Backlight unit and liquid crystal display device

A housing (HG) for a backlight unit (49) includes a bottom section (22), a wall section (23) and a side section (VP), and the side section (VP) is at least a part of a first groove (DH1) which sandwiches a mounting substrate (11).

TECHNICAL FIELD

The present invention relates to a backlight unit including a mounting substrate on which a light emitting block is mounted, and a liquid crystal display device including the backlight unit.

BACKGROUND ART

There have conventionally been developed various types of backlight units for supplying light to a liquid crystal display panel (a non-light-emitting display panel). Backlight units typically include a light source that emits light. For example, the backlight unit149disclosed in Patent Document 1 has the LED (light emitting diode)112mounted on the mounting substrate111as shown in the sectional view ofFIG. 25. The LED112emits light that enters the light guide plate141to travel toward the liquid crystal display panel159via the reflection sheet142and a group of optical sheets146.

Such light is generated by driving the LED112, but when the LED112is driven to generate light, heat is generated as well. The thus generated heat deteriorates the quality of the LED112(for example, the light emitting efficiency of the LED112is degraded or the life of the LED112is shortened). The heat of the LED112is also transferred to the mounting substrate111, and the heat causes early deterioration or warp of the mounting substrate111.

In order to prevent such defects caused by heat, in the backlight unit149described in Patent Document 1, the mounting substrate111on which the LED112is mounted is put in contact with the heat sink substrate172via the heat dissipation sheet171. With this structure, heat of the LED112does not stay in the LED112or the mounting substrate111but escapes to the heat dissipation sheet171and to the heat sink substrate172.

If the backlight unit149is used for a long time, however, the heat generated therein cannot be dealt with by heat dissipation merely by means of the heat dissipation sheet171and the heat sink substrate172, and the mounting substrate111may, for example, warp in the worst case. To prevent this, in the backlight unit149, the LED112and the mounting substrate111are placed between the light guide plate141and the heat sink substrate172, and further, the mounting substrate111is placed between the housing125and the heat sink substrate172of the backlight unit149.

The exploded perspective view ofFIG. 26and the sectional view ofFIG. 27show a backlight unit149as an example of backlight units other than that disclosed in Patent Document 1, and according to this backlight unit149, it is possible to fasten a housing121and a mounting substrate111of the backlight unit149together with screws173(here,FIG. 27is a sectional view taken along line a-a′ inFIG. 26, and a liquid crystal display panel159is additionally illustrated therein).Patent Document 1: JP-A-2006-11242

DISCLOSURE OF THE INVENTION

Problems to be Solved by the Invention

However, with the backlight unit149disclosed in Patent Document 1, the light emission surface of the LED112needs to be in close contact with a side surface of the light guide plate141in order to prevent defects from being caused by heat. This limits the possibilities in designing the product. For example, this makes it impossible to design such that a light emission surface of the LED112is positioned away from a side surface of the light guide plate141in order to reduce nonuniformity in light amount occurring in light (backlight light) coming from the backlight unit149.

Furthermore, with the backlight unit149as shown inFIGS. 26 and 27, tap processing (to form a screw hole174) needs to be applied to a mounting substrate111including wiring of electrodes and the like for the LED112. In particular, if the screw173is made of a conductive material such as metal, the cost of the tap processing will be excessively high to ensure leakage prevention.

The present invention has been made in view of the foregoing. An object of the present invention is to provide a backlight unit in which LEDs are arranged with a higher degree of freedom and that is manufactured easily at low cost, and a liquid crystal display device including the backlight unit.

Means for Solving the Problem

A backlight unit includes: a light emitting block; a mounting substrate on which the light emitting block is mounted; a light guide plate that receives light coming from the light emitting block, the light guide plate allowing the light to pass therethrough and guiding the light to an outside thereof; and a housing in which the light emitting block, the mounting substrate, and the light guide plate are housed.

Here, the housing includes: a bottom section that supports the light guide plate; a wall section that rises from the bottom section; and a protrusion section that is supported by the wall section, protrudes toward the bottom section, and extends in a direction that intersects a direction in which the wall section rises. And the protrusion section is at least part of a first groove in which the mounting substrate is held.

With this structure, the comparatively thick protrusion section holds the mounting substrate in the first groove. As a result, the light emitting block is positioned as desired to be immovable with respect to the light guide plate. Thus, a higher degree of freedom is allowed in the arrangement of the light emitting block (for example, it is unnecessary for the light emitting block to be pressed by a side surface of the light guide plate for the purpose of making the light emitting block immovable with respect to the light guide plate).

Furthermore, since the first groove at least includes the thick protrusion section, it is easy to change the position of the first groove (that is, the first groove can be formed at various locations in the protrusion section). Thus, a higher degree of freedom is securely allowed in the arrangement of the light emitting block.

Moreover, heat resulting from the operation of the light emitting block, the heat typically tending to stay in the light emitting block itself and the mounting substrate, escapes via the first groove (and thus via the protrusion section).

For example, if one of opposite inner surfaces of the first groove that face each other is formed of the protrusion section and another one of the opposite inner surfaces of the first groove is formed of the wall section, heat that tends to stay in the light emitting block itself and the mounting substrate escapes to the protrusion section and to the wall section that form the first groove.

It is desirable that one of the first groove be formed for one of the mounting substrate (this is not meant as a limitation to the present invention). The groove width of the first groove may be either uniform or nonuniform. For example, there may exist along a length of the first groove, a first narrow groove width at which the first groove is in close contact with both a mounting surface and a non-mounting surface of the mounting substrate, and a first wide groove width that is wider than the first narrow groove width.

The first groove whose groove width is not uniform is also capable of holding the mounting substrate therein. Besides, material cost of the protrusion section can be reduced thanks to the wider groove width, and thus backlight cost can also be reduced.

It is desirable that portions of the first groove having the first narrow groove width be positioned corresponding at least to a middle portion and two end portions of the mounting substrate along a length of the mounting substrate. This is because, with this structure, the mounting substrate is efficiently held along its length direction.

A desirable example of a case in which a plurality of grooves are formed as the first groove with respect to one mounting substrate is as follows. That is, a plurality of first grooves each having a length shorter than the length of the mounting substrate are formed with respect to one mounting substrate, and located corresponding at least to a middle portion and two end portions of the mounting substrate along the length of the mounting substrate.

With this structure, not only the mounting substrate is efficiently held along its length, but also the backlight cost is reduced as a result of the length of the first groove being shorter than the length of the mounting substrate.

It is desirable that the protrusion section include a reflection surface that reflects light, and that a space is formed to face at least three surfaces of the reflection surface, a light emission surface of the light emitting block, and a light reception surface of the light guide plate. This is because, with this structure, light travels around inside the space, and this makes it easier for the light to enter the light guide plate.

For example, if the angle formed by the light emission surface of the light emitting block and the reflection surface is an acute angle, and the angle formed by the light reception surface of the light guide plate and the reflection surface is an obtuse angle, when light coming from the light emitting block reaches the reflection surface, the light is reflected thereon to reach an incident surface of the light guide plate.

It is desirable that an optical sheet that transmits light be placed so as to cover the light guide plate, and that the optical sheet be held by the protrusion section. This structure contributes to effective use of the comparatively thick protrusion section.

Even more effective use of the protrusion section can be made if a support portion is formed in the protrusion section so as to support a liquid crystal display panel that receives light from the optical sheet.

The mounting substrate is not limited to be held only in the first groove. That is, the mounting substrate may be held in another groove (a second groove) as well. For example, it is desirable that at least part of the second groove in which the mounting substrate is held be the bottom section of the housing.

With this structure, the mounting substrate is held in the first groove of the protrusion section and the second groove of the bottom section, and thus the mounting substrate is stably housed in the housing.

If one of opposite inner surfaces of the second groove that face each other is formed of the bottom section and another one of the opposite inner surfaces of the second groove is formed of the wall section, heat that tends to stay in the light emitting block itself and the mounting substrate escapes to the bottom section and the wall section that form the second groove.

It is desirable that one of the second groove be formed for one of the mounting substrate (this is not meant as a limitation to the present invention). The groove width of the second groove may be either uniform or nonuniform. For example, there may exist along a length of the second groove, a second narrow groove width at which the second groove is in close contact with both a mounting surface and a non-mounting surface of the mounting substrate, and a second wide groove width that is wider than the second narrow groove width.

The second groove whose groove width is not uniform is also capable of holding the mounting substrate therein. Besides, material cost of the protrusion section can be reduced thanks to the wider groove width, and thus backlight cost can also be reduced.

It is desirable that portions of the second groove having the second narrow groove width be positioned corresponding at least to a middle portion and two end portions of the mounting substrate along a length of the mounting substrate. This is because, with this structure, the mounting substrate is efficiently held along its length direction.

A desirable example of a case in which a plurality of grooves are formed as the second groove with respect to one mounting substrate is as follows. That is, a plurality of second grooves each having a length shorter than the length of the mounting substrate are formed with respect to one mounting substrate, and located corresponding at least to a middle portion and two end portions of the mounting substrate along the length of the mounting substrate.

With this structure, not only the mounting substrate is efficiently held along its length but also the backlight cost is reduced as a result of the length of the second groove being shorter than the length of the mounting substrate.

It can be said that the present invention includes a liquid crystal display device that is provided with any of the backlight units described above and a liquid crystal display panel that receives light from the backlight unit. Also, in such a liquid crystal display device, it is desirable that the liquid crystal display panel be supported by a support portion formed in the protrusion section. That is, in the liquid crystal display device, an optical sheet that transmits light is placed so as to cover the light guide plate, the optical sheet is held by the protrusion section, and the liquid crystal display panel that receives light coming from the optical sheet is supported by the support portion formed in the protrusion section.

Advantages of the Invention

According to the present invention, since the first groove is formed by using the comparatively thick protrusion section, the position of the first groove can be changed as necessary. This allows a higher degree of freedom in the positioning of the mounting substrate that is held in the first groove, and thus in the positioning of the light emitting block.

LIST OF REFERENCE SYMBOLS

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the present invention will be described with reference to the drawings. Hatching, reference signs for members, etc. may sometimes be omitted in a drawing for ease of description, and in such a case, a different drawing is to be referred to. A black dot in a drawing indicates a direction perpendicular to the sheet on which the drawing is drawn.

FIG. 24is an exploded perspective view of a liquid crystal display device69. As shown inFIG. 24, the liquid crystal display device69includes a liquid crystal display panel59and a backlight unit49.

The liquid crystal display panel59is formed by bonding together an active matrix substrate51including a switch element such as a TFT (thin film transistor) and a counter substrate52facing the active matrix substrate51by using a sealing member (not shown). Liquid crystal (not shown) is charged in the gap between the substrates51and52(here, deflection films53,53are attached so as to sandwich the active matrix substrate51and the counter substrate52).

The liquid crystal display panel59, which is a non-light-emitting display panel, exerts its display function by receiving light (backlight light) from the backlight unit49. Accordingly, the display quality of the liquid crystal display panel59can be improved by uniform irradiation of light coming from the backlight unit49over the entire surface of the liquid crystal display panel59.

The backlight unit49includes, for the purpose of generating backlight light, an LED module (a light source module) MJ, a light guide plate41, a reflection sheet42, a diffusion sheet43, optical sheets44and45, and a housing HG.

The LED module MJ is a light emitting module, including: a mounting substrate11; and an LED (light emitting diode)12that emits light by being supplied with electric current via an electrode formed on a mounting surface11A of the mounting substrate11and on which the LED12is mounted (incidentally, a surface of the mounting substrate11on which the LED12is not mounted will be referred to as a non-mounting surface11B).

It is desirable that an LED module MJ include a plurality of LEDs (light emitting blocks, point light sources)12. Furthermore, it is desirable that the LEDs12be aligned parallel to each other in a row. However, only part of the LEDs12are illustrated in the figure for ease of illustration (incidentally, the direction along which the LEDs12are aligned will be referred to as “alignment direction P”).

The light guide plate41is a plate member that has side surfaces41S and a top and bottom surfaces41U and41B, the top and bottom surfaces41U and41B being positioned to sandwich the side surfaces41S. A surface (a light reception surface) among the side surfaces41S faces light emission surfaces of the LEDs12, and thus receives light from the LEDs12. The received light is subjected to mixing inside the light guide plate41, to be emitted out from the top surface41U as surface light.

The reflection sheet42is placed so as to be covered with the light guide plate41. A surface of the reflection sheet42that faces the bottom surface41B of the light guide plate41functions as a reflection surface. Thus, the reflection surface reflects light from the LEDs12and light transmitted in the light guide plate41back to the light guide plate41(specifically, through the bottom surface41B of the light guide plate41) without allowing light to leak out.

The diffusion sheet43is placed so as to cover the top surface41U of the light guide plate41, and diffuses surface light coming from the light guide plate41to deliver light all over the liquid crystal display panel59(incidentally, the diffusion sheet43and the optical sheets44and45will hereinafter be collectively referred to as an optical sheet group46as well).

The optical sheets44and45, each of which has a prism-like surface, are optical sheets that deflect light radiation characteristics, and they are placed so as to cover the diffusion sheet43. Thus, the optical sheets44and45collect light coming from the diffusion sheet43, and thereby increase brightness. Incidentally, the optical sheets44and45are arranged such that directions in which they disperse light that they have collected cross each other.

The housing HG includes: a box-shaped bottom housing member21having a bottom section22; and a top housing member25that covers the bottom housing member21as if a lid. The bottom housing member21houses therein the LED module MJ, the light guide plate41, the reflection sheet42, the diffusion sheet43, the optical sheets44and45, and the like.

Specifically, the reflection sheet42, the light guide plate41, the diffusion sheet43, and the optical sheets44and45are stacked in this order, and housed in the bottom housing member21(hereinafter, the direction along which these members are stacked will be referred to as “stacking direction Q”, and a direction perpendicular to both the alignment direction P of the LEDs12and the stacking direction Q will be referred to as “direction R”).

The non-mounting surface11B of the mounting substrate11is attached to an inner surface of a wall section23of the bottom housing member21via a bonding member BD (incidentally, the mounting substrate11and the wall section23may be in direct contact with each other with no bonding member BD interposed in between). That is, the LED module MJ is attached to the bottom housing member21via the bonding member BD.

And, if the bottom housing member21is formed of a highly heat conductive material (heat dissipating material), heat generated during the operation of the LEDs12does not stay in the LEDs12themselves or in the mounting substrate11, but escapes to the bottom housing member21via the bonding member BD (it is more preferable that the bonding member BD is also highly heat conductive).

In the backlight unit49, light from the LEDs12enters the light guide plate41to be emitted therefrom as surface light, and the surface light passes through the optical sheet group46to be emitted as backlight light having enhanced brightness. The backlight light reaches the liquid crystal display panel59, on which an image is displayed by use of the backlight light.

Now, a detailed description will be given of the housing HG of the backlight unit49, with reference toFIGS. 1 to 3.FIG. 1is an exploded perspective view of the backlight unit49(here, the optical sheet group46is omitted, and the hatching indicates a cross section).FIG. 2is a plan view of the top housing member25.FIG. 3is a sectional view of the liquid crystal display device69(taken along a sectional direction indicated by line A1-A1′ and viewed as indicated by the arrows shown inFIGS. 1 and 2).

The bottom housing member21includes the bottom section22and the wall section23. The bottom section22is a member that supports the light guide plate41and the like, and the circumference of the bottom section22is slightly larger than that of the light guide plate41.

The wall section23rises from the bottom section22, surrounding the bottom section22(it is preferable that the wall section23rises from the bottom section22in the stacking direction Q). And, an LED module MJ is attached to part of the wall section23(for example, to each of opposite sides of the wall section23that face each other) via a bonding member BD.

In the figure, the non-mounting surface11B of a mounting substrate11is in indirect contact with the wall section23with a bonding member BD interposed in between, but this is not meant to limit the present invention. For example, the non-mounting surface11B of a mounting substrate11may be in direct contact with the wall section23(the following description, however, will deal with an example in which the wall section23and a mounting substrate11are in indirect contact with each other with a bonding member BD interposed in between).

The top housing member25is a frame-like member having an outline similar to that of the bottom section22of the bottom housing member21, and the top housing member25is placed so as to cover the bottom housing member21. Thus, it may be said that the top housing member25is a lid of the bottom housing member21.

The top housing member25is also provided with engagement claws CF to be engaged in engagement holes HL of the bottom housing member21. When the top housing member25is placed to cover the bottom housing member21, the engagement claws CF are fitted into the engagement holes HL (seeFIG. 1). Thereby, the top housing member25is immovably fixed to the bottom housing member21(the top and bottom housing members21and25are coupled together).

Furthermore, as shown inFIG. 2(a plan view showing inside of the top housing member25), a side section VP of the top housing member25that forms sides of the frame has a width extending toward the inside of the frame. Thus, when the top housing member25is attached to the bottom housing member21, the side section VP extends (is wide) in directions crossing the direction in which the wall section23rises.

Moreover, when the top housing member25is attached to the bottom housing member21, two portions of the side section VP that are each positioned to overlap an LED module MJ are formed thick toward the bottom section22of the bottom housing member21to face the wall section23(seeFIG. 3). That is, the two portions (protrusion sections) of the side section VP are each a member having a given width and a comparatively large thickness (wall thickness).

Here, as shown inFIGS. 1 to 3, the protrusion sections (hill sections HH) are each a given distance away from an edge of the side section VP and extend in a longitudinal direction of the side section VP, edges of the side section VP serving as external edges of the frame as well. With this structure, if the wall section23is positioned to support the edges of the side section VP when the top housing member25is attached to the bottom housing member21, first grooves DH1are formed one between each of the hill sections HH and the wall section23(that is, the side section VP is at least part of the first grooves DH1).

A first groove DH1has a first groove width W1that is wide enough for a mounting substrate11and a bonding member BD to be held therein. That is, an interval between inner surfaces (that is, an interval between a hill section HH of the side section VP and the wall section23of the bottom housing member21) in a first groove DH1has a length of the same order as the sum of the thickness of a mounting substrate11and the thickness of a bonding member BD.

Moreover, as shown inFIG. 3, when the top housing member25is attached to the bottom housing member21, a hill section HH is so thick as to be able to reach a mounting substrate11attached to the wall section23of the bottom housing member21. That is, a first groove DH1has a groove width W1and a groove height (a groove depth T) that permit a mounting substrate11attached to the wall section23to be held therein.

Thus, when the top housing member25is attached to the bottom housing member21having the LED modules MJ attached to its wall section23with the bonding members BD interposed in between, a mounting substrate11located between the side section VP of the top housing member25and the wall section23is held in a first groove DH1formed with the wall section23and the side section VP.

With this structure, the LEDs12do not have to be pressed by, for example, a side surface41s(in other words, the light emission surfaces12F of the LEDs12and the side surfaces41S of the light guide plate41do not need to be in close contact with each other) to prevent the LED modules MJ from moving. Thus, a higher degree of freedom is allowed in the arrangement of the LEDs12.

Furthermore, since a first groove DH1at least includes a thick-walled portion of the side section VP, it is easy to change the position of a first groove DH1. That is, the position and the shape of a first groove DH1can be changed by changing the shape of a hill section HH (thus making effective use of a comparatively thick-walled portion of the side section VP). Thus, a much higher degree of freedom is securely allowed in the arrangement of the LEDs12.

Moreover, even if the bonding force of a bonding member BD is reduced due to, for example, a long-term use, to cause a mounting substrate11to warp so much away from the bonding member BD that the mounting substrate11tends to come off from the wall portion23of the bottom housing member21, the mounting substrate11is pressed against the wall section23by a hill section HH that forms the inner surface of the first groove DH1. Then, heat in the LEDs12and the mounting substrate11securely escapes to the bottom housing member21(and to the hill section HH as well). This prevents deterioration of the LEDs12from being caused by heat, making long-time driving of the LEDs12possible. This also helps make deterioration of the mounting substrate11less likely to be caused by heat.

Moreover, if the top housing member25including the hill sections HH and the bottom housing member21including the wall section23are both made of resin (insulating material), the inner surface of a first groove DH1is also made of resin (that is, one part of the inner surface of a first groove DH1is formed of the side section VP and the other part thereof is formed of the wall section23). Thus, the height T (the groove depth T) of the portion of a hill section HH that is in contact with a mounting surface11A on which a conductive wiring is formed may be increased, and this makes it easier to increase the area of the portion of the inner surface formed of the hill section HH. Thus, a mounting substrate11is securely pressed against the wall section23of the bottom housing member21.

As shown inFIG. 3, the opposite inner surfaces of a first groove DH1that face each other are formed of a hill section HH (the side section VP) and of the wall section23, respectively. However, this is not meant to limit the present invention. For example, a groove in which a mounting substrate11is to be held may be carved in a hill section HH of the side section VP (that is, a first groove DH1may be entirely formed of the side section VP). However, if a first groove DH1is formed of a hill section HH and the wall section23as shown inFIG. 3, there is no need of performing processing such as carving a groove in a hill section HH of the side section VP.

As shown inFIGS. 1 to 3, the groove width W1of a first groove DH1is uniform along the length thereof, and the groove width W1has a length of the same order as the sum of the thickness of a mounting substrate11and the thickness of a bonding member BD such that a mounting substrate11can be held in a first groove DH1. However, a first groove DH1may be formed otherwise, and one such example will be described with reference toFIGS. 4 to 6.

FIGS. 4 and 5are illustrated in the same manners asFIGS. 1 and 2, respectively, andFIG. 6AandFIG. 6Bare sectional views of a liquid crystal display device69(FIG. 6AandFIG. 6Bare taken along lines A2-A2′ and B2-B2′, respectively, inFIGS. 4 and 5, and viewed from directions indicated by arrows).

As shown inFIG. 4, a hill section HH of the side section VP, the hill section HH forming part of a first groove DH1, extends along the longitudinal direction of the side section VP and protrudes toward the bottom section22of the bottom housing member21. However, as shown inFIG. 5, the width (a short side) of a hill section HH varies along its long side.

This results in a nonuniform width of a first groove DH1, which is a gap between a hill section HH and the wall section23. For example, assume that, as shown inFIG. 5, the width of a first groove DH1is larger at its portions corresponding to the two end portions and the middle portion of a hill section HH than at portions corresponding to the other portions of the hill section HH in the longitudinal direction of the hill section HH.

Then, a groove width (a first narrow groove width) SW1, which is a width of a first groove DH1at its portions corresponding to the two end and middle portions of a hill section HH in its longitudinal direction, is shorter than a groove width (a first broad groove width) BW1, which is a width of the first groove DH1at its portions corresponding to the other portions of the hill section HH in its longitudinal direction.

And, if the comparatively narrow groove width SW1has a length on the same order as the sum of the thickness of a mounting substrate11and the thickness of a bonding member BD, a mounting substrate11is held between the wall section23and three portions corresponding to the two end portions and the middle portion of a hill section HH in its longitudinal direction (seeFIG. 6A). That is, the mounting substrate11is efficiently held at three points in its longitudinal direction.

On the other hand, since the comparatively large groove width BW1is larger than the sum of the thickness of a mounting substrate11and the thickness of a bonding member BD, a mounting substrate11is not in contact with an inner surface of a first groove DH1at portions corresponding to the portions of a hill section HH other than the two ends and middle portions of the hill section HH (seeFIG. 6B).

Even with a backlight unit49including a first groove DH1having a nonuniform groove width, the same operational effect is obtained as is obtained with a first groove DH1having the first groove width W1as shown inFIGS. 1 to 3. Moreover, since a hill section HH may be comparatively small in volume, cost reduction of the top housing member25, and thus cost reduction of the backlight unit49can be achieved.

A first groove DH1does not need to have a length of the same order as the longitudinal length of a mounting substrate11, and two or more first grooves DH1may be formed to hold a mounting substrate11. For example, a plurality of first grooves DH1may hold one mounting substrate11. A description will be given of an example of such a case with reference toFIGS. 7 to 9.

FIGS. 7 and 8are illustrated in the same manners asFIGS. 1 and 2, respectively, andFIGS. 9A and 9Bare sectional views of a liquid crystal display device69(FIGS. 9A and 9Bare taken along lines A3-A3′ and B3-B3′, respectively, inFIGS. 7 and 8, and viewed from directions indicated by arrows).

As shown inFIG. 7, hill sections HH of a side section VP that form part of a first groove DH1are positioned away from each other along the longitudinal direction of the side section VP, and protrudes toward a bottom section22of a bottom housing member21. That is, the length of a hill section HH along the longitudinal direction of the side section VP is shorter than the length of the side section VP, and a plurality of hill sections HH are aligned along the longitudinal direction of the side section VP (inFIGS. 7 to 9, three hill sections HH are formed one at each of the positions corresponding to two end portions and a middle portion of the side section VP, but this is not meant to limit the positions and the number of hill sections HH to be formed).

With this structure, although there are some portions in a mounting substrate11corresponding to which no first groove DH1is formed, and that thus are not held in a first groove DH1, a mounting substrate11is held in the first grooves DH1formed corresponding to three hill sections HH as shown inFIG. 9A. That is, a mounting substrate11is efficiently held at three portions in its longitudinal direction.

Thus, even with a backlight unit49including a first groove DH1formed with hill sections HH arranged away from each other, the same operational effect is obtained as is obtained by use of a first groove DH1having the first groove width W1as shown inFIGS. 1 to 3. Moreover, although three hill sections HH are provided, since the total volume of the three hill sections is smaller than that of the hill section HH that is formed in one piece as shown inFIGS. 1 to 3, cost reduction of the top housing member25, and thus cost reduction of the backlight unit49can be achieved.

The top housing member25is preferably formed of, for example, a reflective white resin. This is for the purpose of reflecting light that fails to enter the light guide plate41through a side surface41S and reaches the top housing member25, to thereby help the light enter the light guide plate41through a side surface41S.

In particular, it is preferable that a surface of a protrusion section rising in the top housing member25is positioned to cover a space between the light emission surfaces12F of LEDs12and a side surface41S of the light guide plate41(that is, it is preferable that a surface of a hill section HH is placed over between the light emission surfaces12F of LEDs12and a side surface41S of the light guide plate41).

With this structure, as shown inFIG. 10, there is formed a space that faces at least three surfaces, namely, the surface of a hill section HH (a reflection surface RS), the light emission surface12F of an LED12, and a side surface41S of the light guide plate41. Light from LEDs12travels around inside the space, and this makes it easier for the light to enter the light guide plate41through the side surface41S of the light guide plate41.

For example, light that does not directly enter the light guide plate41through a side surface41S (see dash-dot line arrows inFIG. 10) is reflected on the reflection surface RS of the hill section HH to enter the light guide plate41through the side surface41S. This contributes to the effective use of light from the LEDs12.

In particular, in order to form the space facing at least the three surfaces of the reflection surface RS of a hill section HH, the light emission surface12F of an LED12, and the side surface41S of the light guide plate41, it is desirable that a hill section HH be thinner as it protrudes (that is, the hill section HH is tapered), that an angle (δ1) formed of the light emission surface12F of an LED12and the reflection surface RS of the hill section HH be an acute angle, and further, that an angle (δ2) formed of the side surface41S of the light guide plate41and the reflection surface RS of the hill section HH be an obtuse angle. This is because this structure allows light to behave as indicated by the dash-dot line arrows inFIG. 10.

Incidentally, in a case in which the top housing member25is formed of a non-reflective material (for example, a black resin that absorbs light), it is preferable that a reflection sheet is attached to the surface RS of a hill section HH. This also allows light to behave as indicated by the dash-dot line arrows shown inFIG. 10.

Second Embodiment

Next, a second embodiment will be described. Such members as function similarly to their counterparts in the first embodiment are identified by common reference signs and no description of them will be repeated.

In the backlight unit49dealt with in the description of the first embodiment, a mounting substrate11is held in a first groove DH1formed of the side section VP of the top housing member25and the wall section23of the bottom housing member21. The following description of the second embodiment will refer toFIGS. 11 and 12, and focus on the feature that a mounting substrate11is held in a second groove which is formed apart from a first groove DH1.

FIG. 11is illustrated in the same manner asFIG. 1, andFIG. 12is illustrated in the same manner asFIG. 3(here,FIG. 12is a sectional view taken along line A4-A4′ inFIG. 11).

As shown inFIGS. 11 and 12, a second groove DH2includes, as part thereof, a level difference DD2formed at an edge portion of a bottom section22of the bottom housing member21. More specifically, an edge portion of the bottom section22of the bottom housing member21that overlap a portion of a side section VP of a top housing member25, the portion including a hill section HH, is formed thinner than the other portions of the bottom section22, and as a result, when the top housing member25is attached to the bottom housing member21, there is generated a height difference between a surface including an edge portion of the bottom section22and a surface including the other portions of the bottom section22, and this height difference is the level difference DD2.

A wall surface having a height equivalent to the level difference DD2(hereinafter referred to as “leve-difference-DD2wall surface”) faces a wall section23of the bottom housing member21, and thereby a second groove DH2is formed between the wall section23and a level-difference-DD2wall surface. That is, a space between a level-difference-DD2wall surface and the wall section23that face each other forms a second groove DH2.

A groove width W2of a second groove DH2is of the same order as the sum of the thickness of a mounting substrate11and the thickness of a bonding member BD (it is preferable that the groove width W2is of the same order as the first groove width W1). With this structure, when a long side of a mounting substrate11is placed in a second groove DH2and a bonding member BD is interposed between a non-mounting surface11B of a mounting substrate11and the wall section23of the bottom housing member21, the mounting substrate11is attached to the wall section23by being fitted into the second groove DH2.

With this structure, since one of long sides of a mounting substrate11is held in a first groove DH1and the other of the long sides is held in a second groove DH2, the mounting substrate11is less likely to warp and less likely to fall away from the wall section23of the bottom housing member21. Also, heat in the LEDs12and the mounting substrate11escapes to the bottom housing member21through the second groove DH2.

As shown inFIG. 12, inner surfaces of a second groove DH2that face each other are a level-difference-DD2wall surface (that is, the bottom section22) and the wall section23. However, this is not meant to limit the present invention. For example, a groove in which a mounting substrate11is to be held may be carved in the bottom section22(that is, the second groove DH2may be entirely formed of the bottom section22).

As shown inFIGS. 11 and 12, in a second groove DH2, the groove width W2is uniform all along the length of the second groove DH2, and the groove width W2is of the same order as the sum of the thickness of a mounting substrate11and the thickness of a bonding member BD. However, the second groove DH2may be formed otherwise, and one such example will be described with reference toFIGS. 13 and 14.

FIG. 13is illustrated in the same manner asFIG. 11, andFIGS. 14A and 14Bare sectional views of a liquid crystal display device69(FIGS. 14A and 14Bare taken along lines A5-A5′ and B5-B5′, respectively, inFIG. 13, and viewed from directions indicated by arrows shown inFIG. 13).

As shown inFIGS. 13 and 14, a second groove DH2has a nonuniform groove width. More specifically, portions of a wall surface corresponding to two end portions and a middle portion of a level difference DD2in its longitudinal direction are closer to the wall section23than portions of the wall surface corresponding to the other portions of the level difference DD2in its longitudinal direction.

Then, a groove width (a second narrow groove width) SW2, which is a distance between the wall section23and a wall surface corresponding to any of the two end portions and the middle portion of a level difference DD2in its longitudinal direction, is shorter than a groove width (a second wide groove width) BW2which is a distance between the wall section23and a wall surface corresponding to a portion of the level difference DD2other than the two end portions and the middle portions in its longitudinal direction.

And, if the comparatively narrow groove width SW2is of the same order as the sum of the thickness of a mounting substrate11and the thickness of a bonding member BD, a mounting substrate11is held between the wall section23and each of three wall surfaces corresponding to two end portions and a middle portion of a level difference DD2(seeFIG. 14A). That is, a mounting substrate11is efficiently held at three portions in its longitudinal direction.

On the other hand, since the comparatively wide groove width BW2is larger than the sum of the thickness of a mounting substrate11and the thickness of a bonding member BD, a mounting substrate11is not in contact with wall surfaces corresponding to portions other than the two ends portions and the middle portion of a level difference DD2along its length direction (seeFIG. 6B).

Even with a backlight unit49including a second groove DH2whose width is not uniform, the same operational effect is obtained as is obtained by use of the second groove DH2having the second groove width W2as shown inFIGS. 11 and 12. Moreover, since the comparatively large groove width contributes to reduction of the volume of the bottom housing member21, cost reduction of the bottom housing member21, and thus cost reduction of the backlight unit49can be achieved.

A second groove DH2is not limited to a groove that is carved down into a surface of the bottom section22of the bottom housing member21. A description will be given of an example of such a case with reference toFIGS. 15 and 16.

FIG. 15is illustrated in the same manner asFIG. 11, andFIG. 16is a sectional view showing a liquid crystal display device69(here,FIG. 16is a sectional view taken along line A6-A6′ inFIG. 15, and viewed from directions indicated by arrows shown inFIG. 15).

As shown inFIGS. 15 and 16, a second groove DH2may be a space between a surface of a bottom section22of a bottom housing member21, in particular a block BK placed along an edge of the bottom section22, and the wall section23(here, a block BK is part of the bottom section22, and is a member that gives a level difference to a surface of the bottom section22). With this structure, as shown inFIG. 16, a mounting substrate11is held in a second groove DH2formed corresponding to a block BK.

Thus, even with a backlight unit49including a second groove DH2formed with a block BK, the same operational effect is obtained as is obtained by use of the second groove DH2having the second groove width W2as shown inFIGS. 11 and 12.

Also, two or more second grooves DH2may be formed to hold a mounting substrate11. For example, a plurality of second grooves DH2may hold one mounting substrate11. For example, a plurality of first grooves DH1may hold one mounting substrate11. A description will be given of an example of such a case with reference toFIGS. 17 and 18.

FIG. 17is illustrated in the same manner asFIG. 11, andFIGS. 18A and 18Bare sectional views of a liquid crystal display device69(FIGS. 18A and 18Bare taken along lines A7-A7′ and B7-7′, respectively, inFIG. 17, and viewed from directions indicated by arrows shown inFIG. 17).

As shown inFIGS. 17 and 18, a second groove DH2is a space between a block BK and a wall section23, a plurality of blocks BK placed away from each other along an edge of the bottom section22(FIGS. 17 and 18show that three blocks BK are formed at two end portions and a middle portion along an edge of the bottom section22, but this is not meant to limit the positioning and the number of the blocks BK).

With this structure, although there are some portions in a mounting substrate11corresponding to which no second groove DH2is formed, and that thus are not held in a second groove DH2, a mounting substrate11is held in the second grooves DH2formed corresponding to three blocks BK as shown inFIG. 18A. That is, a mounting substrate11is efficiently held at three portions in its longitudinal direction.

Thus, even with a backlight unit49including a second groove DH2formed with a block BK, the same operational effect is obtained as is obtained by use of a second groove DH2having the second groove width W2as shown inFIGS. 11 and 12.

The bottom housing member21is preferably formed of, for example, a reflective white resin. This is for the purpose of reflecting light that fails to enter the light guide plate41through the side surfaces41S and reaches the bottom housing member25, to thereby help the light enter the light guide plate41through a side surface41S.

For example, as shown inFIGS. 19 and 20(which are illustrated in the same manners asFIGS. 11 and 12, respectively; andFIG. 20is a sectional view taken along line A8-A8′, and viewed as indicated by arrows inFIG. 19), it is preferable that a top surface US of a block BK is placed so as to cover a space between the light emission surfaces12F of LEDs12and a side surface41S of the light guide plate41(that is, a top surface US of a block BK is placed over between light emission surfaces12F of LEDs12and a side surface41S of the light guide plate41).

With this structure, as shown inFIG. 21, there is formed a space that faces at least three surfaces, namely, the top surface of a block BK (a reflection surface US), the light emission surface12F of an LED12, and a side surface41S of the light guide plate41. Light from LEDs12travels around inside the space, and this makes it easier for the light to enter the light guide plate41through a side surface41S of the light guide plate41.

For example, light that does not enter the light guide plate41directly through a side surface41S thereof (see the dash-dot line arrow) is reflected on the top surface of a block BK to enter the light guide plate41through a side surface41S thereof. This contributes to the effective use of light from the LEDs12.

In particular, in order to generate the space facing at least the three surfaces of the top surface US of a block BK, the light emission surface12F of an LED12, and a side surface41S of the light guide plate41, it is desirable that a block BK be thinner as it protrudes (that is, a block BK is tapered), that an angle (δ3) formed by the light emission surface12F of an LED12and the top surface US of a block BK be an acute angle, and further, that an angle (δ4) formed by the side surface41S of the light guide plate41and the top surface US of the block BK be an obtuse angle. This is because this structure allows light to behave as indicated by the dash-dot line arrows shown inFIG. 21.

Incidentally, in a case in which the bottom housing member21is formed of a non-reflective material, it is preferable that a reflection sheet is attached to the top surface US of a block BK. This is because such a structure also allows light to behave as indicated by the dash-dot line arrows shown inFIG. 21.

Other Embodiments

It should be understood that the embodiments specifically described above are not meant to limit the present invention, and that many variations and modifications can be made within the spirit of the present invention.

For example, it is preferable that a protrusion (a support portion)27is formed to protrude from the side section VP (for example, a portion of the side section VP including a hill section HH) of the top housing member25toward the inside of the frame. And, it is desirable that the protrusion27support a liquid crystal display panel59. Such a protrusion27is also capable of pressing down an optical sheet group46.

However, this is not meant to limit the way the liquid crystal display panel59is supported, and the liquid crystal display panel59may be supported by the entire side section VP. In such a case, the protrusion27is not necessary. However, since edges of the optical sheet group46are held by the side section VP (in particular by the hill sections HH), the side section VP functions also as a positioning member for the optical sheet group46(it goes without saying that even in the case in which the protrusion27is provided, the side section VP functions as the positioning member for the optical sheet group46).

As shown inFIG. 22, there may be interposed a heat dissipation plate31between the reflection sheet42and the bottom housing member21. The heat dissipation plate31is formed of a material such as metal having a comparatively high thermal conductivity, and includes a bottom plate32covered with the reflection sheet, and two wall plates33located such that the bottom plate32is placed between the two wall plates33(incidentally, the section of the heat dissipation plate31along its short side direction has a recessed shape).

In a case in which such a heat dissipation plate31is provided, the non-mounting surface11B of a mounting substrate11is attached to the inside of a wall plate33with a bonding member BD interposed in between (the mounting substrate11and the wall plate33may be in direct contact with each other with the bonding member BD omitted). That is, an LED module MJ is attached to the heat dissipation plate31with a bonding member BD interposed in between. Thus, heat generated during the operation of the LEDs12does not stay in the LEDs12themselves and the mounting substrate11, but escapes to the heat dissipation plate31via the bonding member BD, and further escapes from the heat dissipation plate31to the bottom housing member21.

Also, in the case in which a second groove DH2is fowled in the bottom section22of the bottom housing member21with an LED module MJ attached to a wall plate33of the heat dissipation plate31as shown inFIG. 23, the mounting substrate11, together with the bottom plate32of the heat dissipation plate31, needs to be held in the second groove DH2.

To satisfy this need, the bottom plate32of the heat dissipation plate31includes a level difference DD3similar to the level difference included in the bottom section22of the bottom housing member21. More specifically, a folding line (a valley-folding line) is formed next to an edge of the bottom plate32from which a wall plate33continues, and a reverse folding line (a mountain folding line) is formed next to the folding line (the valley-folding line). That is, a valley fold is formed next to an edge of the bottom plate32from which a wall plate33continues, and further, a mountain fold is formed next to the valley fold. Thereby, there is formed a level difference DD3by the amount of which a front surface32A of the bottom plate32is depressed (in other words, a protruding level difference DD3is formed on a rear surface32B of the bottom plate32).

And, the wall surface of a depressed level difference DD3formed in the front surface32A faces a wall plate33of the heat dissipation plate31to form a third groove DH3between the wall plate33and the wall surface of the level difference DD3. That is, a space between a wall surface of level difference DD3and a wall plate33that face each other is a third groove DH3.

A groove width W3of a third groove DH3has a length of the same order as the sum of the thickness of a mounting substrate11and the thickness of a bonding member BD. Thus, when a long side of a mounting substrate11is placed in a third groove DH3and a bonding member BD is interposed between the rear surface11B of the mounting substrate11and the wall plate33of the heat dissipation plate31, the mounting substrate11is attached to the heat dissipation plate31and held in the third groove DH3.

Furthermore, the depth of a third groove DH3is set to be of the same order as the depth of the second depth DH2, and a projecting level difference DD3having a length of the same order of magnitude as the depth of a second groove DH2is formed on the rear surface32B of the bottom plate32. Moreover, the groove width W2of a second groove DH2is set to be longer than the groove width W3of a third groove DH3. More specifically, the groove width W2of a second groove DH2has the same order of magnitude as the sum of the thickness of a mounting substrate11, the thickness of a bonding member BD, the thickness of the heat dissipation plate31that is in contact with the mounting substrate11, and the thickness of the heat dissipation plate31that is in contact with the bonding member BD.

With this structure, when the heat dissipation plate31having a mounting substrate11set in a third groove DH3is set in the bottom housing member21keeping the wall plates33in contact with the wall section23of the bottom housing member21, a mounting substrate11held in a third groove DH3is set in a second groove DH2(that is, a mounting substrate11is held in a second groove DH2).

As a result, heat generated during the operation of the LEDs12does not stay in the LEDs12themselves and a mounting substrate11, but escapes to the heat dissipation plate31via a bonding member BD, and further escapes from the heat dissipation plate31to the bottom housing member21.

In a case in which a second groove DH2has a complicated shape (see, for example,FIGS. 13 and 17), it is preferable that a third groove DH3of the heat dissipation plate31is formed by using a metal mold (it goes without saying that the heat dissipation plate31including a third groove DH3as shown inFIG. 23may be formed by using a metal mold).

In the descriptions given hereinbefore, an LED module MJ is attached to the bottom housing member21or to the heat dissipation plate31by use of a bonding member BD, but with a first groove DH1or a second groove DH2, it is possible to attach an LED module MJ to the bottom housing member21or to the heat dissipation plate31without using a bonding member BD.

A middle hole MH may be formed in the bottom section22of the bottom housing member21so as to, for example, reduce the weight of the backlight unit49(seeFIGS. 22 and 23).

In the descriptions given hereinbefore, the housing HG is composed of two separate members, namely, the top housing member25and the bottom housing member21. However this is not meant to limit the present invention. That is, the top housing member25and the bottom housing member21may be integrally formed as one housing HG, or instead, the housing HG may be composed with three separate members.

In the descriptions given hereinbefore, LED modules MJ are arranged such that each LED module MJ faces a corresponding one of two opposite side surfaces41S and41S of the light guide plate41that face each other, but this is not meant to limit the present invention. That is, an LED module MJ or LED modules MJ may be provided to face one, three, or four side surfaces41sof the light guide plate41.

It goes without saying that embodiments obtained by appropriately combining technical means disclosed in different embodiments with each other are also included in the technical scope of the present invention. For example, various combinations of a plurality of kinds of top housing members25and a plurality of kinds of bottom housing members21are possible.

The housing HG may include only a first groove DH1, or may include only a second groove DH2. This is because if the housing HG includes at least either a first groove DH1or a second groove DH2, an LED module MJ can be properly mounted in the backlight unit49.