JP6981090B2 - Light guide plate, surface light source device and display device - Google Patents

Description

The present invention relates to an edge light type light guide plate, a surface light source device, and a display device.

A surface light source device is widely used as a backlight that is incorporated in a liquid crystal display device and illuminates the liquid crystal display panel from the back side. The surface light source device is roughly classified into a direct type in which the light source is arranged directly under the optical member and an edge light type in which the light source is arranged on the side of the optical member. The edge light type surface light source device can be easily made thinner than the direct type surface light source device.

For example, Patent Document 1 discloses a display device in which an edge light type surface light source device is backlit and incorporated. In the edge light type surface light source device, a light source such as an LED (Light Emitting Diode) is arranged at a position facing an incoming light surface forming one side surface of the light guide plate. The light emitted by the light source is incident on the light guide plate from the incoming surface, and then the traveling direction is changed while repeatedly reflecting on the light emitting surface (front surface) and the back surface (back surface) of the light guide plate. Then, the light satisfying the angle condition for the light emitted from the light emitting surface is emitted from the light emitting surface and illuminates the liquid crystal display panel from the back side in a plane shape.

Japanese Unexamined Patent Publication No. 2016-12627

In order to change the traveling direction of the light and emit the light from the light emitting surface, various measures are taken on the back surface of the light guide plate. For example, in the surface light source device of Patent Document 1, an inclined surface and a connecting surface are repeatedly formed on the back surface of the light guide plate. The inclined surface is provided so as to be inclined with respect to the plate surface of the light guide plate, whereas the connecting surface is provided so as to extend in the plate surface direction of the light guide plate. Each time the light incident on such a light guide plate is reflected by the inclined surface, the incident angle of the light with respect to the light emitting surface of the light guide plate gradually decreases, and the light emitted from the light emitting surface is promoted.

However, in the light guide plate in which the inclined surface and the non-inclined surface are repeatedly formed on the back surface, only the inclined surface contributes to the change of the incident angle of the light with respect to the light emitting surface, and the non-inclined surface contributes to the change of the incident angle of the light. Not contributing. Therefore, in the light emitting surface of the light guide plate, the degree of light emission varies between the portion corresponding to the inclined surface and the portion corresponding to the non-inclined surface, and moire may occur according to the pitch of the inclined surface and the non-inclined surface. ..

Further, as another type of light guide plate, a wedge-shaped light guide plate is also known, in which the back surface is uniformly inclined and the width gradually narrows as the distance from the light entering surface increases. The wedge-shaped light guide plate has the advantage that the light from the light source can be used efficiently, but it is difficult to uniformly emit light from the entire light emitting surface, and the light emitting surface is relatively relative to the light emitting surface according to the distance from the incoming surface. Bright areas and relatively dark areas tend to appear clearly.

As described above, there is room for further improvement in the light guide plate of the surface light source device in terms of reducing the unevenness of the light emission and increasing the uniformity of the brightness of the entire light emitting surface while efficiently using the light.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a light guide plate, a surface light source device, and a display device capable of reducing luminance unevenness while efficiently using light.

One aspect of the present invention is a light guide plate having a light emitting surface, a back surface arranged to face the light emitting surface, and a first side surface and a second side surface extending in a first direction between the light emitting surface and the back surface. The first side surface is formed larger than the second side surface in the first direction, and the back surface side of the light guide plate is adjacent to the first side surface in the second direction from the first side surface to the second side surface. A second direction from the first side surface to the second side surface, which is a first inclined surface formed by repeatedly forming a plurality of sets of an acute angle portion and a second inclined portion and formed by at least a part of the back surface of the first inclined portion. The acute angle of the first inclined surface that is inclined so as to gradually approach the light emitting surface with respect to the second direction is the second inclined surface formed by the back surface of the second inclined portion and the first side surface. The second inclined surface that inclines toward the light emitting surface gradually with respect to the second direction toward the second side surface is smaller than the acute angle formed with respect to the second direction, and the first inclined surface is with respect to the second direction. When the angle of the acute angle formed by α is represented by α and the angle of the acute angle formed by the second inclined surface with respect to the second direction is represented by β, α <β ≦ 4.2 ° and β − α ≦ 3 ° are satisfied. Regarding the light guide plate.

0 ≦ α ≦ 1.2 ° may be satisfied.

When the size of the first side surface with respect to the first direction is represented by S1 and the size of the second side surface with respect to the first direction is represented by S2, S2 ≦ 2/3 × S1 may be satisfied.

The plurality of first inclined surfaces may be formed on the same plane.

The light guide plate may be further provided with a light diffusing portion formed on the first side surface and diffusing light.

The light diffusing unit may diffuse the light incident on the first side surface in the first direction.

The first inclined portion includes a plurality of stepped portions arranged side by side in the second direction, and the first inclined portion may include a plurality of stepped surfaces formed by at least a part of the back surface of the plurality of stepped portions. good.

The plurality of sets of the first inclined portion and the second inclined portion each occupy the first distance with respect to the second direction, and are continuously arranged in the second direction with the first distance as the arrangement pitch, and the back surface of the light guide plate. Of these, only the second inclined surface may be formed in a range of at least the first distance or more from the second side surface side.

Of the back surface side of the light guide plate, only the second inclined portion may be formed in a range of at least a second distance from the first side surface in the second direction.

On the light emitting surface side of the light guide plate, there are a plurality of light emitting side unit optical units each extending in the second direction, and a plurality of light emitting side units arranged perpendicularly to the first direction and perpendicular to the second direction. An optical portion may be formed.

Each of the plurality of unit optical units on the light emitting side may be formed in a groove shape having a concave curved surface on the back surface side.

Another aspect of the present invention comprises the above-mentioned light guide plate, an optical sheet arranged to face the light emitting surface of the light guide plate, and a light source arranged to face the first side surface of the light guide plate. The present invention relates to a surface light source device in which a prism layer is formed on the surface side of the sheet facing the light emitting surface of the light guide plate.

The surface light source device further includes a reflective sheet arranged to face the back surface of the light guide plate and reflect light, and the surface of the reflective sheet facing the back surface of the light guide plate extends in parallel with a plurality of first inclined surfaces. You may.

Another aspect of the present invention includes the above-mentioned surface light source device, a display panel arranged to face the optical sheet of the surface light source device, and an adhesive layer provided between the surface light source device and the display panel. The surface light source device and the display panel are bonded with an adhesive layer, and the display device is integrally provided via the adhesive layer.

The refractive index of the adhesive layer may be larger than the refractive index of the optical sheet.

The difference between the refractive index of the adhesive layer and the refractive index of the optical sheet may be 0.3 or less.

According to the present invention, it is possible to reduce luminance unevenness while efficiently using light.

FIG. 1 is an exploded cross-sectional view showing a schematic configuration of a display device. FIG. 2 is a cross-sectional view showing a schematic configuration of the light guide plate according to the first embodiment. FIG. 3 is a plan view of the light entering surface. FIG. 4 is a diagram for explaining a surface-side unit optical element, and a cross section of a part of the light guide plate is enlarged and shown. FIG. 5 is a perspective view showing an optical sheet incorporated in the display device of FIG. FIG. 6 is a partial cross-sectional view showing a part of a cross section taken along the VI-VI line of FIG. FIG. 7 is an enlarged cross-sectional view showing an example of the first inclined portion according to the second embodiment. FIG. 8 is a cross-sectional view showing a schematic configuration of the light guide plate according to the third embodiment. FIG. 9 is a cross-sectional view showing a schematic configuration of the light guide plate according to the fourth embodiment.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings. The elements shown in the drawings attached to the present specification include elements whose scales, aspect ratios, and the like are appropriately changed from those of the actual product for the convenience of illustration and comprehension.

[First Embodiment]
FIG. 1 is an exploded cross-sectional view showing a schematic configuration of the display device 10.

The display device 10 is located between the surface light source device 20 that emits light in a planar shape, the liquid crystal display panel 15 that is arranged so as to face the optical sheet 60 of the surface light source device 20, and the surface light source device 20 and the liquid crystal display panel 15. The adhesive layer 17 provided is provided. The surface light source device 20 and the liquid crystal display panel 15 are adhered to each other by an adhesive layer 17, and are integrally provided via the adhesive layer 17. The display device 10 has a display surface 11 for displaying an image. The liquid crystal display panel 15 functions as a shutter that controls the transmission or blocking of light from the surface light source device 20 for each pixel, and is configured to display an image on the display surface 11.

The illustrated liquid crystal display panel 15 is arranged between the upper polarizing plate 13 arranged on the light emitting side, the lower polarizing plate 14 arranged on the incoming light side, and the upper polarizing plate 13 and the lower polarizing plate 14. It has a liquid crystal layer 12. The polarizing plates 13 and 14 decompose the incident light into two orthogonal polarizing components (P wave and S wave) and vibrate in one direction (direction parallel to the transmission axis) (for example, P wave). Has a function of absorbing a linearly polarized light component (for example, an S wave) that vibrates in the other direction (direction parallel to the absorption axis) orthogonal to the one direction.

An electric field can be applied to the liquid crystal layer 12 for each region forming one pixel. Then, the orientation direction of the liquid crystal molecules in the liquid crystal layer 12 changes depending on the presence or absence of the electric field application. As an example, the polarizing component in a specific direction transmitted through the lower polarizing plate 14 arranged on the light entering side rotates its polarization direction by 90 ° when passing through the liquid crystal layer 12 to which an electric field is not applied, while rotating the polarization direction by 90 °. The polarization direction is maintained as it passes through the liquid crystal layer 12 to which an electric field is applied. In this case, whether the polarizing component that vibrates in a specific direction transmitted through the lower polarizing plate 14 further transmits through the upper polarizing plate 13 arranged on the light emitting side of the lower polarizing plate 14 depending on the presence or absence of an electric field applied to the liquid crystal layer 12. Alternatively, it can be controlled whether it is absorbed by the upper polarizing plate 13 and blocked.

In this way, the liquid crystal display panel (liquid crystal display unit) 15 can control the transmission or blocking of light from the surface light source device 20 for each pixel.

The adhesive layer 17 is provided between the surface light source device 20 and the liquid crystal display panel 15, and the surface light source device 20 and the liquid crystal display panel 15 are bonded and integrated. The adhesive layer 17 may contain a light diffusing component inside. It is preferable that an acrylic pressure-sensitive adhesive is used as the pressure-sensitive adhesive layer 17. Further, the thickness of the adhesive layer 17 is preferably 100 μm or less, and more preferably 30 μm or less, considering that the thickness of the display device 10 does not become too thick. The refractive index of the adhesive layer 17 is larger than the refractive index of the optical sheet 60, and the difference between the refractive index of the adhesive layer 17 and the refractive index of the optical sheet 60 is 0.3 or less.

Next, the surface light source device 20 will be described.

The surface light source device 20 has a light emitting surface 21 that emits light in a planar shape, and is used as a device for illuminating the liquid crystal display panel 15 from the back surface side in the present embodiment.

The surface light source device 20 is configured as an edge light type surface light source device, and is formed on a light guide plate 30, an optical sheet 60 arranged to face the light emitting surface 31 of the light guide plate 30, and an incoming surface 33 of the light guide plate 30. A light source 24 arranged to face each other and a reflective sheet 28 arranged to face the back surface 32 of the light guide plate 30 to reflect light are provided.

In the illustrated example, the optical sheet 60 faces the liquid crystal display panel 15 via the adhesive layer 17. The light emitting surface 21 of the surface light source device 20 is defined by the light emitting surface 61 of the optical sheet 60. Further, a prism layer 19 is formed on the surface side of the optical sheet 60 facing the light emitting surface 31 of the light guide plate 30.

In the illustrated example, the light emitting surface 31 of the light guide plate 30 has a rectangular shape (shape seen from the optical sheet 60 side) in a plan view similar to the display surface 11 of the display device 10 and the light emitting surface 21 of the surface light source device 20. It is formed so as to be. As a result, the light guide plate 30 includes four sides defined between the pair of main surfaces. The optical sheet 60 is generally configured as a rectangular parallelepiped member whose side in the thickness direction is smaller than the other sides.

The light guide plate 30 has a light emitting surface 31 composed of one main surface on the liquid crystal display panel 15 side, a back surface 32 composed of the other main surface arranged facing the light emitting surface 31, and the light emitting surface 31 and the back surface. It has an incoming light surface 33 (first side surface) and an opposite surface 34 (second side surface) extending in the first direction D1 from 32. The light guide plate 30 has a wedge shape as a whole, and the light entering surface 33 is formed larger than the opposite surface 34 with respect to the first direction D1. The first direction D1 corresponds to the stacking direction of the surface light source device 20 and the liquid crystal display panel 15, and corresponds to the vertical direction in FIG. Further, the second direction D2 corresponds to the direction from the light entering surface 33 toward the opposite surface 34, and corresponds to the left-right direction in FIG.

The light incident on the light guide plate 30 from the light entry surface 33 travels in the light guide plate 30 substantially along the second direction D2 toward the opposite surface 34 (the right side surface in FIG. 1) facing the light entry surface 33. do.

The light source 24 may be configured in various forms such as a fluorescent lamp such as a linear cold cathode fluorescent lamp, a point LED (light emitting diode), an incandescent lamp, or the like. The light source 24 in the present embodiment is a large number of point-like light emitters arranged side by side along the longitudinal direction of the light entry surface 33 (third direction D3 perpendicular to the first direction D1 and perpendicular to the second direction D2). 25, specifically, it is composed of a large number of light emitting diodes (LEDs).

The reflective sheet 28 is a member for reflecting the light leaked from the back surface 32 of the light guide plate 30 and re-entering the light guide plate 30. The reflective sheet 28 is a white diffuse reflective sheet, a sheet made of a material having a high reflectance such as metal, a sheet containing a thin film made of a material having a high reflectance (for example, a metal thin film) as a surface layer, or an ESR (Enhanced). It may be composed of a reflective polarizing sheet such as Specular Reflector). The reflection on the reflective sheet 28 may be regular reflection (specular reflection) or diffuse reflection. When the reflection on the reflection sheet 28 is diffuse reflection, the diffuse reflection may be isotropic diffuse reflection or anisotropic diffuse reflection. Of the reflective sheet 28, the reflective surface 28a facing the back surface 32 of the light guide plate 30 extends in parallel with a plurality of first inclined surfaces (see the sign “37” in FIG. 2), which will be described later, and is inclined as a whole. .. Therefore, the reflective sheet 28 of the present embodiment has a wedge shape, and when the light guide plate 30 is laminated on the reflective sheet 28, each first inclined surface comes into contact with the reflective surface 28a.

By the way, in the present specification, the “light emitting side” refers to the light source 24, the light guide plate 30, the optical sheet 60, the liquid crystal display panel 15, and the components of the display device 10 without going back from the display device 10. It is the downstream side (the observer side, for example, the upper side of the paper surface in FIG. 1) in the traveling direction of the light emitted toward the observer, and the “light entry side” is the light source 24, the light guide plate 30, and the optical sheet 60. It is the upstream side in the traveling direction of the light emitted from the display device 10 and directed toward the observer by advancing between the liquid crystal display panel 15 and the components of the display device 10 without reversing.

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

Further, in the present specification, the "sheet surface (plate surface, film surface)" coincides with the plane direction of the target sheet-like member when the target sheet-like member is viewed as a whole and in a broad sense. Refers to a surface. In the present embodiment, the sheet surface of the optical sheet 60, the panel surface of the liquid crystal display panel 15, the display surface 11 of the display device 10, and the light emitting surface 21 of the surface light source device 20 are parallel to each other. Further, in the present specification, the normal direction of the sheet-shaped member refers to the normal direction of the target sheet-shaped member to the seat surface. Further, in the present specification, the "front direction" is the normal direction of the surface light source device 20 to the light emitting surface 21, and in the present embodiment, the normal direction of the surface light source device 20 to the light emitting surface 21. It also matches the normal direction to the plate surface on the light emitting surface 31 side of the light guide plate 30, the normal direction to the sheet surface of the optical sheet 60, the normal direction to the display surface 11 of the display device 10, and the like.

Next, the light guide plate 30 will be described in more detail.

FIG. 2 is a cross-sectional view showing a schematic configuration of the light guide plate 30 according to the first embodiment. The light guide plate 30 has a plate-shaped base 40 and a plurality of surface-side unit optical elements 50 formed on one side surface of the base 40 (a surface facing the observer side, an idemitsu side surface). .. The base 40 is configured as a wedge-shaped member having a pair of main surfaces. The back surface 32 of the light guide plate 30 is formed by the other surface of the base 40 located on the side facing the reflective sheet 28.

In addition, the "unit prism", "unit shape element", "unit optical element" and "unit lens" in the present specification exert an optical action such as refraction and reflection on light to indicate the traveling direction of the light. It refers to an element that has a function to change, and is not distinguished from each other based only on the difference in designation.

The other side surface of the base 40 forming the back surface 32 of the light guide plate 30 is formed as an uneven surface. That is, on the back surface 32 side of the light guide plate 30, a plurality of sets of the first inclined portion 41 and the second inclined portion 42 adjacent to each other are repeatedly formed with respect to the second direction D2 from the light entering surface 33 to the opposite surface 34. ing. This "set of the first inclined portion 41 and the second inclined portion 42" constitutes the back surface side unit optical element 51. The first inclined surface 37 is formed by at least a part of the back surface 32 of the first inclined portion 41 (in the present embodiment, the entire back surface 32 (excluding the stepped surface 39)), and is opposite to the light entering surface 33. It is inclined so as to gradually approach the light emitting surface 31 with respect to the second direction D2 toward the surface 34. Further, the second inclined surface 38 is formed by at least a part of the back surface 32 of the second inclined portion 42 (in the present embodiment, the entire back surface 32 (excluding the stepped surface 39)), and is formed from the light entering surface 33. It is inclined so as to gradually approach the light emitting surface 31 with respect to the second direction D2 toward the opposite surface 34. The acute angle angle α formed by the first inclined surface 37 with respect to the second direction D2 is smaller than the acute angle angle β formed by the second inclined surface 38 with respect to the second direction D2. Specifically, these angles α and β satisfy the following conditions.
α <β ≤ 4.2 ° and β-α ≤ 3 °
The angle α is preferably set so as to satisfy 0 ≦ α ≦ 1.2 °.

For example, when the angle β is an angle outside the “α <β ≦ 4.2 °” condition (particularly an angle larger than 4.2 °), the light emitted from the light guide plate 30 becomes too broad. It ends up. Specifically, when the angle β does not satisfy “α <β ≦ 4.2 °”, the FWHM (Full Width at Half Maximum) of the light emitted from the light guide plate 30 may exceed 20 °. Therefore, sufficient directivity of the emitted light cannot be obtained. As a result of diligent research, the inventor of the present invention finds that by setting the angle β so that “α <β ≦ 4.2 °” is satisfied, it is possible to effectively prevent the emitted light from becoming too broad. It came to.

Further, when the difference between the angle α and the angle β becomes large, the amount of light emitted from the light emitting surface 31 reflected by the first inclined surface 37 and the light emitted from the light emitting surface 31 reflected by the second inclined surface 38 are emitted. The difference from the amount of light emitted becomes large, and bright and dark fringes occur on the emitted surface 61 of the surface light source device 20. By interfering between the bright and dark stripes of the surface light source device 20 and the pixels (dots) of the liquid crystal display panel 15, moire that is easily recognized by the human eye may occur on the display surface 11 of the display device 10. As a result of diligent research, the present inventor has set the angle α and the angle β so that “β−α ≦ 3 °” is satisfied, so that the reflection between the first inclined surface 37 and the second inclined surface 38 is satisfied. It has been found that the difference in the amount of light emitted can be suppressed and the occurrence of such moire can be effectively prevented.

Further, the effect brought about by the above-mentioned conditions of "α <β ≦ 4.2 °" and "β-α ≦ 3 °" is, for example, along the first direction D1 from the light entering surface 33 to the opposite surface 34. The light guide distance L is 120 mm, the size of the light entering surface 33 with respect to the first direction D1 (“S1” described later) is 3 mm, and the size of the opposite surface 34 with respect to the first direction D1 (“S2” described later) is 0. The inventor of the present invention has found that it is preferable to set the angle α so that “0 ≦ α ≦ 1.2 °” is satisfied in the case of 5.5 mm.

All the first inclined surfaces 37 provided on the back surface 32 of the light guide plate 30 may have the same angle α, and all the second inclined surfaces 38 have the same angle β. May be good.

Further, when the size of the light entering surface 33 with respect to the first direction D1 is represented by S1 and the size of the opposite surface 34 with respect to the first direction D1 is represented by S2, it is preferable that S1 and S2 satisfy the following conditions. In particular, "S1 = 1.8 mm" and "S2 = 0.7 mm" are preferable.
S2 ≦ 2/3 × S1
1.5 mm ≤ S1 ≤ 3 mm
0 mm ≤ S2 ≤ 2 mm

As a result of diligent research, the inventor of the present invention has come to the conclusion that the light extraction efficiency can be effectively improved by setting S1 and S2 so as to satisfy the above conditions. In particular, when S2 is larger than "2/3 x S1" (that is, when "S2> 2/3 x S1"), the light extraction efficiency becomes poor. For example, when S2 is larger than S1, the light from the light source 24 (that is, the point-shaped light emitter 25 such as an LED) incident on the incoming surface 33 does not enter the light emitting surface 31 or the back surface 32 of the light guide plate 30. It is not preferable because a relatively large amount of light emitted from the opposite surface 34 can be contained. On the other hand, by making S2 smaller than S1 as expressed by the above conditional expression, the probability that the light incident on the light guide plate 30 from the light source 24 via the light incoming surface 33 is incident on the light emitting surface 31 and the back surface 32. Can be increased, and the light extraction efficiency can be effectively improved.

In addition, a plurality of first inclined surfaces 37 (all first inclined surfaces 37 in the example shown in FIG. 2) are formed on the same plane (that is, on the same inclined surface).

The first inclined surface 37 satisfying the above conditions is formed as a gentle slope having a relatively gentle slope, and the second inclined surface 38 is formed as a steep slope having a relatively steep slope. Of the "sets of the first inclined portion 41 and the second inclined portion 42" adjacent to each other, the second inclined surface 38 of one set and the first inclined surface 37 of the other set extend in the first direction D1. It is connected by an existing step surface 39.

The light guide in the light guide plate 30 having the above configuration is based on the total reflection action on the pair of main surfaces 31 and 32 of the light guide plate 30. On the other hand, the first inclined surface 37 and the second inclined surface 38 are inclined so as to approach the light emitting surface 31 as the light entering surface 33 side toward the opposite surface 34 side. Therefore, for the light reflected by the first inclined surface 37 and the second inclined surface 38, the incident angle when incident on the pair of main surfaces 31 and 32 becomes small. By reflecting on the first inclined surface 37 and the second inclined surface 38, when the angle of incidence on the pair of main surfaces 31 and 32 becomes less than the total reflection critical angle, the light is emitted from the light guide plate 30. .. That is, the first inclined surface 37 and the second inclined surface 38 function as elements for extracting light from the light guide plate 30.

By adjusting the distribution of the first inclined surface 37 and the second inclined surface 38 with respect to the second direction D2 which is the light guide direction in the back surface 32, the distribution of the amount of light emitted from the light guide plate 30 along the second direction D2 can be obtained. Can be adjusted. In the light guide plate 30 shown in FIG. 2, the proportion of the second inclined surface 38 of the back surface 32 increases as the light entering surface 33 approaches the opposite surface 34 along the second direction D2. According to the light guide plate 30, the emission of light from the light guide plate 30 is promoted in a region separated from the light entrance surface 33 along the light guide direction, and the amount of emitted light decreases as the distance from the light entrance surface 33 increases. It is possible to effectively prevent it from being stored.

In the illustrated example, the plurality of sets of the first inclined portion 41 and the second inclined portion 42 each occupy the first distance d1 with respect to the second direction D2, and the first distance d1 is set as the arrangement pitch P1. It is continuously arranged in two directions D2. The proportion of the first inclined surface 37 and the second inclined surface 38 with respect to the second direction D2 in each set is different among these plurality of sets. That is, as described above, as the light entering surface 33 approaches the opposite surface 34, the proportion of the first inclined surface 37 with respect to the second direction D2 gradually decreases, while the proportion of the second inclined surface 38 with respect to the second direction D2 gradually decreases. The proportion of light gradually increases. It should be noted that "gradual decrease" and "gradual increase" do not have to be constantly changing, and the first inclined surfaces 37 and the second inclined surfaces 38 between the sets adjacent to each other in the second direction D2 are used. It may occupy the same proportion with respect to the second direction D2.

Further, a light diffusing portion for diffusing the light from the light source 24 is formed on the light entering surface 33 of the light guide plate 30.

FIG. 3 is a plan view of the light entering surface 33. A light diffusing portion 35 is formed on the light entering surface 33 shown in FIG. The light diffusing portion 35 is formed on the entire surface of the incoming light surface 33 or most of the region where the light from the light source 24 is incident, and diffuses the light incident on the incoming light surface 33 in the first direction D1. The light diffusing portion 35 can be realized by, for example, a hairline process of imparting fine scratches extending in the third direction to the light entering surface 33. The light emitted from the light source 24 is diffused in the first direction D1 by the light diffusing unit 35, and then is incident on the light guide plate 30 from the light entering surface 33. Therefore, the light immediately after incident on the light guide plate 30 is effectively guided to the back surface 32 (that is, the first inclined surface 37 and the second inclined surface 38) at a position close to the light entering surface 33. This makes it possible to effectively promote light emission from the light exit surface 31 at a position close to the light entry surface 33. The direction of light diffusion brought about by the light diffusing unit 35 may be a direction other than the first direction D1, and may be, for example, the third direction D3.

Next, a surface-side unit optical element 50 that functions as an emission-side unit optical unit provided on one surface of the base 40 will be described.

FIG. 4 is a diagram for explaining the surface-side unit optical element 50, and a cross section of a part of the light guide plate 30 is enlarged and shown.

On the back surface 32 side of the light guide plate 30, a plurality of back surface side unit optical elements 51 composed of the above-mentioned set of the first inclined portion 41 and the second inclined portion 42 are arranged in the second direction D2, whereas the guide plate 30 is guided. A plurality of surface-side unit optical elements 50 are arranged in the third direction D3 on the light emitting surface 31 side of the light plate 30. Each of the plurality of surface-side unit optical elements 50 extends in the second direction D2.

Each of the front surface side unit optical elements 50 shown in FIG. 4 is formed in a groove shape having a concave curved surface 50a which is concave from the light emitting surface 31 side to the back surface 32 side. At both ends of the concave curved surface 50a in the third direction D3, inclined surfaces 50b inclined from the groove-shaped edge portion 50d to the bottom portion 50c side are formed. In the cross section shown in FIG. 4, the surface-side unit optical element 50 is formed symmetrically (line-symmetrically) with a line passing through the bottom portion 50c and parallel to the thickness direction (that is, the first direction D1) as a boundary.

As a result, the light guide plate 30 of the present embodiment can spread the light guided in the light guide plate 30 in the third direction D3 and emit it. Therefore, it is possible to suppress the occurrence of streak-like unevenness in the central portion of the light emitting surface 31 and the formation of locally brighter spots called hot spots in the vicinity of the incoming light surface 33. Further, foreign matter such as dust adhering to the light emitting surface 31 of the light guide plate 30 can be easily removed by an air blow or the like.

Further, a flat portion 52 substantially parallel to the light emitting surface 31 is provided between the adjacent surface-side unit optical elements 50. In the light emitting surface 31 of the light guide plate 30, since the surface side unit optical element 50 is formed in a groove shape recessed from the light emitting surface 31, this flat portion 52 is formed in the thickness direction (first direction D1) of the light guide plate 30. It becomes a portion located on the light emitting side most, and comes into contact with the optical sheet 60 laminated on the light emitting surface 31. By providing the flat portion 52 between the surface-side unit optical elements 50 in this way, the contact area between the light emitting surface 31 of the light guide plate 30 and the surface of the optical sheet 60 on the light guide plate 30 side can be increased. As a result, it is possible to significantly prevent the boundary portion (flat portion 52) of the surface-side unit optical element 50 and the surface of the optical sheet 60 on the light guide plate 30 side from being damaged or damaged.

Here, the fact that the flat portion 52 is substantially parallel to the light emitting surface 31 is not only when the flat portion 52 is completely parallel to the light emitting surface 31, but also when the flat portion 52 is slightly inclined with respect to the light emitting surface 31 ( For example, the case where the light emitting surface 31 is tilted within a range of ± 5 degrees) is also included. The flat portion 52 is not only a completely flat surface, but also a surface formed into a concave curved surface slightly curved toward the back surface 32 side or a convex curved surface slightly curved toward the light emitting surface 31 side (for example, the radius of curvature is Concave curved surface and convex curved surface of 10 μm or more) are also included.

In FIG. 4, the arrangement pitch of the surface-side unit optical element 50 is represented by "P2", the width of the surface-side unit optical element 50 in the arrangement direction (third direction D3) is represented by "W21", and the arrangement direction (third direction D3). The width of the flat portion 52 in the three directions D3) is represented by "W23". In this embodiment, since the surface side unit optical element 50 and the flat portion 52 are arranged alternately, the arrangement pitch P2 is equal to the sum of the width W21 of the surface side unit optical element 50 and the width W23 of the flat portion 52 (that is,). P2 = W21 + W23).

The arrangement pitch P2 is preferably about 10 to 100 μm. If the arrangement pitch P2 is smaller than this range, it becomes difficult to manufacture the surface-side unit optical element 50, and the shape as designed cannot be obtained. Further, when the arrangement pitch P2 is larger than this range, moire with the pixels of the liquid crystal display panel 15 is likely to occur, and the pitch of the surface unit optical element 50 is easily recognized when used as a surface light source device 20 or the like. Or become. Therefore, the arrangement pitch P2 is preferably in the above range.

Further, it is desirable that the width W23 of the flat portion 52 is formed in the range of 0.5 μm ≦ W23 ≦ 2.5 μm. If the width W23 of the flat portion 52 is less than 0.5 μm, the width of the flat portion 52 becomes too narrow, and the surface of the flat portion 52 and the optical sheet 60 on the light guide plate 30 side is damaged or damaged, which is not desirable. .. Further, when the width W23 of the flat portion 52 is larger than 2.5 μm, damage to the light guide plate 30 and the optical sheet 60 can be avoided, but hot spots may be remarkably generated in the light emitted from the light guide plate 30. Not desirable due to its nature. From the viewpoint of more effectively suppressing the generation of hot spots in the light emitted from the light guide plate 30, the width W23 of the flat portion 52 is 2.0 μm or less (that is, W23 ≦ 2.0 μm). More desirable.

Next, the optical sheet (prism sheet) 60 (see FIG. 1) will be described in more detail. The optical sheet 60 is a member having a function of changing the traveling direction of transmitted light.

As is well shown in FIG. 5, the optical sheet 60 includes a main body portion 65 formed in a plate shape and a plurality of unit prisms (unit shape element, unit optics) formed on the light entrance side surface of the main body portion 65. It has an element (unit lens) 70 and. The main body 65 is configured as a flat plate-like member having a pair of parallel main surfaces. The light emitting surface 61 of the optical sheet 60 is configured by the light emitting side surface 66 of the main body portion 65 located on the side not facing the light guide plate 30.

The plurality of unit prisms 70 are arranged side by side on the light entering side surface 67 of the main body 65. Each unit prism 70 is formed in a columnar shape and extends in a direction intersecting the arrangement direction thereof.

In this embodiment, each unit prism 70 extends linearly. Further, each unit prism 70 is formed in a columnar shape and has the same cross-sectional shape along the longitudinal direction thereof. Further, the plurality of unit prisms 70 are arranged without a gap on the light entrance side surface 67 of the main body portion 65 along the direction orthogonal to the longitudinal direction thereof. Therefore, the light entry surface of the optical sheet 60 is formed by the surfaces (prism surfaces) 71 and 72 of the unit prisms 70 arranged without gaps on the main body portion 65. The plurality of unit prisms 70 are arranged in the prism arrangement direction. Each unit prism 70 extends linearly in a direction orthogonal to the arrangement direction thereof.

The optical sheet 60 is arranged so as to be overlapped with the light guide plate 30, and the unit prism 70 of the optical sheet 60 faces the light emitting surface 31 of the light guide plate 30. Then, in the optical sheet 60, the longitudinal direction of the unit prism 70 is the light guide direction by the light guide plate 30 (the second direction D2 connecting the light entrance surface 33 of the light guide plate 30 and the opposite surface 34 facing the light entrance surface). It is positioned with respect to the light guide plate 30 so as to be non-parallel. The arrangement direction of the unit prisms 70 is parallel to or inclined with respect to the second direction D2 which is the light guide direction. When the optical sheet 60 of the present embodiment is used, the direction in which the luminance peak is generated can be controlled in various directions by inclining the arrangement direction of the unit prism 70 with respect to the second direction D2. In particular, when the arrangement direction of the unit prisms 70 is tilted by 15 ° or more with respect to the second direction D2, the direction in which the luminance peak occurs is set within a range that could not be realized by the surface light source device having a simple configuration. Can be controlled.

As is well shown in FIG. 6, each unit prism 70 has a first prism surface 71 and a second prism surface 72 arranged so as to face each other along the arrangement direction of the unit prism 70. The first prism surface 71 of each unit prism 70 is located on one side (left side in FIG. 6) of the unit prism 70 in the arrangement direction, and the second prism surface 72 is located on the other side (left side of FIG. 6) in the arrangement direction of the unit prism 70. It is located on the right side of FIG. 6).

Therefore, in the surface light source device 20, the first prism surface 71 of each unit prism 70 is located on the side of the light source 24 in the arrangement direction of the unit prism 70 and faces one side (light source side) in the second direction D2. The second prism surface 72 of each unit prism 70 is located on the side separated from the light source 24 in the arrangement direction of the unit prism 70, and faces the other side (opposite side to the light source) in the second direction D2. The first prism surface 71 mainly travels into the light guide plate 30 from the light source 24 arranged on one side in the second direction D2, and then the light emitted from the light guide plate 30 is incident on the optical sheet 60. Functions as a surface. On the other hand, the second prism surface 72 has a function of reflecting the light incident on the optical sheet 60 and correcting the optical path of the light.

The first prism surface 71 and the second prism surface 72 each extend from the main body portion 65 and are connected to each other. The base end portion 75b of the unit prism 70 is defined at a position where the first prism surface 71 and the second prism surface 72 are connected to the main body portion 65, respectively. Further, at a position where the first prism surface 71 and the second prism surface 72 are connected to each other, the tip portion (top) 75a of the unit prism 70 protruding most toward the light entrance side from the main body portion 65 is defined.

A cross section parallel to both the normal direction nd to the sheet surface of the main body 65 (the light receiving side surface 67 of the main body 65, the sheet surface of the optical sheet 60) and the arrangement direction of the unit prism 70 (in the following, simply the optical sheet). The cross-sectional shape of each unit prism 70 in the main cut surface of the unit prism 70 is constant along the longitudinal direction (direction extending linearly) of the unit prism 70.

In the present embodiment, the cross-sectional shape of each unit prism 70 on the main cut surface of the optical sheet 60 is a shape that tapers toward the light entering side (the side of the light guide plate). That is, on the main cut surface of the optical sheet, the width of the unit prism 70 parallel to the sheet surface of the main body portion 65 becomes smaller as it is separated from the main body portion 65 along the normal direction nd of the main body portion 65.

In the illustrated example, it is assumed that the angle formed by the second prism surface 72 forming a part of the outer contour of the unit prism 70 on the main cut surface of the optical sheet 60 with respect to the arrangement direction of the unit prism 70 is an inclination angle θ _{t. The inclination angle θ t} of at least one unit prism 70 is not constant in the second prism surface 72. The inclination angle θ _t of the unit prism 70 is set from the tip end portion 75a of the unit prism closest to the main body portion 65 to the base end portion 75b of the unit prism 70 closest to the main body portion 65 in the second prism surface 72. It changes to become larger. In the region of the second prism surface 72 on the base end portion 75b side, relatively rising light traveling in a direction in which the inclination angle with respect to the front direction is relatively small is likely to be incident. Further, relatively sleeping light traveling in a direction in which the inclination angle with respect to the front direction becomes very large tends to be incident on the region of the second prism surface 72 on the tip end portion 75a side. _{By changing the inclination angle θ t} in the second prism surface 72, the optical sheet 60 can more effectively exert the light condensing function with respect to the light of the light guide plate 30. That is, the light traveling from one unit prism 70 travels in a direction within a narrower angle range.

As a specific configuration, on the main cut surface of the optical sheet 60, the inclination angle θ _t with respect to the arrangement direction of the plurality of unit prisms 70 is directed from the side of the tip portion 75a of the unit prism 70 to the side of the proximal end portion 75b. Each second prism surface 72 includes n (n is a natural number of 2 or more) element surfaces 73, that is, a plurality of element surfaces 73a and 73b arranged so as to gradually increase. The contour of the second prism surface 72 of the illustrated unit prism 70 has a shape formed by joining straight portions on the main cut surface of the optical sheet 60, or by joining the straight portions and chamfering the joints. .. In other words, the outer contour of the second prism surface 72 of the unit prism 70 is formed in a polygonal line shape or in a shape formed by chamfering the corners of the polygonal line. In particular, in the illustrated example, the second prism surface 72 has a first element surface 73a defining the tip portion 75a and a second element surface 73b adjacent to the first element surface 73a from the side of the main body portion 65. Have. _{The inclination angle θ 1} of the first element surface 73a is smaller than _{the inclination angle θ 2} of the second element surface 73b. However, the present invention is not limited to this example, and the second prism surface 72 may have three or more element surfaces, may be a curved surface, or may be a single flat surface (single element surface). It may be.

The above-mentioned tilt angles θ _t , θ ₁ , and θ ₂ are such that the light entry side surface (second prism surface 72) of the unit prism 70 is the arrangement direction of the unit prism 70 on the main cutting surface of the optical sheet 60. The angle to make. More specifically, the angle formed between the element surfaces 73a and 73b forming the polygonal line on the main cut surface of the optical sheet 60 and the arrangement direction of the unit prism 70 (strictly speaking, two formed). The smaller of the two angles (the angle of the inferior angle)) is the inclination angle θ _t , θ ₁ , and θ ₂ .

In the optical sheet 60 having the above configuration, the width W _b of the unit prisms 70 along the arrangement direction of the unit prisms 70 in the main cross-section of the optical sheet, the main body portion 65 in the main cross-section of the optical sheet 60 The ratio of the unit prism 70 to the height H _b along the normal direction nd, that is, the magnitude of the aspect ratio (W _b / H _b ) of the second prism surface 72, and each element surface forming the second prism surface 72. The tilt angles θ ₁ and θ ₂ of 73a and 73b affect the light-collecting property of the optical sheet 60 and the direction in which the optical sheet 60 should be focused, in other words, the direction in which the brightness peak occurs. For example, when the second direction D2 and the direction in which the plurality of unit prisms 70 are arranged are the same direction, the light emitting surface 31 of the light guide plate 30 is inclined from the front direction to the second direction D2 which is the light guide direction. _{The aspect ratio (W b} / H) of the unit prism 70 is required to generate the luminance peak in the direction inclined with respect to the second direction D2 so that the traveling direction of the emitted light advancing from is not returned to the front direction nd. _b ) is 1.15 or more and 1.5 or less, the inclination angle θ ₁ of the first element surface 73a is 38 ° or more and 53 ° or less, and the inclination angle θ ₂ of the second element surface 73b is 43 ° or more and 57 °. The following is preferable. On the other hand, the luminance peak is set by changing the traveling direction of the emitted light traveling from the light emitting surface 31 of the light guide plate 30 beyond the front direction in a direction inclined from the front direction to the second direction D2 which is the light guiding direction. In order to generate it in a direction inclined with respect to the two directions D2, the aspect ratio (W _b / H _b ) of the unit prism 70 is set to 1.1 or more and 1.50 or less, and further, the inclination angle θ of the first element surface 73a is set. _{It is preferable that 1} is 53 ° or more and 68 ° or less, and the inclination angle θ ₂ of the second element surface 73b is 59 ° or more and 72 ° or less.

According to the optical sheet 60 having the above configuration, the second prism surface 72 is inclined with respect to the direction perpendicular to the light emitting surface 21, and is a surface parallel to both the normal direction to the light emitting surface 21 and the prism arrangement direction. In the light guide plate 30, the light incident on the first prism surface 71 and reflected by the second prism surface 72 can be inclined from the direction perpendicular to the light emitting surface 21 to be emitted. Further, the prism arrangement direction is inclined with respect to the second direction D2, and each unit prism 70 extends linearly in a direction inclined with respect to the direction orthogonal to the second direction D2, so that the method for the light emitting surface 21 can be obtained. When the optical sheet 60 is viewed along the linear direction, the light incident on the first prism surface 71 from the light guide plate 30 and reflected by the second prism surface 72 is inclined from the direction parallel to the second direction D2. It can be illuminated. As a result, light having an angular distribution having peak brightness can be emitted in any direction of the light emitting surface 21.

Here, in the present embodiment, the light from the optical sheet 60 is adjusted to be emitted as light having an angular distribution having peak luminance in an arbitrary direction of the light emitting surface 21 as described above. Further, in the angular distribution of luminance in all directions on the light emitting surface 21, the luminance in the direction inclined by 40 ° from the direction in which the peak luminance is obtained to at least one direction is 5.5% or less of the peak luminance. ing. In the angular distribution of luminance in all directions on the light emitting surface 21, the luminance in each direction inclined by 40 ° from the direction in which the peak luminance is obtained to a plurality of directions is 5.5% or less of the peak luminance. It is more preferable that the brightness in each direction inclined by 40 ° from the direction in which the peak brightness is obtained to all directions is 5.5% or less of the peak brightness. In the present embodiment, the brightness in each direction inclined by 40 ° from the direction in which the peak brightness is obtained to all directions is 5.5% or less of the peak brightness.

Other dimensions of the optical sheet 60 can be set as follows, as an example. First, as a specific example of the unit prism 70 having the above configuration, the arrangement pitch of the unit prism 70 ( _{corresponding to the width W b} of the unit prism 70 in the illustrated example) can be set to 10 μm or more and 200 μm or less. .. However, in recent years, the arrangement of the unit prisms 70 has been rapidly improved in definition, and it is preferable that the arrangement pitch of the unit prisms 70 is 10 μm or more and 35 μm or less. _{Similarly, the width W b2} of the second prism surface 72 of the unit prism 70 can be 5 μm or more and 100 μm or less, and in consideration of recent trends, it can be 5 μm or more and 20 μm or less. _{Further, the protruding height Hb} of the unit prism 70 from the main body 65 along the normal direction nd to the sheet surface of the optical sheet 60 can be 5.5 μm or more and 180 μm or less.

The optical sheet 60 having the above structure can be manufactured by imposing the optical sheet 60 on a base material or by extrusion molding. Various materials can be used as the material forming the main body portion 65 of the optical sheet 60 and the unit prism 70. In particular, materials that are widely used as materials for optical sheets incorporated in display devices, have excellent mechanical properties, optical properties, stability, processability, etc., and are inexpensively available, such as acrylics, polystyrenes, and polycarbonates. A transparent resin containing one or more of polyethylene terephthalate, polyacrylonitrile or the like as a main component, or an epoxy acrylate or urethane acrylate-based reactive resin (ionized radiation curable resin or the like) can be preferably used.

When the optical sheet 60 is produced by curing an ionizing radiation curable resin on a base material, a sheet-shaped land portion (for example, a flat plate) located between the unit prism 70 and the base material together with the unit prism 70. The shaped intervening portion) may be formed on the base material. In this case, the main body portion 65 is composed of a base material and a land portion formed of an ionizing radiation curable resin. On the other hand, in the optical sheet 60 manufactured by extrusion molding, the main body portion 65 and the plurality of unit prisms 70 on the light entrance side surface of the main body portion 65 can be integrally formed.

Next, the adhesive layer 17 will be described.

According to the diligent research of the present inventor, it is preferable that the refractive index of the adhesive layer 17 is larger than the refractive index of the optical sheet 60, particularly the main body portion 65 thereof. In this case, the light is more focused in the direction of exhibiting the peak luminance. In particular, when the difference between the refractive index of the adhesive layer 17 and the refractive index of the optical sheet 60, particularly the main body portion 65, is 0.3 or less, it is difficult for light to be visually recognized in a direction inclined by the above-mentioned specific angle or more. The present inventor has confirmed that it becomes easier to play the effect of becoming.

By integrating the surface light source device 20 and the liquid crystal display panel 15 with such an adhesive layer 17, the brightness is reduced in a direction inclined in an arbitrary direction from the direction in which the peak brightness is obtained. That is, it is possible to condense the light from the light source 24 in a specific direction in which the peak luminance is obtained in an arbitrary direction, and suppress the light emission so that it is difficult to see in the other direction.

The effect of providing the adhesive layer 17 between the optical sheet 60 of the surface light source device 20 and the liquid crystal display panel 15 and integrating them is that the space between the optical sheet 60 and the liquid crystal display panel 15 is an air layer. It is played because the difference in refractive index is smaller than in the case. This makes it easier to achieve the effect that the light is less likely to be visually recognized in the direction inclined by the above-mentioned specific angle or more.

As described above, in the display device 10 of the present embodiment, since the first inclined surface 37 and the second inclined surface 38 are formed on the back surface 32 of the light guide plate 30, light is reflected more efficiently and the light emitting surface 31 is formed. Can be emitted from. In particular, by continuously providing the back surface side unit optical element 51 composed of the first inclined portion 41 and the second inclined portion 42 without interruption, most of the back surface 32 provided with the back surface side unit optical element 51 emits light. It contributes to the light emission from the surface 31, reduces the light emission unevenness, and can effectively suppress the occurrence of moire. Further, by using the wedge-shaped light guide plate 30, it is possible to efficiently reflect the light incident on the light guide plate 30 from the light source 24 and improve the light utilization efficiency.

As described above, according to the display device 10, the surface light source device 20, and the light guide plate 30 of the present embodiment, it is possible to provide a surface light source device capable of reducing luminance unevenness while efficiently using light.

The ratio of the angle α of the first inclined surface 37 and the angle β of the second inclined surface 38 can be determined based on an arbitrary viewpoint, for example, from the viewpoint of preventing the occurrence of moire and the brightness distribution of the entire light emitting surface 31. It is possible to determine these angles α and β from the viewpoint of ensuring the uniformity of.

[Second Embodiment]
In the present embodiment, the same or similar elements as those in the first embodiment described above are designated by the same reference numerals, and detailed description thereof will be omitted.

FIG. 7 is an enlarged cross-sectional view showing an example of the first inclined portion 41 according to the second embodiment.

In the present embodiment, each of the plurality of first inclined portions 41 provided on the back surface 32 side of the light guide plate 30 includes a plurality of step portions 80 arranged side by side in a staircase pattern in the second direction D2. Each first inclined portion 41 includes a plurality of stepped surfaces 81 formed by the back surface 32 of the plurality of stepped portions 80.

In the example shown in FIG. 7, each step surface 81 is configured by the first step surface 81a and the second step surface 81b, and a plurality of sets of the first step surface 81a and the second step surface 81b are arranged side by side in the second direction D2. It is arranged continuously. The plurality of first stage surfaces 81a are provided in parallel with each other, and the plurality of second stage surfaces 81b are provided in parallel with each other. With respect to the second direction D2 from the incoming surface 33 (see FIG. 1) to the opposite surface 34, each first stage surface 81a is inclined so as to gradually approach the light emitting surface 31, while each second stage surface 81b is inclined. It is inclined so as to gradually move away from the light emitting surface 31. As described above, the first inclined surface 37 of the present embodiment includes a plurality of stepped surfaces formed by at least a part of the back surface 32 of the plurality of stepped portions 80, and in the light guide plate 30 shown in FIG. 7, each first step is provided. The first inclined surface 37 is formed by the surface 81a.

Therefore, the acute angle angle formed by each of the plurality of first stepped surfaces 81a with respect to the second direction D2 corresponds to "the acute angle angle α formed by the first inclined surface 37 with respect to the second direction D2". Therefore, the acute angle angle α formed by each first stage surface 81a with respect to the second direction D2 satisfies the above-mentioned “α <β ≦ 4.2 °” and “β−α ≦ 3 °” and “0 ≦”. α ≦ 1.2 ° ”is satisfied. When the angle α of each first stage surface 81a satisfies these relationships, the light light guide efficiency is improved, the difference in the amount of light emitted in the light source direction of the light guide plate 30 is reduced, and the difference in the amount of light emitted by the light guide plate 30 is reduced. The present inventor has confirmed that the moire caused by the interference between the light and dark stripes on the light emitting surface 21 of the surface light source device 20 and the pixels of the liquid crystal display panel 15 is improved. The inventor of the present invention has a light guide distance L of 120 mm along the second direction D2 from the incoming surface 33 to the opposite surface 34, a size S1 of the incoming surface 33 with respect to the first direction D1 of 3 mm, and the opposite surface 34. It was actually confirmed that the moire was improved by setting the angle α of each first step surface 81a in the above range when the size S2 with respect to the first direction D1 was 0.5 mm.

Each step 80 thus provided extends in the third direction D3 and has substantially the same cross-sectional shape over the third direction D3. Further, the plurality of first stepped surfaces 81a included in each first inclined portion 41 have different heights h toward the back surface 32 side, and are directed from the light entering surface 33 (see FIG. 1) to the opposite surface 34. The height h of the plurality of first step surfaces 81a of each first inclined portion 41 gradually increases with respect to the two directions D2. Similarly, the plurality of second step surfaces 81b included in each first inclined portion 41 also have different heights h toward the back surface 32 side, and the second direction D2 from the light entering surface 33 toward the opposite surface 34. The height h of the plurality of second step surfaces 81b of each first inclined portion 41 is gradually increasing. The height h toward the back surface 32 is, for example, from a surface parallel to the plate surface of the light guide plate 30 (that is, a surface extending in the second direction D2) through the intersection v of the second inclined surface 38 and the stepped surface 39. The height h can be expressed by the distance to the center point for each of the first step surface 81a and the second step surface 81b.

It should be noted that the intersection c1 on the back surface 32 side of the first step surface 81a and the second step surface 81b included in each first inclined portion 41 has a height h to the back surface 32 side, which is different from each other. The height h of the first step surface 81a and the second step surface 81b included in the 1 inclined portion 41 on the light emitting surface 31 side is also different from each other on the back surface 32 side. In particular, in the example shown in FIG. 7, the height h of the intersection c1 on the back surface 32 side gradually increases with respect to the second direction D2 from the incoming surface 33 to the opposite surface 34, and the intersection c2 on the exit surface 31 side. The height h of is gradually increasing. Therefore, of the intersection c1 on the back surface 32 side of the first step surface 81a and the second step surface 81b included in each first inclined portion 41, the step surface 39 side (that is, the left side of FIG. 7 (light entry surface of FIG. 1). The intersection c1 located on the 33 side)) is arranged on the light emitting surface 31 side most, and the intersection c1 located on the second inclined surface 38 side (that is, the right side of FIG. 7 (opposite surface 34 side of FIG. 1)) is the most back surface 32. It is placed on the side. Similarly, of the intersections c2 on the light emitting surface 31 side between the first step surface 81a and the second step surface 81b included in each first inclined portion 41, the intersection c2 located on the step surface 39 side is the most on the light emitting surface 31 side. The intersection c2 located on the second inclined surface 38 side is arranged on the back surface 32 side most.

Note that such a form shown in FIG. 7 regarding the stepped portion 80 and the stepped surface 81 is only an example, and the stepped portion 80 and the stepped surface 81 of other forms may be provided. For example, the height h of the intersection c1 on the back surface 32 side of the first step surface 81a and the second step surface 81b included in each first inclined portion 41 gradually decreases from the light entering surface 33 toward the opposite surface 34. You may become. Similarly, the height h of the intersection c2 on the light emitting surface 31 side between the first step surface 81a and the second step surface 81b included in each first inclined portion 41 gradually increases from the incoming surface 33 toward the opposite surface 34. May be smaller. In these cases, of the intersection c1 on the back surface 32 side of the first step surface 81a and the second step surface 81b included in each first inclined portion 41, the step surface 39 side (that is, the left side of FIG. 7 (the entry of FIG. 1). The intersection c1 located on the light surface 33 side)) is arranged on the back surface 32 side most, and the intersection c1 located on the second inclined surface 38 side (that is, the right side in FIG. 7 (opposite surface 34 side in FIG. 1)) is the most emitted light. It is arranged on the surface 31 side. Similarly, of the intersections c2 on the light emitting surface 31 side of the first step surface 81a and the second step surface 81b included in each first inclined portion 41, the intersection c2 located on the step surface 39 side is on the back surface 32 side most. The intersection c2 located on the second inclined surface 38 side is arranged on the light emitting surface 31 side most.

Further, in each first inclined portion 41, a portion where the height h of the intersection c1 gradually increases from the incoming surface 33 toward the opposite surface 34, and the height h of the intersection c1 increases from the incoming surface 33 to the opposite surface 34. It may include a portion that gradually becomes smaller toward. Similarly, in each first inclined portion 41, the height h of the intersection c2 gradually increases from the incoming surface 33 toward the opposite surface 34, and the height h of the intersection c2 is opposite to the incoming surface 33. A portion that gradually becomes smaller toward the surface 34 may be included. In addition, from the viewpoint of avoiding the incident of light as much as possible in the portion connecting the two first step surfaces 81a arranged adjacent to each other in each first inclined portion 41 (that is, the second step surface 81b), FIG. 7 shows. As shown, the height h of the intersection c1 on the back surface 32 side is gradually increasing with respect to the second direction D2 from the incoming surface 33 to the opposite surface 34, and the height h of the intersection c2 on the exit surface 31 side. It is more preferable that is gradually increasing.

By providing the stepped portion 80 and the stepped surface 81 in each of the first inclined portions 41, the first inclined surface 37 (that is, a plurality of first stepped surfaces 81a) is not included in the single plane, and the first inclined surface 37 is not included. The contact area between the reflective sheet 28 and the reflective surface 28a of the reflective sheet 28 can be reduced. As a result, moire appearing on the display surface 11 of the display device 10 can be suppressed to display a good image, and uneven brightness in the light guide direction (that is, the second direction D2) of the light guide plate 30 can be suppressed. The surface uniformity of brightness can be improved.

In particular, the slope angle γ of the entire back surface 32 of the light guide plate 30 is set to the light guide distance L with respect to the second direction D2 of the light guide plate 30, the size S1 with respect to the first direction D1 of the light entry surface 33, and the first of the opposite surfaces 34. Based on the magnitude S2 with respect to the direction D1, it is defined as follows.
γ = tan ^-1 ((S1-S2) / L)
In this case, the angle α between the slope angle γ of the entire back surface 32 of the light guide plate 30 and the first inclined surface 37 (that is, the plurality of first step surfaces 81a) is set so that the relationship of “γ ≦ α” is satisfied. This makes it possible to effectively prevent optical adhesion between the back surface 32 of the light guide plate 30 and the reflective surface 28a of the reflective sheet 28. In the light guide plate 30 shown in FIG. 7, the relationship of “γ = α” is satisfied.

In the light guide plate 30 shown in FIG. 7, the plurality of first stepped surfaces 81a included in each first inclined portion 41 have widths equal to each other in the arrangement direction (that is, the second direction D2), and each first inclined portion 41 is inclined. The plurality of second stage surfaces 81b included in the portion 41 also have equal widths with respect to the arrangement direction. However, the plurality of first stepped surfaces 81a included in each first inclined portion 41 may have different widths with respect to the arrangement direction, and the plurality of second stepped surfaces 81b included in each first inclined portion 41 may be arranged. They may have different widths with respect to orientation. Further, in the light guide plate 30 shown in FIG. 7, the angles formed by each of the plurality of first stage surfaces 81a with respect to the second direction D2 (see “α” in FIG. 7) are equal to each other, but the angles are different from each other. May be. Similarly, in the light guide plate 30 shown in FIG. 7, the angles formed by each of the plurality of second step surfaces 81b with respect to the second direction D2 are equal to each other, but the angles may be different from each other.

[Third Embodiment]
In the present embodiment, the same or similar elements as those in the first embodiment described above are designated by the same reference numerals, and detailed description thereof will be omitted.

FIG. 8 is a cross-sectional view showing a schematic configuration of the light guide plate 30 according to the third embodiment.

In the present embodiment, of the back surface 32 of the light guide plate 30, only the second inclined surface 38 is formed within a range of at least the first distance d1 or more from the opposite surface 34. That is, as shown in FIG. 8, the second inclined surface 38 extends from the opposite surface 34. When the distance occupied by the second inclined surface 38 extending from the opposite surface 34 with respect to the second direction D2 is represented by "E1", E1 satisfies the following relational expression.
E1 ≧ d1

As described above, the second inclined surface 38 extending from the opposite surface 34 and located at the position farthest from the light entering surface 33 with respect to the second direction D2 is the first inclined portion 41 and the second inclined surface 38. It occupies a range of a distance equal to or larger than the distance d1 with respect to the second direction D2 of the arrangement pitch P1 of the set of the portions 42 (that is, the back surface side unit optical element 51).

By configuring the second inclined surface 38 extending from the opposite surface 34 as described above, the light incident on the light guide plate 30 from the light source 24 via the light incoming surface 33 can be efficiently emitted from the light guide plate 30. Can be done. In particular, by providing the second inclined portion 42 in a wide range in the vicinity of the opposite surface 34 of the light guide plate 30, which is far from the light entrance surface 33 and the light emission intensity from the light guide plate 30 is likely to be weakened, the light emission surface 31 in the vicinity of the opposite surface 34 is provided. It is possible to suppress the reduction of the brightness and improve the uniformity of the brightness distribution of the entire light emitting surface 31.

[Fourth Embodiment]
In the present embodiment, the same or similar elements as those in the first embodiment described above are designated by the same reference numerals, and detailed description thereof will be omitted.

FIG. 9 is a cross-sectional view showing a schematic configuration of the light guide plate 30 according to the fourth embodiment.

In the present embodiment, of the back surface 32 side of the light guide plate 30, only the second inclined portion 42 is formed in the range E2 of at least the second distance from the light entering surface 33 with respect to the second direction D2. That is, as shown in FIG. 9, the second inclined surface 38 extends from the light entering surface 33.

By configuring the second inclined surface 38 extending from the light incoming surface 33 as described above, the light incident on the light guide plate 30 from the light source 24 via the light incoming surface 33 is efficiently emitted from the light guide plate 30. be able to. In general, the light immediately after entering the light guide plate 30 via the light entry surface 33 is difficult to reach the back surface 32, and the intensity of the light emission tends to be weakened on the light emission surface 31 in the vicinity of the light entry surface 33 of the light guide plate 30. However, by setting the slope extending from the incoming light surface 33 as the second inclined surface 38 which is a steep slope as in the present embodiment, the reduction in the brightness of the light emitting surface 31 in the vicinity of the incoming light surface 33 is suppressed, and the entire light emitting surface 31 is suppressed. It is possible to improve the uniformity of the brightness distribution of.

The size of the distance E2 occupied by the second inclined surface 38 extending from the light entering surface 33 with respect to the second direction D2 is not particularly limited. The larger the range of the second inclined surface 38 extending from the incoming surface 33, the larger the range in the vicinity of the incoming surface 33 where the light emitted from the emitted surface 31 is promoted. For example, a distance equal to or greater than the distance (that is, the first distance d1) of the arrangement pitch P1 of the set of the first inclined portion 41 and the second inclined portion 42 with respect to the second direction D2 is referred to as the above distance E2. It is possible to do.

[Other variants]
The present invention is not limited to the above-described embodiments and modifications, but may include various embodiments to which various modifications that can be conceived by those skilled in the art are added, and the effects produced by the present invention are also described above. It is not limited to the matters of. Therefore, various additions, changes, and partial deletions can be made to the scope of claims and each element described in the specification without departing from the technical idea and purpose of the present invention.

For example, it is also possible to appropriately combine two or more embodiments of the above-mentioned first to fourth embodiments. Therefore, by combining the second embodiment and the third embodiment, the slope extending from the opposite surface 34 is a steep slope while providing the step portion 80 and the step surface 81 (see FIG. 7) in each first inclined portion 41. The second inclined surface 38 may be used (see FIG. 8). Further, by combining the second embodiment and the fourth embodiment, the slope extending from the light entering surface 33 is a steep slope while providing the step portion 80 and the step surface 81 (see FIG. 7) in each first inclined portion 41. The second inclined surface 38 may be used (see FIG. 9). Further, by combining the third embodiment and the fourth embodiment, the slope extending from the opposite surface 34 is set as the second inclined surface 38 which is a steep slope (see FIG. 8), and the slope extending from the light entering surface 33 is a steep slope. The second inclined surface 38 may be used (see FIG. 9). Further, the above-mentioned second embodiment, third embodiment and fourth embodiment may be combined.

The applications of the display device 10, the surface light source device 20, and the light guide plate 30 are not particularly limited, and for example, the display device 10, the surface light source device 20, and the light guide plate 30 can be applied to an in-vehicle display device. Generally, a vehicle occupant observes an in-vehicle display device from a substantially fixed direction. The occupant's observation direction is usually inclined with respect to the normal direction to the display surface of the in-vehicle display device due to space restrictions. Therefore, it is desired that the light from the in-vehicle display device is strongly emitted in a direction other than the front direction. Therefore, the above-mentioned display device 10, the surface light source device 20, and the light guide plate 30 that can set the direction in which the luminance peak occurs in a direction other than the front direction are suitable for an in-vehicle display device, for example, an in-vehicle center console and an in-vehicle rear-view mirror. It can be applied to mirrors, in-vehicle side mirrors, instrument panels, and the like. By controlling the emission direction of the image light in these devices, it is possible to display the image brightly toward the passenger while preventing the reflection of the image on the windshield or the like from being observed by the passenger. ..

The display device 10, the surface light source device 20, and the light guide plate 30 described above can be applied to the following applications as an example.
-Application to in-vehicle display devices By controlling the emission direction of image light, it is possible to display the image brightly to viewers such as drivers while preventing the image from being reflected on the windshield. ..
-Application of an automated teller machine (ATM) to a display device and a surface light source device of the display device It is possible to prevent peeping from the side when operating an ATM.
-Application to digital signage By changing the direction of the unit prism of the optical sheet, optics suitable for the installation location of digital signage (also called electronic signage, electronic billboard, electronic bulletin board, etc.) and the position of the viewer The characteristics can be obtained. Such suitable optical characteristics are, for example, the distribution of the deaf person who matches the luminance peak direction of the emitted light in the direction toward the deaf person assumed from the display surface of the digital signage and also assumes the angular distribution of the luminance. It is possible to set so as to include the range.
-Application to the display device in the train car Since the viewer observes the display device from below, it is preferable to display the image toward the viewer (downward from the installation position). Further, when applied to the position of the hanging advertisement, since the train is elongated, it is not necessary to widen the viewing angle in the lateral direction. Therefore, the image can be efficiently displayed to the viewer.
-Application to display devices such as security rooms Each of many display devices can have light emission characteristics that match the viewer (security guard) located in the center.
-Application to table display The viewer is always located at the same relative position to the desk with the built-in display. Therefore, the light output characteristics can be set according to the position of the viewer.
-Application to amusement facilities For example, when the positional relationship between the installation position and the user is normally constant, such as the display device of a game device installed in a game center, a specific user (observer) from the display surface. It is possible to obtain optical characteristics that match the brightness peak direction of the emitted light in the direction toward.
-Application to lighting Idemitsu characteristics can be set appropriately according to the purpose of lighting such as indirect lighting and desk lights and the installation position of lighting.
・ Application of automatic ticket gate display devices and surface light source devices of the display devices Since the position of the line of sight of passers-by at the ticket gate is limited, the emission peak direction of the emitted light is aligned with that position (or the direction of the line of sight). It is desirable to make it a characteristic.
-Application to wristwatch display devices It is necessary to twist the arm to see from the front, and it is often observed from diagonally below the wristwatch. Therefore, the luminance peak direction and the luminance angle distribution of the emitted light are set so as to include the range of the direction connecting the position of the wristwatch, which is usually used frequently, and the position of the observer's eyes. Moreover, since it is often observed in sunlight, it is desirable to have high brightness.
-As other examples, display devices on the back of seats of airplanes, display devices used for explaining safety equipment such as airplanes, display devices near the ceiling of tourist buses, display devices for operation guidance at airports and stations, etc. It can also be applied to at least one display device of a game machine having a plurality of screens (for example, a screen in a horizontal plane and a screen in a vertical plane), a liquid crystal operation panel (keyboard, etc.), and the like.

10 Display device 11 Display surface 12 Liquid crystal layer 13 Upper polarizing plate 14 Lower polarizing plate 15 Liquid crystal display panel 17 Adhesive layer 19 Prism layer 20 Surface light source device 21 Light emitting surface 24 Light source 28 Reflective sheet 28a Reflective surface 30 Light guide plate 31 Light emitting surface 32 Back surface 33 Incoming surface 34 Opposite surface 35 Light diffusing part 37 First inclined surface 38 Second inclined surface 39 Stepped surface 40 Base 41 First inclined part 42 Second inclined part 50 Surface side unit Optical element 50a Concave curved surface 50b Inclined surface 50c Bottom 50d Edge portion 51 Back surface side unit optical element 52 Flat portion 60 Optical sheet 61 Light emitting surface 65 Main body portion 70 Unit prism 71 First prism surface 72 Second prism surface 75a Tip portion 80 Step portion 81 Step surface 81a First step surface 81b Second stage

Claims (15)

A light guide plate having a light emitting surface, a back surface arranged to face the light emitting surface, and a first side surface and a second side surface extending in a first direction between the light emitting surface and the back surface.
With respect to the first direction, the first side surface is formed larger than the second side surface.
On the back surface side of the light guide plate, a plurality of sets of a first inclined portion and a second inclined portion adjacent to each other are repeatedly formed in a second direction from the first side surface to the second side surface.
A first inclined surface formed by at least a part of the back surface of the first inclined portion, which is inclined so as to gradually approach the light emitting surface with respect to the second direction from the first side surface to the second side surface. The angle of the acute angle formed by the first inclined surface with respect to the second direction is the second inclined surface formed by the back surface of the second inclined portion, from the first side surface to the second side surface. The second inclined surface, which is inclined so as to gradually approach the light emitting surface with respect to the second direction toward the direction, is smaller than the acute angle formed with respect to the second direction.
When the acute angle angle formed by the first inclined surface with respect to the second direction is represented by α, and the acute angle angle formed by the second inclined surface with respect to the second direction is represented by β.
α <β ≤ 4.2 ° and β-α ≤ 3 °
Is satisfied ,
When the size of the first side surface with respect to the first direction is represented by S1 and the size of the second side surface with respect to the first direction is represented by S2.
S2 ≦ 2/3 × S1,
1.5 mm ≤ S1 ≤ 3 mm, and
0 mm ≤ S2 ≤ 2 mm
Is filled with a light guide plate. 0 ≤ α ≤ 1.2 °
The light guide plate according to claim 1. The light guide plate according to claim 1 or 2 , wherein the plurality of first inclined surfaces are formed on the same plane. The light guide plate according to any one of claims 1 to 3 , further comprising a light diffusing portion formed on the first side surface and diffusing light. The light guide plate according to claim 4 , wherein the light diffusing unit diffuses light incident on the first side surface in the first direction. The first inclined portion includes a plurality of step portions arranged side by side in the second direction.
The light guide plate according to any one of claims 1 to 5 , wherein the first inclined surface includes a plurality of step surfaces formed by at least a part of the back surface of the plurality of step portions. A light guide plate having a light emitting surface, a back surface arranged to face the light emitting surface, and a first side surface and a second side surface extending in a first direction between the light emitting surface and the back surface.
With respect to the first direction, the first side surface is formed larger than the second side surface.
On the back surface side of the light guide plate, a plurality of sets of a first inclined portion and a second inclined portion adjacent to each other are repeatedly formed in a second direction from the first side surface to the second side surface.
A first inclined surface formed by at least a part of the back surface of the first inclined portion, which is inclined so as to gradually approach the light emitting surface with respect to the second direction from the first side surface to the second side surface. The angle of the acute angle formed by the first inclined surface with respect to the second direction is the second inclined surface formed by the back surface of the second inclined portion, from the first side surface to the second side surface. The second inclined surface, which is inclined so as to gradually approach the light emitting surface with respect to the second direction toward the direction, is smaller than the acute angle formed with respect to the second direction.
When the acute angle angle formed by the first inclined surface with respect to the second direction is represented by α, and the acute angle angle formed by the second inclined surface with respect to the second direction is represented by β.
α <β ≤ 4.2 ° and
β-α ≤ 3 °
Is satisfied,
The first inclined portion and the plurality of sets of the second inclined portions each occupy a first distance with respect to the second direction, and are continuously arranged in the second direction with the first distance as an arrangement pitch. ,
Wherein among the back surface of the light guide plate, wherein at least said first distance or more in the range of the second side surface, the second inclined surface only light guide plate that will be formed. A light guide plate having a light emitting surface, a back surface arranged to face the light emitting surface, and a first side surface and a second side surface extending in a first direction between the light emitting surface and the back surface.
With respect to the first direction, the first side surface is formed larger than the second side surface.
On the back surface side of the light guide plate, a plurality of sets of a first inclined portion and a second inclined portion adjacent to each other are repeatedly formed in a second direction from the first side surface to the second side surface.
A first inclined surface formed by at least a part of the back surface of the first inclined portion, which is inclined so as to gradually approach the light emitting surface with respect to the second direction from the first side surface to the second side surface. The angle of the acute angle formed by the first inclined surface with respect to the second direction is the second inclined surface formed by the back surface of the second inclined portion, from the first side surface to the second side surface. The second inclined surface, which is inclined so as to gradually approach the light emitting surface with respect to the second direction toward the direction, is smaller than the acute angle formed with respect to the second direction.
When the acute angle angle formed by the first inclined surface with respect to the second direction is represented by α, and the acute angle angle formed by the second inclined surface with respect to the second direction is represented by β.
α <β ≤ 4.2 ° and
β-α ≤ 3 °
Is satisfied,
Wherein one of the back surface side of the light guide plate, said at least a second range of distances from the first side surface with respect to the second direction, the second inclined portion only light guide plate that is formed. On the light emitting surface side of the light guide plate, each of a plurality of light emitting side unit optical units extending in the second direction is arranged perpendicular to the first direction and perpendicular to the second direction. The light guide plate according to any one of claims 1 to 8, wherein a plurality of unit optical units on the light emitting side are formed. The light guide plate according to claim 9 , wherein each of the plurality of unit optical units on the light emitting side is formed in a groove shape having a concave curved surface having a concave surface on the back surface side. The light guide plate according to any one of claims 1 to 10 and the light guide plate.
An optical sheet arranged to face the light emitting surface of the light guide plate and
A light source and a light source arranged to face the first side surface of the light guide plate are provided.
A surface light source device in which a prism layer is formed on the surface side of the optical sheet facing the light emitting surface of the light guide plate. Further provided with a reflective sheet arranged to face the back surface of the light guide plate and reflect light.
The surface light source device according to claim 11 , wherein the surface of the reflective sheet facing the back surface of the light guide plate extends in parallel with the plurality of first inclined surfaces. The surface light source device according to claim 12,
A display panel arranged to face the optical sheet of the surface light source device, and
An adhesive layer provided between the surface light source device and the display panel is provided.
A display device in which the surface light source device and the display panel are adhered to each other by the adhesive layer and integrally provided via the adhesive layer. The display device according to claim 13 , wherein the refractive index of the adhesive layer is larger than the refractive index of the optical sheet. The display device according to claim 14 , wherein the difference between the refractive index of the adhesive layer and the refractive index of the optical sheet is 0.3 or less.

Images