The report determined that the dispensing requirements for digital fabrication and functional printing applications vary widely. Inkjet printing for 3D fabrication requires the deposition of layers that are less than 40 urn along the build Z-axis. Deposit of 30-μm layers for opaque photo polymeric materials and 16-μm layers for transparent polymeric materials have demonstrated that evidence of the layering process is not discernable to the naked eye. The modified Xerox M-series PIJ bend mode head, which has 880 nozzles and ejects drops of 15 or 30 p1, produced even layers and smooth contours without evidence of process artifacts. Similarly, Objet printers using Ricoh Gen3PIJ piston mode printheads produce similarly smooth results, but the production process may require some layer shaving to yield the desired layer thickness. These dimensional targets will satisfy most visual, functional and radiation curing requirements for 3D fabrication applications. The ZPrinters, which use HP TIJ heads to fire polymer into tri-calcium phosphate powder coating, produce Z-layers over 100 μm thick. These typically require some post print curing and finishing. The reports from inkjet printers of electronics indicate that drop volumes of direct printing with metallic nano-particle silver require drops in the range of 1 to 10 p1 depending on the refinement of the circuits lines. The Fujifilm Dimatix DMP inkjet print systems have become standard equipment in almost 700 research and development facilities for testing and producing printed circuits. Dimatix offer its 16-nozzle MEMS cartridge printheads in both 1 and 10 p1 versions. Other companies have developed similar systems. PixDRO has developed production inkjet systems for fabricating solar cells using a variety of printheads to match process requirements. The Company offers Xaar 1001, Fujifilm Dimatix Spectra S-Class SE, SM, SL, (plus hot melt), SE3 and SX3, Konica Minolta KM 204, KM 256, KM 512 (plus hot melt), Trident ITW 256Jet-D. Acid etching and caustics deposit for some circuit printing approaches requires deposition devices with a wide pH tolerance range. We determined that heads that were stainless steel could provide the greatest pH range. The Trident ITW 256Jet-D head offers tolerances in the pH range of 2 to 13, and the ability for a trained end user to dissemble the head for maintenance. The chemical composition of inkjet printheads must have a surface energy that permits the flow of the print fluid with its surface tension through the head. The fluid must also have a surface tension that permits its adhesion with adjacent build layers. More viscose thermoplastic polymers will typically require heating to lower their viscosity to optimal levels for industrial inkjet printing. Heaters and thermistors are available for most industrial head. In addition to providing consistent temperature for jetting fluids, they can also provide hot melt capability. While Dimatix rates its DMC, D-series and most S-series heads at 70°C it also offers heads with ratings to 135°C. Xerox rates its M-series head as capable of handling fluid to 140°C. The MicroFab MJ-SF piezo dispenser and the Geiger SMLD 300G valve jet are rated to handle fluids up to 250°C. Canon Oce has applied for a patent for an inkjet type device that can tolerate fluid temperatures in excess of 1500°C. The ability to dispense liquids at high temperatures greatly extends the range of what is possible with inkjet fabrication and functional printing.
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