JPH11241068A - Nematic liquid crystal composition and liquid crystal display device using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an STN which is less likely to cause an unstable twist structure, has a high yield, and has high contrast and high-speed response.
-To find a liquid crystal composition capable of producing an LCD, and an optimal combination of a liquid crystal composition and a device. SOLUTION: 1,4-phenylene group, trans-1,
5 to 20% by weight of a compound selected from five kinds of 2- to 3-cyclic compounds containing 4-cyclohexylene group etc.
-40% by weight, 10-40% by weight, 10-40% by weight,
A composition containing 5 to 40% by weight, at least 70% by weight.
C, SN at most -20 ° C
A nematic liquid crystal composition having a phase transition temperature, Δn of 0.12 to 0.16 and Δε of 3 or more, and a liquid crystal display device using the same.

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 liquid crystal display (LCD) has been developed as a calculator display, and has been developed in the same way as a computer, and has been changed from a TN-LCD (twisted nematic liquid crystal display) to an STN-LCD (twisted nematic liquid crystal display). (Super Twisted Nematic). STN-LCD is a Schefer (Sche
ffer), etc. [SID '85 Digest, p. 120 (1985)] or Kinukawa et al. [SID '86 Digest, p. 122 (1986)]. It is beginning to spread widely. The STN-LCD is obtained by twisting the twist of about 90 ° more strongly in the TN-LCD. By increasing the twist, the optical response to the applied voltage becomes sharp, and the TN-L
Sufficient contrast in high-density display, which could not be achieved with a CD, can be obtained. On the other hand, because it twisted strongly,
It is difficult to maintain the twisted orientation stably, and it is called the under domain, which is not sufficiently twisted, or called the stripe domain, where the twist is not stable and the molecules in the center of the cell are arranged like wavy and scattering occurs. Then, a state in which the contrast is remarkably deteriorated has occurred. In order to make such an unfavorable state unlikely to occur, it has become important to control the molecular structure of the liquid crystal composition, parameters such as tilt angle, elastic constant, and intermolecular interaction.

[0003]

The most important problem described above is that it is difficult to cause the unstable twisting structure as described above.
An object of the present invention is to find a liquid crystal composition capable of producing an STN-LCD having good yield, high contrast and high-speed response, and an optimum combination of a liquid crystal composition and a device.

The ratio (K33 / K11) between the bending elastic constant (K33) and the spreading elastic constant (K11) of the liquid crystal composition has a great effect on the optical characteristics of the liquid crystal display device (F. LEENHOUTS, M.SCHA).
DT; JAPAN DISPLAY '86 9.2, P388). STN-LC
In D, when K33 / K11 is increased, the contrast is improved, but the response is poor. Conversely, when K33 / K11 is reduced, the response is improved, but the contrast is deteriorated. If the values are excessively increased or decreased as described above, the above problem cannot be solved. The problem to be solved by the present invention is to solve or improve the above problem based on the newly found knowledge. The inventors have prepared many liquid crystal compositions and studied in detail the combination of the polar component and the non-polar component of the liquid crystal composition.As a result, the combination of the liquid crystal materials has a good balance between contrast and response speed, and also has a twisted structure. The present inventors have succeeded in finding a liquid crystal composition which is stable and hardly generate an under domain or a stripe domain, and a combination with the liquid crystal composition, and have completed the present invention.

[0005]

In order to solve the above-mentioned problems, the present invention has examined liquid crystal compositions using various liquid crystal compounds.

[0006]

Embedded image (In the formula, R ₁ represents an alkyl group, an alkenyl group, an oxaalkyl group, an oxaalkenyl group or an alkoxyl group having 1 to 10 carbon atoms, and n represents 0 or 1.) It contains two or more kinds, and its content is in the range of 5 to 20% by weight.
General formula (II)

[0007]

Embedded image (In this formula, R ₂ represents an alkenyl group or an oxaalkenyl group having 1 to 10 carbon atoms.) A compound represented by the formula (I) is contained in an amount of 5 to 40% by weight.
And the general formula (III)

[0008]

Embedded image (In this formula, R ₃ represents an alkyl group having 1 to 10 carbon atoms, an alkenyl group, an oxaalkyl group, an oxaalkenyl group or an alkoxyl group.) Content is 10 to 40
% By weight and further represented by the general formula (IV)

[0009]

Embedded image (In this formula, R ₄ and R ₅ represent an alkyl group, alkenyl group, oxaalkyl group, oxaalkenyl group or alkoxyl group having 1 to 10 carbon atoms, and ring A is substituted by cyclohexylene, phenylene, or a fluorine atom. Phenylene, m represents 0 or 1), and contains one or more compounds represented by the formula
0% by weight, and the general formula (V)

[0010]

Embedded image (In this formula, R ₆ represents an alkyl group having 1 to 10 carbon atoms, an alkenyl group, an oxaalkyl group, an oxaalkenyl group or an alkoxyl group.) A liquid crystal composition having a content in the range of 5 to 40% by weight, wherein at least 70 ° C
Nematic phase-isotropic liquid phase transition temperature, the crystal phase or smectic phase-nematic phase transition temperature of at most -20 ° C., the optical anisotropy Δn of the refractive index is 0.12 to
It has been found that this problem can be solved by using a nematic liquid crystal composition having a relative dielectric anisotropy Δε of 3 or more, and the present invention has been completed.

The present invention also relates to a super-twisted nematic liquid crystal display device having a twist angle of 220 ° to 270 ° using the nematic liquid crystal composition having the above composition. By successfully combining the liquid crystal composition and the liquid crystal composition, the balance between the contrast and the response speed is good, the twist structure is stable, the under domain and the stripe domain are hardly generated, and the present invention is completed. Reached.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an example of the nematic liquid crystal composition of the present invention and a liquid crystal display using the same will be described.

In a preferred embodiment of the liquid crystal composition of the present invention, one to ten compounds are selected from the group of compounds represented by formula (I).
Species, 1 to 6 species from the group of compounds represented by general formula (II),
One to six kinds of compounds represented by the general formula (III), one to six kinds of the compounds of the general formula (IV), and one to six kinds of the compounds of the general formula (V) are selected. It is desirable.
This effect is obtained by adding the compound of the general formula (I) in the range of 5 to 20% by weight, the compound of the general formula (II) in the range of 5 to 40% by weight, and the compound of the general formula (III) by 10%. The compound of the general formula (IV) is added in an amount of 10 to 40% by weight in the range of 40 to 40% by weight.
In the range, the compound of the general formula (V) is preferably contained at 5 to 40% by weight. More preferably, the weight percent of each group is 5 to 10 weight percent, 5 to 20 weight percent, 10 to
A special content is obtained by containing 30% by weight, 20 to 40% by weight, and 10 to 30% by weight.

Hereinafter, the compounds of each group constituting the liquid crystal composition of the present invention will be described in detail.

The compounds of the general formulas (I) to (V) are known compounds and can be easily obtained by those skilled in the art.

The compound of the general formula (I) has a large relative dielectric anisotropy Δε and imparts a low threshold voltage to the composition, which allows a low voltage. The compound of the general formula (II) has an elastic constant ratio of K33 / K11
This has the effect of sharpening the steepness of the electro-optical characteristics in the STN display device and significantly increasing the contrast.
However, when used in a large amount, the response speed is slowed down, the twisted structure is hardly stabilized, and stripe domains are easily generated. The compound of the general formula (III) is a compound having a medium polarity in which the relative dielectric anisotropy Δε is not so large as compared with the compounds of the general formulas (I) and (II). The compound of the general formula (IV) is a low-viscosity compound having a small relative dielectric anisotropy Δε. The compound of the general formula (V) is a low-viscosity compound having a wide nematic temperature range, and has a relatively low elastic constant ratio K33 / K11.

In general formulas (I) to (V), R₁~ R₆
Each independently represents an alkyl group having 1 to 10 carbon atoms,
Alkenyl group, oxaalkyl group, oxaalkenyl group or
Represents an alkoxyl group (R_TwoContains an alkyl group
But the alkyl group and oxaalkyl group have 1 to 1 carbon atoms.
7 is preferred, and particularly preferably 3 to 5. Al
Kenyl group has low viscosity and wide nematic temperature range
Therefore, it is preferable. Especially CH _Two= CH- (CH_Two)_u(U =
Compounds 0 and 2) are preferred. The most preferred embodiment is
R of general formula (I)₁Is an alkyl group, R of the general formula (II)_TwoIs an arche
Nyl group, R of the general formula (III)_ThreeIs an alkenyl group, general formula (IV)
R_FourAnd R_FiveOne or both are alkenyl groups
You. The ring A in the general formula (IV) is most preferably a cyclohexane ring.
Good.

The nematic liquid crystal composition of the present invention has a nematic phase-isotropic liquid phase transition temperature (NI point) of at least 70 ° C., and a crystal phase or a smectic phase-nematic phase at −20 ° C. at the highest. Phase transition temperature (C, S-
N) is a nematic liquid crystal composition. The crystal phase or the smectic phase-nematic phase transition temperature (C, SN) of the liquid crystal composition is preferably −25 ° C.
It is as follows. The relative permittivity of the liquid crystal composition is preferably 3 or more, and more preferably 10 or less.

The liquid crystal display device using the liquid crystal composition obtained in this manner is free from problems such as under domain and stripe domain, and has excellent characteristics of high contrast and good response performance.

The above nematic liquid crystal composition is useful for an STN liquid crystal display device driven by high time division and can be used for a transmission type or reflection type liquid crystal display device.

[0021]

EXAMPLES The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples. Table 1 shows the compositions and characteristic data of the examples and comparative examples.

[0022]

[Table 1] (In the table, the composition of the liquid crystal composition is “% by weight”.) The characteristics measured in the examples are as follows.

Tni: Nematic phase-isotropic liquid phase transition temperature (° C.) Tn: Solid phase or smectic phase-nematic phase transition temperature (° C.) Vth: 90 ° twisted TN cell having a cell thickness d = 6 μm Δn: birefringence η20 ° C .: viscosity at 20 ° C. (mPa · s)

The abbreviations used in the description of the compounds mean the following structures. When the right or left end in the abbreviated formula is a numeral: When the right or left end is a numeral, the terminal of the corresponding compound takes C _n H _{2n + 1-} , but the number shown here is C _n H _{2n + 1}
− Is the value of n.

However, the left end is a numeral (n), followed by d and a numeral (m) (that is, represented by ndm).
Case: ndm (number d number)

[0026]

Embedded image

Means a structure represented by Where n
The number n of dm represents a portion corresponding to n in C _n H _{2n + 1} in the above formula, and the number m of ndm represents a portion corresponding to m in (CH ₂ ) _m-1 in the above formula. . · C: trans-1,4-cyclohexylene group · P: 1,4-phenylene group · E: -COO- · e: -OCO- · A: -CH 2 CH 2 - · t: -C≡C- • 0: oxygen atom • When the right terminal in the abbreviated formula is CN: position 4 in the right terminal ring in the corresponding compound takes a cyano group. -When the right end in the abbreviated formula is F: 4-position in the right end ring in the corresponding compound takes a fluorine atom. -F: Ortho position (3rd position) in the right terminal ring in the corresponding compound takes a fluorine atom.

For example, as the above-mentioned abbreviation example 1, 2PEPfCN in Table 1 is a compound represented by the general formula (I) of the present invention.

[0029]

Embedded image

Represents a compound of the formula:

Further, as the above-mentioned abbreviation example 2, 3CPEP
The compound represented by fF has the formula

[0032]

Embedded image

The compound of the formula:

After adjusting the pitch of the liquid crystal A of Example 1 and the liquid crystal C of Comparative Example with cholesteric nonanoate, the liquid crystal was injected into a liquid crystal display device twisted by 240 °, and the time-division driving waveform (1/1) was adjusted. 240 duty 1/16 bias, 1 /
The device was driven at 480 duty 1 / 23bias) to measure electro-optical characteristics, and to evaluate the orientation stability (under domain and stripe domain generation) at 0 ° C., 25 ° C., and 50 ° C. In the STN liquid crystal display device using the liquid crystal A of Example 1, good contrast and stable alignment were obtained in all temperature ranges, but in the liquid crystal display device using the liquid crystal C of the comparative example, the contrast was inferior. At 50 ° C., abnormal orientation was observed (Table 2).

[0035]

[Table 2] As can be seen from the results in Tables 1 and 2, the general formulas (I) and (I
In Examples 1 and 2 in which compounds selected from I), (III), (IV) and (V) were simultaneously used, the contrast was better than that in Comparative Examples where no compounds were simultaneously used. It can be seen that stripe domains are hardly generated and good alignment stability can be obtained. By using the liquid crystal composition of the present invention, a liquid crystal display device having a high contrast can be manufactured with a high production yield.

[0036]

According to the combination of the liquid crystal materials of the present invention,
A liquid crystal composition having a high contrast when used in an STN liquid crystal display device and capable of producing a good production yield was provided. Further, the STN liquid crystal display device using the liquid crystal composition of the present invention was able to maintain high contrast even in high time division driving.

Claims (2)

[Claims] 1. A compound of the general formula (I) (In the formula, R ₁ represents an alkyl group, an alkenyl group, an oxaalkyl group, an oxaalkenyl group or an alkoxyl group having 1 to 10 carbon atoms, and n represents 0 or 1.) It contains two or more kinds, and its content is in the range of 5 to 20% by weight.
General formula (II) (In this formula, R ₂ represents an alkenyl group or an oxaalkenyl group having 1 to 10 carbon atoms.) One or more compounds represented by the formula (1) are contained in an amount of 5 to 40% by weight. Yes, and the general formula (III) (In the formula, R ₃ represents an alkyl group, an alkenyl group, an oxaalkyl group, an oxaalkenyl group or an alkoxyl group having 1 to 10 carbon atoms.) The amount is in the range of 10 to 40% by weight, and the compound of the general formula (IV) (In this formula, R ₄ and R ₅ represent an alkyl group, alkenyl group, oxaalkyl group, oxaalkenyl group or alkoxyl group having 1 to 10 carbon atoms, and ring A is substituted by cyclohexylene, phenylene, or a fluorine atom. Phenylene, m represents 0 or 1), and contains one or more compounds represented by the formula
0% by weight and further represented by the general formula (V): (In this formula, R ₆ and R ₇ each independently have 1 carbon atom.
And represents an alkyl group, an alkenyl group, an oxaalkyl group, an oxaalkenyl group or an alkoxyl group. )
A liquid crystal composition comprising one or more compounds represented by the formula (I) and having a content in the range of 5 to 40% by weight, having a nematic phase-isotropic liquid phase transition temperature of at least 70 ° C. The crystal phase or the smectic phase-nematic phase transition temperature of at most −20 ° C., the optical anisotropy Δn of the refractive index is 0.12 to 0.16, and the relative dielectric anisotropy Δε is 3 or more. A nematic liquid crystal composition, characterized in that: 2. A super twisted nematic (STN) having a twist angle of 220 ° to 270 ° using the nematic liquid crystal composition according to claim 1.
Liquid crystal display.