Printing smart objects

Photo | Poly IC
Marginal Column

Above: PolyIC prints electronics made from ultra-thin metal layers on plastic films. Photo: Poly IC

Photo | Poly IC

Almost invisible, yet highly conductive: the PolyTC® film. Photo: Poly IC

PolyIC produces transparent conductive films using the web-fed printing process – with a multitude of applications. The IndraMotion system solution provides the necessary manufacturing precision.

 

A transparent heating film that prevents car windows from steaming up in winter. A screen that reacts in a flash to commands given at the touch of one or more fingers. A display in an area where electromagnetic compatibility requirements are especially stringent. Products manufactured by PolyIC GmbH und Co. might be found in any of these applications – although you would not normally notice them. This company, with its headquarters in Fürth, Germany, specializes in printed electronics. The product found in many displays and other applications is a transparent, conductive film called PolyTC®. This film is hardly visible at all after it has been applied, and its production is quite remarkable. Utilizing the roll-to-roll process – the same technology used to print newspapers, for example – PolyIC prints electronics consisting of finely structured, ultra-thin metal coatings.

The material to be printed – also referred to as the substrate – is a transparent polyester film. PolyIC uses as “ink” various materials, deposited on the substrate in a dissolved state using various printing processes. These inks include semi-conductive, conductive and insulating plastics as well as various metal compounds. Continuous roll-to-roll processes like this one are inexpensive and apply the required structure directly, during the manufacturing process. As a rule, the final customer has only to perform a few further processing steps, and sometimes none at all.

Transparent metal coatings

Structured, conductive, high-resolution coatings are of critical importance to almost all components when printed electronics are produced. Modern printing processes make it possible to deposit extremely thin metal coatings at a resolution of just ten microns – one quarter the width of a human hair. Standard printing processes have resolutions in a range of over 100 microns. However, in electronics printing resolutions of under 20 microns are being sought because the resolution in the printing process actively influences the electrical performance of the final product.*

So this is how the machine can print optically transparent films that are, at the same time, electrically conductive. Nowadays, indium tin oxide (ITO) is frequently used for applications like these. The technology based on this compound does, however, have several drawbacks. The ITO coatings are quite brittle and relatively expensive.

The PolyIC company has come up with a flexible and inexpensive alternative: the PolyTC® film. The roll-to-roll process provides ultra-thin, structured metal coatings on plastic substrates. This PolyTC® film is almost completely transparent and provides high conductivity. However, before successfully introducing the product to the market, the company had to overcome several hurdles, especially in manufacturing and processing technology.

Precise processes

Photo | Bosch Rexroth AG

The film is then directed to an accumulator, bringing the sheet to a standstill, without interrupting the ongoing process.

 

The tensile stress on the substrate roll has a significant influence on the precision and stability of the manufacturing process. It also affects the measuring techniques used for quality testing because – in contrast with classic printing processes such as rotogravure – the forces that also guide the web are almost non-existent. A specific pattern in transportation behavior emerges, depending on the substrate’s thickness and material. To achieve a high-precision, stable web, PolyIC installed Rexroth’s IndraMotion system, combining the Motion Control and PLC in a single control unit. Integrated functions such as tensile stress and winding controls helped to speed up customization to match individual requirements. Precise registration is vital to ensuring that the electric structures applied one over another really work. This determines how accurately the individual “ink colors” are positioned in relationship to each other and is thus a quality feature for the printing and for the structure.

The areas where differing sheet tensions prevail are linked to each other by the sheet itself and thus have to be controlled simultaneously. Necessary and precise controls demand complex decoupling of several cascaded tension control units. Engineers combined the process control unit with the machine controls to solve this particular problem. Exact implementation of a complex rule is achieved by real-time integration of process controls and regulating sheet movement with the IndraMotion system solution. Maintaining sheet tension has thus been improved threefold. This represents an immense advance in process stability – and the prerequisite for achieving the desired registration precision of just a few microns.

The film sheet has to be stopped during production so that high-precision testing equipment can monitor electrical functions. To this end, IndraMotion combines the rolling movement of the web feed with the linear movement of a sled. The sled in the so-called web accumulator travels at the same speed as the sheet, but in the opposite direction, and effectively stops the web. This means that a part of the web stands still for a moment for electrical testing, without having to bring the entire production line to a halt and without sacrificing productivity.

Perfect cooperation

Photo | Poly IC

The conductive PolyTC® film on the printing press.

 

Wolfgang Mildner, CEO at PolyIC, is happy with the results of this collaboration. “Cooperation among a variety of partners, who are all experts in their own fields, is of the absolute essence when producing printed electronics. Bosch Rexroth, with its portfolio of automation systems for high-precision web processes, and PolyIC as a leading manufacturer of printed electronics, have achieved an excellent example of such cooperation.” In the future, electronics printed with modern processes will open up new fields for the application of electronics.


* [See: H. Rost, “Vom Polymer-Transistor zur gedruckten Elektronik” (From a Polymer Transistor to Printed Electronic Circuits), Kunststoffe 10, pp. 209-214 (2005)]