JPH09143472A - Liquid crystal composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a guest-host-type liquid crystal composition realizing high- contrast display and low-voltage driving and useful for a liquid crystal display apparatus of an active matrix-type by compounding a liquid crystal raw material with adichroic pigment and suppressing the metal content below a specified value. SOLUTION: This liquid crystal composition is obtained by compounding (A) a liquid crystal raw material of a biphenyl, a phenylcyclohexane, etc., exhibiting a nematic phase or a smectic phase with (B) a dichroic pigment such as an azo or an anthraquinone. The liquid crystal raw material is purified by removing metals through distillation, recrystallization, absorption column chromatography, zone purification, etc., so that the total amounts of metals (e.g. Na, K, Fe, Al, Ca, Mg, Ni, Cu and Cr) included in the composition is suppressed below 50ppb.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal composition containing a liquid crystal material and a dichroic dye, which is used in a guest-host liquid crystal display device.

[0002]

2. Description of the Related Art As one of liquid crystal display systems, there is a guest-host system using a dichroic dye. This uses a liquid crystal composition in which a so-called dichroic dye having anisotropy in absorption of visible light in the major axis direction and the minor axis direction of a molecule is mixed with a liquid crystal material. This guest-host method has a feature that the viewing angle is wider than that of the method that uses the most general polarizing plate in the past and that light utilization efficiency is high because the polarizing plate does not need to be used. This is a great advantage when applied to various types of information devices such as liquid crystal televisions, especially portable devices.

By the way, a liquid crystal material used for such a liquid crystal composition is required to have a high degree of electrical insulation in order to be driven at a low voltage. A method for removing or purifying low molecular impurities or ionic impurities in a liquid crystal material composed of anions such as sulfate ion, nitrate ion, nitrite ion, and chlorine ion has been proposed (JP-A-50-1774, JP-A-58-1774, JP-A-62-210419,
See Japanese Patent Laid-Open No. 64-87685 and the like).

[0004]

However, in recent years, thin film transistors (TFTs) and MIMs (metal insulators) have been developed.
With the widespread use of active matrix type liquid crystal display devices using (e.g., et al.), the properties required for liquid crystal materials have become significantly more advanced. It was not possible to obtain sufficiently satisfactory results for the demand for contrast.

That is, the order parameter (S) indicated by how orderly the molecular alignment of the liquid crystal material is aligned with respect to the ideal alignment, that is, the deviation of the long axis of the liquid crystal molecules from the ideal alignment direction (director). In the case of a guest-host type liquid crystal composition in which a dichroic dye is dissolved, it is considered to be an important index of its performance. Is not suggested at all,
Further, as in this prior art, if the ionic impurities in the liquid crystal material are simply removed, the order parameter (S)
It was not possible to obtain a high-contrast high-contrast color liquid crystal display device.

[0006]

DISCLOSURE OF THE INVENTION As a result of intensive studies on these problems, the present inventors have found that, in particular, in a guest-host type liquid crystal composition used in a color liquid crystal display device,
In the entire liquid crystal composition including the dichroic dye, it has been found that the above-mentioned drawbacks can be solved by reducing the total content of metals that have not been noticed in the past among ionic impurities to an extremely small amount. Came to.

That is, the present invention relates to a liquid crystal composition used in a guest-host liquid crystal display system in which a dichroic dye is mixed with a liquid crystal material, and the total amount of metals contained in the liquid crystal composition is less than 50 ppb. The present invention relates to a liquid crystal composition characterized by the above. In the present invention, an impurity metal that is highly likely to be mixed in the dichroic dye that is always used in the guest-host liquid crystal composition is contained in a specific amount or less from the entire liquid crystal composition containing the liquid crystal material. The purpose is to be achieved by removing it in a quantity.

It has been found that when the amount of these metal impurities is 50 ppb or more, the order parameter of the liquid crystal composition is lowered, which causes a reduction in contrast when incorporated in a liquid crystal display device. It is speculated that the cause of this order parameter decrease is that the thermal energy generated by the charge and the kinetic energy of the molecules during the alignment of the liquid crystal composition causes the metal molecules of the impurities to serve as the heat medium and causes a partial alignment disorder. To be done.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, the metals contained as impurities in the liquid crystal composition are particularly Na, K and Fe.
Has a large effect, but in addition, for example, Al, Ca, Mg,
Metals such as Ni, Cu, and Cr may be contained, and if the sum of any of them is out of the range of the present invention, it is difficult to obtain a liquid crystal composition with high contrast. Becomes

The means for controlling the content of these metals in the liquid crystal composition to less than 50 ppb, which is a requirement of the present invention, is not particularly limited.
Alternatively, after mixing these constituent materials, the content metal content is analyzed by ICP-MS (inductively coupled high frequency argon plasma mass spectrometer) etc. by a method exemplified below or a combination thereof. The value is 50
It is carried out under conditions such that the amount is very small, less than ppb.

That is, specifically, evaporation and concentration are repeated,
Distillation method that separates into components that easily evaporate and components that do not easily evaporate; after dissolving in a solvent in which the object to be purified is dissolved (hereinafter referred to as a solution), add a poor solvent or lower the temperature to adjust the solubility. Recrystallization method to obtain impurities-free crystals by difference; Column chromatography method in which impurities are removed by contacting a solution with activated alumina, silica gel, calcium carbonate, calcium hydroxide, etc. as an adsorbent; There is a zone refining method for removing impurities by repeating the compounding step (see Liquid Crystal Manufacturing Method and Application, P98-99, (1974)). In addition, without using the adsorbent used in the column chromatography method,
There is also a method in which the adsorbent is separated by filtration or the like after simply contacting the solution with stirring.

However, in order to achieve the present invention, even if these methods are combined or carried out by a single method, as described above, the content is in a very small range of less than 50 ppb, It is necessary to perform sufficient separation and purification. The dichroic dye used in the present invention generally has good solubility in liquid crystals, does not impair the performance of liquid crystal materials,
Azo-based, anthraquinone-based, merocyanine-based, styryl-based, azomethine-based, tetrazine-based, quinophthalene-based, perylene-based, indigo-based, thioindigo-based, which have anisotropy in visible light absorption in the major axis direction and the minor axis direction of the molecule Examples thereof include dyes exemplified in Table 1 below, and among them, azo and anthraquinone dyes are particularly preferable.

[0013]

[Table 1]

[0014]

[Table 2]

[0015]

[Table 3]

In the formulas in Table 1, X, Y and Z represent an alkyl group, an alkoxy group, a cyano group and a halogen atom. Further, the hydrogen atom may be substituted with an aromatic ring such as a benzene ring, an aliphatic ring such as a cyclohexane ring, a methyl group, a cyano group, a halogen atom or the like. Moreover, these dichroic dyes may be blended in the liquid crystal composition as a single item, but may be blended in plural kinds as necessary. The procedure at that time is to mix and dissolve a plurality of dichroic dyes in the liquid crystal material first,
The dichroic dyes may be sequentially mixed and dissolved one by one in the liquid crystal material.

The "metal content" in the present invention refers to the total amount in the entire liquid crystal composition including the liquid crystal material and the compounded dichroic dye. The total amount of these dichroic dyes in the liquid crystal composition is usually about 0.5 to 10% by weight, preferably 2% by weight.
It is mixed and dissolved at a ratio of about 7% by weight. Further, the liquid crystal material in the present invention is not only a substance exhibiting liquid crystallinity,
Including those containing various additives such as chiral dopants and viscosity modifiers, specifically, [Liquid Crystal Device Handbook; Japan Society for the Promotion of Science, 142nd Ed. (1989); p.
154 to 192, p715 to 722], and various liquid crystal materials such as a biphenyl-based or phenylcyclohexane-based liquid crystal material exhibiting a nematic or smectic phase.

In the present invention, a fluorine system suitable for an active matrix type liquid crystal display device, for example, in which the terminal groups R and X shown in Table 2 below are substituted with a fluorine atom, a fluoroalkyl group, a fluoroalkoxy group or the like. It is particularly preferable to use it in a liquid crystal composition mainly composed of a liquid crystal material. In this liquid crystal composition, a compound that does not exhibit a liquid crystal phase (that is, does not exhibit a dielectric anisotropy), but is compatible with the liquid crystal material and has a role of adjusting the viscosity or the liquid crystal temperature. , Especially R and X of the terminal groups in Table 2 have 1 carbon atoms
It may contain a compound such as an alkyl group or an alkoxy group having 10 to 10, preferably 3 to 8 carbon atoms.

[0019]

[Table 4]

The liquid crystal composition of the present invention is prepared by dissolving the above dichroic dye in a liquid crystal material containing various additives as necessary. Then, this liquid crystal composition is enclosed in a liquid crystal cell constituted by opposing two substrates each having at least one transparent electrode with a minute gap (space) therebetween, to form a liquid crystal display device (element). To be done. The liquid crystal cell or device may be provided with an alignment film, an active element, or the like depending on the driving method or the like.

[0021]

EXAMPLES The present invention will be described in detail with reference to the following examples, but the present invention is not limited to the following examples as long as the gist thereof is not exceeded. Example 1 First, a dichroic dye shown in Table 3 below was dissolved in a phenylcyclohexane liquid crystal material (trade name: ZLI-1565, manufactured by E. Merck & Co., Inc.) to a concentration of 1% by weight. A liquid crystal composition was prepared. After coating and curing the liquid crystal composition with a polyimide resin on a substrate,
A glass substrate with a transparent electrode, which had been rubbed, was sealed in a cell constituted by facing each other with a gap of 9 μm, and a liquid crystal display element was produced.

The absorbance (A //) of the liquid crystal display device for linear deflection parallel to the alignment direction and the absorbance (A⊥) for linear deflection perpendicular to the alignment direction were measured. The order parameter (S) at the absorption peak (λmax) was calculated by the following formula.

[0023]

S = (A // − A⊥) / (A // + 2A⊥)

The amount of metal in the composition is ICP-MS.
(Inductively coupled high frequency argon plasma mass spectrometer). The above results are shown in Table 3 below.

[0025]

[Table 5] * Dichroic dye Dye I: Azo dichroic dye, trade name "LSY-116", Mitsubishi Chemical Corp. product Dye II: Anthraquinone dichroic dye, trade name "LSB-335", Mitsubishi Chemical ( Products)

Example 2 In the same manner as in Example 1, the dichroic dye was mixed with a fluorine-based liquid crystal material (trade name: ZLI-479).
(2, product of E. Merck) and evaluated.

[0027]

[Table 6] * Dichroic dye Dye I: Azo dichroic dye, trade name "LSY-116", Mitsubishi Chemical Corp. product Dye II: Anthraquinone dichroic dye, trade name "LSB-335", Mitsubishi Chemical ( Products)

[0028]

INDUSTRIAL APPLICABILITY The present invention relates to a guest-host liquid crystal composition suitable for an active matrix color liquid crystal display device, and is capable of high contrast display and low voltage driving. is there.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location C09K 19/60 9279-4H C09K 19/60 J 9279-4H Z G02F 1/13 500 G02F 1/13 500 1/137 500 1/137 500 (72) Inventor Ryoko Kuramoto 1-1 Kurosaki Shiroishi, Hachiman Nishi-ku, Kitakyushu City, Fukuoka Prefecture Mitsubishi Chemical Corporation Kurosaki Development Laboratory

Claims (1)

[Claims] 1. A guest-host type liquid crystal composition comprising a liquid crystal material and a dichroic dye, wherein the total amount of metals contained is less than 50 ppb.