JP2007200741A - Light guide plate for edge light type backlight - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light guide plate for an edge light type backlight capable of increasing light utilization efficiency by returning a component having reached an end surface without being used as emission light to the inside of the light guide plate. <P>SOLUTION: A surface relief structure 12 having a function for reflecting a part of a straight-advancing component 8 in the front or back surface direction of this light guide plate 2 is arranged on an end surface 7. A metal reflecting surface 10 is arranged outside the end surface; and a part of the straight-advancing component refracted, transmitted and scattered by the surface relief structure is reflected by the metal reflecting surface, and is directed in the front or back surface direction of the light guide plate. A metal thin-film layer 11 is formed on a surface of the surface relief structure, and a part of the straight-advancing component is reflected and scattered in the front or back surface direction of the light guide plate by the metal thin-film layer. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a light guide plate used for an edge light type backlight for a liquid crystal display device.

  Currently, liquid crystal display devices for mobile phones and personal digital assistants that are widely used mainly use edge-light type backlights as illumination devices. The backlight of such a liquid crystal display device needs to illuminate the entire plane with high luminance and no luminance unevenness.

  In recent years, a method of processing a V-shaped groove of the order of several tens of μm has become the mainstream as an injection method using a light guide plate used for a backlight, instead of the conventional white dot printing method. Further, in order to reduce luminance unevenness and increase luminance, it is common to use optical sheets such as a scattering diffuser plate and a prism sheet.

  FIG. 1 shows a configuration of an example of a general edge light type backlight. The backlight is provided on the back surface of the liquid crystal panel, and includes a white light source 1 such as a light emitting diode (LED) or a cold cathode tube lamp (CCFL), a light guide plate 2 on which a V-shaped groove emission pattern 3 is disposed, and a light guide. A reflecting plate 4 provided on the back side of the light plate 2, a scattering diffuser plate 5 provided on the front side of the light guide plate 2, and a prism provided on the front side of the scattering plate to collect light It consists of a sheet 6.

  Light from the light source 1 enters the light guide plate 2 from the end face of the light guide plate 2. The light guide plate 2 is a transparent plate for spreading the light incident from the end face and emitting it, and acrylic resin or polycarbonate is mainly used. The light guide plate 2 has a V-shaped groove injection pattern 3 mainly formed on the lower surface thereof. The light incident on the light guide plate 2 propagates by repeating total internal reflection, and is scattered or reflected by the emission pattern 3 and emitted from the upper surface of the light guide plate 2.

  The reflection plate 4 is provided on the back surface side of the light guide plate 2 and functions to return light leaking from the back surface of the light guide plate 2 toward the light guide plate 2.

  The scattering diffuser plate 5 is provided on the exit surface side of the light guide plate 2 and has a role of making the in-plane distribution of luminance uniform. A diffusion pattern may also be provided on the upper surface of the light guide plate 2, and the luminance unevenness is reduced together with the scattering diffuser plate 5.

  The prism sheet 6 is provided on the upper side of the scattering diffuser plate 5 and functions to increase the peak luminance of the exit surface by imparting directivity to the light emitted from the scattering diffuser plate 5. Further, it plays the role of aligning the traveling direction of the light emitted from the scattering diffuser plate 5 in a direction substantially perpendicular to the surface of the light guide plate.

  The problem with edge-lit backlights is that light utilization efficiency is low. Since light is incident from the end face, many components such as a straight component from the light source that escape from the end face are generated without being used. Such components not only reduce the light use efficiency, but also cause uneven brightness near the end face. Here, the termination surface 7 is an end surface facing the end surface on which the light source is arranged.

As a means for solving this problem, it has been conventionally proposed to provide a reflection layer outside the termination surface 7, but this method can recycle the component that escapes from the termination surface of the light guide plate to some extent. Since it is difficult to control the light intensity intentionally, the light utilization efficiency cannot be sufficiently increased, and the generation of noise light and unevenness cannot be prevented. As another means, there is a method of providing a black absorption layer on the end face. According to the method described in Japanese Patent Application Laid-Open No. 2002-131551, light omission and end face reflection can be prevented, but there is no effect of improving the light utilization efficiency.
JP 2002-131551 A

  In the light guide plate used for the edge light type backlight, the component that reaches the end face without being used as the emitted light is returned to the light guide plate, and the light use efficiency is improved. It is an object to provide a light plate.

  In the edge light type backlight light guide plate of the liquid crystal display device according to the present invention, a part of the straight component of light from the light source is reflected in the front or back direction of the light guide plate on the end surface facing the end surface where the light source is arranged. An edge-light type light guide plate for a backlight, which is provided with a surface relief structure having a function of reflecting and scattering and refracting and transmitting other portions.

  In the edge light type backlight light guide plate according to the present invention, the surface relief structure is an optical element structure having a cylindrical lens shape, a prism shape, a sine wave shape, or a rectangular wave cross section. It is the light guide plate for edge light type backlights characterized.

  In the edge light type backlight light guide plate according to the present invention, an inclination angle of the working surface of the optical element structure with respect to a terminal surface is in a range of 15 ° to 22.5 °. This is a light guide plate for an edge light type backlight.

  Further, the present invention is the edge light type backlight light guide plate according to the above invention, wherein the surface relief structure is a unidirectional scattering optical element structure whose main scattering direction is in the front or back direction of the light guide plate. An edge light type light guide plate for backlight.

  Further, the present invention provides the edge light type backlight light guide plate according to the above invention, wherein an inclination angle with respect to the end face in the main scattering direction is in a range of 45 ° to 60 °. Light guide plate.

  Further, the present invention provides the light guide plate for an edge light type backlight according to the above invention, wherein the surface relief structure is an optical element structure having a rough surface of isotropic scattering. It is a light guide plate.

  Further, according to the present invention, in the edge light type backlight light guide plate according to the above invention, a metal reflecting surface is disposed outside the terminal surface, and another part of the rectilinear component refracted and transmitted / scattered by the surface relief structure is added to the metal. An edge-light type light guide plate for backlight, which is reflected by a reflection surface and is directed to the front surface or the back surface of the light guide plate by the surface relief structure.

  Further, the present invention provides the light guide plate for an edge-light type backlight according to the above-mentioned invention, wherein a metal thin film layer is provided on the surface of the surface relief structure, and the other part of the straight traveling component is provided on the surface or back surface of the light guide plate by the metal thin film layer. An edge light type light guide plate for backlight, which reflects and scatters in the direction.

Further, the present invention is the edge light type backlight light guide plate according to the above invention, wherein the surface relief structure is integrally formed on a terminal surface.

  In the edge light type backlight light guide plate according to the present invention, the surface relief structure is provided by bringing a sheet having a surface relief structure into close contact with an end surface. It is a light guide plate for backlight.

  The present invention provides an edge light type backlight in which a surface relief structure having a function of reflecting a part of a straight traveling component of light from a light source toward a front surface or a back surface of a light guide plate is provided on a terminal surface facing an end surface on which a light source is disposed. Therefore, the component that has reached the end face without being used as the emitted light is returned to the light guide plate, and the edge light type backlight light guide plate is improved in light use efficiency.

  In the present invention, a metal reflecting surface is disposed outside the end surface, and another part of the straight component refracted and transmitted / scattered by the surface relief structure is reflected by the metal reflecting surface, and the light guide plate is reflected by the surface relief structure. The light guide plate for the edge-light type backlight that has the front or back direction or a metal thin film layer on the surface of the surface relief structure, and a part of the straight component is reflected or reflected by the metal thin film layer in the front or back direction of the light guide plate. Since it is the edge light type backlight light guide plate to be scattered, it becomes an edge light type backlight light guide plate with further improved light utilization efficiency.

  Hereinafter, embodiments of the light guide plate for an edge light type backlight according to the present invention will be described in detail. FIG. 2 is a conceptual diagram showing a cross section of an edge light type backlight using the light guide plate for the edge light type backlight of the present invention. As shown in FIG. 2, the edge light type backlight includes a white light source 1 such as a light emitting diode (LED) or a cold cathode tube lamp (CCFL), a V-shaped groove injection pattern 3 on the back surface, and a termination surface 7 on the end surface 7. The light guide plate 2 on which the surface relief structure 12 is disposed, the reflection plate 4 provided on the back surface side of the light guide plate 2, the scattering diffuser plate 5 provided on the front surface side of the light guide plate 2, and the light is condensed. For this purpose, the prism sheet 6 is provided on the surface side of the scattering diffuser plate.

As shown in FIG. 3, when light enters the light guide plate 2 from the light source 1 and propagates, the propagating light travels by being repeatedly reflected at an angle that satisfies the total reflection condition. When the light guide plate 2 is made of an acrylic resin, the critical angle θ ₀ is 41.8 ° (≈42 °) when the refractive index is about 1.5, and 42 ° or more is formed on the lower surface 21a and the upper surface 21b of the light guide plate. Light incident at an angle is confined in the light guide plate by total reflection and propagates.

  However, as shown in FIG. 4, for example, most of the light component 8 entering the light guide plate from the light source reaches the end surface 7 without being utilized, causing low light use efficiency. ing. In order to effectively use the straight component 8, it is only necessary to change the traveling direction of the straight component 8 at the end surface 7 into the light guide plate.

  At that time, if converted into a component propagating in the front or back direction of the light guide plate, it is scattered or reflected by the back side injection pattern 3 as shown in FIG. Thus, the utilization efficiency of light can be improved by making it possible to use the component which has reached the end surface 7 without being used as the light emitted from the light guide plate upper surface 21b.

As shown in FIG. 6, as the surface relief structure 12 on the end surface 7, at least one structure (a) having a convex or concave cylindrical lens, at least one structure (b) having a prism, a sinusoidal cross section By providing an optical element structure such as a structure (c) having a shape and a structure (d) having a rectangular wave-like cross-sectional shape, the traveling direction of a part of the light that reaches the end surface 7 without being used can be determined. Or it can be changed to the back side direction. Thereby, the effective guided light component in the light guide plate can be remarkably increased.

  When the straight component 8 reaches the end surface 7 provided with the optical element structure, a part of the light is reflected, reflected / scattered, refracted, and / or transmitted / scattered according to the provided optical element structure. The direction of travel changes. At that time, refraction and transmission scattering mainly occur as shown in FIG. In order to reuse the transmitted light thus generated, it is necessary to dispose a metal reflecting surface 10 such as a metal plate behind the end surface 7. In addition, in order to reuse light more efficiently, the metal thin film layer 11 may be provided on the surface of the end surface provided with the optical element structure. Then, as shown in FIG. 8, when the straight component reaches the terminal surface on which the optical element structure is provided, the light that becomes the main refraction and transmission scattering becomes reflection and reflection scattering, and the light guide plate The direction of travel is changed to the front or back direction of

When the light guide plate is made of acrylic resin, the critical angle θ ₀ is about 42 °, and the desirable angle of light incident on the upper surface 21a or the lower surface 21b of the light guide plate is about 45 ° to 60 °.

As shown in FIG. 9, when it is assumed that the optical element structure 12 is provided on the terminal surface 7 and the linear component is reflected by the action of the optical element structure, the inclination angle of the working surface 17 of the optical element structure 12 with respect to the terminal surface 7 is θ Then, the incident angle with respect to the end surface is θ, the reflection angle is θ, and the angle of reflection and incidence on the lower surface 21a or the upper surface 21b of the light guide plate is 90-2θ. At this time, since the desirable angle of light incident on the lower surface 21a or the upper surface 21b of the light guide plate is about 45 ° to 60 °,
90-2θ = 45 ° -60 °
2θ = 30 ° -45 °
θ = 15 ° to 22.5 °
It becomes.

As shown in FIG. 10, for example, when the optical element structure is at least one cylindrical lens, the pitch is desirably about 100 μm. Further, φ corresponds to a half-angle value, and is preferably within the above θ. The radius of curvature r is r = P / 2 · sinφ
r: radius of curvature P: lens pitch φ: obtained from a half-angle value, for example, when φ = 22.5 ° and P = 100 μm, r = 130 μm.

  As shown in FIG. 11, for example, when the optical element structure is at least one prism, the pitch is preferably about 100 μm. Further, the inclination angle θ of the working surface is preferably 15 ° to 22.5 °.

  As shown in FIG. 12, for example, when the optical element structure has a sinusoidal cross-sectional shape, the pitch is preferably about 100 μm. Further, the inclination angle θ of the working surface is preferably 15 ° to 22.5 °.

  The surface relief structure may be a unidirectional scattering structure in which the scattering direction is limited. At this time, it arrange | positions so that the main scattering structure may be the surface or back surface direction of a light-guide plate.

The unidirectional scattering structure is a structure in which elongated concavo-convex structures having a length, width, depth, etc. of about several microns are randomly arranged, and the minor axis direction of the concavo-convex structure is the thickness direction of the light guide plate. It is assumed that they are installed almost in parallel. In such a structure, since it scatters strongly in the minor axis direction of the elongated concavo-convex structure, by setting the minor axis direction of the concavo-convex structure to substantially coincide with the thickness direction of the light guide plate, it is directed toward the front or back surface of the light guide plate. The scattering effect can be obtained.

  The surface relief structure may be a rough surface that isotropically scatters. Isotropic scattering is uniform scattering in all directions, and scattering occurs in directions other than the front or back direction of the light guide plate, but light that reaches the end surface without being used is converted to light in an effective angular range. We can expect conversion effect.

  For example, in the case of injection molding, the optical element structure as described above can be manufactured by applying an optical element structure to a terminal surface portion of an injection mold by performing die processing by cutting with a metal blade or the like. . Thereby, the optical element structure can be integrally formed on the terminal surface.

  Further, when a metal thin film layer is provided in the optical element structure, vapor deposition is performed with a mask so that the metal thin film layer is not formed except on the end face.

  Or you may arrange | position the sheet | seat in which the optical element structure was formed closely_contact | adhered to the terminal surface of a light-guide plate. At this time, the light guide plate and the optical sheet are in close contact with each other optically. Further, a metal thin film layer may be provided in advance on the surface of the optical sheet by vapor deposition or the like.

It is a conceptual diagram of a general edge light type backlight. It is a conceptual diagram which shows the edge light type backlight using the light guide plate for edge light type backlights of this invention in a cross section. It is explanatory drawing which shows incidence | injection of the light in the light guide plate in this invention, and propagation of the light in a light guide plate. It is explanatory drawing which shows that light leaks from a termination | terminus surface in a general edge light type backlight. It is explanatory drawing which shows the behavior of the light in the termination | terminus surface in this invention. It is explanatory drawing of the surface relief structure in this invention. It is explanatory drawing which shows the behavior of the light in the termination | terminus surface in this invention. It is explanatory drawing which shows the behavior of the light in the termination | terminus surface in this invention. In this invention, it is explanatory drawing which shows a mode that light reflects in a termination | terminus surface. It is explanatory drawing when a surface relief structure is cylindrical lens shape. It is explanatory drawing when a surface relief structure is prism shape. It is explanatory drawing when a surface relief structure is a sine wave form.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Light source 2 ... Light guide plate 3 ... Emission pattern 4 ... Reflection plate 5 ... Scattering diffuser plate 6 ... Prism sheet 7 ... Termination surface 8 ... Straight component 9 ... Extra light 10 ... Metal reflecting surface 11 ... Metal thin film layer 12 ... Surface relief structure (optical element structure)
17 ... Working surface 21a ... Lower surface 21b of the light guide plate ... Upper surface of the light guide plate

Claims (10)

  In the edge light type backlight light guide plate of the liquid crystal display device, a part of the straight component of the light from the light source is reflected, reflected and scattered in the front or back direction of the light guide plate on the end face facing the end face where the light source is arranged. An edge-light type light guide plate for backlight, which is provided with a surface relief structure having a function of refracting and transmitting and scattering another part.   2. The light guide plate for an edge light type backlight according to claim 1, wherein the surface relief structure is an optical element structure having a cylindrical lens shape, a prism shape, a sine wave shape, or a rectangular wave cross section.   The light guide plate for an edge light type backlight according to claim 2, wherein an inclination angle of the working surface of the optical element structure with respect to the terminal surface is in a range of 15 ° to 22.5 °.   2. The light guide plate for an edge light type backlight according to claim 1, wherein the surface relief structure is a unidirectional scattering optical element structure having a main scattering direction in a front or back direction of the light guide plate.   The edge light type backlight light guide plate according to claim 4, wherein an inclination angle of the main scattering direction with respect to the end face is in a range of 45 ° to 60 °.   2. The light guide plate for an edge light type backlight according to claim 1, wherein the surface relief structure is an optical element structure having a rough surface of isotropic scattering.   A metal reflecting surface is arranged outside the terminal surface, and another part of the straight component that is refracted and transmitted / scattered by the surface relief structure is reflected by the metal reflecting surface, and the surface relief structure causes the front or back surface of the light guide plate to The light guide plate for an edge-light type backlight according to claim 1, wherein:   A metal thin film layer is provided on the surface of the surface relief structure, and the metal thin film layer reflects and reflects and scatters another part of the straight component in the front or back direction of the light guide plate. 4. The light guide plate for an edge light type backlight according to 4, or 5.   The light guide plate for an edge light type backlight according to any one of claims 1 to 8, wherein the surface relief structure is formed integrally with a terminal surface.   The edge light type backlight guide according to any one of claims 1 to 8, wherein the surface relief structure is provided with a sheet having a surface relief structure in close contact with a terminal surface. Light board.

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