JP2001011452A - Electrooptical element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an element which has a wide nematic temperature range, stability against light and heat and high retention at a high temperature by making the element contain a compound having a 1,2,3,4- tetrahydronaphthalene-2,6-diyl group which may be substituted with a halogen. SOLUTION: A liquid crystal composition is a liquid crystal display element of STN-LCD or AM-LCD which has a structure of a liquid crystal's being placed between a pair of substrates and is provided with at least an orientation control layer, a transparent electrode and a polarizer. A 1,2,3,4- tetrahydronaphthalene-2,6-diyl group is represented by the formula (wherein U1 to U3 are each independently a hydrogen atom, a fluorine atom or a chlorine atom). The compound having the structure represented by the formula has a molecular weight of 150 to 600 and the liquid crystal composition preferably contains not less than 5% of the compound. The liquid crystal composition has a nematic-isotropic transition temperature (Tni), a dielectric anisotropy of not less than 3 and birefringence of 0.07 to 0.20.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an electro-optical device using a liquid crystal composition containing a compound having a 1,2,3,4-tetrahydronaphthalene-2,6-diyl group, and more particularly to an STN-LC.
D and AM-LCD.

[0002]

2. Description of the Related Art Since the emergence of liquid crystal display devices as calculator displays, in line with the development of computers, STNs (Supertwisted Nematic) have realized large display capacities that could not be achieved in the TN (Twisted Nematic) mode. It has been widely used as an interface between computers and humans, depending on the mode. The active matrix liquid crystal display (AM-LCD), which has a thin film transistor in each pixel, has high image quality that can be used as a CRT, and is expected to be the most promising display with the backing of flattening and energy saving. Have been.

In the AM-LCD, to increase the contrast,
A voltage is supplied to each pixel by attaching a switching element such as a thin film transistor or a diode to each pixel.

The AM-LCD differs from the TN / STN passive drive system in that each pixel passes through several tens of milliseconds through a switching element.
It is driven by supplying a charge every time. For this reason, if the given charge cannot be completely held until the next writing time several tens of milliseconds after the supply of the charge, the display deteriorates. When the charge escapes, the potential between the electrodes decreases, the transmitted light intensity changes, and the contrast decreases. For this reason, a high voltage holding characteristic is required in the AM-LCD. AM-LCD for high voltage holding characteristics
It is necessary to select and use a material that easily maintains a high specific resistance for the liquid crystal composition for use.

[0005] In recent years, the demand for notebook computers intended for portable use has increased.
N-LCD and AM-LCD are required to have characteristics that can withstand outdoor use. For this reason, it has excellent characteristics of high contrast at high temperature, no crystal precipitation at low temperature and no manifestation of smectic phase, and no deterioration of contrast or display failure even when left under exposure to UV light or sunlight. Although strongly sought, conventional liquid crystal compositions and liquid crystal display devices using them have not always met these requirements. In particular, the AM-LCD is susceptible to ambient contamination at high temperatures, making it difficult to maintain high resistance. For this reason, a stable liquid crystal composition having a high voltage holding ratio at a high temperature has been demanded at the same time as the above request.

That is, a liquid crystal composition and a liquid crystal display device which simultaneously satisfy a high nematic-isotropic transition temperature, a low crystal (or smectic) transition temperature, a low viscosity enabling high-speed response, and a high retention at a high temperature are required. Did not.

For example, WO9403558 discloses an example of a liquid crystal composition using a trifluoro compound and a difluoro compound, but has many problems such as a narrow liquid crystal temperature range and a high threshold voltage. At present.

[0008]

SUMMARY OF THE INVENTION It is an object of the present invention to satisfy various characteristics required for the above-mentioned liquid crystal optical element, and to have a wide nematic temperature range, a low viscosity and a high retention rate up to a high temperature. ST using a liquid crystal composition that can be maintained
An object of the present invention is to provide an N-LCD and an AM-LCD, or to provide a liquid crystal display device in which the above-mentioned disadvantages have been conventionally improved.

[0009]

The present invention will be described in detail below. Invention 1 A liquid crystal display device having a structure in which liquid crystal is sandwiched between a pair of substrates and having at least an alignment control layer, a transparent electrode, and a polarizing plate, wherein the liquid crystal may be substituted with halogen 1,2, 3,4-tetrahydronaphthalene-
An electro-optical element using a liquid crystal composition containing a compound having a 2,6-diyl group. Invention 2 The liquid crystal display device according to Invention 1, wherein the electro-optical element is a super twisted liquid crystal display element (STN-LCD) or an active driving liquid crystal display element (AM-LCD). Invention 3 The liquid crystal composition has a nematic-isotropic transition point (Tni) of 60 ° C or higher, a dielectric anisotropy of 3 or higher, 0.07
3. The electro-optical element or the liquid crystal display element according to the invention 1 or 2, having a birefringence of 0.2 to 0.20. Invention 4 The invention 1, in which the liquid crystal composition contains a compound having a 1,2,3,4-tetrahydronaphthalene-2,6-diyl group of two or more components.
4. The electro-optical element or liquid crystal display element according to 2 or 3.

1,2,3,4-tetrahydronaphthalene-2,6-diyl group of the formula (I)

[0011]

[Formula 1]

A compound having the formula (wherein U ¹ , U ² and U ³ each independently represent a hydrogen atom, a fluorine atom or a chlorine atom), is a compound which has been frequently used as a structure of a conventional liquid crystal compound. 1,4-cyclohexylene group (II) or 1,4-phenylene group (III)

[0013]

[Formula 2]

(The hydrogen atom on the ring may be replaced by halogen.) The nematic-isotropic transition temperature (TNi) is higher, and the melting point or the smectic-nematic transition temperature (TN) is higher. Since the temperature tends to be low, the liquid crystal has excellent characteristics such as a wide liquid crystal temperature range. The present invention has intensively studied the most suitable liquid crystal composition for STN-LCD and AM-LCD, and as a result, the electro-optical element using the liquid crystal composition containing the compound having the structure of the formula (I) has the above-mentioned properties. It has been found that means for solving the problems or the above-mentioned problems of the conventional electro-optical element can be reduced.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The feature of the present invention relates to an electro-optical element using a liquid crystal composition containing a compound having the structure of the formula (I), and particularly to an STN-LCD and an AM-LCD. The compound having the structure of the formula (I) can be a compound suitable for a wide range of applications by selecting other structural parts, but the composition containing the compound having the structure of the formula (I) has a wide nematic Temperature range, light and heat stability,
Electro-optic elements with high retention, especially STN-LCD and AM-LC
Very useful because D has favorable characteristics.

In the invention 1, the content of the compound having the structure of the formula (I) is preferably 5% or more, more preferably 10% or more, and the number of components is preferably 1 or more, more preferably 2 or more. The molecular weight of this compound is preferably in the range of 150 to 600, more preferably 500 or less, and the number of rings other than formula (I) of this compound is preferably 0 to 3, more preferably 0 to 2, and particularly preferably 1 to 2. . Further, the compound having the structure of the formula (I) further comprises a compound of the formula (V) or (VI)

[0017]

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(Wherein U ⁴ , U ⁵ , U ⁶ and U ⁷ each independently represent a hydrogen atom, a fluorine atom or a chlorine atom), and the compound contains an aromatic ring at its terminal. It is more preferable that the aromatic ring is substituted by a fluorine atom, and it is more preferable that the aromatic ring is substituted by a cyano group.

In the invention 3, the total number of components of the liquid crystal composition according to the invention 1 is preferably 8 or more, more preferably 10 or more, particularly preferably 15 or more, and Tni is 60 ° C. or more. ° C or higher, more preferably 70 ° C or higher, the dielectric anisotropy is 3 or higher, preferably 3.5 or higher, and the birefringence is in the range of 0.07 to 0.20, preferably 0.07 to 0.18.

Preferred compounds having the structure of formula (I) can be represented by formula (IVa) or (IVb).

[0021]

[Formula 4]

(Wherein R is an alkyl group having 1 to 15 carbon atoms or an alkenyl group having 2 to 15 carbon atoms, and this group is unsubstituted or has at least one halogen as a substituent. cage, and -O as if one or more CH ₂ groups are O atoms each independently present in the group not linked directly to one another -, - S -, - CO -, - COO- , -OC
It may be replaced by O- or -OCO-O-. Ring A, B, C are each independently, 1 or more CH ₂ groups not CH ₂ group or adjacent the present in group may be replaced by -O- and or -S- Trans-1,4-cyclohexylene group,
One CH group or two or more non-adjacent CH groups present in the group may be replaced with -N = 1,4-phenylene group, 1,4-cyclohexenylene, 1,4- Bicyclo (2.2.2) octylene, piperidine-1,4-diyl, naphthalene-2,6-diyl, decahydronaphthalene-2,6-diyl or 1,2,
Represents 3,4-tetrahydronaphthalene-2,6-diyl, which may be substituted with a cyano group or halogen.
Z ¹ and Z ² are each independently -COO-, -OCO-, -CH2O-, -O
CH2-, -CH2CH2-, -CH = CH-, -C≡C-, -CH2CH2CH2CH2-,-
CH = CH-CH2CH2-, -CH2CH2-CH = CH- or a single bond. X ¹ and X ^{2 each} have a ring C having a 1,4-phenylene group and naphthalene-2,6-
Diyl, in the case of a group selected from 1,2,3,4-tetrahydronaphthalene-2,6-diyl, each independently a hydrogen atom,
It is a fluorine atom or a chlorine atom, and the other groups represent a hydrogen atom. l, m and n each independently represent 0, 1 or 2, and l + m + n ≧ 1; U ¹ , U ² and U ³ each independently represent a hydrogen atom, a fluorine atom or a chlorine atom Y represents the same meaning as R, and represents a fluorine atom, a chlorine atom, a trifluoromethyl group, a trifluoromethoxy group, a difluoromethoxy group or a fluoromethoxy group. )
However, in the above description, when ring C is naphthalene-2,6-diyl, 1,2,3,4-tetrahydronaphthalene-2,6-diyl,

[0023]

[Formula 5]

Is

[0025]

[Formula 6]

## EQU1 ## More specifically, preferred compounds having the structure of formula (I) are the following compounds in formula (IV).

[0027]

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[0028]

[Formula 8]

[0029]

[Formula 9]

[0030]

[Formula 10]

(Wherein R has the same meaning as in formula (IV), and R ′ has the same meaning as R)

As described in the examples, the nematic phase-isotropic liquid phase transition temperature of the liquid crystal composition to which these compounds are added is higher than that of a similar compound having no structure of the formula (I). It is high, has a low solid phase-nematic phase transition temperature, and has excellent stability at low temperatures. The liquid crystal display element is often used outdoors where the temperature change is large, and in such a case, the liquid crystal display element of the present invention is extremely useful.

[0033]

EXAMPLES The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples. Further, “%” in the compositions of the following Examples and Comparative Examples means “% by weight”.

The characteristics measured in the examples are as follows.

Tni: Nematic phase-isotropic liquid phase transition temperature (° C.) T → _N : Solid phase or smectic phase-nematic phase transition temperature (° C) Vth: Threshold voltage (V) when a TN-LCD with a cell thickness of 6 μm is constructed Δε: Dielectric anisotropy Δn: Birefringence η: at 20 ° C Viscosity (cp)

The following abbreviations are used for describing the compounds.

[0037]

[Formula 11]

(In the formula, the stereo structure of the cyclohexane ring represents a trans form.)

[0039] _{E -COO- e -OCO- a -CH 2 CH} 2 - t -C≡C- CN -C≡N ( end group) F -F (end group) F attached to the ortho position of the f-terminal groups Atom OCF3 OCF ₃ (terminal group)

(Example 1 and Comparative Example 1) Nematic liquid crystal composition No. 1 for AM-LCD

[0041]

Embedded image

Table 1 shows the results of preparing an AM-LCD liquid crystal display device having the structure shown in FIG.

[0043]

[Table 1] Table 1. Example 1 and Comparative Example 1

As shown in Table 1, the liquid crystal display device for AM of No. 1 has a higher nematic phase-isotropic liquid phase transition temperature and a higher solid phase-nematic phase transition temperature than the display device of Comparative Example 1. It is understood that the liquid crystal display element operates as a liquid crystal display element in an extremely wide temperature range because of its excellent low temperature stability. FIG. 2 shows a temperature-contrast characteristic diagram of this display element. This graph shows that the display element of Example 1 has a contrast difference of about 2 at room temperature as compared with Comparative Example 1 and expands to 10 or more at 80 ° C. Further, the display element of Example 1 showed no image sticking and no display unevenness, and exhibited excellent characteristics as an AM liquid crystal display element.

Example 2 and Comparative Example 2 Nematic liquid crystal composition No. 2 for AM-LCD was prepared, and an AM-LCD liquid crystal display device having the structure shown in FIG. Are shown in Table 1 together with Comparative Example 2.

[0046]

[Table 2] Table 2. Example 2 and Comparative Example 2

As shown in Table 2, the AM liquid crystal display device of No. 2 also has a higher nematic phase-isotropic liquid phase transition temperature than the display device of Comparative Example 2 and thus has an extremely wide liquid crystal phase temperature range. It turns out that it works. In addition, the solid phase-nematic phase transition temperature is low and the stability at low temperatures is excellent. The CR of this liquid crystal display element was better than that of the comparative example, no image sticking and no display unevenness were observed, and exhibited excellent characteristics as an AM liquid crystal display element.

(Example 3 and Comparative Example 3) A liquid crystal composition No. 3 for STN-LCD was prepared, and a chiral substance "S-811" (manufactured by Merck) was added thereto to prepare a mixed liquid crystal. Unlike the AM-LCD liquid crystal display device, an organic film of "Sanever 610" (manufactured by Nissan Chemical Industries, Ltd.) is formed on the opposing flat transparent electrode of the STN liquid crystal display device with the structure shown in Fig. 1, and rubbing is applied. The liquid crystal composition No. 3 for STN-LCD whose twist angle was set and adjusted to 240 degrees was injected. The chiral substance was added so that the intrinsic helical pitch P of the mixed liquid crystal and the cell thickness d of the display cell by the addition of the chiral substance were Δn · d = 0.85 and d / P = 0.50. Table 3 shows the results of measuring various characteristics of the STN liquid crystal display element together with Comparative Example 3.

[0049]

[Table 3] Table 3. Example 3, Comparative Example 3

As shown in Table 3, the STN liquid crystal display device of No. 3 was also different from the liquid crystal display device of Comparative Example 3 in nematic phase.
It can be seen that the liquid crystal has a very wide liquid crystal phase temperature range because of its high isotropic liquid phase transition temperature. In addition, the solid phase-nematic phase transition temperature is low and the stability at low temperatures is excellent. The CR of this display element was better than that of Comparative Example 3, and no burn-in and display unevenness were observed in the display element.
It exhibited excellent characteristics as a liquid crystal display device.

Example 4 and Comparative Example 4 The following composition (B)

[0052]

Embedded image

Composition (A) as a compound having the structure of formula (I)

[0054]

Embedded image

10% was added to (B) to prepare composition No. 4. As a comparative example, the composition (a)

[0056]

Embedded image

10% was added to (B) to prepare a composition, which was designated as Comparative Example 4. Table 4 shows the physical property values of this composition (No. 4) and Comparative Example 4, and the physical property values when a display element was prepared.

[0058]

[Table 4] Table 4. Example 4 and Comparative Example 4

As shown in Table 4, it can be seen that the liquid crystal composition for STN-LCD of No. 4 also has a better liquid crystal temperature range than that of Comparative Example 4.

[0060]

According to the present invention, a liquid crystal composition having a wide liquid crystal phase temperature range of a combination of liquid crystal materials and a low crystal transition temperature provides excellent contrast at high temperatures and no crystal precipitation at low temperatures. was gotten. This liquid crystal display is very practical in both cases of STN-LCD and AM-LCD.

[Brief description of the drawings]

FIG. 1 shows an example of the structure of an electro-optical element according to the present invention.

FIG. 2 is a temperature-contrast characteristic diagram in Example 1 and Comparative Example 1.

[Explanation of symbols]

 1 Polarizer 2 Substrate 3 Transparent electrode or transparent electrode with active element 4 Alignment film 5 Liquid crystal

Continued on the front page F term (reference) 4H027 BA01 BB04 BC04 BD02 BD03 BD24 BE02 BE03 CB01 CB02 CC04 CD04 CL01 CL04 CM01 CM04 CN01 CN04 CP04 CQ01 CQ04 CR01 CR04 CT02 CT04 CW01 CW02 DE04 DK01 DK03 DK04 DK05 DM04

Claims (4)

[Claims] 1. A liquid crystal display device having a structure in which liquid crystal is sandwiched between a pair of substrates and having at least an alignment control layer, a transparent electrode, and a polarizing plate, the liquid crystal may be substituted by halogen. An electro-optical element using a liquid crystal composition containing a compound having a 2,3,4-tetrahydronaphthalene-2,6-diyl group. 2. The liquid crystal display element according to claim 1, wherein the electro-optical element is a liquid crystal display element for super twisting (STN-LCD) or a liquid crystal display element for active driving (AM-LCD). 3. The electro-optical device according to claim 1, wherein the liquid crystal composition has a nematic-isotropic transition point (Tni) of 60 ° C. or more, a dielectric anisotropy of 3 or more, and a birefringence of 0.07 to 0.20. Element or liquid crystal display element. 4. The electro-optical element or liquid crystal display according to claim 1, wherein the liquid crystal composition contains a compound having two or more components having 1,2,3,4-tetrahydronaphthalene-2,6-diyl group. element.