JP2006324169A - Low-profile surface light source and liquid crystal display using this - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a low-profile surface light source which can guide a light irradiated from a light emitter on the light source to the side on a low-profile optical waveguide without any loss utilizing the low-profile optical waveguide shorter than the light emitter on the light source, and a liquid crystal display using this low-profile surface light source. <P>SOLUTION: The liquid crystal display is provided with a surface light source element 10 comprising at least one or more optical outgoing means and a thin plate-shaped optical waveguide 3, and at least one or more light sources 2 for incidence of a light into the side 3a on the optical waveguide 3, which is set to be shorter than a light emitter 2a on the light source 2 in height. In addition, the liquid crystal display incorporates the optical input 6 and optical output 7 which are provided between the light emitter 2a on the light source 2 and the side 3a on the optical waveguide 3, and are different in height respectively depending on the difference in height between both sections mentioned above, as well as a fiber light guide 5 which forms a space in its inside and guides a light incoming from the light emitter 2a on the light source 2 to the side 3a on the optical waveguide 3. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a thin surface light source used for a mobile phone, a personal digital assistant (PDA), a video camera, a car navigation system, a personal computer, a computer monitor, a television receiver, an advertising billboard, and a liquid crystal display using the same. Relates to the device.

  Liquid crystal displays that have come to be widely used as medium and large display devices such as small display devices such as mobile phones, PDAs, video cameras, car navigation systems, personal computers, computer monitors, television receivers, advertising billboards, It consists of a surface light source element (backlight) that emits light in a planar shape and a transmissive or transflective liquid crystal display panel that provides image information, and the light transmittance is controlled by the image information provided by the liquid crystal display panel. Characters and images are displayed.

  Here, in the present specification, a configuration in which a light source composed of a light emitting diode (LED), a cold cathode tube (CCFL), or the like is arranged on a side surface of a light guide in a surface light source element (or a thin surface light source element) is a surface light source ( Alternatively, the surface light source element (or thin surface light source element) is composed of a light guide and at least one light emitting means for emitting light from the light guide.

  As a conventional technique related to this surface light source, there is a method of emitting light from a surface light source using scattered reflection by providing a light emitting means such as dot printing on the back surface of the light guide. Therefore, there is a problem that the brightness in the front direction becomes low (for example, Patent Document 1). On the other hand, in order to increase the luminance, it is necessary to use a light collecting member for controlling the emission angle represented by a prism sheet or the like in which a large number of linear prisms are arranged. However, using these components causes problems such as an increase in the thickness of the surface light source and an increase in cost when the liquid crystal display device is assembled.

  Various surface light sources have been proposed for the above-described problems (for example, Patent Documents 2, 3, and 4), and some have been put into practical use. In these surface light sources, since the functions of the prism sheet and the diffusion sheet can be combined with the surface light source element, it is considered that the surface light source can be thinned. However, it is assumed that the height of the side surface of the light guide used in the surface light source element is larger than the height of the light-emitting portion of the light source, and the surface light source is simply installed on the side surface of the light guide. However, a method for realizing further reduction in thickness is not disclosed.

Moreover, the light guide for converting a point light source into a linear light source other than the method of installing a light source in the side surface of a light guide may be used (for example, patent documents 5 and 6). According to the method using the light guide, it is possible to convert a point light source such as an LED into a corresponding linear light source on the side surface of the light guide, and there is an advantage that the surface light source can emit light uniformly. is there.
JP 2001-43716 A JP 2001-243822 A JP 2001-345008 A JP 2002-131555 A Japanese Patent Laid-Open No. 5-14619 JP-A-9-247368

  Due to recent technological development, components for liquid crystal display devices are being made thinner. Especially for small and medium-sized applications, the market demands reduction in thickness and weight, and proposals have been made to replace the glass substrate of a liquid crystal display panel with a plastic substrate. On the other hand, the surface light source currently occupies most of the liquid crystal display device in terms of thickness and weight, and it can be said that it is a very important issue to make the surface light source thinner and lighter.

  However, since the conventional light guide is based on the premise that the height of the light guide and the light source is approximately the same, the light guide is used on the side of the light guide that is thinner than the light source. There was a problem that it was difficult to make the light incident without loss.

  The present invention solves the above-described problems, and uses a thin light guide whose height is smaller than that of the light emitting portion of the light source, while losing light from the light emitting portion of the light source on the side portion of the thin light guide without loss. An object of the present invention is to provide a thin surface light source that can be guided and a liquid crystal display device using the same.

  In order to achieve the above object, a thin surface light source according to the present invention includes a surface light source element comprising at least one light emitting means and a thin plate-shaped light guide, and light is incident on a side surface portion of the light guide. In the thin surface light source comprising at least one light source for the light source, the height of the side surface portion of the light guide is set to be smaller than the height of the light emitting portion of the light source, Provided between the side surface of the light guide, and having a light incident part and a light emission part having different heights depending on the difference in height between the two, a space is formed inside, A fiber light guide that guides light incident from a light emitting portion of the light source and emits the light to a side portion of the light guide is provided.

  According to this configuration, the fiber light is provided between the light emitting portion of the light source and the side surface portion of the light guide body having a height smaller than the light source, and has different heights depending on the height difference between the two. Since it has a light entrance part and a light exit part, and a space is formed inside, at least the light entrance part and the light exit part according to the height difference between the light emitting part of the light source and the side part of the light guide By making the cross-sectional shapes different, the light from the light emitting portion of the light source can be guided to the side surface portion of the thin light guide without loss.

  Preferably, the light guide is such that the height of the light exit portion is smaller than the height of the light entrance portion. Preferably, the light guide is provided with a diffusing element on its inner wall. In this case, reflection loss on the inner wall can be suppressed.

  Preferably, the surface light source element includes an output light control plate in which the light output means has a plurality of convex portions, and an output surface of the light guide and an apex portion of the convex portions of the output light control plate are bonded to each other. It becomes. In this case, the surface light source element can be made thinner.

  The liquid crystal display device of the present invention uses the above-described thin surface light source. According to this configuration, the thin and light weight of the liquid crystal display device can be achieved by using the above-described thin surface light source.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic perspective view showing a thin surface light source according to an embodiment of the present invention. The thin surface light source 4 includes a thin light guide 3 such as a film and one or more light emitting means 14 such as dot printing that emit light from the light guide 3 (FIG. 2A). ) And a single light source 2 for allowing light to enter the side surface portion 3a of the light guide 3. The height of the side surface portion 3 a of the light guide 3 is set to be smaller than the height of the light emitting portion 2 a of the light source 2.

  The thin surface light source 4 according to the present invention is provided between the light emitting portion 2a of the light source 2 and the side surface portion 3a of the light guide 3, and guides light incident from the light emitting portion 2a of the light source 2 to guide the light. A light guide 5 that emits light to the side surface portion 3 a of the light body 3 is provided. The light guide 5 has a light incident portion 6 and a light exit portion 7 having different heights depending on the height difference between them, that is, has a height corresponding to the light emitting portion 2 a of the light source 2. It has a light incident portion 6 and a light exit portion 7 having a height corresponding to the side surface portion 3a of the light guide 3 having a height different from this, and a space is formed inside (FIG. 3). In this example, the light guide 5 has a tapered shape that gradually decreases in the height direction and gradually increases in the width direction from the light emitting portion 2a of the light source 2 to the side surface portion 3a of the light guide 3. However, the present invention is not limited to this, and any shape can be used as long as it has the light entrance portion 6 and the light exit portion 7 that are opened and a space is formed therein.

  It is preferable that the light incident portion 6 of the light guide 5 has the same shape and size as the light emitting portion 2a of the light source 2 used for the thin surface light source. When the light incident part 6 of the light guide 5 is larger than the light emitting part 2a of the light source 2, the light that has entered the light guide 5 is returned to the light incident part 6 side by regular reflection or scattering reflection on the inner wall. In this case, the light is not irradiated in the direction of the light source 2 and causes light leakage at the light incident portion 6. In particular, when a general surface mount LED is used as the light source 2, the light exit surface of the LED is formed of a light scatterer, so that the light irradiated on the light exit surface is scattered again in the direction of the light guide 5. Will be reflected. Therefore, it is important to make the size of the light incident portion 6 of the light guide 5 the same as that of the light emitting portion 2 a of the light source 2. On the other hand, when the light incident part 6 of the light guide 5 is smaller than the light emitting part 2 a of the light source 2, there is light that is not incident on the light guide 5, so that the light use efficiency decreases. The height of the light output portion 7 of the light guide 5 needs to be the same as or smaller than the height of the side surface portion 3a of the light guide 3 used in the surface light source element 10. Further, the width of the light exiting portion 7 of the light guide 5 may be the same as or smaller than the width of the side surface portion 3 a of the light guide 3. In order to secure the amount of light from the light incident part 6 in the light exit part 7, it is preferable to make the cross sectional area (area of the opening part) of the light incident part 6 larger than the cross sectional area (area of the opening part) of the light exit part 7.

    Examples of the material of the light guide 5 used in the present invention include metals having high visible light reflectivity, and it is particularly preferable to use silver or aluminum. The light guide 5 is obtained by processing these metals into the above-described tapered shape.

  As shown in FIG. 3, it is preferable to provide a diffusion element 8 such as barium sulfate on the inner wall of the light guide 5. When the inner wall is a metal surface, light traveling straight from the light incident part 6 is regularly reflected by the inner wall. Therefore, when the light guide 5 has a tapered shape, the regular reflection of light is repeated, whereby the light incident part 6 is repeated. The problem is that light is returned to the side. Furthermore, although the reflectance of the metal is relatively high, the silver or aluminum exemplified above causes a reflection loss of several percent. That is, even if the light is not returned to the light incident part side by forming fine irregularities on the metal surface, the reflection loss cannot be prevented. On the other hand, by providing the diffusing element 8 on the inner wall, the light traveling straight from the light incident part 6 is scattered and reflected by the inner wall, and the ratio of returning light to the light incident part 6 side is reduced. Can do. Further, if the light is scattered and reflected by the diffusing element 8, almost no reflection loss occurs as in the case of using metal. In addition, the light guide 5 which provides the diffusing element 8 may be the above-described metal or plastic, and the material is not limited.

Hereinafter, the operation of the light guide 5 in the thin surface light source 4 will be described. FIG. 2A is a schematic cross-sectional view showing a thin surface light source 4 according to the present invention.
First, as shown in FIG. 2C, in the conventional surface light source 11, the height of the light emitting portion 12a of the light source 12 such as an LED is smaller than the height of the side surface portion 13a of the light guide 13, so that the light source Light can be incident from 12 to the light guide 13 without loss (incident light on the light guide 13 is indicated by an arrow). On the other hand, in the thin surface light source 4 as an object of the present invention, the height of the light emitting portion 2a of the light source 2 is larger than the height of the side surface portion 3a of the light guide 3 as shown in FIG. In the case where the light source 2 is simply disposed on the side surface portion 3a of the light guide 3 without using the light guide 5 according to the present invention, a part of the light emitted from the light source 2 is the light guide. The light is lost without being incident on the light 3 (the loss light is indicated by a dotted arrow).

  As shown in FIG. 2A, the thin surface light source 4 according to the present invention generally uses the light guide 5 according to the height difference between the light emitting part 2a of the light source 2 and the side surface part 3a of the light guide 3. In correspondence with this, there is a difference in the width of the light emitting part 2a and the side face part 3a of the light guide 3, so that the cross-sectional shapes of at least the light incident part 6 and the light emitting part 7 are different from each other. Shape. In addition, the cross-sectional shape of the internal space also changes continuously from the cross-sectional shape of the light entrance portion 6 to the cross-sectional shape of the light exit portion 7.

  Due to the shape of the light guide 5, the light incident on the light incident part 6 of the light guide 5 without loss from the light emitting part 2 a of the light source 2 travels straight until reaching the inner wall of the light guide 5, and the light reaching the inner wall diffuses. Due to reflection on the wall surface to which the element 8 is applied, the light travels in another direction, propagates through the inside of the light guide 5 without loss while repeating this reflection phenomenon, and reaches the light output portion 7 of the light guide 5. By emitting light from the light emitting portion 7 of the light guide 5 to the side surface portion 3a of the light guide 3 without loss, light is extracted to the viewer side by the light emitting means in the surface light source element 4, so that it functions as a thin surface light source. Fulfill.

  As described above, in the present invention, the light guide 5 is provided between the light emitting portion 2a of the light source 2 and the side surface portion 3a of the light guide 3 having a smaller height than the light guide portion 2a. Accordingly, the light input part 6 and the light output part 7 having different heights are provided, and a space is formed therein, so that the height of the light emitting part 2a of the light source 2 and the side face part 3a of the light guide 3 is increased. By making at least the cross-sectional shapes of the light incident portion 6 and the light exit portion 7 different according to the difference, the light from the light emitting portion 2a of the light source 2 can be guided to the side surface portion 3a of the thin light guide 3 without loss. .

  The surface light source element used in the present invention is not particularly limited as long as it is a system using at least a light guide, and is a dot printing system of a paint in which a diffusing material is added to the back surface of the light guide, the light guide surface and / or the back surface. A surface light source element having a light emitting means of any method, such as a pattern forming method for forming irregularities and grooves on the surface, and a scattering light guide method in which a diffusing material is added to the light guide, can be used. However, since the above surface light source element must use at least one optical sheet such as a reflection sheet, a diffusion sheet, and a prism sheet, the thickness of the surface light source element is increased by that amount. It cannot be said that it is an optimal method for realizing a light source.

  For this reason, the surface light source element 10 shown in FIG. 4 is preferably used so as to realize further thinning. The surface light source element 10 uses an output light control plate 15 having a plurality of convex portions 9 as light output means to control the output angle of the output light, and the output surface (surface) of the light guide 3 and the output light control. The top of the convex portion 9 of the plate 15 is bonded. This surface light source element is referred to, for example, in USP 5,396,350, Japanese Patent Application Laid-Open No. 2005-38749, Japanese Patent Application Laid-Open No. 2005-38750, and the like. Since the surface light source element does not need to use another optical sheet, it is very suitable for the thin surface light source of the present invention.

  A liquid crystal display device can be obtained by disposing a liquid crystal display panel on the exit surface side of the thin surface light source of the present invention. The liquid crystal display panel used here is not particularly limited, but in order to achieve a reduction in the thickness of the liquid crystal display device, a film that is thinner and more flexible than glass can be used as the substrate of the liquid crystal display panel. preferable.

EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited at all by these Examples.
Example 1
A plurality of substantially hemispherical convex portions having a height of 0.02 mm and a width of 0.02 mm were formed on a 40 mm * 30 mm * 0.125 mm PMMA film (Sanduren, Kaneka Co., Ltd.) to produce an outgoing light control plate. . Next, the output light control plate includes a light guide body in which a UV curable adhesive is applied to the surface of a 50 mm * 40 mm * 0.125 mm PMMA film, and a top portion of a convex portion of the produced output light control plate. After bonding so that it might be arrange | positioned at the center part of a light guide, the surface light source element was produced by irradiating UV.

  The light guide has a thickness of 0.125 mm, which is much thinner than an LED light source (CITILED CL432S, Citizen Electronics Co., Ltd.) having a light emitting portion having a height of 0.6 mm. Therefore, a thin surface light source was produced as follows by arranging the light guide between the light guide and the LED light source. Barium sulfate was applied to an aluminum plate having a thickness of 0.1 mm to form a complete diffusion surface. Further, as in FIG. 3, the light incident portion of the aluminum plate is set to 2.8 mm * 0.6 mm having the same area as the light emission size of the LED, and the light emitting portion is 16 mm * to be thinner than the thickness of the light guide. It was set to 0.1 mm. Two light guides were prepared, and two light guides 5 and two LED light sources 2 were installed on the side surface portion 3a of the light guide 3 as shown in FIG.

  When two lamps of the LED light source 2 are turned on in the thin surface light source, the light emitted from the LED light source 2 propagates through the light guide 5 and further enters the surface light source element 10, whereby the thin surface light source. 4 was confirmed to emit light uniformly in the plane.

It is a schematic perspective view which shows the thin surface light source concerning one Embodiment of this invention. (A)-(C) are schematic sectional drawings which show the effect | action of the light guide of this invention. It is the schematic sectional drawing and projection drawing which show the light guide of this invention. It is a schematic perspective view which shows the surface light source element of this invention. It is a schematic plan view which shows the thin surface light source concerning other embodiment of this invention.

Explanation of symbols

2: Light source 3: Light guide 4: Thin surface light source 5: Light guide 6: Light incident part 7: Light emission part 8: Diffusion element 9: Convex part 10: Surface light source element 15: Emission light control plate

Claims (5)

A thin surface light source comprising: a surface light source element comprising at least one light emitting means and a thin plate-shaped light guide; and at least one light source for allowing light to enter the side surface of the light guide. ,
The height of the side part of the light guide is set smaller than the height of the light emitting part of the light source,
Provided between the light emitting part of the light source and the side surface of the light guide, and having a light incident part and a light emitting part having different heights depending on the height difference between the two, and a space inside A thin surface light source comprising: a light guide that guides light incident from a light emitting portion of the light source and emits the light to a side surface portion of the light guide. The thin surface light source according to claim 1, wherein the light guide has a height of the light exit portion smaller than a height of the light entrance portion. 3. The thin surface light source according to claim 1, wherein the light guide has a diffusing element on its inner wall. The surface light source element comprises an output light control plate in which the light emitting means has a plurality of convex portions, and an output surface of the light guide and a top portion of the convex portions of the outgoing light control plate are bonded. The thin surface light source according to any one of claims 1 to 3. A liquid crystal display device using the thin surface light source according to any one of claims 1 to 4.

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