WO2014017488A1

WO2014017488A1 - Illumination device and display device

Info

Publication number: WO2014017488A1
Application number: PCT/JP2013/069923
Authority: WO
Inventors: 一郎梅川; 弘文大澤; 壮史石田; 龍三結城; 昌紀景山; 秀悟八木
Original assignee: シャープ株式会社
Priority date: 2012-07-23
Filing date: 2013-07-23
Publication date: 2014-01-30

Abstract

An illumination device (2) is provided with the following: a light-guide body (31) having a light-entering surface (311) and a light-exiting surface (312); a low refractive index layer (32) that is installed adjacent to the rear face of the light-guide body (31) and that has a lower refractive index than that of the light-guide body (31); and a prism layer (4) that is installed adjacent to the low refractive index layer (32). The illumination device includes a second slope (412, 422) that faces the light-entering surface (311) at a slant, is provided with a plurality of rear face prisms (41, 42) in which the angles of inclination (θ1, θ2) of second slopes are different, and is disposed so that rear face prisms with the same angle of inclination are not adjacent.

Description

Lighting device and display device

The present invention relates to an illumination device using a light guide member that guides light, and relates to a display device including the illumination device.

In a liquid crystal display device (display device) equipped with a non-light emitting liquid crystal panel (display panel), a backlight unit (illumination device) that supplies light is usually mounted on the liquid crystal panel. The backlight unit is configured to emit planar light having uniform luminance over the entire planar liquid crystal panel. Some of the backlight units include a light guide plate (light guide member) that diffuses light from a light source widely and equalizes luminance.

For example, an edge light (side light) type backlight unit is known as a backlight unit including the light guide plate. The light guide plate is a plate-like member that matches the shape of the liquid crystal panel, and is disposed on the back side of the liquid crystal panel. That is, in the light guide plate, a surface (one of the main surfaces) facing the liquid crystal panel is a light output surface that emits light, and at least one of the side surfaces is a light receiving surface on which light from a light source is incident.

The light exit surface of the light guide plate is formed with a prism that reflects light incident at a predetermined angle (critical angle) or more and guides (diffuses) the inside of the light guide plate. Further, a prism that accompanies the inside of the light guide plate and rises light incident at a predetermined angle toward the light exit surface is formed on the surface opposite to the light exit surface.

The prisms are formed on the light exit surface and the opposite surface of the light guide plate, so that uniform light can be emitted from the light guide plate. Since the light guide plate is configured to make the luminance of the planar light uniform, the emission angle (spreading angle) of the light emitted from the light exit surface is narrowed. In other words, the video displayed on the liquid crystal display device has a uniform brightness but a narrow viewing angle. In order to solve such problems, for example, in a liquid crystal display device disclosed in Japanese Patent Application Laid-Open No. 2011-28019, a prism sheet and a lens sheet for adjusting the light spreading angle are provided on the front side of the light exit surface of the light guide plate. I have. By using the prism sheet and the lens sheet, the light spreading angle can be increased, and the viewing angle of the liquid crystal display device is widened.

JP 2011-28019 A

However, the backlight unit of the liquid crystal display device described in Japanese Patent Application Laid-Open No. 2011-28019 requires an optical member for widening the viewing angle, such as a prism sheet and a lens sheet, in addition to the light guide plate and the light source. Will increase. Further, a structure for arranging the optical sheet is required, and the display device becomes thick.

These prism sheets and lens sheets must be accurately positioned with respect to the light guide plate and the liquid crystal panel, so that it takes time and labor to manufacture the backlight unit. Furthermore, although prism sheets and lens sheets are translucent, the intensity of the light is attenuated when light passes through these sheets. In other words, the use efficiency of light is reduced by providing the prism sheet or the lens sheet.

Therefore, an object of the present invention is to provide an illumination device and a display device that can reduce the number of components and can widen the viewing angle while suppressing luminance unevenness.

In order to achieve the above object, the present invention has a light source and a light incident surface facing the light source on a side surface, guides light incident from the light incident surface, and forms planar light from a light exit surface on the front side. A light guide that emits light, and a plurality of light guide prisms that are formed on the light exit surface and include a first inclined surface that is inclined and opposed to the light incident surface, and is arranged in the optical axis direction of the light source, A low refractive index layer that is installed adjacent to the back surface of the light guide and has a lower refractive index than the light guide, and a prism layer that is installed on the opposite side of the low refractive index layer from the light guide. And a second inclined surface formed on the opposite side of the prism layer to the low refractive index layer and inclined and opposed to the light incident surface, wherein the inclined angle of the second inclined surface with respect to the bottom surface is different. And the plurality of back prisms have the same tilt angle. That it is arranged in the optical axis direction of the light source so as not adjacent to an illuminating apparatus according to claim.

According to this configuration, the light incident on the light guide from the light incident surface is the light guide prism,
Light is guided by repeating reflection at the interface between the back surface and the low refractive index layer. In addition, since the rear prisms having different inclination angles are provided, the reflected light from the second inclined surface of the rear prism is reflected at different angles depending on the inclination angles.

The light reflected by the inclined surface passes through the low refractive index layer and the light guide and is emitted from the light exit surface. Therefore, the light reflected by the adjacent back prisms has a back prism having the same angle. Compared with the arrangement, the light irradiation angle becomes wider. Thereby, the viewing angle in the optical axis direction of the light source of the planar light emitted from the light exit surface of the irradiation device is widened. Moreover, the incident angle which injects into the said interface becomes small by repeating reflection with the said light guide prism, the said back surface, and the said low refractive index layer. Thereby, the light incident on the prism layer can be limited to a certain level, and uneven brightness can be suppressed.

Also, since an optical sheet for widening the viewing angle is not used, the number of parts can be reduced, and labor and time required for assembly can be reduced. Thereby, it is possible to reduce the manufacturing cost of an illuminating device. Moreover, since the loss which generate | occur | produces when light passes through these optical sheets can be suppressed, the utilization efficiency of light can be improved and energy saving is also possible.

In the above configuration, a rear prism group in which the rear prisms are arranged so that the inclination angle becomes smaller as the prism layer moves away from the light incident surface may be arranged in the optical axis direction of the light source.

According to this configuration, the rear prism group has a rear prism having a smaller inclination angle as the distance from the light incident surface increases. Thereby, the irradiation direction of the light reflected by each back prism can be made radial, and the viewing angle can be widened while suppressing unevenness in luminance of the emitted light.

In the above configuration, the inclination angle of each rear prism of the rear prism group may be set so that the irradiation area of the light reflected by the inclined surface of each rear prism is continuous.

Thus, by forming the inclination angle of the rear prism, it is possible to suppress uneven brightness due to the overlapping of the light reflected by the inclined surface of each rear prism.

In the above configuration, when the inclination angle of the rear prism is θ _m (m is an integer),
Σθ _n / n = θ _t
| Θ _n −θ _t | = | θ ₁ −θ _t |, | θ _n−1 −θ _t | = | θ ₂ −θ _t |
However, n may be set so that the relational expression of an integer of 3 or more holds.

In the above-described configuration, a plurality of light sources are arranged in the longitudinal direction of the light incident surface, and a plurality of diffusions are arranged on the light guide in the optical axis direction of the light source and arranged in the longitudinal direction of the light incident surface. A prism may be provided.

According to this configuration, for example, even if a point light source such as an LED is used as the light source, the light deflection in the arrangement direction of the light source due to the directivity of the light source can be reduced by the diffusion prism. It is possible to suppress uneven brightness of the planar light emitted more.

In the above-described configuration, a scattering sheet may be provided so as to cover the light exit surface of the light guide plate and scatter light emitted from the light exit surface.

According to this configuration, in order to achieve the required viewing angle or brightness, the light reflected by the inclined surfaces of the adjacent rear prisms overlaps or is not continuous, thereby scattering light having a plurality of peaks. , It is possible to obtain light with a luminance distribution having one peak. Thereby, generation | occurrence | production of the brightness nonuniformity recognized can be suppressed by providing a some peak.

In the above configuration, the low refractive index layer and the prism layer may be integrally formed of a material having a refractive index smaller than the refractive index of the light guide.

According to this configuration, since the low refractive index layer and the prism layer are integrally formed, the number of parts can be reduced. Further, the interface between the low refractive index layer and the prism layer can be omitted, and the manufacture becomes easy. In addition, it is possible to suppress a decrease in the yield of the lighting device by reducing interfaces where defects such as breakage and variations in relative refractive index are likely to occur.

As a device using the above-described illumination device, a display device including a display panel arranged to face the light exit surface of the light guide can be exemplified. In addition, a liquid crystal display device using a liquid crystal display panel can be given as a display panel.

According to the present invention, it is possible to provide an illumination device and a display device that can reduce the number of components and can widen the viewing angle while suppressing luminance unevenness.

It is a disassembled perspective view of an example of the display apparatus concerning this invention. It is a perspective view of the light-guide plate used for the illuminating device concerning this invention. It is an enlarged view of a cut surface parallel to the light incident surface of the light guide plate shown in FIG. FIG. 3 is an enlarged view of the vicinity of a light exit surface of a cut surface orthogonal to the light entrance surface of the light guide plate illustrated in FIG. 2. It is an enlarged view of the prism layer vicinity of the cut surface orthogonal to a light-incidence surface of the light-guide plate shown in FIG. It is sectional drawing of the cut surface orthogonal to the light-incidence surface of the light-guide plate shown in FIG. It is a figure which shows the angle luminous intensity of the light when using the back prism which has a several angle difference. It is a graph which shows the change of the angle luminous intensity by the angle difference of a back prism. It is an expanded sectional view of the other example of the backlight unit which is an illuminating device concerning this invention. It is a graph which shows the change of the angle luminous intensity by the angle difference of a back prism. It is a perspective view of the further another example of the light-guide plate used for the backlight unit which is an illuminating device concerning this invention. It is a side view of the other example of the backlight unit which is an illuminating device concerning this invention. FIG. 3 is an image diagram of the viewing angle of emitted light when the difference in viewing angle is 5 ° in the backlight unit shown in FIG. 2. It is an image figure of the viewing angle of the emitted light when the angle difference of a viewing angle is 5 degrees in the backlight unit shown in FIG.

Embodiments of the present invention will be described below with reference to the drawings.

(First embodiment)
FIG. 1 is an exploded perspective view of an example of a display device according to the present invention. As shown in FIG. 1, the display device A is a liquid crystal display device that includes a liquid crystal panel 1 that is a display panel and a backlight unit 2 that is a lighting device. In the following description, the front and the back may be referred to. The front is the front of the display device, and in FIG. Moreover, the back indicates the reverse of the front. That is, in the display device, it can be said that the liquid crystal panel 1 is disposed on the front side and the backlight unit 2 is disposed on the back side.

The liquid crystal panel 1 includes an array substrate 11 in which switching elements such as TFTs, pixel electrodes, and the like are arranged in an array, and a counter electrode that is disposed at a predetermined interval from the array substrate 11 and faces the pixel electrodes. The substrate 12, the polarizing film 13 disposed in close contact with the outer surfaces of the array substrate 11 and the counter substrate 12, and the liquid crystal disposed (filled) in the gap between the array substrate 11 and the counter substrate 12. 14.

The backlight unit 2 is an edge light type backlight unit, and a light source 21 and a light guide plate 3 are disposed inside a frame-shaped 20. The opening on the back surface of the frame 20 is closed with a reflection sheet 22. The frame 20 is formed of a resin molded product or the like. The frame 20 may be formed of a light absorbing material such as a resin molded product containing a black pigment. Alternatively, a frame 20 in which a light absorbing material such as black paint is applied to a base material such as resin or metal may be employed.

The reflection sheet 22 is a member that reflects light, and is an integrally molded body of white resin. In addition, as a reflection sheet, a light coating material such as a white paint applied to the surface of a sheet formed of resin or metal, a film of a highly reflective metal thin film, etc. Can be widely adopted.

The light source 21 includes an LED 211, and a plurality of LEDs 211 are arranged in one direction (X direction).

The light guide plate 3 is a member that guides light from the LED 211 and emits it as planar light. The light guide plate 3 is a plate-like member formed so as to have a rectangular shape when viewed from the front with a light-transmitting resin or the like. The side surface of the light guide plate 3 faces the light source 21 (LED 211), forms a light incident surface 311 on which light emitted from the light source 21 enters, and the front surface of the light guide plate 3 facing the liquid crystal panel 1 is planar. A light exit surface 312 for emitting light is formed.

In the following description, the longitudinal direction of the light incident surface 311 is the X direction, the direction orthogonal to the X direction and along the optical axis of the LED 211 is the Y direction, and the direction orthogonal to the X direction and the Y direction (thickness direction of the light guide plate 3). This is referred to as the Z direction.

The light guide plate 3 which is a main part of the present invention will be described in more detail with reference to the drawings. 2 is a perspective view of a light guide plate used in the lighting apparatus according to the present invention, FIG. 3 is an enlarged view of a cut surface parallel to the light incident surface of the light guide plate shown in FIG. 2, and FIG. FIG. 5 is an enlarged view of the vicinity of the light exit surface of the cut surface orthogonal to the light incident surface of the light guide plate shown in FIG. 2, and FIG. 5 is an enlarged view of the vicinity of the prism layer of the cut surface of the light guide plate shown in FIG. is there.

As shown in FIG. 2, the light guide plate 3 includes a light guide 31 having a light incident surface 311 and a light exit surface 312, a low refractive index layer 32 disposed on the back side of the light guide 31, and a low refractive index layer. 32 and a prism layer 4 disposed on the back surface of 32. The light guide 31 is made of a resin material having translucency such as acrylic or polycarbonate. The light guide 31 has a light incident surface 311 and a light output surface 312 and guides light emitted from the LED 211.

The light guide 31 is formed in a substantially rectangular parallelepiped. That is, the light guide 31 includes a light exit surface 312 and a substantially parallel back surface 313. In addition, the light incident surface 311 of the light guide 31 is disposed substantially parallel to the light output portion of the light source 21.

The refractive index (n1) of the light guide 31 is preferably 1.42 or more, more preferably 1.59 to 1.65. If the light guide 13 is made of acrylic or the like, the refractive index of the light guide 13 can be about 1.49. If the light guide 31 is made of polycarbonate or the like, the refractive index of the light guide 13 can be about 1.59. In addition, when the light guide 13 is comprised from an acryl, translucency becomes high compared with the case where the light guide 31 is comprised from a polycarbonate.

A plurality of diffusion prisms 33 extending in the Y direction and arranged in the X direction are formed on the light exit surface 312 of the light guide 31. As shown in FIG. 3, the diffusion prism 33 is recessed on the light exit surface 312, and the light guide 31 includes a flat portion 34 parallel to the XY plane between the adjacent diffusion prisms 33. Yes.

As shown in FIG. 3, the diffusion prism 33 includes a pair of inclined surfaces 331 inclined with respect to the flat portion 34. That is, the diffusion prism 33 is formed in a triangular cross section. An angle (vertical angle of the diffusion prism 331) α formed by the pair of inclined surfaces 331 is preferably about 120 ° to about 140 °.

Further, the width of the diffusion prism 33 in the X direction is preferably about 0.1 mm or less, more preferably about 0.010 mm to about 0.030 mm. Furthermore, it is preferable that the width of the diffusing prism 33 in the X direction is larger than the width of the flat portion 34 in the X direction.

In the light guide plate 3 shown in FIG. 2 and the like, the diffusion prisms 33 have the same shape, the same size, and the same pitch regardless of the formation position in the plane of the light guide 31. Preferably it is formed. Moreover, although the thing of the cross-sectional triangle shape is mentioned as the spreading | diffusion prism 33, it is not limited to this, You may have an arc, an elliptical arc, another curve, and polygonal cross-sectional shape.

The light emitted from the light source 21 and incident from the light incident surface 311 is reflected by the diffusion prism 33 so as to diffuse in the longitudinal direction of the light incident surface 311, that is, in the X direction. Thereby, the diffusion prism 33 is used to make the planar light uniform by diffusing the light emitted from the LED 211 as a point light source and incident from the light incident surface 311 in the X direction. If a linear light source extending in the longitudinal direction of the light incident surface 311 is used as the light source 21, the diffusion prism 33 may be omitted.

On the light exit surface of the light guide 31, light guide prisms 35 arranged in the Y direction between adjacent diffusion prisms 33 are provided. A horizontal plane 34 parallel to the XY plane is provided between the light guide prisms 35 adjacent in the Y direction. The light guide prism 35 may be formed continuously (adjacently) and the horizontal plane 34 may be omitted.

The light guide prism 35 includes a vertical surface 351 perpendicular to the XY plane and an inclined surface 352 (first inclined surface) inclined in the YZ plane. The inclined surface 352 is inclined in a direction facing the incident surface 311 and is inclined at an inclination angle β with respect to a direction (Y direction) orthogonal to the incident surface 311. The inclination angle β of the inclined surface 352 with respect to the flat portion 34 is preferably 5 ° or less, and more preferably 0.1 ° to 3.0 °.

The light guide prisms 35 are arranged at a predetermined pitch in the Y direction. The light guide prism 35 is formed to have a predetermined width in the Y direction. The width of the light guide prism 35 in the Y direction is preferably 0.25 mm or less, and more preferably 0.01 mm to 0.10 mm.

In the light guide plate 3, the shape and size of the planar portion 34 and the light guide prism 35 are constant regardless of the distance from the light source 21, but are not limited thereto. For example, the incident angle of the light in the light guide plate 3 with respect to the back surface 313 is a shape that changes according to the distance from the light source 21 or a shape that is different for each predetermined range so that the incident angle decreases as the distance from the light source 21 increases. Also good.

The low refractive index layer 32 is disposed in close contact with the back surface 313 of the light guide 31 so as not to interpose air. The prism layer 4 is formed of a resin containing hollow particles such as a fluorine-based acrylate or a nano-sized inorganic filler. The refractive index (n2) of the low refractive index layer 32 is preferably less than 1.42, more preferably 1.10 to 1.35. Further, it is preferable that a relationship of n1 / n2> 1.18 holds between the refractive index (n1) of the light guide 31 and the refractive index (n2) of the low refractive index layer 32.

For example, if the low refractive index layer 32 is made of a fluorine-based acrylate or the like, the refractive index (n2) of the low refractive index layer 32 can be about 1.35. Further, if the low refractive index layer 32 is made of a resin containing hollow particles such as nano-sized inorganic fillers, the refractive index (n2) of the low refractive index layer 32 can be 1.30 or less. is there. The low refractive index layer 32 has a thickness of about 10 μm to about 50 μm, for example.

The prism layer 4 is closely attached to the back surface of the low refractive index layer 32, that is, the surface opposite to the light guide 31 so that air does not intervene therebetween. When the refractive index of the prism layer 40 is n3, a relationship of n1 ≧ n3> n2 is established between the refractive index (n1) of the light guide 31 and the refractive index (n2) of the low refractive index layer 32. .

The prism layer 4 includes a first back prism 41 and a second back prism 42 having different shapes on the back surface 40 (the back surface of the light guide plate 3). The first back prism 41 and the second back prism 42 are ridges that protrude toward the back side 40 of the prism layer 4 and extend in the X direction. The first back prism 41 and the second back prism 42 constitute a back prism group.

The first rear prism 41 includes a vertical surface 411 perpendicular to the XY plane and an inclined surface 412 (second inclined surface) inclined in the YZ plane. The inclined surface 412 is inclined in a direction opposite to the incident surface 311 (that is, closer to the light guide 31 as the distance from the incident surface 311 increases), and an inclined angle with respect to a direction orthogonal to the incident surface 311 (Y direction). It is inclined at θ1. That is, the first back prism 41 has a right triangle cross section.

Note that the inclination angle θ1 of the inclined surface 412 with respect to the back surface 313 is preferably about 40 ° to about 50 °. The first back prism 41 is formed to have a predetermined width in the Y direction. The length of the first back prism 41 protruding in the Z direction is about 0.1 mm or less, preferably about 0.010 mm to about 0.025 mm.

Similarly to the first back prism 41, the second back prism 42 is a ridge having a right-angled triangular section, and includes a vertical surface 421 and an inclined surface 422 (second inclined surface). The inclined surface 422 is inclined at an inclination angle θ2 with respect to a direction (Y direction) orthogonal to the incident surface 311. The inclination angle θ2 is preferably about 40 ° to about 50 °, similarly to the inclination angle θ1. In the prism layer 4, the relationship θ1> θ2 is established.

And as shown in FIG. 5, the 1st back prism 41 and the 2nd back prism 42 are arrange | positioned adjacently in the Y direction, ie, without passing through a plane part. That is, in the prism layer 4, the inclined surface 412 of the first back prism 41 is adjacent to the vertical surface 421 of the second back prism 42, and the inclined surface 422 of the second back prism 42 is the vertical surface of the first back prism 41. 411 and adjacent structure.

By using the light guide plate 3 formed as described above, the light emitted from the light source 21 (LED 211) is repeatedly reflected between the light guide prism 35 of the light guide 31 and the back surface 313, so that the light guide The light is guided into 31. Then, the light in the light guide 31 is repeatedly reflected by the light guide prism 35, so that the incident angle with respect to the back surface 313 of the light guide 31 is gradually reduced. When the incident angle with respect to the back surface 313 becomes smaller than the critical angle, the light enters the prism layer 4.

In addition, among the light incident on the light guide 31 from the light incident surface 311, the light traveling toward the back surface 311 of the light guide 31 is also reflected by the back surface 313 of the light guide 31 and further back. Reflection is repeated between 313 and the light guide prism 35 and enters the prism layer 4.

Hereinafter, the reflection of light at the light guide 31 will be described with reference to the drawings. 6 is a cross-sectional view of a cut surface orthogonal to the light incident surface of the light guide plate shown in FIG. In the light guide plate shown in FIG. 6, the path of light emitted from the light source 21 (LED 211) and guided into the light guide plate 3 is indicated by a broken line. Note that the light guided through the light guide plate 3 actually has a certain spread, but the broken line in FIG. 6 indicates the center of the spread.

The light emitted from the light source 21 has the highest intensity in the front direction (Y direction) of the light source 21, and has a spread of ± 90 ° in the X direction and the Z direction with respect to the front direction (Y direction). The light emitted from the light source 21 is refracted when entering the light incident surface 311 of the light guide 31. When the refraction angle at this time is γ0 and the critical angle between the light guide 31 and the air layer is φ1, γ0 <φ1. φ1 is arcsin (1 / n1), and the spread angles in the X direction and the Z direction with respect to the front direction (Y direction) of the light incident from the light incident surface 311 are ± φ1. For example, if the refractive index n1 of the light guide 31 is 1.59, φ1 is about 39 °.

Of the light incident from the light incident surface 311, the light traveling toward the light exit surface 312 is incident on the flat surface 34 or the inclined surface 352 of the light guide prism 35. The incident angle of light incident on the flat portion 34 is 90 ° −φ1 or more. Further, the incident angle γ1 of the light Q1 incident on the inclined surface 352 is 90 ° −φ1−β or more. At this time, among the light incident on the flat portion 34 or the inclined surface 352, light having an incident angle smaller than the critical angle φ1 is emitted to the outside from the flat portion 34 or the inclined surface 352, and all the light having the critical angle φ1 or more is emitted. Reflected.

Then, the light Q2 reflected by the inclined surface 352 enters the back surface 313 at an incident angle γ2. The incident angle γ2 is 90 ° −φ1-2 × β or more. At this time, if the critical angle between the light guide 31 and the low refractive index layer 32 is φ2, light incident on the bottom surface 313 at an incident angle smaller than the critical angle φ2 enters the low refractive index layer 32. In addition, light incident at an incident angle greater than the critical angle φ2 is totally reflected at the bottom surface 313 (the interface between the light guide 31 and the low refractive index layer 32). Further, when the critical angle φ2 = arcsin (n2 / n1), for example, when the refractive index n1 = 1.59 of the light guide 31 and the refractive index n2 = 1.35 of the low refractive index layer 32, the critical angle φ2 is It is about 58 °.

Furthermore, the light Q3 reflected by the back surface 313 goes to the light exit surface 312 side. This light Q3 is incident on the plane portion 34 and the inclined surface 352 of the light guide prism 35. The light Q3 enters the flat portion 34 at an incident angle γ2. The incident angle γ3 of the light Q3 incident on the inclined surface 352 is 90 ° −φ1−3 × β or more. As in the case of the light Q1, the light incident on the light exit surface 312 at an incident angle smaller than the critical angle φ1 is emitted to the outside of the light guide 31 and is incident on the light exit surface 31 at an incident angle greater than the critical angle φ1. The light is totally reflected.

At this time, the light Q4 reflected by the inclined surface 352 enters the back surface 313 at an incident angle γ4. The incident angle γ4 of the light Q4 to the back surface 313 is 90 ° −φ1−4 × β or more. As in the case of the light Q2, light having an incident angle γ4 smaller than the critical angle φ2 enters the low refractive index layer 32. Further, light having a critical angle φ2 or more is totally reflected by the back surface 313 and travels toward the light exit surface 312.

As described above, each time the light guided in the light guide 31 is reflected by the inclined surface 352, the incident angle to the light exit surface 312 (plane portion 34) and the back surface 313 gradually decreases. . The incident angle of the light guided through the light guide 21 to the interface between the light guide 31 and the low refractive index layer 32 is reduced by 2 × β ° every time the light is reflected by the inclined surface 352. Then, when the incident angle to the interface between the light guide 31 and the low refractive index layer 32 becomes smaller than the critical angle φ2, the light enters the low refractive index layer 32. Since the refractive index n2 of the low refractive index layer 32 is smaller than the refractive index n1 of the light guide 31, when light enters the low refractive index layer 32, the interface between the light guide 31 and the low refractive index layer 32 Refracts to the side.

As described above, the incident angle of light with respect to the interface between the light guide 31 and the low refractive index layer 32 from the light incident surface 311 is approximately 2 × β each time reflection is repeated in the light guide 31. It gets smaller. For this reason, the spread angle in the Y direction of the light incident on the low refractive index layer 24 is about 2 × β.

In addition, among the light incident from the incident surface 311, the light Q <b> 5 that travels toward the back surface 313 of the light guide 31 is also repeatedly reflected in the light guide 31. That is, by repeating the reflection at the back surface 313 of the light guide 31 and the light guide prism 35, the incident angle with respect to the back surface 313 becomes small and enters the low refractive index layer 32 from the back surface 313.

The light incident on the low refractive index layer 32 passes through the low refractive index layer 32 and enters the prism layer 4. Since the refractive index n3 of the prism layer 4 is formed larger than the refractive index n2 of the low refractive index layer 32 as described above, total reflection does not occur when entering the prism layer 4 from the low refractive index layer 32. Further, when the light is incident on the prism layer 4 from the low refractive index layer 32, the refractive index of the prism layer 4 is large, so that the distance from the interface is opposite to the case where the light is incident on the low refractive index layer 32 from the light guide 31. Refracts on.

The light incident on the prism layer 4 is incident on the inclined surface 412 of the first back prism 41 or the inclined surface 422 of the second back prism 42 as shown in FIG. Of the light incident on the inclined surface 412 or the inclined surface 422, light incident at an incident angle larger than the critical angle φ 3 between the prism layer 4 and the air layer is totally reflected toward the light exit surface 312. Since the critical angle φ3 = arcsin (1 / n3), for example, when n1 = n3 = 1.59, φ3 is about 39 °.

Further, light incident on the inclined surface 412 or the inclined surface 422 at an angle equal to or less than the critical angle φ3 is refracted and emitted from the inclined surface 412 or the inclined surface 422 so as to approach the light guide 31. The light emitted from the inclined surface 412 is refracted and incident on the vertical surface 421 of the second back prism 42. Similarly, the light emitted from the inclined surface 422 is refracted and reincident on the vertical surface 411 of the first back prism 41.

In this way, by repeatedly entering and exiting the first back prism 41 or the second back prism 42 on the back side of the prism layer 4, the incident angle to the inclined surface 412 or the inclined surface 422 gradually increases, Finally, the light is totally reflected by the inclined surface 412 or the inclined surface 422. The light totally reflected by the inclined surface 412 or the inclined surface 422 enters the light guide 31 from the low refractive index layer 32 and the low refractive index layer 32 from the prism layer 4, and from the light exit surface 312 of the light guide 31. Exit.

Since the refractive index n2 of the low refractive index layer 32 is 1.42 (about 1.10 to about 1.35) and the refractive index of the air layer is about 1, the light guide 31 and the air layer have a refractive index n2. The critical angle φ1 is smaller than the critical angle φ2 between the light guide 31 and the low refractive index layer 32. For this reason, almost all the light incident on the light guide 31 is incident on the low refractive index layer 32. That is, the light incident on the light guide 31 from the light incident surface 311 is once incident on the low refractive index layer 32 and the prism layer 4 and reflected by the first back prism 41 or the second back prism 42 to be guided to the light guide. After returning to 31, the light exits from the light exit surface 312.

As described above, the angle of the light incident on the low refractive index layer 32 is gradually decreased by repeating the reflection, so that the light incident on the low refractive index layer 32 is limited. Thereby, it is possible to prevent a large amount of light from entering the low refractive index layer 32 from the light guide 31 or to prevent light from entering, and the luminance distribution in the Y direction of the light emitted from the light exit surface 312. Can be made uniform.

In addition, a plurality of light sources 21 as point light sources are arranged along the X direction, and diffusion prisms 33 extending in the Y direction and arranged in the X direction are formed on the light exit surface 312 of the light guide 31. Thus, since the light incident from the light incident surface 311 is diffused in the X direction by the diffusion prism 33, the luminance distribution in the X direction of the light emitted from the light exit surface 312 can be made uniform.

Next, the viewing angle of light emitted from the backlight unit 2 will be described with reference to the drawings. In FIG. 5, the optical axis of the light reflected by the first back prism 41 and the second back prism 42 is indicated by a one-dot chain line. As shown in FIG. 5, in the backlight unit 2 that is the illumination device according to the present invention, the viewing angle δ is ensured by alternately arranging the first back prism 41 and the second back prism 42 that are inclined surfaces. is doing. Hereinafter, the viewing angle δ of the light emitted from the backlight unit 2 will be described in detail.

As shown in FIG. 5, the inclination angle θ1 of the inclined surface 412 is larger than the inclined surface θ2 of the inclined surface 422. As a result, the incident angles of light incident on the inclined surface 412 and the inclined surface 422 are shifted by θ1−θ2. Thus, even when light having the same angle with respect to the emission surface 312 is incident, the light incident on the inclined surface 412 is incident on the inclined surface 422 on the near side, that is, on the side close to the light incident surface 311. Is reflected to the far side, that is, the side far from the light incident surface 311.

Since the light incident on the low refractive index layer 32 has a spread of about 2 × β in the Y direction, it is reflected by the first back prism 41 and the second back prism 42 and is emitted from the light exit surface 312. Have spread angles of δ1 and δ2, respectively. Since the first back prism 41 and the second back prism 42 are arranged close to each other, the viewing angle δ of the light emitted from the light exit surface 312 of the light guide plate 3 is the first back prism 41 and the second back prism. It is determined by the difference in inclination angle (θ1−θ2) of the prism 42 and the spread angles (δ1, δ2) of the emitted light. Further, the spread angles δ 1 and δ 2 are determined by the inclination angle β of the light guide prism 35.

As described above, the viewing angle δ of the light emitted from the light guide plate 3 is determined by the heights of the first back prism 41 and the second back prism 42, the tilt angles θ1 and θ2, and the tilt angle β of the light guide prism 35. Is done.

For example, assuming that the tilt angle of the back prism that reflects so that the center of the spread of the light emitted from the light exit surface 312 is orthogonal to the light exit surface 312 is θ0 (reference angle), the tilt angle θ1 and the tilt angle θ2. In order to satisfy the following conditions:
(Θ1 + θ2) / 2 = θ0 (1)
θ1> θ2 (2)
Thereby, since the light reflected by the inclined surfaces having different inclination angles is continuously emitted, the viewing angle δ of the emitted light is widened. Further, by determining the inclination angle θ1 and the inclination angle θ2 so as to suppress the overlap of these lights, luminance unevenness due to the overlap of the lights is suppressed.

Then, in the backlight unit 2, the inclination angles of the first back prism 41 and the second back prism 42 were changed, and the effect was verified by simulation. The results of verification will be described below with reference to the drawings. FIG. 7 is a diagram showing the angle luminous intensity when a rear prism having a plurality of angular differences is used, and FIG. 8 is a graph showing the change in angular luminous intensity due to the angular difference of the rear prism. Needless to say, the inclination angle θ1 and the inclination angle θ2 satisfy the above-mentioned (1) and (2).

The vertical axis in FIG. 7 is a normalized value obtained by normalizing the luminance with the peak value, and the horizontal axis indicates the viewing angle on the basis. 7 shows that the difference (θ1−θ2) between the tilt angle θ1 of the first back prism 41 and the tilt angle θ2 of the second back prism 42 is 0 ° (conventional), 2 °, 3 °. The angular distribution in the Y direction of the light emitted from the light exit surface 312 is shown. As shown in FIG. 7, the larger the angle difference (θ1−θ2), the wider the horizontal direction. This indicates that the angular luminous intensity (that is, the viewing angle) is widened by increasing the angular difference (θ1−θ2).

FIG. 8 shows the relationship between the peak half-value angle and the difference between the inclination angles of the back prisms obtained from the diagram shown in FIG. As shown in FIG. 8, the peak half-value angle was about 10.5 ° when the angle difference (θ1−θ2) was 0 °, whereas it was about 14 when the angle difference (θ1−θ2) was 2 °. When the angle difference (θ1−θ2) is 3 °, it is about 17.2 °.

As described above, it is effective to increase the angular luminous intensity of the light emitted from the light exit surface 312 of the light guide 31 by providing the rear prism having different inclination angles and increasing the angle difference. Recognize. Thereby, the viewing angle of the light emitted from the backlight unit 2 can be widened.

Further, by using the illumination device of the present invention, it is possible to suppress luminance unevenness and widen the viewing angle without using an optical sheet such as a prism sheet or a lens sheet.

(Second Embodiment)
Another example of the lighting device according to the present invention will be described with reference to the drawings. FIG. 9 is an enlarged cross-sectional view of another example of a backlight unit which is a lighting device according to the present invention. FIG. 9 is an enlarged view of the prism layer 4b of the backlight unit 2B. The backlight unit 2B shown in FIG. 9 has the same structure as that of the backlight unit 2 except for the light guide plate 3b including the prism layer 4b. Detailed description of the portion is omitted.

As shown in FIG. 9, the prism layer 4b provided in the light guide plate 3b of the backlight unit 2B includes a third back prism 43 in addition to the first back prism 41 and the second back prism 42. Similar to the first back prism 41 and the second back prism 42, the third back prism 43 is a ridge that has a triangular cross section and extends in the X direction. The first back prism 41, the second back prism 42, and the third prism 43 are arranged in this order from the light incident surface 311 side. The first back prism 41, the second back prism 42, and the third back prism 43 form a back prism group, and the back prism group is arranged in the Y direction on the back side of the prism layer 4b.

The third back prism 43 includes a vertical surface 431 and an inclined surface 432 inclined at an inclination angle θ3 with respect to a direction orthogonal to the incident surface 311 (Y direction). The spread angle of the light reflected by the inclined surface 432 and emitted from the light exit surface 312 is δ3.

Further, the inclination angle θ3 of the inclined surface 432 of the third back prism 43 is smaller than the inclination angle θ1 of the first back prism 41 and the inclination angle θ2 of the second back prism 42. That is, θ1> θ2> θ3.

Since the behavior of light incident from the light incident surface 311 (reflection on the light exit surface 312 and the back surface 313) is the same, it is omitted here. The light incident on the low refractive index layer 32 from the light guide 31 is reflected by the inclined surface 412 of the first back prism 41, the inclined surface 422 of the second back prism 42, and the inclined surface 432 of the third back prism 43. The light passes through the refractive index layer 32 and the light guide 31 and exits from the light exit surface 312 of the light guide 31.

At this time, the traveling direction of the light reflected by the inclined surface 412, the inclined surface 422, and the inclined surface 432 is determined by the inclination angles θ1, θ2, and θ3. That is, the light reflected by the inclined surface 412 having the large inclination angle θ1 travels to the side closer to the incident surface 311 and the light reflected from the inclined surface 432 having the small inclination angle θ3 travels to the side far from the incident surface 311. The light reflected by the inclined surface 422 having the inclination angle θ2 between the inclination angle θ1 and the inclination angle θ3 is reflected in the direction between the lights reflected by the other two surfaces.

The light reflected by each inclined surface has a spread of δ1, δ2, and δ3, and θ1, θ2, θ3, and β are determined so that the light having the spread reflected by each surface continues. The viewing angle δ of the light emitted from the light exit surface 312 can be widened.

As described above, the viewing angle δ of the light emitted from the light guide plate 3b includes the heights of the first back prism 41, the second back prism 42, and the third back prism 43, the tilt angles θ1, θ2, θ3, and the light guide. It is determined by the inclination angle β of the prism 35.

For example, assuming that the tilt angle of the back prism that reflects so that the center of the spread of the light emitted from the light exit surface 312 is orthogonal to the light exit surface 312, is the tilt angle θ1 and the tilt angle θ2. And the inclination angle θ3 is formed so as to satisfy the following condition.
(Θ1 + θ2 + θ3) / 3 = θ0 (3)
θ2 = θ0 (4)
| Θ1-θ0 | = | θ3-θ0 | (5)
θ1>θ2> θ3 (6)
Thereby, the light reflected by the inclined surfaces having different inclination angles is emitted in the respective directions at the predetermined spread angles δ1, δ2, and δ3, so that the viewing angle δ of the emitted light is widened. Further, by determining the inclination angle θ1, the inclination angle θ2, and the inclination angle θ3 so that these lights continue and suppress overlapping, luminance unevenness due to discontinuous or overlapping light is suppressed. Is done.

Further, the angle difference (θ1−θ2) between the first rear prism 41 and the second rear prism 42 is the same as that of the backlight unit 2, and further between the first rear prism 41 and the second rear prism 42. Alternatively, the third rear prism 43 having an inclination angle between θ1 and θ2 may be disposed.

In the backlight unit 2B, the tilt angles of the first back prism 41, the second back prism 42, and the third back prism 43 were changed, and the effect was verified. The results of verification will be described below with reference to the drawings. FIG. 10 is a graph showing the change in the angle luminous intensity due to the angle difference of the back prism.

FIG. 10 shows the angle difference (θ1-θ2) between the tilt angle θ1 of the first back prism 41 and the tilt angle θ3 of the second back prism 42 on the horizontal axis, and the peak half-value angle on the vertical axis. Note that the calculation of the peak half-value angle is performed by obtaining the angular distribution of the emitted light by a backlight unit having three different rear prisms in the same manner as in FIG. Needless to say, the above conditions (3) to (6) are satisfied. Since the above condition is satisfied, the angle difference (θ1−θ2) is determined, and (θ2−θ3) is also determined.

As shown in FIG. 10, when the angle difference (θ1-θ2) is 1 °, the peak half-value angle is about 12 °, and when the angle difference (θ1-θ2) is 2 °, the peak half-value angle is about 15 ° and the angle difference ( When θ1-θ2) is 3 °, the peak half-value angle is about 20 °.

As described above, it is possible to increase the angular luminous intensity (that is, the viewing angle) of the light emitted from the light exit surface 312 of the light guide 31 by providing the rear prism having different inclination angles and increasing the angle difference. It turns out that it is effective.

The remaining effects of the second embodiment are the same as those of the first embodiment.

In the above example, the reference angle θ0 is set so that the front of the lighting device is the center of the viewing angle, but the present invention is not limited to this, and the reference angle θ0 is adjusted. It is possible to adjust the center of the viewing angle. For example, by changing the reference angle θ0, it is possible to bring the viewing angle of the emitted light closer to the light source side or the opposite side of the light source.

Furthermore, in this embodiment, the prism layer 4b is configured to include the back prisms having three different tilt angles, but may be configured to include the back prisms having three or more different tilt angles.

In this case, between the tilt angles of the back prisms in the back prism group,
If the inclination angle θm (m = 1, 2,...) Of the m-th rear prism from the light incident surface side is (Σθ _n ) / n = θ _t
| Θ ₁ −θ _t | = | θ _n −θ _t |, | θ ₂ −θ _t | = | θ _n−1 −θ _t |,.
θ _n <θ _n-1
(However, n is an integer of 3 or more)
It is preferable that this relationship is established.

In addition, it is not always necessary to satisfy this condition, and the prism layer having a rear prism having an inclination angle that can widen the angular luminous intensity (viewing angle) of the emitted light and suppress unevenness in luminance of the emitted light is widely used. Can be adopted. Moreover, the structure which equips all the back prisms of a prism layer with the inclination angle different from others may be sufficient. In this case, it is possible that all the back prisms formed in the prism layer form one back prism group.

(Third embodiment)
Still another example of the illumination device according to the present invention will be described with reference to the drawings. FIG. 11 is a perspective view of still another example of the light guide plate used in the backlight unit which is the illumination device according to the present invention. The light guide plate 3c shown in FIG. 11 has the same configuration as that of the light guide plate 3 except that it has a structure in which a low refractive index layer and a prism layer are integrated. A detailed description of the same parts is omitted.

As shown in FIG. 11, the light guide plate 3 c has a prism layer 4 c directly attached to the back surface 313 side of the light guide 31. The prism layer 4 c is made of the same material as the low refractive index layer 32 of the light guide plate 3. That is, the prism layer 4c is configured to also serve as a low refractive index layer.

According to this configuration, since the low refractive index layer can be omitted, the number of parts can be reduced and the structure can be simplified. In addition, there is only one dissimilar material interface between the light guide 31 and the prism layer 4c, which is likely to cause defects (mixing of air, poor contact, etc.), and it is easy to increase the yield of the light guide plate 3c.

Also, since the number of interfaces through which light passes can be reduced, it is possible to suppress attenuation when passing through the interface, and to increase the light utilization efficiency accordingly. The prism layer 4c is made of the same material as that of the low refractive index layer 32. However, the prism layer 4c is not limited to this, and is smaller than the refractive index of the light guide 31, and the critical angle is determined in advance. It is sufficient if it is made of a material having a refractive index that falls within the specified range.

The other effects of the third embodiment are the same as those of the first embodiment and the second embodiment.

(Fourth embodiment)
Still another example of the backlight unit that is the illumination device according to the present invention will be described with reference to the drawings. FIG. 12 is a side view of another example of a backlight unit which is a lighting device according to the present invention. 13 is an image diagram of the viewing angle of the emitted light when the difference in viewing angle is 5 ° in the backlight unit shown in FIG. 2, and FIG. 14 is the angle of viewing angle in the backlight unit shown in FIG. It is an image figure of the viewing angle of the emitted light when a difference is 5 degrees.

As shown in FIG. 12, the backlight unit 2D has the same configuration as the backlight unit 2 except that it includes a scattering sheet 5 on the front side of the light guide plate 3 (so as to face the light exit surface 312). The same parts are denoted by the same reference numerals, and detailed description of the same parts is omitted.

In the backlight unit according to the present invention, the viewing angle δ of the light emitted from the light guide plate 3 is the inclination angle θ1 of the inclined surface 412 of the first back prism 41 and the inclination angle θ2 of the inclined surface 422 of the second back prism 42. Determined by. More specifically, it is determined by the angle difference (θ1−θ2) between the inclination angle θ1 and the inclination angle θ2. That is, as the angle difference (θ1−θ2) increases, the viewing angle δ of light emitted from the light guide plate 3 increases.

When the viewing angle δ becomes larger than a certain angle, that is, when the angle difference (θ1−θ2) becomes larger than a certain value, a region irradiated with the light reflected by the first back prism 41 (a spreading region) ) And the area irradiated with the light reflected by the second back prism 42 may be too far apart. In this case, the portion (peak) where the luminance of each light is the highest is greatly shifted, and two peaks may appear in the viewing angle δ of the light emitted from the light guide plate 3 (see FIG. 13).

If there are two peaks within the viewing angle δ of the emitted light, the luminance increases at the peak, which may be recognized as luminance unevenness. Therefore, in the backlight unit 2D, the dispersion sheet 5 is disposed so as to face the light exit surface 312 of the light guide plate 3 in order to increase the viewing angle δ and disperse two peaks generated within the range of the viewing angle δ. is doing. As shown in FIG. 14, when the light emitted from the light guide plate 3 passes through the dispersion sheet 5, the peak is dispersed, and the general luminance distribution of the light emitted from the backlight unit having the peak at the center portion Become.

The dispersion sheet 5 is an optical sheet that disperses light passing therethrough, and reduces the partial concentration of light by passing through the dispersion sheet 5. Examples of the dispersion sheet 5 include a diffusion film for a liquid crystal display. However, the dispersion sheet 5 is not limited to this, and a wide variety of structures and configurations can efficiently disperse light passing therethrough. Can be adopted.

Further, by adopting such a configuration for the backlight unit 2D, it is possible to widen the viewing angle δ of the emitted light and to suppress uneven brightness.

Further, in the present embodiment, the case of the light guide plate 3 of the first embodiment in which the prism layer 4 including the back prisms having two inclined surfaces having different inclination angles is described, but the present invention is not limited thereto. However, the same effect can be obtained with a structure including three or more back prisms having different inclination angles or a structure in which the low refractive index layer and the prism layer are integrally formed.

In the above-described embodiment, the liquid crystal display device is described as an image display device using the illumination device of the present invention. However, the present invention is not limited to this, and the illumination device according to the present invention is a transmissive image display. It can be widely adopted in the apparatus.

As mentioned above, although embodiment of this invention was described, this invention is not limited to this content. The embodiments of the present invention can be variously modified without departing from the spirit of the invention.

The lighting device and the display device according to the present invention can be used for a display unit of an electronic device such as an information home appliance, a notebook PC, a mobile phone, or a game device.

DESCRIPTION OF SYMBOLS 1 Liquid crystal panel 11 Array substrate 12 Opposite substrate 13 Polarizing film 2 Backlight unit 20 Frame 21 Light source 211 LED
22 Reflective sheet 3 Light guide plate 31 Light guide 311 Light incident surface 312 Light exit surface 313 Back surface 32 Low refractive index layer 33 Diffusion prism 331 Inclined surface 34 Flat portion 35 Light guide prism 351 Vertical surface 352 Inclined surface (first inclined surface)
4 Prism layer 41 First back prism 411 Vertical surface 412 Inclined surface (second inclined surface)
42 Second back prism 421 Vertical surface 422 Inclined surface (second inclined surface)
43 Third back prism 431 Vertical surface 432 Inclined surface (second inclined surface)
5 Scattering sheet

Claims

A light source;
A light guide that has a light incident surface facing the light source on a side surface, guides light incident from the light incident surface, and emits light as planar light from a light exit surface on the front side;
A plurality of light guide prisms formed on the light exit surface, including a first inclined surface that is inclined and opposed to the light incident surface, and is arranged in an optical axis direction of the light source;
A low refractive index layer that is installed adjacent to the back surface of the light guide and has a lower refractive index than the light guide;
A prism layer disposed adjacent to the opposite side of the light guide of the low refractive index layer;
A plurality of back surfaces formed on the opposite side of the low refractive index layer of the prism layer, including a second inclined surface inclined and opposed to the light incident surface, wherein the second inclined surfaces have different inclination angles with respect to the bottom surface; With a prism,
The illumination device, wherein the plurality of rear prisms are arranged in the optical axis direction of the light source so as not to be adjacent to rear prisms having the same inclination angle.
2. The illumination device according to claim 1, wherein a rear prism group in which the rear prisms are arranged in the optical axis direction of the light source is arranged so that the inclination angle becomes smaller as the prism layer moves away from the light incident surface. .
The illuminating device according to claim 2, wherein an inclination angle of each rear prism of the rear prism group is set so that an irradiation area of light reflected by an inclined surface of each rear prism is continuous.
The tilt angle of each back prism in the back prism group is:
When the inclination angle of the m-th rear prism from the light incident surface side is θ m (m is an integer),
Σθ n / n = θ t
| Θ n −θ t | = | θ 1 −θ t |, | θ n−1 −θ t | = | θ 2 −θ t |
(Where n is an integer greater than or equal to 3)
The lighting device according to claim 2 or 3, wherein the relational expression is established.
　 A plurality of the light sources are arranged in the longitudinal direction of the light incident surface,
5. The illumination device according to claim 1, wherein the light guide includes a plurality of diffusion prisms that extend in an optical axis direction of the light source and are arranged in a longitudinal direction of the light incident surface.
The lighting device according to any one of claims 1 to 5, further comprising a scattering sheet that is installed so as to cover the light output surface of the light guide plate and that scatters light emitted from the light output surface.
The lighting device according to any one of claims 1 to 6, wherein the low refractive index layer and the prism layer are integrally formed of a material having a refractive index smaller than a refractive index of the light guide.
A display device comprising: the illumination device according to any one of claims 1 to 7; and a display panel installed to face the light exit surface of the light guide.