JP2014010356A - Sheet for electrophoretic display device and electrophoretic display device including the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sheet for an electrophoretic display device, which is superior in display characteristics while having microcapsules prevented from deformation.SOLUTION: The sheet for an electrophoretic display device according to the present invention includes a substrate, microcapsules, a binder layer for fixing the microcapsules to the substrate, and an overcoat layer laminated on the binder layer. Volume resistivity of the binder layer is higher than that of the overcoat layer, and a maximum thickness of the binder layer is 60 to 92% of a volume average particle size of the microcapsules.

Description

  The present invention relates to a microcapsule electrophoretic display device, and more particularly, to an electrophoretic display device sheet and an electrophoretic display device including the sheet.

  An electrophoretic display device is a device that displays character data, image data, and the like based on the behavior of electrophoretic particles when a voltage is applied by dispersing electrophoretic particles in a solvent. If a plurality of electrophoretic particles having different colors according to charging characteristics are dispersed in a solvent, arbitrary character data and image data can be displayed by an applied voltage.

  Electrophoretic display devices are classified into two types, a microcell system and a microcapsule system, depending on the method of dispersing electrophoretic particles. A microcapsule electrophoretic display device is formed by encapsulating electrophoretic particles in a microcapsule and fixing the microcapsule to a substrate via a binder resin.

  However, since the strength of the microcapsule wall (shell) is usually weak, problems such as deformation of the microcapsule due to external pressure applied to the sheet have occurred when the opposing electrodes are stacked. When the microcapsule is deformed, the display performance may be deteriorated, which is not preferable. Therefore, in recent years, in order to protect the microcapsules, after coating the binder layer and drying the sheet, further laminating an elastic material on the binder layer and absorbing the pressure applied to the microcapsule, A plurality of display devices that deal with the problem are provided (Patent Documents 1 to 6).

Japanese translation of PCT publication No. 2007-525712 (claims 15 to 16) JP 2011-18052 A (Claim 3) JP 2001-242492 A (Claim 17) JP2011-65036A (paragraph 0019) JP 2001-33831 A (Claim 9) JP 2000-352946 A (Claim 12)

  However, if a resin layer is further laminated on the binder layer, the capsule layer becomes thick. When the capsule layer is thick, the voltage does not sufficiently act on the electrophoretic particles, and a high voltage is necessary to display a clear image. For example, the backplane for an electro-optic display described in Patent Document 1 has a thickness of an adhesive layer that is about twice that of an electro-optic medium. A lot of power is required.

  On the other hand, the inventors have found that the voltage applied between the display electrodes can be controlled by making the volume resistivity of the binder layer higher than the volume resistivity of the overcoat layer.

  Therefore, an attempt was made to divert this technique to the display device described above. However, according to the verification by the present inventors, the backplane disclosed in Patent Document 1 has a thick adhesive layer, so that a leak current is generated between the display electrodes, and a clear image cannot be displayed. It was. Further, in the display devices disclosed in Patent Documents 2 to 6, since the binder resin is filled to a height that is almost the same as the particle size of the microcapsules, the effect of improving the display performance by providing the difference in resistivity is sufficient. It was not demonstrated to.

  Under such circumstances, an object of the present invention is to provide a sheet for an electrophoretic display device having excellent display characteristics while preventing deformation of the microcapsules.

As a result of intensive studies to solve the above problems, the present inventors have made the volume resistivity of the binder layer higher than the volume resistivity of the overcoat layer, and further set the maximum thickness of the binder layer to a predetermined value. The inventors have found that adjusting the content within the range can improve the display performance of the electrophoretic display device sheet while protecting the microcapsules, thereby completing the present invention.
That is, the sheet for electrophoretic display device according to the present invention includes a first base material, a microcapsule, a binder layer for fixing the microcapsule to the first base material, and an overcoat layer laminated on the binder layer. An electrophoretic display device sheet comprising a second substrate laminated on the overcoat layer, wherein the binder layer has a volume resistivity higher than a volume resistivity of the overcoat layer, The maximum thickness is 60 to 92% of the volume average particle diameter of the microcapsules. In the capsule layer existing between the first substrate and the second substrate, the volume ratio of the microcapsules is preferably 30 to 75%. Also. More preferably, the difference between the capsule layer thickness and the microcapsule volume average particle diameter is within ± 10 μm. Further, the volume resistivity of the binder layer at 25 ° C. is preferably 1 × 10 ^{7 to} 9 × 10 ¹¹ Ωcm, and the volume resistivity of the overcoat layer is preferably 2 × 10 ^{6 to} 9 × 10 ⁸ Ωcm. . Furthermore, it is desirable that the shell of the microcapsule contains an amino resin.
Furthermore, the present invention includes an electrophoretic display device comprising the electrophoretic display device sheet.

  According to the present invention, the volume resistivity of the binder layer is made higher than the volume resistivity of the overcoat layer, and then the maximum thickness of the binder layer is adjusted within a predetermined range. Therefore, the display device can display a clearer image as compared with the conventional case. Moreover, since the overcoat layer is laminated on the binder layer, the microcapsules can be protected from external pressure.

FIG. 1A shows the state of adjacent microcapsules when the microcapsules are arranged in a hexagonal close-packed manner, and FIG. 1B shows the unit structure when the microcapsules are arranged in a hexagonal close-packed manner. FIG. 2 shows a model used for calculating the volume ratio of the microcapsules in the capsule layer.

≪Electrophoresis display sheet≫
The electrophoretic display device sheet of the present invention includes a first base material, microcapsules, a binder layer for fixing the microcapsules to the first base material, an overcoat layer laminated on the binder layer, and the overcoat Having a second substrate laminated on the layer. Hereinafter, each configuration will be described in detail.

(1) Binder layer and overcoat layer The binder layer is a layer for fixing the microcapsules enclosing the electrophoretic particles to the first substrate. That is, the binder layer is the thickest layer among the layers in contact with the microcapsules. On the other hand, an overcoat layer is a layer laminated | stacked on the said binder layer. That is, the overcoat layer refers to a layer having elasticity or curing among the layers laminated on the binder layer. By providing a difference between the volume resistivity of the binder layer and the volume resistivity of the overcoat layer, an electric field is easily applied to the electrophoretic particles in the microcapsule.

  Other layers may be laminated between the first substrate and the binder layer, between the binder layer and the overcoat layer, and between the overcoat layer and the second substrate, respectively. In the case where a plurality of elastic or cured layers are laminated on the binder layer, the layer closest to the second substrate is used as the overcoat layer of the present invention.

  In the present invention, the volume resistivity of the binder layer is adjusted to be higher than the volume resistivity of the overcoat layer constituting the overcoat layer. Thus, by changing the volume resistivity of the binder layer and the volume resistivity of the overcoat layer, the charging characteristics of the sheet for electrophoretic display devices can be controlled, and an electric field can be easily applied to the sheet. Thereby, the response speed of the electrophoretic particles in the microcapsule is increased, and the display performance of the sheet can be improved.

Specifically, the volume resistivity of the binder layer at 25 ° C. is preferably 1 × 10 ^{7 to} 9 × 10 ¹¹ Ωcm, more preferably 2 × 10 ^{7 to} 6 × 10 ¹¹ Ωcm, and further preferably. 1 × 10 ^{8 to} 9 × 10 ¹⁰ Ωcm.
On the other hand, the volume resistivity of the overcoat layer at 25 ° C. is preferably 2 × 10 ^{6 to} 9 × 10 ⁸ Ωcm, more preferably 3 × 10 ^{6 to} 9 × 10 ⁷ Ωcm, and even more preferably. Is 5 × 10 ^{6 to} 6 × 10 ⁷ Ωcm. If the volume resistivity of the binder layer and the overcoat layer is in the above range, it is preferable because an electrophoretic display device sheet having sufficient display characteristics can be obtained even when the applied voltage is low.

  The binder layer having the volume resistivity is, for example, (meth) acrylic resin, polyvinyl chloride resin, polyvinylidene chloride resin, melamine resin, polyurethane resin, polystyrene resin, alkyd resin, phenol resin, epoxy resin, Synthetic resin binders such as polyester resin, polyvinyl alcohol resin, (meth) acrylic silicone resin, alkylpolysiloxane resin, silicone resin, silicone alkyd resin, silicone polyurethane resin, silicone polyester resin; ethylene-propylene copolymer rubber, polybutadiene rubber, styrene -Synthetic rubber or natural rubber binder such as butanediene rubber, acrylonitrile-butadiene rubber; cellulose nitrate, cellulose acetate butyrate, cellulose acetate, It is formed by using the like; Le cellulose, hydroxypropyl methyl cellulose, thermoplastic or thermosetting polymeric binder such as hydroxyethyl cellulose. These binder resins may be used alone or in combination of two or more. Of these binder resins, polyurethane resins, (meth) acrylic resins, and polyester resins are preferred because of the relatively good dispersibility of microcapsules. Among these, polyurethane resins and (meth) acrylic resins are preferred. Particularly preferred. A polyurethane resin and a (meth) acrylic resin can also be mixed and used.

  On the other hand, as the overcoat resin constituting the overcoat layer, the resin exemplified in the column of the binder resin can be used as appropriate, and the adhesion to the substrate to be bonded to the sheet for electrophoretic display devices and the microcapsule protection From this point, use of a polyurethane resin or a (meth) acrylic resin is preferable. A polyurethane resin and a (meth) acrylic resin can also be mixed and used.

  Furthermore, in order to adjust the volume resistivity of the binder resin and the overcoat resin within a predetermined range, a resistance adjusting agent may be appropriately added to these resins. The resistance adjusting agent is not particularly limited, but it is preferable to use a metal salt that can form ions, a quaternary ammonium salt, or a polymer having conductivity (conductive polymer) because it increases the conductivity of the binder.

Examples of metal salt cations include alkali metal ions such as lithium ions, sodium ions and potassium ions; alkaline earth metal ions such as magnesium ions and strontium ions. The anions of the metal salt include acetate ion, halide ion, perchlorate ion, tetrefluoroborate ion (BF ₄ ⁻ ), hexafluorophosphate ion (PF ₆ ⁻ ), hexafluoroantimonate ion ( Inorganic anions such as SbF ₆ ⁻ ) and hexafluoroarsenate ion (AsF ₆ ⁻ ); polyacrylic acid, polystyrene sulfonate, poly (2-vinylpyridine), poly (4-vinylpyridine), poly (dimethylammonium chloride) , Polymer anions such as poly (dimethylaminoethyl (meth) acrylate) and poly (diethylaminoethyl (meth) acrylate). As the quaternary ammonium salt, for example, quaternary ammonium salts such as tetrabutylammonium hexafluorophosphate and tetrabutylammonium perchlorate can be preferably used. Further, examples of the conductive polymer include conductive polymers such as polyaniline, polythiophene, polypyrrole, poly-3,4-dioxyethylenethiophene, and derivatives of the conductive polymer in an n-doped state or a p-doped state. Can be used.

  In addition, in the present invention, the charging property of the capsule layer is controlled by adjusting the maximum thickness of the binder layer within a predetermined range. In the present invention, the binder layer is desirably coated thinner than the volume average particle diameter of the microcapsules so that a part of the microcapsules is exposed. Specifically, in the present invention, the maximum thickness of the binder layer is adjusted to 60 to 92% of the volume average particle diameter of the microcapsules, and more preferably 65 to 90% in order to improve the charging characteristics. Preferably it is 70 to 88%. If the maximum thickness of the binder layer is less than 60% of the volume average particle diameter of the microcapsules, there is a risk that problems such as inability to display an image clearly and insufficient adhesion of the microcapsules by the binder may occur. On the other hand, if the maximum thickness of the binder layer exceeds 92%, the volume resistivity increases and the image display speed may be inferior. In the present invention, the value of the space filling rate of the binder layer was used as the evaluation of the maximum thickness of the binder layer. The method for measuring the space filling rate of the binder layer will be described in detail in the Examples section.

  The maximum thickness of the binder layer is, for example, preferably 8 to 50 μm, more preferably 10 to 45 μm, and still more preferably 20 to 40 μm. If the maximum thickness of the binder layer is within the above range, it is preferable because the sheet for electrophoretic display devices can display a clear image. In addition, the measuring method of the maximum thickness of a binder layer is explained in full detail in the Example column.

  The binder layer is coated thinner than the particle size of the microcapsule so that a part of the microcapsule is exposed. Therefore, it is desirable that the overcoat layer is filled to a height corresponding to the volume average particle diameter of the microcapsules so as to cover the exposed portions of the microcapsules.

  Specifically, the maximum thickness of the overcoat layer is preferably, for example, 3 to 10 μm, more preferably 4 to 9 μm, and further preferably 5 to 8.5 μm.

  The maximum thickness of the overcoat layer relative to the maximum thickness of the binder layer (maximum thickness of the overcoat layer / maximum thickness of the binder layer) is preferably 0.07 / 1 to 0.7 / 1. More preferably, it is 0.1 / 1 to 0.45 / 1, and further preferably 0.13 / 1 to 0.4 / 1. If the maximum thickness of the overcoat layer is within the above range, an electrophoretic display device sheet excellent in display performance can be obtained, which is preferable.

(2-1) Microcapsule The microcapsule used in the present invention is formed by enclosing a dispersion of electrophoretic particles in a shell.

  In the present invention, since the thickness of the binder layer and the overcoat layer is adjusted to be thinner than that of the conventional product, it is desirable that the shell of the microcapsule has an appropriate strength. Therefore, it is preferable to use a resin having an appropriate strength for the shell of the microcapsule. For example, amino resins such as melamine / formaldehyde resin, urea / formaldehyde resin, melamine / urea / formaldehyde resin, benzoguanamine / formaldehyde resin; polyamide Resins; Polyurethane resins; Polyester resins such as polyethylene terephthalate and polybutylene terephthalate; Polycarbonate resins; Epoxy resins; Acrylic resins; Materials mainly composed of proteins such as gelatin can be preferably used. Among these, it is preferable to use a high-strength amino resin for the shell of the microcapsule, and in particular, the use of melamine / formaldehyde resin, urea / formaldehyde resin, melamine / urea / formaldehyde resin is preferable. These are synthesized from amino compounds such as melamine and urea and formaldehyde, as will be described later.

  Further, the shell of the microcapsule can have a multilayer structure having at least an inner shell and an outer shell in order to increase the strength. For example, as the shell, an inner shell and / or outer shell made of an amino resin can be used as appropriate. In the case where the shell of the microcapsule is formed in such a multilayer structure, it is a more preferable aspect that the inner shell and the outer shell are appropriately combined by crosslinking or the like.

  The volume average particle diameter of the microcapsules is preferably 15 to 60 μm, more preferably 20 to 55 μm, and even more preferably 30 to 50 μm. The true specific gravity of the microcapsule is preferably 1.7 to 2.2, more preferably 1.75 to 2.1, and even more preferably 1.8 to 2.0. Is preferred.

(2-2) Electrophoretic Particles The electrophoretic particles enclosed in the microcapsules may be solid particles having electrophoretic properties, that is, colored particles exhibiting positive or negative polarity in the dispersion, and the pigment particles are used. The electrophoretic particles preferably have a polymer added around the pigment particles in order to enhance dispersion stability in the dispersion.

  The pigment particles are not particularly limited. For example, inorganic pigments such as titanium oxide, barium sulfate, and zinc oxide are used in the white system; yellow iron oxide, cadmium yellow, titanium yellow, chrome yellow, yellow are used in the yellow system. Inorganic pigments such as lead, insoluble azo compounds such as first yellow, condensed azo compounds such as chromophthal yellow, azo complex salts such as benzimidazolone azo yellow, condensed polycycles such as flavans yellow, Hansa Yellow, Organic pigments such as naphthol yellow, nitro compounds, and pigment yellow; in orange, organic pigments such as inorganic pigments such as molybdate orange, azo complex salts such as benzimidazolone azo orange, and condensed polycycles such as perinone orange ; In red, inorganic pigments such as Bengala and Cadmium Red, and dyeing lacquers such as Madare Lake , Soluble azo compounds such as lake red, insoluble azo compounds such as naphthol red, condensed azo compounds such as chromophthalscar red, condensed polycycles such as thioindigo Bordeaux, Shinkasha Red Y, Hosta Palm Red Organic pigments such as quinacridone pigments such as azo pigments such as permanent red and first slow red; in the case of purple, inorganic pigments such as manganese violet, dyed lakes such as rhodamine lakes, and condensed polycycles such as dioxazine violet Organic pigments such as blue; inorganic pigments such as bitumen, ultramarine blue, cobalt blue and cerulean blue; phthalocyanines such as phthalocyanine blue; indanthrenes such as indanthrene blue; organic pigments such as alkali blue; green In the system, emerald green, chrome green, oxidation Organic pigments such as inorganic pigments such as rom and viridian, azo complex salts such as nickel azo yellow, nitroso compounds such as pigment green and naphthol green, and phthalocyanines such as phthalocyanine green; in black, carbon black, titanium black, Examples thereof include particles composed of inorganic pigments such as iron black and organic pigments such as aniline black. These pigment particles may be used alone or in combination of two or more. Of these pigment particles, white pigment particles such as titanium oxide and black pigment particles such as carbon black and titanium black are preferably used.

  In addition, when titanium oxide is used as the pigment particles, the kind thereof is not particularly limited, and any rutile type or anatase type is preferably used as long as it is generally used as a white pigment. it can. In consideration of fading of the colorant due to the photocatalytic activity of titanium oxide, rutile type titanium oxide having low photocatalytic activity can be preferably used.

  In order to reduce the photocatalytic activity, the surface of the titanium oxide particles is preferably subjected to inorganic treatment such as silica treatment, alumina treatment, silica-alumina treatment, zirconium-alumina treatment. Note that silica or alumina present on the particle surface is bonded to a hydroxyl group to form a -Si-OH group or -Al-OH group, and the hydroxyl group serves as a reaction point with the silane coupling agent. Increases the reactivity between the particles and the silane coupling agent.

  In addition, it is preferable to coat the pigment particles with a polymer because the dispersibility in the dispersion is improved. The method for forming the polymer is not particularly limited, but the polymer is preferably formed by polymerizing various monomers.

  In order to increase the amount of polymer addition, in the present invention, a high molecular weight monomer such as a macromonomer or a monomer having a long-chain alkyl group may be used as a polymer raw material.

  Examples of the macromonomer include a silicone macromonomer, a (meth) acrylic macromonomer, and a styrene macromonomer. Among these, a silicone-based macromonomer is preferable because it has a polysiloxane skeleton in the molecule and is excellent in affinity with a silane coupling agent. Specific examples of such macromonomers include the following formula (I):

In the formula, R ¹ is preferably a hydrogen atom or a methyl group, and R ² is preferably a hydrogen atom or an alkyl group having 1 to 4 carbon atoms. In order to increase the polymer addition amount, x is preferably a natural number, more preferably 1 to 10, and further preferably 2 to 6. For the same reason, n is preferably a natural number, more preferably 1 to 130, and still more preferably 5 to 70. In addition, since the terminal of the macromonomer is a (meth) acryloyl group, it can also be called a (meth) acrylic macromonomer.

  As the monomer having a long-chain alkyl group, a (meth) acrylic monomer having 5 to 30 carbon atoms in the long-chain alkyl group is preferable, and a (meth) acrylic monomer having 7 to 25 is more preferable. Specific examples of (meth) acrylic monomers having a long-chain alkyl group include, for example, pentyl (meth) acrylate, isopentyl (meth) acrylate, neopentyl (meth) acrylate, hexyl (meth) acrylate, and heptyl (meth) acrylate. , Octyl (meth) acrylate, nonyl (meth) acrylate, decyl (meth) acrylate, undecyl (meth) acrylate, lauryl (meth) acrylate, hexadecyl (meth) acrylate, heptadecyl (meth) acrylate, stearyl (meth) acrylate, nonadecyl (Meth) acrylate, aralkyl (meth) acrylate, behenyl (meth) acrylate, etc. are mentioned. These monomers having a long-chain alkyl group may be used alone or in combination of two or more. A monomer having a long chain alkyl group may be used in combination with the macromonomer. In the present invention, “(meth) acrylate” means “acrylate” or “methacrylate”.

  Moreover, the monomer which has hydrolyzable groups, such as a cyclic ether group or a hydroxyl group, and a silane coupling agent can also be used as a polymer raw material. By introducing hydrolyzable groups such as cyclic ether groups, hydroxyl groups, and alkoxysilyl groups into the polymer and reacting the hydroxyl groups and hydrolyzable groups present on the surface of the pigment particles, the bond between the pigment particles and the polymer becomes stronger. Therefore, it is preferable.

  Examples of the monomer having a hydrolyzable group such as a cyclic ether group or a hydroxyl group include glycidyl (meth) acrylate, cyclopropylethyl (meth) acrylate, cyclopropyl (meth) acrylate, cyclopentyl (meth) acrylate, and cyclohexyl (meth). Cycloalkyl (meth) acrylates such as acrylate, cyclooctyl (meth) acrylate, cycloundecyl (meth) acrylate, cyclododecyl (meth) acrylate, isobornyl (meth) acrylate, 4-t-butylcyclohexyl (meth) acrylate; Hydrode such as hydroxymethyl (meth) acrylate, hydroxyethyl (meth) acrylate, hydroxypropyl acrylate, hydroxybutyl acrylate, hydroxypentyl acrylate Kishiarukiru (meth) acrylate and the like.

  As the silane coupling agent, use of a silane coupling agent having a vinyl group or a (meth) acryloyl group is preferable. For example, vinyltrimethoxysilane, vinyltriethoxysilane, 3- (trimethoxysilyl) propyl (meth) acrylate , 3- (triethoxysilyl) propyl (meth) acrylate and the like.

  In the present invention, a polyfunctional monomer having two or more polymerizable groups such as a vinyl group or a (meth) acryloyl group can be used as a polymer raw material. Examples of the polyfunctional monomer include aromatic hydrocarbon polyfunctional monomers such as divinylbenzene, divinylnaphthalene, and derivatives thereof; alkanediol di (meth) acrylate (for example, ethylene glycol di (meth) acrylate, 1,4 -Butanediol di (meth) acrylate, 1,6-hexanediol di (meth) acrylate, 1,9-nonanediol di (meth) acrylate, 1,10-decanediol di (meth) acrylate, 1,3-butanediol di Polyfunctional (meth) acrylates such as (meth) acrylate). A polyfunctional monomer may be used independently and may use 2 or more types together.

  Examples of other monomers constituting the polymer include (meth) acrylate monomers other than those exemplified above, styrene monomers, and the like. Examples of (meth) acrylate monomers include methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, n-butyl (meth) acrylate, isobutyl (meth) acrylate, and 2-ethylhexyl (meth) acrylate. Alkyl (meth) acrylates such as: phenyl (meth) acrylate, benzyl (meth) acrylate, tolyl (meth) acrylate, phenethyl (meth) acrylate and other aromatic ring-containing (meth) acrylates, and alkyl (meth) Acrylates are preferred. Examples of styrene monofunctional monomers include styrene; alkyl styrenes such as o-methyl styrene, m-methyl styrene, p-methyl styrene, α-methyl styrene, pt-butyl styrene, o-chlorostyrene, m -Halogen group-containing styrenes such as chlorostyrene and p-chlorostyrene. These monomers may be used alone or in combination of two or more.

  The composition of the high molecular weight monomer in the polymer (the sum of the composition of the macromonomer and the monomer having a long chain alkyl group) is 50 to 95%, more preferably 60 to 90%, and more preferably 70 to 90% by molar ratio. 87%.

  The mass average molecular weight of the polymer is preferably 1000 to 100,000, more preferably 1500 to 50000, and still more preferably 2000 to 20000. The volume average particle diameter of the electrophoretic particles is preferably 400 to 600 nm, and more preferably 450 to 550 nm.

  In the case of white particles (electrophoretic white particles), the zeta potential of the electrophoretic particles obtained by the above method is preferably, for example, +1 to +10 mV, more preferably +2 to +8 mV, and even more preferably +2. 5 to +7 mV. Further, since the black particles (electrophoretic black particles) are required to have a certain response capability with respect to the applied electric field, the black particles preferably have a zeta potential of −2 to −15 mV, more preferably −4. Is −13 mV, and more preferably −5.5 to −12 mV. As a combination of the electrophoretic particles, in order to prevent aggregation of the electrophoretic particles, a combination of black particles having a high zeta potential of −6 to −15 mV and white particles having a low zeta potential of +1 to +6 mV is preferable. The electrophoretic particles may have a combination of opposite charging polarities.

(3) Capsule layer In this invention, the layer which exists between a 1st base material and a 2nd base material is called a capsule layer. That is, the capsule layer is a layer including a binder coat layer, an overcoat layer, a microcapsule layer, and other layers existing between both base materials.

  In the present invention, the higher the ratio (volume ratio) of microcapsules in the capsule layer, the better. For example, in the capsule layer, the volume ratio of the microcapsules is preferably 30 to 75%, more preferably 40 to 70%, and further preferably 52 to 68%. By increasing the volume ratio of the microcapsules, the lines of electric force generated when a voltage is applied become more linear between the opposing electrodes, so that a clear image can be displayed. However, when the volume ratio of the microcapsule exceeds 75%, the microcapsule cannot withstand external force and is deformed, and the display performance may be deteriorated.

  The thickness of the capsule layer is preferably about the same as the volume average particle diameter of the microcapsules. For example, the difference between the thickness of the capsule layer and the volume average particle diameter of the microcapsules is preferably within ± 10 μm. More preferably, it is within ± 5 μm, and further preferably within ± 2 μm.

  The thickness of the capsule layer is preferably within 5% of the volume average particle diameter of the microcapsule, more preferably within 2%, more preferably within the range of 2%, based on the volume average particle diameter of the microcapsule. Preferably, it is within ± 1%. If the thickness of the capsule layer is within the above range, the abundance ratio of the microcapsules is preferably increased.

(4) Base material The first base material is not particularly limited as long as it is substantially conductive. For example, copper, aluminum, nickel, cobalt, platinum, gold, silver, molybdenum, tantalum, or these Metal materials such as alloys, carbon materials such as carbon black, carbon nanotubes, fullerenes, polyacetylene, polypyrrole, polythiophene, polyaniline, poly (p-phenylene), poly (p-phenylenevinylene), polyfluorene, polycarbazole, polysilane Alternatively, in an electroconductive polymer material such as a derivative thereof, polyvinyl alcohol, polycarbonate, polyethylene oxide, polyvinyl butyral, polyvinyl carbazole, vinyl acetate, or the like, NaCl, LiClO ₄ , KCl, H ₂ O, LiCl, LiB r, LiI, LiNO ₃ , LiSCN, LiCF ₃ SO ₃ , NaBr, NaI, NaSCN, NaClO ₄ , NaCF ₃ SO ₃ , KI, KSCN, KClO ₄ , KCF ₃ SO ₃ , NH ₄ I, NH ₄ SCN, NH ₄ ClO ₄ , NH ₄ CF ₃ SO ₃ , MgCl ₂ , MgBr ₂ , MgI ₂ , Mg (NO ₃ ) ₂ , MgSCN ₂ , Mg (CF ₃ SO ₃ ) ₂ , ZnCl ₂ , ZnI ₂ , ZnSCN ₂ , Zn (ClO ₄ ) Ion conductivity high in which ionic substances such as ₂ , Zn (CF ₃ SO ₃ ) ₂ , CuCl ₂ , CuI ₂ , CuSCN ₂ , Cu (ClO ₄ ) ₂ , Cu (CF ₃ SO ₃ ) ₂ are dispersed molecular material, indium tin oxide (ITO), fluorine-doped tin oxide (FTO), tin oxide (SnO _2), various guide such as a conductive oxide material such as indium oxide (IO) Sexual materials include, may be used singly or in combination of two or more of them. In addition, for example, conductive materials (conductive particles) such as gold, silver, nickel, carbon, etc. are mixed in non-conductive materials such as glass materials, rubber materials, polymer materials, etc. Various composite materials such as those added can also be used.

  In addition, as the second base material, the materials exemplified in the column of the first base material may be appropriately used. The first substrate and the second substrate may be the same material or different materials. Moreover, the thickness of a 1st base material and a 2nd base material may be the same, or may differ.

(5) Sheet for electrophoretic display device Since an electric field is easily applied to the electrophoretic display device sheet of the present invention having the above-described configuration, an image can be clearly displayed. In an electrophoretic display device including an electrophoretic display device sheet, for example, the contrast indicating the white reflectance with respect to the black reflectance measured when a DC voltage of 15 V is applied for 0.4 seconds is higher than 8.0. Indicates the value. Moreover, the screen once displayed can be maintained for a long time. That is, black display is performed under the same conditions (DC voltage of 15 V is applied for 0.4 seconds), and the time until the black reflectivity is reduced by 10% (black reflectivity is reduced by 10%) is also better than 30 minutes. Indicates a numerical value.

(6) Electrophoretic Display Device The electrophoretic display device sheet obtained in the present invention is suitable as a display device for a microcell electrophoretic display device. The electrophoretic display device including the sheet of the present invention can display characters and images more clearly.

≪Method for manufacturing sheet for electrophoretic display device≫
Next, the manufacturing method of the sheet | seat for electrophoretic display devices of this invention is demonstrated.

(1) Preparation of binder liquid / overcoat liquid Resin having a predetermined volume resistivity is used for the resin used for the binder layer and the overcoat layer. When the resin does not have a predetermined volume resistivity, it is preferable to add a resistance adjuster to the binder to adjust the volume resistivity. Further, when problems such as aggregation occur during the adjustment, it is preferable to adjust the pH or add a small amount of a solvent or a surfactant.

  Examples of the dispersion medium or solvent used for dispersing or dissolving the resin include water; alcohol solvents such as methanol, ethanol, isopropanol, isobutanol, ethylene glycol, and propylene glycol; ketones such as acetone, methyl ethyl ketone, and cyclohexanone. Solvents: aromatic hydrocarbon solvents such as toluene and xylene; ester solvents such as ethyl acetate, n-butyl acetate and isobutyl acetate; ether solvents such as diisopropyl ether, t-butyl methyl ether and dibutyl ether; Is preferred. These solvents may be used alone or in combination.

  The binder liquid thus prepared preferably has a solid content concentration of 20 to 60% by mass, more preferably 22 to 56% by mass, and even more preferably 25 to 55% by mass. When the solid content concentration of the binder liquid is less than 20% by mass, it is not preferable because it takes a long time to evaporate the liquid or heating at a high temperature. Moreover, if solid content concentration is in the said range, since the maximum thickness of a binder can be adjusted to a predetermined range, it is suitable.

  On the other hand, the overcoat liquid preferably has a solid content concentration of 20 to 50% by mass, more preferably 22 to 46% by mass, and further preferably 25 to 45% by mass. If the solid content concentration of the overcoat liquid is within the above range, the maximum thickness of the overcoat layer after drying can be controlled within a predetermined range.

(2) Preparation of microcapsules (2-1) Preparation of electrophoretic particle dispersion Electrophoretic particles encapsulated in microcapsules are pigment particles having electrophoretic properties and particles in which a polymer is added around pigment particles. Can be used as appropriate.

  The method for producing electrophoretic particles in which a polymer is added around pigment particles is not particularly limited as long as a predetermined amount of polymer is bound around pigment particles. As a method for producing the electrophoretic particles, 1) a method in which a monomer or a monomer and a silane coupling agent are polymerized in advance to form a polymer, and then the formed polymer is reacted with pigment particles; 2) A method in which pigment particles are added to a dispersion in which a monomer and a silane coupling agent are dispersed, and the mixture is heated and reacted; 3) The pigment particles are preliminarily treated with a silane coupling agent, and electrophoretic particle precursors A method of binding a polymer to the electrophoretic particle precursor by reacting with a monomer in the presence of the electrophoretic particle precursor, and the like can be appropriately employed. Since it is easy to adjust the polymer composition and the molecular weight of the polymer, it is preferable to adopt the production method shown in 1) in the present invention.

  For monomer polymerization, 2,2′-azobisisobutyronitrile, 1,1′-azobis (cyclohexanecarbonitrile), bis (4-hydroxybutyl) 2,2′-azobisisobutyrate, 2, 2'-azobis (2-methylbutyronitrile), 2,2'-azobis (2,4-dimethylvaleronitrile), 2,2'-azobis (4-methoxy-2,4-dimethylvaleronitrile), dimethyl Azo polymerization initiators such as 2,2′-azobis (2-methylpropionate); benzoyl peroxide, methyl ethyl ketone peroxide, diisopropyl peroxycarbonate, cumene hydroperoxide, t-butyl hydroperoxide, di-t-butyl peroxide, dialkyl Milperoxide, 2,4-dichlorobenzoyl peroxide, Lauroy Peroxide, 2,2-bis - - (4,4-t- butylperoxy) propane, tris (t-butylperoxy) peroxide polymerization initiators such as triazine; polymerization initiator or the like is used.

  The reaction temperature between the polymer and the pigment particles is, for example, 40 ° C. or higher, more preferably 50 ° C. or higher, and preferably 200 ° C. or lower, more preferably 170 ° C. or lower. The reaction time is not particularly limited, but is preferably 0.5 hours or more, more preferably 1 hour or more, and preferably 24 hours or less, more preferably 12 hours or less.

  The reaction solvent used in the reaction is not particularly limited. For example, benzene, toluene, o-xylene, m-xylene, p-xylene, mixed xylene, ethylbenzene, hexylbenzene, dodecylbenzene, phenylalkyl. Aromatic hydrocarbons such as benzene hydrocarbons such as silylethane; Paraffin hydrocarbons such as n-hexane and n-decane; Isoparaffin hydrocarbons such as Isopar (registered trademark, manufactured by ExxonMobil Chemical); 1 -Olefin hydrocarbons such as octene and 1-decene; aliphatic hydrocarbons such as naphthenic hydrocarbons such as cyclohexane and decalin; kerosene, petroleum ether, petroleum benzine, ligroin, industrial gasoline, coal tar naphtha, petroleum naphtha , Hydrocarbons derived from petroleum and coal such as solvent naphtha Dichloromethane, chloroform, carbon tetrachloride, 1,2-dichloroethane, 1,1,1-trichloroethane, 1,1,2,2-tetrachloroethane, trichlorofluoroethane, tetrabromoethane, dibromotetrafluoroethane, tetrafluorodiiodo Halogenated hydrocarbons such as ethane, 1,2-dichloroethylene, trichloroethylene, tetrachloroethylene, trichlorofluoroethylene, chlorobutane, chlorocyclohexane, chlorobenzene, o-dichlorobenzene, bromobenzene, iodomethane, diiodomethane, iodoform; dimethyl silicone oil, methylphenyl Silicone oils such as silicone oils; fluorinated solvents such as hydrofluoroethers; These organic solvents may be used alone or in combination of two or more. In the present invention, it is preferable to use isoparaffinic hydrocarbons and silicone oils according to the main chain skeleton of the polymer.

  For example, when producing electrophoretic particles by the method shown in 1), a polymer formed by polymerizing a monomer or a monomer and a silane coupling agent in advance is polymer 0.5 to It is good to add 5 mass parts and to react a polymer and pigment particle. The amount of the polymer added is more preferably 0.7 to 3 parts by mass with respect to 10 parts by mass of the pigment particles.

  The electrophoretic particles formed by the above method preferably have a polymer addition amount of 1 to 20% by mass, and more preferably 5 to 12% by mass. A polymer addition amount within the above range is preferable because the dispersion stability of the electrophoretic particles in the dispersion medium can be secured.

  An electrophoretic particle dispersion is obtained by dispersing the obtained electrophoretic particles in a dispersion medium. As the dispersion medium, a nonpolar solvent is preferably used, and any of the reaction solvents described above can be used. These organic solvents may be used alone or in combination of two or more. In addition, as a dispersion medium for electrophoretic particles, a liquid obtained from a reaction solvent may be used as it is. Further, it is possible to use a dispersion medium different from the reaction solvent by substituting the solvent. In the present invention, it is preferable to use isoparaffinic hydrocarbons and silicone oils according to the main chain skeleton of the polymer.

  When black particles and white particles are blended as the electrophoretic particles, the concentration of the black particles is preferably 1 to 10% by mass, more preferably 1.2 to 8% by mass during the electrophoretic particle dispersion. Yes, and more preferably 1.5-7% by mass. On the other hand, the concentration of white particles in the electrophoretic particle dispersion is preferably 10 to 50% by mass, more preferably 12 to 48% by mass, and even more preferably 15 to 45% by mass.

  If necessary, a dye, a dispersant, a charge control agent, a viscosity adjusting agent, or the like may be added to the dispersion medium used for the electrophoretic particle dispersion.

(2-2) Preparation of microcapsules First, in the present invention, the electrophoretic particle dispersion obtained in the above step is used as a core substance, and the core substance is dispersed in an aqueous medium to form a microcapsule shell around the core substance. Form. The aqueous medium is not particularly limited. For example, water or a mixed solvent of water and a hydrophilic organic solvent can be used.

  In order to prepare a microcapsule, first, various raw materials of the shell of the microcapsule are reacted to prepare an initial condensate. The initial condensate can be obtained by partially condensing the raw material of the shell.

  When an amino resin is used as the shell material, the amino resin raw material (amino compound) required for producing the initial condensate is not particularly limited, but the amount of formaldehyde and amino compound added is The mass ratio of amino compound / formaldehyde is preferably 1 / 0.1 to 1/10, and more preferably 1 / 0.5 to 1/2.

  The reaction temperature for carrying out the reaction for obtaining the initial condensate is not particularly limited, but is preferably 55 to 80 ° C, more preferably 60 to 75 ° C, and further preferably 65 to 73 ° C. When the reaction end point is recognized, the reaction may be terminated by an operation such as cooling the reaction solution to room temperature (for example, 25 to 30 ° C.). In addition, reaction time is not specifically limited, According to the preparation amount, it can set suitably.

  Next, a core material containing an electrophoretic dispersion is produced. The core substance may be manufactured by dispersing an electrophoretic dispersion in an aqueous medium.

  The amount in which the core substance (electrophoretic dispersion liquid) is dispersed in the aqueous medium is not particularly limited, but is preferably 5 parts by mass or more, more preferably 8 parts by mass or more with respect to 100 parts by mass of the aqueous medium. More preferably, it is 10 parts by mass or more, preferably 70 parts by mass or less, more preferably 65 parts by mass or less, and still more preferably 60 parts by mass or less. If the amount of the core material dispersed is too small, the concentration of the core material is low, so it takes a long time to form the capsule shell, and the target microcapsules cannot be prepared. Efficiency may be reduced. Conversely, if the amount of the core material dispersed is too large, the core material may aggregate or the aqueous medium may be suspended in the core material, making it impossible to produce microcapsules.

  When dispersing the core substance in the aqueous medium, a dispersant may be used as necessary. Although it does not specifically limit as a dispersing agent, For example, water-soluble polymer (For example, polysaccharides, such as polyvinyl alcohol (PVA), carboxymethylcellulose (CMC), gelatin, gum arabic, soybean polysaccharide, gati gum) And surfactants (for example, anionic surfactants, cationic surfactants, amphoteric surfactants, nonionic surfactants) and the like. These dispersants may be used alone or in combination of two or more. The addition amount of these dispersants is not particularly limited, and may be adjusted as appropriate.

  In addition to water and hydrophilic organic solvents, the aqueous medium may further use other solvents in combination. Examples of other solvents include, but are not limited to, hexane, cyclopentane, pentane, isopentane, octane, benzene, toluene, xylene, ethylbenzene, petroleum ether, terpene, castor oil, soybean oil, paraffin, and kerosene. Etc. These other solvents may be used alone or in combination of two or more.

  The shell of the microcapsule may be formed by adding a preliminarily formed initial condensate to the core material dispersion and then heating.

  In the reaction for forming a shell around the core substance, the reaction temperature is not particularly limited, but is preferably 20 to 60 ° C, more preferably 25 to 55 ° C, and further preferably 30 to 50 ° C. The reaction time is preferably 1 hour or longer, more preferably 2 hours or longer, preferably 12 hours or shorter, more preferably 6 hours or shorter.

  It is also possible to age the reaction solution after completion of the reaction. The aging time is, for example, preferably 0.5 to 12 hours, and more preferably 1 to 6 hours. The aging temperature is preferably 20 to 80 ° C.

  The obtained microcapsules are preferably classified to make the particle diameter uniform. The classification of the microcapsules is carried out as it is for the dispersion containing the microcapsules in the aqueous medium as it is or after dilution with an arbitrary aqueous medium, for example, a sieve type, a filter type, a centrifugal sedimentation, etc. Using a method such as an equation or a natural sedimentation method, the microcapsules may be made to have a desired particle size or particle size distribution. Note that the sieve type is effective for microcapsules having a relatively large particle size.

  Moreover, it is good to wash | clean in order to remove an impurity and to improve product quality.

(3) Production of sheet for electrophoretic display device The method for producing a sheet for electrophoretic display device is as long as a binder layer is formed on the first substrate and an overcoat layer is further formed on the binder layer. The method for producing the sheet is not particularly limited. The method for producing a sheet for an electrophoretic display device includes, for example, a step of producing a paint containing a microcapsule and a binder liquid whose volume resistivity is adjusted; a step of applying the paint to an electrode and drying; It is preferable to include a step of applying and drying an overcoat liquid having an adjusted volume resistivity.

  First, the preparation method of the coating material applied on the 1st base material is demonstrated. The paint is a liquid containing the microcapsules obtained in the above step and a binder liquid whose volume resistivity is adjusted, and the paint comprises the above-described microcapsules and, if necessary, other components as a binder resin. It can be prepared by thoroughly mixing and defoaming if necessary. In preparing the coating material, it is preferable to stir while defoaming using, for example, a rotation / revolution mixer (for example, “Awatori Nertaro (registered trademark) AR-100” manufactured by Sinky).

  The coating concentration is preferably, for example, 35 to 70% by mass, more preferably 40 to 65% by mass, and further preferably 45 to 60% by mass. In order to adjust the coating concentration, water; alcohol solvents such as methanol and ethanol; ketone solvents such as acetone and methyl ethyl ketone; aromatic hydrocarbon solvents such as toluene and xylene; ethyl acetate, n-butyl acetate; An ester solvent such as isobutyl acetate; an ether solvent such as diisopropyl ether may be added.

  Next, the process of applying the paint to the first substrate and drying it will be described. The coating material is preferably dried so that the microcapsules are arranged in a single layer as much as possible after drying the coating film so that the wet film thickness during coating is matched with the volume average particle diameter of the microcapsules. That is, the wet film thickness during coating is preferably 0.015 to 0.1 mm, more preferably 0.045 to 0.09 mm, and even more preferably 0.05 to 0.08 mm.

  When coating the coating material on the first substrate, various coating methods can be appropriately employed. Examples of the coating method include reverse roll coating method, gravure coating method, kiss coating method, die coater method, roll brush method, spray coating method, air knife coating method, wire bar coating method, pipe doctor method, impregnation coating method, curtain coating. Can be used.

  The sheet after coating (coating sheet) is then preferably dried until the binder layer has a predetermined thickness. The coated sheet may be dried by natural drying or a dryer can be used. As the dryer, a known dryer may be used as appropriate.

  Next, a process of applying and drying an overcoat liquid whose volume resistivity is further adjusted after drying will be described. The dried sheet obtained in the above step may be further coated with an overcoat liquid whose volume resistivity is adjusted so that the capsule layer has a laminated structure of a binder layer and an overcoat layer.

  Various coating methods can be used as a method for applying the overcoat liquid.

  After application of the overcoat liquid, the sheet coated with the overcoat liquid may be evaporated by hot drying using natural drying or a dryer.

  A sheet for electrophoretic display devices is obtained by further laminating a second substrate on the surface of the sheet obtained by the above method on the overcoat layer side. The electrophoretic display device sheet is desirably pressure-bonded appropriately using a known pressurizing device in order to enhance adhesion.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited by the following examples, but may be appropriately modified within a range that can meet the purpose described above and below. Of course, it is possible to implement them, and they are all included in the technical scope of the present invention. In the following, “part” means “part by mass” and “%” means “mass%” unless otherwise specified.

<Measurement of particle size>
In the present invention, the average particle diameter means a volume average particle diameter unless otherwise specified. The average particle diameter of the electrophoretic particles was determined by measuring the volume average particle diameter using a dynamic light scattering particle size distribution measuring apparatus (“LB-500” manufactured by Horiba, Ltd.).
In addition, the average particle size of the microcapsules was determined by measuring the volume average particle size using a particle size distribution measuring device particle size distribution measuring device (“Multizer 4” manufactured by Beckman Coulter, Inc.).

<Measurement of zeta potential>
The zeta potential of the electrophoretic particles was measured using an ultrasonic attenuation method measurement apparatus (“DT-1200” manufactured by Dispersion Technology) and the prepared electrophoretic dispersion.

<Measurement of specific gravity and density of capsule, binder layer and overcoat layer>
The true specific gravity of the capsule, the density of the binder layer and the overcoat layer were measured with a dry automatic densimeter (“Acupic II 1340” manufactured by Shimadzu Corporation). The microcapsule sample was dried and powdered, and the binder layer and overcoat layer sample were materials that were sufficiently dried on the release sheet to form a sheet.

<Binder mass ratio>
The binder mass ratio represents the binder solid mass / microcapsule solid mass.

<Binder layer space filling factor>
In the present invention, the calculation was performed on the assumption that the microcapsules are arranged in a hexagonal close-packed manner in one layer. FIG. 1A shows the state of adjacent microcapsules when the microcapsules are arranged in a hexagonal close-packed manner.
FIG. 1B shows a unit structure when the microcapsules are arranged in a hexagonal close-packed manner. In the present invention, in this unit structure, the volume ratio occupied by the microcapsules is assumed to be 0.6 (that is, the volume ratio V of the space filled with the binder resin or the overcoat resin is 0.4).
By using this model, the space filling factor of the binder layer is calculated by the following equation. That is, the space filling rate of the binder layer means the volume ratio v ′ of the filled binder with respect to the volume ratio V of the space where the binder resin can be filled.
F = (v ′ / V) × 100 = (v ′ / 0.4) × 100
As described above, 0.4 was substituted for the volume ratio V of the volume occupied by the binder.
(A) Volume ratio of binder The volume ratio v ′ of the filled binder was calculated by the following equation.
v ′ = (W _B / D _B ) ÷ (W _B / D _B + W _c / D _c )
(W _B : binder layer mass, D _B : binder layer density, W _c : microcapsule mass, D _c : microcapsule true specific gravity)

<Measurement of capsule layer thickness>
The thickness of the electrophoretic display device sheet sufficiently dried and the thickness of the base material before coating were measured with a micrometer (“MDC-SB” manufactured by Mitutoyo Corporation), and the dry film thickness was calculated by the following formula.
(Capsule layer thickness) = (thickness of sheet for electrophoretic display device) − (thickness of base material before coating)
The measurement position was a portion where the coating surface was equally divided into 3 parts in the longitudinal direction and 3 parts in the width direction, and a total of 9 parts were calculated, and the average value and standard deviation were calculated.

<Maximum thickness of binder layer>
The maximum thickness of the binder layer is determined from the space filling rate of the binder layer with respect to the volume average particle diameter of the microcapsules. Specifically, it was calculated by the following formula.
d = R × F
(D: binder layer maximum thickness, R: volume average particle diameter of microcapsules, F: binder layer space filling factor)

<Maximum thickness of overcoat layer>
The maximum thickness of the overcoat layer was calculated by the following formula.
(Maximum thickness of overcoat layer) = (Capsule layer thickness) − (Maximum thickness of binder layer)

<Measurement of volume resistivity>
The amount of current was measured when a DC voltage of 15 V was applied to an electrophoretic display device sheet (electrode portion: length × width = 5 cm × 3 cm) produced in an atmosphere at 25 ° C. The volume resistivity was calculated based on the following formula. In addition, the value calculated | required by the method mentioned above was used for capsule layer thickness.
Volume resistivity ρ (Ω · cm) = (E / I) × (S / d)
(E: applied voltage, I: current, S: electrode area, d: capsule layer thickness)

<Volume ratio of microcapsules in capsule layer>
The volume ratio of the microcapsules in the capsule layer was calculated based on the following formula.
Microcapsule volume ratio = Vc / (Vc + Vb + Vo)
(Vc: Volume of microcapsule, Vb: Volume of binder layer, Vo: Volume of overcoat layer)
The volume of Vc: microcapsule, Vb: volume of binder layer, and volume of Vo: overcoat layer were determined by the following methods.
(A) Microcapsule volume Vc
In the present invention, assuming that the microcapsule is a sphere, the volume of the microcapsule was calculated based on the following equation.
^{Vc = (4πr 3/3)} ÷ 2
In addition, r shows the radius of a microcapsule, and is specifically 1/2 of the volume average particle diameter R of the microcapsule.
(B) Volume Vb of binder layer
The volume Vb of the binder layer was calculated based on the following formula.
Vb = Vr × F / 100
F is the space filling factor of the binder layer.
Here, Vr means the volume of the space filled with the binder resin or overcoat resin in the unit structure when the microcapsules are arranged in a hexagonal manner. That is, Vr is obtained by the following equation. Here, the volume ratio V of the binder is more strictly set to 0.396.
Vr = (volume of triangular prism filled with microcapsules) × (volume ratio V of binder)
= {(√3r / 2) × R × R} × 0.396
(C) Volume Vo of overcoat layer
As shown in FIG. 2, the overcoat layer of the present invention is from the binder layer surface to the maximum microcapsule diameter (in the present invention, the microcapsule volume average particle diameter R is applied to the maximum microcapsule particle diameter). And an overcoat layer II that fills the space from the microcapsule maximum diameter to the second substrate.
That is, the volume Vo of the overcoat layer is obtained by the following equation.
Vo = V _I + V _II
(V _I : Volume of overcoat layer I, V _II : Volume of overcoat layer II)
V _I and V _II are calculated from the following equations, respectively.
V _I = Vr × {(100−F) / 100}
V _II = {(√3r / 2) × R} × (capsule layer thickness−R)
F is a space filling rate of the binder layer.

<White / black reflectance, contrast>
A 15 V DC voltage is applied between the electrodes of the electrophoretic display sheet (the display portion is vertical × horizontal = 5 cm × 3 cm) for 0.4 seconds to display white or black, and a Macbeth spectrophotometer (GretagMacbeth) The reflectance of each display was measured with “SpectroEye” manufactured by the company. Using the reflectance of each display, the contrast (reflectance ratio) was calculated by the following equation.
Contrast (reflectance ratio) = (reflectance for white display) / (reflectance for black display)
The reflectance for white display and black display was measured separately by switching the polarity and applying a voltage. Each reflectance is an average value measured for one entire surface of the electrophoretic display sheet.

<Black reflectance 10% change time>
A dynamic display measuring device including a photosensor amplifier (manufactured by Hamamatsu Photonics), an A / D converter (manufactured by National Instruments), and a personal computer was produced. A sheet for an electrophoretic display device is set in the photosensor section (display portion is vertical × horizontal = 5 cm × 3 cm), a DC voltage of 15 V is applied between both electrodes for 0.4 seconds to display black and hold it as it is, The change in black reflectance was measured, and the time during which the black reflectance changed by 10% was used for evaluation of black retention.
The black reflectance 10% change value was defined by the following formula, and the time when the black reflectance changed to the following black reflectance 10% change value was defined as the black reflectance 10% change time.
Black reflectance 10% change value = black reflectance at start of display + (black reflectance at start of display × 0.1)

1. Electrophoretic dispersion 1-1. Electrophoretic dispersion (A-1)
An acrylic polymer (mass average) composed of lauryl methacrylate, 2-ethylhexyl acrylate, and γ-methacryloxypropyltrimethoxysilane (composition molar ratio 80: 15: 5) was placed in a separable flask equipped with a stirring blade, a thermometer, and a condenser. 2 parts of molecular weight 3,300), 20 parts of titanium black ("Titanium Black 13M" manufactured by Mitsubishi Materials Corporation), 100 parts of isoparaffinic solvent ("Isoper (registered trademark) M" manufactured by ExxonMobil Chemical Co., Ltd.) Was placed in an ultrasonic bath ("BRANSON (registered trademark) 5210" manufactured by Emerson Japan) and dispersed for 3 hours.
The separable flask was transferred to an oil bath, heated to 150 ° C. with stirring, reacted at the same temperature for 5 hours, and a polymer was added to titanium black. After grafting, 100 parts of Isopar M was further added. Next, a series of operations in which the dispersion liquid containing the electrophoretic black particles (polymer-added titanium black) is transferred to a sedimentation tube for centrifugation, and then the electrophoretic black particles are washed with hexane three times are performed. did.
The washed electrophoretic black particles were dispersed in Isopar M to obtain 130 parts of an electrophoretic particle dispersion having a solid content concentration of 15%. The volume average particle diameter of the electrophoretic black particles was 480 nm. The zeta potential of the electrophoretic black particles was −8.7 mV.
On the other hand, in a separable flask equipped with a stirring blade, 50 parts of titanium oxide (“Typaque (registered trademark) CR60” manufactured by Ishihara Sangyo Co., Ltd.), lauryl methacrylate, 2-ethylhexyl acrylate, and γ-methacryloxypropyltrimethoxysilane (composition mol) 5 parts of an acrylic polymer (mass average molecular weight 6,800) consisting of 80: 15: 5) and 100 parts of hexane were placed in an ultrasonic bath (BRANSON 5210), and ultrasonic dispersion was performed for 2 hours while stirring. .
The separable flask after the dispersion treatment was transferred to a 90 ° C. hot water tank, and the solvent was distilled off. The powdered polymer-added titanium oxide was taken out of the flask, transferred to a vat, and then heated for 5 hours at 150 ° C. using a dryer. The operation of dispersing the polymer-added titanium oxide after heating in 100 parts of hexane, centrifuging using a centrifugal sedimentator, and washing the electrophoretic white particles (polymer-added titanium oxide) with hexane is performed three times. The electrophoretic white particles were dried at 100 ° C. In another separable flask, 50 parts of washed electrophoretic white particles are charged into 50 parts of ISOPAR M, placed in an ultrasonic bath (BRANSON 5210), and subjected to ultrasonic dispersion for 2 hours. 100 parts of electrophoretic white particle dispersion were obtained. The volume average particle diameter of the electrophoretic white particles contained in this dispersion was 510 nm. The zeta potential of the electrophoretic white particles was +5.3 mV.
In a sample bottle, 28.7 parts of electrophoretic black particle dispersion liquid, 60 parts of electrophoretic white particle dispersion liquid, and 11.3 parts of Isopar M1 were charged and mixed thoroughly to obtain an electrophoretic dispersion liquid (A-1). . In the electrophoresis dispersion liquid (A-1), the concentration of the electrophoretic black particles was 4.3%, and the concentration of the electrophoretic white particles was 30%.

1-2. Electrophoretic dispersion (A-2)
In a separable flask equipped with a stirring blade, a temperature system, and a cooling tube, an acrylic polymer (mass average molecular weight 3,700) 3 consisting of lauryl methacrylate, 2-ethylhexyl acrylate, glycidyl methacrylate (composition molar ratio 80: 15: 5) 3 Part, carbon black ("M-100A" manufactured by Mitsui Chemicals), 10 parts of ISOPAR M, and 800 parts of zirconia beads having a diameter of 1 mm were further charged. The polymer was added to carbon black by reacting at 150 ° C. for 5 hours while stirring at a rotational speed of 300 rpm. After the reaction, 100 parts of hexane was further added to separate zirconia beads. Next, a series of operations of transferring the dispersion containing the electrophoretic black particles (polymer-added carbon black) to the sedimentation tube for centrifugation, performing the centrifugation operation, and washing the electrophoretic black particles with hexane was performed three times. did.
The washed electrophoretic black particles were dispersed in Isopar M to obtain 98 parts of electrophoretic particle dispersion having a solid content concentration of 10%. The volume average particle diameter of the electrophoretic black particles was 180 nm. The zeta potential of the electrophoretic black particles was −10.1 mV.
In a sample bottle, 20 parts of the electrophoretic black particle dispersion, 40 parts of the electrophoretic white particle dispersion obtained in the column for preparation of (A-1), and 40 parts of Isopar M are mixed and mixed thoroughly. (A-2) was obtained. In the electrophoresis dispersion liquid (A-2), the concentration of the electrophoretic black particles was 2%, and the concentration of the electrophoretic white particles was 20%.

1-3. Electrophoretic dispersion (A-3)
In a separable flask equipped with a stirring blade, a thermometer, and a condenser tube, 3-methacryloxypropyldimethylpolysiloxane (“Jiraplan (registered trademark) FM-0711” manufactured by JNC), 2-ethylhexyl acrylate, γ-methacryloxypropyl 10 parts of an acrylic polymer (mass average molecular weight 5,300) composed of trimethoxysilane (composition molar ratio 80: 15: 5), 20 parts of titanium black ("Titanium Black 13M" manufactured by Mitsubishi Materials Corporation), dimethyl silicone oil (Shin-Etsu) 100 parts of “KF-96-2cs” manufactured by Kagaku Kogyo Co., Ltd. was charged, the separable flask was placed in an ultrasonic bath (BRANSON 5210), and dispersion treatment was performed for 3 hours.
The separable flask was transferred to an oil bath, heated to 150 ° C. with stirring, reacted at the same temperature for 5 hours, and a polymer was added to titanium black. After grafting, 100 parts of silicone oil (KF-96-2cs) was further added. Next, a series of operations of transferring the dispersion containing the electrophoretic black particles (polymer-added carbon black) to the sedimentation tube for centrifugation, performing the centrifugation operation, and washing the electrophoretic black particles with silicone oil three times. Carried out.
The washed electrophoretic black particles were dispersed in silicone oil to obtain 57 parts of electrophoretic particle dispersion having a solid content concentration of 35%. The volume average particle diameter of the electrophoretic black particles was 560 nm. The zeta potential of the electrophoretic black particles was -6.2 mV.
On the other hand, in a separable flask equipped with a stirring blade, 50 parts of titanium oxide (“Typaque (registered trademark) CR60” manufactured by Ishihara Sangyo Co., Ltd.), 3-methacryloxypropyldimethylpolysiloxane (manufactured by JNC, “Shiraplane (registered trademark) FM) -0711 "), 10 parts of an acrylic polymer (mass average molecular weight 8,600) consisting of 2-ethylhexyl acrylate and γ-methacryloxypropyltrimethoxysilane (composition molar ratio 80: 15: 5) and 100 parts of hexane, It put into the ultrasonic bath (BRANSON5210), and ultrasonic dispersion was performed for 2 hours, stirring.
The separable flask after the dispersion treatment was transferred to a 90 ° C. hot water tank, and the solvent was distilled off. The powdered polymer-added titanium oxide was taken out of the flask, transferred to a vat, and then heated for 5 hours at 150 ° C. using a dryer. The operation of dispersing the polymer-added titanium oxide after heating in 100 parts of hexane, centrifuging using a centrifugal sedimentator, and washing the electrophoretic white particles (polymer-added titanium oxide) with hexane is performed three times. The electrophoretic white particles were dried at 100 ° C.
In another separable flask, 50 parts of washed electrophoretic white particles were charged in 50 parts of dimethyl silicone oil (“KF-96-2cs” manufactured by Shin-Etsu Chemical Co., Ltd.), placed in an ultrasonic bath (BRANSON 5210), The sonic dispersion treatment was performed for 2 hours to obtain 100 parts of an electrophoretic white particle dispersion having a solid concentration of 50%. The volume average particle diameter of the electrophoretic white particles contained in this dispersion was 530 nm. The zeta potential of the electrophoretic white particles was +3.9 mV.
A sample bottle is charged with 18 parts of an electrophoretic black particle dispersion, 80 parts of an electrophoretic white particle dispersion, and 2 parts of silicone oil (KF-96-2cs), mixed well, and electrophoretic dispersion (A-3). ) In the electrophoresis dispersion liquid (A-3), the concentration of the electrophoretic black particles was 6.3%, and the concentration of the electrophoretic white particles was 40%.

2. Microcapsule Synthesis Example 1
A separable flask was charged with 8 parts of melamine, 8 parts of urea, 40 parts of 37% formaldehyde aqueous solution, and 2 parts of 25% aqueous ammonia, and allowed to react at 70 ° C. for 1 hour with stirring to obtain an aqueous solution of melamine / urea / formaldehyde initial condensate. (B-1) was obtained. The solid content concentration of the aqueous solution was 53.1%.

  In another container, 120 parts of an aqueous solution in which 20 parts of gum arabic was dissolved was added, and 100 parts of electrophoretic dispersion (A-1) was added under stirring with a disper ("ROBOMIX (registered trademark)" manufactured by Primix). The suspension of the microcapsule particle precursor was obtained by adjusting the stirring speed. The particle diameter of the precursor was visually confirmed using an optical microscope. 100 parts of water was added to the obtained suspension to adjust the concentration.

  The obtained suspension was put into a separable flask equipped with a thermometer and a cooling tube, the temperature of the solution was raised to 40 degrees with stirring, and 48 parts of the aqueous solution (B-1) was added. After 15 minutes, 100 parts of an aqueous solution of 2% L-cysteine was added dropwise over 5 minutes with a dropping funnel. After stirring at 40 ° C. for 4 hours, the temperature was raised to 60 ° C., aged for 2 hours, and then cooled to obtain microcapsules having an amino resin as a wall material. The coarse capsule was removed with a sieve having an opening of 53 μm, and then the microcapsule was washed with a large amount of water. The volume average particle size of the microcapsules for electrophoretic display thus obtained was measured using a particle size distribution measuring device (“Multizer 4” manufactured by Beckman Coulter, Inc.). The microcapsules for electrophoretic display were subjected to suction filtration to obtain microcapsule paste (C-1) for electrophoretic display (nonvolatile content is listed in Table 1). 2 parts of this microcapsule paste (C-1) was dried for 24 hours with a hot air dryer heated to 50 ° C. to obtain a microcapsule powder for electrophoretic display. The true specific gravity of the microcapsules for electrophoretic display was measured for this powder using a dry automatic densimeter (“Accuic II 1340” manufactured by Shimadzu Corporation). The results are shown in Table 1.

Synthesis Example 2 to Synthesis Example 7
A microcapsule paste for electrophoretic display was obtained in the same manner as in Synthesis Example 1 except that the stirring speed of the disper ("ROBOMIX" manufactured by PRIMIX Co., Ltd.) and the opening of the sieve were changed as shown in Table 1. The results are shown in Table 1.

3. Preparation of binder liquid A resistance adjuster was added to an aqueous polyurethane resin dispersion or an acrylic resin aqueous dispersion to prepare a binder liquid. If problems such as agglomeration occur when mixing with a polyurethane resin aqueous dispersion, depending on the type of resistance adjuster, eliminate the problem by adjusting the pH or adding a small amount of solvent or surfactant. did. The properties of the prepared binder liquid are shown in Table 2.

4). Preparation of paint A paint having a composition as shown in Table 3 was prepared using the prepared microcapsule paste for electrophoretic display, a binder liquid and deionized water. The coating material was produced by mixing for 10 minutes using a mixer (“Shintaro Awatori (registered trademark) AR-100” manufactured by Shinky Corporation).

5. Preparation of Overcoat Liquid A resistance adjuster was added to an aqueous polyurethane resin dispersion or an acrylic resin aqueous dispersion to prepare an overcoat liquid. As in the case of preparing the binder resin, depending on the type of resistance adjuster, if problems such as aggregation occur when mixing with the polyurethane resin aqueous dispersion, adjust the pH or add a small amount of solvent or surfactant. The problem was solved by adding it. Table 4 shows the characteristics of the prepared overcoat solution.

6). Examples and Comparative Examples As a slot die type coating apparatus, a desktop die coater (“table die” manufactured by ITOCHU MACHINE TECHNOS), and a slot die (land length 30 mm, land clearance 0.02 mm, discharge width 290 mm, lip length 100 μm) ) Was used. As the substrate, a PET film with an ITO electrode having a substrate thickness of 125 μm (“High Beam (registered trademark) NXC1” manufactured by Toray Film Processing Co., Ltd.) was used.
The coating material was applied on the base material using the coating device. The coating speed was adjusted to 5 mm / s, the gap length was adjusted to 100 μm, and the wet film thickness at the time of coating was adjusted to the microcapsule particle size so that the microcapsules were arranged in one layer as much as possible after the coating film was dried. That is, the apparatus was adjusted so that the wet film thickness at the time of coating was 0.06 to 0.08 mm.
After coating the paint, the coating film was sufficiently dried, and then the overcoat solution was applied onto the coated surface on which the microcapsules were applied using the desktop die coater used for coating the capsule. In Comparative Examples 1 and 2, after the coated overcoat solution was dried, the overcoat solution was further applied to thicken the overcoat layer.
The overcoat solution was sufficiently dried to obtain a coated sheet. Using this coated sheet, the thickness of each layer was evaluated by the method described above. The results are shown in Tables 5-6.

  Further, from the obtained coated sheet, the coated portion was cut out in a state where the coating-uncoated portion was left on one side so that the vertical × horizontal = 5 cm × 3 cm, and the vertical / horizontal = 6 cm × 4 cm as a counter electrode, A 75 μm thick ITO electrode-attached PET film (“High Beam (registered trademark) NXC1” manufactured by Toray Film Processing Co., Ltd.) is bonded, and any two locations are fixed with cello tape (registered trademark), and laminated on a 2 mm thick glass plate. By placing the laminate so that the surface is on the upper roll side and laminating the laminate using a laminating apparatus (manufactured by Taisei Laminator) at a roll temperature of 80 ° C., a feed rate of 5 cm / min, and a laminating pressure of 0.45 MPa, A sheet for electrophoretic display (S-1) was produced. Tables 5 to 6 show the characteristics of the obtained sheet for electrophoretic display devices.

  In the sheets for electrophoretic display devices obtained in Examples 1 to 7, the volume resistivity of the binder layer is higher than the volume resistivity of the overcoat layer, and the maximum thickness of the binder layer is the volume average of the microcapsules. It is 60 to 92% of the particle diameter. Therefore, these sheets can exhibit a contrast of 8.0 or more, and in addition, the black display retention is good.

  On the other hand, in Comparative Example 1, the overcoat layer has a thickness of 40 μm or more, which is about twice the particle size of the microcapsules. In Comparative Example 1, an electrode with ITO is used as a counter electrode, but the value of black reflectance is poor and the contrast is low. In such a sheet, when a segment electrode or a dot electrode typified by TFT is used as the display electrode, a leak current is generated between the display electrodes, and a sufficient electric field does not act on the microcapsules. Therefore, with such a sheet, there is a concern that the display performance is low, the edges between the electrodes are unclear, and the display quality is degraded.

  In Comparative Example 2, the maximum thickness of the binder layer is less than 60% of the volume average particle diameter of the microcapsules. For this reason, when the overcoat layer is applied, it seems that the overcoat layer cannot completely fill the gaps between the microcapsules, and a part of the gaps remain. Therefore, the sheet of this comparative example cannot exert a sufficient electric field on the microcapsules and is inferior in terms of contrast and black display retention.

  In Comparative Example 3, since the thickness of the binder layer exceeds 92% of the volume average particle diameter of the microcapsules and the overcoat layer is thin, the display is due to the difference in volume resistivity between the binder coat layer and the overcoat layer. The performance improvement effect is not fully exhibited. Therefore, the sheet of this comparative example is inferior in terms of contrast and black display retention.

  In Comparative Example 4, as in Comparative Example 2, the maximum thickness of the binder layer is less than 60% of the volume average particle diameter of the microcapsules. Therefore, the sheet of this comparative example cannot exert a sufficient electric field on the microcapsules and is inferior in terms of contrast and black display retention. In addition, in Comparative Example 4, since the volume resistivity of the binder layer is high, the electrophoretic particles in the microcapsules cannot be sufficiently migrated under the conditions of an applied voltage of 15 V and an applied time of 0.4 seconds. For this reason, the sheet of this comparative example has a low contrast and an extremely low value indicating black display retention.

  In Comparative Example 5, the volume resistivity of the overcoat layer is higher than the volume resistivity of the binder layer. In such a case, the reason is unknown, but when black is displayed, a phenomenon is observed in which the reflectance gradually decreases after the reflectance rapidly decreases. Therefore, the sheet of this comparative example is a sheet with low contrast and poor black display retention. In addition, the kickback phenomenon (a phenomenon in which a reverse electric field occurs in the capsule after the electrophoretic black particles adhere to the inner wall of the microcapsule and the attached black particles fall off) is observed because the volume resistivity of the binder layer is low. It was.

1 Sheet for Electrophoretic Display 2 First Base Material 3 Binder Layer 4 Overcoat Layer I
5 Overcoat layer II
6 Microcapsules 7 Second base material

Claims (6)

A first substrate, a microcapsule, a binder layer for fixing the microcapsule to the first substrate, an overcoat layer laminated on the binder layer, and a second substrate laminated on the overcoat layer An electrophoretic display device sheet comprising:
The volume resistivity of the binder layer is higher than the volume resistivity of the overcoat layer,
The electrophoretic display device sheet, wherein the binder layer has a maximum thickness of 60 to 92% of a volume average particle diameter of the microcapsules.   2. The electrophoretic display device sheet according to claim 1, wherein the volume ratio of the microcapsules is 30 to 75% in the capsule layer existing between the first substrate and the second substrate.   The sheet for electrophoretic display devices according to claim 1, wherein a difference between the thickness of the capsule layer and the microcapsule volume average particle diameter is within ± 10 μm. The volume resistivity of the binder layer at 25 ° C. is 1 × 10 ^{7 to} 9 × 10 ¹¹ Ωcm, and the volume resistivity of the overcoat layer is 2 × 10 ^{6 to} 9 × 10 ⁸ Ωcm. The sheet | seat for electrophoretic display devices of any one of these.   The sheet for electrophoretic display devices according to claim 1, wherein the shell of the microcapsule contains an amino resin.   An electrophoretic display device comprising the electrophoretic display device sheet according to claim 1.