JPH04255793A - Nematic liquid crystal composition - Google Patents

Abstract

PURPOSE:To obtain the title composition useful as a STN-LCD material, having a large pretilt angle, an extremely low rate of occurrence of stripe domain and excellent yield in LCD manufacturing, containing specific two kinds of polycyclic aromatic compounds. CONSTITUTION:The objective compound containing 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 5-70wt.% compound shown by formula II (R<2> is 1-10C straight-chain alkyl; m 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)]
The STN (Super Twisted Nematic)-LCD was developed by MIT and has begun to be widely used as a display for high information processing 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 obliquely vapor depositing SiOx on a substrate, but more practically, for example, Nissan Chemical Co., Ltd. A method is known in which the pretilt angle is controlled to about 5° by rubbing an organic film such as "Sunever 150" manufactured by Co., Ltd. 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 well known that the higher the pretilt angle is, the less likely stripe domains will occur and the yield rate will be better when manufacturing a liquid crystal display cell. The current situation is that it is extremely difficult to create a constant and stable alignment film that can be controlled precisely.

On the other hand, STN-LCDs that contain a large amount of information, such as word processors and personal computers, require high time division driving. However, 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.

However, the current situation is that it is extremely complicated and difficult to control the elastic constant and dielectric constant so as to satisfy both the reduction in driving voltage and the display performance for a large amount of information.

The problem to be solved by the present invention is that the pretilt angle of a practical and stable alignment film formed using a rubbing method is higher than about 5° in terms of quality, thereby preventing the occurrence of stripe domains. Moreover, it can meet high time division drive and can be driven at low voltage.
Another object of the present invention is to provide a nematic liquid crystal composition that does not cause precipitation of liquid crystal components at low temperatures and can be operated over a wide temperature range.

0010

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

[0011]

[C3]

(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 general formula (B)

[0013]

[C4]

(In the formula, R2 represents a linear alkyl group having 1 to 10 carbon atoms, and m represents an integer of 1 to 5.)
Provided is a nematic liquid crystal composition containing a compound represented by:

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

[0016]

[Table 1]

[0017]

[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 the 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 the general formula (B) is preferably in the range of 5 to 80% by weight. 70% by weight
A range of 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.

[0020]

[C5]

[0021]

[C6]

(In the above general formula, R3 represents an alkyl group, R4 represents an alkyl group or an alkoxyl group, and
1 represents H or F. ) Table 3 shows nematic liquid crystal composition No. 1 according to the present invention. 12 compounding ratio, nematic phase-isotropic liquid phase transition temperature (TN-I), physical property values of refractive index anisotropy (△n) and dielectric constant anisotropy (△ε), known liquid crystal composition The pretilt angle obtained when the liquid crystal display cell is encapsulated in a liquid crystal display cell, which is known to be able to form a pretilt angle of about 5° when encapsulated with a liquid, is displayed, and for comparison, nematic liquid crystal composition No. ．． The mixed liquid crystal (a) obtained by mixing currently widely used compounds having a similar structure to each of the compounds constituting No. 12 is also posted.

[0023]

[Table 3]

From the data listed in Table 3, nematic liquid crystal composition No. of the present invention. It can be seen that No. 12 can form a pretilt angle that is 1° or more higher than that of the mixed liquid crystal (a) containing structurally similar compounds.

[0025] A difference of 1° in pretilt angle makes it difficult for stripe domains to occur significantly, improving the yield rate when manufacturing an STN liquid crystal display cell. Furthermore, the general formula (A
) and most of the compounds of general formula (B) do not exhibit uniform vertical alignment on a glass surface in a nematic state, but many mixed liquid crystals obtained by mixing these exhibit vertical alignment. was confirmed.

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 a liquid crystal display cell capable of forming a pretilt angle of about 5°. 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
．． 12 or mixed liquid crystal (a) to which a chiral substance "S-811" (manufactured by Merck & Co., Ltd.) was added, was rubbed with an organic film of "Sunever-150" on opposing flat transparent electrodes. Twist angle 2 with alignment film formed by
Each sample was injected into a 20° STN display cell and various characteristics were measured.

Note that the chiral substance is used in such a way 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 are Δn·d=0.85 and d/P=0.53. added to.

[0029] The transmittance of light perpendicular to the display cell surface is 10%.
The voltage when the voltage is 80% is Vth, and the voltage when the voltage is 80% is Vs.
When at, the steepness γ of the electro-optical property is Vsat/
It is defined as Vth, and the closer this value is to 1, the better the high time division characteristics are.

Nematic liquid crystal composition No. according to the present invention
．． The Vth of the STN-LCD using No. 12 was 1.21 V, and the steepness γ was 1.030. Mixed liquid crystal (a)
When using , Vth is 1.98V and steepness γ is 1
．． It was 064.

[0031] From these results, the nematic liquid crystal composition according to the present invention significantly lowers the driving voltage and also improves the steepness.
It became clear that it was an excellent liquid crystal composition.

Therefore, the 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 and reduce the driving voltage, and allows driving by increasing the number of time divisions. This is a liquid crystal composition suitable for STN-LCDs with a large amount of information without adversely affecting circuits.

In order to explain the solubility of the mixed liquid crystal obtained by mixing the compounds used in the present invention, mixed liquid crystals as shown in Table 4 were prepared.

[0034]

[Table 4]

The mixed liquid crystal (b) is a mixed liquid crystal made of typical compounds currently in general use, and is a mixed liquid crystal made of the compounds shown in Table 5.

[0036]

[Table 5]

Further, the compound of formula (c) is No. 1 used in the present invention. It is a known compound having a structure similar to that of No. 11,

[0038]

[C7]

This is a compound represented by: When the viscosity of the mixed liquid crystal (I) shown in Table 4 was measured at 0°C and -20°C, the mixed liquid crystal changed from a nematic phase to a solid phase, making it impossible to measure the viscosity. On the other hand, in mixed liquid crystal (II), 20°C, 0°C and -20°C
Viscosity measurements at °C were possible and had a stable nematic phase.

[0040] The mixed liquid crystal (b) is a mixed liquid crystal consisting of representative compounds that are currently widely used, and since it is a mixture of nine types and many components, it has excellent compatibility with other liquid crystal compounds. It has properties.

Conventionally, it has been known to add a compound such as formula (c) to a mixed liquid crystal in order to expand the temperature range of the nematic phase in a low temperature range. Mixed liquid crystal (I) is 1
No. 0 component and used in the present invention. Nematic liquid crystal composition No. 11 according to the present invention is contained in an amount of 15% by weight. 12 consists of four components, and similarly No.
．． It contains 15% by weight of 11 compounds. However, nematic liquid crystal composition No. 12 is 20℃ and 0
It is possible to perform viscosity measurements at °C.

Furthermore, nematic liquid crystal composition No. Mixed liquid crystal (III) obtained by mixing No. 12 and mixed liquid crystal (b)
When the viscosity was measured, it was found that nematic liquid crystal composition No.
．． It was found that when 12 was 96% by weight or less, the viscosity could be measured at -20°C, and a stable nematic phase was exhibited in the low temperature range.

This dissolution characteristic is different from the known technique of obtaining a liquid crystal composition having a stable nematic phase in a low temperature range by simply increasing the number of components of the liquid crystal compound to be mixed. As has been made clear, this effect can only be obtained by a nematic liquid crystal composition obtained by mixing the compounds represented by the general formula (A) and the general formula (B). Furthermore, by using this technology, it becomes possible to arbitrarily mix the currently widely used compounds or mixed liquid crystals made of these compounds and the nematic liquid crystal composition according to the present invention at a mixing ratio suitable for the purpose of use. .

As is clear from these results, the composition according to the present invention stabilizes the nematic phase at low temperatures,
The STN liquid crystal display device can be driven in a wide temperature range.

General formula (A) and general formula (
The compound represented by B) or the nematic liquid crystal composition obtained by mixing these is chemically stable without any deterioration phenomenon in durability tests such as heating or ultraviolet irradiation. Therefore, it is possible to provide a nematic liquid crystal composition suitable for liquid crystal display devices used under various environments.

[0046]

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

[0047] In the following examples and comparative examples,
"%" represents "% by weight". (Example 1)

[0048]

[Chemical formula 8]

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: 100.1°C △n: 0.130 △ε: 21.5 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 parallel cells and found to be 7.5°. (Example 2)

[0051]

[Chemical formula 9]

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: 78.9°C Δn: 0.136 Δε: 23.8 Using this mixed liquid crystal, the pretilt angle was measured in the same manner as in Example 1, and the result was 7.6°. Ta. (Example 3)

[0054]

[Chemical formula 10]

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: 62.1°C Δn: 0.137 Δε: 19.5 Using this mixed liquid crystal, the pretilt angle was measured in the same manner as in Example 1, and the result was 6.6°. Ta. (Comparative example 1)

[0057]

[Chemical formula 11]

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.

[0060] All of Examples 1 to 3 are 1° lower than Comparative Example 1.
Or the pretilt angle was increased further. Example 1
A mixed liquid crystal obtained by adding a chiral substance "S-811" (manufactured by Merck & Co., Ltd.) to each mixed liquid crystal used in ~3 and Comparative Example 1,
Twist angle 22 with an alignment film formed by rubbing an organic film of "Sunever 150" on opposing flat transparent electrodes
It was injected into a 0° wedge-shaped cell and a display cell, and various characteristics were measured.

[0061] The chiral substance is added so that the inherent helical pitch P of the mixed liquid crystal and the cell thickness d of the display cell become Δn·d=0.85 and d/P=0.53. Added.

Here, Δd/P is the thickness of the wedge-shaped cell at the boundary where no stripe domain occurs, which is d1 and d2.
When (d1 > d2)

[0063]

[Math 1]

[0064] A larger value is 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 6 shows the measurement results of the display characteristics of super twisted nematic liquid crystals prepared by adding chiral substances to the mixed liquid crystals prepared in Examples 1 to 3 and Comparative Example 1.

[0066]

[Table 6]

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.

[0068]

Effects of the Invention: The nematic liquid crystal composition containing the compounds represented by the general formulas (A) and (B) according to the present invention forms a pretilt angle of about 5° when a normal nematic liquid crystal is used. By encapsulating the liquid crystal display cell in a liquid crystal display cell having a flexible alignment film, the pretilt angle can be increased.

Therefore, the nematic liquid crystal composition according to the present invention has a significantly low incidence of stripe domains.
It is extremely useful as a material for STN-LCD, which has a good yield during LCD manufacturing.

Claims (2)

[Claims] Claims: 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 X represents H or F. ), and a compound represented by the general formula [Formula 2] (wherein, R2 is a linear alkyl group having 1 to 10 carbon atoms, and m is an integer of 1 to 5). A nematic liquid crystal composition characterized by: 2. A super twisted nematic liquid crystal display device using the nematic liquid crystal composition according to claim 1.