A tour of the frontiers of printing – Physics World – physicsworld.com

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If you thought innovation in the world of printing was a thing of the past, think again. Joe McEntee goes for a multidisciplinary stroll around the UK’s Centre for Print Research
There can’t be many research environments where scientists in one laboratory are investigating the use of graphene as the basis of high-quality recyclable clothing, while along the corridor their peers are running a course on the ancient Japanese woodblock printing technique Mokuhanga. That, however, is exactly what happens at the Centre for Print Research (CFPR) at the University of the West of England (UWE) in Bristol, where the arts–science and industry–academia divides are bridged on a daily basis.
Following an ethos of convergence, collaboration and co-creation, the CFPR is an interdisciplinary enterprise that brings together senior researchers, postgraduates, technical specialists and apprentices in everything from fine-art print-making and design to physics, materials science and engineering. Their goal is to deliver innovative solutions for the future of print by carrying out empirical investigations into the artistic, historical and industrial significance of creative print practices, processes and technologies.
Adaptability and openness to new research pathways are prerequisites at the CFPR. Take, for example, applied physicist Susanne Klein. Having studied medical physics, Klein shifted to optical research. She then spent two decades as an industrial R&D scientist at HP Labs in Bristol, where her research programme ranged from colloidal chemistry, liquid crystals and advanced display materials to 3D-printing technologies and optical cryptography. Now, Klein is leading a five-year project at the CFPR. Funded to the tune of £1.2 million, its aim is to reimagine various 19th-century printing processes to make them cheaper, faster and more accessible.
One technique Klein is studying and modernizing is Woodburytype, which was the first commercially successful photomechanical printing method to reproduce the continuous tone of photographs. Patented in 1864 by British inventor Walter Woodbury, the process begins with a “wet-collodion” negative, which was the photographic technique used at the time. The negative is placed over a layer of dry, dichromated gelatin and put in sunlight for about 60 minutes. Any gelatin that is not exposed to light through the negative remains water-soluble, and is simply washed away.
The result is an astoundingly robust 3D relief (a mold) of the image, which can be pressed into lead using a hydraulic press. The lead printing plate is then oiled, filled with a warm gelatin pigmented with soot, and covered with paper before going into a printing press. After about five minutes, the paper is pulled off, and once the ink is dry, the print is finally flattened and trimmed. Originally, up to 10 printing plates could be made from a single gelatin relief, and these could be mounted in a printing carousel for mass printing.
“Since Woodburytype prints are based on pigmented gelatin, they are completely archivable because soot or carbon black is extremely ‘light-fast’ and gelatin will not deteriorate or change chemically as long as it is not exposed to extreme humidity,” says Klein. “Although the original process is time-consuming and became obsolete when lithography took off, the image quality is unsurpassed. Even today, Woodburytype is still the only continuous-tone photomechanical reproduction method.”
In revisiting the technique, Klein and her colleagues have developed two alternative routes for creating Woodburytype prints with modern materials. “In one method,” explains Klein, “we follow the original workflow, but replace dichromated gelatin with photopolymer, and lead with silicon.” In this way, the exposure time is reduced from 60 minutes to seconds, while printing plates can be made within hours rather than days. An even faster method uses a laser-cutter to create a relief in acrylic – producing a 10 by 15 cm printing plate in 10 minutes, for example. The precision of the laser-cutter also means the layers of cyan, magenta, yellow and black needed to create full-colour images can be easily printed on top of each other.
Both methods are attractive to fine-arts practitioners for the creation of original works of art, but they are also interesting for companies seeking an environmentally friendly way of creating high-end photographic reproductions for art installations and commercial advertising in public spaces. The advantages are that laser-cutting of printing plates is energy-efficient and produces almost no waste, while the inks are gelatin-based (a waste product of the meat-processing industry). Furthermore, the prints are biodegradable and the ink can be removed from the paper by washing with water.
Another area of investigation for Klein involves the industrial application of “structural colour”, where colour is generated not by pigments but by microscopic patterns reflecting and refracting light in unique ways (as in the wings of a butterfly). One intriguing option is to introduce additional layers of cholesteric (chiral nematic) liquid crystals into the relief of a Woodburytype, to print structural colour. With the appropriate materials, the liquid crystal could be oriented by the layer and the original printed colours changed by applying a magnetic or electric field, not dissimilar to a bistable display.
Possible applications include anticounterfeiting for the labelling of luxury goods, designer fashion and pharmaceuticals. “The commercial opportunity here is significant,” adds Klein. “The challenge is to produce secure packaging with printing inks that will change colour every time an item is authorized at different stages of the supply chain on its way to the customer.”
Klein’s colleague Nazmul Karim – research lead in the centre’s Graphene Application Laboratory – is another academic seemingly made-to-measure for the CFPR’s multidisciplinary melting pot. Before joining UWE in 2019, Karim spent four years working on graphene-based, high-performance functional clothing and wearable electronic textiles (e-textiles) at the National Graphene Institute at the University of Manchester, UK.
His current research interests – which are part of CFPR’s new materials programme – include preparing graphene (via exfoliation and functionalization) graphene and other 2D materials for e-textile applications. Karim is also studying how to make graphene wearables via highly scalable fabrication techniques such as coating and printing (i.e. with graphene “inks” applied directly onto textiles). “My team is passionate about introducing smart materials and artificial intelligence to printed electronics for non-invasive personalized healthcare applications,” says Karim.
The group’s latest results, based largely on work carried out by PhD student Md. Rashedul Islam, demonstrate the tangible commercial opportunity taking shape. Islam has developed a versatile e-textiles platform that is fully printed, highly conductive, flexible and machine-washable. The material can store energy using printed graphene supercapacitors while monitoring a range of physiological indicators, such as heart rate, skin temperature and assorted activity metrics. Even more impressive is that, when fashioned into a separate headband, the prototype e-textile can record brain activity (an electroencephalogram or EEG) to the same standard as conventional rigid electrodes. At the moment the supercapacitors are charged using an external power source, but the goal is to make them self-sufficient in the future by introducing energy-harvesting functionality.
The fabrication process exploits a highly scalable screen-printing technique, in which the graphene-based ink is passed through a custom-designed mesh on to a rough and flexible textile substrate. The conductive tracks are then encapsulated for insulation and protection, to produce a machine-washable e-textiles platform. The hope is that early-stage successes like this will open the way to volume production of multifunctional graphene-based e-textile garments, in which each item of clothing has a network of wearable sensors and is powered by the energy stored in graphene-based textile supercapacitors.
On a related front, the Graphene Application Laboratory is looking into the use of graphene and other functional materials (including antimicrobial coatings) as the basis of high-quality recyclable clothing. Right now, around 55% of textiles are made from synthetic polyesters – most commonly polyethylene terephthalate (PET), which is not biodegradable and can remain in the environment for hundreds of years. “Understandably, there’s growing interest from fashion brands and retailers to move away from virgin PET to recycled polymer (rPET)-based polyester fabrics with reduced environmental impacts,” says Karim.
The trouble is, current iterations of rPET suffer from thermal ageing, and degrade as a result of random mixing with other materials during the recycling process. It’s still early days, notes Karim, but initial results from CFPR show promise, with graphene-enhanced rPET having already been spun into fibres that are lighter, mechanically more robust and easier to recycle. “This will be a long game,” adds Karim, “and we’re going to need sustained collaboration across the innovation ecosystem. That means academic groups like ours working hand-in-hand with graphene suppliers, textile manufacturers, and the big fashion and clothing retailers.”
An altogether different manufacturing opportunity preoccupies Tavs Jorgensen, a craft potter and designer in the ceramics industry before he went on to pursue a career in academia. Jorgensen is in the vanguard of CFPR’s R&D efforts in digital manufacturing, aiming to fast-track the hitherto limited application of 3D-printing technologies, computer-controlled machining and robotics in ceramic production.
Jorgensen and his team are particularly interested in a production process known as extrusion. This is when soft and mouldable clay is forced through a channel, or “die”, that imparts a particular cross-sectional shape to the material, and yields a continuous linear clay strip that can be cut into pieces to produce individual parts such as bricks, tiles, cladding and other architectural components. Industrial extruders are used to make specialized ceramic parts, including filters for catalytic converters and high-temperature components for furnaces and autoclaves. Meanwhile, hand-operated extrusion systems are often found in craft workshops to create handles and one-off decorative elements in support of other production methods such as pressing and casting. “Our challenge,” says Jorgensen, “is how can we exploit digital technologies and robotics to extend the current uses of clay extrusion into more innovative commercial and design-led applications.”
The team’s default setting is based largely on practical experiments. “Sometimes tests are carried out as open-ended explorations with highly unpredictable outcomes, an approach driven largely by curiosity – what happens when we do this?” Fundamental physical and materials insights are an important element in understanding how the clay behaves. For example, during the drying and firing, the extruded clay pieces shrink by around 10–15%, and they can bend and crack due to tensions from the extrusion process.
“The nature of the clay extrusion makes theoretical calculations of the outcome challenging,” says Jorgensen, “although some work has been done to develop algorithms that can help to predict the flow of clay in an extrusion situation.” In an opportunistic cross-disciplinary tie-up, Jorgensen turned to the expertise of Damien Leech – a former CFPR theoretical physicist now based at the Belgian nanoelectronics centre imec – to develop models predicting how particular die geometries might affect the pressures needed to extrude clay. “While empirical testing remains the core methodology with the investigations,” Jorgensen adds, “the theoretical modelling has proved invaluable, providing a basic understanding of which geometries would be best deployed in the real-world physical experiments.”
The team is also creating tooling workflows that allow novel die designs for 3D printing to be quickly prototyped and tested, which is opening up applications for ceramic extrusion in high-performance industrial applications. Front-and-centre is CFPR’s R&D collaboration with the National Composites Centre (NCC) in Bristol. They are interested in the potential for extruding ceramic matrix composites (CMCs), a class of materials in which ceramic paste is mixed with inorganic binders to increase fracture toughness under mechanical or thermomechanical load.
The CFPR/NCC partners are currently defining and iterating the process specifics – including the supporting tools, jigs, components and workflows. Long-term, though, they are eyeing all manner of applications in sectors like power generation and aerospace, where CMCs are increasingly used for high-temperature heat-shield systems. “Extrusion is an entirely novel way of producing CMCs,” says Jorgensen, “and this research opens up the opportunity for us to create CMC parts with exotic geometries, such as pipes and profiles with complex internal structures.” Such CMC pipes are attracting interest for the next generation of nuclear power plants, while the extrusion process has the potential to support the UK’s net-zero carbon target for construction materials, with Jorgensen and colleagues exploring extrusion of unfired clay and fibre mixtures for low-carbon building components.
If convergence, collaboration and co-creation are fundamental to the CFPR research model, so too is the centre’s blend of artists, designers, scientists and technologists, working across both traditional and digital print disciplines.
The group also brings together people from a variety of backgrounds, with researchers from industry as well as academia. This mix of expertise and experience supports the CFPR’s broad international academic and industrial collaborations; with commercial partners including specialist printing companies, ceramic manufacturers and multinational technology firms. Joint R&D projects range from targeted contract research and feasibility studies through to the co-development of advanced materials, processes and full printing systems.
It’s apparent that there’s no hard-and-fast rulebook on collaboration at the CFPR, rather variations on a theme in which open-minded thinking is blended with creativity, science and technology innovation in advanced print practices.
Joe McEntee is a contributing editor based in South Gloucestershire, UK
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