JPH05148483A - Nematic liquid crystal composition - Google Patents

Abstract

PURPOSE:To provide the subject liquid crystal composition containing a specific cyclohexane derivative and a nitrogen-containing heterocyclic compound, having improved response characteristics, low threshold voltage and high potential retention and useful as a material for an active matrix liquid crystal display device, etc. CONSTITUTION:The objective nematic liquid crystal composition having a refractive index of 0.070-0.110, improved response characteristics, a threshold voltage of <=1.8V and high potential retention and useful as an excellent material for active matrix liquid crystal display device is produced by compounding (A) a fluorophenylcyclohexane derivative of formula I [R<1> is 2-5C straight-chain alkyl, 2-5C straight-chain alkenyl or group of formula R<2>-O-(CH2)k (R<2> is 1-3C straight-chain alkyl; (k) is integer of 1-6); (m) is O or l; X<1> is H or F] and (B) a nitrogen-containing heterocyclic compound of formula II (R<3> is 1-3C straight-chain alkyl; (p) is integer of 1-6; (q) is 0 or 1; X<2> is H or F).

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 nematic liquid crystal composition.

[0002]

2. Description of the Related Art An active matrix type liquid crystal display device is attracting attention as the most promising one in the future in application fields such as large area flat-screen televisions and computer displays because of its excellent display quality. Four
Marketed as a ~ 6 inch compact color TV.

An active matrix type liquid crystal display device is driven by a switching element for each pixel, and the switching element is a TFT (thin film transistor) or 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 TFT-LCD) is excellent.

However, at present, such a liquid crystal display device has the following problems. To obtain a uniform, high-contrast, high-quality display in a TFT-LCD,
In the liquid crystal part, the accumulated charge must be retained during the frame period. That is, it is important to have a high voltage holding characteristic with a small “leakage current”. As a factor that affects the voltage holding characteristic, the liquid crystal portion is configured (1).
A liquid crystal material, (2) alignment film, (3) sealing material, (4) spacer and the like can be mentioned.

On the other hand, the unevenness of the substrate surface due to the high definition of the TFT element and the decrease of the pretilt angle due to the high operating temperature cause the disturbance such as the reverse tilt in the alignment of the liquid crystal molecules, which makes it possible to obtain a high quality TFT-LCD. Proposed that a new problem should be suppressed (Proceedings of the 16th Liquid Crystal Symposium, page 212).

It has been proposed to improve the unevenness of the substrate surface by correcting the signal voltage waveform and to improve the pretilt angle by reviewing the alignment film technology. It is said that it must be above ゜.

Furthermore, in order to obtain a high density display TFT-LCD, it is necessary to improve the characteristics that enable high speed response and low voltage driving. Compounds that improve such properties include the following general formulas (III) and (IV)

[0008]

[Chemical 3]

A compound represented by the formula (wherein R ⁴ represents an alkyl group, an alkenyl group or an ether group, and Y represents H or F) is known.
The threshold voltage characteristics required for T-LCD have not been obtained yet.

[0010]

The problem to be solved by the present invention is that it can operate at a high temperature of about 80 ° C.
It has a threshold voltage of 1.8 V or less necessary for active matrix driving, has a large anisotropy of refractive index (Δn) that can be used even with a small cell thickness, and has a sufficiently high voltage holding ratio. A TFT-LCD using a MIM device having a fast response characteristic and free of flicker due to "leakage current".
To provide.

A further problem to be solved by the present invention is, for example, 2 ° from the liquid crystal material side with respect to the pretilt angle which can be formed by rabinking an organic film such as "PIX-5400" manufactured by Hitachi Chemical. It is an object of the present invention to provide a nematic liquid crystal composition capable of preventing the occurrence of reverse tilt by forming a higher pretilt angle as described above and thus obtaining a high quality TFT-LCD.

[0012]

In order to solve the above problems, the present invention provides (1) general formula (I)

[0013]

[Chemical 4]

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

[0015]

[Chemical 5]

(R ³ represents a linear alkyl group having 1 to 3 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
Provided is a matrix type liquid crystal display device.

The liquid crystal composition according to the present invention is suitable for obtaining a high contrast in a wide viewing angle, and the refractive index of the liquid crystal composition can be designed within a preferable range of 0.070 to 0.110. It is an excellent one.

Each liquid crystal compound used in the present invention is distilled,
Remove impurities using methods such as column purification and recrystallization,
Sufficiently purified product should be used.

Representative compounds represented by the general formulas (I) and (II) according to the present invention and their transition temperatures are shown in Tables 1 and 2.

[0020]

[Table 1]

[0021]

[Table 2]

Liquid crystal compounds which can be used as a mixture with the compounds represented by the general formulas (I) and (II) in the liquid crystal composition of the present invention are listed below.

[0023]

[Chemical 6]

[0024]

[Chemical 7]

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

The significance of the present invention will be described below.

[0027]

[Chemical 8]

For the nematic liquid crystal composition No. 1 consisting of, the nematic phase-isotropic liquid phase transition temperature (NI)
Point), anisotropy of refractive index (Δn), and pretilt obtained when the liquid crystal display cell is known to be capable of forming a pretilt angle of about 5 ° when a known liquid crystal composition is enclosed. The angle is posted, and the response time (τ _r = τ _d ) and the voltage holding ratio at which the rise time (τ _r ) and the fall time (τ _d ) are equal in the TN mode of 8 μm are shown below. Listed in.

NI point 91.1 ° C. Threshold voltage 1.71 V Δn 0.098 Response speed (τ _r = τ _d ) 16.0 ms Voltage holding ratio 99.5%

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

[0031]

[Chemical 9]

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

NI point 86.7 ° C. Threshold voltage 2.08 V Δn 0.079 Response speed (τ _r = τ _d ) 20.0 ms Voltage holding ratio 99.5%

From the comparison between the nematic liquid crystal composition No. 1 and the nematic liquid crystal composition (a), the nematic liquid crystal composition No. 1 according to the present invention has a high NI point and a threshold voltage of about 0. It is clear that it is a nematic liquid crystal composition exhibiting excellent characteristics by reducing the voltage of 0.4 V and simultaneously having a high response speed.

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-mentioned nematic liquid crystal compositions No. 1 and (a) were measured. The No. 1 pretilt angle is 2.
It was 1 ° and the nematic liquid crystal composition (a) was 1.8 °. From these results, the nematic liquid crystal composition of the present invention
It is expected that the occurrence of reverse tilt can be prevented.

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

[0037]

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 by these examples.

(Example 1)

[0039]

[Chemical 10]

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

NI point 91.1 ° C. Threshold voltage 1.71 V Δn 0.098 Response speed (τ _r = τ _d ) 16.0 ms Voltage holding ratio 99.5%

(Example 2)

[0043]

[Chemical 11]

A nematic liquid crystal composition No. 2 consisting of was prepared and its physical properties and electro-optical characteristics were measured. The results were as follows. NI point 89.3 ° C Threshold voltage 1.49V △ n 0.095 Response speed (τ _r = τ _d ) 15.4 ms Voltage holding ratio 99.5% Pretilt angle 2.1 °

(Comparative Example 1)

[0046]

[Chemical 12]

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

NI point 86.7 ° C. Threshold voltage 2.08 V Δn 0.079 Response speed (τ _r = τ _d ) 20.0 ms Voltage holding ratio 99.5%

[0049]

INDUSTRIAL APPLICABILITY The nematic liquid crystal composition of the present invention contains the compounds represented by the general formulas (I) and (II) so that the response characteristics can be improved, and the nematic liquid crystal composition sufficient for active matrix driving Has a low threshold voltage,
It has a sufficiently high voltage holding ratio.

The active matrix type liquid crystal display device using the nematic liquid crystal composition of the present invention has no flicker and is excellent as a high-definition TFT-LCD in which the occurrence of reverse tilt is suppressed by the high pretilt angle. It is a thing.

Claims (3)

[Claims] 1. A general formula (I): (R ¹ is a linear alkyl group having 2 to 5 carbon atoms, a linear alkenyl group having 2 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 (2) the general formula (II) (R ³ represents a linear alkyl group having 1 to 3 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 containing a compound described below. 2. The nematic liquid crystal composition according to claim 1, which has a refractive index in the range of 0.070 to 0.110. 3. An active matrix type liquid crystal display device using the nematic liquid crystal composition according to claim 1.