JPH0717910B2 - 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 method, a liquid crystal composition that sandwiches the liquid crystal composition between transparent electrodes and applies a constant voltage to generate a dynamic scattering mode, that is, a DSM type liquid crystal composition is used. To be (JP-A-60-2
No. 13929 gazette) [Problems to be solved by the invention] When this DSM type liquid crystal composition is applied to a large-sized display element, a large area is used, and a cell gap is increased to reduce display unevenness due to nonuniformity of the gap. I often do it. 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. A (Dynamic Scattering Mode) type liquid crystal composition is characterized by containing 1 to 7 parts by volume of di-2-ethylhexyl adipate 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. When the addition ratio of di-2-ethylhexyl adipate 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 it exceeds 7% by volume, the additive and the liquid crystal are separated and not uniform.

The liquid crystal composition also includes an electrolyte compound, Leitsalz235.
Various additives for improving the practical properties of liquid crystal such as (manufactured by Merck & Co., Inc.) can be blended according to 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 di-2-ethylhexyl adipate (special grade reagent) were mixed at various ratios (0, 1, 4, 7% by volume) shown in FIG. 1 to prepare a predetermined liquid crystal composition. In addition,
Here, the volume% means the volume% of di-2-ethylhexyl adipate added when the liquid crystal composition is 100% by volume. When the content exceeds 7% 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 the liquid crystal alignment film, and the alignment treatment is
The rubbing treatment was performed so as to be homogeneous.

(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 increases as the addition rate increases, and in each case of 1, 4 or 7% it is 1.2, 1.9 or 2.5 times faster than in the case of no addition.

(3) 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.) in 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 7% by volume of di-2-ethylhexyl adipate was -10 ° C to about 50 ° 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, when 1% to 7% by volume of di-2-ethylhexyl adipate is added, the upper limit of the liquid crystal operating temperature range is lowered, but it is in a sufficiently practical range and the response speed is increased.
Furthermore, since the present composition contains up to 7% 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 1 to 7 for parts
The present invention is characterized in that a capacity part of di-2-ethylhexyl adipate 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. By adding such a large amount, 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, the 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, this is extremely preferable for a DSM type liquid crystal composition which consumes more energy and has 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 di-2-ethylhexyl adipate added and the response speed in 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. A liquid crystal composition comprising 1 to 7 parts by volume of di-2-ethylhexyl adipate when the composition is 100 parts by volume. 2. The liquid crystal composition according to claim 1, wherein di-2-ethylhexyl adipate is 4 to 7 parts by volume when the liquid crystal composition is 100 parts by volume.