JP4627151B2 - Liquid crystal display device - Google Patents

Description

  The present invention relates to a liquid crystal display device, and more particularly to a technique effective when applied to a direct type backlight used in a liquid crystal display device.

The liquid crystal display module of TFT (T hin F ilm T ransistor ) method is widely used as a display device such as a notebook personal computer.
These liquid crystal display modules are composed of a liquid crystal display panel in which a drain driver and a gate driver are arranged around it, and a backlight that irradiates the liquid crystal display panel.
This backlight is roughly divided into a sidelight type backlight and a direct type backlight.
In the case of a liquid crystal display module used as a display device of a notebook personal computer, a sidelight type backlight is mainly adopted.
In recent years, liquid crystal display modules have become larger and have larger screens and are also used as display devices for monitors. In such large and large screen liquid crystal display modules for monitors, direct-type backlights that can provide high brightness Is employed (see Patent Document 1 and Patent Document 2 below).

FIG. 8 is an exploded perspective view showing a schematic configuration of a liquid crystal display module using a conventional direct type backlight.
As shown in the figure, a conventional liquid crystal display module includes a frame-shaped upper frame (also referred to as a shield case, upper case, or metal upper frame) 1 made of a metal plate, a liquid crystal panel 2, and a backlight (BL). It consists of.
The liquid crystal panel 2 is disposed around a pair of substrates (for example, made of a light-transmitting and electrically insulating material such as glass) stacked with a liquid crystal layer interposed therebetween. A drain circuit board (DPCB) and two gate circuit boards (GPCB).
Each circuit board is mounted with a tape carrier package (DTCP, GTCP) in which a plurality of liquid crystal driving semiconductor integrated circuit elements (driving ICs) are mounted by tape automated bonding (TAB).
Furthermore, these drive ICs have a flexible circuit board (DFPC) for supplying signals or electric power, and a flexible circuit board (GFPC) for connection for connecting the drain circuit board (DPCB) and the gate circuit board (GPCB). .
The pair of substrates are overlapped with a predetermined gap therebetween, and the substrates are bonded together by a sealing material provided in a frame shape in the vicinity of the peripheral edge between the two substrates, and a liquid crystal sealing port provided in a part of the sealing material Liquid crystal is sealed inside the sealing material between the two substrates and sealed, and a polarizing plate is attached to the outside of the two substrates to form the liquid crystal panel 2.
The flexible circuit board (DFPC) is connected to a circuit board (including an integrated circuit element such as a timing converter) (Tcon) provided on the lower surface of the backlight (BL). In FIG. 8, reference numeral 5 denotes a circuit board (Tcon) cover.

FIG. 9 is a developed view showing a schematic configuration of the direct type backlight (BL) shown in FIG.
As shown in FIG. 9, the direct type backlight (BL) shown in FIG. 8 includes a reflecting plate 10 and a plurality of pieces between a mold 7 made of synthetic resin and a lower frame 3 made of metal. A cold cathode fluorescent lamp (CCFL), a diffusion plate 11, a lower diffusion sheet 12, a prism sheet 13, and an upper diffusion sheet 14 are arranged in the order shown in FIG. Two prism sheets 13 may be arranged.
Then, the assembled liquid crystal panel 2 is sandwiched and fixed between the upper frame 1 and the backlight (BL) to complete the liquid crystal display module.
Thus, in the direct type backlight, a plurality of cold cathode fluorescent lamps (CCFL) and optical members (diffuser plates, diffusion sheets, brightness enhancement sheets, etc.) disposed on the top of the plurality of cold cathode fluorescent lamps (CCFL) And a reflecting plate having a reflecting surface for reflecting light emitted from a plurality of cold cathode fluorescent lamps (CCFLs) to the side opposite to the liquid crystal display panel to the liquid crystal display panel side.

As prior art documents related to the invention of the present application, there are the following.
Japanese Patent No. 3262650 Japanese Patent No. 3248890

However, in the cost structure of the direct type backlight, there is a problem that the ratio of the optical members such as the diffusion plate, the diffusion sheet, and the brightness enhancement sheet is as large as about 40 to 70%.
The present invention has been made to solve the problems of the prior art, and an object of the present invention is to provide a luminance uniformity function of a diffusion plate, a diffusion sheet, and the like in a liquid crystal display device including a direct type backlight. Another object of the present invention is to provide a technology that can realize an optical system having a light collecting function such as a brightness enhancement sheet at a low cost and reduce the cost of a direct type backlight.
The above and other objects and novel features of the present invention will become apparent from the description of this specification and the accompanying drawings.

Of the inventions disclosed in this application, the outline of typical ones will be briefly described as follows.
In order to achieve the above object, a liquid crystal display device of the present invention includes a liquid crystal display panel and a backlight, and the backlight has a plurality of light sources and a plurality of light sources opposite to the liquid crystal display panel side. A reflective member disposed on the liquid crystal display panel side and a liquid crystal display panel side surface of the plurality of light sources, and a plurality of micro optical elements disposed on the liquid crystal display panel side surface And a specular reflection surface of the reflecting member having a parabolic shape centered on each of the light sources when cut along a plane orthogonal to the extending direction of the plurality of light sources. The concave portion has a cross-sectional shape in which a plurality of concave portions are connected, and the micro optical element has a cross-sectional shape that reflects light incident on the optical plate in the direction of the reflecting member.
In addition, in the portion where the luminance of light incident on the optical plate is high, the plurality of micro optical elements are densely arranged, and in the portion where the luminance of light incident on the optical plate is low, the plurality of micro optical elements Are sparsely arranged.

The effects obtained by the representative ones of the inventions disclosed in the present application will be briefly described as follows.
According to the present invention, an optical system having a brightness uniformity function such as a diffusion plate and a diffusion sheet and a light collecting function such as a brightness enhancement sheet can be realized at low cost, and the cost of a direct type backlight can be reduced. It becomes possible.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
In all the drawings for explaining the embodiments, parts having the same functions are given the same reference numerals, and repeated explanation thereof is omitted.
The present invention is different in the configuration of the direct type backlight, but the other configuration is the same as the conventional direct type backlight.
FIG. 1 is a cross-sectional view of an essential part showing a configuration of a direct type backlight according to an embodiment of the present invention.
In the figure, 3 is a lower frame, 20 is a reflecting member, 30 is an optical plate, and 31 is a micro optical element formed on the upper surface of the optical plate 30.
Generally, about 50% of the light emitted from the cold cathode fluorescent lamp (CCFL) is applied to the reflecting member 20. By effectively utilizing the light irradiated to the reflecting member 20, the luminance of the light irradiated from the backlight can be improved.
Therefore, the reflecting surface of the reflecting member 20 is a specular reflecting surface, and the reflecting member 20 is composed of, for example, a silver coating product, an aluminum coating product, a mirror finished aluminum sheet polyester resin multilayer structure, or the like.
Further, the cross-sectional shape of the reflecting surface of the reflecting member 20, that is, the cross-sectional shape cut by a surface orthogonal to the extending direction of the cold cathode fluorescent lamp (CCFL) is emitted from the cold cathode fluorescent lamp (CCFL), The light reflected by the reflecting surface is incident on the lower surface of the optical plate 30 perpendicularly, that is, the light is emitted directly above the reflecting member 20 (so-called parabolic shape).
By adopting such a cross-sectional shape, the light emitted from the cold cathode fluorescent lamp (CCFL) is irradiated to the lower surface of the optical plate 30 without loss, and the emission direction from the upper surface of the optical plate 30 is directly above. Thus, the luminance of the liquid crystal display panel can be improved.

The optical plate 30 is made of a transparent material (for example, a transparent acrylic plate) having a total light transmittance of 90% or more.
Here, in addition to the vertical light emitted from the reflecting member 20, the following two lights are incident on the lower surface of the optical plate 30.
The first is an emitted light having an angle directly irradiated from the cold cathode fluorescent lamp (CCFL), and the second is emitted from the cold cathode fluorescent lamp (CCFL) in the lateral direction and reflected by the side plate. Light.
Since the second light is incident on the lower surface of the diffuser plate with a large angle, the utilization efficiency is not good.
The first luminous flux is dense immediately above the cold cathode fluorescent lamp (CCFL), is sparse at the middle portion between the cold cathode fluorescent lamp (CCFL) and the cold cathode fluorescent lamp (CCFL), and is also cold cathode. Incidence is almost perpendicular at the upper part of the fluorescent lamp (CCFL), and incident at a large angle at the intermediate part between the cold cathode fluorescent lamp (CCFL) and the cold cathode fluorescent lamp (CCFL).
Therefore, the luminance distribution due to the light directly incident on the optical plate 30 from the cold cathode fluorescent lamp (CCFL) is high directly above the cold cathode fluorescent lamp (CCFL), and the cold cathode fluorescent lamp (CCFL) and the cold cathode fluorescent lamp (CCFL). The middle part between is lower.
On the other hand, the emitted light from the reflecting member 20 is disturbed by the cold cathode fluorescent lamp (CCFL), and the luminance directly above the cold cathode fluorescent lamp (CCFL) is reduced. The sum of these factors is the luminance distribution on the light emitting surface.

FIG. 10 shows an example of the structure of a direct type backlight in the case where no micro optical element is formed on the upper surface of the optical plate 30. FIG. 11 shows the luminance distribution of light emitted from the optical plate 30 in this case.
In addition, in FIG. 10, the cross-sectional shape of the specular reflective surface of the reflection member 20 is a parabola shape represented by the following formula (1).
[Equation 1]
^{y = (x 2 / d1)} - (d1 / 4)
(1)
Here, d1 is the pitch between the cold cathode fluorescent lamp (CCFL) and the cold cathode fluorescent lamp (CCFL), and the origin is the center of the cold cathode fluorescent lamp (CCFL).
Moreover, each dimension and component structure are as follows.
(1) Distance (h1) between the center of the cold cathode fluorescent lamp (CCFL) and the lower surface of the optical plate (transparent acrylic plate) 30: 13.5 mm
(2) Thickness (h2) of optical plate (transparent acrylic plate) 30: 2.0 mm
(3) Pitch (d1) between the cold cathode fluorescent lamp (CCFL) and the cold cathode fluorescent lamp (CCFL): 27.1 mm
(4) Half the pitch between the cold cathode fluorescent lamp (CCFL) and the cold cathode fluorescent lamp (CCFL) (d2): 13.55 mm
(5) Refractive index of air (n0): 1.0
(6) Number of cold cathode fluorescent lamps (CCFL): 8 (seven) Reflectance of the reflecting surface of the reflecting member 20: 98.0%

In the graph shown in FIG. 11 , the average luminance is 21200 (cd / m ² ), but the luminance step is 33. Here, the luminance step is expressed by (maximum luminance−minimum luminance) / average luminance.
In FIG. 11 , cold cathode fluorescent lamps (CCFLs) are arranged at positions indicated by A, B, and C.
As described above, the direct-type backlight in the case where the micro optical element is not formed on the upper surface of the optical plate 30 has poor luminance uniformity.
Therefore, it is necessary to provide an optical control element on the upper surface of the optical plate 30 in order to control the amount of light.
The function required for the optical control element is to lower the light density of the high-luminance portion or to pass the light beam of the high-luminance portion to the low-luminance portion.
As a means for realizing the former, it is conceivable to roughen the upper surface of the high brightness portion of the optical plate 30. This is also one method, but in order to improve the light utilization efficiency, means for realizing the latter is necessary.
There are several examples of this means, but one of them is extended in the same direction as the extension direction of the cathode fluorescent lamp (CCFL), and its sectional shape (perpendicular to the extension direction of the cathode fluorescent lamp (CCFL)). A case where the micro optical element 31 having a right isosceles triangle is used as an example will be described below.

FIG. 2 shows a configuration in which the micro optical element 31 having a right-angled isosceles triangle cross section is partially installed on the upper surface of the optical plate 30.
In FIG. 2, A part is a part where the light incident on the optical plate 30 is high luminance, and B part is a part where the light incident on the optical plate 30 is low luminance.
The trajectory of light emitted from the cold cathode fluorescent lamp (CCFL) is as follows.
(1) The light is emitted from a cold cathode fluorescent lamp (CCFL) and is incident on the specular reflection surface of the reflection member 20.
(2) Since the cross-sectional shape of the specular reflection surface of the reflecting member 20 is a parabola, the light is reflected directly upward and incident on the lower surface of the optical plate 30 at an incident angle of 0 °. Incident on the slope at an incident angle of 45 °.
(3) Since it is above the critical angle, it is reflected at a reflection angle of 45 °, and is incident on the other inclined surface of the micro optical element 31 at an incident angle of 45 °.
(4) Since the angle is equal to or greater than the critical angle, the light is reflected at a reflection angle of 45 °, reflected directly downward, emitted downward from the lower surface of the optical plate 30, and the above-described (1) of the specular reflection surface of the reflecting member 20 Incident at a position shifted by Lp in the horizontal direction from the position where the light beam hit.
(5) A part of the light is reflected with a slight angle from right above, and when this angle is α0, the light is incident on the lower surface of the optical plate 30 at an incident angle α0.
(6) According to Snell's law, the light is refracted inside the transparent optical plate 30 at a refraction angle α1 expressed by the following equation (2).
[Equation 2]
n0 · Sinα0 = n1 · Sinα1
(2)
Here, n0 is the refractive index of the air layer, about 1.0, and n1 is the refractive index of the transparent optical plate 30. In the case of an acrylic plate, it is about 1.4933.
(7) According to Snell's law, the light is emitted to the air layer at a refraction angle α0 expressed by the above equation (2).

In this way, by placing the micro optical element 31 having a cross-sectional shape of a right isosceles triangle partially on the upper surface of the optical plate 30, the light of the high luminance part is turned to the low luminance part, thereby reducing the luminance step. An improvement in light utilization efficiency can be achieved at the same time.
In this case, if the size of the micro optical element 31 is made too large, the control of the luminance step becomes insufficient, and if the size of the micro optical element 31 is made too small, the workability becomes difficult and the yield is low. High cost.
Therefore, in this embodiment, the micro optical elements 31 are arranged at a constant pitch (for example, 0.3 mm pitch), and as shown in FIG. 4 , the height (h1) is higher in the high luminance portion than in the other portions. The height (h2) is made higher in the low luminance portion than in the other portions, or, as shown in FIG. 3 , in the high luminance portion, the micro optical elements 31 are arranged densely, and the low luminance portion is arranged. Then, the micro optical elements 31 are arranged sparsely.
The cross-sectional shape of the micro optical element 31 is not limited to a right-angled isosceles triangle, but an arc shape shown in FIG. 5A, a parabola shape shown in FIG. 5B, an elliptic shape shown in FIG. The cosine curve shape shown in FIG.

An example of the luminance distribution of light emitted from the optical plate 30 of the present embodiment is shown in FIG. FIG. 6 shows the luminance distribution of the upper half of the display surface, and it can be seen that the luminance is uniform.
Further, the micro optical elements 31 are arranged at a pitch of 0.3 mm, and as shown in FIG. 3, the height is higher in the high luminance part than in the other parts, and the height is different in the low luminance part. FIG. 7 shows the height distribution of the micro optical element 31 at that time.
Each dimension and component configuration are as follows.
(1) Distance (h1) between the center of the cold cathode fluorescent lamp (CCFL) and the lower surface of the optical plate (transparent acrylic plate) 30: 13.5 mm
(2) Thickness (h2) of optical plate (transparent acrylic plate) 30: 2.0 mm
(3) Pitch (d1) between the cold cathode fluorescent lamp (CCFL) and the cold cathode fluorescent lamp (CCFL): 27.1 mm
(4) Half the pitch between the cold cathode fluorescent lamp (CCFL) and the cold cathode fluorescent lamp (CCFL) (d2): 13.55 mm
(5) Refractive index of air (n0): 1.0
(6) Number of cold cathode fluorescent lamps (CCFL): 8 (seven) Reflectance of the reflecting surface of the reflecting member 20: 98.0%

It should be noted that the luminance viewing angle (so-called half-value width) that is 50% of the maximum luminance is about ± 40 ° in the vertical half-width and about ± 45 ° in the horizontal half-width in the conventional one. In this embodiment, the vertical direction may be about ± 10 ° and the horizontal direction may be about ± 45 °.
In such a case, the existing diffusion sheet (12, 14 shown in FIG. 9) can be improved by arranging it on the liquid crystal display panel side of the transparent optical plate 30.
In the present embodiment, the optical plate 30 having the luminance distribution shown in FIG. 6 described above is combined with an existing diffusion sheet, so that the average luminance is 12000 (cd / m ² ), the luminance step is 5, and the vertical half-value width is Was about ± 40 °, and the horizontal half width was about ± 45 °.
As described above, according to the present embodiment, irradiation is performed from the optical plate 30 by partially disposing the micro optical elements 31 having a cross-sectional shape of a right-angled isosceles triangle or an arc shape on the upper surface of the optical plate 30. The amount of emitted light can be controlled to make the luminance uniform and improve the luminance.
Furthermore, by arranging an existing diffusion sheet or the like on the optical plate 30, it is possible to further improve the luminance uniformity and the angle characteristics.

Thereby, various characteristics such as average luminance, luminance step, and angle characteristic can be equal to or higher than those of a conventional direct type backlight, and the reflecting member 20 having a specular reflection surface having a parabolic cross section, a micro optical element With the combination of the optical plate 30 and the diffusion sheet on which 31 is formed, it is possible to achieve an improvement in brightness without an expensive brightness enhancement sheet.
The configuration of the optical member of the conventional direct backlight has required 5 to 7 points such as a milky white diffusion plate, a diffusion sheet, a brightness enhancement sheet, and a reflection member. The board 30, the diffusion sheet, and the reflecting member 20 can be reduced to three points. Not only can the cost of the optical member of the direct type backlight be greatly reduced, but the number of parts can be reduced to less than half, so the reliability Can be improved.
As mentioned above, the invention made by the present inventor has been specifically described based on the above embodiments. However, the present invention is not limited to the above embodiments, and various modifications can be made without departing from the scope of the invention. Of course.

It is principal part sectional drawing which shows the structure of the direct type | mold backlight of the Example of this invention. In the direct type backlight of the embodiment of the present invention, it is a diagram showing a configuration when a micro optical element having a cross-sectional shape of a right isosceles triangle is partially installed on the upper surface of the optical plate. It is a schematic diagram which shows an example of the arrangement | positioning method of the micro optical element of the Example of this invention. It is a schematic diagram which shows the other example of the arrangement | positioning method of the micro optical element of the Example of this invention. It is principal part sectional drawing which shows the other example of the micro optical element of the Example of this invention. 4 is a graph illustrating an example of a luminance distribution of light emitted from an optical plate in a direct type backlight according to an embodiment of the present invention. It is a graph which shows distribution of the height of a micro optical element in the case of the graph shown in FIG. It is a disassembled perspective view which shows schematic structure of the liquid crystal display module using the conventional direct type | mold backlight. It is an expanded view which shows schematic structure of the direct type backlight (BL) shown in FIG. In the direct type backlight shown in FIG. 1, it is principal part sectional drawing which shows an example of a structure in case a micro-optical element is not formed in the upper surface of an optical plate. It is a graph which shows an example of the luminance distribution in the case of the structure shown in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Upper frame 2 Liquid crystal panel 3 Lower frame 5 Circuit board (Tcon) cover 7 Mold 10 Reflecting plate 11 Diffusing plate 12 Lower diffusing sheet 13 Prism sheet 14 Upper diffusing sheet 15 Lamp holder 20 Reflecting member 30 Optical plate 31 Micro optical element BL Backlight DPCB Drain circuit board GPCB Gate circuit board DTCP, GTCP Tape carrier package DFPC, GFPC Flexible circuit board Tcon Circuit board CCFL Cold cathode fluorescent lamp

Claims (8)

A liquid crystal display panel;
A liquid crystal display device comprising a backlight disposed on the opposite side of the display surface of the liquid crystal display panel,
The backlight includes a plurality of light sources,
A reflective member disposed on the side opposite to the liquid crystal display panel side of the plurality of light sources, and the surface on the liquid crystal display panel side being a specular reflection surface;
An optical plate disposed on the liquid crystal display panel side of the plurality of light sources, and having a plurality of micro optical elements partially formed on a surface on the liquid crystal display panel side;
The plurality of micro optical elements of the optical plate reflect incident light toward the reflecting member, and the micro optical elements are densely arranged in a portion where the luminance of light incident on the optical plate is high, The liquid crystal display device , wherein the micro optical elements are sparsely arranged in a portion where the luminance of light incident on the optical plate is low . A liquid crystal display panel;
A liquid crystal display device comprising a backlight disposed on the opposite side of the display surface of the liquid crystal display panel,
The backlight includes a plurality of light sources,
A reflective member disposed on the side opposite to the liquid crystal display panel side of the plurality of light sources, and the surface on the liquid crystal display panel side being a specular reflection surface;
An optical plate disposed on the liquid crystal display panel side of the plurality of light sources, and having a plurality of micro optical elements partially formed on a surface on the liquid crystal display panel side;
The plurality of micro optical elements of the optical plate reflect incident light toward the reflecting member, and the size of the micro optical element is large in the portion where the luminance of the light incident on the optical plate is high, and the optical A liquid crystal display device, wherein the size of the micro optical element is small in a portion where the luminance of light incident on the plate is low. When cut by a plane orthogonal to the extending direction of the plurality of light sources, the specular reflection surface of the reflecting member has a cross-sectional shape in which a plurality of parabolic concave portions centering on each of the light sources are connected. The liquid crystal display device according to claim 1 or 2 . The micro optical element is extended in the same direction as the plurality of light sources, and reflects light incident on the optical plate in the direction of the reflecting member when cut by a plane orthogonal to the extension direction of the plurality of light sources. 4. The liquid crystal display device according to claim 1 , wherein the liquid crystal display device has a cross-sectional shape. 5. The liquid crystal display device according to claim 4 , wherein the cross-sectional shape is a right-angled isosceles triangle shape, an arc shape, a parabola shape, an ellipse shape, or a cosine curve shape. 2. The plurality of micro optical elements are formed on a surface of the optical plate on the liquid crystal display panel side so that the luminance of light emitted from the optical plate is substantially uniform. The liquid crystal display device according to claim 5 . The liquid crystal display device according to any one of claims 1 to 6 , wherein the optical plate is a transparent optical plate having a total light transmittance of 90% or more. The backlight liquid crystal display device according to any one of claims 1 to 7 characterized by having a diffusion sheet to the liquid crystal display panel side of the optical plate.

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