JP2003129052A - Liquid crystal display element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid crystal display element excellent in display quality without giving a flicker of an image and an afterimage. SOLUTION: This element is characterized in that a liquid crystal material is intercalated between two substrates wherein at least one substrate has transparency, one of the substrate has active elements which can drive two or more pixel electrodes and each pixel electrode and continuously supply an electric current to the pixel electrode for a period of a frame cycle and the liquid crystal material contains a compound having a cyano group and an isothiocyanate group in a content of 10-80 mass%.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a liquid crystal display element driven by an active element.

[0002]

2. Description of the Related Art A liquid crystal display device driven by a TFT (thin film transistor) active element has a higher contrast and response speed than passive type TN (twisted nematic) or STN (super twisted nematic) type liquid crystal display elements. And is widely used in televisions, notebook computers, etc. In order to further expand the field of application of the active drive liquid crystal display device in the future, it is necessary to improve the slow response speed as compared with a display device using a cathode ray tube.

In order to improve the response speed of the active driving liquid crystal display element, it is most effective to improve the response speed of the liquid crystal material, but it is becoming difficult to improve the liquid crystal material.

In the current active driving liquid crystal display element, since a high voltage holding ratio is essential for the liquid crystal material in terms of the element structure, a fluorine-based liquid crystal having a fluorine atom, a chlorine atom, OCF _3, etc. as a polar group. The reason is that only liquid crystal materials called ".

Since only a fluorine atom or a chlorine atom can be used as a polar group, the types of chemical structures of liquid crystal materials are limited. As long as liquid crystal materials having these limited chemical structures are used, they are required for liquid crystal display devices. However, there is a limit in improving the response speed, reducing the driving voltage, and expanding the operating temperature range of the display element. We are facing the problem that it is difficult to achieve a large improvement in characteristics while balancing these characteristics at a high level.

On the other hand, a technique capable of solving the retention problem is disclosed in Japanese Patent Laid-Open No. 11-326958. This is an element structure capable of continuously supplying current to the pixel electrode during the frame period. Therefore, it has become possible to reduce the limitation on the voltage holding ratio, which is essential for conventional devices. However, as compared with the conventional device, it is difficult to discharge the charges charged in the pixel electrode, so that there is a problem that an afterimage occurs and it is difficult to obtain a clear image. This problem is disclosed in JP-A-5-107561 by devising a driving method or devising a device circuit such as inserting a resistor for discharging. However, the cost and the aperture related to the brightness of the device are disclosed. There was a problem that the rate was sacrificed.

[0007]

SUMMARY OF THE INVENTION The present invention is an excellent liquid crystal display device using an active element capable of continuously supplying a current during a frame period, in which there is no image flicker and no afterimage. To provide a display.

[0008]

DISCLOSURE OF THE INVENTION As a result of intensive studies made by the present inventors in order to solve the above-mentioned problems, a liquid crystal display using an active element capable of continuously supplying a current during a frame period is obtained. In the device, it was found that the problem can be solved by using a specific compound for the liquid crystal material, and the present invention has been completed.

That is, according to the present invention, in a liquid crystal display element in which a liquid crystal material is interposed between two substrates, at least one of which is transparent, an active element for operating a plurality of pixel electrodes and each pixel electrode on one of the substrates. An element, the active element is capable of continuously supplying a current to the pixel electrode during a frame period,
The liquid crystal material has the general formula (I)

[0010]

[Chemical 4]

(Where R¹Is an alkyl group having 1 to 10 carbon atoms
Or an alkenyl group having 2 to 10 carbon atoms,
Or the alkenyl group is unsubstituted or substituted with
One or more F, Cl, CN, CH₃Or CF₃Have
Present in the alkyl or alkenyl group
1 or 2 or more CH₂The groups are O atoms directly linked to each other.
If not, it may be substituted with O, CO or COO
Ring A and ring B are each independently 1,4-phenylene, 2
Or 3-fluoro-1,4-phenylene, 2,3-difluoro-1,4-
Phenylene, 3,5-difluoro-1,4-phenylene, 2 or 3-
Chloro-1,4-phenylene, 2,3-dichloro-1,4-phenylene
1,3,5-dichloro-1,4-phenylene, pyrimidine-2,5-di
Yl, pyridine-2,5-diyl, trans-1,4-cyclohexyl
Siren, trans-1,4-cyclohexenylene, trans-
1,3-dioxane-2,5-diyl, trans-1-sila-1,4-si
Chlohexylene, trans-4-sila-1,4-cyclohexyl
Naphthalene-2,6-diyl, 1,2,3,4-tetrahydrona
Phthalene-2,6-diyl, decahydronaphthalene-2,6-diyl
Group, phenanthrene-2,7-diyl group or fluorene-2,7-
Represents a diyl group, naphthalene-2,6-diyl and 1,2,3,4-
Is tetrahydronaphthalene-2,6-diyl unsubstituted?
Or one or more F, Cl, CF as a substituent₃, OCF₃or
Is CH₃Where i represents 0, 1 or 2 and Y¹Over
And Y²Are each independently a single bond, -COO-, -OCO-, -CH₂O
-, -OCH₂-, -CH = CH-, -CF = CF-, -C≡C-,-(CH ₂)₂-,-(C
H₂)_Four-, -CH = CH- (CH₂)₂-,-(CH₂)₂-CH = CH-, -CH = N-, -CH
= N-N = CH- or -N (O) = N-, Z¹And Z²Are independent
H, F, Cl, CF₃Or OCF₃X represents -CN, -NCS
You ) Containing 1 to 20 kinds of compounds of 10 to 80 mass%
A liquid crystal display device characterized by the above.

A liquid crystal material containing a compound having a cyano group or an isothiocyanate group represented by the general formula (I) generally has a poor voltage holding ratio, so that it can be continuously used during a frame cycle which is currently widely used. An active element that cannot supply a current (hereinafter, referred to as active element 1) cannot perform good image display such as display failure such as image flicker.

When a voltage is applied to the pixel electrode, an active element (hereinafter, referred to as active element 2) that continuously supplies a current to the pixel electrode even during the period of the frame cycle is expressed by the general formula (I). A liquid crystal material containing the represented compound enables good display without flicker.
However, when the compound represented by the general formula (I) is contained in an amount of 80% by mass or more, flicker also occurs in the active element 2.

Further, in the active element 2, an afterimage becomes remarkable when a fluorine-based liquid crystal material is used. But the general formula
A liquid crystal material containing the compound represented by (I) can achieve excellent display without an afterimage. An afterimage is observed when the content of the compound represented by formula (I) is less than 10% by mass. Therefore, in the active element 2, by using a liquid crystal material containing 10% by mass to 80% by mass of the compound represented by the general formula (I), there is no image flicker and an excellent display without afterimage is provided. can do.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION The liquid crystal display device of the present invention will be described in more detail.

(Transparent Substrate) Examples of the transparent substrate include plastics such as polycarbonate and polyethylene terephthalate, glass, and the like, and examples of the nontransparent substrate include a silicon substrate. You can When a silicon substrate is used, the active element may be directly formed on the substrate.
In addition to the liquid crystal material, a color filter for enabling color display and an optical functional layer for the purpose of improving visibility, such as a light scattering film, may be interposed between the two substrates. .

(Distance between substrates) The distance d between two substrates is
Generally, it can be selected in the range of 1 to 50 μm.
From the viewpoint of achieving both high-speed display and high contrast, 1 to 8 μm is preferable, and 2 to 6 μm is particularly preferable. OCB
In the mode (bend orientation), the distance between the two substrates is 1 to 6
and the pretilt angle on the substrate is preferably 2 to 10 °. More preferably, the distance between the substrates is 2 to 4 μm, and the pretilt angle on the substrates is 3 to 7 °.

(Liquid Crystal Material) In the liquid crystal display device of the present invention, the liquid crystal material interposed between two substrates, at least one of which is transparent, exhibits a nematic liquid crystal phase, a chiral nematic liquid crystal phase or a chiral smectic C phase. A material is preferably used, and a nematic phase or a chiral nematic phase is more preferable. As the display mode of the liquid crystal display element,
TN (Twisted Nematic) mode and STN (Super Twisted Nematic) mode with a twist structure of 0 to 360 degrees, ECB (Electric
ally Controlled Birefringence mode, OCB (Opticall
y Compensated Birefringence) mode, surface-stabilized ferroelectric liquid crystal mode, and PD combined with polymer resin
LC (Polymer Dispersed Liquid Crystal) mode, PNLC (P
Olymer Network Liquid Crystal) mode, polymer-stabilized ferroelectric liquid crystal mode, etc. Among these, it is preferable to use the TN or OCB mode from the viewpoint of enabling high-speed display.

In the TN mode, the twist angle is preferably in the range of 0 to 180 degrees, more preferably 40 to 110 degrees, particularly preferably 45 to 100 degrees. The pretilt angle is preferably 0 to 15 degrees, more preferably 2 to 10 degrees,
Particularly preferred is 3 to 7 degrees. Distance d between substrates of LCD
And the refractive index anisotropy of liquid crystal material Δn, Δn ・ d is 0.1 to 1.6 μm
Is preferable, and it is more preferable that it is 0.1 to 0.6 μm. In particular, when applied to a television, it is preferable to adjust the product Δn · d of the distance d between the substrates of the liquid crystal display element and the refractive index anisotropy Δn of the liquid crystal material within the range of 0.35 to 0.42. When applied to a mold, it is preferable to adjust the range of 0.12 to 0.35.

In STN mode, the twist angle is 180-27
It is preferably in the range of 0 degrees. The pretilt angle is preferably 3 to 10 degrees, more preferably 4 to 9 degrees. △ n ・ d is 0.6 to 1.2
The thickness is preferably μm, more preferably 0.7 to 0.9 μm.

When the twist angle is set to be larger than 270 degrees, the pretilt angle is preferably 0 to 15 degrees, and 2 to 10 degrees.
Is more preferable, and 3 to 7 degrees is particularly preferable. The product of the distance d between the substrates of the liquid crystal display device and the refractive index anisotropy Δn of the liquid crystal material Δn
n ・ d is preferably 0.3 to 2.5 μm, 0.4 to 1.6 μm
Is more preferable.

(Active element) An active element capable of continuously supplying a current to a pixel electrode even during a frame period is disclosed in, for example, Japanese Patent Laid-Open No. 5-107561.
As described in the publication, a voltage supply line is provided in addition to a selection line and a signal line, two transistors are provided for one pixel, the gate of the first transistor is connected to the selection line, and the source is connected. Or one of the drains is connected to the signal line, one of the source or drain of the second transistor is connected to the voltage supply line, the other of the source or drain is connected to the pixel electrode, the source or drain of the first transistor It can be realized by connecting the other to the gate of the second transistor. This concrete circuit diagram is shown in FIG. In addition to these, 27 of the 83rd meeting of the Society of Japan Society for the Promotion of Science "Organic Materials for Information Science, 142nd Committee A Section" (Liquid Crystal Materials)
It is also possible to realize the device configurations as described in paragraphs (1) to (34). This concrete circuit diagram is shown in FIG.

The active element according to the present invention can have two or more transistors for one pixel. As a result, it is possible to provide a driving method that emphasizes display quality. Further, as for the plurality of pixel electrodes on the substrate forming the liquid crystal element and the active element for operating each pixel electrode, the layout as shown in FIG. 3 which is currently widely used can be used without particular limitation. Also,
Active elements are 2 pixel electrodes, 4 pixel electrodes, etc.
A layout in which a plurality of pixel electrodes are integrated in one place may be used. FIG. 4 shows an example of a layout in which active elements are integrated in one place for every four pixel electrodes. The pixel electrode a is driven in the region 1 part of the active element, the pixel electrode b is driven in the region 2 part, the pixel electrode c is driven in the region 3 part, and the pixel electrode d is driven in the region 4 part. .

When two or more transistors are provided for one pixel, if ordinary amorphous silicon is used, the area occupied by the two or more transistors becomes larger than the pixel area, and as a result, the aperture ratio is increased. Tends to be small, so polysilicon or CGS (Co
ntinuous Grain Silicon) is preferably used.

(Compound represented by the general formula (I)) In the liquid crystal display element of the present invention, the liquid crystal material to be interposed between the two substrates is represented by the general formula (I).

[0026]

[Chemical 5]

A cyano-based liquid crystal or an isothiocyanate-based liquid crystal compound represented by is essential.

R ¹ is more preferably an alkyl group having 2 to 7 carbon atoms and an alkenyl group having 2 to 7 carbon atoms. More preferable examples of the alkenyl group include (a) to (e). It is more preferable to select one or more of these compounds. When the ring to which the alkenyl group is directly connected is an aromatic ring such as a benzene ring, a pyridine ring or a pyrimidine ring,
(a) or (b) is particularly preferable, when the ring to which the alkenyl group is directly bonded is an alicyclic ring such as a cyclohexane ring,
(c) and (d) are particularly preferable.

[0029]

[Chemical 6]

(The structural formula is assumed to be connected to the ring at the right end)

More preferred forms of ring A and ring B are 1,4-phenylene, 2 or 3-fluoro-1,4-phenylene, 2,3-difluoro-1,4-phenylene and 3,5-difluoro-. 1,4-phenylene, pyrimidine-2,5-diyl, pyridine-2,5-diyl, trans-1,4-cyclohexylene, trans-1,4-cyclohexenylene, trans-1,3-dioxane- 2,5-diyl, naphthalene-2,6-diyl, 1,2,3,4-tetrahydronaphthalene-2,6-diyl, decahydronaphthalene-2,6-diyl, phenanthrene-2,7-diyl group or It is a fluorene-2,7-diyl group. Where naphthalene-2,6-diyl and 1,2,3,4
-Tetrahydronaphthalene-2,6-diyl may be unsubstituted, but it is preferable to select one or more compounds having one or more F as a substituent.

I is preferably 0 or 1, and i = 0
It is more preferable to select 1 type to 10 types.

A more preferred form of Y ¹ and Y ² is a single bond,
—CH ₂ CH ₂ —, —COO— or —C≡C—, and a particularly preferred form is a single bond, —COO— or —C≡C—.

More preferable forms of Z ¹ and Z ² are independently H and F, and when importance is attached to low voltage drivability, Z ¹ and Z ² are particularly preferably F at the same time.

Since X is a cyano group or an isothiocyanate group, the anisotropy of the dielectric constant of the liquid crystal molecule can be made larger than that of a fluorine atom, and it is easy to reduce the driving voltage. Furthermore, the cyano group and the isothiocyanate group tend to contribute to widen the temperature range of the liquid crystal phase, and when the benzene ring or transcyclohexane ring called mesogen in this technical field is the same, the fluorine atom is used. The liquid crystal phase can be obtained in a wider temperature range as compared with the case where the liquid crystal phase is present. Therefore, the liquid crystal material having the compound represented by the general formula (I) having a cyano group or an isothiocyanate group can contain a large amount of a low-viscosity component,
The response speed is faster than that of a so-called fluorine-based liquid crystal material, and excellent display characteristics can be obtained.

Examples of the compound represented by the general formula (I) include compounds (I-1) to (I-49).

[0037]

[Chemical 7]

[0038]

[Chemical 8]

(In the formula, R ¹ has the same meaning as in formula (I)) Among these compounds, (I-1), (I-2), (I-4), (I -
6), (I-7), (I-12), (I-13), (I-16), (I-20), (I-2
It is preferable to contain a compound selected from 9), (I-31), (I-32), (I-33), and (I-46). From the viewpoint of preventing image sticking of the liquid crystal display element, a pyridine-2,5-diyl group,
Having a pyrimidine-2,5-diyl group (I-3), (I-4), (I-
It is effective to contain the compounds represented by 9), (I-10), (I-15) and (I-16). For the purpose of eliminating burn-in,
It is preferable to add 0.1 to 10 mass% of these compounds.

(Content of Compound Represented by General Formula (I))
The compound represented by the general formula (I) is preferably contained in an amount of 20 to 70% by mass, more preferably 30 to 60% by mass. In particular, it provides an excellent display with no image flicker and no afterimage,
Further, when importance is attached to low voltage driving at about 0.6 to 1.5 V, it is preferable to contain 20 to 80% by mass in the liquid crystal material.
In this case, among the compounds represented by the general formula (I), 1,4-phenylene as ring A and ring B, 2 or 3-fluoro-1,4-phenylene, 2,3-difluoro-1,4- It is preferable to select from phenylene, 3,5-difluoro-1,4-phenylene, trans-1,4-cyclohexylene, it is preferable to select a single bond as Y ¹ and Y ² , and X is -CN. It is preferable from the viewpoints of suppressing the change over time of the liquid crystal display element and ensuring the response speed. In addition, when the response is important,
It is preferable to contain 10 to 25% by mass. in this case,
Among the compounds represented by the general formula (I), it is preferable to select an alkenyl group having 2 to 5 carbon atoms as R ¹ .

In addition to the compound represented by the general formula (I), a polar group having no cyano group or isothiocyanate group in the liquid crystal material is used for the purpose of reducing the viscosity of the liquid crystal material and improving the response speed. It is preferable to include a compound having a small Such compounds include those represented by the general formula (II)

[0042]

[Chemical 9]

(In the formula, R ² and R ³ each independently represent an alkyl group having 1 to 10 carbon atoms or an alkenyl group having 2 to 10 carbon atoms, the alkyl group or the alkenyl group being unsubstituted. One or more than one F, Cl, C as a substituent
One, two or more CH ₂ groups present in the alkyl or alkenyl group, which may have N, CH ₃ or CF ₃ , are O, CO, provided that the O atoms are not directly bonded to each other. Or may be substituted with COO, ring C, ring D and ring E are each independently 1,4-phenylene, 2 or 3-fluoro-1,4-phenylene, 2,3-difluoro-1,4- Phenylene, 3,5-difluoro-1,4-phenylene, 2 or 3-chloro-1,4-phenylene, 2,3-dichloro-1,4-phenylene, 3,5-dichloro-1,4-
Phenylene, pyrimidine-2,5-diyl, pyridine-2,5-diyl, trans-1,4-cyclohexylene, trans-1,4-
Cyclohexenylene, trans-1,3-dioxane-2,5-diyl, trans-1-sila-1,4-cyclohexylene, trans-4-sila-1,4-cyclohexylene, naphthalene-2,6- Diyl, 1,2,3,4-tetrahydronaphthalene-2,6-diyl,
Decahydronaphthalene-2,6-diyl, phenanthrene-2,
7-diyl group or fluorene-2,7-diyl group is represented, naphthalene-2,6-diyl and 1,2,3,4-tetrahydronaphthalene-2,6-diyl are unsubstituted or as a substituent one or more F, Cl, can have a CF _3, OCF ₃ or CH _3, j represents 0, 1 or 2, Y ^3, Y ⁴ are each independently a single bond, -COO -, -OCO-, -CH ₂ O-, -OCH _2- , -CH = CH-,-
CF = CF -, - C≡C - , - (CH 2) 2 -, - (CH 2) 4 -, - CH = CH- (CH 2)
₂ -,-(CH ₂ ) ₂ -CH = CH-, -CH = N-, -CH = NN = CH- or -N (O) = N
-Represents. ) The compound represented by this can be contained.
Examples of the compound represented by the general formula (II) include (II-1)
~ (II-34) can be mentioned.

[0044]

[Chemical 10]

(In the formula, R ² and R ³ have the same meanings as in the general formula (II)) Among these compounds, (II-1), (II-4), (II-5) , (I
I-6), (II-8), (II-9), (II-10), (II-12), (II-14),
(II-17), (II-18), (II-21), (II-22), (II-26), (II-3
It is preferable to contain a compound selected from 3) and (II-34). R ² and R ³ each independently have the same meaning as in formula (II), but an alkyl group having 2 to 5 carbon atoms or an alkenyl group having 2 to 5 carbon atoms is preferable, and at least one of them is More preferably, it is an alkenyl group, and it is even more preferable that both are alkenyl groups.
As the alkenyl group having 2 to 5 carbon atoms,

[0046]

[Chemical 11]

(It is assumed that the structural formula is linked to the ring at the right end). Of these, the ring to which the alkenyl group is directly linked is preferably (a) or (b) when the ring is a benzene ring, a pyridine ring, or a pyrimidine ring, and the ring to which the alkenyl group is directly linked is cyclohexane. In the case of an alicycle such as a ring, (c) and (d) are particularly preferable.

The compound represented by the general formula (II) as described above is preferably contained in the liquid crystal material in an amount of 10 to 80% by mass, more preferably 20 to 70% by mass. When high-speed responsiveness is important, it is preferable to contain 40 to 80% by mass.

As the compound which is preferably used in combination with the compound represented by the general formula (I), the general formula (III)

[0050]

[Chemical 12]

(Where R is^FourIs an alkyl group having 1 to 10 carbon atoms
Or an alkenyl group having 2 to 10 carbon atoms,
Or the alkenyl group is unsubstituted or substituted with
One or more F, Cl, CN, CH₃Or CF₃Have
Present in the alkyl or alkenyl group
1 or 2 or more CH₂The groups are O atoms directly linked to each other.
If not, it may be substituted with O, CO or COO
Ring F, ring G and ring H are independently 1,4-phenylene
, 2 or 3-fluoro-1,4-phenylene, 2,3-difluoro
-1,4-phenylene, 3,5-difluoro-1,4-phenylene, 2
Or 3-chloro-1,4-phenylene, 2,3-dichloro-1,4-phenyl
Nylene, 3,5-dichloro-1,4-phenylene, pyrimidine-2,
5-diyl, pyridine-2,5-diyl, trans-1,4-cyclo
Hexylene, trans-1,4-cyclohexenylene, tiger
Trans-1,3-dioxane-2,5-diyl, trans-1-sila-1,
4-cyclohexylene, trans-4-sila-1,4-cyclohex
Silen, naphthalene-2,6-diyl, 1,2,3,4-tetrahydr
Ronaphthalene-2,6-diyl, decahydronaphthalene-2,6-
Diyl, phenanthrene-2,7-diyl group or fluorene-
Represents a 2,7-diyl group, naphthalene-2,6-diyl and 1,2,
3,4-tetrahydronaphthalene-2,6-diyl is unsubstituted
Or one or more F, Cl, CF as a substituent ₃, OC
F₃Or CH₃Where k represents 0, 1 or 2 and Y
^FiveAnd Y⁶Are each independently a single bond, -COO-, -OCO-, -CH
₂O-, -OCH₂-, -CH = CH-, -CF = CF-, -C≡C-,-(CH₂)₂-,-
(CH₂)_Four-, -CH = CH- (CH₂)₂-,-(CH₂)₂-CH = CH-, -CH = N-,-
CH = N-N = CH- or -N (O) = N-, Z³Is H, F, Cl, CF₃, C
HF₂, OCF₃, OCHF₂, OCH₂Represents F. )
Can be mentioned.

(Retention rate) As a liquid crystal material which is preferably used for the active element 2, a compound represented by the general formula (I) is used.
The liquid crystal material containing 0 to 80 mass% is a conventional active element.
It was found that an excellent display without afterimage can be achieved as compared with the fluorine-based liquid crystal material used in 1. That is, in the case of an active element capable of continuously flowing a current during the period of the frame cycle, the capacitor composed of the pixel and the liquid crystal material does not need to be an ideal capacitor having a voltage holding ratio of 100%. Rather, it was found that it is preferable to design the voltage holding ratio at a moderately lower temperature than this, that is, 40 to 90%.

Liquid crystal materials containing the compound represented by the general formula (I) have been variously developed for TN type and STN type liquid crystal display elements, and the fluorine-based compounds mainly used in the active element 1 are mainly used. Compared with the liquid crystal material as a component, it has excellent characteristics in increasing the response speed, reducing the viscosity, and reducing the driving voltage. By using the compound represented by the general formula (I) for the active element 2, it has become possible to significantly improve the characteristics of the liquid crystal material for active driving according to the present invention.

The liquid crystal material used in the liquid crystal display device of the present invention has a problem that a too high voltage holding ratio causes an afterimage. However, the amount of current that the active element can continuously supply during the frame period is limited by the mobility of the active element, the specific resistance of the wiring material, and the cross-sectional area. The image may flicker, and good display may not be possible. The range of the voltage holding ratio of the liquid crystal material used in the present liquid crystal display device varies depending on the mobility of the active device, the specific resistance of the wiring material and the sectional area, but the voltage holding ratio at 80 ° C. is preferably 50 to 80%.

If the voltage holding ratio is adjusted to a high value of 80 to 90%, unnecessary current flowing through the active element can be suppressed to a low level, and the power consumption of the liquid crystal display element can be reduced. As the voltage holding ratio is adjusted to a low value within the range of 40 to 80%, the current flowing through the active element becomes slightly larger, but the unintended residual charge when no voltage is applied to the pixel is used for special driving. It is possible to suppress without using the method, and it is possible to display a moving image with less afterimage and sharper. Therefore, in applications where battery drive is not expected, the voltage holding ratio should be increased in pursuit of obtaining sharp images with less afterimage than power consumption.
It is preferable to adjust the voltage holding ratio in the range of 40 to 60%, adjust the voltage holding ratio to 80 to 90% in applications where battery operation is assumed, and adjust the voltage holding ratio to 60 to 80% in other applications. . If the voltage holding ratio is reduced to less than 40%, it becomes difficult to supply sufficient current to the pixel due to the mobility of the active element and the impedance of the signal line, and there is a tendency that good images cannot be obtained. Therefore, it is preferable to adjust the voltage holding ratio to at least 40% or more.

From such a viewpoint, in the liquid crystal material used in the liquid crystal display device of the present invention, the liquid crystal material having the high voltage holding ratio, the general formula (I
It is very useful to adjust the voltage holding ratio of the liquid crystal material by adding the compound represented by II). The compound represented by the general formula (III), (III-1) ~ (III-1
Compounds such as 8) can be mentioned.

[0057]

[Chemical 13]

(In the formula, R ⁴ has the same meaning as in formula (III)) Among these compounds, (III-1), (III-2), (III-
It is preferable to contain a compound selected from 8), (III-14), (III-17) and (III-18). R ⁴ has the same meaning as in formula (III), but an alkyl group having 2 to 5 carbon atoms or an alkenyl group having 2 to 5 carbon atoms is more preferable. As the alkenyl group having 2 to 5 carbon atoms,

[0059]

[Chemical 14]

(It is assumed that the structural formula is linked to the ring at the right end). Of these, the ring to which the alkenyl group is directly linked is preferably (a) or (b) when the ring is a benzene ring, a pyridine ring, or a pyrimidine ring, and the ring to which the alkenyl group is directly linked is cyclohexane. In the case of an alicycle such as a ring, (c) and (d) are particularly preferable. The compound represented by the general formula (III) as described above is preferably contained in the liquid crystal material in the range of 0 to 60% by mass,
0 to 50 mass% is more preferable, and 0 to 40 mass% is preferable.

Particularly when importance is attached to low voltage driving at about 0.6 to 1.5 V, (III-2), (III-5), (III-7) and (III-
It is preferable to select a compound selected from 15). In addition, it is preferable to select a compound selected from (III-10), (III-13) and (III-17) particularly when the response is emphasized.

When a desired pitch P is required for the liquid crystal display mode, an optically active compound may be added to the liquid crystal material. As the optically active compound, for example, the general formula (I)
A compound having an optically active group introduced into R ¹ in the formula (II)
A compound having an optically active group introduced into R ² or R ³ , or R ² and R ³ in, or a compound having an optically active group introduced into R ⁴ in the general formula (III) can be used. As the optically active group, for example, cholesteryl group, 2-methylbutyl group, 2-
Methylbutyloxy group, 2-methylbutylcarbonyloxy group, 2-methylbutyloxycarbonyl group, 1-methylheptyl group, 1-methylheptyloxy group, 1-methylheptylcarbonyloxy group, 1-methylheptyloxycarbonyl group Can be mentioned. Furthermore, specifically, the formula
The compounds of (IV-1) to (IV-28) can be mentioned.

[0063]

[Chemical 15]

[0064]

[Chemical 16]

As typical ones, for example, cholesteryl nonananate, C-15, CB-15, S-811 and the like are preferably used.

Temperature Dependence of Induced Pitch P at 0 to 50 ° C.
(The absolute value of the difference between the pitch at 50 ° C and the pitch at 0 ° C is divided by the pitch at 0 ° C and multiplied by 100)
It is preferably 0.5% / ° C or lower, more preferably 0.2% / ° C or lower, particularly preferably 0.1% / ° C or lower. Thus, in order to obtain a liquid crystal composition having a small temperature dependence of the induced pitch P,
In two kinds of optically active compounds that induce the same twist direction, is an optical active compound whose induced pitch P increases with increasing temperature and an optically active compound whose induced pitch P decreases with increasing temperature are mixed as appropriate? , In the two types of materials in which the induced pitch P increases with increasing temperature, the temperature dependence of both is significantly different, and those that induce different twisting directions are mixed appropriately or induced with increasing temperature. In the two types of materials having a small pitch P, the temperature dependences of both materials may be significantly different, and materials that induce different twisting directions may be appropriately mixed.

Preferred physical properties of the liquid crystal material containing the compound as described above will be described below. The crystal phase or smectic phase-nematic phase transition temperature is 0 ° C or lower, preferably -10 ° C or lower, more preferably -20 ° C or lower, and particularly preferably -30 ° C or lower. The nematic phase-isotropic liquid phase transition temperature can be selected from the range of 60 to 150 ° C, preferably 75 ° C or higher, more preferably 85 ° C or higher. The viscosity is preferably in the range of 5 to 150 mPa · s, more preferably in the range of 5 to 60 mPa · s, and particularly preferably in the range of 5 to 40 mPa · s. However, when high-speed response is important, the range of 5 to 20 mPa · s is particularly preferable.
The dielectric anisotropy at 25 ° C. is preferably in the range of 1 ≦ Δε ≦ 60, more preferably in the range of 2 ≦ Δε ≦ 40, and 6 ≦ Δ
The range of ε ≦ 30 is particularly preferable. The refractive index anisotropy is preferably in the range of 0.03 ≦ Δn ≦ 0.40 at 25 ° C., 0.04 ≦ Δn ≦
The range of 0.38 is more preferable, and the range of 0.05 ≦ Δn ≦ 0.35 is particularly preferable. The elastic constant ratio K ₃₃ / K ₁₁ at 25 ° C
It is preferably in the range of 0.3 to 5, more preferably in the range of 0.5 to 4, and even more preferably in the range of 0.5 to 2.5. The optimum values of resistivity and voltage holding ratio vary depending on the mobility of the active element, circuit design, and driving method, but the resistivity is in the range of 1 × 10 ^{9 to} 5.0 × 10 ¹² Ωcm at 25 ° C. Is preferable, and more preferably in the range of 1 × 10 ^{10 to} 5.0 × 10 ¹¹ Ω · cm.

[0068]

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. The characteristics measured in the examples are as follows.

Dielectric Anisotropy: Dielectric Anisotropy (-) at 25 ° C Refractive Index Anisotropy: Birefringence (-) at 589nm at 25 ° C Viscosity: Viscosity at 20 ° C (mPa · s ) Voltage holding ratio: Holding ratio (%) at 80 ° C (The liquid crystal composition was injected into a TN-LCD with a cell thickness of 6 μm, and the voltage was applied at 5 V, frame time 20 ms, pulse width 64 μs. ) Voltage V (20msec)
And the initial applied voltage Vo = 5V expressed as a percentage) Voltage holding ratio = V (20msec) / Vo × 100 (%)

(Embodiment 1) As shown in FIG. 5, one pixel is provided with a selection line, a signal line, a voltage supply line and two transistors, and the gate of the first transistor is connected to the selection line. , The drain is connected to the signal line, the drain of the second transistor is connected to the voltage supply line, the source is connected to the pixel electrode, and the source of the first transistor is connected to the gate of the second transistor. A liquid crystal cell with 4 × 4 pixels, a twist angle of 90 degrees and a cell gap of 3 μm was prepared. This active element is capable of continuously supplying current during the frame period when the pixel electrode is in a voltage applied state. next,

[0071]

[Chemical 17]

A composition (A) consisting of the compound shown in (% represents mass%) was prepared. The crystal-nematic phase transition temperature of this composition (A) is -30 ° C, the nematic-isotropic liquid phase transition temperature is 84 ° C, the dielectric anisotropy is 5.8, and the refractive index anisotropy is 0.15.
8. The viscosity was 14.3 mPa · s, the specific resistance was 1.1 × 10 ¹² Ω · cm, and the voltage holding ratio was 78%. After injecting the composition (A) into the prepared cell, two polarizing films were attached to the liquid crystal cell so as to be normally white, whereby a liquid crystal display element of the present invention was produced. The liquid crystal display device of the present invention can display a moving image without an afterimage, and the image quality of a still image is good. The driving voltage of this liquid crystal display device was 3.7 V, and the response time was 7.8 msec.

(Example 2)

[0074]

[Chemical 18]

A composition (B) consisting of the compound shown in (% represents mass%) was prepared. This composition (B) has a crystal-nematic phase transition temperature of -61 ° C, a nematic-isotropic liquid phase transition temperature of 76 ° C, a dielectric anisotropy of 28, and a refractive index anisotropy of 0.
144, the specific resistance was 2.1 × 10 ¹¹ Ω · cm, and the voltage holding ratio was 65%. After injecting this composition (B) into a liquid crystal cell having the same configuration as that prepared in Example 1 and having a cell gap of 3.3 μm, two polarizing films are bonded to the liquid crystal cell so as to be normally white. Thus, the liquid crystal display element of the present invention was produced. The liquid crystal display device of the present invention can display a moving image without an afterimage, and the image quality of a still image is good. The driving voltage of this liquid crystal display device was 1.2 V, and the response time was 38 msec.

Comparative Example 1 As shown in FIG. 6, a selection line, a signal line and one transistor are provided for one pixel, the gate of the transistor is connected to the selection line, and the drain is connected to the signal line. Then, a liquid crystal cell having 4 × 4 pixels in which a source was connected to a pixel electrode, a twist angle of 90 degrees, and a cell gap of 3 μm was prepared. This active element can supply current to the pixel electrode only when the gate of the transistor is in the selected state. After injecting the composition (A) prepared in Example 1 into this liquid crystal element, two polarizing films were attached to the liquid crystal cell so as to be normally white, whereby a liquid crystal display element was produced. In this liquid crystal display device, the image flicker could not be displayed satisfactorily because the voltage holding characteristics of the liquid crystal composition were insufficient.

Comparative Example 2 After injecting the composition (B) prepared in Example 2 into a liquid crystal cell having the same structure as that prepared in Comparative Example 1 and having a cell gap of 3.3 μm, a normally white color is obtained. A liquid crystal display device was produced by bonding two polarizing films to a liquid crystal cell. In this liquid crystal display device, an image flickers, and a good display cannot be performed.

(Comparative Example 3)

[0079]

[Chemical 19]

A composition (C) comprising the compound shown in (% represents mass%) was prepared. Nematic of this composition (C)
Isotropic liquid phase transition temperature is 87 ℃, dielectric anisotropy is 6.3,
Anisotropy of refractive index is 0.084, viscosity is 25 mPas, specific resistance is 6.0
× 10 ¹³ Ω · cm, voltage holding ratio was 99.4%. After injecting this composition (C) into a liquid crystal cell having a cell gap of 5.6 μm with the same configuration as that prepared in Example 1, two polarizing films were bonded to the liquid crystal cell so as to be normally white, thereby making a comparison. A liquid crystal display element of was produced. In the comparative liquid crystal display device, a burn-in phenomenon was observed in a still image, and a moving image had an afterimage like tailing. The driving voltage of this liquid crystal display element was 4.0 V, and the response time was 44 msec.
Comparison with the characteristics of Examples 1 and 2 of the present invention shows that the response speed is inferior for the drive voltage.

From the comparison between Examples 1 and 2 and Comparative Examples 1 and 2, it can be seen that the liquid crystal display device of the present invention can achieve good moving images. Further, from the comparison between Examples 1 and 2 and Comparative Example 3, the liquid crystal display element of the present invention is excellent in low driving voltage and high-speed response as compared with the conventional liquid crystal display element, and is excellent in no image sticking. You can see that there is something.

(Embodiment 3) As shown in FIG. 2, one pixel is provided with a selection line, a signal line, a voltage supply line and two transistors, and the gate of the first transistor is connected to the selection line. , The drain is connected to the signal line, the drain of the second transistor is connected to the voltage supply line, the source is connected to the pixel electrode, and the source of the first transistor is connected to the gate of the second transistor. Pi-cells with 4 × 4 pixels, pre-tilt angle of 5 degrees and cell gap of 2 μm were prepared. This active element is capable of continuously supplying current during the frame period when the pixel electrode is in a voltage applied state. next,

[0083]

[Chemical 20]

A composition (D) consisting of the compound shown in (% represents mass%) was prepared. The crystal-nematic phase transition temperature of this composition (D) is -31 ° C, the nematic-isotropic liquid phase transition temperature is 98 ° C, the dielectric anisotropy is 9, and the refractive index anisotropy is 0.2.
41, the specific resistance is 1.0 × 10 ¹³ Ω ・ cm, and the elastic constant ratio K33 / K11 is 2.
0, the voltage holding ratio was 82%. After injecting this composition (D) into the liquid crystal cell prepared above, by bonding the retardation film and the two polarizing films to the liquid crystal cell,
An OCB liquid crystal display device of the present invention was produced. The liquid crystal display device of the present invention can display a moving image without an afterimage, and the image quality of a still image is good. The driving voltage of this liquid crystal display device was 6 V, and the response time was 1.2 msec.

[0085]

Since the liquid crystal display device of the present invention can obtain a good display quality with no afterimage as compared with the conventional active driving device, it will be extremely useful as a multimedia display in the future.

[Brief description of drawings]

FIG. 1 is an example of a circuit diagram of an active element that constantly supplies a constant voltage to a pixel electrode when the pixel electrode that is capable of continuously supplying a current during a frame period is in a voltage applied state. . LC in the figure represents a capacitor composed of a pixel electrode and a liquid crystal material.

FIG. 2 is an example of a circuit diagram of an active element that constantly supplies a constant voltage to the pixel electrode when the pixel electrode that can continuously supply current during a frame period is in a voltage application state. . LC in the figure represents a capacitor composed of a pixel electrode and a liquid crystal material.

[Fig. 3] Layout example 1 of pixel electrodes and active elements

[Fig. 4] Layout example 2 of pixel electrodes and active elements

FIG. 5 is a circuit diagram of the first embodiment.

FIG. 6 is a circuit diagram of Comparative Example 1.

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 2H090 LA01 LA04 MA04 MA11                 2H092 JA24 JA45 JB42 KA04 KA05                       NA05                 4H027 BC04 BD04 CB01 CB02 CC04                       CD04 CE04 CM04 CN01 CN04                       CN05 CP04 CT02 CT04 CU01                       CW02 DB04 DE04 DK04

Claims (12)

[Claims] 1. Two sheets, at least one of which is transparent
A liquid crystal display device in which a liquid crystal material is interposed between substrates,
Operate multiple pixel electrodes and each pixel electrode on one side of the substrate
An active element, the active element being a pixel electrode
On the other hand, the current is continuously supplied during the frame period.
Of which the liquid crystal material has the general formula
(I) [Chemical 1] (In the formula, R¹Is an alkyl group having 1 to 10 carbon atoms or a carbon atom
Represents an alkenyl group of the number 2 to 10, and the alkyl group or the alkenyl group
The alkenyl group is unsubstituted or has 1 or 2 substituents.
More than F, Cl, CN, CH₃Or CF₃Can have
1 or 2 existing in the alkyl group or the alkenyl group
CH or more₂The group is such that the O atoms do not bond directly to each other.
And optionally substituted with O, CO or COO, ring A and
Rings B are each independently 1,4-phenylene, 2 or 3-fluoro.
1,4-phenylene, 2,3-difluoro-1,4-phenylene,
3,5-difluoro-1,4-phenylene, 2 or 3-chloro-1,4-
Phenylene, 2,3-dichloro-1,4-phenylene, 3,5-dichloro
Lolo-1,4-phenylene, pyrimidine-2,5-diyl, pyridi
-2,5-diyl, trans-1,4-cyclohexylene, tiger
-1,4-cyclohexenylene, trans-1,3-dioxa
-2,5-diyl, trans-1-sila-1,4-cyclohexyl
, Trans-4-sila-1,4-cyclohexylene, naphthale
-2,6-diyl, 1,2,3,4-tetrahydronaphthalene-2,6-
Diyl, decahydronaphthalene-2,6-diyl, phenane
Represents Tren-2,7-diyl or fluorene-2,7-diyl
Naphthalene-2,6-diyl and 1,2,3,4-tetrahydro
Naphthalene-2,6-diyl is unsubstituted or has a substituent
One or more F, Cl, CF₃, OCF₃Or CH₃Have
Where i represents 0, 1 or 2, and Y¹And Y²Is that
Independently a single bond, -COO-, -OCO-, -CH₂O-, -OCH₂-, -C
H = CH-, -CF = CF-, -C≡C-,-(CH ₂)₂-,-(CH₂)_Four-, -CH = CH
-(CH₂)₂-,-(CH₂)₂-CH = CH-, -CH = N-, -CH = N-N = CH- or-
Represents N (O) = N-, Z¹And Z²Are independently H, F, C
l, CF₃Or OCF₃And X represents -CN and -NCS. )
Liquid containing 10 to 80 mass% of a compound
Crystal display element. 2. The liquid crystal display element according to claim 1, wherein the voltage holding ratio of the liquid crystal material at 80 ° C. is in the range of 40% to 90%. 3. The liquid crystal display device according to claim 1, wherein the liquid crystal material contains the compound represented by the general formula (I) in an amount of 10 to 25% by mass. 4. The liquid crystal display device according to claim 1, wherein the liquid crystal material contains the compound represented by the general formula (I) in an amount of 20 to 80% by mass. 5. The liquid crystal material is represented by the general formula (II): (In the formula, R ² and R ³ each independently represent an alkyl group having 1 to 10 carbon atoms or an alkenyl group having 2 to 10 carbon atoms, wherein the alkyl group or the alkenyl group is unsubstituted or 1 or 2 or more as a substituent, F, Cl, CN, CH ₃ or
One or more CH ₂ groups present in the alkyl or alkenyl group, which may have CF ₃ , are substituted with O, CO or COO, such that the O atoms are not directly bonded to each other. Ring C, ring D and ring E are each independently 1,4
-Phenylene, 2 or 3-fluoro-1,4-phenylene, 2,3-
Difluoro-1,4-phenylene, 3,5-difluoro-1,4-phenylene, 2 or 3-chloro-1,4-phenylene, 2,3-dichloro
-1,4-phenylene, 3,5-dichloro-1,4-phenylene, pyrimidine-2,5-diyl, pyridine-2,5-diyl, trans-
1,4-cyclohexylene, trans-1,4-cyclohexenylene, trans-1,3-dioxane-2,5-diyl, trans
-1-sila-1,4-cyclohexylene, trans-4-sila-1,4-
Cyclohexylene, naphthalene-2,6-diyl, 1,2,3,4-
Tetrahydronaphthalene-2,6-diyl, decahydronaphthalene-2,6-diyl, phenanthrene-2,7-diyl group or fluorene-2,7-diyl group is represented, naphthalene-2,6-diyl and 1,2 , 3,4-tetrahydronaphthalene-2,6-diyl is unsubstituted or has one or more F, C as a substituent.
l, CF ₃ , OCF ₃ or CH ₃ , j represents 0, 1 or 2, Y ³ and Y ⁴ are each independently a single bond, —CO
O-, -OCO-, -CH ₂ O-, -OCH _2- , -CH = CH-, -CF = CF-, -C≡C
_{-, - (CH 2) 2} -, - (CH 2) 4 -, - CH = CH- (CH 2) 2 -, - (CH 2) 2 -CH =
Represents CH-, -CH = N-, -CH = NN = CH- or -N (O) = N-. The liquid crystal display element according to claim 1, further comprising a compound represented by the formula (4). 6. The liquid crystal material is represented by the general formula (III): [Chemical 3] (In the formula, R^FourIs an alkyl group having 1 to 10 carbon atoms or a carbon atom
Represents an alkenyl group of the number 2 to 10, and the alkyl group or the alkenyl group
The alkenyl group is unsubstituted or has 1 or 2 substituents.
More than F, Cl, CN, CH₃Or CF₃Can have
1 or 2 existing in the alkyl group or the alkenyl group
CH or more₂The group is such that the O atoms do not bond directly to each other.
And optionally substituted with O, CO or COO, ring F, ring G
And ring H are each independently 1,4-phenylene, 2 or 3-phenyl.
Luoro-1,4-phenylene, 2,3-difluoro-1,4-phenylene
1,3,5-difluoro-1,4-phenylene, 2 or 3-chloro-
1,4-phenylene, 2,3-dichloro-1,4-phenylene, 3,5-
Dichloro-1,4-phenylene, pyrimidine-2,5-diyl, pi
Lysine-2,5-diyl, trans-1,4-cyclohexylene,
Trans-1,4-cyclohexenylene, trans-1,3-dio
Xan-2,5-diyl, trans-1-sila-1,4-cyclohex
Silen, trans-4-sila-1,4-cyclohexylene, naphth
Thallen-2,6-diyl, 1,2,3,4-tetrahydronaphthalene-
2,6-diyl, decahydronaphthalene-2,6-diyl, fe
Nanthrene-2,7-diyl group or fluorene-2,7-diyl group
Represents naphthalene-2,6-diyl and 1,2,3,4-tetrahi
Dronaphthalene-2,6-diyl is unsubstituted or substituted
One or more F, Cl, CF as a group ₃, OCF₃Or CH₃To
Can have, k represents 0, 1 or 2, and Y^FiveAnd Y⁶Haso
Independently single bond, -COO-, -OCO-, -CH₂O-, -OCH
₂-, -CH = CH-, -CF = CF-, -C≡C-,-(CH₂)₂-,-(CH₂)_Four-,
-CH = CH- (CH₂)₂-,-(CH₂)₂-CH = CH-, -CH = N-, -CH = N-N = CH
-Or-represents N (O) = N-, Z³Is H, F, Cl, CF₃, CHF₂, OC
F₃, OCHF₂, OCH₂Represents F. ) Contains a compound represented by
The liquid crystal display device according to claim 1, wherein the liquid crystal display device is a liquid crystal display device. 7. The liquid crystal material is 2-40 at 25 ° C.
Has a relative dielectric constant anisotropy of 5 to 60 mPa · s,
7. A refractive index anisotropy of 0.04 to 0.38, an elastic constant ratio K33 / K11 of 0.5 to 4.0, and a liquid crystal phase-isotropic liquid phase transition temperature of 60 to 150 ° C. 7. The liquid crystal display device according to claim 1. 8. The method according to claim 1, wherein the distance between the two substrates is 1 to 6 μm, the pretilt angle on the substrates is 2 to 10 °, and the liquid crystal material is in bend alignment. The liquid crystal display device according to claim 1. 9. The twist angle in the liquid crystal display device is
0 ° to 360 °, and the product Δn · d of the distance d between the substrates of the liquid crystal display element and the refractive index anisotropy Δn of the liquid crystal material is 0.1 to 0.6.
9. The liquid crystal display element according to claim 1, wherein the liquid crystal display element has a thickness of μm. 10. The liquid crystal display element according to claim 1, wherein the active element that operates each of the pixel electrodes includes at least two transistors. 11. The active element for operating the pixel electrode has a configuration in which a selection line, a signal line, and a voltage supply line are connected, and a gate of one transistor is connected to the selection line and one of a source and a drain is connected to the selection line. 11. The liquid crystal display element according to claim 10, wherein one of the source and the drain of the other transistor connected to the signal line is connected to the voltage supply line, and the other of the source and the drain is connected to the pixel electrode. 12. The active element according to claim 1, wherein the active element is formed on amorphous silicon or polysilicon.
The liquid crystal display element according to claim 1.