JP2015191818A - Surface light source device and transmission type display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a surface light source device and a transmission type display device capable of improving utilization efficiency of light emitting from an opposing surface of a light guide plate.SOLUTION: A surface light source device 10 includes: a light guide plate 13 which has an incident surface 13a where light enters, an emission surface 13c which crosses the incident surface 13a and from which light emits, a back surface 13d which is opposed to the emission surface 13c and an opposing surface 13b which is opposed to the incident surface 13a, and emits the light entered from the incident surface 13a from the emission surface 13c while guiding the light to a light guide direction; and an opposing surface reflection member 14b which is arranged on the opposing surface side of the light guide plate 13 and reflects the light emitted from the opposing surface 13b of the light guide plate 13 to the light guide plate side. In the opposing surface reflection member 14b, a distance d with the opposing surface 13b of the light guide plate 13 is within a range of 0 mm<d<1.0 mm.

Description

  The present invention relates to a surface light source device and a transmissive display device.

2. Description of the Related Art Conventionally, a transmissive display device that displays an image by illuminating a transmissive display unit such as an LCD (Liquid Crystal Display) panel from the back with a surface light source device (backlight) is known.
Surface light source devices are broadly classified into a direct type in which a light source is arranged directly under an optical member such as various optical sheets and an edge light type in which a light source is arranged on a side surface side of the optical member. This edge light type surface light source device has an advantage that the surface light source device can be made thinner than the direct type because the light source is arranged on the side surface side of the optical member such as a light guide plate, and is widely used. It has been.

Generally, in an edge light type surface light source device, a light source is disposed at a position facing a light incident surface that is a side surface of a light guide plate, and light emitted from the light source enters the light guide plate from the light incident surface, The light advances from the light incident surface to the surface facing the light incident surface while repeating reflection at the light exit surface and the back surface facing the light exit surface (the light traveling direction is referred to as the light guide direction).
In recent years, a light guide plate in which a prism shape having a slope that reflects light and changes an incident angle on a light exit surface and a plurality of V-shaped grooves are arranged on the back surface has been widely used.
In such an edge light type surface light source device, a reflective member such as a reflection sheet is disposed on the back side of the light guide plate or on the opposite side facing the light incident surface, and emitted from the back side or the opposite side of the light guide plate. The light utilization efficiency is increased by returning the light thus returned to the light guide plate from the light exit surface (for example, Patent Document 1).
However, such a surface light source device cannot sufficiently return the light emitted from the opposite surface of the light guide plate to the light guide plate, or cannot sufficiently emit the light from the light exit surface even if the light is returned. In some cases, the light use efficiency is reduced.

JP-A-2005-116268

  The subject of this invention is providing the surface light source device which can improve the utilization efficiency of the light radiate | emitted from the opposing surface of a light-guide plate, and a transmissive display apparatus.

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 includes a light incident surface (13a) on which light is incident, a light output surface (13c) that intersects the light incident surface and emits light, a back surface (13d) that faces the light output surface, A light guide plate (13) that has a facing surface (13b) facing the writing light surface and emits light incident from the light incident surface in the light guide direction (X direction) from the light exit surface; An opposing surface reflecting member (14b) disposed on the opposing surface side of the light guide plate and reflecting light emitted from the opposing surface of the light guide plate to the light guide plate side, wherein the opposing surface reflecting member is A surface light source device (10) characterized in that a distance d between the light plate and the facing surface is in a range of 0 mm <d <1.0 mm.
According to a second aspect of the present invention, in the surface light source device according to the first aspect, the light emitted from the rear surface of the light guide plate is arranged on the rear surface (13d) side of the light guide plate (13). The surface light source device (10) is characterized by including a back reflecting member (14a) for reflecting, and the opposing surface reflecting member (14b) is formed integrally with the back reflecting member.
According to a third aspect of the present invention, in the surface light source device according to the second aspect, the back reflecting member (14a) is joined to the facing surface (13b) side of the back surface (13d) of the light guide plate (13). It is a surface light source device (10) characterized by being.
The invention of claim 4 is the surface light source device (10) according to any one of claims 1 to 3, and a transmissive display unit (11) illuminated from the back side by the surface light source device. Is a transmissive display device (1).

  ADVANTAGE OF THE INVENTION According to this invention, the utilization efficiency of the light radiate | emitted from the opposing surface of a light-guide plate can be improved.

It is a figure explaining the transmissive display apparatus 1 of embodiment. It is a figure explaining the detail of the surface light source device of embodiment. It is a figure explaining the shape of the light-guide plate of embodiment. It is a figure explaining the back side unit optical shape of an embodiment. It is a figure explaining the locus | trajectory of the reflected light by the change of the distance d between the opposing surface of a light-guide plate and an opposing surface reflective member. It is a figure explaining prism sheet 15 of an embodiment. It is a figure explaining the evaluation method of the brightness | luminance of the light of a surface light source device. It is a figure which shows the luminance distribution of the light guide direction of a surface light source device. It is a figure explaining the surface light source device of a deformation | transformation form.

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 this embodiment, words such as plate and sheet are used, but these are generally used in the order of thickness in the order of plate, sheet, and film, and are also used in this specification. It is used following that. However, such proper use has no technical meaning and can be replaced as appropriate.
Numerical values such as dimensions and material names of the respective members 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.

In this specification, terms that specify shape and geometric conditions, for example, terms such as parallel and orthogonal, are strictly meanings, have similar optical functions, and can be regarded as parallel and orthogonal It also includes a state having an error of.
In this specification, the sheet surface (plate surface, film surface) is the planar direction of the sheet (plate, film) when viewed as the entire sheet (plate, film) in each sheet (plate, film). It is assumed that the surface to be

(Embodiment)
FIG. 1 is a diagram illustrating a transmissive display device 1 according to the present embodiment.
FIG. 2 is a diagram illustrating details of the surface light source device of the present embodiment. FIG. 2 is a cross-sectional view of the light guide plate on a plane (XZ plane) parallel to the light guide direction (X direction) and the light exit direction (Z direction).
In addition, in the following drawings including FIG. 1 and the following description, in order to facilitate understanding, when the transmissive display device 1 is in use, the transmissive display device 1 is parallel to the screen of the transmissive display device 1 and orthogonal to each other. The directions are the X direction (X1-X2 direction) and the Y direction (Y1-Y2 direction), and the direction orthogonal to the screen of the transmissive display device 1 is the Z direction (Z1-Z2 direction). In the Z direction, the Z1 side is the back side, and the Z2 side is the observer side.
2, FIG. 5, FIG. 7, and FIG. 9, the unit optical shapes of the light guide plate and the unit prism of the prism sheet are not shown.

The transmissive display device 1 of the present embodiment includes an LCD panel 11, a surface light source device 10, and the like. The transmissive display device 1 illuminates the LCD panel 11 with the surface light source device 10 from the back side, and displays video information formed on the LCD panel 11.
The screen of the transmissive display device 1 of the present embodiment corresponds to the 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 transmissive display device 1 is the display. The normal direction of the surface 11a is parallel to the Z direction, and coincides with the normal direction to the sheet surface of the prism sheet 15 to be described later, the normal direction to the plate surface of the light guide plate 13, and the like.

The LCD panel 11 is a transmissive display unit that is formed of a transmissive liquid crystal display element and forms video information on its display surface.
The LCD panel 11 of the present embodiment is substantially flat. The outer shape of the LCD panel 11 and the display surface 11a are rectangular when viewed from the Z direction, and have two opposite sides parallel to the X direction and two opposite sides parallel to the Y direction.
The transmissive display device 1 is provided on the observer side (Z2 side) of the LCD panel 11 and covers a peripheral edge of the LCD panel 11, and holds a frame-like bezel (not shown), as shown in FIG. In addition, a box-shaped housing portion 20 is provided which holds the LCD panel 11 and the surface light source device 10 disposed therein.

The surface light source device 10 illuminates the LCD panel 11 from the back side, and includes a light source unit 12, a light guide plate 13, a reflection member 14, a prism sheet 15, and a light diffusion sheet 16. The surface light source device 10 is a so-called edge light type surface light source device (backlight).
The light guide plate 13, the reflecting member 14, the prism sheet 15, the light diffusing sheet 16, etc. constituting the surface light source device 10 are rectangular when viewed from the front direction (Z direction) and are opposed to two sides parallel to the X direction. And two opposite sides parallel to the Y direction.

The light source unit 12 is a part that emits light that illuminates the LCD panel 11. The light source unit 12 is disposed along the Y direction at a position facing the light incident surface 13a that is one end surface (X1 side) of the light guide plate 13 in the X direction (X1 side).
The light source unit 12 is formed by arranging a plurality of point light sources 121 at predetermined intervals in the Y direction. The point light source 121 of this embodiment uses an LED (Light Emitting Diode) light source.

The light guide plate 13 is a substantially flat member that guides light. In the present embodiment, the light incident surface 13a and the opposing surface 13b are located at both ends of the light guide plate 13 in the X direction (X1 side end, X2 side end) and from the normal direction (Z direction) of the plate surface. As seen, it extends in the Y direction. The plate surface of the light guide plate 13 is parallel to the XY plane, and the light output surface 13c is a surface parallel to the plate surface.
In the XZ plane, the light guide plate 13 allows light emitted from the light source unit 12 to be incident from the light incident surface 13a and totally reflected by the light output surface 13c and the back surface 13d, while facing the light incident surface 13a. The light is appropriately emitted from the light exit surface 13c to the prism sheet 15 side (Z2 side) while being guided mainly in the X direction (X2 side).

FIG. 3 is a diagram illustrating the shape of the light guide plate 13 of the present embodiment. FIG. 3A is a diagram for explaining the light exit side unit optical shape 135, and FIG. 3B is a diagram for explaining the back side unit optical shape 131. 3A shows an enlarged part of a cross section parallel to the YZ plane of the light guide plate 13, and FIG. 3B shows an enlarged part of a cross section of the light guide plate 13 parallel to the XZ plane. Show.
FIG. 4 is a diagram illustrating the back-side unit optical shape 131 of the present embodiment. In FIG. 4, the back-side unit optical shape 131 in the cross section shown in FIG.
As shown in FIG. 1 and FIG. 3A, the light output side unit optical shape 135 is a triangular prism shape convex to the light output side (LCD panel 11 side, Z2 side), and the longitudinal direction (ridge line direction) is the X direction. And a plurality of them are arranged in the Y direction.
As shown in FIG. 3A, the light exit side unit optical shape 135 has a cross-sectional shape in a cross-section (YZ plane) parallel to the arrangement direction and orthogonal to the plate surface of the light guide plate 13, where the apex angle is γ. The isosceles triangle shape. The arrangement pitch of the light output side unit optical shapes 135 is P2, and the arrangement pitch P2 is equal to the width W2 in the arrangement direction of the light output side unit optical shapes 135 (P2 = W2).

The arrangement pitch P2 of the light exit side unit optical shapes 135 is preferably about 10 to 100 μm.
If the arrangement pitch P2 is smaller than this range, it is difficult to manufacture the light output side unit optical shape 135, and the designed shape cannot be obtained. Further, if the arrangement pitch P2 is larger than this range, moire with the pixels of the LCD panel 11 is likely to occur, or the pitch of the light output side unit optical shape 135 is easily recognized in the usage state as the surface light source device 10 or the like. It becomes. Therefore, the arrangement pitch P2 is preferably in the above range.

  The light output side unit optical shape 135 is not limited to the above example. For example, the cross sectional shape is a polygonal column shape such as a trapezoidal shape or a pentagonal shape, and the long axis is orthogonal to the plate surface (light output surface 13c) of the light guide plate 13. It may be a partial shape of the elliptical cylinder, a partial shape of the cylinder, or a shape formed by combining a plurality of types of curved surfaces and planes.

  The light output side unit optical shapes 135 are arranged in a direction (Y direction) orthogonal to the light guide direction (X direction) of the main light of the light guide plate 13, and the arrangement direction with respect to the light emitted from the light output surface 13c Has a light beam control action. Therefore, the light condensing property in the Y direction of the light emitted from the light guide plate 13 can be improved by the light output side unit optical shape 135. In addition, when such a light beam control action is not required, the light output side unit optical shape 135 may not be formed on the light output surface 13c.

As shown in FIGS. 1 and 3B, the back side unit optical shape 131 is a columnar shape that is convex on the back side (Z1 side), the longitudinal direction (ridge line direction) is the Y direction, and the light guide direction. Are arranged in the X direction.
As shown in FIG. 3B, the back-side unit optical shape 131 has a substantially trapezoidal cross-sectional shape in a cross section (XZ plane) in a direction parallel to the arrangement direction and orthogonal to the plate surface of the light guide plate 13. is there. The back side unit optical shape 131 is located on the light incident surface side (X1 side) and the second inclined surface portion 132, and is located on the opposite surface side (X2 side), and totally reflects at least part of the incident light. It has a slope part 133 and a top face part 134 located between the first slope part 132 and the second slope part 133.
The arrangement pitch of the back side unit optical shapes 131 is P1, and the arrangement pitch P1 is equal to the width W1 in the arrangement direction of the back side unit optical shapes 131 (P1 = W1). Further, the arrangement pitch P1 of the present embodiment is constant in the light guide direction.

The first inclined surface portion 132 forms an angle β with the plate surface of the light guide plate 13 (a surface parallel to the light exit surface 13c, a surface parallel to the XY plane). The second inclined surface portion 133 forms an angle α with the plate surface of the light guide plate 13 (a surface parallel to the light output surface 13c, a surface parallel to the XY plane). The angles α and β satisfy α <β.
The first inclined surface portion 132 is inclined so that the opposite surface side (top surface portion side) end portion is on the back side with respect to the light incident surface side end portion, and the light guided through the light guide plate 13 is incident light. Since it progresses from the surface 13a to the opposing surface 13b (from the X1 side to the X2 side), it does not easily enter the first slope portion 132.

The top surface portion 134 is located between the first slope portion 132 and the second slope portion 133. The top surface portion 134 is a surface parallel to the plate surface (light exit surface 13 c) of the light guide plate 13. Further, the top surface portion 134 is parallel or substantially parallel to the surface (sheet surface) of the back reflecting member 14a of the reflecting member 14 described later.
The second inclined surface portion 133 receives a part of the light guided through the light guide plate 13 and totally reflects at least a part of the incident light. And by the total reflection by the 2nd slope part 133, the advancing direction of the light changes to the direction where the incident angle with respect to the light emission surface 13c (surface parallel to XY surface) becomes small. Therefore, from the viewpoint of improving both the light guiding efficiency and the light extraction efficiency, the angle α preferably satisfies 1 ° <α ≦ 5 °.

When α ≦ 1 °, when the light traveling in the light guide direction (X direction) is totally reflected by the second inclined surface portion 133, the angle formed by the light exit surface 13c (a surface parallel to the XY plane) before and after the total reflection The amount of change in the light intensity becomes too small, so that light cannot be extracted sufficiently, and the light extraction efficiency decreases.
Further, when α> 5 °, when the light traveling in the light guide direction (X direction) is totally reflected by the second slope portion 133, the light exit surface 13c (a surface parallel to the XY plane) before and after the total reflection The amount of change in the angle formed becomes too large, and the light guide efficiency decreases. Further, since the variation in the light output direction from the light guide plate 13 is also increased, the prism sheet 15 described later has an insufficient deflection action in the front direction, the convergence is lowered, and the front luminance is lowered.
From the above, it is preferable that the angle α be in the above range.

The arrangement pitch P1 of the back side unit optical shapes 131 is preferably about P1 = 50 to 300 μm.
If the arrangement pitch P1 is smaller than this range, it becomes difficult to manufacture the back unit optical shape 131, and the designed shape cannot be obtained. Further, when the arrangement pitch P1 is larger than this range, moire tends to occur, and the pitch of the back-side unit optical shape 131 can be easily recognized when used as the surface light source device 10 or the like.
Therefore, the arrangement pitch P1 is preferably in the above range.

As shown in FIG. 4, in the arrangement direction of the back side unit optical shapes 131, the dimension of the top surface part 134 is Wa, and the dimension of both slope parts (the dimension combining the first slope part 132 and the second slope part 133) is Wb. Assuming that the ratio of the back side unit optical shape 131 to the width W1 is the ratio Wa / W1 and the ratio Wb / W1, respectively, these ratios are in the arrangement direction (X direction) of the back side unit optical shape 131. Is changing along.
In the vicinity of the light incident surface 13a, the ratio Wa / W1 is larger than the ratio Wb / W1. However, the ratio Wa / W1 is smaller and the ratio Wb / W1 is larger toward the facing surface 13b, and the ratio Wa / W1 is smaller than the ratio Wb / W1 in the vicinity of the facing surface 13b.
The ratio Wa / W1 and the ratio Wb / W1 may be changed continuously and gradually along the arrangement direction of the back side unit optical shapes 131, or may be changed stepwise.
Thus, by increasing the ratio Wb / W1 occupied by both slope portions (particularly, the second slope portion 133) as it goes to the facing surface side, light can be emitted efficiently in the light guide direction, The uniformity of brightness in the light direction can be improved.

In this embodiment, the ratio Wa / W1 is about 80/100 and the ratio Wb / W1 is about 20/100 on the most incident surface side (X1 side), and the ratio Wa on the most opposed surface side (X2 side). / W1 is about 20/100, and the ratio Wb / W1 is about 80/100.
However, the present invention is not limited to this, and the ratio Wa / W1 and the ratio Wb / W1 can be appropriately set according to the desired optical performance or the like. For example, the ratio Wb / W1 may be set as appropriate as long as it is within a range of about 10/100 on the most light incident surface side and about 90/100 on the most opposite surface side.

The light guide plate 13 is formed by an extrusion molding method, an injection molding method, or the like. The thermoplastic resin to be used is not particularly limited as long as it has high light transmittance, and examples thereof include acrylic resins, COP (cycloolefin polymer) resins, and PC (polycarbonate) resins.
The light guide plate 13 is not limited to this, and the back side unit optical shape 131 and the light exit side unit optical shape 135 are integrally formed on both surfaces of a sheet-like member formed by an extrusion method or the like by an ultraviolet ray forming method. It is good.

1 and 2, the reflecting member 14 is a sheet-like member that can reflect light, and reflects light emitted from the back surface 13 d of the light guide plate 13 and the facing surface 13 b toward the light guide plate side. The light use efficiency of the light source device 10 is improved. As the reflecting member 14, a sheet-like member made of a white resin (PET or the like) having high reflectivity and mainly having diffuse reflectivity is used from the viewpoint of increasing the light utilization efficiency and the like.
However, the present invention is not limited thereto, and for example, a member having mainly specular reflectivity (regular reflectivity) can be used as the reflection member 14. For example, the reflecting member 14 is a sheet-like 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 sheet-like member including a metal thin film as a surface layer can be used.

The reflecting member 14 includes a back reflecting member 14a disposed on the back surface 13d side (Z1 side) of the light guide plate 13, and a facing surface reflecting member 14b disposed on the facing surface 13b side (X2 side) of the light guide plate 13. Has been.
The back reflecting member 14 a is formed in a shape substantially equivalent to the outer shape of the back surface 13 d of the light guide plate 13. The back reflecting member 14 a is arranged so as to overlap the back surface 13 d of the light guide plate 13, thereby reflecting the light emitted from the back surface 13 d of the light guide plate 13 and returning it to the light guide plate 13.

The facing surface reflecting member 14 b is formed in a shape substantially equivalent to the outer shape of the facing surface 13 b of the light guide plate 13. The facing surface reflecting member 14 b is arranged so as to overlap the facing surface 13 b of the light guide plate 13, thereby reflecting the light emitted from the facing surface 13 b of the light guide plate 13 and returning it to the light guide plate 13.
Here, the facing surface reflecting member 14 b is disposed in a state where a predetermined distance d is separated from the facing surface 13 b of the light guide plate 13. This distance d is 0 mm <d <1.0 mm from the viewpoint of reflecting the light emitted from the facing surface 13 b of the light guide plate 13 and returning it to the light guide plate 13 and efficiently emitting it from the light output surface 13 c of the light guide plate 13. It is preferable. Further, it is more preferable that 0.1 mm ≦ d ≦ 0.5 mm.

  FIG. 5 is a diagram illustrating a locus of reflected light due to a change in the distance d between the opposing surface of the light guide plate and the opposing surface reflecting member. FIG. 5A is a diagram showing a locus of reflected light when the distance d is 0 mm <d <1.0 mm, and FIG. 5B is a reflected light when the distance d is d = 0. FIG. 5C is a diagram illustrating the trajectory of the reflected light when the distance d is d> 1.0 mm. In FIG. 5, the light L0 emitted from the light source unit 12 is illustrated as being directed in a direction parallel to the light guide direction (X direction), but the light L0 has a direction parallel to the light guide direction. It is assumed that not only the light that travels but also light that is inclined with respect to the light guide direction to the extent that it is incident on the facing surface 13b of the light guide plate 13 is included.

Here, when the distance d is 0 mm, that is, when the facing surface 13b of the light guide plate 13 and the facing surface reflecting member 14b are in contact with each other, the light is emitted from the light source unit 12 as shown in FIG. Even if the light L0 is emitted from the opposing surface 13b, the reflected light L5 is returned to the light guide plate by the opposing surface reflecting member 14b. It will become difficult to radiate | emit from 13c, and the utilization efficiency of light will fall. Further, even if the light L0 inclined with respect to the light guide direction is reflected by the opposing surface reflecting member 14b, most of the reflected light is not inclined to the extent that it exits from the light output surface 13c of the light guide plate 13. The light is not easily emitted from the surface 13c, and the light use efficiency is reduced.
Further, when the distance d is d> 1.0 mm, as shown in FIG. 5C, the distance between the facing surface 13b of the light guide plate 13 and the facing surface reflecting member 14b is too far from the light source unit 12. Even if the emitted light L0 is emitted from the facing surface 13b of the light guide plate 13 and reflected by the facing surface reflection member 14b, most of the reflected light (G) does not return to the light guide plate 13 and the light use efficiency is reduced. Will end up.

  On the other hand, in the present embodiment, as described above, the distance d between the facing surface 13b of the light guide plate 13 and the facing surface reflecting member 14b is defined as 0 mm <d <1.0 mm. As shown in a), the light L0 emitted from the light source unit 12 is very little reflected light G that does not return to the light guide plate 13 even though it is emitted from the opposed surface 13b and reflected by the opposed surface reflecting member 14b. Most of the light (L1 to L4) returns to the light guide plate 13. Here, the reflected light (L1 to L4) returning to the light guide plate 13 is often incident obliquely with respect to the facing surface 13b. Therefore, the reflected lights (L1 to L4) that have returned to the light guide plate 13 are likely to be emitted from the light exit surface 13c after being repeatedly reflected in the light guide plate 13, and the light use efficiency is improved.

In the reflecting member 14 of the present embodiment, the back reflecting member 14a and the opposing surface reflecting member 14b are integrally formed. Specifically, as shown in FIG. 2, the back surface reflecting member 14a and the counter surface reflecting member 14b are formed by bending one end edge of the sheet-like reflecting member 14 substantially vertically, and the one end bent. The edge becomes the opposing surface reflecting member 14b, and the other part becomes the back reflecting member 14a.
Further, the reflecting member 14 of the present embodiment is joined to the end portion on the opposite surface side (X2 side) of the back surface 13d of the light guide plate 13. Specifically, as shown in FIGS. 1 and 2, the back surface reflection member 14 a of the reflection member 14 and the vicinity of the end portion on the opposite surface side (X2 side) of the back surface 13 d of the light guide plate 13 are joined by the adhesive 17. Has been.

In this way, the back surface reflecting member 14a and the facing surface reflecting member 14b are integrally formed, and the reflecting member 14 is joined to the end portion on the facing surface side (X2 side) of the back surface 13d of the light guide plate 13, thereby absorbing moisture. Even if the light guide plate 13 and the reflection member 14 having different expansion / contraction characteristics due to temperature or the like are individually expanded and contracted, the distance d between the opposing surface 13b of the light guide plate 13 and the opposing surface reflection member 14b can be kept constant, It can suppress as much as possible that the utilization efficiency of the light by expansion / contraction of each member changes.
In the present embodiment, as shown in FIG. 1, the joining of the light guide plate 13 and the reflection member 14 by the adhesive 17 is fixed at both ends in the Y direction of the light guide plate 13 and three points in the center thereof. An example is shown, but the present invention is not limited to this. For example, the adhesive 17 may be provided so as to extend over the entire edge of the light guide plate 13 on the opposite surface side, and the light guide plate 13 and the back reflecting member 14a may be joined.

FIG. 6 is a diagram illustrating the prism sheet 15 of the present embodiment. In FIG. 6, a part of a cross section parallel to the XZ plane of the prism sheet 15 is shown enlarged.
The prism sheet 15 is disposed closer to the LCD panel 11 (Z2 side) than the light guide plate 13 (see FIG. 1). The prism sheet 15 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. It is.
The prism sheet 15 includes a prism base layer 152 and a plurality of unit prisms 151 that are arranged in a plurality on the light guide plate 13 side (Z1 side) of the prism base layer 152.

The prism base material layer 152 is a portion that becomes a base (base material) of the prism sheet 15. For the prism base material layer 152, a resin-made sheet-like member having optical transparency is used.
The unit prism 151 has a triangular prism shape convex toward the light guide plate 13 side (Z1 side), and the longitudinal direction (ridge line direction) is set to the Y direction on the back side (Z1 side) surface of the prism base material layer 152. A plurality are arranged in the direction. That is, the arrangement direction of the unit prisms 151 is parallel to the arrangement direction of the rear unit optical shapes 131 of the light guide plate 13 when viewed from the normal direction (Z direction) of the display surface of the transmissive display device 1, and the light exit side The unit optical shape 135 is orthogonal to the arrangement direction.

The unit prism 151 of the present embodiment is an isosceles triangle whose cross-sectional shape in a cross section (XZ plane) parallel to the arrangement direction (X direction) and the direction orthogonal to the sheet plane (Z direction) is an apex angle ε. The example which is a shape is shown. However, the present invention is not limited to this, and the cross-sectional shape of the unit prism 151 may be an unequal triangular shape. Further, the unit prism 151 may have a bent surface shape in which at least one surface is composed of a plurality of surfaces, or may have a shape in which a curved surface and a flat surface are combined, or a cross-sectional shape that is asymmetric in the arrangement direction. It is good.
The unit prism 151 has an arrangement pitch P3 and a width in the arrangement direction W3, and the arrangement pitch and the lens width in the arrangement direction are equal in the arrangement direction (P3 = W3).
The prism sheet 15 is emitted from the light guide plate 13 and totally reflected by the other surface (for example, the surface 151b) the light L1 incident from one surface (for example, the surface 151a). Z direction) or deflected (condensed) in a direction where the angle formed with respect to the front direction becomes smaller.

The prism sheet 15 is produced, for example, by forming a unit prism 151 with ionizing radiation curable resin such as ultraviolet curable resin on one side of a sheet-like prism base layer 152 made of PET resin or PC resin. The
For example, the prism sheet 15 may be a PC resin, an MBS (methyl methacrylate / butadiene / styrene copolymer) resin, an MS (methyl methacrylate / styrene copolymer) resin, a PET resin, or PS (polystyrene). You may form by extruding thermoplastic resins, such as resin.

Returning to FIG. 1, the light diffusion sheet 16 is a sheet-like member having an action of diffusing light. The light diffusion sheet 16 is provided on the prism panel 15 on the LCD panel 11 side (Z2 side).
By providing such a light diffusing sheet 16, 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 151.
The light diffusing sheet 16 is made of various general-purpose light diffusing members in accordance with the optical performance desired for the surface light source device 10 and the transmissive display device 1, the optical characteristics of the light guide plate 13, and the like. You may select and use.
As such a light diffusing sheet 16, a resin sheet-shaped member containing a diffusing material, or a member in which a binder containing a diffusing material is coated on at least one surface of a resin sheet-like 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.

  In addition, a fine uneven shape is formed on the light output side (Z2 side) surface of the prism base layer 152 of the prism sheet 15 in order to prevent optical adhesion with the light diffusion sheet 16 and to provide a light diffusion function. May be. As such a concavo-convex shape, a layer formed by coating a binder containing a bead-like filler is suitable, but not limited thereto.

In addition, not only the light diffusion sheet 16 but also a polarized light having a function of transmitting light in a specific polarization state to the LCD panel 11 side (Z2 side) from the prism sheet 15 and reflecting light in other polarization states. A selective reflection sheet may be arranged. 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. Such arrangement is preferable from the viewpoint of improving luminance and improving light utilization efficiency. As such a polarization selective reflection sheet, for example, DBEF series (manufactured by Sumitomo 3M Limited) can be used.
In addition to the light diffusion sheet 16, various optical sheets such as a lenticular lens sheet may be disposed.
Further, a polarization selective reflection sheet as described above, various optical sheets, and the like may be further disposed on the LCD panel 11 side of the light diffusion sheet 16.

Next, an evaluation result of a change in luminance of the surface light source device due to a change in the distance d between the opposing surface of the light guide plate and the opposing surface reflecting member will be described.
FIG. 7 is a diagram illustrating a method for evaluating the luminance of light emitted from the surface light source device. FIG. 7A is a schematic diagram for explaining the measurement of the luminance distribution in the light guide direction of the surface light source device, and FIG. 7B shows the measurement points of the luminance measured in evaluating the luminance uniformity. FIG.
FIG. 8 is a diagram illustrating a luminance distribution in the light guide direction of the surface light source device.

(Evaluation of luminance distribution of surface light source device)
First, for a specimen of a surface light source device in which the distance d between the facing surface 13b of the light guide plate 13 and the facing surface reflecting member 14b is different, the brightness distribution in the light guide direction of the surface light source device is measured, and the distance d and the brightness Evaluate the relationship.
As shown in FIG. 7A, the luminance of the surface light source device is measured by laminating the reflection member 14, the light guide plate 13, the prism sheet 15, and the light diffusion sheet 16 on the housing portion 20, and inserting the light guide plate 13. A test body of a surface light source device in which the light source unit 12 is disposed on the light surface 13a side, and a luminance meter from the vertical upper side (Z2 side) of the test body toward the light exit surface (upper surface of the light diffusion sheet 16) And the light source part 12 of the test body was made to emit light.

In this evaluation measurement, the luminance distribution in the light guide direction of the test body was measured by moving the test body with respect to the luminance meter in the light guide direction (X direction) using a transport stage or the like. Note that the measurement of the luminance distribution is not limited to this, and for example, the luminance meter may be moved in the light guide direction with respect to the specimen.
Here, the luminance meter is arranged at a height h = 500 mm from the light exit surface (upper surface of the light diffusion sheet 16) of the test body to the vertical upper side (Z2 side), and on the geometric center of the light exit surface of the test body. From the X1 side end of the test body (light guide plate) (position of −75 mm in the light guide direction from the geometric center) to the X2 side end (+75 mm in the light guide direction from the geometric center). The brightness is measured by moving to the position) at intervals of 5 mm.

The dimensions, specifications, and the like of the reflecting member 14 and the light guide plate 13 used in the evaluation are as follows.
Reflective member 14: 176 mm (X direction) × 300 mm (Y direction), thickness of about 150 μm, white PET sheet (E6QD, manufactured by Toray Industries, Inc.).
Light guide plate 13: 174.5 mm (X direction) × 300 mm (Y direction), thickness of about 550 μm, made of acrylic resin.
Prism sheet 15: 171 mm (X direction) × 300 mm (Y direction), thickness of about 180 μm, reverse prism sheet with apex angle ε = 66 ° formed from a PET film with an acrylic ultraviolet curable resin having a refractive index of 1.51 .
Light diffusion sheet 16: 171 mm (X direction) × 300 mm (Y direction), thickness of about 160 μm, manufactured by Sumitomo 3M Limited.
Luminance meter: BM-7 (manufactured by TOPCON), arranged at a height of h = 500 mm from the light exit surface of the test body vertically upward (Z2 side).

For the measurement of the luminance distribution, a plurality of surface light source device test bodies were prepared in which the distance d between the facing surface 13b of the light guide plate 13 and the facing surface reflecting member 14b was different. That is, seven types of test specimens with distances d = 0 mm, d = 0.1 mm, d = 0.3 mm, d = 0.5 mm, d = 0.8 mm, d = 1.0 mm, and d = 1.2 mm Was prepared, and the luminance distribution in the light guide direction (X direction) of each test specimen was measured and summarized in FIG.
Here, in FIG. 8, the horizontal axis indicates the luminance measurement position in the light guide direction (X direction) of the test body (light guide plate), and the vertical axis indicates the luminance value measured by the luminance meter. The left side of the horizontal axis is the light incident surface 13 a side of the light guide plate 13, and the right side is the opposite surface 13 b side of the light guide plate 13.

As shown in FIG. 8, the luminances on the light incident surface 13 a side of the light guide plate 13 are similar to each other in each test body, but there is a difference in the luminance on the facing surface 13 b side far from the light source unit 12. Specifically, the brightness on the facing surface side tends to decrease as the distance d between the facing surface 13b of the light guide plate 13 and the facing surface reflecting member 14b increases. This is considered that the light returning to the light guide plate 13 out of the reflected light of the opposed surface reflecting member 14b decreases as the distance d increases, and the light use efficiency is reduced.
Note that the luminance when d = 0 is lower than the luminance when d = 0.1 mm, as described above, the light is emitted from the light source unit 12 as shown in FIG. Even if the light is emitted from the facing surface 13b, most of the light returns to the light guide plate by the facing surface reflecting member 14b, but most of the returned light is parallel to the light guide direction (X direction). This is considered to be difficult to emit from the light exit surface 13 c of the light guide plate 13.
From the above, when the distance d is 0.5 mm or less in the light guide direction passing through the geometric center of the light exit surface of the surface light source device, the luminance on the facing surface 13b side is comparable to the luminance on the light incident surface 13a side. It was confirmed that.

(Evaluation of luminance uniformity of surface light source device)
Next, the uniformity of luminance is evaluated for the specimen of the surface light source device in which the distance d between the opposing surface of the light guide plate and the opposing surface reflecting member is different.
In the measurement of the luminance of the surface light source device, the reflection member 14, the light guide plate 13, the prism sheet 15, and the light diffusion sheet 16 are laminated on the housing unit 20 in the same manner as the measurement of the luminance distribution described above. A test body (measurement example 1 to measurement example 7) of a surface light source device in which the light source unit 12 is disposed on the light incident surface 13a side, and a luminance meter is disposed on the vertical upper side (Z2 side) of the test body. The light source unit 12 was made to emit light.
For the measurement of the luminance, a plurality of surface light source device test bodies (measurement examples 1 to 7) having different distances d between the facing surface 13b of the light guide plate 13 and the facing surface reflecting member 14b were prepared. That is, the distance d is d = 0 mm (measurement example 1), d = 0.1 mm (measurement example 2), d = 0.3 mm (measurement example 3), d = 0.5 mm (measurement example 4), d = 0. Seven types of test specimens of 8 mm (Measurement Example 5), d = 1.0 mm (Measurement Example 6), and d = 1.2 mm (Measurement Example 7) were prepared, and the luminance of each test specimen was measured.

As shown in FIG. 7B, the measurement points of the brightness of each test specimen are the geometric center point of the light exit surface (upper surface of the light diffusion sheet 16) of the test specimen, the four corner points of the light exit face, There are 13 points composed of the midpoints of the four corner points and the midpoints of the four corner points and the geometric center point.
The surface light source device of each measurement example used for the evaluation is the same as the test body used for the evaluation of the luminance distribution described above in terms of the dimensions of the reflecting member 14, the light guide plate 13, and the like.
Moreover, the surface light source device of the comparative example was prepared as a comparison object with each test body, and the brightness | luminance measurement similar to each test body (measurement examples 1-7) was performed. The surface light source device of the comparative example is not provided with a facing surface reflecting member, and the inner wall of the casing portion colored in dark color faces the facing surface of the light guide plate.

  Tables 1 and 2 summarize the luminance uniformity of the surface light source devices of the measurement examples 1 to 7 and the surface light source device of the comparative example and the evaluation results of the screen luminance unevenness.

Here, the brightness uniformity in Table 1 is a value obtained by dividing the minimum brightness value by the maximum brightness value among the 13 measurement points (minimum brightness value / maximum brightness value).
The screen brightness unevenness is a result of visual evaluation of the presence or absence of brightness unevenness on the light exit surface of the surface light source device of each measurement example and the surface light source device of the comparative example, and the brightness unevenness is not recognized throughout the light exit surface. It was evaluated as “”, and a product that could be used as a product was evaluated as “good” although some luminance unevenness was observed. Moreover, although the brightness nonuniformity was recognized slightly, the thing which cannot be recommended and used as a product was evaluated as (triangle | delta), and the brightness nonuniformity was recognized and the thing which cannot be used as a product was evaluated as x.

  As shown in Table 1, the surface light source device of the comparative example had a luminance uniformity of 63.1% and an evaluation of screen luminance unevenness of x. This is because, unlike the surface light source device of the present embodiment, the opposed surface reflecting member is not provided on the opposed surface side of the light guide plate, and the inner wall of the housing portion facing the opposed surface is colored in a dark color system. Therefore, it is considered that the light emitted from the opposing surface of the light guide plate is absorbed by the inner wall of the casing and hardly returned to the light guide plate. Therefore, in the surface light source device of the comparative example, it is considered that the luminance of the opposite surface side of the light guide plate is lower than that of the light incident surface side, and both the evaluation of luminance uniformity and screen luminance unevenness are lowered.

The surface light source device of Measurement Example 1 had a luminance uniformity of 70.6%, and the evaluation of screen luminance unevenness was Δ. This is because, unlike the surface light source device of the comparative example, the surface light source device of the measurement example 1 is provided with an opposing surface reflection member, and thus the luminance uniformity is improved as compared with the surface light source device of the comparative example. Conceivable. However, since the distance d between the opposing surface of the light guide plate and the opposing surface reflecting member is 0 mm in the surface light source device of Measurement Example 1, the utilization efficiency of the light emitted from the opposing surface of the light guide plate is low, and Since the brightness was darker than that on the light incident surface side, the evaluation of the screen brightness unevenness is considered to be Δ.
Here, in the evaluation of the luminance distribution of FIG. 8 described above, the surface light source device of Measurement Example 1 has higher luminance on the opposite surface side as compared to the case where the distance d is 0.1 mm. Since it is easy to proceed in the X1 direction, it is difficult to stand up on the outgoing surface side especially at the edge on the opposite surface side of the light guide plate (outside the measurement region in FIG. 8), and black streaks are visually recognized in the edge region on the opposite surface side The evaluation of luminance unevenness was Δ.

In addition, the surface light source device of Measurement Example 6 had a luminance uniformity of 68.8% and a screen luminance unevenness evaluation of Δ. This is because, unlike the surface light source device of the comparative example, the surface light source device of the measurement example 6 is provided with an opposing surface reflection member, so that the luminance uniformity is improved as compared with the surface light source device of the comparative example. Conceivable. However, in the surface light source device of Measurement Example 6, since the distance d between the opposing surface of the light guide plate and the opposing surface reflecting member is too wide as 1.0 mm, most of the reflected light reflected by the opposing surface reflecting member returns to the light guide plate. Since the brightness on the opposite surface side became darker than that on the light incident surface side, it is considered that the evaluation of the screen brightness unevenness was Δ.
The surface light source device of Measurement Example 7 had a luminance uniformity of 64.0% and a screen luminance unevenness evaluation of x. This is because, in the surface light source device of Measurement Example 7, since the distance d between the opposing surface of the light guide plate and the opposing surface reflecting member is greater than 1.0 mm, even if the opposing surface reflecting member is provided, the reflected light is transmitted through the light guide plate. Since the amount returned to is reduced, it is considered that the evaluation was comparable to that of the surface light source device of the comparative example.

  In contrast, the surface light source device of Measurement Example 2 had a luminance uniformity of 75.1% and an evaluation of screen luminance unevenness was ◎. In addition, the surface light source devices of Measurement Examples 3 and 4 also had luminance uniformity of 74.4% and 74.1%, respectively, and the evaluation of screen luminance unevenness was ◎. This is because the surface light source devices of Measurement Examples 2 to 4 emit light from the facing surface of the light guide plate when the distance d between the facing surface of the light guide plate and the facing surface reflecting member is 0.1 to 0.5 mm. Since most of the reflected light reflected by the opposing surface reflecting member returns to the light guide plate, the luminance uniformity is improved, and the evaluation of the screen luminance unevenness is considered to be ◎.

  In addition, the surface light source device of Measurement Example 5 had a luminance uniformity of 72.0% and an evaluation of screen luminance unevenness was good. As in the case of Measurement Examples 2 to 4, since most of the reflected light emitted from the opposing surface of the light guide plate and reflected by the opposing surface reflecting member returns to the light guide plate, the luminance uniformity is improved. Conceivable. However, since the surface light source device of Measurement Example 5 has a distance d farther than that of Measurement Examples 2 to 4, the luminance on the opposite surface side of the light guide plate is slightly darker than that of the light incident surface, resulting in screen luminance. It is probable that the evaluation of unevenness was ○.

  From the above evaluation results, the surface light source device in which the distance d satisfies 0 mm <d <1.0 mm, that is, the surface light source devices in Measurement Examples 2 to 5, have good luminance uniformity of 72% or more, and have uneven screen luminance. It was confirmed that the evaluation was sufficiently suppressed by ◎ or ○. Moreover, in order to more effectively suppress the screen luminance unevenness of the surface light source device, since the evaluation needs to be ◎, it is more preferable that the distance d is 0.1 mm ≦ d ≦ 0.5 mm. confirmed.

As described above, in the surface light source device 10 according to the present invention, the distance d between the facing surface reflecting member 14b and the facing surface 13b of the light guide plate 13 is within the range of 0 mm <d <1.0 mm. The emitted light is emitted from the facing surface 13b and reflected by the facing surface reflecting member 14b, and most of the reflected light returns to the light guide plate 13 to improve the light use efficiency.
Further, in the surface light source device 10, since the opposing surface reflecting member 14b is formed integrally with the back reflecting member 14a, the opposing surface reflecting member 14b can be simultaneously installed in the housing unit 20 together with the back reflecting member 14a. The surface light source device can be easily manufactured as compared with the case where the back surface reflecting member 14a and the opposed surface reflecting member 14b are configured separately.

  Further, in the surface light source device 10, the opposing surface reflecting member 14 b is formed integrally with the back reflecting member 14 a, and the back reflecting member 14 a is joined to the facing surface 13 b side on the back surface 13 d of the light guide plate 13. Even if the light guide plate 13 and the reflection member 14 are individually expanded and contracted by moisture absorption or the like, the distance d between the opposing surface 13b of the light guide plate 13 and the opposing surface reflection member 14b can be kept constant, and the light use efficiency changes. Can be suppressed as much as possible.

(Deformation)
Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications and changes can be made as in the modifications described later, and these are also included in the present invention. Within the technical scope. In addition, the effects described in the embodiments are merely a list of the most preferable effects resulting from the present invention, and the effects of the present invention are not limited to those described in the embodiments. It should be noted that the above-described embodiment and modifications described later can be used in appropriate combination, but detailed description thereof is omitted.
FIG. 9 is a diagram for explaining a modified surface light source device, and corresponds to FIG. 2.

(1) In the embodiment, the example in which the reflecting member 14 includes the back reflecting member 14a and the opposing surface reflecting member 14b has been described, but the embodiment is not limited thereto. For example, as shown in FIG. 9, the reflecting member 14 includes not only the back reflecting member 14 a and the facing surface reflecting member 14 b, but also an upper opening (Z2 side) between the facing surface 13 b and the facing surface reflecting member 14 b of the light guide plate 13. You may make it provide the light emission side reflection member 14c which covers a part. Moreover, you may make it form these reflection members integrally. By providing the light-emitting side reflecting member 14c in this way, the reflected light reflected by the facing surface reflecting member 14b leaks from the upper (Z2 side) opening between the facing surface 13b of the light guide plate 13 and the facing surface reflecting member 14b. While suppressing that it comes out, the reflected light can be returned to the light-guide plate 13, and the utilization efficiency of light can be improved.

(2) In the present embodiment, an example in which the back reflecting member 14a and the opposed reflecting member 14b are integrally formed has been described. However, the present invention is not limited to this. For example, each reflecting member is a separate body. It may be formed.
(3) You may make it form the mat | matte layer which consists of fine uneven | corrugated shape on the surface (surface facing the light-guide plate 13) of the reflection member 14. As shown in FIG. By providing the mat layer, when the light guide plate 13 is laminated on the reflecting member 14, it is possible to suppress the two from being in optical contact.

(4) The back-side unit optical shape 131 is, for example, a staircase in which the top surface portion 134 is a surface parallel to the plurality of light exit surfaces 13c, and the height toward the back surface side increases in the top surface portion 134 toward the opposite surface side. It is good also as the form which has a shape. By adopting such a shape, the contact area between the reflecting member 14 and the light guide plate 13 can be reduced while the optical performance similar to that of the light guide plate 13 having a flat top surface part 134 is obtained, and optical adhesion is further suppressed. it can.
Further, for example, the back surface 13d of the light guide plate 13 is planar, and a plurality of V-shaped grooves are formed to form a back-side unit optical shape, and the inclined surface of the groove is like the second inclined surface portion 133. It is good also as a form which has the effect | action which totally reflects and deflects light.

(5) The back side unit optical shape 131 may be formed in a discontinuous island shape in a direction (Y direction) orthogonal to the light guide direction in the plate surface. For example, the back side unit optical shape 131 is a substantially square trapezoidal shape that is convex on the back side, and may be arranged in a light guide direction and a direction (X direction and Y direction) perpendicular thereto.

(6) The light emission side unit optical shape 135 may have a shape in which the arrangement pitch P2 is larger than the width W2 in the arrangement direction, and a plane portion, a recess, or the like is formed between the light emission side unit optical shapes 135. The same applies to the back unit optical shape 131.
(7) The total thickness of the light guide plate 13 may be a shape in which the light incident surface side (X1 side) is thicker and gradually becomes thinner toward the opposite surface side (X2 side).

(8) The angle α of the back side unit optical shape 131 may be changed stepwise or continuously in the arrangement direction.
(9) Various optical sheets used in combination with the light guide plate 13 as the surface light source device 10 can be appropriately selected and used in accordance with the use environment and desired optical performance. For example, other optical sheets or the like in which various lens shapes or prism shapes are formed may be appropriately combined between the prism sheet 15 and the LCD panel 11. Further, an optical sheet having a deflection action other than the prism sheet 15 may be used.

  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 by the above-described embodiments and the like.

DESCRIPTION OF SYMBOLS 1 Transmission type display apparatus 10 Surface light source device 11 LCD panel 12 Light source part 13 Light guide plate 131 Back side unit optical shape 132 1st slope part 133 2nd slope part 134 Top surface part 14 Reflective member 14a Back surface reflection member 14b Opposite surface reflection member 15 Prism sheet 16 Light diffusion sheet

Claims (4)

A light incident surface on which light is incident; a light exit surface that intersects the light incident surface and emits light; a rear surface that faces the light exit surface; and a facing surface that faces the light incident surface; A light guide plate that emits light from the light exit surface while guiding light incident from the surface in the light guide direction;
An opposing surface reflecting member that is disposed on the opposing surface side of the light guide plate and reflects light emitted from the opposing surface of the light guide plate to the light guide plate side;
The opposing surface reflecting member has a distance d between the opposing surface of the light guide plate and a range of 0 mm <d <1.0 mm;
A surface light source device. The surface light source device according to claim 1,
A rear reflection member that is disposed on the back side of the light guide plate and reflects light emitted from the back side of the light guide plate to the light guide plate side;
The opposing surface reflecting member is formed integrally with the back reflecting member;
A surface light source device. The surface light source device according to claim 2,
The back reflecting member is bonded to the opposite surface side of the back surface of the light guide plate;
A surface light source device. The surface light source device according to any one of claims 1 to 3,
A transmissive display unit illuminated from the back side by the surface light source device;
A transmissive display device.

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