JP3038923B2 - Super twisted nematic liquid crystal display - 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 useful as an electro-optical display material and a liquid crystal display using the same.

[0002]

2. Description of the Related Art A typical TN-LCD is a liquid crystal display cell.
(Twisted, nematic liquid crystal display devices), which are used in watches, calculators, electronic organizers, pocket computers, word processors, personal computers, and the like. In recent years, the amount of information displayed on one screen has been increasing with the increase in the processing information of OA equipment. It is no longer possible to meet the demand for split drive. Under such circumstances, Scheffer et al. [SID '85 Digest, P.12
0 (1985)] or Kinukawa et al. [SID '86 Digest, P.122 (1
986)], an STN (Super Twisted Nematic) -LCD has been developed and has begun to be widely used for high-information processing displays such as word processors and personal computers.

[0003]

In the STN-LCD, the control of the angle between the alignment plane and the liquid crystal molecules, ie, the pretilt angle, is important in producing a liquid crystal display cell, which has a significant effect on display performance and yield. A factor.

As the orientation method, a method of controlling the pretilt angle to a high tilt angle of about 20 ° by oblique deposition of SiOx is known. More practically, for example, “Sun Ever” manufactured by Nissan Chemical Industries, Ltd. is used. A method of controlling the pretilt angle to about 5 ° by rubbing an organic film such as 150 ”is known. In addition, various organic films have been developed and are used by controlling the pretilt angle to 5 to 10 ° by a rubbing method. It is known that the higher the pretilt angle is, the more difficult it is to generate stripe domains and the better the yield during the production of liquid crystal display cells.However, using a rubbing method, the pretilt angle is constant at 5 ° to 10 °. At present, it is extremely difficult to form a stable alignment film.

[0005] The problem to be solved by the present invention is that a pretilt angle which can be formed with a practically stable alignment film using a rubbing method from a quality aspect can be formed with a pretilt angle higher than about 5 °. Another object of the present invention is to provide a super twisted nematic liquid crystal display device using a nematic liquid crystal composition which can be used in a wide temperature range and has improved precipitation phenomenon at a low temperature.

[0006]

In order to solve the above-mentioned problems, the present invention provides a compound represented by the general formula (I)

[0007]

Embedded image

(Wherein, R ¹ represents a linear alkyl group having 1 to 10 carbon atoms, and n represents an integer of 1 to 5)
And a liquid crystal compound having a functional group represented by the following formula (hereinafter, referred to as compound (A)) and the general formula (B)

[0009]

Embedded image

(Wherein R ² represents a linear alkyl group having 1 to 10 carbon atoms, an alkoxy group, an alkenyl group or a group having an ether bond;

[0011]

Embedded image

And Y represents H or F. The present invention provides a super twisted nematic liquid crystal display device using a nematic liquid crystal composition containing the compound represented by the formula (1) and having a pretilt angle exceeding 5.0 °. Table 1 shows the phase transition temperatures of typical compounds (A) used in the present invention.

[0013]

[Table 1]

(In the table, C represents a crystal phase, S represents a smectic phase, N represents a nematic phase, and I represents an isotropic liquid phase.)

The content of the compound (A) in the nematic liquid crystal composition of the present invention is 3 to 40% by weight.
Is preferable.

Table 2 shows the phase transition temperatures of typical compounds represented by formula (B) used in the present invention.

[0017]

[Table 2]

The content of the compound represented by formula (B) used in the present invention in the nematic liquid crystal composition of the present invention is preferably in the range of 5 to 50% by weight.

Examples of the liquid crystal compound which can be used by mixing with the compound (A) and the compound represented by the formula (B) used in the present invention are described below.

[0020]

Embedded image

[0021]

Embedded image

[0022]

Embedded image

(In the above formula, R ³ represents an alkyl group; R ⁴ represents an alkyl group or an alkoxyl group;
Represents a hydrogen atom or a fluorine atom, Y represents a fluorine atom,
Represents a cyano group, an alkyl group or an alkoxyl group. )

Table 3 shows 80% by weight of a mixed liquid crystal (A) having the composition shown in Table 4 which is currently widely used as a nematic liquid crystal material, and a functional group represented by the general formula (I) at the terminal of the molecule. The pretilt angle obtained when a mixed liquid crystal comprising 20% by weight of a compound having the compound is sealed in a liquid crystal display cell capable of forming a pretilt angle of about 5 ° is shown. For comparison, the pretilt angle is represented by the general formula (I). Instead of a compound having a functional group, a butoxy group (C ₄ H ₉ O-)
The pretilt angles of the mixed liquid crystals composed of each of the compounds (a) to (d) shown in Table 5 having the following formulas are also shown.

[0025]

[Table 3]

[0026]

[Table 4]

[0027]

[Table 5]

From the data shown in Table 3, the compounds having a functional group of the general formula (I) at the terminal of the molecule are each similar in structure to the compound liquid crystal having a pretilt angle of (A) of 1 °. It can be understood that the pretilt angle can be increased by 1 ° or more as compared with the mixed liquid crystal containing the compounds (a), (b), (c), and (d) having similar structures.

The difference in the pretilt angle of 1 ° makes it difficult for stripe domains to be remarkably generated, and improves the yield at the time of manufacturing an STN liquid crystal display cell. Furthermore, it was confirmed that most of the compounds containing the functional group of the general formula (I) at the terminal group had a uniform vertical alignment on a glass surface in a nematic state.

The nematic liquid crystal composition used in the present invention is characterized by having a higher pretilt angle than when a conventional liquid crystal composition is sealed, and is capable of forming a pretilt angle of about 5 °. It is not limited to display cells. ST encapsulating the nematic liquid crystal composition of the present invention
When an N-LCD was fabricated, stripe domains were hardly generated, and the yield was confirmed to be improved.

Further, the liquid crystal composition having vertical alignment as in the present invention is extremely useful for vertical alignment required for a display device of, for example, an ECB (birefringence control) system.

Each of the mixed liquid crystals comprising 20% by weight of the compound of No. 1 or No. 2 having a functional group of the general formula (I) at the terminal of the molecule and 80% by weight of the mixed liquid crystal (A) shown in Table 4 20 ° C,
The viscosities at 0 ° C and -20 ° C were measured. For comparison, each mixture obtained by using the compound (a) or (b) shown in Table 5 having a similar structure to these compounds in place of the compound of No. 1 or No. 2 was used. The viscosities of the liquid crystal at 20 ° C, 0 ° C and -20 ° C were measured. The results are shown in Table 6.

[0033]

[Table 6]

In order to examine the stability of the nematic phase at low temperature, an equimolar mixture of No. 1 and No. 3 compounds having a functional group of the general formula (I) at the terminal of the molecule was mixed with a mixed liquid crystal ( The following measurements were performed when the mixture was added to A) and when an equivalent mixture of the compounds (e) and (f) shown in Table 5 having a similar structure to the compound of No. 1 or No. 3 was added. Did.

That is, the addition amount of the equivalent mixture of the No. 1 and No. 3 compounds whose viscosity can be measured at -20 ° C. is 36% by weight, and the pretilt of the liquid crystal material at room temperature at this mixing ratio is 36% by weight. The angle was 7.5 °. On the other hand, the addition amount of the equivalent mixture of the compound (e) and the compound (f) capable of measuring the viscosity at −20 ° C. is 13% by weight, and the pretilt angle at room temperature of the liquid crystal material at this mixing ratio is 5.9. °.

As is clear from the results, the compound having the functional group of the general formula (I) at the terminal of the molecule stabilizes the nematic phase at a low temperature and can operate the STN liquid crystal display device in a wide temperature range. It can be.

[0037]

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

In the following Examples and Comparative Examples,
"%" Represents "% by weight". Examples 1 to 4 Table 7 shows the compositions of the mixed liquid crystals used in Examples 1 to 4. Further, for comparison, the composition of the mixed liquid crystal of Comparative Example 1 containing no compound having a functional group represented by the general formula (I) at the terminal of the molecule is shown.

The _NI transition temperature (T _NI ) and the anisotropy (ΔΔ) of the refractive index of each of the mixed liquid crystals used in Examples 1 to 4 and Comparative Example 1.
n) and the result of measurement of the dielectric anisotropy (Δε)
It is shown in the table.

Further, each mixed liquid crystal was sealed in a cell in which an alignment film formed by rubbing an organic film of "Sanever 150" manufactured by Nissan Chemical Industries, Inc. was vertically and antiparallel, and the pretilt angle was determined by a magnetic field potential method. And measure the result as the eighth.
It is shown in the table.

Each of Examples 1 to 4 was 1 ° more than Comparative Example 1.
Alternatively, the pretilt angle was increased. Example 3 showed a great effect.

Next, a chiral substance (“S-81” manufactured by Merck & Co., Ltd.) was added to each of the mixed liquid crystals used in Examples 1 to 4 and Comparative Example 1.
The mixed liquid crystal to which 1) was added was injected into a wedge-shaped cell having a twist angle of 220 ° and a display cell having an alignment film formed by rubbing an organic film of “Sanever 150” on the opposed flat transparent electrode. Various characteristics were measured.

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

[0044]

(Equation 1)

Was added so that Here, Δd / p
Is given assuming that the thickness of the wedge-shaped cell at the boundary where the stripe domain does not occur is d ₁ and d ₂ , (d ₁ > d ₂ ),

[0046]

(Equation 2)

The larger the value, the better. Further, the transmittance of light perpendicular to the display cell surface is 10% and 80%.
% Is defined as Vsat / Vth, where Vth and Vsat are voltages, respectively, and it is known that the closer to 1, the more excellent the time division characteristic is.

A super twisted liquid crystal obtained by adding a chiral substance to the mixed liquid crystal used in Examples 1 to 4 and Comparative Example 1.
Table 9 shows the measurement results of the display characteristics of the nematic liquid crystal.

In all of Examples 1 to 4, stripe domains are less likely to occur than in Comparative Example 1. Also,
The steepness γ was also close to 1, indicating liquid crystal display characteristics excellent in high time division characteristics.

[0050]

[Table 7]

[0051]

[Table 8]

[0052]

[Table 9]

[0053]

According to the present invention, the nematic liquid crystal composition containing the compound represented by the general formula (I) and the compound represented by the general formula (B) having a functional group of the general formula (I) at the terminal of the molecule is a general nematic liquid crystal. About 5 when used in combination with the composition
By enclosing in a liquid crystal display cell having an alignment film capable of forming a pretilt angle of 1 °, the pretilt angle can be increased.

Therefore, a super twisted nematic liquid crystal display device using the nematic liquid crystal composition according to the present invention and having a pretilt angle exceeding 5.0 ° has a good yield and a striped nematic liquid crystal display device. Domain incidence is significantly lower.

Continuation of the front page (56) References JP-A-57-140737 (JP, A) JP-A-64-56415 (JP, A) JP-A-62-100580 (JP, A) JP-A-59-11387 (JP) JP-A-63-313124 (JP, A) JP-A-2-503446 (JP, A) Japan Display '86, pp. 400-403 (58) Fields investigated (Int. Cl. ⁷ , DB name ) C09K 19/42

Claims (1)

(57) [Claims] 1. A compound of the general formula: embedded image (Wherein, R ¹ represents a linear alkyl group having 1 to 10 carbon atoms, and n represents an integer of 1 to 5), and a liquid crystal compound having a functional group represented by the general formula: (In the formula, R ² represents a linear alkyl group having 1 to 10 carbon atoms, an alkoxy group, an alkenyl group or a group having an ether bond; Y represents H or F; Nematic liquid crystal composition characterized by containing a compound represented by the formula:
And have a pretilt angle exceeding 5.0 °.
Super twisted nematic liquid characterized by the following:
Crystal display device .