Almost invisible and yet so effective: transparent heaters are real problem solvers in a wide variety of areas. The automotive industry is considered a pioneer here with heated headlights and mirrors, among other things. Used in cars, transparent heaters enable vehicle automation sensors to provide precise 3D mapping in all weather conditions. In the meantime, the field of application of transparent heaters has expanded many times over. The technology partner of Bopla Gehäuse Systeme GmbH, the membrane keypad and touch systems manufacturer Kundisch GmbH & Co. KG in Villingen-Schwenningen, uses a special technology for its heating foils.
Harsh weather outdoors, temperature fluctuations in terrariums - optical cameras, together with other sensors, have to withstand the conditions of their field of application. For these cameras to remain active, the field of view must always be free of condensation and ice. Harsh weather or temperature fluctuations can become a real problem and endanger the functionality of the device. The solution: transparent heaters. They protect the field of vision and sensors from external influences - and always with maximum transparency.
Smart Heating: An important future field for Kundisch
The manufacturer of membrane keyboards and touch systems KUNDISCH has been developing solutions for transparent electronics for many years. One area of transparent electronics in which KUNDISCH is experiencing increasing demand is smart heating using transparent foil heaters. For Sebastian Gepp, Development Manager Printed Electronics at KUNDISCH, this is not surprising, because foil heaters based on transparent electronics offer numerous advantages, he says. The biggest advantage of a transparent foil heater compared to today's established heaters, he says, is that it heats up quickly. "With a foil heater, for example, a window pane can be heated to 60 degrees Celsius within a few seconds. Conventional heating systems work by means of a fan and heating wire and primarily heat up the ambient air. This takes considerably longer and also costs a lot of energy."
The metal mesh technology
When manufacturing transparent foil heaters, the challenge is to use a material that has both sufficient conductivity and transparency. At Kundisch, this is where the Metal-Mesh technology comes into play, which fulfils exactly these requirements. This technology produces homogeneous transparent conductive films as printed layers that can be used as heaters for transparent surfaces. For this purpose, the company usually prints two conductors made of silver into the foil. These conduct the current into the foil. Between the two silver-printed lines is a transparent coating. It consists of a mixture of copper and carbon, is highly conductive as well as highly transparent.
"You can imagine it like wafer-thin copper wires on the foil. You can only see these wires with the naked eye if you are skilled," explains Sebastian Gepp. "That is precisely the highlight of this new technology: the wafer-thin, barely visible material enables significantly lower resistances in contrast to other techniques. Because of this, users achieve the same heating power with less electricity." Another advantage of the technology is the possibility to structure the material according to the customer's wishes using printing techniques. This is because it is not always possible to use a rectangular coated surface, for example, in order to achieve a desired heating output with given electrical parameters. With its technology, Kundisch can therefore adapt the products precisely to the application.
The transparent electric heating foil is typically incorporated by "sandwiching" a conductive material between layers of glass or clear plastic, traditionally polycarbonate or acrylic.
The advantage of this method is particularly evident when transparent heating foils need to be produced for large areas, such as windscreens. Today's state of the art for heated windscreens is the laying of wires by robots. A robot lays a thin wire with a centimetre spacing and has to travel over every position to do so. A process that takes more time than the metal mesh technology used by Kundisch, says Sebastian Gepp. Kundisch can print the square metre of heating very homogeneously in seconds, whereas a robot needs several minutes to lay it. "That means the productivity we can achieve with this is many times higher than the current state of the art."
Transparent heaters in different technical variants have been around for a long time. However, the material used by KUNDISCH, which makes the innovative process possible, has only been available on the market for a few years. "There was a procurement problem for many years. You had to use alternative technologies like wires or ITO coatings for Smart Heating in the past," explains Sebastian Gepp.
A problem solver in many areas
The main driver of this technology is the automotive industry. This is because the heating foils are not only transparent to the eye, but also to laser and radar systems. Thus, the transparent heating foils support the functionality of distance measuring devices in vehicles, even when the vehicle is iced over. Whether robots unloading trucks, autonomously driving forklifts or agricultural vehicles - especially areas characterised by a high degree of automation benefit from the transparent heaters. They are also used in medicine, for example in incubators for newborns. Furthermore, they can be installed in various displays, for example in e-paper readers.
But transparent heating foils are also a real problem solver in other areas, says Sebastian Gepp and gives a concrete (extreme) example: "Our customers include lighting manufacturers whose products are used in the Antarctic, among other places. Since it is no longer allowed to use light bulbs that keep ice out with their heat, such a lamp ices up under these conditions. The bulb is then no longer bright enough." Transparent heating foils prevent this.