KR20060066092A - Backlight device - Google Patents

Abstract

An asymmetric prism sheet 15 has a plurality of projections 17 having prism shape on its surface. The projection 17 comprises a first inclined surface 17a having a relatively gentle slope (easy slope) and a second inclined surface 17b having a relatively steep slope (steep slope). A base angle 17d on the side of the second surface 17b is beta° and a base angle 17c on the side of the first surface 17a is beta°. In the case that the light enters into the asymmetric prism sheet 15, which has the above-mentioned structure, from the bottom surface 15a (light guide plate 11), the light is mainly emitted in the substantially vertical direction (a direction inclined by relatively small angle to the vertical direction) in the first inclined surface 17a (arrows X), and is mainly emitted in the inclined direction (a direction inclined by relatively large angle to the vertical direction) in the second inclined surface 17b (arrows Y).

Description

Backlight device and display device having the same {BACKLIGHT DEVICE}

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.

In the transmissive liquid crystal display device or the transflective liquid crystal display device, the light source provided inside the device is mainly used and the 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, the backlight is arranged on the rear side of the liquid crystal cell when viewed from the display side of the device. The backlight is mainly a light guide plate having a major surface that is substantially parallel to the surface of the rear side of the liquid crystal cell and an edge light disposed on the edge surface side of the light guide plate and emitting light to other edge surfaces (metering) Consists of Moreover, the reflective sheet is arrange | positioned on the opposite side to the liquid crystal cell side of this light guide plate.

In such a device, the light from the edge light propagates into the light guide plate and is reflected by the light emitting means provided on the light guide plate and the reflective sheet disposed outside the light guide plate, whereby the transmission direction is changed to the liquid crystal cell side and is incident on the liquid crystal cell side. do.

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

1 shows a conventional prism sheet. The prism sheet 1 has a plurality of prism-shaped protrusions 2 on its surface. Each vertex angle in this protrusion 2 is set to about 90 degrees. Light incident at various angles from the lower side (flat surface) of the light guide plate varies with respect to the direction substantially perpendicular to the protrusion 2 of the prism sheet 1 (see arrows in FIG. 1). By arranging the prism sheet 1 on the liquid crystal cell side of the light guide plate in this way, the light incident from the light guide plate in various directions can be changed in a substantially vertical direction, thereby improving the light condensing characteristics and the luminance in the direction perpendicular to the liquid crystal panel. Can be improved.

On the other hand, in recent years, the liquid crystal display device has been required to improve the luminance in a direction perpendicular to the liquid crystal panel while implementing a wide luminance viewing angle (a viewing angle indicating an appropriate luminance). However, in the prism sheet 1 as described above, the luminance viewing angle is sacrificed because the protrusions are designed especially to improve the vertical luminance. Therefore, it is impossible to realize a wide luminance viewing angle of the liquid crystal display device provided with a backlight by using a conventional prism sheet.

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

The backlight device according to the present invention has a pair of main surfaces and an edge surface facing each other, the light guide means for guiding light from a light source disposed on one of the edge surfaces and disposed on one of the main surfaces of the light guide means. Luminance / luminance-viewing-angle improvement means for emitting light in a direction substantially perpendicular to the main surface and in a direction of a predetermined angle with respect to the perpendicular direction, and reflecting means disposed on the other main surface of the light guiding means.

According to this apparatus, light can be emitted in a direction substantially perpendicular to the main surface and in a direction of a predetermined angle with respect to the right angle direction, thereby improving luminance in a direction of a predetermined angle with respect to the right angle direction, The brightness can be improved. As a result, it is possible to implement a liquid crystal display device capable of achieving an optimum brightness in a wide range.

In the backlight device according to the present invention, the luminance / luminance 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 protrusion of the asymmetric prism 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, preferably, the protrusion of the asymmetric prism sheet has a first bottom angle α of 85 ° and a second bottom angle β of 50 °. In this case, it is preferable that the position of the 1st base angle (alpha) of this protrusion part is a light source side.

In the backlight device according to the present invention, it is preferable that a diffusion means is disposed between the light guiding means and the luminance / luminance viewing angle improving means.

In the backlight device according to the present invention, it is preferable that a symmetrical prism sheet having a plurality of protrusions is disposed on the surface between the diffusion means and the luminance / luminance viewing angle improvement means.

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

The liquid crystal backlight device according to the present invention has a backlight device as described above.

1 is a view showing a part of a conventional prism sheet,

2 is a view showing an embodiment of a backlight device according to an embodiment of the present invention;

3 is a view showing a part of a prism sheet of a backlight device according to an embodiment of the present invention;

4 and 5 show light paths of the prism sheet shown in FIG. 3;

6 is a graph illustrating the effect of a backlight device according to an embodiment of the present invention;

7 (a) and 7 (b) are views showing a mobile phone having a backlight device according to an embodiment of the present invention;

8 illustrates a PDA with a backlight device according to an embodiment of the present invention;

9 illustrates a car navigation system with a backlight device in accordance with an embodiment of the present invention.

Embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

2 is a diagram illustrating an embodiment 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. Edge light (side light) 12 is disposed on one edge surface side of the light guide plate 11. Generally, LED is used as edge light.

A diffusion sheet 13 for diffusing light emitted from the light guide plate 11 is disposed on the main surface 11a of the liquid crystal cell side of the light guide plate 11. Since there is a diffusion sheet 13, the presence of the backlight is not known when viewed from the panel display screen. In addition, the diffusion sheet 13 need not always be disposed.

The symmetrical prism sheet 14 is disposed on the diffusion sheet 13. An example that can be used as the symmetrical prism sheet 14 is BEF (trade name, Sumitomo 3M). The symmetrical prism sheet 14 has a plurality of prismatic protrusions on its surface, which are arranged such that the ridges of the protrusions follow the direction of propagation of light from the light source. In this way, the symmetrical prism sheet controls the light to the right and left of the propagation direction of the light from the light source. Therefore, by providing the symmetrical prism sheet 14, the light collection characteristics in the left and right directions of the propagation direction of the light from the light source are enhanced to improve the luminance. Therefore, the use of the sheet 14 together with the asymmetric prism sheet (described below) further improves the luminance in the vertical direction and the luminance in the wide viewing angle direction.

On the symmetric prism sheet 14 an asymmetric prism sheet 15 is arranged, which is a means for improving luminance / luminance viewing angle. In detail, the asymmetric prism sheet 15 has a configuration as shown in FIG. 3 illustrates a portion of a prism sheet of a backlight device according to an embodiment of the present invention.

The symmetrical prism sheet 15 has a plurality of prismatic protrusions 17 on its surface. The protrusion 17 includes a first sloped surface (low sloped surface) 17a with a relatively gentle slope and a second sloped surface (rapid sloped surface) 17b with a relatively sharp 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 protrusions 17 are disposed along the direction (the depth direction of the sheet as viewed in the drawing) substantially perpendicular to the propagation direction of the light from the light source. That is, 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 propagation direction of the light from the light source.

When light enters the asymmetric prism sheet 15 having the structure described above from the bottom surface 15a (light guide plate 11), the light is substantially perpendicular to the first inclined surface 17a (in the vertical direction). It is emitted in the direction inclined by a relatively small angle with respect to (see arrow X), and mainly in the inclination direction (direction inclined by relatively large angle with respect to the vertical direction) of the second inclined surface 17b (see arrow Y).

The base angles α and β should be set such that the light is mainly emitted in a substantially vertical direction while emitting light mainly in the inclined direction as described above. The inclination direction is determined according to the luminance viewing angle of the backlight device.

Regarding the base angles α and β, each α is preferably 75 ° to 90 °, and each β is preferably 45 ° to 60 °. In addition, it is preferable that angle (alpha) is 85 degrees, for example, and angle (beta) is 50 degrees with respect to the combination of base angle (alpha) and (beta).

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

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

The function of the asymmetric prism sheet of the backlight device according to the present invention will be described below with reference to FIGS. 4 to 5. 4 and 5 are diagrams for explaining an optical path of the prism sheet shown in FIG. In addition, in FIG.4 and FIG.5, as a light source, LED is arrange | positioned at the left side of an observer, and light propagates from the left to the right direction from an observer.

As shown in FIG. 4, light A incident on the asymmetric prism sheet 15 at an angle of θ1 with respect to the vertical direction is refracted by the bottom surface 15a of the asymmetric prism sheet 15, and the protrusion 17 Is further refracted by the first inclined surface 17a to be emitted from the asymmetric prism sheet 15 toward the liquid crystal cell. Here, since the base angle α of the protruding portion 17 is located on the light source side, the emitted light has an angle of θ2 with respect to the vertical direction. Therefore, light is emitted in a substantially vertical direction, thereby improving the brightness in the vertical direction.

In this case, the relationship between the incident angle [theta] 1, the outgoing angle [theta] 2, the base deflection angle [alpha] and the base deflection angle [beta] is expressed by the following equation (1).

... 식(1)

... Expression (1)

N1 is the refractive index of the asymmetric prism sheet.

In addition, as shown in FIG. 5, the light B incident on the asymmetrical prism sheet 15 at an angle of θ1 'with respect to the vertical direction is refracted by the bottom surface 15a of the asymmetrical prism sheet 15. It is further refracted by the first inclined surface 17a of the protrusion 17 and the second inclined surface 17b of the protrusion 17, and is emitted from the asymmetrical prism sheet 15 toward the liquid crystal cell. Here, since the bottom angle α and the bottom angle β of the protrusion 17 are located on the light source side, the emitted light has an angle of 2 'with respect to the vertical direction. Thus, this light is emitted in the oblique direction to improve the wide luminance viewing angle.

In this case, the relationship between the incident angle [theta] 1 ', the exit angle [theta] 2', the base deflection angle [alpha] 'and the base deflection angle [beta] is expressed by the following equation (2).

... 식(2)

... Expression (2)

N1 is the refractive index of the asymmetric prism sheet.

Therefore, in the case of determining the base deflection angles α and β of the protrusion 17 of the asymmetric prism sheet 15 in consideration of the given exit angle θ2 and the exit angle θ2 ', the above-described equation (1) It is preferable to determine this angle based on (2) and (2). In detail, since the luminance viewing angle can be any angle, it is preferable to determine the base deflection angles α and β according to the emission angle θ2 '.

The backlight device having the structure described above is arranged on the rear side (opposite side to the display side) of the liquid crystal cell of the liquid crystal display device. In the liquid crystal display device, light from the edge light 12 of the backlight device is transmitted into the light guide plate 11, and a part of the light is directly emitted to the liquid crystal cell side, and the other part of the light is opposite to the liquid crystal cell of the light guide plate 11. Reflected by the reflective sheet 16 disposed in 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. The light passing through the diffusion sheet 13 is controlled by the symmetrical prism sheet 14 so that the condensing characteristics are enhanced in the left and right directions (left and right in the propagation direction of the light from the light source). The light passing through the symmetrical prism sheet 14 is thus refracted by the protrusion 17 of the asymmetrical prism sheet 15, emitting a substantially perpendicular and oblique direction as described above. That is, the asymmetric prism sheet 15 emits light at a predetermined angle with respect to the perpendicular direction and the perpendicular direction to the main surface of the light guide plate. Thus, the emitted light is 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 the substantially vertical direction while being emitted in the oblique direction, thereby improving the brightness in the vertical direction of the liquid crystal display device while implementing a wide luminance viewing angle. .

Examples that can clearly demonstrate the effects of the present invention will be described below.

On one major surface of the light guide plate, a diffusion sheet, a symmetrical prism sheet and an asymmetric prism sheet are laminated in this order, a reflecting sheet is provided on the other major surface of the light guide plate, and the LED is provided as edge light on one edge surface side of the light guide plate. Three backlights are provided in a manner arranged. For each of the three backlights, the combinations of the base angles α and β of the protrusions of the asymmetric prism sheets are set, respectively (88 °, 45 °) (Example 1), (88 °, 50 °) (Example 2) and ( 88 °, 55 °) (Example 3). Also as a comparative example, a diffusion sheet and two symmetrical prism sheets (BEFs) are laminated in this order on one main surface of the light guide plate, a reflecting sheet is provided on the other main surface of the light guide plate, and the LED is on one edge surface side. One backlight is provided in such a manner that it is disposed as edge light on the top.

The liquid crystal display device is obtained by combining four backlights and one liquid crystal panel. Simulation is performed for the luminance viewing angle of each of the liquid crystal display devices. In this simulation, the brightness of the light on the backlight is measured. The luminance of the light was measured in a widely used luminance meter, and luminance at each angle was obtained. It is assumed here that the perception direction is 0 ° with respect to the light emitting surface of the backlight. 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 has a high vertical luminance while having a wide luminance viewing angle. Specifically, with respect to the vertical luminance, each device has a higher value than the liquid crystal display device of the comparative example. On the other hand, the liquid crystal display device of the comparative example shows high vertical luminance but its luminance viewing angle is narrow.

An application example of the backlight device according to the present invention will be described.

Fig. 7A shows a mobile phone with a conventional backlight device, and Fig. 7B shows a mobile phone with a backlight device according to the present invention. The mobile phone 22 with the backlight device according to the present invention has a wider viewing angle than the mobile phone 21 with the conventional backlight device, thus enabling an image display with a wide range and excellent field of view. do.

8 shows a PDA with a backlight device according to the invention. Even in this case, the PDA 31 has a wider viewing angle than that of a PDA equipped with a conventional backlight device, thus enabling an image display having a wide range and a good field of view.

9 shows a car navigation system with a backlight device according to the invention. Even in this case, the monitor 41 of the car navigation system provided with the backlight device according to the present invention has a wider viewing angle than the monitor provided with the conventional backlight device, and thus provides an image display having a wide range and excellent field of view. Make it possible. For example, as shown in FIG. 9, the image displayed by the monitor 41 installed on the passenger seat side can be seen as a good field of view not only to the person in the passenger seat but also to the person in the driver's seat.

The present invention is not limited to the embodiment described above, and various modifications thereof can be made. For example, the embodiment described above has described a case where the backlight device according to the present invention is applied to a liquid crystal display device for a cellular phone, a PDA and a car navigation system. The present invention can be applied to a liquid crystal display device for all applications requiring luminance in a vertical direction and a wide luminance viewing angle.

Further, this embodiment has described the case where an asymmetric prism sheet is used as the luminance / luminance viewing angle improvement means, but the present invention is not limited to this case. Any member other than an asymmetric prism sheet may be used as long as the member emits light in a substantially vertical direction while emitting light in an oblique direction.

Incidentally, the diffusion sheet and / or the reflection sheet in this embodiment is not limited to the sheet shape, and may be in the shape of a plate or film as long as the luminance effect and / or the reflection effect are exhibited, respectively. The symmetric prism sheet is not limited to the sheet shape as long as its function is exhibited.

As described above, the backlight device of the present invention has a light guide means for guiding light from a light source disposed on one of the pair of edge surfaces, having a pair of main surfaces facing each other and a pair of edge surfaces facing each other; A luminance / luminance viewing angle improving means disposed on one surface side of the light guide plate to emit light in a direction substantially perpendicular to the main surface and in a direction having a predetermined angle to the perpendicular direction, and disposed on the other surface side of the light guide plate Reflective means. As a result, it is possible to implement a liquid crystal display device having improved luminance in a vertical direction and a wide viewing angle.

The present invention can be applied to a backlight device used as a light source of a liquid crystal display device such as a cellular phone, a PDA, a car navigation system, and the like.

Claims (9)

In the backlight device, Light guiding means having a pair of major surfaces and edge surfaces facing each other, the light guide means having an edge surface for guiding light from a light source disposed at one of the edge surfaces; Luminance / luminance-viewing-angle improvement means disposed on one of the main surfaces of the light guiding means to emit light in a direction substantially perpendicular to the main surface and in a direction of a predetermined angle with respect to the right direction; Reflecting means disposed on another major surface of the light guiding means Backlight device comprising a. The method of claim 1, The luminance / luminance viewing angle improving means is an asymmetric prism sheet having a plurality of protrusions. Backlight device. The method of claim 2, The protrusion of the asymmetric prism sheet has a first base angle α of 75 ° to 90 ° and a second base angle β of 45 ° to 60 °. Backlight device. The method of claim 2 or 3, The protrusion of the asymmetric prism sheet has a first base angle α of 85 ° and a second base angle β of 50 °. Backlight device. The method according to claim 3 or 4, The position of the first base angle α of the protruding portion is the light source side. Backlight device. The method according to any one of claims 1 to 5, Diffusion means is disposed between the light guiding means and the luminance / luminance viewing angle improving means. Backlight device. The method of claim 6, A symmetrical prism sheet having a plurality of protrusions is disposed between the diffusion means and the luminance / luminance viewing angle improvement means. Backlight device. The method of claim 7, wherein The asymmetric prism sheet is disposed such that a ridge of the asymmetric prism sheet is substantially perpendicular to the ridge of the symmetric prism sheet. Backlight device. A liquid crystal display device comprising the backlight device as claimed in claim 1.

Images