Dress to impress

Coating – the general process of adding a coat of clear or semi-opaque varnish to a printed sheet or web – has grown massively in the past decade.

Demand has intensified, partly because of the drop in turnaround times – coating, sealing or varnishing a sheet makes it less likely to get scuffed during post-press – and partly because the technology has largely moved inline on an offset press, which reduces the cost and eliminates the handling and floorspace overheads of offline coating. A multicolour sheetfed offset press is now rarely sold without a coating unit or an extra print unit that can be used to seal if needed, and some estimates reckon that around 75% of the UK’s general commercial print output is now sealed.

As for offset, so also for digital: there’s a growing demand for coating in digital environments. With the use of variable data printing set to massively increase over the next couple of years, particularly in the direct mail sector, more customers than ever before are asking for jobs to be protected against the damage to toner-based print – more fragile than ink-based print – caused by mailing lines and postal sorting systems.

Enduring finish
Given the growth in inline coating, it stands to reason that some manufacturers of digital presses should have looked at the same route for the purpose of coating digital print. It’s an area that Xerox recently turned its attention to, with the release last year of the inline UV coater for its iGen3. The CTi-635 unit, made by US corporation Epic, is anilox-roll based, which gives a high-quality, enduring finish. And because it’s specially made for the iGen3, it uses Xerox’s Document Finishing Architecture interface, meaning it can be programmed from the iGen’s control panel.

Likewise, Kodak has offered the Fifth Imaging Unit for its NexPresses (models 2100 upwards) since 2004; the fifth unit is more flexible than the iGen3 dedicated coater approach, because when it’s not coating, it can be used for a fifth colour. The company also offers the Nexglosser glossing unit, which is a dedicated offline coater that puts a high-gloss finish onto prints coated with a clear dry ink on the fifth unit of a NexPress. Other printer manufacturers that have taken the inline route include Xeikon with the PrintProtector, an inline unit that Xeikon claims can help to eliminate static on post-press operations.

However, at a capital outlay of between £30,000 and £65,000 – not to mention click charges and service agreements, which can figure as part of the sales agreement – the average inline coating solution doesn’t come cheap. For users to get their money’s worth, it may be necessary to coat every sheet going through the press, which may not be what the printer in question wants or needs to do. And some coaters slow down the press, despite the instant UV flash curing process. On top of all that, inline digital coaters can be inflexible. For instance, with an anilox-based system, to vary the weight of coating applied it’s necessary to change the anilox for another with the appropriate cell density. And if you’re applying a spot coating, you’ll need an anilox engraved to the spot coating pattern required, which can be expensive.

For printers running digital presses that don’t have the option of an inline coating unit, the solution is to go offline for coating. In fact, there are strong arguments in favour of offline coating even if you do run a press with an optional inline coater, according to Alan Stewart, chief information officer of K2 Systems Group. K2’s A3 Digicoater and A2 Ultracoater offline UV coating systems have been enjoying a big surge in popularity in the light of demand from the digital sector. Stewart argues that an offline coating solution allows for the ultimate in flexibility: both offset and digital jobs can be coated, and the service can even be offered out on a trade basis. “Customers and printers all have widely differing demands, so having a standalone UV coating system allows for immediate address to everyone’s needs,” he says. Interestingly, K2 began its career in coating by making an inline system for hooking up to sheetfed digital presses (it still sells the NexGen inline system), but now focuses on its offline systems for the digital market.

Flexibility is one argument, but what about costs? The capital cost of an offline coater depends on its architecture: simple roller-coaters fall in the region of half to two-thirds the cost of an inline system, where aniloxes are heavier-duty and more expensive. Cost in use, however, is not a simple equation: inline coating incurs none of the handling costs associated with offline, which entails taking a job from one machine to another, plus loading and makeready time, as well as extra ‘overs’ for makeready wastage. The cost of consumables is identical for both methods: an A3 sheet can be coated for between 0.1 and 0.25p per sheet.

Offline and nearline
The offline approach is favoured by HP, whose UV Coater is designed to stand ‘nearline’ to the press. The sheetfed device coats in gloss, matt and satin finishes with ‘virtually’ no drying time, at up to 8,000 A4 sheets per hour. The speed matches the output of most of the HP Indigo press range, so it’s not for speed reasons that Indigo has chosen to go offline: it’s for flexibility. “Finishing is an area of opportunity,” says HP senior vice president for graphics and imaging Stephen Nigro. He adds that the UV Coater has been built in-house by HP from scratch, “as we couldn’t find a strong partner”.

The third-party offline systems currently on the market vary in terms of the type of coatings they can apply (UV or aqueous, and whether the user can switch easily on a job-by-job basis), how those coatings are applied (anilox, plate or simple roller coating), and whether they can only handle all-over ‘flood’ coatings or can additionally handle selective or spot coatings. Epic Products’ offline system, the CT-660, uses an anilox system for flood or spot, aqueous or UV coatings. Prime UV’s Digital Offline UV Coating System uses rollers for all-over flood coatings. Dorn SPE’s offline coating models are all roller coaters with flood capabilities only, as are Olec’s DMC series. Kompac’s Kwik Finish offline coater is a roller-coater, but can take plates for spot coatings in aqueous or UV formulations. Equicoat’s eponymous offline system is a hand-fed roller-coater that carries out only flood coating using UV formulations. UV is the coating formulation of choice for digital work due to its ability to cure instantly, but other machines offer alternative drying solutions for aqueous coating formulations.

Just as the offline coating sector appears to be on the brink of a revival in popularity, manufacturers are beginning to wake up to the possibilities of inkjet technology in the coating world. Inkjet may provide a boost to the sector, bringing the option of in-house, truly flexible offline coating solutions to many digital printers for the first time.

Drop-on-demand
Montreal-based PAT Technology Systems has launched ‘the world’s first truly digital UV coater’, the Varstar, an offline system that applies UV coatings via five Xaar drop-on-demand piezo inkjet printheads. It’s immediately obvious how the inkjet-based application architecture brings immense flexibility to the coating process: coatings can be flood or spot without any need for hardware such as aniloxes, plates or blankets. The fact that the Varstar uses greyscale printheads means that gloss levels can be varied on the run if necessary. The pay-off for all this flexibility, as ever, is speed and format: the Varstar handles a B2 maximum sheet size at a top rate of 1,750 sheets per hour, ie, 7,000 A4 sheets per hour. And the Varstar’s price, while not too exorbitant compared with inline solutions, is high in virtue of its operational flexibility: around £86,000.

While most manufacturers of coating equipment don’t specify the use of particular coatings formulations for use with their equipment when running digital print, it’s worth noting that there are various formulations that have been specially designed to work with digital print. The difficulty in using conventional formulations is twofold: first, the microlayer of fuser oil laid over a digitally-printed sheet means it can be hard for standard coating formulations to adhere to the sheet; and second, the fractionally raised edges of toner-based print (generated by the size of toner particles compared with offset ink) means that a coating or varnish applied to a digitally-printed sheet risks looking lumpy. Last year, Fuji Hunt introduced Ultracoat UV X2, a high-gloss or satin finish varnish designed specifically for toner-based digital printers. Director of marketing Michael Tocci believes the digital market is poorly understood when it comes to varnish products: “The industry is well supported by UV coatings used in the offset process. But Fuji Hunt is committed to developing innovative UV coating solutions to the under-supported digital market,” he says. Ultracoat UV X2 was developed specifically for Xerox’s iGen3, but, Fuji claims, gives “excellent” results in offline coaters as well.
Source: printweek