Function-oriented Knowledge Base \ Electronic paper \ Improve image quality of paper-like display
Electrode matrix records fixed and moving images in electrophoretic layer
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Introduction Flat-panel light-emitting diode and liquid crystal
displays may have a large size, but they are insufficiently
effective in memorizing or recording the displayed images.
Conventional methods of forming images for long-term storage
are based on electrophoresis. In electrophoretic printing,
charged pigment particles contained in a suspension layer
may be transferred to the surface of an electrode or a paper-like
sheet and reproduce a pattern corresponding to the spatial
distribution of an input electric field or an input light
image in a manner similar to that of electrophotography. Applying
a voltage distribution inverse to the initial voltages to
the produced image may erase the image. However, such systems
are designed to reproduce only permanent visible images, not
changeable display systems. In addition, electrophoretic printing
systems do not provide any variation in the optical reflective
property of the suspension itself when a change is made in
the spatial distribution of electrophoretic particles in this
suspension. The image depends upon the shape of the electrode,
so the medium with an electrode pattern must be changed for
each new picture. It is necessary to record and display both
moving and fixed images by means of an electrophoretic suspension
layer in a large, flat and flexible display.
Description To record moving and fixed pictures in an electrophoretic
layer, using an electrode matrix is proposed. The electrode
matrix is comprised of two flat sets of insulated strip electrodes.
The planes of the electrode sets are parallel and separated
by an electrophoretic layer. The electrodes from the two sets
orthogonally intersect. The intersections between the electrodes
divide the image into picture elements (i.e., pixels). The
pixels may be addressably chosen by applying addressing voltages
to a pair of intersecting electrodes that corresponds to the
pixel. It is possible to change or sustain the state of the
pixels within the entire electrophoretic layer by scanning
the electrode matrix with the addressing voltages. After the
voltages are removed, the state of the pixel is preserved,
thereby preserving the newly formed image. The electrode matrix
thus forms and records images of an arbitrary shape.
Additional information White pigment particles are typically made from
titanium dioxide. Black color may be obtained through the
addition of black acetylene particles. The suspending liquid
may (for example) be linseed oil. Pigment particles of other
colors may be used as well. The thickness of the electrophoretic
layer is 25-100 micrometers. The voltage is 25-400 V. At a
frequency below 20 Hertz, the color of the image changes from
white to black at the same frequency. Varying the direct voltage
or the direct voltage pulse width makes it possible to arbitrarily
change the lightness of the electrophoretic layer on one of
the electrodes. During color switching, the average current
is 4*10-9 Amperes per cm2 of the cell. The desired color remains
after switching off the voltage at the required moment of
time. The contrasting pigments may be of other colors. When
the transmission colors of the transparent walls of three
adjacent pixels correspond to the three primary colors (red,
green, and blue), the display is capable of reproducing and
storing color images. Under this condition, only one suspension
that changes the color in the shades of the gray scale between
black and white may be utilized.
