JP2005158427A - Surface light source device and display device using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface light source device having a high luminance used abundantly for a liquid crystal device. <P>SOLUTION: This is a surface light source device which has a light guide body having a light incident surface and a light outgoing surface, a light source provided opposed to the light incident surface, and a light focusing member arranged on the light outgoing surface of the light guide body. A light extraction mechanism of a projection shape in which the relation of the width W and the height H is H/W=0.1-1.5 in the advancing direction of the light from the light source is installed at the light outgoing surface of the light guide body with a pitch of 2H-8H, and the focusing member is constructed of a prism array in which a prism with its apex angle facing the light outgoing surface is arranged with a pitch of 1-500 μm, and the longitudinal direction of the prism array is arranged at right angles to the principally advancing direction of the light from the light source, and the apex angle is 20-48° against the normal line in the angle opposite side to the light source. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a surface light source device and a display device using the same.

  2. Description of the Related Art A transmissive liquid crystal display (display) device is frequently used as a display device such as a monitor for a personal computer or a thin TV. In such a transmissive liquid crystal display device, a planar illumination device, that is, a backlight (surface light source device) is usually provided on the back surface of the liquid crystal element. This surface light source device includes a linear light source such as a cold cathode discharge tube and a mechanism for converting light emitted from the linear light source into planar light.

  Specifically, a method of providing a light source directly under the back surface of the liquid crystal element (direct method), or a light source is installed on the side surface of a light-transmitting light guide such as an acrylic plate, and light is applied in a planar shape using the light guide. A method of obtaining a surface light source by converting (side light method) is representative. Especially in applications where thinning is important, the sidelight system is extremely effective and has been put into practical use. About this sidelight system, it is indicated by patent documents 1 and patent documents 2, for example.

  Various configurations have been proposed to realize a high-luminance surface light source device, but a configuration using a condensing sheet that aligns the direction of light emitted from the light guide as a typical configuration for a startup factory. Are known.

  A configuration example of such a conventional sidelight type surface light source device will be described with reference to FIG. A linear light source 2 is provided at one side end of the light-transmitting substrate, that is, the light guide 1 so as to face the side end face 1a and be substantially parallel. A reflector 3 is attached so as to cover the linear light source 2 so that direct light from the linear light source 2 and reflected light reflected by the reflector are incident on the light guide 1 from the side end surface (light incident surface) 1a. Configured.

  One surface 1b of the light guide 1 is a light emitting surface, and a light collecting sheet (prism sheet) 5 comprising a prism array 4 having a sawtooth cross section is observed on the light emitting surface 1b. It is arranged toward the person side. A light extraction mechanism 6 is provided on the surface 1c of the light guide 1 opposite to the light exit surface 1b. The light extraction mechanism 6 is formed by printing a large number of dots 6a in a predetermined pattern using light scattering ink. Further, a reflection sheet 7 is generally provided on the surface 1c side of the light guide plate 1 in proximity to the surface 1c.

  Another representative example of this type of surface light source device is shown in FIG. 5B, elements having the same functions as those in FIG. 5A are denoted by the same reference numerals, and redundant description is omitted. In the configuration shown in FIG. 5B, the condensing sheet 5 is opposite to the configuration in FIG. 5A on the light emitting surface 1 b with the apex angle facing the light emitting surface 1 b side of the light guide 1. Except that the surface 1c surface of the light guide 1 is provided with a large number of rough surface patterns 6b formed by roughening the light guide plate 1 instead of printing dots as a light extraction mechanism. The configuration is the same as that shown in FIG. About the structure which arrange | positions the apex angle of a condensing sheet | seat toward the light guide body side, it is disclosed also by patent document 3, for example.

  From previous studies, when using a condensing sheet, a triangular prism array with the apex angle directed to the light exit surface side of the light guide is used, and the illumination light is deflected and condensed in the front direction to obtain a surface light source. It is known that a surface light source device with higher performance can be obtained with the configuration of FIG.

JP-A-61-99187 JP 63-62104 A Japanese Patent Laid-Open No. 2-17

  Although the performance of the surface light source device has been improved year by year through attempts to increase the brightness, including the use of a light collecting sheet, there is still a strong demand for higher brightness. On the other hand, demands for so-called narrowing and thinning of display devices are increasing, and further reduction in thickness and size of surface light source devices are required. As a result, the diameter of the light source that can be used is also decreasing, and the need to use light emitted from the light source more efficiently is increasing.

  The present invention has been made in view of such problems, and an object thereof is to realize a surface light source device with higher luminance.

  That is, the gist of the present invention is that a light guide having a light incident surface and a light output surface, a light source provided to face the light incident surface, and a condensing member disposed on the light output surface of the light guide. The light emitting surface of the light guide has a relationship between the width W and the height H in the direction in which light from the light source mainly travels H / W = 0.1-1. Is formed with a prism array in which prisms whose apex angles are directed to the light exit surface are arranged at a pitch of 1 to 500 μm. The prism array is arranged so that the length direction of the prism array is orthogonal to the direction in which light from the light source mainly travels, and the apex angle is 20 to 48 ° at an angle opposite to the light source with respect to the normal line. It exists in the surface light source device characterized by these.

  Another gist of the present invention resides in a display device using the surface light source device of the present invention.

  With such a configuration, the surface light source device according to the present invention can achieve high luminance, and can be suitably used for a display device such as a liquid crystal display device.

Hereinafter, the present invention will be described in detail based on preferred embodiments with reference to the drawings.
FIG. 1 is an exploded perspective view showing an embodiment of a surface light source device according to the present invention. In the present embodiment, the surface light source device includes a substantially rectangular light guide 1, linear light sources 21 and 22 arranged to face a pair of parallel end faces of the light guide 1, a condensing sheet 5, and a reflection. It is composed of a sheet 7.

  The linear light sources 21 and 22 are generally cold-cathode tubes that are easily reduced in size, but are not limited thereto, and light sources such as hot-cathode tubes, LEDs, and EL elements can also be used. It is.

  Further, the arrangement and number of the linear light sources 21 and 22 are also arbitrary. For example, only one of the light sources is arranged, or a light source is further arranged facing the remaining pair of end surfaces of the light guide 1. It is possible.

  Although omitted in FIG. 1 for the sake of simplicity of description, a lamp reflector is actually disposed around the linear light sources 21 and 22 so that light emitted from the light source can be guided as efficiently as possible. 1 is incident on an end surface (light incident surface). The material used for the lamp reflector is not particularly limited as long as it has a high light reflectance. For example, a metal plate having an Ag vapor deposition layer, a white plastic film, or the like is preferably used.

  The light guide 1 is formed of a transparent resin such as PMMA, COP (cycloolefin polymer) and polycarbonate. Further, the thickness can be made substantially constant or a wedge shape in which the thickness decreases as the distance from the light source increases. As shown in FIG. 1, when the wedge shape is applied when the light sources are arranged to face each other, the thickness decreases from the end face facing the linear light sources 21 and 22 toward the center of the light guide 1. do it. As shown in FIG. 1, it is preferable to use a light guide having a substantially constant thickness when the light sources are arranged facing each other, and a wedge-shaped light guide when arranging the light sources so as to face the one end face.

  Light emitted from the linear light sources 21 and 22 is reflected directly or by a lamp reflector and enters the light guide 1 from the end face of the light guide. The incident light beam propagates through the light guide 1 while satisfying the total reflection condition based on Snell's law in geometric optics.

  In the surface light source device of this embodiment, in order to allow light propagating in the light guide 1 to be efficiently emitted from the light exit surface 10 and incident on the light collecting sheet 5, the light exit surface 10 of the light guide 1 has a protruding shape. The light extraction mechanism is provided. The light extraction mechanism is a mechanism that fulfills the function of emitting light rays propagating through the light guide body while satisfying the total reflection condition to the outside of the light guide body.

  In the present embodiment, as a light extraction mechanism, a projection 12 is provided on the light emitting surface 10 of the light guide 1, and a surface facing the light emitting surface 10 of the light guide 1 is processed into a prism array 11 shape. ing. The prism array 11 is formed by arranging a plurality of substantially triangular prisms, and is formed so that the longitudinal direction of the prisms is orthogonal to the length direction of the linear light sources 21 and 22. The apex angle of the prism is preferably 90 to 160 °, and the pitch is preferably 1 to 500 μm.

  The light extracted from the prism array 11 to the lower surface of the light guide 1 is reflected by the reflection sheet 7 made of a material having a highly reflective surface like the lamp reflector and is incident on the light guide 1 again.

  The light extraction mechanism provided on the lower surface of the light guide 1 is not limited to the prism array as shown in FIG. 1, and the light guide is formed by using ink in which light-scattering fine particles such as silica and titania are dispersed as a so-called dot pattern. By printing on the bottom surface, light is emitted outside the light guide by the light scattering phenomenon, and a rough surface is provided on the bottom surface of the light guide, and light is emitted outside the light guide using the light scattering phenomenon at the rough surface. Various configurations are used, such as a mode in which a slight inclined surface portion is provided on the lower surface of the light guide body, a mode in which light incident on the inclined surface portion is emitted outside the light guide body, and a mode in which protrusions are provided on the lower surface of the light guide body Is possible.

  The protrusion 12 that is a light extraction mechanism provided on the upper surface of the light guide 1 and is characteristic of the present invention is a protrusion having a horizontal cross-sectional shape such as a circle, a rhombus, a quadrangle, a triangle, or a semicircle. As shown in FIG. 2, the protrusion 12 preferably has a horizontal cross-sectional shape, preferably a central portion that is convex in the emission direction. Similarly to the prism array 11, the protrusion 12 is integrally formed with the light guide 1 by, for example, injection molding, and the upper end is rounded from the vicinity of H / 2, which is preferably approximately half of the height H of the protrusion. Has a shape. The tip shape of the protrusion 12 can be realized by controlling the mold temperature in the case of injection molding, for example.

  Here, the meaning of the round end of the protrusion 12 will be described. In the present embodiment, the light emitted from the light emitting surface of the light guide 1 is finally aligned in one direction by the light collecting sheet (prism sheet) 5. In order to effectively use the prism constituting the light collecting sheet 5, it is preferable that the light emitted from the protrusion 12 of the light guide 1 is not perpendicular to the light emitting surface but has a certain angle.

  That is, when the tip of the protrusion is not round and the upper surface of the protrusion has the same shape as the base portion, the incident angle of the light emitted from the upper surface of the protrusion to the prism array constituting the condensing sheet 5 is It is small and it becomes difficult to obtain the polarization (condensation) effect in the front direction by the prism array. On the other hand, when the tip of the protrusion is rounded, the light emitted from the tip is incident on the prism array of the condensing sheet 5 at a larger incident angle, so that a polarization (condensing) effect in the front direction is obtained. It becomes easy.

  The protrusion 12 preferably has a width W in the direction perpendicular to the length direction of the linear light sources 21 and 22 of 1 to 200 μm, and the height H is larger than the width W and H / W = 0.1-1. .5 is preferable. The center point distance (pitch) between adjacent protrusions is preferably 2H to 8H with respect to the height H. It is possible to adjust the amount of light extracted from the light guide 1 by changing the size and density of the protrusions 12 according to the distance from the linear light source.

  The portion of the light emitting surface 10 of the light guide 1 where the protrusions 12 are not provided is preferably flat, and specifically, the ten-point average roughness Rz is preferably 0.001 to 1.0 μm. . By flattening this portion, light scattering can be suppressed, and as a result, the light use efficiency is increased.

  The condensing sheet 5 is composed of a prism array formed with the apex angle downward, and the length direction of each prism is equal to the length direction of the linear light source (that is, on the lower surface of the light guide 1). The prism array to be provided and its direction are orthogonal to each other).

  The prism pitch is 1 to 500 μm, and the prism apex angle is preferably 20 to 48 ° with respect to the normal L and the angle θ opposite to the light source as shown in FIG. When two light sources are provided as in the present embodiment, the place where θ should be satisfied changes at the central portion that is the farthest from both light sources (FIG. 3B).

  Although not shown in FIG. 1, a diffusion sheet may be further disposed on the light collecting sheet 5. The diffusion sheet is provided in order to diffuse the light whose direction is aligned by the light collecting sheet 5 and to uniform the in-plane luminance, and is generally a translucent resin film.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to a following example, unless the summary is exceeded.

Example An area light source device having the same structure as that shown in FIG. 1 was manufactured except that there were two light sources on one side and a diffusion sheet was provided on the light collecting sheet 5.

  Specifically, a rectangular acrylic resin plate (manufactured by Mitsubishi Rayon, Acrypet TF8) having a size of 276.4 × 344.0 and a thickness of 8 mm (uniform) was formed as the light guide 1 by injection molding. At this time, a protrusion was integrally formed on the light emitting surface, and a prism array was integrally formed on the lower surface.

  The apex angle of the bottom prism was 140 °, the pitch was 50 μm, and the prism was formed so that the length direction of the prism was perpendicular to the length direction of the light source as shown in FIG. Further, the protrusion on the light emitting surface has a diameter of 54 μm, a height of 27 μm (H / W = 0.5), and a cylindrical shape with a rounded tip, and the length direction of the linear light source (X direction and The pitch in the direction orthogonal to the length direction of the linear light source (Y direction) is fixed at 120 μm (4.44H). Note that the protrusion pitch in the X direction is the closest to the light source and is maximized in a region corresponding to the central portion of the light source, and is minimized in the central portion of the light guide. In order to avoid interference between protrusions adjacent in the Y direction, the protrusion positions were randomly shifted within a radius of 20 μm so that adjacent protrusions on the same straight line in the Y direction were not located.

  The surface roughness of the light emitting surface of the light guide without protrusions was Rz = 2 μm (measured by VK-8500 manufactured by Keyence Corporation).

  As shown in FIG. 4, the linear light source is opposed to each of a pair of end faces corresponding to the long side of the light guide 1, and is a cold cathode tube (Sanken Electric Co., Ltd.) having a tube length of 349 mm, a tube diameter of 2.2 mm, and an electrode material Nb. Two lamps (made by Co., Ltd.) were arranged in parallel such that the lamp center distance was 3.4 mm. The distance between the end face and the light source was 1 mm.

  A plastic film-metal plate composite (Mitsubishi Resin: Alset (registered trademark)) in which a white polyester film (Toray: E60L) and stainless steel with a plate thickness of 0.2 mm were bonded together was used as the lamp reflector.

  As the reflection sheet, a polyester white reflection sheet (Toray, Lumirror E60L) is used, and a light collecting sheet is provided with a triangular prism array (pitch 50 μm, 34 degrees on both sides with respect to the normal line) on the upper part of the light guide. Mitsubishi Rayon's Diamond Art S165) was placed with the apex angle facing the light exit surface side of the light guide so that the length direction of the prism array was parallel to the length direction of the light source. Further, a diffusion sheet (manufactured by Tsujiden Co., Ltd., thickness 120 μm, haze value 74.5% according to JIS K7105) was disposed on the light collecting sheet to constitute an optical system of the surface light source device.

  Using the surface light source device configured as described above, the linear light source is turned on using a dedicated inverter unit so that the tube current becomes constant at 6.5 mA in an environment of room temperature 25 ° C. and humidity 56%, and lighting starts. The brightness was measured 15 minutes after.

  Luminance was measured in 25 points at an interval of 272.6 mm x 338.0 mm on the light exit surface (on the diffusion sheet) of the surface light source device at intervals of 62.6 mm in the Y direction and 79.5 mm in the X direction. Asked. The measuring instrument was a color luminance meter BM-7 manufactured by Topcon Engineering Co., Ltd., with a viewing angle of 1 ° and a measurement distance of 1.5 mm.

As a result of the measurement, the average luminance was 6670 cd / m ² .

Comparative Example A circular projection having a height of 2 μm and a diameter of 123 μm to 176 μm (H / W = 0.016 to 0.011) is provided on the light guide surface of the light guide, and the entire light output surface is blasted to obtain a surface roughness. The surface light source device was configured in the same manner as in Example except that Rz was set to about 0.7 μm (part without projection) and about 1.5 μm (projection part). The protrusions were provided at a fixed pitch of 80 μm (40H) in the X direction and 130 μm (65H) in the Y direction. In order to avoid interference between the protrusions adjacent to each other in the Y direction, the protrusion positions were randomly shifted within a radius of 40 μm so that the protrusions adjacent on the same straight line in the Y direction were not positioned.

When the luminance was measured in the same manner as in Example, the average luminance was 5353 cd / m ² .

It is a disassembled perspective view which shows the structural example of the surface light source device which concerns on embodiment of this invention. It is a figure explaining the shape of the processus | protrusion provided in the light-projection surface of a light guide in the surface light source device which concerns on embodiment of this invention. It is a figure explaining the prism shape of the condensing sheet used in the surface light source device which concerns on embodiment of this invention. It is a figure explaining the light source arrangement | positioning in an Example. It is a figure explaining the structural example of the conventional surface light source device.

Claims (5)

A surface light source device having a light guide having a light incident surface and a light output surface, a light source provided to face the light incident surface, and a light collecting member disposed on the light output surface of the light guide. Because
On the light emitting surface of the light guide, a protrusion shape having a relationship H / W = 0.1 to 1.5 between a width W and a height H in a direction in which light from the light source mainly travels. Are provided at a pitch of 2H to 8H,
The condensing member is composed of a prism array in which prisms whose apex angles are directed to the light exit surface are arranged at a pitch of 1 to 500 μm, and light from the light source mainly travels in the length direction of the prism array. The surface light source device is arranged so as to be orthogonal to a direction, and the apex angle is 20 to 48 ° at an angle opposite to the light source with respect to a normal line. 2. The surface light source device according to claim 1, wherein a tip portion of the light extraction mechanism has a rounded shape.   The prism array that constitutes the condensing member and a prism array whose length directions are orthogonal to each other are provided on a surface of the light guide opposite to the light emitting surface. The surface light source device described.   The surface light source device according to any one of claims 1 to 3, wherein a surface roughness of a portion of the light emitting surface where the protrusion is not present is 0.001 to 1.0 in Rz. .   The display apparatus using the surface light source device of any one of Claim 1 thru | or 4.

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