New process for the production of QR codes

QR codes with shape memory properties are effective for label technology, e.g. for labelling goods at risk of plagiarism.

A new process for the additive production of QR codes with shape memory properties was developed at the Fraunhofer Institute for Applied Polymer Research (IAP) in Potsdam. It is based on 3D printing of shape memory polymers. Very flat and light QR codes can also be produced. This makes them interesting as label technology, for example to protect goods against product piracy. The high-tech polymers can be processed with commercially available 3D printers.

Shape memory polymers are among the intelligent materials. These plastics can retain an imposed shape for a period of time. As soon as the temperature is increased, they can be switched virtually at the push of a button  and thereupon return almost completely to their original shape. One possible application for shape memory polymers comprises certificates of authenticity that release product-related information. These include QR codes developed by the Fraunhofer IAP using additive manufacturing. After printing, the form is changed so that the QR code can no longer be read. The original shape is then only restored by heating via the switching temperature of the shape memory polymer so that the QR code can finally be read out.

Can shape memory polymers be printed?

„In the past, the production of information carriers such as QR codes based on shape memory polymers proved to be complex and labor-intensive,“ explains Dr. Thorsten Pretsch, head of the Shape Memory Polymers working group at the Fraunhofer IAP. „We therefore print the QR codes in 3D using a thermoplastic polyurethane (TPU). This plastic is one of the most intensively studied shape memory polymers. However, there are only a few studies on processing in additive manufacturing using melt layering. We have therefore both produced the filament and optimized the printing process,“ says Pretsch.The 3D printing process used by the research team is called melt layering. Two filaments made of the intelligent plastic are melted in a dual extruder 3D printer, pressed through fine nozzles and the desired object, here the QR code, is then built up in layers. The Fraunhofer IAP scientists produced the required filaments from „pure“ TPU or from TPU dyed with a pigment dye in an extrusion process. The thermoplastic polyurethane used was provided by the firm Covestro Deutschland AG.How is the shape memory introduced?
In test series, a printed QR code was heated to 60 degrees and deformed in various ways. In the resulting state, the QR code was cooled down to -15 degrees and then relieved, as the scientists explain. The deformed state is then stable at room temperature until the QR code is reheated to 60 degrees. This triggers the shape memory effect and the code returns almost completely to its original shape. Depending on the application, the switching temperature of the polymer can expediently be adjusted specifically to a selected level within a wide temperature range.

Shape memory properties on the test bench

As part of the Fraunhofer Cluster „Programmable Materials“, the research team at the Fraunhofer Institute for Industrial Mathematics ITWM in Kaiserslautern analyzed how well the QR codes returned to their original form after the shape memory effect was triggered. They compared the print quality with the originally digitally generated QR codes and mathematically evaluated the surface profiles of the code carriers recorded at the Fraunhofer IAP.

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The new production process for QR codes has several advantages. The extrusion of the polymer to produce the print filament is easy to master and only small amounts of material are required. In addition, commercially available 3D printers can be used to print layers that are thinner than 10 µm. These aspects, together with the low weight of the QR codes, make the process interesting for the industrial sector, especially for the forgery-proof labelling of goods that need to be protected against product piracy.