JP2005085734A - Light guide plate, surface light source and method of manufacturing light guide plate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To emit incident light ahead efficiently without a prism sheet even when a point-like light source is used. <P>SOLUTION: This light guide plate 14 is formed with an incident surface 14a to which light radiated from a point-like light source 15 is injected and an emission surface 18 for emitting the light injected from the incidence surface 14a, wherein a reflection portion 19 for reflecting the light injected to the light guide plate 14 from the point-like light source 15 toward the emission surface 18 is formed on a rear side opposite to the emission surface 18. A plurality of lens-like projecting linear portions 21 are formed on the emission surface 15 in parallel with a virtual surface including the lower end of the incident surface and extending in the direction perpendicular to the incident surface 14a and extending in a direction perpendicular to the incident surface 14a. The projecting linear portion is demarcated with two curved surfaces and has a tangential line parallel with the virtual surface at both ends of an outline shape in a cross section plane perpendicular to the direction that the projecting linear portions extend. Further, a plurality of projecting linear portions having various averages of slopes of the tangential lines on the outline shape exist over whole of the emission surface 18. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a light guide plate, a surface light source device, and a method for manufacturing a light guide plate, and more particularly to a light guide plate, a surface light source device, and a light guide plate manufacturing method. .

  As a liquid crystal display device, there is one in which a surface light source device is disposed as a backlight on the back surface (surface opposite to the display surface) of a liquid crystal display panel (liquid crystal panel). As this type of surface light source device, a device in which a fluorescent tube (cold cathode tube) is arranged along an end surface of a light guide plate formed of a material having high translucency is used. And as the light guide plate, a light guide plate having a prism extending in a direction orthogonal to the end face is proposed (see, for example, Patent Document 1, Patent Document 2, and Patent Document 3).

  As shown in FIG. 8, in the surface light source device 40 described in Patent Document 1, a linear light source 42 is disposed at one end of a light guide plate 41. A reflection layer 44 is provided on one surface of the light guide plate 41. The reflection layer 44 is provided with an irregular reflection pattern formed by a plurality of grooves 43a and 43b. The grooves 43 a and 43 b are formed in parallel so as to follow the direction in which the light from the line light source 42 passes, and are formed in a long groove 43 a formed in the entire length of the light guide plate 41 and in a portion away from the line light source 42. Short grooves 43b are alternately provided.

  As shown in FIG. 9, in the surface light source device described in Patent Document 2, when the convex portion (prism) 53 is formed on the exit surface 52 of the light guide plate 51 or the back surface opposite to the exit surface, the convex portion 53 is formed. Instead of being formed uniformly over the entire length, the convex portion 53 is smoothly formed according to the position of the convex portion 53. Specifically, the convex portion 53 is smoothly formed as it approaches the incident surface 54, and the convex portion 53 is formed smoothly as it approaches the side surface 55.

  As shown in FIG. 10, in the surface light source device described in Patent Document 3, a prism surface is formed on the exit surface of the light guide plate 51 or the surface facing the exit surface 52. The convex portion 53 constituting the prism surface has angles α and β formed by the inclined surfaces 53a and 53b and a virtual plane orthogonal to the incident surface 54 equal in the central portion of the light guide plate 51 and different in inclination on the side surface side. It is formed to become.

Further, it is necessary to make the diameter of the fluorescent tube very small as the liquid crystal display device becomes thinner, and accordingly, the fluorescent tube is easily damaged by a small impact. In addition, since a high voltage is required to cause the fluorescent tube to emit light as a light source, there is a problem that a complicated lighting circuit is required. Therefore, instead of a configuration using a fluorescent tube, as a surface light source device, an LED is arranged facing the end face of the light guide plate, and light is planarized from the surface of the light guide plate (the surface facing the liquid crystal panel). An emitted edge light type (side light type) device has been proposed. However, since LEDs have strong directivity, bright lines, bright parts, dark parts, etc. are likely to occur. As a method of emitting light from the light guide plate in a uniform plane using one or a small number of LEDs, the directivity is relaxed by diffusing with diffusion dots and a diffusion sheet as the light collecting means of the light guide plate, There is a method for obtaining necessary luminance by condensing light with a prism sheet. When this method is used, generally two prism sheets are often used. However, in the configuration using the prism sheet, the number of parts increases, so that the number of assembling steps increases and the cost also increases. Therefore, a prism sheet integrated with a light guide plate has been proposed.
JP-A-8-29624 (paragraphs [0006] and [0014] in FIG. 10, FIG. 10) JP 11-52380 A (paragraphs [0028] to [0032], FIGS. 1 and 2 in the specification) JP-A-11-120810 (paragraphs [0028] to [0032] in FIG. 1, FIG. 1)

  However, in the case of a light guide plate in which a prism (not shown) extending in a direction orthogonal to the incident end face is formed on the exit surface in a configuration using a plurality of point light sources, it is shown in FIGS. 11 (a) and 11 (b). As described above, in the light guide plate 61, the bright portion 64 is generated in the display area 62 near the point light source 63 and in a region corresponding to the space between the point light sources 63. That is, luminance unevenness occurs on the exit surface 65 of the light guide plate 61. This is because the point light source 63 has high directivity, and the amount of light emitted from the point light source 63 is large in the direction toward the front of the point light source, and the amount of light that is inclined from the point light source 63 is small. Therefore, as shown in FIG. 12, when comparing the light emitted from the point light source 63 toward the front and the light emitted obliquely from the point light source 63, the prism 66 has a light-emitting surface in the latter case. After being totally reflected at 67 and proceeding into the prism 66, the ratio of light emitted from the surface of the prism 66 toward the front surface of the light exit surface 65 is increased. As a result, the light emitted from the adjacent point light sources 63 overlaps, and the bright portion 64 is generated in that region.

  In addition, depending on the prism shape, a portion corresponding to the front surface of the point light source 63 near the incident end face is darker than the other areas of the point light source 63, that is, a dark portion is generated near the front surface of the point light source 63. There is also.

  Even if the configuration of Patent Document 1 for linear light sources is applied to the suppression of luminance unevenness in the vicinity of the incident end face of the light guide plate for point light sources (particularly measures against bright portions), the luminance unevenness cannot be suppressed. On the other hand, the configuration of Patent Document 2 is difficult to manufacture a mold, and is intended to increase the luminance of a low-luminance portion, so that it is not effective for measures against bright portions. In addition, the configuration of Patent Document 3 also requires a plurality of tools for manufacturing the mold, which is troublesome to manufacture.

  The present invention has been made in view of the above-mentioned problems, and a first object is to emit incident light efficiently to the front without using a prism sheet even when a point light source is used. It is providing the light-guide plate which can suppress a nonuniformity. The second object is to provide a surface light source device including the light guide plate. A third object is to provide a method for manufacturing the light guide plate.

  In order to achieve the first object, the invention according to claim 1 is a light guide plate that allows light emitted from a light source to enter from an incident surface at one end, and to convert the light into a planar shape and emit the light. In the light guide plate, on the back surface opposite to the exit surface that emits light incident from the entrance surface, the light that is incident from the entrance surface and guided in the light guide plate is emitted in the direction of exiting the exit surface. A reflection part for reflection is formed. A plurality of lenticular ridges are provided on the exit surface so as to extend in parallel to a virtual plane extending in a direction perpendicular to the entrance surface including the lower end of the entrance surface and in the normal direction of the entrance surface. . Each of the ridges is defined by two curved surfaces convex toward the virtual plane side, and has tangent lines parallel to the virtual plane at both ends of the outer shape in a cross section orthogonal to the extending direction of the ridges, The said protruding item | line from which the average value of the inclination of the tangent in an external shape differs exists. Here, “slope of tangent” means the slope of a tangent at a point on the outer shape with respect to the virtual plane. The “average value of the tangential slope in the outer shape” means that the absolute value of the tangent slope obtained for each point on the outer shape is integrated between both ends of the outer shape, and the integrated value is It means the value divided by the distance between both ends of the outer shape.

  In this invention, the light incident from the incident surface is reflected by the reflecting portion while being guided in the light guide plate toward the end surface opposite to the incident surface, and the traveling direction thereof is directed toward the output surface. Deflected. And it is radiate | emitted through the lens-shaped convex strip provided in the output surface. When the ridge is a normal triangular prism, only the light reflected by the reflecting portion is reflected on the front surface of the light guide plate so as to form a predetermined angle with respect to a virtual plane in contact with the vertex of each ridge. Since it is emitted, bright lines are generated when the light guide plate is viewed from the front. However, in the present invention, the ridge is formed as a curve having an outer shape convex toward the imaginary plane and having a tangent parallel to the imaginary plane, and the tangent at each point of the curve There are a plurality of curves having different average values of the slopes. Therefore, even if the angle formed with the virtual plane out of the light reflected by the reflecting portion is deviated from the predetermined angle, it is emitted to the front surface of the light guide plate. As a result, even when a point light source is used, generation of bright lines as occurs in the case of the triangular prism is suppressed, and incident light can be efficiently emitted to the front surface of the light guide plate without using a prism sheet. And the overall luminance is improved.

  According to a second aspect of the present invention, in the first aspect of the invention, the contact pitch between the tangent line and the outer shape is formed constant. In this invention, compared with the case where a pitch is not constant, the process of the metal mold | die for forming a light-guide plate becomes easy.

  According to a third aspect of the present invention, in the first or second aspect of the present invention, a plurality of point light sources are used as the light source, and a curved surface provided at a portion corresponding to the front surface of each point light source. The average value of the tangential slope on the cross section is smaller than the average value of the tangential slope on the cross section of the curved surface provided in the other part.

  Here, “the average value of the slope of the tangent on the cross section of the curved surface provided in the portion corresponding to the front surface of each point light source” is provided in the portion corresponding to the front surface of each point light source. The absolute value of the tangent slope at each point on the cross section of the curved surface is integrated within the width of the point light source, and the integrated value is divided by the width of the point light source. In addition, “the average value of the slope of the tangent line on the cross section of the curved surface provided in the other part” is the above on the cross section of the curved surface provided in the corresponding part between two adjacent point light sources. The absolute value of the slope of the tangent line at each point is integrated between two adjacent point light sources, and the integrated value is divided by the distance between the adjacent point light sources.

  In this invention, the average value of the slope of the tangent of each point on the cross section of the curved surface provided in the portion corresponding to the front surface of each point light source is on the cross section of the curved surface provided in the other portion. The amount of light emitted from the portion corresponding to the front surface of each point light source is relatively larger than when the average value of the tangent slope of each point is formed or when the average value is formed uniformly. Become. As a result, the occurrence of a dark portion in a portion corresponding to the front surface of the point light source is suppressed, and uneven luminance of the light guide plate is suppressed.

  According to a fourth aspect of the present invention, in the first or second aspect of the present invention, a plurality of point light sources are used as the light source, and a curved surface provided at a portion corresponding to the front of each point light source. The average value of the tangential slope at each point on the cross section is formed to be larger than the average value of the tangential slope at each point on the cross section of the curved surface provided in the other part.

  In the present invention, contrary to the invention described in claim 3, the amount of light emitted from the portion corresponding to the front surface of each point light source is relatively reduced. As a result, the occurrence of a bright portion in a portion corresponding to the front surface of the point light source is suppressed due to a relative balance with the amount of light emitted from other portions, and uneven luminance of the light guide plate is suppressed.

  According to a fifth aspect of the present invention, in the invention according to any one of the first to fourth aspects, the back surface of the light guide plate extends along the end surface and emits the incident light. A plurality of grooves constituting a daylighting surface to be reflected in the direction of exiting from the surface are formed.

  In this invention, the light incident from the incident surface is reflected by the daylighting surface while being guided through the light guide plate toward the end surface opposite to the incident surface, and is directed in a direction substantially perpendicular to the emission surface. Thus, the traveling direction is deflected. And it is radiate | emitted through the protruding item | line provided in the output surface. Therefore, compared to the case where dots are provided on the back surface and scattered by the dots, it becomes easier to emit light incident from the incident surface in a direction toward the observer from the emission surface of the light guide plate.

  The invention according to claim 6 is the invention according to any one of claims 1 to 5, wherein the light guide plate is provided with an introduction portion for diffusing incident light, and the introduction portion is It is formed in a shape that expands from the light incident side toward the light guide plate body side. Further, an incident part configured by alternately repeating a plane parallel to a plane extending in the width direction of the introduction part and a diffusion part for diffusing light from the point light source, and facing the point light source, and the diffusion part And a reflection part that reflects the light diffused in step toward the light guide plate body.

  In this invention, the light from the point light source is diffused by the introducing portion, and the directivity and light quantity of the light guided in front of the point light source or between the point light sources are made uniform. Therefore, when a plurality of point light sources are provided, it is possible to further reduce the occurrence of bright or dark portions between the front surfaces of the point light sources or the point light sources, and the luminance unevenness of the light guide plate.

  In order to achieve the second object, a surface light source device according to a seventh aspect includes the light guide plate according to any one of the first to sixth aspects and a light source. According to the present invention, in the side light type surface light source device, the same effect as that obtained when the light guide plate according to any one of claims 1 to 6 is used can be obtained.

  In order to achieve the third object, the invention according to claim 8 is directed to a direction perpendicular to the incident surface including a lower end of the incident surface on an exit surface that emits light incident from an incident surface at one end in a planar shape. A plurality of lens-shaped ridges are provided so as to extend in parallel with a virtual plane extending in the shape, and the outer shape of the ridge in a cross section orthogonal to the direction in which the ridge extends is formed by a convex curve on the virtual plane side. In addition, the light guide plate manufacturing method includes a plurality of curves having tangent lines parallel to the virtual plane as the curves and having different average values of tangent slopes at respective points of the curves. Then, with a single bite having a blade corresponding to the curved surface constituting the ridge, the mother die having the lens-like ridge is cut, and the die is electroformed using the mother die. The light guide plate is manufactured using the mold.

  In this invention, the metal mold used for manufacturing the light guide plate can be processed with a single cutting tool (cutting blade), and the processing of the metal mold becomes easier as compared with the case of using a plurality of cutting tools. At the same time, processing costs can be reduced.

  According to the first to seventh aspects of the present invention, in the surface light source device, even when a point light source is used, incident light is efficiently emitted to the front without using a prism sheet, and luminance unevenness is reduced. Can be suppressed. According to the eighth aspect of the present invention, when a point light source is used, a light guide plate capable of efficiently emitting incident light to the front and suppressing luminance unevenness without using a prism sheet. It can be manufactured easily.

(First embodiment)
Hereinafter, a first embodiment in which the present invention is embodied in a light guide plate of a surface light source device used for a sidelight type backlight of a liquid crystal display device will be described with reference to FIGS. 1A is a schematic perspective view showing the relationship between the light guide plate and the point light source, FIG. 1B is a schematic perspective view of the back surface of the light guide plate as viewed from the exit surface side, and FIG. 2 is a schematic view of the liquid crystal display device. It is. 3 is a schematic front view of the light guide plate, FIG. 4 is a schematic diagram for explaining the manufacturing method, FIG. 5 (a) is a schematic diagram showing the operation of the daylighting surface, and (b) is a case where a triangular prism is provided on the exit surface. (C) is a schematic diagram which shows the effect | action of a lens-shaped convex part.

  As shown in FIG. 2, the liquid crystal display device 11 includes a liquid crystal panel 12 and a surface light source device 13 serving as a backlight disposed on the back surface (surface opposite to the display surface). The surface light source device 13 includes a light guide plate 14 and a plurality of point light sources 15 arranged at positions facing the incident surface 14 a of the light guide plate 14. As the point light source 15, an LED (light emitting diode) is used. The incident surface 14 a is configured by one end surface of the light guide plate 14.

  The surface light source device 13 is located on the opposite side of the liquid crystal panel 12 with the light guide plate 14 interposed therebetween, and a reflective member (reflective sheet) for returning the light leaking from the light guide plate 14 to the light guide plate 14 and using it as outgoing light 16 is provided. A diffusion sheet 17 is disposed between the light guide plate 14 and the liquid crystal panel 12.

  Next, the light guide plate 14 will be described in detail. The light guide plate 14 is made of a highly transparent material such as an acrylic resin. As shown in FIG. 1A, the light guide plate 14 is formed in a substantially square shape, and enters the light incident from the point light source 15 and the light incident from the incident surface 14a. On the back surface opposite to the emission surface 18, a reflection portion 19 that reflects light incident on the light guide plate 14 from the point light source 15 toward the emission surface 18 is formed.

  The reflection part 19 is comprised by the some parallel groove | channel 20 formed so that it might extend along the entrance plane 14a. In the groove 20, a daylighting surface 20a that rises and inclines from the incident surface 14a side toward the opposing surface 14b side, and a waveguide surface (inclined surface) 20b that inclines and descends from the incident surface 14a side toward the opposing surface 14b side are alternately arranged. It is provided to be connected. That is, each groove 20 is formed adjacent to each other so that a cross-sectional shape by a plane orthogonal to the incident surface 14a facing the point light source 15 is a sawtooth shape.

  The daylighting surface 20a is incident on the light guide plate 14 from the incident surface 14a, and the light reaching the daylighting surface 20a is a virtual plane P1 (shown in FIG. 3) extending in a direction perpendicular to the incident surface 14a including the lower end of the incident surface 14a. Is formed at an angle that causes total reflection in the direction of the exit surface 18 at an angle substantially close to the right angle. As shown in FIG. 5 (a), the groove 20 has a predetermined angle in which the angle θ1 formed by the lighting surface 20a and a plane P2 parallel to the virtual plane P1 is in the range of, for example, 35 ° to 50 °, preferably 40 ° to 45 °. The angle θ2 formed by the waveguide surface 20b and the plane P2 is formed at a predetermined angle in the range of 0.3 ° to 2.5 °, for example.

  A plurality of lenticular ridges 21 are formed on the exit surface 18 so as to extend in parallel to a virtual plane P1 including the lower end of the entrance surface 14a and extending in a direction perpendicular to the entrance surface 14a, and in the normal direction of the entrance surface 14a. Is provided. As shown in FIG. 3, each ridge 21 is demarcated by two curved surfaces, and has a tangent L1 parallel to the virtual plane P1 at both ends of the outer shape in a cross section orthogonal to the extending direction of the ridge 21. The entire exit surface 18 is formed such that there are a plurality of ridges having different average values of tangent slopes at each point of the outer shape. In this embodiment, each curve constituting the outer shape in a cross section orthogonal to the extending direction of the ridges 21 forms a part of an elliptical arc, and the curvature of the curve is continuously changed. .

  In this embodiment, each protruding item | line 21 is formed so that it may mutually adjoin, and the output surface 18 becomes the structure by which the protruding item | line 21 extended in the normal line direction of the entrance plane 14a was formed repeatedly. The average value of the slopes of the tangent lines on the cross section perpendicular to the direction in which the curved ridges that define the ridges provided in the portion corresponding to the front surface of the point light source 15 extend is determined by the adjacent point light sources 15. It is formed so as to be smaller than the average value of the slope of the tangent line on the cross section perpendicular to the direction in which the curved ridges defining the ridges provided in the corresponding portions extend.

  The value of the pitch P of the ridges 21 (the distance between both ends of the outer shape defining the ridges 21) is constant, and the value is set to a predetermined size in the range of 10 to 500 μm, preferably 50 to 300 μm. The width of the point light source 15 is, for example, 3 mm. In this specification, the ratio of the shape of the ridges 21 and the size of the point light sources 15 and the ridges 21 are different from the actual for convenience of illustration, and the number of the point light sources 15 is also different from the actual. Only two are shown.

  Each curved surface constituting the ridge 21 is formed in a shape that can be cut with the same tool (blade). The curvature (shape) of each curved surface varies depending on the value of the angle θ1 formed by the lighting surface 20a with the plane P2 and the angle θ2 formed by the waveguide surface 20b with the plane P2 and the directivity of the point light source 15. Accordingly, the projections 21 are formed in a shape in which brightness unevenness is suppressed by eliminating light portions and dark portions generated in the light guide plate 14 in a state where light from the point light source 15 is incident on the light guide plate 14 by simulation or test. Is formed.

  In this embodiment, the light guide plate 14 is manufactured by injection molding using a mold, but the corresponding portion of the convex strip 21 of the mold is manufactured by electroforming. When manufacturing a metal mold | die, as shown in FIG. 4, the matrix 24 which has a lens-shaped convex strip is cut with the single bit | cutting-tool 23 which has the blade part equivalent to the curved surface which comprises the convex strip 21. As shown in FIG. Next, a die is manufactured by electroforming using the mother die 24. And the light-guide plate 14 is manufactured using the metal mold | die. In FIG. 4, an ellipse 23 ′ indicated by a two-dot chain line indicates the tooth shape of the bite 23.

  Next, the operation of the light guide plate 14 configured as described above will be described. For example, as shown in FIG. 2, the light guide plate 14 is used by being incorporated in a surface light source device 13 as a backlight unit of a transmissive liquid crystal display device 11. A plurality of point light sources 15 are provided.

  When the point light source 15 is turned on, the light emitted from the point light source 15 enters the light guide plate 14, and the incident light is emitted from the emission surface 18 of the light guide plate 14 toward the liquid crystal panel 12, and the diffusion sheet 17. Then, the light enters the liquid crystal panel 12. The user of the liquid crystal display device 11 visually recognizes the display on the liquid crystal panel 12 by the emitted light.

  The operation of the light guide plate 14 will be described in detail. Most of the light emitted from the point light source 15 enters the light guide plate 14 from the incident surface 14a. Light incident on the light guide plate 14 is guided in the light guide plate 14. Of these, the light that has reached the daylighting surface 20a exits from the exit surface 18, as shown in FIG.

  The light that has entered the light guide plate 14 from the incident surface 14a does not always travel straight toward the daylighting surface 20a. The light that reaches the daylighting surface 20a is totally reflected by the waveguide surface 20b and the exit surface 18 while being totally reflected. There is also light that reaches the daylighting surface 20 a after being guided through the light 14. However, the waveguide surface 20b is formed so as to be inclined downward from the incident surface 14a side toward the opposing surface 14b side. For this reason, light other than being directly guided toward the lighting surface 20a approaches the direction parallel to the virtual plane P1 while being guided repeatedly. As a result, the light is efficiently transmitted on the lighting surface 20a and perpendicular to the virtual plane P1. Can be totally reflected in the direction of the exit surface 18 at an angle close to.

  As shown in FIG. 5B, when the conventional triangular prism 25 is formed on the emission surface 18, the light L directed to the emission surface 18 side forms a surface perpendicular to the inclined surface 25 a of the triangular prism 25. Refraction proceeds to increase the angle. As a result, the light is collected on the front surface of the light guide plate 14. However, the condensing action of the triangular prism 25 condenses only light incident on the inclined surface 25a at a specific angle toward the front of the light guide plate 14 as shown in FIG. 5B, but at other angles. Incident light is emitted in directions other than the front.

  The light emitted from the point light source 15 and incident on the light guide plate 14 has a spread. Accordingly, the angle at which the light is totally reflected by the lighting surface 20a varies depending on the location. As a result, when the light incident on the lighting surface 20a at a specific angle is emitted from the triangular prism 25, the light is emitted to the front surface of the light guide plate 14. For example, when the apex angle of the triangular prism 25 is 90 ° and the angle θ1 formed by the lighting surface 20a is 45 °, a bright line is generated at a position where the spread angle α from the point light source 15 is about 34 °.

  However, in this embodiment, the ridges 21 are formed such that the surface thereof has a convex curved surface continuous with the back surface side of the light guide plate 14. As a result, as shown in FIG. 5C, in the case of the triangular prism 25, not only the light L incident on the curved surface at a specific angle that refracts and proceeds toward the front of the light guide plate 14 but also other than the specific angle. Even in the light L, a region exiting to the front exists in the ridge 21. Therefore, the light emitted without going to the front surface of the light guide plate 14 is reduced, and the efficiency of emitting the emitted light from the front surface of the emission surface 18 is improved.

This embodiment has the following effects.
(1) The light guide plate 14 is formed with a reflection portion 19 that reflects the incident light in the direction of exiting from the exit surface 18 on the back surface opposite to the exit surface 18 that emits the light incident from the entrance surface 14a. Has been. A plurality of lenticular ridges 21 are provided on the exit surface 18 so as to extend parallel to a virtual plane P1 including the lower end of the entrance surface 14a and extending in a direction perpendicular to the entrance surface 14a and in a direction perpendicular to the entrance surface 14a. It has been. Each of the ridges 21 is defined by two curved surfaces convex toward the two virtual planes P1, and has a tangent line L1 parallel to the virtual plane P1 at both ends of the outer shape in a cross section orthogonal to the extending direction of the ridges 21. The ridges 21 having different average values of tangential slopes in the outer shape are formed. Therefore, even when the point light source 15 is used, incident light can be efficiently emitted to the front surface of the light guide plate 14 without using a prism sheet, and generation of bright lines can be suppressed. That is, compared with the conventional product, the quality is high (the bright line is not noticeable) and the efficiency is high (brightness improvement).

  (2) The said curve is formed by the curve which curvature changes continuously, such as an elliptical arc and a parabola. Accordingly, the light guide plate transmits the emitted light over a wider range of angles of light that is reflected by the lighting surface 20a and incident on the curved surface that forms the ridges 21, as compared to an arc formed with a constant curvature. 14 can be emitted to the front surface.

  (3) The protrusions 21 are formed so that the pitch P of the contacts 22 between the tangent line L1 and the curve is constant. Therefore, compared with the case where the pitch P is not constant, the processing of the mold for forming the light guide plate 14 becomes easier.

  (4) On the back surface of the light guide plate 14, a plurality of grooves 20 are formed that constitute a daylighting surface 20 a that extends along the incident surface 14 a and reflects the incident light in the direction of exiting from the exit surface 18. Therefore, compared to the case where dots are provided on the back surface, it becomes easier to emit light incident from the incident surface 14a in the direction from the exit surface 18 of the light guide plate 14 toward the observer.

  (5) Since it is not necessary to use a prism sheet, the number of parts constituting the surface light source device 13 is reduced, the number of assembling steps can be reduced, and the manufacturing cost can be reduced. It is necessary to form the ridges 21 on the light guide plate 14. However, since the light guide plate 14 is manufactured by injection molding using a mold, the cost of the mold is slightly increased. However, by manufacturing a large number of light guide plates 14, the number of light guide plates 14 per sheet can be increased. The manufacturing cost can be lower than the sum of the manufacturing cost of the light guide plate without the prism and the unit price of the prism sheet.

  (6) The surface light source device 13 includes a diffusion sheet 17. Therefore, even when the bright line cannot be completely prevented in the light guide plate 14, when the light emitted from the light guide plate 14 passes through the diffusion sheet 17 and enters the liquid crystal panel 12, the bright line cannot be distinguished with the naked eye. can do.

  (7) A master die 24 having a lens-like convex strip 21 is cut with a single cutting tool 23 having a blade corresponding to the curved surface constituting the convex strip 21, and electroforming is performed using the master die 24. Then, a mold is manufactured, and the light guide plate 14 is manufactured using the mold. Therefore, it is possible to process the mold used for manufacturing the light guide plate 14 with a single cutting tool 23 (cutting blade), and it is easier to process the mold compared to the case of using a plurality of cutting tools. At the same time, processing costs can be reduced.

  (8) The average value of the slopes of the tangent lines on the cross section perpendicular to the extending direction of the curved ridges defining the ridges provided on the front surface of the point light source 15 is the adjacent point light source 15. Are formed so as to be smaller than the average value of the inclination of the tangent line on the cross section perpendicular to the extending direction of the curved ridges defining the ridges provided in the corresponding portions. Therefore, it is possible to suppress a dark portion from being generated in a portion corresponding to the front surface of the point light source 15 and to suppress luminance unevenness of the light guide plate.

(Second Embodiment)
Next, a second embodiment of the light guide plate 14 embodying the present invention will be described with reference to FIGS. This embodiment is greatly different from the first embodiment in that an introduction portion for allowing light emitted from the point light source 15 to enter the light guide plate 14 is projected. The same parts as those in the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted. 6A is a schematic perspective view showing the relationship between the light guide plate 14 and the point light source 15, and FIG. 6B is a schematic plan view of the introduction part. In addition, illustration of the protruding item | line 21 is abbreviate | omitted in (b).

  As shown in FIG. 6A, a plurality of introducing portions 26 are provided adjacent to the opposite surface 14b of the light guide plate 14, that is, the end surface (incident surface 14a) on the light incident side. The introduction unit 26 includes an incident unit 27 and a reflection unit 28. As shown in FIG. 6B, the introduction portion 26 is formed in a shape that expands from the light incident side toward the main body side of the light guide plate 14, and has a base end (an end on the side facing the point light source 15). ) (Width in the horizontal direction in the drawing) is formed to be larger than the width of the point light source 15. In this embodiment, the introduction part 26 has a symmetrical shape. The incident portion 27 faces the point light source 15 and is parallel to a plane 29 extending in the width direction of the introduction portion 26, and a V-shaped groove 27 b as a diffusion portion for diffusing light from the point light source 15. Are alternately repeated at equal intervals. The value of the angle θ formed by the surface constituting the V-shaped groove 27b and the flat surface 27a in the incident portion 27 is a value between 120 degrees and 155 degrees.

  The reflector 28 is formed so as to reflect the light diffused by the V-shaped groove 27b toward the light guide plate body. The reflection part 28 is planar. The value of the angle Δ formed by the reflecting portion 28 and the surface 29 extending in the width direction of the introducing portion 26 is a value between 35 degrees and 65 degrees. Here, the light guide plate body means a portion excluding the introduction portion 26 of the light guide plate 14.

  In this embodiment, most of the light emitted from the point light source 15 reaches the incident portion 27. A part of the light reaching the incident part 27 is incident on the introduction part 26 from a plane 27 a parallel to the surface 29 extending in the width direction of the introduction part 26. Most of the light incident on the introduction portion 26 from the plane 27a parallel to the surface 29 extending in the width direction of the introduction portion 26 is refracted and introduced in the plane 27a so that its traveling direction approaches a direction perpendicular to the plane 27a. Waveguide 26 and the inside of the light guide plate 14 are guided.

  On the other hand, the remaining part of the light reaching the incident part 27 is refracted toward the reflection part 28 by the V-shaped groove 27b and is incident on the introduction part 26. And most of the light is reflected at the reflecting portion 28 so as to approach a direction perpendicular to the width direction of the light guide plate 14. The light reflected by the reflecting portion 28 is guided through a portion of the light guide plate 14 located between the point light source 15 and the point light source 15.

Therefore, according to the second embodiment, in addition to the same effects as (1) to (8) of the first embodiment, the following effects are obtained.
(9) The light guide plate 14 is provided with an introduction portion 26 for diffusing the incident light, and light from the point light source 15 is diffused by the introduction portion 26, so that the introduction portion 26 is not provided. Thus, the directivity and light quantity of the light guided between the point light sources 15 and the part corresponding to the front of the point light source 15 are made uniform. Therefore, it becomes easy to suppress the occurrence of dark portions or bright portions between the plurality of point light sources 15 or the occurrence of bright portions or dark portions in front of the point light sources 15, and light emitted from the light guide plate 14. The luminance unevenness generated in the vicinity of the point light source 15 can be further reduced.

The embodiment is not limited to the above, and may be embodied as follows, for example.
As shown in FIG. 7, the ridges 21 may have shapes in which the distance between the contact point 22 of each ridge 21 and the virtual plane P <b> 1 is constant and the pitch P is different. In this case, the average value of the slope of the tangent line at each point of the curve in the cross section orthogonal to the ridges 21 of the ridges 21 provided in the portions corresponding to the front of each point light source 15 is provided in the other portions. The projected ridge 21 is formed to be smaller than the average value of the tangential slope at each point of the curve in the cross section. As a result, the amount of light emitted from the portion corresponding to the front surface of each point light source 15 of the ridge 21 is relatively larger than the amount of light emitted from other portions, and the front surface of the point light source 15 and The occurrence of dark portions in the corresponding portions is suppressed, and the luminance unevenness of the light guide plate 14 is suppressed. Further, when forming the mold base, the cutting depth by the cutting tool 23 is made constant, and the pitch P is changed to be a predetermined value for cutting. In this case, since the cutting depth is constant, it is easier to process the die of the mold as compared with the case of changing the cutting depth.

  The average value of the slope of the tangent of each point of the curve in the cross section orthogonal to the ridges 21 of the ridges 21 provided in the portions corresponding to the front surface of each point light source 15 is provided in the other portions. You may form larger than the average value of the inclination of the tangent of each point of the curve in the said cross section of the strip | line 21. FIG. In this case, the amount of light emitted from the portion corresponding to the front surface of each point light source 15 of the ridge 21 is relatively small, and the brightness unevenness of the light guide plate 14 is caused by the balance with the amount of light emitted from other portions. It is suppressed. In such a configuration, in particular, when all the ridges 21 are formed in the same shape, the angle θ1 formed by the daylighting surface 20a and the plane P2, the angle θ2 formed by the waveguide surface 20b and the plane P2, and the ridge This is effective when a bright portion is generated in a portion corresponding to the front surface of the point light source 15 or a dark portion is generated in a portion corresponding to the space between the point light sources 15 due to the relationship of the shape of the curved surface that defines 21. There is.

  O The protruding item | line 21 does not necessarily need the adjacent protruding item | line 21 to continue, and you may arrange | position each protruding item | line 21 at fixed intervals. That is, a flat portion may exist between the adjacent ridges 21. The interval is preferably 1/10 or less of the width of the ridges 21.

  The incident part 27 provided in the introduction part 26 has alternately a plane 27a parallel to the surface 29 extending in the width direction of the introduction part 26 and a V-shaped groove 27b as a diffusion part for diffusing the light from the point light source 15. The V-shaped groove 27b may be continuously repeated without being limited to a configuration that repeats at regular intervals.

  The incident portion 27 may be formed on the incident surface 14 a as an end surface facing the point light source 15 without projecting the introduction portion 26 on the light guide plate 14. In this case, the incident light can be spread in a plane orthogonal to the thickness direction of the light guide plate 14 as compared with the case where the incident surface 14a is flat.

  ○ The configuration in which the light incident from the incident surface 14a is emitted from the output surface 18 of the light guide plate 14 is not limited to the configuration in which the reflecting portion 19 having the configuration in which the daylighting surface 20a and the waveguide surface 20b are continuous in a sawtooth shape is provided on the back surface. For example, you may provide the lighting means using volume scattering. The daylighting means using volume scattering means light (visible light) by dispersing bubbles or beads made of a material having a refractive index different from that of the material of the light guide plate 14 in a highly transparent material constituting the light guide plate 14. Means having a function of reflecting or refracting. A reflective sheet is disposed on the back side of the light guide plate 14. In the case of adopting this configuration, the light guide plate 14 is preferably formed in a substantially wedge shape whose thickness gradually becomes thinner from the incident surface 14a side toward the opposing surface 14b side when viewed macroscopically.

  A configuration in which dots are provided on the exit surface or the back surface of the light guide plate may be adopted as the daylighting means. However, since the configuration in which dots are provided tends to lower the luminance, it can be adopted when the luminance requirement is small or the luminance of the light source is sufficient.

  The thickness of the light guide plate 14 is not constant when viewed macroscopically, and is substantially wedge-shaped and gradually thicker from the incident surface 14a side toward the opposing surface 14b side when viewed macroscopically. It may be formed.

  The diffusion sheet 17 may be omitted from the surface light source device 13. The provision of the diffusion sheet 17 can reduce the luminance unevenness of the entire emission surface of the surface light source device 13. However, depending on the definition of the display unit required for the display device using the surface light source device 13, even if the diffusion sheet 17 is omitted, it is possible to suppress the brightness unevenness from being noticed.

  ○ When manufacturing a die by electroforming, the cutting tool for machining the master die is not limited to a curved shape with a constant curvature such as an ellipse, but a constant curvature such as a circle. It may be formed in a curved shape. However, in the case where the curvature is not constant, the light that is reflected by the daylighting surface 20a and is incident on the curved surface that forms the ridges 21 is emitted from the light guide plate 14 over a wide range of light angles. The light can be emitted to the front.

  ○ After processing the mold used to manufacture the light guide plate 14 with a single tool bit, instead of manufacturing it by electroforming, the mold material is laser processed to process the recesses corresponding to the ridges 21. May be.

The following technical idea (invention) can be understood from the embodiment.
(1) In the invention according to any one of claims 1 to 6, the curve forming the outer shape is a curve in which the curvature of an elliptical arc, a parabola, or the like continuously changes.

  (2) In the invention according to claim 8, the cutting tool is formed of a curve whose curvature changes continuously, such as an elliptical arc or a parabola.

(A) is a model perspective view which shows the relationship between the light-guide plate of 1st Embodiment, and a point light source, (b) is the partial model perspective view which looked at the back surface from the output surface side. 1 is a schematic diagram of a liquid crystal display device. The front view of a light-guide plate. The schematic diagram explaining a manufacturing method. (A) is a schematic diagram which shows the effect | action of a lighting surface, (b) is a schematic diagram which shows the effect | action when a triangular prism is provided in the output surface, (c) is a schematic diagram which shows the effect | action of a lens-shaped convex part. (A) is a schematic perspective view which shows the relationship between the light-guide plate of 2nd Embodiment, and a point light source, (b) is a schematic top view of an introducing | transducing part. The schematic front view of the light-guide plate of another embodiment. The schematic top view of a prior art. The schematic diagram of another prior art. The model perspective view of another prior art. (A), (b) is a schematic top view which shows the state where a bright part appears. The model perspective view which shows the effect | action of a prism.

Explanation of symbols

  L ... light, P ... pitch, L1 ... tangent, P1 ... virtual plane, P2, 27a ... plane, 14 ... light guide plate, 14a ... incident surface, 15 ... point light source, 18 ... output surface, 19, 28 ... reflecting part 20 ... groove, 20a ... lighting surface, 21 ... projection, 22 ... contact, 23 ... bite, 24 ... mother, 26 ... introducing part, 27 ... incident part, 27b ... V-shaped groove as diffusing part, 29 ... surface.

Claims (8)

A light guide plate that emits light emitted from a light source from an incident surface at one end, converts the light into a planar shape, and emits the light.
On the back surface opposite to the exit surface that emits the light incident from the entrance surface, there is a reflecting portion that reflects the light incident from the entrance surface and guided in the light guide plate in the direction of exiting from the exit surface. A plurality of lenticular ridges are formed on the exit surface so as to extend in parallel to a virtual plane extending in a direction perpendicular to the entrance surface including the lower end of the entrance surface and in the normal direction of the entrance surface. Each of the ridges is defined by two curved surfaces convex toward the imaginary plane, and has tangent lines parallel to the imaginary plane at both ends of the outer shape in a cross section perpendicular to the extending direction of the ridges. The light guide plate in which the ridges having different average values of tangent slopes in the outer shape exist.   The light guide plate according to claim 1, wherein a pitch of a contact point between the tangent line and the outer shape is constant.   A plurality of point light sources are used as the light source, and an average value of inclinations of tangent lines on the cross section of the curved surface provided in a portion corresponding to the front surface of each point light source is provided in another portion. The light guide plate according to claim 1, wherein the curved surface is formed to be smaller than an average value of an inclination of a tangent line on the cross section.   A plurality of point light sources are used as the light source, and an average value of inclinations of tangent lines on the cross section of the curved surface provided in a portion corresponding to the front surface of each point light source is provided in another portion. 3. The light guide plate according to claim 1, wherein the curved surface is formed to be larger than an average value of an inclination of a tangent line on the cross section.   5. A plurality of grooves constituting a daylighting surface that extends along the end surface and reflects the incident light in a direction of exiting from the exit surface are formed on the back surface of the light guide plate. The light guide plate according to any one of the above.   The light guide plate is provided with an introduction portion for diffusing incident light, and the introduction portion is formed in a shape extending from the light incident side toward the light guide plate body side, and the width direction of the introduction portion A plane parallel to the surface extending in parallel with the diffusion part for diffusing the light from the point light source, and an incident part facing the point light source, and the light diffused by the diffusion part is guided to the light source. The light guide plate according to any one of claims 1 to 5, further comprising a reflecting portion that reflects toward the optical plate main body.   The surface light source device provided with the light-guide plate as described in any one of Claims 1-6, and the point light source as a light source. A plurality of lens-shaped ridges are provided on the exit surface that emits light incident from the entrance surface of one end in a planar shape so as to extend in parallel with a virtual plane that includes the lower end of the entrance surface and extends in a direction perpendicular to the entrance surface. And the outer shape of the ridge in a cross section perpendicular to the direction in which the ridge extends is formed as a convex curve on the imaginary plane side, and has a tangent line parallel to the imaginary plane as the curve. A method of manufacturing a light guide plate in which there are a plurality of curves having different average values of tangent slopes at each of the points,
Using a single bite having a blade corresponding to the curved surface constituting the ridge, the mother die having the lens-like ridge is cut, and a die is manufactured by electroforming using the mother die. A method of manufacturing a light guide plate using the mold to manufacture a light guide plate.

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