Get functional: applications of inkjet-printed functional fluids
Today’s inkjet printed fluids can extend far beyond simply providing colour. Many different industry sectors now benefit from advances in inkjet technology, including printed electronics, pharmaceutical, biotechnology, medical, food, coatings and packaging with processes including deposition, coating and building structure.
Inkjet printing of electronic devices such as displays and solar cells is an attractive proposition as it can reduce the number of production steps, time, cost and material wastage. Printed functions include conductive, resistive, transparent conductive, dielectric, etch resist, semiconducting, light absorbing and light emitting layers. It is important to be able to print the fluid reliably, as in printed electronics the circuit may be rendered non-functional by printing defects, whilst ensuring that it retains the intended functionality once printed. In addition, most electronics applications require the reproduction of fine details, with circuit performance improved by miniaturisation, and this is limited with inkjet printing. Many groups around the world are working to improve the technology to the level required in production, with high growth predicted for the future. Potential applications for printed electronics include RFID tags, displays and solar cells.
Solid dosage products such as tablets and capsules are ubiquitous, but new developments based around inkjet printing may introduce new possibilities, dispensing highly accurate quantities of pharmaceutical ingredients during manufacture. In the future, patients taking multiple medications could be prescribed a single tablet that contains a bespoke cocktail of medicine. Inkjet printing allows the digital manufacture of tablets for a single patient, and the use of micro-encapsulation also means that different medicines can be released at different places within the body, or at different times of the day.
Medical applications of inkjet printing range from the deposition of cells onto a mesh to form living tissue, to 3D printing for replacement organs and prosthetic limbs. A remarkable recent development was the successful separation of twins born with conjoined skulls, with separate brains but interwoven veins. An inkjet printer was used to produce 3D models of the twins’ skulls so that surgeons could practice the separation and re-routing of the blood supply. Thanks to the use of rapid prototyping, an operation that would have taken 100 hours, with limited chances of survival, was reduced to 22 hours and was a complete success. Rapid prototyping is also being used to manufacture 3D moulds for bone implants and ‘backbones’ for growing replacement organs.
Inkjet printing has also been developed for printing of contact lenses, allowing a wider range of coloured designs to be produced.
Inkjet printing is also being used for bio-medical and biotechnology applications, where the appropriate reagents are accurately dispensed onto sensor strips and into combinatorial chemistry arrays. Array printing removes the risk of cross-contamination present with traditional dispensing methods, speeds up the testing process and reduces the amount of reagent required. Test strips for devices such as those used by diabetics for glucose level detection and for pregnancy testing are now being developed for manufacture using inkjet printing, showing dramatic increases in the consistency of the manufactured strips, giving increased yield and reduced production cost.
Sports Equipment and Bespoke Fashion Accessories
Rapid prototyping with inkjet printing is also used to produce bespoke parts such as cycle helmets and trainers for top athletes. A 3D scan of the body part is fed directly into the printer, creating equipment that is completely tailored to the user. This technique is also being used to create one-off products like high fashion shoes and accessories.
Inkjet printing is being considered for applying food flavourings. For example, the traditional method of applying flavour to crisps is to tumble the crisps with the flavouring agents, which can cause damage and leads to significant downtime when cleaning the machine to accommodate flavour changes. By inkjet printing flavours, food manufacturers can achieve more accurate and predictable results, without damage to delicate products due to the non-contact nature of the printing.
In another dosing application, inkjet printing has been used to apply perfume to household items, such as lampshades and floor mops, so that a pleasant scent is emitted when the light bulb warms the shade, or the mop is pressed to the floor. Again printing allows scents to be mixed, to make each scent different and allow multiple design variations to be introduced simply.
Coatings and Technical Textiles
Fluids applied using inkjet can satisfy functional requirements for a range of applications, including hydrophobic layers for printed circuit boards, anti-scratch coatings for mobile phone displays, hard coatings for automobile headlamp covers, anti-fade, UV and dirt resistant treatments for tents and awnings, flame retardant coatings for aircraft interiors and garments and many others.
Covert coding and marking is being increasingly used for track and trace applications within packaging, where counterfeiting and contamination are damaging to corporate image and public health. Special security fluids with properties such as fluorescence, IR absorption, absorption of specific visible wavelengths and angle-dependent appearance form part of the armoury to counteract these issues.
Inkjet printing can also be used to print intelligent labels on perishable items such as food, which mimic the degradation process and so acts as an active best-before date. An R&D consortium, partly funded by the UK government, has developed an inkjet fluid containing liquid crystals that record temperature stresses. This can be used to manufacture RFID sensor tags for monitoring perishable goods in the supply chain.
Inkjet printing is not just about decoration. Applications of inkjet printing in functional manufacturing, coating and processing show the almost unlimited potential of the technology for revolutionising manufacturing.