JP2007078965A - Image display medium and image display device using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image display medium which attains a reversible display, has a memory property, is especially high in contrast and resolution, is high in response speed, is high in material selectivity, is satisfactory in long term stability and can secure safety in actual use, and to provide an image display device which uses the image display medium, and is power-thrifty and high in visibility. <P>SOLUTION: The image display medium is provided with dispersion liquid (5) at least containing self-dispersible white fine particles (4), self-dispersible colored fine particles (3) and a nonpolar solvent between two conductive layers (1), (2) arranged by providing a desired interval and at least one or both have optical transparency. The dispersion liquid (5) has both of an electrophoretic effect and electric field arrangement effect. The image display device uses the medium. <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 self-dispersing white fine particles or self-dispersing colored fine particles charged by the action of an electric field, and an image display device using the same. The image display medium and the image display apparatus of the present invention can be widely used for functional elements such as a light control element, a light control glass, and a sensor for image display and various recording purposes, and for controlling the amount of transmitted light.

  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, so-called hard copies recorded on paper media by printers are widely used. 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 reflective property and capable of bright display. Among them, the one using an electrophoretic element is excellent in terms of display quality and power consumption during display operation. Patent Document 1 (Japanese Patent Laid-Open No. 5-173194) discloses a set of counter electrodes at least one of which is transparent. Electrophoretic display in which a dispersion system containing electrophoretic particles is enclosed between plates, and the electrophoretic particles are attracted to and separated from the transparent electrode plate by the action of a display driving voltage applied between the electrode plates. Patent Document 2 (Japanese Patent No. 2612472) discloses an apparatus, in which at least one of electrophoretic particles is provided with a porous spacer between a pair of opposingly arranged electrode plates configured to be transparent. An electrophoretic display device is described in which a dispersion system in which is dispersed is divided into discontinuous phases and sealed. A typical form thereof is shown in FIG.

  In FIG. 3, reference numeral (6) is a transparent substrate such as glass, and (7) is a transparent electrode formed in a required pattern on one side of the transparent electrode (7). In the meantime, a dispersion liquid (8) in which a plurality of electrophoretic particles having a color different from the color of the dispersion medium is dispersed in a colored dispersion medium 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 electrophoretic particles and the color of the electrophoretic particles. When a voltage having the same direction as the charge of the migrating particles is applied, the migrating particles move to the opposite side, and 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 the aggregation or adhesion phenomenon of the migrating particles. By arranging a mesh-like or porous perforated spacer (9) between (7), the dispersion (8) is divided discontinuously, and a device for stabilizing the display operation is devised. 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 (FA Waite, J. Oil Col. Chem. Assoc., 54, 342 (1971)) relates to a basic production method of a stable nonaqueous solvent dispersion. In this method, a block or graft copolymer containing a component compatible with particles dispersed in the solvent (insoluble in the solvent) in the solvent and a component dissolved in the solvent is used. It is.

  As a method using this method, Patent Document 3 (Japanese Patent Publication No. 40-7047) discloses a stable polymethyl methacrylate (MMA) by radical polymerization of methyl methacrylate (MMA) in a hydrocarbon solvent in the presence of a degrading rubber. A method for obtaining a (PMMA) dispersion is described. 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. For the purpose of stabilizing the dispersion of particles in electrophoretic display, a pigment molecule and a polymer dispersant shown in Patent Document 4 (US Pat. No. 5,914,806) are used as steric effects. Examples include those that are covalently bonded. 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 (Japanese Patent Publication No. 9-500458) discloses a combination of a pigment having an acidic site and a polymer dispersant having an amino group, thereby improving dispersion stability by both steric effect and electrostatic repulsion. A method is described. 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.

Liquid in which specific solid fine particles are dispersed in an electrically insulating medium (a specific powder in which a hydrophilic powder such as starch, flour, gypsum, carbon, limestone, etc. is suspended in an insulating oil such as mineral oil, olive oil or transformer oil. When a liquid is used and an external electric field is applied thereto, the viscosity of the liquid is significantly increased. This phenomenon is known as the Winslow effect (Patent Document 6 (US Pat. No. 2,417,850)). book)). This phenomenon is expected to be applied to clutches, shock absorbers (dampers), hydraulic control devices, printers, vibration elements, and the like. However, since the electric field responsive fluid composed of starch, wheat flour, etc. disclosed herein has a small shearing force, the apparatus must be enlarged to be put to practical use, and the applied voltage is set to a high voltage. It must be done.
Several proposals have been made to improve liquids (electric field responsive fluids) exhibiting such a phenomenon. To give representative examples, a strongly acidic cation exchange resin or a strongly basic ion exchange resin is used as a particle. That is, a polymer having a dissociable anion group or cation group is used (Patent Document 7 (Japanese Patent Publication No. 52-30273)), and dielectric fine particles in which conductive particles are covered with an electrically insulating thin film are electrically insulated. Used are those dispersed in a conductive oily medium (Patent Document 8 (Japanese Patent Laid-Open No. 64-6093)), and those obtained by laminating a conductive thin film layer and an electrically insulating thin film layer on the surface of organic solid particles are used. (Patent Document 9 (Japanese Patent Laid-Open No. 63-97964)).
However, the following problems remain in these electric field responsive liquids.
That is, in the above, a relatively large shearing force can be obtained in a fluid using an ion exchange resin, but since the specific gravity of the particles is relatively high, a liquid compound that contains a halogen element is not preferable from the viewpoint of safety. Otherwise, the particles cannot be prevented from settling.
Further, in the above, particles in which conductive particles are coated with an insulating layer are used. When a metal such as aluminum is used as the conductive particles, the specific gravity of the particles is remarkably increased, and the particles are rapidly settled. In addition, such a fluid does not always provide a large shearing force, and when an electric field is applied, an abnormally large current flows or particles aggregate on one electrode.
In the above, particles obtained by sequentially laminating a conductive layer and an insulating layer on organic solid particles are used, but a large shearing force is not always obtained. In the same manner as described above, sometimes an abnormal current flows or aggregation of the electrodes occurs.

  On the other hand, a color display device in which a composition containing solid particles having an electric field alignment effect in a medium is filled between electrodes is disclosed. There have been reports of applying an electric field to a colored solid particle dispersion to control the aggregation and dispersion of solid particles (Patent Documents 10 to 13).

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 US Pat. No. 2,417,850 Japanese Patent Publication No.52-30273 JP-A 64-6093 JP-A 63-97964 JP-A-8-190352 Japanese Patent Laid-Open No. 8-21417 Japanese Patent Laid-Open No. 8-21418 JP-A-8-129194 F. A. Waite, J .; Oil Col. Chem. Assoc. , 54, 342 (1971)

  In the image display devices described in Patent Documents 1 to 4, it is expected that solid particles aggregate when an electric field is applied, or aggregate over time. In addition, since a very small amount of water affects the migration of the particles, it is easily affected by temperature and humidity. In addition, inorganic compounds are often used as the solid particles, and it is difficult to stably disperse them in a dispersion medium. Therefore, various dispersion stabilizers have been studied and it is desired to stably disperse the fine particles.

  The present invention has been made in view of the above problems, and its purpose is to enable reversible display, to have a memory property, and in particular, to provide high contrast and resolution, high response speed, and high material selectivity. Another object of the present invention is to provide an image display medium having good long-term stability and ensuring safety in actual use. Another object of the present invention is to provide a power-saving and highly visible image display device using the image display medium.

  The above-mentioned problems are solved by (1) “at least one of self-dispersing white fine particles, self-dispersing colored fine particles and non-dispersible particles between two conductive layers arranged at a desired distance and at least one of which is light transmissive. An image display medium comprising a dispersion containing a polar solvent, and the dispersion having both an electrophoretic effect and an electric field alignment effect ”, (2)“ Each particle in the dispersion is oriented in the vicinity of the conductive layer (3) The self-dispersing white fine particles have a positive charge or a negative charge, and the self-dispersing white fine particles are The self-dispersing colored fine particles have a positive charge when negatively charged, and the self-dispersible colored fine particles have a negative charge when the self-dispersing white fine particles are positively charged. ) Or (2) The image display medium according to any one of (1) to (3), wherein the self-dispersing white fine particles and the self-dispersing colored fine particles have dielectric polarization. Display medium ”, (5)“ The self-dispersing white fine particles or the self-dispersing colored fine particles have positive charges or negative charges generated by acid-base dissociation, and the fine particles have opposite charges. The image display medium according to any one of (1) to (4) above, (6) “The self-dispersing white fine particles or the self-dispersing colored fine particles are generated by an ionic compound, or The image display medium according to any one of the items (1) to (5), which has a negative charge, and the fine particles have opposite charges, and (7) the self-dispersibility. White fine particles or self-dispersing Any one of (1) to (5) above, wherein the colored fine particles have a positive charge or a negative charge generated by a surfactant, and each of the fine particles has an opposite charge. Image display medium ”, (8)“ The self-dispersing white fine particles or the self-dispersing colored fine particles have a positive charge or a negative charge generated by a polymer dispersant, and the fine particles have opposite charges. (9) “The self-dispersing white fine particles and the self-dispersing colored fine particles contain at least a pigment and a resin.” The mass ratio of the pigment and the resin is 0.1 to 300 parts by mass of the pigment with respect to 100 parts by mass of the resin, according to any one of (1) to (8) above. Image display medium ", (10)" Self The image display medium according to any one of (1) to (9) above, wherein the dispersible white fine particles are titanium oxides, and (11) “the self-dispersible colored fine particles are carbon black. The image display medium according to any one of (1) to (9) above, wherein the self-dispersing fine particles are fine particles modified with a surface functional group. The image display medium according to any one of (1) to (11) above, (13) “the self-dispersing white fine particles or the self-dispersing colored fine particles are core-shell polymer fine particles, graft polymer fine particles, The image display medium according to any one of (1) to (11) above, wherein the self-dispersing colored fine particles are acrylic copolymer particles, wherein the image display medium is any one of capsule polymer fine particles The image display medium according to any one of (1) to (13) above, wherein the self-dispersing colored fine particles are silicone polymer grafted carbon black. The image display medium according to any one of (1) to (13) above, (16) “The average particle size of the self-dispersing white fine particles and the self-dispersing colored fine particles is 0.01 μm or more. The image display medium according to any one of (1) to (15) above, wherein the nonpolar solvent is an aliphatic hydrocarbon, an aromatic hydrocarbon, The image display medium according to any one of (1) to (16) above, which is any one of silicone oils.

  In addition, the above-mentioned problems are solved by (18) “an image display device having the image display medium according to any one of (1) to (17)”, (19) “the dispersion”. (20) “The average particle diameter of the microcapsules is 10 μm or more and 150 μm or less”, wherein the liquid is sealed in microcapsules. The image display device according to item (19) or (21), wherein the material of the microcapsule is gelatin or gum arabic. ", (22)" The image display device according to any one of (19) to (21) above, wherein the microcapsules are formed on a sheet ".

According to the present invention, reversible display is possible, it has a memory property, in particular, high contrast and resolution, fast response speed, high material selectivity, good long-term stability, ensuring safety in practical use. It is possible to provide an image display medium capable of In addition, according to the present invention, it is possible to provide a power-saving and highly visible image display device using the image display medium.
That is, according to the image display medium of the present invention, the dispersion liquid composed of the self-dispersing fine particles has an electrophoretic effect and an electric field alignment effect, so that display of memory properties, reflectance, contrast, and the like is possible as compared with the conventional dispersion liquid. It has been found that the properties improve in each stage. In general, an electrophoretic effect appears by charging each of the self-dispersing fine particles to a positive charge or a negative charge. On the other hand, an electric field alignment effect or an electrorheological effect appears by dielectrically polarizing each of the self-dispersing fine particles. In the conventional electrophoresis method based on the electrophoretic effect, the positively charged or negatively charged fine particles move only with respect to the positive or negative electrode due to the electrophoretic effect. It was found that no contrast was obtained. When the self-dispersing fine particles move to the electrode due to the electrophoretic effect, it can be seen that an electrostatic force due to dielectric polarization acts between the self-dispersing fine particles to form a uniformly oriented layer structure near the electrode. It was found that the display characteristics such as reflectance and contrast are improved in each stage when the effect works.
Further, since the self-dispersing white fine particles or self-dispersing colored fine particles having a charge have high dispersion stability, an image display medium capable of reversible display, having a memory property, and good long-term stability can be provided. In addition, acid-base dissociation occurs between the acidic group or basic group on the surface of charged self-dispersing white fine particles or self-dispersing colored fine particles and the basic group or acidic group of a resin soluble in a nonpolar solvent. Therefore, it is possible to provide an image display medium with high response speed and good long-term stability.
Furthermore, since many hydrocarbon solvents and silicone oils can ensure safety in actual use, tolerance for fluctuations in the external environment increases.
In addition, since the selectivity of the resin soluble in the nonpolar solvent is increased, it becomes easy to control the dispersion stability and the response speed of the self-dispersing white fine particles or self-dispersing colored fine particles having a charge. Furthermore, since the dispersion stability of the self-dispersing white fine particles or the self-dispersing colored fine particles having a charge is good even at a small particle size, an image display medium with higher resolution and better long-term stability can be provided.
In addition, since the pigment concentration of the self-dispersing white fine particles or self-dispersing colored fine particles having a charge is high and the dispersion stability is good, an image display medium having a high image density and good long-term stability can be provided.

  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 described in item (1) or (2) is as follows. FIG. 1 is a cross-sectional view schematically showing an example of the image display medium described in item (1) or (2) of the present invention. In the figure, reference numerals (1) and (2) indicate two conductive layers, one or both of which are light transmissive. Between the conductive layers (1) and (2), at least self-dispersing white fine particles (4), self-dispersing colored fine particles (3) and a dispersion (5) containing a nonpolar solvent are provided. The dispersion (5) has both an electrophoretic effect and an electric field alignment effect. The dispersion (5) preferably further contains 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 light transmissive, the color of the self-dispersing white fine particles (4) and the self-dispersing colored fine particles (3) can be seen from above the conductive layer (2). . At this time, the resin soluble in the nonpolar solvent is adsorbed on the white or colored charged fine particles (3), and dispersion stability of the self-dispersing white fine particles (4) or the self-dispersing colored fine particles (3) is caused by the steric effect. Increases the long-term stability.

  On the other hand, FIG. 2 is a schematic diagram showing in principle the mechanism of the display operation when the image display medium of FIG. 1 is actually driven to display an image. In FIG. 2A, self-dispersing colored fine particles having electric charges (1) and (2) having the right half and the left half of the display medium separated from each other by applying charges from the outside by an appropriate means. 3) moves upward along the external electric field as shown in FIG. FIG. 2C shows a state in which a part of the self-dispersing colored fine particles (3) has reached the conductive layer (2). FIG. 2 (d) shows a state in which the conductive layer (2) and the self-dispersing colored fine particles (3) are adhered and moved by electrostatic force. When the state of FIG. 2 (d) is viewed from above the medium (outside the conductive layer (2)), the left half is the color of the self-dispersing white fine particles (4) and the right half is the self-dispersing colored fine particles (3). The color peeks out. The above is the basic operation principle of image display by the image display medium described in the items (1) and (2), but this display mode is reversible and can be used repeatedly.

  Positively charged charged fine particles move by a negative external electric field, and negatively charged charged fine particles move by a positive external electric field.

  In the image display medium described in the items (1) to (8), according to the above aspect, the self-dispersing white fine particles (4) or the self-dispersing colored fine particles (3) are adsorbed on the surface. Charges are generated by the acid-base dissociation between the resin and the solvation effect due to the nonionic polar component, and the synergistic effect of dispersion stability is obtained by the steric effect due to the adsorbed resin. An image display medium with compatible response speeds can be provided. In addition, you may generate | occur | produce an electric charge using either an ionic compound, surfactant, and a polymer dispersing agent so that it may demonstrate below.

  In the image display medium described in item (9), the self-dispersing white fine particles (4) and the self-dispersing colored fine particles (3) having a charge are composed of at least a coloring pigment and a resin, When the mass ratio of the resin is 0.1 to 300 parts by mass of the colorant with respect to 100 parts by mass of the resin, it is possible to display an image with a high image density and a high response speed.

  In the image display medium described in the item (10), since the self-dispersing white fine particles (4) are titanium oxide, an image display medium having good long-term stability and high contrast can be provided.

  In the image display medium described in item (11), since the self-dispersing colored fine particles (3) are carbon black, it is possible to provide an image display medium with good long-term stability and high contrast.

  In the image display medium described in the item (12), the self-dispersing white fine particles (4) and the self-dispersing colored fine particles (3) are fine particles whose surface functional groups are modified, so that long-term stability is good. An image display medium with high contrast can be provided.

  In the image display medium described in item (13), the self-dispersing white fine particles (4) and the self-dispersing colored fine particles (3) are any of core-shell polymer fine particles, graft polymer fine particles, and capsule polymer fine particles. Thus, an image display medium having good long-term stability and high contrast can be provided.

  In the image display medium described in item (14), since the self-dispersing colored fine particles (3) are acrylic copolymer grafted carbon black, an image display medium having good long-term stability and high contrast can be provided.

  In the image display medium described in item (15), since the self-dispersing colored fine particles (3) 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 described in item (16), the self-dispersing white fine particles (4) and the self-dispersing colored fine particles (3) have a particle size of 0.1 μm or more and 1 μm or less. A high-contrast and high-contrast image display medium can be provided.

  In the image display medium according to item (17), the nonpolar solvent is any one of aliphatic hydrocarbon, aromatic hydrocarbon, and silicone oil, thereby providing an image display medium having high material selectivity. can do.

  In the image display device according to any one of (18) to (22), it is possible to provide a power-saving and highly visible image display device by having the image display medium as a constituent element.

Hereinafter, the present invention will be described in more detail.
Self-dispersing white fine particles or self-dispersing colored fine particles (hereinafter sometimes referred to simply as self-dispersing fine particles) are dispersed in a dispersion medium without a dispersant by grafting, encapsulating or core-shelling the fine particles with a polymer, for example. It can be a fine particle in a finished state. The dispersion containing the self-dispersing fine particles has an electrophoretic effect and an electric field alignment effect, and preferably has an electroviscous effect (Winslow effect), so that the reflectivity, contrast, and the like are higher than those of conventional dispersions. It has been found that the display characteristics are improved in each stage. In general, an electrophoretic effect appears by charging each of the self-dispersing fine particles to a positive charge or a negative charge. On the other hand, an electric field alignment effect and an electrorheological effect (Winslow effect) appear by dielectrically polarizing each of the self-dispersing fine particles. Although the mechanism of the electrorheological effect has not yet been fully elucidated, by using fine particles having a dissociative functional group, ions dissociated within the fine particles move when an electric field is applied, and electrostatic force acts between the fine particles. Therefore, it is estimated that the electrorheological effect is manifested. In addition, it is presumed that the surfactant in the fine particles promotes dissociation of these dissociating groups and at the same time has a low electrical conductivity because it does not have a high conductivity like water. In the conventional electrophoresis method based on the electrophoretic effect, the positively charged or negatively charged fine particles move only with respect to the positive or negative electrode due to the electrophoretic effect. It was found that no contrast was obtained. When the self-dispersing fine particles move to the electrode due to the electrophoretic effect, it can be seen that an electrostatic force due to dielectric polarization acts between the self-dispersing fine particles to form a uniformly oriented layer structure near the electrode. It has been found that the memory effect is improved and display characteristics such as reflectance and contrast are improved in each step by the effect.
Regarding the mechanism by which the self-dispersing fine particles are charged to a positive or negative charge, (1) as to the mechanism to charge by acid-base dissociation, in conventional non-aqueous solvents, particularly non-polar aprotic solvent-based dispersions, Existence was unclear. This is presumably because interaction (solvation) between ions and solvent molecules hardly occurs in this type of solvent. Therefore, the present inventors have (a) an organic substance having at least an acidic group, (b) an organic substance having at least a basic group, and (c) a nonionic polar component that is compatible with the solvent. Containing three components of an organic substance [any component of (a) and (b) may be present as a copolymer with component (c)] Results of intensive study on nonpolar aprotic solvent dispersion In the solvent, it was found that the components (a) and (b) caused acid-base ion dissociation. It was also suggested that ion-dipole interaction, ie solvation, exists. That is, when the present inventors have three components (a), (b), and (c), ion dissociation between acid and base via solvation of polar groups in component (c). Thus, it was found that ions can exist stably even in a nonpolar aprotic solvent. This fact was similarly observed whether both components (a) and (b) were soluble or insoluble in the solvent. Further, as described above, the present inventors, in the system containing the three components (a), (b) and (c), when coexisting fixed particles such as pigments and metal oxides, ) Or (b) the acid group or basic group of the component is fixed by chemical bonding, adsorption or the like, and ionic dissociation occurs at the interface between the solid particle surface and the solvent via the solvation of the component (c). It has been found that the solid particles are uniformly charged to a positive or negative polarity, and that the 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 inventors have 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). As a method of charging, (2) a method in which an ionic compound is adsorbed on the surface of the self-dispersing fine particles by adding an ionic compound and positively or negatively charged, and (3) an interface by adding a surfactant. A method in which the active agent is adsorbed on the surface of the self-dispersing fine particles and positively or negatively charged. (4) By adding the polymer dispersant, the polymer dispersant is adsorbed on the surface of the self-dispersing fine particles and becomes positive or negative. There is also a method of charging.

  As a method for expressing the electric field alignment effect and the electrorheological effect (Winslow effect), it is necessary to apply an electrostatic force due to dielectric polarization between the self-dispersing fine particles. What is necessary is just to determine a compounding quantity suitably, confirming expression of a desired effect. When the self-dispersing fine particles themselves are positively charged, if the terminal adsorbing the additive is negatively charged, dielectric polarization occurs between them, and the self-dispersing fine particles themselves may be negatively charged. The same can be considered. There are various other methods for the dielectric polarization of self-dispersing fine particles and the method of applying electrostatic force between self-dispersing fine particles. It is not particularly limited to the method using additives.

  As described above, when the dispersion liquid composed of self-dispersing fine particles has the electric field alignment effect and the electroviscous effect (Winslow effect) in addition to the conventional electrophoretic effect, reversible display is possible, and it has a memory property. In particular, it is possible to provide an image display medium with 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.

  The present invention is based on the above findings.

In the forms of (1) to (8), 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 metal such as Al, Ag, Ni, Cu, or a transparent conductor such as ITO, SnO ₂ , ZnO: Al, etc. formed into a thin film by sputtering, vacuum deposition, CVD, coating, etc., Or what mixed and apply | coated the electrically conductive agent to the 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 layers having pattern-like or multidot-like segments with conductive portions penetrating in the thickness direction. May be. In any case, an electric field can be generated between the conductive layers (1) and (2) by contacting a part of the conductive layers (1) and (2) with the power supply electrode. Can move reliably. In order to perform the display, voltage applying means between the conductive layers (1) and (2) may be prepared, which is convenient.

  First, the dispersion for producing the electric field arrangement effect or the electroviscous effect (Winslow effect) will be described in detail.

Self-dispersing fine particles having a dissociative functional group in the present invention, -COOM in the _{molecule, -SO 3 M, -OM, -SM} , - (R1, R2, R3) NX, - (R1, R2, R3 ) PX (where M is hydrogen or an alkali metal such as sodium, potassium or lithium, ammonium or phosphonium, R1, R2 and R3 are each hydrogen or an alkali group which can have a substituent, X represents an element or functional group that can be an anion such as halogen. Typical examples of these particles include an ion exchange resin obtained by introducing the above functional group into a copolymer of styrene and divinylbenzene, a copolymer of acrylic acid and N, N-methylenebisacrylamide, and the like. Polymers containing acrylic acid, carboxymethyl cellulose, cellulose particles such as those obtained by dyeing cellulose particles with reactive dyes, copolymers of acrylamide and ethylene glycol dimethacrylate, etc. Lumpy aggregates of acrylamide copolymers, acid dyes, direct dyes, basic dyes, and the like. These particles do not necessarily have to be composed of a compound having a dissociative functional group as described above. For example, particles composed of a compound obtained by copolymerizing polyethylene, styrene and divinylbenzene, or the like. Particles in which the compound having the dissociative functional group described above is coated in the vicinity of the surface can also be preferably used.
The particles used in the present invention are particles that hardly contain moisture. More specifically, particles having a water content of 5 mass percent or less, more preferably 1 mass percent or less, are used. The particles from which moisture has been removed can be obtained by synthesizing and purifying the above particles, followed by heat drying, vacuum drying, standing in a dry air stream, freeze-drying, or the like. An electrorheological fluid having a large shear stress can be obtained by adding moisture to the particles as described above, but if such particles are used, the current density becomes high.
The particle size of the particles used in the present invention is preferably 0.01 to 100 μm. If the particle size is less than 0.01 μm or more than 100 μm, a sufficient increase in viscosity due to an electric field cannot be obtained. Especially preferably, it is 0.01-1 micrometer.

The surfactant used in the present invention may be any of anionic, cationic, and nonionic surfactants, but the most preferable for reducing the current that flows when an electric field is applied. It is an activator. In order to obtain a sufficiently large shear stress, it is preferable to use a liquid at room temperature.
Specific examples of the surfactant used in the present invention include polyoxyethylene alkyl ethers, polyoxyethylene alkyl phenyl ethers, polyoxyethylene alkyl esters, polyoxyethylene alkyl sorbitan esters, polyoxyethylene alkyl amines. Glycerin fatty acid esters, decaglycerin fatty acid esters, polyglycerin fatty acid esters, sorbitan fatty esters, propylene glycol fatty acid esters, polyoxyethylene glycol fatty acid esters, polyoxyethylene polyoxypropylene alkyl ethers, poly Examples thereof include oxyethylene polyoxypropylene block polymers, perfluoroalkyl phosphate esters, and perfluoroalkyl betaine acid. Among these nonionic surfactants, it is particularly preferable to use a compound having an ethylene oxide group (polyoxyethylene group) in order to obtain a larger shear stress. In order to obtain a preferable shear stress, a compound in which the length of the ethylene oxide group and the length of the alkyl group are in an appropriate range is selected according to the kind of the particle and the surfactant.

  Next, the nonpolar solvent used in the present invention is an electrically insulating liquid, and a liquid that has been conventionally used for an electrorheological fluid exhibiting the Winslow effect is used as it is. Examples of such liquids include dioctyl phthalate, didecyl phthalate, dibutyl phthalate, diethyl phthalate, dinonyl phthalate, diisononyl phthalate, di-2-ethylhexyl phthalate, ditridecyl phthalate, butyl benzyl phthalate, tri Aromatic carboxylic acid esters such as trioctyl meritate, tridecyl trimellitic acid, butyl sebacate, butyl oleate, butyl stearate, dibutyl adipate, butyl phthalyl ethylene glycolate, methyl phthalyl ethylene glycolate, methyl phthalyl butyl glycolate, monoacetin, Aliphatic carboxylic acid esters such as diacetin, triacetin, vegetable oil, silicone oils such as modified or unmodified polymethylsiloxane, dodecane, 2,2,3-trimethylpentane, hexade , Ligroin, aliphatic hydrocarbons such as refined kerosene, alkylnaphthalene, hydrogenated triphenyl, diphenylmethane, monoethyldiphenyl, triethyldiphenyl, diethyldiphenyl, diphenyl, terphenyl, 1,4-diphenylbenzene, phenyl Alkyl-substituted aromatic hydrocarbons such as xylylethane, toluene and xylene, alkyl-substituted biphenyls, halogen-substituted aliphatic hydrocarbons such as trichloroethylene, tetrachloroethylene, and bromonaphthalene, anisole, phenetole, methoxy Mention may be made of ethers such as toluene, diphenyl ether and veralol, and phosphazenes.

  The essential components of the dispersion in the present invention are the aforementioned self-dispersing fine particles (A) and the nonpolar solvent (B). Each of these components may be formed of a single compound, but several kinds of compounds may be mixed and used depending on the purpose. Various additives can be added depending on the purpose. For example, a gelling agent can be added to adjust the viscosity of the fluid, or an antioxidant can be added to increase the stability of the fluid. When the dispersion according to the present invention is used as an ink for image recording, a colorant such as a dye may be added.

  Next, a method for charging the self-dispersing fine particles will be described.

  Self-dispersing fine particles have at least an acidic group on their surface and a resin soluble in a nonpolar solvent has at least a basic group, or have a basic group on their surface and can be used in a nonpolar solvent. It is preferable that the soluble resin 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 self-dispersing 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 self-dispersing fine particle surface and the solvent via solvation. Solid particles are more stably dispersed than in the past due to the uniform charging of positive or negative polarity and the addition of the electrostatic effect and the steric effect.

  In order to charge the self-dispersing fine particles to positive or negative polarity by a method other than acid-base dissociation, as described above, (2) a method of adding an ionic compound, (3) a method of adding a surfactant, 4) There is a method of adding a polymer dispersant. As for the surfactant, it is also used as a dispersant in the self-dispersing carbon black, as described later. Among these, nonionic surfactants are preferable, and sorbitan fatty acid esters and the like are preferable among them.

  Regarding the polymer dispersant, there are various polymer dispersants, and for example, polyester dispersant Solspers (manufactured by Zeneca) is preferable. Among them, Solspers 17000 (single polyester anchor part: base), Solspers 16000 (single polyester anchor part: base), Solspers 41000 (single polyester anchor part: acid), Solspers 3000 (single polyester anchor part: acid) are preferable. Disperbyk-2050, 2150, 160, 161, 162, 163, 164, 166, 167, 182 (Bicchemy Japan) and the like are also preferable.

  As other polymer dispersants, conventionally known dispersions used for preparing pigment dispersions can be used. Examples of the dispersion include the following. Polyacrylic acid, polymethacrylic acid, acrylic acid-acrylonitrile copolymer, vinyl acetate-acrylic acid ester copolymer, acrylic acid-acrylic acid alkyl ester copolymer, styrene-acrylic acid copolymer, styrene-methacrylic acid copolymer Polymer, styrene-acrylic acid-alkyl acrylate ester copolymer, styrene-methacrylic acid-alkyl acrylate copolymer, styrene-α-methylstyrene-acrylic acid copolymer, styrene-α-methylstyrene-acrylic Acid alkyl ester copolymer, styrene-maleic acid copolymer, vinyl naphthalene-maleic acid copolymer, vinyl acetate-ethylene copolymer, vinyl acetate-fatty acid vinyl ethylene copolymer, vinyl acetate-maleic acid ester copolymer Coalesce, vinyl acetate-crotonic acid copolymer, And vinyl acetate-acrylic acid copolymer. According to a preferred embodiment of the present invention, these copolymers preferably have a weight average molecular weight of 3,000 to 50,000, more preferably 5,000 to 30,000, and most preferably 7,000 to 7,000. 15,000. The amount of the dispersant added may be appropriately determined as long as the pigment is stably dispersed and the other effects of the present invention are not lost. The mass ratio of self-dispersing fine particles: dispersing agent is in the range of 1: 0.006 to 1: 0.3, preferably 1: 0.0125 to 1: 0.3.

  Examples of the self-dispersing 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, methylene blue, Cyan colorants such as Victoria Blue, Methyl Violet, Aniline Blue, Ultramarine Blue, magenta colorants such as Rhodamine 6G Lake, Dimethylquinacridone, Watching Red, Rose Bengal, Rhodamine B, Alizarin Lake, Chrome Yellow, Benzidine Yellow, Conventionally known dyes and mixtures such as yellow colorants such as Hansa Yellow, Naphthol Yellow, Molybdenum Orange, Quinoline Yellow, Tartrazine, etc. have the following acidic groups. Mer, or the like which is dispersed a monomer having a basic group with a non-polar solvent-insoluble particles modified resins having as a component.

  Examples of fine particle modifying resins insoluble in nonpolar solvents having acidic groups (polymers or copolymers comprising monomers having acidic groups as constituents) include (meth) acrylic acid, maleic acid, maleic anhydride, 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 of the following monomers, 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. And a copolymer obtained from at least one alkyl or aryl ester of (meth) acrylic acid. The type of monomer to be combined and the blending ratio at the time of polymerization can be appropriately determined.

  Examples of fine particle modifying resins (polymers or copolymers comprising a monomer having a basic group as a constituent component) insoluble in a nonpolar solvent having a basic group include N-methylaminoethyl (meth) acrylate, N-ethyl Aminoethyl (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-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. The type of monomer to be combined and the blending ratio at the time of polymerization can be appropriately determined.

  In addition, when a substance that can be chemically bonded by grafting or the like, such as carbon black or metal oxide, is used as particles, an acidic group can be obtained by reacting these substances with a monomer having the acidic group or basic group. Alternatively, a basic group may be chemically bonded.

  The amount of the colorant (pigment) used is 0.1 to 300 parts by mass, preferably 1 to 100 parts by mass with respect to 100 parts by mass of the resin.

  As the nonpolar solvent, a known hydrocarbon solvent or silicone oil can be used as described above. Moreover, it is preferable to add white or colored self-dispersing fine particles that are soluble in a nonpolar solvent to the dispersion. Further, as the resin soluble in the nonpolar solvent, a resin having a stronger attractive interaction with the surface of the self-dispersing fine particles than the nonpolar solvent is preferable. When the resin is adsorbed on the self-dispersing fine particles, the dispersion stability of the self-dispersing 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 soluble in hydrocarbon solvents having acidic groups (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 Mono having an acidic group such as styrene And at least one chromatography, the copolymer obtained 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 hydrocarbon solvents having basic groups and resins soluble in silicone oil (polymers or copolymers having 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 Echi At least one monomer having a basic group such as styrene, 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.

  As the compound having a nonionic polar group, a compound that is soluble in a hydrocarbon solvent or silicone oil, has a dielectric constant larger 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 nonpolar solvent is about 0.1 to 10 parts by mass with respect to 100 parts by mass of the nonpolar solvent.

  In order to make the dispersion of the present invention, the above-mentioned components may be mixed and dispersed in a nonpolar 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 the 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) include at least the above ( At least one of the specific examples of the monomer having an acidic group in the embodiment of the present invention of the item 1), 2-hydroxyethyl (meth) acrylate, 2,3-dihydroxypropyl (meth) acrylate, 4-hydroxy Butyl (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-cyano Acrylate, 2-cyanoethyl acrylate, ethyl-2-cyanoacrylate, methacrylacetone, tetrahydrofurfuryl methacrylate, trifluoroethyl methacrylate, p-nitrostyrene, vinylpyrrolidone, acrylamide, methacrylamide, N, N-dimethylmethacrylamide, N, And a copolymer with a polar monomer such as N-dibutylmethacrylamide. Further, it may be a copolymer having, as a component, at least one alkyl or aryl ester of (meth) acrylic acid in the embodiment of item (1).

  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, the self-dispersing fine particles have a nonionic polar group on the surface. Specific examples of the self-dispersing fine particles used in the present invention include a resin that is insoluble in a hydrocarbon solvent or silicone oil containing the monomer having the acidic group and the polar monomer as a component, or the basic group. The thing using the resin insoluble in the hydrocarbon solvent and silicone oil which have a monomer and the said polar monomer as a component is mentioned. In addition, when a substance that can be chemically bonded by grafting or the like, such as carbon black or metal oxide, is used as the solid particle, the monomer having the acidic group or the basic group is reacted with the polar monomer. By doing so, an acidic group or a basic group and a polar group may be chemically bonded.

  In the embodiment of the present invention of item (9), the self-dispersing fine particles comprise at least a pigment and a resin, and the mass ratio of the pigment to the resin is from 0.1 parts by mass of the pigment to 100 parts by mass of the resin. 300 parts by mass. 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, when the resin component responsible for ion generation by acid-base dissociation on the surface of white or 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 of item (10), the self-dispersing white fine particles are preferably titanium oxide. This is because titanium oxide has the highest whiteness among various materials.

In the embodiments of the present invention of the items (11) to (15), description will be given 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 types are generally classified by the production method, and are roughly classified into either pyrolysis of raw material hydrocarbons or incomplete combustion (Table 1), and further subdivided according to the types of raw materials. 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.

(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.
Three major basic characteristics of carbon black (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

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 mass is used. 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.

Further, 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 mass, more preferably in the range of 4.5 to 6.0% by mass, and the 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 mass or more is not clear, but it is presumed 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 mass, the dispersibility tends to be higher than this, so that the volatile content is in the range of 3.5 to 8.5% by mass. 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 so as not to 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.

Where V: Volatile content (%)
WD: mass of dry sample (g)
WR: Mass of the sample after heating (g)

  Such acidic carbon blacks include, for example, MA7, MA8, # 2200B (manufactured by Mitsubishi Chemical), 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.

As for the production method of acidic carbon black, carbon black is generally performed using a channel black method or a 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, and various functional groups can be introduced onto the particle surface. In the following formula, Φ is a condensed aromatic ring, R is an alkyl group, and X is a halogen atom.

(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 interfacial polyoxyethylene alkyl ether acetates, dialkyl sulfosuccinates, polyoxyethylene alkyl ethers, polyoxyethylene alkylphenyl ethers, polyoxyethylene polyoxypropylene block copolymers, and acetylene glycol-based interfaces. An activator is mentioned. More specifically, polyoxyethylene alkyl ether acetate (II) and / or dialkylsulfosuccinic acid (III) having a branched alkyl chain having 5 to 7 carbon chains is used as the anionic surfactant. The dispersion stability of carbon black can be obtained.

  In the formula, R is an alkyl group having 6 to 14 carbon atoms which may be branched, m is 3 to 12, M is an alkali metal ion, quaternary ammonium, quaternary phosphonium or alkanolamine.

In the formula, R ₅ and R ₆ are branched alkyl groups having 5 to 7 carbon atoms, and M is 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 (IV) which are polyoxyethylene alkylphenyl ethers and general formula (V) which are acetylene glycol surfactants.

  In the formula, R is a 6 to 14 carbon chain which may be branched, and k is 5 to 12.

  In the formula, p and q are 0 to 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.
That is, in the present invention, when acidic carbon black is used, good dispersion stability cannot be obtained unless the average molecular weight of the dispersion resin is reduced and the viscosity of the dispersion and the particle size 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. Therefore, if the average molecular weight is too small, the dispersion stability during long-term storage is deteriorated.

  As the water-soluble resin contained in the dispersion liquid of the present invention as a carbon black dispersant, any water-soluble resin that is soluble in an aqueous solution in which an amine is dissolved and has a mass average molecular weight of 3000 to 30000 can be used. 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 in order to enhance both the dispersion stability of the self-dispersing fine particles and the charged 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. Examples of the polymer dispersant include poly (N-vinyl-2-pyrrolidone), poly (N, N′-diethylacrylazide), poly (N-vinylformamide), poly (N-vinylacetamide), poly (N— Vinylphthalamide), poly (N-vinylsuccinamide), poly (N-vinylurea), poly (N-vinylpiperidone), poly (N-vinylcaprolactam), poly (N-vinyloxazoline) and the like. A single or a plurality of 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) 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) Introduction of functional groups on the surface of grafting treatment 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 Asylium perchlorate group
ii Chlormethyl group
iii Benzylium perchlorate c. Anionic graft polymerization
i Potassium carboxylate
ii Carbon black / BuLi composite (OLi group)
iii. Graft reaction with polymer on amino group (c) surface a. Reaction of responsive 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 blacks may be used in combination. In the present invention, it is preferable to contain at least one carbon black having a volatile content of 1.0% 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 or more and 1 μm or less, preferably 0.05 μm or more and 0.1 μm or less. 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.

  The embodiments of the present invention in the items (14) and (15) will be described. Graft carbon black refers to fine particles in which a polymer portion is grafted to a carbon black portion. Graft carbon black 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, graft carbon black allows the polymer portion to effectively enter between the carbon black particles and weaken the cohesive force between the carbon blacks. Further, when the polymer portion has an affinity with the resin material or the like, the graft carbon black can be dispersed in the resin material or the like 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 graft carbon black 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. In the present invention, an acrylic copolymer grafted carbon black grafted with an acrylic copolymer and a grafted carbon black grafted with a silicone polymer are preferred.

  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 the embodiment of the present invention of item (16), the particle size of the white or colored particles is 0.01 μm or more and 1 μm or less. As the particle size is smaller, an image display medium with a higher resolution can be obtained. 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 of item (17), the nonpolar solvent used as the dispersion medium is any one of aliphatic hydrocarbon, aromatic 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, Ciel Petroleum manufactured by Exxon). Cielsol etc. manufactured by the company). 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 of item (18), 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, most preferably. 50-100 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.
Examples of the image display device include digital paper shown in FIG. 4, pocket PC shown in FIG.

In the embodiment of the present invention of item (19), as a display cell for actually enclosing the dispersion liquid, it is very many steps to produce a fine cell with photolithography, etc. Therefore, it is considered preferable to encapsulate in microcapsules.
FIG. 6 is a cross-sectional view for explaining a microcapsule according to the present invention. In FIG. 6, reference numeral (10) denotes a microcapsule in which a dispersion liquid (5) containing self-dispersing white fine particles, self-dispersing colored fine particles and a nonpolar solvent is enclosed. FIG. 7 is an explanatory diagram for explaining an example of an image display medium having the microcapsules of the present invention. In FIG. 7, reference numeral (40) denotes an image display medium, and a microcapsule (10) in which a dispersion liquid (5) is sealed is disposed between the conductive layers (1) and (2).

  In the embodiment of the present invention of item (20), the average particle size 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 of item (21), the material of the microcapsule is most preferably gelatin from the viewpoint 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 of item (22), a flexible display device can be realized by forming the microcapsules on the sheet by a coating method such as coating.

Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to the following examples. The parts used in the examples are all parts by mass.
<Method of synthesizing charged fine particles>
Synthesis Example 1 (Method for producing core-shell titanium oxide fine particles having a basic group)
1. Dispersant synthesis Separable silicone macromer FM0711 (manufactured by Chisso) 36g, dimethylaminoethyl methacrylate DMAEMA (manufactured by Tokyo Chemical Industry) 4g, initiator AIBN (manufactured by Tokyo Chemical Industry) 0.2g, silicone oil KF96L-1cs (manufactured by Shin-Etsu Chemical) It put into the container 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 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-1cs (Shin-Etsu Chemical) are placed in a beaker and stirred for 1 hour with a magnetic stirrer, and then 4 g of titanium oxide CR-90 (Ishihara Sangyo) is added. Stir 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-1cs (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 methacrylic acid MAA (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-1cs (manufactured by Shin-Etsu Chemical) 360 g was put into a separable container and stirred at 200 rpm under an 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)
Synthesis Example 1 1. And 2. (A) was the same, 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 consisting of 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)
Synthesis Example 1 1. And 2. (A) was the same, and 4 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 consisting of 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 group and nonionic polar group)
Synthesis Example 1 1. And 2. (A) was the same, 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 over 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.

<Method of synthesizing 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 115g 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. 1.43 g of sodium nitrite and 10 mL of deionized water are dissolved in advance and added dropwise in about 1 hour. Stir at 65 ° C for 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. Add 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% mass 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. Surface-treated titanium oxide (Silanized Titania) 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 crushed finely, and 750 g is added and stirred. N2 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 fraction is left to dry overnight and then vacuum dried at 70 ° C. for 4 hours. Grafted titanium oxide (LMATiO ₂ ) can be synthesized.

Measurement of dielectric constant and zeta potential of each fine particle In order to show electrophoretic effect and electric field arrangement behavior, each fine particle needs to have a high dielectric constant and zeta potential. Each value was measured. The results are shown in Table 2.
Dielectric constant measurement method Using a dielectric measurement system (126096W type: manufactured by Toyo Technica), measure the chemical impedance of the mixed system containing fine particles from the Cole-Cole plot, and then measure the chemical impedance of the solvent only under the same conditions. The difference was calculated as the dielectric constant of the fine particles.
Method of measuring zeta potential The zeta potential of each fine particle in the solvent was measured using a concentrated zeta potentiometer (ELS-N1000: manufactured by Otsuka Electronics Co., Ltd.).

Preparation of dispersion
By using the combination of self-dispersing fine particles shown in Table 3 below, the dispersion liquids of Examples 1 to 10 were prepared using the fine particles and polymers, surfactants, polymer dispersants, and nonpolar solvents prepared in each of the above synthesis examples. The following composition was prepared. In addition, the following mass part is solid content.

<Composition composition>
Example 1
Titanium oxide (Synthesis example 1): 40 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 41000 (manufactured by Geneca): 0 .47 parts by mass Rheodor SP-O30V (Kao surfactant sorbitan trioleate): 0.53 parts by mass Isopar H (manufactured by Shell Petroleum): 56 parts by mass Total: 100 parts by mass A liquid was prepared and dispersed with an ultrasonic wave for 1 hour, and then used as a dispersion liquid in 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 DeSK008 (manufactured by Tokai Carbon): 2 parts by weight Dispersant Solsperse 17000 (manufactured by Geneca): 0.52 parts by weight Nonion OP-85R (Nippon Yushi surfactant sorbitan trioleate): 0.48 parts by mass Silicone oil KM96-1cs (manufactured by Shin-Etsu Chemical): 76 parts by mass Total: 100 parts by mass Dispersion obtained by mixing these respective compositions A liquid was prepared and dispersed with an ultrasonic wave for 1 hour, and then used as a dispersion liquid in Example 2.

Example 3
Titanium oxide (Synthesis Example 5): 20 parts by mass Basic polymer (Synthesis Example 6): 1 part by mass Self-dispersing carbon black (Synthesis Example 10): 2 parts by mass Dispersant Solsperse 16000 (manufactured by Geneca): 0.30 parts by mass Nonion Surfactant (Wako Pure Chemicals sorbitan trioleate): 0.70 parts by mass Silicone oil SH200-0.65cs (manufactured by Toray Dow Corning): 76 parts by mass Total: 100 parts by mass Dispersion obtained by mixing these respective compositions A liquid was prepared and dispersed with an ultrasonic wave for 1 hour, and then used as a dispersion liquid in Example 3.

Example 4
Titanium oxide (Synthesis Example 7): 40 parts by mass Basic polymer (Synthesis Example 8): 1 part by mass Self-dispersing carbon black (Synthesis Example 10): 2 parts by mass Dispersant Disperbyk-2050 (manufactured by Bicchem Japan): 0. 44 parts by weight Rheodor SP-L10 (Kao surfactant sorbitan monolaurate): 0.56 parts by weight Isopar H (manufactured by Shell Petroleum): 56 parts by weight Total: 100 parts by weight Dispersion obtained by mixing these respective blended compositions A liquid was prepared and dispersed with an ultrasonic wave for 1 hour, and then used as a dispersion liquid in Example 4.

Example 5
Titanium oxide (Synthesis Example 11): 40 parts by mass Self-dispersing carbon black (Synthesis Example 9): 2 parts by mass Acidic polymer (Synthesis Example 2): 1 part by mass Dispersant Disperbyk-2150 (manufactured by Big Chemi Japan): 0.47 Part by weight Rheodor SP-O10V (surfactant sorbitan monooleate manufactured by Kao): 0.53 part by weight Isopar G (manufactured by Shell Petroleum): 56 parts by weight Total: 100 parts by weight A dispersion obtained by mixing these respective composition compositions After producing and dispersing with ultrasonic waves for 1 hour, it was used as a dispersion liquid of Example 5.

Example 6
Titanium oxide (Synthesis example 1): 30 parts by mass Silicone polymer grafted carbon black MX3-GRX-001 (manufactured by Nippon Shokubai): 2 parts by mass Dispersant Solsperse3000 (manufactured by Zeneca): 0.52 parts by mass Rheodor SP-O30V (manufactured by Kao) Surfactant sorbitan monotrioleate): 0.48 parts by mass Isopar H (manufactured by Shell Petroleum): 67 parts by mass Total: 100 parts by mass A dispersion obtained by mixing each of these blended compositions was prepared, and ultrasonically for 1 hour. After dispersion, it was used as Example 6 dispersion.

Example 7
Titanium oxide (Synthesis Example 3): 40 parts by weight Self-dispersing carbon black DeSK009 (manufactured by Tokai Carbon): 2 parts by weight Dispersant Solsperse 17000 (manufactured by Zeneca): 0.47 parts by weight Rheodor SP-L10 (surfactant sorbitan mono from Kao) Laurate): 0.53 parts by mass Silicone oil KM96-1cs (manufactured by Shin-Etsu Chemical): 57 parts by mass Total: 100 parts by mass A dispersion was prepared by mixing each of these blended compositions and dispersed with ultrasound for 1 hour. Later, it was used as Example 7 dispersion.

Example 8
Titanium oxide (Synthesis example 5): 20 parts by mass Self-dispersing carbon black (Synthesis example 9): 2 parts by mass Dispersant Solsperse 16000 (manufactured by Zeneca): 0.47 parts by mass Rheodor AO-10 (surfactant sorbitan monooleate Kao) ): 0.53 parts by mass Isopar G (manufactured by Shell Petroleum): 77 parts by mass Total: 100 parts by mass A dispersion obtained by mixing these respective blended compositions was prepared and dispersed with ultrasound for 1 hour. Used as a dispersion.

Example 9
Titanium oxide (Synthesis Example 7): 40 parts by mass Self-dispersing carbon black (Synthesis Example 9): 2 parts by mass Dispersant Solsperse 17000 (manufactured by Zeneca): 0.40 parts by mass Rheodor AO-15V (surfactant sorbitan sesquiolate manufactured by Kao) ): 0.60 parts by mass Silicone oil KM96-1cs (manufactured by Shin-Etsu Chemical Co., Ltd.): 57 parts by mass Total: 100 parts by mass After preparing a dispersion liquid in which each of these blended compositions was mixed and dispersing with ultrasound for 1 hour, Example 9 Used as a dispersion.

Example 10
Titanium oxide (Synthesis Example 11): 30 parts by mass Self-dispersing carbon black (Synthesis Example 9): 2 parts by mass Dispersant Disperbyk-2050 (manufactured by Big Chemi Japan): 0.50 parts by mass Emazole L-10 (F) (interface) Activator sorbitan monolaurate manufactured by Kao): 0.50 parts by mass Isopar H (manufactured by Shell Petroleum): 67 parts by mass Total: 100 parts by mass After time dispersion, it was used as Example 10 dispersion.

Example 11
Titanium oxide (Synthesis Example 11): 40 parts by mass Self-dispersing carbon black (Synthesis Example 10): 2 parts by mass Dispersant Disperbyk-2150 (manufactured by Big Chemi Japan): 0.55 parts by mass Emazole O-10V (surfactant sorbitan) Monooleate Kao): 0.45 parts by mass Silicone oil SH200-0.65cs (manufactured by Toray Dow Corning): 57 parts by mass Total: 100 parts by mass After dispersing for 1 hour, it was used as Example 11 dispersion.

Comparative Example Titanium oxide (Synthesis Example 7): 10 parts by mass Basic polymer (Synthesis Example 8): 1 part by mass Blue dye MACROLEX BLUE RR GRAN (manufactured by Zeneca): 1 part by mass Isopar H (manufactured by Shell Petroleum): 88 parts by mass Total: 100 parts by mass A dispersion 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.

Here, Nippon Shokubai silicone polymer graft carbon black (silicone-based GCB) and Tokai carbon self-dispersing carbon black are self-dispersing carbon blacks having the following characteristics.
<Nippon Catalyst CB>
Sample name: MX3-GRX-001
CB / RP = 10 / 3wt ratio
Solvent: Silicone oil (Dow Corning SH2001CS)
CB concentration: 20.0%
RP concentration: 6.0%
Solvent concentration: 74.0%
<Tokai Carbon CB>
DeSK008 (10.0%)
DeSK009 (10.0%)

Viscosity change during operation of dispersion liquid Each of the dispersion liquids of Examples 1 to 11 and the dispersion liquid of the comparative example was applied with a voltage of ± 20 V, and the fine particles were in an electric field arrangement state. Each shear stress was measured when the fine particles were in a random state.
For the shear stress, a rotor (name 48 ′ × R24) is attached to a viscosity measuring device RE80L (manufactured by Toki Sangyo Co., Ltd.), and the rotational speed is 100, 50, 20, 10, 5, 1 (rpm) at a temperature of 25 ° C. Measured with Of these, a stable value of 50 or 20 rpm was taken as a measured value. The results are shown in Table 4.

Manufacturing method of display cell Next, a 100 μm thick polyester film having a 1 cm ² opening provided between ^two glass substrates with ITO electrodes 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 Glass cell for reflectance measurement: ITO film formation on one side of the entire surface Glass cell for observation of the movement behavior and orientation of fine particles: Create a 1mm wide line without ITO at the center of one side : Geomat Co., Ltd. Material: Soda glass Dimensions mm: 29.8 ± 0.1 / 39.8 ± 0.1
ITO surface resistance 50 ± 10Ω / □
Or SiO ₂ base treatment (dip)

Display Operation Reflectance Measurement When −20 V was applied to each of the upper ITO electrodes of Examples 1 to 11 and the comparative example, the dispersed particles were rapidly 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.
Using LCD EVALUATION SYSTEM LCD-5000 (manufactured by Otsuka Electronics), the reflectance, contrast, and response speed of each display cell of Examples 1 to 11 and Comparative Example were measured. The results are shown in Table 5.

Observation of movement behavior and orientation of fine particles When -20V is applied to the upper and lower ITO electrodes on the left side of Examples 1 to 11 and the comparative example, the dispersed particles quickly move from the left side to the right side to the right electrode. Electrodeposited. Next, when + 20V was applied to the upper and lower electrodes on the left side, the dispersed particles moved from the right side to the left side. At this time, the movement of the fine particles was visually observed from above with a microscope to observe whether the particles move in a vortex or in a straight line. In addition, the state in which the fine particles adhered to the electrode after the movement was observed, and it was observed whether they were aligned or randomly stacked. 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. The results are shown in Table 6.

Preservation of dispersion and display operation after storage Each dispersion is treated at room temperature (25 ° C.), 50 ° C., 0 ° C., −20 ° C., −20 ° C. to 50 ° C. for one week, two weeks, three weeks, Stored for 4 weeks. The state of the dispersion was examined. In addition, it was confirmed that the display operation could be performed without problems after each storage test. The results are shown in Tables 7 and 8.

It is sectional drawing which shows typically an example of the image display medium of this invention. It is a schematic diagram which shows in principle the mechanism of the display operation | movement of the image display medium of this invention. It is sectional drawing which shows the conventional display apparatus typically. It is a schematic diagram for demonstrating an example of the image display apparatus in this invention. It is a schematic diagram for demonstrating an example of the image display apparatus in this invention. It is sectional drawing for demonstrating the microcapsule in this invention. It is explanatory drawing for demonstrating an example of the image display medium which has the microcapsule of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 2 Conductive layer 3 Self-dispersing colored fine particle 4 Self-dispersing white fine particle 5 Dispersion liquid 10 Microcapsule 40 Image display medium

Claims (22)

  A dispersion liquid containing at least self-dispersing white fine particles, self-dispersing colored fine particles and a nonpolar solvent between two conductive layers at least one or both of which are arranged to be light-transmitted and arranged at a desired interval; and An image display medium, wherein the dispersion has both an electrophoretic effect and an electric field alignment effect.   The image display medium according to claim 1, wherein each fine particle in the dispersion forms a layer oriented in the vicinity of the conductive layer.   When the self-dispersing white fine particles have a positive charge or a negative charge, and the self-dispersing white fine particles have a negative charge, the self-dispersing colored fine particles have a positive charge, and the self-dispersing white fine particles have a positive charge. The image display medium according to claim 1, wherein the self-dispersing colored fine particles have a negative charge.   The image display medium according to claim 1, wherein the self-dispersing white fine particles and the self-dispersing colored fine particles have dielectric polarization.   The self-dispersing white fine particles or the self-dispersing colored fine particles have a positive charge or a negative charge generated by acid-base dissociation, and the fine particles have opposite charges. The image display medium according to any one of the above.   6. The self-dispersing white fine particles or the self-dispersing colored fine particles have positive charges or negative charges generated by an ionic compound, and the fine particles have opposite charges. The image display medium according to any one of the above.   6. The self-dispersing white fine particles or the self-dispersing colored fine particles have a positive charge or a negative charge generated by a surfactant, and the fine particles have opposite charges. The image display medium according to any one of the above.   6. The self-dispersing white fine particles or the self-dispersing colored fine particles have a positive charge or a negative charge generated by a polymer dispersant, and the fine particles have opposite charges. The image display medium according to any one of the above.   The self-dispersing white fine particles and the self-dispersing colored fine particles contain at least a pigment and a resin, and the mass ratio of the pigment to the resin is 0.1 part by mass to 300 parts by mass of the pigment with respect to 100 parts by mass of the resin. The image display medium according to claim 1, wherein the image display medium is provided.   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 white fine particles or the self-dispersing colored fine particles are fine particles modified with a surface functional group.   The image display medium according to claim 1, wherein the self-dispersing white fine particles or the self-dispersing colored 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 grafted carbon black.   The image display medium according to claim 1, wherein an average particle size of the self-dispersing white fine particles and the self-dispersing colored fine particles is 0.01 μm or more and 1 μm or less.   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 dispersion liquid is sealed in a microcapsule.   The image display device according to claim 19, wherein an average particle size of the microcapsules is 10 μm or more and 150 μm or less.   The image display device according to claim 19 or 20, wherein the material of the microcapsule is gelatin or gum arabic. The image display device according to claim 19, wherein the microcapsule is configured on a sheet.

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