JPS62260886A - Liquid crystal display element - Google Patents

Abstract

PURPOSE:To provide a field effect liq. crystal display element which is excellent in time-sharing driving characteristics, exhibits a high transition temp. and is easy to read and to use, and which comprises a liq. crystal comprising an ester cyclohexane liq. crystal material, a phenylcyclohexane liq. crystal material and a particular liq. crystal material. CONSTITUTION:By making use of a liq. crystal obtd. by blending 5-60wt% ester cyclohexane liq. crystal material of formula I (wherein m+n<=6; formula II is a benzene ring; and formula III is a cyclohexane ring) with 5-50wt% phenylcyclohexane of formula IV (wherein n is 2-7) and 5-35wt% liq. crystal material having 3-4 molecules of formulae II and III and having a liq. crystal/liq. transition temp. of 200 deg.C or less, an optically active substance-contg. nematic liq. crystal having positive dielectric anisotropy is sealed in a vertically disposed pair of electrode plates to form a spiral structure in which liq. crystal molecules are twisted by 160-260 deg. in the direction of the liq. crystal thickness, with the polarization axis or absorption axis of a polarizing plate provided so as to sandwich the structure dislocated by 20-70 deg. against the liq. crystal molecule orienting direction of the neighboring electrode plates, thereby obtaining a liq. crystal display element for which the product of the thickness of the liq. crystal layer and the refractive index anisotropy of the liq. crystal is 0.7-1.2mum.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a field effect liquid crystal display device having excellent time-division driving characteristics.

[Conventional technology]

The conventional liquid crystal display element, called the Leystened romatic type, is made of nematic liquid crystal that has positive dielectric anisotropy between two electrode substrates and is twisted by 90 degrees! It had a 1'-rotated structure, and a polarizing plate was placed on the outside of both electrode substrates so that its polarization axis (or absorption axis) was perpendicular or parallel to the liquid crystal molecules adjacent to the electrode substrate. (
Special Publication No. 51-13666).

In order to align the liquid crystal molecules between two electrode substrates so that they form a 90-degree twisted helical structure, for example, the so-called rubbing method (tilt rubbing method), which is a method of rubbing the surface of the electrode substrate in contact with the liquid crystal in one direction with a cloth, etc. angle of 1 to 3 degrees). The rubbing direction at this time, that is, the rubbing direction, becomes the alignment direction of the liquid crystal molecules. The two electrode substrates that have been oriented in this way are placed facing each other with a gap so that their respective rubbing directions intersect with each other at approximately 90 degrees, the two electrode substrates are adhered with a sealant, and the gap is When a nematic liquid crystal having positive dielectric anisotropy is sealed, the liquid crystal molecules are arranged in a helical structure rotated approximately 90 degrees between these electrode substrates. Polarizing plates are provided above and below the liquid crystal cell constructed in this manner, and the polarizing axes or absorption axes thereof are made approximately parallel to the alignment direction of liquid crystal molecules adjacent to each electrode substrate. Here, the fixed reward amount representing the time-sharing drive characteristic, which is necessary for the following explanation, will be briefly explained.

FIG. 2 shows typical voltage-luminance characteristics of a conventional liquid crystal display element having a helical structure of liquid crystal molecules twisted by 90 degrees. This is a relative value of the reflected brightness with respect to the applied voltage, and the initial value of the brightness is 100χ and the final value (value when the applied voltage is sufficiently large) is 0%. In general,
The voltage at which the relative brightness is 90% is the threshold value VJL, 10
% is taken as the saturation value ■sat and is used as a guideline for the characteristics of the liquid crystal. However, in practice, if it is 90% or more, the pixel is sufficiently bright and the liquid crystal is not lit, and if it is 50% or less, the pixel is sufficiently dark and the liquid crystal is lit. The voltages at 90% and 50% are respectively defined as the threshold voltage and saturation voltage Vsat.

Furthermore, the electro-optical characteristics of a liquid crystal display element vary depending on the viewing direction, and these characteristics limit the field of view in which good display quality can be obtained.

Here, the definition of the viewing angle φ will be explained with reference to FIG. In the figure, the rubbing direction of the upper electrode substrate 11 of the liquid crystal display element 1 is 2, the rubbing direction of the lower electrode substrate 12 is 3, and the twist angle of the liquid crystal molecules is 4. Also, liquid crystal display element 1
The orthogonal coordinates XY axes are set on the surface of Let the angle be the viewing angle φ. In this case, for simplicity, the observation direction 5 is
It is assumed that it is within two planes. Further, when φ shown in FIG. 3 is positive, and when viewed from this direction, the contrast becomes high, so this direction is called the viewing direction.

In Figure 2, when the voltage at which the brightness at angle φ-10 degrees is 90% is Vt1, the voltage at which the brightness is 1.50% is v-1, and the voltage at which the brightness at angle φ = 40 degrees is 90% is VAz. , the rise characteristic γ, the angular characteristic Δφ, and the time resolution m are defined as follows.

The time division drive characteristic of a conventional liquid crystal display element is expressed as Δn, where Δn is the refractive index anisotropy of the liquid crystal, and d is the gap between the upper and lower electrode substrates.
-d, and if Δn-d is large (e.g. 0
．． 8μm or more), T is good (small) and Δφ is bad (
small). On the other hand, if Δn・d is small (for example, 0.8
μm or less), T is bad (large) and Δφ is good (large). However, when comparing by time resolution m, Δn
The smaller -d is, the better. Specific examples of the above are shown in Table 1 on the next page.

Table 1 Here, time-division driving will be briefly explained using a dot matrix display as an example. As shown in FIG. 4, striped Y electrodes (signal electrodes) are formed on the lower electrode substrate 12.
13, and an X electrode (scanning electrode) 14 on the upper electrode substrate 11.
The display of characters, etc. is performed by lighting or not lighting the liquid crystal at the intersection of the X and 7 electrodes. In the figure, n scanning electrodes are denoted by X, ,X.

. . . - X7, X, , X, - . . . When a certain scanning electrode is selected, the signal electrode 13 is applied to all pixels on that electrode.
By y, , y2-...-Y, , a selected or non-selected display signal is simultaneously given according to the signal to be displayed.

In this way, lighting or non-lighting of the intersection is selected by the combination of voltage pulses applied to the scanning electrode and the signal electrode. The number of scanning electrodes X in this case corresponds to the number of time divisions.

With conventional liquid crystal display elements, the number of time divisions is 32 or 6 because only the time division drive characteristics shown in Table 1 can be obtained.
4 was the practical limit. However, in recent years, demands for improving the image quality of liquid crystal display elements and increasing the amount of displayed information have become stricter, making it impossible to satisfy the required specifications.

[Problem that the invention seeks to solve]

In order to provide a liquid crystal display device with good image quality even when the number of time divisions is 100 or more, the present inventors previously proposed changing the cell structure of the combination of twist angle and polarizing plate to a completely new system (Unexamined Japanese Patent Publication No. 1986-50511, patent application 1986-
No. 50454, Japanese Patent Application No. 60-70950).

A top view of the cell is shown in FIG. 5, and a perspective view is shown in FIG.

The present invention aims to provide a liquid crystal display element having better time division characteristics and display image quality by selecting a liquid crystal material that is particularly compatible with such a structure.

[Means for solving problems]

As mentioned above, the present inventor first developed a method for determining the characteristics of liquid crystal molecules. ! The twist angle of the helical structure is 160 to 260 degrees, and the polarization axis or absorption axis of the polarizing plate provided on both sides of the helical structure is deviated by 20 to 70 degrees from the liquid crystal molecule alignment direction of the adjacent double yang substrate. Furthermore, the product Δr1·d of the thickness d of the liquid crystal layer expressed in μm and the refractive index anisotropy Δn of the liquid crystal is 0.7 to 1.2.
The present inventors have proposed a structure of a liquid crystal display element having a micrometer scale, but the present inventors have discovered a liquid crystal material that is more suitable for such a structure than conventional ones, and by using this material, both time division characteristics and display image quality can be improved. An excellent liquid crystal display element was obtained.

[Effect]

In the case of an element having a cell structure in which the cell structure is twisted by about 200 degrees, the effect of physical properties when selecting a liquid crystal material tends to be completely different from that in the case of a conventional 90 degree twist, as described below.

First, to see what kind of characteristics a liquid crystal display element with a structure in which the twist angle is increased in this way shows, the viewing angle dependence of the voltage-transmittance characteristics is shown in Figure 1 (a), with a 90 degree twist, and in Figure 1 (b). ) shows the case of 180 degree twist for comparison.

As can be seen from these figures, the element with a 180 degree twisted structure has a falling characteristic (γ characteristic) of transmittance depending on the voltage.
is steep, and the characteristics are clearly improved compared to the conventional 90 degree twist. This tendency becomes more noticeable as the twist angle increases. 160-26 like this
Since an element with a 0 degree twisted element structure has a steep voltage fall characteristic, it is difficult to apply voltage during time-division driving.
The difference in transmittance due to no application of voltage becomes large, making it possible to perform higher time-division driving than in the past. No matter what kind of liquid crystal is used, by increasing the twist angle, the falling characteristics (gamma characteristics) can be greatly improved compared to a 90 degree twist. However, depending on the liquid crystal material, the relationship between the γ characteristics in the case of a 90 degree twist and the γ characteristics in the case of a 160 to 260 degree twist does not show the same tendency, and in the case of a 90 degree twist, the γ characteristics are generally good. The conventional wisdom (Eurodisplay
84. ”Liquid crystal proper
ties in relation to Multi
plex-ing requirements': Gu
A phenomenon has appeared to which the following equation (inter. Bauer) does not apply. This may be due to the relationship of the elastic modulus of twist due to the increase in the twist angle or other factors, but this has not yet been clarified theoretically.

Up until now, it has been thought that the material with the best properties for a 90 degree twist is a material containing a pyrimidine type material (RC static ◎OR) with a small ratio of elastic modulus (k33/k++). In fact, in the case of a 90 degree twist, such a tendency is clearly seen as shown in FIG. Deaf here
The meaning of the line is the γ characteristic (voltage rise characteristic), which is the ratio of the voltage at 80% transmittance and 20% shown in FIG. 1 at an angle of 10 degrees from the normal line.

FIG. 8 shows the relationship between the ratio of elastic modulus and the γ characteristic in the case of 180 degree twist and 230 degree twist. As is clear from the figure, in this case, the pyrimidine type having a small elastic modulus has worse γ characteristics than the PCI (phenylcyclohexane) type. In this way, when twisted by about 2.00 degrees, the previous thinking does not hold, and the PCII
The system shows good results and it is clear that the liquid crystal material needs to be developed in a different way than in the case of a cell structure with a 90 degree twist. Furthermore, as is clear from Fig. 8, the T characteristic is improved when the twist is 230 degrees rather than the 180 degree twist, so it is clear that the larger the twist angle is, the better the γ characteristic is. .

〔Example〕

Hereinafter, the present invention will be explained in more detail with reference to Examples and Reference Examples. In either example, chiral liquid crystal 5811 (manufactured by Merck & Co., Ltd.) is inserted with appropriate twist values (in the case of 180 degree twist, d/p-0, 40-0, 5
0, where p: pitch of chiral liquid crystal, d: cell thickness of liquid crystal cell).

The elements used to measure each side below were those coated with or printed with an organic alignment film such as polyimide and rubbed in a specified direction with gauze or the like. The angle (tilt angle) between the element interface and the liquid crystal molecules in contact with it was approximately 3 degrees.

All the interfaces used to evaluate the liquid crystal material were rubbed to align the liquid crystal material in one direction, but the tilt angle due to rubbing is generally 3 degrees or less, and is thought to be 5 degrees or less at most. In addition, the method for measuring the tilt angle is 5uz
Uki et al.: Appl, Phys.

Let t, , 33 (7), 56.1 (
The same method as in the literature (1978) was used.

Example I Material for the following liquid crystal material composition system (1) (ester cyclohexane ECH type liquid crystal with structural formula "l'2?+-■coo-◎QC1,,'2mvl")
Experiments were conducted by selecting four types of mixed systems. The material of this structure is E
CHnom, the average value of carbon number n + m in the composition (1) containing A, the refractive index anisotropy Δn, and A − · in CP unit, respectively.
39 wLx viscosity, nematic liquid crystal - liquid transition point T
Add N-E. When the average value of carbon number n+m exceeded 6, the viscosity was too high and it could not be adopted as an example.

5 Δn Viscosity ~ For A-1 and A-2 above, the average value of carbon number n0m is 6 or less and the viscosity is within a practical range, but if the average value of carbon number n + m exceeds 6, the viscosity is excessive. Therefore, it could not be put to practical use as a display element. The compositions of ECH-based liquid crystal materials A-3 and 8-4, which have excessive viscosity due to the large sum of carbon numbers, will be described below as reference examples.

"8'D8 Knee 267," a material system containing 30-1 of materials with different molecular weights from 8-1 to A-4, respectively,
The fFS1 diagram (c) shows the data for the case of 18080 degree rice and the case of 900 degree rice. The 180 degree twist and the 90 degree twist show opposite trends. It has been explained that in conventional 90 degree twisted elements, as the value of n+m in the ECH system increases, the ratio of the elastic coefficients of k and/or decreases, resulting in improved 4:γ characteristics and higher contrast. , 180 degree twist, as mentioned above, this concept does not apply at all, indicating that a different concept is required.

Example■ In the following liquid crystal material mixture system, a material with a high transition temperature and an EC
By combining H-based liquid crystals, it is possible to obtain something that exhibits very excellent characteristics. The code, structural formula, and transition point of the high transition point material used here are shown below.

L-1: CsH't-◎◎-coo-◎-θC
,n, 332℃L-2: C3''
? -◎＠-Coo-■-OCd,, 320 ℃
L-3: C, +1. , -◎◎-Coo-@-OC3
H7310"C"'Ct"tp-@◎-coo-◎
-0C3H7291℃ Among these, L-1, L-2,
L-3 is also included in Example ■.

Also, Tolan liquid crystal C, IHz ++ I◎-c=c-◎
QC, Hzwfr is abbreviated as LVFnom.

Composition and transition point TN of Examples n-1, ll-2, ll-3
,! , viscosity at 61125° C., Fuku-w, (180 degree twist), < (voltage that is considered to be substantially in a lighting state when viewed at a viewing angle of 10 degrees) in units of (2) are shown below.

Example n-1 is a simple system in which 30% of Np liquid crystal (Δε≧9−gz) I'CH3 is mixed with the above-mentioned high transition point material and ECH liquid crystal. This yarn has a high content of ECH, so γ
It is a material system with the best properties.

Examples n-2 and 11-3 are systems in which Δn was increased by adding the LVF liquid crystal of Example If-1. LV
As the mixing ratio of F system increases, the γ characteristics decrease, but since the characteristics of Example 11-1 are good, Δn=0.16.
Even in system 11-3, which has been increased to 6, the γ characteristic remains at a good level of 1.054.

Example■ By using the following material as a high-9r point material,
Furthermore, the γ characteristics were improved.

L-5: C,117-9-ecOO-@-0C3H
7318℃L-6: C, H, -θ-θcoo-◎-
θG, 19 325℃ Higher -6 compared to Example ■
In this example, the X-point materials L-3 and L-4 were changed to L-5 and L-6. Both L-5 and L-6, which have three cyclohexane rings, have improved viscosity and γ properties compared to Example (2), suggesting that material selection is important.

Next, as a reference example, the ECH system in Example
When I experimented with the data when replacing it with the 1st system, I got the following.

However, PCI1302: C3+1. -θ-◎0C2Hr
PCH304: C3H,-[phase]-◎0C4H(?P
Compared to CH302 and I'CI (304 is EC), the viscosity is lower due to its lower viscosity, but the TN1 point is lower, and the problem is that the γ characteristics in particular are significantly lower than ECU. PC11 liquid crystal is an important material in terms of reducing viscosity, but ECII liquid crystal is particularly superior in terms of improving gamma characteristics, especially materials in which the sum of carbon numbers n and m in the alkyl group is 6 or less. It is clear from what was shown in Example I that this is superior.

〔Effect of the invention〕

As explained above, according to the present invention, a liquid crystal display element in which the twist angle of the 6M structure of liquid crystal molecules is as large as 160 to 260 degrees can be manufactured using a liquid crystal material according to the present invention (ECH-based low molecular weight liquid crystal with improved γ characteristics). , PGE1 ensures positive dielectric anisotropy as a whole, and the addition of a high transition point liquid crystal material increases the overall transition point), the γ characteristics are good, the transition point is high, It can be made easy to see and use.

[Brief explanation of drawings]

Figure 1(a) shows the voltage of a conventional element with a twist angle of 90 degrees.
A diagram showing the viewing angle dependence of transmittance characteristics. Figure 1(b) is a diagram showing the viewing angle dependence of voltage-transmittance characteristics of an element with a twist angle of 180 degrees. Figure 1(c) is a diagram showing the viewing angle dependence of the voltage-transmittance characteristic of an element with a twist angle of 180 degrees. Sum of numbers (m
+n) and the γ characteristics for a twist angle of 90 degrees and 1
A diagram showing a comparison of the case of 80 degrees, Figure 2 shows the conventional liquid crystal molecules twisted 90 degrees! A diagram showing the typical voltage-luminance characteristics of a liquid crystal display element with a J-circular structure. Figure 3 is an explanatory diagram of the foot chart of viewing angle φ. Figure 4 is an explanatory diagram of time-division driving. Figure 5 is a diagram of twisted display. A top view of an element with a cell structure with thicker corners (and a different combination of polarizing plates), Fig. 6 is a perspective view of the same element, and Fig. 7 shows the ratio of elastic coefficients and γ characteristics of an element with a twist angle of 90 degrees. FIG. 8 is a diagram showing the relationship between the ratio of elastic coefficients and γ characteristics of elements with a twist angle of 180 degrees and a twist angle of 230 degrees according to the present invention.1-Liquid crystal display element, 2.6・-Rubbing direction of upper electrode substrate, 3.7-Rubbing direction of lower electrode substrate, 4
．． 10--twist direction of liquid crystal molecules, 8-direction of absorption axis or polarization axis of upper polarizing plate, 9-direction of absorption axis or polarization axis of lower polarizing plate, 17-liquid crystal molecule. Agent: Patent attorney Katsuma Ogawa-゛h. Fig. 1 (α) (b) Fig. 1 (c) σ 2 4 e /σEC
・Gokubaku no Shini no Delusion (Machi, Figure 2, Figure 3, Figure 7, 5-Kanwosa, Figure 4, d, 5vA, Figure 6, Figure 7, Figure 8)

Claims (1)

[Claims] 1. A nematic liquid crystal having positive dielectric anisotropy and added with an optically active substance is sealed between a pair of upper and lower electrode substrates arranged oppositely, and liquid crystal molecules are distributed in the thickness direction of the nematic liquid crystal. is 160-260
The polarization axis or absorption axis of the polarizing plate that forms a twisted helical structure on both sides of this helical structure is shifted by 20 to 70 degrees from the liquid crystal molecule alignment direction of the adjacent electrode substrate. In a liquid crystal display element in which the product Δn·d of the thickness d of the liquid crystal layer expressed in units and the refractive index anisotropy Δn of the liquid crystal is 0.7 to 1.2 μm, the sum of the carbon numbers m and n is 6 or less Ester cyclohexane liquid crystal material ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼ 5-60% by weight, phenylcyclohexane-based liquid crystal material with n 2-7 ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼ 5-50% by weight, and , a liquid crystal material containing a total of 3 to 4 benzene rings ▲ mathematical formulas, chemical formulas, tables, etc. ▼ and cyclohexane rings ▲ mathematical formulas, chemical formulas, tables, etc. ▼ and a liquid crystal liquid transition temperature of 200°C or higher A liquid crystal display element characterized by using a liquid crystal having a composition of 35% by weight.