JPH10306281A - Nematic liquid crystal composition for plasma-addressed liquid crystal display - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the subject composition having a high resistant value, also fitting to other requirements, and especially not producing an afterimage or substantially not exhibiting the afterimage by including a substance capable of controlling and/or adjusting electric conductivity. SOLUTION: This nematic liquid crystal composition comprises (A) 15-35 wt.% of two or more kinds of compounds selected from components of formulas I and II [R<1> is a 1-5C linear alkyl; L<1> , L<2> are each H, F; X is F, OCF2 H, OCF3 ; (m) is 0, 1], (B) 65-85 wt.% of at least three kinds of compounds selected from compounds of formula IV [R<2> , R<3> are each a 1-5C linear alkyl, an alkoxy; the ring A is a group of formula V, etc.; (n) is 0, 1], and further (C) a substance for controlling and/or adjusting electric conductivity (preferably a crown ether compound).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

FIELD OF THE INVENTION The present invention relates to a substance which regulates or controls the conductivity based on terminal and lateral fluorinated compounds and dielectrically neutral compounds.
The present invention relates to a nematic liquid crystal composition containing a liquid crystal composition containing a liquid crystal composition. This composition is plasma-
Address LCD display device (plasma-addressed
Particularly useful for liquid crystal display devices.

[0002]

2. Description of the Prior Art Plasma-addressed liquid crystal displays (PADs) are particularly preferred as important displays in markets with high information capacity. Such a PAD
Are used not only for TV or video applications, but also for displays with a high information capacity, for example for computer end devices, cars and aircraft, as well as displays for games and game consoles. Some PADs include an active electrical switching element or plasma cell combined with a display cell having a plurality of address lines. Such PADs are described, for example, in EP 0628944, EP 0545
569, USP 4,896,149, USP 5,07
7,553, WO 97/00924 and Kakizaki, T .;
40.4, SID 96 DIGES
T, pages 915-918.

In a PAD, switching elements are addressed in a time division manner. Thus, these switching elements charge the electrodes of the pixels during the active time limit. These elements then become inactive until the next time they are addressed again. Thus, a change in voltage for plasma addressed pixels is undesirable, but is also a very important feature of such displays. The discharge of the electrodes of this pixel is mainly determined by the resistance value of the dielectric substance between the electrodes, that is, by the liquid crystal. This discharge is indexed by a time constant R · C, where the resistance R is primarily the resistance of the liquid crystal and C is the capacitance of a capacitor, which is a pixel filled with liquid crystal as a dielectric. The high resistance of the liquid crystal is a necessary requirement for the slow discharge of charged (addressed) pixels of the display, as it is governed by the time dependence which almost follows the law of Large RC time values are typically good and also high voltage holding ratios (VH
R). This voltage holding ratio (VHR) is defined as the voltage actually present at the pixel as a function of the applied voltage.

Liquid crystal materials customary for active matrix displays, for example thin film transistor (TFT) address twisted nematic liquid crystal displays (TN LCDs), have a high birefringence and a dielectric anisotropy value, so that the PAD Is not suitable. Furthermore, the voltage of the pixels of the PAD can be controlled by other active matrix address LCDs, such as MIM (MIM), which use a solid medium as the electrically active switching medium and do not use a gaseous medium as in the PAD of the present invention. Metal-insulator-metal), diode or TFT AM
(Active matrix) Higher than the voltage applied to the pixels of the LCD. However, for example, TF
The high address voltage of the PAD compared to a TAM LCD leads to a serious problem called afterimages on the display when conventional liquid crystals are used, as for example in WO 97/00924. This is mainly due to the DC charge at the electrodes of the pixels of the display.
Caused by the accumulation of.

[0005] This phenomenon is well known. After a pattern has been displayed for an extended period of minutes or hours, subsequently newly displayed patterns are damaged by residual images, referred to as residual images of previously displayed information. This remaining image can have either positive or negative contrast to the newly displayed pattern.
Thus, in addition to a wide range of nematic mesophases with exceptionally low smectic or crystalline to nematic transition temperatures and other material properties suitable for use in PAD, such as non-crystallization at low temperatures, large resistance values and low residuals There is still a particular need for liquid crystal compositions that have a DC voltage at the same time and that do not produce afterimages. Furthermore, most of the liquid crystal compositions customary for other AMD applications have a birefringence value of Δn> 0.08. There is a need for compositions having a low Δn value, preferably Δn <0.07, and also having a viscosity at 20 ° C. of <20 mm / sec.

[0006]

The object of the present invention is to have a high resistance value and to meet other requirements,
In particular, it is an object of the present invention to provide a liquid crystal composition which does not cause an afterimage or substantially does not show an afterimage. Another object of the invention is to have a small Δn value, preferably Δn <0.07,
Another object is to provide a liquid crystal composition having a viscosity of <20 mm / sec at 20 ° C.

[0007]

SUMMARY OF THE INVENTION According to the present invention, a nematic liquid crystal composition having the following composition and also containing a substance for regulating or controlling the electrical conductivity has been found to be particularly suitable for PAD: 15 to 35% by weight of two or more compounds selected from group 1 consisting of compounds of the formulas 1a and 1b:

[0008]

Embedded image

In each formula, R ¹ is a linear alkyl group having 1 to 5 carbon atoms, L ¹ and L ² are each independently H or F, and X is F , OCF ₂
H or OCF _3, and m is 0 or 1 in some, 65-85 wt% of the following formula 2a and at least three compounds from group 2 consisting of compounds represented by 2b:

[0010]

Embedded image

In each formula, R ² and R ³ are each independently a linear alkyl group or alkoxy group having 1 to 5 carbon atoms,

Embedded image n is 0 or 1.

A very long RC time value, which is a characteristic time related to the discharge of a pixel, can be obtained without causing an afterimage.
D. These compositions also have reduced viscosities, can operate at the primary light transmission minimum in AMD, and do not show any crystallization at -30 ° C. for at least 10 hours in the display. . The LC compositions according to the invention exhibit a dielectric anisotropy of less than 4.0, preferably 1.0 to 3.0, especially 1.5 to 2.5. The clearing point of the composition according to the invention is 8
Higher than 5 ° C., especially higher than 90 ° C. Such compositions are preferably one or more, particularly preferably two,
Contains 3 or 4 compounds from Group 1.
Preferred compositions comprise at least two compounds from Group 1
It is contained at a ratio of 0% by weight.

Compounds from Group 1 are described in European Patent Applications 0387032 and 0280902, European Patents 051738 and 0125653, International Patent Applications WO 89/02884 and WO 85/048.
874, and USP 4,302,352, USP
No. 4,710,315 and US Pat. No. 4,419,264 or can be prepared analogously to known compounds. Compounds from group 2 are for example DE
3321373, DE2500553 and DE320
6269. Preferred compositions also contain one or more compounds from group 0 having two rings:

[0014]

Embedded image

In the formula, R ⁰ represents a linear alkyl group having 2 to 7 carbon atoms, and E ⁰ represents — (CH ₂ ) ₄ —,
— (CH ₂ ) ₂ —, —CO—O— or a single bond;
¹ and L ² are each, independently of one another, H or F, and Q is OCF ₂ , OCFH, CF ₂ , CFH or a single bond. Preferably, E ⁰ is — (CH ₂ ) ₂ —
Or is a single bond, Q is a single bond, and ^one of L ¹ and L ² is H, and the other of L ¹ and L ² is H or F.

Preferred conductivity regulating / controlling substances include compounds from the following group of compounds: Formulas 3, 4 and 5
Compound represented by the formula: Crown ether represented by the formula 3: (-(CH ₂ ) ₀ —O—) _n Formula 3 (where n = 5 to 12, preferably 4 to 10, particularly 6 or 8, and o = 1 to 4, preferably 2 to 3,
Especially 2, and most preferably o, n = 7,6 and 7,8); and a crown ether of formula 4:

[0017]

Embedded image (Where k = 1 or 2, l = 1-10,
And m = 1-3, preferably k = 1, l
= 2-5, and m = 2, especially k = 1, l = 3 or 4, and m = 2); and a quaternary ammonium salt of formula 5:

[0018]

Embedded image Wherein R is each independently of the other alkyl, cycloalkyl, aryl, alkylcycloalkyl or alkylaryl;

Embedded image

The crown ether of the formula 3 is also usually represented by the abbreviation [(0 + 1) ^* n] -crown-n. Particularly preferred examples of the compounds of the formulas 3 and 4 are the compounds of the formulas 3a, 4a, 4b and 5a: Crown ether A

Embedded image

Crown ether B

Embedded image Crown ether C

Embedded image

Tetra-n-butylaluminum bromide, also called TBAB:

Embedded image These compositions and other known compounds having similar functions increase the conductivity of the liquid crystal medium. Thus, they regulate some conductivity for the current. On the other hand, they do not lead to undesirably high mobility of charged carriers in the medium and can be used for controlling the conductivity, whereby the conductivity and the good RC- It allows achieving a balance between conductivity that is small enough to obtain a time value.

The compounds represented by the formulas 3 and 4 are more suitable than the compounds represented by the formula 5 as a conductivity modifier. This compound is particularly small in liquid crystal mixtures.
Keep the ε value. These "small" numbers are preferably less than 3.5, in particular less than 2.5, or even less than 2.0. In these mixtures, the optimal compounds are the compounds of formulas 3 and 4,
Particularly, the compounds represented by 3a, 4a and 4b.
However, liquid-crystal mixtures having a relatively large Δε value, for example of 4 or more, preferably 5 or more, especially 6 or more, can also achieve good results using the compounds of the formula 5a. In particular, compounds of the formula 5a are preferred conductivity controlling / regulating agents in these mixtures. Here and throughout the specification, △ ε
For a thin oriented sample about 5-10 μm thick, 1
Figure 2 represents the dielectric anisotropy of a liquid crystal material measured at a frequency of kHz and 20 ° C.

The compositions according to the invention preferably contain the components from group 1 in an amount of from 20 to 30% by weight, in particular from 25 to 30% by weight. Other groups (if any,
Preferred weight percent ranges for group 0) are as follows: Group 0: 5-15%, especially 5-10% Group 2: 65-85%, especially 70-80%. Conductivity arbitration agent: 0.01 ppm to 2%, preferably 0.1 ppm to 2%.
1 ppm to 1000 ppm, especially 1 ppm to 100 pp
m. Preferably, the components from groups 0, 1 and 2 form the basis of the claimed composition and constitute at least 70% (preferably at least 80%) by weight of the composition. . The conductivity modifier is preferably 1p
pm to 900 ppm, more preferably 10 to 100 p
pm, most preferably at a concentration of 5 to 60 ppm.

However, besides the components from groups 0 to 2 and in small amounts other LC components can also be used to further adapt the properties of the claimed composition. The conductivity adjusting and / or controlling agent can be, for example, a tertiary ammonium salt or can contain a tertiary ammonium salt. Preferably also, the crown ether compound can be used as or as part of a conductivity adjusting and / or controlling agent. In general, the composition comprises 8 to 20, in particular 10 to 17, mesogenic compounds selected from groups 0, 1 and 2 and one, two or three compounds, preferably one or two. It contains a conductivity adjuster consisting of various compounds. In another preferred embodiment, the conductivity modifier is 1
It is a species-only compound. The compositions according to the invention can also contain, for example, chiral dopants or polychromatic dyes in customary amounts.

The preparation of the compositions according to the invention takes place in a customary manner. In general, the desired amount of the components used in the smaller amounts is dissolved in the components making up the main component, preferably at elevated temperature. If this temperature is chosen to be above the clearing point of the main component, the completion of the dissolution process can be seen particularly easily. However, it is also possible to mix the solutions of the various components in an organic solvent, for example acetone, chloroform or methanol, to mix them thoroughly and then to separate the solvent, for example by distillation under reduced pressure. Obviously, in this case, it must be ensured that the solvent does not introduce any contaminants or undesired additional substances. By using suitable additives, the liquid-crystalline media according to the invention can be modified such that they can be used in any of the previously disclosed types of PAD.

[0026]

The following examples illustrate the invention but do not limit it in any way. In these examples, unless otherwise noted,
The melting points and clearing points of liquid crystal materials, as well as other temperatures, are given in degrees Celsius, and percentages are by weight. Throughout the specification, all physical data were measured at 20 ° C. unless otherwise noted.

Comparative Example 1 A liquid crystal composition comprising the following components was prepared: 14% trans, trans-4-propyl-4'-methoxybicyclohexane 13% trans, trans-4-propyl-4'-propoxy Bicyclohexane 13% trans, trans-4-pentyl-4'-methoxybicyclohexane 5% 1- [trans-4- (trans-4-propylcyclohexyl) -cyclohexyl] -2- (3,4
-Difluorophenyl) -ethane 5% 1- [trans-4- (trans-4-pentylcyclohexyl) -cyclohexyl] -2- (3,4
-Difluorophenyl) -ethane 7% 4- (trans-4-propylcyclohexyl) -methoxybenzene 3% 4- (trans-4-propylcyclohexyl) -ethoxybenzene 5% 4- (4-propylphenyl) 4 '-Propylbicyclohexyl-4-yl-1-carboxylate

5% of 4- (4-propylphenyl) 4
'-Butylbicyclohexyl-4-yl-1-carboxylate 4% [4- (trans-4-propylcyclohexyl) -phenyl] 4'-propylbicyclohexyl-4
-Yl-1-carboxylate 4% [4- (trans-4-butylcyclohexyl) -phenyl] 4'-propylbicyclohexyl-4
-Yl-1-carboxylate 4% [4- (trans-4-pentylcyclohexyl) -phenyl] 4'-propylbicyclohexyl-4
-Yl-1-carboxylate 6% 5- [trans-4- (trans-4-ethylcyclohexyl) -cyclohexyl] -1,2,3-trifluorobenzene 6% 5- [trans-4- (trans -4-propylcyclohexyl) -cyclohexyl] -1,2,3-
Trifluorobenzene 6% 5- [trans-4- (trans-4-pentylcyclohexyl) -cyclohexyl] -1,2,3-
Trifluorobenzene

The chiral dopant S-811 from Merck KGaA (Germany) was added in an amount of 0.1% by weight, based on the total weight of the crystal mixture. This composition exhibits the following properties: T (S → N) <− 30 ° C. T (N → I) + 93 ° C. ν (20 ° C.) 17 mm ² / sec ν (0 ° C.) 51 mm ² / sec ν (−30 ° C) 673 mm ² / sec Δn (589 nm, 20 ° C) 0.0668 Δε (1 kHz, 20 ° C) +1.9 This composition, designated LC-0, is shown in Table 1 for comparison. Has a specific resistance of 1.0 × 10 ¹⁴ Ωcm and a VHR of 99.7%.

This VHR is obtained by using a voltage of 5 V,
It was measured as described in rck Liquid Crystal News Letter 9, Part G (1992). This liquid crystal mixture is, for example, Kakiza
Ki, T. et al., 40.4, SID 96 Digest, page 915-918.
The electro-optical properties were measured at room temperature of about 20 ° C. using an illuminometer CA110). This PAD is. It is electrically addressed by a drive circuit developed for home use. These results are shown in FIG. An afterimage is obtained by applying a constant AC-voltage, typically 70 V, to the cell for a certain elapsed time from several minutes (for example, 5 minutes or 10 minutes) to several tens of minutes (about 1 hour). Was evaluated by. These times were taken as representative of the inscription time typical of a practical display. The voltage was then removed, and the display was then addressed with the desired information voltage, eg, 0.30 or 70V, and the resulting transmission measured.

Example 1 Crown Ether A: 1,4,7,10,13,16-hexaoxacyclooctadecane 5 ppm was added to this composition LC-0 of the comparative example. The resulting mixture is called LC-A1. This mixture had the properties summarized in Table 1 and was then used in a plasma addressed LCD, to which an AC voltage was applied and its transmittance was scanned for various address voltages as a function of application time. Example 2 As in example 1, the mixture LC-0 of the comparative example was used together with crown ether A. However, in this example,
50 ppm of crown ether A was added to the mixture LC-0. This mixture is called LC-A2.

Example 3 As in Examples 1 and 2, the mixture LC-0 was used. However, in this example, tetra-n-butylammonium bromide (TBAB) was used as the conductivity adjusting / controlling agent.
Was added. This mixture is called LC-B. In both cases, the results relating to the specific resistance (SR) and the voltage holding ratio (VHR) at 20 ° C. are summarized in Table 1 below: Table 1

[0033]

[Table 1]

The electro-optical properties of these cells are summarized in FIG. The curves for LC-0 (Comparative Example 1) and LC-B are identical within experimental error. Therefore, FIG.
The single curve shown in Figure 2 shows both of these measurements. It is clear that in the case of LC-A1, and also in the case of LC-A2, their voltage-transmission characteristics are moving towards higher voltages with decreasing VHR. 7
The transmission obtained at an applied voltage after an AC voltage of 0 volts has been applied for a period of time is shown in FIGS.
In all cases, the effect of the applied AC voltage on the resulting transmission value is significantly increased at low operating voltages (eg, 0 V), intermediate at intermediate voltages (eg, 30 V), and of the operating time. Interval (writing period)
It is clear that if the same high voltage (i.e., 70V) is applied, no detection is made.

FIG. 2 shows the remarkable decrease in transmittance of the LC mixture of Comparative Example 1 which does not contain the conductivity adjusting / controlling agent (LC-0). Its off-state transmittance is AC
It is significantly reduced after the application of the voltage. This decrease is
It is almost proportional to the time the voltage is applied. 30
At an intermediate voltage of V, this transmittance is also significantly reduced after the application of the AC voltage, the amount of which is proportional to the duration of the application of the AC voltage. As shown in FIG. 3 for LC-A1, the addition of crown ether A in an amount of 5 ppm already already significantly modifies and improves this rather undesirable behavior. However, this off-state transmittance increases almost linearly with the AC-voltage application time. At an intermediate voltage of 30 V, this transmittance is AC
According to the time of application of the voltage, it first decreases slightly, then reaches a minimum transmission at 30 V after an application time of about 30 minutes, and then increases slightly. However,
Even after an application time of 60 minutes, the voltage at its starting point is never reached again.

This is because the liquid crystal LC-A1 uses P
In AD, afterimages are hardly found. As shown in FIG. 4, the minimum effect of the applied AC-voltage on the transmittance of the display is Example 2,
That is, L using 50 ppm of crown ether A
Found in C-A2. It is clear that for this mixture there is virtually no effect of the applied AC-voltage on the residual transmission at all operating voltages. Comparative Example 2 A liquid crystal composition comprising the following components was prepared: 75% L
C-0 (mixture used in Comparative Example 1) and 25% p-trans-4-n-propylcyclohexyl-benzonitrile (PCH-3)

This mixture is called LC2-0. This mixture was evaluated for its voltage holding ratio in the same manner as in Comparative Example 1. Table 2 shows the results. Example 4 Analogously to Example 1, crown ether A (18
-Crown-6 or 1,4,7,10,13,16-
Hexaoxacyclooctadecane), but in this example, it was added at a concentration of 0.5% with respect to LC2-0,
The resulting mixture LC2-A was evaluated for its VHR. Table 2 shows the results. Example 5 As in Example 3, TBAB was added to the liquid crystal mixture, but in this example, a 0.5% concentration was added to LC2-0, and the resulting mixture LC2-B was evaluated for its VHR. . The results are summarized in Table 2.

Table 2

[Table 2]

Comparative Example 3 In the same manner as in Comparative Example 2, a mixture of LC-0 and PCH-3 was prepared. However, in this comparative example, the following mixing ratios were used: 95% LC-0 5% PCH-3 The resulting mixture LC3-0 was converted to its resistance value and its VH
R was evaluated. Example 6 (18-crown-6) (18-
Crown-6) was used. This was added to LC3-0 prepared in Comparative Example 3 at a concentration of 100 ppm. The new mixture LC3-A was evaluated as described in Comparative Example 2.

Example 8 To LC3-0 of Comparative Example 3, 150 ppm of TBAB was added, and the resulting LC3-B was evaluated as described in Comparative Example 2. LC3-0 has a VHR of 92%,
HR is 8 for LC3-A and LC3-B, respectively.
Reduced to 5% and 80%.

[Brief description of the drawings]

FIG. 1: LC-0, LC-A1, L measured at 20 ° C.
9 is a graph showing electro-optical characteristics of C-A2 and LC-B.

FIG. 2 is a graph showing the transmittance of LC-0 measured at 20 ° C. after application of a DC-voltage.

FIG. 3 is a graph showing the transmittance of LC-A1 measured at 20 ° C. after application of a DC-voltage.

FIG. 4 is a graph showing the transmittance of LC-A2 measured at 20 ° C. after application of a DC-voltage.

 ──────────────────────────────────────────────────続 き Continuation of front page (71) Applicant 591032596 Frankfurter Str. 250, D-64293 Darmstadt, Federal Republic of Germany (72) Inventor Hideo Ichinose 1-8-1, Shimomeguro, Meguro-ku, Tokyo Alcotower Merck Jiapan Co., Ltd. (72) Inventor Tomoya Tanino Tokyo Shinagawa, Tokyo 6-7-35 Kita Shinagawa, Ward

Claims (4)

[Claims] 1. Two or three or more compounds selected from Group 1 consisting of 15 to 35% by weight of a compound represented by the following formula: ## STR1 ## In each formula, R ¹ is a linear alkyl group having 1 to 5 carbon atoms, L ¹ and L ² are each independently H or F, and X is F, OCF ₂ H or OCF ₃ and m
Is 0 or 1; 65 to 85% by weight of the following formula 2a
And at least three compounds from group 2 consisting of the compounds represented by 2b: In each formula, R ² and R ³ are each independently a linear alkyl group or alkoxy group having 1 to 5 carbon atoms, A nematic liquid crystal medium containing n is 0 or 1, wherein the medium contains a substance that controls and / or adjusts electric conductivity. Wherein - at least one compound represented by formula 1a, - in formula 1b, L ¹ is H, and at least one compound X is F, - in formula 2a, embedded image At least one compound of the formula: wherein in formula 2a: 2. At least one compound of formula 2b, wherein n is 0, and at least one compound of formula 2b, wherein n is 1. 2. Nematic liquid crystal medium. 3. The at least one of claims 1 and 2, wherein the conductivity controlling and / or regulating substance comprises at least one compound selected from the group consisting of crown ether compounds and ammonium salt compounds. 2. The nematic liquid crystal medium according to 1. 4. A plasma addressed display device comprising the nematic liquid crystal composition according to at least one of claims 1 to 3.