JPH11202784A - Reflection type display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To impart an illumination structure enabling image observation in a dark environment without damaging the image quality in a bright environment, to a reflection type display device. SOLUTION: This reflection type display device is composed of a panel 0, a light transmission plate 20 and a light source 30. The light transmission plate 20 is disposed outside the panel 0 and the light source 30 is disposed at the end part of the light transmission plate 20 and generates illumination light at need. While the light transmission plate 20 normally transmits external light, makes it incident on the panel 0 and emits reflected external light, it transmits the illumination light, makes it incident on the panel 0 and emits reflected illumination light at need. The light transmission plate 20 is provided with mount parts 22 divided in a belt shape and groove parts 21 positioned between the respective mount parts. While the mount parts 22 constitute an emission plate 220, the groove parts 21 constitute a reflection side face 211 and a re-incident side face 212. The reflection side face 211 totally reflects a part of the illumination light led from the light source 30 and makes it be incident on the panel 0. The re-incident side face 212 makes the illumination light of a residual part transmitted through the reflection side face 211 incident on the light transmission plate again. The emission plate 220 emits the illumination light reflected from the panel 0.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reflection type display device which performs display using external light such as natural light. More specifically, the present invention relates to an illumination structure of a reflective display device which is used as an auxiliary when external light is scarce.

[0002]

2. Description of the Related Art A display device using a liquid crystal or the like as an electro-optical material has a flat panel shape, and is characterized in that it is thin and lightweight and consumes low power. Utilizing such features, a flat panel display device is suitable for a display of a portable information device and the like, and is being actively developed at present. The liquid crystal used as the electro-optical material is not of a self-luminous type, and outputs an image by blocking transmission of light incident from outside according to a voltage. For this reason, some kind of illumination structure is required, and it is roughly classified into a transmission type using a back light source and a reflection type using natural light.

[0003]

In a transmissive display device, a flat panel in which a liquid crystal is held as an electro-optical material is formed between a pair of transparent substrates, and a light source for illumination (backlight) is arranged on the back of the flat panel. Meanwhile, an image is observed from the front of the panel. In the case of the transmissive type, a backlight is indispensable and, for example, a cold cathode tube or the like is used. For this reason, the backlight consumes most of the power when viewed as a whole display, and is not suitable for a display of a portable device. On the other hand, in a reflection type display device, while a reflection plate is arranged on the back surface of the panel, external light such as natural light is incident on the front surface, and an image is similarly observed from the front using the reflected light. Unlike the transmissive type, which does not use a light source for backlighting, the reflective type requires relatively low power consumption and is suitable for displays of portable devices. However, the reflective display device cannot observe an image in an environment where external light is poor, such as at night, and 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 have been 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 bonded to the first substrate via a predetermined gap and positioned on the reflective side, an electro-optical material held in the gap, and An electrode is formed on at least one of the first substrate and the second substrate to apply a voltage to the electro-optical material. The light guide plate is made of a transparent material and is disposed outside the first substrate. A light source is disposed at an end of the light guide plate and generates illumination light as needed. As a characteristic feature, the light guide plate usually transmits external light and enters the first substrate and the second light guide plate.
While the external light reflected from the substrate is emitted, the illumination light is guided as needed to be incident on the first substrate and the illumination light reflected from the second substrate is emitted. As a further feature, the light guide plate has a base portion divided into strips and a groove located between the base portions. The pedestal defines an exit plane, while the groove defines a reflective side and a re-incident side. 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 reflecting side surface to re-enter the light guide plate. The emission plane emits the illumination light reflected from the second substrate.

Preferably, the groove has a bottom surface located between the reflection side surface and the re-incident side surface facing each other. Preferably, the angle of inclination of the emission plane with respect to the panel is set small so as not to substantially change the display appearance viewed from the front of the panel. Also preferably,
The reflecting side surface can totally reflect the illumination light guided from the light source toward the light source side from the normal of the first substrate and can totally reflect most of the illumination light reflected from the second substrate toward the light source side. It is set to an appropriate inclination angle. Also, preferably, the re-incident side surface has a larger inclination angle than the facing reflecting side surface, so that the illumination light passing through the reflecting side surface and re-entering can be totally reflected in the light guide plate. Also preferably, the light guide plate and the first substrate are joined to each other via a transparent intervening layer. By appropriately setting the refractive index of the intervening layer, total reflection of illumination light at the interface between the light guide plate and the first substrate is enabled.

According to the present invention, the light guide plate is arranged on the surface of the reflection type panel, and the light source is arranged at the end. In a dark environment, the light source is turned on, and illumination light is incident on the panel side via the light guide plate to display an image. In a bright environment, the light source is turned off, and an image is projected using external light directly through a transparent light guide plate. The light guide plate is basically transparent and does not hinder the observation of an image even in a bright environment. As described above, 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 significantly reduced, which is suitable for a display of a portable device. In addition to the basic functions described above, the present invention devises in particular to make 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 located between the base portions. The base portion forms an emission plane, while the groove portion forms a reflection side surface and a re-incident side surface. As a result, the illumination light incident on the light guide plate from the light source can be efficiently guided farther along the horizontal direction, and uniform illumination is realized.

[0007]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a schematic partial sectional view showing an embodiment of the 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 a transparent first substrate 1 located on the outside light incident side, is bonded to the first substrate 1 via a predetermined gap, and is held in the gap between the second substrate 2 and the two substrates 1 and 2 on the reflection side. The first and second substrates 1 and 2 are provided with electrodes 10 and 11 for applying voltage to the electro-optical material. Depending on the driving method, the electrodes may be formed on at least one of the two substrates 1 and 2. The light guide plate 20 is made of, for example, an injection-molded product of a transparent material such as an acrylic resin, and is disposed outside the first substrate 1 via the polarizing plate 40. The light source 30 is provided at an end of the light guide plate 20 and generates illumination light as needed. The light source 30 is formed of, for example, a cold cathode tube, and is called a so-called edge light. In order to improve the illumination efficiency of the edge light, a reflecting mirror 31 is provided after the cylindrical light source 30. In such a configuration, the light guide plate 2
0 is the first substrate 1 which normally transmits external light and passes through the polarizing plate 40.
While the external light reflected from the second substrate 2 is emitted, and the illumination light is guided as necessary to the first through the polarizing plate 40.
The illumination light that has entered the substrate 1 and reflected from the second substrate 2 is emitted.

The light guide plate 20 has a base portion 22 divided into strips.
And a groove 21 located between the bases. The pedestal portion 22 forms the emission plane 220, while the groove portion 21 forms the reflection side surface 211 and the 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 is the reflective side surface 2
The remaining part of the illumination light that has passed through 11 is re-incident on the light guide plate 20. The emission plane 220 emits the illumination light reflected from the panel 0. In this embodiment, each groove 21 has a substantially V-shape, and a bottom surface 213 is interposed between the reflection side surface 211 and the re-incident side surface 212 facing each other. This bottom 21
Reference numeral 3 is provided for facilitating the processing of the groove 21, and is not an essential component. 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 reflecting side surface 211 can totally reflect the illumination light guided from the light source 30 toward the light source 30 from 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 reflection side surface 211 is set to 58 °. In this case, when the illumination light enters the panel 0, the illumination light is slightly inclined in the direction of the light source 30. This illumination light is reflected from the panel 0, and when it reaches the reflection side surface 211 again, most of the light is totally reflected,
Do not emit to the observer. As a result, an image is displayed only with the illumination light emitted from the emission plane 220, and double shift is eliminated. The return illumination light totally reflected by the reflection side surface 211 is reflected again by the reflection mirror 31 and the like, and is used as illumination light. On the other hand, the re-incident side surface 212 has a larger inclination angle than the facing reflecting side surface 211 and is almost vertical. Most of the illumination light that has passed through the reflection side surface 211 and re-entered the re-incident side surface 212 is totally reflected inside the light guide plate 20 and is guided in the horizontal direction. For example, the illumination light that has re-entered perpendicularly to the re-incident side surface 212 has an inclination angle of 68 ° with respect to the bottom surface of the light guide plate 20 and is totally reflected. On this occasion,
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 appropriately set to enable total reflection of illumination light at the interface between the light guide plate 20 and the polarizing plate 40. ing. For example, when the refractive index of the light guide plate 20 is 1.49, by providing an intervening layer having a refractive index of 1.42,
Illumination light incident on the interface at an inclination angle of 68 ° can be fully totally reflected.

The panel 0 uses a liquid crystal layer 3 mainly composed of nematic liquid crystal molecules 4 having a 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 reflection layer 8. The light reflection 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 functions as a quarter-wave plate. The optical anisotropic axis (optical axis) of this quarter-wave plate is set to form an angle of 45 ° with the polarization axis of the polarizing plate 40. Both substrates 1, 2
A light reflection layer 8 is provided on the second substrate 2 side in the gap. 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.

The light reflecting layer 8 has irregularities on the surface and has light scattering properties. Therefore, not only is the paper white appearance preferable as a display background, but also the incident light is reflected in a relatively wide angle range, so that the viewing angle is enlarged, the display is easy to see, and the brightness of the display is increased in a wide viewing angle range. A transparent flattening layer 12 for filling unevenness is interposed between the light reflecting layer 8 and the alignment film 7. The light reflection layer 8 is composed of a resin film 15 having irregularities formed thereon 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.

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 is patterned into, for example, a cylindrical shape. Then, by heating and performing reflow, the uneven shape can be formed stably. A metal film 16 made of aluminum or the like having a desired film thickness and a good light reflectance is formed on the surface of the concavo-convex shape thus formed. If the depth dimension of the unevenness is set to several μm, good light scattering characteristics can be obtained, and the light reflection layer 8 exhibits white. A flattening layer 12 is formed on the surface of the light reflecting layer 8 to fill the irregularities. The flattening layer 12 is preferably made of a transparent organic material such as an acrylic resin. By interposing the planarizing layer 12, the formation of the alignment film 7 and the rubbing process can be stably performed. 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.

Next, a brief description will be given of the operation when black-and-white display is performed using this reflective display device. 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 state where no voltage is applied (off state), the nematic liquid crystal molecules 4 are horizontally oriented, 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 via the light guide plate 20. The illumination light passing 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 passes through the liquid crystal layer 3 again after being reflected by the light reflection layer 8. At this time, circularly polarized light is converted to 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 vertically aligned along the direction of the electric field, 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 through the liquid crystal layer 3 again to 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 viewer. Therefore, white display is obtained.

FIG. 2 shows a use state of the reflective display device shown in FIG. 1 in a bright environment. In a bright environment, since there is sufficient external light such as natural light, display is performed using this. Therefore, the light source 30 is turned off. Thereby, the power consumption of the entire display can be reduced. The light guide plate 20 transmits the external light incident from the observer side as it is, enters the first substrate 1, and emits the external light reflected from the second substrate 2 from the base 22. The light guide plate 20 is basically transparent and does not hinder any observation of the display. In particular, the emission plane 220 constituted by the platform 22
The angle of inclination with respect to the panel 0 is set to be extremely small so that the display appearance viewed from the front of the panel 0 is not substantially changed, and is substantially close to a horizontal plane.

FIG. 3 is a schematic sectional view showing a reference example of a light guide plate used in a reflection type 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 located between the flat portions. Flat part 22
The inclination angle of a is about 1.5 °, and the inclination angle of the slope 21a is about 45 °. When the light guide plate 20a including the inclined surface 21a having the inclination angle of 45 ° and the almost horizontal flat surface 22a is used, a phenomenon in which the brightness is greatly reduced as the distance from the light source increases is observed. In contrast,
When the light guide plate 20 shown in FIG. 1 is used, the illumination light emitted from the light source can be uniformly guided to a greater distance. In the reference example shown in FIG. 3, numbers are assigned to the slope portions 21 a in order from the closest to the light source. The component L1 of the illumination light L emitted from the light source having a small incident angle (nearly horizontal) is totally reflected at the first slope portion and guided to the panel side. The illumination light component L2 having a slightly large incident angle is totally reflected by the next slope and guided to the panel. Illumination light component L3 having a larger incident angle
Is totally reflected at the slope. 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, so that the total reflection light amount is small. That is, the illuminating light that reaches the slope 21a having a 45 ° inclination angle is blocked at the base of the previous slope 21a as the distance from the light source increases, so that the amount of light that actually reaches the slope 21a decreases. Therefore, the brightness of the light guide plate decreases as the distance from the light source increases.

On the other hand, 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 pedestals divided into strips and grooves located between the pedestals. The pedestal forms the emission plane 220, while the groove forms the reflection side 211 and the re-incident side 212. Reflecting side faces 21 facing each other
The bottom surface 213 is located between the first and the re-incident side surfaces 212.
In this example, the emission plane 2 located between the adjacent groove portions
The width of 20 is set to 201 μm. The inclination angle of the reflection side surface 211 is set to 58 °. The re-incident side surface 212 is a substantially vertical wall having a height dimension of 8.
It is set to 2 μm. The width of the bottom surface 213 is 2 μm
It is. The width of the reflection side surface 211 is 6 μm.

FIG. 5 is a schematic view for explaining the method of use and operation of the light guide plate shown in FIG. As shown, the light guide plate 20 is joined to the panel 0 via an intervening layer 50.
A light source 30 is disposed on an end face of the light guide plate 20 and the illumination light L
Is supplied to the light guide plate 20. The light source 30 is partially covered with a reflecting mirror 31. In the illumination light that has reached the reflection side surface 211, a component L1 having a large incident angle is totally reflected and becomes illumination light L3, and is guided to the panel 0. 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, it reaches the observer with almost no influence. However, when the light reflected from the panel 0 partially reaches the reflection side surface 211, the light is totally reflected due to a large incident angle and does not go to the observer, so that no double image is generated. On the other hand, of the illumination light emitted from the light source 30, the component L2 having a relatively small incident angle is
1 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 inside of the light guide plate 20.
On the other hand, when L4 reaches the reflection side surface 211 in the path guided to the back of the light guide plate 20, a component having a relatively large incident angle is totally reflected, and is guided to the liquid crystal panel 0 as illumination light L5. Thus, the illumination light emitted from the light source 30 is
The panel is guided to a distant position in the horizontal direction while repeating total reflection on the back and front surfaces of the panel 0, so that the panel 0 can be uniformly illuminated over a wide range.

FIG. 6 is a reference diagram schematically showing the operation of the reflection type display device shown in FIG. As shown in the figure, the reflective display device includes a polarizing plate 40, a first substrate 1,
This is equivalent to a stack of the electrode 10, the liquid crystal layer 3, the electrode 11, the light reflection layer 8, and the second substrate 2. In FIG. 6, the left half indicates a voltage applied state (ON state), and white display is performed. The half on the right side indicates a voltage non-applied state (off state), and is displayed in black. In the off state, the nematic liquid crystal molecules 4 contained 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 makes an angle of 45 ° with the polarization axis of the polarizer 40. Accordingly, 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 reflection layer 8, and passes through the liquid crystal layer 3 again. At this time, the circularly polarized light is converted into the output linearly polarized light. However, the polarization directions of the input linearly polarized light and the output linearly polarized light are orthogonal to each other. Therefore,
The output linearly polarized light is absorbed by the polarizing plate 40, so that a 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 without changing the polarization direction, and
Pass through. Therefore, white display is obtained. Although the above-described embodiment is a display mode using the birefringence of one polarizing plate 40 and the liquid crystal layer 3, the present invention is not limited to this, and uses a twisted nematic mode, a guest host mode, or the like. You may.

[0018]

As described above, according to the present invention,
A light guide plate is provided on a reflective panel, and a light source for auxiliary illumination is provided at an end of the light guide plate. The light guide plate normally transmits external light to enter the panel and emits external light reflected from the panel, and, if necessary, guides illumination light to enter the panel and emits illumination light reflected from the panel as necessary. . 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 external light, the light source is turned off to save power. The light guide plate has a pedestal portion divided into strips and a groove located between the pedestals. The pedestal 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 a farther place 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, and shows a use state in a dark environment.

FIG. 2 is a schematic partial cross-sectional view illustrating 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 for 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 use state and functions of the light guide plate shown in FIG.

FIG. 6 is a schematic view for explaining the operation of the reflective display device shown in FIG. 1;

[Description of Signs] 0 ... Panel, 1 ... First substrate, 2 ... Second substrate, 3 ... Liquid crystal layer, 8 ... Light reflection layer, 10 ... Electrode, 11 ... ..Electrode, 20 light guide plate, 21 groove portion, 22 base portion, 40 polarizing plate, 211
Reflection side, 212, re-incident side, 213 ... bottom, 2
20 ・ ・ ・ Emission plane

Claims (6)

[Claims] 1. A transparent first substrate located on an incident side of external light, a second substrate joined to the first substrate via a predetermined gap and located on a reflection side, and electro-optic held in the gap. material,
And a panel formed on at least one of the first substrate and the second substrate and provided with an electrode for applying a voltage to the electro-optical material; a transparent light guide plate disposed outside the first substrate; A light source that is arranged at an end of the light plate and generates illumination light as needed. The light guide plate usually transmits external light, enters the first substrate, and reflects the external light reflected from the second substrate. While emitting light, the illumination light is guided as necessary to be incident on the first substrate and the second
A reflection type display device for emitting illumination light reflected from a substrate, wherein the light guide plate has a base portion divided into strips and a groove located between the base portions, and the base portion is an emission plane. The groove portion constitutes a reflection side surface and a re-incident side surface, and the reflection side surface partially reflects the illumination light guided from the light source and enters the first substrate, and the re-incident side surface is the reflection side surface A reflection type display device, wherein the illumination light of the remaining portion transmitted through the light guide plate is re-entered into the light guide plate, and the emission plane emits the illumination light reflected from the second substrate. 2. The reflection type display device according to claim 1, wherein the groove has a bottom surface located between the reflection side surface and the re-incident side surface facing each other. 3. The reflection surface according to claim 1, wherein the emission plane has a small inclination angle with respect to the panel so as not to substantially change the display appearance viewed from the front of the panel. Type display device. 4. The reflection side surface totally reflects the illumination light guided from the light source toward the light source side with respect to the normal of the first substrate, and reflects most of the illumination light reflected from the second substrate to the light source. 2. The reflection type display device according to claim 1, wherein the inclination angle is set such that the side can be totally reflected. 5. The re-incident side surface has a larger inclination angle than the facing reflecting side surface, and illumination light that has passed through the reflecting side surface and re-entered can be totally reflected in the light guide plate. 2. The reflective display device according to 1. 6. The light guide plate and the first substrate are bonded to each other via a transparent intervening layer, and the refractive index of the intervening layer is appropriately set so that an interface between the light guide plate and the first substrate is formed. 6. The reflection type display device according to claim 5, wherein total reflection of illumination light is enabled.