Developing high speed inkjet

There are three technologies at work, continuous inkjet from Kodak and available through its Prosper heads and presses; drop on demand thermal – which is the core technology behind the HP PageWide presses – and piezo drop on demand, the technology used by every other supplier from FujiXerox to Canon Océ, Ricoh/Screen and KBA. All are using water based inks, some with pigment colourants, some with dyes.

The first applications for this type of inkjet has been as replacement for laser printing in transactional print. The appeal was a lower cost of operation and the opportunity to print colour, which meant the elimination of preprinted litho reels. The colour requirement is not demanding: highlight text, tint blocks, logos and small images. Running on uncoated papers, this has not proved a problem, though more expensive pigmented inks will offer a brighter result.

If this was not a match for litho quality, the saving from no longer discarding out of date preprint reels, waste and storage costs has made the quality more than acceptable. If inkjet has a problem with drying when there is excessive water from the ink present, the low coverage in this type of work ensured that the issue was manageable. Likewise in books, printing black text with small amounts of colour for graphics in textbooks and journals, is well within the capabilities of the technology.

Educational publisher Pearson has endorsed the quality of HP’s technology with the result that many of its suppliers have made investments. These have in turn promoted the print on demand benefits to other customers. If flaws can be detected in tints, publishers of academic books are willing to put up with them for the advantages in terms of print on demand and reduced stock levels.

The question for book printers is whether to run with inline finishing or to rewind the reels and present these to a standalone finishing line.

There is a gain in flexibility, but also an increase in costs, and the market appears evenly divided. Earlier installations with HP PageWide T300 presses ran inline with Muller Martini Sigmalines to fold, cut and gather sections into book blocks for feeding a binder.

Magnum from Canada developed a unit for wider presses able to deliver multi lanes of book blocks. The Timson T-Fold technology has been acquired by Kolbus and will connect inline to any inkjet web. Manroland Web Systems has used experience in handling high speed webs in the FomerLine for book block production and the FoldLine for newspapers and mixed product delivery. Muller Martini will also operate in offline mode as does the Hunkeler Bookline. Some more recent users have preferred to operate offline, particularly when printing colour as they say this allows the web to dry completely and the finishing lines run smoother.

Few installations in either segment are running with reel splicers. This is not a problem in transactional areas where the convention is to stop to offload a printed reel at the same time as loading a fresh reel, nor in books where the advantages the technology brings in terms of print on demand and short production runs mean that there is no imperative for continuous running. But if continuous feed inkjet is to break out into more mainstream commercial print sectors, non-stop printing will be essential.

It is happening. The press suppliers have devised ways to either move inkjet heads away from the web or lift them above it to avoid damage from the splice striking the inkjet array which is positioned just 1mm from the paper.

At the end of last year HP announced a deal with Contiweb to build reel stands for its PageWide T300 and T400 series machines. This will be a preferred partnership, not an exclusive one. Megtec has already supplied reel stands for HP presses in the UK, and in Switzerland where a HP PageWide T410 is being used for newspaper printing. Italian supplier Tecnau has also developed a reel stand, which like Contiweb will offer different levels of automation. Hunkeler in contrast has stated that it will not have an automated reel stand, but that of course may change.

If the mechanics of reel handling have changed in response to the need for greater productivity, so too has press design. The first inkjet machines took their cues from the laser machines they replaced, switching one imaging system for another. They retained the turner bars and twisted web paths of these style of presses, where tension was introduced only at the point of printing. Inkjet needs the web to be under both control and tension, hence the preference for an arched web path adopted by HP and others in the narrow web area.

HP has changed the web path on each of its presses to date and others have done the same, seeking the ideal path for quality and especially for drying the paper. More recent presses are starting to look more like conventional heatset web presses with simplified web paths and the paper under constant tension.

The Ricoh VC60000 (essentially the same press as the Screen TruepressJet HD) typifies the new style. The first generation press clearly showed its roots in the IBM Infoprint laser printers, units could be positioned at right angles to each other for example. The new press can also be installed like this, but it is a much larger machine with a much straighter path.

The paper will be moving faster and greater space is needed to dry it. Drying is infrared and hot air is needed to shift litres of water a minute without harming the paper. Ricoh applies a priming coat to the paper to provide a consistent optimised surface to print on and uses a high pigment ink to minimise the water needed. Screen, which is selling the same machine under its own badge, expects to sell without the priming system because developments in paper and inks will overtake the need for priming.

Presses are being used for direct mail and commercial print applications, calling off small batches of catalogues specific to a retail outlet for example, or for magazines where the cover is changed according to a subscriber’s profile. At one Swedish user a single Ricoh VC60000 is producing the volume that six older Xeikons were needed to print.

The Kodak Prosper 60000 also looks more like a heatset web press than a computer peripheral. It has the highest line production speed at 300m/min, thanks to the intrinsic speed of its continuous inkjet technology.

There are two versions: the Publishing version for newspaper and books, and the Commercial quality version with an additional drying section to cope with higher ink coverages that the quality demands. 

Sales and installations are starting to roll: there are presses in North America and in Europe producing direct mail and customised catalogues, others are printing newspapers and books. The same core technology is also used in hybrid applications, often on newspapers to print a promotional code, lucky numbers or similar. It is also used on web offset presses to add an element of variable information. One customer has added Prosper heads to a Goss M600. The litho press prints the majority of a flyer for a network of corner shops; the Prosper heads print details of each shop, location opening hours and special offers for that shop at press speed with no discernible difference in quality to show two technologies have been used.

Another user has added the heads to the CutStar unit feeding a Heidelberg Speedmaster. It allows production of a mailer complete with customer specific letter and litho quality brochure which can go directly in the envelope without the wastage associated with preprinting the litho brochures and finding there are more than is needed once data for the mailing arrives.

Market leadership in high speed inkjet printing is divided between HP and Canon Océ. The latter can point to legacy installations of laser print machinery that has been replaced by inkjet. It has now developed the PageStream as a press which can deliver high quality colour directly to standard offset papers. It has shipped the first to a German printer who has been producing glove box manuals for cars (inkjet is a far more suitable process for this than toner which is apt to soften and block pages in heat), and bespoke catalogues for online retailers.

The secret for Canon Océ lies in the software and the ink formulations to hold the colour on the surface of the paper rather than allowing it to sink into the fibres. The company is also funding a seven year research project with an Austrian university into how fibres swell and deform in high speed inkjet printing.

The answer for HP lies with a priming coat applied to the paper ahead of the inkjet heads as well as encouraging development of inkjet suitable papers. It too has been pushed into more demanding areas of print quality, led by books and direct mail. It will start the roll out of its High Definition Nozzle Architecture print head this year. This has an additional line of ultra narrow nozzles between the twin rows of 600 nozzles per inch which give HP PageWide presses a 1200dpi resolution.

In high quality applications this is not always enough to render smooth flesh tones or areas of even colour without artefacts. The extra row of droplets smooths out any graininess.

The piezo printheads operate at 600dpi or 1200dpi, while Kodak does not provide an equivalent figure for its prosper heads, only that quality is equivalent to 175lpi litho. Quality is not solely an issue of resolution, droplet size and placement accuracy have an impact as well. Too large a droplet may merge with its neighbour causing unwanted artefacts, yet too small may also result in patchy quality as the smallest details are not rendered.

There is also the issue of blocked nozzles leading to tell-tale stripes down the paper. Developers deploy scanners to pick up these issues and compensate for them by using neighbouring nozzles until the job ends and the heads can be cleaned. Printheads are a consumable item: HP heads are easily replaceable and will require regular changeover; Prosper heads are longer lived and are returned to Kodak for refurbishment; piezo heads may last for a year or more before replacements are necessary.

This is not going to stop the rise of inkjet. The developers do need to reduce the cost of the ink which remains eye wateringly high when ink coverage reaches commercial print levels. Users have become used to applying different ink profiles according to the application; different screening and use of GCR can reduce the amount of ink used.

Paper also remains an issue, caught in the trap between demand making it unattractive for mills to dedicate high speed paper machines to producing, yet too expensive to encourage printers to switch to inkjet printing. The arrival of machines like the HP PageWide T1100S, a 2.8 metre wide press with 260 printheads for corrugated preprint production, as well as take up by newspapers in place of web offset, will tip the balance, encouraging paper producers that inkjet is going to be a big opportunity for them.