JPH0358083A - Electroluminescence element - Google Patents

Abstract

PURPOSE:To lessen the generation of crosstalks and improve the contrast between selected segments and non-selected segments when the element is subjected to duty driving by providing a light emitting layer and a liquid crystal layer between a pair of electrodes. CONSTITUTION:The liquid crystal layer 7 is provided between the transparent electrodes 2 and the light emitting layer 3. The layer is formed by dispersing the liquid crystal layer 8 into a resin 6, such as polyvinyl alcohol or polycarbonate, and imparts steepness to the electrolytic-brightness characteristic of the electrochromic luminescence (EL) element. The transmittance of the layer 7 changes sharply between 0 and 2V/cm impressed voltage to shut off the light emitted by the crosstalks. The contrast is improved is this way.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to electroluminescence phenomenon (hereinafter referred to as E
It is abbreviated as L phenomenon. ) (hereinafter abbreviated as EL element).

[Prior art] The EL phenomenon is a phenomenon in which light emission is obtained by applying an electric field to a certain type of phosphor.
Since L elements are lightweight and thin, they have been commonly used as backlights for non-light emitting elements such as liquid crystal display elements.

FIG. 6 shows an example of an organic dispersion type EL element in which phosphor powder 5 is dispersed in resin 6 to form a light emitting layer 3, and an alternating current electric field is applied to the light emitting layer 3 to emit light.

This organic dispersion type EL element uses a transparent substrate made of glass or the like! A transparent electrode 2 made of indium tin oxide (ITO) or the like, a light emitting layer 3, and a counter electrode 4 made of aluminum or the like are successively laminated on one side of the electrode. Here, the luminescence 113 is produced by adding copper (Cu), manganese (Mn), or fluoride to a base material such as zinc sulfide (ZnS) or a mixture of ZnS and zinc selenide (ZnSe), depending on the luminescent color. Terbium (T bF 3), samarium fluoride (S
The phosphor powder 5 in which a luminescent center is formed by adding an activator such as IllF3) to polyvinyl alcohol (PVA),
It is dispersed in a resin 6 such as polycarbonate (PC) or cyanoethylated cellulose.

For example, a lo
'V/c @ order 50 Hz - 10 kHz
By applying an alternating current electric field of z, light is emitted.

FIG. 7 shows the electric field-luminance characteristics at 400 Hz of the EL element having the above structure.

[Problems to be Solved by the Invention] By the way, when performing matrix display in the EL element of this configuration, as shown in FIG. 7, the electric field Ei of the selected segment and the electric field of the non-selected segment E. Duty driving is performed between
Contrast the brightness Bt at B. :B
, it is necessary to increase .

However, the electric field-luminance characteristics of the EL element with the above configuration are as follows.
As shown in Figure 7, the steepness of the brightness with respect to the applied electric field is small at all frequencies, so the contrast is sufficient to obtain a clear matrix display due to the light emitted due to crosstalk occurring in non-selected segments.・There was an inconvenience that the last part could not be obtained.

The present invention has been made in order to solve the above-mentioned problems, and provides an EL element that causes less crosstalk and has a large contrast between the selected segment 1 and the non-selected segment when driven by a device. It is an object.

[Means for solving the problem] Claims of this invention! The described EL element is provided on a transparent substrate,
A transparent electrode, a liquid crystal layer made of liquid crystal dispersed in resin,
The solution was to sequentially laminate a light-emitting layer made of phosphor powder dispersed in a tree and a counter electrode.

Furthermore, the EL device according to claim 2 of the present invention is formed by sequentially laminating, on a transparent substrate, a transparent electrode, a light-emitting layer made of liquid crystal and phosphor powder dispersed in resin, and a counter electrode. It was used as a solution.

In the EL device according to claim 1 of the present invention, a light emitting layer and a liquid crystal layer are provided between a pair of electrodes, and in the EL device according to claim 2 of the present invention, a light emitting layer and a liquid crystal layer are provided between a pair of electrodes. By providing a light-emitting layer made by dispersing phosphor powder and liquid crystal ε in a resin, the liquid crystal exhibits a steep change in transmittance depending on the applied electric field, resulting in a steep change in the electric field-luminance characteristic of the EL element. This improves the display contrast.

This invention will be explained in detail below.

Figure l is the claim of this invention! An example of the described EL element is shown. No.! The EL element shown in the figure differs from the conventional EL element shown in FIG. 6 in that a liquid crystal 17 is provided between the transparent electrode 2 and the light emitting layer 3.

This liquid crystal layer 7 is provided to give steepness to the electric field-luminance characteristics of the EL element, and is made of a material such as PVA or PC. The liquid crystal 8... is dispersed in the liquid crystal 16. The liquid crystal layer 7 changes its light transmittance greatly depending on the magnitude of the applied electric field, and exhibits characteristics as shown in FIG. 2, for example. In FIG. 2, the horizontal axis indicates the magnitude of the electric field applied to the liquid crystal layer 7, and the vertical axis indicates the transmittance of the liquid crystal layer 7.

Such a liquid crystal layer 7 has an applied electric field of O~2 V/cn
Since the transmittance changes sharply between +, cross l- -
In order to block the light emitted by the EL element, it is possible to give a steepness to the electric field-luminance characteristic of the EL element, thereby increasing the contrast ratio.

Therefore, according to the EL element according to claim 1 of the present invention, the brightness changes sharply when an electric field is applied, so that the electric field difference between the electric field E of the selected segment and the electric field E of the non-selected segment is High contrast can be obtained even with smaller duty driving. As a result,
It is possible to realize a segment or dot matrix driven organic dispersion type EL element, which has been considered difficult in the past.

An EL element having such a configuration can be manufactured, for example, by the following steps.

First, a transparent substrate 1 made of glass, a polymer film, or the like is prepared, and a transparent electrode 2 made of ITO or the like is formed on this transparent substrate l. The transparent electrode 2 is formed by vacuum evaporation or sputtering, and its patterning may be performed by masking or by etching after evaporation. Further, it is preferable that the transparent electrode 2 has a sheet resistance of lkΩ/C or less.

Then, a liquid crystal layer 7 and a light emitting layer 3 are sequentially laminated on this transparent electrode 2. Both the liquid crystal layer 7 and the light emitting layer 3 are formed by dispersing a liquid crystal 8 and a phosphor powder 5 in a solution of a resin 6, respectively, using a thick film forming method such as screen printing or a blade method. After coating, it can be formed by heating and drying. The thickness of the liquid crystal layer 7 is 5
~60 μm 1 The thickness of the light emitting layer 3 is preferably lO ~80 μm.

Here, as the liquid crystal 8..., in addition to twisted nematic liquid crystal, smectic liquid crystal, cholesteric liquid crystal, etc. which are widely used in liquid crystal display elements, polysiloxane polymer liquid crystal may be used singly or in combination. Can be used by mixing seeds. The amount of liquid crystal 8... into the tree finger 6 is selected as appropriate depending on the properties of the limb crystal 8 used, but
Approximately 1 to 30% by weight based on the resin 6 is suitable. If it is less than 1% by weight, it will not be possible to sufficiently block the light emitted from the light emitting layer 3 due to crosstalk, and therefore it will not be possible to provide high contrast. On the other hand, 30
This is because if the amount exceeds % by weight, the dispersibility of the liquid crystal 8 into the resin 6 will decrease. The liquid crystals 8 may be dispersed in the resin 6 by directly dispersing the liquid crystals 8 into the resin 6 or by encapsulating the liquid crystals 8 in microcapsules.

Furthermore, if a dichroic dye that absorbs at least the wavelength of the emitted light color of the phosphor powder 5 is added to the liquid crystal layer 7, the contrast can be further increased.

The phosphor powder 5 used for the light emission 13 is appropriately selected depending on the display color of the EL element, but phosphor powders commonly used as EL elements can be used, such as zinc sulfide (ZnS) or ZnS. and zinc selenide (
Depending on the color of the emitted light, activators such as copper (Cu), manganese (Mn), terbium fubide (TbFs), samarium fluoride (SIF3), etc. are added to the base material such as a mixed product of ZnSe). It is possible to use a material that is added to form a luminescent center. Further, the amount of the phosphor powder 5 dispersed in the resin I16 is appropriately selected depending on the type of the phosphor powder 5 used, but it is preferably 50 to 1500% by weight based on the resin 6. . If it is less than 50% by weight, sufficient brightness cannot be obtained, and if it is more than 1500% by weight, the adhesion of each phosphor powder 5 by the resin 6 to each other becomes incomplete, resulting in uneven light emission, which is not preferable.

Then, a counter voltage Vi4 is formed on the light emitting layer 3. The counter electrode 4 is made of a metal such as aluminum (AI) or a conductive metal oxide such as tTo, and may be deposited by vacuum evaporation or by depositing metal powder such as A1 on an organic resin. It can be formed by applying a conductive paste dispersed therein. After connecting the transparent electrode 2 and the counter electrode 4 with respective lead wires, the entire device is sealed with a moisture-proof organic film such as trifluorochloroethylene. It can be an element.

FIG. 3 shows an example of an EL element according to claim 2 of the present invention. The difference between the EL device shown in FIG. 2 and the EL device shown in FIG. The body powder 5... has just been directly dispersed.

In an EL element with such a configuration, a transparent electrode Wil2
When an electric field is applied between the EL element and the counter electrode 4, the transmittance of the liquid crystal 8 dispersed in the light emitting layer 3 changes sharply. Since it is possible to give a steepness to the electric field-luminance characteristic of the element, light emitted due to crosstalk can be blocked, making it more conducive to condensation.
The last can be made higher.

An EL element having such a configuration can be manufactured by the following steps.

First, just like the EL element shown in FIG.
A transparent electrode 2 is formed on top.

Next, on this transparent electrode 2, a phosphor layer 5... and a liquid crystal 8 are placed.
. . . is dispersed in a resin 6 to form a light-emitting layer 3. This light-emitting layer 3 is made by dispersing a solution of phosphor powder 5... and a liquid product 8... in a resin 6 to form the light-emitting layer 3 and liquid crystal layer 7 of the EL element shown in FIG. It can be formed by applying the film using a thick film forming means and then drying it by heating. The thickness of the light-emitting layer 3 is preferably 10 to 80 μm.

As the phosphor powder 5 and the liquid crystal 8 used here, the same ones as those used in the EL element shown in FIG. 1 can be used, but the phosphor powder in the resin 6 The amount of dispersion of 5... and liquid crystal 8... varies depending on the properties of the phosphor powder 5 and liquid crystal 8 used, but is 50 to 1500% by weight and 1% by weight, respectively, based on the tree 16.
~30% by weight is preferred.

Further, as in the EL element shown in FIG. 1, the contrast can be further increased by adding a dichroic dye that absorbs at least the wavelength of the emitted light color of the phosphor powder 5 to the liquid crystal 8 in the light emitting layer 3. can.

Then, a counter electrode 4 is formed on this light emitting layer 3 in exactly the same manner as the EL element shown in FIG. 1, thereby producing an EL element according to claim 2 of the present invention.

In the EL device according to claim 2 of the present invention, the light-emitting layer 3 is provided between a pair of electrodes, in which phosphor powder 5... and liquid crystal 8... are dispersed. Since the number of layers formed between the electrodes is smaller than that of the EL element according to claim i of the present invention, there is an advantage that the manufacturing process can be simplified.

Note that in the EL element of the present invention, a dielectric layer may be provided between the pair of electrodes. For example, the light emitting layer 3 and the counter electrode 4
The dielectric layer provided between the
Silicon oxide (S i0 2), aluminum oxide (A
I. z03), yttrium oxide (y.03), silicon nitride (si3N.), barium titanate (BaTio3), tantalum oxide (TatO3), etc.
s) etc. are preferably used. By providing such a dielectric layer, dielectric breakdown of the phosphor powder 5 when an electric field is applied can be prevented, and the stability of the EL element can be improved.

[Example 1] After ITO was vacuum-deposited on a glass substrate, a transparent electrode with a predetermined pattern having a sheet resistance of 100Ω/C or less was formed by etching. Next, liquid crystal (EH) was added to the PVA aqueous solution.
After adding chemical E7) and stirring thoroughly, apply this uniformly on the transparent electrode by screen printing method,
Dry for 2 hours at 100°C to coat the liquid crystal in PVA resin.
A liquid crystal layer having a weight percent dispersion was formed to a thickness of 30 μm.

Next, ZnSyCu-based phosphor powder was added to the cyanoethylated cellulose, thoroughly stirred, and then uniformly applied onto the liquid crystal layer by screen printing, dried at 80°C for 1 hour, and formed into a film with a thickness of 40 μm. Formed. On this luminescent layer, a conductive paste containing Ag powder is screen printed and dried to form a counter electrode, and the transparent electrode and this counter electrode are connected with a lead wire, and thus the shape is formed. The entire exposed light-emitting device was sealed with a moisture-proof trifluorochloroethylene film to obtain the EL device of Example 1.

An alternating current electric field was applied to the EL element of Example 1 at a frequency of 40
O to 3 at 0 Hz. When the applied voltage was varied up to O x 10'V/cm and the brightness was measured, the electric field-brightness characteristics as shown in FIG. 4 were obtained.

Moreover, as shown in FIG. 4, the electric field E of the selected segment
,2. 5 X 10'V/c+a, the electric field E of the non-selected segment is set to 0. 9 x 10'V/CI
1. ! :L,, When the dessute drive was performed between these two times, light emission with a contrast of B1:Bt';30:1 was obtained, which was 4.5:I of the conventional organic dispersion type EL element.
It was confirmed that the contrast was significantly improved compared to the previous one.

(Example 2) In the liquid crystal layer of the EL element of Example 1, a yellow dichroic dye G-232 (manufactured by Nippon Kanko Shiki Co., Ltd.) and a red dichroic dye T. ．． , SR-405 (manufactured by Mitsubishi Kasei Corporation) and blue dichroic dye LM
Example 1 except that 5% by weight of the black dichroic dye obtained by mixing B~040 (manufactured by Mitsubishi Kasei Co., Ltd.) at a ratio of l:l:l was added to the crystals. EL in exactly the same way
A device was manufactured and designated as Example 2.

When the EL element of Example 2 was caused to emit light under exactly the same conditions as Example 1, a contrast of 100:1 was obtained.

(Example 3) Encrystalline (EH Chemical E7) and Zn in PVA solution
After adding 10% by weight and 600% by weight of S:Cu-based phosphor powder to PVA resin, and stirring thoroughly,
After applying this on top of transparent IT, it dries to a thickness of 60 μm.
An EL device was prepared as Example 3 in exactly the same manner as in Example 1 except that the light emitting layer was formed in step m.

An alternating current electric field was applied to the EL element of Example 3 at a frequency of 400H.
3 from O at z. When the voltage was applied while varying up to O x t O 'V/am and the brightness was measured, an electric field-brightness characteristic as shown in FIG. 5 was obtained.

Moreover, as shown in FIG. 2.6×1 0
'V/cm, Et to 1. I X I O'V/a
m, and when the duty was driven during this period, B
．． :B,=10+1 was obtained, which was confirmed to be significantly improved compared to the contrast of 4.5:l of a conventional organic dispersion type EL element.

(Example 4) An EL device was produced in exactly the same manner as in Example 3, except that 5% by weight of the black dichroic dye used in Example 2 was added to the light emitting layer of the EL device of Example 3, based on the liquid crystal. A device was manufactured and designated as Example 4.

When the EL device of Example 4 was caused to emit light under the same conditions as in Example 3, a contrast ratio of 40:1 was obtained.

Note that although glass is used as the substrate in this embodiment, the present invention is not limited to this; for example, a polymer film may be used to make a flexible EL element.

[Effects of the Invention] As explained above, the E'L of claim 1 of this invention
The device consists of a transparent electrode, a liquid crystal layer made of liquid crystal dispersed in resin, a light emitting layer made of phosphor powder dispersed in resin, and a counter electrode stacked one after another on a transparent substrate. The EL device according to claim 2 of the present invention is formed by sequentially laminating, on a transparent substrate, a transparent electrode, a light-emitting layer made of liquid crystal and phosphor powder dispersed in a resin, and a counter electrode. Therefore, in any EL element, the liquid crystal shows a steep change in transmittance when an electric field is applied, so by blocking the emitted light due to crosstalk, it is possible to give a steep change to the brightness of the EL element. The display contrast can be made larger.

Therefore, according to the present invention, it becomes possible to perform segment or dot matrix display using the EL element, which has been considered difficult with conventional organic dispersion type EL elements.

Furthermore, in the EL device of the present invention, the contrast can be significantly increased by adding a dichroic dye that absorbs at least the wavelength of the phosphor powder to the liquid crystal in the light emitting layer.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of an example of the EL device according to claim t of the present invention, FIG. 2 is a graph showing electric field-transmittance characteristics of the liquid crystal layer of the EL device shown in FIG. 1, and FIG. The figure is a schematic diagram of an example of the EL element according to claim 2 of the present invention, Figure 4 is a graph showing the electric field-luminance characteristics of the EL element shown in Figure 1, and Figure 5 is the same as Figure 3. 6 is a schematic diagram of the conventional organic dispersion type EL element, and FIG. 7 is the organic dispersion type EL element shown in FIG. 6. This is a graph showing the electric field-luminance characteristics of the device. ! ...Transparent base temporary, 2...Transparent electrode, 3...Light emitting layer, 4...Counter electrode, 5...Phosphor powder, 6...
Tree finger, 7...Liquid crystal layer, 8...Liquid crystal.

Claims (2)

[Claims] (1) A transparent electrode, a liquid crystal layer made of liquid crystal dispersed in resin, a light emitting layer made of phosphor powder dispersed in resin, and a counter electrode are sequentially laminated on a transparent substrate. An electroluminescent element featuring: (2) An electroluminescent device comprising a transparent electrode, a light-emitting layer made of liquid crystal and phosphor powder dispersed in a resin, and a counter electrode, which are successively laminated on a transparent substrate.