JP2009108233A - Liquid crystal composition and ferroelectric liquid crystal composition - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a base liquid crystal composition having a low melting point used in a ferroelectric liquid crystal composition, and provide a ferroelectric liquid crystal composition having a low melting point. <P>SOLUTION: The liquid crystal composition contains a compound given by formulae (I) and (II), where R<SB>1</SB>and R<SB>2</SB>represent independently a straight-chain 1-15C alkyl group while R<SB>3</SB>represents a straight-chain 6C, 7C, or 8C alkyl group. The invention also includes a ferroelectric liquid crystal composition containing the described liquid crystal composition and an optical active compound, and a liquid crystal display element using the ferroelectric liquid crystal composition. These liquid crystal composition and ferroelectric liquid crystal composition are featured by a low melting point, and can preclude effectively the crystal precipitation when they are preserved at a low temperature. The ferroelectric liquid crystal composition is extremely useful when used as a constituent member of a ferroelectric liquid crystal display. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a liquid crystal composition and 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.

The liquid crystal phase that can be a ferroelectric liquid crystal is a tilted chiral smectic liquid crystal phase, but a chiral smectic C phase (hereinafter abbreviated as SmC ^* ) that is practically advantageous in terms of viscosity is most widely used. ing. The operating temperature and storage temperature of the ferroelectric liquid crystal display element are limited by the temperature range of the SmC ^* phase. In order to develop the SmC ^* phase in a wide temperature range, a method of adding an optically active substance to a base liquid crystal composed of a non-chiral compound that exhibits a smectic C phase is known as a general method.

  As the non-chiral compound used as the base liquid crystal, a phenylpyrimidine compound is useful. In particular, the compound represented by the following general formula (I) has a relatively low viscosity as a phenylpyrimidine-based compound and is suitable for high-speed response. Therefore, a composition in which several kinds of the compound are mixed (hereinafter abbreviated as PY base). .) Is widely used as a base liquid crystal.

(In the formula, R ₁ and R ₂ represent a linear alkyl group.)
A PY-based liquid crystal using a phenylpyrimidine compound has a relatively low viscosity, but has a high melting point of usually 0 ° C. or higher.

  As a technique for achieving a low melting point of a PY base liquid crystal, a method of adding a pyrimidine compound having the following branched methyl group in the side chain to the PY base liquid crystal is disclosed (see Patent Documents 1 and 2).

However, the composition described in the cited document has a problem that the substitution position of the methyl group is not optimized in the branched side chain of the pyrimidine-based compound. Therefore, the liquid crystal composition described in the cited document has a melting point as high as about 5 ° C., which is insufficient for practical use of a ferroelectric liquid crystal display. Therefore, development of a low melting point liquid crystal composition used as a base liquid crystal of a ferroelectric liquid crystal composition has been desired.

JP-A 64-79160 JP-A-2-204484

  The problem to be solved by the present invention is to provide a base liquid crystal composition having a low melting point and a ferroelectric liquid crystal composition having a low melting point used for the ferroelectric liquid crystal composition.

  In order to solve the above problems, the inventors of the present application have studied a liquid crystal composition in which pyrimidine compounds having various branched methyl groups in the side chain are added to the PY-based liquid crystal, and have a specific branched side chain. It has been found that the melting point can be effectively reduced by the addition of a pyrimidine-based compound, and the present invention has been completed.

  The present invention relates to general formula (I) and general formula (II).

(In the formula, R ₁ and R ₂ each independently represent a linear alkyl group having 1 to 15 carbon atoms, and R ₃ represents a linear alkyl group having 6, 7 or 8 carbon atoms.) And a ferroelectric liquid crystal composition containing the liquid crystal composition and an optically active compound, together with the ferroelectric liquid crystal composition using the ferroelectric liquid crystal composition. A liquid crystal display device is provided.

  Since the liquid crystal composition and the ferroelectric liquid crystal composition of the present invention are characterized by a low melting point, it is possible to effectively prevent crystal precipitation during low-temperature storage. The ferroelectric liquid crystal composition of the present invention is extremely useful as a constituent member of a ferroelectric liquid crystal display.

The liquid crystal composition of the present invention is composed of compounds represented by general formula (I) and general formula (II). In general formula (I), R ₁ and R ₂ are each independently the number of carbon atoms. A linear alkyl group having 1 to 15 carbon atoms is preferable, but a linear alkyl group having 3 to 12 carbon atoms is preferable, and a linear alkyl group having 5 to 10 carbon atoms is more preferable.
In the general formula (II), R ₃ represents a linear alkyl group having 6, 7 or 8 carbon atoms, preferably a linear alkyl group having 7 or 8 carbon atoms.

The content of the compound represented by the general formula (I) is preferably 40 to 90%, more preferably 50 to 80%, and preferably two or more compounds represented by the general formula (I) are contained.
The content of the compound represented by the general formula (II) is preferably 10 to 60%, more preferably 20 to 50%, and preferably two or more compounds represented by the general formula (II).

When containing the compound represented by the general formula (II) 2 species, a combination of a compound wherein a number of carbon atoms of R ₃ is a compound and 8 are 7 preferred.

The ferroelectric liquid crystal composition of the present invention contains the compound represented by the general formula (I) and the general formula (II) and an optically active compound,
As the optically active compound, a compound having an asymmetric atom or a compound having axial asymmetry can be used, and a compound having an asymmetric carbon or a compound having a carbon-carbon bond as axial asymmetry is preferably used. 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 into which a CF ₃ group is introduced is preferable.
Specifically, the optically active compound is represented by the general formula (III)

（式中、Ｒ_４１及びＲ_４２は、各々独立に炭素原子数１〜１８の直鎖状又は分岐状のアルキル基を表し、該アルキル基中の、１つ又は２つの隣接していない−ＣＨ_２−基は−Ｏ−、−Ｓ−、−ＣＯ−、−ＣＯ−Ｏ−、−Ｏ−ＣＯ−、−ＣＯ−Ｓ−、−Ｓ−ＣＯ−、−Ｏ−ＣＯ−Ｏ−、−ＣＨ＝ＣＨ−、−Ｃ≡Ｃ−、シクロプロピレン基又は−Ｓｉ（ＣＨ_３）_２−で置き換えられてもよく、該アルキル基中の水素原子はフッ素原子又はＣＮ基で置き換えられていてもよく、

(In the formula, each of R ₄₁ and R ₄₂ 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. _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 a hydrogen atom in the alkyl group may be substituted with a fluorine atom or a CN group,

A ₄ , B ₄ and C ₄ are each independently 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, Represents a piperazine-1,4-diyl group, piperazine-2,5-diyl group or naphthalene-2,6-diyl group, and a hydrogen atom in the 1,4-phenylene group and naphthalene-2,5-diyl group a fluorine atom, CF ₃ group, OCF ₃ group, N group, a CH ₃ group, or may be substituted in the OCH ₃ group, a hydrogen atom in xylene group to said trans-1,4-cyclohexylene may be replaced by a CN group or a CH ₃ group,
a ₄ , b ₄ and c ₄ each independently represent 0 or 1, * represents an asymmetric carbon,
L ₄₁ and L ₄₂ 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—
L ₄₃ represents the general formula (III-b), general formula (III-c), or general formula (III-d).

(Wherein d ₄ , e ₄ , and f ₄ each independently represents an integer of 0 or more and 7 or less), Y represents a fluorine atom or a methyl group. ) Is preferred.
Furthermore, the general formula (III-a)

Or general formula (III-e)

(In the formula, R ₄₁ , R ₄₂ , A ₄ , B ₄ , C ₄ , a ₄ , b ₄ , c ₄ , L ₄₁ , L ₄₂ , L ₄₃ and * have the same meaning as in the general formula (III). The compound represented by this is more preferable.
In general formula (III), general formula (III-a) or general formula (III-e), more specifically, a compound having a structure described below as a ring structure is preferable.

Among these structures, particularly preferred structures are the following structures.

Specifically, a compound having the following structure is more preferable as the side chain having an asymmetric carbon atom.

(In the formula, s represents an integer of 1 to 4, r represents an integer of 1 to 10, Q ₃ represents an alkyl group having 3 to 10 carbon atoms, and Q ₄ represents an alkyl group having 2 to 10 carbon atoms. Q ₅ represents an alkyl group having 1 to 10 carbon atoms, Q ₆ represents an alkyl group having 1 to 4 carbon atoms, and * represents an asymmetric carbon.)
More specifically, a compound having the following structure is particularly preferably used as the compound represented by the general formula (III-a).

(In the formula, R ₁ represents an alkyl group having 1 to 10 carbon atoms, n represents the number of methylene groups having 1 to 10 carbon atoms, and * represents an asymmetric carbon.)
The SC * liquid crystal composition of the present invention undergoes a phase transition from the N * phase to the SC * phase through the N * phase and then the SA phase during cooling from the isotropic liquid state. An SC * liquid crystal composition in which the helical pitch appearing in the N * phase from the transition temperature (hereinafter referred to as N * -SA point) to the high temperature side of the N * -SA point once is higher than 3 μm is more preferable. An SC * liquid crystal composition in which the helical pitch is 10 μm or more and the helical pitch divergently increases as it approaches the N * -SA point is preferable. In the half-V application, the SmA phase is not necessary, so that it is preferable to undergo phase transition with the isotropic phase, the N * phase, and the SmC *.

  When a composition comprising an optically active compound having the same twist direction of the spiral appearing in the N * phase when a single optically active compound is added to form an SC * liquid crystal composition, the concentration of the optically active compound is In a practical range, the pitch of the spiral tends to be further shortened. Therefore, it is difficult to obtain an SC * liquid crystal composition having a spiral pitch in the preferable range. Therefore, in order to adjust the helical pitch within the above-mentioned preferable range, optically active compounds in which the directions of the spirals appearing in the N * phase are opposite to each other when added to the base liquid crystal to form an SC * liquid crystal composition are added. It is desirable. More preferably, it is preferable to add a compound in which the pitch of the helix diverges in the N * phase in a single optically active compound without adding optically active substances whose directions of helix are opposite to each other.

  The temperature range showing the N * phase of the SC * liquid crystal composition of the present invention is preferably in the range of 1 degree or more and less than 30 degree. If the temperature range showing the N * phase is less than 1 degree, the phase transitions to the SA phase as soon as the temperature is lowered, which is not preferable because it tends to make it difficult to sufficiently align liquid crystal molecules in the N * phase. In addition, when the temperature range showing the N * phase is 30 ° C. or more, the clearing point of the SC * liquid crystal composition becomes high temperature, and the workability in the process of filling the liquid crystal material into the cell tends to be adversely affected. It is not preferable.

As the optically active compound used in the present invention, it is necessary to induce a certain degree of spontaneous polarization (hereinafter abbreviated as Ps) by adding it to a certain amount of the base liquid crystal. For the SC * liquid crystal composition, the addition amount of the optically active compound may be adjusted so that the value of Ps is in the range of 1 to 30 nC / cm ² particularly near room temperature. However, when the value of P s induced by the optically active compound is small, the amount of addition increases with respect to the base liquid crystal, and this increases the viscosity of the SC * liquid crystal composition. This is not preferable because responsiveness tends to be lost. Accordingly, as the optically active compound used in the present invention, those capable of inducing a Ps of ²⁰ nC / cm ² or more when added to the SC matrix liquid crystal at 10% by weight are preferred, and when added at 5% by weight, 10 nC / cm ² or more. Those capable of inducing Ps are particularly preferred. When high-speed response is required, the value of Ps is preferably 100 nC / cm ² near room temperature.

  By placing 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.

  A liquid crystal display element using a ferroelectric liquid crystal can display a color without using a color filter by using a field sequential driving method, but even if a display method using a color filter is used. Good. The color filter can be produced 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 onto 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 color filter pixel portion can be manufactured. 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. At this time, it is preferable to adjust so that the thickness of the light control layer obtained may be 1-100 micrometers. 2-10 μm is more preferable, and when a deflector 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. When there are two deflecting plates, the deflection axis of each deflecting plate can be adjusted to adjust the viewing angle and contrast. 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 UV curable type and UV-heat combined type curable sealing material is printed on the substrate in a form provided with a liquid crystal injection port, the substrates are bonded together, and the sealing material is cured.

  As a method for sandwiching the liquid crystal composition of the present invention between two substrates, a normal vacuum injection method, an ODF method, or the like can be used. When the injection speed of the liquid crystal is low, vacuum injection or ODF method can be performed while heating. The liquid crystal phase when heated is preferably N * with high fluidity.

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 phase transition temperature was measured using a polarizing microscope equipped with a temperature control stage and a differential scanning calorimeter (DSC). Further, all “%” in the composition represents “% by weight”.

(Examples 1-3)
Three types of phenylpyrimidine compounds having different alkyl chains and alkoxy chains were mixed at the contents shown in Table 1 to obtain PY-based liquid crystals. The melting point of this liquid crystal composition was 9 ° C.
PY base liquid crystal 75% and No. 1 in Table 1. The base liquid crystals of Examples 1 to 3, each comprising 25% of the compounds of 4, 5, and 6, were obtained. Whereas the melting point of the PY base liquid crystal was 9 ° C., the melting points of the base liquid crystal of the present invention were minus 5 ° C. (Example 1), minus 12 ° C. (Example 2), minus 6 ° C. (Example 3). ) Therefore, it is clear that the base liquid crystals of Examples 1 to 3 have a lower melting point than the PY base liquid crystals.
(Comparative Examples 1-2)
PY base liquid crystal 75% and No. 1 in Table 1. Base liquid crystals of Comparative Examples 1 and 2 comprising 25% of each of the compounds 7 and 8 were obtained. The melting points were 3 ° C. (Comparative Example 1) and minus 1 ° C. (Comparative Example 2), respectively. It is clear that the base liquid crystal of the comparative example using compounds having different branch positions of the side chains has a higher melting point than the base liquid crystal of the example.

Example 4
PY base and No. 1 in Table 1. Compounds of 5 and 6, No. Nine chiral compounds were mixed in the proportions shown in Table 1 to prepare a ferroelectric liquid crystal composition of Example 4. The melting point of the ferroelectric liquid crystal composition of Example 4 was −14 ° C., and the low melting point was maintained even in the ferroelectric liquid crystal composition to which the chiral compound was added.
Table 1 summarizes the above examples and comparative examples.

Claims (8)

General formula (I) and general formula (II)

(In the formula, R ₁ and R ₂ each independently represent a linear alkyl group having 1 to 15 carbon atoms, and R ₃ represents a linear alkyl group having 6, 7 or 8 carbon atoms.) The liquid crystal composition containing the compound represented by these. The liquid crystal composition according to claim 1, comprising two or more compounds represented by formula (II). 4. The liquid crystal composition according to claim 3, comprising a compound in which R ₃ has 7 carbon atoms and a compound in which R ₃ is 8 in the general formula (II). The liquid crystal composition according to claim 1, wherein the content of the compound represented by the general formula (II) is 10 to 60%. The liquid crystal composition according to claim 1, wherein the content of the compound represented by the general formula (II) is 20 to 50%. A ferroelectric liquid crystal composition comprising the liquid crystal composition according to any one of claims 1 to 5 and an optically active compound. The optically active compound is represented by the general formula (III)

(In the formula, each of R ₄₁ and R ₄₂ 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. _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 a hydrogen atom in the alkyl group may be substituted with a fluorine atom or a CN group,
A ₄ , B ₄ and C ₄ are each independently 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, Represents a piperazine-1,4-diyl group, piperazine-2,5-diyl group or naphthalene-2,6-diyl group, and a hydrogen atom in the 1,4-phenylene group and naphthalene-2,5-diyl group a fluorine atom, CF ₃ group, OCF ₃ group, N group, a CH ₃ group, or may be substituted in the OCH ₃ group, a hydrogen atom in xylene group to said trans-1,4-cyclohexylene may be replaced by a CN group or a CH ₃ group,
a ₄ , b ₄ and c ₄ each independently represent 0 or 1, * represents an asymmetric carbon,
L ₄₁ and L ₄₂ 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—
L ₄₃ represents the general formula (III-b), general formula (III-c), or general formula (III-d).

(Wherein d ₄ , e ₄ , and f ₄ each independently represents an integer of 0 or more and 7 or less), Y represents a fluorine atom or a methyl group. The ferroelectric liquid crystal composition according to claim 6, which represents a compound represented by: A ferroelectric liquid crystal display device using the ferroelectric liquid crystal composition according to claim 6.