JP2001051625A - Display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To assure a contrast ratio by eliminating the offset in the inversion of a two-color ball and lowering threshold voltage. SOLUTION: This display device has the two-color ball consisting of a pair of hemispherical bodies varying in colors or reflectivity and electrification characteristics from each other and fluid for enclosing this two-color ball. The at least one hemispherical body of the two-color ball is so treated as to decrease asymmetric ion regions. The treatment to decrease the asymmetric ion regions involves the adhesion of a conductive material to the ball or the use of the conductive material, etc., thereby imparting electrical conductivity to at least one hemispherical body of the two-color ball. The electrical conductivity is imparted to the one side of the two-color ball and the charges at the circumference on this hemispherical body side are made uniform to decrease the counter electric field (repulsive force) by the asymmetric ion regions, by which the offset in the rotation of the two-color ball is suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a display device for rotating a two-color ball by the action of an electric field.

[0002]

2. Description of the Related Art In recent years, demands for electronic display devices have been increasing as man-machine interfaces.

[0003] Conventional electronic display devices include:
It is classified into a self-luminous type and a light-receiving type, and as a self-luminous type electronic display device, a cathode ray tube (CRT),
Plasma display (PDP), electroluminescence display (ELD), fluorescent display tube (VFD)
Light emitting diodes (LEDs) and the like are known.

As a light receiving type electronic display device, a liquid crystal display (LCD), an electrochromic display (ECD), an electrophoretic display (ECD)
PID), Dispersed Particle Oriented Display (SPD), 2
A color ball rotating display (TBD) and the like are known.

[0005] Among them, a light-emitting display such as a CRT is said to be unsuitable for reading a document because it tires eyes.

[0006] On the other hand, it is said that a transmissive liquid crystal display using a backlight is apt to cause tired eyes like a CRT due to flickering of a fluorescent tube or the like. Reflective liquid crystal displays that do not use a backlight have poor contrast and impose a considerable burden on the eyes when viewing the screen for a long time.

Further, these CRTs and liquid crystal displays do not have a memory function, and have a drawback that an image disappears when the power is turned off.

[0008] Against this background, displays such as notebook personal computers, electronic book players, and other portable information devices, which are expected to become more widespread in the future, are easy on the eyes, consume less power, and have an image memory. It is considered essential to have the property.

One of the displays satisfying such a demand to some extent is a two-color ball rotating display (T).
BD: Hereinafter, referred to as a two-color ball display device. ).

The two-color ball display device comprises a large number of two-color balls, each of which has a half white color and the other half a black color or the like, and which has a different permittivity between the white hemisphere portion and the black hemisphere portion. This is based on the fact that these two-color balls rotate by the action of an electric field (NKSheridon a
nd MABerkovits, Proc. of the Society of Informat
ion Display 18/3 & 4, 289, 1977).

[0011]

However, even in a two-color ball display device which performs display based on such a method, a high contrast ratio is realized in spite of many years of research since 1977. It was difficult.

One of the causes is that the two-color ball has a clear contrast between the respective hemispheres, but a gap is required between the two-color balls so that a fluid can enter between them in order to rotate the two-color ball. Therefore, there is a problem that the two-color ball cannot be filled most closely.

In order to solve such a defect, there has been proposed a device in which two-color balls are arranged in multiple layers, and a portion where a gap is formed in the first layer is supplemented by a second layer (M. Saitoh). , et.al., Proc. of the Society of Infor
mation Display, Vol. 23, No. 4, pp. 249. 1982).

As a second cause, after the two-color ball is inverted, there is a case where a slight shift occurs instead of stopping only by complete inversion.

The second cause has not been solved yet.

The present invention has been proposed in view of the above-described problems of the two-color ball display device, and eliminates the shift of the inversion of the two-color ball display device and has a low threshold voltage and a high contrast ratio. The purpose is to provide.

[0017]

In order to achieve the above-mentioned object, a display device of the present invention comprises a two-color ball comprising a pair of hemispheres having different colors or reflectances and different charging characteristics, and a two-color ball comprising the same. And a fluid that rotatably surrounds
At least one hemisphere of the colored ball has been treated to reduce the asymmetric ionic region.

In particular, as a treatment for reducing the asymmetric ion region, a conductive material may be attached, or a conductive material may be used to impart conductivity to at least one hemisphere of the two-color ball.

By imparting conductivity to one side of a sphere (two-color ball), making the electric charge around the hemisphere side uniform, and reducing the repulsive electric field (repulsive force) due to the asymmetric ion region, the two-color ball is formed. Rotational deviation is suppressed.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a display device to which the present invention is applied will be described in detail with reference to the drawings.

As shown in FIG. 1, a display device according to the present invention comprises a transparent front substrate 1 such as a glass or plastic film which is a front support member and constitutes a display surface; 1 is provided with a back-side base material 2 serving as a back-side support member opposed to the front-side base material 1 at a predetermined interval. On the front substrate 1, that is,
On the rear surface of the front substrate 1, a transparent front electrode 3 such as an ITO film serving as a front electric field applying means is formed.
On the back substrate 2, that is, on the front surface of the back substrate 2, a back electrode 4 serving as a back electric field applying unit paired with the front electrode 3 is formed.

A fluid 5 is filled between the front-side substrate 1 and the back-side substrate 2.
Two-color balls 6 are dispersed.

Each two-color ball 6 is composed of a pair of first and second hemispherical parts, and these hemispherical parts are colored,
Alternatively, the reflectance and the charging characteristics are different from each other. That is, the first hemispherical portion 6a of each two-color ball has the same color, such as black, or the reflectance for all the two-color balls, and serves as, for example, a black display portion. The second hemispherical portion 6b of each two-color ball serves as a white display portion.

The two-color ball 6 included in the fluid body 5 is, for example, a glass ball filled with a white colorant, a hemispherical portion of which is a black layer (a mixture of antimony sulfide and magnesium fluoride) in a vacuum evaporation chamber. Etc.) can be used.

The fluid 5 includes a non-volatile oil such as alkylnaphthalene, diallylethane, alkylbiphenyl and triallyldimethane, a low-viscosity silicone oil, a vegetable oil,
Those obtained by coloring animal oil or the like with a pigment or the like can be used.
In addition, a charge control agent, a dispersant, a lubricant, a stabilizer, and the like can be added to the fluid 5 as necessary.

The two-color ball and the liquid around the two-color ball are dielectric substances, which are macroscopically electrically neutral, but microscopically around the two-color ball 6. , An electric double layer is formed. Zeta potential is known as a measurable aspect of this electric double layer,
This zeta potential has a function of the two-color ball surface material.
Therefore, the first hemispherical part and the second hemispherical part are colored,
Alternatively, zeta potentials having different characteristics are generated between the first hemispherical portion and the second hemispherical portion by using materials having different properties such as reflectance and charging characteristics. Therefore, when an electric field is applied between the front-side electrode 3 and the back-side electrode 4, the two-color ball operates like a dipole due to the difference in zeta potential between the hemispherical portions, and the dipole moment is reduced by the electric field. It is rotated and oriented until it matches the direction.

In such a two-color ball display device, a DC power supply 7 applies a predetermined voltage between electrodes arranged on an inner surface of a substrate holding a two-color ball 6 serving as a display medium and a fluid 5. When an electric field is applied, the two-color ball rotates according to the polarity, and is colored black as shown in FIG. 1 (A) according to the polarity of the voltage applied to the front electrode 3 or the rear electrode 4 respectively. The hemispherical portion 6a faces the front side substrate 1 which is a transparent substrate, or the white hemispherical portion 6b faces the front side substrate 1 as shown in FIG. 1 (B). The behavior of the two-color ball makes it possible to display white or black.

Further, this two-color ball display device has a memory property that the display is maintained for at least several days even when the application of the voltage is stopped.

By the way, the two-color ball and its surrounding fluid are charged at the interface thereof in an electrokinetic relationship. 2
An electric double layer is formed at the color ball (solid) -fluid (liquid) interface, and the potential distribution in the fluid is as shown in FIG. When it occurs, the pinned layer moves with the two-color ball, so that the electrokinetic phenomenon is dominated by the potential difference between the pinned layer and the interior of the fluid, which is known as the zeta potential.

This zeta potential is a function of only the ball surface material for the same fluid. Therefore, different zeta potentials will be generated for the fluid, depending on each hemisphere and the nature of the material that produces the color or reflectivity associated difference. What makes the ball behave like a dipole when an electric field is present is the difference in zeta potential between each hemisphere of the ball. The ball rotates until its dipole moment matches the direction of the electric field set between the electrodes.

If the stream is a perfect dielectric, the bicolor ball will stop completely at this location. However, a perfect fluid is not present (although it is a matter of definition) and contains some ions. In particular, when an ionic surfactant is applied to the surface of the two-color ball for speeding up, the effect is particularly remarkable due to the asymmetry of each hemisphere surface.

Due to the slight residual ions, an asymmetric ion region exists around the stopped two-color ball.

The mobility of the ions is usually considerably slower than the rotation speed of the two-color ball. For this reason, an electric field is applied, and even when the two-color ball finishes rotating, the bias of the ions before the ball rotation is maintained. Has been saved. This series of states is shown in FIG. 3 (from the initial stage of electric field application to the end of inversion).

Accordingly, an anti-electric field is generated by the ion region, and the two-color ball starts to rotate to the opposite side (FIG. 3: shift after the electric field is turned off). Normally, an electric field of the order of the ions often does not reach the point of inversion, but it is often sufficient to cause a slight shift. In addition, repulsion by ions having the opposite sign must be considered.

This slight displacement of the individual two-color balls significantly reduces the contrast. Further, it is easily presumed that the generation of a dipole larger than the original dielectric difference causes an increase in the applied electric field threshold value at the beginning of the next rotation.

The present inventor has found a method for solving the problem as follows based on these causes. That is, by imparting conductivity to one side of the hemisphere, the charge around the hemisphere is made uniform, and the repulsive electric field (repulsive force) due to the asymmetric ion region is reduced.

Specifically, a conductive substance is applied to one hemisphere on one side by coating or the like (in the case of black, conductive carbon or the like is suitable). Alternatively, a conductive substance is used for one hemisphere.

As a result, as shown in FIG. 4, the bias of the ions after the completion of the rotation is eliminated, and a decrease in the contrast is suppressed. At the same time, an increase in the applied electric field threshold value at the beginning of the next rotation can be suppressed.

[0039]

EXAMPLES Specific examples to which the present invention is applied will be described below based on experimental results.

Example 5 Glass beads having a diameter of 50 μm (manufactured by Toshiba Barodini) were sprayed and fixed on an acrylic plate having an adhesive.

Then, 30% by weight of conductive carbon (ECP-600JD Lion) was mixed with the hot-drying type offset printing ink (black) and adjusted with a roller to a thickness of 1 μm. Using the roller, apply ink with conductivity on the fixed glass beads,
It was dried to produce a two-color ball.

An ITO (Indium Tin Oxide) transparent electrode formed inside by sputtering was 40 mm × 25 mm × 1.
1 mm glass substrate (Corning Co., trade name 705)
9) The gap was controlled by using a spacer having a thickness of 60 μm, and the two sheets were fixed with an ultraviolet curable resin to form a cell.

As the fluid, a silicone oil (KF-995, manufactured by Shin-Etsu Chemical Co., Ltd.) was selected, and an ionic surfactant di-2-ethylhexyl sodium sulfosuccinate was dissolved in an appropriate amount. In this oil, the two-color ball produced by the above method is dispersed, and utilizing the capillary phenomenon,
The sample was injected into a glass cell to obtain a test sample.

A 1 Hz rectangular wave was applied to the test sample, and the threshold value and the contrast ratio were measured.
In determining the threshold value, the applied voltage was gradually increased to a voltage for completely inverting the two-color ball. The contrast was determined by comparing the reflectance in white display and the reflectance in black display.

The threshold value is 7 V and the white level is 20 (ar
b. unit), and the black level was 1 (arb. unit).

Comparative Example For comparison, a sample was prepared in the same manner as in the example except that conductive carbon was not mixed.

The threshold value is 30 V and the white level is 18 (ar
b. unit), the black level was 3 (arb. unit).

[0048]

As is apparent from the above description, according to the present invention, it is possible to eliminate the displacement at the time of stopping the two-color rotating ball, which has made it difficult to increase the contrast.
It is possible to dramatically improve the contrast.

Further, it is possible to reduce the anti-electric field which reduces the effective firing field applied at the beginning of rotation, and it is possible to greatly lower the threshold value.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a basic configuration example of a two-color ball display device and its basic operation.

FIG. 2 is a characteristic diagram illustrating an electrokinetic potential.

FIG. 3 is a schematic diagram illustrating a reversal electric field due to residual ions.

FIG. 4 is a schematic diagram for explaining the elimination of depolarized ions by imparting conductivity.

[Explanation of symbols]

5 Fluid, 6 two-color ball, 6a Black hemispherical part, 6b White hemispherical part

Claims (5)

[Claims] 1. A two-color ball comprising a pair of hemispheres having different colors or reflectances and different charging characteristics, and a fluid rotatably surrounding the two-color ball, wherein at least one hemisphere of the two-color ball is provided. A display device wherein the body has been treated to reduce the asymmetric ionic region. 2. The semiconductor device according to claim 1, wherein at least one hemisphere of said two-color ball has conductivity.
The display device according to the above. 3. The display device according to claim 2, wherein a conductive substance is attached to at least one hemisphere of said two-color ball. 4. The display device according to claim 3, wherein the conductive substance is conductive carbon. 5. The display device according to claim 2, wherein a conductive material is used for at least one hemisphere of said two-color ball.