Tech Talk: Finishing Options: Rollfed Inkjet Book Manufacturing
Nearly every North American book manufacturer that hasn’t already jumped into rollfed inkjet printing has given it serious consideration, and many of those say it’s only a matter of “when” not “if” they’ll adopt this technology for short-run work, in most cases to augment their conventional offset printing.
There are a host of considerations for any book printer planning to enter the production-class, rollfed inkjet market, such as inkjet press quality, speed and web width. IT competency, workflow tools and operator skills are needed to drive the press effectively. But, finishing is key.
Deep and careful consideration of appropriate finishing for the inkjet rollfed press should be equally important to press deliberations, because most legacy postpress is not particularly well-suited to the short-run, quick-changeover, low-waste requirements of profitable inkjet book production.
It’s helpful to segment rollfed inkjet by production band (fpm) and roll width (20˝, 30˝, 40˝+), as different feeding and finishing tools are available and best suited to each. Most comments here apply to 20˝ and 30˝ web widths up to 650 fpm.
In-Line Versus Off-Line Finishing
Most 20˝ inkjet web presses today run between 200-600 fpm. The first postpress decision one faces is whether to finish in-line to the press or run the press roll-to-roll, then finish pre-printed rolls off-line. Each has advantages, and the final decision depends on how you weigh the factors.
Inkjet web presses like to run at full-rated speed, and they don’t like to stop. Most agree that roll-to-roll, on-press is the most reliable way to optimize press productivity: you avoid finishing-related stops (jams, stacking issues), and you eliminate the white-paper waste associated with press rampup during restart.
In-line finishing at 20˝ press speeds is quite stable, but it can get tricky as you move to the outer limits of the media range (≈40 gsm at the lightweight end, ≈250 gsm at the heavyweight end). A lightweight web under tension may run perfectly through an inkjet press, but reliably sheeting and stacking at press speed can be a challenge: how inkjet-printed sheets behave after cutting is influenced by tensile strength, length and direction of the paper fibers, fillers, static, moisture content and other variables.
To complicate things further, different lightweight sheets with the same gsm can behave very differently, so even after you dial everything in for stable finishing on one stock, you might be back to square one on the next job with a different sheet or mill lot.
So, there are genuine advantages to operating postpress near-line, at an optimal speed for the specific media. In most cases, the extra material handling (carting rolls from one system to another) pales in comparison to the low throughput that can result from repeated stops-and-starts.
Of course, in-line finishing presents clear advantages for some applications, especially as you move up into wider and faster inkjet (30˝ and wider, more than 650 fpm). It’s a principle of lean manufacturing that eliminating touchpoints from end-to-end is key to driving labor out of the cost equation. Some purpose-built book finishing lines designed to operate in-line to higher-speed inkjet presses (Hunkeler, Magnum and Muller Martini, for example) can excel on some applications with certain substrates.
In-line book block creation at press speed can involve some trade-offs in format and substrate flexibility. This runs counter to the trend of ultra short-run or book-of-one requirements, which typically demand on-the-fly changeovers to accommodate variable sheet/signature count and cut-lengths. If you expect your inkjet business to lean toward ever shorter runs, be sure your system has the dynamics, automation and agility to support this production.
One U.K. customer realized a 27% lift in total throughput (book blocks/hr.) by simply uncoupling press and finishing. And several book manufacturers have been seduced by the apparent labor and time savings of in-line finishing, only to struggle with less-than-satisfactory, real-world results.
There’s no right answer to the in-line versus off-line question, but there’s every reason to thoroughly research the options and think them through as carefully as you do your inkjet investment.
Cut-Sheet or Glued Book Blocks
Another point to consider is whether book blocks are created cut-sheet (loose-leaf) or unitized (typically using in-line gluing). Glued book block stability can significantly improve downstream efficiency, as cut sheets are easily disheveled during transport (cart or conveyor) and usually require manual jogging — an unnecessary touchpoint — prior to being inserted into a perfect binder.
Unitized book blocks allow efficient, jog-free manual loading of a near-line binder, automatic presentation using a de-stacker, or the books can travel on a conveyor to an in-line perfect binder. Intelligent readers will capture and send all setup parameters needed for automatic changeover of the perfect binder and three-knife trimmer for efficient, zero-makeready production. Books/hr. will vary with degree of book thickness variability, but this touch-free production workflow can efficiently support short-run lengths and even a book-of-one.
End-to-end system control is provided by intelligent marks printed on the web (usually 2D codes) that convey essential data to readers located throughout the system to signal automatic changeovers (cutter form length, folder buckle positions and end-stops, glue on/off, end-of-book, book thickness and format, integrity matching of cover to contents, etc). Dynamic imposition templates — which determine control mark contents and placement — further streamline the production workflow.
Inkjet press manufacturers spend considerable time and effort qualifying various papers. The mills add fillers and apply coatings to optimize “printability,” and most agree that the current state of inkjet image quality is well up-to-par for nearly all book applications. We urge book manufacturers to recognize that not every “inkjet qualified” sheet can be easily finished, and use the term “finishability” to highlight this concept. It’s hard to simulate finishability in a test environment where pre-printed rolls are not fresh off the press, so you don’t have all the attendant issues of moisture, heat and static. The truly best way to avoid media-related production snags is real-world, on-site experience (ask your paper supplier to send a test roll), and talk with peers who are already using your inkjet press and know which stocks run well.
Any book manufacturer starting the journey into production inkjet should put the same careful research into finishing options as they put into the inkjet press. Finishing is not as sexy as workflow or the press, but postpress bottlenecks and downtime can erode margins fast. Consider that already-printed short-run work entering your bindery is — short of finished goods — the highest-value paper in your shop. Any spoilage will require manual intervention and a costly start from scratch for reprints.