JPH06331831A - Light control sheet and planar light emitting device including the same - Google Patents

Abstract

PURPOSE:To eliminate unnecessary emitted light regardless of the edge single lamp system and to realize a horizontally symmetrical distribution of emitted light to obtain sufficient brightness. CONSTITUTION:Many prism parts 5 whose longitudinal sections are non horizontally symmetrical and approximately triangular or many mountain parts 6 which have non horizontally symmetrical cross sections and projecting arcuate top parts and are approximately triangular are provided on one face approximately in parallel, and the other face 1b is an optical plane or a plane provided with minute ruggedness.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a planar light emitting device used for a liquid crystal display such as a personal computer or a word processor, a liquid crystal color television, an electric signboard, a facility lighting, and a light control used for the device. Regarding the seat.

[0002]

2. Description of the Related Art Word processors and personal computers have become smaller, lighter and thinner year after year, and so-called notebook size has become the mainstream. A notebook type or laptop type liquid crystal display device usually does not have a self-luminous property, and therefore a planar light emitting device is provided on the back surface thereof to improve visibility. The planar light emitting device includes a so-called back light source type in which a light source is arranged at the rear part, and an edge light type in which the light source is arranged on one side surface or both side surfaces of the device. At present, the edge-light single-lamp type tends to be used because of its thinness, lightness, and power saving.

A single edge light type planar light emitting device has a basic structure shown in FIG. That is, in this device,
The cathode tube (21) as a light source is a light guide plate (26) made of a transparent plate.
It is arranged on one side. A dot pattern (25) is formed on the back surface of the light guide plate (26). A reflection plate (23) is arranged on the rear side of the light guide plate (26), and a light control sheet (24) described below is provided on the front side of the light guide plate (26).

The dot pattern (25) is a cathode tube (21) on the side surface.
It is a light-scattering print pattern for evenly emitting the light incident on the screen from any position on the screen, and can be called a pseudo light source.

When the liquid crystal display screen is used, the light control sheet (24) is provided with a dot pattern (2) which is a back light source, that is, a pseudo light source in the edge light system, through the liquid crystal display element.
5) is not visually recognized, and functions so that it can be regarded as a surface that uniformly emits light.

Conventionally, as a light control sheet, a sheet made of a resin plate coated with a light diffusing agent or a resin plate kneaded with a light diffusing agent has been used (JP-A-3-78).
701, etc.). Further, as another light control sheet, there is one in which a number of random irregularities are formed on the surface of a plate material which transmits light (Japanese Patent Laid-Open No. 62-291618). Further, there is proposed a so-called prism or wave type sheet in which a large number of parallel prism portions or wave portions having an isosceles triangular cross section are formed on one surface (Japanese Patent Application No. 4-11864).

[0007]

Among the conventional light control sheets described above, those using a light diffusing agent have a problem that sufficient brightness cannot be obtained because of low light transmittance.

In addition, those having innumerable random irregularities have a problem that sufficient brightness cannot be obtained because the ability to collect light from the dot pattern (25) is low.

In addition, the prism of the isosceles triangle in cross section or the wave type has a limited emission direction and can collect light in the direction of the user such as a word processor, that is, the normal direction of the screen, so that the brightness is higher. It can be a screen.

On the other hand, as shown in FIG. 5, in the case of the one-lamp type in which the cathode tube (21) is arranged on one side of the light guide plate (26), the light from the cathode tube (21) is reflected by the reflection plate (23). ), The emitted light has a laterally asymmetric distribution with respect to the normal direction of the screen (FIG. 6).
Therefore, as shown in FIG. 7, when the prism type light control sheet (24) is arranged on the front surface of the light guide plate (26), the cross section of the prism is a symmetrical isosceles triangle, In addition to the effective outgoing light B in the direction, many unwanted outgoing lights such as the outgoing light A occur.

It is an object of the present invention to provide a light control sheet and a planar light emitting device provided with the light control sheet, in which there is no useless emitted light even with a single edge type, and the emitted light distribution is bilaterally symmetrical and sufficient brightness is obtained. To do.

[0012]

The light control sheet of the present invention has, on one surface thereof, a large number of prism portions whose longitudinal cross sections are substantially asymmetrical triangles or whose longitudinal cross sections are asymmetrical and whose tops are convex arcuate triangles. The plurality of ridges are substantially parallel to each other, and the other surface is an optical plane, or the plane is finely roughened.

The planar light emitting device of the present invention includes the above light control sheet. In FIG. 4, θ1
45 ° to 70 ° is suitable, and θ2 is 65 ° to
The range of 80 ° is preferable, and θ2 is made larger than θ1. When θ1 is 70 ° or more, and when θ2 is 80 °
In the above case, it becomes difficult to form the prism portion or the peak portion by compression molding.

[0014]

In the surface light emitting device of the single edge type, the light control sheet of the present invention has a prism portion or a gentle slope of a mountain portion having an isosceles triangular cross section on the cathode tube side, and the prism portion and the cathode tube are If they are arranged so as to be substantially parallel to each other, as shown in FIG. 1, the light emitted from the cathode tube (3) on one side of the light guide plate (4) passes through the reflection sheet (2) and the light control sheet (1). The incident light is surely emitted from the steep slope (5b) in the normal direction of the screen. Therefore, unnecessary emission light is not generated, and effective and uniform emission in the normal direction of the screen is possible.

[0015]

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

FIG. 1 shows an edge-lit type planar light emitting device, in which a transparent light guide plate (4) having a dot pattern (7) on the back is provided on the rear side of the light control sheet (1). A cathode tube (3) is arranged on one side of the light guide plate (4).

The light control sheet (1) is, as shown in FIG.
On the front surface (1a), a large number of substantially triangular prism parts (5) whose longitudinal section is asymmetric are provided in parallel, and the other surface (1b) is an optical plane (prism type). .

FIG. 3 shows another embodiment of the light control sheet,
On the front surface (1a), a large number of ridges (6) whose longitudinal section is asymmetrical and whose top is a substantially triangular shape with a convex arc shape are provided in a substantially parallel shape, and the rear surface (1b) is provided with fine unevenness by matte processing. Has been given (wave type).

Even if any of the prism type and wave type light control sheets of the present invention is used, uniform and sufficient emission characteristics can be obtained. Taking the prism type as an example, as shown in FIG.
If the gentle slope (5a) side of (5) is set to the cathode tube (3) side and the prism part (5) and the cathode tube (3) are arranged substantially parallel, the cathode on one side of the light guide plate (4) The light emitted from the tube (3) is reflected by the reflection sheet (2).
The light is incident on the light control sheet (1) via, and the incident light is reliably emitted from the steep slope (5b) in the normal direction of the screen. Therefore, unnecessary emitted light as shown in FIG. 7 does not occur, and effective and uniform emission in the normal direction of the screen becomes possible. Also,
The same applies to the wave type of the present invention.

Next, regarding the edge-one-lamp type planar light-emitting device, the case where the light control sheets of the above-described first and second embodiments are used, and the conventional prism and wave type light control having an isosceles triangular cross section are used. A performance evaluation test using a sheet was performed. The test conditions and results are as shown in the table. Further, the pitch, depth and angles θ1 and θ2 of the grooves in the prism of the light control sheet are as shown in FIG. 4 (same for wave type). Further, the backlights A and B used were as follows.

Backlight A: Light guide plate thickness 3 mm, long side single light type Backlight B: Light guide plate thickness 2 mm, short side single light type In addition, the light control sheets of Examples 1 and 2 have prism parts ( 5) Or the gentle slope (5a) (6a) of the mountain part (6) is on the cathode tube (3) side, and the prism part (5) or mountain part (6) and the cathode tube (3) are substantially parallel. And

[0022]

[Table 1] As can be seen from the results of the practical data in the table, the front luminance is higher and the useless emitted light is smaller in the examples for both prisms and waves.

[0023]

According to the light control sheet of the present invention, in an edge-lamp type planar light emitting device, the light control sheet of the present invention is such that the gentle slope of the prism portion or the mountain portion is on the cathode tube side, and By arranging the prism part and the cathode tube so as to be substantially parallel to each other, as shown in FIG. 1, the light entering the light control sheet from the cathode tube is surely directed from the steep slope of the prism part in the normal direction of the screen. Is emitted. Therefore, unnecessary emission light is not generated, and effective emission in the normal direction of the screen is possible. Therefore, sufficient brightness can be obtained on the screen, and at the same time, the problem of left-right brightness imbalance seen in the conventional prism or wave-shaped light control sheet having a cross-section of an isosceles triangle can be solved.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a planar light emitting device using a light control sheet of the present invention.

FIG. 2 is a side view showing an embodiment of a light control sheet of the present invention.

FIG. 3 is a side view showing another embodiment of the light control sheet of the present invention.

FIG. 4 is a partially enlarged side view showing the groove pitch, groove depth, etc. of the prism portion of the light control sheet in the evaluation test of the present invention.

FIG. 5 is a cross-sectional view showing the basic structure of the planar light emitting device.

FIG. 6 is a cross-sectional view showing a light emitting state in the one edge light type planar light emitting device.

FIG. 7 is a side view showing emission characteristics of a conventional light control sheet.

[Explanation of symbols]

 (1) Light control sheet (2) Reflective sheet (3) Cathode tube (4) Light guide plate (5) Prism section (6) Mountain section

Claims (2)

[Claims] 1. A large number of prism portions (5) each having a substantially asymmetric vertical cross section on one surface, or a plurality of mountain portions (6) having a substantially asymmetric vertical cross section and a convex arc-shaped top.
Are provided substantially parallel to each other, and the other surface is an optical plane, or the plane is subjected to fine concavo-convex processing. 2. A planar light emitting device comprising the light control sheet according to claim 1.