Is Single-Pass Inkjet a Wide-Format Game Changer?

Before starting a discussion about single-pass printing, it would be helpful to understand just what it is and how it compares to “scan printing.” We spend a lot of time in our industry putting ink onto substrates, from offset presses to the myriad options available in the wide-format arena. At the end of the day, we’re all producing interesting, imaginative and colorful images on a variety of substrates, using a variety of techniques.

For now, let’s focus on the universe of inkjet printing. Scan printing is when the print head moves (or scans) over the substrate and lays down ink using a number of passes to fully form the image. In the case of a roll-to-roll printer, the substrate also moves to advance the substrate for the next pass. In single-pass printing, the print head (or array of print heads) are stationary, and the substrate does all the moving.

MEMS Technology

Because the print head is stationary and able to lay down a tremendous volume of ink droplets (a Memjet 42˝ array can generate more than three billion drops per second), the substrate is able to move quickly, which allows for much higher throughput. In case you are wondering just how they are able to achieve this volume, it’s because of MEMS technology — or Micro-Electro-Mechanical Systems, which are miniaturized mechanical elements.

This technology has been around for a while, and it began with dye-based aqueous inks. The technological hurdles of getting other ink types to work, including UV- and pigment-based aqueous inks, have been overcome, and the single-pass system is one that is working well in the high-speed industrial environment. An example would be ceramic tiles, where the tiles move through the press at high speeds that allows for a high-volume of tiles to be printed in a short timeframe.

Challenges to Consider

There are a few difficulties with this technology, such as print time between maintenance and the problem associated with nozzle drop out. Unlike scan printing, where the multiple passes of the print head can be used to hide the effect of a nozzle dropping out, single-pass printing does not have that luxury and needs a way to overcome this problem.

According to Russ Brown, marketing manager at Fujifilm Dimatix, the SAMBA Single Pass Piezo Drop-on-Demand Inkjet technology has the ability to recirculate the ink at the nozzle plate, which makes for a more stable nozzle ring platform and reduces the need for maintenance between prints to prevent clogging of nozzles. SAMBA print head modules can also print at 1,200 dpi and use VersaDrop to print in grayscale down to 1 picoliter.

HP's T4110 print head.

An additional advantage of the SAMBA technology is the ability to place print head modules end-to-end to form a single, tightly integrated print bar that can vary in length to accommodate a variety of press sizes and diverse printing applications.

Hewlett Packard (HP) is another manufacturer that is making good use of this technology. According to Pat McGrew, HP’s inkjet evangelist, the HP PageWide Web Press group has options as small as 20˝ in width all the way up to 110˝, and it is seen as a good fit in the offset web press world. A typical HP thermal inkjet print head is 4.25˝ long and has five ink drop generators on silicon chips. Each chip or die is approximately 1˝ long and can have 2,100 to 4,200 nozzles per die.

The thermal inkjet heads are capable of running pigmented inks and have a throughput of 150 million to 300 million drops per second, giving them the ability to handle the demands of printing at the high speeds needed in the world of web printing. The print heads are set up with multiple overlapping channels to allow for redundancy to detect nozzle dropout and compensate for it.

A bonding agent is used within its own array of print heads to allow printing on uncoated stock. Dryers then use warm air to dry the media as it passes over the rollers. The print heads are maintained with an automatic print head service station, which serves the purpose of wiping them to help keep the nozzles functioning properly.

Jamie Sirois, HP PageWide XL business development manager, noted that HP’s first goal with the HP PageWide XL printer portfolio was to bring color into the monochrome LED environment. The target for this market was the architect and engineering users, but with the pigmented inks it quickly moved into the GIS mapping and short-term indoor signage arena. The HP PageWide XL printers use eight 5˝ print heads to make up each print bar.

Look for single-pass printing to enter increasingly more areas. Image quality, speed, reliability and lower cost will determine where this technology is adopted next — and packaging, flooring and countertops are likely on the horizon.

This article originally appeared in the SGIA Journal’s September/October 2015 edition.