JP3531696B2 - Liquid crystal composition and liquid crystal display device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nematic liquid crystal composition containing at least one chiral additive and a liquid crystal composition thereof, which are provided in a closed cell formed of two substrates having transparent electrodes. The liquid crystal display element used. More specifically, the present invention relates to a liquid crystal composition for an active matrix LCD and a liquid crystal display device using the composition.

[0002]

2. Description of the Related Art Liquid crystal display devices (LCDs) are capable of lower power consumption, smaller size and lighter weight than CRTs (cathode ray tube displays). Therefore, they are twisted nematic (TN) type and super twisted nematic (LCD) type. STN)
System, thin film transistor (TFT) system, etc.
CD has been put to practical use. Among them, active matrix LCDs such as thin film transistors (TFT) (AM-
LCD) colorization and high definition are progressing, and it is attracting attention as a favorite of flat displays.

The properties required for the liquid crystal composition for AM-LCD are: 1) High voltage holding ratio (VHR) in order to maintain high contrast of LCD. 2) The nematic liquid crystal phase range is large depending on the usage environment. 3) Appropriate refractive index anisotropy (Δn) can be taken according to the cell thickness. 4) An appropriate threshold voltage can be taken according to the driving circuit. Can be mentioned.

The AM-LCD operates as a TN in which the orientation of liquid crystal molecules in the upper and lower substrates is twisted at 90 °.
The display system is adopted. In this TN display method, in order to prevent coloring due to interference of the liquid crystal cell when no voltage is applied and to obtain an optimum contrast, the product Δn · d of the refractive index anisotropy (Δn) and the cell thickness (d) μm. Must be set to a certain value (for example, Δn · d to 0.5 μm). T currently in practical use under these restrictions
The Δn of the liquid crystal composition for FT is 1st. Min. 0.0 in the system
About 7 to 0.11, especially 0.08 to 0.10.

In recent years, notebook personal computers and the like, which are compact and lightweight and can be carried, have been developed, and the applications of LCDs have spread. The LCD for portable use is limited in characteristics by the driving power supply. Since it is necessary to reduce power consumption for long-term use, a liquid crystal composition having a small threshold voltage has been required. Further, in order to further reduce the weight and cost of the driving power source, a liquid crystal having a small threshold voltage has been required.

Further, along with the portability, development for outdoor use has been studied. In order to be able to withstand outdoor use, it is required to exhibit a nematic phase over a region beyond the temperature range of the use environment. From such a viewpoint, the nematic-isotropic phase transition temperature (clearing point: T _NI ) of the liquid crystal composition for TFT currently in practical use is 60 ° C. or higher, and the smectic-nematic phase transition temperature (T _SN ) is −20 ° C. The following are the main subjects.

Under such a background, Japanese Patent Laid-Open No. 2-23
Japanese Patent No. 3626 discloses a trifluoro compound having a relatively large dielectric anisotropy (Δε). For example, Application Example 2 discloses an example of a composition containing 15% by weight of a trifluoro compound and 85% by weight of a difluoro compound. However, the threshold voltage is large, and the compatibility is particularly poor at low temperatures, and the nematic phase range is Since it is small, it has the drawback of lacking in practicality.

WO9403558 discloses an example of a composition of a trifluoro compound and a difluoro compound. However, the compositions disclosed in Examples 1 and 2 have a low clearing point of 50 ° C. or less, and Δn of 0.06 or less, and thus lack practicality. Further, the compositions disclosed in Examples 4 and later are disclosed. The compositions described have the disadvantage of having a high threshold voltage. As described above, although liquid crystal compositions have been earnestly studied according to various purposes, under the present circumstances, new improvements are always required.

[0009]

SUMMARY OF THE INVENTION The object of the present invention is to satisfy various characteristics required for the liquid crystal composition for AM-LCD, while having a nematic phase having a small threshold voltage and excellent compatibility at low temperature. It is to provide a liquid crystal composition having a wide range. The present inventors have diligently studied compositions using various liquid crystal compounds in order to solve these problems, and as a result, have found that this object can be achieved when the liquid crystal composition of the present invention is used in an AM-LCD. I found it.

[0010]

The present invention will be described in detail below.

The first aspect of the present invention is to formulas (I-1) to (I
Among the compounds represented by -7), only at least four each of one or more compounds selected from the group of compounds
And a liquid crystal composition comprising: However, the liquid crystal composition is
It may further contain additives such as laurate and dichroic dye.
Yes. (In the formula, n represents an integer of 1 to 10)

The second aspect of the present invention is to formulas (I-1) to (I
From each compound group represented by -5), only one or more compounds selected from at least four compound groups
And a liquid crystal composition comprising: However, the liquid crystal composition is
It may further contain additives such as laurate and dichroic dye.
Yes. (In the formula, n represents an integer of 1 to 10)

A third aspect of the present invention is that the mixing ratio of the compounds selected from the compound groups represented by the general formulas (I-1) to (I-7) is based on the total weight of the liquid crystal composition. 25% by weight
The present invention relates to the liquid crystal composition according to the first invention, which is 40% by weight or less, 30% by weight or less, 60% by weight or less, 40% by weight or less, 25% by weight or less, and 15% by weight or less.

In a fourth aspect of the present invention, the mixing ratio of the compounds selected from the compound groups represented by the general formulas (I-1) to (I-5) is based on the total weight of the liquid crystal composition. 25% by weight
The present invention relates to the liquid crystal composition according to the second invention, which is 40% by weight or less, 30% by weight or less, 60% by weight or less, and 40% by weight or less.

[0015]

[0016]

The fifth aspect of the present invention relates to a liquid crystal display device using the liquid crystal composition according to any one of the first to fourth aspects.

The trifluoro compound used in the liquid crystal composition of the present invention is a liquid crystal having a large dielectric anisotropy (Δε) and a high chemical stability, as disclosed in JP-A-2-233626. It is a compound. JP-A-2-
From a large number of compounds disclosed in Japanese Patent No. 233626, a compound group having excellent basic properties such as Δn, Δε, and liquid crystal range was selected, and as a result of diligent study on the usage thereof, the present invention was made possible.

The feature of the present invention is that the following general formula (I-1) is used.
To (I-7), each is a liquid crystal composition consisting of at least one trifluoro compound selected from at least four tricyclic compounds. Δn,
Excellent skeleton with excellent basic characteristics such as Δε and liquid crystal range 3
By using four or more cyclic trifluoro compounds, a liquid crystal composition having significantly improved low temperature compatibility can be obtained. Further, the threshold voltage can be effectively reduced by adjusting the liquid crystal composition containing only the trifluoro compound.

The mixing ratio of the compounds represented by the general formulas (I-1) to (I-7) is 25% by weight or less and 30% by weight, respectively.
Hereafter, 30% by weight or less, 60% by weight or less, 40% by weight or less, 25% by weight or less, 15% by weight or less are preferable. Exceeding this mixing ratio is not preferable because the low temperature compatibility may deteriorate.

[0021]

[0022]

The liquid crystal composition used according to the invention is prepared in a manner which is conventional in itself. Generally, a method of dissolving various components with each other at a high temperature is adopted. Further, the liquid crystal material of the present invention is improved and optimized according to the intended use by appropriate additives. Such additives are well known to those skilled in the art, and are described in detail in the literature and the like. Usually, a chiral dopant or the like is added to induce a helical structure of liquid crystal to adjust a necessary twist angle and prevent reverse twist.

Further, the liquid crystal composition used in accordance with the present invention contains a dichroic dye such as merocyanine, styryl, azo, azomethine, azoxy, quinophthalone, anthraquinone and tetrazine as a guest. It can also be used as a liquid crystal composition for the host (GH) mode.
Alternatively, a polymer dispersed liquid crystal display device (PDLCD) typified by NCAP manufactured by encapsulating nematic liquid crystal or a polymer network liquid crystal display device (PNLCD) manufactured by forming a three-dimensional network polymer in the liquid crystal.
It can also be used as a liquid crystal composition. In addition, it can be used as a liquid crystal composition for a birefringence control (ECB) mode or a dynamic scattering (DS) mode.

[0025]

EXAMPLES The present invention is described in detail below with reference to examples, but the present invention is not limited to these examples. Further, the composition ratios of Comparative Examples and Examples are all shown by weight%. Although the measured value of the voltage holding ratio is described, this measurement was carried out based on the method (area method) described in JP-A-5-331464. Also, the T _SN point is 0
The liquid crystal phase was evaluated after leaving it in each of the freezer of ℃, -10 ℃, -20 ℃, -30 ℃ for 30 days.

The symbols of the compounds used in Comparative Examples and Examples are defined as follows.

[Chemical 7]

[Chemical 8]

[Chemical 9]

Comparative Example 1 The following composition disclosed in Application Example 2 of JP-A-2-233626 was prepared. 3-HHB-FFF 15.0% 2-HHB-FF 28.4% 3-HHB-FF 28.3% 5-HHB-FF 28.3% The clearing point of this liquid crystal composition is T _NI = 110.7. (℃), T
The viscosity at _SN <0 ° C and 20 ° C is η ₂₀ = 25.0 (mP
a · s), the refractive index anisotropy at 25 ° C. is Δn = 0.0
The threshold voltage at 77 and 20 ° C. is Vth = 2.32.
(V), V.I. H. R (25 ° C) = 98.8%.
This liquid crystal composition had a large threshold voltage and poor low temperature compatibility (high T _SN ).

Comparative Example 2 The following composition disclosed in Example 1 of WO9403558 was prepared. 7-HB-FFF 10.0% 2-HHB-FFF 25.0% 3-HHB-FFF 35.0% 5-HHB-FFF 18.0% 7-HB-FF 12.0% Clearing point is T _NI = 42.9 (℃), T _SN
The viscosity at <0 ° C. and 20 ° C. is η ₂₀ = 22.2 (mPa
・ S), the refractive index anisotropy at 25 ° C. is Δn = 0.05.
The threshold voltage at 9 and 20 ° C. is Vth = 1.07.
(V), V.I. H. R (25 ° C) = 98.7%.
This liquid crystal composition had a small threshold voltage but a small clearing point and poor low temperature compatibility. In addition, Δn was small and was not practical.

Comparative Example 3 The following composition disclosed in Example 2 of WO9403558 was prepared. 2-HHB-FFF 26.0% 3-HHB-FFF 26.0% 5-HHB-FFF 26.0% 7-HB-FF 12.0% 5-H2B-FF 10.0% Clearing point is T _NI = 46.0 (℃), T _SN
The viscosity at <0 ° C. and 20 ° C. is η ₂₀ = 21.6 (mPa
・ S), the refractive index anisotropy at 25 ° C. is Δn = 0.05.
The threshold voltage at 8 and 20 ° C. is Vth = 1.17.
(V), V.I. H. R (25 ° C) = 98.5%.
This liquid crystal composition had a small threshold voltage but a small clearing point and poor low temperature compatibility. In addition, Δn was small and was not practical.

Comparative Example 4 The following composition disclosed in Example 4 of WO9403558 was prepared. 2-HHB-FFF 10.0% 3-HHB-FFF 10.0% 5-HHB-FFF 10.0% 5-H2B-FF 10.0% 5-HEB-F 7.5% 7-HEB-F 7.5% 2-HHB-FF 11.7% 3-HHB-FF 11.7% 5-HHB-FF 11.6% 3-HHB-F 5.0% 5-HHEB-F 2.5% 7 -HHEB-F 2.5% The clearing point of this liquid crystal composition is T _NI = 71.3 (° C), T _SN
<-20 ° C, viscosity at 20 ° C is η ₂₀ = 19.2 (m
Pa · s) and the refractive index anisotropy at 25 ° C. is Δn = 0.
The threshold voltage at 070 and 20 ° C. is Vth = 1.7.
7 (V), V.I. H. R (25 ° C) = 98.2%. This liquid crystal composition had a large threshold voltage despite a clearing point of about 70 ° C. Δn was a little small.

Comparative Example 5 The following composition was prepared as a composition example selected from two formulas selected from the group of compounds represented by the general formulas (I-1) to (I-7). 3-HHB-FFF 25.0% 5-HHB-FFF 15.0% 3-HBB-FFF 20.0% 5-HBB-FFF 40.0% The clearing point of this liquid crystal composition is T _NI = 64.2. (℃), T _SN
The viscosity at <0 ° C. and 20 ° C. is η ₂₀ = 28.3 (mPa
.S), the refractive index anisotropy at 25 ° C. is Δn = 0.10
The threshold voltage at 3 and 20 ° C. is Vth = 1.38
(V), V.I. H. R (25 ° C) = 98.4%.
Although this liquid crystal composition had a small threshold voltage, it had poor compatibility at low temperatures and lacked practicality.

Example 1 3-H2HB-FFF 7.0% 4-H2HB-FFF 6.0% 5-H2HB-FFF 6.0% 3-HH2B-FFF 5.0% 3-HBB-FFF 28.0 % 5-HHB-FFF 27.0% 3-HBEB-FFF 5.0% 5-HBEB-FFF 3.0% 3-HHEB-FFF 13.0% A liquid crystal composition was prepared. The clearing point of this liquid crystal composition is T _NI = 68.0 (° C.), T _SN <−20 ° C., the viscosity at 20 ° C. is η ₂₀ = 33.5 (mPa · s), and the refractive index anisotropy at 25 ° C. Is Δn = 0.102, the threshold voltage at 20 ° C. is Vth = 1.16 (V), V.I. H. R
(25 ° C) = 98.6%. This liquid crystal composition,
It was excellent in low-temperature compatibility, had a large nematic phase range, had a small threshold voltage, and was highly practical.

Example 2 3-H2HB-FFF 8.0% 4-H2HB-FFF 8.0% 5-H2HB-FFF 8.0% 3-HHB-FFF 8.0% 4-HHB-FFF 4.0 % 3-HH2B-FFF 15.0% 5-HH2B-FFF 10.0% 3-HBB-FFF 20.0% 5-HBB-FFF 19.0% A liquid crystal composition was prepared. The clearing point of this liquid crystal composition is T _NI = 74.3 (° C.), T _SN <−30 ° C., the viscosity at 20 ° C. is η ₂₀ = 28.4 (mPa · s), and the refractive index anisotropy at 25 ° C. Is Δn = 0.094, the threshold voltage at 20 ° C. is Vth = 1.48 (V), V.I. H. R
(25 ° C.) = 98.5%. This liquid crystal composition,
It was excellent in low-temperature compatibility, had a large nematic phase range, had a small threshold voltage, and was highly practical.

Example 3 3-HHB-FFF 10.0% 4-HHB-FFF 5.0% 3-H2HB-FFF 7.0% 4-H2HB-FFF 7.0% 5-H2HB-FFF 6.0 % 3-HBB-FFF 14.0% 5-HBB-FFF 14.0% 3-H2BB-FFF 6.0% 3-HH2B-FFF 10.0% 5-HH2B-FFF 5.0% 3-HHEB- A liquid crystal composition consisting of FFF 10.0% 4-HHEB-FFF 3.0% 5-HHEB-FFF 3.0% was prepared. The clearing point of this liquid crystal composition is T _NI = 75.9 (° C.), T _SN <−30 ° C., the viscosity at 20 ° C. is η ₂₀ = 27.5 (mPa · s), and the refractive index anisotropy at 25 ° C. Is Δn = 0.090, the threshold voltage at 20 ° C. is Vth = 1.33 (V), V.I. H. R
(25 ° C.) = 98.3%. This liquid crystal composition,
It was excellent in low-temperature compatibility, had a large nematic phase range, had a small threshold voltage, and was highly practical.

Example 4 3-HHB-FFF 10.0% 4-HHB-FFF 5.0% 3-H2HB-FFF 7.0% 5-H2HB-FFF 8.0% 3-HH2B-FFF 9.0 % 5-HH2B-FFF 9.0% 3-HBB-FFF 15.0% 5-HBB-FFF 15.0% 3-HBEB-FFF 2.0% 4-HBEB-FFF 2.0% 5-HBEB- A liquid crystal composition consisting of FFF 2.0% 3-HHEB-FFF 10.0% 4-HHEB-FFF 3.0% 5-HHEB-FFF 3.0% was prepared. The clearing point of this liquid crystal composition is T _NI = 81.1 (° C.), T _SN <−30 ° C., the viscosity at 20 ° C. is η ₂₀ = 29.6 (mPa · s), and the refractive index anisotropy at 25 ° C. Is Δn = 0.092, the threshold voltage at 20 ° C. is Vth = 1.21 (V), V.I. H. R
(25 ° C) = 98.2%. This liquid crystal composition,
It was excellent in low-temperature compatibility, had a large nematic phase range, had a small threshold voltage, and was highly practical.

Example 5 3-HHB-FFF 10.0% 4-HHB-FFF 5.0% 3-H2HB-FFF 10.0% 5-H2HB-FFF 9.0% 3-HH2B-FFF 11.0 % 5-HH2B-FFF 7.0% 3-HBB-FFF 8.0% 5-HBB-FFF 8.0% 3-H2BB-FFF 4.0% 5-H2BB-FFF 4.0% 3-HBEB- A liquid crystal composition consisting of FFF 3.0% 4-HBEB-FFF 3.0% 3-HHEB-FFF 10.0% 4-HHEB-FFF 4.0% 5-HHEB-FFF 4.0% was prepared. The clearing point of this liquid crystal composition is T _NI = 83.7 (° C.), T _SN <−30 ° C., the viscosity at 20 ° C. is η ₂₀ = 28.5 (mPa · s), and the refractive index anisotropy at 25 ° C. Is Δn = 0.090, the threshold voltage at 20 ° C. is Vth = 1.21 (V), V.I. H. R
(25 ° C.) = 98.3%. This liquid crystal composition,
It was excellent in low-temperature compatibility, had a large nematic phase range, had a small threshold voltage, and was highly practical.

[0037]

[0038]

[0039]

[0040]

[0041]

[0042]

[0043]

[0044]

The characteristics of the liquid crystal compositions of Comparative Examples and Examples are shown in Table 1. As is apparent from Table 1, according to the present invention,
It is possible to provide a liquid crystal composition having a small threshold voltage, excellent compatibility at low temperature, and a large nematic phase range while satisfying various characteristics required for a liquid crystal composition for AM-LCD.

[0045]

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-6-248268 (JP, A) European patent application publication 688850 (EP, A 1) (58) Fields investigated (Int.Cl. ⁷ , DB name) C09K 19/00-19/46

Claims (5)

(57) [Claims] 1. A liquid crystal composition comprising only one or more compounds selected from at least four compound groups of each compound group represented by formulas (I-1) to (I-7).
However, the liquid crystal composition contains a chiral agent or a dichroic dye.
You may further contain an additive. (In the formula, n represents an integer of 1 to 10) 2. A liquid crystal composition comprising only one or more compounds selected from at least four compound groups among the compound groups represented by formulas (I-1) to (I-5).
However, the liquid crystal composition contains a chiral agent or a dichroic dye.
Additives may further comprise free. (In the formula, n represents an integer of 1 to 10) 3. The compound represented by the general formula (I) based on the total weight of the liquid crystal composition.
-1) to (I-7), the mixing ratios of the compounds selected from the respective compound groups are 25% by weight or less and 40% by weight, respectively.
The liquid crystal composition according to claim 1, wherein the content is 30% by weight or less, 60% by weight or less, 40% by weight or less, 25% by weight or less, and 15% by weight or less. 4. The compound represented by the general formula (I) based on the total weight of the liquid crystal composition.
-1) to (I-5), the mixing ratios of the compounds selected from the respective compound groups are 25% by weight or less and 40% by weight, respectively.
The liquid crystal composition according to claim 2, wherein the content is 30% by weight or less, 60% by weight or less, and 40% by weight or less. 5. A liquid crystal display device using the liquid crystal composition according to claim 1.