JP2011203640A - Reflective display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a reflective display device having a high contrast ratio, wherein white is displayed more whitely and black is displayed more blackly on a scattering display.SOLUTION: In the reflective display device where a scattering display 1 which transmits light from the outside to perform transmission display or scatters the light to perform scattering display and a reflective display 3 which reflects light from the outside to perform reflective display or absorbs the light to perform absorption display are disposed one over the other, the scattering display 1 includes a region (2) which can perform control to perform transmission display or scattering display, and the reflective display 3 includes a region (4) which can perform control to perform reflective display or absorption display, in a position corresponding to the controllable region of the scattering display 1.

Description

  The present invention relates to a display device that enables high-contrast display in a reflective display device that includes a display that displays in two states, a scattering state and a transmission state, and a reflector.

  In recent years, a display that uses a liquid crystal layer that changes between a scattering state and a transmission state, called a polymer dispersion type liquid crystal (PDLC) or a polymer network type liquid crystal (PNLC), as a polymer scattering type liquid crystal has been actively researched. Developed and commercialized. This type of display is often configured with a reflector on the back side of the display in order to achieve higher contrast. Such a display will be described below.

  In general, in a polymer scattering type liquid crystal display, opposing glass substrates, which are kept at a constant interval, are bonded with a sealing material, and a liquid crystal layer is sealed between the two glass substrates. There is a transparent electrode between the glass substrate and the liquid crystal layer, and this transparent electrode can apply an electric field to the liquid crystal layer. A portion where the electrode is applied to the transparent electrode to change the display is a so-called pixel. As the liquid crystal sealed in the liquid crystal layer, a material in which a polymer and a liquid crystal are mixed is used. PDLC has a drop-like liquid crystal in a polymer resin, and PNLC has a liquid crystal in a network-like polymer resin. Two states, a scattering state and a transmission state, appear in these liquid crystal layers depending on the presence or absence of an electric field. Further, a reflective plate such as a metal is placed on the back side of the polymer scattering type liquid crystal display, and external light can be reflected to recognize the display.

  In such a polymer-dispersed liquid crystal display, the refractive index in the major axis direction of the liquid crystal molecules in the liquid crystal layer and the refractive index of the polymer are adjusted to be approximately equal. In the PDLC display, an electric field is applied to the pixel. In this case, almost all of the liquid crystal molecules are aligned parallel to the electric field direction, and the refractive index of the liquid crystal molecules and the refractive index of the polymer are almost equal. Therefore, the light incident on the liquid crystal layer passes straight through to the lower reflector. A part of the light that has arrived and is reflected by the reflector returns to the incident side. I want to reduce this light as much as possible, but usually the reflector is made of metal etc., so light from some angles will not be reflected, but light from other angles will be reflected. Reflection specific to the metal surface occurs. Also, liquid crystal molecules are randomly oriented in a non-electric field where no voltage is applied to the pixels, and the refractive index of the liquid crystal and the refractive index of the surrounding polymer resin are different. Scattering occurs at the resin interface, displaying a white color.

  At this time, the scattering to the opposite side (forward scattering) is generally stronger than the scattering to the light incident side (back scattering). In general, in such a polymer scattering type liquid crystal display, in order to increase the contrast, a metal reflector is arranged on the back side of the liquid crystal panel, and the light rays scattered and emitted to the reflector are re-applied to the liquid crystal layer by the reflector. Returned, scattered again by the liquid crystal layer, and returned to the incident side. Therefore, if a reflector is placed on the back side of the panel, the backscattering and forward scattering eventually come to the incident light side, so that the scattered light intensity to the incident light side can be increased. In addition, since scattering does not have wavelength dependency, scattering at any wavelength is equivalent, so that the scattering state is recognized as white. On the other hand, the transmitted light is reflected by the reflecting plate, passes through the liquid crystal layer again, and returns to the incident side. In general, when the reflecting plate is made of metal, the reflection is a metallic color.

However, since the display contrast is indicated by the ratio between the transmission state and the scattering state display, when a reflector is disposed on the back side of the polymer scattering type liquid crystal display, the scattering state is white display and the transmission state is metal color display. Therefore, it is difficult to increase the contrast ratio, and it is difficult to improve the display quality. In order to increase the contrast, it is desirable to perform black display in the transmissive state. For this reason, conventionally, an absorption plate showing black or a reflection plate for controlling reflection characteristics has been provided on the entire back surface side of the polymer scattering display (see, for example, Patent Document 1).

JP2007-101643 (pages 12-13 and 15-16)

  However, in the prior art, since the absorption plate and the reflection plate are provided on the entire back surface side, the white color in the scattering state becomes dark and it is difficult to control the incident light, and a good contrast cannot be obtained. there were.

  In order to solve the above problems, the present invention adopts the following configuration. A reflective display that displays a transmissive display that transmits light from outside or a scatter display that scatters light, and a reflective display that reflects or absorbs light from the outside. In the display device, the scattering display has an area that can be controlled to perform transmission display or scattering display, and the reflection display is also controlled to perform reflection display or absorption display at a position corresponding to the area of the scattering display. It is characterized by having a possible area.

  In addition, the region where transmission display or scattering display of the scattering display can be controlled includes a plurality of pixels for scattering display to which a voltage can be applied, and reflection display or absorption display of the reflection display is performed. The controllable region also includes a plurality of reflective display pixels to which a voltage can be applied.

  When the controllable area of the scatter display performs transmissive display, the controllable area of the reflective display performs absorption display, and when the controllable area of the scatter display performs scatter display The controllable area of the reflective display performs reflective display. Further, the periphery of the controllable region of the scattering display is in a scatter display state, and the reflection display corresponding to the scatter display state is in a reflection display state. The scattering display is a polymer scattering liquid crystal display element. Alternatively, the reflective display is an electrophoretic display element.

  A reflective display that performs reflection display and absorption display is placed on the back side of the scattering display that performs two-state display of scattering display and transmission display. And when it is set as a scattering display with a scattering type display, the area | region corresponding to a reflection type display is set as a reflection display. By controlling in this way, the light passing through the scattering display is reflected by the corresponding area of the reflective display, returns to the scattering display, passes again through the scattering display, and exits to the incident side. Bright and white display can be implemented. In addition, when a certain area of the scattering display is transmissive display, the corresponding area of the reflective display is absorption display (black display). By controlling in this way, the light that has passed through the scattering display is absorbed by the corresponding region of the reflective display, and black display is possible.

As described above, the display state of the reflective display is changed in accordance with the display state of the scattering display, so that the white display can be displayed in white and the black display can be displayed in black, and the contrast ratio is improved. In addition, if electrodes are arranged in the control area to form pixels and control is possible for each pixel, even when the scattering display and transmission display of the polymer scattering display are changed, the reflection of the reflection display is accompanied accordingly. Since the display area and the absorption display area can also be changed, even when the display content is changed, a display with a high contrast can always be performed.

It is a schematic diagram of the reflective display apparatus of this invention. It is sectional drawing of the reflection type display apparatus of this invention. It is sectional drawing of the electrophoretic display element of a present Example. It is sectional drawing of the electrophoretic display element of a present Example.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic view showing a reflective display device according to an embodiment of the present invention. FIG. 2 is a cross-sectional view of the reflective display device of the present invention.

  The configuration of the reflective display device of the present invention will be described with reference to FIG. FIG. 1 is a schematic view showing a reflective display device of the present invention. As a scattering display capable of performing transmissive display or scattering display, a polymer scattering display 1 using polymer dispersed liquid crystal (PDLC) is provided on the upper side, and reflection display or absorption display is provided on the back side thereof. A reflective display 3 is arranged. In this embodiment, an electrophoretic display element is used for the reflective display 3. Although both are integrated and integrated, in FIG. 1, the polymer scattering display 1 and the reflection display 3 are illustrated in a shifted manner for easy understanding.

  The polymer scattering display 1 includes a region where transmissive display that transmits light from the outside or scattering display that scatters light can be performed. In this embodiment, seven scattering display pixels 2 capable of indicating numbers are arranged as areas where transmissive display or scattered scattering display can be performed, and voltage is applied to each scattering display pixel 2. By applying this, transmissive display or scatter display is performed.

  The reflection type display 3 also has seven reflection type display pixels 4 arranged at positions corresponding to the scattering type display pixels 2 of the polymer scattering type display 1, that is, substantially the same shape and substantially the same position. Yes. Reflection display or absorption display is performed by applying a voltage to each reflection display pixel 4.

  FIG. 2 is a cross-sectional view of the reflective display of this embodiment. The polymer scattering display 1 holds a pair of substrates (11, 12) with a sealant (16, 17) at an interval of about 10 μm, and a PDLC layer is sandwiched between the substrates as a liquid crystal layer 15. The PDLC layer is composed of a material in which a liquid crystal material and a monomer that is polymerized by photocrosslinking are mixed, and is produced by polymerizing the monomer by irradiating ultraviolet rays after sealing between the substrates. The PDLC layer is in a state where liquid crystal molecules are present in the form of droplets between the polymers.

On the liquid crystal layer side of both substrates (11, 12), electrodes formed of a transparent conductive film for applying a voltage are arranged. On the upper substrate 11, scattering type display pixels (13, 14) are arranged as electrodes. The lower substrate 12 has a counter electrode 18 disposed on the entire surface of the substrate. By applying a voltage to each of the scattering display pixels (13, 14), the liquid crystal layer 15 is changed to a transmission state or a scattering state, thereby enabling transmission display or scattering display of the pixel portion to be controlled. In FIG. 2, the area indicated by the hatched portion in the liquid crystal layer 15 indicates the scattering state 15 a, and the area without the hatching is the transmission state 15 b. In this embodiment, PDLC that changes from the scattering state 15a to the transmission state 15b by applying a voltage is used. When a 60 Hz rectangular wave is 0 V, the applied voltage indicates a scattering state. When the applied voltage is increased, the scattering state changes to the transmission state.

  A reflective display 3 is disposed on the back side of the polymer scattering display 1. In FIG. 2, the polymer scattering display 1 and the reflective display 3 are illustrated as being separated from each other, but they may be disposed in close contact with each other. In this embodiment, an electrophoretic display element is used as the reflective display 3. Here, an outline of the configuration and operation of the electrophoretic display element will be described below with reference to FIGS.

  FIG. 3 is an example of a cross section of the electrophoretic display element used in this example. The electrophoretic display element performs display by moving charged particles by electrophoresis. In the reflective display 3, a transparent common electrode (COM) made of an ITO (indium tin oxide) film is formed on the entire back surface of a transparent resin substrate 31, and a microcapsule display called electronic ink is formed thereon. A layer 33 is formed. A flexible printed circuit board (hereinafter abbreviated as FPC) 35 on which segment electrodes SEG are formed is adhered to the surface of the microcapsule display layer 33 as a reflective display pixel by an adhesive layer 34.

  In the microcapsule display layer 33, a large number of microcapsules 30 having a diameter of about several tens of μm are dispersed in a mixture of a binder, a surfactant, a thickener, pure water, and the like. That is, in the electrophoretic display element, a transparent resin substrate 31 and an FPC 35 are disposed as a pair of substrates, a common electrode COM is formed on one of the opposing surfaces, and a segment electrode SEG is formed on the other surface, A microcapsule 30 is enclosed.

  Next, the operation principle of the electrophoretic display element will be described with reference to FIG. In FIG. 4, a microcapsule 40 includes a white particle 43a made of titanium oxide or the like as a charged particle and a black particle 43b made of carbon black or the like as a charged particle inside a capsule shell 41 made of transparent methacrylic resin or the like. It is encapsulated in a state of being dispersed in a transparent dispersion medium 42 having a high density. The white particles 43a are negatively charged, and the black particles 43b are positively charged.

  Of the electrodes arranged so as to sandwich the microcapsule display layer 33, one of the entire common electrodes COM is grounded, and a negative voltage is applied to the segment electrode SEG on the other FPC 35. The negatively charged white particles 43a in the microcapsule 40 move to the transparent common electrode COM side, and the positively charged black particles 43b move to the segment electrode SEG side. Therefore, when viewed from the viewing side (direction of arrow A), Looks white. On the other hand, in the portion where a positive voltage is applied to the segment electrode SEG, the positively charged black particles 43b in the microcapsule 40 by the opposite electric field are transferred to the transparent common electrode COM side, and the negatively charged white particles 43a are segmented. Since it moves to the electrode SEG side, it looks black when viewed from the viewing side.

  Further, as in the central microcapsule 40 in FIG. 4, in the microcapsule 40 at a position straddling the segment electrode SEG to which the negative voltage is applied and the segment electrode SEG to which the positive voltage is applied, one of the white particles 43 a. The portion moves to the common electrode COM side, the rest moves to the segment electrode SEG side, a part of the black particles 43b moves to the segment electrode SEG side, and the rest moves to the common electrode COM side. However, detailed display is also possible.

Therefore, the electrophoretic display element can perform reflection display that is white display or absorption display that is black display, depending on the polarity of the voltage applied between the common electrode COM and the segment electrode SEG. At this time, the white particles 43a and the black particles 43b move in the dispersion medium 42 by electrophoresis. However, since the dispersion medium 42 has a high viscosity, the display state is changed by applying a voltage, and then the application of the voltage is stopped. Even so, the intermolecular force of each particle can provide a memory effect that maintains its display state. Thus, the electrophoretic display element is characterized in that the power consumption is extremely low because the drive voltage only needs to be applied when the display is changed.

  Such an electrophoretic display element is disposed on the back surface of the polymer scattering display as the reflective display 3 as shown in FIG. In FIG. 2, the reflective display 3 is illustrated in a simplified manner. As shown in FIG. 2, the polymer scattering display 1 includes so-called segment pattern scattering display pixels (13, 14), and the reflective display 3 is also a scattering display pixel (13, 14). A segment electrode SEG is disposed as a reflective display pixel at a corresponding position.

  When a voltage is applied to the scattering display pixel 14, the liquid crystal layer 15 is in the transmissive state 15b. In such a case, a voltage is applied to the segment electrode SEG in the reflective display pixel at the corresponding position to perform the absorption display of the black display 33b. At this time, since the scattering display pixel 14 is in the transmission state 15b, the external light L1 passes through the polymer scattering display and is absorbed by the black display 33b of the reflection display. The display is recognized.

  If no voltage is applied to the scattering display pixel 13, the liquid crystal layer 15 is in the scattering state 15a. In such a case, a voltage is applied to the segment electrode SEG at the corresponding position, and the white display 33a is reflected. At that time, since the scattering display pixel 13 is in the scattering state 15a, the outside light L2 is repeatedly scattered in the liquid crystal layer, and the outside light L2 emitted from the polymer scattering display 1 to the back side is Since the light is reflected by the white display 33a of the reflective display and again scattered by the polymer scattering display 1, the white display is recognized from the viewing side.

  In addition, since no electrode is formed in the peripheral region of the scattering display pixels (13, 14) of the polymer scattering display, an electric signal is not applied to the liquid crystal layer 15. Therefore, it is always in the scattering state 15a. A voltage is applied to the segment electrode SEG at a position corresponding to the peripheral region of the scattering display pixel (13, 14) so that the white display 33a is reflected. At that time, since the polymer scattering display is in the scattering state 15a, the external light L2 passes through the liquid crystal layer 15 while being scattered, and the light emitted to the reflective display 3 side is also reflected by the white display 33a. Since the light passes through the liquid crystal layer 15 in the scattering state 15a of the polymer scattering display and returns to the viewing side, white viewing can be recognized on the viewing side.

  Therefore, the black display is recognized in the region where the transmissive display is performed on the polymer scattering display 1, and the white display is recognized in the region where the scatter display is performed on the polymer scattering display 1, and the reflection type of this embodiment. The display device was able to perform display with very high contrast. In particular, in the polymer scattering display 1, even if the scattering display pixel (13, 14) is arbitrarily changed in the scattering state and the transmission state, the reflective display pixel of the reflective display 3 follows the change. Since white display and black display can be changed, high contrast can be maintained even if the display state changes.

  As described above, in this embodiment, seven segment patterns are employed as the scattering display pixels of the polymer scattering display, but a matrix pixel arrangement may be employed. In that case, it is desirable that the reflective display pixels of the reflective display are also arranged in a matrix type correspondingly.

In this embodiment, PDLC is adopted as the polymer scattering display. However, any display such as a display using PNLC may be used as long as the display performs scattering display and transmission display. Similarly, the case where an electrophoretic display element is used as a reflective display has been described. However, the present invention is not particularly limited to this, and any display can be used as long as it can selectively change the areas of reflective display and absorption display. A reflective display may be used.

DESCRIPTION OF SYMBOLS 1 Polymer scattering display 2, 13, 14 Scattering display pixel 3 Reflective display 4 Reflecting display pixel 11 Upper substrate 12 Lower substrate 13, 14 Scattering display pixel 15 Liquid crystal layer 16, 17 Sealing material 15a Scattering State 15b Transmission state 31 Resin substrate 33 Microcapsule display layer 34 Adhesive layer 30, 40 Microcapsule 35 FPC
41 Capsule shell 43a White particles 43b Black particles

Claims (6)

A reflective display that displays a transmissive display that transmits light from outside or a scatter display that scatters light, and a reflective display that reflects or absorbs light from the outside. In the display device,
The scatter display includes an area that can be controlled to perform the transmissive display or the scatter display, and the reflective display also has the reflective display or the position corresponding to the controllable area of the scatter display. A reflective display device comprising a controllable region capable of performing the absorption display.   The region where the transmission display or the scattering display of the scattering display can be controlled includes a plurality of scattering display pixels to which a voltage can be applied, and the reflection display or the absorption of the reflection display. The reflective display device according to claim 1, wherein the display controllable region also includes a plurality of reflective display pixels to which a voltage can be applied.   When the controllable area of the scattering display performs transmission display, the controllable area of the reflection display performs absorption display, and the controllable area of the scattering display is scattered. The reflective display device according to claim 1, wherein when the display is performed, the controllable region of the reflective display performs a reflective display.   The periphery of the controllable region of the scatter display is in a scatter display state, and the reflection display corresponding to the scatter display state is in a reflection display state. 4. The reflective display device according to any one of 3 above.   The reflective display device according to claim 1, wherein the scattering display is a polymer scattering liquid crystal display element.   The reflective display device according to claim 1, wherein the reflective display is an electrophoretic display element.

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