Shellac Ink For Applications in Sustainable Circuits

Unfortunately, successful does not always mean sustainable. The electronic waste becomes more and more from time to time, which is why a team of researchers have come up with a possible solution to this problem – an ink made from a combination of shellac and carbon. An invention that we at drupa definitely view as an exciting step for the printing industry.

The production of electrical circuits using additive processes such as robotic 3D-printing has been very successful. However, the metal particles that make such “inks” electrically conductive are causing more and more electronic waste. In addition, due to the number of new types of disposable sensors, some of which are only used for a few days, it is unfortunately highly likely that the amount of electronic waste will increase in the future.

Gustav Nyström, head of Empa (Swiss Federal Laboratories for Materials, Science, and Technology)’s Cellulose and Wood Materials Laboratory, comments on the current situation as follows: “There is an urgent need for materials that balance electronic performance, cost and sustainability.” To tackle the challenge of electronic waste and thus develop an environmentally friendly ink, the research team established metal-free, non-toxic and biodegradable properties as primary goals.

Optimized for 2D and 3D Printing Processes

As a conductive material, the researchers opted for inexpensive carbon in the form of elongated graphite platelets mixed with tiny soot particles that make electrical contact between these platelets in a matrix of shellac. The advantages here are that shellac matches the desired material profile and is even soluble in alcohol, which evaporates and dries after the ink is applied.

Nevertheless, there is a difficulty in this task. When it is not in use, the ink is somewhat viscous. However, at the moment of printing, when subjected to a lateral shear force, it becomes more fluid. When used in additive manufacturing, such as 3D printing with a robotic arm, an ink that is too viscous is just as unsuitable for printing as one that is too fluid, because the solid components could detach and clog the printer’s nozzle. By optimizing the formulation and relative composition of the components, the team developed several variations of the ink that can be used in different 2D and 3D printing processes.

Diverse Properties for a Wild Range of Applications

To address the ink consistency issues, the team had to experiment extensively with the formulation. One of the researchers, Xavier Aeby, said the biggest challenge was achieving good electrical conductivity while forming shellac, carbon and graphite into a gel-like network. They tested their materials in various formats, including a cuboid with 15 superimposed grids of fine strands only 0.4 mm in diameter. They also constructed several components to test the material’s suitability for real-world applications. These included a sensor for deformation in the form of a thin PET strip on which a structure was printed with shellac ink. The electrical resistance of this device changed when the structure was bent, allowing accurate measurement of deformation. Various material properties were also tested, including tensile strength and stability under water. Finally, several variants of the ink were developed, which can now be used in various 2D and 3D printing processes.

Confident Progress

The research team is confident that the new material could also prove itself in practical applications – and has patented it. 

“We hope that this ink system can be used for applications in sustainable printed electronics,” 

says Gustav Nyström, 

“for example, for conductive tracks and sensor elements in smart packaging and biomedical devices or in the field of food and environmental sensing.”

What do you think of the newly developed environmentally friendly ink? Do you think this can be a big step for the production of sustainable electric circuits?

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