The project NanoMet contained the development of a shielding foil for electromagnetic waves of a defined frequency for the protection of data carriers. The foil can be further processed into a protective cover for RFID bank cards, credit or chip cards. It prevents unauthorized reading as well as damage of the cards due to electromagnetic influences.
The developed foil is a foil-composite consisting of a carrier film (substrate), on which a conductive copper grid is embedded in a CSP-polymer composite (CSP - Core Spike Particle). The used Cu grid has shown a frequency shielding comparable to other commercially available systems.
The shielding foil is sufficiently transparent and thus meets the requirement to read the font of an inserted card and to recognize its color. Furthermore, the flexibility of the polymer foil is greater than the flexibility of a card, similar to a licence holder, with a film thickness less than 0.2 mm. The foil also has a good slipperiness, so it will not stick to a conventional card.
The foil can be further processed in different ways. For example, it is ultrasonically weldable while preserving functionality and it is in silhouette and crush-cut cuttable and punchable. Compared to products on the market, the foil has the same or lower toxicity and particulates emission.
If a self-adhesive carrier foil is used, additional applications arise.
The foil can be produced in a roll-to-roll process, which allows upscaling for large quantities. With this method, larger areas can be produced in a continuous process.
During the development of the foil, different methods of surface activation were tested in order to optimize the adhesion between substrate and CSP polymer composite. Therefore, the carrier foil
was heat treated by IR-irradiation or treated with plasma prior to the coating. Hereby the plasma treatment led to improved connection/adhesion.
For the continuous process of transported foil, a demonstrator was constructed using a roll-to-roll process. The plasma treatment was implemented by a specially designed station on the machine (Figure e).
Following this, the CSPC material is applied to the carrier foil. For this purpose, an automated two-cartridge system was developed, which allows accurate dosing of the CSPC components (c and d). With the help of this system, the ratio of the two polymer components as well as the amount of material to be applied can be adjusted. The Cu grid is then brought together with the liquid CSPC coating followed by distribution to a thin layer with a roller.
Another goal of the project was the development of a flame retardant foi, here silicone proved to be a suitable material. By adding CSP, this property can be enhanced, as shown in the following
figure: As the content of additives increases (from left to right), the burning distance is reduced.
At a maximum layer thickness of 1 mm, the film is also sufficiently flexible, cuttable and can be produced in the R2R-process.
The project was implemented in cooperation with the project partners:
Max Steier GmbH & Co.KG has extensive know-how in the use of foil materials. This company made the selection of suitable carrier foils and provided them. In addition, they performed tests according to further processing of the developed shielding foil for making card-cases and other functional specimens.
Teyfel Automation designed the machine technology which enables a roll-to-roll application. As a machine frame, an old apparatus of the company Steier was used and modified. An automated two-cartridge system as a dosing device enables the application of a viscous medium, in which the microstructures are dispersed, on a carrier foil pretreated with plasma. With the help of an additionally installed rolling device with adjustable contact pressure, viscous media can be distributed to thin films of defined layer thickness.
In the working group 'Functional Nanomaterials' of the Christian-Albrechts-University to Kiel, the basics of ZnO microparticle production were determined. In addition, the mechanical and electrical characterization of the novel foil was carried out.
The Plasma Technology AG of the CAU has many years of experience in the field of surface modification and coating by means of low-temperature plasma processes. Thus, suitable plasma processes could be selected for this specifically application. The plasma is needed to activate the substrate material to ensure better adhesion of the overall composite. As the utilized substrates consist of temperature-sensitive plastics, the temperature load of the substrate was examined and different process parameters were adjusted, such as power, working distance or travel speed of the plasma source.