What is printing?
The process of reproducing text and images using a master form or template, usually with the help of an external device called a printer that accepts text and graphic output from a computer and transfers the information to a surface. Printing can be traced back to early times where cylinder seals were used to imprint images on clay, and modern printing is typically done by using ink on paper (but can also be done on metals, plastics, composite materials and more).
There are many printing technologies, which can be divided into two main categories: impact and non-impact.
Impact printers include a mechanism that touches the paper to create an image. The two main impact technologies are Dot Matrix, in which small pins strike a ribbon coated with ink and cause the ink to transfer to the paper, and Character, which involves a ball with letters embossed on it striking against the ink ribbon and leaving an impression.
Non-impact methods do not touch the paper to create an image. Several methods are included in this category, like inkjet printers that use nozzles to spray drops of ink on the paper, laser printers that use dry ink, static electricity and heat to bond ink onto the paper, solid ink printers, dye sublimation and more.
Common methods of printing include: letterpress, offset lithography, flexography, gravure, screen printing and digital printing (which includes different methods like toner, magnetic digital print, laser and inkjet).
OLED (Organic Light Emitting Diodes) is a flat light emitting technology, made by placing a series of organic thin films (usually carbon based) between two conductors. When an electrical current is applied, light is emitted. OLEDs can be used to make displays and lighting, with possible applications that span TV sets, computer screens, mobile phones, decorative lighting and more. Since OLEDs emit light they do not require a backlight and so they are thinner than LCD displays, and are also more efficient, simpler to make and boast a better color contrast.
While OLED displays excel in color-contrast and efficiency compared to LCDs, they’ve also proven relatively hard to produce on a large scale. Current evaporation-based production techniques involve a lot of wasted material and risk of defects. OLEDs are also extremely sensitive to moisture and oxygen and therefore must be protected with a high performance encapsulating layer. All of these issues hinder OLEDs’ market takeover, but much work is put into resolving them.
OLED ink-jet printing
Current OLED producing methods rely on evaporation processes, in which the organic materials are deposited onto a glass sheet through a thin metal stencil, also known as a "shadow mask”. This process is problematic, as a significant amount of the material is wasted because it disperses all over the mask, in addition to inherent mask changes which expose the sheet to dust and compromise yields (OLEDs are by nature sensitive to contamination).
Inkjet OLED printing has the desirable ability to allow precision deposits without the use of a mask. It also produces less stray particles, thus boosting yields. These significant advantages make this technology interesting to many companies and virtually all OLED makers have active ink-jet printing development projects.
Inkjet methods form films by discharging the required amount of organic material onto large glass substrates in regular atmospheric conditions. This could be done, for example, by placing OLED pixels on glass or plastic using a portable platform and nozzles. Such methods have the potential to increase yields and lower prices, thus enabling OLED technology to take its deserving place in the market.
Unfortunately, OLED inkjet printing is not yet common, as printing OLED displays is a relatively challenging task for many reasons. A number of layers need to be deposited in pixels (the size of the pixels themselves is defined by the overall resolution the display will have). Being able to place the right number of drops of the active materials into the pixels is a challenge, in addition to developing a process in which the ink dries to deliver flat films of materials in the pixel.
Despite major progress, it is maintained that soluble OLED materials (required for inkjet printing) are less effective than evaporable ones. These are some of the challenges that make this technology somewhat scarce in the market, despite its great potential.
Latest OLED inkjet printing developments
Kateeva is a U.S based startup that was established in 2009 to develop OLED ink-jet deposition technology originally developed at MIT. It is currently the most prominent OLED inkjet printing company. In November 2013, Kateeva unveiled their YIELDjet OLED inkjet printing system, which can be used to produce OLEDs in high volume. It is the first one engineered from the ground up for OLED mass production, and should dramatically improve yields and lower production costs. Kateeva reports that this accomplishment was achieved by three major technical breakthroughs: it features a production-worthy pure nitrogen process chamber, which doubles the lifetime in certain applications, it reduces particles by as much as 10X thanks to a specialized mechanical design and it offers exceptional film coating uniformity with a process window that’s 5X wider than standard technologies.
In November 2014, Kateeva announced a new mass production flexible OLED thin film encapsulation (TFE) system, based on their ink-jet technology. The YIELDjet FLEX can offer cost-effective encapsulation deposition. In May 2014, Kateeva expanded its facilities to create a dedicated manufacturing space for building OLED inkjet printing systems. Kateeva already shipped one mass-production to an Asian display maker (probably Samsung, an investor in Kateeva).
In April 2014, AU Optronics developed an OLED inkjet printing technology with Merck’s assistance. AUO developed their own inkjet printer and used it to develop a 14" printable OLED panel. Merck is working closely with AUO to supply them with soluble OLED materials. AUO is still not mass producing commercial AMOLED panels, but the company seems to be close to doing so.
In March 2014, Tokyo Electron announced that it was accepting orders for the Elius 250 OLED inkjet printing system. TEL started collaborating with Seiko Epson on OLED manufacturing technology in 2010 to jointly-develop OLED display manufacturing technology that will integrate Epson's inkjet printing method and TEL's production equipment.
In December 2013, Merck and LG Display agreed to collaborate in developing OLED inkjet printing materials. The two companies are already doing business together (for instance, Merck supplies evaporable OLED materials to LGD’s OLED TVs), so this agreement means that Merck might also supply LGD with soluble materials. The work on this project is presumably ongoing.
In February 2012, Konica Minolta developed a high-accuracy inkjet head capable of 1-picoliter drop size, the first for printed electronics applications. The new print head utilizes the company's proprietary MEMS technologies for the first time. The new print head is resistant to various inks required for industrial applications and suitable to use with low-viscosity inks. It can be used for all sorts of applications, including OLED display patterning and OLED lighting thin air coating.