JP2011129465A - Backlight and liquid crystal display - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a backlight with luminance unevenness alleviated in the vicinity of a frame, and capable of restraining degradation of use efficiency of emission light from a light source. <P>SOLUTION: The backlight is provided with a linear light source, a reflecting member having a reflecting face for reflecting light emitted from the linear light source, an optical element group arranged in opposition to the reflecting face of the reflecting member, and a hollow light guide space formed between the reflective face of the reflecting member and an incident face of the optical element group and equipped with an end part having the linear light source arranged. The optical element group includes a first, a second and a third optical elements sequentially arranged from a side of the light guide space, and the first and the second optical elements have a plurality of prism lenses of a columnar shape aligned having a triangular cross section, with lens faces opposed to the reflecting face of the reflecting member, and with a ridge line of the prism lenses in a crossing relation with the linear light source. The third optical element has a function of diffusing light, and there is a space formed between the second optical element and the third optical element. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a backlight and a liquid crystal display device including the backlight. Specifically, the present invention relates to an edge light type backlight.

  Since the liquid crystal display device is not a self-luminous display device, a backlight is provided behind the liquid crystal display device. There are various types of backlights, but for medium-sized liquid crystal display devices such as notebook PCs (personal computers) and small-sized liquid crystal display devices such as cellular phones, edge-light type backlights are used. Is widely adopted.

  An edge-light type backlight is a system in which light is guided in a direction parallel to the light emitting surface from a linear light source on the back side of the light emitting surface, and the light is refracted, reflected, and diffused and guided to the light emitting surface. It is a backlight. 2. Description of the Related Art Conventionally, as an edge light type backlight, a light guide path method in which radiated light emitted from a linear light source on the back side of a light emitting surface is guided in a direction parallel to the light emitting surface by a light guide plate. However, since this light guide type backlight uses a light guide plate, it is heavy and increases the weight of the electronic device on which the liquid crystal display device is mounted. Therefore, as an edge-light type backlight, a hollow type backlight that guides light in a direction parallel to the light emitting surface by reflecting the radiated light from a linear light source on the back side of the light emitting surface in a hollow light guide space. Has been proposed (see, for example, Patent Documents 1 and 2).

  FIG. 1A is a cross-sectional view showing a configuration of a conventional hollow type edge light type backlight. As shown in FIG. 1A, the edge light type backlight 101 includes an optical element group 110, a large number of point light sources 111, a bottom plate 112, and a middle frame 116. A hollow light guide space 112 a is formed between the reflecting surface Sr of the bottom plate 112 and the incident surface Si of the optical element group 110. A liquid crystal panel 102 is provided on the middle frame 116, and an image is displayed by controlling light emitted from the backlight 101 by the liquid crystal panel 102. A large number of point light sources 111 are arranged in a line to form a linear light source. The optical element group 110 includes a plurality of optical elements selected according to desired characteristics. The optical element group 110 having a general configuration includes an optical element group including a prism sheet 113, a diffusion plate 114, and a diffusion sheet 115.

JP 2007-87658 A

Japanese Patent No. 3549919

  However, in the edge light type backlight having the configuration shown in FIG. 1A, light emitted from the point light source 111 in the liquid crystal panel direction (directly above the point light source 111) leaks from the display surface. Due to this light leakage, as shown in FIG. 2, uneven brightness (also referred to as a hot spot) 121 occurs in the vicinity of the frame of the liquid crystal display device in the vicinity of the point light source 111. Further, due to the above-described light leakage, the emitted light from the point light source 111 is lost, and there is a problem that the utilization efficiency of the emitted light from the point light source 111 is lowered. As a countermeasure against this, as shown in FIG. 1B, it is conceivable to arrange a light shielding portion 116a on the point light source 111 to prevent light leakage. However, even if such a technique is adopted, since the light emitted from the point light source 111 is absorbed by the light shielding portion 116a, the problem of a decrease in the utilization efficiency of the light emitted from the point light source 111 is avoided. It is difficult. In view of this, as shown in FIG. 1C, a technique of arranging a reflecting plate 117 on the light shielding portion 116a is conceivable. However, when the reflecting plate 117 is disposed, the frame unevenness occurs when the reflecting plate 117 is interrupted.

  The above-mentioned luminance unevenness in the vicinity of the frame and the use efficiency of the radiated light from the light source are not only the hollow type edge light type backlight that does not use the light guide plate, but also the light guide type edge light type backlight that uses the light guide plate. The same problem occurs in the light.

  Accordingly, an object of the present invention is to provide a backlight capable of reducing the occurrence of luminance unevenness in the vicinity of the frame and suppressing the use efficiency of radiated light from the light source, and a liquid crystal display device including the backlight. There is.

In order to solve the above-mentioned problem, the first invention
A linear light source that emits light;
A reflective member having a reflective surface for reflecting light emitted from the linear light source;
An optical element group disposed opposite to the reflecting surface of the reflecting member and having an incident surface on which light emitted from the linear light source is incident;
A hollow light guide space formed between the reflecting surface of the reflecting member and the incident surface of the optical element group and having an end portion on which the linear light source is disposed, and
The optical element group includes first, second, and third optical elements that are sequentially arranged from the light guide space side,
The first and second optical elements have lens surfaces on which a large number of prism lenses are arranged,
The prism lens is a columnar body extending in one direction and having a triangular cross section,
The lens surface faces the reflecting surface of the reflecting member, and the ridge line of the prism lens and the linear light source arranged on the end surface of the light guide space are orthogonal to each other,
The third optical element has a function of diffusing light,
This is a backlight in which a space is formed between the second optical element and the third optical element.

The second invention is
A linear light source that emits light;
A reflective member having a reflective surface for reflecting light emitted from the linear light source;
An optical element group disposed opposite to the reflecting surface of the reflecting member and having an incident surface on which light emitted from the linear light source is incident;
A light guide member disposed between the reflection surface of the reflection member and the incident surface of the optical element group, and having an end surface on which the linear light source is disposed,
The optical element group includes first, second, and third optical elements that are sequentially arranged from the light guide space side,
The first and second optical elements have lens surfaces on which a large number of prism lenses are arranged,
The prism lens is a columnar body extending in one direction and having a triangular cross section,
The lens surface faces the reflecting surface of the reflecting member, and the ridge line of the prism lens and the linear light source arranged on the end surface of the light guide member are orthogonal to each other,
The third optical element has a function of diffusing light,
This is a backlight in which a space is formed between the second optical element and the third optical element.

In the present invention, the space formed between the second optical element and the third optical element includes a minute space formed by minute protrusions provided on at least one of the facing surfaces of both. Almost 90 degrees includes 90 degrees.
The first, second, and third optical elements preferably have a sheet shape or a plate shape. The sheet includes a film.

  In the first and second inventions, the first and second optical elements having lens surfaces on which a large number of prism lenses are arranged are arranged so that the lens surface is on the light guide space side on the hollow light guide space. It is arranged. Accordingly, the light from the linear light source is repeatedly refracted by the first and second optical elements, and the incident angle of the light with respect to the back surfaces of the first and second optical elements is set to be close to that of the third optical element. The second optical element can be made larger. Therefore, the second optical element closer to the third optical element among the first and second optical elements can reflect more light on the back surface and return it toward the light guide space. That is, leakage of light emitted from the linear light source in the liquid crystal panel direction (directly above the linear light source) can be reduced. Further, the light reflected on the back surfaces of the first and second optical elements and returned to the light guide space is reflected by the reflecting surface of the reflecting member and can be used again.

  Here, the back surfaces of the first and second optical elements mean surfaces opposite to the prism surface on which many prism lenses are arranged. Further, the incident angle of light with respect to the back surfaces of the first and second optical elements is the normal line of the back surfaces of the first and second optical elements and the light emitted from the linear light source and incident on the back surfaces. Means the angle between

  As described above, according to the present invention, it is possible to reduce the occurrence of luminance unevenness in the vicinity of the frame and to suppress the decrease in the utilization efficiency of the radiated light from the linear light source.

1A to 1C are cross-sectional views illustrating a configuration of a conventional backlight. FIG. 2 is a top view showing luminance unevenness generated near the frame of the liquid crystal display device when a conventional backlight is used. FIG. 3 is an exploded perspective view showing one structural example of the liquid crystal display device according to the first embodiment of the present invention. FIG. 4 is an enlarged sectional view showing an end portion of the liquid crystal display device according to the first embodiment of the present invention. FIG. 5A is a perspective view illustrating a configuration of an optical element group including one prism sheet. FIG. 5B is a perspective view illustrating a configuration of an optical element group including two prism sheets. FIG. 6A is a schematic diagram for explaining a path of emitted light in the optical element group shown in FIG. 5A. FIG. 6B is a schematic diagram for explaining the path of the emitted light in the optical element group shown in FIG. 5B. FIG. 7 is an exploded perspective view showing a configuration example of the liquid crystal display device according to the second embodiment of the present invention. FIG. 8 is an enlarged sectional view showing an end portion of the liquid crystal display device according to the second embodiment of the present invention. FIG. 9A is a plan view showing a lens surface of a prism sheet in a liquid crystal display device according to a third embodiment of the present invention. FIG. 9B is a cross-sectional view taken along the line II shown in FIG. 9A. 9C to 9E are cross-sectional views taken along the line II-II shown in FIG. 9A. FIG. 10 is a graph showing the luminance distribution of the liquid crystal display devices of Example 1 and Comparative Example 1.

Embodiments of the present invention will be described in the following order with reference to the drawings.
1. First embodiment (an example of a liquid crystal display device in which the light guide portion is a hollow light guide space: see FIG. 3)
2. Second Embodiment (Example of a liquid crystal display device in which the light guide portion is a light guide plate: see FIG. 7)

<1. First Embodiment>
[1.1. Configuration of liquid crystal display device]
FIG. 3 is an exploded perspective view showing one structural example of the liquid crystal display device according to the first embodiment of the present invention. FIG. 4 is an enlarged sectional view showing an end portion of the liquid crystal display device according to the first embodiment of the present invention.

  As shown in FIG. 3, the liquid crystal display device includes a backlight 1 that emits light, and a liquid crystal panel 2 that displays an image by temporally and spatially modulating the light emitted from the backlight 1. A front frame (also referred to as a frame) 3 having a display window 3 a is disposed on the liquid crystal panel 2, and the liquid crystal panel and the backlight 1 are integrated.

(LCD panel)
Examples of the liquid crystal panel 2 include a twisted nematic (TN) mode, a super twisted nematic (STN) mode, a vertically aligned (VA) mode, and a horizontal alignment (In-Plane Switching: IPS). Mode, Optically Compensated Birefringence (OCB) mode, Ferroelectric Liquid Crystal (FLC) mode, Polymer Dispersed Liquid Crystal (PDLC) mode, Phase Transition Guest Host (Phase) A display mode such as Change Guest Host (PCGH) mode can be used.

(Backlight)
The backlight 1 is a so-called edge light type hollow backlight. The backlight 1 includes a large number of point light sources 11, a bottom frame 12, an optical element group 10, a middle frame 16, and a housing 17. The casing 17 has a slightly shallow box shape in which one main surface is opened and the other main surface is closed, and a number of point light sources 11, a bottom frame 12, an optical element group 10, The middle frame 16 is accommodated. The bottom frame 12 has a reflecting surface Sr that reflects the radiated light emitted from the light source, and the optical element group 10 has an incident surface Si on which the radiated light emitted from the light source is incident. A hollow light guide space 12 a is formed between the reflective surface Sr of the bottom frame 12 and the incident surface Si of the optical element group 10.

(light source)
A large number of point light sources 11 are linearly arranged at one or both ends of the light guide space 12a to form a linear light source. Examples of the point light source 11 include organic electroluminescence (OEL), inorganic electroluminescence (IEL), and light emitting diode (LED). The light source is not limited to the point light source 11, but instead of a large number of linear light sources 11 arranged in a straight line, a cold cathode fluorescent lamp (CCFL), a hot cathode fluorescent tube ( A linear light source such as Hot Cathode Fluorescent Lamp (HCFL) may be used.

(Bottom frame)
As described above, the bottom frame 12 has the reflecting surface Sr on the surface facing the optical element group 10, and the light emitted from the point light source 11 is reflected by the reflecting surface Sr. Here, the light reflected once or more than once by the reflecting surface Sr of the bottom frame 12 and the optical element group 10 is also referred to as light emitted from the point light source 11.

  For the reflection surface Sr, for example, a reflection sheet (reflection member) can be used. The reflection sheet is for increasing the light utilization efficiency by diffusing or reflecting a part of the light emitted from the point light source 11. Examples of the reflective sheet (reflective film) include a diffuse reflective (white) reflective sheet and a specular reflective reflective sheet, and a specular reflective reflective sheet is preferred. When a specular reflection type reflection sheet is used, the light emitted from the linear light source is incident in the in-plane direction of the prism sheet 13, is repeatedly reflected on the front and back surfaces of the prism sheet 13, and is transmitted from the prism sheet 13 to the diffusion plate 14. Is difficult to be emitted, and the light is repeatedly reflected inside the light guide space 12 a and the prism sheet 13. Thereby, the leakage of the light emitted from the linear light source in the liquid crystal panel direction (directly above the linear light source) can be reduced. Further, the light reflected on the back surface of the prism sheet 13 and returned to the light guide space 12a can be used again by being reflected by the reflecting surface Sr of the reflecting member such as the reflecting sheet. As a result, the luminance is improved. As the diffuse reflection type reflection sheet, for example, a white polyester film or an interface multiple reflection sheet (for example, an ultra-white polyester film) can be used. As the specular reflection type reflection sheet, for example, a metal thin film such as an aluminum (Al) thin film or a silver (Ag) thin film can be used.

  Furthermore, it is preferable to form a dot pattern, which is a large number of diffusion parts for scattering light, on the surface of the reflection sheet. By forming these dot patterns, the light from the linear light source is incident in the thickness direction of the prism sheet 13, so that the light can be efficiently emitted from the prism sheet 13 to the diffusion plate 14. The dot pattern density is preferably adjusted in the screen. For example, it is preferable that the side of the linear light source is sparse and denser as the distance from the linear light source increases. This is because the luminance in the screen can be adjusted uniformly.

(Optical element group)
The optical element group 10 includes two prism sheets (first and second optical elements) 13 and a diffusion plate (third optical element) 14 that are sequentially arranged from the light guide space 12a side. . That is, the diffusion plate 14 is disposed on the liquid crystal panel 2 side, and the two prism sheets 13 are disposed on the reflective surface Sr side. The number of prism sheets 13 is not limited to two, and the number of prism sheets 13 can be three or more according to desired characteristics. The optical element group 10 may further include one or more optical elements 15 disposed between the diffusion plate 14 and the liquid crystal panel 2 from the viewpoint of improving optical characteristics.

  A space is formed between the prism sheet 13 disposed on the diffusion plate 14 side of the two prism sheets 13 and the diffusion plate 14. By forming a space in this way, the refractive index difference with the back surface of the prism sheet 13 as a boundary surface is increased as compared with the case where both are brought into close contact with each other, and the reflectance of light emitted from the point light source 11 is increased. It is because it can improve. This space may be a minute space formed by minute protrusions provided on at least one of the opposing surfaces of the prism sheet 13 and the diffusion plate 14. The minute protrusions are intended to prevent light diffusion or sticking, and the arithmetic average roughness Ra thereof is, for example, not less than 0.01 μm and not more than 5 μm.

  The optical element group 10 may further include one or two or more optical elements disposed between the two prism sheets 13 and the diffusion plate 14 from the viewpoint of improving optical characteristics (not shown). ) In this case, it is preferable to form a space between the one or more optical elements and the two prism sheets 13. Thus, by forming a space between the two, the refractive index difference with the back surface of the prism sheet 13 as the boundary surface is increased as compared with the case where the two are brought into close contact with each other, and the light emitted from the point light source 11 This is because the reflectance can be improved.

  The prism sheet 13 has a lens surface on which many prism lenses are arranged. The prism lens is a columnar body having a triangular cross section that extends in one direction so as to maintain a uniform cross section. The triangular shape of the cross section of the prism lens is preferably an isosceles triangular shape or an equilateral triangular shape. The apex angle of the prism lens is preferably set to approximately 90 degrees. This is because when the angle is set to approximately 90 degrees, light incident in the in-plane direction of the prism sheet 13 is difficult to be emitted to the diffusion plate 14 side.

  In addition, when the prism lens has a triangular cross section, an ideal triangular shape having substantially no curvature at the top is desirable from the viewpoint of improving front luminance. In order to obtain such an ideal triangular prism lens, for example, a laminate transfer method may be used. That is, an ideal triangular shape can be obtained by supplying a base film such as a roll prepared in advance between the master roll and the nip roll and transferring the shape of the master roll.

  In addition, the lens surface of the prism sheet 13 faces the reflecting surface Sr of the bottom frame 12, and the ridgelines of the prism lens of the prism sheet 13 and a number of point light sources arranged linearly at the end of the light guide space 12a. 11 rows are orthogonal to each other. This is because the light incident in the in-plane direction of the prism sheet 13 is not easily emitted to the diffusion plate 14 side. That is, light can be guided in the ridge line direction of the prism sheet 13. The refractive index of the prism sheet 13 is preferably 1.5 or more. When it is less than 1.5, there is a tendency that light emitted to the diffusion plate 14 side increases.

(Diffusion plate)
The diffusing plate 14 has a function of diffusing the emitted light emitted from the multiple point light sources 11 to make the luminance uniform. As the diffusion plate 14, for example, a diffusion plate having a concavo-convex structure for diffusing light on its surface, a diffusing plate containing fine particles having a refractive index different from the main constituent material of the diffusing plate 14, or the above concavo-convex structure And a diffusion plate in which fine particles are combined can be used. As the fine particles, for example, at least one of an organic filler and an inorganic filler can be used. As the fine particles, for example, hollow fine particles and porous fine particles can be used. Moreover, the resin layer containing the concavo-convex structure and / or fine particles is provided on the radiation surface of the diffusion plate 14, for example.

(Other optical elements)
Examples of the optical element 15 disposed between the diffusion plate 14 and the liquid crystal panel 2 include a diffusion sheet, a reflective polarizer, and a prism sheet. When two or more optical elements 15 are arranged, different types of optical elements 15 may be used in combination.

[1.2. Action of optical element group]
FIG. 5A is a perspective view illustrating a configuration example of an optical element group including one prism sheet. FIG. 5B is a perspective view illustrating a configuration example of an optical element group including two prism sheets.
Hereinafter, the operation of the optical element group 10 including one prism sheet (FIG. 5A) and the operation of the optical element group 20 including two prism sheets (FIG. 5B) will be described in comparison.

First, the operation of the optical element group 20 (FIG. 5A) including one prism sheet 13 will be described with reference to FIG. 6A.
First, the light emitted from the point light source 11 in a direction almost immediately above is incident on the inclined surface of the prism sheet 13 at a certain angle. A part of the light incident on the inclined surface is reflected by the inclined surface, and the remaining light enters the prism sheet to form transmitted light. At that time, the transmitted light is refracted and bent so as to rise on the inclined surface. Next, the transmitted light is incident on the back surface of the prism sheet 13, but most of the incident light is not reflected on the back surface but is transmitted and radiated to the diffusion plate 14. This is because the incident angle θ of light with respect to the back surface (the angle formed between the incident light with respect to the back surface and the normal line of the back surface) is small.

  As described above, most of the light emitted from the point light source 11 in the direction immediately above passes through the prism sheet 13 and is diffused by the diffusion plate 14. Therefore, the brightness in the vicinity of the side portion of the liquid crystal panel corresponding to the position just above the point light source 11 is increased. That is, luminance unevenness (hot spot) occurs near the side of the liquid crystal panel.

Next, the operation of the optical element group 10 (FIG. 5B) including the two prism sheets 13 will be described with reference to FIG. 6B.
First, much of the light radiated from the point light source 11 in a direction almost immediately above is transmitted through the prism sheet 13 disposed on the light guide space 12a side, as in the case of the optical element group 20 described above. Next, the light transmitted through the prism sheet 13 enters the inclined surface of the prism sheet 13 disposed on the diffusion plate 14 side. A part of the light incident on the inclined surface is reflected by the inclined surface, and the remaining light enters the prism sheet to form transmitted light. At that time, the transmitted light is refracted and bent so as to rise on the inclined surface. Next, the transmitted light is incident on the back surface of the prism sheet 13, but most of the incident light is reflected on the back surface and returned toward the light guide space. This is because the incident angle θ ₁ of light with respect to the back surface of the prism sheet 13 on the diffusion plate 14 side (the angle formed between the incident light with respect to the back surface and the normal of the back surface) is the back surface of the prism sheet 13 on the light guide space 12 a side. This is because the incident angle θ is larger than the incident angle θ ₂ of the light.

  As described above, when the two prism sheets 13 are arranged in the light guide space, the light emitted from the point light source 11 in the almost right direction guides the one prism sheet 13. Compared with the case where it is arranged in the light space, more of the light is reflected by the prism sheet 13 and returned to the light guide space 12a. Therefore, when two or more prism sheets 13 are arranged on the light guide space 12a, the luminance in the vicinity of the side of the liquid crystal panel corresponding to the position almost directly above the point light source 11 is set to one prism sheet. Compared to the case where 13 is arranged, the height can be lowered. That is, luminance unevenness (hot spot) generated in the vicinity of the side portion of the liquid crystal panel can be reduced.

<2. Second Embodiment>
FIG. 7 is an exploded perspective view showing a configuration example of the liquid crystal display device according to the second embodiment of the present invention. FIG. 8 is an enlarged sectional view showing an end portion of the liquid crystal display device according to the second embodiment of the present invention. In addition, the same code | symbol is attached | subjected to the part similar to the above-mentioned 1st Embodiment, and description is abbreviate | omitted.

  The second embodiment of the present invention is different from the first embodiment in that a light guide plate 18 is provided instead of the hollow light guide space 12a. Examples of the light guide plate 18 include a flat plate shape, a tapered shape, and a wedge shape. When the light guide plate 18 has a tapered shape or a wedge shape, a large number of point light sources 11 are arranged on the end face on one end side with a large thickness. As the material of the light guide plate 18, for example, a transparent plastic such as polymethyl methacrylate (PMMA), polycarbonate (PC), polystyrene (PS), cycloolefin resin (for example, ZEONOR (registered trademark)) is used. it can. Of the main surface of the light guide plate 18, it is preferable to form a dot pattern, which is a large number of diffusion parts for scattering light, on the main surface (back surface) facing the reflecting surface of the bottom frame 12. This dot pattern is formed by, for example, dot printing or injection molding.

<3. Third Embodiment>
FIG. 9A is a plan view showing a lens surface of a prism sheet in a liquid crystal display device according to a third embodiment of the present invention. FIG. 9B is a cross-sectional view taken along the line II shown in FIG. 9A. 9C to 9E are cross-sectional views taken along the line II-II shown in FIG. 9A. The third embodiment of the present invention is different from the first embodiment in that the cross-sectional shape of the prism lens of the prism sheet 13 is different between the both end portions and the central portion of the prism lens. Note that the configuration other than the prism sheet 13 is the same as that of the first embodiment described above, and a description thereof will be omitted.

  The prism lens is a columnar body extending in one direction, and the curvature of the cross-sectional shape becomes gentler from both ends of the prism lens toward the center. In other words, the cross-sectional curvature of the prism lens becomes gentler away from the linear light source. Specifically, for example, the cross-sectional shape of the prism lens at both ends is triangular (see FIG. 10B), whereas the cross-sectional shape of the prism lens at the center is lenticular (see FIG. 10C), and the curvature R is at the top. It is a prism shape (see FIG. 10D) with a mark, or a planar shape (see FIG. 10E). The apex angle of the triangular cross section at both ends is set to, for example, approximately 90 degrees. That is, the cross-sectional shape of both ends is an ideal triangular shape having substantially no curvature at the top. Here, the cross-sectional shape of the prism lens is a cross-sectional shape perpendicular to the ridgeline of the prism lens. The lenticular shape means that the cross-sectional shape perpendicular to the ridge line of the convex portion is an arc shape or a substantially arc shape, or an elliptical arc shape or a substantially elliptical arc part.

  In the third embodiment, the curvature of the cross-sectional shape of the prism lens in the prism sheet 13 is moderated from both ends of the prism lens toward the central portion, so that the luminance unevenness (uniformity) is improved and the whole is improved. Brightness can be improved.

  EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples. However, the present invention is not limited to these examples.

Example 1
First, as an optical element constituting the optical element group, the following two prism sheets, a diffusion plate, and a diffusion sheet were prepared.
Prism sheet (manufactured by Sony Corporation, trade name: LIF): a prismatic prism lens having an isosceles triangle cross section, apex angle of 90 degrees, refractive index of 1.59
Diffuser (made by Teijin Chemicals Ltd., trade name: Panlite Sheet)
Diffusion sheet (Ewa Co., Ltd., trade name: BS912)

Next, a liquid crystal display device having the configuration shown in FIG. 1 was assembled using the prepared optical elements.
In addition, the following were used as a reflection sheet, LED (light source), and a liquid crystal panel.
Reflective sheet (trade name: RF55MGR, manufactured by Tsujiden Co., Ltd.)

(Comparative Example 1)
A liquid crystal panel was assembled in the same manner as in Example 1 except that the number of prism lenses in the optical element group was one.

(Evaluation of luminance uniformity)
First, the backlights of the liquid crystal display devices of Example 1 and Comparative Example 1 were turned on, and it was visually determined whether luminance unevenness occurred in the vicinity of the frame. As a result, in the liquid crystal display device of Example 1, it was found that the luminance unevenness in the vicinity of the frame on the long side of the liquid crystal display device was reduced as compared with the liquid crystal display device of Comparative Example 1.

Next, the luminance distribution in the vertical direction of the liquid crystal display device was measured using a luminance distribution measuring apparatus (Radiant Imaging, Inc., trade name: Prometrics 1200). The result is shown in FIG.
From FIG. 10, it can be seen that, in the liquid crystal display device of Example 1, the increase in luminance near the frame on the long side is reduced as compared with the liquid crystal display device of Comparative Example 1.

  As mentioned above, although embodiment of this invention was described concretely, this invention is not limited to the above-mentioned embodiment, The various deformation | transformation based on the technical idea of this invention is possible.

  For example, the configurations, methods, shapes, materials, numerical values, and the like given in the above-described embodiments are merely examples, and different configurations, methods, shapes, materials, numerical values, and the like may be used as necessary.

  Further, in the above-described embodiment, the optical elements may be integrated by bonding to each other. For example, the diffusion plate and all of the two or more prism sheets may be integrated, or at least two of these optical elements may be integrated. When joining the diffusion plate and the prism sheet on the diffusion plate side, a space is formed between them.

  The configurations of the above-described embodiments can be combined with each other without departing from the gist of the present invention.

  Further, in the above-described embodiment, between the prism sheet disposed on the diffusion plate (third optical element) side of the two prism sheets (first and second optical elements) and the diffusion plate. You may make it contact | adhere both, without forming space. In this case, it is preferable to appropriately select the materials of the two so that the difference in refractive index between the prism sheet and the diffusion plate becomes large.

  In the above-described embodiment, the optical element group has been described as an example in which the two prism sheets are provided on the reflecting surface side of the reflecting member. However, a lens having a three-dimensional shape instead of the two prism sheets. A configuration may be adopted in which one or a plurality of lens sheets having a large number of bodies arranged on one main surface are provided. In this case, the lens sheet is disposed so that one main surface (lens surface) on which the lens bodies are arranged faces the reflecting surface of the reflecting member.

1 Backlight 2 LCD panel 3 Front frame (frame)
DESCRIPTION OF SYMBOLS 10 Optical element group 11 Point light source 12 Bottom frame 12a Light guide space 13 Prism sheet | seat (1st or 2nd optical element)
14 Diffuser (third optical element)
15 Optical element 16 Middle frame 17 Case 18 Light guide plate Sr Reflective surface Si Incident surface

Claims (8)

A linear light source that emits light;
A reflecting member having a reflecting surface for reflecting light emitted from the linear light source;
An optical element group disposed opposite to the reflecting surface of the reflecting member and having an incident surface on which light emitted from the linear light source is incident;
A hollow light guide space formed between the reflecting surface of the reflecting member and the incident surface of the optical element group, and having an end portion on which the linear light source is disposed, and
The optical element group includes first, second, and third optical elements that are sequentially arranged from the light guide space side,
The first and second optical elements each have a lens surface on which a large number of prism lenses are arranged,
The prism lens is a columnar body extending in one direction and having a triangular cross section,
The lens surface is opposed to the reflecting surface of the reflecting member, and the ridgeline of the prism lens and the linear light source disposed on the end surface of the light guide space are orthogonal to each other,
The third optical element has a function of diffusing light,
A backlight in which a space is formed between the second optical element and the third optical element.   The backlight according to claim 1, wherein the linear light source is a number of light emitting diodes arranged linearly along an end surface of the light guide space.   The backlight according to claim 1, wherein a plurality of diffusion portions are provided on the reflection surface of the reflection member.   The backlight according to claim 1, wherein the reflection member is a specular reflection type reflection film.   The backlight according to claim 1, wherein the angle of the top of the prism is approximately 90 degrees. The prism lens is a columnar body extending in one direction and having a triangular cross section at both ends,
The backlight according to claim 1, wherein the curvature of the cross-sectional shape of the columnar body becomes gentler from the both ends of the columnar body toward the central portion. A linear light source that emits light;
A reflecting member having a reflecting surface for reflecting light emitted from the linear light source;
An optical element group disposed opposite to the reflecting surface of the reflecting member and having an incident surface on which light emitted from the linear light source is incident;
A light guide member disposed between a reflection surface of the reflection member and an incident surface of the optical element group, and having an end surface on which the linear light source is disposed,
The optical element group includes first, second, and third optical elements that are sequentially arranged from the light guide space side,
The first and second optical elements each have a lens surface on which a large number of prism lenses are arranged,
The prism lens is a columnar body extending in one direction and having a triangular cross section,
The lens surface is opposed to the reflecting surface of the reflecting member, and the ridge line of the prism lens and the linear light source disposed on the end surface of the light guide member are orthogonal to each other,
The third optical element has a function of diffusing light,
A backlight in which a space is formed between the second optical element and the third optical element.   A liquid crystal display device provided with the backlight described in any one of Claims 1-7.

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