JPH03132720A - Liquid crystal element, polarization converting element using the element and method for driving the element - Google Patents

Abstract

PURPOSE:To obtain the liquid crystal element with which high-speed response and high polarization conversion efficiency are obtaineable by disposing uniaxial double refractive plates having a specific refractive index on the outer side of a liquid crystal layer. CONSTITUTION:The double refractive plates 5A, 5B are is posed on both sides of the liquid crystal cell. Further, a polarizing plate 6A is disposed on the incident light side of this liquid crystal cell in such a manner that the axis of polarization of the polarizing plate nearly parallels with the orienting direction of the liquid crystal molecules on the substrate surface on the incident light side or intersects nearly orthogonally therewith. The liquid crystal element for polarization conversion having the high sped response, a wide visual field angle and excellent polarization convertability is obtd. in this way. This liquid crystal element for polarization conver sion can be constituted to allow the viewing of stereoscopic images by using spectacles provided with the polarizing plates varying in the axis of polarization on the right and left, disposing the liquid crystal element for polarization conversion in front of a display body, such as television, and turning on and off the liquid crystal element in synchronization with the display of the display body to switch the polarization.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a liquid crystal element that repeatedly turns on and off at high speed, a polarization conversion element using the liquid crystal element, and a method for driving the same.

[Prior Art] As a liquid crystal element that repeatedly turns on and off at high speed, a printer head device using a dual-frequency driving method is known.

In this two-frequency driving method, a low frequency up to several KHz and a high frequency up to several tens of KHz are used.

For this reason, in a high frequency region, unless the electrode resistance of the transparent electrode substrate is lowered, the effective voltage applied to the liquid crystal will be reduced, and this has the disadvantage that it is difficult to drive a large area.

In addition, liquid crystal materials suitable for dual-frequency driving have strong interactions in the lateral direction with respect to the molecular axes of liquid crystal molecules, and therefore have extremely high viscosity compared to normal nematic liquid crystals. To get a response, a high voltage is required,
Furthermore, it had the disadvantage of high power consumption.

Therefore, a driving method using a low frequency single signal of up to several KHz is desired.

In this conventional driving method using a single low-frequency signal, in the normal twisted nematic (TN) mode, the response when voltage is applied (on) can be increased by increasing the voltage. , turned off that voltage (
The response speed when off) cannot be increased by changing the voltage; it can be made somewhat faster by thinning the gap between the cell substrates or lowering the viscosity of the liquid crystal, but this response speed cannot be increased at 0°C.
However, it was only a few tens of ff1sec at most. Additionally, due to the thinning of the gap between the substrates and the lowering of the viscosity of the liquid crystal, the polarization conversion efficiency of the liquid crystal element itself may decrease, making it impossible to obtain a liquid crystal element with high polarization conversion efficiency, high speed response, and a wide viewing angle. It wasn't.

[Problems to be Solved by the Invention] In order to solve this problem, the present inventors have developed a pair of transparent electrode substrates with transparent electrodes that have already been horizontally aligned so that the directions of the alignment process are almost perpendicular to each other. a polarizing plate with a nematic liquid crystal sandwiched between them, and the polarization axis on the incident light side of the nematic liquid crystal layer so that it is substantially parallel to or substantially perpendicular to the alignment direction of liquid crystal molecules on the substrate surface on the incident light side. By arranging the nematic liquid crystal, the relationship d/p between the pitch p of the nematic liquid crystal and the substrate gap d is 0.5<d/p<1, and applying a voltage higher than the threshold voltage of the liquid crystal between both transparent electrodes. The liquid crystal molecules assume a vertical alignment state, and then by turning off the voltage, the liquid crystal molecules are in their natural twisted state270
The polarization direction of the incident light is changed to approximately 90" by using the two states, the vertically aligned state of the liquid crystal molecules and the intermediate twisted state of the liquid crystal molecules.
We are proposing a liquid crystal element that can be changed.

As a result, it was possible to obtain a liquid crystal element that is capable of high-speed response without deteriorating polarization conversion efficiency using a driving method using a low-frequency single signal with low power consumption.

However, it was later discovered that although the polarization conversion efficiency is good in the vertical direction, the polarization conversion efficiency decreases when viewed from an oblique direction. Therefore, a liquid crystal element with a wide viewing angle (high polarization conversion efficiency) is desired, and the present invention is aimed at obtaining this.

[Means for Solving the Problems] The present invention has been made to solve these problems, and includes a pair of transparent electrode substrates with transparent electrodes that are horizontally aligned. They are arranged so that the horizontal alignment directions are almost perpendicular, a nematic liquid crystal is sandwiched between them, a polarizing plate is arranged on the incident light side of the nematic liquid crystal layer, and the polarization axis of the polarizing plate on the incident light side is aligned with the polarizing axis of the polarizing plate on the incident light side. The nematic liquid crystal is arranged so as to be substantially parallel to or perpendicular to the alignment direction of liquid crystal molecules on the substrate surface, and the relationship d/p between the pitch p of the nematic liquid crystal and the substrate gap d is 0.5 xn < d/p < 0.
5 X (n + 1) (n: an integer of n≧1), and by applying a voltage higher than the threshold voltage of the liquid crystal between both transparent electrodes, the liquid crystal molecules become vertically aligned, and then the voltage is By turning off, the liquid crystal molecules relax to their natural twisted state, approximately 90° + 180°×m
(m: an integer of n>m≧0), and the polarization direction of the incident light is changed to 90° by using two states: the vertical alignment state of liquid crystal molecules and the intermediate twist state of liquid crystal molecules.
In a liquid crystal element that changes, if the three principal refractive indices of the birefringent plate are nus nx and n, and nl is the refractive index in the thickness direction of the birefringent plate, then nx=n.

>nz, and the refractive index anisotropy Δn1 of the liquid crystal and the substrate gap d
, and the product Δn,・d, the value of Δn2・d2 of the birefringent plate, which is the product of the refractive index anisotropy Δn2 of the birefringent plate and the thickness d2 of the birefringent plate, is 0.1. ×Δn.

A liquid crystal element characterized by disposing a uniaxial birefringent plate such that tL <Δn2・dz <1.5 ×Δn,・d, and the liquid crystal element in which the liquid crystal The d/p of the molecule is 0.5 < d/p < 1,
A liquid crystal element whose natural twist state is 270" and which changes the polarization direction of incident light by 90 degrees by utilizing two states of liquid crystal molecules: a vertical alignment state and a 90 degree intermediate twist state, and In these liquid crystal elements, birefringent plates are arranged on both sides of the liquid crystal layer, and in these liquid crystal elements, the alignment state of liquid crystal molecules is a natural twisted state and is caused by horizontal alignment. A liquid crystal element, characterized in that it is adapted to match a pretilt angle.
And, in these liquid crystal elements, a polarizing plate is also arranged on the output light side of the negative or tick liquid crystal layer, and these liquid crystal elements are arranged in front of the display body. A polarization conversion element for driving a polarization conversion element and a method for driving a liquid crystal element for driving such a liquid crystal element, characterized in that a voltage less than a threshold value of the liquid crystal is applied after the twisted state of the liquid crystal molecules becomes an intermediate twisted state. The present invention provides a method for driving a liquid crystal element.

The present invention does not change the light transmittance by using only the two stable states of voltage on and voltage off, which are used in ordinary liquid crystals, but instead changes the light transmittance by completely turning off the voltage by turning off the voltage for a long time. thicker (relaxed state to twisted natural twisted state approximately 90° + 180°X m (m: n
It changes the polarization direction of incident light by 90@ by using two states: an intermediate twisted state (integer > m ≧ 0) and a vertically oriented state where a voltage higher than the threshold voltage is applied, resulting in a high-speed response. and high polarization conversion efficiency can be obtained.

In addition, in the present invention, the polarization conversion efficiency when viewed from an oblique direction is improved, and the three principal refractive indices of the birefringent plate are reduced to 0.
8, n2, and n8, and when nz is the refractive index in the thickness direction of the birefringent plate, an l-axis birefringent plate such that n4 = nx > nz is arranged outside the liquid crystal layer, Thereby, it is possible to obtain a wide viewing angle and excellent polarization conversion performance.

Furthermore, in the present invention, in order to improve the stability of the intermediate twisted state, the voltage is turned off and after the twisted state of the liquid crystal molecules becomes the intermediate twisted state, a voltage lower than the threshold of the liquid crystal is applied. . As a result, the intermediate twisted state of the liquid crystal molecules continues for a long time, and excellent polarization conversion performance can be obtained.

Since the present invention uses this intermediate twisted state, which is a metastable state, it is suitable for applications in which the polarization direction of polarized light incident on a liquid crystal is repeatedly changed at a relatively high speed of several meters to several seconds.

The orientation processing directions of the liquid crystal element of the present invention are made to be substantially orthogonal between the two substrates. The relationship d/p between the pitch p of the nematic liquid crystal sandwiched between the substrates and the substrate gap d is 0.
．． 5×n <d/p<0.5X(n+1)(n:n
= 1 integer). This results in 270@ for n=1 and 450'' for n=2 in the natural torsion state, where the voltage is left off for a long time.

In the present invention, the liquid crystal molecules are brought into a vertically aligned state by applying a voltage higher than the threshold voltage of the liquid crystal. This state is similar to the case where a voltage higher than the threshold voltage is applied to a conventional 90° twisted liquid crystal display element.

The change between these two stable states is the same for both the liquid crystal element of the present invention and the conventional liquid crystal element. In the present invention, the behavior when the voltage is turned off after the liquid crystal molecules are vertically aligned by applying a voltage equal to or higher than the threshold value is different from that of conventional liquid crystal elements.

In the present invention, when the voltage is turned off, the twist angle of the liquid crystal molecules is large, so in addition to the above two stable states, the natural twist state when the voltage is completely turned off is approximately 9
Approximately 90° + 180° × m (m: n>m), which is a relaxed state to 0° + 180° × n (n + n = 1 integer)
≧0 (integer)).

This intermediate twisted state is reached from the vertically aligned state extremely quickly (specifically, at a high speed of about 1 to several m5ec at room temperature, and is maintained for a certain period of time due to the strong twisting force of the liquid crystal molecules themselves). After that, the natural twisted state is reached.

In the present invention, after the voltage is turned off to enter this intermediate twisted state, by applying a voltage below the threshold value of the liquid crystal, this intermediate twisted state can be maintained stably for a long time.

In the present invention, the device is driven between two states: a vertically oriented state when a voltage equal to or higher than this threshold voltage is applied, and a metastable intermediate twisted state, and is turned on and off at high speed.

In the present invention, it is preferable that this intermediate twist state is 90', so that a high-speed response can be obtained and defects such as circular polarization are less likely to occur. In particular, when d/p is 0.5<d/p×1 and the natural twisted state of the liquid crystal is 270°, the vertical alignment state and 9
It is preferable to change between an intermediate twist state of 0°.

This is because as the twist angle increases, the response speed for transition to the intermediate twist state tends to improve, but the voltage required for driving increases, circular polarization increases, the polarization conversion rate decreases, and the contrast ratio decreases. This is because it is decreasing, and 270'
It is preferable that Furthermore, when the twist angle is increased, there is a tendency for the retardation color to become stronger, which may result in an undesirable color.

In addition, in this case, by aligning the alignment state of the liquid crystal molecules with the pretilt angle due to horizontal alignment in the natural twisted state, it is possible to
It is preferable to transition to this intermediate state at high speed. In this way, it is easy to quickly transition from the intermediate twisted state to the natural twisted state (although in this case, by applying a voltage below the threshold of the liquid crystal, this intermediate twisted state can be stably maintained). do.

An example of this alignment state will be explained using an example in which the natural twist state is 270° and the liquid crystal is twisted counterclockwise when viewed from above.

In this case, when the liquid crystal is twisted 270@ in the counterclockwise direction when viewed from above, the alignment state is achieved. Specifically, in the upper substrate, the left end of the liquid crystal molecules is in contact with the substrate, and in the lower substrate, the near side of the liquid crystal molecules is in contact with the substrate. This makes the pitch of the liquid crystal the same on either side of the liquid crystal molecules, resulting in a stable alignment state. In other words, the left end of the liquid crystal molecule, which was in contact with the upper substrate, now comes to the front as the liquid crystal is twisted 90 degrees counterclockwise, and the far side (the right end of the liquid crystal molecule) comes into contact with the lower substrate. If this happens, it will be in a stable state, which is a consistent state. However, since the opposite front side of the lower substrate is in contact with the substrate, the pitch of the liquid crystal molecules differs between the left end and right end of the liquid crystal molecules, resulting in a mismatched state. On the other hand, if it is twisted by 270 degrees, it will be in a matching state and the pitch of the liquid crystal will be the same. For this reason, 27
This is suitable for a liquid crystal element whose natural twist state is 0'' twist, and it quickly reaches the metastable intermediate twist state of 90°.

The present invention will be explained in more detail below with reference to the drawings.

FIG. 1 is a sectional view showing the basic structure of a liquid crystal element according to the present invention.

In FIG. 1, IA and IB are transparent substrates made of glass, plastic, etc., and transparent electrodes 2A, 2B made of tin oxide, indium oxide-tin oxide, etc. are patterned on their inner surfaces in desired patterns as necessary. It is formed. The surface of this transparent electrode is horizontally aligned by rubbing or diagonal vapor deposition so that the liquid crystal molecules are horizontally aligned in one direction, and the two substrates are placed facing each other so that the horizontal alignment direction is orthogonal to each other. , the periphery is sealed with a sealing material 3, and a nematic liquid crystal 4 is sealed inside to form a liquid crystal cell.

In the present invention, at least one
A number of uniaxial birefringent plates are arranged. In the example shown in this figure, birefringent plates 5A and 5B are arranged on both sides of the liquid crystal cell. In the present invention, one or more uniaxial birefringent plates may be arranged on one side of the liquid crystal layer, or one or more uniaxial birefringent plates may be arranged on both sides of the liquid crystal layer.
Although one or more uniaxial birefringent plates may be arranged,
It is preferable to arrange them on both sides of the liquid crystal layer because the viewing angle becomes wider. Further, a polarizing plate 6A is arranged on the incident light side of this liquid crystal cell so that the polarization axis of the polarizing plate is substantially parallel to or substantially perpendicular to the alignment direction of liquid crystal molecules on the substrate surface on the incident light side.

By doing this, the response is fast and the viewing angle is wide (
A liquid crystal element for polarization conversion with excellent polarization conversion ability can be obtained. This liquid crystal element for polarization conversion uses, for example, glasses with polarizing plates with different polarization axes on the left and right sides, and the liquid crystal element for polarization conversion is placed in front of a display such as a television to synchronize with the display on the display. By turning the liquid crystal element on and off and switching the polarization, you can view a three-dimensional image.

For example, in the case of an NTSC TV, the polarization of the image is changed by 90 degrees for each frame by turning the voltage on and off at a rate of 60 Hz, and glasses with polarizing plates with different polarization axes on the left and right sides are used. It is possible to view stereoscopic images. These glasses only require two polarizing plates (unlike conventional liquid crystal glasses for stereoscopic display, there is no need to drive the liquid crystal glasses in synchronization with the display), so even many people can use the same display. In the present invention, a specific birefringent plate is used to expand the field of view, so that a large number of people can view the image. Suitable for applications such as

Depending on the application, a polarizing plate 6B may be arranged on the output light side of this liquid crystal cell so that the polarization axis of the polarizing plate is substantially parallel to or substantially perpendicular to the alignment direction of liquid crystal molecules on the substrate surface on the output light side. , two polarizing plates may be used so that their polarization axes are orthogonal to each other.

As an example of this, as in the case of conventional stereoscopic display, the image is simply changed at 60Hz on the TV side, and the liquid crystal element of the present invention using two polarizing plates is used on the glasses side.
By controlling the left and right liquid crystal elements to be transparent or opaque at 60 Hz, it is possible to view a stereoscopic image.

Although omitted in this explanation, applications such as those used in general liquid crystal display devices, such as forming metal leads on transparent electrodes and using electroless Ni except for parts that change light transmittance, are possible. An opaque mask is formed by plating, Cr, Al vapor deposition, etc., a color filter is formed, and an overcoat for alignment film such as polyimide, polyamide, polyurethane, silicone resin, silica, alumina, etc. is formed on the transparent electrode. Alternatively, spacers such as glass fibers, alumina particles, plastic particles, etc. may be scattered or a sealing material containing such spacers may be dotted in order to accurately maintain the gap between the substrates within the liquid crystal cell.

FIG. 2 is a perspective view showing the definition of the principal refractive index of the birefringent plate used in the present invention.

In the uniaxial birefringent plate of the present invention, the in-plane direction of the birefringent plate is
The axial direction is the y-axis direction, and the thickness direction is the x-axis direction. Let the refractive index in each direction be nxs nys nz. In the present invention, nx=ny, nx>nz,
The refractive index anisotropy Δn2 of the birefringent plate is Δn2=nx−
It is expressed as nx=ny-ni. In this case, the optical axis direction of this birefringent plate is the X-axis direction. Note that d2 is the thickness of the birefringent plate.

In addition, in the present invention, Δn2・d2 of this birefringent plate
The relationship between and Δn1・d of the liquid crystal layer is the total Δng*
The value of dt is 0.1×Δn+・d+ <Δn,・d.

By setting so that <1.5XΔnx-d, a liquid crystal element with a wide viewing angle can be obtained.

In addition, when using multiple birefringent plates stacked on top of each other, or when using multiple birefringent plates only on one side of the liquid crystal layer,
The total value of Δn2·d2 may be set within the above range. However, as described above, it is preferable to arrange one or more birefringent plates on both sides of the liquid crystal layer, since this provides a wider viewing angle.

As the birefringent plate of the present invention, any transparent plate exhibiting the above-mentioned birefringence can be used, and plastic films, inorganic crystal plates, etc. can be used.

In order to obtain the desired birefringence effect, Δn2・cL = (n
x nx)·d2 may be used, or if adjustment cannot be made with one plate, a plurality of the same uniaxial birefringent plates or different uniaxial birefringent plates may be combined.

Note that the birefringent plate may be provided between the liquid crystal layer and the polarizing plate; for example, the birefringent plate may be provided in a layer between the liquid crystal layer and the electrode, or between the electrode and the substrate, or the birefringent plate itself may be provided in a layer between the liquid crystal layer and the electrode. It may be provided as a plate, as a layer between the substrate and the polarizing plate, or as a combination of these. Note that when a polarizing plate is provided only on one side, a birefringent plate may be provided on the opposite side of the liquid crystal layer to the polarizing plate.

3(A) and 3(B) are a drive waveform diagram and a relative light transmission characteristic diagram of a liquid crystal element, respectively, in which a voltage less than the threshold value of the liquid crystal is applied during the latter half of the voltage-off period according to the present invention; Figure 4 (A)
, (B) are a driving waveform diagram and a relative light transmission characteristic diagram of a liquid crystal element in which the voltage is simply turned off when the voltage is turned off, respectively.

This relative light transmission characteristic diagram was measured by placing another polarizing plate on the outgoing light side of the liquid crystal element so that the polarizing axis of the polarizing plate on the incident light side was orthogonal to the polarizing axis of that polarizing plate. did.

In FIG. 4, during the initial time 1+, a voltage higher than the threshold voltage of the liquid crystal is applied, and the liquid crystal molecules stand up.
It becomes vertically oriented and no light passes through it. Next, time t
In 2, when the applied voltage is turned off, the liquid crystal molecules first shift to an intermediate twisted state, and the angle is approximately 90°+1.
Since the twist is 80° x m, the light is transmitted through it. It will decrease.

For this reason, even if the response speed of the liquid crystal is increased, polarization conversion may become insufficient depending on the repeated on-off cycle.

FIG. 3 is an example of a preferred driving method of the present invention.

In this case as well, as in the example shown in Figure 4, during the initial time t, a voltage higher than the threshold voltage of the liquid crystal is applied, and the liquid crystal molecules stand up and become vertically aligned, and no light passes through. . Next, at time t2, when this applied voltage is turned off, the liquid crystal molecules first shift to an intermediate twisted state,
Since the twist is approximately 90° + 180° x m, light passes through it. This process is also similar to the example shown in Figure 4.

However, in the present invention, after transitioning to this intermediate twisted state, a voltage lower than the threshold voltage of the liquid crystal is applied. That is, after the liquid crystal shifts to the intermediate twisted state during time t2, a voltage lower than the threshold voltage of the liquid crystal is applied during time t3.

As a result, the liquid crystal is stably held in an intermediate twisted state, and polarization is maintained, so that a nearly constant light transmittance can be obtained. Therefore, by increasing the response speed of the liquid crystal,
Higher polarization conversion will occur.

Furthermore, when a voltage equal to or higher than the threshold voltage of the liquid crystal is applied again thereafter, the response speed of the liquid crystal tends to become faster. This is because the liquid crystal is in an intermediate twisted state just before that.

The time for turning off this voltage, that is, the time ts-tt, is usually about the time when the liquid crystal is in an intermediate twisted state,
In terms of light transmittance, it is sufficient if the transmittance reaches approximately 90% or more. Of course, you can leave it for a while after the light transmittance reaches its highest value.

Thereafter, a voltage lower than the threshold voltage of the liquid crystal is applied for a time ts. This voltage also needs to be less than the threshold voltage of the liquid crystal (it is sufficient to experimentally determine the voltage at which the intermediate twisted state is most stably maintained and apply it).

Further, in this example, the voltage below the threshold value of the liquid crystal is kept constant, but two or more different voltages may be applied stepwise or two or more frequencies may be applied.

Note that the intersecting angle of the alignment directions and the relationship between the alignment directions and the polarization axis are not limited to just being exactly parallel or orthogonal, but can also be shifted by about 5°, IO'', or 20°, for example.

Further, a 174-wavelength plate may be arranged between the polarizing plate on the output light side and the liquid crystal cell so that its optical axis is offset by approximately 45'' from the alignment processing direction.

Further, the product Δnx・d of the refractive index anisotropy Δn+ of the liquid crystal used in the present invention and the substrate gap d1 is 0.3 to 2.5 μm.
It is preferable to do this, and thereby a high contrast ratio can be obtained.

The present invention is suitable for applications where this polarization conversion is repeated at high speed.
It is suitable for applications that require polarization conversion up to a degree of 2 or repeating transparent and opaque states.

[Function] The reason why when a voltage equal to or higher than the threshold voltage is applied to the liquid crystal and the liquid crystal molecules are vertically aligned, light leaks and the polarization conversion efficiency decreases when viewed from an oblique direction.

FIGS. 5(A) and 5(B) are perspective views for explaining the present invention in detail.

In FIG. 5(A), the Z axis is the vertical direction of the substrate, and the polarization axes 7A and 7B of the two polarizing plates are the X axis and y axis directions, respectively. When a sufficient voltage is applied, the liquid crystal molecules are oriented approximately in the Z-axis direction. The transmittance of light when light travels through this liquid crystal at the angle shown in FIG. 5(B) is calculated.

If the refractive index of the liquid crystal is no in the molecular axis direction and ns (ns>no) in the direction perpendicular to the molecular axis, then the birefringence Δn*tt exhibited by the liquid crystal from the (θ, ψ) direction is Δn..." (. .・sin・θ+0.・.8・θ
)・, 7n・ (1). The retardation α caused by this birefringence is 2π d ・“−°Δ...°..8e(2)λ, where d is the thickness of the liquid crystal, and the transmission heavy beam in this case is I = 5in22ψ・5in2 (a/2)
(3) becomes.

At θ=0'', Δn*tt=0, so no birefringence is exhibited, but as θ increases, Δn*tt increases, and the transmittance increases.This phenomenon is explained by ψ=45'
It is most noticeable at 135"225', 315°.

In order to eliminate this birefringence, it is sufficient to add a phase difference that cancels out the phase in equation (2).The role of the birefringence plate in the present invention is to use it as a retardation plate that provides this phase difference. The optical anisotropy of this birefringent plate has the opposite sign to that of the liquid crystal, that is, the three principal refractive indices of the birefringent plate are n1% ny+
nz and n8 is the refractive index in the thickness direction of the birefringent plate, then nx = nx > nx By using a uniaxial birefringent plate, light leaks when viewed from an oblique direction, It is possible to prevent the polarization conversion efficiency from decreasing. This enables a liquid crystal element with a wide viewing angle.

In addition, even when driving with a voltage that does not allow the liquid crystal molecules to rise sufficiently, if the average optical axis direction of the liquid crystal molecules when voltage is applied and the optical axis direction of the birefringent plate are arranged to match, the field of view will be the same. A liquid crystal element with wide corners can be obtained.

[Example] Example 1.2, Comparative Example 1.2 Polyimide was applied as an overcoat for an alignment film on the electrode surfaces of a front substrate and a back substrate, each having a transparent electrode patterned on a glass substrate. The film thickness after thermosetting was approximately 80 nm. The surfaces of these polyimide films were horizontally aligned using a rubbing method, and the two substrates were placed so that the rubbing directions were perpendicular to each other so that they were aligned at 270", and the periphery was sealed with a sealant except for the injection port. The cell gap before liquid crystal injection was 6.
0 μm, and Δn1·dl was 1.2 μm.

A nematic liquid crystal to which cholesteryl nonanate was added as a chiral component was injected into this cell so that the helical pitch was 8.0 μm, and the injection port was sealed.

Various uniaxial birefringent plates having refractive indices as shown in Tables 1 and 2 are pasted on each side of this cell (Comparative example 1 = no birefringence plate, Example 1 = 0 (Example 2 = 2 birefringent plates of 0.50 μm, Comparative Example 1 = 2 birefringent plates of 1.00 μm), and a pair of polarizing plates above and below them. A liquid crystal element was manufactured by setting the polarization axis parallel to the rubbing direction of the cell.

In the liquid crystal element manufactured in this manner, the liquid crystal molecules were twisted by 270 degrees when no voltage was applied.

This liquid crystal element was driven at t+=tt=1/60 sec, that is, 60 Hz. Next, when a voltage of 12 V, which is higher than the threshold voltage, was applied, the liquid crystal molecules were vertically aligned. In this state, the liquid crystal cell becomes isodirectional with respect to light, and the light incident on the liquid crystal cell comes out while maintaining the incident polarization. Therefore, almost no light passes through.

Next, when the voltage is turned off, the liquid crystal molecules instantly move 90° within the cell.
The cell was in a twisted intermediate twisted state, and the incident light that passed through the incident side polarizing plate was twisted by 90'' in accordance with the twisted structure of the liquid crystal inside the cell, and the light was transmitted.

After this intermediate twisted state was reached, a voltage of 3 cm, which was less than the threshold voltage, was applied for a time of ts = 0.6 tz. As a result, this intermediate twisted state continues stably,
The light transmittance hardly changed.

For comparison, when the voltage is left off for time t2, the light transmittance gradually decreases to a maximum of 15
%. Therefore, when a voltage lower than the threshold voltage was applied after the intermediate twist state was reached, the time-averaged contrast ratio was improved compared to when no voltage was applied.

Therefore, after reaching the intermediate twisted state, a voltage of 3V, which is less than the threshold voltage, was applied for a time of t2 = 0.6t2 to compare the width of the viewing angle, and the results are shown in Figure 6 ( Comparative Example 1), FIG. 7 (Example 1), FIG. 8 (Example 2), and FIG. 9 (Comparative Example 2).

Note that Figures 6 to 11 are called isocontrast curves, and if the observation direction of the cell is expressed in polar coordinates and the angle is expressed as (θ, ψ), this (θ, ψ) will cause the liquid crystal to θ shows how the contrast ratio of the cell changes.
is shown by changing from 0 to 50'', and ψ from 0 to 360'. Note that ψ is shown by changing from 0 to 360'' counterclockwise, with the main viewing angle direction (downward) of the figure being 0°. and θ was set at 0° at the center, and ranged from 0 to 50″ concentrically. The contrast ratio curves showed only 1, 2, 10, and 20.

In an embodiment of the present invention, as shown in Table 1, 1'l:
nx> nx, and 0.1×Δn+'d+ <Δn
A birefringent plate is used such that x-dz<1.5XΔn1·dl. Therefore, compared to the case where no birefringent plate was used (Comparative Example 1, Figure 6), the contrast ratio indicated by diagonal lines was less than 1, that is, the area where the black and white contrast was reversed was very small. . Furthermore, the region with a high contrast ratio (10 or more) is wide (10 or more), and the viewing angle is wide (a liquid crystal element with excellent polarization conversion ability) has become possible.

On the other hand, even if a birefringent plate such that n It ''ny > n z was used, the total value of Δn2・d2 was larger than 1.5 times the value of Δn1・d of the liquid crystal layer. In the case of Comparative Example 2 (FIG. 9), it was found that the viewing angle was narrower (and the region of high contrast ratio was also narrower) than that of the present invention.

Examples 3 and 4 Two birefringent plates as shown in Table 2 are laminated and pasted on one side of a liquid crystal cell manufactured in the same manner as in Example 1, and a pair of polarizing plates are placed above and below the birefringent plates to reflect the polarized light. It was installed so that the axis was parallel to the rubbing direction of the cell.

Equal contrast curves when driven in the same manner as in Example 1 are shown in FIG. 10 (Example 3) and FIG. 11 (Example 4).

In the present invention, as shown in Table 2, nx=nx>n2, 0.1×Δn+−d+ <input nx·d, <1.
5 × Δn1・dl Since a birefringent plate is used, when the above-mentioned birefringent plate is not used (Comparative Example 1
, FIG. 6), the contrast ratio indicated by diagonal lines was 1 or less, that is, the area where the black and white contrast was reversed was very small. In addition, the region with a high contrast ratio (10 or more) has become wider, and the viewing angle has become wider (a liquid crystal element with excellent polarization conversion ability has become possible).

Example 5 A liquid crystal cell with polarizing plates on both sides manufactured in the same manner as in Example 1 was placed on both glasses, and the liquid crystal elements of the left and right glasses were made transparent to each other at 60 Hz in synchronization with the TV screen.
When controlled to be opaque, a clear three-dimensional image was obtained.

Example 6 A large liquid crystal cell manufactured in the same manner as in Example 1 was laminated with a polarizing plate only on the incident light side and placed in front of a television.The liquid crystal element was driven at 120Hz in synchronization with the television screen to generate polarized light. Conversion was done. When the viewer wore polarized glasses with the left and right polarization axes perpendicular to each other, a clear three-dimensional image was obtained.

Table 1 Table 2 [Effects of the Invention] The present invention has positive dielectric anisotropy, and the liquid crystal pitch p
The relationship d/p between and substrate gap d is 0.5×n < d/p
< 0.5X (n + 1) A nematic liquid crystal was used, and when no voltage was applied, the liquid crystal molecules in the cell assumed a natural twisted state of approximately 90° + 180' × n, and a voltage was applied. At times, the liquid crystal molecules take a vertically aligned state, and when the voltage is subsequently turned off, the liquid crystal molecules take an intermediate twisted state of approximately 90° + 180° × m, which is a relaxed state to the natural twisted state, and when this voltage is applied, The polarization direction of the incident light can be changed to 90" by utilizing two states: the vertically aligned state of the liquid crystal molecules and the almost 90° twisted state of the liquid crystal molecules when the voltage is turned off.
This change has the excellent effect of enabling much faster switching than conventional TN mode liquid crystal elements.

Further, in the present invention, at least one plate is used adjacent to the liquid crystal layer of the liquid crystal element, and the three main birefringence indices of the birefringent plate are nX, nx, and n2, and n8 is the birefringence. When taking the refractive index in the thickness direction of the plate, nx= ny> nx
For Δnl'd1 of the liquid crystal, Δn of the birefringent plate
The value of 2・d2 is 0.1XΔn.

・dl <Δn2・dz <1.5 ×Δn1・dl
A highly uniaxial birefringent plate is placed outside the liquid crystal layer, which provides a wide viewing angle (excellent polarization conversion performance).

Furthermore, in the present invention, after the voltage is turned off and the twisted state of the liquid crystal molecules becomes the intermediate twisted state, by applying a voltage lower than the threshold of the liquid crystal, the intermediate twisted state of the liquid crystal molecules continues for a long time. , excellent polarization conversion performance can be obtained.

In particular, by aligning the natural twisted state so that it matches the natural twisted state, the transition to the intermediate twisted state is also quick. However, as in the present invention, after the voltage is turned off and the twist of the liquid crystal molecules becomes an intermediate twist state, by applying a voltage below the threshold of the liquid crystal to the liquid crystal, this The intermediate twisted state continues stably for a long time.This provides two advantages: high-speed response and high contrast ratio.

Furthermore, by not using a highly twisted state which is a natural twisted state when no voltage is applied, there is little reduction in contrast ratio despite the large twist, and there is little adverse effect due to retardation.

The present invention can be applied in various ways without detracting from the effects of the present invention, and can be applied to applications that require high-speed conversion, such as image selection elements in projection-type stereoscopic televisions.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing the basic structure of a liquid crystal element of the present invention. FIG. 2 is a perspective view showing the definition of the principal refractive index of the birefringent plate used in the present invention. FIGS. 3A and 3B are a drive waveform diagram and a relative light transmission characteristic diagram, respectively, of a liquid crystal element to which a voltage below the liquid crystal threshold is applied in the latter half of the voltage-off period according to the present invention. FIGS. 4A and 4B are a drive waveform diagram and a relative light transmission characteristic diagram, respectively, of a liquid crystal element in which the voltage is simply turned off when the voltage is turned off. FIGS. 5(A) and 5(B) are perspective views illustrating details of the present invention. FIG. 6 to FIG. 11 are diagrams showing equal contrast curves of Examples and Comparative Examples. Transparent substrate: IA, IB Transparent electrode: 2A, 2B Sealing material: 3 Nematic liquid crystal: 4 Birefringent plate: 5A, 5B Polarizing plate: 6A, 6B Polarization axis Near A, 7B Figure 80 Figure 80 Figure 10 Figure 80 Figure 11

Claims (1)

[Claims] (1) A pair of horizontally aligned transparent electrode substrates with transparent electrodes are arranged so that their horizontal alignment directions are substantially orthogonal to each other, and a nematic liquid crystal is placed between them. A polarizing plate is placed on the incident light side of the nematic liquid crystal layer, and the polarization axis of the polarizing plate on the incident light side is approximately parallel to or substantially perpendicular to the alignment direction of the liquid crystal molecules on the substrate surface on the incident light side. The relationship d/p between the pitch p of the nematic liquid crystal and the substrate gap d is 0.5×n<d/p<0.5.
×(n+1) (n: an integer of n≧1), and by applying a voltage higher than the threshold voltage of the liquid crystal between both transparent electrodes, the liquid crystal molecules become vertically aligned, and then the voltage is turned off. , the liquid crystal molecules are in a relaxed state to their natural twisted state, approximately 90° + 180° x m (m: n>m≧0
In a liquid crystal element that changes the polarization direction of incident light by 90 degrees by using two states, the vertically aligned state of liquid crystal molecules and the intermediate twisted state of liquid crystal molecules, the birefringent plate is The three principal refractive indices are n_x, n_y, n_
z and n_z is the refractive index in the thickness direction of the birefringent plate, then n_x=n_y>n_z, and the birefringence is Δn_2・d_ of the birefringent plate, which is the product of the refractive index anisotropy Δn_2 of the plate and the thickness d_2 of the birefringent plate
The value of 2 is 0.1×Δn_1・d_1<Δn_2・d_
A liquid crystal element characterized in that a uniaxial birefringent plate such that 2<1.5×Δn_1·d_1 is disposed outside a liquid crystal layer. 2) In the liquid crystal element according to claim 1, d/ of the liquid crystal molecules is
p is 0.5<d/p<1, and the natural twist state is 2
70°, and is characterized in that the polarization direction of incident light is changed by 90° by utilizing two states of liquid crystal molecules: a vertical alignment state and a 90° intermediate twisted state. (3) A liquid crystal element according to claim 1 or 2, characterized in that birefringent plates are arranged on both sides of the liquid crystal layer. (4) A liquid crystal device according to any one of claims 1 to 3, wherein the alignment state of the liquid crystal molecules is made to match a pretilt angle due to horizontal alignment in a natural twisted state. (5) A liquid crystal device according to any one of claims 1 to 4, characterized in that a polarizing plate is also arranged on the outgoing light side of the nematic liquid crystal layer. (6) A polarization conversion element, characterized in that the liquid crystal element according to any one of claims 1 to 4 is disposed in front of a display. (7) In the method for driving a liquid crystal element according to any one of claims 1 to 5, after the twisted state of the liquid crystal molecules becomes an intermediate twisted state, a voltage lower than a threshold value of the liquid crystal is applied. A method for driving a liquid crystal element, characterized in that: