Editing Inkjet printing (section)

=== Continuous inkjet ===
[[File:INKJET-PRINTER-INDUSTRI.gif|thumb|Schematic diagram of a continuous inkjet printing process]]

The '''continuous inkjet''' (CIJ) method is used commercially for marking and coding of products and packages. In 1867, [[William Thomson, 1st Baron Kelvin|Lord Kelvin]] patented the [[syphon recorder]], which recorded telegraph signals as a continuous trace on paper using an ink jet nozzle deflected by a magnetic coil. The first commercial devices (medical strip [[chart recorder]]s) were introduced in 1951 by [[Siemens]].<ref name="CRC" /> using the patent US2566443 invented by [[Rune Elmqvist]] dated September 4, 1951.

In CIJ technology, a high-pressure pump directs liquid ink from a reservoir through a gunbody and a microscopic nozzle (usually .003 inch diameter), creating a continuous stream of ink droplets via the [[Plateau-Rayleigh instability]]. A piezoelectric crystal  may be used to create an acoustic wave as it vibrates within the gunbody and causes the stream of liquid to break into droplets at regular intervals: 64,000 to 165,000 irregular-sized ink droplets per second may be achieved.<ref name=":2">{{Cite book|last=Kenyon|first=R.W.|title=Chemistry and technology of Printing and Imaging Systems|publisher=Blackie Academic & Professional|year=1996|isbn=978-94-010-4265-9|location=Glasgow UK|pages=114–115, 119–120, 128, 131, 133}}</ref> The ink droplets are subjected to an electrostatic field created by a charging electrode or by a magnetic flux field as they form; the field varies according to the degree of drop deflection desired. This results in a controlled deflection by electrostatic charge on each droplet. Charged droplets may be separated by one or more uncharged "guard droplets" to minimize electrostatic repulsion between neighboring droplets.

The droplets pass through another electrostatic  or magnetic field and are directed (deflected) by electrostatic deflection plates or flux field to print on the receptor material (substrate), or allowed to continue on deflected to a collection gutter for re-use. The more highly charged droplets are deflected to a greater degree. Only a small fraction of the droplets is used to print, the majority being recycled.

CIJ is one of the oldest (1951) ink jet technologies in use and is fairly mature.{{Citation needed|date=October 2022}} Drop-on-demand was not invented until later.{{Citation needed|date=October 2022}} The major advantages of CIJ are the very high velocity (≈20&nbsp;m/s) of the ink droplets, which allows for a relatively long distance between print head and substrate, and the very high drop ejection frequency, allowing for very high speed printing. Another advantage is freedom from nozzle clogging as the jet is always in use, therefore allowing [[Volatility (chemistry)|volatile]] solvents such as [[ketones]] and alcohols to be employed, giving the ink the ability to "bite" into the substrate and dry quickly.<ref name=":2" /> The ink system requires active solvent regulation to counter solvent evaporation during the time of flight (time between nozzle ejection and gutter recycling), and from the venting process whereby air that is drawn into the gutter along with the unused drops is vented from the reservoir. Viscosity is monitored and a solvent (or solvent blend) is added to counteract solvent loss.

In the later 1950s, heated wax inks became popular with CIJ technologies. In 1971, Johannes F. Gottwald patent US3596285A, Liquid Metal Recorder used molten metal ink with a magnetic flux field to fabricate formed symbols for signage. This may have been the first 3D metal object printed using magnetic core memory as data to produce each symbol.