JPH11258593A - Liquid crystal display device and electronic device using the same - Google Patents

Abstract

(57) Abstract: A liquid crystal display device provided with a reflective polarizing plate and an electronic apparatus using the same, in which the reflective performance of the reflective polarizing plate is improved to obtain a brighter display. . The liquid crystal panel includes a liquid crystal panel having a liquid crystal layer, a polarizing plate on one side of the liquid crystal panel, and a reflective polarizing plate on the other side. The direction of the polarization axis of the linearly polarized light transmitted through the liquid crystal panel 2 and incident on the reflection polarizing plate 4 (the long axis direction in the case of elliptically polarized light) and the direction of the reflection axis of the reflection polarization plate 4 are defined by the reflection polarization plate 4. It is characterized in that the directions are substantially the same for each of the wavelengths to be reflected by.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device, particularly to a liquid crystal display device provided with a reflective polarizing plate, and to an electronic device such as a timepiece and a cellular phone using the same.

[0002]

2. Description of the Related Art For example, in a conventional liquid crystal display element using a transmission polarization axis variable optical element such as a TN (Twisted Nematic) liquid crystal or STN (Super-Twisted Nematic) liquid crystal, the polarization axis of which is variable, this liquid crystal display element is used. Since the configuration is sandwiched between two polarizing plates, the light use efficiency is low. In particular, in a reflection type liquid crystal display device, there is a problem that the display becomes dark.

[0003] Therefore, a liquid crystal display in which the reflection efficiency is enhanced by using a reflective polarizer (polarized light separator) instead of one of the two polarizers, thereby obtaining a bright display. A device has been proposed. For example, Japanese Patent Publication No. 9-506985 (International Application Publication: WO /
95/17692) and International Application Publication: WO / 95/2.
Reference numeral 7819 discloses the above-mentioned reflective polarizer as a reflective polarizer or a reflective polarizer, and further discloses a liquid crystal display device using the reflective polarizer.

[0004]

However, even if the above-mentioned reflective polarizing plate is used as it is in a liquid crystal display device, a sufficiently high reflection efficiency cannot always be obtained, and a display having a sufficiently satisfactory brightness can be obtained. It was not obtained.

The present invention has been proposed in view of the above problems, and an object of the present invention is to provide a liquid crystal display device capable of obtaining a brighter display by further improving reflection efficiency, and an electronic device using the same. Aim.

[0006]

In order to achieve the above object, a liquid crystal display device and an electronic apparatus according to the present invention have the following configurations.

That is, a liquid crystal display device according to the present invention is a liquid crystal display device having a liquid crystal panel having a liquid crystal layer, a polarizing plate on one side of the liquid crystal panel, and a reflective polarizing plate on the other side. The vibration direction in which the amplitude of the light transmitted through the liquid crystal panel and incident on the reflective polarizing plate has the maximum amplitude, and the direction of the reflection axis of the reflective polarizing plate are reflected by the reflective polarizing plate. It is characterized in that the directions are substantially the same for each of the wavelengths to be obtained. Here, the vibration direction in which the amplitude is maximum indicates the vibration direction (polarization axis direction) when the light incident on the reflective polarizing plate is linearly polarized light, and the vibration direction when the light is elliptically polarized light. Refers to the major axis direction of elliptically polarized light.

The reflective polarizer is configured to reflect, for example, light having wavelengths corresponding to the three primary colors (R, G, B) of light, and passes through the liquid crystal panel for each wavelength to enter the reflective polarizer. The direction of vibration of which the amplitude is maximum among the directions of vibration of the light and the direction of the reflection axis of the reflective polarizing plate are set to be substantially the same.

The reflective polarizing plate includes, for example, a first film having a birefringent property and a second film having no birefringent property. And a material in which the refractive index of the second film is substantially the same.

Further, a retardation plate may be interposed between the polarizer and the liquid crystal panel or between the liquid crystal panel and the reflective polarizer, and light may be interposed between the liquid crystal panel and the reflective polarizer. A diffusion layer can be interposed.

The liquid crystal display device as described above can be applied to, for example, a display unit of an electronic device such as a clock or a mobile phone.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a liquid crystal display device according to the present invention and an electronic apparatus using the same will be described in detail with reference to the embodiments shown in the drawings.

FIG. 1 is a sectional view showing a schematic configuration of a liquid crystal display device according to the present invention. The illustrated liquid crystal display device has a configuration in which a polarizing plate 1, a liquid crystal panel 2, a light scatterer 3, a reflective polarizing plate 4, and a light absorber 5 are sequentially stacked. As the polarizing plate 1, a conventionally known polarizing plate can be used. The liquid crystal panel 2 has a structure in which a liquid crystal layer 23 is interposed between a pair of substrates 21 and 22 made of glass or the like. As the liquid crystal layer 23, a so-called TN type, STN type, or other conventionally known various liquid crystals are used. be able to.

As the light scattering member 3, for example, a milky white plastic film or sheet can be used. The light scatterer 3 may be provided as needed. When the light scatterer 3 is provided, light is diffused uniformly, and when the light scatterer 3 is not provided, the light scatterer 3 has a specular reflection appearance. Further, the light absorber 5 is for absorbing the light transmitted through the reflective polarizing plate 4, and as the light absorber 5, for example, a black plastic film or sheet having good light absorbency can be used. The material and the like are appropriate and may be omitted in some cases.

As the reflective polarizer 4, for example, as shown in FIG. 2, a laminate of a first film 41 having birefringence and a second film 42 having no birefringence is used. Can be. The first and second films 41 and 42 each have a light-transmitting property and the refractive index of the second film 42 having no birefringence is equal to that of the first film 41 having birefringence. The material and the like are appropriate as long as they are substantially equal to one of the refractive indexes.

Specifically, for example, a first birefringent material
As a film 41 of polyethylene naphthalate (PE
N: polyethylene napthalate (5 times stretched) is used, and as the second film 42 having no birefringence, a copolyester of naphthalene dicarboxylic acid and terephthalic acid (coPEN; copolyester of napht) is used.
halene dicarboxylic acid and terephthalic or
isothalic acid) can be used. The refractive index n _AX of polarized light in the stretching direction of the first film 41 is 1.8.
8. The refractive index n _AY of polarized light orthogonal to the stretching direction is 1.64, and the refractive index n _B of the second film 42 is 1.64.

When light is incident on the reflective polarizing plate 4 in which the first film 41 having birefringence and the second film 42 having no birefringence are laminated as described above, as shown in FIG. The light L1 in the direction orthogonal to the stretching direction of the first film is transmitted as it is because there is no boundary surface between the first and second films 41 and 42. Here, this direction is called a transmission axis. On the other hand, the light L2 in the direction parallel to the stretching direction is transmitted to the first and second films 41 and 42.
Only a predetermined wavelength is selectively reflected at the boundary surface, and the other light is transmitted. Here, this direction is called a reflection axis. The wavelength λ of the reflected light is the refractive index n _AX and n _{B of} the first and second films 41 and 42 (where n _B = n _AY ),
And the thickness d _A of each film 41, 42 is determined by the d _B.

These relationships can be expressed by the following equations (1) and (2).

N _AX · d _A = (１ ／ + m / 2) λ ‥‥‥‥‥ (1) n _B · d _B = (１ ／ + m / 2) λ ‥‥‥‥‥ (2) where m Thus is 0 or a positive integer, the refractive index n _AX of the first and second films 41 and 42, and n _B, the thickness d _a of each film 41, 42, desired be appropriately selected and d _B Light of a wavelength can be reflected. In addition, by appropriately changing one or both of the above-described refractive index and thickness, it is possible to reflect light of different wavelengths, and furthermore, one or both of the refractive index and the thickness are changed. By laminating a plurality of different first and second films, light of a plurality of wavelengths (colors) can be reflected.

FIG. 4 shows an example of the configuration of a reflective polarizer that reflects light of a plurality of wavelengths. First and second films are set to a predetermined thickness so as to reflect a predetermined wavelength λa. One block a is composed of a stack of 41 and 42.
And a plurality of types of blocks a, b, c,... Having different reflection wavelengths are sequentially laminated. In this embodiment, the materials of the first and second films 41 and 42 of each block are the same and differ only in the thickness, and the thicknesses of the films 41 and 42 in each block are set to be the same. Have been.

The first and second films 4 of each of the above blocks
The number of 1.42 is appropriate, but generally, as the number increases, the reflectance of light of a predetermined wavelength can be increased. For example, when the first and second films 41 and 42 made of the above-described materials are used, a reflectance of about 50% can be obtained by laminating about 10 sheets of both films 41 and 42 together, and about 20 layers are laminated. For example, a reflectance of about 80% can be obtained. Also, by appropriately setting the reflectance of each of the plurality of blocks, that is, the reflectance of a plurality of wavelengths, it is possible to adjust the color and brightness of the reflected light. The number (the number of layers) of the first and second films 41 and 42 of each block does not necessarily have to be the same.

When the reflective polarizing plate 4 configured as described above is applied to a liquid crystal display device, it is disposed on the lower surface side of the liquid crystal panel 2 as shown in FIG. 1, and the display principle at that time is a TN type. An example using liquid crystal will be described with reference to FIG. In FIG. 5, the stretching direction of the first film 41 is set to the front-back direction (front-back direction) of the drawing such that the reflection axis direction of the reflective polarizing plate 4 is the front-back direction (front-back direction) of the drawing.

In FIG. 5, as for the light L entering the device from outside the liquid crystal display device, only the light of the linearly polarized component in the direction parallel to the polarization axis (the left-right direction in the drawing) is transmitted by the polarizing plate 1. In the ON state (selection voltage applied state) in the left half of FIG. 5, the light transmitted through the polarizing plate 1 has the liquid crystal molecules oriented almost perpendicular to the substrate surface. After passing through the panel 2 and further through the light scatterer 3 and the reflective polarizer 4, the light is absorbed by the light absorber 5 to provide a dark display.

On the other hand, in the off state (non-selection voltage applied state) of the right half in FIG. 5, the light of the linearly polarized light component in the direction parallel to the polarization axis (left and right directions in the figure) passing through the polarizing plate 1 is a liquid crystal. The polarization direction is twisted by about 90 ° by the panel 2, passes through the light scatterer 3 as it is, and becomes light of a linear polarization component in a direction parallel to the extending direction of the reflection polarization plate 4 (front-back direction in the figure). 4 is incident. The incident light is reflected by the reflective polarizing plate 4 without changing the polarization direction, and is incident on the liquid crystal panel 2 again. Then, the panel 2 twists the polarization direction again by approximately 90 °, and becomes light of a linear polarization component in a direction parallel to the polarization axis of the polarizing plate 1 (the left-right direction in the drawing) and transmits through the polarizing plate 1, so that a bright display is achieved. Becomes

However, as described above, the light incident on the reflective polarizer 4 when reflected by the reflective polarizer 4, that is, the light that is twisted by the liquid crystal panel 2 and enters the reflective polarizer 4 is all polarized. Instead of being oriented in a direction perpendicular to the polarization axis of the plate 1, the direction slightly varies depending on the wavelength. That is, the light that has entered the liquid crystal panel through the polarizing plate 1 changes, for example, in a TN type liquid crystal, in a substantially linearly polarized state due to so-called optical rotation dispersion, and the turning angle changes for each wavelength. Thus, the optical axis varies. Note that in FIG.
Is a wavelength of 650 n representing red, green and blue, respectively.
m, 550 nm, and 450 nm. In FIG. 3A, R, G, and B indicate the directions of the polarization axes of substantially linearly polarized lights r, g, and b.

On the other hand, in the case of STN type liquid crystal, FIG.
As shown in (b), the light is elliptically polarized light having different major axis directions and different eccentricities for each wavelength. In FIG. 6B, r, g, and b represent wavelengths of 650 nm and 550, respectively, representing red, green, and blue.
nm, 450 nm, and R, G, B indicate the major axis directions of r, g, b, which are elliptically polarized light.

Therefore, the direction of the reflection axis of the reflective polarizing plate 4 (the direction of the stretching axis in the case of the reflective polarizing plate 4 shown in FIG. 3) is changed to the direction shown in FIG.
In the case where the light is arranged parallel to the polarization axis direction G of the substantially linearly polarized light g in (a), the amount of g reflected by the reflective polarizer 4 is large, but the polarization axis directions R and B of r and b are different. Since they are not parallel, the reflected light amounts of r and b are smaller than g. Therefore, there is a problem that the reflected light is colored.

Similarly, the direction of the reflection axis of the reflection polarizing plate 4 is shown in FIG.
When the light is arranged in parallel to the major axis direction G of the elliptically polarized light g in (b), the amount of reflection of g by the reflective polarizer 4 is large, but is not parallel to the polarization axis directions R and B of r and b. Therefore, the reflected light amounts of r and b are considerably smaller than g. Therefore, the reflected light is not white but rather colored.

Therefore, in the present invention, the reflection polarizing plate 4
The direction of the reflective axis of the reflective polarizer 4 for each wavelength (color) reflected by the optical axis and the direction of the linear axis of the linearly polarized light transmitted through the liquid crystal panel 2 and incident on the reflective polarizer 4 (in the case of elliptically polarized light, (The major axis direction) is substantially matched (substantially parallel). Specifically, for example, in the reflective polarizer shown in FIG. 4, the block a reflects the wavelength of red (r), the block b reflects the wavelength of green (g), and the block c reflects the wavelength of blue (b). The reflection axis directions (stretching directions) of (c) to (c) are the polarization axis directions (long axis directions in the case of elliptically polarized light) of linearly polarized light of each wavelength incident on the reflective polarizer from the liquid crystal panel in FIG. B may be matched, that is, substantially parallel.

The wavelength (color) reflected by the reflective polarizing plate 4
Are not limited to the three types of R, G, and B described above, and more than three types may be provided. Polarization axis direction of linearly polarized light at the wavelength of interest (long axis direction for elliptically polarized light)
Should be matched.

As described above, for each wavelength reflected by the reflective polarizing plate 4, the direction of the reflection axis of the reflective polarizing plate 4 and the direction of the polarization axis of the linearly polarized light incident on the reflective polarizing plate 4 (long axis in the case of elliptically polarized light) Direction), it is possible to increase as much as possible the amount of light that enters the reflective polarizer 4 from the liquid crystal panel 2 and reflects, thereby obtaining a brighter display. It becomes. In addition, in the case of STN type liquid crystal, not only brightening but also coloring of reflected light can be eliminated.

In addition to the films 41 and 42 described above, the reflective polarizer 4 is a combination of a cholesteric liquid crystal layer and a (1/4) λ plate, and the reflective polarizer 4 uses the Brewster's angle to reflect the reflected polarized light. Separated into transmitted polarized light (SID 92 DIGEST, pages 427 to 4)
29), those utilizing holograms, international applications published internationally (international application publications: WO 95/27819 and W
O95 / 17692) can also be used.

Further, the present invention can be applied to a liquid crystal display device having a retardation plate for eliminating coloring that occurs in the liquid crystal panel 2. FIGS. 7A and 7B show an example thereof, wherein FIG. 7A shows an example in which a retardation plate 6 is interposed between the polarizing plate 1 and the liquid crystal panel 2, and FIG. 3 shows an example in which a phase difference plate 6 is interposed between the phase difference plate 3 and the phase difference plate 3. As the retardation plate 6, various types of conventionally known materials can be used.

Further, the present invention is applicable not only to a so-called reflection type liquid crystal display device but also to a reflection / transmission type liquid crystal display device. FIG. 8 shows an example of this, and FIG.
Is a light transflector 7 instead of the light absorber 5 in FIG.
FIG. 8B shows a configuration in which the light absorber 5 is disposed instead of the light absorber 5 in FIG.
And a backlight 8. FIG. 8
7B, the retardation plate 6 is disposed between the liquid crystal panel 2 and the light scatterer 3, but may be disposed between the polarizing plate 1 and the liquid crystal panel 2 as in FIG. 7A. it can.

The light semi-transmissive member 7 is, for example, a gray translucent film, a black film having a light-transmitting hole formed thereon, or the like. The backlight 8 has a configuration in which a light source 82 and a reflection plate 83 are arranged on the side of a light diffuser 81 in the case of the drawing, but a so-called light guide or other various configurations are applied. It is possible.

The liquid crystal display device according to each of the above embodiments is
For example, if the present invention is applied to the display unit A of the mobile phone T as shown in FIG. 9, it is possible to provide a mobile phone with good display quality, and it can be applied not only to the mobile phone but also to watches and other various electronic devices. .

[0037]

As described above, in the liquid crystal display device according to the present invention, the reflective polarizing plate 4 for reflecting a plurality of wavelengths is disposed on the back side of the liquid crystal panel 2, and the reflected polarized light is transmitted through the liquid crystal panel 2 and reflected. The direction of the polarization axis of the linearly polarized light when entering the plate 4 (the long axis direction in the case of elliptically polarized light)
Is set to be substantially the same direction for each wavelength to be reflected by the reflective polarizing plate 4, so that the reflection efficiency by the reflective polarizing plate 4 can be increased, It is possible to provide a bright liquid crystal display device and an electronic device without any.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a schematic configuration showing one embodiment of a liquid crystal display device according to the present invention.

FIG. 2 is an explanatory diagram illustrating a schematic configuration of a reflective polarizing plate.

FIG. 3 is an explanatory diagram showing the reflection principle of a reflective polarizing plate.

FIG. 4 is a diagram illustrating a laminated configuration of a reflective polarizing plate.

FIG. 5 is an explanatory diagram illustrating a display principle of a liquid crystal display device including a reflective polarizing plate.

FIGS. 6A and 6B are explanatory diagrams of a state of light incident on a reflective polarizer from a liquid crystal panel.

FIG. 7 is an explanatory diagram of a schematic configuration showing another embodiment of the liquid crystal display device according to the present invention.

FIG. 8 is an explanatory diagram of a schematic configuration showing another embodiment of the liquid crystal display device according to the present invention.

FIG. 9 is a perspective view of a mobile phone as an electronic apparatus to which the liquid crystal display device according to the present invention is applied.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Polarizer 2 Liquid crystal panel 4 Reflective polarizer 5 Light absorber

Claims (5)

[Claims] 1. A liquid crystal display device comprising: a liquid crystal panel having a liquid crystal layer; and a polarizing plate on one side of the liquid crystal panel and a reflective polarizing plate on the other side. Of the vibration directions of light incident on the reflective polarizing plate, the vibration direction in which the amplitude is the maximum, and the reflection axis direction of the reflective polarizing plate, for each wavelength to be reflected by the reflective polarizing plate, A liquid crystal display device wherein the directions are substantially the same. 2. The reflection polarizing plate is configured to reflect light having a wavelength corresponding to the three primary colors of light, and the light is transmitted through a liquid crystal panel for each of the wavelengths and is reflected in a vibration direction of light incident on the reflection polarizing plate. 2. The liquid crystal display device according to claim 1, wherein the vibration direction in which the amplitude is maximum is substantially the same as the direction of the reflection axis of the reflection polarizing plate. 3. The first reflective polarizing plate has a birefringent first property.
And a second film having no birefringence, wherein the refractive index of any one of the first film and the refractive index of the second film is substantially equal. 3. The liquid crystal display device according to 1 or 2. 4. The liquid crystal display device according to claim 1, wherein a retardation plate is interposed between the polarizing plate and the liquid crystal panel or between the liquid crystal panel and the reflective polarizing plate. 5. An electronic apparatus comprising a liquid crystal display device as a display portion, wherein the liquid crystal display device has a liquid crystal panel having a liquid crystal layer, a polarizing plate on one side of the liquid crystal panel, and a reflection plate on the other side. What is claimed is: 1. A liquid crystal display device comprising: a polarizing plate; and a vibration direction in which the amplitude of light transmitted through the liquid crystal panel and incident on the reflective polarizing plate is maximized; An electronic device wherein the axial direction is substantially the same for each wavelength to be reflected by the reflective polarizing plate.