JP2002174830A - Reversible image display medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a reversible image display medium which can be repeatedly used and can display high-quality images. SOLUTION: The reversible image display medium 13 houses a developer DL in cells 116 between two substrates 111, 112, and the developer DL contains at least two kinds of dry developer particles WP and BP having triboelectrification property and having different electrification polarity from each other and different optical reflection density from each other [with (the volume average particle size of BP)>=(volume average particle size of WP)]. An electrostatic latent image is formed on one substrate 111 and the developer particles are driven by the electric field produced by the electrostatic latent image to display an image. The ratio of the volume average particle size in the two kinds of dry developer particles WP, BP [=(volume average particle size of the developer particles BP)/(volume average particle size of WP)] is >=1 and <=10.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

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

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

[0004]

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

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

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

In this regard, in the image display on a display such as a CRT display, image display and image deletion can be repeated. However, the image displayed on the display has a lower resolution than the image displayed on a paper or the like by a printer or the like, and there is a limit to obtaining a clear and fine image. Since the resolution is low, it is not suitable for displaying a text document mainly composed of characters. A sentence or the like that fits into about one screen is still good, but a sentence or the like that continues over a plurality of screens is difficult to read and sometimes difficult to understand. In addition, eyes are very apt to be tired in long-term visual work due to relatively low resolution and light emission from the display.

As an image display method capable of repeating image display and image deletion, electrophoretic display (EP
D) and twisted ball type display (TBD) have been proposed. More recently, the method introduced in "Japan Hardcopy '99 Transactions PP249-252" has been proposed.

In the electrophoretic display method, a sealed space is formed by arranging two substrates, at least one of which is transparent, at an interval with a spacer interposed therebetween to form a sealed space, in which particles having electrophoretic ability are formed. It is filled with a display liquid dispersed in a dispersion medium of a different color, and displays images in the color of the particles or the color of the dispersion medium by migrating particles in the display liquid in an electrostatic field. is there.

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

However, in this electrophoretic display,
Since the contrast between the high refractive index particles (inorganic pigment) such as titanium dioxide and the insulating colored liquid is displayed, the degree of concealment of the colored liquid is inevitably low, and the contrast is reduced.

Furthermore, the types of dyes that can be dissolved in a high-concentration nonpolar solvent at a high concentration so as to enable electrophoresis of particles are limited. No black dye is known. Therefore, the background part is inevitably colored, and it is difficult to make the background part white and improve the contrast. When white particles for forming an image are put in the colored liquid, the colored liquid may enter between the substrate and the white particle layer moved to the image observation side substrate, or the colored liquid may be mixed between the white particles. And the contrast is reduced. Also, the resolution of the electrophoretic particles is low because it is difficult for the particles to be uniformly attached to the image observation side substrate.

Further, since 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 agglomerate,
The display contrast tends to decrease, and it is difficult to display images stably for a long period of time, and the previous display afterimage tends to occur. Further, the charging of the particles in the liquid greatly changes with time, and in this respect, the image display stability is also poor.

The twisting ball type display method holds a large number of microcapsules in which microspheres treated so that the half and the other half of the surface show different colors or optical densities together with an insulating liquid inside. Using an image display medium, a microsphere in the microcapsule is rotated by an electric field or a magnetic force to display an image in a predetermined color.

However, in this twisted ball type display, an image is displayed with microspheres in an insulating liquid in the microcapsules, so that it is difficult to obtain a good contrast, and in particular, resolution is low because a gap is formed between the microcapsules. . It is difficult to reduce the size of the microcapsule in order to improve the resolution in manufacturing the capsule.

"Japan Hardcopy '99 Transactions PP249
The image display method introduced in 252252 ”is a method in which two substrates each having an electrode and a charge transport layer laminated thereon are opposed to each other at a predetermined interval to form a sealed space, in which a conductive toner and a conductive toner and a conductive toner are formed. Insulating particles having different colors are enclosed, an electrostatic field is applied to charge and charge the conductive toner, and the conductive toner is moved by Coulomb force to display an image.

However, in the image display method utilizing the charge injection phenomenon, when the charge-injected conductive toner moves,
Insulating particles (for example, white particles that are put together to obtain the background color) hinder the movement of the conductive toner, and some toners stop moving. As a result, sufficient image density and contrast cannot be obtained, and the image display speed decreases. In order to solve this problem, high voltage driving is required. Also, the resolution is limited to the resolution determined by the electrodes. In addition, it is essential to employ an electrode, a charge injection layer, and a conductive toner, and there is a limitation in manufacturing.

Therefore, according to the present invention, image display and image erasure can be repeatedly performed, so that the use of consumables such as an image display medium such as paper and a developer and ink related to the conventional image formation can be reduced. It is an object of the present invention to provide a reversible image display medium capable of responding to today's environmental load reduction.

Another object of the present invention is to provide a reversible image display medium capable of displaying a high-contrast, high-quality image.

It is another object of the present invention to provide a reversible image display medium capable of displaying a high-resolution image with a high resolution.

Another object of the present invention is to provide a reversible image display medium capable of displaying images stably for a long period of time.

Another object of the present invention is to provide a reversible image display medium which is less likely to cause an afterimage and therefore exhibits good reversibility and can display a high quality image in this respect as well.

Still another object of the present invention is to provide a reversible image display medium capable of displaying images at high speed.

Another object of the present invention is to provide a reversible image display medium which requires a low drive voltage for image display.

[0025]

The reversible image display medium according to the present invention basically has the following structure. That is,
Two substrates facing each other with a predetermined gap;
One or two or more developer storage cells formed between two substrates and surrounded by a partition wall, and a dry developer included in each of the cells, wherein the dry developer includes: This is a reversible image display medium containing at least two types of triboelectrically-charged dry-developed particles having different charging polarities and different optical reflection densities.

At least one of the dry developing particles may be a magnetic developing particle.

This reversible image display medium forms an electrostatic field corresponding to an image to be displayed on the developing particles in a state where the developing particles contained in each cell in the image display medium are triboelectrically charged. Thereby, the developing can be performed by moving the developing particles by Coulomb force, and an image can be displayed.

The electrostatic field corresponding to the image to be formed can be obtained by providing electrodes on each of the medium constituting substrates, applying a voltage corresponding to the image to be formed between the electrodes, or forming the image to be formed on one of the substrates. Can be formed by forming an electrostatic latent image corresponding to.

Further, such a reversible image display medium has two substrates facing each other with a predetermined gap therebetween, and one or two substrates formed between the two substrates and surrounded by a partition wall.
It has the above-mentioned developer containing cell and a dry developer contained in each of the cells, and the dry developer has at least two types of charge polarities different from each other and different optical reflection densities from each other. And dry developing particles having triboelectric charging properties. Therefore, even after an image is displayed, a different electrostatic field is applied, an alternating electric field is applied, or an oscillating magnetic field is applied when magnetic development particles are included, thereby erasing an image, or using a different electrostatic field. Can be applied to rewrite the image. Therefore, there is no need to discard the image display medium on which the image has been displayed. Further, the developing particles are contained in the cell, and there is no need to supply the developer from outside. As a result, the use of conventional image display media, such as paper, related to image display, and consumables, such as a developer, can be greatly reduced.

Further, unlike the conventional electrophotographic image formation, it is not necessary to dissolve and fix the toner on a sheet such as paper by heat, and the image forming energy required for this type of conventional image formation is unnecessary. Can save most.

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

According to such a reversible image display medium, the developer contained in the cell has a different optical reflection density (in other words, "different in contrast" or "different in color"). It contains at least two types of developing particles, and the developing particles are dry type developing particles, and the degree of hiding of the other type of developing particles by one type of developing particles is good, so that an image is displayed with good contrast. it can.

The developer contained in the cell contains at least two kinds of mutually frictionally chargeable dry developing particles having mutually different charging polarities. When an image is displayed, the developer is charged to the opposite polarity by friction charging. Since the particles move under the Coulomb force, the particles are easy to move, and in this respect, the image can be displayed with good contrast, the afterimage of the previous display hardly occurs, the image can be displayed at a high speed, and further, low voltage driving is possible. .

Dry developing particles are less likely to settle and agglomerate because they do not involve a liquid, as compared with, for example, electrophoretic particles in a display liquid used for electrophoretic image display as described above. A decrease in contrast is unlikely to occur, and a long-term stable image display can be performed. Since the sedimentation and aggregation of the developing particles hardly occur, the afterimage of the previous display hardly occurs. Further, since dry development particles have less change over time in charging performance than particles in a liquid, stable image display can be performed for a long time in this respect as well.

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

By the way, in the reversible image display medium having the basic structure, from the viewpoint of the image quality of the display image, display is performed by using two types of developing particles having different optical reflection densities (in other words, different colors). In this case, when the particle size difference between the particles increases, the balance of the image density error (color unevenness) between the image area of one particle and the image area of the other particle (hereinafter, “uniformity of image density” may be referred to as “image density uniformity”). ), Graininess is greatly different, and the image quality of the displayed image is degraded.

The present inventor has set out to solve such a problem.
It has been found that the ratio of the volume average particle size of the two types of dry developing particles may be within a certain range.

According to the study of the present inventors, this particle size ratio is 1
If it exceeds 0, the difference in the granularity of image display due to particles having different optical reflection densities becomes large. For example, two types of developing particles of magnetic developing particles and non-magnetic developing particles having different optical reflection densities are used. When used, the difference between the granularity of image display due to the magnetically developed particles and the granularity of image display due to the non-magnetic developed particles becomes large, and the image quality of the displayed image is reduced accordingly.

Therefore, the volume average particle size ratio (= volume average particle size of developing particles a / volume average particle size of developing particles b) (where volume average particle size of particles a ≧ volume average particle size of particles b) is calculated as follows. The number may be 1 or more and 10 or less.

Further, from the viewpoint of image display speed, when one of the two types of developing particles having different optical reflection densities is a magnetic developing particle, a magnetic stirring force is applied to the developer from the outside when displaying an image. It should be able to act to smooth the movement of the developing particles by the electrostatic field and improve the image display speed, but between the two particles having different optical reflection densities, one of the magnetic developing particles is too small, If the stirring force of the particles is weak, the movement resistance of the other developing particles (for example, non-magnetic developing particles) becomes relatively larger than the binding force of one magnetic developing particle due to the magnetic field, and the particles are stirred by the magnetic stirring and Coulomb force. It becomes difficult to control the movement. The other developing particles (eg, non-magnetic developing particles)
Is too small for the one magnetic developing particle, the efficiency of the one magnetic developing particle to scrape off the other developing particle adhering to the image display surface of the substrate in image display decreases.
Anyway, it is not preferable from the viewpoint of the image display speed.

The present inventor has solved the above problem by
Ratio of volume average particle diameter of two types of dry developing particles including magnetic developing particles (= volume average particle diameter of one magnetic developing particle /
It has been found that the volume average particle diameter of the other developing particles should be within a certain range.

According to the study of the present inventors, this particle size ratio is 1
If it exceeds 0, between the two particles having different optical reflection densities, the size of one magnetic developing particle is too small compared to the size of one magnetic developing particle (for example, non-magnetic developing particles), and the other magnetic developing particles cause The scraping efficiency of the developing particles decreases, and the image display speed decreases accordingly. Further, when the particle size ratio is smaller than 0.5, the other developing particles are too large compared to the size of the one magnetic developing particles, and the stirring force by the one magnetic developing particles becomes insufficient. Image display speed decreases.

Therefore, the volume average particle diameter ratio (= the volume average particle diameter of one magnetic developing particle / the volume average particle diameter of the other developing particle) may be set to 0.5 or more and 10 or less.

Based on the above findings, the present invention provides the following first and second reversible image display media employing the above-mentioned basic structure. (1) First reversible image display medium When the two types of dry developing particles are a and b (volume average particle size of a ≧ b volume average particle size of b), the volume average of the developing particles a and b A reversible image display medium having a particle size ratio (= volume average particle size of developing particles a / volume average particle size of developing particles b) of 1 or more and 10 or less.

According to this image display medium, the difference in the granularity of the image display between the two types of developing particles having different optical reflection densities is small. For example, the magnetic developing particles having different optical reflection densities are different from each other. In the case of using two types of developing particles, i.e., non-magnetic developing particles and non-magnetic developing particles, the difference between the granularity of the image display by the magnetic developing particles and the granularity of the image displaying by the non-magnetic developing particles is reduced, and the image can be displayed with high quality. Can be. (2) Second reversible image display medium At least one of the two types of dry developing particles is a magnetic developing particle, and a volume average particle of two types of dry developing particles including the magnetic developing particle among the dry developing particles. A reversible image display medium having a diameter ratio (= volume average particle size of one magnetic developing particle / volume average particle size of the other developing particle) of 0.5 or more and 10 or less.

Examples of the other developing particles include insulating particles (non-conductive particles). In any case, the other developing particles may be non-magnetic particles or magnetic particles.

According to this image display medium, of two types of developing particles including magnetic developing particles having different optical reflection densities from each other, one of the magnetic developing particles is used as the other developing particles (the other developing particles adhered to the substrate). The scraping efficiency is improved, and the image display speed is correspondingly increased. In addition, the stirring force by the one magnetic developing particles is improved, and the image display speed is correspondingly increased.

[0048]

Embodiments of the present invention will be described below.

The reversible image display medium according to the preferred embodiment of the present invention basically has the following structure.

That is, two substrates facing each other with a predetermined gap therebetween, one or more developer storage cells formed between the two substrates and surrounded by partition walls, and This is a reversible image display medium having a dry developer contained in each cell. The dry developer contains at least two types of dry developing particles having triboelectric charging properties, which have different charging polarities and different optical reflection densities.

According to this reversible image display medium, in a state where the developing particles contained in each cell are triboelectrically charged, a predetermined electrostatic field is applied to each pixel corresponding to the image to be displayed on the developing particles. By forming the developing particles, the developing particles are moved by Coulomb force acting between the electrostatic field and the charged developing particles to perform development, and an image can be displayed with a predetermined contrast.

The electrostatic field can be formed based on the electrostatic latent image by forming an electrostatic latent image on any one of the outer surfaces of the two substrates. The formation of the electrostatic field may be performed simultaneously with the formation of the electrostatic latent image, or may be performed after the formation of the electrostatic latent image. Such an electrostatic field may be applied to a substrate opposite to the substrate on which an electrostatic latent image is formed, for example, by applying a bias voltage simultaneously with or after the formation of the electrostatic latent image, or by applying a bias voltage to the opposite substrate. It is obtained by setting the opposite substrate to a predetermined potential for forming an electrostatic field by grounding or the like.

Various materials such as a partition wall for forming a substrate or a cell can be selected and adopted. As the substrate, a glass substrate, a rigid or flexible synthetic resin substrate, or the like can be employed. A flexible film-like substrate can also be employed.

At least one of the two substrates constituting the medium (the one disposed on the image observing side) may have a light transmitting property so that a displayed image can be visually recognized.

When forming an electrostatic latent image on a substrate, the substrate may be an insulating substrate.

The substrate on the side opposite to the substrate on which the electrostatic latent image is formed (for example, the substrate on the non-image observation side) may or may not be an insulating substrate. When an insulating substrate is used, this may be set to the ground potential, or when it is necessary to apply a bias voltage thereto, the insulating substrate may be left as it is.For example, a conductive film may be formed on the outer surface of the substrate, or the entire substrate may be used. It may be formed of a conductive material or a material containing a conductive material. In this way, the substrate can be easily grounded to a ground potential or a bias voltage can be applied to the substrate if necessary. Further, when the opposite substrate is an insulating substrate and a conductive film is formed on the outer surface thereof, or when the opposite substrate itself is a conductive substrate, there is an effect of shielding charges from other components. In addition, even when the media on which images are displayed are overlapped, the images are less likely to collapse, and the images can be held more stably.

The number, size, shape, distribution, arrangement (regular or irregular) of the developer accommodating cells are not particularly limited as long as images can be displayed. A developer movement suppressing member or a spacer for maintaining a gap between the substrates may be provided between the substrates. The partition wall constituting the cell may also serve as the developer movement suppressing member and the spacer.

In the case where an electrostatic latent image is formed on a substrate during image formation, if the gap between the substrates or the thickness of the substrate is large, the electric field applied to the developer is weakened, leading to a decrease in contrast. On the other hand, if the gap between the substrates is too small, the amount of developer that can be included is small, and the contrast is low. If the thickness of the substrate is too small, the substrate is easily bent, and uniformity of the gap between the substrates cannot be obtained,
Image unevenness is likely to occur. Therefore, the thickness of the substrate is 5
μm-100 μm, gap between substrates 20 μm-300
μm, and the thickness of the entire medium is suitably 30 μm to 500 μm.

With respect to the frictional charging of the developing particles, the developing particles may be stored in a developer storage cell and then triboelectrically charged by vibrating the developer particles. However, two or more types of developing particles may be mixed and stirred in advance. The developer particles triboelectrically charged may be accommodated in the cell. This makes it easier to obtain frictionally charged developing particles in a desired state. In any case, the developing particles are triboelectrically charged prior to image display.

In any case, the reversible image display medium is
It may have an electrode or may not have an electrode. When no electrode is provided on the substrate, the medium can be simplified accordingly, and a flexible film substrate or the like can be easily used as the substrate.

As an image display medium having electrodes, an electrode (preferably a transparent electrode) is formed on the inner surface of one substrate having light transmittance, and an electrode facing the electrode is formed on the inner surface of the other substrate. Can be exemplified.

The electrodes on the inner surface of the other substrate may be composed of an individual electrode group formed for each pixel.

For an image display medium having electrodes, leads are connected to the electrodes, and the leads are preferably provided in a non-image display area having a partition wall or the like.

The developer contained in the developer accommodating cell has at least two kinds of different charge polarities and different optical reflection densities (in other words, “different contrast” or “different color”). It is preferable to include dry developing particles. As typical examples, positively chargeable (or negatively chargeable) black particles having light absorbency and negatively chargeable (or positively chargeable) white particles having light reflectivity can be given.

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

Further, at least one of the at least two kinds of developing particles constituting the dry developer may be magnetic developing particles. When the magnetic developing particles are employed in this manner, a magnetic stirring force can be applied to the dry developing particles by a magnetic field in driving the developing particles by the electrostatic field, whereby the developing particles can be smoothly moved by the electrostatic field for image display. This makes it easier to move, further improving the contrast and driving at a lower voltage.

Furthermore, regardless of whether the reversible image display medium has the electrodes or not, the presence of such magnetic particles allows the developer (developed particles) to be stirred by a magnetic field, for example, an oscillating magnetic field. In forming an image (image display) by stirring the developer, it is possible to initialize the medium or erase the previous image, and in the image display, the developing particles can be easily moved by the electrostatic field for the image display. Images can be displayed.

The stirring of the developing particles can be carried out by applying an alternating voltage such as the application of an AC voltage or by applying mechanical vibration. Stirring can be performed by combining two or more of alternating voltage stirring, magnetic stirring, mechanical stirring, ultrasonic irradiation stirring, and the like.

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

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

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

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

Further, the at least two kinds of developing particles constituting the dry developer are a and b (a volume average particle diameter of a ≧ b
When the ratio of the volume average particle diameters of these particles a and b (= volume average particle diameter of the developing particles a / volume average particle diameter of the developing particles b) exceeds 10, when the particles The difference in the granularity of image display due to particles having different optical reflection densities increases. For example, when two types of developing particles of magnetic and nonmagnetic developing particles having different optical reflection densities are used, the The difference between the graininess of the image display and the graininess of the image display due to the non-magnetic developing particles increases, and the image quality of the displayed image is reduced accordingly.

Therefore, the volume average particle size ratio is 1 or more and 10 or more.
The following is preferred.

When at least one of the at least two types of developing particles constituting the dry developer is a magnetic developing particle, the ratio of the volume average particle size of the two types of dry developing particles (= one magnetic particle) Volume average particle size of developing particles /
If the other developing particles (for example, non-magnetic developing particles) have a volume average particle size of more than 10, the other developing particles will be smaller than the size of one magnetic developing particle between the two particles having different optical reflection densities. It is too small, and the efficiency of scraping off the other developing particles (adhering to the substrate) by one magnetic developing particle is low, and the image display speed is reduced accordingly. If the particle size ratio is smaller than 0.5, the size of one magnetic developing particle is too large compared to the size of one magnetic developing particle, and the stirring force of one magnetic developing particle becomes insufficient. Slows down.

Therefore, the volume average particle size ratio in this case is 0.1.
It is preferable that it is 5 or more and 10 or less.

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

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

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

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

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

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

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

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

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

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

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

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

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

These coloring agents can be used alone or in combination.

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

In particular, when the white pigment is kneaded with a molten binder resin (binder resin) to obtain the developing particles from the kneaded product, the amount of the white pigment used is determined in order to obtain a sufficient whiteness. To 100 parts by weight of the starting monomer
The amount is desirably 0 parts by weight or more, preferably 20 parts by weight or more, and is desirably 60 parts by weight or less, preferably 50 parts by weight or less in order to ensure sufficient dispersibility of the white pigment. When the amount of the white pigment exceeds 60 parts by weight, the binding property between the pigment and the binder resin and the dispersibility of the pigment deteriorate. On the other hand, when the amount of the white pigment is less than 10 parts by weight, sufficient development particles of other colors cannot be obtained. No concealing properties are obtained.

[0093] Carbon black is preferable as the black colorant. However, in the case where the developing particles are made to have magnetism, magnetic particles such as magnetite and ferrite and magnetic fine particles can be used as the colorant. -Other internal additives As internal additives preferably used other than the binder resin and the colorant, a magnetic substance, a charge control agent, a resistance adjuster and the like can be mentioned. -Charge control agent The charge control agent is not particularly limited as long as it gives charge to the developing particles by triboelectric charging.

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

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

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

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

[0098] From among the binder resins, magnetic powders, colorants, charge control agents, resistance adjusters and other additives as described above, necessary ones are selected, and they are sufficiently mixed by a predetermined amount and then pressurized. Heat kneading with a kneader or a twin-screw kneading device, etc.
After cooling, it is roughly pulverized by a hammer mill, a cutter mill or the like. Next, after further pulverizing with a jet mill, an ong mill or the like, the particles are classified using an air classifier or the like until the particles have a predetermined average particle size, thereby obtaining developed particles.

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

In particular, fine powders such as silica, aluminum oxide, titanium dioxide and magnesium fluoride are preferable, and a fluidizing agent may be added alone or in combination.

As described above, the formation of an electrostatic field with respect to the developing particles on the reversible image display medium is intended to be displayed on the surface of one of the two substrates (for example, the substrate on the image observation side). An electrostatic latent image corresponding to an image can be formed, or an electrostatic latent image can be formed close to the electrostatic latent image based on the electrostatic latent image. In this case, the formation of the electrostatic field
It may be performed simultaneously with the formation or proximity of the electrostatic latent image, or may be performed after the formation of the electrostatic latent image. The formation of the electrostatic field can be performed, for example, by setting a predetermined potential for forming the electrostatic field on the substrate opposite to the substrate on which the electrostatic latent image is formed. The setting of the predetermined potential can be performed by, for example, applying a bias to the opposite substrate or setting the substrate to the ground potential.

The electrostatic latent image may be formed directly on the medium surface (substrate 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 electrostatic latent image may be formed by transferring the image onto the medium surface (substrate surface). The electrostatic latent image formed outside the medium using the external electrostatic latent image forming apparatus may be brought close to the medium surface (substrate surface).

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

An external electrostatic latent image forming apparatus forms an electrostatic latent image corresponding to an image to be displayed on an electrostatic latent image carrier, and forms the electrostatic latent image on the electrostatic latent image carrier. Is transferred or brought close to the substrate surface. More specifically, an electrostatic latent image corresponding to an image to be displayed is formed on a photoconductor such as a photoconductor, and the electrostatic latent image on the photoconductor is transferred to or brought close to the substrate surface. And an electrostatic latent image corresponding to an image to be displayed on a dielectric, and the electrostatic latent image on the dielectric is transferred to or brought close to the substrate surface.

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

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

Incidentally, for a reversible image display medium having a counter electrode, an electrostatic field for image display can be formed by applying a voltage between the counter electrodes. An electric field forming device for this medium will be exemplified later.

Further, the formation of an electrostatic field for the developing particles in a reversible image display medium without electrodes or a medium having electrodes only on one substrate is performed by arranging electrodes on the outer surface of the medium and applying a voltage through this electrode. Can also be applied.

[0109] Regardless of whether a reversible image display medium with or without electrodes is employed, an image erasing process for erasing the previously displayed image may be performed before the image is displayed.

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

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

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

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

The electric field forming apparatus for erasing an image includes a pair of electrodes (usually a metal) or a dielectric disposed with a reversible image display medium therebetween, and a power supply for applying a bias voltage thereto. Can be exemplified.

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

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

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

This device can be used when at least one of the developer particles contains a magnetic material. A device that irradiates a reversible image display medium with ultrasonic waves. A device that applies mechanical vibration to a reversible image display medium. A device combining two or more of the above devices.

As described above, when the developer (developing particles) is agitated, the charge amount and fluidity of the developing particles are improved, and the next image display is made smoother and more reliably with higher quality. .

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

Therefore, in displaying an image, regardless of whether a reversible image display medium with or without electrodes is employed, the developer may be used together with the image erasing process or separately from the image erasing process. May be stirred.

When employing an image display medium without electrodes or an image display medium having electrodes only on one substrate,
For example, an electrostatic latent image corresponding to an image to be displayed is formed on the surface of the image display medium (substrate surface), and based on the electrostatic latent image, simultaneously with the formation of the electrostatic latent image or the electrostatic latent image. An electrostatic field for image display may be formed after image formation, and the developer may be agitated simultaneously with and / or before the formation of the electrostatic field.

For an image display medium having a counter electrode, a voltage is applied between the electrodes to form an electrostatic field, and the developer is stirred before or simultaneously with the formation of the electrostatic field. be able to. Irrespective of the presence or absence of the electrodes, the developer agitation faces the image display medium conveyance path in the electrostatic field formation region by the electric field formation device or in the upstream side thereof, for example, in the relative conveyance direction of the image display medium to the electric field formation device. This can be done using a stirrer.

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

By stirring the developer in displaying an image as described above, it is possible to further improve the contrast and further reduce the driving voltage.

When an electrostatic latent image is formed on the surface (substrate surface) of an image display medium during image display, the surface of the medium is uniformly charged to a predetermined potential before the electrostatic latent image is formed, and the charged area is charged. An electrostatic latent image corresponding to the image to be displayed may be formed. Then, based on the electrostatic latent image, a predetermined electrostatic field is formed for each pixel corresponding to an image to be displayed on the developer particles in the developer storage cell, thereby moving the developer particles to display an image. Is also good.

The electrostatic latent image on the medium is formed, for example, directly on the surface of the medium charged in the above-mentioned charging step, or by forming the electrostatic latent image formed on the electrostatic latent image carrier outside the medium. It can be formed by transferring and forming on 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 is the same as the charge polarity of the charge area by uniform charging of the medium surface prior to the formation of the electrostatic latent image. The polarity may be different, or 0 [V].

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

According to the various reversible image display media described above, high-contrast, high-resolution, high-quality images can be stably displayed over a long period of time. Further, afterimages are less likely to occur, and therefore, good reversibility is exhibited. In this respect, a high-quality image can be displayed. It is possible to display images at high speed, and it is also possible to reduce the driving voltage. It is also possible to display an image with less image unevenness.

Hereinafter, specific examples of the developing particles and the developer will be described, and specific examples of a reversible image display medium, a reversible image display method, an image forming apparatus, and the like will be described with reference to the drawings. <Developing Particles and Developer> White developing particles WP 100 parts by weight of a thermoplastic polyester resin (softening point 121 ° C., glass transition point 67 ° C.), 40 parts by weight of titanium oxide (CR-50, manufactured by Ishihara Sangyo Co., Ltd.) Zinc salicylate complex (Orient Chemical: Bontron E) as a negative charge control agent
-84) 5 parts by weight were sufficiently mixed with a Henschel mixer, kneaded with a twin-screw extruder, and then cooled. The kneaded product was coarsely pulverized, then pulverized by a jet pulverizer, and classified by wind power to obtain a white fine powder having a volume average particle size of 4.8 μm. Thereafter, 0.3 parts by weight of hydrophobic silica fine particles (manufactured by Nippon Aerosil Co., Ltd .: Aerosil R-972) are added to the white fine powder, and the mixture is mixed by a Henschel mixer to produce white developed particles WP1 having a volume average particle size of 4.8 μm. I got

Similarly, the respective volume average particle diameters are 5.
5 μm, 7.1 μm, 10.1 μm, 14.7 μm, 1
9.1 μm white developing particles WP2, WP3, WP4, W
P5 and WP6 were obtained. Black developing particles BP Styrene-n-butyl methacrylate resin (softening point 13
100 parts by weight, 2 parts by weight of carbon black (Ketjen black manufactured by Lion Yushi Co., Ltd.), and silica (# 200 manufactured by Nippon Aerosil Co., Ltd.)
And 1.5 parts by weight of a magnetite-based magnetic powder (RB-BL
After 500 parts by weight (Titanium Industry Co., Ltd.) were sufficiently mixed with a Henschel mixer, the mixture was kneaded with a vented twin-screw kneader.

The kneaded material was cooled, coarsely pulverized by a feather mill, finely pulverized by a jet mill, and classified by an air classifier to obtain black developing particles BP having a volume average particle size of 5.6 μm.
1 was obtained.

Similarly, each volume average particle diameter was 8 μm.
m, 10 μm, 23 μm, 41 μm, 62 μm, 74 μm
m black developing particles BP2, BP3, BP4, BP5, B
P6 and BP7 were obtained.

Table 1 summarizes the white developing particles WP1 to WP6 and the black developing particles BP1 to BP7.

[0136]

[Table 1]

Preparation of Developer DL Various combinations of the above-mentioned white developing particles and black developing particles,
Regarding each combination, 30 g of white particles and 70 g of black particles were put in a polyethylene bottle, and rotated and mixed and stirred for 30 minutes with a ball mill base to obtain a plurality of types of developers DL. The combinations of the black and white developing particles are shown in Table 2 below. In each of the developers, the white particles were negatively charged and the black particles were positively charged. <Reversible Image Display Medium> The developer DL used in the reversible image display media 11 to 15 ′ described below is composed of white non-magnetic developing particles WP and black magnetic developing particles BP in order to suppress a decrease in image quality. (= Volume average particle size of black developing particles BP / volume average particle size of white developing particles WP) is 1 or more and 10 or less.

Further (or), in order to suppress a decrease in display speed, the ratio of the volume average particle diameter of the white non-magnetic development particles WP and the black magnetic development particles BP (= the volume average particle diameter of the black magnetic development particles BP / (The volume average particle size of the white non-magnetic developing particles WP) is 0.5 or more and 10 or less. -Reversible image display medium 11 Figs. 1 and 2 show an example of a reversible image display medium. FIG.
The medium 11 shown in FIG. 2 includes a first substrate 111 and a second substrate 112. These substrates 111 and 112 face each other with a predetermined gap therebetween. Substrate 11
Partitions 113 are provided between the substrates 1 and 112, and the gap between the substrates is secured to a predetermined value by the partitions 113. That is, the partition 113 is formed of both substrates 111,
Also serves as a spacer between 112. Also, both substrates 111,
112 are connected and fixed to each other by a partition 113.

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

The partition 113 is also provided with a developer accommodating cell 116.
(See FIG. 3). That is, the partitions 113 are formed upright on the inner surface of the first substrate 111 in a grid pattern as shown in FIG.
A plurality of developer accommodating cells 116 are formed in a rectangular shape with a part of 13 as a partition wall.

Each partition wall has a width α and a height h, and the interval between adjacent partition walls is pt.

On the inner surface of the first substrate 111, the first electrode 11
4 are formed. The first electrode 114 is a transparent electrode in which a plurality of individual electrodes 114a are arranged in a grid pattern. Each individual electrode is formed of, for example, a transparent ITO film. The individual electrodes 114 a are arranged in each of the cells 116 at substantially the same interval as the thickness α of the wall 113. That is, here, one cell corresponds to one pixel.

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

A second electrode 115 is provided on the inner surface of the second substrate 112 facing the first substrate 111. Second electrode 1
Reference numeral 15 is continuous over the entire image display area on the inner surface of the substrate 112. The second electrode 115 is not necessarily a transparent electrode, but may be, for example, indium tin oxide (ITO).
It may be formed on a transparent electrode formed as described above.

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

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

The first electrode 1 on the image display medium 11
As shown in FIG. 4, each of the individual electrodes 114a lying laterally has a lead 110 connected thereto, and through these leads, an electrode selection circuit 117 as shown in FIG.
Connected to. A positive drive voltage generation circuit 118a, a negative drive voltage generation circuit 118b, and a display data control unit 119 are connected to the electrode selection circuit 117. A drive voltage is applied to each of the individual electrodes 114a independently from the electrode selection circuit 117, and a display data control unit 119 is provided with display data output means (not shown, such as a computer, a word processor, and a facsimile). Machine)
The display data is input from the controller and the electrode selection circuit 117 is controlled based on the display data. In other words, these electrode selection circuits and the like constitute an example of an electric field forming apparatus or an image forming apparatus for a reversible image display medium having a counter electrode.

Thus, a bias voltage is applied to the second electrode 115 of the image display medium 11 as, for example, a ground electrode or, if necessary, from a bias power supply (not shown) to the electrode 115, and the second electrode 115 is connected to the individual electrode 114a. In the meantime, a predetermined voltage is applied from the positive drive voltage generation circuit 118a or the negative drive voltage generation circuit 118b via the electrode selection circuit 117 which is controlled so that a desired image is displayed by the display data control unit 119, A predetermined electric field is formed for each pixel. Thus, as shown in FIG.
At L, the developing particles WP and BP move from the state where the developing particles are mixed as shown in FIG. 2 according to the electric field.

According to the medium 11, an image can be displayed, for example, as shown in FIG. In FIG. 5, Bk is a black display portion, and W is a white display portion.

The rotating magnetic pole roller R shown by a chain line in FIG.
2 will be described later. -Reversible image display medium 12, 12 'FIG. 6 shows another example of the reversible image display medium.

The reversible image display medium 12 shown in FIG.
In the medium 11 shown in FIG. 1, at least the first substrate 111 is formed of a material having a light transmitting property and an insulating property, and the individual electrodes 114a are omitted.

Other points are the same as those of the medium 11 shown in FIG. In FIG. 6A, the same components and portions as those of the medium 11 are denoted by the same reference numerals as those of the medium 11.

A reversible image display medium 1 shown in FIG.
2 ′ is at least the second in the medium 11 shown in FIG.
The substrate 112 is formed of a material having both light transmittance and insulating properties, and the electrode 115 is omitted. In the medium 12 ', the substrate 112 is an image observation side substrate.

The other points are the same as the medium 11 shown in FIG. In FIG. 6B, the same components and parts as those of the medium 11 are denoted by the same reference numerals as those of the medium 11.

According to the medium 12 (or the medium 12 ′), for example, the electrode 115 of the second substrate 112 (the electrode 114 a for the medium 12 ′) is used as the ground electrode, and the first substrate 111 (the medium 12 ′ is the second electrode). A) arranging an electrode on the outer surface of the substrate 112) and selectively applying a voltage corresponding to an image to be formed between the electrode and the ground electrode;
b) directly forming an electrostatic latent image corresponding to the image to be formed;
c) The image carrier on which the electrostatic latent image corresponding to the image to be formed is formed is brought into contact (including proximity), and the image is displayed by applying a developing particle driving electric field to the developer DL based thereon. be able to.

The electrode 115 for the medium 12 and the electrode 114a for the medium 12 'are preferably electrodes having an intermediate resistance value. -Reversible image display medium 13 FIG. 7A shows another example of the reversible image display medium.

The reversible image display medium 13 shown in FIG.
In the medium 11 shown in FIG. 1, at least the first substrate 111 is formed of a material having a light transmitting property and an insulating property, and a first substrate electrode 114 and a second substrate electrode 115 are formed.
Is omitted.

Other points are the same as the medium 11 shown in FIG. 7, the same components and parts as those of the medium 11 are denoted by the same reference numerals as those of the medium 11. -Reversible image display medium 14 FIG. 8A shows another example of the reversible image display medium.

The reversible image display medium 14 shown in FIG.
In the medium 11 shown in FIG. 1, at least the first substrate 111 is formed of a material having a light transmitting property and an insulating property, and a first substrate electrode 114 and a second substrate electrode 115 are formed.
And a partition 113 composed of a plurality of partition walls 113a extending in parallel with the longitudinal side of the medium 14 is employed instead of the lattice-shaped partition (see also FIG. 9). A developer accommodating cell 116 is provided between each adjacent partition wall 113a. Each cell 116 has a developer D containing white developer particles WP and black developer particles BP frictionally charged with each other.
L is accommodated.

At the periphery of the medium 14, both substrates 111,
112 is heat-sealed to form a sealing portion 140. A portion 140a of the sealing portion 140, which is provided at both ends in the longitudinal direction of the vertical partition wall 113a and seals both ends of each cell, also serves as a partition wall forming the cell 116.

As shown in FIG. 9, each partition wall 113a has a width α and a height h, and the interval between adjacent partition walls 113a is pt.
It is formed as.

According to the media 13 and 14, for example, a) an electrostatic latent image corresponding to an image to be formed is directly formed on the first substrate 111, and b) an electrostatic latent image corresponding to an image to be formed is formed. An image can be displayed by bringing the image carrier into contact with (including proximity to) the first substrate 111 and applying a developing particle driving electric field to the developer DL based on the contact. The second substrate 112 may be set to a ground potential or the like as necessary. -Reversible image display medium 15, 15 'FIG. 10 shows another example of the reversible image display medium.

A reversible image display medium 15 (1) shown in FIG.
5 ′) is a medium 13 (14) in which a conductive film 112A is provided on the outer surface of the second substrate 112.

The other points are the same as the medium 13 (14). In FIG. 10, the same components as the medium 13 (14),
Parts are given the same reference numerals as the medium 13 (14).

The image display using the mediums 15 and 15 ′ is performed by, for example, setting the conductive film 112 A to an appropriate potential such as the ground potential, and a) forming an electrostatic latent image corresponding to the image to be formed on the first substrate 1.
B) an image carrier on which an electrostatic latent image according to an image to be formed is formed is brought into contact with (including proximity to) the first substrate 111, and the developer particles are added to the developer DL based thereon. An image can be displayed by applying a driving electric field.

It is to be noted that, instead of providing the conductive film 112A, the second substrate 112 is made a conductive substrate by making the second substrate 112 a substrate in which a conductive material is dispersed, and this is set to the ground potential. You may do it.

As described above, according to each image display medium described with reference to the drawings and the image display method using the same, image display and image deletion can be repeated. Also, the developing particles W
P and BP are contained in the cell, and do not require an external developer supply. Thus, the use of consumables such as a medium such as paper and a developer related to image display in the related art can be significantly suppressed. Further, since image energy does not require heat energy for fusing the toner to the medium as in the related art, the image forming energy can be reduced accordingly. Therefore, it is possible to meet today's environmental load reduction.

Further, since each of the media 11 to 15 'employs the dry developer DL containing the developing particles WP and BP having different colors, one of the developing particles WP (or BP) is used for the other developing particles BP (or BP). Or WP), the degree of concealment is good, and an image can be displayed with good contrast.

The developing particles W contained in the cell 116
P and BP are frictionally charged to different charging polarities,
In the image display, it is easy to move due to the Coulomb force, and in this regard, the image can be displayed with good contrast, the afterimage of the previous display hardly occurs, the image can be displayed at a high speed, and the driving at a low voltage is possible.

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

Any of the media 11 to 15 ′ can display an image with a higher resolution than the conventional electrophoretic display. In other media except the medium 11, since the resolution does not depend on the size of the pixel electrode 114a unlike the medium 11, an image can be displayed at a higher resolution.

Next, the media 12, 12 ', 13, 14, 1
An example of displaying an image using 5, 15 'will be described together with an image forming apparatus.

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

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

Then, the electrostatic latent image EI on the photosensitive drum PC
For example, the medium 13 or 14 is fed between the drum and the electrode roller R1 in synchronization with the above. At this time, the medium 13
The surface of (14) is uniformly charged to a predetermined potential in advance by a charger CRH such as a corona charger.

Thus, each cell 11 of the medium 13 (14)
An electrostatic field based on the electrostatic latent image EI is formed on the developing particles BP and WP of the developer DL contained in the developer 6, and the developing particles are formed by Coulomb force acting between the electrostatic field and the charged developing particles. Moves. Then, FIG. 7 (A) or FIG.
(A) As shown in FIG.
FIG. 7B or FIG. 8 when the BP is mixed.
As illustrated in (B), the white particles WP and the black particles BP each move according to the electric field. Thus, an image can be displayed with a predetermined contrast.

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

Note that it is not always necessary to previously charge the surface of the medium 13 (14) with the charger CRH.

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

The medium 11 shown in FIGS. 1 and 2 also has a rotating magnetic pole roller R as shown by a chain line in FIG.
2 can be adopted.

Instead of the magnetic pole roller R2, a magnet plate MG having alternately N poles and S poles is provided downstream of the medium transport path as exemplified by a chain line in FIG. A magnetic field may be formed.

The image forming apparatus can also form an image on the mediums 12 and 12 'and the mediums 15 and 15'. When forming an image on the medium 12 or 15, instead of using the electrode roller R1, the second electrode 115 is
For 2 ′, the pixel electrode 114a is connected to the medium 15, 15 ′.
With regard to the above, the conductive film 112A can be grounded, or a bias can be applied thereto.

The image forming apparatus shown in FIG. 12 includes an ion flow type direct electrostatic latent image forming apparatus CR2. Device CR
2 is a corona ion generator c for generating corona ions
2 and corona ions generated in the generating section
3 (or 14) of the writing electrode e2 for leading to the surface of the first substrate 111, and a voltage for leading positive (or negative) corona ions to a pixel corresponding portion of the surface of the substrate 111 in accordance with an image to be displayed. A write electrode control circuit f2 for applying a voltage to the write electrode e2.

The corona ion generator c2 is provided in the shield case c21.
A gold-plated tungsten wire having a diameter of 20 μm is stretched to form a corona wire c22, and a positive (or minus) voltage (for example, 4 kV to 10 kV) is applied to this wire from a power supply Pc2 to generate corona ions.

The write electrode e2 is connected to the medium 13 (or 1
4) The shield case c2 directed to the first substrate 111
1 and includes an upper electrode e21 and a lower electrode e22, through which a corona ion flow can pass.

The electrode control circuit f2 includes a control power supply Pc21,
Including a bias power supply Pc22 and a control unit f21,
The control unit f21 outputs an ion extraction voltage corresponding to the polarity of ions to be extracted toward the medium 13 to the electrodes e21 and e2.
2 can be applied.

Here, when a positive voltage is applied to the upper electrode e21 and a negative voltage is applied to the lower electrode e21 under the instruction of the control unit f21, positive corona ions can be guided to the medium (FIG. 12A). . 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. 12B).

Further, an electrode roller R1 is provided so as to face the writing electrode e2, and a bias voltage is applied to the electrode roller R1 from the power supply PW1, or the roller R1 is set to the ground potential. The roller R1 incorporates a magnetic pole roller R2 that is driven to rotate.

Thus, the surface of the medium 13 (or 14) is uniformly charged in advance to a predetermined potential by a charger such as a corona charger, and the medium 13 (or 14) thus pre-charged is moved relative to the apparatus CR2. Moving the electrode roller R1 in the medium feed direction and rotating the magnetic pole roller R2 in the opposite direction while moving the first substrate in accordance with the image to be displayed, under the instruction of the control unit f21. As shown in FIG. 12A, 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 surface 111, and FIG.
As shown in FIG. In this way, an image can be displayed on the medium 13 or 14 as illustrated in FIG. 7B or FIG. 8B.

It is not always necessary to charge the surface of the medium 13 (14) in advance.

Further, the discharge wire c2 in the device CR2
2 can be replaced by a solid discharge element.

Images can also be formed on the media 12, 12 'and the media 15, 15' by this image forming apparatus. When forming an image on the medium 12 or 15, instead of using the electrode roller R1, the second electrode 115 is
For 2 ′, the second electrode 114a is connected to the medium 15, 15 ′.
In this case, the conductive film 112A may be grounded or an appropriate bias may be applied thereto.

Also, the electrostatic latent image forming apparatus CR2 shown in FIG.
Uses the discharge phenomenon, but in addition to these devices,
Various discharge-type electrostatic latent image forming apparatuses can be used.

The image forming apparatus shown in FIG. 13 includes a multi-stylus type direct electrostatic latent image forming apparatus CR3. The device 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 15 (or 15 ′) and arranged close to the first substrate 111. A signal voltage is applied to apply an electrostatic latent image charge to a portion corresponding to a pixel on the surface of the first substrate 111 according to an image to be displayed on each electrode e3. Medium 15 (15 ')
For example, a bias is applied to the conductive film 112A of the second substrate 112, for example, or the conductive film 112A is grounded.
Then, the sheet is conveyed relatively to the head H3, whereby an image is displayed.

It is to be noted that images can be formed on the mediums 12 and 12 'by this image forming apparatus. In that case, medium 1
A bias may be applied to the second electrode 115 or the electrode 114a of the medium 12 'as necessary.

Also, for the media 13 and 14, an image can be formed by this image forming apparatus by bringing an external electrode to which a bias can be applied or grounded into contact with the outer surface of the second substrate 112 as necessary.

The image forming apparatus shown in FIG. 14 includes a charge injection type direct electrostatic latent image forming apparatus CR4. Device CR4
Is a multi-stylus type device having an electrostatic recording head H4 in which a plurality of recording electrodes e4 are arranged in the main scanning direction with respect to the medium, and adjacent control electrodes e41 are arranged adjacent to the recording electrodes e4. This head is arranged, for example, close to the medium, and a voltage of about の of the voltage (recording voltage) required for image recording is sequentially applied to the control electrode e41 of the head H4 sequentially, and the recording voltage of about 1 is applied to the recording electrode e4. By applying an image signal voltage of / 2, an electrostatic latent image can be formed on the medium located immediately below the recording electrodes.

The image forming apparatus shown in FIG. 15 uses the ion flow type direct electrostatic latent image forming apparatus CR2 shown in FIG. In this image forming apparatus, the image display medium 13 and the like are transported from the entrance side medium transport roller pair RR1 to the exit side media transport roller pair RR2. An ion flow type direct electrostatic latent image forming device CR is provided between these transport roller pairs.
2, a magnet plate MG 'in which N-poles and S-poles are alternately arranged on the downstream side. The ground electrode roller Ea is arranged to face the device CR2. The charger CRH faces the medium transport path on the upstream side of the entrance-side transport roller pair RR1.

According to the image forming apparatus shown in FIG. 15, the surface of the substrate on the electrostatic latent image forming side such as the image display medium 13 is uniformly charged in advance to a predetermined potential by the charger CRH, and the medium thus charged is charged. At 13 or the like, an electrostatic latent image corresponding to an image to be formed by the device CR2 is formed, and then a developer stirring oscillating magnetic field is applied by the rubber magnet plate MG 'with the conveyance of the medium to stir the developer in the medium. To display an image.

Further, as shown in FIG. 10, a conductive film 112 is formed on a substrate 112 opposite to the side on which an electrostatic latent image is formed, such as a medium 15 or 15 '.
In the medium on which A is formed, an appropriate bias may be applied to the medium from the roller R1. When applying the bias, a bias potential between the surface potential of the image portion and the surface potential of the non-image portion on the substrate 111 is applied.

Next, further specific examples of the reversible image display medium and image display using the same will be described. (Reversible image display media D1 to D16) Media D1 to D16
Are the same type of media as the reversible image display medium 13 shown in FIG. 7, and are formed as follows.

That is, a 100-μm-thick film-shaped ultraviolet curable resin was adhered to a first substrate 111 made of a transparent PET (polyethylene terephthalate) film having a thickness of 25 μm, and openings were formed in a predetermined pattern on the resin. A photomask was covered, and ultraviolet light was irradiated from above. Thereafter, development and washing were performed to form lattice-shaped partition walls 113 (see FIG. 3) on the substrate 111. The thickness (width) α of each partition wall 113a forming the partition wall 113 is 50 μm, the height h is 100 μm, and the wall interval pt is 5 mm (FIG. 3, FIG.
(See FIG. 4). This substrate 111 is a substrate on the image observation side (forms an electrostatic latent image).

The developer was put into each concave portion of the substrate 111 surrounded by the lattice-like wall 113.

That is, in the media D1 to D7, the ratio of the volume average particle size of the white non-magnetic developing particles WP and the black magnetic developing particles BP (= volume average particle size of the developing particles BP / volume average particle size of the developing particles WP) ) Is 1 or more and 10 or less.

Further, the media D8 to D11 contained a developer having a particle size ratio of more than 10.

Further, the ratio of the volume average particle diameter (= the volume average particle diameter of the black magnetic developing particles BP / the medium D12, D13)
A developer having a volume average particle size of the white non-magnetic developing particles WP smaller than 0.5 was added, and a developer DL having a particle size ratio of 0.5 or more and 10 or less was added to the media D14 to D16.

Then, a photocurable adhesive 119a (see FIG. 7) is thinly applied only to the top surface of the wall 113 on the first substrate 111, and a PET film containing carbon black having a thickness of 25 μm is applied as the second substrate 112. The film was adhered to the adhesive, and the adhesive was cured by ultraviolet irradiation to adhere the film.

Thereafter, the periphery of the first and second substrates 111 and 112 was heat-sealed instead of being sealed with the epoxy resin adhesive 119b (see FIG. 1) shown in FIG.

Thus, in the medium of the type shown in FIG. 7, the ratio of the volume average particle diameters of the white non-magnetic developing particles WP and the black magnetic developing particles BP differs in the developer DL.
The types of media D1 to D16 were obtained.

Table 2 shows the media D1 to D16.

[0211]

[Table 2]

Among the media D1 to D16, the media D1 to D1
1 was displayed by the image forming apparatus of FIG.

More specifically, the surface of the first substrate 111 is uniformly charged in advance to a negative potential (for example, -500 V) by a corona charger CRH, and the second substrate 112 of the pre-charged medium is set to the ground potential. Set the first substrate 1 of the medium
11, 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, and the portion is set at a positive potential and the negative charging potential (for example, − (500 V) and a potential (for example, +500 V) having the same absolute value as the absolute value, and only the bias potential (ground potential here) was applied to the other pixels.
As a result, the portion charged by the positive coronaine on and the portion not charged by the positive coronaine on are set to potentials of the same magnitude in absolute value (for example, 50
0V) and opposite polarities. Thus, the image was displayed such that the portion on which the positive corona ions were superimposed was displayed white by the negatively chargeable white developing particles WP, and the portion where the positive corona ions were not superimposed was displayed black by the positively charged black developing particles BP. .

When displaying an image, the medium is placed on the magnetic plate M.
By passing above G ′, an oscillating magnetic field was applied to the developing particles in the medium to exert an agitating action on the particles, thereby displaying an image.

For the images formed using the media D1 to D11, the volume average particle diameter ratio of two types of developing particles (white non-magnetic developing particles WP and black magnetic developing particles BP) (= volume average particle diameter of developing particles BP / The relationship between the volume average particle diameter of the developing particles WP) and the uniformity of the image density was examined.

The uniformity of the image density was evaluated as follows.

In displaying an image using the apparatus shown in FIG. 15, the medium is moved in a predetermined direction (X in FIG. 16) as shown in FIG.
Direction), a solid image BT (here, a solid white image (or a solid black image)) is formed on the medium, and its central portion BS
The surface potential is appropriately adjusted so that the reflection density of the image becomes a predetermined density (about 0.35 for a solid white image (or about 1.3 for a solid black image)), and the size (m1 × m2) is 5 cm × 5 cm.
A solid image BT was formed. Here, the image density was measured using a reflection densitometer (Model 310T manufactured by X-Rite). This density is defined as the average value (ID) of the reflection density.

Subsequently, the central portion BS (n1 × n2 = 3c)
m (medium feeding direction X) × 2 mm) is measured in the medium feeding direction X with a microdensitometer (Abe Design Co., Ltd. type 2405; slit width 100 μm (media feeding direction X) × 2 mm), and its maximum value is measured. And the difference between the minimum values (ΔID)
I got FIG. 17 shows an example of the measurement result and the difference (ΔID) between the maximum value and the minimum value.

The ΔID thus obtained was divided by ID to determine the uniformity N of the reflection density.

N = ΔID / ID (Expression 1) As described above, ΔID is the difference between the maximum image density and the minimum image density measured by the microdensitometer, and
Is a reflection densitometer (Model 310 manufactured by X-Rite)
This is the image density measured using T).

Subsequently, the uniformity N of the reflection density is measured for all images that can be displayed (here, a solid black image (or a solid white image)), and the uniformity N of the reflection density is similarly calculated.
The calculated reflection density uniformity N is the uniformity of the reflection density of particles larger or equal to the other as the particles 1 and N _1, the particles towards homogeneity N is less than or equal to the other of the reflection density particles Assuming that the uniformity of the reflection density is N ₂ and the ratio r is obtained.

R = N ₁ (particle 1) / N ₂ (particle 2) (Equation 2) Here, N ₁ ≧ N ₂ and therefore r ≧ 1.

The uniformity N of the reflection density is a value (formula 1) obtained by dividing the difference (ΔID) between the maximum value and the minimum value of the reflection density in the solid image by the average value (ID) of the reflection density.
Is the error of Therefore, the closer the error ratio r (Equation 2) of the ID of the display image (here, the solid white image and the solid black image) to 1 is, the smaller the difference in the uniformity of the image density in the display image is. preferable.

The evaluation criteria for the uniformity of the image density are shown below.

When r is 1.0 or more and 1.5 or less ◎ (very good) When r is more than 1.5 and 2.0 or less ○ (good) When r is more than 2.0 and 2.1 or less Δ (slightly poor) When r exceeds 2.1 × (defective) FIG. 18 shows the volume average particle diameter ratio of two types of developing particles (= volume average particle diameter of developing particles BP / developing particles) for media D1 to D11. The relationship between the WP (volume average particle size) and the uniformity of the image density is shown, and Table 3 shows the results.

[0226]

[Table 3]

With the media D1 to D7 having such a volume average particle diameter ratio in the range of 1 to 10, the same level of image density uniformity was obtained in the displayed images (white solid image and black solid image). Among these, the media D1 to D4 having a volume average particle size ratio in the range of 1 to 6 were particularly effective when the uniformity ratio r of the image density of the white solid image and the black solid image was 1.5 or less. In contrast, media D8 to D8 having a volume average particle size ratio exceeding 10
In No. 11, the difference in image density uniformity became large, and the display image quality was reduced.

In this example, the uniformity of the image density was evaluated by the ratio of the density uniformity of the black particles / the density uniformity of the white particles. May be evaluated. Further, the particles are not necessarily limited only to white particles and black particles.

Next, two types of developing particles (white non-magnetic developing particles W) including magnetic developing particles were used for the media D2 to D16.
The relationship between the volume average particle diameter ratio (= volume average particle diameter of black magnetic development particles BP / volume average particle diameter of white non-magnetic development particles WP) in P and black magnetic development particles BP) and the image display speed was examined.

FIG. 1 shows each of the media D2 to D16.
The image was displayed by the image forming apparatus No. 5 in the same manner as in the evaluation of the image density uniformity. The rubber magnet plate M
G 'is an anisotropic rubber magnet MG manufactured by Shimonishi Manufacturing Co., Ltd.
01016 (11 poles / inch thickness 1.4 mm) was used.

The image display speed was evaluated as follows.

First, a solid image having a predetermined size (here, a solid white image (or a solid black image)) was formed on a medium using the apparatus shown in FIG.

At this time, the image density at the center immediately above the magnetic pole of the rubber magnet plate MG ′ was measured using a reflection densitometer (Mo-X manufactured by X-Rite).
del310T, aperture diameter 2 mm), and the reflection density of the solid image reaches a predetermined density. In other words, the reflection density of the solid white image is 0.35, and the reflection density of the solid black image is 1. The number of magnetic poles passing through the medium on the rubber magnet plate MG ′ required to change the number to 3 was counted.

Here, the reflection density of the solid white image is 0.35.
Is the display speed of a white image, and the number of magnetic poles necessary for the reflection density of a solid black image to reach 1.3 is the display speed of a black image.

The smaller the number of passing magnetic poles, the higher the image display speed, which is preferable.

The evaluation criteria for the image display speed (number of magnetic poles passing) are shown below.

When the display speed (the number of magnetic poles) is 4 or less ◎ When the display speed (the number of magnetic poles) is 5 or more and 6 or less ○ When the display speed (the number of magnetic poles) is 7 or more × In addition, an image of a black image and a white image A comprehensive evaluation of the display speed was performed. The evaluation criteria are shown below.

When the speed evaluations of the black image and the white image are both ◎, one of the speed evaluations of the black image and the white image is ○, and the other is 又 は or ○. Of the speed evaluations of the black image and the white image In the case where one is ◎ and the other is × △ in the other cases × In FIG. 19, the volume average particle diameter ratio (= the volume average of the black magnetic developing particles BP) of the two types of developing particles including the magnetic developing particles for the media D2 to D16 is shown. Particle size / white non-magnetic developing particles W
P shows the relationship between the volume average particle diameter of P) and the image display speed, and Table 4 shows the results. In the “Result” and “Evaluation” of the display speed in Table 4, “Black” indicates the display speed of the black image (the number of passing magnetic poles) and its evaluation, and “White” indicates the display speed of the white image (the number of passing magnetic poles). And its evaluation.

[0239]

[Table 4]

With the media D14 to D16 and D2 to D7 having such a volume average particle size ratio in the range of 0.5 to 10, satisfactory image display speeds were obtained. Among these, the media D16 and D2 to D5 having a volume average particle diameter ratio in the range of approximately 1 to 6 were particularly effective because the display speed of both the white image and the black image was 4 or less. On the other hand, with the media D12 and D13 having a volume average particle diameter ratio of less than 0.5, a satisfactory image display speed was not obtained. It is considered that the reason for this is that the particle size of the non-magnetic particles is larger than the particle size of the magnetic particles, and the stirring power of the magnetic particles is insufficient. In the mediums D8 to D11 having a volume average particle diameter ratio exceeding 10, the display speed of a white image was relatively high, and the display speed of a black image was relatively low. The reason for this is that the black image is displayed by scraping the non-magnetic particles (white particles in this example) attached to the image display surface of the substrate with the magnetic particles (black particles in this example). This is considered to be because the non-magnetic particles and the magnetic particles do not sufficiently contact each other, and the scraping efficiency of the magnetic particles is low, because (= the particle size of the magnetic particles / the particle size of the non-magnetic particles) is larger than 10.

[0241]

As described above, according to the present invention, image display and image erasure can be repeatedly performed, so that image display media such as paper, developer,
The use of consumables such as ink can be reduced, and a reversible image display medium capable of responding to today's environmental load reduction can be provided.

According to the present invention, high contrast
Thus, a reversible image display medium capable of displaying a high-quality image can be provided.

According to the present invention, image display is performed at a higher resolution than conventional electrophoretic image display media and twisted ball image display media, and based on an electrostatic latent image without using a counter electrode. Then, it is possible to provide a reversible image display medium capable of displaying an image with higher resolution and higher quality.

Further, according to the present invention, it is possible to provide a reversible image display medium capable of displaying images stably for a long period of time.

Further, according to the present invention, it is possible to provide a reversible image display medium which hardly generates an afterimage and therefore exhibits good reversibility.

According to the present invention, a reversible image display medium capable of displaying images at high speed can be provided.

Further, according to the present invention, it is possible to provide a reversible image display medium requiring a low drive voltage for image display.

In particular, at least two kinds of triboelectrically-charged developing particles having different charging polarities and different optical reflection densities, which constitute the developer contained in the medium, are a and b (a volume average of a). (Volume average particle size of particle size ≥ b)
When the ratio of the volume average particle size of the two types of dry developing particles (= volume average particle size of developing particles a / volume average particle size of developing particles b) is 1 or more and 10 or less, each particle is For example, when two types of developing particles of magnetic and non-magnetic developing particles having different optical reflection densities from each other are used, the difference in the granularity of image display and the non-magnetic feeling of image display by magnetic developing particles are reduced. The difference in the granularity of the image display due to the magnetically developed particles is reduced, and the image can be displayed with higher quality.

In the case where one of the at least two types of developing particles is a magnetic developing particle, the ratio of the volume average particle size of the two types of dry developing particles (=
By setting the volume average particle size of one magnetic developing particle / the volume average particle size of the other developing particle) to 0.5 or more and 10 or less, the scraping efficiency of the other developing particle by one magnetic developing particle is improved, The image display speed increases accordingly. In addition, the developer stirring force of one of the magnetic developing particles is improved, and the image display speed is correspondingly increased.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of an example of a reversible image display medium with a counter electrode before image display.

FIG. 2 is a cross-sectional view of the medium shown in FIG. 1 in an image display state.

FIG. 3 is a perspective view of a first substrate and a grid-like partition formed on the first substrate in the medium shown in FIG. 1;

FIG. 4 is a plan view of a first substrate and individual electrodes formed on the first substrate in the medium shown in FIG.

FIG. 5 is a diagram showing an example of image display on the medium shown in FIG. 1;

6A is a cross-sectional view of another example of the reversible image display medium, and FIG. 6B is a cross-sectional view of still another example of the reversible image display medium.

7A and 7B show still another example of the reversible image display medium. FIG. 7A is a cross-sectional view of the reversible image display medium before displaying an image, and FIG. It is sectional drawing of an example.

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

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

FIG. 10A is a sectional view of still another example of the reversible image display medium, and FIG. 10B is a sectional view of still another example of the reversible image display medium.

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

FIG. 12 is a diagram illustrating a schematic configuration of an example of an image forming apparatus including an ion flow type direct electrostatic latent image forming apparatus.

FIG. 13 is a diagram illustrating a schematic configuration of an example of an image forming apparatus including a multi-stylus type direct electrostatic latent image forming apparatus.

FIG. 14 is a diagram illustrating a schematic configuration of an example of an image forming apparatus including a multi-stylus type electrostatic latent image forming apparatus having adjacent control electrodes.

FIG. 15 is a diagram illustrating still another example of the image forming apparatus.

FIG. 16 is a diagram showing a solid image formed for evaluating the uniformity of the image density.

FIG. 17 shows an example of the result of measuring the reflection density for evaluating the uniformity of the image density, and the difference between the maximum value and the minimum value (Δ
FIG.

FIG. 18 is a diagram showing a relationship between a volume average particle size ratio and image density uniformity in two types of developing particles.

FIG. 19 is a diagram showing a relationship between a volume average particle diameter ratio and an image display speed in two types of developing particles including magnetic developing particles.

[Explanation of symbols]

Reference Signs List 11 reversible image display medium 111 first substrate 112 second substrate 113 partition 113a partition wall α partition wall thickness pt adjacent partition wall interval h partition wall height 114 first electrode 114a individual electrode (pixel electrode) 115th 2 electrode 116 developer storage 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 DL developer WP white development particles BP black development particles Bk black display portion BT solid Image BS Central part of solid image BT W White display part 12, 12 ', 13, 14, 15, 15' Reversible image display medium 140 Sealing part 140a Part of sealing part 140 112A Conductive film PC Photoconductor drum CH Scorotron charger EX laser image exposure device IR eraser lamp R1 Electrode roller R2 Rotating magnetic pole roller PW1 Bias power supply CRH Charger MG Magnet plate MG 'Rubber magnet plate CR2 Ion flow type direct electrostatic latent image forming device 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 Controller CR3 Multi-stylus type direct electrostatic latent image forming device e3 Electrode H3 Multi-stylus head CR4 Multi-stylus type electrostatic latent image forming device having adjacent control electrodes e4 Recording electrode e41 Control electrode H4 Electrostatic recording head RR1, RR2 Image display medium transport roller pair Ea Ground electrode

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Akihito Ikebe 2-3-113 Azuchicho, Chuo-ku, Osaka-shi, Osaka Inside Osaka International Building Minolta Co., Ltd. (72) Inventor Masaharu Kanazawa Azuchi, Chuo-ku, Osaka-shi, Osaka Osaka International Building Minolta Co., Ltd., 2-313 Machi (72) Inventor Nozomi Yome 2-3-13 Azuchicho, Chuo-ku, Osaka-shi, Osaka Osaka International Building Minolta Co., Ltd. (72) Inventor Kurita Ryuji 52-209-3-2-1 Sayama, Osaka Sayama-shi, Osaka F-term (reference) 5C094 AA06 BA09 BA75 BA76 BA93 CA19 JA08

Claims (2)

[Claims] 1. two or more substrates facing each other at a predetermined gap; one or more developer storage cells formed between the two substrates and surrounded by a partition wall; A dry developer encapsulated in a cell, wherein the dry developer has at least two kinds of dry developing particles a having different charging polarities and different optical reflection densities and having triboelectric charging properties. And b (volume average particle diameter of a ≧ volume average particle diameter of b), and the ratio of the volume average particle diameters of the two types of dry developing particles a and b (= volume average particle diameter of development particles a / A reversible image display medium having a volume average particle size of the developing particles b of 1 or more and 10 or less. 2. Two or more substrates facing each other with a predetermined gap, one or two or more developer storage cells formed between the two substrates and surrounded by a partition wall. And a dry developer encapsulated in the cell, wherein the dry developer has at least two types of dry developing particles having triboelectric charging properties having different charging polarities and different optical reflection densities from each other. Wherein at least one of the two types of dry developing particles is a magnetic developing particle, and a ratio of a volume average particle diameter of the two types of dry developing particles (=
A volume average particle diameter of one magnetic developing particle / a volume average particle diameter of the other developing particle) of 0.5 to 10;