JP2013051149A - Light guide plate, surface light source device and display device - Google Patents

Abstract

Provided is a light guide plate capable of suppressing the occurrence of uneven brightness and side lobes in the vicinity of a light incident surface facing a light source.
A light guide plate 30 includes a main body 40 and a plurality of unit shape elements 50 arranged on one side surface 41 of the main body side by side in an arrangement direction intersecting a light guide direction and forming a light exit surface 31 of the light guide plate. ,including. Each unit shape element extends in a direction intersecting with the arrangement direction. The light exit surface angle θa, which is the angle formed by the outer contour 51 of the unit shape element with respect to one side surface, is 10 ° or more in the region on the outer contour corresponding to 20% to 70% of the total width of the unit shape element. It is 35 degrees or less.
[Selection] Figure 4

Description

  The present invention relates to a light guide plate having a light exit surface, a back surface opposite to the light exit surface, and a light incident surface composed of at least a part of a side surface between the light exit surface and the back surface. The present invention relates to a light guide plate that can be improved. The present invention also relates to a surface light source device including such a light guide plate and a display device in which the surface light source device including such a light guide plate is incorporated as a backlight.

  2. Description of the Related Art A surface light source device that irradiates light in a planar shape is widely used as a backlight that is incorporated in, for example, a liquid crystal display device and illuminates a liquid crystal display panel from the back side (eg, Patent Document 1). Surface light source devices for liquid crystal display devices can be broadly classified into a direct type in which a light source is arranged directly under an optical member and an edge light type in which a light source is arranged on a side of the optical member (also referred to as a side light type). being classified.

  The edge light type surface light source device has a structural feature that enables the surface light source device to be thinner than a direct type surface light source device. Due to this structural feature, the edge light type surface light source device has been mainly applied to a display device for a notebook personal computer (hereinafter, also simply referred to as “notebook PC”). However, in recent years, along with the development of a light source that emits light with good straightness represented by a light emitting diode, an edge light type surface light source device is used in a display device larger than a notebook PC, for example, a home television. Is also being applied.

JP 2004-226503 A

  However, when a light source in which light emitting diodes are arranged in a line is used, in the area on the display surface (light emitting surface) near the light incident surface facing the light source, the brightness (more strictly, luminance) is in the plane. It was confirmed that variation occurred. More specifically, in a region on the display surface (light emitting surface) near the light incident surface, bright portions and dark portions are repeatedly formed at the same pitch as the light emitting diode array pitch along the light emitting diode array direction. Was discovered.

  In addition, it was confirmed that such in-plane variation in brightness becomes more prominent when a light guide plate provided with a linear prism extending along the light guide direction on the light output side is used. Specifically, it has been found that when a light guide plate with a prism is used, the ratio of the area where the in-plane variation in brightness is confirmed increases on the display surface (light emitting surface).

  Furthermore, with the improvement of the light emission intensity of light emitting diodes in the future, the number of light emitting diodes to be used will be reduced by widening the arrangement interval of the light emitting diodes, thereby tending to reduce the cost of display devices. is expected. With such a tendency, it is expected that the in-plane variation in brightness in the region on the display surface (light emitting surface) that is in the vicinity of the light incident surface described above will be confirmed in a clearer and wider region. .

  In addition, when the light guide plate provided with the linear prism on the light output side is used, not only the brightness in-plane variation is likely to occur, but also the second brightness in an angle region greatly inclined from the front direction. There was a case where a peak was generated, a so-called side lobe appeared. On the other hand, light emitted in a direction greatly inclined from the front direction does not form an image that can be effectively observed by an observer.

  In other words, a light guide plate provided with a linear prism extending along the light guide direction on the light output side has been thought to exhibit a condensing function and improve luminance characteristics so far. It was confirmed that the internal distribution and the angular distribution of brightness could vary. In particular, if the occurrence of side lobes can be suppressed, it is very preferable in that the light emitted from the light source can be used effectively and the luminance characteristics can be improved extremely effectively.

  The present invention has been made in consideration of such points, and an object thereof is to provide a light guide plate, a surface light source device, and a display device that can effectively improve luminance characteristics.

The light guide plate according to the present invention comprises:
A light exit surface, a back surface opposite to the light exit surface, at least one light incident surface composed of a part of a side surface between the light exit surface and the back surface, and a part of the side surface along a first direction. A light guide plate having an opposite surface facing the light incident surface,
The main body,
A plurality of unit-shaped elements arranged on one side surface of the main body portion side by side in an arrangement direction intersecting the first direction and forming the light exit surface,
Each of the plurality of unit shape elements extends in a direction intersecting with the arrangement direction thereof,
A light emitting surface angle that forms an angle formed by the outer contour of the unit-shaped element with respect to the one side surface of the main body portion in a main cutting surface parallel to both the normal direction to the one side surface of the main body portion and the arrangement direction. Then, in the region on the outer contour corresponding to 20% to 70% of the width of the unit shape elements along the arrangement direction, the light exit surface angle of the unit shape elements is 10 ° to 35 °. It is as follows.

  In addition, the description about the main cut surface prescribed | regulated in the means for solving a problem, and a claim, for example, "The main cut surface parallel to both the normal line direction to the said one side surface of the said main-body part, and the said array direction. The unit shape elements (or grooves along the arrangement direction) are defined as an angle formed by the outer contour of the unit shape elements (or the light exit side surface of the groove) with respect to the one side surface of the main body. ) In a region on the outer contour (or light-emitting side surface) corresponding to a specific ratio (for example, 20% to 70% or 20% to 35%). The description “the light exit surface angle of the groove) is a specific angle (for example, 10 ° or more and 35 ° or less)” is defined in the description in the main cut sections at all positions in the first direction. Each condition It does not mean that the position be filled by the shape element (each groove).

  In the light guide plate according to the present invention, in the region on the outer contour corresponding to 20% or more and 35% or less of the width of the unit shape elements along the arrangement direction, the light exit surface angle of the unit shape elements is 10%. It is not less than 35 ° and not more than 35 °.

  In the light guide plate according to the present invention, the light exit surface angle of the unit shape element is the most from the top on the outer contour of the unit shape element farthest from the one side surface of the main body portion to the one side surface of the main body portion. You may change so that it may become large toward the edge part on the said outer outline of the said unit shape element which approached.

  In the light guide plate according to the present invention, the light exit surface angle may be 10 ° or more and 60 ° or less in the entire region on the outer contour of the main cutting surface of the unit shape element.

  Furthermore, in the light guide plate according to the present invention, in the region on the outer contour corresponding to 20% to 80% of the width of the unit shape elements along the arrangement direction, the light exit surface angle is larger than 30 °. It may be 60 degrees or less.

  Furthermore, in the light guide plate according to the present invention, a height from the one side surface of the main body portion of the unit-shaped element in the main cutting surface with respect to a width W along the arrangement direction of the unit-shaped elements in the main cutting surface. The H ratio (H / W) may be 0.3 or more and 0.45 or less.

  Furthermore, in the light guide plate according to the present invention, the unit-shaped element has two sides between the top and each end on the outer contour, and one side is located on the one side surface of the main body in the main cutting surface. A pentagonal shape in which a side is located, or a shape formed by chamfering one or more corners of the pentagonal shape, and a top portion that is farthest from the one side surface on the outer contour and each end portion that is connected to the one side surface The light-emitting surface angle of one side of the top portion is 10 ° or more and 35 ° or less, and the light-emitting surface angle of one side of the end portion side is greater than 30 ° and 60 ° or less. There may be.

  Furthermore, in the light guide plate according to the present invention, the main body portion may include a main portion made of resin and a diffusion component dispersed in the main portion.

  In the light guide plate according to the present invention, the unit-shaped element may be configured as a unit-shaped element protruding from the one side surface of the main body, or may be configured as a groove formed in the main body. Also good.

  A surface light source device according to the present invention includes any one of the above-described light guide plates according to the present invention and a light source disposed to face the light incident surface of the light guide plate.

In the surface light source device according to the present invention, the one light incident surface of the light guide plate constitutes a first light incident surface, and the opposite surface of the light guide plate constitutes a second light incident surface,
The light source may include a first light source disposed to face the first light incident surface and a second light source disposed to face the second light incident surface.

  In the surface light source device according to the present invention, the light source may include a plurality of point light emitters arranged at positions facing the light incident surface.

  A display device according to the present invention includes any one of the above-described surface light source devices according to the present invention and a liquid crystal display panel disposed to face the surface light source device.

The display device according to the present invention further comprises a control device,
The light source includes a plurality of point-like light emitters arranged at positions facing the light incident surface, and the control device controls the output of each point-like light emitter, according to an image to be displayed. You may be comprised so that the output of each point-like light-emitting body may be adjusted.

  According to the present invention, the luminance characteristics can be effectively improved.

FIG. 1 is a cross-sectional view illustrating a schematic configuration of a display device and a surface light source device for explaining an embodiment according to the present invention. FIG. 2 is a diagram for explaining the operation of the surface light source device of FIG. FIG. 3 is a perspective view showing a light guide plate incorporated in the surface light source device of FIG. FIG. 4 is a view for explaining the operation of the light guide plate, and is a view showing the light guide plate in a cross section taken along line IV-IV in FIG. 3. FIG. 5 is a cross-sectional view corresponding to FIG. 4 and is a view for mainly explaining the operation of the light guide plate in the vicinity of the light incident surface. FIGS. 6A to 6C are diagrams for explaining the operation of the light guide plate in the vicinity of the light incident surface, and are diagrams showing the optical path of the light source light incident on the main body of the light guide plate. Among these, FIG. 6A is a plan view showing the light guide plate from which the unit shape elements are omitted from the light exit surface side. FIG. 6B is a diagram showing the light guide plate from which the unit shape element is omitted from a direction orthogonal to both the light exit surface and the light entrance surface, that is, from the side. FIG. 6C is a diagram showing the light guide plate from which the unit shape elements are omitted from the light incident surface side. FIG. 7 is a cross-sectional view corresponding to FIG. 4 and is a view for explaining the operation of the light guide plate. FIG. 8 is a view for explaining a modification of the light guide plate in the same cross section as FIG. FIG. 9 is a view for explaining another modification of the light guide plate in the same cross section as FIG. FIG. 10 is a diagram corresponding to FIG. 1 and showing a modification of the surface light source device. FIG. 11 is a diagram corresponding to FIG. 3 and is a diagram for explaining still another modification of the light guide plate. 12 is a view corresponding to FIG. 4 and showing the light guide plate in a cross section taken along line XII-XII in FIG. FIG. 13 is a diagram illustrating a cross-sectional shape of the unit-shaped element in the main cut surface of the light guide plate according to Examples 1 to 5 and Comparative Examples 2 and 3. FIG. 14 is a diagram illustrating a cross-sectional shape of the unit-shaped element in the main cut surface of the light guide plate according to Examples 6 to 10 and Comparative Examples 4 and 5. FIG. 15 is a diagram illustrating a cross-sectional shape of the unit-shaped element on the main cut surface of the light guide plate according to Examples 11 to 15 and Comparative Examples 6 and 7. FIG. 16 is a diagram illustrating a cross-sectional shape of the unit shape element in the main cut surface of the light guide plate according to Comparative Examples 8 to 14. FIG. 17 is a diagram illustrating a cross-sectional shape of the unit shape element in the main cut surface of the light guide plate according to Comparative Example 1. FIG. 18 is a diagram illustrating the luminance distribution on the light exit surface of the surface light source device according to the eleventh embodiment. FIG. 19 is a diagram illustrating the luminance distribution on the light exit surface of the surface light source device according to the twelfth embodiment. FIG. 20 is a diagram illustrating a luminance distribution on the light exit surface of the surface light source device according to Comparative Example 1.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In the drawings attached to the present specification, for the sake of illustration and ease of understanding, the scale, the vertical / horizontal dimension ratio, and the like are appropriately changed and exaggerated from those of the actual product.

  1-7 is a figure for demonstrating one Embodiment by this invention. Among these, FIG. 1 is a cross-sectional view showing a schematic configuration of the liquid crystal display device and the surface light source device, and FIG. 2 is a cross-sectional view for explaining the operation of the surface light source device. FIG. 3 is a perspective view showing a light guide plate included in the surface light source device, and FIGS. 4, 5 and 7 are cross-sectional views showing the light guide plate at the main cutting plane. FIG. 6 is a diagram for explaining the optical path of light from the light source in the vicinity of the light incident surface. Note that the light guide plate in FIGS. 1 and 2 is shown in a cross-section along the line AA in FIG. 3.

  As shown in FIG. 1, the display device 10 includes a liquid crystal display panel 15, a surface light source device 20 that is disposed on the back side of the liquid crystal display panel 15 and illuminates the liquid crystal display panel 15 in a planar shape from the back side, and the liquid crystal display panel 15. And a control device 18 for controlling the surface light source device 20. The display device 10 has a display surface 11.

  The illustrated liquid crystal display panel 15 is disposed between the upper polarizing plate 13 disposed on the light output side, the lower polarizing plate 14 disposed on the light incident side, and the upper polarizing plate 13 and the lower polarizing plate 14. And a liquid crystal cell 12. Among these, the liquid crystal cell 12 includes a pair of support plates made of glass or the like, a liquid crystal disposed between the support plates, and an electrode for controlling the orientation of liquid crystal molecules by an electric field for each region forming one pixel. It is a member having. The control device 18 is configured to control the alignment of liquid crystal molecules for each pixel. As a result, the liquid crystal display panel 15 functions as a shutter that controls transmission and blocking of light from the surface light source device 20 for each pixel, and by selecting and transmitting the planar light from the surface light source device 20, the image is displayed. Will come to form. The details of the liquid crystal display panel 15 are described in various known documents (for example, “Flat Panel Display Dictionary” (supervised by Tatsuo Uchida, Hiraki Uchiike), 2001, Industrial Research Council). Detailed description is omitted.

  Next, the surface light source device 20 will be described. The surface light source device 20 has a light emitting surface 21 that emits light in a planar shape, and illuminates the liquid crystal display panel 15 from the back side. As shown in FIG. 1, the surface light source device 20 is configured as an edge light type surface light source device, and includes a light guide plate 30 and light sources 24 a and 24 b disposed on the sides of the light guide plate 30. . The light guide plate 30 includes a light output surface 31 constituted by a main surface on the liquid crystal display panel 15 side, a back surface 32 formed of the other main surface facing the light output surface 31, and a side surface extending between the light output surface 31 and the back surface 32. And have. Then, at least one light incident surface is formed by a part of the side surface of the light guide plate 30, and the light sources 24a and 24b are arranged to face the light incident surface. In addition, an opposite surface 34 that faces one light incident surface 33 is also formed by a part of the side surface, and the light incident on the light guide plate 30 from the one light incident surface 33 is approximately the light incident surface 33, The light guide plate 30 is guided in the first direction (light guide direction) connecting the opposite surface 34 facing the one light incident surface 33. In addition, the surface light source device 20 further includes a reflection sheet 22 disposed to face the back surface 32 of the light guide plate 30 and an optical sheet 26 disposed to face the light exit surface 31 of the light guide plate 30. ing.

  In the illustrated example, the light exit surface 31 of the light guide plate 30 is formed in a rectangular shape together with the display surface 11 of the liquid crystal display device 10 and the light emitting surface 21 of the surface light source device 20. That is, the light guide plate 30 is generally configured as a quadrangular plate-like member having a pair of main surfaces (light-emitting surface 31 and back surface 32). Therefore, the side surface defined between the pair of main surfaces includes four surfaces. And as shown in FIG. 1, the two surfaces which oppose the 1st direction among the side surfaces comprise the light-incidence surfaces 33 and 34. As shown in FIG. In other words, the one light incident surface described above functions as the first light incident surface 33, and the opposite surface facing the one light incident surface functions as the second light incident surface 34. As shown in FIG. 1, a first light source 24 a is provided to face the first light incident surface 33, and a second light source 24 b is provided to face the second light incident surface 34. In addition, the light guide plate 30 in the present embodiment has a constant cross-sectional shape at each position along the first direction.

  The 1st light source 24a and the 2nd light source 24b can be comprised by various aspects, such as fluorescent lamps, such as a linear cold cathode tube, point-like LED (light emitting diode), and an incandescent lamp, for example. In the present embodiment, each of the first light source 24a and the second light source 24b includes a large number of point light emitters arranged side by side along the longitudinal direction of the corresponding light incident surfaces 33 and 34, specifically, It is comprised by many light emitting diodes (LED). FIG. 3 shows the arrangement positions of a large number of point-like light emitters 25 forming the first light source 24a. The control device 18 determines the output of each point light emitter 25, that is, the brightness at the time of turning on and off each point light emitter 25 and / or the lighting of each point light emitter 25, as another point light emission. It is configured to be adjusted independently of the body output.

  The reflection sheet 22 is a member for reflecting the light emitted from the back surface 32 of the light guide plate 30 so as to enter the light guide plate 30 again. The reflection sheet 22 is composed of a white scattering reflection sheet, a sheet made of a material having a high reflectance such as metal, a sheet containing a thin film (for example, a metal thin film) made of a material having a high reflectance as a surface layer, and the like. obtain.

  The optical sheet 26 is a sheet-like member that changes the traveling direction of the light incident from the light incident side and emits the light from the light output side to intensively improve the luminance in the front direction. In the example shown in FIGS. 1 and 2, the optical sheet 26 has one direction (arrangement direction) on the sheet surface, specifically, the light incident surface 33 (34) of the light guide plate 30 described above and the light incident surface. A plurality of unit prisms 27 arranged side by side in the first direction connecting the opposite surface 34 (33) facing 33 (34). The unit prisms 27 extend linearly on the sheet surface of the optical sheet 30 in a direction orthogonal to the arrangement direction. The unit prism 27 has a triangular cross-sectional shape in a cross section orthogonal to the longitudinal direction. The apex portion 28 formed by the apex angle of the cross section of the unit prism 27 protrudes toward the light incident side, that is, the light guide plate 30 side.

  In the present specification, terms such as “sheet”, “film”, and “plate” are not distinguished from each other only based on the difference in names. Therefore, for example, a “sheet” is a concept including a member that can also be called a film or a plate.

  Further, in this specification, the “sheet surface (plate surface, film surface)” corresponds to the planar direction of the target sheet-like member when the target sheet-like member is viewed as a whole and globally. Refers to the surface. In the present embodiment, the plate surface of the light guide plate 30, the sheet surface of the optical sheet 26, the sheet surface of the reflection sheet 22, the panel surface of the liquid crystal display panel, the display surface 11 of the display device 10, and the surface light source device. The 20 light emitting surfaces 21 are parallel to each other. Further, in the present specification, the “front direction” is a direction nd of a normal to the light emitting surface 21 of the surface light source device 20 (see, for example, FIG. 2 and FIG. 4), and in the present embodiment, the display device 10. This also corresponds to the normal direction to the display surface 11, the normal direction to the plate surface of the light guide plate 30, the normal direction to the light exit surface 31 of the light guide plate 30 when viewed as a whole and as a whole.

  Further, in this specification, the terms “unit shape element”, “prism”, and “lens” are elements having shapes that can exert various optical effects (for example, reflection and refraction) on incident light ( Optical element). Further, terms such as “unit shape element”, “prism”, and “lens” are not distinguished from each other based on only the difference in names as optical elements.

  Next, the light guide plate 30 will be described in detail with reference mainly to FIGS. 2 and 3, the light guide plate 30 includes a main body portion 40 formed in a plate shape and a plurality of unit shapes formed on one side surface (light emission side surface) 41 of the main body portion 40. Element (unit optical element, unit prism) 50. The main body 40 is configured as a flat member having a pair of parallel main surfaces. The back surface 32 of the light guide plate 30 is configured by the surface 42 on the other side of the main body 40 located on the side not facing the optical sheet 26.

  As shown in FIG. 2, the main body portion 40 has a main portion 44 made of resin and a diffusion component 45 dispersed in the main portion 44. The diffusion component 45 referred to here is a component that can exert an action of changing the traveling direction of the light traveling in the main body 40 by reflection or refraction. Such a light diffusing function (light scattering function) of the diffusing component 45 can be achieved, for example, by configuring the diffusing component 45 from a material having a refractive index different from that of the material forming the main portion 44 or with respect to light. It can be applied by constructing the diffusing component 45 from a material that can exert a reflective action. Examples of the diffusion component 45 having a refractive index different from that of the material forming the main portion 44 include a metal compound, a porous material containing a gas, and simple bubbles. Note that the diffusion component 45 is omitted in the drawings other than FIG.

  Next, the unit shape element 50 provided on the one side surface 41 of the main body 40 will be described. As is well shown in FIG. 3, the plurality of unit-shaped elements 50 are arranged on the one side surface 41 of the main body portion 40 along the arrangement direction that intersects the first direction and is parallel to the one side surface 41 of the main body portion 40. Are arranged. Each unit shape element 50 extends linearly on one side surface 41 of the main body 40 so as to intersect the arrangement direction.

  In particular, in the present embodiment, the plurality of unit shape elements 50 are arranged on the one side surface 41 of the main body 40 side by side in the second direction (arrangement direction) orthogonal to the first direction without any gap. Therefore, the light exit surface 31 of the light guide plate 30 is constituted by the light exit side surface 51 of the unit shape element 50. Each unit shape element 50 extends linearly along a first direction orthogonal to the second direction. Furthermore, each unit shape element 50 is formed in a columnar shape and has the same cross-sectional shape along the longitudinal direction. In the present embodiment, the plurality of unit shape elements 50 are configured identically.

  Next, in the cross section shown in FIGS. 4 and 5, that is, in the normal direction nd to the arrangement direction (second direction) of the unit shape elements and the one side surface 41 (plate surface of the light guide plate 30) of the main body 40. A cross-sectional shape of each unit shape element 50 in a cross section parallel to both directions (hereinafter, also simply referred to as “main cut surface”) will be described. In the present embodiment, the outer contour (light-emitting side surface) 51 in the main cutting surface of the unit shape element 50 has a light-emitting surface angle θa that is an angle formed by the outer contour with respect to the one side surface 41 of the main body portion 40. The region (first region) Z1 that is 35 ° or less is included. And this 1st area | region Z1 where the light emission surface angle (theta) a is 10 degrees or more and 35 degrees or less is among the full width W of the unit shape element 50 along the arrangement direction (namely, 2nd direction) of a unit shape element. It occupies a region on the outer contour 51 corresponding to a width of 20% to 70%.

  That is, the first region Z1 in which the light exit surface angle θa is 10 ° or more and 35 ° or less occupies 20% or more and 70% or less of the entire width of the unit shape element 50 when projected in the front direction nd. It becomes like this. In the example shown in FIG. 4, the width Wa of the first region Z1 of the unit shape elements 50 along the arrangement direction of the unit shape elements 50 is 20% or more and 70% or less with respect to the total width W of the unit shape elements 50. It has become. As a result, when the light exit surface 31 of the light guide plate 30 is observed from the front direction nd, in the region of 20% to 70% of the region occupied by the light exit side surface (outer contour) 51 of the unit shape element 50, the unit The light exit surface angle θa of the shape element 50 is not less than 10 ° and not more than 35 °. As described above, the first region Z1 having the light exit surface angle θa of 10 ° to 35 ° is provided on the light exit side surface 51 of the unit-shaped element 50, as will be described in detail later. As proved from the evaluation results of the above, it is possible to prevent the occurrence of uneven brightness in the area of the display surface 11 or the light emitting surface 21 in the vicinity of the light incident surfaces 33 and 34 facing the light sources 24a and 24b. In addition, it is possible to prevent the occurrence of the second peak (side lobe) of luminance (brightness) in a direction greatly inclined from the front direction. Further, when the first region Z1 having the light exit surface angle θa of 10 ° or more and 35 ° or less is projected in the front direction nd, it occupies 20% or more and 35% or less of the entire width of the unit shape element 50. In this case, both unevenness of light and darkness and side lobes can be prevented, and furthermore, excellent front direction luminance can be secured together.

  Here, the light exit surface angle θa is defined by the light exit side surface (outer contour) 51 of the unit-shaped element 50 with respect to the one side surface 41 of the main body 40 in the main cut surface of the light guide plate 30 as described above. Is an angle. As in the example shown in FIG. 4, when the outer contour (light-emitting side surface) 51 in the main cutting surface of the unit shape element 50 is formed in a polygonal line shape, each linear part constituting the polygonal line and one of the main body parts 40. The angle formed between the side surface 41 (strictly speaking, the smaller one of the two formed angles (the minor angle)) is the light exit surface angle θa. On the other hand, the outer contour (light-emitting side surface) 51 in the main cutting surface of the unit shape element 50 may be configured by a curved surface as in a modified example described later (see FIGS. 8 and 9). For the outer contour 51 of the curved unit-shaped element 50, an angle formed between the tangent TL to the outer contour and the one side surface 41 of the main body 40 (strictly, two formed corners). The smaller angle (subordinate angle) is specified as the light exit surface angle θa.

  In the present embodiment, the outer contour (light-emitting side surface) 51 on the main cutting surface of the unit-shaped element 50 further includes a region (second region) Z2 where the light-emitting surface angle θa is greater than 30 ° and equal to or less than 60 °. Contains. And this 2nd area | region Z2 where the light emission surface angle (theta) a is larger than 30 degrees and is 60 degrees or less is the full width W of the unit shape element 50 along the arrangement direction (namely, 2nd direction) of the unit shape element 50. It occupies a region on the outer contour 51 corresponding to a width of 30% to 80%. That is, the second region Z2 in which the light exit surface angle θa is greater than 30 ° and less than or equal to 60 ° is projected in the front direction nd, and is 30% to 80% of the full width W of the unit shape element 50. Occupy. As a result, when the light exit surface 31 of the light guide plate 30 is observed from the front direction, the unit shape is 30% to 80% of the region occupied by the light exit side surface (outer contour) 51 of the unit shape element 50. The light exit surface angle of the element 50 is greater than 30 ° and 60 ° or less. In this way, by providing the second region Z2 in which the light exit surface angle θa is greater than 30 ° and less than or equal to 60 ° on the light exit side surface 51 of the unit shape element 50, as will be described in detail later, the evaluation of the example As shown also from the result, it is possible to exhibit an excellent light collecting function with respect to light components along the arrangement direction (second direction) of the unit shape elements 50.

  Further, in the present embodiment, the light exit surface angle θa is 10 ° or more and 60 ° or less in the entire region on the outer contour (light exit side surface) 51 in the main cutting surface of the unit shape element 50. By using such a light guide plate 30, it is possible to prevent the occurrence of uneven brightness in the area of the display surface 11 or the light emitting surface 12 corresponding to the vicinity of the light incident surfaces 33, 34, and greatly from the front direction nd. It is possible to prevent the occurrence of the second peak of luminance (side lobe) in the inclined direction, and it is excellent in collecting light components along the arrangement direction (second direction) of the unit shape elements 50. An optical function can be exhibited.

  In addition, in the present embodiment, the light exit surface angle θa of the unit shape element 50 is determined such that the unit shape element closest to the main body portion 40 from the top 52a on the outer contour 51 of the unit shape element 50 that is farthest from the main body portion 40. It changes so that it may become large toward the edge part 52b on the outer outline 51 of 50. According to such a light guide plate 30, the function of preventing the occurrence of uneven brightness in the region of the display surface 11 or the light emitting surface 12 corresponding to the vicinity of the light incident surfaces 33, 34 is greatly inclined from the front direction nd. Both the function of preventing the occurrence of the second peak (side lobe) of luminance in the direction and the function of condensing light components along the arrangement direction (second direction) of the unit shape elements 50 are more effective. Will come into play.

  It should be noted that the fact that the light exit surface angle θa changes from the top 52a on the outer contour 51 of the unit shape element 50 toward the end 52b only means that the light exit surface angle keeps changing so as to always increase. It is not a thing. As in the example shown in FIG. 4, even if there is a region where the outer contour 51 of the main cutting surface of the unit-shaped element 50 has a polygonal line shape or a shape obtained by chamfering a bent portion of the polygonal line, and the light exit surface angle θa does not change. Good. That is, the shape that changes so that the light exit surface angle θa increases from the top portion 52a on the outer contour 51 of the unit shape element 50 toward the end portion 52b is larger than the light exit surface angle θa at the top portion 52a. Also included is a shape that does not include a portion where the light exit surface angle θa at the end 52b is larger and the light exit surface angle θa decreases from the top 52a toward the end 52b.

  By the way, the unit shape element 50 as one specific example shown in FIGS. 4 and 5 is located on one side 41 of the main body 40 on the main cutting surface of the light guide plate 30 and on the outer contour 41. It has a pentagonal shape in which two sides are positioned between the top 52a and each end 52b, or a shape formed by chamfering one or more corners of this pentagonal shape. Further, in the illustrated example, the unit shape element 50 is used for the purpose of effectively increasing the luminance in the front direction and imparting symmetry to the angular distribution of the luminance in the plane along the second direction. The cross-sectional shape of the main cutting plane is symmetrical with respect to the front direction nd. That is, as well shown in FIGS. 4 and 5, the light emitting side surface 51 of each unit-shaped element 50 is configured by a pair of bent surfaces 37 and 38 that are configured symmetrically about the front direction. . The pair of folding surfaces 37 and 38 are connected to each other to define a top portion 52a. Each of the folding surfaces 37 and 38 includes first inclined surfaces 37a and 38a that define the top portion 52a, and second inclined surfaces 37b and 38b that are connected to the first inclined surfaces 37a and 38a from the main body 40 side. doing. The pair of first inclined surfaces 37a and 38a have a symmetric configuration with respect to the front direction nd, and the pair of second inclined surfaces 37b and 38b also have a symmetric configuration with respect to the front direction nd.

  And the unit shape element 50 shown by FIG. 4 is 1st inclined surface 37a, 38a among the two sides located between the top part 52a and each edge part 52b on the outer contour 51 in a main cut surface. The side on the top 52a side constituted by the above has a light exit surface angle θa1 of 10 ° to 35 °, and the side on the end 52b side constituted by the second inclined surfaces 37b, 38b is larger than 30 ° and 60 °. The light exit surface angle θa2 is less than or equal to °. That is, the above-described first region Z1 of the light emitting side surface 51 of the unit shape element 50 is a region where a pair of first inclined surfaces 37a and 38a configured symmetrically with respect to the front direction nd is disposed, and the unit shape The above-described second region Z2 on the light output side 51 surface of the element 50 is a region where a pair of second inclined surfaces 37b and 38b configured symmetrically with respect to the front direction is disposed.

  In addition, as a whole structure of the unit shape element 50, the main body portion 40 of the unit shape element 50 on the main cutting surface of the light guide plate 30 with respect to the width W in the arrangement direction of the unit shape elements 50 on the main cutting surface of the light guide plate 30. It is preferable that the ratio (H / W) of the protrusion height H along the front direction from 0.3 to 0.45. According to such a unit shape element 50, an excellent light collecting function is exhibited with respect to light components along the arrangement direction (second direction) of the unit shape elements 50 due to refraction and reflection at the light exit side surface 51. And generation of side lobes can be effectively suppressed.

  In addition, the “pentagonal shape” in the present specification includes not only a pentagonal shape in a strict sense but also a substantially pentagonal shape including limitations in manufacturing technology, errors in molding, and the like. Similarly, terms used in the present specification to specify other shapes and geometric conditions, for example, terms such as “parallel”, “orthogonal”, and “symmetric” are not limited to strict meanings. Interpretation will be made including such an error that a similar optical function can be expected.

  Here, the dimension of the light guide plate 30 may be set as follows as an example. First, as a specific example of the unit shape element 50, the width W (see FIG. 4) can be set to 0.05 mm or more and 0.5 mm or less. In addition, when the outer contour 51 on the main cutting surface of the unit shape element 50 has a shape formed by chamfering the bent portion of the broken line, the value of the radius of curvature of the chamfered portion on the main cutting surface is the unit shape element 50. The width W is preferably equal to or smaller than the value of the width W. This is because when the radius of curvature of the chamfered portion is larger than the value of the width W of the unit shape element 50, the unit shape element 50 cannot exhibit the expected function. On the other hand, the thickness of the main body 40 can be set to 0.5 mm to 6 mm.

  The light guide plate 30 having the above configuration can be manufactured by molding the unit shape element 50 on a base material or by extrusion molding. Various materials can be used as the material forming the main portion 44 of the main body portion 40 of the light guide plate 30 and the unit shape element 50. However, it is widely used as a material for an optical sheet incorporated in a display device, and has excellent mechanical properties, optical properties, stability, workability, and the like, and can be obtained at low cost, such as acrylic, styrene, polycarbonate, Transparent resins mainly composed of one or more of polyethylene terephthalate, acrylonitrile and the like, and epoxy acrylate and urethane acrylate-based reactive resins (ionizing radiation curable resins and the like) can be suitably used. On the other hand, the diffusion component 45 includes particles made of a transparent material such as silica (silicon dioxide), alumina (aluminum oxide), acrylic resin, polycarbonate resin, and silicone resin having an average particle diameter of about 0.5 to 100 μm. Can be used.

  When the light guide plate 30 is produced by curing the ionizing radiation curable resin on the base material, the sheet-shaped land portion that is positioned between the unit shape element 50 and the base material is provided together with the unit shape element 50. It may be formed on a substrate. In this case, the main body portion 40 is composed of a base material and a land portion formed of an ionizing radiation curable resin. Moreover, the board | plate material which consists of a resin material extrusion-molded with the diffusion component as a base material can be used.

  On the other hand, in the light guide plate 30 manufactured by extrusion molding, the main body portion 40 and the plurality of unit shape elements 50 on one side surface 41 of the main body portion 40 can be integrally formed. When the light guide plate 30 is produced by extrusion molding, the unit shape element 50 is composed of the same resin material as the material forming the main portion 44 of the main body 40 and particles forming the diffusion component 45 of the main body 40. May be. Alternatively, the light guide plate 30 is manufactured by so-called coextrusion, and the main body portion 40 is composed of a main portion 44 made of a resin material and a diffusion component 45 dispersed in the main portion 44, while a unit shape The element 50 may be composed of the same resin material as the material forming the main portion 44 of the main body portion 40 and particles having a separate function as the diffusion component 45 of the main body portion 40, or the main body It may be composed of only the same resin material as the material forming the main portion 44 of the portion 40.

  Next, the operation of the display device 10 having the above configuration will be described.

  First, as shown in FIG. 2, the light emitted from the light emitters 25 forming the light sources 24 b and 24 b enters the light guide plate 30 through the light incident surfaces 33 and 34. FIG. 2 shows an example in which light enters the light guide plate 30 from the first light source 24a via the first light incident surface 33 as an example. The operation of the surface light source device 20 and the display device 10 will be described below based on the example shown in FIG. However, the light guide plate 30 has a symmetric configuration with the center position Pc in the first direction as the center. The first light source 24a and the second light source 24b are configured symmetrically with the light guide plate 30 sandwiched in the first direction. Further, the other components of the surface light source device 20 such as the optical sheet 26 and the liquid crystal display panel 15 also have symmetry. Due to the symmetry of such a configuration, the following description applies similarly to the light incident on the light guide plate 30 from the second light source 24b via the second light incident surface 34.

  As shown in FIG. 2, the light L21 and L22 incident on the light guide plate 30 is reflected on the light output surface 31 and the back surface 32 of the light guide plate 30, particularly due to a difference in refractive index between the material forming the light guide plate 30 and air. Then, the total reflection is repeated, and the light proceeds to the first direction (light guide direction) connecting the light incident surface 33 and the opposite surface (the other light incident surface) 34 of the light guide plate 30.

  However, the diffusion component 45 is dispersed in the main body 40 of the light guide plate 30. For this reason, as shown in FIG. 2, the light L21 and L22 traveling in the light guide plate 30 has their traveling directions irregularly changed by the diffusion component 45, and the light exit surface 31 and the back surface 32 at an incident angle less than the total reflection critical angle. May be incident. In this case, the light can be emitted from the light exit surface 31 and the back surface 32 of the light guide plate 30. The light L21 and L22 emitted from the light exit surface 31 travels to the optical sheet 26 disposed on the light exit side of the light guide plate 30. On the other hand, the light emitted from the back surface 32 is reflected by the reflection sheet 22 disposed on the back surface of the light guide plate 30, enters the light guide plate 30 again, and travels through the light guide plate 30.

  The collision between the light traveling in the light guide plate 30 and the diffusion component 45 dispersed in the light guide plate 30 occurs in each area along the light guide direction in the light guide plate 30. For this reason, the light traveling in the light guide plate 30 is gradually emitted from the light exit surface 31. Thereby, the light quantity distribution along the light guide direction (first direction) of the light emitted from the light exit surface 31 of the light guide plate 30 can be made uniform.

  In particular, as shown in FIG. 4, the cross-sectional shape of the main cutting surface of the unit shape element 50 is a pentagonal shape symmetrically arranged around the front direction or a shape formed by chamfering one or more corners of the pentagonal shape. It has become. More specifically, as described above, the light exit surface 31 of the light guide plate 30 is configured as the bent surfaces 37 and 38 that are inclined with respect to the back surface 32 of the light guide plate 30. The light that is totally reflected by the light exit surface 31 formed by the bent surfaces 37 and 38 and travels through the light guide plate 30 and the light that passes through the light output surface 31 formed by the bent surfaces 37 and 38 and is emitted from the light guide plate 30 are as follows. The light-exiting surface 31 composed of the bent surfaces 37 and 38 has an effect described below. First, the effect exerted on the light traveling through the light guide plate 30 after being totally reflected by the light exit surface 31 including the bent surfaces 37 and 38 will be described.

  In FIG. 4, the optical paths of the lights L41 and L42 that travel in the light guide direction (first direction) through the light guide plate 30 while repeating total reflection on the light exit surface 31 and the back surface 32 are shown in the main cut surface of the light guide plate. ing. As described above, the light exit surface 31 of the light guide plate 30 has a pentagonal shape arranged symmetrically with respect to the front direction or a shape formed by chamfering one or more corners of the pentagonal shape as a cross-sectional shape. More specifically, the unit-shaped element 50 includes two kinds of bent surfaces 37 and 38 that are formed by the light-exiting side surface 51 and are inclined opposite to each other across the normal direction nd to the one side surface 41 of the main body 40. It is out. Further, the two types of bent surfaces 37 and 38 that are inclined to the opposite sides are alternately arranged along the second direction. As shown in FIG. 4, the light L41 and L42 that travel in the light guide plate 30 toward the light exit surface 31 and enter the light exit surface 31 are often guided out of the two types of bent surfaces 37 and 38. In the main cutting surface of the optical plate, the light enters the inclined surface inclined to the opposite side to the traveling direction of the light with respect to the normal direction nd to the one side surface 41 of the main body 40.

  As a result, as shown in FIG. 4, the light L41 and L42 traveling in the light guide plate 30 is totally reflected by the bent surfaces 37 and 38 of the light exit surface 31, and the traveling direction of the main cut surface is the front direction nd. Centered on the opposite side. That is, the component along the second direction of the light is not easily directed to the opposite side due to total reflection at the light exit surface 31. In this manner, the light guided in the first direction (light guide direction) in the light guide plate 30 is easily reversed in the traveling direction in the second direction every time it is totally reflected by the light exit surface 31. As a result, light that is emitted from the light emitters 25 of the light sources 24a and 24b in a direction greatly inclined with respect to the first direction and enters the light guide plate 30 is also mainly controlled in the first direction while being restricted from moving in the second direction. Go on to. Thereby, the light quantity distribution along the second direction of the light emitted from the light exit surface 31 of the light guide plate 30 is adjusted by the configuration of the light sources 24 a and 24 b (for example, the arrangement of the light emitters 25) and the output of the light emitter 25. It becomes possible to do.

  Next, the effect exerted from the folding surfaces 37 and 38 on the light that passes through the folding surfaces 37 and 38 and is emitted from the light guide plate 30 will be described. As shown in FIG. 4, the light L41 and L42 emitted from the light guide plate 30 through the unit shape element 50 are inclined surfaces 37 and 38 forming the light output side surface 51 of the unit shape element 50 forming the light output surface 31 of the light guide plate 30. Refracts at. Due to this refraction, the traveling direction (outgoing direction) of the light L41 and L42 traveling in the direction inclined from the front direction nd on the main cut surface is mainly compared with the traveling direction of the light when passing through the light guide plate 30. Thus, it is bent so that the angle formed with respect to the front direction nd is small. By such an action, the unit shape element 50 can narrow the traveling direction of the transmitted light to the front direction nd side with respect to the light component along the second direction orthogonal to the light guide direction. That is, the unit shape element 50 has a light condensing effect on the light component along the second direction orthogonal to the light guide direction. In this way, the emission angle of the light emitted from the light guide plate 30 is narrowed down to a narrow angle range centering on the front direction in a plane parallel to the arrangement direction of the unit shape elements 50 of the light guide plate 30.

  The light L21 and L22 finally emitted from the light exit surface 31 of the light guide plate 30 as described above enters the optical sheet 26 as shown in FIG. As described above, the optical sheet 26 includes the unit prism 27 having a triangular cross section whose apex angle projects toward the light guide plate 30 side. As shown well in FIG. 2, the longitudinal direction of the unit prism 27 intersects with the light guide direction (first direction) by the light guide plate 30, particularly in the present embodiment, the second direction orthogonal to the light guide direction. It is parallel to the direction. Further, due to the refractive index difference between the material forming the light guide plate 30 and air, the emission angle of the first direction component of the light emitted from the light exit surface 31 of the light guide plate 30 (the first direction component of the emitted light and the light guide plate 30). The angle (θc) formed by the normal direction nd to the plate surface tends to be biased within a specific angle range (for example, 65 ° to 85 °).

  For these reasons, as shown in FIG. 2, most of the light emitted from the light exit surface 31 of the light guide plate 30 passes through one prism surface 27 a of the unit prism 27 of the optical sheet 26 and enters the unit prism 27. Then, the optical sheet 26 can be designed so as to be totally reflected by the other prism surface 27b of the unit prism 27. Due to the total reflection at the prism surface 27b of the unit prism 27, the lights L21 and L22 traveling in the direction inclined from the front direction nd in the cross section of FIG. 2 (a cross section parallel to both the first direction and the front direction nd) It is bent so that the angle formed by the traveling direction with respect to the front direction nd is small. By such an operation, the unit prism 27 can narrow the traveling direction of the transmitted light to the front direction nd side with respect to the light component along the first direction (light guide direction). That is, the optical sheet 26 has a light condensing effect on the light component along the first direction.

  The light whose traveling direction is greatly changed by the unit prisms 27 of the optical sheet 26 as described above is mainly a component that travels in the first direction that is the arrangement direction of the unit prisms 27, and is a unit shape element of the light guide plate 30. It is different from the component traveling in the second direction that is collected by the 50 light exit side surfaces 51. Therefore, the front direction luminance can be further improved without harming the front direction luminance raised by the unit shape element 50 of the light guide plate 30 by the optical action of the unit prism 27 of the optical sheet 26.

  As described above, in the surface light source device 20, the distribution of the emitted light amount along the first direction (light guide direction) is made uniform, the front direction luminance is improved, and light is emitted from the light emitting surface 21 in a planar shape. To do. The light emitted from the surface light source device 20 then enters the liquid crystal display panel 15. The liquid crystal display panel 15 selectively transmits light from the surface light source device 20 for each pixel. Thereby, the observer of the liquid crystal display device 10 can observe an image.

  Further, as described above, the light that has entered the light guide plate 30 travels in the first direction while being restricted from moving in the second direction by the bent surfaces 37 and 38 that form the light exit side surface 51 of the unit-shaped element 50. become. That is, the light emitted from each of the multiple light emitters 25 constituting the light sources 24a and 24b is located at a predetermined position in the second direction on the light exit surface 31 of the light guide plate 30, and extends in the first direction. The light is mainly emitted from within the region. Therefore, the control device 18 may adjust the output of each light emitter 25 in accordance with the image displayed on the display surface 11 of the display device 10.

  For example, when nothing is displayed in a certain area within the display surface 11 of the display device 10, in other words, when black is displayed in a certain region within the display surface 11 of the display device 10, this corresponds to the region of the display surface 10. The point light emitter 25 that supplies light to the region of the light exit surface 31 of the light guide plate 30 may be turned off. In this case, it is possible to eliminate conventional problems such as a decrease in contrast caused by the illumination light from the surface light source device 20 being not completely blocked by the display panel 15. Further, the amount of electricity used can be saved, which is preferable from the viewpoint of energy saving.

  Furthermore, the display is not limited to the example of displaying black, and the display level is not dependent on only the display panel 15 by adjusting the output level of each point-like light emitter 25 corresponding to the image displayed on the display surface 11. You may make it adjust the brightness in each area | region of the image | video to be performed. Even in such an example, the contrast of the displayed image can be improved and energy saving can be realized.

  By the way, due to the recent increase in interest in environmental problems, light emitting diodes are attracting attention as light emitters that serve as light sources. From the viewpoint of energy efficiency, light-emitting diodes are much superior to cold-cathode tubes that have been widely used as light-emitting bodies that serve as light sources. However, when the present inventors form a light source by linearly arranging pointed light emitters made of light emitting diodes or the like, and replace the light source made of a cold cathode tube of a conventional surface light source device, the light guide plate Non-uniformity in brightness occurs in the area near the light entrance surface of the light exit surface, or in the region of the light emitting surface of the surface light source device or the display surface of the display device corresponding to the region of the light exit surface of the light guide plate, That is, it was found through the development of a surface light source device that the luminance in-plane variation occurs.

  According to the investigation by the present inventors, when a light source in which point light emitters made of light emitting diodes or the like are arranged in a line is used, the light and darkness in the region on the light guide plate light exit surface near the light entrance surface facing the light source is determined. More specifically, the arrangement pitch of the point light emitters along the arrangement direction (second direction) of the point light emitters in the region on the light guide plate light exit surface in the vicinity of the light incident surface. And bright and dark portions were repeatedly formed at the same pitch.

  In recent years, a light guide plate in which prisms extending linearly along a light guide direction (first direction) are arranged in a direction (second direction) orthogonal to the light guide direction is becoming widespread. This linear prism forms the light exit surface of the light guide plate, and exerts a condensing action on the light emitted from the light guide plate. More specifically, the linear prism has a prism surface (an inclined surface) inclined by about 45 ° with respect to the front direction. By this refraction at the prism surface, the traveling direction of the transmitted light is deflected so that the angle with respect to the front direction becomes small. On the other hand, for light that cannot be deflected in a narrow angle range centered on the front direction, the traveling direction is folded back to the back side by reflection on the prism surface, particularly total reflection.

  When the unit prism that is expected to have such a light condensing function is provided on the light guide plate, unevenness in the second direction of the brightness generated in the vicinity of the light incident surface of the light exit surface of the light guide plate is further increased. It has been found by the present inventors' research that it becomes prominent, and more specifically, that the unevenness generation region along the second direction of brightness becomes wide.

  In addition, as a result of extensive research conducted by the present inventors, in the case where a linear prism having a prism surface (inclined surface) inclined by about 45 ° with respect to the front direction is provided on the light guide plate, in-plane variation in brightness. It has been found that not only is it easy to occur, but that a second brightness peak occurs in an angle region that is greatly inclined from the front direction, that is, a so-called side lobe appears. The light that forms the side lobe is light that travels in a direction greatly inclined from the front direction, and cannot be recognized by the observer as light that effectively forms an image. That is, the occurrence of side lobes is not limited to the fact that the image is brightly observed in a direction that is largely inclined from the front direction, but does not form an image that can be effectively observed by an observer. It cannot be said that the emitted light is used effectively. That is, the generation of side lobes is not preferable in terms of energy efficiency.

  On the other hand, according to the present embodiment described above, it has been confirmed that the occurrence of in-plane luminance variations and side lobes can be effectively suppressed. Although the details of the reason why such a phenomenon occurs are unclear, the reasons presumed through the inventors' research will be described below. In the following, an estimation reason for causing in-plane variation in luminance in the vicinity of the light incident surface facing the light source and an estimation reason for making the luminance variation inconspicuous according to the present embodiment will be described. However, the present invention is not limited to the following estimation.

  As shown in FIGS. 6A to 6C, the pointed light emitters (for example, light emitting diodes) forming the light sources 24a and 24b arranged to face the light incident surfaces 33 and 34 of the light guide plate 30 are light beams. Release radially. 6A to 6C show an example in which light is emitted radially from one light emitting point 25a of the point light emitter 25 around the light guide direction. Accordingly, light emitted from a certain light emitting point 25a becomes a light beam LF spreading in a conical shape indicated by a dotted line in FIGS. 6 (a) to 6 (c). 6A to 6C, the same optical path is observed from the front direction, the second direction (unit shape element arrangement direction), and the first direction (longitudinal direction of unit shape elements), respectively. Show. However, in FIGS. 6A to 6C, the unit shape element 50 is omitted for convenience of understanding.

  Since light is emitted radially as shown in FIGS. 6A to 6C, the light exit surface 31 of the light guide plate 30 (in the drawing, the main body portion 40 of the light guide plate 30 in the immediate vicinity). The light that can be directly incident on the light output side surface 41 (incident on the light output surface 31 without being reflected on the back surface 32 after being incident on the light guide plate 30 from the light sources 25a and 25b) is the arrangement direction of the point light emitters 25 That is, the light L61 does not contain a lot of components along the second direction (in other words, the light does not travel so much in the second direction) L61. On the other hand, among the light emitted radially from the point light emitter 25, the light L63 containing a lot of components along the second direction (in other words, light that travels well in the second direction) L63 has the first direction component. Since it is included only slightly, it can directly enter the light exit surface 31 of the light guide plate 30 (in the drawing, the light exit side surface 41 of the main body 40) at a position P3 far from the light entrance surfaces 33 and 34.

  For this reason, the region A1 where light emitted radially from one point light emitter 25 can be directly incident is a target as shown in FIG. 6A when viewed from the front. This is a region (hereinafter also referred to as a bright region) surrounded by a curve CL closest to the one point-like light emitter 25 at a position P1 facing the one point-like light emitter 25 from the first direction. In particular, the light emitted from one point-like illuminant enters a radial region with the light guide direction (first direction) as the center, as in a normal usage mode in a commercially available edge light type surface light source device. When proceeding, the bright area A1 where the radial light LF can directly enter is an area surrounded by a parabola CL having an extreme value at a position P1 facing the target pointed light emitter 25 from the first direction.

  Therefore, the light exit surface 31 in the vicinity of the light incident surfaces 33 and 34 of the light guide plate 30 faces the intermediate position between the two point-like light emitters 25 adjacent to each other in the second direction, and follows the light guide direction (first direction). The light that enters the light guide plate 30 from the pointed light emitter 25 that emits light in a radial manner does not directly reach the region A2 (hereinafter also referred to as a dark region) that does not reflect on the back surface or the like. . As a result, the amount of light emitted from the dark region A2 is the adjacent region A1, and from the region A1 where the light incident in the light guide plate 30 from the pointed light emitter 25 that emits light radially can reach directly. It is significantly lower than the amount of emitted light.

  As described above, in the vicinity of the light incident surface facing the light source composed of the point light emitters 25, bright and dark stripes are generated at the same pitch as the arrangement pitch of the point light emitters along the arrangement direction of the point light emitters. The reason is considered.

  Further, light that does not contain a lot of the second direction component (for example, the light L61 in FIGS. 6A to 6C) has a relatively large light exit surface angle, specifically, excellent condensing characteristics due to refraction. When the light is incident on a light exit surface having a light exit surface angle of about 45 ° that can be exhibited, it repeats total reflection such as so-called retroreflection to change the traveling direction and move toward the back surface (light in FIG. 5). L51). That is, the second direction component of the light L51 travels in the first direction without largely changing. As a result, the light L51 incident on the clear area A1 is not diffused in the second direction. That is, the light L51 incident on the clear area A1 is restricted from traveling toward the dark area A2.

  On the contrary, even the slightly inclined light (for example, the light L62 in FIGS. 6A to 6C) has a light exit surface angle of about 45 °, similar to the action received from the unit shape element 50 described above. The movement in the second direction is constrained by the reflection on the light exit surface. Therefore, when a light guide plate provided with a unit prism having a relatively large light exit surface angle for the purpose of condensing is used, in-plane variation in luminance occurs along the arrangement direction (second direction) of the point light emitters. It is estimated that the area was confirmed in a larger area.

  Furthermore, with the improvement of the light emission intensity of light emitting diodes in the future, it is predicted that the number of light emitting diodes used will be reduced by widening the arrangement interval of the light emitting diodes, thereby tending to reduce the cost of display devices. Is done. As the arrangement interval of the light emitting diodes increases, it is expected that the in-plane variation in luminance near the light source will be confirmed in a clearer and wider area.

  On the other hand, according to the present embodiment, as described above, on the outer contour corresponding to a width region of 20% to 70% of the total width W of the unit shape elements 50 along the arrangement direction of the unit shape elements 50. The light guide plate 30 is a region (first region Z1), that is, a region Z1 on the outer contour 51 that occupies 20% to 70% of the entire width W of the unit shape element 50 when observed from the front direction. The light exit surface angle θa1, which is the angle formed by the light exit side surface 51 of the unit-shaped element 50 or the tangent to the light exit side surface 51 with respect to the one side surface 41 of the main body 40, is 10 ° or more and 35 ° or less. Yes.

  As a result of extensive research conducted by the present inventors, according to the light emitting side surface 51 of the unit-shaped element 50 having a relatively small light emitting surface angle θa, as shown in FIG. Of the light incident on the light guide plate 30 via 33, the light L52 has little component in the second direction and has a strong component along the direction parallel to the front direction nd, and is very close to the light incident surface 33. It was confirmed that the light L52 directly incident on the light exit surface 31 can be effectively diffused in the second direction. More specifically, in the region on the outer contour 51 corresponding to 20% or more of the total width W of the unit shape elements 50 along the arrangement direction of the unit shape elements 50, the light exit surface angle θa is 10 ° or more and 35 ° or less. In this case, it was confirmed that the in-plane variation in luminance on the light exit surface 31 in the vicinity of the light incident surface 33 can be made inconspicuous to such an extent that it cannot be visually determined. .

  Next, the cause of the occurrence of side lobes is estimated as follows. As already described with reference to FIG. 4, the light L41 and L42 that travel in the light guide plate 30 toward the light exit surface 31 and enter the light exit surface 31 are often out of the two types of bent surfaces 37 and 38. In the main cut surface of the light guide plate, the light enters the inclined surface inclined to the opposite side to the traveling direction of the light with reference to the normal direction nd to the one side surface 41 of the main body 40. However, as shown in FIG. 7, when the angle formed by the traveling direction of the light L71 and the front direction nd is small, the light L71 is inclined to the same side as the traveling direction of the light with respect to the normal direction nd. It can also enter the inclined surface. In this case, the light L71 can be totally reflected by the incident prism surface (inclined surface 37 in FIG. 7), and in many cases, the opposite inclined surface (inclined surface 38 in FIG. 7) facing the prism surface. ).

  At this time, when the light exit surface angle θa of the inclined surface on the opposite side is a relatively large angle that is considered suitable for light collection, it is particularly about 45 ° that is considered to exhibit the most excellent light collection function. In this case, the incident angle of the light on the opposite inclined surface is relatively small. As a result, like the light L71a in FIG. 7, the light is refracted and emitted from the unit shape element without being reflected by the opposite inclined surface. And the emission angle of the said light L71a becomes very large in the main cut surface of a light-guide plate. In order to correct the traveling direction of the light L71a, an optical sheet having unit shape elements arranged in the second direction or a light diffusing sheet having a light diffusing function is arranged on the light output side of the light guide plate. Unless it is not corrected, the direction of travel is not corrected. And it is estimated that such light L71a is a cause which forms a side lobe.

  On the other hand, according to the present embodiment, as described above, the outer region corresponding to the width region of 20% or more and 70% or less of the total width W of the unit shape elements 50 along the arrangement direction of the unit shape elements 50. A region on the contour (first region Z1), that is, a region Z1 on the outer contour 51 that occupies 20% to 70% of the total width W of the unit shape element 50 when observed from the front direction. The light exit surface angle θa1, which is the angle formed by the light exit side surface 51 of the unit-shaped element 50 or the tangent to the light exit side surface 51 with respect to the one side surface 41 of the main body 40 on the main cut surface of the light guide plate 30, is 10 ° or more and 35 ° or less. It has become.

  As a result of extensive research by the present inventors, according to the light emitting side surface 51 of the unit-shaped element 50 having a relatively small light emitting surface angle θa of 10 ° or more and 35 ° or less, as shown in FIG. Light that has traveled in a direction that is not significantly inclined with respect to the front direction nd on the main cutting plane, and that is then totally reflected by an inclined surface that is inclined to the same side as the traveling direction with respect to the normal direction nd as a reference, and is incident on the surface L71 can be totally reflected. In other words, the first region Z1 in which the light exit surface angle θa is relatively small at 10 ° or more and 35 ° or less is effective for the light L71 to be emitted in a direction greatly inclined from the front direction nd forming the side lobe. Can be prevented. The light totally reflected by the first region Z1 of the unit shape element 50 then proceeds again toward the light exit side by reflection on the back surface 32 of the light guide plate 30 or the reflection sheet 22. That is, it is possible to correct the traveling direction of the light that has been formed by wasting side lobes so far and use the light as light for effectively forming an image. As a result of extensive research conducted by the present inventors, in the region on the outer contour 51 corresponding to 20% or more of the total width W of the unit shape elements 50 along the arrangement direction of the unit shape elements 50, the light exit surface angle θa. Is 10 ° or more and 35 ° or less, in the display device having the configuration shown in FIG. 1, that is, the optical sheet for correcting the traveling direction of light along the second direction is a light guide plate. In the display device that is not arranged on the light-emission side, the luminance angle distribution in the plane along the second direction is such that the occurrence of side lobes on the display surface 11 of the display device 10 cannot be visually detected. The second peak at could be made inconspicuous.

  According to the present inventors' confirmation, an area on the outer contour corresponding to a width area of 20% or more of the total width W of the unit shape elements 50 along the arrangement direction of the unit shape elements 50 (first area) In Z1), if the light exit surface angle θa1 is not less than 10 ° and not more than 35 °, the in-plane variation of the brightness on the light exit surface 31 in the vicinity of the light entrance surface 33 and the brightness in the direction greatly inclined from the front direction nd. The peak of 2 could be made inconspicuous. However, when the area where the light exit surface angle θa1 is 10 ° or more and 35 ° or less exceeds 70% of the total width W of the unit shape elements 50 along the arrangement direction of the unit shape elements 50, the unit shape element 50 However, the optical function can no longer be exhibited effectively. For this reason, in the area | region (1st area | region Z1) on the outer contour corresponding to the width area of 20% or more and 70% or less of the total width W of the unit shape elements 50 along the arrangement direction of the unit shape elements 50, the light exit surface If the angle θa1 is not less than 10 ° and not more than 35 °, both the in-plane variation in luminance at the light exit surface 31 in the vicinity of the light incident surface 33 and the second peak of luminance in the direction greatly inclined from the front direction nd are obtained. Not only can it be made inconspicuous, but it is also possible to adjust the brightness in the front direction.

  Further, as demonstrated in the examples described later, according to the research results of the present invention, 20% or more and 35% or less of the total width W of the unit shape elements 50 along the arrangement direction of the unit shape elements 50. If the light exit surface angle θa1 is not less than 10 ° and not more than 35 ° in the region on the outer contour corresponding to the width region (first region Z1), the light exit surface angle θa1 is not less than 10 ° and not more than 35 °. It was confirmed that the brightness in the front direction substantially equivalent to that in the case where the one region Z1 is not provided can be secured. Such a phenomenon is predicted based on the fact that light that has been wasted by forming side lobes so far can be effectively used. Such an effect exceeds the range predicted from the state of the art, where the unit shape element having a right-angled isosceles triangular cross-sectional shape was considered to be able to exhibit the most excellent light collecting function. It can be said that it is remarkable.

  In particular, in the present embodiment, in the region (second region) Z2 on the outer contour corresponding to 30% to 80% of the total width W of the unit shape elements 50 along the arrangement direction of the unit shape elements 50. The light exit surface angle θa2 is greater than 30 ° and 60 ° or less. As a result of extensive studies by the present inventors, when such a light guide plate 30 is used, the unit-shaped element 50 of the light guide plate 30 has a light exit surface angle θa of 10 ° to 35 ° as described above. It was confirmed that the light condensing function can be effectively exhibited along the arrangement direction (second direction) of the unit shape elements 50 even if the light emitting side surface 51 (light emitting surface 31) is included.

  Further, in the present embodiment, the light exit surface angle is 10 ° or more and 60 ° or less in the entire region on the outer contour 51 in the main cutting surface of the unit shape element 50. Thereby, it is possible to prevent light from being emitted from the light guide plate 30 without having any light collecting action on the components along the arrangement direction (second direction) of the unit shape elements 50.

  In addition, in the present embodiment, the light exit surface angle θa of the unit shape element 50 is determined so that the unit shape element closest to the main body portion 40 from the top 52a on the outer contour 51 of the unit shape element 50 that is farthest away from the main body portion 40. It changes so that it may become large toward the edge part 52b on 50 outer contour 51. FIG. Therefore, on the side of the top portion 52a that is separated from the main body portion 40 of the unit shape element 50, the light emission side surface 51 of the unit shape element 50 has a relatively small light emission surface angle θa1. On the other hand, on the side of the end portion 52b close to the main body portion 40, the light exit side surface 51 of the unit shape element 50 has a relatively large light exit surface angle θa2. In particular, according to the present embodiment, the light exit surface angle θa is 10 ° or more and 35 ° or less in the first region Z1 including the top portion 52a of the unit shape element 50, and the diffusion is excellent with respect to the second direction component. A light outgoing side surface 51 (light outgoing surface 31) that can perform the function and can totally reflect the light L71a that can cause a side lobe is formed by the first inclined surfaces 37a and 38a. On the other hand, in the second region Z2 including the end portion 52b of the unit shape element 50, the light exit surface angle θa is greater than 30 ° and less than or equal to 60 °, and the light traveling in the second direction is more effectively suppressed. In addition, the light output side surface 51 (light output surface 31) capable of exhibiting the light collecting function very effectively with respect to the component along the second direction is formed by the second inclined surfaces 37b and 38b.

  Naturally, the light including many components along the second direction (for example, the lights L41 and L42 in FIG. 4) is the region on the end 52b side that is close to the main body 40 in the light emitting side surface 51 of the unit shape element 50. It becomes easy to enter. On the other hand, light (for example, the lights L51 and L52 in FIG. 4) that contains only a small amount of the component along the second direction can be substantially uniformly incident on the entire area of the light emitting side surface 51 of the unit shape element 50. . Therefore, the light incident on the region including the top portion 52a of the light emitting side surface 51 of the unit shape element 50 that is separated from the main body portion 40 is compared with the light incident on the region including the end portion 52b close to the main body portion 40. , A light with a small component along the second direction is included at a higher rate. In addition, the light L71a that can cause a side lobe (for example, the light L71 in FIG. 7) is likely to enter the region near the top 52a of the unit shape element 50. For this reason, the light emission side surface 51 in which the light emission surface angle θa of the light emission side surfaces 51 of the unit-shaped element 50 is 10 ° or more and 35 ° or less is selectively selected with respect to light having a small component along the second direction. Selectively totally reflects light that can diffuse and cause side lobes. As a result, the brightness unevenness in the region on the light exit surface 31 in the vicinity of the light incident surfaces 33 and 34 can be made inconspicuous, and a second peak of luminance occurs in a direction greatly inclined from the front direction nd. This can be effectively prevented.

  As described above, by arranging the light exit side surface 51 having the light exit surface angle θa of 10 ° or more and 35 ° or less at a position separated from the main body 40, unevenness of light and darkness and side lobe in the vicinity of the light incident surfaces 33 and 34 are eliminated. Generation can be effectively inconspicuous. Therefore, when the light exit side surface 51 having the light exit surface angle θa1 of 10 ° or more and 35 ° or less is disposed at a position separated from the main body portion 40, the light incident is compared with the case where the light exit side surface 51 is disposed at a position close to the main body portion 40. The ratio of the light-emitting side surface 51 having the low light-emitting surface angle θa1 out of the total light-emitting surface 51 of the unit-shaped element 50 (first) while suppressing the occurrence of uneven brightness and side lobes in the vicinity of the surfaces 33 and 34 to the same extent. Area ratio). As a result, the light-emitting side surface 51 having a light-emitting surface angle θa larger than 30 ° and less than or equal to 60 ° can be given more to the unit shape element 50. As a result, an excellent light collecting function for components along the second direction can be introduced. It can also be applied to the light plate 30.

  In particular, since it is at the center of the display area that the brightness is easily perceived by the observer, the luminance in the front direction is most important in the center of the light exit surface 31 that is separated from the light entrance surfaces 33 and 34. It becomes an area to include. And the light guided through the light guide plate 30 to the region including the center of the light exit surface 31 separated from the light entrance surfaces 33 and 34 is compared with the light passing through the vicinity of the light entrance surfaces 33 and 34. More components along the second direction are included. Therefore, the central region of the light exit surface 31 that is separated from the light entrance surfaces 33 and 34 where the luminance in the front direction is most important includes the end portion 52b of the light exit side surface 51 of the unit shape element 50 that is close to the main body portion 40. A large amount of light is emitted from the light guide plate 30 through the second region A2, that is, the region on the light output side surface 51 of the unit-shaped element 50 that can exhibit an excellent light collecting function.

  Further, as described above, the light reaching the light exit side surface 51 in the vicinity of the top portion 52a of the unit shape element 50 includes a large amount of light having a relatively small component along the second direction (for example, the light L52 in FIG. 5). It is. In the first place, it is not necessary to exert a strong light condensing effect on the light with few components along the second direction. Therefore, by providing the light exit surface having a light exit surface angle of 35 ° or less in the region including the top portion 52a of the unit shape element 50, the light collecting function by the unit shape element 50 is not significantly adversely affected.

  As a result, the light exit side surface 51 (first inclined surfaces 37a, 38a) having a light exit surface angle θa of which the light condensing function is relatively weak is 10 ° or more and 35 ° or less is disposed at a position separated from the main body 40. In addition, it is possible to effectively avoid significant deterioration of the light collecting function of the unit shape element 50 as a whole due to the provision of the light exit side surface 51 (first inclined surfaces 37a and 38a). That is, when the light exit surface angle θa of the unit shape element 50 increases from the top portion 52a on the outer contour 51 of the unit shape element 50 to the end portion 52b, the light and dark unevenness in the vicinity of the light incident surfaces 33 and 34 is made inconspicuous. In addition, it is possible to prevent the second peak of luminance from being formed in a direction greatly inclined from the front direction nd, and to adjust the front direction luminance. In particular, in a region on the outer contour 51 corresponding to 20% or more and 35% or less of the width W of the unit shape elements 50 along the arrangement direction of the unit shape elements 50, the light exit surface angle θa of the unit shape elements 50 is 10. When the angle is not less than 35 ° and not more than 35 °, it cannot be visually discriminated from the luminance in the front direction when no region where the light exit surface angle θa of the unit shape element 50 is not less than 10 ° and not more than 35 ° is provided. It is possible to ensure a certain degree of brightness in the front direction.

  Note that various modifications can be made to the above-described embodiment. Hereinafter, an example of modification will be described with reference to the drawings. In the drawings used in the following description, the same reference numerals as those used for the corresponding parts in the above-described embodiment are used, and redundant descriptions are omitted.

  For example, the above-described configuration of the unit shape element 50 of the light guide plate 30 is merely an example. As an example, the outer contour 51 of the unit shape element 50 may include a curve on the main cut surface of the light guide plate. As already described, when the cross-sectional shape of the unit-shaped element 50 at the main cutting surface of the light guide plate includes a curve, the light exit surface angle θa is set to the unit-shaped element 50 as shown in FIGS. An angle formed by the tangent TL to the outer contour 51 in the main cut surface and the one side surface 41 of the main body 40, more strictly, the smaller one of the two formed corners (the angle of the inferior angle) )) Value. Also in such a modification, it is preferable that the unit shape element 50 has the above-described configuration. For example, the position of the contact point TP of the tangent TL to the curved outer contour 51 of the unit shape element 50 is 20% or more of the total width W of the unit shape element 50 in the direction parallel to the one side surface 41 of the main body 40. If the light exit surface angle θa is 10 ° or more and 35 ° or less in the region of 70% or less, the light directly incident on the light exit surface 31 in the vicinity of the light entrance surface 33 is effective in the second direction. In the surface of the light exit surface 31 in the vicinity of the light incident surface 33 can be made inconspicuous, and the light L71a that can form a side lobe can be totally reflected. In addition, it is possible to adjust the angular distribution of luminance and to effectively use the light source.

  In the above-described embodiment, the example in which the unit shape elements 50 of the light guide plate 30 are disposed adjacent to each other has been described, but the present invention is not limited thereto. For example, as shown in FIG. 8, a flat portion 58 may be formed between two adjacent unit shape elements 50, and as shown in FIG. 9, a concave portion 59 is provided between two adjacent unit shape elements 50. May be formed.

  Furthermore, in the above-described embodiment, the light emitting surface 31 of the light guide plate 30 is inclined with respect to the plate surface of the light guide plate 30 by providing the unit shape element 50 on the surface 41 on one side of the main body 40. Although the example which included surface 37a, 37b, 38a, 38b was shown, it is not restricted to this. As shown in FIG. 11 and FIG. 12, the light guide plate 30 is inclined by forming a groove having a configuration obtained by inverting the unit-shaped element 50 of the light guide plate 30 described above on one side surface 41 of the main body 40. The surfaces 37a, 37b, 38a, and 38b may be provided. That is, in this example, the groove functions as a unit shape element 50 that exerts an optical action on light. Specifically, a mold having projections and depressions having the same configuration as the light exit surface 31 of the light guide plate 30 described above is prepared, and the main body 40 and the arrangement direction intersecting the first direction are formed by using the mold. A light guide plate 30 having a plurality of grooves 50 formed on one side surface 41 of the main body portion 40, each extending in a direction intersecting with the arrangement direction thereof, is formed. Can do. At this time, the configuration related to the unit shape element as the protruding portion in the embodiment described above can be applied to the unit shape element as the groove. Also in such a light guide plate 30, the inclined surfaces 37a, 37b, 38a, and 38b constituted by the light exit side surfaces (wall surfaces) of the grooves exhibit the same optical functions as those described in the above embodiment. be able to.

  In the example shown in FIGS. 11 and 12, the groove-shaped unit shape element 50 is configured to be complementary to the above-described substantially columnar unit shape element. In FIG. 11 and FIG. 12, the same code | symbol is attached | subjected about the part corresponding to embodiment mentioned above.

  In the example shown in FIGS. 11 and 12, the outer contour of the unit shape element (groove) 50 on the main cutting plane parallel to both the normal direction to the one side surface 41 of the main body 40 and the arrangement direction of the unit shape elements 50. The light exit surface angle θa, which is an angle formed by the (wall surface) with respect to the one side surface 41 of the main body 40, is 20% or more and 70% or less of the width W of the unit shape elements 50 along the arrangement direction of the unit shape elements 50. Is 10 ° to 35 ° in the region on the outer contour 51 corresponding to. Also in the example in which the unit shape elements 50 are formed as grooves, the light exit surface angle θa is an outside corresponding to 20% to 35% of the width W of the unit shape elements 50 along the arrangement direction of the unit shape elements 50. In the region on the contour (wall surface) 51, it is preferably 10 ° or more and 35 ° or less. In the example shown in FIGS. 11 and 12, the light exit surface angle θa of the unit shape element 50 is the top (deepest part) 52a on the outer contour 51 of the unit shape element 50 farthest from the one side surface 41 of the main body 40. It changes so that it may become large toward the edge part (base end part) 52b on the outer outline 51 of the unit-shaped element 50 which approached the one side surface of the main-body part 40 most.

  In the example in which the unit shape elements 50 are formed as grooves, the outer shape 51 on the outer contour 51 corresponding to 30% to 80% of the width W of the unit shape elements 50 along the arrangement direction of the unit shape elements 50 is also illustrated. In the region, the light exit surface angle θa is preferably greater than 30 ° and less than or equal to 60 °, and the light exit surface angle θa is 10 ° or more and 60 ° in the entire region on the outer contour 51 in the main cutting surface of the unit shape element 50. More preferably, it is as follows. Further, in the example in which the unit shape elements 50 are formed as grooves, the unit shape elements 50 on the main cutting surface of the light guide plate 30 with respect to the width W along the arrangement direction of the unit shape elements 50 on the main cutting surface of the light guide plate 30. It is preferable that the ratio (H / W) of the height (depth) H from one side surface 41 of the main body portion 40 is 0.3 or more and 0.45 or less.

  In the example shown in FIGS. 11 and 12, the unit-shaped element 50 as a groove is formed on the one side surface 41 of the main body 40 without a gap. Therefore, in the illustrated example, one side surface 41 of the main body 40 is a surface (virtual surface) defined by the end portion (base end portion) 52 b of the unit shape element 50.

  Furthermore, in the above-described embodiment, an example in which the unit shape element 50 has a constant cross-sectional shape along the longitudinal direction thereof is shown, but the present invention is not limited thereto, and the cross-sectional shape of the unit shape element 50 is the unit shape. You may make it change along the longitudinal direction of an element.

  Further, in the above-described embodiment, the example in which the two opposing surfaces 33 and 34 among the side surfaces of the light guide plate 30 form the light incident surface is shown, but the present invention is not limited thereto. For example, as in the modification shown in FIG. 10, only one surface 33 of the side surfaces of the light guide plate 30 may function as a light incident surface. In such a modification, the emission direction of the emitted light emitted from the light guide plate 30 in the cross section parallel to both the normal direction nd to the light emitting surface 21 of the surface light source device 20 and the first direction is the front direction. It is inclined to only one side with respect to nd. For this reason, the unit prism 27 of the optical sheet 26 does not need to have a symmetrical shape in a cross section parallel to both the normal direction nd and the first direction to the light emitting surface 21 of the surface light source device 20. In the modification shown in FIG. 10, the unit prism 27 includes a transmission surface 27a that transmits light from the light guide plate 30, and a reflection surface 27b that totally reflects light incident on the light guide plate 30 through the transmission surface 27a. The reflection surface 27b is inclined with respect to the front direction nd, whereas the transmission surface 27a extends substantially parallel to the front direction nd.

  Furthermore, in the above-described embodiment, the example in which the light incident on the light guide plate 30 can be emitted from the light guide plate 30 by dispersing the diffusing component 45 in the main body 40 has been described. Not limited. As an example, as shown in FIG. 10, the light exit surface 31 and the back surface 32 of the light guide plate 30 may be inclined with respect to each other. In the example illustrated in FIG. 10, the back surface 32 of the light guide plate 30 has a plurality of adjacent inclined surfaces 32 a that are inclined so as to approach the light exit surface 32 from the light incident surface 33 toward the opposite surface 34. And a step surface 32b connecting the inclined surfaces 32a. Among these, the step surface 32 b extends in the normal direction nd of the plate surface of the light guide plate 30. Therefore, most of the light traveling in the light guide plate 30 from the light incident surface 33 side to the opposite surface 34 side is reflected by the inclined surface 32 a without entering the step surface 32 b of the back surface 32. Become. For this reason, as shown in FIG. 10, when the light L101 travels in the light guide plate 30 after being reflected by the light exit surface 31 and the back surface 32, the incident angle of the light L101 on the light exit surface 31 and the back surface 32 is the back surface 32. It becomes smaller every time it is reflected, and becomes less than the critical angle for total reflection after repeating total reflection. As a result, the light L101 traveling in the light guide plate 30 is emitted from the light guide plate 30 in a region separated from the light incident surface 33 without colliding with the light scattering agent 45 in the main body 40. Thereby, the emitted light quantity along the first direction can be made uniform.

  Furthermore, the present invention is not limited to the example in the above-described embodiment or the example illustrated in FIG. 10, and another configuration (another light extraction configuration) for emitting light incident on the light guide plate 30 from the light guide plate 30 is described above. Instead of the above configuration or in addition to the above-described configuration, it can be adopted. Other than the configuration in which the diffusing component 45 is dispersed and the configuration in which the light exit surface 31 and the back surface 32 are inclined with respect to each other, for example, at least one of the light exit surface 31 and the back surface 32 can be used. Examples of the configuration include a rough surface and a configuration in which a pattern of a white scattering layer is provided on the back surface 32. Further, in the example shown in FIG. 10, the back surface 32 of the light guide plate 30 has the inclined surface 32a and the step surface 32b. However, the present invention is not limited to this. It may be configured as two continuous flat inclined surfaces or one continuous curved surface.

  Furthermore, in the above-described embodiment, an example of the optical sheet 26 disposed on the light output side of the light guide plate 30 has been described. However, the optical sheet 26 described above is merely an example. Instead of the optical sheet 26 described above, various forms of optical sheets can be used. For example, an optical sheet in which a unit prism protrudes on the light output side can be used. In addition, an optical sheet in which the cross-sectional shape of the unit prism 27 is a shape other than a triangular shape, for example, a shape corresponding to a polygon other than a triangle or a part of an ellipse may be used.

  Furthermore, the configurations of the surface light source device 20 and the display device 10 described above are merely examples, and various modifications can be made. For example, a light diffusion sheet having a function of diffusing transmitted light, a polarization separation sheet having a polarization separation function of transmitting only a specific polarization component and reflecting other polarization components, etc. You may make it provide in the side.

  In addition, although the some modification with respect to embodiment mentioned above was demonstrated above, naturally, it is also possible to apply combining a some modification suitably.

  EXAMPLES Hereinafter, although this invention is demonstrated in detail using an Example, this invention is not limited to this Example.

<Surface light source device>
First, the surface light source device which concerns on Examples 1-15 and Comparative Examples 1-14 was prepared. Each surface light source device has a configuration in which a light guide plate, a light source, a reflection sheet, and an optical sheet are arranged in the same positional relationship as in the above-described embodiment. However, unlike the surface light source device shown in FIG. 1, the light guide plate of the surface light source device according to the example and the comparative example has only one light incident surface, and faces the one light incident surface. Only one light source is provided in the surface light source device. As described below, the light source, the reflection sheet, and the optical element are different only in the cross-sectional shapes of the unit-shaped elements of the light guide plate between the prepared surface light source devices according to Examples 1 to 15 and Comparative Examples 1 to 14. The same sheet was used.

(Light guide plate)
The light guide plate has a main body portion and unit shape elements arranged on one side surface of the main body portion. The light guide plate was configured such that one of a pair of side surfaces facing in the first direction forms a light incident surface.

  The unit shape elements are arranged without gaps on one side surface of the main body, as in the above-described embodiment. Each unit shape element has a constant cross-sectional shape and extends linearly along the first direction. And this unit shape element was arranged without the gap along the 2nd direction on one side of the main-body part orthogonal to the 1st direction. The unit shape element was produced by curing an acrylic ultraviolet curable resin. At this time, the land portion was formed between the unit shape element and the base material forming the main body portion by curing the same acrylic ultraviolet curable resin as the unit shape element with a constant thickness.

  On the other hand, the main body portion is formed by a plate material that functions as a base material when the land portion and the unit shape element are molded, and the land portion. The main body portion was formed in a flat plate shape in which the back surface and the light emitting surface were parallel and the thickness was constant. The substrate was a plate made of polymethyl methacrylate (PMMA) containing a light scattering agent as a diffusion component.

  Between the surface light source devices according to Examples 1 to 15 and Comparative Examples 1 to 14, the cross-sectional shape of the main cutting surface of the unit shape element was changed as shown in Table 1 and FIGS. In the light guide plate incorporated in all the surface light source devices, the unit shape element has a cross-sectional shape that is line-symmetric about the front direction. Moreover, in the light guide plate incorporated in all the surface light source devices, the width W at the main cutting surface of the unit shape element was set to 100 μm. 13 to 17, the same reference numerals as those in FIGS. 1 to 12 are used.

  As shown in FIGS. 13-16, in the light-guide plate built in the surface light source device which concerns on Examples 1-15 and Comparative Examples 2-14, a unit shape element is the main cut surface similarly to embodiment mentioned above. In order to form a substantially pentagonal shape. Further, the bent surface extending from the top portion to the end portion in the main cut surface is, as in the above-described embodiment, a gentle slope (37a, 38a) located on the top side, and light emission from the gentle slope arranged on the end side. And steep slopes (37b, 38b) having a large surface angle.

  In the light guide plates incorporated in the surface light source devices according to Examples 1 to 5 and Comparative Examples 2 and 3, the light exit surface angle θa1 of the gentle slope (37a, 38a) is 10 ° as shown in Table 1 and FIG. It was. As shown in the column “ratio (%)” in Table 1, the proportion of the gentle slope with respect to the entire width of the unit shape elements along the arrangement direction of the unit shape elements is shown in Examples 1 to 5 and Comparative Example 2 and It was made to change between three. In the light guide plate incorporated in the surface light source devices according to Examples 6 to 10 and Comparative Examples 4 and 5, the light exit surface angle θa1 of the gentle slope (37a, 38a) is 20 ° as shown in Table 1 and FIG. It was. As shown in the column “ratio (%)” of Table 1, the ratio of the gentle slope to the entire width of the unit shape elements along the arrangement direction of the unit shape elements is shown in Examples 6 to 10 and Comparative Example 4 and It was made to change between 5. In the light guide plates incorporated in the surface light source devices according to Examples 11 to 15 and Comparative Examples 6 and 7, the light exit surface angle θa1 of the gentle slope (37a, 38a) is 35 ° as shown in Table 1 and FIG. It was. As shown in the column “Ratio (%)” of Table 1, the ratio of the gentle slope to the entire width of the unit shape elements along the arrangement direction of the unit shape elements is shown in Examples 10 to 15 and Comparative Example 6 and It was made to change between 7. In the light guide plate incorporated in the surface light source devices according to Comparative Examples 8 to 14, the light exit surface angle θa1 of the gentle slopes (37a, 38a) was set to 40 ° as shown in Table 1 and FIG. The proportion of the gentle slope with respect to the entire width of the unit shape elements along the arrangement direction of the unit shape elements varies between Comparative Examples 8 to 14 as shown in the “Proportion (%)” column of Table 1. I did it.

  On the other hand, as shown in FIG. 17, in the light guide plate incorporated in the surface light source device according to Comparative Example 1, the cross-sectional shape of the unit shape element on the main cut surface is an isosceles triangle shape. About the light-guide plate of the surface light source device which concerns on the comparative example 1, the unit shape element was made into the right-angled isosceles triangle shape including the 90 degree apex angle which protruded in the light emission side in the main cut surface. That is, for the light guide plate of the surface light source device according to Comparative Example 1, the light exit surface angle of the unit shape element was constant at 45 °.

(light source)
Multiple LED chips with a light emitting unit size of 1.6 mm x 0.8 mm are inserted at a pitch of 2.0 mm so that the 0.8 mm side of each LED chip is parallel to the thickness direction of the light guide plate. A light source was configured by arranging in the longitudinal direction of the light surface (the second direction described above). As described above, the light guide plate is provided with only one light incident surface, and the light source formed by arranging a large number of LED chips is provided so as to face the one light incident surface. The light source was arranged so that a gap of 0.8 mm was formed between the light incident surface of the light guide plate.

(Reflective sheet)
A reflective sheet made of a white polyester film having a thickness of 250 μm was disposed so as to face the back surface of the light guide plate.

(Optical sheet)
An optical sheet as a so-called prism sheet was disposed so as to face the light exit surface of the light guide plate. The optical sheet (prism sheet) was formed by forming a plurality of unit prisms from an acrylic ultraviolet curable resin on a 125 μm thick polyester film. The unit prism had an isosceles triangle shape with an apex angle of 66 ° in a cross section orthogonal to the longitudinal direction. In this optical sheet, as in the optical sheet of the above-described embodiment, the unit prisms protrude toward the light guide plate, and the arrangement direction of the unit prisms is parallel to the light guide direction (first direction) of the light guide plate. Arranged.

<Evaluation method>
・ Frontal brightness The frontal brightness was measured. For the measurement, a luminance meter BM-7 (manufactured by TOPCON) was used. The measurement results are shown in the “Luminance Ratio” column of “Evaluation” in Table 1 as the luminance ratio between samples. Further, the surface light source device in a state where the light source emits light was also observed visually at a position 1 m away from the light emitting surface of the surface light source device along the normal direction to the light emitting surface. The surface light source devices according to Examples 1 to 3, Examples 6 to 8, Examples 11 to 13, Comparative Example 1, Comparative Example 2, Comparative Example 4, Comparative Example 6, and Comparative Examples 8 to 11 are visually observed brightest. These surface light source devices were perceived as having the same brightness by visual observation. On the other hand, the surface light source devices according to Comparative Example 3, Comparative Example 5, Comparative Example 7, and Comparative Example 14 were perceived very dark visually as compared with other surface light source devices.

Brightness and darkness unevenness The surface light source device in a state where the light source emits light was visually observed at a position 1 m away from the light emitting surface of the surface light source device along the normal direction to the light emitting surface. It was confirmed whether or not brightness unevenness consisting of repetition of bright and dark portions was observed in a region near the light incident surface of the light emitting surface of each surface light source device. For samples in which unevenness in brightness was clearly observed, an “X” was added to the “brightness / darkness unevenness” column of “Evaluation” in Table 1. Further, although the brightness unevenness was slightly present, the region where the lightness / darkness unevenness occurred was in the range of about 1 to 2 cm along the longitudinal direction of the unit shape element from the light incident surface, and the lightness / darkness unevenness was not problematic in practice. The samples were marked with “◯” in the “Brightness / darkness unevenness” column of “Evaluation” in Table 1. Further, for samples in which no unevenness in brightness was observed, ◯ was marked in the “brightness / darkness unevenness” column of “Evaluation” in Table 1.

-Sidelobe Observation of the light emitting surface of the surface light source device in a state where the light source emits light at a position 1 m away from the light emitting surface from various directions within one plane orthogonal to the longitudinal direction of the unit shape element did. When the observation direction is gradually inclined from the front direction so that the angle formed by the observation direction with respect to the front direction gradually increases from 0 °, the brightness gradually decreases by visual judgment. For the sample, a circle is given in the “side lobe” column of “Evaluation” in Table 1. On the other hand, in the course of gradually inclining the observation direction from the front direction, “x” is added to the “side lobe” column of “Evaluation” in Table 1 for samples that have been changed so that the brightness becomes brighter in visual judgment. .

-Others By the way, the brightness | luminance was measured from various directions on the light emission surface of the surface light source device in the state in which the light source is light-emitted. For the measurement, a luminance meter BM-7 (manufactured by TOPCON) was used. As an example, the measurement result about the surface light source device which concerns on Example 11, Example 12, and the comparative example 1 is shown in FIGS. 18-20, respectively. In addition, in the circular graph shown by FIGS. 18-20, the distribution of the brightness | luminance in each direction is shown as a ratio of the brightness | luminance with respect to the front direction brightness | luminance of each surface light source device. For example, the luminance distribution in the direction connecting “0” and “180” in the circular graph is parallel to both the front direction (normal direction to the light emitting surface) and the first direction (longitudinal direction of the unit shape element). Similarly, the angular distribution of the luminance measured in each measurement direction in the plane is shown. Similarly, the luminance distribution in the direction connecting “90” and “270” in the circular graph is the front direction (to the light emitting surface). The distribution of luminance measured in each measurement direction in a plane parallel to both the second direction (the direction in which the unit shape elements are arranged) and the second direction (the arrangement direction of the unit shape elements) is shown. In addition, the surface light source device that is the measurement target has a light source only on one side along the first direction. In the circular graphs of FIGS. 18 to 20, “0” and “180” are indicated. The “0” side in the connecting direction indicates the luminance in the direction inclined from the front direction to the light source side. 18 to 20, a region CZ1 surrounded by the contour line CL1 is a region in which a luminance of 75% or more of the peak luminance is secured, and a region CZ2 surrounded by the contour line CL2 is a region of 50% or more of the peak luminance. A region CZ3 surrounded by the contour line CL3 is a region where the luminance is secured, and a region CZ4 surrounded by the contour line CL4 is a region where the luminance of 25% or more of the peak luminance is secured. This is a region where the above luminance is secured.

  When the circular graphs shown in FIG. 18 to FIG. 20 are created for each surface light source device, the surface light source device evaluated as “x” in the “side lobe” column of Table 1 has a peak luminance of 50% or more. A contour line CL2 indicating a region where the luminance is secured, a contour line CL3 indicating a region where the luminance of 25% or more of the peak luminance is ensured, and a contour line CL4 indicating a region where the luminance of 15% or more of the peak luminance is ensured, The shape was far from the circular shape. On the other hand, the surface light source device for which the evaluation in the “side lobe” column of Table 1 is “◯” is compared with the measurement result of the surface light source device for which the evaluation in the “side lobe” column of Table 1 is “x”. Then, these contour lines CL2, CL3, and CL4 have a shape close to a circular shape.

DESCRIPTION OF SYMBOLS 10 Display apparatus 15 Liquid crystal display panel 18 Control apparatus 20 Surface light source device 22 Reflection sheet 24a, 24b Light source 25 Light emitter 26 Optical sheet 30 Light guide plate 31 Light emission surface 32 Back surface 33 Light incident surface (1st light incident surface)
34 Opposite surface (second light entrance surface)
37 Folded surface 37a First inclined surface 37b Second inclined surface 38 Folded surface 38a First inclined surface 38b Second inclined surface 40 Main body portion 41 One side surface 44 Main portion 45 Diffusion component 50 Unit shape element 51 Emitting side surface (outer contour)
52a Top 52b End

Claims (13)

A light exit surface, a back surface opposite to the light exit surface, at least one light incident surface composed of a part of a side surface between the light exit surface and the back surface, and a part of the side surface along a first direction. A light guide plate having an opposite surface facing the light incident surface,
The main body,
A plurality of unit-shaped elements arranged on one side surface of the main body portion side by side in an arrangement direction intersecting the first direction and forming the light exit surface,
Each of the plurality of unit shape elements extends in a direction intersecting with the arrangement direction thereof,
A light emitting surface angle that forms an angle formed by the outer contour of the unit-shaped element with respect to the one side surface of the main body portion in a main cutting surface parallel to both the normal direction to the one side surface of the main body portion and the arrangement direction. Then, in the region on the outer contour corresponding to 20% to 70% of the width of the unit shape elements along the arrangement direction, the light exit surface angle of the unit shape elements is 10 ° to 35 °. The light guide plate is as follows.   In a region on the outer contour corresponding to 20% to 35% of the width of the unit shape elements along the arrangement direction, the light exit surface angle of the unit shape elements is 10 ° to 35 °. The light guide plate according to claim 1.   The light exit surface angle of the unit shape element is such that the unit shape element closest to the one side surface of the main body portion from the top on the outer contour of the unit shape element furthest away from the one side surface of the main body portion. The light guide plate according to claim 1, wherein the light guide plate changes so as to increase toward an end portion on the outer contour.   The light guide plate according to any one of claims 1 to 3, wherein the light exit surface angle is not less than 10 ° and not more than 60 ° in the entire region on the outer contour in the main cutting surface of the unit shape element.   In a region on the outer contour corresponding to 30% or more and 80% or less of the width of the unit shape elements along the arrangement direction, the light exit surface angle is greater than 30 ° and 60 ° or less. Item 5. The light guide plate according to any one of Items 1 to 4.   A ratio (H / W) of a height H from the one side surface of the main body portion of the unit-shaped element in the main cutting surface to a width W along the arrangement direction of the unit-shaped elements in the main cutting surface. The light guide plate according to claim 1, which is 0.3 or more and 0.45 or less. The unit-shaped element has, on the main cutting surface, one side located on the one side surface of the main body portion and a top portion that is farthest from the one side surface on the outer contour, and each end portion that is connected to the one side surface. A pentagonal shape in which two sides are located between, or a shape formed by chamfering one or more corners of the pentagonal shape,
Of the two sides located between the top and each end on the outer contour, the light exit surface angle of one side of the top portion is 10 ° to 35 °, and the light exit surface of one side of the end portion The light guide plate according to claim 1, wherein the angle is greater than 30 ° and 60 ° or less.   The light guide plate according to any one of claims 1 to 7, wherein the main body includes a main portion made of a resin and a diffusion component dispersed in the main portion. The light guide plate according to any one of claims 1 to 8,
A surface light source device, comprising: a light source disposed opposite to the light incident surface of the light guide plate. The one light incident surface of the light guide plate constitutes a first light incident surface, and the opposite surface of the light guide plate constitutes a second light incident surface,
The said light source contains the 1st light source arrange | positioned facing the said 1st light-incidence surface, and the 2nd light source arrange | positioned facing the said 2nd light-incidence surface. The surface light source device described in 1.   The surface light source device according to claim 9 or 10, wherein the light source includes a plurality of point-like light emitters arranged at positions facing the light incident surface. A surface light source device according to any one of claims 9 to 11,
A liquid crystal display panel disposed to face the surface light source device. A surface light source device according to claim 11;
A liquid crystal display panel disposed to face the surface light source device;
A control device for controlling the output of each point light emitter,
The said control apparatus is a display apparatus comprised so that the output of each point light emitter may be adjusted according to the image | video which should be displayed.

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