JPH01157091A - Dispersion type electroluminescence element - Google Patents

Abstract

PURPOSE:To provide low power performance and high luminous efficiency by coating a resin composition having a 5 or more induction rate which is lower than that of an induction resin composition used for forming an illuminous layer at a recess on the upper part of the illuminous layer. CONSTITUTION:A resin composition 7 is formed such that its induction ratio is lower than that of a high induction resin composition used for forming an illuminous layer on a recess on the top face of an phosphor 3 and is less than 5. The induction rate difference between the composition for coating the recess and the resin composition to be used for the layer 3 is varied according to the state of the recess, namely the thickenesses and of the resin composition for coating the recess and the layer 3 the like, however, normally it may be about 1 or more, and preferably about 2 or more. It is thus possible to realize low power performance and high illumination efficiency through the low current performance of element.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a distributed electroluminescence light emitting device (hereinafter abbreviated as a distributed EL device) with excellent electrical characteristics, and more specifically relates to a dispersion type electroluminescence light emitting device (hereinafter abbreviated as a “dispersed type EL device”) with excellent electrical characteristics. (Relates to a dispersion type EL element that has excellent luminous efficiency and improved luminance unevenness.)

<Description of Prior Art> Dispersed EL elements are used in light emitting display devices and surface light sources, more specifically, for example, incandescent light bulbs as buff lights for liquid crystal display devices,
Compared to conventional light sources such as flat fluorescent lamps, they are prized for their thinness, uniform brightness, and light weight.

Figure 2 shows a longitudinal cross-sectional view of a conventionally used distributed EL element, in which 1 is a back electrode formed of At foil, 2 is an insulator layer, 3 is a light emitter layer, and 4 is a back electrode formed of At foil or the like. is a transparent electrode, 5
6 indicates a moisture-absorbing film, and 6 indicates a moisture-proof film.

The luminescent layer in a dispersion type EL element is usually made of a cellulose-based dielectric resin composition dissolved in an organic solvent, with a particle size of about 10 to
Approximately 50 μm fluorescent powder is dispersed and mixed, and this is
It is coated and formed on the insulating layer by a doctor blade method, a silk screen method, etc. to a film thickness of about 70 μm.

However, according to this method, it is difficult to uniformly arrange the phosphor particles and coat the surface of the phosphor layer smoothly.
Gaps are formed between the phosphor particles, and areas where there are no phosphor particles become concave portions, so that the surface of the phosphor layer is formed to be uneven.

However, in the conventional method of forming a transparent electrode layer on top of the light emitting layer in this surface state, the distance between the electrodes may differ.
A uniform electric field is applied to the phosphor powder, which not only causes variations in luminance, but also causes current to concentrate in the recesses, causing EL
This is a factor that increases the current density of the light emitting element and deteriorates the luminous efficiency.

(Problems to be Solved by the Invention) In view of the above circumstances, the present inventors have made extensive efforts to obtain a distributed EL light emitting element with low current density, excellent luminous efficiency, and improved luminance unevenness. As a result of the study, it was found that a resin composition having a lower inductivity than the dielectric resin composition used to form the light emitting layer was buried in the recesses on the surface of the light emitting layer, and after the surface of the light emitting layer was almost smoothed, a normal EL light emitting element was formed. The present inventors have discovered that, in some cases, it is possible to obtain a distributed EL element that satisfies the above objectives, and have completed the present invention.

(Means for solving the problems) That is, the present invention provides a dispersion type EL element in which an insulator layer, a luminescent layer, and a transparent electrode layer are laminated on a back electrode layer.
A dispersion type EL obtained by applying a resin composition having a dielectric constant lower than that of the dielectric resin composition used to form the luminescent layer but having a dielectric constant of 5 or more to the recesses existing on the upper part of the luminescent layer. The present invention provides a light emitting device.

Hereinafter, the present invention will be explained in more detail based on the drawings.

FIG. 1 is a longitudinal cross-sectional view of a distributed EL element of the present invention.

In the figure, 1 is a back electrode made of aluminum foil, etc., and 2 is a back electrode made of aluminum foil or the like, and 2 is a mixture of highly insulating powder such as barium titanate dispersed in a highly dielectric resin composition on the top of the back electrode using a roll coater or a doctor. This is an insulating layer formed by coating with a blade or the like.

3 is a typical dielectric constant of cyanoethylated cellulose, cyanoethylated glycidol pullulan, cyanoethylated sucrose, etc., which is made by dissolving a phosphor powder mainly composed of zinc sulfide with an average particle size of about 10 μm to about 50 μm in an organic solvent such as dimethylformamide. A mixture obtained by dispersing and mixing one or more highly dielectric resin compositions of 15 or more is coated on the insulating layer 2 to a thickness of about 20 μm or more using a roll coater or a doctor blade method.
This is a luminescent layer formed by coating approximately 70 mL and heating and drying.

The surface of the luminescent layer 3 formed in this manner is uneven due to variations in particle size of adjacent phosphors and furthermore, due to the dissipation of volatile matter from the resin composition during heating and drying. If a transparent electrode layer is provided on the top surface of the light emitting layer as it is, current will be concentrated in the recessed portions, and in severe cases, there is a risk of short circuit.

Therefore, in the present invention, a low dielectric constant resin is formed by coating the concave portion of the upper surface of the luminescent layer 3 with a resin composition having a lower dielectric constant than the high dielectric constant resin composition used for forming the luminescent layer. A composition layer 7 is formed.

The resin composition may be one having a dielectric constant lower than that of the resin composition used for the light emitting layer 3 and a dielectric constant of 5 or more, and may be a known resin composition such as a cellulose compound or an epoxy resin. , phenoxy resin, or a resin composition containing a mixture of these resins is used.

When a resin composition with a low dielectric constant of less than 5 is used as the resin composition for coating the recesses, the electric field strength applied to the phosphor powder decreases, resulting in deterioration of luminescent properties such as brightness unevenness, which is not preferable.

Furthermore, if the same resin composition as the high dielectric resin composition that forms the phosphor layer is buried in the recess, the effect of reducing the current flowing through the recess is small, and if a large amount is applied to obtain a sufficient effect, This is not preferable because it contributes to a decrease in brightness.

The difference in dielectric constant between the resin composition for coating the recesses and the resin composition used for the luminescent layer is not unique depending on the degree of the recesses, that is, the thickness of the resin composition for coating the recesses, and further the thickness of the luminescent layer. However, it is usually sufficient that there is a difference in dielectric constant of about 1 or more, preferably about 2 or more, and the optimum value can be determined by a simple preliminary experiment depending on the manufacturing conditions to be applied.

In addition, the coating thickness of the low dielectric constant resin composition is sufficient as long as it can fill the recesses, and although it depends on the coating method, it is less than the maximum convex part of the luminescent layer 4 + 5 μm, preferably the maximum convex part + 1 μm.
The following is sufficient.

If the coating film becomes too thick from the largest convex portion, the electric field strength applied to the fluorescent powder will decrease, which is not preferable.

The method of applying the low dielectric constant resin composition is not particularly limited as long as it can form a smooth coating surface, but usually the resin composition is dissolved in a suitable solvent such as dimethylformamide and then a doctor blade method is applied. Alternatively, it may be coated by a silk screen method or the like.

The phosphor layer, which has been coated with a low dielectric resin composition in the recesses on the surface of the phosphor layer and has a smoothed surface, is then coated with ITO by a conventional method.
After forming a transparent electrode layer 4 such as the above, and then covering it with a hygroscopic film 5 if necessary, the entire structure is sealed with a moisture-proof film 6 to form a dispersed EL light emitting device.

When the recesses on the surface of the phosphor layer are coated with a low dielectric resin composition to smooth the surface of the phosphor layer as in the present invention, not only the distance between the electrodes becomes constant, but also the current flowing through the phosphor particles This reduces variations in the resistance of the current flowing through the resin layer, lowers the current, and improves luminous efficiency. It also eliminates local differences in the electric field strength applied to the phosphor powder, reducing variations in luminance. It can be eliminated.

<Effects of the Invention> As described above, according to the present invention, it is possible to provide an EL light-emitting element that has lower current, lower power consumption, and higher luminous efficiency than conventional EL light-emitting elements.

In addition, the drive circuit system has become more compact due to lower power consumption.
It is also possible to reduce costs, and its industrial value is enormous.

<Example> The present invention will be explained in more detail below with reference to Examples.

Note that parts in the examples indicate parts by weight. In addition, in the present invention, the dielectric constant of the resin composition is determined by hot press molding the resin composition to a thickness of 2H, and then measuring the press sheet using a dielectric constant measuring device [Multi-Frequency LCR Meter (manufactured by Yokogawa Heuret Puff Card Co., Ltd.]). The measurement was carried out using the following conditions: 25°C and IKH.

Example 1 and Comparative Examples 1-2 As shown in FIG. 1, aluminum foil 1, BaTiO3
and an insulating layer 2 made of a high conductivity cellulose resin composition.
Zinc sulfide phosphor powder (average particle size of powder 25μ)
40 parts, high dielectric constant cellulose resin (dielectric constant 18) 15
and dimethylformamide (hereinafter abbreviated as DMF).

) was coated by a doctor blade method and dried by heating at 130° C. for 10 minutes to form a phosphor layer 3 of 50 μm.

Next, on the phosphor layer 3, a mixture consisting of 10 parts of a resin composition mixed with a phenoxy resin and a cellulose resin so as to have a dielectric constant of 12, and 90 parts of DMF is applied to an area less than the maximum convexity of the surface of the phosphor layer + 1μ. The coating was applied by a doctor blade method so that the coating was almost the same, and the coating was dried by heating at 130° C. for 10 minutes.

A TTO transparent electrode 4 was formed on the smoothed luminescent layer 3, and the entire structure was coated with polychlorotrifluoroethylene for the purpose of moisture proofing.

The EL light emitting device thus obtained was heated to 115V-40V.
Light was emitted under the driving conditions of 0H2.

The results are shown in Table 1.

For comparison, an EL light emitting element without surface smoothing treatment of the phosphor layer (Comparative Example 1) and Example 1 with surface smoothing treatment are shown.
At the same time, the performance of an EL light emitting element (Comparative Example 2) which was smoothed in the same manner as in Example 1 by replacing the cellulose resin with a dielectric constant of 12 used in Example 1 with a cellulose resin with a dielectric constant of 18 that forms the phosphor was also evaluated. Tested.

The results are also shown in Table 1 as Comparative Examples 1 and 2.

Table 1

[Brief explanation of the drawing]

Figure 1 shows a vertical cross section of a distributed EL device of the present invention, and Figure 2 shows a vertical cross section of a conventionally known distributed EL device. . 3.. Luminous layer, 4.. Transparent electrode. 5. Hygroscopic film. 6. Moisture-proof film. 7 shows a low dielectric resin composition layer. Figure 1 Figure 2

Claims (1)

[Claims] (1) In a distributed electroluminescent device in which an insulator layer, a light emitter layer, and a transparent electrode layer are laminated on a back electrode layer, a recess existing above the light emitter layer is used for forming the light emitter layer. A dispersion type electroluminescent element coated with a resin composition having a dielectric constant lower than that of the conventional dielectric resin composition, but having a dielectric constant of 5 or more.