JP2004070169A - Light guide plate and back light apparatus using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light guide plate with which brightness in a frontage direction of a light emission surface is heightened by improving conversion efficiency of light components in the frontage direction and to provide a back light apparatus using the same. <P>SOLUTION: The back light apparatus is provided with a light source 1, the light guide plate 2, a diffusing sheet 3 and a reflection sheet 4. Light emitted from the light Source 1 is made incident on a light incident surface of the light guide plate 2 as incident light Lin and is emitted from a light emitting surface while being guided in a perpendicular direction. On a reflector bottom face of the light guide plate 2, a plurality of V-grooves 5 extendedly provided directions of which are in parallel to the light incident surface and a plurality of protrusions 6 located near the V-groove 5 at an opposite side of the light incident surface are formed and respectively at least three slopes are formed. Transmitted light Le penetrated to a reflector bottom face side without total reflection by the V-groove 5 is caught by the protrusion 6 and is finally converted to light of almost normal line direction of the reflector bottom face and is emitted as emitting light Lout. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a light guide plate used as a backlight of a display device and a backlight device using the same, and more specifically, a light guide plate used as a backlight of a liquid crystal display device and the like, and a backlight device using the same. About.
[0002]
[Prior art]
In recent years, liquid crystal displays have been widely used as display devices for personal computers, mobile terminals, mobile phones, television devices, and the like. This liquid crystal display is required to be lighter, smaller, thinner, lower in power consumption, higher in brightness, and lower in price. Therefore, a backlight device mounted as a backlight source of the liquid crystal display is also required. Similar improvements are required. Such a backlight device includes a light guide plate that radiates light incident from a light source while reflecting the light on a plurality of reflection surfaces provided near the bottom surface of the member while guiding the light in a direction substantially normal to the bottom surface. Is provided. The same improvement as described above is required for this light guide plate.
[0003]
An example of such a light guide plate used in a conventional backlight device is disclosed (for example, see Patent Document 1). Further, a light guide plate in which a curved protrusion is formed near the edge of a V-shaped groove formed on the bottom surface is disclosed (for example, see Patent Document 2). The structure of the light guide plate disclosed in Patent Document 1 will be described with reference to FIG. FIG. 10 is a schematic side view showing the structure of the light guide plate.
[0004]
In FIG. 10, a light guide plate 102 for guiding light emitted from the reflector 101 and the light source 100 is provided. The light source 100 is configured by a fluorescent lamp or the like, and emits diffused light directly or reflected by the reflector 101 as incident light Lin to one side surface (hereinafter, referred to as a light incident surface) of the light guide plate 102. The light guide plate 102 is a flat light guide member, and a plurality of V-shaped grooves 103 are formed on a bottom surface (hereinafter, referred to as a reflector bottom surface). The extending direction of the V-shaped groove 103 is parallel to the light incident surface, and the inclined surface 103a on the light incident surface forms a reflecting surface. Then, the incident light Lin incident from the light incident surface of the light guide plate 102 propagates in the light guide plate 102 and is totally reflected by the plurality of inclined surfaces 103a, thereby forming an upper surface (hereinafter, referred to as a light exit surface) facing the reflector bottom surface. ) Is emitted as emission light Lout. The emitted light Lout is emitted in a direction substantially normal to the bottom surface of the reflector, and serves as a backlight of a display device (not shown) provided in front of the light emitting surface.
[0005]
[Patent Document 1]
JP-A-7-294745
[Patent Document 2]
JP 2000-89033 A
[0006]
[Problems to be solved by the invention]
However, since the incident light Lin emitted from the light source 100 is a diffused light, light propagating in the light guide plate 102 is reflected within the light guide plate 102 at various angles. Therefore, the incident light Lin nearly parallel to the reflector bottom surface of the light guide plate 102 is totally reflected by the inclined surface 103a as described above, and is emitted as the outgoing light Lout in a direction substantially normal to the reflector bottom surface. The incident light Lin having an angle with respect to the bottom surface may be transmitted to the reflector bottom surface side as transmitted light Le without being totally reflected even if it is incident on the inclined surface 103a. That is, the transmitted light Le causes light to leak from the V-shaped groove 103, so that the light efficiency of the light guide plate 102 is reduced. In addition, it is conceivable to arrange a reflection sheet on the reflector bottom side of the light guide plate 102 to reflect the transmitted light Le to the light guide plate 102 side. However, this reflected light is substantially normal to the reflector bottom surface. Therefore, it does not lead to an improvement in luminance in the front direction of the light emitting surface.
[0007]
On the other hand, the light guide plate disclosed in Patent Literature 2 having a curved projection formed near the edge of a V-groove formed on the bottom surface of the reflector is also disclosed in the above-mentioned Patent Literature. 1, light leakage from the V-groove occurs. Then, the transmitted light transmitted through the V-groove reaches the reflection sheet disposed on the bottom surface side of the light guide plate without being incident on the protrusion, and thus the light guide plate is similar to the light guide plate disclosed in Patent Document 1. Also, the light efficiency decreases. Further, since the projection has a curved shape, most of the light propagated from inside the light guide plate to the projection is transmitted to the bottom surface side of the light guide plate while being diffused. Then, the light transmitted through the protrusion is reflected by the reflection sheet disposed on the bottom surface side of the light guide plate, transmitted through the light guide plate again, and emitted to the upper surface. That is, the light emitted by the light guide plate becomes light having a high diffusivity, the light condensing property of the light emitting surface in the front direction is low, and it does not lead to the improvement of the brightness in the front direction.
[0008]
SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a light guide plate that increases the luminance in the front direction of a light emitting surface by improving the conversion efficiency of a light component in the front direction, and a backlight device using the same. It is.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, the present invention has the following features.
In the light guide plate of the present invention, light emitted from a light source is incident on a side surface, and light incident on the side surface is reflected on a bottom surface and emitted toward an upper surface. The light guide plate has a plurality of grooves and ridges. The plurality of grooves have a V-shaped cross section on the bottom surface, and the extending direction is formed parallel to the side surface. The plurality of ridges have a V-shaped cross section on the bottom surface, and their extending directions are formed in parallel with the side surfaces and near the distant sides of the respective groove grooves. Is done. The groove has a first slope formed closer to the side and a second slope formed farther from the side. The ridge has a third slope formed on the side closer to the side surface and a fourth slope formed on the side farther from the side surface. When the light incident from the side surface is transmitted through the first slope, the light is refracted by the third slope and captured by the ridge, and is totally reflected by the fourth slope, thereby substantially normal to the bottom surface. Emit in the direction.
[0010]
According to the configuration of the present invention described above, each of the grooves is formed by providing a V-shaped ridge in the vicinity of a side far from the side surface on which light is incident, thereby forming the ridge. Light that cannot be totally reflected on the slope is captured by the ridge, and the captured light is totally reflected and emitted as light emitted in a direction substantially normal to the bottom surface. In other words, the light guide plate of the present invention prevents light loss and improves the front luminance of the light exit surface by providing a ridge in the vicinity of a side farther from the light incident side surface for each groove. Can be.
[0011]
Further, the third slope may be formed such that the acute angle with respect to the normal direction of the bottom surface is smaller than the acute angle with respect to the normal direction of the bottom surface of the first slope. The fourth slope may be formed such that an angle on the acute angle side with respect to the normal direction of the bottom surface is substantially equal to the angle on the acute angle side of the first slope. In this case, the light having an angle that cannot be totally reflected by the first slope formed by the groove passes through the first slope and then re-enters the ridge, and the light is refracted by the third slope to cause the light to be refracted. The angle can be converted so as to approach a direction parallel to the bottom surface, and as a result, the light can be totally reflected on the fourth slope.
[0012]
Further, the first and fourth slopes may be formed at an acute angle of 33 ° to 50 °, and the third slope may be formed at an acute angle of 0 ° to 17 °. . In this case, the front luminance of the light emitting surface can be reliably improved as compared with the light guide plate having no projection on the bottom surface.
[0013]
Also, by forming the second and third slopes on the same plane, a set of grooves and protrusions may be formed continuously on the bottom surface. Accordingly, the amount of light captured by the ridges by the third slope increases, and the front luminance can be further improved.
[0014]
Further, the bottom surface may be formed of a plurality of step surfaces formed in steps so that the thickness gradually decreases as the distance from the side surface increases. In this case, a set of the groove and the ridge is formed for each of the step surfaces. Thus, light transmitted through the other side surface opposite to the side surface is reduced, so that the light efficiency of the light guide plate can be further improved.
[0015]
Note that the present invention can also be realized as a backlight device using the above-described light guide plate.
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
A backlight device according to an embodiment of the present invention will be described with reference to FIG. FIG. 1 is a side view showing the structure of the backlight device.
[0017]
In FIG. 1, the backlight device of the present embodiment includes a light source 1, a light guide plate 2, a diffusion sheet 3, and a reflection sheet 4. The light source 1 includes an LED (Light Emitting Diode) that emits diffused light, a fluorescent tube such as a cold cathode tube, an incandescent lamp, an organic or inorganic EL (Electro Luminescence), or the like. The light guide plate 2 is a light guide member made of a transparent resin such as a flat acrylic or polycarbonate, and light emitted from the light source 1 from one side surface (hereinafter, referred to as a light incident surface) is incident light Lin. Incident. The light guide plate 2 emits light propagating therein from a flat plate surface (hereinafter, referred to as a light emission surface) formed in the front direction of the backlight device while guiding the light in a direction perpendicular to the light source 1. . A plurality of grooves 5 whose extending direction is provided in parallel with the light incident surface are formed on a flat surface (hereinafter, referred to as a reflector bottom surface) which is a back surface opposite to the light emitting surface of the light guide plate 2. You. For example, the groove 5 is formed in a V-shape, and is hereinafter referred to as a V-groove 5. A plurality of ridges (hereinafter, referred to as protrusions) 6 having a triangular cross-sectional shape are formed in the vicinity of the light incident surface side of the V groove 5 formed on the bottom surface of the reflector of the light guide plate 2. The plurality of V-grooves 5 and the projections 6 form at least three slopes. The detailed shapes of the V-groove 5 and the protrusion 6 formed on the reflector bottom surface of the light guide plate 2 will be described later.
[0018]
Since the incident light Lin emitted from the light source 1 is a diffused light, the light propagating in the light guide plate 2 is reflected in the light guide plate 2 at various angles. Therefore, the incident light Lin nearly parallel to the reflector bottom surface of the light guide plate 2 is totally reflected by the light incident surface side slope formed by the V-groove 5, so that the reflector is substantially in the normal direction of the reflector bottom surface. The light exits from the light exit surface facing the bottom surface as exit light Lout and is guided to a liquid crystal panel (not shown). Further, as described in the related art, the incident light Lin having an angle with respect to the reflector bottom surface of the light guide plate 2 can be transmitted to the reflector bottom surface side as the transmitted light Le without being totally reflected by the V groove 5. is there. The transmitted light Le that has passed through the V-groove 5 is once emitted from the reflector bottom surface of the light guide plate 2, but is captured by the protrusion 6 provided in the vicinity of the V-groove 5 on the side opposite to the light incident surface, and is incident on the light guide plate 2 again. . The transmitted light Le that has entered the projection 6 is refracted and reflected by the slope formed by the projection 6, and is finally converted into light substantially in the normal direction of the reflector bottom surface, and passes through the light guide plate 2. And is emitted as emission light Lout. The details of the light conversion will be described later.
[0019]
In the vicinity of the light exit surface of the light guide plate 2, the exit light Lout emitted from the light exit surface is made uniform by diffusing, and the bottom surface for guiding the exit light Lout diffused to the liquid crystal panel is flat and the top surface is fine. A diffusion sheet 3 in which various beads are dispersed is provided. In addition, near the reflector bottom surface of the light guide plate 2, there is provided a reflection sheet 4 for reflecting light leaking from the reflector bottom surface of the light guide plate 2 and returning the light to the inside of the light guide plate 2 again. As described above, in the backlight device of the present embodiment, the incident light Lin of the light source 1 is incident from the light incident surface of the light guide plate 2, and the slopes or protrusions on the light incident surface side of the plurality of V-grooves 5 formed on the reflector bottom surface. The inclined surface 6 guides the incident light Lin propagating in the light guide plate 2 in a direction substantially normal to the bottom surface of the reflector and emits the emitted light Lout from the front direction (light emission surface) of the backlight device.
[0020]
Next, a detailed structure of the light guide plate 2 according to the embodiment will be described with reference to FIGS. FIG. 2 is a perspective view of the light guide plate 2 viewed from the light exit surface with the light incident surface in front, and FIG. 3 is a perspective view of the light guide plate 2 viewed from the bottom surface of the reflector. In FIG. 2, a slope formed inside the light guide plate 2 is shown in perspective for explaining the internal structure of the light guide plate 2.
[0021]
2 and 3, a plurality of V-grooves 5 are formed on the bottom surface of the reflector of the light guide plate 2 so as to extend in parallel with the light incident surface. A projection 6 is formed in the light guide plate 2 on the reflector bottom surface in the vicinity of the V-groove 5 on the side opposite to the light incident surface. By forming a V-groove 5 on the bottom surface of the reflector, an inclined surface 5a (shown by a dashed dashed line in FIG. 2) on the light incident surface side and an inclined surface 5b (shown by an oblique line in FIG. 3) on the anti-light incident surface side. Surface) is formed. Further, the projection 6 is formed on the bottom surface of the reflector, so that the slope 5b (the surface shown by oblique lines in FIG. 3) on the light incident surface side and the slope 6a (shown by broken horizontal lines in FIG. 2) on the anti-light incident surface side. Surface) is formed. By forming the plurality of slopes 5a, 5b, and 6a, a plurality of prisms are formed on the reflector bottom surface of the light guide plate 2. In this embodiment, the slope formed on the light incident surface side by forming the projection 6 on the reflector bottom surface is formed on the same plane as the slope 5b formed by the V groove 5. The following description is made on the assumption that the slope formed on the light incident surface side by the V-groove 5 and the slope formed on the light incident surface side by the protrusion 6 are the same slope 5b.
[0022]
Next, the shapes of the slopes 5a, 5b and 6a on the reflector bottom surface of the light guide plate 2 will be described with reference to FIG. FIG. 4 is an enlarged side view of the vicinity of the V-groove 5 and the protrusion 6 formed in the light guide plate 2.
[0023]
In FIG. 4, the reflector bottom surface and the light emission surface of the light guide plate 2 are configured to be parallel to each other. The inclined surface 5a on the light incident surface side of the V-groove 5 formed on the reflector bottom surface of the light guide plate 2 has an angle θ1 on the acute angle side with respect to the normal direction of the reflector bottom surface. ). In addition, the inclined surface 5b provided on the side opposite to the light incident surface of the V groove 5 formed on the bottom surface of the reflector of the light guide plate 2 and on the side of the light incident surface of the projection 6 is formed at an angle θ2 with respect to the normal direction of the bottom surface of the reflector. Is done. Further, the slope 6a on the side opposite to the light incident surface of the projection 6 formed on the reflector bottom surface of the light guide plate 2 is formed at an angle θ3 with respect to the normal direction of the reflector bottom surface. The angle θ1 of the slope 5a and the angle θ3 of the slope 6a are substantially equal to each other.
θ1 = θ3 = 35 ° -50 °
It is. Further, the angle θ2 of the slope 5b is configured to be smaller than the angle θ1, and preferably,
θ1> θ2 = 0 ° -20 °
It is. Then, the depth h1 of the V groove 5 and the height h2 of the projection 6 with respect to the reflector bottom surface are:
h1 ≒ h2
The V-groove 5 and the protrusion 6 are formed such that
[0024]
Next, the propagation of light in the light guide plate 2 will be described with reference to FIG. FIG. 5 is an enlarged side view showing the vicinity of the V-groove 5 and the protrusion 6 for showing the movement of the incident light Lin propagating in the light guide plate 2. Here, as two typical examples of the incident light Lin, the incident light nearly parallel to the reflector bottom surface of the light guide plate 2 is defined as Lin1, and the incident light having an angle θin with respect to the bottom surface is defined as Lin2. The movement of the incident lights Lin1 and Lin2 inside the light plate 2 will be described.
[0025]
In FIG. 5, when the incident light Lin <b> 1 that is nearly parallel to the reflector bottom surface of the light guide plate 2 is incident on the slope 5 a formed by the V-shaped groove 5, the incidence light Lin <b> 1 is close to the angle θ1 with respect to the normal direction of the slope 5 a. The light enters the slope 5a at an angle. Here, since the angle θ1 is set to θ1 = 35 ° to 50 ° as described above, the incident light Lin1 incident on the inclined surface 5a is totally reflected on the inclined surface 5a substantially in the normal direction of the reflector bottom surface. . Then, the incident light Lin1 propagates through the light guide plate 2 substantially in the normal direction of the bottom surface of the reflector, and is emitted from the light emission surface as emission light Lout1.
[0026]
On the other hand, when the incident light Lin2 having an angle θin with respect to the reflector bottom surface of the light guide plate 2 is incident on the slope 5a formed by the V-groove 5, the angle θ1−θin with respect to the normal direction of the slope 5a. Incident on the inclined surface 5a at the incident angle. That is, when the angle θin is close to the angle θ1, the incident angle of the incident light Lin2 on the inclined surface 5a is substantially 0 °, and the incident light Lin2 is transmitted through the inclined surface 5a to be transmitted light Le.
[0027]
The transmitted light Le exits from the V-groove 5 of the light guide plate 2 and enters the projection 6 from the slope 5b at an incident angle having an angle θin + θ2 with respect to the normal direction of the slope 5b. Then, the transmitted light Le is refracted at a refraction angle θr with respect to the normal direction of the inclined surface 5b, and propagates inside the projection 6 as the projection 6 re-incident light Lein. This refraction angle θr is given assuming that the refractive index of the light guide plate 2 is n.
θr = (θin + θ2) / n
It becomes. Here, since the slope 5b is formed at an angle θ2 with respect to the normal direction of the bottom surface of the reflector, the re-incident light Lein is projected at an angle θr−θ2 = (θin + θ2) / n−θ2 with respect to the bottom surface of the reflector. It will propagate inside. That is, the angle θin of the incident light Lin2 with respect to the reflector bottom is converted so that the angle θin approaches a direction parallel to the reflector bottom according to the refractive index n of the light guide plate 2 and the angle θ2 of the inclined surface 5b.
[0028]
The re-incident light Lein is incident on the inclined surface 6a at an incident angle having an angle θ3- (θr−θ2) with respect to the normal direction of the inclined surface 6b. Then, the re-incident light Lein that has entered the slope 6a is totally reflected by the slope 6a in a direction substantially normal to the bottom surface of the reflector, propagates through the light guide plate 2 in a direction substantially normal to the bottom surface of the reflector, and is emitted as a light emission surface Lout2. Is emitted from.
[0029]
That is, the incident light Lin2 having an angle that cannot be totally reflected by the inclined surface 5a formed by the V-groove 5 passes through the inclined surface 5a and then re-enters the protrusion 6, and the angle of the incident light Lin2 with respect to the reflector bottom surface due to refraction on the inclined surface 5b. By being converted so as to approach the parallel direction, the light is totally reflected on the slope 6a. Note that the re-incident light Lein refracted by the inclined surface 5b and re-entered is not propagated to the inclined surface 6b but is incident on another inclined surface 5a formed in the direction of the anti-light incident surface, depending on the incident position on the inclined surface 5b. Is also possible. In this case, the re-incident light Lein is totally reflected by the other inclined surface 5a, propagates substantially in the normal direction of the bottom surface of the reflector, and is emitted from the light emission surface as emission light Lout.
[0030]
As described above, the reflector bottom surface and the light emitting surface of the light guide plate 2 are configured to be parallel to each other, and propagate the incident light Lin while totally reflecting the light inside the light guide plate 2. On the other hand, for example, when the reflector bottom surface and the light exit surface of the light guide plate 2 are not parallel and have an angle such that the anti-light incident surface side becomes narrow, the light propagating in the light guide plate 2 has the reflector bottom surface and the light bottom surface. Each time the light is totally reflected between the light emitting surfaces, the angle of the light to the reflector bottom surface or the light emitting surface increases, and finally the light is transmitted and emitted to the outside of the light guide plate 2. At this time, since the light is emitted obliquely with respect to the normal direction of the bottom surface of the reflector, it does not lead to an increase in luminance in the front direction of the light emission surface. Therefore, the light guide plate 2 can prevent a loss in light propagation by configuring the reflector bottom surface and the light emission surface to be parallel to each other.
[0031]
The amount of light emitted from the light exit surface of the light guide plate 2 is proportional to the area of the slopes 5a and 6a formed on the reflector bottom. Further, since more light propagates in the light guide plate 2 as it is closer to the light source 1, in order to make the luminance emitted from the light emission surface of the light guide plate 2 uniform, the areas of the slopes 5a and 6a are closer to the light source 1. Needs to be gradually reduced. For this reason, in the light guide plate 2, the depth h1 of the V-groove 5 may be gradually reduced as the distance from the light source 1 increases, and the height h2 of the protrusion 6 may be gradually increased. Alternatively, the depth h1 of the V-groove 5 and the height h2 of the protrusion 6 may be kept constant, and the pitch between the V-groove 5 and the protrusion 6 may be gradually reduced as the distance from the light source 1 increases. Alternatively, a gradual change in the depth h1 and height h2 and the pitch of the V-groove 5 and the protrusion 6 may be combined.
[0032]
Next, with reference to FIG. 6 and FIG. 7, a description will be given of the front luminance increase rate of the light guide plate 2 as compared with the conventional light guide plate 102 (see FIG. 10). FIG. 6 is a diagram in which the angle θ2 of the slope 5b of the light guide plate 2 is changed and comparison with the conventional light guide plate 102 is performed by optical simulation. FIG. 7 is a diagram illustrating the slopes 5a and 6a of the light guide plate 2. FIG. 8 is a diagram in which the angles θ1 and θ3 are changed and a comparison with the conventional light guide plate 102 is performed by optical simulation.
[0033]
In FIG. 6, an optical simulation for comparing the light guide plate 2 with the conventional light guide plate 102 is based on the Snell's law of ray tracing based on reflection and refraction within one section of the light guide plate, that is, within the two-dimensional plane shown in FIG. The comparison was made with the average luminance in the light emitting surface direction calculated in the above. In the above optical simulation, the conditions common to the light guide plates 2 and 102 are a light guide plate thickness of 0.4 mm, a length of 45 mm, a groove pitch of 0.35 mm, a luminance uniformity of the entire light exit surface with respect to the light guide plate center of 0.7, and The refractive index of the light guide plate was 1.49. The angle of the opening groove of the V-shaped groove 103 of the light guide plate 102 was fixed at 84 °. Further, the angles θ1 and θ3 of the slopes 5a and 6a in the light guide plate 2 were fixed at θ1 = θ3 = 48 °, and the brightness comparison with the light guide plate 102 was performed by changing the angle θ2 of the slope 5b. Comparing the average brightness in the light emitting surface direction of the light guide plates 2 and 102 under such conditions, the average brightness of the light guide plate 2 is improved with respect to the light guide plate 102 by reducing the angle θ2 of the slope 5b. You can see that For example, by setting the angle θ2 of the light guide plate 2 to 17 ° or less, the average brightness increase rate of the light guide plate 2 can be 10% (1.10.) With respect to the light guide plate 102.
[0034]
In FIG. 7, in an optical simulation for comparing the light guide plate 2 with the conventional light guide plate 102, comparison was performed with the same average luminance as in FIG. In the optical simulation, the conditions common to the light guide plates 2 and 102 are a light guide plate thickness of 0.4 mm, a length of 45 mm, a groove pitch of 0.35 mm, a brightness uniformity of the entire light exit surface with respect to the light guide plate center of 0.7, And the refractive index of the light guide plate was 1.49. The angle of the opening groove of the V-shaped groove 103 of the light guide plate 102 was fixed at 84 °. The angle θ2 of the inclined surface 5b of the light guide plate 2 is fixed at θ2 = 12 °, and the angles θ1 and θ3 of the inclined surfaces 5a and 6a are changed at the same angle (that is, θ1 = θ3 is fixed). A luminance comparison with 102 was performed. Comparing the average luminance in the light emitting surface direction of the light guide plates 2 and 102 under such conditions, the angles θ1 and θ3 of the slopes 5a and 6a are set by setting θ1 = θ3 = 33 ° to 50 °, and the It can be seen that the average luminance of the light plate 2 is improved with respect to the light guide plate 102.
[0035]
In this manner, the light guide plate of the present invention captures the incident light that cannot be totally reflected by the slope formed by the V groove by providing the protrusion on the side of the light receiving surface of the V groove, and captures the light. The incident light is totally reflected and emitted as light emitted from the light emitting surface. That is, the light guide plate of the present invention can prevent light loss and improve the front luminance of the light exit surface by providing the protrusion on the side of the V-groove opposite to the light incident surface.
[0036]
In the above description of the light guide plate 2, the height of the reflector bottom surface is formed to be constant. However, as shown in FIG. 8, by providing a step t behind the V groove 5 and the protrusion 6, the reflector is separated from the light incident surface. The bottom surface of the reflector may be formed stepwise so that the thickness of the light guide plate 2 becomes thinner according to By forming the bottom surface of the reflector in a step-like manner so that the thickness of the light guide plate 2 becomes thinner as the distance from the light incident surface of the light guide plate 2 increases, light transmitted through the anti-light incident surface decreases. 2 can be further improved in light efficiency.
[0037]
Further, in the above description of the light guide plate 2, the slope 5 b formed on the light incident surface side by forming the protrusion 6 on the reflector bottom surface and the slope 5 b formed by the V groove 5 are on the same plane. And one slope 5b. However, these slopes need not be formed on the same plane. That is, as shown in FIG. 9, a reflector bottom portion having a length u is provided between the V-groove 5 and the protrusion 6 on the reflector bottom surface of the light guide plate 2, and the slope 5 c on the side of the V-groove 5 opposite the light incident surface and the protrusion 6 are provided. May be formed separately from the inclined surface 6b on the light incident surface side. In this case, the same function as the slope 5b is realized by the slopes 5c and 6b by forming the slopes 5c and 6b at the angle θ2 of the slope 5b with respect to the normal direction of the reflector bottom surface. Needless to say, we can do it.
[0038]
Further, the light guide plate 2 is made of a transparent resin such as a flat acrylic or polycarbonate, but may be made of glass. Further, in order to prevent the tip of the projection 6 formed on the bottom surface of the reflector of the light guide plate 2 from being chipped, a slightly flat or curved surface may be provided at the tip.
[0039]
【The invention's effect】
The light guide plate of the present invention has a projection on the side opposite to the light incident surface of the V-groove, so that the projection captures incident light that cannot be totally reflected on the slope formed by the V-groove, and collects the captured incident light. The light is reflected and emitted as light emitted from the light emission surface. That is, the light guide plate of the present invention can prevent light loss and improve the front luminance of the light exit surface by providing the protrusion on the side of the V-groove opposite to the light incident surface.
[Brief description of the drawings]
FIG. 1 is a side view showing a structure of a backlight device according to an embodiment of the present invention.
FIG. 2 is a perspective view of the light guide plate 2 of FIG. 1 as viewed from a light emitting surface with a light incident surface in front.
FIG. 3 is a perspective view of the light guide plate 2 of FIG. 1 as viewed from a reflector bottom surface with a light incident surface in front.
FIG. 4 is an enlarged side view of the vicinity of a V-groove 5 and a protrusion 6 formed in the light guide plate 2 of FIG.
FIG. 5 is an enlarged side view showing the vicinity of a V-groove 5 and a protrusion 6 for showing the movement of the incident light Lin of FIG. 1 propagating through the light guide plate 2.
6 is a diagram in which the angle θ2 of the inclined surface 5b of the light guide plate 2 of FIG. 4 is changed and a comparison with the conventional light guide plate 102 is performed by optical simulation.
FIG. 7 is a diagram in which the angles θ1 and θ3 of the slopes 5a and 6a of the light guide plate 2 of FIG. 4 are changed, and comparison with the conventional light guide plate 102 is performed by optical simulation.
FIG. 8 is a diagram showing an example in which the reflector bottom surface is formed in a step-like manner so that the light guide plate 2 of FIG. 1 becomes thinner as the distance from the light incident surface increases.
9 is a diagram showing an example in which a reflector bottom portion having a length u is provided between the V-groove 5 and the protrusion 6 of the light guide plate 2 of FIG.
FIG. 10 is a schematic side view for explaining the structure of a conventional light guide plate disclosed in Japanese Patent Application Laid-Open No. 7-294745.
[Explanation of symbols]
1. Light source
2 ... Light guide plate
3. Diffusion sheet
4: Reflective sheet
5 ... V groove
6 ... Projection
5a, 5b, 5c, 6a, 6b ... slope

Claims (7)

A light guide plate that emits light from a light source from a side surface and reflects the light incident from the side surface on a bottom surface and emits the light toward an upper surface,
A plurality of grooves formed on the bottom surface, the cross section of which has a V-shape, and the extending direction is formed parallel to the side surface;
A plurality of protrusions are formed on the bottom surface, the cross-section of which has a V-shape, the extending direction of which is parallel to the side surface, and each of the grooves is formed near the side far from the side surface. Article is formed,
The groove has a first slope formed on a side closer to the side surface and a second slope formed on a side farther from the side surface,
The light guide plate, wherein the ridge has a third slope formed on a side closer to the side surface and a fourth slope formed on a side farther from the side surface. When the light incident from the side surface is transmitted through the first slope, the light is captured by the ridge by being refracted by the third slope and totally reflected by the fourth slope, whereby The light guide plate according to claim 1, wherein the light is emitted in a substantially normal direction. The third slope is formed such that an acute angle side with respect to a normal direction of the bottom surface is smaller than an acute angle side with respect to a normal direction of the bottom surface of the first slope,
3. The light guide plate according to claim 1, wherein the fourth slope is formed such that an acute angle with respect to a normal direction of the bottom surface is substantially equal to an acute angle of the first slope. The acute angle of the first and fourth slopes is formed at 33 ° to 50 °,
4. The light guide plate according to claim 3, wherein the acute angle of the third slope is 0 ° to 17 °. 5. 5. The method according to claim 1, wherein the second and third slopes are formed on the same plane, so that each set of the groove and the ridge is continuously formed on the bottom surface. 6. Light guide plate. The bottom surface is formed of a plurality of step surfaces formed in a step-like manner so that the thickness gradually decreases as the distance from the side surface increases,
The light guide plate according to claim 1, wherein the set of the groove and the ridge is formed for each of the step surfaces. The light guide plate according to claim 1,
A light source,
And a diffusion sheet for diffusing light emitted from the light guide plate.

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