JP2005079038A - Backlight device using light emitting diode - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a backlight device using a light emitting diode, which prevents deterioration of a light guide plate due to heat, having excellent light entering efficiency to the light guide plate, and restrains color irregularity and luminance irregularity. <P>SOLUTION: This backlight device has: the light guide plate 3 having a light emission surface 3a and a reflecting surface 3b facing to each other, and an end face 3c for connecting those surfaces to each other; an optical sheet 4 installed on the emission surface 3a and the reflecting surface 3b of the guide plate 3; a plurality of light emitting chips 7 arranged in the vicinity of the end face 3c of the guide plate 3; a transparent resin 9 having a nearly flat light emitting surface for sealing the emitting chips 7; and a tubular part surrounding the transparent resin 9 and extended in the end face direction of the guide plate 3 from the light emitting surface of the transparent resin 9. The tubular part of the envelope contacts or adjoins the end face 3c of the guide plate 3. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a backlight device used for liquid crystal displays such as a television, a personal computer, and a car navigation system.

  In recent years, various backlight devices have been used for liquid crystal displays of televisions, personal computers, car navigation systems, and the like.

  Conventional backlight devices have been mainly backlight units using cold cathode fluorescent tubes. On the other hand, backlight units using light-emitting diodes that consume less power and have a longer life than this type of backlight unit have been developed. (For example, refer to Patent Document 1).

  A conventional backlight device will be described with reference to FIG. FIG. 6 is a partially enlarged cross-sectional view of a conventional backlight device. The backlight device includes a light guide unit 101 and a light emitting diode 102. The light guide unit 101 includes a light guide plate 103 having a light emitting surface, a reflective surface, and an end surface, and various optical sheets 104. In the light emitting diode 102, a lead frame 106 is formed on a substrate 105, and a light emitting chip 107 is provided thereon. Further, an envelope 108 is provided on the substrate 105, and a through hole 108 a for accommodating the light emitting chip 107 is formed in the envelope 108. The through hole 108a is filled with a transparent resin 109.

In such a conventional backlight device, the light emitted from the light emitting diode 102 is incident on the end face of the light guide plate 103 and the light emitting surface of the light guide unit 101 is caused to emit light.
Japanese Patent Laid-Open No. 2002-217459 (page 3-4, FIG. 1)

  In the backlight device using the light emitting diode 102, it is necessary to bring the light emitting diode 102 close to the end face of the light guide plate 103 in order to make light efficiently enter the end face of the light guide plate 103. Then, since the envelope 108 is filled with the transparent resin 109 in the conventional light emitting diode 102, the envelope 108 and the transparent resin 109 come close to the end surface of the light guide plate 103. The heat generated and transmitted to the envelope 108 and the transparent resin 109 is also transmitted to the end face of the light guide plate 103. In the case of a power LED, this heat becomes a high temperature of about 80 ° C. on the surface of the envelope 108 and the transparent resin 109. The heat is transmitted to the light guide plate 103 and the light guide plate 103 is deteriorated. Specifically, deterioration occurs particularly near the end face of the light guide plate 103 where the light of the light emitting diode 102 is incident, the transmittance is deteriorated in the vicinity thereof, the light incident efficiency to the light guide plate 103 is deteriorated, and loss occurs. Comes to occur.

  Further, when the distance between the light emitting diode 102 and the end face of the light guide plate 103 is increased, when the light emitted from the light emitting chip 107 exits the transparent resin 109, the refractive index of the transparent resin 109 is different from that of air, and the transparent resin 109 is larger. In addition, the light spreads over a wide angle. Therefore, the light incident efficiency on the end face of the light guide plate 103 is deteriorated.

  In addition, when the light emitted from the light emitting chip 107 enters the slight gap formed when the optical sheet 104 is attached to each surface of the light guide plate 103, the light emitted from the light emitting surface of the light guide plate 103 on which the light enters. There is a phenomenon in which light is emitted with a bias near the end face. In other words, luminance unevenness occurs when light from a white LED enters the gap, and luminance unevenness and color unevenness occur at the light emitting surface of the light guide plate 103 when light from a plurality of LEDs such as red, green, and blue enters. Occur.

  In addition, in the conventional light emitting diode, when a light guide plate 103 having a small thickness is used for weight reduction or cost reduction, light does not enter the light guide plate, and the amount of light leaking outside increases, resulting in very low efficiency. Become. Therefore, if a light emitting diode is used in a small size, it may be impossible to obtain a sufficient amount of light emission from the light emitting chip. Here, the light emission amount of the light emitting chip is proportional to the current applied to the light emitting diode, and the heat generation amount is also proportional to the current. Therefore, if a large amount of current is passed to obtain a sufficient light output, the heat generation amount also increases. . For this reason, the light emitting diode may be destroyed by the amount of generated heat.

  Therefore, an object of the present invention is to provide a backlight device that can solve the above-described problems.

  In order to achieve the above object, a backlight device using a light emitting diode according to the present invention has a light guide plate having opposing light emitting surfaces and reflecting surfaces, and an end surface connecting these surfaces to each other, and the light guide plate. An optical sheet disposed on the light emitting surface and the reflecting surface of the light plate, a light emitting diode chip disposed in the vicinity of the end surface of the light guide plate, and a transparent having a substantially planar light emitting surface, sealing the light emitting diode chip A resin, and an envelope having a body portion surrounding the transparent resin and a cylindrical portion extending forward from the light emitting surface, the envelope contacting the end surface of the light guide plate. Or are arranged close to each other.

  Therefore, even if the light emitting diode is brought close to the end face of the light guide plate, only the cylindrical portion of the envelope of the light emitting diode is close to the end face of the light guide plate, and the light emitting face of the transparent resin is not close. In other words, there is an air layer between the transparent resin and the end face of the light guide plate, and the presence of the air layer makes it difficult to transfer the heat generated from the light emitting chip and transmitted to the transparent resin to the end face of the light guide plate. Can do.

  In the backlight device of the present invention, the light emission width controlled by the cylindrical portion of the envelope of the light emitting diode is less than or equal to the thickness of the end face of the light guide plate, so that the emitted light of the light emitting diode is applied to the end face of the light guide plate. Since light can be prevented from leaking outside without being incident, light can be efficiently incident on the light guide plate.

  Furthermore, the backlight device of the present invention further prevents light from leaking out of the light guide plate by setting the distance between the cylindrical portion of the envelope of the light emitting diode and the end face of the light guide plate to 0 to 1 mm. be able to.

  Therefore, according to the present invention, heat conduction to the light guide plate can be suppressed, and light can be efficiently incident on the light guide plate.

(First embodiment)
In the following, a first embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a perspective view showing a part of a backlight device using a light emitting diode according to the present invention.

  The backlight device of the present invention includes a light guide unit 1 and a light emitting diode 2. The light guide unit 1 includes a light guide plate 3 made of acrylic or the like and various optical sheets 4. The shape of the light guide plate 3 is a flat rectangular shape, and the light guide plate 3 is a flat plate composed of a light emitting surface 3a and a reflecting surface 3b, which are substantially parallel planes, and an end surface 3c. The shape of the light guide plate 3 is not limited to a flat rectangular shape, and may be various, such as a wedge shape. The optical sheet 4 includes a diffusion sheet 4a, a prism sheet 4b, and a reflection sheet 4c.

  In the case of the present invention, in order to prioritize the collection of light in front of the light emitting surface, as a configuration of the optical sheet 4, a diffusion sheet 4 a that diffuses light is condensed on the light emitting surface 3 a of the light guide plate 3. The reflective sheet 4b for reflecting the incident light in the direction of the light emitting surface 3a is affixed to the reflective surface 3b. Here, when a light emitting diode is arranged only on one end face with a flat rectangular light guide plate to form a backlight device, a reflection sheet is also attached to an end face other than the end face on which the light emitting diode is arranged. In addition, there are various combinations of sheets. For example, a combination of sheets that spread light at a wide angle can be used.

  However, the incident light is totally reflected inside the light guide plate 3 by this alone, and the light cannot be efficiently extracted in front of the light emitting surface of the light guide plate 3. Therefore, although not shown in the drawing on the reflecting surface 3b of the light guide plate 3, dot printing, injection processing, or the like is performed as means for extracting incident light to the outside from the light emitting surface 3a of the light guide plate 3. When the incident light hits the portion where these are applied, the direction of the light changes as shown in the enlarged sectional view of the light emitting diode of the backlight device according to the present invention in FIG. Can be taken out.

  The light emitting diode 2 is mounted on the LED mounting substrate 5, and a part of the lead frame 6 is built in the light emitting diode 2. A lower end portion 6a of the lead frame 6 is electrically connected to the LED mounting substrate 5, and a light emitting chip 7 is formed on the lead frame portion 6b. A bonding wire 8 is attached to the light emitting chip 7, and the other end is connected to the lead frame portion 6c. The light emitting chip 7 and the bonding wire 8 are sealed with a transparent resin 9, and the light emission surface of the transparent resin 9 is formed in a substantially flat shape. In general, in the light emitting diode, the transparent resin 9 is formed in a hemispherical dome shape in order to enhance the light condensing property. However, in the present invention, a wide range of emitted light is incident on the light guide plate. However, in order to reduce unevenness on the light emitting surface of the light guide plate, the light emitting surface of the transparent resin 9 is substantially flat. The transparent resin 9 is made of an epoxy resin excellent in translucency and heat resistance. The transparent resin 9 is surrounded by an envelope 10 made of PPA (polyphthalamide) or the like having excellent insulation and heat resistance and high reflectivity. It has the cylindrical part 10a extended rather than the output surface.

  FIG. 3 is a perspective view of one light emitting diode used in the backlight device according to the present invention. Even if the envelope 10 of the light-emitting diode 2 emits light from the light-emitting chip 7 in a wide range, light is leaked outside by the cylindrical portion 10a of the envelope 10 until it enters the end surface 3c of the light guide plate 3. Can not be. However, depending on the emitted light, reflection may be repeated several times until the light enters the end surface 3c of the light guide plate 3, so that the reflection on the inner wall of the cylindrical portion 10a of the envelope 10 is suppressed in order to suppress the light amount loss due to reflection. It is desirable to attach a sheet or paint silver, aluminum, etc. to give it a specularity or high reflectivity.

  A plurality of the light emitting diodes 2 are attached on the same LED mounting substrate 5 as shown in FIG. Here, the light emitting diodes 2 may be provided with monochromatic white LEDs, or may be provided with LEDs of a plurality of colors such as red, green, and blue. Moreover, it is necessary to arrange | position so that the distance of all the light emitting diodes and the end surface 3c of the light-guide plate 3 may become the same.

  FIG. 4 is a side sectional view of a backlight device according to the present invention. A backlight device configured as shown in FIG. 1 is housed and held in a case 11 to form a backlight device. Here, as a configuration of the backlight device, a plurality of light emitting diodes are arranged on one end face, but a plurality of light emitting diodes may be arranged on a plurality of end faces.

  In the first embodiment of the present invention, the light emitting diode 2 is arranged so that the light emitting surface of the transparent resin 9 is parallel to the end surface 3c of the same light guide plate 3 as shown in FIG. A cylindrical portion 10 a is provided in the envelope 10 of the light emitting diode 2, and the cylindrical portion 10 a is in contact with or close to the end surface 3 c of the light guide plate 3. With this configuration, a distance is provided between the end surface 3c of the light guide plate 3 and the transparent resin 9, and heat generated in the light emitting chip 7 and transmitted to the transparent resin 9 can be prevented from being transmitted to the light guide plate 3. Deterioration of the optical plate 3 can be suppressed.

  At this time, the distance between the cylindrical portion 10 a of the envelope 10 and the end surface 3 c of the light guide plate 3 is 0 to 1 mm, and the light output width controlled by the cylindrical portion 10 a of the envelope 10 is the end surface 3 c of the light guide plate 3. Design smaller than the thickness of. The light emission width is determined by the shape of the opening of the cylindrical portion 10a, particularly the vertical width of the opening. Accordingly, when light emitted from the light emitting chip 7 is incident on the end surface 3 c of the light guide plate 3, the end surface 3 c of the light guide plate 3 from the gap between the cylindrical portion 10 a of the envelope 10 of the light emitting diode 2 and the light guide plate 3. It is possible to prevent light from leaking out of the light guide unit 1 without entering the light.

  In addition, the light emitted from the light emitting chip 7 enters the slight gap formed when the optical sheet 4 such as the diffusion sheet 4a, the prism sheet 4b, and the reflection sheet 4c is attached to each surface of the light guide plate 3. Can not be. When light enters the gap, brightness unevenness and color unevenness are generated in which light is biased and emitted near the end surface 3c of the light emitting surface 3a of the light guide plate 3 on which the light is incident. However, such unevenness can also be prevented. .

  In addition, even when a light guide plate 3 having a small thickness is used for weight reduction and cost reduction, a small light emitting diode with a small amount of light emission is used according to the thickness of the light guide plate as in the past. There is no need. In the case of the light emitting diode 2 of the present invention, even if the light guide plate 3 is thin, if the shape of the envelope 10 is changed corresponding to the thickness, the light leaks out of the light guide plate. Therefore, the light-emitting diode used is not limited.

  Here, the envelope 10 acts so that light does not leak until the light emitted from the light emitting diode 2 enters the end surface 3c of the light guide plate 3, and the thickness of the end surface 3c of the light guide plate 3 is If the light emission width controlled by the tubular portion 10a of the envelope 10 is always small, the planar shape of the tubular portion 10a of the envelope 10 in contact with or close to the end surface 3c of the light guide plate 3 is as shown in FIG. Not only a perfect circle but also an ellipse may be used. Further, it may be a quadrilateral or other polygonal shape, and various modifications are possible.

(Second Embodiment)
FIG. 5 is a partial sectional side view of a backlight device according to the second embodiment of the present invention. About each part of this 2nd Embodiment, the same part as each part of the backlight apparatus of 1st Embodiment of FIG. 1 is shown with the same code | symbol, and the description is abbreviate | omitted. This second embodiment is different from the first embodiment in that FIG. 1 is arranged so that the light emission surface of the transparent resin 9 of the light emitting diode 2 is parallel to the end surface 3c of the light guide plate 3. Although the envelope 10 has a shape extending straight as it is, in FIG. 5, the light emitting surface of the transparent resin 9 of the light emitting diode 2 is arranged so as to be perpendicular to the end surface 3 c of the light guide plate 3. 10 has a shape that extends to the end surface 3c of the light guide plate 3 while being bent several times. With this shape, light emitted from the light emitting chip 7 can be incident on the end surface 3 c of the light guide plate 3 while being reflected by the envelope 10. The envelope 10 is shaped so that light is efficiently incident on the light guide plate 3 by simulation or the like.

  Even with this structure, it is possible to maintain a distance between the end surface 3c of the light guide plate 3 and the transparent resin 9, and heat generated in the light emitting chip 7 and transmitted to the transparent resin 9 is transmitted to the light guide plate 3. Can be prevented.

  Further, even in this structure, the envelope 10 is directed toward the end surface 3c of the light guide plate 3 while reflecting the light, so that it is desirable that the envelope 10 has high reflectivity as in the first embodiment. . Moreover, if the light emission width is made smaller than the end face 3c of the light guide plate 3 by the envelope 10, and the distance between the extended tip of the envelope 10 and the end face 3c of the light guide plate 3 is also set to 0 to 1 mm. As in the case of the first embodiment, the light incident efficiency is improved and the luminance unevenness and the color unevenness can be suppressed.

1 is a partially cutaway perspective view of a backlight device according to a first embodiment of the present invention. The expanded sectional view of the light emitting diode part in the backlight apparatus shown in FIG. The perspective view of the light emitting diode used for the backlight apparatus shown in FIG. Sectional drawing of the backlight apparatus shown in FIG. The partial expanded sectional view of the backlight apparatus which is the 2nd Embodiment of this invention. The partial expanded sectional view which shows the structure of the conventional backlight apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,101 Light guide unit 2,102 Light-emitting diode 3, 103 Light-guide plate 3a Light-emitting surface 3b Reflective surface 3c End surface 4, 104 Optical sheet 4a Diffusion sheet 4b Prism sheet 4c Reflective sheet 5 LED mounting substrate 6, 106 Lead frame 7, 107 Light emitting chip 8 Bonding wire 9, 109 Transparent resin 10, 108 Enclosure 10a Tubular part 11 Case

Claims (5)

  A light guide plate having opposing light emitting surfaces and reflecting surfaces and connecting end surfaces to each other, an optical sheet disposed on the light emitting surface and reflecting surface of the light guide plate, and an end surface of the light guide plate A light emitting diode chip arranged in the vicinity, the light emitting diode chip sealed, a transparent resin having a substantially planar light emitting surface, a main body surrounding the transparent resin, and a front portion extending from the light emitting surface An envelope having a cylindrical portion, and the envelope is arranged so that the cylindrical portion is in contact with or close to the end face of the light guide plate. Light equipment.   The cylindrical portion of the envelope controls the light emitted from the light emitting surface so that the light emission width is equal to or less than the thickness of the end surface of the light guide plate. A backlight device using a light emitting diode.   The backlight device using the light emitting diode according to claim 1 or 2, wherein a distance between a cylindrical portion of the envelope and an end surface of the light guide plate is 0 to 1 mm.   The light emitting diode chip is installed such that a light emission surface of the transparent resin is substantially parallel to an end surface of the light guide plate, and the envelope has a substantially straight cylindrical portion. A backlight device using the light emitting diode according to claim 3.   The light emitting diode chip is installed such that a light emitting surface of the transparent resin is substantially perpendicular to an end surface of the light guide plate, and the envelope has a cylindrical portion bent at a substantially right angle. A backlight device using the light emitting diode according to claim 3.

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