many design characteristic with Omet’s label presses, utilising the same basic printing units for example. The principal difference is in the unwind and rewind systems, where different tension controls for less pliable substrates are critical. Also the guide rollers are thicker (six inch diameter) so the substrate has a less angular path through the press. On the converting end of the machine the chasis is 50mm wide to give it a proper robustness in dealing with these more abrasive substrates. A moisturising unit is also incorporated to prevent the board drying out and warping.

Interestingly, TPG chose not to incorporate automatic register control on its Multiboard – usually standard on a press of this specification and which would reduce make-ready waste by as much as a third. TPG’s justification – apart from budgetary constraints – was that it wanted to be sure the press could print in register purely through mechanical stability.

Additionally there is only a single unwind. A non-stop butt splicing unit is commonly specified where longer runs are being undertaken.

Another important development for the Multiboard is a stacker unit incorporating an electronic counter, which can be rolled on or off the press line as required. The unit is based around the folder/stacker originally developed for Omet’s tissue production lines and was built to TPG’s specification.

The option exists to completely automate the post-delivery packaging operation, including strapping, wrapping and palletising. Again, this is already a standard option on Omet’s tissue packaging systems.

Quick change between jobs is achieved via cassettes which are made ready offline. The change cassettes, delivered on trolleys, carry anilox, doctor blade and in tray, delivered with the plate cylinder gears set to a pre-registered position. To make the change, the old cassette is simply slid onto the trolley and the new one slid in. A job change on four printing units takes around nine minutes.

Quick change cassette systems for die cutting and embossing cylinders are available for Omet’s labelling presses, but these are much lighter units than required for carton work. Nonetheless, embossing, cutting, die cutting and creasing units can be removed from the machine fast and easily, with preliminary adjustment carried out outside the press. KDG proofs the embossing cylinders off-line.

TPG’s press is configured with UV curing on the first six units and combination hot air/UV dryers on the last two units, followed by the embossing, die cutting/creasing and automatic rotary stacker. The unwind is followed by an AB Kelva web cleaner, Dan Mekano de-curler and corona treater. A turner bar can be included for reverse side printing. The web scanning unit is a BST system.

The Multiboard is capable of handling boards up to 550 micron thickness with and is available in widths of 420, 520 and 620mm. The press control system can recall historic and statistical data for later analysis.

TPG is looking to bring its years of offset carton experience to flexo production and nowhere is this more evident than in pre-press. TPG does all its pre-press in-house and has become skilled at altering the base process colours where a dominant colour needs to be reproduced and controlled. On the ‘Scala’ pack design demonstrated at the Open Day, a dominant warm red was obtained by modifying the magenta and cyan strengthening the yellow. Although this technique is well established on its offset cartons, TPG is not currently using process colour modification commercially on flexo jobs, although impressive technology demonstrations were on display at the open day.

TPG is mounting its DuPont Cyrel flexo plates onto Polywest sleeves using a DuPont Microflex mounting unit then an off-line pneumatic applicator. The company is using analog plates at least partially for the same reason it does not have register controls on-press – to understand UV flexo’s most basic building blocks before exploring more ‘advanced’ options. Also, since it could not justify the cost of a digital plate-making system, this would mean going to an outside plate supplier, and so losing control of the process. ‘Our pre-press department already has good curves for the flexo press.’

Another potential problem facing carton printers looking to move into in-line flexo production is the high cost of rotary tooling on the converting end of the press, particularly if they already have a high investment in off-line converting tools.

But in the case of TPG its carton production is in only eight formats, from 17.25 to 24 inch repeats, which makes it economic to purchase the full set of rotary converting tools, including die cutting and creasing, stripping, embossing, slitting and stacking.

All change

On its open day, TPG surprised even Omet with its decision to change between four jobs in a morning. TPG was running a range of typical chocolate wraps specially created by design agency KNA Studio. Rotary die cutting units were provided by Rotometrics and the laser engraved embossing units by Keller Dorian Graveurs.

To show the versatility of the press, the first job was set up printing 90 gsm paper foil labels produced on Van Leer’s Valvac transfer metallised papers using six colours, a yellow varnish on station 7 to give a gold appearance to the substrate, plus varnishing, embossing and die cutting at a production speed of 120 m/min. A particular feature of this job were the very fine reverses on the back panel.

The second demonstration showed was a job change to roll to roll process on 115 gsm top coated paper, run as a direct comparison to an offset job. It took 30 minutes to make a complete changeover of all the print units, putting on different materials and dies and change the repeat from 17.25 to 24 inch.

After machine stop, the press was changed over to print 300gsm folding cartons, seven colours plus gloss and matt varnishing followed by in-line embossing, creasing and die cutting.

The third job necessitated a change to 250gsm topcoated board, as well as number of colours – to six colours, a lacquer and gloss on the last stations – and repeat change from 24 to 18 inch. The electronic counter/rotary stacker was bolted on.

The whole machine was changed over including all print units, die cutter, creaser, embossing and stacker plus a change to board stock in half an hour.

The first was an eight-colour job which included an all-over white process and solid blacks and a yellow varnish which on top of the aluminium film creates a gold. Units seven and eight are supplied with combined UV and hot air dryers giving the option to produce waterbased golds – better than UV golds – and water-based lacquers.

The second job involved changing two colour units. Self Adhesive Labels