Planar illumination device

A planar illumination device according to an embodiment, including: a light guiding plate having one of a pair of opposite principal surfaces serving as a light emission surface; a light source arranged at a side surface connecting end edges of the pair of principal surfaces of the light guiding plate; and a frame, in which the light guiding plate is arranged. The frame is formed of plural frame members arranged along side surfaces of the light guiding plate. The plural frame members are configured to include a resin frame member and a metal frame member, and to have a joint portion between the resin frame member and the metal frame member, the joint portion arranged at end portions of the resin frame member and the metal frame member.

CROSS-REFERENCE TO RELATED APPLICATION(S)

The present application claims priority to and incorporates by reference the entire contents of Japanese Patent Application No. 2015-104718 filed in Japan on May 22, 2015.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a planar illumination device including: a light guiding plate; a light source arranged at a side surface of the light guiding plate; and a frame for accommodating therein these components.

2. Description of the Related at

At present, liquid crystal display devices (LCDs) are used as display devices of electronic devices, such as personal computers and mobile phones, and since liquid crystal is not a light emitting type display element, planar illumination devices are widely used as illuminating means used in combination with liquid crystal display devices.

A schematic configuration of a planar illumination device100includes, as illustrated inFIGS. 6A-6C, components, which are: a light guiding plate12, which is formed of a synthetic resin material, has one (surface) of a pair of opposite principal surfaces serving as a light emission surface, and is rectangular in a plan view thereof; a reflecting sheet118arranged on a reverse surface side of the light guiding plate12; and plural plate shaped (or sheet shaped) members, such as an optical sheet18of plural layers (three layers in the example inFIGS. 6A-6C) arranged on a surface side of the light guiding plate12. Inside a frame116, which, in the example ofFIGS. 6A-6C, has a bottomed box shape and is made of sheet metal, these components are stored, together with a light source14, such as a white LED, which is arranged opposite to a side surface (a light incident surface) of the light guiding plate12, the side surface connecting end edges of the pair of principal surfaces.

The frame116made of sheet metal includes a bottom portion116Ma, a first side wall116Mb, and a second side wall116Mc. The first side wall116Mb is arranged along each of a pair of side surfaces12fconnecting end edges of a side surface of the light guiding plate12at a light incident surface12dside with end edges of a side surface12eopposite to the light incident surface12c. The second side wall116Mc is arranged along each of the light incident surface12cof the light guiding plate12and the side surface12eopposite to the light incident surface12c. The bottom portion116Ma is arranged to block a region surrounded by the first side wall116Mb and the second side wall116Mc. Both the first side wall116Mb and the second side wall116Mc are configured to stand up integrally with and from the bottom portion116Ma.

Furthermore, in the frame116made of sheet metal, a pair of resin portions116Ra and116Rb are arranged, which are respectively opposite to the light incident surface12cof the light guiding plate12and the side surface12eopposite to the light incident surface12c. The resin portions116Ra and116Rb are, for example, bar shaped members, having rectangular cross sections. In the example ofFIGS. 6A-6C, the resin portions116Ra and116Rb are integrated with the frame116made of sheet metal, through insert molding (for example, see Japanese Patent Application Laid-open No 2004-240239).

Moreover, a light shielding sheet20prescribing an effective area of the emission surface is used as a means to fix the optical sheet18to the frame116and the planar illumination device100to an LCD (illustration thereof omitted). In the example ofFIGS. 6A-6C, the light shielding sheet20is a double sided adhesive sheet, and one of surfaces thereof (lower surface) is stuck over an upper surface of the optical sheet18and an upper surface of the frame116. The other one of the surfaces (upper surface) is stuck to the LCD (see the specification of Japanese Patent Applioation No. 2014-216444).

One of reasons for using the frame116made of sheet metal like in the example ofFIGS. 6-6Cis to meet a demand for frame narrowing of the display device and the planar illumination device, which is the illuminating means of the display device, in order to downsize the liquid crystal display device and to improve the design. In order to deal with reduction in adhesive area of the light shielding sheet20with respect to the upper surface of the frame116made of metal, the reduction in adhesive area caused by the frame thickness reduction, the pair of resin portions116Ra and116Rb, which are arranged at positions respectively opposite to the light incident surface12cand the side surface12eopposite to the light incident surface12c, are also used as a means to secure the adhesive area of the light shielding sheet20.

However, for the planar illumination device, in addition to the reduction in thickness and securing the necessary rigidity, further frame narrowing is demanded.

The present invention has been made in view of the above described problems, and an object thereof is to balance characteristics with one another even more highly, the characteristics such as frame narrowing, reduction in thickness, and securing necessary rigidity, which are demanded for a planar illumination device.

SUMMARY OF THE INVENTION

A planar illumination device according to an embodiment, including: a light guiding plate having one of a pair of opposite principal surfaces serving as a light emission surface; a light source arranged at a side surface connecting end edges of the pair of principal surfaces of the light guiding plate; and a frame, in which the light guiding plate is arranged.

The frame is formed of plural frame members arranged along side surfaces of the light guiding plate.

The plural frame members are configured to include a resin frame member and a metal frame member, and to have a joint portion between the resin frame member and the metal frame member, the joint portion arranged at end portions of the resin frame member and the metal frame member.

DETAILED DESCRIPTION OP THE PREFERRED EMBODIMENTS

Hereinafter, an embodiment of the present invention will be described, based on the drawings. To portions that are the same as, or to portions corresponding to, those of the conventional technique, the same reference signs will be appended and detailed description thereof will be omitted, as appropriate. Further, “upper” and “lower” directions in the following description mean upper and lower directions in a state where a planar illumination device and a liquid crystal display device in the description have been placed flatly. Furthermore, “front” direction is a direction from a light incident surface12cof a light guiding plate towards a side surface12eopposite to the light incident surface12cin the state where the planar illumination device and the liquid crystal display device in the description have been placed flatly, and “back” direction means a direction reverse to the “front” direction. Hereinafter the light incident surface12cis also referred to as a side surface12c. “Left” and “right” directions mean directions orthogonal to a front-back direction in the state where the planar illumination device and the liquid crystal display device in the description have been placed flatly. Moreover, “inner” at each portion means a central portion side of the devices in the state where the planar illumination device and the liquid crystal display device in the description have been placed flatly, and “outer” means a side opposite to the central portion side of the devices.

InFIGS. 1A-1Cillustrate a planar illumination device10according to an embodiment of the present invention. This planar illumination device10follows the overall configuration of the conventional technique, and thus, description thereof will be made below while referring also to the planar illumination device100according to the conventional technique illustrated inFIGS. 6A-C. This planar illumination device10includes, a light guiding plate12, a light source14, and, in the illustrated example, a frame16for positioning these components. The frame16is formed in a rectangular frame shape in a plan view thereof, and is formed of plural frame members arranged along side surfaces of the light guiding plate12. These plural frame members include resin frame members16Ra and16Rb, and a pair of metal frame members16M, and have, at end portions of the resin frame members16Ra and16Rb and the metal frame members16M, joint portions16J arranged therein, which are for joining the resin frame members16Ra and16Rb and the metal frame members16M together.

The resin frame member16Ra is, similarly to the example inFIGS. 6A-6C, arranged at a position along the light incident surface12cof the light guiding plate12, and the resin frame member16Rb is, similarly to the example inFIGS. 6A-6C, arranged at a position along the side surface12eopposite to the light incident surface120. A front-back direction dimension (width dimension) of the resin frame member16Ra is formed more largely than that of the resin frame member16Rb. By being formed of, preferably, white resin, these resin frame members16Ra and16Rb reflect, towards the light guiding plate12, light leaking from the side surfaces12cand12eof the light guiding plate12opposite to the resin frame members16Ra and16Rb efficiently, and contribute to increase in light emission efficiency from a principal surface12aof the light guiding plate12. Hereinafter the principal surface12ais also referred to as an emission surface12a.

On the contrary, the metal frame members16M are formed by sheet metal forming of a sheet material made of metal, such as aluminum alloy or stainless steel, and are arranged respectively along a pair of side surfaces of the side surfaces of the light guiding plate12, the pair of side surfaces connecting and edges of the light incident surface12cwhere the light source14is arranged with end edges of the side surface12eopposite to the light incident surface12c. The metal frame member16M on the left and the metal frame member16M on the right illustrated inFIG. 1Aare symmetrically formed. Thickness of the metal frame members16M is, for example, 0.1 mm to 0.2 mm. Thickness of the resin frame members16Ra and16Rb is set to an appropriate value equal to or greater than the thickness of the metal frame members16M.

Further, in order to increase the light emission efficiency from the principal surface12aof the light guiding plate12, white ink, silver, or the like may be coated on inner surfaces (surfaces facing the light guiding plate12) of the metal frame members16M.

The joint portions16J between the metal frame members16M and the resin frame members16Ra and16Rb are arranged at all of four corners of the frame16having the rectangular frame shape. Further, at the joint portions16J, the resin frame members16Ra and16Rb and the metal frame members16M have complementary concave and convex shapes. Specifically, they are configured such that a part of the resin frame members16Ra and16Rb is extended so as to go around to the metal frame members16M, and the resin frame members16Ra and16Rb and the metal frame members16M overlap (at least partially) each other in an up-down direction. Or, they are configured such that a part of the metal frame members16M is extended so as to go around to the resin frame members16Ra and16Rb, and the resin frame members16Ra and16Rb and the metal frame members16M overlap (at least partially) each other in the up-down direction. At the joint portions16J, the resin frame members16Ra and16Rb and the metal frame members16M are formed integrally with each other, by insert molding or the like.

The joint portions16J are not necessarily provided at corner portions of the frame16, and as appropriate, may be provided at positions offset from the corner portions in a left-right direction or the front-back direction. Furthermore, as necessary, the resin frame members16Ra and16Rb and the metal frame members16M may be configured to not overlap each other in the up-down direction. Moreover, a concave portion for absorbing thickness of a later described wiring board132(seeFIGS. 5A-5C) of the light source14or thickness of a double sided tape130(see FIGS.5A-5C) or the like used in fixing the wiring board132, may be provided on a lower end surface or an upper end surface of the resin frame member16Ra.

In the example ofFIGS. 1A-1C, both the resin frame members16Ra and16Rb and the metal frame members16M are exposed to form an outer surface of the frame16, at the joint portions16J. On the contrary, in the example ofFIG. 2A, at the joint portions16J between the resin frame members16Ra and16Rb and the metal frame members16M, an end portion of the metal frame member16M is configured to partially cut into the resin frame member16Ra without being exposed to the outer surface of the frame16.

Further, in the example ofFIG. 23, a part of the resin frame member16Ra is extended so as to go around to the metal frame member16M, and furthermore, by formation of a projecting portion16Rap projecting downwards (in a left direction inFIG. 2B) in the resin frame member16Ra and formation of a notched portion16Mr corresponding to the projecting portion16Rap in the metal frame member16M, complementary shapes that are more complicated than those of the example inFIGS. 1A-1Care formed.

In the example ofFIGS. 1A-1C, at a portion along the side surface12eopposite to the light incident surface12c, of the side surfaces of the light guiding plate12, the resin frame member16Rb is arranged, but a metal frame member may be arranged at this portion as illustrated inFIG. 3. In the example ofFIG. 3, the metal frame member16M arranged at a portion along the side surface12eopposite to the light incident surface12c, of the side surfaces of the light guiding plate12, is integrated with the metal frame members16M respectively arranged along the pair of side surfaces connecting the end edges of the light incident surface12cwith the end edges of the side surface12eopposite to the light incident surface12c. The joint portions16J between the resin frame member16Ra and the metal frame members16M are arranged only at two corners of the four corners of the rectangular frame shape, the two corners at a light incident surface12cside of the light guiding plate12.

Further, the planar illumination device10according to the embodiment of the present invention includes optical sheets18and118arranged by being layered over the principal surfaces of the light guiding plate; and the light guiding plate12, together with the optical sheets18and118, is fixed to the metal frame member16M of the frame16via the light shielding sheet20. For the light shielding sheet20, a light shielding property is not necessarily demanded depending on required specifications, and if prevention of light leakage is not demanded, an adhesive sheet (adhesive tape) having a sticking function but not having a light shielding function may be used instead of the light shielding sheet20(and thus, in this description, those including a light shielding sheet, an adhesive sheet (adhesive tape), and the like will also be referred to as “adhesive sheets”).

More specifically, as illustrated inFIG. 4A, of a pair of the principal surface12aand a principal surface12bof the light guiding plate12, the optical sheet18is arranged by being layered on the emission surface12aside, and a reflecting sheet118is arranged by being layered on the other principal surface12bside. Hereinafter the reflecting sheet118is also referred to as an optical sheet118. As the light shielding sheet20, one like a so-called double sided tape is widely used in general, the double sided tape having adhesive layers on both a first surface201, which is an outer surface of the light shielding sheet20, and a second surface202, which is an inner surface of the light shielding sheet20, the inner surface opposite to the light guiding plate12. The second surface202of the light shielding sheet20is stuck such that the second surface202extends from a surface of the optical sheet18on the emission surface12aside to a surface of the reflecting sheet118on the other principal surface12bside so as to wrap around an outer surface16MO of the metal frame member16M of the frame16. The first surface201of the light shielding sheet20is used for fixing an LCD (illustration thereof omitted) to the planar illumination device10. In the example ofFIG. 4A, an upper end surface16MT of the metal frame member16M and a surface18T of the optical sheet18(a third sheet183in the illustrated example) are arranged on the same plane. Further, a lower end surface16MB of the metal frame member16M and a surface118B of the reflecting sheet118are arranged on the same plane.

In the example illustrated inFIG. 4B, an overlap portion OV is formed, where the optical sheet18and the metal frame member16M of the frame16overlap each other at least partially, in a plan view of the optical sheet18. In this overlap portion OV, the upper end surface16MT of the metal frame member16M is arranged below a lower surface18B of the optical sheet18(a lower surface of a first sheet181in the illustrated example, but limitation not being made thereto), and is covered by the optical sheet18at least partially.FIG. 4Billustrates that the optical sheet18has a width dimension such that an end portion of the optical sheet18is partially over the upper end surface16MT of the metal frame member15M, but the width dimension of the optical sheet18may be configured to match a width dimension W16of the metal frame member16M (seeFIG. 6C). Further, in the example ofFIG. 4B, the first sheet181, a second sheet182, and the third sheet183are configured such that their end edge portions are aligned with one another in a plan view thereof and that they have the same width dimension, but they may have width dimensions such that only the third sheet183positioned on the uppermost stage covers, or the third sheet183and second sheet182cover, at least a part of the upper end surface16MT of the metal frame member16M.

Furthermore, inFIG. 4B, the light shielding sheet20is illustrated in a mode of being bent at right angles, but the light shielding sheet20may be stuck such that the light shielding sheet20is bent from a corner portion of the upper end surface16MT of the metal frame member16M towards a corner portion of the upper surface18T of the optical sheet18, and further bent to follow the upper surface18T at the corner portion of the upper surface18T of the optical sheet18. Further, in a bent portion of the light shielding sheet20, perforations, a groove, or the like, may be provided to make the light shielding sheet20easy to be bent.

If a light shielding sheet not having an adhesive layer in a portion arranged on the outer surface16MO of the metal frame member16M and in a portion arranged on the surface of the reflecting sheet118is used the portions of the first surface201of the light shielding sheet20; decrease in handling ability due to unexpected sticking of the light shielding sheet20is able to be prevented.

Further, by use of a film (illustration thereof omitted) for covering and hiding the portion arranged on the outer surface16MO of the metal frame member16M and the portion arranged on the surface of the reflecting sheet118, necessary handling ability may be ensured.

As illustrated inFIGS. 5A-5C, the wiring board132of the light source14is fixed to a lower end surface or an upper end surface (the lower end surface in the illustrated example) of the resin frame member16Ra via the double sided tape130. As described above, since, the front-back direction dimension (width dimension) of the resin frame member16Ra is more largely formed than those of the metal frame members16M and the resin frame member16Rb, a sticking margin for the double sided tape130is sufficiently secured in the resin frame member16Ra.

In addition, since the planar illumination device10follows the overall configuration of the conventional technique, the following description will additionally be made by referring to the planar illumination device100according to the conventional technique illustrated inFIGS. 6A-6C.

In a range of a predetermined width towards a central portion from the light incident surface12c, the range over the emission surface12aof the light guiding plate12, a sloped surface12dis formed, which makes thickness between the pair of opposite principal surfaces thinner towards the central portion of the light guiding plate, and a range over the emission surface12a, the range closer to the central portion than the sloped surface12d, has a constant thickness.

“Effective area” of the emission surface12aprescribed by the light shielding sheet20is an area excluding a “non-effective area”, which is unavoidably generated near an end edge portion of the emission surface12aof the light guiding plate12, due to reduction in uniformity of emission light influenced by reflection of light at the side surface of the light guiding plate12or the like. The planar illumination device described herein maximally achieves effective utilization of the emission light from the effective area by the light shielding sheet20covering and hiding the non-effective area in a plan view of the emission surface12aof the light guiding plate12. For convenience of explanation, inFIG. 6A, illustration of the light shielding sheet20is omitted.

As illustrated inFIG. 6C, the second side wall116Mb and the pair of side surfaces12fjoining the end portions of the light incident surface12cand the end portions of the side surface12eopposite to the light incident surface12ctogether are arranged with a gap therebetween. Further, in the illustrated example, as illustrated inFIG. 6B, the side surface12eof the light guiding plate12and the resin frame member16Rb are arranged with a gap therebetween. The light incident surface12cof the light guiding plate12is adhered closely to the light source14basically, and the light source14and the resin frame member16Ra are arranged with a gap therebetween.

Further, according to this embodiment, the optical sheet18includes the first sheet181, which is the first one of layered stages as counted from the emission surface12aof the light guiding plate12, the second sheet182layered on the first sheet181, and the third sheet183layered on the second sheet182. For example, the first sheet181is a diffusion sheet, the second sheet182is a lower prism sheet, and the third sheet183is an upper prism sheet. These respective optical sheets181,182, and183are formed such that; in a state where end edge portions181b,182b, and183b(seeFIG. 6B) thereof on the side surface12eside opposite to the light incident surface12care aligned with one another in a plan view thereof, the upper the stage of the optical sheet in the layered stages as counted from the emission surface12aof the light guiding plate12is, the more separated the position of the end edge portion161a,182a, or283aon the light incident surface12cside of the light guiding plate12is from the light incident surface12oof the light guiding plate12.

By the embodiment of the present invention configured as described above, the following effects are able to be obtained.

That is, in the planar illumination device10according to the embodiment of the present invention, the frame16includes the resin frame members16Ra and16Rb and the metal frame members16M, and the frame16as a whole is frame shaped, by the respective members being joined together at the joint portions16J arranged at the end portions of the resin frame members16Ra and16Rb and metal frame members16M. Arrangement of the resin frame members16Ra and16Rb and metal frame members16M in the frame shaped frame16is determined in consideration of properties of the resin and metal. Specifically, when the metal frame members16M are formed of sheet metal, reduction in thickness is not limited in terms of formability in contrast to the resin frame members16Ra and16Rb obtained through injection molding or the like of a synthetic resin material. Thus, by arranging the metal frame members16M at a portion, for which frame narrowing is demanded in particular, the portion of the respective portions of the frame shaped frame16, the request for the frame narrowing is met. On the contrary, the resin frame members16Ra and16Rb are arranged at a portion of the frame shaped frame16, the portion where frame narrowing is not particularly demanded. Thereby, through effective utilization of the thickness of the resin frame members16Ra and16Rb, the components accommodated in the frame are able to be stably and infallibly held therein.

At the portion where the resin frame members16Ra and16Rb are arranged, occurrence of contamination is lessened, which is caused by the metal frame members16M coming into contact with the light guiding plate12and the like when a component of the planar illumination device10, such as the light guiding plate12, is assembled and positioned with respect to the frame16(supposing the case where the resin frame members16Ra and16Rb are not present). Further, the resin frame member16Ra, in particular, ensures insulation from the wiring board132of the light source14. Furthermore, when the resin frame member16Rb is arranged at the side surface12eopposite to the light incident surface12cof the light guiding plate12, by the resin frame member16Rb reflecting, towards the light guiding plate12, light leaking from this side surface12e, light emission efficiency from the principal surface12aof the light guiding plate12is increased.

Further, the frame16is formed in a rectangular frame shape in a plan view thereof, the resin frame member16Ra forming one side of the rectangular frame shape is arranged along the light incident surface12cof the light guiding plate12, and the resin frame member16Rb forming another side thereof is arranged along the side surface12eopposite to the light incident surface12cof the light guiding plate12. Furthermore, the metal frame members16M forming the remaining two sides are arranged respectively along the pair of side surfaces12fconnecting the end edges of the light incident surface12cwith the end edges of the side surface12eopposite to the light incident surface12c. Moreover, the joint portions16J are arranged, according to the shapes of the resin frame members16Ra and16Rb and metal frame members16M, at any (seeFIG. 3) or all (seeFIGS. 1A-1C) of the four corners of the rectangular frame shaped frame, and thereby, each piece forming the rectangular frame shaped frame, excluding its end portions (joint portions)16J, is formed of only one of the resin frame members16Ra and16Rb and the metal frame members16M. Therefore, of the rectangular frame shaped frame16, the side at which the metal frame member16M is arranged contributes to the request for frame narrowing, and the side at which the resin frame member16Ra or16Rb is arranged contributes to stable and infallible holding of the components accommodated in the frame.

In addition, by each of the pieces forming the rectangular frame shaped frame being formed of only one of the resin frame members16Ra and16Rb and metal frame members16M, deformation of each the pieces caused by the difference in their thermal expansion coefficients according to the materials forming them is able to be suppressed.

Further, by the complementary concave and convex shapes of the joint portions16J of the resin frame members16Ra and16Rb and the metal frame members16M adhering closely to each other, the resin frame members16Ra and16Rb and the metal frame members16M are infallibly fixed by being meshed with each ether. Furthermore, the mutual positional relation between the resin frame members16Ra and16Rb and metal frame members16M is accurately determined by the joint portions16J having the complementary concave and convex shapes joining together.

At the joint portions16J, the resin frame members16Ra and16Rb and the metal frame members16M are formed integrally with each other, by insert molding or the like, and thereby, a composite frame of metal and resin is formed in a frame shape.

Further, as illustrated inFIGS. 4A-4B, by use of the light shielding sheet20with the adhesive layer provided on the surface thereof, the light guiding plate12, together with the optical sheets18and118, is fixed to the frame16. Specifically, as illustrated inFIG. 4AandFIG. 40, if the optical sheets18and118are arranged by being layered over both of the principal surfaces12aand12bof the light guiding plate12; by sticking the light shielding sheet20such that the light shielding sheet20extends from the surface of the optical sheet on one of the principal surface sides to the surface of the optical sheet on the other principal surface side so as to wrap around the frame, the optical sheets18and118are fixed to the frame16, and the light guiding plate12sandwiched between the optical sheets18and118is also fixed to the frame16. Furthermore, although illustration thereof will be omitted, if the optical sheet is arranged by being layered over one of the principal surfaces (12aor12b) of the light guiding plate, by sticking the light shielding sheet20such that the light shielding sheet20extends from the surface of the optical sheet (18or118) on one of the principal surface sides to the surface of the other principal surface of the light guiding plate12so as to wrap around the frame; the optical sheet (18or118) and the light guiding plate12are fixed to the frame16. Therefore, while having the frame configuration of the rectangular frame shape without a bottom portion, the components, such as the optical sheets18and118and the light guiding plate12, are fixed to the frame16via the light shielding sheet20, and thickness of the planar illumination device10is reduced.

According to the example inFIG. 4B, the end surface of the optical sheet18is positioned above the upper end surface16MT of the metal frame member16M without being covered by the metal frame member16M of the frame16, and is exposed to outside of the metal frame member16M, but the exposed end surface of the optical sheet18is covered and hidden by the light shielding sheet20. Therefore, light leakage from the end surface of the optical sheet18to the outside is not caused, either.

Since the present invention is configured as described above, characteristics, such as frame narrowing, reduction in thickness, and securing necessary rigidity, which are demanded for a planar illumination device, are able to be balanced with one another even more highly.