JP2006195378A - Charged migration particle, dispersion liquid for electrophoresis display and electrophoresis display - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide charged migration particles which do not generate a phenomenon that particles adhere to a wall in a fine container and are not peeled even if voltage is applied to the particles or do not generate mutual flocculation of the particles, and also to provide a dispersion liquid for electrophoresis display, and an electrophoresis display. <P>SOLUTION: The charged migration particles 14 used for the electrophoresis display has two regions A and B consisting of two polymers A and B having grafted chains different from each other on the surfaces of the charged migration particles. The dispersion liquid for electrophoresis display contains the charged migration particles and a dispersion medium dispersing the charged migration particles. The electrophoresis display has a pair of substrates, at least one electrode formed on at least one of the substrates and the dispersion liquid interposed between the substrates and containing the charged migration particles and the dispersion medium dispersing the charged migration particles. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a charged electrophoretic particle, an electrophoretic display device in which display is performed as the charged electrophoretic particle moves between electrodes, and a dispersion for electrophoretic display used in the display device.

  In recent years, with the development of information equipment, the need for low power consumption and thin display devices is increasing, and research and development of display devices that meet these needs are being actively conducted. In particular, liquid crystal display devices are capable of electrically controlling the arrangement of liquid crystal molecules to change the optical characteristics of the liquid crystal, and are actively developed and commercialized as display devices that can meet the above needs.

  Reflective display devices are expected from the viewpoints of low power consumption and reduced burden on the eyes. As one of them, an electrophoretic display device is known in which display is performed when charged electrophoretic particles dispersed in an insulating solvent move between electrodes. For example, Patent Literature 1 and Patent Literature 2 propose an electrophoretic display device.

  The basic structure of the electrophoretic display device is shown in FIGS. 1 and 2 in which the charged electrophoretic particles move horizontally, in FIG. 3 in which the charged electrophoretic particles move in the vertical direction, and in FIG. 4 with the charged electrophoretic particles and the dispersion medium. An example using microcapsules encapsulating a dispersion for electrophoretic display is shown. In FIGS. 1 to 3, the charged electrophoretic particles are encapsulated in a micro container divided by upper and lower substrates and a partition wall. In either case, the charged electrophoretic particles are electrophoresed according to the polarity of the charged electrophoretic particles and the polarity of the voltage applied to both electrodes. As a result, these electrophoretic display devices can realize a high contrast display with a reflection type and a viewing angle.

  In the electrophoretic display device, controlling the electrophoresis of the charged electrophoretic particles brings about high-contrast display performance and display stability. There are Patent Documents 3 to 5 as proposals of the charged electrophoretic particles used in these electrophoretic display devices.

In addition, the charged electrophoretic particles used in the electrophoretic display device are fixed to the wall (including an insulating layer formed on the electrode or a wall other than the insulating layer) inside the micro container when no voltage is applied. In the state where the image is continuously held and a voltage is applied, a characteristic (hereinafter referred to as “memory property”) that promptly peels off the wall and stably migrates is required. As a proposal regarding the memory property of the charged electrophoretic particles in such an electrophoretic display device, there is, for example, Patent Document 6.
JP-A-9-185087 (page 2) Japanese Patent No. 2551783 (first page) JP-A-4-166918 (first page) JP-A-5-173193 (2nd page) JP 2002-287178 A (second page) JP 2002-62545 A (first page)

  The present invention has been made in view of such problems of the prior art, and the particles adhere to the walls in the micro container and do not peel off even when a voltage is applied. Provided are electrophoretic particles that do not cause aggregation, an electrophoretic display device having stable display quality and memory properties, and a dispersion liquid for electrophoretic display used therein, as a result of imparting stable memory properties to the charged electrophoretic particles. To do.

  That is, the first invention of the present invention is a charged electrophoretic particle used in an electrophoretic display device, and has two or more types of regions composed of two or more types of polymer having different graft chains on the surface of the charged electrophoretic particle. This is a charged electrophoretic particle.

  The polymer having different graft chains is a polymer having a repeating structural unit represented by the following general formula (1) and / or a repeating structural unit represented by the following general formula (2). It is selected from high molecular polymers having

(In the formula, R ₁ is a hydrogen atom or a methyl group, R ₂ is —C _p H _{2p + 1} or —C _q H _2q N (C _r H _{2r + 1} ) ₂ (p is an integer of 0 to 30, q is An integer of 1 to 30, r is an integer of 0 to 30, and p, q and r are independent variables.), R ₃ is a hydrogen atom or a methyl group, R ₄ is a hydrogen atom or —C _s H _{2s + 1} (s is an integer of 1 to 30)
The charged electrophoretic particles are a plurality of pigment particles or / and composite particles made of a dye and a polymer.

According to a second aspect of the present invention, there is provided a dispersion for electrophoretic display, comprising the above-described charged electrophoretic particles and a dispersion medium for dispersing the charged electrophoretic particles.
The dispersion medium contains a rosin ester and a rosin ester derivative.

The dispersion medium contains a styrene butadiene copolymer.
According to a third aspect of the present invention, there is provided a pair of substrates, at least one electrode formed on at least one of the substrates, the charged electrophoretic particles sandwiched between the substrates, and a dispersion for dispersing the charged electrophoretic particles. An electrophoretic display device comprising a dispersion containing a medium.

  According to the present invention, since there are two or more types of regions composed of two or more types of high molecular polymers having different graft chains on the surface of the charged electrophoretic particles, in a state where no voltage is applied, the minute container of each pixel The image can be retained on the inner wall, and the image can be held, and when a voltage is applied, the image can be quickly peeled off from the wall and stably migrated. As a result, it is possible to provide an electrophoretic display device having stable display quality and memory properties and an electrophoretic display dispersion used therefor.

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. 1 to 4 are schematic views showing an example of the configuration of an electrophoretic display device according to the present invention.

  The present invention can be applied to an electrophoretic display device (see FIG. 1) in which the charged electrophoretic particles 1 move horizontally, and also to an electrophoretic display device (see FIG. 3) in which the charged electrophoretic particles 1 move vertically. Here, in the horizontal movement type, as shown in FIG. 1, both the first electrode 4a and the second electrode 4b are arranged along one of the substrates 3a or 3b, and the charged electrophoretic particles 1 are disposed on the substrate 3a. , Or that configured to move along 3b. On the other hand, in the vertical movement type, as shown in FIG. 3, the first electrode 4a and the second electrode 4b are arranged on separate substrates so as to sandwich the dispersion medium 2, and the charged electrophoretic particles 1 are disposed on the substrate 3a. , 3b, it is configured to move in the vertical direction (normal direction). It is assumed that the charged electrophoretic particles illustrated in FIGS. 1 and 3 are positively charged.

  On the other hand, the electrophoretic display device of FIG. 2 has a configuration in which the first electrode 4 a is disposed inside the partition wall 5. By using the first electrode 4a as a common electrode and applying a voltage to the second electrode 4b corresponding to each pixel (for example, the pixel 8 and the pixel 9), the charged electrophoretic particles are collected on the side surface of the partition wall 5 (see FIG. )), Or arranged on the second electrode (FIG. 2B) for display. Hereinafter, the electrophoretic display device of FIG. 3 will be described as an example.

  In the electrophoretic display device according to the present invention, as shown in FIGS. 1 to 3, a plurality of charged electrophoretic particles 1 and a dispersion medium 2 in which these charged electrophoretic particles 1 are dispersed include upper and lower substrates (3a, 3b). 1 and 2 are contained in a plurality of minute containers (FIGS. 1 to 3 show one or two minute containers for convenience), and the charged electrophoretic particles 1 are moved by applying a voltage. Is configured to display an image.

The electrophoretic display device of the present invention has charged electrophoretic particles 1 in which two or more types of regions composed of two or more types of polymer having different graft chains are mixed on the surface.
In the charged electrophoretic particle 1 according to the present invention, two or more types of regions composed of two or more types of polymer having different graft chains are mixed on the surface. For example, the surface of the charged electrophoretic particle 14 in FIG. 5 includes a region A formed from the polymer A having a graft chain and a polymer B having a graft chain, which is different from the polymer. The formed region B is mixed. Each of the regions A and B where the polymer polymer graft chains are formed has such an area that the same polymer polymer graft chains are formed and the migration characteristics of the polymer are expressed. ing. As described above, in the present invention, two or more types of regions in which two or more types of polymer polymers having different graft chains are formed are mixed on the surface of the charged electrophoretic particles, so that 2 More than one type of electrophoretic properties can be imparted.

  In the present invention, a region formed from a polymer having the same graft chain can be confirmed by a known method such as surface viscoelasticity measurement using an atomic force microscope or TOF-SIMS method. Here, the same high molecular polymer means that the repeating structural units (monomer units) are the same, and even if the molecular weights of the high molecular polymers are different, they are the same if the repeating structural units are the same. Is a high molecular weight polymer.

The weight average molecular weight of the polymer having a graft chain in the present invention is preferably from 1,000 to 500,000, particularly preferably from 1,000 to 200,000.
In the present invention, the electrophoretic particles are
(A) the force of charged electrophoretic particles adhering to the wall in the micro container when no voltage is applied;
And
(B) The force by which charged electrophoretic particles adhering to the wall are electrophoresed and peeled off the wall in the micro container when a voltage is applied,
By providing both, the memory property of the charged electrophoretic particles can be controlled.

  That is, on the surface of the charged electrophoretic particle of the present invention, the region is high in the region where the polymer polymer graft chain having the characteristic that the particle adheres to the wall of the micro container (the force (a)) is formed, and the particle is high Two or more types of regions in which a polymer polymer graft chain having a charge amount and / or a property of being well dispersed in the dispersion medium (the force (b) is formed) are mixed (FIG. 5). 12, 13). As a result, when the voltage is not applied by the region having the force (a) on the particle surface, the particle does not move by adhering to the wall of the micro container, and when the voltage is applied, the region having the force (b). By this, the particles adhering to the wall can migrate quickly and stably.

  As described above, the charged electrophoretic particles of the present invention continue to be fixed on the wall in the micro container and retain the image in a state where no voltage is applied, and quickly peel off from the wall and stably migrate in a state where the voltage is applied. It can have memory characteristics.

In addition to the control of memory properties, the graft chains of these high molecular polymers
1) The effect of reducing defects (for example, change over time in driving, etc.) that the main component material constituting the particles existing on the particle surface, or the pigment or / and dye as the colorant has on driving the particles,
2) The effect of stabilizing charging,
May be granted.

  The polymer having a graft chain formed on the surface of the charged electrophoretic particle of the present invention is not particularly limited as long as the memory property can be controlled, but is preferably represented by the following general formula (1). Selected from polymer having a repeating structural unit and / or polymer having a repeating structural unit represented by the following general formula (2).

R ₁ represents a hydrogen atom or a methyl group.
R ₂ is —C _p H _{2p + 1} or —C _q H _2q N (C _r H _{2r + 1} ) ₂ (p is an integer of 0-30, q is an integer of 1-30, r is an integer of 0-30. And p, q, and r are independent variables.

R ₃ represents a hydrogen atom or a methyl group.
R ₄ represents a hydrogen atom or —C _s H _{2s + 1} (s is an integer of 1 to 30). ).
The polymer selected from the general formulas (1) and (2) of the present invention may be a single polymer or two or more types of polymer copolymers.

Among the polymer polymers selected from the general formulas (1) and (2) of the present invention, in the general formula (1), (R ₁ , R ₂ ) = (CH ₃ , n—C ₄ H ₉ ), A polymer represented by a repeating structural unit of (CH ₃ , t-C ₄ H ₉ ), (CH ₃ , C ₂₂ H ₄₅ ) or (CH ₃ , C ₂ H ₅ N (CH ₃ ) ₂ ), When the polymer represented by the repeating structural unit of the general formula (2) is used, the charged electrophoretic particles tend to adhere to the wall of the micro container (the force (a) is expressed). .

On the other hand, in the general formula (1), (R ₁ , R ₂ ) = (CH ₃ , CH ₃ ), (CH ₃ , C ₈ H ₁₇ ), (CH ₃ , C ₁₀ H ₂₁ ), (CH ₃ , C ₁₂ When a polymer having a repeating structure of H ₂₅ ) or (CH ₃ , C ₁₈ H ₃₇ ) is used, the charged electrophoretic particles have a high charge amount and / or are well dispersed in the dispersion medium. (The force of (b) is developed).

  Therefore, in the present invention, a combination of these high molecular polymers is preferable. As described above, in the present invention, the memory property and other electrophoretic characteristics can be adjusted by selecting and combining the structure of the polymer.

  The charged electrophoretic particles of the present invention are inorganic pigment organic particles, organic pigment particles, or a plurality of pigment particles or / and composite particles composed of a dye and a high molecular weight polymer. It has a configuration in which two or more types of regions in which a molecular polymer graft chain is formed are mixed.

  First, as particles constituting the electrophoretic particles 1 of the present invention, particles made of an inorganic pigment can be used. Specifically, lead white, zinc white, lithopone, titanium dioxide, zinc sulfide, antimony oxide, calcium carbonate, kaolin, mica, barium sulfate, gloss white, alumina white, talc, silica, calcium silicate, cadmium yellow, cadmium Lipoton yellow, yellow iron oxide, titanium yellow, titanium barium yellow, cadmium orange, cadmium lipotone orange, molybdate orange, bengara, red lead, silver vermilion, cadmium red, cadmium lipoton red, amber, brown iron oxide, zinc iron Chrome brown, chrome green, chromium oxide, viridian, cobalt green, cobalt chrome green, titanium cobalt green, bitumen, cobalt blue, ultramarine, cerulean blue, cobalt aluminum chrome blue, cobalt silver Oret, Mineral Violet, Carbon Black, Iron Black, Manganese Ferrite Black, Cobalt Ferrite Black, Copper Chromium Black, Copper Chromium Manganese Black, Black Low Titanium Oxide, Titanium Black, Aluminum Powder, Copper Powder, Lead Powder, Suzu Powder, Zinc Powder etc. are mentioned. These inorganic pigment particles can be used alone or in combination of two or more as required.

  Moreover, the particle | grains which comprise an organic pigment can also be used as a particle | grains which comprise the electrophoretic particle 1 of this invention. Specifically, fast yellow, disazo yellow, condensed azo yellow, anthrapyrimidine yellow, isoindoline yellow, copper azomethine yellow, quinophthaloin yellow, benzimidazolone yellow, nickel dioxime yellow, monoazo yellow lake, dinitroaniline orange, Pyrazolone orange, perinone orange, naphthol red, toluidine red, permanent carmine, brilliant fast scarlet, pyrazolone red, rhodamine 6G lake, permanent red, resol red, bon lake red, lake red, brilliant carmine, Bordeaux 10B, naphthol red, quinacridone Magenta, condensed azo red, naphthol carmine, perylene scar red, condensed azo scar red, Nido imidazolone carmine, anthraquinonyl red, perylene red, perylene maroon, quinacridone maroon, quinacridone scarred, quinacridone red, diketopyrrolopyrrole red, benzimidazolone brown, phthalocyanine green, Victoria blue lake, phthalocyanine blue, fast sky blue , Alkali blue toner, indanthrone blue, rhodamine B lake, methyl violet lake, dioxazine violet, naphthol violet and the like. If necessary, these organic pigment particles can be used alone or in combination of two or more.

The aforementioned inorganic pigment and organic pigment can be formed into particles by a known method such as pulverization and granulation.
Further, as the particles, a plurality of pigment particles or / and composite particles composed of a dye and a polymer can be used. The polymer used in the composite particles is not particularly limited as long as it is insoluble in the dispersion medium, but polyester, polymethacrylate, polyacrylate, polymethyl methacrylate, polymethyl acrylate, polyethyl methacrylate, polyethyl acrylate , Polyacrylonitrile, polystyrene, divinylbenzene resin, polyurea, nylon, urethane resin, melamine resin, tetrafluoroethylene resin, phenol resin, phenol novolac epoxy resin, cresol novolac epoxy resin, cycloaliphatic epoxy resin, glycidyl ester High molecular polymers such as epoxy resins and polymethacrylic acid esters are exemplified.

  Examples of the pigment particles used for the composite particles include the above-described inorganic pigment particles and organic pigment particles. If necessary, these pigment particles can be used alone or in combination of two or more. In order to adjust the coloring degree of the composite particles, the composite particles may contain a plurality of pigment particles. The size of the pigment particles used for the composite particles is preferably 0.005 μm or more and 1 μm or less in consideration of the average particle diameter of the charged electrophoretic particles.

  The dye used for the composite particles is not particularly limited as long as it can dye a polymer and does not elute in the dispersion medium. For example, azo dyes, anthraquinone dyes, azine dyes are used. Examples include dyes, phthalocyanine dyes, and triphenylmethane dyes. Specifically, Variast Red, Variast Yellow, Oplas Red, Oil Scarlet, Variast Black 3810, Orient Oil Black (manufactured by Orient Chemical Industry Co., Ltd.), Oil Blue V, Oil Green, Bright, Green, Sudan IV, Sudan III (manufactured by Daiwa Chemical Industry Co., Ltd.), Sumiplast Blue, Sumiplast Red HFG, Sumiplast Red F4G, Sumiplast Yellow, Whitefloor B, Sumikaron Brilliant Blue, Sumikaron Violet (manufactured by Sumitomo Chemical Co., Ltd.), Macrolex Red GS (manufactured by Bayer Japan Co., Ltd.), Microris Blue, Giri Japan And Blue, Kayalon Polyster Red [manufactured by Nippon Kayaku Co., Ltd.].

  As a method for preparing a plurality of pigment particles or / and composite particles composed of a dye and a polymer, emulsion polymerization is performed by adding pigment particles and dyes in the polymerization process of the polymer (including when the monomer is charged). A method of performing dispersion polymerization, suspension polymerization, or seed polymerization, a method of dyeing polymer particles themselves with a dye, a method of melt-kneading and pulverizing pigment particles with a polymer, and using a polymer as a solvent Add pigment particles or dye to the dissolved solution, and then remove the solvent, lower the temperature of the solution, or perform reprecipitation using a poor solvent to precipitate and granulate the composite particles. It can be carried out. Further, the polymer or dye constituting the composite particle can be used after being subjected to a crosslinking treatment or an immobilization treatment for the purpose of insolubilization with respect to the dispersion medium. Furthermore, pigment particles and dyes can be mixed and used according to the coloring degree of the composite particles.

  Commercially available particles can be used as the particles of the present invention. For example, Micropearl (manufactured by Sekisui Chemical Co., Ltd.), Natoko Spacer Particles (manufactured by Natco Co., Ltd.), Epocolor Particles (manufactured by Nippon Shokubai Chemical Industry Co., Ltd.), Chemisnow (manufactured by Soken Chemical Co., Ltd.), Tospearl ( GE Toshiba Silicone Co., Ltd.), techpolymer (Sekisui Chemicals Co., Ltd.) and the like are mentioned, but not particularly limited.

  Furthermore, the average particle diameter of the electrophoretic particles 1 of the present invention can be in the range of 0.1 μm to 7 μm, and preferably in the range of 0.1 μm to 3 μm. When it is less than 0.1 μm, handling is reduced, and when it exceeds 7 μm, the display resolution is reduced. In the electrophoretic particles 1 of the present invention, the average particle diameter can be controlled within the range of the present invention by a known method such as dry classification or wet classification, if necessary.

  In the present invention, as a method of forming a polymer having a graft chain on the surface of the charged electrophoretic particle, a method of introducing a functional group to the surface of the particle and selectively grafting different polymer polymers, After the first polymer is grafted using the silane coupling agent, the second polymer different from the first is grafted again using the silane coupling agent, and the third and subsequent high polymers are then grafted. Different from the first method in which the molecular polymer is grafted by the same method, the first polymer is grafted on the particle surface, and the particle surface is irradiated with UV to introduce a functional group. A method of grafting the second polymer, a method of grafting with two or more monomers having a phase separation structure, a method of mixing two or more incompatible monomers and performing a graft reaction, etc. And the like.

  In the present invention, the thickness of the polymer having a graft chain formed on the surface of the charged electrophoretic particles is preferably 1 nm to 200 nm, more preferably 3 nm to 100 nm. When the thickness to cover is less than 1 nm, the influence of the particle | grain surface which is a foundation | substrate may come out. When the coating thickness exceeds 200 nm, the polarity of the charged electrophoretic particles increases and aggregates in the dispersion medium depending on the structure of the selected polymer, or the color of the charged electrophoretic particles themselves is decreased. Absent.

  As the dispersion medium 2 for dispersing the charged electrophoretic particles 1 of the present invention, a highly insulating organic solvent having low 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 2 of the present invention may contain a rosin ester or a rosin derivative in order to stabilize the charging of the charged electrophoretic particles 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) can be mentioned. 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.

  Further, the dispersion medium 2 of the present invention may contain a charge control agent in order to impart charge to the charged electrophoretic particles 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 2 of the present invention may contain a polymer resin that is soluble in the dispersion medium as a dispersion stabilizer for charged electrophoretic particles 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, and for example, commercially available materials include E-SBR, S-SBR (manufactured by JSR Corporation), NIPOL 1502, NIPOL 1712, NIPOL NS112, NIPOL NS116, NIPOL 1006, 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 2 can be used alone 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 dispersion medium 2 used in the present invention can be colored in a different color from the particles in accordance with the display method of the electrophoretic display device used. The colorant is not particularly limited as long as it is an oil-soluble dye that can be dissolved in a dispersion medium.

Further, in the present invention, two or more types of charged electrophoretic particles 1 having different particle diameters, particle components, coloring, etc. may be used in accordance with the display method of the electrophoretic display device.
As described above, the dispersion liquid for electrophoretic display of the present invention contains the charged electrophoretic particles of the present invention and the dispersion medium for dispersing the charged electrophoretic particles, and contains various additives as necessary. Consists of.

  Moreover, the dispersion liquid for electrophoretic display of the present invention can be used by being included in a microcapsule 10 as shown in FIG. Examples of the microcapsule encapsulation method include ordinary methods such as an in-situ method, an interfacial polymerization method, and a coacervation method.

  Microcapsule wall materials include polyurethane, polyurea, polyurea-polyurethane, urea-formaldehyde resin, melamine-formaldehyde resin, polyamide, polyester, polysulfonamide, polycarbonate, polysulfinate, epoxy, polyacrylate, polymethacrylic acid Examples include esters, polyvinyl acetate, polyvinyl alcohol, and gelatin.

The diameter of the microcapsule used in the electrophoretic display device of the present invention is about 1 to 500 μm, preferably about 20 to 100 μm.
The charged electrophoretic particles 1 of the present invention can be used in an arbitrary weight ratio with respect to the dispersion medium 2, but preferably in the range of 0.1 to 20 parts by weight with respect to 100 parts by weight of the dispersion medium. It is.

Next, an electrophoretic display device will be described.
For substrates 3a and 3b, polymer films such as polyethylene terephthalate (PET), polyethersulfone (PES), polyimide (PI), polyethylene naphthalate (PEN), polycarbonate (PC), etc., inorganic materials such as glass and quartz A stainless steel substrate having an insulating layer on the material or 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 3a 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 3a in contact with the dispersion.

The electrodes 4a and 4b are not particularly limited as long as they are conductive materials that can be patterned, and examples thereof include indium tin oxide (ITO), aluminum, titanium, and copper.
Furthermore, an insulating layer 6 may be formed on the surfaces of the electrodes 4a and 4b. When the insulating layer is formed, charge injection from the electrodes 4a and 4b to the charged electrophoretic particles 1 can be prevented. The material used for the insulating layer 6 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.

  Further, a polymer resin may be used for the partition wall 5, and in the case of the electrophoretic display device of FIG. 2, the partition wall is formed on the electrode 4a. Examples of the material to be used include polyimide resin, polyester resin, polyacrylate resin, polymethacrylate resin, polycarbonate resin, polyarylate resin, novolac resin, and epoxy resin.

  As a method of forming the partition wall 5, 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 the substrate after forming the partition wall, a light-transmitting substrate surface The method of forming by a mold can be mentioned. Specific examples of the material include a photosensitive epoxy resin (SU8 Nippon Magder Mid Co., Ltd.).

  Further, the region where either one of the first electrode 4a and the second electrode 4b is arranged has the same color as the charged electrophoretic particle 1, and the region where the other electrode is arranged has a different color. Can be colored. In the case of the apparatus of FIGS. 1 and 2, the first electrode 4a itself may be colored black, or a colored insulating layer may be arranged so as to overlap the electrode.

  In the case of the vertical movement type in FIG. 3, the dispersion medium 2 for dispersing the charged electrophoretic particles can be colored in a color different from that of the particles 1. These enable two-color display. However, the display device as a whole can perform color display by displaying different colors with a plurality of adjacent pixels.

  Hereinafter, the electrophoretic display device shown in FIG. 2 will be described. In addition, the average particle diameter of the particles of the present invention and the formation thickness of the polymer having a graft chain are determined from the average of 20 samples using a transmission electron microscope.

The following two types are used as uncoated particles in the present invention.
(1) Particle A:
Polymerized particles composed of 85 parts by weight of polymethyl methacrylate (PMMA) and 15 parts by weight of carbon black (CB, average particle size 0.02 μm), and the average particle size is 1.5 μm.
(2) Particle B:
Polymerized particles made of polystyrene (PS) are particles dyed black with the dye Varifast Black 3810, Orient Oil Black [manufactured by Orient Chemical Industry Co., Ltd.], and the average particle size is 1.5 μm.

Example 1
The size of one pixel is 100 μm × 100 μm, and the number of pixels is 200 × 200. In FIG. 2, two pixels (pixels 8 and 9) are shown for convenience. The substrate 3b is made of non-alkali glass having a thickness of 1.1 mm, and aluminum is deposited on the surface thereof with a thickness of 100 nm to dispose the second electrode 4b. A polyurethane resin layer whitened by mixing fine titanium oxide particles is disposed as the white scattering layer 7 on the second electrode 4b. A partition wall 5 having a width of 5 μm and a height of 18 μm is disposed at the boundary of the pixel, and a first electrode 4a having a width of 5 μm and a height of 5 μm is disposed below the partition wall 5 as shown in FIG. Then, an insulating transparent resin layer 6 made of polyacrylate resin (manufactured by Optomer SS6699 JSR) is formed on the partition wall 5 including the first electrode 4a and the second electrode. Thereafter, a heat-fusible adhesive layer is formed on the upper surface of the partition wall 5 (bonding surface with the substrate 3a).

Next, on the surface of the particle A, first, polystearyl methacrylate (the (R ₁ , R ₂ ) of the polymer represented by the general formula (1) of the present invention is (− CH ₃ , —C ₁₈ H ₃₇ )) is formed by graft polymerization. Thereafter, the particles are irradiated with UV to make the surface of the non-grafted particles hydrophilic, and then polydimethylaminoethyl as a second polymer is used on the hydrophilic surface using a silane coupling agent. Graft polymerization of methacrylate (when (R ₁ , R ₂ ) of the polymer represented by the general formula (1) is (—CH ₃ , —C ₂ H ₅ N (CH ₃ ) ₂ )) The charged electrophoretic particles of the invention are obtained. The formation thickness of the polymer having a graft chain was 50 nm. The surface composition of the particles was measured by TOF-SIMS, and the weight ratio of polystearyl methacrylate to polydimethylaminoethyl methacrylate was 85:15. Moreover, it is confirmed by the analysis of TOF-SIMS that polystearyl methacrylate partially coats the particle surface and that the remaining uncoated particle surface is coated with polydimethylaminoethyl methacrylate.

  Next, 100 parts by weight of Isopar H (exxon), which is an aliphatic hydrocarbon solvent, is used as a dispersion medium, 2.5 parts by weight of neotol 125H (manufactured by Harima Chemical Co., Ltd.) is used as a rosin ester, and asaprene 1205 is used as a styrene-butadiene copolymer. By mixing 0.8 parts by weight (manufactured by Asahi Kasei Co., Ltd.) for 24 hours with mixing and stirring, and then 3 parts by weight of the above-mentioned charged electrophoretic particles in the liquid filtered under pressure using a 0.2 μm PTFE membrane filter. A dispersion for electrophoretic display is prepared.

  The dispersion liquid thus prepared is filled into the partition walls 5, and a polycarbonate film substrate 3a having a thickness of 100 μm is sealed by heat bonding with an adhesive layer on the top of the partition walls, thereby manufacturing the electrophoretic display device of the present invention. .

In the display device thus manufactured, the first electrode 4a is a common electrode of 0V, and the voltage ± 15V is applied to the second electrode 4b by a rectangular wave having a frequency of 0.25 Hz.
The above-mentioned charged electrophoretic particles are positively charged immediately after voltage application and migrate between the electrodes quickly, and a display with a high black-and-white contrast can be confirmed. 2A shows a case where a voltage of +15 V is applied to the second electrode 4b. Since the charged electrophoretic particles gather on the side surface of the partition wall 5, when the pixels 8 and 9 are observed from the substrate 3a side, the scattering layer is observed. 7 is visually recognized and is displayed in white. On the other hand, FIG. 2B shows a case where a voltage of −15 V is applied to the second electrode 4b. Since the charged electrophoretic particles spread on the second electrode 4b, the pixels 8 and 9 are observed from the substrate 3a side. The charged electrophoretic particles are visually recognized and become black.

  Next, in the white display where the charged electrophoretic particles are collected on the side surfaces of the partition walls 5, the holding state of the charged electrophoretic particles collected on the side surfaces of the partition walls 5 hours after the circuit is opened is observed. As a result, even after 8 hours, the charged electrophoretic particles in the pixel are collected and held on the side surface of the partition wall 5. Thereafter, when a voltage is applied under the same conditions as in the initial stage by connecting the circuit, the charged electrophoretic particles are quickly peeled off from the partition walls 5 and moved between the electrodes, and stable black and white display can be performed.

Example 2
On the surface of the particle B, polylauryl methacrylate as the first polymer (the polymer (R ₁ , R _{2 of the} polymer represented by the general formula (1) of the present invention) was prepared in the same manner as in Example 1. ) Is (—CH ₃ , —C ₁₂ H ₂₅ )), poly-t-butyl methacrylate as the second polymer (the polymer (R) represented by the general formula (1)) ₁ , R ₂ ) (when —CH ₃ , —C ₄ H ₉ ) is introduced to the particle surface to obtain the charged electrophoretic particles of the present invention. In addition, the formation thickness of the high molecular polymer which has a graft chain is 50 nm. The surface composition of the particles was measured by TOF-SIMS, and the weight ratio of polylauryl methacrylate to poly-t-butyl methacrylate was 85:15. Moreover, it is confirmed by TOF-SIMS analysis that polylauryl methacrylate partially covers the particle surface, and that the remaining uncoated particle surface is coated with poly-t-butyl methacrylate.

Next, an electrophoretic display dispersion is prepared from the charged electrophoretic particles by the same method as in Example 1, and the electrophoretic display device of the present invention is manufactured by the same method as in Example 1.
When the first electrode 4a is a common electrode of 0V and the voltage ± 15V is applied to the second electrode 4b with a rectangular wave having a frequency of 0.25 Hz to the display device thus manufactured, the charged electrophoretic particles of the present invention are applied with a voltage. Immediately after that, it is charged positively and migrates quickly between the electrodes, and a display with high black and white contrast can be confirmed.

  Next, in the same manner as in Example 1, when white display is performed to collect the charged electrophoretic particles on the side surfaces of the partition walls 5, the charged electrophoretic particles collected on the side surfaces of the partition walls 8 hours after the circuit is opened are retained. Observe the condition. As a result, even after 8 hours, the charged electrophoretic particles in the pixel are collected and held on the side surface of the partition wall 5. Thereafter, when a voltage is applied under the same conditions as in the initial stage by connecting the circuit, the charged electrophoretic particles are quickly peeled off from the partition walls 5 and moved between the electrodes, and stable black and white display can be performed.

Example 3
On the surface of the particle A, polymethyl methacrylate (the polymer (R ₁ , R _{2 of the} polymer represented by the general formula (1) of the present invention) as the first polymer is formed in the same manner as in Example 1. ) Is (—CH ₃ , —CH ₃ )), polydimethylaminoethyl methacrylate (the polymer represented by the general formula (1) (R ₁ , R ₂ ) is (-CH ₃ , —C ₂ H ₅ N (CH ₃ ) ₂ )) is introduced onto the particle surface to obtain the charged electrophoretic particles of the present invention. The formation thickness of the polymer polymer graft chain is 40 nm. The surface composition of the particles was measured by TOF-SIMS, and the weight ratio of polymethyl methacrylate to polydimethylaminoethyl methacrylate was 90:10. Further, it is confirmed by TOF-SIMS analysis that polymethyl methacrylate partially covers the particle surface, and that the remaining uncoated particle surface is coated with polydimethylaminoethyl methacrylate.

Next, an electrophoretic display dispersion is prepared from the charged electrophoretic particles by the same method as in Example 1, and an electrophoretic display device is manufactured by the same method as in Example 1.
When a voltage is applied to the display device thus manufactured under the same conditions as in Example 1, the charged electrophoretic particles are charged to the positive polarity immediately after the voltage is applied, and quickly migrate between the electrodes, and display with high black and white contrast. Can be confirmed.

  Next, as in Example 1, the holding state of the charged electrophoretic particles collected on the side surface of the partition wall 5 after 8 hours has been observed. As a result, even after 8 hours, the charged electrophoretic particles in the pixel are collected and held on the side surface of the partition wall 5. Thereafter, when a voltage is applied under the same conditions as in the initial stage by connecting the circuit, the charged electrophoretic particles are quickly peeled off from the partition walls 5 and moved between the electrodes, and stable black and white display can be performed.

Example 4
Polystearyl methacrylate as the first polymer (the polymer (R ₁ , R ₂ ) of the polymer represented by the general formula (1) of the present invention is applied to the surface of the particle B in the same manner as in the examples. (In the case of —CH ₃ , —C ₁₈ H ₃₇ ), polymethacrylamide (R ₃ , R _{4 of the} polymer represented by the general formula (2)) as the second polymer. ) Is (-CH ₃ , H)) is introduced into the particle surface to obtain the charged electrophoretic particles of the present invention. In addition, the formation thickness of the high molecular polymer which has a graft chain is 30 nm. The surface composition of the particles was measured by TOF-SIMS, and the weight ratio of polystearyl methacrylate to polymethacrylamide was 90:10. Moreover, it is confirmed by the analysis of TOF-SIMS that polystearyl methacrylate partially coats the particle surface and that the remaining uncoated particle surface is coated with polydimethylaminoethyl methacrylate.

Next, an electrophoretic display dispersion is prepared from the charged electrophoretic particles by the same method as in Example 1, and an electrophoretic display device is manufactured by the same method as in Example 1.
When a voltage is applied to the display device thus manufactured under the same conditions as in Example 1, the charged electrophoretic particles are charged to the positive polarity immediately after the voltage is applied, and quickly migrate between the electrodes, and display with high black and white contrast. Can be confirmed.

  Next, as in Example 1, the holding state of the charged electrophoretic particles collected on the side surface of the partition wall 5 after 8 hours has been observed. As a result, even after 8 hours, the charged electrophoretic particles in the pixel are collected and held on the side surface of the partition wall 5. Thereafter, when a voltage is applied under the same conditions as in the initial stage by connecting the circuit, the charged electrophoretic particles are quickly peeled off from the partition walls 5 and moved between the electrodes, and stable black and white display can be performed.

Comparative Example 1
An electrophoretic display dispersion is prepared from the particles A by the same method as in Example 1, and an electrophoretic display device is manufactured by the same method as in Example 1. When a voltage is applied to the manufactured display device under the same conditions as in Example 1, the charged electrophoretic particles have bipolar particles and migrate between the electrodes irregularly. Furthermore, after 3 hours of electrophoresis, it sticks to the electrode and no longer migrates.

Comparative Example 2
On the surface of the particle A, polystearyl methacrylate (when the polymer (R ₁ , R ₂ ) represented by the general formula (1) of the present invention is (—CH ₃ , —C ₁₈ H ₃₇ )) Is introduced by graft polymerization to obtain charged electrophoretic particles. In addition, the formation thickness of the high molecular polymer which has a graft chain is 30 nm.

Next, an electrophoretic display dispersion is prepared from the charged electrophoretic particles by the same method as in Example 1, and an electrophoretic display device is manufactured by the same method as in Example 1.
When a voltage is applied to the display device thus manufactured under the same conditions as in Example 1, the charged electrophoretic particles are charged to the positive polarity immediately after the voltage is applied, and quickly migrate between the electrodes, and display with high black and white contrast. Can be confirmed.

  Next, as in Example 1, the holding state of the charged electrophoretic particles collected on the side surface of the partition wall 5 after 8 hours has been observed. As a result, after 8 hours, the charged electrophoretic particles in the pixel are peeled off from the side surface of the partition wall 5 and are not held at all.

Comparative Example 3
Polymethacrylamide (when the polymer (R ₃ , R ₄ ) represented by the general formula (2) is (—CH ₃ , H)) is introduced into the surface of the particle A by graft polymerization, Obtain charged electrophoretic particles. The formation thickness of the polymer polymer graft chain is 30 nm.

Next, an electrophoretic display dispersion is prepared from the charged electrophoretic particles by the same method as in Example 1, and an electrophoretic display device is manufactured by the same method as in Example 1.
When a voltage is applied to the display device thus manufactured under the same conditions as in Example 1, the charged electrophoretic particles adhere to the wall in the micro container immediately after the voltage application and do not peel off.

  In the present invention, the surface of the charged electrophoretic particle has two or more regions composed of two or more types of polymer having different graft chains. The image can be retained on the wall, and the image can be held quickly, and when the voltage is applied, it can be quickly peeled off from the wall and stably migrated, and the electrophoretic display device has stable display quality and memory property. Can be used.

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 the schematic which shows the other example of the structure of the electrophoretic display apparatus 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 the schematic which shows the electrophoretic particle which concerns on this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Charged electrophoretic particle 2 Dispersion medium 3a, 3b Substrate 4a 1st electrode 4b 2nd electrode 5 Partition 6 Insulating layer 7 White scattering layer 8 Pixel 9 Pixel 10 Microcapsule 12 Area | region A of the high molecular polymer which has a graft chain
13 Region B of a high molecular polymer having a graft chain
14 Electrophoretic particles 15 Dispersion

Claims (7)

  A charged electrophoretic particle, which is a charged electrophoretic particle used in an electrophoretic display device, and has two or more types of regions composed of two or more types of polymer having different graft chains on the surface of the charged electrophoretic particle. The polymer having a different graft chain has a polymer having a repeating structural unit represented by the following general formula (1) and / or a repeating structural unit represented by the following general formula (2). 2. The charged electrophoretic particles according to claim 1, wherein the charged electrophoretic particles are selected from high molecular weight polymers.

(In the formula, R ₁ is a hydrogen atom or a methyl group, R ₂ is —C _p H _{2p + 1} or —C _q H _2q N (C _r H _{2r + 1} ) ₂ (p is an integer of 0 to 30, q is An integer of 1 to 30, r is an integer of 0 to 30, and p, q and r are independent variables.), R ₃ is a hydrogen atom or a methyl group, R ₄ is a hydrogen atom or —C _s H _{2s + 1} (s is an integer of 1 to 30)   3. The charged electrophoretic particle according to claim 1, wherein the charged electrophoretic particle is a composite particle composed of a plurality of pigment particles or / and a dye and a polymer.   A dispersion liquid for electrophoretic display, comprising the charged electrophoretic particles according to claim 1 and a dispersion medium for dispersing the charged electrophoretic particles.   The dispersion liquid for electrophoretic display according to claim 4, wherein the dispersion medium contains a rosin ester and a rosin ester derivative.   The dispersion liquid for electrophoretic display according to claim 4 or 5, wherein the dispersion medium contains a styrene-butadiene copolymer.   A dispersion medium for dispersing the charged electrophoretic particles and the charged electrophoretic particles according to any one of claims 1 to 3, sandwiched between the pair of substrates, at least one electrode formed on at least one of the substrates, and the substrate. An electrophoretic display device comprising a dispersion containing

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