JP2003279978A - Liquid crystal display - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To uniformize the amount of light emitted from a diffusion plate installed between direct backlights and a liquid crystal display element on the entire surface of the diffusion plate. <P>SOLUTION: The light incident plane SCT1 of the surface facing the light sources (cold cathode fluorescent lamp CFL) of the diffusion plate SCT is worked to a wavy curved surface. The peaks of the wave of the curved surface are made to face a part right above the light sources, and the bottom of the wave is made to face the middle of the light sources, thereby uniformizing the amount of the light emitted from the diffusion plate SCT on the entire surface. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device provided with a light source for illuminating a liquid crystal display element, and more particularly to a liquid crystal display element by controlling the light transmission amount of a diffusion plate provided between the light source and the liquid crystal display element. The present invention relates to a liquid crystal display device capable of irradiating with illumination light of uniform brightness.

[0002]

2. Description of the Related Art Some liquid crystal display devices are provided with a light source for illuminating the liquid crystal panel in order to observe the electronic latent image formed on the liquid crystal panel as a clear visible image. This type of light source illuminates the liquid crystal display element from the backside,
It is a light source called a backlight, and in the following explanation,
This is also called a backlight.

In this backlight, linear lamps (fluorescent lamps, mostly cold cathode fluorescent lamps are used) are provided on the side surface of a light guide plate made of a transparent plate molded of acrylic resin or the like.
A so-called side-edge type in which the above are arranged, and a so-called direct type in which one or a plurality of linear lamps and the like are arranged so as to face the rear surface of the main surface of the liquid crystal panel are known.

The side edge type is widely adopted in notebook type computers and the like which are required to be thin, and many liquid crystal display devices for display monitors also use the side edge type in order to shorten the depth. However, in a large-sized liquid crystal display device such as a display monitor, it is essential to obtain a bright color display image with high contrast, and it is essential that the brightness does not decrease even after long-term use. A liquid crystal display device has been commercialized, which is equipped with a backlight of a type in which the LCDs are arranged directly below a liquid crystal panel.

FIG. 6 is a cross-sectional view for schematically explaining a constitutional example of a liquid crystal display device having a direct type backlight. In FIG. 6, reference numeral PNL is a liquid crystal display element (liquid crystal panel) that electronically generates an image, and includes a pair of glass substrates SUB.
An image is generated by sandwiching a liquid crystal layer LC between 1 and SUB2 and selectively applying a voltage to a pixel selection electrode or a switching element formed on one or both of the glass substrates SUB1 and SUB2.

Polarizing plates PL1 and PL2 are laminated on the outer surfaces of the glass substrates SUB1 and SUB2, respectively, and the polarization of the illumination light from the backlight BL is controlled to allow the light passing through the liquid crystal layer LC to pass upward. An image is displayed by being emitted from the polarizing plate (PL2) or blocked.

The backlight BL includes a plurality of cold cathode fluorescent lamps CFL, a reflector REF, a diffusion plate SCT for controlling the distribution of illumination light emitted from the cold cathode fluorescent lamps CFL, and at least one diffuser for controlling the direction of the illumination light. Sheet S
C and at least one prism sheet PRS, which is an optical sheet OPS.
It is installed on the back of the NL.

FIG. 7 is a sectional view schematically explaining a specific example of the liquid crystal display device shown in FIG. In the direct type backlight BL, a plurality of cold cathode fluorescent lamps CFL that are light sources are used.
A plate-shaped diffusion plate SCT made of an acrylic resin plate, a polycarbonate resin plate, or the like is installed in the vicinity of and above. Also, the cold cathode fluorescent lamp CF of this diffusion plate SCT
On the light incident surface SCT1 which is a surface facing L, a reflection / shielding pattern RCP for correcting uneven brightness is formed by printing or the like. The reflective light-shielding pattern RCP is provided almost directly above the cold cathode fluorescent lamp CFL and is adjusted so that the illumination light that illuminates the liquid crystal display element PNL has an optimum luminance distribution when the diffusion plate SCT is flat.

The cold cathode fluorescent lamp CFL which constitutes the backlight BL is attached along the valley portion of a mountain-shaped reflector REF arranged inside a metal lower frame FLM-D made of an aluminum plate or an iron plate. A prism sheet PRS sandwiched between two diffusion sheets SC-D and SC-U is provided on the light emission surface SCT2 side of the upper surface (liquid crystal display element side) of the diffusion plate SCT arranged above the cold cathode fluorescent lamp CFL. The optical sheets OPS are stacked. One prism sheet PRS may be used, or another prism sheet having the groove directions of the prisms intersect may be used in a stacked manner.

The structure of the laminated body of the diffusion sheet and the prism sheet is not limited to the above example, and only one diffusion sheet,
A combination in which one diffusion sheet and two prism sheets are laminated, a combination in which one diffusion sheet and one prism sheet are laminated, and other combinations are known. A liquid crystal display element PNL is further arranged on the backlight BL having such a configuration, and these are integrated by engaging the upper frame FLM-U and the lower frame FLM-D to form a liquid crystal display device. There is.

Further, in a side-edge type liquid crystal display device of a type different from those shown in FIGS. 6 and 7, the following publications can be cited as documents disclosing the prior art relating to luminance. . That is, for example, in Japanese Unexamined Patent Publication No. 8-146413, the reflection sheet for a planar light emitting device is interposed on the back surface of the light guide plate to concentrate the light output distribution on the front surface of the screen to improve the front luminance and suppress moire fringes. The invention is disclosed.

Similarly, regarding the side-edge type, Japanese Patent Application Laid-Open No. 9-96813 discloses an invention in which a birefringent plate is interposed on the front side of a light control plate to achieve uniform brightness distribution. Further, as a side-edge type, Japanese Patent Application Laid-Open No. 10-3079 discloses an invention in which a light diffusing layer is provided on the surface of the diffusing sheet on the emission surface side to improve the front luminance and widen the viewing angle. ing.

[0013]

As described above, in the liquid crystal display device having the structure shown in FIGS. 6 and 7, a bright display image with high contrast can be obtained, and there is little deterioration in brightness even after long-term use. It has a feature called. However, this configuration has a problem that uneven brightness occurs on the display screen. This will be described with reference to the drawings shown in FIGS. 8 is a plan view of relevant parts of FIG. 7, FIG. 9 is an enlarged cross-sectional view of relevant parts of FIG. 7, and FIG. 10 is an enlarged cross-sectional view of essential parts of FIG. Are given the same reference numerals.

First, in the liquid crystal display device having the structure shown in FIGS. 6 and 7, the plurality of cold cathode fluorescent lamps CFL are arranged at a predetermined pitch p, as shown in detail in FIG.
The distance s1 from the light incident surface SCT1 of the diffuser plate SCT, which is arranged in parallel with each other and is arranged on the upper side, is set to be substantially constant over the entire length of the lamp, as shown in FIGS. t1 represents the thickness of the flat diffusion plate SCT.

Therefore, in such a structure, the brightness of the point P1 of the light incident surface SCT1 of the diffuser plate SCT substantially directly above the cold cathode fluorescent lamp CFL, and the position P approximately in the middle between the adjacent lamps.
2 causes a difference in brightness, and this difference in brightness appears as brightness unevenness on the display screen as it is, resulting in a decrease in the definition of the display screen of the liquid crystal display device, and avoiding a decrease in color purity in the color display. It is a defect that can not be done, and a solution is required.

As one of the solutions, printing of the above-described reflection / light-shielding pattern RCP or the like is used. By arranging the reflection / light-shielding pattern RCP, a temporary display unevenness reducing effect can be expected, but this is still insufficient because of a problem caused by the warp of the diffusion plate SCT described later. Furthermore, even if the pitch of the printing pattern, the ink density, etc. are increased, there is a limit to the control of the brightness difference, and it has not been sufficiently solved.

Further, since the diffusion plate SCT is installed close to the cold cathode fluorescent lamp CFL, a certain amount of time elapses after the cold cathode fluorescent lamp CFL is turned on, a warp occurs due to a temperature rise and flatness is impaired. Tend to be. When the diffuser plate SCT is not flat, it is said that the brightness distribution adjustment by the reflection / shielding pattern RCP formed on the diffuser plate SCT is deviated, and a uniform brightness distribution cannot be obtained for the illumination light to the liquid crystal display element PNL. Another problem arises.

The problem of the warpage of the diffusion plate SCT is that there is a case in which the diffusion plate is added to its own weight and the weight of the laminated optical sheets, and the central portion hangs to cause warpage. Further, a flat acrylic resin plate or a polycarbonate resin plate having a size of several mm or less is usually used as the diffusion plate. However, when the liquid crystal display device receives a vibration or an impact, the diffusion plate vibrates. There is also a risk of damaging adjacent members due to vibration, and there is a need for a solution to this point as well.
This is another one of the problems to be solved in the technical field having the direct type backlight.

An object of the present invention is to solve the above problems and control the light transmission amount of a diffusion plate installed between a direct type light source (backlight) and a liquid crystal display element to make the light uniform with respect to the liquid crystal display element. An object of the present invention is to provide a liquid crystal display device capable of irradiating illumination light having a wide brightness distribution for a long period of time.

[0020]

In order to achieve the above object, the present invention provides a liquid crystal display device by corrugating a surface of a diffuser plate facing a light source and partially controlling the light transmission amount of the diffuser plate. It is possible to irradiate illumination light with a uniform brightness distribution. The typical configurations of the present invention are listed below.

(1) A liquid crystal display element, a diffusion plate arranged on the back side of the liquid crystal display element, an optical sheet arranged between the diffusion plate and the liquid crystal display element, and the diffusion plate sandwiched therebetween. A liquid crystal display device comprising a linear light source arranged on the opposite side of the optical sheet, wherein the diffuser plate has a surface area of a light incident surface of a surface facing the linear light source and an optical sheet facing the optical sheet. The surface area of the light emitting surface of the surface to be turned is different.

(2) The surface area on the light incident surface side of the diffuser plate in (1) is larger than the surface area on the light emitting surface side.

(3) The diffusion plate in (1) or (2) is characterized in that the surface on the light incident surface side has a wavy curved surface.

(4) In the diffuser plate according to any one of (1) to (3), the surface on the light incident surface side has a wavy curved surface, and the wavy top is substantially directly above the linear light source. It is located at.

(5) In the diffuser plate according to any one of (1) to (4), the amount of light transmitted to the light exit surface side is the wavy valley bottom and the top of the wavy curved surface on the light incident surface side. It is different in.

It is needless to say that the present invention is not limited to the above-mentioned constitution and the constitution of the embodiment described later, and various modifications can be made without departing from the technical idea of the present invention.

[0027]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to examples. FIG. 1 is a sectional view schematically explaining an embodiment of a liquid crystal display device according to the present invention, and FIGS. 2 and 3 are enlarged sectional views of the essential part of FIG. 1, each of which is the same as FIG. 6 to FIG. The same parts are denoted by the same symbols.

In this embodiment shown in FIGS. 1 to 3, the direct type backlight BL is arranged on the back side of the liquid crystal display element PNL. The direct type backlight BL is a diffusion plate SCT formed of an acrylic resin plate (which may be polycarbonate resin) in the vicinity of above a plurality of cold cathode fluorescent lamps CFL as a light source and having a relatively large thickness (for example, about 2 mm). And an optical sheet OPS is arranged in front of the diffusion plate SCT.

The diffusion plate SCT is a rectangular plate having the same shape as that of the liquid crystal display element PNL, and its cold cathode fluorescent lamp CF.
The light incident surface SCT1 facing the L is shaped into a wavy curved surface. On the other hand, the light emitting surface SCT2 has a flat surface. Therefore, the surface area of the light entrance surface SCT1 is larger than that of the light exit surface SCT2.

The wavy surface shape of the light incident surface SCT1 of the diffusion plate SCT is such that the wave peak is located almost directly above the cold cathode fluorescent lamp CFL and the wave bottom is located between the adjacent cold cathode fluorescent lamps CFL. It is composed of pitches. 2 and 3, s2 is the distance between the wavy valley bottom of the light incident surface SCT1 and the cold cathode fluorescent lamp CFL, s3 is the distance between the top and the cold cathode fluorescent lamp CFL, and t2 is the wall thickness of the valley bottom. , T3 indicate the wall thickness of the top.

That is, the wall thickness t3 at the point P1 substantially directly above the cold cathode fluorescent lamp CFL is formed thicker than the wall thickness t2 at the point P2 between the adjacent cold cathode fluorescent lamps CFL. And accordingly, the amount of light transmission is point P1 <point P
There is a relationship of 2. Further, the shape and wall thickness of the peripheral portion STC3 that does not contribute to the display of the diffusion plate SCT can be set in consideration of the improvement of the mechanical strength of the diffusion plate SCT.

The wavy surface shape of the light incident surface SCT1 of the diffusion plate SCT can be manufactured by a known means such as a method of heat shaping a raw material plate such as an acrylic resin plate, and a desired shape can be easily obtained. is there. Further, the wavy pitch is preferably matched with the arrangement pitch of the cold cathode fluorescent lamps CFL, but may be variable pitch.

Further, the thickness t2 of the point P2 between the adjacent cold cathode fluorescent lamps CFL, the cold cathode fluorescent lamp CFL.
The thickness t3 at the position of the point P1 substantially immediately above may be determined by the brightness uniformity to be obtained, and when the cold cathode fluorescent lamp CFL itself has a different amount of light emission in its length direction, it is also wavy in that direction. You can also do it. Furthermore, if necessary, the reflection / shielding pattern RCP may be formed by printing or the like at a desired position on the wavy surface of the light incident surface SCT1 of the diffusion plate SCT.

With the configuration of the present embodiment, the light transmission amount of the diffuser plate SCT at the point P1 where the received light amount is large directly above the cold cathode fluorescent lamp CFL is set to the adjacent cold cathode fluorescent lamp CFL.
The light transmission amount of the diffusion plate SCT at the point P2 where the amount of received light is smaller than that at the point P1 almost directly above the center can be the same. Therefore, the light irradiating the liquid crystal display device is not affected by the diffusion plate S
It is possible to make the CT uniform over the entire surface, and as a result, it is possible to eliminate unevenness in the brightness of the display screen of the liquid crystal display device, high definition, and excellent color display with no deterioration in color purity. It has features that can be

Further, with the configuration of this embodiment, due to the effect of the wavy curved surface of the light incident surface SCT1 of the diffusion plate SCT,
Bending rigidity can be improved as compared with the conventional flat plate-shaped diffusion plate SCT. Accordingly, even if the liquid crystal display device is temporarily subjected to vibration or shock, the vibration of the diffusion plate can be suppressed, and damage to adjacent members due to vibration can be prevented. Further, since the warpage of the diffusion plate SCT can be reduced, it is possible to maintain a uniform luminance distribution of the illumination light of the liquid crystal display element and realize a high-quality display even when used for a long time.

FIG. 4 is an exploded perspective view for explaining the structure of the backlight portion of another embodiment of the liquid crystal display device according to the present invention. In FIG. 4, a plurality of cold cathode fluorescent lamps CFL are provided on the upper surface of a lower frame FLM-D generally made of a metal material.
Arrange them so that their longitudinal directions are parallel, cover them with an upper frame FLM-U, and combine them with claws NL, and mold MLD-L (left mold), MLD-of resin material on both sides (left and right). Upper frame FLM- with R (right mold)
The U and lower frame FLM-D are sandwiched and integrated.

A reflection plate REF is provided on the CFL side of the lower frame FLM-D. Then, the upper frame FLM-U
The transparent sheet TPS on the cold cathode fluorescent lamp CFL side
Diffusion plate SCT bonded together, two diffusion sheets SC-
An optical sheet OPS, in which a prism sheet PRS is laminated between D and SC-U, is installed. A liquid crystal display element (not shown) is placed above the backlight, and a power source for driving the cold cathode fluorescent lamp CFL and other necessary circuits and structural members are mounted.

With the structure of this embodiment, the transparent sheet TPS is attached to the light incident surface SCT1 of the diffusion plate SCT, so that the warp of the diffusion plate SCT can be reduced and the light incident surface SCT1 can be reduced. Combined with the effect of the wavy curved surface, it is possible to eliminate the uneven brightness of the display screen of the liquid crystal display device. Furthermore, since the warpage of the diffusion plate SCT can be reduced, it is possible to maintain a uniform luminance distribution of the illumination light of the liquid crystal display element and realize a high-quality display even when used for a long time.

FIG. 5 is an external view showing an example of a display monitor on which the liquid crystal display device according to the present invention is mounted. The backlight constituting the liquid crystal display device mounted on the screen of the monitor, that is, the display unit has the configuration of the embodiment of the present invention described above, and the light transmission amount due to the lighting of the cold cathode fluorescent lamp is the entire surface of the diffusion plate. The brightness distribution of the illumination light of the liquid crystal display element is kept substantially the same, and high-quality display can be realized.

[0040]

As described above, according to the present invention,
The light incident surface of the diffusion plate installed between the direct type light source (backlight) and the liquid crystal display element is formed into a corrugated curved surface, and the illumination light emitted from the light emission surface of this diffusion plate is made uniform over the entire surface of the diffusion plate. At the same time, it is possible to provide a liquid crystal display device capable of irradiating the liquid crystal display element with illumination light having a uniform luminance distribution for a long period of time by suppressing warpage and droop of the diffusion plate.

[Brief description of drawings]

FIG. 1 is a sectional view schematically showing an embodiment of a liquid crystal display device according to the present invention.

FIG. 2 is an enlarged cross-sectional view of an essential part of an embodiment of the liquid crystal display device according to the present invention shown in FIG.

3 is an enlarged cross-sectional view of a main part of an embodiment of the liquid crystal display device according to the present invention shown in FIG.

FIG. 4 is a perspective view of an essential part for schematically explaining another embodiment of the liquid crystal display device according to the present invention.

FIG. 5 is an external view showing an example of a display monitor on which the liquid crystal display device according to the present invention is mounted.

FIG. 6 is a cross-sectional view schematically illustrating a configuration example of a liquid crystal display device including a direct type backlight.

FIG. 7 is a cross-sectional view schematically illustrating a conventional liquid crystal display device.

8 is a plan view of a main part of the liquid crystal display device shown in FIG.

9 is an enlarged cross-sectional view of a main part of the liquid crystal display device shown in FIG.

10 is an enlarged cross-sectional view of a main part of the liquid crystal display device shown in FIG.

[Explanation of symbols]

SCT diffuser SCT1 Light incident surface of diffuser SCT2 Light exit surface of diffuser CFL cold cathode fluorescent lamp (light source) FLM-D lower frame REF reflector SC diffusion sheet PRS prism sheet OPS optical sheet FLM-U upper frame Point just above the cold cathode fluorescent lamp on the P1 diffuser plate The point directly above the middle of the cold cathode fluorescent lamps of the P2 diffusion plate t1, t2, t3 Thickness of diffusion plate.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Shunichi Matsumoto             Hitachi Device, 3681 Hayano, Mobara-shi, Chiba             Engineering Co., Ltd. (72) Inventor Shinji Matsumoto             Hitachi, Ltd. 3300 Hayano, Mobara-shi, Chiba             Factory Display Group F-term (reference) 2H042 AA26 BA03 BA12 BA20 DA21                 2H091 FA14Z FA21Z FA31Z FA34Z                       FA41Z FC12 FD22 LA18

Claims (5)

[Claims] 1. A liquid crystal display element, a diffusion plate arranged on the back side of the liquid crystal display element, an optical sheet arranged between the diffusion plate and the liquid crystal display element, and the optical element sandwiching the diffusion plate. A liquid crystal display device comprising a linear light source arranged on the opposite side of the sheet, wherein the diffusion plate has a surface area of a light incident surface of a surface facing the linear light source and a surface of the surface facing the optical sheet. A liquid crystal display device characterized in that the surface area of a light emitting surface is different. 2. The liquid crystal display device according to claim 1, wherein the diffusion plate has a surface area on the light incident surface side larger than a surface area on the light emission surface side. 3. The liquid crystal display device according to claim 1, wherein the diffusion plate has a wavy curved surface on the light incident surface side. 4. The diffusing plate, wherein the light incident surface side surface has a wavy curved surface, and the wavy top is located substantially directly above the linear light source. The liquid crystal display device according to any one of 1. 5. The diffusion plate according to claim 1, wherein the amount of light transmitted to the light exit surface side is different between the wavy bottom and the top of the wavy curved surface on the light incident surface side. The liquid crystal display device according to any one of claims.