JP6677546B2 - Backlight - Google Patents

Description

  The present invention relates to a backlight including a light guide plate that receives light from the side and emits light from the front.

  In a liquid crystal display device, a backlight having a flat light guide plate may be provided on the back surface of a liquid crystal panel. One main surface of the light guide plate having a large area is a light emitting surface, and the other main surface facing the light emitting surface is a reflective surface. The light guide plate has at least one side surface orthogonal to the main surface as an incident surface, and a light source such as an LED is arranged on the incident surface to face the light source. Light emitted from the light source and entering the light guide plate from the incident surface propagates while repeating reflection in the light guide plate. When a part of this light hits a dot or the like formed on the reflecting surface, the propagation direction is changed and the light is emitted from the light emitting surface. The remaining light tends to exit from the side. Therefore, in order to improve the luminous efficiency on the light emitting surface, a reflection member is arranged facing the side surface, and light to be emitted from the side surface is often returned into the light guide plate.

  However, when the reflection member is arranged on the side surface of the light guide plate so that the light propagating toward the side surface and the light reflected by the side surface and returning are concentrated near the side surface, the vicinity of the side surface of the light emitting surface is brighter than other regions. A phenomenon occurs.

  To cope with such uneven brightness, Patent Document 1 proposes to provide a gap between the side surface of the light guide plate and the reflecting member, make the bottom surface near the side surface a mirror surface, and make the reflecting member a concave mirror. doing.

JP-A-6-289231 (paragraph 0004)

  However, when the distance between the reflecting member and the side surface of the light guide plate varies, the amount of light emission varies, so that the two members are often closely adhered and fixed with a double-sided tape or the like. For this reason, a gap cannot be provided between the light guide plate side surface and the reflection member. Further, since the reflecting member must be formed in a plate shape, it cannot be formed as a concave mirror.

  Also, when the vicinity of the side surface of the light guide plate reflection surface is a mirror surface, even if the brightness when viewed from one direction is uniform, the directivity is different from the other region having reflection dots and the like in the mirror surface region. Since it is difficult to match the characteristics, there is no guarantee that uniformity of luminance can be obtained as a whole. Further, the shape, arrangement, density, and the like of dots and the like are set on the reflection surface in order to eliminate factors that greatly affect non-uniformity of brightness, such as discrete arrangement of light sources. On the other hand, the non-uniform brightness appearing near the side surface is a matter that is positioned as a fine adjustment depending on the characteristics of the employed reflecting member, so the design of the reflecting surface of the light guide plate should be changed each time the reflecting member is changed. Is not realistic.

  Therefore, the present invention has been made in view of the above-described problems, and provides a backlight that can easily eliminate a bright portion generated near the side surface of the light guide plate even when the plate-shaped reflection member is brought close to the side surface of the light guide plate. The purpose is to provide.

The backlight of the present invention is a light guide plate having one main surface as a light emitting surface, the other main surface as a reflective surface, and at least one side surface as an incident surface, a light source disposed to face the incident surface, In a backlight including a first reflecting member disposed to face a side surface other than the incident surface and a second reflecting member attached below the reflecting surface , the first reflecting member is formed in a band shape with the second reflecting member. Is a separate body, has a diffuse reflection surface, is fixed to the side surface other than the incident surface by a double-sided tape , the side surface other than the incident surface, the portion where the double-sided tape is attached and the double-sided tape Is provided, and the reflecting surface, the lower end of the double-sided tape, and the lower end of the first reflecting member are aligned in the height direction .

  In the backlight of the present invention, light emitted from the light source and incident on the light guide plate from the incident surface propagates in the light guide plate while repeating reflection. A part of this light is emitted from the light emitting surface after the propagation direction is changed by dots or the like formed on the reflecting surface. The remaining light tends to exit from the side of the light guide plate. Light to be emitted from a portion of the side surface to which the double-sided tape is attached is diffusely reflected by the reflecting member. On the other hand, a part of the light to be emitted from the part of the side surface to which the double-sided tape is not attached is specularly reflected at the interface between the side surface and the air layer. At this time, the diffusely reflected light exits from the light emitting surface at a high rate near the side surface. On the other hand, the specularly reflected light is emitted from the light emitting surface only at a low rate near the side surface. That is, an interface with the air layer is formed on a part of the side surface to reduce the diffuse reflection, so that a bright portion does not appear near the side surface.

  The double-sided tape may be band-shaped.

  The width of the double-sided tape may vary from place to place.

  The double-sided tape may have a slit.

  The reflection member may have a portion extending from an end of the reflection sheet for a reflection surface facing the reflection surface, and the portion may be bent.

  As described above, in the backlight of the present invention, specular reflection occurs on a side surface other than the incident surface of the light guide plate, and diffuse reflection is weakened. As a result, the amount of light emission in the vicinity of the side surface of the light emitting surface is adjusted, so that even when the plate-shaped reflecting member is brought close to the side surface of the light guide plate, the bright portion generated near the side surface of the light guide plate can be easily eliminated.

FIG. 1 is an exploded perspective view of a backlight shown as a first embodiment of the present invention. FIG. 2 is a partial sectional view of the backlight shown in FIG. 1. FIG. 2 is a side view of the backlight shown in FIG. 1. FIG. 9 is a partial cross-sectional view of a backlight shown as a comparative example. FIG. 2 is a partial sectional view of the backlight shown in FIG. 1. It is a side view of the backlight shown as a 2nd embodiment of the present invention. It is a side view of the backlight shown as a 3rd embodiment of the present invention.

  Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to FIGS. In the description of the drawings, the same or corresponding elements have the same reference characters allotted, and overlapping description will be omitted. The scale of the drawings is appropriately changed for explanation.

(1st Embodiment)
A backlight 10 shown as a first embodiment of the present invention will be described with reference to FIGS. FIG. 1 is an exploded perspective view of the backlight 10. FIG. 2 is a partial cross-sectional view of the backlight 10 taken along line AA ′ in FIG. FIG. 3 is a side view of the backlight 10 drawn for explaining the relationship between the side surface 14a of the light guide plate 14 and the double-sided tape 15a. FIG. 4 is a partial cross-sectional view of a comparative example (backlight 50) drawn to explain a mechanism in which a bright portion occurs near the side surface. FIG. 5 is a partial cross-sectional view of the backlight 10 drawn for explaining a mechanism for eliminating a bright portion near the side surface.

  As shown in FIG. 1, the backlight 10 has a reflection sheet 17 f for a reflection surface disposed on a lower surface side of a light guide plate 14, and a diffusion sheet 13, a prism sheet 12, and a polarizing sheet 11 laminated on an upper surface side. The light guide plate 14 has an upper main surface as a light emitting surface 14e, a lower main surface as a reflection surface 14f, and has four side surfaces. One of the four side surfaces is the incident surface 14d, and the remaining side surfaces are the side surfaces 14a, 14b, and 14c (side surfaces other than the incident surface). Six LEDs 16 (light sources) are opposed to each other on the incident surface 14d. Double-sided tapes 15a, 15b, and 15c are attached to the side surfaces 14a, 14b, and 14c, respectively, and further, the side reflection sheets 17a, 17b, and 17c are attached to the double-sided tapes 15a, 15b, and 15c. The case for accommodating each member is not shown.

  2, the members shown in FIG. 1 will be described in more detail. Dots 18 are formed on the reflection surface 14f of the light guide plate 14 to change the traveling direction of the light that has propagated while repeating reflection in the light guide plate 14 and emit the light from the light emitting surface 14e. On the side surface 14a of the light guide plate 14, a double-sided tape 15a is attached in a lower half area, and further, a side reflection sheet 17a is attached via the double-sided tape 15a. On the light emitting surface 14e of the light guide plate 14, a diffusion sheet 13, a prism sheet 12, and a polarizing sheet 11 are laminated via an air layer (not shown).

  The light guide plate 14 is made of polycarbonate, acrylic, or the like, and has a thickness of 2.0 to 3.0 mm. The dot 18 is a rough surface formed by laser processing, the diameter of the concave portion is 50 to 500 μm, and the diameter is changed depending on the location so that the luminance on the light emitting surface 14 e becomes uniform. The reflection sheet 17f for reflection surface and the reflection sheets 17a, 17b, 17c for side surfaces are made of white PET, and have a thickness of 200 μm. The double-sided tape 15a has an adhesive layer on both sides of a transparent PET sheet, and has a thickness of 100 μm. The diffusion sheet 13 diffuses light with fine particles dispersed and fixed on the transparent sheet, and has a thickness of 120 to 130 μm. The prism sheet 12 adjusts the traveling direction of light by using a large number of fine prisms formed on the upper surface of the transparent sheet, and has a thickness of 155 μm. The polarizing sheet 11 transmits one polarized light while reflecting another polarized light orthogonal to the one polarized light, and has a thickness of 390 μm.

  As shown in FIG. 3, the double-sided tape 15a has a constant width (belt shape) in the vertical direction (the thickness direction of the light guide plate 14) in the figure, and the width is smaller than the thickness of the light guide plate 14; It is pasted. The area to which the double-sided tape 15a is attached in the longitudinal direction of the side surface 14a may be adjusted according to the distribution of the bright portions. The position where the double-sided tape 15a is attached to the short side direction of the side surface 14a may be any position such as an upper portion, a center, and a lower portion. In FIG. 3, since the purpose is to explain the relationship between the side surface 14a and the double-sided tape 15a, the reflection sheet 17f for the reflection surface, the reflection sheets 17a and 17b for the side surfaces, the diffusion sheet 13, the prism sheet 12, the polarizing sheet 11 , The double-sided tape 15b is not drawn. To facilitate understanding, the LED 16 arranged opposite to the incident surface 14d of the light guide plate 14, the light emitting surface 14e which is the main surface of the light guide plate 14, and the side surface 14b opposed to the incident surface 14d are illustrated. Here, the thickness of the LED 16 (in the horizontal direction in the figure) is 1.4 mm.

4 and 5, a mechanism for generating a bright portion near the side surface 14a and a mechanism for eliminating the bright portion will be described. In the sectional view of the backlight 50 (comparative example) shown in FIG. 4, the double-sided tape 15a attached to the lower half of the side surface 14a is different from the sectional view of the backlight 10 shown in FIG. Has been replaced by a double-sided tape 51 attached to the. That is, in the backlight 50, unlike the backlight 10, the side reflection sheet 17 a is adhered to the entire side surface 14 a of the light guide plate 14 via the double-sided tape 51.

  As shown in FIG. 4, the light ray L1 passes through the side surface 14a and the double-sided tape 51, and is diffusely reflected by the side reflection sheet 17a. Due to this diffuse reflection, a light ray L3 directed obliquely upward and to the left is generated. In addition, a light ray L4 which is directed to the lower left by the diffuse reflection, is reflected by the reflection sheet 17f for the reflection surface, and is directed obliquely upward to the left is generated. Similarly, the light ray L2 is diffusely reflected by the side reflection sheet 17a, and a light ray L6 directed diagonally upward and left and a light ray L7 directed diagonally upward and left is reflected by the reflection sheet 17f for the reflection surface which is directed diagonally downward and left at one end. I do. Note that FIG. 4 shows only light rays related to a bright portion generated near the side surface 14a, and does not show other light beams generated by diffuse reflection or light beams emitted from near the side surface before reaching the side surface 14a.

  As described above, in the backlight 50, the light beams L3, L4, L6, and L7 are concentrated near the side surface 14a due to the diffuse reflection of the side reflection sheet 17a, and a bright portion is generated.

  As shown in FIG. 5, in the backlight 10, light rays L6 and L7 are generated for the light ray L2 as in the backlight 50. On the other hand, the light ray L1 (partly) is specularly reflected at the interface between the side surface 14a and the air and becomes a light ray L5. This light ray L5 does not generate a light ray emitted from the light emitting surface 14e near the side surface 14a. As a result, since the light ray L5 is generated in the backlight 10, diffused reflected light is reduced as compared with the backlight 50 shown in FIG. 4, and a bright portion is not generated near the side surface 14a. This mechanism is the same for the other side surfaces 14b and 14c. In addition, a component that is not specularly reflected as the remaining portion of the light ray L1 is diffusely reflected by the side reflection sheet 17a, but is not shown.

  As described above, the backlight 10 has a mixture of diffuse reflection and specular reflection at a portion where the double-sided tapes 15a, 15b, 15c are not attached on the side surfaces 14a, 14b, 14c other than the incident surface 14d of the light guide plate 14. By doing so, the light emission amount near the side surface on the light emitting surface 14e is adjusted. As a result, even if the backlight 10 brings the side-surface reflecting sheets 17a, 17b, 17c, which are plate-shaped reflecting members, close to the side surfaces 14a, 14b, 14c of the light guide plate 14, the side surfaces 14a, 14b, The bright portion generated near 14c can be eliminated. The ratio between diffuse reflection and specular reflection is adjusted by the width of the double-sided tape 15a or the like.

  In the backlight 10, the reflection members facing the side surfaces 14a and the like were the side reflection sheets 17a, 17b, and 17c. In other backlights, the side surface of the light guide plate may be surrounded by a white frame. Even in this case, the ratio of the diffuse reflection and the specular reflection of the frame can be adjusted to eliminate the occurrence of a bright portion. Further, the entire reflecting sheet may be constituted by a reflecting sheet for reflecting surface 17f and a portion extending from the reflecting sheet for reflecting surface 17f, and the extended portion may be bent to be a reflecting member facing the side surface. In this case, the number of components can be reduced.

(2nd Embodiment)
In the backlight 10 shown as the first embodiment, the double-sided tape 15a and the like have a band shape. In the case of a band shape, the ratio of diffuse reflection and specular reflection is equal everywhere in the longitudinal direction of the side surface 14a. However, there are cases where it is desired to change the ratio of diffuse reflection and specular reflection in the longitudinal direction of the side surface 14a depending on the location. Therefore, a backlight 20 in which the ratio of specular reflection is large in a portion of the side surface 14a away from the LED 16 and the ratio of specular reflection is reduced on the LED 16 side will be described as a second embodiment of the present invention with reference to FIG.

  FIG. 6 is a side view of the backlight 20 drawn to explain the relationship between the side surface 14 a of the light guide plate 14 and the double-sided tape 21. FIG. 6 is different from the side view of the backlight 10 shown in FIG. 3 only in the shape of the double-sided tape 21. The members for which drawing is omitted are the same as those in FIG.

  On the side surface 14a, the double-sided tape 21 is wider on the LED 16 side, and becomes narrower as the distance from the LED 16 increases. That is, when the double-sided tape 21 is not used, the double-sided tape 21 functions effectively when a bright portion appears on the LED 16 side far from the side surface 14a. Conversely, when a bright portion is strongly generated near the LED 16 on the side surface 14a, the width of the double-sided tape 21 may be increased as the distance from the LED 16 increases.

(Third embodiment)
In the backlight 20 shown as the second embodiment, the width of the double-sided tape 21 was different depending on the location. For this reason, it may be difficult to manufacture the double-sided tape 21 by processing, pasting, or the like. Further, in the narrow part of the double-sided tape 21, the side reflection sheet 17a may not be fixed firmly. Therefore, according to a third embodiment of the present invention, referring to FIG. 6, a backlight 30 that can solve the above-mentioned problem by keeping the width of the double-sided tape constant while changing the ratio of diffuse reflection and specular reflection in the longitudinal direction of the side surface 14a. explain.

  FIG. 7 is a side view of the backlight 30 drawn for explaining the relationship between the side surface 14 a of the light guide plate 14 and the double-sided tape 31. FIG. 7 differs from the side view of the backlight 10 shown in FIG. 3 only in the shape of the double-sided tape 31. The members for which drawing is omitted are the same as those in FIG.

  As shown in FIG. 7, a slit 32 is formed in the double-sided tape 31. The slit 32 of the double-sided tape 31 has a high density on the LED 16 side, and the density decreases as the distance from the LED 16 increases. That is, in a case where the double-sided tape 31 is not used, the double-sided tape 31 functions effectively when a strong bright portion appears near the side surface 14 a in a region near the LED 16. In the case where a bright portion is strongly generated in a region far from the LED 16 side on the side surface 14a, the density of the slit 32 may be increased as the distance from the LED 16 increases.

  In the backlights 10, 20, and 30, a transparent double-sided tape 15a or the like is attached to a part of the side surface 14a or the like. Then, specular reflection is caused in a portion where the double-sided tape 15a or the like is not adhered, and diffused reflection is reduced, thereby eliminating a bright portion generated near the side surface. However, a transparent double-sided tape may not be able to completely eliminate the bright part. At this time, a reflective double-sided tape may be used instead of the double-sided tape. The reflective double-sided tape is preferably of a specular reflection type or a retroreflection type in which the incident direction and the reflection direction of a light beam coincide with each other. Since the reflective double-sided tape hardly causes diffuse reflection, it is possible to greatly reduce diffuse reflection light without lowering light use efficiency.

10, 20, 30 ... backlight,
11 ... polarizing sheet,
12 ... Prism sheet,
13 ... Diffusion sheet
14 ... light guide plate,
14a, 14b, 14c ... side surfaces,
14d: entrance surface,
14e: Light-emitting surface,
14f: reflective surface,
15a, 15b, 15c, 21, 31 ... double-sided tape,
16 ... LED,
17a, 17b, 17c ... side reflection sheet,
17f ... reflection sheet for reflection surface,
18 ... dot,
32 ... Slit,
L1 to L7: light rays.

Claims (7)

A light guide plate having one main surface as a light emitting surface, the other main surface as a reflective surface, and at least one side surface as an incident surface;
A light source disposed to face the incident surface;
A first reflecting member facing the side surface other than the incident surface ;
A second reflective member mounted below the reflective surface ;
Wherein the first reflecting member, and the second reflecting member in strip be separate, provided with a diffuse reflecting surface, it is fixed to the side surface other than the incident surface by means of a double-sided tape,
The side surface other than the incident surface includes a portion to which the double-sided tape is attached and a portion to which the double-sided tape is not attached ,
The backlight according to claim 1, wherein a height of the reflecting surface, a lower end of the double-sided tape, and a lower end of the first reflecting member coincide with each other . The backlight according to claim 1, wherein the double-sided tape is an integral body extending from one end to the other end in the longitudinal direction of the side surface other than the incident surface. The backlight according to claim 2, wherein the double-sided tape has a constant width in a direction from the light-emitting surface to the reflection surface. The backlight according to claim 2, wherein a width of the double-sided tape in a direction from the light-emitting surface toward the reflection surface changes depending on a location. The backlight according to claim 4, wherein the width increases or decreases as the distance from the incident surface increases. The backlight according to any one of claims 2 to 5, wherein the double-sided tape has a slit. The backlight according to claim 6, wherein the density of the slit varies depending on a location.