JP2005200570A - Nematic liquid crystal composition and liquid crystal display element using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nematic liquid crystal composition which has a threshold voltage of low temperature dependence, steep electrooptical characteristics, and a high response speed; and a liquid crystal display element using the same. <P>SOLUTION: The liquid crystal composition contains compounds represented by general formulas (I), (II), and (III). A liquid crystal display element using the composition has such excellent characteristics as a high contrast, a high response speed, and a display quality hardly influenced by temperature; therefore the composition is useful as a component member of an STN liquid crystal display element. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a liquid crystal composition having steep electro-optical characteristics and a fast response speed and having a small threshold voltage temperature dependency, and a liquid crystal display element using the same.

  Among liquid crystal display elements, a super twisted nematic liquid crystal display element (hereinafter referred to as STN-LCD) is used as a display device for a wide range of applications, and various characteristics are required with the development of applications.

  Particularly in recent years, in a time-division drive for displaying not only characters but also a lot of information such as images in a portable information terminal, more steep electro-optical characteristics are required. With regard to the images, not only still images but also moving images are becoming popular today, and improvement of response speed is also an important issue. Furthermore, at present, in order to withstand use in a wide temperature range, an electrical temperature compensation circuit is added to the drive circuit to reduce the influence on the display quality at the use temperature. However, since an extra circuit is added, the yield is reduced due to process complexity. For this reason, a liquid crystal display element having a small temperature dependency of the threshold voltage is required.

  In response to such demands and problems, a composition containing a difluorocyanophenylbenzoate-based compound constituting the composition of the present invention (see Patent Document 1) has already been known. Although it is described that it can be obtained with a liquid crystal display element having a small size, no specific report has been made regarding the electro-optical characteristics and response speed which are the basis of display quality. On the other hand, it is known that compositions containing bicyclohexyl vinylene compounds (see Patent Document 2 and Patent Document 3) can realize steep electro-optical characteristics. There has been a demand for a liquid crystal composition and a liquid crystal display device using the liquid crystal composition that can simultaneously realize a temperature dependency of a low threshold voltage and a steep electro-optical characteristic, and have a high response speed.

JP 2000-129260 A Japanese National Patent Publication No. 10-501795 JP 2001-11448 A

  The problem to be solved by the present invention is to provide a liquid crystal composition and a liquid crystal display device using the same, which simultaneously realize a temperature dependency of a low threshold voltage, a steep electro-optical characteristic, and a fast response speed.

In order to solve the above problems, the present inventor uses the compounds represented by the general formula (I), the general formula (II) and the general formula (III) at the same time, thereby reducing the temperature dependence of the low threshold voltage, The present invention has been reached based on the knowledge that steep electro-optical characteristics and a fast response speed can be realized simultaneously.
That is, the present invention provides the general formula (I) as the first component.

(Wherein R ¹ represents an alkyl group having 1 to 8 carbon atoms, an alkoxy group having 1 to 8 carbon atoms, an alkenyl group having 2 to 8 carbon atoms or an alkenyloxy group having 2 to 8 carbon atoms, X ¹ and X ² independently represents -H or -F.)
Containing one or more compounds represented by
As the second component, the general formula (II)

(Wherein R ² represents the same meaning as R ¹ in formula (I), p represents an integer of 0 or more and 2 or less, and m represents 0 or 1)
Containing one or more compounds represented by
As the third component, the general formula (III)

(Wherein R ³ and R ⁴ represent the same meaning as R ¹ in formula (I), A represents a trans-1,4-cyclohexylene group or a 1,4-phenylene group, and Z ¹ represents- CH ₂ CH _2- , -COO- or a single bond, X ³ and X ⁴ each independently represent -H or -F, and q represents an integer of 0 or more and 3 or less. A nematic liquid crystal composition containing one or more compounds, and a liquid crystal display device using the liquid crystal composition is also provided.

  The present invention provides a liquid crystal composition having a temperature dependence of a low threshold voltage, steep electro-optical characteristics, and a quick response speed, thereby obtaining an STN-LCD having a greatly improved display quality. Can do. That is, the STN-LCD of the present invention has very excellent characteristics such as high contrast, fast response speed, and being hardly affected by display quality due to temperature.

In the liquid crystal composition of the present invention, the compound selected from the general formula (I) used as the first component contains 1 type or 2 types or more, preferably 1 to 10 types, more preferably 1 to 5 types .
In the compound represented by the general formula (I), R ¹ represents an alkyl group having 1 to 8 carbon atoms, an alkoxy group having 1 to 8 carbon atoms, an alkenyl group having 2 to 8 carbon atoms, or an alkenyloxy group having 2 to 8 carbon atoms. An alkyl group having 1 to 8 carbon atoms or an alkoxy group is preferable, and an alkyl group having 2 to 5 carbon atoms is more preferable. X ¹ and X ² each independently represent -H or -F, preferable.
The content of the compound represented by the general formula (I) in the liquid crystal composition is 5 to 50% by mass, preferably 5 to 40% by mass, and particularly preferably 5 to 30% by mass. .

Further, in the liquid crystal composition of the present invention, the compound represented by the general formula (II) used as the second component contains one or more kinds, preferably 1 to 10 kinds, preferably 1 to 5 kinds. Is more preferable.
In the compound represented by the general formula (II), R ² represents an alkyl group having 1 to 8 carbon atoms, an alkoxy group having 1 to 8 carbon atoms, an alkenyl group having 2 to 8 carbon atoms, or an alkenyloxy group having 2 to 8 carbon atoms. An alkyl group having 1 to 8 carbon atoms or an alkoxy group is preferable. p represents 0 or more and 2 or less, preferably 0 or 1, and particularly preferably 0. m represents 0 or 1; The content of the compound represented by the general formula (II) in the liquid crystal composition is 5 to 50% by mass, preferably 5 to 40% by mass, and particularly preferably 5 to 35% by mass. .

Further, in the liquid crystal composition of the present invention, the compound represented by the general formula (III) used as the third component contains one kind or two or more kinds, preferably 1 to 10 kinds, and preferably 1 to 5 kinds. Further preferred.
In the compound represented by the general formula (III), R ³ and R ⁴ are each independently an alkyl group having 1 to 8 carbon atoms, an alkoxy group having 1 to 8 carbon atoms, an alkenyl group having 2 to 8 carbon atoms, or 2 to Although an alkenyloxy group having 8 carbon atoms is represented, an alkyl group having 1 to 8 carbon atoms, an alkoxy group having 1 to 8 carbon atoms, or an alkenyl group having 2 to 8 carbon atoms is preferable. A represents a trans-1,4-cyclohexylene group or a 1,4-phenylene group. Z ¹ represents —CH ₂ CH ₂ —, —COO— or a single bond, and X ³ and X ⁴ each independently represent —H or —F. q represents 0 or more and 3 or less, preferably 0 or 1. Preferable specific examples of the general formula (III) include compounds represented by the general formulas (III-a) to (III-g).

The content of the compound represented by the general formula (III) in the liquid crystal composition is 5 to 50% by mass, preferably 5 to 40% by mass, and particularly preferably 5 to 35% by mass. .

  Furthermore, the liquid crystal composition of the present invention has the general formula (IV) as the fourth component.

(Wherein R ⁵ represents the same meaning as R ¹ in general formula (I), r represents 0 or more and 2 or less, and n represents 0 or 1). The content is preferably 5 to 35% by mass, more preferably 5 to 25% by mass, and particularly preferably 5 to 15% by mass.

  The nematic phase-isotropic liquid phase transition temperature (hereinafter referred to as Tni) of the liquid crystal composition of the present invention is preferably low in order to increase the contrast of the liquid crystal display element, but if Tni is too low, Since various problems such as display disappearing in an atmosphere of high temperature occur, it is preferably 70 ° C to 140 ° C, more preferably 80 ° C to 120 ° C, and 90 ° C to 110 ° C. Is particularly preferred. Refractive index anisotropy (Δn) is 0.11 to 0.18 for reasons such as keeping the solid phase-nematic phase transition temperature low, obtaining a fast response speed while keeping viscosity low, and steep electro-optical properties. Is preferable, but 0.13-0.18 is more preferable. The dielectric anisotropy (Δε) is preferably 1 or more and 30 or less, and more preferably 8 or more and 20 or less. The rotational viscosity is preferably 35 mPa · s or less, more preferably 30 mPa · s or less, and particularly preferably 25 mPa · s or less in order to obtain a high response speed.

  In addition to the compounds represented by the general formulas (I) to (IV), ordinary nematic liquid crystals, smectic liquid crystals, cholesteric liquid crystals, chiral agents and the like can be used for the liquid crystal composition used in the present invention. Typical examples of the chiral agent include cholesteryl nonanate, C-15, CB-15, S-811, R-811 and the like.

  The liquid crystal composition of the present invention can be used for TN-LCD, STN-LCD, IPS-LCD, OCB-LCD, polymer dispersion type liquid crystal display element, phase change type cholesteric liquid crystal display element, but is particularly useful for STN-LCD. It is.

  When the liquid crystal composition of the present invention is configured as STN-LCD, the twist angle is preferably 180 ° to 270 °, more preferably 220 ° to 260 °, and particularly preferably 230 ° to 250 °. At that time, the chiral agent added to the liquid crystal composition of the present invention preferably has a d / P value (the inherent helical pitch P of the mixed liquid crystal by addition of the chiral agent, the cell thickness d of the display cell) of 0.1 or more and 0.7 or less. 0.3 to 0.6 is particularly preferable.

  The STN-LCD of the present invention is characterized by having a high contrast, and in a time-division drive of 1/32 to 1/480 Duty, more preferably 1/64 to 1/240 Duty required for a portable information terminal. It has very good display characteristics.

  Note that the STN-LCD of the present invention may be any display system such as a transmissive type, a transflective type, and a reflective type.

The STN-LCD using the liquid crystal composition of the present invention is preferably an STN-LCD that satisfies the following conditions.
(i) 1.3v ≦ Vth (25 ℃) ≦ 2.2v
(However, Vth (25 ° C) is the applied voltage when the transmittance change is 10% when a rectangular wave voltage of 100Hz frequency is applied at 25 ° C to a panel with cell thickness d satisfying Δn · d = 0.9. It is preferable that the threshold voltage Vth is represented by a threshold voltage Vth of 1.7V or more and 2.2V or less.
(ii) Vsat (25 ° C) / Vth (25 ° C) ≤ 1.075
(However, Vth (25 ° C) is the applied voltage when the transmittance change is 10% when a rectangular wave voltage of 100Hz frequency is applied at 25 ° C to a panel with cell thickness d satisfying Δn · d = 0.9. Vsat (25 ° C) is the applied voltage when the change in transmittance is 90% when a rectangular wave voltage with a frequency of 100 Hz is applied to a panel with a cell thickness d satisfying Δn · d = 0.9 at 25 ° C. The steepness Vsat (25 ° C.) / Vth (25 ° C.) represented by the following formula is preferable, and 1.065 or less is more preferable.
(iii) τ (25) ≦ 350msec
(However, τ (25) is the change in transmittance from 0% to 90% when the voltage is turned on at 25 ° C and the change from 100% to 10% when the voltage is turned off. It is preferable that the response speed τ (25) expressed by (2), and more preferably 250 msec or less.
(iv) {Vth (-20 ℃) −Vth (50 ℃)} / 70 ≦ 5mV / ℃
(However, Vth (-20 ° C) and Vth (50 ° C) are the values when a rectangular wave voltage with a frequency of 100Hz is applied at -20 ° C and 50 ° C to a panel of cell thickness d satisfying Δn · d = 0.9, respectively. (It represents the applied voltage when the transmittance change is 10%.) The temperature dependence of the threshold voltage is preferably 4 mV / ° C. or less.

  EXAMPLES Hereinafter, although an Example is given and this invention is 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%”.

  In the examples, the measured characteristics are as follows.

Tni: Nematic phase-isotropic liquid phase transition temperature (° C)
Tn: Solid phase or smectic phase-nematic phase transition temperature (° C)
Δn: refractive index anisotropy at 25 ° C. Δε: dielectric anisotropy at 25 ° C. η: rotational viscosity at 20 ° C. (mPa · s)
Vth: threshold voltage (V) at 25 ° C when a STN-LCD with a cell thickness d (μm) and a twist angle of 240 ° is constructed, that is, drive voltage when the transmittance change is 10% .

            The cell thickness d (μm) is determined by the relational expression Δn · d = 0.90.

            The applied drive waveform is a 100Hz rectangular wave.

Vsat: Saturation at 25 ° C when a STN-LCD with a cell thickness d (μm) and a twist angle of 240 ° is constructed.
It represents the sum voltage (V), that is, the drive voltage when the transmittance change is 90%.

            The cell thickness d (μm) is determined by the relational expression Δn · d = 0.90.

            The applied drive waveform is a 100Hz rectangular wave.

γ: Steepness at 25 ° C γ = Vsat / Vth
τ: When STN-LCD with a cell thickness d (μm) and a twist angle of 240 ° is configured at 25 ° C
Response speed (msec).

            The measurement was performed at 1/128 Duty.

    dv / dt: Vth change rate per 1 ° C (mV / ° C) when the temperature is changed from -20 ° C to 50 ° C.

  The STN-LCD was manufactured as follows. A chiral liquid "S-811" (Merck) is added to the nematic liquid crystal composition to prepare a mixed liquid crystal, and an organic film of "Sunever 150" (Nissan Chemical) is rubbed on the opposing flat transparent electrode. Then, it was injected into an STN-LCD with a twist angle of 240 ° on which an alignment film was formed. The chiral agent was added so that the natural helical pitch P of the mixed liquid crystal and the cell thickness d of the display cell were d / P = 0.50 by adding the chiral agent.

The following abbreviations are used in the description of compounds.
-Terminal n (number): -C _n H _{2n + 1} ndm-: C _n H _{2n + 1} -CH = CH- (CH ₂ ) _m-1-
-T-: -C≡C- -ndm:-(C _n H _{2n + 1} -CH = CH- (CH ₂ ) _m-1 )
-F: -F -On: -OC _n H _{2n + 1}
-VO-: -COO- -CN: -C≡N
-D-: -CH = CH-

For example, abbreviations are used as shown below.

(Example 1, Comparative Example 1, Comparative Example 2 and Comparative Example 3)
Liquid crystal composition No. 1 (Example 1), M1 (Comparative Example 1), M2 (Comparative Example 2) and liquid crystal composition M3 (Comparative Example 3) were prepared. In addition, STN-LCDs using these liquid crystal compositions were prepared. Table 1 shows the composition ratios of these liquid crystal compositions and the measured characteristics of STN-LCDs using the liquid crystal compositions.

Liquid crystal composition No. 1 (Example 1) is a combination of general formula (I), general formula (II) and general formula (III) of the present invention. On the other hand, the liquid crystal composition M1 (Comparative Example 1), the liquid crystal composition M2 (Comparative Example 2) and the liquid crystal composition M3 (Comparative Example 3) do not contain all the three components of the present invention. Comparing the characteristics, the STN-LCD of Example 1 shows a faster response speed than that of Comparative Example 1, and the temperature dependence of the threshold voltage is very small. With the liquid crystal composition of the present invention, an STN-LCD that is sufficiently steep, has high-speed response, and has a small change in threshold voltage due to temperature can be obtained. Further, the STN-LCDs of Comparative Example 2 and Comparative Example 3 were insufficient in comparison with the characteristics of Example 1 in the above-described response characteristics and the temperature dependence of the threshold.
(Example 2, Example 3 and Example 4)

Liquid crystal compositions No. 2 (Example 2), No. 3 (Example 3) and No. 4 (Example 4) are also represented by the general formulas (I), (II) and (III) of the present invention. ). As in Example 1, the temperature dependence of the threshold voltage is very small compared to the comparative example, and by using the liquid crystal composition of the present invention, it has high steepness and high-speed response, and depends on the temperature. An STN-LCD with a small change in threshold voltage can be obtained.

Claims (8)

As the first component, the general formula (I)

(Wherein R ¹ represents an alkyl group having 1 to 8 carbon atoms, an alkoxy group having 1 to 8 carbon atoms, an alkenyl group having 2 to 8 carbon atoms or an alkenyloxy group having 2 to 8 carbon atoms, X ¹ and X ² independently represents -H or -F.)
Containing one or more compounds represented by
As the second component, the general formula (II)

(Wherein R ² represents the same meaning as R ¹ in formula (I), p represents an integer of 0 or more and 2 or less, and m represents 0 or 1)
Containing one or more compounds represented by
As the third component, the general formula (III)

(Wherein R ³ and R ⁴ represent the same meaning as R ¹ in formula (I), A represents a trans-1,4-cyclohexylene group or a 1,4-phenylene group, and Z ¹ represents- CH ₂ CH ₂ —, —COO— or a single bond, X ³ and X ⁴ each independently represent —H or —F, and q represents an integer of 0 or more and 3 or less. A nematic liquid crystal composition comprising one or more compounds. The content of the compound represented by the general formula (I) is in the range of 5 to 50% by mass, the content of the compound of the general formula (II) is in the range of 5 to 50% by mass, and the general formula (III) The nematic liquid crystal composition according to claim 1, wherein the content of the compound is in the range of 5 to 50 mass%. As the fourth component, the general formula (IV)

(Wherein R ⁵ represents the same meaning as R ¹ in general formula (I), r is 0 or more and 2 or less, and n is 0 or 1). The nematic liquid crystal composition according to claim 1, wherein the nematic liquid crystal composition contains the above and has a content in the range of 5 to 35 mass%. Nematic phase-isotropic liquid phase transition temperature (T _NI ) is 70 ° C or higher and 140 ° C or lower, solid phase or smectic phase-nematic phase transition temperature (T _{→ N} ) is -30 ° C or lower, and refractive index is different. The nematic according to any one of claims 1 to 3, wherein the isotropic (Δn) is 0.11 or more and 0.18 or less, the dielectric anisotropy (Δε) is 1 or more and 30 or less, and the rotational viscosity is 35 mPa · s or less. Liquid crystal composition. General formula (I) is general formula (Ia)

5. The compound according to claim 1, wherein R ¹ is a compound represented by the formula (wherein R ¹ represents an alkyl group or alkoxy group having 1 to 8 carbon atoms, an alkenyl group or alkenyloxy group having 2 to 8 carbon atoms). The nematic liquid crystal composition described in 1. A liquid crystal display element using the liquid crystal composition according to claim 1. The super twisted nematic (STN) liquid crystal display device according to claim 6, wherein the twist angle is 180 ° to 270 °. The liquid crystal display element according to claim 7, wherein the following conditional expressions (i) to (iii) are satisfied in a driving temperature range of -20 ° C to 50 ° C.
i (ii) Vsat (25 ° C) / Vth (25 ° C) ≤ 1.075
(However, Vth (25 ° C) is the applied voltage when the change in transmittance is 10% when a rectangular wave voltage of 100Hz frequency is applied at 25 ° C to a panel with cell thickness d satisfying Δn · d = 0.9. Vsat (25 ° C) is the applied voltage when the change in transmittance is 90% when a rectangular wave voltage with a frequency of 100 Hz is applied to a panel with a cell thickness d satisfying Δn · d = 0.9 at 25 ° C. Represents.)
(iii) τ (25) ≦ 350msec
(However, τ (25) is the change in transmittance from 0% to 90% when the voltage is turned on at 25 ° C and the change from 100% to 10% when the voltage is turned off. Represents the total time of
(iv) {Vth (-20 ℃) −Vth (50 ℃)} / 70 ≦ 5mV / ℃
(However, Vth (-20 ° C) and Vth (50 ° C) are the values when a rectangular wave voltage with a frequency of 100Hz is applied at -20 ° C and 50 ° C to a panel of cell thickness d satisfying Δn · d = 0.9, respectively. (This represents the applied voltage when the transmittance change is 10%.)
iiv