Digital Laser Transfer Printing for Ceramic Colours
An Innovative Digital Printing Technology LPKF Laser Transfer Printing (LTP) is a laser-based method capable of printing ceramic pigments of the original screen printing size. Compared to the original screen printing paste, only the medium is modified to create an LTP compatible ink. The inorganic part of the ink is not touched. Hence, the resulting enamel on the glass substrate after firing is not different from the one applied by means of screen printing. Furthermore, ceramic colours can be transferred to flat glass with previously unknown precision. This enables introducing digital printing to applications, e.g. printing on automotive glass, where other ditigal methods still have their limitations.
The LTP Process In the LTP process, an endless web is used as a carrier for the ink. The laser beam transfers a defined amount of the ink to a flat substrate. The ink carrier web is transparent for the laser wavelength used. The laser beam is focussed onto the ink and evaporates some portion of the ink solvent. As a consequence a vapour bubble expands and pushes an ink droplet towards the substrate. The ink droplet is released and deposited on the substrate.
The laser focus is scanned in form of a line across the carrier web. The continuous motion between the printing line and the substrate creates a two dimensional print - line by line. Switching the laser on and off during the scan then creates an image.
The laser energy applied determines the amount of ink being transferred and enables to control the ink layer thickness on the substrate.
From Screen Printing to LTP Historically car glass is being bonded to auto body since the 80s. The purpose of printing black colour around the edges is the protection of the glue against the UV radiation. Furthermore, the edge printing is simply supposed to look nice to the outside. Nowadays lorry, bus and train glass is also bonded and printed upon.
Up to today screen printing has been the established method to apply the colour to the glass substrate. Screen printing provides high printing speed independent of the glass size. Hence, it is unbeatable in terms of cycle time on large areas.
However, there are limitations to screen printing. Image resolution is also limited and the layer thickness is fixed with the screen thickness. One screen per window model is required, thus glass-to-glass data variation is impossible. Screen handling from procurement to storage is extensive and costly, in particular with regard to rigging, dismounting, cleaning and storage. This results in high fixed costs making screen printing uneconomical for small runs.
As a result LTP is ideal for producing smaller runs which applies to aftermarket replacement and transportation glass (trains, ships lorries and busses). In addition, where only small areas need to printed, e.g. for logo printing, LTP is a digital method. Above all, as the enamel in screen and LTP printing is the same LTP does not have to be requalified. Serveral inks have already successfully passed the relevant automotive tests.