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Function-oriented Knowledge Base \ Electronic paper \ Improve image quality of paper-like display

Exercises by electrical field and heat improve visual contrast of a gyricon display

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Image forming in addressable, reusable, paper-like visual displays of the gyricon type is based upon rotating a multiplicity of bichromal balls in their micro-cavities by means of an electric field, the distribution of which is set by an electrode matrix in accordance with the displayed image. However, the bichromal balls embedded in the cavities of a gyricon display film stick, or are pressed, to the walls of the micro-cavities. Frequently, such sticking cannot be eliminated during subsequent film swelling in a dielectric fluid, or the penetration of the dielectric fluid into the gap between a micro-cavity wall and a rotating ball. The switching voltage applied for rotating the bichromal balls in order to cause them to face the display surface with another side during the formation of an image is insufficient for rotating all of the necessary balls. The rotatability of the balls is generally insufficient. For this reason, gyricon displays exhibit low resolution and visual contrast. It is necessary to improve the visual contrast of a gyricon display.
To improve the visual contrast of a gyricon display, heating the display and exercising the rotating balls within the display via an electric field is proposed. Applying heat to the display enlarges the cavity surrounding a particle due to the thermal expansion of the cavity. A thermal expansion coefficient mismatch between the materials of the cavity and the ball results in a breaking or loosening of the retaining bonds between the rotating particle and the micro-cavity wall. A simultaneous or subsequent application of an exercising alternating electric field to the rotating balls causes ball rotation cycling and facilitates the breaking or loosening of the bonds between the ball and the micro-cavity wall. Improving the rotatability of the moveable balls improves their respondability within the fluid. The share of the balls rotated by the applied electric field is increased, thereby improving the resolution and visual contrast. Therefore, exercises by an electrical field and heat improve the visual contrast of the gyricon display.
Additional information
During the exercising and heating of the display, the surfaces of the balls and micro-cavity walls are micro-polished due to the temperature dependence of the solubility of the ball material in the dielectric fluid. Over 90 percent of the balls can rotate with the application of an electric field after heating (with the maximum of 85 percent in the prior design). The temperature range is from 35 degrees C for 1-2 hours of heating to 50 degrees C for 2 minutes of heating. The heating may be provided by (for example) radiation. The exercising voltage is one to three times the switching voltage. For example, when the switching voltage is approximately 50 V, the exercising voltage is approximately 100 V. The exercising electric field is reversed at 1 Hz rate and applied for one to two minutes. Heating and exercising can be accomplished by application of ultrasonics. Heating maintains the bistability characteristic of the gyricon displays. The rotating balls have diameters in the 20-40 micron range. A film with such balls in the cavities has a wet thickness of approximately 5-8 mils (0.125-0.200 mm), with a total thickness for the display of 15-18 mils (380-460 microns).
US Patent 6577432; Link >>
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