JP2012079681A - Light guide plate and surface light source device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light guide plate capable of reducing unevenness of incident light near a light source accompanying downsizing of a surface light source device.SOLUTION: The light guide plate includes a substrate which has first and second principal planes and a plurality of side faces surrounding the first and second planes, first optical elements which are mounted on the first principal plane and extended in a direction perpendicular to a first side face of the substrate, and second optical elements 18 which are arranged to be spaced apart from each other over an entire surface of the second principal plane except for a light-incident area. In a cross section perpendicular to the first side face, each second optical element 18 has: a first slope 22, with which a normal line heading for the inside of the substrate intersects the first side surface; and a second slope 24 opposed to the first slope 22. An angle formed between the first side face and each of a face containing the normal line of the first slope 22 and that of the second principal plane and a face containing the normal line of the second slope 24 and that of the second principal plane is in a range of 90°±10°. In a cross section parallel to the first side face, the second optical element has opposed slopes 25, and a range of their projection area to the second principal plane is greater than 0.0001 mmand less than 0.023 mm.

Description

  The present invention relates to a light guide plate and a surface light source device for irradiating a liquid crystal display element or the like from the back.

  The liquid crystal display element does not emit light by itself. Therefore, in order to display an image, a surface light source device that emits illumination light to the back surface of the liquid crystal display element is required. The surface light source device includes a light guide plate that guides light incident from a light source and emits the light from a light exit surface.

  The surface light source device is required to have high luminance and high efficiency without display unevenness. In order to concentrate the emitted light efficiently on the display part of the liquid crystal display element, it has been proposed to make the distribution density of the optical elements arranged on the lower surface of the light guide plate non-uniform, and when using a linear light source, it is diffused. It has been proposed to arrange the pattern elements in parallel with the longitudinal direction of the linear light source (see Patent Document 1). It has also been proposed to use a downward prism sheet or an upward prism sheet on the light exit surface of the light guide plate (see Patent Documents 2, 3 and 4).

  A conventional surface light source device using a downward prism sheet includes a light source, a light guide plate, a reflection member, a downward prism sheet, and a diffusion sheet. The light guide plate is disposed to face the light emitting surface of the light source. The reflection member is disposed on the lower surface of the light guide plate. The downward prism sheet is disposed on the upper surface of the light guide plate. The diffusion sheet is disposed on the downward prism sheet.

  A plurality of point light sources such as light emitting diodes (LEDs) are used as the light source. In the light guide plate, one side surface facing the light source is a light incident surface, one main surface orthogonal to the light incident surface is a light output surface, and the other main surface is a reflection surface. The reflective surface is provided with an optical groove extending in a direction parallel to the light incident surface. In order to make the illumination light uniform, a plurality of fine optical grooves extending in a direction orthogonal to the light incident surface may be arranged on the light exit surface.

  Light emitted from the light source is introduced into the light guide plate from the light incident surface. The light is repeatedly reflected by the optical groove on the reflecting surface in the light guide plate, and is emitted out of the light guide plate through the light output surface when the angle exceeds the critical angle. The light emitted to the outside of the light guide plate is deflected in the normal direction of the light output surface by the downward prism sheet, and further radiated through the diffusion sheet. The diffusion sheet is disposed in order to prevent moiré with the liquid crystal display element. If there is no moiré, no diffusion sheet may be provided.

  On the other hand, a conventional surface light source device using an upward prism sheet includes a light source, a light guide plate, a reflection member, a diffusion sheet, and one or two upward prism sheets. The light guide plate is disposed to face the light emitting surface of the light source. The reflection member is disposed on the lower surface of the light guide plate. The diffusion sheet is disposed on the upper surface of the light guide plate. One or two upward prism sheets are disposed on the diffusion sheet.

  A plurality of point light sources such as light emitting diodes (LEDs) are used as the light source. In the light guide plate, one side surface facing the light source is a light incident surface, one main surface orthogonal to the light incident surface is a light output surface, and the other main surface is a reflection surface. The reflective surface is provided with an optical groove extending in a direction parallel to the light incident surface. In order to make the illumination light uniform, a plurality of fine optical grooves extending in a direction orthogonal to the light incident surface may be arranged on the light exit surface.

  Light emitted from the light source is introduced into the light guide plate from the light incident surface. The light is repeatedly reflected by the optical groove on the reflecting surface in the light guide plate, and is emitted out of the light guide plate through the light output surface when the angle exceeds the critical angle.

  The light emitted to the outside of the light guide plate is diffused by the diffusion sheet in order to make the brightness in the light output surface uniform, and further radiated through the upward prism sheet. The one or two upward prism sheets are arranged to collect the light diffused by the diffusion sheet in the normal direction of the light exit surface and improve the front luminance. Although the upward prism sheet may be arranged in a single sheet, it is possible to improve the light collection efficiency and further improve the front luminance by arranging the two sheets so that the ridge lines of the prisms are almost orthogonal to each other. Two are mainly arranged.

  These proposed surface light source devices achieve high brightness and high efficiency by emitting light with strong directivity from the light guide plate. For this reason, the light diffusion in the light guide plate is weak, and in the vicinity of the light incident surface, each of the light incident portions facing the plurality of light sources has a bright portion, and each of the light incident portions facing the plurality of light sources has a dark portion and an incident portion. Incident light unevenness such as strong bright lines occurs in the vicinity of the light part.

  In order to improve the light incident unevenness, a method has been proposed in which light is reflected from the lower surface of the light guide plate and reflected again to the light guide plate by an optical groove formed on the reflection surface of the reflecting member (see Patent Document 5). The optical groove provided in the reflecting member has a shape that diffuses light in a region corresponding to the vicinity of the light incident surface of the light guide plate.

  In addition, in order to improve the light incident unevenness, a method is adopted in which light is diffused on the light incident surface of the light guide plate so that the light is uniformly incident on the light guide plate. Alternatively, light may be diffused on the light exit surface of the light guide plate so that the light is uniformly emitted from the light exit surface. In this case, a rough surface pattern or a lens pattern processed by blasting or the like is disposed on the light incident surface or the light exit surface. Irradiation unevenness can be improved by a method of diffusing light on the light incident surface.

  However, in recent years, with the downsizing of surface light source devices, the distance from the light incident surface facing a plurality of light sources to the effective light emitting area (display area of the liquid crystal display element) of the surface light source device tends to be shortened. Light unevenness is likely to occur. For this reason, the conventional method cannot sufficiently improve the incident light unevenness.

JP-A-11-231797 JP 2005-142078 A JP 2008-218418 A JP 2006-208869 A International Publication No. 05/061957 Pamphlet

  SUMMARY OF THE INVENTION An object of the present invention is to provide a light guide plate and a surface light source device capable of reducing unevenness in incident light in the vicinity of a light source accompanying downsizing of the device.

To achieve the above object, according to a first aspect of the present invention, there is provided a first and second main surfaces facing each other, a substrate having a plurality of side surfaces surrounding the first and second main surfaces, and a first main surface. A plurality of first optical elements extending in a direction perpendicular to the first side surface of the substrate and a plurality of first optical elements arranged apart from each other over the entire light-excluding area near the first side surface of the second main surface. Each of the plurality of second optical elements includes a first slope on which a normal line toward the inside of the base body intersects the first side face and a first slope in a cross section cut perpendicularly to the first side face. Each of a first plane having a second slope facing each other and including a normal of the first slope and a normal of the second main surface, and a plane including a normal of the second slope and a normal of the second main surface, and the first The angle formed with the side surface is in the range of 90 ° ± 10 °, and the cross-sections cut parallel to the first side surface are inclined to face each other. Has a side surface, the area of each projected onto the second major surface is greater than 0.0001 mm ^2, and summarized in that a light guide plate in the range of less than 0.023 mm ^2.

    According to a second aspect of the present invention, there is provided a surface light source device for irradiating a liquid crystal display element, the light guide plate according to the first aspect of the present invention and a light incident surface opposite to the light incident surface. Arranged to face the light source arranged, the reflecting surface of the light guide plate, the reflecting member that reflects the light incident from the reflecting surface into the light guide plate, and the light exit surface opposite to the reflecting surface The gist of the present invention is a surface light source device including a condensing member that condenses light by controlling the propagation direction of light incident from the light exit surface.

  ADVANTAGE OF THE INVENTION According to this invention, the light-guide plate and surface light source device which can reduce the light reception nonuniformity near the light source accompanying size reduction of an apparatus can be provided.

It is a side schematic diagram showing an example of a surface light source device using a downward prism sheet according to an embodiment of the present invention. It is the side schematic diagram which shows the other example of the surface light source device which uses the upward prism sheet which concerns on embodiment of this invention. It is a bird's-eye schematic showing an example of a light guide plate concerning an embodiment of the invention. It is the schematic which shows an example of the upper surface of the light-guide plate shown in FIG. It is the schematic which shows an example of the AA cross section of the light-guide plate shown in FIG. It is a figure which shows an example of the lower surface of the light-guide plate shown in FIG. It is a plane schematic diagram showing an example of the 2nd optical element concerning an embodiment of the invention. It is the schematic which shows an example of the BB cross section of the light-guide plate shown in FIG. It is the schematic which shows an example of CC cross section of the light-guide plate shown in FIG. It is the side surface schematic diagram which shows the other example of the surface light source device which concerns on embodiment of this invention. It is the side surface schematic diagram which shows the other example of the surface light source device which concerns on embodiment of this invention.

  Next, embodiments of the present invention will be described with reference to the drawings. In the following description of the drawings, the same or similar parts are denoted by the same or similar reference numerals. However, it should be noted that the drawings are schematic, and the relationship between the thickness and the planar dimensions, the ratio of the thickness of each layer, and the like are different from the actual ones. Therefore, specific thicknesses and dimensions should be determined in consideration of the following description. In addition, it goes without saying that the drawings include portions having different dimensional relationships and ratios.

  The embodiments described below exemplify apparatuses and methods for embodying the technical idea of the present invention, and the technical idea of the present invention is subject to various modifications within the scope of the claims. Can be added.

  The light guide plate 3 according to the embodiment of the present invention is used for the surface light source device using the downward prism sheet 5 shown in FIG. 1 and the surface light source device using the two upward prism sheets 6 and 6a shown in FIG. be able to. The light guide plate 3 includes a base body 4, a plurality of first optical elements 16 provided on the first main surface 12 of the base body 4, and a plurality of second optical elements provided on a second main surface 14 facing the first main surface. 18 is provided.

  The structure of the light guide plate 3 is common to the surface light source device shown in FIGS. 1 and 2, and a substantially rectangular base 4 is used as shown in FIGS. 3, 4, and 6. Of the four side surfaces surrounding the first and second main surfaces 12 and 14 of the substrate 4, one side surface is defined as a first side surface and the side surface opposite to the first side surface is defined as a second side surface. In addition, when using for a surface light source device, let the 1st side surface be the light-incidence surface 10. FIG. In the following description, the light guide plate 3 will be described using the rectangular base 4, but the shape of the base 4 is not limited. For example, the base 4 may be a quadrilateral or more polygon. Further, a plurality of polygonal side surfaces used for the substrate 4 may be used as the light incident surface. Below, operation | movement of the light-guide plate 3 is demonstrated using the surface light source device shown in FIG. 1 or FIG.

  As shown in FIGS. 1 and 2, the surface light source device according to the embodiment of the present invention includes a light source 1, a light guide plate 3, a light collecting member 8, a reflecting member 7, and the like. A region of the light guide plate 3 corresponding to a liquid crystal display element (not shown) irradiated by the surface light source device is defined as a display area 34. The area of the light guide plate 3 that includes the display area 34 and in which the second optical element is disposed extends from the light emitting area 30 and the light incident surface 10 of the second optical element 18 that is closest to the light incident surface 10 side of the light emitting area 30. A region up to the end on the light incident surface 10 side, in other words, a region near the first side surface is defined as a light incident area 32. That is, the display area 34 is an effective light emitting area and is arranged in a range smaller than the light emitting area 30.

  The light source 1 is disposed so as to face the light incident surface 10 of the light guide plate 3. The condensing member 8 is disposed so as to face the first main surface 12 that is the light output surface of the light guide plate 3. The condensing member 8 condenses light by controlling the propagation direction of light incident from the first main surface 12. The reflecting member 7 is disposed so as to face the second main surface 14 that is the reflecting surface of the light guide plate 3. The reflecting member 7 reflects the light incident from the second main surface 14 into the light guide plate 3.

  As shown in FIG. 1, the light collecting member 8 includes a downward prism sheet 5 and a diffusion sheet 9. The condensing member 8 is disposed such that the main surface on which the plurality of prism rows 26 of the downward prism sheet 5 are arranged faces the first main surface 12. The diffusion sheet 9 is disposed so as to face the light guide plate 3 with the downward prism sheet 5 interposed therebetween.

  Or the condensing member 8 is provided with the diffusion sheet 28 and the upward prism sheets 6 and 6a, as shown in FIG. The condensing member 8 is disposed such that the diffusion sheet 28 faces the first main surface 12 that is the light exit surface of the light guide plate 3. The upward prism sheet 6 is arranged such that the other main surface facing the main surface on which the plurality of prism rows 27 are arranged faces the light guide plate 3 with the diffusion sheet 28 interposed therebetween. The upward prism sheet 6a is disposed so that the other principal surface facing the principal surface on which the plurality of prism rows 27a are arranged faces the diffusion sheet 28 with the prism sheet 6 interposed therebetween. The upward prism sheets 6 and 6a are arranged so that the ridge lines of the prism row 27 and the prism row 27a are substantially orthogonal to each other. Note that the upward prism sheet 6a may be omitted and a single upward prism sheet 6 may be used.

  A plurality of point light sources, for example, three LEDs, are arranged as the light source 1 so as to face the light incident surface 10 of the light guide plate 3. The light emitted from the light source 1 is introduced into the light guide plate 3 through the light incident surface 10. The light guided in the light guide plate 3 is repeatedly reflected in the light guide plate 3 by the first inclined surface 22 of the second optical element 18 of the second main surface 14.

  For example, as shown in FIG. 1, light having a critical angle or more on the first main surface 12 is emitted toward the downward prism sheet 5 through the first main surface 12 which is a light output surface. The light having a critical angle or more on the second main surface 14 is emitted toward the reflecting member 7 through the second main surface 14. The light emitted from the second main surface 14 is reflected by the reflecting member 7, is again introduced into the light guide plate 3 through the second main surface 14, and is emitted toward the downward prism sheet 5 through the first main surface 12. The The light emitted from the first main surface 12 is deflected in the normal direction of the first main surface 12 by the downward prism sheet 5 and further radiated through the diffusion sheet 9. The diffusion sheet 9 is disposed in order to prevent moiré with the liquid crystal display element. When there is no moiré, the diffusion sheet 9 may not be provided.

  Alternatively, as shown in FIG. 2, the light emitted to the outside of the light guide plate 3 through the first main surface 12 is diffused by the diffusion sheet 28 in order to make the in-plane brightness uniform, and further, the upward prism sheet. 6 and 6a. The upward prism sheets 6 and 6 a are arranged to collect the light diffused by the diffusion sheet 28 in the normal direction of the first main surface 12 and improve the front brightness. One upward prism sheet 6 may be used, but it is preferable to arrange the two upward prism sheets 6 and 6a so that the ridge lines of the respective prism rows are substantially orthogonal to each other. By using the two upwardly facing prism sheets 6 and 6a, the light collection efficiency can be improved and the front luminance can be further improved.

  A transparent thermoplastic such as polymethyl methacrylate (PMMA), polycarbonate (PC), cycloolefin polymer (COP), and cycloolefin copolymer (COC) is used as the base 4 of the light guide plate 3. The first optical element 16 and the second optical element 18 of the light guide plate 3 are formed on the substrate 4 by an injection molding method or the like.

  The light incident surface 10 of the light guide plate 3 is provided with an anisotropic diffusion optical pattern (not shown) that spreads the light emitted from the light source 1 in a direction substantially orthogonal to the traveling direction. The anisotropic diffusion optical pattern is provided so that, for example, a wave shape, an arc shape, a V shape, or the like extends in the thickness direction of the light guide plate 3. In particular, the wavy pattern is preferable because it has strong diffusibility and can suppress generation of bright lines.

  As shown in FIGS. 3 and 4, the first main surface 12 of the base 4 is provided with a plurality of first optical elements 16 extending in a direction orthogonal to the light incident surface 10. The plurality of first optical elements 16 are provided on the entire first main surface 12. As shown in FIG. 5, each first optical element 16 is an isosceles triangle whose cross-sectional shape cut in parallel to the light incident surface 10 has an apex angle θ. The apex angle θ is preferably in the range of more than 80 degrees and less than 150 degrees. In addition, it is desirable that the plurality of first optical elements 16 include isosceles triangles having a plurality of different apex angles θ in the range of more than 80 degrees and less than 150 degrees, preferably 2 or more, preferably 3 or more.

  The first optical element 16 causes light propagating through the light guide plate 3 and tilted in a direction parallel to the light incident surface 10 to be emitted from the light guide plate 3 close to the front direction (normal direction of the light exit surface), It has a function to increase the amount of light in the front direction. By setting the apex angle θ to a range greater than 80 degrees and less than 150 degrees, the amount of light in the front direction can be efficiently increased, and a high-intensity light guide plate can be realized. Further, by using the first optical element 16 having an isosceles triangle having a plurality of apex angles θ having different cross sections, the amount of light in the front direction can be adjusted, and the directivity can be weakened or strengthened, or any light can be emitted. It becomes possible to make it a characteristic.

  The height of the plurality of first optical elements 16 is 5 μm or more, more desirably 6 μm or more. The upper limit of the height is about 50 μm.

  The first optical element 16 can also be a groove. In this case, if the depth of the groove is less than 5 μm, it is likely to be in close contact with the downward prism sheet 5 or the diffusion sheet 28 disposed facing the first main surface 12, and display defects are likely to occur. 5 μm or more, more desirably 6 μm or more.

  As shown in FIGS. 3 and 6, a plurality of second optical elements 18 are provided on the second main surface 14 of the substrate 4 so as to be separated from each other over the entire light emitting area 30. As shown in FIGS. 7 to 9, each of the plurality of second optical elements 18 has a sawtooth shape in cross section cut perpendicular to the light incident surface 10 (cross section cut along line BB in FIG. 7). In addition, the light guide plate 3 has a first inclined surface 22 that intersects the light incident surface 10 and a second inclined surface 24 that faces the first inclined surface 22. That is, the normal line of the second inclined surface 24 toward the inside of the light guide plate 3 faces the surface opposite to the light incident surface 10 and does not intersect with the light incident surface 10. The second optical element 18 has a trapezoidal cross-sectional shape (cross-sectional shape cut along the line CC in FIG. 7) cut parallel to the light incident surface 10, and has inclined side surfaces 25 facing each other.

  The first inclined surface 22 has a rectangular shape, and a width Wa in a direction parallel to the light incident surface 10 is in a range of 0.15 mm or less. The second slope 24 has a trapezoidal shape, and the width Wb of the bottom side is larger than Wa and not more than 0.3 mm. The inclined side surface 25 has a triangular shape, and the width Wc of the base is in a range of 0.3 mm or less. If the widths Wa, Wb, Wc of the second optical element 18 exceed the above range and become too large, the second optical element 18 is visually recognized as a bright spot at the time of light emission, and a display defect occurs.

  The orientation of the second optical element 18 is a plane including the normal line of the first slope 22 and the normal line of the second main surface 14, and a plane including the normal line of the second slope 24 and the normal line of the second main surface 14. The light incident surface 10 and the light incident surface 10 are arranged in a direction substantially perpendicular to the light incident surface 10. That is, the plurality of second optical elements 18 are directed in a fixed direction with respect to the light incident surface 10. Thereby, the light reflected by the first slope 22 spreads in the width direction (direction in which the light sources 1 are arranged), and light incident unevenness near the light incident surface 10 is reduced. Further, the amount of light reflected by the second inclined surface 24 is reduced, and there is an effect of preventing a decrease in the amount of light in the front direction (direction toward the liquid crystal display device). This is because the light reflected by the second slope 24 is emitted in a direction that reduces the luminance in the front direction. Note that the substantially perpendicular direction allows a variation of about ± 10 degrees.

  The angle α formed by the first inclined surface 22 and the normal line of the light incident surface 10 is preferably greater than 0.5 degrees and less than 10 degrees, and more preferably greater than 0.5 degrees and less than 5 degrees. The angle β formed by the second inclined surface 24 and the normal line of the light incident surface 10 is preferably greater than 50 degrees and less than 89 degrees, more preferably greater than 70 degrees and less than 89 degrees.

  When the angle α is 10 degrees or more, a large amount of light is emitted on the light incident surface 10 side, and when it is less than 0.5 degrees, a large amount of light tends to be emitted on the surface side facing the light incident surface. For this reason, in order for the surface light source device to emit light uniformly within the surface, it is preferable to set the angle α within this range.

  If the angle β is less than 50 degrees, the light reflected by the surface facing the light incident surface 10 is reflected by the second inclined surface 24 and emitted out of the light guide plate 3 in a direction inclined from a specified angle. . For this reason, when the surface light source device is viewed from an oblique direction, a display defect occurs in which a bright portion is partially generated. Further, when the angle β is 89 degrees or more, the corner portion is taken by the mold at the time of injection molding, and there is a tendency that molding defects such as chipping occur.

  Further, in a cross section cut parallel to the light incident surface 10, the angle γ formed by the inclined side surface 25 with a line orthogonal to the normal line of the second main surface 14 is preferably in the range of greater than 40 degrees and less than 75 degrees. The inclined side surface 25 causes light propagating in the light guide plate 3 and tilted in a direction parallel to the light incident surface 10 to be emitted from the light guide plate 3 close to the front direction (normal direction of the light exit surface). It has a function to increase the amount of light. By setting the angle γ to be greater than 40 degrees and less than 75 degrees, the amount of light in the front direction can be increased efficiently, and a high-intensity light guide plate can be realized.

  Furthermore, it is preferable that the first inclined surface 22, the second inclined surface 24, and both inclined side surfaces 25 of the second optical element 18 are mirror surfaces. If each surface is not a mirror surface, the light diffuses at the time of reflection, resulting in a decrease in luminance.

The size of each second optical element 18 is substantially constant. It is important that the area of the second optical element 18 projected onto the ^second major surface 14 is in the range of greater than 0.0001 mm ^{2 and} less than 0.023 mm ² , greater than 0.0001 mm ² and 0.001 mm. A range of less than ² is more preferred. When the area is less than 0.0001 mm ² , the number of the second optical elements 18 increases, and it takes much time to process the molding die. On the other hand, if the area is 0.023 mm ² or more, the second optical element 18 becomes too large, and the second optical element 18 is visually recognized as a bright spot at the time of light emission, causing a display defect. Therefore, greater than 0.0001 mm ² area of the second optical element 18, it is essential in reducing the incident unevenness in the range of less than 0.023 mm ^2.

The plurality of second optical elements 18 have the number of second optical elements 18 per unit area in the light emitting area 30 of the second main surface 14 or the surface density on the light incident surface (or first side) 10 side of the light emitting area 30. It arrange | positions so that it may increase in the edge part area | region of the 2nd side surface side which is the opposite side of the light-incidence surface (or 1st side surface) 10 of the light emission area 30 rather than this edge part area | region. Here, when the surface density of the second optical element 18 is projected onto a plane orthogonal to the light incident surface (or first side surface) 10 with respect to the second principal surface 14, the projected area is 1 mm ² . , Defined as the percentage of the projected area of the second optical element 18 included in the projected area. Further, the end region on the light incident surface (or first side surface) 10 side of the light emitting area 30 is a region within 1 mm from the end on the light incident surface (or first side surface) 10 side of the light emitting area 30 inside the light emitting area 30. It is defined as Further, the end region on the second side surface of the light emitting area 30 is defined as a region within 1 mm from the end on the second side surface side of the light emitting area 30 to the inside of the light emitting area 30. Further, when the second main surface 14 is projected onto a plane orthogonal to the light incident surface (or first side surface) 10, the projection is performed in the end region on the light incident surface (or first side surface) 10 side of the light emitting area 30. A projection region having an area of 1 mm ² is defined as a first projection region, an end region on the second side surface side of the light emitting area 30, and a projection region having a projection area of 1 mm ² is defined as a second projection region.

  In the first projection region in the end region on the light incident surface (or first side surface) 10 side of the light emitting area 30, the surface density of the second optical element 18 is preferably in the range of 10% or more and 40% or less. % Or more and 35% or less is more preferable. If the surface density of the second optical element 18 is less than 10% in the end region on the light incident surface (or first side surface) 10 side of the light emitting area 30, the second optical element 18 is recognized as a bright spot, and display defects occur. appear. When the surface density of the second optical element 18 exceeds 40%, a large amount of light is emitted on the light incident surface 10 side, and thus the emitted light in the light emitting area 30 or the display area 34 that is an effective light emitting area is non-uniform. become. Since the projection area of the second optical element 18 is within the above-described range, it is appropriate that there is no unevenness in incident light when the distance from the light incident surface to the effective light emitting area is shortened with the downsizing of the surface light source device. It is possible to find the surface density of the second optical element 18.

  In the second projection region in the end region on the second side surface side of the light emitting area 30, the surface density of the second optical element 18 is preferably in the range of 30% to 65%, preferably 40% to 60%. A range is more preferred. When the surface density of the second optical element 18 is less than 30% in the end region on the second side surface side of the light emitting area 30, the light incident on the light guide plate 3 from the light source 1 is emitted outside the light guide plate 3. Light is reduced, resulting in a decrease in luminance. When the surface density of the second optical element 18 exceeds 65%, more light is emitted from the first inclined surface 22 to the outside of the light guide plate, and enters the light guide plate 3 again from the second inclined surface 24. Since this light is emitted from the light exit surface at an emission angle that is greatly deviated from an appropriate value, the light transmitted through the prism sheet is not emitted to the front, resulting in a decrease in luminance.

  In a general surface light source device, the distance from the light incident surface to the display area is about 4 mm. In consideration of tolerances and the like, it is necessary to prevent display unevenness from occurring in an area exceeding 3 mm from the light incident surface. Moreover, the interval between the plurality of light sources is usually in the range of 6 mm to 15 mm. From this, the interval between the plurality of light sources 1 was set to 6 mm to 15 mm, and the slope ratio capable of suppressing display unevenness was calculated by optical simulation in the region of the light emitting area 30 up to a position 3 mm away from the light incident surface 10. As a result, for example, when a bright portion is generated in the region of the light emitting area 30 near the light incident area 32 facing each of the plurality of light sources 1, the second optical element 18 in the region where the bright portion is generated Reduce density. Moreover, when a dark part generate | occur | produces in the area | region of the light emission area 30 of the vicinity of the light incident area 32 which each opposes between the some light sources 1, the density of the 2nd optical element 18 of a dark part generation | occurrence | production area | region is increased. That is, it was found that display unevenness can be suppressed by optimizing the density of the second optical element 18 in the region between the light emitting area 30 and the display area 34 on the light incident surface 10 side.

  In the surface light source device according to the embodiment, as shown in FIG. 1, the main surface on which the plurality of prism rows 26 of the downward prism sheet 5 are formed faces the light guide plate 3 and the diffusion sheet 9 and the light guide plate. 3 is arranged. Alternatively, as shown in FIG. 2, the diffusion sheet 28 is disposed to face the light guide plate 3, and the surface opposite to the surface on which the plurality of prism rows 27, 27 a of the upward prism sheets 6, 6 a are formed is the diffusion sheet. 28 is disposed opposite the light guide plate 3 with the 28 interposed therebetween. As a result, a surface light source device with high brightness and high efficiency can be realized.

  In the above description, as shown in FIG. 1 or FIG. 2, the first main surface 12 of the light guide plate 3 is the light exit surface and the second main surface 14 is the reflection surface. However, as shown in FIG. 10, even if the second main surface 14 is used as the light exit surface so as to face the prism sheet 5, the same effect can be realized. Alternatively, as shown in FIG. 11, the same effect can be achieved even if the second main surface 14 is used as a light exit surface so as to face the diffusion sheet 28. In this case, the light emitted from the first main surface 12 is reflected by the reflecting member 7 facing the first main surface 12 and introduced again into the light guide plate 3.

(Other embodiments)
As mentioned above, although this invention was described by embodiment of this invention, it should not be understood that the statement and drawing which make a part of this indication limit this invention. From this disclosure, various alternative embodiments, examples and operational techniques will be apparent to those skilled in the art. Accordingly, the technical scope of the present invention is defined only by the invention specifying matters according to the scope of claims reasonable from the above description.

  The light guide plate and surface light source device of the present invention can be used for liquid crystal display devices such as mobile phones, game machines, electronic notebooks, car navigation systems, notebook PCs, and TVs.

DESCRIPTION OF SYMBOLS 1 ... Light source 3 ... Light guide plate 4 ... Base | substrate 5, 6, 6a ... Prism sheet 7 ... Reflective member 8 ... Condensing member 9 ... Diffusing sheet 10 ... Light-incident surface (1st side surface)
DESCRIPTION OF SYMBOLS 12 ... 1st main surface 14 ... 2nd main surface 16 ... 1st optical element 18 ... 2nd optical element 22 ... 1st slope 24 ... 2nd slope 25 ... Inclined side surface 26,27,27a ... Prism row 28 ... Diffusion sheet 30 ... Light emitting area 32 ... Light incident area 34 ... Display area

Claims (15)

A base body having first and second main surfaces facing each other, and a plurality of side surfaces surrounding the first and second main surfaces;
A plurality of first optical elements disposed on the first main surface and extending in a direction perpendicular to the first side surface of the substrate;
A plurality of second optical elements disposed apart from each other except for a light incident area in the vicinity of the first side surface of the second main surface,
Each of the plurality of second optical elements is opposed to the first slope and the first slope where the normal to the inside of the base body intersects the first side in a cross section cut perpendicular to the first side. A plane having a second slope and including a normal line of the first slope and a normal line of the second main surface; and a plane including a normal line of the second slope and a normal line of the second main surface; The angle formed with the first side surface is in a range of 90 ° ± 10 °, and each of the cross-sections cut parallel to the first side surface has inclined side surfaces facing each other and projected onto the second main surface. area greater than 0.0001 mm ^2, a light guide plate which is a range of less than 0.023 mm ^2.   The angle formed by the first slope with the normal line of the first side surface is greater than 0.5 degrees and less than 10 degrees, and the angle formed by the second slope surface with the normal line of the first side surface is 50 degrees. The light guide plate according to claim 1, wherein the light guide plate is in a range of greater than 85 degrees and less than 89 degrees.   3. The guide according to claim 1, wherein an angle γ formed by each of the inclined side surfaces with a line orthogonal to a normal line of the second main surface is in a range of greater than 40 degrees and less than 75 degrees. Light board.   The light guide plate according to any one of claims 1 to 3, wherein the first and second inclined surfaces and the inclined side surface are mirror surfaces.   A region in which the plurality of second optical elements are disposed is defined as a light emitting area, and a side surface opposite to the first side surface is defined as a second side surface, and the plurality of second optical elements are defined in the second area of the light emitting area. 5. The device according to claim 1, wherein the number of the light emitting areas per unit area in the end region on the side surface side is larger than the end region on the first side surface side of the light emitting area. The light guide plate described in 1. Arbitrary projection area of 1 mm ² in a region within 1 mm from the end of the first side surface of the light emitting area to the inside of the light emitting area when the second main surface is projected onto a plane orthogonal to the first side surface The percentage of the projected area of the plurality of second optical elements included in the first projection area with respect to the first projection area is in the range of 10% or more and 40% or less, and the second side surface side of the light emitting area In a region within 1 mm from the end within the light emitting area, the percentage of the projected area of the plurality of second optical elements included in the second projected region is 30% with respect to an arbitrary second projected region having a projected area of 1 mm ^2. The light guide plate according to claim 5, wherein the light guide plate has a range of 65% or less.   Each of the plurality of first optical elements is an isosceles triangle having a cross-sectional shape cut in parallel to the first side surface and having an apex angle in a range greater than 80 degrees and less than 150 degrees. Item 7. The light guide plate according to any one of Items 1 to 6.   The plurality of first optical elements include a plurality of isosceles triangles having cross-sectional shapes cut parallel to the first side surface and having different apex angles in a range of greater than 80 degrees and less than 150 degrees. The light guide plate according to any one of claims 1 to 6. A surface light source device for irradiating a liquid crystal display element,
The light guide plate according to any one of claims 1 to 8,
A light source disposed opposite to the light incident surface with the first side surface as a light incident surface;
A reflective member disposed facing the reflective surface of the light guide plate and reflecting light incident from the reflective surface into the light guide plate;
A surface light source device comprising: a condensing member disposed so as to face a light exit surface opposite to the reflection surface, and condensing light by controlling a propagation direction of light incident from the light exit surface.   A region where the second optical element is arranged is defined as a light emitting area, and a side surface opposite to the first side surface is defined as a second side surface, and the plurality of second optical elements are the second side surface side of the light emitting area. 10. The surface light source device according to claim 9, wherein the surface light source device is arranged so that the number per unit area in the end region of the light emitting area is larger than the end region on the light incident surface side of the light emitting area. Corresponding to the liquid crystal display element, a region of the light guide plate included in the light emitting area is defined as a display area, and the second main surface of the light guide plate is projected onto a plane orthogonal to the light incident surface. The plurality of second projections included in the first projection area with respect to an arbitrary first projection area having a projection area of 1 mm ^{2 in} an area within 1 mm from the end on the light incident surface side of the light emitting area to the inside of the light emitting area. The percentage of the projected area of the optical element is in the range of 10% to 40%, and the projected area is 1 mm ² in a region within 1 mm from the end of the second side surface of the light emitting area to the inside of the light emitting area. The percentage of the projected area of the plurality of second optical elements included in the second projection area with respect to the second projection area is in a range of 30% to 65%. Surface light source .   The surface light source device according to claim 9, wherein the light exit surface is the first main surface.   The surface light source device according to claim 9, wherein the light exit surface is the second main surface.   The said condensing member contains the downward prism sheet arrange | positioned so that the main surface in which the some prism row | line | column was arranged faces the said light emission surface. Surface light source device.   The condensing member is disposed so as to face the light exit surface, and another main surface facing the main surface on which a plurality of prism rows are arranged faces the light exit surface with the diffusion sheet interposed therebetween. The surface light source device according to claim 9, further comprising an upward prism sheet arranged as described above.

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