Next, with reference to
With reference to
As shown in
As shown in
Next, as shown in
In this embodiment, although the color filters were formed by photolithography, the present invention is not limited to the photolithography. In short, the color filters may be formed by other methods such as an ink jet method, a printing method and a transfer method so long as these methods can control the spectral characteristics of the color filters.
For color filter pigment, C. I. Pigment Blue 15:6 and complementary color pigment C. I. Pigment Violet 23 were used for blue. C. I. Pigment Red 254 and complementary color pigment C. I. Pigment Yellow 139 were used for red. For green pigment, generally C. I. Pigment Green 36 (copper brome phthalocyanine green) or C. I. Pigment Green 7 (copper chloro phthalocyanine green) and complementary color pigment C. I. Pigment Yellow 150, C. I. Pigment Yellow 138 or the like are used. In this embodiment, the spectral characteristics can be controlled by adjusting the composition of pigment. By increasing the composition of complementary pigment slightly more than that of comparative examples, it is possible to set the half value wavelength on the longer wavelength side in a range from 590 nm to 600 nm. Although pigment is generally used nowadays, color filters may be made of dye if this coloring matter can control spectroscopy, and can ensure process stability and reliability.
Next, as shown in
Alignment films 22 and 23 made of a dense polyimide film of about 100 nm thick are formed on each of the TFT substrate and color filter substrate, by printing polyamic acid varnish thereon and performing heat treatment for 30 minutes at 210° C. The alignment films were subject to a rubbing process. The material of the alignment film of the embodiment is not particularly limited, but the material may be polyimide using 2,2-bis[4-(p-amino phenoxy) phenyl propane] as diamine, piromerit acid dianhydride as acid hydride, or polyimide using p-phenylene diamine, diaminodiphenyl methane or the like as an amine component, aliphatic tetra carbonic acid dianhydride, piromerit acid dianhydride as an acid anhydride component. Although the rubbing process is used in this embodiment, the process is not limited, but the alignment film may be formed by using photosensitive alignment film material and irradiating a polarized ultraviolet ray. An initial alignment state of liquid crystal, i.e., the alignment direction under no voltage application, was set to a direction of the scan electrode 34 shown in
Next, as shown in
The structure in a region sandwitched between the substrates with the polarizers is called a liquid crystal display panel 13, and the structure in a region of the liquid crystal display panel and a light source unit 14 is called a liquid crystal display apparatus or a liquid crystal display module 15.
The liquid crystal display panel of the embodiment is characterized in the spectral transmittance characteristics of the color filters.
As compared with the usually used filter (first comparative example), the green filter of the embodiment has a shape of the spectral waveform broadened toward the longer wavelength side. This spectrum waveform is represented by the wavelength at the half values as in the following.
The green filter of the embodiment has the maximum transmittance of 82% at a wavelength of 530 nm (indicated by a broken line in
In
In
It was confirmed from these results that the transmittance can be improved more than the conventional one and the color purity can be maintained in the range not influencing the visual perception characteristics, by utilizing the liquid crystal display panel structure of the embodiment. In order to realize both the improvement on the transmittance and the retention of the visual perception characteristics, the longer wavelength in the wavelengths at the half values of the maximum transmittance is set in the range from a minimum of 590 nm and a maximum of 610 nm in the spectral transmittance characteristics of the green color filter. In order to maintain the color purity higher, it is preferable to set in the range from a minimum of 590 nm to a maximum of 600 nm. The shorter wavelength in the wavelengths at the half values of the maximum transmittance is required to be set in the range from a minimum of 470 nm to a maximum of 500 nm, or more preferably in the range from a minimum of 480 nm to a maximum of 490 nm.
From another viewpoint, it is necessary that a transmittance at a wavelength of 600 nm of the green color filter is 40% or larger of the maximum transmittance.
The fine line in
In the second embodiment, a liquid crystal display module was manufactured by disposing a light source on the high transmittance liquid crystal display panel of the first embodiment. A cold cathode three-wavelength fluorescent lamp was used as the light source. For white display of the liquid crystal display module, the chromaticity of the back light unit was adjusted to obtain chromaticity coordinates u′v′ of (0.187, 0.437) by setting a color temperature to 11000 κ.
The fluorescent lamp of the back light unit of the second embodiment utilizes phosphors, BaMgAl10O17: Eu for blue, LaPO4: Tb, Ce for green, and Y2O3: Eu for red, which are used generally in this field. The embodiment is not limited to these materials if the wavelength at the emission center does not differ greatly. For example, in the case of blue phosphor, one or several phosphors may be mixedly used if the emission center is in the wavelength range of 450±15 nm. In the case of green phosphor, if the emission center is terbium (Tb), the chromaticity can be adjusted in the manner similar to this embodiment, because the main peak is near at 545 nm and the sub peaks are near at 490 nm, 590 nm and 625 nm on both sides of the main peak, being influenced hardly by the composition of source materials. Phosphor having the emission center in the wavelength range of 610±5 nm may be used as the red phosphor.
The cold cathode tube is manufactured by a commonly adopted method. Namely, one side of a washed glass tube is immersed in suspension formed by mixing binding agent such as alumina and various phosphors in organic solvent, to coat phosphors on an inner wall of the glass tube through the capillary phenomenon. The material of the glass tube is, for example, kovar glass, a tube diameter is 4 mm and a tube length is 720 mm for a diagonal of 32 inches. These glass tubes are baked to adhere the phosphors to the inner tube wall. Thereafter, metal electrodes are mounted and one side of the glass tube is sealed. Rare gas such as argon and neon is injected into the glass tube from the side opposite to the sealed side, and degassed to adjust a gas pressure. Further, after mercury is filled and the glass tube is sealed and turned up side down to be subjected to an aging process for a predetermined time. The completed cold cathode tubes are disposed flat on a housing 19 whose inner side is covered with reflective agent. In this embodiment, fourteen glass tubes are disposed for a diagonal 32-inch module. An inverter is connected to the cold cathode tube to turn on the tube, or turn on/off for a blink back light to conduct luminance control through trimming in accordance with an average image luminance and an ambient environment illuminance. In this embodiment, although the cold cathode tube is used, the embodiment is not limited to the cold cathode tube. For example, a hot cathode fluorescent lamp may be used which has filaments as metal electrodes, or an external electrode fluorescent lamp (EEFL) may be used whose electrodes are disposed at opposite ends of the tube and wired outside the tube. A diffusion plate 18 is disposed above the cold cathode tube, and a luminance improving film 17 and a diffusion sheet 16 are disposed.
The back light unit was disposed on the back surface of the liquid crystal display panel of the first embodiment to form the liquid crystal display module. A color temperature of white display was 11000 κ as designed, a luminance was 503 cd/m2, and a contrast ratio was 912. In order to compare with a second comparative example to be detailed hereunder, a white luminance of the liquid crystal display module was calculated through conversion of the luminance of the back light unit to 10000 cd/m2, and the calculated value is 578 cd/m2. Namely, if the back light has the same luminance, a luminance of the liquid crystal display module is improved by about 8% and the image quality is improved. Assuming that the while luminance of the liquid crystal display module is constant, a luminance of the back light necessary for obtaining a luminance of, e.g., 500 cd/m2 is 8660 cd/m2 which is improved by about 7%, resulting in a reduction in a consumption power. Whether the liquid crystal display of the embodiment is used as an improved luminance television or a reduced consumption power television is selected in accordance with needs.
It was confirmed from the above-described results that a module realizing both improving the transmittance and maintaining the visual perception characteristics more than a conventional case can be realized even when it is evaluated as a liquid crystal display module.
In the second comparative example, a back light unit made of a cold cathode tube using phosphors similar to those of the first embodiment was mounted on the liquid crystal display panel of the first comparative example. In order to set white display of the liquid crystal display module to 11000 κ, the phosphor composition was adjusted to set the chromaticity coordinates of the back light unit to (0.197, 0.395), and a luminance of 8900 cd/m2 was obtained for the back light unit.
A color temperature of white display of the liquid crystal display module of the comparative example was 11000 κ as designed, and a luminance was 477 cd/m2. In order to compare with the embodiment, a white luminance of the liquid crystal display module calculated through conversion of the luminance of the back light unit to 10000 cd/m2 is 536 cd/m2. It was evidenced that superiority of the high transmittance liquid crystal display panel of the embodiment is retained also for the liquid crystal display module. The chromaticity coordinates of blue, green and red are indicated by black triangles in
This embodiment is similar to the second embodiment except that a red peak in the spectral emission luminance of a light source is shifted to the longer wavelength side. Red phosphor of YVO4 : Eu is used for a cold cathode tube of the light source.
Chromaticity coordinates of the back light of this embodiment were (0.195, 0.387) and a luminance was 8530 cd/m2. The liquid crystal display panel of the first embodiment was used to assemble a liquid crystal display module. Evaluation of this liquid crystal display module showed that a color temperature of white display was 11000 κ and a corresponding luminance was 495 cd/m2. A white luminance of the liquid crystal display module calculated through conversion of the luminance of the back light unit to 10000 cd/m2 was 580 cd/m2, and the luminance efficiency had the advantage equal to that of the second embodiment.
Red chromaticity coordinates are (0.470, 0.514). This means that a color purity is improved more than the chromaticity coordinates (0.460, 0.517) of the second comparative example. If the color purity of red is improved, it is said that red display for the natural world, for example, display of petals of a rose, can be made beautiful. The liquid crystal display module of the embodiment becomes more effective for the improvement on a display quality. Obviously, if a red emission wavelength is shifted more toward the longer wavelength side, a depth of red color increases more and more. However, in this case, in this wavelength range, a spectral luminous efficacy of human being lowers, and it is disadvantageous in terms of a luminance efficiency. For example, as seen from the spectral luminous efficacy characteristics shown in
It has been found from these results that it is possible to improve the transmittance and the color purity, by broadening the range of the green color filter toward the longer wavelength side and shifting the peak wavelength of red of the light source toward the longer wavelength side.
When considering an efficiency and the like of phosphor, it is necessary to set the peak wavelength of red of the light source in a range from 620 nm to 650 nm. From the viewpoint of a transmittance of a color filter, it is necessary that the green color filter has a transmittance of 10% or lower of the maximum transmittance, at a peak wavelength of red of the light source.
This embodiment is similar to the first embodiment except that a transmission range of a red filter among color filters is shifted to the longer wavelength side.
The maximum spectral transmittance of a green filter is 82.5% at a wavelength of 534 nm, and the relative transmittance is 46% at a wavelength of 600 nm. A red filter has a relative transmittance of 9.9% at a wavelength of 590 nm relative to the maximum transmittance (90.6% at a wavelength of 676 nm) of the red filter. As compared with the spectra shown in
More specifically, it is necessary that the red color filter has a transmittance of 10% or lower of the maximum transmittance in a wavelength range from 580 nm to 590 nm.
In the fifth embodiment, the liquid crystal display panel of the fourth embodiment is used with a back light unit using phosphors similar to those of the second embodiment to form a liquid crystal display module. In order to set white display of the liquid crystal display module to 11000 κ, the chromaticity coordinates of the back light unit were set to (0.194, 0.384) and the luminance was set to 8680 cd/m2.
A luminance of white display of the liquid crystal display module was 503 cd/m2. A luminance of white display of the liquid crystal display module calculated through conversion of the luminance of the back light unit to 10000 cd/m2 is 586 cd/m2, and the luminance efficiency has improved.
In the sixth embodiment, the liquid crystal display panel of the forth embodiment is used with a back light unit using red phosphor of YVO4 : Eu similar to that of the third embodiment to form a liquid crystal display module.
The chromaticity coordinates of the back light unit were set to (0.194, 0.385) and the luminance was set to 8420 cd/m2.
A luminance of white display of the liquid crystal display module was 504 cd/m2. A luminance of white display of the liquid crystal display module calculated through conversion of the luminance of the back light unit to 10000 cd/m2 is 588 cd/m2, and the luminance efficiency has improved.
The light source of a back light unit is not limited to phosphors. For example, a light emitting diode, an organic EL or the like may be used, and the advantages similar to those of the present invention can be obtained by adjusting an emission wavelength. In short, the present invention is not limited to the type of a light source, and the important points to obtain the advantages of the present invention are as follows. For blue, an emission intensity is high in the wavelength range of 450 nm to 480 nm, or there is at least one emission peak in the range. For green, even a small emission exists in the range of 550 nm to 590 nm even if a main emission wavelength is near at 520 nm. For red, there is an emission at 611 nm or in a wavelength range of 620 nm to 650 nm.
In this embodiment, a liquid crystal display module of a patterned vertical alignment (PVA) mode shown in
An alkali-free glass substrate 32 having a thickness of 0.7 mm was used as a color filter substrate. A chrome film having a thickness of 160 nm and a chrome oxide film having a thickness of 40 nm were formed on the alkali-free glass substrate by continuous sputtering. A black matrix 44 was formed by coating positive type resist and performing processes of prebake, exposure, develop, etching, stripping and washing. Next, color filters 42 were formed by using color resist of blue, green and red, and by using commonly adopted photolithography involving the processes of coating, prebake, exposure, develop, rinse and postbake. In this embodiment, thicknesses of blue, green and red color filters were set to 3.0 μm, 2.7 μm and 2.5 μm, respectively. However, the thicknesses may be set properly according to a desired color purity or a liquid crystal layer thickness. The spectral characteristics are similar to those of the fourth embodiment.
An overcoat layer 43 made of V-259 manufactured by Nippon Steel Chemical Co., Ltd was formed. Exposure was performed by irradiating an i-line of a high pressure mercury lamp at a dose of 200 mJ/cm2, and then heating was performed for 30 minutes at 200° C. A film thickness was about 1.2 to 1.5 μm above each dot. Although the overcoat layer was formed on the color filter layer, the overcoat layer may not be formed, but ITO may be formed directly by sputtering.
Next, ITO was deposited in vacuum by sputtering to a thickness of 140 nm, crystallized by heating ITO for 90 minutes at 240° C., and was subject to photolithography and etching to form a pattern of a common electrode 33. Openings of the common electrode 33 sandwich the opening of a dot electrode 35 at an intermediate position. Next, post spacers 47 having a height of about 3.5 μm were formed on the black matrix between respective blue dots, by using photosensitive resin and by using commonly adopted photolithography and etching.
An alkali-free glass substrate 31 having a thickness of 0.7 mm was used as an active matrix substrate. A scan electrode (gate electrode) 34 made of molybdenum/aluminum (Mo/Al) was formed on the substrate. In the same layer as that of the scan electrode, a holding capacitor electrode (not shown) may be formed by using chrome and aluminum. A gate insulating film 37 is formed covering these components, and a signal electrode (drain electrode) 36, and a thin film transistor (not shown) were formed similar to the first embodiment. A protective insulating film 38 is formed covering these components. Dot electrodes 35 made of ITO and having an opening pattern were formed on the protective insulating film. Transparent conductor such as indium zinc oxide (IZO) may be used. In this manner, an active matrix substrate (diagonal 32-inch size) having 1366×3×768 dots was obtained being constituted of 1366×3 (corresponding to R, G and B) signal electrodes 36 and 768 scan electrodes 34.
Alignment films 22 and 23 were formed on the TFT substrate and color filter substrate. Liquid crystal material having a negative dielectric constant anisotropy was dropped by one drop filling (ODF) method, and a liquid crystal display panel was assembled. A transmittance of white display of the liquid crystal display panel was 4.4%.
Phase plates 49 and 50 for compensating visual angle characteristics caused by liquid crystal molecule orientation were disposed between upper and lower polarizers 11 and 12 and the substrates 31 and 32. A drive circuit was connected to complete the liquid crystal display panel.
A back light unit is similar to that of the third embodiment except that a diffusion sheet and a luminance improving film are disposed on a diffusion plate. The liquid crystal display module was formed by using this back light unit. Chromaticity coordinates were set to (0.200, 0.422) in order to set white display of the liquid crystal display module to 11000 κ. A luminance on the surface of the back light unit was 8000 cd/m2. Since the luminance improving film is used, a luminance of white display of the liquid crystal display module is improved by about 1.4 times.
A luminance of white display of the liquid crystal display module is 486 cd/m2 which can be understood that it is improved more than the following third comparative example.
In this embodiment, the liquid crystal display apparatus of a patterned vertical alignment (PVA) mode using an ITO notched pattern is used. If a multi domain vertical alignment (MVA) mode forming a projection on a color filter substrate is to be used, after ITO is formed, a projection forming process is executed and then the post spacer forming process is executed.
A liquid crystal display module similar to the seventh embodiment was manufactured by using color filters similar to those of the first comparative example. Phosphors of the back light unit are similar to those of the second embodiment. The chromaticity coordinates were (0.204, 0.432) and a surface luminance was 8000 cd/m2.
A color temperature of white display of the liquid crystal display module is 11000 κ and a luminance is 441 cd/m2. The chromaticity coordinates of green primary color display were (0.121, 0.563), and the chromaticity coordinates of red primary color display were (0.458, 0.517).
The present invention is applicable to all types of liquid crystal display apparatus.
It should be further understood by those skilled in the art that although the foregoing description has been made on embodiments of the invention, the invention is not limited thereto and various changes and modifications may be made without departing from the spirit of the invention and the scope of the appended claims.
Number | Date | Country | Kind |
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2006-266249 | Sep 2006 | JP | national |