The discuss for this edition will bring to conclusion our serial consideration of Introduction to Digital Print Technology. We have discussed in this series that piezoelectric printheads can be grouped into varying types base on the way electric current deforms the activator plates. We have talked about the shear mode and the bend mode. As a continuation plus summary, we are looking at the Push Mode and the squeeze mode.
Push mode is similar to bend mode in that the electrical field between its electrodes is parallel with the piezoplate polarization, and that the piezoceramic pushes against a transducer foot which places pressure on the ink to eject droplets. Dataproduct, Trident and older Epson printers use this technology. It is relatively high energy process which
ejects droplets which are more elongated and may form satellite droplets. These companies have considerable experience with these printers and have steadily improved them.
The idanit 162Ad and other large high production digital print devices employ the Dataproducts heads. Trident has been serving the major marking and coding companies and their industry for a number of years. Its high energy droplet ejection level can be an advantage or disadvantage, depending upon its application and the need for penetration. They are relatively robust and can use inks in the 10 to 20 cp. ranges. Satellite droplets, however, usually compromise image quality.
Multi-layer piezoelectric technology refers to Epson’s technology which first employed push mode for its Stylus Color (1994) and Stylus II (1995) printer printheads. These push mode heads contain 64 nozzles per printhead.
PIEZOELECTRIC SQUEEZE MODE
Squeeze mode refers to technology which S.L. Zoltan of Clevite Corporation developed (1970 announced, 1974 US patent) and Siemens used in its PT-80 printer (1977). In this mode, electrical charge deforms a piezoceramic tube so that it squeezes the ink
within the tube forcing it out through the nozzle end. Siemens successfully marketed this technology for office printing.
SUMMARY OF PIEZOELECTRIC
Hot melt, also known as phase change, technology currently piezoelectric print heads. Teletype Corporation probably initiated hot melt technology in the late 1960s using continuous inkjet technology. Exxon claimed invention of this technology using piezoelectric inkjet.
Dataproducts developed the first commercial application of this technology for monochrome printing. In 1987, Dataproducts acquired Exxon’s rights. Howtek introduced the first color printer using hot melt piezo. Tektronix of Wilsonville, Oregon owns the phase change trademark and manufactures a number of phase change printers. It uses the bender mode piezoelectric driver. Spectra developed its own version of hot melt and licensed Dataproducts rights as well.
Brother has also been active in hot melt piezoelectric printing. The time it takes to refill the ink firing capillary or chamber is the primary factor limiting the speed of a piezoelectric printhead and not the response time of the piezoelectric transducer. Transducers in continuous inkjets operate at hundreds of thousands of cycles per second. Drop on demand printers are constantly stopping and starting the flow of ink, whereas CIJ print heads receive a continuous flow of ink and do not have to overcome inertia constantly as do drop-on-demand print heads. Continuous inkjet also can guide ejected droplets with electrical force, while drop on demand piezoelectric inkjet relies on the force and direction of expulsion and gravity as its only droplet guiding forces.
The advantages of the more robust Xaar, Tektronix, Trident, Calcomp, Dataproducts, and Spectra piezoelectric printheads are their ability to print higher viscosity inks, a wide variety of inks with different solvents, heat sensitive inks and colors, and hot melt thermoplastic and paraffin. Piezoelectric printheads generally have high reliability and will last for months to years of operation. Piezoelectric inkjets generally deposit consistent ink droplets which result in sharp images.
The disadvantages of piezoelectric inkjets have been speed and cost. New configurations of these heads are producing throughput which is much greater than that of comparable thermal inkjet printers as evidenced by the Calcomp CrystalJet, Raster Graphics PiezoPrint 5000 and the Xerox Xpress 36 & 54, which are 2 to 3 times faster than Encad or HP thermal inkjet wide format printers.