Patent Application
20090051846
This application claims priority under 35 U.S.C. §119 to Japanese Patent application No. JP2007-217676 filed on Aug. 23, 2007 and Japanese Patent application No. JP2008-151708 filed on Jun. 10, 2008, the entire contents of which are hereby incorporated by references.
The present invention relates to a planar light unit that illuminates a liquid crystal display panel or the like, and also relates to a display apparatus having the planar light unit.
Liquid crystal display apparatus for image display are widely used in displays of mobile phones, personal digital assistants (PDAs), mobile personal computers (PCs), automatic teller machines (ATMs), etc. These liquid crystal display apparatus employ a backlight unit that applies illuminating light to a light-transmitting liquid crystal display panel from the back thereof to enhance the luminance of the display screen on the front of the display panel.
The backlight unit uses a lightguide plate that guides light from a light source, e.g. a fluorescent lamp or light-emitting diode (LED) light source, and that emits the light toward a liquid crystal display panel from the entire area of a light exiting surface thereof. Japanese Patent Application Publication No. 2006-318830, for example, discloses a backlight unit having a plurality of LEDs opposed close to a side edge surface of a lightguide plate.
In the above-described backlight unit, the LEDs need to be positioned with a high accuracy with respect to the lightguide plate. However, a misalignment between the LEDs and the lightguide plate is likely to occur. If an error occurs in the positioning of the LEDs, the efficiency of light entering the lightguide plate degrades, resulting in a reduction in the luminance at the light exiting surface of the lightguide plate and a degradation of the luminance uniformity.
It has recently been demanded that backlight units should be thinner in order to reduce weight and thickness of end products using them. Under these circumstances, lightguide plates have also been reduced in thickness into a film-like thin structure. A backlight unit employing such a film-shaped lightguide plate also involves the above-described problem of the degradation of light entering efficiency caused by a misalignment between LEDs and the lightguide plate.
The present invention has been made in view of the above-described problems with the conventional art. Accordingly, an object of the present invention is to provide a planar light unit capable of preventing a misalignment between an LED light source and a film-shaped lightguide plate. Another object of the present invention is to provide a display apparatus having the planar light unit of the present invention.
The present invention provides a planar light unit including a film-shaped lightguide plate having at least one light source accommodating hole, and the at least one light source having at least one light-emitting diode element and disposed in the light source accommodating hole. The at least one light source accommodating hole has a peripheral wall surface configured to pressingly engages the peripheral wall surface of the at least one light source to support the light source.
In this planar light unit, the light source is disposed in the light source accommodating hole and supported by the peripheral wall surface of the hole that pressingly engages the peripheral wall surface of the light source. Consequently, the light source is accurately retained in position on the lightguide plate. Thus, it is possible to maintain the efficiency of light entering the lightguide plate satisfactorily and to prevent a reduction in luminance at the light exiting surface of the lightguide plate and degradations in directivity and luminance uniformity.
Specifically, the peripheral wall surface of the at least one light source accommodating hole may be configured to pressingly engage the peripheral wall surface of the light source at a plurality of circumferentially spaced positions of the peripheral wall surface to support the light source. If the peripheral wall surface of the light source accommodating hole is designed to support the light source at a plurality of predetermined positions, it becomes easy to form the profile of the light source accommodating hole for positioning the light source. Hence, it also becomes easy to position the light source accurately.
More specifically, the peripheral wall surface of the at least one light source accommodating hole may have at least one elastic retaining portion extending inward of the hole. The retaining portion pressingly engages the peripheral wall surface of the light source to support the light source. The desired positioning of the light source can be effected, provided that the retaining portion is accurately formed at the predetermined position. Therefore, accurate positioning of the light source is facilitated.
As another specific example, at least one light source accommodating hole may comprise an elongated hole that accommodates and supports a plurality of light sources spaced from each other in a lengthwise direction of the elongated hole. If the light source accommodating hole has a size for accommodating only one light source, the peripheral wall of the hole may not be readily deformed sufficiently to insert and set the light source in the hole. However, such a problem can be solved by forming the light source accommodating hole into an elongated hole that can accommodate a plurality of light sources.
As a more specific example, the at least one light source include a peripheral wall surface which may have a front surface serving as a light exiting surface and a rear surface. The peripheral wall surface of the at least one light source accommodating hole may have a front portion that engages the front surface of the light source, a rear portion that faces the rear surface of the light source and has a retaining portion extending forward therefrom to engage the rear surface of the light source to press the light source toward the front portion.
In this case, the planar light unit may be arranged as follows. The at least one light source may include a single light source and the single light source includes a peripheral wall surface which may have left and right side surfaces extending between the front surface and the rear surface. The peripheral wall surface of the at least one light source accommodating hole has side portions extending rearward from the front portion. The side portions have respective retaining portions extending therefrom toward the light source to pressingly engage the left and right side surfaces of the single light source.
Unlike the above-described arrangement, the planar light unit may be arranged as follows. The at least one light source may include a single light source in the shape of a rectangular parallelepiped and the single light source includes a peripheral wall surface which may have a front surface serving as a light exiting surface, a rear surface and left and right side surfaces extending between the front surface and the rear surface. The peripheral wall surface of the light source accommodating hole has portions that engage corners between the rear surface and at least either one of the left and right side surfaces to press the light source forward.
As still another specific example, the at least one light source may include a single light source and the single light source includes a peripheral wall surface which may have a front surface serving as a light exiting surface and left and right side surfaces extending the front surface. The peripheral wall surface of the at least one light source accommodating hole may have a front portion that engages the front surface of the light source, and left and right side portions extending rearward from the front portion. The side portions have respective retaining portions extending therefrom toward the light source to pressingly engage left and right side surfaces of the single light source.
As a specific example different from the above, the at least one light source may include a single light source and the single light source includes a peripheral wall surface which may have a front surface serving as a light exiting surface, a rear surface and left and right side surfaces extending between the front and rear surfaces. The peripheral wall surface of the at least one light source accommodating hole may have a rear portion that engages the rear surface of the single light source, and side portions extending forward from the rear portion. The side portions have respective retaining portions extending therefrom toward the light source to pressingly engage left and right side surfaces of the single light source.
As still another specific example, the planar light unit may be arranged as follows. The at least one light source may include a single light source in the shape of a rectangular parallelepiped and the single light source includes a peripheral wall surface which may have a front surface serving as a light exiting surface, a rear surface and left and right side surfaces extending between the front surface and the rear surface. The peripheral wall surface of the at least one light source accommodating hole has a rear portion that engages the rear surface of the single light source, and portions that engage corners between the front surface and at least either one of the left and right side surfaces of the single light source to press the light source rearward.
As still another specific example, the planar light unit may be arranged as follows. The at least one light source may include a single light source in the shape of a rectangular parallelepiped and the single light source includes a peripheral wall surface which may have a front surface serving as a light exiting surface, a rear surface and left and right side surfaces extending between the front surface and the rear surface. The peripheral wall surface of the at least one light source accommodating hole is configured to pressingly engage corners of the single light source between the front surface and the side surfaces and corners of the same between the rear surface and at least either one of the side surfaces to support the light source.
In addition, the present invention provides a display apparatus including an image display panel and the above-described planar light unit that is disposed at the front or back of the image display panel. The planar light unit used in the display apparatus is capable of satisfactorily maintaining the efficiency of light entering the lightguide plate and hence capable of preventing a reduction in luminance at the light exiting surface of the lightguide plate and degradations in directivity and luminance uniformity. Accordingly, the display apparatus can realize favorable luminance characteristics with a thin structure.
In the display apparatus, the image display panel may be a liquid crystal display panel.
Embodiments of the present invention will be explained below with reference to the accompanying drawings. It should be noted that the scale of the figures used in the following explanation is properly changed to show each member in a recognizable size.
As shown in
The backlight unit 1 includes LED light sources L having light-emitting diode elements (not shown) and a film-shaped lightguide plate unit 7 having a film-shaped lightguide plate 6 that guides light from the light sources L and that emits the light toward the liquid crystal display panel 2. As shown in
The two strips of double-sided adhesive tape 12 are bonded to the respective lower sides of two longitudinally extending side portions of the support frame 8 and having portions exposed inside the support frame 8. The reflecting sheet 13 is bonded to the lower sides of the two strips of double-sided adhesive tape 12, and the longitudinally extending side edge portions of the lower side of the film-shaped lightguide plate 6 are bonded to the exposed portions at the upper sides of the two strips of double-sided adhesive tape 12. The support frame 8 has other two strips of double-sided adhesive tape 17 bonded to the lower side thereof. The two strips of double-sided adhesive tape 17 also have portions exposed inside the support frame 8. The longitudinally extending side edge portions of the lower side of the film-shaped lightguide plate 6 are bonded to the exposed portions at the upper sides of the two strips of double-sided adhesive tape 17. Each strip of double-sided adhesive tape 17 has a release sheet (not shown) applied to the lower side thereof. When the film-shaped lightguide plate unit 7 is to be mounted in an electronic device such as a mobile phone, the release sheet is removed, and each strip of double-sided adhesive tape 17 is bonded, for example, to the inner surface of the casing of the electronic device.
The diffusing sheet 9 and the first and second prism sheets 10A and 10B each have projections 14 formed on the longitudinally extending side edges thereof. The projections 14 are fitted into recesses 8a formed on the support frame 8. The stack of diffusing sheet 9 and first and second prism sheets 10A and 10B is fitted in the support frame 8 to dispose the projections 14 into the recesses 8a and bonded at the peripheral edge portions thereof with strips of double-sided adhesive tape (12 and 11) bonded to a lower side of the support frame 8.
The support frame 8 is pliable and punched with a press from a large-sized polyethylene terephthalate (PET) or stainless steel (SUS) film, for example. The thickness of the support frame 8 is set substantially equal to a total thickness of the film-shaped lightguide plate 6, the diffusing sheet 9 and the first and second prism sheets 10A and 10B, which are fitted in the support frame 8.
The film-shaped lightguide plate 6 is made of a pliable light-transmitting material. The film-shaped lightguide plate 6 guides light from the LED light sources L throughout it and emits the light from a light exiting surface (upper surface in the figures) thereof. The thickness of the film-shaped lightguide plate 6 is, for example, about 125 μm. In the illustrated film-shaped lightguide plate unit 7, the film-shaped lightguide plate 6 supported by the support frame 8 extends as far as underneath the operation keys 4 to illuminate not only the liquid crystal display panel 2 but also the operation keys 4.
The film-shaped lightguide plate 6 comprises, for example, a substrate layer (not shown) and resin layers (not shown) formed on the upper and lower sides of the substrate layer. Each resin layer has a plurality of microscopic optical configurations (e.g. convex dots) formed on a surface thereof to perform optical path conversion.
The substrate layer and the resin layers are formed by a transparent polycarbonate or acrylic resin, for example. The substrate layer is sheet-formed into a flat sheet shape by using roll forming process, for example. The resin layers are formed as follows. A coating of photo-setting organic resin that sets upon irradiation with ultraviolet (UV) radiation, e.g. one selected from among acrylic, urethane, urethane acrylate and epoxy acrylate resins, is applied to the upper and lower sides of the substrate layer, and microscopic optical configurations are formed on the surface of the resin coating by using a die. Thereafter, the resin coating is set by irradiation with ultraviolet radiation.
In the actual practice, a large-sized sheet formed as stated above is cut with a press or a cutter to obtain a film-shaped lightguide plate 6 of a predetermined shape and size.
The film-shaped lightguide plate 6 has a plurality of light source accommodating holes 6a for accommodating the LED light sources L, which are formed along one end edge (left end edge as seen in
The film-shaped lightguide plate 6 has positioning holes 6c formed at predetermined positions near the light source accommodating holes 6a. The positioning holes 6c are used when each sheet is successively stacked during assembling. It should be noted that the location where the LED light sources L are disposed in the film-shaped lightguide plate 6 is not necessarily limited to the above-described end portion. For example, the LED light sources L may be disposed in the center of the film-shaped lightguide plate 6. It is also possible to dispose LED light sources L in the operation key-side end portion of the film-shaped lightguide plate 6 in addition to the above-described end portion thereof.
The diffusing sheet 9 is formed by dispersing silica particles or the like into a transparent resin, e.g. an acrylic resin, or a polycarbonate resin.
The first prism sheet 10A and the second prism sheet 10B are transparent sheet-shaped members that collect light from the diffusing sheet 9 and direct it upward. The first and second prism sheets 10A and 10B have on their upper sides a plurality of mutually parallel elongated prisms. The respective prisms of the first and second prism sheets 10A and 10B are disposed to intersect each other as viewed from above the prism sheets 10A and 10B, i.e. in plan view. To increase the upward directivity of light transmitted through the first and second prism sheets 10A and 10B, the prisms of the first prism sheet 10A are set in a direction perpendicular to the optical axis of light emitted from the LED light sources L and traveling through the film-shaped lightguide plate 6 from one end toward the other end thereof, and the prisms of the second prism sheet 10B are set parallel to the optical axis of light from the LED light sources L.
The reflecting sheet 13 is a metal sheet, film or foil having a light-reflecting function. In this embodiment, a film provided with an evaporated silver layer is employed as the reflecting sheet 13. It should be noted that an evaporated aluminum layer or the like may be used in place of the evaporated silver layer.
The LED light sources L are white LEDs mounted on a substrate (not shown) for light source. Each white LED is, for example, a semiconductor light-emitting diode element mounted on a substrate and sealed with a resin material. The semiconductor light-emitting element is, for example, a blue (wavelength λ: 470 to 490 nm) LED element or an ultraviolet (wavelength λ: less than 470 nm) LED element, which is formed by stacking a plurality of semiconductor layers of a gallium nitride compound semiconductor (e.g. InGaN compound semiconductor) on an insulating substrate, e.g. a sapphire substrate.
The resin material used to seal the semiconductor light-emitting element is formed by adding, for example, a YAG fluorescent substance into a silicone resin as a main component. The YAG fluorescent substance converts blue or ultraviolet light from the semiconductor light-emitting element into yellow light, and white light is produced by color mixing effect. It should be noted that various LED elements in addition to those described above can be used as the white LEDs. Places where the LED light sources L are mounted are not necessarily limited to the spaces in the light source accommodating holes 6a. The LED light sources L may be mounted at respective positions near an end surface of the film-shaped lightguide plate 6.
The backlight unit 1 is assembled as follows. First, the support frame 8 is fixed on a jig (not shown) serving as a base, and strips of double-sided adhesive tape 12 and 17 are stuck to the upper side of the support frame 8. The release sheets applied to the exposed sides of the strips of double-sided adhesive tape 12 are removed, and the reflecting sheet 13 is stuck to the exposed strips of double-sided adhesive tape 12. It should be noted that the release sheets applied to the strips of double-sided adhesive tape 17 are not removed. Thereafter, the support frame 8 is removed from the jig and turned upside down. The film-shaped lightguide plate 6 is placed on the reflecting sheet 13, and the longitudinally extending side edges of the film-shaped lightguide plate 6 are bonded to the portions of the strips of double-sided adhesive tape 12 that are exposed inside of the support frame 8. Next, a flexible printed substrate (not shown) having the LED light sources L which are mounted thereon is disposed to locate each LED light source L in the corresponding light source accommodating hole 6a of the film-shaped lightguide plate 6.
A sheet unit is assembled in advance which has the second prism sheet 10B, the first prism sheet 10A and the diffusing sheet 9 stuck to the lower side of the rim sheet 11 in the order mentioned. Specifically, after the second prism sheet 10B has been bonded at both longitudinal ends thereof to the rim sheet 11, the first prism sheet 10A and the diffusing sheet 9 are successively laid under the second prism sheet 10B and bonded together by using pieces of double-sided adhesive tape exposed between the projections 14 of these sheets. The sheet unit thus prepared is fitted into the support frame 8 from above, and thus the second prism sheet 10B, the first prism sheet 10A and the diffusing sheet 9 are mounted in the support frame 8. In addition, the rim sheet 11 is stuck to the upper side of the support frame 8. During this assembling process, the projections 14 of each sheet are fitted into the corresponding recesses 8a of the support frame 8. In this way, the backlight unit 1 is produced in which the reflecting sheet 13 and the rim sheet 11 are stuck to the lower and upper sides, respectively, of the support frame 8, and in which the film-shaped lightguide plate 6, the diffusing sheet 9 and the first and second prism sheets 10A and 10B are stacked between the reflecting sheet 13 and the rim sheet 11 inside the support frame 8.
The liquid crystal display panel 2 is a transmissive or semitransmissive liquid crystal display panel. In the case of a semitransmissive liquid crystal display panel 2, for example, it has a panel body having a liquid crystal material, e.g. TN liquid crystal or STN liquid crystal, sealed with a sealant in a gap between an upper substrate and a lower substrate, each having a transparent electrode layer, an alignment film and a polarizer. The semitransmissive liquid crystal display panel 2 further has a semitransmitting-reflecting sheet having both light-transmitting and -reflecting functions, and the semitransmitting-reflecting sheet is provided underneath the panel body.
The mobile phone 5 further includes a sheet-shaped key operation unit 16 having a keypad 18 and a switching mechanism 15 disposed underneath the keypad 18.
The operation keys 4 of the keypad 18 are made of a light-transmitting and pliable resin and have numerals or letters displayed thereon to enter a phone number, etc.
The switching mechanism 15 comprises, for example, a switch substrate 19 and tact switches 20 mounted thereon. When one operation key 4 is depressed, the corresponding tact switch 20 is pressed through the film-shaped lightguide plate 6 to perform an ON/OFF operation.
It should be noted that the keypad 18 is stuck to the upper side of the support frame 8 with double-sided adhesive tape or the like (not shown).
Thus, in the backlight unit 1 of this embodiment, each light source accommodating hole 6a engages the front and rear surfaces of the associated LED light source L at the inner surface of the light source accommodating hole 6a to support the LED light source L. Particularly, the retaining portion 6b of the light source accommodating hole 6a pressingly engages the rear surface of the LED light source L. Therefore, the LED light source L can be positioned with a high accuracy in the direction of the optical axis of light emitted from the LED light source L. In addition, the front surface F of the LED light source L, which is a light exiting surface thereof, is placed in close contact with the inner wall surface of the light source accommodating hole 6a. Therefore, satisfactory light entering efficiency can be obtained.
Accordingly, the display apparatus 3 and the mobile phone 5, which have the backlight unit 1, can be reduced in thickness. In addition, the LED light sources L can be positioned with a high accuracy with respect to the film-shaped lightguide plate 6. Therefore, the light entering efficiency can be maintained satisfactorily, and it is possible to prevent a reduction in luminance and degradations in directivity and luminance uniformity.
Second to sixth embodiments of the lightguide plate according to the present invention will be explained below with reference to parts (a) to (e) of
In the second embodiment shown in part (a) of
In the third embodiment shown in part (b) of
In the fourth embodiment shown in part (c) of
In the fifth embodiment shown in part (d) of
In the sixth embodiment shown in part (e) of
Seventh to ninth embodiments of the lightguide plate according to the present invention will be explained below with reference to
In the seventh embodiment shown in
In a case where one LED light source L is disposed in one light source accommodating hole 6a as in the first embodiment, the retaining portion 6b may not be sufficiently elastic. In such a case, it may be difficult to fit the LED light source L into the light source accommodating hole 6a. In the seventh embodiment, each light source accommodating hole 76a is in the shape of an elongated hole to dispose two LED light sources L therein. Consequently, the peripheral wall of the light source accommodating hole 76a is readily deflectable, as shown in part (a) of
In the eighth embodiment shown in part (a) of
Part (b) of
In the ninth embodiment shown in part (a) of
It should be noted that the present invention is not necessarily limited to the foregoing embodiments but can be modified in a variety of ways without departing from the scope of the present invention.
For example, although it is preferable to provide a retaining portion in a light source accommodating hole, as stated above, a projecting retaining portion need not necessarily be provided. That is, the light source accommodating hole may be configured in accordance with the size of an LED light source to be fitted therein so that flat inner surfaces of the hole engage the front and back surfaces of the LED light source when fitted in the hole. By so doing, the LED light source can be retained by the elasticity of the peripheral wall of the light source accommodating hole and thus can be positioned with a high accuracy.
The diffusing sheet 9 used in the above-described backlight unit 1 may be omitted. Although two prism sheets are used in the foregoing embodiments, the backlight unit 1 may have only one prism sheet.
Although the above-described display apparatus employs the liquid crystal display panel 2 as an image display panel, other types of image display panels may be used, for example, an electronic paper. In this case, the planar light unit according to the present invention is disposed as a front light unit at the front side of the electronic paper body.
| Number | Date | Country | Kind |
|---|---|---|---|
| JP2007-217676 | Aug 2007 | JP | national |
| JP2008-151708 | Jun 2008 | JP | national |
