JP2007103101A - Backlight and liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a backlight without having luminance irregularity by forming an intermediate layer between an LED element unit and a side surface of a light guide plate; and to provide a liquid crystal display device equipped with it. <P>SOLUTION: This backlight unit is characterized by comprising: a light source; the light guide plate; and the intermediate layer formed between the light source and the light guide plate by tightly adhering to the light source and the light guide plate. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a backlight and a liquid crystal display device, and more particularly to a backlight having an extended light emission angle and a liquid crystal display device having the backlight mounted thereon.

LCD panels are installed in various devices such as TVs, car navigation systems, personal computers, and mobile phones. In order to further promote the use of LCD panels, it is important to increase screen size and resolution, and to reduce manufacturing costs. is there.
Most liquid crystal display devices receive light emitted from a backlight unit provided on the back of the liquid crystal display unit and display an image on the screen of the liquid crystal display unit (for example, Patent Document 1).

  If an LED element unit equipped with an LED element (Light Emitting Diode) is used instead of the conventional cold cathode tube as the light source of the backlight unit, the power consumption is reduced and the product life can be extended. Furthermore, since the material does not contain mercury, there are advantages such as environmental friendliness.

  However, if point-emitting LED elements are arranged in a line at a predetermined interval, luminance unevenness such as streak lines or the like is likely to occur between the LED elements in a region with a low luminous intensity or in the light emission direction, and the light efficiency may decrease. Conceivable.

On the other hand, regarding a method for making the light from the LED element unit uniform, for example, a backlight having a light guide plate in which a pattern such as a grating is formed on the opposite side of the light emitting surface of the LED element unit is disclosed ( For example, Patent Document 2).
JP 2001-281654 A JP 2004-111383 A

  The present invention provides a backlight having no luminance unevenness and a liquid crystal display device including the same by providing an intermediate layer between the LED element unit and the side surface of the light guide plate.

According to one aspect of the invention,
A light source;
A light guide plate;
An intermediate layer provided between the light source and the light guide plate in close contact with the light source and the light guide plate;
There is provided a backlight unit characterized in that the backlight unit is provided.

According to another aspect of the present invention,
With the above backlight unit,
A liquid crystal display unit that displays an image by controlling a transmission amount of light emitted from the light guide plate;
A liquid crystal display device is provided.

  According to the present invention, by providing the intermediate layer between the LED element unit and the side surface of the light guide plate, it is possible to provide a backlight having no luminance unevenness and a liquid crystal display device including the same, and the industrial merit is It is a great deal.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1A is a cross-sectional view illustrating a backlight according to this embodiment, and FIG. 1B is a cross-sectional view taken along line AA ′.
As shown in FIG. 1A, the backlight unit 1 of the present embodiment includes a light emitting unit 10, an intermediate layer 15, a light guide plate 20, a reflection sheet 25, and a light amount adjustment sheet 23. Yes. The intermediate layer 15 is made of resin or the like, and is sandwiched between the light emitting surface of the light emitting unit 10 and the side surface of the light guide plate 20. The light guide plate 20 can be formed of a resin such as polymethyl methacrylate (PMMA), silica glass, or the like. In addition, a light amount adjustment sheet 23 is provided on the main surface of the light emitting surface of the light guide plate 20, and an inclined surface is provided on the opposite back side so that the plate thickness decreases as the distance from the intermediate layer 15 increases. A reflective sheet 25 is provided on the inclined surface.

  The light emitting unit 10 has, for example, a structure in which a plurality of SMD (surface mounting device) elements 5 are arranged in a line at a predetermined interval on a mounting substrate 7. Here, the number of SMD elements 5 provided in the light emitting unit 10 is an integer calculated by dividing the required total luminous flux (lumen) by the luminous flux per LED element. For example, in the case of a liquid crystal display device having a diagonal size of 8 inches, the required total luminous flux is about 150 lumens. Therefore, when the luminous flux per SMD element is 12.5 lumens, for example, the number of SMD elements 5 used in the light emitting unit 10 is twelve. If the number of LED elements is reduced in order to reduce the manufacturing cost, the necessary total luminous flux may be reduced, the dark area 18 may be enlarged, and the luminance unevenness of the image may become significant.

FIG. 2 is a cross-sectional view illustrating the structure of the SMD element 5.
The SMD element 5 of this specific example has a pair of leads 51A and 51B, and the LED element 53 is bonded to the lead 51A with a conductive silver paste (not shown) or the like. The electrode 54 provided on the LED element 53 is connected to the other lead 51 </ b> B by a bonding wire 57. The leads 51A and 51B are fixed by a high thermal conductive resin 52, and a high reflection resin 55 is further provided to form a light reflection plate. The LED element 53 is sealed with a sealing resin 58 after the bonding wire 57 is connected. The light 3 emitted from the LED element 53 passes through the sealing resin 58 and is emitted from the substantially circular light emission surface to the outside.

  The size of the SMD element 5 is, for example, about 3.6 mm in length and width, and about 0.8 mm in height, and the opening of the light emitting portion formed in the highly reflective resin 55 has a diameter of 2.6 mm. Can be about.

  Further, for example, by dispersing the phosphor that absorbs light emitted from the LED element 53 and converts the wavelength in the sealing resin 58, various emission colors including white can be achieved. Specifically, an LED element 53 that emits ultraviolet rays is used, and the ultraviolet rays are absorbed to produce red (R) color light, green (G) color light, and blue (B) color light, respectively. By dispersing the phosphor to be emitted in the sealing resin 58, white light is obtained as a mixed color of RGB. Further, the LED element 53 that emits blue light is used, and a phosphor that absorbs the blue light and emits yellow light is dispersed in the sealing resin 58, whereby a mixed color of blue light and yellow light is obtained. As a result, white light is obtained.

  The light 3 radiated from the SMD element 5 enters the light guide plate 20 from the side surface of the light guide plate 20 through the intermediate layer 15 made of resin or the like, is guided to the inclined surface of the light guide plate 20 and the reflection sheet 25, and has an incident angle. The light is reflected in a direction substantially perpendicular to the light and emitted toward the light emitting surface of the light guide plate 20. The light emitted from the light emitting surface of the light guide plate 20 enters a liquid crystal display unit (not shown) via the light amount adjustment sheet 23. Here, the light quantity adjustment sheet 23 is composed of, for example, a plurality of sheets, and can uniformize the light quantity in the plane.

  According to the present embodiment, as shown in FIG. 1, the light distribution characteristic of light is improved by sandwiching the intermediate layer 15 between the SMD element 5 and the side surface of the light guide plate 20. It is possible to suppress the occurrence of luminance unevenness such as the dark region 18 within the effective light emitting surface 22. Here, the “effective light emitting surface” refers to an illumination area having a high degree of uniformity required for displaying a desired image.

FIG. 3 is a schematic view illustrating the main structure of a liquid crystal display device on which the backlight unit of this embodiment is mounted.
The liquid crystal display device 50 includes a backlight unit 1 and a liquid crystal display unit 48. In FIG. 2, the backlight unit 1 and the liquid crystal display unit 48 are separated from each other. However, in an actual liquid crystal display device, these units are almost in close contact with each other.

  The backlight unit 1 has the structure described above with reference to FIG. Here, as the light quantity adjustment sheet 23, for example, a light diffusion film 32, a prism sheet 34, and a brightness enhancement film 36 laminated in order can be used.

  On the other hand, the liquid crystal display unit 48 acts as a matte, with the first polarizing plate 38 that receives light emitted from the backlight unit 1, the liquid crystal cell 40, the phase difference plate 42, and the second polarizing plate 44. The anti-glare film 46 has a structure provided in this order.

  The liquid crystal cell 40 has a structure in which a liquid crystal layer is sandwiched between a drive electrode substrate and a counter electrode substrate. The drive electrode substrate and the counter electrode substrate are each formed using a substrate made of a light-transmitting material such as glass.

  The light emitted from the LED element unit 10 enters from the side surface of the light guide plate 20 and is reflected by the inclined surface and the reflection sheet 25 provided on the back side of the light guide plate 20, and the light diffusion film 32, the prism sheet 34, and the like. The brightness enhancement film 36 is sequentially transmitted, and the amount of light is made uniform. Thereafter, the amount of light incident on the first polarizing plate 38 is controlled through the liquid crystal cell 40, the phase difference plate 42, the second polarizing plate 44, and the anti-glare film 46 in order, and a predetermined image 49 is displayed. .

  FIG. 4 is a schematic diagram for explaining the operation of the intermediate layer 15 provided in the backlight unit of the present embodiment.

FIG. 5 is a schematic view illustrating an optical path when an air layer 17 is provided instead of the intermediate layer 15 as a comparative example.
As shown in FIG. 4, in the present embodiment, an intermediate layer 15 made of resin or the like is sandwiched between the SMD element 5 provided in the light emitting unit and the side surface of the light guide plate 20. When light enters the side surface portion of the light guide plate 20 through the sealing resin 58 of the SMD element 5, the optical path at the interface between the intermediate layer 15 and the light guide plate 20 follows the following formula (1).

sin θt / sin θi = n ₁ / n ₂ (1)

Here, θi is the incident angle, θt is the reflection angle, n ₁ is the refractive index on the incident side, and n ₂ is the refractive index on the reflection angle side.

  According to the present embodiment, the intermediate layer 15 made of resin or the like is inserted between the SMD element 5 and the light guide plate 20 so that no air layer is interposed therebetween. In this way, light can be introduced into the light guide plate 20 at a wide angle.

  That is, as shown in FIG. 5, when an air layer (refractive index n = 1) is provided between the SMD element 5 and the light guide plate 20, the light emitted from the SMD element 5 is air layer 17. The light is refracted when entering the light guide plate 20. Since the refractive index of the light guide plate 20 is about 1.5, for example, the light incident on the light guide plate 20 from the air layer 17 has a narrower spread angle as shown in the figure. That is, even if the SMD element 5 having a wide light distribution characteristic is used, the light distribution characteristic of the light incident on the light guide plate 20 becomes narrow.

  In addition, it is not easy from the viewpoint of manufacture that the SMD element 5 and the light guide plate 20 are always in close contact with each other. It is considered that a gap, that is, an air layer is often generated between the SMD element 5 and the light guide plate 20 due to variations in the thickness of the SMD element 5 and variations in height after mounting on the mounting substrate.

  On the other hand, in the present embodiment, an intermediate layer 15 made of resin or the like is inserted between the SMD element 5 and the light guide plate 20. Then, refraction when light enters the light guide plate 20 from the intermediate layer 15 can be suppressed, and the spread angle of light can be prevented from becoming narrow. That is, as shown in FIG. 4A, light having a wider angle can be introduced into the light guide plate 20. As a result, the light distribution inside the light guide plate 20 can be made uniform, and the dark region 18 formed between the adjacent SMD elements 5 can be reduced.

  As the material of the intermediate layer 15, for example, a silicone resin or an epoxy resin can be used.

  Further, if a resin having elasticity or low hardness is used as the material of the intermediate layer 15 and the light emitting unit 10 and the light guide plate 20 are pressed with the intermediate layer 15 interposed therebetween, the thickness, height, etc. of the SMD element 5 are increased. It is possible to easily prevent the air layer from intervening. That is, the effect described above with reference to FIG. 4 can be obtained with certainty. Examples of such a material for the intermediate layer 15 include a rubber-like silicone resin. In various resins such as a silicone resin, the refractive index and the hardness can be controlled independently.

  The refractive index of the intermediate layer 15 is preferably set between the refractive index of the sealing resin 58 of the SMD element 5 and the refractive index of the light guide plate 20. If it does in this way, wide angle light can be introduced into the light-guide plate 20, and the phenomenon in which a light quantity falls between the SMD elements 5 can be suppressed. For example, when the refractive index of the sealing resin 58 is 1.41 and the refractive index of the light guide plate 20 is 1.51, the refractive index of the intermediate layer 15 may be between 1.41 and 1.51. . If it does in this way, it can enter into light-guide plate 20, suppressing the fall of the spreading angle of the light discharge | released from SMD element 5. FIG.

  Further, when an optical grease such as matching oil is applied between the SMD element 5 and the intermediate layer 15 or between the intermediate layer 15 and the light guide plate 20, formation of an air layer can be prevented.

  FIG. 6A is a cross-sectional view illustrating a comparative example of the backlight unit according to this embodiment, and FIG. 6B is a cross-sectional view taken along line A-A ′. In these drawings, the same elements as those described above with reference to FIGS. 1 to 5 are denoted by the same reference numerals, and detailed description thereof is omitted.

  In this comparative example, an air layer 17 is formed between the light emitting unit 10 and the light guide plate 20.

  In the case of this comparative example, the difference in refractive index between the air layer 17 and the light guide plate 20 contributes, and the light spread angle is narrowed when entering the light guide plate 20.

FIG. 7 is a graph illustrating the refraction angle when light enters the light guide plate 20 (refractive index n = 1) from air (refractive index n = 1).
When the refractive index (n1) of the air layer 17 is 1.0 and the refractive index of the light guide plate 20 is 1.5, when the light enters the intermediate layer 15 at an angle of 45 degrees from the SMD element 5, the light guide plate reflects it. The angle advances at 28 degrees and is narrowed by about 30%. Therefore, a large dark region 18 is generated on the light emitting unit 10 side of the light guide plate 20.

  In order to avoid this dark region 18, the effective light emitting surface 22 must be shortened by a distance ΔL in the optical axis direction of the LED element unit 10, and the effective light emitting surface 22 is reduced. In order to expand the effective light emitting surface 22, it is necessary to increase the number of SMD elements 5, but this measure increases the manufacturing cost.

  Further, the fact that the dark region 18 is large means that there are many portions that are not used as the effective light emitting surface 22. That is, the frame area formed around the image display area is enlarged, which is not desirable from the viewpoint of size reduction, weight reduction, or design.

  FIG. 8 is a graph illustrating the optical characteristics of the SMD element 5 that can be used in the present embodiment. Here, the horizontal axis is the light emission angle (°), and the vertical axis is the relative luminous intensity (a.u.).

In this embodiment, when the SMD element 5 having such a wide light distribution characteristic is used, it is possible to prevent the light distribution characteristic of the light guide plate 20 from being narrowed.
Next, another specific example of the backlight unit according to the present embodiment will be described.

FIG. 9A is a cross-sectional view illustrating a second specific example of the backlight according to this embodiment, and FIG. 9B is a cross-sectional view taken along line AA ′. Also in FIG. 9, the same elements as those described above with reference to FIGS. 1 to 8 are denoted by the same reference numerals, and detailed description thereof is omitted.
In this specific example, a material having a refractive index higher than that of the light guide plate 20 is used as the intermediate layer 15. As a result, when the light emitted from the SMD element 5 enters the light guide plate 20 via the high refractive index intermediate layer 14, the spread angle increases. Therefore, the effective light emitting surface 22 is lengthened by the distance ΔM along the optical axis direction of the LED element unit 10 and the uniformity of the effective light emitting surface 22 is increased, so that the number of SMD elements 5 can be reduced. Here, as a material of the intermediate layer 14, a material having a high refractive index such as a high refractive index silicone resin, a high refractive index epoxy resin, or a high refractive index acrylic resin may be used.

FIG. 10A is a cross-sectional view illustrating a third specific example of the backlight according to this embodiment, and FIG. 10B is a cross-sectional view taken along line AA ′.
In this specific example, a scatterer that scatters light is dispersed in the intermediate layer 15. By using the intermediate layer 15 containing a scatterer, the light emitted from the SMD element 5 diffuses and spreads inside the intermediate layer 15 and enters the light guide plate 20. That is, light having a wider light distribution characteristic can be introduced into the light guide plate 20. As a result, the dark region 18 formed between the adjacent SMD elements 5 can be further reduced. That is, the effective light emitting surface 22 is enlarged in the optical axis direction of the SMD element 5, and the number of SMD elements 5 can be reduced.

Examples of the scatterer in this specific example include powders such as titania (TiO ₂ ) and silica (SiO ₂ ).

Next, examples and comparative examples of the backlight unit according to this embodiment will be described.
(Example)
FIG. 11A is a cross-sectional view illustrating an example of a backlight according to this embodiment, and FIG. 11B is a cross-sectional view taken along line AA ′.
Table 1 is a list showing the result of simulating the luminance distribution for the analysis region C of the backlight unit of this embodiment.
FIG. 12 is a graph schematically showing this luminance distribution.


The backlight unit of this specific example has a structure in which an intermediate layer 15 (refractive index: 1.45, transmission wavelength: 578 nm) made of silicone resin is sandwiched between the SMD element 5 and the light guide plate 20.

Moreover, the detailed conditions of a present Example are as follows.
The SMD element 5 is a white light-emitting element having a light emitting area diameter of 2.6 millimeters and an outer dimension of length 3.6 millimeters × width 3.6 millimeters × thickness 0.8 millimeters. The sealing resin 58 has a refractive index of 1.41 and a transmission wavelength of 578 nanometers.

  The twelve SMD elements 5 were placed in a row on the mounting substrate at intervals of 14.6 millimeters to form the light emitting unit 10. Moreover, the space | interval of the light emission unit 10 and the light-guide plate 20 was 0.5 millimeters, and the intermediate | middle layer 15 was inserted so that a clearance gap might not arise between them.

  On the main surface of the light emitting surface of the light guide plate 20, a light diffusion film 32, a prism sheet 34, and a brightness enhancement film 36 are provided in this order. Here, the light diffusion film 32 has a role of diffusing light from the light guide plate 20 and improving the uniformity of the luminance, and the luminance enhancement film 36 has a role of increasing the luminance.

  Then, as shown in FIG. 11B, the analysis region C (14.6 mm in the parallel direction to the optical axis of the SMD and 10.0 mm in the vertical direction) at the LED element unit side end of the light guide plate. ) For the luminance distribution. Here, the effective light emitting surface 22 is a region excluding a region surrounded between the end portion of the light guide plate 20 and the distance G (3.4 millimeters).

  As a result, as shown in Table 1 and FIG. 12, it was confirmed that according to this example, the light can be introduced into the light guide plate 20 without narrowing the incident angle of the light emitted from the SMD element 5. Further, since the dark region 18 that causes luminance unevenness is formed within a distance G from the end of the light guide plate 20, it has been found that luminance unevenness can be suppressed without reducing the effective light emitting surface 22.

(Comparative example)
FIG. 13A is a cross-sectional view showing a backlight of this comparative example, and FIG. 13B is a cross-sectional view taken along line AA ′.
Table 2 is a list showing the result of simulating the luminance distribution for the analysis region C of this comparative example.
FIG. 14 is a graph schematically showing this luminance distribution.
The basic structure and components of this comparative example are the same as those of the embodiment described above with reference to FIG. 11, but in this comparative example, an air layer 17 (refractive index of 1.0 ) Is pinched.


In the case of this comparative example, as shown in Table 2 and FIG. 14, the light incident on the light guide plate 20 through the air layer 17 is narrowed due to the difference in refractive index between the air layer 17 and the light guide plate 20. The analysis result was obtained. Therefore, it has been found that the dark region 18 is generated in the vicinity of the light emitting unit 10 in the main surface of the light guide plate 20, and the effective light emitting surface 22 is reduced.

The embodiments of the present invention have been described above with reference to specific examples.
However, the backlight and the liquid crystal display device of the present invention are not limited to these specific examples. For example, as long as it has the gist of the present invention, even if it is appropriately changed by those skilled in the art, such as the type of intermediate layer, the number of SMD elements, the type of constituent film, the combination of refractive indexes, etc. Are included within the scope of the present invention.

It is (a) sectional drawing which illustrates the backlight which concerns on this embodiment, and (b) It is sectional drawing of an A-A 'line. 3 is a cross-sectional view illustrating the structure of an SMD element 5. FIG. It is a schematic diagram which illustrates the principal part structure of the liquid crystal display device carrying the backlight unit of this embodiment. It is a schematic diagram for demonstrating the effect | action of the intermediate | middle layer 15 provided in the backlight unit of this embodiment. It is a schematic diagram which illustrates the optical path at the time of providing the air layer 17 instead of the intermediate | middle layer 15 as a comparative example. It is (a) sectional drawing showing the comparative example of the backlight unit which concerns on this embodiment, and (b) It is sectional drawing of an A-A 'line. It is a graph which illustrates the refraction angle in case light injects into the light-guide plate 20 (refractive index n = 1) from air (refractive index n = 1). It is a graph which illustrates the optical characteristic of the SMD element 5 which can be used in this embodiment. It is (a) sectional drawing showing the 2nd specific example of the backlight which concerns on this embodiment, and (b) A-A 'line sectional drawing. It is (a) sectional drawing showing the 3rd specific example of the backlight which concerns on this embodiment, and (b) A-A 'line sectional drawing. It is (a) sectional drawing showing the Example of the backlight concerning this embodiment, and (b) It is sectional drawing of an A-A 'line. It is a graph which represents typically the luminance distribution of an Example. It is (a) sectional drawing showing the backlight of this comparative example, (b) It is sectional drawing of an A-A 'line. It is the graph which represented typically the luminance distribution of the comparative example.

Explanation of symbols

1 Backlight Unit 5 SMD Element 10 Light Emitting Unit (LED Element Unit)
14 high refractive index intermediate layer 15 intermediate layer 16 scatterer-containing resin layer 17 air layer 18 dark region 20 light guide plate 22 effective light emitting surface 23 light amount adjustment sheet 25 reflection sheet 32 light diffusion film 34 prism sheet 36 brightness enhancement film 37 backlight unit 38 Polarizing plate 40 Liquid crystal cell 42 Phase difference plate 44 Polarizing plate 46 Anti-glare film 48 Liquid crystal display unit 49 Image
DESCRIPTION OF SYMBOLS 50 Liquid crystal display device 51A, B Lead wire 52 High heat conductive resin 53 LED element 54 Electrode 55 High reflection resin 57 Bonding wire 58 Sealing resin C Analysis area

Claims (9)

A light source;
A light guide plate;
An intermediate layer provided between the light source and the light guide plate in close contact with the light source and the light guide plate;
A backlight unit characterized by comprising The light source includes a light emitting diode, a sealing resin having a light emitting surface that seals the light emitting diode and emits light to the outside;
Have
The backlight unit according to claim 1, wherein the intermediate layer is in close contact with the light emission surface of the sealing resin.   The backlight unit according to claim 2, wherein the intermediate layer is formed of a material having a refractive index between the refractive index of the light guide and the refractive index of the sealing resin.   The backlight unit according to claim 1, wherein the intermediate layer is made of a resin.   The backlight unit according to claim 4, wherein the resin has a hardness lower than that of the light source that is in close contact with the intermediate layer and lower than that of the light guide plate.   The backlight unit according to claim 4, wherein the resin has rubber-like elasticity.   The said intermediate | middle layer contains the scatterer which scatters light, The backlight unit as described in any one of Claims 1-6 characterized by the above-mentioned.   8. An optical grease is interposed between at least one of the light source and the intermediate layer and between the intermediate layer and the light guide plate. The backlight unit described in. The backlight unit according to any one of claims 1 to 8,
A liquid crystal display unit that displays an image by controlling a transmission amount of light emitted from the light guide plate;
A liquid crystal display device comprising: