EP2130408A1

EP2130408A1 - Electroluminescent layered element

Info

Publication number: EP2130408A1
Application number: EP08734962A
Authority: EP
Inventors: Helmut MÄUSER
Original assignee: Saint Gobain Glass France SAS; Compagnie de Saint Gobain SA
Current assignee: Saint Gobain Glass France SAS; Compagnie de Saint Gobain SA
Priority date: 2007-04-03
Filing date: 2008-04-02
Publication date: 2009-12-09
Also published as: WO2008119554A1; DE102007016401A1; DE202007019199U1

Abstract

The invention relates to an electroluminescent layered element (1) comprising at least one light-permeable substrate (2); a light-permeable surface electrode (3) applied to the substrate (3); a first layer (5) comprising inorganic electroluminescent particles (6) incorporated into an organic binding material, the organic binding material of the first layer (5) having at least approximately identical refractive properties to those of the light-permeable substrate (2); and a rear electrode (9), the transparent surface electrode (3) and the rear electrode (9) being provided to supply the voltage and to produce an electrical field which excites the particles (6) incorporated into the first layer (5) in such a way as to emit light. The aim of the invention is to provide a mechanically stable and permanently durable layered element (1) having very good optical properties, especially avoiding total reflection inside the first layer (5). To this end, the binding material is based on polyvinyl butyral (PVB) or ethylene vinyl acetate (EVA).

Description

Electroluminescent layer element

The invention relates to an electroluminescent layer element with the features of the preamble of patent claim 1.

DE 195 43 205 A1 describes intermediate layers of inorganic materials in electroluminescent arrangements which contain finely divided inorganic particles (nanoparticles or particles) which are dispersed in a polymeric binder. This document initially mentions that it is known to use zinc sulfide (ZnS) particles, but these would have a low luminance, and it would be disadvantageous that a high operating voltage at high frequency must be used to produce the luminous effect.

The document therefore recommends a large number of other materials, preferably with semiconducting properties, and among them preferably titanium dioxide (TiO ₂ ). 1 to 100 nm are given as particle sizes, and the proportion by weight of the nanoparticles in the polymeric binder should be between 0.1 and 90% by weight. As the binder material, amorphous polymers are preferably mentioned which can be processed into transparent layers, for example polycarbonates, polystyrene and various others.

This intermediate layer should then be applied to ITO coated glass. Although the use of undoped ZnS nanoparticles in electroluminescent thin layers is recommended in EP 1 309 013 A2, it is also extensively discussed in the prior art with differently doped ZnS nanoparticles. Mention may be made, among other things, of manganese and copper as doping materials, which may be regarded as relatively good for the environment in comparison with cadmium-containing substances.

No. 6,515,314 describes an enrichment of an electroluminescent layer with photoluminescent (phosphorescent) nanoparticles. The latter are intended to influence the color character of the emitted light. A system with an organic luminescent layer is described, in which nanoscale inorganic particles are incorporated, whereby they have a color-converting function.

Stimulated in the long-wave UV or visible blue. It is necessary for organic light emitting diodes specific holes for holes and electron transport. The particles do not represent scattering centers in the dielectric layer; such are also not required in the teaching of this patent.

EP 1 553 153 A2 discloses dispersion-type electroluminescent elements in which a luminescent layer and an insulating layer or dielectric layer lie between two electrode layers, both having the same organic binder as a matrix. ZnS particles are embedded in the luminescent layer, and barium titanate particles are embedded in the insulating layer. For the size of the ZnS particles, the latter document proposes not to fall below 2 μm, because otherwise the light output would be too low. The barium titanate particles are mixed into the insulating layer mainly because of their dielectric properties; The document makes no explicit statement about its optical properties. However, it is known that barium titanate particles have a bright (white) reflection color. Cyanoethyl cellulose or an epoxy resin are mentioned as two layers of common binder. However, polyethylene (PE) ₁ polypropylene (PP), polystyrene resin, silicone resin, and polyvinyl fluoride resin (PVDF) are also particularly mentioned in addition to cyanoethyl cellulose or epoxy resin. In particular, the use of PVDF as a binder, which has found its way into the practice of producing electroluminescent systems because of its high dielectric constant of about 9 to 11, has proven to be problematic, since the durability of the multi-layer structure thus produced has proven to be inadequate often delamination of the elements are detected after a relatively short time.

It is well known that polyvinyl butyral (PVB) is widely used as an adhesive layer or film between the sheet-to-adhesive rigid sheets in laminated glass, in particular composite glass sheets, because of various advantages. Although its dielectric constant is not very high and is hygroscopic. But it has excellent adhesion to glass and plastic surfaces, is very well translucent, its refractive index is close to that of glass, and unlike, for example, polyurethane it is very resistant to aging (no yellowing or embrittlement). Ethylene vinyl acetate (EVA) has similar properties and is sometimes used in place of PVB. The invention is based on the object to provide a further configuration of an electroluminescent laminating element based on a luminescent layer with embedded in a polymer inorganic particles. This object is achieved with the features of claim 1. The features of the subclaims indicate advantageous developments of this invention.

It is thus created a solution that preferably not only refers to the actual luminescent layer, but also their environment and in particular the adjacent layers, so that overall results in a tuned and optimized layer element. In addition, the layer element according to the invention has excellent strength, since the bond between the individual layers is excellent due to the particularly good adhesive properties of the PVB or EVA. The lifetime of the layer elements according to the invention is very high, especially in mechanical terms.

A key aspect of this invention is the use of PVB or EVA as organic binder, preferably in spreadable or flowable form, with embedded particles for producing the electroluminescent layer by printing, in particular screen printing, if the layer is to have a thickness greater than about 5 μm, such as it is typical in the thick-film process, but also by the inkjet method, the latter especially when the light-emitting particles sufficiently small, ie in particular nanoscale, and the layer thickness then does not exceed the values of the so-called thin-film technology, ie less than e.g. 5 μm. In principle, however, all suitable application methods for the mixtures made of organic binder, the luminous particles and a suitable solvent come into question.

Suitable solvents for the PVB-containing mixture are a large number of substances into consideration, especially those with a high flash point and correspondingly low evaporation rate, namely, when the mixture is applied by screen printing, where large pot life is beneficial. Suitable solvents are, above all, alcohols (methanol, ethanol, propanol, butanol, etc., as well as MEK and THF.

Although with very high surface quality, i. low roughness, the light-emitting first layer is basically a waiver of the electrical second layer between the first layer and the back electrode is possible, the layer element according to the invention according to the present state of the invention

Production technology at least preferably a second layer with dielectric properties, which is disposed between the first layer and the back electrode. The second layer preferably also contains an organic binder material, which should preferably consist of PVB or EVA, ie of the same material as that Binder material of the first layer. In this way, an overall system with very well matched refractive properties is achieved since the refractive properties of both the substrate and the first and second layers are substantially identical. Another particularly great advantage, especially of the PVB, is its hygroscopic property. During the production of PVB as binder material contained layers almost inevitably results in a certain water retention in the PVB material. The water is preferably also still present in the PVB after the production of the electroluminescent layer element according to the invention. The great advantage of the water is that the effective relative dielectric constant of the PVB, which is approximately "only" 4.5 in the "absolutely dry" state, clearly increases in the presence of water (E _n = 80) and values of approx in a range of 10-19, eg 13. By increasing the dielectric constant, as is known, the field strength between the opposing electrodes can be increased without the voltage having to be increased for this purpose. In this case, by suitably conditioning the production conditions of the first or the second layer, it can be ensured that the water content in the PVB in the finished layer element moves within the desired limits. An advantage of the layer element according to the invention in this context also lies in the fact that the water content of the binder material PVB according to the invention has no negative effects on the layer element, neither in terms of optical properties nor durability. Even if one of the two layers or both layers are realized with a comparatively large thickness, due to the high permittivity of the binder materials, a field strength required for the luminous effects can be achieved at a comparatively low voltage. This has favorable consequences, in particular with regard to the production costs and the safety of the end product.

The effective dielectric constant of the second layer is further preferably increased by adding particles of barium titanate to the binder material of the second layer, these particles likewise also having light-scattering properties and thus positively influencing the emission characteristic of the layer element according to the invention.

Barium titanate is a white and thus very color-neutral pigment for optically high demands. The relative dielectric constant of the raw material is up to to 2200. The barium titanate together with the organic binder form a mixed dielectric, resulting in a resulting permittivity of about 80. This mixed dielectric may also be referred to as a paint since it consists of the binder and color pigments. The dielectric layer can also serve as a color filter by using colored pigments. This shifts the color locus of the emitted light in the CIE color system / coordinate system. Its information is known to be represented by the intensity (Y) and the coordinates x and y (color location). In addition, the wavelength and a curve are specified, which describes the color temperature in Kelvin. Of particular interest are colors that produce an effect on emotional states of the human body. One differentiates z. "Warm" shades (orange / white to orange), with a low color temperature, which is usually associated with a feeling of warmth. "Cold" shades (blue / white to blue) with a high color temperature is associated with a feeling of coldness , The basic structure of the electroluminescent system comprises a transparent substrate, for. As glass or plastic, a transparent surface electrode, for. As indium tin oxide (ITO), the actual functional or luminescent layer, preferably or, if necessary, an insulating or dielectric layer, and a flat back electrode. Seen electrically, a capacitor is thus formed. Of course, the two surface electrodes are to be connected to a (alternating) voltage source.

According to the invention, the luminescent layer consists of electroluminescent, preferably doped ZnS: Me particles which are dispersed in a polymer of polyvinyl butyral (PVB) or ethylene vinyl acetate (EVA). Me is metal, and preferably manganese, copper or terbium are used to dope the zinc sulfide. The pigments typically have a diameter between 2 nm and 1 μm. The layer thickness of the light-emitting layer is between a few tens of nanometers and about 13 μm, depending on the choice of particle size. Depending on the technique of the order or the generation of the light-emitting layer are different Pigmentbzw. Particle diameter into consideration. It therefore also discrete diameter ranges for the particles into consideration. An area for very thin layers is between 2 and 30nm. Thicker layers may contain particles between 100 nm and 1 μm. Specifically, with the use of pigments with a diameter of about 10 nm and a spin coating application process, it is possible to produce nanometer thin layers.

Particle sizes of 100 - 1000 nm in combination with an inkjet or inkjet coating process allow layer thicknesses of 1 - 6μm.

Particle sizes of 1 μm, in combination with the classic screen-printing application process, enable layer thicknesses of 5 - 10μm.

In addition, when using organic binders which shrink under the action of heat during solidification / drying, the layer thickness is reduced in defined areas after the drying process. Here, the reduction of the layer thickness should not fall below the highest thickness of the embedded particles, so that the latter remain securely embedded in order to minimize the risk of electrical breakdown.

The dielectric layer as an insulating layer consists of particles of barium titanate (BaTiO ₃ ), which is also dispersed in a binder. The diameter of these particles is between 100nm and 2μm. It is preferably 300nm. It is preferably used the same binder system that also embeds the electroluminescent particles. This also fulfills the requirement that the refractive indices of the binder for the luminescent layer and the dielectric be the same. This is necessary so that the light from the light-emitting layer can be conducted into the dielectric layer without optical losses and supplied to the scattering centers (BaTiO ₃ particles). If the refractive index of the light-emitting layer were greater than the refractive index of the dielectric, then the light would be trapped as in an optical waveguide in the very thin layer by total reflection and the emission would be correspondingly low or virtually zero.

The back electrode may optionally be implemented as an opaque electrical print medium (an electrically conductive screen printing paste), a sputtered layer, or a transparent conductive (conductively doped) polymer (PEDOT) of the prior art.

If the back electrode is to be transparent, a completely transparent inorganic electroluminescent system can be constructed by selecting appropriate (lower) layer thicknesses for the luminescent layer and the insulating layer.

When using a thin light-emitting layer according to the invention, it can be used for total reflection at the boundary layers of the transparent electrode (ITO, otherwise Thin film system) and the dielectric layer can come. According to one embodiment, this problem is to be met with the following mechanisms:

The refractive index of the binder is smaller than the refractive index of the transparent electrode. The binder has a nanoporosity, i. H. it contains smallest air pockets, which due to local inhomogeneities of the refractive index a

Cause light scattering. Scattering centers for light extraction are introduced into the luminescent layer and / or the dielectric layer. For this purpose, BaTiO ₃ pigments can be used as scattering centers.

Finally, scattering centers can be introduced by structuring the transparent electrode (or by deliberately creating a rough surface), if this is possible or carried out without a noticeable change in the sheet resistance.

The structuring is z. B. using a local laser processing possible while the surface roughness z. B. by adjusting the deposition parameters (during sputtering) can be influenced. It is essential for a good luminous efficacy to avoid that within the layer element to total reflections at interfaces occurs.

Further details and advantages of the subject of the invention will become apparent from the drawing of an embodiment and its subsequent detailed description below. It show in a simplified, not to scale representation

1 shows a first partial sectional view through a prior art electroluminescent layer element in which an assumed light refraction state is plotted with non-matching refractive indices of the binder layers; 2 shows an assumed light refraction state in a layer element according to the invention with matching refractive indices of the binder layers.

According to FIG. 1, a layer element 1 is constructed on a transparent rigid plate 2 made of glass or plastic. On the surface of the plate 2, an electrically conductive transparent thin layer 3 made of a TCO (transparent conductive oxide), preferably of indium tin oxide (ITO) is deposited over the entire surface. This electrode layer can be connected by means of a bus bar 4 to the outside to a pole of a voltage source, not shown. On the electrode layer 4, a functional layer 5 made of a transparent organic binder (polymer or silica) is applied in a manner known per se as matrix material and nanoparticles 6, which are incorporated therein and are excitable for electroluminescence. This layer 5 may itself be a dielectric. It is then followed by another dielectric layer 7 made of a likewise transparent binder matrix and light-scattering particles 8 embedded therein.

Finally follows a cover or back electrode layer 9, which need not be transparent, and preferably consists of silver. This electrode can also be connected to the aforementioned voltage source by means of at least one bus bar (not shown). If both electrode layers 4 and 9 are at a suitable alternating voltage, an electric field is created which penetrates the dielectric layers 5 and 7 and excites the particles 6 to emit light.

If the layer element 1 is to be able to emit light on both sides, then of course the cover electrode 9 must also be translucent. In deviation from FIG. 1, it could also consist of a TCO, or be a light-transmitting, electrically conductive multi-layer system with at least one metal layer, or else a conductive doped, light-transmitting polymer (PEDOT).

The nanoparticles 6 in the luminescent layer consist of metal-doped zinc sulfide (ZnS: Me), manganese or copper or terbium being preferred as the doping metal. Their diameters are preferably between 2 and 30 nm or between 100 nm and 1 μm, depending on the thickness of the light-emitting layer 5. This is between a few tens of nanometers and 13 μm, depending on the choice of particle diameter and the application method.

The nanoparticles 8 in the dielectric layer preferably consist of color-neutral barium titanate (BaTiO ₃ ) with respect to the light emitted by the nanoparticles 6. The diameter of the particles 8 is between 100 nm and 2 μm and is preferably 300 nm.

FIG. 1 schematically shows a greatly simplified beam path of light rays which are emitted by some of the particles 6. If the refractive indices of the layers 3, 5 and 7 are not carefully matched, then, as shown in FIG. 1, a total reflection of the emitted light at the interfaces can occur. The layer 5 then acts like an optical waveguide. The particles 8 then have virtually no effect on the light rays, as they did not get to them. It should be noted that the excited in the electric field for lighting pigments naturally emit the light in spherical form in the binder. This is not considered in the schematic diagram.

In the embodiment according to FIG. 2, the brittle indices of the layers 5 and 7 are identical and the index of the layer 3 and the substrate 2 (glass) is not very different or substantially coincides therewith, with an unchanged basic structure. Consequently, the light rays penetrate the interface between the layers 5 and 7 without any significant deflection, and therefore either reach the (mirroring) back electrode or are reflected or scattered on the particles 8. Since the particles 6 themselves have a certain light-scattering effect, so that a total of very homogeneous-surface light emission is possible. It is possible to further improve the scattering effect by mixing a proportion of light-scattering particles into the layer 5 between the zinc sulfide particles 6.

The binder material of both the first layer 5 and the second layer 7 is PVB. When preparing the mixture for the first layer 5, 20% by weight PVB powder (also possible using PVB granules) is mixed with 80% solvent in the form of propanol. From 60% of this binder material and 40% of metal-doped zinc sulfite particles, a paste is then produced, which is applied to the surface electrode 3 by way of the screen-printing method. For the second layer 7, the same binder material is used. In the production of a paste from which the second layer 7 is formed, 40% of the binder material and 60% of barium titanate particles are used (all the above percentages are by weight). Depending on the surface roughness and the ratio of the size of the particles 6 to the thickness of the layer 5, one or more application processes for producing the second layer 7 or the second layers 7 are required.

Claims

claims

An electroluminescent layer element (1) comprising at least one light-transmissive substrate (2), a light-transmitting surface electrode (3) applied thereto, a first layer (5) with inorganic electroluminescent particles (6) embedded in an organic binder material, wherein the organic binder material the first layer (5) has at least approximately the same refractive properties as the transparent substrate (2) and a back electrode (9), wherein the transparent surface electrode (3) and the back electrode (9) for supplying the voltage and for generating an electric field are provided, in the presence of the in the first layer (5) embedded particles (6) are excited to emit light, characterized in that the binder material based on polyvinyl butyral (PVB) or ethylene-vinyl acetate (EVA) or contains one of these polymers.

2. Layer element according to claim 1, characterized in that between the first layer (5) and the rear electrode (9), a second layer (7) is arranged with dielectric properties, wherein the second layer (7) contains an organic binder material, preferably consists of PVB or EVA, or contains one of these polymers.

3. Layer element according to claim 2, characterized in that the second layer (7) embedded in its binder material particles having light-scattering properties, in particular of a material having a high relative dielectric constant, preferably of barium titanate (BaTiO ₃ ).

4. Layer element according to one of claims 1 to 3, characterized in that the first layer (5) by printing, in particular by screen printing, a mixture of the binder material, a solvent and the excitable for emitting light particles (6) on the surface electrode (3) or by application of the mixture by means of an inkjet process.

5. Layer element according to claim 1, characterized in that in the binder material of the light-emitting layer (5) and light-scattering particles are embedded.

6. Layer element according to one of the preceding claims, characterized in that the light-emitting particles (6) zinc sulfite nanoparticles are doped with copper or manganese or terbium.

7. Layer element according to one of the preceding claims, characterized in that either in the first layer (5) and / or the second layer (7) embedded particles (6,8) are nano-particles with a dimension between 2 nm and 1 micron depending on the thickness of the layer (5,7) in which they are embedded.

8. Layer element according to one of the preceding claims, characterized in that the transparent electrode layer (3) with light refractive Structures is provided, in particular with a rough surface and / or with in

the surface introduced bumps.