JP4122555B2 - Reflective display device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a reflective display device that performs display using external light such as natural light. More specifically, the present invention relates to an illumination structure of a reflective display device that is used as an auxiliary when external light is scarce.
[0002]
[Prior art]
A display device using liquid crystal or the like as an electro-optical material has a flat panel shape, and is characterized by being thin and light and low power consumption. Utilizing such characteristics, flat panel display devices are suitable for displays of portable information devices and the like, and are being actively developed. The liquid crystal used as the electro-optical material is not a self-luminous type, and it projects an image by transmitting and blocking light incident from the outside according to the voltage. For this reason, some kind of illumination structure is required, and it is roughly divided into a transmission type using a back light source and a reflection type using natural light.
[0003]
[Problems to be solved by the invention]
In a transmissive display device, a flat panel that holds liquid crystal as an electro-optical material is created between a pair of transparent substrates, and an illumination light source (backlight) is arranged on the back side, while images are displayed from the front of the panel. Observe. In the case of the transmission type, a backlight is essential, and for example, a cold cathode tube is used. For this reason, since the backlight consumes most of the power when viewed as a whole display, it is not suitable for a display of a portable device. On the other hand, in the reflection type display device, a reflection plate is disposed on the back surface of the panel, and external light such as natural light is incident from the front surface, and an image is observed from the front surface using the reflected light. Unlike the transmissive type, a light source for back lighting is not used, so the reflective type requires relatively low power consumption and is suitable for a display of a portable device. However, the reflective display device cannot observe an image in an environment with poor outside light such as at night, which is a problem to be solved.
[0004]
[Means for solving the problems]
In order to solve the above-mentioned problems of the prior art, the following measures were taken. That is, the reflective display device according to the present invention includes a panel, a light guide plate, and a light source as a basic configuration. The panel includes a transparent first substrate positioned on the incident side of external light, a second substrate positioned on the reflective side bonded to the first substrate via a predetermined gap, an electro-optic material held in the gap, and An electrode is formed on at least one of the first substrate and the second substrate and applies a voltage to the electro-optic material. The light guide plate is made of a transparent material and disposed outside the first substrate. A light source is disposed at the end of the light guide plate and generates illumination light as necessary. As a characteristic matter, the light guide plate normally transmits external light, enters the first substrate, and emits external light reflected from the second substrate, while guiding illumination light as necessary to transmit the first light. Illumination light incident on one substrate and reflected from the second substrate is emitted. As a further feature, the light guide plate has a base part divided into strips and a groove part located between the base parts. The base portion constitutes an emission plane, while the groove portion constitutes a reflective side surface and a re-incident side surface. The reflecting side surface partially reflects the illumination light guided from the light source and enters the first substrate. The re-incident side surface re-enters the remaining portion of the illumination light transmitted through the reflective side surface into the light guide plate. The emission plane emits illumination light reflected from the second substrate.
[0005]
Preferably, the groove has a bottom surface located between the reflecting side surface and the re-incident side surface facing each other. Further preferably, the emission plane, so as not substantially change the display appearance viewed from the front of the panel, the inclination angle with respect to the panel that is set smaller. Also preferably, the re-incident side has a large inclination angle than the reflection side facing the illumination light passes through the reflection side is re-incident on the light guide plate, the front planar portion of the re-incident illumination light the light guide plate And totally reflected on the back. Preferably, the light guide plate and the first substrate are joined to each other through a transparent intervening layer. The refractive index of the intervening layer is set appropriately, and the illumination light is totally reflected on the back surface, which is the interface between the light guide plate and the first substrate.
[0006]
According to the present invention, the light guide plate is disposed on the surface of the reflective panel, and the light source is disposed at the end thereof. In a dark environment, the light source is turned on, and illumination light is incident on the panel side through the light guide plate to project an image. In a bright environment, the light source is turned off and images are projected directly using outside light through a transparent light guide plate. The light guide plate is basically transparent and does not hinder any image observation even in a bright environment. Thus, according to the present invention, the light source only needs to be turned on when necessary, and the power consumption of the entire display can be greatly reduced, which is suitable for a display of a portable device. In addition to the basic functions described above, the present invention has been devised in particular to make the illumination of the light guide plate uniform and efficient. That is, the light guide plate has a base portion divided into strips and a groove portion positioned between the base portions. The base portion constitutes an emission plane, while the groove portion constitutes a reflection side surface and a re-incident side surface. Thereby, the illumination light incident on the light guide plate from the light source can be efficiently guided farther in the horizontal direction, and uniform illumination is realized.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic partial sectional view showing an embodiment of a reflective display device according to the present invention. As shown in the figure, the reflective display device includes a panel 0, a light guide plate 20, and a light source 30 as a basic configuration. The panel 0 is held in the gap between the transparent first substrate 1 located on the incident side of the external light, the second substrate 2 located on the reflection side and bonded to the first substrate 1 via a predetermined gap. The electro-optical material and electrodes 10 and 11 formed on each of the first substrate 1 and the second substrate 2 for applying a voltage to the electro-optical material are provided. Depending on the driving method, an electrode may be formed on at least one of the substrates 1 and 2. The light guide plate 20 is made of an injection molded product of a transparent material such as acrylic resin, and is disposed outside the first substrate 1 via the polarizing plate 40. The light source 30 is disposed at the end of the light guide plate 20 and generates illumination light as necessary. The light source 30 is formed of a cold cathode tube, for example, and is called a so-called edge light. In order to improve the illumination efficiency of the edge light, a reflecting mirror 31 is disposed after the cylindrical light source 30. In such a configuration, the light guide plate 20 normally transmits external light, enters the first substrate 1 through the polarizing plate 40, and emits external light reflected from the second substrate 2, while guiding illumination light as necessary. The illumination light is incident on the first substrate 1 through the polarizing plate 40 and is reflected from the second substrate 2.
[0008]
The light guide plate 20 has a base part 22 divided into strips and a groove part 21 located between the base parts. The pedestal portion 22 constitutes an emission plane 220, while the groove portion 21 constitutes a reflection side surface 211 and a re-incident side surface 212. The reflection side surface 211 partially reflects the illumination light guided from the light source 30 and enters the panel 0. The re-incident side surface 212 re-enters the remaining portion of the illumination light transmitted through the reflective side surface 211 into the light guide plate 20. The emission plane 220 emits illumination light reflected from the panel 0. In this embodiment, each groove portion 21 has a substantially V shape, and a bottom surface 213 is interposed between the reflective side surface 211 and the re-incident side surface 212 facing each other. The bottom surface 213 is provided for facilitating the processing of the groove portion 21 and is not necessarily an essential component. The exit plane 220 is set to have a small inclination angle with respect to the panel 0 so that the display appearance viewed from the front of the panel 0 is not substantially changed. For example, the inclination angle is about 2 ° with respect to the horizontal plane. The reflective side surface 211 can totally reflect the illumination light guided from the light source 30 by being inclined toward the light source 30 with respect to the normal line of the panel 0 and can totally reflect most of the illumination light reflected from the panel 0 to the light source 30. The tilt angle is set. For example, the inclination angle of the reflective side surface 211 is set to 58 °. If it does in this way, when illumination light injects into the panel 0, it will incline a little in the direction of the light source 30. FIG. When the illumination light is reflected from the panel 0 and reaches the reflection side surface 211 again, most of the illumination light is totally reflected and is not emitted to the observer. As a result, an image is projected only with the illumination light emitted from the emission plane 220, and double transfer is eliminated. The return illumination light totally reflected by the reflection side surface 211 is reflected again by the reflecting mirror 31 and used as illumination light. On the other hand, the re-incidence side surface 212 has a larger inclination angle than the reflective side surface 211 facing it, and is substantially vertical. Most of the illumination light that has passed through the reflection side surface 211 and reentered the re-incidence side surface 212 is totally reflected in the light guide plate 20 and guided in the horizontal direction. For example, the illumination light re-entered perpendicularly to the re-incident side surface 212 has a tilt angle of 68 ° with respect to the bottom surface of the light guide plate 20 and is totally reflected. At this time, the light guide plate 20 and the polarizing plate 40 are joined to each other via a transparent intervening layer, and the refractive index of the intervening layer is set appropriately to totally reflect the illumination light at the interface between the light guide plate 20 and the polarizing plate 40. Is possible. For example, when the refractive index of the light guide plate 20 is 1.49, the illumination light incident at an inclination angle of 68 ° with respect to the interface is sufficiently totally reflected by providing an intervening layer having a refractive index of 1.42. Can do.
[0009]
The panel 0 uses a liquid crystal layer 3 mainly composed of nematic liquid crystal molecules 4 having positive dielectric anisotropy as an electro-optical material. However, the present invention is not limited to liquid crystals, and other materials can be used as the electro-optical material. The panel 0 further includes a light reflecting layer 8. The light reflecting layer 8 is located on the second substrate 2 side and scatters and reflects external light. The liquid crystal layer 3 is homogeneously aligned by the upper and lower alignment films 6 and 7. As a result, the liquid crystal layer 3 exhibits uniaxial optical anisotropy. By appropriately setting the thickness of the liquid crystal layer 3, the liquid crystal layer 3 is caused to function as a quarter-wave plate. The optical anisotropic axis (optical axis) of the quarter-wave plate is set to form an angle of 45 ° with the polarization axis of the polarizing plate 40. In the gap between the two substrates 1 and 2, a light reflecting layer 8 is provided on the second substrate 2 side. Electrodes 10 and 11 for applying a voltage to the liquid crystal layer 3 are formed on the first substrate 1 side and the second substrate 2 side, respectively.
[0010]
The light reflecting layer 8 has irregularities on the surface and has light scattering properties. Therefore, it has a paper white appearance and is not only preferable as a display background, but also reflects incident light in a relatively wide angle range, so that the viewing angle is enlarged and the display becomes easy to see and the display brightness is increased in a wide viewing angle range. A transparent flattening layer 12 that fills the unevenness is interposed between the light reflecting layer 8 and the alignment film 7. The light reflecting layer 8 is composed of a resin film 15 with unevenness and a metal film 16 such as aluminum formed on the surface thereof. The resin film 15 is a photosensitive resin film having irregularities patterned by photolithography.
[0011]
The photosensitive resin film 15 formed on the surface of the second substrate 2 is made of, for example, a photoresist and is applied to the entire surface of the substrate. This is exposed through a predetermined mask and patterned, for example, in a cylindrical shape. Next, when the substrate is heated and reflowed, the uneven shape can be stably formed. A metal film 16 such as aluminum having a desired film thickness and good light reflectance is formed on the uneven surface thus formed. If the depth dimension of the unevenness is set to several μm, good light scattering characteristics can be obtained, and the light reflecting layer 8 exhibits white. A planarizing layer 12 is formed on the surface of the light reflecting layer 8 to fill the unevenness. The planarizing layer 12 is preferably made of a transparent organic material such as an acrylic resin. By interposing the planarizing layer 12, the alignment film 7 can be formed and rubbed stably. The liquid crystal layer 3 is homogeneously aligned (horizontal alignment) by the alignment film 7 formed on the second substrate 2 side and the alignment film 6 formed on the first substrate 1 side. Instead of this, the liquid crystal layer 3 may be homeotropically aligned (vertical alignment). In this case, nematic liquid crystal molecules 4 having negative dielectric anisotropy are used.
[0012]
Next, the operation when performing monochrome display using this reflective display device will be briefly described. In the case of performing color display, a micro color filter may be formed on the first substrate 1 or the second substrate 2. In a voltage non-application state (off state), the nematic liquid crystal molecules 4 are aligned horizontally, and the liquid crystal layer 3 functions as a quarter-wave plate. Illumination light emitted from the light source 30 enters the polarizing plate 40 through the light guide plate 20. The illumination light that has passed through the polarizing plate 40 becomes linearly polarized light. The linearly polarized light becomes circularly polarized light while passing through the liquid crystal layer 3. The circularly polarized light is reflected by the light reflecting layer 8 and then passes through the liquid crystal layer 3 again. At this time, circularly polarized light is converted into linearly polarized light. However, the polarization axis of the reflected linearly polarized light is rotated by 90 ° from the polarization axis of the incident linearly polarized light. As a result, the reflected linearly polarized light is orthogonal to the transmission axis (polarization axis) of the polarizing plate 40 and is all absorbed. As a result, almost complete black display is obtained. On the other hand, when a voltage is applied (on), the nematic liquid crystal molecules 4 are aligned vertically along the electric field direction, and the liquid crystal layer 3 loses its function as a quarter-wave plate. As a result, the linearly polarized light (illumination light) that has passed through the polarizing plate 40 is not subjected to any modulation as it is, is reflected by the light reflecting layer 8, and passes again through the liquid crystal layer 3 toward the polarizing plate 40. Since the polarization axis of the linearly polarized light is not rotated at all, it passes through the polarizing plate 40 as it is and reaches the observer. Therefore, a white display is obtained.
[0013]
FIG. 2 shows a use state of the reflective display device shown in FIG. 1 in a bright environment. In a bright environment, there is sufficient external light such as natural light, and this is used for display. Accordingly, the light source 30 is turned off. Thereby, the power consumption of the whole display can be reduced. The light guide plate 20 transmits the external light incident from the viewer side as it is, enters the first substrate 1, and emits the external light reflected from the second substrate 2 from the base portion 22. The light guide plate 20 is basically transparent and does not become an obstacle to observing the display. In particular, the exit plane 220 constituted by the pedestal 22 is set to have an extremely small inclination angle with respect to the panel 0 so as not to substantially change the display appearance as viewed from the front of the panel 0, and is substantially close to the horizontal plane.
[0014]
FIG. 3 is a schematic cross-sectional view showing a reference example of a light guide plate used in a reflective display device. The light guide plate 20a according to this reference example includes a flat portion 22a divided into strips and a slope portion 21a positioned between the flat portions. The inclination angle of the flat surface portion 22a is about 1.5 °, and the inclination angle of the inclined surface portion 21a is about 45 °. In this way, when the light guide plate 20a composed of the inclined surface portion 21a having an inclination angle of 45 ° and the almost horizontal flat surface portion 22a is used, a phenomenon is observed in which the brightness is greatly reduced as the distance from the light source is increased. On the other hand, when the light guide plate 20 shown in FIG. 1 is used, the illumination light emitted from the light source can be uniformly guided farther. In the reference example shown in FIG. 3, numbers (1), (2), and (3) are assigned to the slope portions 21a in the order from the light source. The component L1 of the illumination light L emitted from the light source having a small internal incident angle (close to the horizontal) is totally reflected by the first slope portion {circle around (1)} and guided to the panel side. The illumination light component L2 having a slightly larger incident angle is totally reflected at the next inclined surface (2) and guided to the panel. Further, the illumination light component L3 having a larger incident angle is totally reflected by the inclined surface portion (3). However, since the illumination light component L3 has a large incident angle, a part of the illumination light component L3 is kicked at the base of the second slope portion (2), so that the total amount of reflected light is small. That is, the illumination light reaching the slope portion 21a having an inclination angle of 45 ° is blocked at the base portion of the previous slope portion 21a as it moves away from the light source, so that the amount of light actually reaching the slope portion 21a decreases. Therefore, the brightness of the light guide plate decreases as the distance from the light source increases.
[0015]
In contrast, FIG. 4 shows a specific configuration example of the light guide plate 20 made according to the present invention. As shown in the figure, the light guide plate 20 has a base portion divided into strips and a groove portion located between the base portions. The base portion constitutes the emission plane 220, while the groove portion constitutes the reflective side surface 211 and the re-incident side surface 212. A bottom surface 213 is positioned between the reflective side surface 211 and the re-incident side surface 212 facing each other. In this example, the width dimension of the emission plane 220 located between adjacent grooves is set to 201 μm. The inclination angle of the reflective side surface 211 is set to 58 °. The re-incident side surface 212 is a substantially vertical wall, and its height dimension is set to 8.2 μm. The width dimension of the bottom surface 213 is 2 μm. The width dimension of the reflective side surface 211 is 6 μm.
[0016]
FIG. 5 is a schematic diagram for explaining the method of use and operation of the light guide plate shown in FIG. As shown in the figure, the light guide plate 20 is joined to the panel 0 via the intervening layer 50. A light source 30 is disposed on the end surface of the light guide plate 20 and supplies the illumination light L to the light guide plate 20. The light source 30 is partially covered with a reflecting mirror 31. The illumination light that has reached the reflecting side surface 211 is totally reflected at the component L1 having a large incident angle and is led to the panel 0 as illumination light L3. The illumination light L3 is inclined with respect to the normal line of the panel 0 toward the light source 30. When the illumination light L3 is reflected by the panel 0 and reaches the emission plane 220, the illumination light L3 reaches the observer with almost no influence. However, when a part of the light reflected from the panel 0 reaches the reflection side surface 211, the incident angle is large, so that the light is totally reflected and does not go to the observer, and a double image does not occur. On the other hand, the component L2 of the illumination light emitted from the light source 30 having a relatively small incident angle passes through the reflective side surface 211 and enters the re-incident side surface 212. Here, the light is refracted and travels through the light guide plate 20. When this illumination light L4 reaches the intervening layer 50 located at the interface between the light guide plate 20 and the panel 0, it is totally reflected and further proceeds toward the surface of the light guide plate 20. The component L4 that has reached the emission plane 220 is totally reflected here and further guided to the back of the light guide plate 20. On the other hand, when L4 hits the reflective side surface 211 in the path leading to the back of the light guide plate 20, a component having a relatively large incident angle is totally reflected and guided to the liquid crystal panel 0 as illumination light L5. In this way, the illumination light emitted from the light source 30 is guided farther in the horizontal direction while repeating total reflection on the back surface and the front surface of the light guide plate 20, so that the panel 0 can be illuminated uniformly over a wide range.
[0017]
FIG. 6 is a reference diagram schematically showing the operation of the reflective display device shown in FIG. As shown in the figure, the present reflective display device is equivalent to a laminate of a polarizing plate 40, a first substrate 1, an electrode 10, a liquid crystal layer 3, an electrode 11, a light reflecting layer 8, and a second substrate 2 in order from the top. . In FIG. 6, the left half represents a voltage application state (on state) and is displayed in white. The right half represents a state in which no voltage is applied (off state) and is displayed in black. In the off state, the nematic liquid crystal molecules 4 included in the liquid crystal layer 3 are horizontally aligned, and the liquid crystal layer 3 functions as a quarter-wave plate. The optical axis of the quarter-wave plate forms an angle of 45 ° with the polarization axis of the polarizing plate 40. Therefore, the incident linearly polarized light that has passed through the polarizing plate 40 becomes circularly polarized light in the liquid crystal layer 3, is reflected by the light reflecting layer 8, and passes through the liquid crystal layer 3 again. At this time, circularly polarized light is converted into outgoing linearly polarized light. However, the polarization directions of the incident linearly polarized light and the outgoing linearly polarized light are orthogonal to each other. Accordingly, since the output linearly polarized light is absorbed by the polarizing plate 40, black display is obtained. On the other hand, in the ON state, the nematic liquid crystal molecules 4 shift from horizontal alignment to vertical alignment, and the function of the liquid crystal layer 3 as a quarter-wave plate disappears. Therefore, the incident linearly polarized light is reflected as it is without changing the polarization direction and passes through the polarizing plate 40. Accordingly, white display is performed. The above-described embodiment is a display mode using the birefringence of one polarizing plate 40 and the liquid crystal layer 3, but the present invention is not limited to this, and a twisted nematic mode, a guest host mode, or the like is used. May be.
[0018]
【The invention's effect】
As described above, according to the present invention, the light guide plate is disposed on the reflective panel, and the light source for auxiliary illumination is disposed at the end of the light guide plate. The light guide plate normally transmits external light, enters the panel and emits external light reflected from the panel, while guiding the illumination light as necessary, enters the panel, and emits illumination light reflected from the panel . In a dark environment, the light source is turned on so that an image can be observed even with a reflective panel. On the other hand, in a bright environment with abundant outside light, the light source is turned off to save power. The light guide plate has a base portion divided into strips and a groove portion positioned between the base portions. The base portion constitutes an emission plane, while the groove portion constitutes a reflection side surface and a re-incident side surface. With such a configuration, the illumination light traveling in the light guide plate reaches farther while being totally reflected, so that uniform illumination over a wide range is possible.
[Brief description of the drawings]
FIG. 1 is a schematic partial cross-sectional view showing an embodiment of a reflective display device according to the present invention, showing a use state in a dark environment.
FIG. 2 is a schematic partial cross-sectional view showing a use state of a reflective display device according to an embodiment of the present invention in a bright environment.
FIG. 3 is a schematic cross-sectional view showing a reference example of a light guide plate used in a reflective display device.
FIG. 4 is a schematic view showing an example of a light guide plate used in the present invention.
FIG. 5 is an explanatory diagram showing a usage state and functions of the light guide plate shown in FIG. 4;
6 is a schematic diagram for explaining the operation of the reflective display device shown in FIG. 1; FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 0 ... Panel, 1 ... 1st board | substrate, 2 ... 2nd board | substrate, 3 ... Liquid crystal layer, 8 ... Light reflection layer, 10 ... Electrode, 11 ... Electrode, 20 ... light guide plate, 21 ... groove, 22 ... base, 40 ... polarizing plate, 211 ... reflective side, 212 / re-incident side, 213 ... bottom, 220 ... out Plane

Claims (5)

A transparent first substrate positioned on the incident side of external light, a second substrate bonded to the first substrate via a predetermined gap and positioned on the reflecting side, an electro-optic material held in the gap, and the first A panel having an electrode formed on at least one of the first substrate and the second substrate and applying a voltage to the electro-optic material;
A transparent light guide plate disposed outside the first substrate, and a light source that is disposed at an end of the light guide plate and generates illumination light as required.
The light guide plate normally transmits external light, enters the first substrate and emits external light reflected from the second substrate, and guides illumination light as necessary to enter the first substrate. And a reflective display device that emits illumination light reflected from the second substrate,
The light guide plate has a base part divided into strips and a groove part located between the base parts,
The base portion constitutes an emission plane, while the groove portion constitutes a reflective side surface and a re-incident side surface,
The reflective side surface partially reflects the illumination light guided from the light source and enters the first substrate,
The re-incident side surface causes the remaining portion of the illumination light transmitted through the reflective side surface to re-enter the light guide plate,
The reflection type display device characterized in that the emission plane emits illumination light reflected from the second substrate.   2. The reflective display device according to claim 1, wherein the groove has a reflective side surface facing each other and a bottom surface located between the re-incident side surfaces.   2. The reflective display device according to claim 1, wherein the emission plane is set to have a small inclination angle with respect to the panel so as not to substantially change a display appearance viewed from the front of the panel.   The re-incident side surface has a larger angle of inclination than the reflective side surface facing the illumination light. The reflective display device according to claim 1, wherein the reflective display device reflects light.   The light guide plate and the first substrate are joined to each other through a transparent intervening layer, and the refractive index of the intervening layer is set appropriately so that the back surface is the interface between the light guide plate and the first substrate. 5. The reflective display device according to claim 4, wherein the illumination light is totally reflected.

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