JP2006032100A - Inorganic dispersion type electroluminescent element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inorganic dispersion type EL element having a new structure capable of emitting light with high brightness for a long period without spoiling its light weight and flexibility. <P>SOLUTION: The inorganic dispersion type electroluminescent element has a paired electrodes composed of a back face electrode 1 and a transparent electrode 10, and at least a light emitting layer 3 laid between the paired electrodes. The transparent electrode 10 has two or more of transparent conductive layers (12, 13) different from each other, on a flexible transparent base material 11. At least one layer out of the transparent conductive layers is an ITO film 12. At least one transparent conductive layer 13 located at a position nearer to the light-emitting layer side than the ITO layer is composed of tin oxide or zinc oxide which may be doped with one element selected from among fluorine, antimony, aluminum, gallium and boron. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an inorganic dispersion type electroluminescence device.

  An electroluminescence (hereinafter also referred to as “EL”) phosphor is a voltage excitation type phosphor, and a dispersion type EL panel is known in which a phosphor powder is sandwiched between electrodes to form a light emitting panel. The general shape of a dispersion-type EL panel consists of a structure in which phosphor powder is dispersed in a binder with a high dielectric constant, and at least one is sandwiched between two transparent electrodes. Light is emitted by applying an electric field. The light-emitting panel made using phosphor powder can be several millimeters or less in thickness, is a surface light emitter, and has many advantages such as low heat generation, so it can be used for road signs, various interiors and exteriors. Applications include light sources for flat panel displays such as lighting and liquid crystal displays, and illumination light sources for large-area advertisements.

  Since the dispersion type EL panel does not use a high temperature (for example, 300 ° C. or higher) process, it is possible to form a flexible panel using a plastic substrate, and it is a relatively simple process without using a vacuum device. It can be manufactured at low cost, and it is easy to adjust the emission color of the panel by mixing multiple phosphor particles with different emission colors. Has been. However, since the light emission luminance and efficiency are low, and a high voltage of 100 V or higher is required for high luminance light emission, the application range is limited. Conventionally, it is used for light emission with high luminance for a long time (for example, sign and display use) ) Could not be used.

On the other hand, a factor of luminance deterioration of inorganic dispersion type EL is considered to be a decrease in performance of an indium tin oxide film (hereinafter also referred to as “ITO film”) generally used as a transparent electrode. It is considered that the deterioration of the ITO film is caused by the diffusion of ions from the phosphor particles by applying a high electric field (Non-Patent Document 1).
T.IEE Japan, Vo.l.118-A, No.7 / 8, 98 p812-817

  Accordingly, the present invention has been made to solve the above-described problems, and provides an inorganic dispersion type EL element having a novel structure that is lightweight and flexible, and that can emit light with high brightness for a long time. The purpose is to do.

  In order to cause the inorganic dispersion type EL panel to emit light with high luminance, it is necessary to increase the applied voltage or increase the AC frequency. However, when a high voltage is applied, for example, ZnS is decomposed on the surface of the phosphor particles, and S ions generated by the decomposition are diffused to deteriorate the ITO film, and the dispersive EL panel emits light with high luminance emission. It was found that the efficiency is low and most of the input power is consumed by heat generation in high luminance light emission, and heat generation becomes remarkable in high luminance light emission, which can further adversely affect deterioration of the ITO film.

  As a result of various investigations based on such knowledge, the present inventors have found that the above-mentioned problems can be solved by adopting a transparent electrode having a specific configuration as the transparent electrode, and have reached the present invention. . That is, this invention consists of the following structures.

  (1) An inorganic dispersion type electroluminescent device having at least a light emitting layer between a pair of electrodes consisting of a back electrode and a transparent electrode, wherein the transparent electrode has two or more layers on a flexible transparent substrate. Having at least one transparent conductive layer, at least one layer of the transparent conductive layer is an indium tin oxide film, and at least one transparent conductive layer on the light emitting layer side of the indium tin oxide film, Inorganic dispersion characterized by being at least one transparent conductive film selected from tin oxide and zinc oxide, each of which may be doped with at least one element selected from fluorine, antimony, aluminum, gallium and boron Type electroluminescence element.

(2) The inorganic dispersion-type electroluminescent device according to (1), wherein at least one transparent conductive layer on the light emitting layer side of the indium-tin-oxide film is a film made of fluorine-doped tin oxide.
(3) The inorganic dispersion type electroluminescent element according to the above (1) or (2), wherein the back electrode is a graphite sheet.
(4) The inorganic dispersion type electroluminescent device as described in any one of (1) to (3) above, wherein the light emitting layer contains phosphor fine particles having an average sphere equivalent diameter of 0.1 to 15 μm. .

In accordance with the present invention, the transparent electrode of the inorganic dispersion-type EL element has at least two layers, and the ITO film and a specific transparent conductive layer on the light emitting layer side of the ITO film provide chemical resistance and ion diffusion resistance. It is expected that effects such as effective prevention of heat resistance and improvement in heat resistance can be obtained. By these effects, even when a high voltage necessary for high-luminance light emission is applied, deterioration of the transparent electrode can be effectively prevented, and high-luminance light emission for a long time is made possible.
That is, according to the present invention, it is possible to provide an inorganic dispersion-type EL element that has lightness and flexibility and can emit light with high luminance for a long time.
In addition, the EL element of the present invention exhibits a remarkable long life effect when emitting light with high luminance, preferably when emitting light at 300 cd / m ² or more, more preferably at 500 cd / m ² or more.

  Hereinafter, the EL element, EL display device, and manufacturing method thereof of the present invention will be described in detail. In the present specification, “to” is used as a meaning including numerical values described before and after the lower limit value and the upper limit value.

The inorganic dispersion type EL device of the present invention will be specifically described below with reference to FIG.
FIG. 1 is a schematic cross-sectional view showing an example of an inorganic dispersion type EL element of the present invention.

In the inorganic dispersion type EL element of the present invention, a dielectric layer 2, a light emitting layer 3, and a transparent electrode 10 are laminated in this order on a back electrode 1, and a light emitting portion in an EL display device (display panel) described later is formed. To do.
The transparent electrode 10 has two transparent conductive layers on a flexible transparent substrate 11, and the transparent conductive layer 13 on the light emitting layer 3 side is selected from fluorine, antimony, aluminum, gallium, and boron. It is at least one transparent conductive film selected from tin oxide and zinc oxide, each of which may be doped with at least one element, and the transparent conductive layer 12 on the transparent substrate side is an indium tin oxide film (ITO Membrane).

  Examples of the transparent electrode substrate 11 include flexible polymers such as polyethylene terephthalate, polyethylene naphthalate, polyether sulfone, polystyrene, polyethylene, polyarylate, polyether ether ketone, polycarbonate, polypropylene, polyimide, and triacetyl cellulose. The thickness is 10 to 250 μm, and particularly preferably 50 to 200 μm.

  An ITO film 12 serving as a first transparent conductive film is formed on one surface of the transparent substrate 11. The ITO film 12 can be formed by a thin film forming means such as a sputtering method, a CVD method, or a spray pyrolysis deposition method (SPD method). The ITO film 2 has good conductivity and light transmittance, and if the film thickness is thick, the conductivity as the transparent conductive film is preferably increased, but the light transmittance is decreased. It is preferable that it is 5-500 nm, More preferably, it is 10-300 nm.

  On the ITO film 2, for example, a fluorine-doped tin oxide film (hereinafter referred to as FTO film) is formed as the second transparent conductive film. The FTO film 13 is preferably made of tin oxide doped with about several ppm of fluorine.

The thickness of the FTO film 13 is preferably 1 to 200 nm, more preferably 5 to 150 nm. Within this range, the effects of the present invention can be more effectively exhibited.
The FTO film can be formed by a thin film forming means such as an SPD method, a sputtering method, or a CVD method, and is particularly preferably formed using the SPD method.

  In the transparent electrode base material having such a structure, the transparent conductive film made of the FTO film 13 having excellent heat resistance, chemical resistance, and ion diffusion resistance is formed on the first transparent conductive film 12 made of the ITO film. Since the films are laminated and coat the ITO film 12, the ITO film 12 is not deteriorated and the high conductivity of the ITO film 12 is not impaired.

  Further, in the present invention, as the second transparent conductive film 13, in addition to the FTO film, antimony-doped tin oxide (ATO), tin oxide (TO), fluorine-doped zinc oxide (FZO), aluminum dope A transparent conductive film having a thickness of 10 to 200 nm made of zinc oxide (AZO), gallium-doped zinc oxide (GZO), boron-doped zinc oxide (BZO), zinc oxide (ZO), or the like can be used. These transparent conductive films are also films having high ion diffusion resistance and high heat resistance like the FTO film 13.

  Further, a plurality of layers of the third transparent conductive film, the fourth transparent conductive film, and the like, and the transparent conductive film other than the ITO film may be laminated on the second transparent conductive film 13. Further, a transparent conductive film other than the ITO film is formed directly on the transparent substrate 11, an ITO film is formed on the transparent conductive film, and a transparent conductive film other than the ITO film such as an FTO film is formed on the ITO film. May be.

  The resistance value of the transparent conductive sheet preferably used as the transparent electrode 4 is preferably 0.05 to 100Ω / □, and preferably 0.1 to 50Ω / □ from the viewpoint of uniformity of luminance on the light emitting surface. Is more preferable.

  As described above, the transparent electrode 10 may be prepared by any of sputtering, CVD, and the like. However, there are cases where the resistance cannot be sufficiently reduced by these alone. In that case, for example, by arranging fine wires of a metal and / or alloy on a mesh of a comb type or grid type on the transparent substrate 11, and forming the ITO film 12 and the FTO film 13 thereon, It is preferable to improve the electrical conductivity. Copper, silver, aluminum, nickel, etc. are preferably used as the fine wires of metal or alloy. A material having high electrical conductivity and high thermal conductivity is preferable. The thickness of the thin wire of the metal and / or alloy is arbitrary, but is preferably between about 0.1 μm and 100 μm. The fine wires are preferably arranged at a pitch of 50 μm to 1000 μm, and a pitch of 100 μm to 500 μm is particularly preferable. By arranging metal and / or alloy fine wires, the light transmittance is reduced, but it is important that the reduction is as small as possible. The distance between the fine wires is too narrow, and the width and height of the fine wires are increased. It is important to ensure a transmittance of 90% or more and less than 100% without being too much.

Preferred fine wire shapes include a square mesh shape, a rectangular mesh shape, or a rhombus mesh shape. The width of the fine lines may be determined according to the purpose, but typically, the fine line interval is preferably 1 / 10,000 or more and 1/10 or less.
The height of the fine line is the same, but a range of 1/100 or more and 10 times the width of the fine line is preferably used.
As a method for forming a transparent electrode having a fine wire structure portion of metal and / or alloy, the fine metal wire may be bonded to a transparent conductive sheet, or a transparent electrode material such as ITO on a mesh-like fine metal wire formed on the sheet May be applied and evaporated.

  On the other hand, the back electrode 1 on the side that does not take light can be produced using any conductive material. For example, gold, silver, copper, aluminum, beryllium, cobalt, chromium, iron, germanium, iridium, potassium, lithium, magnesium, molybdenum, sodium, nickel, platinum, silicon, tin, tantalum, tungsten, zinc, and other metals, and The EL display panel manufactured from graphite or the like can be appropriately selected according to the form of the EL display panel and the temperature of the manufacturing process. Among them, it is preferable that the thermal conductivity is high from the viewpoint of suppressing temperature rise due to heat generation in the EL element, specifically, it is preferably 100 W / m · K or more, and 200 W / m · K or more. More preferably, it is 280 W / m · K or more. From this viewpoint, gold, silver, copper, aluminum, beryllium, iridium, potassium, magnesium, molybdenum, sodium, silicon, tungsten, zinc, graphite and the like are preferable, and gold, silver, copper, aluminum, beryllium, graphite and the like are more preferable. Moreover, you may use transparent electrodes, such as ITO, if it has electroconductivity.

  The back electrode 1 is preferably formed in a sheet shape, and can be produced using any conductive material. For example, gold, silver, copper, aluminum, beryllium, cobalt, chromium, iron, germanium, iridium, potassium, lithium, magnesium, molybdenum, sodium, nickel, platinum, silicon, tin, tantalum, tungsten, zinc, and other metals, and From a graphite sheet or the like, it can be appropriately selected according to the form of the EL display element to be manufactured and the temperature of the manufacturing process. Among these, it is preferable to use a graphite sheet. This is because the graphite sheet is suitable as an electrode material because it is excellent in electrical conductivity and thermal conductivity, and is lighter and more flexible than a metal such as copper, which is generally used as a back electrode. In the present invention, the graphite sheet is used not only as an electrode but also as a thermal diffusion and heat dissipation sheet. By using the graphite sheet as the back electrode, the heat generation in the light emitting layer is effectively diffused and dissipated, and light emission with high brightness and long time is possible.

The graphite sheet used here is a sheet containing graphite as a main component. In the graphite sheet, carbon atoms are preferably 98.0% by mass or more, more preferably 99.0% by mass or more, and still more preferably. Contains 99.5% by mass or more.
Among the above, the graphite sheet used in the present invention is preferably a highly oriented graphite sheet excellent in electrical conductivity and thermal conductivity, and can be produced by heat-treating a polymer film.

  The highly oriented graphite sheet is obtained, for example, by treating a stretched aromatic imide film at 2600 degrees in an inert gas atmosphere. By stretching the film, it is considered that the aromatic unit is oriented parallel to the film surface, and it becomes easier to obtain oriented graphite. As a reaction process, decomposition and recombination of imide bonds occur at 400 to 600 degrees, and a graphite-like precursor containing nitrogen is obtained. At 1000 degrees or more, dehydrogenation, carbonization by denitrogenation, and bonding of precursors occur, and a larger plane is created. Furthermore, a laminated structure is formed at 2000 degrees or more.

The electrical conductivity of the graphite sheet in the present invention is preferably as high as possible, preferably 1000 S / cm or more, and more preferably 5000 S / cm or more.
Furthermore, from the viewpoint of suppressing temperature rise due to heat generation in the EL display element, it is preferable that the thermal conductivity is high, specifically 200 W / m · K or more, more preferably 300 W / m · K or more, More preferably, it is 400 W / m · K or more.
The thickness of the graphite sheet is preferably 50 μm to 5 nm, more preferably 80 μm to 3 nm, and even more preferably 100 μm to 1 nm.

The light emitting layer 3 is a layer formed by containing EL phosphor particles in a dispersed manner. The EL phosphor particles used in the present invention preferably have an average sphere equivalent diameter of 0.1 to 15 μm, and more preferably 1 to 10 μm. Further, the variation coefficient of the equivalent sphere diameter is preferably 30% or less, and more preferably 5 to 20%.
Here, the “sphere equivalent diameter” means the diameter of the sphere when the EL phosphor particle size is converted to a sphere having the same volume as the EL phosphor particle size.

  As a method for preparing the EL phosphor particles, a firing method, a urea melting method, a spray pyrolysis method, or a hydrothermal synthesis method (Hydrothermal method) can be preferably used. The prepared EL phosphor particles preferably have a multiple twin structure. For example, when the EL phosphor particles are zinc sulfide, the plane spacing of the multiple twins (stacking defect structure) is preferably 1 to 10 nm, and more preferably 2 to 5 nm.

  The EL phosphor particles used in the present invention can be prepared by a firing method (solid phase method) widely used in the industry. For example, in the case of zinc sulfide, a 10-50 nm particle powder (usually called raw powder) is prepared by a liquid phase method, and this is used as a primary particle, and an impurity called an activator is mixed into the powder together with a flux. First baking is performed in a crucible at a high temperature of 900 to 1300 ° C. for 30 minutes to 10 hours to obtain an intermediate fluorescent powder. Next, the obtained intermediate phosphor powder is repeatedly washed with ion-exchanged water to remove the alkali metal or alkaline earth metal, excess activator and coactivator. Next, second baking is performed on the obtained intermediate phosphor powder. The second baking is performed at a temperature of 500 to 800 ° C., which is lower than that of the first baking, and the baking time is 30 minutes to 12 hours and heating (annealing) is performed for a short time.

  Although many stacking faults are generated in the intermediate phosphor particles by the first and second firings, the first firing and the second firing are performed so that the particle size is smaller and more stacking faults are included in the particles. It is preferable to appropriately select the firing conditions.

  Further, by applying an impact force in a certain range to the first fired product, the density of stacking faults can be greatly increased without destroying the particles. As a method of applying impact force, a method of contacting and mixing intermediate fluorescent particles, a method of mixing and mixing spheres such as alumina (ball mill), a method of accelerating and colliding intermediate phosphor particles, a method of irradiating ultrasonic waves, etc. Can be preferably used.

According to the above method, in the present invention, particles having 10 or more stacking faults having a stacking fault density of 5 nm or less can be formed. As a method for evaluating the frequency, when the particles are ground with a mortar and crushed into pieces having a thickness of about 0.2 μm or less and observed with an electron microscope with an acceleration voltage of 200 KV, 10 or more layers of stacking faults of 5 nm or less are observed. It can be evaluated by the frequency of the fragment particles contained. In addition, the said crushing is unnecessary when a particle size is less than 0.2 micrometer.
In the present invention, the above frequency is preferably more than 50%, more preferably more than 70%. The higher the frequency, the better.

  Thereafter, the intermediate phosphor particles are etched with an acid such as HCl to remove the metal oxide adhering to the surface, and the copper sulfide adhering to the surface is removed by washing with a KCN solution. Subsequently, the intermediate phosphor is dried to obtain EL phosphor particles.

  In the case of zinc sulfide and the like, it is preferable to use a hydrothermal synthesis method as a method for forming phosphor particles because a multiple twin structure is introduced into the phosphor crystal. In the hydrothermal synthesis system, the particles are dispersed in a well-stirred aqueous solvent, and the zinc ions and / or sulfur ions that cause particle growth are determined from the outside of the reaction vessel at a controlled flow rate with an aqueous solution. Added for hours. Therefore, in this system, particles can move freely in an aqueous solvent, and added ions can diffuse in water and cause particle growth uniformly. For this reason, according to the hydrothermal synthesis method, the concentration distribution of the activator or the coactivator inside the particles can be changed, and particles that cannot be obtained by the firing method can be obtained. In the adjustment of the particle size distribution, the nucleation process and the growth process can be clearly separated, and the particle size distribution can be adjusted by freely controlling the degree of supersaturation during particle growth. Zinc sulfide particles can be obtained. It is preferable to insert an Ostwald ripening step between the nucleation process and the growth process in order to adjust the grain size and realize a multiple twin structure.

  For example, zinc sulfide crystals have very low solubility in water, which is very disadvantageous when growing particles by ionic reaction in aqueous solution. The solubility of zinc sulfide crystals in water increases as the temperature rises, but at 375 ° C. or higher, water becomes supercritical and the solubility of ions drastically decreases. Therefore, the particle preparation temperature is preferably 100 to 375 ° C, and more preferably 200 to 375 ° C. The time required for particle size adjustment is preferably within 100 hours, more preferably 5 minutes to 12 hours.

  Specifically, the matrix material of the EL phosphor particles preferably used in the present invention includes one or more elements selected from the group consisting of Group II elements and Group VI elements, Group III elements and Group V elements. These are semiconductor fine particles composed of one or more elements selected from the group consisting of group elements, and are arbitrarily selected depending on the necessary emission wavelength region. Examples thereof include CdS, CdSe, CdTe, ZnS, ZnSe, ZnTe, CaS, MgS, SrS, GaP, GaAs, and mixed crystals thereof. ZnS, CdS, CaS, and the like can be preferably used.

Furthermore, as the base material of the EL phosphor particles, BaAl ₂ S ₄ , CaGa ₂ S ₄ , Ga ₂ O ₃ , Zn ₂ SiO ₄ , Zn ₂ GaO ₄ , ZnGa ₂ O ₄ , ZnGeO ₃ , ZnGeO ₄ , ZnAl ₂ O ₄ , CaGa ₂ O ₄ , CaGeO ₃ , Ca ₂ Ge ₂ O ₇ , CaO, Ga ₂ O ₃ , GeO ₂ , SrAl ₂ O ₄ , SrGa ₂ O ₄ , SrP ₂ O ₇ , MgGa ₂ O ₄ , Mg ₂ GeO ₄ , MgGeO ₃ , BaAl ₂ O ₄ , Ga ₂ Ge ₂ O ₇ , BeGa ₂ O ₄ , Y ₂ SiO ₅ , Y ₂ GeO ₅ , Y ₂ Ge ₂ O ₇ , Y ₄ GeO ₈ , Y ₂ O ₃ , Y ₂ O ₂ S, or the like can be preferably used SnO ₂ and mixed crystals thereof.

  In addition, as an activator for the EL phosphor particles used in the present invention, at least one ion selected from copper, manganese, silver, gold and rare earth elements can be preferably used. As the coactivator, at least one ion selected from chlorine, bromine, iodine and aluminum can be preferably used.

  By appropriately selecting the matrix material, activator and emission center of the above EL phosphor particles and using a plurality of phosphor particles, 0.3 <x on the chromaticity diagram without using dyes or fluorescent dyes. White light emission in the range of <0.4 and 0.3 <y <0.4 can be substantially obtained.

The light emitting layer 3 can be formed by dispersing the phosphor particles described above in a dispersant. Examples of the dispersant used for dispersing the phosphor particles in the light emitting layer 3 include a polymer having a relatively high dielectric constant such as a cyanoethyl cellulose resin, polyethylene, polypropylene, polystyrene resin, silicone resin, and epoxy resin. A resin such as vinylidene fluoride can be used. In addition, the dielectric constant can be adjusted by appropriately mixing fine particles having a high dielectric constant such as BaTiO ₃ or SrTiO ₃ with these resins. As a dispersing method of the dispersant, a homogenizer, a planetary kneader, a roll kneader, an ultrasonic disperser, or the like can be used. It is preferable that the weight ratio of the particle | grains and a dispersing agent in a light emitting layer is 5.0-20.

  The thickness of the light emitting layer 3 is preferably thin, preferably 1 to 25 μm, and more preferably 3 to 20 μm. The light emitting layer 3 has the surface of the light emitting layer 3 with respect to the thickness d of the light emitting layer 3 when the variation in the distance between the back electrode 1 and the transparent electrode 4 is viewed as the center line average roughness Ra. It preferably has a smoothness of (d × 1/8) or less.

Next, the dielectric layer 2 will be described. The dispersion type EL element in the present invention can be formed by adjoining the light emitting layer 3 with the dielectric layer 2 containing an inorganic dielectric substance, if necessary. As the inorganic dielectric substance, any material can be used as long as it has a high dielectric constant and insulation and has a high dielectric breakdown voltage. As the inorganic dielectric material, various metal oxides and nitrides can be used. For example, SiO ₂ , TiO ₂ , BaTiO ₃ , SrTiO ₃ , PbTiO ₃ , KNbO ₃ , PbNbO ₃ , Ta ₂ O ₃ , BaTa _2. O ₆ , LiTaO ₃ , Y ₂ O ₃ , Al ₂ O ₃ , ZrO ₂ , AlON, ZnS, or the like can be used. These can be used alone or in combination. The dielectric layer 2 may be formed as a uniform film or may be formed as a film having a particle structure. Furthermore, the dielectric layer 2 may be a single layer or a laminate of different insulating layers.

  The dielectric layer 2 may have any structure of a thin film crystal layer structure and a particle shape structure, and may also have a combination thereof. The dielectric layer 2 may be provided only on one side of the light emitting layer 3 as shown in FIG. 1, but it is preferably provided on both sides of the light emitting layer 3 from the viewpoint of obtaining high luminance. When the dielectric layer 2 has a thin film crystal layer structure, the dielectric layer 2 may be a thin film formed by a vapor phase method such as sputtering or a sol-gel film using an alkoxide such as Ba or Sr. When the dielectric layer 2 has a particle shape structure, the size of the dielectric substance is preferably sufficiently small compared to the phosphor particle size. Specifically, the particles of the dielectric material are preferably 1/3 to 1/1000 the average particle size of the phosphor particles.

  The EL element of the present invention has a structure having a light emitting layer containing a phosphor material sandwiched between a pair of opposing electrodes, at least one of which is transparent. Therefore, the total thickness (hereinafter also referred to as “element thickness”) of the light emitting layer 3 and the dielectric layer 2 is equal to or larger than the average sphere equivalent diameter of the EL phosphor particles, but ensures the smoothness of the element. For this purpose, the element thickness is preferably 1.1 to 10 times, more preferably 2 to 10 times, and more preferably 3 to 5 times the average sphere equivalent diameter of the EL phosphor particles. Further preferred.

  Further, the contact point is increased by covering the part of the upper part of the particle, that is, by coating the part of the light emitting layer 3 so that the dielectric layer 2 is partly inserted, or the smoothness of the element surface is improved. It is preferable because an effect such as improvement appears.

  The dielectric material contained in the dielectric layer 2 and the phosphor particles contained in the light emitting layer 3 can be in direct contact with the dielectric material, but the dielectric material is a non-light emitting shell. It is preferred to contact the phosphor particles that are completely or partially covered with a layer. Further, the contact between the dielectric material and the phosphor material may be merely contact, but the upper part of the phosphor particles is completely or partially covered, that is, the dielectric layer 2 is entirely formed on the light emitting layer 3. Coating or contacting the light-emitting layer 3 with the dielectric layer 2 partially in contact with the light-emitting layer 3 increases the contact point and improves the smoothness of the element surface. It is preferable from the viewpoint that effects such as

  The dielectric layer 2 and the light emitting layer 3 are preferably formed by coating using a spin coating method, a dip coating method, a bar coating method, a spray coating method, or the like. In particular, it is preferable to use a method that does not select a printing surface, such as a screen printing method, or a method that allows continuous application, such as a slide coating method. For example, in the screen printing method, a dispersion liquid in which fine particles of phosphor or dielectric are dispersed in a polymer solution having a high dielectric constant is applied through a screen mesh. The film thickness can be controlled by appropriately selecting the thickness of the screen mesh, the aperture ratio, and the number of coatings. By adjusting the dispersion liquid, not only the dielectric layer 2 and the light emitting layer 3 but also the back electrode 1 can be formed, and further, the area can be easily increased by changing the size of the screen mesh. The method for preparing the dielectric layer 2 may be a vapor phase method such as sputtering or vacuum deposition. Further, by coating so that the dielectric layer 2 partially enters the light emitting layer 3, the contact point between the light emitting particles and the dielectric substance can be increased, and the smoothness of the EL element is further improved. It is preferable because effects such as the above can be obtained.

  The light emission color of the EL display device using the dispersion type EL element used in the present invention is preferably white in consideration of the use as a light source. As a specific method for making the emission color white, for example, a method using phosphor particles that emit white light alone, such as a ZnS phosphor activated with manganese and gradually cooled after firing, or three primary colors Alternatively, it is preferable to use a method of mixing a plurality of phosphors that emit light of complementary colors (for example, a blue-green-red combination, a blue-green-orange combination, etc.). In addition, light is emitted at a short wavelength such as blue described in JP-A-7-166161, JP-A-9-245511, and JP-A-2002-62530, and light emission is performed using a fluorescent pigment or a fluorescent dye. It is also preferable to use a method of converting the wavelength of the part into green or red and then whitening it. Further, the CIE chromaticity coordinates (x, y) preferably have an x value in the range of 0.30 to 0.4 and a y value in the range of 0.30 to 0.40.

Usually, the distributed EL display device is driven by an alternating current, and is typically driven by using an alternating current power source of 100 V and 50 to 400 Hz. When the area of the distributed EL display device is small, the luminance increases almost in proportion to the applied voltage and frequency. However, in the case of an EL display panel having a large area of 0.25 m ² or more, the capacitance component of the EL display panel increases, and there is a shift between the EL display panel and the impedance matching of the power source, or storage in the EL display panel. The time constant required for the charge may increase. For this reason, in an EL display panel with a large area, power supply may be insufficient even when the voltage is increased, particularly the frequency is increased. In particular, in an EL display panel having a large area of 0.25 m ² or more, for AC driving of 500 Hz or more, the applied voltage is often lowered with an increase in driving frequency, and the luminance is often lowered.
On the other hand, even when the EL element of the present invention has a large area of 0.25 m ² or more, it can be driven at a high frequency, preferably at 500 Hz to 5 KHz, more preferably at 800 Hz to 4 KHz. Therefore, high luminance can be obtained.

  An EL display panel using the EL element of the present invention can be used, for example, as a backlight of a backlight display film for inkjet recording on which an image is recorded by an inkjet recording method.

  In addition, the EL display panel using the EL element of the present invention can be used as a backlight of a high-quality transmission print image having a maximum density of 1.5 or more, for example, for high-quality large-area advertisements. Can be realized.

  Although the specific Example of the EL element of this invention is described below, this invention is not restrict | limited to this Example.

Example 1
Phosphor particles (ZnS; Cu, Cl) having an average particle diameter of 25 μm and a red pigment manufactured by Sinloi Co., Ltd. having an average particle diameter of 4 μm (Sinloi FA-001) are dispersed in a 30% by mass cyanoethyl cellulose solution to form a light emitting layer. A paste was used. Further, barium titanate powder having an average particle size of 0.2 μm was uniformly dispersed in a 30% by mass cyanoethyl cellulose solution to obtain a dielectric paste.
The dielectric paste was applied on an aluminum sheet (thickness 75 μm) so that the film thickness after drying was 35 μm, and dried at 110 ° C. for 4 hours with a hot air dryer. Further, the light emitting layer paste was applied thereon so that the film thickness after drying was 35 μm, and dried at 110 ° C. for 6 hours by a hot air dryer.

Next, as a transparent substrate having flexibility, polyethylene terephthalate having a thickness of 100 μm was used, and ITO was uniformly deposited on the substrate by sputtering to a thickness of 50 nm. Further, antimony-doped tin oxide ( ATO) film was similarly deposited and used as a transparent electrode. A silver paste as a power supply line was printed on the conductive surface side of the film by screen printing and dried, and a lead electrode made of a lead piece made of a copper aluminum sheet was attached.
The application surface of the aluminum sheet and the conductive surface of the transparent conductive film were bonded together and thermocompression bonded to obtain an EL element.
The size of the light emitting surface of the element was set to 500 mm × 500 mm.

(Example 2)
The same procedure as in Example 1 was performed except that a fluorine-doped tin oxide (FTO) film was used instead of the ATO film.

Example 3
The same operation as in Example 2 was performed except that the thickness of the FTO film was 25 nm.

Example 4
The back electrode was formed in the same manner as in Example 2 except that a graphite sheet (manufactured by Matsushita Electronic Components, thermal conductivity: 800 W / m · K) was used instead of the aluminum sheet.

(Example 5)
The same procedure as in Example 4 was performed except that phosphor particles (ZnS; Cu, Cl) having an average particle diameter of 10 μm were used to produce a light emitting layer paste.

(Comparative Example 1)
The same procedure as in Example 1 was performed except that the ATO film was not attached.

(Comparative Example 2)
It carried out similarly to the comparative example 1 except having made the film thickness of the said ITO film | membrane into 100 nm.

Table 1 shows various characteristics of the EL display panels of Examples 1 to 5 and Comparative Examples 1 and 2. The EL display panel was evaluated by fixing the frequency of the driving AC power source to 1 KHz and adjusting the applied voltage so that the initial luminance was 600 cd / m ² . In the case of the EL display panel of Example 1, the applied voltage was about 200V. Table 1 shows the relative luminance (relative luminance after 300 hours) with respect to the initial luminance when the EL display panels of Examples 1 to 5 and Comparative Examples 1 and 2 are continuously driven for 300 hours in an environment where the temperature is 20 ° C. and the humidity is 60%. Shown in

  From the above results, it can be seen that the EL element of the present invention can emit light with high brightness for a long time.

It is a schematic plan view which shows an example of the dispersion type EL element of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Back electrode 2 Dielectric layer 3 Light emitting layer 10 Transparent electrode 11 Transparent base 12 Transparent conductive layer (ITO film)
13 Transparent conductive layer (FTO film)

Claims (4)

  An inorganic dispersion type electroluminescent device having at least a light emitting layer between a pair of electrodes composed of a back electrode and a transparent electrode, wherein the transparent electrode has two or more layers of different transparent conductive materials on a flexible transparent substrate. At least one of the transparent conductive layers is an indium tin oxide film, and at least one transparent conductive layer on the light emitting layer side of the indium tin oxide film is fluorine, antimony Inorganic dispersive electroluminescence characterized by being at least one transparent conductive film selected from tin oxide and zinc oxide, each of which may be doped with at least one element selected from aluminum, gallium and boron element.   2. The inorganic dispersion type electroluminescence device according to claim 1, wherein at least one transparent conductive layer located closer to the light emitting layer than the indium tin oxide film is a film made of fluorine-doped tin oxide.   The inorganic dispersion type electroluminescent device according to claim 1, wherein the back electrode is a graphite sheet.   The inorganic dispersion type electroluminescence device according to any one of claims 1 to 3, wherein the light emitting layer contains phosphor fine particles having an average sphere equivalent diameter of 0.1 to 15 µm.

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