Continuous inkjet printers are small character devices that are used to code and mark products and packaging.

These are still inkjet devices and produce output in the raster format of a series of straight lines arranged in a grid. However, output is through a single nozzle, typically 60 micron size. Micro versions with 40 micron nozzles are also available, producing very fine print on small items such as electrical cable. These micro versions are capable of faster speeds but are more expensive.

Small character industrial printers use the same processing methods as large character equivalents in terms of sensing products and setting time delays to position marking correctly (see other new article here). But, with only one nozzle, they have a totally different ink delivery method that enables them to handle fast moving products, which do not have to be as close to the print head (up to one inch away).

Continuous inkjet typically handles font sizes from 0.6 mm to 12 mm, output up to eight lines of text and can be used where space is limited. Resolution is not as good as for large character, high resolution devices but is sufficient for product identification and traceability.

Continuous inkjets create a continuous stream of ink droplets that are emitted from the single tiny nozzle by a high pressure pump that forces the ink out of a reservoir. A piezo electric crystal vibrates and creates an acoustic wave that breaks the ink into droplets at the rate of around 64,000-165,000 per second.
An electronic field is created by a charging electrode and is applied to the ink droplets, with the field varying depending on the degree of deflection needed. Droplets therefore have a controlled and variable electrostatic charge applied and are kept separate by uncharged droplets.

The charged droplets go through an electrostatic field where they are deflected, depending on the degree of charge, to print on the substrate. Most droplets are uncharged, passing through undeflected to the return block where they are recycled to the ink module for re-use.

This technology is well-established and has very high drop ejection frequency with the droplets ejected at high velocity. This allows for high speed marking, with a relatively large gap between the nozzle and the substrate. Since the single nozzle is in constant use, it is resistant to clogging, allowing volatile solvents that dry quickly to be used. However, the solvent has to be regulated to replace any that is lost by evaporation after ejection from the nozzle and before return for recycling. Any air that is drawn in with unused drops has to be vented from the system.