CN100414327C - Backlight device - Google Patents

Abstract

The asymmetric prism sheet 15 has a plurality of protrusions 17 having a prismatic shape on its surface. The protruding portion 17 includes a first inclined surface 17a having a relatively small slope (gentle slope) and a second inclined surface 17b having a relatively steep slope (steep slope). The base angle 17d on the side of the second surface 17b is α °, and the base angle 17c on the side of the first surface 17a is β °. In the case where light enters the asymmetric prism sheet 15 having the above-described structure from the bottom surface 15a (light guide plate 11), the light is mainly emitted in a substantially vertical direction (a direction inclined by a relatively small angle with respect to the vertical direction) in the first inclined surface 17a (arrow X), and is mainly emitted in an inclined direction (a direction inclined by a relatively large angle with respect to the vertical direction) in the second inclined surface 17b (arrow Y).

Description

Backlight device

technical field

The present invention relates to a backlight device used as a light source of a liquid crystal display device, and more particularly to a backlight device using a brightness improving film.

Background technique

In a transmissive liquid crystal display device or a transflective liquid crystal display device, a light source provided inside the device is mainly used while external light is partially used. As a light source, a backlight is used.

In order to supply light from the rear side of the liquid crystal cell, a backlight is disposed on the rear side of the liquid crystal cell when viewed from the display side of the device. The backlight is mainly composed of a light guide plate whose main surface is opposed to and arranged substantially parallel to the surface on the rear side of the liquid crystal cell, and an edge light (side light) which is arranged on one side of one edge surface of the light guide plate and emit light toward the edge surface. In addition, a reflective sheet is provided on the side opposite to the liquid crystal cell side of the light guide plate.

In this arrangement, the light from the edge lamps propagating inside the light guide plate is reflected by the light reflection means provided on the light guide plate and the reflective sheet provided outside the light guide plate, thereby changing the direction of propagation toward the liquid crystal cell, and incident on the liquid crystal cell.

In a conventional backlight, in order to collect light from the light guide plate to enhance the brightness of the liquid crystal panel, a prism sheet having prism-shaped protrusions on its surface is provided on the liquid crystal cell side of the light guide plate.

Figure 1 shows a conventional prism sheet. The prism sheet 1 has a plurality of protrusions 2 in a prism shape on its surface. In the protruding part 2, each top angle is set to about 90 degrees. By the protruding portion 2 of the prism sheet 1, the direction of light incident in various directions from the lower side (flat surface) of the light guide plate is changed to a substantially vertical direction (see arrows in FIG. 1). Therefore, by arranging the prism sheet 1 on the liquid crystal cell side of the light guide plate, the light in all directions of the light guide plate can be changed into a substantially vertical direction, thereby improving the light collection characteristics and improving the brightness in the vertical direction of the liquid crystal panel.

Meanwhile, in recent years, liquid crystal display devices are required to increase luminance in the vertical direction of the liquid crystal panel while realizing a wide luminance viewing angle (viewing angle exhibiting sufficient luminance). However, as described above, in the prism sheet 1, since the protrusion is specially designed to increase the brightness in the vertical direction, the brightness viewing angle is sacrificed. Therefore, it is impossible to realize a wide brightness viewing angle in a liquid crystal display device provided with a backlight using a conventional prism sheet.

Contents of the invention

An object of the present invention is to provide a backlight device capable of realizing a liquid crystal display device exhibiting an improvement in luminance in a vertical direction and having a wide luminance viewing angle.

A backlight device according to the present invention includes: a light guide device having a pair of main faces and edge faces facing each other, and capable of guiding light from a light source provided at one of the edge faces; brightness/brightness viewing angle improving means, which be arranged on one side of a main surface of the light guide, and emit light in a substantially normal direction of the main surface and in a direction having a predetermined angle with the normal direction; and reflecting means, which are arranged on the other side of the light guide main face.

According to this structure, light can be emitted in a direction substantially normal to the main surface and in a direction having a predetermined angle with respect to the normal direction, so that brightness in the vertical direction can be improved while enhancing brightness in a direction having a predetermined angle with respect to the normal direction. . As a result, a liquid crystal display device capable of exhibiting sufficient brightness over a wide range can thereby be realized.

In the backlight device according to the present invention, the brightness/brightness viewing angle improving means is preferably an asymmetric prism sheet having a plurality of protrusions on its main surface.

In the backlight device according to the present invention, the protruding portion of the asymmetric prism sheet preferably has a first base angle α of 75° to 90° and a second base angle β of 45° to 60°. In the backlight device of the present invention, the protruding portion of the asymmetric prism sheet preferably has a first base angle α of 85° and a second base angle β of 50°. In this case, the first base angle α of the protruding portion is preferably on the side of the light source.

In the backlight device according to the present invention, a diffusion device is preferably provided between the light guide device and the brightness/brightness viewing angle improving device.

In the backlight device according to the present invention, a symmetrical prism sheet having a plurality of protrusions on its principal surface is preferably provided between the diffusion means and the brightness/brightness viewing angle improving means.

In the backlight device according to the present invention, the asymmetric prism sheet is preferably arranged such that the ridges of the protrusions of the asymmetric prism sheet are perpendicular to the ridges of the protrusions of the symmetrical prism sheet.

A liquid crystal display device according to the present invention has the backlight device as described above.

Description of drawings

Figure 1 shows a part of a conventional prism sheet;

Figure 2 schematically shows the arrangement of a backlight device according to an embodiment of the present invention;

FIG. 3 shows a part of a prism sheet in a backlight device according to an embodiment of the present invention;

Figures 4 and 5 have shown the light paths in the prism sheet shown in Figure 3;

FIG. 6 shows graphs for explaining the effect of a backlight device according to an embodiment of the present invention;

7(a) and 7(b) show a mobile phone with a backlight device according to one embodiment of the present invention;

Figure 8 shows a PDA with a backlight arrangement according to one embodiment of the present invention; and

FIG. 9 shows a car navigation system with a backlight device according to an embodiment of the present invention.

best mode

An embodiment of the present invention will be specifically described below with reference to the accompanying drawings.

FIG. 2 is a view schematically showing the arrangement of a backlight device according to an embodiment of the present invention. The backlight device of the present invention has a light guide plate 11 having a main surface 11a and an edge surface 11b. An edge light (side light) 12 is provided on one side of one edge surface of the light guide plate 11 . LEDs are generally used as edge lights.

On the main surface 11 a of the light guide plate 11 on the liquid crystal cell side, a diffusion sheet 13 for diffusing light emitted from the light guide plate 11 is provided. The diffusion sheet 13 can make the presence of the backlight invisible when viewed from the panel display screen. Furthermore, it is not always necessary to provide the diffusion sheet 13 .

A symmetrical prism sheet 14 is disposed on the diffusion sheet 13 . An example used as the symmetrical prism sheet 14 is BEF (trade name, Sumitomo 3M). The symmetrical prism sheet 14 has a plurality of protrusions in a prism shape on its surface, and is arranged such that the ridges of the protrusions are along the traveling direction of light from the light source. In this way, the symmetrical prism sheet can control light on the left and right sides of the traveling direction of the light from the light source. Thus, by providing the symmetrical prism sheet 14, light collection characteristics can be improved on the left and right sides of the traveling direction of light from the light source, thereby improving brightness. Therefore, using the sheet 14 together with an asymmetric prism sheet (described later) can further improve brightness in the vertical direction and improve brightness in each wide viewing angle direction.

An asymmetric prism sheet 15 is arranged on the symmetrical prism sheet 14 as a brightness/brightness viewing angle improving device. Specifically, the asymmetric prism sheet 15 has a structure as shown in FIG. 3 . FIG. 3 shows a part of a prism sheet of a backlight device according to an embodiment of the present invention.

The asymmetric prism sheet 15 has a plurality of protruding portions 17 having a prism shape on its surface. The protruding portion 17 includes a first inclined surface (slow-slope inclined surface) 17a having a relatively small slope and a second inclined surface (steep-slope inclined surface) 17b having a relatively steep slope. The base angle 17d on the side of the second surface 17b is α°, and the base angle 17c on the side of the first surface 17a is β°. The ridges of the protruding portion 17 are arranged along a direction substantially perpendicular to the traveling direction of light from the light source (the depth direction of the sheet when viewed in the figure). In other words, the asymmetric prism sheet 15 is arranged such that the ridges of the protrusions 17 are substantially perpendicular to the ridges of the protrusions of the symmetrical prism sheet. Thus, the asymmetric prism sheet 15 controls the light in the traveling direction of the light from the light source.

When light enters the asymmetric prism sheet 15 having the above-mentioned structure from the bottom surface 15a (light guide plate 11), the light is mainly in a substantially vertical direction (a direction inclined at a relatively small angle with respect to the vertical direction) in the first inclined surface 17a. ) (see arrow X), and in the second inclined surface 17b mainly emit in an oblique direction (a direction inclined at a relatively large angle relative to the vertical direction) (see arrow Y).

It is desirable to set the base angles α and β to emit light primarily in a substantially vertical direction, while emitting light primarily in an oblique direction, as described above. The tilting direction is determined according to the brightness viewing angle of the backlight device.

For the base angles α and β, it is desirable that the angle α ranges from 75° to 90°, while the angle β preferably ranges from 45° to 60°. Furthermore, as for the combination of the base angles α and β, for example, it is preferable that the angle α is 85° and the base angle β is 50°.

A preferable material of the asymmetric prism sheet 15 is a material having a refractive index of 1.4 to 1.6. Examples of the material of the asymmetric prism sheet 15 include resin materials such as acrylic-based resins, norbornene-based resins, and polycarbonate.

A reflective sheet 16 is provided in the direction opposite to the liquid crystal cell side of the light guide plate 11 (the side where the diffusion sheet 13 is not provided).

The function of the asymmetric prism sheet in the backlight device according to the present invention will be described in detail below with reference to FIGS. 4 and 5 . 4 and 5 are views for explaining optical paths in the prism sheet shown in FIG. 3 . Furthermore, in FIGS. 4 and 5 , an LED as a light source is provided on the observer's left side, and light travels in a left-to-right direction viewed by the observer.

As shown in FIG. 4, the light A incident on the asymmetric prism sheet 15 at an angle θ1 with respect to the vertical direction is refracted by the bottom surface 15a of the asymmetric prism sheet 15, and then refracted by the first inclined surface 17a of the protruding portion 17, And emit from the asymmetric prism sheet 15 toward the liquid crystal unit. At this time, since the base angle α of the protruding portion 17 is on the light source side, the emitted light has an angle θ2 with respect to the vertical direction. Light is thus emitted in a substantially vertical direction, thus promoting brightness improvement in the vertical direction.

In this case, the following equation (1) expresses the relationship among the incident angle θ1, the outgoing angle θ2, the base angle α, and the base angle β:

θ2＝β+sin ^-1 [n1xsin{β-sin ^-1 (sinθ1)/n1}] Equation (1)

Where n1 represents the refractive index of the asymmetric prism sheet.

In addition, as shown in FIG. 5, the light B incident on the asymmetric prism sheet 15 at an angle θ1' with respect to the vertical direction is refracted by the bottom surface 15a of the asymmetric prism sheet 15, and then is refracted by the first inclined surface of the protruding portion 17. 17a, and then refracted by the second inclined surface 17b, and emitted from the asymmetric prism sheet 15 toward the liquid crystal cell. At this time, since the base angle α of the protruding portion 17 is on the light source side, the emitted light has an angle θ2' with respect to the vertical direction. Light is thus emitted in an oblique direction, thus facilitating improvement of a wide brightness viewing angle.

In this case, the following equation (2) expresses the relationship between the incident angle θ1', the outgoing angle θ2', the base angle α, and the base angle β:

θ2'＝-α+sin ^-1 [n1xsin{α+2β-180-sin ^-1 (sinθ1')/n1}] Equation (2)

Where n1 represents the refractive index of the asymmetric prism sheet.

Therefore, in the case of determining the base angles α and β of the protruding portion 17 of the asymmetric prism sheet 15, it is desirable to determine the angles according to the above-mentioned equations (1) and (2) in consideration of the outgoing angles θ2 and θ2'. In particular, since the luminance viewing angle is arbitrary, it is desirable to determine the base angles α and β from the angle θ2'.

The backlight device having the above structure is provided on the rear side (opposite to the display side) of the liquid crystal cell in the liquid crystal display device. In the liquid crystal display device, light from the edge lamp 12 of the backlight device propagates inside the light guide plate 11, a part of the light is directly emitted to the liquid crystal cell side, while another part of the light is disposed on the opposite side of the light guide plate 11 to the liquid crystal cell side The reflection sheet 16 on the reflection. The light reflected by the reflective sheet 16 passes through the light guide plate 11 and is emitted to the liquid crystal cell side. Light emitted from the light guide plate 11 is diffused by the diffusion sheet 13 . Light passing through the diffusion sheet 13 is controlled by the symmetric prism sheet 14, thereby enhancing light collection characteristics in left-right directions (left and right directions of the traveling direction of light from the light source). Then, the light passing through the symmetrical prism sheet 14 is refracted by the protruding portion 17 of the asymmetrical prism sheet 15, and is emitted in a substantially vertical direction while being emitted in an oblique direction, as described above. In other words, the asymmetric prism sheet 15 emits light in a direction normal to the main surface of the light guide plate and in a direction forming a predetermined angle from the normal direction. The emitted light is thus incident on the liquid crystal cell.

In this way, according to the asymmetric prism sheet of the backlight device of the present invention, the light is emitted in a substantially vertical direction and simultaneously emitted in an oblique direction, thereby improving the brightness of the liquid crystal display device in the vertical direction and realizing a wide brightness at the same time perspective.

Examples executed to clarify the effects of the present invention will be described below.

Three backlights were prepared by sequentially laminating a diffusion sheet, a symmetrical prism sheet, and an asymmetrical prism sheet on one main surface of the light guide plate, providing a reflective sheet on the other main surface of the light guide plate, and An LED is provided on one side of the edge surface as an edge light. Each combination (88 °, 45 °) (example 1), (88 °, 50 °) (example 2) and (88 °, 55 °) ( Example 3) Set the three backlights. Also, as a comparative example, a backlight was prepared in which a diffusion sheet and two symmetrical prism sheets (BEF) were sequentially laminated on one main surface of the light guide plate, a reflection sheet was provided on the other main surface of the light guide plate, and An LED is provided on one side of an edge surface as an edge light.

A liquid crystal display device is obtained by combining four backlights and a liquid crystal panel. The brightness viewing angle of each liquid crystal display device was simulated. The brightness of the light on the backlight is measured in this simulation. Measure the luminance with a commonly used luminance meter and obtain the luminance at each angle. It is assumed here that the normal direction of the light emitting surface of the backlight is a viewing angle of 0°. Figure 6 shows the simulation results.

As can be seen from FIG. 6, each of the liquid crystal display devices (Examples 1 to 3) using the backlight according to the present invention exhibited high luminance in the vertical direction while having a wide luminance viewing angle. In particular, each device had a higher value for luminance in the vertical direction than the liquid crystal display device of the comparative example. On the other hand, the liquid crystal display device of the comparative example exhibited high luminance in the vertical direction, but its luminance viewing angle was narrow.

Application examples of the backlight device according to the present invention will be described below.

FIG. 7(a) is a view showing a mobile phone with a conventional backlight device, and FIG. 7(b) is a view showing a mobile phone with a backlight device according to the present invention. The mobile phone 22 with the backlight device of the present invention has a wider luminance viewing angle than the mobile phone 21 with the conventional backlight device, and therefore, can realize image display with a wide range and excellent viewing characteristics.

FIG. 8 is a view showing a PDA having a backlight device according to the present invention. Also in this example, the PDA 31 with the backlight device of the present invention has a wider brightness viewing angle than the PDA with the conventional backlight device, and therefore, image display with a wide range and excellent viewing characteristics can be realized.

FIG. 9 is a view showing a car navigation system having a backlight device according to the present invention. Also in this example, the monitor 41 of the car navigation system with the backlight device of the present invention has a wider luminance viewing angle than the monitor 41 of the car navigation system with the conventional backlight device, therefore, a wide range and Image display with excellent viewing characteristics. For example, as shown in FIG. 9, for a person on the driver's seat and a person next to the driver's seat, all information on the monitor 41 mounted on the passenger side can be seen in an excellent viewing state. displayed image.

The present invention is not limited to the foregoing embodiments, but it can be put into practice with various modifications. For example, the foregoing embodiments have described cases where the backlight device according to the present invention is used for liquid crystal display devices of mobile phones, PDAs, and car navigation systems. The present invention can also be used in liquid crystal display devices for all applications requiring luminance in the vertical direction and a wide luminance viewing angle.

Furthermore, this embodiment describes the case of using an asymmetric prism sheet as the brightness/brightness viewing angle improving means, but the present invention is not limited to this case. Any member other than a symmetrical prism sheet may be used as long as one member emits incident light in a substantially vertical direction while emitting light in an oblique direction.

Moreover, the diffusion sheet and/or the reflection sheet in this embodiment are not limited to the shape of a sheet, and may also be in the shape of a plate or a film, as long as they respectively exhibit a diffusion effect and/or a reflection effect. Symmetrical prism sheets are not limited to sheets, as long as they can exhibit their functions.

As described above, the backlight device of the present invention includes: a light guide device having a pair of main faces facing each other and a pair of edge faces facing each other and capable of guiding light from a light source provided on one of the edge faces Brightness/brightness viewing angle improving device, which is provided in one side of one main surface of the light guide plate, and can emit light in a direction substantially normal to the main surface and in a direction having a predetermined angle with the normal direction; and reflection means, which are arranged on the other major face of the light guide. Thereby, a liquid crystal display device exhibiting enhanced luminance in the vertical direction and having a wide luminance viewing angle can be realized.

Industrial applicability

The present invention is applicable to a backlight device used as a light source of a liquid crystal display device of a mobile phone, a PDA (Personal Digital Assistant), a car navigation system, or the like.

Claims (7)

1. backlight device comprises:

Light guide, it has a pair of interarea that faces with each other and edge surface, is used to guide the light from the light source that is arranged on an edge surface place;

Device is improved at the luminance/luminance visual angle, and it is set on the side of an interarea of described light guide, and launches light having on the direction of predetermined angular on the basic normal direction of this interarea and with this normal direction; With

Reflection unit, it is set on another interarea of described light guide,

Wherein between described light guide and described luminance/luminance visual angle raising device, disperser is set, and between described disperser and described luminance/luminance visual angle raising device, a symmetric prism with a plurality of outshots is set.

2. according to the backlight device described in the claim 1, it is an asymmetric prism sheet with a plurality of outshots that device is improved at wherein said luminance/luminance visual angle.

3. according to the backlight device described in the claim 2, the described outshot of wherein said asymmetric prism sheet has 75 ° to 90 ° first base angle and 45 ° to 60 ° the second base angle β.

4. according to the backlight device described in claim 2 or 3, the described outshot of wherein said asymmetric prism sheet has 85 ° first base angle and 50 ° the second base angle β.

5. backlight device according to claim 3, wherein described first base angle of outshot is positioned at a side of described light source.

6. according to the backlight device described in the claim 2, wherein said asymmetric prism sheet is configured such that the ridge of described asymmetric prism sheet is basically perpendicular to the ridge of described symmetric prism.

7. liquid crystal indicator comprises the backlight device described in any one of claim 1 to 7.

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