JP2001345010A - Surface light source element and display device using it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a surface light source element wherein the generation of dark lines is reduced and display quality is improved. SOLUTION: The surface light source element is equipped with a light source 2, a reflector 4 which is arranged around the light source 2, a light guide body 3 into which light from the light source 2 reflected by the reflector 4 is made to enter through at least one end face, and an emitting light control board 10 which is arranged on an emitting surface 6 side of the light guide body 3 and through plural convex parts installed at its face opposing the light guide body 3 makes the lights from the emitting surface 6 of the light guide body 3 head for a front side direction of the emitting surface 6. A curvature radius of the top and bottom corner parts 8 to a direction parallel in a longitudinal direction of the light source on a side where the light source 2 of the light guide body 3 is arranged and/or a corner part 9 in a thickness direction of the light guide body on the side where the light source 2 of the light guide body 3 is arranged, is not more than 0.1 mm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface light source element used for a personal computer, a computer monitor, a video camera, a television receiver, a car navigation system, and the like, and a direct-view display device using the same.

[0002]

2. Description of the Related Art A transmissive display device typified by a liquid crystal panel is composed of a backlight which emits light in a plane and a display panel in which pixels are arranged in a dot form. Characters and images are displayed by controlling the transmittance. As the backlight, a combination of a halogen lamp, a reflector, a lens, and the like is used to control the luminance distribution of the emitted light. A fluorescent tube is provided on the end face of the light guide, and light from the fluorescent tube is perpendicular to the end face. And a fluorescent tube provided inside the light guide (direct type). A backlight using a halogen lamp is mainly used for a liquid crystal projector requiring high luminance. On the other hand, since a backlight using a light guide can be made thin, it is often used for a direct-view type liquid crystal TV, a display of a personal computer, and the like.

[0003]

In a backlight used for a liquid crystal TV, a notebook personal computer, and the like, it is required to reduce power consumption and to have high luminance. Higher brightness can be realized by increasing the number of light sources such as cold cathode tubes, but this method is not practical because it leads to an increase in power consumption. Therefore, a surface light source element having a configuration in which an emission light control plate having a microprism array is arranged on a light guide has been proposed (US Pat. No. 5,39,39).
6,350). According to this surface light source element, since total reflection of light by the microprism array is used, light loss is small and high luminance can be realized, but a light guide parallel to the longitudinal direction of the light source 2 Dark lines are generated from the upper and lower corners 8 of the light guide 3 and the corner 9 in the thickness direction of the light guide 3, and the display quality may be greatly reduced. FIG. 2 is a diagram illustrating each corner portion, and FIG. 3 is a diagram illustrating a position where a dark line occurs.

[0004] The present invention has been made in view of the above problems, and has as its object to provide a surface light source element with reduced occurrence of dark lines and improved display quality. Also, the present invention
It is an object of the present invention to provide a display device having high luminance using the surface light source element.

[0005]

The above object is achieved by a light source,
A reflector disposed around the light source, a light guide to which light from the light source reflected by the reflector is incident from at least one end face, and is disposed on an emission surface side of the light guide,
An emission light control plate for directing light from the emission surface of the light guide to a front direction of the emission surface by a plurality of protrusions provided on a surface facing the light guide, and a light source of the light guide is provided. The problem is solved by the surface light source element in which the radius of curvature of the upper and lower corners in the direction parallel to the longitudinal direction of the light source on the arranged side is 0.1 mm or less. A light source, a reflector disposed around the light source, a light guide into which light from the light source reflected by the reflector is incident from at least one end face, and a light guide disposed on an emission surface side of the light guide. An emission light control plate for directing light from the emission surface of the light guide toward a front direction of the emission surface by a plurality of projections provided on a surface facing the light guide, and a light source of the light guide. The surface light source element in which the radius of curvature of the corner portion in the thickness direction of the light guide on the side where is disposed is 0.1 mm or less. Further, the upper and lower corners in the direction parallel to the longitudinal direction of the light source and the curvature radius of the corners in the thickness direction of the light guide are each 0.1 mm.
It is more preferred that:

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a schematic configuration diagram of an example of the surface light source element of the present invention. The surface light source element includes a light guide 3 provided with a light source 2 such as a cold cathode tube at both end surfaces, and an emission light control plate 10 for controlling an angular distribution of light emitted from the light guide 3. . The emission light control plate 10 is provided on the emission surface 6 of the light guide 3.
On the incident surface of the emission light control plate 10, a number of convex portions (microprism arrays) are formed. The cross-sectional shape of the convex portion is parabolic, triangular, or the like. The convex portion in this example is a one-dimensional pattern, and the ridge line of the convex portion is arranged so as to be parallel to the light guide end face on the side where the light source is arranged. Around the light source 2, there is provided a reflector 4 that reflects light traveling in the direction opposite to the end face of the light guide 3 and travels toward the end face of the light guide 3. Light incident on the light guide 3 from the end face propagates through the light guide while repeating total reflection. This propagating light is emitted from the output light control plate 1.
The light is introduced into the emission light control plate 10 from a contact portion between the projection of No. 0 and the emission surface of the light guide 3. Thereby, the light propagating in the light guide 3 is sequentially extracted from the contact portion to the emission light control plate 10, and the extracted light is collected while being totally reflected in the projection of the emission light control plate 10.

In the surface light source element of the type using the emission light control plate, the light is extracted using the total reflection on the inner surface of the projection of the emission light control plate. Is emitted in a specific direction. That is, the light emitted from the surface light source element in a specific direction is only the light that has propagated through the light guide in a specific direction corresponding to the direction. Therefore, when the surface light source element is observed from a direction in which light propagating in a certain direction exits in the light guide, a dark line appears when there is no light propagating in a direction parallel to that direction.

The occurrence of dark lines will be described with reference to FIGS. As shown in FIG. 6A, the light traveling in the light guide has a refractive index n of the light guide, a refractive index of air of 1, and a refractive index of the air of 1.
Assuming that the incident angle from air to the light guide is θi and the angle in the light guide is θo, the angle is limited by the following equation (1): sin (θi) = n · sin (θo) (1) For example, n = 1.4 as the light guide
In the case of using an acrylic plate of No. 9, −42.2 ° <θo <42.2 °.

In the case where the radius of curvature of the upper and lower corners of the light guide parallel to the longitudinal direction of the light source and the corner in the thickness direction of the light guide on the side where the light source is arranged is large, the corner of the light guide is 6 (b) will be described with reference to FIG. Light incident on the point A at a certain angle is totally reflected at the point B and propagates in the C direction. On the other hand, the light propagating in the BC direction at the point F (the FG direction) is light to be propagated in the EF direction and also in the DE direction. However, as described above, since the light propagation angle is limited in the light guide, the DE
Light propagating in the direction is not actually present. That is, light does not propagate in the FG direction. Further, light (HI direction) propagating from the point H in the BC direction can enter the light guide due to refraction by air and the light guide, and therefore can exist. Therefore, light does not propagate in the BC direction in a region between BC and HI in the figure, and light propagates in a region outside the BC direction. Therefore, when the light propagating in the light guide is observed from the direction in which the light propagating in the BC direction is emitted, a dark line appears in a region where there is no light propagating in the direction parallel to the BC direction. When the corner shown in FIG. 6B is the corner 9 in the thickness direction of the light guide, a dark line appears in the area shown in FIG. 7A. FIG.
In the case where the corners shown in (b) are the upper and lower corners 8 of the light guide parallel to the longitudinal direction of the light source, the points C ′ and I ′ shown in FIG. A dark line appears in a region extending in a direction parallel to the direction.

Here, when the radius of the corner portion of the light guide becomes small, the area taking the optical path such as DEFG in FIG. 6B becomes small, and the area where the dark line occurs becomes small. Therefore, dark lines are difficult to see. As a result of the study by the present inventors, it has been found that by setting the radius of curvature of the corner portion to 0.1 mm or less, the dark line can be regarded as substantially disappearing. In order to reduce the curvature of the light guide corner to 0.1 mm or less, the end face may be subjected to cutting or polishing using a buff. When the light guide is manufactured by injection molding or the like using a mold, the radius of curvature of the corner of the mold may be 0.1 mm or less.

As the light guide used for the surface light source element of the present invention, a resin obtained by processing a resin having excellent transparency such as an acrylic resin, a polycarbonate resin, and a polystyrene resin and glass into a predetermined shape can be used. Among them, it is preferable to use an acrylic resin in terms of lightness and transparency.
As a processing method, a method of cutting out from an extruded plate or a cast plate or a melt molding method such as a hot press or an injection molding is suitably used. FIG. 5 shows an example of a light guide that can be used in the present invention. The light guide of FIG. 5A is a light guide of a type in which light is incident from both side surfaces, and is provided with a convex portion 7 for fixing the light guide to a frame and preventing a positional shift. The shape of the convex portion 7 may be a concave portion. FIG. 5B illustrates a light guide of a type in which light is incident from one side surface, and the thickness of the light guide is changed between the light incident portion side and the opposite light incident portion side of the light guide to reduce the weight. In this case, the control of the radius of curvature of each corner may be performed only at the corner where the light source is disposed.

Further, the surface shape of the emission light control plate is determined by using a stamper or a female mold, etc., using a hot press method, a 2P method using ultraviolet curing, a casting method using thermal curing, an injection molding method, or the like.
It can be formed on a transparent substrate by an extrusion method or the like. As the transparent substrate, a resin such as an acrylic resin, a polycarbonate resin and a polystyrene resin or glass is used. The stamper used for producing the emission light control plate is, for example, to coat a negative or positive photosensitive resin on a glass substrate, expose the photosensitive resin through a photomask, and perform electroforming after development. And can also be made by cutting. The emission light control plate does not need to be in the form of a plate, but may be in the form of a film. The pattern of the projections of the emission light control plate may be arranged not only one-dimensionally but also two-dimensionally. A microlens array may be provided on the light emission surface of the emission light control plate.

An image display device can be constructed by using the surface light source element described above as a backlight and providing a transmissive display element on the emission surface. As the transmissive display element, a liquid crystal panel such as an STN, a TFT, and a MINI can be used.

[0014]

FIG. 4 shows an embodiment of the present invention. In this embodiment, a light source 2 as a cold cathode tube is disposed at both ends of an acrylic light guide 3, and the light source 2 is covered with a reflector 4. The light emitted from the light source 2 and the light emitted from the light source 2 and reflected by the reflector 4 enter from the end face of the light guide 3. Light guide 3
An emission light control plate 10 for taking out light propagating through the inside and controlling emission light is provided on the emission surface.

The light guide is cut out from an acrylic plate having a thickness of 6 mm, and the length of the end on the side where the light source is disposed is 319 mm.
It was manufactured by cutting so that the length in the direction in which light propagated was 241 mm. The emission light control plate was manufactured as follows. First, a stamper of an emission light control plate in which a concave and convex pattern having a depth of about 20 μm was formed in a one-dimensional array having a parabolic cross-sectional shape by cutting was formed. 200 μm thick
Using a polycarbonate film as a base material, an acrylic ultraviolet curable resin was applied thereon at 100 μm, pressed against a mold, and then irradiated with ultraviolet light from the film side to obtain an emission light control plate. The obtained emission light control plate is processed into the same size as the light guide, and is closely adhered so that the convex ridge line is parallel to the end face of the light guide on which the light source is arranged, and the light source and the reflector are attached to the surface. A light source element was used.

The light guide used in the present embodiment has upper and lower corners parallel to the light source on the side where the light source of the light guide is arranged, and the radius of curvature of the corner in the thickness direction of the light guide. 0.
The end face was polished with a buff so as to have a thickness of 03 mm. With respect to the above light guide, corner portions were polished with a buff to produce light guides having several types of radii of curvature, and the occurrence of dark lines from each corner portion was evaluated. The radius of curvature was measured using an optical microscope. .

[0017]

[Table 1]

From the above results, by setting the radius of curvature of the upper and lower corners parallel to the light source on the side where the light source of the light guide is arranged and the corner in the thickness direction of the light guide to 0.1 mm or less. It can be understood that the dark line generated in parallel with and the dark line generated in an oblique direction from the corner can be eliminated. When the radius of curvature of the corner is 0.05 mm or less,
It turns out that the effect is higher.

[0019]

According to the surface light source device of the present invention, it is possible to reduce dark lines generated parallel to the light source and dark lines generated obliquely from the corners. Further, in a display device using this surface light source element, a high-quality image can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an example of a surface light source element of the present invention.

FIG. 2 is a diagram illustrating each corner.

FIG. 3 is a diagram illustrating a position where a dark line occurs.

FIG. 4 is an embodiment of the present invention.

FIG. 5 is an example of a light guide that can be used in the present invention.

FIG. 6 is a diagram illustrating the principle of generation of dark lines.

FIG. 7 is a diagram illustrating the occurrence of dark lines.

[Explanation of symbols]

2 light source, 3 light guide, 4 reflector, 6 light guide light emission surface, 8 corner portion parallel to the light source, 9 corner portion of light guide in thickness direction 10 emission light control plate

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Yoichi Hashimoto 41 Miyukigaoka, Tsukuba, Ibaraki Prefecture Kuraray Co., Ltd. F-term (reference) 2H038 AA52 AA55 BA06 2H091 FA14Z FA21Z FA23Z FA28Z FA42Z FB02 FB07 FD22 FD23 LA18 LA30

Claims (5)

[Claims] 1. A light source, a reflector disposed around the light source, a light guide to which light from the light source reflected by the reflector enters from at least one end face, and an emission surface of the light guide An emission light control plate that is disposed on the side and directs light from the emission surface of the light guide toward the front direction of the emission surface by a plurality of protrusions provided on the surface facing the light guide; A surface light source element in which a radius of curvature of upper and lower corners in a direction parallel to a longitudinal direction of a light source on a side where a light source of a body is arranged is 0.1 mm or less. 2. A light source, a reflector disposed around the light source, a light guide to which light from the light source reflected by the reflector enters from at least one end face, and an emission surface of the light guide An emission light control plate that is disposed on the side and directs light from the emission surface of the light guide toward the front direction of the emission surface by a plurality of protrusions provided on the surface facing the light guide; A surface light source element in which a radius of curvature of a corner portion in a thickness direction of a light guide on a side of a body where a light source is arranged is 0.1 mm or less. 3. A light source, a reflector disposed around the light source, a light guide to which light from the light source reflected by the reflector enters from at least one end face, and an emission surface of the light guide An emission light control plate that is disposed on the side and directs light from the emission surface of the light guide toward the front direction of the emission surface by a plurality of protrusions provided on the surface facing the light guide; On the side where the light source of the body is arranged, the curvature of the upper and lower corners in a direction parallel to the longitudinal direction of the light source is 0.1 mm or less, and on the side where the light source of the light guide is arranged,
The radius of curvature of the corner in the thickness direction of the light guide is 0.1 mm
The following is a surface light source element. 4. A display device comprising a combination of the surface light source device according to claim 1 and a transmissive display device. 5. The display device according to claim 4, wherein the transmission type display element is a liquid crystal panel.