JP3077334B2 - Nematic liquid crystal composition - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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 same.

[0002]

2. Description of the Related Art Active matrix type liquid crystal display devices have attracted attention as the most promising devices in the field of applications such as large-area flat-screen televisions and computer displays because of their excellent display quality. 4
It is marketed as a small color TV of up to 6 inches.

The active matrix type liquid crystal display device is driven by using a switching element for each pixel, and the switching element includes a TFT (thin film transistor) or a MIM (metal insulator.
Metal) etc. are used. In terms of display quality,
In particular, a liquid crystal display device using a TFT as a switching element (hereinafter referred to as a TFT-LCD) is excellent.

However, at present, such a liquid crystal display has the following problems. To obtain a uniform, high-contrast, high-quality display in a TFT-LCD,
In the liquid crystal section, the accumulated charge during the frame period must be held. That is, it is important to have a high voltage holding characteristic with a small “leakage current”. The factor that affects the voltage holding characteristic is to configure the liquid crystal unit (1).
Examples include a liquid crystal material, (2) an alignment film, (3) a seal material, and (4) a spacer.

On the other hand, unevenness of the substrate surface due to the high definition of the TFT element and a decrease in the pretilt angle due to a high operating temperature cause disturbances such as reverse tilt in the liquid crystal molecular alignment, so that a high quality TFT-LCD can be obtained. Raised the necessity of suppressing this, and raised a new problem (Proceedings of the 16th Liquid Crystal Symposium, p. 212).

Improvements in the unevenness of the substrate surface have been proposed by correcting the signal voltage waveform, and improvements in the reduction of the pretilt angle have been proposed by reviewing the alignment film technology.゜ It is necessary to make it more.

Further, in order to obtain a TFT-LCD for high-density display, it is necessary to improve characteristics that enable high-speed response and low-voltage driving.

[0008]

The problem to be solved by the present invention is that operation is possible even at a high temperature of about 80 ° C.
It has a threshold voltage of 2.0 V or less necessary for active matrix driving, has a large refractive index anisotropy (Δn) that can be used even with a small cell thickness, and has a sufficiently high voltage holding ratio. To provide a nematic liquid crystal composition having
It is an object of the present invention to provide a TFT-LCD using an MIM element which has a fast response characteristic and does not generate flicker due to "leakage current" by using this nematic liquid crystal composition.

Another problem to be solved by the present invention is that the pretilt angle which can be formed by rubbing an organic film such as “PIX-5400” manufactured by Hitachi Chemical Co., Ltd. is 2 ° from the liquid crystal material side. An object of the present invention is to provide a nematic liquid crystal composition capable of preventing occurrence of reverse tilt by forming a higher pretilt angle as described above and thus obtaining a high-quality TFT-LCD.

[0010]

In order to solve the above-mentioned problems, the present invention provides (1) a compound represented by the following general formula (I):

[0011]

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(R ¹ represents a linear alkyl group having 1 to 5 carbon atoms, a linear alkenyl group having 1 to 5 carbon atoms or R ² —O— (CH ₂ ) _k —; ² has 1 carbon atom
Represents a linear alkyl group of 3 to 3, k represents an integer of 1 to 6, m represents 0 or 1, and X ¹ represents H or F. And a compound represented by the general formula (II):

[0013]

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(R ³ represents a linear alkyl group having 1 to 5 carbon atoms, p represents an integer of 1 to 6, q represents 0 or 1, and X ² represents H or F. A nematic liquid crystal composition characterized by containing a compound represented by the following formula:
Provided is a matrix type liquid crystal display device.

The liquid crystal composition according to the present invention has a high light-shielding property and is therefore suitable for obtaining a high contrast. In particular, the liquid crystal composition has a refractive index of 0.160 to 0.2.
It is an excellent one which can be designed in a preferable range of 20.

Each of the liquid crystal compounds used in the present invention is distilled,
Column purification, removal of impurities using methods such as recrystallization,
A sufficiently purified product shall be used.

Tables 1 and 2 show typical compounds represented by the general formulas (I) and (II) and their transition temperatures according to the present invention.

[0018]

[Table 1]

[0019]

[Table 2]

In the liquid crystal composition of the present invention, liquid crystal compounds which can be used by mixing with the compounds represented by formulas (I) and (II) are listed below.

[0021]

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[0022]

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(In the formula, R represents a linear alkyl group having 1 to 7 carbon atoms, n represents 1 or 2, and X represents H or F.)

Hereinafter, the significance of the present invention will be described.

[0025]

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The nematic liquid crystal composition No. 1 comprising the nematic phase-isotropic liquid phase transition temperature (NI)
Point), anisotropy of refractive index (Δn), pretilt obtained when sealed in a liquid crystal display cell known to be able to form a pretilt angle of about 5 ° when a known liquid crystal composition is sealed. The threshold voltage, the response time (τ _r = τ _d ) at which the rise time (τ _r ) and the fall time (τ _d ) are equal in the TN mode of 8 μm, and the voltage holding ratio are as follows. Raised.

NI point 80.9 ° C. Threshold voltage 1.42 V Δn 0.218 Response speed (τ _r = τ _d ) 19 ms Voltage holding ratio 99.4%

On the other hand, a liquid crystal composition using the same amount of the compound represented by the general formula (I) in place of the compound represented by the general formula (II) according to the present invention in the nematic liquid crystal composition No. 1 is used. So,

[0029]

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The physical properties and electro-optical properties of the nematic liquid crystal composition (a) comprising the following are as follows.

NI point 84.3 ° C. Threshold voltage 1.87 V Δn 0.224 Response speed (τ _r = τ _d ) 23.8 ms Voltage holding ratio 99.4%

From a comparison between the above nematic liquid crystal composition No. 1 and the nematic liquid crystal composition (a), it was found that the compound containing the compound represented by the general formula (I) and the compound represented by the general formula (II) according to the present invention were contained. Nematic liquid crystal composition No.1
However, it is clear that the response speed is high, the threshold voltage is low, and it is excellent.

A cell having an alignment film formed using "PIX-5400" manufactured by Hitachi Chemical Co., Ltd. was prepared, and the pretilt angles of the above nematic liquid crystal compositions No. 1 and (a) were measured. The pretilt angle of No.1 is 2.
3 °, and that of the nematic liquid crystal composition (a) was 2.0 °. From these results, the nematic liquid crystal composition of the present invention,
It is expected that occurrence of reverse tilt can be prevented.

Further, when a TFT-LCD containing the nematic liquid crystal composition according to the present invention was produced, it was confirmed that the TFT-LCD was excellent in that "leakage current" was small and flicker did not occur.

[0035]

EXAMPLES The present invention will be specifically described below with reference to examples, but the gist and scope of the present invention are not limited to these examples.

(Example 1)

[0037]

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A nematic liquid crystal composition No. 1 was prepared, and its physical properties and electro-optical properties were measured. The results were as follows.

NI point 80.9 ° C. Threshold voltage 1.42 V Δn 0.218 Response speed (τ _r = τ _d ) 19 ms Voltage holding ratio 99.4%

Comparative Example 1

[0041]

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A nematic liquid crystal composition (a) was prepared, and its physical properties and electro-optical properties were measured. The results were as follows.

NI point 84.3 ° C. Threshold voltage 1.87 V Δn 0.224 Response speed (τ _r = τ _d ) 23.8 ms Voltage holding ratio 99.4%

[0044]

The nematic liquid crystal composition of the present invention has a large Δn which can be used even with a small cell thickness by containing the compounds represented by the general formulas (I) and (II). It can operate at a high temperature, has a sufficiently low threshold voltage necessary for active matrix driving, and has a sufficiently high voltage holding ratio.

The active matrix type liquid crystal display device according to the present invention using the nematic liquid crystal composition of the present invention has a fast response, is free from flicker, and has a high pretilt angle of 2 ° or more, so that it can be reversed. This is excellent as a high-definition TFT-LCD that suppresses the occurrence of tilt.

Continuation of front page (56) References JP-A-63-310838 (JP, A) JP-A-61-260031 (JP, A) JP-A-4-352740 (JP, A) JP-A-4-82854 (JP) JP-A-5-43877 (JP, A) JP-A-4-356468 (JP, A) JP-A-5-148241 (JP, A) JP-A-5-148483 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) C09K 19/42

Claims (3)

(57) [Claims] (1) General formula (I) (R ¹ is a linear alkyl group having 1 to 5 carbon atoms, a linear alkenyl group having 1 to 5 carbon atoms, or R ² —O—
(CH _{2) k} - represents, R ² represents a straight-chain alkyl group having 1 to 3 carbon atoms, k represents an integer of 1-6,
m represents 0 or 1, and X ¹ represents H or F. And a compound represented by the general formula (II): (R ³ represents a linear alkyl group having 1 to 5 carbon atoms, p represents an integer of 1 to 6, q represents 0 or 1, and X ² represents H or F.) Nematic liquid crystal composition, characterized by containing a compound to be prepared. 2. The nematic liquid crystal composition according to claim 1, wherein the refractive index is in the range of 0.160 to 0.220. 3. An active matrix type liquid crystal display device using the nematic liquid crystal composition according to claim 1.