JP2001284053A - Electroluminescent element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electroluminescent element without lowering brightness, for example, keeping 50 cd/m2 or more, with effectively improved luminous efficiency and life. SOLUTION: The electroluminescent element is composed of a transparent conductive layer, a binder formed at the back of the transparent conductive layer, a luminous layer including a number of luminous particles buried in the binder, an insulation layer including particles of insulation material formed at the back of the luminous layer, and a back surface electrode formed at the back of the insulation layer. The ratio of the thickness of the luminous layer T [μm] to the maximum diameter of the luminous particle Dm [μm]; (T/Dm) is 1.2 or more and less than 2.0.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electroluminescent device (hereinafter, also referred to as "EL device"), and more particularly, to a coating type luminescent layer formed by applying a coating material containing luminescent particles and a binder. And an improvement in an EL element.

[0002]

2. Description of the Related Art An EL device having a coating type light emitting layer formed by applying a coating material prepared by dispersing light emitting particles such as a phosphor in a resin binder is known from the following documents. Have been. JP-B-59-14878 discloses a transparent base material, a transparent electrode layer, an insulating layer composed of only a vinylidene fluoride binder, a light emitting layer composed of a vinylidene fluoride binder and phosphor particles, and the same insulating layer as described above. , And a back electrode are laminated in this order, and an EL light emitting element is disclosed. In addition, Japanese Patent Publication 62-59879
Japanese Patent Application Laid-Open No. H10-209,199 discloses an EL light emitting device in which a polyester film, an ITO electrode, a light emitting layer composed of a cyanoethylated ethylene-vinyl alcohol copolymer (binder) and phosphor particles, and an aluminum foil (back electrode) are laminated in this order. An element is disclosed.

On the other hand, there is known an EL device provided with a “stacked light emitting layer” as a coating light emitting layer that does not use a dispersion type paint. For example, U.S. Pat. Nos. 5,019,748 and 5,045,755 describe (1) a first high dielectric constant adhesive layer applied over a transparent conductive layer of a transparent substrate;
Almost a single layer (layer thickness does not exceed the largest fluorescent particle size) formed by placing dry fluorescent particles (luminescent particles) electrostatically applied on the high dielectric constant adhesive layer An EL device comprising: a) a fluorescent particle layer; and (3) a laminate of three layers of a second dielectric constant layer, which includes a high dielectric constant material applied on the fluorescent particle layer and fills a gap between adjacent fluorescent particles. Is disclosed. A back electrode is directly provided on the surface of the second dielectric layer, that is, the second dielectric layer functions as an insulating layer.

However, in any of the above publications or patent specifications, a terminal (bus) for supplying electricity (voltage) to the transparent conductive layer from the outside is provided during the production process of the roll-shaped EL element. No specific means for providing such a structure so as to extend continuously in the longitudinal direction of the device is disclosed. For example, in achieving a large area of an EL element, it is important to provide a terminal (bus) for supplying electricity (voltage) to the transparent conductive layer from the outside in any form. For example, in an EL element for a small area display, a bus that is not electrically connected to the back electrode can be provided on the transparent conductive layer by effectively repeating screen printing. However, none of the above-mentioned publications or patent specifications disclose the formation of the bus so as to extend continuously along the length direction and no means for that.

[0005]

By the way, the conventional EL
In the device, the luminescent particles formed a substantially single layer in the luminescent layer. That is, the ratio T / Dm between the thickness T [μm] of the light emitting layer and the maximum particle size Dm [μm] of the light emitting particles was 1.0. This was mainly because the thickness of the entire EL element was made as small as possible to reduce the thickness. On the other hand, such a structure was advantageous in increasing the luminance, but the luminous efficiency and the lifetime (luminance half-life: Time to Half Lum
It was disadvantageous to simultaneously improve inescence = THL). For example, the luminous efficiency is a value defined by the following equation 1, and this value is set to 3 [lm / W] or more,
Further, it was very difficult to make the life (luminance half-life) 700 hours or more.

## EQU1 ## Luminous efficiency η [lm / W] = L × π × S / P (1) where P is power consumption (effective power) (unit: W), and L is luminance measured using a luminance meter. (Unit: cd / m ² ), S
Is the area of the light emitting surface (unit: m ² ), and π is the pi.

[0006] Low luminous efficiency means that the luminance per unit effective power is low, which means that the power efficiency is low. For example, in the EL device having the above-mentioned stacked type light emitting layer, compared with the EL device having the light emitting layer formed by applying the dispersion paint, when the power source of the same frequency and the same voltage is connected, the light emitting device has the same or higher luminance. I do.
However, there is a problem that the luminous efficiency and the life are rather reduced. Therefore, an object of the present invention is to improve the luminous efficiency and lifetime effectively without lowering the luminous luminance (for example, maintaining the luminance at 50 cd / m ² or more) in order to solve the problems of the conventional EL element. To provide an EL device.

[0007]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides: a) a transparent conductive layer; and b) a binder and a plurality of binders embedded in the binder disposed on the back surface of the transparent conductive layer. A light emitting layer containing light emitting particles; c) an insulating layer containing insulator particles disposed on the back side of the light emitting layer; and d) a back electrode disposed on the back side of the insulating layer. The ratio (T / Dm) between the thickness T [μm] of the light emitting layer and the maximum particle diameter Dm [μm] of the light emitting particles is 1.2 or more and less than 2.0. An electroluminescent element is provided.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION (EL Element) First, the EL element of the present invention will be described from the viewpoint of operation. EL of the present invention
In the device, the light-emitting layer includes a binder and a plurality of light-emitting particles embedded in the binder, and has a thickness T [μm] of the light-emitting layer and a maximum particle diameter Dm [μm] of the light-emitting particles.
Is not less than 1.2 and less than 2.0. In the light emitting layer, the fact that the light emitting particles are embedded in the binder layer acts to improve the efficiency (luminous efficiency) of the luminous brightness with respect to the effective power. Further, the thickness T [μm] of the light emitting layer and the maximum particle diameter Dm [μm
m], and T / Dm within the above-mentioned range acts to effectively increase the lifetime (luminance half-life: THL) without impairing the luminous efficiency and the luminous luminance. That is,
According to the present invention, the emission luminance is not reduced to a practical level or less (for example, maintained at 50 cd / m ² or more),
It is possible to provide a practical EL element in which luminous efficiency and lifetime are effectively increased, and these three characteristics are balanced at a high level. From such a viewpoint, the ratio of the thickness of the light emitting layer to the maximum particle size of the light emitting particles, T / Dm, is preferably 1.3.
The range is not less than 1.8 and not more than 1.8.

In a preferred aspect of the present invention, the luminescent particles have a structure that is not substantially buried in the insulating layer. Thereby, the luminous efficiency can be more effectively increased. Such an operation is considered as follows. For example, in an EL device having a stacked type light emitting layer, a gap between light emitting particles such as phosphor particles is filled with a filler (insulator particles or the like) having a very high dielectric constant, so that the gap between the phosphors is reduced. Capacitance increases. Therefore, the dielectric loss in the gap becomes large, and a power loss occurs due to the generation of Joule heat. As a result, the luminous efficiency is deteriorated. Usually, the dielectric constant of the insulator particles is
It is at least 100, and a relatively high insulating effect such as a typical barium titanate may be 1,000 or more. On the other hand, the dielectric constant of an organic polymer or a high dielectric constant polymer that can be used as a binder (also referred to as a “matrix resin”) for an EL element is usually 5
It is less than 0, and is in the range of 5 to 30 even for a suitable high dielectric constant polymer such as a vinylidene fluoride resin or a cyano resin. The “dielectric constant” in this specification is a relative dielectric constant measured by applying an alternating voltage of 1 kHz unless otherwise specified.

That is, if the layer of the luminescent particles is not substantially buried in the insulating layer, the gap between the phosphor particles (luminescent particles) is filled with a very high dielectric filler (such as insulating particles). Is not filled. Therefore, an increase in dielectric loss in the gap and a power loss due to generation of Joule heat can be reduced as much as possible, and luminous efficiency can be improved. Such a structure, for example,
A coating material composed of a slurry containing luminescent particles dispersed in a binder is applied and solidified (dried, cured, or the like), and the ratio T / Dm between the luminescent layer thickness and the luminescent particle maximum diameter falls within a predetermined range. The light emitting layer can be easily formed by preventing the particle surface from being exposed from the surface (back surface) of the light emitting layer in contact with the insulating layer.

According to another preferred embodiment of the present invention, in the EL device, the transparent conductive layer, the light emitting layer, the insulating layer, and the back electrode extend continuously along a length direction of the transparent conductive layer. And further electrically connected to the back surface of the transparent conductive layer, having a width dimension smaller than the width dimension of the transparent conductive layer, and extending continuously along the length direction of the transparent conductive layer. Characterized by comprising at least one existing bus. The bus is not electrically connected to the back electrode. This facilitates forming a roll-shaped EL element capable of forming a large light-emitting display. Further, when the bus is not directly connected to the light emitting layer (electrically connected via the transparent conductive layer), it becomes easier to form a large-area roll-shaped EL element. This is because the back electrode can be arranged on substantially the entire back surface of the light emitting layer, and substantially the entire surface of the light emitting layer can emit light. For example, it is possible to directly connect the bus near the edge of the light-emitting layer and the bus. In such a case, the electrode-free portion on the back surface of the light-emitting layer where the bus and the back electrode are not provided is referred to as the back electrode and the bus. Must be provided so as to be separated from each other (so as not to be electrically connected). The light emitting surface of the light emitting layer corresponding to the electrode non-arranged portion hardly emits light, and thus it may be difficult to increase the light emitting area.

The EL device according to the present invention can be manufactured by various methods. For example, it is preferable to carry out as follows. That is, i) a slurry paint for forming a light emitting layer is applied on one of the back surface of the transparent conductive layer and the surface of the insulating layer and solidified, and the ratio T / Dm falls within the above range. The light emitting layer is formed as described above, and at this time, the light emitting particles are embedded in the light emitting layer containing the binder so that the surface thereof is not exposed. Ii) The transparent conductive layer and the insulating layer are formed on the light emitting layer. Is a manufacturing method including each step of arranging one of the other. This makes it possible to manufacture an EL element with improved luminous efficiency and lifetime effectively without lowering the luminous brightness to a practical level or less with high productivity. Also,
It is easy to manufacture a large-area sheet-shaped or roll-shaped EL element.

(Structure of EL Element) The structure of an EL element (10) according to one embodiment of the present invention will be described with reference to FIG. The EL element of the illustrated example has a transparent conductive layer (1) adhered on a transparent substrate (7), a back electrode (6), and a transparent conductive layer (1) and a back electrode (6). Light emitting layer (2). The light emitting layer (2) is a coating layer that is in close contact with the transparent conductive layer (1). The coating layer includes a binder layer (4) and a layer of luminescent particles (3) embedded in the binder layer (4). In the illustrated example, the back electrode (6) and the insulating layer (5) are in close contact with each other, and the contact surface is substantially a smooth surface. Thereby, the luminous efficiency and the life can be effectively improved.

In the illustrated example, the layer of the luminescent particles (3) is completely buried in the binder layer (4) containing the binder, and is in contact with the insulating layer (5) containing the insulating particles. There is no or point contact. That is, most of the plurality of light-emitting particles (3) (such as particles having a relatively large particle diameter) make point contact with the insulating layer, and the insulating layer (5) penetrates between the adjacent light-emitting particles. Not. The surfaces of the insulating layer (5) and the transparent conductive layer (1) facing each other are substantially parallel to each other and are substantially smooth surfaces. The fact that these two surfaces are smooth parallel surfaces is advantageous for increasing the luminous efficiency.

Further, in the illustrated example, the luminescent particles (3)
Forms a multilayer composed of a first layer arranged on the side of the insulating layer (5) and a second layer arranged on the side of the transparent conductive layer (1), in which a plurality of luminescent particles (3 ) Are in contact with each other. Thereby, the energy (voltage) applied to the light emitting layer (2) is uniformly applied to each of the light emitting particles (3), so that the luminous efficiency and the life can be more effectively improved without lowering the luminance. Can be done.
Further, such an overlapping layer of the luminescent particles forms a binder layer (4).
It is also very advantageous to improve the luminous efficiency and the lifetime by being buried inside and being close to both the insulating layer (5) and the transparent conductive layer (1).

The thickness of the entire EL element is usually 100 to 3,
000 μm, preferably in the range of 120 to 2,000 μm. The length of the EL element is usually 1 m or more when it is in a roll shape.

On the other hand, in an EL element having a structure suitable for forming a roll-shaped EL element, in the element having a structure as shown in FIG. Also form at least one bus having a large width dimension. The light emitting layer non-arranged portion is formed as an exposed surface that is not covered with the light emitting layer even after the light emitting layer is arranged on the surface of the transparent conductive layer, since the surface area of the transparent conductive layer is larger than the surface area of the light emitting layer. You. The bus is not directly connected to the light emitting layer and is not electrically connected to the back electrode. In such a form, the normal bus is
It is arranged near both ends in the width direction of the transparent substrate, and has two stripe shapes substantially parallel to the light emitting layer with the back electrode extending along the length direction of the transparent substrate.

The bus is not limited to the above shape and arrangement as long as it functions as a terminal for supplying electricity (voltage) from the outside to the transparent conductive layer when the EL element is used. For example, a bus composed of a combination of a plurality of small buses (bus parts) and continuously extending in the bar code shape along the length direction, or a plurality of circular bus parts continuously existing in the length direction May be used. That is, as long as the effects of the present invention are not impaired, even if a small bus exists discontinuously along the length direction, it may be continuous as a whole. The bus can be formed by using, for example, a conductive material that is also used when forming the back electrode, and an application unit. As an application means, application of a paint containing a conductive material, vapor deposition, sputtering and the like are preferable.

In the EL device according to the preferred embodiment of the present invention, as described above, the light emitting layer is not substantially embedded in the insulating layer. Here, “not substantially embedded in the insulating layer” means that the light emitting layer is not in contact with the insulating layer at all, is in point contact, or is in contact with the insulating layer.
As there is no insulator particle between adjacent luminescent particles,
It means a state in contact with the insulating layer. The above state includes, for example, a state in which the luminescent particles of the luminescent layer are in point contact with the insulating layer. Furthermore, as long as the effects of the present invention are not impaired, light-emitting particles having a relatively wide particle size distribution may be used, and some of the light-emitting particles may be embedded in the insulating layer.

As mentioned above, the dielectric constant of the insulator particles is usually at least 100, whereas the dielectric constant of the binder is usually less than 50. According to the above configuration, since the luminescent particles are embedded in the binder layer and are not substantially embedded in the insulating layer, the capacitance of the gap can be effectively reduced. Examples of the polymer that can be used as the binder include a tetrafluoroethylene-hexafluoropropylene-vinylidene fluoride copolymer (THV).

(Method for Manufacturing EL Element) The EL element of the present invention can be preferably formed as follows. In the following description, the numbers of the components are those shown in FIG. First, a paint for forming a light emitting layer is applied to the back surface of the transparent conductive layer (1) formed on the back surface of the transparent substrate (7), and the applied paint is solidified. The light emitting layer (2) is preferably formed using a paint (slurry) containing a binder such as a high dielectric constant polymer and luminescent particles dispersed and contained in the binder. In this case, for example, using a coating method such as a bar coating method, a curtain coating method, a die coating method, a gravure coating method, and a rotary silk printing method, a ratio (T / Dm) between the maximum particle diameter of the luminescent particles and the thickness of the luminescent layer.
Is within a predetermined range. For the solidification of the paint (coating), ordinary means, for example, drying, cooling, curing and the like can be used. Subsequently, on the light emitting layer (2) (on the back side),
An insulating layer (5) is arranged. The insulating layer is preferably formed by applying a coating for the insulating layer containing a resin and insulating particles dispersed in the resin to the back surface of the binder layer and drying the coating. Finally, a back electrode (6) is brought into close contact with the back surface of the insulating layer (5) to complete the EL element.

On the other hand, a method of starting fabrication from the opposite side, that is, a light emitting layer is laminated on the smoothed surface of the insulating layer formed on the back electrode first, and finally the transparent conductive layer (or transparent conductive layer) A method of laminating a transparent substrate with a conductive layer) may be used.

According to the above-described method, it is particularly easy to form a high-brightness EL device having improved luminous efficiency and lifetime continuously and at high speed, that is, with high productivity. For example, usually 5 mpm (m / min) or more, preferably 10 to 2
It can be produced at a coating speed of 00 mpm, particularly preferably between 12 and 100 mpm.

The light-emitting layer may contain particles other than light-emitting particles, for example, transparent beads such as glass and ceramic, and color pigment particles. However, the ratio of the luminescent particles contained in the whole particles is preferably 40% by volume or more.
If it is less than 40% by volume, the light emission luminance may be reduced. Luminance, luminous efficiency and lifetime are most improved when the particles consist only of luminescent particles. Therefore, a particularly suitable ratio of the luminescent particles is in the range of 50 to 100% by volume.

(Method of Manufacturing Roll EL Element) As described above, a preferred embodiment of the present invention is an EL element which can be formed into a roll.
An element is provided. In the roll-shaped EL element, a transparent conductive layer, a light-emitting layer, an insulating layer, a back electrode, and a bus, which are arranged on a transparent base material extending continuously in the length direction, are arranged in the length direction of the transparent base material. Extend continuously along. Therefore, it is extremely easy to obtain an EL element having a light-emitting layer or the like having a large area (planar dimension) continuous in the length direction. That is,
A roll-shaped EL element as a raw material having a light emitting layer continuous in the length direction is manufactured and stored, and an EL element having a desired length is obtained by simply cutting the raw material as necessary. Can be.

In the conventional production using screen printing,
The laminated portion, such as the light emitting layer and the bath, disposed on the transparent base material is formed only discontinuously along the length direction. Further, according to the conventional technique, only an EL element having a size (length) that does not include the discontinuous portion can be obtained from a raw material of an EL element manufactured using screen printing. On the other hand, when the roll-shaped EL device of the present invention is used as a raw material, application to products having various dimensions as described above becomes extremely easy.

The roll-shaped EL element is, for example, as follows:
It is preferable that the transparent conductive layer is produced by a production method comprising the following steps: 1) preparing a transparent substrate having a transparent conductive layer disposed on one surface; and 2) forming a transparent conductive layer on the transparent conductive layer. A light emitting layer and an insulating layer are arranged so as to have a width dimension smaller than the width dimension of the transparent conductive layer; and 3) the light emitting layer of the transparent conductive layer of the substrate with the light emitting layer is not formed. A masking having a smaller dimension in the width direction than the light-emitting layer non-arranged portion is arranged along the length direction of the transparent substrate on the remaining exposed portion (ie, the “light-emitting layer non-arranged portion”) 4). A conductive material is applied on the light-emitting layer-attached base material, and the masking is interposed, or the light-emitting layer non-arranged portion where the masking is removed is directly interposed between the light-emitting layer and the back electrode. Is not connected, the conductive material And a back electrode made of the conductive material. One of the features of this method is that the light emitting layer and the back electrode and the bus are directly connected to each other by the interposition of the masking or the interposition of the light emitting layer non-arranged portion of the transparent conductive layer from which the masking has been removed. The point is that the back electrode and the bus can be formed so as not to be electrically connected.

In this method, the masking may be removed as needed, and need not be removed unless the back electrode and the bus are electrically connected to each other.
For example, applying a first conductive material forming a back electrode and a second conductive material forming a bus simultaneously (but in separate application devices) or in separate steps,
If the bus formed of two conductive materials and the back electrode are not electrically connected on the masking, it is not necessary to remove the masking. In addition, the thickness of the light emitting layer and the masking is sufficiently larger than the thickness of the bus to be formed, and the conductive material applied at the same time does not electrically connect the bus portion and the back electrode portion. In some cases, it is not necessary to remove the masking. However,
Preferably, the masking is removed. This is because the back electrode and the bus, which are not electrically connected to each other, can be particularly easily formed. Further, even if the first and second conductive materials are the same material,
Different materials may be used. However, preferably,
The bus and the back electrode are preferably formed at the same time. This is because the manufacturing steps can be easily simplified and the productivity can be easily improved.

Next, components such as materials used in the present invention will be described in detail. (Transparent substrate) It is preferable to use a transparent substrate as a support for the transparent conductive layer. As the transparent base material, any base material such as glass and plastic film used in conventional EL elements can be used. Plastic film
For example, polyester resins such as polyethylene terephthalate (PET) and polyethylene naphthalate (PEN); acrylic resins such as polymethyl methacrylate and modified polymethyl methacrylate; fluororesins such as polyvinylidene fluoride and acrylic-modified polyvinylidene fluoride; polycarbonate resins; Vinyl chloride resin such as vinyl copolymer; polyolefin resin.

As the transparent substrate, a single-layer film can be used, but a multilayer film can also be used. For example, one of the multilayer films may have a high degree of transparency and include a dye that develops a color complementary to the emission color of the light-emitting layer, thereby increasing the whiteness of light. Such a dye is preferably a red or pink fluorescent dye such as rhodamine 6G, rhodamine B, or a perylene dye when the emission color of the light emitting layer is blue-green. A processed pigment formed by dispersing these dyes in a resin can also be used. The front and back surfaces of the transparent substrate are generally flat, but the surface that is not in contact with the transparent conductive layer may have a prism-shaped protrusion as long as the effects of the present invention are not impaired.

The light transmittance of the transparent substrate is usually 60% or more,
It is preferably at least 70%, particularly preferably at least 80%.
Here, the “light transmittance” in this specification refers to an ultraviolet / visible spectrophotometer “U best V-” manufactured by JASCO Corporation.
"560" means the light transmittance measured using 550 nm light. The thickness of the transparent substrate is usually 10 to 1,000 μm when a roll-shaped EL element is formed.
It is. Further, as long as the effects of the present invention are not impaired, additives such as an ultraviolet absorber, a moisture absorbent, a coloring agent, a fluorescent substance, and a phosphorescent substance may be contained in the transparent substrate.

(Transparent Conductive Layer) The transparent conductive layer is disposed so as to be in close contact with the back surface of the transparent substrate. For the transparent conductive layer, ITO (indium.
A transparent electrode such as a (tin / oxide) film can be used. The thickness of the transparent conductive layer is usually 0.01 to 1,000 μm, and the surface resistance is usually 500 Ω / □ or less, preferably 1
３００300Ω / □. The light transmittance is usually 70% or more, preferably 80% or more.

The ITO film is formed by a film forming means such as ordinary vapor deposition, sputtering, or application of a paste. In the illustrated embodiment, the ITO film is provided directly on the transparent substrate, but after a primer layer is provided on the transparent substrate, an ITO film may be formed on the primer layer. The thickness of the primer layer is usually 0.1 to 100 μm. Further, instead of the primer layer, the surface of the transparent substrate may be subjected to an easy adhesion treatment such as a corona treatment. Alternatively, ITO on the light emitting layer
After providing the film, a transparent substrate can be laminated on the ITO film. Further, the ITO film provided on the release treatment surface of the temporary base material can be transferred to the back surface of the transparent base material via a transparent adhesive. As such a temporary base material, a release paper, a release film, a low molecular weight polyethylene film or the like can be used.

(Back Electrode) The back electrode is arranged on the back side of the light emitting layer (on the insulating layer side of the light emitting layer). In the embodiment shown in FIG. 1, the light emitting layer is disposed so as to be in direct contact with the light emitting layer. Further, an adhesive layer may be provided between the light emitting layer and the light emitting layer for the purpose of increasing the adhesive strength to the back electrode. As the resin of the adhesive layer, for example, the same resin as a binder described later is used. In addition, the adhesive layer may contain insulating inorganic particles.

As the back electrode, a metal film such as aluminum, gold, silver, copper, nickel or chromium used for a dispersion type EL device; a transparent conductive film such as an ITO film; a conductive film such as a conductive carbon film Can be used. Such a conductive film is preferably provided by application means such as application of a paint containing a conductive material (bar coating, spray coating, curtain coating, etc.), vapor deposition, sputtering, and the like. The metal film is, for example, a deposited film, a sputtered film,
Or a metal foil or the like. Further, as the back electrode, an electrode film obtained by providing the above conductive film on a support such as a polymer film can also be used. The thickness of the back electrode is usually 5 nm to 1 mm. When the back electrode is also made of a transparent conductive film and the insulating layer is transparent, it is possible to emit light on both the front and back surfaces of the EL element.

The back electrode is usually formed of the light emitting layer (ie,
It is continuously arranged on the entire back surface (of the insulating layer). However, it can be partially provided according to the purpose. For example, a continuous image (pattern,
(Characters, symbols, etc.). Thus, the EL element can emit light so as to represent an image. For the same purpose, the light emitting layer may be repeatedly formed in the longitudinal direction so as to represent a continuous image.

(Binder) The binder is usually made of a light-transmitting polymer. The light transmittance of the polymer is usually 6
0% or more, preferably 70% or more. Further, as the binder, a high dielectric constant polymer can be suitably used. The high dielectric constant polymer usually has a dielectric constant of about 5 or more, preferably 7 to
25, particularly preferably in the range of from 8 to 18 polymers.
If the dielectric constant is too low, the light emission luminance may not be increased, and if it is too high, the light emission efficiency may not be increased. Examples of the high dielectric constant polymer include, for example, a vinylidene fluoride resin (such as the above-described THV), a cyano resin, and a polyvinylidene chloride resin, or a mixture of two or more thereof. The vinylidene fluoride resin is, for example, a vinylidene fluoride monomer,
It is obtained by copolymerization of a mixture with at least one other fluorine-based monomer. Other fluorine-based monomers include, for example, ethylene tetrafluoride, ethylene trifluoride chloride, and propylene hexafluoride. Examples of the cyano-based resin include cyanoethyl cellulose, cyanoethylated ethylene-vinyl alcohol copolymer, cyanoethyl pullulan, and cyanoethyl polyvinyl alcohol.

Usually, the light-emitting layer contains, except for containing light-emitting particles,
It consists only of a binder, but as long as the effects of the present invention are not impaired, other resins, fillers, bubbles,
Additives such as hollow or solid glass microspheres, surfactants, ultraviolet absorbers, antioxidants, fungicides, rust inhibitors, moisture absorbers, coloring agents, phosphorescent substances, etc. can also be included. For example, when the emission color of the light-emitting particles is blue-green, a red or pink fluorescent dye such as rhodamine 6G, rhodamine B, or a perylene dye may be contained. Further, the other resin may have curability or tackiness as long as the transparency is not impaired. In order to lower the dielectric constant of the binder portion existing on the insulating layer side, bubbles and hollow glass microspheres can be filled.

(Insulating Layer) The insulating layer is indispensable for effectively preventing the dielectric breakdown of the light emitting layer. Therefore, the insulating particles contained in the insulating layer are, for example, the conventional dispersion type EL
The dielectric constant of the insulating inorganic particles used in the device is 100
These are the particles. The insulating layer is usually a coating layer formed from a paint formed by dispersing insulating particles in a resin. As the resin for the insulating layer, a high dielectric constant polymer used for the binder layer is preferable. The insulator particles are, for example, inorganic particles such as titanium dioxide and barium titanate. The insulating layer can be provided, for example, by coating on the back electrode or the light emitting layer.

When the insulating layer is a coating layer containing insulating particles and a high dielectric constant polymer, the mixing ratio thereof is 100 parts by mass of the high dielectric constant polymer (Parts by Weigh
The amount of the insulating particles is in the range of 1 to 400 parts by mass, preferably 10 to 350 parts by mass, particularly preferably 20 to 300 parts by mass with respect to t). If the amount of the insulating particles is too small, the insulating effect is reduced, and dielectric breakdown may occur when a relatively high voltage is applied. Conversely, if the amount is too large, application of the paint may be difficult.

The insulating layer can be formed by applying a coating material for forming the insulating layer containing the above-mentioned materials and drying the coating material. The coating thickness of the insulating layer is selected so that the dry thickness falls within a predetermined range.
The dry thickness of the insulating layer is usually 2 to 1,000 μm. Further, the solid content concentration of the coating material is usually in the range of 5 to 70% by mass. By using a paint having such a solid concentration, it is easy to smooth the surface of the insulating layer (the surface facing the transparent conductive layer). The solvent used for the paint is selected from ordinary organic solvents so that the insulating particles can be uniformly dissolved or dispersed. For the preparation and application of the paint, those described above can be used. The drying conditions depend on the type of the solvent and the solid content of the paint, but are usually from room temperature (about 25 ° C.) to 150 ° C.
° C, 5 seconds to 1 hour. The insulation layer
Additives such as fillers, surfactants, antioxidants, fungicides, rust inhibitors, moisture absorbers, coloring agents, phosphorescent substances, curable resins, adhesives, etc., as long as the insulation is not impaired. Can also.

(Light-Emitting Layer) The light-emitting particles in the light-emitting layer are particles that emit light when placed in an alternating electric field.
Phosphor particles used in a light emitting layer of a conventional EL element can be used. The phosphor is, for example, ZnS, CdZn
Simple substance of a fluorescent compound such as S, ZnSSe, CdZnSe,
Alternatively, Cu, I, Cl, Al, Mn, Nd
It is composed of a complex to which auxiliary components such as F ₃ , Ag and B are added. Alternatively, a phosphor having a coating film of glass, ceramics, or the like on the surface of the particle-shaped phosphor may be used. The maximum particle size (Dm) of the luminescent particles is usually 10 to 120 µm, preferably 20 to 100 µm. The maximum particle size (diameter: Dm) of the luminescent particles is determined by measuring the diameters of all the particles observed in one visual field by microscopic observation, and the largest one among them is defined as the maximum particle size (Dm). The measurement is usually performed so that the number of particles that can be observed in one visual field is about 50. Further, it is usually preferable to use a scanning electron microscope (SEM) for the microscope. The thickness of the light emitting layer can be appropriately determined within a range where the above-described ratio T / Dm is within a predetermined range.
Usually, it is 30 to 190 μm.

Further, the light emitting layer may include two or more kinds of light emitting particles. For example, a light-emitting layer with high whiteness can be formed by mixing at least two kinds of light-emitting particles that emit light of colors such as blue, blue-green, green, and orange and have spectra that are independent of each other. The light-emitting layer may contain one or more particles (particles made of glass, a coloring material, a phosphor, a polymer, an inorganic oxide, or the like) other than the light-emitting particles. For example, a light-emitting particle that emits blue-green light and a pink colorant (particles containing rhodamine 6G, rhodamine B, perylene dye, etc.) having a complementary color to the light are mixed to obtain a high whiteness. A light-emitting layer can be formed.

As described above, the light emitting layer is formed by solidifying a coating film formed by applying a slurry containing a binder and light emitting particles dispersed in the binder. The filling rate of the particles including the luminescent particles is usually at least 60% by volume, preferably at least 70% by volume, particularly preferably at least 80% by volume. This is because a decrease in the filling rate may cause a decrease in light emission luminance and light emission efficiency. For example, a transparent base material having a transparent conductive layer laminated on the back surface is prepared, and slurry is applied to the back surface of the transparent conductive layer. At this time, the rear surface of the transparent conductive layer is usually preferably set to a substantially smooth surface. When a bus is provided, the light emitting layer is formed so as to have a smaller width dimension than the transparent conductive layer. The drying conditions when the slurry contains a solvent depend on the type of the solvent and the solid concentration of the paint, but are usually at room temperature (about 2
5 ° C.) to 150 ° C., for 5 seconds to 1 hour. The solid content of the slurry is preferably relatively high, usually 60 to 97% by mass, and preferably 70 to 95% by mass.
Range.

(Method of Using EL Element) The EL element of the present invention can be used for internally illuminated signboards, road signs, decorative displays, etc.
Can be used as a light source for large displays. For example,
Images such as characters and designs are provided on the surface of the light-transmitting sheet, and the light-transmitting sheet is arranged and used so that the back surface of the sheet faces the light emitting surface of the EL element. For the light-transmitting sheet, for example, the same material as the above-mentioned transparent substrate can be used, and its light transmittance is usually 20% or more. At this time, the back of the seat and E
It is preferable that the light emitting surface of the L element is in close contact with the light emitting surface. In order to make them adhere to each other, a light-transmitting adhesive is used. Such an adhesive is, for example, an acrylic pressure-sensitive adhesive, an acrylic heat-sensitive adhesive, or the like.

Further, a light-transmitting sheet is used as the above-mentioned transparent substrate, a transparent conductive layer is directly provided on the back surface of the light-transmitting sheet, and a light-emitting layer is laminated on the conductive layer to form a display device with a built-in EL. You can also. Further, a prism type retroreflective sheet can be used as a light-transmitting sheet (or a transparent substrate). Combination with a retroreflective sheet
The retroreflective property and the self-luminous performance can be provided to the EL built-in display body.

Light emission of the EL element is usually performed by connecting a power supply to a bus on the transparent conductive layer and a terminal provided on the back electrode layer.
This is performed by applying a voltage to the element. For example, a battery such as a dry battery, a storage battery, or a solar battery is used, or an alternating current supplied from a power transmission line is converted through an inverter (a device that changes the magnitude of a voltage or frequency or converts between AC and DC). E
Supply to L element. AC frequency is usually 50 to 1,000
The range is 0 Hz. The applied voltage is usually 3 to 20.
It is in the range of 0V. Since the EL element of the present invention has a high luminous efficiency, a voltage lower than that of the conventional dispersion type (for example, 100
V or less) (for example, 50 cd / m ²⁾
Above). When the EL element is used outdoors, E
It is preferable that the L element is used after being covered with a water catching film made of a polyamide resin or the like or a moisture-proof film made of a polytetrafluoroethylene film or the like.

In the EL element of the present invention, a coloring material such as a dye or a pigment is included in a component such as a transparent base material and a binder layer, which is located in an optical path of light from luminescent particles, for the purpose of adjusting luminescent color. You can also. In addition, a wavelength conversion layer containing a fluorescent dye or a fluorescent pigment, which is excited by light from the luminescent particles and emits light of a different wavelength from the light from the luminescent particles, can be arranged in the optical path of the light from the luminescent particles. . As the wavelength conversion layer, a component located in the above optical path containing a fluorescent dye or a fluorescent pigment can also be used.

[0049]

EXAMPLE 1 Formation of EL Element In this example, an EL element having a light emitting layer having the structure shown in FIG. 1 was formed. 320mm width as transparent substrate,
60m long PET film with ITO (Oike Industry Co., Ltd.)
TCF KPC300-75A (thickness: 75 μm, light transmittance: 81%) was used. This film was obtained in the form of a roll, and a transparent conductive layer made of ITO (indium-tin-oxide) was laminated on one surface by a sputtering method. The thickness of the ITO layer is 50n.
m, and the surface resistance was 250 Ω / □.

A slurry for forming a light emitting layer was applied to the ITO surface of the transparent substrate using a bar coater along the length of the transparent substrate. This paint was prepared by dispersing luminescent particles (300 parts by mass) composed of the following phosphors in a binder solution (100 parts by mass) composed of a high dielectric constant polymer. Phosphor particles: Durel phosphor particles, product number: 615
A high dielectric constant polymer solution: 15 mass% solution of tetrafluoroethylene-hexafluoropropylene-vinylidene fluoride copolymer “THV200P” (dielectric constant 10 (1 kHz), light transmittance 96%) manufactured by 3M (solvent is acetic acid) ethyl/
Methyl isobutyl ketone = 1: 1).

The coating film of the above slurry was dried at 65 ° C. for about 1 minute and then at 125 ° C. for about 3 minutes to obtain a dry thickness (T).
Formed a 48 μm light emitting layer. The maximum particle size (Dm) of the phosphor particles measured by the above-described method (microscope observation method) was 35 μm, and the ratio T / Dm was 1.37. The particle size measurement sample was not dispersed in the light emitting layer, but was observed at a magnification of 500 times using powdery phosphor particles. Also, about 30 parts at both ends in the width direction of the ITO surface
The light emitting layer was applied so that an exposed portion having a width of mm (a portion where the light emitting layer was not disposed) was formed.

Subsequently, a coating for forming an insulating layer was applied on the back surface of the light emitting layer, and the coating was dried to form an insulating layer. The composition of the coating material for forming the insulating layer is the above-mentioned THV200.
G: barium titanate: ethyl acetate: methyl isobutyl ketone = 11: 26: 31: 31 (weight ratio), applied by a bar coater, and dried under the same conditions as in the case of the light emitting layer described above. The barium titanate was “HPBT-1” manufactured by Fuji Titanium Co., Ltd. The total thickness of the light emitting layer and the insulating layer after drying was 53 μm. On the other hand, a 3M application tape “SCPM7Y” (18 mm) is formed so that an exposed portion having a width of about 5 mm is formed in a portion where the light emitting layer is not disposed on the ITO surface of the transparent substrate with the light emitting layer.
Width) was applied along the length direction of the transparent substrate and masked.

Lastly, after vacuum-depositing aluminum on the surface to be coated of the transparent substrate with the light-emitting layer (the surface comprising the light-emitting layer, the masking, and the exposed ITO surface), the masking is removed, and the aluminum-deposited film is formed. Formed simultaneously with the back electrode and the bus (two at both ends). Thus, a roll-shaped EL element of this example was obtained. The vacuum deposition of aluminum is performed at a degree of vacuum (pressure in the chamber) of 3.0 × 1.
0 ^{-4 to} 5.0 × 10 ^-4 Torr, line speed 90m
/ Min.

A non-deposited portion was formed between the back electrode and the two buses, and these buses were not electrically connected to both the light emitting layer and the back electrode. Further, the bus was a striped bus extending continuously in the length direction and having no discontinuous portions. When the cross section of the light emitting layer of the EL element of this example was observed using a scanning electron microscope, a binder was filled between the phosphor particles adjacent to each other, and no insulator particles were observed. A first layer in which phosphor particles are arranged on the insulating layer side;
An overlying layer composed of the second layer arranged on the transparent conductive layer side was formed, and it was confirmed that a plurality of luminescent particles were in contact with each other in the overlying layer. In this way, the light emitting layer was formed such that the layer of the light emitting particles was completely embedded in the binder layer and was not substantially embedded in the insulating layer. The surfaces of the insulating layer and the transparent conductive layer that face each other were substantially parallel to each other and were substantially smooth.

Light emission from EL element From the roll-shaped EL element (raw material) thus obtained,
Cut out the rectangular EL element and set 100 between the back electrode and the bus.
When an AC voltage of 400 V was applied to the EL element to emit light, uniform light emission was obtained over the entire light emitting surface. The plane size of the light emitting surface of the rectangular EL element is
It was 100 mm (vertical) x 100 mm (horizontal). EL
In order to emit light from the element, a power supply (“PCR500L” manufactured by Kikusui Electronics Corporation) was connected between the ITO surface and the back electrode, and a sine wave of 100 V and 400 Hz was applied. Using a luminance meter (“LS110” manufactured by Minolta Co., Ltd.), the effective power P [W] and the luminance L [cd / m ² ] during light emission were measured in a dark room, and the light emission luminance and light emission efficiency η [Im / W] was calculated using the aforementioned equation (1). As a result, the emission luminance was 51 cd / m ² , and the emission efficiency was 3.3 lm (lumen) /
W. When the device was continuously driven under the same conditions, the luminance half-life (THL) was 1000 hours or more.

(Example 2) The EL of this example was manufactured in the same manner as in Example 1 except that the amount of the phosphor particles was changed to 600 parts by mass.
An element was manufactured. The dry thickness (T) of the light emitting layer was 52 μm, and the ratio T / Dm was 1.48. The emission luminance measured in the same manner as in Example 1 was 51 cd / m ² , and the emission efficiency was 3.9 lm (lumen) / W. Further, when continuously driven under the same conditions, the luminance half-life was 88.
It was 0 hours.

Example 3 The EL device of this example was manufactured in the same manner as in Example 1 except that the concentration of the binder (THV) solution was changed to 10% by mass and the amount of the phosphor particles was changed to 1200 parts by mass. Produced. The dry thickness (T) of the light emitting layer is 53μ
m and the ratio T / Dm was 1.51. The emission luminance measured in the same manner as in Example 1 was 56 cd /
m ² , and luminous efficiency was 3.7 lm (lumens) / W. When the device was continuously driven under the same conditions, the luminance half-life was 860 hours.

Comparative Example 1 An EL device of this example was manufactured in the same manner as in Example 1, except that the concentration of the binder (THV) solution was changed to 10% by mass. Dry thickness of light emitting layer (T)
Was 34 μm and the ratio T / Dm was 0.97.
In addition, when the cross section of the light emitting layer of the EL element of this example was observed with a scanning electron microscope, it was confirmed that the phosphor particles substantially formed a single layer. The emission luminance measured in the same manner as in Example 1 was 70 cd / m ² , and the emission efficiency was 1.
It was 9 lm (lumen) / W. When the device was continuously driven under the same conditions, the luminance half-life was 630 hours.

Comparative Example 2 The same procedure as in Example 1 was carried out except that the concentration of the binder (THV) solution was changed to 10% by mass and the amount of the phosphor particles was changed to 900 parts by mass.
An L element was produced. The dry thickness (T) of the light emitting layer is 39 μm
And the ratio T / Dm was 1.11. In addition, when the cross section of the light emitting layer of the EL element of this example was observed with a scanning electron microscope, it was confirmed that the phosphor particles substantially formed a single layer. The emission luminance measured in the same manner as in Example 1 was 81 cd / m ² , and the luminous efficiency was 1.31 lm.
(Lumens) / W. When the device was continuously driven under the same conditions, the luminance half-life was 460 hours.

[0060]

According to the present invention, there is provided an EL device in which the luminous efficiency and the lifetime are effectively improved without lowering the luminous brightness.
An element can be provided. In the EL device according to the present invention, for example, the luminous efficiency is maintained at 3 lumen / W or more and the lifetime (luminance half-life) is maintained while maintaining the luminous luminance at 50 cd / m ² or more.
Can be improved to 700 hours or more.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of an EL device according to one embodiment of the present invention.

[Explanation of symbols]

1: transparent conductive layer, 2: light-emitting layer, 3: light-emitting particles, 4: binder layer, 5: insulating layer, 6: back electrode, 7: transparent substrate,
10: EL element

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Makoto Sekiguchi 3-8-8 Minamihashimoto, Sagamihara-shi, Kanagawa F-term in Sumitomo 3M Limited (Reference) 3K007 AB02 AB03 AB11 CA06 CB01 CC01 DA05 DB02 DC01 EA02 EB04 FA01

Claims (3)

[Claims] 1. a) a transparent conductive layer; b) a light-emitting layer comprising a binder and a plurality of light-emitting particles embedded in the binder disposed on the back of the transparent conductive layer; c) a light-emitting layer And d) a back electrode disposed on the back side of the insulating layer, wherein the light emitting layer has a thickness T The ratio (T / Dm) of [μm] to the maximum particle diameter Dm [μm] of the luminescent particles is 1.2 or more.
An electroluminescent element, which is less than 0. 2. The electroluminescent device according to claim 1, wherein the luminescent particles are not substantially buried in the insulating layer. 3. The light-emitting particles form a multilayer composed of a first layer arranged on the insulating layer side and a second layer arranged on the transparent conductive layer side, in which the light-emitting particles are The electroluminescent device according to claim 1, wherein the electroluminescent device is in contact with each other.