JPH0393191A - Electroluminescence element - Google Patents

Abstract

PURPOSE:To obtain an electroluminescence element with no intensity irregularity by using the conducting fine powder mainly made of carbon black for the conducting fine powder of current limiting layers. CONSTITUTION:A transparent electrode 2 is formed on a glass substrate 1, then ZnS doped with Mn is formed as a light emitting layer 3. Carbon black is dispersed in a mixed solvent solution of an aluminum coupling agent, a mixed liquid of binder resin and a thinner is added so that the volume ratio between carbon black and binder resin after solidification is set to 2:8, then it is filtered with a filter, and the filtered paint is coated by spraying and dried to form a current limiting layer 4. Al is formed into a film as a back electrode 5, and the current limiting layer 4 and the Al film 5 are concurrently scribed to form a preset back electrode pattern. An EL element with no intensity irregularity is obtained.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to hybrid electroluminescence (hereinafter referred to as EL).
The purpose is to improve the device (hereinafter referred to as "abbreviation"), and in particular to modify the material of the conductive fine powder of the current limiting layer.

[Conventional technology]

EL displays, which utilize EL elements, are one of the promising flat displays that are rapidly becoming popular in portable computer terminals and the like. For EL elements, light meditation! Two types of EL devices are known: IIEL devices and powder-type EL devices, but recently hybrid FF! EL. IIl
Child (Hybrid EL element or Compos1
t (also called EL element) is one of the leading EL elements.
It has started to attract attention as a species (for example, GB
2176340, QB2176-341) Figure 1 is a diagram showing the configuration of a hybrid EL element. The structure and manufacturing method of the hybrid EL4 child will be explained using this figure. A transparent electrode material such as ITO is formed into a film as a transparent electrode 2 on a glass substrate l by a method such as sputtering or vacuum evaporation. A light emitting layer 3 is formed thereon by vacuum evaporation method, spatter method, M
Formed using a method such as OCVD. Examples of materials for the light emitting layer include ZnS, ZnSe, and Cd.
Group 1 compounds such as S, transition metals such as Mn and Cu, Tb, Sm. Those doped with rare earth elements such as Dy or their fluorides, chlorides, etc. as luminescent centers are often used. On top of the current limiting layer 4, a powder layer of about several tens of micrometers made of conductive fine powder hardened with an organic binder is formed by a method such as a spray method. Finally, the EL element is completed by depositing a metal such as A1 as the upper electrode 5 by vacuum evaporation or sputtering. When manufacturing a dot matrix type display panel, patterning is then performed by mechanical scratching using a diamond needle or the like. Therefore, the thickness of the current limiting layer 4 is preferably in the range of 5 Bm to 30 μm. The current limiting layer 4 serves to prevent the resistivity of the light-emitting layer from decreasing during light emission and excessive current flowing through the EL element, thereby preventing the element from being thermally destroyed. However, the larger the resistance of the current limiting layer, the more stable it becomes against destruction, but if it is too large, the voltage drop in the current limiting layer becomes large, which leads to an increase in the driving voltage of the EL element. There is a limit naturally, and in the film thickness range of 5 μm to 30 μm mentioned above, 10 Ω to 2 Ω per unit recommended area (jam') in the film thickness direction.
000Ω resistance box, that is, IXIO'Ω”cm to 2
A resistivity of approximately ×106Ω●Cm is preferable. The material of the conductive fine powder needs to have the above-mentioned resistivity after being hardened with a binder, so I
It is required to have a resistivity of about 'Ω●Cm to 2X10''Ωscm.Initially, the above hybrid EL element was coated with Cu, which was conventionally used in powder type EL elements, as the material for the conductive fine powder. ZnS powder was often used, but recently MnO2 has been used because its black color increases display contrast and its resistance does not change over time due to the movement of Cu.

[Problem II to be solved by the invention]

However, the above conventional hybrid! ! ! In the case of EL elements, there was a serious problem of 7f when uneven brightness and shortened lifespan occurred during use.

[Means to resolve divisions]

The present invention was made to solve the problems of the previous generation, and includes a current limiting layer and a back electrode in which a transparent electrode, a light emitting layer, and a conductive fine powder are fixed with a binder resin on a transparent insulating substrate. of,
In sequentially laminated electroluminescent elements,
The conductive fine powder of the current limiting layer is a conductive fine powder whose main component is carbon black. First of all, there are various types of carbon black, such as channel black, furnace black, and acetylene black, which are named according to the manufacturing method, and their physical properties are quite different, but if the particle size is 3 μm or less, these It doesn't matter which one you use. Examples of conductive powder containing carpon black as a main component include conductive fine powder consisting only of carbon black, and powder containing carbon black mixed with conductive fine powder other than carbon black. Among these, a mixture of carbon black and barium titanate semiconductor is preferred because the temperature coefficient of electrical resistance of the mixture tends to be 0 or more. This barium titanate-based semiconductor is made by adding small amounts of yttrium, cerium, etc. to ferroelectric materials such as barium titanate, strontium titanate, and lead titanate to give it conductivity. be. It is also preferable that the particle size is 3 μm or less. The resistivity of these two types of substances in fine powder form is measured, for example, when they are sandwiched between brass electrodes and a load of 8 kg is applied.
lO-2~10'Ω◆C ms with carbon black
It shows a value of about 10' to 10 eΩ·cm for barium titanate-based semiconductors. Since the resistivity of the conductive fine powder preferable for the current limiting layer is 104 to 106 Ω·am, the resistivity within this range can be obtained by mixing these powders. Mixtures of these powders are used in the form of ordinary powder or solvent-dispersible sol, and these are fixed using a binder resin. It can also be treated with a coupling agent to improve dispersibility before being dispersed in the binder resin solution, and in this case, an aluminum-based coupling agent provides the most favorable effect. Examples of binder resins include vinyl resins, polyester resins, polyamide resins, cellulose resins, polyurethane resins, urea resins, epoxy resins, melamine resins, silicone resins, etc.
Polymer materials having polar groups such as hydroxyl, carboxyl, sulfonyl, and nitro groups, and reactive groups such as epoxy, isocyanuric, and silanol groups are preferably used.
Further, the binder resin, carbon black fine powder,
It is preferable that the volume mixing ratio of each of the barium titanate-based semiconductor fine powder satisfies all of the following formulas Φ to ■. C a 1. 5 ■A B 150% ■C
15% (However, A is the ratio of the actual volume of barium titanate to the volume of the current limiting layer, B is the ratio of the actual volume of the binder resin to the volume of the current limiting layer, and C is the ratio of the actual volume of carbon black to the current limiting layer volume. (ratio to volume) The above actual volume refers to the true volume, which is not an apparent volume, in the case of powder materials, and the volume in the solidified state excluding solvent, etc., in the case of resin materials. If the above formulas (■) and (■) are not satisfied, the resistance of the current limiting layer tends to increase. If the formula (■) is not satisfied, the film forming properties will deteriorate, such as cracks appearing in the current limiting layer. Furthermore, the most important thing in the internal structure of the current limiting layer is the local uniformity of electrical resistance, and in the present invention,
Carbon black clusters tend to form, and it is necessary to use a dispersion method that prevents this from occurring, or to remove it. Removal of large particles of carpon black is possible after dispersing it in a binder resin solution.
This is achieved by filtration with a filter of less than m.

[Effect]

The present invention solves the problem of uneven brightness and short lifespan of conventional hybrid EL elements during use. This invention was developed in view of the fact that the temperature rise is caused by a vicious cycle of "progressive temperature rise", and according to the present invention, carbon black and barium titanate based semiconductors have a positive or very small change in electrical resistance with respect to temperature rise. or carbon black as the current limiting layer, compared to the conventional M n
Breakdown due to heat generation when using O 2 is prevented.

【Example】

Below, some examples of the present invention will be introduced. Example 1 ITO was formed as a transparent electrode 2 on a glass substrate 1 to a thickness of about 500 nm using a reactive sputtering method, and then patterned into a predetermined shape using a photolithography method. Subsequently, as a light-emitting layer 3, a film of ZnS doped with 0.3ffi of Mn was formed using an electron beam evaporation method for about 19 ms. Next, carbon black (product name SEAST 9H:
Tokai h-1) was dispersed in a mixed solvent solution of an aluminum coupling agent (product name: L-M: Ajinomoto), carbon black and a binder resin (product name: ATO HO).
: Add a mixture of binder resin and thinner so that the volume ratio after assimilation is 2:8, and then pass through a 10μm Teflon membrane filter, and then pass through a 5μm Teflon membrane filter. The filtered paint was applied by spraying and dried, and the resistivity was 4X10'Ω.
●A current limiter 714 with a film thickness of 16 μm was formed in cm.
The current limiting layer 4 made in the fabricated layer 11 is made of wood H with no visible voids.
It was fixed as a black layer of almost uniform thickness. Next, as the back electrode 5, an AI film of about 1 μm is formed by vacuum evaporation, and then the current limiting layer 4 and the AI film 11f5 are formed.
A predetermined background electrode pattern was formed by scribing the time and date using a diamond needle. When the EL element prepared in this way was connected to a drive circuit and emitted light, it emitted light uniformly over the entire surface, and no unevenness in brightness was observed. Example-2 Carbon black (product name SEAST 98: bundle 11
1h-reference and barium titanate semiconductor (product name P
TC-SN: A mixture of 6:l (volume ratio) of Kyoritsu kiln slip raw material) was mixed with an aluminum-based coupling agent (trade name AL-M).
: Ajinomoto) in a mixed solvent solution, and mix with the binder resin so that the ratio of the total volume of the powder to the volume of the binder resin (trade name MR-110: Japan 1-on) is 1.75:8.25. After adding the mixture with thinner, it was filtered with a 10 μm Teflon membrane filter as in Example 1, and then filtered with a 5 μm Teflon membrane filter to prepare a paint. A light-emitting layer 3 was prepared using the paint in the same manner as in Example-1. Painted on glass substrate 1 with 2 transparent electrodes by spray method, dried, and resistivity was 1 x 1 oaΩ・c.
A current limiting layer 4 with a MW of 15 μm is formed at 1:! ．． Next, a back electrode 5 was formed as in Example 1, and a predetermined back electrode pattern was formed by scribing with a diamond needle. When the EL element thus prepared was connected to a drive circuit and emitted light, it emitted light uniformly over the entire surface, and there was no unevenness in brightness. Example-3 Carpon rack (product name SEAST 9H: Tokai Car Honshi) and barium titanate semiconductor (product name PTC)
-SN: Kyoritsu Ceramic Raw Materials) at a ratio of 11:5 (volume ratio) is dispersed in a mixed solvent solution of an aluminum coupling agent (trade name AL-M: Ajinomoto), and the total volume of the powder and the binder resin ( Product name MR-110: Japan 1Iin>
After adding a mixture of binder resin and thinner so that the volume ratio of
Filter with a μm Teflon membrane filter, then 6 μm
A paint was prepared by filtering with a Teflon membrane filter. The luminescent layer 3 was prepared using the paint in the same manner as in Example-1.
, painted by spray method on glass substrate 1 with 2 transparent electrodes,
After drying, the resistivity is axio'Ω・am and the film thickness is 15μ.
A current limiting layer 4 of m was formed. Next, a back electrode 6 was formed as in Example 1l, and a predetermined back electrode pattern was formed by scribing with a diamond needle. When the EL element prepared in this way was connected to a drive circuit and emitted light, it emitted light uniformly over the entire surface, and no unevenness in brightness was observed. Here, changes in resistivity due to temperature of the current limiting layer produced in Example 3 above were measured. The measurement results are shown in Figure 2. As is clear from FIG. 2, the resistivity of the current limiting layer of this example exhibited a nearly constant value regardless of temperature. Comparative Example MnO2 powder produced by electrolytic method was pulverized with a ball mill to give an average particle size of 0.3 μm, and the ratio of the volume of MnO2 powder to the volume of binder resin (trade name MR-110: Nippon Seon) was calculated. After adding a mixture of binder resin and thinner in a ratio of 3:7, Example-1
Filtered with the same 10μm Teflon membrane filter,
Next, a paint was prepared by filtering through a 5 μm Teflon membrane filter. The paint was applied by spraying onto a glass substrate l with a light-emitting layer 3 and transparent electrodes 2 prepared in the same manner as in Example-1, dried, and current-limited with a resistivity of 5 x 10' Ω cm and a film thickness of 20 μm. Layer 4 was formed. Next, Example-
A back electrode 5 was formed in the same manner as in Example 1, and a predetermined back electrode pattern was formed by scribing using a diamond needle. When the EL elements fabricated in this way were connected to a drive circuit and emitted light, as the brightness increased, the temperature of the panel rose, and breakdown occurred sequentially starting from the brightest elements in the panel. The change in resistivity of the current limiting layer due to temperature was measured in the same manner as in Example 3, and the results are shown in Figure 2. From FIG. 2, it can be seen that the resistivity of the current limiting layer of Example 3 was constant regardless of temperature.

【Effect of the invention】

According to the present invention, it is possible to improve the brightness unevenness of an EL element using a current limiting layer, prevent breakdown, and improve the reliability of the EL element. Further, in the EL element of the present invention, since the resistivity of the current limiting layer is constant regardless of temperature,
There is little temporal variation in the required power, and there is also little temporal variation in brightness.

[Brief explanation of drawings]

FIG. 1 is a schematic cross-sectional view of a hybrid electroluminescent device according to the present invention, and FIG. 2 is a diagram showing temperature changes in resistivity of current limiting layers fabricated in Example 13 and Comparative Example. 1. Glass substrate 2. Transparent electrode 3. Light emitting layer 4. Current limiting layer 5. Back electrode 1st Figure 2.25 2,50 2.75 1l Absolute temperature 2.59 (κ) / 10000 324 Figure 2

Claims (3)

[Claims] (1) In an electroluminescent element in which a transparent electrode, a light-emitting layer, a current-limiting layer in which conductive fine powder is fixed with a binder resin, and a back electrode are sequentially laminated on a transparent insulating substrate, the conductive fine powder in the current-limiting layer An electroluminescent element characterized by using conductive fine powder whose main component is carbon black. (2) The electroluminescent device according to claim 1, wherein the conductive fine powder is a mixture of carbon black and a barium titanate semiconductor. (3) The current limiting layer is composed of a mixture of a binder resin, a carbon black fine powder, and a barium titanate semiconductor fine powder that satisfy all the conditions of formulas (1) to (3) below. The electroluminescent device described. C/A≧1.5 (1) B≧50% (2) C≧5% (3) (However, A is the ratio of the actual volume of barium titanate to the current limiting layer volume, and B is the actual volume of the binder resin. (C is the ratio of the actual volume of carbon black to the volume of the current limiting layer)