Smart labels with an excellent memory

Smart labels based on line or bar codes are an essential part of today's commerce. These one- and two-dimensional codes must all be error free, machine-readable and as tamper-proof as possible.

A team of scientists of BAM was the first to show that smart labels can be produced from polymers with shape memory. In numerous test studies they examined their applicability as a function of shape memory and developed a thermo-mechanical method which can make the codes temporarily unreadable.

The required quality for the legibility of the codes can be achieved by a strong colour contrast. Therefore the BAM scientists developed a new dyeing process which can improve the reading of the QR codes. QR means quick response and is known from shipping documents or tickets as a square matrix of black and white rectangles.

The code is engraved into the two- to three-millimetre thick shape memory polymer layer by a laser. BAM scientists have now managed to produce a sufficiently high colour contrast between the untreated and cut-out areas by dyeing the polymer surface with the midnight blue dye "Victoria Blue B" to a depth of 100 micrometres [1]. The QR code could be read error-free with an optical reader such as a smartphone.

To reduce the availability of the QR code thus increasing security, the polymers are deformed after colouring and engraving and temporarily stabilised in different shapes where the code is no longer able to be deciphered. For the code to be made readable again, the polymer is heated above its switching temperature whereby the shape memory effect is triggered. The polymer "remembers" its original form and almost takes it up again. The colour contrast remains as high as ever.

In this way, labels with shape memory can be used to store information for the characterisation and identification of goods. If the shape memory effect is triggered, the product reveals information: for example, about its manufacturer or authenticity.

Source: Federal Institute for Materials Research and Testing (BAM)