JP2006113390A - Electrophoretic particle, its manufacturing method, and electrophoretic display device using electrophoretic particle dispersion liquid - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve problems, wherein generally a pigment has poor dispersibility and electrophoretic particles obtained in steps of dispersing a pigment in a solution, in which a polymer is dissolved, baking and pulverizing shows a very poor coloring state of particles, because of the aggregation and turning into an inhomogeneous state of the pigment in the polymer. <P>SOLUTION: The electrophoretic particles contain a pigment dispersed uniformly in polymer fine particles by uniformly dispersing a polymer-grafted pigment in a polymerizable monomer, and polymerizing the obtained composition. By copolymerization of the polymer grafted to the pigment with the polymerizable monomer, the pigment is fixed within the particles. Moreover, a shell layer which prevents mutual aggregation of particles is formed on the particle surface. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an electrophoretic display element using an electrophoretic particle dispersion containing an electrophoretic particle, a method for producing the same, and an electrophoretic particle dispersion containing the electrophoretic particle.

  In recent years, with the development of information equipment, the need for low power consumption and thin display elements has increased, and research and development of display elements that meet these needs has been actively conducted. Among them, the liquid crystal display element can change the optical characteristics of the liquid crystal by electrically controlling the arrangement of liquid crystal molecules, and has been actively developed and commercialized as a display element that can meet the above needs. . However, these liquid crystal display elements sufficiently solve the problem that it is difficult to see characters on the screen due to the angle and reflected light when viewing the screen, or the visual burden caused by flickering of the light source, low luminance, etc. Absent. For this reason, research on display elements with less visual burden has been actively studied.

  As one of such display elements, an electrophoretic display element invented by Evans et al. Is known (see Patent Document 1). The electrophoretic display element includes a pair of substrates arranged with a predetermined gap therebetween, and electrodes are formed on each substrate. The gap between the substrates is filled with a large number of electrophoretic particles that are positively charged and colored, and a dispersion medium that is colored with a color different from the electrophoretic particles. Further, the partition is arranged so as to divide the gap into a large number of pixels along the surface direction of the substrate, and is configured to prevent the uneven distribution of the electrophoretic particles and to define the substrate gap.

  In such an electrophoretic display element, when a positive voltage is applied to the electrode on the viewer side and a negative voltage is applied to the opposite electrode, the positively charged electrophoretic particles are applied to the opposite electrode. When the display element is viewed from the observer, the same color as the dispersion medium is displayed. On the other hand, when a negative voltage is applied to the electrode on the viewer side and a positive voltage is applied to the electrode on the opposite side, the electrophoretic particles gather to cover the electrode on the viewer side, and the display element is moved from the viewer. When viewed, the same color as the electrophoretic particles is displayed. By performing such driving in units of pixels, an arbitrary image or character is displayed by a large number of pixels.

As a method for producing electrophoretic particles used in conventional electrophoretic display elements, a pigment is mixed into a solution obtained by dissolving a polymer in a highly volatile organic solvent, and then subjected to steps such as baking and pulverization, and then the pigment is polymerized. Is disclosed (see Patent Document 2).
US Pat. No. 3,612,758 Japanese Patent Publication No. 61-25139

  Pigments are generally poorly dispersible, and it is extremely difficult to uniformly disperse pigments in a solution in which a polymer is dissolved by conventional methods for producing electrophoretic particles. As a result, the electrophoretic particles produced by such a method have a problem that the pigments aggregate in the polymer and become non-uniform so that the degree of coloring of the particles may be lowered. In addition, when the pigment is exposed on the surface of the electrophoretic particles, there is a problem that the electrophoretic particles aggregate.

  An object of the present invention is to provide an electrophoretic particle excellent in coloring degree and dispersibility, a method for producing the same, and an electrophoretic display element excellent in using such an electrophoretic particle.

  As a result of various studies to solve such problems, the present inventor has found electrophoretic particles having better coloring and dispersibility than conventional electrophoretic particles, and has led to the present invention. is there.

That is, the electrophoretic particle of the present invention is an electrophoretic particle in which a pigment is dispersed in a polymer fine particle, and the polymer fine particle is copolymerized with the first polymer portion grafted to the pigment and the first polymer portion. A pigment having a polymer grafted with the polymer to be the first polymer part dispersed in a polymerizable monomer for forming the second polymer part in a state of being dispersed in the polymerizable monomer for forming the second polymer part. It is an electrophoretic particle obtained by polymerizing a polymerizable monomer.

The method for producing an electrophoretic particle of the present invention is a method for producing an electrophoretic particle in which a pigment is dispersed in polymer fine particles, and includes a pigment grafted with a polymer, a polymerization initiator, and a polymerizable monomer. A first polymer portion comprising a polymer grafted to the pigment by polymerizing the polymerizable monomer in a state where the composition in which the grafted pigment is dispersed is suspended in a suspension medium; An electrophoretic particle comprising: a step of obtaining an electrophoretic particle in which the pigment is dispersed in a polymer fine particle having a second polymer portion obtained from the polymerizable monomer copolymerized with the first polymer portion. It is a manufacturing method.

  The electrophoretic particle dispersion of the present invention is an electrophoretic particle dispersion characterized by containing the above electrophoretic particles and an electrophoretic particle dispersion medium.

An electrophoretic display element of the present invention includes a container for storing an electrophoretic particle dispersion containing electrophoretic particles and an electrophoretic particle dispersion medium, a display unit provided in at least a part of the container, and the display unit. An electrophoretic particle having a voltage applying means for causing movement of the electrophoretic particle according to display information, and performing display based on the presence or absence of the electrophoretic particle in the display unit. An electrophoretic display element, wherein the dispersion is the electrophoretic particle dispersion according to claim 9.

  In the electrophoretic particle of the present invention, a pigment grafted with a polymer is dispersed in a composition containing a polymerization initiator and a polymerizable monomer, and the composition in which the pigment is dispersed is further converted into a particulate state to form a polymerizable monomer. The pigment is coated with a polymer and is uniformly dispersed in the polymer fine particles. In addition, the pigment is immobilized in the particles by copolymerization of the polymer grafted to the pigment and the polymerizable monomer. Furthermore, a shell layer that prevents aggregation of the electrophoretic particles may be formed on the surface of the electrophoretic particles. From the above, the present invention can provide an electrophoretic particle having a better coloring degree and dispersibility than conventional electrophoretic particles, and a method for producing the same.

  An embodiment of an electrophoretic display element using electrophoretic particles of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view showing one embodiment of an electrophoretic display element using electrophoretic particles of the present invention. In the electrophoretic display element of FIG. 1A, the first substrate 1a provided with the first electrode 1c and the second substrate 1b provided with the second electrode 1d are opposed to each other at a predetermined interval through the partition wall 1g. Is arranged. An electrophoretic particle dispersion liquid composed of at least electrophoretic particles 1e and an electrophoretic particle dispersion medium 1f is enclosed in a cell (space) partitioned by the first substrate 1a, the second substrate 1b, and the partition walls 1g. An insulating layer 1h is formed on each electrode. That is, a container for storing the electrophoretic particle dispersion is formed by the first substrate 1a, the second substrate 1b, and the partition walls 1g. In the electrophoretic display element, the side on which the second substrate 1b is provided is a display surface.

  FIG. 1B shows an electrophoretic display element using microcapsules. A microcapsule 1i enclosing the electrophoretic particle dispersion is disposed on the first substrate 1a and covered with the second substrate 1b. When the microcapsule 1i is used, the insulating layer 1h may not be provided.

  In FIG. 1, the first electrode 1c is a pixel electrode that can independently apply a desired electric field to the electrophoretic particle dispersion in each cell (or microcapsule), and the second electrode 1d is the same over the entire surface. It is a common electrode applied with a potential. These electrodes constitute voltage applying means. This pixel electrode is provided with a switch element, a selection signal is applied to each row from a matrix drive circuit (not shown), and a control signal and an output from the drive transistor are applied to each column. A desired electric field can be applied to the electrophoretic particle dispersion in the cell (or microcapsule). The electrophoretic particles 1e in each cell (or microcapsule) are controlled by the electric field applied by the first electrode 1c, and each pixel has a color of the electrophoretic particles (for example, white) and a color of the dispersion medium (for example, blue). Is displayed. By performing such driving in units of pixels, an arbitrary image or character can be displayed by a large number of pixels.

(Configuration of electrophoretic display element)
The first substrate 1a is an arbitrary insulating member that supports the electrophoretic display element, and glass, plastic, or the like can be used. For the first electrode 1c, a metal vapor-deposited film such as ITO (Indium Tin Oxide), tin oxide, indium oxide, gold, or chromium can be used, and a photolithography method is used for pattern formation of the first electrode 1c. be able to.
As the second substrate 1b, an insulating member such as a transparent glass substrate or a plastic substrate can be used. A transparent electrode such as ITO or an organic conductive film can be used for the second electrode 1d.
As the insulating layer 1h, a colorless and transparent insulating resin can be used. For example, acrylic resin, epoxy resin, fluorine resin, silicone resin, polyimide resin, polystyrene resin, polyalkene resin, or the like can be used.

  A polymer resin can be used as the material of the partition wall 1g. Any method may be used for forming the partition wall. For example, a method of forming a partition wall by a photolithography method using a photosensitive resin, a method of bonding a partition wall prepared in advance to a substrate, or a partition wall by a mold. A forming method or the like can be used.

  The method of filling the electrophoretic particle dispersion into the cell is not particularly limited, but an inkjet type nozzle can be used.

(Micro capsule)
The microcapsule 1i enclosing the electrophoretic particle dispersion can be obtained by a known method such as an interfacial polymerization method, an in situ polymerization method, or a coacervation method. The material that forms the microcapsule 1i is preferably a material that transmits light sufficiently. Specifically, urea-formaldehyde resin, melamine-formaldehyde resin, polyester, polyurethane, polyamide, polyethylene, polystyrene, polyvinyl alcohol, gelatin, or These copolymers can be mentioned.

  Further, the method for disposing the microcapsule 1i on the first substrate 1a is not particularly limited, but an ink jet type nozzle can be used.

  For the purpose of preventing the displacement of the microcapsule 1i disposed on the substrate, the gap between the microcapsules 1i may be impregnated with a light-transmitting resin binder and fixed on the substrate. Examples of the light-transmitting resin binder include water-soluble polymers, such as polyvinyl alcohol, polyurethane, polyester, acrylic resin, and silicone resin.

When sealing the first substrate 1a and the second substrate 1b, the microcapsule 1i is pressed down so that the length in the horizontal direction is longer than the length in the vertical direction with respect to the first substrate 1a. It is preferable to seal between the substrates. (See Fig. 1 (b))
(Electrophoretic particle dispersion medium)
Examples of the electrophoretic particle dispersion medium 1f include highly insulating and colorless and transparent liquids. For example, aromatic hydrocarbons such as toluene, xylene, ethylbenzene, and dodecylbenzene, aliphatic hydrocarbons such as hexane, cyclohexane, kerosene, normal paraffin, and isoparaffin can be used. These can be used alone or in combination of two or more. It may be used.

(dye)
In order to color the electrophoretic particle dispersion medium 1f, oil-soluble dyes having colors such as R (red), G (green), B (blue), C (cyan), M (magenta), and Y (yellow) are used. be able to. These oil-soluble dyes include azo dyes, anthraquinone dyes, quinoline dyes, nitro dyes, nitroso dyes, penoline dyes, phthalocyanine dyes, metal complex dyes, nafur dyes, benzoquinone dyes, cyanine dyes, indigo dyes, and quinoimine dyes. Dyes are preferred, and these may be used in combination.

  For example, the following oil-soluble dyes can be mentioned. Bali First Yellow (1101, 1105, 3108, 4120), Oil Yellow (105, 107, 129, 3G, GGS), Bali First Red (1306, 1355, 2303, 3304, 3306, 3320), Oil Pink 312, Oil Scarlet 308, Oil Violet 730, Bali First Blue (1501, 1603, 1605, 1607, 2606, 2610, 3405), Oil Blue (2N, BOS, 613), Macrolex Blue RR, Sumiplast Green G, Oil Green (502 BG) and the like, and the concentration of the oil-soluble dye is preferably 0.1 to 3.5% by weight with respect to the electrophoretic particle dispersion medium 1f.

(Electrophoretic particles)
The electrophoretic particle according to the present invention has a structure in which a pigment is dispersed in a polymer layer, the first polymer in which the polymer layer is grafted to the pigment, and the second polymer copolymerized with the first polymer. Is included. The electrophoretic particles are formed by a suspension polymerization method, which will be described later, so that the pigment is uniformly dispersed in the polymer layer and the pigment layer is not exposed on the surface of the polymer layer. Furthermore, the electrophoretic particles of the present invention may have a shell layer that prevents aggregation of the electrophoretic particles outside the polymer layer, and the shell layer is a polymer having a high affinity for the electrophoretic particle dispersion medium. Preferably there is. In the case of having this shell layer, the portion made of the polymer layer becomes the core.

  In the electrophoretic particle according to the present invention having the above-described configuration, a pigment grafted with a polymer is dispersed in a phase containing a polymerization initiator and a polymerizable monomer, and this phase is suspended in a suspension medium as particles. It can be obtained by polymerizing a polymerizable monomer in a heated state. As a suspension medium for carrying out this suspension polymerization, an aqueous suspension medium containing a suspension stabilizer can be preferably used. A polymer in which the pigment is uniformly dispersed in the polymer fine particles, and the polymer grafted to the pigment is used. Electrophoretic particles in which a polymerizable monomer is copolymerized can be obtained. Furthermore, an electrophoretic particle having a core / shell structure can be obtained by forming a shell layer on the outer surface of the electrophoretic particle as a core.

  Hereinafter, an example of manufacturing electrophoretic particles having a core / shell structure will be described.

(Core formation)
The core of the electrophoretic particle 1e is obtained by suspending a core composition containing a polymer-grafted pigment, a core polymerization initiator, and a core polymerizable monomer in an aqueous suspension medium containing a suspension stabilizer. By polymerizing, the pigment is uniformly dispersed in the polymer fine particles, and a core in which the polymer grafted to the pigment and the polymerizable monomer are copolymerized can be formed. In this case, the polymer grafted on the pigment becomes the first polymer portion described above, and the polymerizable monomer is polymerized to become the second polymer portion described above.

  More specifically, the pigment grafted with the polymer is uniformly dispersed with a dispersing device in the core composition containing the core polymerization initiator and the core polymerizable monomer. As a device for dispersing the grafted pigment in the composition containing the polymerizable monomer for the core, a shear type dispersion device such as a homogenizer, a homomixer or a biomixer, a media type dispersion device such as a ball mill, an attritor or a sand mill, A sonic dispersion device or the like can be used.

  The core composition in which the pigment is dispersed is put into a suspension medium, and granulated to a particle size close to the target particle size using a dispersing device. As a device for suspending the core composition in the suspension medium, a dispersing device such as a homogenizer, a homomixer, or a line mixer can be used. Any suspension medium may be used as long as it can suspend the core composition. If the core composition is suspended in water, an aqueous suspension medium containing a suspension stabilizer is preferably used. be able to.

  The polymerizable monomer is polymerized from the suspension under an inert gas. Nitrogen gas or argon gas can be used as the inert gas. The polymerization temperature varies depending on the type of core polymerization initiator used, but is preferably in the range of about 50 to 90 ° C. The polymerization time is preferably 0.5 to 30 hours, and more preferably 2 to 10 hours.

(Suspension stabilizer)
Suspension stabilizers include phosphates such as calcium phosphate, magnesium phosphate, aluminum phosphate and zinc phosphate, pyrophosphates such as calcium pyrophosphate, magnesium pyrophosphate, aluminum pyrophosphate and zinc pyrophosphate, calcium carbonate, carbonate Water-insoluble inorganic compounds such as magnesium, calcium hydroxide, magnesium hydroxide, aluminum hydroxide, calcium sulfate, barium sulfate, and colloidal silica; water-soluble materials such as polyvinyl alcohol, carboxymethyl cellulose, hydroxyethyl cellulose, methyl cellulose, starch, and sodium polyacrylate A functional polymer. The suspension stabilizer is preferably from 0.01 to 30% by weight, more preferably from 0.1 to 20% by weight, based on the core composition.

(Surfactant)
In addition, a surfactant such as an anionic surfactant, a cationic surfactant, a nonionic surfactant, and an amphoteric surfactant may be added to the suspension medium as necessary.

  Anionic surfactants include alkyl sulfates, alkyl sulfonates, fatty acid salts, polyoxyethylene alkyl phenyl ether sulfates, polyoxyethylene alkyl sulfates, alkyl naphthalene sulfonates, alkane sulfonates, alkyl phosphates. Salt and the like can be used.

As the cationic surfactant, an alkylamine salt, a quaternary ammonium salt, or the like can be used.
As the nonionic surfactant, polyoxyethylene alkyl phenyl ether, polyoxyethylene alkyl ether, polyoxyethylene fatty acid ester, sorbitan fatty acid ester, polyoxysorbitan fatty acid ester, glycerin fatty acid ester and the like can be used. As the amphoteric surfactant, lauryldimethylamine oxide can be used.

  The surfactant is preferably 0.01 to 10% by weight, more preferably 0.05 to 5% by weight, based on the core composition in which the pigment is dispersed.

  In addition, a thickener such as glycerin or ethylene glycol may be added to the suspension medium as necessary for the purpose of preventing coalescence of particles obtained by polymerization.

(Pigment)
As the pigment, an organic pigment, an inorganic pigment, or the like can be used. Examples of organic pigments include azo pigments, phthalocyanine pigments, quinacridone pigments, isoindolinone pigments, isoindoline pigments, dioxazine pigments, perylene pigments, perinone pigments, thioindigo pigments, quinophthalone pigments, anthraquinone pigments, nitro pigments, and nitroso pigments. Specifically, red pigments such as quinacridone red, lake red, brilliant carmine, perylene red, permanent red, toluidine red, madder lake, green pigments such as diamond green lake, phthalocyanine green, pigment green B, Victoria Blue pigments such as Blue Lake, Phthalocyanine Blue, Fast Sky Blue, Hansa Yellow, Fast Yellow, Disazo Yellow, Isoindolinone Yellow, Quinophthalo Yellow pigments such as yellow, aniline black, black pigments such as diamond black.

  Examples of inorganic pigments include white pigments such as titanium oxide, aluminum oxide, zinc oxide, lead oxide, tin oxide, and zinc sulfide, black pigments such as carbon black, manganese ferrite black, cobalt ferrite black, and titanium black, and cadmium red. Red pigments such as red iron oxide and molybdenum red, green pigments such as chromium oxide, viridian, titanium cobalt green, cobalt green and victoria green, blue pigments such as ultramarine blue, Prussian blue and cobalt blue, cadmium yellow and titanium yellow Yellow pigments such as yellow iron oxide, yellow lead, chrome yellow, and antimony yellow can be used.

  The average particle size of the pigment is preferably 10 to 500 nm, more preferably 20 to 200 nm. If the average particle diameter of the pigment is less than 10 nm, handling is extremely lowered, which is not preferable. In addition, when the average particle diameter of the pigment exceeds 500 nm, it is not preferable because the coloring degree of the pigment is lowered or the electrophoretic particles are not suitable for reducing the particle diameter.

(Polymer grafting of pigment)
The cohesive force between the pigments is extremely large when compared with the affinity between the pigment and the other medium. Therefore, it is difficult to disperse the pigment in the medium on the submicron order. However, when a polymer is grafted on the pigment, aggregation of the pigments can be inhibited.

  Grafting a polymer with a pigment means that the polymer is irreversibly bound to the primary particles of the pigment or an aggregate of several primary particles.

  When the grafted polymer has a high affinity with the medium, the pigment grafted with the polymer can be dispersed in the medium on the submicron order. That is, by coating the pigment surface with the grafted polymer, the core polymerizable monomer having high affinity with the grafted polymer and the pigment can be uniformly dispersed in the polymerized layer, and the pigment is coated on the polymer layer surface. It can have a structure that is not exposed.

  As a method for grafting a polymer to a pigment, a conventionally known method can be used. For example, a method of polymerizing a polymerizable monomer in the presence of a pigment, a method of reacting a polymer having a reactive group that reacts with a functional group present on the pigment surface and the pigment, a radical generating group such as an azo group or a peroxide group. Introduced to the pigment surface, decomposes radical generating groups on the pigment surface in the presence of polymerizable monomers to generate radicals, and polymerizes the polymerizable monomer on the pigment surface via these radicals, azo groups, peroxide groups, etc. And a method in which a polymer having a radical generating group is thermally decomposed in the presence of a pigment and the generated polymer radical is radical trapped in the pigment.

  As the graft polymer (polymer used for grafting), a polymer having a high affinity with the core polymerizable monomer described later is desirable. Here, the high affinity means that the graft polymer and the polymerizable monomer for the core are excellent in compatibility without phase separation. For example, when the core polymerizable monomer is a styrene monomer, a styrene polymer is preferable as the graft polymer. Further, when the polymerizable monomer for the core is a (meth) acrylic acid ester monomer, a (meth) acrylic acid ester polymer is preferable as the graft polymer.

  The polymer used for grafting preferably contains at least one of a methine group and a methylene group. That is, in a graft polymer containing either a methine group or a methylene group, a hydrogen atom is extracted by a free radical generated by thermal decomposition of a core polymerization initiator described later, and a radical is generated on the graft polymer. The pigment is fixed in the particles by copolymerizing the radical on the graft polymer and the polymerizable monomer for the core. The ease with which the hydrogen atom is extracted by the core polymerization initiator is that the hydrogen atom of the methine group (tertiary hydrogen) is easier than the hydrogen atom of the methylene group (secondary hydrogen). More preferably, the graft polymer contains a methine group.

  As a graft polymer, you may use the monomer described below individually or in mixture of 2 or more types. For example, 4-isobutylstyrene, 4- (2-methylbutyl) styrene, 4-isoamylstyrene, 4- (3-methylpentyl) styrene, 4- (n-propyl) styrene, 4- (n-butyl) styrene, 4 -Styrene monomers such as (n-pentyl) styrene and 4- (n-hexyl) styrene, isopropyl (meth) acrylate, 1-methylpropyl (meth) acrylate, 2-methylpropyl (meth) acrylate, ( 1-ethylpropyl (meth) acrylate, 2-methylbutyl (meth) acrylate, 2-ethylbutyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, n-propyl (meth) acrylate, (meth) acrylic acid (Meth) acrylic such as n-butyl, n-pentyl (meth) acrylate, n-hexyl (meth) acrylate Ester monomers, isopropyl vinyl ether, 1-methylpropyl vinyl ether, 1-ethylpropyl vinyl ether, isobutyl vinyl ether, 2-methylbutyl vinyl ether, 2-ethylbutyl vinyl ether, propyl vinyl ether, butyl vinyl ether, and other vinyl ether monomers, propyl vinyl ketone, butyl Examples thereof include vinyl ketone monomers such as vinyl ketone, pentyl vinyl ketone, hexyl vinyl ketone, isobutyl vinyl ketone, and 2-methylbutyl vinyl ketone. The weight average molecular weight of the polymer grafted to the pigment is not particularly limited, but can be selected from the range of 1000 to 500,000. The amount of the polymer grafted to the pigment relative to the pigment can be selected from the range of 0.01 to 90% by weight.

  The pigment grafted with the polymer is preferably 1 to 50% by weight based on the polymerizable monomer for the core.

(Polymerizable monomer for core)
As the polymerizable monomer for the core, those capable of dispersing the pigment, forming suspended particles in the suspension medium, and further copolymerizing with the polymer grafted on the pigment are used. Among them, those having affinity for the polymer grafted to the pigment and favorably proceeding with the polymer drafted to the pigment in the core composition are preferable. As such a polymerizable monomer for the core, various vinyl monomers can be used. Specifically, styrene, 2-methylstyrene, 3-methylstyrene, 4-methylstyrene, 2-ethylstyrene, 3-ethylstyrene, 4-ethylstyrene, 3- (n-propyl) styrene, 4- (n -Propyl) styrene, 3-isopropylstyrene, 4-isopropylstyrene, 4- (n-butyl) styrene, 4- (2-methylbutyl) styrene, 4-isoamylstyrene, 4- (n-pentyl) styrene, 4- ( 3-methylpentyl) styrene, 4- (n-hexyl) styrene, 4-tert-butylstyrene, 2,3-dimethylstyrene, 3,4-dimethylstyrene, 2,4-dimethylstyrene, 2,6-dimethylstyrene 2,3-diethylstyrene, 3,4-diethylstyrene, 2,4-diethylstyrene, 2,6-diethyls Styrene monomers such as len, 2-methyl-3-ethylstyrene, 2-methyl-4-ethylstyrene, α-methylstyrene, methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate , (Meth) acrylic acid isopropyl, (meth) acrylic acid n-butyl, (meth) acrylic acid 1-methylpropyl, (meth) acrylic acid 2-methylpropyl, (meth) acrylic acid n-pentyl, (meth) acrylic (Meth) acrylate esters such as 1-ethylpropyl acid, 2-methylbutyl (meth) acrylate, n-hexyl (meth) acrylate, 2-ethylbutyl (meth) acrylate, 2-ethylhexyl (meth) acrylate Monomer, isopropyl vinyl ether, 1-methylpropyl vinyl ether, 1-ethylpropyl vinyl Ether, isobutyl vinyl ether, 2-methylbutyl vinyl ether, 2-ethylbutyl vinyl ether, butyl vinyl ether, propyl vinyl ether, methyl vinyl ether, ethyl vinyl ether and other vinyl ether monomers, methyl vinyl ketone, ethyl vinyl ketone, propyl vinyl ketone, butyl vinyl ketone, Examples thereof include vinyl ketone monomers such as pentyl vinyl ketone, hexyl vinyl ketone, isobutyl vinyl ketone and 2-methylbutyl vinyl ketone, and these may be used alone or in admixture of two or more. Furthermore, it is preferable to select and use those having an affinity for the polymer drafted into the pigment. The weight average molecular weight of the polymer obtained from the core polymerizable monomer can be selected from 10,000 to 5,000,000.

  Moreover, you may use a crosslinking agent together as needed. Examples of the crosslinking agent include divinylbenzene, divinylnaphthalene, ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, tetraethylene glycol di (meth) acrylate, and trimethylolpropane triacrylate. , Allyl (meth) acrylate, 1,3-butanediol di (meth) acrylate, N, N-divinylaniline, divinyl ether and the like, and these may be used alone or in combination of two or more. Good.

(Core polymerization initiator)
The core polymerization initiator is required to be soluble in the core polymerizable monomer and to extract a hydrogen atom from the pigment graft polymer. For the core polymerization initiator, for example, an organic peroxide can be used.

The organic peroxide is generally regarded as a derivative of hydrogen peroxide (H ₂ O ₂ ), and has a structure in which one or two hydrogen atoms of hydrogen peroxide are substituted with an organic atomic group. Since organic peroxide has an —O—O— bond in the molecule, it is thermally decomposed at a relatively low temperature and easily generates free radicals. The generated free radical causes an addition reaction to an unsaturated double bond and a hydrogen atom abstraction reaction. The organic peroxide that can be used in the present invention is diacyl peroxide, dialkyl peroxide, peroxy ketal, peroxy ester and the like. Diacyl peroxide is represented by the following general formula (I), and has a structure in which two hydrogen atoms of hydrogen peroxide are substituted with an acyl group. R and R _{1 in} the general formula (I) are each independently an alkyl group or an aralkyl group.

ジアルキルパーオキサイドは下記の一般式（ＩＩ）で表され、過酸化水素の２個の水素原子をアルキル基、又はアラルキル基で置換した構造を有する。一般式（ＩＩ）のＲ₂、Ｒ₃はそれぞれ独立してアルキル基又はアラルキル基である。

The dialkyl peroxide is represented by the following general formula (II), and has a structure in which two hydrogen atoms of hydrogen peroxide are substituted with an alkyl group or an aralkyl group. R ₂ and R _{3 in} the general formula (II) are each independently an alkyl group or an aralkyl group.

パーオキシケタールは下記の一般式（ＩＩＩ）で表される構造を有する。一般式（ＩＩＩ）のＲ₄、Ｒ₅、Ｒ₆、Ｒ₇はそれぞれ独立してアルキル基である。

Peroxyketal has a structure represented by the following general formula (III). R ₄ , R ₅ , R ₆ and R ₇ in the general formula (III) are each independently an alkyl group.

パーオキシエステルは下記の一般式（ＩＶ）で表され、過酸化水素の１個の水素原子をアルキル基又はアラルキル基で、他方の水素原子をアシル基で置換した構造を有する。一般式（ＩＶ）のＲ₈はアルキル基、アラルキル基、又はアリール基であり、Ｒ₉はアルキル基である。

The peroxyester is represented by the following general formula (IV), and has a structure in which one hydrogen atom of hydrogen peroxide is substituted with an alkyl group or an aralkyl group, and the other hydrogen atom is substituted with an acyl group. R _{8 in the} general formula (IV) is an alkyl group, an aralkyl group, or an aryl group, and R ₉ is an alkyl group.

有機過酸化物として、具体的には、ベンゾイルパーオキサイド、ジ−（３−メチルベンゾイル）パーオキサイド、ベンゾイル（３−メチルベンゾイル）パーオキサイド、ジステアロイルパーオキサイド、ラウロイルパーオキサイド、オクタノイルパーオキサイド、ジ−（３，５，５−トリメチルヘキサノイル）パーオキサイド等のジアシルパーオキサイド、ジ−tert−ブチルパーオキサイド、ジ−tert−ヘキシルパーオキサイド、ジクミルパーオキサイド、tert−ブチルクミルパーオキサイド等のジアルキルパーオキサイド、１，１−ジ（ｔｅｒｔ−ブチルパーオキシ）シクロヘキサン、１，１−ジ（ｔｅｒｔ−ブチルパーオキシ）−２−メチルシクロヘキサン、ｎ−ブチル−４，４−ジ（ｔｅｒｔ−ブチルパーオキシ）バレレート、２，２−ジ（ｔｅｒｔ−ブチルパーオキシ）ブタン、２，２−ジ（４，４−ジ−（ｔｅｒｔ−ブチルパーオキシ）シクロヘキシル）プロパン、１，１−ビス（ｔｅｒｔ−ヘキシルパーオキシ）−３，３，５−トリメチルシクロヘキサン等のパーオキシケタール、クミルパーオキシネオデカノエート、１，１，３，３−テトラメチルブチルパーオキシネオデカノエート、１−シクロヘキシル−１−メチルエチルパーオキシネオデカノエート、tert-ヘキシルパーオキシネオデカノエート、tert-ブチルパーオキシネオデカノエート、tert-ヘキシルパーオキシピバレート、tert-ブチルパーオキシピバレート、１，１，３，３−テトラメチルブチルパーオキシ−２−エチルヘキサノエート、２，５−ジメチル−２，５−ジ（２−エチルヘキサノイルパーオキシ）ヘキサン、tert-ヘキシルパーオキシ−２−エチルヘキサノエート、tert-ブチルパーオキシ−２−エチルヘキサノエート、tert-ブチルパーオキシイソブチレート、tert-ブチルパーオキシ−３，５，５−トリメチルヘキサノエート、tert-ブチルパーオキシラウレート、２，５−ジメチル−２，５−ジ（３−メチルベンゾイルパーオキシ）ヘキサン、tert-ヘキシルパーオキシベンゾエート、２，５−ジメチル−２，５−ジ（ベンゾイルパーオキシ）ヘキサン、tert-ブチルパーオキシアセテート、tert-ブチルパーオキシベンゾエート、tert-ブチルパーオキシ−３−メチルベンゾエート等のパーオキシエステルが挙げられる。

Specific examples of the organic peroxide include benzoyl peroxide, di- (3-methylbenzoyl) peroxide, benzoyl (3-methylbenzoyl) peroxide, distearoyl peroxide, lauroyl peroxide, octanoyl peroxide, Diacyl peroxide such as di- (3,5,5-trimethylhexanoyl) peroxide, di-tert-butyl peroxide, di-tert-hexyl peroxide, dicumyl peroxide, tert-butyl cumyl peroxide, etc. Dialkyl peroxide, 1,1-di (tert-butylperoxy) cyclohexane, 1,1-di (tert-butylperoxy) -2-methylcyclohexane, n-butyl-4,4-di (tert-butylper) Oxy) valerate, 2,2-di tert-butylperoxy) butane, 2,2-di (4,4-di- (tert-butylperoxy) cyclohexyl) propane, 1,1-bis (tert-hexylperoxy) -3,3,5- Peroxyketals such as trimethylcyclohexane, cumylperoxyneodecanoate, 1,1,3,3-tetramethylbutylperoxyneodecanoate, 1-cyclohexyl-1-methylethylperoxyneodecanoate, tert -Hexylperoxyneodecanoate, tert-butylperoxyneodecanoate, tert-hexylperoxypivalate, tert-butylperoxypivalate, 1,1,3,3-tetramethylbutylperoxy-2 -Ethylhexanoate, 2,5-dimethyl-2,5-di (2-ethylhexanoylperoxy) hexa Tert-hexylperoxy-2-ethylhexanoate, tert-butylperoxy-2-ethylhexanoate, tert-butylperoxyisobutyrate, tert-butylperoxy-3,5,5-trimethyl Hexanoate, tert-butyl peroxylaurate, 2,5-dimethyl-2,5-di (3-methylbenzoylperoxy) hexane, tert-hexyl peroxybenzoate, 2,5-dimethyl-2,5- Examples thereof include peroxyesters such as di (benzoylperoxy) hexane, tert-butyl peroxyacetate, tert-butyl peroxybenzoate, and tert-butylperoxy-3-methylbenzoate.

  Among these organic peroxides, those having a high hydrogen abstraction ability include, for example, perbutyl-based organic peroxides that generate tert-butoxy radicals. On the other hand, examples of the organic peroxide having a small hydrogen abstraction ability include a perhexyl organic peroxide that generates a tert-hexyloxy radical.

  The polymerization initiator for the core can be appropriately selected depending on the hydrogen abstraction ability and the solubility in the polymerizable monomer for the core. The core polymerization initiator is preferably 0.1 to 10% by weight based on the core polymerizable monomer.

(Formation of shell layer)
Electrophoretic particles having a core-shell structure can be obtained by adding a polymerizable monomer for shell and a polymerization initiator for shell to the core and polymerizing. Specifically, a shell layer is formed on the surface of the core by adding a polymerizable monomer for shell and a polymerization initiator for shell to the reaction system of the polymerization reaction for forming the core and continuously polymerizing. When the polymerizable monomer for shell and the polymerization initiator for shell are added, these may be added simultaneously, or after adding the polymerizable monomer for shell, the polymerization initiator for shell may be added.

  When reacting with the core, the polymerizable monomer for the shell is preferably controlled to droplets smaller than the average particle diameter of the core. That is, when the particle diameter of the droplets of the polymerizable monomer for the shell is larger than the average particle diameter of the core, it is not preferable because the polymerizable monomer for the shell cannot be uniformly adsorbed on the core surface. In order to control the polymerizable monomer for shell to droplets smaller than the average particle diameter of the core, a mixture of the polymerizable monomer for shell and the aqueous dispersion medium is finely dispersed using, for example, an ultrasonic emulsifier. The dispersion thus obtained is preferably added to the reaction system in which the core is present. In this case, the polymerization conversion rate of the polymerizable monomer for the core in the core composition is preferably 80% or more, and more preferably 90% or more. When the polymerization conversion rate of the core polymerizable monomer is less than 80%, the core polymerizable monomer remaining in the reaction system is relatively copolymerized with the added shell polymerizable monomer, and the shell layer is formed on the core surface. Is not preferable because it cannot be formed effectively.

  The polymerization temperature varies depending on the type of core polymerization initiator used, but is preferably in the range of about 50 to 90 ° C. The polymerization time is preferably 0.5 to 30 hours, and more preferably 2 to 10 hours.

  The ratio between the core and the shell of the electrophoretic particles of the present invention is preferably in the range of 60:40 to 99.9: 0.01 in terms of the weight ratio of the polymerizable monomer for the core and the polymerizable monomer for the shell. When the ratio of the polymerizable monomer for shell is larger than this, the coloring degree of the electrophoretic particles 1e is lowered, which is not preferable. On the other hand, if the ratio of the polymerizable monomer for shell is smaller than this, the effect of eliminating the steric stericity of the shell is not sufficiently exhibited, which is not preferable.

  After completion of the reaction, the generated particles are collected by an appropriate method such as washing, filtration, decantation, and centrifugation, dried and classified to obtain electrophoretic particles 1e.

(Polymerizable monomer for shell)
The shell layer used in the present invention is a polymer having a high affinity with the electrophoretic particle dispersion medium 1f. That is, the shell layer of the present invention exhibits a steric exclusion effect that prevents aggregation between particles by spreading in the electrophoretic particle dispersion medium 1f.

  As the polymerizable monomer for shell, the polymer is preferably a polymer having high affinity with the electrophoretic particle dispersion medium 1f described above. Here, the high affinity means that the shell layer and the electrophoretic particle dispersion medium 1f are excellent in compatibility without phase separation.

  Examples of the shell polymerizable monomer include styrene, 4-methylstyrene, 4-ethylstyrene, 2-ethylhexyl (meth) acrylate, hepsyl (meth) acrylate, octyl (meth) acrylate, and (meth) acrylic acid. Nonyl, decyl (meth) acrylate, undecyl (meth) acrylate, dodecyl (meth) acrylate, tridecyl (meth) acrylate, tetradecyl (meth) acrylate, pentadecyl (meth) acrylate, hexadecyl (meth) acrylate , Heptadecyl (meth) acrylate, octadecyl (meth) acrylate, 1-hexene, 1-heptene, 1-octene, 1-decene, etc., and these may be used alone or in combination of two or more. Good.

  The weight average molecular weight of the polymer obtained from the polymerizable monomer for gel can be selected from the range of 1000 to 1000000.

(Polymerization initiator for shell)
In the formation of the shell layer, the shell polymerization initiator added together with the shell polymerizable monomer is preferably a water-soluble polymerization initiator. That is, it is preferable to use a water-soluble polymerization initiator because the water-soluble polymerization initiator enters the shell polymerizable monomer adsorbed on the core surface and a shell layer is easily formed on the core surface.
Polymeric initiators for shells include potassium persulfate, ammonium persulfate, 2,2′-azobis- (2-amidinopropane) dihydrochloride, 4,4′-azobis- (4-cyanovaleric acid), 2, Examples thereof include water-soluble polymerization initiators such as 2′-azobis-2-methyl-N-1,1-bis (hydroxymethyl) -2-hydroxyethylpropioamide. The polymerizable initiator for shell is preferably 0.1 to 10% by weight based on the polymerizable monomer for shell.

  The average particle diameter of the electrophoretic particles is preferably in the range of 0.5 to 10 μm, more preferably 0.5 to 3 μm. If the average particle size exceeds 10 μm, high resolution display may not be possible. Further, when the average particle size is less than 0.5 μm, it may be difficult to produce electrophoretic particles.

(Electrophoretic particle dispersion)
The electrophoretic particle dispersion contains at least electrophoretic particles and an electrophoretic particle dispersion medium, and a charge control agent, a charge auxiliary agent, and the like may be added as necessary. Either or both of the charge control agent and the charge auxiliary agent may be added to the electrophoretic particle dispersion medium.

  The charge control agent is not particularly limited as long as it is soluble in the electrophoretic particle dispersion medium. For example, cobalt naphthenate, zirconium naphthenate, copper naphthenate, iron naphthenate, lead naphthenate, manganese naphthenate, naphthene Naphthenic acid metal soaps such as zinc acid, cobalt octenoate, zirconium octenate, iron octenoate, lead octenoate, nickel octenate, manganese octenoate, zinc octenoate, stearic acid metal soap And the like, such as metal soaps such as polyaminopolybuterosuccinimide, lecithin and the like. Among these charge control agents, metal soap is preferable. The addition amount of the charge control agent is appropriately determined depending on the kind thereof, but is preferably 0.0001 to 5% by weight, and more preferably 0.001 to 1% by weight with respect to the electrophoretic particle dispersion medium.

  Examples of the charging aid include rosin esters and rosin derivatives. The rosin ester or rosin derivative is not particularly limited as long as it is soluble in the electrophoretic particle dispersion medium. For example, gum rosin, wood rosin, tall oil rosin, rosin modified maleic acid, rosin modified pentaerythritol, rosin glycerin ester, partial hydrogen Added rosin methyl ester, partially hydrogenated rosin glycerin ester, partially hydrogenated rosin triethylene glycol ester, fully hydrogenated rosin pentaerythritol ester, maleic acid modified rosin ester, fumaric acid modified rosin ester, acrylic acid modified rosin ester, maleic acid modified Rosin pentaerythritol ester, fumaric acid modified rosin pentaerythritol ester, acrylic acid modified rosin glycerin ester, maleic acid modified rosin glycerin ester, fumaric acid modified Jin glycerol esters, acrylic acid-modified rosin glycerin ester. The addition amount of the charging auxiliary agent is appropriately determined depending on the type thereof, but is preferably 0.001 to 10% by weight, and more preferably 0.01 to 5% by weight with respect to the electrophoretic particle dispersion medium 1f. .

The concentration of the electrophoretic particles in the dispersion varies depending on the hue and particle size, but is preferably 1 to 40% by weight, more preferably 3 to 20% by weight, based on the electrophoretic particle dispersion medium. When the concentration of the electrophoretic particles 1e is less than 1% by weight, the display contrast of the electrophoretic particles becomes light, which is not preferable. On the other hand, when the concentration of the electrophoretic particles exceeds 40% by weight, the display contrast of the colored electrophoretic particle dispersion medium becomes unpreferable.
(Electrophoretic display)
A display example in each cell of the electrophoretic display element using the electrophoretic particles is shown in FIG. FIG. 2 is a display example when the cell is filled with an electrophoretic particle dispersion liquid composed of white electrophoretic particles 1e and an electrophoretic particle dispersion medium 1f colored with a blue dye. The electrophoretic particle 1e is assumed to be negatively charged. When the second electrode 1d is set to 0 V and a negative voltage is applied to the first electrode 1c, the electrophoretic particles 1e gather at the second electrode 1d, and when the cell is observed from above, the distribution of the white electrophoretic particles 1e causes white (Fig. 2 (a)). On the other hand, when the second electrode 1d is set to 0 V and a positive voltage is applied to the first electrode 1c, the electrophoretic particles 1e gather on the first electrode 1c, and when the cell is observed from above, it looks blue (FIG. 2 ( b)). By performing such driving in units of pixels, an arbitrary image or character can be displayed by a large number of pixels.

  Another embodiment of the electrophoretic display element using the electrophoretic particles of the present invention will be described with reference to the drawings. FIG. 3 is a cross-sectional view showing another embodiment of the electrophoretic display element using the electrophoretic particles of the present invention. In the electrophoretic display element of FIG. 3A, a first electrode 3c and a second electrode 3d are provided on a first substrate 3a, and insulating layers 3h and 3i are formed between the electrodes and on the second electrode 3d, respectively. ing. The insulating layer 3h may be colored or colorless and transparent, but the insulating layer 3i is colorless and transparent. The 1st board | substrate 3a and the 2nd board | substrate 3b are arrange | positioned so that it may oppose at predetermined intervals through the partition 3g. An electrophoretic particle dispersion liquid including at least electrophoretic particles 3e and an electrophoretic particle dispersion medium 3f is enclosed in a cell (space) including the first substrate 3a, the second substrate 3b, and the partition walls 3g. In the electrophoretic display element, the side on which the second substrate 3b is provided is a display surface.

  FIG. 3B shows an electrophoretic display element using microcapsules. A microcapsule 3j containing the electrophoretic particle dispersion is disposed on the first substrate 3a and covered with the second substrate 3b. Note that when the microcapsule 3j is used, the insulating layer 3i may not be provided.

  In FIG. 3, the second electrode 3d is a pixel electrode that can independently apply a desired electric field to the electrophoretic particle dispersion in each cell (or microcapsule), and the first electrode 3c is the same over the entire surface. It is a common electrode applied with a potential. This pixel electrode is provided with a switch element. A selection signal is applied to each row from a matrix drive circuit (not shown), and a control signal and an output from the drive transistor are applied to each column. A desired electric field can be applied to the electrophoretic particle dispersion in the cell (or microcapsule). The electrophoretic particles 3e in each cell (or microcapsule) are controlled by the electric field applied by the second electrode 3d, and each pixel has a color of the electrophoretic particles (for example, black) and a color of the insulating layer 3h (for example, white). ) Is displayed. By performing such driving in units of pixels, an arbitrary image or character can be displayed by a large number of pixels.

(Configuration of electrophoretic display element)
The first substrate 3a is an arbitrary insulating member that supports the electrophoretic display element, and glass, plastic, or the like can be used. An insulating member such as a transparent glass substrate or plastic substrate can be used for the second substrate 3b. As the material of the first electrode 3c, a light reflective metal electrode such as Al is used. As the insulating layer 3h formed on the first electrode 3c, a fine particle for scattering light, such as aluminum oxide, titanium oxide or the like mixed with a colorless and transparent insulating resin can be used. Examples of the colorless and transparent insulating resin include the insulating resin described above. Or you may use the method of scattering light using the unevenness | corrugation of the metal electrode surface, without using microparticles | fine-particles.

  The second electrode 3d can be made of a conductive material that looks dark black when viewed from the viewer side of the display element, such as titanium carbide, blackened Cr, Al or Ti with a black layer formed on the surface. Further, a photolithography method can be used for pattern formation of the second electrode 3d.

  Subsequently, an insulating layer 3i is formed on the second electrode 3d. As the insulating layer 3i, the above-described colorless and transparent insulating resin can be used.

  Since the display contrast of this embodiment greatly depends on the area ratio between the second electrode 3d and the pixel, it is necessary to reduce the exposed area of the second electrode 3d with respect to that of the pixel in order to increase the contrast. It is preferably about 1: 2 to 1: 5. For the partition 3g, the same partition formation method and material as described above can be used. The method of filling the electrophoretic particle dispersion into the cell is not particularly limited, but the above-described inkjet nozzle can be used.

(Micro capsule)
As described above, the microcapsule 3j containing the electrophoretic particle dispersion can be obtained by a known method such as an interfacial polymerization method, an in situ polymerization method, a coacervation method, and the like. Can use the same polymer materials as described above.

  The method for disposing the microcapsule 3j on the first substrate 3a is not particularly limited, but the above-described ink jet type nozzle can be used.

For the purpose of preventing displacement of the microcapsules 3j arranged on the substrate, the gap between the microcapsules 3j may be impregnated with a light-transmitting resin binder and fixed on the substrate as described above. As the light transmissive resin binder, the above-described resins can be used.
When the first substrate 3a and the second substrate 3b are sealed, the microcapsule 3j is pressed so that the length in the horizontal direction is longer than the length in the vertical direction with respect to the first substrate 3a. It is preferable to seal between the substrates. (See Fig. 3 (b))
(Electrophoretic particle dispersion medium)
For the electrophoretic particle dispersion medium 3f, the same liquid as described above can be used.

(Electrophoretic particles)
As the electrophoretic particles 3e, black particles obtained by the same method as described above can be used. The concentration of the electrophoretic particles 3e in this embodiment is preferably 0.5 to 10% by weight, more preferably 1 to 5% by weight with respect to the electrophoretic particle dispersion medium 3f, although it varies depending on the particle size. When the concentration of the electrophoretic particles 3e is less than 0.5% by weight, it is not preferable because the first electrode 3c cannot be completely hidden and the display contrast becomes light. On the other hand, if the concentration of the electrophoretic particles 3e exceeds 10% by weight, it overflows from the colored second electrode 3d and the display contrast is deteriorated.

(Electrophoretic display)
A display example of an electrophoretic display element using the electrophoretic particles of the present invention is shown in FIG. FIG. 4 is a display example when a cell is filled with an electrophoretic particle dispersion liquid composed of black electrophoretic particles 3e and a colorless and transparent electrophoretic particle dispersion medium 3f. The electrophoretic particles 3e are assumed to be negatively charged. In addition, the insulating layer 3h is white and the second electrode 3d is black. When the first electrode 3c is set to 0V and a positive voltage is applied to the second electrode 3d, the electrophoretic particles 3e gather on the second electrode 3d, and when the cell is observed from above, it looks white (FIG. 4A). ).

  On the other hand, when the first electrode 3c is set to 0V and a negative voltage is applied to the second electrode 3d, the electrophoretic particles 3e gather on the first electrode 3c, and when the cell is observed from above, it looks black (FIG. 4 ( b)). By performing such driving in units of pixels, an arbitrary image or character can be displayed by a large number of pixels.

Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to these examples.
Example 1
A polymerizable monomer of 2-methylpropyl acrylate (196 parts by weight) containing 2,2′-azobisisobutyronitrile (16 parts by weight) and isopropenyl oxazoline (4 parts by weight) The mixture is put into alcohol (400 parts by weight), stirred at high speed to prepare a uniform suspension, and then polymerized at 80 ° C. for 7 hours in a nitrogen atmosphere. Separation and purification yields a 2-methylpropyl acrylate copolymer whose reactive group is an oxazoline group. This 2-methylpropyl acrylate copolymer (40 parts by weight) and titanium oxide having a hydroxyl group as a functional group (average particle diameter of 80 nm, 25 parts by weight) were used at 150 ° C. and 90 rpm under a kneader. For 20 minutes. When the reaction product is cooled and then pulverized, titanium oxide grafted with 2-methylpropyl acrylate copolymer is obtained.

  Titanium oxide grafted with 2-methylpropyl acrylate copolymer (30 parts by weight), benzoyl peroxide (4 parts by weight) and methyl methacrylate (130 parts by weight) were mixed with a homogenizer, and 2-methyl acrylate was mixed. A mixture in which the titanium oxide grafted with the propyl copolymer is uniformly dispersed is obtained. In the suspension medium obtained by dispersing calcium phosphate (20 parts by weight) in 0.05% by weight sodium dodecyl sulfate aqueous solution (400 parts by weight), the above mixture (core composition in which the grafted pigment is dispersed) ). This is stirred at high speed using a homogenizer to prepare a uniform suspension. The average particle size of the suspended core composition is about 2.0 μm. Next, polymerization is performed at 80 ° C. in a nitrogen atmosphere. When the polymerization conversion of the polymerizable monomer for the core reaches about 90%, a shell layer is subsequently formed.

  The shell polymerizable monomer, dodecyl methacrylate (5 parts by weight) and ion-exchanged water (100 parts by weight) are finely dispersed by an ultrasonic emulsifier to prepare an aqueous dispersion of the shell polymerizable monomer. At this time, the average particle diameter of the droplets of the polymerizable monomer for shell is about 0.1 μm. After adding an aqueous dispersion in which a polymerizable monomer for shells was dispersed to this reaction system, potassium persulfate (0.03 parts by weight) as a polymerization initiator for shells was dissolved in ion-exchanged water (40 parts by weight). Add aqueous solution and continue polymerization for 5 hours.

  After completion of the polymerization, the target electrophoretic particles are obtained through washing, drying, and classification steps. Its average particle size is about 2.1 μm.

  The synthesized electrophoretic particles are coated with a metal and embedded in an epoxy resin, then cut into a thickness of 1 mm with a microtome, and when the cut surface is observed with a transmission electron microscope, titanium oxide is uniformly dispersed in the polymer fine particles. It can be confirmed that a shell layer having a thickness of about 0.1 μm is formed on the surface.

  In addition, acetone was added to the electrophoretic particles and stirred at room temperature for 1 hour, and when the amount of titanium oxide efflux was measured, the amount of effluent was very small, so the graft polymer of titanium oxide and the core polymerizable monomer were copolymerized. In addition, it can be confirmed that the titanium oxide is immobilized in the particles.

  5% by weight of electrophoretic particles (white particles), 0.1% by weight of oil blue N (Aldrich), 2.5% by weight of rosin ester (charging aid, Neotol 125H, Harima Kasei), Isopar H as an electrophoretic particle dispersion medium (Exxon Chemistry) Using 92.4% by weight, an electrophoretic particle dispersion composed of these was injected into a cell using an inkjet nozzle, and a voltage application circuit was connected to the electrophoresis shown in FIG. A display element is manufactured.

  When contrast display is performed at a driving voltage of ± 10 V, the electrophoretic particles 1e are excellent in coloring degree and dispersibility, and can display clear blue and white.

(Example 2)
Using the electrophoretic particle dispersion obtained in the same manner as in Example 1, microcapsules 1i enclosing the dispersion are produced by an in situ polymerization method. The membrane material of the microcapsule is urea-formaldehyde resin. The microcapsule 1i is arranged on the first substrate 1a using an inkjet nozzle, and a voltage application circuit is connected to produce the electrophoretic display element shown in FIG. When contrast display is performed at a driving voltage of ± 10 V, the electrophoretic particles 1e are excellent in coloring degree and dispersibility, and can display clear blue and white.

(Example 3)
A polymerizable monomer of 2-methylbutyl methacrylate (195 parts by weight) and glycidyl methacrylate (5 parts by weight) containing 2,2′-azobisisobutyronitrile (16 parts by weight) and 0.05% by weight polyvinyl alcohol (400 parts by weight) and stirring at high speed to prepare a uniform suspension, followed by polymerization at 80 ° C. for 7 hours in a nitrogen atmosphere. Separation and purification yields a 2-methylbutyl methacrylate copolymer in which the reactive group is an epoxy group. Using a kneader, this 2-methylbutyl methacrylate copolymer (40 parts by weight) and carbon black having a hydroxyl group and a carboxyl group as a functional group (average particle size 22 nm, 20 parts by weight) at 150 ° C. and 100 rpm React for 20 minutes under conditions. When the reaction product is cooled and then pulverized, carbon black grafted with 2-methylbutyl methacrylate copolymer is obtained.

  A core composition comprising carbon black (30 parts by weight) grafted with 2-methylbutyl methacrylate copolymer, di-tert-butyl peroxide (4 parts by weight), and ethyl methacrylate (130 parts by weight) with a homogenizer Disperse uniformly. The above core composition is put into a suspension medium obtained by dispersing calcium phosphate (90 parts by weight) in 0.05% by weight aqueous sodium dodecyl sulfate solution (1800 parts by weight). This is stirred at high speed using a homogenizer to prepare a uniform suspension. The average particle size of the suspended core composition is about 1.5 μm. Next, polymerization is performed at 80 ° C. in a nitrogen atmosphere. When the polymerization conversion of the polymerizable monomer for the core reaches about 90%, a shell layer is subsequently formed.

  The shell polymerizable monomer, dodecyl methacrylate (5 parts by weight) and ion-exchanged water (100 parts by weight) are finely dispersed by an ultrasonic emulsifier to prepare an aqueous dispersion of the shell polymerizable monomer. At this time, the average particle diameter of the droplets of the polymerizable monomer for shell is about 0.1 μm. After adding an aqueous dispersion in which a polymerizable monomer for shells was dispersed to this reaction system, potassium persulfate (0.03 parts by weight) as a polymerization initiator for shells was dissolved in ion-exchanged water (40 parts by weight). Add aqueous solution and continue polymerization for 5 hours.

  After completion of the polymerization, the target electrophoretic particles 3e are obtained through washing, drying, and classification steps. The average particle size is about 1.6 μm.

  Similar to Example 1, when the synthesized electrophoretic particles 3e are observed with a transmission electron microscope, carbon black is uniformly dispersed in the polymer fine particles, and a shell layer having a thickness of about 0.1 μm is formed on the core surface. Can be confirmed.

  Similarly to Example 1, acetone was added to the synthesized electrophoretic particles 3e and stirred for 1 hour at room temperature. Then, when the outflow amount of carbon black was measured, the outflow amount was extremely small. It can be confirmed that the polymer and the polymerizable monomer for the core are copolymerized and the carbon black is fixed in the particles.

  1% by weight of the above electrophoretic particles (black particles), 0.5% by weight of rosin ester (charging aid, Neotol 125H, Harima Kasei), and 98.5% by weight of Isopar H as the electrophoretic particle dispersion medium. The electrophoretic particle dispersion is injected into the cell using an inkjet nozzle, and a voltage application circuit is connected to produce the electrophoretic display element shown in FIG. When contrast display is performed at a drive voltage of ± 10 V, the electrophoretic particles 3e are excellent in coloring degree and dispersibility, and can perform clear black and white display.

Example 4
Using the electrophoretic particle dispersion obtained in the same manner as in Example 3, microcapsules 3j enclosing the dispersion are produced by an interfacial polymerization method. The membrane material of the microcapsule is a polyamide resin. The microcapsule 3j is placed on the first substrate 3a using an inkjet nozzle, and a voltage application circuit is connected to produce the electrophoretic display element shown in FIG.
When contrast display is performed at a drive voltage of ± 10 V, the electrophoretic particles 3e are excellent in coloring degree and dispersibility, and can perform clear black and white display.

  The electrophoretic particles of the present invention can be utilized in industrial fields such as electrophotography using electrophoretic display elements and liquid toner. In the electrophoretic particles of the present invention, the pigment is uniformly dispersed in the polymer fine particles by polymerizing a composition in which a polymer-grafted pigment is uniformly dispersed in a polymerizable monomer. In addition, the pigment is immobilized in the particles by copolymerization of the polymer grafted to the pigment and the polymerizable monomer. Further, a shell layer for preventing aggregation of particles is formed on the particle surface. From the above, the present invention can provide an electrophoretic particle that is more excellent in coloring degree and dispersibility than conventional electrophoretic particles. Therefore, the present invention can provide an electrophoretic display element and an electrophotography with high contrast using such electrophoretic particles.

It is sectional drawing which shows the example of 1 embodiment of the electrophoretic display element using the electrophoretic particle of this invention. It is the schematic which shows the example of a display of the electrophoretic display element using the electrophoretic particle of this invention. It is sectional drawing which shows the other embodiment example of the electrophoretic display element using the electrophoretic particle of this invention. It is the schematic which shows the example of a display of the electrophoretic display element using the electrophoretic particle of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1a 1st board | substrate 1b 2nd board | substrate 1c 1st electrode 1d 2nd electrode 1e Electrophoretic particle 1f Electrophoretic particle dispersion medium 1g Partition 1h Insulating layer 1i Microcapsule 3a 1st board | substrate 3b 2nd board | substrate 3c 1st electrode 3d 2nd electrode 3e Electrophoretic particle 3f Electrophoretic particle dispersion medium 3g Partition wall 3h Insulating layer 3i Insulating layer 3j Microcapsule

Claims (10)

In electrophoretic particles in which pigments are dispersed in fine polymer particles,
The polymer fine particle has a first polymer portion grafted to a pigment and a second polymer portion copolymerized with the first polymer portion, and the polymer to be the first polymer portion is grafted. An electrophoretic particle obtained by polymerizing a polymerizable monomer in a state where a pigment is dispersed in the polymerizable monomer for forming the second polymer portion.   The electrophoretic particle according to claim 1, wherein the polymer grafted to the pigment has an affinity for the polymerizable monomer.   The electrophoretic particle according to claim 1, wherein the polymer grafted to the pigment contains at least one of a methine group and a methylene group.   The electrophoretic particle according to claim 1, wherein the surface of the electrophoretic particle further has a shell layer.   The electrophoretic particle according to claim 1, wherein the shell layer is a polymer having an affinity for the electrophoretic particle dispersion medium. A method for producing electrophoretic particles in which pigments are dispersed in polymer fine particles,
The polymerizable monomer is polymerized by suspending a composition in which a pigment grafted with a polymer, a polymerization initiator, and a polymerizable monomer and the pigment grafted with the polymer is dispersed in a suspension medium. By letting
Electricity in which the pigment is dispersed in polymer fine particles having a first polymer portion made of a polymer grafted to the pigment and a second polymer portion obtained from the polymerizable monomer copolymerized with the first polymer portion. A method for producing electrophoretic particles, comprising a step of obtaining electrophoretic particles.   The method for producing electrophoretic particles according to claim 6, further comprising forming a shell layer on a surface of the electrophoretic particles.   The method for producing electrophoretic particles according to claim 6, wherein the polymerization initiator is an organic peroxide.   6. An electrophoretic particle dispersion liquid comprising the electrophoretic particles according to claim 1 and an electrophoretic particle dispersion medium. A container for storing an electrophoretic particle dispersion containing electrophoretic particles and an electrophoretic particle dispersion medium, a display unit provided in at least a part of the container, and a display of movement of the electrophoretic particles to the display unit In an electrophoretic display element having a voltage application means for generating according to information, and performing display by the presence or absence of the electrophoretic particles in the display unit,
The electrophoretic display element according to claim 9, wherein the electrophoretic particle dispersion is the electrophoretic particle dispersion.

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