JPH08327993A - Liquid crystal element - Google Patents

Abstract

PURPOSE: To provide a liquid crystal element which can modulate light with enough contrast without using plural liquid crystal cells different in cell gap in the wavelength range of the light modulated by a polarized light-controlling type smectic liquid crystal element for optical modulation or even when the wavelength of light to be modulated is changed. CONSTITUTION: A phase difference plate is disposed in the optical path of a polarized light-controlling type smectic liquid crystal element for optical modulation in such a manner that the phase difference produced by the liquid crystal cell and the phase difference plate during modulating is controlled to satisfy the following relation. 0.8 × (wavelength λa/wavelength λb)<|(phase difference to transmitted light of wavelength λa)/(phase difference to transmitted light of wavelength λb)|<1.2 × (wavelength λa/wavelength λb).

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a smectic liquid crystal device.

[0002]

2. Description of the Related Art In recent years, various light modulators and display devices have been reduced in weight and power consumption, and in connection with this, there is an increasing tendency to use liquid crystal elements in these devices. Among liquid crystal elements, attention is paid to smectic liquid crystal elements such as ferroelectric liquid crystal elements and antiferroelectric liquid crystal elements because they have a wider viewing angle and faster response speed than commonly used TN liquid crystal elements. In particular, a liquid crystal element that performs light modulation by reversing the polarity of the voltage applied to the liquid crystal cell has attracted attention. In particular,
In the antiferroelectric liquid crystal element, since the liquid crystal material filled in the liquid crystal cell is used in the antiferroelectric liquid crystal state, the liquid crystal cell has excellent impact resistance, and the problem such as burn-in does not easily occur in the liquid crystal cell. It's getting a lot of attention.

A smectic liquid crystal element having the above-mentioned features is basically constituted by including a liquid crystal cell having a pair of substrates with electrodes and a liquid crystal material exhibiting a smectic phase (including a chiral smectic phase), and is required. According to the above, various polarization control means are provided. Of these, in the liquid crystal cell,
The distance between the electrodes of the pair of substrates with electrodes is adjusted to several μm or less, and a liquid crystal material exhibiting a smectic phase is sandwiched between the electrodes.

Conventionally, in order to perform light modulation with a sufficient contrast using a smectic liquid crystal element, the phase difference generated in the liquid crystal cell at the time of light modulation has a desired value corresponding to the wavelength of the light to be modulated. In addition, it was necessary to adjust the thickness of the liquid crystal cell. In particular, in optical switches for optical communication, optical shutters for stereoscopic image display, optical shutters used in welding glasses, etc., it is necessary to modulate light of a plurality of wavelengths or wavelengths of several tens of nm or more. When constructing the device, it was necessary to appropriately combine and use liquid crystal cells having different thicknesses. For this reason, there have been problems that it is difficult to reduce the size of these devices and the cost is increased.

Further, in the smectic liquid crystal element, there has been a demand for a liquid crystal element capable of modulating light with sufficient contrast even when the wavelength of modulated light or the wavelength of modulated light changes. .

As described above, it is necessary to change the cell gap of the liquid crystal cell according to the wavelength of the light modulated by the smectic liquid crystal element which modulates the light by inverting the polarity of the voltage applied to the liquid crystal cell. For some reason.

In order to modulate light with a sufficient contrast using a smectic liquid crystal element, the absolute value of the phase difference (wavelength shift) of the light generated in the liquid crystal cell during light modulation is proportional to the wavelength of the modulated light. Then you need to make it bigger. On the other hand, the magnitude of the retardation changes according to the absolute value of the birefringence of the liquid crystal material contained in the liquid crystal cell, and this birefringence value is large on the short wavelength side in the visible region and on the long wavelength side. It becomes smaller as it becomes. Furthermore, in the infrared region, it exhibits a complicated behavior due to the presence of absorption peaks of liquid crystals.

For this reason, for example, the wavelength λ
When a light of a and a light of wavelength λb are modulated by a smectic liquid crystal element, in order to obtain a liquid crystal cell that acts as a ½ wavelength plate for each light, two types of cell gaps da and db shown below are used. A liquid crystal cell having the following is required: da = λa / (2 * Δna) db = λb / (2 * Δnb) (where Δna is the birefringence index (birefringence index of the liquid crystal for light of wavelength λa). Difference), and Δnb represents the birefringence of the liquid crystal with respect to light of wavelength λb).

[0009]

SUMMARY OF THE INVENTION The present invention has been made in order to solve the above-mentioned problems that have occurred in the conventional smectic liquid crystal element, and is used in various fields such as optical communication and stereoscopic image display. When performing optical modulation using the electro-optical effect of the phase, without using a plurality of liquid crystal cells with different cell gaps, and in the wavelength range of the modulated light,
Alternatively, it is an object of the present invention to provide a liquid crystal element that can modulate light with sufficient contrast even when the wavelength of modulated light changes.

[0010]

SUMMARY OF THE INVENTION A liquid crystal device according to the present invention comprises a polarization control means and a smectic phase (including a chiral smectic phase).
And a liquid crystal cell filled with a liquid crystal material exhibiting a liquid crystal material, wherein the liquid crystal material performs a light modulation by reversing the polarity of a voltage applied to the liquid crystal cell in a state where the liquid crystal material exhibits a smectic phase. A phase difference plate or a plurality of phase difference plates is attached in the middle of the optical path in which the phase difference of the transmitted light generated by the liquid crystal cell and the phase difference plate or the plurality of phase difference plates at the time of the light modulation is the transmitted light of the wavelength λa. On the other hand, Ra, and Rb for transmitted light of wavelength λb (where λ
a and λb are included in the wavelength range in which light is modulated. ), The following formula:
0.8 × (λa / λb) <| Ra / Rb | <1.2
It is characterized in that x (λa / λb) is satisfied.

[0011]

DETAILED DESCRIPTION OF THE INVENTION The liquid crystal element according to the present invention comprises a polarization control means and a liquid crystal cell filled with a liquid crystal material exhibiting a smectic phase, preferably a chiral smectic phase.

Further, in the liquid crystal element according to the present invention, the light modulation is performed by reversing the polarity of the voltage applied to the liquid crystal cell, and a single or a plurality of phase difference plates are provided in the optical path where the light modulation is performed. It is attached.

In these phase difference plates, the phase difference of the transmitted light generated by the liquid crystal cell and the one or more phase difference plates at the time of the light modulation is Ra (nm) with respect to the transmitted light of the wavelength λa (nm). ), And becomes Rb (nm) for the transmitted light of wavelength λb (nm) (however, λa and λb are included in the wavelength range to be optically modulated), and 0.8 × (λa / λb) <| Ra /Rb|<1.2×
(Λa / λb) Preferably, 0.9 × (λa / λb) <| Ra / Rb | <1.1 ×
It is adjusted to be (λa / λb).

Therefore, in the liquid crystal element according to the present invention, λ
It is possible to perform light modulation with sufficient contrast for light having any wavelength of a and λb. The phase difference represented by the above relational expression is adjusted as follows, for example.

First, in a state where the liquid crystal material filled in the liquid crystal cell exhibits a smectic phase, a retardation plate having a wavelength dispersion property opposite to that of the liquid crystal material is used. A retardation plate having such a property is obtained by stacking a retardation plate having a large wavelength dispersion and a retardation plate having a small wavelength dispersion in the wavelength range of light to be modulated so that their fast axes are orthogonal to each other. It is made by combining. At this time, by selecting the material of the retardation plate, a retardation plate having an appropriate size of wavelength dispersion can be obtained.

In order to satisfy the relationship of the retardation represented by the above formula, for example, the cell gap of the liquid crystal cell and the thickness of the retardation plate (for example, when the retardation plate is the above laminated plate, the above wavelength dispersion is used). The thickness of the retardation plate having a large property and the thickness of the retardation plate having a small wavelength dispersion are adjusted as follows.

The light having a specific wavelength λo included in the wavelength range of the light modulated by the liquid crystal element is used to determine the cell gap of the liquid crystal cell so that the phase difference generated only by the liquid crystal cell exhibits a desired value. This cell gap is, for example, approximately 1 to 3 μ if the wavelength range of light modulated by the liquid crystal element is in the visible range.
It is about m.

Next, one or a plurality of retardation plates are arranged in the optical path where the light modulation is performed, for example, on the light incident side and / or the light emitting side of the liquid crystal cell. At this time, the retardation plate may be in close contact with the substrate of the liquid crystal cell or may be separated from the liquid crystal cell.

In this state, the phase difference is measured by changing the wavelength of the light passing through the liquid crystal cell and the retardation plate, and λo (nm)
The phase difference becomes 0, and the thickness of the phase difference plate is set so that (R + RLC) (the sum of the phase difference R of the phase difference plate and the phase difference RLC of the liquid crystal cell) shows a desired value at the desired shortest and longest wavelengths. Adjust.

The above (R + RLC), that is, the phase difference Ro at an arbitrary wavelength λo included in the wavelength range to be optically modulated.
Is approximately λo / 2m (where λo is the wavelength of light transmitted through the light modulation optical path formed by the liquid crystal element, and m is 0
It is an integer excluding. ) Is preferable, and particularly, it is preferable that the wavelength is ½ wavelength or ¼ wavelength over the entire visible range. Note that approximately λo / 2m is 0.85 ×
λo / 2m to 1.15 × λo / 2m, preferably 0.9
It means within the range of × λo / 2m to 1.1 × λo / 2m.

In particular, a liquid crystal element in which the above (R + RLC) is adjusted to be a ½ wavelength or a ¼ wavelength over the entire visible range is suitable for use in fields such as stereoscopic image display and optical communication. .

The retardation plate used in the liquid crystal device of the present invention is, for example, a plate-shaped retardation plate such as a retardation plate obtained by processing a crystal such as quartz or calcite into a plate or a polymer stretched film. A film-like retardation film is used.

When the wavelength range of the light modulated by the liquid crystal element is in the visible range, examples of the material used for forming the retardation plate having a large wavelength dispersion include polycarbonate, polysulfonate, polyethylsulfone. Examples thereof include polyvinyl alcohol, polymethylmethacrylate, quartz, and calcite. Examples of the material used for forming the retardation plate having a small wavelength dispersion property include polyacrylate, polyarylate, and various liquid crystal polymers.

As the polarization control means used in the liquid crystal element of the present invention, a polarizing film, a Nicol prism and the like can be mentioned. Further, the substrate of the liquid crystal cell used in the liquid crystal element according to the present invention, soda glass, borosilicate glass, alkali-free glass, a glass substrate such as quartz, or a plate made of a transparent resin such as polyolefin, polyester, polystyrene or A film substrate may be used. Here, when a substrate made of a material other than quartz glass is used, in order to prevent impurities such as metal ions and stabilizers contained in the substrate from eluting into the liquid crystal material inside the liquid crystal cell, SiO 2 is formed on the substrate. It is preferable that a base film such as _{2 is} formed in advance by a dipping method, a vapor deposition method, a sputtering method or the like, and then an electrode is formed on this base film.

The electrode formed directly on the substrate or through the underlying film is preferably transparent or almost transparent to the entire wavelength range of the light modulated by the liquid crystal element. When the light modulated by the liquid crystal element is visible light, for example, an indium oxide-tin oxide-based conductive film or a zinc oxide-based conductive film known as ITO is used for the CV method.
The electrode can be formed by a method such as D method, sputtering method, ion plating method, or vacuum deposition method.

Further, an insulating film such as SiO ₂ may be formed on one surface or both surfaces of the electrode with a film thickness of 100 to 1000 Å by a vacuum deposition method, a sputtering method or the like for the purpose of preventing a short circuit.

Furthermore, on one or both of the electrodes, an alignment film may be formed on the uppermost surface in contact with the liquid crystal material inside the liquid crystal cell. Examples of the alignment film include an organic alignment film made of a polymer thin film such as polyimide, polyamide, or polyvinyl alcohol, and an inorganic alignment film made of SiO ₂ or the like. Among them, the organic alignment film is formed with a film thickness of 50 to 3000 Å by a method such as a printing method, a spin coating method, a vapor deposition polymerization method, and a dipping method. In particular, it is preferable to use a polyimide thin film for stable operation for a long period of time as an element. The surface of this organic alignment film is preferably subjected to an alignment treatment such as rubbing in a certain direction with a cloth such as nylon, cotton, or rayon which has been subjected to a raising treatment.

On the other hand, the inorganic alignment film is subjected to a desired alignment treatment by being formed by an oblique vapor deposition method, that is, a method of vapor deposition from an oblique direction with respect to the substrate. The cell used in the liquid crystal element according to the present invention (the liquid crystal cell before encapsulating the liquid crystal material) has a pair of electrode-attached substrates each of which may have an alignment film or the like formed on one or both of them as described above. It is manufactured by making electrodes formed on a substrate face each other, stacking them via a spacer, and bonding in this state except for a liquid crystal material injection port. At this time, as the spacer, a resin film having a thickness substantially equal to a desired cell gap with a liquid crystal filling portion and an injection port cut out, alumina having a diameter substantially equal to the desired cell gap, silica, a true spherical spacer such as resin, Alternatively, a columnar spacer made of glass or the like having a diameter substantially equal to a desired cell gap is used. When using a resin film as a spacer,
An adhesive is applied between the substrate and the spacer to bond the spacer and both substrates together. When using spherical spacers, the spacers are sprinkled on one substrate, then the other substrate is stacked and bonded with an adhesive. In the case of using the columnar spacer, the spacer is kneaded in an adhesive and applied to a necessary portion of one substrate, and the other substrate is bonded.

The liquid crystal cell used in the liquid crystal element according to the present invention is filled with a liquid crystal material exhibiting a smectic phase in a temperature range in which the liquid crystal cell can be driven. The liquid crystal material exhibiting the smectic phase is not particularly limited as long as it is a liquid crystal material exhibiting the smectic phase in a temperature range in which the liquid crystal cell can be driven, such as a ferroelectric liquid crystal material or an antiferroelectric liquid crystal material. However, the antiferroelectric liquid crystal material is preferable in that the liquid crystal cell is resistant to impact and the image sticking of the liquid crystal material is unlikely to occur in a portion in contact with the liquid crystal material inside the liquid crystal cell. Among the antiferroelectric liquid crystals, the liquid crystal material can be driven in a wide temperature range, and when the liquid crystal cell is driven, good operation characteristics can be obtained. The liquid crystal material is represented by the following formula [I]: R'- (AX) _p- (BY) _q- (CZ) _r- R ^* ... [I] (In the formula, R'is an alkyl group, an alkoxy group, a halogenated alkyl group and a halogenated alkoxy group. A group having 3 to 20 carbon atoms, wherein A, B and C are each independently

[0030]

[Chemical 3]

And a group in which some or all of the hydrogen atoms of these groups are substituted with halogen atoms, methyl groups, ethyl groups, methoxy groups, ethoxy groups, hydroxyl groups, trifluoromethyl groups, difluoromethyl groups, monofluoromethyl groups, etc. At least one of A, B and C is selected from

[0032]

[Chemical 4]

And a group in which some or all of the hydrogen atoms of these groups are substituted with halogen atoms, methyl groups, ethyl groups, methoxy groups, ethoxy groups, hydroxyl groups, trifluoromethyl groups, difluoromethyl groups, monofluoromethyl groups, etc. X, Y and Z are each independently -COO.
-, - OCO -, - CH 2 CH 2 -, - CH 2 O -, - O
_{CH 2 -, - S-S} -, - CO-CH 2 - and -CH ₂
Represents a group selected from —CO—, and R ^* represents an optically active group having at least one asymmetric carbon atom and having 4 to 20 carbon atoms (a hydrogen atom bonded to a carbon atom constituting the optically active group is a halogen atom; Optionally substituted), and p, q and r each independently represent 0 or 1. Particularly preferably, the compound is represented by

[0034]

According to the present invention, a phase difference plate is provided in the middle of the optical path, and the following formula: 0.8 × (λa / λb) <| Ra / Rb | <1.2 ×
A smectic liquid crystal element is provided at the time of light modulation so as to satisfy (λa / λb) (where Ra represents a phase difference with respect to transmitted light of wavelength λa and Rb represents a phase difference with respect to transmitted light of wavelength λb). Since the phase difference of the transmitted light generated by the liquid crystal cell and the retardation plate is adjusted, it is possible to modulate the light in the wavelength range of the modulated light without using a plurality of liquid crystal cells having different cell gaps. Provided is a smectic liquid crystal device capable of modulating light with sufficient contrast even when the wavelength of light changes.

The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

[0036]

[Example] IT having a thickness of 1000 angstrom on one side
A polyimide film having a thickness of 600 angstroms was formed on each of the two glass substrates having O (Indium Tin Oxide) transparent electrodes formed thereon by spin coating. Then
The polyimide film was rubbed with a napped nylon cloth, and spherical silica with a diameter of 2.4 μm was sprayed as a spacer on the transparent electrode of one of the glass substrates.
The above-mentioned two glass substrates were attached so that their polyimide films face each other, to produce a cell.

Next, a liquid crystal composition prepared by mixing liquid crystal compounds represented by the following formulas (1) and (2) in a weight ratio of 8: 2 is injected between the polyimide films of the cells thus produced. And a liquid crystal cell was produced.

[0038]

[Chemical 5]

After the liquid crystal cell manufactured as described above was inserted between two polarizing plates arranged in the crossed Nicols position, the darkest state was obtained when a voltage of +15 V was applied between the transparent electrodes of the liquid crystal cell. That is, the liquid crystal cell was arranged so that the amount of light transmitted through the polarizing plate / liquid crystal cell / polarizing plate was minimized. Then, the above-mentioned two polarizing plates were arranged in a para-Nicol position, and an optical spectrum transmitted through the polarizing plate / liquid crystal cell / polarizing plate was measured while applying a voltage of −15 V between the transparent electrodes of the liquid crystal cell. The transmission spectrum shown in the curve (a) of was obtained. The minimum value of the transmittance shown by the curve (a) in FIG. 1 coincided with the minimum value of the transmittance when the two polarizing plates were arranged in the crossed Nicols position. This result indicates that the liquid crystal cell acts as a ½ wavelength plate for incident light near the wavelength of 600 nm.

Next, a polycarbonate (hereinafter referred to as PC) sheet having a thickness adjusted to have a phase difference of 1334 nm when transmitting a light having a wavelength of 550 nm, and a thickness of the sheet having the phase difference of 1294 nm were prepared. Adjusted polymethylmethacrylate (hereinafter referred to as PMMA)
A retardation plate was produced by combining the sheets made so that the respective fast axes were orthogonal to each other.

This retardation plate was inserted between the liquid crystal cell and the polarizing plate (specify either the light incident side, the light emitting side, or both), and the two polarizing plates were arranged in the para-Nicol position. After that, the retardation plate was arranged so as to be in the darkest state when a voltage of −15 V was applied between the transparent electrodes of the liquid crystal cell.
In this state, the light spectrum transmitted through the two polarizing plates, the liquid crystal cell and the retardation plate was measured, and the transmission spectrum shown by the curve (b) in FIG. 1 was obtained. This result is
Liquid crystal cell is 1/2 for incident light of 450-700 nm
It shows that it is acting as a wave plate.

By the way, the phase difference of transmitted light generated by the liquid crystal cell and the retardation plate under the above-mentioned conditions is a wavelength of 500 nm.
For transmitted light of 249 nm (hereinafter referred to as Ra).
And 328 nm for transmitted light with a wavelength of 650 nm.
(Hereinafter, referred to as Rb), and | Ra / Rb | = 0.
759 and 0.8 × (500/650) = 0.61
5, 1.2 × (500/650) = 0.923, so the following equation: 0.8 × (500/650) <| Ra /
Rb | <1.2 × (500/650) was satisfied.

[0043]

[Comparative Example] A PC sheet having a thickness adjusted to have a phase difference of 1360 nm when transmitting light having a wavelength of 550 nm and a PMMA sheet having a thickness adjusted to have the phase difference of 1260 nm. A light transmission spectrum was measured in the same manner as in the example except that a retardation plate was prepared and the phase difference generated when light having a wavelength of 550 nm was transmitted through the liquid crystal cell and the retardation plate was shifted by 20% or more from the half wavelength. did.
As a result, it became clear that the transmittance exceeded 5% for incident light of any wavelength of 450 to 700 nm, and the transmitted light was changed to elliptically polarized light.

By the way, the phase difference of the transmitted light generated by the liquid crystal cell and the retardation plate under the above conditions is a wavelength of 500 nm.
For transmitted light of 286 nm (hereinafter referred to as Ra).
And 283 nm for transmitted light with a wavelength of 650 nm
(Hereinafter, referred to as Rb), and | Ra / Rb | = 1.
01> 0.923 = 1.2 × (500/650).

[Brief description of drawings]

FIG. 1 is a graph showing a spectral transmittance for explaining an effect of a liquid crystal element according to the present invention.

Claims (5)

[Claims] 1. A polarization control means and a liquid crystal cell filled with a liquid crystal material exhibiting a smectic phase, wherein the polarity of a voltage applied to the liquid crystal cell is reversed in the state where the liquid crystal material exhibits the smectic phase to generate light. In a liquid crystal element that performs modulation, a single or a plurality of phase difference plates are attached in the middle of the optical path in which the light modulation is performed, and the transmitted light generated by the liquid crystal cell and the single or a plurality of phase difference plates at the time of the light modulation. The phase difference is Ra for the transmitted light of wavelength λa and Rb for the transmitted light of wavelength λb (where λa and λb
Is included in the wavelength range that is optically modulated. ) And satisfying the following formula: 0.8 × (λa / λb) <| Ra / Rb | <1.2 ×
(Λa / λb) 2. The liquid crystal device according to claim 1, wherein the smectic phase is a chiral smectic phase. 3. A phase difference Ro at an arbitrary wavelength λo included in a wavelength range to be optically modulated is approximately λo / 2m (λo is a wavelength of light passing through the optical modulation optical path, and m is an integer except 0). .) The liquid crystal element according to claim 1. 4. The liquid crystal element according to claim 2, wherein the retardation plate is a laminate of layers having different wavelength dispersions of birefringence. 5. The liquid crystal material has the following formula [I]: R '-(AX) _p- (BY) _q- (CZ) _r- R ^* ... [I] (wherein R'is a group having 3 to 20 carbon atoms selected from an alkyl group, an alkoxy group, a halogenated alkyl group and a halogenated alkoxy group, and A, B and C are each independently And part or all of the hydrogen atoms of these groups are halogen atom, methyl group, ethyl group, methoxy group, ethoxy group, hydroxyl group, trifluoromethyl group, difluoromethyl group,
Selected from groups substituted with a monofluoromethyl group and the like, at least one of A, B and C is And part or all of the hydrogen atoms of these groups are halogen atom, methyl group, ethyl group, methoxy group, ethoxy group, hydroxyl group, trifluoromethyl group, difluoromethyl group,
A group substituted with a monofluoromethyl group or the like, X, Y and Z are each independently -COO-, -O.
_{CO -, - CH 2 CH 2} -, - CH 2 O -, - OCH 2 -,
Represents a group selected from —SS—, —CO—CH ₂ — and —CH ₂ —CO—, and R ^* has 4 to 2 carbon atoms having at least one asymmetric carbon.
0 represents an optically active group (a hydrogen atom bonded to a carbon atom constituting the optically active group may be substituted with a halogen atom), and p, q and r each independently represent 0 or 1. Represent 5. The liquid crystal device according to claim 1, which is composed of a compound represented by the formula (4).