The problems of developing ink jet sheet-fed presses

At Drupa 2008 Screen and Fujifilm both showed prototype B2 ink jet presses.  These will be launched at the forthcoming IPEX trade show at the NEC, Birmingham, UK 18-25 May, 2010.  Up until now all ink jet printers aimed at commercial printing have been web-based.

We already have the smaller format B3 format digital presses, in particular from HP Indigo. These are based on Indigo’s Electroink process which is a variant of electrophotography.  So why have we never had B2 versions?  Well, having spent the earlier part of my career designing and developing photocopiers and printers based on the EPG process, I can tell you that the cost goes up rapidly as you increase the process width.  Although it is possible to build wider machines, with multiple process steps the products would be very expensive.

Fujifilm Jetpress gripper drum

In theory ink jet is better suited to increases in width.  You just stack more printheads across the machine and the costs should be proportional to the width. However there is a snag.  The ink jet printheads have to positioned very close to the substrate and the substrate needs to be moved precisely.  This means that conventional gripper drums used within offset presses can’t be used, as the grippers would collide with the relatively fragile printheads.

From the patent literature we can see that the Fuji Jet Press 720 uses a variation on a gripper drum, but this only works on the leading edge, so there is also an internal vacuum system to help keep the substrate flat around the drum.  The vacuum is switched on and off with the rotation of the drum to allow the substrate to be gripped and released.

The Screen SX paper transport - a series of vacuum tables

Again from patents we believe that the Screen Jet SX uses a series of flat trays that are circulated around the lower part of the machine by chains.  The paper is fed on to the tray by an offset-type feeder, and is held flat during the printing process using a vacuum system.  The chain drive can’t move the tables past the printheads with enough precision of speed, so a series of linear motors take over for this part of the travel.  A vacuum picker system then lifts the sheets into the output stacker.

So why bother with sheet feed if a web-based paper feed is easier?  Well, the B2 sheet paper format is the most popular with commercial print shops.  They are used to the capability of quickly changing paper from one job to another.  They also have an existing investment in finishing equipment around the B2 size.  So we expect to see a lot of interest in these new machines at IPEX and will keep our blog readers posted.