JP2001093318A - Light guide plate, surface light source device and display - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a surface light source device capable of obtaining a light having angle-of-visibility property of concentration in two directions after injected from one linear light source, a light guide plate to be used for the surface light source device, and a display to be suitably used for a vehicle mounted display with the surface light source device. SOLUTION: Diffuser is contained in a light guide plate 2, on the backside 23 of which a groove 25 is provided in opposition to an incident plane 21, with its slope 25a inclined to the direction of moving away from the incident plane 21 as moving away from the backside 23. A light reflected from the slope 25a is emitted from an emission plane, as a light having an inclination to the incident plane. With the scattering operation of the diffuser, a light having angle-of- visibility property of concentration in two directions is emitted from the emission plane 22.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a surface light source device for emitting light having a viewing angle characteristic concentrated in a specific direction, a light guide plate used for the surface light source device, and the surface light source device. The present invention relates to a display device.

[0002]

2. Description of the Related Art In a non-light-emitting display device represented by a liquid crystal display device, for example, when it is incorporated into a product such as a digital still camera, a video camera, or a liquid crystal television, a surface is provided on the rear surface of the device for illumination. A backlight unit as a light source device is provided. As one structure of the backlight unit, a linear light source, a light guide plate for emitting light from the light source from the side and emitting from the emission surface, and a reflector for efficiently making the light from the light source enter the light guide plate A lens sheet for condensing light (emitted light) emitted from the surface of the light guide plate within a viewing angle to improve luminance, and provided on the back surface side of the light guide plate to return light exiting from the back surface into the light guide plate again. Is known.

[0003] Normally, it is desired that a backlight emits as uniform light as possible in all directions from an emission surface.
Depending on the purpose of use, for example, a liquid crystal color TV for personal use having a small viewing angle is required to have a viewing angle characteristic concentrated in a certain direction and to be capable of obtaining a uniform amount of emitted light over the entire emission surface. You. Therefore, Patent No. 27397
In No. 30, light having an inclination with respect to a normal direction of the light emitting surface in a surface direction orthogonal to both the light incident surface and the light emitting surface is emitted from the light emitting surface of the light guide plate, and the light emitted is made into a lens sheet. By further deflecting in the normal direction,
Light having a viewing angle characteristic concentrated in a specific direction is obtained.

[0004]

In a vehicle-mounted liquid crystal display, such as a liquid crystal color TV or a car navigation system, the display is often observed from two directions from the driver's seat side and the passenger seat side. ,
Therefore, a backlight unit incorporated in a liquid crystal display is required to emit light having viewing angle characteristics concentrated in the two directions.

[0005] However, in general, the above-mentioned Patent No. 2
No. 7,379,730, there is only one direction of concentration, so that light having viewing angle characteristics concentrated in two directions could not be obtained. Further, by providing two linear light sources and obtaining light having a viewing angle characteristic that is concentrated in another direction with respect to light from each linear light source, a viewing angle concentrated in two directions is obtained. It is conceivable to obtain emission light having characteristics, but in this case, two linear light sources are required.
In the backlight unit, the linear light source accounts for a relatively large percentage of the cost, so providing two linear light sources increases the cost.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has a surface capable of receiving light from one linear light source and obtaining light having a viewing angle characteristic concentrated in two directions. It is an object of the present invention to provide a light source device, a light guide plate used for the surface light source device, and a display device suitable for use in a vehicle-mounted display including the surface light source device.

[0007]

According to a first aspect of the present invention, there is provided a light guide plate comprising a light-transmitting material containing a light diffusing agent, a light source opposed to the light source, and a light incident surface on which light from the light source is incident. ,
It has an exit surface from which light incident from the entrance surface is emitted, and an opposing surface facing the exit surface, and the opposing surface is inclined in a direction facing the incident surface and moving away from the incident surface as the distance from the opposing surface increases. An emission direction control means having an inclined surface is provided.

According to a second aspect of the present invention, in the light guide plate according to the first aspect, the inclined surface has an angle of 45 degrees with respect to the emission surface.
It has an angle of at least 90 ° and less than 90 °.

According to a third aspect of the present invention, in the light guide plate according to the first or second aspect, the distance between the exit surface and the facing surface in the direction perpendicular to the exit surface is greater than that near the entrance surface. It is characterized in that the portion near the surface opposite to the surface is shorter.

According to a fourth aspect of the present invention, there is provided a surface light source device comprising: the light guide plate according to any one of the first to third aspects; and a linear light source provided to face an incident surface of the light guide plate. It is characterized by.

According to a fifth aspect of the present invention, there is provided a display device comprising the surface light source device according to the fourth aspect and a non-light emitting type display means provided on an emission surface side of the light guide plate.

[0012]

FIG. 1 is a schematic diagram showing one embodiment of a light guide plate, a surface light source device and a display device according to the present invention.

Reference numeral 1 denotes a linear light source such as a cold-cathode fluorescent lamp or the like. The longitudinal axis of the linear light source 1 is provided in parallel with one side (one side on the incident side) of an emission surface of a light guide plate described later. . The linear light source is not limited to a fluorescent lamp, and a point light source such as an LED may be arranged linearly at appropriate intervals and function as a substantially linear light source.

Reference numeral 2 denotes a light guide plate made of a light-transmitting material such as an acrylic resin. The light guide plate 2 is formed so as to contain a diffusing agent substantially uniformly throughout, and has a scattering particle diameter of 0.5 μm, for example.
(For those containing a diffusing agent, see, for example, JP-A-7-17-1).
99856). The light guide plate 2 has an entrance surface 21 on which the linear light source 1 is disposed to face and light from the light source 1 is incident on.
And an emission surface 22 for emitting light incident from the incidence surface 21
And a back surface 23 as a facing surface facing the light emitting surface, and a facing side surface 24 which is a surface on the opposite side of the light emitting surface 22 via the light emitting surface 22.

A plurality of grooves 25 are formed on the back surface 23 as emission direction control means. The grooves 25 face the incident surface 21 and are inclined in a direction away from the incident surface 21 as the distance from the back surface 23 increases. Inclined surface 25a. The inclined surface 25a emits light that is reflected by the inclined surface 25a and emitted from the emission surface 22 out of the light that has traveled inside the light guide plate 2 so as to be emitted as having an inclination closer to the incidence surface 21. 22 at an angle α of 45 °. However, the angle α is 45 ° or more and less than 90 °, desirably in the range of 45 ° or more and about 70 °, even if the light reflected from the inclined surface 25a and emitted from the emission surface 22 is
The light can be emitted as having an inclination near the incident surface 21. The depth and interval at which the groove 25 is formed are:
The distance may be constant irrespective of the distance from the incident surface 21, or may be increased as the distance from the incident surface 21 increases (for example, 5 to 100 μm) or the distance may be reduced (for example, 10 to 200 μm). (Either depth and / or spacing may vary),
It is appropriately determined according to the dimensions and light quantity required for the surface light source device.

The distance between the light exit surface 22 and the back surface 23 in the direction perpendicular to the light exit surface 22, that is, the thickness of the light guide plate 2, depends on the light incident surface in order to improve the light emission efficiency. Opposing side surface 24 which is a surface opposite to the incident surface than near 21
The vicinity is formed shorter, so that the exit surface 22 has a surface parallel to a lens sheet or a liquid crystal display panel described later, and the rear surface 23 is inclined (or stepped) with respect to the exit surface 22. Formed.

Such a light guide plate is usually formed by injection molding using a thermoplastic resin such as an acrylic resin or a polycarbonate. Integrally and easily by a simple molding process.

Reference numeral 3 denotes a reflector for efficiently causing the light from the linear light source 1 to enter the incident surface 21. The reflector has an inner surface formed of a white or silver foil reflecting surface.
And the light from the light source is directed to the incident surface 21. Reference numeral 4 denotes a reflecting plate which is provided to face the back surface 23 which is the facing surface, and serves as a reflecting member for returning light leaked from the back surface 23 into the light guide plate 2 again.
On the surface facing the back surface 23, a white diffuse reflection surface is formed. In addition, regarding each of the three surfaces other than the entrance surface 21, the exit surface 22, and the back surface 23, a reflection member such as the reflection plate 4 is provided so as to face each surface as necessary.

Reference numeral 5 denotes a lens sheet comprising a prism array having a light emitting surface having a triangular cross section and each of its ridges being arranged in parallel.
The light component, which is provided on the upper side and spreads in the same direction as the axial direction of the linear light source 1 included in the light emitted from the emission surface 22 in a plane parallel to the incidence surface 21, is collected in a predetermined direction.

Reference numeral 6 denotes a transmissive liquid crystal display panel as non-light emitting display means provided on the light exit surface 22 side through the lens sheet 5.

In this embodiment, the linear light source 1, the light guide plate 2, the reflector 3, the reflection plate 4, and the lens sheet 5 constitute a backlight as a surface light source device.

In the apparatus shown in FIG. 1, when the linear light source 1 is turned on, light from the linear light source 1 is directly or reflected by the reflector 3 and enters the light guide plate 2 from the incident surface 21. The light incident from the incident surface 21 is scattered by the diffusing agent while traveling in the light guide plate 2 or the rear surface 2.
The light is emitted from the emission surface 22 after being reflected by 3 and the reflection plate 4.

Here, with reference to FIG. 2, the light emitted from the emission surface 22 by the scattering effect of the diffusing agent without being reflected on the inclined surface 25a of the back surface 23 will be described. Since the scattering by the diffusing agent is Mie scattering, the light is scattered with directivity, and the scattered light from the diffusing agent S is directed in the direction along the light traveling direction, that is, the light traveling from the incident surface 21 side. The light is scattered to the opposite side surface 24 side. Therefore, most of the light emitted from the emission surface 22 by being scattered by the diffusing agent S without being reflected by the inclined surface 25a of the back surface 23 has an inclination closer to the opposite side surface 24 (A in FIG. 3). Become.
In addition, having the inclination near the opposing side surface 24 means having directivity in a direction from the output surface 22 to an extension of the opposing side surface 24 in a plane perpendicular to the incident surface 21 and the output surface 22. Means

Next, light emitted from the emission surface 22 after being reflected by the inclined surface 25a of the back surface 23 will be described. Most of the light reflected on the inclined surface 25a has an inclination (B in FIG. 3) close to the incident surface 21 due to the inclination angle (angle α) of the inclined surface 25a even if it is scattered by the diffusing agent S on the way. In this state, the light is emitted from the emission surface 22. As described above, the inclination closer to the entrance surface 21 has directivity in a direction from the exit surface 22 to an extension of the entrance surface 21 in a plane perpendicular to the entrance surface 21 and the exit surface 22. Means that.

Therefore, when the linear light source 1 is turned on, the emission surface 2
2 and 3, as shown in FIGS. 2 and 3, light having a tilt toward the opposite side surface 24 and light having a tilt toward the incident surface 21, that is, having viewing angle characteristics concentrated in two directions. Light is emitted.

The light emitted from the emission surface 22 passes through the lens sheet 5 and is condensed in the axial direction of the linear light source 1, and illuminates the liquid crystal display panel 6 from the back in a state where the brightness is improved. I do. At this time, the liquid crystal display panel 6
Illumination light has a viewing angle characteristic concentrated in two directions, that is, the inclination toward the opposite side surface 24 and the inclination toward the incident surface 21, so that even if it is used as a liquid crystal display for in-vehicle use, A high-luminance display screen can be provided for observation from any direction from the passenger seat side.

Also, light having viewing angle characteristics concentrated in two directions can be obtained with one linear light source.
The surface light source device can further contribute to cost reduction as a display device.

It should be noted that the present invention is not limited to use in a vehicle-mounted liquid crystal display, but is suitably applied to a case where one display screen is viewed from a symmetrical position (such as line symmetry). It is something that can be done.

Further, in this embodiment, a separate lens sheet 5 is provided on the light guide plate 2, but a prism array having a triangular cross section similar to the lens sheet is formed on the exit surface of the light guide plate. The light guide plate may have the function of the lens sheet integrally.

[0030]

According to the present invention, as is apparent from the above description, the light guide plate contains a diffusing agent, and the inclined surface which is opposed to the incident surface on the rear surface and which is inclined away from the incident surface as the distance from the rear surface increases. The light reflected by this inclined surface is emitted from the exit surface as light having an inclination near the entrance surface, so that the viewing angle characteristics are concentrated in two directions from the exit surface together with the scattering action of the diffusing agent. Can be emitted. This makes it possible to provide a surface light source device and a display device suitable for use in a display for a vehicle.

Further, since light having a viewing angle characteristic concentrated in two directions can be obtained by one linear light source, it is possible to contribute to cost reduction of the apparatus.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing one embodiment of a light guide plate, a surface light source device, and a display device according to the present invention.

FIG. 2 is a diagram illustrating the behavior of light by a light guide plate according to one embodiment of the present invention.

FIG. 3 is a diagram showing viewing angle characteristics of an example according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Linear light source 2 Light guide plate 21 Incident surface 22 Outgoing surface 23 Back surface (facing surface) 24 Facing side surface 25 Groove (outgoing direction control means) 25a Inclined surface 3 Reflector 4 Reflecting plate 5 Lens sheet 6 Liquid crystal display panel (Non-light emitting display means) )

Claims (5)

[Claims] A light-transmitting material containing a light-diffusing agent, wherein a light source is disposed opposite to the light-receiving surface, and an incident surface on which light from the light source is incident;
An emission surface control means having an opposite surface facing the emission surface, wherein the opposite surface is provided with an emission direction control means having an inclined surface facing the incident surface and inclined in a direction away from the incident surface as away from the opposite surface. A light guide plate characterized by the above-mentioned. 2. The inclined surface is at least 45 ° and 90 ° with respect to the emission surface.
The light guide plate according to claim 1, wherein the light guide plate has an angle of less than °. 3. The distance between the exit surface and the opposing surface in a direction perpendicular to the exit surface is shorter near the surface opposite to the incident surface than near the incident surface.
3. The light guide plate according to claim 1. 4. A surface light source device comprising: the light guide plate according to claim 1; and a linear light source provided to face an incident surface of the light guide plate. 5. A display device, comprising: the surface light source device according to claim 4; and a non-light-emitting type display unit provided on an emission surface side of the light guide plate.