JP2002182216A - Video display unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a video display unit which has a bright and good display grade by improving the use efficiency of illuminating light. SOLUTION: The video display unit is provided with a liquid crystal display element 50 which consists of at least one layer of liquid crystal layer including liquid crystal which shows a cholesteric phase, a sheet lighting system 10 consisting of a light source unit 11 and a light guide plate 15, and a λ/4 wavelength plate 30. The λ/4 wavelength plate 30 is interposed between the light guide plate 15 and the liquid crystal display element 50 so that an angle formed by the prism ridgeline 15e of a lagging axis and a prism is ±45 deg..

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image display device, and more particularly to an image display device in which a reflective liquid crystal display element and a planar illumination device functioning as a front light are combined.

[0002]

2. Description of the Related Art In recent years, with the spread of mobile phones and PDAs (Personal Digital Assistants), it has been desired to provide a small, light, thin and low power consumption video display device. As a display element capable of realizing this, attention has been paid to a reflective liquid crystal display element.

[0003] This type of reflective liquid crystal display element uses external light as illumination light in a bright place, so that a transmissive liquid crystal display element and a transflective liquid crystal display element require a necessary auxiliary light source (backlight). By not doing so, low power consumption can be achieved. On the other hand, a reflection type liquid crystal display element requires an auxiliary light source (front light) for illuminating the display surface of the display element from above in order to improve visibility in a dark place.

A liquid crystal exhibiting a cholesteric phase at room temperature (a chiral nematic liquid crystal is known as a representative example thereof) is a reflective liquid crystal that selectively reflects visible light of a specific wavelength, and has a high reflectance. Attention has been paid to the fact that a high bright display element can be formed. Furthermore, the chiral nematic liquid crystal has a memory property that maintains the display even after the power supply is stopped after the display is completed. As a result, lower power consumption can be achieved. In addition, the chiral nematic liquid crystal reflects or transmits either clockwise circularly polarized light (right circularly polarized light) or counterclockwise circularly polarized light (left circularly polarized light) depending on its component (that is, any one of them). Display the image (by switching the circular polarization).

Conventionally, a front light combined with a reflection type liquid crystal display device is disclosed in Japanese Patent Application Laid-Open No. 11-218575.
As described in Japanese Patent Application Laid-Open Publication No. H11-209, there is known a light guide plate in which the surface (the observer's eye side) is configured by a prism array. The illumination light on the liquid crystal display element by the front light includes right circularly polarized light and left circularly polarized light in substantially equal amounts,
Since the cholesteric liquid crystal reflects either clockwise or counterclockwise circularly polarized light, the light use efficiency is approximately 50%.

Accordingly, an object of the present invention is to provide a video display device capable of improving the utilization efficiency of illumination light.

Another object of the present invention is to provide an image display device capable of bright display.

It is still another object of the present invention to provide an image display device which has a small ghost due to light leakage and has good display quality.

[0009]

In order to achieve the above objects, a first image display device according to the present invention sandwiches a liquid crystal exhibiting a cholesteric phase having a selective reflection wavelength in a visible light region between a pair of substrates. A liquid crystal display element including at least one liquid crystal layer, and a light source unit and a light guide plate. The light guide plate has a flat surface on the display surface side of the liquid crystal display element, and has a light source unit on a surface facing the flat surface. A planar illuminating device having a prism array for transmitting incident light to the display surface through the plane, and a slow axis and a prism ridge line of the prism array between the light guide plate and the liquid crystal display element And a λ / 4 wavelength plate interposed therebetween so that the angle between them and becomes ± 45 °.

A second image display device according to the present invention is characterized in that the liquid crystal display device, the planar illumination device, a λ / 4 wavelength plate interposed between the light guide plate and the liquid crystal display device,
The λ / 4 wavelength plate has a slow axis inclined with respect to the prism ridge line of the prism array, and converts linearly polarized light emitted from the light guide plate into circularly polarized light.

Illumination light on the liquid crystal display element by the planar illumination device includes polarized light vibrating in a direction parallel to the prism ridge line on the reflection surface to the element of the prism array, and illuminating light on the prism ridge line on the reflection surface of the prism array. Polarized light that oscillates in a vertical direction (herein, the former is called S-polarized light,
The latter is referred to as P-polarized light).

The incident angle of light on the reflecting surface to the element of the prism array is substantially in the range of 30 to 50 °, and this incident angle is near the Brewster angle. The reflection intensity of S-polarized light is stronger than the reflection intensity of P-polarized light. On the other hand, liquid crystals exhibiting a cholesteric phase selectively reflect only clockwise or counterclockwise circularly polarized light. The λ / 4 wavelength plate is disposed between the light guide plate and the liquid crystal display element in the first image display device such that the angle between the slow axis and the prism ridge line of the prism array is ± 45 °. In the image display device of No. 2, since the slow axis is interposed in a state inclined with respect to the prism ridge line of the prism array so as to convert linearly polarized light emitted from the light guide plate into circularly polarized light, the S polarized light is Is converted into circularly polarized light that is selectively reflected.

As described above, according to the first and second image display devices according to the present invention, S having a higher intensity than the P-polarized component is used.
Since the polarized light component is converted into circularly polarized light that is selectively reflected by the liquid crystal, light use efficiency is improved. Therefore, bright display becomes possible. In addition, since the intensity of unnecessary light (circularly polarized light in a direction in which liquid crystal is not selectively reflected) is reduced, generation of ghost due to unnecessary light can be suppressed, leading to improvement in contrast.

In the first and second video display devices according to the present invention, the liquid crystal display element has two or more liquid crystal layers having different selective reflection wavelengths and reflecting circularly polarized light in the same direction. They may be stacked. By laminating two or more liquid crystal layers, the display can be multicolored. For example, full-color display is possible if three layers of selectively reflected light of R, G, and B are laminated. In addition, by configuring all the liquid crystal layers to reflect circularly polarized light in the same direction, it is possible to improve the illumination efficiency for all the liquid crystal layers, and at the same time, to increase the contrast.

It is preferable that the λ / 4 wavelength plate is bonded to a display surface of a liquid crystal display element and / or is bonded to a plane of a light guide plate. It is possible to suppress generation of ghost light due to inter-surface reflection between the λ / 4 wavelength plate and the liquid crystal display surface and / or generation of ghost light due to inter-surface reflection between the light guide plate and the λ / 4 wavelength plate. it can.

Further, a polarizing plate transmitting S-polarized light and reflecting P-polarized light may be disposed on an end face of the light guide plate on which light is incident from the light source unit. The P-polarized light is emitted to the outside as leakage light from the light guide plate and becomes ghost light, and even when it becomes illumination light for the liquid crystal display element, it is converted into circularly polarized light in the opposite direction to the selectively reflected light of the liquid crystal. This causes the liquid crystal contrast to decrease. However, if a polarizing plate that transmits S-polarized light and reflects P-polarized light is disposed on the incident end face of the light guide plate, unnecessary light, P-polarized light, can be prevented from entering the light guide plate, thereby reducing ghost light and improving display quality. It can be good.

Further, a reflection polarizer for transmitting S-polarized light may be arranged on an end face of the light guide plate on which light is incident from the light source unit. With this configuration, P-polarized light unnecessary as illumination light is returned into the light source unit, and the returned light is converted into S-polarized light while being scattered in the light source unit, and is used as illumination light. Therefore, the utilization efficiency of the illumination light can be further improved.

Further, the light source unit may include a converter for converting P-polarized light reflected from the reflective polarizing plate into S-polarized light. With this configuration, the P-polarized light returned to the light source unit can be reliably converted to S-polarized light, and the utilization efficiency of illumination light can be further improved.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the video display device according to the present invention will be described with reference to the accompanying drawings.

(First Embodiment, see FIGS. 1 to 3) An image display device 1 shown in FIG. 1 is a combination of a planar illumination device 10 and a reflection type liquid crystal display element 50, and a λ is provided between them. /
The four-wavelength plate 30 is interposed.

The planar lighting device 10 includes a linear light source unit 1.
1 and a light guide plate 15. The light guide plate 15 has a flat bottom surface 15a and a light guide surface 1 with a small inclination on the top surface.
A prism array composed of 5b and the reflecting surface 15c is formed in a sawtooth cross section. The linear light source unit 11 is composed of a light guide 12 and a point light source (for example, a light emitting diode) (not shown) disposed at an end thereof, and diffuses light emitted from the point light source in the light guide 12. Incident surface 1 of light guide plate 15
Light is emitted toward 5d.

The spread illuminating apparatus 10 has a λ with the bottom surface 15 a of the light guide plate 15 facing the display surface of the liquid crystal display element 50.
It is arranged via a 波長 wavelength plate 30.

On the other hand, the reflection type liquid crystal display element 50 is composed of a pair of substrates having a cholesteric phase at room temperature, for example, a chiral nematic liquid crystal obtained by adding a sufficient amount of a chiral agent to the nematic liquid crystal to exhibit a cholesteric phase. This enables full-color display in which a red display layer 51R, a green display layer 51G, and a blue display layer 51B sandwiched therebetween are stacked.

Each of the display layers 51R, 51G, and 51B is composed of a plurality of pixels in a matrix.
Each pixel (liquid crystal) is driven by a pulse voltage applied from a scanning electrode and a signal electrode formed on each substrate, and selectively reflects a transparent state (focal conic state) and visible light R, G, and B selectively. State (planar state) and display an image. Each display layer 51R, 51
The liquid crystals included in G and 51B are prepared so as to selectively reflect circularly polarized light in the same direction.

Further, a light absorbing layer 52 is disposed on the lowermost surface, and absorbs light not reflected by each of the display layers 51R, 51G, 51B.

In the image display apparatus 1 having the above structure, light incident on the light guide 12 from the point light source is totally reflected and diffused in the light guide 12, so that the light becomes a pseudo-linear light source. Irradiates the light incident surface 15d of the light guide plate 15 from above. The light that has entered the light guide plate 15 is totally reflected by the light guide surface 15b of the prism array, is reflected by the reflection surface 15c, emerges as planar light from the planar bottom surface 15a, and passes through the λ / 4 wavelength plate 30. To illuminate the display surface of the liquid crystal display element 50. This illumination light is reflected on the display surfaces of the display layers 51R, 51G, and 51B, and transmits through the light guide plate 15 as image light.

Here, the operation (polarization state) of the λ / 4 wavelength plate 30 will be described with reference to FIG. Since the light emitted from the light source is unpolarized, it can be considered after being decomposed into orthogonal linearly polarized lights having equal amplitude intensities. That is, FIG.
As shown in part A, the light can be decomposed into an S-polarized component and a P-polarized component having the same amplitude intensity. Reflective surface 15 of light guide plate 15
In the light reflected by c, the amplitude intensity of the S-polarized light is greater than the amplitude intensity of the P-polarized light, as shown in part B. Incidentally, the leakage light from the reflection surface 15c is
The amplitude intensity of the P-polarized light is larger than the amplitude intensity of the S-polarized light.

FIG. 3 shows the relationship between the incident angle θ (see FIG. 2) on the reflection surface 15c of the light guide plate 15 and the reflectance. The incident angle of the light with respect to the reflecting surface 15c of the prism array is substantially 30 to 50 °. As shown in FIG. 3, at the incident angle in this range, the reflection intensity of the S-polarized light is smaller than that of the P-polarized light. It turns out to be strong. If a material having a small birefringence is used as the light guide plate 15, polarization separation is ensured, and the light use efficiency is improved.

Here, when the slow axis of the λ / 4 wavelength plate 30 is inserted so as to be inclined at 45 ° with respect to the prism ridge 15e, the S-polarized light component and the P-polarized light component of the reflected light are respectively
It becomes left-handed circularly polarized light and right-handed circularly polarized light. The intensity of the left circular polarization component corresponds to the intensity of the S polarization component, and the intensity of the right circular polarization component corresponds to the intensity of the P polarization component. That is, the intensity of the left circularly polarized light component is stronger than the intensity of the right circularly polarized light component.

Therefore, each of the liquid crystal display layers 51R, 51G, 5
If all the directions of circularly polarized light selectively reflected in 1B are set to left circularly polarized light, 50% or more of the illumination light is used as image light. Note that the right circularly polarized light is absorbed by the light absorbing layer 52 disposed on the lowermost surface. Further, the light absorbing layer 52 also absorbs all the light transmitted through the liquid crystal (black display) in the focal conic state.

On the other hand, if the λ / 4 wavelength plate 30 is inserted with its slow axis rotated by 90 °,
That is, if the prism ridge 15e is rotated by 45 ° (-45 °) in the opposite direction to the above example, the S-polarized light component and the P-polarized light component of the reflected light are clockwise circularly polarized light and It becomes counterclockwise circularly polarized light. Therefore, each display layer 51
The directions of circularly polarized light selectively reflected by R, 51G, and 51B may be set to right circularly polarized light.

When an air layer exists between the λ / 4 wavelength plate 30, the light guide plate 15, and the liquid crystal display element 50, the λ /
It is preferable to perform an antireflection treatment on the interface between the four-wavelength plate 30 and the air layer.

(Second Embodiment, see FIGS. 4 and 5) The image display device 2 according to the second embodiment includes a planar illumination device 10, a liquid crystal display element 50, and a λ / And a four-wavelength plate 30. Therefore, in FIGS. 4 and 5, the same members as those in FIGS. 1 and 2 are denoted by the same reference numerals, and the operation of each member is the same as in the first embodiment.

The difference is that the λ / 4 wavelength plate 30 is bonded to the uppermost surface of the liquid crystal display element 50 via the bonding layer 31 and that the light guide 12 and the light guide plate 15 are The point is that a polarizing plate 41 that transmits S-polarized light and absorbs P-polarized light is arranged. The adhesive layer 31 is composed of the λ / 4 wavelength plate 30 and the liquid crystal display element 5.
This has the effect of preventing inter-plane reflection occurring between zero.

Here, the operation (polarization state) of the λ / 4 wavelength plate 30 in the second embodiment will be described with reference to FIG.

Almost all the light emitted through the polarizing plate 41 is S-polarized light, and the S-polarized light component is reflected on the reflecting surface 15c of the prism array, and the slow axis is the prism ridge 15e.
Through the λ / 4 wave plate 30 inserted so as to be inclined at 45 ° with respect to, all of the light is turned to the left-handed circularly polarized light. Therefore, if all the directions of circularly polarized light selectively reflected by the liquid crystal display layers 51R, 51G, and 51B are set to left circularly polarized light, right circularly polarized light that does not contribute to switching is not included in principle, and unnecessary scattering or the like is eliminated. Accordingly, a high-contrast image with little ghost light and high contrast can be displayed. Also, P
Since almost no polarized light component is incident on the light guide plate 15, leakage light from the light guide plate 15 is reduced.

Instead of the polarizing plate 41, a reflective polarizing plate 42 (for example, 3M) that transmits S-polarized light and reflects P-polarized light.
(D-BEF). Since the P-polarized light returned to the light guide 12 by the reflective polarizing plate 42 is scattered in the light guide 12 and converted into S-polarized light, and emitted to the light guide plate 15, the light use efficiency is further improved. Can be.

(Refer to the third embodiment, FIG. 6) As in the second embodiment, the image display device 3 according to the third embodiment includes a spread illuminating device 10, a liquid crystal display element 50, and a λ / 4 wavelength. It is composed of a plate 30 and a polarizing plate 41. Therefore, FIG.
In FIG. 7, the same reference numerals are given to the same members as in FIG.

The difference is that the λ / 4 wavelength plate 30 is bonded to the bottom surface 15a of the light guide plate 15 via the bonding layer 32. The adhesive layer 32 has an effect of preventing inter-plane reflection generated between the λ / 4 wavelength plate 30 and the light guide plate 15. It is preferable that the refractive index of the adhesive layer 32 is smaller than the refractive index of the light guide plate 15 in order to ensure the condition of total reflection of the light guide plate 15.

(Refer to the fourth embodiment, FIG. 7) The video display device 4 according to the fourth embodiment has a configuration in which the second embodiment and the third embodiment are combined. Accordingly, in FIG. 7, the same members as those in FIGS. 4 and 6 are denoted by the same reference numerals, and the operation of each member is the same as in the second and third embodiments.

That is, in the fourth embodiment, the upper and lower surfaces of the λ / 4 wavelength plate 30 are bonded to the uppermost surface of the liquid crystal display element 50 and the bottom surface 15 a of the light guide plate 15 via the adhesive layers 31 and 32. The functions of the adhesive layers 31 and 32 are as described in the second and third embodiments.

(Fifth Embodiment, see FIG. 8) The video display device 5 of the fifth embodiment is characterized by the configuration of the light source unit 11, and includes a light guide plate 15, a liquid crystal display element 50, and a λ / 4.
The wave plate 30 may adopt any configuration of the first, second, third, and fourth embodiments.

That is, the reflection polarizing plate 42 was arranged on the emission surface 12a of the light guide 12, and the λ / 4 wavelength plate 43 and the reflection plate 44 were arranged on the surface 12b facing the emission surface 12a.

As described above, the S-polarized light propagating in the light guide 12 passes through the reflective polarizer 42 and enters the light guide 15. On the other hand, the P-polarized light is reflected by the reflection polarizing plate 42, further reflected by the reflection plate 44, and returns to the reflection polarizing plate 42 again.
At this time, the P-polarized light is transmitted back and forth through the λ / 4 wavelength plate 43 and is converted into S-polarized light. The light converted to S-polarized light is transmitted through the reflective polarizer 42 this time, and
5 is incident.

Therefore, according to the fifth embodiment, the P-polarized light is converted into the S-polarized light by the
% Of the light can be incident on the light guide plate 15, and the light use efficiency is further improved.

(Sixth Embodiment, FIG. 9) The image display device 6 of the sixth embodiment is characterized by the configuration of the light guide plate 15, and includes a light source unit 11, a liquid crystal display element 50, and a λ / 4.
The wave plate 30 may adopt any configuration of the first to fifth embodiments.

That is, the prism ridge 15e is inclined with respect to the light incident surface 15d from the light source unit 11.
Since the prism ridge 15e has an inclination as described above, generation of moiré fringes can be suppressed.

(Other Embodiments) The video display device according to the present invention is not limited to the above embodiments, but can be variously modified within the scope of the gist.

For example, the details of the light source unit and the light guide plate are arbitrary, and it is a matter of course that the reflection type liquid crystal display device can have various structures.

[Brief description of the drawings]

FIG. 1 is a schematic perspective view showing a first embodiment of a video display device.

FIG. 2 is an explanatory diagram showing a polarization state of light in the first embodiment.

FIG. 3 is a graph showing a relationship between an incident angle and a reflectance at a reflecting portion of the light guide plate.

FIG. 4 is a schematic side view showing a second embodiment of the video display device.

FIG. 5 is an explanatory diagram showing a polarization state of light in the second embodiment.

FIG. 6 is a schematic side view showing a third embodiment of the video display device.

FIG. 7 is a schematic side view showing a fourth embodiment of the video display device.

FIG. 8 is a schematic side view showing a main part of a fifth embodiment of the video display device.

FIG. 9 is a schematic perspective view showing a sixth embodiment of the video display device.

[Explanation of symbols]

 1,2,3,4,5,6 image display device 10 planar illumination device 11 light source unit 15 light guide plate 15e prism ridge line 30 λ / 4 wavelength plate 31, 32 adhesive layer 41 polarizing plate 42 ... Reflection polarizing plate 43 ... λ / 4 wavelength plate 44 ... Reflection plate 50 ... Liquid crystal display element

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H04N 5/64 511 H04N 5/64 511Z F term (Reference) 2H038 AA52 AA55 BA06 2H089 HA25 HA28 QA16 RA11 TA12 TA14 TA15 TA17 TA20 2H091 FA01Y FA08X FA11X FA14Y FA21X FA23X FA45X FD06 FD10 HA11 LA18 5G435 AA02 AA03 BB12 BB16 CC09 FF02 GG03 HH05

Claims (9)

[Claims] 1. A liquid crystal display device comprising at least one liquid crystal layer sandwiching a liquid crystal exhibiting a cholesteric phase having a selective reflection wavelength in a visible light region between a pair of substrates, a light source unit and a light guide plate. And a light guide plate having a planar surface on the display surface side of the liquid crystal display element, and a planar illumination having a prism array for transmitting light incident from the light source unit to the display surface through the flat surface on a surface facing the flat surface. And a λ / 4 wavelength plate interposed between the light guide plate and the liquid crystal display element such that the angle between the slow axis and the prism ridge line of the prism array is ± 45 °. An image display device characterized by the following. 2. A liquid crystal display device comprising at least one liquid crystal layer sandwiching a liquid crystal exhibiting a cholesteric phase having a selective reflection wavelength in a visible region between a pair of substrates, a light source unit and a light guide plate, The light guide plate has a flat surface on the display surface side of the liquid crystal display element, and a planar illumination device having a prism array on a surface facing the flat surface for transmitting light incident from the light source unit to the display surface through the flat surface. And λ / interposed between the light guide plate and the liquid crystal display element.
A four-wave plate, wherein the λ / 4-wave plate has a slow axis inclined with respect to the prism ridge of the prism array, and converts linearly polarized light emitted from the light guide plate into circularly polarized light. Characteristic video display device. 3. The liquid crystal display device according to claim 1, wherein two or more liquid crystal layers having different selective reflection wavelengths and reflecting circularly polarized light in the same direction are laminated. The image display device according to claim 2. 4. The image display device according to claim 1, wherein the λ / 4 wavelength plate is adhered to a display surface of the liquid crystal display device. 5. The image display device according to claim 1, wherein the λ / 4 wavelength plate is adhered to a plane of the light guide plate. 6. The image display device according to claim 5, wherein said λ / 4 wavelength plate is further adhered to a display surface of said liquid crystal display device. 7. A polarizing plate for transmitting S-polarized light is disposed between the light source unit and an end face of the light guide plate on which light is incident from the light source unit. 7. The video display device according to claim 2, claim 3, claim 4, claim 5, or claim 6. 8. A reflection polarizer that transmits S-polarized light and reflects P-polarized light is disposed between the light source unit and an end face of the light guide plate on which light is incident from the light source unit. The image display device according to claim 1, 2, 3, 4, 5, or 6, wherein 9. The image display device according to claim 8, wherein the light source unit includes a converter for converting P-polarized light reflected from the reflective polarizer to S-polarized light.