JP2001236810A - Illumination device and liquid crystal display using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a compact illumination device which is used as a front light of a reflective liquid crystal display (LCD), that has low power consumption. SOLUTION: The illumination device 30 comprises light sources 20 and light transmissive plate 10. The light transmissive plate 10 sends out the light rays incident on light incident end surfaces 10a, 10b through a rear surface 10d to a front surface 10c. Light-emitting bodies 20, consisting of organic EL elements as the light sources, are mounted on the incident end surfaces 10a and 10b of the light transmissive plate 10.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lighting device suitable as a front light for a liquid crystal display device.

[0002]

2. Description of the Related Art Conventionally, there has been known a reflection type liquid crystal display device having a structure in which a front light (illumination device) is provided on a display surface side of a liquid crystal display panel and a reflection plate is provided on a back surface side of the liquid crystal display panel. I have. FIG. 2 is a schematic configuration diagram of an example of a reflection type liquid crystal display device as viewed in cross section. The device in this example is
It comprises a front light 3 having a light guide plate 1 and a light source 2, a liquid crystal display panel 4, and a reflector 5. In this device, the light guide plate 1 is laminated on one surface of the liquid crystal display panel 4, and the reflection plate 5 is laminated on the other surface. The light source 2 is arranged along the end face of the light guide plate 1, and a light direction control member 2 a is provided around the light source 2 except for the side of the light guide plate 1, and light emitted from the light source 2 transmits the end face of the light guide plate 1. Is configured to be efficiently incident on the inside thereof. The back surface of the light guide plate 1, that is, the surface in contact with the liquid crystal display panel 4, is formed flat. On the other hand, the light guide plate 1
The surface of the light guide plate 1 is formed with fine irregularities.
Light incident from the end face of the light guide plate 1
The light is efficiently emitted from the back surface of the liquid crystal display panel 4 toward the liquid crystal display panel 4, and the light reflected by the reflection plate 5 is transmitted through the surface of the light guide plate 1 and emitted from the display surface of the liquid crystal display device. ing.

[0003]

In the conventional front light 3, the light source 2 is a cold cathode tube or an LE.
However, in order to make the light emitted from the light source 2 incident into the light guide plate 1 without waste, the light direction control member 2a is provided around the light source 2. It was necessary to provide. For this reason, when configuring the liquid crystal display device, a relatively large space for accommodating the light source 2 must be provided outside the display surface, which has been a problem in reducing the size of the device. In particular, a cold cathode tube requires an inverter and has a problem that power consumption is relatively large.

[0004] The present invention has been made in view of the above circumstances, and has as its object to reduce the size and power consumption of a front light.

[0005]

According to another aspect of the present invention, there is provided an illuminating apparatus including a light source and a light guide plate, wherein the light guide plate transmits light incident from an incident end face from a back surface. It has a characteristic of emitting light emitted from the back surface and emitting light incident from the back surface, and a luminous body made of an organic EL element is provided as the light source on the incident end face of the light guide plate. I do. The front surface of the light guide plate is formed in a stepped shape in which inclined portions that reflect light incident from the incident end face toward the rear surface and flat portions that transmit light incident from the rear surface are alternately arranged. Is preferred. A pair of opposing end surfaces of the light guide plate may both be incident end surfaces, and a luminous body made of an organic EL element may be provided on each of the incident end surfaces. In this case, the front surface of the light guide plate, an inclined portion that reflects the light incident from the incident end surface toward the back surface,
A shape in which flat portions that transmit light incident from the back surface are stepwise arranged alternately, and the thickness of the light guide plate gradually decreases from one incident end surface to the other incident end surface, and then gradually increases. It is preferable that Further, when the pair of incident end surfaces are on the left and right sides, it is preferable that the shape of the light guide plate is symmetric. In addition, it is preferable that the width of the flat portion in the light guide plate is configured to gradually decrease as the distance from the light source increases. A liquid crystal display device according to the present invention includes the lighting device according to the present invention.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail.
FIGS. 1A and 1B show an embodiment of a reflection type liquid crystal display device provided with a lighting device of the present invention as a front light, where FIG. 1A is a plan view, and FIG. 1B is a cross-sectional view along line BB. It is. 1, the same components as those in FIG. 2 are denoted by the same reference numerals, and description thereof will be simplified. In the present embodiment, reference numeral 30 in the figure denotes a front light (illumination device), and a light guide plate 10 having a rectangular planar shape, and an organic EL provided on a pair of incident end faces 10a and 10b of the light guide plate 10 facing each other. A light-emitting body (light source) 20 composed of an element (organic electroluminescence element). In the figure, reference numeral 4a denotes a polarizing plate of the liquid crystal display panel 4, and 5a denotes a reflection film of the reflection plate 5, respectively.

The organic EL device constituting the light emitting body 20 has a structure in which an anode, a hole transporting layer made of an organic compound, a light emitting layer made of an organic compound, and a cathode are sequentially laminated.
When electrons are injected from the cathode to the light-emitting layer and holes are injected from the anode to the light-emitting layer via the hole transport layer, excitons are generated in the light-emitting layer by recombination of electrons and holes. It emits light in the process of radiation deactivation. As the luminous body 20 in the present embodiment, an anode made of a well-known transparent material and a hole transport layer, a light-emitting layer, and a cathode made of a well-known material are sequentially stacked on a transparent substrate 20a made of glass or the like. And a transparent substrate 20a having a light-emitting surface.
a and the incident end faces 10a and 10b of the light guide plate 10 are arranged so as to face each other. In the stacking direction of the luminous body 20 composed of the organic EL element (incident end faces 10a, 1
The thickness T1 (in the direction perpendicular to 0b) is preferably thinner in order to reduce the size of the liquid crystal display device. However, there is a limit to the reduction in thickness in manufacturing. The thickness is about 3 to 1.0 mm, and the thickness of the stacked body 20b thereon is about 0.3 to 1.0 mm. Light guide plate 1
If the size W1 of the luminous body 20 in the thickness direction of 0 is smaller than the thickness T2 of the light guide plate 10, the distribution of incident light on the incident end faces 10a and 10b of the light guide plate 10 becomes non-uniform. It is preferably larger. On the other hand, if W1 is too small, it becomes difficult to manufacture the luminous body 20, while if W1 is larger than the total thickness T3 of the light guide plate 10, the liquid crystal display panel 4, and the reflection plate 5, the storage efficiency in the liquid crystal display device is reduced. Since it is bad, it is set in the range of T2 ≦ W1 <T3.

The light guide plate 10 is made of a light transmissive material such as an acrylic resin, a polycarbonate resin, a methacrylic resin or the like, and has a fine unevenness on the surface 10c. The back surface 10d of the light guide plate 10 is a flat surface, and all four end surfaces including the incident end surfaces 10a and 10b are flat surfaces perpendicular to the back surface 10d. In the present embodiment, the front surface 10c of the light guide plate 10 is
0d and an inclined portion 12 inclined at a certain angle α with respect to the flat portion 11
It is formed in a stepped shape alternately arranged in the normal direction of a and 10b. That is, the flat portion 11 and the inclined portion 1
Reference numeral 2 denotes a band extending in the direction along the incident end faces 10a and 10b, and the inclined portions 12 are arranged so as to intersect the normals of the incident end faces 10a and 10b. The thickness of the light guide plate 10 is
It is the largest at the incident end faces 10a and 10b on both sides, and increases gradually after decreasing from the one incident end face 10a toward the other incident end face 10b.
Are formed in a substantially valley shape. Further, in the present embodiment, the shape of the light guide plate 10 is formed so as to be symmetric when viewed from the right and left sides of the incident end faces 10a and 10b, and at the center in the normal direction of the incident end faces 10a and 10b, The distance between the flat portion 11 and the back surface 10d of the light guide plate 10 is the smallest. Inclined part 1 with respect to flat part 11
2 is preferably set so that the light incident from the incident end faces 10a and 10b can be most efficiently reflected toward the rear face 10d.
It is formed at 45 °. Also, the incident end faces 10a, 10b
The width W3 of the inclined portion 12 in the normal direction of the light guide plate 10
Although it is constant throughout, the width W4 of the flat portion 11 is formed so as to gradually decrease as the distance from the incident end faces 10a and 10b increases. That is, the incident end faces 10a, 1
In the normal direction of 0b, the interval between the inclined portions 12 becomes closer as it approaches the center.

The thickness T2 of the light guide plate 10 at the incident end faces 10a and 10b increases as the thickness increases, but the size of the illuminating device increases. In the present embodiment, 1.0 to 3.
It is set to 0 mm, preferably about 2 mm. The length L of the light guide plate 10 in the normal direction of the incident end faces 10a and 10b can be set as needed. However, if it is too long, the light source light is insufficient and the light is emitted from the surface 10c of the light guide plate 10. Light may be non-uniform. In the present embodiment, since the light source light is incident on the light guide plate 10 from two directions facing each other, the length L of the light guide plate 10 can be relatively large, and specifically, Luminous body 20
Generally, the length L is 20 to 200 m, although it depends on the amount of emitted light.
m. Also, the incident end face 10
Light incident from a and 10b is reflected by the inclined portion 12 and finally emitted from the flat portion 11 toward the viewer, and the portion of the inclined portion 12 on the display screen darkens in a streak shape. If the width W3 is too large, the slope 12
Is conspicuous and may cause a problem in display characteristics. On the other hand, if the width W3 of the inclined portion 12 is too small, one inclined portion 12
In this case, the amount of light reflected by the light guide plate is reduced, so that the amount of light emitted from the light guide plate surface 10c is reduced. To compensate for this, if the inclined portions 12 are densely provided, the total area of the flat portion 11 is reduced as a result. In addition, the light emission area on the light guide plate surface 10c is reduced. Therefore, the width W of the flat portion 11
4 and the width W3 of the inclined portion 12 are equal to the surface 1 of the light guide plate 10.
It is preferable that the setting be made in a well-balanced manner so that light can be emitted most efficiently from 0c. In the present embodiment, the width W3 of the inclined portion 12 is about 5 to 10 μm, and the width W4 of the flat portion 11 is
Is about 150 to 250 μm at the widest outside, about 100 to 150 μm at the narrowest center, and 150 to 200 μm on average
It is designed to be about m. The minimum value of the distance between the flat portion 11 and the back surface 10d of the light guide plate 10, that is, the thickness T4 of the light guide plate 10 at the center in the normal direction of the incident end surfaces 10a and 10b, the thinner the light source light utilization efficiency. However, if the thickness is too small, the production of the light guide plate 10 becomes difficult, and the shape retention is deteriorated. Therefore, the thickness is designed to be 0.1 mm or more, preferably about 0.2 to 0.3 mm.

The lighting device 30 of the present embodiment includes a light guide plate 10
Is formed by a molding method such as injection molding, and separately, a luminous body 20 is formed by forming the laminate 20b on a transparent substrate 20a.
a, the transparent substrate 20a of the luminous body 20
Can be manufactured by bonding and fixing with an acrylic adhesive or the like. The illuminating device 30 obtained as described above is laminated on one surface of the liquid crystal display panel 4 as a front light, and a reflection plate 5 is provided on the other surface side of the liquid crystal display panel 4 to provide a reflection type liquid crystal display. A device is obtained.

According to this embodiment, the light source 20 made of an organic EL element is used as a light source for making light incident on the light guide plate 10, so that the light source itself can be downsized.
The protrusion of the light source 20 to the outside of the light guide plate 10 can be reduced. Therefore, downsizing of the lighting device 30 and downsizing of the liquid crystal display device can be achieved. In addition, since the luminous body 20 composed of the organic EL element does not require an inverter and can obtain high-luminance illumination light with relatively small power consumption, the power consumption of the lighting device 30 and the liquid crystal display device can be reduced. The life can be improved. Furthermore, since the light emitting body 20 made of an organic EL element emits surface light and can be formed on the entire surface of the incident end faces 10a and 10b of the light guide plate 10, the light direction control member 2a is not provided around the light source. Also, light can be efficiently incident on the incident end faces 10a and 10b of the light guide plate 10, and the uniformity of incident light on the incident end faces 10a and 10b is high. Moreover, since the luminous body 20 is made of a laminate, it is easy to mold and change the shape of the luminous surface. Therefore, even if the thickness T2 of the light guide plate 10 is increased, it is possible to easily cope with the increase, and it is possible to secure high incidence efficiency and uniformity of incident light, so that the degree of freedom in designing the light guide plate 10 is high.

Further, according to the present embodiment, as indicated by the arrow in FIG. 1, of the light incident from the incident end faces 10a and 10b of the light guide plate 10, the light that reaches the inclined portion 12 of the front surface 10c is the rear surface 10d. And is emitted from the back surface 10d. Then, the light passes through the liquid crystal display panel 4 and passes through the reflector 5.
The reflected light passes through the liquid crystal display panel 4 again, enters the light guide plate 10 from the back surface 10d thereof, and exits from the flat portion 11 of the front surface 10c of the light guide plate 10. Therefore, in the light guide plate 10 of the present embodiment, the incident end face 1
The light transmitted between the front surface 10c and the back surface 10d at the center in the normal direction of 0a and 10b is not used because it is not reflected by the inclined portion 12, but the front surface 10c and the back surface 1d are not used.
Since the distance from 0d is formed sufficiently small, the utilization efficiency of the incident light is sufficiently high. In the present embodiment, the light-emitting bodies 20 are provided on both left and right sides in the normal direction of the incident end faces 10a and 10b of the light guide plate 10, and the light guide plate 1
Since the shape of the 0 surface 10c is symmetrical, the amount of incident light can be increased and the amount of emitted light can be increased as compared with the case where the light source 20 has only one side.
Therefore, even if the area of the light guide plate 10 increases, sufficiently bright illumination light can be obtained. Further, in the present embodiment, the width W4 of the flat portion 11 is relatively large on both sides where the amount of incident light from the incident end surfaces 10a and 10b is relatively large in the normal direction of the incident end surfaces 10a and 10b of the light guide plate 10,
Since the width W4 of the flat portion 11 is gradually reduced as approaching the center, the interval between the inclined portions 12 becomes denser as the distance from the light source 20 increases, and the area for reflecting light gradually increases. Therefore, even in the normal direction of the incident end faces 10a and 10b, even if the light guiding distance becomes longer and the amount of light reaching the inclined portion 12 decreases, the amount of light reflected toward the back surface 10d can be made uniform. Surface 10
The uniformity of the light emitted from c is high.

The luminous body 20 composed of an organic EL element in the present embodiment is different from the light guide plate 10 in the present embodiment.
In addition to this, the lighting device can be configured by combining with a light guide plate of any shape, making the lighting device compact, reducing the size of the liquid crystal display device, reducing the power consumption, improving the battery life, and making the incident light highly uniform. Effects such as sex are obtained. In addition, the light guide plate 10 in the present embodiment can also constitute an illumination device in combination with a light source other than the light emitting body 20 made of an organic EL element. However, like the light guide plate 10 of the present embodiment, the unevenness of the surface 10c is stepped, and
When c is formed so as to have a valley shape as a whole, the thickness T2 of the incident end faces 10a and 10b tends to be large. Preferably, it is used. Further, in the present embodiment, the light guide plate 10 is formed in a symmetrical shape, and the light emitting bodies 2 are provided on both end surfaces (incident end surfaces 10a and 10b).
Although 0 is provided, the shape may be changed to a shape that is not symmetrical. Further, the shape of the light guide plate 10 may be appropriately changed to provide the light emitting body 20 on only one side.

[0014]

As described above, according to the present invention,
By using a light-emitting body made of an organic EL element as a light source for allowing light to enter from the end face of the light guide plate, the illumination device and the liquid crystal display device using the same can be reduced in planar size and consumed. Power consumption can be reduced and battery life can be improved. Further, the surface of the light guide plate is formed in a stepped shape in which an inclined portion that reflects light incident from the incident end face toward the back surface and a flat portion that transmits light incident from the back surface are alternately arranged. Thereby, light use efficiency can be improved. Further, a pair of opposing end surfaces of the light guide plate are both set as incident end surfaces,
By providing a luminous body made of an organic EL element on each of the incident end faces, it is possible to increase the amount of incident light,
Brighter illumination can be realized. Also, by gradually reducing the width of the flat portion in the light guide plate as the distance from the light source increases, the area of the reflection portion can be changed in accordance with the light amount distribution in the light guide plate,
The amount of emitted light can be made uniform.

[Brief description of the drawings]

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

FIG. 2 is a schematic configuration diagram showing an example of a conventional reflective liquid crystal display device.

[Explanation of symbols]

1, 10 light guide plate, 2, 20 light source (light emitting body), 3, 3
0: front light (illumination device), 10a, 10b: incident end face, 10c: front surface, 10d: back surface, 11: flat portion,
12: Inclined part.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H05B 33/14 H05B 33/22 C 33/22 G02F 1/1335 530 F term (Reference) 2H038 AA55 BA06 2H091 FA23X FA44X FB02 LA11 LA30 3K007 AB02 AB05 CA01 CB01 DA00 DB03 EB00 FA01 5G435 AA00 AA16 AA18 BB05 BB12 BB16 FF03 FF08 GG25

Claims (7)

[Claims] 1. A lighting device comprising a light source and a light guide plate, wherein the light guide plate emits light incident from an incident end face from a back surface and emits light incident from the back surface from a front surface. A lighting device, wherein a luminous body composed of an organic EL element is provided as the light source on the incident end face of the light guide plate. 2. The front surface of the light guide plate has an inclined portion that reflects light incident from the incident end face toward a back surface and a flat portion that transmits light incident from the back surface, which are alternately arranged. The lighting device according to claim 1, wherein the lighting device is formed in a step shape. 3. The light guide plate according to claim 1, wherein a pair of opposing end faces of the light guide plate are both incident end faces, and a luminous body made of an organic EL element is provided on each of the incident end faces. Lighting equipment. 4. The front surface of the light guide plate has an inclined portion for reflecting light incident from the incident end face toward a back surface and a flat portion for transmitting light incident from the back surface, which are alternately arranged. The lighting device according to claim 3, wherein the lighting device has a step shape, and the thickness of the light guide plate gradually increases from one incident end face to the other incident end face, and then gradually increases. 5. The lighting device according to claim 3, wherein the shape of the light guide plate is bilaterally symmetric when the pair of incident end faces are on the left and right sides. 6. A width of the flat portion in the light guide plate,
The lighting device according to claim 2, wherein the distance gradually decreases as the distance from the light source increases. 7. A liquid crystal display device comprising the lighting device according to claim 1.