JPH06260284A - Dispersion type el element - Google Patents

Abstract

PURPOSE:To increase luminance and improve luminous efficiency by providing a light emitting layer in which a granular high dielectric layer having a specified average particle size is laminated on the back surface of a phosphor layer. CONSTITUTION:On the back surface of a transparent conductive electrode 1, a light emitting layer 3 consisting of a layer having a granular phosphor 6 dispersed in a binder and a layer having a granular high dielectric body 8 dispersed in the binder which is laminated on the back surface thereof is formed. Further, an insulating layer 4 and a back plate 5 are arranged on the back surface, and the whole laminated body is sealed by a moisture-proof resin 2. The average particle size of the granular dielectric body 7 is 0.5 time or more the average particle size of the phosphor 6. The phosphor situated on the upper part of the high dielectric body particle having a relatively large particle size is enhanced in field strength, and the high dielectric body can be sufficiently used in a small amount. Since the increase of electrostatic capacity of the light emitting layer is thus also minimized, the luminance is improved with a little increase of power consumption.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dispersion-type EL (electroluminescence) device, and more specifically, a half or more of the average particle size of the phosphor is below the dispersion layer of the phosphor (on the back side of the device). The present invention relates to a dispersion type EL device having a light emitting layer formed by laminating a dispersion layer of a granular high dielectric material having a size of, and having sufficiently improved brightness.

[0002]

2. Description of the Related Art Generally, a conventional dispersion type EL element has a high dielectric resin as a binder between a transparent conductive electrode (1) and a back electrode (5) of aluminum foil, as shown in the cross section of FIG. A light emitting layer (3) in which a phosphor is dispersed, and an insulating layer (4) in which a highly dielectric resin, which is a binder, is highly filled with ultrafine granular high dielectric material such as submicron barium titanate.
It consists of and. The outside is covered with a moisture-proof resin (2), and when a voltage is applied between the transparent conductive electrode and the back electrode, the phosphor in the light emitting layer emits light.

In such a dispersion type EL element, in order to improve the brightness, an electric field applied to the phosphor in the light emitting layer is increased. In general, when a voltage is applied to a substance composed of two kinds of dielectrics, the strength of the electric field is higher in the low dielectric constant dielectric material than in the high dielectric constant dielectric material.

Utilizing this fact, a resin having a higher dielectric constant has been used as the high dielectric resin in the light emitting layer. Although cyanoethylated cellulose and the like are used as the high dielectric resin, the dielectric constant of the resin is generally lower than that of the inorganic material, and even cyanoethylated cellulose has a dielectric constant of about 20. For this reason, a substance having a higher dielectric constant is mixed and dispersed in the high dielectric resin to increase the apparent dielectric constant of the high dielectric resin. As an example of this, Japanese Patent Publication No. 38-20651 discloses a reflective high dielectric constant inorganic material such as barium titanate, and Japanese Patent Publication No. 3-171591 discloses a nonlinear optical material such as P-nitroaniline.
In JP 7-189496, PZT (PbO.ZrO.T
iO ₂ mixed sintered body), in JP-A-3-297092 Publication being performed using each granular high dielectric such as a composite oxide of barium, titanium and zirconium. The conventional method of mixing and dispersing the granular high dielectric material in the light emitting layer is to increase the apparent permittivity of the high dielectric resin, and is generally used to reduce the loss due to the reflection and absorption of light in the light emitting layer. A granular high dielectric material having an average particle size of about 1 μm is used. For this reason, the particle size of the high dielectric material is usually smaller than that of the phosphor (average particle size of about 30 μm). Also, as disclosed in Japanese Patent Publication No. 4-34893, a method has been proposed in which a phosphor is coated with a liquid high dielectric resin and the outer surface of the phosphor is covered with a thermosetting resin to form a capsule structure.

[0005]

In the conventional technique of further mixing and dispersing a high dielectric material in a high dielectric resin, the apparent dielectric constant of the high dielectric resin, which is a binder, becomes large, so that the concentration of an electric field on the phosphor is reduced. Therefore, the brightness is improved, but the electrostatic capacity of the light emitting layer is also increased, so that there is a drawback that the current is increased and the power consumption is also increased. Therefore, the Japanese Examined Patent Publication 3-29
As shown in Japanese Patent Publication No. 7092, the luminous efficiency (lumen / watt) was almost the same as that of the conventional product. Further, the method of coating the phosphor with a high dielectric resin does not sufficiently improve the brightness.

An object of the present invention is to provide a dispersion type EL element which can concentrate an electric field on a phosphor with almost no increase in current and has high brightness.

[0007]

The inventors of the present invention have made extensive studies in view of the above problems, and as a result, in an EL device, a layer of a granular high dielectric material having a specific average particle size is laminated on the back surface of a phosphor layer. It was found that when the above structure is formed in the light emitting layer, the electric field can be concentrated on the phosphor with almost no increase in current and the brightness is improved, and the present invention has been completed.

That is, according to the present invention, a layer in which a granular phosphor is dispersed in a binder and a layer in which a granular high dielectric material is dispersed in a binder are laminated, and the latter layer is an element for the former. The present invention relates to a dispersive electroluminescent device having a light emitting layer located on the back surface side and having an average particle diameter of the granular high dielectric material that is at least ½ of that of the granular phosphor.

The average particle diameter in the present invention is the number average particle diameter measured by a microscope as described on pages 12 to 13 of the Handbook of Powder Engineering (Nikkan Kogyo). E of the present invention
An example of the L element is schematically shown in FIG. Figure 1
In the above, a layer in which the granular phosphor (6) is dispersed in a binder and a layer in which the granular high dielectric material (7) is dispersed in a binder are laminated, and the latter layer is the back surface of the device with respect to the former. There is a light emitting layer (3) located on the side, and an insulating layer (4) is further laminated on the back side thereof. The front transparent conductive electrode (1) and the back electrode (5) are arranged so as to sandwich the light emitting layer (3) and the insulating layer (4). The entire laminated body is sealed with the moisture-proof resin (2).

In the light emitting layer of the EL device of the present invention, a method of laminating a layer in which a granular phosphor is dispersed in a binder and a layer in which a granular high dielectric material is dispersed in a binder are laminated on a high dielectric resin solution which is a binder. A phosphor paste and a high-dielectric paste are prepared by mixing and dispersing the phosphor and the granular high-dielectric, respectively, and a method in which the high-dielectric paste and then the phosphor paste are sequentially laminated and applied on the base material according to a conventional method.
Alternatively, there is a method in which the phosphor paste and the dielectric paste are applied on different base materials according to a conventional method, and then both are adhered with the base material outside. It is considered that the former method is easier to handle the current commercialization process than the latter method and is suitable for continuous processing.

Examples of the phosphor used in the present invention include zinc sulfide-based phosphors obtained by doping a phosphor such as zinc sulfide with an activator such as manganese or copper and an activator such as chlorine or bromine. Without being limited to this, any II-IV group compound that can be used as a phosphor for a dispersion-type EL device can be used. The average particle size of the granular phosphor used in the present invention is not limited to this, but is usually 1 to 40 μm.

The high dielectric used in the light emitting layer in the present invention is generally a metal oxide having a dielectric constant of about 100 or more, and examples thereof include titanium dioxide and barium titanate. Besides, PZT (described above), PL
Lead-based composite oxides such as ZT (PZT with La added) can also be used. The average particle size of the granular high dielectric material used here is not limited to this, but is usually 10
Is about 200 μm. Such a high-dielectric material having a relatively large average particle diameter can be obtained by a known method such as sieving a small one. The particle shape of the granular high dielectric material used in the present invention includes any shape such as a plate shape as well as a spherical shape and a shape close to a sphere. In the present invention, the ratio of the average particle size of the granular high dielectric material to the average particle size of the phosphor is 1: 2 to 3: 1, more preferably 1: 1 to 2: 1. If the average particle diameter of the high dielectric material is smaller than half that of the phosphor, the improvement of the brightness of the device is not sufficient.

In the light emitting layer of the present invention, the ratio of the high dielectric resin as a binder, the phosphor and the high dielectric used is preferably about 1: 1 to 1: 5: 5. In the light emitting layer, the thickness of the layer containing a high dielectric material is usually 10 to 200 μm.
m, preferably about 20 to 100 μm, and the thickness of the layer containing the phosphor is usually 10 to 200 μm, preferably 20.
It is about 100 μm. The dispersion type EL element of the present invention is
A configuration known in the related art as shown in FIG. 2 can be adopted except that the light emitting layer is as described above. That is, in the present invention, the insulating layer is formed by filling the binder with an ultrafine granular high dielectric material such as conventionally known submicron barium titanate and having a thickness of usually 10 to 200 μm, preferably 20 to 100 μm. Stuff used. Further, as the binder in the light emitting layer or the insulating layer, a high dielectric resin such as conventionally known cyanoethylated cellulose is used.
As the transparent conductive electrode, any of the conventionally known electrodes having the same purpose can be used. For example, transparent synthetic resin such as polymethylmethacrylate or polyester, or indium oxide on the surface of a glass sheet, A transparent conductive material such as tin oxide or indium-tin oxide (ITO) coated on the entire surface or in a pattern is used. The opaque electrode layer used on the back surface of the device may be a conventionally known one, for example, a vapor deposition film of aluminum, silver, gold or the like is used.

The conventional method of mixing and dispersing the granular high dielectric material in the light emitting layer is to increase the apparent dielectric constant of the high dielectric resin, and to reduce the loss due to the reflection and absorption of light in the light emitting layer. Therefore, a granular high dielectric material having an average particle size of about 1 μm is generally used. For this reason, the particle size of the high dielectric material is usually smaller than that of the phosphor (average particle size of about 30 μm).

When high dielectric particles are not present in the light emitting layer,
The electric field distribution in the light emitting layer is almost uniform, and the electric field strength is almost the same in any part of the light emitting layer. On the other hand, when the high-dielectric particles are present in the light emitting layer, the electric field distribution around the high-dielectric particles changes, and a portion having a high electric field strength and a portion having a low electric field strength appear around the high-dielectric particles.

The high dielectric substance in the light emitting layer of the dispersion type EL device of the present invention is used to locally change the electric field in the light emitting layer to create a portion having a large electric field strength around the phosphor. When the high-dielectric-constant particles having a large particle size are present in the lower part (back side) in the light-emitting layer as in the present invention, the electric field strength in the light-emitting layer above the high-dielectric particle becomes large. Since the phosphor is located in the light emitting layer above the high dielectric particles, the electric field strength of the phosphor is effectively increased, and the brightness of the EL device of the present invention is improved. As described above, according to the conventional method of mixing and dispersing the high dielectric material in the light emitting layer, since the average particle diameter of the high dielectric material used is smaller than that of the phosphor, the appearance of the high dielectric resin in the light emitting layer is Although it is possible to increase the dielectric constant, it is not possible to disturb the electric field distribution around the high-dielectric-constant particles and increase the electric field strength of the phosphor located at a specific portion in the light emitting layer.

In the present invention, the amount of the granular high dielectric material in the light emitting layer is small compared to the conventional method of mixing and dispersing the high dielectric material in the light emitting layer, and the capacitance of the light emitting layer is increased. Since it is small, the increase in current is small and the increase in power consumption is also small.

[0018]

EXAMPLES Examples of the present invention will be shown below, but the present invention is not limited thereto. Example 1 and Comparative Example 1 A cyanoethylated cellulose-based high dielectric resin was dissolved in dimethylformamide as a solvent to prepare a solution containing 20% by weight of the cyanoethylated cellulose-based high dielectric resin. 20 g of a dispersion type EL element phosphor (zinc sulfide-based) having an average particle size of about 20 μm was mixed and dispersed in 50 g of this solution to prepare a phosphor paste. Further, 20 g of high-dielectric particles were mixed and dispersed in 50 g of a solution containing 20% by weight of the cyanoethylated cellulose-based high-dielectric resin to prepare a high-dielectric paste.
High dielectric particles are obtained by crushing a barium titanate sintered body,
It is classified by a sieve, and has a particle size distribution of 45 to 74 μm, an average particle size of 50 μm, and a dielectric constant of about 400.
0 was used. Next, a dispersion type EL device for observing the emission intensity as shown in FIG. 3 was prepared by the following procedure. The phosphor paste was applied by an applicator onto a polyester film having a thickness of about 100 μm on which a transparent electrode of indium-tin oxide was formed, and dried at 120 ° C. for 5 minutes to be in a semi-dried state.

A high dielectric paste is applied by an applicator onto a polyester film having a thickness of about 100 μm on which a transparent electrode of indium-tin oxide is formed, and 1
It was dried at 20 ° C. for 5 minutes to be semi-dried. A polyester film having a phosphor layer formed thereon is superposed on a polyester film having a semi-dried high dielectric layer formed thereon.
It was passed between two roll laminators heated to 0 ° C. Then, it was dried at 60 ° C. for 8 hours to prepare a dispersion type EL device for observing emission intensity.

As Comparative Example 1, a dispersion type EL device for observing emission intensity as shown in FIG. 4 was prepared. It was prepared in the same manner as in Example 1 except that a blank paste (not containing a high dielectric material) was used in place of the high dielectric material paste.

The internal structure of the light emitting layer of the dispersion type EL device for observing the emission intensity of Example 1 was observed by observing the cross section of the device with an electron microscope, and it was confirmed that the structure as shown in FIG. 3 was formed. The thickness of the light emitting layers of Example 1 and Comparative Example 1 was 139, respectively, based on the measurement results by the micrometer.
μm and 115 μm. In the light emitting layer of Example 1, the thickness ratio of the high dielectric layer and the phosphor layer is approximately 6: 4. The transparent electrodes of the dispersion-type EL devices for observing the emission intensity of Example 1 and Comparative Example 1 were connected to an AC power source, and 100 V, 4
A sine wave voltage of 00 Hz was applied and the brightness and current were measured. As a result, in the dispersion type EL device of Example 1, the current increased by about 1.1 times and the brightness increased by about 2.8 times as compared with Comparative Example 1.

[0022]

EFFECT OF THE INVENTION The dispersion type EL device of the present invention has a smaller increase in current as compared with the conventional product, and the brightness is improved by the electric field concentration on the phosphor. Since the increase in power consumption due to the increase in current is small, not only the brightness is improved, but also the luminous efficiency (lumen / watt) can be improved.

[Brief description of drawings]

FIG. 1 is a sectional view showing an example of a dispersion type EL device of the present invention.

FIG. 2 is a cross-sectional view of a conventional general dispersion type EL device.

FIG. 3 is a cross-sectional view showing a dispersion type EL element for luminescence intensity observation of Example 1.

4 is a cross-sectional view showing a dispersion type EL device for observing emission intensity of Comparative Example 1. FIG.

[Explanation of symbols]

 1. Transparent conductive electrode 2. Moisture-proof resin 3. Light-emitting layer 4. Insulating layer 5. Back electrode (aluminum foil, etc.) 6. Phosphor particles 7. High dielectric particles 8. Polyester film

Claims (1)

[Claims] 1. A layer in which a granular phosphor is dispersed in a binder and a layer in which a granular high dielectric material is dispersed in a binder are laminated, and the latter layer is located on the back side of the device with respect to the former. In addition, the dispersion type electroluminescence device is characterized by having a light emitting layer in which the average particle size of the granular high dielectric material is 1/2 or more of that of the granular phosphor.