JPH04220996A - EL element - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thick film EL device which is particularly capable of producing stable light emission.

0002

2. Description of the Related Art FIG. 3 is a diagram showing the structure of a conventional thick film EL element. In the figure, 1 is a back electrode formed of aluminum foil;
2 is an insulating layer interposed between the back electrode 1 and the light-emitting layer 3, 4 is a transparent conductive film provided on the surface of the light-emitting layer 3, 5 is a water-trapping film made of nylon or the like, and 6 is a package. It is a moisture-proof film for.

Both the insulating layer 2 and the light emitting layer 3 use a thermoplastic resin whose dielectric constant has been increased by cyanoethylation etc. as a binder, and the insulating layer 2 is made by adding barium titanate powder to this resin in a solvent. The light-emitting layer 3 is formed by coating this resin with zinc sulfide powder, which is a phosphor, dispersed in the same manner and drying it. It has been done. and,
On this light-emitting layer 3, an electrically conductive transparent electrode material is applied to the polyester resin. T. O. Transparent conductive film 4 deposited with
are bonded together by thermocompression bonding, this element is layered with water-trapping films 5 from above and below, and further packaged with a moisture-proof film 6.

0004

[Problems to be Solved by the Invention] However, in the conventional EL device as described above, the same thermoplastic resin is used as a binder for the insulating layer and the light-emitting layer. Considering the thermal deformation of the transparent conductive film substrate when bonding, the usable binders are limited and the range of selection is narrow, and the properties of EL are inevitably influenced by the properties of the binder, especially at high temperatures.
When driven in high humidity conditions, impedance changes are large and stable light emission cannot be obtained.

[0005] The present invention was made in view of the above-mentioned problems, and provides an EL element that has a wide selection range of binders for the light-emitting layer, has a small change in impedance over time, and can emit stable light. It is intended to.

[0006]

[Means for Solving the Problems] The EL element of the present invention is
In an EL element in which a light-emitting layer is provided on the front side of a back electrode via an insulating layer, and a transparent conductive film is provided as a transparent electrode on the surface of this light-emitting layer, the insulating layer is made of a binder having a higher glass transition point than the binder of the light-emitting layer. It was formed using

[0007]

[Function] In the EL device of the present invention, since the insulating layer uses a binder having a higher glass transition point than the binder of the light emitting layer, changes in impedance are suppressed.
Further, the binder of the light-emitting layer does not need to take into account the glass transition point.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a structural diagram showing an embodiment of the present invention. In the figure, 1 is a back electrode formed of aluminum foil;
4 is a polymer resin containing I. T. O. 7 is an insulating layer interposed between the back electrode 1 and the light-emitting layer 8, and is formed using a binder having a higher glass transition point (secondary transition point) than the binder of the light-emitting layer 8. The transparent conductive film 4 is provided as a transparent electrode on the surface of the light emitting layer 8. Note that the other configuration is the same as that in FIG. 3.

[0009] In the EL element constructed as described above, since the binder of the insulating layer 7 uses a binder having a higher glass transition point than the binder of the light emitting layer 8, changes in impedance are small and stable light emission can be achieved. In addition, since the binder of the light-emitting layer 8 does not necessarily have to take into account the glass transition point, the range of selection is widened.

That is, as a transparent electrode of an EL element, I
．． T. O. There are two types in which I. powder is dispersed in a polymer resin (binder), and one in which I. T
．． O. There are two types: a type that uses vapor-deposited polyester film, and a type that uses a polyester film, which has a low sheet resistance, in the case of an element with a relatively large light-emitting area where uniformity of brightness is a problem. (transparent conductive film 4) is used. And in this case, I. T. O
．． The transparent conductive film 4 on which the transparent conductive film 4 is vapor-deposited and the light-emitting layer 8 are bonded by thermocompression bonding, so the binder used for the light-emitting layer 8 is selected in consideration of the heat resistance temperature, thermal expansion, and ease of adhesion of the transparent conductive film. There must be. For this reason,
If the binder of the insulating layer 7 under the light emitting layer 8 is the same as that of the light emitting layer 8, as in the conventional case, satisfactory characteristics cannot necessarily be obtained. For example, even if the binder for the light-emitting layer 8 has excellent properties such as good adhesion with the transparent conductive film 4 and high luminance, if a binder with a low glass transition point is used, it will not last long. When zinc sulfide decomposes over time or when driven at high temperatures and high humidity, and zinc ions become present, these ions begin to move around the glass transition temperature, and the impedance of the element increases significantly around the glass transition temperature. Changes to This results in negative effects such as increased power consumption and mismatch with the self-excited inverter, resulting in no lighting. Therefore, in this example, a binder with a glass transition point higher than that of the binder of the light emitting layer 8 is used for the insulating layer 7, and by raising the temperature at which the above-mentioned adverse effects occur, a highly reliable thick film EL element is realized. .

FIG. 2 shows how the impedance of the EL element changes. The broken line in the figure shows the case of the conventional example, and shows the characteristics of an EL element using cyanoethylpoval for both the insulating layer 2 and the light emitting layer 3. Further, the solid line in the figure shows the case of this example, where the light emitting layer 8 is made of cyanoethylpoval, and the insulating layer 7 has a glass transition point (approximately 100°C) higher than the glass transition point (approximately 50°C) of this cyanoethylpoval.
The characteristics of EL devices using cyanoethyl pullulan with In addition, both are under the same conditions (60
It shows the change in impedance over time at 60° C. when driven at 60° C. (90%).

As is clear from FIG. 2, when cyanoethyl pullulan, which has a high glass transition point, is used as a binder in the insulating layer 7, the change in impedance with respect to the drive time of the EL element is smaller, and stable light emission can be obtained. This change in impedance is important because it has negative effects such as an increase in power consumption and a sudden decrease in brightness due to mismatching with the inverter, as described above. Moreover, the selection range of the binder for the light-emitting layer 8 is also expanded.

[0013]

As described above, according to the present invention, since a binder having a glass transition point higher than that of the light-emitting layer is used for the insulating layer, the time change in impedance is small and stable light emission is obtained. This has the effect of widening the selection range of binders for the layer.

[Brief explanation of the drawing]

[Fig. 1] Structural diagram showing one embodiment of this invention

[Figure 2] EL
Characteristic diagram showing changes in element impedance

[Figure 3] Structural diagram of a conventional EL element

[Explanation of symbols]

1　Back electrode 4 Transparent conductive film 7 Insulating layer 8 Luminescent layer

Claims (1)

[Claims] 1. An EL element in which a light-emitting layer is provided on the front side of a back electrode with an insulating layer interposed therebetween, and a transparent conductive film is provided as a transparent electrode on the surface of the light-emitting layer, in which the insulating layer is bonded to a binder for the light-emitting layer through glass transition. An EL element characterized in that it is formed using a binder with a high point.