JP6500613B2 - Light guide plate, surface light source device, transmission type display device - Google Patents

Description

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

BACKGROUND Conventionally, there has been known a transmissive display device that illuminates a transmissive display unit such as an LCD (Liquid Crystal Display) panel or the like with a surface light source device (backlight) from the back surface to display an image.
Surface light source devices are roughly classified into a direct type in which a light source is disposed immediately below an optical member such as various optical sheets, and an edge light type in which a light source is disposed on the side of an optical member. Since this edge light type surface light source device arranges the light source on the side of the optical member such as a light guide plate, it has the advantage of being able to make the surface light source device thinner compared to the direct type. It is used.

Generally, in the edge light type surface light source device, the light source is disposed at a position facing the light incident surface which is the side surface of the light guide plate, and the light emitted from the light source is incident on the light guide plate from the light incident surface. While repeating the reflection on the light exit surface and the back surface opposite to the light exit surface, the light travels in the direction (light guide direction) substantially orthogonal to the light entrance surface. Then, by changing the traveling direction of light by a diffusion pattern, a prism shape, or the like provided on the back surface of the light guide plate, light is emitted little by little to each side of the LCD panel from each position along the light guide direction of the light emission surface. Go.
In recent years, a light guide plate in which a plurality of unit optical shapes such as a prism shape are arranged on the back surface is widely used (Patent Documents 1 and 2).

JP, 2005-259361, A Unexamined-Japanese-Patent No. 9-166713 gazette

The unit optical shape of the back surface of the light guide plate is, for example, a surface which is parallel to the light output surface and reflects light so as to be incident at a critical angle or more with respect to the light output surface to guide the light to the opposing surface side. It is known to have an inclined surface which is inclined with respect to the light exit surface, and has an inclined surface which allows the reflected light to be incident at less than a critical angle with respect to the light exit surface and to be emitted from the light exit surface.
Since such a light guide plate does not diffuse and reflect light, the front luminance can be increased, and even in the region away from the light source in the light guide direction, the light can be sufficiently guided. The uniformity is also good.

In the light guide plate as described above, the light is mainly reflected by the inclined surface, and most of the light incident at less than the critical angle with respect to the light exit surface exits from the light exit surface. Further, a plurality of slopes are arranged in the light guide direction. Therefore, the amount of light emitted from the light guide plate repeatedly changes in the light guiding direction, such as increasing or decreasing.
As a result, bright and dark stripes are generated on the light emitting surface of the surface light source device, and the interference between the bright and dark stripes and the pixels of the liquid crystal panel causes moire on the display surface of the transmissive display device to significantly reduce the image quality of the display. There was a problem of causing
Patent Literatures 1 and 2 do not disclose any measures against the bright and dark stripes produced on the light emitting surface of the surface light source device as described above and the moire produced on the display surface of the transmissive display device.

  An object of the present invention is to provide a light guide plate capable of significantly reducing the occurrence of moiré and displaying a good image, and a surface light source device and a transmissive display device provided with the same.

The present invention solves the above problems by the following solution means. In addition, in order to make an understanding easy, although the code | symbol corresponding to embodiment of this invention is attached and demonstrated, it is not limited to this.
The invention according to claim 1 has a light entrance surface (13a) on which light is incident, a light exit surface (13c) which intersects the light entrance surface and emits light, and a back surface (13d) opposite to the light exit surface. A light guide plate that emits light from the light exit surface while guiding light incident from the light entrance surface to the surface side facing the light entrance surface, and the back surface has a unit optical shape (131) on the back surface. A plurality of light emitting units are arranged in the light guiding direction, and the back side unit optical shape is a pillar that is convex on the back side, and is a cross section in a cross section parallel to the arranging direction and parallel to the thickness direction of the light guiding plate A first slope portion (132) positioned on the light entrance surface side, and a second slope portion (133 for total reflection of at least part of incident light positioned on the other side opposite to the first slope portion); And a top surface located on the most rear side between the first slope and the second slope 134, 234), and the top surface is inclined such that the end on the first slope side is positioned more on the back side than the end on the second slope side, and the second slope Let .beta. Be the angle parallel to the plate surface of the light guide plate be .beta., And let .gamma. Be the angle between the top surface portion and the plane parallel to the plate surface of the light guide plate be 0.2.degree. <. Gamma. <0. A light guide plate (13, 23) characterized by satisfying the relationships of 7 °, 1 ° <β <5 °, (β−γ) <2 °.
The invention according to claim 2 is the light guide plate according to claim 1, wherein the rear side unit optical shape (131) has a constant array pitch P1, and the second sloped portion (with respect to the array pitch P1). The light guide plate (13, 23) is characterized in that the ratio Wa / P1 of the dimension Wa occupied by 133) in the arrangement direction of the back side unit optical shape increases with distance from the light incident surface (13a). .
The invention according to claim 3 relates to the light guide plate according to claim 1 or 2, wherein the top surface portion (234) has a plurality of surfaces (234a to 234d) having different heights on the back side. The plurality of surfaces form an angle γ with the surface parallel to the plate surface of the light guide plate, and the surface (234a) located closest to the first inclined surface side in the light guide direction has the smallest height to the back surface side. (2) The light guide plate (23) is characterized in that the height to the back side increases as it goes to the slope portion side.
The invention of claim 4 is provided at a position facing the light guide plate (13, 23) according to any one of claims 1 to 3 and the light incident surface (13a) of the light guide plate. A light source unit (12) for projecting light onto the light entrance surface, and a light exit surface side of the light guide plate, and the light emitted from the light guide plate is in the normal direction or the normal direction of the sheet surface A deflecting optical sheet (15) having a deflecting action to turn in a direction in which the angle decreases, and a reflecting member (14) disposed on the back side of the light guide plate and reflecting light emitted from the back side of the light guide plate to the light guide plate side. A surface light source device (10).
The invention of claim 5 is a transmission type display device (1) including the surface light source device (10) according to claim 4 and a transmission type display unit (11) illuminated from the back side by the surface light source device. It is.

  According to the present invention, it is possible to provide a light guide plate capable of significantly reducing the occurrence of moiré and displaying a good image, and a surface light source device and a transmissive display device provided with the same.

It is a figure explaining the transmissive display apparatus 1 of 1st Embodiment. It is a figure explaining the light-guide plate 13 of 1st Embodiment. It is a figure explaining the mode of the light in back side unit optical shape 131. FIG. It is a figure explaining the prism sheet 15. FIG. It is a figure explaining light guide plate 13B, 13C of comparative examples 1 and 2. It is a figure explaining the light guide plate 23 of 2nd Embodiment. It is a figure explaining the light-and-dark stripes which give a moiré.

Embodiments of the present invention will be described below with reference to the drawings and the like.
In addition, each figure shown below including FIG. 1 is a figure shown typically, and the magnitude | size of each part and the shape are suitably exaggerated in order to make an understanding easy.
In the present specification, the terms plate, sheet and the like are used, but as a general usage, these are used in the order of thickness, in the order of plate, sheet and film, and this specification Above all, it is used according to it. However, since such proper use has no technical meaning, the wording of the sheet, the plate, and the film can be replaced as appropriate. For example, the optical sheet may be an optical film or an optical plate.

Numerical values such as dimensions of respective members and material names described in the present specification are merely examples as an embodiment, and the present invention is not limited to these and may be appropriately selected and used.
In the present specification, terms specifying shape and geometrical conditions, for example, terms such as parallel and orthogonal, have similar optical functions in addition to strictly meaning, and the degree to which it can be regarded as parallel or orthogonal It also includes a state with an error of
In the present specification, the sheet surface (plate surface, film surface) means, in each sheet (plate, film), a plane direction of the sheet (plate, film) when viewed as the whole sheet (plate, film) It is assumed that the surface is

First Embodiment
FIG. 1 is a view for explaining the transmission type display device 1 according to the first embodiment.
The transmission type display device 1 according to the first embodiment includes an LCD panel 11 and a surface light source device 10. The transmissive display device 1 illuminates the LCD panel 11 with the surface light source device 10 from the back side, and displays image information formed on the LCD panel 11.
In the following drawings and in the following description including FIG. 1, in order to facilitate understanding, in use of the transmissive display device 1, it is parallel to the screen of the transmissive display device 1 and orthogonal to each other 2 Let the direction be the X direction (X1-X2 direction) and the Y direction (Y1-Y2 direction), and let the direction orthogonal to the screen of the transmissive display 1 be 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.

  The screen of the transmissive display device 1 corresponds to the surface (hereinafter referred to as a display surface) 11 a of the LCD panel 11 closest to the Z2 side (observer side). The “front direction” of the transmission type display device 1 is the normal direction of the display surface 11 a and is parallel to the Z direction, and the normal direction of the plate surface of the light guide plate 13 described later or the prism sheet 15 It corresponds to the normal direction of the sheet surface. The display surface 11 a of the transmission type display device 1 is parallel to the XY plane, and parallel to the plate surface of the light guide plate 13 described later and the sheet surface of the prism sheet 15.

  The LCD panel 11 is a substantially plate-like member formed of a transmissive liquid crystal display element, and is a transmissive display unit that forms image information on the display surface 11 a. The outer shape and display surface 11a of the LCD panel 11 of the present embodiment is substantially rectangular when viewed from the Z direction, and has two opposing sides parallel to the X direction and two opposing sides parallel to the Y direction. ing.

The surface light source device 10 illuminates the LCD panel 11 from the Z1 side (rear side), and is a so-called edge light type surface light source device (backlight).
The surface light source device 10 includes a light source unit 12, a light guide plate 13, a reflection sheet 14, a prism sheet 15, and an optical sheet 16. The light guide plate 13, the reflection sheet 14, the prism sheet 15, the optical sheet 16 and the like are substantially rectangular when viewed from the Z direction, and include two opposing sides parallel to the X direction and two opposing sides parallel to the Y direction. have.

The light source unit 12 is a portion that emits light for illuminating the LCD panel 11. The light source unit 12 is disposed along the Y direction at a position facing the light incident surface 13 a which is an end surface on one side (X1 side) of the light guide plate 13 in the X direction.
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 is a light emitting diode (LED) light source.
The light source unit 12 may be, for example, a linear light source such as a cold cathode tube extending in the Y direction, or may have a light source disposed on the end face of the light guide extending in the Y direction. Further, from the viewpoint of improving the utilization efficiency of the light emitted from the light source unit 12, a reflecting plate (not shown) may be provided to cover the outer side (X1 side or Z2 side) of the light source unit 12.

The light guide plate 13 is a substantially flat plate-like member for guiding light, and has a light incident surface 13a, an opposing surface 13b, a light exit surface 13c, and a back surface 13d. The light guide plate 13 makes the light emitted from the light source unit 12 incident from the light incident surface 13a and totally reflects the light emitted from the light incident surface 13c and the back surface 13d to the opposing surface 13b side (X2 side) facing the light incident surface 13a. It is suitably emitted from the light exit surface 13c to the side of the prism sheet 15 (Z2 side) while guiding light mainly in the X direction.
The light incident surface 13a and the opposing surface 13b of the light guide plate 13 of the present embodiment are located at both ends (X1 side end, X2 side end) of the light guide plate 13 in the X direction. In addition, unless otherwise noted, the light exit surface 13 c and the back surface 13 d of the light guide plate 13 are the surface on the light exit side and the surface on the back side, respectively, when viewed as the entire light guide plate 13. It is assumed that it is parallel to the plate surface.
Hereinafter, each part of the light guide plate 13 will be described.

FIG. 2 is a view for explaining the light guide plate 13 of the first embodiment. FIG. 2A is a view for explaining the light emission side unit optical shape 135, and FIG. 2B is a view for explaining the back side unit optical shape 131. In FIG. 2A, a part of a cross section parallel to the YZ plane of the light guide plate 13 is shown enlarged, and in FIG. 2B a part of the cross section parallel to the XZ plane of the light guide plate 13 is enlarged It shows.
As shown in FIG. 1 and FIG. 2A, the light emission side unit optical shape 135 is a column that is convex on the light emission side (the LCD panel 11 side, the Z2 side), and the viewer side (Z2 side) of the light guide plate 13 On the surface of), the longitudinal direction (the ridge line direction) is taken as the X direction, and a plurality of Y electrodes are arrayed.

As shown in FIG. 2A, the light emission side unit optical shape 135 has a substantially pentagonal 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 as shown in FIG. is there.
The apex angle of the light output side unit optical shape 135 is δ1, and the angle between the slope on the valley side and the Z direction is δ2. Moreover, the arrangement pitch of the light emission side unit optical shape 135 is P2. The arrangement pitch P2 of this embodiment is equal to the width W2 of the light emission side unit optical shape 135 in the arrangement direction (P2 = W2).

The arrangement pitch P2 of the light emission side unit optical shape 135 is preferably about 10 to 100 μm.
If the arrangement pitch P2 is smaller than this range, manufacture of the light emission side unit optical shape 135 will become difficult, the shape as designed may not be obtained, and desired optical performance may not be obtained. If the arrangement pitch P2 is larger than this range, moire with the pixels of the LCD panel 11 is likely to occur, or when the surface light source device 10 or the like is used, the pitch of the light output side unit optical shape 135 is streaky. It becomes easy to be recognized. Therefore, the arrangement pitch P2 is preferably in the above range.

In addition, the light emission side unit optical shape 135 may change the shape according to not only the above-mentioned example but the desired optical performance. For example, the light output side unit optical shape 135 has a polygonal prism shape whose cross sectional shape is an isosceles triangle shape or a trapezoidal shape, or a part of an elliptic cylinder whose major axis is orthogonal to the plate surface of the light guide plate 13 (light emission surface 13c) It may be a shape, or may be a partial shape of a cylinder. Moreover, the light emission side unit optical shape 135 may be a shape formed by combining a plurality of types of curved surfaces or planes.
A plurality of light emitting side unit optical shapes 135 are arranged in the direction (Y direction) in which the longitudinal direction (ridge direction) is parallel to the light guiding direction (X direction) of the main light of the light guide plate 13 It is done. The light emission side unit optical shape 135 has a light beam control action in the arrangement direction with respect to the light emitted from the light guide plate 13 and improves the light collecting property etc. of the light emitted from the light guide plate 13 in the Y direction. it can. In addition, when such a light ray control action is not required, it is good also as a form which does not form the light emission side unit optical shape 135 in the light emission surface 13c.

The back side unit optical shape 131 is a pillar which is convex on the back side (Z1 side) as shown in FIG. 1 and FIG. 2 (b), and is long on the back side (Z1 side) of the light guide plate 13. The direction (ridge direction) is taken as the Y direction, and a plurality of the light guide directions are arranged in the X direction.
As shown in FIG. 2B, the back side unit optical shape 131 has a substantially rectangular 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 a first slope portion 132 located on the light incident surface side (X1 side), and a second inclined surface located on the opposite surface side (X2 side) and totally reflecting at least a part of the incident light. It has a slope portion 133 and a top surface portion 134 located between the first slope portion 132 and the second slope portion 133.
The arrangement pitch of the back side unit optical shape 131 is P1. The arrangement pitch P1 of this embodiment is equal to the width W1 of the back side unit optical shape 131 in the arrangement direction (P1 = W1).

The arrangement pitch P1 of the back side unit optical shape 131 is preferably about P1 = 80 to 300 μm.
If the arrangement pitch P1 is smaller than this range, it may be difficult to manufacture the back side unit optical shape 131, the shape as designed may not be obtained, and desired optical performance may not be obtained. If the arrangement pitch P1 is larger than this range, moire with the pixels of the LCD panel 11 is likely to occur, or the pitch of the back side unit optical shape 131 becomes streaky in the state of use as the surface light source device 10 or the like. It becomes easy to be recognized.
Accordingly, the arrangement pitch P1 is preferably in the above range.

FIG. 3 is a view for explaining the appearance of light in the back side unit optical shape 131.
As shown in FIG. 2, the first slope portion 132 forms an angle α with the plate surface (XY plane) of the light guide plate 13. Further, the second slope portion 133 forms an angle β with the surface of the light guide plate 13. Further, the top surface portion 134 forms an angle γ with the plate surface of the light guide plate 13. The angles α, β and γ are α>β>γ> 0 °.
As shown in FIG. 2 (b) and FIG. 3, the first slope section 132 has an end on the opposite surface side (an end on the top surface 134 side) than the end on the light incident surface side as the back side (Z2 side) It is inclined to become. An angle α between the first slope portion 132 and the plate surface of the light guide plate 13 (a plane parallel to the light emitting surface 13c) is about 50 to 85 °. The light guided in the light guide plate 13 to the opposing surface side (X2 side) travels from the light incident surface 13a to the opposing surface 13b (from the X1 side to the X2 side), but the first slope portion 132 has the shape as described above Therefore, it is difficult to enter the first slope portion 132.

As shown in FIG. 2 (b) and FIG. 3, the second slope portion 133 is inclined so that the light incident surface side end portion is on the back side (Z2 side) than the opposing surface side end portion. With the surface (XY plane) of the light guide plate 13.
The second slope portion 133 is a slope on which a part of light guided in the light guide plate 13 is incident and at least a part of the incident light is totally reflected. As shown in FIG. 3, the light (light L1) totally reflected by the second slope portion 133 changes its traveling direction in the direction in which the incident angle with respect to the light exit surface 13c (surface parallel to the XY plane) decreases due to total reflection. Do. Then, light totally incident on the light exit surface 13c after being totally reflected by the second slope portion 133 continues to be guided but at least a portion of the light incident on the light exit surface 13c at an angle less than the critical angle The light L 1) is emitted from the light guide plate 13.

As shown in FIG. 2 (b) and FIG. 3, the top surface portion 134 has an end on the second slope portion 133 side (facing surface side, X2 side) on the first slope portion 132 side (light entrance surface side, It inclines so that it may be located in the light emission surface side (Z2 side) rather than the edge part of X1 side, and the plate surface (XY surface) of the light-guide plate 13 has made the angle (gamma).
As shown in FIG. 3, at least a part of the light advancing in the light guide direction (X direction) and entering the top surface portion 134 is totally reflected and travels to the light exit surface 13 c side. At this time, the traveling direction of light changes in the direction in which the incident angle with respect to the light emitting surface 13c is smaller with respect to the light emitting surface 13c due to the total reflection.

A lot of light (light L2) is totally reflected by the light exit surface 13c and continues to be guided to the opposite surface side, but a part of light (light L3) is incident on the light exit surface 13c at an angle smaller than the critical angle The light is emitted from the light guide plate 13.
However, since γ <β, the change in angle before and after the total reflection at the top surface portion 134 is smaller than the change in angle before and after the total reflection at the second slope portion 133. Therefore, the light totally reflected on the top surface portion 134 and emitted from the light guide plate 13 is less than the light totally reflected on the second inclined surface portion 133 and emitted from the light guide plate 13.

In such a light guide plate 13, the angle β preferably satisfies 1 ° <β <5 ° from the viewpoint of improving both the light guiding efficiency and the light extraction efficiency.
In addition, satisfying the condition of 0.2 ° <γ <0.7 ° increases the light guiding efficiency of light and reduces the difference in the amount of emitted light in the light guiding direction of the light guiding plate 13, thereby It is preferable from a viewpoint of improving the moire by interference with the bright-dark stripes of the light emission surface of the surface light source device and the pixel of LCD panel 11 resulting from the light emission difference of 13. FIG.
Furthermore, that the angle γ and the angle β satisfy (β−γ) <2 ° is an interference between the bright and dark stripes of the light emitting surface of the surface light source device and the pixels of the LCD panel 11 due to the difference in the light emitting amount of the light guide plate 13 It is preferable from the viewpoint of improving moire due to
Details of these reasons will be described later.

As shown in FIG. 2B, assuming that the dimension of the second inclined surface portion 133 in the arrangement direction of the back side unit optical shape 131 is Wa, the ratio Wa / P1 of the dimension Wa to the arrangement pitch P1 is in the light guide direction It becomes large as it goes to the opposing surface side from the light incident surface side.
The ratio Wa / P1 in the present embodiment is 0 at the side closest to the light incident surface 13a (X1 side) and gradually increases toward the opposing surface 13b side, and is approximately 0.5 at the side closest to the opposing surface (X2). It has become.
As for this ratio Wa / P1, when the angle γ is γ> 0 ° as described above, the minimum value on the light incident surface side is about 0, and the maximum value on the opposing surface side is about 0.5. If it is in such a range, the value is not limited to the above example, but can be set appropriately according to the desired optical performance and the like.
As in the present embodiment, when the angle γ is 0.2 ° <γ <0.7 °, part of the light incident on the top surface portion 134 is totally reflected by the top surface portion 134 and is critical to the light exit surface 13 c. Since the light is incident at less than an angle and emitted from the light guide plate 13, even if a region where the ratio Wa / P1 = 0 is provided (for example, the rear side unit optical shape 131 is provided with a region without the second slope portion 133) ), The light can be emitted from the light guide plate 13.

By increasing the ratio Wa / P1 toward the facing surface side, the proportion of the second sloped portion 133 in the back side unit optical shape 131 is increased. Thereby, the light guiding efficiency to the facing surface side (X2 side) is improved, and light can be efficiently emitted from the light guide plate 13 also on the facing surface side where the light amount decreases, and the brightness in the light guiding direction Uniformity can be improved.
In the present embodiment, the ratio Wa / P1 changes continuously and gradually along the arrangement direction (light guide direction, X direction) of the back side unit optical shape 131, but the present invention is not limited thereto. For example, the form may be changed stepwise.

The light guide plate 13 is manufactured by cutting a concave mold for shaping the back side unit optical shape 131 with a cutting tool or the like, and is formed by extrusion molding or injection molding using the mold. Ru. The thermoplastic resin to be used is not particularly limited as long as it has high light permeability, and examples thereof include acrylic resin, COP (cycloolefin polymer) resin, PC (polycarbonate) resin and the like.
The light guide plate 13 is not limited to this, and the back side unit optical shape 131 and the light emission side unit optical shape 135 are integrally formed on both sides of the sheet-like member formed by extrusion molding or the like by the ultraviolet ray molding method. The light guide plate 13 may be used.

Returning to FIG. 1, the reflection sheet 14 is a sheet-like member capable of reflecting light, and is disposed on the back side (Z1 side) of the light guide plate 13. The reflection sheet 14 has a function of reflecting light directed from the light guide plate 13 toward the Z1 side and directing the light toward the light guide plate 13 side.
The reflection sheet 14 may be, for example, a sheet-like member made mainly of white resin having diffuse reflectance and high reflectance.
The reflection sheet 14 may be mainly one having specular reflectivity (regular reflectivity) from the viewpoint of, for example, enhancing the utilization efficiency of light. For example, the reflection sheet 14 is a sheet-like member at least a reflection surface (surface on the light guide plate 13 side) formed of a material having high reflectance such as metal, a thin film formed of a material having high reflectance (for example, A sheet-like member containing a metal thin film as a surface layer can be used.

FIG. 4 is a view for explaining the prism sheet 15. In FIG. 4, a part of a cross section parallel to the XZ plane of the prism sheet 15 is shown in an enlarged manner.
The prism sheet 15 is disposed closer to the LCD panel 11 (Z2 side, observer side) than the light guide plate 13 (see FIG. 1). The prism sheet 15 emits light from the light exit surface 13c of the light guide plate 13 and advances the light traveling in the direction forming an angle with the Z direction (front direction) in the direction forming a small angle with the Z direction or the Z direction. It is a deflection optical sheet having a deflection (condensing) action.
The prism sheet 15 includes a prism base layer 152, and a plurality of unit prisms 151 formed in a plurality on the Z1 side (light guide plate 13 side) of the prism base layer 152.

The prism base layer 152 is a portion to be a base (base) of the prism sheet 15. As the prism base layer 152, a sheet-like member made of resin having light transparency is used.
The unit prism 151 has a columnar shape that is convex on the Z1 side (light guide plate 13 side), and the longitudinal direction (the ridge line direction) in the surface on the back side (Z1 side) of the prism base layer 152 is Y direction. Multiple are arranged in the direction. The arrangement direction of the unit prisms 151 is parallel to the arrangement direction of the back side unit optical shape 131 of the light guide plate 13 when viewed from the normal direction (Z direction) of the display surface of the transmission type display device 1. It is orthogonal to the arrangement direction of the optical shapes 135.

The unit prism 151 of the present embodiment has a substantially triangular prism shape, and has a surface 153 on the light incident surface side and a surface 154 on the opposing surface side. The cross-sectional shape of the unit prism 151 in a cross section (XZ plane) parallel to the arrangement direction (X direction) and the direction (Z direction) orthogonal to the sheet surface is a substantially triangular shape with an apex angle ε.
The surface 153 on the light entrance surface side forms an angle θ3 with a surface (XY surface) parallel to the sheet surface.
The surface 154 on the opposite surface side is in the form of a bent surface convex outward, and has a first surface 154a on the prism base layer side and a second surface 154b on the apical angle side. The first surface 154a forms an angle θ1 with a surface (XY surface) parallel to the sheet surface, and the second surface 154b forms an angle θ2 with a surface (XY surface) parallel to the sheet surface.

The unit prism 151 has an arrangement pitch of P3 and a width in the arrangement direction of W3. The unit prism 151 of this embodiment has a configuration in which the arrangement pitch P3 and the lens width W3 in the arrangement direction are equal in the arrangement direction (P3 = W3).
The arrangement pitch P3 of the unit prisms 151 can generally be 10 to 200 μm. However, in recent years, high definition of the arrangement of the unit prisms 151 has rapidly progressed, and in order to more efficiently direct the light from the light guide plate 13 in the front direction, the arrangement pitch P3 is preferably 10 to 40 μm. . If the arrangement pitch P3 is smaller than 10 μm, manufacture is difficult and favorable optical performance can not be obtained. If the arrangement pitch P3 is larger than 40 μm, moire due to interference with the pixels of the LCD panel 11 is likely to occur, or the pitch of the unit prisms 151 is recognized as streaks in the use state as the surface light source device 10 or the like. It becomes easy. Therefore, the arrangement pitch P1 of the unit prisms 151 is preferably in the above range.

Most of the light emitted from the light guide plate 13 is emitted in a direction at a large angle on the X2 side with respect to the front direction (Z direction) in the XZ plane. As shown in FIG. 4, the prism sheet 15 causes the light L (lights L 4 and L 5) emitted from the light guide plate 13 to be incident from the surface 153 on the light incident surface side, and totally reflected on the surface 154 on the opposing surface side. The light beam is deflected (condensed) in the direction in which the traveling direction is smaller in the front direction (Z direction) or in the front direction.
The unit prism 151 is not limited to the above example, and may have an isosceles triangular prism shape or another polygonal prism shape. Further, the unit prism 151 may be in the form of a broken surface in which the surface 154 on the opposing surface side is formed of three or more surfaces, and the surface on the light incident side may also be in the shape of a broken surface formed of a plurality of surfaces. Also, the unit prism 151 may have a shape in which a curved surface and a flat surface are combined.

The prism sheet 15 is made of, for example, PET (polyethylene terephthalate) resin, PC resin, etc., and ionizing radiation curable resin such as ultraviolet curable resin or electron beam curable resin on one side of the sheet-like prism base layer 152. Thus, a plurality of unit prisms 151 are formed.
Not limited to this, for example, the prism sheet 15 may be PC resin, MBS (methyl methacrylate butadiene styrene copolymer) resin, MS (methyl methacrylate styrene copolymer) resin, PET resin PS (polystyrene) It may be formed by extruding a thermoplastic resin such as a resin.

Returning to FIG. 1, the optical sheet 16 is a polarization selective reflection sheet having a function of transmitting light of a specific polarization state and reflecting light of the other polarization states. The optical sheet 16 is provided on the LCD panel 11 side (the Z2 side, the observer side) of the prism sheet 15.
The optical sheet 16 may be arranged such that the transmission axis thereof is parallel to the transmission axis of a polarizing plate (not shown) located on the light entrance side (Z1 side) of the LCD panel 11, thereby improving the luminance and the light utilization efficiency. It is preferable from the viewpoint of improvement.
As the optical sheet 16 having such polarization selective reflectivity, for example, DBEF series (manufactured by Sumitomo 3M Limited) can be used.

The optical sheet 16 is a sheet-like member having various general-purpose light diffusing properties, optical performance desired for the surface light source device 10 and the transmissive display device 1, and optics of other optical members such as the light guide plate 13 It may be appropriately selected and used according to the characteristics and the like.
For example, the optical sheet 16 may be a light diffusion sheet having an action of diffusing light. By using a light diffusion sheet as the optical sheet 16, the effect of appropriately widening the viewing angle and reducing moiré and the like generated by the pixels (not shown) of the LCD panel 11 and the unit prism 151 can be obtained.
Such a light diffusion sheet is a resin sheet-like member containing a diffusion material, or a member obtained by coating a binder containing a diffusion material on at least one side of a resin sheet-like member serving as a base material, It is possible to use various types of optical sheets such as a microlens sheet, a lenticular lens sheet, and the like in which a microlens array is formed on one side or the like of a sheet-like member made of resin serving as a substrate.

Further, on the surface on the light output side (Z2 side) of the prism base layer 152 of the above-mentioned prism sheet 15, a fine concavo-convex shape is formed for the purpose of preventing optical adhesion with the optical sheet 16 and providing a light diffusion function. May be As such an uneven | corrugated shape, although the mat | matte layer etc. which were formed by coating the binder containing a bead-like filler etc. are suitable, it is not this limitation.
Furthermore, a sheet having light diffusivity as described above may be disposed on the back side (Z1 side) of the optical sheet 16 having polarization selective reflectivity.

FIG. 7 is a diagram for explaining light and dark stripes causing moiré. FIG. 7 shows the light guide plate 13B and the prism sheet 15 having the back side unit optical shape 131b at the angle γ = 0 °. For ease of understanding, the prism sheet 15 is simply shown with its unit prism 151 omitted.
When the back side unit optical shape is a triangular prism shape which is convex on the back side, there is a problem that the apex angle may damage the reflective sheet 14 or the apex angle may be broken. Therefore, a light guide plate having a quadrangular prism shape as shown in FIG. 7 and having a back surface unit optical shape 131b whose top surface 134 is parallel (γ = 0 °) to the light exit surface 13c (XY surface) is used. It has
In the light guide plate having such a rear side unit optical shape 131b, the light totally reflected mainly by the second inclined surface portion 133 is emitted from the light emission surface 13c, but the light totally reflected by the top surface portion 134 is before and after the total reflection. Because the angle with respect to the light exit surface 13c does not change, many of them continue to be guided. Therefore, the amount of light emitted from the light guide plate 13B is large in the region where the light totally reflected by the second slope portion 133 is incident on the light emitting surface 13c, small in the other regions, and large or small in the light guide direction. repeat.

The prism sheet 15 for raising the light emitted from the light guide plate 13B in the front direction is disposed closer to the viewer (Z2 side) than the light guide plate 13B, but when the prism sheet 15 is observed from the front direction, Light and dark stripes are generated due to the difference in the amount of light emitted from the light guide plate 13B. The bright and dark stripes have a form in which a bright line and a dark line whose longitudinal direction is a direction (Y direction) orthogonal to the light guide direction repeatedly appear in the light guide direction.
Fine light and dark stripes due to the difference in the amount of light emitted from the light guide plate 13B are not eliminated by various optical sheets used for the surface light source device such as a light diffusion sheet, and are also produced on the light emitting surface of the surface light source device.
The bright lines of the bright and dark stripes are mainly due to the light emitted by being reflected by the second slope portion 133 of the back side unit optical shape 131b, and the pitch of the bright lines is the pitch of the second slope portions 133 It substantially corresponds to the arrangement pitch of the unit optical shape 131b. Since the arrangement pitch of the second slope portion 133 is very small (P1 = 80 to 300 μm), the pitch of the light and dark stripes is also small, and the light and dark stripes on the light exit surface of the surface light source device are hardly visible to human eyes.

  However, when an LCD panel is stacked on the surface light source device in which the bright and dark stripes occur, and an image is displayed on the display surface as a transmissive display device, transmission is caused by interference between the bright and dark stripes and pixels (dots) of the LCD panel. On the display surface of the type display device, moiré occurs in which bright lines brighter than the bright lines of bright and dark stripes occur at a pitch of 400 to 500 μm. Since the bright lines of this moiré are bright and the arrangement pitch thereof is large enough to be recognized by human eyes, there is a problem that the image quality of the display is significantly reduced. And this moire tends to be recognized more notably on the light incident surface side.

Therefore, the present invention significantly reduces the above-mentioned bright and dark stripes and substantially improves the moiré by satisfying the following three expressions regarding the angle γ and the angle β of the back side unit optical shape 131. Video was displayed.
0.2 ° <γ <0.7 ° (Expression 1)
1 ° <β <5 ° (Equation 2)
(Β-γ) <2 ° (Equation 3)

With regard to Equation 1, when γ ≦ 0.2 °, the change in angle with respect to the light emitting surface 13 c before and after total reflection at the top surface portion 134 becomes too small, and light totally reflected at the top surface portion 134 and emitted from the light guide plate 13 Will be reduced. Therefore, most of the light emitted from the light guide plate 13 becomes the light totally reflected by the second slope portion 133. Therefore, the bright and dark stripes resulting from the difference in the amount of emitted light in the light guide direction of the light guide plate 13 are not improved.
Further, when the angle γ0.70.7 °, the change in the angle with respect to the light emitting surface 13c before and after total reflection at the top surface portion 134 becomes large, and light totally reflected at the top surface portion 134 and emitted from the light guide plate 13 increases. . Therefore, the light guiding efficiency is lowered, and the surface uniformity of brightness is lowered, for example, the opposing surface side becomes dark.
From the above, it is preferable that the angle γ satisfy the equation 1 above.

With regard to Equation 2, when β ≦ 1 °, when light traveling in the light guiding direction (X direction) is totally reflected by the second slope portion 133, a light exit surface 13c (a plane parallel to the XY plane) before and after total reflection. The amount of change in the angle with)) is too small. Therefore, when β ≦ 1 °, light incident on the light exit surface 13c at an angle smaller than the critical angle decreases, so that light can not be sufficiently extracted from the light guide plate 13, and the light extraction efficiency decreases.
In addition, when the light traveling in the light guide direction (X direction) is totally reflected by the second slope portion 133 as β と 5 °, the amount of change in the angle formed with the light exit surface 13c before and after the total reflection becomes large. However, although the amount of light emitted from the light incident surface side is increased, the amount of light emitted from the opposite surface side is decreased, and the light guiding efficiency is lowered. Moreover, since dispersion | variation in the light emission direction from the light-guide plate 13 will also become it large that it is (beta)> = 5, the deflection action in the front direction (Z direction) in the prism sheet 15 becomes inadequate, and the convergence of light falls. Front brightness decreases.
From the above, it is preferable that the angle β satisfy the equation 2 above.

  With regard to Equation 3, when (β−γ) ≧ 2 °, the difference between the angle β and the angle γ is large, and the light totally reflected by the second slope portion 133 and emitted, and totally reflected by the top surface portion 134 There is a large difference in the amount of light emitted from the light emitted, and the bright and dark stripes are not reduced. Therefore, it is preferable that the angle β and the angle γ satisfy the range of Expression 3.

Here, the light guide plate 13 of the example of the first embodiment and the light guide plates of Comparative Examples 1, 2 and 3 were prepared, the transmission type display device was assembled, and the presence or absence of moire was examined.
FIG. 5 is a view for explaining the light guide plates 13B and 13C of the first and second comparative examples.
5A shows a light guide plate 13B of Comparative Example 1, and FIG. 5B shows a light guide plate 13C of Comparative Example 2. As shown in FIG. In FIG. 5, a part of a cross section parallel to the XZ plane of the light guide plates 13B and 13C of Comparative Examples 1 and 2 is shown enlarged.
Hereinafter, details of the light guide plate of the example and the comparative examples 1 to 3 will be described.
The back side unit optical shape 131 of the light guide plate 13 of the embodiment has an arrangement pitch P1 = 148 μm, an angle β = 1.8 °, an angle γ = 0.4 °, and β−γ = 1.4 °, as described above. Formulas 1 to 3 are satisfied.

The light guide plate 13B of the comparative example 1 has substantially the same form as the light guide plate 13 of the example except that the angle γ = 0 ° of the back side unit optical shape 131b. The back side unit optical shape 131b of the light guide plate 13B of the comparative example 1 has an arrangement pitch P1 = 148 μm, an angle β = 2.3 °, an angle γ = 0 ° <0.2 °, and β−γ = 2.3 °. It is> 2 °, which satisfies Equation 2, but does not satisfy Equation 1 and Equation 3.
The light guide plate 13C of the comparative example 2 has substantially the same form as the light guide plate 13 of the example except that the angles β and γ of the back side unit optical shape 131c are (β−γ)> 2 °. The back side unit optical shape 131c of the light guide plate 13C of the comparative example 2 has an arrangement pitch P1 = 148 μm, an angle β = 2.5 °, an angle γ = 0.4 °, and β−γ = 2.1 °> 2 °. And satisfy Equations 1 and 2 but not Equation 3.

  Although not shown, the light guide plate of Comparative Example 3 has substantially the same form as the light guide plate 13 of the example except that the angle γ> 0.7 ° of the back side unit optical shape. The rear side unit optical shape of the light guide plate of this comparative example 3 has an arrangement pitch P1 = 148 μm, an angle β = 2.4 °, an angle γ = 0.8 °> 0.7 °, and β-γ = 1.6 ° Although Equation 1 is not satisfied, Equations 2 and 3 are satisfied.

Each of the light guide plate 13 of the embodiment, the light guide plates 13B and 13C of the comparative examples 1 and 2 and the light guide plate of the comparative example 3 is made of acrylic resin, and the refractive index thereof is 1.49. The thickness of the light guide plate 13 of the embodiment, the light guide plates 13B and 13C of the comparative examples 1 and 2 and the light guide plate of the comparative example 3 is about 600 μm.
The ratio Wa / P1 of the light guide plate 13 of the example, the light guide plate 13C of the comparative example 2, and the light guide plate of the comparative example 3 is 0 at the most incident surface side and about 0.5 at the opposite surface side. It is continuously enlarged from the surface side to the opposing surface side. The ratio Wa / P1 of the light guide plate 13B of Comparative Example 1 is about 0.2 on the light incident surface side and about 0.8 on the opposite surface side, and continuously increases from the light incident surface to the opposing surface. It has become.
In the light guide plate 13 of the embodiment, the light guide plates 13B and 13C of the comparative examples 1 and 2, and the light guide plate of the comparative example 3, the light output side unit optical shape 135 is a pentagonal prism shape as shown in FIG. The arrangement pitch P2 = 36 μm, the angle δ1 = 140 °, and the angle δ2 = 45 °.

The light guide plate 13 of these examples, the light guide plates 13B and 13C of Comparative Examples 1 and 2, and the light guide plate of Comparative Example 3 are respectively incorporated into the surface light source device 10 to create the transmission type display device 1 ) Was displayed, and the presence or absence of moiré was examined visually.
In the transmission type display device 1 incorporating the light guide plate 13 of the embodiment, the light guide plates 13B and 13C of the comparative examples 1 and 2, and the light guide plate of the comparative example 3, the other members other than the light guide plates are the same. There is.
The light source unit 12 uses an LED light source (white light) as the point light source 121.
The reflective sheet 14 is a white sheet made of PET resin.

Prism sheet 15:
The prism base layer 152 is a sheet-like member having a thickness of 125 μm and made of PET resin.
The unit prism 151 is made of an acrylic urethane resin (ultraviolet curable resin) and has a substantially triangular prism shape. The unit prism 151 has an arrangement pitch P3 = 18 μm, an angle θ1 = 58.5 °, an angle θ2 = 56 °, an angle θ3 = 58.3 °, and an angle ε = 65.7 °.
The optical sheet 16 is a polarization selective reflection sheet (Sumitomo 3M Co., Ltd. DBEF-D3-260).
The LCD panel 11 has an effective display screen of 8 inches, an arrangement pitch of pixels (not shown) of 90 μm, and a ratio of a transmissive portion (color filter) in the light guide direction (X direction) is 78%.

  The moire evaluation method prepares each transmission type display 1 incorporating the light guide plate 13 of the embodiment, the light guide plates 13B and 13C of the comparative examples 1 and 2 and the light guide plate of the comparative example 3 in a dark room environment and displaying Display a white screen on the surface. Then, the observer observes the display surface from a position 20 cm away on the Z2 side from the center of the display surface along the Z direction, and the subject visually determines whether or not moiré is visually recognized. Moiré was evaluated in a dark room environment because it is easier to observe in a dark room environment than in a bright room environment.

Table 1 shows moire in the case where the light guide plate 13 of the example and the light guide plates 13B and 13C of the comparative examples 1 and 2 and the angles β and γ of the light guide plate of the comparative example 3 are incorporated in the transmissive display Is a table summarizing the strengths of
As shown in Table 1, in the transmission type display device using the light guide plate 13B of the comparative example 1, the interference between the bright and dark stripes due to the difference in the amount of light emitted from the light guide plate 13B and the pixels of the LCD panel 11 is displayed on the screen. Moiré was significantly generated on the entire screen. This moiré is strong, greatly hinders the recognition of a good image, and significantly reduces the image quality.
In the transmission type display device using the light guide plate 13C of Comparative Example 2, moiré having a weaker intensity than that of the transmission type display device using the light guide plate 13B of Comparative Example 1 was generated, and the image quality was deteriorated.
In the transmission type display device using the light guide plate of Comparative Example 3, moire was generated on the screen, but the intensity was weaker than that of the transmission type display devices of Comparative Example 1 and Comparative Example 2. However, the luminance on the opposite surface side is lowered to be dark and uneven luminance is generated, and the surface uniformity of the brightness is deteriorated.

  Further, in the transmission type display device using the light guide plate 13C of Comparative Example 2 and the light guide plate of Comparative Example 3, the area where the ratio Wa / P1 of the light incident surface side (light source part side) of the light guide plate is about 0-10%. In this case, no moiré occurred, and moiré occurred toward the opposite surface side, and the intensity was increased. This is because in the region where the ratio Wa / P1 is approximately 0 to 10%, the second slope portion 133 is small, the amount of light incident on the second slope portion 133 is small, and most of the light emitted from each light guide plate is the top surface portion The light is totally reflected at 134 and is incident on the light exit surface 13c at less than the critical angle, and the difference in the amount of emitted light is small.

On the other hand, in the transmission type display device 1 of the embodiment using the light guide plate 13 of the embodiment, although moire was generated, it is very weak, the influence on the visual recognition of the image is very small, and a good image is visually recognized .
In addition, in the transmission type display device 1 using the light guide plate 13 of the example, the light guiding efficiency was high, and the surface uniformity of the brightness was high.
Furthermore, also in the transmission type display device 1 using the light guide plate 13 of the example, no moire occurs in the area where the ratio Wa / P1 of the light incident surface side of the light guide plate is about 0 to 10%, and the opposing surface Although moire was generated toward the side, the intensity was small, the image quality was hardly affected, and a good image was observed.

From the above, according to the present embodiment, the change in the amount of emitted light in the light guide direction of the light guide plate 13 is reduced, the difference between the bright and dark stripes is significantly reduced, the occurrence of moire is improved, and a good image is displayed. it can.
Further, according to the present embodiment, it is possible to significantly suppress the unevenness in brightness in the light guide direction, and to provide the transmission type display device 1 with good surface uniformity of brightness.

Second Embodiment
FIG. 6 is a view for explaining the light guide plate 23 of the second embodiment. In FIG. 6, the cross section of the light guide plate 23 in a plane parallel to the XZ plane is shown enlarged.
The light guide plate 23 of the second embodiment is substantially the same as the light guide plate 13 of the first embodiment, except that the top surface portion 234 has a step-like shape formed by a plurality of slopes. Therefore, the same reference numeral or the same reference numeral is attached to the end of the part that achieves the same function as that of the first embodiment described above, and the overlapping description is appropriately omitted.
In the light guide plate 23 of the second embodiment, a plurality of light emission side unit optical shapes 135 are arrayed on the surface on the Z2 side, and a plurality of back surface side unit optical shapes 231 are formed on the surface on the Z1 side.

The back side unit optical shape 231 is a columnar shape that is convex on the back side (Z1 side), and a plurality of longitudinal directions (ridge directions) are taken as a Y direction, and a plurality of light units are arrayed in the X direction. As shown in FIG. 5, the back side unit optical shape 231 has a substantially rectangular 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.
The back side unit optical shape 231 is a first slope portion 132 located on the light incident surface side (X1 side), and a second inclined surface located on the opposite surface side (X2 side) and totally reflecting at least a part of the incident light. It has a slope portion 133 and a top surface portion 234 located between the first slope portion 132 and the second slope portion 133.

The top surface portion 234 has a plurality of surfaces having different heights h on the back side (Z1 side). Here, the height h on the back side (Z1 side) is the back side (Z1 side) from the plane parallel to the plate surface of the light guide plate 13 passing the point v located at the valley bottom between the back side unit optical shapes 231 It shall be the dimension to the point which becomes the center of each surface located in).
As an example, the top surface 234 shown in FIG. 5 has four faces 234a, 234b, 234c, 234d. The surfaces 234a to 234d form an angle γ with respect to a surface (XY surface) parallel to the light exit surface 13c, and the opposite surface side end has a height h smaller than the light entrance surface side end (Z2 side Is located in the The respective surfaces 234a to 234d are arranged in a direction parallel to the arrangement direction (X direction) of the back side unit optical shapes 231, with the longitudinal direction (Y direction) of the back side unit optical shapes 231 as the longitudinal direction.

Of the surfaces 234a to 234d, the surface 234a located closest to the first inclined surface 132 (light entrance surface side, X1 side) is located closest to the light exit surface (Z2 side) in the Z direction, and the second inclined surface 133 side As it goes to (the opposite surface side, X2 side), it becomes the back surface side (Z1 side) gradually, and the surface 234d located on the second slope section 133 side is located most on the back surface side (Z1 side). The top surface portion 234 has a step-like shape along the arrangement direction (X direction) by the surfaces 234 a to 234 d. Therefore, the light guide plate 23 has a small contact area with the reflective sheet 14.
Also, a slope 234e is formed between the surfaces 234a to 234d. The inclined surface 234 e forms an angle α with the surface of the light guide plate 13 (surface parallel to the XY plane) and is parallel to the first inclined surface 132.
The light guide plate 23 of the second embodiment satisfies the above-described Equations 1 to 3 regarding the angle γ and the angle β.

  In the present embodiment, the surfaces 234a to 234d will be described by giving an example in which the widths in the arrangement direction are equal, but the widths in the arrangement direction may not be equal. The difference in height h on the back side between the surfaces may be constant or may be different. Furthermore, the angle γ that the surfaces 234 a to 234 d form with the plate surface of the light guide plate 13 may be different depending on each surface as long as the above-described Expression 1 to Expression 3 are satisfied.

According to the present embodiment, it is possible to suppress moire appearing on the display surface of the transmissive display device, and to display a good image.
Moreover, according to the present embodiment, it is possible to suppress the uneven brightness in the light guide direction, and to improve the surface uniformity of the brightness.

(Modified form)
Various modifications and changes are possible without being limited to the embodiments described above, and they are also within the scope of the present invention.
(1) In the surface light source device 10, the facing surface 13b may be the second light incident surface 13b, and the light source unit 12 may be further disposed at a position facing this surface.
In this case, for example, the back side unit optical shape 131 is the shape of the above embodiment from the light incident surface 13a to the central point of the light guide plate 13 in the arrangement direction (X direction). Up to the second light entrance surface 13b, the X direction in the above embodiment is reversed. At this time, it is preferable that the ratio Wa / P1 gradually decreases toward the X2 side from the central point to the second light incident surface 13b. The back surface 13d of the light guide plate 13 has a symmetrical shape with a straight line parallel to the Z direction passing through the center in the X direction (light guide direction) as an axis in a cross section parallel to the XZ plane.

(2) The light guide plate 13 may have a shape in which the light incident surface side (X1 side) is thick and the light guide plate 13 becomes thinner gradually as it proceeds to the opposing surface side (X2 side).

(3) The light emission side unit optical shape 135 may be a shape in which the arrangement pitch P2 is larger than the width W2 in the arrangement direction, and a flat portion, a recess and the like are formed between the light emission side unit optical shapes 135. The arrangement pitch P1 may be larger than the width W1 for the back side unit optical shapes 131 and 231 as well.

(4) Although the surface light source device 10 shows the example in which the reflective sheet 14 is disposed on the back side (Z1 side) of the light guide plate 13, the present invention is not limited thereto. For example, the surface light source device 10 is not the reflective sheet 14 Alternatively, a paint or metal foil having light reflectivity such as white or silver may be applied or transferred to the surface of the transmission type display device 1 located on the back side of the light guide plate 13 of the casing. .

(5) Various optical sheets and the like used in combination with the light guide plate 13 as the surface light source device 10 can be appropriately selected and used according to the use environment and desired optical performance. For example, an optical sheet having a deflection function other than the prism sheet 15 may be used. In addition, an optical sheet having a diffusion function, another optical sheet having various lens shapes or a prism shape, or the like may be combined and disposed between the prism sheet 15 and the LCD panel 11.

  In addition, although this embodiment and a modification can also be combined and used suitably, detailed description is abbreviate | omitted. Further, the present invention is not limited by the embodiments described above.

DESCRIPTION OF SYMBOLS 1 transmission type display apparatus 10 area light source device 11 LCD panel 12 light source part 13, 23 light-guide plate 131, 231 back side unit optical shape 132 1st slope part 133 2nd slope part 134, 234 top face part 135 light emission side unit optical shape 14 Reflective sheet 15 Prism sheet 151 Unit prism 16 Optical sheet

Claims (5)

It has a light incident surface on which light is incident, a light emitting surface intersecting the light incident surface and a light emitting surface, and a back surface opposite to the light emitting surface, and light incident from the light incident surface is incident on the light incident surface. A light guide plate that emits light from the light exit surface while guiding light to the opposite surface side,
On the back side, a plurality of back side unit optical shapes are arranged in the light guiding direction of light,
The back side unit optical shape is a pillar which is convex on the back side, and in a cross section parallel to the arrangement direction and parallel to the thickness direction of the light guide plate, the cross sectional shape is located on the light entrance surface side A first slope portion, a second slope portion positioned on the other side opposite to the first slope portion and totally reflecting at least a part of incident light, and the first slope portion and the second slope portion And a back surface located on the most rear side,
The top surface portion is inclined such that the end on the first slope side is located on the back side of the end on the second slope side,
When an angle formed by the second inclined surface portion with a plane parallel to the plate surface of the light guide plate is β, and an angle formed by the top surface portion with a plane parallel to the plate surface of the light guide plate is γ.
0.2 ° <γ <0.7 °
1 ° <β <5 °
(Β-γ) <2 °
To satisfy the relationship
A light guide plate characterized by In the light guide plate according to claim 1,
In the back side unit optical shape, the arrangement pitch P1 is constant,
The ratio Wa / P1 of the dimension Wa occupied by the second inclined surface portion in the arrangement direction of the back side unit optical shape with respect to the arrangement pitch P1 increases with distance from the light incident surface;
A light guide plate characterized by In the light guide plate according to claim 1 or 2,
The top surface portion has a plurality of surfaces having different heights on the back side,
The plurality of faces are
Make an angle γ with a plane parallel to the plate surface of the light guide plate,
The surface closest to the first inclined surface side in the light guide direction has the smallest height to the rear surface side, and the height to the rear surface side increases toward the second inclined surface side,
A light guide plate characterized by A light guide plate according to any one of claims 1 to 3;
A light source unit which is provided at a position facing the light incident surface of the light guide plate and projects light onto the light incident surface;
A deflecting optical sheet disposed on the light emitting surface side of the light guide plate and having a deflecting action of directing light emitted from the light guide plate in a direction normal to the sheet surface or in a direction forming a smaller angle with the normal direction;
A reflective member disposed on the back side of the light guide plate and reflecting light emitted from the back side of the light guide plate to the light guide plate side;
A surface light source device comprising The surface light source device according to claim 4;
A transmissive display unit illuminated from the back side by the surface light source device;
A transmissive display comprising:

Images