JP2009300939A - White resin particle and image display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide white resin particles having a sufficient whiteness degree and to provide an image display device which is capable of displaying an image superior in contrast even when being repeatedly driven. <P>SOLUTION: The white resin particles contain a rutile type titanium oxide and an optical whitening agent. The image display device has display particles enclosed between two substrates, at least one of which is transparent, in a powdery form and has the display particles moved by generation of an electric field between the substrates to display an image, wherein the white resin particles are used as the display particles. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to white resin particles, particularly white resin particles suitable for use as display particles in an image display device that displays images by moving display particles in a gas phase, and an image display device.

  2. Description of the Related Art Conventionally, image display apparatuses that display images by moving display particles in a gas phase are known. In the image display device, display particles are sealed in a powder form between two substrates, at least one of which is transparent, and an electric field is generated between the substrates to move and attach the display particles to at least one substrate. The image is displayed. In general, resin particles of at least two colors including white resin particles are used as the display particles. When driving such an image display device, a voltage is applied between the substrates to generate an electric field, and the display particles move based on the electric field direction. At this time, the resin particles of two or more colors included in the display particles move to one substrate side or move to the other substrate side based on the difference in charge polarity of the resin particles of each color. As a result, image display is achieved, and image display and deletion can be repeatedly executed by appropriately selecting the electric field direction. Therefore, resin particles used as display particles of an image display device are required to have excellent colorability in order to obtain a clear image with high contrast. In particular, since the white resin particles serve as a base for image display, the white density of the layer composed of the white resin particles is important, and white resin particles having excellent whiteness have been demanded.

  White resin particles are generally produced by dispersing a high refractive index material such as titanium oxide, zinc oxide, zinc sulfide in a low refractive index material such as a resin (polymer), and reflecting / reflecting due to the difference in refractive index. It looks white due to scattering. However, there is a problem that sufficient whiteness cannot be obtained even if such white resin particles are used.

  Therefore, a technique for improving the whiteness by adding a fluorescent whitening agent in addition to the pigment has been proposed (Patent Document 1). However, even with such a technique, sufficient white color was still not obtained.

On the other hand, the image display apparatus has a problem that the contrast is lowered when it is repeatedly driven.
JP 2004-3138008 A

  An object of this invention is to provide the white resin particle which shows sufficient whiteness.

  The present invention also provides a white resin particle capable of displaying an image having excellent contrast even when it is repeatedly driven in an image display device that displays an image by moving display particles in a gas phase, and an image including the white resin particle An object is to provide a display device.

  The present invention relates to a white resin particle having rutile titanium oxide and a fluorescent brightening agent.

  The present invention also provides an image display in which display particles are encapsulated in a powder form between two substrates, at least one of which is transparent, and an image is generated by moving the display particles by generating an electric field between the substrates. The present invention relates to an image display apparatus using the white resin particles as display particles.

The white resin particles according to the present invention exhibit sufficient whiteness. For this reason, when the white resin particles according to the present invention are used in an image forming apparatus employing a conventional electrophotographic method, a white image having excellent whiteness can be provided.
The white resin particles according to the present invention suppress an increase in charge amount during repeated driving, particularly when used as display particles in an image display device that displays images by moving the display particles in the gas phase. . As a result, the image display device using the white resin particles as display particles has excellent contrast due to the synergistic effect of the excellent whiteness improvement effect and the charge suppression effect of the white resin particles according to the present invention. Images can be displayed repeatedly.

[White resin particles]
The white resin particles according to the present invention are characterized by having rutile-type titanium oxide and a fluorescent brightening agent.

  The rutile-type titanium oxide and the optical brightener may be independently added to the resin particles and present inside the resin particles, or may be externally added to the resin particles and exist outside the resin particles. Also good. The presence in the resin particles means that the resin particles are added during the production process of the resin particles and dispersed or compatible with the resin particles. Presence outside the resin particles means that the resin particles are attached to and / or immobilized on the surface of the resin particles once added to the produced resin particles.

  Titanium oxide generally has three crystal forms, a so-called rutile type, anatase type, and brookite type. Of these, the rutile type and the anatase type are used industrially, but the rutile type is used in the present invention. Even if anatase-type or brookite-type titanium oxide or other white pigment is used in combination with a fluorescent brightening agent, the whiteness cannot be sufficiently improved.

The rutile type titanium oxide has a reflection characteristic that does not show reflection in the wavelength region of about 410 nm or less in the wavelength-reflectance curve. Specifically, when the wavelength is shifted to the long wavelength side, the reflection from the wavelength of about 410 nm. After that, a relatively large constant reflectance is exhibited over the entire visible light wavelength region to a wavelength region of 800 nm. An example of the wavelength-reflectance curve of such rutile titanium oxide is shown in FIG. The wavelength-reflectance curve of rutile-type titanium oxide can be measured from a rutile-type titanium oxide simple substance, for example, with a measuring device such as CM-3600d (manufactured by Konica Minolta) under the following conditions.
Measurement condition;
Light source: Xenon lamp (D65)
Measurement mode: reflectance measurement, SCI mode (measured including specular reflection light)
Target mask: Φ4mm
Measurement including specular reflection (SCI)
Observation field 10 °

  As long as the rutile titanium oxide has the above-described reflection characteristics, it may be treated with a surface treatment agent or may not be treated. In particular, when rutile type titanium oxide is internally added to the resin, in order to improve the dispersibility of the titanium oxide in the resin, it can be treated with an inorganic substance such as alumina (Al) or silica (Si), or a silicone resin. , Treatment with organic substances such as polyol resin) is preferably performed. In general, inorganic treatment is used for the purpose of imparting hydrophilicity, and organic treatment is used for the purpose of imparting water repellency, and the hydrophilicity and water repellency of titanium oxide can be adjusted by these treatments. Thereby, the titanium oxide dispersibility in the resin can be improved.

  Any rutile titanium oxide can be used as long as it is commercially available as a so-called rutile type. For example, R-630, R-550, CR-60 (Ishihara Sangyo Co., Ltd.), JR-600A, JR-800 (Manufactured by Teica), TR-600, TR-700 (manufactured by Fuji Titanium), R-101, R-102, R103 (manufactured by Dupont) and the like.

  The average primary particle size of rutile-type titanium oxide is not particularly limited, and is preferably 50 to 500 nm, particularly preferably 100 to 300 nm, from the viewpoint of further improving whiteness.

In this specification, the average primary particle size of titanium oxide is the number average particle size of primary particles, and a value measured by Microtrac UPA-150 (manufactured by Nikkiso Co., Ltd.) is used.
As a measurement procedure, 0.1 g of inorganic fine particles for measurement is placed in a 50 ml measuring cylinder, 25 ml of pure water is added, and dispersed for 3 minutes using an ultrasonic cleaner “US-1 (manufactured by asone)”. Prepare a sample. Next, 3 ml of the measurement sample is put into the cell of “Microtrack UPA-150”, and it is confirmed that the value of Sample Loading is in the range of 0.1-100. And it measures on the following measurement conditions.
Measurement condition;
Transparency: Yes
Refractive Index (refractive index): 1.59
Particle Density: 1.05g / cm3
Spherical Particles: Yes
Solvent conditions
Refractive Index (refractive index): 1.33
Viscosity (Viscosity): Height (temp) 0.797x10-3Pa · S, Low (temp) 1.002x10-3Pa · S

  The blending amount of rutile type titanium oxide is not particularly limited as long as the object of the present invention is achieved, and is, for example, 10 to 200 parts by weight, preferably 30 to 150 parts by weight with respect to 100 parts by weight of the resin. The compounding amount of rutile type titanium oxide is 100 weight of resin used when producing resin particles, regardless of whether rutile type titanium oxide is internally added or externally added to resin particles. This is the value for the part.

  The fluorescent whitening agent is conventionally added to laundry detergent, paper, fiber, resin, wallpaper, etc., and is used for the purpose of making white stand out or maintaining white. In the present invention, a fluorescent whitening agent having a reflectance peak in the wavelength-reflectance curve of 440 nm or less, particularly 360 to 440 nm, preferably 360 to 420 nm, more preferably 380 to 410 nm is used. By using such a fluorescent whitening agent in combination with rutile type titanium oxide, the whiteness can be sufficiently improved. As shown in FIG. 1, the fluorescent whitening agent having a reflectance peak in the above-mentioned wavelength range complements the reflection characteristics moderately with the rutile titanium oxide, and the total reflectance thereof is in the visible light region (380 to 780 nm). Can be made sufficiently uniform. Therefore, the whiteness of the color attributed to the reflected light is further increased, and as a result, the whiteness of the white resin particles is improved. On the other hand, the wavelength-reflectance curve of anatase-type titanium oxide is as shown in FIG. 7 and shows no reflection in the wavelength region of about 380 nm or less, but when the wavelength is shifted to the long wavelength side. Reflects from a wavelength of about 380 nm, and then exhibits a relatively large constant reflectance over the entire visible light range. Therefore, when anatase-type titanium oxide and a fluorescent brightening agent are used in combination, their reflection characteristics are not complemented with each other, and as shown in FIG. 8, the total reflectance shows a relatively large maximum. Therefore, it is considered that a color other than white is added by that amount, and the whiteness is lowered.

The wavelength-reflectance curve of the fluorescent brightener can be measured from the fluorescent brightener alone using the same measuring apparatus as described above.
The wavelength-reflectance curve of anatase-type titanium oxide can be measured from the anatase-type titanium oxide alone by the same measuring device as described above.

  Examples of the fluorescent brightener include benzoxazoyl compounds, coumarin compounds, styrene biphenyl compounds, pyrazolone compounds, and the like. In particular, the benzoxazoyl compounds further include those classified into stilbene, naphthalene, thiophene, and the like depending on the substituent. From the viewpoint of weather resistance, stilbene compounds are preferred. The reflectance peak wavelength in the wavelength-reflectance curve is unique to each compound. In particular, the above-described various compounds have various reflectance peak wavelengths that vary depending on the presence or type of substituents. Therefore, in the present invention, among the above compounds, those having a reflectance peak in the above wavelength range may be appropriately selected and used.

  Examples of fluorescent brighteners having a reflectance peak in the above wavelength range include commercially available Hostalux KSN (reflectance peak wavelength: about 400 nm, stilbenebenzoxazoyl-based compound), KS (same; about 400) nm. , Stilbene benzoxazoyl compounds), KCB (same; about 400) nm, naphthalene benzoxazoyl compounds (above, manufactured by Clariant), UVITEX OB (same; about 400 nm, thiophene benzoxazoyl group, Ciba Specialty Chemicals), Kayalight B, Kayalight OS (same; about 420 nm), Kayalight OSN (same: about 420 nm) (above, Nippon Kayaku Co., Ltd.), etc.

  The optical brightener has a solid form with a particle size of several tens of microns. When it is internally added to the resin particles, it dissolves and becomes compatible with the resin, and when it is externally added to the resin particles, it easily disintegrates. -Since it is fixed, the particle size is not particularly limited.

  The blending amount of the optical brightener is not particularly limited as long as the object of the present invention is achieved, and is, for example, 0.01 to 10 parts by weight, particularly 0.1 to 2 parts by weight with respect to 100 parts by weight of the resin. preferable. The compounding amount of the optical brightener is 100 weight of the resin used when producing the resin particles, even when the optical brightener is added internally to the resin particles or externally added. This is the value for the part. Two or more kinds of optical brighteners may be used in combination, and in such a case, the total blending amount thereof may be within the above range.

  The blending ratio of the fluorescent whitening agent and the rutile type titanium oxide is not particularly limited as long as the respective blending amounts are within the above-mentioned ranges. From the viewpoint of further improving the whiteness, the weight of the titanium oxide / fluorescent whitening agent. The ratio is preferably 5 to 1000, particularly 10 to 300.

  The resin constituting the white resin particles is not particularly limited, and a polymer called a vinyl resin shown below is typical, and in addition to the vinyl resin, for example, a polyamide resin or a polyester resin And condensation resins such as polycarbonate resin and epoxy resin. Specific examples of vinyl resins include, for example, polyolefin resins formed from ethylene monomers and propylene monomers, in addition to polystyrene resins, polyacrylic resins, polymethacrylic resins, and styrene acrylic resins. Examples of resins other than vinyl resins include polyether resins, polysulfone resins, polyurethane resins, fluorine resins, and silicone resins in addition to the above-described condensation resins.

  The polymer constituting the resin that can be used for the white resin particles is produced by combining a plurality of types of polymerizable monomers in addition to those obtained by using at least one type of polymerizable monomer that forms these resins. You can also. When a resin is produced by combining a plurality of types of polymerizable monomers, for example, a method of forming a copolymer such as a block copolymer, a graft copolymer or a random copolymer, or a mixture of a plurality of types of resins. There is also resin formation by a polymer blending method.

The weight average molecular weight of the resin constituting the white resin particles is preferably from 5,000 to 200,000, particularly preferably from 15,000 to 100,000, from the viewpoints of heat resistance and fixation of external additives.
In this specification, the value measured by HLC-8220 (made by Tosoh Corporation) is used for the weight average molecular weight.

  The white resin particles of the present invention may have additives such as a charge control agent and a fluidizing agent as desired. The charge control agent may be internally added to the white resin particles, or may be externally added. The fluidizing agent is externally added to the white resin particles.

  The charge control agent is not particularly limited. For example, a charge control agent known in the field of electrophotographic toner is used. Specific examples include negative charge control agents such as salicylic acid metal complexes, metal-containing azo dyes, quaternary ammonium salt compounds, and nitriliimidazole derivatives, and positive charge control agents such as nigrosine dyes, triphenylmethane compounds, and imidazole derivatives. Can be mentioned. For example, when the charge control agent is added internally to the resin particles, the amount is preferably 0.1 to 5 parts by weight with respect to 100 parts by weight of the resin. 0.5-2 weight part is preferable with respect to weight part.

  Examples of the fluidizing agent include particulate titanium oxide, particulate silica, calcium carbonate, and the like. The average primary particle size of the fluidizing agent is usually 5 to 100 nm. The blending amount of the fluidizing agent is preferably 0.1 to 10 parts by weight with respect to 100 parts by weight of the white resin particles. At this time, since the added part of the fluidizing agent is smaller than that of the white pigment, the influence on the white density is small. Therefore, anatase type titanium oxide can also be used as a fluidizing agent.

The method for producing the white resin particles is not particularly limited. For example, it can be dealt with by applying a known method for producing resin particles such as a toner production method used for electrophotographic image formation. Is possible. Specific examples of the method for producing the white resin particles include the following methods.
(1) Kneading and pulverizing and classifying the resin and a predetermined internal additive component, and then mixing the external additive component as desired to produce white resin particles;
(2) A polymerizable monomer and a predetermined internal additive component are mechanically stirred in an aqueous medium to form droplets, polymerized, and then mixed with external additive components as desired to form white resin particles. Manufacture (suspension polymerization method);
(3) An internally added component other than a polymerizable monomer and rutile type titanium oxide is dropped into an aqueous medium containing a surfactant, and a polymerization reaction is carried out in a micelle to produce polymer particles of 100 to 150 nm. After that, rutile type titanium oxide particles and an aggregating agent are added to agglomerate and fuse these particles. Thereafter, if desired, external resin components are mixed to produce white resin particles (emulsion polymerization aggregation method).

  The volume average particle diameter of the white resin particles is not particularly limited, and may be appropriately determined according to the use. For example, when white resin particles are used as display particles of an image display device, the volume average particle size of the white resin particles is usually 1 to 50 μm, preferably 1 to 30 μm.

The volume average particle diameter of the white resin particles is a volume-based median diameter (d50 diameter), and is measured and calculated using a device in which a computer system for data processing is connected to Multisizer 3 (manufactured by Beckman Coulter). be able to.
As a measurement procedure, 0.02 g of a sample is conditioned with 20 ml of a surfactant solution (for dispersing particles, a surfactant solution obtained by diluting a neutral detergent containing a surfactant component 10 times with pure water). After that, ultrasonic dispersion is performed for 1 minute to prepare a dispersion. This dispersion is poured into a beaker containing ISOTON II (manufactured by Beckman Coulter, Inc.) in a sample stand with a pipette until the measured concentration reaches 10%, and measurement is performed with a measuring machine count set to 2500 pieces. The aperture size of the multisizer 3 is 50 μm.

[Usage]
The white resin particles of the present invention may be used, for example, as a toner in an image forming apparatus employing a conventional electrophotographic method, or in an image display apparatus that displays an image by moving display particles in a gas phase. It may be used as display particles. Preferably, it is used as display particles of an image display device. This is because the excellent whiteness of the white resin particles is not only used for improving the density during white display, but also because the rutile titanium oxide has a high dielectric constant, it leads to stabilization of repeated display. Specifically, in the image display device, the display particles are brought into frictional contact with each other when the display particles are moved by an electric field. Therefore, when the display particles are repeatedly driven, the charge amount of the display particles is increased by frictional charging. As the charge amount increases, the voltage required to drive the display particles increases, and the contrast at the same voltage decreases. Since the white resin particles of the present invention use rutile type titanium oxide having a high dielectric constant and charge accumulation is suppressed, when the white resin particles are used as display particles, repeated display can be stabilized.

[Image display device]
The image display device according to the present invention uses at least the above-described white resin particles as display particles. Hereinafter, the image display apparatus of the present invention will be described in detail. The image display device according to the present invention is also called a “powder display”.

  The image display device according to the present invention encloses the display particles described above in a powder form between two substrates, at least one of which is transparent, and moves the display particles by generating an electric field between the substrates. An image is displayed.

  FIG. 2 shows a typical cross section of the image display apparatus according to the present invention. FIG. 2A shows a structure in which an electrode 15 having a layer structure is provided on the substrates 11 and 12 and an insulating layer 16 is provided on the surface of the electrode 15. The image display device shown in FIG. 2 (b) has a structure in which no electrode is provided in the device, and an electric field is applied through an electrode provided outside the device so that the display particles can be moved. It is. The same reference numerals in FIGS. 2A and 2B denote the same members. FIG. 2 is meant to include FIGS. 2 (a) and 2 (b). As shown in the figure, the image display device 10 in FIG. 2 is supposed to visually recognize an image from the substrate 11 side. However, in the present invention, the image display device 10 is not limited to the one that visually recognizes an image from the substrate 11 side. Further, the type shown in FIG. 2B has an advantage that the structure of the device can be simplified and the manufacturing process can be shortened because the electrode 15 is not provided on the device itself. FIG. 4 shows a state in which voltage application is performed by setting the image display device 10 of the type shown in FIG. The cross-sectional configuration of the image display apparatus according to the present invention is not limited to that shown in FIGS. 2 (a) and 2 (b).

  At the outermost part of the image display device 10 in FIG. 2 (a), two substrates 11 and 12 that are casings constituting the image display device are arranged to face each other. In the substrates 11 and 12, an electrode 15 for applying a voltage is provided on the surface on which both faces each other, and an insulating layer 16 is provided on the electrode 15. The substrates 11 and 12 are provided with an electrode 15 and an insulating layer 16, and display particles exist in a gap 18 formed by facing the surfaces having the electrode 15 and the insulating layer 16. In the image display device 10 shown in FIG. 2, two kinds of display particles, black display particles (hereinafter referred to as black particles) 21 and white display particles (white resin particles; hereinafter referred to as white particles) 22, are displayed in the gap 18 as display particles. Exist. Note that other colored particles may be used instead of the black particles. Further, in the image display device 10 of FIG. 2, the gap 18 is surrounded by the substrates 11 and 12 and the two partition walls 17, and the display particles are present in a state of being enclosed in the gap 18.

  The thickness of the gap 18 is not particularly limited as long as the enclosed display particles can move and maintain the contrast of the image, and is usually 10 μm to 500 μm, preferably 10 μm to 100 μm. The volume occupation ratio of the display particles in the gap 18 is 5% to 70%, preferably 30% to 60%. By setting the volume occupancy of the display particles within the above range, the display particles can move smoothly in the gap 18 and an image with good contrast can be obtained.

Next, the behavior of display particles in the gap 18 of the image display device 10 will be described.
In the image display device according to the present invention, when a voltage is applied between two substrates to form an electric field, the charged display particles move based on the direction of the electric field. In this way, when a voltage is applied between the substrates on which the display particles exist, the charged display particles move between the substrates to display an image.

The image display in the image display apparatus according to the present invention is performed by the following procedure.
(1) The display particles used as the display medium are charged by a known method such as frictional charging with a carrier.
(2) Display particles are sealed between two opposing substrates, and a voltage is applied between the substrates in this state.
(3) An electric field is formed between the substrates by applying a voltage between the substrates.
(4) The display particles are attracted to the surface of the substrate along the direction of the electric field opposite to the polarity of the display particles by the action of the electric field force between the electrodes, so that image display can be performed.
(5) Further, the moving direction of the display particles is switched by changing the electric field direction between the substrates. The image display can be changed variously by switching the moving direction.

The display particles can be charged by the above-described known methods, for example, a method in which the display particles are charged by contact with a carrier by frictional charging, or two color display particles having different charging polarities are mixed and stirred. In the present invention, it is preferable to use a carrier and enclose the charged display particles in a substrate.
The image display device can also be manufactured by an electrophotographic developing method.

Examples of the movement of the display particles accompanying voltage application between the substrates are shown in FIGS.
FIG. 3A shows a state before a voltage is applied between the substrates 11 and 12, and the positively charged white particles 22 exist in the vicinity of the viewing-side substrate 11 before the voltage is applied. In this state, the image display device 10 displays a white image. FIG. 3B shows a state after a voltage is applied to the electrode 15, and the black particles 21 that are negatively charged by applying a positive voltage to the substrate 11 are near the substrate 11 on the viewing side. The white particles 22 have moved to the substrate 12 side. In this state, the image display device 10 displays a black image.

  FIG. 4 shows a state before the voltage is applied in this state in which the image display device 10 shown in FIG. 2B is set to the voltage application device 30 having no electrode (FIG. 4A). ) And the state after the voltage is applied (FIG. 4B). In the image display device 10 of the type shown in FIG. 2B, the black particles 21 negatively charged by applying a positive voltage to the substrate 11 as well as the image display device 10 having the electrode 15 are in the vicinity of the substrate 11 on the viewing side. The positively charged white particles 22 have moved to the substrate 12 side.

  Next, the substrates 11 and 12, the electrode 15, the insulating layer 16, and the partition wall 17 constituting the image display device 10 illustrated in FIG. 2 will be described.

  First, the substrates 11 and 12 constituting the image display device 10 will be described. In the image display device 10, the observer visually recognizes the image formed by the display particles from at least one side of the substrates 11 and 12, and therefore the substrate provided on the side viewed by the observer is required to be made of a transparent material. . Therefore, the substrate used on the side where the observer visually recognizes the image is preferably a light-transmitting material having a visible light transmittance of 80% or more, for example, and has a visible light transmittance of 80% or more. Sex is obtained. Of the substrates constituting the image display device 10, the material of the substrate provided on the opposite side of the image viewing side is not necessarily transparent.

  The thicknesses of the substrates 11 and 12 are each preferably 2 μm to 5 mm, and more preferably 5 μm to 2 mm. When the thicknesses of the substrates 11 and 12 are in the above range, sufficient strength can be given to the image display device 10 and the distance between the substrates can be kept uniform. In addition, since the image display device can be provided in a compact and lightweight manner by setting the thickness of the substrate within the above range, the use of the image display device in a wide field is promoted. Further, by setting the thickness of the substrate on the side where the image is viewed to be in the above range, the display image can be accurately viewed without impeding the display quality.

  Examples of the material having a visible light transmittance of 80% or more include an inorganic material having no flexibility such as glass and quartz, an organic material typified by a resin material described later, a metal sheet, and the like. Among these, organic materials and metal sheets can impart a certain degree of flexibility to the image display device. Examples of the resin material having a visible light transmittance of 80% or more include polyester resins typified by polyethylene terephthalate and polyethylene naphthalate, polycarbonate resins, polyethersulfone resins, and polyimide resins. . In addition, a transparent resin obtained by radical polymerization of a vinyl polymerizable monomer such as an acrylic resin or a polyethylene resin, which is a polymer of acrylic acid ester or methacrylic acid ester represented by polymethyl methacrylate (PMMA). It is done.

  The electrode 15 is provided on the surfaces of the substrates 11 and 12, and forms an electric field between the substrates, that is, the gap 18 by applying a voltage. As with the above-described substrate, it is necessary to provide a transparent electrode 15 on the side where the observer visually recognizes the image.

  The thickness of the electrode provided on the side for visually recognizing the image is required to ensure conductivity and at a level that does not hinder the light transmittance. Specifically, the thickness is preferably 3 nm to 1 μm, and preferably 5 nm to 400 nm. More preferred. Note that the visible light transmittance of the electrode provided on the side where the image is viewed is preferably 80% or more, like the substrate. The thickness of the electrode provided on the side opposite to the side where the image is viewed is also preferably within the above range, but it is not necessary to be transparent.

  Examples of the constituent material of the electrode 15 include metal materials, conductive metal oxides, and conductive polymer materials. Specific examples of the metal material include aluminum, silver, nickel, copper, and gold. Specific examples of the conductive metal oxide include indium tin oxide (ITO), indium oxide, and antimony tin. An oxide (ATO), a tin oxide, a zinc oxide, etc. are mentioned. Furthermore, examples of the conductive polymer material include polyaniline, polypyrrole, polythiophene, polyacetylene, and the like.

  As a method of forming the electrode 15 on the substrate 11 or 12, for example, when an electrode on a thin film is provided, a sputtering method, a vacuum evaporation method, a chemical vapor deposition method (CVD method), a coating method, or the like can be used. Can be mentioned. There is also a method of forming an electrode by mixing a conductive material with a solvent or a binder resin and applying the mixture to a substrate.

  The insulating layer 16 is provided on the surface of the electrode 15 and is in contact with the display particles 21 and 22 on the surface of the insulating layer 16, but is not necessarily provided. The insulating layer 16 has a role of relaxing the change in the charge amount by the voltage applied when the display particles 21 and 22 are moved. Further, by imparting a resin having a highly hydrophobic structure and unevenness, it is possible to reduce the physical adhesion with the display particles and to reduce the driving voltage. The material constituting the insulating layer 16 is an electrically insulating material that can be made into a thin film, and has transparency as desired. The insulating layer provided on the image viewing side preferably has a visible light transmittance of 80% or more, like the substrate. Specific examples include silicone resin, acrylic resin, and polycarbonate resin.

  The thickness of the insulating layer 16 is preferably 0.01 μm or more and 10.0 μm or less. That is, when the thickness of the insulating layer 16 is in the above range, the display particles 21 and 22 can move without applying a very large voltage between the electrodes 15. For example, a voltage at a level applied in image formation by electrophoresis is applied. It is preferable because the image can be displayed by applying.

  The partition wall 17 secures a gap 18 between the upper and lower substrates, and can be formed not only at the edges of the substrates 11 and 12 but also inside as needed, as shown in the right and left diagrams in the upper part of FIG. . The width of the partition wall 17, particularly the thickness of the partition wall on the image display surface 18 a side, is preferably as thin as possible from the viewpoint of ensuring the clarity of the display image, as shown in the right side of FIG.

The partition walls 17 formed inside the substrates 11 and 12 may be formed continuously or intermittently in the front and back directions in the right and left drawings in the upper part of FIG.
By controlling the shape and arrangement of the partition walls 17, the cells in the gap 18 partitioned by the partition walls 17 can be arranged in various shapes. An example of the shape and arrangement of the cells when the gap 18 is viewed from the viewing direction of the substrate 11 is shown in the lower diagram of FIG. As shown in the lower drawing of FIG. 5, a plurality of cells can be arranged in a rectangular shape, a triangular shape, a line shape, a circular shape, a hexagonal shape or the like in a honeycomb shape or a mesh shape. )

  The partition wall 17 can be formed, for example, by processing the substrate on the side opposite to the side on which the image is viewed using the following method. Examples of the method for forming the partition wall 17 include embossing with a resin material or the like, uneven formation by hot press injection molding, photolithography, screen printing, and the like.

Experimental example 1
[Production of white resin particles]
<Example 1>
The resin and titanium oxide described below were put into a Henschel mixer (manufactured by Mitsui Miike Mining Co., Ltd.), the peripheral speed of the stirring blade was set to 25 m / second, and the mixture was mixed for 5 minutes to obtain a mixture.
Styrene acrylic resin (weight average molecular weight 20,000) 100 parts by weight Rutile type titanium oxide 30 parts by weight (R-630; manufactured by Ishihara Sangyo Co., Ltd., average primary particle size 240 nm)
Optical brightener (Hostalux KSN, manufactured by Clariant Co., Ltd.) 0.5 parts by weight The above mixture is kneaded with a twin-screw extruder kneader, then coarsely pulverized with a hammer mill, and then pulverized with a turbo mill pulverizer (Turbo Kogyo Co., Ltd.) Further, fine powder classification was performed with an airflow classifier utilizing the Coanda effect to produce white resin particles having a volume average particle size of 10.0 μm.

<Example 2>
Resin particles were produced by the same method as the production method of the white resin particles of Example 1 except that the optical brightener was not used. Next, 0.5 parts by weight of a fluorescent whitening agent (Hostalux KSN, manufactured by Clariant) is added to 100 parts by weight of the resin particles, and the mixture is put into a hybridizer apparatus (manufactured by Nara Machinery Co., Ltd.), and mixed. White resin particles were obtained.

<Example 3>
Resin particles were produced by the same method as the white resin particle production method of Example 1, except that rutile titanium oxide was not used. Next, 30 parts by weight of rutile type titanium oxide (R-630; manufactured by Ishihara Sangyo Co., Ltd., average primary particle size 240 nm) is added to 100 parts by weight of the resin particles, and the mixture is put into a hybridizer apparatus (manufactured by Nara Machinery Co., Ltd.). Then, a mixing process was performed to obtain white resin particles. )

<Example 4>
Resin particles were produced by the same method as the white resin particle production method of Example 1, except that rutile titanium oxide and fluorescent brightener were not used. Next, 100 parts by weight of resin particles, 30 parts by weight of rutile type titanium oxide (R-630; manufactured by Ishihara Sangyo Co., Ltd., average primary particle size 240 nm) and 0.5 parts by weight of optical brightener (Hostalux KSN, manufactured by Clariant) Part was added and charged into a hybridizer apparatus (manufactured by Nara Machinery Co., Ltd.) and mixed to obtain white resin particles.

<Example 5>
White resin particles were produced by the same method as the white resin particle production method of Example 1, except that 30 parts by weight of JR-600A (Taika Corp., average primary particle size 250 nm) was used as the rutile titanium oxide. . )

<Example 6>
White resin particles were produced by the same method as the white resin particle production method of Example 1, except that 30 parts by weight of R-102 (Dupont, average primary particle size 230 nm) was used as rutile titanium oxide. . )

<Example 7>
White resin particles were produced by the same method as the white resin particle production method of Example 1, except that 0.5 parts by weight of Hostalux KCB (manufactured by Clariant) was used as the fluorescent whitening agent.

<Example 8>
White resin particles were produced by the same method as the white resin particle production method of Example 1, except that 1 part by weight of UVITEX OB (manufactured by Ciba Specialty Chemicals) was used as the fluorescent whitening agent.

<Comparative Example 1>
White resin particles were produced by the same method as the production method of the white resin particles of Example 1 except that the fluorescent brightener was not used.

<Comparative Example 2>
White resin particles were produced by the same method as the white resin particle production method of Example 1, except that anatase titanium oxide (TA-200, manufactured by Fuji Titanium Industry Co., Ltd.) was used instead of rutile titanium oxide. .

<Comparative Example 3>
White resin particles were produced by the same method as the production method of the white resin particles of Comparative Example 2 except that no fluorescent brightener was used.

[Evaluation]
White resin particles were encapsulated in a transparent glass substrate, and the concentration was measured with black paper laid on the back of the substrate. For density measurement, a reflection densitometer (Konica's reflection densitometer: SakuraDENSITMETER PDA-65) was used. The reflection density of 0.42 or less is a practically problematic range, 0.40 or less is a preferred range, and if it exceeds 0.42, there is a practical problem.

  It turned out that the white resin particle of this invention is excellent in whiteness. As a result, high contrast can be obtained when used in an image display apparatus.

Experimental example 2
[Manufacture of white display particles]
5 parts by weight of silica particles (RA200; manufactured by Aerosil Co., Ltd.) having an average primary particle size of 15 nm are added as a fluidizing agent to 100 parts by weight of the white resin particles manufactured in Experimental Example 1, and a hybridizer apparatus (manufactured by Nara Machinery Co., Ltd.). ) And mixed, and used as white display particles.

[Production of black display particles]
The resin and carbon black described below were put into a Henschel mixer (manufactured by Mitsui Miike Mining Co., Ltd.), the peripheral speed of the stirring blade was set to 25 m / sec, and the mixture was mixed for 5 minutes to obtain a mixture.
Styrene acrylic resin (weight average molecular weight 20,000) 100 parts by weight Carbon black (average primary particle size 25 nm) 10 parts by weight The above mixture is kneaded with a twin-screw extrusion kneader, then coarsely pulverized with a hammer mill, and then turbo milled. Coarse powder was pulverized with a machine (manufactured by Turbo Kogyo Co., Ltd.), and fine powder classification was performed with an airflow classifier utilizing the Coanda effect to produce black resin particles having a volume average particle size of 10.0 μm. Next, 4 parts by weight of silica particles (R-805; manufactured by Aerosil Co., Ltd.) having an average primary particle size of 15 nm are added as a fluidizing agent to 100 parts by weight of the black resin particles, and a hybridizer apparatus (manufactured by Nara Machinery Co., Ltd.). ) And mixed to produce black display particles.

[Carrier A for charging white display particles]
Conditions in which 2 parts of fluorinated acrylate resin particles are added to 100 parts by weight of ferrite core having an average particle diameter of 80 μm, and these raw materials are put into a horizontal rotary blade type mixer so that the peripheral speed of the horizontal rotary blade is 8 m / sec. Was mixed and stirred at 22 ° C. for 10 minutes, and then heated to 90 ° C. and stirred for 40 minutes to produce Carrier A.

[Carrier B for charging black display particles]
Under the condition that 2 parts of cyclohexyl methacrylate resin particles are added to 100 parts by weight of a ferrite core having an average particle diameter of 80 μm, and these raw materials are put into a horizontal rotary blade type mixer so that the peripheral speed of the horizontal rotary blade is 8 m / sec. After mixing and stirring at 22 ° C. for 10 minutes, carrier B was produced by heating to 90 ° C. and stirring for 40 minutes.

[Manufacture of image display devices]
The image display device was manufactured according to the electrophotographic development method so as to have the same structure as that shown in FIG. Two glass substrates 11 having a length of 80 mm, a width of 50 mm, and a thickness of 0.7 mm are prepared, and each substrate surface is made of an indium tin oxide (ITO) film (resistance 30 Ω / □) having a thickness of 300 nm. The electrode 15 was formed by a vapor deposition method. On the electrode, a coating solution prepared by dissolving 12 g of polycarbonate resin in a mixed solvent of 80 ml of tetrahydrofuran and 20 ml of cyclohexanone is applied by spin coating to form an insulating layer 16 having a thickness of 3 μm. Got.

  The display particles were charged by mixing 1 g of black display particles and 9 g of carrier B with a shaker (manufactured by YS-LD Co., Ltd., Yayoi) for 30 minutes. As shown in FIG. 6A, the obtained mixture (21, 210) was placed on a conductive stage 100, and one substrate with electrodes was placed at an interval of about 2 mm from the stage 100. Between the electrode 15 and the stage 100, a DC bias of +50 V, an AC bias of 2.0 kV, and a frequency of 2.0 kHz were applied for 10 seconds to deposit the black display particles 21 on the insulating layer 16.

  The display particles were charged by mixing 1 g of white display particles and 9 g of carrier A for 30 minutes with a shaker (manufactured by Yayoi, YS-LD Co., Ltd.). As shown in FIG. 6B, the obtained mixture (22, 220) was placed on a conductive stage 100, and the other substrate with electrodes was placed at an interval of about 2 mm from the stage 100. Between the electrode 15 and the stage 100, a DC bias of −50 V, an AC bias of 2.0 kV, and a frequency of 2.0 kHz were applied for 10 seconds to adhere the white display particles 22 on the insulating layer 16.

  As shown in FIG. 6C, the substrate with electrodes to which black display particles are attached and the substrate with electrodes to which white display particles are attached are adjusted and overlapped with a partition so as to have an interval of 50 μm. Were bonded with an epoxy adhesive to obtain an image display device. The volume occupation ratio between the two types of display particles between the glass substrates was 50%. The content ratio of the white display particles and the black display particles is approximately 1/1 in the number ratio of the white display particles / black display particles.

[Evaluation]
Display characteristics were evaluated by alternately applying +100 V and −100 V DC voltage to the image display device and measuring the reflection density of the display image obtained by the voltage application. It was confirmed that when a positive voltage was applied in the white display state, the display changed from white to black. The voltage applied to the electrode on the upstream side in the visual recognition direction of the image display device was changed, and the other electrode was electrically grounded.

(Contrast durability)
Contrast was measured after alternating voltage application of +100 V and −100 V was repeated 10,000 times.
Contrast is the difference between black density and white density, i.e.
Evaluation was based on a density difference defined by contrast = black density−white density.
The black density is the reflection density of the display surface obtained when a voltage of +100 V is applied to the electrode on the upstream side in the viewing direction of the image display device.
The white density is a reflection density of the display surface obtained when a voltage of −100 V is applied to the electrode on the upstream side in the viewing direction of the image display device.
The density was averaged by measuring five locations on the display surface at random using a reflection densitometer “RD-918 (manufactured by Macbeth)”.
Regarding the contrast, the density difference of 1.20 or more was the best “◎”, 0.95 or more was “good”, 0.70 or more was “Δ”, and less than 0.70 was “x”. In the present invention, a level having no practical problem is “◯” or more, and “Δ” and “x” are levels having a practical problem.

It is a graph which shows the wavelength-reflectance curve for demonstrating the reflective characteristic of the white resin particle which concerns on this invention. It is the schematic which shows an example of the cross-sectional structure of an image display apparatus. It is a schematic diagram which shows the example of the movement of the display particle by the voltage application between base | substrates. It is a schematic diagram which shows the example of the movement of the display particle by the voltage application between base | substrates. It is a schematic diagram which shows the example of a shape of an image display surface. It is a schematic diagram which shows an example of the sealing method of a display particle. It is a graph which shows the wavelength-reflectance curve for demonstrating the reflective characteristic of a rutile type titanium oxide and an anatase type titanium oxide. It is a graph which shows the wavelength-reflectance curve for demonstrating the reflective characteristic of the white resin particle which concerns on a prior art.

Explanation of symbols

  10: image display device, 11:12: substrate, 15: electrode, 16: insulating layer, 17: partition, 18: gap, 18a: image display surface, 21: black display particles, 22: white display particles (white resin particles) ).

Claims (6)

  White resin particles comprising rutile-type titanium oxide and a fluorescent brightening agent.   The white resin particles according to claim 1, wherein the rutile-type titanium oxide and the fluorescent brightening agent are independently or internally added to the resin particles.   The white resin particles according to claim 1 or 2, wherein the rutile type titanium oxide has an average primary particle size of 50 to 500 nm.   The white resin particles according to claim 1, wherein the peak wavelength of the reflectance of the fluorescent whitening agent is 440 nm or less.   As display particles of an image display apparatus that encloses display particles in a powder form between two substrates transparent at least one and generates an electric field between the substrates to move the display particles and display an image It is used, The white resin particle in any one of Claims 1-4 characterized by the above-mentioned.   An image display device that displays an image by moving display particles by encapsulating display particles in a powder form between two substrates, at least one of which is transparent, and generating an electric field between the substrates, The image display apparatus which uses the white resin particle in any one of Claims 1-4 as a display particle.

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