WO2020203941A1 - Backlight - Google Patents

Abstract

A backlight (1) comprises: a back case (2); a light guide plate (3) which has one major surface serving as a light-output surface, another major surface opposite the light-output surface serving as reflective surface, and one side surface serving as an input-light surface, and which is disposed on the back case (2) with the reflective surface facing downward; a light source (4) which is disposed in the back case (2) opposite the input-light surface of the light guide plate (3); and a diffusing sheet (6) which is disposed on the light-output surface of the light guide plate (3) and includes a reflecting portion (6c) provided in an end portion opposite the light source (4). The diffusing sheet (6) is disposed on the light-output surface of the light guide plate (3) in such a way that a direction in which the diffusing sheet (6) may extend due to thermal expansion coincides with a direction from the side surface of the light guide plate (3) opposite the light source (4) to the light source (4).

Description

Backlight

The present disclosure relates to a backlight for irradiating the back surface of a liquid crystal panel with light.

Backlights are widely used in smartphones and the like. The backlight has a back case, a light guide plate, a light source, and an optical sheet. The back case houses the light guide plate, the light source and the reflective sheet. In the light guide plate, one main surface is the light emitting surface, the other main surface facing the light emitting surface is the reflecting surface, one or two side surfaces are the light receiving surfaces, and the reflecting surface of the light guide plate is placed below the back case. Is placed. The light source has a light emitting element such as an LED (Light-Emitting Diode), and is arranged in the back case so as to face the light entering surface of the light guide plate.

The optical sheet has a rectangular diffusion sheet whose surface holographic shape functions as a minute and random lens array. The diffusion sheet is a heat-expandable resin material such as a polycarbonate film or polyethylene terephthalate, that is, it extends in a direction perpendicular to the end face of the light guide plate facing the light source as the ambient temperature rises and faces the light source as the ambient temperature decreases. It is composed of a material that contracts in the direction perpendicular to the end face of the light guide plate.

Conventionally, there has been proposed a backlight in which a pressing member is formed on a light source and a specular reflection layer formed on one end of an optical sheet is inserted between the light source and the pressing member (for example, Japanese Patent Application Laid-Open No. 2007-234412). reference).

A light source having a light emitting element such as an LED used for a backlight has a characteristic that the luminous efficiency decreases as the ambient temperature rises. Therefore, there is a disadvantage that the brightness of the backlight decreases as the ambient temperature rises.

An object of the present disclosure is to provide a backlight capable of keeping the brightness constant even if the ambient temperature rises.

In the backlight according to the present disclosure, the back case and one main surface are light emitting surfaces, the other main surface facing the light emitting surface is a reflecting surface, the first side surface is an incoming surface, and the back case has a reflecting surface. A light guide plate arranged with the light source facing down, a first light source arranged in the back case facing the light entering surface of the light guide plate, and a first light source arranged on the light emitting surface and facing the first light source. An optical sheet having a first reflecting portion provided at an end thereof, and the extension direction of the optical sheet due to thermal expansion is from the first side surface of the light guide plate facing the first light source to the first light source. It is characterized in that the optical sheet is arranged on the light emitting surface so as to coincide with the direction toward.

The backlight according to the present disclosure further includes a frame member fixed to the back case, and a fixing portion for fixing the optical sheet to the frame member at an end portion opposite to the side provided with the first reflecting portion. You may.

In the backlight according to the present disclosure, the light guide plate has a protrusion for fixing the optical sheet, the optical sheet is formed with a hole for inserting the protrusion, and the fixing portion has the protrusion. The optical sheet may be fixed by fixing it to the frame member.

In the backlight according to the present disclosure, the light guide plate has a first convex portion formed at the end opposite to the end portion of the light guide plate facing the first light source, and the protrusion is the first convex portion. The optical sheet is formed in a portion and has a second convex portion in which a hole is formed while corresponding to the first convex portion, and the frame member has an opening formed in a portion corresponding to the protrusion. You may.

The backlight according to the present disclosure covers the first reflective sheet arranged between the back case and the reflective surface, the first light source, and the lower portion of the end surface of the light guide plate facing the first light source. It may further have a second reflective sheet disposed between the case and the first reflective sheet.

In the backlight according to the present disclosure, the back case may have a first groove for accommodating the second reflective sheet.

In the backlight according to the present disclosure, the first reflective sheet may be fixed to the back case at the center of the end opposite to the end of the light guide plate facing the first light source.

The backlight according to the present disclosure further includes a second light source arranged in the back case so as to face a second light receiving surface corresponding to a second side surface opposite to the first side surface of the light guide plate. However, the optical sheet may further have a second reflecting portion provided at an end facing the second light source.

The backlight according to the present disclosure may further include a frame member fixed to the back case and a fixing portion for fixing the optical sheet to the frame member at the center of the first reflecting portion and the second reflecting portion. Good.

In the backlight according to the present disclosure, the light guide plate has a protrusion for fixing the optical sheet, the optical sheet is formed with a hole for inserting the protrusion, and the fixing portion has the protrusion. The optical sheet may be fixed by fixing it to the frame member.

In the backlight according to the present disclosure, the light guide plate is formed at the center of the end portion of the light guide plate facing the first light source and the end portion of the light guide plate perpendicular to the end portion of the light guide plate facing the second light source. The first convex portion is formed, the protrusion is formed on the first convex portion, and the optical sheet has a second convex portion corresponding to the first convex portion and having a hole formed therein. , The frame member may have an opening formed at a position corresponding to the protrusion.

The backlight according to the present disclosure may further have a pressing member that is arranged between the frame member and the optical sheet and presses the optical sheet toward the light guide plate by fixing the frame member to the back case. ..

The backlight according to the present disclosure covers the first reflective sheet arranged between the back case and the reflective surface, the first light source, and the lower portion of the end surface of the light guide plate facing the first light source. The back case and the first are covered with a second reflective sheet arranged between the case and the first reflective sheet, and the lower part of the end face of the second light source and the light guide plate facing the second light source. It may further have a third reflective sheet arranged between the reflective sheet and the reflective sheet.

In the backlight according to the present disclosure, the back case may have a second groove for accommodating the third reflective sheet.

In the backlight according to the present disclosure, the first reflective sheet is fixed to the back case at the end of the light guide plate facing the first light source and the central portion of the end of the light guide plate facing the second light source. May be good.

According to the present disclosure, the brightness of the backlight can be kept constant even if the ambient temperature rises.

It is a front view of the backlight of 1st Embodiment by this disclosure. It is an exploded perspective view of the backlight of FIG. FIG. 1 is a cross-sectional view taken along the line AA of FIG. It is a cross-sectional view of BB of FIG. It is an enlarged view of the part X of FIG. It is a bottom view of the diffusion sheet of the backlight of FIG. It is a figure which shows typically the thermal expansion and contraction of the diffusion sheet of FIG. It is a front view of another embodiment of the backlight by this disclosure. It is an exploded perspective view of the backlight of FIG. FIG. 6 is a sectional view taken along the line CC of FIG. It is a cross-sectional view of C'-C'of FIG. FIG. 6 is a sectional view taken along line DD of FIG. It is an enlarged view of the part Y of FIG. It is a bottom view of the diffusion sheet of the backlight of FIG. It is a graph which shows the contribution of the reflection part of FIG. 2 and FIG. 4 to the brightness of the backlight, and the contribution of the reflection part of FIGS. 7 and 9 to the brightness of the backlight. It is a figure which showed more concretely the thermal expansion and contraction of the diffusion sheet shown in FIG. It is a graph which showed the simulation result which calculated the change of the brightness of the backlight when the temperature of the backlight was changed. It is a graph which showed that the brightness decrease of LED with temperature rise, and the decrease in brightness of LED is partially compensated by using the backlight of this embodiment. It is a figure for demonstrating use of the modification of the holding member of FIG. It is a figure for demonstrating use of the modification of the holding member of FIG. It is a figure for demonstrating use of the modification of the holding member of FIG. It is a figure for demonstrating use of the modification of the holding member of FIG. It is a figure for demonstrating use of the transparent plate which can be used for the backlight by this disclosure. It is a figure for demonstrating use of another transparent plate which can be used for the backlight by this disclosure. It is a figure for demonstrating another structure for suppressing the movement of an optical sheet in the direction perpendicular to an optical sheet. It is a front view of the backlight of the 3rd Embodiment by this disclosure. It is an exploded perspective view of the backlight of FIG. FIG. 21 is a cross-sectional view taken along the line AA of FIG. FIG. 21 is a cross-sectional view taken along the line BB of FIG. It is an enlarged view of the part X of FIG. It is a partial cross-sectional view of FIG. 22 and an enlarged view thereof. It is a figure which shows typically the thermal expansion and contraction of the reflective sheet of FIG. It is a front view of another embodiment of the backlight by this disclosure. It is an exploded perspective view of the backlight of FIG. FIG. 26 is a cross-sectional view taken along the line CC of FIG. It is a cross-sectional view of C'-C'of FIG. 26. FIG. 26 is a sectional view taken along line DD of FIG. It is an enlarged view of the part Y of FIG. It is a partial cross-sectional view of FIG. 27 and an enlarged view thereof. It is a figure which showed typically an example of the structure of the light source used for the backlight of this disclosure. It is an enlarged sectional view which showed the modification of the light guide plate, the diffusion sheet, and the reflection part used for the backlight of this disclosure. It is an enlarged plan view which showed another modification of the light guide plate, the diffusion sheet, and the reflection part used for the backlight of this disclosure.

The embodiment of the backlight according to the present disclosure will be described in detail with reference to the drawings. However, it should be noted that the technical scope of the present disclosure is not limited to those embodiments, but extends to the inventions described in the claims and their equivalents. In addition, the same member is designated by the same reference numeral.

(First Embodiment)
FIG. 1 is a front view of an embodiment of the backlight according to the present disclosure, FIG. 2 is an exploded perspective view of the backlight of FIG. 1, and FIG. 3A is AA of FIG. It is a sectional view, FIG. 3B is a sectional view taken along the line BB of FIG. 1, and FIG. 3C is an enlarged view of a portion X of FIG. In FIG. 3C, a part of the member shown in FIG. 2 is omitted for clarity.

The backlight 1 is an edge light type backlight for irradiating the back surface of a liquid crystal panel (not shown) with light, and includes a back case 2, a light guide plate 3, a light source 4, a reflective sheet 5, and diffusion. It has an optical sheet 9 having a sheet 6 and prism sheets 7 and 8, a frame member 10, and a pressing member 11. The light source 4 is an example of the first light source.

The back case 2 accommodates a light guide plate 3, a light source 4, a reflective sheet 5, an optical sheet 9, and a holding member 11, and has a screw insertion hole 2c into which a screw 13 is inserted to fix the frame member 10 to the back case 2. Have.

The light guide plate 3 is arranged in the back case 2 with one main surface as a light emitting surface, another main surface facing the light emitting surface as a reflecting surface, one side surface as an incoming surface, and the back case 2 with the reflecting surface facing down. To. The light entry surface is an example of a first light entry surface corresponding to the first side surface. Further, the light guide plate 3 has a convex portion 3a formed at the end opposite to the end portion of the light guide plate 3 facing the light source 4, and a protrusion 3b formed on the convex portion 3a. The convex portion 3a is an example of the first convex portion, and the convex portion 3b is an example of the fixed portion. The light guide plate 3 is made of a resin such as polycarbonate or acrylic, glass having high light resistance, or the like. The protrusion 3b is made of the same material as the light guide plate 3 or a resin such as silicone that does not generate gas while the backlight 1 is lit. The protrusion 3b may be formed of a threaded pin or the like.

As shown in FIG. 3A, the light source 4 has a light emitting element 4a arranged so as to face the light entering surface of the light guide plate 3 and a light emitting element 4a attached to the light emitting element 4a in the back case 2 and a double-sided tape (not shown). It has a flexible printed circuit board (FPC) 4b fixed to the back case 2 by.

The reflective sheet 5 is arranged between the back case 2 and the reflective surface of the light guide plate 3, and is made of a heat-expandable resin material such as polyethylene terephthalate. In order to make the extension direction of the reflective sheet 5 due to thermal expansion coincide with the direction from the side surface of the light guide plate 3 facing the light source 4 toward the light source 4, the flow direction (MD direction) of the reflective sheet 5 is set to the y direction. The vertical direction (TD direction) of the reflective sheet 5 is defined as the x direction. Further, the reflective sheet 5 has a convex portion 5a corresponding to the convex portion 3a.

The reflective sheet 5 is fixed to the back case 2 at the center of the end opposite to the end of the light guide plate 3 facing the light source 4 by fixing the convex portion 5a to the back case 2 with double-sided tape. There is. Therefore, the central portion of the end portion on the opposite side of the end portion of the light guide plate 3 facing the light source 4 serves as a position reference for the extension of the reflective sheet 5.

The diffusion sheet 6 may be arranged on the light emitting surface of the light guide plate 3 and may function as a lens array having a minute and random holographic shape on the surface. The diffusion sheet 6 is made of a heat-expandable resin material such as a polycarbonate film or polyethylene terephthalate. In order to make the extension direction of the diffusion sheet 6 due to thermal expansion coincide with the direction from the side surface of the light guide plate 3 facing the light source 4 toward the light source 4, the MD direction of the diffusion sheet 6 is set to the y direction, and the diffusion sheet 6 is set. Let the TD direction of be the x direction.

FIG. 4 is a bottom view of the diffusion sheet of FIG. The diffusion sheet 6 includes a convex portion 6a corresponding to the convex portion 3a, a hole 6b for inserting the protruding portion 3b formed in the convex portion 6a, and a reflecting portion 6c provided at an end portion facing the light source 4. Have. The reflecting portion 6c is an example of the first reflecting portion.

As shown in FIG. 2B, the diffusion sheet 6 has a central portion of an end portion opposite to the end portion of the light guide plate 3 facing the light source 4 by fixing the convex portion 5a to the back case 2 as described later. It is fixed to the back case 2 with. Therefore, the central portion of the end portion on the opposite side of the end portion of the light guide plate 3 facing the light source 4 serves as a position reference for the elongation of the diffusion sheet 6. By setting the extension position reference of the diffusion sheet 6 at the center of the end opposite to the end of the light guide plate 3 facing the light source 4 in this way, it is advantageous to narrow the frame of the backlight 1.

The reflective portion 6c is formed of a reflective sheet made of a heat-expandable resin material such as polyethylene terephthalate, and is adhered, crimped or attached to the main body of the diffusion sheet 6. The reflection portion 6c may be provided by printing white on the end portion of the diffusion sheet 6 facing the light source 4. To prevent wrinkles, kinks, etc. of the main body of the diffusion sheet 6 and the reflection portion 6c caused by the difference between the linear expansion coefficient of the portion of the diffusion sheet 6 excluding the reflection portion 6c and the coefficient of thermal expansion of the reflection sheet forming the reflection portion 6c. In addition, the MD direction of the reflective sheet forming the reflective portion 6c is the y direction, and the TD direction of the reflective sheet forming the reflective portion 6c is the x direction.

The prism sheet 7 has microprisms parallel to one side formed on one side, the prism sheet 8 has microprisms parallel to the other side formed on one side, and the prism sheets 7 and 8 are stacked and diffused sheets. Placed on top of 6. The prism sheet 7 has a convex portion 7a corresponding to the convex portion 3a and a hole 7b for inserting the convex portion 3b formed in the convex portion 7a. The prism sheet 8 has a convex portion 8a corresponding to the convex portion 3a and a hole 8b for inserting the convex portion 3b formed in the convex portion 8a. The convex portions 6a, 7a, 8a are examples of the second convex portions.

The frame member 10 is fixed to the back case 2 from above the optical sheet 9 by screws 13. The frame member 10 is made of a metal having a relatively high reflectance (for example, 95% or more) (for example, a silver-coated aluminum material), a resin having a relatively high reflectance (for example, 95% or more), or the like. Further, the frame member 10 may be made of a metal or resin having a relatively high reflectance (for example, less than 95%) and may be provided with white printing, a reflective sheet or the like on the lower surface. The frame member 10 has an opening 10a formed at a position corresponding to the protrusion 3b, and a screw insertion hole 10b into which a screw 13 is inserted to fix the frame member 10 to the back case 2. Since the opening 10a is formed outside the display area of the backlight 1, the convex portions 3a, 5a, 6a, 7a, 8a are formed outside the display area of the backlight 1.

The pressing member 11 is rectangular and is arranged between the frame member 10 and the optical sheet 9. The pressing member 11 may have another shape such as a circular shape or a polygonal shape. The pressing member 11 is made of an elastic body such as rubber or elastomer or a resin such as plastic. As shown in FIG. 3C, the pressing member 11 is arranged on the optical sheet 9, and the frame member 10 is fixed to the back case 2, so that the pressing member 11 presses the optical sheet 9 toward the light guide plate 3 and the diffusion sheet. 6 can be fixed to the back case 2.

As a result, the movement of the optical sheet 9 housed in the back case 2 in the z direction, that is, the movement of the optical sheet 9 in the direction perpendicular to the optical sheet 9 can be suppressed. The pressing member 11 may be fixed to the optical sheet 9 with double-sided tape (not shown). Further, by arranging the pressing member 11 on the optical sheet 9 corresponding to the outside of the display area of the backlight 1, the protrusion 3b serves as a reference position for the elongation of the optical sheet 9, and the heat of the optical sheet 9 in the x-direction and the y-direction becomes the reference position. Since the expansion and contraction is not suppressed by the pressing member 11, the influence of the generation of wrinkles and the like due to the thermal expansion and contraction of the optical sheet 9 is not exerted.

FIG. 5 is a diagram schematically showing the thermal expansion and contraction of the diffusion sheet of FIG. When the ambient temperature is substantially the same as room temperature (for example, 25 ° C.), the reflecting unit 6c does not reflect the light from the light source 4, as shown by the arrow in FIG. 5A. On the other hand, as the ambient temperature rises, the expansion of the diffusion sheet due to thermal expansion increases so that the reflecting portion 6c covers at least a part of the light source 4, as shown by the arrow in FIG. 5B. 6c reflects the light from the light source 4. The amount of light from the light source 4 that is reflected by the reflecting unit 6c and taken into the light source plate 3 increases as the extension of the diffusion sheet 6 in the direction from the side surface of the light source plate 3 facing the light source 4 toward the light source 4 increases.

According to the present embodiment, as the brightness of the backlight 1 decreases as the ambient temperature rises, the diffusion sheet 6 extends significantly from the side surface of the light guide plate 3 facing the light source 4 toward the light source 4. Become. As a result, the amount of light from the light source 4 that is reflected by the reflecting unit 6c and taken into the light guide plate 3 also increases, so that the brightness of the backlight 1 can be kept constant even if the ambient temperature rises.

Further, the diffusion sheet 6 is fixed to the back case 2 at the center of the end opposite to the end of the light guide plate 3 facing the light source 4, and is fixed to the back case 2 on the opposite side of the end of the light guide plate 3 facing the light source 4. Since the central portion of the end portion serves as a position reference for the elongation of the diffusion sheet 6, the elongation of the diffusion sheet 6 can be satisfactorily controlled in the y direction.

6 is a front view of another embodiment of the backlight according to the present disclosure, FIG. 7 is an exploded perspective view of the backlight of FIG. 6, and FIG. 8A is a sectional view taken along the line CC of FIG. 8B is a cross-sectional view taken along the line C'-C'of FIG. 6, FIG. 8C is a cross-sectional view taken along the line DD of FIG. 8, and FIG. 8D is an enlarged view of a portion Y of FIG. In FIG. 8D, some of the members shown in FIG. 6 are omitted for clarity.

The backlight 21 is an edge light type backlight for irradiating the back surface of a liquid crystal panel (not shown) with light, and is a back case 22, a light guide plate 23, light sources 24, 24', and a reflective sheet 25. An optical sheet 29 having a diffusion sheet 26 and prism sheets 27 and 28, a frame member 30, and a pressing member 31. The light source 24 is an example of the first light source, and the light source 24'is an example of the second light source.

The back case 22 accommodates the light guide plate 23, the light sources 24, 24', the reflective sheet 25, the optical sheet 29, and the holding member 31, and the screw 33 is inserted to fix the frame member 30 to the back case 22. It has a hole 22c.

The light guide plate 23 is arranged on the back case 22 with one main surface as an light emitting surface, the other main surface facing the light emitting surface as a reflecting surface, two side surfaces as an incoming surface, and the back case 22 with the reflecting surface facing down. To. These incoming surfaces are examples of a first incoming surface corresponding to the first side surface and a second incoming surface corresponding to the second side surface. Further, the light guide plate 23 is formed on the convex portion 23a formed at the end portion of the light guide plate 23 facing the light source 24 and the central portion of the end portion of the light guide plate 23 facing the light source 24', and the convex portion 23a. It has a protrusion 23b. The convex portion 23a is an example of the first convex portion, and the convex portion 23b is an example of the fixed portion. The light guide plate 23 is made of a resin such as polycarbonate or acrylic, glass having high light resistance, or the like. The protrusion 23b is made of the same material as the light guide plate 23 or a resin such as silicone that does not generate gas while the backlight 21 is lit. The protrusion 23b may be configured by a pin with a screw or the like.

As shown in FIG. 8A, the light source 24 has a light emitting element 24a arranged so as to face one of the light receiving surfaces of the light guide plate 23 and a double-sided tape (shown). It has an FPC 24b fixed to the back case 22 by (1).

As shown in FIG. 8B, the light source 24'is attached with a light emitting element 24a'arranged in the back case 22 so as to face the other light receiving surface of the light guide plate 23, and a double-sided tape. It has an FPC 24b'fixed to the back case 22 by (not shown).

The reflective sheet 25 is arranged between the back case 22 and the reflective surface of the light guide plate 23, and is made of a heat-expandable resin material such as polyethylene terephthalate. In order to make the extension direction of the reflective sheet 25 due to thermal expansion coincide with the direction from the side surface of the light guide plate 23 facing the light source 24 toward the light source 24, the flow direction (MD direction) of the reflective sheet 25 is set to the x direction. The vertical direction (TD direction) of the reflective sheet 25 is defined as the y direction. Further, the reflective sheet 25 has a convex portion 25a corresponding to the convex portion 23a.

By fixing the convex portion 25a to the back case 22 with double-sided tape, the reflective sheet 25 is formed at the end portion of the light guide plate 23 facing the light source 24 and the central portion of the end portion of the light guide plate 23 facing the light source 24'. It is fixed to the back case 2. Therefore, the end portion of the light guide plate 23 facing the light source 24 and the central portion of the end portion of the light guide plate 23 facing the light source 24'are used as a position reference for the extension of the reflective sheet 25.

The diffusion sheet 26 may be arranged on the light emitting surface of the light guide plate 3 and may function as a lens array having a minute and random holographic shape on the surface. The diffusion sheet 26 is made of a heat-expandable resin material such as a polycarbonate film or polyethylene terephthalate. The extension direction of the diffusion sheet 26 due to thermal expansion coincides with the direction from the side surface of the light guide plate 3 facing the light source 24 toward the light source 24 and the direction from the side surface of the light guide plate 23 facing the light source 24'toward the light source 24'. The MD direction of the diffusion sheet 26 is set to the x direction, and the TD direction of the diffusion sheet 26 is set to the y direction.

FIG. 9 is a bottom view of the diffusion sheet of FIG. 7. The diffusion sheet 26 includes a convex portion 26a corresponding to the convex portion 23a, a hole 26b for inserting the protruding portion 23b formed in the convex portion 26a, and a reflecting portion 26c provided at an end portion facing the light source 24. A reflecting portion 26d provided at an end facing the light source 24'. The reflection unit 26c is an example of the first reflection unit, and the reflection unit 26d is an example of the second reflection unit.

As will be described later, the diffusion sheet 26 has a convex portion 26a fixed to the back case 2, so that the end portion of the light guide plate 23 facing the light source 24 and the light guide plate facing the light source 24'as shown in FIG. 8C. It is fixed to the back case 22 at the center of the end of the 23. Therefore, the end portion of the light guide plate 23 facing the light source 24 and the central portion of the end portion of the light guide plate 23 facing the light source 24'are used as a position reference for the extension of the diffusion sheet 6. The convex portions 26a and the holes 26b may be provided on both of the sides of the diffusion sheet 26 facing each other. In this case, similarly, the convex portions 23a of the light guide plate 23 provided on both of the opposite sides of the light guide plate 23. Each may be fixed by the protrusion 23b.

The reflective portions 26c and 26d are formed of a reflective sheet made of a heat-expandable resin material such as polyethylene terephthalate, and are adhered, crimped or attached to the main body of the diffusion sheet 26. Reflecting portions 26c and 26d may be provided by white printing on the end portion of the diffusion sheet 26 facing the light source 24 and the end portion of the diffusion sheet 26 facing the light source 24'. Wrinkles in the main body of the diffusion sheet 26 and the reflection portions 26c and 26d caused by the difference between the linear expansion coefficient of the portion of the diffusion sheet 26 excluding the reflection portions 26c and 26d and the coefficient of thermal expansion of the reflection sheet forming the reflection portions 26c and 26d. In order to prevent twisting and the like, the MD direction of the reflective sheet forming the reflective portions 26c and 26d is set to the x direction, and the TD direction of the reflective sheet forming the reflective portions 26c and 26d is set to the y direction.

The prism sheet 27 has microprisms parallel to one side formed on one side, the prism sheet 28 has microprisms parallel to the other side formed on one side, and the prism sheets 27 and 28 are stacked and diffused sheets. It is placed on top of 26. The prism sheet 27 has a convex portion 27a corresponding to the convex portion 23a and a hole 27b for inserting the protruding portion 23b formed in the convex portion 27a. The prism sheet 28 has a convex portion 28a corresponding to the convex portion 23a and a hole 28b for inserting the protruding portion 23b formed in the convex portion 28a. The convex portions 26a, 27a, 28a are examples of the second convex portions.

The frame member 30 is fixed to the back case 22 from above the optical sheet 29 by screws 33. The frame member 30 is made of a metal having a relatively high reflectance (for example, 95% or more) (for example, a silver-coated aluminum material), a resin having a relatively high reflectance (for example, 95% or more), or the like. Further, the frame member 30 may be made of a metal or resin having a relatively high reflectance (for example, less than 95%) and may be provided with white printing, a reflective sheet or the like on the lower surface.

The frame member 30 has an opening 30a formed at a position corresponding to the protrusion 23b, and a screw insertion hole 30b into which a screw 33 is inserted to fix the frame member 30 to the back case 22. Since the opening 30a is formed outside the display area of the backlight 1, the convex portions 23a, 25a, 26a, 27a, 28a are formed outside the display area of the backlight 21.

The pressing member 31 is rectangular and is arranged between the frame member 30 and the optical sheet 29. The pressing member 31 may have another shape such as a circular shape or a polygonal shape. The pressing member 31 is made of an elastic body such as rubber or elastomer or a resin such as plastic. As shown in FIG. 8D, the pressing member 31 is arranged on the optical sheet 9, and the frame member 30 is fixed to the back case 22, so that the pressing member 31 presses the optical sheet 29 toward the light guide plate 23 and the diffusion sheet. 26 can be fixed to the back case 22.

As a result, the movement of the optical sheet 29 housed in the back case 22 in the z direction, that is, the movement of the optical sheet 29 in the direction perpendicular to the optical sheet 29 can be suppressed. The pressing member 31 may be fixed to the optical sheet 29 with double-sided tape (not shown). Further, by arranging the pressing member 31 on the optical sheet 29 corresponding to the outside of the display area of the backlight 21, the influence of wrinkles and the like due to the expansion and contraction of the optical sheet 29 is not exerted.

According to the present embodiment, as the brightness of the backlight 21 decreases as the ambient temperature rises, the diffusion sheet 26 extends from the side surface of the light guide plate 3 facing the light source 24 toward the light source 24 and the light source. The extension of the diffusion sheet 26 in the direction from the side surface of the light guide plate 3 facing the 24'toward the light source 24'is increased. As a result, the amount of light from the light sources 24 and 24'reflected by the reflecting portions 26c and 26d and taken into the light guide plate 23 also increases, so that the brightness of the backlight 21 can be kept constant even if the ambient temperature rises. ..

Further, the diffusion sheet 26 is fixed to the back case 22 at the end of the light guide plate 23 facing the light source 24 and the center of the end of the light guide plate 23 facing the light source 24', and is fixed to the back case 22 and faces the light source 24. Since the end of the 23 and the center of the end of the light guide plate 23 facing the light source 24'are the position reference for the elongation of the diffusion sheet 26, the elongation of the diffusion sheet 26 should be well controlled in the x direction. Can be done.

FIG. 10 is a graph showing the contribution of the reflecting portion of FIGS. 2 and 4 to the brightness of the backlight and the contribution of the reflecting portion of FIGS. 7 and 9 to the brightness of the backlight. In FIG. 10, a straight line a indicates a change in the ratio of the brightness of the backlight 1 to the brightness of the backlight having the same configuration as that of the backlight 1 except that the reflection portion 6c is not provided, according to the ambient temperature. The change according to the ambient temperature of the ratio of the brightness of the backlight 21 to the brightness of the backlight having the same configuration as the backlight 21 except that it does not have 26c and 26d is shown by a straight line b.

As shown by the straight line a in FIG. 10, the brightness of the backlight having the same configuration as that of the backlight 1 except that the brightness of the backlight 1 does not have the reflecting portion 6c at 90 ° C. corresponding to the ambient temperature at the time of lighting. It can be seen that it is 1.2% higher than that.

Further, as shown by the straight line b in FIG. 10, the backlight 21 has the same configuration as the backlight 21 except that the brightness of the backlight 21 does not have the reflecting portions 26c and 26d at 90 ° C. corresponding to the ambient temperature at the time of lighting. It can be seen that it is 2.5% higher than the brightness of the backlight.

11 (a) to 11 (c) are views showing the thermal expansion and contraction of the diffusion sheet 6 shown in FIG. 5 more concretely. 11 (a) to 11 (c) show in the horizontal direction so that the reflecting portion 6c covers the upper part of the light source 4 as the diffusion sheet 6 is stretched by heat in the configuration of the backlight 1 shown in FIG. It shows a state of moving in the (y direction in the figure) and reflecting the light from the light source 4.

FIG. 11A shows the state of the reflecting portion 6c when the temperature of the backlight 1 is room temperature T0 (for example, 25 ° C.). At room temperature T0, the horizontal separation distance from the reflecting portion 6c to the back case 2 is d (for example, 0.90 mm), and the light emitted from the light source 4 leaks from this gap d, resulting in low light utilization efficiency. , The brightness of the backlight 1 is suppressed.

FIG. 11B shows the state of the reflecting portion 6c when the temperature of the backlight 1 rises to T1 (for example, 60 ° C.). When the diffusion sheet 6 is stretched as the temperature rises, the reflecting portion 6c moves in the horizontal direction so as to cover the upper part of the light source 4. As a result, the separation distance from the reflecting portion 6c to the back case 2 is reduced (for example, 0.42 mm), and the light emitted from the light source 4 is reflected by the reflecting portion 6c to increase the light utilization efficiency. Therefore, the backlight 1 is used. Brightness is improved.

FIG. 11C shows the state of the reflective portion 6c when the temperature of the diffusion sheet 6 rises to T2 (for example, 100 ° C.) higher than T1. When the diffusion sheet 6 is further extended with the further temperature rise, the reflective portion 6c comes into contact with the side surface of the back case 2. As a result, since the upper part of the light source 4 is completely covered by the reflecting portion 6c, all the light emitted upward from the light source 4 is reflected by the reflecting portion 6c, and the brightness of the backlight 1 is further improved.

FIG. 12 is a graph showing the simulation results of calculating the change in the brightness of the backlight 1 when the temperature of the backlight 1 is changed. The simulation result shown in FIG. 12 is a calculation of the brightness of the backlight 1 in the three states of the reflecting portion 6c shown in FIGS. 11A to 11C. The horizontal axis of FIG. 12 indicates the temperature (° C.) of the backlight 1, and the vertical axis of FIG. 12 is the relative brightness (%) of the backlight 1 based on the brightness of the backlight 1 at room temperature T0 (25 ° C.). Is shown. The horizontal length of the diffusion sheet 6 was set to 300 mm. It can be seen that the relative brightness a1 of the backlight 1 shown in FIG. 12 increases as the temperature of the backlight 1 rises, as described with reference to FIGS. 11 (a) to 11 (c).

The simulation result shown in FIG. 12 is a simulation result obtained on the assumption that the brightness of a light emitting element such as an LED used as the light source 4 is constant regardless of the temperature. However, it is known that the brightness of LEDs decreases as the temperature rises.

FIG. 13 is a graph showing that the decrease in LED brightness due to the temperature rise and the decrease in LED brightness are partially compensated by using the backlight 1 of the present embodiment. The relative brightness b0 shown by the broken line indicates a decrease in the brightness of the LED as the temperature rises. On the other hand, the relative brightness b1 shown by the solid line shows the simulation result of the brightness of the backlight 1 calculated on the assumption that the brightness of the light source 4 decreases like the relative brightness b0 as the temperature rises. It can be seen that the relative brightness b1 of the backlight 1 of the present embodiment is improved as compared with the relative brightness b0 indicating the decrease in the brightness of the LED with the increase in temperature. For example, the relative luminance b1 at 100 ° C. is improved by about 3.6% as compared with the relative luminance b0. Therefore, it can be seen that by using the backlight 1 of the present embodiment, the decrease in the brightness of the light source 4 due to the temperature rise is partially compensated, though not completely.

(Second Embodiment)
Conventionally, a backlight in which a holding member for holding an optical sheet is arranged on the side of a reflecting surface of a light guide plate has been proposed. When the front case is attached to the back case, a clearance is created between the optical sheet housed in the back case and the front case. Therefore, it is difficult to suppress the movement of the optical sheet in the direction perpendicular to the optical sheet (z-axis direction).

An object of the present embodiment is to provide a backlight capable of suppressing the movement of the optical sheet in the direction perpendicular to the optical sheet housed in the back case.

14 to 17 are diagrams for explaining the use of a modified example of the pressing member 11 of FIG. 3C. As shown in FIG. 14 corresponding to FIG. 3C, the pressing member 11A in which the hole 11a into which the protrusion 3b is inserted may be formed may be used instead of the pressing member 11. Further, as shown in FIG. 15 corresponding to FIG. 3C, a pressing member 11B having holes 11b formed in the y direction may be used instead of the pressing member 11.

Further, as shown in FIG. 16 corresponding to FIG. 3C, instead of the pressing member 11, a pressing member 11C having a recess 11c formed in the protrusion 3b may be used. Further, as shown in FIG. 17 corresponding to FIG. 3C, two triangular pressing members 11D and 11D'may be used instead of the pressing member 11.

FIG. 18 is a diagram for explaining the use of a transparent plate that can be used for the backlight according to the present disclosure. 18A shows a front view of the transparent plate 12, FIG. 18B shows a side view of the transparent plate 12, and FIG. 18C shows a point having a hole into which a screw 13'is inserted to fix the transparent plate 12. It is a figure which shows the state which attached the transparent plate 12 to the backlight 1'which has the same structure as the backlight 1 except that.

As shown in FIG. 18B, the transparent plate 12 has a step corresponding to the step formed by the back case 2 of the backlight 1', the frame member 10, and the optical sheet 9. By attaching the transparent plate 12 to the backlight 1'so that the transparent plate 12 is in contact with the optical sheet 9, the entire surface of the optical sheet 9 is pressed down, so that the movement of the optical sheet 9 in the direction perpendicular to the optical sheet 9 is suppressed. can do. Further, even when the backlight 1'does not have the protrusion 3b and the frame member 10, the movement of the optical sheet 9 in the direction perpendicular to the optical sheet 9 can be suppressed. Preferably, the frame member 10 is made of the same material as the optical sheet 9. When the frame member 10 is made of the same material as the optical sheet 9, the amount of thermal expansion and contraction of the frame member 10 is the same as the amount of thermal expansion and contraction of the optical sheet 9, and the influence of wrinkles and the like is not exerted. Further, even when the frame member 10 is softer or thinner than the optical sheet 9, the influence of wrinkles and the like due to thermal expansion and contraction of the optical sheet 9 is not exerted.

FIG. 19 is a diagram for explaining the use of a transparent plate that can be used for the backlight according to the present disclosure. 19A shows a front view of the transparent plate 12', FIG. 19B shows a side view of the transparent plate 12, and FIG. 19C shows a point having a pin 2a' for insertion into the hole 12a of the transparent plate 12'. It is a figure which shows the state which attached the transparent plate 12'to the backlight 1" which has the same structure as the backlight 1 except that.

As shown in FIG. 19B, the transparent plate 12'has a step corresponding to a step formed by the back case 2, the frame member 10 and the optical sheet 9 of the backlight 1'. By attaching the transparent plate 12'to the backlight 1'so that the transparent plate 12'contacts the optical sheet 9, the entire surface of the optical sheet 9 is pressed down, so that the movement of the optical sheet 9 in the direction perpendicular to the optical sheet 9 is performed. Further, even when the backlight 1 "does not have the protrusion 3b and the frame member 10, the movement of the optical sheet 9 in the direction perpendicular to the optical sheet 9 can be suppressed. Preferably, the frame member 10 is made of the same material as the optical sheet 9. When the frame member 10 is made of the same material as the optical sheet 9, the amount of thermal expansion and contraction of the frame member 10 is the same as the amount of thermal expansion and contraction of the optical sheet 9, and the influence of wrinkles and the like is not exerted. Further, even when the frame member 10 is softer or thinner than the optical sheet 9, the influence of wrinkles and the like due to thermal expansion and contraction of the optical sheet 9 is not exerted.

The pressing member 11 may have other shapes such as a circle and a polygon, and examples of other shapes have been described above with reference to FIGS. 14 to 17.

As a result, the movement of the optical sheet 29 in the z direction, that is, the movement of the optical sheet 29 in the direction perpendicular to the optical sheet 29 can be suppressed.

According to the present embodiment, the frame member 30 fixed to the back case 22 from above the optical sheet 29 and the protrusion 23b for fixing the optical sheet 29 allow the optical sheet 29 in the direction perpendicular to the optical sheet 29. Movement can be suppressed.

Further, the diffusion sheet 26 is fixed to the back case 22 at the end of the light guide plate 23 facing the light source 24 and the center of the end of the light guide plate 23 facing the light source 24', and is fixed to the back case 22 and faces the light source 24. Since the end of the 23 and the center of the end of the light guide plate 23 facing the light source 24'are the position reference for the elongation of the diffusion sheet 26, the elongation of the diffusion sheet 26 should be well controlled in the x direction. Can be done.

FIG. 20 is a diagram for explaining another structure for suppressing the movement of the optical sheet in the direction perpendicular to the optical sheet. FIG. 20 is formed in the light guide plate 23 so as to face the elongated holes 29b and the protrusions 23b formed in the optical sheet 29 so as to face the holes 26b, 27b, 28b in the backlight 21 shown in FIG. The protrusion 23b'inserted into the elongated hole 29b is shown.

By forming these elongated holes 29b and the protrusion 23b'to face the holes 26b, 27b, 28b and the protrusion 23b, it is possible to prevent the optical sheet 29 from rotating around the protrusion 23b. ..

(Third Embodiment)
Conventionally, there has been proposed a backlight in which a pressing member is formed on a light source and a specular reflection layer formed on one end of a reflective sheet is inserted between the light source and the pressing member (for example, Japanese Patent Application Laid-Open No. 2007-2344412 reference). In the backlight, the reflective sheet made of a heat-expandable resin material is designed so as not to come into contact with the back case even when stretched according to an ambient temperature substantially the same as the maximum temperature when the backlight is lit.

For this reason, there is light from a light source that the position of the edge of the reflective sheet changes according to the ambient temperature and cannot be reflected by the reflective sheet due to heat shrinkage of the reflective sheet. That is, it can be reflected by a reflective sheet that is stretched according to the ambient temperature that is substantially the same as the maximum temperature when the backlight is lit, but is reflected by the heat-shrinked reflective sheet when the ambient temperature is lower than the maximum temperature. There is light from a light source that cannot.

Therefore, light loss may occur due to the presence of light from a light source that cannot be reflected by the reflective sheet due to heat shrinkage of the reflective sheet. When such light loss occurs, the optical performance of the backlight deteriorates.

An object of the present embodiment is to provide a backlight in which the optical performance does not deteriorate even if the reflective sheet is heat-shrinked.

21 is a front view of the backlight according to the third embodiment according to the present disclosure, FIG. 22 is an exploded perspective view of the backlight of FIG. 21, and FIG. 23A is a sectional view taken along the line AA of FIG. 23B is a sectional view taken along line BB of FIG. 21, FIG. 23C is an enlarged view of a portion X of FIG. 21, and FIG. 24 is an enlarged sectional view of a part of FIG. 2 and an enlarged view thereof.

In FIG. 23C, a part of the member shown in FIG. 22 is omitted for clarity, and in FIGS. 24A to 24C, a cross section at the substantially center of the backlight of FIG. 21 in a plane parallel to the yz plane is shown for clarity. Therefore, a part of the members shown in FIG. 22 is omitted.

The backlight 1 is an edge light type backlight for irradiating the back surface of a liquid crystal panel (not shown) with light, and includes a back case 2, a light guide plate 3, a light source 4, a reflective sheet 5, and diffusion. It has an optical sheet 9 having a sheet 6 and prism sheets 7 and 8, a frame member 10, a pressing member 11, and a lower reflection sheet 14. The light source 4 is an example of a first light source, the reflective sheet 5 is an example of a first reflective sheet, and the lower reflective sheet 14 is an example of a second reflective sheet.

The back case 2 houses the light guide plate 3, the light source 4, the reflective sheet 5, the optical sheet 9, the pressing member 11, and the lower reflective sheet 14, and has a groove portion 2a for accommodating the lower reflective sheet 14. The groove 2a is an example of the first groove.

The groove 2a is provided with a double-sided tape 2b for fixing the lower reflective sheet 14 to the groove 2a. Further, the back case 2 has a screw insertion hole 2c into which a screw 13 is inserted in order to fix the frame member 10 to the back case 2.

The light guide plate 3 is arranged in the back case 2 with one main surface as a light emitting surface, another main surface facing the light emitting surface as a reflecting surface, one side surface as an incoming surface, and the back case 2 with the reflecting surface facing down. To. The light entry surface is an example of a first light entry surface corresponding to the first side surface.

Further, the light guide plate 3 has a convex portion 3a formed at the end opposite to the end portion of the light guide plate 3 facing the light source 4, and a protrusion 3b formed on the convex portion 3a. The light guide plate 3 is made of a resin such as polycarbonate or acrylic, glass having high light resistance, or the like. The protrusion 3b is made of the same material as the light guide plate 3 or a resin such as silicone that does not generate gas while the backlight 1 is lit. The protrusion 3b may be formed of a threaded pin or the like.

As shown in FIG. 23A, the light source 4 has a light emitting element 4a arranged so as to face the light entering surface of the light guide plate 3 and a light emitting element 4a attached to the light emitting element 4a in the back case 2 and a double-sided tape (not shown). It has a flexible printed circuit board (FPC) 4b fixed to the back case 2 by.

The reflective sheet 5 is arranged between the back case 2 and the reflective surface of the light guide plate 3, and is made of a heat-expandable resin material such as polyethylene terephthalate. In order to make the extension direction of the reflective sheet 5 due to thermal expansion coincide with the direction from the side surface of the light guide plate 3 facing the light source 4 toward the light source 4, the flow direction (MD direction) of the reflective sheet 5 is set to the y direction. The vertical direction (TD direction) of the reflective sheet 5 is defined as the x direction. Further, the reflective sheet 5 has a convex portion 5a corresponding to the convex portion 3a.

The reflective sheet 5 is fixed to the back case 2 at the center of the end opposite to the end of the light guide plate 3 facing the light source 4 by fixing the convex portion 5a to the back case 2 with double-sided tape. There is. Therefore, the central portion of the end portion on the opposite side of the end portion of the light guide plate 3 facing the light source 4 serves as a position reference for the extension of the reflective sheet 5.

The diffusion sheet 6 may be arranged on the light emitting surface of the light guide plate 3 and may function as a lens array having a minute and random holographic shape on the surface. The diffusion sheet 6 is made of a heat-expandable resin material such as a polycarbonate film or polyethylene terephthalate.

In order to make the extension direction of the diffusion sheet 6 due to thermal expansion coincide with the direction from the side surface of the light guide plate 3 facing the light source 4 toward the light source 4, the MD direction of the diffusion sheet 6 is set to the y direction, and the diffusion sheet 6 is set. Let the TD direction of be the x direction. Further, as shown in FIG. 4, the diffusion sheet 6 faces the convex portion 6a corresponding to the convex portion 3a, the hole 6b for inserting the convex portion 3b formed in the convex portion 6a, and the light source 4. It has a reflecting portion 6c provided at the end portion. The reflecting portion 6c is an example of the first reflecting portion.

As shown in FIG. 22B, the diffusion sheet 6 has a central portion of an end portion opposite to the end portion of the light guide plate 3 facing the light source 4 by fixing the convex portion 6a to the back case 2 as described later. It is fixed to the back case 2 with.

Therefore, the central portion of the end portion on the opposite side of the end portion of the light guide plate 3 facing the light source 4 serves as a position reference for the elongation of the diffusion sheet 6. By setting the extension position reference of the diffusion sheet 6 at the center of the end opposite to the end of the light guide plate 3 facing the light source 4 in this way, it is advantageous to narrow the frame of the backlight 1.

The reflective portion 6c is formed of a reflective sheet made of a heat-expandable resin material such as polyethylene terephthalate, and is adhered, crimped or attached to the main body of the diffusion sheet 6. The reflection portion 6c may be provided by printing white on the end portion of the diffusion sheet 6 facing the light source 4. To prevent wrinkles, kinks, etc. of the main body of the diffusion sheet 6 and the reflection portion 6c caused by the difference between the linear expansion coefficient of the portion of the diffusion sheet 6 excluding the reflection portion 6c and the coefficient of thermal expansion of the reflection sheet forming the reflection portion 6c. In addition, the MD direction of the reflective sheet forming the reflective portion 6c is the y direction, and the TD direction of the reflective sheet forming the reflective portion 6c is the x direction.

The prism sheet 7 has microprisms parallel to one side formed on one side, the prism sheet 8 has microprisms parallel to the other side formed on one side, and the prism sheets 7 and 8 are stacked and diffused sheets. Placed on top of 6.

The prism sheet 7 has a convex portion 7a corresponding to the convex portion 3a and a hole 7b for inserting the convex portion 3b formed in the convex portion 7a. The prism sheet 8 has a convex portion 8a corresponding to the convex portion 3a and a hole 8b for inserting the convex portion 3b formed in the convex portion 8a.

The frame member 10 is fixed to the back case 2 from above the optical sheet 9 by screws 13. The frame member 10 is made of a metal having a relatively high reflectance (for example, 95% or more) (for example, a silver-coated aluminum material), a resin having a relatively high reflectance (for example, 95% or more), or the like. Further, the frame member 10 may be made of a metal or resin having a relatively high reflectance (for example, less than 95%) and may be provided with white printing, a reflective sheet or the like on the lower surface.

The frame member 10 has an opening 10a formed at a position corresponding to the protrusion 3b, and a screw insertion hole 10b into which a screw 13 is inserted to fix the frame member 10 to the back case 2. Since the opening 10a is formed outside the display area of the backlight 1, the convex portions 3a, 5a, 6a, 7a, 8a are formed outside the display area of the backlight 1.

The pressing member 11 is rectangular and is arranged between the frame member 10 and the optical sheet 9. The pressing member 11 may have another shape such as a circular shape or a polygonal shape. The pressing member 11 is made of an elastic body such as rubber or elastomer or a resin such as plastic. As shown in FIG. 23C, the pressing member 11 is arranged on the optical sheet 9 corresponding to the outside of the display area of the backlight 1, and the frame member 10 is fixed to the back case 2, so that the pressing member 11 holds the optical sheet 9. The diffusion sheet 6 can be fixed to the back case 2 by pressing it toward the light guide plate 3.

As a result, the movement of the optical sheet 9 housed in the back case 2 in the z direction, that is, the movement of the optical sheet 9 in the direction perpendicular to the optical sheet 9 can be suppressed. The pressing member 11 may be fixed to the optical sheet 9 with double-sided tape (not shown). Further, by arranging the pressing member 11 on the optical sheet 9 corresponding to the outside of the display area of the backlight 1, the influence of wrinkles and the like due to the expansion and contraction of the optical sheet 9 is not exerted.

As shown in FIGS. 22A, 24A, 24B, and 24C, the lower reflective sheet 14 reflects with the groove 2a of the back case 2 so as to cover the lower part of the end surface of the light source 4 and the light guide plate 3 facing the light source 4. It is arranged between the sheet 5 and the sheet 5.

The lower reflective sheet 14 is made of a heat-expandable resin material such as polyethylene terephthalate. The MD direction of the lower reflection sheet 14 is the x direction, and the TD direction of the lower reflection sheet 14 is the y direction.

FIG. 25 is a diagram schematically showing the thermal expansion and contraction of the reflective sheet of FIG. 22. Light from the light source 4, which cannot be reflected by the heat-shrinkable reflective sheet 5 at an ambient temperature below substantially the same temperature as the maximum temperature when the backlight 1 is lit, is reflected downward as shown by the arrow in FIG. 25A. After being reflected by the sheet 14, it is incident on the light guide plate 3. On the other hand, the light from the light source 4 that cannot be reflected by the heat-shrinkable reflective sheet 5 when the ambient temperature is lower than the maximum temperature when the backlight 1 is lit is shown by the arrow in FIG. 25B. After being reflected by the reflective sheet extended according to the ambient temperature substantially the same as the maximum temperature when the backlight is turned on, the light is incident on the light guide plate 3.

According to the present embodiment, there is no loss of light due to the presence of light from the light source 4 that cannot be reflected by the reflective sheet 5 due to heat shrinkage of the reflective sheet 5. Therefore, even if the reflective sheet 5 is thermally shrunk, the optical performance does not deteriorate.

Further, since the lower reflective sheet 14 is provided in the groove portion 2a formed in the back case 2, it is not necessary to increase the size of the backlight 1 in order to provide the lower reflective sheet 14. Further, the reflective sheet 5 is fixed to the back case 2 at the center of the end opposite to the end of the light guide plate 3 facing the light source 4, and is fixed to the back case 2 on the opposite side of the end of the light guide plate 3 facing the light source 4. The central portion of the end portion of the reflective sheet 5 serves as a position reference for the extension of the reflective sheet 5. Therefore, the elongation of the reflective sheet 5 can be satisfactorily controlled in the y direction.

26 is a front view of another embodiment of the backlight according to the present disclosure, FIG. 27 is an exploded perspective view of the backlight of FIG. 26, and FIG. 28A is a sectional view taken along the line CC of FIG. 26. 28B is a cross-sectional view taken along the line C'-C'of FIG. 26, FIG. 28C is a cross-sectional view taken along the line DD of FIG. 28, and FIG. 28D is an enlarged view of a portion Y of FIG. 29 is a partial cross-sectional view of FIG. 26 and an enlarged view thereof.

In FIG. 28D, a part of the member shown in FIG. 22 is omitted for clarity, and in FIGS. 29A to 29C, a substantially central cross section of the backlight of FIG. 21 in a plane parallel to the yz plane is shown for clarity. Therefore, a part of the members shown in FIG. 27 is omitted.

The backlight 21 is an edge light type backlight for irradiating the back surface of a liquid crystal panel (not shown) with light, and is a back case 22, a light guide plate 23, light sources 24, 24', and a reflective sheet 25. The optical sheet 29 having the diffusion sheet 26 and the prism sheets 27 and 28, the frame member 30, the pressing member 31, and the lower reflection sheets 34 and 34'are included. The light source 24 is an example of a first light source, the light source 24'is an example of a second light source, the reflective sheet 25 is an example of a first reflective sheet, and the lower reflective sheet 34 is a second. The lower reflective sheet 34'is an example of a third reflective sheet.

The back case 22 accommodates the light guide plate 23, the light sources 24, 24', the reflective sheet 25, the optical sheet 29, the pressing member 31 and the lower reflective sheets 34, 34', and has a groove portion 22a for accommodating the lower reflective sheet 34. , A groove portion 22a'for accommodating the lower reflective sheet 34'. The groove portions 22a and 22a'are examples of the first groove portion and the second groove portion.

The groove portion 22a is provided with a double-sided tape 32b for fixing the lower reflective sheet 34 to the groove portion 22a. The groove portion 22a'is provided with a double-sided tape 32b for fixing the lower reflection sheet 34'to the groove portion 22a'. Further, the back case 22 has a screw insertion hole 22c into which a screw 33 is inserted in order to fix the frame member 30 to the back case 22.

The light guide plate 23 is arranged on the back case 22 with one main surface as an light emitting surface, the other main surface facing the light emitting surface as a reflecting surface, two side surfaces as an incoming surface, and the back case 22 with the reflecting surface facing down. To. These incoming surfaces are examples of a first incoming surface corresponding to the first side surface and a second incoming surface corresponding to the second side surface.

Further, the light guide plate 23 is formed on the convex portion 23a formed at the end portion of the light guide plate 23 facing the light source 24 and the central portion of the end portion of the light guide plate 23 facing the light source 24', and the convex portion 23a. It has a protrusion 23b. The light guide plate 23 is made of a resin such as polycarbonate or acrylic, glass having high light resistance, or the like. The protrusion 23b is made of the same material as the light guide plate 23 or a resin such as silicone that does not generate gas while the backlight 21 is lit. The protrusion 23b may be configured by a pin with a screw or the like.

As shown in FIG. 28A, the light source 24 has a light emitting element 4a arranged so as to face one of the light receiving surfaces of the light guide plate 23 and a double-sided tape (shown). It has an FPC 24b fixed to the back case 22 by (1).

As shown in FIG. 28B, the light source 24'is attached with a light emitting element 4a'arranged so as to face the other light receiving surface of the light guide plate 23 and the light emitting element 4a'in the back case 22, and is also a double-sided tape. It has an FPC 24b'fixed to the back case 22 by (not shown).

The reflective sheet 25 is arranged between the back case 22 and the reflective surface of the light guide plate 23, and is made of a heat-expandable resin material such as polyethylene terephthalate. In order to make the extension direction of the reflective sheet 25 due to thermal expansion coincide with the direction from the side surface of the light guide plate 23 facing the light source 24 toward the light source 24, the flow direction (MD direction) of the reflective sheet 25 is set to the x direction. The vertical direction (TD direction) of the reflective sheet 25 is defined as the y direction. Further, the reflective sheet 25 has a convex portion 25a corresponding to the convex portion 23a.

By fixing the convex portion 25a to the back case 22 with double-sided tape, the reflective sheet 25 is formed at the end portion of the light guide plate 23 facing the light source 24 and the central portion of the end portion of the light guide plate 23 facing the light source 24'. It is fixed to the back case 2. Therefore, the end portion of the light guide plate 23 facing the light source 24 and the central portion of the end portion of the light guide plate 23 facing the light source 24'are used as a position reference for the extension of the reflective sheet 25.

The diffusion sheet 26 may be arranged on the light emitting surface of the light guide plate 3 and may function as a lens array having a minute and random holographic shape on the surface. The diffusion sheet 26 is made of a heat-expandable resin material such as a polycarbonate film or polyethylene terephthalate.

The extension direction of the diffusion sheet 26 due to thermal expansion coincides with the direction from the side surface of the light guide plate 3 facing the light source 24 toward the light source 24 and the direction from the side surface of the light guide plate 23 facing the light source 24'toward the light source 24'. The MD direction of the diffusion sheet 26 is set to the x direction, and the TD direction of the diffusion sheet 26 is set to the y direction. Further, as shown in FIG. 9, the diffusion sheet 26 faces the convex portion 26a corresponding to the convex portion 23a, the hole 26b for inserting the convex portion 23b formed in the convex portion 26a, and the light source 24. It has a reflecting portion 26c provided at an end portion and a reflecting portion 26d provided at an end portion facing the light source 24'. The reflection unit 26c is an example of the first reflection unit, and the reflection unit 26d is an example of the second reflection unit.

As will be described later, the diffusion sheet 26 has a convex portion 26a fixed to the back case 2, so that the end portion of the light guide plate 23 facing the light source 24 and the light guide plate facing the light source 24'as shown in FIG. 28C. It is fixed to the back case 22 at the center of the end of the 23. Therefore, the end portion of the light guide plate 23 facing the light source 24 and the central portion of the end portion of the light guide plate 23 facing the light source 24'are used as a position reference for the extension of the diffusion sheet 6.

The reflective portions 26c and 26d are formed of a reflective sheet made of a heat-expandable resin material such as polyethylene terephthalate, and are adhered, crimped or attached to the main body of the diffusion sheet 26. Reflecting portions 26c and 26d may be provided by white printing on the end portion of the diffusion sheet 26 facing the light source 24 and the end portion of the diffusion sheet 26 facing the light source 24'. Wrinkles in the main body of the diffusion sheet 26 and the reflection portions 26c and 26d caused by the difference between the linear expansion coefficient of the portion of the diffusion sheet 26 excluding the reflection portions 26c and 26d and the coefficient of thermal expansion of the reflection sheet forming the reflection portions 26c and 26d. In order to prevent twisting and the like, the MD direction of the reflective sheet forming the reflective portions 26c and 26d is set to the x direction, and the TD direction of the reflective sheet forming the reflective portions 26c and 26d is set to the y direction.

The prism sheet 27 has microprisms parallel to one side formed on one side, the prism sheet 28 has microprisms parallel to the other side formed on one side, and the prism sheets 27 and 28 are stacked and diffused sheets. It is placed on top of 26.

The prism sheet 27 has a convex portion 27a corresponding to the convex portion 23a and a hole 27b for inserting the convex portion 23b formed in the convex portion 27a. The prism sheet 28 has a convex portion 28a corresponding to the convex portion 23a and a hole 28b for inserting the protruding portion 23b formed in the convex portion 28a.

The frame member 30 is fixed to the back case 22 from above the optical sheet 29 by screws 33. The frame member 30 is made of a metal having a relatively high reflectance (for example, 95% or more) (for example, a silver-coated aluminum material), a resin having a relatively high reflectance (for example, 95% or more), or the like. Further, the frame member 30 may be made of a metal or resin having a relatively high reflectance (for example, less than 95%) and may be provided with white printing, a reflective sheet or the like on the lower surface.

The frame member 30 has an opening 30a formed at a position corresponding to the protrusion 23b, and a screw insertion hole 30b into which a screw 33 is inserted to fix the frame member 30 to the back case 22. Since the opening 30a is formed outside the display area of the backlight 1, the convex portions 23a, 25a, 26a, 27a, 28a are formed outside the display area of the backlight 21.

The pressing member 31 is rectangular and is arranged between the frame member 30 and the optical sheet 29. The pressing member 31 may have another shape such as a circular shape or a polygonal shape. The pressing member 31 is made of an elastic body such as rubber or elastomer or a resin such as plastic. As shown in FIG. 28D, the pressing member 31 is arranged on the optical sheet 9, and the frame member 30 is fixed to the back case 22, so that the pressing member 31 presses the optical sheet 29 toward the light guide plate 23 and the diffusion sheet. 26 can be fixed to the back case 22.

As a result, the movement of the optical sheet 29 housed in the back case 22 in the z direction, that is, the movement of the optical sheet 29 in the direction perpendicular to the optical sheet 29 can be suppressed. The pressing member 31 may be fixed to the optical sheet 29 with double-sided tape (not shown). Further, by arranging the pressing member 31 on the optical sheet 29 corresponding to the outside of the display area of the backlight 21, the influence of wrinkles and the like due to the expansion and contraction of the optical sheet 29 is not exerted.

As shown in FIGS. 28A and 29A, the lower reflective sheet 34 is between the groove portion 22a of the back case 22 and the reflective sheet 25 so as to cover the lower part of the end surface of the light source 24 and the light guide plate 23 facing the light source 24. Be placed.

As shown in FIGS. 28A, 29A, 29B and 29C, the lower reflective sheet 34'covers the lower portion of the end surface of the light source 24' and the light guide plate 23 facing the light source 24', and the groove portion of the back case 22 is formed. It is arranged between 22a'and the reflective sheet 25.

The lower reflective sheets 34, 34'are made of a heat-expandable resin material such as polyethylene terephthalate. The MD direction of the lower reflection sheets 34, 34'is the y direction, and the TD direction of the lower reflection sheets 34, 34'is the x direction.

According to the present embodiment, the heat shrinkage of the reflective sheet 25 eliminates the loss of light due to the presence of light from the light source 24 that cannot be reflected by the reflective sheet 25, and the heat shrinkage of the reflective sheet 25 causes the reflective sheet 25 to cause light loss. There is no loss of light due to the presence of light from the light source 24 that cannot be reflected. Therefore, even if the reflective sheet 5 is thermally shrunk, the optical performance does not deteriorate.

Further, since the lower reflective sheet 34 is provided in the groove portion 22a formed in the back case 22 and the lower reflective sheet 34'is provided in the groove portion 22a'formed in the back case 22, the lower reflective sheets 34, 34'are provided. There is no need to increase the size of the backlight 21.

Further, the reflective sheet 25 is fixed to the back case 22 at the end of the light guide plate 23 facing the light source 24 and the center of the end of the light guide plate 23 facing the light source 24', and is fixed to the back case 22 and faces the light source 24. The end portion of the 23 and the central portion of the end portion of the light guide plate 23 facing the light source 24'are used as a position reference for the extension of the reflective sheet 25. Therefore, the elongation of the reflective sheet 25 can be satisfactorily controlled in the x direction.

FIG. 30A is a perspective view schematically showing an example of the configuration of the light sources 4, 24, 24'(hereinafter, simply referred to as the light source 4) used in the backlight 1 of the present disclosure, and is a perspective view of FIG. 30 (b). ) Is a plan view schematically showing the configuration of the light source 4, and FIG. 30 (c) is a cross-sectional view taken along the line AA'of the light source 4 shown in FIG. 30 (b). The light source 4 has a substrate 40 in which light emitting elements 4a such as LEDs are arranged side by side.

The board 40 has a mounting board 40a and a circuit board 40b that are bonded to each other. The mounting board 40a and the circuit board 40b shown in FIG. 30B both have an elongated linear planar shape, but the mounting board 40a and the circuit board 40b have a rectangular planar shape such as a square or a rectangle. You may. When both the mounting board 40a and the circuit board 40b have a linear planar shape, the longitudinal direction of the mounting board 40a and the circuit board 40b coincides with the longitudinal direction of the light source 4, and the width direction of the mounting board 40a and the circuit board 40b is , Consistent with the width direction of the light source 4. Further, the circuit board 40b has an opening 49, the longitudinal direction of the opening 49 coincides with the longitudinal direction of the light source 4, and the width direction of the opening 49 coincides with the width direction of the light source 4.

The mounting substrate 40a is formed of a metal such as aluminum or copper, or a material having high thermal conductivity mainly composed of ceramics. The mounting board 40a has a flat surface, and a plurality of light emitting elements 4a are directly arranged on the flat surface of the mounting board 40a exposed to the opening 49 of the circuit board 40b. As a result, in the light emitting state in which the plurality of light emitting elements 4a are emitting light, the heat generated by the light emitting elements 4a is efficiently dissipated by conducting through the mounting substrate 40a having high thermal conductivity.

The circuit board 40b is formed of a highly insulating resin containing a resin such as phenol, epoxy, polyimide, or polyester as a main component. A pair of wirings 45a and 45b are formed on the surface of the circuit board 40b so as to extend in the longitudinal direction of the circuit board 40b at intervals in the width direction so as to sandwich the opening 49 of the circuit board 40b. Connector 42a, 42b is formed at at least one end of the wiring 45a, 45b in the longitudinal direction. The connectors 42a and 42b supply positive and negative potentials supplied via the cable 43 to the light emitting element 4a via the wirings 45a and 45b, respectively. The wirings 45a and 45b and the connectors 42a and 42b are formed by patterning a metal such as gold or copper on the circuit board 40b, for example. The wirings 45a and 45b and the connectors 42a and 42b may be further covered and protected by a solder resist or the like which is an insulating film.

The light emitting element 4a is formed, for example, after an LED die or the like is bonded onto the surface of the mounting substrate 40a by a die bond, and then the cathode terminal and the anode terminal of the LED are electrically connected to the wirings 45a and 45b by a wire or the like. Ru. The plurality of light emitting elements 4a shown in FIG. 30B are arranged so that their sides face each other, but the light emitting elements 4a are rotated by 45 degrees and their vertices are arranged so as to face each other. You may. It is preferable that the plurality of light emitting elements 4a are arranged so that the upper surface thereof is parallel to the surface of the mounting substrate 40a. The light emitting element 4a emits visible light such as purple, blue, green, and red, but may contain invisible light such as infrared light, or may contain a combination of these.

The plurality of light emitting elements 4a are electrically connected to each other by wires to form one row. In the example shown in FIG. 30B, eight light emitting elements 4a are connected in series in one row, but the number of light emitting elements 4a connected in one row is determined via the cable 43. It may be appropriately determined according to the supplied voltage and the like. For example, when eight light emitting elements 4a having a forward voltage of about 3 V are connected in series to form one row, it is preferable that a power supply voltage exceeding at least 24 V is supplied. The light emitting elements 4a located at both ends of each row are electrically connected to the wiring 45a or the wiring 45b via a wire. In FIG. 30B, for convenience, the light emitting element 4a and the wire sealed by the sealing material 47 are shown by solid lines instead of broken lines. The light emitting element 4a is supplied with a voltage from the cable 43 via the connectors 42a and 42b, the wirings 45a and 45b, and the wire to emit light. A Zener diode or the like that prevents an overvoltage from being applied to the light emitting element 4a may be connected between the wiring 45a and the wiring 45b.

The frame body 46 is formed by arranging a continuous body such as a dam material in an annular shape or a rectangular shape so as to surround the opening 49 of the circuit board 40b. The frame 46 is made of, for example, a silicone resin or an epoxy resin. The frame 46 is preferably formed of a white resin in which fine particles such as titanium oxide, which easily reflects light, are dispersed. As a result, the light emitted from the light emitting element 4a is reflected above the light source 4, so that the utilization efficiency of the light emitted from the light emitting element 4a is improved.

The sealing material 47 protects the light emitting element 4a by sealing the opening 49 of the mounting substrate 40a surrounded by the frame body 46. The region sealed by the sealing material 47 functions as a light emitting region 41 of the light source 4. The sealing material 47 is formed of a resin such as epoxy or silicone having translucency with respect to the light emitted by the light emitting element 4a. The sealing material 47 may contain a phosphor that converts the light emitted by the light emitting element 4a into light having a longer wavelength. This phosphor can be, for example, a particulate phosphor material such as YAG (Yttrium aluminum garnet) that absorbs blue light emitted by the light emitting element 4a and emits yellow light. The blue light emitted by the light emitting element 4a and the yellow light whose wavelength is converted by the phosphor are mixed to obtain white light. The encapsulant 47 may have a phosphor that converts blue light into, for example, red light or green light other than yellow light, or may have no phosphor at all. After forming the sealing material 47, the frame body 46 may be removed to use only the sealing material 47.

31 (a) to 31 (c) show light guide plates 3, 23, diffusion sheets 6, 26, and reflectors 6c, 26c, 26d (hereinafter, simply light guide plate 3, diffusion, respectively) used in the backlight 1 of the present disclosure. It is an enlarged sectional view which showed the modification of the sheet 6 and the reflection part 6c).

The reflective portion 6c may be fixed to the upper surface of the end portion of the diffusion sheet 6. In this case, as shown in FIG. 31A, the reflective portion 6c is arranged on the upper surface of the end portion of the diffusion sheet 6 so as not to overlap with the optical sheet such as the prism sheet 7 arranged on the upper surface of the diffusion sheet 6. Is preferable. As a result, it is possible to prevent the reflective portion 6c from entering between the optical sheet such as the prism sheet 7 and the diffusion sheet 6 to form a gap and deteriorate the optical performance of the optical sheet.

Further, the reflective portion 6c may be fixed to the lower surface of the end portion of the diffusion sheet 6. Also in this case, it is preferable that no gap is formed between the light guide plate 3 and the diffusion sheet 6. Therefore, as shown in FIG. 31B, the reflecting portion 6c is the lower surface of the end portion of the diffusion sheet 6 so that the back light 1 does not overlap with the light guide plate 3 even if the backlight 1 becomes low temperature and the diffusion sheet 6 contracts. It is preferable that the light guide plate 3 is arranged apart from the light guide plate 3. Alternatively, as shown in FIG. 31 (c), the reflecting portion 6c may be arranged so as to be housed in the upper space having a step shape by cutting the corner portion of the end portion of the reflecting portion 6c. ..

FIG. 32 is an enlarged plan view showing another modified example of the light guide plate 3, the diffusion sheet 6, and the reflecting portion 6c used in the backlight 1 of the present disclosure. The planar shape of the reflecting portion 6c is not limited to the rectangular shape as shown in FIGS. 4 and 9, and may be determined according to, for example, the light directivity of the light source 4. For example, when an elongated linear light source 4 as shown in FIGS. 30 (a) to 30 (c) is used as the light source 4, the amount of light emitted from the end portion of the light source 4 is emitted from the central portion of the light source 4. Less than the amount of light. Therefore, as shown in FIG. 32, the reflecting portion 6c may have a narrow width in the region facing the end portion of the light source 4 and a wide width in the region facing the central portion of the light source 4. As a result, the brightness of the backlight 1 is more likely to be maintained constant when the ambient temperature changes.

The present disclosure is not limited to the above embodiment, and many modifications and modifications can be made. For example, in the above embodiment, the backlight having one or two incoming surfaces has been described, but the present disclosure can also be applied to a backlight having three incoming surfaces.

Further, in the above embodiment, the case where the light source has a light emitting element has been described, but a linear light source such as a line bar may be used instead of the light emitting element. Further, although the case where the rectangular pressing member is used in the above embodiment has been described, a pressing member having a shape other than the rectangular shape may be used. Further, the case where the pressing member shown in FIGS. 14 to 17 is used for the backlight having one light entering surface has been described, but the pressing member shown in FIGS. 14 to 17 is used for the backlight having two or three light entering surfaces. You may use it.

Claims (15)

1. Back case and
   A light guide plate arranged on the back case with the reflective surface facing down, with one main surface as the light emitting surface, the other main surface facing the light emitting surface as the reflecting surface, and the first side surface as the light entering surface. When,
   In the back case, a first light source arranged to face the light entry surface of the light guide plate and
   An optical sheet arranged on the light emitting surface and having a first reflecting portion provided at an end facing the first light source, and an optical sheet.
   Have,
   The optical sheet has a light emitting surface so that the extension direction of the optical sheet due to thermal expansion coincides with the direction from the first side surface of the light guide plate facing the first light source toward the first light source. Placed on top of
   The backlight is characterized by that.
2. The frame member fixed to the back case and
   A fixing portion for fixing the optical sheet to the frame member at an end portion opposite to the side on which the first reflecting portion is provided, and a fixing portion.
   The backlight according to claim 1, further comprising.
3. The light guide plate has a protrusion for fixing the optical sheet, and has a protrusion.
   The optical sheet is formed with a hole for inserting the protrusion.
   The backlight according to claim 2, wherein the fixing portion fixes the optical sheet by fixing the protrusion to the frame member.
4. The light guide plate has a first convex portion formed at an end portion opposite to the end portion of the light guide plate facing the first light source.
   The protrusion is formed on the first protrusion.
   The optical sheet has a second convex portion corresponding to the first convex portion and having the hole formed therein.
   The frame member has an opening formed at a position corresponding to the protrusion.
   The backlight according to claim 3.
5. A first reflective sheet arranged between the back case and the reflective surface,
   A second reflective sheet arranged between the back case and the first reflective sheet so as to cover the lower portion of the end surface of the first light source and the light guide plate facing the first light source. The backlight according to any one of claims 1 to 4, further comprising.
6. The backlight according to claim 5, wherein the back case has a first groove for accommodating the second reflective sheet.
7. The first reflective sheet according to claim 5 or 6, wherein the first reflective sheet is fixed to the back case at a central portion of an end opposite to the end of the light guide plate facing the first light source. Backlight.
8. In the back case, it further has a second light source arranged so as to face a second light entry surface corresponding to a second side surface opposite to the first side surface of the light guide plate.
   The optical sheet further has a second reflective portion provided at an end facing the second light source.
   The backlight according to claim 1.
9. The frame member fixed to the back case and
   The backlight according to claim 8, further comprising a fixing portion for fixing the optical sheet to the frame member at a central portion between the first reflecting portion and the second reflecting portion.
10. The light guide plate has a protrusion for fixing the optical sheet, and has a protrusion.
    The optical sheet is formed with a hole for inserting the protrusion.
    The backlight according to claim 9, wherein the fixing portion fixes the optical sheet by fixing the protrusion to the frame member.
11. The light guide plate is formed at the center of an end portion of the light guide plate facing the first light source and an end portion of the light guide plate perpendicular to the end portion of the light guide plate facing the second light source. Has a first convex part
    The protrusion is formed on the first protrusion.
    The optical sheet has a second convex portion corresponding to the first convex portion and having the hole formed therein.
    The frame member has an opening formed at a position corresponding to the protrusion.
    The backlight according to claim 10.
12. 2. The second aspect of the present invention, further comprising a pressing member which is arranged between the frame member and the optical sheet and presses the optical sheet toward the light guide plate by fixing the frame member to the back case. The backlight according to any one of 4, 9 to 11.
13. A first reflective sheet arranged between the back case and the reflective surface,
    A second reflective sheet arranged between the back case and the first reflective sheet so as to cover the lower portion of the end surface of the first light source and the light guide plate facing the first light source.
    A third reflective sheet arranged between the back case and the first reflective sheet so as to cover the lower portion of the end surface of the second light source and the light guide plate facing the second light source.
    The backlight according to claim 8, further comprising.
14. The backlight according to claim 13, wherein the back case has a second groove for accommodating the third reflective sheet.
15. The first reflective sheet is fixed to the back case at an end portion of the light guide plate facing the first light source and a central portion of the end portion of the light guide plate facing the second light source. , The backlight according to claim 13 or 14.

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