JPH07119417B2 - 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 while maintaining liquid crystal characteristics.

[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 a method. As the liquid crystal composition used in the DS method, a liquid crystal composition that sandwiches the liquid crystal composition between transparent electrodes and a constant voltage is applied to generate a dynamic scattering mode, 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 device, it is necessary to increase the cell area and increase the cell gap in order to reduce display unevenness such as nonuniform gap. Many. 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.

As a solution to this problem, it is conceivable to add an inexpensive additive to the liquid crystal to reduce the amount of the liquid crystal used, but in this case, the characteristics are generally deteriorated such as an increase in current consumption.

The present invention solves the above problems, and an object of the present invention is to provide a DSM type liquid crystal composition containing an inexpensive additive that does not deteriorate the characteristics of the liquid crystal.

[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. A (Dynamic Scattering Mode) type liquid crystal composition is characterized by containing 5 to 11 parts by volume of n-butylcyclohexane when the above liquid crystal composition is 100 parts by volume.

Any liquid crystal compound may be used as long as it has a negative dielectric anisotropy and produces a dynamic 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. If the addition ratio of n-butylcyclohexane is less than 5% by volume or exceeds 11% by volume, power consumption increases, which is not preferable.

In addition, various additives for improving practical liquid crystal properties such as an electrolyte compound and a dichroic dye can 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 n-butylcyclohexane (special grade reagent) were mixed at various ratios (0 to 14% by volume) shown in Fig. 1 to prepare a predetermined liquid crystal composition. In addition, in volume% here,
It means the added volume% of n-butylcyclohexane when the liquid crystal composition is 100% by volume.

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 was used as the film and the alignment film, and the alignment treatment was a rubbing treatment so as to be homogeneous.

(2) Measurement of current consumption AC voltage 30V (64H
The current consumption when z) was applied was measured, and the relationship between the amount of n-butylcyclohexane added and the current consumption is shown in FIG.

As this figure shows, the current consumption increases as the amount added increases, reaching the peak at 4%, and then starting to decrease again at 9%.
It showed a minimum at and gradually increased, and started to increase sharply at 11%. From the above, when the added amount was 5 to 11%, the current consumption was almost the same as when it was not added, or the increase was slight. Particularly, in the case of 6 to 11%, the current consumption was almost the same as that in the case where it was not added.

(3) Measurement of response speed Next, measurement was carried out on each of the above liquid crystal cells using the apparatus shown in FIG. 3 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, whether the predetermined voltage is applied (solid line in the figure) or not applied (dotted line in the figure), the response speed becomes faster when the addition rate is increased, and is saturated at about 7%. To do.

(4) Measurement of liquid crystal operating temperature range This temperature range of the liquid crystal "ZLI-1623" (ester-based mixed liquid crystal, manufactured by Merck & Co., Inc.) to which the above additives are not added is -10 ° C to 80 ° C.
It was ℃.

On the other hand, the operating temperature range of the liquid crystal composition containing 11% by volume of n-butylcyclohexyne was −10 ° C. to about 50 ° C., and the upper limit was only lowered by about 30 ° C., which was still a practical range. When the addition ratio is less than the above, the operating temperature range condition is considered to be a larger value.

(5) Summary From the above, when n-butylcyclohexane is added in an amount of 5 to 11% by volume, the upper limit of the liquid crystal operating temperature range is lowered, but it is within a practical range, the current consumption is lowered, and the response speed is further increased. , The characteristics of liquid crystal are sufficiently maintained. Further, since the present composition contains up to 11% by volume of an inexpensive additive as compared with an expensive liquid crystal, it becomes an extremely inexpensive liquid crystal composition. In particular, if the composition is applied to a large-sized liquid crystal panel, the cost will be greatly reduced.

[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. 5 to 11
It is characterized in that a volume part of n-butylcyclohexane is blended.

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. Even if added in such a large amount, the characteristics of the liquid crystal can be maintained or improved, and the cost of the liquid crystal composition can be greatly reduced. Especially when the composition is applied to a large-sized liquid crystal panel, the cost reduction becomes extremely large.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the amount of n-butylcyclohexane added and the current consumption in Examples. FIG. 2 is a graph showing the relationship between the amount of n-butylcyclohexane added and the response speed in the examples. FIG. 3 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. A liquid crystal composition comprising 5 to 11 parts by volume of n-butylcyclohexane when the composition is 100 parts by volume. 2. The liquid crystal composition according to claim 1, wherein n-butylcyclohexane is 7 to 11 parts by volume when the liquid crystal composition is 100 parts by volume.