Patent Application
20160091760
1. Field of the Invention
The present disclosure relates to a direct type LED backlight device which is used for a liquid crystal display in a liquid crystal television, a liquid crystal display monitor, and the like.
2Description of the Related Art
The LED backlight device is typically configured such that a backlight device as a surface light source is disposed on the rear side of a flat liquid crystal display panel; and there are two light emission types of the backlight device, which are an edge type and a direct type.
A backlight device of the edge type is a backlight device of a method in which LEDs (light emitting diodes) are arranged on an edge part of a backlight device and light is emitted to a front surface through a light guide plate. In contrast, a backlight device of the direct type is a backlight device of a method in which the LEDs are arranged immediately back of the liquid crystal display panel and the light is directly emitted to the front surface. A backlight device of the direct type is disclosed in PTL 1, for example.
When the edge type and the direct type are compared, the edge type has a feature of being more suitable for thin LED backlight devices but being higher in cost, and the direct type has a feature of making LED backlight devices thicker but being lower in cost.
PTL 1; Unexamined Japanese Patent Publication No. 2011-90977
The present disclosure provides a direct type LED backlight device and a direct type liquid crystal display in which unevenness of brightness is reduced and uniformity of brightness is improved.
A backlight device in the present disclosure is equipped with: a plurality of LEDs disposed lengthwise and widthwise; a substrate on which the plurality of LEDs are mounted; and a light-blocking member configured to prevent a predetermined amount of part of light from passing through, wherein the part of light is part of light emitted from an LED, of the plurality of LEDs, disposed on an outermost circumference and is emitted to an outer circumferential side.
The backlight device of the present disclosure reduces, by using the light-blocking member, an amount of light from the LED which is directed to a liquid crystal panel via a reflection sheet so that the backlight device adjusts an amount of light on a part on which light overlaps on the liquid crystal panel, thereby restraining spot unevenness from occurring.
An exemplary embodiment will be described below in detail with reference to the drawings as necessary. However, unnecessarily detailed description will be omitted in some cases. For example, a well-known fact and a duplicated explanation of substantially the same configuration will not be described in detail in some cases. This is to prevent the following description from being unnecessarily redundant and to facilitate a person skilled in the art to understand.
The attached drawings and the following description are provided for a person skilled in the art to sufficiently understand the present disclosure, and are not intended to limit the subject matter defined by the claims.
Before the exemplary embodiment is described in the following, the following items will be described to clarify the feature of the present disclosure: (1) A configuration of a direct type backlight device, (2) A relationship between a cost-oriented design method and first and second spot unevenness, (3) A first conventional measure against the second spot unevenness, and (4) A second conventional measure against the second spot unevenness.
In television markets in emerging countries, cost-oriented relatively inexpensive television (TV) sets are being rapidly spread. In order to make television sets for emerging countries more cost-competitive, there is a demand for lower-cost LED backlight devices to be developed. As described above, especially from the point of view of cost, the direct type, which is the direct type, is used as an LED backlight device for a liquid crystal display in a TV or other devices in many cases, and television sets equipped with the backlight device of the direct type are beginning to spread in the emerging country markets.
Rear frame 101 is located on a rear surface of LED substrate 102 to support LED substrate 102. LED substrate 102 is fixed on rear frame 101 with a double-sided adhesive tape, a bolt, or the like. On LED substrate 102, reflection sheet 103 is mounted such that LEDs 100 are exposed through LED holes 113. Reflection sheet 103 has, in order to deliver light to an edge part of liquid crystal panel 106 and to make the light exit to the front side, inclined parts 123 which is bent to be inclined in vicinities of edges of LED substrate 102.
Diffuser plate 104 is mounted at a position a predetermined distance away from LEDs 100 to play a role of diffusing the light from LEDs 100. Optical sheet 105 is mounted on diffuser plate 104. Optical sheet 105 is formed of a diffuser sheet aiming to diffuse light, a prism sheet aiming to improve brightness, a micro-lens sheet, a reflective polarization sheet, and the like. Regarding a number and configuration of optical sheet 105, various configurations are possible to meet a target specification of the backlight device of the liquid crystal display, and the present disclosure does not limit the configuration of the sheet.
Further, support frame 107 is mounted to fix optical sheet 105 and to fix liquid crystal panel 106. As support frame 107, a molded resin article is widely used, but can be replaced by various materials such as silicone rubber. Further, on an outer side of liquid crystal panel 106 and support frame 107, there is mounted cabinet 108. As materials for cabinet 108, either of a metal component and a resin component can be used. Cabinet 108 is doubled as an outer cabinet at the front-most side of a TV set in many cases and is painted or decorated as an external component.
What is described above is a schematic configuration of liquid crystal display 10 equipped with common direct type backlight device 111. Other than described above, there are used many small components such as a bolt, a double-sided adhesive tape, a cushion, and a conductive tape for electrostatic countermeasure, but these components do not directly relate to the present disclosure and will not be described.
As describe above, the direct type backlight device has an advantage that the cost can be reduced, and especially the number of LEDs largely affects the cost. Therefore, the reduction of the number of LEDs largely contributes to cost-cutting, and is thus one technical point in the direct type backlight device.
In general, it is a thickness of the LED backlight device that closely relates to the number of LEDs. In the direct type backlight device, decrease in the number of LEDs indicates increase in the array pitch (LED pitch) of LEDs 100; therefore, if the LED pitch is large, spot unevenness (light and shade in black and white) of the LEDs is likely to occur.
Further, in the case that the LED pitch and the optical configuration are fixed, the spot unevenness is more likely to occur as the thickness of the LED backlight device is thinner (as LEDs 100 are closer to diffuser plate 104). The distance from LEDs 100 to diffuser plate 104 is commonly called an “optical thickness.” As a result, the technical point is how to reduce the number of LEDs 100 and to control the spot unevenness while keeping the optical thickness of the LED backlight device.
Regarding the spot unevenness, there are some types. One of the typical types is spot unevenness (first spot unevenness) which appears on entire liquid crystal panel 106 and occurs simply depending on the relationship between the LED pitch and the optical thickness. Another one is spot unevenness (second spot unevenness) which appears on an outer circumferential part (edge part) of liquid crystal panel 106 and occurs depending on the relationship among the LED pitch, the optical thickness, a distance from LEDs 100 to inclined part 123 of reflection sheet 103, and an angle of inclined part 123.
In general, the second spot unevenness is more likely to appear; and in many cases, while the LEDs are arranged at a constant pitch, the spot unevenness does not appear in the central part of the screen but occurs in the edge part.
With reference to
In order to solve the second spot unevenness, in the conventional art, there are techniques of printing black on and making holes in inclined part 123 of reflection sheet 103. In the following, these two types of conventional arts will be described.
[3. A first Conventional Measure Against the Second Spot Unevenness]
First, the technique of painting black on the reflection sheet will be described with reference to
Next, the technique of making holes in reflection sheet 103 will be described with reference to
In addition, there is an additional issue with this technique that, due to reflection adjusting holes 501 made in inclined part 123 of reflection sheet 103, light leaks from the rear surface and that dust or small bugs enter. Particularly with the issue of the dust and the bugs entering, if the dust or the bug once enters in the backlight device, it is impossible to remove the dust or the bug without disassembling, and in addition, the dust or the bug is projected on the screen, which directly leads to a serious problem. However, different from the case of black print 401 in the first conventional measure, reflection adjusting holes 501 can be made simultaneously when LED holes 113 are made in reflection sheet 103; therefore, cost does not increase in many cases.
As describe above, when the second spot unevenness is solved by the conventional arts described in the first and second conventional measures, the following three issues arise as side effects. Specifically, the issues are (1) the decrease in the brightness, due to the loss of light, on the outer circumferential part of the TV set, (2) the increase in cost of the reflection sheet and (3) the decrease in the image quality due to the dust or the bug entering.
The present disclosure is to solve these three issues and will be described below through an exemplary embodiment.
In the following, a first exemplary embodiment will be described with reference to
First, a configuration of a backlight device according to the first exemplary embodiment will be described with reference to the drawings.
As shown in
Cabinet 108 is a frame part, which is the outermost layer at the front side of a TV set. In general, many TV sets are made of resin, but some are made of metal. Liquid crystal panel 106 is made of two glass plates laminated with liquid crystal sealed between the plates.
Support frame 107 is a component for supporting liquid crystal panel 106 and at the same time supporting optical sheet 105 and diffuser plate 104 located under liquid crystal panel 106. Optical sheet 105 is selected depending on a target image quality of a TV set, and various combinations can be used. Typical examples include diffuser sheets, prism sheets, reflective polarization sheets, and micro-lens films, and brightness and a viewing angle are adjusted depending on how these components are combined. Diffuser plate 104 is made of resin, and examples include one having reflective beads inside to obtain a diffusion function and one having voids inside to obtain a diffusion function.
As shown
On LED substrate 102 are mounted LED packages 305 and secondary lenses 306. Rear frame 101 can be made of resin or metal. In general, since when a resin rear frame is used, dissipation of heat of the LEDs is poor, a metal rear frame is often used. In the above, the configurations and the materials of the components of the present exemplary embodiment are described; however, the present disclosure does not limit the configurations or the materials.
Here, the outermost circumferential LEDs will be described with reference to
The second spot unevenness tends to be more noticeable as the distance from LEDs 100 to inclined part 123 of reflection sheet 103 is smaller. Therefore, depending on the designed value of the distance, in some cases, the second spot unevenness occurs on the upper and lower edge parts of the liquid crystal display but does not occur on the left and right edge parts, for example. In that case, if light-blocking members 802 shown in
With reference to
In the first configuration, light-blocking members 802 are disposed on an inclined part 123 side from outer LEDs 901 as shown in
Regarding a color of light-blocking members 802, various colors can be used, but a high-reflectance color such as white and silver or a specular surface is desirable. A color such as whitish brown, which reflects light and at the same time transmits part of the light, is also desirable. If a color such as black, which absorbs light, is used, light is lost, whereby the brightness on the edge part is reduced.
As a material for light-blocking members 802, heat resistant materials are preferable because light-blocking members 802 are disposed in the vicinities of LEDs 100. Materials which become discolored or deforms due to application of heat are not preferable.
Light-blocking members 802 of the first configuration are provided to flat portion 133 of reflection sheet 103. Since flat portion 133 has a flat surface, light-blocking members 802 can be easily mounted; therefore, this arrangement is preferable.
Alternatively, light-blocking members 812 may be provided on or inside secondary lenses 306. For example, light-blocking members 812 may be configured such that the surfaces of secondary lenses 306 are colored or roughened to reduce transmittance. However, because, from the point of view of cost, it is generally preferable to use the same secondary lenses 306 for all the LEDs used in the backlight device, the former means is more preferable than the latter one.
Also as light-blocking members 812, in the same way as in the case of light-blocking members 802 of the first configuration shown in
As a material for light-blocking member 822, preferable is a component which is made of resin and which is of a type capable of being clamped on LED substrate 102, a dummy chip (which is not conductive and does not affect electric characteristics of LED substrate 102), or others. Since light-blocking members 822 of the third configuration can be mounted on LED substrate 102 simultaneously when LED packages 305 and secondary lenses 306 are mounted, the process cost can be relatively low.
With this arrangement, the light once reflected on light-blocking members 842 is returned again back into secondary lenses 306 of outer LEDs 901. Because the surface of LED substrate 102 is typically in white color, the light having returned into secondary lenses 306 is reflected on the surface of substrate 102 and is emitted again through secondary lenses 306 while being spread. This arrangement provides an effect that the second spot unevenness is not likely to occur.
With this arrangement, the shape of light-blocking members 832 can be simultaneously formed in a punching step of forming LED holes 113; therefore, additional material cost or processing cost is not necessary to provide light-blocking members 832, thereby providing advantages in cost. Further, since reflection sheet 103 is bent and used, a step of providing a dashed-line perforation in bending part 143 is commonly included. Thus, it is possible to provide a dashed-line perforation also in bending parts 153 of light-blocking members 832 in this step.
Although light-blocking members 832 shown in the fourth configuration are previously bent in a bending step at bending parts 153 shown in
Next, a sixth configuration will be described with reference to
As shown in
In addition, it is not easy for a worker to bend, in an actual mass production process, light-blocking members 842 at such an angle that light-blocking members 842 overlap secondary lenses 306 as in the fifth configuration shown in
Since bending parts 153 of light-blocking members 862 are each formed away from each LED hole 113, when reflection sheet 103 is put on LEDs 100, light-blocking members 862 can be automatically bent, and can automatically form a structure in which light-blocking members 862 overlap secondary lenses 306 as shown in
Specifically, there is no need for the step in which a worker bends light-blocking members 862 to mount reflection sheet 103, and the structure in which light-blocking members 862 overlap secondary lenses 306 is thus formed stably; therefore, backlight device 601 equipped with this light-blocking member 862 can be manufactured in the same work as in the conventional process.
With the arrangement described above, light-blocking member 862 can be made simultaneously in the conventional working process of the reflection sheet, and the present disclosure is preferable in this respect. Further, since light-blocking members 832, 842, and 862 formed by using reflection sheet 103 shown in the fourth to sixth configurations are commonly a reflective sheet or a sheet in white color or silver color, there is no need for additional coloring, and there is no need for material cost for a separate component, thereby providing advantages in cost.
As described above, backlight device 601 of the present disclosure is equipped with: a plurality of LEDs 100 disposed lengthwise and widthwise; LED substrate 102 on which the plurality of LEDs 100 are mounted; and light-blocking members 802, 812, 822, 832, 842, and 862 configured to prevent a predetermined amount of part of light from passing though, wherein the part of light is part of light emitted from outer LEDs 901, of the plurality of LEDs 100, disposed on an outermost circumference and is emitted to an outer circumferential side. With this arrangement, a light amount of indirect light 301 directed to inclined part 123 of reflection sheet 103 is reduced; thus, a light amount on a part on which light overlaps on liquid crystal panel 106 is reduced, whereby the second spot unevenness is eliminated without reducing the brightness on the edge part.
In addition, when light-blocking member is made of high-reflectance material which is in white or silver in color, reflected light is not absorbed, whereby light is not lost.
Further, when light-blocking member is made by using a part of reflection sheet 103, which reflect light from LEDs 100, no additional members are necessary. Further, it is not necessary to make a special hole such as reflection adjusting hole 501 in reflection sheet 103, and therefore, dust or small bugs do not enter.
As described above, by using the light-blocking member of the present disclosure, it is possible to eliminate the second spot unevenness without causing the side effect occurring in the conventional art shown in
In addition, since there is a technical trend that the number of LEDs used will be further reduced along with the spread of flip-chip in the future, the expansion of the present disclosure is thought to be accelerated.
The present disclosure can be applied to a direct type LED backlight device in which LEDs are laid out lengthwise and widthwise just under the screen and to a liquid crystal display in a liquid crystal television, a liquid crystal display monitor, and the like.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2014-195445 | Sep 2014 | JP | national |
| 2015-165328 | Aug 2015 | JP | national |
