JPH04292686A - Liquid crystal composition - Google Patents

Abstract

PURPOSE:To obtain a liquid crystal composition suitable for ferroelectric liquid crystal display element by surface stabilization, having high contrast ratio, quick response speed and stable memory characteristics, containing specific three kinds of liquid crystal compounds. CONSTITUTION:The objective composition containing liquid crystal compounds shown by formulae I, II and III (R<1> is 6-14C straight-chain alkyl; R<2> is 4-8C asymmetric carbon-containing alkyl; R<3> is 6-14C straight-chain alkyl; R<4> is 4-14C straight-chain alkyl; R<5> is 6-14C straight-chain alkyl; R<6> is 4-8C asymmetric carbon-containing alkyl; X is F or H; n is 0-5) wherein a phase transfer line is an isotropic phase-smectic A phase-chiral smectic C phase and the smectic A phase is shown at >=20 deg.C.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal composition, and more particularly to a liquid crystal composition suitable for use in liquid crystal displays and the like.

0002

[Background Art] With the progress of office automation, flat panel display devices are desired.
Liquid crystal displays (LCDs) have become widely used. Conventional LCD displays are mainly used for laptop personal computers and notebook computers with relatively small display capacities, and the most common LCD display is 640 x 400 dots (in Japan).
Or, it has a display capacity of 640 x 480 dots (foreign countries).

However, as office automation progresses and notebook computer hardware and software technology becomes more sophisticated, display devices become more sophisticated, particularly in terms of increased display capacity, increased response speed, and improved contrast (ease of viewing). It is desired to improve the ratio, enlarge the display screen (display area), and reduce viewing angle dependence. Among these, improved visibility and increased response speed can be achieved by using a TFT active matrix panel LCD in which a thin film transistor is incorporated in each picture element, rather than a conventional liquid crystal display (super twisted nematic (STN) type display). However, with regard to expansion of display capacity and display area, TFT-LCDs are practically difficult or extremely difficult to manufacture in terms of their manufacturability. Furthermore, regarding the reduction of viewing angle dependence, conventional T
FT-LCD is insufficient.

On the other hand, liquid crystal displays using surface-stabilized ferroelectric liquid crystals (SSFLC) are capable of large capacity, large area, wide viewing angle, high contrast ratio, and high speed response in principle. Practical application is being actively considered. However, with conventional ferroelectric liquid crystals, uniform liquid crystal molecular alignment cannot be obtained and zigzag-like alignment defects occur, resulting in a low contrast ratio and an inability to obtain high-speed response. In addition, because the memory state was unstable, large-capacity display was not possible, which was a fatal problem in practical terms.

[0005]

SUMMARY OF THE INVENTION Accordingly, the present invention solves the above-mentioned problems of the prior art and provides a high contrast ratio,
It is an object of the present invention to provide a liquid crystal composition suitable for a surface-stabilized ferroelectric liquid crystal display device having fast response speed and stable memory characteristics.

[0006]

[Means for Solving the Problems] According to the present invention, the formula (I
), (II) and (III):

[0007]

[C4]

[0008]

[C5]

[0009]

[C6]

(In the formula, R1 is a straight chain alkyl group having 6 to 14 carbon atoms, R2 is an alkyl group having at least one asymmetric carbon atom having 4 to 8 carbon atoms, and R3 is a straight chain alkyl group having 6 to 14 carbon atoms.
R4 is a straight-chain alkyl group having 4 to 14 carbon atoms, R5 is a straight-chain alkyl group having 6 to 14 carbon atoms, R
6 is an alkyl group containing at least one asymmetric carbon having 4 to 8 carbon atoms, X is a fluorine atom or a hydrogen atom, and n is 0 to 5.
) and (III), particularly in a temperature range in which the phase transition series is isotropic phase - smectic A phase - chiral smectic C phase - crystalline phase, and exhibits smectic A phase. Provided is a liquid crystal composition in which the temperature is 20°C or higher.

A liquid crystal display using a ferroelectric liquid crystal displays information by inverting the spontaneous polarization of the liquid crystal by an externally applied electric field and visualizing the resulting birefringence. Therefore, it is basically a binary display and is a memory-driven device that utilizes a bistable state. Therefore, as a first premise, it is clear that the bistable state must be sufficiently stable. Generally, in order to stabilize a bistable state, it is first necessary to make the alignment of liquid crystal molecules uniform. In other words, if the molecular orientation is not uniform, the directions of the permanent dipole moments of individual liquid crystal molecules will not be aligned, and if the directions of the permanent dipole moments are not aligned, the spontaneous polarization of the liquid crystal as a whole will decrease. First, when an electric field is applied from the outside, each molecule moves in a different direction, making it impossible to obtain an easy-to-see display with a high contrast ratio. In particular, in conventional ferroelectric liquid crystals, zigzag defects occur, and the liquid crystal molecules around these defects cannot be inverted with the same phase during polarization reversal, leading to phenomena such as a low contrast ratio and a decrease in response speed. It could not be put to practical use as a display.

[0012] Therefore, in order to use ferroelectric liquid crystal as a practical liquid crystal display, it is necessary to use a ferroelectric liquid crystal that does not generate zigzag defects.
It is necessary to develop liquid crystal materials that enable uniform molecular alignment. As a result of studies from this point of view, the present inventors found that, in general, the phase transition series of liquid crystal materials is isotropic phase (I) - smectic A phase (SA) - chiral smectic C phase (
S C * ), and the temperature range of the SA phase is 2
It has been found that when the temperature is wide at 0° C. or higher, the molecular orientation of the SC* phase, which is a ferroelectric phase, becomes uniform. Although the relationship between the temperature range of the SA phase and the molecular orientation of the SC* phase has not yet been fully elucidated, it is assumed that the enthalpy change accompanying the SA-SC* phase transition is involved in the molecular orientation of the SC* phase. Suppose.

Specific examples of liquid crystals having the effects of the present invention as tolan-based liquid crystals are the compounds of the general formulas (I) and (II). Tolan-based liquid crystals represented by general formulas (I) and (II) and ester-based liquid crystals represented by general formula (III), respectively, are
By mixing and using the compositions shown in Table 2, it is possible to obtain a liquid crystal composition that exhibits excellent electro-optical properties that cannot be obtained with conventional liquid crystals as shown in Table 2.

Formulas (I), (II) and (III
) Preferably, the optically active tolan liquid crystal represented by the general formula (I) is mixed in an amount of 25 to 90% by weight, more preferably 35 to 7% by weight based on the entire composition.
5% by weight, 5 to 70% by weight, more preferably 15 to 30% by weight of optically inactive tolan liquid crystal represented by general formula (II).
It is also effective to blend 5 to 40 weight %, more preferably 10 to 30 weight % of the ester liquid crystal represented by the general formula (III).

[0015]

[Operation] Based on the above assumption, the present inventors investigated various ferroelectric liquid crystals, and found that a liquid crystal mixture containing tolan liquid crystal represented by the above formula (I) as a main component is I-SA.
-SC * -Cr shows the phase transition series, and also SA
It was also found that the temperature range of the phase was as wide as 20°C or higher. As a result of fabricating a liquid crystal display using this liquid crystal material and observing the molecular alignment, they found that a clean, uniform alignment without zigzag defects was obtained.

[0016]

[Examples] The present invention will be specifically explained below with reference to Examples, but it goes without saying that the present invention is not limited to the following Examples.

[0017] A round solid transparent electrode with a diameter of 20 mm was provided.
A glass substrate of 0 x 60 x 1.1 mm (thickness) was coated with 3% by weight polyvinyl alcohol (PV) using a spin coater.
A) After applying the aqueous solution at 2500 rpm,
It was baked at ℃ for 2 hours. Two of these substrates were used, and a solution in which silica beads having an average particle size of 1.8 μm were dispersed in Freon was applied to the surface of one substrate by a spray method to disperse the spacer material. Thereafter, the two substrates were bonded together using silica beads as spacers. Note that, before bonding, the PVA on the surface of the substrate was rubbed three times so that they were antiparallel to each other. A mixed ferroelectric liquid crystal containing tolan-based liquid crystal as the main component shown in Table 1 was injected into this panel, and after once forming the I phase, the temperature was lowered at a rate of 2° C./min to room temperature.

[0018]

[Table 1]

As a result of observing the state of molecular orientation of this liquid crystal panel using a polarizing microscope, uniform orientation was obtained without any defects including zigzag defects. next,
In order to measure the electro-optical response characteristics of this liquid crystal panel, a bipolar pulse with a peak value of 15 V and a pulse width of 300 μs was applied. Note that the interval between the +15V and -15V pulses was 0.5s. When a pulse voltage of 15V is applied, the time required for the transmittance to change from 10 to 90%, that is, the response time of this liquid crystal panel is 51.0 μs, and the transmittance when voltage is applied (when pulse voltage is applied) and when no voltage is applied The ratio is 3
The ratio was 5:1. Furthermore, the transmittance ratio in the memory state (see FIG. 1) 0.5 s after the application of the pulse voltage was 30:1. These characteristic values are expressed by the formula (IV) of the most commonly used ferroelectric liquid crystal:

[0020]

[C7]

Table 2 shows the results of comparison with a phenylpyrimidine mixed liquid crystal panel.

[0022]

[Table 2]

Table 2 Footnote Contrast ratio during response Transmittance when pulse voltage is applied/Transmittance when no voltage is applied (before application) Contrast ratio during memory After voltage application 0.5
Transmittance after s/Transmittance response time when no voltage is applied (before application) Transmittance 1
Time required for 0 to 90% change Applied voltage Peak value 15V, pulse width 300μs Presence of zigzag defect Polarizing microscope observation Memory stability Reproducibility of memory state after voltage application If reproducible If memory is not stable
Memory is unstable SA phase temperature range SA phase temperature range when the temperature is lowered at a rate of 2°C/min after heating up to isotropic phase Measurement by polarizing microscope and DSC

[0024] As is clear from Table 2, the liquid crystal display using the mixed liquid crystal composition containing tolan-based liquid crystal as a main component of the present invention has a higher contrast ratio, faster response, and better memory state than conventional liquid crystals. A high contrast ratio can be obtained. In particular, a high contrast ratio in the memory state means higher bistability and stability, and the memory-driven ferroelectric liquid crystal display (SSFL)
This is an extremely essential characteristic for C-LCDs.

On the other hand, as a result of investigating the characteristics as a liquid crystal material for liquid crystal displays that exhibit the excellent characteristics described above,
The liquid crystal mixture composition according to the present invention has a phase transition series of I-SA.
-SC*-Cr, and the temperature range showing the SA phase is wide from 78°C to 50.5°C, extending to 27.5°C. In contrast, conventional ferroelectric liquid crystals generally have a phase transition series of I-N*-SA-
SC*-Cr and SA phase temperature range is at most 10°C, and in most cases as narrow as about 5°C. In addition,
Here, N* indicates a cholesteric phase. The above measurements were similarly performed on other tolan-based liquid crystal compositions shown in Tables 3-1, 3-2, and 3-3.

[0026]

[Table 3]

[0027]

[Table 4]

[0028]

[Table 5]

As shown in Table 2, the results show clearly superior electro-optic response characteristics compared to conventional liquid crystals.

Next, as comparative examples, the formulas (I) to (II
Table 4-1 and Table 4- below, in which one of the components of I) is missing
The above measurements were performed on liquid crystal compositions E and F shown in No. 2.

[0031]

[Table 6]

[0032]

[Table 7]

The results for compositions E and F are both SC*
It was confirmed that the SC* phase does not appear in a two-component system that does not show any phase. Therefore, it is clear that the ternary system of the present invention is essential to obtain the SC* phase.

[0034]

[Effect of the invention] Formulas (I) and (II) according to the present invention
By using a liquid crystal composition containing the compound (III) as a main component, conventional liquid crystal compositions suffer from low contrast, slow response, and unstable memory characteristics due to alignment defects such as zigzag defects. I couldn't get it,
By surface stabilization, a ferroelectric liquid crystal display element can be made to have high contrast (at least 4 times that of the conventional one), fast response, and stable memory characteristics.

[Brief explanation of the drawing]

FIG. 1 is a graph diagram for measuring the electro-optical response characteristics of a liquid crystal panel using a liquid crystal composition (composition A) according to an example of the present invention.

Claims (2)

[Claims] [Claim 1] General formulas (I), (II) and (II)
I): [Formula 1] [Formula 2] [Formula 3] (wherein, R1 is a straight-chain alkyl group having 6 to 14 carbon atoms, R
2 is an alkyl group containing at least one asymmetric carbon atom having 4 to 8 carbon atoms, R3 is a straight chain alkyl group having 6 to 14 carbon atoms, R4 is a straight chain alkyl group having 4 to 14 carbon atoms, R5
is a straight chain alkyl group having 6 to 14 carbon atoms, and R6 is a straight chain alkyl group having 4 carbon atoms.
an alkyl group containing at least one asymmetric carbon of ~8,
represents a fluorine atom or a hydrogen atom, and n is 0 to 5)
Liquid crystal compounds (I), (II) and (II
A liquid crystal composition comprising at least one type of each of I). Claim 2: The phase transition series is isotropic phase - smectic A phase - chiral smectic C phase, and the temperature range showing the smectic A phase is 20°C or higher.
The liquid crystal composition described.