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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Introduction 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.
Description 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).
