JPH0826318B2 - Liquid crystal composition - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Outline] The present invention relates to a ferroelectric liquid crystal composition, which contains the following two components at the same time for the purpose of reducing the viscosity of the liquid crystal composition in order to shorten the response time. And a liquid crystal composition.

(Here, R ₁ is an alkyl or alkoxy group having 6 to 16 carbon atoms, Is an alkyl group containing at least one asymmetric carbon atom having 4 to 12 carbon atoms. ) (Here, R ₂ is an alkyl or alkoxy group having 6 to 16 carbon atoms, Is an alkyl group containing at least one asymmetric carbon atom having 4 to 12 carbon atoms. The present invention relates to a liquid crystal composition, and more specifically to a liquid crystal composition in which the response time of a ferroelectric liquid crystal is shortened.

[Problems to be Solved by Prior Art and Invention]

Liquid crystal displays (LCDs), which have been put to practical use as display displays for watches and calculators, have rapidly developed as display devices for small portable information devices in recent years by taking advantage of their features of low power consumption and thin and light weight. However, recently, a liquid crystal display capable of displaying a large amount of information (large capacity) has been demanded.

In the conventional simple matrix TN type liquid crystal display,
Since the response of the liquid crystal is slow and the display contrast is low, the display capacity of about 640 × 400 pixels is the limit, and it is not possible to increase the capacity further, and clear moving image display is impossible.

In recent years, research on active matrix type display elements that can display large capacity and high contrast using TN type liquid crystal has been actively conducted. In this method, transistors and diodes are formed in each pixel. However, it is difficult to manufacture a large-capacity, defect-free panel, and it is not suitable for a large-area, large-capacity display because the cost is high for mass-production.

On the other hand, the ferroelectric liquid crystal display (FLCD) is capable of displaying large-capacity and high-contrast moving images by a simple matrix method that can be manufactured at low cost. The FLCD eliminates the spiral structure by enclosing the liquid crystal in a panel with a space between the glass substrates of about 2 μm, and arranges the liquid crystal molecules in parallel with the substrate by the orientation control force by rubbing, and further, a layer structure perpendicular to the substrate And the permanent dipole moments perpendicular to the long axis of the molecule are oriented in the same direction to cause spontaneous polarization. The FLCD is a TM-type liquid crystal because the spontaneous polarization of the liquid crystal is directly coupled to the applied electric field.
It is possible to have a response time of 1/1000 or less. Further, since it has a memory property (bistability) that maintains the state even when the applied electric field is cut off, the number of pixels can theoretically be infinite. From the above characteristics, FLCD
Enables simple matrix type large-capacity, high-contrast moving image display.

However, in order to enable the FLCD as described above, there are alignment problems that align the directions of spontaneous polarization, problems that make the memory appearance stable, and further, those characteristics change with changes in environmental temperature. There are driving problems caused by the above, and these problems must be solved in order to realize a real device.

The present invention is directed, inter alia, to reducing the response time of FLCDs.

[Means for solving problems]

In the present invention, the following two components are simultaneously included in a liquid crystal composition in order to shorten the response time of FLCD.

(Here, R ₁ is an alkyl or alkoxy group having 6 to 16 carbon atoms, Is an alkyl group containing at least one asymmetric carbon atom having 4 to 12 carbon atoms. ) (Here, R ₂ is an alkyl or alkoxy group having 6 to 16 carbon atoms, Is an alkyl group containing at least one asymmetric carbon atom having 4 to 12 carbon atoms. ) The response time τ _r of the ferroelectric liquid crystal is generally represented by the following equation.

Here, η is viscosity, P _S is spontaneous polarization, and E is electric field strength. To shorten the response time with constant electric field strength,
It is effective to reduce the viscosity or increase the spontaneous polarization. However, the viscosity of the liquid crystal generally increases as the temperature decreases, resulting in a slow response. Spontaneous polarization increases as the temperature decreases. The spontaneous polarization is large and the response is almost fast, but at low temperature the increase rate of the viscosity is larger and the response becomes slower.

From the above, as a means to shorten the response time,
It is considered effective to mix (1) a liquid crystal having the effect of decreasing the viscosity or (2) mix a liquid crystal having a large spontaneous polarization. The present invention has developed means for decreasing the viscosity without changing the magnitude of spontaneous polarization so much.

In the liquid crystal composition of the present invention, the total amount of the compound (1) and the compound (2) is 10 to 50% by weight based on the whole liquid crystal composition.
Is appropriate. If this amount exceeds 50% by weight, good bistability cannot be obtained, and if it is less than 10% by weight, the effect of lowering the viscosity cannot be sufficiently exhibited. Further, the ratio of the compound (1) to the compound (2) is appropriately 5 to 75% by weight of (1) with respect to the total amount of (1) and (2). When the amount of the compound (1) exceeds 75% by weight, the liquid crystal composition becomes an unstable smectic C phase or does not exhibit a smectic C phase,
On the other hand, if it is less than 5% by weight, the effect of lowering the viscosity does not sufficiently appear.

In the liquid crystal composition of the present invention, a typical ferroelectric liquid crystal can be used as a component other than the compounds (1) and (2). In particular, a component having large spontaneous polarization and a component exhibiting bistability. It is preferably used together with. As a component having a large spontaneous polarization, for example, (Here, R ₃ is an alkoxy group or alkyl group having 6 to 16 carbon atoms, ▲ R ^* ₃ ▼ is an alkyl group containing at least one asymmetric carbon atom having 4 to 12 carbon atoms, and at least one asymmetric group. Carbon is directly bonded to oxygen bonded to ▲ R ^* ₃ ▼, n is 1 or 2.), and the component exhibiting bistability is, for example, (Here, R ₄ is an alkoxy group or alkyl group having 6 to 16 carbon atoms, R ₄ ^* is an alkyl group having 4 to 12 carbon atoms having at least one asymmetric carbon atom, and n is 1 or 2 , M
= 1 to 6, X = COO or 0. ) And the like.

[Action]

It is considered that the compound (1) weakens the bonding force between the liquid crystal molecules by introducing a fluorine atom in the minor axis direction of the molecule, thereby lowering the viscosity of the liquid crystal composition. However, when only the compound (1) is added, the liquid crystal composition does not show the smectic C phase necessary for the ferroelectric liquid crystal, but by using the compound (2) together, the smectic C phase is exhibited while the viscosity is reduced. become.

〔Example〕

A panel having a gap of 2 μm was prepared using rubbed polyvinyl alcohol as an alignment film, and mixed liquid crystals of compositions I, II and III shown in Table 1 were enclosed.

The above composition I comprises compounds (1) and (2)
II contains only the compound (2), and the composition III contains only the compound (1).

Of these, Composition III did not exhibit a smectic C phase.

Liquid Crystal Response Time τ for Composition I and Composition II
_r (20 V applied) and spontaneous polarization P _s were measured. The results are shown in FIGS. 1 and 3 for the composition I, respectively.
Composition II is shown in FIGS. 2 and 4.

Comparing FIG. 1 and FIG. 2, composition I is the composition
It is recognized that the response is faster than II (less than 1/2 at 35 ° C or lower). On the other hand, comparing FIG. 3 and FIG. 4, when looking at the temperature range of about 20 to 35 ° C., the spontaneous polarization of both is equivalent. Therefore, since the spontaneous polarization of the composition I is the same as that of the composition II, it is recognized that the response time is shortened by the viscosity reduction.

The components effective for shortening the response time in the composition I are the following components.

and Further, in the liquid crystal composition of the examples, a liquid crystal having a straight-chain alkoxy group having 8 to 12 carbon atoms in the 4-position substituent of the phenyl group was used, but the essential structure for reducing the viscosity of the liquid crystal is as described above. General formulas are represented by the structural formulas (1) and (2), and if the liquid crystal phase temperature range is sufficiently wide, the 4-position substituent of the phenyl group is a straight chain having 6 to 16 carbon atoms or It may be an alkoxy group.

EFFECTS OF THE INVENTION According to the present invention, in a liquid crystal composition used for a ferroelectric liquid crystal display, it is possible to reduce the response time of the liquid crystal by reducing the viscosity of the liquid crystal.

[Brief description of drawings]

1 and 2 are graphs showing the temperature dependence of the response times of the compositions I and II of the examples, FIG. 3, and FIG. 4, respectively.
The figures are graphs showing the temperature dependence of the spontaneous polarization of the compositions I and II, respectively.

Front page continuation (72) Inventor Akihiro Mochizuki 1015 Kamiodanaka, Nakahara-ku, Kawasaki, Kanagawa Prefecture Fujitsu Limited (72) Inventor Masakatsu Nakatsuka 2882 Iijima-cho, Sakae-ku, Yokohama-shi, Kanagawa

Claims (3)

[Claims] 1. A liquid crystal composition for use in a ferroelectric liquid crystal display in which a helical structure of liquid crystal is eliminated by parallel processing and a sufficiently thin panel gap, wherein the following two compounds are contained at the same time. (Here, R ₁ is an alkyl or alkoxy group having 6 to 16 carbon atoms, Is an alkyl group containing at least one asymmetric carbon atom having 4 to 12 carbon atoms. ) (Here, R ₂ is an alkyl or alkoxy group having 6 to 16 carbon atoms, Is an alkyl group containing at least one asymmetric carbon atom having 4 to 12 carbon atoms. ) 2. The liquid crystal composition according to claim 1, wherein the total amount of the compounds (1) and (2) is 10 to 50% by weight with respect to the entire liquid crystal composition. 3. The composition according to claim 1 or 2, wherein the composition ratio of the compound (1) is 5 to 75% by weight based on the total amount of the compounds (1) and (2). Liquid crystal composition.