JP2008103272A - Highly efficient planar light source element using planar side face light source - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a planar light source that is highly efficient and environment-friendly by adhering the whole side of a light guide body having an emitting light control sheet to a planar side light source which uses electroluminescence (EL). <P>SOLUTION: By optically coupling the whole side of the light guide body into which light is made incident from at least one side face where the emitted light control sheet is installed with the planar side light source as the incident light by means of physical sticking or scientific adhesion, light loss caused by the total reflection of the emitted light from the light source to the side face of the light guide body is prevented, and the light from the light-emitting face of the light guide body can be taken out efficiently toward the front direction while brightness unevenness is made less. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a high-efficiency, environmentally friendly surface light source element used in a direct-view liquid crystal display device such as a personal computer, a monitor for a portable terminal, a video camera, a television receiver, a car navigation system, and a manufacturing method thereof.

  A transmissive display device typified by a liquid crystal panel includes a surface light source element (backlight) that emits light in a planar shape and a display panel in which pixels are arranged in a dot shape. Characters and images are displayed by controlling the transmittance. As a surface light source element to be used, a cold cathode tube (CCFL), a reflector, a lens or the like is used to control the luminance distribution of emitted light, a cold cathode tube is provided on the end face of the light guide, The incident light from the cold cathode tube is emitted from a surface perpendicular to the end face of the light guide, and the cold cathode tube is provided at the lower part of the light guide (direct type). A surface light source element using a cold cathode tube is mainly used in a liquid crystal projector that requires high luminance. On the other hand, since a surface light source element using a light guide can be thinned, it is often used for a direct-view liquid crystal TV, a display of a personal computer, and the like.

  Surface light source elements used in displays such as liquid crystal TVs, notebook personal computers, and portable terminal monitors are required to reduce power consumption and to have high luminance and low luminance unevenness. Furthermore, recent displays are strongly required to be thin and consider the environment. Conventional surface light source elements generally scatter light from the light source by providing a reflective sheet on the back side of the light guide, printing dots on the back side of the light guide, or forming an uneven pattern (molding). This improves the light extraction efficiency of the light source. Furthermore, it is possible to increase the luminance of the surface light source element by increasing the number of light sources such as cold cathode fluorescent lamps, but this method is not practical because it leads to an increase in power consumption. Therefore, a surface light source element having a configuration in which an outgoing light control sheet capable of efficiently extracting light is provided on a light guide as shown in FIG. 3 has been proposed (see Patent Document 1, Patent Document 2, and the like). According to this surface light source element, total reflection of light is utilized, and there is little loss of light and high brightness can be realized. However, the volume of the light source is still reduced by using a cold cathode tube (CCFL). There is a limit to reducing the incident light loss from the cold cathode fluorescent lamp to the light guide body.

  On the other hand, a surface light source element composed of a light emitting diode (LED) as a point light source and a light guide as shown in FIG. 4 has been proposed (see Patent Document 3 and the like). According to this surface light source element, the luminance is improved by using a large number of LED light sources according to the size of the display element. It is difficult to eliminate unevenness completely. Further, FIG. 5 proposes a surface light source element in which the light emitting surface of the LED light source and the incident end surface of the light guide are in optical contact (see Patent Document 4 and the like). According to this surface light source element, the light from the point light source is transmitted through the mediator whose refractive index difference between the light emitting surface of the LED that is the point light source and the material constituting the light guide is 0.1 or less. Although a surface light source element that suppresses total reflection and has a uniform brightness in the light guide surface is intended, it is a point light source, but has not yet solved the luminance unevenness of the light guide surface. FIG. 6 also proposes a surface light source element in which the light emitting surface of a stripe-shaped electroluminescent element (OLED) and the incident end face of the light guide are in optical contact with each other with respect to the thickness of the light guide ( (See Patent Document 5). According to this surface light source element, when a conventional CCFL is used as a side light source, the side surface of the light guide (1.0 mm) of 1.5 mm or less, which was technically difficult, and the longitudinal direction of the side surface of the light guide A light emitting surface (OLED) having a linear shape (stripe shape, width 0.1 mm) along the surface is optically bonded to provide a thin surface light source, but the light emitting surface used as incident light guides light. Since the stripe shape is thinner than the thickness of the body, the luminance of the light guide is not improved and the luminance unevenness is not solved.

JP-A-8-2221013 JP 2001-307524 A JP 2001-155524 A JP 2005-38755 A Japanese Patent Laid-Open No. 10-050124

  In recent years, there has been a strong demand for reducing the thickness of a transmissive display element, reducing the power consumption, and improving the environment. On the other hand, the EL light source is thin, and if the EL light source is used as a backlight of the display element, a transmissive display element or the like can be thinned. However, the EL light source has a problem of low luminance. On the other hand, in a surface light source element composed of a light guide having an output light control sheet having a plurality of convex portions on one surface, light is propagated using total reflection of light at the output light control sheet and the light guide. Therefore, there is little loss of light and high brightness can be realized. However, the desired luminance may not be obtained depending on the type of the light guide.

  The present invention has been made in view of the above problems, and is a highly efficient and environmentally friendly planar light source capable of efficiently extracting incident light from a side EL light source in the front direction of the light guide and its manufacture. It aims to provide a method.

  The surface light source element of the present invention that solves the above-mentioned problems is the entire at least one side surface of the light guide including an outgoing light control sheet having a plurality of uneven portions on at least one surface in order to efficiently extract light in the front direction. A planar light source having an electroluminescence (EL) element as a side light source is optically coupled. According to the present invention, it is possible to prevent light loss due to total reflection of incident light from the side light source with the side surface of the light guide, and to efficiently extract light from the output surface in the front direction of the light guide. .

  The light guide is provided with a plurality of convex portions (double-sided molding) on both sides with respect to at least one outgoing surface for outgoing light control, or a plurality of convex portions are provided on at least one outgoing surface. A light guide provided with the emitted light control sheet is used, and light incident on the top of the convex portion from the light guide at an angle greater than a critical angle is extracted by the convex portion. A plurality of convex portions may be provided on the surface opposite to the surface facing the light source of the emission light control sheet.

  Of the light emitted from the light emitting layer, the electroluminescence light source is incident on the transparent substrate covering the light emitting layer at a critical angle or more, and is totally reflected from the air layer and is not emitted from the transparent substrate. In the present invention, the entire side surface of the light guide and the electroluminescent side light source are optically joined without an air layer, thereby preventing total reflection from the side EL light source and improving the incident efficiency to the light guide. Thus, the light extraction efficiency of the surface light source element can be improved. This can increase the luminance of the surface light source element (improve the luminance with respect to the front direction of the light guide by about 30% at the maximum).

  According to the present invention, the entire side surface of the light guide including the double-sided shaped type having the outgoing light control unit and the outgoing light control sheet and the light emitting surface of the electroluminescence (EL) element are optically arranged without an air layer. The surface light source can be obtained with high efficiency and environment-friendliness without causing unevenness of brightness.

The principle of the present invention will be described with reference to FIGS. FIG. 2 shows a light source (EL light source 1) having a general electroluminescence composed of a transparent substrate 5 typified by transparent glass, a transparent electrode 6 typified by ITO and the like, a light emitting layer 7 and a metal layer 8. FIG. When the refractive index of the transparent substrate 5 is n and the emission side is air, the critical angle is obtained by θc = Sin ⁻¹ (1 / n) (however, the refractive index of air is 1). In the light that reaches the interface between the transparent substrate 5 and air, when the incident angle to the transparent substrate 5 is smaller than the critical angle, the light is refracted and emitted at the interface between the transparent substrate 5 and air (FIG. 2). Light ray L1) shown in FIG. Light incident at an angle larger than the critical angle propagates again through the transparent substrate 5 by total reflection. This reflected light is reflected again at the interface between the EL light-emitting layer 7 and the metal electrode 8. When the surface layer of the metal electrode 8 is parallel to the surface of the transparent substrate, the surface of the transparent substrate 5 and the metal electrode 8 are reflected. Multiple reflections are repeated with the surface layer, and the light is not emitted from the transparent substrate 5 (light ray L2 shown in FIG. 2).

  On the other hand, in the case of a surface light source element in which the LED side surface light source of the point light source is integrated with the light guide, it is possible to increase the brightness of the surface light source by increasing the number of the LEDs used. Due to the presence of a dark space between them, there is a concern about the occurrence of uneven brightness of the surface light source and an increase in power consumption due to an increase in the number of LEDs. In addition, it is difficult to solve the above problem even in a surface light source in which a planar stripe-shaped EL light source thinner than the thickness of the side surface of the light guide is used as side surface incident light. In the present invention, the material for forming the electroluminescent layer of the EL light source used as the planar side light source may be any of an organic material, an inorganic material, and an organic / inorganic hybrid material. Further, according to the present invention, light confined in the EL light source due to total reflection occurring in the EL light source covered with the transparent substrate can be taken out by adhering to or adhering to the entire surface of the light guide body. It can be used regardless of the configuration.

  FIG. 1 is a schematic view of a surface light source element of the present invention obtained by adhering to a light emitting surface of the transparent substrate 4 of an EL light source and a side surface of a light guide provided with an emitted light control sheet 3. A surface of the EL side light source that faces the transparent substrate 4, that is, a light guide body in which a plurality of convex portions are formed on the top and bottom for controlling emitted light, or an output light control sheet 3 in which a plurality of convex portions are formed. The light incident surface of the light guide is adhered and integrated with the exit surface of the transparent substrate 4 of the EL light source 1. The light generated from the light emitting layer 6 of the EL light source 1 shown in FIG. 1 propagates through the transparent substrate 4 and reaches the light emitting surface.

  The cross-sectional shape of the convex pattern may be constituted by either a straight line or a curved line. In the case of a curved line, a parabola, an ellipse, or a combination of these curves is desirable. It should be noted that by changing the shape of the convex portion provided on the incident surface side of the outgoing light control plate and the shape of the convex portion provided on the outgoing surface side, the luminance peak is oblique to the outgoing surface of the planar light source element. Can be directed.

  In the present invention, the plurality of convex portions (microprism array) provided in the outgoing light control unit may not have periodicity, but may have a one-dimensional or two-dimensional periodic structure. When the plurality of convex portions provided on the outgoing light control plate have periodicity, it is desirable that the ratio of the height of the convex portion to the period (pitch) of the convex portion is in the range of 1/3 to 2. If it is smaller than this range, refraction and reflection at the convex wall surface may be difficult to occur, and if it is larger than this range, EL emitted light from other than the close contact portion of the convex portion may be refracted by the convex portion. Because. The period is preferably in the range of 10 μm to 5 cm. When the convex portion is a one-dimensional pattern, the angular distribution only in the direction orthogonal to the groove direction of the convex portion can be controlled. However, when the convex portion is a two-dimensional pattern, the angular distribution in both directions is controlled. Can be controlled.

  When providing a convex portion of a one-dimensional pattern on both the surface facing the light source of the outgoing light control plate and the surface opposite to the surface (exit surface), the convex portions of the one-dimensional pattern are in a direction perpendicular to each other It is desirable to be provided. By providing a convex portion on the exit surface, the exit light control plate can have a function of controlling the angular distribution of the exit light from the planar light source element as well as taking out the light from the EL light source. . Brightness can be increased by configuring the projections provided on the exit surface side of the exit light control plate to form a prism array.

  The convex portions on the surface of the emission light control can be formed by a hot press method, a 2P method by ultraviolet curing, a 2P method by thermal curing, an injection molding method using a female mold, or the like. For example, a stamper used for producing an outgoing light control plate is obtained by coating a negative or positive photosensitive resin on a glass substrate, exposing the photosensitive resin through a photomask, and performing electroforming after development. Can be produced. The outgoing light control plate does not have to be plate-shaped and may be sheet-shaped. Since both the plate shape and the sheet shape are rich in mass productivity, they can be manufactured in large quantities at a low cost. Moreover, the pattern of the convex part of the emitted light control plate may be arranged not only one-dimensionally but also two-dimensionally. A microlens array may also be provided on the light exit surface of the exit light control plate.

  Examples of the resin used for forming the light guide include those having excellent transparency such as polycarbonate resin and polystyrene resin in addition to the acrylic resin. The light guide can be formed by cutting using a panel saw and an NC milling machine. In this case, for example, after cutting a few millimeters larger than the reference dimension using a panel saw, rough cutting is performed using a Compaqs blade on an NC milling machine, and further precision cutting is performed using a diamond blade on the NC milling machine. .

  The said convex part of the emitted light control sheet used by this invention is produced by press-molding an acrylic board, for example. In addition, an ultraviolet curable resin is applied on a transparent film such as a TAC film, an acrylic film, a PET film, a PC film, and the ultraviolet curable resin is irradiated by irradiating ultraviolet rays (UV) by pressing a female mold against the film. It can also be produced by peeling the molded product from the female mold after curing. A light guide provided with an outgoing light control sheet can also be produced by injection molding using a transparent resin. The contact portion between the projection tip of the outgoing light control sheet and the light guide body needs to be optically coupled to take light from the light guide body into the outgoing light control sheet. By selecting and using UV curable adhesives, adhesives such as hot melt adhesives, pressure sensitive adhesives and double-sided tapes, or by using a direct bonding method such as a melt pressure bonding method realizable.

  The close contact between the transparent substrate of the side EL light source and the entire side surface of the light guide needs to be optically coupled in order to capture the light emitted from the EL light source from the transparent substrate to the side of the light guide. There is a physical and chemical adhesion as such an adhesion method. Of the adhesives such as UV curable adhesives, hot melt adhesives, adhesive materials such as polyvinyl alcohol, and double-sided tapes, select one with excellent transparency, or use a direct bonding method such as a melt pressure bonding method. This can be realized by using Alternatively, bonding can be performed using an ultraviolet (UV) curable adhesive.

  The surface light source elements described above can be used for liquid crystal backlights, advertising backlights, room lighting, signs, and the like. In particular, a display device can be configured by using the surface light source element described above as a backlight and providing a transmissive display element on the emission surface. Examples of the transmissive display element include liquid crystal panels such as STN, TFT, and MINI.

<Example 1>
Hereinafter, the present invention will be described in more detail with reference to examples. As the light guide, a PMMA light guide (50 mm (L) × 50 mm (W) × 5 mm (t)) manufactured by Kuraray Co., Ltd. having dots printed on the reflection surface was used. A film tape with an Al reflective film is applied to the side of the light guide except for the side where the side light source is in close contact, a reflection film made by Kimoto is placed on the reflective surface, and a diffusion sheet made by Kimoto is made on the outgoing light surface. A prism sheet was placed. The electroluminescence light source used as side light is a TPD (triphenylamine-based hole transport material) and Alq3 (8-aluminum quinolinol, electron transporting light-emitting material) on a transparent substrate (glass) with a transparent electrode ITO by vapor deposition. After laminating (film thickness is 500 nm), an Al electrode is formed by vapor deposition (film thickness is 1000 nm) and sealed with a glass cap in a glove box, and the side surface has the same area as the thickness of the light guide. A light source (light emitting area 50 mm (L) × 5 mm (W)) was obtained. For adhesion of the transparent substrate of the obtained EL light source and the light incident surface side of the light guide, an appropriate amount of an aqueous solution of polyvinyl alcohol manufactured by Kuraray Co., Ltd. was used as an adhesive, and after dropping an appropriate amount on the light incident surface of the light guide, The transparent substrate side was bonded (optically bonded) and left at room temperature for 1 hour. The evaluation of the planar light source uses a luminance-voltage-current (LVI) measuring device dedicated to the EL light source, and first sets the current density so that a certain luminance can be obtained by applying an electric field to the EL light source, The front luminance of the outgoing light from the center of the light guide and the luminance unevenness due to the exit location of the light guide were measured with constant luminance as incident light.

<Example 2>
A PMMA light guide (50 mm (L) x 50 mm (W) x 5 mm (t)) manufactured by Kuraray Co., Ltd. was used as the light guide. As the outgoing light control sheet, an outgoing light control sheet using an OP film (Mirabu light) manufactured by Kuraray Co., Ltd., in which a plurality of convex portions for controlling the outgoing light from the light guide is patterned on a PET film (thickness: 125 μm). Generated from a high-pressure mercury lamp after applying UV curable resin to the thickness of about 10μm on the convex portion of the light guide and one side of the light guide, and bonding the UV curable resin surface and the acrylic light guide with a laminator A weak ultraviolet ray to be irradiated is irradiated from the PET film side (120 mJ) to obtain a semi-cured ultraviolet curable resin layer. Thereby, it can prevent that a convex part is embed | buried in an ultraviolet curable resin layer, and can make only the front-end | tip of this convex part point-bond. Then, the PET film is peeled off to obtain a state where an adhesive is applied on the light guide plate. The outgoing light control sheet is pressed from above (pressure 29419.95 Pa) and pasted using a laminator. Finally, ultraviolet rays emitted from a high-pressure mercury lamp were irradiated from the outgoing light control sheet side (2.0 J), and the ultraviolet curable resin was completely cured to obtain a light guide with an OP film. A film tape with an Al reflective film was attached to the side surface of the light guide except for the side surface to which the side light source was bonded, and a reflection film made by Kimoto was placed on the reflective surface. The method for producing the side EL light source and the method for bonding the light guide and the method for evaluating the obtained surface light source were evaluated in the same manner as in Example 1.

<Comparative Example 1>
For comparison with Example 1 above, using the light guide described in Example 1 and the EL side light source, contact the light incident side of the light guide and the transparent substrate of the EL light source without complete adhesion (optical coupling). A planar light source was obtained. The evaluation method of the obtained surface light source was evaluated by the same method as in Example 1.

<Comparative example 2>
For comparison with Example 2, the surface light source is obtained by using the light guide described in Example 2 and the EL side light source and bringing the light incident side of the light guide into contact with the transparent substrate of the EL light source without completely bonding them. Got. The evaluation method of the obtained surface light source was evaluated by the same method as in Example 1.

  Table 1 shows the results of measuring and comparing the center front luminance of the surface light source for the EL side light source in Example 1 and Comparative Example 1, and in Example 2 and Comparative Example 2.

  From the above results, the central front luminance of the surface light source in which the transparent substrate of the EL side light source and the light guide side surface are completely bonded (optically coupled) using an adhesive of an aqueous PVA solution (Example 1, 2) It was found that the front luminance of the surface light source (Comparative Examples 1 and 2) in which the transparent substrate of the EL side light source was in contact with the light guide side surface was improved by 80% or more. In addition, as for the luminance unevenness of the light guide, since the side light source is a planar light source regardless of the bonding method between the side EL light source and the light guide, the luminance unevenness due to the measurement place was less than 3% and was hardly recognized. .

<Comparative Example 3>
For comparison with the second embodiment, the stripe-shaped EL light source having a light emitting area (50 mm (L) × 5 mm (W)) of 25% of the side surface of the light guide as a side light source and a side light source described in the second embodiment. A planar light source having the same amount of incident light (total luminous flux) as in Example 2 was prepared. The method for producing the side surface EL light source and the method for bonding the light guide and the method for evaluating the obtained surface light source were evaluated in the same manner as in Example 1. From the above results, it was found that the emission-side front luminance of the light guide is only 80% of the light guide of Example 2. It was also found that the luminance unevenness of the light guide was large as 10% or more depending on the measurement location.

It is a schematic structure perspective view of the surface light source element of this invention. It is a ray tracing figure in the conventional surface light source element using EL. It is a schematic sectional drawing which shows the structure of the conventional surface light source element. It is a schematic perspective view which shows the structure of the conventional surface light source element. It is a schematic perspective view which shows the structure of the conventional surface light source element. It is a schematic sectional drawing which shows the structure of the conventional surface light source element.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Electroluminescence (EL) side light source 2 Adhesive layer 3 Light guide 4 Emission light control sheet 5 Transparent substrate 6 Transparent electrode 7 EL light emitting layer 8 Electrode layer 9 Light guide emission surface 10 Cathode-ray tube fluorescent lamp light source (CCFL)
11 Reflector 12 Light source (LED)
13, 14 Up and down convex recess

Claims (5)

  A primary light source, a light guide that guides light from the primary light source, and an outgoing light control sheet having a plurality of uneven portions on at least one surface of the light guide, A planar light source element, wherein at least one entire side surface and a planar light source having an electroluminescence element (hereinafter sometimes referred to as an EL element) as a side light source are optically coupled.   As a method of optically coupling at least one side surface of the light guide and the side light source, a physical method by heat fusion or the like without using an air layer in order to prevent total reflection and scattering of the side light source, or 2. The surface according to claim 1, wherein the adhesion layer or the adhesion layer is provided by a chemical method using an adhesive having a refractive index higher than that of the substrate of the side light source and lower than that of the light guide. Light source element.   The said light guide body consists of a transparent member which has an output surface in at least one direction and is provided with a plurality of concave and convex portions having a function of diffuse reflection or regular reflection of internal propagation light from external light. The planar light source element described.   The planar light source element according to any one of claims 1 to 3, wherein an electroluminescent element using an organic material, an inorganic material, or an organic / inorganic hybrid material as a light emitting layer is used as the side light source.   The surface according to any one of claims 1 to 6, wherein a light emission source is a bottom emission type in which emitted light is extracted from the transparent substrate side or a top emission type electroluminescence extracted from the transparent electrode side as the side light source. Light source element.