Diamond micro engraving of gravure roller mould for roll-to-roll printing of fine line electronics

Printing electronics has attracted great attention in recent years due to its various superior performances compared with conventional silicon-based semiconductor industry. Roll-to-Roll gravure printing is able to transfer conductive nanoparticle ink onto the flexible film substrate to form continuous fine metal lines using a gravure roller mould with tens of thousands of tiny gravure cells on its surface. However, it is difficult to scale down the printed line width, which is crucial for the film's circuit density, resolution and transparency, because the market-available rollers fabricated by conventional engraving techniques for graphic printing usually have gravure cells larger than 25 μm. Hence, in this study, a novel method based on ultraprecision machining technology, Diamond Micro Engraving (DME), is introduced to miniaturize the gravure cells in order to reduce the ink volume transfer during the printing process. A V-shape sharp diamond tool is used to continuously generate concave inverted micro pyramidal structures on the gravure roller surface using the Slow Slide Servo technology. Geometrical modelling of the engraving process is conducted to help programming the tool path to realize accurate control of the instantaneous position of two linear axes and one rotatory axis. Through applying the DME process, generation of consistent cell structure is achieved. The engraved gravure cell width is successfully miniaturized to 7 μm. With the optimized cell spacing value, the DME-machined roller moulds are used in gravure printing of metal mesh film, which works as a potential transparent conductive film to replace the expensive indium-tin-oxide (ITO). The printed line width is reduced from 47 μm to 19 μm, and the transmittance of the printed metal mesh film for visible light is increased from 65.2% to 80.4% accordingly, which is comparable to the transmittance of ITO film.