JPH086009A - Color liquid crystal display element - Google Patents

Abstract

PURPOSE:To provide the color liquid crystal display element which has a high contrast and a bright screen even in high time-vision driving constitution. CONSTITUTION:This color liquid crystal display element consists of a couple of substrates 6 and 10 which are arranged opposite each other, transparent electrodes 4 and 7 provided on the opposite surfaces of the couple of substrates 6 and 10, the color filter 26 which consists of an R filter 25, a G filter 26, and a B filter 27 provided on the reverse surface of the electrode 7 of the upper substrate 10 so that the G filter 26 is formed thinner in thickness than the R filter 25 and the B filter 27 is formed thinner in thickness than the G filter 26, and liquid crystal 24 which is twisted and oriented within a range of 100+ or -5 deg. between the couple of substrates 6 and 10. The gamma characteristics of the liquid crystal 24 are improved and the contrast ratio is high even at the time of high time-division driving; and the transmissivity in an ON state where the contrast is maximum is increased and the screen becomes bright.

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 element used in a color liquid crystal display device.

[0002]

2. Description of the Related Art Conventionally, as a color liquid crystal display device, there is a simple matrix type TN (twisted nematic) type color liquid crystal display device having a simple structure and low manufacturing cost. As shown in FIG. 3, this color liquid crystal display device includes a color liquid crystal cell (color liquid crystal display element) 1
The upper polarizing plate 2 and the lower polarizing plate 3 are arranged so as to be sandwiched between the upper polarizing plate 2 and the lower polarizing plate 3. Color liquid crystal cell 1 is IT
One electrode 4 made of a transparent conductive material such as O and a lower substrate 6 on which a lower alignment film 5 covering the electrode 4 is formed;
The other electrode 7 that is orthogonal to and opposed to the one electrode 4, the color filter 8 that covers the electrode 7, and the upper substrate 10 on which the upper alignment film 9 that covers the color filter 8 is formed, and the upper and lower substrates 6 respectively. 10 and a liquid crystal 11 enclosed in a region surrounded by a sealing material (not shown). In this color liquid crystal display device, light is incident from the lower substrate 6 and light is emitted from the upper substrate 10.

The alignment films 5 and 9 formed on the surfaces of the lower substrate 6 and the upper substrate 10 facing each other are subjected to an alignment treatment such as rubbing. That is, as shown in FIG. 4B, the upper alignment film 9 of the upper substrate 10 is formed from the lower left to the upper right with respect to horizontal horizontal lines when the color liquid crystal cell 1 is observed from the front (the upper substrate 10 side). The alignment treatment is performed in a direction having an inclination of 45 ° (hereinafter, referred to as an emission side alignment treatment direction) 9a. The lower alignment film 5 of the lower substrate 6 is subjected to the alignment treatment in a direction (hereinafter referred to as an incident side alignment treatment direction) 5a which is rotated counterclockwise by approximately 90 ° with respect to the emission side alignment treatment direction 9a. By such an alignment treatment, the molecules of the liquid crystal 11 are twisted counterclockwise by 90 ° when viewed from the exit side. The lower polarizing plate 3 is shown in FIG.
As shown in (c), the absorption axis 3a is arranged so as to be substantially orthogonal to the incident side alignment treatment direction 5a of the color liquid crystal cell 1. As shown in FIG. 4A, the upper polarizing plate 2 has its absorption axis 2a arranged substantially parallel to the exit side alignment treatment direction 9a of the color liquid crystal cell 1. Therefore, in this color liquid crystal display device, when no voltage is applied, the linearly polarized light that has passed through the lower polarizing plate 3 is rotatably emitted by about 90 ° in the liquid crystal layer of the color liquid crystal cell 1, and the emitted light is emitted. It is absorbed by the upper polarizing plate 2. That is, it is a negative type (normally black) liquid crystal display element.

On the other hand, the color filter 8 corresponds to the electrode 7 for the red (R) filter 13 and the green (G) filter 1.
4, a blue (B) filter 15, and upper and lower electrodes 4,
The filters 13 to 15 are provided in a mosaic pattern corresponding to the points where 7 intersect. Further, the filters 13 to 15 have different film thicknesses. That is, the refractive index anisotropy Δn of light has wavelength dependence,
Therefore, the phase difference Δn · d generated when the light passes through the color liquid crystal cell 1 is different for each wavelength, and it is difficult to apply a predetermined voltage to obtain a desired color. Therefore, in order to compensate for the difference in Δn · d for each wavelength light, the thicknesses of the filters 13 to 15 are made different so that the wavelength dependence of Δn · d is eliminated. In this example, the film thickness T _R of the R filter 13 is 1.30 μm (of which the dye content is 0.50 μm), and the film thickness T _G of the G filter 14 is 1.00 μm (of which the dye content is 0.34 μm). The filter 13 is formed thinner than the film thickness of the filter 13, and the film thickness TB of the _B filter 15 is 0.55 μm.
m (of which the dye content is 0.27 μm), and is formed thinner than the film thickness of the G filter 14. In this case, the refractive index anisotropy Δn of the liquid crystal 11 is 0.115 at 35 ° C., and the gap d of the liquid crystal layer corresponding to the G filter 14 is 5.85 μm.

In this color liquid crystal display device, an alignment of liquid crystal molecules is changed by applying an electric field between the electrodes 4 and 7 facing each other by time division driving with a 1/75 duty and a 1/10 bias, and this alignment is performed. Is visualized by the upper and lower polarizing plates 2 and 3, whereby desired color display is performed.

[0006]

By the way, in such a color liquid crystal display device, high time division driving is required when the number of pixels increases in order to perform high definition display.
When the color liquid crystal display device is driven in a high time division manner in response to such a demand, since the molecules of the liquid crystal 11 of the color liquid crystal cell 1 are twist-aligned at about 90 °, the gamma characteristic of the liquid crystal 11 (light with respect to the applied voltage) There is a problem that the rising characteristic of the transmittance curve) is poor, the contrast ratio is low, the transmittance in the ON state at the maximum contrast is low, and the screen becomes dark. By the way, the measured value at 35 ° C shows that the contrast ratio is 7.4 and the backlight is 100%.
Then, the transmittance in the ON state is 1.3%. Further, in this color liquid crystal display device, since the thickness of each of the filters 13 to 15 of the color filter 8 is only determined according to the wavelength dependence of Δn, the voltage of each wavelength of R, G, and B- There is also a problem that the contrast ratio becomes low because the voltage of the bounce minimum value in the transmittance curve becomes uneven, and light leakage occurs in the off state. The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a color liquid crystal display device having a high contrast and a bright screen even in high time division driving.

[0007]

In order to achieve the above object, the invention according to claim 1 includes a pair of substrates arranged to face each other, and a transparent electrode provided on each of the facing surfaces of the pair of substrates. , The R filter, the G filter, and the B filter provided on the electrodes of one of the substrates, and the G filter is thinner than the R filter, and the B filter is thinner than the G filter. A color filter having a thin film thickness, a liquid crystal twisted in a range of 100 ° ± 5 ° between a pair of substrates, and a pair of polarizing plates arranged on both sides of the pair of substrates. It is characterized by having. In the invention according to claim 2, the thickness of the liquid crystal layer corresponding to the G filter of the color filter provided on the transparent electrode is formed to be 5.85 ± 0.5 μm,
The thickness of the R filter is 0.7 μm thicker than that of the G filter, and the thickness of the B filter is 0.2 μm than that of the G filter.
It is characterized in that it is formed to be thin by μm.
Further, according to the invention of claim 3, a pair of polarizing plates provided on both outer sides of the liquid crystal display element are arranged so that their absorption axes are parallel to each other, and a negative type color display is obtained. It is characterized by.

[0008]

According to the first aspect of the present invention, by twisting the liquid crystal between the pair of substrates in the range of 100 ° ± 5 °, the gamma characteristic of the liquid crystal is improved, and the contrast is improved even in the high time division driving. The ratio is high, the transmittance is high in the ON state with the maximum contrast, and the screen is bright. According to the second aspect of the invention, the thickness of the G filter that contributes most to the brightness is set to 5.85 ±
The wavelength difference between the G filter and the R filter is set to 0.7 μm, and the thickness difference between the G filter and the B filter is set to 0.2 μm. The voltage of the bounce minimum value on the voltage-transmittance curve coincides with each other, so that the transmittance in the off state in which no voltage is applied decreases, and the contrast ratio improves. In this case, the film thickness of each of the R and B filters becomes thicker than the conventional one, but since the film thickness of the G filter that contributes to the most brightness is the same as the conventional one, the decrease in the brightness is minimized. It can be suppressed.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a color liquid crystal display device to which the present invention is applied will be described below with reference to FIGS. The same parts as those of the conventional example shown in FIGS. 3 and 4 are designated by the same reference numerals, and the description thereof will be appropriately omitted. As shown in FIG. 1, this color liquid crystal display device has a structure in which an upper polarizing plate 2 and a lower polarizing plate 3 are arranged outside a color liquid crystal cell (color liquid crystal display element) 20 so as to sandwich it. The color liquid crystal cell 20 includes one electrode 4 and a lower substrate 6 on which a lower alignment film 21 that covers the electrode 4 is formed.
The other substrate 7 that is orthogonal to the one electrode 4 and is opposed thereto, the color filter 22 that covers the electrode 7, and the upper substrate 10 on which the upper alignment film 23 that covers the color filter 22 is formed.
And a liquid crystal 24 enclosed in a region surrounded by the upper and lower substrates 6 and 10 and a sealing material (not shown). Also in this color liquid crystal display device, light is assumed to be incident from the lower substrate 6 and emitted from the upper substrate 10.

The alignment films 21 and 23 formed on the opposing surfaces of the lower substrate 6 and the upper substrate 10, respectively, are subjected to an alignment treatment such as rubbing. That is, the upper substrate 1
As shown in FIG. 2B, the upper alignment film 23 of 0 has an inclination of 40 ° from the lower left to the upper right with respect to the horizontal horizontal reference line when the color liquid crystal cell 20 is observed from the front. A direction (hereinafter, referred to as an outgoing side alignment process direction) 23a is subjected to the alignment process. The lower alignment film 21 of the lower substrate 6 is subjected to an alignment treatment in a direction from the lower right to the upper left (hereinafter referred to as an incident side alignment treatment direction) 21a at a position rotated by 140 ° counterclockwise with respect to the same horizontal reference line. Has been done. By such an alignment treatment, the molecules of the liquid crystal 24 are twisted and arranged in the range of 100 ° ± 5 ° counterclockwise as viewed from the emission side. As shown in FIG. 2C, the lower polarizing plate 3 has its absorption axis 3a substantially perpendicular to the incident side alignment processing direction 23a of the color liquid crystal cell 20, that is, a horizontal reference line in the horizontal direction. 45 ° from lower left to upper right
It is arranged so that it becomes the angle of. As shown in FIG. 2A, the absorption axis 2a of the upper polarizing plate 2 is substantially parallel to the exit side alignment treatment direction 23a of the color liquid crystal cell 20, that is, the absorption axis 3a of the lower polarizing plate 3. Are arranged as follows. Therefore, also in this color liquid crystal display device, when no voltage is applied, the linearly polarized light transmitted through the lower polarizing plate 3 is almost 1 in the liquid crystal layer of the color liquid crystal cell 20.
The light is rotated by 00 ° and emitted, and the emitted light is absorbed by the upper polarizing plate 2, and a negative display is performed.

On the other hand, the color filter 22 has a structure in which an R filter 25, a G filter 26, and a B filter 27 are provided in a mosaic pattern corresponding to the positions where the upper and lower electrodes 4 and 7 intersect. The film thickness of each of the filters 25 to 27 is formed as follows. That is,
The G filter 26 contributes most to the brightness, and the film thickness T _G of the G filter 26 is determined by the product Δn · d of the gap d of the color liquid crystal cell 20 and the refractive index anisotropy Δn, for example, 1.00. ± 0.5 μm (of which dye content is 0.34 μm)
The thickness of the liquid crystal layer corresponding to the G filter 26 is 5.85 ± 0.5 μm. The film thickness T _R of the R filter 25 is 1.70 μm (of which the dye content is 0.54 μm)
The thickness of the G filter 26 is about 0.7 μm. Further, the film thickness T _B of the B filter 27 is
The thickness is 0.80 μm (of which the dye content is 0.37 μm), which is thinner than the film thickness of the G filter 26 by about 0.2 μm. In this case, the refractive index anisotropy Δn of the liquid crystal 24 is 0.135 at 35 ° C.

In this color liquid crystal display device, the gamma characteristic of the liquid crystal 24 is improved by twisting the liquid crystal 24 between the pair of substrates 6 and 10 within a range of 100 ° ± 5 °, and even in high time division driving. , High contrast ratio,
On-state transmittance at maximum contrast is high,
The screen can be brightened. Moreover, since the twist angle of the liquid crystal 24 is 100 ° ± 5 °, the left and right viewing angles are expanded and the viewing angle is improved. Further, in this color liquid crystal display device, the thickness of the liquid crystal layer corresponding to the G filter 26 that contributes most to the brightness is 5.85 ± 0.5 μm, the thickness of the G filter 26 is 1.00 μm, and the R filter 25 is used. Film thickness of 1.70 μm, B filter 27 film thickness of 0.80 μm
Therefore, the voltage of the bounce minimum value in the voltage-transmittance curve of each wavelength is the same, so that the transmittance in the off state where no voltage is applied is reduced and the contrast ratio is improved. Further, the film thickness of each of the R and B filters 25 and 27 becomes thicker than the conventional one, but the film thickness of the G filter 26, which contributes to the most brightness, is the same as the conventional one. Can be kept to a minimum. By the way, in this color liquid crystal display device, the actually measured value at 35 ° C. is that the contrast ratio is 8.7, and the transmittance in the ON state is 1.6% when the backlight is 100%. (The contrast ratio is 7.4, and the transmittance in the ON state is 1.3.
%) Is better than

In the above embodiment, the case where the color filter 22 is provided on the side of the upper substrate 10 through which light is emitted has been described, but the present invention is not limited to this. For example, the color filter is provided on the side of the lower substrate 6 through which light is incident. May be. Further, the present invention is
The present invention can be applied not only to the negative type color liquid crystal display element as in the above embodiment but also to a positive type color liquid crystal display element.

[0014]

As described above, according to the invention of claim 1, the liquid crystal has a gamma characteristic improved by twisting the liquid crystal between the pair of substrates in the range of 100 ° ± 5 °. Therefore, even in the high time-division driving, the contrast ratio is high, the transmittance in the ON state at the maximum contrast is high, and the screen becomes bright. According to the second aspect of the invention, the thickness of the G filter that contributes to the most brightness is set to 5.85 ± 0.5 μ when the thickness of the corresponding liquid crystal layer is
It is formed so as to have a thickness of m
By forming the thickness of the filter to be 0.7 μm and making the thickness of the B filter to be 0.2 μm thinner than that of the G filter, the voltage of the bounce minimum value in the voltage-transmittance curve of each wavelength can be made uniform. As a result, the transmittance in the off state where no voltage is applied is reduced, the brightness is not reduced even if the filter film thickness is increased, and the contrast ratio is improved.

[Brief description of drawings]

FIG. 1 is an enlarged sectional view of an essential part of a color liquid crystal display device to which the present invention is applied.

2A and 2B show an absorption axis and an alignment treatment direction of the color liquid crystal display device of FIG. 1, FIG. 2A is a diagram showing an absorption axis direction of an upper polarizing plate, and FIG. 2B is an upper substrate and a lower substrate of a color liquid crystal cell. And (c) is a diagram showing the direction of the absorption axis of the lower polarizing plate.

FIG. 3 is an enlarged cross-sectional view of a main part of a conventional color liquid crystal display device.

4A and 4B show an absorption axis and an alignment treatment direction of the color liquid crystal display device of FIG. 3, FIG. 4A shows a direction of an absorption axis of an upper polarizing plate, and FIG. 4B shows an upper substrate and a lower substrate of a color liquid crystal cell. And (c) is a diagram showing the direction of the absorption axis of the lower polarizing plate.

[Explanation of symbols]

 4, 7 electrodes 6 lower substrate 10 upper substrate 20 color liquid crystal cell 22 color filter 24 liquid crystal 25 R filter 26 G filter 27 B filter

Claims (3)

[Claims] 1. A pair of substrates arranged to face each other, transparent electrodes provided on each of the facing surfaces of the pair of substrates, and a red filter and a green filter provided on the electrodes of the one substrate. A filter for blue, and the film thickness of the green filter is thinner than the film thickness of the red filter, and the film thickness of the blue filter is thinner than the film thickness of the green filter. A color filter, a liquid crystal twisted in a range of 100 ° ± 5 ° between the pair of substrates, and a pair of polarizing plates arranged on both sides of the pair of substrates so as to sandwich the liquid crystal. And color liquid crystal display device. 2. The thickness according to claim 1, wherein the liquid crystal layer corresponding to the green filter has a thickness of 5.85 ± 0.5 μm,
The difference in film thickness between the red filter and the green filter is 0.
A color liquid crystal display device having a thickness of 7 μm and a difference in film thickness between the green filter and the blue filter of 0.2 μm. 3. The color liquid crystal display device according to claim 1, wherein the pair of polarizing plates are arranged such that their absorption axes are parallel to each other.