JPH09311331A - Color liquid crystal display - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a color liquid crystal display device in which the range of displayed colors is wide and which is of bright by specifying the product between the anisotropy of the refractive index of liquid crystal and the thickness of a liquid crystal layer as a liquid crystal element and using the optimum combination of a color filter, a polarizing plate, a back light and the liquid crystal element. SOLUTION: This device is constituted of a liquid crystal element 3 which is provided with a color filter 1 and a polarizing plate 2 and which is to become an optical shutter and a back light 4. Then, a liquid crystal element in which the product >=.d between the difference between the refractive index of the long axial direction and the refractive index of the short axial direction of a liquid crystal molecular, that is, the anisotropy >=n of the refractive index of liquid crystal and the thickness (d) of the liquid crystal layer is 0.45-0.70 is used. Moreover, a color filter in which stimulating purities are thought important or a color filter in which stimulating purities and brightnesses are balanced is used as the color filter 1 and plural number of three wavelength type lights are used as light sources of the back light 4. Moreover, it is desirable for the color filter 3 that peak values of transmissivities in the wavelength area of 450-650nm of respective color elements of green, blue and red are large in the order of green, blue and red.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color liquid crystal display device having a color filter having wavelength selective transmittance in the visible light wavelength range and a backlight.

[0002]

2. Description of the Related Art A conventional color liquid crystal display device is disclosed in Japanese Patent Laid-Open No.
-210481, JP-A-59-208577, etc., using a three-wavelength light-emitting fluorescent lamp as a light source;
Each color element of the color filter and the peak characteristic of the spectral distribution of the light source are matched, and the half width of the light source is made smaller than the half width of each color element of the color filter. However, no consideration is given to the combination of the optimal spectral distribution of the backlight, the spectral transmittance of the liquid crystal element including the polarizing plate, and the spectral transmittance of the color filter.

A conventional device uses the three-wavelength light source described in the above two cases as a backlight and combines a color filter with a three-wavelength light source. Is greatly dependent on the spectral transmittance of the polarizing plate and the liquid crystal other than the color filter and the backlight.

Here, the term "liquid crystal which affects color reproducibility" refers to the difference between the refractive index in the major axis direction and the minor axis direction of the liquid crystal molecules, that is, the refractive index anisotropy of the liquid crystal and the thickness of the liquid crystal layer. The relationship is

[0005]

In order to achieve a wide color display range and a bright display in a color liquid crystal display, it is necessary to optimize a liquid crystal element including a polarizing plate in addition to a color filter and a backlight. This is an important issue.

[0006] Also, in the combination of a color filter and a backlight, in the above two conventional devices, only the combination of the backlight having a spectral characteristic in which the half width of the backlight is smaller than the half width of each color element of the color filter is obtained. When a bright color filter is used, even if a backlight having a spectral distribution with a half width smaller than the half width of the color filter is used, color mixing is likely to occur because the spectral transmittance characteristic of the color filter is not sharp. And the color reproducibility decreases.

[0007] In a color liquid crystal display, it is desired that a color specification range is wide and bright even in a backlight with low power consumption.

The object of the present invention is to provide a color filter, a polarizing plate,
An object of the present invention is to provide a bright color liquid crystal display having a wide color specification range in a combination of a backlight and a liquid crystal element.

[0009]

According to the present invention, in a color liquid crystal display including a color filter, a polarizing plate, a backlight and a liquid crystal element, each component and color reproducibility,
In particular, by clarifying the relationship between colorimetric range, stimulus purity and brightness by experiments and finding the optimum combination of color filter, polarizing plate, backlight and liquid crystal element,
Provided is a bright color liquid crystal display having a wide color range.

As a liquid crystal element, the refractive index anisotropy Δ of the liquid crystal is
The product Δn · d of n and the thickness d of the liquid crystal is 0.45 to 0.70.

As the color filter, a filter in which importance is attached to stimulation purity or a filter in which stimulation purity and brightness are balanced is used.

As the light source, a plurality of three-wavelength lights are used.

As shown in FIG. 1, a color liquid crystal display device capable of displaying a full color is composed of a liquid crystal element 3 which is an optical shutter provided with a polarizing plate 2 of a color filter 1 and a backlight 4.

FIG. 1A shows a case in which a liquid crystal element 3 serving as an optical shutter is of a TN (twisted, nematic) type, and in many cases, a color filter 1 and a liquid crystal element 3 are sandwiched between two polarizing plates 2. However, it goes without saying that the color filter 1 can be provided outside the polarizing plate 2. Also, the light source 4
A configuration in which the color filter 1 is provided on the diffusion plate described above is also possible.

When the liquid crystal element 3 shown in FIG. 1A is of the TN type, there is a disadvantage that the brightness and the hue change depending on the viewing direction.

FIG. 1B shows an optical shutter. The liquid crystal element 3 is a GH (guest, host) type, and generally includes a color filter, a single polarizing plate 2, a liquid crystal element 3, and a backlight 4.

When the GH type liquid crystal element is used, the dependence on the viewing angle that the brightness and the hue change from the viewing direction is small, but there is a drawback that it is dark.

Therefore, the liquid crystal element 3 is set to TN depending on the application.
It should be decided whether it is a type or a GH type. Generally, a TN type liquid crystal element 3 is used for those not displaying gradation and a GN type liquid crystal element 3 is used for those displaying gradation. There are many examples.

FIG. 1 shows only a transmission type configuration in which the light source 4 is disposed on the back side of the liquid crystal element 3 serving as an optical shutter, but a reflection type configuration in which the light source 4 is disposed in front of the liquid crystal element 3 serving as an optical shutter is also shown. Of course it is possible.

However, actually, in the case of the reflection type,
Since it is dark and the stimulus purity is low, there are generally many transmission types.

As shown in FIG. 2, when the color filter 1 and the liquid crystal element 3 serving as an optical shutter are additively mixed, the color filter disperses red (R), green (G), and blue (B) in a plane. Are arranged as follows.

FIG. 1 shows only the case of additive color mixture, but of course subtractive color mixture is also possible. In that case, the configuration is such that cyan, yellow, and magenta are superposed.

In any case of additive color mixture and subtractive color mixture, by combining a backlight having a light emission peak at a wavelength corresponding to each color element and a color filter, high brightness and stimulus purity and excellent color reproducibility are obtained. Aiming to realize a color liquid crystal display.

As described above, the use of a backlight having an emission peak at a wavelength corresponding to each color element has the advantage that the range of colors that can be displayed is not largely affected by the performance of the color filter, and the sharp characteristic of the emission peak is obtained. The development of a three-wavelength fluorescent tube with is being advanced in each direction.

FIG. 3 shows red (R) and green color filters.
The CIE chromaticity diagram shows the colorimetric range of a system combined with a backlight having an emission peak at a wavelength corresponding to each of (G) and blue (B) color elements.

In FIG. 2, the color range of the color liquid crystal display is indicated by a solid line, and the color range of the CRT is indicated by a broken line. None have perfect color reproduction. In particular, a color liquid crystal display device cannot reproduce a color with high stimulus purity because of the use of dye absorption, and has a narrow color specification range.

The present invention has been made in view of these drawbacks, and has emission peaks at wavelengths corresponding to red (R), green (G) and blue (B). Optimized by combining the backlight and the color filter, as well as the interference color due to the birefringence of the TN type liquid crystal element and the color of the polarizer, to provide a bright, high stimulus purity, and excellent color reproducibility color liquid crystal display. Is what you do.

[0028]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the drawings. First, FIG. 4 shows a color filter used in an experiment for finding the present invention. As shown in the figure, a color element of 120 μm square arranged in dots at a pitch of 125 μm was used.

In order to clarify the effect on the color range and brightness of the color filter, three types of stimulus purity priority type, stimulus purity, brightness balance type and brightness priority type were used. FIG. 5 shows the spectral transmittance of the color filter. FIG. 3A shows the spectral transmittance of a color filter emphasizing stimulus purity, FIG. 2B shows the spectral transmittance of a color filter in which stimulus purity and brightness are balanced, and FIG. 2C shows the spectrum of a color filter emphasizing brightness. The transmittance.

As shown in the figure, the spectral characteristics of the color filter emphasizing the stimulus purity are lower than the spectral characteristics of the color filter emphasizing the brightness. The rate is also low. On the other hand, a color filter emphasizing brightness has a high transmittance for each color element.
However, it can be seen that the transmittance of the portion to be shielded is also high.

In order to clarify the relationship between the spectral transmittance and the color range and brightness of a polarizing plate, experiments were conducted on commercially available neutral and blue polarizers. As shown in FIG. The polarizing plate shown in the figure has a relatively small wavelength-dependent spectral transmittance. In the figure, 1 is the characteristic of the polarizing plate alone, and 2 is
Is a so-called open state characteristic in which the transmission axes are matched by two polarizing plates, and 3 is a so-called closed state characteristic in which the transmission axes are orthogonalized by two polarizing plates. In any of the cases 1, 2, and 3, the transmittance is high in the long wavelength region.

Next, FIG. 7 shows the spectral distribution of the backlight used in the experiment. FIG. 1A shows a photographic light source having a spectral distribution having relatively small wavelength dependence, and FIG. 2B shows a three-wavelength planar light source having an emission peak in a wavelength region of each color element of a color filter.

The liquid crystal element used was a TN liquid crystal. FIG. 8 shows a configuration including the liquid crystal element used in an experiment of a color liquid crystal display.

As shown in FIG. 1, the color filter 1, the polarizing plate 2, the liquid crystal element 3, and the backlight 4 were provided.

FIG. 9 shows an optical system for measuring the color specification range and brightness. As shown in the figure, the optical measuring system was composed of a color filter 1, a polarizing plate 2, a liquid crystal element 3, a backlight 4, and a spectral radiation measuring device 5.

First, the color specification range of each color filter in the combination of the color filter and the backlight is shown in FIG.
Shown in FIG. 1A shows a combination of a photographic light source and a color filter, which is a color filter 1 that emphasizes stimulus purity, a color filter 2 that balances stimulus purity and brightness, and a color filter 3 that emphasizes brightness. ) Is a combination of a three wavelength type flat light source and a color filter.

As can be seen from the figure, there is no significant difference in the color specification range between any combination of the color filter, the photographic source, the three-wavelength type planar light source, and the like. However, the change in hue between the color filters is smaller in the combination with the three-wavelength type flat light source than in the combination with the photographic light source.

FIG. 11 shows the relationship between the stimulus purity and the transmittance in the combination of the color filter and the backlight. FIG. 3A shows a combination with a photographic light source, and FIG. 3B shows a combination with a three-wavelength planar light source.

In the figure, 1 is a color filter emphasizing stimulus purity, 2 is a color filter that balances stimulus purity and brightness, and 3 is a characteristic of a color filter emphasizing brightness.

As can be seen from the figure, when compared with the combination with the photographic light source, the combination with the three-wavelength type planar light source is superior in both the stimulus purity and the transmittance, and is a color filter with emphasis on brightness. Appearing noticeably.

Next, FIG. 12 shows a change in color temperature in a combination of a polarizing plate and a backlight. In the figure,
An open state in which the transmission axes of the photographic light source 1 and the three-wavelength planar light source 2 are matched with one polarizing plate and two polarizing plates.
The decrease in the color temperature to a closed state in which the transmission axes are orthogonal to each other becomes large. Also, as can be seen from the figure, the decrease in color temperature is smaller when the three-wavelength flat light source is combined than when the photographic light source and the polarizing plate are combined.

Next, FIG. 13 shows the relationship between the stimulus purity and the transmittance in a combination of a color filter, a polarizing plate, and a backlight. FIG. 3A shows a case where a photographic light source is used as a backlight, and FIG. 3B shows a case where a three-wavelength planar light source is used as a backlight.

As can be seen from the figure, the stimulus purity and transmittance are higher when a three-wavelength planar light source is used than when a photographic light source is used for the backlight.

From the above examination results, the three-wavelength type of the spectral distribution having a light emission peak in the wavelength region of each color element of the color filter is compared with the light source having the spectral distribution with small wavelength dependence as the backlight of the color liquid crystal display. It was confirmed that the light source was excellent in color reproducibility.

Next, since it was confirmed that the three-wavelength planar light source of the backlight was excellent in color reproducibility, the influence of the polarizing plate on the color reproducibility was examined. First, FIG. 14 shows the relationship between stimulus purity and transmittance in commercially available neutral polarizing plates and blue polarizing plates.

FIG. 4A shows a blue polarizing plate, and FIG. 4B shows a neutral polarizing plate. As can be seen from the figure, the neutral type polarizing plate has a higher stimulating purity than the blue type polarizing plate.

From the results of this study, it has become clear that the spectral transmittance of the polarizing plate is excellent in color reproducibility due to its spectral characteristics having small wavelength dependence.

Therefore, the relationship between the stimulus purity and the transmittance was examined using a polarizing plate having a spectral transmittance much smaller than the wavelength of a commercially available polarizing plate.

FIG. 15 shows the spectral transmittance of the polarizing plate used in this experiment. As shown in the figure, it has a spectral transmittance with small wavelength dependence.

FIG. 16 shows the relationship between the stimulus purity and the transmittance using this polarizing plate. As shown in the figure, compared to the stimulus purity when the color filter and the three-wavelength type planar light source are combined, it is clear that the combination of a polarizing plate having a small wavelength-dependent spectral transmittance does not lower the stimulus purity. Became.

FIG. 17 shows a change in color temperature when a backlight of a three-wavelength light source and a polarizing plate having a spectral transmittance with small wavelength dependence are combined. As shown in the figure, even when the open state in which the transmission axes are matched by one polarizing plate and two polarizing plates, and the closed state in which the transmission axes are orthogonal by two polarizing plates are combined with the polarizing plate, the color temperature can be maintained. Hardly drops.

As described above, a color liquid crystal display having excellent color reproducibility cannot be achieved by using only a color filter and a backlight, and a polarizing plate is a major factor affecting color reproducibility.

Next, FIG. 18 shows the color temperature and the transmittance temperature in a combination of a color filter, a polarizing plate, a liquid crystal element, and a backlight including a TN liquid crystal element. The color filter used in this experiment emphasized the stimulation purity, the polarizing plate was a neutral neutral commercially available product, the liquid crystal was the difference Δn = 0.123 between the refractive index in the major axis direction and the minor axis direction, and the thickness of the liquid crystal layer was 6
μm, 7 μm, 8 μm, and 10 μm.

As shown in the figure, 1 is a color filter,
A combination of a polarizing plate and a backlight; 2 to 5, a combination of a color filter, a polarizing plate, a liquid crystal element, and a backlight; 2, a liquid crystal layer thickness d = 6 μm; 3, a d = 7 μm;
Is a characteristic of d = 8 μm, and 5 is a characteristic of d = 10 μm.

As can be seen from the figure, the color temperature changes greatly depending on the thickness of the liquid crystal layer. Therefore, a color liquid crystal display having excellent color reproducibility cannot be achieved unless these four components are optimized such as a color filter, a polarizing plate, a liquid crystal element, and a backlight. Therefore, the liquid crystal element must optimize the refractive index anisotropy Δn of the liquid crystal and the thickness d of the liquid crystal layer. The relationship between the transmittance T of the liquid crystal element, the refractive index anisotropy Δn of the liquid crystal, and the thickness d of the liquid crystal layer can be expressed by the following equation.

[0056]

[Equation 1]

FIG. 19 shows an example of the relationship between the transmittance T and Δn, where d = 10 μm and λ = 550 nm. In the figure, Δ at which the initial transmittance T is minimized
The combination of n and d has wide viewing angle dependence and high contrast.

Since the spectral transmittance of the liquid crystal element affects the stimulus purity, the combination of Δn and d must be such that the spectral transmittance has as small a wavelength dependence as possible.

FIG. 20 shows an example of the relationship between the wavelength and the transmittance of the liquid crystal element. In the figure, the refractive index anisotropy Δn = 0.062
And the thickness of the liquid crystal layer d = 6 μm, 7 μm, 8 μm, 9 μm
m, 10 μm. As can be seen from the figure, the spectral transmittance greatly changes depending on the relationship between Δn and d.

In this experiment, the above-mentioned polarizing plate having a small wavelength dependence was used. However, if a commercially available polarizing plate is used, the change will be even larger.

Therefore, it is necessary to combine a polarizing plate and a liquid crystal element to obtain a spectral transmittance with small wavelength dependence. From this, the relationship between the refractive index anisotropy Δn of the liquid crystal element, the thickness d of the liquid crystal layer, and the stimulus purity was examined.

FIG. 21 shows the relationship between the product Δn · d of the refractive index anisotropy Δn of the liquid crystal element and the thickness d of the liquid crystal layer and the stimulation purity. As can be seen from the figure, the range between Δn · d = 0.45 and 0.70 is a range where there is almost no coloring.

Therefore, in the liquid crystal element, the product Δn · d of the refractive index anisotropy Δn of the liquid crystal and the thickness d of the liquid crystal layer is 0.45 to 0.4.
By setting it to 70, it becomes suitable for a color liquid crystal display.

As described above, in the combination of the color filter, the polarizing plate, the liquid crystal element and the backlight, a plurality of three wavelength type light sources are used for the backlight so that there is no spectral distribution other than the spectral transmittance characteristics of each color element of the color filter. . As the color filter, a filter that emphasizes stimulation purity or a filter that balances stimulation purity and brightness is used. In the liquid crystal element, the product Δn · d of the difference Δn between the refractive index in the major axis direction and the refractive index in the minor axis direction of the liquid crystal molecule and the thickness d of the liquid crystal layer is 0.45 to 0.70.
Range. By combining these components, a bright color liquid crystal display having a wide color range can be achieved.

[0065]

According to the present invention, there is an effect that a bright color liquid crystal display having a wide color range can be achieved.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing components of a color liquid crystal display for explaining the present invention.

FIG. 2 is a perspective view showing a general example of a color filter.

FIG. 3 is an explanatory diagram showing a color specification range of a CRT and a color LCD.

FIG. 4 is a configuration diagram of a color filter used to find the present invention.

FIG. 5 is an explanatory diagram showing a spectral transmittance of the color filter.

FIG. 6 is a diagram showing the spectral transmittance of a polarizing plate used to find the present invention.

FIG. 7 is a spectral distribution diagram of a backlight used to find the present invention.

FIG. 8 is a block diagram of the components used to find the present invention.

FIG. 9 is an explanatory diagram showing an optical measurement system.

FIG. 10 is an explanatory diagram showing a color specification range in a combination of a color filter and a backlight.

FIG. 11 is a diagram showing the relationship between stimulus purity and transmittance in a combination of a color filter and a backlight.

FIG. 12 is an explanatory diagram showing a color temperature change in a combination of a polarizing plate and a backlight.

FIG. 13 is a diagram showing a relationship between stimulus purity and transmittance in a combination of a color filter, a polarizing plate, and a backlight.

FIG. 14 is a diagram showing the relationship between the stimulus purity and transmittance of a blue polarizing plate and a neutral polarizing plate.

FIG. 15 is a diagram showing the spectral transmittance of the polarizing plate of the present invention.

FIG. 16 is a diagram showing the relationship between stimulus purity and transmittance when this polarizing plate is used.

FIG. 17 is an explanatory diagram showing a color temperature change when this polarizing plate is used.

FIG. 18 is an explanatory diagram illustrating a color temperature change due to a difference in Δn · d of the liquid crystal element.

FIG. 19 is a relationship diagram of Δn and transmittance of a TN liquid crystal element.

FIG. 20 is an explanatory diagram showing Δn · d and spectral transmittance of a liquid crystal element.

FIG. 21 shows Δn · d of a liquid crystal element which is a point of the present invention.
FIG. 4 is a diagram illustrating the relationship between product and stimulus purity.

[Explanation of symbols]

1 ... Color filter, 2 ... Polarizing plate, 3 ... Liquid crystal element, 4 ...
Backlight, 5 ... Spectral emission measurement device.

Claims (4)

[Claims] 1. A liquid crystal molecule comprising a pair of substrates arranged at a predetermined interval and provided with electrodes on opposite surfaces thereof, and a liquid crystal layer of a predetermined thickness sandwiched between the pair of substrates. A liquid crystal element having a product Δn · d of the difference Δn between the refractive index in the axial direction and the refractive index in the minor axis direction and the thickness d of the liquid crystal layer is 0.45 to 0.70, and one of the pair of substrates. Three types of color filters provided on the substrate and having different color elements, a pair of polarizing plates provided on opposite sides of the liquid crystal layer of the pair of substrates, and color elements of the three types of color filters. A three-wavelength type light source having a spectral distribution having an emission peak in a corresponding wavelength region, wherein the color filter uses a stimulus purity-oriented one or a stimulus purity and brightness balance, Is one of the pair of polarizing plates Serial color liquid crystal display device which comprises using a plurality of three-wavelength type of light positioned on the opposite side of the liquid crystal layer. 2. The color filter according to claim 1, wherein the peak value of the transmittance of each color element of green, blue and red in the wavelength region of 450 nm to 650 nm is larger in the order of green, blue and red. Color liquid crystal display device. 3. The color liquid crystal display device according to claim 2, wherein the transmittance of each color element of the color filter in the light-shielding wavelength region is approximately 5% or less. 4. A color liquid crystal display device according to claim 1, wherein the liquid crystal constituting the liquid crystal layer is a twisted nematic liquid crystal.