JPS6238838B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a distributed electroluminescent device with improved brightness, lifetime and stability.

Currently, liquid crystals, light-emitting diodes, and fluorescent display tubes are used as display elements, taking advantage of their respective characteristics, and electroluminescent elements are used for only a limited number of displays that require low brightness. There is only one, but it is hardly ever put into practical use. The reason for this is that, as is well known, the brightness and lifespan have not reached practical levels. However, electroluminescent devices are planar light sources that can emit light in various colors, and they have features that other display devices do not have, such as being able to manufacture relatively large area devices at extremely low cost, low power consumption, and a large degree of freedom in design. home appliances, measuring instruments,
Expectations continue to be high for use in displays for vehicles, ships, aircraft, various displays, and flat-screen TVs. The problem is brightness and lifespan, but a brightness of 20 to 30ft-L is required for practical display purposes, and a half-life of brightness is required to be at least 3,000 hours and a usable time of at least 10,000 hours. Ru.

However, at present, no dispersion polar electroluminescent device in which ZnS-based phosphor powder is dispersed in resin or ceramic, which is expected to have low cost and practical brightness, satisfies the above conditions. Although the brightness can be increased by changing the frequency and voltage of the applied electric field, the current situation is that the lifetime becomes even shorter.

In addition, resin-type light emitting devices with improved brightness using high dielectric constant resins have been experimented with in the past, but the binder resins used in these devices have problems in terms of film formation and stability after film formation. Relative permittivity 20~
It was around 25, maybe 30 at most. Considering the apparent permittivity of the ZnS-based phosphor when it emits light, a binder with a relative permittivity of 40 or higher is desired, but most of these high permittivity materials are in liquid form, and the film forming surface and There were problems with subsequent stability and disturbance of the light-emitting surface due to aggregation of phosphor particles during operation as a light-emitting device, and it could not be used alone as a practical binder for electroluminescent devices. Also,
The deterioration of the above ZnS-based phosphor is accelerated by moisture, so when it is manufactured as a light-emitting element, it is common to take appropriate moisture-proof sealing measures. For example, in resin-type devices that use resin as a binder, moisture-proof sealing is performed with a moisture-proof glass plate using an adhesive such as epoxy resin.
The purpose can be achieved to some extent by using an appropriate heat-curing epoxy resin and devising a moisture-proofing process. However, as long as resin is used for adhesion, the adhesive layer gradually absorbs moisture due to moisture in the air during storage or lighting operation, causing interfacial delamination between the adhesive layer and the glass, causing rapid This may cause severe deterioration.

Furthermore, enamel-type electroluminescent devices are already well known, in which phosphor powder is sintered on an iron substrate using low-melting glass. Since the process is carried out at high temperatures, the brightness of the phosphor itself is greatly reduced, and glasses suitable as binders for ZnS-based phosphors are limited to those that do not contain lead, bismuth, antimony, etc. Its dielectric constant is about 8 to 10 at most, which is insufficient for use as a binder for electroluminescent devices. Therefore, the luminance of the enamel type is about 1/10 lower than that of the one using high dielectric constant resin, making it unsatisfactory for display purposes. In addition, enamelled molds whose light emitting layers are made by sintering have many defects and voids in the light emitting layer, which may lower the dielectric strength and cause short circuits, which may cause the device to become moisture-proof. For protection, a moisture-proof cover coat layer was provided using a material such as low-melting glass that could be treated at a temperature that would not damage the light-emitting layer. However, it is not possible to directly use lead-based or bismuth-based glass, which has a low melting point and high fluidity, for this coating, and as a result, the coating layer is not free of defects and pinholes, and as a result, the dielectric strength is low. Not only does it deteriorate, but moisture that enters through them can cause small spots on the light emitting surface during lighting operation, and blackening progresses from there, resulting in a decrease in brightness. It was hot.

An object of the present invention is to eliminate the above-mentioned drawbacks of the prior art and to provide a high-brightness phosphor powder-dispersed sintered electroluminescent device using a high dielectric constant binder and a moisture-proofing method therefor. Furthermore, for more details,
A practical distributed electroluminescent element with high brightness and stability that uses a high dielectric constant liquid material with a dielectric constant of at least 20 as a void filling material, and which can not only suppress the decrease in dielectric strength voltage and the occurrence of non-luminescent spots. Another object of the present invention is to provide a moisture-proof electroluminescent device that also has the effect of improving brightness.

The feature of the dispersion sintered electroluminescent device of the present invention is that the interelectrode constituent material layer consisting of a phosphor layer or a phosphor layer and a high dielectric constant insulating reflective layer is made of a metal that is harmless to the phosphor. The material is sintered with oxide and fixed to prevent the phosphor from moving or aggregating during application of an electric field and lighting.Next, the sintered layer is coated with a high-carbon material that is harmless to the phosphor. The device is impregnated with a liquid substance having a dielectric constant, and further, the device is sealed in a glass container to make it moisture-proof.

The method for sintering the phosphor layer and high dielectric constant insulating layer is to mix an organic complex of a metal that is harmless to the phosphor, such as a metal alkoxide solution, with these film-forming pastes or slurries, After coating and forming a film on a glass plate with a transparent conductive film called Nesa film, heating and drying, the above-mentioned metal alkoxide solution was added and impregnated, and heat treatment was performed at 400 to 450°C. There is a method in which the organic components are completely burned out and at the same time, the phosphor layer and the like are sintered using the generated metal oxide. Other methods include mixing the phosphor with a harmless neutral salt solution and firing it, or adding harmless low-melting point glass fine powder to the phosphor, although the sintering temperature will be slightly higher. A sintered type can also be obtained by forming a film using a paste or slurry and firing at a temperature of around 600°C. Materials suitable for the above sintering include, of course, those that are harmless to the phosphor, but which convert into oxides when heated at high temperatures of 400°C or higher, such as:
The material needs to be able to maintain its transparent or white color without reacting with the currently used ZnS-based phosphor to become a light-absorbing color such as black, and it is also desirable to have a dielectric constant as high as possible. From the above points, for example,
Complexes and neutral salts of metals such as titanium, zinc, tin, indium, barium, strontium, calcium, aluminum, boron, silicon, and rare earth elements such as europium, yttrium, terbium, and samarium, although they are slightly more expensive. is applicable. In addition, low melting point glasses include ZnO−B ₂ O ₃ −SiO ₂ series, B ₂ O ₃ −
SiO ₂ type etc. can be used.

After forming a sintered light-emitting layer on the Nesa glass plate as described above, a back electrode is formed on this by means such as vacuum evaporation of aluminum or sputtering, and then sintered as shown in Figure 1. Make a type light emitting element. In the figure, 1 is a glass substrate, 2 is a transparent conductive film, 3 is a sintered light emitting layer, 4 is a back electrode,
In some cases, a high dielectric constant insulating reflective layer may be provided between the light emitting layer 3 and the back electrode 4. Then,
The entire interelectrode constituent material layer may be impregnated with a liquid material that has as high a dielectric constant as possible and is as nonvolatile as possible. Examples of liquids with a high dielectric constant and a high boiling point for impregnation include cyanoethyl saccharose, α-cyanoethyl phthalate, and β-cyanoethyl phthalate, which have a dielectric constant of 20 or higher and a boiling point of 150°C or higher. It is suitable as a material for the purpose of the present invention. By impregnating this high dielectric constant liquid material, all the voids and defects in the emissive layer that were unavoidable in the conventional sintered type are filled with the high dielectric constant liquid and bonded with an oxide with a relatively high dielectric constant. The phosphor powder is in a fixed and dispersed form within the liquid having a higher dielectric constant. As a result, not only the dielectric strength between the electrodes is increased, but also an electric field is effectively applied to the phosphor, making it possible to obtain a distributed sintered electroluminescent device with high brightness and improved lifetime. It turns out.

The present invention will be explained in detail below using examples.

Example 1 7 parts by weight of electroluminescent ZnS phosphor, 2 parts by weight of fine barium titanate powder,
Titanium tetraisopropoxide solution stabilized with acrylic ester SA (manufactured by Mitsubishi Rayon Co., Ltd.) 0.5
Parts by weight were added, and an appropriate amount of α-terpineol was further diluted to prepare a paste for forming a light-emitting layer. This paste is printed on the transparent conductive film 2 of the glass substrate 1 by screen printing method to form a film,
After heating and drying at 150 to 200°C, vacuum impregnation of the titanium tetraisopropoxide stabilizing solution into the membrane, heating, and drying are repeated several times, followed by heating at a maximum of 430°C for about 60 minutes. A firing process was performed. By this firing treatment, the organic components in the film are burnt out, and at the same time, an electroluminescent layer 3 is obtained in which the phosphor powder is sintered with titanium oxide produced by thermal decomposition of titanium tetraisopropoxide. Next, a back electrode 4 was formed on the light emitting layer 3 by vacuum evaporation of aluminum to obtain a conventional sintered electroluminescent element (see FIG. 1). An alternating current electric field was applied between the transparent conductive film 2 and the back electrode 4 of this element to confirm that this element emits light and its dielectric strength. Next, the light emitting element was heated to about 130° C. in a reduced pressure atmosphere, and the entire light emitting layer 3 of the light emitting element was sufficiently impregnated with cyanoethyl sucrose. The electroluminescent device according to the present invention obtained in this way has a voltage of 250Hz and 100V.
When lit, it had a brightness of 20 to 30 ft-L, although it varied slightly depending on the phosphor used and its film thickness.

However, if left as is, it will deteriorate due to moisture in the air, so it is necessary to make it a moisture-proof element for practical use.

Below, a method for making the electroluminescent device of the above type completely moisture-proof will be described.

Example 2 First, as shown in FIG. 1, a sintered electroluminescent layer 3 and a back electrode 4 were formed on a transparent conductive film 2 of a glass substrate 1 having a transparent conductive film 2 formed on its surface. A sintered electroluminescent device of this type is produced using the method described above.

FIG. 2a is a plan view of the lid-shaped glass plate 5 used for moisture-proofing the light emitting element, and FIG.
FIG. This lid-shaped glass plate 5 is made by etching a single glass plate using a hydrofluoric acid etching method, leaving a side wall 6 of a predetermined thickness and width on the periphery thereof, forming a concave portion 7, and at the same time forming a concave portion 7 at an appropriate location on the side wall 6. A small groove 8 for injecting a high dielectric liquid material is provided. Note that the size of the recess 7 is slightly larger than that in order to sufficiently cover the light emitting layer 3 shown in FIG. 1, and its depth is also slightly larger than the thickness of the light emitting layer 3 and the back electrode 4. For example, the depth is about 50 to 100 μm, the depth of the small groove 8 is almost the same as the depth of the recess 7, and the width is about 1 to 2 mm.
This processing was performed simultaneously with the formation of the recess 7.
Furthermore, the outer dimensions of the lid-shaped glass plate 5 are smaller than the glass substrate 1. Next, a lead glass-based low melting point glass paste layer is formed by printing on the end face of the side wall 6 of the lid-shaped glass plate 5, avoiding the small groove 8, and after drying, as shown in FIG. The lid-shaped glass plate 5 is used as a light-emitting layer 3 and a back electrode 4 of a light-emitting element.
The glass substrate 1 and the lid-like glass plate 5 were bonded together by the low melting point glass layer 9 by placing the glass plate in an electric furnace at a maximum temperature of 430° C. and firing it. Next, the light-emitting element made into the state shown in FIG. 3 by the above method was
10 ^-1 to 10 ^-2 mmHg, 2 to 3 in a reduced pressure atmosphere at 140℃
Heating and drying for hours, immersing in molten cyanoethyl sugar rose in the same atmosphere,
After sufficiently impregnating the light-emitting layer 3 of the device with cyanoethyl saccharose through the small grooves 8 of the lid-shaped glass plate 5, the small grooves 8 of the lid-shaped glass plate 5 are heated in the same atmosphere as shown in FIG. By closing with the hardening epoxy resin 10, a moisture-proof electroluminescent device according to the present invention can be obtained.

The moisture-proof electroluminescent device according to the present invention described above does not have minute non-luminous spots (stains) or roughness on the light emitting surface, which is seen in the conventional enamel electroluminescent device which is moisture-proofed with a cover coat/glass layer.
Fully homogeneous, 60-70℃, relative humidity 95%
Even during continuous lighting in the above atmosphere, no abnormality occurred on the light emitting surface. In addition, since the voids and defects in the light emitting layer 3 and the voids 10 in the lid-shaped glass plate 5 are all filled with an insulating liquid with a dielectric constant of 40, the dielectric strength voltage is large, and the thickness of the light emitting layer ( Since the distance between the electrodes can be reduced, the brightness is approximately 20% lower than that of the conventional wax type.
I was able to double the improvement. The brightness itself is
The type of phosphor to be used, the structure of the emissive layer and the thickness of that layer, the creation process conditions and the electric field strength to be applied,
It varies depending on the frequency, but according to the results of experiments by the inventors, for example, 250Hz, 100V (RMS)
When lit, it is 20 to 25 ft-L and can be used for a long time.
Showed more than 10000 hours.

In the above examples, it is desirable to use a material with a large dielectric constant as a sintering agent for the phosphor particles, etc.
We have described an example in which a sintered light-emitting layer was formed by blending a stabilizing solution of a titanium-based organic complex into a paste. For example, zinc, tin,
Organic complexes such as indium, magnesium, calcium, strontium, barium, aluminum, boron, silicon, etc. can all be used as means for fixing phosphor particles and the like in the same manner as above.

In addition to the above, examples of the high dielectric constant liquid to be impregnated into the light emitting layer include α-cyanoethyl phthalate and β-cyanoethyl phthalate. These have higher fluidity than the above-mentioned cyanoethyl saccharose, and can be easily injected and impregnated into the small grooves of a moisture-proof glass plate, and the effects of impregnation in improving dielectric strength and brightness are also large.

Example 3 2 parts by weight of ethyl cellulose, 5 parts by weight of titanium tetraisopropoxide, acrylic ester SA
(Product name manufactured by Mitsubishi Rayon Co., Ltd.) 5 parts by weight, 125 parts by weight of electroluminescent phosphor powder, 25 parts by weight of titanium oxide,
To this, 68 parts by weight of α-terpineol as a solvent,
A phosphor paste prepared by adding 20 parts by weight of ethyl alcohol was printed to a predetermined size on a Nesa glass substrate by screen printing to form a phosphor layer with a thickness of about 35 μm. Next, ethyl cellulose 2
Parts by weight, 5 parts by weight of Tetin tetraisopropoxide, 5 parts by weight of acrylic ester SA (trade name manufactured by Mitsubishi Rayon Co., Ltd.), 330 parts by weight of barium titanate powder, 68 parts by weight of α-tetopineol as a solvent, and 20 parts by weight of ethyl alcohol. A barium titanate paste was used to print and form a film on the phosphor layer to a thickness of about 5 μm to form a two-layer light-emitting layer with a total thickness of about 40 μm. Next, the light-emitting layer forming substrate is subjected to a heat treatment at about 200°C for 30 minutes, and then a titanium complex consisting of 1 part by weight of titanium tetraisopropoxide, 1 part by weight of acrylic ester SA, and 2 parts by weight of ethyl alcohol as a diluent. The operation of impregnation and heating, which consists of impregnating the luminescent layer with a liquid and heating it at 200°C for 30 minutes, is repeated several times, followed by baking at about 420°C for 45 minutes to remove the organic matter in the luminescent layer. While the components were burnt out, the phosphor particles, titanium oxide powder, and barium titanate powder were bound together by titanium oxide produced by thermal decomposition of the titanium complex, thereby converting it into a sintered light-emitting layer. Next, a titanium oxide sintered electroluminescent device was created by forming a back electrode on the light emitting layer using an aluminum vacuum evaporation method.At this point, the NESA substrate electrode (transparent conductive film) and the back electrode When an AC electric field of 250Hz and 100V was applied between
It showed a brightness of ~8ft-L. Next, this electroluminescent device was kept in a heated state of about 120° C., and the entire light emitting layer was impregnated with cyanoethyl sucrose, which is a high dielectric constant liquid. As a result, this electroluminescent device is
When an AC electric field of 250 Hz and 100 V was applied, the luminance was about 25 ft-L.

Example 4 After creating a titanium oxide sintered electroluminescent device using the same method as described in Example 3 and confirming its light emitting operation, impregnation with a high dielectric constant liquid and moisture-proof sealing were performed as follows. That's how I did it.

First, as shown in FIG. 2, a side wall 6 with a width of approximately 5 nm is left on the entire periphery of a single glass plate, and a portion corresponding to the light emitting layer of the light emitting element is etched to a depth using a hydrofluoric acid etching method. A recess 7 of approximately 0.08 mm is formed, and a portion of the side wall 6 is also approximately 0.08 mm deep and approximately 1 mm wide.
A small groove 8 for injecting a high dielectric constant liquid was formed, and a moisture-proof lid-shaped glass plate 5 was created. The end surface of the side wall 6 of this moisture-proof lid-like glass plate 5 is a so-called "gluing margin", and a low melting point glass paste is printed on the "gluing margin" except for the small groove 8 part, and then 420 ℃ for 40 minutes to form a low melting point glass layer 9 on the "glue" part.
was formed. Next, the titanium oxide sintered electroluminescent element on which the back electrode has been formed is covered with the moisture-proof lid glass plate 5 on which the low-melting point glass layer has been formed, and the device is heated at 420°C for 30 minutes while being held with a suitable jig. Heating was performed for a minute to weld the moisture-proof lid-shaped glass plate to the Nesa glass substrate of the sintered light emitting element using the low melting point glass layer of the "glue" portion.

Next, the light emitting element with the moisture-proof glass plate welded to it was thoroughly dehumidified in a reduced pressure heating atmosphere of 10 ^-2 mmHg and 120°C, and then thoroughly dehumidified in the same atmosphere. After immersing the light emitting element in a cyanoethyl sucrose liquid, injecting the cyanoethyl sucrose liquid into the light emitting layer of the light emitting element by injecting it through a small groove provided in the side wall of the moisture-proof glass plate in a vacuum impregnation manner. , Fill the small groove part of the moisture-proof lid glass plate used for injection with a heat-curing epoxy resin (for example, 100 parts of epoxy base resin, 8 parts of dicyandiamide), and harden it by heating and drying at 150 ° C. for 5 hours. The small groove was occluded. By the above method, a titanium oxide sintered electroluminescent device impregnated with a high dielectric constant liquid and subjected to moisture-proof sealing can be produced by applying an alternating current electric field of 250Hz and 100V to a height of 25 to 30 feet.
It exhibited a luminance of L, and its service life was over 10,000 hours.

As is clear from the above explanation, by the present invention, α-cyanoethyl phthalate and β-cyanoethyl phthalate, which are high dielectric constant liquid substances that could only be used as plasticizers by blending with an appropriate base resin, can be produced. , cyanoethyl sucrose, etc. can now be used to fill voids, defects, etc. in the sintered light emitting layer, making it possible to manufacture high brightness dispersion sintered electroluminescent elements whose light emitting surface is not disturbed even when lit at relatively high temperatures. It became possible.

Furthermore, with moisture-proof treated products, moisture-proof sealing with low melting point glass can be done at a relatively low temperature of around 400℃, so there is almost no damage to the phosphor like with conventional enamel molds, and , it has become possible to withstand continuous lighting for long periods of time in a humid atmosphere, and it has become possible to produce high-luminance and stable dispersion sintered electroluminescent elements using currently available phosphors, and its practical use. This will pave the way for further development.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a sintered electroluminescent device, and FIGS. 2 to 4 are schematic illustrations of the manufacturing process of the moisture-proof electroluminescent device according to the present invention. In the figure, 1... Glass substrate, 2... Transparent conductive film, 3... Sintered electroluminescent layer, 4... Back electrode, 5... Moisture-proof lid-shaped glass plate, 6... Side wall, 7
... Concavity, 8 ... Small groove for injection, 9 ... Low melting point glass layer, 10 ... Heat-curing epoxy resin, 11 ...
...Gap in the lid-shaped glass plate 5.

Claims (1)

[Scope of Claims] 1. A transparent glass substrate having a transparent conductive film serving as a front electrode on one surface, and a light emitting device formed by dispersing and sintering phosphor powder in a dielectric material on the front electrode. A structure having a high dielectric constant insulating reflective layer provided on the light emitting layer or the light emitting layer by sintering, and a back electrode made of a conductive metal layer provided on the light emitting layer or the reflective layer. In the distributed electroluminescent device, a colorless or translucent high dielectric constant liquid that is harmless to the interelectrode constituent material is contained in the sintered luminescent layer or the interelectrode constituent material layer consisting of the sintered luminescent layer and the sintered reflective layer. A distributed electroluminescent device characterized by being impregnated with a substance. 2. A transparent glass substrate having a transparent conductive film serving as a front electrode on one surface, and a light-emitting layer formed by dispersing and sintering phosphor powder in a dielectric material on the front electrode, or further the light-emitting layer. In a distributed electroluminescent device having a structure having a high dielectric constant insulating reflective layer provided thereon by sintering, and a back electrode made of the light emitting layer or a conductive metal layer provided on the reflective layer. , a two-layer film consisting of the light-emitting layer and the back electrode or a three-layer film consisting of the light-emitting layer, the reflective layer and the back electrode is formed on the front electrode side of the substrate with a peripheral exposed portion of a predetermined width left; A lid-like glass plate having a recess sufficient to cover the multi-layer film or three-layer film with some margin is placed over the two-layer film or three-layer film, and the end face of the side wall of the lid-like glass plate is exposed to the substrate. A layer of low-melting glass is used to adhere the material on the substrate, and a small groove provided in the side wall of the glass lid is inserted into the space formed between the substrate and the glass lid, and the material is harmless to the material between the electrodes. 1. A distributed electroluminescent device characterized in that a colorless or translucent high dielectric constant liquid material is injected to sufficiently impregnate the interelectrode material and then the small grooves are sealed.