Reflection type display device

Description: TECHNICAL FIELD [Detailed description of the invention]

【0001】

[Technical field to which the invention belongs]

The present invention relates to a reflective display device that displays using external light such as natural light. More specifically, the present invention relates to an illumination structure of a reflective display device used as an auxiliary when external light is scarce.

【0002】

[Conventional technology]

Flat panel type display devices represented by liquid crystal displays are roughly classified into transmissive type and reflective type. In a transmissive display device, a panel in which a liquid crystal or the like is held as an electro-optical substance is created between a pair of transparent substrates, and a light source (backlight) for lighting is arranged on the back surface of the panel, while an image is displayed from the front of the panel. Observe. In the case of the transmissive type, a backlight is indispensable, and for example, a fluorescent tube is used. For this reason, the backlight consumes most of the power when viewed as a whole display, and is not suitable for the display of portable devices. On the other hand, in the reflection type display device, while a reflector is arranged on the back surface of the panel, external light such as natural light is incident from the front and the reflected light is used to observe the image from the front as well. Unlike the transmissive type, it does not use a light source for rear lighting, so the reflective type requires relatively low power consumption and is suitable for displays in portable devices.

【0003】

[Problems to be Solved by the Invention]

However, the reflective display device cannot observe an image in an environment where there is little outside light such as at night. In order to solve this drawback, a reflective display device equipped with a front light that is turned on as needed such as at night has been proposed, and this is shown in FIG. A light guide plate 20 is attached to the surface of the reflective panel 0. A light source 30 is arranged at the end of the light guide plate 20, and the light source 30 is partially covered with a reflecting mirror 31. As the light source 30, a long-shaped fluorescent tube (line light source) can be used. For example, a slope portion 21 having an inclination angle of 45 ° and a substantially flat trapezoidal portion 22 are formed on the surface of the light guide plate 20. The illumination light emitted from the light source 30 is totally reflected by the slope portion 21 formed on the surface of the light guide plate 20 and guided to the panel 0 located below the light guide plate 20. Therefore, the image of the panel 0 can be projected by the illumination of the light source 30 even in a dark environment.

【0004】

FIG. 8 is a functional explanatory view of the front light incorporated in the reflective display device shown in FIG. 7. As shown in the figure, the front light includes a light guide plate 20 and a light source 30 arranged at an end thereof and generating illumination light as needed. The light guide plate 20 normally transmits external light and is incident on panel 0 and emits external light reflected from panel 0, while guiding illumination light as necessary to be incident on panel 0 and reflected from panel 0. Emits the illuminated illumination light. Specifically, the light guide plate 20 has a trapezoidal portion 22 divided into strips and an inclined slope portion 21 located between the trapezoidal portions 22, and the illumination light emitted from the light source 30 is emitted from each slope. It is reflected by the unit 21 and incident on the panel 0, and the illumination light reflected from the panel 0 is emitted from each trapezoidal unit 22 toward the observer.

【0005】

FIG. 9 is a schematic plan view showing an improved example of the reflective display device with a front light shown in FIG. In this example, a plurality of light sources 30 made of light emitting diodes (LEDs) and the like are arranged at the ends of the light guide plate 20 having a striped slope and trapezoidal portions, instead of a line light source such as a fluorescent tube. .. LEDs are usually regarded as point light sources, and are used as substitutes for fluorescent tubes by arranging a plurality of LEDs along the end of the light guide plate 20. However, although a point light source such as an LED has the advantages of being easier to handle and more compact than a line light source such as a fluorescent tube, as shown in the figure, a sujimura is formed on the surface of the light guide plate 20 due to the reflection of the illumination light. There is a problem that it occurs.

【0006】

White LEDs have been developed in recent years and can replace fluorescent tubes in some applications. In fact, as shown in FIG. 10, a backlight using a point light source 30 and a light guide plate 20 is supplied to the market in combination with a transmissive panel 0. In the case of a backlight, even if an LED that tends to cause streaks or unevenness is used as the light source, it is possible to eliminate the streaks and unevenness by applying some kind of diffusion system to the back surface of the light guide plate 20. In the example of FIG. 10, a diffusion layer 29 is arranged on the bottom surface of the light guide plate 20 to eliminate streaks and unevenness. In the case of the backlight, since it is located on the back side of the panel 0 regardless of the diffusion means, the observer cannot see it and the image quality is not adversely affected. On the other hand, since the front light combined with the reflective display device is arranged on the observer side who sees the panel, if the light guide plate is directly diffused, the image quality is deteriorated. Therefore, the current situation is that the light guide plate itself of the front light can hardly be expected to have the function of erasing the sujimura. In fact, if the LED is directly attached to the end of the light guide plate of the front light, streaks are generated along the light flux emitted from the point light source as shown in FIG. 9, and the image quality is significantly impaired. From the above, in the past, only fluorescent tubes, which are line light sources, could be used for the front light. An object of the present invention is to solve the above-mentioned problem of Sujimura and to provide a front light using a point light source that satisfies light utilization efficiency, uniformity and image quality.

【0007】

[Means for solving problems]

The following measures were taken in order to solve the above-mentioned problems of the prior art and to achieve the object of the present invention. That is, the reflective display device according to the present invention basically includes a panel, a light guide plate, and a light source. The panel is a reflective type, a transparent first substrate located on the incident side of external light, a second substrate joined to the first substrate through a predetermined gap and located on the reflective side, and held in the gap. It includes an electro-optical material and electrodes formed on at least one of the first and second substrates to apply a voltage to the electro-optical material. The light guide plate is arranged on the outside of the first substrate of the panel to form a front light. The light source is arranged at one end of the light guide plate and generates illumination light as needed. As a feature, a reflective member is arranged at the other end of the light guide plate (opposite to one end where the light source is arranged). The light source is composed of a light emitting diode arranged at one end of the light guide plate. In such a configuration, the light guide plate functions as an integrator that homogenizes the illumination light emitted from the light source and guides the light from one end to the other. The reflective member reflects the uniformed illumination light and folds back from the other end to one end of the light guide plate. The light guide plate guides the folded illumination light to enter the first substrate of the panel and emits the illumination light reflected from the second substrate of the panel. Therefore, this light guide plate functions as a front light. When the light source is not lit, the light guide plate transmits external light, enters the first substrate of the panel, and emits external light reflected from the second substrate. That is, in an environment with abundant outside light such as daytime, the light guide plate merely exists in front of the panel as a transparent plate.

【0008】

Preferably, the light guide plate has a trapezoidal portion divided into strips and an inclined slope portion located between the trapezoidal portions, and the illumination light folded back by the reflecting member is reflected by each slope portion. Then, it is incident on the first substrate of the panel, and the illumination light reflected from the second substrate of the panel is emitted from each trapezoidal portion. Preferably, the inclination angle of the slope portion is shifted from 45 degrees to remove unnecessary reflection of the illumination light from one end to the other end of the light guide plate from the normal direction of the panel. Alternatively, a polarizing plate may be arranged on one side or both sides of the light guide plate on one end side of the light guide plate to remove the S polarization component from the illumination light and suppress unnecessary reflection by the slope portion. Alternatively, an optical means for narrowing the incident angle of the illumination light entering one end of the light guide plate from the light emitting diode can be provided, and leakage of the illumination light guided from one end to the other end of the light guide plate can be prevented. Alternatively, a light absorption band can be arranged in a predetermined range on one side or both sides of the light guide plate on one end side of the light guide plate, and the component of the illumination light leaking from the light guide plate can be removed in advance.

【0009】

In the above-mentioned reflective display device, the light guide plate itself has both an integrator function for a point light source and a front light function. The present invention also includes a structure in which the functions of the integrator and the front light are separated into separate light guide plates. That is, this reflective display device is arranged on a panel, transparent first and second light guide plates arranged on the outside thereof, and one end of the first light guide plate, and emits illumination light as needed. It includes a light source that generates light, and a connecting member that optically connects the other end of the first light guide plate and the other end of the second light guide plate. The light source comprises a light emitting diode arranged at one end of the first light guide plate. The first light guide plate homogenizes the illumination light emitted from the light source and guides the light from one end to the other end. That is, this first light guide plate functions as an integrator. The connecting member turns back the homogenized illumination light and introduces it from the other end of the first light guide plate to the other end of the second light guide plate. The second light guide plate normally transmits external light and is incident on the panel and emits external light reflected from the panel, while, if necessary, guides the folded illumination light and is incident on the panel. The illumination light reflected from the panel is emitted. That is, the second light guide plate functions as a front light. The structure is such that the integrator and the front light are connected to each other via a connecting member. Preferably, the first light guide plate also serves as a touch sensor to be combined with the panel. Also preferably, an additional connecting member for optically connecting one end of the first and second light guide plates to each other is arranged, and the first and second light guide plates are returned from the other end toward one end. The rest of the illuminating light is introduced again into one end of the first light guide plate for reuse.

【0010】

According to the present invention, an auxiliary front lighting system for a reflective display device is constructed by using a single point light source composed of light emitting diodes or a plurality of point light sources composed of light emitting diodes arranged in a row. An integrator is used to eliminate the sujimura peculiar to the point light source. In other words, the integrator converts one or a plurality of point light sources arranged discretely into a single line light source. Further, the line light source is converted into a surface light source for a panel to be used as a front light. In the present invention, a compact and high-quality auxiliary lighting system is obtained by integrating a light guide plate that functions as an integrator and a light guide plate that functions as a surface light source of a front light. Alternatively, the light guide plate that functions as an integrator and the light guide plate that functions as a surface light source of the front light may be separated and the two may be overlapped.

【0011】

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic cross-sectional view showing a first embodiment of the reflective display device according to the present invention. As shown in the figure, the present reflection type display device includes a panel 0, a light guide plate 20, a light source 30, and a reflection member 40. Panel 0 is a reflective type, and is a transparent first substrate 1 located on the incident side of external light, a second substrate 2 bonded to the first substrate 1 through a predetermined gap and located on the reflective side, and inside the gap. It is provided with an electro-optical material such as a liquid crystal held in the above and an electrode formed on at least one of the first substrate 1 and the second substrate 2 to apply a voltage to the electro-optical material. The light guide plate 20 is arranged on the surface side of the panel 0 (outside the first substrate 1). The light source 30 is partially covered with a reflector 31 and is arranged at one end (right side in the drawing) of the light guide plate 20 to generate illumination light as needed, such as at night. The reflective member 40 is arranged at the other end (left side in the drawing) of the light guide plate 20. In other words, the light source 30 and the reflecting member 40 face each other via the light guide plate 20. Here, the light source 30 is composed of a plurality of point light sources discretely arranged along one end of the light guide plate 20. For example, a light emitting diode (LED) that emits white illumination light can be used as the point light source 30. The light guide plate 20 homogenizes a plurality of illumination lights emitted from the plurality of point light sources 30 and guides the light from one end (right side in the drawing) to the other end (left side in the drawing). That is, the light guide plate 20 functions as an integrator and converts the point light sources 30 arranged discretely into an apparent overline light source. The converted line light source will come to the position of the reflecting member 40. The reflective member 40 reflects the uniformed illumination light and folds back from the other end on the left side of the light guide plate 20 toward the one end on the right side of the drawing. At this time, the light guide plate 20 guides the folded illumination light to enter the first substrate 1 of the panel 0 and emits the illumination light reflected from the second substrate 2. That is, the light guide plate 20 converts the line light source apparently arranged at the position of the reflection member 40 into a surface light source with respect to the panel 0. When the light source 30 is not lit, the light guide plate 20 transmits external light, enters the first substrate 1 of the panel 0, and is reflected from the second substrate 2 of the panel 0. It emits the outside light. At this time, the light guide plate 20 merely exists on the surface of the panel 0 as a transparent plate.

【0012】

A detailed description will be given below for each component of this reflective display device. First, the light guide plate 20 has a trapezoidal portion 22 divided into strips and an inclined slope portion 21 located between the trapezoidal portions 22, and the illumination light folded back by the reflecting member 40 is emitted to each slope portion. It is totally reflected by 21 and incident on the first substrate 1 of the panel 0, and the illumination light reflected from the second substrate 2 is emitted from each trapezoidal portion 22. The inclination angle of the slope portion 21 is, for example, 45 °, and the illumination light folded back from the reflecting member 40 is almost totally reflected and directed to the panel 0. On the other hand, the trapezoidal portion 20 has an inclination angle of about 1 ° and is almost flat. Therefore, the illumination light emitted from the point light source 30 can be almost totally reflected, and it functions sufficiently as an integrator. The light source 30 is composed of a white LED as described above. When the light guide plate 20 is made of PMMA resin having a refractive index of n = 1.49, the total reflection critical angle of the upper and lower surfaces is 42.2 °. In this case, if the illumination light emitted from the light source 30 is within an angle range of ± 47.8 ° in the vertical direction, it reaches the reflective member 4 side after being totally reflected by the upper and lower surfaces of the light guide plate 20 and made uniform. To do. In order to adjust this angle range, the LED lens constituting the light source 30 may have a desired directivity, or a cylindrical lens or the like may be inserted between the light source 30 and one end of the light guide plate 20. The reflective member 40 facing the light source 30 may be specularly reflective or diffusely reflective. In some cases, a concave mirror or a convex mirror may be used to completely parallelize the illumination light.

【0013】

FIG. 2 schematically shows the function of the light guide plate 20 shown in FIG. 1 as an integrator. The light guide plate 20 is made of a transparent resin having a high refractive index, for example, a PMMA plate having a thickness of 1 mm. A point light source 30 composed of four white LEDs is arranged at one end of the light guide plate 20 at an interval of 1: 2: 2: 1. The luminous flux emitted from each point light source 30 repeats multiple total reflections on the upper and lower surfaces of the light guide plate 20 that functions as an integrator to form a pseudo line light source. When it reaches the reflective member 40 side, it is almost completely uniform. Moreover, since total reflection is used, 100% light utilization efficiency can be achieved theoretically. The longer the size of the integrator, the more multiple reflections and the better the uniformity. However, if the LED has wide directivity, it is short and sufficient, and it may be about the same size as the panel. In FIG. 2, (A) is a side view of the light guide plate 20, and (B) is a plan view of the light guide plate 20.

【0014】

As described above, according to the present invention, by providing the integrator function to the light guide plate itself of the front light, the illumination light emitted from the point light source is made uniform. The front light of the present invention uses a light guide plate as a highly efficient integrator. That is, an LED light source is arranged at the end opposite to the normal one, the illumination light is incident, and when the homogenization is performed, the illumination light is folded back at the other end having a reflection function and used as a front light. In particular, compared to fluorescent tubes, white LEDs do not require an inverter, are lightweight and compact, have bright brightness in cold weather, and have no risk of non-lighting. In addition, there are merits such as low power consumption and no breakage. Therefore, it is much more suitable as a light source for portable devices than a fluorescent tube.

【0015】

In a small liquid crystal panel, a single light emitting diode may provide a sufficient front lighting effect. Even in such a case. By applying the present invention, sufficient uniformity of front illumination light and screen brightness can be obtained. By using the light guide plate as an integrator, it is possible to obtain front lighting with good uniformity even with a small panel size and a single light emitting diode. For reference, Fig. 3 shows a small structure of a conventional liquid crystal panel using a single light emitting diode as a light source. Since the light guide plate is not used as an integrator as in the conventional example shown in FIG. 8, the illumination light emitted from the light emitting diode 30 does not spread sufficiently to the effective panel area and is shaded. Even in this case, according to the present invention, since the light guide plate is used as an integrator, the illumination light can be made uniform by arranging the point light source 30 composed of the light emitting diode on the opposite side of FIG. 3, as shown in FIG. There is no shadow. Therefore, the present invention is effective not only when there are a plurality of light emitting diodes but also when there is only one light emitting diode.

【0016】

FIG. 4A schematically reprints the cross-sectional structure of the reflective display device according to the first embodiment. As shown in the figure, a light source 30 made of a light emitting diode is arranged on one end side of the light guide plate, and a reflecting member 40 is arranged on the other end side. In the figure, depending on the design of the inclination angle θ2 of the trapezoidal portion 22 formed on the light guide plate 20, the component of the illumination light exceeding the critical angle leaks from the light guide plate 20 without being totally reflected by the trapezoidal portion 22. The streaks may be conspicuous due to the reflection when this unnecessary component re-enters the slope portion 21 having the inclination angle θ1.

【0017】

As shown in (B), in principle, the light incident from the light source 30 at a certain incident angle α0 has a first reflection angle α1, a second reflection angle α2, ........., and an nth reflection angle. As αn and the trapezoidal portion 22 repeat all reflections, the reflection angle becomes smaller due to the influence of the inclination angle θ2 of the trapezoidal portion 22. In the range from the incident side at one end to the reflection side at the other end of the light guide plate 20, when the reflection angle αn falls below the critical angle at the nth time and cannot be totally reflected, the illumination light leaks from the light guide plate 20. The position on the light guide plate 20 where the incident light from the light source 30 cannot satisfy the critical angle is determined by the incident angle α0. The smaller the incident angle α0, the farther it reaches without leaking due to repeated total reflection. By the way, in order to prevent leakage of the illumination light, as shown in (B), there is a method of adjusting the inclination angle θ1 of the slope portion 21 to remove unnecessary reflected light from the normal direction (effective field of view) of the panel. is there. That is, it is unnecessary by shifting the inclination angle θ1 of the slope portion 21 from 45 degrees and removing unnecessary reflection of the illumination light from one end portion to the other end portion of the light guide plate 20 by the slope portion 21 from the normal direction of the panel. It is possible to prevent the reflection from entering the observer's field of view.

【0018】

As another means, as described above, there is a method of reducing the incident angle α0 and making it close to parallel light by using a cylindrical lens or sharpening the directivity of the lens integrated with the light emitting diode. In order to adjust the incident angle range, the LED lens constituting the light source 30 has a desired directivity, or a cylindrical lens or the like is inserted between the light source 30 and one end of the light guide plate 20. By providing an optical means for narrowing the incident angle of the illumination light entering one end of the light guide plate from the light emitting diode, it is possible to prevent leakage of the illumination light guided from one end to the other end of the light guide plate.

【0019】

As another means, since the range of the incident angle α0 at which the above-mentioned streaks are generated from the incident port on one end side of the light guide plate 20 to the other end side is fixed, the problem can be solved by removing the light component in this range. That is, as shown in (C), it is a method in which a light absorption band 33 is stretched on one side or both sides of the light guide plate 20 with the minimum necessary width to absorb light of an unnecessary component. A light absorption band 33 is arranged in a predetermined range on one side or both sides of the light guide plate 20 on one end side of the light guide plate 20, and a component of illumination light leaking from the light guide plate 20 is removed in advance. For example, black tape is used for the light absorption band 33.

【0020】

Alternatively, as shown in (D), instead of a light absorption band such as black tape, a polarizing plate is attached to one side or both sides with the minimum necessary width to absorb only the S polarization component that is an unnecessary component. is there. FIG. 4D shows an optical path diagram in the light guide plate 20. As shown in the figure, the illumination light emitted from the light source 30 composed of light emitting diodes arranged at one end of the light guide plate 20 repeats total internal reflection on the upper and lower surfaces of the light guide plate 20 and reaches the reflection member 40 located on the other end side. .. In principle, most of the unnecessary components reflected on the observer side on the slope portion 21 are S polarization components, and the P polarization component passes through the slope portion 21 without being reflected and re-enters the light guide plate 20. Therefore, it is sufficient to absorb only the S polarization component, which is an unnecessary component, at the time when the illumination light is incident on the light guide plate 20. For this purpose, the polarizing plate 35 is attached to the upper and lower surfaces of the light guide plate 20.

【0021】

As shown in (E) of FIG. 4, the absorption axis of the polarizing plate 35 is parallel to the arrangement of a plurality of aligned point light sources 30. As a result, most of the S polarization component can be absorbed. In this way, the illumination light emitted from the light source 30 composed of the light emitting diode initially contains the P-polarizing component and the S-polarizing component, but the polarizing plate 35 guides almost only the P-polarizing component to the light guide plate 20. Even if the P-polarized light component is subsequently incident on the slope portion 21, it is almost transmitted, and the unnecessary reflected light reflected from the slope portion 21 can be reduced to only a minute remaining S-polarized light component. This method can suppress the light loss to about half as compared with the absorption band using black tape or the like. That is, since about half of the P-polarized light component contributes to illumination as effective light, the effect of eliminating streaks is equivalent to that of the absorption band, but the illumination of the panel can be brighter than that of the absorption band. The polarizing plate 35 and the absorption band 33 may be provided in a band shape as shown in (E), but a desired streak may be formed even if the polarizing plate 35 and the absorption band 33 are fragmented and attached only to the portion corresponding to each light emitting diode as shown in (F). The effect of erasing can be obtained. In this way, the loss of light can be further reduced.

【0022】

FIG. 5 is a schematic cross-sectional view showing a second embodiment of the reflective display device according to the present invention. Unlike the first embodiment described above, in this embodiment, the light guide plate that functions as an integrator and the light guide plate that functions as a surface light source of the front light are separated. As shown in (A), this reflective display device includes a reflective panel 0, transparent first and second light guide plates 60 and 20 arranged on the surface side thereof, and a first light guide plate. A light source 30 arranged at one end of 60 (right side in the drawing) to generate illumination light as needed, and the other end of the first light guide plate 60 (left side in the drawing) and the other end of the second light guide plate 20. It has a connecting member 41 that optically connects the portion (left side in the drawing). Similar to the first embodiment described above, the light source 30 is covered with a reflector 31 and is composed of a plurality of point light sources discretely arranged along one end of the first light guide plate 60. For example, a point light source is a light emitting diode that emits white illumination light. The first light guide plate 60 functions as an integrator, homogenizes a plurality of illumination lights emitted from the plurality of point light sources 30, and guides the light from one end on the right side of the drawing to the other end on the left side of the drawing. The first light guide plate 60 functions as an integrator, and a transparent plate having a high refractive index can be used. In this example, the first light guide plate 60 also serves as a touch sensor to be combined with the panel 0, and has a pattern of a transparent conductive film 61 made of ITO or the like on the surface. The connecting member 41 is composed of a reflecting prism or the like, and the illumination light homogenized by the first light guide plate 60 is folded back and introduced from the other end of the first light guide plate 60 to the other end of the second light guide plate 20. .. The second light guide plate 20 functions as a surface light source of the front light, guides the illumination light folded back by the connecting member 41, enters the panel 0, and emits the illumination light reflected from the panel 0. Specifically, the second light guide plate 20 has a trapezoidal portion 22 divided into strips and an inclined slope portion 21 located between the trapezoidal portions 22, and is folded back by the connecting member 41. The illumination light is totally reflected by each slope portion 21 and incident on the panel 0, and the illumination light reflected from the panel 0 is emitted from each trapezoidal portion 22 toward the observer.

【0023】

As described above, in the present embodiment, in the configuration in which the touch sensor is arranged on the light guide plate 20 for the front light, the first light guide plate 60 also serving as the touch sensor is used as an integrator. Here, too, the illumination light emitted from the LED point light source can be made uniform with high efficiency and incident on the second light guide plate 20 which is the surface light source of the front light. The reflecting surface of the reflecting prism constituting the connecting member 41 has an angle of 45 °, but it is generally necessary to optimize it according to the directivity characteristics of the LED light. The touch sensor has a transparent electrode 61 formed in a sheet shape on the surface of a transparent plate such as glass due to its structure. When LED light is incident on the transparent electrode 61, turbidity occurs. Therefore, the transparent electrode 61 is shortened by several mm from one end of the light guide plate 60 as indicated by Z, and the LED light is blocked so as not to enter the transparent electrode 61.

【0024】

(B) is a schematic cross-sectional view showing a modified example of the second embodiment shown in (A). In this modification, an additional connecting member 42 is used to optically connect one ends (right side in the drawing) of the first and second light guide plates 60 and 20 to each other. This additional connecting member 42 also comprises, for example, a reflecting prism. Further, the second light guide plate 20 has a structure in which the thickness gradually decreases from the left end portion on the drawing toward the right end portion on the drawing. With this configuration, the rest of the illumination light returned from the other end of the second light guide plate 20 (left side in the drawing) toward one end (right side in the drawing) is again applied to one end of the first light guide plate 60. It can be introduced and reused. As a result, the illumination brightness of panel 0 can be improved, and cost reduction and power consumption can be reduced by reducing the number of LEDs used as point light sources. The angle of inclination of the reflecting prism used as the additional connecting member 42 is set to 45 °, but in reality it is necessary to optimize it according to the directivity characteristics of the LED light, so it is not limited to this and it is made spherical. In some cases, some ingenuity is required. As described above, the second light guide plate 20 has a shape that is thinned from the other end side to the one end side, and by making the cross-sectional size of the incident portion and the exit portion of the reflecting prism constituting the connecting member 42 the same, the light It is possible to minimize the loss.

【0025】

Finally, FIG. 6 is a schematic partial cross-sectional view showing a specific configuration example of the panel incorporated in the reflective display device according to the present invention. This example is TN-ECB (Twist Nematic-Electrically Controlled) Birefringence) mode liquid crystal panel. As shown in the figure, a polarizing plate 70 and a quarter wave plate 80 are arranged on the surface of the panel 0. Panel 0 is formed by joining a first substrate 1 made of transparent glass or the like located on the incident side of external light to a second substrate 2 located on the reflection side through a predetermined gap. The nematic liquid crystal layer 3a is held in the gap between the two substrates 1 and 2. The liquid crystal molecule 4 is twist-oriented by the upper and lower alignment films 6 and 7. Electrodes 10 and 11 are formed on the inner surfaces of the substrates 1 and 2, respectively, and a voltage is applied to the nematic liquid crystal layer 3a for each pixel. In this example, the electrodes 10 formed on the first substrate 1 side are patterned in a stripe shape, and the electrodes 11 formed on the second substrate 2 are also formed in a stripe shape. Both electrodes 10 and 11 are orthogonal to each other, and pixels are defined at the intersections, which is a so-called simple matrix type. The polarizing plate 70 and the quarter wave plate 80 are arranged on the first substrate 1 side of the panel 0. The reflective liquid crystal display device having such a configuration is a TN-ECB system and a normal white mode. That is, when no voltage is applied, the nematic liquid crystal layer 3a maintains the twist orientation and functions as a quarter wave plate, and cooperates with the polarizing plate 70 and the quarter wave plate 80 to allow outside light to pass through. Is displayed in white. When a voltage is applied, the nematic liquid crystal layer 3a shifts to vertical orientation and loses its function as a quarter wave plate, and blocks external light in cooperation with the polarizing plate 70 and the quarter wave plate 80. Display in black.

【0026】

Each component will be described in detail with reference to FIG. As described above, the polarizing plate 70 is arranged on the surface of the first substrate 1 of the panel 0. A quarter wave plate 80 is interposed between the polarizing plate 70 and the first substrate 1. The quarter wave plate 80 is made of, for example, a uniaxially stretched polymer film, and gives a phase difference of one quarter wavelength between normal light and abnormal light. The optical axis (uniaxial anisotropic axis) of the quarter wave plate 80 is arranged so as to form an angle of 45 ° with the polarizing axis (transmission axis) of the polarizing plate 70. When external light passes through the polarizing plate 70, it becomes linearly polarized light. This linearly polarized light becomes circularly polarized light when it passes through the quarter wave plate 80. Once again, when it passes through the quarter wave plate, it becomes linearly polarized light. In this case, the polarization direction is rotated by 90 ° from the original polarization direction. As described above, the quarter wave plate can rotate the polarization direction by combining with the polarizing plate, and this is used for the display.

【0027】

Panel 0 basically uses a nematic liquid crystal layer 3a composed of horizontally oriented nematic liquid crystal molecules 4 having a positive dielectric anisotropy as an electro-optical material. The nematic liquid crystal layer 3a functions as a quarter wave plate by appropriately setting its thickness. In this example, the refractive index anisotropy Δn of the nematic liquid crystal layer 3a is about 0.7, and the thickness of the nematic liquid crystal layer 3a is about 3 μm. Therefore, the retardation Δn · d of the nematic liquid crystal layer 3a is 0.2 to 0.25 μm. As shown in the figure, by twist-orienting the nematic liquid crystal molecule 4, the above-mentioned retardation value becomes substantially 0.15 μm (150 nm). This value is approximately 1/4 of the central wavelength of external light (about 600 nm), and the nematic liquid crystal layer 3a can optically function as a quarter wave plate. By sandwiching the nematic liquid crystal layer 3a between the upper and lower alignment films 6 and 7, a desired twist orientation can be obtained. On the first substrate 1 side, the liquid crystal molecules 4 are aligned along the rubbing direction of the alignment film 6, and on the second substrate 2 side, the liquid crystal molecules 4 are aligned along the rubbing direction of the alignment film 7. By shifting the rubbing directions of the alignment film 6 and the alignment film 7 by 60 ° to 70 °, a desired twist orientation can be obtained.

【0028】

A light reflecting layer 8 is formed below the electrode 11 on the second substrate 2 side. The light reflecting layer 8 has irregularities on its surface and has light scattering properties. Therefore, not only the appearance of paper white is preferable as a display background, but also the incident light is reflected in a relatively wide angle range, so that the viewing angle is widened to make the display easier to see and the brightness of the display 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 electrode 11. The light reflecting layer 8 is composed of a resin film 15 on which irregularities are formed and a metal film 16 such as aluminum formed on the surface thereof. The resin film 15 is a photosensitive resin film in which irregularities are patterned by photolithography. The photosensitive resin film 15 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 into, for example, a columnar shape. Then, if it 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 formed in this manner. 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 color. A flattening layer 12 is formed on the surface of the light reflecting layer 8 to fill the unevenness. It is preferable to use a transparent organic substance such as acrylic resin for the flattening layer 12. By interposing the flattening layer 12, the electrode 11 and the alignment film 7 can be stably formed.

【0029】

[Effect of the invention]

As described above, according to the present invention, a reflective display device having a front light structure using, for example, an LED as a point light source is realized. LED light is incident from one end of the light guide plate that constitutes the front light, and the light guide plate functions as an integrator to remove streaks and unevenness peculiar to the point light source. Further, the illumination light uniformed by the mirror arranged on the other end side of the light guide plate is returned to guide the panel. With the above configuration, it is possible to efficiently convert a point light source such as an LED into a surface light source without streaks and put it into practical use for front light applications. Point light sources such as LEDs are easier to handle than line light sources such as fluorescent tubes. Further, if the integrator and the surface light source for the front light are combined with the light guide plate, it is possible to realize a thin, lightweight and low-cost reflective display device with auxiliary front lighting with a small number of parts.

[Simple explanation of drawings]

[Figure 1]

It is sectional drawing which shows the 1st Embodiment of the reflection type display device which concerns on this invention.

[Figure 2]

It is sectional drawing and plan view of the light guide plate incorporated in the reflection type display device which concerns on 1st Embodiment.

[Fig. 3]

It is a top view which shows the reference example of the reflection type display device.

[Fig. 4]

It is sectional drawing and plan view which show the improvement example of the reflection type display device which concerns on 1st Embodiment.

[Fig. 5]

It is sectional drawing which shows the 2nd Embodiment of the reflection type display device which concerns on this invention, and the modification | modification thereof.

[Fig. 6]

It is a partial cross-sectional view which shows the specific example of the panel incorporated in the reflective display device which concerns on this invention.

[Fig. 7]

It is a perspective view which shows the reference example of the reflection type display device provided with a front light.

[Fig. 8]

It is a schematic diagram provided for the operation explanation of the reference example shown in FIG.

[Fig. 9]

It is a top view which shows the appearance of the reflection type display device which used the point light source for the front light.

[Fig. 10]

It is sectional drawing which shows the conventional example of the transmission type display device provided with a backlight.

[Explanation of symbols]

0 ... panel, 1 ... 1st substrate, 2 ... 2nd substrate, 20 ... light guide plate, 21 ... slope, 22 ... trapezoidal, 30 ... light source, 31 Reflector, 33 Absorption band, 35 Polarizing plate, 40 Reflector, 41 Connecting member, 42 Connecting member, 60 Light guide plate, 61 Transparent electrode