JP5136807B2 - Reversible image display medium - Google Patents

Description

The present invention relates to an image display medium. In particular the image display, relates to reversible image display medium capable of repeatedly performing image erasing.

  Today's image display uses a pencil, pen, paint, etc. to manually write characters, figures, etc. on an image display medium such as paper, or a document, figure, etc. created by a computer, word processor, etc., such as a CRT display Or by displaying it on a medium such as paper with a printer.

  Also, manually create documents and graphics on paper and other media such as paper, and documents and graphics on paper and other media that have been output to a printer on another paper or other media using a copier, etc. Alternatively, it is transmitted by a facsimile machine or the like, and is copied and output on a medium such as paper at the transmission destination.

  Among these image displays, image display for displaying characters, figures, etc. on an image display medium such as paper using a pencil, pen, etc., printers, copiers, facsimiles using electrophotography, ink spraying, thermal transfer, etc. In an image display in which characters, graphics, and the like are displayed on an image display medium such as paper by an image forming apparatus such as a machine, the image can be clearly displayed at a high resolution, and the image is friendly to human eyes when viewing the image.

An electrophoretic display has been proposed as an image display method capable of repeating image display and image erasure (see, for example, JP-A-4-221990). In this display method, two substrates, at least one of which is transparent, are arranged to face each other with a gap between them to form a sealed space, in which electrophoretic particles are dispersed in different colors. A display liquid dispersed in a medium is filled, and 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 an isoparaffin-based dispersion medium, particles such as titanium dioxide, a dye for imparting a color contrast with the particles, a dispersant such as a surfactant, and an additive such as a charge imparting agent.

JP-A-4-221990

  However, image display and image erasure cannot be repeated on an image display medium such as paper. When writing a character using a pencil, the character can be erased to some extent by using an eraser. However, if the character is thinly written, it is completely erased when written at a normal density. It is difficult to leave, and it is difficult to reuse a medium such as paper once image-displayed, except for the case where an image is also displayed on the back side of the medium that has not yet been image-displayed.

  For this reason, media such as paper on which images are displayed are discarded or incinerated after they are used up, and many 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 production energy of the medium are required. This is contrary to the reduction in environmental load that is required today.

  In this respect, image display and image erasure can be repeated in image display by a display such as a CRT display. However, an image displayed on a display has a lower resolution than an image displayed on a paper or the like by a printer or the like, and there is a limit in obtaining a clear and fine image. In addition, the eyes are very tiring when viewing for a long time due to the relatively low resolution and the light emission from the display.

  In the electrophoretic display, since the contrast between the high refractive index particles such as titanium dioxide and the insulating colored liquid is displayed, the degree of concealment of the colored liquid by the particles (the degree to which the colored liquid can be hidden by the particles) is inevitably poor. Therefore, the contrast is lowered. In addition, the specific gravity difference between the particles and the dispersion medium in the display liquid is very large, and the particles are likely to settle and aggregate. Therefore, the display contrast is likely to decrease, and it is difficult to display images stably for a long period of time. In addition, the last display afterimage is likely to occur. Furthermore, the charging of the particles in the liquid varies greatly with time, and the image display stability is also inferior in this respect.

Therefore, an object of the present invention is to provide a reversible image display medium having the following advantages. (1) Image display and image erasure can be performed repeatedly. Therefore, it is possible to reduce the use of image display media such as paper, developer, ink and other consumables related to conventional image display. It can respond to the environmental load reduction.
(2) An image with excellent contrast, high resolution and high quality can be stably displayed over a long period of time.
(3) Afterimages are unlikely to occur, thus exhibiting good reversibility, and a high-quality image can be displayed in this respect.
(4) The drive voltage is low.

Another object of the present invention is to provide a reversible image display medium that can display an image with little image unevenness.

The present invention provides a sixth reversible image display medium described later . In the following, reference first to fifth reversible image display media and first, second and third reversible image display methods will be described.
(1) A first reversible image display medium and a first reversible image display method.
(1-1) First reversible image display medium (reference medium)
Two sheets facing each other with a predetermined gap, at least one of which is light transmissive,
One or more developer containing cells formed between the two sheets and surrounded by a partition wall;
A dry developer contained in each cell;
Have
The dry developer contains at least two types of dry developing particles having triboelectric charging properties having different charging polarities and different optical reflection densities.
Reversible image display medium.
(1-2) First reversible image display method (reference method)
The first reversible image display medium, wherein at least two types of the dry developer particles constituting the dry developer in the developer containing cell are frictionally charged to different charging polarities. Preparing an image display medium;
The developer particles contained in the cells are moved by forming a predetermined electrostatic field for each pixel corresponding to the image to be displayed on the developer particles in a state in which the developer particles are frictionally charged. A step of displaying an image;
A reversible image display method comprising:
(2) Second reversible image display medium and second reversible image display method
(2-1) Second reversible image display medium (reference medium)
Two sheets facing each other with a predetermined gap, at least one of which is light transmissive,
One or more developer containing cells formed between the two sheets and surrounded by a partition wall;
A dry developer contained in each cell;
An electrode (preferably a transparent electrode) formed on the inner surface of one of the sheets having light permeability;
An electrode facing the electrode formed on the inner surface of the other sheet;
Have
The dry developer contains at least two types of dry developing particles having triboelectric charging properties having different charging polarities and different optical reflection densities.
A reversible image display medium characterized by the above.

The electrode on the inner surface of the other sheet may be composed of an individual electrode group formed for each pixel.
(2-2) Second reversible image display method (reference method)
In the second reversible image display medium, at least two types of the dry developer particles constituting the dry developer in the developer containing cell are frictionally charged to different charging polarities. Preparing an image display medium;
A predetermined electrostatic field is formed for each pixel corresponding to an image to be displayed between the electrodes by applying a voltage between the electrodes while the developing particles contained in the cells are frictionally charged. A step of moving the developing particles to display an image;
A reversible image display method comprising:

In the reversible image display medium used in this reversible image display method, the electrode on the other sheet inner surface may be composed of an individual electrode group formed for each pixel.
(3) Third to fifth reversible image display media and third reversible image display method
(3-1) Third reversible image display medium (reference medium)
Two sheets facing each other with a predetermined gap, at least one of which is light transmissive,
One or more developer containing cells formed between the two sheets and surrounded by a partition wall;
A dry developer contained in each cell;
Have
The dry developer includes at least two types of dry developing particles having triboelectric charging properties having different charging polarities and different optical reflection densities from each other.
The thickness of each sheet is 5 μm to 100 μm,
The gap between the two sheets is 20 μm to 300 μm,
The overall thickness is 30 μm to 500 μm.
Reversible image display medium.
(3-2) Fourth reversible image display medium (reference medium)
Two sheets facing each other with a predetermined gap, at least one of which is light transmissive,
One or more developer containing cells formed between the two sheets and surrounded by a partition wall;
A dry developer contained in each cell;
Have
The dry developer includes at least two types of dry developing particles having triboelectric charging properties having different charging polarities and different optical reflection densities from each other.
The surface resistivity of the outer surface of at least one of the two sheets is 10 ¹⁰ Ω / □ to 10 ¹⁶ Ω / □.
Reversible image display medium.
(3-3) Fifth reversible image display medium (reference medium)
Two sheets facing each other with a predetermined gap, at least one of which is light transmissive,
One or more developer containing cells formed between the two sheets and surrounded by a partition wall;
A dry developer contained in each cell;
Have
The dry developer includes at least two types of dry developing particles having triboelectric charging properties having different charging polarities and different optical reflection densities from each other.
The surface resistivity of the outer surface of at least one of the two sheets is 10 ⁷ Ω / □ or less.
Reversible image display medium.
(3-4) Third reversible image display method (reference method) The reversible image display medium according to any one of third to fifth, wherein the dry developer in the developer containing cell is configured. Providing a reversible image display medium in which at least two types of dry developing particles are frictionally charged to different charging polarities, and developing the image in a state in which the developing particles contained in each cell are frictionally charged. A reversible image display method comprising: a step of forming a predetermined electrostatic field for each pixel in correspondence with an image to be displayed on the particles to move the developing particles to display an image.

In any reversible image display medium and a reversible image display method using the same, an image to be displayed on the developer particles in a state in which the developer particles contained in each cell of the image display medium are frictionally charged. (A second reversible image display medium having the electrode and a second reversible image display method using the same, a voltage is applied between the electrodes. And by forming a predetermined electrostatic field for each pixel corresponding to the image to be displayed between the electrodes), developing the image by moving the developing particles by Coulomb force and displaying the image. Can do.

In any reversible image display medium and reversible image display method using the same, even after an image is displayed once, a different electrostatic field is formed or an alternating electric field is formed as will be described later to erase the image. The image can be rewritten by forming a different electrostatic field. Therefore, it is not necessary to discard the image display medium once displayed. Further, the developer particles are contained in the cell, and therefore, it is not necessary to supply the developer from the outside. As a result, the use of conventional image display media such as paper and image consumables such as developer can be greatly reduced.

  In addition, it is unnecessary to melt and fix toner on a sheet of paper or the like as in conventional electrophotographic image formation, and image forming energy required for this type of conventional image forming apparatus. Can save most of it.

  Thus, today's environmental burden can be reduced.

Further, in any reversible image display medium and a reversible image display method using the same, the developer contained in the cell has a different optical reflection density (in other words, “different contrast” Or “different colors”) containing at least two kinds of developing particles, and the developing particles are dry developing particles, and the concealment degree of the developing particles of the other type by the developing particles of one type is good. Therefore, the image can be displayed with good contrast.

  The developer contained in the cell includes at least two types of chargeable dry developing particles that are mutually triboelectrically chargeable with different charging polarities. When displaying an image, the developing particles that are oppositely charged by triboelectric charging are coulombs. Since it moves under the force, an image can be displayed with good contrast at this point, and an afterimage of the previous display hardly occurs.

  Compared with, for example, the conductive toner in the display liquid used for the electrophoretic image display described above, the dry developing particles are less likely to settle and aggregate because they do not intervene in the liquid, and this also causes a decrease in image display contrast. It is difficult and can display images stably for a long time. Since the settling and agglomeration of developer particles are unlikely to occur, the afterimage of the previous display is unlikely to occur. Further, since the dry developing particles have less change with time in the charging performance as compared with the toner in the liquid, stable image display can be performed for a long time also in this respect.

  In addition, compared with image display using a conventional CRT display or the like, the image can be displayed with high resolution and kind to the eyes.

Further, according to the reversible image display medium and the reversible image display method using the same, at least two kinds of developing particles contained in each cell are charged in opposite polarities by frictional charging. Image display by forming an electrostatic field on the second electrode (in the second reversible image display medium having the electrode and the second reversible image display method using the electrode, a voltage is applied between the electrodes to generate an image. Since the display is performed), the particles are easy to move, and accordingly, the driving voltage for displaying the image is low.

It said third reversible image display medium, i.e., the thickness of each sheet is 5 m to 100 m, the gap between the two sheets 20Myuemu～300myuemu, the reversible image display medium and which is a total thickness of 30μm~500μm The reversible image display method used has the following advantages.

  That is, if the gap between sheets or the thickness of each sheet is too large, the electric field applied to the developer between the sheets becomes weak and developability deteriorates, resulting in a decrease in contrast and a decrease in resolution. On the other hand, if the gap between the sheets is too small, the amount of developer that can be contained in the developer containing cell is reduced, and it becomes difficult to obtain the necessary contrast. Also, if the thickness of each substrate, and thus the overall thickness of the medium based on the thickness of each substrate, is too small, the medium is likely to bend, the uniformity of the gap between sheets cannot be obtained, and image unevenness is likely to occur.

  In this respect, the thickness of each sheet is set to 5 μm to 100 μm, the gap between both sheets is set to 20 μm to 300 μm, and the overall thickness is set to 30 μm to 500 μm, so that such a problem is solved, so that the contrast is good and the resolution is high. Images can be displayed with little unevenness.

In the reversible image display medium and the reversible image display method using the same in which the thickness of the sheet is defined in this way, an electrode (on the inner surface of one of the sheets having light transparency in the reversible image display medium) Preferably, a transparent electrode) may be formed, and an electrode facing the electrode may be formed on the inner surface of the other sheet. In this case, a voltage is applied between the electrodes to form a predetermined electrostatic field for each pixel corresponding to the image to be displayed between the electrodes, thereby moving the developer particles by Coulomb force. Development can be performed, and an image can be displayed. You can also erase or rewrite images. The other electrode on the inner surface of the sheet may be composed of an individual electrode group formed for each pixel.

Further, the fourth reversible image display medium, i.e., at least one of the surface resistivity of the outer surface of the sheet ^{10 10 Ω / □ ~10 16 Ω} / □ and the reversible image display of the two sheets medium and reversible image display method using the same, or the fifth reversible image display medium, i.e., a surface resistivity of at least one of the outer surfaces of the two sheets and 10 ⁷ Ω / □ or less The reversible image display medium and the reversible image display method using the same have the following advantages.

  If the surface resistance value of the sheet, particularly the surface resistance value of the sheet on the side where the electrostatic field is formed, is small, an electrostatic latent image can be formed directly on the surface of the sheet to form an electrostatic field for image display. In any of the cases where the electrostatic latent image formed in (1) is transferred to the sheet surface, the electrostatic latent image is liable to collapse.

In this respect, by setting the surface resistivity of the outer surface of at least one of the two sheets to 10 ¹⁰ Ω / □ to 10 ¹⁶ Ω / □, such a problem can be solved, and the image display can be reliably ensured. It can be easily performed and stable image display can be performed over a long period of time.

  On the other hand, if the sheet surface resistance value, particularly the surface resistance value on the side opposite to the side on which the electrostatic field is formed, is too large, it will hinder image formation and its holding. In particular, when an electrostatic latent image is directly formed on the sheet surface on the electrostatic field forming side, the latent image charge is difficult to be applied, and when an electrostatic latent image formed externally is transferred, it is difficult to obtain a uniform electric field. Image unevenness is likely to occur. Furthermore, when the media after image formation are overlapped, electrostatic shielding between adjacent media becomes difficult, and the image tends to collapse and is difficult to hold.

In this respect, by setting the surface resistivity of the outer surface of at least one of the two sheets to 10 ⁷ Ω / □ or less (a resistivity equivalent to or less than that of paper), this problem can be solved. Image display can be performed reliably and easily, stable image display can be performed over a long period of time, and image unevenness can be reduced.

From the above, the surface resistivity of the outer surface of one of the two sheets is 10 ¹⁰ Ω / □ to 10 ¹⁶ Ω / □, and the surface resistivity of the outer surface of the other sheet is 10 ⁷ Ω / □. It is good also as follows.
Accordingly, the present invention provides the following sixth reversible image display medium.
Two sheets facing each other with a predetermined gap, at least one of which is light transmissive,
One or more developer containing cells formed between the two sheets and surrounded by a partition wall;
A dry developer contained in each cell;
A reversible image display medium on which an image is formed by forming an electrostatic latent image on one outer surface of the two sheets,
The dry developer includes at least two types of dry developing particles having triboelectric charging properties having different charging polarities and different optical reflection densities from each other.
The surface resistivity of the outer surface of the sheet on the side where the electrostatic latent image is formed is 10 ¹⁰ Ω / □ to 10 ¹⁶ Ω / □,
A reversible image display medium in which the surface resistivity of the outer surface of the sheet opposite to the side on which the electrostatic latent image is formed is 10 ⁷ Ω / □ or less.

The thickness of each sheet is 5 μm to 100 μm, the gap between both sheets is 20 μm to 300 μm, the total thickness is 30 μm to 500 μm, and the outer surface of one of the two sheets The surface resistivity may be 10 ¹⁰ Ω / □ to 10 ¹⁶ Ω / □, and the surface resistivity of the outer surface of the other sheet may be 10 ⁷ Ω / □ or less.

According to the reversible image display medium described above and the reversible image display method using the same, high-resolution and high-quality images can be stably displayed over a long period of time with good contrast. In addition, afterimages are unlikely to occur, and therefore show good reversibility, and a high-quality image can be displayed in this respect. Furthermore, the drive voltage for image display can be low.

Further, according to the reversible image display medium described above and the reversible image display method using the same, it is possible to display an image with display characteristics close to the display characteristics of the paper medium. Compared with an electrophoretic display (EPD), the contrast can be made higher.

As described above, according to the present invention, a reversible image display medium having the following advantages can be provided.
(1) Image display and image erasure can be performed repeatedly. Therefore, it is possible to reduce the use of image display media such as paper, developer, ink and other consumables related to conventional image display. It can respond to the environmental load reduction.
(2) An image with excellent contrast, high resolution and high quality can be stably displayed over a long period of time.
(3) Afterimages are unlikely to occur, thus exhibiting good reversibility, and a high-quality image can be displayed in this respect.
(4) The drive voltage is low.
Further, according to the present invention, it is possible to provide a reversible image display medium that can display an image with little image unevenness.

Each of FIG. (A) to FIG. (I) is a diagram showing an example of the shape of a developer containing cell. FIGS. (A) to (H) are diagrams showing examples of the shape and arrangement of the developer movement suppressing members. FIG. (I) is a diagram showing an example of the medium unit area Sb and the image portion area Sa by the cells therein. It is sectional drawing before the image display of an example of the reversible image display medium with an electrode. FIG. 4 is a cross-sectional view of the image display state of the medium shown in FIG. 3. It is a perspective view of the 2nd sheet | seat in the medium shown in FIG. 3, and the grid | lattice-like partition formed in this. It is a top view of the 2nd sheet | seat in the medium shown in FIG. 3, and the individual electrode formed in this. FIG. 4 is a diagram illustrating an image display example of the medium illustrated in FIG. 3. It is sectional drawing of the other example of a reversible image display medium. FIG. 8A is a cross-sectional view of the reversible image display medium before image display, and FIG. 8B is a cross-sectional view of an example during image display. It is a top view which notches and shows a part of medium shown in FIG. It is a figure which shows the example of an image display of the medium shown in FIG. It is a figure which shows schematic structure of the example of an image forming apparatus provided with the external electrostatic latent image forming apparatus. It is sectional drawing of the further another example of a reversible image display medium . Fig. (A) is a plan view showing still another example of image display, and Fig. (B) is a graph showing the relationship between the ratio of non-image area (non-image area / medium unit area) and the reflection density ratio. It is. It is a figure which shows schematic structure of the example of an image forming apparatus provided with the direct electrostatic latent image forming apparatus of an ion flow system. It is a figure which shows schematic structure of the other example of an image forming apparatus provided with the direct electrostatic latent image forming apparatus of an ion flow system. It is a figure which shows schematic structure of the further another example of the image forming apparatus provided with the direct electrostatic latent image forming apparatus of an ion flow system. 1 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. It is a figure which shows schematic structure of the example of an image forming apparatus provided with the multi-stylus type electrostatic latent image forming apparatus which has an adjacent control electrode. It is a figure which shows the equivalent circuit of the image forming apparatus provided with the external electrostatic latent image forming apparatus. FIG. (A) is an equivalent circuit in a state where the image carrier and the image display medium are separated from each other. FIG. (B) 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 occurs due to dielectric breakdown, and FIG. (D) is an equivalent circuit in a state where the image carrier and the medium are separated after charge transfer. 1 is a diagram illustrating a schematic configuration of an example of an image forming apparatus including an image erasing apparatus. It is a figure which shows schematic structure of the other example of the image forming apparatus provided with the image erasing apparatus. It is a figure which shows schematic structure of the further another example of the image forming apparatus provided with the image erasing apparatus. It is a figure which shows schematic structure of the example of an image forming apparatus provided with the developer stirring apparatus. It is a figure which shows schematic structure of the other example of the image forming apparatus provided with the developing agent stirring apparatus. It is a figure which shows schematic structure of the further another example of the image forming apparatus provided with the developer stirring apparatus. It is a figure which shows schematic structure of the further another example of the image forming apparatus provided with the developer stirring apparatus. It is a figure which shows schematic structure of the further another example of the image forming apparatus provided with the developer stirring apparatus. It is a figure which shows schematic structure of the further another example of the image forming apparatus provided with the developer stirring apparatus. It is a figure which shows schematic structure of the further another example of the image forming apparatus provided with the developer stirring apparatus. 1 is a diagram illustrating a schematic configuration of an example of an image forming apparatus provided with a preliminary charging device. It is a figure which shows schematic structure of the other example of the image forming apparatus provided with the preliminary charging device. FIG. 3 is a diagram showing an equivalent circuit when a medium is charged before forming an electrostatic latent image in an image forming apparatus provided with an external electrostatic latent image forming apparatus. FIG. (A) is an equivalent circuit in a state where the image carrier and the image display medium are separated from each other. FIG. (B) 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, FIG. (D) is an equivalent circuit in which the image carrier and the medium are separated from each other after charge transfer, and FIG. (E) is when the counter electrode roller is grounded. Is an equivalent circuit. FIG. 10 is a partial cross-sectional view of still another example of the reversible image display medium. FIG. 10 is a partial cross-sectional view of still another example of the reversible image display medium.

Embodiments of the present invention will be described below.
A reversible image display medium according to a preferred embodiment of the present invention basically has the following configuration.
That is, one or two or more developments formed between two sheets facing each other with a predetermined gap, at least one of which is light transmissive, and surrounded by a partition wall It is a reversible image display medium having an agent storage cell and a dry developer contained in each cell. The dry developer contains at least two types of dry developer particles having triboelectric charging properties having different charging polarities and different optical reflection densities.

The reversible image display method shown for reference uses 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 types of developer particles in the dry developer are frictionally charged to different charging polarities, and the inclusion in each cell. A step of moving the developed particles to display an image by forming a predetermined electrostatic field for each pixel in correspondence with an image to be displayed on the developed particles in a state in which the developed particles are frictionally charged; Is a reversible image display method.

  According to these reversible image display media and a reversible image display method using the same, an image to be displayed on the developer particles in a state where the developer particles contained in each cell of the image display medium are frictionally charged. By forming a predetermined electrostatic field for each pixel in correspondence with each other, development is performed by moving the developing particles with a Coulomb force acting between the electrostatic field and the charged developing particles, and an image is displayed with a predetermined contrast. can do.

  The electrostatic field can be formed based on the electrostatic latent image by forming an electrostatic latent image on the outer surface of one of the two sheets, for example. The electrostatic field may be formed simultaneously with the formation of the electrostatic latent image or after the formation of the electrostatic latent image. Such an electrostatic field is used for forming an electrostatic field by applying a bias voltage to a sheet opposite to the sheet on which the electrostatic latent image is formed or by grounding the opposite sheet. May be set to a 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 permeability, and an electrode facing the transparent electrode may be provided on the inner surface of the other sheet.

  In a reversible image display medium provided with an electrode and a reversible image display method using the same, a voltage is applied between the two electrodes in a state where developer particles included in each cell of the medium are frictionally charged. By developing a predetermined electrostatic field for each pixel corresponding to the image to be displayed between both electrodes, the developing particles are moved by the Coulomb force acting between the electrostatic field and the charged developing particles for development. The image can be displayed with a predetermined contrast.

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

  In any type of the reversible image display medium (including the display medium employed in the reversible image display method), in order to obtain a state in which the developer particles contained in the cell are triboelectrically charged, the developer particles are placed in the cell. Prior to encapsulating, it is triboelectrically charged by mixing and stirring, etc., and then encapsulated in the cell, or after encapsulating the developer particles in the cell and mixing and stirring in the cell by applying some energy, triboelectrically charged, or both What is necessary is just to carry out friction charging.

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

  By further mixing and stirring the developer particles and charging them, the contrast can be further improved and the driving voltage can be further reduced.

  In any type of the reversible image display medium (including the display medium employed in the reversible image display method), each of the two sheets has a larger area than the thickness and has a wide area. It can be made of various materials such as synthetic resin and glass, and can be any of a flexible material, a flexible material, a glass plate with poor flexibility, etc. It suffices that at least one of the sheets (sheet on the image observation side) has light transmittance so that the image can be visually recognized. Both sheets may have optical transparency.

  Further, a developer movement suppressing member for suppressing the lateral movement of the dry developer in the developer containing 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.

  Further, the partition wall forming the developer containing 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, unevenness of the developing particles in the cell is suppressed, and a high-quality image with less image unevenness can be displayed. Further, since the gap between the two sheets is maintained at a predetermined value by the spacer, it is possible to display an image with little image unevenness. 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 electrodes, the number, size, shape, distribution, arrangement (regular, irregular), etc. of the developer containing cells in the reversible image display medium are not particularly limited as long as the image can be displayed. 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 can be integrally formed by, for example, bonding and fixing at least a part to at least one of the two sheets by bonding or the like, or by forming the sheet and the like. . However, each of the partition wall, the developer movement suppressing member, and the dedicated spacer is not bonded and fixed to one or both of the two sheets, or formed integrally with the sheet, and between the two sheets, It may be arranged so as not to move with respect to at least one sheet.

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

  The independent type cell CE2 has, for example, a grid pattern (FIG. 1 (D)), a brick fence shape (FIG. 1 (E)), a honeycomb shape (FIG. 1 (F)), and a mode in which triangles are connected (FIG. 1 (G)). ), An embodiment in which corrugated sections are connected (FIG. 1H), an embodiment in which continuous grooves each surrounded by a partition wall are connected (FIG. 1I), and the like.

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

  In any case, as shown in FIG. 1 (A) to FIG. 1 (I), each cell may be continuously formed in other cells so as to be adjacent to other cells, but apart from other cells. It may be formed. The cell arrangement may be regular or irregular. The number of cells may be one. Further, the partition wall w1 may also serve as a spacer for maintaining a predetermined gap between sheets.

  As for the pixels for image display, there may be one case where there is one pixel for one cell, when there are a plurality of pixels in one cell, and when there is one pixel for a plurality of cells. .

  The shape of the developer movement suppressing member may be any of a columnar shape (such as a cylinder, a quadrangular column, or a triangular column), a cone shape (such as a cone, a quadrangular pyramid, a truncated cone, or a quadrangular pyramid), or a wall shape. Various types of developer movement restraining members may be used. The arrangement may be regular or irregular. The columnar member is convenient for firmly bonding it to the sheet. A long wall-like member can be expected to have a large effect of suppressing developer movement. A thin plate-like member among the wall-like members is convenient for securing a desired developer capacity. The height of the developer movement suppressing member is arbitrary. Therefore, it may be arranged so as not to move to either one of the sheets. When it has a height that extends between two sheets, it may also serve as a spacer that maintains the gap between the sheets at a predetermined value.

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

  FIG. 2 (A) shows a state in which a plurality of member rows in which columnar suppressing members CL1 having a rectangular cross section are arranged at intervals in a predetermined direction are arranged in parallel. FIG. 2B shows a state in which the columnar suppressing members CL2 having a circular cross section are arranged in a distributed manner. FIG. 2C shows a state in which a plurality of thin plate-like (wall-like) suppression members CL3 are arranged in parallel. FIG. 2D shows a state in which the columnar suppressing members 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 members CL2 and the thin plate-like (wall-shaped) suppressing members CL3 having the same length are regularly distributed to some extent. FIG. 2F shows a state in which a plurality of columnar suppressing members CL4 each having a rectangular cross section are arranged in an island shape in each of the continuous groove type cells CE1 shown in FIG. FIG. 2 (G) shows a state where one columnar suppressing member 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. 1 (D). Each suppressing member CL1, CL2, CL3, CL4 can also serve as a spacer. In these drawings, 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. In FIG. 2 (F), δ indicates an interval between 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 the non-image display area is too large, it becomes difficult to display an image or the image quality deteriorates. On the other hand, if it is too small, the result is that the area where the spacers are provided is reduced, resulting in non-uniform gaps between the sheets and image unevenness.

  Therefore, the ratio Sn / So of the area Sn of the non-image part in the unit area So (for example, the region of γ1 × γ2 in FIGS. 2A and 2H) provided by the image display medium regardless of the presence or absence of electrodes. It is preferable to set it to 0.0001 or more and 0.5 or less. The unit area So can be set arbitrarily, but may be set so that both the area where the image can actually be displayed and the non-image part area are included. Further, for example, it may be set in a repeating unit in which both an area where an image can actually be displayed and a non-image area are included and repeatedly appear on the medium.

  Alternatively, an image display area provided by one developer containing cell (or a plurality of developer containing cells) in any one developer containing cell (or a plurality of successive developer containing cells). Is the area surrounded by the center line of the partition wall forming the outer contour of the one developer containing cell (or the partition forming the outer contour of the plurality of developer containing cell groups). When the area surrounded by the center line of the wall is Sb, the value of (1-Sa / Sb) relating to the one developer accommodating cell (or the plurality of developer accommodating cell groups) is 0.0001 or more and 0.00. 5 or less is preferable (see FIG. 2I).

  As a result, an image display area area that does not hinder image display can be secured and a high-quality image can be displayed with good contrast, while a spacer such as a spacer by a partition wall, a spacer by a developer movement restraining member, a dedicated spacer, etc. This area can be secured and the gap between the two sheets can be maintained at a predetermined value, thereby suppressing the occurrence of image unevenness.

  In addition, for an image display medium with an electrode, a lead is connected to the electrode, and the lead is preferably provided in a non-image display area such as a partition wall.

  The material of the sheet, cell partition wall, developer movement suppressing member, spacer, etc. is 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 with or without electrodes. In the case where an insulating sheet is used, when it is necessary to apply a bias voltage to the ground potential, 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. The whole may be formed of a conductive material or a material containing a conductive material. In this way, if necessary, the sheet can be easily grounded to the ground potential, or a bias voltage can be applied to the sheet. In addition, when the opposite side sheet is an insulating sheet and a conductive film is formed on its outer surface, regardless of the presence or absence of electrodes, or when the opposite side sheet itself is a conductive sheet, Therefore, even when the image-displayed media are stacked, the image is not easily collapsed, and the image can be held stably.

  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 becomes weak and developability deteriorates, resulting in a decrease in contrast and a decrease in resolution. On the other hand, if the gap between the sheets is too small, the amount of developer that can be contained in the developer containing cell is reduced, and it becomes difficult to obtain the necessary contrast. Further, if the thickness of each sheet, and thus the thickness of the entire medium based on the thickness of each sheet, is too small, the medium is likely to be bent, the uniformity of the gap between sheets cannot be obtained, and image unevenness is likely to occur.

  Therefore, in a reversible image display medium without electrodes, the thickness of each sheet is preferably 5 μm to 100 μm, the gap between both sheets is preferably 20 μm to 300 μm, and the total thickness is preferably 30 μm to 500 μm. .

  Also for the reversible image display medium with electrodes, in order to secure the developer amount and maintain the uniformity of the gap between sheets, the thickness of each sheet is 5 μm to 100 μm, and the gap between both sheets is not limited thereto. May be 20 μm to 300 μm, and the total thickness may be 30 μm to 500 μm.

  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, the surface resistance of the sheet When the value, particularly the surface resistance value of the sheet on the side where the electrostatic field is formed, is small, an electrostatic latent image is formed directly on the surface of the sheet to form an electrostatic field for image display, In any case where the electrostatic latent image is transferred to the surface of the sheet, the electrostatic latent image tends to collapse.

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 / □.

  On the other hand, if the sheet surface resistance value, particularly the surface resistance value on the side opposite to the side on which the electrostatic field is formed, is too large, it will hinder image formation and its holding. In particular, when an electrostatic latent image is directly formed on the sheet surface on the electrostatic field forming side, the latent image charge is difficult to be applied, and when an electrostatic latent image formed externally is transferred, it is difficult to obtain a uniform electric field. Image unevenness is likely to occur. Furthermore, when the media after image formation are overlapped, electrostatic shielding between adjacent media becomes difficult, and the image tends to collapse and is difficult to hold.

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

From the above, in the electrodeless reversible image display medium, the surface resistivity of the outer surface of one of the two sheets is 10 ¹⁰ Ω / □ to 10 ¹⁶ Ω / □, and the outer surface of the other sheet is It is recommended that the surface resistivity be 10 ⁷ Ω / □ or less.

The thickness of each sheet is 5 μm to 100 μm, the gap between both sheets is 20 μm to 300 μm, the total thickness is 30 μm to 500 μm, and the surface resistance of the outer surface of one of the two sheets is within the range without any problem. The rate may be 10 ¹⁰ Ω / □ to 10 ¹⁶ Ω / □, and the surface resistivity of the outer surface of the other sheet may be 10 ⁷ Ω / □ or less.

  The surface resistivity of each sheet can be adjusted, for example, by containing conductive materials (for example, conductive carbon) having different resistance values in the sheet, or by applying a surfactant to the sheet surface.

  For both reversible image display media with and without electrodes, the developers contained in the developer containing cells have different charge polarities and different optical reflection densities (in other words, “contrast It is preferable that at least two types of dry developing particles are included. Representative examples include positively chargeable (or negatively chargeable) black particles having light absorptivity and negatively charged (or positively charged positive) white particles having light reflectivity.

  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 or not the image display medium has an electrode, the presence of such non-conductive particles makes it possible to easily and reliably frictionally charge the two kinds of developing particles, and thus to display a good image. Can be done.

  Further, at least one of the at least two kinds of developing particles constituting the dry developer may be magnetic particles. Regardless of whether the image display medium has electrodes or not, the presence of such magnetic particles allows the developer (development particles) to be stirred by a magnetic field, for example, an oscillating magnetic field, as will be described later. This agitation makes it possible to erase the previous image prior to image formation (image display) and to make the developer particles move easily in the electrostatic field for image display in the image display, and display the image as well.

  In any case, if the developing particles are too small, the adhesion force becomes very large, causing adhesion between the developing particles and a decrease in developing efficiency. 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 must be increased for image display, and thus a high driving voltage is required.

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

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

  One type of developing particles may be 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. What can be used for these is as follows.
-Binder resin A colorant, a magnetic body, etc. can be disperse | distributed and will not be specifically limited if normally used as a binder. A typical example is a binder resin used in 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 Resins, fluorine-based resins, silicon-based resins, copolymers thereof, block polymers, graft polymers, polymer blends, and the like can be used.

The glass transition point Tg may be quite high and in some cases 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 black pigments include carbon black, copper oxide, manganese dioxide, aniline black, and activated carbon.

  Yellow pigments include yellow lead, zinc yellow, cadmium yellow, yellow iron oxide, mineral fast yellow, nickel titanium yellow, navel yellow, naphthol yellow S, banza yellow G, banza yellow 10G, benzidine yellow G, benzidine yellow GR, There are quinoline ero lakes, permanent ero NCGs, tartarine rakes, etc.

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

  Examples of red pigments include bengara, cadmium red, red lead, mercury sulfide, cadmium, permanent red 4R, risol red, pyrazolone red, watching red, calcium salt, lake red D, brilliant carmine 6B, eosin lake, rhodamine lake B, There are Alizarin Lake and Brilliant Carmine 3B.

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

  Examples of blue pigments include bitumen, cobalt blue, alkali blue lake, Victoria blue lake, phthalocyanine blue, metal-free phthalocyanine blue, phthalocyanine blue partially chlorinated, first sky blue, and induslen blue BC.

  Examples of the green facial department include chrome green, chromium oxide, pigment green B, malachite green lake, final yellow green G, and the like.

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

  Examples of extender pigments include barite powder, barium carbonate, clay, silica, white carbon, talc, and alumina white.

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

  These colorants can be used alone or in combination.

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

  In particular, when a white pigment is kneaded with a melt binder resin (binder resin) to obtain developed particles from the kneaded product, the amount of white pigment used is a raw material monomer for white particles in order to obtain sufficient whiteness. 10 parts by weight or more, preferably 20 parts by weight or more with respect to 100 parts by weight. In order to ensure sufficient dispersibility of the white pigment, 60 parts by weight or less, preferably 50 parts by weight or less. It is desirable to be. When the white pigment exceeds 60 parts by weight, the binding property between the pigment and the binder resin and the dispersibility of the pigment deteriorate, and when the white pigment is less than 10 parts by weight, sufficient development particles of other colors can be obtained. Cannot be concealed.

Carbon black is preferable as the black colorant. However, in the case where the developing particles are made magnetic, magnetic particles such as magnetite and ferrite and magnetic fine powders can be used as the colorant.
Other internal additives Examples of internal additives that are preferably used in addition to the binder resin and the colorant include a magnetic material, a charge control agent, and a resistance adjusting agent.
-Charge control agent There is no restriction | limiting in particular as a charge control agent, if a charge is given to a developing particle by triboelectric charge.

  Examples of the positive charge control agent include nigrosine dyes, triphenylmethane compounds, quaternary ammonium salt compounds, polyamine resins, and imidazole derivatives.

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

In addition, metal oxides such as ultrafine silica, ultrafine titanium oxide, ultrafine alumina, nitrogen-containing cyclic compounds such as pyridine and derivatives and salts thereof, various organic pigments, resins containing fluorine, chlorine, nitrogen, etc. are also charged. It can be used as a control agent.
Magnetic substance Magnetic particles and magnetic fine powders can be used, such as ferromagnetic elements and alloys, compounds, etc. containing these, for example, iron such as magnetite, hematite, ferrite, cobalt, nickel, It is sufficient that a conventionally known magnetic material such as an alloy or a compound such as manganese or other ferromagnetic alloy is contained. These magnetic powders have various shapes such as granular, needle-like, and flake-like shapes, and can be appropriately selected and used.
・ Resistance modifiers Some resistance modifiers are equivalent to the above-mentioned magnetic powder and colorant, and metal oxides such as flakes, fibers and powders, graphite, carbon black, etc. are preferably used. Can do.

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

  Necessary ones are selected from the binder resin, magnetic powder, colorant, charge control agent, resistance adjusting agent and other additives as described above, and after mixing them by a predetermined amount, a pressure kneader or 2 Heat kneading with a shaft kneader or the like, and after cooling, coarsely pulverize with a hammer mill, cutter mill or the like. Next, after further finely pulverizing with a jet mill, ang mill, etc., classification is performed using an air classifier or the like until a predetermined average particle diameter is obtained, whereby developer particles are obtained.

A developer having a predetermined charge amount can be prepared by mixing and stirring the particles having different charge polarities and different contrasts (optical reflection densities) thus obtained at a predetermined ratio. At this time, a third component (particles) such as a fluidity improver may be added and mixed.
-About such fluidizers Examples of fluidity improvers include 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, bengara, 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.

  Formation of an electrostatic field for developing particles for image display employing an electrodeless reversible image display medium is intended to be displayed on the surface of one of the two sheets (for example, the image observation side sheet), for example. An electrostatic latent image corresponding to the image to be formed can be formed and formed based on the electrostatic latent image. In this case, the electrostatic field may be formed simultaneously with the formation of the electrostatic latent image or after the electrostatic latent image is formed. The electrostatic field can be formed, for example, by setting a predetermined potential for forming the electrostatic field on a sheet opposite to the sheet on which the electrostatic latent image is formed. The predetermined potential can be set, for example, by 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 may be formed outside the medium using an external electrostatic latent image forming apparatus. The image may be formed by transferring it to the medium surface (sheet surface).

  As a direct electrostatic latent image forming apparatus, various discharge-type electrostatic latent image forming apparatuses that discharge an electrostatic latent image charge on a medium surface according to an image to be displayed and put an electrostatic latent image charge on it, depending on the image to be displayed. Various types of charge injection type electrostatic latent image forming devices that inject charges onto the surface of the medium to place electrostatic latent image charges 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 apparatus having an electrostatic recording head in which recording electrodes are arranged in a predetermined direction (for example, main scanning direction when a sheet is scanned by the apparatus) and adjacent control electrodes are arranged adjacent to the recording electrodes. Can be mentioned.

  As an external electrostatic latent image forming apparatus, an electrostatic latent image corresponding to an image to be displayed is formed on an electrostatic latent image carrier, and the electrostatic latent image on the electrostatic latent image carrier is transferred to the sheet. What is transferred to the surface can be exemplified. Furthermore, an electrostatic latent image corresponding to an image to be displayed on a photoconductor such as a photoconductor is formed, and the electrostatic latent image on the photoconductor is transferred to the sheet surface, For example, an electrostatic latent image corresponding to an image to be displayed on a dielectric is formed, and the electrostatic latent image on the dielectric is transferred to the sheet surface.

  For image display, an electric field forming device including any one of the electrostatic latent image forming devices can be employed.

  As described above, when an electrostatic latent image is formed on an image display medium, whether it is transfer or direct formation, image retention is improved as will be described in detail later. In particular, it is advantageous in terms of image retention when a developer having high fluidity or a developer whose fluidity is enhanced by a developer stirring process prior to image display is used.

  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 apparatus 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 displaying the image.

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

  Accordingly, when displaying an image, the image erasing device includes, for example, an electric field forming device that forms an electric field for moving the developed particles, an image erasing device that includes an agitating device that applies a stirring force to the developed particles, and such an electric field. What contains both the formation apparatus and the stirring apparatus etc. can be employ | adopted suitably.

  For example, while collecting developer particles having the same optical reflection density (in other words, “same contrast” or “same color”) of one of the two types of developer particles under an electric field to one sheet side, If the other developer particles having the same optical reflection density are collected on the other sheet side, the image can be erased, and when the next image is formed, it is only necessary to move the developer particles only in the image portion. Therefore, the image display is smooth, sure, and high quality.

  Further, for example, when the developer (development particles) is stirred, the image is erased, and the charge amount and fluidity of the development particles are improved. In this case, the next image display is smoothly, reliably and high quality. The

  Examples of such an electric field forming device include a device including a pair of electrodes (usually metal) or a dielectric disposed with a reversible image display medium therebetween, and a power supply device for applying a bias voltage thereto.

  In addition, various discharge type electric field forming devices that discharge an image display medium to form an electric field and various charge injection type electric field forming devices that form an electric field by injecting electric charge into a reversible image display medium can be exemplified. 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, and examples of the latter include arranging electrodes in a predetermined direction. In addition, a multi-stylus type electric field forming apparatus having a head in which adjacent control electrodes are arranged adjacent to the electrodes can be exemplified.

Moreover, the following can be illustrated as a stirring apparatus.
A device that forms an alternating electric field on a reversible image display medium.

This apparatus can be used when at least one of the developer particles is insulative.
A device that generates an oscillating magnetic field for a reversible image display medium.

This apparatus 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 (development particles) is stirred, the charge amount and fluidity of the development particles are improved, and the next image display is smoothly and reliably made high quality.

  In addition, when the developer is stirred prior to image display, the charge amount of the developer particles is stabilized, and in this respect, image display can be performed satisfactorily. Furthermore, there is an advantage that the allowable range of chargeability and fluidity of the developer is widened.

  Therefore, for image display, regardless of whether a reversible image display medium with or without electrodes is used, the developer is used together with the image erasing process or separately from the image erasing process. You may stir.

  When an image display medium without electrodes is adopted, for example, an electrostatic latent image corresponding to an image to be displayed on the surface (sheet surface) of the image display medium is formed, and the electrostatic latent image is based on the electrostatic latent image. An electrostatic field for image display is formed simultaneously with image formation or after formation of the electrostatic latent image, and the developer is agitated simultaneously with and / or before formation of the electrostatic field. That's fine.

  For an image display medium having electrodes, an electrostatic field is formed by applying a voltage between the electrodes, and the developer may be stirred before or simultaneously with the formation of the electrostatic field. Regardless of the presence or absence of electrodes, the developer agitation faces the image display medium conveyance path in the electrostatic field formation region by the electric field forming device or the upstream side in the relative conveyance direction of the image display medium with respect to the electric field forming device, for example. This can be done using a stirrer.

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

  In this way, the contrast can be further improved and the driving voltage can be further lowered by stirring the developer for image display.

  When an electrostatic latent image is formed on the surface (sheet surface) of the image display medium when displaying the image in the case of employing the reversible image display medium without electrodes, the surface of the medium is predetermined before the electrostatic latent image is formed. An electrostatic latent image corresponding to an image to be displayed in the charged area may be formed by charging the potential uniformly. Based on the electrostatic latent image, a predetermined electrostatic field is formed for each pixel corresponding to the image to be displayed on the developer particles in the developer containing cell, thereby moving the developer particles to display an image. Also good.

Such an image display method is:
Charged charged developer particles having 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 developer particles are opposed to each other with a predetermined gap, at least one of which is light transmissive The present invention can also be applied to a reversible image display medium sealed between two sheets having the above.

  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 surface of the charged medium, and each pixel corresponding to the image to be displayed on the charged developing particles dispersed in the insulating liquid in the medium based on the electrostatic latent image. A predetermined electrostatic field is formed on the surface.

The image display method is as follows:
Among the outer surfaces, the other half of the surface opposite to the half is different in color and the spherical developer particles different in ion adsorption amount are surrounded by an insulating liquid layer in the insulating holding medium. The present invention can also be applied to an embedded reversible image display medium.

  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 surface of the charged medium, and a predetermined electrostatic field is formed for each pixel corresponding to an image to be displayed on the spherical developer particles based on the electrostatic latent image. An image is displayed by controlling the directions of the surfaces of the spherical developing particles having different colors. More specifically, the spherical developer particles that are surrounded by the insulating liquid layer and are rotatable are reversed by the influence of the electrostatic field, and an image is displayed. The reversal of the spherical developer particles is that the other half of the outer surface of the spherical developer particles is different from the other half in terms of the amount of ion adsorption, and therefore 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 developer particle is opposite in color to the other half, the image can be displayed.

  The electrostatic latent image on the medium is directly formed on, for example, the surface of the medium charged in the charging step, regardless of whether the medium includes cell-encapsulated developer particles, developer particles in an insulating liquid, or rotatable spherical particles. Alternatively, the electrostatic latent image formed on the electrostatic latent image carrier outside the medium can be formed by transfer onto the surface of the medium charged in the charging step.

  The charge polarity of the area of the electrostatic latent image formed on the medium has a different polarity even if it is the same polarity as the charge polarity of the charge area due to uniform charging of the medium surface prior to the formation of the electrostatic latent image. 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 grounding the medium.

  As described above, when the surface of the image display medium is uniformly charged to a predetermined potential in advance and an electrostatic latent image is written in the charged area, the charged developer particles in the developer containing cells or The charged developing particles in the insulating liquid can be moved, or the spherical developing particles can be reversed. Further, an electrostatic field sufficient to hold the moved developer particles and the inverted developer particles at the position is formed. In other words, when the surface of the image display medium is uniformly charged to a predetermined potential in advance and then an electrostatic latent image is written in the charged area, the image retention is improved. In particular, it is advantageous in terms of image retention when a developer having high fluidity or a developer whose fluidity is enhanced by a developer stirring process prior to image display is used. As a result, high-quality images with excellent contrast can be stably displayed over a long period of time.

  It should be noted that the image can be erased by forming a different electrostatic field or forming an alternating electric field for both the medium in which the charged developer particles are dispersed in the insulating liquid and the medium containing the spherical developer particles. The image can be rewritten by forming an electrostatic latent image.

  According to the various reversible image display media described above and the reversible image display method using the same, high-resolution and high-quality images can be stably displayed over a long period of time with good contrast. In addition, afterimages are unlikely to occur, and therefore show good reversibility, and a high-quality image can also be displayed in this respect. It is also possible to reduce the driving voltage. It is also possible to display an image with little image unevenness.

Hereinafter, specific examples of the developing particles and the developer will be described, and specific examples of the reversible image display medium, the reversible image display method, the image forming apparatus, and the like will be described with reference to the drawings.
<Development particles and developer>
・ White developer particles WP
100 parts by weight of thermoplastic polyester resin (softening point 121 ° C., glass transition point 67 ° C.), 40 parts by weight of titanium oxide (manufactured by Ishihara Sangyo Co., Ltd .: CR-50), zinc salicylate complex (Orient Chemical Co., Ltd.) as a negative charge control agent (Product: Bontron E-84) 5 parts by weight were sufficiently mixed with a Henschel mixer, then kneaded with a twin screw extruder and cooled. The kneaded material was coarsely pulverized, then pulverized by a jet pulverizer, and classified by wind to obtain a white fine powder. White fine powders having a volume average particle size of 0.7 μm, 2.1 μm, 10.1 μm, 46.2 μm, and 55.3 μm were obtained.

  Thereafter, 0.3 part by weight of hydrophobic silica particles (Aerosil R-972, manufactured by Nippon Aerosil Co., Ltd.) is added to the white fine powder of each particle size, and mixed with a Henschel mixer to obtain a white particle having substantially the following particle size. Developer particles WP (WP1 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 developer particles BP
100 parts by weight of a styrene-n-butyl methacrylate resin (softening point 132 ° C., glass transition point 65 ° C.), 4 parts by weight of carbon black (manufactured by Lion Oil & Fats, Ketjen Black EC), silica (manufactured by Nippon Aerosil Co., Ltd., # 200) ) And 500 parts by weight of magnetite-based magnetic powder (RB-BL Titanium Kogyo Co., Ltd.) were sufficiently mixed with a Henschel mixer and then kneaded with a bent biaxial kneader.

  The kneaded product was cooled, coarsely pulverized with a feather mill, then finely pulverized with a jet mill, and classified with an air classifier to obtain black particles BP (BPo, BP1 to BP5) having the following volume average particle diameter. .

Particle BPo: Volume average particle diameter 25.0 μm
Particle BP1: Volume average particle diameter 0.8 μm
Particle BP2: Volume average particle diameter 3.0 μm
Particle BP3: Volume average particle diameter 25.1 μm
Particle BP4: Volume average particle diameter 87.7 μm
Particle BP5: Volume average particle diameter 121.0 μm
These black developing particles are magnetic particles.
・ Developer DL
The white particles WP3 (10.1 μm) and the black particles BPo (25.0 μm) are placed in a polyethylene bottle at a ratio of 20 g of white particles and 80 g of black particles, rotated on a ball mill stand and mixed for 30 minutes for development. Agent DL (DLo) was obtained.

  Further, white particles and black particles are combined in the following manner, and 20 g of white particles and 80 g of black particles are put in a polyethylene bottle, rotated on a ball mill base and mixed and stirred for 30 minutes. While making (DL1 to DL9), the following developers De1 to De16 were made as comparative developers.

  In any developer, white particles were negatively charged and 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 Example Developer De1: WP1 (0.7 μm) + BP1 (0.8 μm)
Comparative Example Developer De2: WP2 (2.1 μm) + BP1
Comparative Example Developer De3: WP3 (10.1 μm) + BP1
Comparative Example Developer De4: WP4 (46.2 μm) + BP1
Comparative Example Developer De5: WP5 (55.3 μm) + BP1
Comparative Example 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 Example Developer De9: WP5 (55.3 μm) + BP3
Comparative Example Developer De10: WP1 (0.7 μm) + BP4 (87.7 μm)
Comparative Example Developer De11: WP5 (55.3 μm) + BP4
Comparative Example Developer De12: WP1 (0.7 μm) + BP5 (121 μm)
Comparative Example Developer De13: WP2 (2.1 μm) + BP5
Comparative developer De14: WP3 (10.1 μm) + BP5
Comparative Example Developer De15: WP4 (46.2 μm) + BP5
Comparative developer De16: WP5 (55.3 μm) + BP5
The following developer was also prepared as a comparative developer.
Comparative developer d1
1 g of Sudan Black X60 (trade name, manufactured by BASF) was added to 100 ml of isoparaffin hydrocarbon (trade name: Isopa G, manufactured by Exxon Chemical Co., Ltd.) and sufficiently dissolved and mixed to prepare a colored liquid.

  To this, 10 g of titanium dioxide particles (Ishihara Sangyo Co., Ltd .: CR-50) and 70 g of an IP solvent 1620 solution of 0.5 wt% sulhole Ba-30N (barium sulfonate manufactured by Matsumura Oil Research Co., Ltd.) were mixed. , Sand grinder (manufactured by IGARASHI KIKAI SEIZO CO., Ltd.), 1 mm diameter glass beads (1500 cc) as media, 1/8 GL Bessel with water jacket, cooling water temperature 20 ° C., disk rotation speed Wet grinding was performed by treating at 2000 rpm for 15 hours.

To 100 parts by weight of this concentrated liquid developer, 900 parts by weight of IP solvent 1620 was added for dilution. K. A developer d1 was obtained by carrying out a dispersion treatment at 10,000 rpm for 5 minutes using an auto homomixer type M (manufactured by Tokushu Kika Kogyo Co., Ltd.).
<Reversible image display medium>
・ Reversible image display medium 11
3 and 4 show an example of a reversible image display medium. The medium 11 shown in FIGS. 3 and 4 includes a first sheet 111 and a second sheet 112. These sheets 111 and 112 face each other with a predetermined gap therebetween. A partition wall 113 is provided between the sheets 111 and 112, and a gap between both sheets is secured by the partition wall 113. That is, the partition wall 113 also serves as a spacer between the sheets 111 and 112. Both sheets 111 and 112 are connected and fixed to each other by a partition wall 113.

  The first sheet 111 is formed of, for example, a light transmissive plate such as 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. The first electrode 114 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 indium tin oxide (ITO), for example.

  The second sheet 112 is not necessarily transparent, but is formed of, for example, a light transmissive plate such as 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. Here, the second electrode 115 is 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 wall 113 is formed upright in a grid pattern on the inner surface of the second sheet 112, so that a plurality of developments, each of which is partitioned into a square shape with a part of the partition wall 113 as a partition wall, are formed. An agent storage cell 116 is formed, and one individual electrode 115 a is arranged in each of the cells 116. That is, here, one cell corresponds to one pixel.

  Further, a dry developer DL containing white developer particles WP and black developer particles BP that are frictionally charged with each other is contained in each cell.

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

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

  The individual electrodes 115a that lie along the second electrode 115 in the image display medium 11 have lead portions 110 connected to each other as shown in FIG. 6, and the electrodes as shown in FIG. Connected to the selection circuit 117. 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 from the electrode selection circuit 117, and the display data control unit 119 displays display data output means (for example, 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 one example of an electric field forming apparatus or an image forming apparatus for a reversible image display medium with electrodes.

  Thus, the first electrode 114 in the image display medium 11 is used as a ground electrode, and an electrode that is controlled so that a desired image display is performed by the display data control unit 119 between the electrode 114 and each individual electrode 115a. By applying a predetermined voltage from the positive drive voltage generation circuit 118a or the negative drive voltage generation circuit 118b via the selection circuit 117 and forming a predetermined electric field for each pixel, as shown in FIG. As shown in FIG. 4, the developer particles WP and BP move from the state where the developer particles are mixed in accordance with 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. 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
8 and 9 show other examples of the image display medium. FIG. 8A is a cross-sectional view of the reversible image display medium 12 before image display, and FIG. 8B is a cross-sectional view of an example during image display. FIG. 9 is a plan view in which a part of the medium 12 is cut away.

  The image display medium 12 shown in FIGS. 8 and 9 is a rectangular medium as a whole, and includes a first sheet 121, a second sheet 122, and a partition wall 123 between these sheets.

  The first sheet 121 and the partition wall 123 are integrally formed by heat-molding 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 containing cell 124 is provided between the adjacent vertical partition walls. Each cell 124 contains a developer DL containing white developer particles WP and black developer particles BP that are frictionally charged with each other.

  Both sheets 121 and 122 are heat-sealed at the peripheral edge of the medium 12 to form a sealing portion 120. Of the sealing portion 120, a portion 120 a connected to both ends in the longitudinal direction of the vertical partition wall 123 a and sealing 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 with an interval between adjacent vertical partition walls 123a as pt.

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

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

  As described above, it is preferable that any of the sheets 121 and 122 is formed in the thickness range of 5 μm to 100 μm, and the height h of the partition wall 123a (in other words, the gap between the sheets) is preferably 20 μm to 300 μm. The thickness of the entire medium 12 is preferably 30 μm to 500 μm.

Further, the surface resistivity of the first sheet 121 forming the electrostatic latent image 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 medium 12 can be displayed as an image by the image forming apparatus shown in FIG.

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

  After the surface of the photosensitive drum PC is charged by the charger CH, an image is exposed to the charged area by the exposure apparatus 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, in synchronization with the electrostatic latent image EI on the photosensitive drum PC, the medium 12 is fed between the drum and the electrode roller R1.

  Thus, a predetermined electrostatic field is formed for each pixel on the developer particles BP and WP of the developer DL contained in each cell 124 of the medium 12, and thereby, the Coulomb force acting between the electrostatic field and the charged developer particles. The developing particles move at. Then, as shown in FIG. 8A, the white particles WP and the black particles BP move in accordance with the electric field from the state where the black and white particles WP and BP are mixed in the developer DL as shown in FIG. 8B. To do. 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 display 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 printing.

  In this image display, if the magnetic pole roller R2 is provided and rotated, the developer DL in each cell 124 is agitated and the developer particles BP and WP are easily moved, and a better image can be displayed. The drive voltage can be reduced.

Such a rotating magnetic pole roller R2 can also be adopted for the medium 11 shown in FIG.
-Reversible image display medium 13
FIG. 12 shows 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 a 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.

The medium 13 can also be displayed with a predetermined contrast using, for example, the image forming apparatus shown in FIG. 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 Medium Examples of the other reversible image display medium include the following.
a) A medium in which the developer containing cell has another shape selected from FIG. 1A to FIG.
b) A medium in which the developer movement suppressing member shown in any of FIGS. 2 (A) to 2 (H) is provided in the developer containing cell in the mediums 11 to 13;
c) A medium that employs a developer accommodating cell other than those employed in the mediums 11 to 13 and employs any developer movement suppressing member.

  As described above, each image display medium described with reference to the drawings and the other medium just described can repeat image display and image erasure. Further, the developer particles WP and BP are contained in the cell, and it is not necessary to supply the developer from the outside. As a result, the use of conventional media such as paper and consumables such as developer can be significantly suppressed. In addition, the image forming energy can be reduced by not requiring the heat energy for fusing the toner to the medium unlike the conventional case. Therefore, today's environmental load can be reduced.

  Further, since each medium 11, 12, 13, etc. employs the dry developer DL containing developer particles WP, BP having different colors, the other developer particles BP (or WP) by one developer particle WP (or BP). ) Has a good concealment degree and can display an image with good contrast.

  Further, since the developing particles WP and BP contained in the cells are charged with different charging polarities, and accordingly can easily move by receiving the Coulomb force when displaying the image, the image can be displayed with good contrast in this respect, The previous afterimage is unlikely to occur.

  Further, since the dry developer DL is employed as the developer, the settling and aggregation of the developed particles are difficult to occur, and the contrast is not reduced much in the image display, and stable image display can be performed over a long period of time. Since settling and agglomeration of developing particles are unlikely to occur, an afterimage of the previous display image is also unlikely to occur. Since the dry developer DL has little change with time, a stable image display can be performed for a long time in this respect.

  In addition, since one pixel can be reduced, an image can be displayed with high resolution by doing so.

  As a result, it is possible to stably display an image with excellent contrast, high resolution and high quality over a long period of time.

Next, a specific example medium (example medium) of the reversible image display medium and image display using the medium will be described.
Example 1
A reversible image display medium with electrodes of the type shown in FIGS. 3 to 7 and formed as follows.

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

  Next, using a PET film with an AL deposition layer formed on the entire surface, applying a photoresist, patterning it by exposure, development, and etching, stripping and removing the photoresist layer, and two-dimensionally arranged individual pixels A second sheet 112 having a group of electrodes 115a is formed.

  In the transparent individual pixel electrode group 151a thus formed, for example, as shown in FIG. 6, square electrodes having a length and width of 5 mm are arranged in a grid pattern with an electrode interval of 0.5 mm. The lead part 110 is patterned between the individual electrodes so that a voltage can be applied.

  A portion other than the individual electrodes on the second sheet 112 (a thick film resist was repeatedly applied between the individual electrodes and the surrounding area to form partition walls 113 having a height of 90 μm in a grid pattern (see FIG. 5). Each concave portion of the grid-like partition wall 113 is used as a space of the cell 116, and the developer DL is put up to a height of 90% in the developer 116. The developer DL is a developer DL (DLo) among several examples of the developer described above. Yes, it contains white developing particles WP (WP3 10.1 μm) and black developing particles BP (BPo 25.0 μm).

  Next, after thinly applying the photocurable adhesive 119a only on the partition wall 113, the first sheet 111 is brought into close contact, and the adhesive is cured by ultraviolet irradiation to adhere the sheet 111.

  Thereafter, the periphery of the first and second sheets 111 and 112 was sealed and sealed with an epoxy adhesive 119b as shown in FIG. 3 and the like, and the reversible image display medium of Example 1 was obtained.

  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 each cell space was filled with the developer dl so that no bubbles would enter.

  For the medium of Example 1 described above, +100 V was applied to the electrode corresponding to the pixel to be displayed in black among the individual electrodes 115a, 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 display could be performed as illustrated in FIG.

  Similarly to the medium of Example 1, voltages of +100 V and −100 V were applied to the image display medium E1 (not shown) to display an image, and the image contrast was evaluated together with the medium of Example 1.

  For the evaluation of contrast, the image density of the black part Bk and the white part W was measured using a reflection densitometer (manufactured by Konica: SAKURA DENSITOMETER PDA-65), and the ratio (BK / W) was evaluated. A reflection density ratio of 10.0 or more was judged good (◎), 7.0 or more and less than 10.0 was acceptable (◯), and less than 7.0 was judged as bad (x). Note that the contrast evaluation method is the same in this specification unless otherwise specified.

The evaluation results were as follows.
-Medium of Example 1 The reflection density (BK) of the black part was 1.5, the reflection density (W) of the white part was 0.1, and the reflection density ratio was 15.0 (good).
Comparative medium E1
The black portion had a reflection density of 0.6, the white portion had a reflection density of 0.1, and the reflection density ratio was 6.0, which was poor (×).
(Example 2)
An electrodeless reversible image display medium of the type shown in FIGS. 8 to 10 and formed as follows.

  A base material made of transparent PET was heated and stamped to integrally form a partition wall 123 composed of a plurality of partition walls 123a parallel to the first sheet 121 having an average thickness of 25 μm. Each partition wall 123a has a width α = 20 μm, a height h = 100 μm, and an interval between adjacent partition walls pt = 200 μm.

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

The developer DL is the developer DL (DLo) described above, and includes white developer particles WP (WP3 10.1 μm) and black developer particles BP (BPo 25.0 μm).
(Example 3)
In the medium 12 of the second embodiment, a conductive film 122A is formed on the outer surface of the second sheet 122 by aluminum deposition as shown in FIG. 12, and the other points are the same as those of the medium 12 of the second embodiment.

  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 an image is exposed to the charged area to form an electrostatic latent image EI, while a bias +500 V is applied to the electrode roller R1, and the photosensitive drum PC and the electrode roller R1 The medium 12 was passed between them. 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 constant at θ = 1.

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

  As a comparative example for the media of Examples 2 and 3, a comparative example was made in the same manner as these media, except that each cell space of the media of Example 2 was filled with the developer dl so that no bubbles would enter. A medium E2 (not shown) was also formed.

  For the media of Examples 2 and 3 and the comparative example media E2, images were 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 part was 1.5, the reflection density (W) of the white part was 0.1, and the reflection density ratio was 15.0 (good).
-Medium of Example 3 The reflection density (Bk) of the black part was 1.6, the reflection density (W) of the white part was 0.1, and the reflection density ratio was 16.0, which was good (◎).
-Comparative example medium E2
The black portion had a reflection density of 0.6, the white portion had a reflection density of 0.1, and the reflection density ratio was 6.0, which was poor (×).

Next, the ratio Sn / So of the non-image area Sn in the unit area So provided by the image display medium is set to 0.0001 or more and 0.5 or less, or the value of (1-Sa / Sb) is set. Example media (Examples 4 to 9) and comparative example media E3 to E4, which show that it is preferably 0.0001 or more and 0.5 or less, will be described.
Example 4
In the medium of Example 2 (partition wall thickness α = 20 μm, adjacent partition wall interval pt = 200 μm), the medium has Sn / So of 0.091. This medium has substantially the same structure as the medium of Example 2.

  Evaluation of the image contrast was performed using the image forming apparatus shown in FIG. 11 and displaying an image of the black portion Bk on the right half and the white portion W on the left half as shown in FIG. 13A. . For image formation, the surface of the photosensitive drum PC is charged to +1000 V by the charger CH, and the electrostatic latent image EI is formed by exposing the charged area to the charged area, while a bias of +500 V is applied to the electrode roller R1, A 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 constant at θ = 1.

As a result of the image contrast evaluation, the reflection density of the black part was 1.65, the reflection density of the white part was 0.133, and the reflection density ratio (Bk / W) was 12.4 (◎).
(Example 5)
In the medium of Example 2, the shape and arrangement of the developer containing cells are grid-like as shown in FIG. 1D, the thickness (width) α of the partition walls forming the cells is 20 μm, and the spacing between adjacent partition walls pt Is 200 μm (in other words, the cell size is 200 μm × 200 μm), and Sn / So is 0.174. Others are the same as the medium of Example 2.

  A similar image was formed on this medium using the same image forming apparatus and image forming conditions as those of the medium of Example 4.

As a result of image contrast evaluation, the reflection density of the black part was 1.52, the reflection density of the white part was 0.135, and the reflection density ratio (Bk / W) was 11.2 (（).
(Example 6)
In the electrode-attached medium of Example 1 (cells having a grid pattern), the spatial dimension of the cells 116 is 200 μm × 200 μm, the thickness (width) of the partition wall 113 also serving as the partition wall forming the cells is 20 μm, and Sn / So is a medium with 0.174. Others are the same as the medium of Example 1. .

  With respect to this medium, an image similar to that in FIG. 13A was formed using the same electric field forming apparatus and image forming conditions as those of the medium of Example 1.

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

  A similar image was formed on this medium using the same image forming apparatus and image forming conditions as those of the medium of Example 4.

As a result of the image contrast evaluation, the reflection density of the black part was 1.80, the reflection density of the white part was 0.130, and the reflection density ratio (Bk / W) was 13.8 (◎).
(Example 8)
In the medium of Example 2, as shown in FIG. 2F, a medium in which developer movement suppression column members having vertical and horizontal dimensions β1 × β2 = 60 μm × 10 μm are erected at intervals of δ = 1000 μm in each cell. Sn / So is 0.101. Others are the same as the medium of Example 2.

  A similar image was formed on this medium using the same image forming apparatus and image forming conditions as those of the medium of Example 4.

As a result of evaluating the image contrast, the reflection density of the black part was 1.63, the reflection density of the white part was 0.133, and the reflection density ratio (Bk / W) was 12.3 (◎).
Example 9
In the medium of Example 2, the shape and arrangement of the developer containing cells are grid-like as shown in FIG. 1D, the thickness (width) α of the partition walls forming the cells is 50 μm, and the spacing between adjacent partition walls pt Is a medium in which a developer movement suppression column member having vertical and horizontal dimensions β1 × β2 = 60 μm × 10 μm is set up one by one in each cell, in other words, the cell size is 150 μm × 150 μm. Sn / So is 0.468. Others are the same as the medium of Example 2.

  A similar image was formed on this medium using the same image forming apparatus and image forming conditions as those of the medium of Example 4.

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

  A similar image was formed on this medium using the same image forming apparatus and image forming conditions as those of the medium of Example 4.

  As a result of image contrast evaluation, the reflection density of the black part was 0.90, the reflection density of the white part was 0.186, and the reflection density ratio (Bk / W) was 4.8, which was poor (×).

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

  A similar image was formed on this medium using the same image forming apparatus and image forming conditions as those of the medium of Example 4.

  As a result of image contrast evaluation, the reflection density of the black part was 0.84, the reflection density of the white part was 0.146, and the reflection density ratio (Bk / W) was 5.8, which was poor (×).

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

  The configurations of the media of Examples 4 to 9 described above are summarized in Table 1.

  Table 2 summarizes the image contrast evaluation results for the media of Examples 4 to 9 and the comparative media E3 and E4.

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

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

  In the comparative example medium E3, since the ratio of the non-image portion is too small, the gap between the sheets cannot be maintained, the image unevenness occurs, and the reflection density of the black portion is decreased and the reflection density of the white portion is increased. .

  In the comparative example medium E4, since the ratio of the non-image area is too large, sufficient contrast cannot be obtained. This is because the black solid is displayed in black and white stripes in the black display, and thus the reflection density is lowered. On the other hand, in the white display, the reflection density of the non-image area is large and the white solid has a high reflection density. .

Next, in the reversible image display medium, the thickness of each sheet is 5 μm to 100 μm, the gap between both sheets is 20 μm to 300 μm, the total thickness is 30 μm to 500 μm, one of the two sheets of the medium Example medium showing that the surface resistivity of the outer surface of the sheet is preferably 10 ¹⁰ Ω / □ to 10 ¹⁶ Ω / □, and the surface resistivity of the outer surface of the other sheet is preferably 10 ⁷ Ω / □ or less. Examples 10 to 21) and comparative example media E5 to E12 will be described.
(Examples 10-14, Comparative Example Media E5-E8)
An image display medium in which the surface resistivity of the first sheet 121 and the surface resistivity of the second sheet 122 are variously changed while the thickness of each sheet is 25 μm and the gap between sheets is 100 μm. The medium is the same as that of Example 2 except that the sheet surface resistivity is variously changed.

  In addition to these media, the surface resistivity of the first sheet 121 was adjusted by applying a surfactant to the sheet surface for the media of Examples 15 to 21 to be described later. The surface resistivity of the second sheet 122 was adjusted by making the second sheet contain conductive carbon and changing its content. The surface resistivity was measured in a 65% RH environment according to the measurement method ASTM D-257.

Table 3 shows the media of Examples 10 to 14 and the comparative media E5 to E8.
(Example 15)
In the medium of Example 3 (the medium having the Al deposited film on the second sheet), the surface resistivity of the first sheet 121 is 1.20 × 10 ¹⁵ Ω / □, and the surface resistivity of the second sheet 122 is 8. Medium set to 50 × 10 ⁻¹ Ω / □. Others are the same as the medium of Example 3.
(Examples 16 to 21, Comparative Example Media E9 to E12)
In the medium of Example 15, the medium is obtained by changing the thickness of each sheet and the gap between sheets in various ways while keeping the surface resistivity of each sheet as it is. Others are the same as the medium of Example 15.

  The media of Examples 16 to 21 and the comparative media E9 to E12 are shown together in Table 3.

  For each of the example media (Examples 10 to 21) and the comparative example media E5 to E12, an image as shown in FIG. 13 is formed using the image forming apparatus shown in FIGS. 16 (A) and 16 (B). 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 explained later.

  In this evaluation, the maximum reflection density and the minimum reflection density are measured for each of the black part and the white part, and the average reflection density of each of the black part Bk and the white part W is obtained based on these. From this, the reflection density ratio was obtained. Also in this case, when the reflection density ratio was 10.0 or more, it was judged as good (◯), and when it was smaller than 10.0, it was judged as defective (x).

  Also, image unevenness was evaluated. For the evaluation of image unevenness, the image density of the black portion is measured using a reflection densitometer (manufactured by Konica: SAKURA DENSITOMETER PDA-65), and the difference between the maximum value and the minimum value of the image density is obtained. A value of 2 or less was evaluated as good (◯), and a value larger than that was determined as defective (×).

  These evaluation results are summarized in Table 4. Table 4 also shows a defect mark for those with poor contrast.

From this evaluation result, the thickness of each sheet is 5 μm to 100 μm, the gap between both sheets is 20 μm to 300 μm, the total thickness is 30 μm to 500 μm, and the outer surface of one of the two sheets of the medium is It can be seen that the surface resistivity is preferably 10 ¹⁰ Ω / □ to 10 ¹⁶ Ω / □, and the surface resistivity of the outer surface of the other sheet 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 an electrodeless type in which one sheet is provided with a conductive film like the medium 13 in FIG.

  The image forming apparatus of FIG. 14 includes an ion flow type direct electrostatic latent image forming apparatus CR1. The apparatus CR1 includes a corona ion generating part c1 for generating corona ions, a writing electrode e1 for guiding the corona ions generated in the generating part to the surface of the sheet 121, and an image for displaying positive or negative corona ions. Accordingly, it includes a write electrode control circuit f1 that applies a voltage to the write electrode e1 to guide the pixel 121 on the surface of the sheet 121. The electrode control circuit f1 includes a control power supply and a bias power supply (not shown).

  The corona ion generation part c1 is not limited to this in the shield case c11, but, for example, a gold-plated tungsten wire having a diameter of 60 to 120 μm is stretched to form a corona wire c12. A positive or negative voltage is applied to the wire from the power supply Pc1. (For example, 4 kV to 10 kV) is applied to generate corona ions.

  The write electrode e1 is provided adjacent to the portion of the shield case c11 facing the first sheet 121 of the medium (for example, the medium 13), and the corona ion flow can pass through the through hole provided in the center.

  The electrode control circuit f1 can apply to the electrode e1 an ion extraction voltage corresponding to positive and negative ions to be derived toward the medium 13.

  Thus, the medium 13 is displayed with the second sheet 122 as the ground potential (or by applying a bias voltage having the same polarity as the latent image polarity and smaller than the latent image potential) relative to the apparatus CR1. Depending on the image, the positive or negative corona ions are guided to the pixel-corresponding portion on the surface of the sheet 121, thereby applying an electrostatic latent image charge to the surface of the first sheet 121, and simultaneously forming an electrostatic field. Then, the developed particles in each cell of the medium 13 can be moved to display an image.

  The image forming apparatus shown in FIG. 15 is suitable for an image display medium having no electrode and having no conductive film on one sheet, like the medium 12 shown in FIG. The image forming apparatus of FIG. 15 includes an electrode Ea that contacts the sheet 122 on the side opposite to the sheet 121 on the side on which the electrostatic latent image is formed. Similarly to the case of FIG. 14, a bias voltage may be applied to the electrode Ea. The other points are the same as in the apparatus of 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 part c2 for generating corona ions, a writing electrode e2 for guiding the corona ions generated in the generating part to the surface of the sheet 121, and a positive (or negative) corona ion. And a write electrode control circuit f2 that applies a voltage to the write electrode e2 to guide the pixel 121 on the surface of the sheet 121 in accordance with the image.

  The corona ion generator c2 stretches a corona wire c22 similar to that in the apparatus CR1 shown in FIG. 14 in the shield case c21, and applies a positive (or negative) voltage from the power source Pc2 to the corona ion to generate corona ions. It is something to be made.

  The write electrode e2 is provided adjacent to the portion of the shield case c21 facing the first sheet 121 of the medium 12 or 13 type medium (the medium 12 is shown as a representative example in the figure). It consists of an electrode e22, and a corona ion stream can pass through the central through hole.

  The electrode control circuit f2 includes a control power source Pc21, a bias power source Pc22, and a control unit f21. The control unit f21 applies an ion extraction voltage to the electrodes e21 and e22 according to the polarity of ions to be derived toward the medium 12. 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).

  Further, an electrode roller R1 is provided so as to face the writing electrode e2, and a positive bias voltage is applied thereto from the power source PW1. The roller R1 incorporates a magnetic pole roller R2 that is rotationally driven.

  Thus, according to the image to be displayed while moving the medium 12 relative to the apparatus CR2, and rotating the electrode roller R1 in the medium feeding direction and the magnetic pole roller R2 in the opposite direction, the control unit f21 Under the instruction, for 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. As for the pixel of, the outflow of ions is prevented as shown in FIG.

  In the image evaluation experiment, a positive corona ion is led 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, the portion is charged to + 500V to + 600V, and the like. Only the bias voltage + 250V was applied to the pixels of. As a result, the portion where the positive corona ions are placed is displayed white by the negatively charged white developer particles WP, and the portion where the positive corona ions are not placed is displayed black by the positively charged black developer particles BP, thus displaying an image. It was.

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

  The electrostatic latent image forming apparatuses CR1 and CR2 shown in FIGS. 14 to 16 use the discharge phenomenon. In addition to these apparatuses, various discharge type electrostatic latent image forming apparatuses can be used.

  Further, the image can be displayed even if the image forming apparatus shown in FIGS. 17 and 18 is adopted instead of the image forming apparatus shown in FIGS.

  The image forming apparatus in FIG. 17 includes a multi-stylus type direct electrostatic latent image forming apparatus CR3. The apparatus CR3 includes, for example, a multi-stylus head H3 having a plurality of electrodes e3 arranged in the main scanning direction with respect to the medium 13 and arranged close to the first sheet 121. 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 according to an image to be displayed on each electrode e3. For example, a bias is applied to the second sheet 122 on the opposite side, and the medium 13 is conveyed relative to the head H3, 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. The 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 an adjacent control electrode e41 is arranged adjacent to the recording electrode e4. For example, this head is disposed close to the medium 13, and a voltage about half of the voltage (recording voltage) necessary for image recording (recording voltage) is sequentially applied to the control electrode e41 of the head H4, and the recording voltage about the recording voltage is applied to the recording electrode e4. By applying a half of the image signal voltage, an electrostatic latent image can be formed on the medium located immediately below the recording electrode.

  Here, it will be described that the latent image formation is advantageous by taking an image forming apparatus having an external electrostatic latent image forming apparatus as shown in FIG. 11 as an example.

  An equivalent circuit of the device is shown in FIGS. In these drawings, electrostatic capacitances of an electrostatic latent image carrier such as a photosensitive drum, an image display medium, and an air layer therebetween are denoted as C1, C2, and C0, respectively.

  Assume that an electrostatic latent image carrier (hereinafter referred to as “image carrier”) is applied with a latent image charge Q (potential V at that time) by a charging charger and an image exposure apparatus.

  FIG. 19A shows an equivalent circuit in a state where the image carrier and the image display medium are separated from each other. Since C1 and C2 are much larger than C0, the charge Q does not move, and the medium is static. Not affected by the electrostatic latent image.

  When the image carrier and the medium approach from this state, C0 increases, and the charges charged in C1 and C2 are induced by electrostatic induction, resulting in the state of FIG. 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 of FIG. 19B, the potential differences V1, V2, and V0 induced in the image carrier, the medium, and the air layer by the induced charges are expressed by the following equations (1), (2), and (3). It can be expressed as

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

  A developer is included in the medium. Since the developer particles carry charge under an electric field, the developer layer apparently approximates a conductive layer. That is, the electrostatic capacity C2 of the medium approximates the combined capacity of the upper and lower resin sheets.

  Here, in order to transfer the latent image charge of the image carrier to the medium, it is necessary for the air layer to cause dielectric breakdown and to move the charge. If dielectric breakdown does not occur, when the image carrier and the medium are separated from each other, the state returns to the state shown in FIG. 19A and the latent image is not transferred.

  That is, for example, when V0 is small, particle movement occurs due to an 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 needs to be about 370 V or more according to Paschen's law.

Here, when the bias value Vb = 11000V, V = 1000V, and the ratio of each capacitance is C1: C2: C0 = 18: 5: 12, V0 (potential difference of the air layer) = 480V, Dielectric breakdown occurs and the latent image is transferred.
(However, the ratio of the respective capacitances is considered assuming that the image carrier is a normal organic photoreceptor, the medium is the combined capacity of the above structure, and the air layer has a gap of about 10 μm where dielectric breakdown is likely to occur.)
Thus, the latent image is transferred under the condition that V-Vb is about 1500 V or more. Conversely, under these conditions, electrostatic induction is performed in a state where the image carrier and the medium are close to each other, but the latent image is not transferred.

  In the electrostatic latent image on the image bearing member, charge transfer occurs between the charging unit (1) and the medium, and charge transfer does not occur in the non-charging unit (exposure unit) (2). For this reason, a difference occurs in the surface potential on the medium. The surface potential of the medium after the charge transfer of the charging portion (1) is expressed by the following equation (4), and that of the non-charging portion (2) is expressed by the preceding equation (3).

  FIG. 19C shows an equivalent circuit in a state where charge transfer occurs due to dielectric breakdown. In this state where charge transfer occurs due to dielectric breakdown, the following equation (4) holds.

  In Expression (4), V′0 is the minimum potential difference that can be discharged, and V1 and V2 are Expressions (2) and (3).

  For example, under the set conditions, the surface potential on the medium is about + 265V in the region (1) corresponding to the charged portion and about -340V in the region (2) corresponding to the non-charged portion.

  Here, when an arbitrary bias (or ground) is applied to the counter electrode roller, electric fields in opposite directions are formed in the charged portion (1) and non-charged portion (2) regions, and the developer particles follow the electric field. It can be moved to form an image.

  Thereafter, when the image carrier and the medium are separated from each other, the induced charge is moved, and the surface potential of the medium is changed. The (1) part returns to about +275 V, and the (2) part returns to approximately 0 V, and a latent image can be formed on the medium.

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

  In this way, not only the latent image is brought close to the medium, but also by forming the electrostatic latent image on the medium by transfer, direct formation, etc., even after passing through the opposing area of the electrostatic latent image carrier and the counter electrode. It can be seen that image retention is improved because electrostatic attracting force is generated between the developer particles and the reversible image display medium. In short, it is advantageous to form an electrostatic latent image on the medium. In particular, it is advantageous in terms of image retention when a developer having high fluidity or a developer whose fluidity is enhanced by a developer stirring process prior to image display is used.

  Next, the particle size of the developer particles contained in the developer is preferably an example medium indicating that a volume average particle size of 1 μm to 50 μm is preferable for non-conductive developer particles and a volume average particle size of 1 μm to 100 μm is preferable for magnetic developer particles ( Examples 22 to 30) and comparative example media E13 to E28 will be described.

  All of these media were the same as those in Example 2, except that 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. Is a medium having the same structure as the medium of Example 2.

  These were also evaluated for image contrast. At that time, using the image forming apparatus shown in FIG. 11, as shown in FIG. 13 (A), an image in which the right half was a black portion (Bk) and the left half was a white portion (W) was formed and evaluated.

  The contrast evaluation here is very good (◎) when the reflection density ratio (Bk / W) is 9.0 or more, good (良好) when smaller than 9.0, or better than (7.0), smaller than 7.0. A value of .0 or higher was evaluated as slightly defective (.DELTA.), And a value smaller than 5.0 was determined as defective (x).

  These media and evaluation results are summarized in Table 5. In Table 5, WP1 to WP5 and BP1 to BP5 are non-conductive white developer particles and magnetic black developer particles having the above-described particle sizes, respectively. In Examples 22 to 30, the above-described developers DL1 to DL9 were used, and in Comparative Examples E13 to E28, the above-described comparative developers De1 to De16 were used.

  In each cell showing the examples and comparative examples in Table 5, the upper right side shows the contrast evaluation result, the middle side shows the reflection image density ratio, the lower side shows the reflection density of the black image portion, and the left side shows the reflection of the white image portion. The concentration is shown.

  As can be seen from Table 5, the developer particles contained in the developer have a volume average particle size of 1 μm to 50 μm for non-conductive developer particles (here, white particles) and magnetic developer 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 image erasure processing before image display will be described. In implementing this image display method, the image display medium of Example 2 (herein referred to as medium 12) was employed.

  Each of FIG. 20 to FIG. 22 shows an example of an image forming apparatus that implements this image display method. In particular, an image forming apparatus provided with an image erasing apparatus is shown.

  The image forming apparatus shown in FIG. 20 is the same as the image forming apparatus shown in FIG. 11 (provided that the rotating magnetic pole roller R2 is not provided). The image erasing apparatus EL1 is arranged on the upstream side (in the direction of the straight arrow in the figure).

  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 source PW3. The electrode roller R3 may be grounded. The lower electrode roller R4 is connected to the bias power source PW4. The electrode roller R4 may be grounded.

  According to this image forming apparatus, an electric field corresponding to the potential difference of the bias applied to the electrode rollers R3 and R4 of the image erasing apparatus EL1 is formed on the medium 12 prior to image display, thereby developing particles having different charged polarities. Of the 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. The medium 12 is fed between the photosensitive drum PC and the counter electrode roller R1 after the image erasing process, and a new image is displayed.

  An experiment of image erasure and image formation was performed using the apparatus of FIG. 20 under the following conditions.

  That is, the charged portion potential of the electrostatic latent image on the photosensitive drum PC was −800 V, the uncharged portion (exposed portion) potential was −100 V, and the bias applied to the counter electrode roller R1 was −100 V. In the erasing apparatus EL1, the electrode roller R4 is grounded, and the bias applied to the electrode roller R3 is + 1000V. The developer receives a coulomb at 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, the black particles move to the lower side in the figure, and the previously displayed image is the entire surface. Will be erased. At this time, when the medium 12 was viewed from the upper side in the figure, the entire surface was white.

  Thereafter, on the medium 12 on which the entire image has been erased, an electric field is formed in accordance with 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 a coulomb. The charged portion on the photoconductive drum PC generates a 700V upward electric field in the figure due to the potential difference from the bias of the electrode roller R1, the white particles move downward, and the non-charged portion has no potential difference, so the particles move. The white particles remained on the top surface. When the image formed in this way was viewed from the upper side in the figure, the area corresponding to the charged part was a black part, and the area corresponding to the non-charged part was a white part.

  In this way, an image can be formed simply by moving the developing particles according to the charging portion. For this reason, 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 port R1 was −800 V. In the erasing apparatus EL1, the bias of the electrode roller R4 is +1000 V, and the electrode roller R3 is grounded.

  In this case, after the medium 12 passed between the electrode rollers R4 and R3, the white particles moved to the lower side in the figure and the black particles moved to the upper side in the figure, and the previously displayed image was erased over the entire surface. At this time, when the medium 12 was viewed from the upper side in the figure, the entire surface was black.

  Thereafter, a non-charged portion of the photosensitive drum PC forms a downward electric field of 700 V in the figure due to a potential difference from the bias of the counter electrode roller R1, and white particles move upward. It did not move and the white particles remained below. When the image formed in this way was viewed from the upper side in the figure, the region 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 of FIG. 21, the electrode roller R1 is opposed to the ion flow type electrostatic latent image forming apparatus CR1 shown in FIG. 14, and the same image erasing apparatus EL1 as shown in FIG. Is provided.

  The image forming apparatus shown in FIG. 22 is the same as the image forming apparatus shown in FIG. 20, except that a rotating magnetic pole roller R2 is built in the lower electrode roller R4 of the erasing device EL1. The other points are the same as the apparatus of FIG. The rotating magnetic pole roller R2 is rotationally driven in one direction or reciprocally rotated to form an oscillating magnetic field with respect to the medium 12. As a result, the developer DL is agitated by affecting the black magnetic developer particles BP. This developer agitation increases the triboelectric charge amount of the developing particles, increases the moving speed due to the Coulomb force in image display, improves the fluidity of the developing particles, and increases the moving efficiency of the developing particles.

  The image erasing apparatus can also be applied to the image forming apparatus shown in FIGS.

  Next, an image display method for stirring the developer for image display will be described. In implementing this image display method, the image display medium of Example 2 (herein referred to as medium 12) was employed.

  Each of FIG. 23 to FIG. 29 shows an example of an image forming apparatus that implements this image display method. In particular, an image forming apparatus including a developer stirring device is shown. In the image forming apparatus shown in FIG. 4, the rotating magnetic pole roller R2 is provided. In the image forming apparatus shown in FIG. 11, the rotating magnetic pole roller R2 is built in the developing electrode roller R1 facing the photosensitive drum PC. The magnetic roller R2 also functions as a developer stirring device when the R2 is rotationally driven in one direction or reciprocally rotated.

  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 charged portion potential of the photosensitive drum PC was + 500V, the non-charged portion (exposed portion) potential was + 100V, and the bias applied to the developing electrode roller R1 was + 300V. Further, the magnetic pole roller R2 inside the electrode roller R1 was rotated in the left direction (counterclockwise) in the drawing, with a maximum magnetic flux density of 400 gauss, a magnetic pole number of 8, and a rotational speed of about 100 rpm.

  Under such conditions, the white particles WP corresponding to the charged sites are subjected to a force upward in the figure against the direction of the electric field, and the black particles BP are subjected to a force downward in the figure along the direction of the electric field, and at the same time, the black particles BP Was disturbed by the oscillating magnetic field, and the developed particles moved efficiently.

  The image forming apparatus of FIG. 23 has a developing electrode roller R1 disposed opposite to the ion flow type electrostatic latent image forming apparatus CR1 in the image forming apparatus shown in FIG. 14, and a rotating magnetic pole roller R2 is incorporated in the roller. Is.

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

  Under such conditions, the white particles WP corresponding to the charged sites are subjected to a force upward in the figure against the direction of the electric field, and the black particles BP are subjected to a force downward in the figure along the direction of the electric field, and at the same time, the black particles BP Was stirred by the oscillating magnetic field, and the developed particles moved efficiently.

  The image forming apparatus described above can be broadly grasped as a static image corresponding to an image to be displayed on the outer surface of one of the two sheets of the reversible image display medium. In this example, an electrostatic latent image is formed and formed simultaneously with the formation of the electrostatic latent image based on the electrostatic latent image, and the developer is stirred simultaneously with the formation of the electrostatic field.

  The image forming apparatus shown in each of FIGS. 24 and 25 to be described next broadly captures the electrostatic field formed in the image display process on either outer surface of two sheets of the reversible image display medium. After forming an electrostatic latent image corresponding to the image to be displayed, the electrostatic latent image is formed based on the electrostatic latent image, and the developer is stirred to form the electrostatic latent image and then simultaneously with the electrostatic field formation. Is.

  In the image forming apparatus of FIG. 24, a transfer electrode roller R5 for transferring an electrostatic latent image is disposed at a position where the developing electrode roller R1 is located in the image forming apparatus of FIG. 11, and the photosensitive drum PC, the transfer electrode roller R5, and the like. A developing electrode roller R1 for forming an electrostatic field and a rotating magnetic pole roller R2 built in the developing electrode roller R2 are disposed downstream of the facing region.

  A bias power source PW5 is connected to the transfer electrode roller R5, and a bias power source PW1 is connected to the electrode roller R1.

  In the image forming apparatus of FIG. 25, the counter electrode roller R5 for transferring the electrostatic latent image is disposed at the position where the developing electrode roller R1 is 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 incorporated in the developing electrode roller R2 are arranged downstream of the region facing the roller R5.

  A bias power source PW5 is connected to the counter electrode roller R5, and a bias power source PW1 is connected to the electrode roller R1.

  24 and 25, after the electrostatic latent image is formed on the medium 12 in the region where the photosensitive drum PC or the electrostatic latent image forming device CR1 and the transfer (counter) electrode roller R5 face each other. When the medium comes into contact with the developing electrode roller R1, an electrostatic field for each pixel is formed according to the electrostatic latent image, thereby displaying an image. At this time, the magnetic pole roller R2 is rotationally driven in one direction or reciprocally driven to generate an oscillating magnetic field, and an image is displayed while developing particles are stirred by the influence of the magnetic field. As the developer particles are stirred, the charge amount of the developer particles is increased, and the fluidity of the developer particles is improved. As a result, images are displayed smoothly and satisfactorily.

  The magnetic pole roller R2 may be disposed between the electrode rollers R1 and R5.

  The image forming apparatus shown in FIG. 26 and FIG. 27 to be described next will display the electrostatic field formed in the image display process on the outer surface of one of the two sheets of the reversible image display medium. An electrostatic latent image corresponding to the image to be formed is formed, and formed based on the electrostatic latent image simultaneously with the electrostatic latent image formation or after the electrostatic latent image formation. This is an example performed before forming a latent image.

  The image forming apparatus shown in FIG. 26 does not include a magnetic pole roller in the electrode roller R1 in the image forming apparatus shown in FIG. 11, and a rotating magnetic pole roller R2 is disposed upstream of the region where the photosensitive drum PC and the electrode roller R1 are opposed to each other. Is. The magnetic pole roller R2 is rotationally driven in one direction or reciprocally rotated, thereby forming an oscillating magnetic field for stirring the developer.

  A bias power supply PW1 is connected to the electrode roller R1.

  In this image forming apparatus, when the charged portion potential of the photosensitive drum PC is +500 V, the non-charged portion (exposure portion) potential is +100 V, and the bias applied to the developing electrode roller R1 is +300 V, the white particles corresponding to the charged portion have an electric field. The black particles moved upward along the direction of the electric field and downward along the direction of the electric field. Since the developing particles are agitated in advance, the charge amount is increased and the fluidity is improved, and the developer particles move efficiently.

  The image forming apparatus in FIG. 27 is the same as the image forming apparatus in FIG. 24 except that the rotating magnetic pole roller R2 is disposed upstream of the region where the photosensitive drum PC and the electrode roller R5 are opposed. The magnetic pole roller R2 is rotationally driven in one direction or reciprocally rotated, 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 developer particles BP may be biased to any one in the developer containing cell due to the magnetic field generated by one magnetic pole roller R2. If this apparatus is grasped extensively, a plurality (two in this case) of developer agitating devices that form an oscillating magnetic field are sequentially provided along the medium conveyance direction.

  In the example shown in FIG. 28, in the image forming apparatus shown in FIG. 11, two developing magnetic pole rollers R1 incorporating a rotating magnetic pole roller R2 are arranged opposite to the photosensitive drum PC. Power sources PW1, PW 'are connected to the rollers R1, R1. The two rotating magnetic pole rollers R2 are rotationally driven in opposite directions. Thereby, the bias | inclination in the cell of a magnetic developing particle (here black particle BP) can be suppressed.

  In the image forming apparatus shown in FIG. 29, in place of the developing electrode roller R1 and the magnetic pole roller R2 in the image forming apparatus shown in FIG. 24, a magnet member Mg provided with alternating N and S poles is provided downstream of the photosensitive drum PC. Further, it is arranged so as to be in contact with the incoming medium 12, and a developing bias power supply PW1 "is connected to the member Mg.

  As the medium 12 moves relative to the member Mg, an oscillating magnetic field is formed on the medium 12.

  Next, when an image is displayed, an electrostatic latent image is formed on the surface (sheet surface) of the image display medium, and the surface of the medium is uniformly charged to a predetermined potential before the electrostatic latent image is formed. An image display method for forming a latent image will be described. In implementing this image display method, the image display medium of Example 2 (herein referred to as medium 12) was employed.

  Each of FIG. 30 and FIG. 31 shows an example of an image forming apparatus that implements this image display method. In particular, an image forming apparatus including a charging device that uniformly charges a medium surface to a predetermined potential before forming an electrostatic latent image is shown.

  The image forming apparatus shown in FIG. 30 does not include the magnetic pole roller R2 in the developing electrode roller R1 in the image forming apparatus shown in FIG. 11, and the preliminary charging device 2 is located upstream from the region where the photosensitive drum PC and the electrode roller R1 face each other. It is equipped with. The charging device 2 includes a charger 21 facing the surface of the conveyed medium 12 on the electrostatic latent image forming side, and a ground electrode 22 facing the medium passage with the medium passage therebetween. The electrode roller R1 may be grounded depending on circumstances.

  The image forming apparatus shown in FIG. 31 is the same as the image forming apparatus shown in FIG. 21, except that the image erasing apparatus EL1 on the upstream side of the electrostatic latent image forming apparatus CR1 is provided with the same preliminary charging device 2 as described above. The electrode roller R1 may be grounded depending on circumstances.

  In these image forming apparatuses, the surface of the medium 12 is uniformly charged in advance by a preliminary charging device prior to image display. 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, the electrostatic latent image is written by the electrostatic latent image forming apparatus CR1. In any example, the area charged uniformly in advance and the area where the electrostatic latent image is written later have opposite polarities. By setting the bias of the electrode roller R1 to the ground or appropriately setting the potential, the direction of the electric field differs 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, the dielectric breakdown inside the medium 12 can be prevented by charging the surface of the medium 12 uniformly with a polarity opposite to the polarity of the electrostatic latent image formed later. The latent image can be transferred reliably. As described above, since the electrostatic latent image is reliably transferred, the image retention is improved.

  In the example shown in FIG. 31, the potential difference between the image portion and the non-image portion can be increased when forming the electrostatic latent image. For example, the negatively charged uniform charged portion by preliminary charging by the charging device 2 is set to -1000 V, the positive charged portion by electrostatic latent image writing is set to +1000 V, and the bias of the electrode roller R1 is grounded, thereby preventing the image portion from being non-imaged. Each image portion has a potential difference of 1000 V, which can drive the developing particles. Thus, the developing particle driving electric field can be increased, and the moving speed of the developing particles can be increased.

  It should be noted that the area charged uniformly in advance and the area where the 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 direction of the electric field is 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, since the medium 12 passes through the photosensitive drum PC or the area where the electrostatic latent image forming apparatus CR1 and the electrode roller R1 face each other, an electrostatic attracting force is generated between the developer particles and the sheet of the medium. Good retention.

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

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

  Further, the electrostatic latent image forming apparatus is not limited to the one shown in FIGS. 30 and 31, and the other electrostatic latent image forming apparatus described above can be adopted.

  Here, it is advantageous to uniformly charge the surface of the medium before forming the electrostatic latent image on the surface of the medium and form an electrostatic latent image in the charged area, as shown in FIG. An image forming apparatus provided with an electrostatic latent image forming apparatus will be described as an example.

  An equivalent circuit of the device is shown in FIGS. In these drawings, electrostatic capacitances of an electrostatic latent image carrier such as a photosensitive drum, an image display medium, and an air layer therebetween are denoted as C1, C2, and C0, respectively.

  The electrostatic latent image carrier (hereinafter referred to as “image carrier”) is charged with a charging charger and an image exposure device, and the latent image charge Q (the potential V at that time) is preliminarily charged to the medium with a preliminary charging device. Is applied.

  FIG. 32A shows an equivalent circuit in which the image carrier and the image display medium are separated from each other. Since C1 and C2 are very large compared to C0, the charge Q does not move, and the medium is static. Not affected by the electrostatic latent image.

  When the image carrier and the medium approach from this state, C0 increases, and the 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 of FIG. 32B, the potential differences V1, V2, and V0 induced in the image carrier, the medium, and the air layer by the induced charges are expressed by the following equations (5), (6), and (7). It can be expressed as Here, let us consider a case where a ground is applied without applying a bias.

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

  A developer is included in the medium. Since the developer particles carry charge under an electric field, the developer layer apparently approximates a conductive layer. That is, the electrostatic capacity C2 of the medium approximates the combined capacity of the upper and lower resin sheets.

  Here, in order to transfer the latent image charge of the image carrier to the medium, it is necessary for the air layer to cause dielectric breakdown and to move the charge. If dielectric breakdown does not occur, when the image carrier and the medium are separated from each other, the state returns to the state shown in FIG. 32A and the latent image is not transferred.

  That is, for example, when V0 is small, particle movement occurs due to an 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 needs to be about 370 V or more according to Paschen's law.

Here, when V = 1000 V, V ′ = − 1000 V, and the ratio of the respective capacitances is C1: C2: C0 = 18: 5: 12, V0 (potential difference of the air layer) = 480 V, and dielectric breakdown occurs. Then, the latent image is transferred. Further, the potential difference applied to the medium is about 200 V, and dielectric breakdown inside the medium can be prevented. (However, the ratio of the respective capacitances is considered assuming that the image carrier is a normal organic photoreceptor, the medium is the combined capacity of the above structure, and the air layer has a gap of about 10 μm where dielectric breakdown is likely to occur.)
In the electrostatic latent image on the image bearing member, the charge portion (1) moves between the medium and the non-charged portion (exposure portion) (2). For this reason, a difference occurs in the surface potential on the medium. The surface potential of the medium after the charge transfer of the charged part (1) is expressed by the following expression (8), and that of the non-charged part (2) is expressed by the previous expression (7).

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

  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 set conditions, the surface potential on the medium is about + 260V in the region (1) corresponding to the charged portion and about -340V in the region (2) corresponding to the non-charged portion.

  Here, when the counter electrode roller is grounded, electric fields in opposite directions are formed in the areas of the charging portion (1) and the non-charging portion (2), and the developer particles move along the electric field to form an image. be able to.

  Thereafter, when the image carrier and the medium are separated from each other, the induced charge is moved, and the surface potential of the medium is changed. The (1) part returns to about -720 V, and the (2) part returns to about -1000 V, so that 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 in a grounded state, an appropriate bias can be applied to the roller. In this case, V ′ may be replaced with V ′ + Vb. FIG. 32E shows an equivalent circuit in this case.

  Further, 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 charged polarity of the developer particles may be reversed.

  In this way, 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, thereby suppressing the potential difference inside the medium. This can improve the image retention.

  Next, still another example of the reversible image display medium will be described with reference to FIGS. 33 and 34. FIG.

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

  The medium 14 includes an electric field coloring layer 140 supported on a transparent support substrate 146. The electric field coloring layer 140 is obtained by sealing a liquid layer 143 in which charged colored particles 141 are dispersed in an insulating liquid 142 between the transparent conductive layer 144 and the insulating layer 145. The insulating liquid 142 is obtained by mixing an organic substance containing an ionic surfactant and a dye with high-purity petroleum (trade name Isopar, Esso). The ionic surfactant is adsorbed on the organic colored particles 141 containing the pigment, and the particles are stably charged electrochemically. The charged colored particles 141 are dispersed in the liquid 142 and exhibit electrophoretic properties.

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

  For the image display on the medium 14, for example, using the image forming apparatus shown in FIG. 30 or FIG. 31, the surface of the medium 14 is uniformly charged to a predetermined potential in advance before the image display. An electrostatic latent image EI is formed and corresponds to an image to be displayed on charged developing particles (here, charged colored particles) 141 dispersed in the insulating liquid 142 in the medium based on the electrostatic latent image. An image can be displayed by forming a predetermined electrostatic field for each pixel.

  In this way, the surface of the medium 14 is charged in advance prior to the formation of the electrostatic latent image, and the electrostatic latent image is formed in the charged region, so that the preliminary charging is performed as in the image display by the conventional electrophoretic image display medium. As compared with the case where the image is formed without the image retention, the image retention is improved.

  A reversible image display medium 15 shown in FIG. 34 is an example of a rotating particle sphere display medium.

  This medium 15 has an electric field coloring layer 150 supported by a transparent support substrate 156. The electric field coloring layer 150 surrounds a single-sided colored sphere 151 colored 151a on one side with an insulating liquid 152 and embeds the liquid together in an insulating holding medium 153, and a transparent conductive layer 154 on one side of the medium 153 and an opposite side. An insulating layer 155 is formed.

The single-sided colored sphere 151 is produced, for example, by uniformly disposing glass white spheres containing TiO ₂ as a main component on a suitable table and evaporating chromium or the like from the upper surface. The size may be in the range of 30 μm to 100 μm, but if it is 10 μm or less, the resolution becomes higher.

  The single-sided colored sphere 151 is dispersed in an insulating holding medium 153 such as an elastomer, and the medium 153 is swollen by immersing it in a solution obtained by dissolving an ionic surfactant in an organic solvent such as toluene. Thereby, the insulating liquid 152 is accumulated around the single-sided colored sphere 151. Thus, the single-sided colored sphere 151 is surrounded by the insulating liquid layer 152, and a state where the liquid is embedded in the insulating holding medium 153 in a rotatable state is obtained.

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

  For the image display using the medium 15, for example, using the image forming apparatus shown in FIGS. 30 and 31, the surface of the medium 15 is uniformly charged to a predetermined potential in advance before the image display. An electrostatic latent image EI is formed, and a predetermined electrostatic field is generated for each pixel corresponding to an 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. An image can be displayed by forming. As a result, the image can be displayed with good image retention.

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

  Note that the mediums 14 and 15 may form images with the other image forming apparatuses described above as long as the images can be displayed satisfactorily.

  The present invention can be used to provide a reversible image display medium and a reversible image display method capable of repeatedly performing image display and image erasure.

CE1 Continuous groove shaped developer containing 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 Inhibitor of developer movement Members β1, β2 Vertical and horizontal dimensions γ1, γ2 of the columnar developer movement suppressing member Vertical and horizontal dimensions DL, DLo of one unit of the image display area Developer WP White developer particle BP Black developer particle 11 Reversible image display medium 111 First Sheet 112 Second sheet 113 Partition 114 First electrode 115 Second electrode 115a Individual electrode (pixel electrode)
116 Developer accommodating cell 110 Lead section 117 Electrode selection circuit 118a Positive drive voltage generation circuit 118b Negative drive voltage generation circuit 119 Display data control section Bk Black display portion W White display portion 12 Reversible image display medium 121 First sheet 122 Second sheet 123 Partition 123a Vertical partition wall 124 Developer containing cell 120 Sealing portion 120a Sealing portion 120 PC Photosensitive 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 apparatus c1 Corona ion generation unit c11 Shield case c12 Corona wire e1 Write electrode f1 Write electrode control circuit Ea Ground electrode CR2 Ion flow type Directly Electro-latent image forming apparatus c2 Corona ion generator 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 power supply Pc22 Bias power supply f21 Control part R3 Electrode roller PC20 Power supply CR3 Multi-stylus system Direct electrostatic latent image forming device e3 electrode H3 multi-stylus head CR4 multi-stylus type electrostatic latent image forming device e4 having adjacent control electrode recording electrode e41 control electrode H4 electrostatic recording head EL1, EL2 image erasing device R5 transfer electrode roller PW5 Power source Mg Member PW1 ′ provided alternately with N and S poles Development bias power source 2 Precharging device 21 Charger 22 Ground electrode 14 Electrophoretic reversible image display medium 140 Electric field coloring layer 141 Charged colored particles 142 Insulating liquid 43 Liquid layer 144 Transparent conductive layer 145 Insulating layer 146 Support substrate 15 Rotating particle sphere type reversible image display medium 150 Electric field coloring layer 151 Single-sided colored sphere 151a Coloring 152 Insulating liquid 153 Insulating holding medium 154 Transparent conductive layer 155 Insulating layer 156 Support substrate

Claims (1)

Two sheets facing each other with a predetermined gap, at least one of which is light transmissive,
One or more developer containing cells formed between the two sheets and surrounded by a partition wall;
A reversible image display medium in which an image is formed by forming an electrostatic latent image on one outer surface of the two sheets. ,
The dry developer includes at least two types of dry developing particles having triboelectric charging properties having different charging polarities and different optical reflection densities from each other.
The surface resistivity of the outer surface of the side of the sheet on which an electrostatic latent image is formed on Ri ^{10 10 Ω / □ ~10 16 Ω} / □ der,
A reversible image display medium characterized in that the surface resistivity of the outer surface of the sheet opposite to the side on which the electrostatic latent image is formed is 10 ⁷ Ω / □ or less .

Images