JP2010270088A - Electrophoretic particle dispersion, image display medium, and image display device - Google Patents

Abstract

Disclosed is an electrophoretic particle dispersion that has a high white reflectance and is less likely to settle in a dispersion medium than an inorganic white pigment.
An electrophoretic particle dispersion obtained by dispersing electrophoretic particles mainly comprising an alkylene bismelamine derivative represented by general formula (I) in a nonpolar solvent.

Wherein R is a hydrogen atom, a lower alkyl group having 1 to 4 carbon atoms or an alicyclic group, R ₁ , R ₂ , R ₃ and R ₄ are each independently a hydrogen atom or a lower alkyl group having 1 to 4 carbon atoms. R ₁ and R ₂ , R ₃ and R ₄ may form a heterocyclic group together with the nitrogen atom, and X represents a lower alkylene group having 2 to 3 carbon atoms)
[Selection figure] None

Description

  The present invention relates to an electrophoretic particle dispersion, an image display medium using the same, and an image display device.

  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. They can display and rewrite digital data instantly, but it is difficult to always carry the device around, and it has many drawbacks such as eye fatigue when working for a long time and display when turning off the power. is there. On the other hand, when a character or a still image is distributed or stored as a document, it is recorded on a paper medium by a printer. This paper medium is widely used as a so-called hard copy. 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, the hard copy is discarded and recycled after being used, but since the recycling requires a lot of labor and cost, there remains a problem in terms of resource saving.

  There is a great need for a rewritable paper-like display medium that has the advantages of both the above display and hard copy, a polymer-dispersed liquid crystal as a display medium that has a reflective and bright display, and a memory property. A display medium using a bistable cholesteric liquid crystal, an electrochromic element, an electrophoretic element, or the like has attracted attention. Among these, those using electrophoretic elements are excellent in terms of display quality and power consumption during display operation (see, for example, Patent Document 1 and Patent Document 2). In an electrophoretic display medium, a dispersion liquid in which a plurality of electrophoretic particles having a color different from the color of a dispersion medium is dispersed in a colored dispersion medium is sealed between a pair of transparent electrodes. In this case, the electrophoretic particles (also simply referred to as “electrophoretic particles”) have a charge on the surface in the dispersion medium, and when a voltage opposite to the charge of the electrophoretic particles is applied to one of the transparent electrodes. When the electrophoretic particles are deposited there and the color of the electrophoretic particles is observed, and the voltage is applied in the same direction as the electrophoretic particles, the electrophoretic particles move to the opposite side, so the color of the dispersion medium is observed. . As a result, display can be performed.

  The electrophoretic particles are required to have optical properties such as white and coloring relating to the display / non-display state, and good charging performance to move quickly in response to an external electric field. Among them, inorganic pigments such as titanium oxide, which have high light scattering ability, have been conventionally used as particles having white color in order to exhibit whiteness like paper, and these can be used as they are or as additives such as particle dispersants. May be used after improving the dispersion stability. However, these pigments are generally not perfect insulators and have a lower volume resistivity than insulators. Therefore, it is difficult to migrate well along the direction of the electric field in the range of the external electric field in electrophoretic display, and in particular, it is inferior in terms of repeated display switching stability. Furthermore, since the specific gravity of the inorganic pigment is significantly larger than that of the dispersion medium, precipitation cannot be prevented, the display state changes with time, and there is a problem in terms of display memory properties. On the other hand, from the viewpoint of insulation and specific gravity, various kinds of polymer particles are preferable as the charged particles, and many particles migrate well even with an external electric field. However, the conventional polymer particles have no white particles having a satisfactory optical function as a display material.

  In order to satisfy these two requirements, conventionally, the above pigment and polymer are combined by heating and melting and then finely pulverized (for example, see Patent Document 3). However, even in this case, the specific gravity of the particles and the dispersion medium does not completely match, and there is a limit to atomization by pulverization, and the migration speed becomes slower as the particle size becomes larger. There is a problem. Furthermore, since the pigment is not completely encapsulated in the polymer and is also present on the surface to some extent, the charging of the particles varies, and the above problem cannot be completely solved.

  As an attempt to solve the above problem, a particle dispersion composition in which a self-dispersing polymer compound is adsorbed on the outer surface of a particulate material in a dispersion composition in which the particulate material is dispersed in an organic solvent has been proposed. (For example, see Patent Document 4). However, in the particle dispersion composition of Patent Document 4, in the production method, a particulate material is added to the polymer compound dissolved in the good solvent, and the poor solvent of the polymer compound is further added thereto. Since the polymer compound is deposited and adsorbed on the particulate matter, it is difficult to control the equilibrium of dissolution and deposition in the two-solvent system of the polymer compound, and the product is stably dispersed in the poor solvent without agglomerating. However, there is a problem that the composition of the polymer compound is very limited and the room for selecting a good solvent is limited.

  In addition, a method has been reported in which a pigment and a monomer are added to an organic solvent and a reaction is performed in the organic solvent to form a polymer layer on the surface of the pigment (for example, see Non-Patent Document 1). However, in this case, the reaction solvent used is methanol, which is a polar organic solvent, and the resulting particles are particles that are stably dispersed in methanol. Therefore, it is difficult to stably disperse the particles used in Non-Patent Document 1 with an insulating organic solvent used in electrophoretic display, and a particle dispersant is added to stabilize the particles. Then, there is a problem that a very large amount of use is required and the electrophoretic characteristics of the particles are impaired.

  On the other hand, grafted particles are disclosed in which polymer chains compatible with the dispersion medium are chemically bonded to the particle surfaces (see, for example, Patent Documents 5, 6 and 7). However, both of these improve the dispersibility of the particles, but since the polymer chain is compatible with the dispersion medium, the interface between the particles and the dispersion medium is substantially the surface of the solid particles, which is required for electrophoretic particles. Therefore, good electrophoretic characteristics cannot be obtained.

  In order to improve the above problems, a method for producing composite particles having a small particle size and excellent dispersion stability and chargeability has been disclosed (for example, see Patent Document 8). In particular, fine particles having vinyl naphthalene as a constituent element have been disclosed as means for solving the above-mentioned problem particularly with respect to white particles (see, for example, Patent Document 9). These fine particles have a high refractive index and an excellent light scattering effect, and are extremely white in polymer fine particles. Further, since it is a polymer, it has a small specific gravity and excellent dispersion stability, and is suitable for an electrophoretic display medium. However, since the refractive index is smaller than that of titanium oxide, a large number of particles must be present on the display surface side in order to exhibit the same or higher whiteness. For this reason, there is a problem that the distance between the electrodes becomes large and the voltage required for driving becomes high. Further, it is a copolymer containing vinyl naphthalene as a monomer element and having a basic group or an acidic group (see, for example, Patent Document 10), or a coated pigment that wraps titanium oxide as a coating resin (for example, Patent Document). 11) has also been proposed.

  Furthermore, as these combinations, composite particles in which titanium oxide is encapsulated with polyvinyl naphthalene are also disclosed (for example, see Non-Patent Document 2). In this case, however, the polyvinyl naphthalene film is not dense and is not completely covered with the polymer film. Therefore, there is a problem that the pigment surface is partially exposed and the insulating property is lowered.

  An object of the present invention is to provide an electrophoretic particle dispersion that has a high white reflectance and is less likely to settle in a dispersion medium as compared to an inorganic white pigment, and an image display medium and device excellent in display memory properties. It is to provide.

  In order to solve the above problems, the electrophoretic particle dispersion of the present invention is obtained by dispersing electrophoretic particles mainly composed of an alkylene bismelamine derivative represented by the general formula (I) in a nonpolar solvent. is there.

(In the formula, R represents a hydrogen atom, a lower alkyl group having 1 to 4 carbon atoms or an alicyclic group, and R ₁ , R ₂ , R ₃ and R ₄ are the same or different, and each represents a hydrogen atom or 1 carbon atom. Represents a lower alkyl group of ˜4, and R ₁ and R ₂ or R ₃ and R ₄ may form a heterocyclic group together with a nitrogen atom, and X represents a lower alkylene group of 2 to 3 carbon atoms. )

  The electrophoretic particle dispersion of the present invention may further contain a basic polymer dispersant or may further contain a nonionic surfactant.

  The image display medium of the present invention is obtained by sealing the electrophoretic particle dispersion liquid between two conductor layers.

  The image display device of the present invention has the image display medium as a component.

  In the electrophoretic particle dispersion of the present invention, an electrophoretic particle having an alkylene bismelamine derivative represented by the general formula (I) as a main component is used, so that the white reflectance is high and an inorganic white pigment is used. Compared to sedimentation in a dispersion medium. Therefore, in an image display medium using the electrophoretic particle dispersion and an image display apparatus having the image display medium, visibility can be improved and excellent display memory performance can be obtained.

It is sectional drawing of the image display medium which shows one embodiment of this invention. It is sectional drawing of the image display medium which shows other one Embodiment of this invention. It is a schematic diagram of an image display device showing an embodiment of the present invention.

  The electrophoretic particle dispersion of the present invention is obtained by dispersing electrophoretic particles mainly composed of an alkylene bismelamine derivative represented by the above general formula (I) in a nonpolar solvent.

[Alkylene bismelamine derivatives]
In the alkylene bismelamine derivative represented by the general formula (I), examples of the group R include a hydrogen atom, a lower alkyl group having 1 to 4 carbon atoms (for example, a methyl group, an ethyl group, a propyl group, or a butyl group), an aliphatic group. Examples thereof include a cyclic group (for example, a cyclohexyl group). In addition, the groups R ₁ , R ₂ , R ₃ and R ₄ in the formula (I) are the same or different and are each a hydrogen atom, a lower alkyl group having 1 to 4 carbon atoms (for example, a methyl group, an ethyl group, a propyl group). Or a butyl group). Further, the groups R ₁ and R ₂ , or R ₃ and R ₄ may form a heterocyclic group together with the nitrogen atom. Examples of such a heterocyclic group include a piperidyl group and a morpholino group. be able to. Further, X in the formula (I) is a lower alkylene group having 2 to 3 carbon atoms, for example _-CH 2 CH ₂ - or _-CH 2 _CH 2 CH ₂ - and the like.

  The alkylene bismelamine derivative represented by the general formula (I) is a white crystal and generally has a high melting point (300 ° C. or higher) and is excellent in heat resistance. In addition, the alkylene bismelamine derivative has high whiteness, good concealment, and is an organic compound, and thus has a low specific gravity. Furthermore, the alkylene bismelamine derivative has excellent characteristics as an electrophoretic particle used in an electrophoretic particle dispersion liquid, such as being hardly soluble in various solvents and thus having good solvent resistance.

  The alkylene bismelamine derivative represented by the general formula (I) can be produced, for example, by the following method. First, 1 equivalent of cyanuric halide is dispersed in ice water together with a small amount of a surfactant. Specific examples of the cyanuric halide include cyanuric chloride. Next, an aqueous solution containing 4 equivalents of ammonia (or lower mono- or dialkylamine) is dropped into the dispersion while stirring at a temperature of 0 to 5 ° C. After completion of the dropwise addition, the mixture is heated to a temperature of 40 to 45 ° C. and reacted for about 3 hours. Here, examples of amines to be reacted with cyanuric halide include ammonia, mono- (or di-) methylamine, mono- (or di-) ethylamine, dipropylamine, dibutylamine, morpholine, piperidine and the like. it can. Next, the precipitated white crystals are filtered. The 2,4-diamino (or di-lower mono- or dialkylamino) -6-halogeno-1,3,5-triazine filter cake thus obtained was dispersed in an appropriate amount of water, 1/2 equivalent of alkylene diamine (or substituted alkylene diamine) is added. Examples of the alkylene diamine include ethylene diamine, N, N′-dimethylethylene diamine, N, N′-dicyclohexyl ethylene diamine, and propylene diamine. Next, when the reaction is carried out with stirring at a temperature of 95 to 100 ° C., the alkali gradually disappears, so an aqueous solution containing 2 equivalents of caustic soda is dropped over about 2 hours while maintaining the same temperature. The pH of the reaction mixture becomes about 8, and the content once becomes a transparent solution, but white crystals are soon deposited. Furthermore, after maintaining the reaction at 95-100 ° C. for about 3 hours, the reaction is allowed to cool, and when the temperature reaches about 50 ° C., the pH of the reaction mixture is adjusted to a weak alkalinity of about 10, and the precipitated crystals are filtered. Then, after sufficiently washing with water and drying, an alkylene bismelamine derivative can be obtained. In addition, about the alkylene bismelamine derivative shown by general formula (I), the content of an indication of patent document 12 can be referred, for example.

  The alkylene bismelamine derivative particles represented by the general formula (I) as the electrophoretic particles preferably have a particle size of, for example, 100 nm or more and 1 μm or less. When the particle diameter exceeds 1 μm, the dispersion stability in the nonpolar solvent is lowered and the liquid crystal tends to settle, which may adversely affect the display memory property of the electrophoretic display medium. Further, when the particle size is 100 nm or less, Mie scattering of white particles cannot be expected, and the white particles hardly function as light scattering particles. Moreover, as an alkylene bismelamine derivative shown by general formula (I), it is also possible to use a commercial item, for example, ShigenoxOWP (brand name, the product made by Hakkor Chemical Co., Ltd.), Opt beads (brand name, Nissan). Chemical Industry Co., Ltd.) can be preferably used.

[Electrophoretic particles]
The electrophoretic particles only need to contain the alkylene bismelamine derivative of the above general formula (I) as a main component. The electrophoretic particles can contain other components such as a surfactant and a dispersant as long as the effects of the present invention are not impaired.

[Nonpolar solvent]
The nonpolar organic solvent used in the electrophoretic particle dispersion of the present invention functions as a dispersion medium, for example, paraffinic hydrocarbons such as pentane, hexane, heptane, octane, nonane, decane, dodecane, isohexane, Isoparaffin hydrocarbons such as isooctane and isododecane, alkyl naphthenic hydrocarbons such as liquid paraffin, aromatic hydrocarbons such as benzene, toluene, xylene, alkylbenzene, and solvent naphtha, dimethyl silicone oil, phenyl methyl silicone oil, dialkyl silicone oil, Examples thereof include silicone oils such as alkylphenyl silicone oil, cyclic polydialkylsiloxane, and cyclic polyalkylphenylsiloxane.

  In addition to the above essential components, the electrophoretic particle dispersion of the present invention includes, for example, basic polymer dispersants, nonionic surfactants, dye resins, charge control agents, additives, alcohols and other solvents. An arbitrary component such as can be blended. Moreover, electrophoretic particles (for example, a well-known pigment etc.) other than the electrophoretic particles containing the alkylene bismelamine derivative of general formula (I) can be contained.

[Basic polymer dispersant]
A basic polymer dispersant is a compound that is soluble in a solvent in a particle dispersion and has an adsorptive property to the particles when the particles are present. Has the effect of preventing aggregation. By blending a basic polymer dispersant, the electrophoretic particles are stably dispersed in the electrophoretic particle dispersion due to the steric effect of the polymer compound, and the dispersibility is improved. In the electrophoretic particle dispersion of the present invention, the merit of blending a “basic” polymer dispersant is as follows. For example, when a pigment such as carbon black is used in the electrophoretic particle dispersion, the basic polymer dispersant is adsorbed on the surface of the pigment and acts as a positive charge control agent, thereby positively charging the pigment surface. It is thought that there is. In this case, the particles of the alkylene bismelamine derivative behave as negatively charged particles. This is because the behavior of the particles is determined by the relative strength of the charge of the particles, and even when the two particles have the same charge, one behaves as a positively charged particle and the other as a negatively charged particle. Therefore, by blending the basic polymer dispersant together with the pigment, an effect of facilitating the behavior of the alkylene bismelamine derivative as the negatively charged particle while making the pigment behave as the positively charged particle can be obtained.
In addition, when a dye is used in the electrophoretic particle dispersion, a basic polymer dispersant may not be blended, but by blending, a basic polymer is added to the dye aggregate existing in a micelle state. It is thought that a dispersing agent acts and can promote the stabilization. As a result, similar to the above, an effect of facilitating the behavior of the alkylene bismelamine derivative as electrophoretic particles whose surface is negatively charged can be obtained.

  Examples of the basic polymer dispersant that can be blended in the electrophoretic particle dispersion of the present invention include those that are soluble in a nonpolar solvent. Examples of such basic polymer dispersants include N-methylaminoethyl (meth) acrylate, N-ethylaminoethyl (meth) acrylate, N, N-dimethylaminoethyl (meth) acrylate, and N, N. -Diethylaminoethyl (meth) acrylate, N, N-dibutylaminoethyl acrylate, N, N-di-tert-butylaminoethyl acrylate, N-phenylaminoethyl methacrylate, N, N-diphenylaminoethyl methacrylate, aminostyrene, dimethyl Aminostyrene, N-methylaminoethylstyrene, dimethylaminoethoxystyrene, diphenylaminoethylstyrene, N-phenylaminoethylstyrene, 2-N-piperidylethyl (meth) acrylate, 2-vinylpyridine, 4-vinylpyridine Examples include polymers obtained from at least one monomer having a basic group such as 2-vinyl-6-methylpyridine and at least one alkyl ester or aryl ester of (meth) acrylic acid described later. it can. In addition, these can synthesize | combine resin soluble in a nonpolar organic solvent by adjusting suitably the kind of monomer to combine, and the compounding ratio at the time of superposition | polymerization.

  As the basic polymer dispersant, commercially available products can be used. For example, Solspers17000 (single polyester anchor portion: base), Solspers16000 (single polyester anchor portion: base), Solspers41000 manufactured by Nippon Lubrizol Co., Ltd. (Single polyester anchor part: acid), Solspers 3000 (single polyester anchor part: acid) and the like are preferable. Further, as another example of a commercially available basic polymer dispersant, Disperbyk-2050, 2150, 160, 161, 162, 163, 164, 166, 167, 182 (manufactured by Big Chemie Japan) and the like can be preferably used. .

[Nonionic surfactant]
Nonionic surfactants that can be blended in the electrophoretic particle dispersion of the present invention include, for example, sorbitan trioleate, sorbitan laurate, sorbitan palmitate, sorbitan stearate, sorbitan tristearate, sorbitan trioleate, sorbitan tribehe Nate, sorbitan caprylate and the like. Furthermore, as a normal nonionic surfactant, polyoxyethylene alkyl ether, polyoxyethylene alkyl allyl ether, polyoxyethylene alkyl phenyl ether, polyoxyethylene glycol ester, polyoxyethylene fatty acid amide, polyoxyethylene fatty acid ester, polyoxyethylene alkyl ether Oxyethylene polyoxypropylene glycol, glycerin ester, sorbitan ester, sucrose ester, glycerin ester polyoxyethylene ether, sorbitan ester polyoxyethylene ether, sorbitol ester polyoxyethylene ether, fatty acid alkanolamide, amine oxide, polyoxy Ethylene alkylamine, glycerin fatty acid ester, sorbitan fatty acid ester, polyoxyethylene Tail fatty acid esters, polyoxyethylene sorbitol fatty acid esters and alkyl (poly) Gurikokishido like. The nonionic surfactant is added for the purpose of improving the dispersion stability of the electrophoretic particles and obtaining a sufficient migration speed and memory property. If an ionic surfactant or amphoteric surfactant other than nonionic surfactants is used, the ionic active agent may be adsorbed on the surface of the electrophoretic particles and may adversely affect the behavior of the electrophoretic particles. Since the nonionic surfactant does not have such a concern, it can be preferably used in the electrophoretic particle dispersion of the present invention.

[Electrophoretic particle dispersion]
In the electrophoretic particle dispersion of the present invention, the alkylene bismelamine derivative particles of the formula (I) may be mixed with the nonpolar organic solvent, and an optional component may be added and mixed and dispersed as necessary. The dispersing means in this case is not particularly limited, and known dispersing means such as a homogenizer, a ball mill, a sand mill, and an attritor can be used. The weight ratio of the solid content in the electrophoretic particle dispersion of the present invention is appropriately set so as to obtain a desired concentration of color, and for example, about 0.1 to 25% by weight is appropriate.

[Action]
The electrophoretic particle dispersion using the alkylene bismelamine derivative of the general formula (I) is excellent when used in an image display device because the electrophoretic particles are organic polymer, so that the particles do not settle in the dispersion. Display memory performance can be imparted. For example, the specific gravity of ethylenebismelamine in which R, R ₁ , R ₂ , R ₃ and R ₄ in general formula (I) are all hydrogen atoms and X is a —CH ₂ CH ₂ — group, Table 1 shows the specific gravity of the inorganic pigment component. The specific gravity of ethylene bismelamine shown in Table 1 was measured by a measurement method using a specific gravity bottle among the solid specific gravity measurement methods in JIS Z8807.

  The alkylene bismelamine derivative of the formula (I) is excellent in terms of whiteness and hiding properties, and can impart excellent visibility and discrimination when used in an image display element. For example, as in Table 1, with respect to an aqueous dispersion composition in which ethylene bismelamine is dispersed (pigment component content = 40 wt%, particle size of 5 μm or less), the same concentration and composition of calcium carbonate and clay ( Table 2 shows the results of comparing the whiteness of the aqueous dispersion compositions in which HG-90) or fired clay was dispersed. In this test, the wire rod: No. 14. Coating temperature: room temperature, drying conditions: The whiteness of blackboard paper and gold sand paper obtained by coating and drying at 120 ° C. for 1 minute was compared. In Table 2, it means that whiteness is excellent, so that a numerical value is large.

W (Lab) in Table 2 is Hunter whiteness according to the L, a, b method, and WB means whiteness obtained from the reflectance of the optical fiber from the sample. W (Lab) and WB can be calculated based on the following formulas (1) and (2), respectively. In addition, the numerical value of Table 2 is an average value of the value obtained by measuring arbitrary five places of each coated paper using “Colorimetry System Σ90” manufactured by Nippon Denshoku Industries Co., Ltd.
W (Lab) = 100 − [(100−L) ² + a ² + b ² ] ^1/2 (1)
WB = Z × 0.847 (2)

  In formula (1), L, a, and b are scales for expressing the color (whiteness) on the solid coordinates, and are numerical values measured by a color difference meter. When the intersection of the vertical axis and the horizontal axis intersecting at right angles on the same plane is 0, and the axis perpendicular to the plane is taken from the intersection 0, the height from the plane is represented by L. This L means lightness (brightness). “a” and “b” represent hues, and “a” has a higher degree of redness in the right direction from the vertical axis, that is, on the (+) side, and a greater degree of redness in the left direction, that is, on the (−) side. Is shown. On the other hand, b shows the degree of yellowishness on the (+) side from the horizontal axis and the degree of blueness on the (−) side. When comparing the whiteness of two samples, the difference in distance from the reference point on the solid coordinates is the “color difference” between the samples. A larger value of L, a greater on the (+) side, and b greater on the (−) side means higher whiteness.

  Moreover, Z in Formula (2) represents the reflectance of the optical fiber from a sample.

  As apparent from Table 2 above, the whiteness of the blackboard paper and gold sand paper coated with the dispersion containing the alkylene bismelamine derivative of the formula (I) is inorganic regardless of W (Lab) or WB. It is understood that it is superior to the other three white pigments and also has good hiding properties.

[Image display medium]
The image display medium of the present invention is obtained by encapsulating an electrophoretic particle dispersion containing an alkylene bismelamine derivative of the formula (I) between two conductor layers. An embodiment of the image display medium of the present invention will be described with reference to FIG. In FIG. 1, reference numerals 1 and 2 denote conductive layers, at least one of which is light transmissive. As the conductive layers 1 and 2, for example, a metal such as Al, Ag, Ni, or Cu or a transparent conductor such as ITO, SnO ₂ , or ZnO: Al is formed into a thin film by sputtering, vacuum deposition, CVD, coating, or the like. Or formed by mixing a conductive agent with a solvent or a synthetic resin binder. Examples of the conductive agent include cationic polymer electrolytes such as polymethylbenzyltrimethyl chloride and polyallylpolymethylammonium chloride, anionic polymer electrolytes such as polystyrene sulfonate and polyacrylate, and electron conductive zinc oxide. Tin oxide, indium oxide fine powder, or the like is used. The conductive layers 1 and 2 may be thick enough to have a self-holding function, or the conductive layers 1 and 2 may be provided on a substrate having a self-holding function (not shown). Can also be suitably used. In addition, the conductive layers 1 and 2 may be layers showing anisotropic conductivity, or may be layers having pattern-like or multidot-like segments with conductive portions penetrating in the thickness direction. In either case, if a power supply electrode is connected to a part of the conductive layers 1 and 2, an electric field can be generated between the conductive layers 1 and 2, so that white or colored particles can be moved.

  In FIG. 1, reference numeral 3 denotes a microcapsule. However, the microcapsule 3 is not essential in the present invention, and a particle dispersion described later may be enclosed in a cell provided with fine partition walls by, for example, photolithography. As described above, it is preferable to divide the two electrodes by a large number of fine cells because it can prevent the deviation of particles due to gravity and the aggregation of particles. Examples of the method for producing the microcapsule 3 include known methods such as a coacervation method and a phase separation method, but are not particularly limited. In FIG. 1, reference numeral 4 denotes white particles. As the white particles, particles containing an alkylene bismelamine derivative represented by the above formula (I) can be used.

  In FIG. 1, the code | symbol 5 is a coloring dispersion medium, and the nonpolar organic solvent is colored in the color different from the color of a white particle. In order to control the dispersibility of the dispersed particles, a dispersing agent or the like can be added to the colored dispersion medium as necessary. Examples of the dye used for coloring the nonpolar organic solvent include oil-soluble dyes soluble in the nonpolar solvent. For example, dyes classified as Solvent dye in Color Index are preferably used. These dyes include azo dyes, anthraquinone dyes, phthalocyanine dyes, and triallylmethane dyes. These oil-based dyes include, for example, Spirit Black (SB, SSBB, AB), Nigrosine Base (SA, SAP, SAPL, EE, EEL, EX, EXBP, EB), Oil Yellow (105, 107, 129, 3G, GGS) , Oil orange (201, PS, PR), Fast orange, Oil red (5B, RR, OG), Oil scarlet, Oil pink 312, Oil violet # 730, Macrolex blue RR, Sumiplast green G, Oil brown (GR 416), Sudan Black X60, Oil Green (502, BG), Oil Blue (613, 2N, BOS), Oil Black (HBB, 860, BS), Bali First Yellow (1101, 1105, 3108, 4120), Bali First ole Di (3209, 3210), Bali First Red (1306, 1355, 2303, 3304, 3306, 3320), Bali First Pink 2310N, Bali First Brown (2402, 3405), Bali First Blue (3405, 1501, 1603, 1605, 1607, 2606, 2610), Bali First Violet (1701, 1702), Vari First Black (1802, 1807, 3804, 3810, 3820, 3830) are typical examples, as long as they are not contrary to the object of the present invention. Oil-based dyes or oil-soluble dyes other than the dyes described herein may be used.

  In FIG. 1, reference numeral 6 denotes an adhesive support layer that holds the microcapsule 3 between the conductive layers 1 and 2. Although any known material that adheres to the conductive layers 1 and 2 can be used for the adhesive support layer 6, it is preferably transparent and excellent in electrical insulation. A solvent-free curable material is particularly preferable. Examples of such a material include a photo-curable epoxy resin, a urethane resin, and an acrylic resin.

  Another embodiment of the image display medium of the present invention will be described with reference to FIG. In FIG. 2, reference numerals 1 and 2 are conductive layers, and at least one of them is light transmissive. As the conductive layers 1 and 2, the same material as described in FIG. 1 can be used. In FIG. 2, reference numerals 4A and 4B are white or colored particles, and the colors and charging polarities of the reference numerals 4A and 4B are different from each other. In FIG. 2, reference numeral 7 denotes a dispersion medium, and it is preferable that the transparent medium is colorless and transparent because it does not adversely affect the contrast of the image based on the color difference between the white or colored particles 4A and 4B. In order to control the dispersibility of the dispersed particles, a dispersant or the like may be added to the dispersion medium 7 as necessary. As an example of the white particles constituting the particle dispersion, electrophoretic particles containing an alkylene bismelamine derivative represented by the above formula (I) can be used. Examples of the colored particles include known electrophoretic particles other than white. If a power supply electrode is connected to a part of the conductive layers 1 and 2, an electric field can be generated between the conductive layers 1 and 2, and the two kinds of particles 4A and 4B can be moved in opposite directions.

  In order to manufacture the image display medium in the present embodiment, a mixture obtained by mixing the particle dispersion-containing microcapsules obtained above and an adhesive serving as an adhesive support layer is applied to an electrode substrate, and the counter electrode substrate is bonded to the electrode substrate. . As a coating method, for example, a known coating film forming method such as blade, wire bar, dipping or spin coating can be used, and it is not particularly limited. An image display medium can be easily manufactured by these steps.

[Image display device]
An embodiment of the image display device of the present invention will be described with reference to FIG. As shown in FIG. 3, the image display device 10 of the present invention includes an image display medium 11, and includes a drive circuit, an arithmetic circuit, an internal memory, a power supply, and the like (not shown). The electrodes in the display medium form a dot matrix and display an image as a whole by displaying ON a specified dot. In FIG. 3, reference numeral 12 denotes a casing, and reference numeral 13 denotes information input means. As the image display medium 11 in the image display device 10, the one shown in FIG. 1 or 2 can be applied.

  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. In addition, all the expressions of “parts” used in the following examples are “parts by weight”.

<White organic pigment fine particles>
Shigenox OWP (trade name, average particle size 0.66 μm, manufactured by Hackol Chemical Co., Ltd.) was used. The white organic pigment fine particles correspond to a compound having the following structure in the general formula (I).
—N (R ₁ ) (R ₂ ): —NH ₂
—N (R ₃ ) (R ₄ ): —NH ₂
-R: -H
_{-X -: - CH 2 CH 2} -

<Synthesis of graft carbon black>
1. Carbon black surface treatment Into a reaction vessel made of 4 L glass, 3.0 L of deionized water was added and stirred at 250 rpm. Next, 115 g of carbon black (Printex A (trade name), manufactured by Degussa) was added. Subsequently, 3.0 mL of 37% hydrochloric acid was added. Next, 2.5 g of 4-vinylaniline was added and stirred at 65 ° C. for 30 minutes or more. 1.43 g of sodium nitrite and 10 mL of deionized water were dissolved in advance and added dropwise in about 1 hour, and then stirred at 65 ° C. for 3 hours. This was returned to room temperature and stirred overnight. The resulting black dispersion was centrifuged at 30000 rpm / 20 minutes and decanted. To the black powder obtained by such an operation, 500 mL of deionized water was added, stirred and redispersed. The black dispersion was centrifuged at 30000 rpm / 20 minutes and decanted. The black powder was left to dry overnight and then vacuum dried at 40 ° C. for 4 hours. As a result, surface-treated carbon black (VAnCB) could be synthesized.

2. Synthesis of Graft Carbon Black 50 g of surface-treated carbon black (VAnCB) synthesized as described above was charged into a 1 L glass reaction vessel, 100 mL of toluene was added, and 100 mL of 2-ethylhexyl methacrylate was further added. 0.65 g of azobisisobutyronitrile (AIBN) was added, stirred at 250 rpm, purged with N ₂ for 20 minutes, heated to 70 ° C. in about one hour, stirred for 7 hours, and cooled to room temperature. 500 mL of THF was added and stirred, re-precipitated in 3 L methanol, and suction filtered.

  Subsequently, 1.5 L of THF was added to the obtained black polymer, stirred, redispersed, and cooled to 10 ° C. The black dispersion was centrifuged at 30,000 rpm / 20 minutes and decanted. This operation was repeated three times. The black powder thus obtained was vacuum dried at 70 ° C. for 4 hours. The graft carbon blacks of Examples and Comparative Examples were synthesized by the operation described above. In addition, the measurement by TG / DTA was performed using the differential thermothermal weight simultaneous measurement apparatus, and the weight reduction measurement of the graft polymer was performed. When the weight ratio of the graft polymer was calculated, the graft amount was 8.8%.

<Synthesis of grafted titanium oxide>
3. Surface treatment of titanium oxide 930.7 g of ethanol was charged into a 4 L glass reaction vessel. 69.3 g of deionized water was added and stirred at 150 rpm. Glacial acetic acid was added dropwise to adjust the pH to 4.5. After adding 160 g of 3- (trimethoxysilyl) propyl methacrylate and stirring at 150 rpm for 5 minutes, the speed was adjusted to 250 rpm. Thereafter, 1000 g of titanium oxide (R-960, manufactured by Dupont) was added, and the mixture was stirred at 250 rpm for 10 minutes and then set to 200 rpm. Thereafter, 1826.6 g of methanol was added and stirred at 200 rpm for 1 minute. The white dispersion was centrifuged at 3000 rpm / 20 minutes and decanted. The white powder was left to dry overnight and then vacuum dried at 70 ° C. for 4 hours. Surface-treated titanium oxide (Silanized Titania) was synthesized by the above-described operation.

4). Synthesis of Grafted Titanium Oxide Fine Particles 960 g of lauryl methacrylate was charged into a 4 L glass reaction vessel, 1386 g of toluene was charged, stirred at 200 rpm, brought to 50 ° C., and then 300 rpm. 3. above. The surface-treated titanium oxide synthesized in (1) was finely crushed, 750 g was added and stirred, and N ₂ purge was performed for 20 minutes. AIBN 5.64 g and toluene 500 g were dissolved in advance, dropped in about 1 hour, heated to 70 ° C. in about 1 hour, and continuously stirred at 70 ° C. overnight. The white dispersion (thick liquid) obtained by the above operation was centrifuged at 10000 rpm / 30 minutes and decanted.

Subsequently, 1000 g of toluene was added to the white powder and stirred and redispersed. The white dispersion was centrifuged at 3000 rpm / 30 minutes and decanted. This operation was repeated twice. The white powder obtained by the above operation was left to dry overnight and then subjected to a vacuum drying treatment at 70 ° C. for 4 hours. Thereby, grafted titanium oxide (LMATiO ₂ ) was synthesized. Similarly, the graft amount was measured and found to be 9.7%.

Dispersions mixed with the following composition were dispersed for 1 hour with ultrasonic waves to obtain sample dispersions for each of the examples and comparative examples.
<Dispersion composition>
(1) White fine particles:
Organic white fine particles (Examples 1 and 2) 20 parts Grafted titanium oxide (Comparative Examples 1 and 2) 20 parts (2) Black particles:
In the case of dyes, those dissolved to a saturated concentration (Example 1 and Comparative Example 1)
Graft carbon black (Example 2 and Comparative Example 2) 1 part (3) Basic polymer dispersant:
Solsperse 17000 (trade name, manufactured by Nippon Lubrizol Co., Ltd.) 0.5 parts (4) Nonionic surfactant:
Sorbitan triolate (manufactured by Wako Pure Chemical Industries, Ltd.) 0.5 parts (5) Nonpolar solvent:
Isopar G (manufactured by ExxonMobil Corporation) Remaining amount The total of the above (1) to (5) was taken as 100 parts.

Example 1
(Production and operation of image display medium)
A solution prepared by dissolving 10 parts of urea, 1 part of resorcinol and 10 parts of ethylene-maleic anhydride copolymer in 290 parts of water was adjusted to pH 3.5 with an aqueous sodium hydroxide solution. Separately, 79 parts of a saturated solution of an isoparaffin-based hydrocarbon solvent, Isopar G (trade name, manufactured by ExxonMobil), a saturated solution of Macrolex Blue RR (trade name, manufactured by Bayer), organic white pigment Shigenox OWP (trade name, Happa) 20 parts of Cole Chemical Co., Ltd. and 0.50 parts of dispersant Solsperse 17000 (trade name, manufactured by Nippon Lubrizol Co., Ltd.) and 0.50 parts of nonionic surfactant / sorbitan triolate (manufactured by Wako Pure Chemical Industries, Ltd.) In addition, an ultrasonic dispersion was prepared as a particle dispersion. This dispersion was added to the aqueous solution, and 25 parts of a formaldehyde solution was further added, followed by heating and stirring at 50 ° C. for 3 hours.

  After completion of the reaction, the microcapsules were collected by suction filtration, washing with water and drying. The microcapsules obtained above were dispersed in an ultraviolet curable epoxy resin ThreeBond 3121 (trade name, manufactured by ThreeBond Co., Ltd.) and coated on a glass substrate with an ITO electrode with a wire bar. Next, the coating film was sandwiched with another ITO electrode so that the distance between the electrodes was 100 μm, and then cured by irradiation with ultraviolet rays. When a voltage of +15 V was applied to the upper ITO electrode, the white fine particles were quickly electrodeposited on the upper electrode side and looked white when viewed from the upper substrate surface. Next, when a voltage of −15 V was applied to the upper electrode, the white fine particles moved to the lower electrode side, and when viewed from the upper substrate side, the coloring state due to the color of the dye was clearly seen. The white reflectance during white display (ratio of the amount of reflected light with respect to the amount of white incident light) was 45%. When this white state was left unattended for 1 day, there was almost no change in the white reflectance.

Comparative Example 1
(Production and operation of image display medium)
An image display medium was prepared in the same manner as in Example 1 except that grafted titanium oxide (shown in the above dispersion composition) was used as the white migrating particles, and the display was switched by applying a voltage. The reflectivity was 48% at first, but decreased to 20% when left for one day.

Example 2
(Production and operation of image display medium)
Except for preparing a dispersion of particles (shown in the above-mentioned dispersion blend composition) prepared by changing the dye, Macrolex Blue RR (trade name, manufactured by Bayer) into graft carbon black, as a particle dispersion. An image display medium was produced in the same manner as in Example 1. When a voltage of +15 V was applied to the upper ITO electrode of this image display medium, the white fine particles were quickly electrodeposited on the upper electrode side, while the black particles moved to the lower electrode side and looked white when viewed from the upper substrate surface. . Next, when a voltage of −15 V was applied to the upper electrode, the white fine particles moved to the lower electrode side, while the black particles moved to the upper electrode side, and looked black when viewed from the upper substrate side. Further, the white reflectance at the time of white display was 40%, and when this white state was left for one day without applying voltage, the white reflectance was hardly changed.

Comparative Example 2
(Production and operation of image display medium)
An image display medium was prepared in the same manner as in Example 2 except that titanium oxide (shown in the dispersion composition) was used as the white migrating particles, and the display was switched by applying a voltage. The reflectivity was 42% at first, but decreased to 25% when left for one day.

DESCRIPTION OF SYMBOLS 1 Conductive layer 2 Conductive layer 3 Microcapsule 4, 4A, 4B White thru | or colored particle 5 Colored dispersion medium 6 Adhesive support layer 7 Dispersion medium 10 Image display apparatus 11 Image display medium 12 Housing 13 Information input means

JP-A-5-173194 Japanese Patent No. 2612472 Japanese Patent Publication No.51-46396 JP 2001-98206 A JP-A-3-258866 JP-A-5-173193 Special table 2004-526210 gazette JP 2005-265938 A JP 2006-96985 A JP 2007-231208 A JP 2008-122468 A Japanese Patent Laid-Open No. 6-122684

9th International Display Workshop (IDW'02) Proceedings p. 1361 (2002) 2005 The 54th Annual Meeting of the Polymer Society, Japan

Claims (5)

An electrophoretic particle dispersion obtained by dispersing electrophoretic particles mainly composed of an alkylene bismelamine derivative represented by the general formula (I) in a nonpolar solvent.
(In the formula, R represents a hydrogen atom, a lower alkyl group having 1 to 4 carbon atoms or an alicyclic group, and R ₁ , R ₂ , R ₃ and R ₄ are the same or different, and each represents a hydrogen atom or 1 carbon atom. Represents a lower alkyl group of ˜4, and R ₁ and R ₂ or R ₃ and R ₄ may form a heterocyclic group together with a nitrogen atom, and X represents a lower alkylene group of 2 to 3 carbon atoms. ) The electrophoretic particle dispersion according to claim 1, further comprising a basic polymer dispersant. The electrophoretic particle dispersion liquid according to claim 1, further comprising a nonionic surfactant. The image display medium formed by enclosing the electrophoretic particle dispersion liquid according to any one of claims 1 to 3 between two conductor layers. An image display device having the image display medium according to claim 4 as a component.