JP2006220969A - Suspension for electrophoresis display and electrophoresis display apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrophoresis display apparatus having electrooptical characteristics of high contrast and display image memory properties after an electric field is applied. <P>SOLUTION: In the electrophoresis display apparatus having a pair of substrates 4a and 4b, at least one electrode 5a and 5b formed on at least one substrate of the substrates and a suspension containing colored charged migration particles 1 absorbing light, transparent particles 2 transmitting light and a dispersion medium 3 dispersing the colored charged migration particles and the transparent particles, the suspension has ≤0.01 Pa s shear viscosity η<SB>0</SB>at ≥10 sec<SP>-1</SP>shear rate at 20°C and the shear viscosity η of the suspension at 20°C satisfies η≥η<SB>0</SB>in at least the range of 1 to 10 sec<SP>-1</SP>shear rate. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a suspension for electrophoretic display and an electrophoretic display device, and more particularly to the use of a suspension and electrophoretic particles used in an electrophoretic display device utilizing a phenomenon in which charged particles in a medium move by application of a voltage. The present invention relates to an electrophoretic display device.

  In recent years, with the development of information equipment, the market demand for low power consumption and thin display devices has increased, and research and development of display devices in response to these market demands have been actively conducted. For example, liquid crystal display devices can change the optical characteristics of liquid crystals by electrically controlling the arrangement of liquid crystal molecules, and are actively developed and commercialized as display devices that meet the above market requirements.

  In addition, a reflective display device is expected from the viewpoint of low power consumption and reduction of the burden on the eyes. As one of them, an electrophoretic display device in which display is performed by moving charged electrophoretic particles dispersed in an insulating solvent between electrodes is known. Electrophoresis exemplified in Patent Document 1 and Patent Document 2 Display devices have been proposed.

  FIG. 4 shows an example of the basic structure of an electrophoretic display device that moves charged electrophoretic particles in the horizontal direction of the display surface. In the electrophoretic display device, the charged electrophoretic particles migrate between the pixel opening portion and the pixel concealing portion according to the charging polarity of the particles and the polarity applied to the electrode of the display device. Since the electrophoretic display device does not use a polarizer known as an optical modulation member such as a liquid crystal display device, the use efficiency of light incident on the display element is high, and the high reflectivity and wide field of view suitable for reflective display A corner and a high-contrast display can be realized.

In addition, a low power consumption reflective display device is required to have long-term storage performance of a written image. As a proposal to realize this performance requirement, a method using electrophoretic particles capable of expressing interatomic attractive force such as close adhesion force, remote hydrogen bond, dipole-dipole interaction, Van der Waals force, etc., for example, patent There is literature 3. The written image after voltage application in the electrophoretic display device can be stored and resisted against environmental disturbances such as micro-Brownian motion of the electrophoretic particles, impact on the display device, and vibration by an exemplary method.
JP-A-11-202804 JP 2001-249366 A JP 2000-259102 A

  In an electrophoretic display device using electrophoretic particles capable of expressing attractive force between particles, represented by Patent Document 3, the performance of storing a display image after voltage application is charged electrophoresis occupying the electrophoretic liquid filling portion in the display device The volume fraction of particles increases and increases.

  However, the volume of electrophoretic particles in the electrophoretic liquid for the purpose of improving the long-term storage performance of the written image in the method represented by Patent Documents 1 and 2, in which the charged electrophoretic particles travel between the opening and the concealing portion in the display surface. When the fraction is increased, there is a problem that the area covered by the charged electrophoretic particles at the time of bright display becomes large, and the effective aperture ratio at the time of bright display is reduced.

  The present invention has been made in view of such problems of the prior art, and an electrophoretic display device that satisfies both high-contrast electro-optical characteristics and display image storage after application of an electric field, and an electric device used therefor A suspension containing electrophoretic display particles and a dispersion medium is provided.

That is, the present invention relates to a suspension used in an electrophoretic display device, wherein the suspension disperses colored charged electrophoretic particles that absorb light, transparent particles that transmit light, and colored charged electrophoretic particles and transparent particles. And the suspension has a shear viscosity η _{0 at a} shear rate of 10 sec ⁻¹ or more at 20 ° C. of 0.01 Pa · s or less, and the suspension has a shear viscosity η at 20 ° C. of at least shear. The suspension for electrophoretic display, wherein η ≧ η ₀ in the range of speed 1 to 10 sec ⁻¹ .

  The present invention also provides a pair of substrates, at least one electrode formed on at least one of the substrates, colored charged electrophoretic particles that absorb light, sandwiched between the substrates, transparent particles that transmit light, and An electrophoretic display device having a suspension containing colored charged electrophoretic particles and a dispersion medium for dispersing transparent particles, wherein the suspension is composed of the above-described electrophoretic display suspension. It is a display device.

  The electrophoretic display device of the present invention includes a pair of substrates, at least one electrode formed on at least one of the substrates, and a coloring colored to absorb light having a desired wavelength sandwiched between the substrates. Electric charge containing charged electrophoretic particles, transparent particles that transmit light of a desired wavelength, a dispersion medium that disperses the charged electrophoretic particles and the transparent particles, and a suspension composed of the charged electrophoretic particles, the transparent particles, and the dispersion medium In the electrophoretic display device, the charged electrophoretic particles and the transparent particles exhibit thixotropy in the suspension.

  “Thixotropic property” used in the description of the present invention indicates “a phenomenon in which the viscosity temporarily decreases when shearing is applied to a certain suspension system, and the viscosity increases again when left standing”. It also includes “isothermal reversible sol-gel transition phenomenon in a certain suspension system”.

The present invention is an electrophoretic display suspension used in the above electrophoretic display device. The suspension containing the electrophoretic display device particles composed of the colored charged electrophoretic particles and the transparent particles has a shear viscosity η _{0 at a} shear rate of 10 sec ⁻¹ or more at 20 ° C. of 0.01 Pa · s (Pa · sec) or less. And, the shear viscosity η at 20 ° C. of the suspension is η ≧ η ₀ , more preferably η ≧ 2 × η ₀ , at least in the range of the shear rate of 1 to 10 sec ⁻¹ .

The volume percentage of the colored charged electrophoretic particles and the transparent particles in the electrophoretic display suspension is preferably 0.1% by volume or more and 20% by volume or less.
Polystyrene, polystyrene sulfonic acid, polyacrylic acid ester, polymethacrylic acid ester, polyfluoroalkyl acrylic acid, polyfluoroalkyl methacrylic acid, polyacrylic acid, polymethacrylic acid, polyacrylonitrile on the surface of the above colored charged electrophoretic particles and transparent particles, It is preferable that at least one component of polymethacrylonitrile, polyacrylamide, polymethacrylamide, polyvinyl esters, polyvinyl ethers, and silanol is modified and exhibits thixotropic properties in the dispersion medium. More preferably, modification of polystyrene, polystyrene sulfonic acid, polyfluoroalkyl acrylic acid, polyfluoroalkyl methacrylic acid, and silanol is effective for the expression of thixotropy.

The charged state of the transparent particles is not particularly limited as long as the electrophoretic properties of the colored charged electrophoretic particles are not hindered.
Colored electrophoretic particles and transparent particles are polystyrene, polystyrene sulfonic acid, polyacrylic acid ester, polymethacrylic acid ester, polyfluoroalkylacrylic acid, polyfluoroalkyl when the particles themselves do not exhibit thixotropic properties in the dispersion medium. Particles containing additives containing at least one of methacrylic acid, polyacrylic acid, polymethacrylic acid, polyacrylonitrile, polymethacrylonitrile, polyacrylamide, polymethacrylamide, polyvinyl esters, polyvinyl ethers and silanols as components It may be adsorbed on the surface to induce thixotropic properties. More preferably, an additive containing at least one component of polystyrene, polystyrene sulfonic acid, polyfluoroalkyl acrylic acid, polyfluoroalkyl methacrylic acid, and silanol is effective for the expression of thixotropy.

Transparent particles, n ₁ the refractive index of the particles, when the refractive index of the dispersion medium and n _2, which satisfies the relationship of _{1.14n 2 ≧ n 1 ≧ 0.86n 2} .

  According to the present invention, by using a suspension composed of a group of colored charged electrophoretic particles having thixotropy and transparent particles, and a dispersion medium, a plane transfer type electric power generation is achieved by increasing the viscosity of the suspension in a low shear region. A high contrast electro-optical characteristic can be realized by reconciling the effect of improving the display memory property of the electrophoretic element and the effect of improving the effective aperture ratio by optimizing the amount of the colored particles filled in the display pixel.

Hereinafter, the present invention will be described in detail.
An embodiment of the present invention will be described with reference to FIGS. Note that these drawings are diagrams showing the configuration of the electrophoretic display device and the configuration of the charged electrophoretic particles according to the present invention, but an example is schematically shown for convenience.

FIG. 1 is a schematic view showing an example of the configuration of an electrophoretic display device according to the present invention.
The present invention is applied to an electrophoretic display device (see FIG. 1) in which colored charged electrophoretic particles 1 move horizontally. Here, in the horizontal movement type, as shown in FIG. 1, both the first electrode 5a and the second electrode 5b are arranged along one of the substrates 4a or 4b, and the colored charged electrophoretic particles 1 are the substrates. It means what is configured to move along 4a and 4b. Note that the colored charged electrophoretic particles exemplified in FIG. 1 are charged positively.

Hereinafter, the electrophoretic display device of FIG. 1 will be described as an example.
As shown in FIG. 1, an electrophoretic display device according to the present invention includes colored charged electrophoretic particles 1 (hereinafter abbreviated as colored particles), transparent particles 2, and dispersion in which these colored particles 1 and transparent particles 2 are dispersed. A suspension containing the medium 3 is provided, and an image is displayed by moving the colored particles 1 by applying a voltage.

  The colored particles 1 in the present invention must be filled with a particle amount capable of concealing the pixel surface when the pixel surface concealment state is selected. The amount of particles is an amount corresponding to at least one layer, more preferably two layers or more, in a close-packed arrangement of colored particles with respect to the pixel surface.

  The colored particles have interparticle attractive forces derived from hydrogen bonds, dipole-dipole interactions, Van der Waals forces and the like in the dispersion medium, and develop thixotropic properties by these interparticle attractive forces. The colored particles are preferably modified with a functional group capable of generating an attractive force between particles on the particle surface by a known technique such as a graft polymerization method or a coupling agent treatment. The functional group chemically modified on the particle surface is preferably one that expresses thixotropy by attractive force between particles. For example, as described in Patent Document 3, polyacrylic acid ester, polymethacrylic acid ester, polyacrylic acid, polyacrylic acid, Electronegative atoms Y such as methacrylic acid, polyacrylonitrile, polymethacrylonitrile, polyacrylamide, polymethacrylamide, polyvinyl esters, polyvinyl ethers, silanol (Si—OH), etc. (eg O, N, F, Cl) ), And a polystyrene or polystyrene sulfone containing a benzene ring structure that causes an overlap of the ring structure by exchange of π electrons, a group of X-H in which hydrogen is covalently bonded to the same atom X (for example, O, N) as above) Acid, especially polyfluoroalkylacrylic acid, polyfluoroalkylmethacrylic acid And the like, preferably includes at least one or more of the foregoing components.

  The viscosity of the colored particles increases with increasing volume fraction in the suspension, and the viscosity of the suspension in the low shear rate region is greater than the viscosity of the suspension in the high shear region. As a result, the display image memory property after the application of an electric field in the electrophoretic display device has the effect of preventing the movement of colored particles due to environmental disturbance as well as the viscosity of the suspension.

  On the other hand, when the volume fraction of the colored particles in the suspension increases, the retreat area of the colored particles on the pixel surface of the display device increases when the bright display state is selected in the electrophoretic display device. Narrow the effective pixel aperture area at the time. This phenomenon results in a decrease in the maximum reflectance during bright display in the electrophoretic display device, and thus a decrease in the contrast of the written image, thereby degrading the image quality of the display device.

  Thus, in the electrophoretic display device, when the thixotropic property is imparted to the colored particles, and the particles are added to the suspension in an amount sufficient to prevent the colored particles from moving due to environmental disturbance after image writing, the display element There was a problem that the reflectance and contrast performance deteriorated during bright display.

  As a means for solving this technical problem, the present invention is characterized by mixing colored particles having thixotropic properties and transparent particles in a suspension. This eliminates the decrease in effective aperture ratio due to the excessive addition of colored particles in the conventional suspension, and maintains the thixotropy of the suspension that can prevent the movement of the colored particles due to environmental disturbance after writing the display image. it can.

  The transparent particles 2 of the present invention are insoluble in the dispersion medium and have thixotropic properties derived from the attractive force between the particles as in the case of the colored particles 1. As a means for imparting thixotropy to transparent particles, a method of chemically modifying the particle surface in the same manner as colored particles can be employed. The functional group to be modified is preferably one that expresses thixotropy, such as polyacrylic acid ester, polymethacrylic acid ester, polyacrylic acid, polymethacrylic acid, polyacrylonitrile, polymethacrylonitrile, polyacrylamide described in Patent Document 3. Hydrogen to an atom X (for example, O, N) similar to an electronegative atom Y (for example, O, N, F, Cl) such as polymethacrylamide, polyvinyl ester, polyvinyl ether, silanol (Si—OH), etc. XH group (hereinafter referred to as hydrogen bond) covalently bonded to polystyrene, polystyrene having a benzene ring structure causing a ring structure to overlap by exchange of π electrons, polystyrene sulfonic acid, and particularly polyfluoroalkylacrylic acid and polyfluoroalkylmethacrylic Examples include acids. At least one of the aforementioned components is contained on the particle surface. Further, two or more sets of transparent particles that are contained on the particle surface with different composition ratios of the aforementioned components may be mixed and used.

Transparent particles 2, the refractive index n ₁ of the transparent particles, the refractive index n ₂ of the dispersion medium, satisfies _{1.14n 2 ≧ n 1 ≧ 0.86n 2} . Furthermore, the absorbance A in the suspension state consisting only of transparent particles and a dispersion medium, from which the colored particles are removed from the suspension for the electrophoretic display element (the thickness of the suspension layer at the time of the absorbance measurement is determined by the electrophoretic display device). A ≦ 0.1505 is suitable for the liquid layer thickness when the suspension is filled. Since the transparent particle size needs not to hinder the pixel surface hiding by the colored particles 1, it is allowed to be less than the average layer thickness when the pixel surface is hidden by the colored particles.

  Specific examples of the transparent particles satisfying these properties include commercially available products such as Chemisnow MS, SS (manufactured by Soken Chemical Co., Ltd.) and Hi-Pureshka (Ube Nitto Kasei Co., Ltd.). The electrophoretic properties of the transparent particles with respect to the applied electric field are not essential, and the charging polarity of the transparent particles is not particularly limited as long as the electrophoretic properties of the colored particles 1 are not hindered.

  In addition, when one or both of the colored particles 1 and the transparent particles 2 do not have thixotropic properties, an additive that induces thixotropic properties is adsorbed on the surface of the non-thixotropic particles, and the thixotropic properties are expressed in the particle-containing dispersion medium. May be.

  Additives adsorbed on either or both of colored particles and transparent particles are polyacrylic acid ester, polymethacrylic acid ester, polyacrylic acid, polymethacrylic acid, polyacrylonitrile, polymethacrylonitrile, polyacrylamide, polymethacrylamide Hydrogen is covalently bonded to atom X (for example, O, N) similar to electronegative atom Y (for example, O, N, F, Cl) such as polyvinyl ester, polyvinyl ether, silanol (Si-OH), etc. Component of polystyrene, polystyrene sulfonic acid, and particularly polyfluoroalkylacrylic acid and polyfluoroalkylmethacrylic acid containing a benzene ring structure that causes an overlap of the ring structure caused by exchange of π electrons. It is preferable to contain at least one kind. Specifically, organic polymer fine particles such as crosslinked polymethyl methacrylate and crosslinked polystyrene, inorganic polymer fine particles such as fine silica, and swellable layered viscosity minerals such as smectite can be used. Examples of commercially available materials include Chemisnow (Soken Chemical Co., Ltd.), AEROSIL (Nihon Aerosil Co., Ltd.), and Lucentite (Coop Chemical Co., Ltd.).

The colored particles 1 that adsorb the additive for inducing thixotropy are insoluble in the dispersion medium, and there are no particular restrictions on the material as long as the electrophoretic property against the external electric field and the light concealing property are maintained even after the additive adsorption. The transparent particles 2 to adsorb additives for inducing thixotropy, insoluble in the dispersion medium, at least 20 ℃, λ = 1.14n ₂ at the refractive index n ₂ of the refractive index n ₁ and a dispersion medium of the transparent particles in 589nm ≧ n ₁ ≧ 0.86n ₂ , and the absorbance A in the suspension state consisting only of transparent particles and a dispersion medium (the thickness of the suspension layer at the time of measuring the absorbance is determined by the electrophoretic display device) The liquid layer thickness in the case of filling is applied) is A ≦ 0.1505, and the material is not particularly limited as long as the migration of the colored particles 1 against the external electric field is not hindered.

  As the dispersion medium 3 for dispersing the colored particles 1 and the transparent particles 2 of the present invention, a highly insulating organic solvent having a low electrical conductivity is used. Specifically, aromatic hydrocarbon solvents such as benzene, ethylbenzene, dodecylbenzene, toluene, xylene, naphthenic hydrocarbons, hexane, cyclohexane, kerosene, paraffinic hydrocarbon solvents and aliphatic hydrocarbons of isoparaffinic hydrocarbon solvents Examples of the solvent include halogenated hydrocarbon solvents such as chloroform, trichloroethylene, tetrachloroethylene, dichloromethane, trichlorotrifluoroethylene, and ethyl bromide, or silicon oil and high-purity petroleum. Among them, aliphatic hydrocarbon solvents are preferably used. Specifically, Isopar G, H, M, L, P, V (all manufactured by Exxon Chemical Co., Ltd.), Shellsol (Showa Shell Japan), IP Solvent 1016, 1620, 2028, 2835 (Idemitsu Petrochemical), Nisseki Eye Tetrazole 200, 300, 400 (all manufactured by Nippon Petrochemicals) and the like. These can be used alone or in admixture of two or more.

  The dispersion medium 3 used in the present invention can be colored in a color different from the particles according to the display method of the electrophoretic display device to be used. The colorant is not particularly limited as long as it is an oil-soluble dye that can be dissolved in a dispersion medium.

  The dispersion medium 3 of the present invention contains a rosin ester or a rosin derivative in order to stabilize the charging of the colored particles 1 of the present invention. The rosin ester or rosin derivative used is not particularly limited as long as it is soluble in the dispersion medium. For example, gum rosin, wood rosin, tall oil rosin, rosin modified maleic acid, rosin modified pentaerythritol, rosin glycerin ester, partially hydrogenated rosin Methyl ester, partially hydrogenated rosin glycerin ester, partially hydrogenated rosin triethylene glycol ester, fully hydrogenated rosin pentaerythritol ester, maleic acid modified rosin ester, fumaric acid modified rosin ester, acrylic acid modified rosin ester, maleic acid modified rosin penta Erythritol ester, fumaric acid modified rosin pentaerythritol ester, acrylic acid modified rosin glycerin ester, maleic acid modified rosin glycerin ester, fumaric acid Sex rosin glycerin esters, acrylic acid-modified rosin glycerin ester. Specifically, for example, neotol (Harima Kasei), pencel, ester gum, superester (all of which are Arakawa Chemical Industries, Ltd.) can be mentioned. When the rosin ester or rosin derivative is not contained in the dispersion medium, the charging of the colored particles 1 may not be stable, and the charging polarity of the particles 1 may be reversed or the particles 1 may not be electrophoresed. The rosin ester or rosin derivative can be contained in the range of 0.01 to 5 parts by weight, preferably 0.05 to 3 parts by weight, with respect to 100 parts by weight of the dispersion medium.

  The dispersion medium 3 of the present invention may contain a charge control agent in order to impart charge to the colored particles 1 or to assist charging. The charge control agent is not particularly limited as long as it is soluble in the dispersion medium, but, for example, naphthenic acid type of cobalt naphthenate, zirconium naphthenate, copper naphthenate, iron naphthenate, lead naphthenate, manganese naphthenate, zinc naphthenate Metal soaps such as metal soaps, cobalt octoate, zirconium octoate, iron octoate, lead octoate, nickel octoate, manganese octoate, zinc octoate octanoate metal soap, stearic acid metal soap, polyaminopolypropyl Well-known things, such as tersuccinimide and a lecithin, are mentioned.

  Furthermore, the dispersion medium 3 of the present invention may contain a polymer resin that is soluble in the dispersion medium as a dispersion stabilizer for the colored particles 1 or an adhesion inhibitor to the wall. Specific examples include polybutadiene, polyisoprene, polyisobutylene, polybutene, styrene butadiene copolymer, styrene isoprene copolymer, styrene maleic anhydride copolymer, norbornene resin, and polyethylene wax. Among them, a styrene butadiene copolymer is preferable. For example, commercially available materials include E-SBR, S-SBR (manufactured by JSR Corporation), NIPOL 1502, NIPOL 1712, NIPOL NS112, NIPOL NS116, NIPOL 1006, and NIPOL 1009 ( Nippon Zeon Co., Ltd.), Tuffden, Tuffprene, Asaprene (Asahi Kasei Co., Ltd.), Sumitomo SBR (Sumitomo Chemical Co., Ltd.) can be used.

  In the present invention, the above components contained in the dispersion medium 3 can be used singly or in combination of two or more. The dispersion medium of the present invention contains an anionic surfactant, a cationic surfactant, an amphoteric surfactant, a nonionic surfactant, and a fluorosurfactant that are soluble in the dispersion medium as necessary. These may be used alone or in combination of two or more.

  The viscosity (thixotropic property) of the suspension composed of the colored particles 1, the transparent particles 2 and the dispersion medium 3 of the present invention is determined by the volume fraction obtained by adding the colored particles 1 and the transparent particles 2 in the suspension. Change. The total volume percentage of particles suitable for the practice of the present invention is in the range of 0.1% to 20% by volume, preferably 4% to 16% by volume.

Further, the viscosity of the suspension containing the colored particles 1 and the transparent particles 2 and the dispersion medium is 0.01 Pa · s or less, more preferably 0,0 at a shear viscosity η ₀ at a shear rate of 10 sec ⁻¹ or more at 20 ° C. In the range of 005 Pa · s or less and the shear viscosity η of the suspension at least in the range from 1 to 10 sec ⁻¹ , η ≧ η ₀ , more preferably η ≧ 2 × η ₀ .

  The substrates 4a and 4b are made of polyethylene terephthalate (PET), polyethersulfone (PES), polyimide (PI), polyethylene naphthalate (PEN), polycarbonate (PC), or other inorganic films such as glass or quartz. Alternatively, a stainless steel substrate having an insulating layer on the surface can be used. Note that a material having a high visible light transmittance, such as a transparent polymer film or glass, may be used for the substrate 4a on the viewer side. Further, a polymer material having a rubber hardness in the range of 10 or more and 90 or less, specifically silicon resin, natural rubber, thermoplastic elastomer resin, or the like may be formed on the surface of the substrate 4a in contact with the dispersion.

  The electrodes 5a and 5b are not particularly limited as long as they are conductive materials that can be patterned, and examples thereof include indium tin oxide (ITO), aluminum, and titanium. In the horizontal movement type electrophoretic display device shown in FIG. 1, one electrode 5b is formed over the entire pixel, and the other electrode 5a is formed at a height different from that of the electrode 5b, Of course, the electrodes 5a and 5b may be formed at the same height. In this case, the electrode 5b cannot be formed on the entire pixel, and the electrode 5a is not limited to this. , 5b do not overlap. Alternatively, the electrode may be divided for each pixel.

  Furthermore, the insulating layer 8 may be formed so as to cover the electrodes 5a, 5b and the like, and when the insulating layer is formed, charge injection from the electrodes 5a, 5b to the colored particles 1 and the transparent particles 2 can be prevented. The material used for the insulating layer 8 is preferably a thin film that is difficult to form pinholes. Specific examples include a highly transparent polyimide resin, polyester resin, polyacrylate resin, polymethacrylate resin, polycarbonate resin, polyarylate resin, novolac resin, and epoxy resin.

  A polymer resin may be used for the partition wall 6. Specific examples include polyimide resins, polyester resins, polyacrylate resins, polymethacrylate resins, polycarbonate resins, polyarylate resins, novolac resins, and epoxy resins.

  As a method of forming the partition wall 6, a method of performing exposure and wet development after applying a photosensitive resin layer, a method of forming by a printing method, a method of bonding to a substrate after forming the partition wall, a light-transmitting substrate surface The method of forming by a mold can be mentioned.

  Of the first electrode 5a and the second electrode 5b described above, the same color as the colored particles 1 is applied to the region where one of the electrodes is disposed, and the region where the other electrode is disposed is colored differently. can do. In this case, the electrode itself may be colored, or a colored layer may be provided separately from the electrode, and the insulating layer may be disposed so as to overlap the electrode, and the insulating layer may be colored.

FIG. 2 is a schematic view showing another example of the configuration of the electrophoretic display device according to the present invention.
FIG. 2 shows a horizontal movement type electrophoretic display element in which a structural barrier is provided in order to give a threshold characteristic to the voltage value at which the migrating particles move.

  Hereinafter, the present invention will be described in more detail with reference to examples and comparative examples of a horizontal movement type electrophoretic display device. The suspension viscosity was evaluated using a rheometer DAR-100 (Reologica).

The following two types are used as particles in the present invention.
Colored particles A1:
Particles obtained by dyeing polymer particles made of polystyrene (PS) in black with the dye Variifast Black 3810, Orient Oil Black [manufactured by Orient Chemical Co., Ltd.], and further coating the surface of the particles with polytrifluoromethyl methacrylate by a graft polymerization method And the average particle size is 2.5 μm. Viscosity at the time of the dispersion C1 the particles were charged 10 wt% of the ^{later, 1.88 × 10 -2 Pa · s} (20 ℃) at a shear rate of 1 sec ^-1, shear rate 10 ³ sec ^{- 1} in 3. 5 × 10 ⁻³ Pa · s (20 ° C.).

Transparent particles B1:
Polymerized particles made of crosslinked polymethylmethacrylate, and the average particle size is 0.1 to 1.5 μm. Viscosity at the time of the dispersion C1 the particles were charged 10 wt% will be described later, at a shear rate of ^{1sec -1 1.83 × 10 -2 Pa ·} s (20 ℃), at a shear rate 10 ³ sec ^-1 3. 1 × 10 ⁻³ Pa · s (20 ° C.).

The refractive index of the transparent particles is 20 ° C., λ = 589 nm, and n _D = 1.49. The refractive index is measured by immersion method measurement.
The present invention uses the following dispersion.

Dispersion C1:
Isopar H (Exxon) 100 parts by mass as an aliphatic hydrocarbon solvent as a dispersion medium, Neotol 125H (Harima Kasei Co., Ltd.) 2.5 parts by mass as a rosin ester, Asaprene 1205 (Asahi Kasei) as a styrene butadiene copolymer (Made by Co., Ltd.) 0.8 parts by mass is mixed and stirred for 1 hour. The refractive index of the dispersion alone is 20 ° C., λ = 589 nm, and n _D = 1.40.

Example 1
FIG. 3 shows a method for manufacturing the electrophoretic display device of this embodiment.
First, the second electrode 5b is formed by depositing aluminum with a thickness of 100 nm on the surface of the polyimide (PI) film of the substrate 4b (see FIG. 3A). A polyimide film having a size of 50 mm × 50 mm and a thickness of 200 μm is used.

Next, a polyurethane resin layer whitened by mixing fine titanium oxide particles is formed on the surface of the second electrode 5 b to form an insulating layer 8.
On the surface of the insulating layer 8, the first electrode 5a is formed in a partial region of one pixel so as to overlap the second electrode 5b as shown in FIG. 3B. Then, the insulating transparent resin layer 10 made of polyacrylate resin (Optomer SS6699, manufactured by JSR Corporation) is formed on the insulating layer 8 so as to cover the first electrode 5a. The first electrode 5a is formed by forming dark black titanium carbide and patterning it in a line shape by photolithography and dry etching. The first electrode 5a has a thickness of 50 nm and a line width of 35 μm.

  A partition wall 6 is formed on the surface of the insulating layer 8 so as to partition the pixels. The partition wall 6 is formed with a height of 30 μm, a width of 12 μm, and an interval of 120 μm by performing steps of application of a photosensitive epoxy resin (SU8, manufactured by Nippon Magdermid Co., Ltd.), exposure, and wet development. Thereafter, a heat-fusible adhesive layer 9 is formed on the upper surface of the partition wall 6 (bonding surface with the substrate 4a).

  Next, 1 part by weight (1.4% by volume) of colored particles A1, 1 part by weight (1.4% by volume) of transparent particles B1, and 103.5 parts by weight of dispersion C1 were mixed and stirred for 1 hour. Prepare a suspension for electrophoretic display.

The shear viscosity η ₀ of the suspension at 20 ° C. and a shear rate of 1 sec ⁻¹ is 6.3 × 10 ⁻³ Pa · s. Moreover, the shear viscosity η at 20 ° C. and 10 ³ sec ⁻¹ of the suspension is 3.18 × 10 ⁻³ Pa · s.

The suspension thus prepared is filled into the partition wall 6 (see FIG. 3C).
Further, after aligning the substrate 4a made of a polycarbonate film having a thickness of 100 μm and the adhesive layer 9 (see FIG. 3D), the substrate 4a is heat-bonded to the partition wall (end support member) 6 to thereby form the present invention. The electrophoretic display device is manufactured (see FIG. 3E). In addition, the upper part of the 1st electrode 5a is visually recognized in black, and the white of the insulating layer 8 is visually recognized in the upper part of the area | region where the 1st electrode 5a is not arrange | positioned.

  After applying and writing a rectangular wave having a voltage of ± 15 V and a frequency of 0.25 Hz to the display device thus manufactured, the applied voltage is attenuated to 0 V over 20 s. Table 1 shows the reflectance of the display element immediately after stopping the voltage application and after 5 minutes.

  In the present invention, the particles in the suspension have thixotropic properties for both the colored particles and the transparent particles, and the migration of the migrating particles after writing due to disturbance such as micro Brownian motion is suppressed. As a result, this example shows a display state with a high black-and-white contrast immediately after the voltage application is stopped, and it can be confirmed that the display state is maintained even 5 minutes after the voltage application is stopped.

Comparative Example 1
In Comparative Example 1, the following colored particles A2 are used.
Colored particles A2:
Polymerized particles made of polystyrene (PS) are dyed black with the dye Variifast Black 3810, Orient Oil Black [manufactured by Orient Chemical Industry Co., Ltd.], and polystearyl methacrylate (PStMA) is grafted onto the particle surface at a thickness of 20 nm. The average particle size is 2.5 μm. Particles 10 mass% to the dispersion C1 (13.8 vol%) viscosity when charged, the shear rate 10 to 10 ³ sec ^{- 1} in ^{3.5 × 10 -3 Pa · s (} 20 ℃), Thixotropic properties are not recognized.

  Following Example 1, an electrophoretic display device was produced under the same conditions except that the colored particles contained in the suspension for electrophoretic display were changed to electrophoretic particles A2 having no thixotropic property. The display element reflectance under the same conditions was measured. The results are shown in Table 2. The negative value of the reflectance in the white display and the condition 5 minutes after stopping the voltage application in the table indicates that the reflectance is lower than the black display in the voltage applied state.

The shear viscosity η ₀ of the suspension at 20 ° C. and a shear rate of 1 sec ⁻¹ is 3.6 × 10 ⁻³ Pa · s. Moreover, the shear viscosity η at 20 ° C. and a shear rate of 10 ³ sec ⁻¹ of the suspension is 3.18 × 10 ⁻³ Pa · s.

  In this example, only transparent particles in the suspension have thixotropic properties, and migration of electrophoretic particles due to disturbance such as micro Brownian motion cannot be sufficiently suppressed. As a result, as compared with the embodiment, the display state after writing rapidly deteriorates with time.

Comparative Example 2
In Comparative Example 2, the following transparent particle B2 is used.
Transparent particle B2:
Polymerized particles made of crosslinked polystyrene, and the particle size is 0.1 to 1.5 μm. Viscosity when 10% by mass (13.8% by volume) of the particles were added to the dispersion C1 was 1.25 × 10 ⁻¹ Pa · s (20 ° C.) at a shear rate of 1 sec ⁻¹ , and 10 ³ sec ^{− 1} is 6.8 × 10 ⁻³ Pa · s (20 ° C.). The refractive index at 20 ° C. and λ = 589 nm is n _D = 1.60 (immersion method measurement).

  Following Example 1, an electrophoretic display device was produced under the same conditions except that the transparent particles contained in the suspension for electrophoretic display were changed to B2, and the reflectance of the display device under the same conditions as in Example 1. Measure. The results are shown in Table 3.

The shear viscosity η ₀ of the suspension at 20 ° C. and a shear rate of 1 sec ⁻¹ is 1.41 × 10 ⁻² Pa · s. Further, the shear viscosity η at 20 ° C. and a shear rate of 10 ³ sec ⁻¹ of the suspension is 3.74 × 10 ⁻³ Pa · s.

From Table 3, the white display reflectance at 5 minutes after stopping the voltage application is higher than that of Comparative Example 1, and the effect that the migrating particles A2 and the transparent particles B2 have thixotropic properties appears.
Table 4 shows the results of comparing the relative reflectances of Example 1 and Comparative Example 2.

(Note) The white reflectance of Comparative Example 2 is 100, and the black reflectance of Comparative Example 2 is 0.
When the relative reflectances of Example 1 and Comparative Example 2 are compared in Table 4, the white display reflectance of Comparative Example 2 remains at more than 50% of the white display reflectance of Example 1. This phenomenon has a large refractive index difference between the transparent particles and the dispersion medium, and the concentration of the transparent particles in the suspension is high, so that part of the light beam incident on the display element is scattered and dissipated in the suspension layer. By doing.

To prevent the incident light dissipation to such display device, the refractive index n ₂ of the refractive index n ₁ and the dispersion medium of the transparent particles is preferably from _{1.14n 2 ≧ n 1 ≧ 0.86n 2} , more Preferably, 1.05n ₂ ≧ n ₁ ≧ 0.95n ₂ is good.

Moreover, A ≦ 0.1505 is suitable for the absorbance A in the suspension state consisting of only transparent particles and a dispersion medium.
Example 2
In Example 2, the colored particles A2 and the following transparent particles B3 are used.

Transparent particle B3:
The surface of polymer particles made of polystyrene (PS) is coated with polystearyl methacrylate (PStMA) with a thickness of 20 nm by a graft polymerization method, and the average particle size is 2.5 μm. The viscosity at the time of charging 10% by mass (13.8% by volume) of the particles into the dispersion C1 is 3.5 × 10 ⁻³ Pa · s (20 ° C.) at a shear rate of 10 to 10 ³ sec ⁻¹ . Thixotropic properties are not recognized.

In Example 2, the preparation of the dispersion for electrophoretic display is changed as follows.
Dispersion C2:
Isopar H (Exxon) 100 parts by mass as an aliphatic hydrocarbon solvent as a dispersion medium, Neotol 125H (Harima Kasei Co., Ltd.) 2.5 parts by mass as a rosin ester, Asaprene 1205 (Asahi Kasei) as a styrene butadiene copolymer Co., Ltd.) 0.8 parts by mass and zirconium octoate (Nikka Octix Zircon, Nippon Chemical Industry Co., Ltd.) 0.25 parts by mass are mixed and stirred for 1 hour to prepare a dispersion. The refractive index of the dispersion medium excluding the colored particles A2 and the transparent particles B3 is 20 ° C., λ = 589 nm, and n _D = 1.41.

  Next, an electrophoretic display suspension is prepared. 1 part by weight (1.4% by volume) of colored particles A2, 0.17 parts by weight (0.3% by volume) of transparent particles B3, 103.55 parts by weight of dispersion C2, and colored particles A2 and transparent particles B3 1 part by mass of Aerosil R972 (manufactured by Nippon Aerosil Co., Ltd.) is added as additive D for imparting thixotropy and stirred for 1 hour.

The shear viscosity η ₀ of the suspension at 20 ° C. and a shear rate of 1 sec ⁻¹ is 1.76 × 10 ⁻² Pa · s. Further, the shear viscosity η at 20 ° C. and a shear rate of 10 ³ sec ⁻¹ of the suspension is 3.65 × 10 ⁻³ Pa · s.

  According to Example 1, an electrophoretic display device is produced under the same conditions except that the electrophoretic dispersion C2 is used, and the reflectance of the display device is measured. The results are shown in Table 5.

  In Example 5, the additive C in the suspension forms an adsorption equilibrium state between the colored particles and the transparent particles and the dispersion medium, and imparts thixotropic properties to the colored particles and the transparent particles in the suspension. The movement of colored particles after writing due to disturbance such as motion is suppressed. As a result, Example 2 shows a display state with a high black-and-white contrast immediately after the voltage application is stopped, and the display state is maintained even 5 minutes after the voltage application is stopped.

  Since the electrophoretic display device of the present invention satisfies both high-contrast electro-optical characteristics and display image storage after application of an electric field, it can be used for display screens of electronic books, electronic maps, portable information terminals, and the like. .

It is the schematic which shows an example of the structure of the electrophoretic display device which concerns on this invention. It is the schematic which shows the other example of the structure of the electrophoretic display apparatus which concerns on this invention. It is process drawing which shows the manufacturing method of the electrophoretic display device which concerns on this invention. It is the schematic which shows the structure of the conventional electrophoretic display apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Colored particle 2 Transparent particle 3 Dispersion medium 4a, 4b Substrate 5a 1st electrode 5b 2nd electrode 5c Control electrode 6 Partition 7 Structure partition 8 Insulating layer 9 Adhesive layer 10 Transparent resin layer

Claims (6)

A suspension used in an electrophoretic display device, the suspension containing colored charged electrophoretic particles that absorb light, transparent particles that transmit light, and a dispersion medium that disperses colored charged electrophoretic particles and transparent particles. And the shear viscosity η ₀ at a shear rate of 10 sec ⁻¹ or more at 20 ° C. of the suspension is 0.01 Pa · s or less, and the shear viscosity η at 20 ° C. of the suspension is at least a shear rate of 1 to 10 sec ^−1. A suspension for electrophoretic display, wherein η ≧ η ₀ in the range up to.   2. The electrophoretic display according to claim 1, wherein the volume percentage of the volume sum of the colored charged electrophoretic particles and the transparent particles contained in the suspension is 0.1% by volume or more and 20% by volume or less. Suspension.   The colored charged electrophoretic particles and the transparent particles have a surface of polystyrene, polystyrene sulfonic acid, polyacrylic acid ester, polymethacrylic acid ester, polyfluoroalkyl acrylic acid, polyfluoroalkyl methacrylic acid, polyacrylic acid, polymethacrylic acid, poly 3. For electrophoretic display according to claim 1 or 2, comprising at least one component selected from acrylonitrile, polymethacrylonitrile, polyacrylamide, polymethacrylamide, polyvinyl esters, polyvinyl ethers, and silanol. Suspension.   At least polystyrene, polystyrene sulfonic acid, polyacrylic acid ester, polymethacrylic acid ester, polyfluoroalkyl acrylic acid, polyfluoroalkyl methacrylic acid, polyacrylic acid, polymethacrylic acid, polyacrylonitrile, polymethacrylonitrile, polyacrylamide, polymethacrylic 4. An additive containing at least one component selected from amides, polyvinyl esters, polyvinyl ethers, and silanols is adsorbed on the surfaces of the colored charged electrophoretic particles and transparent particles. The suspension for electrophoretic display according to any one of the above. _{2. The} suspension for electrophoretic display according to claim 1, wherein the refractive index n ₁ of the transparent particles is 1.14n ₂ ≧ n ₁ ≧ 0.86n ₂ with respect to the refractive index n ₂ of the dispersion. Muddy liquid.   A pair of substrates, at least one electrode formed on at least one of the substrates, colored charged electrophoretic particles that absorb light, transparent particles that transmit light, and colored charged electrophoretic particles and transparent An electrophoretic display device comprising a suspension containing a dispersion medium for dispersing particles, wherein the suspension comprises the suspension for electrophoretic display according to any one of claims 1 to 5. An electrophoretic display device.

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