JP2003280051A - Image display medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image display medium which has a couple of substrates, at least one cell formed between those substrates and contains a dry developer, and barriers formed between those substrates and adjacent to the cell and can display an image with a good contrast. <P>SOLUTION: The image display medium MD1 has the substrates S1 and S2, a plurality of cells CL formed between those substrates and containing the dry developer DV, and barriers W1 formed between those substrates and adjacent to the cells CL. The observation-side substrate S1, the substrate S2 arranged on the opposite side from the observation side, and the barriers W1 are all colorless and transparent. On the substrate S2, a white layer 41 is formed. Between the substrate S2 arranged on the opposite side to the observation side and barriers W1, black light absorbing films (dark color layer) 31 are provided. Consequently, the quantity of white light emitted from medium areas corresponding to the barriers W1 to an observer is reduced. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pair of substrates, at least one cell formed between these substrates and containing a dry developer, and a partition formed between these substrates and adjacent to the cells. And an image display medium having.

[0002]

2. Description of the Related Art In recent years, a rewritable image display medium called electronic paper or digital paper has been proposed as an image display medium (image recording medium) for recording an image and replacing the paper for displaying the recorded image. ing.

Various types of image display media have been proposed, and one of them is one that displays an image using a dry developer. A schematic sectional view of an example of this type of medium is shown in FIG.

The image display medium MDp shown in FIG. 15A has a pair of substrates S1 and S2 and a plurality of cells CL formed between the substrates. The dry developer DV is contained in each cell CL. Media MD using dry developer DV
An image is formed on p. The display image by the medium MDp is observed from the substrate S1 side. Substrate S1 arranged on the observation side
Is usually colorless and transparent.

Cell CL for containing the dry developer DV
In order to form a closed space used as a space between the substrates,
A plurality of partition walls Wp are formed between the substrates. Each partition W
p is usually colorless and transparent.

As the dry developer DV in the cell CL, for example, a developer composed of two kinds of developing particles of white developing particles Pw and black developing particles Pk is adopted. These developing particles P
The charging polarities of w and Pk are different from each other.

As shown in FIG. 15 (B), when an electric field E is applied to the dry developer DV in the cell CL, the developing particles Pw charged with opposite polarities to each other depending on the direction of the electric field E. One of the development particles of Pk moves toward the substrate S1, and the other of the development particles moves toward the substrate S2.

As a result, in the medium region where the white developing particles Pw are gathered toward the observing side substrate S1, the substrate S1
The light incident on the medium from the side is the white developing particles P in the cell CL.
Reflected by w, white display is performed. Further, in the medium region where the black developing particles Pk are gathered toward the substrate S1,
Light incident on the medium from the substrate S1 side is absorbed by the black developing particles Pk in the cell CL, and black display is performed.

[0009]

However, in the image display medium MDp, since the partition wall Wp is usually colorless and transparent, the following problems occur depending on the color of the substrate S2 arranged on the side opposite to the observation side. May occur.

The substrate S2 arranged on the side opposite to the observation side is
For example, it is conceivable that the substrate S1 on the observation side is made colorless and transparent. In this case, a part of the light incident on the inside of the medium from the substrate S2 side passes through the transparent substrate S2, the transparent partition Wp, and the transparent substrate S1, and is emitted from the medium region corresponding to the partition Wp to the observer. Go to When the black developer particles Pk in the cell CL are collected on the substrate S1 side to perform black display, when light is emitted from the medium region corresponding to the partition wall Wp adjacent to the cell CL, the black image density displayed. And the contrast of the displayed image is reduced. When the light that passes through the partition wall Wp and is emitted from the substrate S1 side is white light, the black color displayed during black display becomes whitish. In addition, a transparent partition Wp
The object arranged on the back side of the medium MDp can be seen through the above, and the contrast, color tone, etc. of the displayed image change depending on the place where the medium MDp is arranged.

As the substrate S2 arranged on the side opposite to the observing side, it is conceivable to employ a white substrate or a transparent substrate having a white layer formed thereon. In this case, the substrate S
A part of the light incident on the inside of the medium from the side 1 is reflected by the white surface of the substrate S2, emitted from the medium region corresponding to the partition Wp, and travels toward the observer. Black developer particles P in the cell CL
When black is displayed by collecting k on the substrate S1 side,
When white light is emitted from the medium region corresponding to the partition wall Wp adjacent to the cell CL, the density of the displayed black image is reduced and the contrast of the displayed image is reduced.

Such a problem occurs not only when black display is performed by black developing particles, but also when red display is performed by a color other than black, for example, red developing particles.

Therefore, the present invention has a pair of substrates, at least one cell formed between these substrates and containing a dry developer, and a partition wall formed between these substrates and adjacent to the cells. An object of the present invention is to provide an image display medium that can display an image with good contrast.

[0014]

[Means for Solving the Problems] §1. Image Display Medium In order to solve the above-mentioned problems, the present invention provides the following two types of image display mediums, first and second. First, items common to both the first and second types of image display media will be described. After that, characteristic items of each type of medium will be described.

§1.1. Both the first and second types of image display media have a first substrate, a second substrate, at least one cell, at least one partition and a dry developer.

The first substrate and the second substrate are arranged with a space therebetween. The display image by the medium is observed from the first substrate side. That is, the first substrate is an observation-side substrate (a substrate arranged near the observer who observes the display image). The second substrate is a substrate arranged on the side opposite to the observation side (a substrate arranged on the side farther from the observer who observes the display image than the first substrate). The first substrate arranged on the observation side is transparent. The first substrate is typically colorless and transparent, but may be colored and transparent. The second substrate may be opaque,
It may be transparent.

The first and / or second substrate may be, for example, a resin substrate (for example, a resin film substrate), a glass substrate, or the like. If resin substrates are used as the first and second substrates, damage to the medium can be suppressed more than when glass substrates are used, and the medium can be made lighter and thinner. If resin film substrates are used as the first and second substrates,
The medium can be made flexible.

At least one cell is formed between the first substrate and the second substrate. A cell is a closed space (closed space) for containing a dry developer. Typically, a plurality of cells may be provided between the substrates. The shape of the cell is not limited and may be, for example, a line shape. When a plurality of cells are provided between the substrates, all the cells may or may not have the same shape. The dry developer is stored in each cell.

The partition wall is formed between the first substrate and the second substrate so as to form a closed space used as a cell.
It is provided between the substrate and the second substrate. The partition walls are for forming cells. Typically, a plurality of partition walls may be provided between the substrates. The partition is adjacent to at least one cell. The partition walls can maintain a predetermined space between the substrates. Further, the partition walls can increase the strength of the entire medium. Further, the partition walls can suppress the bias of the dry developer in the cells in the direction parallel to the substrate surface. The partition wall may be integrally formed with the first or second substrate.

The dry developer in the cell contains two types of developing particles, a first type and a second type. The first developing particles and the second developing particles have different optical reflection densities (for example, colors) from each other. Both the first and second developing particles have a triboelectric charging property. The charging polarities of the first developing particles and the second developing particles are opposite to each other. Note that the first and second developing particles may not be charged when the medium is stored, but when the image is formed on the medium, the first and second developing particles are charged as described above. Need to be
The first or / and second developer particles may be magnetic developer particles. The dry developer may contain developing particles other than the first and second developing particles. That is, the dry developer contains at least two types of developing particles, and may contain three or more types of developing particles. When the dry developer contains three or more kinds of developing particles, any two kinds of developing particles are two kinds of developing particles (first and second developing particles) having the above-mentioned properties and relationships. ).

Image formation on the medium and image display on the medium are performed using the dry developer in the cell.

For example, by applying an electric field in the direction perpendicular or almost perpendicular to the substrate surface to the dry developer in the cell,
The medium can be imaged. As described above, the charging polarities of the first developing particles and the second developing particles in the dry developer are opposite to each other. Therefore, when such an electric field is applied to the dry developer, the first developing particles are moved toward one of the first and second substrates relative to the second developing particles according to the direction of the electric field. The second developer particles can be moved toward the other substrate relative to the first developer particles.

As a result, the first or second developing particles gather on the side of the first substrate on the observation side depending on the direction of the applied electric field. When the dry developer is composed of first and second types of developing particles and the first substrate is colorless and transparent, the first developing particles are present in the cell region where the first developing particles gather on the first substrate side. Is displayed, and the color of the second developer particles is displayed in the cell area where the second developer particles are gathered on the first substrate side.

A desired image can be formed on the medium by applying an electric field in the direction corresponding to the image information (image data) of each pixel of the image to be formed to the dry developer of the pixel. When forming an image, one cell may correspond to one pixel, one cell may correspond to a plurality of pixels, or a plurality of pixels may correspond to one cell.

In order to apply the electric field to the dry developer in the cell as described above, the first and / or the second, as required.
At least one electrode may be formed on the substrate.

The characteristic features of the first and second types of image display media will be described below.

§1.2. First type image display medium The first type image display medium is transparent and is disposed at a distance from the first substrate, which is disposed on the observation side, and is more observable than the first substrate. A second substrate disposed on the side farther from the side, at least one cell formed between the first substrate and the second substrate, and a cell formed between the first substrate and the second substrate. A partition wall adjacent to the cell for forming the cell and a dry developer housed in the cell, which have different optical reflection densities, different charge polarities, and both have triboelectric chargeability. And a dry developer containing developing particles, and at least the bottom surface of the partition wall facing the second substrate is colored in a dark color.

In the first type medium, at least the bottom surface of the partition wall facing the second substrate is colored dark. The entire partition may be colored dark.

For example, by forming a dark color layer on the bottom surface of the partition wall so that the dark color layer is disposed between the bottom surface of the partition wall and the second substrate, the bottom surface of the partition wall facing the second substrate can be colored darkly. Good. In this case, the partition wall itself may be typically colorless and transparent. The dark color layer may be, for example, a dark color coating film (film formed by paint). When the partition wall and the second substrate are bonded with an adhesive, a dark adhesive (for example, an adhesive in which a dark colorant is dispersed) is used as the adhesive,
The layer formed by the dark adhesive may be a dark layer.

When the entire partition is colored in dark color, for example, a dark material (for example, a resin material in which a dark colorant is dispersed) is used as the partition material, and the partition itself is darkened. Instead of this, the partition walls may be coated with a dark paint so that the entire partition walls are colored in a dark color.

In any case, the dark color is preferably a color having a lightness of 2 or less when it is close to an achromatic color in the Munsell color system, a color saturation of 05 or less when it is a chromatic color, and a lightness of 1 or less. The dark color is, for example, black or gray. The same applies to the dark color in the following description.

In the medium of the first type, since at least the bottom surface of the partition wall facing the second substrate is colored dark in this way, light emitted from the region corresponding to the partition wall of the medium and directed toward the observer. It is possible to reduce the amount of As a result, when black display is performed by the first type medium, for example, the black image density can be improved, and the image display can be performed with good contrast. Further, when displaying black with the black developing particles, it is possible to display a color more faithful to the color of the black developing particles. The same applies when displaying the color by using developing particles of a color other than black (for example, red).

Since at least the bottom surface of the partition wall facing the second substrate is colored dark, even if the second substrate is transparent, the light incident on the inside of the medium from the second substrate side is
No light is emitted from the first substrate region corresponding to the partition. Therefore, even in such a case, the contrast or the color tone of the image displayed by the place where the medium is placed, the object arranged on the back side of the medium, or the like does not change.

In the first type medium, the viewing angle dependency can be reduced by coloring only the bottom surface of the partition wall facing the second substrate, rather than by coloring the entire partition wall in a dark color.

In the first type medium, when the partition wall and the partition wall which are arranged on the observation side are integrally formed, the area corresponding to the partition wall of the medium is larger than that in the case where the partition wall and the partition wall are formed separately. It is possible to reduce the amount of light that is emitted from the light source and travels toward the observer. When the first substrate and the partition wall are separate bodies, even if the partition wall is colorless and transparent, a part of the light entering the medium from the first substrate side is reflected at the interface between the first substrate and the partition wall, Light may be emitted toward the observer from the region corresponding to the partition wall of the medium. On the other hand, the first
If the substrate and the partition are integrally formed, the interface where such reflection occurs is eliminated, so that the amount of light emitted from the region corresponding to the partition of the medium toward the observer is reduced.

The second substrate arranged on the side farther from the observation side in the first type medium may be opaque, for example. More specifically, the second substrate may have an opaque bright color, for example. As the light color, an achromatic white color or a chromatic color a light color can be used. The achromatic white color is preferably a lightness of 8 to 9 or more in the Munsell color system, and a chromatic light color having a saturation of 04 to 03 or less and a lightness of 5 to 6 or more in the Munsell color system. The bright color is white, for example. What has been described here regarding the bright color is the same in the following description.

When the light-colored second substrate is used, the medium looks bright when viewed from the side opposite to the observation side, and the medium can have a paper-like texture. When the medium is viewed from the side opposite to the observing side, the medium looks lighter than the dark color such as black, rather than the dark color, for example, reduces the discomfort caused by the difference between the medium and the user. be able to.

A transparent second substrate is used so that the medium looks bright when viewed from the side opposite to the viewing side.
An opaque light color layer may be formed on the second substrate. Even in this case, the medium can have a paper-like texture. The bright color layer may be formed on the surface of the second substrate opposite to the observation side or may be formed on the observation side surface. The light color layer may be a coating film, for example.

§1.3. Second type image display medium The second type image display medium is transparent and is arranged with a space between the first substrate and the first substrate which is disposed on the observation side, and which is more observable than the first substrate. A second substrate disposed on the side farther from the side, at least one cell formed between the first substrate and the second substrate, and a cell formed between the first substrate and the second substrate. A partition wall adjacent to the cell for forming the cell and a dry developer housed in the cell, which have different optical reflection densities, different charge polarities, and both have triboelectric chargeability. And a dry developer containing developing particles, the partition wall is transparent, and at least a region of the second substrate facing the partition wall is colored dark.

In the second type medium, the partition wall is transparent (typically colorless and transparent), and at least the region of the second substrate facing the partition wall is colored dark. The entire area of the surface of the second substrate facing the partition wall (the surface of the second substrate on the observation side) may be colored dark.

For example, by forming a dark layer (film) only on the region of the second substrate facing the partition wall, or by forming a dark layer (film) on the entire region of the surface of the second substrate facing the partition wall. By forming at least, the region of at least the partition wall of the second substrate may be colored in a dark color. The dark color layer (dark color film) may be a coating film, for example.

The second substrate is made of a dark material (for example, a resin in which a dark colorant is dispersed), the second substrate itself is dark, and the entire region of the second substrate facing the partition wall is dark. May be.

In the second type medium, since at least the region of the second substrate facing the partition wall is colored dark in this way, the light emitted from the region corresponding to the partition wall of the medium and directed toward the observer. It is possible to reduce the amount of As a result, when black display is performed using the second type medium, for example, it is possible to improve the black image density and display images with good contrast. Further, when displaying black with the black developing particles, it is possible to display a color more faithful to the color of the black developing particles. The same applies when displaying the color by using developing particles of a color other than black (for example, red).

Similarly to the first type medium, in the second type medium, when the first substrate and the partition disposed on the observation side are integrally formed, the first substrate and the partition are separated from each other. Also, it is possible to reduce the amount of light emitted from the region corresponding to the partition wall of the medium and traveling toward the observer.

In the second type medium, when the dark color layer is formed on the second substrate as described above (for example, when the dark color layer is formed only on the region of the second substrate facing the partition wall, or When a dark layer is formed on the entire region of the surface of the second substrate facing the partition wall), the second substrate itself may be opaque, for example. More specifically, the second substrate may have an opaque bright color, for example. When a light-colored second substrate such as white is used, the medium looks bright when viewed from the side opposite to the observation side, and the medium can have a paper-like texture.

When a dark color layer is formed on the second substrate,
The second substrate itself may be transparent. In this case, an opaque bright color layer may be formed on the second substrate so that the medium looks bright when viewed from the side opposite to the viewing side.
Even in this case, the medium can have a paper-like texture. The bright color layer may be formed on the surface of the second substrate opposite to the observation side or may be formed on the observation side surface. When the light-colored layer is provided on the observation-side surface of the second substrate, these layers may be formed in this order from the second substrate side to the light-colored layer and the dark-colored layer. The light color layer may be a coating film, for example.

As described above, the second substrate itself may have a dark color. In this case, by forming a light color layer on the surface of the second substrate opposite to the observation side, the medium looks bright when viewed from the side opposite to the observation side, giving the medium a paper-like texture. be able to.

[0048]

BEST MODE FOR CARRYING OUT THE INVENTION §2. Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following description, specific numerical values, material names, etc. are shown, but the image display medium of the present invention is not limited thereto.

A schematic plan view and a schematic sectional view of an example of the image display medium according to the present invention are shown in FIGS. 1 and 2, respectively.

The image display medium MD1 shown in FIGS. 1 and 2 has a pair of substrates S1 and S2t arranged at a predetermined interval. A plurality of partition walls W1 and a plurality of cells CL are provided between these substrates. The dry developer DV is contained in each cell CL.

The display image by the medium MD1 is observed from the upper side of the medium in FIG. 2, that is, the substrate S1 side.

The substrate S1 on the observation side is colorless and transparent, and is made of polypropylene (PP) in this example. The substrate S2t on the side far from the observation side is also colorless and transparent in this example, and is made of polyethylene terephthalate (PET). A white layer 41 is formed on the surface of the substrate S2t on the observation side (the surface facing the substrate S1). The white layer 41 is made of white paint on the substrate S.
It is a coating film formed by applying 2t. Substrate S2
A transparent electrode Ec is formed on the surface opposite to the observation side of t. The electrode Ec is made of ITO.

The partition walls W1 are formed between the substrates in the predetermined pattern shown in FIG. More specifically, an annular partition wall and a plurality of line-shaped partition walls are formed between the substrates. The partition W1 and the substrates S1 and S2t form a plurality of line-shaped sealed spaces between the substrates. Each of these closed spaces is used as a cell CL for containing the dry developer DV.

The partition W1 is, in this example, the substrate S1 on the observation side.
It is formed integrally with. PP using a mold
By forming the film, the partition W1 having a predetermined pattern is formed integrally with the substrate S1. Therefore, in this example, the partition W1 is made of polypropylene like the substrate S1 and is colorless and transparent.

More specifically, between the partition W1 and the substrate S2t, a black light absorbing film 31 is formed between the partition W1 and the white layer 41 on the substrate S2t. The black light absorbing film 31 is formed by applying a black paint to the bottom surface of the partition W1 facing the substrate S2t. After the black light absorbing film (black coating film) 31 is formed on the bottom surface of the partition W1, the partition W1 and the substrate S2t are bonded to each other with a colorless and transparent adhesive (not shown).

In this example, the size of each part of the medium MD1 is as follows. The thickness of the substrate S1 is 50 μm, and the partition W1
Has a height of 200 μm, and the substrate S2t has a thickness of 25 μm. The width of the partition W1 is 50 μm, and the width between the adjacent partition W1 is 300 μm. Therefore, the width of each cell CL is 300 μm, the height is 200 μm, and the pitch is 350 μm.
m. The medium MD1 itself is approximately A4 size.

The dry developer DV contained in the cell is composed of two kinds of developing particles, white developing particles Pw and black developing particles Pk. The developing particles Pw and Pk are particles made of a binder resin in which a colorant or the like is dispersed.

More specifically, white developing particles Pw
In this example, is manufactured as follows. First, a styrene-acrylic copolymer resin as a binder resin, titanium oxide as a white pigment, and a quaternary ammonium salt as a charge control agent are mixed at a predetermined ratio. After thoroughly kneading the mixture, the kneaded product is ground. The ground product (particles) is subjected to air classification to obtain white developing particles Pw having a predetermined particle size. The average particle size of the white developing particles Pw is about 15 μm.

The black developing particles Pk are produced as follows, like the white developing particles Pw. First, a polyester resin as a binder resin, magnetite as a magnetic colorant / black colorant, and carbon black as a black colorant are mixed at a predetermined ratio. After thoroughly kneading the mixture, the kneaded product is ground. The crushed material (particles)
Is subjected to air classification to obtain black developing particles Pk having a predetermined particle diameter. The average particle size of the black developing particles Pk is about 20 μm. The black developing particles Pk have magnetism because they contain a magnetic substance.

The white developing particles Pw and the black developing particles Pk thus prepared were mixed at a weight ratio of white particles 27: black particles 73 and stirred, and the dry developer DV contained in the cell CL was used. is there. A filling rate of about 33 in the cell CL
%, The developer DV is stored. The white developer particles Pw and the black developer particles Pk of the developer DV are frictionally charged in positive and negative polarities, respectively, by stirring before being stored in the cell CL.

§4. An image can be formed on the image display medium MD1 as follows. In forming an image, as shown in FIG. 3, an electric field E perpendicular or almost perpendicular to the medium substrate surface is applied to the dry developer DV in the cell CL.

As described above, the white developing particles Pw and the black developing particles Pk constituting the dry developer DV are positively and negatively charged, respectively. Therefore, when an electric field is applied, the developing particles are generated in accordance with the direction of the electric field. One of the development particles of Pw and Pk moves toward the substrate S1, and the other development particle moves toward the substrate S2t.

More specifically, in the region to which the upward electric field E is applied in FIG. 3, the positively charged white developing particles Pw move toward the substrate S1 relative to the black developing particles Pk. In the region where the downward electric field E is applied in FIG. 3, the negatively charged black developer particles Pk move toward the substrate S1 relative to the white developer particles Pw.

By applying an electric field in the direction corresponding to the image information (image data) of each pixel of the image to be formed to the dry developer DV (developing particles Pw and Pk) of the pixel,
A desired image can be formed. In this example, image formation is performed by associating a plurality of pixels with one cell.

An oscillating magnetic field may be applied to the dry developer DV at the same time as or before and / or before the application of the electric field to the dry developer DV in the cell. Since the dry developer DV contains the black developing particles Pk having magnetism as described above,
When the oscillating magnetic field is applied to the developer DV, the developer DV can be stirred and vibrated. By this agitation, the charge amount of the developing particles Pw and Pk having frictional charging properties is increased, the electrostatic force acting on the developing particles Pw and Pk is increased when an electric field is applied, and the developing particles Pw and Pk act. It becomes easy to move in the direction of the electrostatic force. Further, by vibrating the developer DV (developing particles Pw and Pk), the fluidity of the developer is improved, which also contributes to the development particles Pw.
And Pk easily move when an electric field is applied.

FIG. 4 shows an example of an image forming apparatus capable of forming an image on the medium MD1. Image forming apparatus A of FIG.
P1 uses the electrode Ec formed on the substrate S2t of the medium MD1 to apply an electric field to the dry developer in the cell to form an image.

The image forming apparatus AP1 has a drum-shaped photosensitive member 8
1, and a charging device 82, a laser exposure device 83, a developer agitating device 84, a bias voltage applying device 85, and an erasing device 86 are arranged around it.

In the image forming apparatus AP1, the image is formed on the medium MD1 conveyed through the predetermined path as follows.

First, the charging device 82 uniformly charges the surface of the photoconductor 81 which is driven to rotate counterclockwise in the drawing. The photoconductor 81 is charged by the conductive brush roller 821 which is in contact with the photoconductor 81 and to which a high voltage is applied from the power source 822. At this time, the brush roller 821 is rotationally driven in the clockwise direction in the figure at a peripheral speed about 2 to 3 times the peripheral speed of the photoconductor 81. In this example, the surface potential Vo is about -800.
The photoconductor 81 is charged to V.

Then, by the laser exposure device 83,
The exposed surface of the photoreceptor is exposed according to the image to be formed. The potential of the surface area of the photoconductor that is exposed to the light is attenuated. In this example, the potential Vi after the attenuation on the surface of the photoconductor is about −5.
It will be about 0V. As a result, an electrostatic latent image corresponding to the image to be formed is formed on the photoconductor 81.

The medium MD1 is provided between the photosensitive member 81 holding the electrostatic latent image and the magnet roller 841 of the stirring device 84,
Further, it is conveyed between the photoconductor 81 and the bias roller 851 of the bias voltage applying device 85. Substrate S2
The medium MD1 is transported so that the electrode Ec on t contacts the bias roller 851.

Magnet roller 841 of agitator 84
Are contained in a cylindrical sleeve 842 made of aluminum. The sleeve 842 is used to convey the medium M to be conveyed.
It is pressed by D1 with a predetermined pressure, and is driven to rotate clockwise in the figure at the same peripheral speed as the peripheral speed of the photoconductor 81. The sleeve 842 may be driven to rotate. Magnet roller 84
1 is driven to rotate clockwise in the figure at a predetermined peripheral speed independently of the sleeve 842. The magnet roller 841 may typically be rotationally driven at a peripheral speed higher than the peripheral speed of the photoconductor 81. Specifically, although depending on the number of poles of the magnet roller 841, the rotation speed (peripheral speed) may be set so that the developer DV receives a magnetic force of about 5 to 10 times by the magnetic poles of the magnet roller 841. Magnet roller 841
Due to the rotation, the oscillating magnetic field is applied to the dry developer DV in the cells of the medium MD1 facing the roller 841. The vibrating magnetic field causes the dry developer DV to be agitated and vibrated.

A bias voltage (-400 V in this example) is applied to the bias roller 851 of the bias voltage applying device 85 from the power source 852. When the bias roller 851 contacts the electrode Ec of the medium MD1, the potential of the electrode Ec is set to the bias voltage. As a result, the potential is Vo
An electric field in the direction from the substrate S2t to S1 is applied to the dry developer DV in the cells of the medium MD1 facing the surface area of the photoconductor (about −800 V in this example). Further, an electric field directed from the substrate S1 toward S2t is applied to the dry developer DV in the cells of the medium MD1 facing the surface area of the photoconductor having the potential Vi (about -50V in this example). Since the electrostatic latent image corresponding to the image to be formed is formed on the photoconductor 81, in other words, the surface potential of the photoconductor becomes the potential Vo or Vi depending on the image to be formed. Therefore, an electric field having an orientation corresponding to the image information of each pixel of the image to be formed is applied to each region of the medium. With these, a desired image is formed on the medium MD1.

The magnet roller 841 and the bias roller 851 are arranged at a predetermined distance from each other, and the magnetic field of the magnet roller 841 has almost no influence in the area where the dry developer DV in the cell faces the bias roller 851. In this region, the developer DV is not stirred by the oscillating magnetic field of the magnet roller 841. Therefore, after the electric field is applied to the dry developer DV in the cell together with the oscillating magnetic field, the electric field is further applied in a state where there is almost no influence of the oscillating magnetic field.

The surface of the photoreceptor 81 is bias roller 85.
After passing through the area facing 1, the light is erased from the erase device 86 in preparation for the next image formation. The erase device 86 includes an LED, and the light emitted from the LED erases the photoconductor 81.

The image forming apparatus AP1 can form a desired image on the medium even if the electrode is not formed on the medium. However, in that case, the bias roller 8
The electric field is applied to the dry developer in the cell only in the area where 51 faces the photoconductor 81. If a bias voltage applying member is formed by adding a conductive belt member that is wound around the bias roller 851 and the sleeve 842, the medium on which the electrodes are formed and the image forming apparatus AP.
Similar to the case of forming an image by the combination with 1, the electric field may be applied to the region facing the bias roller after the electric field is applied together with the oscillating magnetic field.

§4. In the image display medium MD1, the bottom surface of the partition wall W1 facing the substrate S2t is colored in black, and the black light absorption film 31 is formed between the partition wall W1 and the substrate S2t, and thus is reflected by the white layer 41. The amount of white light emitted from the region corresponding to the partition W1 of the medium and traveling toward the observer can be reduced as compared with the medium without the light absorption film 31. Therefore, when the black developing particles Pk in the cells CL are collected on the substrate S1 side in the medium MD1 to perform black display, the amount of white light emitted from the area adjacent to the cells CL is reduced, and a black image is displayed. The concentration can be increased. The contrast of the display image by the medium MD1 is improved by that much.

In the medium MD1, since the dry developer contained in the cell CL is composed of two kinds of developing particles, that is, the black developing particles Pk and the white developing particles Pw, the two-color display of black and white is performed. Done. If, for example, a dry developer containing red developing particles and white developing particles is adopted as the dry developer contained in the cell, two-color display of red and white can be performed. In this case, the black light absorption film 31 between the partition W1 and the substrate S2t reduces the amount of white light emitted from the medium region corresponding to the partition, so that the red color displayed by the red developing particles becomes whitish. Can be suppressed. That is, the amount of white light emitted from the medium region corresponding to the partition wall can be reduced by the black light absorbing film 31, which means that the colors of the developing particles themselves (colors corresponding to the colors of the developing particles) such as black and red can be reduced. It means that it can be displayed more faithfully and more accurately.

A medium MD shown in FIG. 2 and further shown in FIG.
5, instead of coloring the bottom surface of the partition W1 black, the entire partition W2 may be colored black as in the medium MD2 of FIG. 5B, or the medium of FIG. Even if the top surface of the partition W3 facing the substrate S1 is colored black like MD3, the amount of white light emitted from the medium region corresponding to the partition can be reduced as in the case of the medium MD1. Note that FIG.
The medium MD2 of (B) is substantially the same as the medium MD1 except that the entire partition W2 is colored black. In addition, the medium MD3 of FIG. 5C is substantially the same as the medium MD1 except that the top surface of the partition W3, not the bottom surface, is colored black.

However, as shown in FIGS. 5B and 5C, when the display images of the media MD2 and MD3 are viewed obliquely with respect to the surface of the media substrate, the fields of view are visible on the partition walls W2 and W3 whose top surfaces are black. It will be blocked. Therefore, the media MD2 and MD
In No. 3, the viewing angle dependency of the light and shade of the image becomes large.
On the other hand, as shown in FIG. 5A, in the medium MD1, since the upper portion of the partition W1 facing the substrate S1 is colorless and transparent, the field of view is not obstructed by the partition W1 and only the field of view of the display image is increased. The angle dependence can be reduced.

In the medium MD1, the substrate S1 on the observation side and the partition W1 are integrally formed, but instead of this, the substrate S1 and the partition W4 may be separate bodies as in the medium MD4 in FIG. The medium MD4 includes the substrate S1 and the partition W4.
Is substantially the same as the medium MD1 except that is a separate body.

In the medium MD4, the partition W4 is made of ultraviolet (UV) curable resin and is formed as follows. First, a UV curable resin is uniformly applied on the substrate S1 to form a UV curable resin film. By irradiating this resin film with ultraviolet rays through a mask having holes corresponding to the partition wall pattern, the portion of the resin film to be the partition wall is cured. Then, the uncured resin film portion is removed to form the partition W4 having a predetermined pattern on the substrate S1. The partition W4 itself is colorless and transparent. In the medium MD4 as well, similar to the medium MD1, the black light absorption film 31 between the partition W4 and the substrate S2t is formed by coloring the bottom surface of the partition W4 facing the substrate S2t with black paint. As the substrate S1, for example, a PET film may be adopted instead of the PP film.

Instead of the above, the partition wall is formed as follows on the substrate S1.
It may be formed on top. For example, an ultraviolet curable resin or a thermosetting resin is poured into a molding die having pattern irregularities corresponding to the partition pattern, and a resin film to be the substrate S1 is pressure-bonded to this resin. After that, the curable resin is cured to form the partition W4 made of the curable resin on the substrate S1. Alternatively, the partition W4 may be formed on the substrate S1 by adhering a plurality of transparent tapes split to the partition height on the substrate S1. Alternatively, a portion of the resin film corresponding to the cell is punched out to form a plurality of linear holes corresponding to the cell in the resin film, and the resin film having the holes is thermocompression-bonded to the resin film serving as the substrate S1. The partition W4 may be formed on the substrate S1. In this case, the partition wall W4 is a portion of the resin film which is not a hole.

In any case, in the medium MD4, since the black light absorbing film 31 is formed between the transparent partition W4 and the substrate S2t, it is reflected by the white layer 41 and formed on the partition W4 similarly to the medium MD1. The amount of white light emitted from the corresponding medium area can be reduced. However, medium M
At D4, the light incident on the inside of the medium from the substrate S1 side may be reflected at the interface between the substrate S1 on the observation side and the partition W4, and may be emitted from the medium region corresponding to the partition. The emitted light due to this interface reflection also reduces the black image density when performing black display.

On the other hand, in the medium MD1 of FIG. 2 etc., the substrate S1 on the observation side and the partition W1 are integrally formed, and there is no interface between the substrate S1 and the partition W1.
The interface reflection that occurs in the medium MD4 does not occur. Therefore, the amount of light emitted from the medium MD1 from the medium region corresponding to the partition wall is smaller than that of the medium MD4.
To that extent, the black image density when displaying black becomes higher.

In the medium MD1, since the black light absorption film 31 is formed between the transparent substrate S2t arranged on the opposite side of the observation side and the partition W1, the light incident on the inside of the medium from the substrate S2t side is The light does not pass through the partition W1 and is emitted from the substrate S1 side and does not go toward the observer. This allows
The contrast, color tone, etc. of the image displayed by the medium do not change depending on the place where the medium MD1 is placed.

In the medium MD1, as described above, the substrate S
The white layer 41 is formed on 2t, and when the medium MD1 is viewed from the side opposite to the observation side (substrate S2t side), the white layer 41 is visible through the colorless transparent electrode Ec and the colorless transparent substrate S2t. That is, when viewed from the side opposite to the observation side, the medium MD1
Looks white. As a result, the medium MD1 can give the user a paper-like impression, and the discomfort with the paper of the medium MD1 can be reduced.

The white layer 41 may be formed on the back side surface (the surface opposite to the observation side) of the transparent substrate S2t like the medium MD5 of FIG. 7A. Alternatively, instead of providing the white layer 41 on the transparent substrate S2t, the medium MD of FIG.
The substrate S2w itself, which is arranged on the side opposite to the observation side as in 6, may be white. In any case, when viewed from the side opposite to the observation side, the media MD5 and MD6 appear white, and these media can give the user a paper-like impression.

§5. Experiment in which a medium having the same structure as the image display medium MD1 shown in FIGS. 1 and 2 and having a black light absorbing film 31 between the partition W1 and the substrate S2t is actually manufactured to examine the image display performance (Experimental Example 1) I went. The size and material of each part of the manufactured medium are the same as those described in the description of the medium MD1.

As the image display performance, the black image density when performing black display and the white image density when performing white display were measured. The black image density indicates that the larger the value, the darker the black. The smaller the white image density, the higher the whiteness. The contrast (reflection density ratio) was calculated from the measured black image density Db and white image density Dw. The contrast is 10 ^Db / 10 ^Dw . Contrast indicates that the larger the value, the easier it is to view the displayed image.

For comparison with the medium of Experimental Example 1, an experiment (Comparative Example 1) was conducted in which a conventional medium having no black light absorbing film 31 was prepared and its image display performance was examined. Comparative Example 1
The medium is the black light absorption film 3 between the partition W1 and the substrate S2t.
The medium is the same as that of Experimental Example 1 except that 1 is absent.

The results are shown in Table 1 below. Table 1                 Black image density White image density Contrast Experimental Example 1 1.441 0.383 11.43 Comparative Example 1 1.160 0.340 6.61

It can be seen from Table 1 that the medium of Experimental Example 1 according to the present invention has a greatly improved black image density as compared with the medium of the conventional Comparative Example 1. It is considered that the black light absorption film between the substrate and the partition arranged on the side opposite to the observation side reduces the white light emitted from the region of the medium corresponding to the partition, thereby improving the black image density. On the other hand, it can be seen that the medium of Experimental Example 1 has a slightly increased white image density value (that is, the degree of white when displaying white is slightly reduced) as compared with the medium of Comparative Example 1. It is considered that this is also because the black light absorbing film reduced white light emitted from the region corresponding to the partition wall of the medium. Although the white image density of the medium of Experimental Example 1 was slightly deteriorated, the black image density was significantly improved, and as a result, the contrast was significantly improved as compared with the medium of Comparative Example 1.

§6. In the medium MD1 of FIG. 2, by forming a black coating film on the bottom surface of the partition wall W1 facing the substrate S2t as described above, the bottom surface of the partition wall W1 facing the substrate S2t is colored black, and the partition wall W1 and the substrate S2t are colored. The black light absorption film 31 is disposed between the two.

Instead of this, a black adhesive, for example, an adhesive in which a black colorant such as carbon black is dispersed is used as an adhesive for adhering the partition W1 and the substrate S2t,
The bottom surface of the partition W1 facing the substrate S2t may be colored black with this adhesive. Alternatively, a black coating film may be formed only on the region of the substrate S2t that faces the partition W1. Whichever is adopted, the black light absorbing film is arranged between the bottom surface of the partition wall W1 and the substrate S2t like the medium MD1.
The same effect as the medium MD1 is obtained.

§7. FIG. 8 shows a schematic sectional view of still another example of the image display medium. The medium MD7 in FIG. 8 is substantially the same as the medium MD1 in FIG. 2 except as described below.

In the medium MD7, the substrate S of the partition W5
The bottom face facing 2t is not colored black. Instead, the partition W5 of the substrate S2t arranged on the side opposite to the observation side
Is colored black with a black paint, and a black light absorbing film 32 is formed in this region. Also,
A region of the substrate S2t that does not face the partition W5 is colored white with a white paint, and a white film 42 is formed in this region.

In the medium MD7 as well, as in the medium MD1, the black light absorption film 32 disposed between the partition W5 and the substrate S2t can reduce the amount of light emitted from the medium region corresponding to the partition W5. it can. Also, the medium MD7
When viewed from the side opposite to the observation side, the white film 42 and the black light absorption film 32 can be seen through the transparent electrode Ec and the transparent substrate S2t. Since the white film 42 is wider than the black film 32,
When viewed from the side opposite to the observation side, the medium MD7 looks almost white. As a result, the medium MD7 can give the user a paper-like impression.

§8. A schematic sectional view of still another example of the image display medium is shown in FIG. The medium MD8 of FIG. 9A is substantially the same as the medium MD1 of FIG. 2 except as described below.

In the medium MD8, the substrate S of the partition W5
The bottom face facing 2t is not colored black. Instead, the black light absorption film 3 is formed on the entire surface of the substrate S2t on the observation side.
3 is formed. The black light absorbing film 33 is formed on the substrate S
It is formed by applying a black paint to 2t. Further, in the medium MD8, the white layer 43 is formed on the surface of the substrate S2t opposite to the observation side.

Also in the medium MD8, the amount of light emitted from the medium portion corresponding to the partition W5 can be reduced by the black light absorption film 33, similarly to the medium MD1. As described above, the black light absorption film 33 is formed on the entire surface of the substrate S2 as in the medium MD8, as compared with the case where the black light absorption film is formed only in the region of the substrate S2t facing the partition W1. Can be formed easily and efficiently.

When the medium MD8 is viewed from the side opposite to the observing side,
Since the white layer 43 can be seen through the transparent electrode Ec, the medium M
D8 looks white. Therefore, the medium MD8 is also the medium M.
Similar to D1, it is possible to give the user a paper-like impression.

It should be noted that the white layer 43 is the medium M of FIG.
It may be provided on the surface of the transparent substrate S2t on the observation side as in D9. Alternatively, as in the medium MD10 in FIG. 9C, the substrate S2w itself arranged on the side far from the observation side may be white. In any case, when viewed from the side opposite to the observation side, the media MD9 and MD10 appear white, and these media can give the user a paper-like impression.

§9. FIG. 10 shows a schematic sectional view of still another example of the image display medium. The medium MD11 of FIG. 10 is substantially the same as the medium MD1 of FIG. 2 except as described below.

In the medium MD11, the bottom surface of the partition W5 is not colored black. Instead, a black substrate S2k is adopted as the substrate arranged on the side opposite to the observation side, instead of the colorless transparent substrate S2t. A white layer 43 and a transparent electrode Ec are formed on the back side surface of the substrate S2k.

According to the medium MD11, since the substrate S2k arranged on the side far from the observing side is black, the partition W
The amount of light emitted from the medium region corresponding to 5 can be reduced. The white layer 4 when viewed from the side opposite to the observation side
By 3, the medium MD11 looks white, and the medium MD11 can give the user a paper-like impression.

§10. The above-described media MD1 to MD11
In each of the above cases, the cell shape was a line shape, but the cell shape is not limited to this. For example, the cells CL may have a lattice shape like the medium MD12 of FIG.
The cells CL may have a honeycomb shape like the medium MD13 of FIG.

Whatever the cell shape may be, by coloring at least the bottom surface of the partition wall in a dark color such as black as described above, or at least the substrate arranged on the side opposite to the observation side. By coloring the surface facing the partition wall in a dark color such as black, the amount of light emitted from the medium region corresponding to the partition wall can be reduced.

§11. In the medium MD1 and the like described above, the electrode Ec is provided on the substrate arranged on the side opposite to the observation side, but the electrode Ec may be provided on the observation side substrate S1. Further, the electrode may be provided on the medium substrate, if necessary, in more detail, depending on the image forming method on the medium (method of applying an electric field to the dry developer in the cell) and the like. As described above, according to the image forming apparatus AP1 of FIG.
A desired image can be formed on the medium even if the electrode is not formed on the medium. The method of applying an electric field to the dry developer in the cell to form an image on the medium is not limited to the method by the image forming apparatus AP1 of FIG. 4 described above, and may be performed as follows, for example.

§11.1. The medium MD1 shown in FIG.
An image can be formed by the image forming apparatus AP2 in FIG. 12 instead of the image forming apparatus AP1.

In the image forming apparatus AP2, the medium MD1
The image is formed while being conveyed in a predetermined direction. The image forming apparatus AP2 has a plurality of stylus electrodes 70 that are brought close to the medium substrate S1 and a magnet roller 75. Although not shown, the plurality of stylus electrodes 70 are arranged at a predetermined pitch in a direction orthogonal to the medium transport direction.

When forming an image, the stylus electrode 7
A predetermined voltage is applied to 0 to discharge from the stylus electrode 70 toward the medium substrate S1 to give an electrostatic charge on the substrate S1. As a result, an electrostatic latent image corresponding to the image to be formed is formed on the substrate S1. At this time, the medium substrate S
The electrode Ec on 2t is set to a predetermined bias potential.
This bias potential is a potential between the potential of the region of the substrate S1 to which the electrostatic charge is applied and the potential of the region of the substrate S1 to which the electrostatic charge is not applied. With these, an electric field oriented in accordance with the pixel is applied to the dry developer corresponding to each pixel, and the medium M
A desired image can be formed on D1. At the same time when the electric field is applied, an oscillating magnetic field is also applied to the dry developer by the magnet roller 75.

The electrostatic latent image can be formed on the medium substrate by applying the electrostatic charge as described above, instead of using the multi-stylus type device described above, for example, using an ion flow type device.

§11.2. Image display medium MD1 of FIG.
4, electrodes are formed on the substrates S1 and S2t respectively, and a voltage is applied between the electrodes on the substrate S1 and the substrate S2t to apply an electric field to the dry developer in the cell. Then, an image may be formed.

The medium MD14 is substantially the same as the medium MD1 in FIG. 2 except that the electrodes are formed as follows. Individual electrodes Ei are formed on the substrate S1 of the medium MD14 so as to correspond to the respective pixels. Further, a common electrode Ec facing any of these individual electrodes Ei is formed on the substrate S2t. Both the individual electrode Ei and the common electrode Ec are transparent electrodes.

An image can be formed on the medium MD14 by the image forming apparatus AP3 shown in FIG. 13, for example. The image forming apparatus AP3 has a voltage application controller 71 for applying a voltage to each individual electrode Ei of the medium MD14, and a magnet sheet 72 for applying an oscillating magnetic field to the dry developer DV in the cell. .

When performing image formation, with the common electrode Ec grounded, a voltage having a polarity corresponding to the image information of the pixel corresponding to the individual electrode Ei is applied to each individual electrode Ei. As a result, the electric field E oriented according to the image information of the pixel is applied to the dry developer DV in the region corresponding to each pixel, and a desired image can be formed on the medium MD14. By vibrating the magnet sheet 72 in a plane parallel to the medium substrate surface at the same time as applying the electric field, or
An oscillating magnetic field is applied to the dry developer DV by moving the magnet sheet 72 relative to the medium.

§11.3. Image display medium M shown in FIG.
A float electrode is formed on the substrate like D15,
Electric charges may be injected into the float electrode, and an electric field may be applied to the dry developer in the cell by utilizing the injected charges.

The medium MD15 is substantially the same as the medium MD1 of FIG. 2 except that the electrodes are formed on the substrate as follows. On the substrate S1 of the medium MD15, a plurality of float electrodes Ef are formed corresponding to each pixel. Further, a common electrode Ec facing any of the float electrodes Ef is formed on the substrate S2t. Both the float electrode Ef and the common electrode Ec are transparent.

An image can be formed on the medium MD15 by the image forming apparatus AP4 shown in FIG. 14, for example.
The image forming apparatus AP4 includes the float electrode E of the medium MD15.
A plurality of injection electrodes 73 for injecting charges into f, a voltage application controller 74 for selectively applying a positive or negative voltage to these injection electrodes, and an oscillating magnetic field applied to the dry developer DV in the cell. It has a magnet roller 75 for Although not shown, the plurality of injection electrodes 73 are arranged side by side at a predetermined pitch in a direction orthogonal to the medium transport direction.

The image formation is performed while the medium MD15 is conveyed in a predetermined direction with the common electrode Ec grounded. The injection electrode 73 is a float electrode E on the medium substrate to be transported.
contact f sequentially. A voltage having a polarity corresponding to the image information of the pixel corresponding to the contacting float electrode Ef is applied to the injection electrode 73. As a result, charges having a polarity corresponding to the image information of the pixel corresponding to the float electrode are injected into the float electrode Ef. Therefore, the electric field E oriented in accordance with the polarity of the charges injected into the float electrode is applied to the dry developer DV that faces the float electrode Ef. Thereby, a desired image can be formed on the medium MD15. An oscillating magnetic field is applied to the dry developer DV by rotating the magnet roller 75 at the same time as applying the electric field.

[0122]

As described above, according to the present invention, a pair of substrates, at least one cell formed between these substrates and containing a dry developer, and the cells formed between these substrates are provided. It is possible to provide an image display medium having adjacent partition walls and capable of displaying an image with good contrast.

[Brief description of drawings]

FIG. 1 is a schematic plan view of an example of an image display medium according to the present invention.

FIG. 2 is a schematic sectional view of the image display medium of FIG.

FIG. 3 is a diagram showing a state in which an electric field is applied to a dry developer in cells of the image display medium of FIG. 1 to form an image.

FIG. 4 is a schematic configuration diagram of an example of an image forming apparatus capable of forming an image on the image display medium of FIG.

5 (A) shows a state in which a display image by the image display medium of FIG. 1 is viewed obliquely. FIG. 5 (B)
2C and 2C are schematic cross-sectional views of another example of the image display medium according to the present invention, showing a state in which a display image by the medium is viewed obliquely.

FIG. 6 is a schematic sectional view of still another example of the image display medium according to the present invention.

7A and 7B are schematic sectional views of still another example of the image display medium according to the present invention.

FIG. 8 is a schematic cross-sectional view of still another example of the image display medium according to the present invention.

9 (A), (B) and (C) are schematic cross-sectional views of still another example of the image display medium according to the present invention.

FIG. 10 is a schematic cross-sectional view of still another example of the image display medium according to the present invention.

11A and 11B are schematic plan views of still another example of the image display medium according to the present invention.

12 is a schematic configuration diagram of another example of an image forming apparatus capable of forming an image on the image display medium of FIG.

FIG. 13 is a schematic sectional view of still another example of the image display medium according to the present invention and a schematic configuration diagram of an example of an image forming apparatus capable of forming an image on the medium.

FIG. 14 is a schematic sectional view of still another example of the image display medium according to the present invention and a schematic configuration diagram of an example of an image forming apparatus capable of forming an image on the medium.

15A is a schematic cross-sectional view of an example of a conventional image display medium, and FIG. 15B is a diagram showing a state in which an image is formed on the medium.

[Explanation of symbols]

MD1 to MD15 image display medium S1 Observation side substrate S2t Substrate placed on the side opposite to the observation side (colorless transparent) S2w Substrate placed on the side opposite to the observation side (white) S2k Substrate placed on the side opposite to the observation side (black) W1-W5 partition CL cell DV dry developer Pw White developer particles Pk Black developer particles Ec electrode Ei individual electrode Ef float electrode E electric field 31, 32, 33 Black light absorption film 41, 42, 43 White layer AP1 to AP4 image forming apparatus 70 stylus electrode 71 Voltage application controller 72 Magnet sheet 73 Injection electrode 74 Voltage application controller 75 magnet roller 81 photoconductor 82 Charging device 821 Charging brush roller 822 High voltage power supply 83 Exposure equipment 84 developer stirring device 841 Magnet roller 842 sleeve 85 Bias voltage applying device 851 bias roller 852 power supply 86 Erase device

Claims (5)

[Claims] 1. A transparent first substrate disposed on the observation side, and a second substrate disposed at a distance from the first substrate and farther from the observation side than the first substrate. A substrate, at least one cell formed between the first substrate and the second substrate, and a partition wall formed between the first substrate and the second substrate and adjacent to the cell for forming the cell And a dry developer contained in the cell, the dry developer containing two types of developing particles having different optical reflection densities, different charging polarities, and both having triboelectric charging properties. The image display medium is characterized in that at least the bottom surface of the partition wall facing the second substrate is colored dark. 2. A transparent first substrate disposed on the observation side, and a second substrate disposed at a distance from the first substrate and farther from the observation side than the first substrate. A substrate, at least one cell formed between the first substrate and the second substrate, and a partition wall formed between the first substrate and the second substrate and adjacent to the cell for forming the cell And a dry developer contained in the cell, the dry developer containing two types of developing particles having different optical reflection densities, different charging polarities, and both having triboelectric charging properties. The image display medium is characterized in that the partition wall is transparent, and at least a region of the second substrate facing the partition wall is colored dark. 3. The image display medium according to claim 1, wherein the second substrate is opaque. 4. The image display according to claim 1, wherein the second substrate has an opaque dark color, and an opaque bright color layer is formed on the surface of the second substrate opposite to the observation side. Medium. 5. The second substrate is transparent and is opaque on the second substrate such that the image display medium looks bright when viewed from the side opposite to the viewing side. The image display medium according to claim 1, wherein a color layer is formed.