JP2007298596A - Liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal display device that gives high-quality display images having high color reproducibility and no luminance unevenness all over the entire display screen of a liquid crystal display panel by using a plurality of cold cathode fluorescent lamps having a short tube length so as to obtain light from a surface light source having high uniformity of luminance from the backlight at low cost. <P>SOLUTION: The plurality of cold cathode fluorescent lamps CFL in a backlight BL disposed on the back face of the liquid crystal display panel PNL include first cold cathode fluorescent lamps CFL1 having a long tube length and second cold cathode fluorescent lamps CFL2 having a shorter tube length than the first lamps, alternately arranged in parallel in rows and columns at a predetermined interval D in such a manner that the interval D is present within the range of the tube length of the first cold cathode fluorescent lamp CFL1 in the arrangement in a columnar direction. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a liquid crystal display device having a backlight, and in particular, a liquid crystal display device using a cold cathode fluorescent lamp direct type backlight that is installed on the back side of the liquid crystal display panel and irradiates the liquid crystal display panel with light source light. It is about.

  In recent years, liquid crystal display devices are widely used as display means for various information terminal monitors such as personal computers and mobile phones, or television receivers. This type of liquid crystal display device is made visible by applying light to an electronic image formed on a liquid crystal display panel. Small information equipment has a structure that uses ambient light as a light source for visualization, but a liquid crystal display is used to observe a good image regardless of the ambient light condition or on a relatively large screen. In many cases, the panel includes an illumination light source, and an electronic image formed on the liquid crystal display panel is illuminated with illumination light from the illumination light source.

  A small liquid crystal display device has a structure in which a so-called front light is installed as an illumination light source in front of or in the vicinity of the liquid crystal display panel. However, in a notebook computer, a computer monitor, and a television receiver, An illumination light source called a backlight to be installed is employed.

  There are roughly two types of backlights, one of which is a side-edge type backlight used in notebook computers and computer monitors where the depth of the equipment is limited, and the other one requires high brightness. A relatively large computer monitor or television receiver is a direct type backlight installed directly under the back of a liquid crystal display panel.

  In these backlights, a cold cathode fluorescent lamp is mainly used as an illumination light source. A side edge type backlight using this cold cathode fluorescent lamp can be constructed relatively compactly because the cold cathode fluorescent lamp is arranged on the side of the light guide installed on the back of the liquid crystal display panel. Although it has advantages, it has the disadvantage that light utilization efficiency is low, and the direct type backlight is configured with a plurality of cold cathode fluorescent lamps installed without a light guide on the back of the liquid crystal display panel. Therefore, there is an advantage that the light use efficiency is high, but there is a disadvantage that the thickness of the backlight itself becomes large.

  A plurality of straight tube type cold cathode fluorescent lamps as light sources, a light diffusion plate arranged on the liquid crystal display panel side of each of these cold cathode fluorescent lamps, a polarization conversion film and a prism sheet, and each cold cathode fluorescent lamp A backlight composed of a lamp and a reflector installed on the back side is disclosed in, for example, “Patent Document 1” below. Also, for a liquid crystal display device configured to install this type of backlight device on the back side of the liquid crystal display panel and irradiate the light source light on the back side of the liquid crystal display panel, see, for example, “Patent Document 2” below. It is disclosed.

JP 2002-82626 A JP-A-6-75216

  However, the backlight with the above configuration requires a cold cathode fluorescent lamp with a long tube length as the liquid crystal display panel becomes larger. Since this type of cold cathode fluorescent lamp has a small tube diameter and a long tube length, there are problems such as high manufacturing cost and being easily damaged by handling during the manufacture of the backlight.

  In addition, the backlight with the above configuration can improve the luminance by increasing the number of cold cathode fluorescent lamps, but it increases the power consumption of the backlight and increases the temperature of the backlight. There was a problem that it would end up.

  In addition, if the arrangement distance of the cold cathode fluorescent lamps in the central portion of the display screen of the liquid crystal display panel is reduced without increasing the number of cold cathode fluorescent lamps, the arrangement interval of the cold cathode fluorescent lamps in the peripheral portion of the display screen is relatively reduced. Increases, the luminance of the peripheral portion decreases, and the luminance uniformity of the display screen decreases.

  Furthermore, the problem of brightness uniformity can be solved to some extent by using an optical sheet, a cold cathode fluorescent lamp having a long tube length, a reflector made of a highly reflective member, etc., but the material cost is high. A new problem arises.

  Accordingly, the present invention has been made to solve the above-described conventional problems, and its purpose is to reduce planar light source light with high luminance uniformity from a backlight using a plurality of cold cathode fluorescent lamps having a short tube length. It is an object of the present invention to provide a liquid crystal display device which can obtain a high-quality display image with high color reproducibility over the entire display screen of a liquid crystal display panel and which does not cause luminance unevenness by being obtained at low cost.

  In order to achieve such an object, a liquid crystal display device according to the present invention includes a liquid crystal display panel configured by sandwiching a liquid crystal layer between a pair of transparent substrates having electrodes for forming pixels on the inner surface, and the liquid crystal display. A backlight installed on the back of the panel, and this backlight is arranged in parallel facing the back of the diffusion plate and a diffusion plate having an illumination surface for irradiating the back of the liquid crystal display panel with diffused light. A plurality of cold cathode fluorescent lamps that irradiate the back surface of the diffusion plate with light source light, and a light source that is installed opposite to the back surfaces of the plurality of cold cathode fluorescent lamps and irradiated from the plurality of cold cathode fluorescent lamps A plurality of cold cathode fluorescent lamps having a long tube length and a second tube length shorter than that of the first cold cathode fluorescent lamp. Cold cathode fluorescent lamp Are arranged alternately in parallel in the row direction and the column direction with a predetermined interval, and the intervals are arranged to be within the range of the tube length of the first cold cathode fluorescent lamp in the column direction arrangement. It is a feature.

  Another liquid crystal display device according to the present invention is installed on the back surface of a liquid crystal display panel configured by sandwiching a liquid crystal layer between a pair of transparent substrates having pixels for forming electrodes on the inner surface. A backlight, and the backlight is installed with a diffusion plate having an illumination surface for irradiating diffused light on the back surface of the liquid crystal display panel, and arranged in parallel facing the back surface of the diffusion plate. A plurality of cold cathode fluorescent lamps that irradiate the back surface of the light source light and a plurality of cold cathode fluorescent lamps facing the back surface of the plurality of cold cathode fluorescent lamps, and the light source light irradiated from the plurality of cold cathode fluorescent lamps on the back surface of the diffusion plate A plurality of cold cathode fluorescent lamps, the first cold cathode fluorescent lamp and the second cold cathode fluorescent lamp having substantially the same tube length are reflected corresponding to the central portion of the display screen of the liquid crystal display panel. In the center of the board The first cold cathode fluorescent lamp and the second cold cathode fluorescent lamp are arranged in the row direction and the column direction with a predetermined interval, and the arrangement interval in the column direction of the first cold cathode fluorescent lamp and the second cold cathode fluorescent lamp is a peripheral portion corresponding to the periphery of the display screen. It is characterized by being set smaller than the arrangement interval.

  In the liquid crystal display device according to the present invention, preferably, in the above configuration, a reflector having a convex cross section toward the diffusion plate along the arrangement direction of the intervals is provided on the inner surface corresponding to the central portion of the reflection plate. It is characterized by being.

  In the liquid crystal display device according to the present invention, preferably, in the above configuration, a reflector having a concave cross section toward the diffusion plate along the arrangement direction of the intervals is provided on the inner surface corresponding to the central portion of the reflection plate. It is characterized by having.

  In the liquid crystal display device according to the present invention, preferably, in the above configuration, the arrangement interval in the column direction of the first cold cathode fluorescent lamp and the second cold cathode fluorescent lamp is gradually increased from the central portion toward the peripheral portion. It is characterized by being installed.

  In the liquid crystal display device according to the present invention, preferably, the first cold cathode fluorescent lamp and the second cold cathode fluorescent lamp in the above-described configuration are arranged so that the end portions in the column direction of the first cold cathode fluorescent lamp and the lower side of the display screen are substantially parallel to each other. It is characterized by having.

  The present invention is not limited to the above-described configuration, and various modifications can be made without departing from the technical idea of the present invention.

  According to the liquid crystal display device of the present invention, the surface light source with high luminance uniformity is irradiated from the backlight using a plurality of cold cathode fluorescent lamps having a short tube length to the back surface of the liquid crystal display panel. It has extremely excellent effects such as a high luminance display image that is high and has no luminance unevenness.

  Hereinafter, specific embodiments of a liquid crystal display device having a backlight according to the present invention will be described in detail with reference to the drawings of the respective examples.

  FIG. 1 is a longitudinal sectional view of an essential part for explaining a configuration according to a first embodiment of a liquid crystal display device equipped with a backlight according to the present invention. In FIG. 1, reference numeral PNL is a liquid crystal display panel as a display panel configured by sandwiching a liquid crystal layer between a pair of translucent substrates each having an electrode for pixel formation on the inner surface. A liquid crystal layer is sandwiched between the first substrate SUB1 and the second substrate SUB2, and pixels are formed on both or one inner surface of the first substrate SUB1 and the second substrate SUB2 made of a light-transmitting glass plate. It has electrodes for formation or active elements. Note that the first substrate SUB1 on which an active element such as a thin film transistor (TFT) is formed is also referred to as an active matrix substrate, and a substrate using a thin film transistor is also referred to as a TFT substrate.

  In addition, the first polarizing plate POL1 is laminated on the first main surface (backlight side), and the second polarizing plate POL2 is laminated on the second main surface (display surface side). Has been. Further, an optical compensation sheet laminate OPS is installed on the back side of the liquid crystal display panel PNL. The optical compensation sheet laminate OPS is a first from the side facing the diffusion plate DEP of the backlight BL described later. The diffusion sheet DF1, the first prism sheet PRZ1, the second prism sheet PRZ2, and the second diffusion sheet DF2 are laminated in this order, for example.

  In addition, a direct backlight BL is disposed on the back side of the optical compensation sheet laminate OPS so as to be opposed thereto. The backlight BL has a cold-cathode fluorescent lamp CFL1 having a long tube length and a cold-cathode having a short tube length inside a reflector REF made of a molded body of, for example, an acrylic or polycarbonate white resin material whose inner wall surface is mirror-finished. Fluorescent lamps CFL2 are alternately arranged in parallel. Further, a diffusion plate DEP having an illumination surface for diffusing light source light on the liquid crystal display panel PNL side is disposed at the upper opening end of the reflection plate REF so as to face the plurality of cold cathode fluorescent lamps CFL.

  In such a configuration, a plurality of cold cathode fluorescent lamps CFL in which a cold cathode fluorescent lamp CFL1 having a long tube length and a cold cathode fluorescent lamp CFL2 having a short tube length are alternately arranged in parallel are arranged inside the reflector REF. 2 shows a first cold cathode fluorescent lamp CFL1 having a long tube length in the row direction and a second tube length shorter than that of the first cold cathode fluorescent lamp CFL, as shown in a plan view seen from above the backlight BL in FIG. The cold cathode fluorescent lamps CFL2 are combined in series with a predetermined interval D and arranged in the row direction and arranged in parallel in the column direction, and the first cold cathode fluorescent lamps are arranged in the column direction. It is installed so as to be within the range of the tube length of the lamp CFL.

  The backlight configured as described above is provided with a cold cathode fluorescent lamp CFL1 having a long tube length and a cold cathode fluorescent lamp CFL2 having a short tube length arranged alternately in parallel in the column direction. Without using fluorescent lamps and without increasing the number of cold cathode fluorescent lamps, the luminance is improved over the entire illumination surface, luminance reduction is corrected, and planar light source light with high luminance uniformity can be obtained. .

  In addition, the liquid crystal display device configured as described above can obtain diffused light having high luminance uniformity over the entire surface of the diffusion plate DEP corresponding to the display screen, so that the luminance uniformity is provided on the back surface of the liquid crystal display panel PNL. Since high planar light source light is irradiated, a high-luminance display image with high color reproducibility and no luminance unevenness can be obtained.

  FIG. 3 is a plan view of a main part for explaining another configuration of the backlight according to the second embodiment of the liquid crystal display device equipped with the backlight according to the present invention. The same parts as those shown in FIG. The description is omitted. 3 is different from FIG. 2 in that the plurality of cold cathode fluorescent lamps CFL includes a first cold cathode fluorescent lamp CFL3 and a second cold cathode fluorescent lamp CFL, which have substantially the same tube length, in the display screen of the liquid crystal display panel. The first cold cathode fluorescent lamp CFL4 and the second cold cathode fluorescent lamp CFL4 are arranged in the row direction and the column direction with a predetermined interval d at the center portion of the reflector REF corresponding to the center portion. The arrangement interval is set to be smaller than the arrangement interval of the peripheral portion corresponding to the periphery of the display screen in the central portion.

  In the liquid crystal display device configured in this way, the first cold cathode fluorescent lamp CFL3 and the second cold cathode fluorescent lamp CFL4 are arranged radially from the central part to the peripheral part of the reflector REF. Therefore, the diffused light having high luminance uniformity over the entire surface of the diffusion plate DEP corresponding to the display screen using the first cold cathode fluorescent lamp CFL3 and the second cold cathode fluorescent lamp CFL4 having a short tube length. Since the planar light source light with high luminance uniformity is irradiated on the back surface of the liquid crystal display panel, a high luminance display image with high color reproducibility and no luminance unevenness can be obtained.

  FIG. 4 is a plan view of a principal part for explaining another configuration of the backlight according to the third embodiment of the liquid crystal display device equipped with the backlight according to the present invention. The same parts as those shown in FIG. The description is omitted. 4 differs from FIG. 3 in that the first cold-cathode fluorescent lamp CFL3 and the second cold-cathode fluorescent lamp CFL4 have a distance d substantially parallel to the lower side of the display screen at the extreme ends in the column direction. It is installed in a straight line.

  In the liquid crystal display device configured as described above, the first cold-cathode fluorescent lamp CFL3 and the second cold-cathode fluorescent lamp CFL4 are linearly arranged in the row direction at the extreme end in the column direction. In addition to the function and effect of Example 2, the brightness of display positions such as subtitles and telops displayed on the display screen can be made uniform.

  FIG. 5 is a cross-sectional view of an essential part for explaining another configuration according to the fourth embodiment of the liquid crystal display device equipped with the backlight according to the present invention, and FIG. 6 is a plan view seen from above the backlight BL in FIG. The same parts as those in the above-mentioned figure are denoted by the same reference numerals, and the description thereof is omitted. 5 and 6, the difference from FIG. 3 is that the distance d between the first cold cathode fluorescent lamp CFL3 and the second cold cathode fluorescent lamp CFL4 is provided on the inner surface corresponding to the central portion of the reflector REF. A reflector REM1 having a convex cross section toward the diffusion plate DEF along the arrangement direction is integrally installed. The reflector REM1 can be integrally formed by a drawing process of the reflector REF.

  In the liquid crystal display device configured as described above, a part of the light condensed on the central portion of the reflector REF is diffused by the reflector REM1, and the first cold cathode fluorescent lamp CFL3 and the second cold cathode fluorescent lamp CFL4. Since the brightness change at the portion where the brightness difference occurs at the joint portion is suppressed and the brightness at the center portion is improved, the first cold cathode fluorescent lamp CFL3 and the second cold cathode fluorescent lamp CFL4 having a short tube length are provided. The diffused light with high luminance uniformity is obtained on the entire surface of the diffusion plate DEP corresponding to the display screen, and the surface light source light with high luminance uniformity is irradiated on the back surface of the liquid crystal display panel PNL. A high-luminance display image with high performance and no luminance unevenness can be obtained.

  FIG. 7 is a cross-sectional view of an essential part for explaining another configuration according to the fifth embodiment of the liquid crystal display device equipped with the backlight according to the present invention, and FIG. 8 is a plan view seen from above the backlight BL of FIG. The same parts as those in the above-mentioned figure are denoted by the same reference numerals, and the description thereof is omitted. 7 and 8 are different from FIGS. 5 and 6 in that the first cold cathode fluorescent lamp CFL3 and the second cold cathode fluorescent lamp CFL4 are disposed on the inner surface corresponding to the central portion of the reflector REF. A reflector REM2 having a concave cross section toward the diffusion plate DEF along the arrangement direction of the distance d is integrally installed. The reflector REM2 can be integrally formed by a press forming method of the reflector REF.

  The liquid crystal display device configured as described above is provided with a reflector REM2 having a concave cross section between the first cold cathode fluorescent lamp CFL3 and the second cold cathode fluorescent lamp CFL4 arranged in the column direction. A part of the light condensed on the central portion of the plate REF is diffused by the reflector REM2, and a sudden change in luminance at the joint portion between the first cold cathode fluorescent lamp CFL3 and the second cold cathode fluorescent lamp CFL4 is suppressed. Therefore, the diffused light having high luminance uniformity over the entire surface of the diffusion plate DEP corresponding to the display screen using the first cold cathode fluorescent lamp CFL3 and the second cold cathode fluorescent lamp CFL4 having a short tube length. Since the planar light source light with high luminance uniformity is irradiated on the back surface of the liquid crystal display panel PNL, a high luminance display image with high color reproducibility and no luminance unevenness can be obtained.

  In the first embodiment described above, the liquid crystal display device configured by interposing the optical compensation sheet laminate OPS between the liquid crystal display panel PNL and the backlight BL has been described, but the present invention is not limited to this. However, the present invention can be applied to a liquid crystal display device including the liquid crystal display panel PNL and the backlight BL.

  In the above-described embodiment, the case where the cold cathode fluorescent lamp direct type backlight device is applied to a liquid crystal television receiver mounted with a liquid crystal display panel has been described. However, a large-sized liquid crystal monitor using the backlight device having the above configuration, The same effects as described above can be obtained even when applied to display devices such as in-vehicle liquid crystal displays (liquid crystal car navigation), mobile phone displays, game machine liquid crystal displays, medical liquid crystal monitors, and printing / design liquid crystal monitors.

It is a principal part longitudinal cross-sectional view explaining the structure by Example 1 of the liquid crystal display device carrying the backlight by this invention. It is the top view seen from the upper direction of the backlight shown in FIG. It is a principal part top view which shows the other structure of the backlight by Example 2 of the liquid crystal display device by this invention. It is a principal part top view which shows the other structure of the backlight by Example 3 of the liquid crystal display device by this invention. It is principal part sectional drawing which shows the other structure by Example 4 of the liquid crystal display device by this invention. It is the top view seen from the upper direction of the backlight shown in FIG. It is principal part sectional drawing which shows the other structure by Example 5 of the liquid crystal display device by this invention. It is the top view seen from the upper direction of the backlight shown in FIG.

Explanation of symbols

PNL ... liquid crystal display panel, SUB1 ... first substrate, SUB2 ... second substrate, POL1 ... first polarizing plate, POL2 ... second polarizing plate, OPS ... Optical compensation sheet laminate, DF1... First diffusion sheet, DF2... Second diffusion sheet, PRZ1... First prism sheet, PRZ2. Backlight, REF ... reflector, CFL ... cold cathode fluorescent lamp, CFL1 ... cold cathode fluorescent lamp, CFL2 ... cold cathode fluorescent lamp, CFL3 ... cold cathode fluorescent lamp, CFL4 ... Cold cathode fluorescent lamp, DEP ... diffusion plate, REM1 ... reflector, REM2 ... reflector.

Claims (6)

A liquid crystal display panel configured by sandwiching a liquid crystal layer between a pair of transparent substrates having electrodes for pixel formation on the inner surface;
A backlight installed on the back of the liquid crystal display panel;
A liquid crystal display device comprising:
The backlight includes a diffusing plate having an illumination surface that irradiates the back surface of the liquid crystal display panel with diffused light;
A plurality of cold-cathode fluorescent lamps that are arranged in parallel facing the back surface of the diffusion plate, and irradiate the back surface of the diffusion plate with light source light;
A reflector that is installed opposite to the back of the plurality of cold cathode fluorescent lamps and reflects the light source light emitted from the plurality of cold cathode fluorescent lamps to the back of the diffuser;
With
In the plurality of cold cathode fluorescent lamps, a first cold cathode fluorescent lamp having a long tube length and a second cold cathode fluorescent lamp having a tube length shorter than that of the first cold cathode fluorescent lamp are provided at a predetermined interval. A liquid crystal display device, wherein the liquid crystal display device is arranged alternately in parallel in a direction and a column direction, and the interval exists within a range of a tube length of the first cold cathode fluorescent lamp in the column direction. A liquid crystal display panel configured by sandwiching a liquid crystal layer between a pair of transparent substrates having electrodes for pixel formation on the inner surface;
A backlight installed on the back of the liquid crystal display panel;
A liquid crystal display device comprising:
The backlight includes a diffusing plate having an illumination surface that irradiates the back surface of the liquid crystal display panel with diffused light;
A plurality of cold-cathode fluorescent lamps that are arranged in parallel facing the back surface of the diffusion plate, and irradiate the back surface of the diffusion plate with light source light;
A reflector that is installed opposite to the back of the plurality of cold cathode fluorescent lamps and reflects the light source light emitted from the plurality of cold cathode fluorescent lamps to the back of the diffuser;
With
The plurality of cold cathode fluorescent lamps include a first cold cathode fluorescent lamp and a second cold cathode fluorescent lamp having substantially the same tube length in a central portion of the reflecting plate corresponding to a central portion of the display screen of the liquid crystal display panel. The first cold cathode fluorescent lamp and the second cold cathode fluorescent lamp are arranged in the row direction and the column direction with a predetermined interval, and the arrangement interval in the column direction of the first cold cathode fluorescent lamp and the second cold cathode fluorescent lamp corresponds to the periphery of the display screen. A liquid crystal display device, wherein the liquid crystal display device is installed smaller than the arrangement interval of the peripheral portions.   The reflector having a convex cross section toward the diffuser plate is disposed along the arrangement direction of the intervals on an inner surface corresponding to the central portion of the reflector plate. Liquid crystal display device.   3. The reflector having a concave cross section toward the diffuser plate along the arrangement direction of the intervals is disposed on an inner surface corresponding to the central portion of the reflector plate. Liquid crystal display device.   The arrangement interval of the first cold cathode fluorescent lamp and the second cold cathode fluorescent lamp in the column direction is gradually increased from the central portion toward the peripheral portion, and is installed. Item 5. A liquid crystal display device according to any one of Items 4 to 5. 6. The column-endmost ends of the first cold cathode fluorescent lamp and the second cold cathode fluorescent lamp are disposed substantially parallel to the lower side of the display screen. A liquid crystal display device according to any one of the above.

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