Real-time Drop Analysis for Inkjet Printing

In April, Krüss will unveil its new Drop Shape Analyzer – DSA Inkjet, a measuring instrument for analysing the properties and flight behaviour of ink drops after exiting the print head. Presentations will take place at two parallel conferences, the IMI Inkjet Ink Development Conference held in Hamburg from 8-11 April, and the InPrint show held in Louisville, KY from 9-11 April.

During ink development and quality assurance, the interaction between the print head control and the ink must be perfectly adjusted and monitored. The DSA Inkjet was specifically designed for this task. With its integrated printer electronics, it communicates directly with the print head installed in the instrument and analyses the ink drops in real time.

Once the print head has been inserted into the instrument in a just few simple steps, the intuitive waveform editor realistically simulates the electronic control in a printing process. The microscopic lens depicts the drop beam in a sharp and high-contrast manner. The DSA Inkjet uses an imaginative method to precisely analyse ink drops of just a few picolitres at flight speeds of up to 40 m/s: two different-coloured light flashes in swift succession provide double exposure of the drop in a single colour camera video image. By separating the colour channels, discrete images of the same drop are obtained at intervals of a few milliseconds.

This method opens up unprecedented opportunities for filming the drop flight live, automatically analysing the drops and obtaining result parameters that are relevant for the print quality. To name but a few examples, the software-controlled measurement provides mean values for the drop’s volume and speed, trajectory (deviation from the vertical), length of the ligament and number of possible unwanted satellite drops. The data is generated as immediate feedback on the dynamically adjustable print parameters and is particularly suitable for checking an ink or optimising the printing process. Easy-to-create automation programs also enable measurements under repeatable conditions to test ink formulations in a standardised manner.

Wetting the print head during printing can deflect the drop jet and clog the nozzles by drying out. A separate lens observes the nozzles from below to make unwanted ink drops visible on the rows of nozzles. Another innovative development makes it easier to measure real drop dimensions such as volume or ligament length. The image scale is automatically determined with the aid of a calibration grid regularly projected into the camera image. This eliminates the need for image calibration when changing the zoom, saving time and ensuring reliable results.

The DSA Inkjet is designed for easy, versatile, and safe use. Inserting the print head and focusing on individual nozzles is a matter of a few simple steps thanks to the 3D fine positioning. The instrument is also equipped with a storage tank to supply the print head with ink during long-term measurements, whereby the drops are collected in a waste container. A suction device prevents harmful vapours. Thanks to a UV protection cover, UV-curing inks such as those used for 3D printing can also be examined.