WO2010106934A1

WO2010106934A1 - Dispersion-type electroluminescence device

Info

Publication number: WO2010106934A1
Application number: PCT/JP2010/053746
Authority: WO
Inventors: Masashi Shirata
Original assignee: Fujifilm Corporation
Priority date: 2009-03-17
Filing date: 2010-03-02
Publication date: 2010-09-23
Also published as: TW201041437A; JP2010218891A

Abstract

A dispersion-type electroluminescence device, containing: a pair of electrodes including a back electrode and a transparent electrode; and at least an insulating layer and a light-emitting layer provided between the pair of electrodes, wherein the insulating layer contains dielectric particles, an average particle size of the dielectric particles contained in the insulating layer is in a range of from 0.40 to 1.0 μm, and a volume ratio of the dielectric particles contained in the insulating layer is 30 to 60%.

Description

DESCRIPTION

DISPERSION-TYPE ELECTROLUMINESCENCE DEVICE

Technical Field

The present invention relates to a dispersion-type electroluminescence device (hereinafter referred to as "EL device" in some cases) having a light-emitting layer formed by dispersion-coating electroluminescence (EL) powder particles of high brightness and long life.

Background Art

EL phosphors are voltage excitation type phosphors, and a dispersion-type EL device of sandwiching the phosphor powder between electrodes as a light- emitting device, and a thin film EL device are known. Ordinary dispersion-type EL devices take the structure of sandwiching phosphor powder dispersed in a binder having a high dielectric constant between two electrodes, at least one of which is transparent, and light is emitted by applying AC electric field between both electrodes. It is possible for light-emitting devices manufactured with EL phosphor powder to have a thickness of several millimeters or less, and they have many advantages such that they are plane emitters, little in heat generation, and good in light emitting efficiency, so that various uses are expected of EL devices such as road signs, various indoor and outdoor illuminations, light sources for flat panel displays such as liquid crystal display, and light sources of illuminations for advertisement of large area.

However, light-emitting devices manufactured with phosphor powder have drawbacks such that they are low in light emission brightness and light emitting life is short as compared with light-emitting devices manufactured on the basis of other principles. Therefore, various improvements have been tried.

For the purpose of increasing light emission brightness of a dispersion-type EL device, for example, it is considered to heighten the voltage to be applied to the device, but mere heightening of the voltage of the device results in increase of consumed electric power. Further, heightening of the voltage is not only related to the costs of peripheral power circuits but also lowers light emitting life, and breaking of the device is liable to occur due to high electric field. JP-A-2005-158491 (the term "JP-A" as used herein refers to an "unexamined published Japanese patent application") discloses increasing the dielectric constant of an insulating layer and reducing the thickness of the insulating layer for the purpose of reinforcing effective electric field strength of a phosphor.

However, there are problems such that sufficient light emitting characteristics (compatibility of brightness and life) cannot be obtained, for example, when the ratio of dielectric particles is increased to raise the dielectric constant of an insulating layer, the ratio of the binder relatively lowers and coating property deteriorates, and when the thickness of the insulating layer is decreased, insulation resistance reduces.

JP-A-2005-302693 discloses to form a light-scattering layer with the same material as used in an insulating layer, and shift the wavelength of a color conversion wavelength to the longer side by a red conversion material by generating multi- scattering.

Summary of Invention However, there are almost no descriptions in JP-A-2005-302693 about the fact that the insulating layer does not function as the insulating layer according to the technique, and about the characteristics of the material to be used in the insulating layer.

Accordingly, an object of the invention is to provide a dispersion-type EL device excellent in light emission brightness and improved in light emitting life.

As a result of earnest examinations, the present inventors have found that high brightness and long life are achieved by properly setting the average particle size and the filling ratio of particles having high dielectric constant in an insulating layer, thus the invention has been accomplished.

(1) A dispersion-type electroluminescence device, containing: a pair of electrodes including a back electrode and a transparent electrode; and at least an insulating layer and a light-emitting layer provided between the pair of electrodes, wherein the insulating layer contains dielectric particles, an average particle size of the dielectric particles contained in the insulating layer is in a range of from 0.40 to 1.0 μm, and a volume ratio of the dielectric particles contained in the insulating layer is 30 to 60%.

(2) The dispersion-type electroluminescence device as described in (1), wherein the light-emitting layer contains phosphor particles, an average particle size of the phosphor particles contained in the light-emitting layer is in a range of 1 μm or more and less than 20 μm, and a variation coefficient with respect to particle sizes is 3% or more and less than 40%.

(3) The dispersion-type electroluminescence device as described in (1) or (2), wherein either of the layers of the dispersion-type electroluminescence device contains a red conversion material. (4) The dispersion-type electroluminescence device as described in (1) or (2), wherein the light-emitting layer contains red light-emitting phosphor particles besides the phosphor particles.

(5) The dispersion-type electroluminescence device as described in (3), wherein a red conversion material layer containing a red conversion material is provided between the light-emitting layer and the back electrode.

(6) The dispersion-type electroluminescence device as described in (4), wherein an average particle size of the red-emitting phosphor particles is 1 μm or more and less than 20 μm, and a variation coefficient with respect to the particle sizes is 3% or more and less than 40%.

Incidentally, in the invention, "phosphor particles" means particles that emit light by the application of voltage.

Description of Embodiments

The invention will be described in detail below. Dielectric particles:

The insulating layer of the EL device in the invention contains dielectric particles (hereinafter also referred to as "high dielectric material" or "particles having a high dielectric constant" in some cases). As the high dielectric material, arbitrary materials are used so long as they are materials having a high dielectric constant, a high insulating property, and high dielectric breakdown voltage. A material having a high dielectric constant forms an insulating layer as particles with the later-described organic binder. It is preferred for a material having a high dielectric constant to have high light reflectance. A material having a high dielectric constant has a function of reflecting and scattering the light generated from a phosphor in an EL device and taking out the light forward. As a result of heightening of the function, light emission brightness can be raised.

As the examples of the materials having a high dielectric constant, BaTiO₃, KNbO₃, LiNbO₃, LiTaO₃, Ta₂O₃, BaTa₂O₆, Y₂O₃, Al₂O₃, and AlON are exemplified. BaTiO₃ powder, Palceram (manufactured by Nippon Chemical Industrial Co., Ltd.) is preferably used.

The average particle size of the materials having a high dielectric constant is 0.40 to 1.0 μm. When the average particle size is less than 0.40 μm, the average particle size is smaller than visible light wavelength, and Rayleigh scattering is predominant as light scattering, so that the effect of scattering is lessened. Contrary to this, when the average particle size is 0.40 μm or more, Mie scattering is predominant and light emission of a phosphor can be efficiently scattered. When the average particle size exceeds 1.0 μm, the compatibility with the binder lowers and a coating property is reduced, and so not preferred. The average particle size is preferably 0.42 to 0.80 μm, and is more preferably 0.44 to 0.65 μm.

The average particle size of a high dielectric constant material can be measured according to a method by laser scattering with, for example, a laser diffraction/scattering system particle size distribution measuring apparatus LA-920 (manufactured by Horiba Seisakusho Co., Ltd.). Here, the particle size indicates a median diameter. Phosphor particles:

Phosphor particles preferably used in the invention are specifically particles of semiconductors including compounds selected from the group consisting of compounds containing one or plural elements belonging to the Group II elements and one or plural elements belonging to the Group VI elements of the periodic table, and compounds containing one or plural elements belonging to the Group III elements and one or plural elements belonging to the Group V elements of the periodic table, and they are arbitrarily selected according to necessary light emission wavelength region. For example, CdS, CdSe, CdTe, ZnS, ZnSe, ZnTe, CaS, SrS, GaP, and GaAs are exemplified. ZnS, CdS and CaS are preferably used of them.

Phosphor particles for use in the invention can be formed according to a baking method (a solid phase method) well known in the industry. For example, in the case of zinc sulfide, fine particle powder having a particle size of 10 to 50 run (generally called crude powder) is manufactured by a solid phase method, and the obtained powder is used as primary particles, i.e., a base material. Zinc sulfide includes two crystal systems of a high temperature stable type hexagonal system and a low temperature stable type cubic system, and either may be used, and mixture of them may be used. The base material is baked in a crucible with impurities called activator and co-activator, and a flux at a high temperature of 900 to 1,300⁰C for 30 minutes to 10 hours to obtain intermediate phosphor particles. The baking temperature for obtaining phosphor particles having proper average particle size and low variation coefficient of particle sizes is preferably 950 to 1,250⁰C, and more preferably 1,000 to 1,200⁰C. The baking time is preferably 30 minutes to 6 hours, and more preferably 1 to 4 hours. Further, in the invention, it is preferred that the average particle size is 1 μm or more and less than 20 μm, and the variation coefficient is 3% or more and less than 40%.

The average particle size and the variation coefficient of particle sizes of phosphor particles can be measured according to a method by laser scattering with, for example, a laser diffraction/scattering system particle size distribution measuring apparatus LA-920 (manufactured by Horiba Seisakusho Co., Ltd.) similarly to the measurement of the above high dielectric constant material.

As the flux, the use amount is 20% by mass or more, preferably 30% by mass or more, and more preferably 40% by mass or more. The proportion of the flux here is shown as follows: The proportion of the flux (% by mass) = the mass of the flux/(the mass of the raw material phosphor primary particles + the mass of the flux). For example, when copper that is an activator is mixed with crude powder in advance as the later-described copper-activated zinc sulfide phosphor, the copper of activator and the raw material powder of phosphor are mixed in one, and in such a case, the raw material powder of phosphor including the copper is measured as the mass of the raw material powder of phosphor.

The mass of a flux at room temperature and that at a baking temperature differ in some cases. For example, barium chloride is present in the state of BaCl₂ • 2H₂O at room temperature, but it is considered that water of hydration is lost at a baking temperature and becomes BaCl₂. However, the proportion of the flux here is computed on the basis of the mass of the flux in a stable condition at room temperature.

Further, in the invention, for removing excessive activator and co-activator contained in the intermediate phosphor powder obtained by baking, it is preferred to wash the intermediate phosphor powder with ion exchange water.

Plane-like stacking fault (a twin crystal structure) naturally occurred is present in the intermediate phosphor particle obtained by baking. By applying a certain range of impact force thereto, the density of the stacking fault can be greatly increased without destroying the particle. As the methods of applying impact force, a method of bringing the intermediate phosphor particles into contact and mixing, a method of mixing the particles by means of the mixture of spheres such as alumina (a ball mill), and a method of accelerating and impinging the particles are conventionally known. In particular in the case of zinc sulfide, two crystal systems of a cubic system and a hexagonal system are present, and the closest atomic plane ((111) face) in the former takes three-layer structure of ABCABC ... , and the closest atomic plane perpendicular to c axis in the latter forms two-layer structure of ABAB.... Accordingly, when impact force is applied to zinc sulfide crystal by a ball mill and the like, sliding on the closest atomic plane occurs in the cubic system and, when C planes come out, the cubic system partly becomes hexagonal system of ABAB, and edge dislocation occurs, or AB planes are reversed, which causes twin crystal in some cases. Since impurities in a crystal are generally concentrated at lattice defect parts, when zinc sulfide having stacking fault is heated and an activator such as copper sulfide is diffused, the activator precipitates at the stacking fault. The interface between the precipitated part of the activator and the zinc sulfide of the base material is the center of the emitter of electroluminescence, so that stacking fault density is preferably high in the invention for the improvement of brightness.

In the next place, the obtained intermediate phosphor powder is subjected to the second baking. The second baking is performed at 500 to 800⁰C that is lower than the first baking, and heating (annealing) for 30 minutes to 3 hours of shorter time, by which the activator can be convergently precipitated at the stacking fault.

After that, the intermediate phosphor is subjected to etching with acid, e.g., hydrochloric acid, to remove adhered metal oxide from the surface, and further, washing with KCN and the like to eliminate adhered activator from the surface. Subsequently, the intermediate phosphor is dried to obtain an electroluminescence phosphor.

By means of these methods, particles having an average particle size of 1 μm or more and less than 20 μm, and a variation coefficient of particle sizes of 3% or more and less than 40% can be obtained, and it is preferred to use such particles in the invention.

As other forming methods of phosphors, vapor phase methods such as methods of combinations of a laser ablation method, a CVD method, a plasma method, sputtering, resistance heating, or an electron beam method with flowing oil level deposition, liquid phase methods such as a double decomposition method, a method by thermal decomposition reaction of a precursor, a reverse micelle method, methods of combinations of these methods with high temperature baking, and a freeze drying method, in addition, a urea melting method, and a spray thermal decomposition method can also be used.

It is also preferred that the phosphor powder in the invention is zinc sulfide containing copper as an activator, and contains at least one kind of metal element belonging to the second transition metals of Group VI to Group X of the periodic table. Molybdenum, platinum and iridium are especially preferred. These metals are preferably contained in zinc sulfide in the range of 1 x 10^"7 mol to 1 x 10^"3 mol per mol of zinc sulfide, and more preferably in the range of 1 x 10 ⁶ mol to 5 x 10^"4 mol. It is preferred that these metals are added to deionized water together with zinc sulfide fine powder and a prescribed amount of copper sulfate, thoroughly mixed in a slurry state, dried, and baked with an activator and a flux to be contained in zinc sulfide particles, and it is also preferred that complex powder containing these metals is mixed in advance with a flux, and baking is carried out by using the co-activator and a flux to be contained in zinc sulfide particles. In either case, an arbitrary compound containing a metal element to be used as the raw material compound at the time of addition of the metal, but it is more preferred to use a complex of a metal or a metal ion coordinated with oxygen or nitrogen. The ligands may be inorganic compounds or organic compounds. Brightness can further be improved and life can be prolonged by these operations.

The phosphor particles may have non-luminous shell layer on the surfaces of the particles. With regard to the details of the non-luminous shell layer, JP-A-2005- 283911, paragraphs [0028] to [0033] can be referred to. Insulating layer:

The insulating layer in the EL device of the invention contains the above particles having a high dielectric constant and is generally formed with an organic binder. The content of the high dielectric particles in the insulating layer is 30 to 60% in a volume ratio. When the content is less than 30%, since the ratio of the high dielectric particles is low, the dielectric constant of the insulating layer itself lowers and electric field is not effectively applied to the light-emitting layer, and so not preferred. When the content is 30% or more, it is expected that the dielectric constant as the insulating layer becomes high and electric field is effectively applied to the light-emitting layer. However, as a result of earnest examinations by the present inventors, it has been found that if the content exceeds 60%, a coating property suddenly lowers, a smooth coated plane cannot be formed, unevenness occurs in light emission, and durability is worsened. Further, it has been surprisingly found that when an insulating layer is formed with the content exceeding 60%, the probability of contact of high dielectric particles to each other heightens, the course of the beam of light is closed as a result the light is shut in the layer and cannot come out, and the effect of improving the brightness is almost lost. The volume ratio is preferably 35 to 57%, and more preferably 40 to 55%.

From these facts, it is considered that the invention properly prescribing the average particle size and volume ratio of the high dielectric particles in the insulating layer is contributable to the improvement of EL device.

The thickness of the insulating layer is preferably 10 μm or more and less than 35 μm, more preferably 12 μm or more and less than 33 μm, and still more preferably 15 μm or more and less than 33 μm. When the insulating layer is too thin, insulation breakdown is liable to occur, while when the insulating layer is too thick, the voltage applied to the light-emitting layer reduces and light emitting efficiency substantially diminishes, and so not preferred.

As the organic binders usable in the insulating layer, polymers having a relatively high dielectric constant, e.g., cyanoethyl pluran, cyanoethyl polyvinyl alcohol, cyanoethyl cellulose-based resins, and resins, e.g., polyethylene, polypropylene, polystyrene-based resins, silicone resins, epoxy resins, and vinylidene fluoride are exemplified. Fine particles having a high dielectric constant, such as BaTiO₃ and SrTiO₃ are mixed to the above exemplified resins and dispersed by adjusting the volume ratio in the insulating layer to the above range so as to be capable of obtaining a desired dielectric constant. As dispersing methods of the fine particles in the resins, a homogenizer, a planetary kneader, a roll kneader, and an ultrasonic wave disperser can be used. Light-emitting layer:

In manufacturing an EL device with phosphor particles, these particles are dispersed in an organic dispersion medium, and the resulting dispersion is coated to form a light-emitting layer.

As the organic dispersion media, organic polymeric materials and organic solvents having a high boiling temperature can be used, but an organic binder mainly containing an organic polymeric material is preferably used. As the organic binders, materials having a high dielectric constant are preferred, for example, fluorine-containing polymeric compounds (e.g., ethylene fluoride, polymeric compounds containing ethylene trifluoride monochloride as the polymer unit), polysaccharides having a cyanoethylated hydroxyl group (e.g., cyanoethyl pluran, cyanoethyl cellulose), polyvinyl alcohols (e.g., cyanoethyl polyvinyl alcohol), and resins, e.g., phenol resins, polyethylene, polypropylene, polystyrene-based resins, silicone resins, epoxy resins, and vinylidene fluoride are exemplified, and it is preferred for the light-emitting layer to contain all or a part of these as the organic binder. It is also possible to adjust the dielectric constant by properly mixing fine particles having a high dielectric constant, e.g., BaTiO₃ and SrTiO₃, to these binders.

As the dispersing methods of the phosphor particles in the binders, a homogenizer, a planetary kneader, a roll kneader, and an ultrasonic wave disperser can be used.

It is preferred to determine the blending proportion of the binders and the phosphor particles so that the content of the phosphor particles in the light-emitting layer is 30 to 90% by mass to all the solids content, and more preferably 60 to 85% by mass. By such a constitution, the surface of the light-emitting layer can be made smooth.

As the binder, it is preferred to use the polymeric compound having a cyanoethylated hydroxyl group in an amount of 20% or more in mass ratio of the organic dispersion medium in the light-emitting layer as a whole, and more preferably 50% or more.

The thickness of the thus-obtained light-emitting layer is preferably 20 μm or more and less than 80 μm, and more preferably 25 μm or more and less than 75 μm. When the thickness is 20 μm or more, good smoothness of the light-emitting layer surface can be obtained, and when it is less than 80 μm, electric field can be effectively applied to the phosphor particles, and so preferred. In particular, when the later-described cut-off layer is provided, reduction of initial brightness can be recovered and sufficient durability effect can be obtained by thinning the film thickness of the insulating layer and thickening the film thickness of the light- emitting layer. For obtaining good initial brightness, the film thickness of the light- emitting layer is preferably 70 μm or less. Cut-off layer:

The EL device of the invention may have a cut-off layer between a transparent electrode and a light-emitting layer. With regard to the details of the cutoff layer, JP-A-2007- 12466, paragraphs [0013] to [0020] can be referred to. Red color material:

When phosphor particles that emit light in blue green are used in the electroluminescence device of the invention, a light-emitting material emitting light in red is used besides the phosphor particles that emit light in blue green in order to produce white-emitting light. The red light-emitting material may be any of an organic material absorbing light emission of phosphor particles emitting light in blue green and converting the absorbed light emission to red, and an inorganic material showing red electroluminescence. As the former, organic fluorescent dyes and fluorescent pigments are especially used, and these materials may dispersed in a light-emitting layer or in an insulating layer, or may be positioned between the light- emitting layer and a transparent electrode or on the opposite side of the light-emitting layer to the transparent electrode. The latter can be contained in the light-emitting layer, similarly to the phosphor material that emits light in blue green, or can be introduced as a red inorganic phosphor material layer between the transparent electrode and the insulating layer separately from a layer containing a phosphor material emitting light in blue green.

As the phosphor particles emitting light in red preferably used in the invention, similarly to the phosphor material that emits light in blue green, the base material is selected form the group consisting of compounds containing one or plural elements belonging to the Group II elements and one or plural elements belonging to the Group VI elements of the periodic table, and compounds containing one or plural elements belonging to the Group III elements and one or plural elements belonging to the Group V elements of the periodic table, and they are arbitrarily selected according to necessary light emission wavelength region. Activators are not especially restricted and selected from, for example, transition metals such as Cu and Mn, and co-activators are selected from the elements belonging to Group VII, e.g., F, Cl, Br and I, and the elements belonging to Group III, e.g., Al, Ga and In. It is also preferred that rare earth elements such as Ce, Eu and Sm are also doped, specifically, ZnS:Cu, In and CaSrEu, Ce are applied thereto.

Red conversion organic materials will be particularly described in detail below.

In the electroluminescence device of the invention, light emission wavelength of a red color at the time of white light emission is preferably 590 nm or more and 650 nm or less. For obtaining red-emitting wavelength included in this range, a red conversion material may be contained in a light-emitting layer, may be contained between the light-emitting layer and a transparent electrode, or may be contained on the opposite side of the light-emitting layer with the transparent electrode as center, but it is most preferred to be contained in an insulating layer. As the insulating layer containing the red conversion material, it is preferred that all the insulating layers in the electroluminescence device of the invention contain the red conversion material, but it is more preferred to divide the insulating layer in the device into two or more and a part of the divided insulating layers contains the red conversion material. The layer containing the red conversion material is preferably positioned between the insulating layer not containing the red conversion material and the light-emitting layer, and it is also preferred that the layer containing the red conversion material is positioned so as to be flanked on both sides with the insulating layers not containing the red conversion material.

When the layer containing the red conversion material is positioned between the insulating layer not containing the red conversion material and the light-emitting layer, the thickness of the layer containing the red conversion material is preferably 1 μm or more and 20 μm or less, and more preferably 3 μm or more and 17 μm or less. When the layer containing the red conversion material is positioned so as to be flanked on both sides with the insulating layers not containing the red conversion material, the thickness of the layer containing the red conversion material is preferably 1 μm or more and 20 μm or less, and more preferably 3 μm or more and 10 μm or less. When the layer containing the red conversion material is positioned so as to be flanked on both sides with the insulating layers not containing the red conversion material, it is also preferred for the layer containing the red conversion material not to contain dielectric particles and to contain only a binder having a high dielectric constant and the red conversion material.

The light emission wavelength at the time when the red conversion material used here is in a powder state is preferably 590 nm or more and 750 nm or less, more preferably 600 nm or more and 650 nm or less, and most preferably 605 nm or more and 630 nm or less. When the red conversion material is added to the electroluminescence device, the light emission wavelength of red at the time of light emission is preferably 590 nm or more and 650 nm or less as described above, more preferably 595 nm or more and 630 nm or less, and most preferably 600 nm or more and 620 nm or less.

As the binder in the layer containing the red conversion material, polymers having a relatively high dielectric constant, e.g., cyanoethyl pluran, cyanoethyl polyvinyl alcohol, cyanoethyl cellulose-based resins, and resins, e.g., polyethylene, polypropylene, polystyrene-based resins, silicone resins, epoxy resins, and vinylidene fluoride are preferred.

As the red conversion materials of the invention, fluorescent dyes and fluorescent pigments can be preferably used. As these compounds occupying the position of the center of light emission, rhodamine, lactone, xanthene, quinoline, benzothiazole, triethylindoline, perylene, triphennine, and compounds having a dicyanomethylene structure are preferably used. In addition to the above, cyanine dyestuffs, azo dyes, polyphenylene vinylene polymers, disilane oligo-ethynylene polymers, ruthenium complexes, europium complexes and erbium complexes are also preferably used. These compounds may be used alone or a plurality of kinds of compounds may be used in combination. These compounds may be used after being dispersed in a polymer. As the fluorescent pigment having light emission maximum in the above range, "SEL-1003" (manufactured by SINLOIHI CO., LTD.) can be used.

The above fluorescent pigments or fluorescent dyes can be adjusted to have light emission maximum in the above range by using a filter such as a band reflection filter. Transparent electrode:

A transparent electrode can be obtained by uniformly adhering and film forming by a method of depositing, coating, or printing a transparent conductive material, such as indium tin oxide (ITO), tin oxide, antimony-doped tin oxide, zinc- doped tin oxide, or zinc oxide on a transparent film such as polyethylene terephthalate or triacetyl cellulose, to say nothing of a glass substrate.

A multilayer structure comprising a silver thin film sandwiched with high refractive index layers may be used. Further, it is possible to preferably use conductive polymers such as conjugate polymers, e.g., polyaniline and polypyrrole.

These transparent conductive materials are described in Denjiha Shield Zairyo no Genjo to Shorai (The Present Situation and The Future of Electromagnetic Wave-Shielding Materials), published by Research Center, Toray Industries Inc., and JP-A-9- 147639.

As the transparent electrode, it is possible to use a transparent conductive sheet improved in conductivity that is obtained by forming a conductive plane in which a fine line structural part of a metal and/or an alloy of a uniform network-like, a comb-type, or a grid-type is arranged on a transparent conductive sheet or a conductive polymer manufactured by adhering a transparent conductive material on the above transparent film and film-forming.

When the above fine line is used in combination, as the materials of the fine lines of the metal and alloy, copper, silver, nickel, and aluminum are preferably used, but according to purposes, the above transparent conductive materials may be used in place of metal and alloy. Such conductive materials are preferably materials high in electric conductivity and thermal conductivity. The width of the fine line is arbitrary but between 0.1 μm or so and 1,000 μm is preferred. The fine lines are preferably arranged by the pitch of distance of 50 μm to 5 cm, and a pitch of 100 μm to 1 cm is especially preferred.

The height (thickness) of the fine line structural part is preferablyO.l μm or more and 10 μm or less, and especially preferably 0.5 μm or more and 5 μm or less. Either of the fine line structural part and transparent conductive film may be the obverse, but the smoothness (unevenness) of the conductive plane is preferably 5 μm or less. From the viewpoint of adhesion, the weight is preferably 0.01 μm or more and 5 μm or less, and especially preferably 0.05 μm or more and 3 μm or less.

The smoothness of the conductive plane (unevenness) shows the average amplitude at the unevenness part when the area of 5 mm square is measured with a three dimensional surface roughness meter (e.g., SURFCOM 575A-3DF, manufactured by Tokyo Seimitsu). When the smoothness cannot be obtained by the resolution of the surface roughness meter, the smoothness is found by measurement with an STM and an electron microscope.

With regard to the relationship of the width and height and the distance of the fine lines, the width of the fine lines may be determined according to purposes, but the width is typically preferably 1/10,000 or more and 1/10 or less of the fine line distance.

The height of the fine line is also the same and the height is preferably in the range of 1/100 or more and 10 times or less of the fine line width.

The surface resistivity of the transparent electrode for use in the invention is preferably 1 Ω/G or more and 100 Ω/α or less, and more preferably 1 Ω/α or more and 80 Ω/α or less. The surface resistivity of the transparent electrode is a value measured according to the method described in JIS K6911.

When a metal and/or alloy fine line structural parts is arranged as the transparent electrode, it is preferred to control the reduction of light transmittance. It is preferred to secure 90% or more light transmittance by bringing the distance of fine lines, width and height of fine lines into the above ranges.

It is preferred in the invention that light transmittance of the transparent electrode is 70% or more to the light of 550 nm, more preferably 80% or more, and most preferably 90% or more.

For the purpose of improving brightness and realizing white light emission, it is preferred that the transparent electrode is capable of transmitting the light in the region of wavelength of 420 nm to 650 nm by 80% or more, more preferably by 90% or more. In realizing white light emission, it is more preferred that the transparent electrode is capable of transmitting the light in the region of wavelength of 380 nm to 680 nm by 80% or more. The light transmittance of a transparent electrode can be measured with a spectrophotometer. Back electrode:

As the back electrode on the side not taking out light, arbitrary materials having conductivity can be used. The material is any time selected from metal such as gold, silver, platinum, copper, iron and aluminum, and graphite, according to the shape of the device manufactured, and the temperatures of the manufacturing processes. A transparent electrode such as ITO may be used so long as it has conductivity. Further, for improving durability, it is important that the heat conductivity of a back electrode is high, which is preferably 2.0 W/cm-deg or more, and especially preferably 2.5 W/cm-deg or more.

Further, for securing high heat dissipating property and current-carrying property at the peripheral parts of the EL device, it is preferred to use a metal sheet and a metal mesh as the back electrode. Manufacturing method:

The manufacturing method of the EL device of the invention is not especially restricted, and the methods disclosed in detail in JP-A-2007- 12466, paragraphs [0046] to [0049] can be adopted. Sealing:

It is preferred that the dispersion-type EL device of the invention is finally processed to exclude the influence of humidity and oxygen from the outside environment with a sealing film. The details of sealing are disclosed in JP-A-2007- 12466, paragraphs [0050] to [0055].

The invention is especially effective in the uses to use the EL device for light emission at high brightness (e.g., 600 cd/m² or more). Specifically, the invention is effective in the case for use on the driving condition of applying voltage of 100 V or more and 500 V or less between the transparent electrode and the back electrode of the EL device, or the case for use on the driving condition by AC power of frequency of 800 Hz or more and 4,000 KHz or less.

Examples

The examples of the distributed EL devices of the invention are shown below, but the distributed EL devices of the invention are not restricted thereto.

EXAMPLE 1

On the aluminum electrode (back electrode) having a thickness of 70 μm, an insulating layer (first layer, thickness: 25 μm) and a light-emitting layer (second layer, thickness: 55 μm) are coated in this order.

Cyanoethyl pluran and cyanoethyl polyvinyl alcohol are mixed in mass ratio of 1/1 and the resulting mixture is used in each layer as the organic binder. BaTiO₃ having an average particle size as shown in Table 1 below (Palceram BT, manufactured by Nippon Chemical Industrial Co., Ltd.) is used in the insulating layer as high dielectric particles in the volume ratio as shown in Table 1.

The light-emitting layer is manufactured by adjusting the phosphor particles prepared as shown below in the volume ratio to the organic binder of 1/1.

The viscosity of the coating solution for forming each layer is adjusted by adding dimethylformamide and the layer after coating is dried at 110⁰C for 10 hours.

Polyethylene terephthalate (thickness: 75 μm) sputtered with indium tin oxide to form a transparent electrode having a thickness of 40 run is pressure-bonded by means of a heat roller at 190⁰C in the nitrogen atmosphere so that the transparent electrode side (conductive face side) faces the aluminum electrode side and the transparent electrode and phosphor particles-containing layer (light-emitting layer) as the second layer are contiguous to each other.

The aluminum electrode and the transparent electrode are respectively wired for an electrode terminal (an aluminum plate having a thickness of 60 μm) and the obtained product is sandwiched between moisture-proof films (GX film, manufactured by Toppan Printing Co., Ltd.) and sealed by thermally pressure- bonding while vacuum deaeration to manufacture the EL device shown in Table 1. Preparation of phosphor particles:

Water is added to 150 g of ZnS (purity: 99.999%, manufactured by Furuuchi Chemical Corporation) to make a slurry, an aqueous solution containing 0.538 g of CuSO₄-5H₂O and sodium chloroaurate in an amount of 0.0001 mol% based on the zinc are added to the slurry to obtain ZnS crude powder (having an average particle size of 100 run) partly substituted with Cu (1.4*10^"3 mol of Cu per mol of ZnS). To 25.0 g of the obtained crude powder are added 2.1 g of BaCl₂-2H₂O, 4.25 g of MgCl₂-OH₂O, and 1.0 g of SrCl₂-OH₂O, and the mixture is baked at 1,200⁰C for 4 hours to obtain phosphor intermediate. The above particles are washed with ion exchange water 10 times and dried. The obtained intermediate is crushed with a ball mill and then annealed at 700⁰C for 4 hours.

The obtained phosphor particles are washed with a 10% KCN aqueous solution to remove extra copper on the surface (copper sulfide), and then washed five times with water to obtain phosphor particles A having an average particje size of 24 μm and a variation coefficient of particle sizes of 36%.

In connection with Cu content, phosphor particles are dissolved in aqua regia, and the content is measured from the percentage to Zn by ICP emission analysis. Further, the average particle size and the variation coefficient of particle sizes are measured with a laser diffraction/scattering system particle size distribution measuring apparatus LA-920 (manufactured by Horiba Seisakusho Co., Ltd.).

The particle size of BaTiO₃ used in each device and the volume ratio are shown in Table 1.

With respect to the thus-obtained EL devices, relative value of initial brightness of each device with respect to the emission brightness of EL device 101 driven by 120 V and 1.4 kHz being 100, and emission brightness of each device after continuously driving for 150 hours on a condition where the driving voltage of each device is adjusted by fine control so as to obtain the same initial brightness and the initial brightness is taken as 100. The results are shown in Table 1. TABLE 1

OJ

Since the average particle sizes OfBaTiO₃ of EL devices 101 to 103 and 110 are small, light scattering performance of these devices is low, initial brightness is also relatively low, and relative brightness after continuous driving at the same brightness is also low. In particular, the volume ratio Of BaTiO₃ of EL device 101 is low, so that the relative brightness is low. Although the volume ratio of BaTiO₃ of EL device 103 is large, initial brightness and relative brightness after continuous driving are equal or lower as compared with EL device 102 having the volume ratio smaller than that of EL device 103, and the effect of the improvement of brightness is not seen. Further, when EL device 103 is bent with the back electrode side of the device being concave side, peeling is generated at the interface in the layer, and emission became uneven after that. EL device 103 is also reduced in flexibility. For the reasons that EL device 104 is low in the volume ratio Of BaTiO₃, EL device 108 is high in the volume ratio Of BaTiO₃, and EL device 109 is large in the average particle size Of BaTiO₃, they are low in the initial brightness and the brightness after continuous driving, and all of these devices are out of the range of the invention. Contrary to these, since the average particle sizes and the volume ratios of BaTiO₃ of EL devices 105 to 107, 111 and 112 are in proper ranges, they all show good values of initial brightness and relative brightness after continuous driving.

EXAMPLE 2

Phosphor particles B having an average particle size of 17 μm and a variation coefficient of the particles of 31% is obtained in the same manner as in the manufacture of phosphor particles A in Example 1 except for changing the use amounts of fluxes, BaCl₂-2H₂O to 4.2 g, MgCl₂-OH₂O to 11.2 g, and SrCl₂ OH₂O to 9.O g.

EL device 201 is manufactured with phosphor particles B in the same condition as EL device 106. The initial brightness and relative brightness after 150 hours of EL device 201 are evaluated in the same manner as in Example 1. The effects of improvement of 10% or so are obtained in both items.

EXAMPLE 3

EL device is manufactured in the same manner as in Example 2 except for adding 3.0 g/m² of red fluorescent dye (SEL-1003, manufactured by SINLOIHI CO., LTD.) to the insulating layer in the EL device. As a result, as compared with EL device 106, not only the initial brightness and relative brightness after 150 hours are improved but also white light emission excellent in a color rendering property (Ra 80 or more) can be obtained.

Industrial Applicability

The dispersion-type EL device in the invention is a device reconciling high brightness and long life. Further, it shows excellent color reproducibility (a color rendering property) when it is tried to obtain light emission in white by combination with a red coloring material.

This application is based on Japanese patent application JP 2009-064411, filed on March 17, 2009, the entire content of which is hereby incorporated by reference, the same as if set forth at length.

Claims

1. A dispersion-type electroluminescence device, comprising: a pair of electrodes including a back electrode and a transparent electrode; and at least an insulating layer and a light-emitting layer provided between the pair of electrodes, wherein the insulating layer contains dielectric particles, an average particle size of the dielectric particles contained in the insulating layer is in a range of from 0.40 to 1.0 μm, and a volume ratio of the dielectric particles contained in the insulating layer is 30 to 60%.

2. The dispersion-type electroluminescence device according to claim 1, wherein the light-emitting layer contains phosphor particles, an average particle size of the phosphor particles contained in the light-emitting layer is in a range of 1 μm or more and less than 20 μm, and a variation coefficient with respect to particle sizes is 3% or more and less than 40%.

3. The dispersion-type electroluminescence device according to claim 1 or 2, wherein either of the layers of the dispersion-type electroluminescence device contains a red conversion material.

4. The dispersion-type electroluminescence device according to claim 1 or 2, wherein the light-emitting layer contains red light-emitting phosphor particles besides the phosphor particles.