JP2621385C - - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an electro-optical device such as a super twisted nematic liquid crystal display device. [Prior Art] A conventional super twisted nematic liquid crystal display device has a twist angle of a liquid crystal molecule of 180 degrees or more and an optical anisotropy Δn of the liquid crystal and a liquid crystal as disclosed in Japanese Patent Application Laid-Open No. 60-50511. The product Δn · d with the layer thickness d was from 0.7 μm to 1.1 μm. [Problems to be Solved by the Invention] Therefore, coloring due to birefringence occurs. However, when time-division driving is performed, the color becomes yellow when a non-selection voltage is applied, becomes blue when a selection voltage is applied, and becomes the color shown in FIG. 16 when an intermediate voltage is applied. As shown in the chromaticity diagram (CIE standard chromaticity diagram), the color ranged from yellow to slightly blue-green to blue, and other multicolors could not be obtained. Therefore, a sufficient multi-color display cannot be performed by the gradation display driving in which an intermediate voltage other than the selection voltage and the non-selection voltage is applied. In addition, there is a multi-color display having a color filter. However, three pixels of three primary colors R, G, and B are required, and the production is very troublesome. The present invention has been proposed in view of the above problems, and can easily perform multi-color display by gradation display operation, and can be time-division driven at a low duty ratio of 1/100 or less, for example. It is an object of the present invention to provide an electro-optical device capable of obtaining a sufficient contrast even in a case. [Means for Solving the Problems] To achieve the above object, an electro-optical device according to the present invention has the following configuration. That is, a liquid crystal cell comprising a pair of polarizing plates disposed on both sides of the pair of substrates, sandwiching nematic liquid crystal twisted between a pair of substrates having electrodes formed on opposing inner surfaces, and In the electro-optical device, wherein the twist angle of the nematic liquid crystal is in a range of 180 degrees to 360 degrees, the nematic liquid crystal is a PCH liquid crystal, a trans liquid crystal, or a liquid crystal obtained by adding a trans liquid crystal to the PCH liquid crystal. And the value of the product Δn · d of the optical anisotropy Δn of the nematic liquid crystal and the liquid crystal layer thickness d (μm) of the nematic liquid crystal is 1.1 μm or more, and the liquid crystal cell comprises: By changing the effective voltage applied between the electrodes within a range of 2.44 V or less, a characteristic of exhibiting at least three colors including blue or red among blue, green, yellow, red, and violet. To Time-division driving by selectively applying at least three different voltages between the electrodes in addition to a selection voltage and a non-selection voltage and an intermediate voltage that is an intermediate value of their effective voltages. Thus, multicolor display can be performed on the same screen without using a color filter. [Operation] In the so-called STN electro-optical device as described above, Δn · d of the nematic liquid crystal layer of the liquid crystal cell is set to 1.1 μm or more, and a selection voltage and a non-selection voltage are applied between a pair of substrates of the liquid crystal cell. In addition, by selectively applying at least three different voltages to an intermediate voltage that is an intermediate value of the effective voltages and performing time-division driving, a blue-based, green-based, Multicolor display of three or more of yellow, red, and purple can be easily performed, and for example, the duty ratio is 1 /
Even when time-division driving is performed at a low duty ratio of 100 or less, a sufficient contrast can be obtained. EXAMPLES Hereinafter, the present invention will be specifically described based on examples shown in the drawings. FIG. 1 is a sectional view of a schematic configuration of a liquid crystal display device as an electro-optical device according to an embodiment of the present invention. In the figure, 1 is a lower polarizing plate, 2 is an upper polarizing plate, and 10 is a liquid crystal cell disposed between the two polarizing plates 1 and 2. The liquid crystal cell 10 has a nematic liquid crystal 13 sandwiched between a lower electrode substrate 11 having an electrode 11a on an upper surface and an upper electrode substrate 12 having an electrode 12a on a lower surface. The nematic liquid crystal 13 is twisted by subjecting the upper and lower electrode substrates 11 and 12 to rubbing treatment or the like. Reference numeral 14 denotes a spacer interposed in the peripheral portion between the two electrode substrates 11 and 12. The spacer 14 holds the nematic liquid crystal 13 between the two electrode substrates 11 and 12, , That is, the liquid crystal layer thickness is kept constant. The two substrates 11
A spacing member such as glass fiber or glass ball may be sprayed between the twelve. In the figure, reference numeral 3 denotes a driving circuit for the liquid crystal cell 10 connected to the electrodes 11a and 12a. In this example, a time-division driving circuit is used, and a selection voltage and a non-selection voltage are applied between the two electrode substrates. The configuration is such that grayscale display driving can be performed by selecting a voltage of three or more values such as an intermediate voltage in addition to the selection voltage. FIG. 2 is an explanatory diagram showing the relationship between the molecular axis of liquid crystal molecules near the electrode substrate and the absorption axis of the polarizing plate in the liquid crystal display device of FIG. In the present invention, the means for aligning the liquid crystal molecules is not limited to the rubbing treatment, but for convenience of explanation, the direction of alignment of the long axis of the liquid crystal molecules near the electrode base will be described as the rubbing direction. The same applies to the embodiments described later. In the figure, R11 and R12 are rubbing directions on the lower electrode substrate 11 and the upper electrode substrate 12 side of the liquid crystal cell 10, respectively, and T is the first liquid crystal molecule in the liquid crystal cell 10.
In the figure, the twist direction and angle from top to bottom, P1 and P2 are the directions of the absorption axes (polarization axes) of the lower polarizing plate 1 and the upper polarizing plate 2, respectively, and θ1 is the absorption axis of the lower polarizing plate 1. The angle between the direction P1 and the rubbing direction R11 of the lower electrode substrate 11, and θ2 indicates the angle between the direction P2 of the absorption axis of the upper polarizing plate 2 and the rubbing direction R12 of the upper electrode substrate 12. In the above configuration, the upper electrode substrate and the lower electrode substrate are arranged to face each other such that the twist angle T of the liquid crystal molecules is in a range from 180 degrees to 360 degrees. In this case, the twist direction and the angle T of the liquid crystal molecules are defined by the rubbing directions R11 and R12 and the type and amount of the optical rotatory substance added to the nematic liquid crystal 13. The angles θ1 and θ2 between the rubbing direction and the absorption axis of the polarizing plate are preferably in the range of 15 to 75 degrees. The product of the optical anisotropy Δn of the liquid crystal and the thickness d (μm) of the liquid crystal layer Δn · d
Is 1.1 μm or more. In the above configuration, by changing the voltage applied to the pair of electrode substrates 11 and 12, the retardation of the liquid crystal layer changes and decreases. When the retardation changes, the color of the transmitted light changes. Therefore, in order to increase this color change, it is sufficient to increase the change in retardation.
It is necessary to increase n · d. Therefore, in order to obtain a multi-color display, it was found that Δn · d at the initial stage should be 1.1 μm or more, so that sufficient multi-color display by gradation display driving can be simplified. What can be done. The upper limit of the value of Δn · d is not particularly limited, and a multi-color display can be performed no matter how large the value becomes. However, at present, Δn is 0.2 at most, and Δnd is preferably 2.0 or less in consideration of response speed and the like. In order to increase the display capacity, time-division driving is required. However, with the above-described configuration, a sufficient contrast can be obtained even in a low-duty-ratio drive of, for example, a duty ratio of 1/100 or less. Further, the present invention positively utilizes the birefringence of the liquid crystal, and it is necessary that the alignment direction and the direction of the absorption axis (polarization axis) of the polarizing plate are shifted. When the angles θ1 and θ2 between the direction and the direction of the absorption axis are in the range of 15 ° to 75 ° as described above, a multicolor display with high contrast and good color purity can be obtained. Hereinafter, a specific example based on the above embodiment will be described. Specific Example 1 In the configuration shown in FIGS. 1 and 2, a PCH-based liquid crystal is used as the nematic liquid crystal 13, the optical anisotropy Δn is 0.13, the liquid crystal layer thickness d is 10 μm, and Δn · d is The thickness was 1.3 μm. Further, the twist angle T of the liquid crystal was 180 degrees, and the angles θ1 and θ2 between the rubbing direction and the absorption axis of the polarizing plate were 30 degrees and 30 degrees, respectively. When four gradation driving is performed by the driving circuit (time-division driving circuit) 3 of the liquid crystal cell 10 at a duty ratio of 1/100, when a non-selection voltage (effective voltage 2.10 V) is applied, blue-green and a selection voltage (effective voltage) 2.32V) Red when applied, intermediate value of its two values, ie, effective voltage 2.1
Four colors of blue and purple were displayed when 7 V and 2.25 V were applied, respectively. However, the response time was 600 ms or more, resulting in a considerably slow response. Specific Example 2 Instead of the liquid crystal of the above specific example 1, a translanic liquid crystal is used, and the optical anisotropy Δn is 0.
. 18, the liquid crystal layer thickness d was 8 μm. Other configurations were the same as in Example 1,
Four colors were displayed in the same manner as in Example 1, and the response time was also 300 ms. Example 3 Using the liquid crystal of Example 2 above, the twist angle T of the liquid crystal was 220 degrees, and the angles θ1 and θ2 between the rubbing direction and the absorption axis of the polarizing plate were each 45 degrees. The other configuration is the same as that of the specific example 2. When four gradation driving is performed by the driving circuit 3 at a duty ratio of 1/100, four colors are displayed also in this case, as shown in the chromaticity diagram of FIG. became. Example 4 In Example 3 above, the twist angle T of the liquid crystal was changed to 230 degrees. The other configuration was the same as that of the specific example 3, and the driving circuit 3 performed four gradation driving at a duty ratio of 1/100. FIG. 4 shows the color tone at this time. As is apparent from the figure, the three primary colors of green, blue and red could be further displayed in yellow. Specific Example 5 In the specific example 4, when the driving circuit 3 performs eight gradation driving at a duty ratio of 1/200, the driving circuit 3 turns green when a non-selection voltage (effective voltage 2.24 V) is applied, and selects a selection voltage (effective voltage 2.4 V). ) Yellow when applied, its intermediate voltage, ie, effective voltage 2.26V, 2.2
When 9V, 2.31V, 2.33V, 2.35V, and 2.38V were applied, they turned blue-green, blue, purple, red, orange, and yellow, respectively. FIG. 5 shows the color tone at this time. As is apparent from FIG. 5, all the eight gradation displays showed different color tones.
The response time at this time was 400 ms. Specific Example 6 In the specific example 5, the liquid crystal layer thickness d was 5.5 μm instead of the trans liquid crystal having an optical anisotropy Δn of 0.21. Then, the response time showed a good response of 250 ms. Specific Example 7 In the specific example 6, the twist angle T of the liquid crystal was set to 260 degrees, and a pair of polarizing plates 1 and
The angle between the two absorption axes was 10 degrees. The duty ratio 1 /
When eight gradation driving was performed at 200, red was applied when a non-selection voltage (effective voltage 2.28 V) was applied, and blue-green, yellow, and other colors were gradually applied when a selection voltage (effective voltage 2.44 V) was applied. Was displayed. FIG. 6 shows the color tone at this time. When the angle between the absorption axes of the pair of polarizing plates 1 and 2 is set to 80 degrees, eight tones having a complementary color relationship with each of the above colors (each point and the white point 0 in FIG. Color tone). Specific Example 8 In the specific example 7, the twist angle T of the liquid crystal molecules is further increased, for example, to 330
I did it. Note that oblique deposition was performed instead of the rubbing treatment as the alignment treatment of the liquid crystal molecules. As a result, a wider viewing angle was obtained than in Example 7. In the other specific examples 1 to 6, the same effect can be obtained by increasing the twist angle T. Specific Example 9 As the liquid crystal 13, a liquid crystal obtained by adding a trans liquid crystal to a PCH liquid crystal is used.
The optical anisotropy Δn is 0.18, the liquid crystal layer thickness d is 9 μm, and Δn · d is 1.62 μm.
m. Further, the twist angle T of the liquid crystal was 180 degrees, and the angles θ1 and θ2 between the rubbing direction and the absorption axis of the polarizing plate were 30 degrees and 60 degrees, respectively. And the driving circuit 3
As a result, when four gradation display driving was performed at a duty ratio of 1/100, four colors of green, blue, red, and yellow were displayed. However, the response time was 1000 ms, which was a considerably slow response. Specific Example 10 In the specific example 9, the concentration of the tolanic liquid crystal was increased, and the optical anisotropy Δn was 0.1.
22, the same test as in Example 9 was performed with the liquid crystal layer thickness d set to 7 μm. Then, four colors were displayed in the same manner as in Example 9, and the response time was also 400 ms. Example 11 The liquid crystal of Example 10 was used, the liquid crystal layer thickness was 9 μm, and the twist angle T of the liquid crystal was 2
The angle between the rubbing direction and the absorption axis of the polarizing plate was set to 45 degrees. Then, the driving circuit 3 performed eight gradation driving at a duty ratio of 1/200. FIG. 7 is a chromaticity diagram showing the color tone at this time, and eight colors such as light green, green, blue, red, and yellow could be displayed. Specific Example 12 The same test as in Specific Example 11 was performed except that the twist angle T of the liquid crystal was 260 degrees. FIG. 8 is a chromaticity diagram showing the color tone at this time. As is apparent from FIG. 8, both point A and point B are yellow, but point A has higher color purity than point B. Yellows with different color purities were obtained. Specific Example 13 In the specific example described above, the twist angle T of the liquid crystal molecules was further increased, for example, to 330 degrees. Note that oblique deposition was performed instead of the rubbing treatment as the alignment treatment of the liquid crystal molecules. As a result, a wider viewing angle was obtained than in Example 12. In the above Examples 9 to 11, the same effect can be obtained by increasing the twist angle T. The driving circuit 3 of the liquid crystal cell for performing the above-described gradation display includes a pulse gradation display driving circuit for controlling a pulse width in a selection period, and a frame gradation display driving for changing the number of selections in a plurality of frames. There are circuits and the like. In the above specific examples 1 to 13, the frame gradation display driving circuit is used. However, the same result as described above can be obtained with the pulse gradation display driving circuit. REFERENCE EXAMPLE FIG. 9 is a cross-sectional view of a schematic configuration of a liquid crystal display device as an electro-optical device in which two liquid crystal cells are provided between a pair of polarizing plates as a reference example. In the figure, reference numeral 1 denotes a lower polarizing plate, 2 denotes an upper polarizing plate, and 10 denotes a liquid crystal cell (hereinafter referred to as a first cell) provided between the two polarizing plates. ing. Reference numeral 20 denotes a second liquid crystal cell (hereinafter, referred to as a second cell) provided between the first cell 10 and the upper polarizing plate 2, and a lower electrode substrate 21 having an electrode 21a on the upper surface and an electrode on the lower surface. A nematic liquid crystal 23 is sandwiched between the upper electrode substrate 22 having the upper electrode substrate 22a. The liquid crystal 23 is twisted by subjecting the upper and lower electrode substrates 21 and 22 to a rubbing process or the like. 24 is a spacer, 4 is the electrode 21a.2
This is a drive circuit of the second cell 20 connected to 2a. In this example, a static drive circuit is used, and an arbitrary voltage can be applied to the electrodes 21a and 22a. FIG. 10 is an explanatory diagram showing the relationship between the rubbing direction (the direction of the molecular axis of the liquid crystal molecules approaching the electrode substrate) and the absorption axis of the polarizing plate in the liquid crystal display device of FIG. In the figure, R11 and R12 denote the rubbing directions of the lower electrode substrate 11 and the upper electrode substrate 12 of the first cell 10, respectively, and R21 and R22 denote the second cell 20 respectively.
Rubbing direction of the lower electrode substrate 21 and the upper electrode substrate 22, θ is the first cell 10
The angle T1 between the rubbing direction R12 of the upper electrode substrate 12 and the rubbing direction R21 of the lower electrode substrate 21 of the second cell 20 is T1 from top to bottom in FIG. 9 of the liquid crystal molecules in the first cell 10. , T2 is the twist direction and angle of the liquid crystal molecules in the second cell 20, and P1 and P2 are the lower polarizing plate 1 and the upper polarizing plate 2, respectively.
Is the angle between the absorption axis direction P1 of the lower polarizing plate 1 and the rubbing direction R11 of the lower electrode substrate 11 of the first cell 10, and θ2 is the direction of the polarizing axis of the upper polarizing plate 2. The angle between P2 and the rubbing direction R22 of the upper electrode substrate 22 of the second cell 20 is shown. In the above configuration, the twist direction and the angle T1 of the liquid crystal molecules of the first cell 10 are determined by the rubbing directions R11 and R12 and the type and amount of the optically active substance added to the nematic liquid crystal 13 as in the case of the first embodiment. The angle is set to be in the range of 180 degrees to 360 degrees, and the optical anisotropy Δn of the liquid crystal of the first cell 10 and the liquid crystal layer thickness d (
μm) is set to a range of 1.1 μm or more. As described above, in the liquid crystal display device having the liquid crystal cell (first cell) 10 interposed between the pair of polarizing plates 1 and 2, a second liquid crystal cell (second cell) is provided separately from the first cell 10.
When 20 is provided, the color tone that can be displayed on the display device can be changed by an electric signal. In addition, the black and white display required by personal computers
It can be realized by switching by the electric signal of the cell 20. The twist angle T2 of the nematic liquid crystal of the second cell 20 is 90 degrees × n ± 40 degrees (
(n is 0 or an integer) is desirable to obtain a black-and-white display with high contrast. The angle θ is desirably 90 degrees. Further, the twist direction of the liquid crystal of the second cell is preferably opposite to the twist direction of the liquid crystal of the first cell. REFERENCE EXAMPLE 1 A PCH-based liquid crystal to which a tran-based liquid crystal is added is used as the liquid crystal 13 of the first cell 10 in FIGS. Then, Δn · d was set to 1.44. The twist angle T1 of the liquid crystal molecules of the first cell 10 was set to 220 degrees to the left, and the twist angle T2 of the liquid crystal molecules of the second cell was set to 90 degrees to the right. Further, the angles θ1 and θ2 are each set to 45 degrees, and the angle θ is set to 90 degrees. The driving circuit (static driving circuit) 4 of the second cell 20 applies an effective voltage of 10 V to the second cell, and the driving circuit (time division driving circuit) 3 of the first cell 10 displays four gradations at a duty ratio of 1/100. Drive was performed. At this time, four colors were displayed, as shown in the chromaticity diagram of FIG. That is, there are four colors of blue-green, blue-violet, red, and yellow. Next, the second cell 2
When the switch of the drive circuit 4 of 0 is turned off, as shown in FIG. 12, point A is when a non-selection voltage (effective voltage 2.24 V) is applied, and point B is when a selection voltage (effective voltage 2.4 V) is applied. Color tone. Point A was slightly bluish black, and point B was slightly yellowish white, almost black and white display. The contrast ratio at this time was 1:10. Reference Example 2 In the above-described Reference Example 1, the twist angle T1 of the liquid crystal molecules of the first cell 10 is shifted to the left by 230
Each time, the twist angle T2 of the liquid crystal molecules of the second cell 20 was changed to the right to 270 degrees, and the other configuration was the same as that of the reference example 1. Then, the driving circuit 4 of the second cell 20 applies an effective voltage of 10 V to the second cell, and the driving circuit 3 of the first cell 10 applies a duty ratio of 1/200.
8 gradation display drive was performed. FIG. 13 shows the color tone at this time. As is clear from the figure, all the eight gradation displays showed different color tones. When the switch of the drive circuit 4 of the second cell 20 is turned off, as shown in FIG. 14, a point A is applied with a non-selection voltage (effective voltage 2.28 V), and a point B is applied with a selection voltage (effective voltage 2.28 V). 44V) The color tone upon application of voltage was obtained. Point A is slightly bluish black, point B is yellowish white,
The display became almost black and white. The contrast ratio at this time was 1:15. Reference Example 3 In Reference Example 2, the effective voltage applied to the second cell 20 by the drive circuit 4 of the second cell 20 was changed from 10V to 0V. As a result, green (x, y) = (0.197, 0.386) shown in FIG. 13 became blue, red, and black as shown in FIG. The other colors shown in FIG. 13 also correspond to the driving circuit 4 of the second cell 20.
Was changed from 10 V to 0 V, a color change could be caused. REFERENCE EXAMPLE 4 In the reference example 2, the torsion angle T1 of the liquid crystal molecules of the first cell 10 is shifted to the left by 330
At the same time, the twist angle T2 of the liquid crystal molecules of the second cell 20 is changed to 450 degrees to the right, and an effective voltage of 10 V is applied to the second cell 20 by the driving circuit 4 as in the second embodiment. Drive circuit 3 performs 8-gradation display driving at a duty ratio of 1/200. Then, the viewing angle was wider than in Reference Example 2. When the switch of the drive circuit 4 of the second cell 20 was turned off, a black-and-white display was obtained, and the contrast ratio was improved to 1:52. In the above Reference Examples 1 to 4, the twist direction of the liquid crystal molecules in the second cell 20 is set to the left, and the twist direction of the liquid crystal molecules in the first cell 10 is set to the right. . Although the twist directions of the liquid crystal molecules of the first cell and the second cell are made the same, almost the same results can be obtained though they are insufficient. In the above embodiment and the reference examples 1 to 4, a static driving circuit was used as the driving circuit 4 of the second cell 20, but any means for applying a voltage to the electrodes 21a and 22a may be used. It may be a drive circuit, a sine waveform application circuit, or a triangular waveform application circuit. [Effects of the Invention] As described above, according to the present invention, multi-color display can be easily performed by gradation display, and color display can be performed very simply and inexpensively as compared with the conventional one using a color filter. There is an effect that an electro-optical device capable of performing the above can be provided.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view of a schematic configuration of a liquid crystal display device as an electro-optical device according to a first embodiment of the present invention, and FIG. FIG. 3, FIG. 4, FIG. 5, FIG. 6, FIG. 7, FIG. 8 are illustrations showing the relationship with the rubbing direction and the like, showing the color tones displayed by the specific example based on the first embodiment. FIG. 9 is a cross-sectional view of a schematic configuration of a liquid crystal display device as an electro-optical device according to a reference example.
FIG. 0 is an explanatory view showing the relationship between the absorption axis of the polarizing plate and the rubbing direction and the like in the liquid crystal display device. FIGS. 11, 12, 13, 13, 14 and 15 show the above reference examples. FIG. 16 is a chromaticity diagram showing a color tone that can be displayed by a conventional liquid crystal display device. 1 and 2 are polarizing plates, 10 is a liquid crystal cell, 11 and 12 are electrode substrates, 13 is liquid crystal, 20
Is a second liquid crystal cell, 21 and 22 are electrode substrates, and 23 is a liquid crystal.

Claims (1)

Claims: (1) A pair of polarizing plates disposed on both sides of a pair of substrates, sandwiching a twist-aligned nematic liquid crystal between a pair of substrates having electrodes formed on opposing inner surfaces thereof. An electro-optical device comprising a liquid crystal cell, wherein the twist angle of the nematic liquid crystal is in a range of 180 degrees to 360 degrees, wherein the nematic liquid crystal is a PCH-based liquid crystal or a trans-based liquid crystal, or
It is a liquid crystal obtained by adding a trans liquid crystal to a PCH liquid crystal, and the value of the product Δn · d of the optical anisotropy Δn of the nematic liquid crystal and the liquid crystal layer thickness d (μm) of the nematic liquid crystal is 1. 1 μm or more, and the liquid crystal cell changes the effective voltage applied between the electrodes within a range of 2.44 V or less to thereby provide a blue-based, green-based, yellow-based, red-based, or purple-based Having a characteristic of exhibiting at least three colors including a reddish color, and at least three different values of an intermediate voltage that is an intermediate value of those effective voltages in addition to a selection voltage and a non-selection voltage between the electrodes. An electro-optical device characterized in that multi-color display can be performed on the same screen without using a color filter by selectively applying and driving in a time-division manner. (2) The direction of the absorption axis (polarization axis) of the pair of polarizing plates is shifted within a range of 15 degrees to 75 degrees with respect to the liquid crystal molecule alignment direction of the adjacent substrates. Item 2. An electro-optical device according to Item 1.