JPH04252290A - Nematic liquid crystal composition - Google Patents

Abstract

PURPOSE:To obtain the title composition useful for an electro-optical display material, having a large pretilt angle, extremely low occurrence ratio of stripe domain and excellent yield in LCD manufacture, containing a mixture of specific polycyclic aromatic compounds. CONSTITUTION:The objective composition containing (A) preferably 3-80wt.% compound shown by formula I (R<1> is 1-10C straight-chain alkyl; n is 1-5 integer; X is H or F) and (B) preferably 5-70 wt.% compound shown by (i) formula II (R<2> is 1-10C straight-chain alkyl; m is 2-5 integer; Y is H or F) and/or (ii) formula III (R<3> is 1-10C straight-chain alkyl; P is 1-5 integer).

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 useful as an electro-optical display material and a liquid crystal display device using the composition.

0002

[Prior Art] A typical type of liquid crystal display cell is TN-L.
There is a CD (twisted, nematic liquid crystal display), which is used in watches, calculators, electronic notebooks, pocket computers, word processors, personal computers, etc. In recent years, with the increase in information processed by OA equipment, the amount of information displayed on one screen has increased, and conventional TN-LC
In D, from the viewpoint of display quality such as contrast and viewing angle,
In particular, it is no longer possible to meet the demands for high time division drive of word processors, personal computers, and the like.

Under these circumstances, Schaefer (Sc.
heffer) etc. [SID '85 Digest,
P. 120 (1985)] or Kinugawa et al. [SID'
86 Digest, P. 122 (1986)] by STN (Super Twisted Nematic)
-LCDs have been developed and are beginning to be widely used as displays for high information processing applications such as word processors and personal computers.

0004

[Problems to be Solved by the Invention] In STN-LCD, controlling the angle between the alignment plane and the liquid crystal molecules, that is, the pretilt angle, is an important issue in manufacturing the liquid crystal display cell, which has a large impact on display performance and yield. Become a factor.

As an orientation method, a method is known in which the pretilt angle is controlled to a high tilt angle of about 20° by oblique evaporation of SiOx. A method is known in which the pretilt angle is controlled to about 5° by rubbing an organic film such as "150". In addition, various organic films have been developed and are used by controlling the pretilt angle to 5 to 10 degrees by a rubbing method.

It is known that the higher the pretilt angle is, the less likely stripe domains are to occur and the yield rate when manufacturing a liquid crystal display cell is improved. The current situation is that it is extremely difficult to create a constant and stable alignment film.

On the other hand, high time division driving is required for STN-LCDs used in word processors, personal computers, etc. that contain a large amount of information. An increase in the number of time divisions causes an increase in drive voltage, which greatly affects the drive circuit. To meet this demand, it is necessary to lower the driving voltage of the liquid crystal material. Physical properties such as the elastic constant and dielectric constant of the liquid crystal material are important factors for controlling the driving voltage, but at the same time, they also need to be optimized to prevent the occurrence of stripe domains. Therefore, the current situation is that it is extremely complicated and difficult to control the elastic constant and dielectric constant so as to satisfy both a reduction in driving voltage and display performance with a large amount of information.

[0008] The problem to be solved by the present invention is to form striped domains by forming a pretilt angle higher than about 5°, which can be formed with a practically stable alignment film using a rubbing method in terms of quality. To provide a nematic liquid crystal composition which is capable of preventing the occurrence of such a phenomenon, can be driven at a low voltage suitable for high time division driving, is free from precipitation of liquid crystal components at low temperatures, and can be driven in a wide temperature range. There is a particular thing.

[0009]

[Means for Solving the Problems] In order to solve the above problems, the present invention provides (1) general formula (A)

0010

[C4]

(wherein, R1 represents a linear alkyl group having 1 to 10 carbon atoms, n represents an integer of 1 to 5,
X represents H or F. ) and (2
) (a) General formula (B)

0012

[C5]

(In the formula, R2 represents a linear alkyl group having 1 to 10 carbon atoms, m represents an integer of 2 to 5, and Y
represents H or F. ) or (b)
General formula (C)

[0014]

[C6]

(In the formula, R3 represents a linear alkyl group having 1 to 10 carbon atoms, and p represents an integer of 1 to 5.)
Provided is a nematic liquid crystal composition containing a compound selected from the group consisting of compounds represented by:

General formula (A) used in the present invention, general formula (
Tables 1 and 2 list the phase transition temperatures of typical compounds represented by B) and (C).

[0017]

[Table 1]

[0018]

[Table 2]

(In the table, C is a crystalline phase, N is a nematic phase,
I each represent an isotropic liquid phase. ) The content of the compound represented by general formula (A) in the nematic liquid crystal composition of the present invention is preferably in the range of 3 to 80% by weight, and the content of the compound represented by general formula (B) and general formula (C) is preferably in the range of 3 to 80% by weight. The content of the compound selected from the group consisting of: 5 to 70% by weight is preferred.

Examples of liquid crystal compounds that can be used in combination with the liquid crystal composition of the present invention are listed below.

[0021]

[C7]

[0022]

[Chemical formula 8]

(In the above general formula, R4 represents an alkyl group, R5 represents an alkyl group or an alkoxyl group, and
1 represents a hydrogen atom or a fluorine atom. )

[0024]
Table 3 shows nematic liquid crystal composition No. 1 according to the present invention.
16 compounding ratio, N-I transition temperature (TNI), physical property values of refractive index anisotropy (△n) and dielectric constant anisotropy (△ε), when a known liquid crystal composition is encapsulated, approximately The pretilt angle obtained when the cell is sealed in a liquid crystal display cell that is known to be able to form a pretilt angle of 5° is displayed, and for comparison, a currently widely used compound with a similar structure related to the present invention is shown. Similar data is posted for the mixed liquid crystal (a) obtained by mixing.

[0025]

[Table 3]

From the data listed in Table 3, nematic liquid crystal composition No. of the present invention. It can be seen that No. 16 can form a pretilt angle that is 1° or more higher than that of the mixed liquid crystal (a) containing a compound having a similar structure.

A difference of 1° in pretilt angle makes it difficult for stripe domains to occur significantly, improving the yield rate when manufacturing STN liquid crystal display cells. Furthermore, the general formula (A
), (B) and (C) do not exhibit uniform vertical alignment on the glass surface in the nematic state, but many mixed liquid crystals obtained by mixing these do not exhibit vertical alignment. It was confirmed that it has.

The nematic liquid crystal composition of the present invention is characterized in that it has a higher pretilt angle than when conventional liquid crystal compositions are encapsulated, and is capable of forming a pretilt angle of about 5° in a liquid crystal display cell. It is not limited to. STN-LC encapsulating the nematic liquid crystal composition of the present invention
When Sample D was produced, stripe domains were significantly less likely to occur, and it was confirmed that the yield was improved.

Nematic liquid crystal composition No. shown in Table 3
．． Chiral substance “S-8” is added to each mixed liquid crystal of 16 or (a).
An S with a twist angle of 220° has an alignment film formed by rubbing an organic film of "Sunever-150" on the opposing flat transparent electrode with a mixed solution containing "11" (manufactured by Merck & Co., Ltd.).
Each was injected into a TN display cell and various characteristics were measured.

Note that the chiral substance is used so that the inherent helical pitch P of the mixed liquid crystal and the cell thickness d of the display cell due to the addition of the chiral substance become Δn·d=0.85 and d/p=0.53. added to.

[0031] The transmittance of light perpendicular to the display cell surface is 10%.
The steepness γ of the electro-optical characteristic is expressed as Vsat/Vth
The closer this value is to 1, the better the high time division characteristics are.

Nematic liquid crystal composition No. of the present invention. 16
The Vth of the STN-LCD using the above was 1.39, and the steepness γ was 1.029. When mixed liquid crystal (a) is used, Vth is 1.98 and steepness γ is 1.064.
Met.

From these results, it is clear that the nematic liquid crystal composition according to the present invention is excellent in that the driving voltage is greatly improved and the steepness is close to 1.

Therefore, the nematic liquid crystal composition of the present invention eliminates the trouble of optimizing the physical properties of a mixed liquid crystal, makes it possible to prevent the occurrence of stripe domains, reduce the driving voltage, and increase the number of time divisions. This liquid crystal composition is suitable for STN-LCDs with a large amount of information, without adversely affecting the drive circuit.

The following experiment was conducted to explain the dissolution characteristics of the mixed liquid crystal obtained by mixing the compounds used in the present invention. No. of Table 2 15% by weight of compound No. 15 and the following No. 4
2 of each mixed liquid crystal consisting of 85% by weight of the mixed liquid crystal shown in the table.
When the viscosity was measured at 0°C, 0°C and -20°C, the phase of this mixed liquid crystal changed from a nematic phase to a solid phase, making it impossible to measure the viscosity. No. 20° C. of a mixed liquid crystal obtained by using the following compound (b) having a similar structure to these compounds in place of compound No. 15,
Viscosity measurements at 0<0>C and -20<0>C showed a possible and stable nematic phase.

[0036]

[Chemical formula 9]

[0037] The mixed liquid crystal shown in Table 4 is a mixed liquid crystal consisting of representative compounds that are currently widely used.Since it is a mixture of nine types and many components, it has high compatibility with other liquid crystal compounds. It has the following characteristics.

[0038]

[Table 4]

Nematic liquid crystal composition No. 1 according to the present invention shown in Table 3. No. 16 is a mixture of four types and a small number of ingredients. Although it contains 15% by weight of 15 compounds, the same amount as the above-mentioned mixed liquid crystal,
It is possible to carry out viscosity measurements at 20°C and 0°C.

Furthermore, when the viscosity of the mixed liquid crystal obtained by mixing the liquid crystals shown in Table 3 and those shown in Table 4 was measured, the nematic liquid crystal composition No. 3 shown in Table 3 was measured. 1
It has been found that when 6 is 92% by weight or less, it becomes possible to measure at -20°C and exhibits a nematic phase that is stable at low temperatures.

This excellent dissolution property is different from the known technique of obtaining a stable nematic phase at low temperatures by simply increasing the number of components of the liquid crystal compound to be mixed.
As clarified in the present invention, it is obtained by mixing a compound selected from the group consisting of (1) a compound represented by general formula (A) and (2) a compound represented by general formulas (B) and (C). This is the first time that a nematic liquid crystal composition has been obtained.

[0042] Furthermore, by using this technique,
It becomes possible to arbitrarily mix it with currently widely used compounds or mixed liquid crystals made of them at a mixing ratio suitable for the purpose of use.

As is clear from these results, the nematic liquid crystal composition of the present invention stabilizes the nematic phase at low temperatures and is capable of driving an STN liquid crystal display over a wide temperature range.

The following compounds (c) and (d) having a similar structure to the compound represented by the general formula (B) used in the present invention
The nematic liquid crystal composition is chemically unstable, with the phase transition temperature of the nematic-isotropic liquid decreasing and liquid crystallinity being lost even under nitrogen-substituted storage conditions at room temperature. It is an unsuitable compound to mix with substances.

[0045]

[Chemical formula 10]

[0046]

[Chemical formula 11]

However, the general formula (
A), the compounds represented by general formulas (B) and general formulas (C), and the nematic liquid crystal composition of the present invention are chemically stable without deterioration phenomena when subjected to durability tests such as heating or ultraviolet irradiation. It is.

Therefore, it is possible to provide a nematic liquid crystal composition suitable for liquid crystal display devices used under various environments.

[0049]

EXAMPLES The present invention will be explained in detail with reference to Examples below, but the present invention is not limited to these Examples.

[0050] In the following examples and comparative examples,
"%" represents "% by weight". (Example 1)

[0051]

[Chemical formula 12]

A mixed liquid crystal consisting of the following was prepared. Nematic phase-isotropic liquid phase transition temperature (TN-I) of this mixed liquid crystal
, refractive index anisotropy (△n) and dielectric constant anisotropy (△ε)
was as follows.

TN-I: 113.5°C △n: 0.136 △ε: 20.3 This mixed liquid crystal was turned upside down with an alignment film formed by rubbing an organic film of “Sunever 150” manufactured by Nissan Chemical Co., Ltd. The pretilt angle was measured by the magnetic field potential method after being sealed in a parallel cell and found to be 7.1°. (Example 2)

[0054]

[Chemical formula 13]

A mixed liquid crystal consisting of the following was prepared. Nematic phase-isotropic liquid phase transition temperature (TN-I) of this mixed liquid crystal
, refractive index anisotropy (Δn) and dielectric constant anisotropy (Δε)
was as follows.

TN-I: 90.0°C Δn: 0.141 Δε: 22.3 The pretilt angle was measured in the same manner as in Example 1, except that this mixed liquid crystal was used. As a result, the pretilt angle was 7.2°. there were. (Example 3)

[0057]

[Chemical formula 14]

A mixed liquid crystal consisting of the following was prepared. Nematic phase-isotropic liquid phase transition temperature (TN-I) of this mixed liquid crystal
, refractive index anisotropy (Δn) and dielectric constant anisotropy (Δε)
was as follows.

TN-I: 69.2°C Δn: 0.141 Δε: 18.6 The pretilt angle was measured in the same manner as in Example 1, except that this mixed liquid crystal was used, and the result was 6.4°. there were. (Comparative example 1)

[0060]

[Chemical formula 15]

A mixed liquid crystal consisting of the following was prepared. Nematic phase-isotropic liquid phase transition temperature (TN-I) of this mixed liquid crystal
, refractive index anisotropy (Δn) and dielectric constant anisotropy (Δε)
was as follows.

TN-I: 71.3°C Δn: 0.139 Δε: 12.6 Using this mixed liquid crystal, the pretilt angle was measured in the same manner as in Example 1, and the result was 5.2°. Ta.

[0063] All of Examples 1 to 3 are 1° lower than Comparative Example 1.
Or the pretilt angle was increased more than that.

(Example 4) A mixed liquid crystal obtained by adding a chiral substance "S-811" (manufactured by Merck & Co., Ltd.) to each of the mixed liquid crystals used in Examples 1 to 3 and Comparative Example 1 was placed on opposing flat transparent electrodes. “Sunever 150
A wedge-shaped cell with a twist angle of 220° and a display cell each having an alignment film formed by rubbing an organic film of ``100'' were injected into a display cell and various characteristics were measured.

Note that the chiral substance has the characteristic helical pitch P of the mixed liquid crystal and the cell thickness d of the display cell due to the addition of the chiral substance.

[0066]

[Math 1]

It was added in such a manner that: Here, Δd/p
is when the thickness of the wedge-shaped cell at the boundary where no striped domain occurs is d1 and d2 (d1 > d2).

[
0068

[Math 2]

[0069] The larger the value, the better. In addition, the transmittance of light perpendicular to the display cell surface is 10% and 80%.
The steepness γ of the electro-optical characteristics is defined as Vsat/Vth, where the voltages at which the voltages are Vth and Vsat are respectively defined as Vsat/Vth, and the closer this value is to 1, the better the high time division characteristics are.

Table 5 shows the measurement results of the display characteristics of super twisted nematic liquid crystals obtained by adding chiral substances to the mixed liquid crystals prepared in Examples 1 to 3 and Comparative Example 1.

[0071]

[Table 5]

All of the mixed liquid crystals of Examples 1 to 3 have significantly improved Δd/p than the mixed liquid crystal of Comparative Example 1, and stripe domains are less likely to occur. Furthermore, the driving voltage was lowered by 35% or more, the steepness γ was also close to 1, and liquid crystal display characteristics with excellent high time division characteristics were exhibited.

[0073]

Effects of the Invention The nematic liquid crystal composition of the present invention can be encapsulated in a liquid crystal display cell having an alignment film which is known to be able to form a pretilt angle of about 5° when a normal nematic liquid crystal is encapsulated. It is a liquid crystal composition that can increase the pretilt angle, has a low threshold voltage, and is free from precipitation in a low temperature region.

Therefore, the nematic liquid crystal composition according to the present invention has a significantly low incidence of stripe domains.
It has a good yield when manufacturing LCDs and is extremely useful as a material for STN-LCDs that can be driven in a wide temperature range.

Claims (2)

[Claims] Claim 1: (1) General formula [Formula 1] (wherein R1 represents a linear alkyl group having 1 to 10 carbon atoms, n represents an integer of 1 to 5, ) and (2) (a) a compound represented by the general formula (wherein R2 represents a linear alkyl group having 1 to 10 carbon atoms, and p represents 1 1. A nematic liquid crystal composition comprising a compound selected from the group consisting of compounds represented by (representing an integer from 1 to 5). 2. A super twisted nematic liquid crystal display device using the nematic liquid crystal composition according to claim 1.