JPH10325952A - Reflection type liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To brighten a picture display and to enhance contrast. SOLUTION: A liquid crystal layer 3 is provided between a pair of transparent substrates 1, 2 opposite to each other, and polarizing plates 5, 6 are provided respectively on the outside of a pair of these transparent substrates 1, 2, and a reflector 20 constituted of forming plural stripe grooves lengthening to one direction on its surface is provided on the outside of the polarizing plate 6 of a side opposite to a display side facing to the polarizing plate 6. Then, angles between directions of many stripe grooves formed on the reflection surface of the reflector 20 and the direction of the axis of polarization of the polarizing plate 6 is made 0 to 15 deg..

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reflection type liquid crystal display device having a bright display surface and good display quality over a wide range of viewing angles.

[0002]

2. Description of the Related Art In recent years, a reflection type liquid crystal display device has been widely used as a display unit of a handy type computer or the like because of particularly low power consumption. In this reflection type liquid crystal display device, a reflector for displaying light by reflecting light incident from the display surface side is arranged. As the conventional reflector, a reflector having a mirror-finished surface or a reflector having an irregular surface on random irregularities has been used. As shown in FIG. 11, this conventional random uneven reflector 60 has
For example, glass spheres having an average particle size of 1 to several tens of μm are sprayed on the surface of a flat resin base material 61 made of acrylic or the like by compressed air to form an uneven surface 61 a having a large number of unevenness having a height of about several tens μm. The reflection film 62 made of aluminum, silver, or the like is formed on the uneven surface 61a by vapor deposition or the like.

Next, an example of a reflection type liquid crystal display device using the reflector 60 will be described with reference to FIG. As shown in FIG. 12, a conventional reflection-type liquid crystal display device 50 includes a pair of glass substrates 5.
The transparent electrode layers 53, 54
Are provided, and liquid crystal alignment films 55 and 56 are provided on the transparent electrode layers 53 and 54, respectively, and a liquid crystal layer 57 is provided between the pair of glass substrates 51 and 52. Furthermore, first and second glass substrates 51 and 52 are provided outside the glass substrates 51 and 52, respectively.
Are provided, and a reflector 60 is attached outside the second polarizing plate 59 with the uneven surface of the uneven reflecting film 62 facing the second polarizing plate 59 side. In such a conventional reflective liquid crystal display device 50, light incident from the first polarizing plate 58 is linearly polarized by the first polarizing plate 58,
The polarized light passes through the liquid crystal layer 57 to be elliptically polarized. The elliptically polarized light is linearly polarized again by the second polarizing plate 59, and the linearly polarized light is reflected by the reflector 60, passes through the second polarizing plate 59 and the liquid crystal layer 57 again, and is then linearly polarized. The light exits from the first polarizing plate 58.

[0004]

In the above-mentioned conventional reflection type liquid crystal display device 50, the range of the reflection direction is widened because the incident light is reflected in the random direction by the uneven reflector 60. In other words, the viewing angle is increased. On the other hand, there is a problem that it is difficult to guide desired reflected light within a specific angle range which is originally a viewing angle range. That is, there is a problem that the display surface is dark. The present invention has been made in view of this problem, and has as its object to provide a reflective liquid crystal display device in which the brightness of a display surface is significantly improved as compared with a conventional reflective liquid crystal display device. is there.

[0005]

According to the reflection type liquid crystal display device of the present invention, a liquid crystal layer is provided between a pair of transparent substrates facing each other, and a polarizing plate is provided outside each of the pair of transparent substrates. A reflector having a reflecting surface formed by forming a plurality of grooves extending in one direction on the outside of the one polarizing plate is provided toward the one polarizing plate, and the polarizing axis of the one polarizing plate and the groove of the reflector are provided. Is set to 0 to 15 degrees. According to such a reflection type liquid crystal display device, the screen display can be made bright and the contrast can be increased.

In a reflection type liquid crystal display device according to the present invention, a liquid crystal layer is provided between a pair of opposed transparent substrates, and a polarizing plate is provided on an outer surface of one of the pair of transparent substrates. A reflector having a plurality of grooves extending in one direction formed on the outer surface of the other transparent substrate is provided with a reflector facing the other transparent substrate, and the other transparent substrate is incident from the polarizing plate. The angle between the major axis direction of the elliptically polarized light passing through and the direction in which each groove of the reflecting surface extends is 0 to 1
5 degrees. Since only one polarizing plate is used in such a reflective liquid crystal display device, the amount of light can be effectively used, and the screen display can be further brightened as compared with the reflective liquid crystal display device having the pair of polarizing plates.

Furthermore, in the reflection type liquid crystal display device according to the present invention, a liquid crystal layer is provided between a pair of opposing transparent substrates,
A polarizing plate is provided on the outer surface of one of the pair of transparent substrates, and a reflection surface formed by forming a plurality of grooves extending in one direction inside the other transparent substrate of the pair of transparent substrates is formed on the one of the one transparent substrate. A reflector facing the transparent substrate is provided, and the angle between the major axis direction of the elliptically polarized light that enters from the polarizing plate and passes through the liquid crystal layer and the direction in which each groove of the reflection surface extends is 0 to 15 degrees. . According to such a reflective liquid crystal display device, in addition to improving the brightness of the screen display, light passing through the liquid crystal layer is reflected by the reflector without passing through the other transparent substrate, so that the display image is doubled. It is possible to brighten the screen display without causing the problem of so-called parax phenomenon.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the reflection type liquid crystal display device according to the present invention will be described below with reference to the drawings. As shown in FIG. 1, the reflection type liquid crystal display device injects liquid crystal between a display side glass substrate 1 and a back side glass substrate 2 which are a pair of transparent substrates having a thickness of, for example, 0.7 mm. The display-side glass substrate 1 is provided with a retardation plate 4 made of a polycarbonate resin, a polyarylate resin, or the like, and a first polarizing plate is provided on the top surface of the retardation plate 4. 5 are provided. Back glass substrate 2
A second polarizing plate 6 and a plate-like reflector 20 are sequentially provided on the lower surface of the first substrate. The reflector 20 is laminated on the lower surface of the second polarizing plate 6 with the uneven reflecting film 22 facing the surface, and between the second polarizing plate 6 and the reflecting film 22, refraction of light such as fluorine-containing epoxy resin is performed. An adhesive 7 made of a material having a refractive index equivalent to that of glass is filled.

[0009] Further, on the opposing surface side of both glass substrates 1 and 2,
Transparent electrode layers 8 and 9 made of ITO (indium tin oxide) or the like are formed, and alignment films 10 and 11 made of a polyimide resin or the like are provided on the transparent electrode layers 8 and 9 respectively. The liquid crystal in the liquid crystal layer 3 has a twisted arrangement of 240 degrees due to the relationship between these alignment films and the like. In FIG. 1, reference numeral 12 denotes a sealing body for sealing the liquid crystal layer 3 between the substrates 1 and 2.

As shown in FIG. 2, a plurality of stripe grooves 21a extending in one direction are formed on the surface of a flat resin substrate 21 made of a resin material. The reflection film 22 is formed by vapor deposition or printing. Stripe groove 2
1a is formed by changing the width of adjacent stripe grooves and repeatedly forming a group of stripe grooves with a certain period. The cross-sectional shape of each stripe groove is the same R, and the R is 30 to 100 μm. The groove depth of the stripe groove is approximately 1 to 2 μm. When R exceeds 100 μm, the stripe groove is visually recognized, and the display quality of the liquid crystal display element is greatly reduced. Therefore, R is preferably 100 μm or less. When R is less than the order of visible light, that is, smaller than 0.4 μm, effective reflection characteristics cannot be obtained.
It is desirable that the thickness be at least μm.

The reflector is manufactured by the manufacturing method shown in FIG. First, as shown in FIG. 3A, a flat plate-shaped matrix 30 made of, for example, a copper alloy or an iron alloy has a flat surface.
Is cut in a straight line by a grinding jig 31 such as a cutting tool having a radius R of the cutting edge 31a of 30 to 100 μm shown in FIG. 4 while changing the feed pitch in a direction orthogonal to the groove direction. , A master die 30 having a die surface in which adjacent stripe grooves 30a shown in FIG.
To form Feed pitch P during grinding of grinding jig 31
Are four types, for example, P1 of 13 μm, P2 of 16 μm, P3 of 17 μm and P4 of 18 μm, and send these four kinds of feed pitches P while changing them irregularly. For example, the feed pitch is 18 μm, 13 μm, 13 μm, 16 μm, 17
As shown in FIG. 5, cutting is performed using a cutting tool having the same depth at a cutting edge of R30 μm for each of the μm, 13 μm, 13 μm, 17 μm, and 13 μm units. The shape of the cutting edge 31a of the grinding jig 31 for grinding may be not only an arc-shaped surface but also various other curved surfaces, but an arc-shaped surface is preferable because the jig itself is most easily processed. The feed pitch is not limited to the above-described four types of dimensions, and several types of dimensions may be combined in an irregular order.

3B is obtained by repeatedly cutting a unit having a predetermined number of stripe grooves with the same feed pitch and a different cutting depth for each stripe groove.
To form a matrix 30 having a mold surface in which adjacent stripe grooves 30a have different groove widths from each other.
0 may be manufactured. Furthermore, by repeatedly cutting a unit consisting of a certain number of stripe grooves, while changing the feed pitch and changing the cutting depth for each stripe groove, the groove widths of adjacent stripe grooves 30a have different mold surfaces from each other. The matrix 20 may be formed, and the reflector 20 may be manufactured by this.

Next, as shown in FIG. 3 (c), the matrix 30 is placed in a box-shaped container 32, and a resin material 33 such as silicone is poured into the container 32 and left to cure at room temperature. The cured resin product is taken out of the container 32 and unnecessary portions are cut off, and the mold 30 as shown in FIG.
A transfer mold 40 having a mold surface having a large number of reverse stripe grooves 40a having a concave and convex shape opposite to the large number of stripe grooves 30a forming the mold surface is obtained. Further, as shown in FIG. 3E, the mold surface of the transfer mold 40 is pressed against the surface of the resin base material 21 made of the resin material for the reflector, and the resin base material 21 is cured, whereby the resin base material 21 is cured. f) As shown in FIG.
2. The stripe groove 21a shown in FIG.
To form Finally, for example, aluminum is formed on these stripe grooves 21a by electron beam evaporation or the like to form the reflection film 22, thereby forming the reflector 20.
To manufacture.

As shown in FIG. 6, the reflector 20 has a groove direction (indicated by a dotted arrow M) of the stripe groove on the surface of the reflection film 22 corresponding to each of the plurality of stripe grooves 21a, and a second polarizing plate. 6 with respect to the direction of the deflection axis (indicated by a solid arrow L) is arranged with respect to the polarizing plate 6 so as to be within the range of 0 to 15 degrees.

In such a reflection type liquid crystal display device, when no voltage is applied between the transparent electrode layers 8 and 9,
The incident light from the display surface side is linearly polarized in the direction of its polarization axis by the first polarizing plate 5, subsequently passes through the retardation plate 4 and the liquid crystal layer 3, and the birefringence effect of the liquid crystal layer 3 is obtained. As a result, the light is in an elliptically polarized state. If this elliptically polarized light is close to linearly polarized light and the major axis direction is aligned with the direction of the polarization axis of the second polarizing plate 6, light can efficiently pass through the second polarizing plate 6, The transmitted light is reflected by the reflection film 22 of the reflector 20, and passes through the second polarizing plate 6, the liquid crystal layer 3, the phase difference plate 4, and the first polarizing plate 5 again. Thus, the incident light is reflected by the reflector 20 and returns as reflected light, so that the display screen of the liquid crystal display device is in a bright state, that is, a white state.

On the other hand, when a voltage is applied between the transparent electrode layer 8 on the display side and the transparent electrode layer 9 on the back side, the refractive index of the liquid crystal in the liquid crystal layer 3 at the point where the voltage is applied becomes transparent. The liquid crystal changes its refractive index to be different from the birefringence of the liquid crystal when no voltage is applied between the electrode layers 8 and 9. Therefore, the state of the elliptically polarized light transmitted through the liquid crystal layer 3 changes from the state in which no voltage is applied between the transparent electrode layers 8 and 9, and the major axis direction of the elliptically polarized light turns. The light that has passed through the liquid crystal portion has almost no component in the polarization axis direction of the second polarizing plate 6 as the rotation angle of the major axis of the elliptically polarized light is closer to 90 degrees and the elliptically polarized light state is closer to linearly polarized light.
It hardly passes through the second polarizing plate 6. Therefore, the incident light hardly returns as reflected light, and the display screen is in a dark state, that is, a black state. As described above, by controlling the voltage application between the transparent electrode layers 8 and 9, the display screen can be switched between light and dark, that is, black and white, and various displays can be performed.

In the reflection type liquid crystal display device according to the present invention, a color filter is printed between the rear glass substrate 2 and the transparent electrode layer 9 or between the display glass substrate 1 and the transparent electrode 8. The reflection type liquid crystal display device may be configured to be able to perform color display by being formed as described above.

Next, the reflection characteristics of the above-mentioned reflection type liquid crystal display device with respect to incident light will be described with reference to FIGS. FIGS. 7 and 8 are graphs showing reflection characteristic curves with the vertical axis representing the reflectance and the horizontal axis representing the reflection angle. The solid line a shown in FIG. 7 indicates the reflection characteristic curve of the reflector 20 itself,
(2) When the incident light from the point light source arranged above is fixed at an incident angle of 30 degrees from a direction perpendicular to the surface of the reflector 20 and perpendicular to the stripe groove 21a, the angle of the reflected light is changed from 0 degrees to 50 degrees. It is a plot of the reflectance when changed. The reflection characteristic curve shown by the dotted line b is shown in FIG.
1 is related to the conventional reflection plate 60 shown in FIG.
When the incident light from the point light source disposed above is made to enter the normal to the surface of the reflective film 62 at a constant incident angle of 30 degrees from an arbitrary direction, the angle of the reflected light with respect to the normal is 0 °.
It is a plot of the reflectance when the angle is changed from 50 degrees to 50 degrees. 1. The reflective liquid crystal display device shown in FIG.
For the conventional reflection type liquid crystal display device shown in FIG. 2, plots of similar reflectances are shown by a solid line c and a dotted line d in FIG. 8, respectively. The above-mentioned reflectance was measured by using a liquid crystal panel evaluation device (LCD5000 model manufactured by Otsuka Electronics Co., Ltd.) to reflect reflected light at a regular reflection angle of 30 ° when a white plate (a plate having an MgO standard white surface) was irradiated at an angle of 30 °. This is a value expressed as a percentage (%) by dividing the output of the reflected light by the quasi-output with reference to the output.

As is clear from the solid line a in FIG. 7, the reflector 20 has a range of up to ± 15 degrees around the reflection angle of 30 degrees as compared with the dotted line b of the conventional reflector 60. It can be seen that high reflectance can be maintained over a very wide range. As is clear from the solid line c in FIG.
The liquid crystal display device according to the present invention using 0 is compared with the dotted line d for the conventional liquid crystal display device to have a reflection angle of 30 degrees as a center and a reflection angle of up to ± 15 degrees, particularly a range of ± 10 degrees. Sufficiently high reflectivity is obtained throughout. That is,
Very wide viewing angles and good reflectivity can be provided.

The relationship between the brightness and the contrast of the reflection type liquid crystal display device shown in FIG. 1 is shown by the angle between the direction of the stripe groove on the surface of the reflection film 22 of the reflector 20 and the direction of the polarization axis of the polarizing plate 6. Table 1 shows the results. In Table 1, the brightness was such that light was incident at an incident angle of 30 degrees with respect to a perpendicular to the display surface of the reflective liquid crystal display device, and a reflection angle of 2 with respect to this perpendicular.
When the reflected light of 0 degree is received, the reflectance (50
%), The evaluation was "good" when the reflectance was 60% or more, and the evaluation was "impossible" when the reflectance was 40% or less. Further, the contrast in Table 1 is a ratio between the above-defined reflectance Ron when black display is performed when an ON voltage is applied to the reflective liquid crystal display device and the above-defined reflectance Roff when white display is performed when an OFF voltage is applied. The value of Roff / Ron is represented by a value at which the value becomes maximum. In Table 1, the evaluation "good" indicates a contrast greater than 6, "acceptable" indicates a contrast of 4 to 6, and "impossible" indicates a contrast less than 4. As is clear from Table 1, the reflection type liquid crystal display device shown in FIG.
When the angle formed between the polarization axis of (1) and the direction of the stripe groove on the surface of the reflection film 22 of the reflector 20 is 0 to 15 degrees, the brightness is evaluated as “good”, and the contrast is evaluated as “good” and “good”. Met.

[0021]

Although the present invention has been described with reference to the STN mode liquid crystal display device, the present invention is not limited to the above-described embodiment. For example, the twist angle of the liquid crystal molecules in the liquid crystal layer is set to 90 degrees. Of course, the present invention can be applied to a TN (Twisted Nematic) type liquid crystal display device.

FIG. 9 shows another embodiment of the reflection type liquid crystal display device according to the present invention. The reflection type liquid crystal display device shown in FIG. 9 has the same structure as the reflection type liquid crystal display device shown in FIG. 1 except that a polarizing plate is not provided between the glass substrate 2 on the back side and the reflector 20. is there. 9, the same members as those of the reflection type liquid crystal display device shown in FIG. 1 are denoted by the same reference numerals as those in FIG. 1, and the description thereof is omitted. In this reflection type liquid crystal display device, a retardation plate 4 and a polarizing plate 5 are sequentially arranged on the upper surface side of the display side glass substrate 1, and only the reflector 20 is provided on the lower surface side of the back side glass substrate 2. This is a structure in which only one polarizing plate is arranged.

In the reflection type liquid crystal display device, the incident light linearly polarized by the polarizing plate 5 passes through the phase difference plate 4 and the liquid crystal layer 3 and is elliptically polarized, and the elliptically polarized incident light is reflected by the reflector 20. Reflected light again, passes through the liquid crystal layer 10 and the phase difference plate 4 and returns to the polarizing plate 5, and whether the major axis direction of the returned elliptically polarized light matches the direction of the polarizing axis of the polarizing plate 5? A black and white display can be performed depending on whether or not the image is displayed. In this reflective liquid crystal display device, the direction of a large number of stripe grooves formed on the surface of the reflective film 22 of the reflector 20 and the major axis direction of elliptically polarized light that passes through the liquid crystal layer 3 and enters the reflector 20 are determined. By setting the angle formed by 0 to 15 degrees,
The screen display can be made even brighter than the reflective liquid crystal display device shown in FIG.

FIG. 10 shows another embodiment of the reflection type liquid crystal display device according to the present invention. This reflection type liquid crystal display device has the same structure as that of the reflection type liquid crystal display device shown in FIG. 9 except that a reflector is formed between the rear glass substrate 2 and the liquid crystal layer 3. 10, the same components as those of the reflection type liquid crystal display device of FIG. 9 are denoted by the same reference numerals as those of FIG. 9, and the description thereof is omitted.

This reflection type liquid crystal display device is a so-called reflector built-in type liquid crystal display device in which the reflector 70 is provided on the inner surface side of the rear glass substrate 2. This reflector 70 is shown in FIG.
The reflective film 72 is formed by vapor deposition or the like on the surface of the substrate 71 having the same number of stripe grooves as the number of stripe grooves on the substrate 21 shown in FIG. Base material 71
Is composed of a photosensitive resist resin layer applied on the glass substrate 2. The transparent electrode layer 9 and the alignment film 11 are placed on the reflector 70 via an overcoat layer 13 having a flat surface.
Are sequentially formed. In such a reflective liquid crystal display device,
The incident light is reflected by the reflection film 71 without passing through the rear glass substrate 2, and depends on whether or not the major axis direction of the elliptically polarized light of the reflected light coincides with the direction of the polarization axis of the polarizing plate 5. Black and white display can be performed.

The reflection type liquid crystal display device has a reflector 70.
The angle between the direction of the many stripe grooves formed on the surface of the reflection film 72 and the major axis direction of the elliptically polarized light of the light passing through the liquid crystal layer 10 and entering the reflector 70 is set to 0 to 15 degrees. Thereby, the problem that the display image becomes double can be prevented, and the screen display can be further brightened as compared with the reflective liquid crystal display device of FIG.

[0028]

According to the reflection type liquid crystal display device of the present invention,
Compared with the conventional reflection type liquid crystal display device, the screen display can be brightened and the contrast can be increased.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating an embodiment of a reflective liquid crystal display device according to the present invention.

FIG. 2 is a schematic view showing the reflector shown in FIG.

FIG. 3 is a sectional view showing a manufacturing process of the reflector shown in FIG. 2;

FIG. 4 is a partially cutaway perspective view showing a cutting jig.

FIG. 5 is a cross-sectional view showing a cutting example at the time of cutting a master block using the cutting jig shown in FIG.

FIG. 6 is a plan view showing a relationship between a groove direction of a stripe groove on a reflection film surface of a reflector and a polarization axis of a polarizing plate in the reflection type liquid crystal display device shown in FIG.

FIG. 7 is a graph showing the reflection characteristics of the reflector shown in FIG.

8 is a graph showing the reflection characteristics of the reflection type liquid crystal display device shown in FIG.

FIG. 9 is a sectional view showing another embodiment of the reflection type liquid crystal display device according to the present invention.

FIG. 10 is a sectional view showing another embodiment of the reflection type liquid crystal display device according to the present invention.

FIG. 11 is a perspective view of a conventional reflector.

FIG. 12 is a cross-sectional view illustrating an example of a conventional reflective liquid crystal display device.

[Explanation of symbols]

 1, 2 Transparent substrate 3 Liquid crystal layer 5, 6 Polarizer 20, 70 Reflector 21, 71 Reflector base material 21a Stripe groove 22, 72 Reflective film

Claims (3)

[Claims] 1. A liquid crystal layer is provided between a pair of opposed transparent substrates, a polarizing plate is provided outside each of the pair of transparent substrates, and a plurality of grooves extending in one direction outside the one polarizing plate. Is provided with a reflection surface facing the one polarizing plate, and the angle between the polarization axis of the one polarizing plate and the direction in which the groove of the reflector extends is 0 to 15;
A reflection type liquid crystal display device characterized in that: 2. A liquid crystal layer is provided between a pair of opposing transparent substrates, a polarizing plate is provided on an outer surface of one of the pair of transparent substrates, and a liquid crystal layer of the other of the pair of transparent substrates is provided. Provide a reflector facing the other transparent substrate the reflection surface formed by forming a plurality of grooves extending in one direction on the outer surface,
A reflection-type liquid crystal display, wherein an angle between a major axis direction of the elliptically polarized light that enters from the polarizing plate and passes through the other transparent substrate and a direction in which each groove of the reflection surface extends is 0 to 15 degrees. apparatus. 3. A liquid crystal layer is provided between a pair of transparent substrates facing each other, a polarizing plate is provided on an outer surface of one of the pair of transparent substrates, and a liquid crystal layer of the other of the pair of transparent substrates is provided. A reflector facing the one transparent substrate is provided with a reflection surface formed with a plurality of grooves extending in one direction inside,
A reflection-type liquid crystal display device, wherein an angle between a major axis direction of the elliptically polarized light that enters from the polarizing plate and passes through the liquid crystal layer and a direction in which each groove of the reflection surface extends is 0 to 15 degrees. .