The best known e-paper devices are without a doubt those based on E Ink’s display technology. Devices such as the Sony, Amazon and iRex readers all use this technology to great affect, and have sold tons of devices with it. But, just because they’ve made a lot of money doesn’t necessarily mean it will stand the test of time. How long can E Ink dominate the current e-paper landscape? Let’s take a look.
Most people who are interested in e-readers know the basics of how the technology works, but it may be useful and interesting to take a deeper look into an E Ink patent to see what really makes it tick. The patents are all public domain, and looking at the right ones can give us a quick peek into how these things work. They show how the particles (black, white and color) are made, turned into a fluid, encapsulated and then turned into a film.
Looking at precisely how this technology works is key to understanding how well it will fare in the far (and very near) future. Before we explore the technology’s impact I will provide an overview on how E Ink particles are made and how the technology works. For those of you who are not interested in the technical specifics of the technology, you may skip over this section.
How E Ink Particles are Made
The patent itself is a bit dense to read in one bite, so we’re going to simplify things even further. The way the white particles work is pretty much the simplest to follow and the other particles are used in pretty much the same way.
To make the white particles, titanium dioxide pigment particles are coated with silicon dioxide. These are the types of pigments used in paints and coatings. A reaction is then done to make the surface carbon based, and then a polymer reacts on the surface. So what you end up with is an “onion like” particle with many layers, starting with a titanium dioxide core to give the whiteness and a hairy polymer surface which stops the particles from sticking together. The hairs can also give the particles charge needed to move in a device.
How E Ink Particles are Used to Make Electrophoretic Fluid
This is a simple step in essence, but it is actually very tricky to get just right. The dry particles are mixed with a solvent and a surfactant(s) to create the fluid. The solvent used is very hydrophobic (water-hating). The end results are extremely small (less than 1000nm) particles which are dispersed in a fluid. At this stage different colors can be mixed to give a 2-particle system, like you see in current E Ink displays. This is what is known as an Electrophoretic Fluid. If step is done incorrectly, there can be many long term problems such as aggregation of particles, or the particles can even carry the wrong charge mixing up your black and white particles and creating a big mess.
How E Ink Microencapsulates Electrophoretic Fluids
The electrophoretic fluids can be emulsified by surrounding drops of the electrophoretic fluid in water. Using some clever chemistry, a solid polymer at the interface of the water and electrophoretic fluid is formed. This provides solid capsules which now contain the fluid. The conditions must be just right. If they’re not, the capsules won’t be the same size, and if the capsules are not the same size, the electrodes can’t connect, won’t hold a charge, and will effectively be a dead capsule on the display.
Making the Film
Making the film is a very simple step, but tricky to get right as the engineering required for it has to be precise. The capsules are mixed with a binder, formed into a film and dried. Then it can be optionally laminated onto another binder. The binders used are sometimes based on PVA, which is a well known type of polymer. The binder and capsule must also be very flexible. The backplane electronics need to be applied to them and they need to conduct some electricity. All of these criteria must be in place in order to perform the electrophoretic manipulation of the particles to display images in a flexible display.
Coming Full Circle and Moving to the Future
You should not underestimate the amount of science used in an E Ink display. Many of the steps are extremely tricky to get just right, and if you get them even slightly wrong you are left with film which doesn’t perform well and a horrible mess to clean up afterwards.
The final film has some excellent properties. It shows good contrast ratio, the switching speed is quite high and it is bistable. Most importantly, it works time and time again in real devices.
The films on the market at the moment from E Ink are black and white. The real future of e-paper is color. People want moving video, faster refresh rates, cheaper devices with more features, but the first step to most of these is color. The main drawback is that E Ink technology has only been proven for 2 particle systems giving just black and white films.
Even if you could incorporate other colors, a mixture of either red, green, blue, cyan, magenta, yellow, black and white particles would be needed. To get the full color spectrum, at least 3 colors, plus white or black are needed. Recent announcements on color displays use color filters over a black/white display. These look washed out, usually producing pastel shades.
What does this mean for the future of E Ink type devices? They work well now, they have a dominant market share, but the technology does not seem well suited for color applications. The particles and films described above can be found in patents over 10 years old and not much has changed in the patents on the synthesis during this time. Improvements made in the patents are on bistability, switching speeds and lower switching voltages, but the question of full color devices is still open.
Until we see this, electrophoretic displays of this type will always be in a weak position when colored technologies enter the market this year. However, history has shown us that when technologies go head to head it is often a battle won in the marketing departments. If this is to be the case with e-paper, judging by the current market, expect E Ink to be here to stay.
By W Y Scott
Bio - W Y Scott has a strong background in materials chemistry. With many years experience in the industry and a PhD in Chemistry, his main expertise is in the physics and chemistry behind many e-paper modes.
Good article. E Ink is such a dominant player in the e-paper market - it will be interesting to see what happens once we see more color displays. Since PVI bought E Ink, perhaps no more technology patents will be filed by E Ink - rather PVI might file them and/or buy up companies that have invented good bistable color technologies.
Yeah I second that- I think e-readers are just the start.
I’ve been researching the E-ink technology, trying to discover the palette of greys. As a web designer in the ’90’s this was critical to a good display, and I had presumed similar principles would hold for E-ink. However this information seems to be unavailable, and experiments with blocks of greys seem to indicate clusters of greys look better, followed by crosshatched (rather than dithered) clusters.
I’m wondering if you can shed any light on this question?
You say that “The films on the market at the moment from E Ink are black and white.”
Well, I have got one, and it is black and grey.
Before color, what is needed is real white.
Those screens are just too dark, which makes them very inferior to real books. Real books are much more readable in normal lighting conditions.
Real books are not true white though??? They are usually quite far from white and I expect that on a true colour space chart, the e-ink white is much closer to white than paper. You’re getting mistaken over what you consider to be “real” white.
It’s due to the reflectivity… Papers can reflect ~80% light, and E-ink only ~40%. That caused we to perceive a not true white colorJonathan Scott said:
.