Continous Inkjet system work by expelling electrically charged ink droplets from a printhead nozzle and passing them through an electric field.
Continuous inkjet printers are used mainly to print variable information on individual products – such as dates, times, specific text, batch codes, product names and logos.
The print head contains an ink drop-generator with a vibrating drive rod. This creates ultrasonic pressure waves in the inkjet ink, breaking it up into individual droplets. When these droplets fall between a set of electrodes, individual droplets are intermittently charged. The size of the charge given to each droplet determines how far it will be deflected out of the stream when passing through the deflector plates. This determines its placement on the product.
By placing a collection of these droplets close together, a variety of characters are printed as the product passes the print head. Ink droplets not deflected out of the stream are re-circulated to repeat the process. This is a highly efficient use of ink jet ink allowing many millions of characters to be printed from a litre of ink.
Drop on demand (DOD) is a broad classification of inkjet printing technology where drops are ejected from the print head only when required. The drops are formed by the creation of a pressure pulse within the print head. The particular method used to generate this pressure pulse creates the primary sub-categories within DOD, namely thermal and piezoelectric (piezo)
With piezo DOD, a piezoelectric crystal undergoes distortion when an electric field is applied. This distortion creates a pressure pulse in the ink chamber within the print head, which in turn, causes an ink droplet to be ejected from the nozzle onto the substrate.