JP2003233092A - Image display device and method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image display device which is formed by sealing particles between two substrates facing each other, moves the particles with a low driving voltage, is inexpensive and is excellent in stability and a method for the same. <P>SOLUTION: The image display device is formed by sealing the particles between the opposite substrates, at least one of which is transparent, and displays images by applying an electric field between the substrates and moving the particles. The composite particles composed of mother particles and at least one kind of child particles are adopted as the particles of the device and the particle diameter ratio, particle diameter distribution, etc., are managed, by which the compatibility of the reduction in driving voltage with the improvement in the stability during repetition of display and during preservation can be attained. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image display device and an image display method capable of repeatedly displaying and erasing an image by moving particles using Coulomb force or the like.

[0002]

2. Description of the Related Art As an image display device replacing liquid crystal (LCD), an image display device (display) using a technique such as an electrochromic system, a thermal system, and a two-color particle rotation system has been proposed. These image display devices
Compared with LCD, it can be considered as a next-generation inexpensive display device because it has a wide viewing angle similar to ordinary printed matter, consumes less power, and has a memory function. It is expected to be applied to electronic paper.

Recently, an electrophoretic method has been proposed in which a dispersion liquid composed of dispersed particles and a coloring solution is formed into microcapsules and the microcapsules are arranged between opposed substrates. However, in the electrophoretic method, particles of high specific gravity such as titanium oxide are dispersed in a solution of low specific gravity, so it is easy to settle down, it is difficult to maintain the stability of the dispersed state, and the solution for coloring is added. Due to the addition of a dye or the like to the above, there is a problem in long-term storability, and there is a problem that the image repeating stability is lacking. Even in the case of microencapsulation, the cell size is set to the microcapsule level, and such defects are apparently difficult to appear, and no essential problem is solved.

In contrast to the electrophoretic method utilizing the behavior in a solution as described above, a method using no solution at all has been proposed. These are dry display devices that utilize the behavior of particles in a gas consisting of particles and a substrate. Since no solution is used at all, problems such as sedimentation and aggregation of particles, which have been problems in the electrophoretic method, are solved. To be done. However, in the dry type display device, the driving voltage is significantly increased, and the particles can be moved by several tens of volts in the electrophoretic method, but there is a new problem that the particles cannot be moved unless it is several hundreds of volts or more. (See, for example, Non-Patent Document 1).

[0005]

[Non-Patent Document 1] Japan Imaging Society "Japan Hardcopy '99"
Proceedings July 21, 1999, p. 249-252

[0006]

SUMMARY OF THE INVENTION The present invention relates to an image display method in which particles are moved by a Coulomb force or the like, which has been earnestly studied in view of the above circumstances, to display an image. It is an object of the present invention to provide an image display device and method which are inexpensive and excellent in stability.

[0007]

Means for Solving the Problems As a result of intensive studies to achieve the above-mentioned object, the present inventors have found that in an image display device composed of opposed substrates and particles, the particles are mother particles and child particles. The present invention has been found out that the use of the composite particles made of (1) makes it possible to obtain an image display device that is inexpensive and achieves both improved stability and reduced drive voltage.

That is, the present invention provides the following image display device and method. 1. An image display device in which particles are enclosed between opposing substrates, at least one of which is transparent, and an electric field is applied between the substrates to move the particles to display an image. The image display device includes mother particles and at least one kind of child particles. An image display device using composite particles. 2. The image display device according to 1 above, wherein the ratio (B / A) of the average particle diameter d _0.5 (B) of the mother particles to the average particle diameter d _0.5 (A) of the child particles is 20 or more. (However, d _0.5 is 50 of particles
% Is larger than 50%, and 50% is smaller than 50%. ) 3. The image display device according to 1 or 2 above, wherein the average particle diameter d _0.5 of the child particles is 1 μm or less. (However, d _0.5 is 50% of particles
Is larger than this and 50% is smaller than this, and shows the numerical value expressed in μm. ) 4. The image display device according to any one of 1 to 3 above, wherein the particle size distribution Span of the mother particles represented by the following formula is less than 5. Particle size distribution Span = (d _0.9 −d _0.1 ) / d _0.5 (where d _0.5 is a numerical value expressed in μm, which is the particle size in which 50% of the particles are larger than this and 50% are smaller than this, d
_0.1 is the particle size where the ratio of particles below this is 10% is μm
And d _0.9 is the numerical value in μm of the particle diameter of which 90% or less of the particles are. ) 5. The image display device according to any one of 1 to 4 above, wherein the solvent insolubility of the composite particles represented by the following formula is 50% or more. Solvent insolubility rate (%) = (D / C) × 100 (where C is the weight of the composite particles before soaking in the solvent, and D is the weight of the composite particles after soaking the composite particles in a good solvent at 25 ° C. for 24 hours. Shown) 6. The image display device according to any one of 1 to 5 above, wherein the mother particles and the child particles are combined by any one of a mechanochemical method, a mechanofusion method, and a graft method. 7. The particles for image display according to any one of 1 to 6 above, wherein the particles are insulating particles having a volume resistivity of 1 × 10 ¹⁰ Ω · cm or more. 8. The image display device according to any one of 1 to 7 above, wherein the volume occupancy of the composite particles is 10 to 80% of the space volume between the opposing substrates. 9. 9. The image display device according to any one of 1 to 8 above, wherein the space between the opposing substrates is filled with a gas having a relative humidity at 25 ° C. of 60% RH or less. 10. 10. The image display device according to any one of 1 to 9 above, which comprises a plurality of display cells formed by partition walls located between opposed substrates. 11. The partition walls are screen-printed, sandblasted,
10. The image display device according to 10 above, which is formed by either a photoconductor paste method or an additive method. 12. The image display device according to 10 or 11 above, wherein the partition wall has a one-sided rib structure. 13. A composite particle composed of mother particles and at least one or more child particles is enclosed between opposing substrates, at least one of which is transparent, and an electric field is applied between the substrates to move the composite particles to display an image. An image display method characterized by:

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION In the image display method of the present invention, charges are applied to the surface of a substrate by some means in a display device in which particles are enclosed between opposing substrates. Negatively charged particles are attracted by the Coulomb force toward the positively charged substrate site, and positively charged particles are attracted by the Coulomb force toward the negatively charged substrate site. An image is displayed by reciprocating between the substrates facing each other. Therefore, it is necessary to design the display device so that the particles encapsulated between the substrates move so as to maintain stability during repetition or storage, and that the display can be driven at a low voltage. Here, the force exerted on the particles may be a force attracting each other by Coulomb force between particles, an intermolecular force, a Coulomb force with an electrode plate, a liquid bridge force, gravity, and the like.

However, until now, when trying to achieve stability during repeated use or during storage, the so-called dry type in which particles and substrates are the basic constituent elements without using the solution, which is the main factor that inhibits the stability If, on the contrary, the electrostatic display is selected and it is attempted to realize the reduction of the driving voltage, the particles, the substrate, and the sufficient solution for the particles to migrate using the electrophoresis in the solution are the basic constituent elements. There was no choice but to select a so-called wet type electrostatic display. That is,
There was a trade-off between improving stability during storage, avoiding sedimentation and aggregation, and improving stability during storage, and it was difficult to achieve both at the same time. The present invention, in a dry image display device composed of a substrate and particles facing each other, by forming a composite particle consisting of mother particles and child particles, moreover, by managing the particle size ratio, particle size distribution, etc., It has been found that, as compared with both the conventional dry type and the wet type, it is possible to achieve both the improvement in stability at the time of repetition and storage and the reduction in driving voltage as described above.

The present invention relates to a dry type image display method in which particles are enclosed between opposing substrates, at least one of which is transparent, and particles are moved by Coulomb force or the like to display an image. This image display is performed by moving two or more types of particles having different colors and different charging characteristics in a direction perpendicular to the substrate as shown in FIG. 1, and one type of particles as shown in FIG. There is a display method by moving it in the direction parallel to, and it can be applied to any of them,
From the viewpoint of stability, it is preferable to apply the former method.
FIG. 3 is an explanatory diagram showing an example of the structure of the image display device.
It is formed by the substrate 1, the substrate 2 and the particles 3 facing each other, and a partition wall 4 is provided as necessary.

Regarding the substrate, at least one of the substrate 1 and the substrate 2 is a transparent substrate from which the color of particles can be confirmed from the outside of the device, and a material having a high visible light transmittance and a high heat resistance is suitable. Whether or not the image display device is flexible is appropriately selected depending on the application. For example, for an application such as electronic paper, a flexible material, a mobile phone, a PDA, and a display of a portable device such as a notebook computer are used. An inflexible material is used.

Examples of the substrate material include polyethylene terephthalate, polyether sulfone, polyethylene,
Examples include polymer sheets such as polycarbonate and inorganic sheets such as glass and quartz. Substrate thickness is 2-5
000 μm, preferably 5 to 1000 μm is suitable, and when it is too thin, it becomes difficult to maintain strength and uniformity of spacing between substrates, and when it is too thick, sharpness as a display function and deterioration of contrast occur. It lacks flexibility in paper applications.

In the image display device of the present invention, the electrodes may be provided on the substrate or may be provided at other portions, for example, both ends, partition walls, or the outside of the substrate, apart from the substrate. When the electrodes are not provided on the substrate but are provided separately from the substrate, an electrostatic latent image is given to the outer surface of the substrate, and an electric field generated according to the electrostatic latent image causes the electrostatic charge of a color charged to a predetermined characteristic. By attracting or repelling the picked-up particles to the substrate, the particles arranged corresponding to the electrostatic latent image are visually recognized from the outside of the display device through the transparent substrate. The electrostatic latent image is formed by a method of transferring and forming the electrostatic latent image on the substrate of the image display device, which is performed in a normal electrophotographic system using an electrophotographic photosensitive member,
There is a method of directly forming an electrostatic latent image on a substrate by ion flow.

When an electrode is provided on the substrate, an external voltage is applied to the electrode portion to cause an electric field generated at each electrode position on the substrate to attract or repel particles of a color charged to a predetermined characteristic. The particles arranged corresponding to the electrostatic latent image are visually recognized from the outside of the display device through the transparent substrate. The electrode at this time is formed of a transparent and patternable conductive material, and, for example, indium oxide,
Metals such as aluminum, conductive polymers such as polyaniline, polypyrrole, polythiophene, etc.,
A forming method such as vacuum deposition or coating can be exemplified. In addition, the electrode thickness may be 3 to 1000 nm, preferably 5 to 400 nm, as long as the conductivity can be secured and the light transmittance is not hindered. In this case, the external voltage input may be DC or AC superimposed.

In the present invention, if necessary, a partition wall located between opposed substrates can be formed to form the display portion from a plurality of display cells. The shape of the partition wall is appropriately set appropriately according to the size of the particles involved in the display and is not particularly limited, but the width of the partition wall is 10 to 1000 μm, preferably 30 to 1000 μm.
The partition wall height is 10 to 5000 μm, preferably 10 μm.
Adjusted to ~ 500 μm. In forming the partition walls, a two-rib method in which ribs are formed on each of the opposing substrates and then joined, and a one-rib method in which ribs are formed only on one substrate are conceivable, but they prevent misalignment during joining. From the aim, it is preferable to form the partition wall by the one-rib method. The partition wall may have a gap as long as it can prevent lateral movement of particles. As shown in FIG. 4, the display cell formed by the partition wall composed of these ribs has a quadrangular shape, a triangular shape, a line shape, and a circular shape as viewed from the substrate plane direction. It is better to make the portion (area of the frame portion of the display cell) corresponding to the partition wall cross-sectional portion visible from the display side as small as possible, so that the sharpness of image display is increased. Examples of the method of forming the partition wall include a screen printing method, a sandblast method, a photoconductor paste method, and an additive method.

A concrete process of the screen printing method comprises the following steps as illustrated in FIG. (1) Prepare a paste that will be the partition wall material. (2) Stainless mesh that can print the partition pattern,
Preparing a plate-making plate made of polyester mesh or the like (3) A paste is applied and transferred onto a substrate on one side (a substrate on which the above-mentioned electrode pattern is formed, if necessary) through the plate-making plate. (4) Harden by heating. (5) The steps (3) to (4) are repeated until a predetermined thickness (corresponding to the height of the partition wall) is obtained, and a desired partition wall shape is produced.

Here, the plate-making may be any as long as a predetermined partition wall pattern can be printed. For example, meshes plated for ensuring high tension, metal meshes such as high tension material meshes, polyester meshes, tetron meshes, etc. The chemical fiber mesh, or a combination type mesh in which a polyester mesh is joined between the plate frame and the printing area can be used. An ordinary screen printing machine can be used for the screen printing, and the paste is transferred onto the substrate through the plate making using a squeegee and a scraper. In this case, the attack angle of the squeegee is 10 to 30 degrees, preferably 15 to 25 degrees, and the squeegee speed is 5 to 500 mm / se.
c, preferably 20 to 100 mm / sec, squeegee printing pressure is 0.1 to 10 kg / cm ² , preferably 0.5 to 3 kg
/ Cm ² is preferable.

As a concrete process of the sand blast method, as shown in FIG. (1) Prepare a paste that will be the partition wall material. (2) A paste is applied on one side of the substrate (the substrate on which the above-mentioned electrode pattern is formed, if necessary), and dried and cured. (3) Stick a dry film photoresist on it. (4) Only the pattern part which will be the partition wall is left by exposure and etching. (5) The pattern portion from which the resist has been removed is etched by sandblasting until it has a predetermined rib shape. When sandblasting, it is important to keep in mind that the balance between the air pressure applied to the abrasive and the injection amount of the abrasive is adjusted to ensure the straightness of the abrasive injected from the sandblasting device nozzle as much as possible. As a result, since the excessive diffusion of the abrasive is reduced, the final shape of the partition wall formed becomes clean, and especially the side edge of the partition wall is reduced. Further, as the abrasive used for sandblasting, glass beads, talc, calcium carbonate, metal powder or the like can also be used.

A concrete process of the photoconductor paste method includes the following steps as illustrated in FIG. (1) Prepare a photosensitive paste containing a photosensitive resin. (2) A photosensitive paste is applied on one side of the substrate (the substrate on which the above-mentioned electrode pattern is formed, if necessary). (3) Using a photomask, only the portion corresponding to the partition wall is exposed to light to cure the photosensitive paste. (If necessary, repeat (2) and (3) until the desired partition height is reached.) (4) Develop and remove the uncured part. (5) Bake the cured part as needed. The photosensitive paste contains at least an inorganic powder, a photosensitive resin, and a photoinitiator, and also contains a solvent, a resin, and an additive.

A concrete process of the additive method includes the following steps as illustrated in FIG. (1) Stick a photoresist film on the substrate. (2) The photoresist film is left only on the portions between the partition walls to be formed by exposure etching. (3) A paste that becomes a partition wall material is prepared and cured. (4) Remove the photoresist film to form a predetermined partition wall shape.

The paste for partition walls contains at least inorganic powder and resin, and also contains solvent, additives and the like. The inorganic powder is ceramic powder or glass powder, and one kind or a combination of two or more kinds is used.
Examples of the ceramic powder include ZrO ₂ , Al ₂ O ₃ ,
Examples thereof include oxide-based ceramics such as CuO, MgO, TiO ₂ and ZnO _2, and non-oxide-based ceramics such as SiC, AlN and Si ₃ O ₄ . As an example of glass powder,
Examples include raw materials of SiO ₂ , Al ₂ O ₃ , B ₂ O ₃ , and ZnO, which are melted, cooled, and pulverized. The glass transition point Tg of the glass powder is preferably in the range of 300 to 500 ° C. In this range, the temperature can be lowered in the firing process, and there is an advantage that the resin is less damaged.

Here, the particle size distribution Span represented by the following formula of the partition wall inorganic paste powder is preferably 8 or less, more preferably 5 or less. Particle size distribution Span = (d _0.9 −d _0.1 ) / d _0.5 (where d _0.5 is a numerical value expressed in μm, which is the particle size in which 50% of the particles are larger than this and 50% are smaller than this, d
_0.1 is the particle size where the ratio of particles below this is 10% is μm
And d _0.9 is a numerical value in μm in which the particle diameter of 90% or less of the particles is 90 μm. ) By setting the particle size distribution Span of the partition wall paste inorganic powder within the range of 8 or less, the sizes of the inorganic powder in the paste are made uniform, and even if the above-mentioned process of applying and curing the paste is repeatedly laminated. Therefore, the partition wall can be formed with high accuracy.

The particle size of the inorganic powder in the paste is
The thickness is preferably 0.1 to 20 μm, more preferably 0.3 to 10 μm. By setting the thickness in such a range, similarly, it is possible to form the partition wall with high accuracy during repeated stacking. The above particle size distribution and particle size can be determined by a laser diffraction / scattering method or the like. When a particle to be measured is irradiated with a laser beam, a light intensity distribution pattern of diffracted / scattered light is spatially generated. Since this light intensity pattern has a correlation with the particle size, the particle size and the particle size distribution can be measured. . The particle size and the particle size distribution are obtained from the volume standard distribution. Specifically, Master
Using a sizer2000 (Malvern Instruments Ltd.) measuring machine, put the particles into a nitrogen stream and use the included analysis software (Ma
The particle size and particle size distribution can be measured with software based on the volume standard distribution using the il theory).

The resin contained in the partition paste may contain any of the above-mentioned inorganic powders as long as it can form a predetermined partition shape, and examples thereof include thermoplastic resins, thermosetting resins and reactive resins. Considering the required physical properties of the bulkhead,
The higher the molecular weight and the higher the glass transition point, the better. For example, acrylic, styrene, epoxy, phenol, urethane, polyester, urea and the like are mentioned, and acrylic, epoxy, urethane and polyester are particularly preferable.

Any solvent may be added to the partition paste so long as it is compatible with the above-mentioned inorganic powder and resin. For example, an aromatic solvent such as phthalate ester, toluene, xylene, benzene, or oxy Examples thereof include alcohol solvents such as alcohol, hexanol, and octanol, and ester solvents such as acetic acid ester, and usually 0.1 to 50 parts by weight is added to the inorganic powder. In addition, a dye, a polymerization inhibitor, a plasticizer, a thickener, a dispersant, an antioxidant, a curing agent, a curing accelerator, and an anti-settling agent may be added to the paste, if necessary. The paste material composed of these is a kneader, a stirrer,
Dispersed and mixed with this roller. Taking workability into consideration, the viscosity is preferably 500 to 300,000 cps.

In the present invention, the particles to be enclosed between the substrates are composite particles composed of mother particles having a large particle diameter and child particles having a small particle diameter. A plurality of child particles are used so as to cover the surface of the mother particle, and one kind or a plurality of kinds are used. The ratio (B / A) of the average particle diameter d _0.5 (B) of the mother particles to the average particle diameter d _0.5 (A) of the child particles in the composite particles is 20 or more, preferably 100 or more, more preferably 300 or more. is important. The average particle diameter d _0.5 of the child particles is 1 μm.
Or less, preferably 0.1 μm or less, more preferably 0.
It should be less than 05 μm. The average particle diameter d _0.5
In the particle size distribution of each particle, 50% of particles are larger than 50% and smaller than 50% of the particles are numerical values expressed in μm.

Regarding the particle size distribution of the mother particles, the particle size distribution Span represented by the following formula is less than 5, preferably 3
Less than Particle size distribution Span = (d _0.9 −d _0.1 ) / d _0.5 (where d _0.5 is 50% larger than 50%
Is the numerical value of the particle size that is smaller than this, expressed in μm, d
_0.1 is the particle size where the ratio of particles below this is 10% is μm
And d _0.9 is a numerical value in μm in which the particle diameter of 90% or less of the particles is 90 μm. ) By setting the particle size distribution Span of the mother particles within the range of 5 or less, the size of each particle becomes uniform, and uniform particle movement becomes possible.

With respect to the particle size of the mother particles, the average particle size d _0.5 is preferably 0.1 to 50 μm.
The particle size distribution and the particle size can be measured in the same manner as the particle size distribution and the particle size of the partition paste inorganic powder. By designing the mother particles and the child particles in this way, the driving voltage can be significantly reduced while maintaining stability. The reason for this is not clear, but by arranging minute child particles having a particle size of 1/20 or less on the surface of the mother particles having a uniform particle size distribution, the particle size is almost uniform in a macroscopic view, In addition, microscopically, it is presumed that the surface of the mother particle can be a composite particle in which fine irregularities are formed due to the arrangement of the child particles. Therefore, the macroscopic uniformity of particle size contributes to the repeated stability during particle movement, that is, the improvement in stability during durability storage, and the microscopic unevenness on the particle surface contributes to the adhesion force to the substrate. It is considered that this contributes to the reduction, that is, the reduction of the driving voltage. Therefore, it is not necessary to simply combine the mother particles and the child particles, and it is important to properly manage and design them within the range described above.

The composite method of the mother particles and the child particles is a mechanochemical method in which the mother particles are fixed by applying mechanical energy such as driving the mother particles on the surface of the mother particles, or the child particles are mechanically fixed on the surface of the mother particles. A mechanofusion method in which thermal energy is added in addition to energy for diffusion and fixation, or a graft method in which child particles are chemically bonded to the surface of mother particles can be used. In addition, the mother particles themselves and the child particles themselves are prepared by kneading and pulverizing the necessary resin, charge control agent, colorant, and other additives, polymerizing from a monomer, or existing particles are resin-charged. Control agent, colorant,
It may be coated with other additives.

Examples of resins, charge control agents, colorants, and other additives are shown below. Examples of the resin include urethane resin, acrylic resin, polyester resin, urethane-modified acrylic resin, silicone resin, nylon resin, epoxy resin, styrene resin, butyral resin, vinylidene chloride resin, melamine resin, phenol resin, and fluororesin. It is also possible to mix two or more kinds, and in particular, in order to control the adhesive force with the substrate, an acrylic urethane resin,
Acrylic urethane silicone resin, acrylic urethane fluororesin, urethane resin, and fluororesin are suitable.

Examples of the charge control agent include quaternary ammonium salt compounds, nigrosine dyes, triphenylmethane compounds and imidazole derivatives in the case of imparting a positive charge, and in the case of imparting a negative charge. Examples thereof include metal-containing azo dyes, salicylic acid metal complexes, and nitroimidazole derivatives. Examples of colorants include basic and acidic dyes such as nigrosine, methylene blue, quinoline yellow, and rose bengal. Examples of inorganic additives include titanium oxide, zinc oxide, zinc sulfide, antimony oxide, calcium carbonate, lead white, talc,
Silica, calcium silicate, alumina white, cadmium yellow, cadmium red, cadmium orange, titanium yellow, navy blue, ultramarine blue, cobalt blue, cobalt green, cobalt violet, iron oxide, carbon black, manganese ferrite black, cobalt ferrite black, copper powder , Aluminum powder and the like.

Although the child particles may be made from the above-mentioned materials, it is preferable to use the existing powder as it is. For example, titanium oxide, zinc oxide, zinc sulfide, antimony oxide and calcium carbonate are used. , Lead white, talc, silica, calcium silicate, alumina white, cadmium yellow, cadmium red, cadmium orange, titanium yellow, dark blue, ultramarine, cobalt blue,
Examples thereof include cobalt green, cobalt violet, iron oxide, carbon black, manganese ferrite black, cobalt ferrite black, copper powder and aluminum powder, and titanium oxide, zinc white and carbon black are particularly preferable.

By controlling the water content and solvent insolubility of these particles, the durability against repeated use is improved. The water content of the particles is preferably 3% by weight or less, and particularly preferably 2% by weight or less. The water content is measured by AS
The measurement is performed according to TM-D570, and the measurement conditions are 23 ° C. and 24
Time. Regarding the solvent insolubility of the particles, the solvent insolubility of the particles represented by the following relational expression is 50% or more, particularly 70
% Or more is preferable. Solvent insolubility rate (%) = (D / C) × 100 (where C is the weight of the particles before soaking in the solvent, and D is the weight after soaking the particles in a good solvent at 25 ° C. for 24 hours). If the ratio is less than 50%, bleeding may occur on the surface of the particles during long-term storage, which may affect the adhesive force with the particles, hinder the movement of the particles, and may impair the durability of image display. As a solvent (good solvent) when measuring the solvent insolubility rate, methyl ethyl ketone or the like in a fluororesin, methanol or the like in a polyamide resin, methyl ethyl ketone, toluene or the like in an acrylic urethane resin, acetone or isopropanol in a melamine resin, or a silicone resin Toluene and the like are preferable.

Regarding the filling amount of the particles, the volume occupancy of the particles is 10 to 10 with respect to the space volume between the substrate 1 and the substrate 2.
The volume should be 80%, preferably 10 to 60%. Here, the space volume of the substrate 1 and the substrate 2 is so-called particle filling, which is provided between the opposing substrate 1 and the substrate 2 except the occupied portion of the partition wall 4 and the device sealing portion, which are provided as necessary. It shall refer to the possible volume. Since the particles are required to retain the charged electric charge, insulating particles having a volume resistivity of 1 × 10 ¹⁰ Ω · cm or more are preferable, and insulating particles having a volume resistivity of 1 × 10 ¹² Ω · cm or more are particularly preferable.

Further, in the present invention, it is important to control the gas in the space surrounding the particles between the substrates, which contributes to the improvement of display stability. Specifically, regarding the humidity of the gas in the space, it is important to set the relative humidity at 25 ° C. to 60% RH or less, preferably 50% RH or less, and more preferably 35% RH or less. In FIG. 3, the space portion is defined as a portion sandwiched between the substrate 1 and the substrate 2 facing each other.
The so-called gas portion in contact with particles, excluding the occupied portion of the particles 3, the occupied portion of the partition wall 4, and the device sealing portion, is meant. The gas in the space may be of any type as long as it is in the above-mentioned humidity range, but dry air, nitrogen, argon, helium or the like is preferable. This gas needs to be enclosed in the device so that its humidity is maintained,
For example, it is important to assemble particles, substrates and the like under a predetermined humidity environment, and further to apply a sealing material and a sealing method for preventing moisture from entering from the outside.

The image display device of the present invention includes a display unit of a mobile device such as a notebook computer, a PDA and a mobile phone, an electronic book, an electronic paper such as an electronic newspaper, a signboard,
It is used for posters, bulletin boards such as blackboards, copiers, rewritable paper as a substitute for printer paper, calculators, display parts for home appliances, and display parts for point cards.

[0038]

EXAMPLES Next, the present invention will be described more specifically by showing Examples and Comparative Examples. However, the present invention is not limited to the following examples. The characteristics of the particles and the image display device obtained in Examples and Comparative Examples were evaluated according to the following criteria.

(1) Average particle size and particle size distribution of mother particles and child particles Span Mastersizer2000 (Malvern instruments Ltd.) Each particle was put into a measuring machine, and attached analysis software (particle size distribution based on volume standard distribution) The following values were determined using software for calculating the particle size). Particle size distribution Span = (d _0.9 −d _0.1 ) / d _0.5 (where d _0.5 is a numerical value expressed in μm, which is the particle size in which 50% of the particles are larger than this and 50% are smaller than this, d
_0.1 is the particle size where the ratio of particles below this is 10% is μm
And d _0.9 is a numerical value in μm in which the particle diameter of 90% or less of the particles is 90 μm. The average particle diameter (μm) was set to the value of d _0.5 described above, and the particle diameter ratio (B / A) of the mother particles (B) and the child particles (A) was determined.

(2) Solvent insolubility rate Each particle was immersed in a methyl ethyl ketone solvent at 25 ° C. for 24 hours and dried at 100 ° C. for 5 hours, and the weight was measured. From the weight change before and after immersion, the solvent insolubility was measured according to the following formula. Solvent insolubility rate (%) = (D / C) × 100 (where C is the weight of the particles before soaking in the solvent, and D is the resin weight after soaking the particles in the MEK solvent)

(3) Evaluation of display function The voltage applied to the manufactured display device was gradually increased, and the voltage at which particles moved to enable display was measured as the minimum drive voltage. In the specific example, as shown in FIG. 9, a voltage that becomes a threshold value in the relationship between the applied voltage and the reflection density is the minimum driving voltage. Next, by applying a voltage of the lowest driving voltage +10 V and reversing the polarity, black to white display was repeated. For the evaluation of the display function, the contrast ratio was measured using a reflection image densitometer for the initial display after repeating 10,000 times and after standing for 5 days in black and white. Here, the contrast ratio is the reflection density at the time of black display with respect to the time of white display (contrast ratio = reflection density at the time of black display / reflection density at the time of white display). In addition, the contrast ratio after 10000 times the initial contrast ratio and after standing for 5 days was expressed as a retention rate.

Example 1 A display device was manufactured as follows. First, a substrate with electrodes having a partition wall was prepared. 200 μm height on a glass substrate with an indium oxide electrode of about 500 Å thickness
Ribs were formed to form a stripe-shaped rib structure. Ribs were formed as follows. First, the paste is prepared by melting, cooling and crushing a glass powder of a mixture of SiO ₂ , Al ₂ O ₃ , B ₂ O ₃ and ZnO as an inorganic powder, and a thermosetting epoxy resin as a resin.
A paste prepared to have a viscosity of 12,000 cps with a solvent was prepared. Next, this paste is applied to the entire surface of the above-mentioned substrate, heat-cured at 150 ° C., and this application to curing is repeated to obtain a thickness (corresponding to the height of the partition wall) of 20.
It was adjusted to be 0 μm. A dry photoresist is attached, and the line is 50μ by exposure and etching.
A mask having a partition pattern of m, space 200 μm, pitch 250 μm was formed. Excessive portions were removed by sandblasting so as to have a predetermined partition shape, and predetermined stripe-shaped partition walls were formed. Further, particles A and particles B were prepared. In the particle A, urethane particles (average particle diameter 5.8 μm) are used as mother particles, carbon (average particle diameter 0.03 μm) is used as child particles, and Bontron No. 10 is used as a charge control agent. 7 was mixed and the child particles and the charge control agent were fixed on the surface of the mother particles by the mechanofusion method to form composite particles. In particle B, urethane particles (average particle size 5.8 μm) are used as mother particles and TiO 2 is used as child particles.
₂ (average particle diameter 0.015 μm) and Bontron E89 as a charge control agent were mixed, and the child particles and the charge control agent were immobilized on the surface of the mother particles by the mechanofusion method to form composite particles. The above-mentioned particles A and B are put between the glass substrates with electrodes having the ribs and the glass substrate having the indium oxide electrode with a thickness of about 500Å prepared by the spacer so that the distance between them is 400 μm. An image display device was produced by adhering the periphery of the glass substrate with an epoxy adhesive and enclosing the particles. Particle A
The mixing ratios of the particles and the particles B were the same weight, and the volume occupancy ratio of the particles between the glass substrates was adjusted to be 60% by volume. The gas filling the space was air with a relative humidity of 35% RH. Particle size and particle size distribution Span of each particle (simply Span
And the particle diameter ratio of the mother particles and the child particles, the solvent insolubility ratio, and the evaluation result of the display function of the obtained image display device.
Shown in the table.

Example 2 A display device was manufactured in the same manner as in Example 1 except that the material of the mother particles of the particles A was carbon microbeads ICB. The characteristics of each particle and the evaluation results are shown in Table 1. Since the particle size distribution Span was large, the durability was slightly deteriorated.

Example 3 A display device was manufactured in the same manner as in Example 1 except that the material of the child particles of particle B was acrylic acid containing titanium oxide (TiO ₂ ). The characteristics of each particle and the evaluation results are shown in Table 1. Since the particle diameter ratio of the mother particles and the child particles of the particles B was large, the minimum driving voltage was slightly increased, and the initial contrast ratio and the holding ratio were slightly lowered.

Example 4 A display device was manufactured in the same manner as in Example 1 except that the partition wall was not formed. The characteristics of each particle and the evaluation results are shown in Table 1. Since there is no partition wall, durability deteriorated a little.

Comparative Example 1 In Example 1, the material of the mother particle of particle A was Bontron No. 7 was added, Bontron E89 was added to the material of the mother particles of particle B, and the child particles were not used, and a display device was manufactured in the same manner. The characteristics of each particle and the evaluation results are shown in Table 1. Since the child particles are not used, the driving voltage is significantly deteriorated.

[0047]

[Table 1]

[0048]

According to the present invention, in a dry image display device composed of a substrate and particles facing each other, the particles are composite particles composed of a mother particle and a child particle, so that they are excellent in repeated durability at a low driving voltage. An image display device that can display an image, is inexpensive, and achieves both improved stability and reduced drive voltage can be obtained.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a display system in an image display device of the present invention.

FIG. 2 is an explanatory diagram showing a display system in the image display device of the present invention.

FIG. 3 is an explanatory diagram showing an example of the structure of the image display device of the present invention.

FIG. 4 is a diagram showing an example of the shape of partition walls in the image display device of the present invention.

FIG. 5 is an explanatory diagram of a process of forming partition walls by a screen printing method in the image display device of the present invention.

FIG. 6 is an explanatory diagram of a process of forming partition walls by a sandblast method in the image display device of the present invention.

FIG. 7 is an explanatory diagram of a process of forming partition walls by a photoconductor paste method in the image display device of the present invention.

FIG. 8 is an explanatory diagram of a process of forming partition walls by an additive method in the image display device of the present invention.

FIG. 9 is an explanatory diagram showing a method of measuring the minimum driving voltage in the example.

[Explanation of symbols]

1, 2: substrate 3: Particle 4: Partition wall

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Kazuya Murata             3-5-5 Ogawahigashi-cho, Kodaira-shi, Tokyo (72) Inventor Yakushiji Manabu             3-2- 6-408 Ogawahigashi-cho, Kodaira-shi, Tokyo (72) Inventor Hajime Kitano             3-5-5 Ogawahigashi-cho, Kodaira-shi, Tokyo (72) Inventor Takahiro Kawagoe             1302-57 Aobadai, Tokorozawa, Saitama Prefecture

Claims (13)

[Claims] 1. An image display device in which particles are enclosed between opposing substrates, at least one of which is transparent, and an electric field is applied between the substrates to move the particles to display an image, wherein mother particles and at least one child are used as particles. An image display device characterized by using composite particles composed of particles. 2. The image display device according to claim 1, wherein the ratio (B / A) of the average particle diameter d _0.5 (B) of the mother particles to the average particle diameter d _0.5 (A) of the child particles is 20 or more. (However, d _0.5 represents a numerical value expressed in μm of the particle diameter in which 50% of the particles are larger than this and 50% are smaller than this.) 3. The image display device according to claim 1, wherein the average particle diameter d _0.5 of the child particles is 1 μm or less.
(However, d _0.5 represents a numerical value expressed in μm of the particle diameter in which 50% of the particles are larger than this and 50% are smaller than this.) 4. A particle size distribution Sp of a mother particle represented by the following formula
The image display device according to claim 1, wherein an is less than 5. Particle size distribution Span = (d _0.9 −d _0.1 ) / d _0.5 (where d _0.5 is a numerical value expressed in μm, which is the particle size in which 50% of the particles are larger than this and 50% are smaller than this, d
_0.1 is the particle size where the ratio of particles below this is 10% is μm
And d _0.9 is the numerical value in μm of the particle diameter of which 90% or less of the particles are. ) 5. The image display device according to claim 1, wherein the solvent insolubility of the composite particles represented by the following formula is 50% or more. Solvent insolubility rate (%) = (D / C) × 100 (where C is the weight of the composite particles before soaking in the solvent, and D is the weight of the composite particles after soaking the composite particles in a good solvent at 25 ° C. for 24 hours. Show) 6. A mother particle and a child particle are mechanochemical methods,
The image display device according to claim 1, wherein the image display device is compounded by any one of a mechanofusion method and a graft method. 7. The particles have a volume resistivity of 1 × 10 ¹⁰ Ω · cm.
The particles for image display according to any one of claims 1 to 6, which are the above insulating particles. 8. The image display device according to claim 1, wherein the volume occupancy of the particles is 10 to 80% of the space volume between the opposing substrates. 9. The image display device according to claim 1, wherein the space between the opposing substrates is filled with a gas having a relative humidity at 25 ° C. of 60% RH or less. 10. The image display device according to claim 1, comprising a plurality of display cells formed by partition walls located between opposed substrates. 11. The image display device according to claim 10, wherein the partition wall is formed by any one of a screen printing method, a sandblast method, a photoconductor paste method, and an additive method. 12. The partition wall has a one-sided rib structure.
Alternatively, the image display device according to claim 11. 13. A composite particle composed of mother particles and at least one kind of child particles is enclosed between opposing substrates, at least one of which is transparent, and an electric field is applied between the substrates to move the composite particles. An image display method characterized by displaying an image.