When considering conventional printing methods there are a few technologies which immediately come to mind, lithographic offset printing, flexographic printing and gravure or rotogravure as it is known. Each of them has their own benefits and applications and have reached a certain level of quality which makes it stand out in its respective field.
As printing goes, lithography is by far the oldest of the three systems and was devised as a development of the letterpress process. Lithography was invented in 1796 with the first rotary press being developed in 1814 by Koenig & Bauer. Gravure is the second oldest of these processes and dates back to around 1852. Flexography is the youngest of the systems having been invented in around 1890. Lithography and flexography have continued to develop over the years, but gravure is much the same process now as it was when it was first invented. The only real developments have come in the speed and quality of the engraving process and in the speeds of the printing presses.
As such, gravure is considered a mature printing process. It is widely used for very long-run and extremely high-quality printing applications, due to the fact that the image is essentially ‘fixed’ in the engraved cylinder. Items such as glossy woman’s magazines with extremely long runs, or packaging printing where hundreds of thousands are printed are examples of items which can be printed using the gravure process. Due to the formulation of its inks, gravure printing can be used with a wide range of substrates from paper and board to films and foils.
This would therefore, seem to be the extent of the capabilities of gravure. However, various universities and research organisations around the world are looking at gravure as an option for the production of printed circuitry. This is due to the way in which the ink layer is laid down by a gravure press. The only requirement is the production of an ink which is capable of conducting electric current. Tests have shown that this can be done with high-viscosity inks incorporating silver, gold and copper.
Although tests are still underway, the results appear positive for the mid-scale production of low-power devices such as photovoltaics. The limitation is the control of the ink viscosity and the fact that the press needs to be run at lower speeds in order to achieve consistent conductive ink lines.
Printed electronics is a new and potentially expansive market for the graphic communications industry. Combining traditional printing processes with conductive, metal-based inks allows for the production of functional electronic devices. These include flexible displays, smart labels, photovoltaic devices, organic light emitting diodes and RFID tags. Printing electronic circuitry offers dramatic increases in productivity. While other processes such as flexography, silkscreening and even lithography have been looked at, the extremely high-resolution of gravure makes it the most ideal process. Gravure also has the ability to print a continuous image.
Gravure has another advantage over other printing techniques, it is a mechanical process with fewer variables to control which results in a more consistent image. What does influence the quality of the printed electronic circuitry is the method of etching or engraving used to create the image on the copper cylinder. More research will be required to find the best method. Electro-mechanical engraving is the most widely used method, but cells are limited to a fixed aspect ratio defined by the geometry of the diamond stylus used to engrave the cells into the cylinder. Direct laser engraving uses a laser beam focused onto the surface of the cylinder to create cells. This method allows for a free selection of cell dimension which optimises ink transfer. Chemical etching also uses laser technology by imaging the mask area. Each cell produced has the same depth resulting in tonal variation being achieved by controlling the diameter of the cells.
Gravure’s ability to handle fast, high-resolution image transfer make it ideal for the mass production of printed electronics. While the quality of gravure printing can be affected by a number of variables, there are numerous techniques available to control quality. Most importantly, gravure is capable of putting down a comparably thicker layer of ink film providing the necessary flow of electrons through the conductive ink.
While it is still early days in the development of this solution, it offers a degree of hope to gravure printers who are feeling the effects of the decline in print volumes. While conventional print volumes continue to decline, there will be an increasing demand for printed electronics and this could offer gravure the opportunity to move into a new market for which it is ideally suited. Watch this space for more on this development.