JP2001215902A - Reversible image display method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a reversible image display method capable of repetitively displaying and erasing images and therefore capable of decreasing the paper, ink etc., used for the conventional image display and stably displaying the images having an excellent contrast, high resolution and high quality for a long period of time. SOLUTION: The image display medium, which has two sheets 121 and 112 having light transparency, developer housing cells which are formed therebetween and circumferentially enclosed by partition walls and the dry process developer included in the respective cells and in which the developer contains triboelectrified dry process developing particles varying in electrostatic charge polarities from each other and varying in optical reflection density from each other, is prepared. Prescribed static electric fields are formed by each of pixels in correspondence to the images to be displayed for the developing particles included in the respective cells, by which the developing particles are transferred and the images are displayed. The static electric fields formed in this image display stage form the electrostatic latent images corresponding to the images to be displayed and form the images in accordance with the electrostatic latent images on the surface of a medium.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to an image display method. In particular, the present invention relates to a reversible image display method capable of repeatedly performing image display and image deletion.

[0002]

2. Description of the Related Art Today's image displays include pencils, pens,
Manually write characters and graphics on an image display medium such as paper using paints, etc .; display documents and graphics created by a computer, word processor, etc. on a display such as a CRT display; This is done by, for example, displaying an output on a medium.

Further, a document, a figure, or the like, which is manually created on a medium such as paper, or a document, a figure, or the like on a medium such as paper output by a printer is printed on another medium such as paper using a copying machine or the like. In some cases, a copy is made, or transmitted by a facsimile machine or the like, and copied and output on a medium such as paper at a transmission destination.

[0004]

Among these image displays, characters, characters and the like are displayed on an image display medium such as paper using a pencil, a pen or the like.
Image display for displaying figures, etc., and image display for displaying characters, figures, etc. on an image display medium such as paper by an image forming apparatus such as an electrophotographic system, an ink spraying system, a thermal transfer system, etc., such as a printer, a copying machine, or a facsimile machine. Then, a clear image can be displayed at a high resolution, and the image is easy to see when viewing the image.

However, it is not possible to repeat image display and image deletion on an image display medium such as paper. When writing letters and the like using a pencil, the letters and the like can be erased to some extent with an eraser, but if the letters etc. are thinly written, they will be completely erased if they are written with normal darkness. It is difficult to leave, and it is difficult to reuse a medium, such as paper, on which an image has been displayed, unless the image is also displayed on the back side of the medium on which an image has not been displayed.

[0006] Therefore, a medium such as paper on which an image is displayed is discarded or incinerated after it has been used up, and a lot of resources are consumed. In printers and copiers, consumables such as toner and ink are also consumed. Further, in order to obtain a display medium such as new paper, toner, ink, and the like, resources such as a medium and energy for manufacturing the medium are further required. This is contrary to the demand for environmental load reduction required today.

In this regard, in the image display on a display such as a CRT display, image display and image deletion can be repeated. However, the image displayed on the display has a lower resolution than the image displayed on a paper or the like by a printer or the like, and there is a limit to obtaining a clear and fine image. In addition, eyes are very apt to be tired in long-term visual work due to relatively low resolution and light emission from the display.

An electrophoretic display has been proposed as an image display method capable of repeating image display and image deletion. In this display method, at least one is transparent.
A sealed space was formed by arranging two substrates facing each other with a space between them, and filled with a display liquid in which particles having electrophoretic ability were dispersed in a dispersion medium of a different color from the sealed space. An image is displayed in the color of the particles or the color of the dispersion medium by applying an electrostatic field and causing the particles in the display liquid to migrate.

Such a display liquid usually comprises a dispersion medium such as isoparaffin, particles such as titanium dioxide, a dye for imparting color contrast with the particles, a dispersant such as a surfactant, and additives such as a charge imparting agent. Is done.

However, in this electrophoretic display,
Because of the contrast display between the high-refractive-index particles such as titanium dioxide and the insulating colored liquid, the degree of hiding of the colored liquid (the degree of hiding the colored liquid by the particles) by the particles is inevitably low, and therefore the contrast is reduced. I will. Further, since the difference in specific gravity between the particles and the dispersion medium in the display liquid is very large, sedimentation of the particles and aggregation are likely to occur, the contrast of the display is likely to decrease, and stable image display for a long time is difficult. In addition, the previous display afterimage easily occurs.
Further, the charging of the particles in the liquid greatly changes with time, and in this respect, the image display stability is also poor.

Accordingly, an object of the present invention is to provide a reversible image display method having the following advantages. (1) Image display and image deletion can be repeatedly performed,
Therefore, image display media such as paper related to the conventional image display,
It is possible to reduce the use of consumables such as a developer and ink, and it is possible to respond to today's environmental load reduction. (2) A high-resolution, high-quality image with excellent contrast can be stably displayed over a long period of time. (3) Afterimages are less likely to occur, and therefore exhibit good reversibility. In this respect, a high-quality image can be displayed. (4) A low driving voltage is required.

[0012]

According to the present invention, there are provided two sheets which are opposed to each other with a predetermined gap, at least one of which has a light transmitting property, and is formed between the two sheets;
One or two or more developer storage cells surrounded by a partition wall, and a dry developer contained in each of the cells, wherein the dry developers have different charging polarities, and A reversible image display medium comprising at least two kinds of dry development particles having triboelectricity, each having a different optical reflection density, wherein the dry developer in the developer storage cell is constituted. Preparing a reversible image display medium in which at least two kinds of dry developing particles are frictionally charged to different charging polarities; and developing the developing particles in a state where the developing particles contained in each of the cells are frictionally charged. Moving the developing particles to form an image display by forming a predetermined electrostatic field for each pixel corresponding to the image to be displayed on the particles, and displaying the electrostatic field formed in the image display step. The formed electrostatic latent image corresponding to the image to be displayed on either the outer surface of the two sheets is formed based on the electrostatic latent image, it provides a reversible image displaying method.

[0013] In the reversible image display method according to the present invention, in a state where the developing particles contained in each cell of the image display medium are triboelectrically charged, display is performed on one of the outer surfaces of the two sheets. An electrostatic latent image corresponding to the image to be formed is formed, and based on this, a predetermined electrostatic field is formed for each pixel corresponding to the image to be displayed on the developing particles in the cell. The formation of the electrostatic field may be performed simultaneously with the formation of the electrostatic latent image, or may be performed by, for example, applying a bias voltage to the medium after the formation of the electrostatic latent image.
The development is performed by moving the developing particles by the Coulomb force due to the electrostatic field, and an image is displayed.

According to the reversible image display method of the present invention, an image can be erased by forming a different electrostatic field even after displaying the image once, or by forming an alternating electric field or the like as described later in detail. The image can be rewritten by forming a different electrostatic latent image. Therefore, there is no need to discard the image display medium on which the image has been displayed. Further, the developer is contained in the cell, is not consumed, and does not require an external supply of the developer. As a result, the use of conventional image display media, such as paper, related to image display, and consumables, such as a developer, can be greatly reduced.

Further, unlike the conventional electrophotographic image formation, it is not necessary to dissolve and fix the toner on a sheet such as paper by heat, and it is not necessary to perform the work required in the conventional image formation of this type. Most of the image energy can be saved.

Thus, it is possible to meet today's reduction in environmental load.

According to the reversible image display method of the present invention, the developers contained in the cells have different optical reflection densities (in other words, "different contrast" or "color difference"). Different)) at least two types of developing particles, and the developing particles are dry type developing particles, and the degree of hiding of the other type of developing particles by one type of developing particles is good, so that good contrast is obtained. Can be displayed on the screen.

The developer contained in the cell contains at least two kinds of mutually dry triboelectrically chargeable dry developing particles having different charging polarities. When an image is displayed, the developer is charged to the opposite polarity by friction charging. Since the particles move under the Coulomb force, an image can be displayed with good contrast at this point, and an afterimage of the previous display hardly occurs.

Dry developing particles are less likely to settle and accumulate because they do not involve a liquid, as compared with, for example, the conductive toner in a display liquid used for electrophoretic image display as described above.
Also in this respect, the contrast of the image display is hardly reduced, and stable image display can be performed for a long time. Since the sedimentation and accumulation of the developing particles hardly occur, the afterimage of the previous display hardly occurs. Further, the dry developing particles have a small change over time in charging performance as compared with the toner in the liquid, so that even in this respect, stable image display can be performed for a long time.

Further, since the electrostatic latent image on the sheet surface can be formed with a high resolution, an image can be displayed with a higher resolution and easier on the eyes than a conventional CRT display or the like.

Further, according to the reversible image display method of the present invention, at least two types of developing particles contained in each cell of the image display medium to be used are charged in the opposite polarity by friction charging. Therefore, since the image is displayed by forming an electrostatic field, the particles are easy to move, so that the driving voltage for displaying the image is correspondingly low.

As described above, according to the reversible image display method according to the present invention, a high-resolution, high-quality image can be stably displayed over a long period with good contrast. Further, afterimages are less likely to occur, and therefore, good reversibility is exhibited. In this respect, a high-quality image can be displayed. Further, an image can be displayed with less image unevenness. Further, the driving voltage for displaying an image can be reduced.

According to the reversible image display method of the present invention, it is possible to display an image having display characteristics close to those of a paper medium. The contrast can be increased as compared with an electrophoretic display (EPD).

The electrostatic latent image may be formed directly on the sheet surface using, for example, a direct electrostatic latent image forming apparatus.
An electrostatic latent image formed outside the medium using an external electrostatic latent image forming apparatus may be transferred to the sheet surface and formed.

[0025] Thus, whether transferred or directly formed,
When an electrostatic latent image is formed on an image display medium, the image holding properties are improved. This is particularly advantageous in terms of image retention when using a highly fluid developer or a developer whose fluidity is increased by a developer stirring process prior to image display.

As a direct electrostatic latent image forming apparatus, various discharge-type electrostatic latent image forming apparatuses for discharging an electrostatic latent image charge on the sheet surface in accordance with an image to be displayed are to be displayed. Various charge-injection-type electrostatic latent image forming apparatuses in which charge is injected onto the sheet surface according to an image to be charged and an electrostatic latent image charge is applied can be exemplified. Examples of the former include an ion flow type apparatus and a multi-stylus type apparatus having an electrostatic recording head in which recording electrodes are arranged in a predetermined direction (for example, a main scanning direction when a sheet is scanned by the apparatus). As an example of the latter, a multi-stylus type device having an electrostatic recording head in which recording electrodes are arranged in a predetermined direction (for example, a main scanning direction when a sheet is scanned by the device) and adjacent control electrodes are arranged adjacent to the recording electrodes. Can be mentioned.

An external electrostatic latent image forming apparatus forms an electrostatic latent image corresponding to an image to be displayed on an electrostatic latent image carrier, and forms the electrostatic latent image on the electrostatic latent image carrier. Is transferred to the sheet surface. Furthermore, forming an electrostatic latent image corresponding to an image to be displayed on a photoconductor such as a photoconductor, and transferring the electrostatic latent image on the photoconductor to the sheet surface, An example is one in which an electrostatic latent image corresponding to an image to be displayed is formed on a dielectric, and the electrostatic latent image on the dielectric is transferred to the sheet surface.

[0028]

Embodiments of the present invention will be described below.

The reversible image display medium used for carrying out the method of the present invention has the following constitution.

That is, two sheets which are opposed to each other with a predetermined gap, at least one of which is light-transmitting, and one or two sheets formed between the two sheets and surrounded by a partition wall. A reversible image display medium having the above-mentioned developer storage cells and a dry developer contained in each of the cells. The dry developer has at least two different charge polarities and different optical reflection densities.
And dry developing particles having triboelectric properties.

A reversible image display method according to a preferred embodiment of the present invention utilizes the reversible image display medium, and is basically the following method.

That is, a step of preparing the reversible image display medium, wherein the at least two kinds of developing particles in the dry developer are frictionally charged to different charging polarities from each other; In a state where the developing particles contained in the cell are triboelectrically charged, a predetermined electrostatic field is formed for each pixel corresponding to the image to be displayed on the developing particles, thereby moving the developing particles to display an image. And a reversible image display method.

According to the reversible image display medium and the reversible image display method using the same, the developing particles contained in each cell in the image displaying medium are displayed on the developing particles in a state of being triboelectrically charged. By forming a predetermined electrostatic field for each pixel corresponding to the image to be developed, the developing particles are moved by Coulomb force acting between the electrostatic field and the charged developing particles to perform development, and with a predetermined contrast. Images can be displayed.

The electrostatic field can be formed based on the electrostatic latent image by forming an electrostatic latent image on the outer surface of either of the two sheets, for example. The formation of the electrostatic field may be performed simultaneously with the formation of the electrostatic latent image, or may be performed after the formation of the electrostatic latent image.
Such an electrostatic field is generated by applying a bias voltage to a sheet on the side opposite to the sheet on which an electrostatic latent image is formed, or by grounding the opposite side sheet to form an electrostatic sheet. May be set to the predetermined potential.

The reversible image display medium may include an electrode.

That is, a transparent electrode may be formed on the inner surface of one of the sheets having light transmittance, and an electrode facing the transparent electrode may be provided on the inner surface of the other sheet.

In the reversible image display medium provided with the electrodes and the reversible image display method using the same, a voltage is applied between the two electrodes while the developing particles contained in each cell of the medium are frictionally charged. Then, by forming a predetermined electrostatic field for each pixel corresponding to the image to be displayed between the two electrodes, the developing particles are moved by Coulomb force acting between the electrostatic field and the charged developing particles. To develop an image and display an image with a predetermined contrast.

The electrodes on the inner surface of the other sheet may be composed of a group of individual electrodes formed for each pixel.

In any of the reversible image display media (including the display media employed in the reversible image display method) of any of the above types, the developing particles contained in the cells are required to have a triboelectrically charged state. Prior to encapsulation in the cell, frictionally charged by mixing and stirring, etc., and then encapsulated in the cell, or developing particles are encapsulated in the cell, and then mixed and agitated in the cell by applying some energy to triboelectrically charge them, or May be used for triboelectric charging.

Specific examples of the mixing and stirring of the developing particles include mixing and stirring by applying an alternating electric field (for example, an AC electric field).
Mixing and stirring by magnetic force when at least one of the developing particles is magnetic particles, mixing and stirring by ultrasonic irradiation or application of mechanical vibration, and mixing and stirring by a combination of two or more of these.

By mixing and agitating the developing particles and charging them well, it is possible to further improve the contrast and further reduce the driving voltage.

In either type of the reversible image display medium (including the display medium employed in the reversible image display method), each of the two sheets has an area larger than the thickness, Refers to things that are spread, synthetic resin,
It can be formed of various materials such as glass, and may be any of a flexible material, a flexible material, a material having poor flexibility such as a glass plate, and at least one of two sheets. It is only necessary that the (sheet on the image observation side) has a light transmitting property so that an image can be visually recognized. Both sheets may have optical transparency.

Also, a developer movement suppressing member for suppressing the lateral movement of the dry developer in the developer accommodating cell may be provided between the two sheets. As a matter of course, the partition walls forming the cells also suppress the lateral movement of the developer.

The partition wall forming the developer accommodating cell and / or the developer movement suppressing member may also serve as a spacer for maintaining the gap between the two sheets at a predetermined gap. A dedicated spacer for maintaining the gap between the two sheets at a predetermined gap may be provided separately from the partition wall and the developer movement suppressing member.

By providing such a developer movement suppressing member, the bias of the developing particles in the cell is suppressed, and a high quality image with less image unevenness can be displayed. In addition, since the gap between the two sheets is maintained at a predetermined value by the spacer, image display with less image unevenness can be performed. The shape of the developer movement suppressing member is arbitrary such as a columnar member or a wall member.

Regardless of the presence or absence of the electrodes, the number, size, shape, distribution, arrangement (regular or irregular) of the developer containing cells in the reversible image display medium is not particularly limited as long as the image can be displayed. There is no. The same applies to the developer movement suppressing member and the dedicated spacer.

Each of the partition wall, the developer movement suppressing member, and the dedicated spacer is, for example, at least partially fixed to at least one of two sheets by bonding or the like, or is integrally formed with the sheet by molding or the like. be able to. However, each of the partition wall, the developer movement suppressing member, and the dedicated spacer is not adhesively fixed to one or both of the two sheets, and is not integrally formed with the sheets. It may be arranged so as not to move with respect to at least one sheet.

The shape of the developer accommodating cell can be roughly classified into a continuous groove type and an independent type. As illustrated in FIGS. 1A, 1B, and 1C, the continuous groove type cell CEl is a cell in which each partition w1 extends without intersecting with another partition w1. For example, it is a cell formed by extending between the sealing portions cw of the peripheral portion of the medium S facing each other. In this case, the sealing portion cw can also serve as a partition wall forming a cell. The continuous groove type cell CE1 may extend parallel to two parallel sides of the medium S (FIG. 1A) or extend in a direction intersecting each side of the medium S (FIG. 1B), Even if it extends in a wave shape (Fig. 1
(C)) or may extend in other manners.

The independent type cell CE2 is, for example, a grid (FIG. 1 (D)), a brick wall (FIG. 1 (E)), a honeycomb (FIG. 1 (F)) or a series of triangles (FIG. 1). (G)),
A mode in which corrugated sections are connected (FIG. 1 (H)), and a mode in which continuous grooves each surrounded by a partition wall are connected (FIG. 1)
(I)) and the like.

In these figures, α represents the thickness of the partition wall, and pt represents the interval between adjacent partition walls.

In any case, the individual cells are shown in FIGS.
As shown in FIG. 1 (I), it may be continuously formed in another cell so as to be adjacent to another cell, or may be formed separately from the other cell. The arrangement of the cells may be regular or irregular. The number of cells may be one. In addition, partition wall w
1 may also serve as a spacer for maintaining a predetermined gap between sheets.

The pixels for image display are as follows:
Either a case where there is one pixel for one cell, a case where there is a plurality of pixels for one cell, or a case where there is one pixel for a plurality of cells may be used.

The shape of the developer transfer suppressing member may be any of a columnar shape (a cylinder, a quadrangular prism, a triangular prism, etc.), a cone shape (a cone, a square pyramid, a truncated cone, a truncated pyramid, etc.), a wall shape, and the like. Various types of developer movement suppressing members may be used. The arrangement can be regular or irregular. The columnar member is convenient for firmly joining it to the sheet. A long wall-shaped member can be expected to have a large developer transfer suppressing effect. A thin plate-shaped wall-shaped member is convenient for securing a desired developer storage amount. The height of the developer movement suppressing member is arbitrary. Therefore, it may be arranged so as not to move on one of the sheets.
When the sheet has a height extending between two sheets, it may also serve as a spacer for maintaining the gap between sheets at a predetermined value.

FIGS. 2A to 2H illustrate the shape and arrangement of the developer movement suppressing member.

FIG. 2A shows a columnar restraining member C having a rectangular cross section.
A state is shown in which a plurality of member rows, each of which is formed by arranging L1 at predetermined intervals, are arranged in parallel. FIG. 2B shows a state in which columnar suppressing members CL2 having a circular cross section are dispersedly arranged. FIG. 2C shows a thin plate-shaped (wall-shaped) restraining member C.
A state where a plurality of L3s are arranged in parallel is shown. FIG.
(D) shows a state in which the columnar suppressing member CL2 and the thin plate-like (wall-shaped) suppressing members CL3 having various lengths are irregularly distributed. FIG. 2E shows a state in which the columnar suppressing member CL2 and the thin plate-like (wall-shaped) suppressing member CL3 having the same length are dispersed and arranged to some extent. FIG.
(F) shows a plurality of column-shaped suppressing members CL4 each having a rectangular cross section in each of the continuous groove type cells CE1 shown in FIG.
This shows a state where they are arranged in an island shape. FIG. 2 (G) is FIG.
(D) shows a state in which one of the columnar suppressing members CL4 having a rectangular cross section is arranged in an island shape in each of the independent cells CE2 having a grid-like arrangement of the type shown in FIG. Each restraining member CL1,
CL2, CL3, and CL4 can also serve as spacers. In these figures, β1 and β2 indicate vertical and horizontal dimensions of the columnar suppressing member. γ1 and γ2 indicate the vertical and horizontal dimensions of one unit of the image display area. FIG. 2 (F)
Represents the distance between the adjacent members CL4. By the way, in the image display medium, a non-image display area is generated by the partition wall, the developer movement suppressing member, the spacer, and the like as described above. If the total area of such non-image display areas is too large, image display becomes difficult or image quality deteriorates. On the other hand, if it is too small, the area of the region where the spacers are provided becomes small, which results in non-uniform gap between sheets and further image unevenness.

Therefore, regardless of the presence or absence of the electrodes, the unit area So provided by the image display medium (for example, FIG. 2A,
It is preferable that the ratio Sn / So of the area Sn of the non-image portion in the region (γ1 × γ2 in (H)) is 0.0001 or more and 0.5 or less. Note that the unit area So can be arbitrarily set, but may be set so as to include both an area where an image can be actually displayed and a non-image area. Furthermore, for example, it is preferable to set both in a repetition unit that includes both a region where an image can be actually displayed and a non-image portion region and that appears repeatedly in a medium.

Alternatively, in any one of the developer storage cells (or a plurality of successively-arbitrary developer storage cell groups), one developer storage cell (or a plurality of developer storage cell groups) is provided. The area of the image display area is Sa, and the area surrounded by the center line of the partition wall forming the outer contour of the one developer containing cell (or the outer contour of the plurality of developer containing cell groups is formed. When the area surrounded by the center line of the partition wall is Sb, the value of (1-Sa / Sb) for the one developer storage cell (or the plurality of developer storage cells) is 0.0001. It is desirable to set the value to 0.5 or more (see FIG. 2I).

As a result, a high-quality image can be displayed with good contrast by securing an image display area area that does not hinder image display. On the other hand, a spacer by a partition wall, a spacer by a developer movement suppressing member, and a dedicated spacer Thus, the gap between the two sheets can be maintained at a predetermined value by securing a spacer region such as the above, and the occurrence of image unevenness can be suppressed.

In the case of an image display medium having electrodes, leads are connected to the electrodes, and the leads are preferably provided in a non-image display area having a partition wall or the like.
The materials such as the sheet, the cell partition wall, the developer movement suppressing member, and the spacer are not particularly limited. However, for example, when an electrostatic latent image is formed on the medium surface (sheet surface) for image display, at least the sheet on which the electrostatic latent image is formed is an insulating sheet. The sheet on the opposite side may or may not be an insulating sheet, regardless of the presence or absence of electrodes. When an insulating sheet is used, this may be set to the ground potential, and when it is necessary to apply a bias voltage to the sheet, the insulating sheet may be left as it is.For example, a conductive film may be formed on the outer surface of the sheet, or the opposite sheet may be used. The whole may be formed of a conductive material or a material containing a conductive material. This makes it possible to easily ground the sheet to a ground potential or apply a bias voltage to the sheet if necessary. Regardless of the presence or absence of electrodes, when the opposite sheet is an insulating sheet and a conductive film is formed on its outer surface, or when the opposite sheet itself is a conductive sheet, Has the effect of shielding the charge of
Even when the media on which images are displayed are overlapped, the images are hardly distorted, and the images can be stably held.

In the case of a medium without electrodes, if the gap between the sheets or the thickness of each sheet is too large, the electric field applied to the developer between the sheets is weakened, so that the developability is deteriorated, and the contrast and the resolution are reduced. Invite. On the other hand, if the gap between the sheets is too small, the amount of developer that can be included in the developer accommodating cell decreases, and it becomes difficult to obtain a necessary contrast. On the other hand, if the thickness of each sheet, and hence the thickness of the entire medium based on the thickness of each sheet, is too small, the medium is likely to bend, the uniformity of the gap between sheets cannot be obtained, and image unevenness tends to occur.

Therefore, in the reversible image display medium without electrodes, the thickness of each sheet is not limited to 5%.
μm to 100 μm, the gap between the two sheets is 20 μm
m to 300 μm, and the entire thickness is desirably 30 μm to 500 μm.

For the reversible image display medium having electrodes, the thickness of each sheet is not limited to 5 μm to 100 μm in order to secure the developer amount and maintain the uniformity of the gap between sheets. 20 gaps between
μm to 300 μm, total thickness 30 μm to 500 μm
It may be.

In a reversible image display medium without electrodes, for example, when an electrostatic latent image is formed on the medium surface (sheet surface) and an electrostatic field is formed based on the electrostatic latent image, a sheet If the surface resistance of the sheet on which the electrostatic field is formed is small, especially if the surface resistance of the sheet on which the electrostatic field is formed is small, an electrostatic latent image is formed directly on the sheet surface to form an electrostatic field for image display, In any case where the formed electrostatic latent image is transferred to the sheet surface, the electrostatic latent image is easily broken.

Therefore, in the reversible image display medium without electrodes, it is preferable that the surface resistivity of the outer surface of at least one of the two sheets is 10 ¹⁰ Ω / □ to 10 ¹⁶ Ω / □.

If the resistance value of the sheet surface, especially the surface resistance value of the sheet on the side opposite to the side on which the electrostatic field is formed, is too large, there is a problem in image formation and its holding. In particular, when forming an electrostatic latent image directly on the sheet surface on the electrostatic field forming side, the latent image charge is difficult to ride, and when transferring an externally formed electrostatic latent image, it is difficult to obtain a uniform electric field. And image unevenness is likely to occur. Furthermore, when the media after the image formation are overlapped, it becomes difficult to shield the electrostatic between the adjacent media, the image is easily broken, and it is difficult to hold the image.

Therefore, it is preferable that the surface resistivity of at least one outer surface of the two sheets is set to 10 ⁷ Ω / □ or less (a resistivity equal to or less than that of paper).

From the above, in the reversible image display medium without electrodes, the surface resistivity of the outer surface of one of the two sheets is 10 ¹⁰ Ω / □ to 10 ¹⁶ Ω / □, and that of the other sheet is It is recommended that the surface resistivity of the outer surface be 10 ⁷ Ω / □ or less.

The thickness of each sheet is set to 5 μm within a range where no trouble is caused.
m to 100 μm, gap between both sheets 20 μm to 3
00 μm, and the total thickness is 30 μm to 500 μm
Both surfaces of the outer surface of one of the two sheets
10 resistivity^TenΩ / □ -10 ¹⁶Ω / □, of the other sheet
Surface resistivity of outer surface is 10⁷Ω / □ or less.

The surface resistivity of each sheet can be adjusted by, for example, adding a conductive material (eg, conductive carbon) having a different resistance value to the sheet or applying a surfactant to the sheet surface. In both reversible image display media with and without electrodes, the developers contained in the developer accommodating cells have different charging polarities and different optical reflection densities (in other words, "contrast of contrast"). "Differential" or "different colors"). As representative examples, positively chargeable (or negatively chargeable) black particles having light absorbency and negatively chargeable (or positively chargeable) white particles having light reflectivity can be given.

At least one of the at least two types of developing particles constituting the dry developer may be non-conductive particles. In this case, regardless of whether the image display medium has an electrode or not, the presence of the non-conductive particles causes
Various kinds of developing particles can be easily and reliably triboelectrically charged, so that a good image display can be performed.

Further, at least one of the at least two types of developing particles constituting the dry developer may be magnetic particles. Regardless of whether or not the image display medium has electrodes, the presence of such magnetic particles allows the developer (developing particles) to be agitated by a magnetic field, for example, an oscillating magnetic field, as described below. By agitation, the previous image prior to image formation (image display) can be erased, and in the image display, the developing particles can be easily moved in the electrostatic field for image display.

In any case, if the developing particles are too small, the adhesive force becomes extremely large, causing sticking between the developing particles and lowering the developing efficiency. On the other hand, if the developing particles are too small, the charge amount of the particles becomes very large, so that an electric field for moving the particles in displaying an image must be made large, and therefore a high driving voltage is required.

If the size of the developing particles is too large, triboelectric charging cannot be performed well, and a sufficient moving speed of the developing particles cannot be obtained in an electrostatic field for displaying an image, or good contrast cannot be obtained.

In light of these facts and materials for obtaining developing particles having predetermined characteristics, it is appropriate that the non-conductive developing particles have a particle size of 1 μm to 50 μm, and the magnetic developing particles have a particle size of 1 μm to 100 μm. .

It should be noted that one type of developing particles may be both non-conductive particles and magnetic particles.

The developing particles can be formed from, for example, a binder resin, a colorant, or the like, or a colorant alone.
The following can be used for these. -Binder resin There is no particular limitation as long as it can disperse a colorant, a magnetic substance, and the like, and is usually used as a binder. A typical example is a binder resin used for an electrophotographic toner.

For example, polystyrene resin, poly (meth) acrylic resin, polyolefin resin, polyamide resin, polycarbonate resin, polyether resin, polysulfone resin, polyester resin, epoxy resin, urea resin, urethane Resin, urea resin, fluorine resin, silicon resin and copolymers thereof,
A block polymer, a graft polymer, a polymer blend, or the like can be used.

The glass transition point Tg may be quite high,
In some cases, it need not be a thermoplastic resin. -Colorant As the colorant, various organic or inorganic pigments and dyes as shown below can be used.

Examples of the black pigment include carbon black, copper oxide, manganese dioxide, aniline black, activated carbon and the like.

Examples of the yellow pigments include graphite, zinc yellow, cadmium yellow, yellow iron oxide, mineral fast yellow, nickel titanium yellow, navels yellow, naphthol yellow S, banza yellow G, banza yellow 10G, benzidine yellow G, and benzidine. Yellow GR,
There are quinoline yellow lake, permanent yellow NCG, tartrazine lake and the like.

Examples of the orange pigment include red yellow lead, molybdenum orange, permanent orange GTR, pyrazolone orange, vulcan orange, indaslen brilliant orange RK, benzidine orange G, and indaslen brilliant orange GK.

Examples of red pigments include red iron, cadmium red, leadtan, mercury sulfide, cadmium, permanent red 4R, lithol red, pyrazolone red, watching red, calcium salt, lake red D, brilliant carmine 6B, eosin lake, and rhodamine. Lake B, Alizarin Lake, Brilliant Carmine 3B and the like.

Examples of purple pigments include manganese purple, fast violet B, and methyl violet lake.

As blue pigments, navy blue, cobalt blue, alkali blue lake, Victoria blue lake,
Phthalocyanine blue, metal-free phthalocyanine blue,
Phthalocyanine blue partially chlorinated products, Fast Sky Blue, Indaslen Blue BC and the like.

The green subjects include chrome green, chromium oxide, pigment green B, malachite green lake, and final yellow green G.

As white pigments, zinc white, titanium oxide,
Examples include antimony white and zinc sulfide.

The extender includes baryte powder, barium carbonate, clay, silica, white carbon, talc, alumina white and the like.

Various dyes such as basic, acidic, disperse, and direct dyes include nigrosine, methylene blue, rose bengal, quinoline yellow, and ultramarine blue.

These coloring agents can be used alone or in combination of two or more.

Particularly in black and white display, carbon black is preferred as a black colorant, and titanium dioxide is preferred as a white colorant.

In particular, when the white pigment is kneaded with a molten binder resin (binder resin) to obtain the developing particles from the kneaded product, the amount of the white pigment used is determined in order to obtain a sufficient whiteness. To 100 parts by weight of the starting monomer
The amount is desirably 0 parts by weight or more, preferably 20 parts by weight or more, and is desirably 60 parts by weight or less, preferably 50 parts by weight or less in order to ensure sufficient dispersibility of the white pigment. When the amount of the white pigment exceeds 60 parts by weight, the binding property between the pigment and the binder resin and the dispersibility of the pigment are deteriorated. No concealing properties are obtained.

[0092] Carbon black is preferable as the black colorant. However, in the case where the developing particles are made to have magnetism, magnetic particles such as magnetite and ferrite and magnetic fine particles can be used as the colorant. -Other internal additives As internal additives preferably used other than the binder resin and the colorant, a magnetic substance, a charge control agent, a resistance adjuster and the like can be mentioned. -Charge control agent The charge control agent is not particularly limited as long as it gives charge to the developing particles by triboelectric charging.

Examples of the positive charge control agent include a nigrosine dye, a triphenylmethane compound, a quaternary ammonium salt compound, a polyamine resin, and an imidazole derivative.

Examples of the negative charge control agent include salicylic acid metal complexes, metal-containing azo dyes, oil-soluble dyes containing gold (including metal ions and metal atoms), quaternary ammonium salt compounds, calixarene compounds, and boron-containing compounds. (Boron benzylate complex), nitroimidazole derivatives and the like.

In addition, metal oxides such as ultrafine silica, ultrafine titanium oxide and ultrafine alumina, nitrogen-containing cyclic compounds such as pyridine and derivatives and salts thereof, various organic pigments,
Resins containing fluorine, chlorine, nitrogen and the like can also be used as charge control agents. -Magnetic substance Magnetic particles and magnetic fine powder can be used, and examples thereof include ferromagnetic elements and alloys and compounds containing these, such as magnetite, hematite, iron such as ferrite, cobalt, nickel, and the like. Conventionally known magnetic materials such as alloys and compounds such as manganese and other ferromagnetic alloys may be contained. The shape of these magnetic powders is various, such as a granular shape, a needle shape, and a flake shape, and can be appropriately selected and used. -Resistance adjuster As the resistance adjuster, there are also the same as the above-mentioned magnetic powders and colorants, and it is preferable to use metal oxide, graphite, carbon black, etc. in various shapes such as flake, fiber, powder, etc. Can be.

Next, a production example of the developing particles will be described.

[0097] From among the binder resin, magnetic powder, colorant, charge control agent, resistance adjuster and other additives as described above, necessary ones are selected, and they are sufficiently mixed by a predetermined amount and then pressurized. Heat kneading with a kneader or a twin-screw kneading device, etc.
After cooling, it is roughly pulverized by a hammer mill, a cutter mill or the like. Next, after further pulverizing with a jet mill, an ong mill or the like, the particles are classified using an air classifier or the like until the particles have a predetermined average particle size, thereby obtaining developed particles.

The different charging polarities thus obtained,
By mixing and stirring particles having different contrasts (optical reflection densities) at a predetermined ratio, a developer having a predetermined charge amount can be prepared. At this time, a third component (particle) such as a fluidity improver may be added and mixed. -About such fluidizers As fluidity improvers, for example, silica, alumina, titanium oxide, barium titanate, magnesium titanate, calcium titanate, strontium titanate, zinc oxide, silica sand, clay, mica, wollastonite Diatomaceous earth, chromium oxide, cerium oxide, red iron oxide, antimony trioxide, magnesium oxide, zirconium oxide, barium sulfate, barium carbonate, calcium carbonate, silicon carbide, silicon nitride and the like.

In particular, fine powders such as silica, aluminum oxide, titanium dioxide and magnesium fluoride are preferable, and a fluidizing agent may be added alone or in combination. The formation of the electrostatic field on the developing particles for image display using the electrodeless reversible image display medium is performed, for example, by using one of the two sheets (for example, the image observation side sheet).
An electrostatic latent image corresponding to the image to be displayed can be formed on the surface of the device and formed based on the electrostatic latent image.
In this case, the formation of the electrostatic field may be performed simultaneously with the formation of the electrostatic latent image, or may be performed after the formation of the electrostatic latent image. The electrostatic field can be formed, for example, by setting a predetermined potential for forming the electrostatic field on a sheet on the opposite side of the sheet on which the electrostatic latent image is formed. The setting of the predetermined potential can be performed by, for example, applying a bias to the opposite sheet or grounding the sheet.

The electrostatic latent image may be formed directly on the medium surface (sheet surface) using, for example, a direct electrostatic latent image forming apparatus, or formed outside the medium using an external electrostatic latent image forming apparatus. The electrostatic latent image may be formed by transferring the image onto the medium surface (sheet surface).

As the direct electrostatic latent image forming apparatus, various discharge-type electrostatic latent image forming apparatuses which discharge an electrostatic latent image charge by discharging to the surface of a medium in accordance with an image to be displayed are to be displayed. Various charge-injection-type electrostatic latent image forming apparatuses that charge an electrostatic latent image by injecting charge into the medium surface according to an image can be exemplified. As an example of the former, an ion flow type apparatus, a predetermined direction (for example, a main scanning direction when a sheet is scanned by the apparatus)
A multi-stylus-type device having an electrostatic recording head with recording electrodes arranged therein can be cited. As an example of the latter, recording electrodes are arranged in a predetermined direction (for example, a main scanning direction when a sheet is scanned by the device). A multi-stylus type device having an electrostatic recording head in which adjacent control electrodes are arranged adjacent to the recording electrodes can be mentioned.

The external electrostatic latent image forming apparatus forms an electrostatic latent image corresponding to an image to be displayed on an electrostatic latent image carrier, and forms the electrostatic latent image on the electrostatic latent image carrier. Is transferred to the sheet surface. Furthermore, forming an electrostatic latent image corresponding to an image to be displayed on a photoconductor such as a photoconductor, and transferring the electrostatic latent image on the photoconductor to the sheet surface, An example is one in which an electrostatic latent image corresponding to an image to be displayed is formed on a dielectric, and the electrostatic latent image on the dielectric is transferred to the sheet surface.

In displaying an image, an electric field forming apparatus including any one of the electrostatic latent image forming apparatuses can be employed.

As described above, whether the image is transferred or directly formed,
When an electrostatic latent image is formed on an image display medium, the image holding property is improved as will be described later in detail. This is particularly advantageous in terms of image retention when using a highly fluid developer or a developer whose fluidity is increased by a developer stirring process prior to image display.

Incidentally, for a reversible image display medium having electrodes, an electrostatic field for image display can be formed by applying a voltage to the electrodes. An electric field forming device for this medium will be exemplified later. Regardless of whether a reversible image display medium with or without electrodes is employed, an image erasing process for erasing the previously displayed image may be performed before the image is displayed.

The image erasing process can be performed by, for example, forming an electric field for moving the developing particles constituting the developer in the image display medium, applying a stirring force to the developer, or both. The application of the stirring force, for example, to form an alternating electric field to the developer, to form an oscillating magnetic field,
Irradiation of ultrasonic waves, application of mechanical vibration, and combination thereof can be performed.

Therefore, in displaying an image, the image erasing device includes, for example, a device including an electric field forming device for forming an electric field for moving the developing particles, and a device including a stirring device for applying a stirring force to the developing particles. A device that includes both the electric field forming device and the stirring device can be appropriately used.

For example, under the electric field, one of the two types of developing particles having the same optical reflection density (in other words, “same contrast” or “same color”) is transferred to one sheet side. By collecting and collecting the other developing particles having the same optical reflection density on the other sheet side, the image can be erased, and when a new image is formed next, only the developing particles need to be moved only in the image area. Therefore, the image display can be performed smoothly, reliably, and with high quality.

Further, for example, when the developer (developing particles) is stirred, the image is erased, and the charge amount and the fluidity of the developing particles are improved. In this case, the next image display is smoother.
High quality is ensured.

As such an electric field forming apparatus, a pair of electrodes (usually metal) arranged with a reversible image display medium in between
Alternatively, a device including a dielectric and a power supply device for applying a bias voltage thereto can be exemplified.

In addition, various discharge-type electric field forming devices for forming an electric field by discharging to an image display medium, and various charge injection-type electric field forming devices for forming an electric field by injecting charges into a reversible image display medium are exemplified. it can. Examples of the former include a corona charging device, an ion flow type electric field forming device, and a multi-stylus type electric field forming device having a head in which electrodes are arranged in a predetermined direction. As the latter example, electrodes are arranged in a predetermined direction. And a multi-stylus type electric field forming apparatus having a head in which adjacent control electrodes are arranged adjacent to the electrodes.

The following can be exemplified as the stirring device. A device for forming an alternating electric field on a reversible image display medium.

This device can be used when at least one of the developer particles is insulating. A device for forming an oscillating magnetic field on a reversible image display medium.

This device can be used when at least one of the developer particles contains a magnetic material. A device that irradiates a reversible image display medium with ultrasonic waves. A device that applies mechanical vibration to a reversible image display medium. A device combining two or more of the above devices. As described above, when the developer (developing particles) is agitated, the charge amount and the fluidity of the developing particles are improved, and the next image display is performed smoothly, reliably, and with high quality.

When the developer is stirred prior to the image display, the charge amount of the developing particles is stabilized, and the image can be displayed well in this respect. Further, there is an advantage that the allowable range of chargeability and fluidity of the developer is widened.

Therefore, in the case of image display, regardless of whether a reversible image display medium with or without electrodes is employed, the above-described image erasing process is also used, or separately from the image erasing process. The developer may be agitated.

When an image display medium without electrodes is employed, for example, an electrostatic latent image corresponding to an image to be displayed is formed on the surface (sheet surface) of the image display medium, and based on the electrostatic latent image, To form an electrostatic field for image display simultaneously with or after the formation of the electrostatic latent image,
The developer may be agitated simultaneously with and / or before the formation of the electrostatic field.

For an image display medium having electrodes, a voltage is applied between the electrodes to form an electrostatic field, and the developer is stirred before or simultaneously with the formation of the electrostatic field. Good. Regardless of the presence or absence of the electrode, the developer stirring
For example, this can be performed using a stirrer facing the image display medium transport path in the electrostatic field formation area by the electric field generator or upstream thereof in the direction of transport of the image display medium relative to the electric field generator.

As the developer stirring method and the stirring apparatus, the same stirring method and apparatus as those exemplified in connection with the image erasing process can be employed.

By stirring the developer in displaying an image as described above, it is possible to further improve the contrast and further reduce the driving voltage. When an electrostatic latent image is formed on the surface (sheet surface) of the image display medium when displaying an image in the case of using the reversible image display medium without the electrodes, the surface of the medium is determined before forming the electrostatic latent image. The electrostatic latent image corresponding to the image to be displayed in the charged area may be formed by uniformly charging to the potential. Then, based on the electrostatic latent image, a predetermined electrostatic field is formed for each pixel corresponding to an image to be displayed on the developer particles in the developer storage cell, thereby moving the developer particles to display an image. Is also good.

In such an image display method, charged charged developing particles of a color different from the color of the liquid are dispersed in an insulating liquid of a predetermined color, and the insulating liquid and the charged developing particles are separated by a predetermined gap. The present invention can also be applied to a reversible image display medium sealed between two opposing sheets, at least one of which has a light transmitting property.

That is, before the image is displayed, the surface of the image display medium is uniformly charged to a predetermined potential. Thereafter, an electrostatic latent image is formed on the surface of the charged medium, and based on the electrostatic latent image, each of the pixels corresponding to the image to be displayed on the charged developing particles dispersed in the insulating liquid in the medium. Thus, a predetermined electrostatic field is formed.

Further, in this image display method, the half of the outer surface and the other half of the surface opposite to each other are different in color from each other, and spherical developing particles having different ion adsorption amounts are surrounded by an insulating liquid layer. The present invention can also be applied to a reversible image display medium embedded in an insulating holding medium in a state where it is performed.

That is, prior to image display, the surface of the image display medium is uniformly charged to a predetermined potential. Thereafter, an electrostatic latent image is formed on the charged medium surface, and a predetermined electrostatic field is formed for each pixel corresponding to an image to be displayed on the spherical developing particles based on the electrostatic latent image. The images are displayed by controlling the directions of the different colored surfaces of the spherical developing particles. In addition, the rotatable spherical developing particles surrounded by the insulating liquid layer are inverted by the influence of the electrostatic field, and an image is displayed. The reversal of the spherical developing particles is caused by the fact that half of the outer surface of the spherical developing particles and the other half surface on the opposite side are different in ion adsorption amount, and thus the direction of the surface changes depending on the direction of the electric field. Occur. In addition, since half of the outer surface of the spherical developing particles and the other half of the surface opposite to each other are different in color, images can be displayed.

Regardless of the medium employing any of the developing particles contained in the cell, the developing particles in the insulating liquid, and the rotatable spherical particles, the electrostatic latent image on the medium is, for example, on the surface of the medium charged in the charging step. It can be formed by directly forming, or by transferring and forming an electrostatic latent image formed on the electrostatic latent image carrier outside the medium on the surface of the medium charged in the charging step.

Even if the charge polarity of the area of the electrostatic latent image formed on the medium is the same as the charge polarity of the charge area by uniform charging of the medium surface prior to the formation of the electrostatic latent image, The polarity may be different, or 0 [V].

The formation of the electrostatic field may be performed simultaneously with the formation of the electrostatic latent image, or may be performed by applying a bias voltage to the medium after forming the electrostatic latent image, or by grounding the medium. Is also good.

When the surface of the image display medium is uniformly charged in advance to a predetermined potential and an electrostatic latent image is written in the charged area, the charge in the developer accommodating cell according to the medium structure is determined. The developing particles or the charged developing particles in the insulating liquid can be moved, or the spherical developing particles can be inverted.
Further, an electrostatic field sufficient to hold the moved and inverted developing particles in that position is formed. In other words, if the surface of the image display medium is uniformly charged to a predetermined potential in advance, and then the electrostatic latent image is written in the charged area, the image holding property is improved. This is particularly advantageous in terms of image retention when using a highly fluid developer or a developer whose fluidity is increased by a developer stirring process prior to image display. As a result, a high-quality image with excellent contrast can be stably displayed for a long time.

It is to be noted that an image can be erased by forming a different electrostatic field or an alternating electric field in any of the medium in which the charged developing particles are dispersed in the insulating liquid and the medium including the spherical developing particles. However, the image can be rewritten by forming a different electrostatic latent image. According to the various reversible image display media described above and the reversible image display method using the same, a high-resolution, high-quality image can be stably displayed with good contrast for a long period of time. Further, afterimages are less likely to occur, and therefore, good reversibility is exhibited. In this respect, a high-quality image can be displayed. It is also possible to reduce the driving voltage. It is also possible to display an image with less image unevenness. Hereinafter, specific examples of the developing particles and the developer will be described, and specific examples of a reversible image display medium, a reversible image display method, an image forming apparatus, and the like will be described with reference to the drawings. <Developing Particles and Developer> White developing particles WP 100 parts by weight of a thermoplastic polyester resin (softening point 121 ° C., glass transition point 67 ° C.), 40 parts by weight of titanium oxide (CR-50, manufactured by Ishihara Sangyo Co., Ltd.) Zinc salicylate complex (Orient Chemical: Bontron E) as a negative charge control agent
-84) 5 parts by weight were sufficiently mixed with a Henschel mixer, kneaded with a twin-screw extruder, and then cooled. The kneaded material was roughly pulverized, then pulverized by a jet pulverizer, and subjected to air classification to obtain a white fine powder. The white fine powder has a volume average particle size of 0.3.
7 μm, 2.1 μm, 10.1 μm, 46.2 μm, 5
5.3 μm was obtained.

[0130] After the white fine powder of each particle size, hydrophobic silica particles (Aerosil R-9, manufactured by Nippon Aerosil Co., Ltd.)
72) 0.3 parts by weight were added, and the mixture was mixed with a Henschel mixer to give white developing particles WP (W
P1 to WP5) were obtained.

Particle WP1: Volume average particle diameter 0.7 μm Particle WP2: Volume average particle diameter 2.1 μm Particle WP3: Volume average particle diameter 10.1 μm Particle WP4: Volume average particle diameter 46.2 μm Particle WP5: Volume average particle diameter 55.3 μm These white developing particles are non-conductive particles. Black developing particles BP Styrene-n-butyl methacrylate resin (softening point 13
100 parts by weight at 2 ° C., glass transition point 65 ° C.) and carbon black (Ketjen Black E, manufactured by Lion Yushi Co., Ltd.)
C) and 4 parts by weight of silica (Nippon Aerosil Co., Ltd.
00) and 1.5 parts by weight of magnetite magnetic powder (RB).
-BL Titanium Industry Co., Ltd.) and 500 parts by weight with a Henschel mixer, and then kneaded with a vented biaxial kneader.

The kneaded material was cooled, coarsely pulverized by a feather mill, finely pulverized by a jet mill, and classified by an air classifier to obtain black particles BP (BPo, B
P1 to BP5) were obtained.

Particle BPo: Volume average particle size 25.0 μm Particle BP1: Volume average particle size 0.8 μm Particle BP2: Volume average particle size 3.0 μm Particle BP3: Volume average particle size 25.1 μm Particle BP4: Volume average particle size 87.7 μm Particle BP5: Volume average particle diameter 121.0 μm These black developing particles are magnetic particles.・ Developer DL White particles WP3 (10.1 μm) and black particles BPo
(25.0 μm) was placed in a polyethylene bottle at a ratio of 20 g of white particles and 80 g of black particles, and mixed and stirred for 30 minutes while being rotated on a ball mill base to perform developer DL (D
Lo) was obtained.

Further, 20 g of white particles and 80 g of black particles were placed in a polyethylene bottle in the following combination of white particles and black particles, and the mixture was rotated and mixed and stirred for 30 minutes by a ball mill stand. Developer DL
(DL1 to DL9) and the following developers De1 to De16 were prepared as comparative developers.

In each developer, the white particles were negatively charged and the black particles were positively charged.

Developer DL1: WP2 (2.1 μm) + BP2 (3.0 μm) Developer DL2: WP3 (10.1 μm) + BP2 Developer DL3: WP4 (46.2 μm) + BP2 Developer DL4: WP2 + BP3 (25.1 μm) Developer DL5: WP3 + BP3 Developer DL6: WP4 + BP3 Developer DL7: WP2 + BP4 (87.7 μm) Developer DL8: WP3 + BP4 Developer DL9: WP4 + BP4 Comparative developer De1: WP1 (0.7 μm) + BP1 (0.8 μm) + BP1 Comparative developer De3: WP3 (10.1 μm) + BP1 Comparative developer De4: WP4 (46.2 μm) + BP1 Comparative developer De5: WP5 (55.3 μm) + BP1 Comparative developer De6: WP1 (0.7 μm) + BP2 (3.0 μm) Comparative example developer De7: WP5 (55.3 μm) + BP2 Comparative example developer De8: WP1 (0.7 μm) + BP3 (25.1 μm) Comparative developer De9: WP5 (55.3 μm) + BP3 Comparative developer De10: WP1 (0.7 μm) + BP4 (87.7 μm) Comparative developer De11: WP5 (55.3 μm) + BP4 Comparative developer De12: WP1 ( 0.7 μm) + BP5 (121 μm) Comparative Example Developer De13: WP2 (2.1 μm) + BP5 Comparative Example Developer De14: WP3 (10.1 μm) + BP5 Comparative Example Developer De15: WP4 (46.2 μm) + BP5 Comparative Example Developer De16: WP5 (55.3 μm) + BP5 The following developer was also prepared as a comparative developer. Comparative Example Developer d1 Sudan Black X6 in 100 ml of isoparaffinic hydrocarbon (trade name: Isopa G, manufactured by Exxon Chemical Co., Ltd.)
0 (manufactured by BASF, trade name) was added and dissolved and mixed well to prepare a colored liquid.

The titanium dioxide particles (Ishihara Sangyo Co., Ltd .:
CR-50) with 10 g and 0.5 wt% of sulfol B
a-30N (barium sulfonate manufactured by Matsumura Petroleum Institute Co., Ltd.) was mixed with 70 g of IP Solvent 1620 solution, and the mixture was mixed with a sand grinder (IGARASHI KIKA).
I SEIZO CO. , Ltd. Using a glass bead (1500 cc) having a diameter of 1 mm as a medium, a 1/8 GL vessel with a water jacket, a cooling water temperature of 20 ° C., and a disk rotation speed of 2000 rpm.
m for 15 hours to perform wet grinding processing.

To 100 parts by weight of the concentrated liquid developer, IP
Solvent 1620 was added and diluted by 900 parts by weight.
K. Auto homomixer type M (manufactured by Tokushu Kika Kogyo Co., Ltd.)
Was dispersed at 10,000 rpm for 5 minutes to obtain a developer d1. <Reversible Image Display Medium> Reversible Image Display Medium 11 FIGS. 3 and 4 show an example of a reversible image display medium. FIG.
The medium 11 shown in FIG. 4 includes a first sheet 111 and a second sheet 112. These sheets 111, 11
Numeral 2 faces each other with a predetermined gap therebetween. A partition 113 is provided between the sheets 111 and 112, and the partition 113 ensures a predetermined gap between the sheets. That is, the partition 113 also serves as a spacer between the sheets 111 and 112. The two sheets 111 and 112 are connected and fixed to each other by a partition 113.

The first sheet 111 is formed of, for example, a light-transmitting plate such as a transparent glass, a transparent resin film, or the like. This sheet 111 is a sheet on the image observation side.

A first electrode 114 is provided on the inner surface of the sheet facing the second sheet 112. First electrode 11
4 is continuous over the entire image display area on the inner surface of the sheet 111. The first electrode 114 is a transparent electrode formed of, for example, indium tin oxide (ITO) or the like.

The second sheet 112 is not necessarily required to be transparent, but is formed of, for example, a light-transmitting plate such as a transparent glass, a resin film, or the like.

A second electrode 115 is formed on the inner surface of the second sheet 112 facing the first sheet 111. Second
The electrode 115 has a plurality of individual electrodes 115a arranged in a grid pattern. Each individual electrode is not necessarily a transparent electrode, but is formed of, for example, a transparent ITO film.

As shown in FIG. 5, the partition walls 113 are formed upright on the inner surface of the second sheet 112 in the form of a lattice. As a result, each of the partition walls 113 is partitioned into a square shape using a part of the partition wall 113 as a partition wall. A plurality of developer accommodating cells 116 are formed, and one of the individual electrodes 115a is arranged in each of the cells 116. That is, here, one cell corresponds to one pixel.

Furthermore, a dry developer DL containing white developer particles WP and black developer particles BP frictionally charged in each cell.
Is housed.

Each cell is sealed, and the developer DL does not leak from the cell.

The gap between the sheets, the height of the partition 113, or the distance between the first electrode 114 and the second electrode 115 is not limited thereto, but may be, for example, 20 μm to 1 mm.
Is set between

The second electrode 1 on the image display medium 11
As shown in FIG. 6, each of the individual electrodes 115a lying horizontally has a lead 110 connected thereto, and through these leads, an electrode selection circuit 117 as shown in FIG.
Connected to. A positive drive voltage generation circuit 118a, a negative drive voltage generation circuit 118b, and a display data control unit 119 are connected to the electrode selection circuit 117. A drive voltage is applied to each of the individual electrodes 115a independently of the electrode selection circuit 117, and the display data control unit 119 includes a display data output unit (not shown, such as a computer, a word processor, Display data is input from a facsimile machine or the like, and the electrode selection circuit 117 is controlled based on the display data. In other words, these electrode selection circuits and the like constitute an example of an electric field forming apparatus or an image forming apparatus for a reversible image display medium with electrodes.

Thus, with the first electrode 114 of the image display medium 11 serving as a ground electrode, a display data control section 119 is provided between the electrode 114 and each of the individual electrodes 115a.
A predetermined voltage is applied from the positive drive voltage generation circuit 118a or the negative drive voltage generation circuit 118b via the electrode selection circuit 117 which is controlled so that a desired image is displayed, and a predetermined electric field is generated for each pixel. By the formation, the developing particles WP and BP respectively move according to the electric field from the state where the developing particles are mixed in the developer DL as shown in FIG. 3 as shown in FIG. Thus, an image can be displayed with a predetermined contrast. For example, an image can be displayed as shown in FIG. In FIG. 7, Bk is a black display portion, and W is a white display portion.

The roller R2 shown in FIG. 4 will be described later. -Reversible image display medium 12 FIGS. 8 and 9 show another example of the image display medium. FIG.
8A is a cross-sectional view of the reversible image display medium 12 before displaying an image, and FIG. 8B is a cross-sectional view of one example when displaying an image. FIG. 9 is a plan view showing a part of the medium 12 cut away.

The image display medium 12 shown in FIG. 8 and FIG.
The whole is a rectangular medium, and includes a first sheet 121, a second sheet 122, and a partition 123 between these two sheets.

The first sheet 121 and the partition 123 are formed integrally by heating and pressing a synthetic resin base material.
At least the first sheet 121 is transparent and is a sheet on the image observation side. The second sheet 122 is also a synthetic resin sheet.

The partition wall 123 is composed of a plurality of vertical partition walls 123a extending in parallel with the vertical side of the medium 12, and a developer accommodating cell 124 is provided between each adjacent vertical partition wall. Each cell 124 contains a developer DL containing mutually frictionally charged white developing particles WP and black developing particles BP.

At the periphery of the medium 12, both sheets 12
Reference numerals 1 and 122 are heat-sealed to form a sealing portion 120. A portion 120a of the sealing portion 120 which is provided at both ends in the longitudinal direction of the vertical partition wall 123a and seals both ends of each cell also serves as a partition wall forming the cell 124.

Each partition wall 123a has a width α and a height h, and is formed such that the interval between adjacent vertical partition walls 123a is pt.

Each cell is sealed, and the developer DL does not leak from the cell.

The partition 123 (partition wall 123a) also serves as a spacer for maintaining a predetermined gap between the sheets 121 and 122.

As described above, any of the sheets 121, 1
22 is also preferably formed with a thickness in the range of 5 μm to 100 μm, and the height h (in other words, the gap between sheets) of the partition walls 123 a is preferably 20 μm to 300 μm. The thickness of the entire medium 12 is preferably 30 μm to 500 μm.

The first sheet 12 on which an electrostatic latent image is formed
The surface resistivity of No. 1 is preferably 10 ¹⁰ Ω / □ to 10 ¹⁶ Ω / □, and the surface resistivity of the second sheet 122 is preferably 10 ⁷ Ω / □ or less.

The image of the medium 12 can be displayed by, for example, the image forming apparatus shown in FIG.

The image forming apparatus shown in FIG. 11 includes a photosensitive drum PC driven to rotate in the direction of the arrow in the figure. A scorotron charger CH is provided around the photosensitive drum PC.
A laser image exposure apparatus EX and an eraser lamp IR are arranged. An electrode roller R1 that is driven to rotate is disposed below the photosensitive drum PC. The electrode roller R1 is a developing electrode roller for forming an electrostatic field for displaying an image. A bias voltage can be applied to the roller R1 from the power supply PW1. The roller R1 may include a rotating magnetic pole roller R2 that is driven to rotate in the opposite direction to the roller R1 (or is driven to reciprocate).

The surface of the photosensitive drum PC is charged to the charger CH.
Then, the charged area is image-exposed by an exposure device EX to form an electrostatic latent image EI on the drum PC.
On the other hand, a bias is applied to the electrode roller R1 from the power supply PW1.

Then, the electrostatic latent image EI on the photosensitive drum PC
The medium 12 is fed between the drum and the electrode roller R1 in synchronization with the above.

In this way, a predetermined electrostatic field is formed for each pixel with respect to the developing particles BP and WP of the developer DL contained in each cell 124 of the medium 12, and thereby, between the electrostatic field and the charged developing particles. The developing particles move due to the acting Coulomb force. Then, as shown in FIG. 8A, the state where the black and white particles WP and BP are mixed in the developer DL is changed from FIG.
As shown in (B), the white particles WP and the black particles BP move according to the electric field. Thus, an image can be displayed with a predetermined contrast. For example, an image can be displayed as shown in FIG. In FIG. 10, Bk is a black display portion, and W is a white display portion.

After the image is displayed as described above, the charge on the surface of the photosensitive drum PC is erased by the eraser lamp IR in preparation for the next print.

In this image display, when the magnetic pole roller R2 is provided and rotated, the developer DL in each cell 124 is agitated, and the developing particles BP and WP are easily moved, so that a better image can be obtained. The display can be performed, and the driving voltage can be reduced.

The rotating magnetic pole roller R2 can also be employed for the medium 11 shown in FIG. Reversible Image Display Medium 13 FIG. 12 is a cross-sectional view of still another example of the reversible image display medium. The image display medium 13 shown in FIG. 12 is the same as the medium 12 except that the conductive film 122A is formed on the outer surface of the second sheet 122 of the medium 12 shown in FIG.
The same parts as those of the medium 12 are denoted by the same reference numerals.

As for the medium 13, an image can be displayed with a predetermined contrast by using, for example, the image forming apparatus shown in FIG. Note that instead of using the electrode roller R1, the conductive film 122A on the surface of the second sheet 122 may be grounded. -Other reversible image display media The following are examples of other reversible image display media. a) a medium in which the shape of the developer accommodating cell in the mediums 11 to 13 is another shape selected from FIGS. 1A to 1I; b) a medium in the mediums 11 to 13 A medium provided with a developer transfer suppressing member shown in any of FIGS. 2A to 2H in a developer storage cell; c) a developer storage cell other than that used in the media 11 to 13 is used; A medium that employs any of the developer movement suppressing members. The image display medium described above with reference to the drawings and the other medium just described can repeat image display and image deletion. Further, the developing particles WP and BP are contained in the cell, and do not require an external developer supply. Thus, the use of consumables such as a medium such as paper and a developer related to image display in the related art can be significantly suppressed.
Further, since image energy does not require heat energy for fusing the toner to the medium as in the related art, the image forming energy can be reduced accordingly. Therefore, it is possible to meet today's environmental load reduction.

Each of the media 11, 12, 13 and the like employs the dry developer DL containing the developing particles WP and BP of different colors, so that one of the developing particles BP (or BP) is used for the other developing particles BP. (Or WP), the degree of concealment is good, and an image can be displayed with good contrast.

The developing particles W contained in the cells
Since P and BP are charged with different charging polarities, and can be easily moved by receiving Coulomb force in displaying an image, P and BP can also be displayed with good contrast in this respect, and the afterimage of the previous time hardly occurs.

Further, since the dry developer DL is employed as the developer, sedimentation and agglomeration of the developing particles hardly occur.
As a result, a decrease in contrast in image display is small and stable image display can be performed for a long period of time. Since the sedimentation and aggregation of the developing particles hardly occur, the afterimage of the previously displayed image is hardly generated. Since the dry developer DL has little change with time, stable image display can be performed for a long time in this respect as well.

Since one pixel can be made smaller, an image can be displayed with high resolution by doing so.

As a result, an image can be stably displayed over a long period of time with excellent contrast, high resolution and high quality. Next, a more specific example of a reversible image display medium (example medium) and image display using the medium will be described. (Embodiment 1) A reversible image display medium with electrodes of the type shown in FIGS. 3 to 7 and formed as follows.

That is, transparent PET having a thickness of 100 μm
First made of (polyethylene terephthalate) film
An ITO film is formed on the entire surface of the sheet 111 as the first electrode 114 to a thickness of 500 ° by a sputtering method.

Next, a PE having an AL vapor deposition layer formed on the entire surface is used.
Using a T film, applying a photoresist, exposing,
After patterning by development and etching, the photoresist layer is separated and removed to form a second sheet 112 having a two-dimensionally arranged group of individual pixel electrodes 115a.

The transparent individual pixel electrode group 15 thus formed
1a, for example, as shown in FIG. 6, a square electrode of 5 mm in length and width is arranged in a grid pattern with an electrode interval of 0.5 mm, and a lead portion is provided so that a voltage can be applied to each individual electrode. 110 is patterned between the individual electrodes.

A portion other than the individual electrodes on the second sheet 112 (a thick film resist was repeatedly applied between the individual electrodes and a region around them, to form 90 μm high partition walls 113 in a grid pattern (see FIG. 5). Each of the recesses of the grid-like partition 113 is used as a space for the cell 116 and the developer DL is added to them 90
% Height. The developer DL is a developer DL (DLo) among some examples of the developer described above, and includes white developing particles WP (WP310.1 μm) and black developing particles BP
(BPo 25.0 μm).

Next, the photocurable adhesive 119a is thinly applied only on the upper part of the partition wall 113, and then the first sheet 111 is brought into close contact therewith.
Glue.

Thereafter, the first and second sheets 111, 11
2 and the like, as shown in FIG.
b) Sealing and sealing were performed to obtain the reversible image display medium of Example 1.

As a comparative example for the medium 11, a comparative medium E1 was also formed in the same manner as the medium 11, except that the developer dl was filled in each cell space so that air bubbles did not enter.

With respect to the medium of Embodiment 1 described above,
Of the individual electrodes 115a, +100 V was applied to the electrode corresponding to the pixel to be displayed in black, and -100 V was applied to the electrode corresponding to the pixel to be displayed in white. In this way, a voltage corresponding to the display data was applied, and a desired image could be displayed as illustrated in FIG.

Comparative Example Image display medium E1 (not shown) was applied with a voltage of +100 V and -100 V similarly to the medium of Example 1 to display an image, and the image contrast of the medium of Example 1 was evaluated. .

The contrast was evaluated by measuring the image density of the black portion Bk and the white portion W with a reflection densitometer (manufactured by Konica: SAKURA).
DENSITOMETER PDA-65) and the ratio (B
K / W). A reflection density ratio of 10.0 or more is good (◎), 7.0 or more and less than 10.0 is acceptable (○),
Less than 7.0 was regarded as defective (x). Unless otherwise specified, the method of evaluating the contrast is the same in each of the present specification.

The evaluation results were as follows. The medium of Example 1 The reflection density (BK) of the black portion is 1.5, the reflection density (W) of the white portion is 0.1, and the reflection density ratio is 15.0 (good).
Met. Comparative Example Medium E1 The reflection density of the black portion was 0.6, and the reflection density of the white portion was 0.1.
And the reflection density ratio was 6.0 (poor). (Embodiment 2) A reversible image display medium without electrodes of the type shown in FIGS. 8 to 10 and formed as follows.

A transparent PET substrate is heated and pressed.
A partition 123 composed of a plurality of partition walls 123a parallel to the first sheet 121 having an average thickness of 25 μm was integrally formed. Each partition wall 123a has a width α = 20 μm and a height h = 1.
00 μm, and the interval between adjacent partition walls pt = 200 μm.

The developer DL is put into the cell 124 provided between each adjacent partition wall 123a to 90% of its space height, and then the photocurable adhesive 123b is applied only on the upper part of the partition wall 123. A 25 μm-thick second sheet 122 was adhered thereon, and then the adhesive was cured by irradiation with ultraviolet rays. The peripheral portions of the sheets 121 and 122 were heat-sealed to form a sealing portion 120. Thus, a reversible image display medium of Example 2 was formed.

The developer DL is the same as the developer DL (DL
o) and the white developing particles WP (WP3 10.1 μm)
m) and black developing particles BP (BPo 25.0 μm). (Example 3) In the medium 12 of Example 2, a conductive film 122A was formed on the outer surface of the second sheet 122 by aluminum evaporation as shown in FIG. Same thing as.

Images of the media of Examples 2 and 3 were displayed as follows using the image forming apparatus shown in FIG.

The surface of the photosensitive drum PC is charged to +1000 V by the charger CH, and the charged area is exposed to an image to form an electrostatic latent image EI. On the other hand, a bias of +500 V is applied to the electrode roller R1 so that the photosensitive drum PC is charged. The medium 12 was passed between the electrode roller R1. At this time, the ratio (peripheral speed ratio) θ between the peripheral speed of the photosensitive drum PC and the peripheral speed of the counter electrode roller R1 was kept constant at θ = 1.

Thus, an image as shown in FIG. 10 could be displayed.

As a comparative example with respect to the media of Examples 2 and 3, the same procedures as those of the media of Example 2 were carried out except that each cell space of the medium of Example 2 was filled with the developer dl so as to prevent air bubbles from entering. Thus, a comparative medium E2 (not shown) was also formed.

The images of the media of Examples 2 and 3 and Comparative Example Medium E2 were also displayed using the image forming apparatus shown in FIG. 11, and the image contrast was evaluated.

The evaluation results were as follows. -Medium of Example 2 The reflection density (Bk) of the black portion is 1.5, the reflection density (W) of the white portion is 0.1, and the reflection density ratio is 15.0 (good).
Met. Medium of Example 3 The reflection density (Bk) of the black portion is 1.6, the reflection density (W) of the white portion is 0.1, and the reflection density ratio is 16.0 (good).
Met. Comparative Example Medium E2 The reflection density of the black portion was 0.6, and the reflection density of the white portion was 0.1.
And the reflection density ratio was 6.0 (poor). Next, the ratio Sn / So of the area Sn of the non-image portion in the unit area So provided by the image display medium is set to 0.0001 or more and 0.5 or less, or (1-Sa / S
Example media (Examples 4 to 9) and Comparative Example media E3 to E4 showing that the value of b) is preferably 0.0001 or more and 0.5 or less will be described. Example 4 The medium of Example 2 (partition wall thickness α = 20 μ)
m, Sn / So is 0.091 at an interval between adjacent partition walls (pt = 200 μm). This medium has substantially the same structure as the medium of the second embodiment.

The image contrast was evaluated by using the image forming apparatus shown in FIG. 11 to display an image of a black portion Bk on the right half and a white portion W on the left half as shown in FIG. 13A. I went. For image formation, change CH
To charge the surface of the photosensitive drum PC to +1000 V and form an electrostatic latent image EI by exposing the charged area to an image, while applying a bias of +500 V to the electrode roller R1.
The medium was passed between the photosensitive drum PC and the electrode roller R1. At this time, the ratio (peripheral speed ratio) θ between the peripheral speed of the photosensitive drum PC and the peripheral speed of the counter electrode roller R1 is θ =
It was fixed at 1.

The image contrast evaluation results show that the reflection density of the black part is 1.65, the reflection density of the white part is 0.133,
The reflection density ratio (Bk / W) was 12.4 (◎). (Example 5) In the medium of Example 2, the shape and arrangement of the developer accommodating cells were set in a grid pattern as shown in FIG. 1 (D), and the thickness (width) α of the partition wall forming the cell was 20 μm, The matching partition wall interval pt is 200 μm (in other words, the cell size is 200 μm × 200 μm), and Sn / So is 0.17.
The medium designated as 4. Others are the same as the medium of the second embodiment.

With this medium, the same image was formed under the same image forming apparatus and image forming conditions as those of the medium of Example 4.

The image contrast evaluation results show that the reflection density of the black portion is 1.52 and the reflection density of the white portion is 0.135.
The reflection density ratio (Bk / W) was 11.2 (◎). (Embodiment 6) In the medium with electrodes of Embodiment 1 (cells having a grid pattern), the space dimension of the cell 116 was set to 200 μm.
× 200 μm, the thickness (width) of the partition 113 serving also as a partition wall for forming cells is 20 μm, and Sn / So is 0.174. Others are the same as the medium of the first embodiment. .

An image similar to that of FIG. 13A was formed on this medium under the same electric field forming apparatus and image forming conditions as those of the medium of Example 1.

The image contrast evaluation results show that the reflection density of the black part is 1.59 and the reflection density of the white part is 0.135.
The reflection density ratio (Bk / W) was 11.8 (◎). (Embodiment 7) In the medium of the embodiment 2, as shown in FIG. 2A, developer movement restraining column members having vertical and horizontal dimensions β1 × β2 = 60 μm × 10 μm are dispersed and erected, and the medium unit area γ1 × γ2 = a medium in which a pattern in which the suppression members are arranged one by one within 1000 μm × 800 μm is repeated. Sn / So is 0.0008. Others are the same as the medium of the second embodiment.

The same image was formed on this medium under the same image forming apparatus and image forming conditions as those of the medium of Example 4.

The image contrast evaluation results show that the reflection density of the black portion is 1.80 and the reflection density of the white portion is 0.130.
The reflection density ratio (Bk / W) was 13.8 (◎). (Eighth Embodiment) In the medium of the second embodiment, in each cell,
As shown in FIG. 2F, the vertical and horizontal dimensions β1 × β2 = 60 μ
m × 10 μm developer transfer suppressing column member
Medium standing at m intervals. Sn / So is 0.101. Others are the same as the medium of the second embodiment.

The same image was formed on this medium under the same image forming apparatus and image forming conditions as those of the medium of Example 4.

The image contrast evaluation results show that the reflection density of the black part is 1.63 and the reflection density of the white part is 0.133.
The reflection density ratio (Bk / W) was 12.3 (◎). (Example 9) In the medium of Example 2, the shape and arrangement of the developer accommodating cells were set in a grid pattern as shown in FIG. 1D, and the thickness (width) α of the partition wall forming the cell was 50 μm, A medium in which a matching partition wall interval pt is set to 150 μm (in other words, a cell size is 150 μm × 150 μm), and a developer movement suppressing column member having vertical and horizontal dimensions β1 × β2 = 60 μm × 10 μm is provided in each cell. Sn / So is 0.468
It is. Others are the same as the medium of the second embodiment.

With this medium, the same image was formed under the same image forming apparatus and image forming conditions as those of the medium of Example 4.

The image contrast evaluation results show that the reflection density of the black part is 1.03 and the reflection density of the white part is 0.144.
The reflection density ratio (Bk / W) was 7.2 (○). (Comparative Example Medium E3) In the medium of Example 2, FIG.
As shown in (H), vertical and horizontal dimensions β1 × β2 = 20 μm ×
20 μm developer movement suppressing pillar members are dispersed and erected, and
Medium unit area γ1 × γ2 = 5000 μm × 2000 μm
A medium in which a pattern in which the suppression members are arranged one by one is repeated. Sn / So is 0.00004.
Others are the same as the medium of the second embodiment.

With this medium, the same image was formed under the same image forming apparatus and image forming conditions as those of the medium of Example 4.

The image contrast evaluation results show that the reflection density of the black part is 0.90 and the reflection density of the white part is 0.186.
The reflection density ratio (Bk / W) was 4.8, which was poor (x).

Both the black solid image portion and the white solid image were images having uneven density. (Comparative Example Medium E4) In the medium of Example 2, the partition wall thickness α = 160 μm, and the interval between adjacent partition walls pt = 140.
μm and Sn / So of 0.53. This medium has substantially the same structure as the medium of the second embodiment.

With this medium, the same image was formed under the same image forming apparatus and image forming conditions as those of the medium of Example 4.

The image contrast evaluation results show that the reflection density of the black part is 0.84 and the reflection density of the white part is 0.146.
The reflection density ratio (Bk / W) was 5.8, which was poor (x).

A solid black image portion formed between the partition walls was obtained only in a stripe shape.

Table 1 summarizes the structures of the media of Examples 4 to 9 described above.

Table 2 shows the image contrast evaluation results of the media of Examples 4 to 9 and the comparative media E3 and E4.
Are shown together.

[0213]

[Table 1]

[0214]

[Table 2]

FIG. 13 is a graph showing the relationship between the ratio of the non-image portion area (non-image portion area / medium unit area) and the reflection density ratio.

As described above, according to the image display media of Examples 4 to 8, there was obtained an image having no image unevenness and high contrast. In the image display medium of Example 9, since the area ratio of the non-image portion is increased, the contrast is slightly deteriorated, but is practically acceptable.

In the comparative example medium E3, since the ratio of the non-image portion was too small, the gap between the sheets could not be maintained, and image unevenness occurred, and the reflection density of the black portion decreased.
An increase in the reflection density of the white portion was observed.

In Comparative Example Medium E4, a sufficient contrast was not obtained because the ratio of non-image portions was too large. The reason for this is that, while black solids are displayed in black and white stripes in black display, the reflection density decreases, while white solids have high reflection densities in the non-image area, and the solid white reflection density increases. . Next, in the reversible image display medium, the thickness of each sheet is 5 μm to 100 μm,
The gap between the two sheets is 20 μm to 300 μm, the total thickness is 30 μm to 500 μm, and the surface resistivity of the outer surface of one of the two sheets of the medium is 10 μm.
Example media (Examples 10 to 21) and Comparative example media showing that it is preferable that the surface resistivity of the outer surface of the other sheet be ¹⁰ Ω / □ to 10 ¹⁶ Ω / □ and the surface resistivity of the other sheet be 10 ⁷ Ω / □ or less. E
5 to E12 will be described. (Examples 10 to 14, Comparative Example Media E5 to E8) Example 2
Wherein the thickness of each sheet is 25 μm and the gap between sheets is 100 μm, and the surface resistivity of the first sheet 121 and the surface resistivity of the second sheet 122 are variously changed. It is the same as the medium of Example 2 except that the sheet surface resistivity was variously changed.

In addition to these media, the media of Examples 15 to 21 to be described later, etc.
The surface resistivity of No. 21 was adjusted by applying a surfactant to the sheet surface. The surface resistivity of the second sheet 122 is
The sheet was made to contain conductive carbon, and the content was adjusted by changing the content. Surface resistivity is measured by AST
It was measured in a 65% RH environment according to MD-257.

Media of Examples 10 to 14 and Comparative Example Medium E
Table 3 summarizes 5-E8. (Example 15) In the medium of Example 3 (medium having an Al vapor deposited film on the second sheet), the surface resistivity of the first sheet 121 was set to 1.20 × 10 ¹⁵ Ω / □, and the second sheet 122 was used.
Medium having a surface resistivity of 8.50 × 10 ⁻¹ Ω / □. Others are the same as the medium of the third embodiment. (Examples 16 to 21, Comparative Example Mediums E9 to E12) The medium of Example 15 except that the surface resistivity of each sheet was unchanged and the thickness of each sheet and the gap between sheets were variously changed. Others are the same as the medium of Example 15.

Mediums of Examples 16 to 21 and Comparative Example Medium E
Tables 9 to E12 are shown in Table 3.

[0222]

[Table 3]

For each of the above-mentioned example media (Examples 10 to 21) and comparative example media E5 to E12, FIG.
An image as shown in FIG. 13 was formed using the image forming apparatus shown in FIGS. 16A and 16B, and the image contrast was evaluated. Note that the image forming apparatus shown in FIG. 16 is an image forming apparatus using an ion flow type direct electrostatic latent image forming apparatus. This will be described later.

In this evaluation, the maximum reflection density and the minimum reflection density were measured for both the black portion and the white portion.
Based on these, the average reflection densities of the black portion Bk and the white portion W were determined, and the reflection density ratio was calculated from these average reflection densities. Also in this case, a reflection density ratio of 10.0 or more was regarded as good (○), and a reflection density ratio of less than 10.0 was regarded as poor (x).

Further, image unevenness was also evaluated. In the evaluation of image unevenness, the image density of the black portion was measured using a reflection densitometer (manufactured by Konica Corporation: SAKURA DENSITOMETER PDA-65), and the difference between the maximum value and the minimum value of the image density was determined. 2 or less was evaluated as good (○), and larger than 2 was evaluated as poor (x).

Table 4 shows the results of these evaluations.
Table 4 also shows defective marks for those having poor contrast.

[0227]

[Table 4]

From the evaluation results, it was found that the thickness of each sheet was 5 μm.
m to 100 μm, gap between both sheets 20 μm to 3
00 μm, the total thickness is 30 μm to 500 μm, the surface resistivity of the outer surface of one of the two sheets of the medium is 10 ¹⁰ Ω / □ to 10 ¹⁶ Ω / □, and the outer surface of the other sheet is It can be seen that the surface resistivity of is preferably 10 ⁷ Ω / □ or less.

The image forming apparatus shown in FIGS. 16A and 16B is a development of the image forming apparatus whose principle is shown in FIGS.

The image forming apparatus shown in FIG. 14 is suitable for an image display medium of a type in which one sheet has a conductive film and has no electrodes, like the medium 13 in FIG.

The image forming apparatus shown in FIG. 14 includes an ion flow type direct electrostatic latent image forming apparatus CR1. Device CR
1 is a corona ion generator c for generating corona ions
1 and corona ions generated in the generating section
The writing electrode e1 for guiding to the surface and the sheet 121 according to the image to display the positive or negative corona ions.
The voltage for guiding the surface to the pixel-corresponding portion is a write electrode e.
1 and a write electrode control circuit f1 to be applied to the circuit. The electrode control circuit f1 includes a control power supply and a bias power supply, not shown.

The corona ion generator c1 is provided in the shield case c11.
A gold-plated tungsten wire having a diameter of 20 μm is stretched to form a corona wire c12, and a positive or negative voltage (for example, 4 kV to 10 kV) is applied to this wire from a power supply Pc1 to generate corona ions.

The writing electrode e1 is a medium (for example, medium 1).
3) The shield case c directed to the first sheet 121
The corona ion flow can pass through a through hole provided at the center of the portion 11.

The electrode control circuit f1 can apply an ion extraction voltage to the electrode e1 according to the positive or negative of the ions to be extracted toward the medium 13.

Thus, the medium 13 is transferred to the second sheet 122.
As a ground potential (or by applying a bias voltage having the same polarity as the latent image polarity and a value smaller than the latent image potential)
In accordance with the image to be displayed, positive or negative corona ions are guided to a portion corresponding to a pixel on the surface of the sheet 121 while being moved relatively to the surface of the first sheet 121, whereby an electrostatic latent image charge is formed on the surface of the first sheet 121. The developing particles in each cell of the medium 13 can be moved and an image can be displayed by forming an electrostatic field at the same time.

The image forming apparatus shown in FIG. 15 does not have a conductive film on one sheet as in the medium 12 shown in FIG.
It is suitable for an image display medium without electrodes. FIG.
Of the sheet 12 on which the electrostatic latent image is formed
1 has an electrode Ea that contacts the sheet 122 on the opposite side. As in the case of FIG. 14, a bias voltage may be applied to the electrode Ea. The other points are the same as those of the apparatus shown in FIG.

The image forming apparatus shown in FIGS. 16A and 16B used in the evaluation experiment includes an ion flow type direct electrostatic latent image forming apparatus CR2. The device CR2 attempts to display a corona ion generating section c2 for generating corona ions, a writing electrode e2 for guiding the corona ions generated by the generating section to the surface of the sheet 121, and a positive (or negative) corona ion. A write electrode control circuit f2 for applying a voltage to the write electrode e2 to guide the pixel 121 to a portion corresponding to a pixel on the surface of the sheet 121 according to an image.

In the corona ion generating section c2, a corona wire c22 similar to that in the device CR1 shown in FIG. 14 is stretched in a shield case c21, and a positive (or negative) voltage is applied to this wire from a power source Pc2 to generate a corona wire. It generates ions.

The write electrode e2 is provided on the shield case c21 facing the first sheet 121 of a medium of the type of the mediums 12 and 13 (the medium 12 is shown as a representative example in the figure). e21 and lower electrode e22
And a corona ion flow can pass through the central through hole.

The electrode control circuit f2 includes a control power supply Pc21,
Including a bias power supply Pc22 and a control unit f21,
The control unit f21 outputs an ion extraction voltage corresponding to the polarity of ions to be extracted toward the medium 12 to the electrodes e21 and e2.
2 can be applied.

Here, when a positive voltage is applied to the upper electrode e21 and a negative voltage is applied to the lower electrode e21 under the instruction of the control unit f21, positive corona ions can be guided to the medium (FIG. 16A). . When a negative voltage is applied to the upper electrode e21 and a positive voltage is applied to the lower electrode e21, positive corona ions can be confined (FIG. 16B).

An electrode roller R1 is provided so as to face the write electrode e2, and a positive bias voltage is applied to the electrode roller R1 from the power supply PW1. The roller R1 incorporates a magnetic pole roller R2 that is driven to rotate.

Thus, while moving the medium 12 relatively to the apparatus CR2, rotating the electrode roller R1 in the medium feeding direction and rotating the magnetic pole roller R2 in the opposite direction, control is performed according to the image to be displayed. Under the instruction of the section f21, a positive corona ion is applied to a predetermined pixel corresponding portion corresponding to an image to be displayed among a plurality of pixel corresponding portions on the surface of the first sheet 121 as shown in FIG. Then, the outflow of ions is prevented for the other pixels as shown in FIG.

In the image evaluation experiment, the first sheet 121
A positive corona ion is guided to a predetermined pixel corresponding portion corresponding to an image to be displayed among a plurality of pixel corresponding portions on the surface,
The portion was charged to +500 V to +600 V, and only the bias voltage of +250 V was applied to the other pixels.
As a result, the portion on which the positive corona ions are mounted is displayed white by the negatively chargeable white developing particles WP, and the portion on which the positive corona ions are not mounted is displayed black by the positively charged black developing particles BP, thus displaying an image. Was.

The discharge wires c12 and c22 in the devices CR1 and CR2 can be replaced with solid-state discharge elements.

Although the electrostatic latent image forming devices CR1 and CR2 shown in FIGS. 14 to 16 use a discharge phenomenon, various discharging type electrostatic latent image forming devices can be used in addition to these devices.

Images can also be displayed by employing the image forming apparatus shown in FIGS. 17 and 18 instead of the image forming apparatus shown in FIGS.

The image forming apparatus shown in FIG. 17 includes a multi-stylus type direct electrostatic latent image forming apparatus CR3. The device CR3 includes, for example, a plurality of electrodes e arranged in the main scanning direction with respect to the medium 13 and arranged close to the first sheet 121.
3 including a multi-stylus head H3.
In accordance with an image to be displayed on each electrode e3, a signal voltage is applied to apply an electrostatic latent image charge to a pixel corresponding portion on the surface of the first sheet 121. The medium 13 is conveyed relatively to the head H3 by applying, for example, a bias to the second sheet 122 on the opposite side, whereby an image is displayed.

The image forming apparatus shown in FIG. 18 includes a charge injection type direct electrostatic latent image forming apparatus CR4. Device CR4
Is a multi-stylus type device having an electrostatic recording head H4 in which a plurality of recording electrodes e4 are arranged in the main scanning direction with respect to the medium, and adjacent control electrodes e41 are arranged adjacent to the recording electrodes e4. This head is disposed, for example, close to the medium 13, and a voltage of about の of a voltage (recording voltage) required for image recording is sequentially applied to the control electrode e41 of the head H4 sequentially, and a recording voltage of about の is applied to the recording electrode e4. 1/2
By applying the image signal voltage, an electrostatic latent image can be formed on the medium located immediately below the recording electrodes.

Here, the advantage of forming a latent image will be described with reference to an image forming apparatus provided with an external electrostatic latent image forming apparatus as shown in FIG.

FIGS. 19A to 19D show equivalent circuits of the device. In these figures, the electrostatic latent image carrier such as a photosensitive drum, the image display medium, and the capacitance of the air layer therebetween are denoted by C1, C2, and C0, respectively.

It is assumed that a latent image charge Q (potential V at that time) is applied to an electrostatic latent image carrier (hereinafter, referred to as an "image carrier") by a charger and an image exposure device.

FIG. 19A shows an equivalent circuit in a state where the image carrier and the image display medium are separated from each other.
Since it is much larger than 0, the charge Q does not move and the medium is not affected by the electrostatic latent image.

In this state, when the image carrier comes close to the medium, C0 increases, and the electric charges charged in C1 and C2 are induced by electrostatic induction, resulting in the state of FIG. 19B. FIG. 19B is an equivalent circuit in a state where the image carrier is brought close to the image display medium and electrostatically induced.

In the state shown in FIG. 19B, the potential difference V1, induced in the image carrier, medium, and air layer by the induced charge,
V2 and V0 can be expressed as in the following equations (1), (2) and (3).

[0256]

(Equation 1)

[0257]

(Equation 2)

[0258]

(Equation 3)

Here, V is the surface potential of the latent image on the image carrier, Vb
Is a bias value.

The medium contains a developer. Since the developer particles carry electric charges under an electric field, the developer layer is apparently similar to the conductive layer. That is, the capacitance C2 of the medium is close to the combined capacitance of the upper and lower resin sheets.

Here, in order for the latent image charges on the image carrier to be transferred to the medium, the air layer needs to be subjected to dielectric breakdown and charge transfer. If the dielectric breakdown does not occur, when the image carrier is separated from the medium, the state returns to the state of FIG. 19A again, and the latent image is not transferred.

That is, for example, when V0 is small, particles move due to the induced electrostatic field, but the latent image is not transferred.

For example, in order for an air layer having a gap of 10 μm to cause dielectric breakdown, V0 is about 37 according to Paschen's rule.
0 V or more is required.

Here, the bias value Vb is set to 1000 V, V = 1000 V, and the ratio of each capacitance is C1: C
When 2: C0 = 18: 5: 12, V0 (potential difference of the air layer) = 480 V, dielectric breakdown occurs, and the latent image is transferred. (However, the image carrier is a normal organic photoreceptor,
Assuming that the medium has a combined capacity of the above-described configuration and the air layer has a gap of about 10 μm in which dielectric breakdown easily occurs, and the ratio of the respective capacitances is considered. As described above, the latent image is transferred under the condition that V-Vb is about 1500 V or more. Conversely, under other conditions, electrostatic induction is performed in a state where the image carrier and the medium are close to each other, but no latent image is transferred.

In the electrostatic latent image on the image bearing member, charge transfer occurs between the charged portion and the medium, and the non-charged portion (exposed portion)
Does not cause charge transfer. This causes a difference in the surface potential on the medium. The surface potential of the medium after the charge transfer of the charged portion is performed is represented by the following expression (4), and that of the non-charged portion is represented by the above expression (3).

FIG. 19C shows an equivalent circuit in a state where charge transfer has occurred due to dielectric breakdown. In such a state where charge transfer has occurred due to dielectric breakdown, the following equation (4) is established.

[0267]

(Equation 4)

In equation (4), V'0 is the minimum potential difference at which discharge is possible, and V1 and V2 are equations (2) and (3).

For example, under the above-mentioned setting conditions, the surface potential on the medium is approximately +265 V in the area corresponding to the charged portion.
The area corresponding to the non-charged portion is about -340V.

Here, when an arbitrary bias (or ground) is applied to the counter electrode roller, electric fields are formed in the charged and uncharged areas in directions opposite to each other, and the developing particles move along the electric field. An image can be formed.

Thereafter, when the image carrier is separated from the medium, the induced charges move, and the surface potential of the medium changes.
The part returns to about +275 V and the part returns to approximately 0 V, and a latent image can be formed on the medium.

Although the case where the electrostatic latent image carrier is a photosensitive drum (photoconductor) has been described above, a dielectric drum may be used. The polarity of the electrostatic latent image may be negative. The charge polarity of the developing particles may be reversed.

As described above, in addition to bringing the latent image close to the medium, the electrostatic latent image is formed on the medium by transfer, direct formation, or the like, so that the opposing region between the electrostatic latent image carrier and the counter electrode is formed. It can be seen that, even after the passage, the developer particles and the reversible image display medium generate an electrostatic attraction force, so that the image retention is improved. In short, it is advantageous to form an electrostatic latent image on a medium. This is particularly advantageous in terms of image retention when using a highly fluid developer or a developer whose fluidity is increased by a developer stirring process prior to image display.

Next, the particle diameter of the developing particles contained in the developer is 1 μm to 50 μm for the non-conductive developing particles.
m is a volume average particle diameter of 1 μm to 1
Example medium showing that 00 μm is preferable (Example 22
30) and Comparative Examples E13 to E28.

In each of these media, the height h of the partition wall 123 was changed to 150 μm, the interval pt between the adjacent partition walls 123a was changed to 250 μm, and the developing particles contained in each cell 124 were variously changed. The medium has the same structure as that of the medium of Example 2 except that the medium is changed.

With respect to these, the image contrast was evaluated. At this time, using the image forming apparatus shown in FIG. 11, as shown in FIG.
k) An image having a white portion (W) formed on the left half was evaluated.

Here, the contrast evaluation was very good (◎) when the reflection density ratio (Bk / W) was 9.0 or more.
If the value was smaller than 9.0 and not less than 7.0, the result was good (○), and the value was smaller than 7.0 and not less than 5.0 was slightly defective (不良).

Table 5 summarizes these media and evaluation results. In Table 5, WP1 to WP5, BP1 to BP5
Are non-conductive white developing particles and magnetic black developing particles having the particle diameters described above. In Examples 22 to 30, the above-described developers DL1 to DL9 were used instead of Comparative Examples E13 to E28.
Used the comparative developer De1 to De16 described above.

In each of the cells showing the examples and comparative examples in Table 5, the upper part on the right shows the results of the contrast evaluation, the middle part shows the reflection image density ratio, the lower part shows the reflection density of the black image part, and the left part shows the white image. 2 shows the reflection density of the portion.

[0280]

[Table 5]

As can be seen from Table 5, the non-conductive developing particles (here, white particles) contained in the developer had a volume average particle diameter of 1 μm to 50 μm, while the magnetic developing particles (here, black particles) It can be said that the volume average particle diameter is preferably 1 μm to 100 μm. Next, an image display method for performing an image erasing process before displaying an image will be described. In carrying out this image display method, the second embodiment is used.
(Hereinafter referred to as medium 12).

Each of FIGS. 20 to 22 shows an example of an image forming apparatus for implementing this image display method. Particularly, the figure shows an image forming apparatus provided with an image erasing device.

The image forming apparatus shown in FIG. 20 is the same as the image forming apparatus shown in FIG. 11 (provided that the rotary magnetic pole roller R2 is not provided).
In this embodiment, the image erasing device EL1 is disposed on the upstream side in the relative transport direction of the medium 12 (the direction of the straight arrow in the figure) from the area where the photosensitive drum PC and the electrode roller R1 face each other.

The image erasing device EL1 includes a pair of upper and lower electrode rollers R3 and R4. The upper electrode roller R3 is connected to a bias power supply PW3. The electrode roller R3 may be grounded. Lower electrode roller R4 is bias power source PW4
Connected to. The electrode roller R4 may be grounded.

According to this image forming apparatus, prior to image display, an electric field corresponding to the potential difference of the bias applied to each of the electrode rollers R3 and R4 of the image erasing apparatus EL1 is formed on the medium 12, thereby changing the charging polarity. Of the developed particles BP and WP, one particle BP gathers on one sheet side and the other particle WP gathers on the other sheet side, thereby erasing the image. After the image erasing process, the medium 12 is sent between the photosensitive drum PC and the counter electrode roller R1, and a new image is displayed.

Using the apparatus shown in FIG. 20, an experiment of image deletion and image formation was performed under the following conditions.

That is, the potential of the charged portion of the electrostatic latent image on the photosensitive drum PC was -800 V, the potential of the non-charged portion (exposed portion) was -100 V, and the bias applied to the counter electrode roller R1 was -100 V. In the erasing device EL1, the electrode roller R4 was grounded, and the bias applied to the electrode roller R3 was + 1000V. The developer receives Coulomba by an electric field when passing between the electrode rollers R3 and R4. In this case, since the white particles WP are negatively charged and the black particles BP are positively charged, the white particles move to the upper side in the figure and the black particles move to the lower side in the figure. Erased over At this time, when the medium 12 was viewed from the upper side in the figure, the entire surface was white.

Thereafter, in the area of the medium 12 from which the entire image has been erased, an electric field is formed according to the electrostatic latent image in a region where the photosensitive drum PC and the electrode roller R1 face each other, and the developer DL receives Coulomba. In the charging section on the photoconductor drum PC, an electric field of 700 V upward is formed in the figure due to the potential difference from the bias of the electrode roller R1, and the white particles move downward.
Since there was no potential difference in the non-charged part, the particles did not move, and the white particles remained on the upper surface. In the image thus formed, when viewed from the upper side in the drawing, the area corresponding to the charged portion was a black portion, and the region corresponding to the non-charged portion was a white portion.

As described above, an image can be formed only by moving the developing particles in accordance with the charged portion, and the electric field strength for moving the developing particles can be increased.

The experiment was also performed under the following conditions. That is,
The charged portion potential of the photosensitive drum PC was -800 V, the non-charged portion (exposed portion) potential was -100 V, and the bias applied to the counter electrode opening R1 was -800 V. Erasing device EL
In No. 1, the bias of the electrode roller R4 is set to +1000.
V, the electrode roller R3 was grounded.

In this case, the medium 12 has the electrode rollers R4, R
After passing between the three, the white particles moved to the lower side in the figure, the black particles moved to the upper side in the figure, and the previously displayed image was completely erased. At this time, when the medium 12 was viewed from the upper side in the figure, the entire surface was black.

Thereafter, in the non-charged portion of the photosensitive drum PC, a downward electric field of 700 V is formed in the figure due to the potential difference from the bias of the counter electrode roller R1, white particles move upward, and the charged portion has no potential difference. Therefore, the particles did not move, and the white particles remained on the lower side. In the image thus formed, when viewed from the upper side in the drawing, the area corresponding to the charged portion was a black portion, and the region corresponding to the non-charged portion was a white portion.

In the image forming apparatus shown in FIG. 21, the electrode roller R1 is opposed to the ion flow type electrostatic latent image forming apparatus CR1 shown in FIG.
The same image erasing device EL1 is provided as shown in FIG.

The image forming apparatus shown in FIG. 22 is different from the image forming apparatus shown in FIG. 20 in that the rotating magnetic pole roller R2 is incorporated in the lower electrode roller R4 of the erasing apparatus EL1. The other points are the same as those of the apparatus shown in FIG. The rotating magnetic pole roller R <b> 2 is driven to rotate in one direction or reciprocatingly rotates to form an oscillating magnetic field on the medium 12. As a result, the developer DL is stirred while affecting the black magnetic developing particles BP. The stirring of the developer increases the amount of triboelectric charging of the developing particles, increases the moving speed due to Coulomb force in image display, improves the flowability of the developing particles, and increases the moving efficiency of the developing particles.

The image erasing apparatus can be applied to the image forming apparatuses shown in FIGS. Next, an image display method of stirring the developer in displaying an image will be described. In carrying out this image display method, the image display medium of Embodiment 2 (herein, described as medium 12) was employed.

FIGS. 23 to 29 show an example of an image forming apparatus for implementing this image display method. In particular, an image forming apparatus provided with a developer stirring device is shown. In the image forming apparatus shown in FIG. 4, a rotating magnetic pole roller R2 is provided, or in the image forming apparatus shown in FIG. 11, the developing magnetic roller R1 opposed to the photosensitive drum PC incorporates the rotating magnetic pole roller R2. When the R2 is driven to rotate in one direction or reciprocally, the magnetic pole roller R2 functions as a developer stirring device.

First, an experimental example in which the developer is stirred and an image is displayed using the image forming apparatus shown in FIG. 11 will be described.

The potential of the charged portion of the photosensitive drum PC is set to +500
V, the potential of the non-charged portion (exposed portion) was +100 V, and the bias applied to the developing electrode roller R1 was +300 V. The magnetic pole roller R2 inside the electrode roller R1 was rotated leftward (counterclockwise) in the figure at a maximum magnetic flux density of 400 gauss, 8 magnetic poles, and a rotation speed of about 100 rpm.

Under these conditions, the white particles WP corresponding to the charged portions receive a force upward in the figure against the direction of the electric field, and the black particles BP receive a force downward in the figure along the direction of the electric field. Since the black particles BP were disturbed by the oscillating magnetic field, the developing particles moved efficiently.

The image forming apparatus shown in FIG. 23 is different from the image forming apparatus shown in FIG. 14 in that a developing electrode roller R1 is arranged so as to face an ion flow type electrostatic latent image forming apparatus CR1, and a rotating magnetic pole roller R2 is provided in the roller. Is built-in.

In this apparatus, experiments of developer stirring and image display were performed under the following conditions. That is, the charged portion potential of the medium 12 is +500 V, and the non-charged portion (exposed portion) potential is about 0 V.
V, the bias applied to the electrode roller R1 was + 300V. The magnetic pole roller R2 has a maximum magnetic flux density of 400 gauss,
The number of magnetic poles was 8 and the rotation speed was about 100 rpm.

Under these conditions, the white particles WP corresponding to the charged portions receive a force upward in the figure against the direction of the electric field, and the black particles BP receive a force downward in the figure along the direction of the electric field. Since the black particles BP were stirred by the oscillating magnetic field, the developing particles moved efficiently.

The image forming apparatus described above, if broadly considered, converts an electrostatic field formed in the image display step into an image to be displayed on one of the outer surfaces of the two sheets of the reversible image display medium. This is an example in which a corresponding electrostatic latent image is formed, formed simultaneously with the formation of the electrostatic latent image based on the electrostatic latent image, and further, the developer is stirred simultaneously with the formation of the electrostatic field. .

The image forming apparatus shown in each of FIGS. 24 and 25, which will be described next, can broadly grasp the electrostatic field formed in the image display step by using any one of the two sheets of the reversible image display medium. After forming an electrostatic latent image corresponding to the image to be displayed on the outer surface, the electrostatic latent image is formed based on the electrostatic latent image, and stirring of the developer is performed simultaneously with the formation of the electrostatic field after forming the electrostatic latent image. It is something to be done.

In the image forming apparatus of FIG. 24, a transfer electrode roller R5 for transferring an electrostatic latent image is arranged at a position where the developing electrode roller R1 was located in the image forming apparatus of FIG. A developing electrode roller R1 for forming an electrostatic field and a rotating magnetic pole roller R2 built therein are arranged downstream of a region facing the roller R5.

A bias power source PW is applied to the transfer electrode roller R5.
5, a bias power source PW1 is connected to the electrode roller R1.

In the image forming apparatus shown in FIG. 25, a counter electrode roller R5 for transferring an electrostatic latent image is arranged at a position where the developing electrode roller R1 was located in the image forming apparatus shown in FIG. A developing electrode roller R1 for forming an electrostatic field and a rotating magnetic pole roller R2 built therein are arranged downstream of a region facing the counter electrode roller R5.

A bias power supply PW is applied to the counter electrode roller R5.
5, a bias power source PW1 is connected to the electrode roller R1.

According to the image forming apparatuses of FIGS. 24 and 25,
After an electrostatic latent image is formed on the medium 12 in a region where the photosensitive drum PC or the electrostatic latent image forming device CR1 and the transfer (opposite) electrode roller R5 oppose each other, the medium is transferred to the developing electrode roller R
By contacting with the number 1, an electrostatic field is formed for each pixel in accordance with the electrostatic latent image, whereby an image is displayed. At this time, whether the magnetic pole roller R2 is driven to rotate in one direction,
Alternatively, an oscillating magnetic field is generated by the reciprocating rotation driving, and the image is displayed while the developing particles are stirred by the influence of the magnetic field. The agitation of the developing particles increases the charge amount of the developing particles and improves the fluidity of the developing particles. As a result, images are displayed smoothly and well.

[0310] The magnetic pole roller R2 is an electrode roller R1,
It may be arranged between R5.

The image forming apparatus shown in FIGS. 26 and 27, which will be described next, broadly considers an electrostatic field formed in an image display step by using an outer surface of one of two sheets of a reversible image display medium. Forming an electrostatic latent image corresponding to the image to be displayed, and forming the electrostatic latent image based on the electrostatic latent image simultaneously with or after the formation of the electrostatic latent image, and stirring the developer. Is performed before forming an electrostatic latent image.

The image forming apparatus shown in FIG. 26 is different from the image forming apparatus shown in FIG. 11 in that a magnetic pole roller is not built in the electrode roller R1 and a rotating magnetic pole roller R2 is provided upstream of a region where the photosensitive drum PC and the electrode roller R1 face each other. Is arranged.
The magnetic pole roller R2 is driven to rotate in one direction or to reciprocate, thereby forming an oscillating magnetic field for stirring the developer.

[0313] A bias power source PW1 is connected to the electrode roller R1.

In this image forming apparatus, when the potential of the charged portion of the photosensitive drum PC is +500 V, the potential of the non-charged portion (exposed portion) is +100 V, and the bias applied to the developing electrode roller R1 is +300 V, the white color corresponding to the charged portion is obtained. The particles moved upward in the figure against the direction of the electric field, and the black particles moved downward in the figure along the direction of the electric field. Since the developing particles were previously stirred, the charge amount was increased and the fluidity was improved, so that the developing particles moved efficiently.

The image forming apparatus shown in FIG. 27 is different from the image forming apparatus shown in FIG. 24 in that a rotating magnetic pole roller R2 is disposed upstream of a region where the photosensitive drum PC and the electrode roller R5 face each other. The magnetic pole roller R2 is driven to rotate in one direction or to reciprocate, thereby forming an oscillating magnetic field for stirring the developer.

The image forming apparatus shown in FIG. 28 is an image forming apparatus provided when there is a possibility that the magnetic developing particles BP may be biased to one side in the developer accommodating cell due to the magnetic field generated by one magnetic pole roller R2. This device, if viewed broadly,
A plurality (here, two) of developer agitators for forming an oscillating magnetic field are sequentially provided in the medium transport direction.

In the example shown in FIG. 28, in the image forming apparatus shown in FIG. 11, two developing magnetic pole rollers R1 each having a built-in rotary magnetic pole roller R2 are arranged to face the photosensitive drum PC. Power supplies PW1, PW 'are connected to the rollers R1, R1. The two rotating magnetic pole rollers R2 are driven to rotate in opposite directions. Thereby, the bias of the magnetic developing particles (here, the black particles BP) in the cells can be suppressed.

The image forming apparatus shown in FIG. 29 differs from the image forming apparatus shown in FIG. 24 in that a magnet member Mg provided with N poles and S poles alternately is replaced with a photosensitive drum PC in place of the developing electrode roller R1 and the magnetic pole roller R2. Downstream of the incoming medium 12
And a developing bias power source PW1 ″ is connected to the member Mg.

The oscillating magnetic field is formed on the medium 12 by moving the medium 12 relative to the member Mg. Next, in displaying an image, an electrostatic latent image is formed on the surface of the image display medium (sheet surface), and before the electrostatic latent image is formed, the medium surface is uniformly charged to a predetermined potential. An image display method for forming a latent image will be described. In carrying out this image display method, the image display medium of Embodiment 2 (herein, described as medium 12) was employed.

FIGS. 30 and 31 show examples of an image forming apparatus for implementing this image display method. In particular, the figure shows an image forming apparatus provided with a charging device for uniformly charging the surface of a medium to a predetermined potential before forming an electrostatic latent image.

The image forming apparatus shown in FIG. 30 is different from the image forming apparatus shown in FIG. 11 in that the magnetic pole roller R2 is not built in the developing electrode roller R1, and the photosensitive drum PC and the electrode roller R1 are not provided.
The preliminary charging device 2 is provided on the upstream side of a region facing the above. The charging device 2 includes a charger 21 facing the surface of the transported medium 12 on the side where the electrostatic latent image is formed, and a ground electrode 22 opposed to the medium path with the medium path interposed therebetween. The electrode roller R1 may be grounded in some cases.

The image forming apparatus shown in FIG. 31 is different from the image forming apparatus shown in FIG. 21 in that the same preliminary charging device 2 as that described above is used instead of the image erasing device EL1 on the upstream side of the electrostatic latent image forming device CR1. . The electrode roller R1 may be grounded in some cases.

In these image forming apparatuses, the surface of the medium 12 is uniformly charged by the preliminary charging device before displaying an image. Thereafter, in the example of FIG. 30, the electrostatic latent image formed on the photosensitive drum PC is transferred and written in the charged area. In the example of FIG. 31, an electrostatic latent image is written by the electrostatic latent image forming device CR1. In each case, the region uniformly charged in advance and the region where the electrostatic latent image is written later have opposite polarities. By setting the bias of the electrode roller R1 to ground or appropriately setting the potential, the direction of the electric field is different between the area where the electrostatic latent image is written and the area where the electrostatic latent image is not written, thereby moving the developing particles to form an image. be able to.

In the example shown in FIG. 30, by uniformly charging the surface of the medium 12 to the polarity opposite to the polarity of the electrostatic latent image formed later, dielectric breakdown inside the medium 12 can be prevented, and Thus, the latent image can be reliably transferred to the medium 12. As described above, since the electrostatic latent image is reliably transferred, the image holding property is improved.

In the example shown in FIG. 31, when forming an electrostatic latent image,
The potential difference between the image portion and the non-image portion can be increased.
For example, by setting the uniform charging portion of the negative polarity by the preliminary charging by the charging device 2 to -1000 V, the charging portion of the positive polarity by the writing of the electrostatic latent image to +1000 V, and the bias of the electrode roller R1 to the ground, the non-contact with the image portion Image part is 1000 each
A potential difference of V is generated, so that the developing particles can be driven. As described above, the developing particle driving electric field can be increased, and the moving speed of the developing particles can be increased.

It is to be noted that a region uniformly charged in advance and a region where an electrostatic latent image is written later may have the same polarity.
In this case, by setting the bias of the electrode roller R1 to an intermediate potential between the area where the electrostatic latent image is written and the area where the electrostatic latent image is not written, the directions of the electric fields are different in both areas, and an image can be formed. .

The area where the electrostatic latent image is written later may be 0V. Also in this case, by setting the bias of the electrode roller R1 to an intermediate potential between the area where the electrostatic latent image is written and the area where the electrostatic latent image is not written, the direction of the electric field is different in both areas, and an image can be formed.

Thus, even after the medium 12 has passed the area where the electrode drum R1 and the photosensitive drum PC or the electrostatic latent image forming apparatus CR1 are opposed, an electrostatic attraction force is generated between the developer particles and the sheet of the medium. Therefore, the image retention is improved.

The polarity of the electrostatic latent image to be formed may be negative.

The charge polarity of the black and white developing particles may be reversed.

The electrostatic latent image forming apparatus is not limited to those shown in FIGS. 30 and 31, and the other electrostatic latent image forming apparatuses described above can be employed. Here, an external static image as shown in FIG. 11 shows that it is advantageous to uniformly charge the medium surface before forming an electrostatic latent image on the medium surface and to form an electrostatic latent image in the charged area. An image forming apparatus provided with an electrostatic latent image forming apparatus will be described as an example.

FIGS. 32A to 32E show equivalent circuits of the device. In these figures, the electrostatic latent image carrier such as a photosensitive drum, the image display medium, and the capacitance of the air layer therebetween are denoted by C1, C2, and C0, respectively.

An electrostatic latent image carrier (hereinafter referred to as an "image carrier") is charged with a latent image charge Q (potential V at that time) by a charging charger and an image exposure device, and a medium is charged beforehand by a preliminary charging device with a charge Q '. It is assumed that (the potential V 'at that time) is applied.

FIG. 32A shows an equivalent circuit in a state where the image carrier and the image display medium are separated from each other.
Since it is much larger than 0, the charge Q does not move and the medium is not affected by the electrostatic latent image.

In this state, when the image carrier comes close to the medium, C0 increases, and the electric charges charged in C1 and C2 are induced by electrostatic induction, resulting in the state of FIG. FIG. 32B is an equivalent circuit in a state where the image carrier is brought close to the image display medium and electrostatically induced.

In the state shown in FIG. 32B, the potential difference V1, which is induced in the image carrier, the medium, and the air layer by the induced charge,
V2 and V0 can be expressed as in the following equations (5), (6), and (7). Here, it is assumed that a ground is applied without applying a bias.

[0337]

(Equation 5)

[0338]

(Equation 6)

[0339]

(Equation 7)

Here, V is the latent image surface potential of the image carrier, V '
Is the surface potential of the medium.

The medium contains a developer. Since the developer particles carry electric charges under an electric field, the developer layer is apparently similar to the conductive layer. That is, the capacitance C2 of the medium is close to the combined capacitance of the upper and lower resin sheets.

Here, in order for the latent image charges of the image carrier to be transferred to the medium, the air layer needs to be subjected to dielectric breakdown and charge transfer. If the dielectric breakdown does not occur, when the image carrier is separated from the medium, the state returns to the state of FIG. 32A again, and the latent image is not transferred.

That is, for example, when V0 is small, the particles move due to the induced electrostatic field, but the latent image is not transferred.

For example, in order for an air layer having a gap of 10 μm to cause dielectric breakdown, V0 is about 37 according to Paschen's rule.
0 V or more is required.

Here, V = 1000 V, V ′ = − 1000
V, the ratio of each capacitance is C1: C2: C0 = 18:
When 5:12, V0 (potential difference of air layer) = 480
V, causing dielectric breakdown and transferring the latent image. Further, the potential difference applied to the medium is about 200 V, and dielectric breakdown inside the medium can be prevented. (However, the image carrier is assumed to be a normal organic photoreceptor, the medium is assumed to have a combined capacity of the above configuration, and the air layer is assumed to have a gap of about 10 μm where dielectric breakdown is likely to occur, and the respective capacitance ratios are considered.) In the electrostatic latent image on the image carrier, charge transfer occurs between the charged portion and the medium, and no charge transfer occurs in the non-charged portion (exposed portion). This causes a difference in the surface potential on the medium. The surface potential of the medium after the charge transfer of the charged portion is performed is represented by the following expression (8), and that of the non-charged portion is represented by the following expression (7).

FIG. 32 (C) shows an equivalent circuit in a state where charge transfer has occurred due to dielectric breakdown. In this state where charge transfer has occurred due to dielectric breakdown, the following equation (8) is established.

[0347]

(Equation 8)

In equation (8), v0 is the minimum potential difference that can be discharged, and V1 and V2 are equations (6) and (7).

For example, under the above-mentioned setting conditions, the surface potential on the medium is approximately +260 V in the area corresponding to the charged portion.
The area corresponding to the non-charged portion is about -340V.

Here, when the counter electrode roller is grounded, electric fields in opposite directions are formed in the charged portion and the non-charged portion, and the developing particles move along the electric field to form an image. .

Thereafter, when the image carrier is separated from the medium, the induced charges move, and the surface potential of the medium changes.
The part returns to about -720V, the part returns to about -1000V,
A latent image can be formed on the medium (see FIG. 32D).

Although the above description has been made with the counter electrode roller R1 grounded, an appropriate bias may be applied to the roller. In this case, V ′ may be replaced with V ′ + Vb. FIG. 32E shows an equivalent circuit in this case.

Although the case where the electrostatic latent image carrier is a photosensitive drum (photoconductor) has been described, a dielectric drum may be used. The polarity of the electrostatic latent image may be negative. The charge polarity of the developing particles may be reversed.

As described above, before the latent image is transferred by causing dielectric breakdown between the electrostatic latent image carrier and the medium, the surface of the medium is uniformly charged to a predetermined potential in advance, so that the inside of the medium can be charged. The potential difference can be suppressed, thereby improving the image retention. Next, still another example of the reversible image display medium will be described with reference to FIGS.

A reversible image display medium 14 shown in FIG. 33 is an example of an electrophoretic medium.

The medium 14 has an electric field coloring layer 140 supported on a transparent support substrate 146. Electric field coloring layer 1
Reference numeral 40 denotes a transparent conductive layer 144 and an insulating layer 145 in which a liquid layer 143 in which charged coloring particles 141 are dispersed in an insulating liquid 142 is formed.
It is sealed between. The insulating liquid 142 is obtained by mixing an organic substance containing an ionic surfactant and a dye with high-purity petroleum (Isoper, trade name of Esso). The ionic surfactant is adsorbed on the pigmented organic coloring particles 141 and the particles are electrochemically stably charged. The charged colored particles 141 are dispersed in the liquid 142 and exhibit electrophoretic properties.

When no electric field is applied to the medium 14 or when an electric field opposite to a predetermined electric field is applied, the color of the dye in the insulating liquid 142 is visible, but an electrostatic latent image is written. Then, the charged colored particles 141 move toward the transparent conductive layer 144, and the pigment is visible.

[0358] Regarding the image display by the medium 14,
For example, prior to image display, the surface of the medium 14 is uniformly charged to a predetermined potential in advance, and an electrostatic latent image EI is formed on the charged medium surface using the image forming apparatus illustrated in FIGS. Charged developing particles (here, charged colored particles) 1 dispersed in the insulating liquid 142 in the medium based on the electrostatic latent image
An image can be displayed on the image 41 by forming a predetermined electrostatic field for each pixel corresponding to the image to be displayed.

As described above, the surface of the medium 14 is charged before the formation of the electrostatic latent image, and the electrostatic latent image is formed in the charged area. As compared with the case where an image is formed without pre-charging, the image holding property is improved.

The reversible image display medium 15 shown in FIG.
It is an example of a rotating particle spherical display medium.

This medium 15 has an electric field coloring layer 150 supported on a transparent support substrate 156. Electric field coloring layer 1
Reference numeral 50 denotes a single-sided colored sphere 151 having one side colored 151a surrounded by an insulating liquid 152, and the insulating holding medium 1 is disposed together with the liquid.
The transparent conductive layer 15 is embedded on one side of the medium 153.
4 is obtained by forming an insulating layer 155 on the opposite side.

The single-sided colored sphere 151 is produced by, for example, uniformly disposing a white sphere of glass containing TiO ₂ as a main component on an appropriate table, and depositing chromium or the like from the upper surface. The size may be in the range of 30 μm to 100 μm, but 10 μm
If the following is set, the resolution will be higher.

The single-sided colored spheres 151 are dispersed in, for example, an insulating holding medium 153 such as an elastomer, and the medium 153 is immersed in a solution in which an ionic surfactant is dissolved in an organic solvent such as toluene. Swell, thereby causing the insulating liquid 152 to collect around the single-sided colored sphere 151. Thus, the single-sided colored sphere 151 is made of the insulating liquid layer 15.
2, the liquid is embedded in the insulating holding medium 153 together with the liquid in a rotatable state.

Since the one-sided colored sphere 151 has different properties on one hemisphere and the other hemisphere, the amount of adsorbed ions is different on both surfaces. Therefore, when an electric field is applied to the medium 15, the direction of the surface of the single-sided colored particles 151 changes depending on the direction of the electric field. Accordingly, an image is displayed by seeing the colored surface of the single-sided colored sphere 151 or an uncolored surface.

The image display by the medium 15 is also
For example, prior to image display, the surface of the medium 15 is uniformly charged to a predetermined potential in advance, and an electrostatic latent image EI is formed on the charged surface of the medium using an image forming apparatus illustrated in FIGS. Displaying an image by forming a predetermined electrostatic field for each pixel corresponding to the image to be displayed on the single-sided colored sphere 151 floating in the insulating liquid 152 in the medium based on the electrostatic latent image Can be. Thereby, an image can be displayed with good image retention.

Image display and image deletion can be repeated for the media 14 and 15 as well.

The mediums 14 and 15 may be formed by another image forming apparatus as long as the images can be displayed well.

[0368]

As described above, according to the present invention, a reversible image display method having the following advantages can be provided. (1) Image display and image deletion can be repeatedly performed,
Therefore, image display media such as paper related to the conventional image display,
It is possible to reduce the use of consumables such as a developer and ink, and it is possible to respond to today's environmental load reduction. (2) A high-resolution, high-quality image with excellent contrast can be stably displayed over a long period of time. (3) Afterimages are less likely to occur, and therefore exhibit good reversibility. In this respect, a high-quality image can be displayed. (4) A low driving voltage is required.

In particular, according to the present invention, since an electrostatic latent image is formed on an image display medium when an image is displayed, there is an advantage that image retention is improved.

[Brief description of the drawings]

FIGS. 1A to 1I are diagrams showing examples of the shape of a developer accommodating cell. FIG.

FIGS. 2A to 2H are diagrams illustrating examples of shapes and arrangements of developer movement suppressing members, respectively. FIG. 1I shows the unit area Sb of the medium and the area Sa of the image part by the cells in the medium unit area Sb.
It is a figure showing an example of.

FIG. 3 is a cross-sectional view of an example of a reversible image display medium with electrodes before image display.

4 is a cross-sectional view of the medium shown in FIG. 3 in an image display state.

FIG. 5 is a perspective view of a second sheet of the medium shown in FIG. 3 and lattice-like partition walls formed thereon;

FIG. 6 is a plan view of a second sheet of the medium shown in FIG. 3 and individual electrodes formed thereon.

FIG. 7 is a diagram showing an image display example of the medium shown in FIG. 3;

FIG. 8 is a cross-sectional view of another example of the reversible image display medium.
FIG. 8A is a cross-sectional view of the reversible image display medium before displaying an image, and FIG. 8B is a cross-sectional view of one example when displaying an image.

FIG. 9 is a plan view showing a part of the medium shown in FIG.

10 is a diagram showing an example of image display on the medium shown in FIG. 8;

FIG. 11 is a diagram illustrating a schematic configuration of an example of an image forming apparatus including an external electrostatic latent image forming apparatus.

FIG. 12 is a sectional view of still another example of the reversible image display medium according to the present invention.

FIG. 13A is a plan view showing still another example of image display, and FIG. 13B is a diagram showing the ratio of the non-image area (non-image area / medium unit area) to the reflection density ratio. It is a graph which shows a relationship.

FIG. 14 is a diagram illustrating a schematic configuration of an example of an image forming apparatus including an ion flow type direct electrostatic latent image forming apparatus.

FIG. 15 is a diagram illustrating a schematic configuration of another example of an image forming apparatus including an ion flow type direct electrostatic latent image forming apparatus.

FIG. 16 is a diagram illustrating a schematic configuration of still another example of an image forming apparatus including an ion flow type direct electrostatic latent image forming apparatus.

FIG. 17 is a diagram illustrating a schematic configuration of an example of an image forming apparatus including a multi-stylus type direct electrostatic latent image forming apparatus.

FIG. 18 is a diagram illustrating a schematic configuration of an example of an image forming apparatus including a multi-stylus type electrostatic latent image forming apparatus having adjacent control electrodes.

FIG. 19 is a diagram illustrating an equivalent circuit of an image forming apparatus including an external electrostatic latent image forming apparatus. FIG. 1A is an equivalent circuit in a state where the image carrier is separated from the image display medium, and FIG. 2B is an equivalent circuit in a state where the image carrier is brought close to the image display medium and electrostatically induced. (C) is an equivalent circuit in a state where charge transfer has occurred due to dielectric breakdown, and FIG. (D) is an equivalent circuit in a state where the image carrier and the medium are separated after the charge transfer.

FIG. 20 is a diagram illustrating a schematic configuration of an example of an image forming apparatus including an image erasing device.

FIG. 21 is a diagram illustrating a schematic configuration of another example of the image forming apparatus including the image erasing device.

FIG. 22 is a diagram illustrating a schematic configuration of still another example of the image forming apparatus including the image erasing device.

FIG. 23 is a diagram illustrating a schematic configuration of an example of an image forming apparatus including a developer stirring device.

FIG. 24 is a diagram illustrating a schematic configuration of another example of an image forming apparatus including a developer stirring device.

FIG. 25 is a diagram illustrating a schematic configuration of still another example of an image forming apparatus including a developer stirring device.

FIG. 26 is a diagram illustrating a schematic configuration of still another example of an image forming apparatus including a developer stirring device.

FIG. 27 is a diagram illustrating a schematic configuration of still another example of an image forming apparatus including a developer stirring device.

FIG. 28 is a diagram illustrating a schematic configuration of still another example of the image forming apparatus including the developer stirring device.

FIG. 29 is a diagram illustrating a schematic configuration of still another example of the image forming apparatus including the developer stirring device.

FIG. 30 is a diagram illustrating a schematic configuration of an example of an image forming apparatus including a preliminary charging device.

FIG. 31 is a diagram illustrating a schematic configuration of another example of the image forming apparatus including the preliminary charging device.

FIG. 32 is a diagram illustrating an equivalent circuit when a medium is charged before forming an electrostatic latent image in an image forming apparatus including an external electrostatic latent image forming apparatus. FIG. 1A is an equivalent circuit in a state where the image carrier is separated from the image display medium, and FIG. 2B is an equivalent circuit in a state where the image carrier is brought close to the image display medium and electrostatically induced. (C) is an equivalent circuit in which charge transfer has occurred due to dielectric breakdown, FIG. (D) is an equivalent circuit in which the image carrier is separated from the medium after charge transfer, and FIG. (E) is a case where the counter electrode roller is grounded. Is an equivalent circuit.

FIG. 33 is a partial cross-sectional view of still another example of the reversible image display medium.

FIG. 34 is a partial cross-sectional view of still another example of the reversible image display medium.

[Explanation of symbols]

CE1 Continuous groove-shaped developer accommodating cell w1 Partition wall S Image display medium CE2 Independent type cell α Partition wall thickness pt Adjacent partition wall spacing h Partition wall height CL1, CL2, CL3, CL4 Developer movement suppression Members β1, β2 Vertical and horizontal dimensions of the columnar developer movement suppressing member γ1, γ2 Vertical and horizontal dimensions of one unit of the image display area DL, DLo Developer WP White developing particles BP Black developing particles 11 Reversible image display medium 111 First Sheet 112 Second sheet 113 Partition wall 114 First electrode 115 Second electrode 115a Individual electrode (pixel electrode) 116 Developer storage cell 110 Reed part 117 Electrode selection circuit 118a Positive drive voltage generation circuit 118b Negative drive voltage generation circuit 119 Display Data control unit Bk Black display part W White display part 12 Reversible image display medium 121 Sheet 122 Second sheet 123 Partition wall 123a Vertical partition wall 124 Developer storage cell 120 Sealing portion 120a Sealing portion 120 PC Photoconductor drum CH Scorotron charger EX Laser image exposure device IR eraser lamp R1 Electrode roller R2 Rotating magnetic pole roller PW1 Bias power supply 13 Reversible image display medium 122A Conductive film CR1 Ion flow type direct electrostatic latent image forming device c1 Corona ion generator c11 Shield case c12 Corona wire e1 Write electrode f1 Write electrode control circuit Ea Ground electrode CR2 Ion flow Direct electrostatic latent image forming apparatus c2 Corona ion generating section e2 Write electrode f2 Write electrode control circuit c21 Shield case c22 Corona wire Pc2 Power supply e21 Upper electrode e22 Lower electrode Pc21 Control Source PC22 Bias power supply f21 Control unit R3 Electrode roller PC20 Power supply CR3 Multi-stylus type direct electrostatic latent image forming device e3 Electrode H3 Multi-stylus head CR4 Multi-stylus type electrostatic latent image forming device having adjacent control electrodes e4 Recording electrode e41 Control Electrode H4 Electrostatic recording head EL1, EL2 Image erasing device R5 Transfer electrode roller PW5 Power Mg Member provided with alternating N and S poles PW1 'Developing bias power supply 2 Pre-charging device 21 Charger 22 Ground electrode 14 Electrophoretic reversibility Image display medium 140 Electric field coloring layer 141 Charged colored particles 142 Insulating liquid 143 Liquid layer 144 Transparent conductive layer 145 Insulating layer 146 Support substrate 15 Rotating particle spherical reversible image display medium 150 Electric field coloring layer 151 Single-sided colored sphere 151a Colored 152 Insulated Liquid Body 153 Insulating holding medium 154 Transparent conductive layer 155 Insulating layer 156 Support substrate

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Ryuji Kurita, Inventor 5-2232-3-2-1-1 Sayama, Osaka Sayama City, Osaka Prefecture (72) Hidetoshi Miyamoto 2-3-13 Azuchicho, Chuo-ku, Osaka City, Osaka Osaka International Building Minolta Co., Ltd. (72) Inventor Nozomi Youme 2-13-13 Azuchicho, Chuo-ku, Osaka-shi, Osaka F-term in Osaka International Building Minolta Co., Ltd. 2H029 DB00 DB04 DB11 5C094 AA06 AA24 AA31 AA53 AA56 BA09 BA75 BA76 BA84 CA19 DA12 EA04 EA05 EB02 EC04 FA01 FA02 FB01 FB02 FB15 GA10 HA10

Claims (3)

[Claims] 1. Two sheets facing each other at a predetermined gap, at least one of which is light transmissive, and one or two sheets formed between the two sheets and surrounded by a partition wall. And a dry developer contained in each of the cells. The dry developer has at least two types of different charge polarities and different optical reflection densities. A reversible image display medium, comprising: dry developing particles having a triboelectric charging property, wherein at least two types of the dry developing particles constituting the dry developer in the developer accommodating cell are mutually separated. Preparing a reversible image display medium that is frictionally charged to a different charging polarity, and corresponding to an image to be displayed on the developing particles in a state where the developing particles contained in each of the cells are frictionally charged. Picture Moving the developing particles to form an image by forming a predetermined electrostatic field for each element; and displaying the image, wherein the electrostatic field formed in the image displaying step is one of the two sheets. A reversible image display method, comprising: forming an electrostatic latent image corresponding to an image to be displayed on an outer surface, and forming based on the electrostatic latent image. 2. The reversible image display method according to claim 1, wherein said electrostatic latent image is formed directly on said sheet surface using a direct electrostatic latent image forming apparatus. 3. The reversible image display method according to claim 1, wherein the electrostatic latent image is formed by transferring an electrostatic latent image formed outside the medium to the sheet surface using an external electrostatic latent image forming apparatus. .