Planar lighting device

Abstract

To provide a planar illumination device with a further narrowed frame.SOLUTION: A planar illumination device of an embodiment includes a light guide plate, a light source, one or more optical sheets, a bottom frame, and a top frame. The light guide plate receives light from a light incident side. The light source emits light to the light incident side of the light guide plate. The optical sheet is disposed on a light exit side of the light guide plate. The bottom frame houses the light guide plate, the light source, and the optical sheet. The top frame includes an opening, engages with the bottom frame and covers a light exit side of the optical sheet. An end portion on the opening side of a side wall of the bottom frame forms a space with a frame portion of the top frame, where the space corresponds to a clearance for an end portion of the optical sheet.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to a surface lighting device. [Background technology]

[0002] A so-called edge-light type planar illumination device is known in which light is incident from a light-entering side surface of a light guide plate and the light is emitted from one main surface of the light guide plate (see, for example, Patent Documents 1 and 2). Such planar illumination devices are used as backlights in liquid crystal display devices.

[0003] In addition, in general surface lighting devices, a top frame with an opening for emitting light is often used as part of the housing, and the part of the top frame that forms the opening for emitting light is called a frame. Recently, mainly from the viewpoint of design, there has been a demand for narrower frames.

[0004] Since the light guide plate and optical sheet, which are components of the surface illumination device, expand and contract due to temperature, a clearance is required in the direction of expansion and contraction between the side wall of the bottom frame that houses them and the light guide plate and optical sheet. If the clearance is too small, the expansion and contraction of the light guide plate and optical sheet cannot be absorbed, making it difficult to hold them and causing deterioration of the optical properties. Moreover, if the clearance is too large, it becomes difficult to achieve a narrow frame.

[0005] Incidentally, the linear expansion coefficient of DBEF (Dual Brightness Enhancement Film), which is widely used as an optical sheet, is anisotropic in two perpendicular directions, with the larger linear expansion coefficient being greater than that of a typical light guide plate, so the relationship between the optical sheet and the bottom frame is dominant in the clearance design. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2003-5160 A [Patent Document 2] JP 2016-213090 A Summary of the Invention [Problem to be solved by the invention]

[0007] However, the arrangement of optical sheets within a typical bottom frame has already been optimized to narrow the frame, and it is becoming difficult to narrow the frame further.

[0008] The present invention has been made in view of the above, and an object of the present invention is to provide a planar lighting device capable of achieving a further narrowing of the frame. [Means for solving the problem]

[0009] In order to solve the above-mentioned problems and achieve the object, a planar lighting device according to one aspect of the present invention includes a light guide plate, a light source, one or more optical sheets, a bottom frame, and a top frame. The light guide plate receives light from a light-entering side. The light source irradiates light onto the light-entering side of the light guide plate. The optical sheet is disposed on the light-exiting side of the light guide plate. The bottom frame houses the light guide plate, the light source, and the optical sheet. The top frame engages with the bottom frame, covers the light-exiting side of the optical sheet, and has an opening. The end of the opening side of the side wall of the bottom frame forms a space between the frame portion of the top frame and the opening side to provide a clearance for the end of the optical sheet. The light guide plate has long sides and short sides in a plan view, and the height of the side wall of the bottom frame facing the short side of the light guide plate is The height does not reach the optical sheet. The height of the side wall of the bottom frame facing the long side of the light guide plate is the height of the side wall of the bottom frame facing the short side of the light guide plate than It is tall and reaches the back of the frame part of the top frame.

[0010] A surface illumination device according to an aspect of the present invention can achieve a further narrowing of the frame of the surface illumination device. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 is a perspective view of the appearance of a surface illumination device according to one embodiment. [Diagram 2] FIG. 2 is an exploded perspective view of the main components of the surface illumination device. [Diagram 3] FIG. 3 is a cross-sectional view of the surface illumination device shown in FIG. [Figure 4] 4 is a cross-sectional view of the surface illumination device shown in FIG. 1 taken along the line YY. [Diagram 5] FIG. 5 is a cross-sectional view of a surface illumination device of a comparative example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, a planar lighting device according to an embodiment will be described with reference to the drawings. Note that the present invention is not limited to this embodiment. In addition, the dimensional relationship of each element in the drawings, the ratio of each element, etc. may differ from reality. The drawings may also include parts with different dimensional relationships and ratios. In principle, the contents described in one embodiment or modified example are similarly applied to other embodiments or modified examples.

[0013] Fig. 1 is an external perspective view of a surface lighting device 1 according to an embodiment, as viewed from the light emission surface side. For convenience of explanation, in Fig. 1, the direction along the long side of the housing of the surface lighting device 1 is defined as the X-axis direction, the direction along the short side of the housing is defined as the Y-axis direction, and the direction along the thickness of the housing is defined as the Z-axis direction.

[0014] In FIG. 1, the surface lighting device 1 has a substantially rectangular (although it is substantially rectangular in the illustrated example, it may be substantially square) substantially plate-like external shape, and a top frame 2B is exposed at the end of the light emission surface side on the front side in the figure. A bottom frame (2A) is present on the back side, which is not visible in the figure. The top frame 2B has an opening 2d through which light is emitted on the inside. The surrounding area of ​​the opening 2d is a frame portion 2e. A part of the light source board 5 is provided extending from the surface lighting device 1 in the positive direction of the X-axis, and a connection portion 5a is provided at the tip of the light source board 5, which is used for electrical connection with the outside. The top frame 2B is formed of sheet metal such as stainless steel. When the surface lighting device 1 is used as a backlight for a liquid crystal display device or the like, the liquid crystal display device or the like is attached to the opening 2d and frame portion 2e side.

[0015] Fig. 2 is an exploded perspective view of the main components of the planar lighting device 1, and is a view seen from the light output surface side, similar to Fig. 1. In Fig. 2, the planar lighting device 1 is configured such that a reflector 3A, a partial reflector base 3B, a light guide plate 4, a light source substrate 5, and optical sheets 7A to 7C are laminated in this order on a bottom frame 2A on the upper side of the figure, and a top frame 2B is disposed thereon to cover them.

[0016] 3 is a cross-sectional view of the surface lighting device 1 in FIG. 1 taken along line XX, and FIG. 4 is a cross-sectional view of the surface lighting device 1 in FIG. 1 taken along line YY.

[0017] The bottom frame 2A has a bottom 2a and four side walls 2b surrounding the bottom. The top frame 2B has a frame 2e with an opening 2d formed therein and four side walls 2f surrounding the frame. The side walls 2b of the bottom frame 2A are provided with protrusions 2c formed by bending a cut in the side walls 2b, and when the top frame 2B is attached to the bottom frame 2A, the protrusions 2c of the side walls 2b of the bottom frame 2A are engaged with holes 2g provided in the side walls 2f of the top frame 2B. On the side not on the light-entering side (FIG. 4), a reflector 110 is attached to the inner surface of the side walls 2b of the bottom frame 2A via a fixing member 109 made of double-sided tape or the like. Alternatively, instead of the fixing member 109 and the reflector 110, an end of the reflector 3A may be bent and a part of the reflector 3A may be disposed between a side surface of the light guide plate 4 other than the light incident side surface 4a and the side wall 2b of the bottom frame 2A. Alternatively, instead of the fixing member 109 and the reflector 110, a reflector that is a separate member from the reflector 3A may be attached to a side surface of the light guide plate 4 other than the light incident side surface 4a.

[0018] The light guide plate 4 is an optical member that guides the light incident from the light-entering side surface 4a to the inside and emits it from the main surface opposite to the reflector 3A. The light guide plate 4 is made of a transparent resin such as polycarbonate. On the light-entering side edge (FIG. 3), the light source substrate 5 is fixed to the bottom frame 2A on the light-entering side surface 4a side of the light guide plate 4 via a fixing member 106 such as double-sided tape. The light source substrate 5 is made of an FPC (Flexible Printed Circuit) or the like. A plurality (a large number) of light sources 5b such as LEDs are arranged along the longitudinal direction of the light-entering side surface 4a on the portion of the light source substrate 5 facing the light-entering side surface 4a. Note that, although the illustrated example shows a case of a top-view type LED that emits light from the top surface, a side-view type LED that emits light from the side surface can also be used.

[0019] On the light-entering side (FIG. 3), the reflector 3A and the partial reflector base 3B are disposed between the light guide plate 4 and the bottom 2a of the bottom frame 2A. The end of the reflector 3A and the partial reflector base 3B are fixed to the bottom 2a of the bottom frame 2A via a fixing member 101 such as a white, highly adhesive double-sided tape. The partial reflector base 3B is fixed to the light guide plate 4 via a fixing member 105 such as a thermocompression tape, and a base material 104 is disposed around the fixing member 105. The fixing member 105 is disposed in a scattered island shape to avoid the portion facing the light source 5b, so as to reduce the influence on the optical characteristics of the light guide plate 4 (the influence on the optical characteristics due to total reflection at the contact surface between the fixing member 105 and the light guide plate 4), and the comb-shaped base material 104 surrounds the periphery. The base material 104 is fixed (bonded) to the partial reflector base 3B, and is not fixed (bonded) to the light guide plate 4. With this configuration, the light guide plate 4 is fixed to the bottom frame 2A at the edge on the light incident side. The reflector 3A, the fixing member 101, and the base material 104 function as optical members that reflect light that has leaked onto the surface opposite to the exit surface of the light guide plate 4 and emits it towards the exit surface side.

[0020] The optical sheet 7A is an optical member such as a diffusion sheet. The optical sheet 7B is an optical member such as a BEF (Brightness Enhancement Film) as a prism sheet. The optical sheet 7C is an optical member such as a DBEF (Dual Brightness Enhancement Film) as a reflective polarizing film. At the light incident side edge (FIG. 3), the ends of the optical sheets 7A to 7C are fixed to the back surface of the frame portion 2e of the top frame 2B via fixing members 108 such as double-sided tape. That is, like the light guide plate 4, the optical sheets 7A to 7C are fixed to the top frame 2B at the light incident side edge.

[0021] As is clear from Figures 3 and 4, the height of the side wall 2b of the bottom frame 2A is different between the side on the light incident side (Figure 3) and the side perpendicular to the side on the light incident side (Figure 4). That is, on the side on the light incident side (Figure 3), the side wall 2b of the bottom frame 2A has a height that reaches the rear surface of the frame portion 2e of the top frame 2B, but on the side perpendicular to the side on the light incident side (Figure 4), the side wall 2b of the bottom frame 2A has a height that does not reach the optical sheet 7A.

[0022] The reason for this difference is due to the relationship between the long and short sides of the light guide plate 4 and the optical sheets 7A to 7C, and the anisotropy of the linear expansion coefficient of the DBEF used as the optical sheet 7C, for example. The linear expansion coefficient α1 of the DBEF in one axial direction is different from the linear expansion coefficient α2 in the axial direction perpendicular to the axial direction by, for example, α1=5.6×10 -5 / K, α2=8×10 -5 / K, where α1<α2. The axis direction of DBEF needs to be aligned with the axis direction of the polarizing plate on the planar lighting device 1 side of the liquid crystal panel attached to the emission surface side of the planar lighting device 1, so the axis direction of DBEF with a large linear expansion coefficient α2 is generally assigned to the long side direction (X-axis direction) of the planar lighting device 1. Therefore, expansion and contraction in the long side direction (X-axis direction) is dominated by the optical sheets 7A to 7C, and how to deal with the clearance therebetween is important for narrowing the frame in the long side direction (X-axis direction).

[0023] In addition, in the short side direction (Y-axis direction) of the surface illumination device 1, the general linear expansion coefficient α of the light guide plate 4 is isotropic, and is, for example, α=6.5×10 -5 / K, which is larger than the linear expansion coefficient α1 of DBEF, the expansion and contraction in the short side direction (Y-axis direction) is dominated by the light guide plate 4, but since it is the short side, the amount of expansion and contraction of the light guide plate 4 is small, and the effect of the clearance on narrowing the frame is small. Therefore, in this embodiment, no measures are taken in the short side direction (Y-axis direction) by changing the height of the side wall 2b of the bottom frame 2A.

[0024] Therefore, when the direction of the mounted liquid crystal panel is changed to a perpendicular direction, a measure based on the height of the side wall 2b of the bottom frame 2A is similarly taken for the short side direction (Y-axis direction). However, when the light guide plate 4 and the optical sheets 7A to 7C are fixed on the light-entering side, a measure based on the height of the side wall 2b of the bottom frame 2A is not necessary for the light-entering side. Also, a measure based on the height of the side wall 2b of the bottom frame 2A may be taken for both the long side direction (X-axis direction) and the short side direction (Y-axis direction). In this case, when the light guide plate 4 and the optical sheets 7A to 7C are fixed on the light-entering side, a measure based on the height of the side wall 2b of the bottom frame 2A is not necessary for the light-entering side.

[0025] Fig. 5 is a cross-sectional view of a surface illumination device 1' of a comparative example, and corresponds to the cross-sectional view of a side perpendicular to the side on the light-entering side in Fig. 4. In Fig. 5, the bottom frame 2A', the top frame 2B', the bottom 2a', the side wall 2b', the protruding portion 2c', the opening 2d', the frame portion 2e', the side wall 2f', the hole 2g', the reflector 3', the light guide plate 4', the optical sheets 7A' to 7C', the fixing member 109', and the reflector 110' correspond to the bottom frame 2A, the top frame 2B, the bottom 2a, the side wall 2b, the protruding portion 2c, the opening 2d, the frame portion 2e, the side wall 2f, the hole 2g, the reflector 3A, the light guide plate 4, the optical sheets 7A to 7C, the fixing member 109, and the reflector 110, respectively.

[0026] In FIG. 5, the side wall 2b' of the bottom frame 2A' has a height that reaches the rear surface of the frame portion 2e' of the top frame 2B'. Therefore, the clearance for the expansion and contraction of the optical sheets 7A' to 7C' is the distance from the end of the optical sheets 7A' to 7C' to the side wall 2b' of the bottom frame 2A'. On the other hand, in the embodiment of FIG. 4, the end of the opening side of the side wall 2b of the bottom frame 2A forms a space between the frame portion 2e of the top frame 2B and the opening side of the side wall 2b of the bottom frame 2A, which serves as a clearance for the ends of the optical sheets 7A to 7C. Therefore, the ends of the optical sheets 7A to 7C can be brought closer to the side wall 2b of the bottom frame 2A and the side wall 2f of the top frame 2B. Therefore, the opening 2d of the top frame 2B can be shifted toward the side wall 2f, and the frame can be narrowed. In the specific design by the inventors, 0.3 mm was saved for the thickness of the side wall 2b of the bottom frame 2A, and 0.1 mm was saved for the clearance for engagement between the bottom frame 2A and the top frame 2B, resulting in a total frame narrowing of 0.4 mm.

[0027] Although the embodiment of the present invention has been described above, the present invention is not limited to the above embodiment, and various modifications are possible without departing from the spirit of the present invention.

[0028] As described above, the planar lighting device according to the embodiment includes a light guide plate for receiving light from a light-entering side, a light source for irradiating the light-entering side of the light guide plate, one or more optical sheets arranged on the light-exiting side of the light guide plate, a bottom frame for housing the light guide plate, the light source, and the optical sheets, and a top frame that engages with the bottom frame, covers the light-exiting side of the optical sheets, and has an opening, and the end of the opening side of the side wall of the bottom frame forms a space between the frame of the top frame and the edge of the optical sheets as a clearance. This makes it possible to further narrow the frame of the planar lighting device.

[0029] Furthermore, when the light guide plate is a rectangle consisting of long and short sides in a plan view, and one or more optical sheets have anisotropic linear expansion coefficients, the end of the opening side of the side wall of the bottom frame perpendicular to the axial direction with a large linear expansion coefficient forms a space between the frame of the top frame and the opening side of the optical sheet, which serves as a clearance for the end of the optical sheet. This makes it possible to apply frame narrowing measures wherever possible.

[0030] In addition, the axial direction in which the linear expansion coefficient is large is the direction of the longer side of the light guide plate, which makes it possible to narrow the frame of the planar lighting device on the shorter side.

[0031] In addition, the larger linear expansion coefficient of the anisotropic optical sheet is larger than the linear expansion coefficient of the light guide plate, which makes it possible to target DBEF, which is widely used as an optical sheet.

[0032] In addition, the height of the side wall of the bottom frame facing the short side of the light guide plate is lower than the height of the side wall of the bottom frame facing the long side of the light guide plate, which allows measures to narrow the frame to be applied in an effective location.

[0033] In addition, the height of the side wall of the bottom frame facing the short side of the light guide plate is set so as not to reach the optical sheet, thereby forming a sufficient space as a clearance for the edge of the optical sheet.

[0034] Furthermore, the present invention is not limited to the above-mentioned embodiment. The present invention also includes a configuration in which the above-mentioned components are appropriately combined. Further effects and modifications can be easily derived by those skilled in the art. Therefore, the broader aspects of the present invention are not limited to the above-mentioned embodiment, and various modifications are possible. [Explanation of symbols]

[0035] 1 Planar lighting device, 2A bottom frame, 2B top frame, 3A reflector, 3B partial reflector base, 4 light guide plate, 4a light entrance side, 5 light source substrate, 5a connection portion, 5b light source, 7A to 7C optical sheets

Claims

1. A light guide plate into which light enters from a light-entering side; a light source that irradiates light onto a light-entering side surface of the light guide plate; One or more optical sheets arranged on the exit surface side of the light guide plate; a bottom frame that accommodates the light guide plate, the light source, and the optical sheet; a top frame that engages with the bottom frame, covers the light exit surface side of the optical sheet, and has an opening; Equipped with an end portion of the side wall of the bottom frame on the opening side forms a space between the end portion of the side wall of the bottom frame and a frame portion of the top frame, the space being a clearance for an end portion of the optical sheet; The light guide plate has long sides and short sides in a plan view, a height of a side wall of the bottom frame facing a short side of the light guide plate does not reach the optical sheet; a height of a side wall of the bottom frame facing a long side of the light guide plate is higher than a height of a side wall of the bottom frame facing a short side of the light guide plate, and the height reaches a rear surface of a frame portion of a top frame; Surface lighting device.

2. Any one of the one or more optical sheets has anisotropy in linear expansion coefficient, an end portion of the bottom frame on an opening side of a side wall of a side perpendicular to the axial direction in which the linear expansion coefficient is large forms a space between the end portion and a frame portion of the top frame to serve as a clearance for an end portion of the optical sheet; 2. The spread illuminating device according to claim 1.

3. The axial direction in which the linear expansion coefficient is large is the long side direction of the light guide plate.

3. The spread illuminating device according to claim 2.

4. The larger linear expansion coefficient of the optical sheet having anisotropy is larger than the linear expansion coefficient of the light guide plate.

3. The spread illuminating device according to claim 2.

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