JP2003140152A - Semitransmissive liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the availability of the light from a backlight in the case of a transmissive display in a semitransmissive liquid crystal display device. SOLUTION: A polarization changing layer 13 is disposed between a transflective film 10 and a quarter-wave plate 14. The polarization changing layer 13 converts the light from the backlight, emitted from the backlight unit 17 and modulated to circularly polarized light by successively passing through a rear side polarizing plate 15 and the quarter-wave plate 14, into elliptically polarized light. The elliptically polarized light is reflected and is converted into counterrotating elliptically polarized light on a reflection region of the transflective film 10, passes through the quarter-wave plate 14 while being converted into elliptically polarized light with a shape different from, and with handedness identical to, the counterrotating elliptically polarized light, subsequently passes through the rear side polarizing plate 15 and is converted into linearly polarized light and again returns to the backlight unit 17. The light from the backlight is made to be reusable by reflecting the linearly polarized light on a reflection plate 16 equipped on the backlight unit 17.

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, and more particularly to a transflective liquid crystal display device having a transmissive region and a reflective region.

[0002]

2. Description of the Related Art In recent years, liquid crystal display elements used for portable information terminals are required to have low power consumption, and development of a reflective liquid crystal display device that does not require backlight light (utilizes external light) has been developed. It is active. However, since such a liquid crystal display device cannot recognize the display in a dark place, it uses external light in a bright place like a normal reflection type liquid crystal device, and displays in a dark place where the external light is insufficient by a backlight light. A recognizable transflective liquid crystal display device has been proposed.

A liquid crystal module structure of a conventional transflective liquid crystal display device as disclosed in Japanese Patent Laid-Open No. 11-337931 will be described with reference to FIG.

The liquid crystal module structure of the above-mentioned transflective liquid crystal display device has a front polarizing plate 301, a retardation plate 302, and a front substrate 3.
03, transparent electrode (transparent conductive thin film) 304, alignment film 30
5, STN (Super Twisted Nemat)
ic) Liquid crystal layer 306, overcoat layer 307, color filter layer 308, transflective film 309, diffusion film 31
0, back substrate 311, quarter-wave plate (phase difference plate) 312,
The back polarizing plate 313 and the backlight unit 315 are provided.

The front polarizing plate 301 and the back polarizing plate 313 are
Out of light vibrating in all directions of 360 °, light vibrating in only one direction is extracted. Phase plate 3
Reference numeral 02 is for optically compensating the polarization state due to the birefringence of the STN liquid crystal layer 306 to optimize the optical characteristics of the panel. The front substrate 303 and the back substrate 311 are generally non-alkali glass substrates excellent in flatness. The transparent electrode (transparent conductive thin film) 304 is a film having a high visible light transmittance and conductivity, and is usually ITO (Indi).
um Tin Oxide) film. Alignment film 30
Reference numeral 5 is a rubbed polyimide thin film for controlling the arrangement of liquid crystal molecules in the STN liquid crystal layer 306. ST
The N liquid crystal layer 306 is composed of a nematic liquid crystal having a predetermined twist angle. The overcoat layer 307 is
A resin film that protects the color filter layer 308. The color filter layer 308 includes R (red), G (green), and B (blue).
Is a resin film in which the three colored layers are arranged in a predetermined pattern, and is a filter for colorizing the liquid crystal display. The semi-transmissive reflective film 309 is a perforated reflective film formed on the back substrate 311 and having an opening for transmitting light.

Here, the pixel 401 shown in FIG.
It has a transmissive region 402 which is an opening of the semi-transmissive reflective film 309 shown in FIG. 2B, and a reflective region 403 where the reflective film is present.

The diffusion film 310 uniformly illuminates the liquid crystal display with backlight light. The 1/4 wavelength plate 312 is a retardation plate having a phase difference corresponding to 1/4 of the wavelength. The backlight unit 315 is provided with a reflection plate 314 on the back surface for reflecting light to the back substrate 311 side in order to provide backlight light in a dark place where external light is insufficient.

7 (a) and 7 (b) show how the external light 501 entering the liquid crystal display device is reflected, and FIG. 7 (c) shows the backlight light 50 from the backlight unit 315.
2 shows the state of transmission of 2 and reflection of backlight light 503. 7 (a), (b), and (c) show only the front substrate 303, the STN liquid crystal layer 306, the semi-transmissive reflective film 309, the back substrate 311, and the backlight unit 315 among the members shown in FIG. Is extracted and described.

FIG. 7 shows a reflective display utilizing external light.
As shown in (a) and (b), the front substrate 303 and the back substrate 3
External light 501 is introduced into a cell sandwiched between 11 and 11, and the inside of the cell ((FIG. 7A)) or the outside of the cell ((FIG.
The color filter layer 308 and the STN are reflected by the reflection region 403 of the semi-transmissive reflection film 309 arranged in (b)).
A reflective display is performed through the liquid crystal layer 306. On the other hand, at the time of transmission using the backlight light, as shown in FIG. 7C, the backlight light 502 transmits through the opening (the transmissive region 402) formed in the semi-transmissive reflective film 309, and the same as above. Color filter layer 308 and STN liquid crystal layer 306
Is displayed transparently. However, the other backlight light 503 is reflected by the reflection area 4 of the semi-transmissive reflection film 309.
It is reflected at 03.

[0010]

FIG. 8 shows a configuration in which a quarter-wave plate 312 and a back polarizing plate 313 are added to FIG. 7 (c) at the time of transmission using backlight light.

FIG. 8 shows polarization states of the backlight light emitted from the backlight unit 315 in the transmissive region 402 and the reflective region 403.

As shown in the figure, the backlight light 502 in the transmissive region 402 is generated by the back polarizing plate 313 and the quarter wavelength plate 312.
And the opening of the semi-transmissive reflective film 309 (transmissive region 402)
Through. On the other hand, the backlight light 5 of the reflection area 403
After passing through the back polarizing plate 313 and the quarter-wave plate 312, the light beam 03 is reflected by the semi-transmissive reflection film 309, and the quarter-wave plate 3 is reflected.
It is absorbed by being transmitted through 12 and the back polarizing plate 313. For this reason, when the transmissive display is performed using the backlight light of the backlight unit 315, the backlight light 503 is not used at all.

Therefore, it is an object of the present invention to allow the backlight light 503 during the transmissive display to be reused and improve the utilization efficiency of the backlight light during the transmissive display.

[0014]

A liquid crystal layer, a pair of substrates sandwiching the liquid crystal layer, and a back light having a reflecting plate on the back surface for irradiating the liquid crystal layer with light from the back side are provided on the substrate. A polarizing plate that transmits linearly polarized light from the light from the backlight, a quarter wavelength plate that converts the linearly polarized light from the polarizing plate into circularly polarized light, and a transmission region that transmits circularly polarized light from the quarter wavelength plate. A semi-transmissive liquid crystal display device provided with a semi-transmissive reflective film having a reflective region for reflecting, wherein the polarization state change layer is provided between the semi-transmissive reflective film and the ¼ wavelength plate. And

According to the above arrangement, the backlight light from the backlight unit becomes linearly polarized light after passing through the polarizing plate, and becomes circularly polarized light after passing through the quarter wavelength plate. Become. After passing through the polarization state changing layer, circularly polarized light changes to become elliptically polarized light, but the elliptically polarized light in the transmissive region passes through the liquid crystal layer to perform transmissive display. On the other hand, the elliptically polarized light in the reflection region is reflected by the semi-transmissive reflective film and becomes elliptically polarized light which is the opposite of the elliptically polarized light before being reflected, and the reverse elliptically polarized light is different after passing through the polarization state change layer. It becomes the reverse elliptically polarized light of, and after passing through the quarter-wave plate,
It becomes another state of reverse elliptical polarization. After passing through the polarizing plate, the reverse elliptically polarized light becomes linearly polarized light and returns to the backlight unit. Then, the returned backlight light is reflected by a reflection plate included in the backlight unit and is reused.

The polarization state changing layer has a plurality of refractive indexes and has birefringence, which is a property of shifting the phase of light, in the same direction with respect to the surface direction of the semi-transmissive reflective film. It is characterized by being a layer (film). Therefore, the layer having a plurality of refractive indexes can have the property of changing the polarization state of light, and moreover, can change the circular polarization state to the elliptically polarized light uniformly on the entire surface of the polarization state change layer. You can

On the other hand, the elliptically polarized light incident on the polarization changing layer is changed to another elliptically polarized light. Therefore, the reverse elliptically polarized light reflected by the semi-transmissive reflection film passes through the polarization state changing layer to be in a different reverse elliptically polarized state, and is absorbed by the quarter wavelength plate and the polarizing plate. Instead, the backlight unit can be reached.

Here, in the above configuration, the polarization state changing layer is provided on the entire surface between the semi-transmissive reflective film and the quarter-wave plate. In that case, the reflection of the semi-transmissive reflective film is performed. This not only changes the polarization state of the reflected light in the area, but also changes the circular polarization state of the backlight light that is transmitted without being reflected by the semi-transmissive reflection film in the transmission area. Therefore, by forming the polarization state changing layer only in a region facing the reflection region, it is possible to prevent the polarization state of the backlight light in the transmission region portion from changing.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described below with reference to FIGS. In the embodiment of the present invention, the transflective liquid crystal display device is applied to a transflective color liquid crystal display device. As shown in FIG. 1, the transflective color liquid crystal display device includes a front polarizing plate 1, a first retardation film 2, a second retardation film 3, in order from the observer side of the liquid crystal display screen.
Front substrate 4, transparent electrode 5, alignment film 6, STN liquid crystal layer 7, alignment film 6, transparent electrode 5, overcoat layer 8, color filter layer 9, semi-transmissive reflective film 10, diffusion film 11, back substrate 1
2, a polarization state changing layer 13, a quarter-wave plate 14, a back polarizing plate 15, and a backlight unit 17.

The front polarizing plate 1 and the back polarizing plate 15 respectively take out light (linearly polarized light) vibrating in only one direction out of light vibrating in all directions of 360 °. . The first retardation plate 2 and the second retardation plate 3 are for optically compensating the polarization state due to the birefringence of the STN liquid crystal layer 7 to optimize the optical characteristics of the panel,
Here, the compensation is facilitated by dividing into two first and second retardation films. The front substrate 4 and the back substrate 12 may be transparent glass substrates made of, for example, soda glass, or both surfaces thereof are smooth, or may be transparent plastic substrates. The quarter-wave plate used here is such that the slow axis of a film having a specific retardation is arranged at 45 ° with respect to the polarization axis of the polarizing plate,
By combining with a polarizing plate, linearly polarized light is changed to circularly polarized light.

In the present embodiment, the semi-transmissive reflective film 10 is formed by laminating, for example, a metal (or alloy) film on the uneven diffusion film (organic film) 11. The semi-transmissive reflective film 10 is formed of, for example, an aluminum film formed by a sputtering method. Although the aluminum film has total light reflectivity, the aluminum film is patterned with aluminum by a photolithography method to form an opening for transmitting light.

Here, the opening is formed as shown in FIG.
It is shown in 402 of (b). In this embodiment, the total area of the openings 402 in the pixel 401 of FIG. 2A is set to 30% of the total area of one pixel (401). However, although the total area was set to 30% as described above, it is preferably 2
It is from 0 to 80% (when less than 20%, the transmitted light is less utilized and the screen for transmissive display becomes dark, and when it is 80% or more, the reflective display screen becomes dark and there is a problem in visibility). Further, on the semi-transmissive reflective film 10, R (red), G (green), and B (blue)
A color filter layer 9 is formed in which colored layers of colors are arranged in stripes as shown by R, G, and B in FIG.

In this embodiment, the semi-transmissive reflective film 10 is used.
Is disposed inside the cell sandwiched between the front substrate 4 and the back substrate 12 as described above, but may be disposed outside the cell.

On the semi-transmissive reflective film 10, for example, silicon oxide (SiO 2) is used as a protective film for the surface of the semi-transmissive reflective film 10.
₂ ) A film is formed. A polarization state change layer 13 is provided on the side of the back substrate 12 different from the STN liquid crystal layer 7.
In the polarization state changing layer 13, the backlight light from the backlight unit 17 is sequentially transmitted through the back polarizing plate 15 and the quarter wavelength plate 14, and is reflected by the semi-transmissive reflection plate 10 in the circularly polarized state. Reverse circular polarization state, again 1 /
As a result of preventing the light from being transmitted through the four-wave plate 14 and the back polarizing plate 15 in this order to be absorbed, changing the phase of each light forming the circularly polarized light variously, and collecting the lights having the various changed phases. Is a film that becomes elliptically polarized light. The polarization state change layer 13 has a plurality of refractive indexes and has birefringence which is a property of shifting the phase of light uniformly in the same direction with respect to the surface direction of the semi-transmissive reflective film. The layer having a plurality of refractive indices has a property of changing the polarization state of light, and here, for example, a circular polarization state is an elliptically polarized state and an elliptically polarized state is another elliptically polarized state. The state is a layer that can change the linearly polarized state to the elliptically polarized state. Further, the polarization state changing layer 13 is provided with an opening having the same area as the opening of the semi-transmissive reflection film by laser processing or the like at the same position as the opening of the semi-transmissive reflection film having the opening. May be used.

In this embodiment, the polarization state changing layer 13 is arranged outside the cell, but it may be arranged inside the cell, for example, directly below the semi-transmissive reflector film, or the back substrate 12 itself is refracted. It may have a rate anisotropy.

The surface of the color filter layer 9 becomes uneven due to the overlapping portion with the color filter layer 9 or the film thickness difference of each color, and the orientation of the STN liquid crystal is deteriorated. Therefore, the acrylic resin-based overcoat layer 8 is formed on the color filter layer 9.

The transparent electrode 5 is formed of indium tin oxide (ITO) on the front substrate 4 and the overcoat layer 8 of the back substrate 12.
Are vapor-deposited and etched to form stripes. Then, polyimide is applied on the transparent electrode 5 and baked to form the alignment film 6.
The alignment film 6 is rubbed so that the twist angle of the liquid crystal molecules of the STN liquid crystal film 7 becomes 240 °.

Further, the front substrate 4 and the back substrate 12 are adhered together by a sealing resin, and in order to prevent light confusion, a refractive index anisotropy Δ which is a difference in refractive index between the major axis and the minor axis of the liquid crystal is provided therebetween.
The STN liquid crystal cell is formed by injecting liquid crystal in which n and the twist pitch of the liquid crystal are adjusted. The STN liquid crystal cell includes a first retardation plate 2, a second retardation plate 3, a quarter wavelength plate 14, a front polarizing plate 1 and a back polarizing plate 15.
Are attached to the STN liquid crystal cell so as to form a predetermined axis. Here, the first retardation plate 2, the second retardation plate 3, the quarter-wave plate 14, the front polarizing plate 1 and the back polarizing plate 15 are polycarbonate, which is a polymer material having a desired retardation Δn · d. It consists of a film.

The retardation Δn · d is the product of the refractive index anisotropy Δn and the thickness d of the STN liquid crystal layer, and the degree of phase shift between the incident light and the emitted light of the STN liquid crystal layer. It represents.

Further, a backlight unit 17 is arranged on the back side of the back polarizing plate 15. A reflection plate 16 is provided on the back surface of the light guide plate of the backlight unit 17. When the backlight light reflected by the semi-transmissive reflection film 10 passes through the quarter-wave plate 14 and the back polarizing plate 15 and returns, it is reflected again on the liquid crystal display screen side.

Here, a state in which the backlight light emitted from the backlight unit 17 is reused by providing the semi-transmissive reflection film 13 is shown in FIG.
An explanation will be given using (b).

FIGS. 3A and 3B show a semi-transmissive reflective film 10, a polarization state changing layer 13, a quarter-wave plate 14 and a back surface of the liquid crystal module structure of the semi-transmissive liquid crystal display device shown in FIG. Only the polarizing plate 15 and the backlight unit 17 are described, and each polarization state of light transmitted through each layer thereof is shown.

Backlight light 201 from the backlight unit 17 in the reflection area 403 of FIG.
Is natural light (randomly polarized light) 203 immediately after being emitted from the backlight unit 17, but the back polarizing plate 15
After being transmitted, it becomes a linearly polarized light 204, and after passing through the quarter-wave plate 14, it is changed from the linearly polarized light to a polarized light having a phase difference corresponding to 1/4 of the wavelength, that is, a circularly polarized light 205.

Next, the circularly polarized light 205 becomes elliptically polarized light 206 by passing through the polarization state changing layer 13, is reflected by the reflection region 403 of the semi-transmissive reflection film 10, and is changed to reverse elliptically polarized light 207. Then, the reverse elliptically polarized light 207 is transmitted through the polarization state changing layer 13 again and becomes the same reverse elliptically polarized light 208 although the shape is different. Further, the reverse elliptical polarization 208
Of the same shape as the reverse elliptical polarized light 207, but the same reverse elliptical polarized light 208 is transmitted through the quarter-wave plate 14.

The quarter-wave plate 14 is, as described above,
It is a retardation plate that shifts the phase by 1/4 wavelength of light,
Even if the phase of elliptically polarized light is shifted by 1/4 wavelength, it remains elliptically polarized light.

The reverse elliptically polarized light 209 is converted to linearly polarized light 210 after passing through the back polarizing plate 15 and returns to the backlight unit 17. Therefore, the returned backlight light can be reflected and reused by the reflection plate 16 provided in the backlight unit 17.

In the structure shown in FIG. 3A, the polarization state changing layer 13 includes the semi-transmissive reflection film 10 and the quarter-wave plate 14.
In this case, in addition to disturbing the polarization state of the reflected light in the reflection area 403 of the semi-transmissive reflection film 10, the circularly polarized light 211 to the elliptically polarized light 212 in FIG. The change in the circular polarization state of the backlight for the transmissive display in the transmissive region 402 of the semi-transmissive reflective film 10 changes. Therefore, by forming a hole 131 at the same position as the transmissive region 402 of the semi-transmissive reflective film 10, the polarization state changing layer 13 is formed only in the reflective region. This makes it possible to prevent the polarization state of the circularly polarized light 132 transmitted through the quarter-wave plate 14 in the transmission region 402 from changing.

In any case, the polarization state changing layer 13
By including the above, the backlight light reflected by the reflection area 403 can be returned to the backlight unit 17 and can be reflected again to the liquid crystal display screen, so that the backlight light can be effectively used.

Here, the axis angle of each optical element in one embodiment of the present invention is shown in FIGS. 4 (a) and 4 (b).

FIG. 4A shows a front side of the transflective liquid crystal display module of the present invention (a side where the backlight unit 17 is not provided) viewed from an observer of the liquid crystal display screen. Further, FIG. 4B shows a view of the back side of the transflective liquid crystal display module (the side provided with the backlight unit 17) as seen from the viewer side of the liquid crystal display screen.

The twist angle of the liquid crystal molecules of the STN liquid crystal layer 7 is 240 °, and the angle between the slow axis 701 of the first retardation plate 2 and the slow axis 702 of the second retardation plate 3 is 40 °. Second
The angle formed by the slow axis 702 of the retardation plate 3 and the orientation direction 703 of the liquid crystal molecules on the front substrate side is 60 °, and the absorption axis 7 of the front polarizing plate 1 is
04 and the slow axis 701 of the first retardation plate 2 is 10
Set to 5 °. In addition, the orientation direction of the liquid crystal molecules on the back substrate side 70
The angle formed by 5 and the slow axis 706 of the quarter-wave plate 14 is 20
The angle formed between the slow axis 706 of the quarter-wave plate 14 and the absorption axis 707 of the back polarizing plate 15 is 45 °.

Furthermore, the retardation (Δ
n ・ d) value is set to S for the measurement wavelength of 550 nm.
The TN liquid crystal layer 7 is 800 nm, and the first retardation plate 2 is 675 n.
m, the second retardation plate 3 is 175 nm, and the quarter-wave plate 14 is 140 nm, which constitutes a liquid crystal display device which is in a normally black mode during reflection / transmission.

In addition, a retardation plate having a retardation value of 270 nm is provided in the polarization state changing layer 13, and a slow axis 708 of the retardation plate and an orientation direction 705 of liquid crystal molecules on the back substrate side are
It is configured to form an angle of 85 °.

Next, Table 1 shows the optical characteristic evaluation results of the transflective liquid crystal display device of this embodiment and a comparative example.

In the comparative example, the polarization state changing layer 1 is provided between the semi-transmissive reflective film 10 and the quarter-wave plate 14 in the reflective region 403.
A semi-transmissive liquid crystal display device having the same structure as that of the above-described embodiment except that 3 is not provided.

[0046]

[Table 1]

As can be seen from Table 1, 1/66 Duty,
When driven at ⅙ Bias, frame frequency, the characteristic at the time of reflected diffuse light is equivalent to that of the conventional case, and the contrast at the time of transmitted diffuse light is from Comparative Example 25.0 to Embodiment 31.
0% and 24% increase, and the transmittance increased from 2.8% of the comparative example to 3.7% of the embodiment and 32%.

Here, FIGS. 5A and 5B show a measuring device used for evaluating the optical characteristics of the semi-transmissive liquid crystal display device of this embodiment and a comparative example.

FIG. 5A shows a measuring device used for the reflected and diffused light shown in Table 1. First, a diffused light generation device 802 that generates diffused light is installed so as to face the display screen of the semi-transmissive liquid crystal display device 801. The inner wall surface of the diffused light generation device 802 is coated with barium sulfate, and the light source 803
The light that is emitted from the and reflected by the coating becomes reflected diffuse light 804. Then, the diffused light generation device 80
The reflected diffused light 804 emitted from the No. 2 is reflected by the semi-transmissive liquid crystal display device 801, and the reflected light 805 reflected by the light receiver 807 installed in the normal direction 806 (DMS- The light is received at 703) and the contrast and reflectance of the semi-transmissive liquid crystal display device 801 are measured. In the measurement with the reflected diffused light in FIG. 5A, the backlight of the semi-transmissive liquid crystal display device 801 is turned off.

On the other hand, FIG. 5 (b) shows the measuring device used for the transmitted diffused light in Table 1. Transflective liquid crystal display device 801
The transmitted diffused light 811 from the backlight unit 810 provided in the above is received by a light receiver 813 (BM-5A described in Note 1 of Table 1) installed in the normal direction 812, and is a semi-transmissive type. The contrast and reflectance of the liquid crystal display device 801 are measured. A cylindrical cover 814 is installed so that the transmitted diffused light 811 can block external light.

[0051]

EFFECT OF THE INVENTION A liquid crystal layer, a pair of substrates sandwiching the liquid crystal layer, and a backlight having a reflecting plate on the back surface for irradiating the liquid crystal layer with light from the back side are provided, and the backlight is provided on the substrate. Polarizing plate that transmits linearly polarized light from the above light, a quarter wavelength plate that converts linearly polarized light from the polarizing plate into circularly polarized light, and a transmission region that transmits circularly polarized light from the quarter wavelength plate and a reflection region that reflects Is provided, and the polarization state change layer is further provided between the semi-transmissive reflection film and the quarter-wave plate.

With the above arrangement, the backlight light from the backlight unit is emitted from the polarizing plate and the 1 /
After passing through the four-wave plate in order, it becomes circularly polarized light, and after passing through the polarization changing layer, the circularly polarized light changes to become elliptically polarized light. Then, the elliptically polarized light in the reflection region is reflected by the semi-transmissive reflection film, and becomes elliptically polarized light opposite to the elliptically polarized light before being reflected, and the reverse elliptically polarized light is separated after passing through the polarization state change layer. The reverse elliptically polarized light of (1) becomes the other elliptically polarized light, and after passing through the quarter-wave plate, it becomes another state of the reverse elliptically polarized light. Then, the reverse elliptically polarized light becomes linearly polarized light after passing through the polarizing plate and returns to the backlight unit. Therefore, the returned backlight light can be reflected to the liquid crystal display screen side by the reflection plate provided in the backlight unit and reused, and the efficiency of use of the backlight light can be improved. Like

The polarization state changing layer is a layer (film) having birefringence uniformly in the same direction as the surface direction of the semi-transmissive reflective film. Therefore, the polarization state change layer can have the property of changing the polarization state of light, and moreover, the circular polarization state can be changed uniformly to the elliptically polarized light over the entire surface of the polarization state change layer. You can On the other hand, the incident light of elliptically polarized light has a property of changing to another elliptically polarized light. Therefore, the reverse elliptically polarized light reflected by the semi-transmissive reflection film is in the same reverse elliptically polarized state after passing through the polarization state changing layer but has a different shape, and is transmitted through the polarizing plate and the ¼ wavelength plate. The backlight unit can be reached without being absorbed by the backlight unit. Therefore, it is possible to reflect the light toward the liquid crystal display screen side for reuse by the reflection plate provided in the backlight unit, and improve the utilization efficiency of the backlight light.

Here, in the above structure, the polarization state changing layer is provided on the entire surface between the semi-transmissive reflective film and the quarter-wave plate. In that case, in the reflective region of the semi-transmissive reflective film. This not only changes the polarization state of the reflected light, but also changes the circular polarization state of the backlight light that is transmitted without being reflected by the semi-transmissive reflective film in the transmissive region. Therefore, by forming the polarization state change layer only in a region facing the reflection region, it is possible to prevent the polarization state of the backlight light in the transmission region from changing, and to improve the utilization efficiency of the backlight light. Due to the polarization state change layer provided for improving, it is possible to prevent the conventional efficiency of the backlight light in the transmissive region from being lowered.

[Brief description of drawings]

FIG. 1 is a structural diagram of a liquid crystal module of a transflective liquid crystal display device according to an embodiment of the present invention.

2A and 2B are diagrams showing a transmissive region and a reflective region in one pixel of a transflective liquid crystal display device according to an embodiment of the present invention.

3A and 3B are diagrams showing a polarization state of light in a transflective liquid crystal display device according to an embodiment of the present invention.

4 (a) and 4 (b) are diagrams showing respective axis angles in the embodiment of the present invention.

5 (a) and 5 (b) are diagrams showing a measuring device used for evaluating optical characteristics of a semi-transmissive liquid crystal display device according to an embodiment of the present invention and a comparative example.

FIG. 6 is a structural diagram of a liquid crystal module of a conventional transflective liquid crystal display device.

7A and 7B are diagrams showing reflection of external light of a conventional transflective liquid crystal display device, and FIG. 7C is a view of transmission of backlight light of the conventional transflective liquid crystal display device. FIG.

FIG. 8 is a diagram showing a polarization state of light in a conventional transflective liquid crystal display device.

[Explanation of symbols]

7 STN liquid crystal layer (liquid crystal layer) 10 Semi-transmissive reflective film 13 Polarization change layer 14 1/4 wave plate 15 Back polarizing plate (polarizing plate) 16 Reflector 17 Backlight unit (backlight)

Claims (3)

[Claims] 1. A liquid crystal layer, a pair of substrates sandwiching the liquid crystal layer, and a backlight having a reflective plate on the back surface for irradiating the liquid crystal layer with light from the back side, the backlight being provided on the substrate. Polarizing plate that transmits linearly polarized light from the above light, a quarter wavelength plate that converts linearly polarized light from the polarizing plate into circularly polarized light, and a transmission region that transmits circularly polarized light from the quarter wavelength plate and a reflection region that reflects In a semi-transmissive liquid crystal display device provided with a semi-transmissive reflective film having: a polarization state change layer for changing the circularly polarized light into different polarized light, between the semi-transmissive reflective film and the quarter-wave plate. A transflective liquid crystal display device comprising: 2. The transflective liquid crystal display device according to claim 1, wherein the polarization state changing layer has birefringence in the same direction as the surface direction of the transflective film. 3. The transflective liquid crystal display device according to claim 1, wherein the polarization state changing layer is formed only in a region facing the reflection region.