JP2005283982A - Display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a display device having an organic EL panel with which display colors are effectively switched and to enhance display quality of the display device having the organic EL panel. <P>SOLUTION: A liquid crystal panel 104 is a guest-host type liquid crystal panel having a liquid crystal layer in which dichroic coloring matter is dissolved. When the liquid crystal panel 104 is at an OFF state, namely, an electric field is not impressed to the layer consisting of liquid crystal and the dichroic coloring matter, white light from the organic EL panel 101 is visually recognized as red light. When the liquid crystal panel 104 is at an ON state, namely, the electric field is impressed to the liquid crystal layer, the white light from the organic EL panel 101 is visually recognized as the white light. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a display device, and more particularly to a display device that changes a display color of an organic EL (Electro Luminescence) panel using a liquid crystal panel including a liquid crystal and a dichroic dye.

With the recent rapid technological development in the information and communication field, there is a great expectation for a flat display replacing CRT. In particular, organic EL (Electro Luminescence) displays are highly researched because they are excellent in terms of high-speed response, visibility, brightness, and the like. The original organic EL element structure has a two-layer structure of organic thin films, uses trisaluminum for the light emitting layer, emits green light when driven at a low voltage of 10 V or less, and has a luminance of 1000 cd / m ^2. It was.

  In recent researches, various stacked organic EL devices having about 1 to 10 organic layers sandwiched between a hole injection electrode and an electron injection electrode have been developed. With respect to organic EL materials, those using low molecules or those using polymers have been studied. As a method for producing an organic EL element, not only a method of forming a thin film of a low molecular compound by a vacuum deposition method, but also a method of forming a thin film of a polymer compound by a method such as spin coating, ink jet, die coating, flexographic printing, etc. A method for forming an element has been proposed.

  The organic EL element causes the organic EL element to emit light by current driving by applying a voltage between the hole injection electrode and the electron injection electrode sandwiching the organic thin film layer. As a driving method, active driving using a switching element for selecting an organic EL element constituting a pixel, or passive driving not using a switching element is known.

  As the organic EL display, there are known an organic EL display that performs display by monochromatic light emission, an area color display that displays partially different colors, or a display that performs full color display. The monochromatic organic EL display includes a monochromatic organic EL element. For example, an organic EL element that emits red, blue, green, or white light is known.

  On the other hand, the organic EL element that performs color display divides the display area into a plurality of areas, and displays an organic EL display that performs area color display that displays different colors in each area, and each pixel displays RGB colors. An organic EL display that performs color display is known. In order to display different colors of RGB at the pixel level, the organic layer of the organic EL element emits light in one of RGB colors, or an RGB color filter layer is formed in front of the organic EL element that performs white display What performs color display by doing so is known.

  It is known that a color image display device is configured using a guest-host type liquid crystal (see Patent Document 1). The display device disclosed in Patent Document 1 includes a backlight, a back polarizing plate, a back electrode substrate, a guest-host type liquid crystal layer configured by adding dye molecules to a liquid crystal material, a front electrode substrate, and a front polarizing plate 6 in this order. It has an arrayed configuration. A wavelength cut filter with a light wavelength region different from the light wavelength region emitted by the backlight is attached to the front surface of the liquid crystal display element, and the drive voltage waveform of the guest-host type liquid crystal layer is the n-line inverted drive voltage waveform And

  A liquid crystal having a guest-host type liquid crystal layer having the above-described structure, which has improved light resistance without deteriorating the display quality of the liquid crystal display element, and has a long life by using an AC drive voltage waveform as an n-line inversion drive voltage waveform. A display element can be provided.

JP 2001-033829 A

  As an application of a display device, there is a case in which a display with a specific color is performed in a normal display operation and the display color is switched in a predetermined case. In such a display device, it is an extremely important factor that display quality is excellent or that display color conversion is realized with a simple structure.

  Accordingly, one object of the present invention is to provide a display device having an organic EL panel that can effectively switch display colors. Another object of the present invention is to improve the display quality of a display device having an organic EL panel. Another object of the present invention is to realize display color switching and display quality improvement in a display device having an organic EL panel with an efficient configuration.

  A display device according to a first aspect of the present invention includes an organic EL panel having a display region for displaying information, a retardation plate disposed on the viewing side of the display region, and a viewing side of the retardation plate. And a liquid crystal panel that is disposed on the viewing side of the retardation plate and controls the color of transmitted light by applying an electric field to a layer containing liquid crystal and a dichroic dye. By having this configuration, it is possible to effectively switch the display color of light from the organic EL panel. Preferably, in the liquid crystal panel, the liquid crystal when there is no electric field is substantially twisted by 90 ° between the substrates. Or it is preferable from the point of display quality that the angle between the transmission axis of the said polarizing plate and the orientation axis | shaft of the liquid crystal in the side facing the said polarizing plate of the said liquid crystal panel is substantially parallel.

  The retardation plate is preferably a λ / 4 plate. Furthermore, it is preferable that the polarizing plate is disposed on the non-viewing side of the liquid crystal panel, and an angle between the stretching axis of the retardation plate and the transmission axis of the polarizing plate is substantially 45 °. Thereby, it is possible to effectively suppress the reflected light from the organic EL panel from being visually recognized. Alternatively, it is preferable that the display area of the organic EL panel displays information with monochromatic light. Thereby, the effect of switching the display color by the liquid crystal panel containing the dichroic dye can be enhanced.

  According to the present invention, display colors can be effectively switched in a display device having an organic EL panel.

  Hereinafter, embodiments to which the present invention can be applied will be described. The following description is to describe the embodiment of the present invention, and the present invention is not limited to the following embodiment. For clarity of explanation, the following description and drawings are omitted and simplified as appropriate. Moreover, those skilled in the art can easily change, add, and convert each element of the following embodiments within the scope of the present invention.

  FIG. 1 is a cross-sectional view illustrating a schematic configuration of a display device 100 according to the present embodiment. In FIG. 1, 101 is an organic EL (Electro Luminescence) panel (OLED (Organic Light Emitting Diode)) capable of displaying information, 102 is a λ / 4 plate as an example of a phase difference plate, and 103 is a predetermined direction. A polarizing plate selectively transmits linearly polarized light that vibrates in the direction of 1. A liquid crystal panel 104 controls the color (wavelength) of transmitted light for switching display colors.

  The liquid crystal panel 104 is a guest / host type liquid crystal panel including a liquid crystal layer in which a predetermined dichroic dye is mixed with a liquid crystal material. In this embodiment, as a preferred example, the liquid crystal material is nematic liquid crystal, and is aligned so as to be in a twisted state of 90 ° when no electric field is applied. The liquid crystal panel 104 will be described later. In the display device 100, the liquid crystal panel 104, the polarizing plate 103, the λ / 4 plate 102, and the organic EL panel 101 are laminated in this order from the viewing side.

  The organic EL panel 101 typically performs display with monochromatic light. Preferably, an organic EL panel using an organic EL element that emits white light (including an organic light emitting layer and an anode and a cathode sandwiching the organic light emitting layer) is used. The organic EL panel 101 can display information such as images or characters by dot display or segment display. In the following description, this white light emitting organic EL panel will be described as an example. The organic EL panel can be passive or active.

  The liquid crystal panel 104 similarly controls the color (wavelength) of transmitted light over the entire display area. Specifically, one transparent electrode layer is formed over the entire display area on each of the two transparent substrates of the liquid crystal panel 104, and the liquid crystal layer is driven statically. In response to a signal from the outside, a similar electric field is applied to the liquid crystal layer in the entire display region by the transparent electrode pair.

  As described above, the liquid crystal panel 104 of the present embodiment includes a guest-host (GH) type liquid crystal having a liquid crystal layer in which a dichroic dye (guest) having different absorption in the molecular direction is dissolved in a liquid crystal material (host). It is a panel. In the guest-host type liquid crystal panel, when the alignment direction of liquid crystal molecules is changed by an electric field, the alignment of the dye changes according to the movement. Thereby, color control of transmitted light can be performed by applying voltage (electric field) (colorless) and applying no voltage (electric field) (coloring).

  In this embodiment, a liquid crystal panel in which a red dichroic dye is dissolved as a dichroic dye will be described below as an example. The liquid crystal material is a nematic liquid crystal like the TN mode liquid crystal panel, and is oriented so as to be twisted by 90 ° between the substrates when there is no electric field. When no electric field is applied between the substrates, the polarization direction of the linearly polarized light incident on the liquid crystal panel is rotated by 90 ° according to the twist of the liquid crystal material. Further, when passing through the liquid crystal panel, light having a predetermined wavelength is absorbed by the molecules of the dichroic dye, and only light having the predetermined wavelength is transmitted. In this example, an example in which red light is transmitted will be described.

  On the other hand, when an electric field is applied between the substrates, the liquid crystal molecules are arranged along the electric field direction, and the dichroic dye molecules are also arranged in the electric field direction accordingly. The light transmitted through the liquid crystal layer including the liquid crystal molecules and the dichroic dye molecules passes through the liquid crystal panel 104 without changing the polarization direction and without being substantially absorbed by the dichroic dye.

  FIG. 2 is a diagram for explaining the display operation of the display device 100. As shown in FIG. 2, white light from the organic EL panel 101 is displayed on the viewer side as white light or red light depending on the state of the liquid crystal panel 104. When the liquid crystal panel 104 is in an OFF state, that is, when an electric field is not applied to the liquid crystal layer that is a layer made of a liquid crystal and a dichroic dye, white light from the organic EL panel 101 is visually recognized as red light ( Red display state).

  On the other hand, when the liquid crystal panel 104 is in an ON state, that is, when an electric field is applied to the liquid crystal layer, white light from the organic EL panel 101 is visually recognized as white light (white display state). The display device 100 can be applied to, for example, an automobile instrument panel. For example, the display device 100 normally displays the speed and the like in white, and can change the display color to red in an emergency or the like.

  The optical operation of the display device 100 will be described. FIG. 3 shows the optical axis direction of the constituent elements of the display device 100. As shown in FIG. 3, the stretching axis of the λ / 4 plate 102 and the transmission axis of the polarizing plate 103 are preferably arranged at an angle of substantially 45 °. Thereby, the reflected light by the organic panel 101 can be effectively suppressed. It is preferable that the transmission axis of the polarizing plate 103 and the alignment axis direction on the surface of the liquid crystal panel 104 on the side close to the polarizing plate are substantially parallel.

  That is, the alignment axis direction (rubbing direction) of the back substrate 104a of the liquid crystal panel 104 is substantially parallel to the transmission axis of the polarizing plate 103. Thereby, vivid color display and color display conversion can be performed effectively. Further, as described above, the alignment axis direction (rubbing direction) of the front substrate 104b of the liquid crystal panel 104 is twisted by approximately 90 ° with respect to the alignment axis direction of the back substrate 104a. In addition, the above has shown one of the preferable relationship of the optical axis direction of each component, and the angle of each axis | shaft is not limited to this.

  With reference to FIG. 4, the display operation by the display device 100 will be described. In FIG. 4, the constituent elements such as the dichroic dye and the liquid crystal are schematically shown for explanation of the invention, and do not necessarily reflect the actual configuration accurately. FIG. 4A shows the display device 100 in which the liquid crystal panel 104 is in an OFF state. FIG. 4B shows the display device 100 in which the liquid crystal panel 104 is ON. The optical axis direction of each component in FIG. 4 is the same as the preferred example shown in FIG.

  As shown in FIG. 4A, when the liquid crystal panel 104 is in an OFF state, light having a predetermined wavelength among white light from the organic EL panel 101 is transmitted through the liquid crystal panel 104. In this example, red light is transmitted through the liquid crystal panel 104, and a display screen with a red display color is shown to the user. On the other hand, when the liquid crystal panel 104 is in an ON state, as shown in FIG. 4B, white light from the organic EL panel is transmitted through the liquid crystal panel 104, and a display screen with a white display color is displayed to the user. Indicated.

  First, the antireflection function by the polarizing plate 103 and the λ / 4 plate 102 will be described. When light enters the organic EL panel 101 from the viewing side, the incident light is reflected by a metal electrode or the like in the organic EL panel 101. This reflected light causes a decrease in the visibility of the display image or a decrease in contrast. For this reason, it is preferable to suppress the reflected light by the organic EL panel 101. Reflected light from the organic EL panel 101 can be blocked by the λ / 4 plate 102 disposed in front of the organic EL panel 101 and the polarizing plate 103 disposed in front of the λ / 4 plate 102.

  Of the light incident from the viewing side, only the linearly polarized light component parallel to the transmission axis direction of the polarizing plate 103 is transmitted through the polarizing plate 103. In the example of FIG. 4, only linearly polarized light in a direction parallel to the paper surface is transmitted through the polarizing plate 103, and the polarizing plate 103 does not transmit light of other components. The linearly polarized light transmitted through the polarizing plate 103 is converted into circularly polarized light by the λ / 4 plate 102 and enters the organic EL panel 101.

  The light reflected by the organic EL panel 101 enters the λ / 4 plate 102 again, and is converted from a circularly polarized state to a linearly polarized state. The polarization direction of this linearly polarized light is 90 ° shifted from the linearly polarized light incident on the λ / 4 plate 102 from the polarizing plate 103, and these are perpendicular to the paper surface. Since the polarization direction of the light converted into the linearly polarized light by the λ / 4 plate 102 is perpendicular to the transmission axis of the polarizing plate 103, the reflected light from the organic EL panel 101 does not pass through the polarizing plate 103, and the polarizing plate 103 To be absorbed. Thereby, the reflection of light by the organic EL panel can be effectively prevented.

  Next, a change in the state of white light from the organic EL panel 101 will be described. First, the state where the liquid crystal panel 104 is OFF will be described with reference to FIG. White light irradiated from the organic EL panel 101 passes through the λ / 4 plate 102 and enters the polarizing plate 103. The light of the linearly polarized light component that vibrates in the transmission axis direction of the polarizing plate 103 is selectively transmitted by the polarizing plate 103. In this example, linearly polarized light having a polarization direction parallel to the paper surface is transmitted through the polarizing plate 103.

  The linearly polarized light is transmitted through the back transparent substrate 104a of the liquid crystal panel 104, and the light in the predetermined wavelength region of the incident light is absorbed by the dichroic dye molecules contained in the liquid crystal layer, and the light in the predetermined wavelength region is selectively transmitted. To do. In this example, red light is transmitted. Red light is transmitted through the front transparent substrate 104b and displayed on the display surface.

  Next, the case where the liquid crystal panel 104 is in the ON state will be described with reference to FIG. When the liquid crystal panel 104 is set in the ON state and an electric field is applied to the liquid crystal layer, the major axes of the liquid crystal molecules are aligned in a direction parallel to the electric field (perpendicular to the substrate plane). Accordingly, the dichroic dye molecules are similarly arranged. Therefore, the incident light passes through the liquid crystal panel 104 without changing its polarization state and color. The blocking of the reflected light by the organic EL panel 101 is the same as when the liquid crystal panel 104 is in the OFF state.

  Specifically, white light irradiated from the organic EL panel 101 passes through the λ / 4 plate 102 and enters the polarizing plate 103. The light of the linearly polarized light component that vibrates in the transmission axis direction of the polarizing plate 103 is selectively transmitted by the polarizing plate 103. In this example, linearly polarized light having a polarization direction parallel to the paper surface is transmitted through the polarizing plate 103.

  The linearly polarized light is transmitted through the back transparent substrate 104a of the liquid crystal panel 104, and is further transmitted by the applied electric field through the liquid crystal layer in which liquid crystal molecules and dichroic dye molecules are arranged in a direction perpendicular to the substrate surface (parallel to the electric field). To do. The linearly polarized light passes through the liquid crystal layer without being absorbed by the dichroic dye molecules. White light is transmitted through the front transparent substrate 104b, and white display is visually recognized on the display surface.

  As described above, the polarizing plate 103 disposed between the organic EL panel 101 and the liquid crystal panel 104 contributes to the antireflection function of the organic EL panel 101 and the function of changing the display color of light from the organic EL panel. . By using a liquid crystal panel in which dichroic dye is dissolved in a liquid crystal material, a polarizing plate, and a λ / 4 plate, the display color can be switched by light from the organic EL panel and the display quality can be improved with few optical elements. Can be achieved.

  Note that the liquid crystal panel 104 can include a plurality of display segments by having the separated transparent electrodes. By performing different control for each segment, it is possible to more effectively perform display by changing the display color.

  In the configuration of the display device 100, the λ / 4 plate 102 and the polarizing plate 103 can be attached to either the organic EL panel 101 or the liquid crystal panel 104. For example, the display device 100 can be configured by attaching both the λ / 4 plate 102 and the polarizing plate 103 to the organic EL panel 101 and laminating the organic EL panel 101 and the liquid crystal panel 104. The relationship of the optical axes shown above is a preferable example, and the present invention is not limited to this.

  Alternatively, the display device 100 can be configured by attaching both the λ / 4 plate 102 and the polarizing plate 103 to the liquid crystal panel 104 and laminating the liquid crystal panel 104 and the organic EL panel 101. The polarizing plate 103 is preferably attached to the liquid crystal panel 104. Thus, the liquid crystal panel 104 can be effectively inspected at the manufacturing stage.

  Several display devices were evaluated. FIG. 5 shows an axial arrangement of each component in the evaluated display device. Each example will be described below with reference to FIG.

Example 1.
2% SI-426 (maximum absorption wavelength 525 nm) manufactured by Mitsui Chemicals, Inc. as a dichroic dye, and G-207 manufactured by Hayashibara Biochemical Research Laboratories, Inc. (Maximum absorption wavelength: 395 nm) was added at 0.5%, adjusted so that a good red color was displayed, and injected into a GAP = 9 μm liquid crystal panel with a left twist of 90 °. SR-W062AP manufactured by Sumitomo Chemical Co., Ltd. was used as the polarizing plate 103. As the λ / 4 plate 102, a λ / 4 plate of ΔnF · dF = 138 nm was used. The angle between the orientation axis on the non-viewing side (back side) of the liquid crystal panel and the transmission axis of the polarizing plate is substantially parallel, and the angle between the transmission axis of the polarizing plate and the stretching axis of the λ / 4 plate is substantially 45 °. Each element was arranged as follows. The stacking order of the components and the arrangement of the optical axes are the same as those shown in FIG.

  When the liquid crystal panel for switching the display color is driven by static driving at 10V with respect to the white luminescent color of the organic EL panel, as shown in the table below, the white luminescent color when ON and the good red image when OFF are displayed. Display was performed, and good display color switching was possible.

  In Table 1, “No LCD” means that there is no liquid crystal panel, “LCD-OFF” means that there is a liquid crystal panel, and “LCD-ON” means that the liquid crystal panel is in an OFF state. Is present and the liquid crystal panel is in the ON state. x and y indicate x and y coordinate values in the xy chromaticity coordinates, respectively. These points are the same in other tables below.

Example 2
2% of M-86 (maximum absorption wavelength: 550 nm) manufactured by Mitsui Chemicals, Inc. as a dichroic dye, and G-207 manufactured by Hayashibara Biochemical Lab. (Maximum absorption wavelength: 395 nm) was added at 0.5%, adjusted so that a good red color was displayed, and injected into a GAP = 9 μm liquid crystal panel with a left twist of 90 °. As the λ / 4 plate 102, a λ / 4 plate of ΔnF · dF = 138 nm was used. Other conditions are the same as in the first embodiment. As shown in the following table, an image was displayed with a white emission color at ON and a good blue color at OFF, and a good display color switching could be performed.

It is a disassembled perspective view which shows schematic structure of the display apparatus in this embodiment. It is a figure which shows the display operation of a display apparatus in this embodiment. It is a figure which shows the optical axis arrangement | positioning of the component of a display apparatus in this embodiment. It is a figure which shows the state change of the white light from the organic electroluminescent panel in the display operation of the display apparatus in this embodiment. It is a figure which shows the optical axis arrangement | positioning of the component in an Example.

Explanation of symbols

100 display device, 101 organic EL panel, 102 1 / 4λ plate,
103 polarizing plate, 104 liquid crystal panel, 104a rear transparent substrate,
104b Front transparent substrate

Claims (6)

An organic EL panel having a display area for displaying information;
A phase difference plate disposed on the viewing side of the display area;
A polarizing plate disposed on the viewing side of the retardation plate,
A liquid crystal panel that is arranged on the viewing side of the retardation plate and controls the color of transmitted light by applying an electric field to a layer containing liquid crystal and a dichroic dye;
A display device comprising:   The display device according to claim 1, wherein in the liquid crystal panel, the liquid crystal when there is no electric field is substantially twisted by 90 ° between the substrates.   The display device according to claim 1, wherein an angle between a transmission axis of the polarizing plate and a liquid crystal alignment axis on a side of the liquid crystal panel facing the polarizing plate is substantially parallel.   The display device according to claim 1, wherein the retardation plate is a λ / 4 plate. The polarizing plate is disposed on the non-viewing side of the liquid crystal panel,
The angle between the stretching axis of the retardation plate and the transmission axis of the polarizing plate is substantially 45 °.
The organic EL display device according to claim 1.   The display device according to claim 1, wherein the display area of the organic EL panel emits monochromatic light.

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