Electronic Ink

Electronic ink is a special type of ink that can display different colors when exposed to an electric field. It is made through a two step process that involves creating two-toned charged particles and encapsulating them in a transparent polymeric shell. The resulting nanoparticle shells are suspended in a solvent until the ink can be applied to a surface. First developed in the early 1990s, electronic ink promises to revolutionize the printing industry and maybe even change the way we interact with the world.

Background

Ink has been around for centuries and for the purposes of displaying an idea, ink on paper has many advantages over electronic displays. Paper is easy to carry around and can be read almost anytime and anywhere. It does not require a power source and is relatively durable. However, ink on paper has the disadvantage of not being able to be updated. Electronic ink has been designed to maintain the advantages of traditional paper and ink while providing the added advantages of updating and high capacity data storage.

Electronic ink is like traditional ink in that it is a colored liquid that can be coated onto nearly any surface. Suspended in the liquid are millions of microcapsules that contain tiny, two-toned polymeric particles. One side of the particle is a dark color while the other is a contrasting light color. Similar to a magnet, the dark colored side of the particle has an electric charge that is opposite that of the light colored side. When the ink is exposed to an electric field, the particles realign themselves, depending on the charge of the field. When all of the dark colored sides are attracted to the surface, the ink looks dark. When an opposite electric charge is applied, the light colored sides orient face forward and the surface looks light. This ability to change from white to black or visa versa whenever desired makes electronic ink extremely useful. When a book or other surface is coated with electronic ink, it can be reprogrammed to display different words or pictures.

It has long been known in the printing industry that letters and pictures can be displayed using distinct dots, or pixels. The more pixels that can be placed closer together, the better the image looks. On a standard newspaper about 300 pixels are used in the area of a square inch. When electronic ink is coated on a surface in specific quantities, each of these pixels can be made light or dark depending on how the electronic field is applied. Printing technology is already available to cover surfaces with over 1,200 pixels per square inch of electronic ink. This resolution makes electronic ink suitable for almost any printed work.

The way that an electronic ink display would work is much like a computer screen. Each pixel of ink could be controlled by an attached computer. Groups of adjoining pixels could be turned on or off to creates letters, number, and pictures. While this might be difficult to achieve on a piece of standard paper, a specially designed paper is being developed which will feel and look like paper but actually be a mini-computer complete with a vast array of electric circuits to control each pixel. This special paper would not be essential however because a special scanner could also be developed to have the same effect.

One of the most useful characteristics of electronic ink is that after the electric field is removed, the ink remains in its configuration. This means that only a small amount of power is required as compared to typical electronic displays. The configuration can be changed however, by applying a new electric field whenever desired. This means that if a book was printed with electronic ink, it could contain the words of one book on one day and another book the next. If fitted with memory storage, a single electronic book could contain thousands of different texts.

History

While the printed word has been around for centuries, the idea of electronic ink is a relatively recent invention. In the late 1970s, researches at Xerox PARC developed a proto-type of an electronic book. The device used millions of tiny magnets that had oppositely colored sides (black on one, white on the other) embedded on a thin, soft, rubber surface. When an electric charge was introduced the magnets flipped making either a black or white mark similar to pixels on a video screen. The device was never a commercial success because it was large and difficult to use.

Over the next decade various screens were introduced and the idea of an electronic book became a reality. However, these devices still remain more cumbersome than printed paper. In 1993, Joe Jacobson, a researcher at MIT, began investigating the idea of a book that typeset itself. He conceived a variation of the PARC idea using reversible particles. Eventually, he created electronic ink, which utilizes colored polymers encased in a transparent shell. He submitted his idea for patent in 1996 and was eventually rewarded one in 2000.

Jacobson formed E Ink Corporation which was designed to bring electronic ink to the marketplace. The first commercial product is the Immedia display. It is an advertising sign that looks and feels just like a paper sign. However, this sign is coated with electronic ink allowing it to be programmed to change its message. E ink anticipates that electronic ink will eventually be utilized in an area where traditional ink is used such as newspapers, books, magazines and even clothes.

Raw Materials

A variety of raw materials are used in the production of electronic ink. These include polymers, reaction agents, solvents, and colorants.

Polymers are high molecular weight materials which are made up of chemically bonded monomers. To make the charged, colored portions of the electronic ink polyethylene, polyvinylidene fluoride or other suitable polymers are used. These materials are useful because they can be made liquid when heated, solidify when cooled, and will maintain stable dipoles which are long lasting.

Filler materials are added to the polymers to alter their physical characteristics. Since polymers are generally colorless, colorants are added to them to produce the contrast needed for electronic ink. These may be soluble dyes or comminuted pigments. To produce a white color, an inorganic material such as titanium dioxide may be used. Iron oxides can be used to produce other colors like yellow, red, and brown. Organic dyes such as pyrazolone reds, quinacridone violet, and flavanthrone yellow may also be utilized. Other fillers such as plasticizers can be added to modify the electrical characteristics of the polymers. This is particularly important for electronic ink. During production the polymer is heated. For this reason stabilizers are added to prevent it from breaking down. Heat stabilizers include unsaturated oils like soy bean oil. Protective materials that are added include UV protectors such as benzophenones and antioxidants such as aliphatic thiols. These materials help prevent UV degradation and environmental oxidation respectively.

During the electronic ink encapsulation process various compounds are used. Water is used to create an emulsion and provide a vehicle for the encapsulation reaction to take place. Monomers are added to produce the encapsulation shell. Cross-linking agents which cause the monomers to react are utilized. Silicone oil is the hydrophobic material that gets incorporated with the colored particles in the encapsulate. This material provides a liquid medium for the particles to travel through when the electric field is applied. It is clear, colorless and extremely slippery. Other gel or polymeric materials can be added to the encapsulate to improve the stability of the system.

The Manufacturing Process

Electronic ink is made in a step-wise fashion. First, two contrasting inks are given opposite charges. Then the inks are encapsulated in conductive micro spheres and applied to the desired surface.

Producing charged ink

• 1 Two contrasting liquid polymers are loaded into separate containers which have attached atomizing nozzles. The materials are kept heated so they remain liquid. One of the nozzles has a positively charged potential while the other has a negative potential. Pressure is then used to force the inks through the nozzles causing them to break into tiny particles and also acquire the opposing charges. The containers are situated next to each other so when the inks exit the nozzles they come in contact. Since they have opposite charges, they are attracted to each other and form larger, neutral particles.
• 2 After the larger particles are formed, the materials are allowed to cool which causes them to solidify. This results in a small two-toned solid particle which has a positive and negative side. The particles are then run past a heating element which reduces surface tension and creates a more perfect sphere.
• 3 The particles are then run through a set of electrodes to separate out the ones that are imperfectly charged. As they pass the electrodes, the imperfect particles are attracted to the corresponding electrode and then removed. The rest of the particles are transferred to the encapsulating area.

Encapsulating ink

• 4 The particles are moved into a tank which contains a liquid solution of monomer in a silicone oil. The particles are mixed thoroughly so they are evenly dispersed. This solution is combined with an aqueous phase which creates an emulsion. An emulsion is a semi-stable mixture of oil and water. The electronic ink particles remain in the silicone oil which is surround by water.
• 5 A cross-linking agent is added to the solution which causes the monomer to react with itself. This produces tiny spheres which contain some silicone oil and the electronic ink particles. The ink particles can then be separated from the aqueous phase for various applications. This can be done by evaporation with subsequent solvent washing.
• 6 After the reactions are complete, the electronic ink articles are stored in a liquid solvent until they can be applied. Depending on the final product, this application process can involve spreading the liquid ink on specialized paper, fabric, or other kinds of fibers.

Quality Control

To ensure the quality of the electronic ink, each phase of the production process is monitored. Since it is a relatively new technology, electronic ink is not made in large, rapid quantities. For this reason each step can be thoroughly tested before proceeding to the next. Inspections begin with an evaluation of the incoming raw materials. These materials are tested for things such as pH, viscosity, and specific gravity. Also, color and appearance are evaluated. After the electronic ink is finished, it is tested to ensure that it will properly react to an electric field. The material may be spread on a thin surface and have an electric field applied. The color of the surface should change accordingly. The particle size is also tested using various mesh screens.

The Future

The first products utilizing electronic ink are just being introduced. They are simple two-toned devices that are not more impressive than flat paneled electronic displays. However, future generations promise to have broad applications and may significantly impact the way we interact with the world. The hope that electronic ink manufacturers have is that this material will initially be incorporated into outdoor billboards, hand-held computer devices, books, and newspapers. But ultimately, electronic ink will be put onto any surface such as clothes, walls, product labels, and bumper stickers. It will then become ubiquitous to the environment so that any message can be displayed any-where at anytime.

Since the current electronic ink product is made up of only two colors, the products made with it can not create a full colored display. In the future, more colors of electronic ink will be developed. Scientists still have to work out how to display these differing colors at the proper time, but once accomplished, any surface coated with electronic ink could become as interesting to look at as a television screen.

Where to Learn More

Periodicals

Gregory, P. "Coloring the Jet Set." Chemistry in Britain (August 2000): 39-2.

Johnston, M. "Lucent, E Ink Demo Electronic Ink Prototypes." Digit (November 21,2000).

Peterson, I. "Rethinking Ink." Science News (June 20, 1998):396-97.

Wilkinson, S. "E-Books Emerge." Chemical & Engineering News (August 21, 2000): 49-4.

Other

E Ink. http://www.eink.com (January 2001).

MIT Media Laboratory. http://www.media.mit.edu/micromedia (January 2001).

—PerryRomanowski