Browse Prior Art Database

Electrophoretic/Photochromic Hybrid Device for Multi-Colored Displays

IP.com Disclosure Number: IPCOM000033735D
Publication Date: 2004-Dec-23
Document File: 4 page(s) / 95K

Publishing Venue

The IP.com Prior Art Database

Abstract

Electrophoretic inks consist of charged particles dispersed in a suspending fluid. Only 2 colored states are possible. This disclosure describes a hybrid device, consisting of a photochromic layer superimposed on top of a 1-particle electrophoretic device. The addition of this photochromic layer provides an additional handle for color change of the device, enabling a wider color gamut. Moreover, the coloration intensity of the photochromic film can be tuned, enabling a grayscale effect on the device.

This text was extracted from a Microsoft Word document.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 53% of the total text.

Electrophoretic/Photochromic Hybrid Device for Multi-Colored Displays

Electrophoretic inks consist of charged particles dispersed in a suspending fluid.  Only 2 colored states are possible.  The result is a monochrome device (i.e.:  black and white, blue and white, red and white, blue and red, etc.).  For the realization of electronic paper, a wider range of colors is essential.  To date, most electrophoretic display devices are limited to the monochrome arrangement.  Relatively complex designs are required for full color displays, such as segmented lateral electrodes with colored backplanes or color filters.  All these schemes suffer from diminished intensity of reflection, and a faded color appearance.

This disclosure describes a hybrid device, consisting of a photochromic layer superimposed on top of a 1-particle electrophoretic device.  The addition of this photochromic layer provides an additional handle for color change of the device, enabling a wider color gamut.  Moreover, the coloration intensity of the photochromic film can be tuned, enabling a grayscale effect on the device.  Shown below in Figure 1 are side and top views of the hybrid device concept.

Microcapsules containing a green dye and white particles are mixed with a binder and spread onto a conductive substrate to create a thin film of capsules.  Next, a solution containing a mixture of polymer and spiropyran molecules is coated onto the capsule film.  The solvent is allowed to evaporate, leaving a dry photochromic film layer on top of the capsules.  The spiropyran/polymer film is initially transparent.  Upon irradiation with long wave UV light, the spiropyran undergoes a ring opening to create a highly colored form, and the film becomes dark purple.  The superposition of this colored film over the capsule film makes the device look darker.  By heating the film, or allowing the film to stand in ambient light, the film eventually reverts back to the colorless state.  The electrophoretic film can be switched between the light and dark states, and, by superimposing the photochromic film over this, a 4-color scheme may be realized.  Moreover, the coloration intensity of the photochromic top film can be varied to create a grayscale effect, as shown below in Figure 2.

Figure 2: Possible Color Schemes with Hybrid Electrophoretic/Photochromic Device.

In a second configuration, the spiropyran material can be embedded directly into the binder material containing the microcapsules, as illustrated in Figure 3 to create a single-layered hybrid device.

Figure 3:  Single-layered Hybrid Electrophoretic/Photochromic Device.

Preparation of Electrophoretic Ink

5.5g of a white pa...