JP3676425B2 - Light guide plate - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to a light guide plate used in, for example, a surface light source device that illuminates a liquid crystal display surface.
[0002]
[Prior art]
Liquid crystal, which has been attracting attention as a flat display, does not emit light itself and must be illuminated in some way. As an illumination method, a reflection type using reflection of external light and a transmission type using a backlight or the like are known. Among them, it is common to use a transmissive type, particularly an edge light type light guide plate in which a light source is arranged in the vicinity of the side surface of the light guide plate in terms of brightness and thinness.
[0003]
Previously, the present applicants proposed Japanese Patent Application Laid-Open No. 6-3529 as a light guide plate having a low luminance and a low luminance. FIG. 8 is a configuration diagram of a light guide plate in Japanese Patent Laid-Open No. 6-3529. In the figure, reference numeral 81 denotes a light guide plate including a transmission surface 82 and a reflection surface 83 that faces the transmission surface 82 and reflects light to the transmission surface 82. A linear light source 84 that emits light into the light guide plate 81 is disposed on an incident surface 89 that is substantially orthogonal to the reflection surface 83 of the light guide plate 81. Reference numeral 85 denotes a reflector that reflects light emitted from the light source 84 toward the light guide plate 81.
[0004]
A diffusion sheet 86 that diffuses light emitted from the transmission surface 82 is disposed on the transmission surface 82 side of the light guide plate 81. On the other hand, on the reflecting surface 83 side of the light guide plate 81, a plurality of strips 87 having the same shape facing the light source 84 are formed at intervals of 0.1 mm or more and 5 mm or less. The protrusion 87 is composed of a reflective slope a 92 having an angle of 90 ° with the transmission surface 82 and a reflection slope b 91 having an angle of 33 ° with the transmission surface 82. In the figure, when a light beam passing from the left to the right is incident on the protrusion 87, the light strikes the reflecting slope b91. Further, a reflective vapor deposition film 88 is formed on the reflective surface 83 of the light guide plate 81.
[0005]
Next, the operation of the above configuration will be described. Part of the light emitted from the light source 84 is reflected by the reflecting plate 85, and the other part directly enters the light guide plate 81 from the incident surface 89. The light beam incident on the ridge 87 hits the reflection inclined surface b91 from the shape of the ridge 87, is specularly reflected in the direction of the transmission surface 82 by the reflective vapor deposition film 88, and is emitted from the transmission surface 82. The light emitted from the transmission surface 82 is diffused by the diffusion sheet 86.
[0006]
[Problems to be solved by the invention]
However, the angular distribution of the light beam incident on the reflecting slope b91 of each protrusion 87 differs depending on the distance from the light source. FIG. 9 is a diagram showing the angular distribution of light rays incident on the reflective inclined surface b of the ridge at a position 20 mm from the incident surface in the light guide plate of the first embodiment of the present invention, and FIG. 10 is the guide of the first embodiment of the present invention. It is a figure which shows the angle distribution of the light ray which injects into the reflective slope b of the protrusion of the position of 150 mm from the entrance plane in an optical plate. As can be seen from these figures, the further away from the light source 84, the more the peak angle of the angular distribution of the light rays incident on the protrusion 87 moves in the 0 ° direction. That is, the ratio of the light rays incident on the protrusion 87 far from the light source 84 is close to 0 °. The definition of the ray angle in these figures is shown in FIG.
[0007]
However, in the light guide plate 81 configured as described above, all the protrusions 87 have the same shape, that is, the angle formed by the reflection inclined surface b91 with respect to the transmission surface 82 is the same for each protrusion 87. The traveling direction of the light beam traveling in the direction of the transmission surface 82 varies depending on the distance from the light source 84. That is, the emission characteristics of the light group on the transmission surface 82 vary depending on the location, and the luminance peak is not suitable for the front direction (direction orthogonal to the transmission surface 82) at all locations.
[0008]
In addition, since the arrangement pitch of the protrusions 87 of the light guide plate 81 having the above configuration is as large as 0.1 mm or more and 5 mm or less, only the protrusions 87 are bright, the periphery of the protrusions 87 is dark, and the place where the pitch becomes large is dark and dark. This is not preferable as a surface light source. Therefore, in the configuration shown in FIG. 8, in consideration of the visual influence as a surface light source, a diffusion sheet 86 is disposed on the transmission surface 82 of the light guide plate 81 to diffuse the light beam group. However, the provision of the diffusion sheet 86 causes another problem that the luminance in the front direction decreases.
[0009]
The present invention has been made in view of the above problems, and an object of the present invention is to provide a light guide plate that has no luminance unevenness, has high luminance in the front direction, and has a simple configuration.
[0010]
[Means for Solving the Problems]
The present invention provides a light guide plate that guides light incident from an incident surface facing a linear light source to the outside through a transmission surface substantially orthogonal to the incident surface.
A reflective portion is provided that has a protrusion or groove formed on a reflective surface that faces the transmissive surface and reflects light to the transmissive surface.
Increasing the inclination angle formed by the reflecting portion and the transmission surface as the distance from the light source increases.
The interval between adjacent reflecting portions is set to 100 μm or less.
[0011]
In the above invention, the light guide plate is preferably made of a plastic material.
Further, it is desirable that each surface of the light guide plate and each surface of the groove or the protrusion is a substantially smooth surface.
[0012]
It is desirable that the projected area of the reflecting portion on the reflecting surface in the unit area of the reflecting surface increases as the distance from the light source increases.
[0013]
It is desirable that the thickness of the light guide plate decreases as the distance from the light source increases.
[0014]
[Action]
In the light guide plate of the present invention, as the light from the light source moves away from the light source, the peak angle of the angular distribution moves in the 0 ° direction as shown in FIGS. Therefore, by increasing the inclination angle between the reflecting portion and the transmitting surface as the distance from the light source increases, the light beam reflected by the reflecting portion so that the peak angle of the light angle distribution is directed in the same direction and transmitted through the transmitting surface. The maximum value of brightness goes in the front direction.
[0015]
In addition, when the interval between the adjacent reflecting portions is set to 100 μm or less, bright and dark stripes cannot be seen. In addition, by forming the reflection portions at a random pitch, it is possible to prevent moiré from occurring in a wide range. By these, the diffusion sheet of a surface light source device can be made unnecessary.
[0016]
Furthermore, as the light in the light guide plate gets farther from the light source, the amount of light reaching the reflecting portion decreases, but as shown in FIG. 11, the projected area on the reflecting surface of the reflecting portion occupying the unit area of the reflecting surface (the hatched line in the figure Since the decrease in the light amount is covered by increasing the area of the portion surrounded by (), the light amount transmitted through the transmission surface is substantially constant regardless of the position from the light source.
[0017]
【Example】
Next, embodiments of the present invention will be described with reference to the drawings. 1 is a block diagram for explaining a first embodiment of the present invention, FIG. 2 is a diagram for explaining a reflecting portion in FIG. 1, FIG. 3 is a view in the direction of arrow A in FIG. 1, and FIG. FIG. 5 is a diagram for explaining the relationship between the inclination angle of the reflecting portion and the distance from the incident surface of the reflecting portion, and FIG. 5 shows the ratio of the projected area of the reflecting portion to the reflecting surface in the unit area of the reflecting surface in FIG. FIG. 6 is a diagram for explaining the relationship between the distance from the light source of the light guide plate configured as shown in FIG. 1 and the front luminance at that location, and FIG. 7 is a diagram showing the configuration of another embodiment of the ridge. 12 is a diagram for explaining the random pitch in FIG. 1, FIG. 13 is a block diagram for explaining the second embodiment of the present invention, and FIG. 14 is a diagram for explaining the reflection part in FIG.
[0018]
First, in FIG. 1, reference numeral 1 denotes a light guide plate including a transmission surface 2 and a reflection surface 3 that faces the transmission surface 2 and reflects light to the transmission surface 2. A linear light source 4 that emits divergent light is disposed on an incident surface 11 that is substantially orthogonal to the reflecting surface 3 of the light guide plate 1. Reference numeral 5 denotes a reflecting plate that reflects divergent light emitted from the light source 4 toward the light guide plate 1. In addition, the light guide plate 1 of the present embodiment is formed so that the thickness is gradually reduced according to the distance from the light source 4. The thickness here is the distance between the transmission surface 2 and the reflection surface 3, and the protrusion 8 portion is not limited to this.
[0019]
On the reflective surface 3 side of the light guide plate 1, a ridge 8 is formed that is a reflective portion 6 having a reflective slope a9 and a reflective slope b10 substantially parallel to the light source 4. The reflection part 6 may have any shape that is concave and convex with respect to the reflection surface 3, and has a function of transmitting the light beam specularly reflected by the reflection part 6 from the transmission surface.
[0020]
In addition, the magnitude | size of the light-guide plate 1 of a present Example shown in FIG. 1 is as follows.
L = 160mm
h1 = 3mm
h2 = 2mm
d = 20 μm or more and 60 μm or less The plurality of protrusions 8 are formed with a random pitch of 100 μm or less. Here, the random pitch means a pitch that is a completely uncorrelated sequence when the pitch is expressed by a sequence as shown in FIG. Further, a reflective vapor deposition film 7 is formed on the reflective surface 3 of the light guide plate 1 as a reflective film that absorbs less light, such as aluminum or silver. Under the condition that there is no limitation on the film thickness uniformity on the uneven surface, it is advantageous for mass production to form a reflective film by vapor deposition. Further, a liquid crystal display surface 14 is disposed on the light transmission plate 2 side of the light guide plate 1.
[0021]
FIG. 2 is a view for explaining a protrusion as a reflecting portion. Each ridge 8 has a reflection slope a9 and a reflection slope b10, and light rays incident on each ridge 8 are reflected by the shape of the ridge 8, that is, the inclination angle a12 of the reflection slope a9 and the inclination angle b13 of the reflection slope b10. A route is obtained.
[0022]
As the light ray group in the light guide plate 1 moves away from the light source 4, the peak angle of the angular distribution of the light ray incident on the ridge 8 moves in the 0 ° direction as shown in FIGS. Therefore, the inclination angle b13, which is the angle formed between the transmission surface 2 and the reflection slope b10 shown in FIG. 2, is increased as the distance from the light source 4 increases, and the peak of the angular distribution of the light beam reflected by the reflection slope b10 that is each reflector 6 is obtained. The corners are set to face in the same direction (front direction). By doing so, the luminance peak of the light beam that passes through the transmission surface 2 is directed in the front direction regardless of the position from the light source 4.
[0023]
Further, as the distance from the light source 4 increases, the pitch of the protrusions 8 is narrowed, or the width d of the protrusions 8 is increased, and the protrusions 8 occupy the unit area of the reflecting surface 3 shown by the hatched portion in FIG. The ratio of the projected area onto the reflecting surface 3 is increased as the distance from the light source 4 increases as shown in FIG.
[0024]
The light guide plate 1 of the present embodiment is a molded product such as compression molding because it forms the narrow protrusions 8. From the cost, the internal transmittance of light, and the reproducibility of the product, acrylic, polycarbonate, etc. The optical plastic material was used. If the mold of the light guide plate is processed with a smooth surface, it is possible to simulate from which position on the transmission surface 2 and at what angle the light incident from the incident surface 11 of the light guide plate 1 is emitted by the ray tracing method. If a sheet or shape having a diffusing action exists in the light guide plate as in Japanese Patent Laid-Open No. 6-3529, the simulation cannot be performed accurately by the ray tracing method. The metal mold of the reflecting surface 3 of the light guide plate 1 was cut with a diamond tool, R tool, and sharp tool with a V-shaped tip on a flat-polished tool to form a ridge 8.
[0025]
As a method of changing the inclination angle of the reflective slope a9 and the reflective slope b10, there are a method of changing the attachment angle of the cutting tool for each place, a method of using a plurality of cutting tools having different tip shapes appropriately for each place, and the like.
[0026]
Next, the operation of the above configuration will be described. A part of the light emitted from the light source 4 is reflected by the reflecting plate 5, and the other part directly enters the light guide plate 1 from the incident surface 11.
[0027]
Then, a part of the light beam is directly reflected on the protrusion 8 which is the reflecting portion 6 of the reflecting surface 3 and the other part is totally reflected several times on the transmitting surface 2 and the reflecting surface 3 in the light guide plate 1 and then reflected. The light enters the ridge 8 that is the reflecting portion 6 of the surface 3. In this embodiment, the inclination angle b13, which is the angle formed between the reflective inclined surface b10 and the transmission surface 2, is set to 32 ° to 36 °, and the apex angle of the ridge is set to 90 °, so that the light incident on the ridge 8 is reflected. It hits slope b10. Since the incident light beam has the reflective vapor deposition film 7, it is specularly reflected by the reflective inclined surface b 10 which is the reflective portion 6 and reflected in the direction of the transmissive surface 2 to illuminate the liquid crystal display surface 14.
[0028]
According to the above configuration, the following effects could be obtained.
(1) The angular distribution of the light rays incident on each protrusion 8 is obtained by simulation, and the inclination angle b13, which is the angle formed by the reflective inclined surface b10 that is the reflecting portion 6 and the transmitting surface 2, is changed depending on the distance from the light source 4. By doing so, the maximum luminance value can be obtained in the front direction, which is the viewer direction, regardless of the location.
[0029]
(2) Further, since the interval between the adjacent reflecting portions 6 is set to 100 μm or less, unevenness in brightness and darkness is eliminated. Thereby, a diffusion sheet becomes unnecessary and can further prevent a decrease in luminance in the front direction.
[0030]
(3) Although the amount of light reaching the light guide plate 1 decreases as the distance from the light source 4 increases, the projected area onto the reflection surface of the reflecting portion increases as the distance from the light source 4 increases, so Regardless, the amount of light transmitted through the transmission surface 2 is substantially constant, and uneven brightness is eliminated as shown in FIG.
[0031]
(4) Since the arrangement pitch of the ridges 8 is a random pitch, even if the refraction of light rays intensifies the interference between two ridges 8, the adjacent ridges 8 are adjacent to each other. The probability of intensifying interference with the light beam is low, so that the generation of amore in a wide range can be prevented.
[0032]
The present invention is not limited to the above embodiment. In the above embodiment, since the light source 4 emits diverging light, the light is guided into the light guide plate 1 using the reflection plate 5. However, if the light source is directional, the reflection plate 5 is unnecessary. is there.
[0033]
The thickness of the light guide plate 1 is formed so as to be gradually reduced according to the distance from the light source 4 for reasons such as weight reduction and securing of an arrangement space for an IC or the like. Needless to say, the thickness may be uniform.
[0034]
When a light beam passing through the light guide plate 1 from the left to the right hits the ridge 8, it hits only the reflecting slope b 10. However, the ridge 8 may also hit the reflecting slope a 9. In this case, at least one of the inclination angle a12 and the inclination angle b13 may be changed as the distance from the light source 4 increases.
[0035]
Although the protrusion 8 of the said Example was formed substantially parallel to the light source 4, it is not limited to this. For example, as shown in FIG. 7 (a), the ridges 17 may be formed in an arc shape, or as shown in FIG. 7 (b), the ridges 18 may be formed as a broken line, As shown in FIG. 7 (c), the ridges 19 intersecting at an angle may be used. By making such protrusions non-parallel to the light source, it is possible to reduce the influence of moire fringes generated by light beam interference.
[0036]
Further, in the above embodiment, the reflective vapor deposition film 7 is formed over the entire reflective surface 3 of the light guide plate 1, but it is sufficient to form the reflective vapor deposition film on the minimum reflective slope b10. In this case, since the reflectance of the light beam on the reflecting surface is increased, a light guide plate with higher luminance can be obtained.
[0037]
Furthermore, in the above embodiment, the reflecting portion is a protrusion, but the reflecting portion may be a groove, as shown in FIG. In this case, as shown in FIG. 14, the apex angle 65 of the groove 57 may be increased by 90 °, and the inclination angle a63 of the reflective inclined surface a55 may be increased as the distance from the light source 53 increases as shown in FIG.
[0038]
【The invention's effect】
As described above, according to the present invention, the reflection portion of the light guide plate is provided with the reflection portion in which the peak angle of the angle distribution of the light from the light source is in the same direction. Head in place. By making the interval between adjacent reflecting portions 100 μm or less, bright and dark stripes are not visible. In addition, by forming the reflection portions at a random pitch, it is possible to prevent moiré from occurring in a wide range. Accordingly, the diffusion sheet can be omitted and the configuration is simplified.
[0039]
The amount of light that reaches the light guide plate decreases as it moves away from the light source, but the projected area on the reflecting surface of the reflecting part increases as the distance from the light source increases so that the decrease in light amount is covered. Regardless of the position, the amount of light transmitted through the transmission surface is substantially constant.
[Brief description of the drawings]
FIG. 1 is a configuration diagram illustrating a first embodiment of the present invention.
FIG. 2 is a diagram for explaining a reflecting portion in FIG. 1;
3 is a view in the direction of arrow A in FIG.
4 is a diagram for explaining a relationship between an inclination angle of a reflective slope b in FIG. 1 and a distance from an incident surface of a reflective portion.
5 is a diagram for explaining a ratio of a projected area of a reflecting portion to a reflecting surface in a unit area of the reflecting surface in FIG. 1 and a distance from an incident surface. FIG.
6 is a diagram for explaining the relationship between the distance from the light source of the light guide plate configured as shown in FIG. 1 and the front luminance at that location. FIG.
FIG. 7 is a configuration diagram of another embodiment of a ridge.
FIG. 8 is a configuration diagram of a light guide plate in Japanese Patent Laid-Open No. 6-3529.
FIG. 9 is a diagram showing the angular distribution of light rays incident on the reflective inclined surface b of the protrusion at a position 20 mm from the incident surface in the light guide plate of the first embodiment of the present invention.
FIG. 10 is a diagram showing the angular distribution of light rays incident on the reflective inclined surface b of the ridge at a position 150 mm from the incident surface in the light guide plate of the first embodiment of the present invention.
FIG. 11 is a diagram for explaining a projected area of a reflecting portion on a reflecting surface in a unit area of the reflecting surface.
12 is a diagram for explaining a random pitch in FIG. 1; FIG.
FIG. 13 is a configuration diagram illustrating a second embodiment of the present invention.
FIG. 14 is a diagram for explaining a reflection part in FIG. 13;
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Light guide plate 2 Transmission surface 3 Reflection surface 4 Light source 5 Reflection plate 6 Reflection part 7 Reflection vapor deposition film 8 Projection 9 Reflection slope a
10 Reflective slope b

Claims (5)

In the light guide plate that guides the light incident from the incident surface facing the linear light source to the outside through the transmission surface substantially orthogonal to the incident surface,
A reflective portion is provided that has a protrusion or groove formed on a reflective surface that faces the transmissive surface and reflects light to the transmissive surface.
Increasing the angle of inclination between the reflecting portion and the transmitting surface as the distance from the light source increases,
A light guide plate, wherein an interval between adjacent reflecting portions is 100 μm or less.   The light guide plate according to claim 1, wherein the light guide plate is made of a plastic material. The light guide plate according to claim 1, wherein each surface of the light guide plate and each surface of the groove or the ridge are substantially smooth surfaces. The light guide plate according to any one of claims 1 to 3, wherein a projected area of the reflecting portion on a unit area of the reflecting surface onto the reflecting surface increases as the distance from the light source increases . The light guide plate according to claim 1 , wherein the thickness of the light guide plate decreases as the distance from the light source increases .

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