JP2005228719A - Light guide plate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light guide plate of a side-light type surface light source preventing emission lines and brightness unevenness near the light source and uniformalizing intensity distribution of light after incidence into the light guide plate. <P>SOLUTION: The light guide plate is provided with a side face of a platy member having a polygonal shape and translucency as a light-incident face, and irradiates illumination light on an illumination object from its top face by changing optical paths of the light from the light source arranged in opposition to the light-incident face. In the plate, at least one corner part of the platy member is chamfered to make a side face formed by the chamfering a light-incident face, on which concavities and convexities consisting of a smoothly continuing curved surface are formed. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a light guide plate used for a sidelight type planar light source that irradiates a liquid crystal panel from the back side, for example, and more particularly to a light guide plate for a sidelight type planar light source suitable for a small liquid crystal panel such as a cellular phone.

  2. Description of the Related Art In recent years, a liquid crystal display device having a thin and easy-to-see backlight mechanism has been used as a display device for small and thin information devices such as book-type word processors, computers, mobile phones, and portable TVs. As such a backlight mechanism, a planar light source that irradiates the entire surface of the liquid crystal panel from behind is used. As this planar light source, a light source composed of a fluorescent lamp or an LED (light emitting diode) and a light flux of the liquid crystal are used. In general, a light guide plate that converts a planar light beam to be irradiated on the panel is used. Among these, particularly in recent years, a planar light source using an LED or the like as a light source has been increasingly used for the purpose of further miniaturization, thinning and long life. In addition, these planar light sources are roughly classified into a direct type in which the light source is disposed directly under the light guide plate and a side light type in which the light source is disposed on the side of the light guide plate. The sidelight type is adopted exclusively for the equipment where emphasis is placed on manufacturing.

  As a specific example of such a prior art, one corner of a light guide plate made of a plate-like transparent material is chamfered, and a side surface formed by this chamfering is used as a light incident surface, and is opposed to the light incident surface. A light guide plate of a side light type planar light source is disclosed in which light from a light source arranged is converted into an optical path and planar illumination light is emitted from the upper surface to an illumination object (see, for example, Patent Document 1). ). 5A and 5B show a main part of a conventional sidelight type planar light source. FIG. 5A is a plan view, and FIG. 5B is a cross-sectional view taken along the line CC in FIG. FIG. 6 is a partially enlarged plan view showing the vicinity of the light incident surface of the light guide plate. Hereinafter, the side light type planar light source in the above-described prior art will be described with reference to the drawings.

As shown in FIG. 5A, the side light type planar light source includes a light guide plate 1 and a light source 2 as a light emitting diode (LED). The light guide plate 1 is made of a colorless and transparent plastic material or the like, and chamfers one corner 1d of a plate-like member having a substantially rectangular parallelepiped shape. A side surface formed by the chamfering is used as a light incident surface 1a, and the light incident surface 1a. The light source 2 is arranged at a position facing the. Further, as shown in FIG. 5B, the upper surface of the light guide plate 1 is a light exit surface 1b, and the light after entering the light guide plate 1 on the lower surface 1c facing the light exit surface 1b. As a means for reflecting 6b toward the light emitting surface 1b, a plurality of minute embossments or a plurality of hemispherical dots are provided on the surface, and the lower surface 1c is a light reflecting surface.
The light guide plate 1 is disposed on the back side of the liquid crystal panel 7, and in many cases, a light reflecting sheet 3 for directing light from the light source 2 toward the liquid crystal panel is provided on the lower surface side of the light guide plate 1. ing. Further, the light guide plate 1 is often provided with a diffusion sheet 4 for uniformly dispersing the light from the light source 2 and a prism sheet 5 for condensing the light.

  The irradiation light 6a emitted from the light source 2 is incident from the light incident surface 1a and propagates toward the light emitting surface 1b while being repeatedly reflected inside the light guide plate as light 6 after entering the light guide plate 1. A component having a critical angle or less is emitted to the outside as illumination light 8 from the light emitting surface 1 b of the light guide plate 1. At this time, the illumination light 8 is dispersed by the diffusion sheet 4 and the prism sheet 5 to illuminate the liquid crystal panel 7 from behind. As a result, the side light type planar light source forms a light emitting surface on the light emitting surface 1b of the light guide plate 1 and forms a side light type planar light source by the irradiation light 6a emitted from the light source 2. Has been made.

  In such a sidelight type planar light source, as shown in FIG. 6, when the irradiation light 6 a from the light source 2 is incident on the light guide plate 1 at an incident angle a, light is refracted, and the light is generated inside the light guide plate 1. The incident light 6b is incident at an angle b that is a normal line. Since the acrylic resin, polycarbonate resin, or the like, which is the material of the light guide plate 1, has a refractive index larger than that of air, the angle b formed with the normal line is smaller than the incident angle a. At this time, the irradiation light 6a irradiated from the light source 2 has directivity of the light emitting diode (LED) itself, and the irradiation light 6a having this directivity is refracted and incident on the light incident surface 1a. The directivity of the light 5 after entering the inside becomes narrower than the directivity of the irradiation light of the light source 2, and the light region 9 after entering the inside of the light guide plate 1 becomes narrow as shown in FIG. .

  FIG. 7 shows the directivity of the irradiation light 6 a from the light source 2 and the light 6 b after entering the light guide plate 1. 7A shows the directivity of the irradiation light 6a of the light emitting diode (LED) itself as the light source 2, and FIG. 7B shows the irradiation light 6a of the light source 2 from the light incident surface 1a to the inside of the light guide plate 1. FIG. The directivity of the light 6b after entering is shown. The irradiation light 6a of the light emitting diode (LED) itself that is a point light source as the light source 2 has directivity as shown by a curve 101 in FIG. The directivity of the light 6b after the irradiation light 6a having the directivity is incident on the inside of the light guide plate 1 shows the directivity as shown by the curve 102 in FIG. 7B. As described above, the light guide plate 1 The directivity of the light 6b after entering the LED becomes narrower than the directivity of the irradiation light 6a of the LED itself. For this reason, in the conventional light guide plate 1 in which the light incident surface is formed by a flat surface, there is a problem that the intensity distribution of the light 6b after entering the light guide plate 1 becomes non-uniform.

  In order to solve such a problem, an example of a light guide plate is disclosed in which one side surface of a substantially rectangular parallelepiped light guide plate is used as a light incident surface, and the light incident surface is provided with irregularities made of a plurality of uniform prisms. (For example, refer to Patent Document 2). There is also an example in which the light incident surface formed by chamfering the corner portion of the light guide plate is provided with unevenness made up of a plurality of uniform prisms. This light guide plate is different in the shape of the light incident surface and is otherwise the same as the light guide plate 1 described above, so the light incident surface will be described and the other description will be omitted. 8 shows a light guide plate, FIG. 8 (a) is a plan view of the light guide plate, and FIG. 8 (b) is a partially enlarged perspective view showing a light incident surface in part A of FIG. 8 (a). FIG. 9 is a partially enlarged plan view showing a light incident surface in a portion A of FIG. Hereinafter, the light guide plate will be described with reference to the drawings.

  As shown in FIG. 8A, the light guide plate 11 is chamfered at a corner portion 11d, and a light incident surface 11a is formed on a side surface formed by the chamfering. As shown in FIG. 8B, the light incident surface 11 a has a plurality of prism-like convex portions 12 that run in the thickness direction of the light guide plate 11 and are unevenly formed. Here, between the convex part 12 and the convex part 12, there are a plurality of scale-like plane parts 13 substantially parallel to the thickness direction of the light guide plate 11. The prism-shaped convex portion 12 has a substantially triangular cross section by connecting a pair of inclined surfaces 12a and 12b.

  Further, in the light guide plate 11, as shown in FIG. 9, the light incident surface 11a is regarded as a pseudo plane due to the effect of the pair of inclined surfaces 12a and 12b in the prism-shaped convex portion 12 provided on the light incident surface 11a. At this time, even for light having a large incident angle incident on the light incident surface 11a, the angle formed between the normal lines of the light 15 and 17 after entering the light guide plate 11 is increased as compared with the light guide plate 1 as a result. With respect to the entire light incident surface 11a, the angle range of the light after entering the light guide plate 11 can be increased, and the light region 19 after entering the light guide plate 11 as shown in FIG. Becomes wider. Further, the planar portion 13 is incident on the light guide plate 11 as light 16 after entering the light guide plate 11 as in the case of the planar light incident surface 1 a of the light guide plate 1 described above.

JP 2003-262734 A (2nd page, FIG. 6) Japanese Patent Laid-Open No. 2002-196151 (page 3-5, FIG. 2)

However, in the light guide plate 11 described above, the light incident surface 11a formed by the prism-shaped convex portion 12 and the flat portion 13 is discontinuous as shown in FIG. The directivity of the light 15, 16, 17 after entering the inside of the optical plate 11 has a distorted shape as shown in FIG. 10. 9, the light 16 after entering the light guide plate 11 from the flat surface portion 13 of the light guide plate 11 exhibits the directivity indicated by the curve 104 in FIG. 9, the light 17 after entering the light guide plate 11 from one inclined surface 12a of the convex portion 12 exhibits the directivity indicated by the curve 105 in FIG. In addition, the light 15 after entering the light guide plate 11 from the other inclined surface 12b of the convex portion 12 in FIG. 9 exhibits the directivity indicated by the curve 103 in FIG. Thus, the directivity of the light 15, 16, 17 after entering the light guide plate 11 from the light incident surface 11 a is distorted, and the light after entering the light guide plate 11 corresponding to this directivity. There was a problem that the intensity distribution became non-uniform.
Further, in such a liquid crystal display device using a side-light type planar light source using the light guide plate 11 with non-uniform light intensity distribution, bright lines from the light source are generated, or luminance unevenness is generated on the display screen. There was a problem that the quality of the screen was remarkably lowered.

(Object of invention)
An object of the present invention is to solve the above-mentioned problems in the prior art, prevent the generation of bright lines near the light source, prevent uneven brightness, and make the light intensity distribution after entering the light guide plate uniform. It is providing the light-guide plate of a type | mold planar light source.

  In order to achieve the above object, the light guide plate of the present invention has a polygonal shape and has a light-transmitting surface as a light incident surface, and transmits light from a light source disposed facing the light incident surface. In the light guide plate that changes the optical path and emits planar illumination light from the upper surface to the illumination object, at least one corner of the corner of the plate member is chamfered, and the side surface formed by this chamfering Is a light incident surface, and unevenness including a smoothly continuous curved surface is formed on the light incident surface.

Further, the unevenness formed on the light incident surface is characterized in that concave portions made of smooth curved surfaces and convex portions made of smooth curved surfaces are alternately and repeatedly formed in the longitudinal direction of the light incident surface of the light guide plate. .
The curved surface formed on the light incident surface is a quadratic curved surface.
Further, the curved surface is roughened.
Further, the plate-like member has a substantially rectangular parallelepiped shape.

  As described above, in the light guide plate of the present invention, the corners of the plate-like member are chamfered, the side surface formed by the chamfering is used as a light incident surface, and the shape of the light incident surface is a continuous curved surface with a smooth surface. Thus, the directivity of light after entering the light guide plate can be corrected smoothly. Thereby, the intensity distribution of the light after entering the light guide plate is made uniform, and generation of bright lines and luminance unevenness in the vicinity of the light source can be prevented. As a result, a high-quality side light type planar light source can be configured by the light guide plate and the light emitting diode of the present invention. Further, if the liquid crystal display panel is illuminated by a sidelight type planar light source using the light guide plate of the present invention, it is possible to reduce the luminance unevenness on the display screen of the liquid crystal display device and display a high quality display screen.

  Hereinafter, embodiments of the present invention will be described in detail with reference to FIGS. 1 to 4. 1A and 1B are diagrams showing a sidelight type planar light source using a light guide plate according to the present embodiment. FIG. 1A is a plan view, and FIG. 1B is a cross-sectional view taken along the line DD in FIG. FIG. The light guide plate in the present embodiment is different from the prior art in the shape of the light incident surface, and the other basic configuration is similar to the above-described prior art. Therefore, the same components as those in the conventional example are given the same reference numerals and description thereof is omitted.

  As shown in FIG. 1, the side light type planar light source in the present embodiment includes a light guide plate 21 and a light source 2 as a light emitting diode (LED). The light guide plate 21 is made of a colorless and transparent plastic material or the like, and chamfers one corner 21d of a plate-like member having a substantially rectangular parallelepiped shape. A side surface formed by the chamfer is used as a light incident surface 21a, and the upper surface of the light guide plate 21 is formed. Is a light exit surface 21b. On the lower surface 21c opposite to the light emitting surface 21b, a plurality of minute wrinkles or a plurality of fine wrinkles are formed on the surface as means for reflecting the light 26 after entering the light guide plate 21 toward the light emitting surface 21b. The lower surface 21c is a light reflecting surface.

  The light source 2 is disposed at a position facing the light incident surface 21 a of the light guide plate 21. Irradiation light 25 emitted from the light source 2 enters from the light incident surface 21 a and then enters as light 26 after entering the light guide plate 21, and travels toward the light exit surface 21 b while being repeatedly reflected inside the light guide plate 21. The component having a critical angle or less is emitted from the light exit surface 21b of the light guide plate 21 as illumination light 28 to the outside. The illumination light 28 emitted to the outside illuminates the liquid crystal panel 7 from behind. Thereby, the sidelight type planar light source in the present embodiment forms a light emitting surface on the light emitting surface 21 b of the light guide plate 21, and forms a sidelight type planar light source by the irradiation light 25 irradiated from the light source 2. It is made like that.

  2 is an enlarged view of part B of FIG. 1, FIG. 2 (a) is a partially enlarged plan view showing a light incident surface 21a of the light guide plate 21, and FIG. 2 (b) is a partially enlarged perspective view of the light incident surface 21a. It is. As shown in FIG. 2, the light incident surface 21 a of the light guide plate 21 has a convex portion 22 made of a smooth curved surface extending in the thickness direction of the light guide plate 21 and a concave portion made of a smooth curved surface similarly extended in the thickness direction. 23 are alternately and repeatedly formed in the longitudinal direction of the light incident surface 21 a of the light guide plate 21, thereby forming unevenness including a smoothly continuous curved surface. Here, the unevenness is formed by directly connecting the convex portion 22 and the concave portion 23. Further, the convex portion 22 and the concave portion 23 are formed with smooth secondary curved surfaces, and are formed with a constant cross-sectional shape in the thickness direction of the light guide plate 21. Therefore, the cross-sectional shape of the convex portion 22 and the concave portion 23 is a quadratic curve.

The quadratic curve is not particularly limited. In the present embodiment, as shown in FIG. 3, the radius C in the x-axis direction and the y-axis direction are centered on the intersection 24 of the x-axis and the y-axis. The cross-sectional shape of the convex part 22 and the concave part 23 was formed by a quadratic curve composed of an elliptical arc of an ellipse 27 represented by an equation of x ² / C ² + y ² / D ² = 1 with a radius D of. That is, the ellipse 27 is divided by the y-axis passing through the center 24 of the ellipse 27, a quadratic curve made of one elliptical arc is used as the cross-sectional shape of the convex portion 22, and a quadratic curve made of the other elliptical arc is taken as the cross-sectional shape of the concave portion 23. It is a shape. Further, when the y-axis direction of the ellipse 27 at this time regards the light incident surface 21 a as a macroscopic plane, the shapes of the convex portions 22 and the concave portions 23 are formed so as to be parallel to the plane. Further, the radii C and D of the ellipse 27 are preferably set to predetermined values in the range of 30 to 500 μm.

  As described above, the light guide plate 21 in the present embodiment is guided by the incident light of the light source 2 from the light incident surface 21a formed of a continuous quadratic smooth quadratic curve as shown in FIG. The intensity distribution of the light 26 after entering the inside of the optical plate 21 is made uniform, and the directivity thereof is corrected to a smooth directivity as shown by the curve 106 in FIG. Thereby, generation of bright lines and luminance unevenness in the vicinity of the light source 2 can be prevented. Note that the curves 107 and 108 shown in FIGS. 4B and 4C change the value of D / C, which is the ratio of the radii C and D of the ellipse 27, and the convex portions 22 forming the light incident surface 21a. The directivity of the light 26 after entering the light guide plate 21 when the shape of the recess 23 is changed is shown. Thus, the directivity of the light 26 after entering the light guide plate 21 can be controlled by changing the shapes of the convex portions 22 and the concave portions 23. Therefore, the shape of the light incident surface 21a is optimized by changing the value of D / C which is the ratio of the radii C and D of the ellipse 27 in accordance with the positional relationship between the light guide plate 21 and the light source 2, and the like. The directivity of the light 26 after entering the light guide plate 21 can be corrected smoothly.

  Further, as shown in FIG. 1B, the light 26 after entering the inside of the light guide plate 21 propagates while being repeatedly reflected between the light emitting surface 21b and the lower surface 21c, and consists of a component having a critical angle or less. Illumination light 28 is emitted from the light exit surface 21 b and illuminated from behind the liquid crystal display panel 7. As a result, luminance unevenness on the display screen of the liquid crystal display panel 7 can be reduced and a high-quality display screen can be displayed.

In addition, in this embodiment, although the example which made the shape of the plate-shaped member the substantially rectangular parallelepiped was demonstrated, it is not limited to this, The case where a light-guide plate is formed from the other polygon-shaped plate-shaped member may be used. Applicable.
Moreover, although the corner part of one place of the plate-shaped member was chamfered to form a light incident surface, and one light source was disposed opposite to the light incident surface, the plurality of corner parts of the plate-shaped member were described. The present invention can also be applied to a side light type planar light source having a light guide plate that is chamfered to form a plurality of light incident surfaces and a light source that is disposed to face each light incident surface.

Further, the case where the convex portion and the concave portion having a quadratic cross section are alternately and repeatedly formed has been described, but the present invention is not limited to this, and for example, the convex portion having a multi-order curve such as a cubic or quadratic cross section. The portions and the recesses may be alternately and repeatedly formed.
Moreover, although the example which directly connects a convex part and a recessed part was demonstrated, it is not limited to this, You may connect between a convex part and a recessed part with a smooth curved surface.
Moreover, although the example which forms a convex part or a recessed part with one type of curved surface demonstrated, you may form a convex part or a recessed part combining several curved surfaces.

In this embodiment, the example in which the light incident surface of the light guide plate is not subjected to the surface treatment has been described. However, the present invention is not limited to this, and the light incident surface may be formed as a rough surface to be a light diffusion surface. Thereby, luminance unevenness can be further reduced.
In addition, the case where one type of convex portion and concave portion are alternately and repeatedly formed on the light incident surface has been described. However, the present invention is not limited thereto, and the convex portion is further away from the light source according to the directivity of irradiation light emitted from the light source. In addition, the shape of the recess may be gradually changed. Thereby, directivity can be made smoother.

  Further, in the present embodiment, the case where the light guide plate of the present invention is applied to the sidelight type surface light source of the liquid crystal display device has been described. However, the present invention is not limited to this, and the sidelight type surface light source of various lighting devices, display devices, and the like. Can be widely applied to.

It is a figure which shows the sidelight type planar light source using the light-guide plate in embodiment of this invention, Fig.1 (a) is a top view, FIG.1 (b) is DD sectional drawing of Fig.1 (a). is there. FIG. 2B is an enlarged view of a portion B in FIG. 1, FIG. 2A is a partially enlarged plan view showing a light incident surface, and FIG. 2B is a partially enlarged perspective view of the light incident surface. It is a partial enlarged plan view which shows the light-incidence surface of the light-guide plate in embodiment of this invention. It is a figure which shows the directivity of the light after injecting into the inside of the light-guide plate in embodiment of this invention. The principal part of the sidelight type planar light source in a prior art is shown, Fig.5 (a) is a top view, FIG.5 (b) is CC sectional drawing in Fig.5 (a). It is the elements on larger scale which show the light-incidence surface vicinity of the light-guide plate in a prior art. FIG. 7A shows the directivity of the light in the prior art, FIG. 7A shows the directivity of the irradiation light of the light source itself, and FIG. 7B shows the directivity of the light after entering the light guide plate. It is. FIG. 8A is a plan view of the light guide plate, and FIG. 8B is a partially enlarged perspective view showing a portion A of FIG. 8A. It is the elements on larger scale which show the light-incidence surface vicinity of the light-guide plate in a prior art. It is a figure which shows the directivity of the light after injecting into the inside of the light-guide plate in a prior art.

Explanation of symbols

1
Light guide plate 1a Light incident surface 1b Light exit surface 1c Lower surface 1d Corner 2 Light source (LED)
DESCRIPTION OF SYMBOLS 3 Reflective sheet 4 Diffusion sheet 5 Prism sheet 6a Irradiation light 6b from a light source Light 7 after entering the inside of a light guide plate 7 Liquid crystal panel 8 Illumination light 9 irradiated from a light guide plate Light region 11
Light guide plate 11a Light incident surface 11b Light exit surface 11c Lower surface 11d Corner portion 12 Protrusions 12a, 12b Slope 13 Plane portions 15, 16, 17 Light 19 after entering the inside of the light guide plate 21 Light guide plate 21a Light incidence Surface 21b Light exit surface 21c Lower surface 21d of light guide plate Corner 22 Projection 23 Concave 24 Ellipse center 25 Illumination light 26 Light after entering inside light guide plate 27 Ellipse 28 Illumination light 29 emitted from light guide plate Light region

Claims (5)

The side surface of a plate-shaped member having a polygonal shape and having translucency is used as a light incident surface, and light from a light source arranged opposite to the light incident surface is converted into an optical path from the upper surface to the illumination object. In the light guide plate that emits the illumination light of
A chamfer is applied to at least one of the corners of the plate-like member, and a side surface formed by the chamfering is used as a light incident surface, and irregularities including a smoothly continuous curved surface are formed on the light incident surface. A light guide plate characterized by comprising:   The unevenness formed on the light incident surface is characterized in that a concave portion made of a smooth curved surface and a convex portion made of a smooth curved surface are alternately and repeatedly formed in the longitudinal direction of the light incident surface of the light guide plate. The light guide plate according to claim 1.   The light guide plate according to claim 1, wherein the curved surface formed on the light incident surface is a quadratic curved surface. The light guide plate according to any one of claims 1 to 3, wherein the curved surface is a rough surface. The light guide plate according to claim 1, wherein the plate-like member has a substantially rectangular parallelepiped shape.

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