JP2003344853A - Reflective liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a reflective liquid crystal display device with which a uniform and bright display screen is obtainable by preventing Moire fringes from being generated. <P>SOLUTION: In the reflective liquid crystal display device equipped with a liquid crystal display element and a front light to illuminate the liquid crystal display element wherein the front light is provided with at least a light guide body with a plurality of fine prisms on the surface opposite to the liquid crystal display element and a light source placed along the width direction of an end part of the light guide body, the reflective liquid crystal display device is characterized by having a ridge line 22c of the fine prisms of the light guide plate 22 made to be a curved line or a straight line with a projecting and recessing shape. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reflective liquid crystal display device, and more particularly to a reflective liquid crystal display device having a front light arranged in front of a liquid crystal display element.

[0002]

2. Description of the Related Art In a conventional reflective liquid crystal display device,
The front light is used to illuminate the liquid crystal display element. The front light of this reflective LCD is
A light source and a light guide plate that introduces light from an end surface facing the light source into the inside and diffuses it, and irradiates the reflected light reflected by the prism surface to the outside to illuminate a liquid crystal display element that is an illuminated object. Have and.

An example of a reflection type liquid crystal display device using a front light in the prior art will be described below with reference to FIGS. 7 to 13. FIG. 7 is a cross-sectional view schematically showing an outline of a conventional reflective liquid crystal display device. FIG. 8 is a plan view of the reflective liquid crystal display device. As shown in FIGS. 7 and 8, the reflective liquid crystal display device 10 includes a liquid crystal display element 1
5, the front light 16 is provided. The front light 16 is disposed on the liquid crystal display element 15 and includes an LED (light emitting diode) 11 as a light source and a light guide 12, and the light guide 1 is made of a transparent synthetic resin plate for guiding light.
LEDs (light emitting diodes) 11 are arranged close to each other along the side surface of No. 2. In addition, the light guide plate 12 has a prism surface 12b on which a step-like fine prism on which gentle wavy projections are formed is formed. It is arranged so as to be the upper surface of the light plate 12.

Further, FIG. 7 schematically shows the locus of light incident on the inside of the light guide plate 12. As shown in FIG. 7, the light from the LED (light emitting diode) 11 that has entered the inside of the light guide plate 12 from the end face 12a of the light guide plate 12 has a stepwise fine prism formed as shown by a ray A. The light is totally reflected by the prism surface 12b (upper surface) that is present, goes downward, and is emitted from the smooth surface 12d that is the lower surface of the light guide plate 12 to irradiate the liquid crystal display element 15 located therebelow as irradiation light. Thereafter, the irradiation light is reflected by the liquid crystal display element 15 and again enters from the lower surface 12d of the light guide plate 12, goes upward, passes through the light guide plate 12, and reaches the eyes of the observer.

The light ray B is totally reflected by the lower surface 12d of the light guide plate 12, and then totally reflected by the prism surface 12b on which the step-like fine prisms are formed, and travels downward. An example of light reaching the observer's eye in the optical path of is shown.

FIG. 9 is a plan view of the light guide plate 12, and FIG. 10 is a partially enlarged side view of the light guide plate 12 showing a main optical path. As shown in FIGS. 9 and 10, the light guide plate 12 has fine prisms 12b formed on the fine prism surface 12b of the light guide plate 12, and the prisms are gentle slopes. a and a steep slope b, and the ridge lines 12c of this prism are formed in parallel.

FIG. 11 is a plan view of the liquid crystal display element 15, FIG.
2 is a partially enlarged cross-sectional view showing the outline of the BB cross section in FIG. 11. As shown in FIGS. 11 and 12, in the liquid crystal display element 15, a plurality of electrodes 15a and 15b are provided so as to intersect with each other, and pixels 15c are formed in a matrix.

FIG. 13 is a view showing a state in which the liquid crystal display element 15 and the light guide plate 12 are arranged so as to overlap each other. The pixel repeating direction of the liquid crystal display element 15 and the prism ridge line 12c of the light guide plate 12 are shown.
Shows the relationship with the direction of. As shown in FIG. 13, in the conventional reflective liquid crystal display device, between the light guide 12 and the liquid crystal display element 15, the direction of the ridgeline 12c of the light guide plate 12 is the repeating direction of the pixels 15c of the liquid crystal display element 15, They were arranged almost in parallel.

[0009]

However, the direction of the prism ridgeline 12c of the light guide plate 12 and the liquid crystal display element 15 are to be solved.
When the repeating directions of the pixels 15c are arranged substantially parallel to each other, moire fringes (striped pattern) may appear on the screen depending on the pitch size of the prism ridge lines 12c.
In the conventional light guide plate 12 and the liquid crystal display element 15, as shown in FIGS. 10 and 12, there are a portion where light is shown by hatching and a portion where light is not shown without hatching, respectively. However, these are repeated at a certain specific pitch, forming a so-called striped pattern. These striped patterns have no problem when the pitches are exactly the same, but when striped patterns having two different pitches are overlapped with each other, moire fringes are generated and visibility is deteriorated.

The reflection type liquid crystal display device in the prior art is
As shown in FIG. 13, the prism ridgeline 1 of the light guide plate 12
Although the direction of 2c is arranged substantially parallel to the repeating direction of the pixels of the liquid crystal display element 15, the prism ridgeline 12c of the light guide plate 12 and the repeating direction of the pixels of the liquid crystal display element 15 are
There is a slight angle shift due to an assembly error or the like, and in reality, they are not perfectly parallel.

Therefore, the prism ridgeline 1 of the light guide plate 12
When the direction of 2c is arranged substantially parallel to the repeating direction of the pixels of the liquid crystal display element 15, interference may occur with the pixel pitch in the repeating direction of the pixels of the liquid crystal display element 15 depending on the size of the pitch of the prism ridge lines 12c. However, there is a problem that moire fringes are generated on the screen of the liquid crystal display element 15.

Therefore, conventionally, in order to prevent this moire fringe, the pitch of the prism ridge lines 12c of the light guide plate 12 is adjusted, or the prism ridge lines 12c of the light guide plate 12 and
Pixel 15c or electrodes 15a, 15b of liquid crystal display element 15
A measure such as rotating the light guide plate 12 so that and intersect at a predetermined angle has been adopted. However, there are few kinds of light guide plates that are actually produced, and if the pitch dimension of the prism ridges 12c is prioritized to prevent moire fringes, the usable light guide plates are limited, and the brightness of the front light cannot be prioritized. there were.

(Object of the Invention) An object of the present invention is to prevent the occurrence of moire fringes due to the interference between the light guide plate and the liquid crystal display element to obtain a uniform display screen regardless of the pitch dimension of the prism ridgelines of the light guide plate. An object of the present invention is to provide a low-cost reflective liquid crystal display device capable of improving the brightness of the front light and obtaining a bright display screen.

[0014]

In order to achieve the above-mentioned object, a reflection type liquid crystal display device according to a first aspect of the present invention includes a liquid crystal display element and an illumination for the liquid crystal display element. At least a light guide body having a plurality of fine prisms on the surface opposite to the liquid crystal display element, and a light source arranged along the width direction of the end portion thereof. In the reflective liquid crystal display device having the above, the ridge lines of the fine prisms of the light guide plate are curved lines or concave and convex straight lines.

The reflective liquid crystal display device according to the second aspect of the present invention is characterized in that the ridge lines of the fine prisms of the light guide plate are arc-shaped curves.

Further, the reflection type liquid crystal display device according to the invention of claim 3 is characterized in that the ridges of the fine prisms of the light guide plate are composed of a plurality of curves.

A reflection type liquid crystal display device according to a fourth aspect of the present invention comprises a liquid crystal display element and a front light for illuminating the liquid crystal display element.
In a reflective liquid crystal display device, wherein the front light has at least a light guide body having a plurality of fine prisms on a surface opposite to the liquid crystal display element, and a light source arranged along a width direction of an end portion thereof, The ridges of the fine prisms of the light guide plate are formed by combining straight lines and curved lines.

The reflective liquid crystal display device according to a fifth aspect of the present invention is the reflective liquid crystal display device according to the fourth aspect, wherein at least one of the straight line and the curved line is plural. It is characterized by

(Operation) Moire fringes are generated by overlapping fringes of two different periods, and the period T can be obtained by the following formula. 1 / T = | 1 / T1 −1 / T2 | (where T1 and T2 are the periods of two striped patterns, respectively). Therefore, one of the shapes is a curve, a straight line having an uneven shape, or
The cycle T can be made fine by using a shape that combines a curved line and a straight line. As a result, the moire fringes generated by the interference of the two fringe patterns with each other are finer than the resolution of the eyes of the observer, and the moiré patterns can be finally eliminated. Hereinafter, a detailed description will be given based on the embodiment.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION (First Embodiment) A first embodiment of the present invention will be described below with reference to FIGS. The reflective liquid crystal display device according to the present embodiment is characterized in that the stepwise fine prism ridge lines of the light guide plate arranged on the liquid crystal display element are formed into arc-shaped curves. Therefore, the basic structure of the reflection type liquid crystal display device is similar to that of the prior art, and the components other than the light guide plate are the same as those of the prior art.

FIG. 1 shows a light guide plate 22, FIG. 1 (a) is a plan view, and FIG. 1 (b) is a partially enlarged cross-sectional view showing the AA cross section in FIG. 1 (a). Further, FIG. 2 shows a liquid crystal display element 1.
5 is a diagram showing a state in which the light guide plate 22 and the light guide plate 22 are overlapped with each other, and the repeating direction of the pixels 15c of the liquid crystal display element 15 and the light guide plate 2
2 shows the relationship with the direction of the prism ridgeline 22c.
As shown in FIG. 1, the light guide plate 22 has a smooth surface 22 on its lower surface.
d, the upper surface is a fine prism surface 22b, and the material is a transparent plate such as polycarbonate. A large number of step-like fine prisms are formed on the fine prism surface 22b of the light guide plate 22.

When the light guide plate 22 is arranged on the liquid crystal display element 15, as shown in FIG. 2, the prism ridge line 22c formed by the arc-shaped curve is the pixel 15c of the liquid crystal display element 15.
It is possible to obtain a reflection type liquid crystal display device in which moire fringes do not occur without overlapping in parallel with the repeating direction (arrows A and B).

The curvature and center position of the arc-shaped curve of the prism ridge line 22c described in this embodiment are not particularly limited. Further, in the present embodiment, the prism ridge line 22c has been described by taking an arc-shaped curve as an example, but the same effect can be obtained also in the case of a multi-order curve such as a quadratic curve or a cubic curve.

As described above, according to the reflective liquid crystal display device of this embodiment, it is possible to prevent the generation of moire fringes and obtain a uniform display screen. In addition, a slight angle deviation caused by an assembly error or the like does not pose a problem and the manufacturing cost can be reduced. Furthermore, since the pitch dimension of the prism ridgeline 22c of the light guide plate 22 is not related to the occurrence of moire fringes, it is possible to select the pitch dimension of the prism ridgeline 22c with priority given to the brightness of the front light.
As a result, the brightness of the liquid crystal display element 15 due to the illumination light from the front light can be increased and a bright liquid crystal display screen can be obtained.

(Second Embodiment) A second embodiment of the present invention will be described with reference to FIGS. The reflection type liquid crystal display device according to the present embodiment is different from that of the first embodiment in the shape of the prism ridge line of the light guide plate, and is otherwise the same as that of the first embodiment, and the description thereof will be omitted. FIG. 3 is a plan view of a light guide plate according to the second embodiment, and FIG. 4 is a plan view of a light guide plate showing another example of the present embodiment.

As shown in FIG. 3, in the reflection type liquid crystal display device according to the present embodiment, the fine prism ridge lines 3 of the light guide plate 32 are used.
It is characterized in that 2c is formed by two arc-shaped curves 31 and 33 having the same shape. Light guide plate 3 in the present embodiment
In the same manner as in the first embodiment, the prism ridge line 32
c does not overlap in parallel with the repeating direction of the pixels 15c of the liquid crystal display element 15, and a reflection type liquid crystal display device in which moire fringes do not occur can be obtained.

In FIG. 4, the ridgeline 42c of the fine prism of the light guide plate 42 is divided into two arc-shaped curves 41 having different shapes.
The example formed by 43 is shown. In this case as well, a reflective liquid crystal display device in which moire fringes are not generated can be obtained.

The curvature and center position of the arc-shaped curves of the prism ridge lines 32c and 42c described in this embodiment are not particularly limited. In addition, the prism ridgeline 32
Although c and 42c are described using two arc-shaped curves as an example,
The number of arc-shaped curves is not particularly limited, and a plurality of arc-shaped curves can be freely selected. Further, in the present embodiment, the prism ridge lines 32c and 42c are described by taking an arc-shaped curve as an example, but similar effects to the case of a multi-order curve such as a quadratic curve and a cubic curve as in the first embodiment. Can be obtained.

As described above, also in the reflection type liquid crystal display device of this embodiment, the same effect as that of the first embodiment can be obtained.

(Third Embodiment) A third embodiment of the present invention will be described with reference to FIG. The reflection type liquid crystal display device according to the present embodiment is different from that of the first embodiment in the shape of the prism ridge line of the light guide plate, and is otherwise the same as that of the first embodiment, and the description thereof will be omitted. FIG. 5 is a plan view of the light guide plate according to the third embodiment.

As shown in FIG. 5, the reflection type liquid crystal display device according to the present embodiment is characterized in that the ridge line 52c of the fine prism of the light guide plate 52 is formed by two straight lines 51 and 53 having an uneven shape. That is, the prism ridge line 52c is formed by a zigzag straight line as in the first embodiment.
It is possible to obtain a reflective liquid crystal display device in which the moire fringes do not occur in the liquid crystal display element 15 without overlapping in parallel with the repeating direction of the pixels 15c.

The straight line 51 described in this embodiment is used.
The inclination angle of the straight line 53 with respect to is not particularly limited. Further, although the prism ridge line 52c has been described by taking as an example two concave and convex straight lines, the number of straight lines is not particularly limited and a large number of straight lines can be freely selected.

As described above, also in the reflection type liquid crystal display device of this embodiment, the same effect as that of the first embodiment can be obtained.

(Fourth Embodiment) A fourth embodiment of the present invention will be described with reference to FIG. The reflection type liquid crystal display device according to the present embodiment is different from that of the first embodiment in the shape of the prism ridge line of the light guide plate, and is otherwise the same as that of the first embodiment, and the description thereof will be omitted. FIG. 6 is a plan view of the light guide plate according to the fourth embodiment.

As shown in FIG. 6, the reflection type liquid crystal display device in this embodiment is characterized in that the ridge lines 62c of the fine prisms of the light guide plate 62 are formed by the straight line 61 and the arc-shaped curve 63. Similar to the first embodiment, the prism ridge line 62c does not overlap in parallel with the repeating direction of the pixels 15c of the liquid crystal display element 15, and a reflection type liquid crystal display device in which moire fringes do not occur can be obtained.

It should be noted that either one of the straight line 61 of the prism ridgeline 62c and the arc-shaped curve 63 described in the present embodiment may be plural, or both of them may be plural. Further, the curvature, center position, etc. of the arc-shaped curve 63 are not particularly limited as in the first embodiment.
It goes without saying that the arc-shaped curve 63 can also obtain the same effect in the case of a multi-dimensional curve such as a quadratic curve or a cubic curve.

As described above, also in the reflection type liquid crystal display device in this embodiment, the same effect as in the first embodiment can be obtained.

In the first to fourth embodiments, the fine prisms provided on the light guide body have been described by taking the stepwise fine prisms having the gentle wavy projections as an example. It goes without saying that the same effect can be obtained also in the case of a so-called V-groove prism in which a V-shaped groove is provided on the surface.

[0039]

As described above, according to the reflection type liquid crystal display device of the present invention, the ridge lines of the fine prisms of the light guide plate arranged on the liquid crystal display element are arranged with respect to the repeating direction of the pixels of the liquid crystal display element. Since it has an inclination angle, it is possible to prevent the generation of moire fringes due to the interference between the light guide plate and the liquid crystal display element and obtain a uniform display screen.

Further, since the pitch dimension of the prism ridgeline of the light guide plate is not related to the generation of moire fringes, the pitch dimension of the prism ridgeline should be selected with priority on the front light brightness without paying attention to the generation of moire fringes. Is possible. As a result, the brightness of the liquid crystal display element due to the illumination light from the front light can be increased and a bright liquid crystal display screen can be obtained.

Further, the production cost can be reduced without the generation of moire fringes due to a slight angle deviation caused by an assembly error or the like.

[Brief description of drawings]

1A and 1B are views for explaining a reflective liquid crystal display device according to a first embodiment of the present invention, FIG. 1A is a plan view of a light guide plate, and FIG. 1B is a plan view of FIG. 1A. It is a partial expanded sectional view which shows the AA cross section.

FIG. 2 is a diagram showing an arrangement of a liquid crystal display element and a light guide plate according to the first embodiment of the present invention.

FIG. 3 is a plan view of a light guide plate according to a second embodiment of the present invention.

FIG. 4 is a plan view of a light guide plate showing another example of the second embodiment of the present invention.

FIG. 5 is a plan view of a light guide plate according to a third embodiment of the present invention.

FIG. 6 is a plan view of a light guide plate according to a fourth embodiment of the present invention.

FIG. 7 is a cross-sectional view schematically showing an outline of a reflective liquid crystal display device in the related art.

FIG. 8 is a plan view of a reflection type liquid crystal display device in the related art.

FIG. 9 is a plan view of a light guide plate in the related art.

FIG. 10 is a partially enlarged side view of a light guide plate in the related art and a diagram showing a main optical path.

FIG. 11 is a plan view of a liquid crystal display element according to a conventional technique.

12 is a partially enlarged cross-sectional view showing the outline of the BB cross section in FIG.

FIG. 13 is a diagram showing an arrangement of a liquid crystal display element and a light guide plate in a conventional technique.

[Explanation of symbols]

10 Reflective Liquid Crystal Display Device 11 LED 12 Light Guide 12a End Face 12b of Light Guide Prism Surface 12c of Light Guide Prism Ridge 12d Smooth Surface of Light Guide 15 Liquid Crystal Display Device 15a, 15b Electrode 15c Pixel 16 Front Light 22 , 32, 42, 52, 62 light guides 22c, 32c, 42c, 52c, 62c prism ridge lines 31, 33, 41, 43, 63 arc-shaped curves 51, 53, 61 straight line a gentle slope b steep slope

Claims (5)

[Claims] 1. A light guide body comprising a liquid crystal display element and a front light for illuminating the liquid crystal display element, the front light having a plurality of fine prisms on a surface opposite to the liquid crystal display element. A reflection type liquid crystal display device having at least a light source arranged along the width direction of the end portion thereof, characterized in that the ridge lines of the fine prisms of the light guide plate are curved or concave and convex straight lines. Type liquid crystal display device. 2. The reflective liquid crystal display device according to claim 1, wherein the ridges of the fine prisms of the light guide plate are arc-shaped curves. 3. The reflection type liquid crystal display device according to claim 1, wherein the ridges of the fine prisms of the light guide plate are composed of a plurality of curves. 4. A light guide body comprising a liquid crystal display element and a front light for illuminating the liquid crystal display element, the front light having a plurality of fine prisms on a surface opposite to the liquid crystal display element. A reflection type liquid crystal display device having at least a light source arranged along the width direction of the end portion thereof, wherein the ridge lines of the fine prisms of the light guide plate are composed of a combination of straight lines and curved lines. Type liquid crystal display device. 5. The reflective liquid crystal display device according to claim 4, wherein at least one of the straight line and the curved line is plural.