Optical-sheet supporting structure, lighting device and display device

In a backlight device, a diffuser plate and a plurality of optical sheets are disposed above a base tray that includes a plurality of cold-cathode tubes therein. The diffuser plate is sandwiched in between a base member, which holds the bottom surface thereof, and a facing portion of an inner frame disposed on the top surface side thereof. A holding protrusion is arranged on the facing portion so as to abut on an exposed portion located on the periphery of the diffuser plate. According to this construction, even when the backlight device is used in an upright orientation, the diffuser plate can be prevented from leaning forward, and thereby pressure applied on the optical sheets can be prevented.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an optical-sheet supporting structure, a lighting device and a display device.

2. Description of the Related Art

A backlight device used for a liquid-crystal display device or the like is widely known, and includes an optical component having a plurality of optical sheets stacked on a panel, such as a diffuser plate or a light guide plate (as described in JP-A-2002-341345, for example). The optical component is disposed on the front or side of a light source in order that light from the light source may be uniformly radiated to a liquid-crystal panel. A structure shown inFIG. 7is provided as an example of its supporting structure, which supports a panel10and optical sheets11by sandwiching in the periphery thereof between a base member15and a holding member16. According to this supporting structure, assembly can be readily achieved by simply laying the parts on top of one another.

In the supporting structure, preferably, a predetermined gap is formed between the holding member16and the optical sheets11. In the case that the optical sheets11are held so as to be subjected to direct intense pressure, the optical sheets11may vault (SeeFIG. 8) when the optical sheets11expand or contract due to change of ambient temperature or the like. This could result in failing to uniformly radiate light from the light source to the liquid-crystal panel. However, actually the holding member16may apply direct pressure on the optical sheets11due to the following two reasons, and this should be improved.

The first reason is that the panel10can move due to the gap. That is, when the backlight device is used in an upright orientation, for example, the panel10may lean forward within the gap (or play) provided between the holding member16and the optical sheets11. In recent years in particular, panels10have been getting larger along with increasing size of display devices. Therefore, once the panel10leans forward, the periphery of the optical sheets11may be sandwiched in between the leaning panel10and the holding member16so as to be subjected to intense pressure.

The second reason is that the holding member16can lean inwardly. Other components may be disposed on the holding member16. In this case, if the holding member16is not adequately supported, the distal end portion16A thereof may lean inwardly (SeeFIG. 9). In recent years in particular, components have been growing in size. This could result in increasing the tendency of the holding member16to be made of resin. In this case, high-accuracy components cannot be expected, and therefore the gap between the holding member16and the optical sheets11may be originally narrower than designed. In this instance, the distal end portion16A of the holding member16may apply intense pressure on the periphery of the optical sheets11, if it leans inwardly as described above.

SUMMARY OF THE INVENTION

In order to overcome the problems described above, preferred embodiments of the present invention provide an optical-sheet supporting structure that is capable of supporting a panel and therefore optical sheets so as not to apply pressure on the optical sheets, and provide a lighting device and a display device therewith.

An optical-sheet supporting structure according to a preferred embodiment of the present invention includes a flat panel, an optical sheet placed on the panel so that an exposed portion is left on the periphery thereof, a base-side panel support that abuts the periphery of the panel so as to hold the panel, a holding-side panel support having a frame-like shape which is disposed on the opposite side of the base-side panel support so as to hold the periphery of at least the panel in cooperation with the base-side panel support and therebetween, and a holding protrusion that is disposed on and projects from at least one of the exposed portion of the panel and a portion of the holding-side panel support opposite to the exposed portion so as to abut on the other. According to this construction, the holding protrusion restricts movement of the panel between the panel supports, and thereby the panel can be supported stably. Therefore, the panel can be prevented from leaning forward, even when the panel is used in an upright orientation.

Preferably, the present invention is embodied as follows.

The holding protrusion is preferably integrated with the holding-side panel support or the panel. Thereby, the production costs can be reduced, compared to the case in which the holding protrusion is provided as a separate component.

The holding-side panel support preferably includes a facing portion which is cantilevered and extends so as to overlap with the periphery of the optical sheet. The holding protrusion preferably is disposed on and projects from the facing portion. The projecting length of the holding protrusion is preferably larger than the thickness of the optical sheet, so that a gap is maintained between the optical sheet and the facing portion. Thus, the facing portion can be disposed so as to maintain a distance from the periphery of the optical sheet.

An escape portion corresponding to the holding protrusion preferably is formed as a notch on the optical sheet, so that a portion of the panel is exposed as the exposed portion. According to this construction, a conventional panel can be used directly.

A posture retaining portion preferably is provided, and is disposed on one of the base-side panel support and the facing portion, and abuts on the other so as to provide two-point support for the facing portion together with the holding protrusion. Thereby, the facing portion can be prevented from leaning inward, and therefore the distal end of the facing portion can be prevented from interfering with the optical sheet.

An optical-sheet supporting structure according to a preferred embodiment of the present invention includes a flat panel, an optical sheet placed on the panel so that an exposed portion is left on the periphery thereof, a base-side panel support that abuts on the periphery of the panel so as to hold the panel, and a holding-side panel support which is disposed on the opposite side of the base-side panel support and includes a facing portion positioned so as to hold the periphery of the panel and the optical sheet in cooperation with the base-side panel support and therebetween. The holding-side panel support preferably has a frame-like shape as a whole. Further included are at least two posture retaining portions arranged to retain the posture of the facing portion so that the facing portion extends along the surface of the optical sheet. According to this construction, two-or-more-point support for the facing portion is provided, and thereby firm support can be achieved.

According to a preferred embodiment of the present invention, other components can be prevented from applying intense pressure on the optical sheet. Therefore, the optical sheet can be prevented from vaulting, even when ambient temperature or the like changes. Thereby light from the light source can be radiated uniformly, which contributes to quality improvement of a lighting device.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

First Preferred Embodiment

FIG. 1is an exploded perspective view of a display device20. The display device20preferably includes a liquid crystal panel30having a planar surface capable of image display, and a backlight device (corresponding to a lighting device of a preferred embodiment of the present invention)40. The liquid-crystal panel30includes a pair of glass substrates, liquid crystal filled between the glass substrates, and a pair of polarizing plates applied to the outer surfaces of the respective glass substrates. It is placed on a backlight device40with an overlap, and held by a substantially rectangular-shaped outer frame35.

The backlight device40preferably is a so-called direct-light-type backlight device, in which a plurality of cold-cathode tubes65positioned beneath the liquid-crystal panel30are arranged in a row sideways. A base tray60that contains the cold-cathode tubes65therein is provided, and a diffuser plate (corresponding to a panel of a preferred embodiment of the present invention)51and three optical sheets55A-55C are disposed thereon so as to cover the opening thereof from above.

The three optical sheets (i.e., from bottom up, a diffusing sheet55A, a lens sheet55B and a brightness enhancement sheet55C, for example) are formed so as to be substantially of the same size as the diffuser plate51, and placed on the diffuser plate51with an overlap. The optical sheets55A-55C and the diffuser plate51convert substantially-linear light emitted from each cold-cathode tube65into flat light, so that the light is uniformly radiated to the liquid-crystal panel30. Each of them preferably has a substantially rectangular flat shape, and the size thereof is larger than the display area of the display device20.

InFIG. 1, symbol80designates a substantially rectangular-shaped inner frame (corresponding to a holding-side panel support of a preferred embodiment of the present invention), which holds the diffuser plate51and the three optical sheets55A-55C in cooperation with the base tray60and therebetween. Hereinafter, a supporting structure for the optical sheets55A-55C and the diffuser plate51will be explained in detail with reference toFIGS. 2 to 4.FIG. 2is a typical sectional view of the display device20.FIG. 3Ais a plan view of the backlight device40, andFIG. 3Bis an enlarged view of Section “C” shown inFIG. 3A. InFIGS. 3A and 3B, the inner frame80is shown by the chain lines.

As shown inFIG. 2, the base tray60includes a metallic base panel61of an open-topped box shape, and a base member (corresponding to a base-side panel support of a preferred embodiment of the present invention)71made of synthetic resin. The base member71preferably has, as a whole, a frame-like shape following the contour of the diffuser plate51, and is fitted on the inner circumference of the base panel61so as not to form any clearance. The upper surface of the base member71is provided as a flat bearing surface71A, on which the periphery (shown as right and left edge portions inFIG. 2) of the diffuser plate51is held.

Further, the base member71includes, on the edge portion of its upper surface, a raised portion (corresponding to a posture retaining portion of a preferred embodiment of the present invention)72which projects upward in the figure. The raised portion72is arranged to extend along the entire circumference of the base member71as shown inFIG. 3A, and partially expands inward so as to form positioning portions73. More specifically, a pair of positioning portions73A are formed on the sides shown as the right and left sides inFIG. 3A, while five positioning portions73B are formed on each of the upper and lower sides.

On the other hand, slits53A and53B corresponding to the positioning portions73A and73B are provided on the periphery of the diffuser plate51. The concave portion of each slit53A or53B is engaged with the convex portion of the positioning portion73A or73B, so that the diffuser plate51is positioned in the planar directions (i.e., right and left, and upward and downward directions inFIG. 3A). The positioning portions73and slits53are spaced away from the display area of the display device20.

Slits57A and57B corresponding to the positioning portions73A and73B are also provided on each of the optical sheets55stacked on the diffuser plate51. Among the slits57of the optical sheets55, the right and left slits57A preferably have the same shape as the slits53A of the diffuser plate51, while some (e.g., a slit shown in Section “C”) of the upper and lower slits57B have a slit width (shown as Dimension F2inFIG. 3B) larger than the slit width (shown as Dimension F1inFIG. 3B) of the diffuser plate51.

Thus, some of the slits57B of the optical sheets55have a larger slit width, and thereby the extended portions (shown by the hatching inFIG. 3B, and corresponding to an escape portion of a preferred embodiment of the present invention) are formed so that areas exposed therethrough are provided as exposed portions54on the top surface of the diffuser plate51.

FIG. 4is a cross-sectional view along the line A-A ofFIG. 3B(i.e., a cross-sectional view of an exposed portion).

The inner frame80is preferably made of synthetic resin, and includes a mounting portion81extending vertically inFIG. 4and a facing portion (corresponding to a facing portion of a preferred embodiment of the present invention)83extending horizontally and inwardly (i.e., toward the left inFIG. 4) from the close-to-upper-end portion of the mounting portion81, so as to have a substantially L-shaped cross section. On the other hand, the raised portion72projecting upward in the figure is provided on the periphery of the base member71as described above. The height thereof is preliminarily set so that the distal end thereof properly abut on the proximal end portion87of the facing portion83of the inner frame80. Thereby, the raised portion72supports the facing portion83from below.

Along the entire circumference of the inner frame80, a holding base84opposite to the periphery of the diffuser plate51and the optical sheets55is formed on the facing portion83so as to sag downwards in the figure. The holding base84extends widthwise so as to have an area (shown as Section G inFIG. 4) overlapping with the periphery of the optical sheets55, while a holding protrusion85opposite to the exposed portion54of the diffuser plate51is provided on the right edge portion of the lower surface84A so as to project downward in the figure and abut on the exposed portion54.

The holding protrusion85is integrated with the inner frame80. The projecting length (shown as Dimension H1inFIG. 4) from the lower surface84A is set so as to be larger than the thickness (shown as Dimension H2inFIG. 4) of the three optical sheets. Thereby, a gap is kept between the optical sheets55and the holding base84, while the holding protrusion85directly holds the top surface of the diffuser plate51.

Screw through holes (not shown) are formed on the inner frame80, while the corresponding screw holes are formed on the opposing base member71. Thereby, the inner frame80can be screwed, from above in the figure, to the base member71. Thus, the diffuser plate51is immovably held between the base member71and the holding base84of the facing portion83.

The holding protrusion85is provided as described above, and thereby two-point support for the cantilevered facing portion83can be achieved. That is, the support by the raised portion72is firstly provided as described above, and the second support is provided by the holding protrusion85abutting on the exposed portion54.

Thus the two-point support for the facing portion83is provided, and thereby the following effects can be obtained. The inner frame80is made of resin as described above, and therefore has inadequate rigidity in itself. Further, there has been the problem that its component accuracy is not quite high. However, as shown inFIG. 2, the upper surface of the facing portion83is provided as a panel bearing surface83A for the liquid-crystal panel30, so as to support the periphery of the liquid-crystal panel30.

Therefore, if support for the facing portion83is inadequate, the facing portion83may lean inward under the weight of the liquid-crystal panel30. This could result in the anterior end of the holding base84applying pressure on the top surface of the optical sheets55. (Particularly, in the case that a narrower gap is originally formed due to component variations, interference may occur even due to slight leaning.) However, the two-point support for the facing portion83is provided as described above, so that sufficient supporting strength against the weight of the liquid-crystal panel30can be secured. Thereby, leaning of the facing portion83can be restricted.

According to the present preferred embodiment, the holding protrusion85directly holds the top surface of the diffuser plate51. Therefore, leaning of the diffuser plate51can be prevented, even when the display device20is used in an upright orientation, for example. Further, the two-point support for the facing portion83of the inner frame80is provided, and thereby leaning of the facing portion83can be effectively restricted.

In this way, the optical sheets55can be prevented from interfering with neighboring components such as the facing portion83, and thereby prevented from being subjected to pressure. Therefore, the optical sheets55can be prevented from vaulting, even when the optical sheets55expand or contract due to change of ambient temperature or the like. Thereby, light from the light source can be uniformly radiated to the liquid-crystal panel.

Second Preferred Embodiment

Next, a second preferred embodiment of the present invention will be explained with reference toFIG. 5.

In the first preferred embodiment, the holding protrusion85is provided on the lower surface of the holding base84so that its end surface abuts on the exposed portion54of the diffuser plate51. Conversely, in the second preferred embodiment, a holding protrusion95is arranged on a diffuser plate90so that its end surface abuts on the lower surface84A of a holding base84. According to this construction, operation and effects similar to those of the first preferred embodiment can be achieved. InFIG. 5, the same components as the first preferred embodiment are designated by the same symbols, and redundant explanation is omitted.

Third Preferred Embodiment

Next, a third preferred embodiment of the present invention will be explained with reference toFIG. 6.

In the first preferred embodiment, two-point support for the facing portion83is provided by the raised portion72and the holding protrusion85. In the third preferred embodiment, instead of the holding protrusion85, a posture retaining protrusion (corresponding to a posture retaining portion of the present invention)100is additionally provided on the base member71, so that two-point support for the facing portion83is provided by the posture retaining protrusion100and the raised portion72both abutting on the lower surface of the facing portion83. The other constructions are similar to the first preferred embodiment.

Other Preferred Embodiments

The present invention is not limited to the preferred embodiments described above with reference to the drawings. The following preferred embodiments are included in the technical scope of the present invention, for example.

(1) In the first to third preferred embodiments, a direct-light-type backlight device, in which cold-cathode tubes65as a light source are arranged beneath the liquid-crystal panel30, is shown as an illustrative example. However, a backlight device of another type, in which a light source is arranged on the lateral sides, can be used.

(2) In the first and second preferred embodiments, the holding protrusion85or95is provided on one side. That is, the holding protrusion85preferably is provided on the holding base84in the first preferred embodiment, while the holding protrusion95is provided on the diffuser plate90in the second preferred embodiment. However, the holding protrusion85or95is not limited to these constructions. For example, that may be provided on each of the holding base84and the diffuser plate90so as to abut on each other. Further, in the first and second preferred embodiments, the holding protrusion85or95is integrated with the inner frame80or the diffuser plate90. However, that may be provided as a separate component.

(3) In the first to third preferred embodiments, two-point support for the facing portion83of the inner frame80is provided. However, in the case that two-point support is not required for securing the sufficient supporting strength (e.g., in the case that the inner frame80is made of metal), one-point support can be used (i.e., support by the raised portion72may be eliminated).

(4) In the first and second preferred embodiments, the height of the holding protrusion85or95is purposely set to be larger than the thickness of the optical sheets55, so that the gap is formed between the holding base84and the optical sheets55. However, preferably, the gap is set to be as narrow as possible. Therefore, contact therebetween may be formed so that pressure is not applied on the optical sheets55.