WO2005031450A1

WO2005031450A1 - Electronic paint with charge memory

Info

Publication number: WO2005031450A1
Application number: PCT/IB2004/051854
Authority: WO
Inventors: Anthonie H. Bergman; Murray F Gillies; Mark T. Johnson; Guofu Zhou
Original assignee: Koninklijke Philips Electronics, N.V.; U.S. Philips Corporation
Priority date: 2003-09-29
Filing date: 2004-09-24
Publication date: 2005-04-07

Abstract

The invention provides an electronic paint (10) comprising a lower conductive layer (20), a layer of electrophoretic ink (22) disposed on the lower conductive layer (20), ,a plurality of floating electrodes (24) disposed on the layer of electrophoretic ink (22), a photoconductive layer (26) disposed on the plurality of floating electrodes (24), and an upper conductive layer (28) disposed on the photoconductive layer (26). Light (36) directed onto a portion of the photoconductive layer (26) and a bias voltage (30) applied to the upper conductive layer (28) allow a transfer of a predetermined charge (32) onto at least one floating electrode (24). Activation of the electrophoretic ink (22) is based on the predetermined charge (32) on the floating electrode (24) and a reference voltage (34) that is applied to the lower conductive layer (20).

Description

ELECTRONIC PAINT WITH CHARGE MEMORY

This invention relates generally to electrophoretic displays, and more specifically to an electronic paint including electrophoretic ink and methods of activation thereof. Large displays having electrophoretic materials are being developed for whiteboards. signage, billboards and the like. Bi-stable, reflective displays technologies such as electrophoretic image displays (EPID) and suspended particle displays (SPD) offer the possibility of low power, high contrast displays having flexible substrates that are especially suited for large area applications, which often are updated only infrequently. Emergent electronic-ink technologies based on electrophoresis have been used for displays that are activated by writing a desired image onto the so-called electronic or digital ink. Electrophoretic displays can be bi-stable, in that their display elements have first and second display states that differ in at least one optical property such as lightness or darkness of a color. In recent electrophoretic displays, the display states occur after microencapsulated particles in the electronic ink have been driven to one state or another by means of an electronic pulse of a finite duration, and the driven state persists after the activation voltage has been removed. Such displays can have attributes of good brightness and contrast, wide -viewing angles, state stability for two or more states, and low power consumption when compared with liquid crystal displays (LCDs). Multi-stable electronic inks have a continuum of optical states into which the electronic ink can be switched, allowing gray-scale images and potentially full -color electrophoretic displays. Current research is moving towards developing commercially viable encapsulated, electrophoretic materials for thin electronic -ink displays that look and feel like pieces of paper. Electronic-ink displays are attractive because they can be more than six times brighter than reflective liquid-crystal displays (LCDs) and can be seen at any angle without a change in contrast, unlike LCDs. Researchers are also working on applying this digital- or electronic -ink technology to a large electronic wall display of a so-called electronic wallpaper, poster or wall screen, which could consist of a thin electrophoretic film placed on a wall. A large electronic -ink display would be appropriate where semi -permanent images are required, such as a large electronic advertisement medium. This electronic low -cost electronic ink application also could be us ed, for example, for putting a shopping list, the latest vacation pictures, or family pictures on a home wall Methods, systems and related devices for addressing and writing to electronic -ink displays are actively being developed for large electrophoretic displays with a handheld charge - transfer device. One challenge in developing effective methods of and systems for writing to these displays is the switching speed of the display material to its intended display state. Current electronic inks require one second or so to switch at room temperature with an approximately 10V drive. Applying higher voltages provides faster switching time, and increasing the temperature will also improve switching time. While a handheld charge-transfer device that is used to address the display may be able to travel over the surface of the display with a velocity on the order often centimeters per second, writing a spot with a pixel size of one millimeter allows only ten milliseconds to switch the electronic ink. An exemplary large electrophoretic display with a size on the order of one meter by one meter would therefore require a long time to write the image when the activation times for the electronic ink are long. Thus, the present speeds of addressing electronic ink with a handheld device and activation needs of large electrophoretic displays are mismatched. Using active-matrix addressing methods with transistors, photo- diode/transistors or any complicated structuring in the display to increase switching speed are workable yet are cost prohibitive for large, inexpensive applications, particularly those with low refresh rates on the order of days, weeks, or even months. One active matrix electrophoretic display having a switching element for turning the writing of data on and off is described in "Display Device and Recording Medium," Inoue, U.S. Patent Application No. 2002/0036616 published March 28, 2002. The device has a thin film transistor (TFT) built in the switching element and an associated driver to control the tu rning off and on of the TFT. Whenever an electrophoretic display has integrated electrodes, the electrode must be protected from potential mechanical or electrochemical damage. A description of an exemplary electrode employed in an electrophoretic display is described in "Protective Electrodes for Electrophoretic Displays," Drzaic et al., International Patent No. WO0038001 issued June 29, 2000. A layer of material is designed to protect a vapor permeable electrode that has a reticulated electrically conductive structure such as a metal screen or wire mesh, or a reticulated structure coated or impregnated with a conductive material. An electric reusable paper sheet that uses a pattern of conductive charge -retaining islands on its outer surface is described in "Field Addressed Displays Using Charge Discharging in Conjunction with Charge Retaining Island Structures," Howard et al., U.S. Patent No. 6,456,272 issued September 24, 2002, and in "Charge Retention Islands for Electric Paper and Applications Thereof," Howard et al., United States Patent No. 6,222,513 issued April 24, 2001. The first of two thin layers encapsulates the conductive charge -retaining islands in an electric reusable paper substrate, which interact with conductive areas in the encapsulating sheet. Electric charges from an external charge-transfer device help create an electric field in the electric reusable paper sufficient to cause an image change. A display having an electrophoretic dispersion layer and a capacitive element for storing charge is described in "Electrophoretic Device, Electronic Sheet including the Same, Electronic Book including the Electronic Sheet, and Manufacturing Method Thereof," Shimoda et al., U.S. Patent Application No. 2002/0105600 published August 8, 2002. External signals are transmitted to a driver region of the display to change display contents on the display region. While smaller electrophoretic displays often receive data and are addressed by driving an active matrix of the display, large electrophoretic displays may have no intrinsic addressing schemes to accurately write text and graphics. Thus, an approach is needed that allows rapid strokes of a handheld activation device to accommodate relatively slow transition times of electronic inks. What a larger electrophoretic display needs is a system and process by which the display can receive data in a short period of time from a handheld writing device while allowing the electronic paint or ink to switch its display state more slowly. Such a desirable system would be cost effective for large area applications where data is updated infrequently, and its associated methods would be time effective. The aforementioned and other features and advantages of the invention will become further apparent from the follo ing detailed description of the presently preferred embodiments, read in conjunction with the accompanying drawings. The detailed description and drawings are merely illustrative of the invention rather than limiting, the scope of the invention being defined by the appended claims and equivalents thereof. One aspect of the invention is an electronic paint. The electronic paint includes a lower conductive layer, a layer of electrophoretic ink disposed on the lower conductive layer, a plurality of floating electrodes disposed on the layer of electrophoretic ink, a photoconductive layer disposed on the plurality of floating electrodes, and an upper conductive layer disposed on the photoconductive layer. Light directed onto a portion of the photoconductive la yer and a bias voltage applied to the upper conductive layer allow a transfer of a predetermined charge onto at least one floating electrode. Activation of the electrophoretic ink is based on the predetermined charge on the floating electrode and a reference voltage that is applied to the lower conductive layer. Another aspect of the invention is a method of activating an electronic paint. A bias voltage and a reference voltage are applied to the electronic paint. Light is received on a portion of a photoconductive layer. A predetermined charge is transferred through the lit portion of the photoconductive layer to at least one floating electrode based on the received light and the applied bias voltage. The electrophoretic ink is activated based on the predetermined charge and the applied reference voltage. Another aspect of the invention is an electronic paint activation system. The electronic paint activation system includes an electronic brush and an electronic paint including a lower conductive layer, a layer of electrophoretic ink disposed on the lower conductive layer, a plurality of floating electrodes disposed on the layer of electrophoretic ink, a photoconductive layer disposed on the plurality of floating electrodes, and an upper conductive layer disposed on the photoconductive layer. Light directed from the electronic brush onto a portion of the photoconductive layer and a bias voltage applied to the upper conductive layer allow a transfer of a predetermined charge onto at least one floating electrode. Activation of the electrophoretic ink is based on the predetermined charge on the floating electrode and a reference voltage that is applied to the lower conductive layer. The aforementioned and other features and advantages of the invention will become further apparent from the following detailed description of the presently preferred embodiments, read in conjunction with the accompanying drawings. The detailed description and drawings are merely illustrative of the invention rather than limiting, the scope of the invention being defined by the appended claims and equivalents thereof. Various embodiment of the present invention are illustrated by the accompanying figures, wherein: FIG. 1 is an illustration of an electronic paint, in accordance with one embodiment of the current invention; FIG. 2 is a cross -sectional view of an electronic paint, in accordance with one embodiment of the current invention; FIG. 3a, FIG.3b, FIG.3c, FIG.3d, FIG.3e, and FIG.3f are illustrations of a method for activating an electronic paint, in accordance with one embodiment of the current invention; FIG. 4 is a graph of voltage on a floating electrode within an electronic paint, in accordance with one embodiment of the current invention; FIG. 5 is a block diagram of an electronic paint activation system, in accordance with one embodiment of the current invention; and FIG. 6 is a flow diagram of a method for activating an electronic paint, in accordance with one embodiment of the current invention. FIG. 1 shows an exploded illustration of an electronic paint 10, in accordance with on embodiment of the present invention. Electronic paint 10 includes a first or lower conductive layer 20, a layer of electrophoretic ink 22 disposed on the lower conductive layer 20, a plurality of spaced-apart floating electrodes 24 disposed on the layer of electrophoretic ink 22, a photoconductive layer 26 disposed on the plurality of floating electrodes 24, and a second or upper conductive layer 28 disposed on the photoconductive layer 26. The optical state of electrophoretic ink 22 is adjusted by shining or directing light onto selective portions of photoconductive layer 26, causing charge to be transferred from upper conductive layer 28 and stored on one or more floating electrodes 24. A bias voltage is applied to upper conductive layer 28, which allows the transfer of a predetermined charge onto at least one floating electrode 24. The transferred charge generates an attractive force and an electric field to twist and re -orient electrophoretic ink 22, providing a variable color or gray -level display from which text, graphics, images, photographs and other image data can be viewed. With this material, faster pulses or scanned beams of light can be used to control the transfer of charge onto floating electrodes 24, which in turn activate electrophoretic ink 22 on a slower time scale to a desired optical state. Activation of electrophoretic ink 22 is based on the predetermined charge on one or more floating electrodes 24 and a reference voltage that is applied to lower conductive layer 20. Floating electrodes 24 and lower conductive layer 20 serve as electrodes in a parallel plate capacitor, with electrophoretic ink 22 serving as the dielectric layer. This capacitor is charged by temporally and locally connecting one or more floating electrodes 24 to upper conductive layer 28 with an applied bias voltage. Striking photoconductor layer 26 with, for example, a scanned or pulsed beam of laser light can make this connection. The capacitor c an hold its voltage for a longer time than the optical addressing time, allowing electrophoretic ink 22 to switch to the desired state. Charge stored on floating electrodes 24 retains a driving force on electrophoretic ink 22, acting as a local memory until the desired optical state is set. Gray tones, for example, can be achieved with electrophoretic ink 22 by controlling the bias voltage, the intensity and timing of the addressing laser, the leakage through the layer of electrophoretic ink 22 and photoconductor layer 26, and by the selective quenching of the charge stored on floating electrodes 24. Electrophoretic ink 22 comprises one of several commercially available electrophoretic inks, commonly referred to as electronic inks or e-ink. The layer of electrophoretic ink 22 comprises, for example, a thin electrophoretic film with millions of tiny microcapsules in which positively charged white particles and negatively charged black particles are suspended in a clear fluid. When a negative electric field is applied to the display, the white particles move to the top of the microcapsule where they become visible to the user. This makes the surface appear white at the top position or surface of the microcapsule. At the same time, the electric field pulls the black particles to the bottom of the microcapsules where they are hidden. When the process is reversed, the black particles appear at the top of the microcapsule, which makes the surface appear dark at the surface of the microcapsule. When the activation voltage is removed, a fixed image remains on the display surface. Before another image is written, the so-called electronic ink of the display material may need to be reset to a well -defined state, such as an all white surface with white particles moved to the top of the microcapsules, prior to re-addressing the ink. This can be accomplished by, for example, applying short pulses of relatively high voltage across lower conductive layer 20 and upper conductive layer 28 of electronic paint 10, forcing the ink into an initialized or reset optical state through the applied electric field. In another example, electrophoretic ink 22 contains an array of colored electrophoretic materials selectively positioned under floating electrodes 24 to allow generation and display of colored images. FIG.2 shows a cross -sectional view of an electronic paint 10, in accordance with one embodiment of the present invention. A layer of electrophoretic ink 22 is sandwiched between lower conductive layer 20 and an array of floating electrodes 24. Lower conductive layer 20 may comprise, for example, a reflective metal such as aluminum, platinum or chrome. Alternatively, lower conductive layer 20 may comprise a transparent electrode material such as indium tin oxide (ITO) or other suitably conductive material. A photoconductive layer 26 is sandwiched between the array of floating electrodes 24 and upper conductive layer 28. The plurality of floating electrodes 24 is configured, for example, in a periodic array of small, rectangular conductive pads, square conductive pads, circular conductive pads, or squares of conductive pads with rounded corners. Alternatively, floating electrodes 24 may be configured randomly with small, locally isolated regions of conductive islands. In one example, the size of individual floating electrodes 24 is on the order of the pixel size for the display. In another example, the size of individual floating electrodes 24 may be appreciably smaller than the pixel size for the display, such that more than one electrode is locally charged with an applied laser beam to activate electrophoretic ink 22. The array of floating electrodes may be configured to encompass, for examples: an array of magenta, yellow, and cyan electrophoretic materials; an array of magenta, yellow, cyan and black electrophoretic materials, or an array of red, green and blue electrophoretic materials for transmissive displays. Floating electrodes 24 comprise, for example, patterned ITO or an insulative polymer including polyethylenedioxythiophene (PEDOT) with locally doped regions of polyphenylene sulfide (PPS). Upper conductive layer 28 comprises a transparent optical material such as ITO for topside viewing and for charging floating electrodes 24. Upper conductive layer 28 is at least transparent to the wavelength of the activation laser light. A plastic or glass backing may be added to either or both sides of electronic paint 10 to increase the strength while retaining the desired flexibility. Reflected displays comprising electronic paint 10 with a metallic backing are viewed from the top, as illustrated. Alternatively, electronic paint 10 may be viewed through lower conductive layer 20, and can be addressed from this side. In other configurations such as a transmissive display, lower conductive layer 20 is transparent over the visible light range and electrophoretic ink 22 is selectively absorbent, allowing backside viewing of written images or the option of backlighting the display. A bias voltage 30 and a reference voltage 34 may be applied to upper conductive layer 28 and lower conductive layer 20, respectively, to allow the initialization and activation of electrophoretic ink 22. FIG.3a, FIG.3b, FIG.3c, FIG.3d, FIG. 3e, and FIG.3f show illustrations of a method for activating an electronic paint, in accordance with one embodiment of the present invention. These cross -sectional views show an electronic paint 10 under various electrical and optical influences. FIG.3a shows a randomized electrophoretic ink 22 between lower conductive layer 20 and a floating electrode 24, with a positive bias voltage 30 applied to upper conductive layer 28 and a reference voltage 34 such as ground or common applied to lower conductive layer 20. In this cross-section, no light is applied to photoconductive layer 26. Most of the voltage drop occurs across the photoconductive layer, and the electrophoretic particles remain largely in their initial orientations. In FIG.3b, an incident beam of light 36 (λj) is absorbed in a portion of photoconductive layer 26, a conductive path is generated between upper conductive layer 28 and floating electrode 24, and a predetermined charge 32 is transferred from upper conductive layer 28 with applied bias voltage 30 onto floating electrode 24. As charge accumulates on floating electrode 24, an electric field is generated between floating electrode 24 and lower conductive layer 20 with applied reference voltage 34, and electrophoretic ink 22 is driven accordingly. In FIG. 3c, the light is removed or directed elsewhere, and charge 32 on floating electrode 24 in coordination with reference voltage 34 applied to lower conductive layer 20 continue to generate an electric field that further orients electrophoretic particles within electrophoretic ink 22. Even when bias voltage 30 is removed from upper conductive layer 28 as in FIG.3d, the electrophoretic particles will continue their path towards orientation. One method of quenching the charge on floating electrode 24 is to allow the charge to bleed away via parasitic resistance paths between floating electrode 24 and upper conductive layer 28, lower conductive layer 20, or other floating electrodes, thus locking in or "freezing" electrophoretic ink 22 to a desired optical state. Alternatively, as seen in FIG. 3e, incident laser light 36 (λi) is applied to a portion or all of photoconductive layer 26, forming conductive paths between floating electrode 24 and upper conductive layer 28, thereby removing all the charge from floating electrode 24 when bias voltage 30 is set equal to reference voltage 34. When the charge has been removed from floating electrode 24, the electrophoretic particles in electrophoretic ink 22 stabilize and are locked in to a desired optical state, as seen in FIG.3f. FIG. 4 shows a graph of voltage on a floating electrode with an electronic paint, in accordance with one embodiment of the present invention. In this graph, floating electrode voltage 38 varies between the reference voltage and the bias voltage. The bias voltage is shown as a positive voltage with respect to the reference voltage, though the bias voltage may be negative as well to switch or drive the electrophoretic material in an opposite direction. At time t = t₀, the bias voltage and the reference voltage are set to ground or zero, indicated as v_refgnd, and the floating electrode voltage is also to zero. The electrophoretic particles under the floating electrode have been previously reset or initialized, for example, into a white optical state, and then they can be set to a gray or black optical state as the particles are activated. At time t = ti, a positive bias voltage, indicated as V_b,_as,hi_gh5 is applied to the upper conductive layer. At time t = t₂, light is applied to a portion of a photoconductive layer, and charge is transferred from the upper conductive layer to the floating electrode, pulling the voltage towards the bias voltage. As charge is transferred, the voltage on the floating electrode reaches the bias voltage and is retained there until the light is removed. The light is removed at t = t₃, and the floating electrode voltage decreases as charge leaks away. The bias voltage may be adjusted to another value, removed, or turned off as indicated at t = t4. While the floating electrode is charged, the electrophoretic ink continues to re -orient and modify its viewable color and intensity. At t = t₅, a second light is applied with the bias voltage on the upper conductor set equal to the reference voltage on the lower conductor, thereby discharging any remaining charge on the floating electrode. At t = tβ, the charge is removed, locking in or freezing the color and intensity of the electrophoretic ink. This plot indicates that the electrophoretic ink can continue to re-orient or "develop" after the beam of light is removed. Secondly, the graph shows that the amount of charge transferred to the floating electrode is in part determined by the bias voltage, such that the bias voltage can be adjusted as the laser light is scanned to transfer a predetermined charge onto the floating electrodes. Thirdly, the graph shows that the driving force for the electrophoretic ink, when necessary, can be rapidly quenched by the application of a flooding light source, though controlled bleeding of the charge leads to a similar result. FIG. 5 shows a block diagram of an electronic paint activation system, in accordance with one embodiment of the present invention. Electronic paint activation system 40 includes an electronic brush 50 and an electronic paint 10. Electronic brush 50 includes a laser scanner 52 and a position detector 54. Electronic paint 10 includes a lower conductive layer 20, a layer of electrophoretic ink 22, a plurality of floating electrodes 24, a photoconductive layer 26, and an upper conductive layer 28. Light directed from electronic brush 50 onto a portion of photoconductive layer 26 allows a transfer of a predetermined charge onto at least one floating electrode 24 when a bias voltage 30 is applied to upper conductive layer 28. Electrophoretic ink 22 is activated based on the predetermined charge on floating electrode 24 and on a reference voltage 34 that is applied to lower conductive layer 20. Electronic paint activation system 40 may include a controller 42 such as a central processing unit (CPU), a dedicated controller or other suitable electronic circuit electrically coupled to electronic brush 50. Controller 42 controls laser scanner 52 and light 36 striking photoconductive layer 26 based on a determined position of electronic brush 50. Controller 42 may be wired or wirelessly connected to electronic brush 50. For example, controller 42 may be contained within a personal computer (PC), a laptop computer, or a personal digital assistant (PDA) and connected to electronic brush 50 via a cable or a short-range wireless link such as

Bluetooth™ or 802.11 protocols. Alternatively, controller 42 may be contained within electronic brush 50 and image data provided to electronic brush 50 and controller 42 via a memory device such as a memory stick, or an uplink from a PC, laptop computer or PDA that is optionally connected to the Internet 44. As electronic brush 50 is stroked or swept across the surface of electronic paint 10, light

36 from laser scanner 52 is directed preferentially at portions of photoconductive layer 26 to write the image data. Bias voltage 30 and reference voltage 34 may be set to a fixed level as laser scanner 52 optically addresses electronic paint 10. Alternatively, bias voltage 30 may be continuously varied as light 36 from laser scanner 52 is scanned across the surface of electronic paint 10, while position detector 54 provides sensor information that allows controller 42 to determine the location and rotation of electronic brush 50. The image data may be provided in real time as the image is written with electronic brush 50, or stored within electronic brush 50 until written. FIG. 6 shows a flow diagram of a method for activating an electronic paint, in accordance with one embodiment of the present invention. Various steps are described to initialize and activate electronic paint, such as the exemplary electronic paint shown in FIG. 1. An electrophoretic ink is initialized or reset to a predetermined optical state, as seen at block 60. The predetermined optical state may be white, black, or a predefined color depending on the type of electrophoretic ink and the applied voltages. Initialization of the electrophoretic ink may be accomplished, for example, by setting a bias voltage to a large negative potential 10

while grounding the reference voltage, and then flooding the photoconductive layer with light to activate and switch the electrophoretic ink to the predetermined optical state. From the initialized optical state, the electrophoretic can be adjusted in one common direction based on the driving forces applied to the electrophoretic ink. Alternatively, the electrophoretic ink may be initialized by applying high frequency voltage waveforms or voltage pulses of one polarity or the other to generate a sufficient el ectric field across the electrophoretic material that induces a transition to the desired optical state. A large, static voltage applied between the lower conductor and upper conductor will also initialize or reset the electrophoretic ink. A bias voltage and a reference voltage are applied to the electronic paint, as seen at block 62. The bias voltage may be a fixed positive voltage or a fixed negative voltage. Alternatively, the bias voltage may vary in voltage level based on the image data and the position of a scanned beam of laser light so that the amount of charge transferred onto the floating electrodes is controlled. Light is received on a portion of the photoconductive layer, as seen at block 64. For example, a scanned beam of laser light from an electronic brush is directed towards and received on a portion of the photoconductive layer. As light energy is absorbed, a conductive path is generated between the upper conductive layer and the floating electrodes. A charge, which is transferred through the lit portion of the photoconductive layer to the floating electrodes, may be predetermined based on the received light, the applied bias voltage, the applied reference voltage, and the capacitance of the floating electrodes. The electrophoretic ink is activated based on the predetermined charge that is transferred to the floating electrodes and the applied reference voltage, as seen at block 66. The charged floating electrodes and the lower conductive layer generate an electric field that provides a force to set at least a portion of the electrophoretic ink into a predetermined optical state while the electrophoretic ink is activated. As the electrophoretic ink reaches its desired optical state, the charge may be removed from the floating electrodes to stabilize the electrophoretic ink in a predetermined optical state, such as at a predetermined gray level corresponding to the image data, as seen at block 68. In one example, the charge is removed from the floating electrodes by setting the bias voltage equal to the reference voltage and shining light on at least the previously lit portion of the photoconductive layer with, for example, a second pass of an electronic brush. When the charge has been removed, the electrophoretic ink is stabilized or frozen into the desired optical state, providing a viewable display of the image data. In another example, the bias voltage is set equal to the reference voltage and a floodlight is applied to the display. In another example, the charge 11

is removed from the floating electrodes by controlling the decay of the charge through the photoconductive material and the electrophoretic material. To write image data to all portions of the electronic paint, the steps for activating one portion can be performed in series, in parallel, or some combination thereof with the steps for activating another portion so that the optical state of each portion of the electrophoretic ink is set at the desired level. In one example having an electronic brush, the image data is written ont o additional portions of the electronic paint as the electronic brush is moved across the surface of the electronic paint or is lifted from the surface and new strokes are started. While the embodiments of the invention disclosed herein are presently consi dered to be preferred, various changes and modifications can be made without departing from the spirit and scope of the invention. The scope of the invention is indicated in the appended claims, and all changes that come within the meaning and range of equivalents are intended to be embraced therein.

Claims

An electronic paint (10), comprising: a lower conductive layer (20); a layer of electrophoretic ink (22) disposed on the lower conductive layer (20); a plurality of floating electrodes (24) disposed on the layer of electrophoretic ink

(22); a photoconductive layer (26) disposed on the plurality of floating electrodes (24); and an upper conductive layer (28) disposed on the photoconductive layer (26); wherein light (36) directed onto a portion of the photoconductive layer (26) and a bias voltage (30) applied to the upper conductive layer (28) allow a transfer of a predetermined charge (32) onto at least one floating electrode (24), and wherein activation of the electrophoretic ink (22) is based on the predetermined charge (32) on the floating electrode (24) and a reference voltage (34) that is applied to the lower conductive layer (20).

2. The electronic paint of claim 1 wherein the lower conductive layer (20) comprises one of a reflective metal and a transparent electrode material.

3. The electronic paint of claim 1 wherein the plurality of floating electrodes (24) comprises one of indium tin oxide and a conductive polymer including polyethylenedioxythiophene with locally doped regions of polyphenylene sulfide.

4. The electronic paint of claim 1 wherein the plurality of floating electrodes (24) is configured in a periodic array of rectangular conductive pads.

5. The electronic paint of claim 1 wherein the plurality of floating electrodes (24) is configured in a periodic array of square conductive pads.

6. The electronic paint of claim 1 wherein the upper conductive layer (28) comprises a transparent electrode material.

7. A method of activating an electronic paint, comprising: applying a bias voltage (30); applying a reference voltage (34); receiving light (36) on a portion of a photoconductive layer (26); transferring a predetermined charge (32) through the lit portion of the photoconductive layer (26) to at least one floating electrode (24) based on the received light (36) and the applied bias voltage (30); and activating an electrophoretic ink (22) based on the predetermined charge (32) and the applied reference voltage (34).

8. The method of claim 7 wherein receiving light (36) on the portion of the photoconductive layer (26) comprises absorbing light energy from a scanned beam of laser light (36) from an electronic brush.

9. The method of claim 7 further comprising: setting an optical state of at least a portion of the electrophoretic ink (22) while the electrophoretic ink (22) is activated.

10. The method of claim 7 further comprising: removing the predetermined charge (32) from the at least one floating electrode (24); and stabilizing the electrophoretic ink (22) in a predetermined optical state.

11. The method of claim 10 wherein removing the predetermined charge (32) from the at least one floating electrode (24) comprises setting the bias voltage (30) equal to the reference voltage (34), and shining light (36) on at least the previously lit portion of the photoconductive layer (26).

12. The method of claim 7 further comprising: initializing the electrophoretic ink (22) to a predetennined optical state.

13. An electronic paint activation system (40), comprising: an electronic brush (50) including a laser scanner (52) and a position detection means (54); and an electronic paint (10) including a lower conductive layer (20), a layer of electrophoretic ink (22) disposed on the lower conductive layer (20), a plurality of floating electrodes (24) disposed on the layer of electrophoretic ink (22), a photoconductive layer (26) disposed on the plurality of floating electrodes (24), and an upper conductive layer (28) disposed on the photoconductive layer (26); wherein light (36) directed from the electronic brush (50) onto a portion of the photoconductive layer (26) and a bias voltage (30) applied to the upper conductive layer (28) allow a transfer of a predetermined charge (32) onto at least one floating electrode (24), and wherein activation of the electrophoretic ink (22) is based on the predetermined charge (32) on the floating electrode (24) and a reference voltage (34) that is applied to the lower conductive layer (20).

14. The electronic paint activation system of claim 13 wherein the lower conductive layer (20) comprises one of a reflective metal and a transparent electrode material.

15. The electronic paint activation system of claim 13 wherein the plurality of floating electrodes (24) comprises one of indium tin oxide and a conductive polymer including polyethylenedioxythiophene with locally doped regions of polyphenylene sulfide.

16. The electronic paint activation system of claim 13 wherein the plurality of floating electrodes (24) is configured in a periodic array of rectangular conductive pads.

17. The electronic paint activation system of claim 13 wherein the plurality of floating electrodes (24) is configured in a periodic array of square conductive pads.

18. The electronic paint activation system of claim 13 wherein the upper conductive layer (28) comprises a transparent electrode material.

19. The electronic paint activation system of claim 13 further comprising: a controller (42) electrically coupled to the electronic brush (50), wherein the controller (42) controls the light (36) directed from the electronic brush (50).

20. The electronic paint activation system of claim 19 wherein the controller (42) is wired or wirelessly connected to the electronic brush (50).