JP2004070094A - Contrast increasing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent contrast of a display light image from being decreased by incidence of external light in an active image display device. <P>SOLUTION: The contrast increasing device is constructed so as to be arranged on the front face side of the active image display device 1 having on the rear side rear face electrodes 11 serving also as a reflecting mirror, and to consist of the multiple layers of a polarizing plate 2, a quarter-wave plate 3, and a polarized isolation reuniting film 4 in order of the incident direction of the external light. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an active image display device that emits light by itself, and more particularly to a contrast enhancement device that increases the contrast of light and dark of a display image of an electroluminescence display device (hereinafter abbreviated as EL).
[0002]
[Prior art]
A liquid crystal display (LCD) is a passive image display that does not emit light by itself, of a flat or sheet display device called a flat display. That is, image display occurs when external light incident on the display device is modulated. Accordingly, it is preferable that the outside light is generally strong because the contrast of the displayed image is large.
[0003]
In contrast, a plasma display device (PDP) or EL is an active image display device that emits light by itself, so that no external light is required for display, and an image can be displayed in a dark place without a light source.
By the way, PDPs emit light by causing discharge of a rare gas or the like in a large number of minute cells arranged in a grid, and recently, an ultraviolet-excited phosphor is generated by ultraviolet rays generated by the discharge. 2. Description of the Related Art A color PDP that emits light to display full color has been regarded as a promising image display device to replace a large-sized color CRT.
[0004]
On the other hand, it has long been known that the electroluminescence phenomenon that occurs when an electric field is applied to a phosphor may be applied to an active image display device that emits light by itself when an electric field is applied. This electroluminescence started with the emission of ZnS, but since the invention of a transparent conductive film of SnO ₂ called a Nesa film, it was possible to realize a thin image display device, and the possibility of practical use was increased. It came out.
[0005]
EL can be classified into four types according to a combination of powder or thin film used for the phosphor film, and whether the applied voltage is AC or DC. However, practically, there are an AC dispersion type, an AC thin film type, and a DC organic thin film type (hereinafter, abbreviated as “organic EL”).
In the AC dispersion type EL, a phosphor powder is dispersed in an organic binder to form a film having a thickness of, for example, 50 to 100 μm, and is driven by AC. In order to efficiently apply an electric field to the dispersed phosphor powder, for example, cyanoethyl cellulose having a large dielectric constant is used as a binder, and BaTiO ₃ or the like is used when an acrylic resin having a low dielectric constant is used. Is dispersed in a binder to increase the luminous efficiency.
[0006]
The AC thin film EL is one in which a phosphor is formed into a film having a thickness of, for example, about 1 μm by vapor deposition or sputtering, and is driven by AC. As compared with the dispersion type, a dense film of only the phosphor can be formed, so that the luminous efficiency is high. However, in order to prevent the dielectric breakdown of the film and prolong the service life, a configuration is practically adopted in which the upper and lower sides of the phosphor film are sandwiched by insulating layers.
[0007]
The organic EL has a structure in which a layer having a function of transporting electrons, for example, a layer having a thickness of 50 nm and a function of transporting holes, for example, a layer having a thickness of 20 nm are stacked. I have. Light emission is generated as a result of recombination light emission by injection of holes into the electron transport layer or injection of electrons into the hole transport layer, and is injection light similar to a light emitting diode. For example, an organic compound such as a triphenyldiamine derivative is used for the electron transport layer, for example, an oxadiazole derivative, and for the hole transport layer, which is why an organic EL is called.
[0008]
Furthermore, recently, a light emitting layer made of an organic light emitting material that emits light of various colors is provided between a hole transport layer and an electron transport layer, and a color organic material capable of displaying three primary colors of RGB depending on the selection of the light emitting material. The configuration is such that EL can be realized. As a result, the organic EL has made remarkable progress in terms of luminous efficiency, color display, lifespan, and the like, and has been put to practical use in display devices for mobile phones and monitor displays of several inches.
[0009]
FIG. 3 is a schematic sectional view showing the configuration of the EL. Although the basic configuration of the EL 100, which is one of the active image display devices, is shown upside down in FIG. 3, a transparent substrate such as glass provided with a transparent electrode 12 made of a transparent conductive film is provided. The light emitting layer 14 is provided on the light emitting layer 13, and the back electrode 11 is provided on the light emitting layer 14. That is, the light emitting layer 14 is configured to be sandwiched between the transparent electrode 12 and the back electrode 11.
[0010]
Although not shown, the transparent electrode 12 and the back electrode 11 are patterned in a grid shape orthogonal to each other. Then, in the case of general simple matrix driving, when an intersection of both electrodes 11 and 12 corresponding to a display image is selected and a voltage: V is applied, images such as characters and pictures are displayed. Has become.
The light emitting layer 14 differs depending on the form of the EL 100. In the case of an AC dispersion type EL, the phosphor powder is dispersed in an organic binder. In the case of an AC thin film EL, a phosphor is formed by vapor deposition or sputtering. Further, in the case of the organic EL, the electron transport layer and the hole transport layer are laminated.
[0011]
The transparent substrate 13 is provided on the side where the light image 5 emitted from the light emitting layer 14 of the EL 100 is viewed, and generally, transparent glass is used. However, when flexibility is given, a polyester film or the like is used. Plastics film is also used.
The transparent electrode 12 is provided on the substrate 13. The transparent electrode 12 is called a transparent conductive film, and uses In ₂ O ₃ , SnO _2, or the like. When fine patterning is required, the transparent electrode 12 is a solid solution of In ₂ O ₃ and SnO _2. ITO films are frequently used.
[0012]
The back electrode 11 also serves as a reflector for reflecting a light image displayed by the light emitting layer 14 of the EL 100, and an Al film having a high reflectance and a low specific resistance is often used. Generally, it is used as a vapor deposition film. However, when flexibility is required in a dispersion type, an Al foil is also used.
FIG. 4 is a schematic diagram showing the behavior of external light when the EL is viewed under daylight. When the form of the EL 100 is a dispersion type, the light emitting layer 14 in which the phosphor is dispersed has a thickness of several tens to several hundreds of micrometers, and the light emitting layer 14 is often opaque. However, when the EL 100 is of a thin film type, the thickness of the light emitting layer 14 is, for example, about 1 μm. In particular, when the EL 100 is an organic EL, the thickness of the light emitting layer 14 is, for example, several tens nm. The light emitting layer 14 becomes transparent at such a thickness.
[0013]
Therefore, when the EL 100 is used as a display device under daylight, particularly under strong light such as sunlight, external light 6 indicated by an arrow passes through the transparent electrode 12 from the transparent substrate 13 on the front side. Then, the light passes through the light emitting layer 14 and reaches the back electrode 11 also serving as a reflecting mirror, is reflected, and returns through the light emitting layer 14, the transparent electrode 12, and the transparent substrate 13.
Here, the optical image 5 and the external light 6 are illustrated in a separated positional relationship for easy understanding. However, it actually indicates that the external light 6 is incident on the same position, that is, the position where the light emitting layer 14 emits light.
[0014]
That is, the external light 6 enters the EL 100 and is reflected by the back electrode 11 and returns. Therefore, the light image 5 displayed by light emission in the light emitting layer 14 is reduced to the external light 6, and a decrease in contrast as viewed from the eyes 7 of the viewer is inevitable. Therefore, a proposal has been made to suppress the malfunction of the external light 6.
[0015]
[Problems to be solved by the invention]
FIG. 5 is a schematic diagram of an example of a measure for preventing reflection of external light incident on the EL. In this case, the EL 100 is assumed to be an organic EL, but in FIG. 5, a method in which a polarizing plate 2 and a quarter-wave plate 3 are arranged on the front surface of the EL 100 is proposed.
The external light 6 to be incident on the EL 100 becomes linearly polarized light by the polarizing plate 2, and becomes circularly polarized light having a phase advanced by 45 ° by the ４ wavelength plate 3 and enters the EL 100. After passing through the glass substrate, the transparent electrode, and the light emitting layer, the external light 6 is reflected by the back electrode 11, travels backward, and is emitted to the outside of the EL 100. Then, it becomes linearly polarized light advanced by 45 ° in the quarter-wave plate 3, and enters the polarizing plate 2 in the direction of the absorption axis orthogonal to the transmission axis of the polarizing plate 2.
[0016]
Therefore, the reflected light of the external light 6 is absorbed by the polarizing plate 2 and does not enter the eye 7 of the viewer of the EL 100. That is, it is intended that the external light 6 does not cause a problem that the light image 5 displayed by the EL 100 is thinned to lower the contrast.
However, in the light image 5 emitted by the EL 100, only linearly polarized light parallel to the transmission axis direction enters the viewer's eyes with the polarizing plate 2. For this reason, only about 45% of the light image 5 is observed as a whole together with the light absorption of the polarizing plate 2, and the light image 5 of the EL 100 is greatly reduced. That is, the measure for suppressing the unsatisfactory behavior of the external light 6 also diminishes the light image 5 itself emitted from the EL 100 and lowers the contrast.
[0017]
Therefore, the present invention provides a polarizing plate and a quarter-wave plate and a polarization separation / recombination film interposed therebetween, and repeatedly reflects a light image displayed and emitted by an active image display device such as an EL by forming an optical image. It is an object of the present invention to provide a contrast enhancement device for increasing the amount of light and increasing the contrast.
[0018]
[Means for Solving the Problems]
The above-mentioned problem is solved in claim 1 in that the polarizing plate and the polarizing plate are arranged on the front side of the active image display device having a back electrode also serving as a reflecting mirror on the back side, in order from the incident direction of external light. The problem is solved by a contrast enhancement device configured to have a multilayer structure of a four-wave plate and a polarization separation / recombination film.
[0019]
That is, in the present invention, a polarizing plate is used to reduce the contrast of a light-emitting display light image caused by external light reflected from the active image display device and emitted from the display device. In order to prevent the four-wavelength plate from absorbing or reflecting the essential light-emitting display light image and dimming it, the polarization separation / recombination film is stacked on the polarization plate and the quarter-wave plate. ing.
[0020]
The effect of the polarizing plate, the quarter-wave plate, and the polarization separation / recombination film is as follows. Among the display light images emitted from the EL light emitting layer, the display light image that has not passed through the polarization separation / recombination film is the back surface. The display light image reflected and returned by the electrode and not transmitted again through the polarization separation / recombination film is repeatedly reflected and returned by the back electrode a plurality of times, so that the integrated light amount of the display light image is increased.
[0021]
On the other hand, the display light image transmitted through the polarization separation / recombination film becomes linearly polarized light whose phase is advanced by 45 ° by a で wavelength plate, and transmits through the polarization plate.
The display light image emitted from the EL light-emitting layer as described above is transmitted through the polarizing plate sequentially and is emitted to the outside of the device while going back and forth between the back electrode a plurality of times by providing the polarization separation / recombination film. I will do it.
[0022]
As a result, while external light such as sunlight is dimmed by the polarizing plate and the quarter-wave plate, the dimming of the display light image can be suppressed by the interposition of the polarization separation and recombination film. Image contrast can be increased.
Then, in claim 2, the polarization separation and recombination film is configured to reflect the S wave of the incident light and transmit the P wave, thereby solving the problem of the contrast enhancement device according to the claim 1. .
[0023]
That is, in the polarization separation / recombination film, an electric vector of linearly polarized light having a phase advance of 45 ° passing through the polarizing plate and the １ ／ wavelength plate reflects an S wave perpendicular to the incident surface, and is parallel to the incident surface. The P wave is transmitted.
Therefore, of the display light image emitted from the EL light emitting layer, the S-polarized light component reflected by the polarization separation / recombination film is reflected by the back electrode, converted back into elliptically polarized light, and returned. The elliptically polarized P-polarized light component passes through the polarization separation / recombination film and is visually recognized as a display light image.
[0024]
On the other hand, the S-polarized component is reflected again by the polarization separation / recombination film, returns to the EL, is reflected by the back electrode, is converted into elliptically polarized light, returns to the polarization separation / recombination film again, and repeats the same phenomenon. Has become.
As a result, while external light such as sunlight is dimmed by the polarizing plate and the quarter-wave plate, the integrated light amount of the display light image is increased due to the polarization separation and recombination film, and the dimming is suppressed. The contrast of the display light image can be increased.
[0025]
Then, in claim 3, the problem is solved by the contrast enhancement device according to claim 1, wherein the active image display device is configured to be an EL.
There are PDPs and the like in the active image display device, but the effect of the present invention is exerted in EL. In other words, in an EL having a structure in which the light emitting layer is transparent and the back electrode also functions as a reflecting mirror, the incident external light passes through the EL, is reflected by the reflecting mirror, and transmits again in the EL in the opposite direction. As a result, the contrast of the display light image is degraded.
[0026]
On the other hand, in the present invention, the contrast is increased by effectively emitting the EL display light image by the interaction of the polarizing plate, the quarter-wave plate, and the polarization separation / recombination film. .
Then, in claim 4, the problem is solved by the contrast enhancement device according to claim 2, wherein the EL is an organic EL of a recombination emission type.
[0027]
In other words, in the present invention, the contrast is increased by suppressing the external light from being reflected back to the EL which is transparent and transmits the external light and transmits to the back electrode serving as a reflector. I have to.
As a result, in the present invention, a remarkable increase in contrast can be achieved in a recombination light-emitting organic EL in which external light enters the back electrode and is reflected because the light-emitting layer of the EL is transparent.
[0028]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 1 is a schematic sectional view showing an embodiment of the present invention, and FIG. 2 is a schematic enlarged perspective view of a polarization separation / recombination film.
In the figure, 1 is an active image display device, 2 is a polarizing plate, 3 is a 波長 wavelength plate, 4 is a polarization separation / recombination film, 5 is an optical image, 10 is a contrast enhancement device, 11 is a back electrode, and 51 is a back electrode. A first light image, 52 is a second light image, 53 is a third light image, 511, 512, 513 are display images, 41 is S polarized light, 42 is P polarized light, 411 is first S polarized light, 412 Is the second S-polarized light, 421 is the first P-polarized light, 422 is the second P-polarized light, and 423 is the third P-polarized light 423.
[0029]
1 and 2, the active image display device 1 has a structure in which the back electrode 11 also serves as a reflecting mirror made of an Al thin film or the like so that light emitted toward the back can be efficiently emitted. That is, the emitted light image 5 is integrated with the light emitted directly and the light reflected and emitted by the back electrode 11 also serving as a reflecting mirror, so that the amount of emitted light can be visually recognized with as little loss as possible.
[0030]
By the way, in the prior art, in order to prevent daylight such as sunlight from entering the active image display device 1 and reflecting on the back electrode 11 to lower the contrast of the optical image 5, the polarizing plate 2 is used. And the quarter-wave plate 3 are provided on the front surface of the active image display device 1. In addition, in the present invention, the polarization separation / recombination film 4 is interposed between the active image display device 1 and the 波長 wavelength plate 3.
[0031]
As shown in FIG. 2, the polarization separation / recombination film 4 reflects S-polarized light 41, which is linearly polarized light whose electric vector is perpendicular to the plane of incidence, of the light incident on the surface of the polarization separation / recombination film 4. The P-polarized light 42, which is linearly polarized light parallel to the incident surface, has a function of transmitting through the film. Here, a DBEF film manufactured by Sumitomo 3M Limited is used as a sample (claim 2).
[0032]
Returning to FIG. 1, the first light image 51 indicated by the solid line is emitted toward the polarization separation / recombination film 4, and the first P-polarized light 421 is transmitted through the polarization separation / recombination film 4, and The light passes through the wave plate 3 and the polarizing plate 2 and is visually observed as a display image 511.
On the other hand, of the first light image 51, the first S-polarized light 411 emitted toward the polarization separation / recombination film 4 is reflected by the polarization separation / recombination film 4 and returned, and is reflected again by the back electrode 11 to be an ellipse. The light is converted into polarized light and becomes a second light image 52 indicated by a dashed line.
[0033]
The second light image 52 is emitted toward the polarization separation / recombination film 4, and the second P-polarized light 422 transmits through the polarization separation / recombination film 4 and transmits through the １ ／ wavelength plate 3 and the polarization plate 2. The display image 512 is combined with the display image 511 and visually observed, and the light amount is integrated.
On the other hand, of the second light image 52, the second S-polarized light 412 emitted toward the polarization separation / recombination film 4 is reflected by the polarization separation / recombination film 4 and returns, and is reflected again by the back electrode 11 to form an ellipse. The light is converted into polarized light and becomes a third light image 53 indicated by a two-dot broken line.
[0034]
Similarly, the third light image 53 is emitted toward the polarization separation / recombination film 4, the third P-polarized light 423 is transmitted through the polarization separation / recombination film 4, and the Ｐ wavelength plate 3 and the polarizing plate 2 is transmitted to form a display image 513, which is combined with the display image 511 and the display image 512, is visually observed, and is integrated as a light amount.
In FIG. 1, each of the display images 511, 512, and 513 is schematically illustrated by being horizontally expanded and separated for easy understanding. However, considering that the display images 511, 512, and 513 each have a light-emitting layer with a thickness of at most 100 nm and a size of one pixel of about several tens of μm square, the first by the polarization separation / recombination film 4 is used. The repetition of the reflection of each of the light images 51, 52, and 53 may be visually regarded as being repeated within one pixel. This is why the display images 511, 512, and 513 are combined and visually observed.
[0035]
In this way, with only the polarizing plate 2 and the quarter-wave plate 3, more than half of the emitted light is reflected or absorbed and is dimmed, and the light image 5 itself is dimmed by the amount that the reflected light of external light is suppressed. However, by repeating the reflection by the polarization separation / recombination film 4, the light amount of the light image 5 can be greatly increased, and as a result, the contrast can be increased.
[0036]
Incidentally, when the increase of the light image 5 obtained by the two reflections by the polarization separation / recombination film 4 is actually measured, the visible light amount of the first light image 51 transmitted by the first P-polarized light indicated by the broken line is The visible light amount of the second light image 52 transmitted by the second P-polarized light indicated by the one-dot broken line is 20%, and the visible light amount of the third light image 53 transmitted by the third P-polarized light indicated by the two-dot broken line is 46%. The visible light amount was 10%.
[0037]
That is, it can be confirmed that the total amount of light of the light image 5 is increased by 76/46 = 1.65 times by introducing the polarization separation / recombination film 4, and as a result, the contrast can be increased correspondingly. Was.
By the way, PDPs, fluorescent display tubes (VFD), and the like have been put into practical use as active image display devices. However, in order for the back electrode to function as a reflecting mirror, it is an essential condition that the light emitting layer is transparent, and in the present invention, the EL has a more effective configuration (claim 3).
[0038]
That is, the opaque AC dispersion type EL of the light emitting layer in which the phosphor is dispersed in the binder cannot exert the effect, and the transparent AC thin film EL of the light emitting layer in which the phosphor is formed as a thin film can exert the effect. However, in order to obtain a further effect, an organic EL in which the thickness of the light emitting layer is thin and the material itself is transparent can exert the most effect.
Here, the repeated reflection of S-polarized light by the polarization separation / recombination film is schematically illustrated up to two times, but this number is not uniquely determined, and various modifications are possible.
[0039]
Although the polarizing plate, the quarter-wave plate, and the polarization separation / recombination film are separately illustrated in order to schematically understand the behavior of the optical image, each is a thin film, which is practical. Each has a close integral structure.
[0040]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to the contrast enhancement apparatus which becomes this invention, the polarizing plate and 1/4 wavelength plate arrange | positioned so that external light may be reduced and it may be visually recognized with good contrast with respect to an active image display apparatus, such as an organic EL. However, it is possible to prevent the emission light image of the EL itself from dimming.
[0041]
As a result, the present invention is directed to an increase in the contrast of an active image display device, such as an organic EL used for a display of a mobile phone which is frequently used in daylight, which is expected to be increasingly used in the future. Is a major contributor.
[Brief description of the drawings]
FIG. 1 is a schematic sectional view showing an embodiment of the present invention.
FIG. 2 is a schematic enlarged perspective view of a polarization separation / recombination film.
FIG. 3 is a schematic cross-sectional view illustrating a configuration of an EL.
FIG. 4 is a schematic diagram showing the behavior of external light when the EL is viewed under daylight.
FIG. 5 is a schematic view of an example of a measure for preventing reflection of external light incident on the EL.
[Explanation of symbols]
REFERENCE SIGNS LIST 1 active image display device 11 back electrode 2 polarizing plate 3 波長 wavelength plate 4 polarization separation / recombination film 41 S polarization 42 P polarization 411 first S polarization 412 second S polarization 421 first P polarization 422 2 P-polarized light 423 Third P-polarized light 5 Optical image 51 First optical image 52 Second optical image 53 Third optical image 511, 512, 513 Display image 10 Contrast increasing device

Claims (4)

Arranged on the front side of an active image display device having a back electrode also serving as a reflecting mirror on the back side,
A contrast enhancement device comprising a laminated structure of a polarizing plate, a quarter-wave plate, and a polarization separation / recombination film in order from the incident direction of external light. 2. The contrast enhancement device according to claim 1, wherein the polarization separation / recombination film reflects an S-wave of the incident light and transmits a P-wave. 2. The contrast enhancement device according to claim 1, wherein said active image display device is electroluminescence (EL). 4. The contrast enhancement device according to claim 3, wherein the EL is a recombination luminescence type organic EL.

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