JPH0121519Y2 - - Google Patents

Description

[Detailed Description of the Invention] This invention relates to the structure of an electroluminescent element that emits electroluminescence by applying a voltage.

The phosphor layer is sandwiched between first and second electrodes and supported and held on an insulating transparent substrate, and a regular alternating current voltage is applied between the first and second electrodes to cause light emission within the phosphor layer. A distributed electroluminescent element or light emitting layer that emits electroluminescence by exciting the center is sandwiched between first and second insulating layers, which is further sandwiched between first and second electrodes to be supported and held on an insulating transparent substrate. However, a thin film (vapor deposition) type electroluminescent device that emits electroluminescence by exciting a luminescent center in a luminescent layer by applying a regular alternating current voltage between the first and second electrodes is well known. When used as a flat display device for displaying characters, figures, etc., compared to liquid crystal display elements, which are similar flat displays, they can operate in a wide temperature range from low to high temperatures, and have high brightness. Since it is a self-luminous type, it does not require any other illumination light source, and has advantages such as excellent responsiveness. In recent years, its practical use has been rapidly advanced, and various types have been proposed.

It is a well-known fact that the brightness life of these electroluminescent elements can be extended by providing a moisture barrier layer that prevents moisture from the surrounding atmosphere, especially moisture containing OH groups. Note that the brightness life here is defined as the time until the brightness of light emission becomes 1/2 of the initial brightness.

As a moisture-proof layer for such an electroluminescent device, methods such as coating with a resin adhesive such as Araldite or sealing with an inert gas with good electrical insulation properties such as dehumidified Freon sulfur hexafluoride have been known for some time. However, heat curing is required to form a coating with a resin adhesive, which may cause excessive thermal history to be applied to the phosphor layer or luminescent layer, which may deteriorate brightness characteristics. . Further, complete sealing is required to seal inert gas and provide a moisture-proof layer, which is difficult to perform and difficult to confirm the sealing state from the outside.

Furthermore, some electroluminescent devices have a structure that uses a desiccant in the moisture barrier layer to address these conventional problems, but since the desiccant is a solid powder, it cannot be completely isolated from the surrounding atmosphere. Moreover, it is not possible to obtain a sufficient moisture-proof structure without using a considerable amount of desiccant, which requires a large space to contain the desiccant, which increases the overall size of the electroluminescent device and makes it easier to make it thinner. A problem has arisen in that the most important feature of an electroluminescent device is lost.

This invention was devised by focusing on the above-mentioned conventional problems, and aims to provide an electroluminescent device having a structure in which liquid crystal is used as a moisture-proof layer of the electroluminescent device.

This invention will be described below based on embodiments shown in the accompanying drawings.

Figure 1 is a cross-sectional view of a distributed electroluminescent device showing its structure. 1 is a transparent glass substrate that constitutes the display surface, and 2 is a film of tin oxide as an electrode material on the glass substrate 1 to a thickness of about 2000 Å. The transparent electrode 3 is formed by electron beam evaporation and heat treatment, and the transparent electrode 3 is made by dispersing zinc sulfide powder to which copper is added as an active substance to form luminescent centers on the transparent electrode 2 in a suitable binder. A phosphor layer was formed by coating or printing the phosphor material produced by the process using a silk screen method to a thickness of about 10 μm. 4 was formed by forming aluminum on the phosphor layer 3 to a thickness of about 3000 Å by an electron beam evaporation method. The glass substrate 1, the transparent electrode 2, the fluorescent layer 3, and the back electrode 4 constitute an EL cell 5, which is a reflective metal back electrode. 6 is a cover made of polycarbonate resin that seals and surrounds the EL cell 5 except for the display surface of the EL 5; 7 is a liquid crystal interposed between the EL cell 5 and the cover 6;
After the cover 6 is fixed, the liquid is injected through an injection port (not shown) provided in the cover 6.

In this structure, by applying a regular alternating current voltage of several KHz between the electrodes 2 and 4, an electric field generated in the phosphor layer 3 excites the electrons of copper, which is the luminescent center, and emits green electroluminescence. The light emitted from this emission is emitted directly or reflected by the back electrode 4 and irradiated to the outside through the glass substrate 1.

Figure 2 is a diagram for comparing the brightness characteristics of electroluminescent elements using a desiccant (activated alumina) and liquid crystal 7 in the moisture barrier layer, with the horizontal axis representing the current application time and the vertical axis representing the luminance. , when the liquid crystal 7 is used as the moisture-proof layer, the luminescent display is stable for a long time. This is LCD 7
Because it does not contain OH groups, which are the major enemies of the fluorescent layer 3, and is in a liquid phase, it is able to isolate the EL cell 5 from the surrounding atmosphere more reliably than a desiccant that is in a solid phase and is a powder. This is thought to be due to

In the above embodiments, a dispersion type electroluminescent device has been described, but it goes without saying that a thin film (vapor deposition) type electroluminescent device can also be used and the same functions and effects as described above can be obtained.

In addition to the synthetic resin, the cover 6 may be made of metal, glass, or any other material as long as the liquid crystal 7 does not leak.If only the portion facing the display surface is transparent, the cover 6 may be made of metal or glass.
It may have a shape that surrounds the entire cell 5. Furthermore, like a general liquid crystal display element, the glass substrate 1 is used as one substrate, and the other substrate is provided so as to sandwich the transparent electrode 2, fluorescent layer 3, and back electrode 4 formed on this substrate 1, and the gap between the two substrates is It is also possible to form an empty cell by providing an epoxy sealant mixed with a spacer and fixedly adhering it, and then injecting the liquid crystal into the empty cell.

As described above, in the electroluminescent element according to this invention,
By injecting liquid crystal between the EL cell and the cover that covers the EL cell, it is possible to isolate the EL cell from the surrounding atmosphere, thereby eliminating the negative effect of moisture on the light emitting display, compared to the conventional structure. The luminance lifespan can be extended compared to other electroluminescent devices.

In addition, there is no additional heat history to the fluorescent layer or luminescent layer that occurs when forming a moisture-proof layer by coating with a resin adhesive, and there is no risk of adversely affecting brightness characteristics, eliminating variations in performance during device manufacturing. ,
It is possible to easily produce stable products.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing the structure of a distributed electroluminescent device that is an embodiment of this invention, and FIG. 2 is a diagram showing changes in luminance with respect to current application time due to differences in the moisture-proof structure of the same electroluminescent device. be. 1...Transparent glass substrate, 2...Transparent electrode, 3...
...fluorescent layer, 4...metal back electrode, 5...EL cell,
6...Cover, 7...LCD.

Claims (1)

[Scope of utility model registration request] An EL cell that emits electroluminescence when voltage is applied;
1. An electroluminescent device comprising a cover that hermetically surrounds the EL cell, characterized in that a liquid crystal is injected between the EL cell and the cover.