JP2015191091A - Dispersion, electrophoretic display device and electronic apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a dispersion capable of suppressing the aggregation of charged particles and suppressing deterioration of moving speed, and an electrophoretic display device and electronic apparatus having the dispersion and capable of displaying a high quality image.SOLUTION: A dispersion comprises: electrophoretic particles 31 having color particles 32 and polymer chains 33 modifying the surfaces of the color particles; and a dispersion medium for dispersing the electrophoretic particles. The electrophoretic particles have a plurality of first particles and a plurality of second particles. The first particles have first color particles and are positively charged, and the second particles have second color particles and are negatively charged. A number average molecular weight of the polymer chains is 5000 or more and 100000 or less. The total amount of a number average molecular weight of the polymer chains stuck to the surfaces of the first color particles and a number average molecular weight of the polymer chains stuck to the surfaces of the second color particles is 25000 or more and 200000 or less.

Description

  The present invention relates to a dispersion, an electrophoretic display device, and an electronic apparatus.

  Conventionally, a configuration of an electrophoretic display device in which a dispersion liquid in which a plurality of white particles and a plurality of black particles having different charging characteristics are dispersed is sandwiched between a pair of substrates is known. In such an electrophoretic display device, charged white particles and black particles (charged particles) are moved by an electric field applied between substrates, and a monochrome image is displayed (for example, see Patent Document 1).

JP 2010-210812 A

  By the way, in an electrophoretic display device, it is known that the dispersion state of charged particles contained in a dispersion strongly affects the display quality. This is because if the charged particles are difficult to disperse in the dispersion, the charged particles may unintentionally aggregate and display quality may be deteriorated.

  On the other hand, it is known that the ease of movement of the charged particles strongly affects the display quality. This is because when charged particles are difficult to move, the response speed of display switching is reduced.

  Such quality requirements are not limited to the case where the charged particles are white particles and black particles, and the charged particles may be color particles used in electrophoretic display devices for color display such as red, blue, and green. The same is required.

  Therefore, in electrophoretic display devices, there has been a demand for a dispersion liquid that suppresses aggregation of charged particles and suppresses a decrease in moving speed of charged particles.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a dispersion liquid in which aggregation of charged particles is suppressed and a decrease in moving speed is suppressed. Another object of the present invention is to provide an electrophoretic display device and an electronic apparatus that have such a dispersion and can display a high-quality image.

In order to solve the above-described problem, one embodiment of the present invention provides an electrophoretic particle having color particles, a polymer chain that modifies the surface of the color particle, a dispersion medium that disperses the electrophoretic particles, The electrophoretic particles have a plurality of first particles and a plurality of second particles, and the first particles have first color particles and are positively charged, and the second particles Has a second color particle and is negatively charged, the number average molecular weight of the polymer chain is 5000 or more and 100000 or less, and the polymer chain attached to the surface of the first color particle A dispersion in which the sum of the number average molecular weight and the number average molecular weight of the polymer chain attached to the surface of the second color particle is 25,000 or more and 200,000 or less is provided.
According to this configuration, it is possible to improve the light reflectance during white display by suppressing the aggregation of particles, and it is possible to suppress a decrease in response speed. Therefore, a high-contrast image display is possible, and a dispersion having high display performance can be provided.

In one aspect of the present invention, the polymer chain that modifies the color particles having a relatively small total surface area by comparing the total surface area of the first color particles and the total surface area of the second color particles, Alternatively, the number average molecular weight may be smaller than that of the polymer chain that modifies the color particles having a relatively large total surface area.
According to this configuration, a good response speed can be realized.

In one aspect of the present invention, the polymer chain may be attached in an amount of 3% to 10% with respect to the mass of the color particles.
According to this configuration, aggregation of particles is suppressed, leading to an improvement in white reflectance. Also, a good response speed can be realized.

One embodiment of the present invention provides an electrophoretic display device that includes a pair of substrates and an electrophoretic layer sandwiched between the pair of substrates, and the electrophoretic layer includes the dispersion liquid.
According to this configuration, since the above-described dispersion liquid is included, it is possible to provide an electrophoretic display device capable of displaying a high-quality image with high display image contrast.

One embodiment of the present invention provides an electronic device including the electrophoretic display device.
According to this configuration, since the above-described electrophoretic display device is included, it is possible to provide an electronic device capable of displaying a high-quality image with high contrast of a display image.

1 is a cross-sectional view illustrating a schematic configuration of an electrophoretic display device according to an embodiment. It is a top view which shows the structural example of a cell matrix. It is a schematic diagram which shows the electrophoretic particle of embodiment. It is process drawing which shows the manufacturing process of an electrophoretic display device. It is process drawing which shows the manufacturing process of an electrophoretic display device. It is a perspective view explaining the specific example of the electronic device to which the electrophoretic display device of this invention is applied. It is a graph which shows the result of an Example. It is a graph which shows the result of an Example. It is a graph which shows the result of an Example. It is a graph which shows the result of an Example.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In all the drawings below, the dimensions and ratios of the constituent elements are appropriately changed in order to make the drawings easy to see.

[Electrophoretic display device]
FIG. 1 is a cross-sectional view illustrating a schematic configuration of the electrophoretic display device according to the present embodiment. As shown in the drawing, an electrophoretic display device 100 includes an element substrate 1, a counter substrate 2, a cell matrix 4 provided on the element substrate 1 and having a plurality of cells 15, and an electrophoretic layer accommodated in the cells 15. (Dispersion) 11, sealing film 5 provided to cover electrophoretic layer 11 and cell matrix 4, and counter electrode disposed on sealing film 5 and sandwiched between sealing film 5 and counter substrate 2 6 are provided. The element substrate 1 and the counter substrate 2 correspond to “a pair of substrates” in the electrophoretic display device of the present invention.

  The element substrate 1 includes a base material 1A and a plurality of pixel electrodes 12 provided on the electrophoretic layer 11 side of the base material 1A. As the base material 1A, either a transparent substrate or an opaque substrate can be used. Examples of opaque substrates include ceramics such as alumina, metal sheets such as stainless steel that have been subjected to insulation treatment such as surface oxidation, thermosetting resins and thermoplastic resins, and films thereof (plastic films). It is done. As the transparent substrate, for example, an inorganic substance such as glass, quartz glass, or silicon nitride, or an organic polymer (resin) such as an acrylic resin or a polycarbonate resin can be used. In addition, a composite material formed by laminating or mixing the above materials can be used as long as it has optical transparency.

  A plurality of pixel electrodes 12 are provided in a matrix corresponding to the plurality of cells 15 included in the cell matrix 4. The pixel electrode 12 is an electrode in which nickel plating and gold plating are laminated in this order on a Cu foil, or an electrode formed of Al, ITO (indium tin oxide), or the like. Although not shown, between the pixel electrode 12 and the substrate 1A, wiring such as scanning lines and data lines, a selection transistor, and the like form a layer structure. Each wiring and transistor are appropriately insulated by an insulating layer. With these configurations, a potential can be independently applied to the pixel electrode 12.

  The counter substrate 2 is composed of the above-described transparent base material. A counter electrode 6 having a planar shape facing the plurality of pixel electrodes 12 is formed on the electrophoretic layer 11 side of the counter substrate 2. The counter electrode 6 is a transparent electrode made of MgAg, ITO, IZO (indium / zinc oxide, registered trademark) or the like.

  The cell matrix 4 includes a base portion 13 and a partition wall 14 disposed on the base portion 13. The cell matrix 4 is attached to the element substrate 1 via an adhesive layer 20 disposed in a region between the plurality of pixel electrodes 12.

  The base portion 13 forms the bottom surface of the cell matrix 4 and is composed of a sheet-like (that is, flat plate) member. There is no restriction | limiting in the thickness of the base 13, For example, a thin film about several micrometers-several tens of micrometers may be sufficient.

  Further, the partition wall 14 forms a side wall of the cell matrix 4 and divides the electrophoretic layer 11 into a plurality of parts. The partition 14 divides the element substrate 1 into a plurality of cells 15 corresponding to the pixel electrodes 12, and the electrophoretic layer 11 is disposed in each of the plurality of cells 15. In the present embodiment, the partition wall 14 has a tapered shape in which the cross-sectional structure tapers toward the distal end side opposite to the base portion 13 side.

  The shape of the partition wall 14 in plan view (hereinafter also referred to as a planar shape) is, for example, a square lattice shape, a hexagonal lattice shape, or a triangular lattice shape. FIG. 2 is a plan view showing a configuration example of the cell matrix 4. As shown in FIG. 2A, when the planar shape of the partition 14 is a square lattice, the planar shape of the cell 15 is a square. Further, as shown in FIG. 2B, when the planar shape of the partition 14 is a hexagonal lattice, the planar shape of the cell 15 is a hexagon.

  In the cell matrix 4, the base portion 13 and the partition wall 14 may be integrally formed. The partition wall 14 and the plate-like base portion 13 are separately formed, and the partition wall is formed on one surface of the plate-like base portion 13. 14 may be fixed. Further, the cell matrix 4 may be configured by only the partition wall 14 without the base portion 13. In that case, the partition wall 14 may be directly attached to the element substrate 1.

  In the cell matrix 4, when the base 13 and the partition 14 are integrally formed, the base 13 and the partition 14 are made of the same material. Moreover, when the base 13 and the partition 14 are formed separately, the base 13 and the partition 14 may be comprised with the same material, and may be comprised with a different material.

  The material constituting the base portion 13 may be either a flexible material or a hard material. For example, various materials such as an epoxy resin, an acrylic resin, a urethane resin, a melamine resin, and a phenol resin. Examples thereof include resin materials and various ceramic materials such as silica, alumina, and titania. When plasticity is imparted to the electrophoretic display device 100, it is preferable to select a resin material having plasticity for the base portion 13. Examples of the material constituting the partition wall 14 include various resin materials such as epoxy resin, acrylic resin, urethane resin, melamine resin, and phenol resin, and various ceramic materials such as silica, alumina, and titania. Can be mentioned.

  The electrophoretic layer 11 is composed of a dispersion liquid including a dispersion medium 30 and a plurality of electrophoretic particles 31 dispersed in the dispersion medium 30. The electrophoretic layer 11 relates to an embodiment of the dispersion liquid of the present invention.

The dispersion medium 30 is, for example, aliphatic hydrocarbons such as pentane, hexane, octane, paraffin, and isoparaffin;
Cycloaliphatic hydrocarbons such as cyclohexane, methylcyclohexane, naphthene;
Benzenes having a long-chain alkyl group such as benzene, toluene, xylene, hexylbenzene, heptylbenzene, octylbenzene, nonylbenzene, decylbenzene, undecylbenzene, dodecylbenzene, tridecylbenzene, tetradecylbenzene (alkylbenzene derivatives) Aromatic hydrocarbons such as
Aromatic fluorinated rings such as pyridine, pyrazine, furan, pyrrole, thiophene, methylpyrrolidone;
Esters such as methyl acetate, ethyl acetate, butyl acetate, ethyl formate;
Ketones such as acetone, methyl ethyl ketone, diethyl ketone, methyl isobutyl ketone, methyl isopropyl ketone, cyclohexanone;
Nitriles such as acetonitrile, propionitrile, acrylonitrile;
Amides such as N, N-dimethylformamide and N, N-dimethylacetamide;
Carboxylate;
Alternatively, silicone oil or the like can be used. These may be used alone or as a mixture.

  Moreover, as aliphatic hydrocarbons that can be used as the dispersion medium 30, those that are commercially available as isoparaffinic solvents can be used, and examples of such commercially available products include Isopar (registered trademark). . The dispersion medium 30 is, for example, a liquid obtained by mixing one or two or more kinds selected from the group consisting of Isopar E, Isopar G, Isopar H, Isopar L, and Isopar M, or these and other hydrocarbons described above. Mixed liquids can be used.

  In the present embodiment, the electrophoretic particles 31 are charged particles including, for example, white particles 31a and black particles 31b. The white particles 31a are particles made of a white pigment such as titanium oxide, zinc white, and antimony trioxide, and are used, for example, by being negatively charged. The black particles 31b are particles made of a black pigment such as carbon black, aniline black, titanium black, or copper chromite, and are used, for example, by being positively charged.

  The sealing film 5 is a film for sealing the electrophoretic layer 11 in the cell 15. On the surface of the electrophoretic layer 11, the sealing film 5 is formed with a constant film thickness along the surface, and the concave shape of the surface of the electrophoretic layer 11 appears on the surface of the sealing film 5. Examples of the material constituting the sealing film 5 include water-soluble polymers, and specifically, any one of polyvinyl alcohol (also referred to as PVA), gelatin, gum arabic, carboxymethyl cellulose, and chaotic cellulose, Alternatively, two or more of these are included. In the present embodiment, the sealing film 5 is formed using PVA.

  When a hydrocarbon-based dispersion medium (for example, Isopar) is selected as the dispersion medium 30 and a water-soluble polymer film (for example, PVA) is selected as the sealing film 5, the following advantages are obtained. There is. That is, both hydrocarbon-based dispersion media (for example, Isopar) and PVA are inexpensive.

  For this reason, the manufacturing cost of the electrophoretic display device 100 can be reduced. In addition, the sealing film 5 can be formed to be colorless and transparent, and a light transmittance of about 90% can be secured. Since the attenuation of light by the sealing film 5 is small, the visibility of characters, images, and the like displayed on the screen covered with the sealing film 5 (that is, the aggregate of the plurality of cells 15) can be improved. In addition, since the compatibility between the sealing film 5 and the electrophoretic layer 11 is extremely low, the electrophoretic layer 11 can be sealed in the cell 15 with high airtightness.

  Based on this configuration, in the electrophoretic display device 100, for example, when a voltage is applied between the pixel electrode 12 and the counter electrode 6, the electrophoretic particles 31 (white particles 31a and The black particles 31b) are electrophoresed toward one of the electrodes (pixel electrode 12, counter electrode 6). For example, when the white particles 31a are negatively charged, if the pixel electrode 12 is set to a positive potential, the white particles 31a move to the pixel electrode 12 side (lower side) and gather to display black. Thereby, the electrophoretic display device 100 can display a desired image.

[Dispersion]
Next, the dispersion liquid of this embodiment will be described. The dispersion liquid of the present embodiment includes the electrophoretic particles 31 and the dispersion medium 30 that disperses the electrophoretic particles 31 as described above. In addition, the electrophoretic particles 31 included in the dispersion liquid of the present embodiment include a plurality of first particles and a plurality of second particles. For example, in the above description, the positively charged black particles 31b correspond to the first particles, and the negatively charged white particles 31a correspond to the second particles in the present invention.

  FIG. 3 is a schematic diagram showing the electrophoretic particles 31 of the present embodiment. As shown in the figure, the electrophoretic particle 31 includes a color particle 32 and a polymer chain 33 that modifies the surface of the color particle 32.

(Color particles)
As the color particles 32, particles made of a pigment itself, a core particle (hereinafter sometimes referred to as a core particle) colored with a coloring material such as a pigment or a dye, or a polymerizable dye is polymerized. Examples thereof include particles using a polymer as a forming material. As the “coloring”, a method of coating the surface of the core particle with a pigment, or a method of mixing a coloring material with the core particle forming material can be employed.

  As a material for forming the core particles, a resin material or an inorganic material can be used. Examples of the resin material that is a material for forming the core particles include acrylic resin, urethane resin, urea resin, epoxy resin, polystyrene, polyester, and polyolefin. These may be used alone or in combination of two or more. Moreover, titanium oxide can be mentioned as an inorganic material which is a formation material of a nucleus particle.

  Various coloring materials such as pigments and dyes can be used according to the purpose. For example, examples of the black color material include black pigments and black dyes such as aniline black, carbon black, and titanium black. Examples of the white color material include white pigments such as titanium oxide and antimony oxide. Examples of the yellow color material include azo pigments such as monoazo, yellow pigments such as isoindolinone and yellow lead, and yellow dyes. Examples of the red color material include red pigments and red dyes such as quinacridone red and chrome vermilion. Examples of the blue color material include blue pigments and blue dyes such as phthalocyanine blue and indanthrene blue. Examples of the green color material include green pigments such as phthalocyanine green and green dyes.

(Polymer chain)
The polymer chain 33 modifies the surface of the color particle 32 and modifies the dispersibility of the color particle 32. As the polymer chain 33, a polymer chain having a high affinity with the dispersion medium used in the dispersion is selected. High affinity means that the polymer chain and the dispersion medium are excellent in compatibility without phase separation. Such polymer chains have a steric exclusion effect that prevents aggregation between particles by spreading in the dispersion medium. In FIG. 3, a circle indicated by a broken line indicates the spread of the polymer chain 33 in the dispersion medium.

  When the dispersion medium to be used is a hydrocarbon solvent, the polymer chain 33 preferably includes a hydrocarbon chain such as a polyolefin chain. The polyolefin chain may be linear or branched, but is preferably linear. The straight-chain type is advantageous when the steric exclusion effect is exhibited.

  Examples of the monomer corresponding to the polyolefin chain include 1-hexene, 1-heptene, 1-octene, 1-decene, butadiene, isoprene, and isobutylene. The polyolefin chain may be a homopolymer of these monomers, or may be a copolymer obtained by polymerizing two or more of these monomers.

  When the dispersion medium to be used is silicone oil, the polymer chain 33 preferably contains a polysiloxane chain. The polysiloxane chain may have an alkyl group having 1 to 3 carbon atoms such as a methyl group, an ethyl group, or a propyl group in the side chain. The polymer chain 33 may include a polysiloxane chain in the main chain or may be included in the side chain, but is preferably a linear type in which the polysiloxane chain is included in the main chain. The straight-chain type is advantageous when the steric exclusion effect is exhibited.

  The polymer chain 33 may have a charge control group that appropriately controls the charge of the electrophoretic particles 31 in the dispersion medium 30. Examples of the charge control group include a polarization group having a main skeleton in which electrons are unevenly distributed, and a charge group having a main skeleton that forms an ion pair. By having these groups, the polymer chain 33 changes in electrical bias and electric charge, so the chargeability of the entire electrophoretic particle 31 is controlled by controlling the type and amount of the charge control group. can do.

The dispersion of this embodiment has the following two requirements.
(Requirement 1) The number average molecular weight (Mn) of the polymer chain 33 is 5000 or more and 100,000 or less (Requirement 2) The number average molecular weight of the polymer chain 33 attached to the surface of the first color particle and the second color particle The sum of the number average molecular weight of the polymer chains 33 adhering to the surface of 25,000 or more and 200000 or less

(Requirement 1)
The number average molecular weight of the polymer chain 33 defined in the above requirement 1 corresponds to the spreading range of the polymer chain 33 in the electrophoretic particles 31 in the dispersion, and is a value that affects the steric exclusion effect. That is, requirement 1 defines the range of the “stereoscopic exclusion effect” described above. When the number average molecular weight of the polymer chain 33 is 5000 or more, a sufficient steric exclusion effect can be expected, and when the number average molecular weight is 100,000 or less, the movement of the electrophoretic particles is not inhibited in the dispersion medium.

(Requirement 2)
The value specified in the above requirement 2 corresponds to the length of the polymer chain 33 interposed between the first color particles and the second color particles in the dispersion. The first color particles and the second color particles that are charged with different polarities are likely to aggregate in the dispersion medium, but if the total of the polymer chains 33 that modify the surface is 25000 or more, aggregation is suppressed. Can do. The upper limit of the polymer chain 33 is a value when the polymer chain 33 included in each of the first particle and the second particle exhibits the maximum value in the requirement 1 requirement.

  In the present specification, the “number average molecular weight” refers to the number average molecular weight in terms of polystyrene measured using gel permeation chromatography (GPC).

  In the electrophoretic particles contained in the dispersion liquid of the present embodiment, the molecular weight of the polymer chain 33 can be controlled as follows, for example. Here, a case where the polymer chain includes a polysiloxane chain will be described as an example.

  First, a silicone oil having a molecular weight corresponding to the polymer chain 33 is prepared. A functional group having a carbon-carbon double bond such as a vinyl group or an allyl group is bonded to the silicon atom at the terminal of the silicone oil. Examples of such silicone oil include compounds represented by the following formula (1).

  The above formula (1) is a compound (silicone oil) having a polysiloxane chain, a vinyl group bonded to a terminal silicon atom, and a side chain organic group being a methyl group. In the formula, n is a natural number indicating the degree of polymerization.

  Next, the silicone oil of the above formula (1) and the compound represented by the following formula (2) are mixed with a platinum catalyst in an organic solvent and heated to react (hydrosilylation reaction) to obtain a reaction product. In the reaction formula represented by the following formula (3), the reaction between the compound represented by the above formula (1) and trimethoxyhydrosilane as an example of the compound represented by the following formula (2) is shown.

（式中、Ｒはアルキル基、Ｘはハロゲン原子、ヒドロキシ基およびアルコキシ基から選ばれる基であり、ａは１から３の自然数である。Ｘを複数有する場合、複数のＸは互いに同じであってもよく異なっていてもよい）

(In the formula, R is an alkyl group, X is a group selected from a halogen atom, a hydroxy group and an alkoxy group, and a is a natural number from 1 to 3. When there are a plurality of X, the plurality of X are the same as each other. Or it may be different)

  Next, the reaction product obtained by the above formula (3) and the color particles are mixed in an organic solvent and heated to form particles (first particle or second particle) having polymer chains attached to the surface of the color particles. Particles).

  In the above reaction, the number average molecular weight of the polymer chain 33 can be easily controlled by controlling the number average molecular weight of the starting silicone oil. Moreover, the electrophoretic particle contained in the dispersion liquid of this embodiment can be adjusted by preparing 1st particle | grains and 2nd particle | grains by said reaction, respectively, and mixing suitably.

  The method for adjusting the polymer chain 33 is not limited to the above method. First, a compound (referred to as compound B) for attaching or bonding a polymer chain such as the compound of the above formula (2) to the surface of the color particle is attached or bonded to the surface of the color particle. Thereafter, a compound (referred to as compound A) that defines the number average molecular weight of the “polymer chain”, such as the compound of the above formula (1), is reacted with compound B attached or bonded to the surface of the color particle to perform chemical reaction. You may adjust by the method of producing a coupling | bonding. Also in this case, by using a compound having a desired number average molecular weight as the compound A, the number average molecular weight of the polymer chain 33 can be easily controlled.

  Such electrophoretic particles are prevented from agglomerating in the dispersion, and the inter-particle distance between charged particles having different signs is increased, so that separation during application of voltage is facilitated. As a result, when a dispersion having such electrophoretic particles is used in an electrophoretic display device, the white reflectance is improved. In addition, a decrease in response speed can be suppressed.

  In the electrophoretic particle 31, when the total surface area of the first color particle and the total surface area of the second color particle are compared, the polymer chain 33 that modifies the surface of the color particle having a relatively small total surface area. The number average molecular weight is preferably smaller than that of the polymer chain 33 that modifies the surface of the color particle having a relatively large total surface area. Further, the color particles having a relatively small total surface area are preferably particles having a relatively low reflectance as compared with the other color particles. The total surface area of the particles means the total surface area of the first or second color particles contained in the dispersion.

  In the dispersion liquid of this embodiment, black particles 31b are used as the first particles, and white particles 31a are used as the second particles. Since the black particles 31b absorb light and develop color, a small amount of clear black is developed. On the other hand, since the white particles 31a are colored by scattering light, particles having a relatively larger volume than the black particles are required to shield the color of the coexisting black particles. Therefore, it is preferable that the electrophoretic particles 31 contain more white particles 31a than the black particles 31b. In such a case, it is advantageous in terms of response speed to perform display by positively migrating the relatively small amount of black particles 31b among the two kinds of charged particles contained in the dispersion.

  In that case, when the total surface area of the color particles (first color particles) included in the black particles 31b and the total surface area of the color particles (second color particles) included in the white particles 31a are compared, The color particles of 1 are blended so that the total surface area is smaller than that of the second color particles, and the surface of the color particles contained in the black particles 31b is more number-average molecular weight than the polymer chains of the white particles 31a. It may be modified with a polymer chain having a small. The black particles having such a polymer chain are less likely to be entangled with the polymer chains of the adjacent particles, and migration is not easily inhibited by the polymer chain 33, and a good response speed can be realized.

Further, in the electrophoretic particles 31, the amount of polymer chains 33 attached is preferably 3% or more and 10% or less with respect to the mass of the color particles 32. When the adhesion amount of the polymer chain 33 is 3% or more, the surface of the color particle is modified with a sufficient amount of the polymer chain 33 to express the steric exclusion effect. Therefore, particle aggregation is suppressed, leading to an improvement in white reflectance. Further, when the adhesion amount of the polymer chain 33 is 10% or less, the polymer chain is less likely to be entangled with the polymer chain of the adjacent particle, migration is not easily inhibited by the polymer chain 33, and a good response speed is realized. can do.
The dispersion liquid of this embodiment has the above configuration.

[Method for Manufacturing Electrophoretic Display Device]
Next, a method for manufacturing the electrophoretic display device 100 using the electrophoretic particles 31 formed as described above will be described with reference to FIGS. 5 and 6 are cross-sectional views showing the manufacturing process of the electrophoretic display device 100. FIG.

  First, as shown in FIG. 4A, first, a cell matrix 4 is prepared. In the present embodiment, a substrate in which the element substrate 1 is attached to the surface of the cell matrix 4 on the base 13 side in advance through an adhesive layer 20 is used.

  Next, as shown in FIG. 4B, the electrophoretic layer 11 is supplied into each cell 15 of the cell matrix 4. In the present embodiment, a dispersion liquid having a plurality of electrophoretic particles 31 and a dispersion medium 30 is disposed in each cell 15.

  The electrophoretic layer 11 is supplied into each cell 15 by various application methods such as a dropping method using a dispenser, an ink jet method (droplet discharge method), a spin coating method, a dip coating method, a spray coating method, and the like. Among these, it is preferable to use a dropping method or an ink jet method. According to the dropping method or the ink jet method, since the electrophoretic layer 11 can be selectively supplied to the intended storage portion, it can be supplied into the cell 15 more reliably and without waste.

  Next, as shown in FIG. 4C, the opening side of the cell matrix 4 to which the electrophoretic layer 11 is supplied is covered with PVA which is a material for forming the sealing film 5, and each cell 15 of the cell matrix 4 is covered. The electrophoretic layer 11 is enclosed inside. In this embodiment, after supplying the electrophoretic layer 11 into the cell 15, the sealing process is performed after a certain waiting time is provided. Thereby, the surface (namely, liquid level) of the electrophoretic layer 11 can be reduced in the center part of the cell 15, and the shape by the cross-sectional view can be made concave.

A method for forming the sealing film 5 is, for example, as follows. That is, PVA is dissolved in, for example, water or a hydrophilic liquid (for example, methanol or ethanol) to form a liquid, and a sealing liquid is created. For example, PVA is dissolved in water to create a sealing liquid of 3% by mass to 40% by mass. Next, this sealing liquid 5 A is applied to the opening side of the cell matrix 4. The electrophoretic layer 11 is lipophilic, the sealing liquid 5A is hydrophilic, and the electrophoretic layer 11 and the sealing liquid 5A are not miscible.
In the application process of the sealing liquid 5A, for example, the sealing liquid 5A is uniformly applied to the entire surface on the opening side of the cell matrix 4 using the squeegee 17. Further, the coating method of the sealing liquid 5A may be other methods, for example, a coating method using a die coater or a comma coater.

  A cross-linking agent may be added to the sealing liquid 5A. As the cross-linking agent, for example, an aqueous boric acid solution is added. The boric acid aqueous solution contains borate ions. In the sealing liquid 5A, borate ions connect (ie, gel) PVA molecules together. This gelation is due to multipoint intermolecular forces (hydrogen bonds, coordination bonds, covalent bonds, etc.). Thereby, the viscosity of 5A of sealing liquid can be 1000 mPa * s or more, for example, and a gel-like PVA aqueous solution can be obtained. Thereby, handling of sealing liquid 5A becomes easy and a manufacturing process can be simplified.

Next, as shown in FIG. 5A, the applied sealing liquid 5A is dried and cured. For example, the sealing liquid 5A is left in a temperature environment of about room temperature to about 50 ° C., and is dried and cured.
Although the time required for the drying process depends on the thickness of the sealing liquid 5A, it is, for example, about several minutes to several hours. Since the concentration of PVA in the film of the sealing liquid 5A is high, the sealing liquid 5A can be dried naturally or at a relatively low temperature. As described above, the sealing film 5 is formed on the exposed portion of the electrophoretic layer 11 supplied into the cell 15. As a result, the electrophoretic layer 11 is sealed in the cell 15 with high airtightness. In this drying process, the moisture contained in the sealing liquid 5A is volatilized (that is, evaporated), so that the thickness of the sealing film 5 becomes thinner than that immediately after the application (FIG. 4 (c), FIG. 5 (a). )reference).

Next, as shown in FIG. 5B, a counter substrate 2 having a counter electrode 6 is prepared. In the present embodiment, a flexible resin substrate is selected as the counter substrate 2 in order to impart flexibility to the electrophoretic display device 100. Then, the counter substrate 2 is attached to the cell matrix 4 using an adhesive layer (not shown). Thereafter, a sealing material (not shown) is disposed so as to surround the outer periphery of the counter substrate 2.
Through the above steps, the electrophoretic display device 100 shown in FIG. 1 is completed.

  According to the dispersion liquid having the above-described configuration, it is possible to improve the light reflectance during white display by suppressing the aggregation of particles, and it is possible to suppress a decrease in response speed. Therefore, a high-contrast image display is possible, and a dispersion having high display performance can be provided.

  Moreover, according to the electrophoretic display device having the above-described configuration, since the above-described dispersion liquid is included, high-contrast image display is possible and high-quality display performance is achieved.

[Electronics]
Next, an embodiment of the electronic device of the present invention will be described.
FIG. 6 is a perspective view illustrating a specific example of an electronic apparatus to which the electrophoretic display device of the present invention is applied.
FIG. 6A is a perspective view illustrating an electronic book which is an example of the electronic apparatus. The electronic book (electronic device) 400 includes a book-shaped frame 401, a cover 402 that can be rotated (openable and closable) with respect to the frame 401, an operation unit 403, and the electrophoretic display of the present invention. And a display unit 404 configured by the apparatus.

  FIG. 6B is a perspective view illustrating a wrist watch that is an example of an electronic apparatus. The wristwatch (electronic device) 500 includes a display unit 501 configured by the electrophoretic display device of the present invention.

  FIG. 6C is a perspective view illustrating an electronic paper which is an example of the electronic apparatus. This electronic paper (electronic device) 600 includes a main body portion 601 composed of a rewritable sheet having the same texture and flexibility as paper, and a display portion 602 composed of an electrophoretic display device of the present invention.

  According to the electronic book 400, the wristwatch 500, and the electronic paper 600 described above, the electrophoretic display device according to the present invention is employed. Therefore, an electronic device that can display an image with high contrast and display a high quality. It becomes.

  In addition, said electronic device illustrates the electronic device which concerns on this invention, Comprising: The technical scope of this invention is not limited. For example, the electrophoretic display device according to the present invention can be suitably used for display units of electronic devices such as mobile phones and portable audio devices, business sheets such as manuals, textbooks, problem collections, information sheets, and the like. it can.

  The preferred embodiments of the present invention have been described above with reference to the accompanying drawings, but it goes without saying that the present invention is not limited to such examples. Various shapes, combinations, and the like of the constituent members shown in the above-described examples are examples, and various modifications can be made based on design requirements and the like without departing from the gist of the present invention.

  For example, in the above-described embodiment, the electrophoretic display device 100 is exemplified by a structure in which the electrophoretic layer (dispersion liquid) 11 is accommodated in the cell 15 provided between the element substrate 1 and the counter substrate 2. However, the present invention is not limited to this, and a configuration in which the microcapsules containing the dispersion liquid are disposed between the element substrate 1 and the counter substrate 2 may be employed.

  EXAMPLES The present invention will be described below with reference to examples, but the present invention is not limited to these examples.

  In this example, the following dispersion was used.

<Dispersion>
(particle)
A particle (white particle): The surface of titania (CR97, manufactured by Ishihara Sangyo Co., Ltd.) is modified with a polymer having a siloxane structure with a number average molecular weight of 10,000 in the main chain. Primary particle diameter 250nm
B particles (black particles): The surface of titanium black (SC-13M-T, manufactured by Mitsubishi Materials Corporation) is modified with a polymer having a siloxane structure with a number average molecular weight of 10,000 in the main chain. Primary particle diameter 75nm
C particles (black particles): The surface of titanium black is modified with a polymer having a siloxane structure with a number average molecular weight of 16000 in the main chain.
D particles (white particles): The surface of titania is modified with a polymer having a siloxane structure with a number average molecular weight of 25,000 in the main chain.
E particles (white particles): The surface of titania is modified with a polymer having a siloxane structure with a number average molecular weight of 60000 in the main chain.
The particle size of white particles and black particles is measured using the dynamic light scattering method as the measurement principle.
(Dispersion medium)
Dispersion medium: Silicone oil (KF-96L-2cs, manufactured by Shin-Etsu Silicone)
(Dispersion)
The above A particles to E particles are appropriately mixed (described later) and dispersed in the dispersion medium for adjustment. Particle concentration of dispersion: 40% by mass

<Level 1>
(Example 1)
About the dispersion liquid 1 mixed by A particle | grains: C particle | grains = 7: 1 (mass ratio), the light reflectivity was measured with the following method.

The dispersion liquid was measured with a color luminance meter (manufactured by Topcon Co., Ltd., BM-5A), and the light reflectance was determined. Specifically, a ring light source was used as a light source, light emitted from the ring light source was reflected by a test cell, and the amount of reflected light was measured with a color luminance meter.
(Test cell)
Test cell: A sealed space is formed with a pair of glass substrates (0.5 mm thick, with ITO electrodes)
Separation distance between substrates 30μm
Voltage at the time of measurement: After applying a predetermined voltage, the reflectance is measured after a sufficient time for the particles to move.

(Comparative Example 1)
The light reflectance of the dispersion was measured in the same manner as in Example 1 except that the dispersion 2 mixed at A particle: B particle = 7: 1 (mass ratio) was used.

  FIG. 7 is a graph showing the relationship between the applied voltage and the light reflectance during white display for dispersions 1 and 2 of Example 1 and Comparative Example 1. In FIG. 7, the horizontal axis represents the applied voltage (unit: V) at the time of measurement, and the vertical axis represents the light reflectance (unit:%). The value on the vertical axis represents a relative value with the measurement result under the condition of the applied voltage of 10 V as 100 in Comparative Example 1.

  FIG. 8 is a graph showing the increase rate of the light reflectance of the dispersion liquid of Example 1 with respect to the dispersion liquid of Comparative Example 1 based on the result shown in FIG. In FIG. 8, the light reflectance of the dispersion liquid of Comparative Example 1 at each applied voltage is shown as 100%.

  As shown in the figure, according to the dispersion liquid of Example 1, it was confirmed that the light reflectance was improved as compared with the dispersion liquid of Comparative Example 1.

FIG. 9 is a graph obtained by measuring the display response performance of the dispersions 1 and 2 of Example 1 and Comparative Example 1, and is a graph showing the relationship between the voltage application time and the light reflectance. FIG. 9A shows the display response performance when changing from black display to white display, and FIG. 9B shows the display response performance when changing from white display to black display.
In FIG. 9, the horizontal axis represents voltage application time (unit: seconds), and the vertical axis represents light reflectance (unit%).

  As shown in the figure, it has been found that even if the number average molecular weight of the polymer chain of the black particles is increased from 10,000 to 16000, the response speed is not substantially affected.

  From the results shown in FIGS. 7 to 9, it was found that the dispersion of Example 1 can improve the light reflectance while maintaining the response speed as compared with the dispersion of Comparative Example 1.

<Level 2>
(Example 2)
The light reflectance of the dispersion was the same as in Example 1 except that the dispersion 3 mixed at D particles: B particles = 12: 1 (mass ratio) was used, and the applied voltage at the time of measurement was 10 V. Was measured.

(Example 3)
The light reflectance of the dispersion was measured in the same manner as in Example 1 except that the dispersion 4 mixed with E particles: B particles = 12: 1 (mass ratio) was used.

  FIG. 10 shows the light reflectance during white display for Examples 2 and 3. The light reflectance in the figure is a relative value when the value measured for Example 2 is taken as 100%.

  As shown in the figure, it was found that the light reflectance during white display is improved by increasing the molecular weight of the polymer chain that modifies the surface of the white particles. When the light reflectance during black display was measured separately, it was found that there was no difference between Examples 2 and 3, so that the contrast (white reflectance / black reflectance) was improved.

  From the above results, it was confirmed that the present invention is useful.

  1, 2, 3, 4 ... dispersion, 11 ... electrophoretic layer (dispersion), 30 ... dispersion medium, 31 ... electrophoretic particles, 32 ... colored particles, 33 ... polymer chain, 100 ... electrophoretic display device, 400 ... electronic book (electronic device), 500 ... watch (electronic device), 600 ... electronic paper (electronic device)

Claims (6)

Electrophoretic particles having colored particles and polymer chains that modify the surface of the colored particles;
A dispersion medium for dispersing the electrophoretic particles,
The electrophoretic particles have a plurality of first particles and a plurality of second particles,
The first particles have first color particles and are positively charged;
The second particles have second color particles and are negatively charged;
The number average molecular weight of the polymer chain is 5000 or more and 100,000 or less,
The sum of the number average molecular weight of the polymer chain attached to the surface of the first color particle and the number average molecular weight of the polymer chain attached to the surface of the second color particle is 25000 or more and 200000 or less. A dispersion.   Comparing the total surface area of the first color particles and the total surface area of the second color particles, the polymer chain that modifies the color particles having a relatively small total surface area has a relatively large total surface area. The dispersion according to claim 1, wherein the number average molecular weight is smaller than that of the polymer chain that modifies the color particles.   The dispersion according to claim 1 or 2, wherein the amount of the polymer chain attached is 3% or more and 10% or less with respect to the mass of the color particles.   The dispersion according to any one of claims 1 to 3, wherein the polymer chain is linear. A pair of substrates;
An electrophoretic layer sandwiched between the pair of substrates,
An electrophoretic display device, wherein the electrophoretic layer comprises the dispersion liquid according to claim 1.   An electronic apparatus comprising the electrophoretic display device according to claim 5.

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