JPH0717909B2 - 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 M method. As the liquid crystal composition used in this DSM method, a liquid crystal composition in which a dynamic scattering mode is generated when this 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-60-21392
No. 9 bulletin).

[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 often increased in order to reduce display unevenness due to uneven 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.

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. However, in this case, the characteristic is 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 10 to 17 parts by volume of n-tetradecane (hereinafter, simply referred to as tetradecane) when the 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. Further, when the addition ratio of tetradecane is less than 10% by volume, the current consumption increases, and when it exceeds 17% by volume, the additive and the liquid crystal are separated from each other and are not 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 tetradecane (special grade reagent) were mixed at various ratios (0, 4, 7, 10, 13, 17% by volume) shown in FIG. 1 to prepare a predetermined liquid crystal composition. Here, volume%
The term "added volume% of tetradecane" (hereinafter simply referred to as "%") when the liquid crystal composition is 100% by volume. Again 17
If it is added in excess of%, the additive and the liquid crystal are separated from each other and are not uniform.

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 current consumption AC voltage 30V (64H
The current consumption when z) was applied was measured, and the relationship between the amount of tetradecane 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 begins to decrease.
An inflection point was shown in%, and reached saturation at 13%. From the above,
When the added amount was 10 to 17%, the current consumption was almost the same as that in the case where it was not added, or the increase was slight. In particular, in the case of 13 to 17%, the current consumption was almost the same as that in the case without addition.

(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 increases as the amount of addition is increased, and the response is almost saturated at about 7%. To do.
When the added amount is 10%, the response speed is 2.4 times faster when voltage is applied, 2.3 times faster when no voltage is applied, and 2.7 times faster when not applied when 17%.

(4) 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 17% of tetradecane was −10 ° C. to 52 ° C., and the upper limit was only lowered by about 30 ° C., which was still a practical range. If the addition ratio is less than the above, the upper limit of the operating temperature range is considered to be a larger value.

(5) Summary From the above, when tetradecane is added in an amount of 10 to 17% by volume, the upper limit of the liquid crystal operating temperature range is lowered, but it is in a sufficiently practical range, the current consumption is lowered, and the response speed is 2.3 to
It is about 2.7 times faster and maintains the liquid crystal characteristics sufficiently. Furthermore, since the present composition contains up to 17% 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 10 to 17
It is characterized by being mixed with tetradecane in the capacity part.

On the other hand, in the conventional liquid crystal composition, the amount of the additive compounded for improving the characteristics 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. 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.

In addition, the present composition consumes less current and can increase the response speed, and therefore is extremely preferable for a DSM type liquid crystal composition which generally 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 tetradecane added and the current consumption in Examples. FIG. 2 is a graph showing the relationship between the amount of tetradecane 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 10 to 17 parts by volume of n-tetradecane when the composition is 100 parts by volume. 2. The amount of n-tetradecane is 13 to 17 parts by volume when the liquid crystal composition is 100 parts by volume.
Item 6. A liquid crystal composition according to item.