JPH0978068A - Liquid crystal composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a guest-host-type liquid crystal composition free from the lowering of solubility of a dichroic pigment in a liquid crystal material and capable of keeping a high absorbance and suitable for a color liquid-crystal- display apparatus by compounding the liquid crystal material with the dichroic pigment so that the total content of metals is at a specified amount. SOLUTION: A liquid crystal material such as a biphenyl compound or a phenylsiloxane compound exhibiting a nematic or smectic phase is compounded with a dichroic pigment of a compound of the formula, etc., preferably in an amount of 0.5-10wt.%, so that the total amount of contained metals such as Na, K and Fe is in the range of 50-1000ppb.

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 spread of active matrix type liquid crystal display devices using (etal) etc., the properties required for liquid crystal materials have also become significantly more advanced.
There is a demand for higher electrical insulation properties and a demand for high reliability such as storage stability for a long period of time including the state of being incorporated in a liquid crystal display device.

In the case of a guest-host liquid crystal composition in which a dichroic dye is dissolved, the solubility of the dichroic dye in the host liquid crystal material is important. In particular, the host liquid crystal material of the liquid crystal composition used in the above active matrix type liquid crystal display device is often a fluorine-based compound, which is generally dichroic as compared with a conventional cyano-based liquid crystal material. Dye solubility is low. When the solubility of the dye is low, the amount of the dye used is limited and a sufficient coloration state cannot be obtained, or the dye is deposited at a low temperature and cannot be used as a display.

[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,
Impurities of metals in liquid crystal compositions including dichroic dyes are related to their storage stability, and when the content is within a specific range, the solubility of dichroic dyes in liquid crystal materials is improved. The inventors have found that they can do so and have reached the present invention.

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 50 ppb or more and 1000 ppb or less. The present invention relates to a liquid crystal composition characterized in that When the amount of these metal impurities exceeds 1000 ppb, the absorption of the liquid crystal composition is lowered. This is because in the presence of a metal, the metal acts as an oxidation catalyst to decompose the liquid crystal material and adversely affect the dichroic dye, or the dichroic dye is directly decomposed, and It is considered that the coloring state of the pigment may be inhibited.

Further, when this liquid crystal composition is incorporated in a liquid crystal display device, if the amount of metal impurities exceeds 1000 ppb, the leak current when a voltage is applied becomes large, and in this case, the drive voltage is compared with the threshold voltage. Inevitably, the liquid crystal display element consumes less power, which is the greatest feature. If the amount of these ionic impurities is less than 50 ppb, the solubility of the dichroic dye dissolved in the liquid crystal composition tends to decrease, and the amount of the dichroic dye used must be reduced. In some cases, the dichroic dye may not be obtained or may be unusable as a liquid crystal display device during storage at low temperature.

[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 having excellent storage stability.

The content of these metals in the liquid crystal composition is 50
The object of the present invention is achieved if the content is ppb or more and 1000 ppb or less, but the content is 50 ppb or more and 300 ppb.
It is more preferable that it is b or less because the solubility of the dichroic dye is not decreased and the absorbance is hardly decreased which is considered to be caused by decomposition of the dichroic dye. The means for adjusting the content of the metal, which is a requirement of the present invention, to 50 ppb or more and 1000 ppb or less is not particularly limited, but is exemplified below for each of the constituent materials of the liquid crystal composition or after mixing these constituent materials in advance. Any method or a combination thereof may be used.

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.

The dichroic dye used in the present invention generally has good solubility in liquid crystal, does not impair the performance of the liquid crystal material, and absorbs visible light in the major axis direction and the minor axis direction of the molecule. Anisotropic dyes such as azo, anthraquinone, merocyanine, styryl, azomethine, tetrazine, quinophthalene, perylene, indigo, and thioindigo are listed in Table 1 below. However, of these, 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, among these liquid crystal materials, particularly suitable for active matrix type liquid crystal display devices, for example, the terminal groups shown in Table 2 below are fluorine atoms,
It is particularly preferable to use it in a liquid crystal composition mainly composed of a fluorine-based liquid crystal material substituted with a fluoroalkyl group or a fluoroalkoxy group. 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. In particular, the terminal groups R and X in Table 2 have 1 to 10 carbon atoms, preferably 3 carbon atoms.
The compound may be an alkyl group, an alkoxy group or the like of 8 to 8.

[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 sealed in a liquid crystal cell constituted by facing two substrates having at least one transparent electrode through a minute gap (space), and a liquid crystal display device (element) is formed. Composed.
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. First, 5 parts by weight of each of the dichroic dyes shown in Table 3 below was dissolved in 100 parts by weight of a fluorinated liquid crystal material (trade name: ZLI-4792, manufactured by E. Merck & Co., Inc.) and shaken at 25 ° C for 1 hour.・ Observe the insoluble matter in the mixed solution after stirring with a microscope of 50 times, and if there is an obvious insoluble matter, compatibility x, if there is an extremely small amount of insoluble matter △, if no insoluble matter is observed, ○ It was evaluated.

Further, the liquid crystal composition was exposed to a temperature of 80 ° C. for 30 days, dissolved in chloroform, and given a predetermined concentration (dye I: 7 ppm, dye II: 14 ppm) in terms of dye.
Prepare the solution so that it becomes, and use a spectrophotometer to measure the absorbance (λmax
Was measured. The amount of metal in the composition is IC
It analyzed by P-MS (dielectric coupling high frequency argon plasma mass spectrometer).

The above results are shown in Table 3 below. As a result, when the metal content was less than 50 ppb, the solubility of the dye in the liquid crystal composition was low, and precipitation of insoluble matter was observed. When the amount is more than 1000 ppb, insoluble matter is not observed, but the absorbance of the solution in which the liquid crystal material and the dye are dissolved is reduced W, and a large amount of metal may adversely affect the coloring of the dye. Recognize.

[0024]

[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)

[0025]

INDUSTRIAL APPLICABILITY The present invention relates to a guest-host type liquid crystal composition which is particularly suitable for an active matrix type color liquid crystal display device, and the solubility of a dichroic dye in a liquid crystal material is not lowered and is high. The absorbance can be maintained,
Moreover, it can be driven at a low voltage.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical indication location C09K 19/60 9279-4H C09K 19/60 J 9279-4H Z (72) Inventor Ryoko Kuramoto Fukuoka Prefecture 1-1 Kurosaki Shiroishi, Hachimannishi-ku, Kitakyushu City 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 in the range of 50 ppb to 1000 ppb.