Planar lighting device

Abstract

To realize both screen quality and narrow frame.SOLUTION: A planar lighting device comprises a light guide plate, a light source, a rear frame, an intermediate material, and a fixing member. The light guide plate receives light from a light incident side surface. The light source irradiates the light incident side surface of the light guide plate with light. The rear frame houses the light guide plate and the light source. A part of the intermediate material is laser-welded to an end part on the light incident side of the main surface of the light guide plate on the rear frame side. The fixing member is arranged between the intermediate material and the bottom of the rear frame.SELECTED DRAWING: Figure 2

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 front frame (top frame) with an opening for emitting light is often used as part of the housing, and the part of the front 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 frame widths.

[0004] In addition, since the light guide plate, which is a component of the surface lighting device, expands and contracts due to temperature changes, a clearance is required between the side wall of the rear frame (bottom frame) that houses them and the light guide plate in the expansion and contraction direction. If the light guide plate is simply placed on the surface lighting device due to the presence of the clearance, the light guide plate will hit the rear frame due to vibrations applied to the surface lighting device, generating rattle noise and causing discomfort to the user. For this reason, in the past, the corners of the light guide plate on the non-light-entering side were generally supported by an elastic member such as rubber, and the light guide plate was pressed against the light-entering side to prevent vibration and absorb the expansion and contraction of the light guide plate due to temperature changes. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2011-171208 A [Patent Document 2] JP 2019-153566 A Summary of the Invention [Problem to be solved by the invention]

[0006] However, when supporting the light guide plate with the above-mentioned elastic member, the thickness of the elastic member in the expansion and contraction direction needs to be an amount corresponding to the clearance, making it difficult to reduce the width of the frame portion covering the area where the elastic member is placed, and making it difficult to narrow the frame.

[0007] It is also possible to fix the light guide plate using a fixing member such as double-sided tape instead of the elastic member, but it is difficult to narrow the frame while maintaining the screen quality. That is, at the contact interface between the light guide plate and the fixing member, the optical characteristics such as scattering and absorption of light by the fixing member and the contact state between the light guide plate and the fixing member affect the screen quality, so it is desirable that the contact area between the light guide plate and the fixing member is extremely small. However, a fixing member such as double-sided tape requires a large contact area to exert sufficient force to fix the light guide plate, so it is difficult to achieve both screen quality and narrow the frame.

[0008] The present invention has been made in view of the above, and has an object to provide a surface illumination device that can achieve both high image quality and a narrow frame. [Means for solving the problem]

[0009] In order to solve the above-mentioned problems and achieve the object, a surface lighting device according to one aspect of the present invention comprises a light guide plate, a light source, a rear frame, an intermediate material, and a fixing member. Light enters the light guide plate from a light entrance side. The light source irradiates light onto the light entrance side of the light guide plate. The rear frame houses the light guide plate and the light source. A portion of the intermediate material is laser welded to an end of the light entrance side of the main surface of the light guide plate facing the rear frame. The fixing member is disposed between the intermediate material and a bottom of the rear frame. The intermediate member is made of the same material as the light guide plate.

[0010] A surface illumination device according to an aspect of the present invention can achieve both high image quality and a narrow frame. [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 a cross-sectional view taken along line XX in FIG. [Diagram 3] FIG. 3 is a cross-sectional view taken along line YY in FIG. [Figure 4] FIG. 4 is a diagram showing an example of a laser welded portion as viewed from the light guide plate side. [Diagram 5] FIG. 5 is a diagram showing how light is absorbed in a portion where a laser weld is present. [Figure 6] FIG. 6 is a diagram showing how light is absorbed in a portion where there is an air gap. [Figure 7] FIG. 7 is a diagram showing an example of the luminance distribution over the entire surface of the light guide plate. [Figure 8] FIG. 8 is a cross-sectional view showing the configuration of the light incident side of a surface illumination device of a comparative example. [Figure 9] FIG. 9 is a cross-sectional view taken along line YY in FIG. [Figure 10] FIG. 10 is a diagram showing how light is diffusely reflected within a light guide plate that is attached solidly with a transparent double-sided tape. [Figure 11] FIG. 11 is a diagram showing an example of luminance distribution over the entire surface of a light guide plate 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, in which a light emission surface is viewed from an oblique direction. 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 illumination device 1 has a substantially rectangular and substantially flat outer shape, and a front frame (top frame) 3 is exposed at the end of the light emission surface side on the upper side in the figure. In addition, a rear frame (bottom frame) 2 is provided on the back side. The front frame 3 has an opening 3a through which light is emitted. The front frame 3 and the rear frame 2 are made of resin, metal, or the like. When the surface illumination 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 3a side. Although a substantially flat plate-shaped housing is shown in FIG. 1, the housing may be a curved plate-shaped one. In this case, in addition to the rear frame 2 and the front frame 3, the internal light guide plate, which will be described later, also has a curved shape.

[0015] Fig. 2 is an XX cross-sectional view in Fig. 1, showing a cross-sectional configuration along the light guide direction on the light input side. Fig. 3 is a YY cross-sectional view in Fig. 2, showing a cross-sectional configuration along a direction perpendicular to the light guide direction on the light input side. Note that in Figs. 2 and 3, the front frame 3 and optical sheets (diffusion sheet, prism sheet, etc.) arranged on the output surface side of the light guide plate are omitted from the illustration.

[0016] 2 and 3, a substrate 10 such as an FPC (Flexible Printed Circuits) is fixed to a side wall 2b on the light-entering side of the rear frame 2, and a plurality of light sources 11 such as LEDs (Light Emitting Diodes) are arranged on the substrate 10. A light-emitting portion 11a of the light source 11 faces a light-entering side surface 9c of the light guide plate 9. Although a top-view type LED that emits light from the top surface of the chip is illustrated, a side-view type LED that emits light from the side surface of the chip can also be used by changing the arrangement of the substrate 10.

[0017] Meanwhile, a black sheet 6 as an intermediate material is fixed to the inner surface of the bottom 2a of the rear frame 2 on the light-entering side via a white double-sided tape 4 as a fixing member, and a reflector 5 is fixed toward the terminal end side in the light guide direction with a small gap therebetween. The white double-sided tape 4 has a strip-like shape extending along the light-entering side, and is a highly reflective white color in order to reflect leaked light from the light guide plate 9 and the light source 11 toward the exit surface side and improve light efficiency. The reflector 5 returns light leaked from the light guide plate 9 to the back side (non-exiting side) toward the light guide plate 9, and has a highly reflective white surface.

[0018] An end of the rear principal surface 9a of the light guide plate 9 is placed on the black sheet 6 serving as an intermediate material, and the light guide plate 9 and the black sheet 6 are fixed together by a laser welded portion 7. The light guide plate 9 has a substantially rectangular and flat outer shape and is made of a transparent resin such as a typical polycarbonate, and guides light incident from the light entrance side surface 9c to the terminal end side, and emits the light from the opposite principal surface 9b by the action of the optical elements on the rear principal surface 9a.

[0019] The black sheet 6 as an intermediate material is made of the same material as the light guide plate 9, such as polycarbonate, so that it can be easily welded to the light guide plate 9. That is, since it is difficult to directly weld the light guide plate 9 made of polycarbonate or the like to the rear frame 2 made of metal or the like, the black sheet 6 made of the same material as the light guide plate 9 is disposed as an intermediate material, and the black sheet 6 and the light guide plate 9 are welded to each other. In addition, the black sheet 6 is black so that it can easily absorb laser energy and can be efficiently welded to each other by laser welding.

[0020] Although it is expected that there will be some concerns about the strength of the intermediate material, sufficient strength can be obtained by fixing the opposite side of the welding surface with a large area of ​​white double-sided tape 4. In addition, since the intermediate material is black, the optical properties and adhesion state of the white double-sided tape 4 are not important, which offers advantages in tape selection and assembly processes.

[0021] 3, the laser welded portion 7 is in the form of a scattered island that avoids the position facing the light source 11, and an air gap 8 is formed in the portion without the laser welded portion 7. The air gap 8 may be one that is naturally formed in the black sheet 6 by the formation of the laser welded portion 7 (there is an air layer because the light guide plate 9 and the black sheet 6 are only lightly in contact with each other in the portion other than the laser welded portion 7), or it may be a recess that is intentionally provided on the surface of the black sheet 6. The presence of the air gap 8 reduces the light absorbed by the black sheet 6 as an intermediate material, and reduces the impact on the screen quality. In particular, when the intermediate material is the black sheet 6, which has a large absorption of light, the presence of the air gap 8 prevents the absorption of light.

[0022] Furthermore, as shown in FIG. 3, when laser welded portion 7 is located away from the position facing the light source, the effect on the light incident from light source 11 is small. However, even if laser welded portion 7 is located in a position facing the light source, it has been confirmed that there is almost no effect on the light incident from light source 11, as will be described later.

[0023] 4 is a diagram showing an example of the laser welded portion 7 as viewed from the light guide plate 9 side. In FIG. 4, line L1 corresponds to the light incident side surface 9c of the light guide plate 9, and line L2 corresponds to the inner end face of the black sheet 6.

[0024] As shown in Fig. 4, the outline of the laser welded part 7 is substantially circular, and macroscopically, it is dot-like. The laser welded part 7 may be composed of one or more dot-like welds as shown in Fig. 4, or may be composed of one or more linear welds formed by a series of dot-like welds, and the laser welded part 7 may have any outline. Laser welding is performed at a heating temperature at which gas is sealed inside the laser welded part 7, and the gas acts as an air gap to reduce the light that passes through the laser welded part 7 and is absorbed by the black sheet 6 as the intermediate material, thereby minimizing the impact on the image quality.

[0025] Moreover, it is sufficient that the laser welding is performed within a predetermined range at approximately the center of the side of the light-entering side of the light guide plate 9. This allows the laser welding work to be simplified while ensuring sufficient fixing strength by the laser welding. Furthermore, the fixing of the black sheet 6 as an intermediate material and the bottom 2a of the rear frame 2 by the white double-sided tape 4 as a fixing member is performed within a predetermined range at approximately the center of the side of the light-entering side of the light guide plate 9. This prevents the white double-sided tape 4 as a fixing member from peeling off due to the difference between the expansion and contraction of the rear frame 2 at the end of the side of the light-entering side (expansion and contraction of metal is sufficiently smaller than that of resin) when the light guide plate 9 and the black sheet 6 as an intermediate material expand and contract due to temperature changes (the light guide plate 9 and the black sheet 6 expand and contract at the same rate because they are made of the same material).

[0026] Fig. 5 is a diagram showing how light is absorbed in the area where the laser welded portion 7 is located. In Fig. 5, the light that has traveled inside the light guide plate 9 as indicated by the solid line with an arrow is partly absorbed by the black sheet 6 and is reflected as indicated by the dashed line with an arrow. As described above, the proportion of the area where the laser welded portion 7 is provided is small, and furthermore, the amount of light absorbed by the black sheet 6 due to the gas sealed inside the laser welded portion 7 is small, so the effect is small.

[0027] Fig. 6 is a diagram showing how light is absorbed in the area with air gap 8. In Fig. 6, light that has traveled inside light guide plate 9 as indicated by the solid lines with arrows is not affected by black sheet 6 due to air gap 8, and is reflected multiple times inside light guide plate 9.

[0028] Fig. 7 is a diagram showing an example of the luminance distribution over the entire surface of the light guide plate 9. In Fig. 7, in the comparative examples (Figs. 8 to 11) described later, linear portions with high luminance called light bars are generated at the end of the light incident side of the light guide plate, which reduces the screen quality, but in Fig. 7, no light bars are generated at the end P of the light guide plate 9, and the luminance distribution is uniform over the entire surface.

[0029] FIG. 8 is a cross-sectional view showing the configuration of the light incident side of a surface illumination device 1" of a comparative example. FIG. 9 is a cross-sectional view taken along line YY in FIG. 8. In FIGS. 8 and 9, the rear frame 2", bottom 2a", side wall 2b", white double-sided tape 4", reflector 5", light guide plate 9", main surfaces 9a", 9b", light incident side surface 9c", substrate 10", light source 11" and light-emitting section 11a" correspond to the rear frame 2, bottom 2a, side wall 2b, white double-sided tape 4, reflector 5, light guide plate 9, main surfaces 9a", 9b, light incident side surface 9c, substrate 10, light source 11 and light-emitting section 11a in FIGS. 2 and 3. The black sheet 6 in FIGS. 2 and 3 is replaced by transparent double-sided tape 6" in FIGS. 8 and 9, the laser welded portion 7 and air gap 8 in FIGS. 2 and 3 are eliminated, and the transparent double-sided tape 6" is solidly attached to the end of the main surface 9a" of the light guide plate 9".

[0030] FIG. 10 is a diagram showing how light is diffusely reflected within a light guide plate 9" that is solidly attached with transparent double-sided tape 6". In FIG. 10, when transparent double-sided tape 6" is solidly attached to the light guide plate 9", light that has traveled through the light guide plate 9 as indicated by the solid lines with arrows is diffusely reflected at the boundary surface, which causes light bars and reduces the screen quality.

[0031] FIG. 11 is a diagram showing an example of the luminance distribution over the entire surface of a light guide plate 9" in a comparative example. In FIG. 11, a light bar LB occurs at the end of the light incident side of the light guide plate 9", which is one factor that reduces the screen quality. In the luminance distribution in the above-described embodiment (FIG. 7), no light bar occurs, and the screen quality can be improved.

[0032] 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.

[0033] As described above, the planar illumination device according to the embodiment includes a light guide plate that receives light from a light-entering side surface, a light source that irradiates light onto the light-entering side surface of the light guide plate, a rear frame that houses the light guide plate and the light source, an intermediate material that is partially laser-welded to the light-entering side end of the main surface of the light guide plate on the rear frame side, and a fixing member that is disposed between the intermediate material and the bottom of the rear frame. This makes it possible to achieve both high screen quality and narrower frame. That is, the light guide plate and the intermediate material are firmly fixed with a small contact area by laser welding, and the intermediate material is fixed to the bottom of the rear frame by the fixing member with any contact area required, so that it is possible to contribute to narrower frame while maintaining screen quality.

[0034] In addition, the intermediate material is made of the same material as the light guide plate, which makes it easy to laser weld the light guide plate and the intermediate material together, and also makes them expand and contract in response to temperature changes equivalently, enabling the light guide plate and the intermediate material to be firmly fixed together.

[0035] In addition, the intermediate material is black in color, which allows it to easily absorb the energy of the laser and allows efficient laser welding.

[0036] Moreover, the light guide plate and the intermediate material are made of polycarbonate, which allows the light guide plate and the intermediate material to be made of common materials.

[0037] The fixing member is a double-sided tape, which makes it possible to easily fix the intermediate material.

[0038] Moreover, the laser welding is performed within a predetermined range approximately in the center of the side of the light input side of the light guide plate, which makes it possible to simplify the laser welding work while ensuring sufficient fixing strength by the laser welding.

[0039] Furthermore, the intermediate material is fixed to the bottom of the rear frame by the fixing member within a predetermined range approximately in the center of the side of the light-entering side of the light guide plate, which makes it possible to prevent peeling of the fixing member due to the difference in expansion and contraction between the bottom of the rear frame and the intermediate material at the end of the side of the light-entering side when the light guide plate and the intermediate material expand and contract due to temperature changes.

[0040] Moreover, the laser welding is performed by welding one or more dots or one or more lines in a plan view from the main surface side of the light guide plate, which allows laser welding with any contour.

[0041] In addition, the laser welding is performed while avoiding the position facing the light source, or without considering the position facing the light source. This allows laser welding to be performed at any position. Although laser welding performed while avoiding the position facing the light source has less effect on the light incident from the light source, it has been confirmed that even if laser welding is performed at a position facing the light source, there is almost no effect on the light incident from the light source.

[0042] In addition, an air gap is formed in the boundary between the light guide plate and the intermediate material where laser welding is not performed. This reduces the amount of light absorbed by the intermediate material, minimizing the impact on the screen quality. In particular, when the intermediate material is black, light absorption is high, so the presence of the air gap prevents light absorption.

[0043] Laser welding is performed at a heating temperature that allows gas to be sealed inside the welded part, which acts as an air gap, reducing the amount of light that passes through the laser welded part and is absorbed by the intermediate material, minimizing the impact on screen quality.

[0044] The fixing member fixes the light-entering end of the reflector disposed on the non-emission surface side of the light guide plate, which eliminates the need for another member for fixing the reflector, thereby reducing the number of parts.

[0045] 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]

[0046] REFERENCE SIGNS LIST 1 Planar lighting device, 2 Rear frame, 2a Bottom, 2b Side wall, 3 Front frame, 3a Opening, 4 White double-sided tape, 5 Reflector, 6 Black sheet, 7 Laser welded portion, 8 Air gap, 9 Light guide plate, 9a, 9b Main surface, 9c Light-entering side, 10 Substrate, 11 Light source, 11a Light-emitting portion

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; a rear frame that accommodates the light guide plate and the light source; an intermediate material having a portion laser welded to an end portion on a light-entering side of a main surface of the light guide plate on the rear frame side; a fixing member disposed between the intermediate member and a bottom portion of the rear frame; Equipped with The intermediate material is formed from the same material as the light guide plate. Surface lighting device.

2. 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; a rear frame that accommodates the light guide plate and the light source; an intermediate material having a portion laser welded to an end portion on a light-entering side of a main surface of the light guide plate on the rear frame side; a fixing member disposed between the intermediate member and a bottom portion of the rear frame; Equipped with a welded portion formed between the light guide plate and the intermediate material by the laser welding has a gas sealed therein in order to reduce light absorbed by the intermediate material from the light guide plate; Surface lighting device.

3. The intermediate material is black.

3. A spread illuminating device according to claim 1 or 2.

4. The light guide plate and the intermediate material are made of polycarbonate.

4. The spread illuminating device according to claim 1.

5. The fixing member is a double-sided tape.

5. The spread illuminating device according to claim 1.

6. The laser welding is performed within a predetermined range at approximately the center of the side of the light input side of the light guide plate.

6. The spread illuminating device according to claim 1.

7. The fixing of the intermediate member and the bottom portion of the rear frame by the fixing member is performed within a predetermined range approximately at the center of the side of the light input side of the light guide plate.

7. The spread illuminating device according to claim 1.

8. The laser welding is, in a plan view from the main surface side of the light guide plate, one or more dot-like welding or one or more line-like welding.

8. The spread illuminating device according to claim 1.

9. The laser welding is performed while avoiding a position facing the light source, or without taking into consideration a position facing the light source.

9. The spread illuminating device according to claim 1.

10. An air gap is formed in a portion of the boundary between the light guide plate and the intermediate material where the laser welding is not performed.

10. The spread illuminating device according to claim 1.

11. the fixing member fixes a light-entering-side end portion of a reflector disposed on a non-light-exiting surface side of the light guide plate; The spread illuminating device according to any one of claims 1 to 10.

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