JPH0160196B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a liquid crystal composition for a display element, and particularly to a liquid crystal composition that has a fast response speed and is suitable for a liquid crystal display element with a wide displayable temperature range. Recently, liquid crystal display devices have come to be used not only for watches and calculators but also for measuring instruments. Since measuring instruments are installed not only indoors but also outdoors, they need to have a wide displayable temperature range and are also required to have high-speed response. Therefore, the viscosity of the liquid crystal used for this purpose is required to be extremely low. Among the liquid crystals known to date, liquid crystal compounds with extremely low viscosity are shown in Table 1 along with their characteristic values.

[Table] As can be seen from Table 1, these liquid crystals have an extremely low viscosity, but have the disadvantage of a low nematic-isotropic transition temperature (N-I point) and an extremely narrow usable temperature range. . In order to expand the usable temperature range and maintain high-speed response, it is necessary to combine a liquid crystal compound with a high N-I point and low viscosity with the liquid crystal compounds in Table 1. Become. The present applicant has previously filed a patent application for one of such compounds [Patent Application No. 49689/1989 (Patent Application No. 49689/1989)
-Refer to Publication No. 39136)] General formula (In the above formula, R represents an alkyl group having 1 to 10 carbon atoms, and R' represents an alkyl group or an alkoxy group having 1 to 10 carbon atoms). The compound represented by formula () has an N-I point of 150°C or higher, and its viscosity at 20°C (η20°C) is extremely low at 20 cp (extrapolated value), so it can be used as a liquid crystal without increasing the viscosity of the composition. The temperature range can be widened. Furthermore, since it has virtually no absorption in the visible region, it does not color the composition. It also has excellent water resistance and weather resistance. Table 2 has the preferred liquid crystal temperature range ()
Some of the compounds of formula and their characteristic values are shown.

[Table] When a liquid crystal is actually used in a display device, the dielectric anisotropy is not sufficiently large with the above two components alone, so it is necessary to further add a liquid crystal compound with a large absolute value of the dielectric anisotropy value. In this case, either positive or negative dielectric anisotropy is selected and used depending on the display method used. The general formula for such compounds with positive dielectric anisotropy is (R represents an alkyl group having 1 to 10 carbon atoms) is the most representative and preferred compound, and as a compound having negative dielectric anisotropy, the general formula The most preferred compound is (R and R' represent an alkyl group having 1 to 10 carbon atoms). The present invention is a liquid crystal composition containing the above three components as essential components. These three components, namely, the compound in Table 1 (this is the component (a)), the compound of formula () (this is the component (b)), and the liquid crystal compound with large dielectric anisotropy (this is the component (c) By combining components (), an excellent display element liquid crystal composition having an N-I point of 75° C. or higher and a viscosity of 25 cp or lower at 20° C. can be easily obtained. The proportion of each component (a), (b), and (c) in the final composition is 20 to 50% of component (a).
(weight, the same below), preferably 30 to 40%, component (b) 25 to 50%, preferably 35 to 45%, component (c) 15 to 40%
It may be determined in the range of 40%, preferably 20 to 30%, taking into account the type of display device and other factors. Particularly preferred specific examples of the compositions of the present invention are shown below as examples. Example 1 As a compound of component (a) (b) As a compound of component (c) As a liquid crystal compound with a large positive dielectric anisotropy A liquid crystal composition consisting of six components in total was prepared, and its liquid crystal temperature range was measured to be -5°C to 89°C, and the viscosity at 20°C was 17 cp. The response speed when applying a voltage of 32Hz5V is the rise time at 0℃.
It has an extremely fast fall time of 80ms and a fall time of 80ms, making it suitable for use in measuring instruments. Example 2 As a compound of component (a) (b) As a compound of component (c) As a liquid crystal compound with large positive dielectric anisotropy A liquid crystal composition consisting of seven components in total was prepared, and the liquid crystal temperature range was measured to be -30°C or lower to 78°C, and the viscosity at 20°C was 19 cp. The response speed when applying a voltage of 32Hz5V is the rise time at 0℃.
It exhibited extremely fast characteristics suitable for use in measuring instruments, with a fall time of 60 ms and a fall time of 100 ms. Example 3 As a compound of component (a) (b) As a compound of component (c) As a liquid crystal compound with large positive dielectric anisotropy A liquid crystal composition consisting of seven components was prepared, and the liquid crystal temperature range was measured to be -15℃ to 80℃, which was 20℃.
The viscosity at °C was 21 cp. The response speed when applying a voltage of 32Hz and 5V is a rise time of 95ms at 0℃,
The rise time was 120 ms, which was sufficiently fast, and showed characteristics suitable for use in measuring instruments. Example 4 As a compound of component (a) (b) As a compound of component (c) As a liquid crystal compound with large negative dielectric anisotropy A liquid crystal composition consisting of nine components was prepared, and the liquid crystal temperature range was measured to be -20°C to 88°C,
The viscosity at 20°C was 21 cp. 1% of an azo dye was added to this liquid crystal composition, and the mixture was injected into a cell subjected to vertical alignment treatment, and a voltage of 32 Hz and 8 V was applied.
The response speed at 0℃ is a rise time of 350ms,
The fall time was 450ms, and it exhibited characteristics suitable for use in measuring instruments.

Claims (1)

[Scope of Claims] 1. A liquid crystal composition containing the following three components (a), (b), and (c) as essential components. (a) Component is the general formula (R and R' represent an alkyl group having 1 to 10 carbon atoms) or general formula (R, R' are the same as above) or general formula (R is the same as above) at least one type of compound or a mixture thereof, and component (b) is the general formula (R represents an alkyl group having 1 to 10 carbon atoms, and R' represents an alkyl group or an alkoxy group having 1 to 10 carbon atoms), or a mixture thereof; component (c) is a liquid crystal compound or mixture with an absolute value of dielectric anisotropy of 6 or more. 2 (c) component is general formula (R represents an alkyl group having 1 to 10 carbon atoms) The liquid crystal composition according to claim 1. 3 (c) component is general formula (R and R' represent an alkyl group having 1 to 10 carbon atoms) The liquid crystal composition according to claim 1. 4 Claim 1 in which component (a) is 20 to 50%, component (b) is 25 to 50%, and component (c) is 15 to 40%.
The liquid crystal composition according to item 1 or 2 or 3.