JP2013214379A - Light guide plate, surface light source device, and display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light guide plate in which leakage of light from an opposed surface opposed to a light-incident surface is reduced in a guiding direction of light, and utilization efficiency of light is excellent, as well as a surface light source device and a display device which have this.SOLUTION: A light guide plate 13, provided with a light-incident surface 13a from which light enters and a light-emitting surface 13c which crosses the light-incident surface 13a and from which the light is emitted, and emitting light entering from the light-incident surface from the light-emitting surface 13c by guiding it in the light guide direction, is further provided with: a retroreflection part 131 for performing retroreflection of guided light provided on an opposed surface 13b opposed to the light-incident surface 13a in a light guiding direction, the retroreflection part 131 being formed of an array of a plurality of first unit optical elements 132; and a light guide direction control part 133 which is provided in the light-emitting surface 13c or a rear surface 13d opposed to the light-emitting surface 13c and brings an advancing direction of light close to the light guide direction.

Description

  The present invention relates to a light guide plate that guides light, a surface light source device including the same, and a display device.

2. Description of the Related Art A transmissive display device that displays an image by illuminating an LCD (Liquid Crystal Display) panel from the back side with a surface light source device is widely used. As the surface light source device used in this display device, an edge light type, a direct type and the like are known.
An edge light type surface light source device is a form in which a light source is arranged at a position facing at least one side of a light guide plate that guides light, and a direct type surface light source in which a light source is arranged on the back side of various optical sheets. Compared with the device, the surface light source device has an advantage that the thickness can be reduced, and is widely used.

In general, light projected from a light source is incident from a light incident surface that is one side surface of the light guide plate, and is repeatedly reflected between the light exit surface and the back surface of the light guide plate, and substantially perpendicular to the light incident surface. Proceed to (light guiding direction). At this time, the light traveling direction gradually changes depending on the diffusion pattern provided on the back side of the light guide plate, the mat shape, the lens shape, etc., and light is gradually emitted from each position along the light guide direction of the light exit surface. Light is emitted to the panel side.
With respect to this light guide plate, various shapes of light guide plates have been developed for the purpose of improving light utilization efficiency and light guide distance, improving brightness unevenness (brightness unevenness), thinning, and the like (for example, Patent Documents 1 to 3). 3).

JP-A-9-43433 JP 2007-227405 A Japanese Patent No. 4453516

In recent years, along with the reduction in thickness and weight of surface light source devices and the development of various light sources, a small and bright point light source such as an LED (Light Emitting Diode) is used as a light emitting part of the light source of the surface light source device. Has become mainstream.
The light emitted from the LED has a characteristic of relatively high directivity (the light distribution direction is narrow). When such highly directional light is projected onto the light guide plate, most of the light incident on the light guide plate travels straight in the light guide direction, and the light guide distance becomes longer. However, there is a problem that a part of the light is emitted from the opposite surface to cause light leakage and the light use efficiency is lowered.

Patent Documents 1 to 3 describe a light guide plate with a diffusion pattern for diffusing light on the back surface, a structure in which a diffraction grating or the like is formed on the back surface of the light guide plate, and a reflective material is provided outside the light guide plate. .
However, none of the patent documents discloses a countermeasure against light leakage from the facing surface as described above.

  An object of the present invention is to provide a light guide plate that reduces light leakage from a facing surface that faces a light incident surface in the light guiding direction and has high light use efficiency, and a surface light source device and a display device including the same. It is to be.

The present invention solves the above problems by the following means. In addition, in order to make an understanding easy, although the code | symbol corresponding to embodiment of this invention is attached | subjected and demonstrated, it is not limited to this.
The invention of claim 1 has a light incident surface (13a) on which light is incident and a light output surface (13c) that intersects the light incident surface and emits light, and guides light incident from the light incident surface. A light guide plate that emits light from the light exit surface while guiding in the light direction, and is provided on a facing surface (13b) that faces the light entrance surface in the light guide direction, and a first unit optical element (132) is provided. A plurality of arranged retroreflecting portions (131) that retroreflect light that has been guided and a rear surface (13d) that opposes the light exiting surface and that faces the light exiting surface. And a light guide direction control unit (133) that approaches the light guide plate.
The invention according to claim 2 is the light guide plate according to claim 1, wherein the first unit optical element (132) has a triangular prism shape with an apex angle of 90 degrees that protrudes outward from the light guide plate. It is a light-guide plate (13) characterized by these.
According to a third aspect of the present invention, in the light guide plate according to the second aspect, the longitudinal direction of the first unit optical element (132) is parallel to the normal direction of the light exit surface (13c). The light guide plate (13).
According to a fourth aspect of the present invention, in the light guide plate according to any one of the first to third aspects, the light guide direction control unit (133) is provided on the light exit surface (13c), and the light guide plate A plurality of second unit optical elements (134) having a columnar shape protruding outward and having a direction perpendicular to the light incident surface (13a) as a longitudinal direction. It is an optical plate (13).
The invention of claim 5 is provided at a position facing the light guide plate (13) according to any one of claims 1 to 4 and the light incident surface (13a), to the light incident surface. The light source part (12) for projecting light and the light exit surface (13c) side of the light guide plate are arranged, and the angle between the light from the light guide plate and the normal direction or normal direction of the sheet surface is small. And a deflecting optical sheet (14) having a deflecting action to be emitted in the direction of the surface light source device (10).
Invention of Claim 6 is a display apparatus (1) provided with the surface light source device (10) of Claim 5, and the transmissive display part (11) illuminated from the back side by the said surface light source device. .

  According to the present invention, a light guide plate that reduces light leakage from a facing surface facing a light incident surface in the light guide direction and has high light use efficiency, and a surface light source device and a display device including the light guide plate are provided. It is to be.

It is a figure explaining the display apparatus 1 of embodiment. It is a figure explaining the shape of the light-guide plate 13 of embodiment. It is a figure explaining the shape of the light-guide plate 13 of embodiment. It is a figure explaining the deflection | deviation optical sheet 14 of embodiment. It is a figure which shows the mode of the light in the opposing surface 13b.

Embodiments of the present invention will be described below with reference to the drawings.
In addition, each figure shown below including FIG. 1 is the figure shown typically, and the magnitude | size and shape of each part are exaggerated suitably for easy understanding.
In addition, in this specification, terms such as plate and sheet are used, but these are generally used in the order of thickness, plate, sheet, and film in order of increasing thickness. This is also used in the specification. However, such proper use has no technical meaning, and the terms “sheet”, “plate”, and “film” can be appropriately replaced.
Furthermore, numerical values such as dimensions and material names of each member described in the present specification are examples of the embodiment, and the present invention is not limited thereto, and may be appropriately selected and used.

Further, in this specification, the sheet surface (plate surface, film surface) is the plane of the sheet (plate, film) when viewed as the entire sheet (plate, film) in each sheet (plate, film). Suppose that it shows the surface used as a direction.
Furthermore, in the present specification, terms specifying shape and geometric conditions, for example, terms such as parallel and orthogonal, have the same optical functions in addition to strictly meaning, and can be regarded as parallel and orthogonal. A state having a certain degree of error is also included.

(Embodiment)
FIG. 1 is a diagram illustrating a display device 1 according to the present embodiment.
The display device 1 of this embodiment is a transmissive display device that includes an LCD panel 11 and a surface light source device 10 that illuminates the LCD panel 11 from the back side. In addition, although description etc. are abbreviate | omitted in the display apparatus 1, in addition to this, the normal apparatus required in order to operate | move as a display apparatus, the housing | casing part etc. which hold | maintain various members are provided.
The surface light source device 10 is an edge light type surface light source device (backlight) including a light source unit 12, a light guide plate 13, a deflection optical sheet 14, a light diffusion sheet 15, a reflection plate 16, and the like.

In addition, in the following drawings including FIG. 1 and the following description, in order to facilitate understanding, in the use state of the display device 1, two directions that are parallel to the screen of the display device 1 and are orthogonal to each other are X direction (X1-X2 direction) and Y direction (Y1-Y2 direction), and a direction orthogonal to the screen of the display device 1 is a Z direction (Z1-Z2 direction).
At this time, the light emitted from the surface light source device 10 is incident on the LCD panel 11 from the Z1 side (back side) and is emitted to the Z2 side (observer side). The observer O observes an image on the screen of the display device 1 from the Z2 side on the observer side toward the Z1 side on the back side.
The screen of the display device 1 according to the present embodiment corresponds to a surface 11a closest to the viewer (hereinafter referred to as a display surface) 11a of the LCD panel 11, and the “front direction” of the display device 1 refers to the display surface 11a. It is a normal direction, parallel to the Z direction, and coincides with the normal direction to the sheet surface of the deflecting optical sheet 14 (to be described later), the plate surface of the light guide plate 13 (light exit surface 13c, back surface 13d), and the like. .

The LCD panel 11 is a transmissive display unit and is a flat member. The LCD panel 11 is illuminated from the back side (Z1 side) by the surface light source device 10 and displays an image.
In the present embodiment, the outer shape of the LCD panel 11 and the display surface 11a are rectangular when viewed from the Z direction. The LCD panel 11 and each member constituting the LCD panel 11 have two opposite sides parallel to the X direction and two opposite sides parallel to the Y direction when viewed from the Z direction.

The light source unit 12 is a part that emits light that illuminates the LCD panel 11. The light source unit 12 is provided at a position facing the light incident surface 13a which is one end surface (X1 side) of the light guide plate 13 in the X direction.
The light source unit 12 is formed by using an LED (not shown), which is a point light source, as a light emitting unit 121, and a plurality of the light emitting units 121 are arranged at predetermined intervals in the Y direction along the light incident surface 13a. From the viewpoint of improving the light use efficiency of the light source unit 12, a reflection member (not shown) or the like may be provided so as to cover the outside of the light source unit 12.
In addition, the light emission part 121 of the light source part 12 is good also as a form with which the longitudinal direction is arrange | positioned along the light-incidence surface 13a using not a point light source as mentioned above but linear light sources, such as a cold cathode tube.

2 and 3 are views for explaining the shape of the light guide plate 13 of the present embodiment. FIG. 2A is a perspective view of the light guide plate 13. 2B is an enlarged view of a part of the cross section parallel to the YZ plane of the light guide plate 13, and FIG. 2C is an enlarged view of a part of the cross section of the light guide plate 13 parallel to the XZ plane. Show. FIG. 3A is a view of the facing surface 13b of the light guide plate 13 as viewed from the normal direction (X direction). FIG. 3B shows an enlarged part of a cross section of the facing surface 13b parallel to the XY plane.
The light guide plate 13 is a substantially flat member that guides light. The light guide plate 13 causes light emitted from the light source unit 12 to enter from the light incident surface 13a and guide it mainly in the X direction to the opposite facing surface 13b side (X2 side) while totally reflecting the light output surface 13c and the back surface 13d. The light is appropriately emitted from the light exit surface 13c to the deflecting optical sheet 14 side (Z2 side). Further, the light guide plate 13 reflects at least a part of the light reaching the facing surface 13b by the facing surface 12b and guides it again in the X direction.

As shown in FIGS. 1 to 3, the light guide plate 13 of the present embodiment includes a retroreflective portion 131 formed by arranging a plurality of first unit optical elements 132 on the facing surface 13 b, and the light exit surface 13 c. Has a light guide direction control unit 133 formed by arranging a plurality of second unit optical elements 134. Further, the back side 13d of the light guide plate 13 of the present embodiment has a back side optical shape part 135 formed by arranging a plurality of third unit optical elements 136.
The light guide plate 13 includes a main body 137 that is a substantially flat portion in which these unit optical elements are not formed. The main body 137 includes a retroreflecting unit 131, a light guide direction control unit 133, The back side optical shape part 135 is integrally formed.

  The light incident surface 13a of the light guide plate 13 of the present embodiment is planar. The present invention is not limited to this, and a plurality of columnar unit optical elements may be arranged on the light incident surface 13a on the light source unit 12 side. For example, the unit optical element may have a triangular prism shape that is convex toward the light source unit 12 or a partial shape of a cylinder or an elliptical column, or a partial shape of a cylinder or elliptical column that is concave toward the light source unit 12.

A retroreflective portion 131 is formed on the facing surface 13b of the light guide plate 13 of the present embodiment. The retroreflective portion 131 is formed by arranging a plurality of first unit optical elements 132.
The first unit optical element 132 has a columnar shape, and as shown in FIG. 3A, the longitudinal direction (ridge line direction) is parallel to the Z direction when viewed from the normal direction (X direction) of the facing surface 13b. And a plurality are arranged in the Y direction. The first unit optical element 132 totally reflects light incident on the facing surface 13b from the X1 side in the XY plane in the light guide plate 13 on one inclined surface (for example, the inclined surface 132a), and further on the other inclined surface. (For example, it has the effect | action (retroreflection effect | action) which totally reflects by the slope 132b and returns to the light-incidence surface 13a side (X1 side).

The first unit optical element 132 is not limited to the above example, and a plurality of first unit optical elements 132 may be arranged such that the ridge line direction is an angle θ (0 ° <θ <90 °) with respect to the Z direction. . In this case, the total reflection at each slope changes the light traveling direction in the Z direction, increasing the light emitted from the light exit surface 13c in the vicinity of the facing surface 13b, and the light source in the light guide direction (X direction). A decrease in the amount of emitted light on the side far from the portion 12 can be suppressed.
In the present embodiment, as shown in FIG. 3A, the retroreflective portion 131 is an area where the second unit optical element 134 is formed in the Z direction as viewed from the X direction (light guide direction control). An example in which the second unit optical element 134 is formed is not limited thereto, but may be formed in a region where the second unit optical element 134 is formed.
Further, in the present embodiment, in FIG. 3A, an example is shown in which the first unit optical elements 132 and the second unit optical elements 134 have the same pitch, and the positions of the ridge lines in the arrangement direction match. However, the present invention is not limited to this, and the arrangement pitch may be different, the width in the arrangement direction may be different, or the ridge line position in the arrangement direction may be different.

In the present embodiment, the first unit optical element 132 will be described by taking an example of a triangular prism shape that protrudes outward (X2 side) of the light guide plate 13.
As shown in FIG. 3B, the first unit optical element 132 has an isosceles triangle shape having a cross-sectional shape in a cross section parallel to the XY plane as shown in FIG. The first unit optical elements 132 have an arrangement pitch P1 and are equal to the width W1 in the arrangement direction (P1 = W1). The apex angle α1 is preferably α1 = 90 ° from the viewpoint of obtaining good retroreflectivity.
The first unit optical element 132 may have an unequal triangular shape in cross section in a cross section parallel to the XY plane.

The light guide direction control unit 133 is provided on the light exit surface 13c of the light guide plate 13, and is formed by arranging a plurality of second unit optical elements 134.
As shown in FIGS. 2 and 3, the second unit optical element 134 has a columnar shape that is convex on the light output side (Z2 side), and a plurality of second unit optical elements 134 are arranged in the Y direction with the longitudinal direction (ridge line direction) being the X direction. Yes.
The second unit optical element 134 of the present embodiment has a triangular prism shape, and has an isosceles triangular shape whose cross-sectional shape parallel to the YZ plane is an apex angle α2. The second unit optical element 134 has an arrangement pitch P2 and is equal to the width W2 in the arrangement direction (P2 = W2).

The second unit optical element 134 is not limited to the above example. For example, the second unit optical element 134 may have a partial shape of an elliptic cylinder whose major axis is orthogonal to the sheet surface of the light guide plate 13 or a partial shape of a cylinder. However, the shape may be a combination of a plurality of types of curved surfaces and planes.
The second unit optical element 134 formed on the light exit surface 13c is configured such that, in the light guide plate 13, light traveling obliquely with respect to the light guide direction (X direction) in the XY plane is incident on the light exit surface 13c at a critical angle or more. When light is incident at an angle, it is totally reflected on one slope and further totally reflected on the other slope, thereby guiding the light traveling direction closer to the light guide direction (X direction) while guiding it to the X2 side. have.
Moreover, since the 2nd unit optical element 134 is arranged in the direction (Y direction) orthogonal to the light guide direction (X direction) of the light of the light-guide plate 13 on the light emission surface 13c, the light radiate | emitted from the light emission surface 13c. Has a light beam control action in the arrangement direction. Therefore, the light emitted from the light guide plate 13 is subjected to the light beam control action of the second unit optical element 134, is diffused and collected, and the brightness uniformity in the Y direction can be improved.
In addition, not only the above-mentioned shape but the light emission surface 13c is good also as substantially planar shape.

The back-side optical shape portion 135 is formed by arranging a plurality of third unit optical elements 136 on the back surface 13 d of the light guide plate 13.
As shown in FIGS. 2 and 3, the third unit optical element 136 has a substantially triangular prism shape that is convex on the back side (Z1 side), and the longitudinal direction (ridge line direction) is the Y direction, which is the light guiding direction. A plurality are arranged in the X direction.
As shown in FIG. 2C, the third unit optical element 136 has a substantially triangular cross section in a cross section parallel to the XZ plane, an apex angle of α3, and base angles of β1, β2 ( β1> β2). Therefore, in the third unit optical element 136, the inclined surface 136a that forms a large angle with respect to the plate surface of the light guide plate 13 is located on the light incident surface 13a side (X1 side), and the inclined surface 136b that forms a small angle faces the surface. It is located on the 13b side (X2 side). The third unit optical element 136 has an arrangement pitch P3 and is equal to the width W3 in the arrangement direction (P3 = W3).

In the present embodiment, the light guide direction control unit 133 (second unit optical element 134), the back side optical shape unit 135 (third unit optical element 136), and the main body 137 are integrally extruded using a thermoplastic resin, A tape-like member in which the first unit optical element 132 is formed by ionizing radiation curable resin or the like on one side of a base material (not shown) is attached to the surface on the facing surface 13b side of the main body 137. Bonding via an adhesive or the like, the retroreflective portion 131 is integrally formed, and the light guide plate 13 is produced. At this time, it is preferable that the thermoplastic resin, the ionizing radiation curable resin, the base material, the adhesive, the pressure-sensitive adhesive, and the like to be used have a small difference in refractive index to such an extent that the refractive index is equal or the refractive index can be regarded as equal.
The light guide plate 13 is not limited to the above example, and the light guide direction control part 133 (second unit optical element 134), the back side optical shape part 135, and the main body part 137 are integrally extruded to form the main body part 137. The first unit optical element 132 may be formed on the surface on the opposite surface 13b side by cutting or the like, and the retroreflective portion 131 may be formed.
In addition, for example, the light guide plate 13 may be formed by integrally forming each unit optical element and the main body portion 137 by extrusion molding or injection molding, or by forming the main body portion 137 by extrusion molding or the like. May be formed by ionizing radiation curable resin on each surface of the main body 137, and the manufacturing method thereof may be appropriately selected according to the characteristics of the resin used.
Examples of the thermoplastic resin used include acrylic resins, PC (polycarbonate) resins, and COP (cycloolefin polymer) resins. Examples of the ionizing radiation resin used include acrylic ultraviolet curable resins such as urethane acrylate and epoxy acrylate.

The reflection plate 16 is a plate-like member capable of reflecting light, and is disposed on the back side (Z1 side) of the light guide plate 13. The reflecting plate 16 has a function of reflecting light traveling toward the Z1 side and directing it toward the light guide plate 13.
The reflector 16 preferably has a specular reflectivity (regular reflectivity) from the viewpoint of increasing the light utilization efficiency. The reflecting plate 16 is, for example, a member in which at least the reflecting surface (the surface on the light guide plate 13 side) is formed of a material having a high reflectance such as metal, or a thin film (for example, a metal thin film) formed of a material having a high reflectance. A member or the like containing as a surface layer can be used.

The deflection optical sheet 14 is disposed on the LCD panel 11 side (Z2 side) with respect to the light guide plate 13. The deflecting optical sheet 14 has a function of deflecting (condensing) the traveling direction of light emitted from the light exit surface 13c of the light guide plate 13 in the front direction (Z direction) or in a direction having a small angle with the Z direction. ing.
FIG. 4 is a diagram illustrating the deflecting optical sheet 14 of the present embodiment. In FIG. 4, a part of a cross section parallel to the XZ plane of the deflecting optical sheet 14 is shown enlarged.
The deflection optical sheet 14 includes a base material layer 141 and a plurality of unit prisms 142 that are formed and arranged on the light guide plate 13 side (Z1 side) of the base material layer 141.

The base material layer 141 is a portion that becomes a base (base material) of the deflecting optical sheet 14.
The unit prism 142 has a triangular prism shape that protrudes toward the light guide plate 13 side (Z1 side) on the back side (Z1 side) surface of the base material layer 141, and the longitudinal direction (ridge line direction) is defined as the Y direction. A plurality are arranged in the direction.
The unit prism 142 of the present embodiment shows an example in which the cross-sectional shape is an isosceles triangular shape with the apex angle α4, but the present invention is not limited to this, and the cross-sectional shape may be an unequal triangular shape. Further, the unit prism 142 may have a bent surface shape in which at least one surface is composed of a plurality of surfaces.
In addition, the unit prism 142 of the present embodiment has an arrangement pitch of P4 and an arrangement direction width of W4, and the arrangement pitch is equal to the lens width of the arrangement direction (P4 = W4).
As shown in FIG. 4, the deflecting optical sheet 14 emits light L from the light guide plate 13 and totally reflects the light L incident from one surface (for example, the slope 142b) on the other surface (for example, the slope 142a). The traveling direction is deflected (condensed) in a front direction (Z direction) or a direction in which an angle with respect to the front direction is reduced.

The deflecting optical sheet 14 of the present embodiment has a unit prism 142 formed on one side of a sheet-like base material layer 141 made of PET resin or PC resin by using an ionizing radiation curable resin such as an ultraviolet curable resin. Have been made.
For example, the deflecting optical sheet 14 may be PC resin, MBS (methyl methacrylate / butadiene / styrene copolymer) resin, PET resin, MS (methyl methacrylate / styrene copolymer) resin, PS (polystyrene). ) It may be formed by extruding a thermoplastic resin such as a resin.

Returning to FIG. 1, the light diffusion sheet 15 has an action of diffusing light. The light diffusion sheet 15 is provided on the LCD panel 11 side (Z2 side) of the deflection optical sheet 14.
By providing such a light diffusion sheet 15, it is possible to obtain an effect of appropriately widening the viewing angle or reducing moire or the like caused by pixels (not shown) of the LCD panel 11 and the unit prism 142.
The light diffusing sheet 15 is appropriately selected from various general-purpose light diffusing sheet-like members in accordance with optical performance desired for the surface light source device 10 and the display device 1, optical characteristics of the light guide plate 13, and the like. May be used.
As such a light diffusing sheet 15, a member made of a resin sheet containing a diffusing material, or a member coated with a binder containing a diffusing material on at least one surface of a resin sheet member serving as a base material Alternatively, a microlens sheet or the like in which a microlens array is formed on one surface of a resin sheet-like member serving as a substrate can be used.

It has a function of transmitting light in a specific polarization state to the LCD panel 11 side (Z2 side) rather than the light diffusion sheet 15 and reflecting light in other polarization states than the light diffusion sheet 15. A polarization selective reflection sheet may be disposed. When such a polarization selective reflection sheet is used, the transmission axis of the polarization selective reflection sheet is parallel to the transmission axis of a polarizing plate (not shown) located on the light incident side (Z1 side) of the LCD panel 11. It is preferable to arrange in such a manner.
As this polarization selective reflection sheet, for example, DBEF series (manufactured by Sumitomo 3M Limited) can be used.
In addition to the light diffusion sheet 15, various optical sheets such as a lenticular lens sheet may be disposed.
Further, the light diffusion sheet 15 is not limited to the separate light diffusion sheet 15, and a light diffusion layer that diffuses light may be laminated on the light output side (Z2 side) surface of the deflection optical sheet 14.

Here, the retroreflection part 131 of the opposing surface 13b of the light guide plate 13 of the present embodiment will be further described.
FIG. 5 is a diagram showing a state of light on the facing surface 13b. Fig.5 (a) shows the opposing surface 13b of this embodiment, FIG.5 (b) shows the conventional planar opposing surface 13b. FIG. 5 is a view of the light guide plate 13 viewed from the Z direction. In FIG. 5, the second unit optical element 134 and the like are omitted for easy understanding.
As described above, the light guide direction control for bringing the light traveling direction in the XY plane closer to the light guide direction (X direction) by the plurality of second unit optical elements 134 arranged on the light exit surface 13c of the present embodiment. A portion 133 is formed. A part of the light traveling in the light guide plate 13 in the direction forming an angle with respect to the X direction in the XY plane gradually progresses by total reflection on the inclined surface of the second unit optical element 134 as it proceeds in the light guide direction. The direction is deflected so that the angle formed with respect to the light guide direction (X direction) becomes small, and the traveling direction approaches the X direction as it proceeds toward the X2 side. Due to the action of the light guide direction control unit 133, the light is sufficiently guided also to the facing surface 13b side away from the light source unit 12, and the brightness in the region away from the light source unit 12 (region on the X2 side) is sufficient. Can be secured.

However, since the light traveling direction is close to the X direction, a large amount of light that is parallel to the X direction or has a small angle with the X direction is incident on the facing surface 13b. At this time, when the facing surface 13b is planar, as shown in FIG. 5B, a part of the light incident on the facing surface 13b is separated from the facing surface 13b as shown by the lights L21 and L22. Light exits from the light guide plate 13 to cause light leakage. Such light leakage is not preferable because it reduces the light utilization efficiency and causes a decrease in luminance and an increase in power consumption.
However, the opposing surface 13b of the present embodiment is configured so that the first unit optical element 132 causes the light incident on the inclined surface as shown in FIG. Can be totally reflected at the interface and retroreflected to the X1 side. As a result, as shown in FIG. 5B, a part of the light incident on the facing surface 13b is emitted from the facing surface 13b to the outside of the light guide plate 13 to cause light leakage, thereby reducing the light use efficiency. The phenomenon can be greatly improved.

Further, in the conventional surface light source device, a member having a reflective action is provided at a position facing the outer surface of the light guide plate (for example, inside the housing), or white tape material or metal vapor deposition is provided on the opposite surface of the light guide plate. There are some which aim at improvement of light leakage by pasting tape material etc.
However, when a reflective material is provided outside the light guide plate, the light emitted once to the outside of the light guide plate is made to enter the light guide plate again. Positioning with the facing surface is required, and the manufacturing becomes complicated. Also, when white tape material or metallized tape material is provided on the opposite surface of the light guide plate, the reflectivity is low, the loss of light amount due to reflection is large, or when diffuse reflection with white tape etc. In this case, light is emitted unnecessarily in the vicinity of the facing surface 13b from the light emitting surface 13c due to the diffuse reflection component due to diffuse reflection, and the vicinity of the facing surface 13b becomes brighter than necessary, resulting in uneven brightness.

On the other hand, in the light guide plate 13 of the present embodiment, the light reaching the facing surface 13b is incident on the inclined surfaces 132a and 132b of the first unit optical element 132 of the retroreflective portion 131 as shown in FIG. Totally reflected and headed to the X1 side. At this time, since the light is totally reflected by the inclined surfaces 132a and 132b of the first unit optical element 132, the light is not emitted to the outside of the light guide plate 13, and the reflectance is high, and the light is emitted from the light guide plate and reincident. And light loss due to reflection can be greatly reduced. In addition, alignment of the light guide plate 13 and the reflecting material is not necessary, and manufacturing is easy. Further, the first unit optical element 132 can be totally reflected by the inclined surfaces 132a and 132b and directed toward the X1 side, and the retroreflective unit 131 retroreflects the light, so that it is opposed by the irregular reflection component generated in the diffuse reflection or the like. It is possible to suppress the vicinity of the surface 13b from becoming too bright and causing uneven brightness.
Therefore, according to the present embodiment, light leakage from the facing surface 13b is significantly improved, and a good light guide plate with high light utilization efficiency can be obtained. Moreover, by using the surface light source device 10 and the display device 1 including the light guide plate 13 as described above, it is possible to obtain a good surface light source device and display device with high light use efficiency and high brightness.

(Evaluation of Examples and Comparative Examples)
Here, a light guide plate serving as an example of the present embodiment and a light guide plate serving as a comparative example were prepared, and the presence / absence of a hot spot, the amount of light flux on the light exit surface, and the like were evaluated.
The light guide plate of the example has the same shape as the light guide plate 13 of the present embodiment.
The first unit optical elements 132 have an arrangement pitch P1 = 50 μm and an apex angle α1 = 90 °, and the longitudinal direction (ridge line direction) is parallel to the Z direction and is arranged in the X direction.
The first unit optical element 132 is formed of an acrylic ultraviolet curable resin on a base material (not shown), cut to a predetermined width and processed into a tape shape, and an acrylic having the same refractive index as the main body 137. The base material 137 is bonded to the surface on the light incident surface 13a side of the main body 137 through a system adhesive material.

The second unit optical elements 134 are arranged in the Y direction with the arrangement pitch P2 = 50 μm and the apex angle α2 = 90 °, with the longitudinal direction (ridge line direction) as the X direction (light guide direction).
The third unit optical element 136 has an apex angle α3 = 100 °, a base angle β1 = 79.4 °, β2 = 0.6 °, an arrangement pitch P3 = 175 μm, and its ridge line direction is the Y direction. They are arranged in the X direction.
The thickness of the main body 137 is 2 mm.
The light incident surface 13a has a planar shape and is mirror-finished by mechanical polishing.
The main body 137, the second unit optical element 134, and the third unit optical element 136 are formed by extruding acrylic resin (refractive index 1.49).

The light guide plates of Comparative Examples 1 and 2 have the same shape as the light guide plate of the above-described embodiment except that the shape of the facing surface 13b is different.
The light guide plate of Comparative Example 1 has a flat opposing surface 13b, and a white reflective layer is provided outside the light guide plate 13 at a position facing the opposing surface 13b. This white reflective layer is a white polyester film.
As for the light-guide plate of the comparative example 2, the opposing surface 13b is planar shape and the white tape material is bonded on the opposing surface 13b via the adhesive agent. The white tape material is a white polyester film, the adhesive is an acrylic resin adhesive, has optical transparency, and has the same refractive index as the light guide plate.

  The light leakage is evaluated by visual observation of light leakage from the facing surface 13b. The observation position of light leakage passes through the geometric center of the light exit surface 13c of the light guide plate 13 and is a position 600 mm in the Z2 direction from the apex of the second unit optical element 134. Observing light from the opposing surface 13b, such as when the opposing surface 13b appears to shine white through the light exit surface 13c of the light guide plate 13 when observed from this position, is impossible, and no light leakage occurs. Even if it occurred, it was evaluated as good.

The amount of light flux means the light flux emitted in all directions from the light exit surface of the light guide plate. The higher this value, the higher the light extraction efficiency.
Here, using a viewing angle characteristic evaluation apparatus, the amount of luminous flux, which is the amount of light emitted at nine points on the light exit surface of the light guide plates of Examples and Comparative Examples 1 and 2, is measured and the average value is calculated. Were compared and evaluated.
The conditions and apparatus used for the measurement are as follows.
Measuring device: ELDIM EZcontrast160R
Evaluation screen size: incident side length (dimension in Y direction) 520 mm,
Light guide length (dimension in X direction) 320mm
Light emitting part 121 (LED) arrangement: LED length / gap length = 3 mm / 2.5 mm
(However, the LED length is the dimension in the Y direction of the light emitting part 121, and the gap length is the dimension between the light emitting parts 121 in the Y direction.)
Measurement position: 9 points which are intersections of lines equally divided vertically and horizontally (X direction and Y direction) on the light exit surface of each light guide plate Comparison method: Compare the average values of the above 9 points

Table 1 is a table showing the presence or absence of light leakage of Examples and Comparative Examples 1 and 2, the average value of 9 points of the luminous flux, and the like.
As shown in Table 1, light leakage was remarkably observed in the light guide plates of Comparative Examples 1 and 2 in which the facing surface 13b was flat and a white light reflecting layer, a white tape material, or the like was used. On the other hand, in the light guide plate of the example including the retroreflective portion 131 in which a plurality of first unit optical elements 132 are arranged on the opposing surface 13b, almost no light leakage from the opposing surface 13b was observed.
Therefore, by providing the retroreflective portion 131 in which a plurality of first unit optical elements 132 are arranged on the opposing surface 13b, light leakage from the opposing surface 13b can be reduced.
Further, as shown in Table 1, in the light guide plate of Comparative Examples 1 and 2 using the facing surface 13b as a flat surface and using a white light reflecting layer or a white tape material, the amount of light emitted from the light exit surface 13c is small. Small and dark was observed. In contrast, the light guide plate of the example has a large amount of light emitted from the light exit surface 13c and is brightly observed.
Therefore, by providing the retroreflective portion 131 on the facing surface 13b, light leakage from the facing surface 13b can be significantly reduced and the light utilization efficiency can be improved.
In addition, this effect is the light traveling direction in a direction close to the light guide direction as in this embodiment having the light guide direction control unit 133 in which a plurality of second unit optical elements 134 are arranged on the light exit surface 13c. This is particularly effective when light is incident on the facing surface 13b from a direction substantially parallel to the X direction or a direction having a small angle with the X direction.

(Deformation)
The present invention is not limited to the embodiment described above, and various modifications and changes are possible, and these are also within the scope of the present invention.
(1) In the present embodiment, the second unit optical element 134 has an example in which the arrangement pitch and the width in the arrangement direction are equal, but the present invention is not limited thereto, and the arrangement pitch is larger than the width in the arrangement direction. It is good also as a shape by which the plane part, the recessed part, etc. were formed between each unit optical element.

(2) In the present embodiment, the light guide plate 13 has an example in which the back surface 13d has a planar shape. However, the present invention is not limited to this. For example, the third unit optical element has a substantially triangular prism shape that is convex on the back surface side. Yes, the longitudinal direction (ridgeline direction) is the X direction, and a plurality of them are arranged in the Y direction, and may have a function as a light guide direction control unit that brings the light traveling direction closer to the light guide direction (X direction). .
Further, the thickness of the light guide plate 13 (particularly, the dimension in the Z direction of the main body 137) extends from the light incident surface 13a side (X1 side) to the opposing surface 13b (X2 side) along the light guide direction (X direction). It is good also as a shape which becomes thin gradually as it goes to.
The light guide plate 13 may have a form in which dots having a diffusing action are formed on the back surface 13d. In the case of such a configuration, it is preferable to use a deflecting optical sheet having a configuration in which unit prisms that are convex on the light output side (Z2 side) are arranged.
The light guide plate 13 may have a shape obtained by appropriately combining these shapes.

(3) In the present embodiment, an example in which the light diffusion sheet 15 is provided between the deflecting optical sheet 14 and the LCD panel 11 is shown. However, the present invention is not limited to this. A polarization selective reflection sheet may be further provided on the Z2 side).

  In addition, although this embodiment and modification can also be used in combination as appropriate, detailed description is abbreviate | omitted. Further, the present invention is not limited to the embodiment described above.

DESCRIPTION OF SYMBOLS 1 Display apparatus 10 Surface light source device 11 LCD panel 12 Light source part 121 Light emission part 13 Light guide plate 13a Light incident surface 13b Opposite surface 13c Light emission surface 13d Back surface 131 Retroreflection part 132 1st unit optical element 133 Light guide direction control part 134 2nd Unit optical element 14 Deflection optical sheet 15 Light diffusion sheet

Claims (6)

It has a light incident surface on which light is incident and a light exit surface that intersects the light incident surface and emits light. The light incident from the light incident surface is emitted from the light exit surface while being guided in a light guide direction. A light guide plate,
A retroreflecting portion that is provided on a facing surface facing the light incident surface in the light guiding direction, is formed by arranging a plurality of first unit optical elements, and retroreflects the light guided;
A light guide direction control unit that is provided on the light exit surface or the back surface facing the light exit surface and makes the traveling direction of light approach the light guide direction;
Providing
A light guide plate characterized by The light guide plate according to claim 1,
The first unit optical element has a triangular prism shape with an apex angle of 90 degrees that is convex to the outside of the light guide plate;
A light guide plate characterized by The light guide plate according to claim 2,
The longitudinal direction of the first unit optical element is parallel to the normal direction of the light exit surface;
A light guide plate characterized by The light guide plate according to any one of claims 1 to 3,
The light guide direction control unit is provided on the light exit surface, and is formed with a plurality of second unit optical elements having a columnar shape protruding outward from the light guide plate and having a direction perpendicular to the light entrance surface as a longitudinal direction. Being formed,
A light guide plate characterized by The light guide plate according to any one of claims 1 to 4,
A light source unit provided at a position facing the light incident surface and projecting light onto the light incident surface;
A deflecting optical sheet that is disposed on the light exit surface side of the light guide plate and has a deflecting action that emits light from the light guide plate in a normal direction of the sheet surface or a direction in which an angle with the normal direction is reduced. When,
A surface light source device comprising: A surface light source device according to claim 5;
A transmissive display unit illuminated from the back side by the surface light source device;
A display device comprising:

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