JP3576662B2 - Reflective liquid crystal display - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a reflection-type liquid crystal display device which can obtain a bright image without using a backlight only by using external light and consumes less power, and in particular, stands up against a laptop or notebook personal computer. The present invention relates to a reflective liquid crystal display device suitable for use.
[0002]
[Prior art]
2. Description of the Related Art There are two types of liquid crystal display devices used in conventional laptop and notebook personal computers, a transmissive type having a backlight on the back of a liquid crystal panel and a reflective type having a light reflector on the back of a liquid crystal panel. First of all, among these, the transmission type has the problem that the power consumption is large and the battery operation is problematic, while the reflection type has the problem that the brightness is insufficient and it is dark and difficult to see. As a result, in the prior art, it was difficult to achieve both long battery life and good visibility at the time of battery operation.
[0003]
Here, when analyzing the cause of the darkness and difficulty in viewing in the conventional reflection type liquid crystal display device, it is found that mainly the light use efficiency is low and the incident external light does not sufficiently reach the eyes of the user (viewer). It turns out that there is. That is, only a small part of the external light incident on the liquid crystal panel returns to the direction of the user's eyes.
[0004]
In particular, in a liquid crystal display device that is used standing up like a laptop or notebook personal computer, in an environment where incident light is particularly strong from above, such as in a normal office, most of the available incident light can be applied to a liquid crystal panel. The light is placed diagonally downward in front by the light reflector installed on the back of the camera, and the light cannot reach the user.
[0005]
In order to solve this, for example, in EP0490132A2, by using a reflector having an angle with respect to the liquid crystal display device surface, the display device is tilted from above with respect to the display device like a ceiling light, and with respect to the display surface. A method has been proposed in which the incident light is reflected in the direction of the user to make it brighter. In Japanese Patent Application Laid-Open No. Sho 63-30825, a reflector having a saw-shaped groove at this time is used. A method for obtaining the same effect has been proposed.
[0006]
[Problems to be solved by the invention]
In the above-mentioned conventional technology, it cannot be said that sufficient consideration is given to the improvement of the external light use efficiency, and there is a problem that it is difficult to obtain a bright display.
SUMMARY OF THE INVENTION An object of the present invention is to provide a liquid crystal display device that can make more external light incident on a liquid crystal panel and return more reflected light from the liquid crystal panel to a user direction, and that is bright and has good visibility. Is to do.
[0007]
[Means for Solving the Problems]
The object of the present invention is to provide a reflection type liquid crystal display device having a light scattering layer and a light reflection surface on the back surface of a normally open liquid crystal display device, and operating as external light incident on the display surface of the liquid crystal display device as illumination light. In the above, the light-scattering layer is a transparent medium, and an adhesive in which particles of a transparent body having a different refractive index from the transparent medium are put in the transparent medium, and the light-reflecting surface is blazed mirror-reflective. The light-reflecting surface and the liquid crystal display are constituted by a layer and are directly bonded and joined by the light- scattering layer with the light- scattering layer interposed therebetween.
At this time, the difference between the refractive indexes of the transparent medium and the transparent body may be 0.01 to 0.30.
At this time, the blazed specular reflecting surface further reflects external light incident from a direction having an inclination angle exceeding 0 degree with respect to the normal direction of the display surface in substantially the normal direction. The reflection intensity in the normal direction may be set to be higher than the reflection light intensity in the direction having the same inclination angle and the opposite sign.
[0008]
As a result, the effects obtained by the present invention are shown below as compared with the prior art.
First, in the prior art, a reflector having a rough surface of a metal having high light reflectance such as aluminum or silver was used.
At this time, the reflection surface is roughened for the following reason. In other words, if the reflecting surface remains a mirror surface, even if a blazed reflecting surface is used, for example, a light source such as a fluorescent lamp on the ceiling will be reflected in its original shape and will be visually recognized as a background, As a result, the display becomes difficult to see.
[0009]
Here, the reflectance on the mirror-finished metal surface is as high as 90% or more, for example, but when the surface is roughened, multiple reflections occur, and as a result, the reflectance decreases by the number of times of multiple reflection. That is, the reflectance on the polished surface is significantly lower than the reflectance on the mirror surface, and as a result, the brightness is reduced in the related art.
[0010]
Therefore, in the present invention, instead of roughening the specular reflection surface, a light scattering layer made of a transparent medium having a different refractive index is used to easily obtain a high transmittance of, for example, 99% or more. The light is scattered by the light-scattering layer, and the light is scattered by the light-scattering layer so that the light is reflected only once on the mirror-reflecting surface. This greatly reduces the absorption loss on the reflecting surface. , The reflectance can be increased, and the brightness can be greatly increased.
[0011]
In addition, a mold is often used for the transfer of the blaze shape. At this time, if the surface of the mold is roughened to roughen the reflection surface, the mold is clogged and the reflection surface is formed. At the time of preparation, cleaning is required over and over again, resulting in poor workability and high cost. However, with a mirror surface, there is no danger of clogging. Is obtained.
[0012]
Next, usually, for example, many light sources in an office or the like are installed on a ceiling. Therefore, most of the illumination light for office equipment such as a laptop personal computer (hereinafter abbreviated as a personal computer) and a notebook personal computer is emitted from above to below.
[0013]
On the other hand, a display device of a laptop computer or a notebook computer to which the present invention is applied is usually used by leaning on the display device, and as a result, the display surface is irradiated per unit area. The energy of light is significantly smaller than in the case of a desktop calculator or the like in which the plane of the display device is directed right above.
[0014]
Further, in the reflection plate used in the prior art, most of the light emitted from above is reflected downward, transmitted through the display panel, and the intensity of light transmitted to the user's eyes under the control of brightness is further reduced. As a result, only an extremely dark display can be obtained.
[0015]
Therefore, in the prior art, even in the case of battery operation, a transmissive liquid crystal display device having a backlight has to be mainstream, despite the remarkable reduction of its life.
[0016]
However, according to the present invention, since the reflecting surface is a blazed mirror surface, the reflecting direction can be controlled even under the path of the light from the light source in such a general office, and the incident light amount can be controlled. Light emitted from above the office can be directed toward the front of the panel, that is, toward the user's eyes. As a result, the intensity of light reaching the user's eyes increases, and the brightness of the display device increases. Can be improved.
[0017]
Further, at this time, in the present invention, the liquid crystal display means including the liquid crystal and the pair of polarizing films has a configuration having normally open characteristics, so that the transmittance in the incident direction of external light can be increased. As a result, the intensity of the incident light further increases, and a brighter display can be obtained.
[0018]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, a reflective liquid crystal display device according to the present invention will be described in detail with reference to the illustrated embodiments.
[0019]
FIG. 1 shows an embodiment in which a reflection type liquid crystal display device 1 according to the present invention is applied as a display device of a laptop personal computer. Reference numeral 4 denotes a main body (processing unit) of the personal computer, and reference numeral 2 denotes a liquid crystal display unit. Reference numeral 3 denotes a reflection unit.
Then, in this embodiment, Yes liquid crystal display part 2 is set to the angle theta 60 degrees formed by the horizontal plane, in this state, the incident light L _A from above as the illumination light source, toward the normal direction of the display surface display by the reflected light L _B is obtained, a bright screen display viewing direction E is adapted to obtain.
[0020]
The liquid crystal display unit 2 includes two polarizing films (polarizing plates) 21 and a liquid crystal display element 22 sandwiched between them. Although not shown in this figure, a retardation plate is disposed between the polarizing film 21 and the liquid crystal display element 22.
The reflecting portion 3 is composed of a blazed mirror-like reflector 31 formed by aluminum evaporation and a light scattering layer 32, and the light scattering layer 32 is sandwiched between the blazed mirror-like reflector 31 and the liquid crystal display 2. Are located.
[0021]
The liquid crystal display element 22 is manufactured as follows.
First, two transparent glass plates are prepared as substrates.
Each of them has a thickness of 1.1 mm and the surface is optically polished. Further, inside these substrates, XY matrix transparent electrodes connected to a driver IC are formed. Thus, a display portion of 640 × 480 pixels is obtained, and the display area size at this time is 9.4 inches (about 24 cm) in diagonal length.
[0022]
Next, a liquid crystal composition in which a small amount of a chiral substance S-811 (manufactured by Merck) is added to the nematic liquid crystal ZLI-2293 (manufactured by Merck) is sandwiched between these two substrates and sealed.
Here, the natural pitch of the liquid crystal composition is 10.5 μm, and the gap between the substrates is 6.1 μm. At this time, a bead spacer made of divinylbenzene having a diameter of 6.3 μm is sandwiched. A constant gap of 6.1 μm is maintained.
[0023]
A polyimide-based alignment film LQ-1800 (manufactured by Hitachi Chemical Co., Ltd.) is applied on the transparent electrodes of these substrates to a thickness of about 500 ° by a spin coating method and surface-treated by a rubbing method. The material has a pre-tilt angle of about 5 degrees and a twist angle of 240 degrees.
[0024]
The polarizing film 21 and the phase difference plate are made of, for example, NPF-F1225DU manufactured by Nitto Denko Corporation, and are configured so that the liquid crystal display means 2 is provided with normally open characteristics.
Here, the normally open characteristics are characteristics in which the transmittance is high while the voltage applied to the liquid crystal is low, and the transmittance decreases as the voltage is increased. FIG. 5 shows the viewing angle characteristics of the liquid crystal display means 2 having.
As is apparent from the characteristics shown in FIG. 5, in this embodiment, the transmittance to the light b (FIG. 1) incident from an oblique direction is reduced by using the liquid crystal display means 2 having such normally open characteristics. Higher, which results in a further increase in brightness.
[0025]
The light scattering layer 32 is made as follows.
First, a bisphenol A type epoxy resin (EP827, epoxy equivalent 180) was prepared at a weight ratio of 50, and methylhexahydrophthalic anhydride (NH8210, acid equivalent 162) was prepared at a weight ratio of 50, and these were mixed to form a transparent medium. Get.
Next, a small amount of 2-ethyl-4-methylimidazole is added as a curing agent to the transparent medium, and a transparent material having a particle size of about 20 μm and made of PMMA (polymethyl methacrylate) which is a material having a different refractive index from the transparent medium. Was also mixed in a weight ratio of 20 to form a film having a thickness of about 50 μm between the blazed specular reflection plate 31 and the polarizing film 20, and then cured at 100 ° C. for 2 hours.
[0026]
Here, the transparent medium made of EP827 and NH8210 has a refractive index of 1.53, and the transparent body made of PMMA has a refractive index of 1.49. The refractive index difference of 0.04 makes it possible to function as a light scattering layer. You get it.
The transparent medium made of EP827 and NH8210 in this embodiment is a thermosetting resin, but is not limited to the thermosetting resin as long as it is a mixture of transparent media having different refractive indexes.
[0027]
The light scattering layer 32 thus formed is made of only a transparent medium, and thus scatters light without absorbing it.
Therefore, the reflectance can be further increased in combination with the specular reflection characteristics of the blazed specular reflection plate 31.
That is, in the case of this embodiment in which the light scattering layer 32 is combined with the blazed specular reflector 31, the intensity of the reflected light b increases in the visual recognition direction d compared to when the blazed reflector is grounded. Brightness improved 1.3 times.
[0028]
In this example, the layer thickness of the light scattering layer 32 was set to 50 μm. However, by increasing the difference in refractive index between the transparent medium and the transparent body or increasing the density of particles to be mixed, The thickness can be further reduced.
At this time, although the magnitude of the refractive index of the transparent particles mixed in the transparent medium does not matter, it is preferable that the back scattering by the light scattering layer 32 is small. This is because, if the backscattering is large, the directivity of the light reflected by the blazed specular reflector 31 is lost, and the brightness is reduced.
[0029]
Therefore, in order to reduce the back scattering by the light scattering layer 32, the particle size of the transparent body is set to be larger than 0.5 μm, and the difference in the refractive index from the transparent medium is set to 0.01 or more and 0.3 or less. It is desirable.
[0030]
The blazed specular reflector 31 is made as follows.
First, a blazed mold is manufactured by machining. Next, the blaze shape is transferred to the thermosetting resin using the mold. Then, aluminum is vapor-deposited on the surface to obtain a reflection surface composed of a blazed mirror surface.
At this time, the blaze angle (inclination angle) was 20 degrees and the groove width of the blaze was 35 μm.
[0031]
According to blazed specular reflector 31 thus obtained, as shown in FIG. 2, the incident light L _A is scattered by the light scattering layer 32, is reflected directionally by the blaze angle with blazed specular reflector 31, it is possible to obtain reflected light L _B having a peak value of the intensity in the normal direction of the display surface, as shown in FIG. 1, under illumination by the incident light L _a from above, bright display in the viewing direction E Can be obtained.
[0032]
Then, at this time, according to this embodiment, since the reflecting portion 3 in which the light scattering layer 32 is combined with the blazed specular reflecting plate 31 is used, under the high reflectivity by the mirror surface and the high transmissivity. Can be provided, and as a result, the light use efficiency is greatly improved, and under a sufficient brightness, it is possible to easily obtain a clear display with no fear of the background being reflected. it can.
[0033]
Next, another embodiment of the present invention will be described.
First, FIG. 3 shows one embodiment of the present invention in a case where the polarizing film 21 is integrated with the blazed mirror-like reflecting plate 31 by using the light scattering layer 32 as an adhesive to produce a film-like polarizing reflecting plate. This is an example.
According to the embodiment of FIG. 3, since the polarizing film 21 and the blazed specular reflector 31 are integrated, reflection loss at the interface between them can be prevented, and the brightness can be further improved. .
[0034]
Next, FIG. 4 shows that one surface (the surface opposite to the surface in contact with the polarizing film 21, the back surface) of the light scattering layer 32 is molded in a blazed shape, and aluminum is vapor-deposited on the molded surface. This is an embodiment of the present invention in which a reflecting surface is used as a blazed mirror-like reflecting plate 31.
In this embodiment, as the material for transferring the shape from the blaze molding die, the above-described thermosetting resin, that is, a thermosetting resin obtained by mixing transparent particles PMMA into a transparent medium (EP827 and NH8210) is used. After the resin is molded and cured by a mold, aluminum is vapor-deposited on the molding surface to obtain a blazed specular reflector 31 integrated with the light scattering layer 32 as shown in FIG.
[0035]
According to the embodiment of FIG. 4, since aluminum is directly deposited on the light scattering layer 32, it is not necessary to consider thermal expansion between the blazed specular reflector 31 and the light scattering layer 32. Therefore, a display device that is bright, has good visibility, and has stable characteristics can be easily obtained.
[0036]
Therefore, by using the reflection type liquid crystal display device according to the above embodiment as a display unit of a laptop computer or a notebook computer, and a display unit of a palmtop computer or a PDA (personal digital assistant), a high contrast ratio is obtained. In addition, a bright and highly visible display can be obtained, and an information processing apparatus with low power consumption can be easily provided.
[0037]
By the way, as a liquid crystal element, there is a liquid crystal element in which a liquid crystal and a dichroic dye are mixed in a polymer without using a polarizing film, and the present invention relates to a reflection type liquid crystal display device using such a display element. Can also be applied.
Also in this case, although the contrast ratio is not as high as that of the above-described embodiment, the brightness which is a problem in the reflection type liquid crystal display device is sufficiently improved.
[0038]
【The invention's effect】
According to the present invention, a light-scattering layer is combined with a mirror-like blazed reflection surface, and a liquid crystal element having normally open characteristics is used, so that incident light from oblique directions can be efficiently used as illumination light. In other words, a reflective liquid crystal display device that is sufficiently bright, has good visibility, and consumes low power can be obtained as a reflective type device that does not require a backlight.
[0039]
As a result, when the battery is operated, the battery life can be prolonged, which can greatly contribute to the improvement of the performance of the battery operated laptop personal computer and the notebook personal computer.
[Brief description of the drawings]
FIG. 1 is a sectional view showing one embodiment of a reflection type liquid crystal display device according to the present invention.
FIG. 2 is a cross-sectional view showing one embodiment of a reflecting section according to the present invention.
FIG. 3 is a cross-sectional view showing another embodiment of the reflection section in the present invention.
FIG. 4 is a cross-sectional view showing still another embodiment of the reflection section in the present invention.
FIG. 5 is a characteristic diagram of the liquid crystal display means according to one embodiment of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Reflection type liquid crystal display device 2 Liquid crystal display part 3 Reflection part 4 PC main body (processing part)
21 polarizing film 22 liquid crystal display device 31 blazed specular reflector 32 light scattering layer _{L A} incident light _{L B} reflected light E viewing direction

Claims (3)

A reflection type liquid crystal display device having a light scattering layer and a light reflecting surface on the back surface of the liquid crystal display means having normally open characteristics and operating as external light incident on the display surface of the liquid crystal display means as illumination light.
The light-scattering layer is a transparent medium, an adhesive in which transparent particles having a different refractive index from the transparent medium are put in the transparent medium,
The light reflecting surface is constituted by a blazed specular reflecting layer,
The reflection type liquid crystal display device, wherein the light reflection surface and the liquid crystal display unit are directly bonded and joined by the light scattering layer with the light scattering layer interposed therebetween. In the invention of claim 1,
The difference between the refractive index of the transparent medium and the refractive index of the transparent body is 0.01 to 0.30. In the invention of claim 1 or claim 2,
The blazed specular reflection surface reflects external light incident from a direction having an inclination angle exceeding 0 degree with respect to the normal direction of the display surface substantially in the normal direction, and also reflects the external light in the normal direction. Wherein the reflection intensity is higher than the reflection light intensity in the direction having the same angle as the tilt angle and the opposite sign.

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