JP7273646B2 - Planar lighting device - Google Patents

Description

The present invention relates to a planar illumination device.

2. Description of the Related Art A so-called edge-light type planar lighting device is known, in which light is incident from a light incident end surface of a light guide plate and light is emitted from one main surface of the light guide plate. In addition, there is a planar illumination device provided with two light guide plates in order to improve the brightness and enable switching of the viewing angle (for example, see Patent Documents 1 to 3).

In order to hold the two light guide plates in the housing, generally, the first light guide plate is arranged at the bottom of the bottom frame, and the second light guide plate is provided at the stepped portion inside the side wall surrounding the bottom of the bottom frame. is placed on the end of the light guide plate.

Japanese Patent Application Laid-Open No. 2004-118207 JP 2014-26282 A WO2016/163176

However, in the configuration in which the end portion of the second light guide plate is placed on the stepped portion provided inside the side wall of the bottom frame, the first light guide plate and the second light guide plate cannot be separated from each other in order to narrow the frame. There was a limit to reducing the frame width due to the arrangement of

SUMMARY OF THE INVENTION It is an object of the present invention to provide a planar illumination device capable of achieving a narrow frame.

In order to solve the above-described problems and achieve an object, a planar illumination device according to one aspect of the present invention includes first and second light guide plates, first and second light sources, a bottom frame, and a holding part. The first and second light sources irradiate respective light incident end surfaces of the first and second light guide plates with light. The bottom frame houses the first and second light guide plates and the first and second light sources. The holding portion is arranged at a stepped portion inside the side wall of the bottom frame. The first light guide plate is mounted on the bottom of the bottom frame. The end portion of the second light guide plate in a direction orthogonal to the light guide direction is placed on the inner protruding portion of the holding portion that protrudes inward from the side wall of the bottom frame.

A planar lighting device according to one embodiment of the present invention can achieve a narrow frame.

FIG. 1 is a perspective view showing an example of the appearance of a planar lighting device according to an embodiment. FIG. 2 is a cross-sectional view taken along the line XX in FIG. FIG. 3 is a cross-sectional view along YY in FIG. FIG. 4 is a ZZ cross-sectional view in FIG. FIG. 5 is a cross-sectional view of a planar illumination device according to Comparative Example #1. FIG. 6 is a cross-sectional view of a planar illumination device according to Comparative Example #2. FIG. 7 is a diagram showing a usage example of the light source substrate. FIG. 8 is a cross-sectional view of a planar illumination device according to Comparative Example #3. FIG. 9 is a diagram illustrating an example of the width of the holding portion of the light guide plate according to the embodiment;

A planar illumination device according to an embodiment will be described below with reference to the drawings. In addition, this invention is not limited by this embodiment. In addition, the dimensional relationship of each element in the drawings, the ratio of each element, and the like may differ from reality. Even between the drawings, there are cases where portions with different dimensional relationships and ratios are included. In principle, the contents described in one embodiment and modification are similarly applied to other embodiments and modifications.

FIG. 1 is a perspective view showing an example of the appearance of a planar illumination device 1 according to one embodiment. In FIG. 1, a planar illumination device 1 has a substantially rectangular and substantially plate-like outer shape, and a bottom frame 2 is covered with a top frame 3 to form a housing. The bottom frame 2 has a floor (2a) not visible in the drawing and four side walls 2b surrounding the floor. The top frame 3 has a frame portion 3b provided with an opening 3a inside, and four side walls 3c surrounding the frame portion 3b.

FIG. 2 is a cross-sectional view taken along the line XX in FIG. 1, viewed from a direction orthogonal to the light guiding direction. In FIG. 2, a concave portion 2c is provided at one end (left side in the figure) of the floor portion 2a of the bottom frame 2, and the light source is bent in a substantially L shape across the concave portion 2c and the inner surface of the side wall 2b. A substrate 4 is attached with a double-sided tape or the like. The light source substrate 4 is formed of FPC (Flexible Printed Circuit) or the like, and the light sources 5 in the first row and the light sources 6 in the second row are arranged on the light source substrate 4 from the side of the floor portion 2a. ing. The light sources 5 and 6 are light emitting elements such as LEDs (Light Emitting Diodes). It is arranged to face the light incident end surface 15 a of the light plate 15 . A plurality of LEDs and the like are arranged at predetermined intervals in both the first row and the second row. The light guide plate 8 is an example of a first light guide plate. The light guide plate 15 is an example of a second light guide plate. Although the illustrated example shows 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.

A light guide plate 8 is placed on the floor portion 2 a of the bottom frame 2 with a reflective sheet 7 interposed therebetween. The reflective sheet 7 has its ends bent so as to cover three side surfaces of the light guide plate 8 excluding the light incident side. In order to allow thermal expansion due to temperature changes, the reflection sheet 7 and the light guide plate 8 are not fixed to the floor 2a, and are secured to the light entrance side by elastic members at the corners opposite to the light entrance side. is pressed and held. Various optical sheets 9 to 13 are laminated on the side of the light guide plate 8 opposite to the floor portion 2a. The optical sheets 9 to 13 include diffusion sheets, prism sheets, brightness enhancement sheets, viewing angle (light distribution) control sheets, and the like.

On the other hand, a stepped portion 2d is provided on the inner side of the side wall 2b except for one surface on the light incident side of the bottom frame 2, and an inner frame 14 having a substantially square shape in a plan view is arranged on the stepped portion 2d. there is The inner frame 14 is an example of a holding portion. Four peripheral edges of the light guide plate 15 are mounted on the inner frame 14 . In order to allow thermal expansion due to temperature change, the light guide plate 15 is not fixed to the inner frame 14, and is pressed toward the light incident side by an elastic member at the corner portion opposite to the light incident side. there is A top frame 3 having a frame portion 3b and side walls 3c is covered and fixed to the opening of the bottom frame 2 opposite to the floor portion 2a. Exposed.

FIG. 3 is a cross-sectional view taken along the line YY in FIG. 1, viewed from the light guiding direction. In FIG. 3, a groove 2e is provided in the inner stepped portion 2d of the side wall 2b of the bottom frame 2, and one end of the outer wall 14a of the inner frame 14 is fitted into the groove 2e. The inner frame 14 is stably held by the bottom frame 2 by fitting one end of the outer wall 14a into the groove 2e. The inner frame 14 is made of a resin or the like having an expansion coefficient close to that of the bottom frame 2, thereby minimizing the clearance between the edge of the outer wall 14a and the groove 2e, thereby providing an effect for positioning the inner frame 14. Is possible.

FIG. 4 is a cross-sectional view taken along line ZZ in FIG. 3, viewed from the direction of light emission. In FIG. 4 , the light guide plate 15 is placed on the inner projecting portion 14 b of the inner frame 14 . A dashed line 14 d is the inner end of the inner protruding portion 14 b of the inner frame 14 . A plurality of recesses 14e are provided on the light incident side of the inner frame 14, and the light sources 6 of the light source substrate 4 are arranged at positions corresponding to these recesses 14e. An elastic member 16 made of rubber or the like is provided at a corner of the light guide plate 15 opposite to the light entrance side, and presses the light guide plate 15 toward the light entrance side. The light guide plate 8 is similarly provided with an elastic member.

FIG. 5 is a cross-sectional view of a planar illumination device 1A according to Comparative Example #1, which is viewed from a direction perpendicular to the light guiding direction, as in FIG. In FIG. 5, the planar lighting device 1A of Comparative Example #1 has a light source substrate 4A-1 bent in a substantially L shape extending from the inner surface of the recessed portion 2Ac of the floor portion 2Aa of the bottom frame 2A to the inner surface of the side wall 2Ab. A light source substrate 4A-2 is attached to the inner surface of the side wall 2Ab at a distance L1 in the thickness direction from the light source substrate 4A-1. The light sources 5A in the first row are arranged on the light source substrate 4A-1 so as to face the light entrance end surface 8Aa of the light guide plate 8A, and the light sources 6A in the second row are arranged on the light source substrate 4A-2. 15A is opposed to the light incident end surface 15Aa.

When two rows of light source substrates 4A-1 and 4A-2 are attached to the inner surface of the side wall 2Ab, which is the same attachment surface, a certain distance L1 must be provided from the design of the clearance between the light source substrates. It is not possible to use the entire width of the mounting surface. As a result, the total thickness of the planar illumination device 1A is increased, which greatly restricts the wiring design.

FIG. 6 is a cross-sectional view of a planar lighting device 1B according to Comparative Example #2, which is viewed from a direction perpendicular to the light guiding direction, like FIG. In FIG. 6, the planar illumination device 1B of Comparative Example #2 has a light source substrate 4B-1 attached to the inner surface of the thick portion of the side wall 2Bb of the bottom frame 2B. of light sources 5B are arranged and face the light entrance end surface 8Ba of the light guide plate 8B. A side wall 2Bb of the bottom frame 2B is provided with a raised portion 2Bc that once sinks from the outside and rises, and the light source substrate 4B-2 is attached to the inner wall of the portion that once sinks from the outside. A second row of light sources 6B is arranged on the light source substrate 4B-2 and faces the light incident end face 15Ba of the light guide plate 15B.

By attaching the light source substrates 4B-1 and 4B-2 to different surfaces, it is possible to secure the width necessary for the wiring of the light source substrates 4B-1 and 4B-2, but the side wall 2Bb of the bottom frame 2B is limited. Since the thickness is increased by the distance L2 between the light source substrates 4B-1 and 4B-2 compared to the case of FIG. 5, narrowing the frame becomes difficult.

In contrast to Comparative Example #1 above, in the embodiment shown in FIG. , the clearance between the two rows becomes unnecessary, and the width of the attachment surface can be used as the width of the light source substrate 4 entirely. Therefore, the total thickness of the planar illumination device 1 can be reduced, and restrictions on wiring design can be reduced. In addition, the side wall 2b of the bottom frame 2 can be made thinner than the comparative example #2, and a narrow frame can be achieved.

FIG. 7 is a diagram showing an example of use of the light source substrate 4. A thermistor 17 for temperature detection is provided between the light source 5 in the first row and the light source 6 in the second row. The thermistor 17 is used for control to prevent the light sources 5 and 6 from overheating. When two rows of light source substrates are provided as shown in FIGS. 5 and 6, a thermistor is required adjacent to each light source substrate. The number of thermistors 17 is sufficient, which contributes to a reduction in the number of parts.

FIG. 8 is a cross-sectional view of a planar illumination device 1C according to Comparative Example #3, which is viewed from the light guide direction, as in FIG. In FIG. 8, in the planar illumination device 1C of Comparative Example #3, the light guide plate 8C is arranged on the floor portion 2Ca of the bottom frame 2C, and the end portion of the light guide plate 15C is placed on the stepped portion 2Cc provided inside the side wall 2Cb. placed. A reflecting member 18C for reflecting light leaking from the end of the light guide plate 15C is provided on the inner surface of the side wall 2Cb facing the end of the light guide plate 15C.

Here, the frame width L10 is
・L11: Thickness and clearance of the side wall of the top frame ・L12: Thickness of the outer side wall of the stepped portion of the bottom frame considering the strength of the housing ・L13: The second guide plate considering the thermal expansion of the light guide Clearance between the edge of the light guide plate and the opposing inner wall ・L14: Width above the step on which the edge of the second light guide plate is placed (held) considering the thermal expansion of the light guide plate ・L15: Heat of the light guide plate Clearance between the edge of the first light guide plate and the opposing inner wall, considering expansion L16: Considering the appearance of lighting, the edge of the first light guide plate cannot be seen from the opening side of the top frame. Efforts have been made to reduce the distances from the ends of the first light guide plate to the openings, but further reduction beyond the current situation cannot be expected.

On the other hand, FIG. 9 is a diagram showing an example of the width of the holding portion of the light guide plate 15 according to the embodiment. Distances L01-L06 correspond to and are numerically equivalent to distances L11-L16 in FIG. 8, respectively, except that distance L03 is changed to the inner wall of the inner frame 14 instead of the inner wall of the bottom frame. Become. Here, in the embodiment, due to the presence of the inner frame 14, the thickness of the outer wall 14a of the inner frame 14 is newly included in the frame width L00. The total frame width L00 is considerably smaller than the frame width L10 in FIG. 8 after ensuring a sufficient width L14 on the stepped portion on which the end portion of the light plate is placed (held). That is, in FIG. 8, the distance L14 of the holding portion of the light guide plate 15C was outside the portion accommodating the light guide plate 8C, but in FIG. (In other words, by effectively using the inevitably generated dead space as a mounting space for the second light guide plate), the total frame width can be reduced. Therefore, it is possible to contribute to the narrowing of the frame.

In addition, by forming the inner frame 14 from a material such as white resin, a reflecting member (reflecting member 18C in FIG. 8) for reflecting light leaking from the end of the light guide plate 15 becomes unnecessary, and the number of parts is reduced. You can also try to reduce it.

Although the embodiments of the present invention have been described above, the present invention is not limited to the above embodiments, and various modifications can be made without departing from the scope of the invention.

As described above, the planar illumination device according to the embodiment includes the first and second light guide plates, and the first and second light guide plates for irradiating the light incident end surfaces of the first and second light guide plates with light. a light source, a bottom frame that houses the first and second light guide plates, and the first and second light sources; , the second light guide plate is placed on the bottom of the bottom frame, and the end portion of the second light guide plate is placed on the inner protruding portion of the holding portion that protrudes in the light guiding direction from the side wall side of the bottom frame toward the inside of the housing. be done. As a result, the holding portion of the end portion of the second light guide plate arranged on the output surface side can be inserted into the portion accommodating the first light guide plate, so that the total frame width can be reduced. A narrow frame can be achieved.

In addition, the holding portion includes a side wall having a height in the thickness direction of the second light guide plate and an inner projecting portion projecting from the side wall. are placed in engagement. Thereby, the holding portion can be stably held on the bottom frame.

Also, the holding portion is made of a material having an expansion coefficient similar to that of the bottom frame. As a result, the clearance between the holding portion and the bottom frame can be minimized, and an effect for positioning the holding portion can be obtained.

Moreover, the holding portion is formed of a white material. This eliminates the need for a reflecting member for reflecting the light leaking from the end of the second light guide plate, thereby reducing the number of parts.

Further, the end surface of the inward projecting portion of the holding portion is located between the opening end portion of the top frame covering the bottom frame and the end surface of the first light guide plate when viewed from above. As a result, the end face of the inner projecting portion does not optically affect the output surface side, and a sufficient width for placing (holding) the end portion of the second light guide plate can be secured.

Further, the end face of the second light guide plate is located outside the end face of the first light guide plate. Thereby, two light guide plates can be easily accommodated in the bottom frame, and a sufficient width for placing (holding) the end portion of the second light guide plate can be secured.

Also, the first and second light sources are mounted on one light source substrate. As a result, the entire width of the attachment surface can be used as the width of the light source substrate, reducing restrictions on wiring design.

Moreover, the present invention is not limited by the above embodiments. The present invention also includes those configured by appropriately combining the respective constituent elements described above. Further effects and modifications can be easily derived by those skilled in the art. Therefore, broader aspects of the present invention are not limited to the above-described embodiments, and various modifications are possible.

Reference Signs List 1 planar illumination device 2 bottom frame 3 top frame 4 light source substrate 5, 6 light source 7 reflection sheet 9 to 13 optical sheet 14 inner frame 8a, 15a light entrance end surface 8, 15 light guide plate

Claims (7)

first and second light guide plates;
first and second light sources for irradiating the light incident end surfaces of the first and second light guide plates with light;
a bottom frame housing the first and second light guide plates and the first and second light sources;
a holding portion arranged at a stepped portion inside the side wall of the bottom frame;
with
The first light guide plate is mounted on the bottom of the bottom frame,
The end portion of the second light guide plate in a direction perpendicular to the light guide direction is placed on an inner projecting portion of the holding portion projecting inward from the side wall of the bottom frame.
Planar lighting device. The holding portion includes a side wall having a height in the thickness direction of the second light guide plate, and the inward projecting portion projecting from the side wall,
an end portion of the side wall of the holding portion is arranged in engagement with a groove provided in a stepped portion inside the side wall of the bottom frame;
The planar lighting device according to claim 1 . The holding part is made of a material having an expansion coefficient similar to that of the bottom frame,
The planar illumination device according to claim 1 or 2. The holding part is formed of a white material,
The planar lighting device according to any one of claims 1 to 3. The end surface of the inward projecting portion of the holding portion is located between the opening end of the top frame covering the bottom frame and the end surface of the first light guide plate when viewed from the top.
The planar lighting device according to any one of claims 1 to 4. The end face of the second light guide plate is outside the end face of the first light guide plate,
The planar lighting device according to any one of claims 1 to 5. wherein the first and second light sources are mounted on a single light source substrate;
The planar lighting device according to any one of claims 1 to 4.

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