JP2003332068A - Electroluminescence element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electroluminescence (EL) element having high visibility. <P>SOLUTION: The EL element 10 has a circularly polarizing filter 3 where an absorption type linear polarizing plate 1 and 1/4-wavelength plate 2 constituted by one or a plurality of phase difference plates. Of the phase difference plates constituting the 1/4-wavelength plate 2, at least one or more phase difference plates satisfies ny<nz, where ny is a refractive index in the direction orthogonal to the direction having the maximum refractive index on a surface and nz is a refractive index in the thickness direction. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a self-luminous flat panel display, as well as an electroluminescence element (hereinafter referred to as an EL element) used for various light emitters, lighting, etc., and particularly, visibility and light utilization efficiency. Relates to an excellent organic EL device.

[0002]

2. Description of the Related Art An EL element which has a light emitting layer between electrodes and emits light when a voltage is applied to the light emitting layer is a flat type illumination, a light source for an optical fiber, a backlight for a liquid crystal display, a backlight for a liquid crystal projector, a display device or the like. Research and development are being actively pursued as various light sources of. Among them, in particular, the organic EL element has a light emitting efficiency, low voltage driving,
It is an element that is excellent in terms of light weight and low cost, and is an element that has received a great deal of attention in recent years.

The organic EL device is a device in which electrons are injected from the cathode and holes are injected from the anode, and both are recombined in the light emitting layer to generate visible light emission corresponding to the light emitting characteristics of the light emitting layer. . Among the transparent conductive materials that can be used at present, the anode is mainly made of ITO because it has the highest electric conductivity, a relatively large work function, and a high hole injection efficiency. On the other hand, the cathode has
Usually a metal electrode is used, but considering the electron injection efficiency,
From the viewpoint of work function, Mg, MgAg, MgIn, A
Materials such as l and LiAl are used. These metal materials have a high light reflectance and, in addition to the function as an electrode (cathode), also have the function of reflecting the light emitted from the light emitting layer and increasing the amount of emitted light (luminance). That is, the light emitted toward the cathode is specularly reflected on the surface of the metal material that is the cathode,
The emitted light is taken out from the transparent ITO electrode (anode).

In the organic EL element having such a structure, since the cathode has a mirror surface having a strong light reflectivity, external light reflection becomes noticeable in a state where no light is emitted. That is,
There is a fatal problem in that the interior room lighting is severely reflected and black color cannot be expressed in a bright place, and that the bright room contrast is extremely low for use as a light source for a display device.

However, by utilizing the fact that the cathode of the organic EL element is a smooth specular reflection surface, it is possible to remarkably suppress the reflection of external light at the cathode by installing a circular polarization filter. is there. The use of a circular polarization filter for preventing reflection of external light on a mirror surface is a known technique, and the use of a circular polarization filter for an organic EL element is also disclosed in JP-A-8-321381 and JP-A-9-12788.
No. 5, for example.

The circular polarization filter is usually formed by laminating an absorption type linear polarization plate and a quarter wavelength plate so that their optical axes intersect at 45 degrees or 135 degrees. Here, when the quarter-wave plate is formed of, for example, a single stretched film, the retardation of the stretched film is different for each wavelength due to the wavelength dispersion that is different for each wavelength. Although it can be exactly 1/4 wavelength, it does not function as a 1/4 wavelength plate because the phase difference at other wavelengths deviates from the 1/4 wavelength. As a result, the circular polarization filter using such a quarter wave plate does not function as a perfect circular polarization filter over the entire visible light range. Therefore,
For example, when functioning as a quarter-wave plate for green light of 550 nm, it becomes difficult to completely prevent reflection of red light having a longer wavelength and blue light having a shorter wavelength. However, there is a problem that the phase difference of blue light having a large wavelength dispersion is large and the reflected color becomes bluish.

As means for improving the wavelength dependence of such a quarter-wave plate, Japanese Patent Laid-Open Nos. 5-27118 and 5-100114 disclose two retardation plates having different phase differences. By forming a quarter-wave plate with laminated wave plates, the wavelength dependence of the phase difference is improved, and the quarter-wave plate can function as a quarter-wave plate in the entire visible light wavelength region.
Wave plates have been proposed. In addition, Japanese Patent Laid-Open No. 2001-249
In JP-A-222-222, it is proposed to obtain a quarter-wave plate that does not depend on the wavelength in the visible light wavelength region, from a single polymer oriented film having a smaller retardation as the wavelength becomes shorter.

[0008] 1 / which improves the wavelength dependence described above.
By using a four-wave plate, over the entire visible light,
It is possible to obtain a circular polarization filter that can prevent reflection at the cathode. However, this is the case where the incident light from the outside and the reflected light from the cathode are perpendicularly incident on the surface of the circular polarization filter, and the light obliquely incident is the light that passes through the quarter-wave plate. The optical path length becomes long, and as described above, it does not function as an ideal circular polarization filter. In other words, if the organic EL element is viewed from the front (the circular polarization filter is viewed from the front), the portion not emitting light is displayed in black due to the function of the circular polarization filter, but the portion is viewed obliquely. As a result (the circular polarization filter is viewed from an oblique direction), there is a problem that the metallic luster of the cathode is visually recognized.

On the other hand, as another problem, in a solid-state light emitting device such as an EL device that emits light from the light emitting layer itself, of the emitted light, the refractive index of the light emitting layer and the refraction of the emitting medium in contact with the light emitting layer. Light having an incident angle larger than the critical angle determined by the index may be totally reflected at the interface between the light emitting layer and the emission medium, may be trapped inside the light emitting layer, and may not be extracted to the outside. Here, when the refractive index of the light emitting layer is n, it is known that the extraction efficiency η of the light extracted to the outside of the light generated in the light emitting layer is approximated by η = 1 / (2 · n ² ). Has been. For example, if the refractive index of the light emitting layer is 1.7, then η≈17%, and 1/5 or more of the light is lost as lost light. further,
When the circular polarization filter is installed as described above to prevent reflection of external light, about half of the light emitted from the light emitting layer is absorbed by the absorption type linear polarization plate that constitutes the circular polarization filter, and thus the EL element The light utilization efficiency of is calculated to be only 1/10.

As a method of improving the extraction efficiency, for example, as described in JP-A-63-314795, the extraction efficiency is improved by making the substrate itself constituting the EL element have a light-collecting property. How to improve,
As described in Japanese Patent Application Laid-Open No. 10-321371, a method of improving front directivity of a light ray itself by forming a light emitting layer with a discotic liquid crystal,
As described in Japanese Patent Application Laid-Open No. 11-214162, a method of forming an electrode forming an EL element into a concave shape, and as described in Japanese Patent Application Laid-Open No. 11-214163, an electrode forming an EL element. Various methods have been proposed, such as a method of forming an inclined surface on the substrate, and a method of forming a diffraction grating or the like on the electrodes constituting the EL element as described in Japanese Patent Application Laid-Open No. 11-283751. However, these proposals have problems such that the EL element has a complicated structure and the luminous efficiency of the light emitting layer itself is deteriorated.

A relatively simple method for improving the extraction efficiency is to form a light diffusion layer on the EL element to diffuse the light and reduce the light that satisfies the condition of total reflection. be able to. Such methods include
For example, as described in JP-A-6-347617, a diffusion plate in which particles having a refractive index distribution structure having different refractive indexes inside and on the surface are dispersed and contained in a transparent substrate,
As described in JP-A-001-356207, it is possible to use a diffusing member in which a light diffusing layer containing translucent particles arranged in a single particle layer is provided on a translucent substrate. As described in JP-A-151061, various proposals have been made such as a method of dispersing scattering particles in the same material as the light emitting layer of the EL element.

However, when such a light diffusing layer is inserted between the light emitting layer and the circularly polarizing plate, the organic EL device is improved in luminance due to the improved extraction efficiency, but it passes through the circularly polarizing filter. There is a problem that the polarized light is canceled and the function of the circularly polarized light filter is hindered by the scattering of the external light by the light diffusion layer. Therefore, in order to avoid this, it is necessary to design the light diffusion layer so that the polarization state is not eliminated as much as possible. That is, if the light diffusing power is increased, the brightness is improved, but the function as a circular polarization filter is lowered. Conversely, if the light diffusing power is decreased, the function as a circular polarization filter is easily exhibited, but the brightness is There was a trade-off between the two, as it would be difficult to improve.

[0013]

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems of the prior art.
A first object is to provide an EL device having excellent visibility by efficiently preventing external light reflection in an oblique direction due to a cathode (metal electrode), which is a problem in the device. In addition, high light utilization efficiency (high brightness) is achieved by improving the light extraction efficiency while exhibiting the external light reflection prevention function.
The second object is to provide an EL element.

[0014]

In order to solve the first problem, the present invention comprises an absorption type linear polarizing plate and one or more retardation plates as described in claim 1. 1 /
An electroluminescence element comprising a circular polarization filter laminated with a four-wave plate, wherein at least one phase-difference plate among the phase-difference plates constituting the quarter-wave plate has the maximum in-plane refraction. When the refractive index in the direction orthogonal to the direction having the refractive index is ny and the refractive index in the thickness direction is nz, ny
An electroluminescent element characterized by satisfying <nz.

According to the first aspect of the present invention, the function as a quarter-wave plate can be achieved even for the light incident on the quarter-wave plate in an oblique direction. That is, the optical path length is given by the product of the refractive index of the medium in which light propagates and the physical distance,
In the quarter-wave plate according to claim 1, since at least one retardation plate is formed so as to satisfy ny <nz, the light passing through the retardation plate is incident from the front direction. The light has a smaller refractive index with respect to the light incident from the diagonal direction, and the difference in the physical distance between them (the light entering from the diagonal direction has a longer physical distance) is just compensated for, and the optical path length is compensated. It is possible to make both equal. Therefore, by constructing a quarter-wave plate with such a retardation plate, the function of a circular polarization filter for both the light incident from the front direction and the light incident from the oblique direction (external light reflection prevention function) Thus, it is possible to provide an EL element which can exhibit high brightness and high visibility in a bright room.

Further, in order to solve the second problem, according to the present invention, as described in claim 2, light diffusion formed between the light emitting layer of the electroluminescence element and the circular polarization filter. The present invention provides an electroluminescent device including a layer.

According to the second aspect of the present invention, the circular polarization filter not only solves the first problem, but also includes a light diffusion layer between the light emitting layer of the electroluminescence element and the circular polarization filter. Since it is formed, light is diffused by the light diffusion layer, and the light that satisfies the condition of total reflection is reduced, so that the light extraction efficiency is improved, resulting in high light utilization efficiency (high brightness). It is possible to provide an EL element. Even if the light diffusion layer is formed in this way, a normal retardation plate (nx> ny = nz)
It is possible to improve the external light reflection preventing function as compared with the case where the quarter wavelength plate is formed.

Preferably, at least one retardation plate among the retardation plates constituting the ¼ wavelength plate has a maximum in-plane refractive index of nx and an in-plane retardation plate. The refractive index in the direction orthogonal to the direction having the maximum refractive index of ny,
When the refractive index in the thickness direction is nz, 0 <(nx-n
z) / (nx-ny) <1 is formed. If (nx-nz) / (nx-ny) is too small, the correction of the phase difference of the light incident on the quarter-wave plate from the oblique direction becomes too large, and conversely, (nx-nz) /
If (nx-ny) is too large, the correction may be too small (it is difficult to obtain a phase difference of 1/4 wavelength for the light), so it is more preferable that 0 is set as described in claim 4. .3 <(nx-nz) / (nx-ny) <
It is formed so as to satisfy 0.7.

Further, as described in claim 5, the 1/4
The wave plate satisfies nx = ny <nz, where nx is the maximum in-plane refractive index, ny is the refractive index in the direction orthogonal to the direction having the maximum in-plane refractive index, and nz is the thickness direction refractive index. And a retardation plate satisfying nx> ny = nz.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 shows an E according to the first embodiment of the present invention.
It is a longitudinal cross-sectional view showing a schematic configuration of an L element. As shown in FIG. 1, an EL element 10 according to the present embodiment is a 1 / # composed of an absorption type linear polarizing plate 1 and one or a plurality of retardation plates.
A circular polarization filter 3 in which a four-wave plate 2 is laminated is provided. Here, the absorptive linear polarizing plate 1 and the 1/4 wavelength plate 2 are arranged so that their optical axes intersect at 45 degrees or 135 degrees, and a straight line transmitted through the absorptive linear polarizing plate 1 The polarized light will be converted into circularly polarized light by the quarter-wave plate 2. Further, the EL element 10 includes a transparent substrate 4 arranged to face the circular polarization filter 3, an anode 5 formed on the transparent substrate 4, a cathode 6 arranged to face the anode 5, and an anode 5.
And a light emitting layer 7 disposed between the cathode 6.
In the EL element 10 having such a structure, electrons are injected from the cathode 6 and holes are injected from the anode 5, and both are recombined in the light emitting layer 7 to emit visible light corresponding to the light emitting characteristics of the light emitting layer 7. Occurs. The light generated in the light emitting layer 7 is directly or after being reflected by the cathode 6, and is extracted to the outside via the anode 5, the transparent substrate 4, and the circular polarization filter 3.

On the other hand, the external light I1 (external light incident from the direction perpendicular to the surface of the absorption type linear polarizing plate 1) incident from the outside of the EL element 10 due to indoor lighting or the like is halved by the absorption type linear polarizing plate 1. It is absorbed and the other half is transmitted as linearly polarized light and is incident on the quarter-wave plate 2. The light incident on the quarter-wave plate 2 is transmitted to the absorption linear polarizing plate 1 /
Since the optical axes of the four-wavelength plate 2 and the four-wavelength plate 2 are arranged to intersect each other at 45 degrees or 135 degrees, the light is converted into circularly polarized light by passing through the quarter-wave plate 2. The circularly polarized light emitted from the quarter-wave plate 2 has a phase of 180 when specularly reflected by the cathode 6.
It is inverted and reflected as circularly polarized light of the opposite direction. The reflected light R1 is incident on the quarter-wave plate 2 again,
Since it is converted into linearly polarized light parallel to the absorption axis (axis orthogonal to the optical axis) of the absorptive linear polarization plate 1, it is completely absorbed by the absorptive linear polarization plate 1 and is not emitted to the outside.

On the other hand, external light I incident from an oblique direction
In the conventional case, when the light passes through the quarter-wave plate 2, the light of No. 2 becomes longer than the circularly polarized light and becomes elliptically polarized light. Therefore, a part of the reflected light R2 (Fig. The light indicated by the dotted line in 1) leaked to the outside and was visually recognized by the observer. However, the quarter-wave plate 2 according to the present embodiment has at least one of the phase difference plates constituting the quarter-wave plate 2.
One or more retardation plates have a refractive index ny in the direction orthogonal to the direction having the maximum in-plane refractive index and a refractive index nz in the thickness direction.
Is formed so as to satisfy ny <nz. Therefore, the function as a quarter-wave plate can be achieved even with respect to the external light I2 incident from the oblique direction. That is,
The optical path length is given by the product of the refractive index of the medium through which the light propagates and the physical distance, and the quarter wavelength plate 2 according to the present embodiment is used.
Because at least one retardation film is formed so as to satisfy ny <nz, the refractive index for external light I2 incident from the oblique direction is smaller than that of external light I1 incident from the front direction. , The difference in physical distance between the two (the physical distance of the external light I2 is longer) is just compensated,
Both can be made equal as the optical path length. Therefore, by constructing the quarter-wave plate 2 with such a retardation plate, an external light reflection preventing function is exhibited for both external light I1 incident from the front direction and external light I2 incident from the oblique direction. It is possible to

The absorption type linear polarizing plate 1 is not limited as long as it is an absorption type linear polarizing plate, and various forms can be applied. Generally, a film made of a hydrophilic polymer such as polyvinyl alcohol is treated with a dichroic dye such as iodine and stretched, or a plastic film such as polyvinyl chloride is treated to remove polyene. In addition to the oriented polarizing film, a polarizing film covered with a sealing film for protection and the like are used.

The quarter-wave plate 2 can be formed of a single birefringent film (retardation plate), but the wavelength dependence of the retardation is reduced to 1 /
In order to function as a four-wave plate, it is preferable that a plurality of birefringent films are laminated and formed. However, from the viewpoint of cost reduction, it is preferable to form two birefringent films by laminating. For example, a birefringent film that gives a phase difference of ½ wavelength to monochromatic light and a birefringent film that gives a phase difference of ¼ wavelength have their optical axes functioning as a ¼ wavelength plate. If the quarter-wave plate 2 is formed by stacking by intersecting at a predetermined angle so as to play,
The wavelength dependence of the phase difference can be reduced. As described above, the quarter-wave plate 2 according to the present embodiment has at least one of the phase difference plates constituting the quarter-wave plate 2.
One or more retardation plates have a refractive index ny in the direction orthogonal to the direction having the maximum in-plane refractive index and a refractive index nz in the thickness direction.
In such a case, it may be formed so as to satisfy ny <nz. In particular, when a plurality of birefringent films are laminated to form the quarter-wave plate 2, all the birefringent films have the above relations. The configuration to satisfy (ny <nz) is
It is preferable in that the function of preventing reflection of external light is sufficiently exerted.

When a stretched film is used as the birefringent film, the maximum in-plane refractive index of the stretched film is nx, the refractive index in the direction orthogonal to the direction having the maximum in-plane refractive index is ny, and the thickness is When the refractive index in the direction is nz, from the viewpoint of angle correction of the quarter-wave plate 2, it is preferable that 0 <(nx-nz) / (nx-ny) <1 be satisfied, and it is further preferable. , 0.3 <(nx-nz)
It is formed so as to satisfy /(nx-ny)<0.7.

The specific material of the stretched film is not particularly limited, and a polymer film is uniaxially or biaxially.
It can be formed by performing a stretching process or the like by an appropriate method such as a shaft. The refractive index in the thickness direction of the stretched film can be controlled by stretching the polymer film while adhering the heat-shrinkable film, but the method is not particularly limited.

As a specific material of the polymer film, as long as it is a material having excellent transparency and capable of being stretched,
Various things can be applied. Examples of such materials include polycarbonate-based polymers, polyester-based polymers, polysulfone-based polymers, polyethersulfone-based polymers, polystyrene-based polymers, polyolefin-based polymers, polyvinyl alcohol-based polymers, and cellulose acetate-based polymers. Examples thereof include polymers, polyvinyl chloride polymers, polymethylmethacrylate polymers, polyarylate polymers, polyamide polymers and the like.

The birefringent films constituting the quarter-wave plate 2 and the absorption type linear polarizing plate 1 can be compounded by using an acrylic transparent pressure-sensitive adhesive or adhesive having no optical anisotropy. .

It should be noted that the quarter wave plate 2 has nx = ny <n
It is also possible to stack and form a retardation film satisfying z and a retardation film satisfying nx> ny = nz. Examples of such a quarter-wave plate 2 include, for example, a normal stretched film (nx> n) in which the refractive index in the thickness direction is not controlled.
y = nz) and a film in which liquid crystal molecules are vertically aligned (n
x = ny <nz).
In addition, a film in which liquid crystal molecules are horizontally aligned (nx> n
y = nz) and a vertically oriented film (nx = ny <
nz) can also be formed in combination.

Here, as the material for the homeotropic alignment liquid crystal layer, for example, Chemical Review 44 (surface modification,
A general nematic liquid crystal compound that can be homeotropically aligned by a vertical aligning agent, as described in Chemical Society of Japan, pp. 156 to 163) can be used. Such a homeotropic alignment liquid crystal layer has an optical axis in the Z-axis direction (thickness direction) and has a maximum in-plane refractive index nx.
And the refractive index ny in the orthogonal direction is substantially the same, and nx
= Ny <nz, which can be suitably used as a retardation plate forming the quarter-wave plate 2. A specific method for producing the homeotropically aligned liquid crystal layer is described in detail in, for example, Japanese Patent Application No. 2001-136848, but there is no particular limitation regarding the producing method and the material.

Incidentally, in order to ensure the prevention of external light reflection, the surface of the circular polarization filter 3 can be further subjected to antireflection treatment. Examples of such antireflection treatment include, for example,
In addition to directly forming the multilayer film on the surface of the circular polarization filter 3, it is also possible to attach a separately prepared antireflection film. Also, an appropriate anti-glare treatment may be applied.

Next, a second embodiment of the present invention will be described.

FIG. 2 shows an E according to the second embodiment of the present invention.
It is a longitudinal cross-sectional view showing a schematic configuration of an L element. As shown in FIG. 2, the EL element 10 ′ according to this embodiment also includes an absorption type linear polarizing plate 1 and one or more retardation plates.
A circular polarization filter 3 having a quarter wavelength plate 2 laminated thereon is provided. In addition, the transparent substrate 4, the anode 5, the cathode 6, and the light emitting layer 7 are provided in the same manner as in the first embodiment.

However, in the EL element 10 'according to the present embodiment, in order to improve the light extraction efficiency and improve the brightness of the EL element 10', the light emitting layer 7 and the circular polarization filter 3 are provided.
Between the circular polarization filter 3 and the transparent substrate 4 in FIG. 2 is provided, which is different from the first embodiment.

In the EL element 10 ′ according to this embodiment, external light I 1 (external light incident from a direction perpendicular to the surface of the absorption type linear polarizing plate 1) incident from the outside is scattered by the light diffusion layer 8. Accordingly, there is a case where the light is obliquely reflected (reflected light R1), or conversely, the external light I2 incident from the oblique direction is scattered by the light diffusion layer 8 and reflected in the front direction (reflected light R2). . Even in such a case, for the same reason as described in the first embodiment, in the conventional case, a part of the reflected lights R1 and R2 (light indicated by a dotted line in FIG. 2) leaks to the outside, It was visually recognized by the observer. However, the quarter-wave plate 2 according to this embodiment is also the quarter-wave plate 2
In the case where at least one or more of the phase difference plates constituting the above-mentioned structure has a refractive index in the direction orthogonal to the direction having the maximum in-plane refractive index as ny and a refractive index in the thickness direction as nz, n
Since it is formed so as to satisfy y <nz, it is possible to exhibit the external light reflection preventing function for both the external light I1 incident from the front direction and the external light I2 incident from the oblique direction. .

The light diffusing layer 8 can be applied without particular limitation as long as it can diffuse light to some extent, and the position of the light diffusing layer 8 is between the light emitting layer 7 and the circular polarization filter 3. There is no particular limitation as long as it is arranged in.

More specifically, as the light diffusing layer 8, in addition to those in which fine particles having different refractive indexes are dispersed in a matrix, various lens sheets, physical uneven surfaces, matte treated surfaces, etc. may be applied. It is possible.

However, if a light diffusing layer having a large light diffusing power to such an extent that the polarization state is completely eliminated, the effect of improving the brightness is enhanced, but the function of the circular polarization filter 3 is
That is, the external light reflection preventing function is impaired. Therefore, for example, it is preferable to find the optimum light diffusion layer 8 by appropriately optically designing the refractive index difference between the matrix and the fine particles, the particle diameter of the fine particles, the particle addition amount, the number of particles in the thickness direction, and the like.

The characteristics of the present invention will be further clarified by showing Examples and Comparative Examples below.

(Reference Example 1) ITO was formed on one surface of a glass substrate.
A 120 nm-thick ITO transparent film anode was formed from a ceramic target (In ₂ O ₃ : SnO ₂ = 90% by weight: 10% by weight) by the DC sputtering method. Then, after performing ultrasonic cleaning, cleaning was performed by an ultraviolet ozone method. Next, on the ITO surface, N, N′-diphenyl-N, N′-bis- (3-methylphenyl) -disposed in a molybdenum boat in a resistance heating type vacuum deposition apparatus.
[1,1'-biphenyl] -4,4'-diamine (TP
D) and tris (8-quinolinol) aluminum (Alq) placed in another molybdenum processing boat, the vacuum chamber was evacuated to 1 × 10 ⁻⁴ Pa and the TPD was heated to 220 ° C. After forming a hole transport layer made of a 60 nm TPD film, 275 Alq is formed thereon.
The Alq film having a thickness of 60 nm was formed by heating to ° C. Next, a two-source simultaneous vapor deposition method is performed in which a vacuum chamber is evacuated to a pressure of 2 × 10 ⁻⁴ Pa via magnesium placed on a molybdenum boat and silver placed on another molybdenum boat. The Mg / Ag alloy (M
g / Ag = 9/1) forming a 100 nm-thick cathode and emitting green (main wavelength 513 nm) organic EL
A device was created. The emission area of the created organic EL element is 2
It was cm × 3 cm. Moreover, 6V is applied to this organic EL element.
The front luminance when applying the DC voltage of 1230 cd / m
^{Was 2} .

Reference Example 2 Refractive Index 1.59, Thickness 50μ
m polycarbonate film was stretched at 150 ° C. for 5% under adhesion of a heat-shrinkable film, and a wavelength of 550
Nz (= which gives a phase difference of ½ wavelength for nm light)
A half-wave plate having (nx-nz) / (nx-ny)) of 0.5 was prepared.

Reference Example 3 Refractive Index 1.59, Thickness 50μ
The polycarbonate film of m was stretched by 5% at 150 ° C. to prepare a half-wave plate having Nz of 1 (that is, ny = nz) that gives a half-wave retardation to light having a wavelength of 550 nm.

(Reference Example 4) Refractive index 1.51, thickness 100
μm cyclic polyolefin film (AR made by JSR, AR
TON) under adhesion of heat shrinkable film
25% stretching treatment at ℃, 1 for light of wavelength 550nm
A quarter wave plate having Nz of 0.9 giving a phase difference of / 4 wavelength was prepared.

Reference Example 5 Refractive Index 1.51, Thickness 100
μm cyclic polyolefin film (AR made by JSR, AR
TON) is stretched by 25% at 175 ° C. and the wavelength is 550n.
A quarter-wave plate having Nz of 1 that gives a quarter-wave retardation to m light was created.

(Reference Example 6)

[Chemical 1] The above chemical formula (in the formula, n = 35, mol% of the monomer unit is shown, and is represented by a block for convenience,
A solution of 25 parts by weight of a side chain type liquid crystal polymer having a weight average molecular weight of 5000) dissolved in 75 parts by weight of cyclohexanone is a plastic film (20 μm) using a norbornene-based polymer (trade name: Zeonex, manufactured by Zeon Corporation) as a polymer material. Was applied by spin coating. Next, the liquid crystal polymer is homeotropically aligned by heating at 130 ° C. for 1 minute and then cooled to room temperature all at once, and the homeotropically aligned liquid crystal layer is fixed while maintaining the alignment to obtain an in-plane refractive index. Is constant and the refractive index in the thickness direction is large (that is, nx = n
y <nz) A retardation plate was prepared.

Reference Example 7 2 g of silicone particles having a refractive index of 1.43 and a particle size of 3 μm was added to 10 g of toluene,
Stir well. Further, an acrylic pressure-sensitive adhesive having a refractive index of 1.47 was added and dissolved in toluene so that the concentration became 20% by weight. Such a solution is added to a toluene solution in which silicone particles are dispersed so that the silicone concentration with respect to the adhesive is 20% by weight, and the concentration is adjusted so that the concentration of the adhesive with respect to toluene is 20%. Stir well. Using the applicator, apply the solution prepared on the separator and dry it,
A light diffusion adhesive having a thickness of 25 μm was prepared.

(Example 1) A half-wave plate prepared in Reference Example 2 and a quarter-wave plate prepared in Reference Example 4 were acrylic with their stretching axes (optical axes) intersecting each other. A 1/4 wavelength plate was prepared by laminating via a pressure-sensitive adhesive. Next, the half-wave plate side and a polarizing plate (NPF manufactured by Nitto Denko Corporation) were laminated in the same manner with an acrylic pressure-sensitive adhesive between them to form a circular polarization filter. The crossing angle of the optical axis with respect to the polarization axis of the polarizing plate was 1 for the half-wave plate prepared in Reference Example 2.
2 degrees, the quarter-wave plate prepared in Reference Example 4 was 69 degrees. Furthermore, the quarter-wave plate side of this circular polarization filter is
The organic EL device of this example was prepared by sticking the glass substrate of the organic EL device prepared in Reference Example 1 with an acrylic adhesive.

(Example 2) The half-wave plate prepared in Reference Example 2 and the quarter-wave plate prepared in Reference Example 5 were acrylic with their stretching axes (optical axes) intersecting each other. A 1/4 wavelength plate was prepared by laminating via a pressure-sensitive adhesive. Next, the half-wave plate side and a polarizing plate (NPF manufactured by Nitto Denko Corporation) were laminated in the same manner with an acrylic pressure-sensitive adhesive between them to form a circular polarization filter. The crossing angle of the optical axis with respect to the polarization axis of the polarizing plate was 1 for the half-wave plate prepared in Reference Example 2.
2 degrees, the quarter-wave plate prepared in Reference Example 5 was 69 degrees. Furthermore, the quarter-wave plate side of this circular polarization filter is
The organic EL device of this example was prepared by sticking the glass substrate of the organic EL device prepared in Reference Example 1 with an acrylic adhesive.

(Example 3) The half-wave plate prepared in Reference Example 3 and the quarter-wave plate prepared in Reference Example 5 were acrylic with their stretching axes (optical axes) intersecting each other. A 1/4 wavelength plate was prepared by laminating via a pressure-sensitive adhesive. Next, the half-wave plate side and the plastic film side of the retardation plate on which the homeotropic liquid crystal layer prepared in Reference Example 6 was fixed were laminated in the same manner with an acrylic adhesive, Further, the homeotropic liquid crystal layer side and a polarizing plate (NPF manufactured by Nitto Denko Corporation) were laminated via an acrylic pressure-sensitive adhesive to prepare a circular polarization filter. The crossing angle of the optical axis with respect to the polarization axis of the polarizing plate was 1/2 as prepared in Reference Example 3.
The wave plate is 12 degrees, and the quarter wave plate prepared in Reference Example 5 is 6
It was 9 degrees. Further, the quarter-wave plate side of this circularly polarizing filter was adhered to the glass substrate of the organic EL element prepared in Reference Example 1 via an acrylic pressure-sensitive adhesive to obtain the organic E of this example.
An L element was created.

(Comparative Example 1) A half-wave plate prepared in Reference Example 3 and a quarter-wave plate prepared in Reference Example 5 were acrylic with their stretching axes (optical axes) intersecting each other. A 1/4 wavelength plate was prepared by laminating via a pressure-sensitive adhesive. Next, the half-wave plate side and a polarizing plate (NPF manufactured by Nitto Denko Corporation) were laminated in the same manner with an acrylic pressure-sensitive adhesive between them to form a circular polarization filter. The crossing angle of the optical axis with respect to the polarization axis of the polarizing plate was 1 for the ½ wavelength plate prepared in Reference Example 3.
2 degrees, the quarter-wave plate prepared in Reference Example 5 was 69 degrees. Furthermore, the quarter-wave plate side of this circular polarization filter is
The glass substrate of the organic EL device prepared in Reference Example 1 was attached via an acrylic adhesive to prepare an organic EL device of this comparative example.

Example 4 In Example 1, reference example 1
When the glass substrate of the organic EL element prepared in step 1 and the quarter-wave plate side of the circularly polarized light filter are stuck together, except that two diffusion adhesives prepared in Reference Example 7 are laminated between them. Produced an organic EL device similar to that of Example 1.

(Comparative Example 2) In Comparative Example 1, reference example 1
When the glass substrate of the organic EL element prepared in step 1 and the quarter-wave plate side of the circularly polarized light filter are stuck together, except that two diffusion adhesives prepared in Reference Example 7 are laminated between them. Produced an organic EL device similar to that of Comparative Example 1.

Organic EL of Examples 1 to 4 and Comparative Examples 1 and 2
The following three evaluation tests were performed on the device.

(1) Measurement of Luminance Using a commercially available luminance meter (manufactured by Topcon, product name BM9), the front luminance was measured with a DC voltage of 5 V applied to the organic EL element.

(2) Evaluation of external light reflection preventing effect The organic EL element was placed in an environment with an illuminance of about 100 lx without applying a voltage to the organic EL element, and the blackness level of the reflected color was visually evaluated. did. The blackness level is 4 below.
It was evaluated according to which one of the two conditions it corresponds to. ◎: A state in which external light reflection disappears almost completely and exhibits a black color ○: Inferior to ◎, but a state in which external light reflection is sufficiently suppressed and exhibits a substantially black color Δ: External light reflection is visually recognized and slightly noticeable Condition x: External light reflection is visible and extremely disturbing

(3) Evaluation of Angle Dependence of External Light Reflection Preventing Effect The organic EL element was placed in an environment with an illuminance of about 100 lx without applying voltage to the organic EL element, and was placed in front of the diagonal 4
The blackness level of the reflected color was visually evaluated from the direction of 5 degrees, and the difference was compared. In addition, the comparison result was evaluated according to which of the following four states was applicable. ◎: No change in external light reflection is seen between the front and squint ○: A slight difference in external light reflection is seen between the front and squint, but not noticeable △: Difference in external light reflection between the front and squint Anxious state ×: A state in which the difference in external light reflection between the front and the perspective is extremely anxious

Table 1 shows the results of the three evaluation tests described above.

[Table 1]

As shown in Table 1, the organic EL devices of Examples 1 to 3 are excellent not only in the basic function of the circularly polarized light filter to prevent reflection of external light on the front surface, but also in their angular dependence. Therefore, it was found that even in an oblique direction, it has a sufficient external light reflection preventing function. On the other hand, the organic EL device of Comparative Example 1 is excellent in the effect of preventing reflection of external light on the front surface, but has a large angle dependency, and external light reflection on the cathode was clearly recognized from the oblique direction.

The organic EL device of Example 4 in which the diffusion adhesive layer is formed for the purpose of improving the light extraction efficiency is the same as Example 1
It was found that the brightness was increased by about 1.5 times as compared with the organic EL device of. Further, it was found that although the effect of preventing reflection of external light was slightly lowered by the formation of the diffusion pressure-sensitive adhesive layer, it was at a level at which there was no particular problem, and there was almost no change in perspective. On the other hand, in the organic EL element of Comparative Example 2, the luminance increased as in the organic EL element of Example 4, but the effect of preventing reflection of external light by the circular polarization filter was significantly impaired.

[0061]

As described above, according to the electroluminescence element of the present invention, at least one of the phase difference plates constituting the quarter wavelength plate of the circular polarization filter is used.
Since one or more retardation plates are formed so as to satisfy ny <nz, the function as a substantially 1/4 wavelength plate can be obtained even for light incident on the 1/4 wavelength plate in an oblique direction. Therefore, the function of the circular polarization filter (external light reflection preventing function) can be exhibited for both the light incident from the front direction and the light incident from the oblique direction, and the bright room contrast is high and the visibility is excellent. An electroluminescent device is provided.

In particular, when a light diffusing layer is formed between the light emitting layer of the electroluminescent element and the circular polarization filter, the light extraction efficiency is improved while maintaining the external light reflection preventing function. In addition, it is possible to obtain an electroluminescence device having high light utilization efficiency (high brightness).

[Brief description of drawings]

FIG. 1 is an EL according to a first embodiment of the present invention.
It is a longitudinal cross-sectional view which shows the schematic structure of an element.

FIG. 2 is an EL according to a second embodiment of the present invention.
It is a longitudinal cross-sectional view which shows the schematic structure of an element.

[Explanation of symbols]

1 ... Absorption type linear polarizing plate 2 ... 1/4 wavelength plate 3 ... Circular polarizing filter 4 ... Transparent substrate 5 ... Anode 6 ... Cathode 7 ... Emitting layer 8 ...
Light diffusing layers 10, 10 '... Electroluminescent element

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Minoru Miyatake             1-2 1-2 Shimohozumi, Ibaraki City, Osaka Prefecture Nitto             Electric Works Co., Ltd. (72) Inventor Sadahiro Nakanishi             1-2 1-2 Shimohozumi, Ibaraki City, Osaka Prefecture Nitto             Electric Works Co., Ltd. F-term (reference) 2H049 BA02 BA03 BA07 BA42 BB03                       BB63 BC22                 3K007 AB02 AB03 AB17 BB06 DB03

Claims (5)

[Claims] 1. An electroluminescence element comprising a circular polarization filter in which an absorption type linear polarizing plate and a quarter wavelength plate composed of one or a plurality of retardation plates are laminated, At least one of the phase difference plates constituting the wave plate has a refractive index n y in the direction orthogonal to the direction having the maximum in-plane refractive index and a refractive index n in the thickness direction.
An electroluminescent element characterized by satisfying ny <nz when z. 2. The electroluminescent element according to claim 1, further comprising a light diffusion layer formed between the light emitting layer of the electroluminescent element and the circular polarization filter. 3. At least one retardation plate among the retardation plates constituting the quarter wavelength plate has a maximum in-plane refractive index of nx and is orthogonal to a direction having a maximum in-plane refractive index. When the refractive index in the direction of ny is ny and the refractive index in the thickness direction is nz, 0 <(nx-nz) / (nx-ny) <1 is satisfied. Electroluminescent device. 4. At least one retardation plate among the retardation plates constituting the quarter-wave plate is orthogonal to a direction having a maximum in-plane refractive index nx and a maximum in-plane refractive index. When the refractive index in the direction of the arrow is ny and the refractive index in the thickness direction is nz, 0.3 <(nx-nz) / (nx-ny) <0.7 is satisfied. The electroluminescent element described. 5. The quarter-wave plate has a maximum in-plane refractive index of nx, a refractive index in a direction orthogonal to a direction having a maximum in-plane refractive index of ny, and a thickness-wise refractive index of nz. At this time, it is comprised from the phase difference plate which satisfy | fills nx = ny <nz, and the phase difference plate which satisfies nx> ny = nz, The electroluminescent element of Claim 1 or 2 characterized by the above-mentioned.