JPH0716923U - Liquid crystal display - Google Patents

Abstract

(57) [Summary] [Object] To provide a liquid crystal display device having a wide viewing angle with sufficient display brightness as a reflection type liquid crystal display device. [Structure] A liquid crystal cell 10 comprising a TN type or STN type liquid crystal cell 10, a polarizing plate 30 and a reflecting plate 31.
The polarizing plate 30 is arranged on the front side of the liquid crystal cell, the reflecting plate 31 is arranged on the rear side of the liquid crystal cell 10, and the reflecting plate 31 is
The structure is such that the fine particles 33 are adhered to the surface of the base sheet 32 almost entirely, and the metal film 34 is adhered thereon.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a reflective liquid crystal display device.

[0002]

[Prior art]

 As a liquid crystal display device, a liquid crystal cell using a TN (twisted nematic) type or STN (super twisted nematic) type liquid crystal cell in which liquid crystal molecules are twist-aligned is generally used.

This liquid crystal display device includes a transmissive type that uses light from a backlight arranged on the back side thereof and a type of liquid crystal display that uses outside light to direct light incident from the front side to the back side. There is a reflection type that reflects and displays with a reflector placed, and a reflection type liquid crystal display device is generally used as a display device of portable electronic equipment such as a calculator, an electronic notebook and an electronic wrist watch. There is.

FIG. 6 is a sectional view of a conventional reflective liquid crystal display device. This liquid crystal display device is composed of a TN type or STN type liquid crystal cell 10, two polarizing plates 21 and 22, and a reflection plate 23. The polarizing plates 21 and 22 sandwich the liquid crystal cell 10 and have their surfaces sandwiched therebetween. Side and the back surface side, and the reflection plate 23 is arranged on the back surface of the back surface side polarizing plate 22.

In the liquid crystal cell 10, a pair of transparent substrates 11 and 12 made of glass or the like are joined at their peripheral portions via a frame-shaped sealing material 17, and the sealing material 17 between the substrates 11 and 12 is used. Liquid crystal 18 is enclosed in the enclosed area, and transparent electrodes 13 and 14 are formed on the surfaces of both substrates 11 and 12 facing each other, and the alignment direction of liquid crystal molecules is regulated thereon. Alignment films 15 and 16 are formed.

The molecules of the liquid crystal 18 are aligned by the alignment films 15 and 16 of the substrates 11 and 12 with a certain pretilt angle with respect to the film surfaces, and a predetermined twist angle is provided between the substrates 11 and 12. (The TN type is approximately 90 °, and the STN type is 180 to 270 °).

As the reflection plate 23, the surface of a base sheet 24 made of PET (polyethylene terephthalate) or the like is subjected to a matte treatment (roughening treatment), and a metal film such as Al (aluminum) is formed on the surface thereof. The thing which vapor-deposited 25 is used.

The above liquid crystal display device is driven by displaying the alignment state of the liquid crystal molecules by controlling the alignment state of the liquid crystal molecules by applying a voltage between the electrodes 13 and 14 of the liquid crystal cell 10. In accordance with the voltage applied between the electrodes 14, the initial twist orientation state and the rising arrangement state in which it rises almost upright with respect to the surfaces of the substrates 11 and 12 are changed.

On the other hand, external light that enters the liquid crystal display device from its front surface side is linearly polarized by the front surface side polarizing plate 21 and enters the liquid crystal cell 10, and passes through the liquid crystal cell 10 and the rear surface side polarizing plate 22. Incident on. The light incident on the back surface side polarization plate 22 is light polarized according to the alignment state of the liquid crystal molecules corresponding to the applied voltage in the process of passing through the liquid crystal cell 10, and the back surface side polarization plate according to the polarization state. It is either transmitted through 22 or absorbed.

The light transmitted through the back-side polarizing plate 22 is reflected by the reflecting plate 23, passes through the back-side polarizing plate 22, the liquid crystal cell 10, and the front-side polarizing plate 21, and is emitted to the front side of the liquid crystal display device. Then, due to the emission of this light and the absorption of light by the back surface side polarizing plate 22, the display pattern is displayed in bright and dark.

[0011]

[Problems to be solved by the device]

 However, in the above-mentioned conventional liquid crystal display device, the display is entirely dark due to the absorption of light by the two polarizing plates, and the brightness of the display when viewed from the front direction (the normal direction of the display device) is high. Although the brightness is relatively high, the brightness of the display is extremely reduced when viewed from an oblique direction, so there is a problem that the viewing angle range (hereinafter referred to as the viewing angle) where the display can be viewed with sufficient contrast is narrow. . An object of the present invention is to provide a liquid crystal display device having a wide viewing angle with sufficient display brightness as a reflection type liquid crystal display device.

[0012]

[Means for Solving the Problems]

 The present invention comprises a liquid crystal cell in which a liquid crystal is sealed between a pair of transparent substrates having transparent electrodes, and the molecules of the liquid crystal are twist-aligned between the two substrates, a polarizing plate, and a reflector. The polarizing plate is arranged on the front surface side of the liquid crystal cell, the reflecting plate is arranged on the rear surface side of the liquid crystal cell, and the reflecting plate is formed by adhering fine particles almost entirely on the surface of the base sheet. It is characterized by having a structure in which a metal film is adhered to.

In the present invention, it is desirable that the fine particles adhered to the surface of the base sheet of the reflection plate have a particle diameter of 10 μm or less, and the metal film have a thickness of about ⅔ or less of the particle diameter of the fine particles. . Further, in the present invention, in order to increase the brightness of the display, a retardation plate may be provided between the liquid crystal cell and the reflection plate arranged on the back side thereof.

[0014]

[Action]

 In the liquid crystal display device of the present invention, the light linearly polarized by the polarizing plate disposed on the surface side of the liquid crystal cell and incident on the liquid crystal cell is reflected by the reflecting plate through the liquid crystal cell, and then again passes through the liquid crystal cell and the polarizing plate. Incident on. This light is polarized according to the alignment state of the liquid crystal molecules corresponding to the applied voltage in the process of passing through the liquid crystal cell, and is transmitted through or absorbed by the polarizing plate depending on the polarization state. The display pattern is displayed in bright and dark by the emission of the light transmitted through the plate and the absorption of the light by the polarizing plate.

Further, in this liquid crystal display device, since the reflection plate has a structure in which fine particles are adhered to the surface of the base sheet almost entirely and a metal film is adhered thereon, The reflection surface (metal film surface) of the plate has unevenness according to the particle size of the fine particles, and therefore the light reflected by the reflection plate is diffused and the brightness of the display when viewed from an oblique direction is increased. As a result, the change in display brightness depending on the viewing angle becomes slower, and the viewing angle becomes wider.

If the particle size of the fine particles adhered to the surface of the base sheet of the reflection plate is 10 μm or less and the film thickness of the metal film is about ⅔ or less of the particle size of the fine particles, the metal film surface is Results in an uneven surface that diffuses the reflected light satisfactorily, and a display with a gentle change in display brightness depending on the viewing angle and without "glare" can be obtained.

Moreover, in this liquid crystal display device, only one polarizing plate is provided, and both of the polarizer for linearly polarizing the incident light and the analyzer for transmitting / absorbing the light passing through the liquid crystal cell are provided on the polarizing plate. Since it has the function of, the light loss due to the polarizing plate is extremely small, and the display becomes brighter accordingly.

Therefore, this liquid crystal display device has sufficient display brightness and a wide viewing angle. Further, in the above liquid crystal display device, if a retardation plate having retardation for compensating for the phase difference of each wavelength light transmitted through the liquid crystal cell is provided between the liquid crystal cell and the reflection plate arranged on the back surface side of the liquid crystal cell, The light that has changed the polarization state due to the phase difference of each wavelength light in the process of passing through is reflected by the reflection plate after being converted to linearly polarized light by the phase difference plate, so the light loss is reduced and the display The brightness becomes brighter.

[0019]

【Example】

 Hereinafter, a first embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a sectional view of a liquid crystal display device. This liquid crystal display device comprises a liquid crystal cell 10, a single polarizing plate 30, and a reflecting plate 31, the polarizing plate 30 being arranged on the front surface side of the liquid crystal cell 10, and the reflecting plate 31 being a liquid crystal. It is arranged on the back side of the cell 10.

The liquid crystal cell 10 is a TN type or STN type in which liquid crystal molecules are twist-aligned, and its configuration is the same as that of the conventional liquid crystal display device shown in FIG. Therefore, the description will be omitted by attaching the same reference numerals to the drawings.

On the other hand, the reflection plate 31 has fine particles 33 such as glass beads adhered to the surface of a base sheet 32 made of a resin film such as PET over almost the entire surface thereof, and a metal film 34 made of Al or the like thereon. The reflecting plate 31 is provided with its reflecting surface, that is, the surface of the metal film 34, facing the rear substrate 12 of the liquid crystal cell 10.

FIG. 2 is an enlarged cross-sectional view of a part of the reflection plate 31. The fine particles 33 are arranged in a base sheet at an interval equal to or smaller than the particle diameter so that the particles do not vertically overlap with each other. It is attached to the surface of 32. Further, the particle size of the fine particles 33 is set to 10 μm or less, and the metal film 34 is deposited to a thickness of about 2/3 or less (about 7 μm or less) of the particle size of the fine particles 33. .

The reflection plate 31 is formed, for example, by applying an adhesive on the surface of the base sheet 32, and by spraying fine particles 33 on the adhesive to adhere the fine particles 33 to the base sheet 32. It is manufactured by a method of depositing the metal film 34 by a vapor deposition method, a sputtering method, or a plating method.

In this liquid crystal display device, the light linearly polarized by the polarizing plate 30 arranged on the surface side of the liquid crystal cell 10 and incident on the liquid crystal cell 10 is reflected by the reflection plate 31 through the liquid crystal cell 10 and is again reflected. And enters the polarizing plate 30. This light is polarized according to the alignment state of the liquid crystal molecules corresponding to the applied voltage in the process of passing through the liquid crystal cell 10, and is transmitted or absorbed by the polarizing plate 30 depending on the polarization state. The display pattern is displayed in bright and dark by the emission of the light transmitted through the polarizing plate 30 and the absorption of the light by the polarizing plate 30.

In this liquid crystal display device, the reflection plate 31 has a structure in which the fine particles 33 are adhered to the surface of the base sheet 32 over substantially the entire surface thereof, and the metal film 34 is adhered thereon. The reflecting surface (the surface of the metal film 34) of the reflecting plate 31 has irregularities according to the particle size of the fine particles 33 as shown in FIG. 2, and therefore the light reflected by the reflecting plate is diffused. However, the brightness of the display when viewed from an oblique direction is improved, and the change in the display brightness depending on the viewing angle becomes gradual.

That is, the reflection plate 23 used in the conventional liquid crystal display device shown in FIG. 6 is obtained by performing a matte treatment on the surface of the base sheet 24 and depositing the metal film 25 thereon. On the reflection plate 23, most of the light incident on the reflection surface (the surface of the metal film 25) is reflected at the same reflection angle as the incident angle, so the diffusivity of the reflected light is small, and therefore the front surface The brightness of the display is high when viewed from the direction (normal direction of the display device), but the brightness of the display is extremely reduced when viewed from an oblique direction.

On the other hand, in the reflection plate 31 used in the liquid crystal display device of the above-described embodiment, the reflection surface (the surface of the metal film 34) has unevenness according to the particle size of the fine particles 33, and therefore this reflection is caused. Most of the light incident on the reflection surface of the plate 31 is reflected at a reflection angle θ2 different from the incident angle θ1 (angle with respect to the normal line Z of the reflection plate 31) as shown in FIG.

Therefore, in the above liquid crystal display device, the light reflected by the reflection plate 31 is diffused in a wide range, and this diffused light is emitted to the surface side of the liquid crystal display device. The brightness of the display is improved, and the brightness of the display when viewed from the diagonal direction is the same as the brightness of the display when viewed from the front direction.

In this embodiment, the particle size of the fine particles 33 attached to the surface of the base sheet of the reflection plate 31 is 10 μm or less, and the thickness of the metal film 34 deposited on the fine particles 33 is less than 10 μm. Since the particle size is about ⅔ or less (7 μm or less) of the particle size, the surface of the metal film 34 is an uneven surface that favorably diffuses the reflected light, and the change in the display brightness depending on the viewing angle is gentle. Moreover, it is possible to obtain a display without "glare".

That is, FIG. 3 shows the incident angle of light on the reflection plate 31 (angle with respect to the normal line of the reflection plate 31) and the front luminance of the reflected light (luminance viewed from the normal line direction of the reflection plate 31). FIG. 7 is a reflection characteristic diagram showing the relationship in comparison with the reflector used in the conventional liquid crystal display device shown in FIG. 6 and the Mg O reflector formed by forming Mg 2 O (magnesium oxide) into a sheet. Here, as the reflection characteristics of the reflection plate 31, the reflection characteristics of four types of reflection plates in which the particle diameters of the fine particles 33 are 5 μm, 10 μm, 40 μm, and 80 μm are shown.

As shown in FIG. 3, the reflector used in the conventional liquid crystal display device (hereinafter referred to as the conventional reflector) has a small incident angle of light of about 10 °, that is, the reflector is opposed to the reflector. The front brightness is very high when light is incident at an angle close to vertical, but as the incident angle is increased from 10 ° to 20 °, the front brightness drops sharply and the incident angle becomes 30 °. When it exceeds, the front luminance is hardly obtained. Therefore, the liquid crystal display device using the reflection plate having such a reflection characteristic has a considerably high display brightness when viewed from the normal direction, but the viewing angle is slightly changed from 10 ° to 20 °. However, the brightness of the display is extremely reduced, and when the viewing angle exceeds 30 °, the display becomes dark and almost invisible.

On the other hand, the MgO reflector is known as a diffuse reflector, and in this MgO reflector, the front luminance hardly changes even if the incident angle of light is changed, but on the other hand, However, since the reflected light with sufficient brightness cannot be obtained within the incident angle range of 0 to 20 °, which requires relatively high brightness, when used as a reflector of a liquid crystal display device, the display is dim as a whole. turn into.

Next, looking at the reflection characteristics of four types of reflectors in which the particle size of the fine particles 33 is 5 μm, 10 μm, 40 μm, and 80 μm, among them, the reflector plate in which the particle size of the fine particles 33 is 80 μm is The front brightness is high when the incident angle of light is as small as about 10 °, and the reflection characteristics are improved compared to the conventional reflector, but the incident angle of light is increased from 10 ° to 30 °. In the meantime, the front luminance is greatly reduced, and when the incident angle exceeds 40 °, almost no front luminance is obtained. In addition, since the particle size of the fine particles 33 is large in this reflecting plate, and therefore the unevenness of the reflecting surface (metal film surface) is large, when this reflecting plate is used, "glare" occurs in the display of the liquid crystal display device. .

On the other hand, in all of the reflectors in which the particle size of the fine particles 33 is 5 μm, 10 μm, and 40 μm, the front brightness when the incident angle of light is as small as about 10 ° is lower than that of the conventional reflector. However, its brightness is sufficient, and the decrease in frontal brightness with increasing incident angle is extremely gentle.

Among these reflection plates, the reflection plate in which the fine particles 33 have a particle size of 40 μm has large irregularities on its reflection surface (metal film surface), so that “glaring” is displayed on the liquid crystal display device. However, the reflection plate having the fine particles 33 having a particle size of 5 μm or 10 μm does not cause “glitter” in the display of the liquid crystal display device.

Therefore, if the particle size of the fine particles of the reflection plate 31 is set to 10 μm or less (the film thickness of the metal film 34 is about ⅔ or less of the particle size of the fine particles), the brightness of the display changes depending on the viewing angle. It is possible to obtain a wide viewing angle and a display without "glare".

Moreover, in the above liquid crystal display device, the number of the polarizing plates 30 is only one, and the polarizing plate 30 includes a polarizer for linearly polarizing the incident light and an analyzer for transmitting / absorbing the light passing through the liquid crystal cell 10. Since the polarizing plate 30 has both the above functions, the light loss by the polarizing plate 30 is extremely small, and the display becomes brighter by that much.

That is, in the conventional liquid crystal display device shown in FIG. 6, since the polarizing plates 21 and 22 are arranged on the front surface side and the back surface side of the liquid crystal cell 10, light incident on this liquid crystal display device is , The front-side polarizing plate 21 and the back-side polarizing plate 22 are emitted through each two times, so that the light amount loss according to the transmittance of the polarizing plates 21 and 22 is repeated four times in total. The loss will increase. Further, in the conventional liquid crystal display device, as described above, since the diffusivity of the reflected light by the reflecting plate 23 is small, the brightness of the display is extremely reduced when viewed from an oblique direction. As a result, the brightness of the display is further reduced when viewed from an oblique direction.

On the other hand, in the liquid crystal display device of the above embodiment, since only one polarizing plate 30 is provided, the light amount loss corresponding to the transmittance of the polarizing plate 30 is once for each of the incident path and the outgoing path. Since it only occurs, the loss of light by the polarizing plate 30 is extremely small.

Therefore, this liquid crystal display device has a wide viewing angle with sufficient display brightness when viewed from an oblique direction. FIG. 4 shows the relationship between the viewing angle (angle with respect to the normal line of the liquid crystal display device) and the display brightness in the liquid crystal display device as compared with the conventional liquid crystal display device. In the figure, the + viewing angle represents the viewing angle in one direction from the normal line of the liquid crystal display device, and the − viewing angle represents the viewing angle in the opposite direction.

As shown in FIG. 4, the conventional liquid crystal display device shows the viewing angle-brightness characteristics as shown by the broken line, but the liquid crystal display device of the above-mentioned embodiment shows the viewing angle-brightness characteristics as shown by the solid line. The change in brightness on the display has a gradual viewing angle-brightness characteristic, and thus has a wide viewing angle.

Next, another embodiment of the present invention will be described. FIG. 5 is a sectional view of a liquid crystal display device showing a second embodiment of the present invention. In the liquid crystal display device of this embodiment, a retardation plate 35 is provided between the liquid crystal cell 10 and a reflection plate 31 arranged on the back surface side thereof, and other configurations are the same as those of the first embodiment described above. Is the same as. The retardation plate 35 is for compensating the phase difference of each wavelength light transmitted through the liquid crystal cell 10 and returning it to linearly polarized light.

In the liquid crystal display device of this embodiment, the linearly polarized light incident through the polarizing plate 30 passes through the liquid crystal cell 10 of the TN type or the STN type to generate a phase difference in each wavelength light and become elliptically polarized light. However, since the elliptically polarized light is returned to the linearly polarized light by the retardation plate 35 and then reflected by the reflecting plate 31, the loss of light is reduced, and therefore the brightness of the display becomes brighter.

Moreover, according to the liquid crystal display device of this embodiment, since the phase difference of the light of each wavelength transmitted through the liquid crystal cell 10 is compensated by the retardation plate 35, the display is not colored. .

That is, in a liquid crystal display device using a TN type or STN type liquid crystal cell, linearly polarized light that has entered through the polarizer becomes elliptically polarized light in the process of passing through the liquid crystal cell, and this elliptically polarized light enters the polarizer. Therefore, the light transmitted through this analyzer absorbs light in a certain wavelength range by the analyzer to become colored light, and the display is colored. The color band of this display is particularly remarkable in the liquid crystal display device using the STN type liquid crystal cell, but a slight band color is generated also in the liquid crystal display device using the TN type liquid crystal cell.

However, according to the liquid crystal display device of the above-described embodiment, since the light that has become elliptically polarized light while passing through the liquid crystal cell 10 is returned to the linearly polarized light by the phase difference plate 35, the display becomes colored. Nothing. The light reflected by the reflection plate 31 is emitted through the retardation plate 35, the liquid crystal cell 10 and the polarizing plate 30. At this time, the position of each wavelength light generated by the polarization action of the retardation plate 35 is increased. The liquid crystal cell 10 compensates for the phase difference.

Further, since the phase difference plate 35 has a polarization function but does not absorb light, even if the phase difference plate 35 is provided in a liquid crystal display device, the display brightness does not decrease.

Therefore, according to the liquid crystal display device of the embodiment shown in FIG. 5, as in the liquid crystal display device of the first embodiment, the brightness of the display when viewed from an oblique direction is made sufficient and the viewing angle is improved. In addition to widening the display, it is possible to further improve the brightness of the display and eliminate the banding of the display. The liquid crystal cell is not limited to the TN type and the STN type, and the present invention can be applied to the case of using a ferroelectric liquid crystal cell, for example.

[0049]

[Effect of device]

 The liquid crystal display device of the present invention comprises a liquid crystal cell in which liquid crystal is sealed between a pair of transparent substrates having transparent electrodes, a polarizing plate and a reflector, and the polarizing plate is provided on the front side of the liquid crystal cell. And the reflection plate is arranged on the back surface side of the liquid crystal cell, and the reflection plate has a structure in which fine particles are adhered to almost the entire surface of the base sheet and a metal film is deposited thereon. Therefore, the brightness of the display is sufficient and the viewing angle can be widened.

Further, in the present invention, if the particle size of the fine particles attached to the surface of the base sheet of the reflection plate is 10 μm or less and the film thickness of the metal film is about ⅔ or less of the particle size of the fine particles, The surface of the metal film becomes an uneven surface that favorably diffuses the reflected light, and a display with a gradual change in display brightness depending on the viewing angle and without "glare" can be obtained.

Further, in the present invention, if a retardation plate is provided between the liquid crystal cell and the reflection plate arranged on the back surface side of the liquid crystal cell, a phase difference is generated in each wavelength light in the process of passing through the liquid crystal cell, and the polarization state is changed. The changed light is returned to the linearly polarized light by the retardation plate and then reflected by the reflection plate, so that the loss of light is reduced and the display brightness becomes brighter.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a liquid crystal display device showing a first embodiment of the present invention.

FIG. 2 is an enlarged cross-sectional view of a part of the reflection plate.

FIG. 3 shows the relationship between the incident angle of light on the reflection plate and the front luminance of the reflected light, which is obtained by comparing the reflection plate and M of the conventional liquid crystal display device.
The reflection characteristic figure shown in comparison with the gO reflector.

FIG. 4 is a view angle-brightness characteristic diagram showing the relationship between the view angle and the display brightness in the liquid crystal display device of the first embodiment in comparison with the conventional liquid crystal display device.

FIG. 5 is a sectional view of a liquid crystal display device showing a second embodiment of the present invention.

FIG. 6 is a sectional view of a conventional liquid crystal display device.

[Explanation of symbols]

 10 ... Liquid crystal cell 11, 12 ... Transparent substrate 13, 14 ... Transparent electrode 15, 16 ... Alignment film 18 ... Liquid crystal 30 ... Polarizing plate 31 ... Reflection plate 32 ... Base sheet 33 ... Fine particles 34 ... Metal film 35 ... Retardation plate

Claims (3)

[Scope of utility model registration request] 1. A liquid crystal cell in which liquid crystal is sealed between a pair of transparent substrates having transparent electrodes, a single polarizing plate and a reflector, and the polarizing plate is arranged on the front surface side of the liquid crystal cell. ,
The reflection plate is arranged on the back surface side of the liquid crystal cell, and the reflection plate has a structure in which fine particles are adhered to almost the entire surface of a base sheet and a metal film is adhered thereon. Liquid crystal display device. 2. The particle size of the fine particles attached to the surface of the base sheet of the reflector is 10 μm or less, and the film thickness of the metal film is about ⅔ or less of the particle size of the fine particles. 1
The liquid crystal display device according to item 1. 3. The liquid crystal display device according to claim 1, wherein a retardation plate is provided between the liquid crystal cell and the reflection plate arranged on the back surface side of the liquid crystal cell.