Flexo printing has a future in printed electronics

The words “printed electronics” tend to mean different things to different people. Some may say that printed electronics refers to a process in which a conventional technology, like gravure, inkjet, screen, offset-litho or (increasingly) flexography, is used to produce electronic items and components like electronic circuits or sensors. Others might add that they are produced in a way that brings process and commercial advantages to the manufacturers and supply chain providers.

The more technically savvy printer may be able to expand a little. Maybe they know printing technologies are replacing photolithography and etching processes or that rapid development is taking place with regard to printing support technologies such as the development of low viscosity conductive inks that can be printed by flexography.

Most printing and converting practitioners would probably admit their interest in the printed electronics market and knowledge thereof is, at best, cursory. The reason perhaps is that it is still regarded as a speciality market , albeit one showing strong growth – its value is predicted to expand to a worldwide value of USD 40.2 billion over the next five year period.

Less theoretically inclined and more grounded in process and commercial reality than in the past, the future for many narrow web printers and converters will be in printed electronics. Advances in fabrication techniques and the use of organic semi-conductors are drivers of change, providing the potential for their use in inks to allow circuitry printing.

The printed electronic market is dynamic and has the attention of governments and industry at the highest level. Progress in this sector has been rewarding, but it’s worth remembering that printed electronics is still in its infancy. It’s also worth reminding ourselves of some of the important developments that have laid the foundation for future developments.

For the most part, inorganic semi-conductor fabrication required the deposition of slabs of semiconductor films followed by the lithographic impression of the desired device structure and removal of unwanted elements via physical and chemical etching. That has changed – the ability to create and employ organic polymers has redefined process parameters. It has turned a subtractive process based on the growth of films and selective etching into a more simplified and additive process based on the selective deposition of multi-layered structures of a desired geometry.

The fact that printed electronics no longer needs to rely on film growth to control crystal and electronic structure provides developers with unprecedented freedom in the choice of substrates used for device fabrication. For instance, flexible substrates can now be employed, and, most importantly, the substrate can be selected according to the specific requirements of the target application rather than what had  been the case – restricted by the choice of device material and lattice matching of a semi-conductor material or building block.

The dynamics with regard to printing electronics and plastic printed electronics has changed, opening up possibilities for flexography. Screen and inkjet have been favoured processes until recently. The former is a low cost, single pass technology suited to the relatively low-batch, slow manufacturing regime that until now has been prevalent. Inkjet is much more the upstart. It does have the advantage of being non-contact technology but is comparatively slow in terms of both throughput and curing.

Flexography offers enormous potential in that it is a roll-to-roll print technology, which could speed product throughput, making the production of devices such as flexible displays, bio-sensors, disposable electronics and even intelligent textiles a batch printing process that would be commercially more viable than at present. Complementing the increase in production output is the fact that flexo has the ability to provide the necessary resolution and precision that current and yet-to-be developed electronic devices will require.

Printed electronics will create many new markets for printing technology rather than just competing with existing ones. The anticipated scale of the market and the opportunities it will create are exciting for those engaged in the manufacture of print machinery and its complimentary technology and accessories. It’s likely most print technologies, whether inkjet, gravure, offset-litho and flexo (or hybrid combo), will continue, each gaining a degree of market share.

Production possibilities include small, low-cost RFID tags, smart packaging, and disposable sensors; and large, rugged and inexpensive electronics such as signage displays, integrated photovoltaic panels, smart shelving and EMI/RF shielding devices. Some application areas will have demanding material requirements. Inks are a particularly area where R&D will be ongoing. For instance, flexible displays – those that roll up – will require not only flexible substrates but inks that will not crack when dry or repeatedly flexed.

RK Print Coat Instruments FlexiProof 100 and the associated FlexiProof UV and FlexiProof LED UV are being used for a variety of purposes connected with optimising the flexo printing of electronics, according to the company. These flexo prepress devices are being used for conducting feasibility trials, R&D purposes and monitoring ink/substrate interaction. RK Print Coat Instruments says one advantage of the FlexiProof concept is that they are cost-effective, multi-tasking devices that replicate the processing conditions likely to be experienced in the real world.

A compact LED UV curing system for use with LED optimized flexographic inks completes the company’s lineup of FlexiProof devices. The FlexiProof LED UV features lamps that offer a tailored output either at the 385nm or 395nm wavelength. The company reports that regardless of the FlexiProof chosen, each occupy the minimum of bench top space in a laboratory, prepress production environment, R&D department or educational facility.

The FlexiProof unit is a scaled-down yet component-critical version of a full-sized flexographic production press. Used for trialling new products, it can be used instead of a production press for pilot runs, determining printability on a wide range of substrates, colour matching, preparation of customer presentation samples and ensuring accuracy in batch production situations. According to the company, proofing and curing inline with the FlexiProof UV offers additional benefits in that it highlights any problems associated with the use of UV inks frequently missed when proofing using a conventional offline UV conveyor.

RK Print Coat Instruments says it has other equipment and systems being used for the development of new products and for quality control, including the Rotary Koater and Versatile Converting Machine. In each of these systems the users may select from almost two dozen different print and coating head technologies. Systems can include hot air, infrared drying or UV curing, and laminating possibilities include both wet and dry.

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