JP5143475B2 - Nematic liquid crystal composition and bistable nematic liquid crystal display device - Google Patents

Description

  The present invention relates to a nematic liquid crystal composition that can be suitably applied to a bistable nematic liquid crystal display device, and a bistable nematic liquid crystal display device using the same.

A liquid crystal display element (LCD) is thin, light, and has low power consumption, and thus has been applied to various applications. This LCD has a structure in which a liquid crystal composition is sandwiched between two substrates having at least one transparent substrate, and the two substrates have liquid crystal compositions on their inner surfaces (surfaces facing each other). An electrode layer and an alignment film subjected to an alignment process for aligning liquid crystals are applied so that an electric field can be applied to the object. This alignment treatment has a function of anchoring (anchoring force) at the same time as arranging the liquid crystal composition in the alignment film.
When an electric field equal to or higher than the Fredericksz transition voltage is applied to the liquid crystal composition, the orientation direction of the liquid crystal composition changes, an optical change occurs due to the birefringence of the liquid crystal composition, and a display is obtained by using a polarizing plate. Functions as an element.

An LCD as described above (referred to as a “classic” LCD) has the following characteristics.
(1) After applying an external electric field to display information, the display disappears when the electric field is turned off.
(2) The alignment film functions to align liquid crystal molecules horizontally with respect to the alignment film, and has a very strong anchoring force for the liquid crystal molecules. For this reason, even when an electric field is applied, the liquid crystal molecules in the vicinity of the alignment film are not aligned in the direction of the electric field, but are substantially maintained in the horizontal direction with respect to the alignment film.
(3) When the electric field is turned off, the state before the application of the electric field is restored.

  In these “classic” LCD liquid crystal compositions, various studies have been made to optimize the characteristics such as temperature range, viscosity, elastic constant, birefringence, dielectric anisotropy, and threshold characteristics and enhance the characteristics of the LCD. Has been made. In order to optimize the above characteristics, a single compound cannot be achieved, and it is necessary to combine a plurality of compounds (Non-Patent Document 1).

Further, in this “classic” LCD, the anchoring force for the alignment film with respect to the liquid crystal molecules does not require a strict design, and a strong anchoring force is required, in other words, a certain strength or more is required (approximately L _Z <15 nm, _LZ will be described later.) Studies have already been made on alignment films that can provide such strong anchoring force, and several types of alignment film materials are currently used (Non-Patent Document 2).

  In recent years, a new nematic liquid crystal display element called a bi-stable nematic display has been studied. In this display, the liquid crystal molecules have two stable alignment states, and voltage application is necessary only when switching between the two alignment states, and it is not necessary to continue to apply voltage to maintain the display. In this display principle, the power consumption is proportional to the number of switching of the display, and the power consumption approaches 0 as the switching period becomes longer. Therefore, it is very useful for a mobile display where low power consumption is required.

  Two bi-stable displays that are stabilized by the action of an alignment film on the substrate have been proposed. One has two alignment states on the alignment film (bistable), and the other has one alignment state on the alignment film (monostable). . These displays switch between two stable states by breaking the anchoring of the liquid crystal molecules on at least one alignment film. By applying a voltage, the liquid crystal molecules on the alignment film are oriented in a direction where the interface torque is zero and the energy is maximized. When the voltage is turned off, the liquid crystal molecules on the alignment film return to a stable alignment state, and the bulk liquid crystal shifts to one or another stable state.

  A display developed by ZBD Displays (Non-Patent Document 3) uses an alignment film having two stable states. The liquid crystal molecules on the alignment film have two stable states, an alignment state substantially horizontal to the substrate and an alignment state substantially vertical to the substrate. In Orsay Solid State Physics Laboratory, a bi-stable nematic display having a bi-stable orientation state with two different tilt angles is proposed. One is a technique using a flexoelectric effect (Patent Document 1), and the other is a technique using an electronic chiral effect (Patent Document 2).

  These two bi-stable nematic displays use a monostable alignment film and switching due to anchoring breakage, BiNem (registered trademark) by Nemoptic, France (Patent Documents 3 to 5), and SBiND display Further improvements have been made by LICET in Italy (Patent Documents 6-8).

FIG. 1 shows a switching method of a bistable nematic display by Nemoptic. This display uses two states. One state is a uniform or slightly twisted state (T ₀ ), in which the liquid crystal molecules are substantially horizontal (0 ± 20 °) to each other. Another state is a state twisted by 180 (± 20) ° (T ₁₈₀ ). The natural pitch P ₀ of the liquid crystal composition is adjusted to be four times the cell thickness so that these two states are energetically equal. When no voltage is applied, the above two states are energy minimum values, and a stable alignment state is maintained. When a high voltage is applied, anchoring breakage occurs on at least one of the substrates (specifically, on the alignment film), and the liquid crystal molecules are almost in homeotropic alignment (H). This orientation state (H) is in a transition state and can be switched to one of two stable states (T ₀ , T ₁₈₀ ). When the voltage is turned off slowly, the state can be changed to the T ₀ state by the elastic coupling effect, and when the voltage is turned off quickly, the state can be changed to the T ₁₈₀ state by the hydrodynamic coupling.

  Bistable displays that are switched by breaking anchoring require liquid crystal materials and alignment films with special characteristics.

1) Anchoring of at least one of the alignment films needs to be weak enough that the anchoring is broken by an applied voltage that matches the electrical and electrochemical characteristics of the nematic liquid crystal compound.
2) The anchoring of the alignment film should not be too weak so that the liquid crystal material becomes stable by anchoring. In order to maintain the texture, the torque due to anchoring needs to be larger than the elastic torque of the liquid crystal on the alignment film due to the bulk liquid crystal in a stable state.

3) The electrochemical stability of the liquid crystal material needs to be higher than the normal “classic LCD”. In an actual “classic LCD”, only bulk liquid crystals are moving. The voltage is close to 2-3 times the Fredericks transition voltage, and the minimum voltage is determined by the nematic elastic constant. When operating by anchoring destruction, considering the texture stability condition, approximately 10 times the Fredericks transition voltage is required.

4) The optical response of the display is determined by the viscosity and elastic constant of the liquid crystal material. When the stable state is determined by hydrodynamic coupling, the viscosity and elastic constants are fundamental constants in driving.
5) Since a cell thickness thinner than that of “classic LCD” is used, a high refractive index anisotropy (0.14 to 0.20) is necessary to obtain a good contrast. In the bi-stable display using the anchoring breakdown using the liquid crystal material and the alignment film as described above, the anchoring breakdown voltage is proportional to the cell thickness, that is, the voltage is low at a small cell thickness.

6) The temperature range of the nematic liquid crystal needs to be wider than the operating temperature range. In fact, not all of the above characteristics are satisfied over the entire temperature range of nematic liquid crystals. Nematic temperature range (ΔT _N ) is T _N-I (nematic _- isotropic transition temperature) and T _X-N (transition temperature from nematic to higher liquid crystal phase, or transition temperature from crystalline layer to glass state) It is between. The nematic temperature range (ΔT _N ) needs to be wider than the operating temperature range in order to obtain the above characteristics in a technically acceptable temperature range (temperature range of 50 to 80 ° C. centering on room temperature).

The anchoring force design is very sophisticated and accurate. This anchoring force is caused by the anisotropy of the interaction between the interface and the liquid crystal compound. Anchoring is characterized by the directionality and its strength induced by the adjacent interface of the liquid crystal molecules. This direction is called an easy axis, and the easy axis direction n ₀ is represented by an azimuth angle (φ ₀ ) and a polar angle (θ ₀ ) (see FIG. 2). The average alignment direction of the nematic liquid crystal is along this easy axis. In the absence of external influences, the liquid crystal molecules are aligned parallel to the easy axis in order to minimize the interaction energy from the interface. This interaction energy (anchoring energy) is expressed by Equation (1) using a first-order approximation (Non-Patent Document 4).

In Equation (1), phi represents the azimuth angle of the nematic liquid crystal on the interface to (azimuthal angle), θ represents the polar angle of the nematic liquid crystal on the interface of the (zenithal angle), _{W A} represents azimuthal anchoring energy , W _Z represents polar angle anchoring energy.

The azimuthal anchoring energy W _A from the nature of the nematic liquid crystal, depends on the anisotropy excited in the alignment film according to the process of alignment or the like. Even if sufficient azimuth anchoring is required to maintain the twist texture, this issue will not be addressed here.
In bi-stable displays driven by anchoring destruction, polar anchoring destruction is important, and we pay attention to this phenomenon.
Zenithal anchoring energy W _Z is chemical properties of the alignment films, and depends strongly on the nematic liquid crystal material. In most solid alignment films, the polar angle anchoring energy is 1 to 2 digits higher than the azimuth angle anchoring energy. When the direction of the director of the liquid crystal composition deviates from the easy axis, the interfacial energy is not zero, and also has energy derived from the elastic constant. This interfacial energy is associated with an extrapolation length that is the ratio of the elastic energy and anchoring energy of the bulk liquid crystal. The extrapolation length L _Z of polar angle anchoring is represented by L _Z = K ₃₃ / W _Z. Here _{K 33} is the bending elastic constant. When L _Z <15 nm, it is considered “strong polar angle anchoring”, and when L _Z > 25 nm, it is considered “weak polar angle anchoring”.

The alignment direction of the liquid crystal molecules can be changed by an external electric field or magnetic field. For example, when an electric field perpendicular to the substrate surface is applied, the liquid crystal molecules inside the cell are aligned along the electric field direction (ie, θ = 0) if they have positive dielectric anisotropy, and the substrate if there is no electric field. Oriented almost parallel to the surface (ie, θ = about 90 °). The polar angle θ of the liquid crystal molecule director on the substrate surface is given as a function of the electric field and varies continuously. When the electric field exceeds the critical electric field intensity E _C , θ becomes 0, and the director of the liquid crystal molecules on the substrate surface becomes independent of the anchoring torque and the electric torque. This state is called a state in which polar angle anchoring destruction (polar angle anchoring break) has occurred. The critical electric field strength E _C is expressed by Equation (2).

In Formula (2), W _Z represents polar angle anchoring energy, K ₃₃ represents bending elastic constant, and Δε represents dielectric anisotropy (however, relative ratio to dielectric constant ε ₀ of vacuum).

This critical electric field strength E _C is an electric field necessary for driving a device utilizing polar angle anchoring breakdown. Therefore, a large Δε, a large flexural modulus and a small polar anchoring energy are required to control this device.

In fact, what is important in displays using zenithal anchoring breaking is a voltage U _Z cause zenithal anchoring breaking. That is, the product of the critical electric field and the cell thickness. Usually, the birefringence magnitude of the cell of the bi-stable nematic display is adjusted to be equal to the half wavelength of the center wavelength of the light passband. When polar angle anchoring is defined, threshold break voltage U _{λ / 2} is used. This is the value of the breakdown voltage U _Z in optical thickness lambda / 2 cells. U _{λ / 2} is expressed by Equation (3).

In Equation (3), λ is the center wavelength of the light passband, W _Z is polar angle anchoring energy, L _Z is the extrapolation length of polar angle anchoring, Δn is the refractive index anisotropy at wavelength λ, and K ₃₃ Is a bending elastic constant, and Δε is a dielectric anisotropy. The inventors believe that this polar angle anchoring falls into a weak category if U _{λ / 2} in the operating temperature range is a voltage that can be supplied by a driver that is currently in common use. _{If λ / 2} is 25 V or less, it can be said that the anchoring is low.

The polar angle anchoring energy depends on the material of the alignment film, the surface treatment method, the liquid crystal composition used, and the temperature.
The properties of the alignment film greatly affect the polar angle anchoring energy. Polyimide alignment films used in “classic” LCDs exhibit strong polar angle anchoring energy for most nematic liquid crystal materials. For example, a commercially available polyimide alignment film (SE140, manufactured by Nissan Chemical Industries, Ltd.) has L _Z = 7 nm with respect to pentylcyanobiphenyl (5CB), and polar anchoring is strong.

On the other hand, Patent Document 9 and Patent Document 11 report the development of a copolymer film having a weak polar angle anchoring against 5CB and other nematic liquid crystal materials by Nemoptic (at 20 ° C for 5CB). L _Z> 25nm). In both patents, moderate to strong azimuth anchoring is obtained by normal rubbing treatment, and textures of T ₀ and T ₁₈₀ are stably obtained.

Patent Document 10 discloses an example of a liquid crystal composition having a small polar angle anchoring. According to this, it is described that a liquid crystal composition having a low _{Uλ / 2} is obtained by a combination of specific liquid crystal compounds, and further, a combination having a wide temperature range of a nematic phase is described. In fact, the anchoring characteristic optimized in the bi-stable display depends on the alignment film and the liquid crystal material. However, in a bi-stable nematic display that uses polar anchoring breakdown, the temperature range of the nematic phase and the operating temperature range of the display are not proportional. That is, even if the operating voltage is low at room temperature, if the temperature dependency is large, the operating temperature range is substantially narrowed. In fact, no bi-stable nematic display that can operate in a wide temperature range is currently available. Therefore, it was necessary to find a combination of liquid crystal compositions that can be driven over a wide operating temperature range.
Handbook of Liquid Crystals, 1988, Wiley-VCH Weinheim Liquid Crystals—Applications and Uses, 1990, World Scientific Publishing Co. Pte. Ltd. Singapore G. P. Bryan-Brown et al., Nature, 399, 338, 1999. A. Rapini and M.M. Papoular, J. et al. Phys. (Fr), C4, Vol. 30, pp. 54-56, 1969 French Patent Application Publication No. 2663770 French Patent Application Publication No. 2567699 French Patent Application Publication No. 2740893 French Patent Application Publication No. 2740894 US Pat. No. 6,327,017 European Patent Application No. 0773468 US Pat. No. 5,993,173 JP-A-9-274205 European Patent Application No. 1259854 JP 2005-133057 A US Pat. No. 7,067,180

  The present invention has been made in view of the above circumstances, and provides a nematic liquid crystal composition having a wide operating temperature range when used in a bi-stable nematic liquid crystal display device, and a bi-stable nematic liquid crystal display device using the same. This is the issue.

  The present invention has found the following findings as a result of studying various combinations of liquid crystal compounds in order to solve the above problems. That is, from general formulas (A1) to (A6)

(In the formulas (A1) to (A6), R ¹ represents an alkyl group or alkenyl group having 2 to 7 carbon atoms (one or two or more methylene groups present in the alkyl group or alkenyl group represent an oxygen atom) Are each independently substituted with an oxygen atom, —COO—, or —OCO— as those that are not directly bonded to each other.
X ¹ represents a cyano group, a fluorine atom, a chlorine atom, a trifluoromethyl group, a trifluoromethoxy group, or a difluoromethoxy group (—OCHF ₂ ),
Z ¹ and Z ² are each independently —COO—, —OCO—, —CH ₂ O—, —OCH ₂ —, —CF ₂ O—, —OCF ₂ —, —C≡C—, or a single bond Represents
Z ³ and Z ⁴ are each independently —CH ₂ CH ₂ —, —COO—, —OCO—, —CH ₂ O—, —OCH ₂ —, —CF ₂ O—, —OCF ₂ —, or Represents a bond,
Z ⁵ _{is, -CH 2 CH 2 -, -} CH = CH -, - COO -, - OCO -, - CH 2 O -, - OCH 2 -, - CF 2 O -, - OCF 2 -, or a single bond Represents
Y ¹ to Y ⁶ each independently represent a hydrogen atom, a fluorine atom, a chlorine atom, a trifluoromethyl group, or a trifluoromethoxy group,
Ring T ¹ is a 1,4-phenylene group or a 1,4-cyclohexylene group (among these groups, the 1,4-phenylene group is unsubstituted or substituted with a fluorine atom, a chlorine atom, a methyl group, Which can have one or more trifluoromethyl groups or trifluoromethoxy groups).
m represents 0 or 1;
p and q represent 0 or 1, where p + q is 0 or 1. )
Containing 20% by mass or more of one or more compounds selected from the compound group A represented by: and containing 3% by mass or more of the compound represented by the general formula (A6),

  From general formulas (B1) to (B11)

(In the formulas (B1) to (B11), R ² and R ³ are each independently an alkyl group having 1 to 7 carbon atoms or an alkenyl group having 2 to 7 carbon atoms (in the alkyl group or alkenyl group). 1 or 2 or more methylene groups present may be each independently substituted with an oxygen atom, —COO— or —OCO— as if oxygen atoms were not directly bonded to each other.
Z ⁶ represents —COO—, —OCO—, —CH ₂ O—, —OCH ₂ —, —CF ₂ O—, —OCF ₂ —, —C≡C—, or a single bond,
Z ⁷ represents —CH ₂ CH ₂ —, —COO—, —OCO—, —CH ₂ O—, —OCH ₂ —, —CF ₂ O—, —OCF ₂ —, or a single bond,
Z ⁸ _{is, -CH 2 CH 2 -, -} CH = CH -, - COO -, - OCO -, - CH 2 O -, - OCH 2 -, - CF 2 O -, - OCF 2 -, or a single bond Represents
Z ⁹ and Z ¹⁰ each independently represent —CH ₂ CH ₂ —, —COO—, —OCO—, or a single bond,
Y ⁷ to Y ¹⁴ each independently represents a hydrogen atom, a methyl group, a fluorine atom, a chlorine atom, a trifluoromethyl group, or a trifluoromethoxy group,
Rings T ² and T ³ are each independently a 1,4-phenylene group or a 1,4-cyclohexylene group (among these groups, the 1,4-phenylene group is unsubstituted or fluorine as a substituent). Which can have one or more atoms, chlorine atoms, methyl groups, trifluoromethyl groups or trifluoromethoxy groups),
n represents 0 or 1. )
A nematic liquid crystal composition containing 5 to 50% by mass of one or more compounds selected from the compound group B represented by:

The relative proportions of the compounds used in the nematic liquid crystal composition are as follows for the composition:
-The nematic-isotropic transition temperature (T _N-I ) of the liquid crystal composition is 60 ° C or higher,
The temperature range (ΔT _N ) in which the liquid crystal composition exhibits a nematic phase is 70 ° C. or higher,
The dielectric anisotropy at 20 ° C. is 8 × 10 ⁻¹¹ F / m or more,
For a bi-stable nematic liquid crystal display element in which the product (Δn · d) of refractive index anisotropy Δn and thickness d at 20 ° C. is 275 nm and at least one substrate has a weak polar anchoring force The anchoring breakdown voltage U _{λ / 2} when supported between the substrates is 25 V or less.
A nematic liquid crystal composition characterized in that it is determined to be obtained simultaneously is provided.

  The liquid crystal composition of the present invention is used for a bi-stable nematic liquid crystal display device in which at least one substrate is supported on two substrates having a weak polar anchoring force, and has a wide operating temperature range. A display element can be obtained.

Hereinafter, an example of the present invention will be described.
In the liquid crystal composition of the present invention, the compounds of the general formulas (A1) to (A6) belonging to the compound group A are compounds having a polar group at the terminal, and are important compounds for causing anchoring destruction. In particular, by including the compound represented by the general formula (A6), the temperature dependency of the driving voltage can be improved and the operating temperature range can be widened.

The case where it is especially preferable about the compound represented by general formula (A1) to (A6) is illustrated below.
X ¹ is preferably a cyano group or a fluorine atom.
Z ¹ and Z ² are preferably —COO—, —OCO—, or a single bond.
Z ³ and Z ⁴ are preferably —COO—, —OCO—, —CH ₂ CH ₂ —, or a single bond, and more preferably a single bond.
Z ⁵ is preferably —COO—, —OCO—, —CH ₂ CH ₂ —, or a single bond, and more preferably a single bond.
Y ¹ to Y ⁶ are preferably a hydrogen atom or a fluorine atom.
The ring T ¹ is preferably a 1,4-cyclohexylene group.

R ¹ is an alkyl group or alkenyl group having 2 to 6 carbon atoms (one or two or more methylene groups present in the alkyl group or alkenyl group are those in which oxygen atoms are not directly bonded to each other. Independently substituted with an oxygen atom, -COO- or -OCO-) is preferred, and an alkyl group or alkenyl group having 2 to 5 carbon atoms is more preferred.

Moreover, more preferable cases are illustrated below for each of the general formulas (A1) to (A6).
In the general formulas (A1) and (A2), it is preferable that X ¹ is a fluorine atom, and Y ¹ to Y ⁵ each independently represent a hydrogen atom or a fluorine atom.
In General Formula (A3), m represents 0, Z ¹ represents —COO—, —OCO—, or a single bond, X ¹ represents a cyano group, and Y ¹ to Y ⁶ each independently represent a hydrogen atom. Or it is preferable to represent a fluorine atom.
In General Formula (A4), m represents 1, Z ¹ and Z ³ each independently represent —COO—, —OCO—, or a single bond, X ¹ represents a cyano group, and Y ¹ to Y ⁴ Each independently represents a hydrogen atom or a fluorine atom.
In general formula (A5), p represents 0, q represents 1, ring T ¹ represents a 1,4-cyclohexylene group, and Z ⁴ and Z ⁵ each independently represent —CH ₂ CH ₂ —, or a single group. It is preferable that X ¹ represents a fluorine atom or a cyano group, and Y ¹ and Y ² each independently represent a hydrogen atom or a fluorine atom.
In General Formula (A6), X ¹ is preferably a fluorine atom or a cyano group, and Y ¹ and Y ² each independently represent a hydrogen atom or a fluorine atom.

  More specifically, the following compounds are preferable.

(In the formulas (I-1) to (I-69), R ⁴ represents an alkyl group or alkenyl group having 2 to 6 carbon atoms (one or two or more methylene groups present in the alkyl group or alkenyl group). Represents an oxygen atom that is not directly bonded to each other, and may be independently substituted with an oxygen atom.) Further, R ⁴ is preferably an alkyl or alkenyl group having 2 to 6 carbon atoms. Furthermore, these alkyl groups or alkenyl groups are preferably linear alkyl groups or alkenyl groups.

The liquid crystal composition of the present invention contains 20% by mass or more of one or more compounds selected from the compound group A represented by the general formulas (A1) to (A6), and is represented by the general formula (A6). It is necessary to contain 3% by mass or more of the compound.
Further, the liquid crystal composition contains 30% by mass or more of one or more compounds selected from the compound group A represented by the general formulas (A1) to (A6) and is represented by the general formula (A6). It is more preferable to contain 5% by mass or more of the compound and 20% by mass or more of the compound represented by the general formula (A3) or (A4).
The liquid crystal composition contains 50% by mass or more of one or more compounds selected from the compound group A represented by the general formulas (A1) to (A6), and is represented by the general formula (A6). It is even more preferable to contain 5% by mass or more of the compound and 30% by mass or more of the compound represented by the general formula (A3) or (A4).
In addition, the liquid crystal composition contains 20% by mass or more of two or more compounds selected from the compound group A represented by the general formulas (A1) to (A6), and the compound represented by the general formula (A6) It is more preferable to contain 5 mass% or more.
Of the compound group A represented by the general formulas (A1) to (A6), the content of the compound having a dielectric anisotropy of 3.5 × 10 × 10 ⁻¹⁰ F / m or more is 25% by mass or less. It is preferable.

In these exemplifications, when two or more compounds corresponding to the compound group A or each of the general formulas are blended, the above numerical values mean the total content of the two or more compounds. In addition, when two or more compounds represented by the general formulas (A1) to (A6) are contained, R ¹ , X ¹ , Y ¹ to Y ⁶ , Z ¹ to Z ⁵ , T ¹ , m of each compound , P and q may be the same or different from each other.

  In the liquid crystal composition of the present invention, the compounds of the general formulas (B1) to (B11) belonging to the compound group B are compounds having no polar group at the terminal.

The case where it is especially preferable about the compound represented by general formula (B1) to (B11) is illustrated below.
R ² and R ³ are each an alkyl group having 1 to 6 carbon atoms or an alkenyl group having 2 to 6 carbon atoms (one or two or more methylene groups present in the alkyl group or alkenyl group are oxygen The atoms may be independently substituted with an oxygen atom, -COO- or -OCO- as those in which the atoms are not directly bonded to each other), preferably an alkyl group having 1 to 6 carbon atoms or 2 to 6 carbon atoms. The alkenyl group is more preferable.
Z ⁶ is preferably —COO—, —OCO—, —C≡C—, or a single bond, more preferably —COO—, —OCO—, or a single bond.
Z ⁷ , Z ⁸ , Z ⁹ and Z ¹⁰ are preferably —COO—, —OCO—, —CH ₂ CH ₂ —, or a single bond.
As the rings T ² and T ³ , a 1,4-cyclohexylene group is preferable.
Y ⁷ to Y ¹⁴ are preferably a hydrogen atom or a fluorine atom.

  More specifically, the following compounds are preferable.

(In the formulas (II-1) to (II-26), R ⁵ and R ⁶ are an alkyl group having 1 to 6 carbon atoms or an alkenyl group having 2 to 6 carbon atoms (present in the alkyl group or alkenyl group). 1 or 2 or more methylene groups may be independently substituted with oxygen atoms as oxygen atoms are not directly bonded to each other), and Y ³¹ to Y ³⁵ are hydrogen atoms, fluorine Represents an atom or a methyl group.)

The liquid crystal composition of the present invention needs to contain 5 to 50% by mass of one or more compounds selected from the compound group B represented by the general formulas (B1) to (B11).
Moreover, it is more preferable that a liquid crystal composition contains 5-40 mass% of 1 or 2 or more compounds chosen from the compound group B represented by general formula (B1) to (B11).

In these exemplifications, when two or more compounds corresponding to the compound group B or each of the general formulas are blended, the above numerical values mean the total content of the two or more compounds. When two or more compounds represented by the general formulas (B1) to (B11) are contained, R ² , R ³ , Y ⁷ to Y ¹⁴ , Z ⁶ to Z ¹⁰ , T ² , T of each compound ³ and n may be the same as or different from each other.

The nematic-isotropic transition temperature (T _N-I ) of these liquid crystal compositions needs to be 60 ° C. or higher. As for a liquid-crystal composition, it is more preferable that _TN-I is 70 degreeC or more.
In addition, in order for the liquid crystal display element to realize a wide driving temperature range, it is essential that the temperature range (ΔT _N ) itself in which the liquid crystal composition exhibits a nematic phase is also wide. For this reason, the difference between the upper limit temperature T _N-I (nematic _- isotropic transition temperature) and the lower limit temperature T _X-N (transition temperature at which the nematic phase transitions to a higher-order liquid crystal phase, glass state, or crystalline state). in defined temperature range [Delta] T _N is preferably at 70 ° C. or more, more preferably 80 ° C. or higher, still more preferably not less 90 ° C. or higher.
Further, the lower limit temperature T _{X-N at} which the liquid crystal composition exhibits a nematic phase is preferably −10 ° C. or lower, more preferably −20 ° C. or lower.

Since the driving voltage decreases as the dielectric anisotropy (ε ₀ Δε) increases, the dielectric anisotropy of the liquid crystal composition at 20 ° C. needs to be 8 × 10 ⁻¹¹ F / m or more. If it is too large, a problem occurs in reliability. Therefore, as dielectric anisotropy (value at 20 ° C.), 8 × 10 ^{−11 to} 6 × 10 ⁻¹⁰ F / m is preferable, and 1.3 × 10 ^{−10 to} 4.5 × 10 ⁻¹⁰ F / m m is more preferable, and 1.7 × 10 ^{−10 to} 3.5 × 10 ⁻¹⁰ F / m is even more preferable. Further, as ε ₀ Δε, 1.3 × 10 ^{−10 to} 3.0 × 10 ⁻¹⁰ F / m (Δε is 15 to 35) is more preferable. Note that ε ₀ is the dielectric constant of vacuum.

The refractive index anisotropy (Δn) at 20 ° C. is preferably 0.13 to 0.19, more preferably 0.14 to 0.18, and even more preferably 0.15 to 0.18.
Further, two bi-stable nematic liquid crystal display elements in which the product (Δn · d) of refractive index anisotropy Δn and thickness d at 20 ° C. is 275 nm and at least one substrate has a weak polar anchoring force It is necessary that the anchoring breakdown voltage U _{λ / 2} (represented by Equation 3) when supported between the substrates is 25V or less. U _{λ / 2 at} this temperature of 20 ° C. and Δn · d = 275 nm is more preferably 20 V or less, and even more preferably 15 V or less.

The liquid crystal composition of the present invention comprises
a) The substrate so that at least one substrate has a liquid crystal composition sandwiched between two substrates having a weak polar anchoring force, and an electric field can be applied to the liquid crystal composition between the two substrates. Are provided with electrodes on the inner surfaces facing each other, at least one of the substrate and the electrode is optically transparent,
b) aligning the liquid crystal composition and being subjected to a treatment capable of forming at least two alternative different textures that are stable or metastable in the absence of an electric field, one of the textures not being twisted, or The twist is in the range of -90 ° to + 90 °, the other texture is twisted at an angle close to 180 °,
c) the product at 20 ° C. d · [Delta] n (d is the liquid crystal composition layer thickness, [Delta] n denotes the refractive index anisotropy of the liquid crystal composition.) is, λ _0/2 (although lambda ₀ is the display device Represents the center wavelength of the effective spectral band), or an integer multiple of λ ₀ , or designed to approach either one of these two values,
d) By breaking anchoring on at least one of the two substrates, it is possible to switch between the different textures described above, and to maintain either texture after the electric field is removed. It is useful for a bi-stable nematic liquid crystal display element (for example, BiNem (registered trademark) display manufactured by Nemoptic, see FIG. 1).

In the liquid crystal display element having the structure shown in FIG. 1, the substrate 1 includes a glass substrate having an electrode layer 2 made of a transparent conductor such as indium tin oxide (ITO). Both anchoring by the alignment films 3 and 4 of the two substrates 1 and 1 are preferably monostable. Further, at least one alignment film has a weak polar angle anchoring force. Here, when the extrapolation length of polar angle anchoring is L _Z , it has “strong polar angle anchoring force” when L _Z <15 nm, and “weak polar angle anchoring force when L _Z > 25 nm. ".

Examples of the alignment film 3 having a strong polar angle anchoring force include commonly used alignment film materials such as polyimide, polyamide, and SiO deposited film. As the alignment film 4 having a weak polar angle anchoring force, a film made of polyvinyl chloride (homopolymer) or a vinyl chloride copolymer (copolymer) is suitable as described in Patent Document 9, for example. Examples of monomers other than vinyl chloride used in the vinyl chloride copolymer include vinyl acetate, vinyl ether, acrylic acid ester and the like.
In the present invention, since the liquid crystal composition of the present invention described above is used as the liquid crystal composition supported between the substrates of the liquid crystal display element, a bistable nematic liquid crystal display element having a wide operating temperature range can be obtained.

The alignment film 4 having a weak polar angle anchoring force has an anchoring breakdown voltage U in a cell having a thickness d in which the product (Δn · d) of the refractive index anisotropy Δn and the thickness d at 20 ° C. is 275 nm. It is preferable to have a weak polar anchoring force defined as _{λ / 2} being 25 V or less. Thereby, the liquid crystal composition can take at least two different stable states by a weak polar angle anchoring force, and switching between at least two different stable states when an appropriate electrical signal is applied to the electrode layer 2. Can be achieved. This switching is preferably an anchoring destruction type.

Further, as at least two different stable states, as shown in FIG. 1, the first stable texture (T ₀ ) in which the molecules in the liquid crystal composition are arranged at least substantially parallel to each other and twisted uniformly or slightly, and 2 It is preferred to have a second stable texture (T ₁₈₀ ) that takes a twisted texture between the substrates at an angle of 180 ° or close thereto. Thus, switching between T ₀ and T ₁₈₀ can be achieved when an appropriate electrical signal is applied to the electrode layer 2. This switching is preferably achieved by the destruction of polar angle anchoring in at least one substrate.

  In the bistable nematic liquid crystal display element of the present invention, the cell preferably has a product (Δn · d) of refractive index anisotropy Δn and thickness d at 20 ° C. of 200 to 300 nm, and 220 to 280 nm. It is more preferable. Since Δn at 20 ° C. is determined by the liquid crystal composition to be used, a desired Δn · d can be obtained by adjusting the gap between the substrates with a spacer.

  EXAMPLES Hereinafter, although an Example is given and this invention is further explained in full detail, this invention is not limited to these Examples. Further, “%” in the compositions of the following Examples and Comparative Examples means “mass%”. The nematic phase temperature range means a temperature range (temperature difference) from a solid phase or smectic phase-nematic phase transition temperature to a nematic phase-isotropic liquid phase transition temperature unless otherwise specified.

T _N-I : Nematic phase-isotropic liquid phase transition temperature T _X-N : Solid phase or smectic phase-nematic phase transition temperature Δε: Dielectric anisotropy at 20 ° C. Δn: Refractive index anisotropy at 20 ° C.

Example 1
Two glass substrates with ITO are prepared as substrates for supporting the liquid crystal composition, and SiO ₂ (thickness: 107 nm) is deposited on one glass substrate with ITO in order to obtain a strong polar angle anchoring force with high tilt. On the other hand, to obtain a weak polar angle anchoring force, the equation (G)

(Vinyl chloride-isobutyl vinyl ether copolymer) was coated at a thickness of 20 nm by the following method.

Step 1: A 0.75% solution of the above polymer dissolved in a 50/50 mixture of N-methyl-pyrrolidone / butoxyethanol is deposited by spin coating.
Step 2: Annealing is performed at 150 ° C. for 1.5 hours.
Step 3: UV irradiation (λ = 254 nm) for 2 hours using a 100 watt mercury lamp.
Step 4: Annealing is performed at 150 ° C. for 30 minutes.
Step 5: Brushing (rubbing) with a roller coated with a fabric velvet to induce azimuth anchoring.

  The two substrates are bonded together through a spacer of 1.5 μm, a BiNem (registered trademark) type cell is assembled, and a chiral agent is added so that the natural pitch at 25 ° C. becomes 6 μm in the liquid crystal composition (H) shown below. After adding S-811 (Merck), it was injected into the cell.

  A plurality of measurement temperatures are set to measure the operating temperature, a voltage with a pulse width of 5 ms is applied to the cell at each temperature up to 30 V in increments of 1 V, and the driving voltage is measured by measuring the anchoring breakdown voltage. The operating temperature range was evaluated.

The liquid crystal composition (H) is a liquid crystal composition containing 8% by mass of the compound represented by the general formula (A6), and the physical properties of this liquid crystal composition are T _N−I = 85.0 ° C., T _{X The} nematic liquid crystal phase temperature range ΔT _N was 113 ° C. at _−N = −28 ° C. The dielectric anisotropy ε ₀ Δε = 0.53 × 10 ⁻¹⁰ F / m and the refractive index anisotropy Δn = 0.156. Therefore, Δn · d of this cell is 234 nm.

The operating temperature range of this liquid crystal composition (H) in a BiNem (registered trademark) cell was −3 to 69 ° C., and the operating temperature range was 72 ° C. The threshold voltage _{U Z} at 20 ° C. was 13V. This threshold voltage _{U Z,} in terms of U _{lambda / 2} when the 275nm to [Delta] n · d, is 15.3V. U _{λ / 2} when Δn · d was 275 nm was converted by the following formula (4).

(Example 2)
The liquid crystal composition (H) in Example 1 was changed to the liquid crystal composition (I) shown below, and the same evaluation was performed.

This liquid crystal composition (I) is a liquid crystal composition containing 8% by mass of the compound represented by the general formula (A6). The physical properties of this liquid crystal composition are as follows: T _N−I = 67.8 ° C., T _X-N = −35 ° C. and nematic liquid crystal phase temperature range ΔT _N = 102.8 ° C. The dielectric anisotropy ε ₀ Δε = 1.88 × 10 ⁻¹⁰ F / m and the refractive index anisotropy Δn = 0.172. Therefore, Δn · d of this cell is 258 nm.

The operating temperature range of this liquid crystal composition (I) in a BiNem (registered trademark) cell was −5 to 60 ° C., and the operating temperature range was 65 ° C. The threshold voltage _{U Z} at 20 ° C. was 15.2V. This threshold voltage _{U Z,} in terms of U _{lambda / 2} when the 275nm to [Delta] n · d, is 16.2 V.

(Example 3)
The same evaluation was performed by changing the liquid crystal composition (H) in Example 1 to the liquid crystal composition (J) shown below.

This liquid crystal composition (J) is a liquid crystal composition containing 15% by mass of the compound represented by the general formula (A6). The physical properties of this liquid crystal composition are T _N-I = 70.4 ° C., T _X-N = −28 ° C., nematic liquid crystal phase temperature range ΔT _N = 98.4 ° C. The dielectric anisotropy ε ₀ Δε = 2.31 × 10 ⁻¹⁰ F / m and the refractive index anisotropy Δn = 0.175. Therefore, Δn · d of this cell is 262.5 nm.

The operating temperature range of this liquid crystal composition (J) in a BiNem (registered trademark) type cell was −8 to 64 ° C., and the operating temperature range was 72 ° C. The threshold voltage _{U Z} at 20 ° C. was 12.2V. This threshold voltage _{U Z,} in terms of U _{lambda / 2} when the 275nm to [Delta] n · d, is 12.8V.

Example 4
The same evaluation was performed by changing the liquid crystal composition (H) in Example 1 to the liquid crystal composition (K) shown below.

This liquid crystal composition (K) is a liquid crystal composition containing 8% by mass of the compound represented by the general formula (A6). The physical properties of this liquid crystal composition are as follows: T _N−I = 73.9 ° C., T in _X-N = -28 ℃, nematic liquid crystal temperature range ΔT _N = 101.9 ℃. In addition, dielectric anisotropy ε ₀ Δε = 3.41 × 10 ⁻¹⁰ F / m, and refractive index anisotropy Δn = 0.153. Therefore, Δn · d of this cell is 229.5 nm.

The operating temperature range of this liquid crystal composition (K) in a BiNem (registered trademark) type cell was −5 to 68 ° C., and the operating temperature range was 73 ° C. The threshold voltage _{U Z} at 20 ° C. was 11.8V. This threshold voltage _{U Z,} in terms of U _{lambda / 2} when the 275nm to [Delta] n · d, is 14.1 V.

(Example 5)
The same evaluation was performed by changing the liquid crystal composition (H) in Example 1 to the liquid crystal composition (L) shown below.

This liquid crystal composition (L) is a liquid crystal composition containing 7% by mass of the compound represented by the general formula (A6). The physical properties of this liquid crystal composition are T _N-I = 61.5 ° C., T in _X-N = -30 ℃, nematic liquid crystal temperature range ΔT _N = 91.9 ℃. The dielectric anisotropy ε ₀ Δε = 2.2 × 10 ⁻¹⁰ F / m and the refractive index anisotropy Δn = 0.169. Therefore, Δn · d of this cell is 253.5 nm.

The operating temperature range of this liquid crystal composition (L) in a BiNem (registered trademark) cell was −8 to 68 ° C., and the operating temperature range was 64 ° C. The threshold voltage _{U Z} at 20 ° C. was 14.8V. This threshold voltage _{U Z,} in terms of U _{lambda / 2} when the 275nm to [Delta] n · d, is 16.1V.

(Comparative Example 1)
The liquid crystal composition (H) in Example 1 was changed to the liquid crystal composition (P) shown below, and the same evaluation was performed.

This liquid crystal composition (P) is a liquid crystal composition not containing a compound corresponding to the general formula (A6), and the physical properties of this liquid crystal composition are T _N-I = 61.3 ° C., T _X-N = At −25 ° C., the nematic liquid crystal phase temperature range ΔT _N = 86.3 ° C. The dielectric anisotropy ε ₀ Δε = 2.28 × 10 ⁻¹⁰ F / m and the refractive index anisotropy Δn = 0.157. Therefore, Δn · d of this cell is 235.5 nm.

The operating temperature range of this liquid crystal composition (P) in the BiNem (registered trademark) type cell was −0 to 50 ° C., and the operating temperature range was 50 ° C. The threshold voltage _{U Z} at 20 ° C. was 14.1 V. This threshold voltage _{U Z,} in terms of U _{lambda / 2} when the 275nm to [Delta] n · d, is 16.5V.

(Comparative Example 2)
The same evaluation was performed by changing the liquid crystal composition (H) in Example 1 to the liquid crystal composition (Q) shown below.

This liquid crystal composition (Q) is a liquid crystal composition not containing a compound corresponding to the general formula (A6), and the physical properties of this liquid crystal composition are as follows: T _N−I = 61.0 ° C., T _X−N = At −20 ° C., the nematic liquid crystal phase temperature range ΔT _N = 81.0 ° C. Further, the dielectric anisotropy ε ₀ Δε = 2.57 × 10 ⁻¹⁰ F / m and the refractive index anisotropy Δn = 0.156. Therefore, Δn · d of this cell is 234 nm.

The operating temperature range of this liquid crystal composition (Q) in the BiNem (registered trademark) type cell was 5 to 50 ° C., and the operating temperature range was 45 ° C. The threshold voltage _{U Z} at 20 ° C. was 14.2V. This threshold voltage _{U Z,} in terms of U _{lambda / 2} when the 275nm to [Delta] n · d, is 16.7V.

  Table 1 shows the results of evaluating the physical properties of the liquid crystal compositions prepared in the above Examples and Comparative Examples, and the results of evaluating the characteristics by producing liquid crystal display elements using these liquid crystal compositions.

  Comparing the example and the comparative example, it can be seen that the example has a wider operating temperature range by the BiNem (registered trademark) type cell. That is, a liquid crystal composition having a wide operating temperature range in the bistable nematic liquid crystal display device could be obtained by the combination of the liquid crystal materials of the present invention.

  The liquid crystal composition of the present invention can be suitably used for a bi-stable nematic liquid crystal display device in which at least one substrate is supported on two substrates having a weak polar anchoring force, and has an operating temperature range. A wide bistable nematic liquid crystal display element can be obtained.

It is a figure which shows typically operation | movement of the bistable nematic liquid crystal display element by anchoring destruction. It is a figure explaining the direction of anchoring.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Glass substrate, 2 ... ITO electrode layer, 3 ... Strong anchoring alignment film, 4 ... Weak anchoring alignment film.

Claims (8)

From general formulas (A1) to (A6)

(In the formulas (A1) to (A6), R ¹ represents an alkyl group or alkenyl group having 2 to 7 carbon atoms (one or two or more methylene groups present in the alkyl group or alkenyl group represent an oxygen atom) Are each independently substituted with an oxygen atom, —COO—, or —OCO— as those that are not directly bonded to each other.
X ¹ represents a cyano group, a fluorine atom, a chlorine atom, a trifluoromethyl group, a trifluoromethoxy group, or a difluoromethoxy group (—OCHF ₂ ),
Z ¹ and Z ² are each independently —COO—, —OCO—, —CH ₂ O—, —OCH ₂ —, —CF ₂ O—, —OCF ₂ —, —C≡C—, or a single bond Represents
Z ³ and Z ⁴ are each independently —CH ₂ CH ₂ —, —COO—, —OCO—, —CH ₂ O—, —OCH ₂ —, —CF ₂ O—, —OCF ₂ —, or Represents a bond,
Z ⁵ _{is, -CH 2 CH 2 -, -} CH = CH -, - COO -, - OCO -, - CH 2 O -, - OCH 2 -, - CF 2 O -, - OCF 2 -, or a single bond Represents
Y ¹ to Y ⁶ each independently represent a hydrogen atom, a fluorine atom, a chlorine atom, a trifluoromethyl group, or a trifluoromethoxy group,
Ring T ¹ is a 1,4-phenylene group or a 1,4-cyclohexylene group (among these groups, the 1,4-phenylene group is unsubstituted or substituted with a fluorine atom, a chlorine atom, a methyl group, Which can have one or more trifluoromethyl groups or trifluoromethoxy groups).
m represents 0 or 1;
p and q represent 0 or 1, where p + q is 0 or 1. )
Containing 20% by mass or more of one or more compounds selected from the compound group A represented by: and containing 3% by mass or more of the compound represented by the general formula (A6),
From general formulas (B1) to (B11)

(In the formulas (B1) to (B11), R ² and R ³ are each independently an alkyl group having 1 to 7 carbon atoms or an alkenyl group having 2 to 7 carbon atoms (in the alkyl group or alkenyl group). 1 or 2 or more methylene groups present may be each independently substituted with an oxygen atom, —COO— or —OCO— as if oxygen atoms were not directly bonded to each other.
Z ⁶ represents —COO—, —OCO—, —CH ₂ O—, —OCH ₂ —, —CF ₂ O—, —OCF ₂ —, —C≡C—, or a single bond,
Z ⁷ represents —CH ₂ CH ₂ —, —COO—, —OCO—, —CH ₂ O—, —OCH ₂ —, —CF ₂ O—, —OCF ₂ —, or a single bond,
Z ⁸ _{is, -CH 2 CH 2 -, -} CH = CH -, - COO -, - OCO -, - CH 2 O -, - OCH 2 -, - CF 2 O -, - OCF 2 -, or a single bond Represents
Z ⁹ and Z ¹⁰ each independently represent —CH ₂ CH ₂ —, —COO—, —OCO—, or a single bond,
Y ⁷ to Y ¹⁴ each independently represents a hydrogen atom, a methyl group, a fluorine atom, a chlorine atom, a trifluoromethyl group, or a trifluoromethoxy group,
Rings T ² and T ³ are each independently a 1,4-phenylene group or a 1,4-cyclohexylene group (among these groups, the 1,4-phenylene group is unsubstituted or fluorine as a substituent). Which can have one or more atoms, chlorine atoms, methyl groups, trifluoromethyl groups or trifluoromethoxy groups),
n represents 0 or 1. )
A nematic liquid crystal composition containing 5 to 50% by mass of one or more compounds selected from the compound group B represented by:
The relative proportions of the compounds used in the nematic liquid crystal composition are as follows for the composition:
-The nematic-isotropic transition temperature (T _N-I ) of the liquid crystal composition is 60 ° C or higher,
The temperature range (ΔT _N ) in which the liquid crystal composition exhibits a nematic phase is 70 ° C. or higher,
The dielectric anisotropy at 20 ° C. is 8 × 10 ⁻¹¹ F / m or more,
For a bi-stable nematic liquid crystal display element in which the product (Δn · d) of refractive index anisotropy Δn and thickness d at 20 ° C. is 275 nm and at least one substrate has a weak polar anchoring force The anchoring breakdown voltage U _{λ / 2} when supported between the substrates is 25 V or less.
A nematic liquid crystal composition, which is determined to be obtained simultaneously. The nematic liquid crystal composition according to claim 1, wherein the dielectric anisotropy at 20 ° C. is 1.3 × 10 ^{−10 to} 3.0 × 10 ⁻¹⁰ F / m. In general formulas (A1) and (A2), X ¹ is a fluorine atom,
In the general formula (A3), m represents 0, Z ¹ represents —COO—, —OCO—, or a single bond, X ¹ represents a cyano group,
In General Formula (A4), m represents 1, Z ¹ and Z ³ each independently represent —COO—, —OCO—, or a single bond, and X ¹ represents a cyano group,
In general formula (A5), p represents 0, q represents 1, ring T ¹ represents a 1,4-cyclohexylene group, and Z ⁴ and Z ⁵ each independently represent —CH ₂ CH ₂ —, or a single group. Represents a bond, X ¹ is a fluorine atom or a cyano group,
In General Formula (A6), X ¹ is a fluorine atom or a cyano group,
2. The nematic liquid crystal composition according to claim 1, wherein in general formulas (A1) to (A6), Y ¹ to Y ⁶ each independently represent a hydrogen atom or a fluorine atom. The nematic liquid crystal composition according to claim 1 is supported between two substrates forming a cell, and has an alignment film and an electrode structure on an inner surface of these substrates,
The alignment film of the at least one substrate has an anchoring breakdown voltage U _{λ / 2 in} a cell having a thickness d in which a product (Δn · d) of a refractive index anisotropy Δn and a thickness d at 20 ° C. is 275 nm. Has a weak polar angle anchoring force defined as being 25 V or less, and the liquid crystal composition can take at least two different stable states by the weak polar angle anchoring force,
A bistable nematic liquid crystal display device in which switching between at least two different stable states is achieved when an appropriate electrical signal is applied to the electrode structure.   The bistable nematic liquid crystal display element according to claim 4, wherein the bistable nematic liquid crystal display element is an anchoring destruction type. As the at least two different stable states, a first stable texture in which molecules in the liquid crystal composition are arranged substantially parallel to each other in a range of at least ± 20 ° and are twisted uniformly or slightly, and between the two substrates A second stable texture with a twisted texture at 180 ± 20 °,
The bistable nematic liquid crystal display device according to claim 4, wherein switching between the first stable texture and the second stable texture is achieved when an appropriate electrical signal is applied to the electrode structure.   The bistable nematic liquid crystal display device according to claim 6, wherein the switching between the two stable textures is achieved by destruction of polar angle anchoring of at least one substrate.   5. The bi-stable nematic liquid crystal display device according to claim 4, wherein both anchoring by the alignment films of the two substrates is monostable.

Images