JP5424020B2 - Ferroelectric liquid crystal composition and display device using the same - Google Patents

Description

  The present invention relates to a ferroelectric liquid crystal composition useful as a constituent member of a ferroelectric liquid crystal display.

  The surface-stabilized ferroelectric liquid crystal display device proposed by Clark and Lagerwall et al. Has (1) high-speed response, (2) memory property, (3) wide viewing angle, (4) Since it exhibits characteristics such as being capable of passive drive, it has attracted attention as a next-generation display element. However, a problem has been pointed out that high-quality display cannot be performed due to a seizure phenomenon or switching failure due to reversal abnormality (see, for example, Patent Documents 1 and 2). In Patent Documents 1 and 2, by adding a cyclic or cage-like lipophilic or oleophilic compound to the ferroelectric liquid crystal composition, the ionic impurities contained in the ferroelectric liquid crystal composition are captured. Although an example in which the seizure phenomenon of the ferroelectric liquid crystal display element and the switching failure due to the inversion abnormality are reduced is shown, the performance is still insufficient. For this reason, it has been desired to develop a means effective for preventing a switching failure due to a seizure phenomenon or a reversal abnormality seen in a ferroelectric liquid crystal display element.

Japanese Patent Laid-Open No. 3-180815 Japanese Patent Laid-Open No. 4-227685

  A problem to be solved by the present invention is to provide a ferroelectric liquid crystal composition exhibiting a preferable switching behavior in which inversion anomaly is suppressed without causing baking, and a display element using the ferroelectric liquid crystal composition is provided. That is.

In order to solve the above-mentioned problems, the present inventors have studied various additives, and as a result, they have been subject to aggressive removal, trapping, and association because they have caused baking, inversion abnormality, or crystallization. Among the ions, the ionic liquid was found to be preferable as an additive for realizing a preferable switching behavior in which the ionic liquid was not baked and the reversal abnormality was suppressed, and the present invention was completed.
The present invention provides a ferroelectric liquid crystal composition characterized by comprising a liquid crystal mixture containing at least two or more liquid crystal compounds and at least one ionic liquid, and the ferroelectric liquid crystal. A ferroelectric liquid crystal display device using the composition is provided.

  Since the ferroelectric liquid crystal composition of the present invention exhibits a preferable switching behavior in which inversion abnormality is suppressed without causing baking, a display element with good display quality can be manufactured with high productivity. The ferroelectric liquid crystal composition of the present invention is extremely useful as a constituent member of a ferroelectric liquid crystal display.

The ferroelectric liquid crystal composition of the present invention contains an ionic liquid.
The “ionic liquid” is a salt composed only of ions, and the salt is characterized by being a liquid at an extremely low temperature. Various names such as “ionic liquid” and “room temperature molten salt” are used as the name of “ionic liquid”, which is equivalent to “Ionic liquid” in English, but is called by these names. The compounds corresponding to the above definition are collectively referred to as “ionic liquid” in the present invention.
In the ion-binding salt, ions are bonded to each other by electrostatic interaction, and the melting point thereof is generally high, and the melting point of salt is 800 ° C. or higher. Ionic liquids are characterized by having a remarkably low melting point compared to general salts, but generally the boiling point of water is used as a guideline, and indicates a melting point at 100 ° C or lower. However, the definition is not clear.
In the present invention, specifically, the melting point of the ionic liquid is preferably 100 ° C. or lower, more preferably 60 ° C. or lower, further preferably 30 ° C. or lower, and particularly preferably liquid at room temperature.
Unlike general salts, ionic liquids have a high affinity with organic substances and are known to conduct ions. By utilizing this property, ions that can easily move in the liquid crystal medium or near the liquid crystal cell interface. This produces an effect of improving display quality and productivity by suppressing display defects such as burn-in and reversal abnormality.
The ionic liquid added to the ferroelectric liquid crystal composition of the present invention is an imidazolium-based ionic liquid, a pyridinium-based ionic liquid, a pyrrolidinium-based ionic liquid, a phosphonium-based ionic liquid, or an ammonium-based ionic liquid. It is preferable.
Specific examples of the imidazolium-based ionic liquid include the following compounds.

ピリジニウム系イオン性液体の具体例は、次に記載する化合物が挙げられる。

Specific examples of the pyridinium-based ionic liquid include the compounds described below.

ピロリジニウム系イオン性液体の具体例は、次に記載する化合物が挙げられる。

Specific examples of the pyrrolidinium-based ionic liquid include the compounds described below.

ホスホニウム系イオン性液体の具体例は、次に記載する化合物が挙げられる。

Specific examples of the phosphonium-based ionic liquid include the compounds described below.

アンモニウム系イオン性液体の具体例は、次に記載する化合物が挙げられる。

Specific examples of the ammonium-based ionic liquid include the compounds described below.

これらの中でも、ハロゲンをアニオンとしないイオン性液体は、脱ハロゲン化の観点から好ましい。さらに好ましくは、イミダゾリム系イオン性液体が好ましい。

Among these, an ionic liquid that does not use halogen as an anion is preferable from the viewpoint of dehalogenation. More preferably, an imidazolim ionic liquid is preferable.

  The addition amount of the ionic liquid has a preferable content in order to exhibit a stable liquid crystal phase or to effectively suppress switching defects such as baking or inversion abnormality. The following contents are expressed in ppm or% by weight with respect to the ferroelectric liquid crystal composition. The content of the ionic liquid is preferably 0.01 ppm to 10%, more preferably 0.01 to 1%, still more preferably 0.05 to 0.1%, Particularly preferred is -100 ppm.

  Although the ferroelectric liquid crystal composition of the present invention contains a liquid crystal mixture and an ionic liquid, the liquid crystal mixture used is not particularly limited, and a known and commonly used liquid crystal mixture is used. Among them, the liquid crystalline mixture has the following general formula (Ia)

(In the formula, R ¹¹ and R ¹² each independently represent a linear or branched alkyl group having 1 to 18 carbon atoms, provided that at least one of the alkyl groups is a branched alkyl group. And one or two non-adjacent —CH ₂ — groups in the alkyl group are —O—, —CO—, —CO—O—, —O—CO—, —O—CO—O—. , —CH═CH— or —C≡C—, wherein one or more hydrogen atoms in the alkyl group may be replaced with a fluorine atom or a CN group, and A ¹ , B ¹ and Each C ¹ is independently a 1,4-phenylene group in which one or two hydrogen atoms may be replaced by a fluorine atom, a CF ₃ group, an OCF ₃ group, or a CN group, or a plurality of these groups, or It represents 1,4-cyclohexylene group, ^{a 1} is 0, 1, or It represents, ^{b 1} and ^{c 1} is an integer of 0 or ^1, a 1, the sum of ^{b 1} and ^{c 1} is 1 or 2.) The compound represented by, and the following formula (I-b)

(In the formula, R ¹³ and R ¹⁴ each independently represent a linear or branched alkyl group having 1 to 18 carbon atoms or a fluorine atom, provided that R ¹³ and R ¹⁴ may simultaneously become a fluorine atom. And one or two non-adjacent —CH ₂ — groups are —O—, —S—, —CO—, —CO—O—, —O—CO—, —CO—S—, — S—CO—, —O—CO—O—, —CH═CH—, —C≡C—, a cyclopropylene group or —Si (CH ₃ ) ₂ — may be substituted, and one of the alkyl groups Or more hydrogen atoms may be replaced by fluorine atoms or CN groups, X ^{11 to} X ¹⁷ each independently represent a hydrogen atom, a fluorine atom, a CF ₃ group, or an OCF ₃ group, and L ^{11 to} L ¹⁴ are each independently a single bond, -O -, - S -, - CO-, _{CH 2 O -, - OCH 2} -, - CF 2 O -, - OCF 2 -, - CO-O -, - O-CO -, - CO-S -, - S-CO -, - O-CO- O—, —CH ₂ CH ₂ —, —CH═CH— or —C≡C—, and d ¹ , e ¹ , f ¹ and g ¹ each independently represent an integer of 0 or 1, provided that d ¹ + e ¹ + f ¹ + g ¹ is 1, 2 or 3, and when d ¹ is 0, g ¹ is 0, and when d ¹ is 1, f ¹ is 0. A liquid crystalline mixture containing at least two kinds of compounds selected from the group consisting of:
In terms of stabilization by widening the temperature range of the ferroelectric liquid crystal phase, the following general formula (IV)

(R ⁴¹ represents a linear or branched alkyl group having 1 to 18 carbon atoms, and one or two non-adjacent —CH ₂ — groups in the alkyl group are —O—, —CO. —, —CO—O—, —O—CO—, —O—CO—O—, —CH═CH— or —C≡C—, may be replaced by one or more in the alkyl group In which A ⁴ , B ⁴ and C ⁴ are each independently one or two hydrogen atoms are fluorine atoms, CF ₃ groups, OCF ₃ groups, or CN 1,4-phenylene group which may be replaced by a plurality of groups, pyrazine-2,5-diyl group or pyridazine-3 in which one or two hydrogen atoms may be replaced by fluorine atoms , 6-diyl group, pyridine-2,5-diyl group, pyrimidine- , 5-diyl group, trans-1,4-cyclohexylene group in which one or two hydrogen atoms may be replaced by cyano group or methyl group or both, or 1,3,4-thiadiazole-2 , 5-diyl group, 1,3-dioxane-2,5-diyl group, 1,3-dithian-2,5-diyl group, 1,3-thiazole-2,4-diyl group, 1,3-thiazole -2,5-diyl group, thiophene-2,4-diyl group, thiophene-2,5-diyl group, piperazine-1,4-diyl group, piperazine-2,5-diyl group, naphthalene-2,5- A diyl group, L ⁴¹ and L ⁴² each independently represent a single bond, —O—, —CO—, —CH ₂ O—, —OCH ₂ —, —CF ₂ O—, —OCF ₂ —, —CO; -O-, -O-CO-, -O-CO-O-,- CH ₂ CH ₂ —, —CH═CH— or —C≡C— is represented, a ⁴ , b ⁴ , and c ⁴ represent 0 or 1, and the sum of a ⁴ , b ^4, and c ⁴ is 2 or 3 R ⁴² represents a single bond or a linear or branched alkylene group having 1 to 18 carbon atoms, and one or two non-adjacent —CH ₂ — groups in the alkylene group are —O —, —CO—, —CO—O—, —O—CO—, —O—CO—O—, —CH═CH— or —C≡C— may be substituted, and one of the alkylene groups Alternatively, a compound represented by the formula (1) may be preferably used as a component of the liquid crystalline mixture.

  The ferroelectric liquid crystal composition of the present invention contains an optically active compound in order to exhibit ferroelectricity, and a known and commonly used optically active compound can be used as the optically active compound. For example, a compound having an asymmetric atom, a compound having axial asymmetry, or a compound having plane asymmetry can be used, and a compound having an asymmetric carbon or a compound having a carbon-carbon bond as an axis asymmetry is used. It is preferable that a compound having an asymmetric carbon atom is more preferable.

In an optically active compound having an asymmetric carbon, the asymmetric carbon may be introduced into a part of a chain structure or a part of a cyclic structure, and a fluorine atom or a methyl group may be present on the asymmetric carbon. Alternatively, a compound having a CF ₃ group introduced therein or a compound having an oxirane ring structure having an asymmetric carbon is preferable.
Specifically, the optically active compound is represented by the general formula (V)

(In the formula, R ⁵¹ and R ⁵² each independently represent a linear or branched alkyl group having 1 to 18 carbon atoms, and one or two non-adjacent —CH in the alkyl group. _{The 2-} group is replaced by —O—, —S—, —CO—, —CO—O—, —O—CO—, —O—CO—O—, —CH═CH— or —C≡C—. The hydrogen atom in the alkyl group may be replaced with a fluorine atom or a CN group, and A ⁵ , B ⁵ and C ⁵ are each independently a 1,4-phenylene group, pyrazine-2,5 -Diyl group, pyridazine-3,6-diyl group, pyridine-2,5-diyl group, pyrimidine-2,5-diyl group, trans-1,4-cyclohexylene group, 1,3,4-thiadiazole- 2,5-diyl group, 1,3-dioxane-2,5-diyl group, 1,3-dithiane 2,5-diyl group, 1,3-thiazole-2,4-diyl, 1,3-thiazole-2,5-diyl, thiophene-2,4-diyl group, thiophene-2,5-diyl group, piperazine -1,4-diyl group, piperazine-2,5-diyl group or naphthalene-2,6-diyl group, provided that the hydrogen atom in the 1,4-phenylene group and naphthalene-2,5-diyl group May be substituted by a fluorine atom, a CF ₃ group, an OCF ₃ group, a CN group, a CH ₃ group, or an OCH ₃ group, and the hydrogen atom in the trans-1,4-cyclohexylene group is a CN group or Optionally substituted with a CH ₃ group, a ⁵ , b ⁵ , and c ⁵ each independently represent 0 or 1, L ⁵¹ and L ⁵² each independently represent a single bond, —O—, —CO—. _{, -CH 2 O -, - OCH} 2 -, - CF 2 O -, - _{CF 2 -, - CO-O} -, - O-CO -, - O-CO-O -, - CH 2 CH 2 -, - CH = CH- or an -C≡C-, L ⁵³ is generally Formula (V-1), General Formula (V-2), or General Formula (V-3)

（式中、ｄ^５、ｅ^５、及びｆ^５は、各々独立に０以上７以下の整数を表す。）のいずれかで表される構造を有し、Z^５１は、一般式（V−４）又は一般式（V−５）

(Wherein d ⁵ , e ⁵ , and f ⁵ each independently represents an integer of 0 or more and 7 or less), Z ⁵¹ has the general formula (V-4 ) Or general formula (V-5)

(However, Z ⁵² represents a fluorine atom, a methyl group or a CF ₃ group, R ⁵³ and R ⁵⁴ each independently represent a hydrogen atom or a linear or branched alkyl group having 1 to 10 carbon atoms, * Represents an asymmetric carbon). ) Is preferred.

Among the compounds represented by the general formula (V), in particular, Z ⁵¹ has a structure of the general formula (V-4) and Z ⁵² is a fluorine atom, or Z ⁵¹ is the general formula (V-5). More preferred is a compound having the structure: R ⁵³ and R ⁵⁴ are hydrogen atoms.
Among the compounds represented by the general formula (V), Z ⁵¹ has the structure of the general formula (V-4) and Z ⁵² is a fluorine atom, and the following general formula (Vb)

(Wherein R ⁵⁷ and R ⁵⁸ each independently represents a linear or branched alkyl group having 1 to 18 carbon atoms, and one or two non-adjacent —CH in the alkyl group) _{The 2-} group is replaced by —O—, —S—, —CO—, —CO—O—, —O—CO—, —O—CO—O—, —CH═CH— or —C≡C—. The hydrogen atom in the alkyl group may be replaced with a fluorine atom or a CN group, and L ⁵⁴ is represented by the general formula (Vb-1) or the general formula (Vb-2).

（式中、ｇ^５、及びｈ^５は、各々独立に０以上７以下の整数を表す。）のいずれかで表される構造を有する。）で表される化合物、又は、下記一般式（V−ｃ）

(Wherein, g ⁵ and h ⁵ each independently represent an integer of 0 or more and 7 or less). ) Or a compound represented by the following general formula (Vc)

(In the formula, R ⁵⁹ and R ⁵¹⁰ each independently represents a linear or branched alkyl group having 1 to 18 carbon atoms, provided that at least one of the alkyl groups is a branched alkyl group. And one or two non-adjacent —CH ₂ — groups in the alkyl group are —O—, —CO—, —CO—O—, —O—CO—, —O—CO—O—. , —CH═CH— or —C≡C—, wherein one or more hydrogen atoms in the alkyl group may be replaced with a fluorine atom or a CN group, and X ⁵¹ and X ⁵² are Each independently represents a hydrogen atom or a fluorine atom, d ⁵ represents an integer of 0 or 1, and L ⁵⁵ represents a general formula (Vc-1), a general formula (Vc-2), or a general formula ( V-c-3)

（式中、ｊ^５、ｋ^５、及びｍ^５は、各々独立に０以上７以下の整数を表す。）のいずれかで表される構造を有する。）の構造を有することが好ましい。

(Wherein j ⁵ , k ⁵ , and m ⁵ each independently represents an integer of 0 or more and 7 or less). ).

Among these compounds, in the case of the compound represented by the general formula (Vb), R ⁵⁷ and R ⁵⁸ are more preferably a linear or branched alkyl group, and particularly preferably a linear alkyl group. On the other hand, in the case of the compound represented by the general formula (Vc), R ⁵⁹ is more preferably a linear or branched alkyl group, alkoxy group, alkenyl group or alkenyloxy group, and R ⁵¹⁰ is linear or A branched alkyl group is preferable, and a linear alkyl group is particularly preferable.
Among the compounds represented by the general formula (V), examples of compounds in which Z ⁵¹ has the structure of the general formula (V-5) as an asymmetric carbon structure, and R ⁵³ and R ⁵⁴ are hydrogen atoms. Listed below.

(Wherein R ⁵³¹ is an alkyl group or alkoxy group having 4 to 14 carbon atoms, R ⁵³² is an alkyl group having 1 to 8 carbon atoms, R ⁵³³ is an alkyl group having 4 to 14 carbon atoms, L ⁵³¹ and L ⁵³² are Each independently represents a carbonyl group or a methylene group.)
Among the compounds represented by the general formula (V), examples of compounds in which Z ⁵¹ has a structure of the general formula (V-4) as an asymmetric carbon structure are given below.

(Wherein R _aa is a linear or branched alkyl group or alkoxy group having 1 to 18 carbon atoms, R _bb is a linear or branched alkyl group having 1 to 18 carbon atoms, and M _aa is the number of carbon atoms. 1 to 3 methylene groups, and M _bb represents a methylene group having 1 to 2 carbon atoms.)

When a cation other than the ionic liquid is contained in the liquid crystal mixture used in the ferroelectric liquid crystal composition of the present invention, the cation is not preferable because it causes a switching failure due to seizure or inversion abnormality. In order to eliminate this influence, it is desired to sufficiently purify the liquid crystal mixture or the compound that is a component of the liquid crystal mixture. At that time, for the purpose of removing impurities and the like, it is also preferable to perform a purification treatment with silica, alumina or the like. As the liquid crystalline mixture, it is preferable to use a liquid crystalline mixture having a specific resistance value of 1 × 10 ¹¹ to 1 × 10 ¹⁵ Ωcm. Considering ease of production and purification, 1 × 10 ¹¹ to 1 × 10 It is more preferable to use a liquid crystalline mixture that is ¹⁴ Ωcm. The specific resistance value of the ferroelectric liquid crystal composition is preferably from ^{1 × 10 10 ~1 × 10 14} Ωcm, more preferably ^{1 × 10 10 ~1 × 10 13} Ωcm. In addition to using a liquid crystal mixture with a high specific resistance as the liquid crystal mixture, the use of a liquid crystal mixture containing a cation clathrate compound in the liquid crystal mixture also prevents the influence of cations present as impurities in the liquid crystal mixture. This method is preferably used. There is no restriction | limiting in particular as a cation inclusion compound, A well-known and usual compound is used. Of these, podand, coronand, or cryptand is preferred as the compound, but the following general formula (VI),

(In the formula, Z ⁶ is an oxygen atom or a sulfur atom, a ⁶ and b ⁶ are integers greater than 0, a ⁶ + b ⁶ is 2 to 6, and X ⁶¹ and X ⁶² are the same or different groups. , Oxygen atom, sulfur atom, or the following structure,

(Wherein R ⁶ is a non-adjacent —CH ₂ — group may be substituted by —COO—, —CO—, —O—, —S—, —CONH—, or —CH═CH—. An alkyl group having 1 to 15 carbon atoms or a halogenated alkyl group, a hydrogen atom, a cyclohexyl group, a phenyl group, a benzyl group, or a benzoyl group), or X ⁶¹ and X ⁶² are The following structure together,

(Wherein, Z ⁶¹ and Z ⁶² are an oxygen atom or a sulfur atom, and c ⁶ and d ⁶ are 1 or 2). ) Is more preferable.

  If the association force between the cation and the cation clathrate compound present as an impurity in the liquid crystal mixture is too strong, the clathrate clathrate compound is difficult to move in both molecular weight and shape, and therefore the cation mobility deteriorates. As a result, it becomes difficult to relax the electric field formed by the cations inside the cell, which is not preferable for suppressing seizure and inversion abnormality. If there is no association force between the cation and the cation clathrate compound present as impurities in the liquid crystal mixture, the cation strongly adsorbs directly to the polar cell interface, and the cation has low solubility in the liquid crystal medium, so it strongly resists the interface. It becomes difficult to relax the electric field formed inside by the adsorbed cations. Therefore, in order to reduce the adverse effects of cations present as impurities in the liquid crystal mixture, a combination of a cation having a weak associating force and a cation inclusion compound is particularly preferred, and the cation encapsulation represented by the general formula (VI) is used. One or more of the oxygen atoms that are the source of the strong associative force of the close contact compound are replaced by nitrogen atoms that are electrically positive and consequently have the effect of appropriately weakening the association force with the cation. Compounds are particularly preferred. In such a weak association state, it is considered that the cation and the cation clathrate compound dynamically form a molecular assembly. Therefore, the cation is easily dissolved in the liquid crystal medium, and as a result, the cation mobility is also increased. It is believed to improve and prevent the formation of undesirable internal electric field due to local accumulation of cations.

  As the cation inclusion compound having a weak associating force as described above, a compound having one or two nitrogen atoms is preferably used as shown in the following structure.

Wherein R ⁶¹¹ and R ⁶¹² are not adjacent to each other by a —CH ₂ — group substituted by —COO—, —CO—, —O—, —S—, —CONH—, or —CH═CH—. And may be an alkyl group having 1 to 15 carbon atoms or a halogenated alkyl group, a hydrogen atom, a cyclohexyl group, a phenyl group, a benzyl group, or a benzoyl group, and e ⁶ is 0 or 1.)
The content of the cation clathrate compound is preferably 0.01 ppm to 10%, more preferably 0.1 ppm to 5%, and more preferably 1 ppm to 5% in terms of the weight ratio with respect to the ferroelectric liquid crystal composition. It is particularly preferred. The content of the cationic clathrates, be selected amount, such as T _AC point of the liquid crystal mixture before addition of (smectic C- smectic A phase transition temperature) does not change 10 ° C. or higher by the addition of cationic inclusion compound Is preferred.

  The liquid crystal mixture used in the ferroelectric liquid crystal composition of the present invention is represented by the general formula (Ia), general formula (Ib), general formula (IV), or general formula (V). A compound can be used, but the temperature range of the liquid crystal is widened, the transition temperature is maintained in a preferable temperature range, a preferable liquid crystal phase series is developed, the tilt angle is maintained in a preferable range, and a high-speed response is performed. In order to keep the spontaneous polarization within a preferable range so that the viscosity can be lowered or a high-speed response can be achieved, there is a preferable content with respect to the entire ferroelectric liquid crystal composition. The content of the compound represented by the general formula (Ia) or (Ib) is preferably 20% to 98%, more preferably 30% to 95%, and more preferably 40% with respect to the liquid crystal mixture. -90% is particularly preferred. The content of the compound represented by the general formula (IV) is preferably 2 to 40%, more preferably 3 to 30%, and particularly preferably 4 to 20%. If the content of the compound represented by the general formula (V) is too small, the value of the spontaneous polarization becomes small and the response becomes slow. On the other hand, if the content is too large, an undesirable twist of the molecular arrangement based on the chiral effect occurs. Therefore, the content of the compound represented by the general formula (V) is preferably 1% to 40%, more preferably 3 to 30%, and particularly preferably 5 to 25%. In addition, when the content of the compound represented by the general formula (V) per compound is 1% to 10%, it is possible to suppress undesired crystallization and disorder of the phase series due to too many single components. It is still good because you can.

When the ferroelectric liquid crystal composition is used as an actual display device, the components of the liquid crystal mixture are adjusted so that the temperature range of the (chiral) smectic C phase, which is a ferroelectric phase, is a wide range including room temperature. It will be. Regarding the low temperature side temperature, it is preferable not to crystallize at −20 ° C., and as a display application used outdoors, it is more preferable not to crystallize at −30 ° C. For the upper temperature, T _AC point of the ferroelectric liquid crystal composition (smectic C- smectic A phase transition temperature) is preferably above room temperature, more preferably from 50 ° C. to 100 ° C.. In particular, it is preferable that the _TAC point is high for use outdoors. However, the _TAC point is determined according to a preferable temperature range of the clearing point described below. Regarding the clearing point (liquid crystal-liquid phase transition temperature) as the high temperature side temperature, the ferroelectric liquid crystal composition is a smectic phase that exhibits a ferroelectric property, which is a liquid crystal phase close to a solid, when producing a liquid crystal display device. Therefore, it is difficult to inject liquid crystal into the display cell in this smectic phase, and it is necessary to raise the temperature to the liquid phase or nematic phase. Therefore, if the clearing point is high, there is a possibility that the liquid crystal material due to heat, the member used for the liquid crystal display element, the sealing agent, etc. may be altered, and heating and cooling require energy and time, which is not preferable as a process. Therefore, the clearing point is preferably 75 to 120 ° C, and more preferably 75 to 95 ° C as a display for indoor use. In order to obtain good alignment, it is preferable that the temperature range of the nematic phase and smectic A phase is sufficiently wide for applications other than half V-type displays. Specifically, each of the nematic phase and smectic A phase is different from each other. The temperature range shown independently without coexisting with the above phase is preferably 1 ° C. or higher, more preferably 3 ° C. or higher. In a half-V display application, in order to obtain good alignment, the smectic A phase does not exist or its temperature range is within 3 ° C, preferably within 1 ° C, and the nematic phase coexists with other phases. It is preferable that the temperature range shown independently is 1 degreeC or more, and it is more preferable that it is 3 degreeC or more.

  Further, as a component of the ferroelectric liquid crystal composition, if necessary, other than the compound represented by the general formula (Ia), the general formula (Ib), the general formula (IV), or the general formula (V) These liquid crystalline compounds can be used in combination. The compound that can be used in combination is not particularly limited, but in order to stabilize the ferroelectric liquid crystal phase, it is preferable to use a liquid crystalline compound exhibiting a smectic C phase or a chiral smectic C phase. (In this specification, the name of the liquid crystal phase includes the corresponding chiral liquid crystal phase unless otherwise specified.) In addition, the phase series of the ferroelectric liquid crystal phase or the temperature range of each liquid crystal phase is defined. In order to adjust, it is preferable to select a liquid crystal compound as appropriate. Specifically, in order to develop a nematic phase or expand the temperature range of the nematic phase, it is preferable to use a compound exhibiting a nematic phase in combination, or to develop a smectic A phase or a smectic A phase. When it is desired to expand the temperature range, it is preferable to use a compound exhibiting a smectic A phase, or, when a smectic A phase is not required, such as a half V material, a compound that does not exhibit a smectic A phase. It is preferable to use together. In order to obtain good alignment, it is necessary to stabilize the nematic phase. In that case, it is preferable to add a compound that exhibits a nematic phase having a good compatibility with the smectic liquid crystal and a wide temperature range. Such a compound preferably has a temperature range of 5 ° C. to 120 ° C. showing a nematic phase, more preferably 10 ° C. to 120 ° C., particularly preferably 20 ° C. to 120 ° C. The clearing point is preferably 70 ° C to 220 ° C. As specific examples, the following general formula (VII),

(In the formula, R ⁷⁶¹ and R ⁷⁶² each independently represent a linear alkyl group or alkoxy group having 1 to 8 carbon atoms, and A ⁷ , B ⁷ and C ⁷ are 1,4-phenylene group or 1 , 4-cyclohexylene group, a ⁷ represents 0, 1 or 2, b ⁷ and c ⁷ represent an integer of 0 or 1, and the sum of a ⁷ , b ⁷ and c ⁷ represents 1 or 2 Wherein R ⁷⁶¹ is a linear alkyl group having 1 to 8 carbon atoms when A ⁷ is a 1,4-cyclohexylene group, and R ⁷⁶² is carbon when C ⁷ is a 1,4-cyclohexylene group. Represents a linear alkyl group having 1 to 8 atoms.)
A compound having the structure shown in FIG. Among these, R ⁷⁶¹ and R ⁷⁶² are more preferably each independently a linear alkyl group having 1 to 5 carbon atoms or an alkoxy group.

  In order to obtain a display element with good contrast, it is necessary to adjust the tilt angle according to the display method. In order to increase the tilt angle, it is preferable to select a compound so as to increase the upper limit temperature of the smectic C phase or to narrow the temperature range of the smectic A phase. To reduce the tilt angle, the smectic C phase is preferred. It is preferable to use a compound that lowers the upper limit temperature of the phase or widens the temperature range of the smectic A phase.

  One kind of chiral compound may be used, or a plurality of compounds having different structures may be used. In order to suppress the helical structure in the liquid crystal phase generated based on the chiral effect and obtain a good alignment state, it is preferable to use a combination of a plurality of chiral compounds having different twist directions to be generated. At this time, if the combination of chiral compounds is selected so that the directions of spontaneous polarization are aligned, or if a combination of a compound that generates sufficiently large spontaneous polarization and a compound that induces a twisted structure but has a small spontaneous polarization value is selected, The value is preferred because it is not canceled. It is also preferable to introduce a plurality of chiral structures having different twist directions to be introduced into the same compound in order to suppress the generation of a helical structure that occurs in the liquid crystal phase based on the chiral effect. At this time, if a combination of chiral structures is selected so that the directions of spontaneous polarization are aligned, or if a combination of structures that induce sufficiently large spontaneous polarization and a torsional structure is induced but has a small spontaneous polarization value, The value is preferred because it is not canceled.

  Furthermore, a dopant such as a dye can be added to the liquid crystal composition according to the purpose. In addition, antioxidants, UV absorbers, non-reactive oligomers and inorganic fillers, organic fillers, polymerization inhibitors, antifoaming agents, leveling agents, plasticizers, silane coupling agents, etc. are added as necessary. You may do it.

The ferroelectric liquid crystal composition of the present invention can be produced by adding an ionic liquid to a liquid crystalline mixture. The ionic liquid may be added alone, or may be produced by dissolving in a soluble solvent and adding to the liquid crystalline mixture and then removing the solvent. In the production of the ferroelectric liquid crystal composition, the specific resistance value of the liquid crystalline mixture is 1 × 10 ¹¹ to 1 × for the purpose of expressing the effect of the ionic liquid without being affected by the impurities in the liquid crystalline mixture. It is preferable to produce a ferroelectric liquid crystal composition using a liquid crystal mixture having a density of 10 ¹⁵ Ωcm. In consideration of ease of production and purification, a liquid crystal mixture having a density of 1 × 10 ¹¹ to 1 × 10 ¹⁴ Ωcm is preferable. Is more preferable, and it is particularly preferable to use a liquid crystalline mixture of 1 × 10 ¹¹ to 1 × 10 ¹³ Ωcm. The ferroelectric liquid crystal composition preferably has a specific resistance value of 1 × 10 ¹⁰ to 1 × 10 ¹⁴ Ωcm, and more preferably 1 × 10 ¹⁰ to 1 × 10 ¹³ Ωcm.

  By putting the composition of the present invention in a liquid crystal cell, a liquid crystal display element can be produced. The two substrates of the liquid crystal cell can be made of a transparent material having flexibility such as glass or plastic, and one of them can be an opaque material such as silicon. A transparent substrate having a transparent electrode layer can be obtained, for example, by sputtering indium tin oxide (ITO) on a transparent substrate such as a glass plate. For the purpose of aligning the liquid crystal on the substrate, it is desirable to form a well-known liquid crystal alignment layer. As the alignment layer, an alignment layer material of polyimide or other organic polymer is formed on a substrate such as a glass substrate and then subjected to alignment treatment such as rubbing treatment, photo-alignment treatment, ion beam treatment, SiOx, CaF, etc. Formed on a substrate such as a glass substrate by vapor deposition or sputtering, or a photo-alignment layer formed by polarization irradiation, non-polarization oblique irradiation using a photo-alignment material as an alignment layer substance, or a combination of both Can be used.

  A liquid crystal display element using a ferroelectric liquid crystal composition can display a color without using a color filter by using a field sequential driving method, but a display method using a color filter is used. May be. The color filter can be prepared by, for example, a pigment dispersion method, a printing method, an electrodeposition method, or a dyeing method. A method for producing a color filter by a pigment dispersion method will be described as an example. A curable coloring composition for a color filter is applied on the transparent substrate, subjected to patterning treatment, and cured by heating or light irradiation. By performing this process for each of the three colors red, green, and blue, a pixel portion for a color filter can be created. In addition, a pixel electrode provided with an active element such as a TFT, a thin film diode, or a metal insulator metal specific resistance element may be provided on the substrate.

  The said board | substrate is made to oppose so that a transparent electrode layer may become an inner side. In that case, you may adjust the space | interval of a board | substrate through a spacer. In this case, it is preferable to adjust the thickness of the obtained cell to be 1 to 100 μm. The cell thickness is more preferably 1 to 10 μm, still more preferably 1 to 4 μm. When a polarizing plate is used, it is preferable to adjust the product of the refractive index anisotropy Δn of the liquid crystal and the cell thickness d so that the contrast is maximized. In view of manufacturing the display element, it is preferable that the cell thickness is thick. In that case, it is necessary to use a liquid crystal having a small Δn. In that case, it is desirable to use cyclohexyl or a compound having a 1,3,4-thiadiazole-2,5-diyl structure in combination. One or two cyclohexyl structures are preferably present in one molecule, and one 1,3,4-thiadiazole-2,5-diyl is preferably present in one molecule. In addition, when there are two polarizing plates, the polarizing axis of each polarizing plate can be adjusted so that the viewing angle and contrast are good. Furthermore, a retardation film for widening the viewing angle can also be used. Examples of the spacer include glass particles, plastic particles, alumina particles, and a photoresist material. Thereafter, a sealant such as an epoxy thermosetting composition is screen-printed on the substrates with a liquid crystal inlet provided, the substrates are bonded together, and heated to thermally cure the sealant.

  As a method for sandwiching the polymer-stabilized ferroelectric liquid crystal composition between two substrates, a normal vacuum injection method, an ODF method, or the like can be used. At this time, the liquid crystal composition is preferably in a uniform isotropic state or in a (chiral) nematic phase. In the smectic phase, handling during device fabrication becomes difficult.

Hereinafter, the liquid crystal composition of the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples. In this example, the evaluation of reversal abnormality was performed according to the following procedure. Two polarizing plates were placed in crossed Nicols, the light intensity when nothing was placed in the optical path was defined as 0%, and the light intensity when placed in parallel Nicols was defined as 100%. The two polarizing plates were arranged in crossed Nicols, and the liquid crystal cell was arranged so that the light transmittance of the liquid crystal cell after applying one pulse of -5 V and 1 Hz between the two polarizing plates was minimized. One pulse of 5 V and a pulse width of 0.1 ms was applied, and the transmittance was measured. Next, after applying a rectangular wave of -5 V and 1 Hz again, a pulse with a voltage of 5 V having a different pulse width was applied, and the transmittance was measured. This was repeated, and the pulse width was sequentially changed to 5 ms, and the transmittance when each pulse was applied was measured. The pulse width when 90% of the total change in transmittance of the liquid crystal cell was changed was defined as the saturation voltage pulse width. Next, -5V, 1Hz rectangular wave is applied again, and a pulse of saturation voltage pulse width of 1.5V, which does not change the transmittance with one pulse, is applied 3000 times at 100Hz. Each transmittance before and after was measured. When a change of 0.5% or more occurred in the transmittance before and after 3000 times application, it was judged that a reversal abnormality occurred. Evaluation of image sticking is based on the pulse width (time) required to change the liquid crystal cell left in the dark state for one week from the dark state to the bright state and the pulse required to change from the initial dark state to the bright state. Evaluation was made by comparing width (time). That is, when both values were close, there was no seizure, and the greater the difference between the two values, the stronger the seizure phenomenon that occurred. The specific resistance value was obtained by dissolving the measurement target in toluene and measuring the specific resistance value and extrapolating the measurement target to 100%. Further, “parts” in the composition all represent “parts by mass”, and “ppm,%” indicating the content ratios are all expressed on a mass basis.
Example 1
A compound having the following structure was mixed at the ratio shown below to prepare a liquid crystal mixture (LC-1).

The specific resistance value of this liquid crystalline mixture (LC-1) was 5 × 10 ¹² Ωcm. A ferroelectric liquid crystal composition (FLC-1) was prepared by adding 5 ppm of 1-ethyl-3-methylimidazolium trifluoromethanesulfonate as an ionic liquid to the liquid crystalline mixture (LC-1).
The specific resistance value of this ferroelectric liquid crystal composition (FLC-1) was 5.1 × 10 ¹¹ Ωcm. Next, FLC-1 was injected into a cell having a cell gap of 2 μm that had been subjected to polyimide-rubbing treatment by a vacuum injection method to obtain a ferroelectric liquid crystal element (FLCD-1). Using the thus obtained ferroelectric liquid crystal element (FLCD-1), the burn-in and inversion abnormalities were evaluated. FLCD-1 did not cause seizure, and the transmittance change showing reversal abnormality was 0.2%, which was preferable because reversal abnormality did not occur.

(Comparative Example 1)
The liquid crystal mixture (LC-1) has the same composition as the ferroelectric liquid crystal composition (FLC-1) of Example 1 except that it does not contain 1-ethyl-3-methylimidazolium trifluoromethanesulfonate. Since the liquid crystal is a liquid crystal, a ferroelectric liquid crystal element (LCD-1) was produced in the same manner as in Example 1 using (LC-1) for comparison. When the ferroelectric liquid crystal element (LCD-1) thus obtained was evaluated for burn-in and reversal abnormality, seizure occurred and the transmittance change indicating reversal abnormality was 7.6%. It was clear that the reversal abnormality was clearly observed and was inferior to Example 1.
(Example 2)
A compound having the following structure was mixed at the ratio shown below to prepare a liquid crystalline mixture (LC-2).

The specific resistance value of this liquid crystalline mixture (LC-2) was 4.8 × 10 ¹² Ωcm. A ferroelectric liquid crystal composition (FLC-2) was prepared by adding 5 ppm of 1-ethyl-3-methylimidazolium trifluoromethanesulfonate as an ionic liquid to the liquid crystal mixture (LC-2). The specific resistance value of this ferroelectric liquid crystal composition (FLC-2) was 2.5 × 10 ¹¹ Ωcm. A ferroelectric liquid crystal element (FLCD-2) was produced in the same manner as in Example 1. Using the thus obtained ferroelectric liquid crystal element (FLCD-2), the burn-in and inversion abnormalities were evaluated. FLCD-2 did not cause seizure, and the transmittance change indicating reversal abnormality was 0.1%, which was preferable because reversal abnormality did not occur.

(Comparative Example 2)
The liquid crystal mixture (LC-2) has the same composition as the ferroelectric liquid crystal composition (FLC-2) of Example 2 except that it does not contain 1-ethyl-3-methylimidazolium trifluoromethanesulfonate. Since the liquid crystal composition was (LC-2), a ferroelectric liquid crystal device (LCD-2) was produced in the same manner as in Example 1 using (LC-2) for comparison. The ferroelectric liquid crystal element (LCD-2) thus obtained was evaluated for burn-in and reversal abnormality. As a result, seizure occurred and the transmittance change indicating reversal abnormality was 4.6%. It was clear that a reversal abnormality was clearly observed and was inferior to Example 2.
(Example 3)
A compound having the following structure was mixed at the ratio shown below to prepare a liquid crystalline mixture (LC-3).

The specific resistance value of this liquid crystalline mixture (LC-3) was 6.2 × 10 ¹² Ωcm. A ferroelectric liquid crystal composition (FLC-3) was prepared by adding 10 ppm of 1-ethyl-3-methylimidazolium trifluoromethanesulfonate as an ionic liquid to the liquid crystal mixture (LC-3).
The specific resistance value of this ferroelectric liquid crystal composition (FLC-3) was 1.1 × 10 ¹¹ Ωcm. A ferroelectric liquid crystal element (FLCD-3) was produced in the same manner as in Example 1. The ferroelectric liquid crystal element (FLCD-3) thus obtained was used to evaluate burn-in and reversal abnormalities. FLCD-3 did not cause seizure, and had a transmittance change of 0% indicating reversal abnormality, and was suitable without causing reversal abnormality.

(Comparative Example 3)
The liquid crystal mixture (LC-3) has the same composition as the ferroelectric liquid crystal composition (FLC-3) of Example 3 except that it does not contain 1-ethyl-3-methylimidazolium trifluoromethanesulfonate. Since the liquid crystal composition was (LC-3), a ferroelectric liquid crystal device (LCD-3) was produced in the same manner as in Example 1 using (LC-3) for comparison. When the ferroelectric liquid crystal element (LCD-3) thus obtained was evaluated for burn-in and reversal abnormality, seizure occurred and the transmittance change indicating reversal abnormality was 10.5%. It was clear that the reversal abnormality was clearly observed and was inferior to Example 3.
Example 4
In the liquid crystalline mixture (LC-1) described in Example 1, 1 ppm of 1-ethyl-3-methylimidazolium trifluoromethanesulfonate as an ionic liquid, and a compound (I-aa) having the following structure as a cation inclusion compound,

Was added to prepare a ferroelectric liquid crystal composition (FLC-4). The specific resistance value of this ferroelectric liquid crystal composition (FLC-4) was 1.9 × 10 ¹¹ Ωcm.
A ferroelectric liquid crystal element (FLCD-4) was produced in the same manner as in Example 1. The ferroelectric liquid crystal element (FLCD-4) thus obtained was used to evaluate burn-in and reversal abnormalities. FLCD-4 did not cause seizure, and the transmittance change indicating reversal abnormality was 0%, which was preferable because reversal abnormality did not occur.

Claims (4)

A ferroelectric liquid crystal composition comprising at least one liquid crystal mixture containing at least two liquid crystal compounds and an ionic liquid ,
The ionic liquid is an imidazolium ionic liquid, a pyridinium ionic liquid, a pyrrolidinium ionic liquid, a phosphonium ionic liquid or an ammonium ionic liquid, and the content of the ionic liquid is 0.01 ppm to 10%,
The liquid crystalline mixture has the following general formula (Ia)

(In the formula, R ¹¹ and R ¹² each independently represent a linear or branched alkyl group having 1 to 18 carbon atoms, provided that at least one of the alkyl groups is a branched alkyl group. And one or two non-adjacent —CH ₂ — groups in the alkyl group are —O—, —CO—, —CO—O—, —O—CO—, —O—CO—O—. , —CH═CH— or —C≡C—, wherein one or more hydrogen atoms in the alkyl group may be replaced with a fluorine atom or a CN group, and A ¹ , B ¹ and Each C ¹ is independently a 1,4-phenylene group in which one or two hydrogen atoms may be replaced by a fluorine atom, a CF ₃ group, an OCF ₃ group, or a CN group, or a plurality of these groups, or It represents 1,4-cyclohexylene group, ^{a 1} is 0, 1, or It represents, ^{b 1} and ^{c 1} is an integer of 0 or ^1, a 1, the sum of ^{b 1} and ^{c 1} is 1 or 2.) The compound represented by, and the following formula (I-b)

(In the formula, R ¹³ and R ¹⁴ each independently represent a linear or branched alkyl group having 1 to 18 carbon atoms or a fluorine atom, provided that R ¹³ and R ¹⁴ may simultaneously become a fluorine atom. And one or two non-adjacent —CH ₂ — groups are —O—, —S—, —CO—, —CO—O—, —O—CO—, —CO—S—, — S—CO—, —O—CO—O—, —CH═CH—, —C≡C—, a cyclopropylene group or —Si (CH ₃ ) ₂ — may be substituted, and one of the alkyl groups Or more hydrogen atoms may be replaced by fluorine atoms or CN groups, X ^{11 to} X ¹⁷ each independently represent a hydrogen atom, a fluorine atom, a CF ₃ group, or an OCF ₃ group, and L ^{11 to} L ¹⁴ are each independently a single bond, -O -, - S -, - CO-, _{CH 2 O -, - OCH 2} -, - CF 2 O -, - OCF 2 -, - CO-O -, - O-CO -, - CO-S -, - S-CO -, - O-CO- O—, —CH ₂ CH ₂ —, —CH═CH— or —C≡C—, and d ¹ , e ¹ , f ¹ and g ¹ each independently represent an integer of 0 or 1, provided that d ¹ + e ¹ + f ¹ + g ¹ is 1, 2 or 3, and when d ¹ is 0, g ¹ is 0, and when d ¹ is 1, f ¹ is 0. A ferroelectric liquid crystal composition which is a liquid crystalline mixture containing at least two kinds of compounds selected from the group consisting of: The ferroelectric liquid crystal composition according to claim 1, wherein the ionic liquid has a melting point of 100 ° C. or lower. The ferroelectric liquid crystal composition according to claim 1, wherein the specific resistance value is 1 × 10 ¹⁰ to 1 × 10 ¹⁴ Ωcm. A ferroelectric liquid crystal display element using the ferroelectric liquid crystal composition according to claim 1.