JPH0717911B2 - Liquid crystal composition - Google Patents

Description

TECHNICAL FIELD The present invention relates to a liquid crystal composition, and more specifically to an inexpensive liquid crystal composition having improved response characteristics of liquid crystal.

[Prior Art] Although there are various liquid crystal display methods, the TN (Twist Nematic) method is often used from the viewpoint of high contrast and low voltage driving. When this TN method is used, its characteristics depend largely on the cell gap, so that highly accurate gap control is required. Therefore, for curved display elements or large display elements where gap control is difficult
It becomes difficult to use the TN method. Therefore, as a display method applicable to such a poor gap accuracy, DS
There is M method. As the liquid crystal composition used in this DSM system, a liquid crystal composition in which a dynamic scattering mode is generated when the liquid crystal composition is sandwiched between transparent electrodes and a constant voltage is applied, that is, a DSM type liquid crystal composition is used. (JP-A-60-213
No. 929 publication).

[Problems to be Solved by the Invention] When this DSM type liquid crystal composition is applied to a large-sized display element, the cell gap is often made large in order to reduce the display unevenness due to non-uniformity of the gap. . Therefore, since a large amount of DSM type liquid crystal composition is used in this display device, the ratio of liquid crystal to the cost becomes very large. Further, there is a problem that the response of the liquid crystal display element is deteriorated due to the size of the cell gap.

The present invention solves the above-mentioned problems, and an object of the present invention is to provide an inexpensive DSM type liquid crystal composition having improved liquid crystal response characteristics.

[Means for Solving the Problems] The liquid crystal composition of the present invention is a DSM containing a liquid crystal compound having a negative dielectric anisotropy in which the dielectric constant of liquid crystal molecules in the minor axis direction is larger than the dielectric constant in the major axis direction. In a (Dynamic Scattering Mode) type liquid crystal composition, when the above liquid crystal composition is 100 parts by volume, 1 to 13 parts by volume of trans (hereinafter abbreviated as t) -1, 4
-It is characterized in that it contains dimethylcyclohexane.

Any liquid crystal compound may be used as long as it has a negative dielectric anisotropy and produces a random scattering mode when a constant voltage is applied, and various compounds are selected and used according to the purpose and application. Further, the present liquid crystal composition may contain one kind of liquid crystal compound or may be a mixed liquid crystal of two or more kinds. Usually, mixed liquid crystals are used from the viewpoint of practical liquid crystal characteristics. When the addition ratio of t-1,4-dimethylcyclohexane is less than 1% by volume, the response characteristics are not sufficiently improved, and the effect of reducing the cost of the liquid crystal composition is small. If this content exceeds 13% by volume, the additive and the liquid crystal will not separate and become uniform.

In addition, various additives for improving practical liquid crystal properties such as an electrolyte compound and a dichroic dye may be added to the present liquid crystal composition depending on the purpose and application.

[Examples] Hereinafter, the present invention will be described with reference to Examples.

(1) Preparation of liquid crystal cell Nematic liquid crystal with negative dielectric anisotropy (“ZLI-1 manufactured by Merck Ltd.
623 ") and t-1,4-dimethylcyclohexane (special grade reagent) at various ratios (0, 1, 2, 4,
7, 10, 13% by volume) to prepare a predetermined liquid crystal composition. Here, the volume% means the volume% of n-putylcyclohexane added when the liquid crystal composition is 100% by volume. If it exceeds 13% by volume, the additive and the liquid crystal are separated from each other, which is not preferable.

Next, a pair of glass substrates, a transparent electrode formed on the glass substrate, a liquid crystal alignment film formed on the transparent electrode,
A cell before injection of liquid crystal, which was composed of a spacer arranged between the glass substrates and a peripheral sealing member, was prepared by a usual method. The glass substrate has a size of 30 × 50 mm and its cell gap is 20 μm. Then, the above liquid crystal compositions were injected by a vacuum injection method to prepare a liquid crystal cell. ITO (Indium-Tin-Oxide) as this transparent electrode
Polyimide is used as the film and liquid crystal compounding film, and the compounding process is
The rubbing treatment was performed so as to be pomodious.

(2) Measurement of response speed Next, measurement was performed on each of the above liquid crystal cells using the device shown in FIG. 2 under the conditions of a measurement temperature of 0 ° C. and an applied AC voltage of 30 V (64 Hz). The results are shown in FIG. The response time was the time when 90% of the total change in transmittance was changed.

According to this figure, the response speed becomes faster as the amount of addition is increased, and it is almost saturated at about 4%. This addition amount is 1, 2, 4,
In each case of 7, 10 or 13%, compared to the case of no addition
1.3, 1.5, 2.1, 2.5, 3.0 or 3.4 times faster response speed. Especially when the added amount is 4-10%, 2.1-3.4
It's twice as fast.

(3) Measurement of liquid crystal operating temperature range The temperature range of the liquid crystal "ZLI-1623" (ester-cyclohexane mixed liquid crystal, manufactured by Merck & Co., Inc.) to which the above additives were not added was -10 ° C to 80 ° C.

On the other hand, the operating temperature range of the liquid crystal composition containing 13% by volume of t-1,4-dimethylcyclohexane was −10 ° C. to 48 ° C., and the upper limit was only lowered by about 30 ° C., which is still a practical range. It was When the ratio of addition is smaller than the above, the upper limit of the operating temperature range is considered to be a larger value.

(4) Summary From the above, 1 to 13 of t-1,4-dimethylcyclohexane was added.
Addition by volume% lowers the upper limit of the liquid crystal operating temperature range, but is in a practically sufficient range, and the response speed becomes faster. Furthermore, since the present composition contains up to 13% by volume of an inexpensive additive as compared with an expensive liquid crystal, it becomes an extremely inexpensive liquid crystal composition.

[Effects of the Invention] The liquid crystal composition of the present invention is a liquid crystal compound having a negative dielectric anisotropy in which the dielectric constant of the liquid crystal molecule in the short axis direction is larger than the dielectric constant in the long axis direction, and the total composition is 100 vol. 1 to 13
It is characterized by being mixed with t-1,4-dimethylcyclohexane in a capacity part.

On the other hand, in conventional compositions, the amount of additives added to improve the properties is generally very small. However, in the present liquid crystal composition, contrary to common sense as the additive amount, a large amount of an inexpensive additive is added to the liquid crystal. By adding a large amount in this way, the response characteristics of the liquid crystal can be improved, and the cost of the liquid crystal composition can be greatly reduced. In particular, when the composition is applied to a large-sized liquid crystal panel (in particular, a DSM type liquid crystal composition is often used for a large-sized panel), the cost reduction becomes extremely large.

Further, since the composition can accelerate the response speed,
Generally, it is extremely preferable for a DSM type liquid crystal composition having a thicker liquid crystal layer than the TN type.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the amount of t-1,4-dimethylcyclohexane added and the response speed in the examples.
FIG. 2 is an explanatory view schematically showing the response speed measuring device.

Claims (2)

[Claims] 1. A DSM (Dynamic Scattering mode) type liquid crystal composition containing a liquid crystal compound having a negative dielectric anisotropy in which the dielectric constant of liquid crystal molecules in the minor axis direction is larger than the dielectric constant in the major axis direction. When the composition is 100 parts by volume, 1 to 13 parts by volume of t
A liquid crystal composition comprising rans-1,4-dimethylcyclohexane. 2. The liquid crystal composition according to claim 1, wherein trans-1,4-dimethylcyclohexane is 4 to 13 parts by volume when the liquid crystal composition is 100 parts by volume.