JP2007033637A - Image display medium and image display apparatus using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image display medium capable of performing reversible display and having a memory property, especially high contrast and high resolution and high response speed and to provide the image display medium further having high material selectivity and satisfactory long time stability and capable of securing security also in practical use. <P>SOLUTION: A dispersion liquid 5 comprising at least self dispersable white fine particles 4 and self dispersable colored fine particles 3, a nonpolar solvent, a resin soluble in the nonpolar solvent, a resin dispersant and a compound having a non-ionic polar group is contained between two conductive layers which are disposed at a desired interval and at least one or both of which are light transmissive. The self dispersable white fine particles 4 have positive or negative charges generated by acid/base dissociation and the self dispersable colored fine particles 3 have positive charges (when the self dispersable white fine particles 4 have negative charges) or negative charges (when the self dispersable white fine particles have positive charges) generated by a method except the acid/base dissociation. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image display medium capable of reversibly changing a visual state by moving white fine particles and colored fine particles charged by the action of an electric field, and an image display device using the image display medium.

Conventionally, a CRT or a liquid crystal display is used as a terminal for displaying so-called images such as characters, still images, and moving images.
These can display and rewrite digital data instantly, but it is difficult to always carry the device, many eyes are tired from long-term work, and cannot be displayed when the power is turned off. There is also.
On the other hand, when characters and still images are distributed and stored as documents, they are widely used as so-called hard copies recorded on paper media by printers.
Hard copy is easier to read than display, less fatigue, and can be read freely. Furthermore, it has the characteristics that it is lightweight and can be carried freely.
However, hard copies are discarded and recycled after they are used. However, this requires a lot of labor and cost, so that a problem remains from the viewpoint of resource saving.

For this reason, there is a great need for a rewritable paper-like display medium that has the advantages of both the above-mentioned display and hard copy. To date, polymer dispersed liquid crystals, bistable cholesteric liquid crystals, electrochromic devices, electrophoresis A device using an element has been proposed, and has attracted attention as a display medium having a memory property and having a reflective and bright display.
Among them, the one using an electrophoretic element is superior in terms of display quality and power consumption during display operation. Patent Document 1 discloses a dispersion including electrophoretic particles between a pair of counter electrode plates, at least one of which is transparent. An electrophoretic display device is described in which a system is enclosed and electrophoretic particles are adsorbed and separated from the transparent electrode plate side by the action of a display driving voltage applied between the electrode plates to perform a display operation. 2 includes a dispersion system in which electrophoretic particles are dispersed with a porous spacer interposed between a pair of opposed electrode plates, at least one of which is configured to be transparent, and divided into discontinuous phases and enclosed. An electrophoretic display device is described. A typical form thereof is shown in FIG.

In FIG. 3, 6 is a transparent substrate such as glass, 7 is a transparent electrode formed in a required pattern on one side, and a colored dispersion medium is interposed between the pair of transparent electrodes 7 arranged opposite to each other. A dispersion liquid 8 in which a plurality of electrophoretic particles having a color different from the color of the dispersion medium is dispersed is enclosed.
The electrophoretic particles are charged on the surface in the dispersion medium, and when a voltage opposite to the electrophoretic particle charge is applied to one of the transparent electrodes 7, the electrophoretic particles accumulate on the surface and the color of the electrophoretic particles is observed. When a voltage having the same direction as the charge of the electrophoretic particles is applied, the electrophoretic particles move to the opposite side, so that the color of the dispersion medium is observed. As a result, display can be performed.
Here, in the structure in which the dispersion liquid 8 is simply enclosed between the electrodes 7 and 7, display unevenness may occur due to aggregation or adhesion phenomenon of the migrating particles. By arranging the perforated spacer 9 in a shape, the dispersion liquid 8 is discontinuously divided so as to stabilize the display operation. However, in the case of such a structure, there has been a problem that it is difficult to uniformly enclose the dispersion liquid, or it is difficult to obtain reproducibility by changing the characteristics of the dispersion liquid at the time of encapsulation.

  It is known that the stability of dispersed particles is generally obtained by the action of an electrostatic effect or a steric effect (also referred to as an adsorption layer effect). The DLVO theory has been established for the electrostatic effect. In this theory, the spread of the electric double layer and the interface potential (so-called ζ potential) are important factors. Therefore, the presence of ions that form these is required, and some studies have been made on aqueous solvent systems in which the presence of ions is clear.

On the other hand, a steric effect corresponding to the DLVO theory has not yet been established, but the following researches are known for non-aqueous solvent systems (mainly petroleum solvents), for example.
That is, the research described in Non-Patent Document 1 relates to a basic production method of a stable non-aqueous solvent dispersion, and this method is compatible with particles dispersed in a solvent (insoluble in a solvent) in the solvent. A block or graft copolymer containing a soluble component and a component soluble in the solvent is produced and used.

As a method utilizing this method, Patent Document 3 describes a method of obtaining a stable polymethyl methacrylate (PMMA) dispersion by radical polymerization of methyl methacrylate (MMA) in a hydrocarbon solvent in the presence of degradable rubber. Has been. It is unlikely that the degraded rubber is adsorbed to the PMMA particles by this method. From the fact that the PMMA particles are dispersed and stabilized, it is considered that MMA is graft-polymerized on the degraded rubber. Further, in this graft polymer, it is considered that the insoluble part is associated with the particle surface and the dissolved part has a steric effect, and as a result, the dispersion stability of the particle is maintained.
Examples of a method that aims to stabilize the dispersion of particles in electrophoretic display include a method in which a pigment molecule and a polymer dispersant described in Patent Document 4 are bonded by a covalent bond as a method that utilizes a steric effect. However, in this case, although dispersion stability based on the steric effect due to the polymer chain can be expected, the effect due to electrostatic repulsion cannot be expected, so that the dispersion stability is insufficient.
Patent Document 5 describes a method for enhancing dispersion stability by both a steric effect and electrostatic repulsion by combining a pigment having an acidic site and a polymer dispersant having an amino group. However, in this case, the pigment itself must have an acid in the molecule, and its selection is limited. In addition, since acid-base dissociation in a nonpolar solvent is very small unlike polar solvents such as water, the electrostatic effect is usually small.

  As described above, in the electrophoretic display medium so far, positive and negative charged fine particles are mixed together, and fine particles having different charges move in different directions according to the positive and negative electrodes. In this case, if fine particles having different charges are blended in the same dispersion, positive and negative charged particles attract each other and the stability of the fine particles in the dispersion is impaired and aggregated, or positively charged fine particles are applied to the electrode. Various problems have arisen, such as the movement of negatively charged fine particles, and conversely the movement of negatively charged fine particles to the electrode.

JP-A-5-173194 Japanese Patent No. 2612472 Japanese Patent Publication No. 40-7047 US Pat. No. 5,914,806 Japanese National Patent Publication No. 9-500458 F. A. Waite, J .; Oil Col. Chem. Assoc. , 54, 342 (1971)

In view of the above-described prior art, the object of the present invention is to enable reversible display by combining positively charged self-dispersing fine particles and negatively charged self-dispersing fine particles, have a memory property, and in particular, contrast. And providing an image display medium with high resolution and high response speed.
Another object of the present invention is to provide an image display medium having high material selectivity, good long-term stability, and ensuring safety in actual use.

The first aspect of the present invention includes at least self-dispersing white fine particles and self-dispersing colored fine particles, a non-polar solvent, a nonpolar solvent, between two conductive layers that are disposed at a desired interval and at least one or both are light transmissive. Contains a dispersion composed of a resin soluble in a polar solvent, a resin dispersant, and a compound having a nonionic polar group, and the self-dispersing white fine particles have a positive or negative charge generated by acid-base dissociation. The self-dispersing colored fine particles have a positive charge (when the self-dispersing white fine particles are negatively charged) or a negative charge (when the self-dispersing white fine particles are positively charged) generated by a method other than acid-base dissociation. The present invention relates to an image display medium.
A second aspect of the present invention includes at least self-dispersing white fine particles and self-dispersing colored fine particles, a nonpolar solvent, a non-polar solvent, and at least one or both of the light-transmitting conductive layers disposed at a desired interval. Contains a dispersion composed of a resin soluble in a polar solvent, a resin dispersant, and a compound having a nonionic polar group, and the self-dispersing colored fine particles have a positive or negative charge generated by acid-base dissociation. The self-dispersing white fine particles have a positive charge (when the self-dispersing colored fine particles are negatively charged) or a negative charge (when the self-dispersing colored fine particles are positively charged) generated by a method other than acid-base dissociation. The present invention relates to an image display medium.
A third aspect of the present invention relates to the image display medium according to claim 1 or 2, wherein the method other than the acid-base dissociation is a surfactant.
A fourth aspect of the present invention relates to the image display medium according to claim 3, wherein the surfactant is a nonionic surfactant.
A fifth aspect of the present invention relates to the image display medium according to claim 1, wherein the method other than the acid-base dissociation is based on a polymer dispersant.
According to a sixth aspect of the present invention, the self-dispersing white fine particles having a charge or the self-dispersing colored fine particles having a charge have at least an acidic group on the surface, and at least a resin soluble in the nonpolar solvent. It has a basic group, It is related with the image display medium in any one of Claims 1-5 characterized by the above-mentioned.
According to a seventh aspect of the present invention, the self-dispersing white fine particles having electric charge or the self-dispersing colored fine particles having electric charge have a basic group at least on the surface and are soluble in the nonpolar solvent. It has an acidic group at least, It is related with the image display medium in any one of Claims 1-5 characterized by the above-mentioned.
According to an eighth aspect of the present invention, the compounding ratio (weight) of the self-dispersing white fine particles having a charge or the self-dispersing colored fine particles having a charge and a resin soluble in the nonpolar solvent is 1 to 1 to 50 pairs. 8. The image display medium according to claim 1, wherein the image display medium is in a range of 1.
According to a ninth aspect of the present invention, the self-dispersing white fine particles having electric charge and the self-dispersing colored fine particles having electric charge are composed of at least a pigment and a resin, and the weight ratio of the pigment to the resin is 100 parts by weight of the resin. The image display medium according to claim 1, wherein the pigment content is 0.1 to 300 parts by weight with respect to the pigment.
The tenth aspect of the present invention relates to the image display medium according to any one of claims 1 to 9, wherein the self-dispersing white fine particles are titanium oxide.
The eleventh aspect of the present invention relates to the image display medium according to any one of claims 1 to 10, wherein the self-dispersing colored fine particles are carbon black.
The twelfth aspect of the present invention relates to the image display medium according to any one of claims 1 to 11, wherein the self-dispersing fine particles are fine particles modified with a surface functional group.
The thirteenth aspect of the present invention relates to the image display medium according to any one of claims 1 to 12, wherein the self-dispersing fine particles are any of core-shell polymer fine particles, graft polymer fine particles, and capsule polymer fine particles. .
A fourteenth aspect of the present invention relates to the image display medium according to any one of claims 1 to 13, wherein the self-dispersing colored fine particles are acrylic copolymer graft carbon black.
The fifteenth aspect of the present invention relates to the image display medium according to any one of claims 1 to 14, wherein the self-dispersing colored fine particles are silicone polymer graft carbon black.
16. The image display according to claim 1, wherein the self-dispersing white fine particles and the self-dispersing colored fine particles have an average particle size of 0.01 μm to 1 μm. It relates to the medium.
The seventeenth aspect of the present invention relates to the image display medium according to any one of claims 1 to 16, wherein the nonpolar solvent is any one of an aliphatic hydrocarbon, an aromatic hydrocarbon, and a silicone oil. .
An eighteenth aspect of the present invention relates to an image display apparatus having the image display medium according to any one of claims 1 to 17.
The nineteenth aspect of the present invention relates to the image display device according to claim 18, wherein the image display device includes a microcapsule in which an image display medium is enclosed.
The twentieth aspect of the present invention relates to the image display device according to claim 18 or 19, wherein the average particle diameter of the microcapsules is 10 μm to 150 μm.
The twenty-first aspect of the present invention relates to the image display device according to any one of claims 18 to 20, wherein the material of the microcapsule is gelatin or gum arabic.
The twenty-second aspect of the present invention relates to the image display device according to any one of claims 18 to 21, wherein the microcapsules are formed on a sheet.

Hereinafter, the present invention will be described in detail with reference to the drawings.
The operation principle of image display by the image display medium of the present invention is as follows.
FIG. 1 is a cross-sectional view showing an example of the display medium of the present invention.
In the figure, reference numerals 1 and 2 denote two conductive layers, one or both of which are light transmissive, and are internally charged positively charged self-dispersing colored fine particles 3 and negatively charged self-dispersing particles. It has a dispersion 5 composed of white fine particles 4, a nonpolar solvent, a resin soluble in the nonpolar solvent, a resin dispersant, and a compound having a nonionic polar group.
Here, when the conductive layer 2 is translucent, when the medium is viewed from above the conductive layer 2, the color of the self-dispersing white fine particles 4 can be seen. At this time, the resin soluble in the nonpolar solvent is adsorbed on the charged self-dispersing colored fine particles 3 or the charged self-dispersing white fine particles 4, and the dispersion stability of the charged white and colored fine particles is increased by the steric effect. Enables long-term stability.

On the other hand, FIG. 2 is a cross-sectional view showing an example of an operation mechanism when an image is displayed by actually driving the medium of FIG.
In FIG. 2A, when a charge is applied from the outside to the conductive layers 1 and 2 in which the right half and the left half of the display medium are partitioned, the positively charged self-dispersing colored fine particles 3 are It moves upward along the external electric field as shown in FIG.
FIG. 2C shows a state in which positively charged self-dispersing colored fine particles 3 have reached the conductive layer 2. Here, the conductive layer 2 and the positively charged self-dispersing colored fine particles 3 are attached by the electrostatic force and the movement is completed.
When the state of FIG. 2C is viewed from above the medium (outside the conductive layer 2), the left half is negatively charged self-dispersing white fine particles 4 and the right half is positively charged self-dispersing colored fine particles. You can expect 3 colors.
In addition, as shown in FIG. 2C, some charged colored fine particles 3 may remain inside.
This is presumably because the charged colored fine particles 3 and the charged white fine particles 4 have insufficient fluidity, and therefore there is a portion where the mechanical resistance to movement of the charged colored fine particles 3 is large.
In order to prevent this phenomenon, it is conceivable to improve the fluidity of the particles. However, if the fluidity of the particles is excessively improved, the colored fine particles 3 and the charged white fine particles 4 are charged by external impact or vibration. It may move and the display image may be damaged.
Ideally, the fluidity of the particles is good during the rewriting operation of the image, and it is desired that the fluidity deteriorates at the end of the rewriting operation, but it is difficult to obtain such characteristics for the particles themselves.
In the present invention, the fluidity of the fine particles is improved by blending the surfactant and the polymer dispersant, and the colored charged fine particles 3 are easily moved in the surface direction during the rewriting operation. The same can be said for the white charged fine particles. As a result, as shown in FIG. 2D, the colored charged fine particles 3 staying in the dispersion 5 are reduced, and the display contrast is improved.
The above is the basic operation principle of image display by the image display medium of the present invention, but this display mode is reversible and can be used repeatedly.
When the charged fine particles are positively charged, they move by a negative external electric field, and when the charged fine particles are negatively charged, they move by a positive external electric field.
FIG. 4 is a schematic diagram of digital paper which is the display medium itself in the present invention.
FIG. 5 is an apparatus diagram in which a display medium such as a pocket PC is mounted in the present invention.
FIG. 6 is a partial cross-sectional explanatory view of a microcapsule showing an embodiment of the present invention.
In the microcapsule 30, white and colored fine particles 23 are dispersed in a dispersion medium 24, and the periphery thereof is covered with a microcapsule film 25.
FIG. 7 is a partial cross-sectional explanatory view of an image display medium showing an embodiment of the present invention.
In the image display medium 40, microcapsules 36 are closely packed between two conductive layers 31 and 32. Each microcapsule has white and colored fine particles 33 dispersed in a dispersion medium 34. The periphery is covered with a microcapsule film 35.

In the image display medium of the present invention, charge is generated due to the acid-base dissociation between the surface of the white and colored fine particles and the resin adsorbed on the fine particles and the solvation effect due to the nonionic polar component, and the adsorbed resin A synergistic effect of dispersion stability can be obtained by the three-dimensional effect, and an image display medium having both long-term stability and fast response speed can be provided.
In the image display medium of the present invention, the white and colored fine particles comprise at least a pigment and a resin, and the weight ratio of the pigment to the resin is 0.1 to 300 parts by weight of the pigment with respect to 100 parts by weight of the resin. By being a part, it is possible to display an image with high image density and high response speed.
In the image display medium of the present invention, since the white fine particles are titanium oxide, it is possible to provide an image display medium with good long-term stability and high contrast. Further, since the colored fine particles are carbon black, an image display medium having good long-term stability and high contrast can be provided.
Further, since the charged white and colored self-dispersing fine particles are fine particles modified with surface functional groups, an image display medium having good long-term stability and high contrast can be provided.
Since the self-dispersing fine particles are any of core-shell polymer fine particles, graft polymer fine particles, and capsule polymer fine particles, it is possible to provide an image display medium with good long-term stability and high contrast, and the self-dispersing colored fine particles are acrylic copolymer grafted carbon black. Therefore, an image display medium with good long-term stability and high contrast can be provided.
Since the self-dispersing colored fine particles are silicone polymer grafted carbon black, an image display medium having good long-term stability and high contrast can be provided.
In the image display medium of the present invention, when the particle size of the white and colored self-dispersing fine particles is 0.01 μm to 1 μm, it is possible to provide an image display medium with good long-term stability and high contrast.
When the nonpolar solvent is any one of an aliphatic hydrocarbon, an aromatic hydrocarbon, and a silicone oil, an image display medium with high material selectivity can be provided.
Since the compound having a nonionic polar group is a nonionic surfactant, it is possible to provide an image display medium having high long-term stability of charged self-dispersing colored fine particles and charged self-dispersing white fine particles and high contrast. .
In the image display device, by having the image display medium as a constituent element, it is possible to provide a power-saving and highly visible display device.

Self-dispersing fine particles refer to fine particles in a state where the fine particles are grafted, encapsulated, or core-shelled with a polymer and dispersed in a solvent in the same manner as a dye dissolved without a dispersant.
When these positively charged self-dispersing fine particles and negatively charged self-dispersing fine particles are moved by electrophoresis in a nonpolar solvent, display characteristics such as reflectance and contrast are different from those of conventional dispersions. It was found that it was improved.
As described above, regarding the mechanism of charging by acid-base dissociation, the presence of ions or charges was unclear in conventional non-aqueous solvents, particularly non-polar aprotic solvent dispersions.
This is presumably because interaction (solvation) between ions and solvent molecules hardly occurs in this type of solvent.
Therefore, the present inventor has (a) an organic material having at least an acidic group, (b) an organic material having at least a basic group, and (c) an organic material that is compatible with the solvent and has a nonionic polar component. As a result of intensive studies on a nonpolar aprotic solvent-based dispersion containing three components of the substance [any component of (a) and (b) may be present as a copolymer with component (c)] It was found that the components (a) and (b) caused acid-base ion dissociation in the solvent.
It was also suggested that ion-dipole interaction, ie solvation, exists.
That is, the present inventor, when the three components (a), (b), and (c) are present in the solvent, the ion-base dissociation between the acid and base via the solvation of the polar group in the component (c). It was found that ions can exist stably even in nonpolar aprotic solvents.
This fact was similarly observed whether both components (a) and (b) were soluble or insoluble in the solvent. Further, as described above, the present inventor, in the system containing the three components (a), (b) and (c), when coexisting fixed particles such as pigments and metal oxides, Or the acidic group or basic group of component (b) is fixed by chemical bonding, adsorption, etc., and ionic dissociation occurs at the interface between the solid particle surface and the solvent via the solvation of component (c), resulting in solid It has been found that the particles are uniformly charged to a positive or negative polarity, and that solid particles are more stably dispersed than before due to the coherent action of this electrostatic effect and further the steric effect.
Furthermore, the present inventor has found that the amount of ions and the amount of charge can be controlled by the types and amounts of the components (a), (b), and (c). The present inventor found that when positively charged self-dispersing fine particles and negatively charged self-dispersing fine particles were blended in the same dispersion and moved by an external electric field, the long-term stability was very good, and at the same time the contrast The present inventors have found that very high display characteristics can be obtained.

The reason why the display characteristics are improved by the combination of positively charged self-dispersing fine particles and negatively charged self-dispersing fine particles is as follows.
In conventional electrophoretic display media, positive and negative charged fine particles are mixed together, and fine particles having different charges move in different directions according to positive and negative electrodes.
In this case, if fine particles having different charges are blended in the same dispersion, positive and negative charged particles attract each other and the stability of the fine particles in the dispersion is impaired and aggregated, or positively charged fine particles are applied to the electrode. Various problems have arisen, such as the movement of negatively charged fine particles, and conversely the movement of negatively charged fine particles to the electrode.
In contrast, in the combination of positively charged self-dispersing fine particles and negatively charged self-dispersing fine particles, one fine particle has a positive or negative charge generated by acid-base dissociation, and the other fine particle has Because it has a positive or negative charge generated by a method other than acid-base dissociation, it has no effect on the charged fine particles blended together, and it has no adverse effects such as hindering movement or aggregation. It is.
As a result, it is possible to provide an image display medium capable of reversible display, having a memory property, and particularly having high contrast and resolution and high response speed. It is also possible to provide an image display medium with high material selectivity, good long-term stability, and safety in practical use.
When one of the self-dispersing fine particles is charged by acid-base dissociation, the other self-dispersing fine particles are affected by the same kind of charge generation principle, affecting each other, preventing movement and aggregating. It is impossible to charge by acid-base dissociation because of the high possibility of giving.
Therefore, the charge of other dispersible fine particles needs to be generated by a method other than acid-base dissociation.
As a method other than the acid-base dissociation,
(1) Charge due to the surface potential of the fine particles themselves,
(2) a method using a charge control agent used in wet toner,
(3) a method using an ionic surfactant;
(4) There is a method using an ionic polymer dispersant.
Among these, it is particularly preferred to be charged by the surface potential of the fine particles themselves.
(1) The fine particles themselves originally have a positive or negative potential as the surface potential, and the degree depends on the fine particles. The required charge can be obtained by selecting fine particles having a preferable surface potential.
(2) The required charge can be obtained by blending a charge control agent typified by 2-ethylhexylzirconium.
(3) The required charge can be obtained by adsorbing the ionic surfactant to the self-dispersing fine particles.
(4) The required charge can be obtained by adsorbing the ionic polymer dispersant to the self-dispersing fine particles.

Hereinafter, embodiments of the present invention will be described in detail.
In the embodiment of the present invention, reference numerals 1 and 2 in FIG. 1 are conductive layers, and at least one of them is light transmissive.
As the conductive layer, a transparent conductor such as a metal such as Al, Ag, Ni, Cu or indium tin oxide (ITO), SnO ₂ , ZnO: Al is formed into a thin film by sputtering, vacuum deposition, CVD, coating, or the like. The one formed into a shape or the one coated with a conductive agent mixed with a solvent or synthetic resin fine particle modification is used.
Conductive agents include cationic polyelectrolytes such as polymethylbenzyltrimethyl chloride and polyallylpolymethylammonium chloride, anionic polyelectrolytes such as polystyrene sulfonate and polyacrylate, and electronically conductive zinc oxide and tin oxide. Indium oxide fine powder or the like is used. The conductive layer itself may be thick enough to have a self-holding function, or the conductive layer may be provided on a substrate having a self-holding function (not shown), which can be preferably used in either case.
In addition, the conductive layers 1 and 2 may be layers having anisotropic conductivity, or may be layers having pattern-shaped or multi-dot segments in which conductive portions penetrate in the thickness direction.
In any case, if the power electrode is brought into contact with a part of the conductive layers 1 and 2, an electric field can be generated between the conductive layers 1 and 2, so that the white and colored particles 3 can move reliably.
In order to perform the display, a voltage applying means between the conductive layers 1 and 2 may be prepared, which is convenient.

White or colored fine particles are white or colored fine particles having at least an acidic group on the surface, and a resin soluble in a nonpolar solvent has at least a basic group, or white or colored fine particles on at least the surface. The resin having a basic group and soluble in a nonpolar solvent has at least an acidic group.
At this time, acid-base dissociation occurs between the acidic group or basic group on the surface of the white or colored fine particles and the basic group or acidic group of the resin soluble in the nonpolar solvent.
In addition, the presence of a compound having a nonionic polar group in the dispersion causes ion generation to occur at the interface between the white and colored fine particle surface and the solvent via solvation. The particles are uniformly charged to a positive or negative polarity, and solid particles are more stably dispersed than in the past due to the coherent action of this electrostatic effect and further the steric effect.

In order for white or colored fine particles to be charged to a positive or negative polarity by acid-base dissociation,
There are (I) a method of synthesizing charged fine particles having a core-shell structure, and (II) a method of using a nonionic surfactant.
In the method (I), resin fine particles are adsorbed on the surface of fine particles by dispersion polymerization to synthesize charged fine particles having a core-shell structure.
The method (II) is achieved by adding a nonionic surfactant.

  Examples of white and colored fine particles used in the present invention include metal oxides such as silica, titania and alumina, black colorants such as carbon black, aniline black, furnace black and lamp black, phthalocyanine blue and methylene blue. , Cyan colorants such as Victoria Blue, Methyl Violet, Aniline Blue, Ultramarine Blue, Rhodamine 6G Lake, Dimethylquinacridone, Watching Red, Rose Bengal, Rhodamine B, Alizarin Lake, Magenta Colorant, Chrome Yellow, Benzidine Yellow , Hansa Yellow, Naphthol Yellow, Molybdenum Orange, Quinoline Yellow, Yellow Colorants such as Tartrazine, etc., conventionally known dyes and pigments have the following acidic groups Monomer, or a monomer having a basic group in a non-polar solvent having a component include those dispersed in insoluble particulate modified resin.

Examples of the fine particle modifying resin having an acidic group insoluble in a non-polar solvent (a polymer or copolymer having a monomer having an acidic group as a constituent component) include (meth) acrylic acid, maleic acid, maleic anhydride, and itacon. Acid, itaconic anhydride, fumaric acid, cinnamic acid, crotonic acid, vinyl benzoic acid, 2-methacryloxyethyl succinic acid, 2-methacryloxyethyl maleic acid, 2-methacryloxyethyl hexahydrophthalic acid, 2-methacryloxyethyl Trimellitic acid, vinyl sulfonic acid, allyl sulfonic acid, styrene sulfonic acid, 2-sulfoethyl methacrylate, 2-acrylamido-2-methylpropane sulfonic acid, 3-chloroamidophosphoxypropyl methacrylate, 2-methacryloxyethyl acid phosphate, Has acidic groups such as hydroxystyrene At least one monomer and 2-ethylhexyl (meth) acrylate, octyl (meth) acrylate, nonyl (meth) acrylate, decyl (meth) acrylate, lauryl (meth) acrylate, stearyl (meth) acrylate, vinyl laurate, Methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, hexyl (meth) acrylate, cyclohexyl (meth) acrylate, benzyl (meth) acrylate, phenyl (meth) acrylate, styrene, vinyltoluene, etc. ) Copolymers obtained from at least one alkyl or aryl ester of acrylic acid.
A fine particle-modified resin that is insoluble in a nonpolar solvent may be produced by suitably determining the types of monomers to be combined and the blending ratio during polymerization.

  Examples of the fine particle modifying resin having a basic group insoluble in a nonpolar solvent (a polymer or copolymer having a monomer having a basic group as a constituent component) include N-methylaminoethyl (meth) acrylate, N- Ethylaminoethyl (meth) acrylate, N, N-dimethylaminoethyl (meth) acrylate, N, N-diethylaminoethyl (meth) acrylate, N, N-dibutylaminoethyl acrylate, N, N-di-tert-butylamino Ethyl acrylate, N-phenylaminoethyl methacrylate, N, N-diphenylaminoethyl methacrylate, aminostyrene, dimethylaminostyrene, N-methylaminoethylstyrene, dimethylaminoethoxystyrene, diphenylaminoethylstyrene, N-phenylaminoethylstyrene, 2 At least one monomer having a basic group such as N-piperidylethyl (meth) acrylate, 2-vinylpyridine, 4-vinylpyridine, 2-vinyl-6-methylpyridine, and alkyl of the above (meth) acrylic acid Or the copolymer obtained from at least 1 sort (s) of an aryl ester is mentioned. A fine particle-modified resin that is insoluble in a nonpolar solvent may be produced by suitably determining the types of monomers to be combined and the blending ratio during polymerization.

Further, when a substance that can be chemically bonded by carbon black or grafting of a metal oxide is used as the solid particles, an acidic group or a basic group can be reacted with the monomer having the acidic group or basic group. A basic group may be chemically bonded.
The amount of the pigment used is 0.1 to 300 parts by weight, preferably 1 to 100 parts by weight, based on 100 parts by weight of the fine particle modifying resin.
As the nonpolar solvent, a known hydrocarbon solvent or silicone oil can be used.
As the resin soluble in the nonpolar solvent, a resin having a stronger attractive interaction with the surface of the white and colored charged fine particles than the nonpolar solvent is preferable.
By adsorbing the resin to the charged white and colored fine particles, the dispersion stability of the charged white and colored fine particles is increased by the steric effect.

Specific examples of the resin soluble in the hydrocarbon solvent or silicone oil used in the present invention are as follows.
Examples of resins having acidic groups soluble in hydrocarbon solvents (polymers or copolymers having monomers having acidic groups as constituents) include (meth) acrylic acid, maleic acid, maleic anhydride, itaconic acid , Itaconic anhydride, fumaric acid, cinnamic acid, crotonic acid, vinyl benzoic acid, 2-methacryloxyethyl succinic acid, 2-methacryloxyethyl maleic acid, 2-methacryloxyethyl hexahydrophthalic acid, 2-methacryloxyethyltri Merit acid, vinyl sulfonic acid, allyl sulfonic acid, styrene sulfonic acid, 2-sulfoethyl methacrylate, 2-acrylamido-2-methylpropane sulfonic acid, 3-chloroamidophosphoxypropyl methacrylate, 2-methacryloxyethyl acid phosphate, hydroxy Monomers having acidic groups such as styrene And at least one copolymer obtainable from at least one alkyl or aryl esters of (meth) acrylic acid. A resin that is soluble in a hydrocarbon solvent or silicone oil may be prepared by suitably determining the type of monomer to be combined and the blending ratio during polymerization.

  Examples of resins having basic groups that are soluble in hydrocarbon solvents and silicone oils (polymers or copolymers comprising monomers having basic groups as constituents) include N-methylaminoethyl (meth) acrylate N-ethylaminoethyl (meth) acrylate, N, N-dimethylaminoethyl (meth) acrylate, N, N-diethylaminoethyl (meth) acrylate, N, N-dibutylaminoethyl acrylate, N, N-di-tert -Butylaminoethyl acrylate, N-phenylaminoethyl methacrylate, N, N-diphenylaminoethyl methacrylate, aminostyrene, dimethylaminostyrene, N-methylaminoethylstyrene, dimethylaminoethoxystyrene, diphenylaminoethylstyrene, N-phenylamino ethyl At least one monomer having a basic group such as tylene, 2-N-piperidylethyl (meth) acrylate, 2-vinylpyridine, 4-vinylpyridine, 2-vinyl-6-methylpyridine, and the above (meth) Mention may be made of copolymers obtained from at least one alkyl or aryl ester of acrylic acid. A resin that is soluble in a hydrocarbon solvent or silicone oil may be prepared by suitably determining the type of monomer to be combined and the blending ratio during polymerization.

The compound having a nonionic polar group is preferably a compound that is soluble in a hydrocarbon solvent or silicone oil, has a dielectric constant greater than that of the hydrocarbon solvent or silicone oil, and does not ionically dissociate itself.
Examples of the compound having a nonionic polar group used in the present invention include ethers, esters, alcohols, ketones and amides.
The mixing ratio of these compounds and the hydrocarbon solvent is about 0.1 to 10 parts by weight with respect to 100 parts by weight of the hydrocarbon solvent.
In order to make the dispersion of the present invention, the above-mentioned components may be mixed and dispersed in a hydrocarbon solvent. In this case, a ball mill, a sand mill, an attritor or the like may be used as the dispersing means. The mixing order is not particularly limited.

In the embodiment of the present invention, a resin soluble in a hydrocarbon solvent or silicone oil has a nonionic polar group.
Specific examples of the resin soluble in the hydrocarbon solvent or silicone oil used in the present invention are as follows.
Examples of a resin having an acidic group and having a nonionic polar group (a copolymer having a monomer having an acidic group and a monomer having a nonionic polar group as a constituent component) At least one of specific examples of the monomer having, 2-hydroxyethyl (meth) acrylate, 2,3-dihydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, 2-hydroxy-3-propyl methacrylate , Methoxypolyethylene glycol methacrylate, methoxypolypropylene glycol methacrylate, 2-chloroethyl (meth) acrylate, 2,3-dibromopropyl (meth) acrylate, (meth) acrylonitrile, isobutyl-2-cyanoacrylate, 2-cyanoethyl acrylate, ethyl Polar monomers such as 2-cyanoacrylate, methacrylacetone, tetrahydrofurfuryl methacrylate, trifluoroethyl methacrylate, p-nitrostyrene, vinylpyrrolidone, acrylamide, methacrylamide, N, N-dimethylmethacrylamide, N, N-dibutylmethacrylamide And a copolymer.
Moreover, the copolymer which has at least 1 or more types of the alkyl or aryl ester of the said (meth) acrylic acid as a component may be sufficient.
Examples of a resin having a basic group and having a nonionic polar group (a copolymer having a monomer having a basic group and a monomer having a nonionic polar group as a constituent component) Among the specific examples of the monomer having a basic group, a copolymer of at least one kind and the polar monomer may be mentioned.
Further, it may be a copolymer having at least one or more alkyl or aryl esters of (meth) acrylic acid as a component.

In the embodiment of the present invention, positively charged fine particles and negatively charged fine particles have an ionic polar group on the surface.
Specific examples of the positively charged fine particles and the negatively charged fine particles used in the present invention include a monomer having the acidic group and a resin insoluble in a hydrocarbon solvent or silicone oil having the polar monomer as a component, Or the thing using the insoluble resin in the hydrocarbon solvent and silicone oil which have the monomer which has the said basic group, and the said polar monomer as a component is mentioned.
In addition, when substances that can be chemically bonded, such as carbon black or grafting of metal oxide, are used as the solid particles, by reacting these substances with a monomer having an acidic group or basic group and a polar monomer. Alternatively, an acidic group or basic group and a polar group may be chemically bonded.

In the embodiment of the present invention, the white and colored particles are composed of at least a pigment and a resin, and the weight ratio of the pigment to the resin is 0.1 to 300 parts by weight of the pigment with respect to 100 parts by weight of the resin. It is preferable.
When the proportion of the pigment as the coloring component is large, the image density when displayed as an image is high, and an image display medium with good contrast can be obtained.
On the other hand, if the resin component responsible for ion generation due to acid-base dissociation on the surface of white and colored particles decreases, the amount of generated charges decreases and it becomes difficult to increase the response speed.
Conversely, when the proportion of the pigment as the coloring component is small, the response speed increases, but it becomes difficult to display an image with good contrast.
In the embodiment of the present invention, the white fine particles are preferably titanium oxide. This is because titanium oxide has the highest whiteness among various materials.

One embodiment of the present invention will be described below.
Carbon black is defined as an aggregate of fine spherical particles obtained by incomplete combustion of various hydrocarbons or carbon-containing compounds, and is a generic name for carbon materials that are nearly pure and have a chemical composition of 98% or more. It is.
The type is generally classified by the production method, and is roughly classified into either pyrolysis of raw material hydrocarbons or incomplete combustion (Table 1), and further subdivided according to the type of raw material. The contact method is a manufacturing method in which a flame is brought into contact with iron or stone, and includes a channel method and a gas black method (roller method) which is an improved method thereof. Channel black is a representative product of the contact method, and is collected by bringing a flame into contact with the bottom surface of channel steel.
The furnace method is a method of generating carbon black by continuously pyrolyzing raw material hydrocarbons by combustion heat of fuel air, and is classified into a gas furnace method and an oil furnace method.
The thermal method is a special production method in which natural gas is used as a raw material carbon source and combustion and thermal decomposition are repeated periodically. The feature is that carbon black having a large particle size can be obtained.
Acetylene black is a kind of thermal process that uses acetylene as a raw material. However, the thermal decomposition of acetylene is an exothermic reaction while other raw materials are endothermic, so it is possible to omit the combustion cycle in the thermal process. Continuous operation is possible. The characteristics of acetylene black are that it develops crystallinity compared to ordinary carbon black and has a high structure, so it has excellent conductivity, and is used as a conductivity-imparting agent for dry batteries and various rubbers and plastics. Yes.
The carbon black production method and main raw materials are shown in Table 1 below.

(1) Basic characteristics of carbon When carbon black is blended and dispersed in rubber, resin, paint and ink vehicles, the important factors for imparting functions such as reinforcement, blackness, and conductivity are particle size and structure. In addition, it is the physicochemical properties of the particle surface, which is usually called the three major characteristics of carbon black, and various carbon blacks are produced by combining these.
The three basic characteristics of carbon black are:
(I) Particle size: Particle size and surface area (II) Structure: DBP oil supply (ml / 100g) and structure index (III) Surface chemical properties: Volatile content (%) and pH
It is.
In the present invention, acidic carbon black means carbon black having an acidic group on its surface, among which carbon black having a pH of 5 or less and carbon black having a volatile content of 3.5 to 8.0% by weight. It is preferable to use it.
The reason why the dispersibility is high when the pH of the carbon black is 5 or less is not clear, but it is estimated that such carbon black has many surface acidic groups that influence the pH, and therefore the carbon black particles themselves The affinity for the solvent is increased, which enables fine dispersion, and as a result, dispersibility is expected to increase.

Here, the pH of the carbon black referred to in the present invention means a value obtained by the following measurement method.
That is, 1 to 10 g of carbon black sample is weighed into a beaker, water is added at a rate of 10 ml per 1 g of sample, covered with a watch glass, and boiled for 15 minutes (to make the sample easy to wet, several drops of ethanol may be added) ). After boiling, the mixture is cooled to room temperature, and the supernatant is removed by a gradient method or a centrifugal separation method to leave a mud.
An electrode of a glass electrode pH meter is put in this mud and the pH is measured by JISZ8802 (pH measuring method). In this case, the measured value may change depending on the electrode insertion position. Therefore, move the beaker to change the electrode position, carefully measure the electrode surface so that the muddy surface is in full contact, and maintain a constant pH value. Read the value when.
In addition, the dispersion liquid of the present invention is prepared using carbon black having a volatile content in the range of 3.5 to 8.0% by weight, more preferably in the range of 4.5 to 6.0% by weight, and an image display medium. Can be used to obtain an image display body with high contrast.
The reason why the dispersibility is high when the volatile content of the carbon black is 3.5% by weight or more is not clear, but it is estimated that the carbon black particles themselves have many surface acidic groups. It is believed that the affinity of the solvent to the solvent is increased, thereby enabling fine dispersion, and as a result, the dispersibility is improved.
Furthermore, even if a dispersion is prepared with carbon black having a volatile content of more than 8.0% by weight, the dispersibility does not increase any more, so the volatile content is in the range of 3.5 to 8.5% by weight. It is particularly desirable to use carbon black. This is considered to be because if too much volatile component is present, it will cause an inhibition of the dispersibility of carbon black.

Here, the volatile matter of carbon black referred to in the present invention means a value obtained by the following measuring method.
That is, a dry sample of carbon black is packed into a platinum crucible or a porcelain crucible of the same shape and capacity with a drop lid by shaking it so that it does not exceed 2 mm below the lid, and its mass is measured.
Cover it, put it in an electric furnace, heat it at 950 ± 25 ° C for exactly 7 minutes, take it out, let it cool to room temperature in a desiccator, weigh the mass after heating, and calculate the volatile content by the following formula calculate.
V = (WD−WR) / WD × 100
[In the formula, V represents volatile matter (%), WD represents the mass (g) of the dried sample, and WR represents the mass (g) of the sample after heating. ]
Such acidic carbon blacks include, for example, MA7, MA8, # 2200B (manufactured by Mitsubishi Kasei), RAVEN1255 (manufactured by Colombia), REGAL400R, MOGUL L (manufactured by Kibot), Color Black FW1, Color Black FW18, Color Black S170. , Color Black S150, Printex U (manufactured by Degussa Co., Ltd.) and other commercial products can be used, and those newly produced for this purpose can also be used.

The production method of acidic carbon black is generally performed using carbon black by the channel black method or the furnace black method.
In the channel black method, natural gas, town gas and hydrocarbons are partially burned as raw materials and collided with cold surfaces. In the furnace black method, natural gas or petroleum fraction is used as a raw material, kept in a high temperature atmosphere, and the raw material is sprayed into a closed reactor and thermally decomposed.
Further, these carbon blacks are oxidized with nitric acid or the like to obtain a desired acidity.
In addition, the surface treatment of carbon black can improve properties such as dispersion stability, surface wettability, rheological properties, and electrical properties.

Examples of the surface treatment method include the following.
The surface of carbon black particles has a condensed aromatic ring and can be subjected to various surface treatments described below.
(1) Surface oxidation treatment When carbon black is treated with an oxidizing agent, a carboxyl group or a phenolic hydroxyl group is introduced into the condensed aromatic ring on the particle surface.
(2) Surfactant dispersion Carbon black can be dispersed in a film-forming solution with a normal anionic surfactant, nonionic surfactant, cationic surfactant, amphoteric surfactant, and the like.
(3) Dispersion Stabilization by Polymer (Resin) Dispersion Stabilizer Carbon black can be dispersed and stabilized in a film forming solution by steric hindrance repulsion of the chain portion of the polymer dispersion stabilizer.
(4) Encapsulation treatment Carbon black is coated with a resin and dispersed in a solvent, or the resin is impregnated with carbon black, that is, the surface layer or the inside, or the carbon black exists in the whole. Can be used.
Its characteristics can improve properties such as dispersion stability, surface wettability, rheological properties and electrical properties.
In particular, with regard to dispersion stability, the dispersibility of the graft chain in a good solvent (easily dispersible in the dispersion medium and stability after dispersion) is remarkably improved, and in terms of electrical properties, the carbon black particles are polymer matrix. Since it is easily and uniformly dispersed in the inside, there is a feature that a constant resistance value can be obtained over a wide area.

(5) Grafting treatment Carbon black grafting treatment can be classified as follows based on the grafting mechanism.
(A) Graft polymerization on the surface of carbon black In this method, a vinyl monomer is polymerized using a polymerization initiator in the presence of carbon black, and the growing polymer chain generated in the system is captured on the particle surface.
(B) Graft polymerization from the carbon black surface This is a method of growing a graft chain from a polymerization initiating group introduced into the carbon black surface.
(C) Graft reaction between carbon black surface and polymer This is a method based on a reaction between a functional group on the carbon black surface and a reactive polymer.
Among these, the method (a) can be most easily performed, but since a non-grafted polymer is predominantly produced, a product having a large graft ratio cannot be obtained.
On the other hand, the system (b) is characterized in that a polymer (graft chain) grows outward from the carbon black surface, so that a product having a high graft rate can be obtained. Furthermore, according to the method (c), there is a great feature that the molecular weight and number of graft chains can be controlled, and a graft having a relatively large graft ratio can be obtained.
(6) Gas Phase Oxidation Method This is an oxidation treatment method of the carbon black surface by ozone treatment or plasma treatment. By irradiating the carbon black with plasma, a hydroxyl group or a carboxyl group can be attached to the carbon black surface by high energy of plasma.

More specifically, (1) Surface oxidation treatment When carbon black is treated with an oxidizing agent, a carboxyl group or a phenolic hydroxyl group is introduced into the condensed aromatic ring on the particle surface.
Furthermore, the condensed aromatic ring on the surface of carbon black reacts with the following various reagents as described below, and various functional groups can be introduced onto the particle surface.

(2) Surfactant dispersion As the types of anionic surfactant, nonionic surfactant, cationic surfactant, and amphoteric surfactant, those having the following structure can be used.
Preferred surfactants include polyoxyethylene alkyl ether acetates, dialkyl sulfosuccinates, polyoxyethylene alkyl ethers, polyoxyethylene alkyl phenyl ethers, polyoxyethylene polyoxypropylene block copolymers, and acetylene glycol surfactants. Agents.
More specifically, the anionic surfactant is a polyoxyethylene alkyl ether acetate general formula (2) and / or a dialkyl sulfosuccinic acid having a branched alkyl chain having 5 to 7 carbon chains. By using the chemical formula (3), dispersion stability of carbon black can be obtained.
R—O— (CH ₂ CH ₂ O) _m CH ₂ COOM (2)
(In the formula, R represents an alkyl group having 6 to 14 carbon atoms which may be branched, M represents an alkali metal ion, quaternary ammonium, quaternary phosphonium or alkanolamine, and m represents an integer of 3 to 12).
(In the formula, R ₅ and R ₆ are branched alkyl groups having 5 to 7 carbon atoms, M represents an alkali metal ion, quaternary ammonium, quaternary phosphonium or alkanolamine.)

Further, the use of lithium ions, quaternary ammonium, and quaternary phosphonium as counter ions of the surfactant of the present invention shows excellent dissolution stability of the surfactant.
Preferred nonionic surfactants include those represented by general formula (4) which is polyoxyethylene alkylphenyl ether and those represented by general formula (5) which are acetylene glycol surfactants.
(In the formula, R represents an alkyl group having 6 to 14 carbon atoms which may be branched, and k represents an integer of 5 to 12).
(In formula, p and q show the integer of 0-40.)

(3) Dispersion Stabilization with Polymer (Resin) Dispersion Stabilizer Generally, when the average molecular weight of a polymer dispersed resin increases, the viscosity when the same amount is dissolved in a water-soluble organic solvent increases.
In addition, since the dispersion resin has a role of adsorbing around the carbon black when the carbon black is dispersed and stably dispersing the carbon black due to steric hindrance, the molecular weight of the dispersion resin is increased. Means that the particle diameter of the dispersion increases.
In particular, carbon black showing acidity has a repulsive relationship with the carboxyl group added to the dispersion resin used in the present invention because it has many acidic groups on its surface, and its particle size tends to further expand. It is in.
In other words, when acidic carbon black is used as in the dispersion of the present invention, good dispersion stability is obtained unless the average molecular weight of the dispersion resin is reduced and the viscosity of the dispersion and the particle diameter of the dispersion are reduced. In addition, as described above, the dispersion resin must be adsorbed around the carbon black and act as a steric hindrance, so if the average molecular weight is too small, the dispersion stability in long-term storage will deteriorate. .

  The water-soluble resin contained in the dispersion liquid of the present invention as a carbon black dispersant can be used as long as it is soluble in an aqueous solution in which an amine is dissolved and has a weight average molecular weight of 3000 to 30000. Acrylic acid copolymer, styrene-acrylic acid-alkyl acrylate ester copolymer, styrene-maleic acid copolymer, styrene-maleic acid-alkyl acrylate copolymer, styrene-methacrylic acid copolymer, styrene- Examples thereof include methacrylic acid-acrylic acid alkyl ester copolymers, styrene-maleic acid half ester copolymers, vinyl naphthalene-acrylic acid copolymers, vinyl naphthalene-maleic acid copolymers, and salts thereof.

In the present invention, a resin dispersant can be further added to enhance both the dispersion stability of the positively charged self-dispersing fine particles and the negatively charged self-dispersing fine particles.
Although it will not specifically limit as a dispersing agent if the objective of this invention is met, For example, a polymeric dispersing agent is mentioned.
Polymer dispersing agents include poly (N-vinyl-2-pyrrolidone), poly (N, N′-diethylacrylamide), poly (N-vinylformamide), poly (N-vinylacetamide), poly (N-vinyl). Phthalamide), poly (N-vinylsuccinamide), poly (N-vinylurea), poly (N-vinylpiperidone), poly (N-vinylcaprolactam), poly (N-vinyloxazoline) and the like. One or more polymer dispersants can be added.
In addition, resin (polymer) dispersants, surfactants, and various dispersion stabilizers can be used within the scope of the object of the present invention.

(4) Introduction of functional groups on the grafted surface The phenolic hydroxyl groups and carboxyl groups present on the surface of carbon black can be used as scaffolds for grafting reactions as they are, but based on this, they are converted to more reactive functional groups. Then, it can utilize for the graft reaction of various polymers.
(A) Graft polymerization on the surface When radical polymerization of a vinyl monomer is performed in the presence of carbon black, a part of the produced polymer is grafted on the particle surface.
(B) Graft polymerization from the surface a. Radical polymerization i peroxide and peroxyester groups
ii an azo group b. Cationic graft polymerization i Acylium perchlorate group
ii Chlormethyl group
iii Benzylium perchlorate c. Anionic graft polymerization i Potassium carboxylate group
ii Carbon black / BuLi composite (OLi group)
iii. Graft reaction with polymer on amino group (c) surface a. Reaction of reactive carbon black with polymer b. Reaction of carbon black with reactive polymer i Reaction with living polymer
ii Reaction with terminal isocyanate group polymer Preferably, a polymer (resin) dispersion type, a graft type, or an encapsulation type is preferred.
As carbon black, channel black or furnace black is preferable.
About furnace black, what used the oxidation process improves the dispersibility to a solvent, Therefore The thing which performed the oxidation process suitably is preferable.

Examples of the carbon black used in the present invention include furnace black, ketjen black, channel black and the like, and a single type or a plurality of types of carbon black may be used in combination.
In the present invention, it is preferable to contain at least one carbon black having a volatile content of 3.5 to 8.0% by weight or more.
Such carbon blacks include Degussa Color Black FW200, Color Black FW2, Color Black FW2V, Color Black FW1, Color Black FW18, Special Black 6, Color Black S170, Color Black S160, Special Black 5, Special Black 4, Special Black 4A, Printex 150T, Printex U, Printex V, Printex 140U, Printex 140V, Special Black 550, Special Black 350, Special Black 250, Special Black 100, Mitsubishi Chemical Corporation MA7, MA77 , MA8, MA11, MA100, MA100R, MA230, MA220, MONARCH700, MONARC manufactured by Cabot Corporation 800, MONARCH880, MONARCH900, MONARCH1000, MONARCH1300, MONARCH1400, MOGUL-L, REGAL400R, and the like VULCAN XC-72R.

The carbon black used in the present invention has an average particle size of 0.01 μm to 1 μm, preferably 0.05 μm to 0.1 μm.
Those having an average particle diameter of less than 0.01 μm are substantially difficult to obtain. When the average particle diameter exceeds 1 μm, the dispersion containing the carbon black has whiteness, blackness, contrast, This is because it is difficult to obtain a practically satisfactory one from the viewpoint of response speed and the like.
The said average particle diameter shows the average particle diameter based on the primary particle diameter measured with the electron microscope etc. The carbon black may be oxidized on the surface of the carbon black particles by grafting the surface of the particles with a polymer such as styrene or methyl methacrylate, encapsulating, or forming a core shell.

An embodiment of the present invention will be described.
The carbon black graft polymer refers to fine particles in which a polymer part is grafted on a carbon black part. The carbon black graft polymer is obtained by grafting a polymer to primary particles or several aggregates of carbon black. Addition reactions that can be used for “grafting” include electrophilic addition reactions, radical addition reactions, nucleophilic addition reactions, and cycloaddition reactions.
Carbon black usually has a particle size of several nm to several hundred nm. However, since carbon black has a large cohesion force between particles, it is usually handled as an aggregate having a particle diameter of several microns or more.
In addition, the cohesive strength between carbon blacks is significantly greater than the affinity between carbon black and other substances such as resin-based materials, and it is very difficult to disperse carbon black in resin-based materials etc. in submicrons. A stable resistance value cannot be obtained.
On the other hand, in the carbon black graft polymer, the polymer portion can effectively enter between the carbon black particles, and the cohesive force between the carbon blacks can be weakened.
Furthermore, when the polymer portion has an affinity with the resin-based material, the carbon black graft polymer can be dispersed in the resin-based material, etc. in submicrons.
However, even if the polymer portion has a high affinity with the resin-based material or the like, if the polymer portion is not effectively grafted to the carbon black portion, the characteristics will not be stable. As a result, the dispersion of carbon black does not become a good dispersion, and if a certain level of affinity is obtained, the content of the carbon black portion in the carbon black graft polymer is lowered. The blackness which it has will be impaired remarkably.

The carbon black graft polymer according to the present invention can be obtained by reacting a carbon black reactive polymer with carbon black.
The polymer having reactivity with carbon black may be any polymer having a reactive group reactive with the surface functional group of carbon black, for example, and the reactive group is present on the surface of carbon black. The reactive group is not particularly limited as long as it can react with the functional group and contribute to the grafting of the polymer onto carbon black, and various reactive groups can be used.
Here, in order to make the grafting more reliable and stable, it is desired that the polymer portion is bonded to the carbon black through a covalent bond, in particular, an ester bond, a thioester bond, an amide bond, an amino bond, An at least one bond selected from the group consisting of an ether bond, a thioether bond, a carbonyl bond, a thiocarbonyl bond and a sulfonyl bond, and at least one bond selected from the group consisting of an ester bond, a thioester bond and an amide bond It is desirable to be. Considering such points, the reactive group is preferably at least one or more selected from the group consisting of an epoxy group, a thioepoxy group, an aziridine group and an oxazoline group.
Although the reactive group with respect to carbon black is not necessarily limited to these, when the polymer which has groups other than these reactive groups is used, the kind of carbon black which can be used may restrict | limit.

The reason why it is preferable that the polymer has the reactive group is that carbon black and the polymer are added with very high grafting efficiency even under mild conditions regardless of the type and state of carbon black that can be used. It is to react.
In particular, when carbon black has a carboxyl group as a surface functional group as described above, the carboxyl group undergoes an irreversible addition reaction in a high yield by thermal reaction with an epoxy group, thioepoxy group, aziridine group or oxazoline group. The addition reaction is desirable because the above-described covalent bond is formed between the carbon black portion and the polymer portion.

In another embodiment of the present invention, the particle size of the white and colored particles is 0.01 μm to 1 μm. As the particle size is smaller, an image display medium with higher resolution can be obtained. On the other hand, the cohesive force of the particles is increased, and it is difficult to obtain dispersion stability. On the contrary, when the particle size is large, the dispersion stability is improved, but it is difficult to realize high resolution.
In the embodiment of the present invention, the nonpolar solvents used as the dispersion medium are hydrocarbon and silicone oil.
Many hydrocarbons can ensure safety in practical use in terms of volatility.
Examples of the aliphatic hydrocarbon used in the present invention include pentane, hexane, heptane, octane, nonane, decane, dodecane, ligroin, and solvent naphtha (commercially available products are Isobar H, G, L, K, Shell Petroleum manufactured by Exxon). And the like.
Aromatic hydrocarbon solvents generally have a high resin solubilizing ability, increasing the selectivity of resins soluble in hydrocarbon solvents.
Examples of the aromatic hydrocarbon used in the present invention include benzene, toluene, xylene, alkylbenzene and the like. Examples of the silicone oil include various dimethylpolysiloxanes including modification.
In the embodiment of the present invention, a nonionic surfactant is preferably used, and the surfactant can be used in the structure mentioned above. Among these, sorbitan trioleate is preferable.

In the embodiment of the present invention, the gap between the two conductive layer electrodes constituting the display medium, that is, the desired gap is 5 to 300 μm, more preferably 10 to 200 μm, and most preferably 50 to 100 μm.
When the width is smaller than 5 μm, the image contrast may not be sufficient. When the width is larger than 300 μm, the applied voltage often needs to be excessive.
In the embodiment of the present invention, as a display cell that actually encloses an image display medium, it is very many steps to produce a fine cell by photolithography or the like, and there are many loads in equipment and environmental measures. It may be preferable to encapsulate.
In the embodiment of the present invention, the average particle diameter of the microcapsules is preferably 10 to 150 μm.
Of these, 100 μm is preferable because of high contrast, and 50 μm is preferable because of its high response speed. Practically, this average particle size of 50 to 100 μm is most preferable.
In the embodiment of the present invention, the material of the microcapsule is most preferably gelatin because of transparency and softness.
Other than gelatin, gum arabic, urethane, melamine, acrylic, polyester, and other various synthetic and natural polymers can be used.
In the embodiment of the present invention, a flexible display device is possible because the microcapsules are formed on a sheet by a coating method such as coating.

According to the present invention, in view of the above prior art, the combination of positively charged self-dispersing fine particles and negatively charged self-dispersing fine particles enables reversible display, has memory properties, and in particular, contrast and resolution. Image display medium having a high response speed and a high response speed and an image display apparatus using the same can be provided.
In addition, it was possible to provide an image display medium having high material selectivity, good long-term stability, and safety in practical use, and an image display apparatus using the image display medium.

Hereinafter, the present invention will be described in more detail with reference to examples and comparative examples. However, the present invention is not limited to these examples.
All parts used in the examples are parts by weight.

1. Synthesis method 1 of charged fine particles
(Method for producing core-shell titanium oxide fine particles having a basic group)
(1) Dispersant synthetic silicone macromer FM0711 (manufactured by Chisso) 36 g, dimethylaminoethyl methacrylate DMAEMA (manufactured by Tokyo Chemical Industry) 4 g, initiator AIBN (manufactured by Tokyo Chemical Industry) 0.2 g, silicone oil KF96L-1cs (manufactured by Shin-Etsu Chemical) 360 g was placed in a separable container and stirred at 200 rpm in a nitrogen atmosphere. Then, temperature was raised to 60 degreeC in 30 minutes, and the polymerization reaction was performed at 60 degreeC for 7 hours. Thereafter, the temperature was raised to 80 ° C. in 30 minutes and maintained at 80 ° C. for 1 hour. Thereafter, the temperature was returned to room temperature. The silicone oil in the synthesized dispersant solution was removed by an evaporator. It dried for 24 hours with the vacuum dryer and it was set as the dispersing agent.
(2) Synthesis of core-shell titanium oxide fine particles (a) 4 g of the dispersant synthesized above and 200 g of silicone oil KF96L-lcs (manufactured by Shin-Etsu Chemical) were placed in a beaker and stirred with a magnetic stirrer for 1 hour, and then titanium oxide CR- 4 g of 90 (Ishihara Sangyo) was added and stirred for 1 hour. Thereafter, it was dispersed for 2 hours with an ultrasonic disperser to obtain a titanium oxide dispersion.
(B) 3 g of silicone macromer FM0725 (manufactured by Chisso), 6.9 g of methyl methacrylate MMA (manufactured by Tokyo Chemical Industry), 0.1 g of dimethylaminoethyl methacrylate DMAEMA (manufactured by Tokyo Chemical Industry), 0.05 g of initiator AIBN (manufactured by Tokyo Chemical Industry) Stir in a beaker.
It put into the separable container with the said titanium oxide dispersion liquid, and stirred at 200 rpm under nitrogen atmosphere. Then, temperature was raised to 60 degreeC in 30 minutes, and the polymerization reaction was performed at 60 degreeC for 7 hours. Thereafter, the temperature was raised to 80 ° C. in 30 minutes and maintained at 80 ° C. for 1 hour. Thereafter, the temperature was returned to room temperature. The synthesized core-shell titanium oxide fine particle solution was separated using a centrifuge at a speed of 2000 to 3000 rpm. It melt | dissolved in silicone oil KF96L-lcs (made by Shin-Etsu Chemical), and isolate | separated similarly with the centrifuge. This operation was repeated three times. It dried for 24 hours with the vacuum dryer and it was set as the core shell titanium oxide microparticles | fine-particles.

Synthesis example 2
(Method for producing resin soluble in silicone oil having acidic group)
Silicone macromer FM0711 (manufactured by Chisso), 1 g of MAA methacrylate (manufactured by Tokyo Chemical Industry), 1 g of vinylpyrrolidone (manufactured by Tokyo Chemical Industry), 0.2 g of initiator AIBN (manufactured by Tokyo Chemical Industry), silicone oil KF96L-lcs (manufactured by Shin-Etsu Chemical) 360 g was placed in a separable container and stirred at 200 rpm in a nitrogen atmosphere. Then, temperature was raised to 60 degreeC in 30 minutes, and the polymerization reaction was performed at 60 degreeC for 7 hours. Thereafter, the temperature was raised to 80 ° C. in 30 minutes and maintained at 80 ° C. for 1 hour. Thereafter, the temperature was returned to room temperature. The silicone oil in the synthesized dispersant solution was removed by an evaporator. It was dried in a vacuum dryer for 24 hours to obtain an acid polymer.

Synthesis example 3
(Method for producing core-shell titanium oxide fine particles having acidic groups)
The same applies up to (1) in Synthesis Example 1 and (a) in (2), and twice the amount of the titanium oxide dispersion prepared in (a) was used for the following synthesis.
In a reaction vessel equipped with a stirrer, a thermometer and a reflux condenser, 200 parts of toluene was taken and heated to 85 ° C. A solution comprising 16 parts of methyl methacrylate, 4 parts of methacrylic acid, a titanium oxide dispersion, and 0.1 part of azobisisobutyronitrile was added dropwise over 1 hour.
The mixture was stirred at this temperature for 4 hours to complete the reaction. After completion of the reaction, the solvent was removed to obtain a fine particle modified resin.

Synthesis example 4
(Production of a resin soluble in a hydrocarbon solvent having a basic group)
In a reaction vessel, 200 parts of Isopar H was taken and heated to 85 ° C. A solution comprising 19 parts of lauryl methacrylate, 1 part of N, N-diethylaminoethyl methacrylate and 0.1 part of azobisisobutyronitrile was added dropwise over 1.5 hours. Subsequently, the temperature was raised to 90 ° C., and the mixture was stirred at this temperature for 4 hours to complete the reaction. A uniform and transparent resin solution was obtained.

Synthesis example 5
(Method for producing core-shell titanium oxide fine particles having a basic group)
The same applies to (a) in Synthesis Example 1 and (a) in (2), and four times the amount of the titanium oxide dispersion prepared in (a) was used for the following synthesis. 500 parts of Isopar H was taken in the reaction vessel used in Synthesis Example 1 and heated to 80 ° C. A solution comprising 10 parts of lauryl methacrylate, 80 parts of ethyl methacrylate, 10 parts of di-tert-butylaminoethyl acrylate, 0.2 part of azobisisobutyronitrile, and a titanium oxide dispersion was added dropwise over 1 hour.
Next, the temperature was raised to 85 ° C., and the mixture was stirred at this temperature for 4 hours to complete the reaction. After completion of the reaction, the solvent was removed to obtain a fine particle modified resin.

Synthesis Example 6
(Method for producing resin soluble in hydrocarbon solvent having acidic group and nonionic polar group)
500 parts of Isopar H was taken in a reaction vessel and heated to 80 ° C. A solution consisting of 50 parts of 2-ethylhexyl methacrylate, 5 parts of methacrylic acid, 5 parts of hydroxyethyl methacrylate and 0.1 part of azobisisobutyronitrile was added dropwise over 1 hour. Next, the temperature was raised to 85 ° C., and the mixture was stirred at this temperature for 4 hours to complete the reaction. A uniform and transparent resin solution was obtained.

Synthesis example 7
(Method for producing titanium oxide fine particles having acidic groups and nonionic polar groups)
The same applies up to (1) in Synthesis Example 1 and (a) in (2), and 60 times the amount of the titanium oxide dispersion prepared in (a) was used for the following synthesis.
400 parts of toluene was placed in the reaction vessel used in Synthesis Example 1 and heated to 90 ° C. In this, 50 parts of butyl acrylate, 70 parts of methyl methacrylate, 40 parts of cyclohexyl methacrylate, 85 parts of 2-hydroxyethyl methacrylate, 50 parts of 2,3-dibromopropyl acrylate, titanium oxide dispersion, 5 parts of styrene sulfonic acid, benzoyl peroxide A solution of 3 parts was added dropwise over 5 hours. Subsequently, the reaction was completed by stirring at 95 ° C. for 2 hours. The solvent was removed to obtain a fine particle modified resin.

Synthesis example 8
(Production of a resin soluble in a hydrocarbon solvent having a basic group)
Take 500 parts of Isopar H in a reaction vessel and heat to 90 ° C. A solution consisting of 80 parts of stearyl methacrylate, 10 parts of methoxypolypropylene glycol methacrylate (molecular weight 482), 5 parts of dimethylaminoethyl methacrylate and 5 parts of benzoyl peroxide is added dropwise in 1 hour, followed by stirring at the same temperature for 3 hours. In this way, a uniform transparent resin solution was obtained.

Synthesis Example 9
(Method for producing core-shell oxidized carbon black fine particles having a basic group)
Core-shell oxidized carbon black fine particles having basic groups were synthesized under the same conditions as in Synthesis Example 1 except that carbon black (Printex A, degussa) was used instead of titanium oxide.
<Synthesis method of self-dispersing fine particles>

Synthesis Example 10
(Synthesis method of acrylic copolymer grafted carbon black)
(1) Carbon black surface treatment A reaction vessel made of 4 L glass is charged with 3.0 L of deionized water and stirred at 250 rpm.
Add 115 g of carbon black (Printex A, degussa). Add 3.0 mL of 37% hydrochloric acid. Add 2.5 g of 4-vinylaniline and stir at 65 ° C. for 30 minutes or more.
Be careful because vinylaniline is jelly-like and sticky at room temperature and is difficult to handle.
Sodium nitrite 1.43 g and deionized water 10 mL are dissolved in advance and added dropwise in about 1 hour. Stir at 65 ° C./3 hours. Return to room temperature and stir overnight. The black dispersion is centrifuged at 30,000 rpm / 20 minutes. Decant. Add 500 mL of deionized water to the black powder and stir and redisperse. The black dispersion is centrifuged at 30,000 rpm / 20 minutes. Decant. The black powder is left to dry overnight and then vacuum dried at 40 ° C. for 4 hours. Surface treated carbon black (VAnCB) can be synthesized.
(2) Synthesis of graft carbon black 50 g of surface-treated carbon black (VAnCB) is charged into a 1 L glass reaction vessel. Charge 100 mL of toluene. Add 100 mL of 2-ethylhexyl methacrylate. Add 0.65 g of AIBN. Stir at 250 rpm, N2 purge for 20 minutes, heat to 70 ° C. in about one hour, stir for 7 hours, and cool to room temperature. Add 500 mL of THF and stir. Reprecipitate in 3 L methanol and filter with suction. “Add 1.5 L of THF to the black polymer, stir, redisperse, and cool to 10 ° C. Centrifuge the black dispersion at 30,000 rpm / 20 minutes. Decant.” Repeat this operation three times in total. . The black powder is vacuum dried at 70 ° C. for 4 hours. Graft carbon black (2EHMACB) can be synthesized. (12.3% weight loss with TG / DTA)

Synthesis Example 11
(Synthesis method of acrylic copolymer grafted titanium oxide)
(1) Titanium oxide surface treatment 930.7 g of ethanol is put into a 4 L glass reaction vessel. Charge 69.3 g of deionized water and stir at 150 rpm. Glacial acetic acid is adjusted to pH 4.5 and added dropwise. 160 g of 3- (trimethoxysilyl) propyl methacrylate is added and stirred at 150 rpm for 5 minutes, and then 250 rpm. 1000 g of titanium oxide (R-960, Dupont) is added and stirred at 250 rpm for 10 minutes and then 200 rpm. Add 1826.6 g of methanol and stir at 200 rpm for 1 minute. The white dispersion is centrifuged at 3,000 rpm / 20 minutes. Decant. The white powder is left to dry overnight and then vacuum dried at 70 ° C. for 4 hours. A surface-treated titanium oxide can be synthesized.
(2) Synthesis of grafted titanium oxide fine particles 960 g of lauryl methacrylate is charged into a 4 L glass reaction vessel. 1386 g of toluene is added and stirred at 200 rpm to a temperature of 50 ° C. Set to 300 rpm. Surface-treated titanium oxide (Silanized Titania) is finely crushed, and 750 g is added and stirred. N ₂ purge 20 minutes. AIBN 5.64 g and toluene 500 g are dissolved in advance and dropped in about 1 hour. Heat to 70 ° C. in about an hour. Stir overnight at 70 ° C.
The white dispersion (thick liquid) is centrifuged at 10,000 rpm / 30 minutes. Decant. “1000 g of toluene is added to the white powder and stirred and redispersed. The white dispersion is centrifuged at 3,000 rpm / 30 minutes. Decanted.” This operation is repeated twice in total. The white powder is left to dry overnight and then vacuum dried at 70 ° C. for 4 hours. Grafted titanium oxide (LMATiO ₂ ) can be synthesized.

2. Preparation of Dispersion Dispersions of Examples 1 to 5 were prepared with the composition shown in Table 2 using the fine particles and polymers prepared in each of Synthesis Examples 1 to 11. Below, a weight part is solid content.

<Composition composition>
Example 1
Titanium oxide (Synthesis example 1) 20 parts by weight Acid polymer (Synthesis example 2) 1 part by weight Silicone polymer grafted carbon black MX3-GRX-001 (manufactured by Nippon Shokubai) 2 parts by weight Dispersant Solsperse 16000 (manufactured by Geneca) 0.47 parts by weight interface Activator sorbitan trioleate (manufactured by Wako Pharmaceutical Co., Ltd.) 0.53 parts by weight Silicone oil KF96L-lcs (manufactured by Shin-Etsu Chemical Co., Ltd.) 76 parts by weight A total of 100 parts by weight After being dispersed for 1 hour, it was used as a dispersion liquid of Example 1.

Example 2
Titanium oxide (Synthesis example 3) 20 parts by weight Basic polymer (Synthesis example 4) 1 part by weight Self-dispersing carbon black (Synthesis example 10) 2 parts by weight Dispersant Solsperse 3000 (manufactured by Geneca) 0.47 parts by weight Surfactant sorbitan monolauri Rate (manufactured by Nippon Oil & Fats Co., Ltd.) 0.53 parts by weight Silicone oil SH200-lcs (manufactured by Toray Dow Corning) 76 parts by weight Total 100 parts by weight And then used as a dispersion in Example 2.

Example 3
Titanium oxide (Synthesis Example 5) 20 parts by weight of acid polymer (Synthesis Example 6) 1 part by weight of silicone polymer grafted carbon black
MX3-GRX-001 (manufactured by Nippon Shokubai) 2 parts by weight Dispersant Solsperse 41000 (manufactured by Zeneca) 0.5 parts by weight surfactant sorbitan monooleate (manufactured by NOF Corporation) 0.5 parts by weight silicone oil SH200-0.65cs (Toray Industries, Inc.) Made by Dow Corning) 76 parts by weight Total 100 parts by weight A dispersion obtained by mixing each of these blended compositions was prepared, dispersed for 1 hour with ultrasonic waves, and then used as a dispersion in Example 3.

Example 4
Titanium oxide (Synthesis example 7) 20 parts by weight Basic polymer (Synthesis example 8) 1 part by weight Self-dispersing carbon black (Synthesis example 10) 2 parts by weight Dispersant Solsperse 17000 (manufactured by Geneca) 0.5 part by weight Surfactant sorbitan monostea Rate (manufactured by NOF Corporation) 0.5 parts by weight Isopar H (manufactured by Shell Petroleum) 76 parts by weight Total 100 parts by weight A dispersion obtained by mixing each of these blended compositions was prepared and dispersed for 1 hour with ultrasonic waves, and then carried out. Example 4 Used as a dispersion.

Example 5
Titanium oxide (Synthesis Example 9) 20 parts by weight acid polymer (Synthesis Example 2) 1 part by weight self-dispersing carbon black (Synthesis Example 11) 2 parts by weight Dispersant Solsperse 17000 (manufactured by Geneca) 0.5 part by weight surfactant sorbitan palmitate ( 0.5% by weight silicone oil KF96L-lcs (manufactured by Shin-Etsu Chemical Co., Ltd.) 76 parts by weight Total 100 parts by weight After preparing a dispersion obtained by mixing each of these blended compositions and dispersing with ultrasound for 1 hour, Example 5 Used as a dispersion.

Comparative example Titanium oxide (Synthesis example 7) 20 parts by weight Basic polymer (Synthesis example 8) 1 part by weight Blue dye MACROLEX BLUE RR GRAN (manufactured by Zeneca) 1 part by weight Isopar H (manufactured by Shell Petroleum) 78 parts by weight Total 100 parts by weight A dispersion liquid in which each of these blended compositions was mixed was prepared and dispersed with an ultrasonic wave for 1 hour, and then used as a comparative dispersion liquid.
Here, Nippon Shokubai's silicone polymer grafted carbon black (silicone GCB) is a self-dispersing carbon black having the following characteristics.
Sample name: MX3-GRX-001
CB / RP = 10 / 3wt ratio
Solvent: Silicone oil (SH2001CS manufactured by Dow Corning)
CB concentration: 20.0%
RP concentration: 6.0%
Solvent concentration: 74.0%

3. Method for producing display cell Next, a 100 μm thick polyester film provided with an opening of 1 cm ² between ^two glass substrates with an ITO electrode is used to create a space.
The dispersion was ultrasonically dispersed in the space, and then sealed with a microsyringe by capillary action.
Specifications of ITO solid electrode substrate Manufacturer: Geomatek Co., Ltd. Material: Soda glass Dimensions: 29.8 ± 0.1 / 39.8 ± 0.1 Chamfered outer periphery ITO surface resistance 50 ± 10Ω / □
ITO film is formed on the entire surface of one surface. SiO ₂ base treatment (dip)

4). Display Operation When −20 V was applied to each of the upper ITO electrodes of Examples 1 to 5 and the comparative example, the dispersed particles were quickly electrodeposited on the lower electrode.
Next, when +20 V was applied to the upper electrode, the dispersed particles moved to the upper electrode. This polarity switching was performed about 100 times, but could be stably repeated. Further, the electrodeposited state was maintained even when the voltage was removed.
Table 3 shows the results of measuring the reflectance, contrast, and response speed of each of the display cells of Examples 1 to 5 and the comparative example using LCD EVALUATION SYSTEM LCD-5000 (manufactured by Otsuka Electronics).

5. Dispersibility of storage liquid and display operation after storage Each dispersion liquid is stored at room temperature (25 ° C.), 50 ° C., 0 ° C., −20 ° C. and 5 levels of a cycle test in which the temperature is changed between −20 ° C. and 50 ° C. for 4 weeks. saved. It was confirmed whether display operation could be performed without any problem after each storage test.
Table 4 shows the state of the dispersion after the storage test.
Further, Table 5 shows the test results regarding the display operation after the storage test.

1 is a cross-sectional view schematically showing an example of an image display medium of the present invention. The schematic diagram which shows in principle the mechanism of the display operation | movement of the image display medium of this invention. (A), (b), (c), (d) is a figure for demonstrating the movement state of a charge fine particle, respectively. Sectional drawing which shows the conventional display apparatus typically. It is a schematic diagram of the digital paper which is the display medium itself in the present invention. In the present invention, it is an apparatus diagram in which a display medium such as a pocket PC is mounted. The partial cross section explanatory view of the microcapsule which shows one embodiment of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a partial cross-sectional explanatory view of an image display medium showing an embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Conductive layer 2 Conductive layer 3 Positively charged self-dispersing colored fine particles 4 Negatively charged self-dispersing white fine particles 5 Dispersion liquid 6 Transparent substrate 7 Transparent electrode 8 Dispersion liquid 9 Perforated spacer 23 White and colored fine particles 24 Dispersion medium 25 Microcapsule film 30 Microcapsule 31 Conductive layer 32 Conductive layer 33 White and colored fine particles 34 Dispersion medium 35 Microcapsule film 36 Microcapsule 40 Image display medium

Claims (22)

  At least self-dispersing white fine particles and self-dispersing colored fine particles, a non-polar solvent, a resin soluble in the non-polar solvent, between two conductive layers that are light-transmitting at least one or both arranged with a desired interval A dispersion composed of a resin dispersant and a compound having a nonionic polar group, and the self-dispersing white fine particles have a positive or negative charge generated by acid-base dissociation, and the self-dispersing colored fine particles Image having a positive charge (when the self-dispersing white fine particles are negative) or a negative charge (when the self-dispersing white fine particles are positive) generated by a method other than acid-base dissociation Medium.   At least a self-dispersing white fine particle and a self-dispersing colored fine particle, a nonpolar solvent, a resin soluble in the nonpolar solvent, between two conductive layers that are light-transmitting at least one or both arranged with a desired interval A self-dispersing white fine particle containing a dispersion composed of a resin dispersant, a compound having a nonionic polar group, the self-dispersing colored fine particles having a positive or negative charge generated by acid-base dissociation Display having a positive charge (when the self-dispersing colored fine particles are negatively charged) or a negative charge (when the self-dispersing colored fine particles are positively charged) generated by a method other than acid-base dissociation Medium.   The image display medium according to claim 1, wherein a method other than the acid-base dissociation is based on a surfactant.   The image display medium according to claim 3, wherein the surfactant is a nonionic surfactant.   The image display medium according to claim 1, wherein the method other than the acid-base dissociation is performed by a polymer dispersant.   The self-dispersing white fine particles having a charge or the self-dispersing colored fine particles having a charge have at least an acidic group on the surface, and the resin soluble in the nonpolar solvent has at least a basic group. The image display medium according to claim 1, wherein the image display medium is characterized in that   The self-dispersing white fine particles having a charge or the self-dispersing colored fine particles having a charge have at least a basic group on the surface, and the resin soluble in the nonpolar solvent has at least an acidic group. The image display medium according to claim 1, wherein the image display medium is characterized in that   The blending ratio (weight) of the self-dispersing white fine particles having a charge or the self-dispersing colored fine particles having a charge and a resin soluble in the nonpolar solvent is in the range of 1: 1 to 50: 1. 8. The image display medium according to claim 1, wherein the image display medium is characterized in that   The self-dispersing white fine particles having a charge and the self-dispersing colored fine particles having a charge are composed of at least a pigment and a resin, and the weight ratio of the pigment to the resin is 0.1 parts by weight of the pigment to 100 parts by weight of the resin. The image display medium according to any one of claims 1 to 8, wherein the image display medium is in a range of parts by weight to 300 parts by weight.   The image display medium according to claim 1, wherein the self-dispersing white fine particles are titanium oxide.   The image display medium according to claim 1, wherein the self-dispersing colored fine particles are carbon black.   The image display medium according to claim 1, wherein the self-dispersing fine particles are fine particles modified with a surface functional group.   The image display medium according to any one of claims 1 to 12, wherein the self-dispersing fine particles are any of core-shell polymer fine particles, graft polymer fine particles, and capsule polymer fine particles.   The image display medium according to claim 1, wherein the self-dispersing colored fine particles are acrylic copolymer grafted carbon black.   The image display medium according to claim 1, wherein the self-dispersing colored fine particles are silicone polymer graft carbon black.   The image display medium according to claim 1, wherein an average particle diameter of the self-dispersing white fine particles and the self-dispersing colored fine particles is 0.01 μm to 1 μm.   The image display medium according to claim 1, wherein the nonpolar solvent is any one of an aliphatic hydrocarbon, an aromatic hydrocarbon, and a silicone oil.   An image display device comprising the image display medium according to claim 1.   The image display device according to claim 18, wherein the image display medium is configured by an encapsulated microcapsule.   20. The image display device according to claim 18, wherein an average particle diameter of the microcapsules is 10 μm to 150 μm.   21. The image display device according to claim 18, wherein the material of the microcapsule is gelatin or gum arabic. The image display device according to claim 18, wherein the microcapsule is configured on a sheet.