JP2003279979A - Liquid crystal display device - Google Patents

Abstract

(57) [Problem] To uniformly uniform chromaticity of light emitted from a diffusion plate provided between a direct light source and a liquid crystal display element. SOLUTION: A light incident surface SCT1 of a diffuser plate SCT facing a light source lamp (cold cathode fluorescent lamp CFL) has a smooth surface shape, and a reflective light-shielding pattern RCP having light scattering properties is provided on this surface. The light emitted from the diffusion plate SCT was made to have a uniform color tone with no chromaticity difference.

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 having a light source for illuminating a liquid crystal display element from the rear side, and more particularly, controlling a diffusion plate installed between the light source for illuminating the liquid crystal display element and the liquid crystal display element. The present invention relates to a liquid crystal display device capable of irradiating a liquid crystal display element with illumination light of uniform chromaticity.

[0002]

2. Description of the Related Art A liquid crystal display device includes a light source that illuminates a liquid crystal display element (hereinafter, also referred to as a liquid crystal panel) in order to observe a latent electronic image as a clear visible image. is there. This type of light source is a light source for illuminating a liquid crystal display element, which is a so-called backlight, from the back side, and is also referred to as a backlight in the following description.

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

The side edge type is widely adopted in the notebook type computer which is required to be thin, and in many liquid crystal display devices for display monitors, the side edge type is used in order to reduce the depth.

However, in a large-sized liquid crystal display device such as a display monitor, it is indispensable 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, which is generally called a direct type, has been commercialized in which linear lamps are arranged directly below the main surface of a liquid crystal panel. Here, such a backlight will be described as a direct-type backlight.

FIG. 7 is a cross-sectional view for schematically explaining a structural example of a liquid crystal display device having a direct type backlight. In the figure, reference numeral PNL is a liquid crystal display element (liquid crystal panel) that electronically generates an image, and a liquid crystal layer LC is sandwiched between a pair of substrates SUB1 and SUB2, which are preferably glass plates,
An image is generated by 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.
Here, the substrates SUB1 and SUB2 are made of glass plates, and the substrates SUB1 and SUB2 are described as 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 so that the light passing through the liquid crystal layer LC is on the upper side. The light is emitted from the polarizing plate (PL2) or blocked.

The backlight BL includes a plurality of cold cathode fluorescent lamps CFL, a reflector REF, a diffuser 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. The optical sheet OPS is composed of a laminated body of the sheet SC and at least one prism sheet PRS, and is installed on the back surface of the liquid crystal display element PNL.

FIG. 8 is an enlarged cross-sectional view of an essential part for schematically explaining a specific example of the liquid crystal display device shown in FIG. In the direct type backlight BL, a flat diffuser plate SCT made of an acrylic resin plate, a polycarbonate resin plate, or the like is installed in the vicinity of and above a plurality of cold cathode fluorescent lamps CFL that are light sources. In addition, substantially the entire light incident surface SCT1 on the surface of the diffusion plate SCT facing the cold cathode fluorescent lamp CFL is
A reflective light-shielding pattern RCP for correcting uneven brightness is formed by printing or the like. This reflection shading pattern RCP
Is a liquid crystal display element PN when the diffuser plate SCT is flat and is provided on substantially the entire surface including just above the cold cathode fluorescent lamp CFL.
The illumination light for illuminating L is adjusted so as to have an optimum luminance distribution.

The cold cathode fluorescent lamp CFL which constitutes the backlight BL is attached along the valley portion of a mountain-shaped reflector REF which is 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, only one diffusion sheet is a combination of one diffusion sheet and two prism sheets laminated, one diffusion sheet and one diffusion sheet. A combination of laminated prism sheets and other combinations are known.

A liquid crystal display element PNL is further arranged on the backlight BL having such a structure, and these are integrated by engaging the upper frame FLM-U with the lower frame FLM-D to form a liquid crystal display device. I am configuring.

Further, for example, the following invention has been disclosed as a prior art relating to a side edge type liquid crystal display device of a type different from that shown in FIGS. 7 and 8. That is, the surface of mica is coated with titanium dioxide, and the colored pearlescent pigment with the composition of titanium complex oxide is coated on the surface of the light emitting surface of the diffuser plate to improve the light diffusing performance and the light transmitting performance. The invention to be made is disclosed in JP-A-10-3911.
No. 6 publication. In addition, JP-A-2000-180
Japanese Patent No. 634 discloses an invention in which a light diffusion layer of titanium dioxide-coated transparent spherical powder is provided on the light exit surface of a transparent light guide plate to improve the light utilization efficiency.

Further, in Japanese Patent Laid-Open No. 2001-174609, a printing ink in which a light diffusing agent made of a metal oxide is dispersed is applied to the end portion of the surface of an optical sheet, and a bright line due to a side edge type light source is applied. An invention to suppress is disclosed. Furthermore,
Japanese Patent Application Laid-Open No. 7-42475 discloses an invention in which a dielectric interference film made of a titanium dioxide film is provided between a light guide plate and a panel.

[0014]

In the liquid crystal display device having the structure as shown in FIGS. 7 and 8 described above, a bright display image with high contrast can be obtained as described above, and the brightness is not deteriorated even after long-term use. It has the characteristics of being few. However, this configuration has a problem of uneven brightness on the display screen. This will be described with reference to the drawing shown in FIG.

First, in the above-described liquid crystal display device having the structure shown in FIG. 8, a plurality of cold cathode fluorescent lamps CFL are arranged in parallel at a predetermined pitch p, as shown in detail in FIG. The distance s1 between the diffuser plate SCT disposed on the upper side and the light incident surface SCT1 is set to be substantially constant over the entire length of the lamp. Further, t1 is the thickness of the flat diffusion plate SCT, L1
Is a ray of light to a point P1 just above the cold cathode fluorescent lamp CFL on the light incident surface SCT1 of the diffuser plate SCT, and L2 is a diffuser plate SCT.
Of light from the liquid crystal display element PNL corresponding to a point P1 substantially directly above the cold cathode fluorescent lamp CFL. , L21 respectively indicate the light emission from the liquid crystal display element PNL corresponding to the position P2 approximately in the middle between the adjacent lamps of the cold cathode fluorescent lamp CFL.

When a liquid crystal display device having such a direct type backlight is driven, a chromaticity difference occurs in the light emission of L11 and L21, and this chromaticity difference directly causes uneven brightness on the display screen. This appears, and as a result, the definition of the display screen of the liquid crystal display device is lowered, and further, the color display is inevitably lowered in color purity, which is one of the problems to be solved.

As a solution to this problem, means for changing the characteristics of the printing ink of the above-mentioned reflection / shading pattern RCP, the pitch of the printing pattern, the ink density, etc. are used.
However, with such means alone, the above L11 and L2
The correction of the chromaticity difference from 1 is insufficient. In particular, it is more conspicuous on a monitor or the like for visually observing a still image, and a measure for preventing the occurrence of uneven brightness due to the difference in chromaticity is required. This has been a problem to be solved in the technical field having a direct type backlight.

An object of the present invention is to solve the above-mentioned problems and to control a diffusion plate installed between a direct type light source (backlight) and a liquid crystal display element so that there is no difference in chromaticity 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 uniform luminance distribution for a long period of time.

[0019]

[Means for Solving the Problems] In order to achieve the above object, the inventors of the present invention conducted various experiments and studies and obtained the following findings. That is, (a), in the diffuser plate having the unevenness on the surface of the light incident surface SCT1 of the diffuser plate and having no reflection / light-shielding pattern RCP, there is no chromaticity difference in light emission between L11 and L21.

(B) In the diffusion plate having the light incident surface SCT1 of the diffusion plate having a smooth surface and having no reflection / light-shielding pattern RCP, chromaticity difference occurs in light emission between L11 and L21.

(C) The light-incident surface SCT1 of the diffuser has a structure in which irregularities are present on the light-incident surface SCT1, and the light-shielding pattern RCP is provided.
In the diffusion plate printed with, a chromaticity difference occurs in the light emission of L11 and L21.

(D) In the diffuser plate in which the light incident surface SCT1 of the diffuser plate has a smooth surface and the reflection / light-shielding pattern RCP is printed, a chromaticity difference occurs in the light emission of L11 and L21.

In (e), (b) and (d), the chromaticity is reversed. Based on such knowledge, the inventors of the present invention found out that the surface shape of the light incident surface SCT1 of the diffuser plate and the presence / absence of the reflection / light-shielding pattern RCP are the causes of the chromaticity difference, and determined the diffuser plate. It is possible to irradiate the liquid crystal display element with illumination light having a uniform luminance distribution by controlling it. 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 light diffusion surface of the diffusion plate facing the linear light source is smooth, and light is incident on the surface. It is characterized by having a reflective light-shielding pattern having a scattering property.

In (2) and (1), the reflection-shielding pattern having the light-scattering property is characterized in that the film surface has an uneven shape.

In (3), (1) or (2), the light-shielding reflective light-shielding pattern has light-scattering particles.

In (4) and (3), the light-scattering particles have a particle diameter of 0.1 to 0.4 μm.

In the above (5), (3) or (4), the light scattering particles are titanium oxide.

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

[0030]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will now be described in detail with reference to the drawings of the embodiments.

FIG. 1 is a sectional view schematically explaining an embodiment of the liquid crystal display device according to the present invention, and FIG. 2 is an enlarged sectional view of the essential parts of the embodiment of the liquid crystal display device according to the present invention shown in FIG.
1 and 2, the same parts as those in FIGS. 7 and 8 described above are designated by the same reference numerals. In this embodiment, as shown in FIG. 1, the direct type backlight BL is arranged on the back side of the liquid crystal display element PNL. The direct type backlight BL is provided with a diffuser plate SCT having a configuration described later in proximity to and above a plurality of cold cathode fluorescent lamps CFL which are light sources, and an optical sheet OPS is provided in front of the diffuser plate SCT. ing.

As shown in detail in FIG. 2, which is an enlarged schematic view of the main part of FIG. 1, this diffuser plate SCT is made of an acrylic resin plate (polycarbonate resin may be used) and has a relatively large thickness. With a rectangular plate like the liquid crystal display element PNL, and has a smooth surface shape of the light incident surface SCT1 facing the cold cathode fluorescent lamp CFL and has a light scattering property. It has a reflective light-shielding pattern RCP1 made of a film. On the other hand, the light exit surface SCT
2 is a plane.

The reflection / light-shielding pattern RCP1 is provided on substantially the entire surface including substantially directly above the cold cathode fluorescent lamp CFL, and its pattern size, pattern pitch, etc. are determined by the liquid crystal display element PNL when the diffusion plate SCT is flat. The illumination light for illumination is adjusted so as to have an optimum luminance distribution, and the film itself has a light scattering property.

Reflecting / shielding pattern RCP1 having light scattering property
The configuration will be described with reference to the examples of FIGS. 3 and 4 which schematically show the details of the main part of FIG. 2 in an enlarged manner. First, FIG.
FIG. 3 is a cross-sectional view schematically showing an enlarged main part of FIG. 1, in which the same parts as those in the above-mentioned drawings are denoted by the same symbols. In FIG.
The light incident surface SCT1 of the diffusion plate SCT has a smooth surface shape,
A reflective light shielding pattern RCP11 having a light scattering property is formed on this surface. This reflection / light-shielding pattern RCP11 uses ink having the same composition as the conventional one, and its pattern size, pattern pitch, etc. are optimum for the illumination light for illuminating the liquid crystal display element PNL when the diffusion plate SCT is flat as described above. The brightness distribution is adjusted and the surface of the film has an uneven shape.

This uneven shape has a cold cathode fluorescent lamp CFL.
Array pitch p, the distance s between this lamp and the diffuser plate SCT
1. The thickness may be set based on the film thickness of the reflection / shading pattern RCP and the like, but it is preferably about 400 nm or more. With this configuration, the light ray L1 to the point P1 substantially directly above the cold cathode fluorescent lamp CFL goes straight, passes through the reflection / shielding pattern RCP11, and then enters the diffusion plate SCT from the smooth surface of the diffusion plate SCT. And emits light as L12.

On the other hand, the light ray L2 traveling toward the intermediate point P2 is inclined and strikes the reflection / shading pattern RCP11. Therefore, it goes without saying that the light ray L2 has a difference in optical path length from the light ray L1. The colliding light beam L2 is scattered and disappears at this position as shown by an arrow, and the scattered light beam L2 travels into the reflection / shielding pattern RCP11 and disappears here.
Although it is divided into various optical paths, such as one that passes through this film and further passes through the diffusion plate SCT to emit light as L22, the light emission of L22 has a chromaticity close to that of L12. This L22 and L1
The difference in chromaticity of the light emission with that of No. 2 was improved compared with the conventional one, and it was possible to discriminate that the colors were practically the same on a still screen.

Here, the light incident surface SCT1 of the diffusion plate SCT
The smooth surface shape can be produced by a known means such as a method of heating and shaping a raw material plate such as an acrylic resin plate, and a desired shape can be easily obtained.

FIG. 4 is a sectional view schematically showing an enlarged main part corresponding to FIG. 3 of another embodiment of the liquid crystal display device according to the present invention. Is attached. In FIG. 4, the light incident surface SCT of the diffusion plate SCT
The surface shape of No. 1 is smooth, and a reflective light shielding pattern RCP12 having a light scattering property is formed on this surface. This reflection / shading pattern RCP12 has titanium oxide (Ti
It contains light scattering particles S such as O ₂ ) particles. or,
As described above, the pattern size, the pattern pitch and the like are adjusted so that the illumination light that illuminates the liquid crystal display element PNL has the optimum luminance distribution when the diffusion plate SCT is flat.

Here, the light-scattering particles S have a property of reflecting and scattering light and have a reflective light-shielding pattern RC.
Any material having a function of controlling the amount of light transmission, which is the original purpose of P, may be used, and silver, resin beads, or the like may be used in addition to the titanium oxide. Further, the particle size is preferably about 0.1 μm to 0.4 μm, which allows a change in chromaticity, and more preferably 0.2 μm to 0.3 μm.

With the configuration as in this embodiment, it is possible to obtain a desired reflection / shielding pattern RCP simply by mixing the light scattering particles S in the film-forming ink, and the light scattering particles S are incident. The light is scattered and reflected, and the chromaticity of the emitted light is changed in combination with the smooth surface shape of the light incident surface SCT1 of the diffusion plate SCT to be adjacent to the light emission L12 just above the cold cathode fluorescent lamp CFL. It is possible to eliminate the chromaticity difference between the cold cathode fluorescent lamp CFL and the light emission L22 that is located directly above and in the middle.

Therefore, it becomes possible to make the chromaticity of the irradiation light to the liquid crystal display element uniform over substantially the entire surface of the diffusion plate SCT.
As a result, it is possible to eliminate the difference in chromaticity of the display screen of the liquid crystal display device, eliminate the unevenness in brightness, have high definition, and further, in color display, it is possible to perform excellent display without deterioration in color purity.

Next, an example of specific specifications of the configuration shown in FIG. 4 will be described. First, the light scattering particles S have an average particle size of 0.25 μm.
m of titanium oxide particles, the light-scattering particles S and the polyester-based oligomer and acrylate monomer are 7:
Mix at a ratio of 2: 1 and use this mixture to diffuse plate SC
A film thickness of 15 μ is formed on the entire smooth surface of the light incident surface SCT1 of T.
m reflection / shading pattern RCP was formed.

The diffuser plate SCT having the reflection / light-shielding pattern RCP having such specifications is used as a cold cathode fluorescent lamp CFL having a diameter of 2.6 mm, the above-mentioned interval s1: 8 mm, and p: 30 m.
The chromaticity of the light emission L12 and L22 was measured by incorporating it into the direct backlight BL of m and operating it. As a result, the light emission L
No chromaticity difference between 12 and L22 was detected, and this is shown in FIG.
As a result of being mounted on the liquid crystal display device shown in FIG. 2 and measuring both moving images and still images, the occurrence of uneven brightness due to the chromaticity difference was not observed in any of the images.

FIG. 5 is a developed 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. 5, 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.
The lower frame FLM-D has a reflector REF on the CFL side.

On the upper frame FLM-U, a diffusion plate SCT having a transparent sheet TPS attached on the opposite side of the cold cathode fluorescent lamp CFL, and a prism between the two diffusion sheets SC-D and SC-U. An optical sheet OPS in which sheets PRS are laminated is installed. A liquid crystal panel (not shown) is placed above the backlight, and a power source for driving the CFL, other necessary circuits, and structural members are mounted.

As in this embodiment, by attaching the transparent sheet TPS to the light exit surface SCT2 of the diffusion plate SCT, the "warpage" of the diffusion plate SCT can be reduced. Further, the smooth surface shape of the light incident surface SCT1 and the effect of having the reflection / shielding pattern having the light scattering property are combined, so that the uneven brightness due to the chromaticity difference of the display screen of the liquid crystal display device can be eliminated.

Further, since the warpage of the diffusion plate SCT can be reduced, it is possible to realize a high-quality display by keeping the luminance distribution of the illumination light of the liquid crystal display element uniform even when used for a long time.

FIG. 6 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 display monitor, that is, the display unit has the configuration of the embodiment of the present invention described above, and the color of the light emitted from the diffuser plate by the lighting of the cold cathode fluorescent lamp. Since the liquid crystal display element is irradiated with the light having substantially the same degree on the entire surface, it is possible to realize high-quality display without causing uneven brightness on the screen due to the difference in chromaticity.

[0049]

As described above, according to the present invention,
The light-incident surface of the diffusion plate installed between the so-called direct type light source (backlight) and the liquid crystal display element has a smooth surface shape, and the surface has a reflective light-shielding pattern having a light-scattering property. As a result, the illumination light emitted from the light emitting surface of the diffuser plate is made to have uniform chromaticity over the entire surface of the diffuser plate, and the warp and droop of the diffuser plate are suppressed to provide uniform chromaticity illumination to the liquid crystal display element. A liquid crystal display device capable of irradiating light for a long period of time can be provided.

[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.

FIG. 3 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.

FIG. 4 is an enlarged sectional view of an essential part of another embodiment of the liquid crystal display device according to the present invention.

FIG. 5 is a perspective view of relevant parts for schematically explaining still another embodiment of the liquid crystal display device according to the present invention.

FIG. 6 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. 7 is a cross-sectional view schematically illustrating a configuration example of a liquid crystal display device including a direct type backlight.

8 is an enlarged cross-sectional view of an essential part for schematically explaining a specific example 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 RCP reflection shading pattern CFL cold cathode fluorescent lamp (light source) L1 and L2 rays L11, L12, L21, L22 light emission 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 P2 The point directly above the middle of the cold cathode fluorescent lamps on the diffusion plate.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Yasuhisa Shiraishi             Hitachi Elect, 3350 Hayano, Mobara-shi, Chiba             Within Ronic Devices Co., Ltd. F-term (reference) 2H042 AA26 BA02 BA03 BA20 DA21                 2H091 FA14Z FA21Z FA23Z FA31Z                       FA34Z FA41Z LA15 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 smooth light-incident surface on a surface facing the linear light source, and has a light-scattering property on the surface. A liquid crystal display device having a reflective light-shielding pattern having 2. The reflective light-shielding pattern having the light-scattering property,
The liquid crystal display device according to claim 1, wherein the film surface has an uneven shape. 3. The reflective light-shielding pattern having the light-scattering property,
A light-scattering particle is included, The claim 1 or 2 characterized by the above-mentioned.
The liquid crystal display device according to item 1. 4. The light scattering particles have a particle size of 0.1 μm to
The liquid crystal display device according to claim 3, wherein the liquid crystal display device has a thickness of 0.4 μm. 5. The liquid crystal display device according to claim 3, wherein the light scattering particles are titanium oxide.